Surface-crosslinked polyaspartic acid particles, water-absorbing agent, absorber, and absorbent article

Abstract

To provide a surface cross-linked polyaspartic acid cross-linked body particle excellent in all of water retentivity, liquid permeability, and moisture absorption blocking resistance, a water absorbent containing the surface cross-linked polyaspartic acid cross-linked body particle, and an absorber and an absorbent article containing the water absorbent.SOLUTION: In the surface-crosslinked polyaspartic acid particle, the surface of a polyaspartic acid crosslinked particle containing at least one selected from the group consisting of a polyaspartic acid crosslinked product and a salt thereof is surface-crosslinked with a surface-crosslinking agent, and the surface-crosslinking agent contains a polyfunctional epoxy compound.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to surface-crosslinked polyaspartic acid crosslinked particles, a water-absorbing agent, an absorbent body, and an absorbent article. [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 of water-absorbent resins (Patent Document 1). Because they are not biodegradable, disposal (incineration or 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. For example, Patent Document 2 describes a water-absorbent resin containing a crosslinked polyaspartic acid. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-112474 [Patent Document 2] International Publication No. 2023 / 155523 Summary of the Invention [Problem to be solved by the invention]

[0005] When used as a water-absorbent resin, it is desirable that the balance between water retention and liquid permeability is good. Furthermore, when a water-absorbent resin absorbs water, adjacent water-absorbent resin particles may bond together, causing blocking. Therefore, when used as a water-absorbent resin, it is also desirable that the resin have good resistance to moisture absorption blocking.

[0006] Therefore, an object of the present invention is to provide surface-crosslinked polyaspartic acid crosslinked particles that are excellent in all of water retention, liquid permeability, and moisture absorption blocking resistance, a water-absorbing agent containing the surface-crosslinked polyaspartic acid crosslinked particles, and an absorbent body and absorbent article that contain the water-absorbing agent. [Means for solving the problem]

[0007] The present invention includes the following aspects. [1] Surface-crosslinked crosslinked polyaspartic acid particles, which comprise at least one member selected from the group consisting of crosslinked polyaspartic acids and salts thereof, and whose surfaces are surface-crosslinked with a surface-crosslinking agent, wherein the surface-crosslinking agent comprises a polyfunctional epoxy compound. [2] The surface-crosslinked polyaspartic acid crosslinked particle according to [1], wherein the polyaspartic acid crosslinked product has an amino group, and the surface crosslinking includes a structure in which the amino group is bonded to an epoxy group of the polyfunctional epoxy compound. [3] The surface-crosslinked polyaspartic acid crosslinked particle according to [1] or [2], wherein the surface crosslinking agent further contains a polyfunctional amine compound, and the surface crosslinking comprises a structure in which an epoxy group of the polyfunctional epoxy compound and an amino group of the polyfunctional amine compound are bonded to each other. [4] The surface-crosslinked polyaspartic acid crosslinked particle according to [3], wherein the polyfunctional amine compound comprises at least one selected from the group consisting of polyaspartic acid derivatives in which a polyfunctional amine compound is bonded to polyaspartic acid, and polyethyleneimine. [5] The surface-crosslinked polyaspartic acid crosslinked particles according to any one of [1] to [4], wherein the crosslinked polyaspartic acid contains a structure in which polyaspartic acid is crosslinked with lysine and a polyfunctional epoxy compound. [6] Surface-crosslinked polyaspartic acid crosslinked particles according to any one of [1] to [5], wherein the ratio of the polyfunctional epoxy compound to 10 parts by mass of the polyaspartic acid crosslinked particles is 0.001 to 1 part by mass. [7] A water-absorbing agent containing the surface-crosslinked polyaspartic acid crosslinked particles according to any one of [1] to [6]. [8] An absorbent body comprising the water-absorbing agent according to [7] and a fiber layer containing a fibrous material. [9] An absorbent article comprising a liquid-impermeable sheet, the absorbent body described in [8], and a liquid-permeable sheet, wherein the liquid-impermeable sheet, the absorbent body, and the liquid-permeable sheet are arranged in this order. [Effects of the Invention]

[0008] According to the present invention, there are provided surface-crosslinked polyaspartic acid crosslinked particles having good water retention, liquid permeability, and moisture absorption blocking resistance, a water-absorbing agent containing the surface-crosslinked polyaspartic acid crosslinked particles, and an absorbent body and an absorbent article containing the water-absorbing agent. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic diagram showing the general configuration of a liquid permeability measuring device used in the examples. DETAILED DESCRIPTION OF THE INVENTION

[0010] A numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits.

[0011] [Surface-crosslinked polyaspartic acid particles] A first aspect of the present disclosure is surface-crosslinked crosslinked polyaspartic acid particles. The surface-crosslinked crosslinked polyaspartic acid particles comprise at least one polyaspartic acid selected from the group consisting of crosslinked polyaspartic acid and salts of the crosslinked polyaspartic acid, the surfaces of which are surface-crosslinked with a surface-crosslinking agent. The surface-crosslinking agent includes a polyfunctional epoxy compound.

[0012] "Surface-crosslinked polyaspartic acid crosslinked particles" are particles having a structure in which at least a portion of the particle surface of the crosslinked polyaspartic acid particles is crosslinked by a surface crosslinking agent. In the surface-crosslinked polyaspartic acid crosslinked particles, at least a portion of the crosslinked polyaspartic acid present on the particle surface and in the vicinity of the surface is further crosslinked by a surface crosslinking agent. The surface-crosslinked polyaspartic acid particles may have, for example, a core layer and a shell layer. The shell layer is a region having a structure crosslinked by a surface crosslinking agent. The surface-crosslinked polyaspartic acid particles may have, for example, a structure in which at least a portion of the core layer surface is covered with the shell layer. The crosslink density in the shell layer may be higher than the crosslink density in the core layer, but is not limited to this. For example, the core layer may partially have a region having a higher crosslink density than the shell layer.

[0013] The term "surface cross-linking" refers to cross-linking by a surface cross-linking agent on the surface and in the vicinity of the surface of the surface-cross-linked cross-linked polyaspartic acid particles, and the cross-linked structure formed by the cross-linking.

[0014] <Surface cross-linking agent> The surface cross-linking agent used for surface cross-linking the cross-linked polyaspartic acid particles includes a polyfunctional epoxy compound. 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.

[0015] As the polyfunctional epoxy compound, di- to tetrafunctional epoxy compounds are preferred. As the difunctional epoxy compound, alkylene glycol diglycidyl ether is preferred, and ethylene glycol diglycidyl ether is more preferred. As the trifunctional epoxy compound, poly(alkylene glycol) polyglycidyl ether is preferred, and glycerol polyglycidyl ether is more preferred. As the tetrafunctional epoxy compound, alkane polyol polyglycidyl ether is preferred, and sorbitol polyglycidyl ether is more preferred.

[0016] When the crosslinked polyaspartic acid has an amino group, the epoxy group of the polyfunctional epoxy compound bonds to the amino group of the crosslinked polyaspartic acid. This forms a surface crosslink including a structure in which the amino group of the crosslinked polyaspartic acid and the epoxy group of the polyfunctional epoxy compound are bonded. The structure in which an amino group and an epoxy group are bonded refers to a structure generated by a bonding reaction between an amino group and an epoxy group. An example of the structure in which an amino group and an epoxy group are bonded is a structure represented by the following formula (A).

[0017] [ka]

[0018] The surface cross-linking agent may include, in addition to the polyfunctional epoxy compound, other surface cross-linking agents, such as polyfunctional amine compounds. A polyfunctional amine compound is a compound containing two or more amino groups. The amino groups contained in the polyfunctional amine compound are preferably primary amino groups, and amino groups that substitute hydrogen atoms of aliphatic hydrocarbon groups are preferred because they have high reactivity with epoxy groups. Examples include alkylamino groups, aralkylamino groups, and benzylamino groups. Examples of the amine compound include aliphatic polyamines such as ethylenediamine, propylenediamine, 1,4-butanediamine, pentamethylenediamine, hexamethylenediamine, heptamethylenediamine, octamethylenediamine, nonamethylenediamine, decamethylenediamine, undecamethylenediamine, dodecamethylenediamine, tetradecamethylenediamine, hexadecamethylenediamine, 1-amino-2,2-bis(aminomethyl)butane, tetraaminomethane, diethylenetriamine, triethylenetetramine, and polyethyleneimine; norbornenediamine, 1,4-diaminosilanediamine, and 1,4-diaminosilanediamine; Examples of suitable polyamines include alicyclic polyamines such as cyclohexane, 1,3,5-triaminocyclohexane, and isophoronediamine; aromatic polyamines such as phenylenediamine, tolylenediamine, and xylylenediamine; polyamines such as basic amino acids or their esters, and compounds in which one or more molecules of monoamino compounds such as cystamine are bonded via one or more disulfide bonds, and derivatives thereof; polyamino acid derivatives in which a polyfunctional amine compound is bonded to a polyamino acid; and amino acids having two or more amino groups such as lysine, cystine, and ornithine, or salts or esters thereof.

[0019] The polyfunctional amine compound is preferably a polymer having an amino group in a side chain. The polyfunctional amine compound is preferably a polyalkyleneimine or a polyamino acid derivative. The polyalkyleneimine is preferably polyethyleneimine, and more preferably branched polyethyleneimine. The polyamino acid derivative is preferably a polyaspartic acid derivative in which a polyfunctional amine compound is bonded to polyaspartic acid, and more preferably a polyaspartic acid derivative in which lysine is bonded to polyaspartic acid. The polyfunctional amine compound preferably includes at least one selected from the group consisting of a polyaspartic acid derivative in which a polyfunctional amine compound is bonded to polyaspartic acid, and polyethyleneimine.

[0020] The amino group of the polyfunctional amine compound bonds with the epoxy group of the polyfunctional epoxy compound, thereby forming a surface crosslink including a structure in which the amino group of the polyfunctional amine compound and the epoxy group of the polyfunctional epoxy compound are bonded.

[0021] The surface crosslinking of the crosslinked polyaspartic acid particles can be carried out by a known method. For example, the surface of the crosslinked polyaspartic acid particles can be brought into contact with a surface crosslinking treatment liquid containing a surface crosslinking agent dissolved therein, thereby carrying out a surface crosslinking reaction, thereby carrying out the surface crosslinking of the crosslinked polyaspartic acid particles. Examples of methods for bringing the surface crosslinking treatment liquid into contact with the surface of the crosslinked polyaspartic acid particles include a method of spraying or dropping the surface crosslinking treatment liquid onto the surface of the crosslinked polyaspartic acid particles, and a method of immersing the crosslinked polyaspartic acid particles in the surface crosslinking treatment liquid. Specific examples of the surface crosslinking method include a method of immersing the crosslinked polyaspartic acid particles in a surface crosslinking treatment liquid containing a surface crosslinking agent dissolved therein (treatment method A), and a method of mixing the surface crosslinking treatment liquid containing a surface crosslinking agent dissolved therein with the crosslinked polyaspartic acid particles (treatment method B).

[0022] Processing Method A In treatment method A, crosslinked polyaspartic acid particles are immersed in a surface crosslinking treatment liquid to adhere the surface crosslinking treatment liquid to the crosslinked polyaspartic acid particles. A mixed solvent of water and alcohol can be used as the solvent for the surface crosslinking treatment liquid. Ethanol, for example, can be used as the alcohol. The ratio of water to 100 parts by mass of the mixed solvent can be, for example, 10 to 50 parts by mass. The ratio of alcohol to 100 parts by mass of the mixed solvent can be, for example, 50 to 90 parts by mass. The amount of the polyfunctional epoxy compound added to 100 parts by mass of the mixed solvent is, for example, 0.1 to 10 parts by mass, and preferably 0.2 to 5 parts by mass. When only a polyfunctional epoxy compound is used as the surface crosslinking agent, the amount of the polyfunctional epoxy compound added to 100 parts by mass of the mixed solvent is preferably 0.1 to 1 part by mass, and more preferably 0.1 to 0.5 parts by mass. When a polyfunctional epoxy compound and a polyfunctional amine compound are used as the surface cross-linking agent, the amount of the polyfunctional epoxy compound added relative to 100 parts by mass of the mixed solvent is preferably 0.1 to 10 parts by mass, more preferably 0.3 to 5 parts by mass. When a polyfunctional epoxy compound and a polyfunctional amine compound are used as the surface cross-linking agent, the amount of the polyfunctional amine compound added relative to 100 parts by mass of the mixed solvent is preferably 0.1 to 20 parts by mass. When the polyfunctional amine compound is polyethyleneimine, the amount of the polyfunctional amine compound added relative to 100 parts by mass of the mixed solvent is preferably 0.1 to 5 parts by mass. When the polyfunctional amine compound is a polyaspartic acid derivative, the amount of the polyfunctional amine compound added relative to 100 parts by mass of the mixed solvent is preferably 5 to 20 parts by mass.

[0023] The method for immersing the crosslinked polyaspartic acid particles in the surface crosslinking treatment solution is not particularly limited. For example, the crosslinked polyaspartic acid particles may be placed in a container such as a stainless steel mesh and immersed in the surface crosslinking treatment solution. The crosslinked polyaspartic acid particles are completely immersed in the surface crosslinking treatment solution. The amount of the crosslinked polyaspartic acid particles added per 100 parts by mass of the mixed solvent may be 1 to 20 parts by mass, and preferably 1 to 10 parts by mass.

[0024] The immersion time may be long enough to allow the surface cross-linking treatment liquid to adhere sufficiently to the entire surface of the cross-linked polyaspartic acid particles. The immersion time may be 10 to 200 seconds or more, preferably 30 to 200 seconds or more, more preferably 50 to 200 seconds or more, and even more preferably 60 to 200 seconds or more. After immersion, the mesh container is pulled up and excess surface cross-linking treatment liquid is removed. Next, a surface cross-linking reaction is carried out by heat treatment.

[0025] The temperature for the heat treatment may be 100 to 200°C, preferably 120 to 180°C, and more preferably 140 to 180°C. The heat treatment time may be 10 to 100 minutes, preferably 15 to 60 minutes, and more preferably 20 to 40 minutes.

[0026] Processing method B: In treatment method B, the surface cross-linking treatment liquid and the cross-linked polyaspartic acid particles are stirred and mixed to adhere the surface cross-linking treatment liquid to the cross-linked polyaspartic acid particles. Water can be used as the solvent for the surface cross-linking treatment liquid. Alternatively, the solvent may be water to which a small amount of an aqueous solvent such as alcohol or alkylene glycol has been added. Examples of alcohol that can be used include ethanol and isopropyl alcohol. Examples of alkylene glycol that can be used include propylene glycol. The amount of the solvent used in the surface cross-linking treatment liquid may be such that the surface cross-linking agent can be dissolved in it. The amount of the surface treatment agent added relative to 100 parts by mass of the surface cross-linking agent is, for example, 50 to 200 parts by mass.

[0027] The method for mixing and stirring the surface cross-linking treatment liquid and the cross-linked polyaspartic acid particles is not particularly limited. Examples of the mixing method include a method in which the surface cross-linking treatment liquid is sprayed or dropped onto the cross-linked polyaspartic acid particles, and then mixed and stirred until uniform.

[0028] The surface cross-linking treatment liquid and the cross-linked polyaspartic acid particles may be mixed and stirred using a mixer. The mixer preferably has a torque required to uniformly and reliably mix the cross-linked polyaspartic acid particles and the surface cross-linking treatment liquid. The mixer is preferably a high-speed stirring mixer, more preferably a high-speed stirring continuous mixer. The rotation speed of the high-speed stirring mixer may be, for example, 100 rpm to 10,000 rpm.

[0029] The ratio of the polyfunctional epoxy compound to 10 parts by mass of the crosslinked polyaspartic acid particles is 0.001 to 1 part by mass, preferably 0.01 to 1 part by mass, and more preferably 0.01 to 0.6 parts by mass.The ratio of the polyfunctional amine compound to 10 parts by mass of the crosslinked polyaspartic acid particles is 0.01 to 5 parts by mass.

[0030] The surface cross-linking treatment liquid and the cross-linked polyaspartic acid particles are mixed and stirred until homogeneous, and then the surface cross-linking reaction is carried out by heat treatment.

[0031] The temperature for the heat treatment may be 100 to 250°C, preferably 120 to 200°C, and more preferably 140 to 180°C. The heat treatment time may be 10 to 100 minutes, preferably 15 to 60 minutes, and more preferably 20 to 40 minutes.

[0032] <Crosslinked polyaspartic acid particles> The "crosslinked polyaspartic acid particles" are particles containing at least one selected from the group consisting of crosslinked polyaspartic acid and salts thereof as a main component. The crosslinked polyaspartic acid particles can be obtained by drying and pulverizing the crosslinked polyaspartic acid.

[0033] (Structural unit containing a cross-linked structure: structural unit (a)) A crosslinked polyaspartic acid is a polymer in which one or more side chains of polyaspartic acid are crosslinked. The crosslinked polyaspartic acid is, for example, a polymer containing a structural unit (a) having a crosslinked structure represented by the following general formula (1).

[0034] [ka] [In the formula, R 1 represents a divalent linking group.

[0035] The structural unit (a) containing a crosslinked structure contains a structure in which two aspartic acid side chains are crosslinked with a crosslinking agent. Examples of the crosslinked structure include a structural unit containing a structure in which two aspartic acid side chains are crosslinked with the compound (A) described below and a polyfunctional epoxy compound. Examples of the structural unit (a) containing such a crosslinked structure include a structural unit represented by the following general formula (2):

[0036] [ka] [In the formula, L 1 and L 2 are each independently a divalent linking group. The carboxy group in the formula may form a salt.]

[0037] L in the formula (2) 1 Examples of the divalent linking group in L include a linear or branched alkylene group, a combination of a linear or branched alkylene group and an ether bond, and a combination of a methylene group and an ester bond. 1 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.

[0038] L in the formula (2) 2 Examples of the divalent linking group in L include a linear or branched alkylene group, a combination of a linear or branched alkylene group and an ether bond, and a combination of a methylene group and an ester bond. 2is preferably a polyalkyleneoxy group, more preferably a polyethyleneoxy group or a polypropyleneoxy group, and even more preferably a polyoxyethylene group. The polyalkyleneoxy group preferably has 1 to 10 carbon atoms, more preferably 2 to 8 carbon atoms, and even more preferably 2 to 4 carbon atoms.

[0039] The carboxy group in the formula (2) may form a salt. Examples of the salt include the same salts as those described above. The salt formed by the carboxy group in the formula (2) is preferably an alkali metal salt, more preferably a sodium salt or a potassium salt.

[0040] The structural unit (a) containing a crosslinked structure includes a structure in which two aspartic acid side chains are crosslinked with lysine and a polyfunctional epoxy compound. The structural unit (a) is preferably a structural unit represented by the following formula (3):

[0041] [ka] [The carboxy group in the formula may form a salt.]

[0042] The carboxy group in the formula (3) may form a salt. Examples of the salt include the same salts as those described above. The salt formed by the carboxy group in the formula (3) is preferably an alkali metal salt, more preferably a sodium salt or a potassium salt.

[0043] (Structural unit containing an uncrosslinked aspartic acid side chain: structural unit (b)) The crosslinked polyaspartic acid may contain, in addition to the structural unit (a) containing the crosslinked structure represented by the above general formula (1), a structural unit (b) containing an uncrosslinked aspartic acid side chain. The structural unit (b) is a structural unit represented by the following general formula (4):

[0044] [ka] [In the formula, G represents a carboxy group or a carboxylate group.]

[0045] In the formula (4), 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.

[0046] (Structural unit having an amino group introduced into the side chain: structural unit (c)) In addition to the structural units (a) and (b), the crosslinked polyaspartic acid may contain a structural unit (c) in which an amino group has been introduced into the asparagine side chain. It may also contain uncrosslinked aspartic acid monomer units (b). Examples of the structural unit (c) include monomer units represented by the following general formula (5):

[0047] [ka] [In the formula, R 2 represents a divalent linking group. 3 represents a valence of one.]

[0048] The structural unit (c) is preferably a structural unit having the below-described compound (A) introduced into its side chain. Examples of the structural unit (c) include structural units represented by the following general formula (6).

[0049] [ka] [In the formula, L represents a divalent linking group, and G represents a carboxy group or a carboxylate group.]

[0050] In the formula (6), 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.

[0051] In the formula (6), 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.

[0052] The structural unit (c) is preferably a structural unit in which lysine has been introduced into the side chain of aspartic acid. The structural unit (c) is preferably a structural unit represented by the following formula (7).

[0053] [ka]

[0054] (Method of producing crosslinked polyaspartic acid) The crosslinked polyaspartic acid can be prepared, for example, by reacting polysuccinimide with a crosslinking agent to partially crosslink it, and then subjecting the uncrosslinked imide ring portion to alkaline hydrolysis; or by reacting polyaspartic acid with a crosslinking agent to partially crosslink it. Known crosslinking agents can be used, such as basic polyamine compounds and polyfunctional epoxy compounds.

[0055] A polyaspartic acid crosslinked body containing the structural unit (a), the structural unit (b), and the structural unit (c) can be obtained by reacting polysuccinimide (PSI), a compound (A) having a first functional group (a1) and a second functional group (a2), and a multifunctional epoxy compound (B) (International Publication No. 2023 / 155523). In the compound (A), the second functional group does not react with polysuccinimide (PSI) or has lower reactivity with polysuccinimide (PSI) than the first functional group.

[0056] The crosslinked polyasparagine contains a PSI-a1(A) bond formed by an addition reaction between a first functional group (a1) and polysuccinimide (PSI), and a B-a2(A) bond formed by a reaction between the second functional group (a2) and a polyfunctional epoxy compound (B). The crosslinked polyaspartic acid contains a crosslinked structure (PABAP) represented by PSI-a1-A1-a2-B-a2-A1-a1-PSI, and a portion of the crosslinked structure (PABAP) (e.g., the unreacted portion of PSI) is hydrolyzed.

[0057] Compound (A): The first functional group (a1) of the compound (A) is preferably an amino group (NH2-), and more preferably an NH2-CH2- amino group.

[0058] The second functional group (a2) of the compound (A) is preferably an amino group (NH2-) or a phosphonooxy group ((OH)2P(=O)-O-), and more preferably an amino group (NH2-). When the second functional group (a2) is an amino group (NH2-), the amino group of the second functional group (a2) is preferably an amino group in a structure represented by the following formula (8):

[0059] [ka] [In the formula, G represents a carboxy group or a carboxylate group, and * represents a bond.]

[0060] 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.

[0061] When the first functional group (a1) and the second functional group (a2) of the compound (A) are both amino groups (NH2-), it is preferable that the amino group of the second functional group of the compound (A) has lower reactivity with polysuccinimide (PSI) than the amino group of the first functional group. Examples of such a compound (A) include diamines having different terminal structures containing the respective amino groups. For example, asymmetric diamines are included.

[0062] The compound (A) may be a compound in which the first functional 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 formula (8). Such a compound (A) may be a compound represented by the following formula (9).

[0063] [ka] [In the formula, L represents a divalent linking group.]

[0064] In the formula (9), 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.

[0065] In compound (A), the carboxy group of the compound represented by formula (9) 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.

[0066] The compound (A) may be a compound represented by the following formula (10).

[0067] [ka] [In the formula, n represents an integer of 1 to 10.]

[0068] In the formula (10), n is preferably an integer of 2 to 8, and more preferably an integer of 3 to 5.

[0069] In compound (A), the carboxy group of the compound represented by formula (10) 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.

[0070] When the first functional group (a1) of the compound (A) is an amino group and the second functional group (a2) is a phosphonooxy group ((OH)2P(=O)-O-), examples of the compound (A) include compounds represented by the following formula (11).

[0071] [ka] [In the formula, L represents a divalent linking group.]

[0072] Examples of the divalent linking group for L in the formula (11) include the same as the divalent linking group for L in the formula (9). L in the formula (11) 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.

[0073] In compound (A), the phosphonooxy group of the compound represented by formula (11) 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.

[0074] Specific examples of the compound (A) include lysine, ornithine, arginine, phosphorylethanolamine, and the like.

[0075] When compound (A) contains an amino group, an acid salt of compound (A) may be used as a raw material. Examples of the acid salt of compound (A) include hydrochlorides such as lysine hydrochloride, ornithine hydrochloride, and arginine hydrochloride, as well as similar sulfates.

[0076] Dipeptides may be used as compound (A). Examples of the dipeptides include dipeptides having a basic amino acid residue at the C-terminus, such as glycine-lysine (isopeptide bond), alanine-lysine (isopeptide bond), glycine-lysine-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.

[0077] Multifunctional epoxy compound (B): 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.

[0078] A polyaspartic acid crosslinked body, which is a reaction product of polysuccinimide (PSI), compound (A), and polyfunctional epoxy compound (B), can be produced by the method described in WO 2023 / 155523. For example, the polyaspartic acid crosslinked material can be produced by reacting polysuccinimide (PSI), compound (A), and polyfunctional epoxy (B) in water or a water-containing solvent to produce a crosslinked material. The order of reaction of polysuccinimide (PSI), compound (A), and polyfunctional epoxy (B) is not particularly limited, and examples thereof include the following three production methods. (i) A production method comprising the steps of: reacting polysuccinimide (PSI) with a compound (A) to obtain a reaction product (P1) of polysuccinimide (PSI) and the compound (A); and reacting the reaction product (P1) with a polyfunctional epoxy compound. (ii) A production method in which polysuccinimide (PSI) and compound (A) are first mixed and reacted, and then a polyfunctional epoxy compound is added at a constant rate. (iii) A production method in which polysuccinimide (PSI), compound (A), and a polyfunctional epoxy compound are mixed and then reacted.

[0079] From the viewpoint of ease of controlling the structure of the crosslinked polyaspartic acid, method (i) or method (ii) is preferred, and method (i) is more preferred.

[0080] In the step of obtaining the reaction product (P1) in the method (i), it is preferable to first dissolve the compound (A) in water. For example, 5 to 50 parts by mass of water is preferable, and 10 to 30 parts by mass of water is more preferable, per 1 part by mass of the compound (A). Polysuccinimide is then mixed with this aqueous solution. The compounding ratio is preferably 0.5 to 20 parts by mass of the compound (A) per 100 parts by mass of the polysuccinimide, more preferably 1 to 15 parts by mass, and even more preferably 1.5 to 10 parts by mass.

[0081] After blending, the pH of the resulting mixture is preferably adjusted to 8 to 13 by adding an organic or inorganic base compound such as NaOH or an amine, more preferably to 9 to 12, and even more preferably to 11 to 11.5. In the resulting product, the proportion of units to which compound (A) is added is preferably 2 to 30%, more preferably 5 to 15%, and even more preferably 8 to 12% of all units. The proportion of units to which compound (A) is added is determined by the ratio (Ib / Ia) of the integral value Ia of the peak derived from the -CH- protons in the polyaspartic acid main chain to the integral value Ib of the peak derived from the -CH- protons in compound (A) in proton NMR. Alternatively, it can be determined by the ratio (Ic × 2 / Ia) of the integral value Ic of the peak derived from the -CH- protons in compound (A) to twice the integral value Ic.

[0082] In the method (i), in the step of reacting the reactant (P1) with a polyfunctional epoxy compound, the amount of the polyfunctional epoxy compound is preferably 0.1 to 10 parts by mass, more preferably 0.5 to 5 parts by mass, and even more preferably 0.5 to 3 parts by mass, per 100 parts by mass of the reactant (P1).

[0083] The reactant (P1) may be a solid reactant (P1) obtained by isolating the reactant (P1) from the reaction liquid obtained in the step of producing the reactant (P1). In this case, it is preferable to prepare an aqueous solution of the reactant (P1) before blending it with the polyfunctional epoxy compound.

[0084] As the reactant (P1), the polyfunctional epoxy compound can be blended directly in a solution state from the reaction solution obtained in the reactant (P1) production step without isolating the reactant (P1).

[0085] The reaction temperature between the reactant (P1) and the polyfunctional epoxy compound can be 30°C to 100°C, preferably 40 to 80°C, and more preferably 50 to 70°C. When the reaction temperature is 60°C, for example, the reaction time can be 40 to 600 minutes, and more preferably 60 to 300 minutes.

[0086] The crosslinked polyaspartic acid produced by the reaction can be isolated by known ordinary isolation procedures such as recrystallization, reprecipitation, filtration, concentration, etc.

[0087] The degree of crosslinking of the crosslinked polyaspartic acid (the ratio of crosslinked units to all units) is not particularly limited. For example, in the case of a crosslinked polyaspartic acid which is a reaction product of polysuccinimide (PSI), compound (A), and polyfunctional epoxy compound (B), the ratio of units to which compound (A) is added (addition ratio) to all units in the polysuccinimide (PSI) is preferably 1 to 20%, more preferably 3 to 15%, and even more preferably 5 to 10%. The addition ratio can be measured by NMR.

[0088] (Method of producing crosslinked polyaspartic acid particles) Crosslinked polyaspartic acid particles can be produced by drying a crosslinked polyaspartic acid and physically pulverizing it. The drying method is not particularly limited, and any known method can be used, such as heat drying, freeze drying, reduced pressure (vacuum) drying, and reduced pressure heat drying. In the case of heat drying, the drying temperature is usually 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 usually 50°C to 200°C, preferably 60°C to 150°C, and more preferably 70°C to 120°C. The size (average particle size) of the crosslinked polyaspartic acid particles is preferably 1 to 5000 μm, more preferably 10 to 2000 μm, even more preferably 50 to 1500 μm, and particularly preferably 100 to 1000 μm. The particle size distribution of the crosslinked polyaspartic acid particles may be adjusted by performing a procedure such as particle size adjustment using sieve classification.

[0089] The surface-crosslinked polyaspartic acid crosslinked particles of this embodiment are surface-crosslinked with a surface crosslinking agent containing a polyfunctional epoxy compound. The polyfunctional epoxy compound is surface-crosslinked by the amino groups of the crosslinked polyaspartic acid particles and the epoxy groups of the polyfunctional epoxy compound. Therefore, the surface-crosslinked structure does not contain an ester bond and is resistant to hydrolysis. When the crosslinked polyaspartic acid particles are crosslinked with the above-mentioned compound A and a polyfunctional epoxy compound, the crosslinked polyaspartic acid particles also do not contain an ester bond and are resistant to hydrolysis. Therefore, surface-crosslinked polyaspartic acid crosslinked particles that are resistant to hydrolysis can be obtained.

[0090] The surface-crosslinked polyaspartic acid crosslinked particles of this embodiment have a good balance between water retention and liquid permeability, and are excellent in both water retention and liquid permeability. In addition, the surface-crosslinked polyaspartic acid crosslinked particles of this embodiment also have good resistance to moisture absorption blocking. Therefore, they are suitable for use as a water absorbent.

[0091] [Water absorbent] A second aspect of the present disclosure is a water-absorbing agent, which contains the surface-crosslinked polyaspartic acid crosslinked body particles according to the first aspect.

[0092] The water-absorbing agent of the present embodiment may contain other components in addition to the surface-crosslinked polyaspartic acid crosslinked particles. Examples of the other components include water-absorbing resins other than the surface-crosslinked polyaspartic acid crosslinked particles, known additives, and the like. Examples of the additives include gel stabilizers, metal chelating agents, and flow-improving agents (lubricants). The other components may be located inside the surface-crosslinked polyaspartic acid crosslinked particles, on the surface of the particles, or both. For example, the water-absorbing agent may contain a flow-improving agent (lubricant) as another component. Examples of the flow-improving agent include inorganic particles. Examples of the inorganic particles include silica particles such as amorphous silica, talc, and mica.

[0093] The water-absorbing agent may contain a plurality of inorganic particles arranged on the surface of the surface-crosslinked crosslinked polyaspartic acid particles. For example, the inorganic particles can be arranged on the surface of the surface-crosslinked crosslinked polyaspartic acid particles by mixing the surface-crosslinked crosslinked polyaspartic acid particles with inorganic particles. The inorganic particles may be silica particles such as amorphous silica. The ratio of the inorganic particles to the mass of the surface-crosslinked crosslinked polyaspartic acid 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, or 5.0% by mass or less, or 3.5% by mass or less. By adding the inorganic particles in the above-mentioned range, a water-absorbing agent having favorable water-absorbing properties of the surface-crosslinked crosslinked polyaspartic acid particles can be easily obtained.

[0094] The water-absorbing agent of the present embodiment can be used in various products that require water absorption, moisture absorption, and the like. pet supplies such as pet sheets; daily necessities and clothing such as disposable body warmers, sweat absorbent fibers, deodorizing and dehumidifying 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;

[0095] [Absorbent] A third aspect of the present disclosure is an absorbent body. The absorbent body includes the water-absorbing agent according to the second aspect and a fiber layer containing fibrous material. The absorbent body is, for example, a mixture containing the water-absorbing agent and the fibrous material. The absorbent body may be configured, for example, in such a manner that the water-absorbing agent and the fibrous material are uniformly mixed, or in such a manner that surface-crosslinked polyaspartic acid crosslinked particles are sandwiched between fibrous material formed in a sheet or layer, or in other configurations.

[0096] The mass proportion of the water-absorbing agent in the absorbent body of the present embodiment may be 2 to 100 mass %, 10 to 90 mass %, or 10 to 80 mass % relative to the total mass of the water-absorbing agent and fibrous material.

[0097] The shape of the absorbent body of this embodiment 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.

[0098] The absorbent of this embodiment contains the surface-crosslinked polyaspartic acid crosslinked particles according to the first aspect. The absorbent of this embodiment may contain other known water-absorbent resin particles in addition to the surface-crosslinked polyaspartic acid crosslinked particles according to the first aspect. It is preferable that the absorbent of this embodiment contains only the surface-crosslinked polyaspartic acid crosslinked particles according to the first aspect as the water-absorbent resin particles.

[0099] The content of the surface-crosslinked polyaspartic acid crosslinked particles in the absorbent body of this embodiment is 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 below. 2 ), and more preferably 100 to 1000 g / m 2 In order to ensure that the absorbent article exhibits sufficient liquid absorption performance and, in particular, to prevent liquid leakage, the content of the surface-crosslinked polyaspartic acid crosslinked particles is 50 g / m 2 From the viewpoints of suppressing the occurrence of gel blocking, exhibiting the liquid diffusion performance of the absorbent article, and further improving the liquid permeation rate, the content of the surface-crosslinked polyaspartic acid crosslinked particles is preferably 2000 g / m or more. 2 It is preferable that: [Fibrous material]

[0100] 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.

[0101] 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 2 In 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 It is preferable that

[0102] 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.

[0103] 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.

[0104] 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.

[0105] 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.

[0106] [Additives] The absorbent body of the present embodiment may contain various additives commonly used in the relevant 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 body. Examples of the inorganic powders include silicon dioxide, zeolite, mica, kaolin, clay, etc. When the water-absorbing agent contains inorganic particles, the absorbent body may contain the inorganic powder in addition to the inorganic particles in the water-absorbing agent.

[0107] (Absorbent articles) A fourth aspect of the present disclosure is an absorbent article. The absorbent article includes a liquid-impermeable sheet, an absorbent body according to the third aspect, and a liquid-permeable sheet. In the absorbent article, the liquid-impermeable sheet, absorbent body, and 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.

[0108] In the absorbent article, a liquid-impermeable sheet, an absorbent body, and a liquid-permeable sheet are laminated in this order.

[0109] The absorbent article of this embodiment includes the absorbent body according to the third aspect. The absorbent article of this embodiment may include other known absorbents in addition to the absorbent body according to the third aspect. It is preferable that the absorbent article of this embodiment uses only the absorbent body according to the third aspect as the absorbent body.

[0110] [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.

[0111] 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.

[0112] 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.

[0113] 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.

[0114] 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.

[0115] 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.

[0116] 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.

[0117] 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.

[0118] [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.

[0119] 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.

[0120] 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.

[0121] 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]

[0122] The present invention will be described below with reference to examples, but the present invention is not limited to the following examples.

[0123] [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)

[0124] [Liquid permeability measurement] Measurements were performed using a measuring device whose schematic configuration is shown in Figure 1. The measurement unit consists of a cylindrical acrylic resin container (A) with an inner diameter of 19 mm, an outer diameter of 25 mm, and a height of 120 mm, to which a stainless steel mesh sheet (250 mesh) is attached, a cylindrical acrylic resin container (B) with an inner diameter of 26 mm, an outer diameter of 36 mm, and a height of 80 mm, to which a similar stainless steel mesh sheet is attached, and a swollen water-absorbent resin particle gel (C). The measurement unit is placed on a metal mesh (D) with a mesh size of 2 mm. The inner diameter of the Petri dish (E) below the measurement unit is approximately 110 mm.

[0125] The measurement was carried out at a room temperature of approximately 25°C. 0.20 g of water-absorbent resin particles, which had been previously classified into sizes of 150 to 710 μm, was uniformly placed in a cylindrical container (B), and the cylindrical container (A) was inserted from above to form a measurement unit. The mesh side of the measurement unit was immersed in a petri dish containing an appropriate amount of physiological saline and allowed to swell for 30 minutes, forming a swollen water-absorbent resin particle gel. Next, the entire measurement unit was moved onto an empty petri dish, and a 200 g weight was slowly placed on top of the cylindrical container (A), and the swollen gel was loaded for 3 minutes. The mass (W1) of an empty Petri dish (E) was measured in advance. A metal mesh (D) with 2 mm openings was placed on the Petri dish (E), and then the measurement unit containing the swollen gel (C) was placed on top of the Petri dish (E). Next, physiological saline was added from the top of the cylindrical container (A) and a stopwatch was started at the same time. Thereafter, physiological saline was added appropriately until the end of the measurement so that the liquid level remained 6 to 7 cm above the bottom of the cylindrical container (A). The mass (W2) of the Petri dish (E) containing the physiological saline that had flowed through the swollen gel (C) within 30 seconds (0.5 minutes) after the addition was measured, and the liquid flow rate (g / min) was calculated using the following equation.

[0126] Liquid passing rate (g / min)=(W2-W1) / 0.5

[0127] [Measurement of moisture absorption blocking resistance] 0.3 g of water-absorbent resin particles was weighed into a 5 mL glass container (opening diameter: 10 mm). The glass container with the lid open was placed in a thermo-hygrostat previously set at a temperature of 70°C and a relative humidity of 95%, and treated for 24 hours. After 24 hours, the glass container was removed from the thermo-hygrostat. After cooling to room temperature, the glass container was turned upside down, and the change in appearance of the swollen water-absorbent resin particles was observed. The moisture absorption blocking resistance was evaluated according to the following evaluation criteria. Evaluation criteria: A: The entire absorbent resin particle falls off from the bottom. B: Some absorbent particles fall off from the bottom. C: The water-absorbent resin particles do not peel off from the bottom of the container and do not move.

[0128] [Synthesis example of polysuccinimide reaction product] <Synthesis Example 1: Synthesis of polysuccinimide> 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 became neutral, and then vacuum dried at 80°C to obtain 115 parts of polysuccinimide having a weight-average molecular weight of 80,000.

[0129] <Synthesis Example 2: Synthesis of polysuccinimide reaction product> 8.47 parts of L-lysine hydrochloride was added to 195 parts of distilled water and dissolved with stirring. Next, 100 parts of the polysuccinimide obtained in Synthesis Example 1 was added to this L-lysine hydrochloride solution. Next, 82.6 parts of a 48% aqueous NaOH solution was added dropwise to the solution with stirring at room temperature while adjusting the pH to 11 to 11.5. After the dropwise addition was completed, the solution was stirred for an additional 15 hours at room temperature. The resulting reaction solution was filtered using a 59 μm nylon mesh to obtain a lysine-added polysodium aspartate solution (solid content: 40%).

[0130] [Production example of crosslinked polyaspartic acid particles] (Production Example 1: Production of Crosslinked Polyaspartic Acid Particles 1) 25.0 parts of the lysine-added sodium polyaspartate solution (solid content 40%) obtained in Synthesis Example 2 above and 0.27 parts of a multifunctional epoxy compound (Denacol (registered trademark) EX-810, Nagase ChemteX Corporation) were mixed and subjected to a crosslinking reaction at 60°C. The resulting crosslinked product was vacuum-dried at 60°C under reduced pressure, and the dried composition was pulverized in a mortar and sieved through a stainless steel sieve (JIS Z-8801) to obtain particles of 150 to 710 μm. These were designated polyaspartic acid crosslinked particles 1. The water retention and liquid permeability of the crosslinked polyaspartic acid particles 1 were 33.0 g / g and 0 g / min, respectively.

[0131] (Production Example 2: Production of Crosslinked Polyaspartic Acid Particles 2) Water-absorbent resin particles 2 were obtained in the same manner as in Production Example 1, except that 0.32 parts of a polyfunctional epoxy compound (Denacol EX-810, Nagase ChemteX Corporation) was used. The water retention and liquid permeability of the polyaspartic acid crosslinked particles 2 were 28.5 g / g and 2.2 g / min, respectively.

[0132] (Production Example 3: Production of Crosslinked Polyaspartic Acid Particles 3) Water-absorbent resin particles 3 were obtained in the same manner as in Production Example 1, except that 0.42 parts of a polyfunctional epoxy compound (Denacol EX-810, Nagase ChemteX Corporation) was used. The water retention and liquid permeability of the crosslinked polyaspartic acid particles 3 were 24.5 g / g and 45.6 g / min, respectively.

[0133] [Example of production of surface-crosslinked polyaspartic acid crosslinked particles] The crosslinked polyaspartic acid particles were surface crosslinked by the following treatment method A or treatment method B.

[0134] <Processing Method A> A surface cross-linking treatment solution containing a surface cross-linking agent was prepared, and a predetermined amount was weighed into a glass Petri dish. A predetermined amount of weighed polyaspartic acid cross-linked particles was placed on a stainless steel mesh, and the stainless steel mesh was immersed in the glass Petri dish. After immersion for a predetermined time, the stainless steel mesh was slowly pulled up to filter off the excess treatment solution. This resulted in a mixture in which the surface-crosslinking treatment solution adhered to the surface of the crosslinked polyaspartic acid particles. Subsequently, the mixture was heated for a predetermined time and at a predetermined temperature to obtain surface-crosslinked crosslinked polyaspartic acid particles.

[0135] <Processing method B> A predetermined amount of crosslinked polyaspartic acid particles was weighed into a glass container. A surface crosslinking treatment solution containing a surface crosslinking agent was prepared, added to the crosslinked polyaspartic acid particles, and mixed until uniform. This resulted in a mixture in which the surface crosslinking treatment solution adhered to the surfaces of the crosslinked polyaspartic acid particles. Subsequently, the mixture was heat-treated for a predetermined time and at a predetermined temperature to obtain surface-crosslinked crosslinked polyaspartic acid particles.

[0136] (Examples 1 to 9, Comparative Examples 1 to 3) In Examples 1 to 9, surface cross-linking was carried out by Treatment Method A. Example 1 A surface cross-linking treatment solution was prepared by mixing 0.34 parts of a multifunctional epoxy compound (Denacol EX-810, Nagase ChemteX Corporation), 20.0 parts of ion-exchanged water, and 80.0 parts of ethanol, and the solution was placed in a glass Petri dish. 5.0 parts of polyaspartic acid cross-linked particles 1 were weighed onto a stainless steel mesh, which was then immersed in the Petri dish for 60 seconds. The stainless steel mesh was slowly lifted, and the excess surface cross-linking treatment solution was filtered. This resulted in a mixture in which the surface cross-linking treatment solution adhered to the surface of polyaspartic acid cross-linked particles 1. The mixture was then heated at 140°C for 40 minutes to obtain surface-cross-linked polyaspartic acid cross-linked particles.

[0137] Examples 2 to 9 The surface-crosslinked polyaspartic acid crosslinked particles of Examples 2 to 9 were obtained in the same manner as in Example 1, except that the composition of the surface-crosslinking treatment solution, and the heat treatment temperature and heating time were changed as shown in Tables 1 and 2.

[0138] <Comparative Examples 1 to 3> In Comparative Examples 1 to 3, polyaspartic acid crosslinked particles 1 to 3, which had not been subjected to a surface crosslinking treatment, were used, respectively.

[0139] [Table 1]

[0140] [Table 2]

[0141] (Examples 10 to 20, Comparative Examples 4 to 9) In Examples 10 to 20 and Comparative Examples 8 and 9, surface crosslinking was carried out by Treatment Method B.

[0142] Example 10 5.0 parts of 10.0 parts of crosslinked polyaspartic acid particles 1 were weighed into a glass container. 0.2 parts of a multifunctional epoxy compound (Denacol EX-810, Nagase ChemteX Corporation) and 0.2 parts of ion-exchanged water were mixed to prepare a surface crosslinking treatment liquid. The surface crosslinking treatment liquid was added to the crosslinked polyaspartic acid particles 1 and mixed until uniform. This resulted in a mixture in which the surface crosslinking treatment liquid adhered to the surfaces of the crosslinked polyaspartic acid particles 1. Next, the mixture was heated at 140°C for 40 minutes to obtain surface-crosslinked crosslinked polyaspartic acid particles.

[0143] Examples 11 to 20 Surface-crosslinked polyaspartic acid crosslinked particles of Examples 11 to 20 were obtained in the same manner as in Example 10, except that the composition of the surface-crosslinking treatment solution, and the heat treatment temperature and heating time were changed as shown in Tables 3 and 4.

[0144] <Comparative Examples 4 to 6> In Comparative Examples 4 to 6, polyaspartic acid crosslinked particles 1 to 3, which had not been subjected to a surface crosslinking treatment, were used, respectively.

[0145] Comparative Examples 7 and 8 Surface-crosslinked polyaspartic acid crosslinked particles of Comparative Examples 7 and 8 were obtained in the same manner as in Example 10, except that the composition of the surface-crosslinking treatment solution, and the heat treatment temperature and heating time were changed as shown in Table 5.

[0146] [Table 3]

[0147] [Table 4]

[0148] [Table 5]

[0149] The abbreviations in Tables 1 to 3 above represent the following components. (pAsp)-1: the above-mentioned polyaspartic acid crosslinked particle 1 (pAsp)-2: The above polyaspartic acid crosslinked particle 2 (pAsp)-3: The above polyaspartic acid crosslinked particle 3 (E)-1: Multifunctional epoxy compound (Denacol (registered trademark) EX-810, Nagase ChemteX Corporation) (E)-2: Multifunctional epoxy compound (Denacol (registered trademark) EX-313, Nagase ChemteX Corporation) (E)-3: Multifunctional epoxy compound (Denacol (registered trademark) EX-614B, Nagase ChemteX Corporation) (A)-1: Lysine-added polyaspartic acid synthesized in Synthesis Example 2 (aqueous solution with a solid content of 40%) (A)-2: Polyethyleneimine (Epomin® HM-2000, Nippon Shokubai Co., Ltd.) (S)-1: Silane coupling agent (amine-modified silicone; KBE-9007, Shin-Etsu Chemical Co., Ltd.) (S)-2: Modified silicone oil (3-isocyanatepropyltriethoxysilane; KF-880, Shin-Etsu Chemical Co., Ltd.) DW: Ion-exchanged water EtOH: ethanol PG: Propylene glycol IPA: Isopropyl alcohol

[0150] [evaluation] The surface-crosslinked polyaspartic acid crosslinked particles or polyaspartic acid crosslinked particles of Examples 1 to 19 and Comparative Examples 1 to 8 were used as water-absorbent resin particles, and the water retention, liquid permeability, and moisture absorption blocking resistance were measured by the methods described above. The results are shown in Tables 6 to 11. Tables 6 to 11 also show the polyaspartic acid crosslinked particles, surface crosslinking agents, and surface crosslinking treatment methods used.

[0151] [Table 6]

[0152] [Table 7]

[0153] [Table 8]

[0154] [Table 9]

[0155] [Table 10]

[0156] [Table 11]

[0157] For moisture-absorbing resin particles, a water retention of 25 g / g or more, a liquid permeability of 3 g / min or more, and a moisture absorption blocking resistance of A can be considered to have good performance. The surface-crosslinked polyaspartic acid crosslinked particles of Examples 1 to 19 satisfied all of the above performance standards, whereas the surface-crosslinked polyaspartic acid crosslinked particles or polyaspartic acid crosslinked particles of Comparative Examples 1 to 8 did not satisfy one or more of the above performance standards. [Industrial Applicability]

[0158] According to the present invention, there are provided surface-crosslinked polyaspartic acid crosslinked particle having good water retention, liquid permeability, and moisture absorption blocking resistance, a water-absorbing agent containing the surface-crosslinked polyaspartic acid crosslinked particle, and an absorbent body and an absorbent article containing the water-absorbing agent.

Claims

1. Surface-crosslinked polyaspartic acid crosslinked particles, the surfaces of which contain at least one selected from the group consisting of crosslinked polyaspartic acids and salts thereof, are surface-crosslinked with a surface crosslinking agent, The surface cross-linking agent comprises a multifunctional epoxy compound. Surface-crosslinked polyaspartic acid particles.

2. The crosslinked polyaspartic acid has an amino group, the surface crosslinking includes a structure in which the amino group and the epoxy group of the polyfunctional epoxy compound are bonded together; The surface-crosslinked polyaspartic acid crosslinked particle according to claim 1 .

3. the surface cross-linking agent further comprises a polyfunctional amine compound, the surface crosslinking comprises a structure in which an epoxy group of the polyfunctional epoxy compound and an amino group of the polyfunctional amine compound are bonded to each other; 3. The surface-crosslinked polyaspartic acid crosslinked particle according to claim 1 or 2.

4. The polyfunctional amine compound includes at least one selected from the group consisting of a polyaspartic acid derivative in which a polyfunctional amine compound is bonded to polyaspartic acid, and polyethyleneimine. The surface-crosslinked polyaspartic acid crosslinked particles according to claim 3 .

5. The polyaspartic acid crosslinked product has a structure in which polyaspartic acid is crosslinked with lysine and a polyfunctional epoxy compound.

3. The surface-crosslinked polyaspartic acid crosslinked particle according to claim 1 or 2.

6. the ratio of the polyfunctional epoxy compound to 10 parts by mass of the crosslinked polyaspartic acid particles is 0.001 to 1 part by mass; 3. The surface-crosslinked polyaspartic acid crosslinked particle according to claim 1 or 2.

7. A water-absorbing agent comprising the surface-crosslinked polyaspartic acid crosslinked particles according to claim 1 or 2.

8. The water-absorbing agent according to claim 7, a fiber layer containing fibrous material; An absorbent comprising:

9. A liquid-impermeable sheet, the absorbent body according to claim 8, and a liquid-permeable sheet, The liquid-impermeable sheet, the absorbent body, and the liquid-permeable sheet are arranged in this order. Absorbent articles.

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