JP2016121287A - Water-absorbing resin and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a water-absorbing resin which is formed of a cross-linked body of γ-polyglutamic acid partially neutralized product and is excellent in a saturation absorption amount and an absorption amount under load.SOLUTION: A water-absorbing resin includes a cross-linked body in which γ-polyglutamic acid partially neutralized product is crosslinked with a polyvalent glycidyl compound. The γ-polyglutamic acid constituting the γ-polyglutamic acid partially neutralized product is γ-polyglutamic acid which is prepared by cultivation of Bacillus natto and has a weight average molecular weight of 1,000,000 to 30,000,000, and pH of the γ-polyglutamic acid partially neutralized product is 3.5-6.8.SELECTED DRAWING: None

Description

  The present invention relates to a water absorbent resin using γ-polyglutamic acid (hereinafter referred to as “γ-PGA”).

  Since the water-absorbent resin can absorb water several hundred times its own weight and can retain the absorbed water, the water-absorbing resin is used for various applications taking advantage of such characteristics. As such a water-absorbing resin, Patent Documents 1 to 5 propose using a polyamino acid as a raw material.

  In Patent Literature 1 and Patent Literature 3, γ-PGA described in Patent Literature 6 is used (see Patent Literature 1 (paragraph [0010])). Note that γ-PGA according to Patent Document 6 has a molecular weight of 500 to 1,000,000 (see Patent Document 6 (page 3, lower left column, lines 14 and 15)). As the water-absorbent resin of Patent Document 2, polyaspartic acid having a molecular weight of 200,000 is used (see Patent Document 2 (paragraph [0053])). Patent Document 4 describes that the number average molecular weight of the polyamino acid is preferably 3,000 to 2,000,000, and the weight average molecular weight is preferably 6,000 to 4,000,000, but the molecular weight of what is used in the examples is not described (patent Reference 4 (see paragraphs [0025] and [0030])). Patent Document 5 does not describe the molecular weight of the polyamino acid.

  In addition to Patent Document 6, a technique related to γ-PGA has been proposed. For example, Patent Document 7 describes γ-PGA having an average molecular weight of 5000 kDa or more produced by a salt-tolerant strain, Bacillus subtilis var. Chungkokjang, KCTC0697BP.

Japanese Patent No. 2005-179534 JP-A-10-298282 JP-A-11-343339 Japanese Patent Laid-Open No. 10-330478 JP 2001-131283 A Japanese Patent Laid-Open No. 1-174397 JP 2008-202043 A

  Conventionally, water-absorbing resins using polyamino acids as raw materials have been proposed, but all use γ-PGA having a low molecular weight as a raw material. When γ-PGA having a small molecular weight is used as described above, the absorption capacity under load and the saturated absorption capacity of the resulting water-absorbent resin tend to be inferior. Even when γ-PGA having a small molecular weight is used, the amount of absorption under load can be increased by increasing the crosslinking density. However, when the crosslinking density is increased, the saturated absorption amount tends to decrease. This invention is made | formed in view of the said situation, and consists of the bridge | crosslinking body of the partially neutralized substance of (gamma) -PGA, and aims at providing the water absorbing resin excellent in the absorption amount under load and the saturated absorption amount. .

  The water-absorbent resin of the present invention that has been able to solve the above problems comprises a crosslinked product obtained by crosslinking a partially neutralized product of γ-PGA with a polyvalent glycidyl compound, and constitutes the partially neutralized product of γ-PGA. γ-PGA is a γ-PGA having a weight average molecular weight of 1,000,000 to 30,000,000 produced by culture of Bacillus natto, and the pH of the partially neutralized product of γ-PGA is 3.5 to 6.8. It is characterized by being.

  Using γ-PGA having a weight average molecular weight of 1,000,000 to 30,000,000 produced by culture of Bacillus natto, the pH of the partially neutralized product of γ-PGA is adjusted to 3.5 to 6.8. The obtained water-absorbent resin can obtain a sufficient amount of absorption and saturation absorption under load.

  The cationic component of the partially neutralized product of γ-PGA is preferably sodium and / or potassium, more preferably sodium. The polyvalent glycidyl compound is preferably a divalent glycidyl compound. The crosslinked body constituting the water-absorbent resin of the present invention is preferably subjected to surface crosslinking treatment with a surface crosslinking agent. The surface cross-linking agent is preferably a glycidyl ether compound, and more preferably polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, or polyglycerin diglycidyl ether. The water-absorbing resin of the present invention preferably has a saturated absorption of 30 g / g to 100 g / g and an absorption under load of 7 g / g to 30 g / g.

  In the present invention, a step of producing γ-PGA having a weight average molecular weight of 1,000,000 to 30,000,000 by culturing Bacillus natto; the γ-PGA and a cation source are mixed, and the pH is 3.5 to 6. And a step of obtaining a partially neutralized product of γ-PGA of 8; and a step of producing a crosslinked product by crosslinking the partially neutralized product of γ-PGA with a polyvalent glycidyl compound. included.

  ADVANTAGE OF THE INVENTION According to this invention, it consists of the bridge | crosslinking body of the partially neutralized substance of (gamma) -PGA, and the water absorbing resin excellent in the saturated absorption amount and the absorption amount under load is obtained.

[Water absorbent resin]
The water-absorbent resin of the present invention comprises a crosslinked product obtained by crosslinking a partially neutralized γ-PGA with a polyvalent glycidyl compound. The γ-PGA constituting the partially neutralized product of γ-PGA is a γ-PGA having a weight average molecular weight of 1,000,000 to 30,000,000 produced by culture of Bacillus natto, and the γ-PGA part. The neutralized product has a pH of 3.5 to 6.8.

(Γ-PGA)
The partially neutralized product of γ-PGA will be described. The γ-PGA is preferably obtained by culturing Bacillus natto.

  The microorganism producing γ-PGA is not particularly limited as long as it is a microorganism producing γ-PGA having a weight average molecular weight of 1 million or more. For example, Bacillus subtilis, Bacillus anthracis, Bacillus licheniformis, Bacillus megaterium, Bacillus subtilis var. Chungkookjang, Bacillus halodurans, Bacillus subtilis var. Further, Bacillus subtilis var. Natto, and Bacillus natto used in the production of commercially available natto, can be obtained from these natto bacterium manufacturers.

  The γ-PGA has a weight average molecular weight (Mw) of preferably 1 million or more, more preferably 2 million or more, further preferably 2.3 million or more, particularly preferably 2.5 million or more, and preferably 30 million or less. More preferably, it is 20 million or less, More preferably, it is 13 million or less. If the weight average molecular weight is 1 million or more, the synthesized water-absorbing resin has sufficient absorption and saturated absorption under load, and if it is 30 million or less, the viscosity of the aqueous solution does not become too high. Can be done easily.

  In the γ-PGA, the proportion of molecules having a molecular weight of 1 million or more is preferably 80% by mass or more, more preferably 90% by mass or more, and still more preferably 95% by mass or more. The γ-PGA preferably has a molecular weight of less than 600,000, preferably 20% by mass or less, more preferably 10% by mass or less, and still more preferably 5% by mass or less.

  The cationic component constituting the partially neutralized product of γ-PGA is not particularly limited. The cation component may be any of ammonium ion, metal ion, and organic cation. Examples of metal ions include monovalent metal ions such as lithium, sodium, potassium, rubidium, cesium, francium, silver; beryllium, magnesium, calcium, strontium, barium, zinc, cadmium, copper, cobalt, nickel, manganese, and the like And divalent metal ions such as aluminum and iron; and other ions such as tin, zirconium and titanium. As said metal ion, a sodium ion and a potassium ion are preferable. The metal ions may be used alone or as a mixture of two or more.

  The organic cation is a cation having a carbon chain. The organic cation is not particularly limited, and examples thereof include organic ammonium ions. Examples of the organic ammonium ion include primary ammonium ions such as stearyl ammonium ion, hexyl ammonium ion, octyl ammonium ion, and 2-ethylhexyl ammonium ion, and secondary such as dodecyl (lauryl) ammonium ion and octadecyl (stearyl) ammonium ion. Ammonium ion; tertiary ammonium ion such as trioctyl ammonium ion; quaternary ammonium ion such as dioctyl dimethyl ammonium ion and distearyl dimethyl ammonium ion. These organic cations may be used alone or in combination of two or more.

  The pH of the partially neutralized product of γ-PGA is 3.5 or more, preferably 3.6 or more, more preferably 3.7 or more, 6.8 or less, preferably 6.7 or less, more preferably 6.6 or less. When the pH of the partially neutralized product of γ-PGA is less than 3.5 or more than 6.8, sufficient absorption under load and saturated absorption cannot be obtained for the synthesized water absorbent resin. The pH of γ-PGA can be adjusted by the amount of cationic component used or by dialysis. The pH of unneutralized γ-PGA is 3.3.

(Polyvalent glycidyl compound)
The crosslinked body constituting the water-absorbent resin of the present invention is obtained by crosslinking a partially neutralized product of γ-PGA with a polyvalent glycidyl compound. The polyvalent glycidyl compound is not particularly limited as long as it has two or more glycidyl groups in the molecule. Examples of the polyvalent glycidyl compound include ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, glycerol polyglycidyl ether, diglycerol polyglycidyl ether, polyethylene diglycidyl ether, polyglycerol polyglycidyl ether, polypropylene glycol diglycidyl ether, and the like. And divalent glycidyl compounds such as glycerin triglycidyl ether and polyglyceryl polyglycidyl ether. The said polyvalent glycidyl compound may be used independently and may use 2 or more types together. Among these, as the polyvalent glycidyl compound, a divalent or trivalent glycidyl compound is preferable, and a divalent glycidyl compound is more preferable.

(Additive)
The water-absorbent resin may contain additives such as preservatives, fungicides, antibacterial agents, antioxidants, ultraviolet absorbers, colorants, fragrances, deodorants, inorganic powders, and organic fibrous materials. When the additive is contained, the content of the additive in the crosslinked body is preferably 0.001% by mass or more, more preferably 0.01% by mass or more, still more preferably 0.05% by mass or more, particularly preferably. Is 0.1% by mass or more, preferably 10% by mass or less, more preferably 5% by mass or less, still more preferably 1% by mass or less, and particularly preferably 0.5% by mass or less.

(Surface cross-linking agent)
The crosslinked body is preferably subjected to a surface crosslinking treatment with a surface crosslinking agent. By performing the surface crosslinking treatment, the water absorption performance can be further improved. Examples of the surface cross-linking agent used in the surface cross-linking treatment include compounds having two or more functional groups capable of reacting with a carboxy group and a carboxylate group, such as a glycidyl ether compound, a haloepoxy compound, and an aldehyde compound. It is done. Among these, diglycidyl ether compounds such as polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, and polyglycerin diglycidyl ether are suitable. In particular, diethylene glycol diglycidyl ether is used as a carboxylate group in the water absorbent resin. Most suitable due to reactivity.

  The addition amount of the surface cross-linking agent is usually 10 ppm to 100,000 ppm, preferably 50 ppm to 5000 ppm with respect to the cross-linked product.

(Surface modifier)
The crosslinked body may be further treated with a surface modifier. Surface modifiers include aluminum sulfate, potassium alum, ammonium alum, sodium alum, (poly) aluminum chloride, polyvalent metal compounds such as hydrates thereof; polycation compounds such as polyethyleneimine, polyvinylamine, polyallylamine Inorganic fine particles; surface modifiers containing hydrocarbon groups; surface modifiers containing hydrocarbon groups having fluorine atoms; and surface modifiers having a polysiloxane structure.

  The shape of the crosslinked body is not particularly limited, but is preferably particulate. What is necessary is just to adjust the weight average particle diameter of the said crosslinked body suitably according to the use of water absorbing resin.

  For example, when a water absorbent resin is used for an absorbent article, the weight average particle diameter (μm) of the crosslinked body is preferably 100 μm or more, more preferably 200 μm or more, still more preferably 250 μm or more, particularly preferably 300 μm or more. It is preferably 800 μm or less, more preferably 700 μm or less, still more preferably 600 μm or less, and particularly preferably 500 μm or less. When the weight average particle diameter (μm) of the water absorbent resin particles is within the above range, the absorption performance is further improved. In addition, the weight average particle diameter was measured using a low-tap test sieve shaker and a standard sieve (JIS Z8801-1: 2006), Perry's Chemical Engineers Handbook, 6th edition (McGlow Hill Book Company, 1984). , Page 21). In the medical field, the agricultural field, the cosmetic field, the electrical / electronic field, the civil engineering field, etc., it may be preferable that the thickness is less than 100 μm.

  The saturated absorption amount of the water-absorbing resin is preferably 30 g / g or more, more preferably 33 g / g or more, still more preferably 35 g / g or more, preferably 100 g / g or less, more preferably 95 g / g or less, More preferably, it is 90 g / g or less. The saturated absorption amount is a scale indicating how much the water absorbent resin can absorb water.

  The absorption amount under load of the water absorbent resin is preferably 7 g / g or more, more preferably 8 g / g or more, and still more preferably 9 g / g or more. The amount of absorption under load is absorbed in a state where a predetermined load is applied to the water absorbent resin. It is a scale showing how much water can be absorbed under load.

  The water retention amount of the water-absorbent resin is preferably 20 g / g or more, more preferably 22 g / g or more, still more preferably 25 g / g or more, preferably 90 g / g or less, more preferably 85 g / g or less, Preferably it is 80 g / g or less. The water retention amount is a scale indicating how much the liquid absorbed by the water absorbent resin can be retained. When the water retention amount is 20 g / g or more, the body fluid retention capacity can be maintained at a predetermined level with a small amount of water-absorbing resin.

[Method for producing water-absorbing resin]
Hereinafter, the manufacturing method of a water absorbing resin is demonstrated. The method for producing a water absorbent resin of the present invention comprises a step of producing a partially neutralized product of γ-PGA (generation step); the γ-PGA and a cation source and / or anion source are mixed, A step of adjusting the pH of the partially neutralized product (pH adjusting step); and a step of crosslinking the partially neutralized product of γ-PGA with a polyvalent glycidyl compound to produce a crosslinked product (crosslinking step).

(Generation process)
In the step of producing γ-PGA, γ-PGA having a weight average molecular weight of 1 million to 30 million is produced by culturing natto bacteria.

  The culture method of Bacillus natto is not particularly limited as long as Bacillus natto can produce γ-PGA, but liquid culture is preferable for easily recovering γ-PGA.

  As a medium used for culturing Bacillus natto, a medium containing a carbon source, a nitrogen source, inorganic salts, and other necessary nutrient sources is used. Examples of the carbon source include saccharides (such as glucose). Examples of the nitrogen source include amino acids and salts thereof (such as glutamic acid and sodium glutamate), peptides and salts thereof (such as soybean peptide), and the like. Examples of inorganic salts include sodium chloride and magnesium sulfate heptahydrate. Examples of nutrient sources include phosphates (disodium hydrogen phosphate, 12 hydrate, potassium dihydrogen phosphate, etc.) and vitamins (biotin, etc.). A partially neutralized product of γ-PGA having a pH of 3.5 to 6.8 can also be obtained by adding a cation source to the medium. In this case, a pH adjustment step described later can be omitted.

  The culture temperature is preferably 30 ° C or higher, more preferably 35 ° C or higher, still more preferably 40 ° C or higher, preferably 50 ° C or lower, more preferably 45 ° C or lower. It is also preferable to perform the culture at a culture temperature of 40 ° C. to 50 ° C. and change the culture temperature to less than 40 ° C. during the culture. By changing the culture temperature to less than 40 ° C. during the culture, production of γ-PGA degrading enzyme can be suppressed. Examples of the time for changing the culture temperature to less than 40 ° C. include the middle to late phase of the logarithmic growth phase.

(PH adjustment step)
In the pH adjustment step, γ-PGA or a partially neutralized product thereof and a cation source and / or anion source are mixed, or the partially neutralized product of γ-PGA is dialyzed to have a pH of 3.5 to 6. 8 partially neutralized γ-polyglutamic acid is obtained. The partially neutralized product of γ-PGA may be mixed with a cation source and / or an anion source after dialysis. Specifically, a method of mixing γ-PGA and a cation source; a method of mixing a partially neutralized product of γ-PGA and an anion source; And a method of mixing γ-PGA after acid dialysis and then mixing with a cation source.

  Examples of the method for mixing the γ-PGA with the cation source and / or the anion source include a method for mixing the γ-PGA with the cation source and / or the anion source in the presence of a solvent. Examples of the solvent include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylmorpholine, and mixtures thereof. The amount of the cation source used is preferably 0.1 equivalents or more and less than 10 equivalents with respect to 1 equivalent of carboxylic acid contained in γ-PGA.

  Examples of the cation source include compounds containing the cation component. Examples of such a cation source include metal hydroxides, metal carbonates, and organic acid salts containing the metal ions. Examples of the metal hydroxide include lithium hydroxide, sodium hydroxide, potassium hydroxide and the like. Examples of the metal carbonate include sodium carbonate and potassium carbonate. Examples of the organic acid salt include sodium citrate, sodium lactate, sodium tartrate, and sodium fumarate. Examples of the anion source include inorganic acids and organic acids. Examples of the inorganic acid include hydrochloric acid, sulfuric acid, nitric acid and the like. Examples of the organic acid include citric acid.

  The method for dialyzing the partially neutralized product of γ-PGA is not particularly limited. For example, after an aqueous solution of the partially neutralized product of γ-PGA is put into a dialysis membrane tube, the dialysis membrane tube is deionized water or an acidic solution. The method of immersing in is mentioned. As the dialysis membrane, one that can pass a cation component without passing γ-PGA molecules can be used. Examples of the acidic solution include hydrochloric acid, sulfuric acid, and nitric acid.

(Crosslinking process)
In the step of producing a crosslinked product, the partially neutralized product of γ-PGA is crosslinked with a polyvalent glycidyl compound. A method for performing the crosslinking reaction is not particularly limited, and examples thereof include a method in which γ-PGA and a polyvalent glycidyl compound are mixed and heated in the presence of a solvent. The solvent is not particularly limited as long as it dissolves or disperses the glycidyl compound. For example, water, alcohol solvents (for example, methanol, ethanol, isopropanol, ethylene glycol, glycerin, etc.), ketone solvents (for example, acetone, Methyl ethyl ketone, methyl isobutyl ketone, etc.), ether solvents (eg, ethyl cellosolve, tetrahydrofuran, propylene glycol monomethyl ether, etc.), amide solvents (eg, dimethylformamide, dimethylacetamide, N-methylmorpholine, etc.), sulfoxide solvents (eg, , Dimethyl sulfoxide and the like) and mixtures thereof. It is also preferable to use a buffer as a solvent. Buffers include citrate buffer (mixed solution of citrate and sodium citrate), acetate buffer (mixed solution of acetic acid and sodium acetate), phosphate buffer (mixed of phosphate and sodium phosphate) Solution).

  As a mixing method, after dissolving γ-PGA in a solvent, a method of adding a polyvalent glycidyl compound to the γ-PGA solution; after dissolving γ-PGA and a polyvalent glycidyl compound in separate solvents, And a method of mixing these solutions. Particularly preferred is a method in which γ-PGA is dissolved in a buffer solution, and this γ-PGA solution and an aqueous solution of a polyvalent glycidyl compound are mixed.

  The blending amount of the polyvalent glycidyl compound is preferably 0.5 parts by mass or more, more preferably 1.5 parts by mass or more, further preferably 2.0 parts by mass or more, with respect to 100 parts by mass of γ-PGA. 115 parts by mass or less is preferable, more preferably 55 parts by mass or less, and still more preferably 15 parts by mass or less. If the blending amount of the polyvalent glycidyl compound is 0.5 parts by mass or more, the absorbed amount and the saturated absorption amount of the synthesized water absorbent resin are improved, and if it is 115 parts by mass or less, the synthesized water absorbent resin is excessive. The occurrence of internal crosslinking is suppressed.

  The pH of the reaction solution during the crosslinking reaction is preferably 3.5 or more, more preferably 4.0 or more, still more preferably 5.0 or more, and preferably 6.8 or less, more preferably 6.7. Hereinafter, it is more preferably 6.6 or less. If the pH of the reaction solution is less than 3.5 or more than 6.8, the synthesized water-absorbent resin has poor absorption and saturation absorption under load. The pH of the reaction solution can be measured with a pH meter (Model “HI-98109” manufactured by HANNA).

  The temperature of the reaction solution during the crosslinking reaction is preferably 60 ° C. or higher, more preferably 70 ° C. or higher, further preferably 80 ° C. or higher, preferably 120 ° C. or lower, more preferably 110 ° C. or lower, and still more preferably. It is 100 degrees C or less. The reaction time is preferably 0.5 hours or more, more preferably 0.75 hours or more, further preferably 1 hour or more, preferably 80 hours or less, more preferably 24 hours or less, still more preferably 6 hours or less. .

  After the crosslinking reaction, an excess solvent is removed from the reaction solution to obtain a crosslinked hydrous gel. The hydrous gel is composed of a crosslinked body and water. The water content of the hydrogel is not particularly limited, but is usually 30% by mass to 99.9% by mass. The hydrogel can be shredded as necessary. The size (longest diameter) of the gel after shredding is preferably 50 μm to 10 cm, more preferably 100 μm to 2 cm, and even more preferably 1 mm to 1 cm. Within this range, the drying property in the drying process is further improved. Shredding can be performed by a known method. For example, the shredding can be performed using a conventional shredding device such as a Bex mill, a rubber chopper, a pharma mill, a mincing machine, an impact grinder, and a roll grinder.

  When a solvent (such as an organic solvent or water) is used for the crosslinking reaction, the solvent is distilled off after the reaction to obtain a dried product of the crosslinked product. As a method of distilling off the solvent (including water), a method of distilling (drying) with hot air at a temperature of 80 ° C. to 230 ° C., a thin film drying method using a drum dryer heated to 100 ° C. to 230 ° C., etc. (Heating) A vacuum drying method, a freeze drying method, a drying method using infrared rays, decantation, filtration, and the like can be applied. Furthermore, after dehydrating using a hydrophilic solvent such as methanol or ethanol, it may be dried by the above method.

  The dried product of the crosslinked product can be pulverized. The pulverization method is not particularly limited, and for example, a normal pulverizer such as a hammer pulverizer, an impact pulverizer, a roll pulverizer, and a shet airflow pulverizer can be used. The pulverized crosslinked product can be adjusted in particle size by sieving or the like, if necessary.

  The cross-linked product may be subjected to surface cross-linking treatment as necessary. In the case of subjecting the crosslinked body to a surface crosslinking treatment, the surface crosslinking treatment can be achieved by a method of spraying or impregnating the crosslinked body with an aqueous solution containing a surface crosslinking agent and then performing a heat treatment.

  The surface cross-linking treatment is preferably performed by reacting the cross-linked product with the surface cross-linking agent in the presence of water and a water-soluble leveling agent. By using the water-soluble leveling agent, the surface crosslinking agent can be more uniformly dispersed on the surface of the crosslinked body. Therefore, the surface of the crosslinked body can be more uniformly surface-crosslinked. Examples of such a method include a method of spraying or impregnating a crosslinked body with a solution containing a surface crosslinking agent, a water-soluble leveling agent and water and then heat-treating; a liquid containing a surface crosslinking agent and a water-soluble leveling agent Is sprayed onto a crosslinked product containing water, followed by heat treatment.

  The amount of the surface crosslinking agent used is preferably 0.005 parts by mass or more, more preferably 0.008 parts by mass or more, and still more preferably 0.01 parts by mass or more with respect to 100 parts by mass of the crosslinked product. 0.5 mass part or less is preferable, More preferably, it is 1.2 mass parts or less, More preferably, it is 1.0 mass part or less. If the blending amount of the polyvalent glycidyl compound is in the range of 0.005 to 1.5 parts by mass, gel blocking can be prevented and a sufficient absorption amount can be obtained.

  The water-soluble leveling agent is not particularly limited as long as it can dissolve the surface crosslinking agent and is not substantially absorbed by the crosslinked body. Examples of the water-soluble leveling agent include alcohols such as methanol, ethanol, and isopropanol. The amount of the water-soluble leveling agent used is preferably 0.05 parts by mass or more, more preferably 0.08 parts by mass or more, still more preferably 0.1 parts by mass or more, based on 100 parts by mass of the water absorbent resin. The amount is preferably at most 10 parts by mass, more preferably at most 13 parts by mass, even more preferably at most 10 parts by mass.

  The heating temperature in the surface cross-linking treatment is preferably 30 ° C. or higher, more preferably 40 ° C. or higher, 150 ° C. or lower, more preferably 130 ° C. or lower. The heating time is preferably 10 minutes or longer, more preferably 20 minutes or longer, preferably 60 minutes or shorter, more preferably 40 minutes or shorter.

  The surface of the crosslinked body may be treated with a surface modifier as necessary. The method for treating with the surface modifier is not particularly limited as long as the method is performed so that the surface modifier is present on the surface of the crosslinked body. However, the surface modifier is not a water-containing gel of the cross-linked polymer or a polymer solution before polymerizing the cross-linked polymer, but is mixed with the dried product of the cross-linked polymer to control the amount of the surface modifier. It is preferable from the viewpoint. The mixing is preferably performed uniformly. When performing the surface treatment, it is preferable to adjust the water content of the crosslinked product to 15% by mass to 25% by mass.

  The water-absorbent resin of the present invention can be used in hygiene fields such as disposable diapers, sanitary napkins, incontinence pads, medical fields, agricultural fields, cosmetics fields, electrical / electronic fields, civil engineering fields, and the like.

  Hereinafter, the present invention will be described in detail by way of examples. However, the present invention is not limited to the following examples, and all modifications and embodiments without departing from the gist of the present invention are not limited thereto. Included in range.

1. Evaluation method 1-1. Weight average molecular weight The weight average molecular weight of (gamma) -polyglutamic acid was measured on condition of the following using gel permeation chromatography (GPC).
measuring device;
Pump: PU-2089 Plus (manufactured by JASCO)
Degasser: PU-2089 Plus (manufactured by JASCO)
Mixer: PU-2089 Plus (manufactured by JASCO)
Autosampler: AS-2057 Plus (manufactured by JASCO)
Column oven: CO-2065 Plus (manufactured by JASCO)
Detector: RI-2031 Plus (manufactured by JASCO)
Analysis software: ChromNAV (manufactured by JASCO)
Measurement condition;
Column used: TSKgel GMPW _XL (7.8 mm ID × 30 cm) (manufactured by Tosoh Corporation)
Column temperature: 40 ° C
Detection method: differential refractometer (RI detector), multi-angle light scattering detector (MALS)
Mobile phase: 50 mM phosphate buffer (pH = 8.0)
Sample concentration: 0.5 mg / mL
Sample volume: 100 μL
Calibration curve; pullulan

1-2. pH of partially neutralized product of γ-PGA
The pH of the partially neutralized product of γ-PGA is such that γ-PGA is dissolved in water, and the pH of this γ-PGA solution (concentration: 1.0% by mass) is adjusted to a pH meter (Model “HI-98109” manufactured by HANNA). Measured with

1-3. Saturated absorption amount The saturated absorption amount was measured according to JIS K7223 (1996). Nylon mesh (JIS Z8801-1 (2000)) with a mesh size of 63 μm is cut into a rectangle with a width of 10 cm and a length of 40 cm, folded in half at the center in the longitudinal direction, and both ends are heat-sealed to give a width of 10 cm (inner size: 9 cm), A nylon bag having a length of 20 cm was produced. 1.00 g of a measurement sample was precisely weighed and placed uniformly at the bottom of the produced nylon bag. The nylon bag containing the sample was immersed in physiological saline. After 60 minutes from the start of soaking, the nylon bag was taken out from the physiological saline, and the mass R1 (g) after being drained by hanging in a vertical state for 1 hour was measured. Further, the same operation was performed without using a sample, and the mass R0 (g) at that time was measured. And the target saturated absorption amount was computed from these mass R1, R0 and the mass of the sample according to following Formula.
Saturated absorption (g / g) = (R1-R0-mass of sample) / mass of sample

1-4. Absorption under load Weigh 0.1 g of measurement sample in a cylindrical plastic tube (inner diameter 30 mm, height 60 mm) with a nylon mesh with a mesh opening of 63 μm (conforming to JIS Z8801-1 (2006)) on the bottom. The measurement sample was arranged on the nylon net with a vertical tube so that the thickness was almost uniform, and a weight of 29.5 mm × 22 mm in outer diameter was placed on the measurement sample so that a load of 60 g / cm ² was applied. . In a petri dish (diameter: 12 cm) containing 60 ml of physiological saline (salt concentration 0.9%), place a plastic tube containing a measurement sample and a weight vertically, immerse the nylon mesh side on the bottom, and let it stand, After 10 minutes, the plastic tube containing the sample and the weight is weighed, the weight of the measurement sample absorbed by the physiological saline is calculated, and the weight increased by 10 times the increased weight under the load with respect to the physiological saline (g / G). The physiological saline used and the temperature of the measurement atmosphere were 25 ° C. ± 2 ° C.

1-5. Water retention amount The water retention amount was measured according to JIS K 7223 (1996). Nylon mesh (JIS Z8801-1 (2000)) with a mesh size of 63 μm is cut into a rectangle with a width of 10 cm and a length of 40 cm, folded in half at the center in the longitudinal direction, and both ends are heat-sealed to give a width of 10 cm (inner size: 9 cm), A nylon bag having a length of 20 cm was produced. 1.00 g of a measurement sample was precisely weighed and placed uniformly at the bottom of the produced nylon bag. The nylon bag containing the sample was immersed in physiological saline. After 60 minutes from the start of immersion, the nylon bag was taken out from the physiological saline, suspended in a vertical state for 1 hour, drained, and then dehydrated using a centrifugal dehydrator (Kokusan Co., Ltd., model H-130C special model). The dehydrating condition was 143 G (800 rpm) for 2 minutes. The mass F1 (g) of the sample after dehydration was measured. Moreover, the same operation was performed without using a sample, and the mass F0 (g) at that time was measured. And from these masses F1 and F0 and the mass of the sample, the target absorption ratio was calculated according to the following equation.
Water retention amount (g / g) = (F1-F0) / sample mass

1-6. Absorption speed under no load, reversal amount A cylindrical tube (inner diameter 60 mm, height 50 mm) was installed in a portion corresponding to the center of the absorbent body on the top sheet of the absorbent article. 80 mL of physiological saline (saline concentration: 0.9%) was injected into this cylindrical tube over 10 seconds. The time from the start of physiological saline injection until the physiological saline was absorbed by the absorbent article and disappeared from the cylindrical tube was measured. This measured time was defined as an absorption rate (seconds) under no load.

  Next, 5 minutes after starting the injection of physiological saline, the cylindrical tube was removed from the absorbent article, and a filter paper (size 100 mm × 100 mm) whose mass was measured in advance was placed on the absorbent article. A weight (size 100 mm × 100 mm, weight 3.5 kg) was placed on the filter paper. Three minutes after placing the weight, the weight was removed, and the mass of the filter paper was measured. And the return amount of the absorbent article was calculated from the mass before and after placing on the absorbent article.

  The injection and absorption of the physiological saline and the measurement of the amount of return to the filter paper after absorption of the physiological saline were performed three times, and the absorption rate (seconds) and the amount of return (g) in the third measurement were recorded. In each measurement, the interval from the start of physiological saline injection to the start of the next physiological saline injection was 10 minutes.

1-7. Absorption speed under load, reversal amount A cylindrical tube (inner diameter 60 mm, height 50 mm) was installed in a portion corresponding to the center of the absorbent body on the top sheet of the absorbent article. Moreover, the weight was installed so that the load of 60 g / cm < ² > might be applied to the part in which the said cylindrical tube of an absorber is not installed. 80 mL of physiological saline (salt concentration: 0.9%) was injected into the cylindrical tube over 10 seconds. The time from the start of physiological saline injection until the physiological saline was absorbed by the absorbent article and disappeared from the cylindrical tube was measured. This measured time was taken as the absorption rate under load (seconds).

  Next, 5 minutes after starting the injection of physiological saline, the cylindrical tube and the weight were removed from the absorbent article, and a filter paper (size 100 mm × 100 mm) whose mass was measured in advance was placed on the absorbent article. A weight (size 100 mm × 100 mm, weight 3.5 kg) was placed on the filter paper. Three minutes after placing the weight, the weight was removed, and the mass of the filter paper was measured. And the return amount of the absorbent article was calculated from the mass before and after placing on the absorbent article.

  The injection and absorption of the physiological saline and the measurement of the amount of return to the filter paper after absorption of the physiological saline were performed three times, and the absorption rate under load (seconds) and the amount of return (g) in the third measurement were recorded. In each measurement, the interval from the start of physiological saline injection to the start of the next physiological saline injection was 10 minutes.

2. Preparation of γ-PGA (1) In distilled water, glucose; 2.0% by mass, sodium glutamate; 5.0% by mass, soybean peptide; 0.2% by mass, disodium hydrogen phosphate 12 hydrate; 0 .42% by mass, potassium dihydrogen phosphate; 0.27% by mass, sodium chloride; 0.05% by mass, magnesium sulfate heptahydrate; 0.05% by mass, biotin; 0.0001% by mass A liquid medium (pH 6.4) was prepared. This liquid medium was inoculated with Bacillus subtilis var. Natto. The medium was stored at 37 ° C. for 4 days and cultured in liquid to obtain a Bacillus natto culture solution. Ethanol was added to 100 mL of the Bacillus natto culture solution to cause precipitation, and this precipitate was collected by filtration and dried under vacuum to obtain 1 g of a partially neutralized product of γ-PGA (1). Further, this partially neutralized product of γ-PGA (1) was placed in a dialysis tube (Dialysis Membranes size 36, manufactured by Wako Pure Chemical Industries, Ltd.) and dialyzed against deionized water for 10 days. The pH of the partially neutralized product of γ-PGA (1) obtained was 6.8, and the weight average molecular weight of γ-PGA (1) was 1.2 million (content of molecules having a molecular weight of 1 million or more, 92 mass%, molecular weight 100). The content of molecules less than 10,000 was 8% by mass).

3. 3. Synthesis of water absorbent resin powder 3-1. Water-absorbent resin powder No. 1
1 g of the partially neutralized product of γ-PGA (1) obtained above was dissolved in a citrate buffer (pH 5.3), and then the volume was adjusted to 100 mL with the same buffer to prepare a γ-PGA solution. The pH of the partially neutralized product of γ-PGA (1) in the γ-PGA solution after preparation was 5.3. 0.25 g of glycerol polyglycidyl ether (manufactured by Nagase ChemteX Corporation, “Denacol (registered trademark) EX-313”) was dissolved in deionized water, and the volume was adjusted to 100 mL to prepare a crosslinking agent solution. 9 parts by mass of the γ-PGA solution and 1 part by mass of the cross-linking agent solution were mixed, and the mixture was incubated at 80 ° C. for 1 hour. Thereafter, ethanol was added to the mixture to cause precipitation. The precipitate was collected and dried in vacuum to obtain a dried product of a crosslinked product.

  After the dried product of the crosslinked product was pulverized with a juicer mixer (Osterizer Blender, manufactured by Oster), a dried product powder was obtained by adjusting the particle size to 150 μm to 710 μm using a sieve having openings of 150 μm and 710 μm. .

  An ethylene glycol diglycidyl ether solution (ethylene glycol diglycidyl ether concentration; 2% by mass, solvent; water) while 100 parts by mass of the dry powder was stirred at high speed (manufactured by Hosokawa Micron Corporation, high-speed stirring turbulizer: rotation speed 2000 rpm). / Methanol weight ratio = 70/30) 5 parts by weight were added by spraying. Then, it left still for 30 minutes at 150 degreeC, and surface bridge | crosslinked. The weight average particle diameter of the obtained powder was adjusted to 400 μm, and the water absorbent resin powder No. 1 was obtained.

3-2. Water-absorbent resin powder No. 2
1 g of the partially neutralized product of γ-PGA (1) obtained above was dissolved in water and then made up to a volume of 100 mL with water to prepare a γ-PGA solution. 0.5 g of glycerol polyglycidyl ether (manufactured by Nagase ChemteX Corporation, “Denacol (registered trademark) EX-313”) was dissolved in deionized water, and the volume was adjusted to 100 mL to prepare a crosslinking agent solution. 9 parts by mass of the γ-PGA solution and 1 part by mass of the cross-linking agent solution were mixed, and the mixture was incubated at 80 ° C. for 1 hour. Thereafter, ethanol was added to the mixture to cause precipitation. The precipitate was collected and dried in vacuum to obtain a dried product of a crosslinked product.

  After the dried product of the crosslinked product was pulverized with a juicer mixer (Osterizer Blender, manufactured by Oster), a dried product powder was obtained by adjusting the particle size to 150 μm to 710 μm using a sieve having openings of 150 μm and 710 μm. .

  An ethylene glycol diglycidyl ether solution (ethylene glycol diglycidyl ether concentration; 2% by mass, solvent; water) while 100 parts by mass of the dry powder was stirred at high speed (manufactured by Hosokawa Micron Corporation, high-speed stirring turbulizer: rotation speed 2000 rpm) / Methanol weight ratio = 70/30) 5 parts by weight were added by spraying. Then, it left still for 30 minutes at 150 degreeC, and surface bridge | crosslinked. The weight average particle diameter of the obtained powder was adjusted to 400 μm, and the water absorbent resin powder No. 2 was obtained.

3-3. Water-absorbent resin powder No. 3
Commercially available water-absorbent resin powder (manufactured by Nippon Shokubai Co., Ltd., “AQUALIC (registered trademark) CA101”, polyacrylic acid base) was used.

3-4. Water-absorbent resin powder No. 4
Commercially available water-absorbent resin powder (manufactured by SDP Global, “Sunwet (registered trademark) IM720”, polyacrylic acid base) was used.

  Absorbent resin powder no. The evaluation results of 1 to 4 are shown in Table 1.

4). Production of Absorbent Article Absorbent Article No. 1
A synthetic rubber-based hot melt adhesive was applied on the liquid-impermeable sheet, and tissue paper was laminated thereon. After applying a synthetic rubber-based hot melt adhesive on the tissue paper, pulp and water-absorbing resin powder No. 1 were used. 1 in a mixed state (weight of pulp 200 g / m ² , weight of water-absorbent resin powder 200 g / m ² ), and a synthetic rubber-based hot melt adhesive is applied thereon, and tissue paper is further laminated to 400 mm. An absorber having a size of × 200 mm was formed. A synthetic rubber-based hot melt adhesive was further applied onto tissue paper, and a liquid-permeable nonwoven fabric (top sheet) was laminated to form an absorbent article.

Absorbent article no. 2
The water absorbent resin powder is designated as water absorbent resin powder No. Except for having changed to 2, the absorbent article no. Absorbent article No. 1 was prepared in the same manner as the production method of No. 1. 2 was formed.

Absorbent article no. 3
The water absorbent resin powder is designated as water absorbent resin powder No. Except for the change to No. 3, the absorbent article no. Absorbent article No. 1 was prepared in the same manner as the production method of No. 1. 3 was formed.

Absorbent article no. 4
The water absorbent resin powder is designated as water absorbent resin powder No. Except for having changed to No. 4, the absorbent article no. Absorbent article No. 1 was prepared in the same manner as the production method of No. 1. 4 was formed.

  The evaluation results for each absorbent article are shown in Table 2.

  The water-absorbent resin of the present invention can be used in hygiene fields such as disposable diapers, sanitary napkins, incontinence pads, medical fields, agricultural fields, cosmetics fields, electrical / electronic fields, civil engineering fields, and the like.

Claims (10)

It consists of a crosslinked product obtained by crosslinking a partially neutralized product of γ-polyglutamic acid with a polyvalent glycidyl compound,
The γ-polyglutamic acid constituting the partially neutralized product of γ-polyglutamic acid is γ-polyglutamic acid having a weight average molecular weight of 1 to 30 million produced by culturing Bacillus natto,
A water-absorbent resin, wherein the pH of the partially neutralized product of γ-polyglutamic acid is 3.5 to 6.8.   The water-absorbent resin according to claim 1, wherein the cationic component of the partially neutralized product of γ-polyglutamic acid is sodium and / or potassium.   The water-absorbent resin according to claim 1, wherein the cationic component of the partially neutralized product of γ-polyglutamic acid is sodium.   The water-absorbent resin according to any one of claims 1 to 3, wherein the polyvalent glycidyl compound is a divalent glycidyl compound.   The water-absorbent resin according to any one of claims 1 to 4, wherein the surface cross-linking treatment is performed with a surface cross-linking agent.   The water absorbent resin according to claim 5, wherein the surface crosslinking agent is a glycidyl ether compound.   The water absorbent resin according to claim 5 or 6, wherein the surface cross-linking agent is polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether or polyglycerin diglycidyl ether.   The water-absorbent resin according to any one of claims 1 to 7, which has a saturated absorption amount of 30 g / g to 100 g / g. A step of producing γ-polyglutamic acid having a weight average molecular weight of 1 to 30 million by culture of Bacillus natto;
Mixing the γ-polyglutamic acid and a cation source to obtain a partially neutralized product of γ-polyglutamic acid having a pH of 3.5 to 6.8; and
A method for producing a water-absorbent resin, comprising: a step of producing a crosslinked product by crosslinking the partially neutralized product of γ-polyglutamic acid with a polyvalent glycidyl compound. The water-absorbent resin according to claim 9, further comprising a step of subjecting the crosslinked body to a surface crosslinking treatment by reacting the crosslinked body with a surface crosslinking agent in the presence of water and a water-soluble leveling agent after the crosslinked body is made into particles. Manufacturing method.