Water-absorbing resin composition and use of same

Abstract

Provided is a water-absorbing resin composition which contains a water-absorbing resin, a hydrophobic substance, and a hydrophilic substance, the hydrophobic substance being contained in an amount more than 0.16 parts by weight but less than 0.60 parts by weight with respect to 100 parts by weight of the water-absorbing resin, and the hydrophilic substance being contained in an amount more than 0.20 parts by weight but less than 0.50 parts by weight with respect to 100 parts by weight of the water-absorbing resin. The water-absorbing resin composition improves the fluidity of a gel obtained by solidifying a waste liquid.

Description

Water-absorbent resin composition and use thereof

[0001] The present invention relates to a water-absorbent resin composition and its use.

[0002] In recent years, the volume of wastewater discharged from various industrial fields has been steadily increasing. Examples of wastewater include industrial wastewater, beverage wastewater, bodily fluid wastewater, and medical wastewater. In particular, liquid medical wastewater containing amniotic fluid and blood discharged during hospital surgery and childbirth is collected in wastewater containers and then either (a) incinerated or (b) treated with chemicals and then disposed of in a septic tank. This is to prevent the spread of infectious diseases to medical personnel and waste disposal companies. However, in both (a) and (b) treatment methods, disposing of medical wastewater in its liquid form poses the risk of damage to the wastewater container in the event of an accident or secondary infection due to the dispersion of the wastewater. Therefore, it is desirable to solidify (also known as gelation) the medical wastewater before disposal. Specifically, a wastewater treatment method that solidifies the wastewater into a gel by adding a treatment agent to the wastewater is desired.

[0003] Waste liquid solidifying agents for solidifying waste liquid are disclosed, for example, in Patent Documents 1 and 2. The waste liquid solidifying agent disclosed in Patent Document 1 is a water-absorbent resin composition containing a water-absorbent resin and a hydrophobic substance. The waste liquid solidifying agent disclosed in Patent Document 2 is a water-absorbent resin composition containing a water-absorbent resin, a hydrophobic substance, and a hydrophilic substance.

[0004] Japanese Patent Publication No. 2007-538110 Japanese Patent Publication No. 2016-203106

[0005] The waste liquid solidification agents of Patent Documents 1 and 2 address the issue of shortening the solidification time of waste liquids, particularly waste liquids containing blood or bodily fluids. However, the fluidity of the gel obtained by solidifying the waste liquid (hereinafter sometimes simply referred to as gel fluidity) was not evaluated for the waste liquid solidification agents of Patent Documents 1 and 2, leaving room for improvement. If the gel obtained by solidifying the waste liquid has high fluidity, the gel may scatter when the waste liquid container is damaged, causing the spread and leakage of harmful substances, viruses, etc., which may lead to secondary infection. Furthermore, since flowable gels spread over a wide area when they leak from the container, recollection of the leaked gel (by wiping, etc.) is time-consuming, increasing the risk of secondary infection and making it difficult to handle.

[0006] An object of one aspect of the present invention is to provide a water-absorbing resin composition capable of improving the fluidity of a gel obtained by solidifying a waste liquid, and to realize use of the composition as a waste liquid solidifying agent.

[0007] In order to solve the above problems, the present inventors have focused on the contents of the hydrophobic substance and the hydrophilic substance in the water-absorbent resin composition and conducted extensive research. As a result, the present inventors have found that by setting the contents of the hydrophobic substance and the hydrophilic substance in a specific numerical range different from conventional ones, gel fluidity, which has not been noticed before, is improved and the composition can be appropriately used as a waste liquid solidifying agent, and have arrived at the present invention.

[0008] That is, a water-absorbent resin composition according to one aspect of the present invention comprises a water-absorbent resin having a constitutional unit derived from an acid group-containing unsaturated monomer, a hydrophobic substance, and a hydrophilic substance, wherein the hydrophobic substance is contained in an amount of more than 0.16 parts by weight and less than 0.60 parts by weight relative to 100 parts by weight of the water-absorbent resin, and the hydrophilic substance is contained in an amount of more than 0.20 parts by weight and less than 0.50 parts by weight relative to 100 parts by weight of the water-absorbent resin.

[0009] According to one aspect of the present invention, it is possible to obtain an effect of improving the fluidity of a gel obtained by solidifying a waste liquid.

[0010] The present invention will now be described with reference to the best mode. Throughout this specification, singular expressions should be understood to include the plural concept unless otherwise specified. Therefore, singular articles (e.g., "a," "an," "the," etc. in English) should be understood to include the plural concept unless otherwise specified. Furthermore, terms used in this specification should be understood to have the meaning commonly used in the art unless otherwise specified. Therefore, unless otherwise defined, all technical and scientific terms used in this specification have the same meaning as commonly understood by those skilled in the art to which this invention belongs. In the event of a conflict, this specification (including definitions) shall prevail. The present invention is not limited to the following embodiments and can be variously modified within the scope of the claims. Furthermore, in this specification, unless otherwise specified, "A to B" representing a numerical range means "greater than or equal to A (including A and greater than A)" or "less than or equal to B (including B and less than B)."

[0011] [1. Definition of Terms] [1-1. Water-Absorbent Resin] In the present embodiment, the term "water-absorbent resin" refers to a water-swellable, water-insoluble polymer gelling agent that satisfies the following physical properties: That is, the term "water-swellable" refers to a polymer gelling agent that satisfies the physical properties of having a CRC of 5 g / g or more as defined in NWSP 241.0. R2(15) and an Ext of 50 wt% or less as defined in NWSP 270.0. R2(15).

[0012] The water-absorbent resin can be appropriately designed depending on its application, and is not particularly limited, but is preferably a hydrophilic cross-linked polymer obtained by cross-linking an unsaturated monomer having a carboxyl group. In addition, the water-absorbent resin is not limited to a form in which the entire amount (100% by weight) of the water-absorbent resin is a polymer, and may be a water-absorbent resin composition containing additives and the like within a range that satisfies the above physical properties (CRC, Ext).

[0013] Furthermore, the water-absorbent resin in the present embodiment is not limited to a final product, but may refer to an intermediate in the manufacturing process of the water-absorbent resin (for example, a hydrogel-like crosslinked polymer after polymerization, a dried polymer after drying, a water-absorbent resin powder before surface crosslinking, etc.), and all of these are collectively referred to as a "water-absorbent resin." Note that, examples of the shape of the water-absorbent resin include a sheet, a fiber, a film, a particle, a gel, etc., but a particle-like water-absorbent resin is preferred in the present embodiment.

[0014] [1-2. "NWSP"] "NWSP" stands for "Non-Woven Standard Procedures-Edition 2015", which was jointly issued by EDANA (European Disposals and Nonwovens Associations) and INDA (Association of the Nonwoven Fabrics Industry) to standardize evaluation methods for nonwoven fabrics and their products in the United States and Europe, and indicates a standard measurement method for water-absorbent resins. Unless otherwise specified, in the present invention, the physical properties of a water-absorbent resin are measured in accordance with "NWSP".

[0015] [1-2-1. "CRC" (NWSP241.0.R2(15))] "CRC" is an abbreviation for Centrifuge Retention Capacity, and means the water absorption capacity of a water-absorbent resin under no load (sometimes referred to as "water absorption capacity").

[0016] Specifically, it refers to the water absorption capacity (unit: g / g) after 0.2 g of a water-absorbent resin is placed in a nonwoven bag, the bag is immersed in a large excess of a 0.9 wt % aqueous solution of sodium chloride for 30 minutes to allow free swelling, and then the bag is centrifuged (250 G) to remove water.

[0017] [1-2-2. "PSD" (NWSP241.0.R2(15))] "PSD" is an abbreviation for Particle Size Distribution, and means the particle size distribution of a water-absorbent resin measured by sieve classification.

[0018] The weight-average particle diameter (D50) and the logarithmic standard deviation (σζ) of particle size distribution are measured in the same manner as in "(3) Mass-Average Particle Diameter (D50) and Logarithmic Standard Deviation (σζ) of Particle Diameter Distribution" described in U.S. Pat. No. 7,638,570.

[0019] [1-2-3. "Density" (NWSP241.0.R2(15))] "Density" means the bulk specific gravity of the water-absorbent resin. The density is measured in accordance with NWSP 251.0.R2(15).

[0020] [1-3. Other] In this application, the term "X to Y" indicating a range means "X or more and Y or less," and "greater than X" is treated as a synonym for "exceeding X." Unless otherwise noted, the unit of mass "t (ton)" means "metric ton," and "ppm" means "ppm by mass" or "ppm by weight." Furthermore, "mass" and "weight," "parts by mass" and "parts by weight," "mass %" and "weight %" are treated as synonyms, respectively. Furthermore, "acid (salt)" means "acid and / or its salt," and "(meth)acrylic" means "acrylic and / or methacrylic," respectively.

[0021] [2. Water-absorbent resin] In this embodiment, from the viewpoint of absorption characteristics, the water-absorbent resin has a structural unit derived from an acid group-containing unsaturated monomer (hereinafter, sometimes simply referred to as a monomer) having an acid group, particularly a carboxyl group. That is, the water-absorbent resin has a crosslinked structure obtained by polymerizing an acid group-containing unsaturated monomer. In this embodiment, the water-absorbent resin is essentially a single type or a mixture, but from the viewpoint of water absorption speed, it is preferably a poly(meth)acrylic acid partially neutralized polymer having a structural unit derived from a monomer mainly composed of (meth)acrylic acid and / or its salt (neutralized product). That is, the water-absorbent resin is preferably a poly(meth)acrylic acid (salt)-based water-absorbent resin. Furthermore, in this embodiment, in order to improve salt resistance, a water-absorbent resin having a structural unit derived from an acid group-containing water-soluble ethylenically unsaturated monomer may be used in combination with a nonionic water-absorbent resin such as a polyethylene oxide crosslinker and / or a cationic water-absorbent resin such as a polyethyleneimine crosslinker.

[0022] [2-1. Physical Properties of Water-Absorbent Resin] It is preferable that the water-absorbent resin contained in the water-absorbent resin composition according to this embodiment further satisfies the following physical properties.

[0023] (CRC) The lower limit of the water-absorbent resin's absorption capacity (CRC) is 10 g / g or more, preferably 20 g / g or more, and more preferably 30 g / g or more. If the CRC is less than 10 g / g, a large amount of waste liquid solidifying agent may be required for solidification. The upper limit of the absorption capacity (CRC) is preferably 60 g / g or less, more preferably 50 g / g or less, and even more preferably 45 g / g or less. If the CRC is 60 g / g or more, the amount of waste liquid absorbed by the gel increases, the gel itself becomes soft, and the gel may become more fluid.

[0024] The CRC of the water-absorbent resin is preferably in the range of 10 g / g to 60 g / g, more preferably 20 g / g to 50 g / g, and even more preferably 30 g / g or more and less than 45 g / g. The CRC can be controlled by the type and / or amount of the internal cross-linking agent.

[0025] (Weight average particle diameter (D50)) The water-absorbent resin is in a particulate form. In the water-absorbent resin, particles having a size of 106 μm or more and less than 850 μm account for 90% by mass to 100% by mass of the entire water-absorbent resin, more preferably 95% by mass to 100% by mass, and even more preferably 98% by mass to 100% by mass. The weight average particle diameter (D50) of the water-absorbent resin is 150 μm to 700 μm, preferably 200 μm to 600 μm, and more preferably 300 μm to 500 μm.

[0026] A weight-average particle diameter (D50) exceeding 700 μm is undesirable because it causes problems such as a slow gelation rate. Furthermore, a weight-average particle diameter (D50) of less than 150 μm leads to poor working conditions for solidifying waste liquid due to dusting, etc. The weight-average particle diameter (D50) can be appropriately adjusted by granulating, pulverizing, or classifying the water-absorbent resin, or controlling the reverse-phase polymerization of the monomer solution.

[0027] (Bulk specific gravity and true specific gravity) The bulk specific gravity of the water-absorbent resin (defined in U.S. Patent No. 6,562,879) is usually 0.30 g / cm ３ ~0.90 g / cm ３ , preferably 0.50 g / cm ３ ~0.80 g / cm ３ , more preferably 0.60 g / cm ３ ~0.80 g / cm ３ The true specific gravity of the water-absorbent resin (defined in European Patent No. 736060) is usually 1.1 g / cm ３ ~2.0 g / cm ３ , preferably 1.2 g / cm ３ ~1.8g / cm ３ The water-absorbing resin composition according to this embodiment has a true specific gravity of 1.1 g / cm ３ Even if it contains a water-absorbent resin exceeding 1.0 g / cm ３ ) and has the characteristic of floating.

[0028] The bulk density and true density, especially the true density, can be appropriately controlled by adjusting the monomer composition. Furthermore, the bulk density can be appropriately controlled by adjusting the weight average particle diameter (D50) of the water absorbent resin by adjusting the monomer composition. If the bulk density and true density are outside the above-mentioned ranges, it may be difficult to control the solidification and floating of the waste liquid solidifying agent, or problems may occur during transportation.

[0029] (Shape) Examples of the shape of the water-absorbent resin include the following shapes (a) to (c): (a) A spherical and / or ellipsoidal or Vienna sausage-like primary particle shape obtained by inverse suspension polymerization as described in Figures 1 and 2 of U.S. Patent No. 5,244,735. (b) A shape of a primary particle granule formed by agglomeration of spherical particles and / or ellipsoidal particles, such as agglomerated beads, as described in Figure 1 on page 75 of NONWOVENSWORLD October-November 2000 (published by Marketing Technology Service, Inc.). (c) An amorphous shape derived from a crushed hydrogel polymer obtained by polymerizing an aqueous monomer solution, such as the crystals shown in Figures 2, 3 and 4 of U.S. Patent No. 5,981,070 or Figure 1 on page 75 of NONWOVENSWORLD, October-November 2000, or the shape of a granulated product thereof.

[0030]

[0033] In addition, the shape of the water absorbent resin composition according to the present embodiment may be any of spherical primary particles, oval-spherical (ellipsoidal) primary particles, granules of spherical or ellipsoidal particles, irregular shapes derived from crushed products of a hydrogel polymer obtained by polymerizing monomer particles, or the shape of granules thereof. In the water absorbent resin composition according to the present embodiment, the water absorbent resin is preferably granulated simultaneously with or separately from the surface cross-linking step described later in [3. Method for producing water absorbent resin] in order to adjust the floating.

[0031] 3. Method for Producing Water-Absorbent Resin Hereinafter, steps 3-1 to 3-8 for producing a water-absorbent resin used in one embodiment of the present invention will be described.

[0032] [3-1. Step of preparing aqueous monomer solution] This step is a step of preparing an aqueous solution containing an acid group-containing unsaturated monomer as a main component as a monomer (hereinafter referred to as "aqueous monomer solution"). Note that a slurry liquid of the monomer can also be used within a range that does not deteriorate the water absorption performance of the obtained water absorbent resin.

[0033] (Acid Group-Containing Unsaturated Monomer) As the acid group-containing unsaturated monomer, it is preferable to use (meth)acrylic acid (salt) as the main component, but other monomers may be used in combination, or the water-absorbent resin may be obtained using other monomers as the main component. Examples of the monomer other than acrylic acid include acid group-containing unsaturated monomers such as methacrylic acid, maleic acid (anhydride), fumaric acid, crotonic acid, itaconic acid, vinyl sulfonic acid, 2-(meth)acrylamide-2-methylpropanesulfonic acid, (meth)acryloxyalkanesulfonic acid and alkali metal salts and ammonium salts thereof, N-vinyl-2-pyrrolidone, N-vinylacetamide, (meth)acrylamide, N-isopropyl(meth)acrylamide, 2-hydroxyethyl(meth)acrylate, methoxypolyethylene glycol (meth)acrylate, polyethylene glycol (meth)acrylate, and N,N-dimethyl(meth)acrylamide. Furthermore, the water-absorbing resin may be obtained by copolymerizing these acid group-containing unsaturated monomers with hydrophobic unsaturated monomers such as isobutylene and lauryl (meth)acrylate.

[0034] In the present embodiment, when (meth)acrylic acid (salt) is used as a monomer, the amount of other monomers other than the (meth)acrylic acid (salt) may be 0 mol % to 50 mol %, preferably 0 mol % to 30 mol %, and more preferably 0 mol % to 10 mol %, relative to the total amount of the other monomers and the (meth)acrylic acid (salt) used as the main component. Within this range, in addition to solidification performance, other functions such as antibacterial properties and deodorizing properties can be imparted, and a water-absorbing resin composition can be obtained at a lower cost.

[0035] "Using (meth)acrylic acid (salt) as the main monomer component" means that, of all monomers (excluding the internal crosslinking agent) used in polymerization, (meth)acrylic acid (salt) accounts for 50 mol% to 100 mol%, more preferably 70 mol% to 100 mol%, even more preferably 90 mol% to 100 mol%, and particularly preferably substantially 100 mol%. "Poly(meth)acrylic acid (salt)-based water-absorbent resin" means a water-absorbent resin having (meth)acrylic acid (salt) as a repeating unit as the main component.

[0036] In addition, as the acid group-containing unsaturated monomer, a neutralized salt in which the acid group is neutralized can be used. In this case, examples of the salt (neutralized salt) of the acid group-containing unsaturated monomer include alkali metal salts, alkaline earth metal salts, and ammonium salts. From the viewpoints of the performance of the obtained water absorbent resin, ease of industrial availability, safety, etc., the salt of the acid group-containing unsaturated monomer is preferably an alkali metal salt, and among them, sodium salts and potassium salts are particularly preferred.

[0037] Furthermore, from the viewpoint of the water absorption performance of the obtained water absorbent resin, it is preferable to use an acid group-containing unsaturated monomer and a neutralized salt of the acid group-containing unsaturated monomer in combination. When an acid group-containing unsaturated monomer and a neutralized salt of the acid group-containing unsaturated monomer are used in combination, from the viewpoint of water absorption performance, the number of moles of the neutralized salt relative to the total number of moles of the acid group-containing unsaturated monomer and its neutralized salt (100 mol%) (hereinafter referred to as "neutralization rate") is preferably 10 mol% to 100 mol%, more preferably 30 mol% to 90 mol%, and even more preferably 40 mol% to 80 mol%. In addition, when a water absorbent resin is polymerized using a neutralized salt of an acid group-containing unsaturated monomer, (i) a neutralized salt may be generated by neutralizing a state of the acid group-containing unsaturated monomer, (ii) a non-neutralized acid group-containing unsaturated monomer and a neutralized salt of the acid group-containing unsaturated monomer may be mixed, (iii) a polymer during or after polymerization of the acid group-containing unsaturated monomer may be neutralized to generate a neutralized salt, or (iv) (i) to (iii) may be used in combination.

[0038] (Internal Crosslinking Agent) The water-absorbent resin must have a crosslinked structure. It is more preferable that the water-absorbent resin has a structural unit derived from the internal crosslinking agent. That is, it is more preferable that the water-absorbent resin is obtained by polymerizing or reacting a monomer in the presence of an internal crosslinking agent, or by reacting a functional group contained in a polymer obtained by polymerization with an internal crosslinking agent. The internal crosslinking agent is a compound having two or more polymerizable unsaturated groups and / or reactive groups in one molecule. The internal crosslinking agent may be used alone or in a mixture of two or more types. It may also be added all at once or in portions to the reaction system before, during, or after polymerization. Considering the absorption characteristics of the final water-absorbent resin or waste liquid solidification agent, it is preferable that the internal crosslinking agent is used during polymerization, and it is preferable to use an internal crosslinking agent having two or more polymerizable unsaturated groups in one molecule. The water-absorbent resin may also be a self-crosslinked crosslinked polymer that does not have a structural unit derived from the internal crosslinking agent (i.e., does not use an internal crosslinking agent).

[0039] The internal crosslinking agent used in this embodiment is a compound described in U.S. Patent No. 6,241,928. One or more compounds are selected from these compounds in consideration of reactivity.

[0040] The amount of the internal crosslinking agent used is preferably 0.0001 mol % to 10 mol %, more preferably 0.001 mol % to 1 mol %, based on the total amount of monomers. By setting the amount used within the above range, a desired water-absorbent resin can be obtained. If the amount used is too small, the gel strength tends to decrease and the water-soluble content tends to increase, while if the amount used is too large, the water absorption capacity may decrease.

[0041] In the present embodiment, in order to form a crosslinked structure of the water absorbent resin, a method is preferably applied in which a predetermined amount of an internal crosslinking agent is added in advance to the aqueous monomer solution, and a crosslinking reaction is carried out simultaneously with polymerization. On the other hand, other than this method, a method of crosslinking by adding an internal crosslinking agent during or after polymerization, a radical crosslinking method using a radical polymerization initiator, a radiation crosslinking method using active energy rays such as electron beams or ultraviolet rays, etc. can also be employed. These methods can also be used in combination.

[0042] (Polymerization initiator) The polymerization initiator used in the present embodiment is not particularly limited as it is appropriately selected depending on the polymerization form and the like, and examples thereof include a thermally decomposable polymerization initiator, a photodecomposable polymerization initiator, or a redox-based polymerization initiator used in combination with a reducing agent that promotes the decomposition of these polymerization initiators. Specifically, one or more of the polymerization initiators disclosed in U.S. Pat. No. 7,265,190 are used. Note that, from the viewpoint of the handleability of the polymerization initiator and the physical properties of the water-absorbent resin, preferably a peroxide or an azo compound, more preferably a peroxide, and even more preferably a persulfate is used as the polymerization initiator.

[0043] The amount of the polymerization initiator used is preferably 0.001 mol % to 1 mol %, more preferably 0.001 mol % to 0.5 mol %, based on the total amount of the monomers, and the amount of the reducing agent used is preferably 0.0001 mol % to 0.02 mol %, based on the total amount of the monomers.

[0044] In the polymerization of the monomer, the polymerization reaction may be carried out by irradiating with active energy rays such as radiation, electron beams, and ultraviolet rays instead of the above-mentioned polymerization initiator, and these active energy rays and the polymerization initiator may be used in combination.

[0045] [3-2. Polymerization Step] This step is a step in which the aqueous monomer solution obtained in the aqueous monomer solution preparation step is polymerized to obtain a hydrogel-like crosslinked polymer (hereinafter referred to as "hydrogel"). In this embodiment, the polymerization method applied to the monomer polymerization step is not particularly limited, but from the viewpoints of water absorption characteristics, ease of polymerization control, etc., preferred examples include spray droplet polymerization, aqueous solution polymerization, and reversed-phase suspension polymerization, more preferably aqueous solution polymerization and reversed-phase suspension polymerization, and even more preferably aqueous solution polymerization. Furthermore, among aqueous solution polymerizations, continuous aqueous solution polymerization is particularly preferred, and as continuous aqueous solution polymerization, either continuous belt polymerization or continuous kneader polymerization can be applied.

[0046] As specific polymerization modes, continuous belt polymerization is disclosed in U.S. Pat. Nos. 4,893,999, 6,241,928, U.S. Patent Application Publication No. 2005 / 215734, etc., and continuous kneader polymerization is disclosed in U.S. Pat. Nos. 6,987,151, 6,710,141, etc. By employing these continuous aqueous solution polymerizations, the production efficiency of a water absorbent resin is improved.

[0047] Furthermore, preferred forms of the continuous aqueous solution polymerization include "high-temperature initiated polymerization" and "high-concentration polymerization." "High-temperature initiated polymerization" refers to a form in which polymerization is initiated at a temperature of the aqueous monomer solution of preferably 30°C or higher, more preferably 35°C or higher, even more preferably 40°C or higher, and particularly preferably 50°C or higher (the upper limit is the boiling point). "High-concentration polymerization" refers to a form in which polymerization is carried out at a monomer concentration of preferably 30% by weight or higher, more preferably 35% by weight or higher, even more preferably 40% by weight or higher, and particularly preferably 45% by weight or higher (the upper limit is the saturated concentration). These polymerization forms can also be used in combination.

[0048] In the present embodiment, the polymerization can be carried out in an air atmosphere, but from the viewpoint of the color tone of the obtained water-absorbent resin, it is preferable to carry out the polymerization in an inert gas atmosphere such as nitrogen or argon. In this case, for example, it is preferable to control the oxygen concentration to 1% by volume or less. It is also preferable to replace the dissolved oxygen in the aqueous monomer solution with an inert gas (for example, dissolved oxygen: less than 1 mg / L).

[0049] In this embodiment, foam polymerization can also be employed, in which polymerization is carried out by dispersing bubbles (particularly the above-mentioned inert gas or the like) in the aqueous monomer solution.

[0050] [3-3. Gel Crushing Step] The water-absorbent resin obtained after the polymerization step is usually a hydrogel. In this step, the hydrogel obtained in the polymerization step is crushed using, for example, a screw extruder such as a kneader or a meat chopper; and / or a gel crusher such as a cutter mill; to obtain a particulate hydrogel (hereinafter referred to as "particulate hydrogel"). When kneader polymerization is employed in the polymerization step, the polymerization step and the gel crushing step are carried out simultaneously. Furthermore, when gas phase polymerization, reverse phase suspension polymerization, or the like is employed in the polymerization step and the particulate hydrogel is obtained directly during the polymerization process, the gel crushing step may not be carried out.

[0051] [3-4. Drying Step] This step is a step of drying the particulate hydrogel obtained in the polymerization step and / or the gel-pulverization step to a desired resin solid content to obtain a dried polymer. The resin solid content is determined from the loss on drying (the weight change when 1 g of the water-absorbent resin is heated at 180°C for 3 hours), and is preferably 80 wt% or more, more preferably 85 wt% to 99 wt%, even more preferably 90 wt% to 98 wt%, and particularly preferably 92 wt% to 97 wt%.

[0052] The method for drying the particulate hydrogel is not particularly limited, and examples thereof include heat drying, hot air drying, reduced pressure drying, fluidized bed drying, infrared drying, microwave drying, drum dryer drying, drying by azeotropic dehydration with a hydrophobic organic solvent, and high-humidity drying using high-temperature water vapor, etc. Among these, from the viewpoint of drying efficiency, hot air drying is preferred, and band drying in which hot air drying is performed on a ventilated belt is more preferred.

[0053] The drying temperature (hot air temperature) in the hot air drying is preferably 120°C to 250°C, more preferably 150°C to 200°C, from the viewpoint of the color tone of the water-absorbent resin and drying efficiency. The drying conditions other than the drying temperature, such as the hot air speed and drying time, may be appropriately set depending on the water content, total weight, and target resin solid content of the particulate hydrogel to be dried. When band drying is performed, the conditions described in International Publication Nos. 2006 / 100300, 2011 / 025012, 2011 / 025013, 2011 / 111657, and the like, are appropriately applied.

[0054]

[0111] (3-5. Pulverization step, classification step) This step is a step of pulverizing the dried polymer obtained in the drying step (pulverization step), and adjusting the particle size distribution to a predetermined range (classification step), to obtain a water absorbent resin powder (a powdery water absorbent resin before being subjected to surface crosslinking is conveniently referred to as "water absorbent resin powder").

[0055] Examples of equipment used in the pulverization step in this embodiment include high-speed rotary pulverizers such as roll mills, hammer mills, screw mills, and pin mills, vibration mills, knuckle-type pulverizers, and cylindrical mixers. These may be used in combination as needed.

[0056] Furthermore, the method for adjusting the particle size distribution in the classification step in the present embodiment is not particularly limited, and examples thereof include sieve classification using a JIS standard sieve (JIS Z8801-1 (2000)), air flow classification, etc. The adjustment of the particle size distribution of a water absorbent resin is not limited to the pulverization step and the classification step, and can be appropriately performed in a polymerization step (particularly, reverse phase suspension polymerization or spray droplet polymerization) or other steps (for example, a granulation step, a fine powder recovery step).

[0057]

[0222] (3-6. Surface cross-linking step) This step is a step of providing a portion with higher cross-link density on a surface layer (a portion several tens of µm from the surface of a water absorbent resin powder) of a water absorbent resin powder obtained through the above-mentioned step, and is composed of a mixing step, a heat treatment step and a cooling step (optional).

[0058] In the surface cross-linking step, a surface-cross-linked water-absorbent resin (water-absorbent resin particles) is obtained by radical cross-linking, surface polymerization, cross-linking reaction with a surface cross-linking agent, or the like on the surface of the water-absorbent resin powder.

[0059] The surface cross-linking agent used in the present embodiment is not particularly limited, and examples thereof include organic or inorganic surface cross-linking agents. Among them, from the viewpoint of the physical properties of the water-absorbent resin and the handling of the surface cross-linking agent, organic surface cross-linking agents that react with carboxyl groups are preferred. For example, one or more surface cross-linking agents disclosed in U.S. Patent No. 7,183,456 can be used. More specifically, examples thereof include polyhydric alcohol compounds, epoxy compounds, haloepoxy compounds, polyvalent amine compounds or condensates thereof with haloepoxy compounds, oxazoline compounds, oxazolidinone compounds, polyvalent metal salts, alkylene carbonate compounds, and cyclic urea compounds.

[0060]

[0073] The amount of the surface crosslinking agent used (when a plurality of agents are used, the total amount used) is preferably 0.01 to 10 parts by weight, more preferably 0.01 to 5 parts by weight, relative to 100 parts by weight of a water absorbent resin powder. Further, the surface crosslinking agent is preferably added as an aqueous solution, and in this case, the amount of water used is preferably 0.1 to 20 parts by weight, more preferably 0.5 to 10 parts by weight, relative to 100 parts by weight of a water absorbent resin powder. Furthermore, when a hydrophilic organic solvent is used as necessary, the amount used is preferably 10 parts by weight or less, more preferably 5 parts by weight or less, relative to 100 parts by weight of a water absorbent resin powder.

[0061]

[0133] In addition, in the case where a water absorbent resin is obtained by reverse phase suspension polymerization, the surface crosslinking agent is added during azeotropic dehydration after completion of polymerization and / or after completion of azeotropic dehydration, for example, in a state where the water content of the water absorbent resin is preferably 5 wt% to 50 wt%, more preferably 5 wt% to 40 wt%, and the mixture is mixed and heated, whereby a water absorbent resin the surface of which is crosslinked can be obtained.

[0062]

[0111] (Mixing Step) This step is a step of mixing a water absorbent resin with the surface crosslinking agent. A method of mixing the surface crosslinking agent is not particularly limited, but includes a method of preparing a surface crosslinking agent solution in advance, and mixing the liquid with a water absorbent resin powder, preferably by spraying or dropping the liquid, more preferably by spraying.

[0063] The device for carrying out the mixing is not particularly limited, but is preferably a high-speed stirring mixer, more preferably a high-speed stirring continuous mixer.

[0064] (Heat Treatment Step) This step is a step in which heat is applied to the mixture obtained from the mixing step to cause a crosslinking reaction on the surface of the water absorbent resin powder.

[0065] The device for carrying out the crosslinking reaction is not particularly limited, but preferably includes a paddle dryer. Moreover, the conditions in the heat treatment step are appropriately set depending on the type of the surface crosslinking agent used. As the conditions, the heat treatment temperature of the water absorbent resin or the heat medium temperature for the water absorbent resin is usually 60°C to 280°C, preferably 100°C to 250°C, more preferably 150°C to 240°C. Moreover, the heating time is preferably 1 minute to 2 hours.

[0066] (Cooling Step) This step is an optional step that is performed as necessary after the heat treatment step, and is a step of cooling the water-absorbent resin heated in the heat treatment step to a desired temperature.

[0067] The cooling device is not particularly limited, but is preferably a device with the same specifications as the device used in the heat treatment step, and more preferably a paddle dryer. This is because the device can be used as a cooling device by changing the heat medium to a refrigerant. Note that the water-absorbent resin particles obtained in the heat treatment step are forcibly cooled, as necessary, to preferably 40°C to 80°C, more preferably 50°C to 70°C in the cooling step.

[0068] [3-7. Granulation step] The water-absorbent resin used in the water-absorbent resin composition of the present embodiment is obtained by subjecting the surface to crosslinking treatment in the above-mentioned surface crosslinking step. The water-absorbent resin is preferably adjusted to a specific particle size distribution in order to achieve the effects of rapid and uniform solidification of waste liquid and / or solidification of waste liquid in a small amount. The particle size distribution of the water-absorbent resin in the present embodiment will be described later.

[0069] Furthermore, the particle size of the water-absorbent resin or the waste liquid solidifying agent may be adjusted by adding and mixing insoluble fine particles and / or a hydrophilic solvent and further granulating, depending on the purpose or need. When the granulation step is performed together with the surface cross-linking step, the granulation step and the surface cross-linking step may be performed simultaneously or separately. In the granulation step, water and a polyhydric alcohol may be added.

[0070]

[0033] In addition, in the granulation step, irregular granules may be produced. Examples of methods for producing irregular granules include (1) the method described in JP-A-11-106514, that is, a method in which a water-absorbent resin fine powder (150 μm or less) is mixed with a preheated aqueous liquid at high speed for a short period of time, followed by drying and pulverization to obtain irregular granules, and (2) a method in which the vicinity of the surface of the irregular granules obtained in (1) above is crosslinked. Further, examples include (3) a method in which a water-absorbent resin crosslinked in the vicinity of the surface is mixed with an aqueous liquid at room temperature, followed by drying and pulverization to adjust the particle size as necessary.

[0071] Furthermore, when reversed-phase suspension polymerization is performed, the hydrogel dispersed in the hydrophobic solvent may be aggregated during or after polymerization to form granules, for example, by adding inorganic fine particles (e.g., hydrophilic silica fine particles) (U.S. Patent No. 4,732,968) or by two-stage polymerization (European Patent No. 807,646).

[0072] The presence or absence of granulated matter can be easily confirmed by an increase in particle size distribution before and after the granulation step, a decrease in the amount of fine particles, etc. Furthermore, the presence or absence of granulated matter can also be easily confirmed by a microscopic photograph of the product (water-absorbent resin, waste liquid solidifying agent) obtained by the granulation step.

[0073] [4. Water-absorbent resin composition] The water-absorbent resin composition according to the present embodiment contains the above-mentioned water-absorbent resin, a hydrophobic substance, and a hydrophilic substance. The contents of the hydrophobic substance and the hydrophilic substance are as shown in (I) and (II) below.

[0074] (I) The hydrophobic substance is contained in an amount of more than 0.16 parts by weight and less than 0.60 parts by weight, preferably more than 0.16 parts by weight and less than 0.50 parts by weight, and more preferably more than 0.16 parts by weight and less than 0.30 parts by weight, relative to 100 parts by weight of the water-absorbent resin. The lower limit of the content of the hydrophobic substance is more than 0.16 parts by weight, preferably 0.17 parts by weight or more, and more preferably 0.18 parts by weight or more, relative to 100 parts by weight of the water-absorbent resin. The upper limit is less than 0.60 parts by weight, preferably 0.50 parts by weight or less, and more preferably 0.30 parts by weight or less.

[0075] (II) The hydrophilic substance is contained in an amount of more than 0.20 parts by weight and less than 0.50 parts by weight, preferably more than 0.20 parts by weight and less than 0.45 parts by weight, more preferably more than 0.20 parts by weight and less than 0.35 parts by weight, relative to 100 parts by weight of the water-absorbent resin. The lower limit of the content of the hydrophilic substance is more than 0.20 parts by weight, preferably 0.21 parts by weight or more, more preferably 0.22 parts by weight or more, relative to 100 parts by weight of the water-absorbent resin. The upper limit is less than 0.50 parts by weight, preferably 0.45 parts by weight or less, more preferably 0.35 parts by weight or less.

[0076] The water-absorbent resin composition of the present invention is preferably used as a waste liquid solidifying agent for treating waste liquid contained in a container. In this case, when the water-absorbent resin composition is poured into the waste liquid, the water-absorbent resin composition (waste liquid solidifying agent) that has settled in the waste liquid partially sinks and partially floats, and solidification proceeds from the top and bottom of the waste liquid. When the container containing the waste liquid is a bulky, vertically elongated cylindrical container (20 cm to 100 cm in height), the water-absorbent resin composition that has settled in the container swells from the bottom, gradually expanding to the middle and finally to the top of the container. The water-absorbent resin composition that was floating in the container swells from the top and gradually expanding to the middle of the container. With conventional waste liquid solidifying agents, the gelation of the waste liquid proceeds from both the top and bottom as described above, and although the gelation rate is fast, solidification of the waste liquid gel is insufficient. When the container is turned sideways, the gel fails to maintain its shape and may flow out of the container. The waste liquid solidifying agents disclosed in Patent Documents 1 and 2 have not been evaluated for their gel fluidity, leaving room for improvement. As mentioned above, the term "gel fluidity" means that even though the waste liquid itself has gelled and lost its liquid fluidity, the solidified gel is soft and will flow if the container is tilted or vibrated.

[0077] Here, by controlling the balance between hydrophilicity and hydrophobicity of the water-absorbent resin composition within the specific range prescribed in the present application, it is thought that, although the reason is not clear, hydrophilic sites and hydrophobic sites are mixed between and / or on the surfaces of water-absorbent resin particles that have absorbed liquid and gelled, thereby enabling the gel particles to swell uniformly, and realizing a structure in which the elasticity of the entire gel is maintained in such a way that even if some of the gel particles try to flow, other parts buffer this, and the flow of gel particles that have absorbed liquid and swollen can be suppressed, thereby improving gel fluidity.

[0078] Therefore, in order to suppress the gel fluidity of the waste liquid, adjustment of the amounts of the hydrophobic substance and the hydrophilic substance in the water-absorbent resin composition is an important factor. In the water-absorbent resin composition according to the present embodiment, the amount of the hydrophobic substance relative to the water-absorbent resin is specified within the numerical range of (I) above, and the amount of the hydrophilic substance relative to the water-absorbent resin is specified within the numerical range of (II) above, so that the effect of suppressing the gel fluidity is achieved.

[0079] Furthermore, a preferred embodiment of the water-absorbent resin composition according to the present embodiment is an embodiment in which a hydrophobic substance and a hydrophilic substance are attached to the surface of the water-absorbent resin. In the attachment step of attaching a hydrophobic substance and a hydrophilic substance to the surface of the water-absorbent resin, the hydrophilic substance and the hydrophobic substance may be attached in separate steps, or may be attached in the same step. Since there are optimal attachment conditions for the hydrophilic substance and the hydrophobic substance, respectively, it is preferable to attach the hydrophilic substance and the hydrophobic substance to the surface of the water-absorbent resin in separate steps.

[0080] [5. Method for producing water-absorbent resin composition] The method for producing the water-absorbent resin composition according to the present embodiment is not particularly limited as long as it can substantially immobilize both a hydrophobic substance and a hydrophilic substance to the water-absorbent resin, and examples thereof include any of methods 1 to 5 described in paragraphs

[0068] to

[0072] of JP 2016-203106 A. The method for producing the water-absorbent resin composition according to the present embodiment preferably includes a step of mixing the water-absorbent resin, a hydrophobic substance, and a hydrophilic substance, and more preferably includes a step of mixing the water-absorbent resin, a hydrophilic substance, and a hydrophobic substance in separate steps.

[0081] (Mixing method) In the case where a hydrophobic substance and a hydrophilic substance are in the form of powders, examples of the mixing method include: (1) a method in which a hydrophobic substance and a hydrophilic substance are directly mixed in a powder state as they are to a water absorbent resin, for example, like a dry blending method; (2) a method in which a hydrophobic substance and a hydrophilic substance are dispersed in a slurry state in a surface crosslinking agent solution in which the surface crosslinking agent and water and, if necessary, a hydrophilic organic solvent are mixed, and the resultant is mixed with a water absorbent resin; and (3) a method in which a hydrophobic substance and a hydrophilic substance are dispersed in a slurry state in water or a hydrophilic organic solvent, and the resultant is mixed with a water absorbent resin.

[0082] When a hydrophobic substance and a hydrophilic substance are dispersed in a slurry form and mixed with a water-absorbent resin, the optimal amount of water, or an aqueous dispersion containing water and a hydrophilic organic solvent, to be added as needed, varies depending on the type and particle size distribution of the water-absorbent resin. Typically, in the case of an aqueous dispersion, the amount of water used is 10 parts by weight or less, preferably in the range of 1 to 5 parts by weight, per 100 parts by weight of the solid content of the water-absorbent resin. Similarly, the amount of hydrophilic organic solvent used is typically 10 parts by weight or less, preferably in the range of 0.1 to 5 parts by weight, per 100 parts by weight of the solid content of the water-absorbent resin. The concentrations of the hydrophobic substance and hydrophilic substance in the slurry to be mixed with the water-absorbent resin are appropriately selected depending on the type of the hydrophobic substance and hydrophilic substance and dispersion solvent used, and the viscosity of the slurry, and are not particularly limited, but are typically in the range of 0.001 to 30% by weight, preferably 0.01 to 10% by weight.

[0083]

[0123] The powder temperature of a water absorbent resin when mixed with a hydrophobic substance and a hydrophilic substance is usually room temperature or higher, but in order to obtain stable liquid absorption characteristics and fluidity at the time of moisture absorption of a water absorbent resin composition, the temperature is preferably 40°C to 180°C, more preferably 50°C to 100°C.

[0084] In the method for producing a water-absorbent resin composition according to the present embodiment, the amount of the hydrophobic substance added is more than 0.16 parts by weight and less than 0.60 parts by weight, preferably more than 0.16 parts by weight and less than 0.50 parts by weight, and more preferably more than 0.16 parts by weight and less than 0.30 parts by weight, relative to 100 parts by weight of the water-absorbent resin. When the amount of the hydrophobic substance added is 0.16 parts by weight or less, or 0.60 parts by weight or more, the hydrophobicity of the water-absorbent resin composition is insufficient or excessive, so that swelling of the gel particles during gelation becomes non-uniform, or the elasticity of the gel as a whole may decrease, which may cause gel fluidity.

[0085] Furthermore, the amount of the hydrophilic substance added is more than 0.20 parts by weight and less than 0.50 parts by weight, preferably more than 0.20 parts by weight and less than 0.45 parts by weight, and more preferably more than 0.20 parts by weight and less than 0.35 parts by weight, relative to 100 parts by weight of the water-absorbent resin. Similarly, when the amount of the hydrophilic substance added is 0.20 parts by weight or less, or 0.50 parts by weight or more, the hydrophilicity of the water-absorbent resin composition is insufficient or excessive, so that there is a risk that swelling varies among gel particles during gelation, or that the elasticity of the entire gel is reduced, which becomes a factor causing gel fluidity.

[0086] In the present embodiment, a conventionally known mixing device can be adopted as a device used when mixing a liquid, powder, and / or slurry solution containing a water absorbent resin, a hydrophobic substance, and a hydrophilic substance. Examples of the mixing device include a cylindrical mixer, a screw mixer, a screw extruder, a turbulizer, a Nauta mixer, a V-type mixer, a ribbon mixer, a double-arm kneader, a fluid mixer, an airflow mixer, a rotating disk mixer, a roll mixer, and a rolling mixer. In addition, in these mixers, the speed at the time of mixing may be either high or low. Note that these mixers can also be used in a mixing step of mixing a water absorbent resin and a surface crosslinking agent in surface crosslinking treatment.

[0087] [6. Hydrophobic Substance] Next, the hydrophobic substance will be described. The hydrophobic substance used in this embodiment is a water-insoluble or poorly water-soluble substance, and is a non-volatile hydrophobic substance that is stably non-water-absorbent (non-water-swellable). Regarding the water-insolubility or poorly water-soluble nature of the hydrophobic substance, the solubility of the hydrophobic substance in water at 26.7°C is 10 －１ g / L or less, preferably 10 －３ g / L or less, more preferably 10 －４ g / L or less, more preferably 10 －５ Furthermore, non-water absorbing (non-swellable in water) means that the water absorption capacity (CRC) described below is 1 g / g or less, preferably 0.5 g / g or less.

[0088] Furthermore, the hydrophobic substance is a substance containing a hydrophobic group in the molecule. The hydrophobic group mainly includes chain hydrocarbons and aromatic hydrocarbons, and the hydrophobicity increases as the hydrocarbon chain becomes longer. The number of carbon atoms in the hydrophobic group is preferably 7 or more. If the number of carbon atoms is less than 7, the hydrophobicity becomes insufficient, and the waste liquid solidification performance of the water absorbent resin composition may become insufficient. In addition to chain hydrocarbons and aromatic hydrocarbons, the hydrophobic group may also be a halogenated alkyl group (RX-), an organosilicon group (e.g., RSi(CH ３ ) ２ -), fluorocarbon groups (e.g., C ｎ F ２ｎ＋１ ) also belong to this category.

[0089] These hydrophobic substances need to remain or be immobilized in the water-absorbent resin. Therefore, in this embodiment, a substance that is solid or non-volatile at room temperature (25°C) and normal pressure is used as the hydrophobic substance. Here, a non-volatile substance is a substance whose boiling point at normal pressure is essentially 150°C or higher, preferably 200°C or higher, more preferably 250°C or higher, and even more preferably 300°C or higher. Furthermore, a solid is preferably used as the hydrophobic substance, and its melting point is 25°C or higher, preferably 50°C or higher, more preferably 75°C or higher, and even more preferably 100°C or higher. When a volatile substance is used as the hydrophobic substance, it becomes difficult to immobilize it in the water-absorbent resin, and odor problems may also occur.

[0090] When the hydrophobic substance is a powder, the particle size of the hydrophobic substance is not particularly limited, but is usually smaller than the weight average particle size of the water-absorbent resin, and 90% to 100% by weight of the powder is 200 μm or less, preferably 100 μm or less, more preferably 50 μm or less, and particularly preferably 20 μm or less. The lower limit of the particle size of the hydrophobic substance is usually about 0.001 μm.

[0091] (Methanol Index) The hydrophobic substance used in this embodiment is not particularly limited, but preferably has a methanol index of 20 or more, more preferably 50 or more, and even more preferably 100 or more. The methanol index refers to the volume (ml) of methanol at 25°C required to wet a solid hydrophobic substance when 1 g of the hydrophobic substance is added to 50 ml of pure water at 25°C, or the volume (ml) of methanol at 25°C required to disperse and / or emulsify a liquid hydrophobic substance when the hydrophobic substance is solid. Wetting means that the hydrophobic substance is wetted to the point where no floating matter on the liquid surface has disappeared (all has settled). Specifically, the methanol index can be evaluated by the method described in the Examples.

[0092] When the methanol index is less than 20, a large amount of a hydrophobic substance is required to impart hydrophobicity to the water-absorbent resin composition in order to use it as a waste liquid solidifying agent, which may result in a decrease in the liquid absorption performance as a waste liquid solidifying agent, and further an increase in the raw material cost.

[0093] Examples of hydrophobic substances include hydrocarbons, fatty acids, fatty acid esters, fatty acid amides, metal soaps, silicon compounds, and surfactants, and the hydrophobic substances described in JP-A-2007-538110 can be used.

[0094] (Metal soap) Metal soap is a metal salt other than an alkali metal salt of an organic acid such as a fatty acid, a petroleum acid, or a polymeric acid. There are no particular limitations on the metal soap. This metal soap also acts as a stabilizer.

[0095] Examples of organic acids that constitute metal soaps include long-chain or branched fatty acids such as caproic acid, octylic acid, decanoic acid, lauric acid, myristic acid, palmitic acid, oleic acid, and stearic acid; petroleum acids such as benzoic acid, myristic acid, naphthenic acid, naphthoic acid, and naphthoxyacetic acid; and polymeric acids such as poly(meth)acrylic acid and polysulfonic acid. Among these, the organic acid is preferably an organic acid having a carboxyl group in the molecule, and more preferably a fatty acid such as caproic acid, octylic acid, decanoic acid, lauric acid, myristic acid, palmitic acid, oleic acid, stearic acid, cow's fatty acid, and hardened castor fatty acid.

[0096] More preferably, the organic acid is a fatty acid having no unsaturated bond in the molecule, such as caproic acid, octylic acid, decanoic acid, lauric acid, myristic acid, palmitic acid, and stearic acid. Most preferably, the organic acid is a long-chain fatty acid having 12 or more carbon atoms in the molecule and no unsaturated bond in the molecule, such as lauric acid, myristic acid, palmitic acid, and stearic acid.

[0097] Even when a fatty acid having an unsaturated bond in the molecule is used as the organic acid, it is possible to suppress gel fluidity. However, when such a fatty acid is used as the organic acid of the metal soap, the waste liquid solidifying agent may become discolored, emit an odor, or the like if it is subjected to heat and / or oxidation during storage.

[0098] Furthermore, it is preferable to use an organic acid containing 7 or more carbon atoms in the molecule. Using an organic acid with fewer than 7 carbon atoms in the molecule is undesirable because the solubility of the hydrophobic substance in water increases, which may lead to the hydrophobic substance leaching into medical waste fluids containing blood and / or body fluids. Furthermore, when using an organic acid with fewer than 7 carbon atoms in the molecule, such as oxalic acid or citric acid, the metal salts of these acids have high hardness, so that, for example, when subjected to mechanical impact, the waste fluid solidifying agent may suffer a decrease in its liquid absorption properties.

[0099] The metal salt constituting the metal soap is not particularly limited as long as it is a metal salt other than an alkali metal salt, such as an alkaline earth metal salt or a transition metal salt. Examples of such metal salts include magnesium salts, calcium salts, strontium salts, barium salts, zinc salts, cadmium salts, aluminum salts, tin salts, and lead salts. Among these, barium salts, calcium salts, magnesium salts, aluminum salts, and zinc salts are preferred due to their ease of availability. The combination of the organic acid and the metal salt constituting the metal soap is not particularly limited. Furthermore, the metal soap may be used alone or in combination of two or more types within the range of the combination of the organic acid and the metal salt.

[0100] The methanol index of zinc stearate (manufactured by NOF Corporation) is 200 or more.

[0101] (Zinc Stearate) In the water absorbent resin composition according to the present embodiment, the hydrophobic substance is particularly preferably zinc stearate among the above-mentioned metal soaps. The zinc stearate is not particularly limited and may be obtained by a dry method or a wet method. The "wet method" refers to a method in which zinc stearate particles are produced by reacting an alkali metal salt or ammonium salt of stearic acid with an inorganic zinc salt in an aqueous solution, and is also called a metathesis method. The "dry method" refers to a method in which zinc stearate particles are produced by directly heating and reacting an alkali metal salt or ammonium salt of stearic acid with zinc oxide or zinc hydroxide, and is also called a direct method, direct melting method, or melting method.

[0102] In the water-absorbent resin composition according to the present embodiment, the zinc stearate is preferably obtained by a wet method. When the water-absorbent resin composition is used as a waste liquid solidifying agent, the gel is more uniformly solidified and the elasticity of the entire gel is maintained by using zinc stearate obtained by a wet method as the hydrophobic substance, rather than using zinc stearate obtained by a dry method as the hydrophobic substance. Therefore, by using zinc stearate obtained by a wet method as the hydrophobic substance, the fluidity of the gel of the resulting waste liquid can be further reduced. One preferred embodiment of the water-absorbent resin composition includes a water-absorbent resin having a structural unit derived from an acid group-containing unsaturated monomer and a metal soap obtained by a wet method, and the metal soap is contained in an amount of more than 0.16 parts by weight and less than 0.60 parts by weight per 100 parts by weight of the water-absorbent resin.

[0103] When zinc stearate obtained by the dry method is used as the hydrophobic substance, the water-absorbent resin composition according to the present embodiment has excellent water dispersibility and high water diffusibility while being hydrophobic. One preferred embodiment of the water-absorbent resin composition includes a water-absorbent resin having constitutional units derived from an acid group-containing unsaturated monomer and a metal soap obtained by the dry method, and the metal soap is contained in an amount of more than 0.16 parts by weight and less than 0.60 parts by weight relative to 100 parts by weight of the water-absorbent resin.

[0104] Zinc stearate obtained by the wet process can be distinguished from zinc stearate obtained by the dry process by the concentration of sodium chloride contained as a constituent characteristic.

[0105] The water-absorbent resin composition according to the present embodiment is suitable as a waste liquid solidifying agent, but can also be used for other purposes. For example, it can be used for absorbents in absorbent articles such as paper diapers (for infants and adults), sanitary napkins, and incontinence pads, as a water retention agent, a soil water retention agent, a seedling raising sheet, a seed coating material, a dew condensation prevention sheet, a drip absorbent, a freshness-preserving material, a disposable warmer, a cooling bandana, an ice pack, a soil solidifying material, a water-damage preventing waste liquid gelling agent, a water-absorbing sandbag, a portable toilet for disasters, a compress, a thickener for cosmetics, a water-stop material for communication cables of electric and electronic materials, a gasket packing, and a sustained-release agent for fertilizers. It can be suitably used in various sustained-release agents (air disinfectants, air fresheners, etc.), waterproof nursing care sheets, pet sheets, cat litter, wound protection dressings, anti-condensation building materials, oil moisture removers, paints, adhesives, resin additives (anti-blocking agents, light diffusing agents, matting agents, decorative panel additives, artificial marble additives, toner additives, etc.), moisture absorbents, deodorizers, printer ink absorbents, solidifying agents for waste liquid discharged when manufacturing three-dimensional objects with 3D printers, etc.

[0106] [7. Hydrophilic Substance] The water-absorbent resin composition according to this embodiment contains a hydrophilic substance together with a hydrophobic substance. In the water-absorbent resin composition according to this embodiment, the water-absorbent resin (having a true density of about 1.6 g / cm ３ The density of the water-absorbent resin (before and after) is greater than that of water or aqueous waste liquid. The above-mentioned hydrophobic substance has the effect of making such a water-absorbent resin hydrophobic, thereby allowing the water-absorbent resin to float in the waste liquid, but has the undesirable effect of causing the water-absorbent resin to swell and gel, thereby preventing the waste liquid from gelling. In the water-absorbent resin composition according to this embodiment, the contents of the hydrophobic substance and the hydrophilic substance are defined within the numerical ranges (I) and (II), respectively, so that the effect of suppressing gel fluidity is achieved. The hydrophilic substance is preferably in the form of a powder, more preferably in the form of an inorganic powder, and even more preferably in the form of water-insoluble inorganic fine particles.

[0107] Examples of hydrophilic substances include metal oxides such as silicon dioxide and titanium oxide; silicic acid (salts) such as natural zeolite and synthetic zeolite; inorganic compounds such as kaolin, talc, clay, and bentonite; and other organic compounds. Among these, water-insoluble inorganic fine particles in the form of powder, which are hydrophilic substances listed as metal oxides, silicic acid (salts), and inorganic compounds, can be preferably used. Among these, silicon dioxide (silica) is more preferred, and fine particle amorphous silica such as Aerosil 200 manufactured by Nippon Aerosil Co., Ltd. is even more preferred.

[0108] The water-absorbent resin and the hydrophilic substance can be mixed by the method described in the section (Mixing Method) in [5. Method for Producing Water-Absorbent Resin Composition].

[0109] [8. Use as a waste liquid solidifying agent] The water absorbent resin composition according to the present embodiment is used in a method for treating waste liquid, in which the water absorbent resin composition is poured into waste liquid in a container to solidify the waste liquid into a gel state. By using the water absorbent resin composition according to the present embodiment as a waste liquid solidifying agent in this way, an effect is achieved in that the fluidity of the gel obtained by solidifying the waste liquid can be suppressed.

[0110] When used as a waste liquid solidifying agent, the water-absorbent resin composition according to the present embodiment preferably contains a water-absorbent resin as a main component, and the content of the water-absorbent resin in the waste liquid solidifying agent is 50 to less than 100% by weight, preferably 70 to 99% by weight, and more preferably 80 to 98% by weight. As components other than the water-absorbent resin powder, the above-mentioned hydrophobic substance and the above-mentioned hydrophilic substance are used.

[0111] Furthermore, when used as a waste liquid solidifying agent, the water absorbent resin composition according to the present embodiment may contain, as other additives as necessary, additives that impart various functions, such as deodorants, antibacterial agents, fragrances, foaming agents, pigments, dyes, plasticizers, adhesives, surfactants, fertilizers, oxidizing agents, protein cross-linking agents, reducing agents, water, salts, chelating agents, disinfectants, hydrophilic polymers, polyester resins, thermosetting resins such as urea resins, etc., within the scope that does not impair the above-mentioned effects. Examples of the hydrophilic polymers include polyethylene glycol, polyethyleneimine, etc.

[0112] When the water absorbent resin composition according to the present embodiment is used as a waste liquid solidifying agent, the constitution of the waste liquid solidifying agent described in the following [9. Method for treating waste liquid and method for disposing of waste liquid] can be applied.

[0113] [9. Method for Treating Waste Liquid and Method for Disposing of Waste Liquid] The method for treating waste liquid according to this embodiment is a method for solidifying waste liquid into a gel state by adding the above-mentioned water-absorbent resin composition to waste liquid in a container. When used as a waste liquid solidifying agent, the water-absorbent resin composition according to this embodiment can be used to solidify various types of waste liquid such as beverage waste liquid, food waste liquid, industrial waste liquid, radioactive waste liquid, feces and urine waste liquid, and medical waste liquid. The waste liquid may contain organic matter, solid dispersions, and the like. Here, the waste liquid refers to an aqueous liquid to be disposed of or a filtered aqueous liquid.

[0114] In particular, medical waste fluids are liquid waste fluids containing amniotic fluid, blood, etc., discharged during surgery or childbirth in hospitals. To prevent infectious diseases among medical personnel and waste disposal companies, such medical waste fluids are collected in waste fluid containers and then incinerated or treated with chemicals before being disposed of in a septic tank. However, in either case, if medical waste fluids are disposed of in their liquid form, there is a risk of secondary infection due to damage to the waste fluid container in the event of an accident or the scattering of the waste fluid.

[0115] Because the waste liquid solidifying agent solidifies quickly and uniformly, the waste liquid treatment method according to this embodiment is preferably used for solidifying medical waste liquid, which has many problems as described above. Therefore, in the waste liquid treatment method according to this embodiment, the waste liquid is preferably medical waste liquid.

[0116] In the waste liquid treatment method according to this embodiment, the container for holding the waste liquid can be of various shapes, such as a vertically long or horizontally long shape. Furthermore, the waste liquid solidifying agent can be added to the waste liquid in various ways, such as adding it all at once or in portions, or adding it before or after the waste liquid. In the waste liquid treatment method according to this embodiment, solidifying the waste liquid in a vertically long container is preferable because the waste liquid solidifying agent solidifies quickly and uniformly. When added, the waste liquid solidifying agent may be in powder form or may be contained in a water-soluble, water-breakable, or water-permeable container or bag.

[0117] According to conventional knowledge, when a waste liquid solidifying agent is added to a waste liquid, some of it sinks, some of it floats, and the agent swells while remaining floating, so that solidification proceeds from the top and bottom of the waste liquid. Therefore, particularly when a vertically elongated container is used, it is possible to significantly shorten the time until the entire waste liquid solidifies. By using the water-absorbent resin composition according to the present embodiment in combination with this swelling mechanism, it is possible to shorten the time until solidification and improve gel fluidity, which is preferable.

[0118] The waste liquid disposal method according to this embodiment is a method of disposing of the waste liquid solidified by the waste liquid treatment method described above together with the container. The solidified waste liquid may be removed from the container. However, as in the waste liquid disposal method according to this embodiment, by disposing of the entire container containing the waste liquid (however, in the case of a multi-container, only the inner container in contact with the waste liquid), hygienic disposal can be achieved.

[0119] An embodiment of the present invention may include the following inventions [1] to [8].

[0120] [1] A water-absorbent resin composition comprising a water-absorbent resin having a constitutional unit derived from an acid group-containing unsaturated monomer, a hydrophobic substance, and a hydrophilic substance, wherein the hydrophobic substance is contained in an amount of more than 0.16 parts by weight and less than 0.60 parts by weight relative to 100 parts by weight of the water-absorbent resin, and the hydrophilic substance is contained in an amount of more than 0.20 parts by weight and less than 0.50 parts by weight relative to 100 parts by weight of the water-absorbent resin.

[0121] [2] The water-absorbing resin composition according to [1], wherein the hydrophobic substance is zinc stearate.

[0122] [3] The water-absorbing resin composition according to [2], wherein the zinc stearate is obtained by a wet method.

[0123] [4] The water-absorbing resin composition according to any one of [1] to [3], wherein the hydrophilic substance is water-insoluble inorganic fine particles.

[0124] [5] The water-absorbent resin composition according to any one of [1] to [4], wherein the water-absorbent resin has a CRC of 10 g / g to 60 g / g.

[0125] [6] The water-absorbing resin composition according to any one of [1] to [5], wherein the weight average particle diameter (D50) of the water-absorbing resin is 150 μm to 700 μm.

[0126] [7] The bulk density of the water-absorbent resin is 0.30 g / cm ３ ~0.90 g / cm ３ The water-absorbing resin composition according to any one of [1] to [6],

[0127] [8] The water-absorbing resin composition according to any one of [1] to [7], which is used in a method for treating waste liquid, in which the water-absorbing resin composition is poured into waste liquid in a container to solidify the waste liquid into a gel state.

[0128] [9] A method for treating waste liquid, comprising adding the water-absorbing resin composition according to any one of [1] to [8] to the waste liquid to solidify the waste liquid into a gel state.

[0129]

[10] The method for treating waste liquid according to [9], wherein the waste liquid is medical waste liquid.

[0130]

[11] The method for treating waste liquid according to [9] or

[10] , wherein the waste liquid is medical waste liquid containing blood.

[0131]

[12] A method for disposing of waste liquid, comprising disposing of the waste liquid solidified by the method for treating waste liquid according to any one of [9] to

[11] together with the container.

[0132] The present invention will be explained in more detail with reference to the following experimental examples. However, the present invention is not limited to these explanations, and experimental examples obtained by appropriately combining the technical means disclosed in each experimental example are also included in the scope of the present invention.

[0133] Hereinafter, a powder obtained by pulverizing and classifying a dried product obtained by drying will be referred to as a "water absorbent resin powder", and particles obtained by surface cross-linking the water absorbent resin powder will be referred to as "water absorbent resin particles". Furthermore, the "water absorbent resin" includes the dried product, the water absorbent resin powder, and the water absorbent resin particles.

[0134] In the following Production Examples, Examples and Comparative Examples, unless otherwise specified, the operations were carried out under the conditions of room temperature (20 to 25° C.) and relative humidity of 45 to 55% RH.

[0135] Unless otherwise noted, the electrical equipment used in the following Production Examples, Examples, and Comparative Examples (including measurements of the physical properties of the water-absorbent resin) used a power supply of 200V or 100V.

[0136] <Measurement of physical properties of water absorbent resin> (1) Water absorption capacity (CRC / Centrifuge Retention Capacity) The CRC of a water absorbent resin powder or a water absorbent resin particle was measured in accordance with NWSP 241.0.R2(15). Specifically, 0.2 g of the water absorbent resin powder was placed in a nonwoven bag, and then immersed in a large excess of a 0.9 mass % aqueous sodium chloride solution for 30 minutes to allow the water absorbent resin powder to freely swell, and then dehydrated using a centrifuge (250 G), and then the absorption capacity (CRC) (unit: g / g) was measured.

[0137] (2) Particle Size Distribution, Weight Average Particle Diameter (D50), and Logarithmic Standard Deviation (σζ) of Particle Size Distribution The particle size distribution, weight average particle diameter (D50), and logarithmic standard deviation (σζ) of particle size distribution of a water absorbent resin particle were measured in accordance with “(3) Mass-Average Particle Diameter (D50) and Logarithmic Standard Deviation (σζ) of Particle Diameter Distribution” described in columns 27 and 28 of U.S. Pat. No. 7,638,570.

[0138] (3) Bulk Specific Gravity The bulk specific gravity of the water-absorbent resin particles was measured in accordance with JIS K 3362 using a bulk specific gravity measuring instrument (manufactured by Kuramochi Scientific Instruments Manufacturing Co., Ltd.) with reference to International Publication No. 2010 / 095427. In order to eliminate bias in particle size distribution, 100.0 g of water-absorbent resin particles were thoroughly mixed. Then, 100.0 g of the water-absorbent resin particles were placed in a funnel with a damper closed, and the damper was quickly opened, and the water-absorbent resin particles were poured into a funnel with an internal volume of 100 cm. ３ The water-absorbent resin particles that had risen from the receiver were scraped off with a glass rod, and then the weight of the receiver containing the water-absorbent resin particles (weight W2 [g]) was accurately measured to the nearest 0.1 g, and the bulk specific gravity was calculated according to the following formula. The temperature of the environment in which the measurement was carried out was 23.2°C, and the relative humidity was 31% RH. Bulk specific gravity [g / cm ３]=(W2-W1) / 100cm ３ .

[0139] <Measurement of Physical Properties of Hydrophobic Substances> (5) Methanol Index 50 ml of pure water at 25°C and a stirrer tip (25 mm long x 8 mm diameter, tapered on both sides, made of Teflon (registered trademark)) were placed in a 300 ml glass beaker (inner diameter 78 mm x height 103 mm), and 1 g of hydrophobic substance was added thereto. The mixture was then stirred at 750 rpm with a stirrer. Methanol at 25°C was continuously added dropwise at 10 ml / min using a burette. Methanol was added dropwise until the hydrophobic substance was wetted and all floating matter on the liquid surface disappeared (all had settled). The volume (ml) was read using the burette's scale, and this value was taken as the methanol index. If the hydrophobic substance was not wetted and floating matter on the liquid surface disappeared even when the volume of methanol at 25°C exceeded 200 ml, the methanol index was determined to be 200 or greater.

[0140] <Performance Evaluation as Waste Liquid Solidifying Agent> (7) Solidification State (Solidification Test) An acrylic cylindrical container (inner diameter 104 mm, height 460 mm) containing 3500 ml of a 2.5 wt % sodium chloride aqueous solution (23±1°C) was placed on a horizontal stand. A funnel for measuring apparent density as specified in JIS K3362 was placed on top of the cylindrical container so that its lower opening was 50 mm above the liquid surface. With the lower opening of the funnel open, 120 g of each water-absorbent resin composition was poured into the funnel over 10 seconds to solidify (gel) the aqueous sodium chloride solution in the cylindrical container. One hour after the water-absorbent resin composition was poured, the cylindrical container was tilted 5° from the vertical direction to check for the presence or absence of flowing liquid in the cylindrical container, and the solidification state was evaluated. The evaluation criteria are as follows: "Good": No flowing liquid. "Poor": Flowing liquid was present.

[0141] (8) Gel fluidity After evaluating the solidification state as described above, the cylindrical container was laid horizontally (tilted 90°) and, after 1 minute, the gel state (gel fluidity) was observed. The evaluation criteria are as follows: "Excellent": When the cylindrical container is inverted, the solid gel does not flow out of the cylindrical container. "Good": When the cylindrical container is inverted, the solid gel and swollen gel flow out of the cylindrical container. "Poor": When the cylindrical container is inverted, the swollen gel flows out of the cylindrical container. Here, "solid gel" means a gel that does not lose its shape under its own weight, and "swollen gel" means a gel that loses its shape under its own weight.

[0142] Regarding the evaluation of gel fluidity, "excellent" and "good" were considered to be acceptable.

[0143] [Production Example 1] A reactor formed by attaching a lid to a double-armed jacketed stainless steel kneader having an internal volume of 10 L and two sigma-type blades was used as a reaction apparatus.

[0144] 5,500 g of an aqueous solution of sodium acrylate with a neutralization rate of 75 mol% (monomer concentration 38% by mass) was mixed with 5.1 g of polyethylene glycol diacrylate (average number of moles of ethylene oxide added: 9) as an internal crosslinking agent to prepare an aqueous monomer solution. The aqueous monomer solution was degassed for 30 minutes under a nitrogen gas atmosphere. Next, the aqueous monomer solution was charged into the reactor, and while maintaining the liquid temperature at 30°C, nitrogen gas was blown into the aqueous monomer solution in the reactor until the dissolved oxygen level reached 1 ppm or less, thereby degassing the solution.

[0145] Subsequently, while the aqueous monomer solution was being stirred with a kneader, 29.8 g of a 10% by mass aqueous solution of sodium persulfate and 6.0 g of a 0.2% by mass aqueous solution of L-ascorbic acid were separately added as polymerization initiators. Then, about 1 minute after the addition, the temperature of the aqueous monomer solution began to rise, and polymerization began.

[0146] Then, polymerization was carried out while stirring and the jacket temperature was changed from 30°C to 60°C and maintained at that temperature, and 19 minutes after the addition of the polymerization initiator, the polymerization peak temperature reached 88°C. 60 minutes after the start of polymerization, the hydrogel-like crosslinked polymer (1) was removed. The obtained hydrogel-like crosslinked polymer (1) was fragmented to particles having diameters of about 1 to 5 mm.

[0147] The hydrogel crosslinked polymer (1) was spread on a wire net with an opening of 300 μm (50 mesh) and dried with hot air at 180° C. for 45 minutes to obtain a dried product (1).

[0148] Subsequently, the dried product (1) was pulverized using a roll mill, and further classified using JIS standard sieves with mesh sizes of 600 μm and 106 μm to obtain an irregularly pulverized water-absorbent resin powder (1a) having a particle diameter of 106 μm or more and less than 600 μm. The coarse particles remaining on the 600 μm mesh sieve were again pulverized using a roll mill to produce a pulverized product (1b1). The particles that passed through the 106 μm mesh sieve (fine powder, 12% by weight of the total amount used for pulverization) were mixed with 90 ° C. hot water, then dried under the above-mentioned drying conditions, and pulverized under the above-mentioned pulverization conditions to produce a pulverized product (1b2). Then, the pulverized product (1b1) and the pulverized product (1b2) were combined and classified again using JIS standard sieves with mesh sizes of 600 μm and 106 μm, to obtain an irregularly pulverized water-absorbent resin powder (1b) having a particle size of 106 μm or more and less than 600 μm. Particles remaining on the sieve with a mesh size of 600 μm and particles passing through the sieve with a mesh size of 106 μm were removed. The water-absorbent resin powder (1a) and the water-absorbent resin powder (1b) were mixed to obtain an irregularly pulverized water-absorbent resin powder (1). The water absorption capacity of the water-absorbent resin powder (1) was 41.9 g / g.

[0149] A surface cross-linking agent solution (1) consisting of 0.05 parts by weight of ethylene glycol diglycidyl ether, 1 part by weight of propylene glycol, 3 parts by weight of water, and 1 part by weight of isopropyl alcohol was mixed with 100 parts by weight of the obtained water absorbent resin powder (1), and the mixture was heated at 180°C for 40 minutes to obtain surface cross-linked water absorbent resin particles (A). The water absorbent resin particles (A) have a water absorption capacity of 34.8 g / g, a weight average particle diameter (D50) of 408 µm, and a bulk specific gravity of 0.67 g / cm. ３ It was.

[0150] [Production Example 2] A mixed solution (a) was prepared by charging 291 parts by weight of acrylic acid, 0.63 parts by weight of polyethylene glycol diacrylate (molecular weight 523) as an internal crosslinking agent, 1.80 parts by weight of a 1.0 wt% aqueous solution of trisodium diethylenetriaminepentaacetic acid, and 3.60 parts by weight of a 1.0 wt% solution of IRGACURE (registered trademark) 184 in acrylic acid into a 1 L polypropylene container covered with expanded polystyrene as a heat insulating material.

[0151] Separately, 247 parts by weight of a 48.5 wt % aqueous sodium hydroxide solution and 255 parts by weight of ion-exchanged water adjusted to 50°C were placed in a 1 L polypropylene container covered with another insulating polystyrene foam to prepare a mixed solution (b).

[0152] The mixed solution (b) was added to the mixed solution (a) while stirring at 800 rpm using a magnetic stirrer (length: 5 cm) to obtain an aqueous monomer solution (2). The temperature of the aqueous monomer solution (2) rose to approximately 100°C due to the heat of neutralization and heat of dissolution. The neutralization rate of acrylic acid was 73.5 mol%. The content of trisodium diethylenetriaminepentaacetic acid (chelating agent) was 0.005 wt% (50 ppm) based on the solid content of the monomer.

[0153] Subsequently, 1.8 parts by weight of a 3% by weight aqueous solution of sodium persulfate was added as a polymerization initiator to the aqueous monomer solution (2) to prepare a reaction solution (2).

[0154] After stirring the reaction mixture (2) for about 3 seconds, it was immediately poured into a stainless steel vat-type reactor (bottom: 340 x 340 mm, height: 25 mm, inner surface: Teflon (registered trademark) coated) in an open-to-air system. At the same time, ultraviolet light was irradiated using an ultraviolet irradiation device. After about 10 seconds, the polymerization reaction started. The peak temperature was reached within about 1 minute.

[0155] After 3 minutes had elapsed since the start of polymerization, the ultraviolet irradiation was stopped and the hydrogel crosslinked polymer (2) was taken out. The above series of operations were carried out in an open-air system.

[0156] Next, the hydrogel crosslinked polymer (2) was gel-crushed using a meat chopper (MEAT-CHOPPER TYPE 12VR-400KSOX; die hole diameter: 6.4 mm, number of holes: 38, die thickness: 8 mm / manufactured by Iizuka Kogyo Co., Ltd.) to obtain a particulate hydrogel crosslinked polymer (2).

[0157] Next, the particulate hydrogel crosslinked polymer (2) was spread on a wire mesh with an opening of 300 μm (50 mesh) and dried with hot air at 180° C. for 45 minutes. Subsequently, it was pulverized using a roll mill, and the pulverized product was classified using JIS standard sieves with openings of 850 μm and 150 μm. By this series of operations, an irregularly pulverized water-absorbent resin powder (2) having a particle size of 150 μm or more and less than 850 μm was obtained. The solid content of the water-absorbent resin powder (2) was 97% by weight.

[0158] Subsequently, a surface crosslinking agent solution (2) consisting of 0.024 parts by weight of ethylene glycol diglycidyl ether, 0.52 parts by weight of propylene glycol, 2.1 parts by weight of ion-exchanged water, and 0.31 parts by weight of ethylene carbonate was uniformly mixed with 100 parts by weight of the water absorbent resin powder (2), and the mixture was heated at 176°C for 40 minutes to obtain surface-crosslinked water absorbent resin particles (B). The water absorbent resin particles (B) have a water absorption capacity of 38.8 g / g, a weight average particle diameter (D50) of 362 µm, and a bulk specific gravity of 0.65 g / cm. ３ It was.

[0159] [Production Example 3] A water absorbent resin powder (3) was obtained in the same manner as in Production Example 1, except that the amount of polyethylene glycol diacrylate (average number of moles of ethylene oxide added: 9) was changed to 2.4 g. The fine powder accounted for 14 wt % of the total amount subjected to pulverization. The water absorption capacity of the obtained water absorbent resin powder (3) was 54.3 g / g.

[0160] Next, 3.33 parts by weight of a surface cross-linking agent aqueous solution (3) was mixed with 100 parts by weight of the water absorbent resin powder (3). The surface cross-linking agent aqueous solution (3) consisted of 0.02 part by weight of ethylene glycol diglycidyl ether, 0.2 part by weight of 1,4-butanediol, 0.5 part by weight of propylene glycol, and 2.1 parts by weight of water. This mixture was heated for 40 minutes while stirring in a mortar mixer heated to 175°C, thereby obtaining surface-cross-linked water absorbent resin particles (C). The water absorbent resin particles (C) had a water absorption capacity of 47.1 g / g, a weight average particle diameter (D50) of 408 μm, and a bulk specific gravity of 0.64 g / cm. ３ It was.

[0161] Example 1 100 parts by weight of water-absorbent resin particles (A) were uniformly mixed with 0.30 parts by weight of silicon dioxide (Aerosil 200, manufactured by Nippon Aerosil Co., Ltd.) and 0.20 parts by weight of zinc stearate (zinc stearate, manufactured by NOF Corporation) as hydrophilic substances. That is, 100 parts by weight of water-absorbent resin particles (A) were placed together with 0.30 parts by weight of silicon dioxide in a mayonnaise bottle (Mayonnaise 450, manufactured by Nippon Yamamura Glass Co., Ltd.) having an outer diameter of 8 cm and a height of 13 cm, and the mixture was shaken at 800 (cycles / min) for 1 minute using a paint shaker (No. 488 test disperser, manufactured by Toyo Seiki Seisakusho Co., Ltd.). Then, 0.20 parts by weight of zinc stearate was added as a hydrophobic substance to the mayonnaise bottle, and the mixture was further shaken for 3 minutes to obtain a water-absorbent resin composition (1).

[0162] Example 2 A water-absorbent resin composition (2) was obtained in the same manner as in Example 1, except that the water-absorbent resin particles (A) were replaced with the water-absorbent resin particles (B).

[0163] Example 3 A water-absorbent resin composition (3) was obtained in the same manner as in Example 1, except that the water-absorbent resin particles (A) were replaced with the water-absorbent resin particles (C).

[0164] Example 4 The same procedure as in Example 2 was carried out, except that zinc stearate (zinc stearate, manufactured by NOF Corporation) was replaced with zinc stearate (SZ-TF, manufactured by Sakai Chemical Industry Co., Ltd.), to obtain a water-absorbent resin composition (4).

[0165] Example 5 A water-absorbing resin composition (5) was obtained in the same manner as in Example 2, except that the amount of silicon dioxide added was changed to 0.40 parts by weight and the amount of zinc stearate added was changed to 0.31 parts by weight.

[0166] Example 6 A water-absorbent resin composition (6) was obtained in the same manner as in Example 2, except that the amount of silicon dioxide added was changed to 0.23 parts by weight and the amount of zinc stearate added was changed to 0.18 parts by weight.

[0167] Example 7 A water-absorbent resin composition (7) was obtained in the same manner as in Example 2, except that the amount of silicon dioxide added was changed to 0.36 parts by weight and the amount of zinc stearate added was changed to 0.48 parts by weight.

[0168] Example 8 A water-absorbent resin composition (8) was obtained in the same manner as in Example 3, except that the amount of silicon dioxide added was changed to 0.45 parts by weight and the amount of zinc stearate added was changed to 0.55 parts by weight.

[0169] Comparative Example 1 The same procedure as in Example 1 was carried out except that the amount of silicon dioxide added was changed to 0.20 parts by weight, to obtain a comparative water-absorbing resin composition (1).

[0170] Comparative Example 2 The same procedure as in Example 1 was carried out except that the amount of silicon dioxide added was changed to 0.50 parts by weight, to obtain a comparative water-absorbent resin composition (2).

[0171] Comparative Example 3 The same procedure as in Example 1 was carried out except that the amount of zinc stearate added was changed to 0.10 parts by weight, to obtain a comparative water-absorbent resin composition (3).

[0172] Comparative Example 4 A comparative water-absorbent resin composition (4) was obtained in the same manner as in Example 1, except that the amount of zinc stearate added was changed to 0.60 parts by weight.

[0173] Comparative Example 5 The same procedure as in Example 1 was carried out except that zinc stearate was not added, to obtain a comparative water-absorbent resin composition (5).

[0174] Comparative Example 6 The same procedure as in Example 3 was carried out except that the amount of silicon dioxide added was changed to 0.20 parts by weight, to obtain a comparative water-absorbent resin composition (6).

[0175] Comparative Example 7 The same procedure as in Example 3 was carried out except that the amount of silicon dioxide added was changed to 0.50 parts by weight and the amount of zinc stearate added was changed to 1.00 parts by weight, to obtain a comparative water-absorbent resin composition (7).

[0176] Comparative Example 8 The same procedure as in Example 3 was carried out except that the amount of zinc stearate added was changed to 0.01 parts by weight, to obtain a comparative water-absorbent resin composition (8).

[0177] Comparative Example 9 The same procedure as in Example 3 was carried out except that the amount of zinc stearate added was changed to 10.00 parts by weight, to obtain a comparative water-absorbent resin composition (9).

[0178] Hereinafter, the physical properties of the water-absorbent resin particles A to C produced in Production Examples 1 to 3 are shown in Table 1, and the evaluation results of the solidification states and gel fluidity of the water-absorbent resin compositions (1) to (7) and the comparative water-absorbent resin compositions (1) to (9) are shown in Table 2.

[0179] The methanol indexes of the zinc stearates ((Zinc Stearate, manufactured by NOF Corporation) and (SZ-TF, manufactured by Sakai Chemical Industry Co., Ltd.)) used in the Examples and Comparative Examples were measured and found to be 200 or more. Of these zinc stearates, zinc stearate is zinc stearate obtained by a wet method, and SZ-TF is zinc stearate obtained by a dry method.

[0180] As shown in Table 2, in the water-absorbent resin compositions (1) to (8) produced in Examples 1 to 8, the hydrophobic substance was contained in an amount of more than 0.16 parts by weight and less than 0.60 parts by weight relative to 100 parts by weight of the water-absorbent resin particles, and the hydrophilic substance was contained in an amount of more than 0.20 parts by weight and less than 0.50 parts by weight relative to 100 parts by weight of the water-absorbent resin particles. Therefore, the water-absorbent resin compositions (1) to (8) correspond to the water-absorbent resin composition of the present invention. On the other hand, in the comparative water-absorbent resin compositions (1) to (9) produced in Comparative Examples 1 to 9, the hydrophobic substance was contained outside the range of more than 0.16 parts by weight and less than 0.60 parts by weight relative to 100 parts by weight of the water-absorbent resin particles, and / or the hydrophilic substance was contained outside the range of more than 0.20 parts by weight and less than 0.50 parts by weight relative to 100 parts by weight of the water-absorbent resin particles. Therefore, the comparative water-absorbent resin compositions (1) to (9) do not correspond to the water-absorbent resin composition of the present invention.

[0181] In addition, it was found that the water-absorbing resin compositions (1) to (8) had improved gel fluidity compared to the comparative water-absorbing resin compositions (1) to (9).

[0182] The present invention can be used to treat wastewater discharged from various industrial fields.

Claims

1. A water-absorbent resin composition comprising a water-absorbent resin having a constituent unit derived from an acid group-containing unsaturated monomer, a hydrophobic substance, and a hydrophilic substance, wherein the hydrophobic substance is contained in an amount of more than 0.16 parts by weight and less than 0.60 parts by weight relative to 100 parts by weight of the water-absorbent resin, and the hydrophilic substance is contained in an amount of more than 0.20 parts by weight and less than 0.50 parts by weight relative to 100 parts by weight of the water-absorbent resin.

2. The water-absorbent resin composition according to claim 1, wherein the hydrophobic substance is zinc stearate.

3. The water-absorbing resin composition according to claim 2, wherein the zinc stearate is obtained by a wet method.

4. The water-absorbing resin composition according to any one of claims 1 to 3, wherein the hydrophilic substance is water-insoluble inorganic fine particles.

5. The water-absorbent resin composition according to any one of claims 1 to 4, wherein the water-absorbent resin has a CRC of 10 g / g to 60 g / g.

6. The water-absorbent resin composition according to any one of claims 1 to 5, wherein the water-absorbent resin has a weight-average particle diameter (D50) of 150 μm to 700 μm.

7. The bulk density of the water-absorbent resin is 0.30 g / cm ３ ~0.90 g / cm ３ The water-absorbing resin composition according to any one of claims 1 to 6, 8. The water-absorbing resin composition according to any one of claims 1 to 7, which is used in a method for treating waste liquid, in which the composition is poured into waste liquid in a container to solidify the waste liquid into a gel state.

9. A method for treating waste liquid, which comprises adding the water-absorbing resin composition according to any one of claims 1 to 8 to the waste liquid to solidify the waste liquid into a gel state.

10. The method for treating waste liquid according to claim 9, wherein the waste liquid is medical waste liquid.

11. The method for treating waste liquid according to claim 9 or 10, wherein the waste liquid is medical waste liquid containing blood.

12. A method for disposing of waste liquid, comprising disposing of the waste liquid solidified by the method for treating waste liquid according to any one of claims 9 to 11 together with the container.

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