Method for selecting water-absorbing resin used for solidifying waste liquid of 3D printer

Abstract

To provide a method for selecting a water-absorbing resin used for solidifying an aqueous waste liquid discharged when manufacturing a three-dimensional molding by a 3D printer.SOLUTION: There is provided a method for selecting a water-absorbing resin used for solidifying an aqueous waste liquid discharged when manufacturing a three-dimensional molding by a 3D printer, wherein the water-absorbing resin is selected based on the result of measuring a liquid absorption rate by using the aqueous waste liquid. Also provided is the method for selecting a water-absorbing resin based on the result of measuring the specific volume by using the aqueous waste liquid.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for selecting a water-absorbent resin used to solidify waste liquid generated when manufacturing a three-dimensional object with a 3D printer. [Background technology]

[0002] Known methods of 3D printers include a fused deposition modeling method, an inkjet ultraviolet curing method, a photolithography method, a laser sintering method, etc. Among these, in the fused deposition modeling method and the inkjet ultraviolet curing method, in order to form a three-dimensional object of a complex shape, a modeling material constituting the three-dimensional object and a support material for supporting the three-dimensional structure of the modeling material are laminated to obtain a three-dimensional object precursor, and then the support material is removed from the three-dimensional object precursor to obtain the desired three-dimensional object.

[0003] As a method for removing a support material from a three-dimensional object precursor, there is a method in which a compound having a high affinity for water, such as polyvinyl alcohol, polyvinylpyrrolidone, poly(2-ethyl-2-oxazoline), or polyalkylene glycol, is used as the support material, and the support material is removed by immersing the three-dimensional object precursor in water (Patent Documents 1 to 3). Meanwhile, like the model material, the support material is a curable resin composition and therefore contains highly reactive compounds. Depending on the type of support material, it may be dissolved using an alkaline aqueous solution, etc., which poses a risk of contact or leakage when disposing of the support material dissolving solution.

[0004] Even 3D printers that do not use support materials still produce a significant amount of waste ink, and devices have been proposed to safely collect this waste ink (Patent Document 4). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special Publication No. 2002-516346 [Patent Document 2] JP 2019-089323 A [Patent Document 3] Special Publication No. 2018-509501 [Patent Document 4] Special Publication No. 2018-520919 Summary of the Invention [Problem to be solved by the invention]

[0006] It is already known that the waste ink generated during nozzle cleaning of inkjet printers can be absorbed into absorbent resins, but as mentioned above, 3D printers generate large amounts of waste liquid, so it is necessary to absorb it quickly and efficiently.

[0007] Therefore, the present inventors attempted to solidify aqueous wastewater using a polyacrylic acid-based water-absorbing resin, which is used in mass-produced paper diapers and is designed to provide consumers with value such as comfort and convenience, and a wide variety of products have been developed to achieve the performance required for such paper diapers. However, the results showed behavior completely different from that of evaluations using water or saline, which are widely used in paper diapers. Therefore, the present inventors began to develop an evaluation method for treating wastewater from 3D printers.

[0008] In the process of examining this evaluation method, the specific gravity of a water absorbent resin that has absorbed a test liquid having a specific gravity of about 1 was measured, and it was found that a certain type of water absorbent resin has a high specific gravity, and the value of the particularly high water absorbent resin exceeds 1, that is, a surprising result was shown in which the volume of a water absorbent resin that has absorbed 100 ml of a test liquid becomes 100 ml or less, leading to the completion of the present invention.

[0009] That is, an object of the present invention is to provide a method for selecting a water-absorbent resin suitable for treating aqueous waste liquid discharged when manufacturing a three-dimensional object using a 3D printer.

[0010] Another object of the present invention is to provide a method for safely and simply treating aqueous waste liquid discharged when manufacturing a three-dimensional object using a 3D printer.

[0011] Furthermore, it is clear that the above findings can be applied not only to the treatment of 3D printer wastewater, but also to the treatment of wastewater in standard containers.

[0012] That is, an object of the present invention is to provide a method for selecting a water-absorbent resin suitable for efficiently treating an aqueous waste liquid in a fixed-size container.

[0013] Another object of the present invention is to provide a method for efficiently treating an aqueous waste liquid in a fixed-size container. [Means for solving the problem]

[0014] In order to solve at least one of the above problems, one method according to the present invention provides a method for selecting a water-absorbent resin to be used for solidifying aqueous waste liquid discharged when manufacturing a three-dimensional object with a 3D printer, the method selecting a water-absorbent resin based on the results of measuring the absorption rate using the aqueous waste liquid.

[0015] In order to solve at least one of the above problems, one method according to the present invention provides a method for treating aqueous waste liquid discharged when manufacturing a three-dimensional object with a 3D printer, which comprises absorbing the aqueous waste liquid using a water-absorbent resin having an absorption speed of 15 seconds or less when using a polypropylene glycol-containing test liquid, and solidifying the aqueous waste liquid.

[0016] In order to solve at least one of the above problems, one method according to the present invention provides a method for selecting a water-absorbing resin used to solidify an aqueous waste liquid in a fixed-size container, the aqueous waste liquid containing at least a polymer component, and a water-absorbing resin is selected based on the result of measuring the liquid absorption rate using a model evaluation liquid containing a component contained in the waste liquid.

[0017] In order to solve at least one of the above problems, one method according to the present invention is a method for treating an aqueous waste liquid in a fixed-size container, comprising the steps of: The aqueous waste liquid contains at least a polymer component, The aqueous waste liquid is absorbed and solidified using a water-absorbing resin having an absorption speed of 15 seconds or less and a specific volume of 0.50 to 1.20 ml / g when used with the aqueous waste liquid. Effect of the Invention

[0018] According to the present invention, aqueous waste liquid discharged during the manufacture of three-dimensional objects using a 3D printer, for example, can be safely and simply treated. Furthermore, when a more preferable water-absorbing resin is used, the specific volume after absorbing the liquid is smaller than that of the waste liquid alone, which is expected to result in the miniaturization of the liquid-absorbing treatment container and the reduction of the storage space required until disposal. [Brief description of the drawings]

[0019] [Figure 1] This is a method for measuring the liquid absorption rate of the present invention. [Diagram 2] This is a method for measuring the amount of absorbed liquid according to the present invention. [Diagram 3] This is a method for measuring the specific volume after liquid absorption. [Figure 4] This is a graph comparing the relationship between absorption speed and specific volume for saline and 3D printer waste liquid. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] The present invention will now be described in further detail.

[0021] <Measurement conditions> In the present invention, the measurement of the absorption rate, the absorption amount, and the specific volume is carried out by adjusting the liquid temperature to a practical use using an actually generated aqueous waste liquid or a model liquid prepared according to the composition of the aqueous waste liquid. In the present specification, unless otherwise specified, the actually generated aqueous waste liquid and the model liquid prepared according to the composition of the aqueous waste liquid are not distinguished and are described as aqueous waste liquid. In the present invention, the amount of the water-absorbing resin and the aqueous waste liquid used for measuring the absorption rate and the specific volume are determined according to the practical use. Specifically, although it varies depending on the type of the aqueous waste liquid, it is set to a degree that the water-absorbing resin can solidify the aqueous waste liquid. The amount of the aqueous waste liquid that the water-absorbing resin can solidify can be known by, for example, measuring the absorption amount of the aqueous waste liquid.

[0022] <How to make model liquid> When the structure of the modeled object changes, the amount of support agent used during modeling and the amount of water required to remove the modeled object change. Therefore, it is most preferable to measure the amount of absorbed liquid using the actually generated aqueous waste liquid. However, this method is inefficient because it requires measurement for each treatment. Therefore, it is convenient to select the water-absorbing resin to be used for solidification in advance using a model liquid with an average composition.

[0023] When preparing the model liquid, the model liquid may be adjusted to contain a component that can be contained in the aqueous waste liquid and that is dissolved in water in the largest amount. Furthermore, if a component that is not the largest component but has a content of 1 mass% or more can be contained, it is preferable to adjust the model liquid to contain that component.

[0024] <Test solution containing polypropylene glycol> In the present invention, the polypropylene glycol-containing test liquid is a 10% by weight dispersion liquid obtained by mixing acryloylmorpholine, polypropylene glycol (average molecular weight 400), and polypropylene glycol (average molecular weight 1000) in a weight ratio of 1:2:2, polymerizing them, and adding the resulting polymer to ion-exchanged water. Details will be described in the Examples.

[0025] In one embodiment of the present invention, the aqueous waste liquid discharged when manufacturing a three-dimensional object with a 3D printer may be a polypropylene glycol-containing test liquid. Hereinafter, the measurement method will be described in detail using the polypropylene glycol-containing test liquid as an example.

[0026] <Method for measuring liquid absorption rate> In one embodiment of the present invention, the temperature of the polypropylene glycol-containing test liquid may be 30±1° C. In one embodiment of the present invention, 50 g of the test liquid is weighed into a 100 mL beaker (a glass beaker with an inner diameter of 5 cm and a height of 7 cm), and 2.00 g of a sample is added while stirring at 600 rpm with a cylindrical stirrer with a length of 40 mm and a width of 8 mm. The liquid absorption rate (seconds) is measured by measuring the time (seconds) from when the sample is added until the sample absorbs the test liquid and the test liquid covers the stirrer tip.

[0027] <Method for measuring the amount of absorbed liquid> The following changes were made with reference to NWSP240.0.R2(15) “Determination of the Free Swell Capacity in Saline by Gravimetric Measurement,” which is an evaluation method for the amount of liquid absorption of absorbent resins used in disposable diapers, etc.

[0028] 0.100 g of sample (weight W0(g)) was weighed out and evenly placed in a 60 x 85 mm nonwoven bag. The bag was heat sealed and then immersed in 300 mL of polypropylene glycol-containing test liquid adjusted to 23 ± 2°C. After 5 minutes, the bag was pulled up with tweezers and hung for 10 minutes to drain. The weight of the bag (W1(g)) was then measured. The same operation was performed without the sample, and the weight of the bag (W2(g)) was measured. The amount of liquid absorption was calculated from the obtained W0(g), W1(g), and W2(g) according to the following formula.

[0029] Liquid absorption amount (g / g)={(W1-W2) / W0}-1 <Method of measuring specific volume> In one embodiment of the present invention, 50 g of polypropylene glycol-containing test liquid is weighed into a 100 mL beaker (a glass beaker with an inner diameter of 5 cm and a height of 7 cm), and then the mixture is stirred at 600 rpm with a cylindrical stirrer with a length of 40 mm and a thickness of 8 mm, and 2.00 g of sample is added. After stirring for 1 minute, 20 g of the swollen hydrogel is weighed out and placed evenly on the bottom surface of a cylindrical container with an inner diameter of 6 cm, and a cylindrical weight of 590 g and a diameter of 5.96 cm is placed on top so that the weight is evenly applied to the hydrogel, and the weight is applied for 1 minute. After 1 minute, the height of the compressed hydrogel is measured with the weight still placed on it. The specific volume is calculated by the following calculation method.

[0030] Specific volume (cm 3 / g) = Height of the above hydrous gel (cm) × Bottom area of ​​the cylindrical container (cm 2 ) ÷ mass of hydrous gel (g) <Selection of water-absorbent resin> The water-absorbent resin used in the present invention has an absorption capacity of at least 5 g / g of aqueous waste liquid.

[0031] Hereinafter, a method for selecting a water-absorbent resin suitable for treating an aqueous waste liquid will be described, taking the aqueous waste liquid as an example, which is a test liquid containing polypropylene glycol.

[0032] The water-absorbent resin used in one embodiment of the present invention has a liquid-absorption capacity capable of measuring the liquid-absorption rate using at least a polypropylene glycol-containing test liquid, that is, capable of solidifying 50 g of a polypropylene glycol-containing test liquid with 2 g of the water-absorbent resin.

[0033] The water-absorbing resin used in the treatment method of the present invention is selected by measuring the liquid absorption rate using aqueous waste liquid. The water-absorbing resin used in the treatment method of the present invention has a liquid absorption rate using a polypropylene glycol-containing test liquid of 15 seconds or less, preferably 9 seconds or less, more preferably 8 seconds or less, and even more preferably 5 seconds or less. If the liquid absorption rate using a polypropylene glycol-containing test liquid is 15 seconds or less, the work can be completed in a short time, which is efficient and there is little risk of leakage. In addition, it has been found that when an aqueous waste liquid is absorbed using a water-absorbing resin selected based on its high liquid absorption rate, the gel obtained is surprisingly compact. Specifically, the specific volume using a polypropylene glycol-containing test liquid is 1.20 ml / g or less, which tends to make a compact gel. If the liquid absorption rate using a polypropylene glycol-containing test liquid is 9 seconds or less, it tends to make an even more compact gel.

[0034] The water-absorbing resin used in the treatment method of the present invention is preferably selected by measuring the specific volume using an aqueous waste liquid in addition to the liquid absorption speed. The water-absorbing resin used in the treatment method of the present invention has a specific volume using a polypropylene glycol-containing test liquid of preferably 1.20 ml / g or less, more preferably 1.15 ml / g or less, even more preferably 1.10 ml / g or less, particularly preferably 1.05 ml / g or less, and most preferably 1.00 ml / g or less. The smaller the specific volume using a polypropylene glycol-containing test liquid, the more compact the gel becomes, and the smaller the liquid-absorbing treatment container and the smaller the storage space until disposal. On the other hand, the lower limit of the specific volume using a polypropylene glycol-containing test liquid is 0.50 ml / g, and preferably 0.80 ml / g or more.

[0035] The water-absorbing resin used in the treatment method of the present invention may be in the form of particles (powder), fibers, or blocks, but the particles (powder) are preferred from the viewpoints of ease of handling and availability.

[0036] The water-absorbent resin used in the treatment method of the present invention has an average particle diameter of preferably 10 to 1000 μm, more preferably 20 to 850 μm, further preferably 30 to 500 μm, and particularly preferably 40 to 400 μm. The average particle diameter is measured in the same manner as the "Mass-Average Particle Diameter (D50)" described in U.S. Pat. No. 7,638,570. If the "Mass-Average Particle Diameter (D50)" is less than 150 μm, the average particle diameter is measured in the same manner as the "Particle Diameter Measurement Method" described in JP-A-2015-48386 (paragraph

[0037] ) and the volume average particle diameter is the average particle diameter of the water-absorbing resin used in the present invention. When the average particle diameter is within this range, the liquid absorption rate using not only polypropylene glycol-containing test liquid but also aqueous waste liquid is likely to be in a preferred range, and handling is also easy. When the average particle diameter is too large, the liquid absorption rate using not only polypropylene glycol-containing test liquid but also aqueous waste liquid is likely to decrease. When the average particle diameter is too small, the liquid absorption rate using not only polypropylene glycol-containing test liquid but also aqueous waste liquid decreases, or the water-absorbing resin absorbs moisture during storage, causing adhesion between the water-absorbing resins themselves or between the water-absorbing resin and the container, making handling difficult.

[0038] The water-absorbent resin used in the treatment method of the present invention does not contain water-insoluble inorganic fine particles on the surface of the water-absorbent resin, or contains water-insoluble inorganic fine particles in an amount of less than 0.1 parts by weight per 100 parts by weight of the water-absorbent resin. If the surface of the water-absorbent resin does not contain water-insoluble inorganic fine particles, the specific volume of the water-absorbent resin using not only polypropylene glycol-containing test liquid but also aqueous waste liquid is likely to be small. However, if the water-absorbent resin absorbs moisture during storage and the water-absorbent resin adheres to itself or to the container, making it difficult to handle, the surface of the water-absorbent resin can be made to contain a small amount of water-insoluble inorganic fine particles within the above range, making it easier to handle. If the surface of the water-absorbent resin contains a large amount of water-insoluble inorganic fine particles, the specific volume of the water-absorbent resin using not only polypropylene glycol-containing test liquid but also aqueous waste liquid is unlikely to be small.

[0039] The water-absorbing resin used in the treatment method of the present invention is preferably a water-absorbing resin containing nonionic monomer units in an amount of preferably 50 mol % or more, more preferably 60 mol % or more, and even more preferably 70 mol % or more relative to the total monomer units forming the resin. If the nonionic monomer units are contained in the above ratio, the specific volume using a polypropylene glycol-containing test liquid tends to be small.

[0040] <Method of manufacturing water-absorbent resin> There are many known methods for producing water-absorbent resins, and the method is not limited as long as it can produce the water-absorbent resin used in the present invention.

[0041] As an example, the method for producing a water absorbent resin includes a step of preparing an aqueous monomer solution, a polymerization step, a gel crushing step, a drying step, a crushing step, a classification step, a surface cross-linking step, a re-moistening step, and an additive addition step. Each step will be described below.

[0042] (Preparation of Monomer Aqueous Solution) This step is a step of preparing an aqueous monomer solution containing a monomer and an internal crosslinking agent in the method for producing the water-absorbing resin used in the present invention.

[0043] The monomer component used in this process is a water-soluble monomer having an ethylenically unsaturated group, and examples thereof include (meth)acrylic acid, (anhydrous) maleic acid, itaconic acid, cinnamic acid, vinyl sulfonic acid, allyl toluene sulfonic acid, vinyl toluene sulfonic acid, styrene sulfonic acid, 2-(meth)acrylamido-2-methylpropanesulfonic acid, 2-(meth)acryloylethanesulfonic acid, 2-(meth)acryloylpropanesulfonic acid, 2-hydroxyethyl (meth)acryloylphosphat, and the like. Examples of the anionic unsaturated monomers include anionic unsaturated monomers and their salts, such as phosphate; mercaptan group-containing unsaturated monomers; phenolic hydroxyl group-containing unsaturated monomers; amide group-containing unsaturated monomers, such as (meth)acrylamide, N-ethyl (meth)acrylamide, and N,N-dimethyl (meth)acrylamide; and amino group-containing unsaturated monomers, such as N,N-dimethylaminoethyl (meth)acrylate, N,N-dimethylaminopropyl (meth)acrylate, and N,N-dimethylaminopropyl (meth)acrylamide. The monomers used in this step preferably contain 50 mol% or more, more preferably 60 mol% or more, and even more preferably 70 mol% or more of nonionic monomers relative to the total monomers. If the nonionic monomer is contained in the above ratio, the specific volume using the polypropylene glycol-containing test solution tends to be small. When an anionic unsaturated monomer is used, it is preferably in the form of an alkali metal salt or ammonium salt, more preferably in the form of a sodium salt or potassium salt, and even more preferably in the form of a sodium salt.

[0044] Examples of the internal crosslinking agent used in this step include ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, trimethylolpropane di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol di(meth)acrylate, pentaerythritol tri(meth)acrylate, and pentaerythritol tetra(meth)acrylate. Compounds having two or more ethylenically unsaturated groups in one molecule, such as N,N'-methylenebis(meth)acrylamide, triallyl isocyanurate, trimethylolpropane di(meth)allyl ether, triallylamine, tetraallyloxyethane, and glycerolpropoxytriacrylate; ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, glycerin, polyglycerin, propylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, neopentyl alcohol, etc. Polyhydric alcohols such as ethanol, diethanolamine, tridiethanolamine, polypropylene glycol, polyvinyl alcohol, pentaerythritol, sorbitol, sorbitan, glucose, mannitol, mannitan, sucrose, and glucose; polyglycidyl ethers such as ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, and glycerin triglycidyl ether; haloepoxy compounds such as epichlorohydrin and α-methylchlorohydrin; polyaldehydes such as glutaraldehyde and glyoxal; ethylene Examples of the internal crosslinking agent include polyamines such as diamines; hydroxides, halides, carbonates, oxides, and borates such as borax of metals in Groups 2A, 3B, and 8 of the periodic table, such as calcium hydroxide, calcium chloride, calcium carbonate, calcium oxide, magnesium chloride borax, magnesium oxide, aluminum chloride, zinc chloride, and nickel chloride; and polyvalent metal compounds such as aluminum isopropylate. One or more of these can be used in consideration of reactivity, but it is preferable to use a compound having two or more ethylenically unsaturated groups in one molecule as the internal crosslinking agent.

[0045] The amount of the internal crosslinking agent used is preferably 0.0001 to 10 mol %, more preferably 0.001 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 liquid absorption speed is likely to decrease, and if the amount used is too large, the amount of liquid absorption is likely to be insufficient.

[0046] In the present invention, from the viewpoint of improving the physical properties of the resulting water-absorbent resin, substances other than those mentioned above may also be added during preparation of the aqueous monomer solution.

[0047] Specifically, hydrophilic polymers such as starch, starch derivatives, cellulose, cellulose derivatives, polyvinyl alcohol, polyacrylic acid (salts), and crosslinked polyacrylic acid (salts) can be added in amounts of preferably 50% by weight or less, more preferably 20% by weight or less, even more preferably 10% by weight or less, and particularly preferably 5% by weight or less (the lower limit is 0% by weight); and foaming agents such as carbonates, azo compounds, and bubbles, surfactants, chelating agents, chain transfer agents, etc. can be added in amounts of preferably 5% by weight or less, more preferably 1% by weight or less, and even more preferably 0.5% by weight or less (the lower limit is 0% by weight).

[0048] In this step, the concentration of the monomer component in the aqueous monomer solution is not particularly limited, but from the viewpoint of the physical properties of the water absorbent resin, it is preferably 10 to 80% by weight, more preferably 20 to 75% by weight, and even more preferably 30 to 70% by weight.

[0049] (Polymerization process) This step is a step of polymerizing the aqueous monomer solution obtained in the above-mentioned aqueous monomer solution preparation step to obtain a hydrous gel crosslinked polymer (hereinafter referred to as "hydrous gel").

[0050] Examples of the polymerization initiator used in this step include thermal decomposition initiators (e.g., persulfates: sodium persulfate, potassium persulfate, ammonium persulfate; peroxides: hydrogen peroxide, t-butyl peroxide, methyl ethyl ketone peroxide; azo compounds: azonitrile compounds, azoamidine compounds, cyclic azoamidine compounds, azoamide compounds, alkylazo compounds, 2,2'-azobis(2-amidinopropane)dihydrochloride, 2,2'-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride), and photodecomposition initiators (e.g., benzoin derivatives, benzyl derivatives, acetophenone derivatives, benzophenone derivatives, azo compounds). Persulfates are preferred in terms of cost and residual monomer reduction ability. In addition, a reducing agent that promotes the decomposition of these polymerization initiators can be used in combination to form a redox initiator by combining the two. Examples of the reducing agent include (bis)sulfites (salts) such as sodium sulfite and sodium hydrogensulfite, L-ascorbic acid (salts), reducing metals (salts) such as ferrous salts, and amines.

[0051] The amount of the polymerization initiator used is preferably 0.001 to 1 mol %, more preferably 0.001 to 0.5 mol %, based on the monomers, and the amount of the reducing agent used is preferably 0.0001 to 0.02 mol %, based on the monomers.

[0052] The polymerization form applied to this step is preferably spray-drop polymerization, aqueous solution polymerization, or reversed-phase suspension polymerization, more preferably aqueous solution polymerization, or reversed-phase suspension polymerization, and even more preferably aqueous solution polymerization, from the viewpoint of water absorption characteristics, ease of polymerization control, etc. Among them, continuous aqueous solution polymerization is particularly preferred, and either continuous belt polymerization or continuous kneader polymerization can be applied.

[0053] As specific polymerization forms, continuous belt polymerization is disclosed in U.S. Patent 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. Patent Nos. 6,987,151, 6,710,141, etc. By adopting these continuous aqueous solution polymerizations, the production efficiency of the water absorbent resin is improved.

[0054] In this step, the polymerization can be carried out under an air atmosphere, but from the viewpoint of polymerizability, it is preferable to carry out the polymerization under 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).

[0055] (Gel crushing process) In this step, the hydrogel obtained in the polymerization step is gel-pulverized by a screw extruder such as a kneader or a meat chopper, or a gel pulverizer such as a cutter mill, to obtain a particulate hydrogel (hereinafter referred to as a "particulate hydrogel"). When the polymerization step is kneader polymerization, the polymerization step and the gel pulverization step are carried out simultaneously. When a particulate hydrogel is obtained directly in the polymerization process, such as gas phase polymerization or reversed phase suspension polymerization, the gel pulverization step may not be carried out.

[0056] (drying process) This step is a step of drying the particulate hydrogel obtained in the above polymerization step and / or gel crushing step to a desired resin solid content to obtain a dry polymer. The resin solid content is determined from the loss on drying (weight change when 1 g of the water-absorbent resin is heated at 180°C for 3 hours), and is preferably 80% by weight or more, more preferably 85 to 99% by weight, even more preferably 90 to 98% by weight, and particularly preferably 92 to 97% by weight.

[0057] 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, 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 ventilation belt is more preferred.

[0058] From the viewpoint of drying efficiency, the drying temperature (hot air temperature) in the hot air drying is preferably 120 to 250° C., more preferably 150 to 200° C. The drying conditions other than the above drying temperature, such as the hot air speed and drying time, may be appropriately set depending on the water content and total weight of the particulate hydrogel to be dried and the intended resin solid content, and when band drying is performed, the various conditions described in WO 2006 / 100300, WO 2011 / 025012, WO 2011 / 025013, WO 2011 / 111657, etc. are appropriately applied.

[0059] (Crushing process, classification process) This step is a step in which the dried polymer obtained in the drying step is pulverized (pulverization step) and adjusted to a particle size within a predetermined range (classification step) to obtain a water-absorbent resin powder.

[0060] Examples of equipment used in the grinding step include high-speed rotary grinders such as roll mills, hammer mills, screw mills and pin mills, vibration mills, knuckle-type grinders, cylindrical mixers, flash mills and jet mills, which may be used in combination as necessary.

[0061] The method for adjusting the particle size in the classification step is not particularly limited, but examples thereof include sieve classification using a JIS standard sieve (JIS Z8801-1 (2000)) and air flow classification.

[0062] The water absorbent resin powder obtained in this step has an average particle size of preferably 10 to 1000 μm, more preferably 20 to 850 μm, further preferably 30 to 500 μm, and particularly preferably 40 to 400 μm.

[0063] (Surface crosslinking process) This step is a step of providing a part with a higher crosslink density on the surface layer (a part several tens of μm from the surface of the water absorbent resin powder) of the water absorbent resin powder obtained through the above-mentioned steps, and is composed of a mixing step, a heat treatment step, and a cooling step (optional). In the surface crosslinking step, a water absorbent resin that is surface crosslinked by radical crosslinking or surface polymerization on the surface of the water absorbent resin powder, a crosslinking reaction with a surface crosslinking agent, or the like is obtained. When acrylic acid is the main component (50 mol % or more of the total monomers) as a monomer, this step is preferably carried out. This step may improve the handleability and liquid absorption speed of the water absorbent resin.

[0064] The surface cross-linking agent used in this step is not particularly limited, but may be an organic or inorganic surface cross-linking agent. Among them, from the viewpoint of the physical properties of the water-absorbent resin and the handling of the surface cross-linking agent, an organic surface cross-linking agent that reacts with a carboxyl group is preferred. For example, one or more surface cross-linking agents disclosed in U.S. Patent No. 7,183,456 may be mentioned. More specifically, polyhydric alcohol compounds, epoxy compounds, haloepoxy compounds, polyamine compounds or their condensates with haloepoxy compounds, oxazoline compounds, oxazolidinone compounds, polyvalent metal salts, alkylene carbonate compounds, cyclic urea compounds, etc. may be mentioned.

[0065] 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 the water absorbent resin powder. 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 the 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 the water absorbent resin powder.

[0066] The mixing step is a step of mixing the surface crosslinking agent with the water absorbent resin powder. The method of mixing the surface crosslinking agent includes a method of preparing a surface crosslinking agent solution in advance, and preferably spraying or dropping the liquid onto the water absorbent resin powder, more preferably spraying and mixing. As an apparatus for performing the mixing, preferably a high-speed stirring type mixer, more preferably a high-speed stirring type continuous mixer, is included.

[0067] The heat treatment step is a step of applying heat to the mixture discharged from the mixing step to cause a crosslinking reaction on the surface of the water absorbent resin powder. The device for carrying out the crosslinking reaction is not particularly limited, but a paddle dryer is preferable. The reaction temperature in the crosslinking reaction is appropriately set depending on the type of surface crosslinking agent used, and is preferably 50 to 300°C, more preferably 100 to 200°C.

[0068] The cooling step is an optional step that is performed as necessary after the heat treatment step.

[0069] The cooling device is not particularly limited, but is preferably a device having the same specifications as the device used in the heat treatment step, and more preferably a paddle dryer. This is because it can be used as a cooling device by changing the heat medium to a refrigerant. The water-absorbent resin particles obtained in the heat treatment step are forcibly cooled, if necessary, to preferably 40 to 80°C, more preferably 50 to 70°C in the cooling step.

[0070] (Rehumidification process) This step is a step of adding water or an aqueous solution or aqueous dispersion of at least one additive selected from the group consisting of polyvalent metal salt compounds, cationic polymers, chelating agents, inorganic reducing agents, and α-hydroxycarboxylic acid compounds to the surface-crosslinked water-absorbent resin obtained in the surface-crosslinking step. When the water-absorbent resin is excessively dried in the heat treatment step of the surface-crosslinking step, the impact resistance stability and liquid absorption speed may be improved by adding water, an aqueous solution, or an aqueous dispersion. In addition, various functions can be imparted by adding the additives simultaneously with water.

[0071] (Additive addition process) In the manufacturing method of the water-absorbent resin used in the present invention, additives other than the additives described above can also be added to impart various functions to the water-absorbent resin. Specific examples of the additives include surfactants, compounds having phosphorus atoms, oxidizing agents, organic reducing agents, water-insoluble inorganic fine particles, organic powders such as metal soaps, deodorants, antibacterial agents, pulp, thermoplastic fibers, etc. In addition, the surfactants are compounds disclosed in International Publication No. 2005 / 075070, and the water-insoluble inorganic fine particles are compounds disclosed in "(5) Water-insoluble inorganic fine particles" in International Publication No. 2011 / 040530, both of which are applicable to the present invention.

[0072] The amount of the additive used (added amount) is not particularly limited since it is appropriately determined depending on the application, but is preferably 3 parts by weight or less, more preferably 1 part by weight or less, relative to 100 parts by weight of the water absorbent resin powder. In addition, the additive can also be added in a step different from the above step.

[0073] In the method for producing the water-absorbent resin used in the present invention, it is preferable that no water-insoluble inorganic fine particles are added, or that the content of the water-insoluble inorganic fine particles is less than 0.1 part by weight per 100 parts by weight of the water-absorbent resin.

[0074] (Other processes) In the method for producing the water absorbent resin used in the present invention, in addition to the above-mentioned steps, a granulation step, a sizing step, a fine powder removal step, a fine powder reuse step, etc. can be provided as necessary. In addition, one or more steps such as a transport step, a storage step, a packaging step, and a storage step may be further included. The "sizing step" includes a fine powder removal step subsequent to the surface crosslinking step, and a step of classifying and pulverizing the water absorbent resin when it aggregates and exceeds a desired size. In addition, the "fine powder reuse step" includes a form in which the fine powder is added as it is, as well as a step of making it into a large hydrous gel and adding it to any step in the production process of the water absorbent resin.

[0075] <Method for treating aqueous waste liquid using water-absorbing resin> (Aqueous waste liquid) The 3D printer waste liquid treated in the present invention is usually an aqueous waste liquid containing a polymer component. Specifically, the polymer component may include polyvinyl alcohol, polyvinylpyrrolidone, poly(2-ethyl-2-oxazoline), polyalkylene glycol, etc. The concentration of the polymer in the 3D printer waste liquid is preferably 5% by mass to 20% by mass. As a solvent other than water, other solvents may be contained as long as they are compatible with water.

[0076] (container) In the present invention, containers for treating 3D printer waste liquid include waste liquid storage tanks installed in 3D printers, plastic containers such as polyethylene tanks, and metal containers such as drums and 18L cans. A vinyl bag with appropriate strength may be set as an inner bag so that the gel-like material can be easily removed after treatment.

[0077] (Stirring means) When the aqueous waste liquid is brought into contact with the water-absorbing resin, it is preferable to carry out the contact while stirring, since this shortens the absorption time. Also, when the water-absorbing resin is supplied in advance to the bottom of the container, the water-absorbing resin at the top absorbs the aqueous waste liquid and swells, causing a blocking phenomenon in which the aqueous liquid is difficult to pass downward, which may result in a longer absorption time or the generation of wasted water-absorbing resin that does not absorb the aqueous waste liquid. However, contact while stirring has the effect of preventing these problems.

[0078] The stirring method includes a method of inserting a stirring blade or a stirring bar into a container and rotating it, and a method of applying vibration to a container. The rotation speed (vibration frequency) depends on the size of the container and the stirring mechanism, but is preferably 10 to 1000 rpm, and more preferably 60 to 600 rpm. If the rotation speed (vibration frequency) is too high, the 3D printer waste liquid may be scattered. If the rotation speed (vibration frequency) is too low, the stirring effect may be low, and the absorbent resin may not be able to efficiently absorb the 3D printer waste liquid. These operations may be automatic or manual.

[0079] In order to reduce the volume of the water-absorbent resin that has absorbed the aqueous waste liquid, the resin may be compressed by applying pressure from above.

[0080] (Amount of water-absorbent resin) The amount of the water-absorbing resin used to treat the 3D printer waste liquid in the present invention may be set with reference to the value obtained by absorbing the above-mentioned aqueous waste liquid. As a guideline, the amount is preferably 0.5 to 40% by mass, more preferably 1 to 30% by mass, even more preferably 2 to 20% by mass, and particularly preferably 4 to 10% by mass, relative to the aqueous waste liquid. When the amount of the water-absorbing resin is the above amount, it can be solidified without waste or leakage.

[0081] In addition, when the amount of the necessary water absorbent resin exceeds 5 mm when it is previously supplied to the container, the above-mentioned blocking phenomenon is likely to occur even in a form in which the water absorbent resin is supplied to the stored aqueous waste liquid. When using such a large amount of water absorbent resin, the water absorbent resin may be supplied in several batches.

[0082] In the case of supplying in multiple portions, for example, the amount of the stored aqueous waste liquid may be measured with an integrating flow meter or the like, the mass of the aqueous waste liquid stored in the storage container may be measured with a mass meter, the amount of the stored aqueous waste liquid may be measured with a liquid level meter, or the like, and additional water absorbent resin may be supplied at an appropriate timing.

[0083] (temperature) The treatment of the present invention can be carried out at room temperature, preferably at a liquid temperature of the aqueous waste liquid of 15 to 35°C, more preferably 20 to 30°C. EXAMPLES

[0084] The present invention will be described in more detail below with reference to examples, but the present invention is not limited thereto.

[0085] Unless otherwise specified, experiments were conducted in an environment with a temperature of 25°C and a relative humidity of 40–60%.

[0086] <Test solution containing polypropylene glycol> In the present invention, the polypropylene glycol-containing test liquid is a 10% by mass dispersion liquid obtained by mixing acryloyl morpholine, polypropylene glycol (average molecular weight 400), and polypropylene glycol (average molecular weight 1000) in a weight ratio of 1:2:2, polymerizing the polymer, and adding ion-exchanged water to the polymer. In detail, 10 g of acryloyl morpholine, 20 g of polypropylene glycol (average molecular weight 400), 20 g of polypropylene glycol (average molecular weight 1000), and 1.5 g of Irgacure 184 (Nagase & Co., Ltd.) were mixed. The liquid temperature of the obtained mixture was 25°C. This mixture was poured into a 15 cm square Teflon (registered trademark) tray and photopolymerized by irradiating with a UV lamp for 1 minute. 450 g of water was added to the obtained polymer and mixed to obtain a polypropylene glycol-containing test liquid.

[0087] <Method for measuring liquid absorption rate using polypropylene glycol-containing test solution> The temperature of the polypropylene glycol-containing test liquid was adjusted to 30±1°C. 50 g of this test liquid was weighed into a 100 mL beaker (glass beaker with an inner diameter of 5 cm and a height of 7 cm). This test liquid was stirred at 600 rpm with a cylindrical stirrer with a length of 40 mm and a width of 8 mm, and 2.00 g of sample was added. The time (seconds) from when the sample was added until the sample absorbed the test liquid and the test liquid covered the stirrer tip was measured.

[0088] <Method for measuring the amount of absorbed liquid using a test liquid containing polypropylene glycol> The following changes were made with reference to NWSP240.0.R2(15) “Determination of the Free Swell Capacity in Saline by Gravimetric Measurement,” which is an evaluation method for the amount of liquid absorption of absorbent resins used in disposable diapers, etc.

[0089] 0.100 g of sample (weight W0(g)) was weighed out and evenly placed in a 60 x 85 mm nonwoven bag. The bag was heat sealed and then immersed in 300 mL of polypropylene glycol-containing test liquid adjusted to 23 ± 2°C. After 5 minutes, the bag was pulled up with tweezers and hung for 10 minutes to drain. The weight of the bag (W1(g)) was then measured. The same operation was performed without the sample, and the weight of the bag (W2(g)) was measured. The amount of liquid absorption was calculated from the obtained W0(g), W1(g), and W2(g) according to the following formula.

[0090] Liquid absorption amount (g / g)={(W1-W2) / W0}-1 <Method for measuring specific volume using polypropylene glycol-containing test solution> 50 g of polypropylene glycol-containing test liquid adjusted to a liquid temperature of 30°C was weighed into a 100 mL beaker (glass beaker with an inner diameter of 5 cm and a height of 7 cm), and then stirred at 600 rpm with a cylindrical stirrer with a length of 40 mm and a thickness of 8 mm, and 2.00 g of sample was added. After stirring for 1 minute, 20 g of the hydrogel swollen 25 times was weighed out and placed evenly on the bottom of a cylindrical container with an inner diameter of 6 cm, and a cylindrical weight of 590 g and a diameter of 5.96 cm was placed on top so that the load was applied evenly to the hydrogel, and the load was applied for 1 minute. After 1 minute, the height of the compressed hydrogel was measured with the weight still placed on it. The specific volume is calculated by the following calculation method.

[0091] Specific volume (cm 3 / g) = Height of the above hydrous gel (cm) × Bottom area of ​​the cylindrical container (cm 2 ) ÷ mass of hydrous gel (g) (Production Example 1) (Preparation of Monomer Aqueous Solution) 241.8 parts by mass of 40% by mass acrylamide aqueous solution (copper content <1 ppb), 148.2 parts by mass of 37% by mass sodium acrylate aqueous solution, and 27.8 parts by mass of deionized water were mixed. 29.7 parts by mass of 1.5% by mass methylenebisacrylamide aqueous solution as an internal crosslinking agent was dissolved in the resulting mixture to obtain reaction liquid (1).

[0092] (Polymerization process, gel crushing process) The reaction solution obtained was bubbled with nitrogen gas (10 L / min) for 30 minutes and degassed. Next, the reaction solution (1) was supplied to a jacketed stainless steel double-arm kneader having two sigma-type blades, and the inside of the system was replaced with nitrogen gas while maintaining the temperature at 20°C. Next, 2.7 parts by mass of a 25% by mass aqueous solution of sodium persulfate and 3.4 parts by mass of a 2% by mass aqueous solution of L-ascorbic acid were added while stirring the reactor, and polymerization started about 1 minute later. Sodium persulfate and L-ascorbic acid are polymerization initiators. The maximum temperature during polymerization was 95°C. After reaching the polymerization peak temperature, the mixture was stirred for 20 minutes at a jacket temperature of 60°C, and after stopping the stirring, 32.6 parts by mass of a 5% by mass aqueous solution of sodium hydrogen sulfite was added, and the mixture was stirred for another 10 minutes at a jacket temperature of 60°C, and a hydrogel polymer (1) was obtained.

[0093] (drying process) This hydrous gel polymer (1) was spread on a wire net with a mesh size of 50 mesh (opening size of 300 μm) and dried at 160° C. for 130 minutes to obtain a dried polymer (1) with a moisture content of 4%.

[0094] (Crushing process, classification process) The dried polymer (1) was pulverized with a pin mill to obtain a pulverized product (1). The pulverized product (1) was classified with a sieving device having a metal sieve with an opening of 250 μm to obtain a water-absorbent resin powder (1) that passed through a 250 μm sieve. The volume average particle diameter of the water-absorbent resin powder (1) was 135 μm.

[0095] (Production Example 2) The water-absorbent resin powder (1) was further pulverized by a jet mill to obtain a water-absorbent resin powder (2) having a volume average particle size of 45 μm.

[0096] (Production Example 3) (Preparation of Monomer Aqueous Solution) Reaction liquid (3) was prepared by dissolving 2.22 g of polyethylene glycol diacrylate (average number of moles of ethylene oxide added: 8) in 5,500 g of an aqueous solution of sodium acrylate having a neutralization rate of 75 mol % (monomer concentration: 38 mass %).

[0097] (Polymerization process, gel crushing process) The reaction liquid (3) was fed into a reactor formed by attaching a lid to a jacketed stainless steel twin-arm kneader having an internal volume of 10 L and two sigma-type blades, and the system was replaced with nitrogen gas to remove dissolved oxygen while maintaining the reaction liquid at 25°C. Next, 2.4 g of sodium persulfate and 0.12 g of L-ascorbic acid were added while stirring the reaction liquid, and polymerization began about 1 minute later. The polymerization peak temperature was 95°C, and 40 minutes after the start of polymerization, a hydrogel polymer (3) was taken out. The obtained hydrogel (3) was broken down into particles of about 5 mm.

[0098] (drying process) This finely divided hydrogel (3) was spread on a wire net with a mesh size of 50 mesh (opening size: 300 μm) and dried with hot air at 170° C. for 70 minutes to obtain a dried polymer (3).

[0099] (Crushing process, classification process) The obtained dried polymer (3) was pulverized using a roll mill, and further continuously classified using wire meshes with openings of 850 μm and 106 μm. By such operations, irregularly pulverized water absorbent resin powder (3) was obtained.

[0100] (Production Example 4) (Surface crosslinking process) 4.13 parts by mass of a surface cross-linking agent aqueous solution consisting of 0.03 parts by mass of ethylene glycol diglycidyl ether, 0.8 parts by mass of propylene glycol, 2.5 parts by mass of water, and 0.8 parts by mass of ethyl alcohol was mixed with 100 parts by mass of the water absorbent resin powder (3) obtained in Production Example 3. The mixture was heat-treated for 45 minutes in a mortar mixer heated to 195°C, thereby obtaining surface-cross-linked water absorbent resin particles (4).

[0101] (Additive addition process) 0.3 parts by mass of fine particles of silicon dioxide (trade name: Aerosil 200) as an inorganic powder was added to 100 parts by mass of the obtained water-absorbent resin particles (4) and mixed (dry blended) to obtain a water-absorbent resin powder (4).

[0102] (Production Example 5) (Preparation of Monomer Aqueous Solution) In a polypropylene container with an inner diameter of 80 mm and a capacity of 1 liter, covered with polystyrene foam as a heat insulating material, 291 g of acrylic acid, 0.43 g (0.02 mol % relative to the carboxyl group-containing unsaturated monomer) of polyethylene glycol diacrylate (average number of moles of ethylene oxide added: 9) as an internal crosslinking agent, 1.80 g of a 1.0 mass % aqueous solution of diethylenetriaminepentaacetate·pentasodium, and 3.60 g of a 1.0 mass % acrylic acid solution of IRGACURE (registered trademark) 184 (1-hydroxycyclohexyl phenyl ketone) as a photopolymerization initiator were mixed to prepare a solution (A1), and a solution (B1) was mixed with 247 g of a 48.5 mass % aqueous solution of sodium hydroxide and 255 g of ion-exchanged water adjusted to 50° C. The monomer aqueous solution (5) was obtained by quickly adding and mixing the solution (B1) to the solution (A1) stirred at 800 rpm using a magnetic stirrer with a length of 5 cm. The temperature of the aqueous monomer solution (5) rose to about 100° C. due to the heat of neutralization and the heat of dissolution. The neutralization rate of acrylic acid was 73.5 mol %.

[0103] (Polymerization process) 1.8 g of a 3% by mass aqueous solution of sodium persulfate was added to the aqueous monomer solution (5), and after stirring for about 1 second, the solution was immediately poured in an open system into a stainless steel vat-type container with Teflon (registered trademark) attached to the inside. The aqueous monomer solution was poured into the stainless steel vat-type container and simultaneously irradiated with ultraviolet light. Polymerization started shortly after the aqueous monomer solution was poured into the vat (temperature at the start of polymerization was 98°C), and the polymerization reached a peak temperature within about 1 minute. After 3 minutes, the irradiation of ultraviolet light was stopped, and the hydrogel (5) was taken out. This series of operations was carried out in a system open to the atmosphere.

[0104] (Gel crushing process) The obtained hydrous gel (5) was pulverized using a meat chopper (MEAT-CHOPPER TYPE: 12VR-400KSDX, Iizuka Kogyo Co., Ltd., die hole diameter: 6.4 mm, number of holes: 38, die thickness: 8 mm) to obtain a hydrous gel having a particle diameter of about 1 mm (particulate hydrous gel (5)).

[0105] (drying process) The particulate hydrogel (5) was spread on a wire net with a mesh size of 50 mesh (opening size of 300 μm) and dried with hot air at 180° C. for 30 minutes to obtain a dried polymer (5).

[0106] (Crushing process, classification process) The obtained dried polymer (5) was pulverized by a roll mill and further classified by JIS standard sieves with meshes of 850 μm and 150 μm to obtain irregularly pulverized water absorbent resin powder (5).

[0107] Example 6 (Surface crosslinking process) 4.03 parts by mass of a surface cross-linking agent aqueous solution consisting of 0.03 parts by mass of ethylene glycol diglycidyl ether, 1.0 parts by mass of propylene glycol, and 3.0 parts by mass of water was mixed with 100 parts by mass of the water absorbent resin powder (5) obtained in Production Example 5. The mixture was heat-treated at 100° C. for 45 minutes to obtain surface cross-linked water absorbent resin particles (6).

[0108] (Additive addition process) To 100 parts by mass of the obtained water absorbent resin particles (6), 0.3 parts by weight of hydrotalcite (product name: DHT-6, manufactured by Kyowa Chemical Industry Co., Ltd., MgAl(OH)CO·4HO, volume average particle diameter: 0.5 μm) was added and mixed (dry blended), thereby obtaining a water absorbent resin powder (6).

[0109] Example 7 (Preparation of Monomer Aqueous Solution) In Production Example 5, 380 g of acrylic acid was used instead of reaction liquid (A1), 1.53 g (0.055 mol % relative to the carboxyl-containing unsaturated monomer) of polyethylene glycol diacrylate (average number of moles of ethylene oxide added: 9) as an internal crosslinking agent, 1.17 g (0.075 mol % relative to the monomer component) of a 30 wt % aqueous solution of lauryl dimethylaminoacetate betaine (Amphitol 20BS, Kao Corporation, active ingredient: 30 wt %), and 23.4 g of a 0.1 wt % aqueous solution of pentasodium diethylenetriamine pentacetate were used instead of reaction liquid (A2), and 320 g (B2) of a 48.5 wt % aqueous solution of sodium hydroxide was used instead of reaction liquid (B1) to obtain an aqueous monomer solution (4). The temperature of the aqueous monomer solution (4) rose to about 80° C. due to the heat of neutralization and the heat of dissolution. The neutralization rate of acrylic acid was 74 mol %.

[0110] Furthermore, in Production Example 5, 18.58 g of a 4% by mass aqueous solution of sodium persulfate was used instead of 1.8 g of a 3% by mass aqueous solution of sodium persulfate, and a hydrous gel (7) was taken out.

[0111] (Gel crushing process) The obtained hydrogel crosslinked polymer was pulverized by a meat chopper (No. 32 type, Hiraga Manufacturing Co., Ltd., die hole diameter: 3.2 mm) to obtain a finely divided hydrogel crosslinked polymer (particulate hydrogel (7)). The gel pulverization was performed by feeding 4.6 (kg / min) of the hydrogel (7) into the meat chopper with the screw shaft rotation speed of the meat chopper set to 130 rpm.

[0112] (drying process) The particulate hydrogel (7) was spread on a wire net with a mesh size of 50 mesh (opening size of 300 μm) and dried with hot air at 185° C. for 30 minutes to obtain a dried polymer (7).

[0113] (Crushing process, classification process) The obtained dried polymer (7) was pulverized by a roll mill, and sieved with sieves having openings of 850 μm, 600 μm, 500 μm, 300 μm, and 150 μm. Then, the particles passing through 850 μm and not passing through 600 μm were mixed at 3 weight %, the particles passing through 600 μm and not passing through 500 μm were mixed at 10 weight %, the particles passing through 500 μm and not passing through 300 μm, 54 weight %, the particles passing through 300 μm and not passing through 150 μm, and 2 weight % of the particles passing through 150 μm and not passing through 45 μm, to obtain an irregularly pulverized water absorbent resin powder (7A).

[0114] (Surface crosslinking process) The obtained water absorbent resin powder (7A) was transferred to a rotary mixer manufactured by Lödige AG of Germany, and a surface crosslinking agent aqueous solution consisting of 0.025 parts by mass of ethylene glycol diglycidyl ether, 0.3 parts by mass of ethylene carbonate, 0.5 parts by mass of propylene glycol, and 2.0 parts by mass of water was uniformly mixed with 100 parts by mass of the water absorbent resin powder, and heat treatment was performed for 25 minutes at 200° C. Thereafter, the particles were sized using a JIS standard sieve with an opening of 850 μm, thereby obtaining water absorbent resin particles (7B) whose surfaces were crosslinked.

[0115] (Rehumidification process) 100 parts by mass of the obtained water absorbent resin particles (7B) was added with 1 part by weight of 1% by mass DTPA (pentasodium diethylenetriaminepentaacetate) aqueous solution while stirring, and mixed for 1 minute. Then, the mixture was left in a hot air dryer at 60°C for 30 minutes, and then passed through a wire mesh with an opening of 850 μm to obtain re-humidified water absorbent resin particles (7C).

[0116] (Additive addition process) The re-humidified water absorbent resin particles (7C) were mixed with 0.6 parts by weight of fumed silica (Aerosil 200, manufactured by Nippon Aerosil Co., Ltd.). For mixing, 30 g of the water absorbent resin was placed in a mayonnaise bottle (Mayonnaise 225, manufactured by Nippon Yamamura Glass Co., Ltd.) having an outer diameter of 6 cm and a height of 11 cm together with the fumed silica, and the mixture was shaken for 3 minutes at 800 (cycles / min) using a paint shaker (No. 488 test disperser / manufactured by Toyo Seiki Seisakusho Co., Ltd.), to obtain a water absorbent resin powder (7).

[0117] (Production Example 8) (Preparation of Monomer Aqueous Solution) A reaction solution (8) was obtained by the same procedure as in Example 3, except that 7.5 g of polyethylene glycol diacrylate (average number of moles of ethylene oxide added: 9) was used instead of 2.22 g of polyethylene glycol diacrylate (average number of moles of ethylene oxide added: 8).

[0118] (Polymerization process) The reaction liquid (8) was fed into a reactor formed by attaching a lid to a jacketed stainless steel twin-arm kneader having an internal volume of 10 L and two sigma-type blades, and the reaction liquid was kept at 30°C while the system was replaced with nitrogen gas to remove dissolved oxygen. Next, 29.8 g of a 10% by mass aqueous solution of sodium persulfate and 1.5 g of a 1% by mass aqueous solution of L-ascorbic acid were added while stirring the reaction liquid, and polymerization started about 1 minute later. The polymerization peak temperature reached 86°C 17 minutes after the start of polymerization, and the hydrogel (8) was taken out 60 minutes after the start of polymerization. The obtained hydrogel (8) was fragmented into particles of about 1 to 4 mm.

[0119] (drying process) This finely divided hydrogel (8) was spread on a wire net with a mesh size of 50 mesh (opening size: 300 μm) and dried with hot air at 160° C. for 60 minutes to obtain a dried polymer (5).

[0120] (Crushing process, classification process) The obtained dried polymer (8) was pulverized using a roll mill, and further classified continuously using wire meshes with mesh sizes of 450 μm and 106 μm. Particles with a size of 450 μm or more were pulverized again using a roll mill. Particles that passed through the 106 μm wire mesh accounted for 13 mass% of the total amount of particles pulverized. The water-absorbent resin fine particles that passed through the 106 μm wire mesh were mixed with the same amount of water heated to 90° C., dried again under the same conditions, and pulverized. By such operations, an irregularly pulverized water-absorbent resin powder (8A) was obtained at a yield of 98%.

[0121] (Surface crosslinking process) 100 parts by mass of the obtained water absorbent resin powder (8A) was mixed with 0.7 parts by mass of a surface cross-linking agent aqueous solution consisting of 0.1 parts by mass of ethylene glycol diglycidyl ether, 0.3 parts by mass of propylene glycol, and 0.3 parts by mass of water. The mixture was heat-treated for 20 minutes in a mortar mixer heated to 210°C to obtain surface cross-linked water absorbent resin particles (8B).

[0122] (Rehumidification process) A mixed solution consisting of 0.01 parts by mass of sodium diethylenetriaminepentaacetate, 0.1 parts by mass of a 15% by mass aqueous solution of a leaf extract of a plant of the family Theaceae (product name: FS-80MO, sold by Shiraimatsu Pharmaceutical Co., Ltd. (location: 37-1 Ukawa, Minakuchi-cho, Koka-gun, Shiga Prefecture)) and 3 parts by mass of water was sprayed and mixed into 100 parts by mass of the obtained water absorbent resin particles (8B). The obtained mixture was heated and cured at 60° C. for 1 hour while maintaining a moisture content of 3% by mass, and passed through a wire mesh with an opening of 600 μm to obtain rehumidified water absorbent resin particles (8C).

[0123] (Additive addition process) To 100 parts by mass of the re-humidified water absorbent resin particles (8C), 0.3 parts by mass of fine particle-like silicon dioxide (product name: Aerosil 200) as an inorganic powder was added and mixed (dry blended), thereby obtaining a water absorbent resin powder (8) containing 35% by mass of granulated particles.

[0124] (Production Example 9) The water absorbent resin powder (9) was taken out from a commercially available disposable diaper (HUGGIES Ginso (L size, Lot 20200212 ND3 00:05:06), manufactured by Kimberly-Clark, purchased in 2020). When taking out, only the water absorbent resin was taken out so as not to mix with cotton-like pulp. The taken out water absorbent resin powder (9) was dried under reduced pressure until the moisture content of the water absorbent resin was 8% by mass.

[0125] Examples 1 to 7 The polypropylene glycol-containing test liquid used to measure the absorption rate was used as a model liquid for 3D printer waste liquid, and water-absorbent resin powders (1) to (7) were used as the water-absorbent resin, and the model liquid for 3D printer waste liquid was absorbed and solidified while also measuring the absorption rate, resulting in Examples 1 to 7. Furthermore, instead of the polypropylene glycol-containing test liquid, measurements were also performed using physiological saline (0.9 wt% sodium chloride aqueous solution), which is widely used to evaluate water-absorbent resins, as the absorption liquid.

[0126] The absorption speed, absorption amount, and specific volume of the polypropylene glycol-containing test liquid, and the absorption speed and specific volume of physiological saline are respectively: water-absorbent resin powder (1) used in Example 1: 3 seconds, 106 g / g, 0.85 cm 3 / g, 7 seconds, 0.99cm 3 / g, Water-absorbent resin powder (2) used in Example 2: 9 seconds, 89 g / g, 1.07 cm 3 / g, 15 seconds, 1.15cm 3 / g, Water-absorbent resin powder (3) used in Example 3: 8 seconds, 251 g / g, 1.07 cm 3 / g, 26 seconds, 1.00cm 3 / g, Water-absorbent resin powder (4) used in Example 4: 11 seconds, 271 g / g, 1.13 cm 3 / g, 24 seconds, 1.12cm 3 / g, Water-absorbent resin powder (5) used in Example 5: 8 seconds, 246 g / g, 0.99 cm 3 / g, 30 seconds, 1.06cm 3 / g, Water-absorbent resin powder (6) used in Example 6: 14 seconds, 221 g / g, 1.05 cm 3 / g, 32 seconds, 1.13cm 3 / g, Water-absorbent resin powder (7) used in Example 7: 9 seconds, 215 g / g, 1.13 cm 3 / g, 14 seconds, 1.08cm 3 / g.

[0127] Comparative Examples 1 and 2 The polypropylene glycol-containing test liquid used to measure the liquid absorption rate was used as a model liquid of 3D printer waste liquid, and water-absorbent resin powders (8) to (9) were used as the water-absorbent resin. The model liquid of 3D printer waste liquid was absorbed and solidified while also measuring the liquid absorption rate, to give Comparative Examples 1 and 2, respectively.

[0128] The absorption speed, absorption amount, and specific volume of the polypropylene glycol-containing test liquid, and the absorption speed and specific volume of physiological saline were, respectively, 16 seconds, 207 g / g, and 1.41 cm for the water-absorbent resin powder (8) used in Comparative Example 1. 3 / g, 34 seconds, 1.34cm 3 / g, water-absorbent resin powder (9) used in Comparative Example 2: 19 seconds, 201 g / g, 1.56 cm 3 / g, 25 seconds, 1.35cm 3 / g, The treatment results of the model liquid waste from 3D printers and the performance of the water-absorbent resin powder used are summarized in Table 1.

[0129] [Table 1] As shown in Table 1, there is no correlation between the measurement results using physiological saline, which is widely used to evaluate water-absorbent resins, and the measurement results using a polypropylene glycol-containing test liquid as a model test liquid. In addition, it is found that a water-absorbent resin with a high liquid absorption rate has a low specific volume after absorbing liquid, and can store waste liquid compactly. [Industrial Applicability]

[0130] According to the present invention, not only can aqueous waste liquid discharged when manufacturing three-dimensional objects with a 3D printer be safely and simply treated, but the waste liquid treatment container can be made smaller and the storage space required until disposal can be reduced, which is expected to be particularly effective when manufacturing a large number of three-dimensional objects. [Explanation of symbols]

[0131] 11 100mL beaker 12 Cylindrical stirrer 13 Gel dispersion 14. Stirrer 21 Container 22 Non-woven bag containing sample 23 clips 31 A cylindrical container with an inner diameter of 6 cm 32 Cylindrical weight 33 Gel 34 Height measuring device 100 samples (water-absorbent resin) 200 3D printer waste fluid (or model fluid)

Claims

1. A method for selecting a water-absorbent resin to be used for solidifying aqueous waste liquid discharged when manufacturing a three-dimensional object with a 3D printer, the method selecting a water-absorbent resin based on the results of measuring the absorption rate using the aqueous waste liquid.

2. The method according to claim 1, wherein the water-absorbing resin is selected based on the result of measuring the specific volume using the aqueous waste liquid.

3. A method for treating aqueous waste liquid discharged when manufacturing a three-dimensional object with a 3D printer, comprising absorbing the aqueous waste liquid with a water-absorbent resin having an absorption speed of 15 seconds or less using a polypropylene glycol-containing test liquid, and solidifying the aqueous waste liquid.

4. The treatment method according to claim 3, wherein the specific volume of the water-absorbent resin using a polypropylene glycol-containing test liquid is 0.50 to 1.20 ml / g.

5. 5. The method according to claim 3, wherein the water-absorbent resin has an average particle size of 10 to 1000 μm.

6. The treatment method according to any one of claims 3 to 5, wherein the surface of the water absorbent resin does not contain water-insoluble inorganic fine particles, or contains less than 0.1 parts by weight of water-insoluble inorganic fine particles per 100 parts by weight of the water absorbent resin.

7. The treatment method according to any one of claims 3 to 6, wherein the water-absorbing resin contains nonionic monomer units in an amount of 50 mol % or more of the total monomer units.

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