Water-absorbent resin and its manufacturing method

Abstract

To provide a water-absorbing resin and a method for producing the same.SOLUTION: A method for producing a water-absorbing resin includes: a step of obtaining a gel body by subjecting a water-absorbing resin composition comprising an aqueous solution of an acid-based monomer, a polymerization initiator, and a radical polymerization crosslinking agent to radical polymerization; a step of cutting the gel body using a mincer equipped with a perforated plate with variable hole diameters, where a first hole diameter at a material inlet is larger than a second hole diameter at a material outlet, to obtain a plurality of water-absorbing resin particles; and a step of subjecting the water-absorbing resin particles to surface crosslinking treatment to obtain a water-absorbing resin. This enables improvement in the bulk density, absorption rate, and liquid flow conductivity of the resulting water-absorbing resin.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a water-absorbent resin and a method for producing the same, and more particularly to a water-absorbent resin produced by using a mincer having a variable diameter hole plate and a method for producing the same. [Background technology]

[0002] Super absorbent polymers (SAPs) are water-insoluble polymers that are used in a variety of applications, including absorbent articles such as disposable diapers and sanitary napkins, water retention agents for agriculture and forestry, and industrial waterproofing agents.

[0003] The production process of a water-absorbent resin requires the use of large amounts of monomers and hydrophilic polymers, and polyacrylic acid (salt)-based water-absorbent resins using acrylic acid and / or its salts as monomers are mainly produced industrially. As the performance of disposable diapers, which are the main application of water-absorbent resins, improves, more functions (e.g., high cost performance) are also required of water-absorbent resins. Specifically, in addition to the basic physical properties of absorption capacity without load and absorption capacity under load, various physical properties such as gel strength, water-soluble components, moisture content, water absorption rate, antibacterial properties, abrasion resistance, powder flowability, deodorizing properties, color resistance, low dust generation, and low residual monomer content are also required of water-absorbent resins. In particular, in the application of sanitary products such as disposable diapers, as products become thinner, it is desired to further increase the water absorption rate of water-absorbent resins.

[0004] Generally, industrial production methods for powdered or particulate water absorbent resins include a polymerization step, a gel crushing (atomization) step carried out after or simultaneously with polymerization, a drying step of the atomized gel, a crushing step of the dried product, a sieving step of the crushed product, and a surface cross-linking step of the classified water absorbent resin powder. Currently proposed methods for producing water absorbent resins include a production method in which the polymerization step and the gel crushing step are carried out simultaneously using a polymerization apparatus equipped with a crushing device. In the case of the above production method, the liquid monomer is polymerized, and at the same time, the produced hydrogel is crushed, and the atomized hydrogel is discharged from the polymerization apparatus.

[0005] However, the size of the gel particles obtained by the above-mentioned device is approximately several millimeters to several centimeters. Since the size of the above-mentioned gel particles cannot meet the demand for further improvement of the water absorption rate, a gel crushing device must be added. For example, a water-absorbent resin can be produced into gel particles having a specific particle size or relatively smaller size by a wet crushing method using a batch kneader or a continuous kneader. However, the known gel crushing device is too large in size and is difficult to apply to an industrial production line.

[0006] In view of this, there is an urgent need to provide a water-absorbent resin and a method for producing the same in order to crush the gel body to a size as required during the production process. Summary of the Invention [Means for solving the problem]

[0007] One aspect of the present invention provides a method for producing a water-absorbent resin, which comprises crushing a gel body using a mincer's variable diameter hole plate, and further improving the absorption rate and liquid conductivity of the produced water-absorbent resin.

[0008] Another aspect of the present invention provides a water-absorbent resin produced by the above-mentioned aspect.

[0009] According to one aspect of the present invention, there is provided a method for producing a water-absorbent resin, the method comprising: obtaining a gel body by radical polymerization of a water-absorbent resin composition comprising an acid-based monomer aqueous solution, a polymerization initiator, and a radical polymerization crosslinking agent; cutting the gel body using a mincer having a diameter-variable hole plate including a material supply hole having a first diameter and a material discharge hole having a second diameter smaller than the first diameter, to obtain a plurality of water-absorbent resin particles; and performing a surface crosslinking reaction on the water-absorbent resin particles to obtain a water-absorbent resin.

[0010] According to one embodiment of the present invention, the first diameter is between 8 mm and 20 mm, and the second diameter is between 6 mm and 18 mm.

[0011] According to one embodiment of the present invention, the thickness of the variable diameter hole plate is 20 mm to 40 mm.

[0012] According to one embodiment of the present invention, the first diameter, the second diameter and the thickness of the variable diameter hole plate have the following relationship:

number

[0013] According to one embodiment of the present invention, the step of crushing the gel body further includes a step of screening a plurality of micro gel bodies having an average particle size of 2.00 mm or less.

[0014] According to one embodiment of the present invention, the water-absorbing resin particles have an average particle size of 0.06 mm to 1.00 mm.

[0015] According to one embodiment of the present invention, the method further comprises the step of adding a surface cross-linking agent and an aluminum salt compound to the water-absorbent resin particles before the step of carrying out the surface cross-linking reaction.

[0016] According to one embodiment of the present invention, the amount of the aluminum salt compound added is 0.1 wt % to 1.0 wt % with respect to 100 wt % of the water absorbent resin particles.

[0017] According to one embodiment of the present invention, the aluminum salt compound comprises aluminum sulfate, aluminum lactate, aluminum citrate, or any combination thereof.

[0018] According to another aspect of the present invention, there is provided a water-absorbent resin produced by the above method. [Effects of the Invention]

[0019] When the water-absorbent resin and the manufacturing method thereof of the present invention are applied, the gel body is crushed by a mincer having a diameter-variable hole plate, thereby improving the density and surface roughness of the gel body, and further improving the apparent specific gravity, absorption rate, and liquid conductivity of the manufactured water-absorbent resin. [Brief explanation of the drawings]

[0020] Aspects of the present disclosure may be better understood by reference to the following detailed description, taken in conjunction with the drawings, in which: It should be noted that, as is standard practice in the industry, many features are not drawn to scale, and in fact, sizes of many features may be arbitrarily scaled for clarity of discussion. [Figure 1] 1 is a flowchart of a method for producing a water-absorbent resin according to some embodiments of the present invention. [Figure 2] 1 is a side view of a material inlet end and a material outlet end of a variable diameter hole plate according to some embodiments of the present invention. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0021] As used herein, "around," "about," "approximately," or "substantially" generally means within 20%, or within 10%, or within 5% of the value or range.

[0022] The making and using of embodiments of the present invention are discussed in detail below. However, it will be understood that the embodiments provide many applicable inventive concepts that can be embodied in a variety of specific contexts. The specific embodiments discussed are for illustrative purposes only and are not intended to limit the scope of the invention.

[0023] As described above, the present invention provides a water-absorbent resin and a method for producing the same, and by pulverizing a gel body using a mincer having a diameter-variable hole plate, the density and surface roughness of the gel body are improved, and further the apparent specific gravity, absorption rate and liquid conductivity of the produced water-absorbent resin are improved.

[0024] Please refer to Fig. 1. Fig. 1 shows a flowchart of a method 100 for producing a water-absorbent resin according to some embodiments of the present invention. First, an operation 110 is performed in which a water-absorbent resin composition is subjected to a radical polymerization reaction to obtain a gel body. In some embodiments, the water-absorbent resin composition includes an acid-based monomer aqueous solution, a polymerization initiator, and a radical polymerization crosslinking agent.

[0025] In some embodiments, the aqueous acid monomer solution in the water absorbent resin composition contains a water-soluble monomer having an unsaturated double bond, such as acrylic acid. In some embodiments, the aqueous acid monomer solution may be methacrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, malic acid (cis-butenedioic acid), cis-butenyl acid anhydride, fumaric acid (trans-butenedioic acid), and trans-butenedioic acid anhydride. The aqueous acid monomer solution may contain one type of monomer, but is not limited thereto, and two or more types of the above-mentioned aqueous monomer solutions may be selected.

[0026] In some embodiments, the concentration of the acidic monomer aqueous solution may be 20 wt% to 55 wt% relative to 100 wt% of the water absorbent resin composition, but is not limited thereto, and is preferably 30 wt% to 45 wt%. Generally, when the concentration of the acidic monomer aqueous solution is 20 wt% to 55 wt%, the viscosity of the product after polymerization is appropriate, machining is easy, and the reaction heat when performing a radical polymerization reaction is easily controlled.

[0027] In other embodiments, other hydrophilic monomers having an unsaturated double bond, such as acrylamide, methacrylamide, 2-carboxyethyl acrylate, 2-carboxyethyl methacrylate, methyl acrylate, ethyl acrylate, dimethylamine acrylamide, trimethylamine chloride acrylamide, etc., can be selectively added. However, the amount of the hydrophilic monomer to be added should not impair the physical properties (e.g., centrifugation retention capacity and absorption rate) of the water absorbent resin.

[0028] In some embodiments, in order to reduce production costs, a water-soluble polymer can be selectively added to the water-absorbent resin composition, and the water-soluble polymer may be partially or fully saponified polyvinyl alcohol, polyethylene glycol, polyacrylic acid, polyacrylamide, starch or a starch derivative (e.g., methyl cellulose, methyl cellulose acrylate, ethyl cellulose), etc., and preferably, starch and partially or fully saponified polyvinyl alcohol are used alone or in combination. In the above embodiments, the molecular weight of the water-soluble polymer is not limited, and when the amount of the acid-based monomer aqueous solution used is taken as 100 wt%, the amount of the water-soluble polymer added is, in principle, not to deteriorate the physical properties of the water-absorbent resin, and is usually 20 wt% or less, preferably 10 wt% or less, and more preferably 5 wt% or less.

[0029] In some embodiments, the acidic monomer aqueous solution may be directly polymerized, or may first be partially neutralized using a neutralizing agent to render the acidic monomer aqueous solution neutral or weakly acidic, and then polymerized. In some embodiments, the neutralizing agent may include hydroxides or carbonates of alkali metals or alkaline earth metals (e.g., sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate), amine compounds, and combinations thereof. In some embodiments, the neutralization concentration of the acidic monomer aqueous solution is 45 mol% to 85 mol%, preferably 50 mol% to 75 mol%. When the neutralization concentration is within the above range, the acidic monomer aqueous solution can have an appropriate pH value and is not harmful to humans even if it accidentally comes into contact with them. It should be noted that the neutralization concentration described herein is defined as the ratio of the moles of the alkaline solution to the moles of the acidic monomer aqueous solution, and may be the percentage at which the acidic groups in the acidic monomer aqueous solution are neutralized. In some embodiments, the pH value of the acidic monomer aqueous solution is 5.5 to 7.0, preferably 5.5 to 6.5. When the pH value of the acidic monomer aqueous solution is 5.5 to 7.0, a large amount of unreacted monomer is unlikely to remain in the aqueous solution after polymerization, and the water absorbent resin produced later has good physical properties and a large absorption capacity.

[0030] The prepolymerization reaction begins with the decomposition of the polymerization initiator to generate radicals. In some embodiments, the amount of the polymerization initiator used is 0.001 wt% to 10 wt%, preferably 0.1 wt% to 5 wt%, relative to 100 wt% of the acid-based monomer aqueous solution. When the amount of the polymerization initiator used is within the above range, the radical polymerization reaction speed is appropriate, economic benefits are good, reaction heat can be easily controlled, and the formation of a gel-like solid due to excessive polymerization can be avoided.

[0031] In some embodiments, the polymerization initiator includes a thermal decomposition initiator, a redox initiator, and a combination thereof. In some embodiments, the thermal decomposition initiator includes a peroxide such as hydrogen peroxide, di-t-butyl peroxide, peroxide amide, or persulfate (including ammonium salts and alkali metal salts), and an azotide such as 2,2-azobis(2-amidinopropane) dihydrochloride or 2,2-azobis(N,N-dimethyleneisobutylamidine) dihydrochloride. In some embodiments, the redox initiator includes an acid sulfite, ascorbic acid, or a ferrous salt. The polymerization initiator preferably includes a combination of a thermal decomposition initiator and a redox initiator. The redox initiator is first reacted to generate radicals, and the radicals are transferred to the monomer, initiating the polymerization reaction. The large amount of heat released by the polymerization reaction increases the temperature. When a certain temperature is reached, the decomposition of the thermal decomposition initiator can be further initiated to make the polymerization reaction more complete, thereby avoiding leaving excess unreacted monomer.

[0032] The radical polymerization reaction crosslinking agent in the water absorbent resin composition can provide the water absorbent resin composition with an appropriate degree of crosslinking, and can improve the processability of the water absorbent resin composition after the polymerization reaction. In some embodiments, the radical polymerization reaction crosslinking agent can be, for example, N,N-bis(2-propenyl)amine, N,N-methylenebisacrylamide, N,N-methylenebismethacrylamide, allyl acrylate, ethylene glycol diacrylate, polyethylene glycol diacrylate, ethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, glycerin trismethacrylate, triacrylate or trimethacrylate of glycerin-ethylene oxide adduct, trimethylolpropane trimethacrylate, trimethylolpropane triacrylate, N,N,N-tris(2-propenyl)amine, ethylene glycol diacrylate, ethylene glycol dimethacrylate, ethylene glycol diacrylate, ethylene glycol dimethacrylate, glycerin trismethacrylate, ethylene glycol diacrylate, ethylene glycol dimethacrylate, ethylene glycol diacrylate, ethylene glycol dimethacrylate, ethylene glycol trismethacrylate, ethylene glycol diacrylate, ethylene glycol trismethacrylate, ethylene glycol tri ... Alternatively, a compound containing two or more compounds having an unsaturated double bond, such as ethylene glycol diacrylate, polyoxyethylene glyceryl triacrylate, diethyl polyoxyethylene glyceryl triacrylate, or triethylene glycol diacrylate, may be selected. Alternatively, a compound containing two or more compounds having an epoxy group, such as sorbitol polyglycidyl ether, polyglycerol polyglycidyl ether, ethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, or diglycerol polyglycidyl ether, may be selected. Two or more radical polymerization crosslinking agents may be used alone or in combination. In some embodiments, the amount of radical polymerization crosslinking agent is 0.001 wt% to 5 wt%, preferably 0.01 wt% to 3 wt%, relative to 100 wt% of the aqueous acid monomer solution. When the amount of radical polymerization crosslinking agent added is within the above range, the viscosity of the aqueous polymer solution after the reaction is appropriate, machining is easy, and the resulting water-absorbent resin has good water absorption properties.

[0033] In some embodiments, the radical polymerization reaction can be carried out in a batch reactor (eg, a tank reactor) or a conveyor reactor.

[0034] Next, operation 120 is performed in which the gel body is cut using a mincer to obtain water-absorbent resin particles. The mincer has a plate with variable diameter holes. By using a mincer with this variable diameter hole plate, the number of times the gel body is cut can be reduced, and the gel body after cutting can be aggregated, making the obtained water-absorbent resin particles denser, further reducing eluates in the water-absorbent resin particles, and improving the apparent specific gravity of the water-absorbent resin particles. In addition, the surface roughness of the gel body can be improved, which contributes to achieving the effects of improving the surface porosity and absorption rate of the water-absorbent resin particles and further improving the liquid conduction performance.

[0035] Please refer to Figure 2. Figure 2 shows a side view of a material supply end 210 and a material discharge end 220 of a variable diameter hole plate 200 according to some embodiments of the present invention. The material supply end 210 includes a plurality of material supply holes 215, and the material discharge end 220 includes a plurality of material discharge holes 225. The material supply holes 215 have a first diameter D1, and the material discharge holes 225 have a second diameter D2. In some embodiments, the first diameter D1 is larger than the second diameter D2, so that the resulting water-absorbent resin particles have a good adhesion effect.

[0036] In some embodiments, the first diameter D1 is about 8 mm to about 20 mm, and preferably about 10 mm to about 20 mm. When the first diameter D1 is in the above range, the operation of the device becomes smooth, and a lot of friction occurs between the gel bodies, which increases the surface roughness of the gel bodies, and further improves the apparent specific gravity and absorption rate of the obtained water-absorbent resin particles. In some embodiments, the second diameter D2 is about 6 mm to about 18 mm, and preferably about 8 mm to about 16 mm. When the second diameter D2 is in the above range, the operation of the device becomes smooth, and the obtained water-absorbent resin particles have a good adhesive effect.

[0037] The variable diameter hole plate 200 has a thickness L, and in some embodiments, the thickness L is about 20 mm to about 40 mm, preferably 30 mm. When the thickness L is in the above range, the obtained water-absorbent resin particles have a good adhesive effect and an appropriate material discharge speed.

[0038] The first diameter D1, the second diameter D2, and the thickness L of the variable diameter hole plate 200 have the following relationship: D1=D2 / L / L.

number

[0039] In some embodiments, the microgel bodies obtained after cutting with a mincer need to be subjected to steps such as drying, grinding, and screening. In the above embodiments, the temperature of the drying step is about 100°C to about 250°C. By performing the drying process within this temperature range, the drying time and the degree of crosslinking can be effectively controlled, thereby preventing a large amount of unreacted monomer from remaining.

[0040] In some embodiments, the screening step involves screening microgel particles having an average particle size of about 2.0 mm or less, preferably about 0.05 mm to about 1.50 mm. Gel particles with an average particle size larger than 2.0 mm must be returned to the mincer and crushed again. The particle size must be controlled within this range to avoid the generation of a high amount of fine powder in subsequent processes, and the particle size must have good thermal conductivity to prevent excess unreacted monomer from remaining, which could result in poor physical properties. Generally, the narrower the particle size distribution of the microgel particles, the better the physical properties and the easier it is to control the drying time and temperature.

[0041] In some embodiments, after the screening step, the microgel bodies can be dried again, and optionally, the microgel bodies can be subjected to another drying process. In such embodiments, the drying process is performed at a temperature of about 100°C to about 180°C. By performing the drying process within this temperature range, the drying time and the degree of crosslinking can be effectively controlled, and a large amount of unreacted monomer can be prevented from remaining.

[0042] In some embodiments, the particle size of the water-absorbent resin particles is screened to 0.06 mm to 1.00 mm, preferably 0.10 mm to 0.85 mm. By controlling the particle size of the water-absorbent resin particles within the above range, the amount of fine powder in the finished product can be reduced and the absorption performance of the water-absorbent resin can be improved.

[0043] In some embodiments, the produced water absorbent resin particles have a centrifugation retention capacity of about 34.0 g / g to about 35.0 g / g, a 1-minute pure water absorption capacity of about 130 g / g to about 160 g / g, a 1-hour water soluble portion of about 4.7% to about 6.0%, a surface porosity of about 0.033 cc / g to about 0.045 cc / g, an apparent specific gravity of about 600 g / L to about 640 g / L, and a free swelling rate of about 0.35 g / g / s to about 0.53 g / g / s.

[0044] Next, operation 130 is performed to obtain a water-absorbent resin by subjecting the water-absorbent resin particles to a surface cross-linking reaction. Because water-absorbent resins are insoluble hydrophilic polymers, they have a uniform cross-linked structure within the resin. Generally, further cross-linking is performed on the surface of the resin to improve its absorption rate, gel strength, blocking resistance, liquid permeability, and other properties. The surface cross-linking reaction is performed using a surface cross-linking agent having a functional group capable of reacting with an acid group. In some embodiments, the surface cross-linking agent includes a polyol, a polyamine, a compound having two or more epoxy groups, and an alkylene carbonate. The polyol may be, for example, glycerol, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, or propylene glycol. The polyamine may be, for example, ethylenediamine, diethylenediamine, or triethylenediamine. The epoxy group-containing compound may be, for example, sorbitol polyglycidyl ether, polyglycerol polyglycidyl ether, ethylenediamine, or propylene glycol. The alkylene carbonate may be, for example, ethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, or diglycerol polyglycidyl ether. The alkylene carbonate may be, for example, ethylene glycol carbonate, 4-methyl-1,3-dioxolan-2-one, 4,5-dimethyl-1,3-dioxolan-2-one, 4,4-dimethyl-1,3-dioxolan-2-one, 4-ethyl-1,3-dioxolan-2-one, 1,3-dioxan-2-one, 4,6-dimethyl-1,3-dioxan-2-one, or 1,3-dioxepan-2-one. The reaction may be carried out using a single surface cross-linking agent or a mixture of two or more surface cross-linking agents. Depending on the selected surface cross-linking agent, the surface cross-linking agent may be added directly or may be prepared in an aqueous solution or a hydrophilic organic solution and then added. Hydrophilic organic solvents include, but are not limited to, methanol, ethanol, propanol, isobutanol, acetone, methyl ether, ethyl ether, and the like.

[0045] In some embodiments, the amount of the surface cross-linking agent added is about 0.001 wt% to about 10 wt%, preferably about 0.005 wt% to about 5 wt%, relative to 100 wt% of the total solid content of the reaction product. When the amount of the surface cross-linking agent added is within the above range, the surface of the water absorbent resin has a cross-linked structure, and further improved absorption performance can be achieved.

[0046] In some embodiments, the surface cross-linking reaction further comprises adding an aluminum salt compound simultaneously with the addition of the surface cross-linking agent to further improve the liquid conduction performance of the water-absorbent resin. In some specific examples, the aluminum salt compound comprises aluminum sulfate, aluminum lactate, aluminum citrate, or a combination thereof. In some embodiments, the amount of the aluminum salt compound added is 0.1 wt% to 1.0 wt%, preferably about 0.3 wt% to about 0.7 wt%, relative to 100 wt% of the water-absorbent resin particles. By adding the aluminum salt compound in the amount within the above range, the water absorption capacity under pressure and the liquid conduction performance of the obtained water-absorbent resin can be improved.

[0047] As described above, the water absorbent resin produced using the above-described method for producing a water absorbent resin 100 has a high apparent specific gravity, a low water-soluble portion, and a high surface porosity. In some embodiments, the water absorbent resin of the present invention has an apparent specific gravity of about 600 g / L to about 650 g / L, a water-soluble portion after 16 hours of about 5.9% to about 8.6%, and a surface porosity of about 0.033 cc / g to about 0.045 cc / g.

[0048] Furthermore, the water-absorbent resin must have a good centrifuge retention capacity (CRC) and absorption against pressure (AAP) so that the water-absorbent resin will not be damaged or have its liquid absorption capacity affected by pressure applied from the outside to the absorbent body after absorbing liquid. In some embodiments, the water-absorbent resin of the present invention has a centrifuge retention capacity of 25 g / g or more, preferably about 28.0 g / g to about 29.0 g / g. In some embodiments, the water-absorbent resin of the present invention has an absorption against pressure greater than 23 g / g, preferably about 25 g / g to 26 g / g.

[0049] The water-absorbent resin produced by method 100 can have a good absorption rate, which can be evaluated using the free swelling rate (FSR). The free swelling rate of the water-absorbent resin of the present invention is 0.35 g / g / s or more, preferably about 0.35 g / g / s to about 0.55 g / g / s. It is necessary to further explain that a water-absorbent resin with a high free swelling rate can rapidly absorb liquid without applying pressure.

[0050] The ability of a dry water-absorbent resin to absorb a liquid when first contacting the liquid can be indicated by the T20 value. A low T20 value of a water-absorbent resin indicates that the dry water-absorbent resin easily absorbs a liquid. The T20 value of the water-absorbent resin of the present invention is about 150 seconds or less, for example, about 100 seconds to about 150 seconds. It is necessary to further explain that the T20 value is defined as the time required for 1 gram of the water-absorbent resin to absorb 20 grams of saline and 0.01 wt% aqueous solution of an alcohol ethoxy compound under a pressure of 0.3 psi, and the alcohol ethoxy compound has 12 to 14 carbon atoms.

[0051] The permeability of a water-absorbent polymer can be measured using urine permeability measurement (UPM). UPM typically measures the flow resistance of a pre-swollen layer of a water-absorbent polymer. Thus, a water-absorbent polymer with a high UPM value can exhibit good permeability when the polymer is wetted with a liquid. The UPM value of the water-absorbent polymer of the present invention is about 45×10 -7 cm 3 -s / g ~ approx. 65×10 -7 cm 3 -s / g.

[0052] The liquid conductance properties of a water-absorbent resin can also be measured using fixed height absorption (FHA) and free swell gel bed permeability (free swell GBP). The FHA value measures the amount of fluid absorbed by a water-absorbent resin when the resin absorbs fluid up to a specific height against gravity. In some embodiments, the water-absorbent resin produced using method 100 has an FHA value of about 25.3 g / g to about 35.0 g / g. The free swell gel bed permeability is used to measure the permeability of the expanding substrate of the water-absorbent resin. As will be understood, the so-called "free swell" state means that the water-absorbent resin is allowed to expand and there is no expansion-restraining load. In some embodiments, the free swell gel bed permeability of a water-absorbent resin produced using method 100 is about 22.7 x 10 -9 cm 2 ~Approx. 32.5×10 -9 cm 2 is.

[0053] The following examples are provided to illustrate the application of the present invention, but are not intended to limit the scope of the present invention. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Manufacture of water-absorbent resin Manufacturing example

[0054] 437.5 g of 48 wt% sodium hydroxide aqueous solution was slowly added to a 2000 cc Erlenmeyer flask containing 540 g of acrylic acid and 583.2 g of water, the sodium hydroxide / acrylic acid dropwise ratio was set to 0.85-0.95, the dropwise addition time was 2 hours, and the temperature of the neutralization reaction system in the flask was maintained within the range of 15°C-40°C to obtain a monomer aqueous solution with a monomer concentration of 42 parts by weight, in which 70 mol% of acrylic acid was partially neutralized to sodium acrylate, and then added to a 2-liter tank reactor (manufactured by Taiwan Jin Lei Precision Industries).

[0055] Next, 0.9 g of N,N'-methylenebisacrylamide (radical polymerization reaction crosslinking agent) was added to the acidic monomer aqueous solution, and after maintaining the temperature at about 20°C, nitrogen gas was introduced through a pipe to remove oxygen for 30 minutes.

[0056] Next, 0.3 g of hydrogen peroxide as a polymerization initiator, 4.15 g of sodium hydrogen sulfite, 23.4 g of 10% sodium carbonate foaming agent, and 3.6 g of ammonium persulfate were added to carry out a radical polymerization reaction. After leaving to stand for 30 minutes, a gel was obtained. Example 1

[0057] The gel body of the manufacturing example was cut using a mincer (Model 200, manufactured by Taichung Nikki Co., Ltd.) with a variable diameter hole plate (manufactured by Kinlei Precision Industries, Taiwan). The first diameter D1 of the material supply hole of the variable diameter hole plate was 10 mm, the second diameter D2 of the material discharge hole was 8 mm, and the thickness L of the hole plate was 20 mm. The α value calculated according to the above relational expression was 0.05.

[0058] The gel bodies having a particle size of 2 mm or less were screened. Then, the gel bodies were dried at a temperature of 130°C for 2 hours. The gel bodies were screened using a mesh with a fixed particle size of 0.1 mm to 0.85 mm to obtain water-absorbent resin particles.

[0059] Subsequently, 100 g of water-absorbent resin particles were weighed, and an aqueous solution prepared by mixing 5 g of ethylene glycol, 1,4-butanediol (manufactured by Taiwan Plastics Co., Ltd.) and methanol in a volume ratio of 1:1:0.5 was added as a surface cross-linking agent, and the mixture was heat-treated at a temperature of 200° C. for 1 hour. After cooling, a water-absorbent resin was obtained. Examples 2 to 24

[0060] The water-absorbent resins of Examples 2 to 24 were manufactured using the same process steps as in Example 1. The only differences were the first diameter D1 of the material supply hole of the diameter-variable hole plate, the second diameter D2 of the material discharge hole, and the thickness L of the hole plate, as well as the calculated α value. The first diameter D1 of the material supply hole, the second diameter D2 of the material discharge hole, and the thickness L of the hole plate of Examples 2 to 24 are shown in Table 1, respectively. Comparative Example 1

[0061] According to the method described in Chinese Patent CN1206365A, an aqueous monomer solution was prepared by mixing 83.2 parts of acrylic acid, 1662.8 parts of a 37% by weight aqueous sodium acrylate solution, 5.5 parts of polyethylene glycol diacrylate (average total ethylene oxide (EO) moles: 8), and 654.5 parts of deionized water. The neutralization rate of the acrylic acid in the aqueous monomer solution was 85%, and the monomer concentration was 30%. Nitrogen gas was blown into the aqueous monomer solution to remove dissolved oxygen from the aqueous monomer solution, while the temperature of the aqueous monomer solution was maintained at 24°C.

[0062] Next, 77 parts of a 10 wt% solution of 2,2'-azobis(2-methylpropionamidine) dihydrochloride was added, while the aqueous monomer solution was stirred. Three minutes after stirring began, the aqueous monomer solution containing the 2,2'-azobis(2-methylpropionamidine) dihydrochloride solution became cloudy white, and white particulate solids with an average particle size of approximately 9 μm were produced. This particulate solid was 2,2'-azobis(2-methylpropionamidine) diacrylate, which served as a blowing agent. Five minutes after stirring began, 10.8 parts of a 10 wt% aqueous solution of sodium persulfate and 0.5 parts of a 1 wt% aqueous solution of L-ascorbic acid were added as radical polymerization initiators under nitrogen gas, while the aqueous monomer solution was stirred. The aqueous monomer solution was thoroughly stirred and then allowed to stand. Three minutes after the addition of the 10 wt% aqueous solution of sodium persulfate and the 1 wt% aqueous solution of L-ascorbic acid, the polymerization reaction began. The polymerization reaction was carried out in a warm bath, and the temperature of the warm bath was controlled as the temperature of the aqueous monomer solution increased. 26 minutes after adding the 10 wt% aqueous sodium persulfate solution to the aqueous monomer solution, the temperature of the aqueous monomer solution reached 97°C. Next, the aqueous monomer solution was again allowed to stand for 20 minutes, and its temperature was maintained within the range of 70°C to 90°C to complete the polymerization reaction of the acrylate monomer. A crosslinked hydrogel polymer having bubbles (hereinafter referred to as hydrogel (A)) was obtained as a porous crosslinked polymer.

[0063] The obtained hydrogel (A) was continuously pulverized using a rotary pulverizer as disclosed in Chinese Patent CN1206365A. During pulverization, the average residence time of the hydrogel (A) in the rotary pulverizer 31, i.e., the pulverization time, was approximately 0.25 minutes. The particle size range of the hydrogel particles obtained by pulverizing the hydrogel (A) was approximately 1 to 15 mm. The pulverized hydrogel was dried for 1 hour at 160°C using a circulating hot air dryer. The dried hydrogel was then pulverized using a roller mill and sieved using a standard sieve conforming to JIS standards. Particles that passed through an 850 μm sieve but not a 150 μm sieve were obtained as water-absorbent resin particles.

[0064] Subsequently, a secondary crosslinking treatment liquid was applied to carry out a surface crosslinking reaction, thereby producing a water-absorbent resin. Specifically, 100 parts of water-absorbent resin particles were mixed with a treatment liquid for secondary crosslinking treatment, and the resulting mixture was then heated at 195°C for 30 minutes to obtain a water-absorbent resin. The secondary crosslinking treatment liquid was prepared as a composition obtained by mixing 0.05 parts of ethylene glycol glycidyl ether, 0.5 parts of lactic acid, 0.02 parts of polyoxyethylene sorbitan monostearate, 0.75 parts of isopropanol, and 3 parts of water. Comparative Examples 2 to 8

[0065] The water-absorbent resins of Comparative Examples 2 to 8 are also manufactured using the same process steps as in Example 1. The only differences are the first diameter D1 of the material supply hole of the diameter-variable hole plate, the second diameter D2 of the material discharge hole, the thickness L of the hole plate, and the calculated α value. The first diameter D1 of the material supply hole, the second diameter D2 of the material discharge hole, and the thickness L of the hole plate of Comparative Examples 2 to 8 are respectively shown in Table 1. Evaluation method

[0066] In order to evaluate the properties of the water-absorbent resin of the present invention, its physical properties are analyzed by the following test methods, and unless otherwise specified, the following measurement conditions are all at room temperature of 23±2°C and a relative humidity of 45±10%. The water-absorbent resin should be thoroughly mixed before analysis. Centrifuge Retention Volume

[0067] The Centrifuge Retention Capacity (CRC) is tested in accordance with the test method ERT 241.2(12) specified by the European Disposables and Nonwovens Association (EDANA). The test results of the centrifuge retention capacity of the water-absorbent resin particles and the water-absorbent resin are shown in Tables 2 and 3, respectively. 1 minute pure water absorption rate

[0068] The one-minute pure water absorption capacity is tested in accordance with the test method of ERT 240.2(12) specified in EDANA, where the saline solution is replaced with deionized water (pure water) and the absorption time is changed from 30 minutes to 1 minute. The test results of the one-minute pure water absorption capacity of the water-absorbent resin particles and the water-absorbent resin are shown in Table 2 and Table 3, respectively. Bulk specific gravity

[0069] The bulk density is tested in accordance with the test method ERT 251.0(12) specified in EDANA. The test results of the bulk density of the water-absorbent resin particles and the water-absorbent resin are shown in Tables 2 and 3, respectively. Surface Porosity

[0070] The surface porosity was tested using a mercury porosimeter (micromeritics AutoPore® IV 9520), and the standard packing pressure was about 4 kPa. The test results of the water-absorbent resin particles and the water-absorbent resin are shown in Tables 2 and 3, respectively. Free Swelling Rate

[0071] The free swelling rate (FSR, unit: g / g / s) was measured and calculated according to the method described in Patent No. WO2012 / 174026A1, in which 4 g of the water-absorbent resin was first dried for 48 hours at a temperature of 23±2°C and a pressure of 0.01 torr or less, and then approximately 1 g was weighed and placed in a beaker and dispersed at the bottom of the beaker. 20 g of a 0.9 wt% aqueous sodium chloride solution was then poured into the beaker, and the elapsed time from when the liquid contacted the water-absorbent resin until the liquid was completely absorbed by the water-absorbent resin was measured. The free swelling rate was calculated by dividing the amount of liquid by the weight of the water-absorbent resin and then by the elapsed time. The average results of three repeat measurements for the water-absorbent resin particles and the water-absorbent resin are shown in Tables 2 and 3, respectively. 1-hour and 16-hour water-soluble portions

[0072] The 1-hour and 16-hour water extractable content are tested in accordance with the test method ERT 470.2(02) specified in EDANA. The test results for the 1-hour water extractable content of water absorbent resin particles and the 16-hour water extractable content of water absorbent resin are shown in Table 2 and Table 3, respectively. Water absorption rate under pressure

[0073] Absorption against pressure (AAP) was tested in accordance with the test method of ERT 442.3(10) specified in EDANA, which tests the absorption against pressure for 60 minutes against a 0.9% sodium chloride aqueous solution under a pressure of 4.9 kPa. The test results for the water-absorbent resin particles and the water-absorbent resin are shown in Tables 2 and 3, respectively. T20 value

[0074] The T20 value (unit: seconds) was measured and calculated according to the method described in U.S. Patent No. 9,285,302, and is the time required for 1 gram of this water-absorbent resin to absorb 20 grams of physiological saline and 0.01 wt% aqueous solution of an alcohol ethoxy compound under a pressure of 0.3 psi, and the alcohol ethoxy compound has 12 to 14 carbon atoms. The average results of three repeated tests of the water-absorbent resin particles and the water-absorbent resin are shown in Table 2 and Table 3, respectively. Urine permeability measurement

[0075] The urine permeability measurement is performed according to the method described in Patent No. WO2012 / 174026A1. The test results of the water-absorbent resin particles and the water-absorbent resin are shown in Tables 2 and 3, respectively. Fixed Height Absorption Value

[0076] The fixed height absorption value is tested according to the method described in US Patent US 7108916. The test results of the water-absorbent resin particles and the water-absorbent resin are shown in Table 2 and Table 3, respectively. Free-swelling gel bed permeability

[0077] The free swelling gel bed permeability is tested according to the method described in US Patent US8021998B2. The test results of the water absorbent resin particles and water absorbent resin are shown in Table 2 and Table 3, respectively.

[0078] [Table 1]

[0079] [Table 2]

[0080] [Table 3]

[0081] In Comparative Example 4, the second diameter of the material discharge hole of the diameter variable hole plate was too small, so that the gel body could not be discharged smoothly and the mincer motor overheated, so that it was not possible to produce water-absorbent resin particles and water-absorbent resin, and it was also not possible to measure various physical properties in Tables 2 and 3.

[0082] According to Tables 2 and 3, in Comparative Example 1 using the conventional technology, the absorption properties of the water-absorbent resin produced were clearly inferior to those of Examples 1 to 24. In Comparative Example 2, the thickness of the perforated plate was too small and the extrusion path was too short, making it difficult to form a water-absorbent resin with good absorption properties. In contrast, when the thickness of the perforated plate in Comparative Example 3 was too large, wear increased and the surface porosity of the water-absorbent resin decreased, so properties such as absorption rate were good. In both Comparative Examples 7 and 8, the diameter of the material supply hole was equal to the diameter of the material discharge hole, and the pressing force was insufficient, resulting in a high water-soluble portion of the water-absorbent resin.

[0083] According to Table 2, compared with Comparative Examples 1 to 8, the water-absorbent resin particles of Examples 1 to 24 clearly had a lower water-soluble portion, and higher one-minute pure water absorption capacity, surface porosity and free swelling rate.

[0084] According to Table 3, the absorbency under load, urine permeability (UPM), fixed height absorption (FHA) and free swelling gel bed permeability (GBP) were all high and the T20 value was low in Examples 1 to 24 compared with Comparative Examples 1 to 8. Therefore, the water absorbent resins of Examples 1 to 24 easily absorbed liquid under dry conditions and also had good liquid permeability and conductance.

[0085] Therefore, by applying the method for producing a water-absorbent resin of the present invention, the gel body is cut using a mincer with a diameter-variable hole plate, and the diameter of the material supply hole is controlled to be larger than the diameter of the material discharge hole, thereby improving the density and surface roughness of the gel body, and further improving the apparent specific gravity, absorption rate, and liquid conductivity of the produced water-absorbent resin, and reducing the water-soluble portion.

[0086] Although the present invention has been disclosed in a number of embodiments as described above, they are not intended to limit the present invention, and anyone skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be limited to the scope of the patent application to be attached later. [Explanation of symbols]

[0087] 100: Method 110, 120, 130: Operation 200: Variable diameter hole plate 210: Material supply end 215: Material supply hole 220: Material discharge end 225: Material discharge hole D1: 1st diameter D2: Second diameter L: Thickness

Claims

1. A step of obtaining a gel body by radical polymerization of a water-absorbing resin composition including an acid-based monomer aqueous solution, a polymerization initiator, and a radical polymerization crosslinking agent; a step of cutting the gel body using a mincer having a diameter-variable hole plate including a material supply hole having a first diameter and a material discharge hole having a second diameter smaller than the first diameter, to obtain a plurality of water-absorbent resin particles; performing a surface cross-linking reaction on the water-absorbent resin particles to obtain the water-absorbent resin; Including, the first diameter is between 8 mm and 20 mm, and the second diameter is between 6 mm and 18 mm; The thickness of the variable diameter hole plate is 20 mm to 40 mm.

2. The first diameter, the second diameter, and the thickness of the variable diameter hole plate have the following relationship: [Equation 1] In the above formula, D1 represents the first diameter, D2 represents the second diameter, and L represents the thickness of the diameter variable hole plate, and the α value is 0.05 to 0.

35. The method for producing a water-absorbent resin according to claim 1.

3. The step of cutting the gel body includes: The method for producing a water-absorbent resin according to claim 1, further comprising the step of screening a plurality of microgel bodies having an average particle size of 2.00 mm or less.

4. 4. The method for producing a water-absorbent resin according to claim 3, wherein the water-absorbent resin particles have an average particle size of 0.06 mm to 1.00 mm.

5. Before the step of carrying out the surface cross-linking reaction, The method for producing a water-absorbent resin according to claim 1, further comprising the step of adding a surface cross-linking agent and an aluminum salt compound to the water-absorbent resin particles.

6. 6. The method for producing a water-absorbent resin according to claim 5, wherein the amount of said aluminum salt compound added is 0.1 wt % to 1.0 wt % with respect to 100 wt % of said water-absorbent resin particles.

7. The method for producing a water-absorbent resin according to claim 5, wherein the aluminum salt compound includes aluminum sulfate, aluminum lactate, aluminum citrate, or any combination thereof.

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