Water-absorbing resin and method for producing the same

Abstract

The present invention provides a water-absorbent resin and a method for producing the same. [Solution] A method comprising: performing a radical polymerization reaction on a water-absorbent resin composition containing an aqueous solution of an unsaturated monomer, a polymerization initiator, and a radical polymerization crosslinking agent to obtain a gel; shearing the gel using a twisting machine having a blade with a parallelogram cross-section and a perforated plate containing multiple holes to obtain multiple water-absorbent resin particles; and performing a surface crosslinking reaction on the multiple water-absorbent resin particles to obtain a water-absorbent resin. This makes it possible to improve the surface porosity, absorption rate, and liquid conductivity of the obtained water-absorbent resin.

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 obtained by a twisting machine having special blades and a method for producing the same. [Background technology]

[0002] Super absorbent polymers (SAPs) are polymers that do not contain water and are mainly used in a variety of fields, such as absorbent products like disposable diapers and sanitary cotton, water-retaining agents for agriculture, forestry, and horticulture, and water-stopping agents for industry.

[0003] The manufacturing process of superabsorbent polymers requires the use of large quantities of monomers and hydrophilic polymers. Industrially, polyacrylic acid (salt)-based superabsorbent polymers, primarily using acrylic acid and / or its salts as monomers, are produced. With the increasing demand for high performance in disposable diapers, a major application, more functionality (e.g., high cost-effectiveness) is required for superabsorbent polymers. Specifically, in addition to the basic physical properties of water absorption ratio under no pressure and water absorption ratio under pressure, various other physical properties are required for superabsorbent polymers, such as gel strength, water-soluble components, water content, water absorption rate, antibacterial properties, abrasion resistance, powder flowability, deodorizing properties, color resistance, low dust, and low residual monomers. In particular, for hygiene products such as disposable diapers, there is a growing desire to improve the water absorption rate of superabsorbent polymers as products become thinner.

[0004] Generally, industrial manufacturing methods for powdered or particulate superabsorbent polymers include a polymerization step, a gel pulverization (fine pulverization) step performed after or simultaneously with polymerization, a drying step for the finely pulverized gel, a pulverization step for the dried material, a sieving step for the pulverized material, and a surface crosslinking step for the classified superabsorbent polymer powder. Conventionally proposed methods for manufacturing superabsorbent polymers include a method in which the polymerization step and the gel pulverization step are performed simultaneously using a polymerization apparatus equipped with pulverization equipment. In the aforementioned manufacturing method, the resulting hydrogel is pulverized while the liquid monomer is polymerized, and the finely pulverized hydrogel is discharged from the polymerization apparatus. Specifically, it is known that pulverization is performed using an intermittent kneader or a continuous kneader.

[0005] However, the size of the gel particles obtained by the above apparatus is approximately a few millimeters to a few centimeters. Under the requirement to further improve the water absorption rate, the aforementioned gel particle size cannot meet this requirement, and therefore, a gel grinding device needs to be added. For example, intermittent and continuous kneaders can be used to process the water-absorbing resin into gel particles of a specific particle size or relatively small particles using a wet grinding method. However, conventional gel grinding devices are too large and therefore difficult to apply to industrial production lines. [Overview of the project] [Problems that the invention aims to solve]

[0006] In light of this, there is an urgent need to provide an absorbent resin for crushing the gel to a size that meets the requirements during the process, and a method for manufacturing the same. [Means for solving the problem]

[0007] One aspect of the present invention provides a method for producing a water-absorbent resin, which involves crushing a gel with special blades of a twisting machine to further improve the absorption rate and liquid conduction performance of the resulting water-absorbent resin.

[0008] According to one aspect of the present invention, a method for producing a water-absorbent resin is provided, comprising: performing a radical polymerization reaction on a water-absorbent resin composition containing an aqueous solution of an unsaturated monomer, a polymerization initiator, and a radical polymerization crosslinking agent to obtain a gel; shearing the gel using a twisting machine including a blade with a parallelogram cross-section and a perforation disc having a plurality of holes 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.

[0009] According to one embodiment of the present invention, the parallelogram has a first side length and a second side length that are parallel to each other in a first direction, the endpoints of the first side length and the second side length on the same side are the first endpoint and the second endpoint, the first side length is equal to the sum of the first length and the second length, the first length is the distance between the first endpoint of the first side length and the second endpoint of the second side length in the first direction, and the ratio of the first length to the second length is 0.1 to 0.8.

[0010] According to one embodiment of the present invention, the angle between the first side length and the adjacent side is a bounding angle with a tangent value of 0.1 to 0.9.

[0011] According to one embodiment of the present invention, the first length is 40 mm to 120 mm, and the second length is 190 mm to 210 mm.

[0012] According to one embodiment of the present invention, each of the holes has a diameter of 8 mm to 22 mm.

[0013] According to one embodiment of the present invention, the blade and the hole press are separated by a pitch of 0.01 mm to 0.09 mm.

[0014] According to one embodiment of the present invention, the specific mechanical energy of the twisting machine is 25 kWh / t to 65 kWh / t.

[0015] According to one embodiment of the present invention, the surface crosslinking agent and an aluminum salt compound are further added to the water-absorbing resin particles before the surface crosslinking reaction.

[0016] According to an embodiment of the present invention, with respect to 100 wt% of the water-absorbing resin, the addition amount of the aluminum salt compound is 0.1 wt% to 1.0 wt%.

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

Advantages of the Invention

[0018] By using the water-absorbing resin and the method for producing the same according to the present invention, the gel is pulverized by a twisting machine having a perforated plate with different pore diameters, thereby improving the compactness and surface roughness of the gel. Further, the surface porosity, absorption rate, and liquid conduction performance of the obtained water-absorbing resin are improved, and the water-soluble part is reduced.

Brief Description of the Drawings

[0019] The aspects of the present disclosure can be better understood by reading the following detailed description in conjunction with the drawings. It should be noted that, unlike the standard methods in the industry, many features are not drawn proportionally. In fact, for the purpose of clear discussion, the sizes of many features may be arbitrarily scaled. [Figure 1] It is a flowchart of a method for producing a water-absorbing resin according to some embodiments of the present invention. [Figure 2A] It is a plan view of a blade of a twisting machine according to some embodiments of the present invention. [Figure 2B] It is a side view of a blade of a twisting machine according to some embodiments of the present invention. [Figure 2C] It is a cross-sectional view of a blade of a twisting machine according to some embodiments of the present invention.

Modes for Carrying Out the Invention

[0020] As used herein, "around", "about", "approximately" or "substantially" generally refers to within 20%, or within 10%, or within 5% of the above numerical value or range.

[0021] Hereinafter, the production and use of the examples of the present invention will be examined in detail. However, it can be understood that the examples provide many applicable invention concepts that can be implemented in various specific contents. The specific examples discussed are for illustrative purposes only and are not used to limit the scope of the present invention.

[0022] Known methods for producing water-absorbing resins involve pulverizing a crosslinkable hydrogel and performing drying and pulverization in order to improve drying efficiency. The aforementioned pulverization step can, for example, pulverize the hydrogel using a screw extruder or a meat grinder after the polymerization reaction, pulverize it all at once during the polymerization reaction using the cutter of a kneader, cut the hydrogel into pieces using pliers or a cutter knife in the laboratory, or cut it into pieces by pressing a circular cutting blade against a roller.

[0023] From the above, the present invention provides a water-absorbing resin and a method for producing the same, pulverizes the gel with a twisting machine having a special blade, improves the compactness and surface roughness of the gel, and further improves the surface porosity, absorption rate and liquid conduction performance of the obtained water-absorbing resin, thereby reducing the water-soluble part.

[0024] Please refer to FIG. 1, which is a flowchart of a method 100 for producing a water-absorbing resin according to some embodiments of the present invention. First, operation 110 is performed to carry out a radical polymerization reaction on a water-absorbing resin composition to obtain a gel. In some embodiments, the water-absorbing resin composition includes an unsaturated monomer aqueous solution, a polymerization reaction initiator, and a radical polymerization reaction crosslinking agent.

[0025] The term "unsaturated monomer" as used in this invention refers to a water-soluble monomer having an unsaturated double bond. In some examples, the aqueous solution of the unsaturated monomer in the water-absorbent resin composition includes a water-soluble monomer having an acid group, such as acrylic acid. In some examples, the aqueous solution of the unsaturated monomer may be methacrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, fumaric acid (cis-butenioic acid), cis-butenioic anhydride, fumaric acid (anti-butenioic acid), and anti-butenioic anhydride. The aqueous solution of the unsaturated monomer may contain one monomer, but is not limited to that, and may contain two or more of the above-mentioned aqueous solutions of monomers.

[0026] In some examples, the concentration of the aqueous solution of the unsaturated monomer may be 20 wt% to 55 wt% relative to 100 wt% of the water-absorbent resin composition, but is not limited to this, and is preferably 30 wt% to 45 wt%. Generally, if the concentration of the aqueous solution of the unsaturated monomer is 20 wt% to 55 wt%, the viscosity of the product after polymerization is appropriate, making it easy to process mechanically, and the reaction heat during the radical polymerization reaction is easy to control.

[0027] In some other embodiments, other hydrophilic monomers having unsaturated double bonds, such as acrylamide, methacrylamide, 2-carboxyethyl acrylate, 2-carboxyethyl methacrylate, methyl acrylate, ethyl acrylate, dimethylamide acrylamide, and chloride acrylamide trimethylamine, may be selectively added. However, the amount of hydrophilic monomer added should, in principle, not impair the physical properties of the water-absorbing resin (e.g., retention capacity and absorption rate).

[0028] In some embodiments, a water-soluble polymer may be selectively added to the water-absorbent resin composition to reduce manufacturing costs. The water-soluble polymer may be partially saponified or fully saponified polyvinyl alcohol, polyethylene glycol, polyacrylic acid, polyacrylamide, starch, or starch derivatives (e.g., methylcellulose, methylcellulose acrylate, ethylcellulose), and preferably starch and partially saponified or fully saponified polyvinyl alcohol are used alone or in combination. In the embodiments described above, the molecular weight of the water-soluble polymer is not limited, and when the amount of unsaturated monomer aqueous solution used is 100 wt%, the amount of water-soluble polymer added is usually 20 wt% or less, preferably 10 wt% or less, and more preferably 5 wt% or less, in principle not to degrade the physical properties of the water-absorbent resin.

[0029] In some embodiments, the aqueous solution of the unsaturated monomer may undergo direct polymerization, or it may be partially neutralized using a neutralizing agent to make the aqueous solution neutral or weakly acidic before polymerization. In these embodiments, the neutralizing agent includes alkali metal group or alkaline earth metal group hydroxyl compounds or carbonate compounds (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 aqueous solution of the unsaturated monomer is 45 mol% to 85 mol%, preferably 50 mol% to 75 mol%. When the neutralization concentration is within this range, the aqueous solution of the unsaturated monomer can have an appropriate pH value and will not cause harm even if it comes into accidental contact with the human body. Supplementarily, the neutralization concentration described herein is defined as the ratio of moles of the alkaline solution to moles of the aqueous solution of the unsaturated monomer, and may be the percentage at which the acidic groups of the aqueous solution of the unsaturated monomer are neutralized. In some embodiments, the pH value of the aqueous solution of the unsaturated monomer is 5.5 to 7.0, preferably 5.5 to 6.5. If the pH value of the unsaturated monomer aqueous solution is between 5.5 and 7.0, a large amount of unreacted monomer is less likely to remain in the aqueous solution after polymerization, resulting in a water-absorbing resin with good physical properties and high absorption capacity.

[0030] The preliminary polymerization reaction begins with the decomposition of the polymerization initiator, which generates radicals. In some examples, the appropriate amount of polymerization initiator used is 0.001 wt% to 10 wt%, preferably 0.1 wt% to 5 wt%, per 100 wt% of the unsaturated monomer aqueous solution. When the amount of polymerization initiator used is within the aforementioned range, the rate of the radical polymerization reaction is appropriate, economic benefits are good, the heat of reaction is easy to control, and the formation of a gel-like solid due to excessive polymerization can be avoided.

[0031] In some embodiments, polymerization initiators include pyrolysis initiators, redox initiators, and combinations thereof. In some embodiments, pyrolysis initiators include peroxides [e.g., hydrogen peroxide, di-tert-butyl peroxide, peroxide amides, or persulfates (including ammonium salts and alkali metal salts)] and azo compounds [e.g., 2,2-azobis(2-amidinepropane) dihydrochloride, 2,2-azobis(N,N-diolmethylisobutylazine) dihydrochloride]. In some embodiments, redox initiators include acidic sulfites, ascorbic acid, or ferrous salts. Polymerization initiators are preferably used in combination with pyrolysis initiators and redox initiators. First, the redox initiator reacts to generate radicals, and when the radicals are transferred to monomers, the polymerization reaction begins, and the temperature rises due to the large amount of heat released by the polymerization reaction. Once a certain temperature is reached, the decomposition of the pyrolysis initiator can be further initiated to make the polymerization reaction more complete, thus avoiding the retention of excess unreacted monomers.

[0032] The radical polymerization crosslinking agent in the water-absorbent resin composition can give the water-absorbent resin composition an appropriate degree of crosslinking and improve the processability of the water-absorbent resin composition after the polymerization reaction. In some examples, the radical polymerization crosslinking agent is a compound having two or more unsaturated double bonds, such as N,N-bis(2-propenyl)amine, N,N-methylenebisacrylamide, N,N-methylenebismethacrylamide, propylene acrylate, ethylene glycol diacrylate, polyethylene glycol diacrylate, ethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, glycerin trimethacrylate, triacrylate or trimethacrylate of ethylene oxide with glycerol, trimethylolpropane trimethacrylate, trimethylol Propane triacrylate, N,N,N-tri(2-propenyl)amine, ethylene glycol diacrylate, polyoxyethylene glyceryl triacrylate, diethyl polyoxyethyl glycerol triacrylate, dipropylene triglycol ester, etc. may be used, as well as compounds having two or more epoxy groups, such as sorbitol polyglycidyl ether, polyglycerol polyglycidyl ether, ethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, diglycerol polyglycidyl ether, etc. They may be used alone or in mixtures of two or more radical polymerization crosslinking agents. In some examples, the amount of radical polymerization crosslinking agent is 0.001 wt% to 5 wt%, preferably 0.01 wt% to 3 wt%, per 100 wt% of an unsaturated monomer aqueous solution. When the amount of radical polymerization crosslinking agent added is within the above range, the viscosity of the polymer aqueous solution after the reaction is appropriate and mechanical processing is easy, and the water absorption of the water-absorbing resin obtained thereafter is good.

[0033] In some embodiments, the radical polymerization reaction can be carried out in a batch reaction vessel (e.g., a kettle reactor) or a conveyor belt reactor.

[0034] Next, operation 120 is performed to shear the gel with a twisting machine to obtain superabsorbent resin particles. The material discharge port of the aforementioned twisting machine has special blades and a perforation plate. The twisting machine with special blades can compress the gel, improving its roughness and compactness, further improving the short-time absorption rate of the superabsorbent resin particles, reducing water-soluble matter, and improving liquid conductivity.

[0035] Please refer to Figures 2A to 2C. Figure 2A is a plan view of the blade 200 of a twisting machine according to some embodiments of the present invention, Figure 2B is a side view of the blade 200 of a twisting machine according to some embodiments of the present invention, and Figure 2C is a cross-section 210 of the blade 200 of a twisting machine according to some embodiments of the present invention. Compared to known blades consisting of a rectangle, the blade 200 consists of two parallelogram blades, and unlike known blades with a rectangular cross-section, the cross-section 210 of the blade 200 used in the present invention is a parallelogram as shown in Figure 2B. When the cross-section 210 is a parallelogram, there is a large friction and pressing force when cutting the gel, and a lot of friction is generated between the gels, so the roughness and compactness of the obtained water-absorbing resin particles can be improved, and the false specific gravity and absorption rate of the obtained water-absorbing resin particles can be improved.

[0036] The cross section 210 has a first side length 215 and a second side length 220 that are parallel to each other in direction X, and the endpoints on the same side of the first side length 215 and the second side length 220 are the first endpoint P1 and the second endpoint P2, respectively. The first side length 215 consists of a first length R1 and a second length R2, where the first length R1 is the distance between the first endpoint P1 and the second endpoint P2 in direction X. In some embodiments, the first length R1 is about 40 mm to about 120 mm, and the second length R2 is about 190 mm to about 210 mm (preferably about 200 mm).

[0037] In some embodiments, the ratio R1 / R2 of the first length R1 to the second length R2 is about 0.1 to about 0.8, preferably about 0.2 to about 0.7. When the ratio R1 / R2 is within the aforementioned range, the twisting machine can be given appropriate pressing and shearing forces and good specific mechanical energy.

[0038] The cross section 210 has a first side length 215 and an adjacent side 225 that intersects at the first endpoint P1, and the first side length 215 and the adjacent side 225 have an enclosed angle θ. In some embodiments, the tangent value of the enclosed angle θ (i.e., tanθ) is about 0.1 to about 0.9, preferably about 0.2 to about 0.6. When tanθ is within the aforementioned range, the twisting machine can be given appropriate frictional and shear forces and good specific mechanical energy.

[0039] The perforated plate of the twisting machine has multiple holes, and in some embodiments, the diameter of the holes is about 8 mm to about 22 mm, preferably about 10 mm to about 20 mm. When the hole diameter is within the aforementioned range, the operating time of the twisting machine can be reduced and an appropriate frictional force can be applied to the gel.

[0040] The blade and the perforator are connected and spaced apart by a pitch, which in some embodiments is about 0.01 mm to about 0.09 mm, preferably about 0.02 mm to about 0.08 mm. When the pitch is within the aforementioned range, the twister can apply appropriate shear and frictional forces to the gel, thus having appropriate specific mechanical energy, effectively shearing the gel and avoiding the generation of metal shavings from the blade or perforator. Supplementary information, specific mechanical energy is the motor output power of the twister divided by the flux of the gel. In some embodiments, the specific mechanical energy of the twister is about 25 kWh / t to about 65 kWh / t, preferably about 25 kWh / t to 60 kWh / t. Using the appropriate specific mechanical energy described above, the gel can be effectively sheared.

[0041] In some embodiments, the small gels obtained after shearing with a twisting machine require steps such as drying, grinding, and sieving. In the embodiments described above, the temperature for the drying step is approximately 100°C to 250°C. By performing the drying process within the aforementioned temperature range, the drying time can be effectively controlled, and the degree of crosslinking can be effectively controlled to avoid the retention of large amounts of unreacted monomers.

[0042] In some embodiments, the sieving step described above involves sieving small gels with an average particle diameter of about 2.0 mm or less, preferably about 0.05 mm to about 1.50 mm. Gels with an average particle diameter greater than 2.0 mm must be sent back to the twisting machine for further shredding. The particle diameter must be controlled within the aforementioned range to avoid the generation of a higher amount of fine powder in subsequent processes, allowing for better thermal conductivity and avoiding the retention of too much unreacted monomer, which can lead to poor physical properties. Generally, the narrower the particle size distribution of small gels, the better the physical properties and the more advantageous it is for controlling drying time and temperature.

[0043] In some embodiments, after the sieving step, the small gels can be dried again, allowing for selective re-drying of the small gels. In the embodiments described above, the drying process is carried out at a temperature of approximately 100°C to 180°C. By performing the drying process within the aforementioned temperature range, the drying time can be effectively controlled, and the degree of crosslinking can be effectively controlled to avoid the retention of large amounts of unreacted monomers.

[0044] In some embodiments, the particle size of the water-absorbing resin particles is sieved to be between 0.06 mm and 1.00 mm, preferably between 0.10 mm and 0.85 mm. By controlling the particle size of the water-absorbing resin particles within the aforementioned range, the amount of fine powder in the product can be reduced, and the absorption performance of the water-absorbing resin can be improved.

[0045] In some examples, the resulting superabsorbent resin particles have a holding capacity of approximately 33.0 g / g to approximately 35.0 g / g, a purified water absorption rate of approximately 120 g / g to approximately 150 g / g per minute, a water-soluble portion of approximately 5.0% to approximately 7.0% per hour, a surface porosity of approximately 0.030 cc / g to approximately 0.050 cc / g, and a free swelling rate of approximately 0.30 g / g / s to approximately 0.50 g / g / s.

[0046] Next, operation 130 is performed to perform a surface crosslinking reaction on the water-absorbent resin particles to obtain a water-absorbent resin. Since the water-absorbent resin is an insoluble hydrophilic polymer, it has a uniform crosslinked structure inside the resin, and is further crosslinked on the resin surface in order to improve the absorption rate, improve gel strength, and improve properties such as blocking resistance and transmittance. The surface crosslinking reaction is carried out using a surface crosslinking agent having a functional group that can react with an acid group. In some examples, the surface crosslinking 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, and propylene glycol, the polyamine may be, for example, ethylenediamine, diethylenediamine, and triethylenediamine, and the compound containing an epoxy group may be, for example, sorbitol polyglycidyl ether, polyglycerol polyglycidyl ether, etc. The surface crosslinking agents may be ethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, and diglycerol polyglycidyl ether, and the alkylene carbonate may be, for example, ethyl methyl carbonate, 4-methyl-1,3-dioxolan-2-one, 4,5-dimethyl-1,3-dioxolan-2-one, 4,4-dimethyl-1,3-didioxolan-2-one, 4-ethyl-1,3-dioxolan-2-one, 1,3-dioxan-2-one, 4,6-dimethyl-1,3-dioxan-2-one, and 1,3-dioxepane-2-one. The reaction can be carried out by using one or more surface crosslinking agents together. Depending on the selected surface crosslinking agent, it may be added directly, or it may be prepared as an aqueous solution or hydrophilic organic solution before addition. Hydrophilic organic solvents include, but are not limited to, methyl alcohol, ethanol, propanol, isobutanol, acetone, methyl ether, and ether.

[0047] In some examples, the amount of surface crosslinking agent added is approximately 0.001 wt% to 10 wt%, preferably approximately 0.005 wt% to 5 wt%, relative to 100 wt% of the total solid content of the reactant. When the amount of surface crosslinking agent added is within the above range, a crosslinked structure can be formed on the surface of the water-absorbing resin, and even better absorption performance can be achieved.

[0048] In some embodiments, the surface crosslinking reaction further includes adding an aluminum salt compound along with a surface crosslinking agent to further improve the liquid conductivity of the water-absorbent resin. In some specific examples, the aluminum salt compound includes aluminum sulfate, aluminum lactate, aluminum citrate, or a combination thereof. In some embodiments, the amount of aluminum salt compound added per 100 wt% of water-absorbent resin particles is 0.1 wt% to 1.0 wt%, preferably about 0.3 wt% to about 0.7 wt%, and optimally about 0.6 wt%. By adding an amount of aluminum salt compound within the aforementioned range, the water absorption ratio and liquid conductivity of the resulting water-absorbent resin under pressure can be improved.

[0049] As described above, the water-absorbing resin obtained by the water-absorbing resin manufacturing method 100 can have a high absorption rate, a low water-soluble portion, and a high surface porosity. In some examples, the water-soluble portion of the water-absorbing resin of the present invention after 16 hours is about 5.0% to about 8.0%, and the surface porosity is about 0.030 cc / g to about 0.050 cc / g.

[0050] Furthermore, the water-absorbing resin must possess good centrifuge retention capacity (CRC) and absorption against pressure (AAP) so that it is not damaged or affected by external pressure applied to the absorbent after absorbing liquid. In some embodiments, the centrifuge retention capacity of the water-absorbing resin of the present invention is 28 g / g or more, preferably about 28.0 g / g to about 31.0 g / g. In some embodiments, the absorption against pressure of the water-absorbing resin of the present invention is greater than 23.0 g / g, preferably about 25.0 g / g to 27.0 g / g. The effective capacity (EFFC) of the water-absorbing resin is the average value of the retention capacity and the absorption against pressure, and can be calculated using the following formula.

number

[0051] The ability of a dry superabsorbent polymer to absorb liquid upon initial contact may be expressed as a T20 value. A low T20 value of a superabsorbent polymer indicates that the dry polymer absorbs liquid easily. The T20 value of the superabsorbent polymer of the present invention is approximately 150 seconds or less, for example, approximately 90 seconds to approximately 130 seconds. Supplementary information: The T20 value is defined as the time required for 1 gram of superabsorbent polymer to absorb 20 grams of physiological saline and a 0.01 wt% aqueous solution of an alcohol ethoxy compound under a pressure of 0.3 psi, where the alcohol ethoxy compound has 12 to 14 carbon atoms.

[0052] The permeability of the superabsorbent polymer may be detected by urine permeability measurement (UPM). UPM typically measures the flow resistance of the pre-swelled layer of the superabsorbent polymer. Therefore, when the superabsorbent polymer is wet with liquid, a superabsorbent polymer with a high UPM value can exhibit better permeability. The UPM value of the superabsorbent polymer of the present invention is approximately 20 × 10⁻⁶ -7 cm3 -s / g ~ approx. 50×10 -7 cm 3 -s / g

[0053] Furthermore, the liquid conductivity of the superabsorbent polymer may be detected by fixed height absorption (FHA) and free swell gel bed permeability (free swell GBP). The FHA value measures the amount of fluid absorbed when the absorbent fluid reaches a specific height after the superabsorbent polymer has overcome gravity. In some embodiments, the FHA value of the superabsorbent polymer obtained by Method 100 is approximately 20 g / g to approximately 30 g / g. Free swell gel bed permeability is used to measure the permeability of the swollen base of the superabsorbent polymer. It should be understood that the so-called "free swell" state means that swelling of the superabsorbent polymer is permitted and there is no swelling limiting load. In some embodiments, the free swell gel bed permeability of the superabsorbent polymer obtained by Method 100 is approximately 5 × 10⁻⁶. -9 cm 2 ~Approx. 20×10 -9 cm 2 That is the case.

[0054] The following examples illustrate the application of the present invention, but are not intended to limit the invention, and those skilled in the art can make various modifications and changes without departing from the spirit and scope of the invention. Manufacturing of water-absorbent resins Manufacturing example

[0055] 437.5 g of a 48 wt% sodium hydroxide aqueous solution was slowly added to a 2000 c.c. tapered bottle containing 540 g of acrylic acid and 583.2 g of water, with a sodium hydroxide / acrylic acid dropping ratio within the range of 0.85 to 0.95, a dropping time of 2 hours, and the temperature inside the bottle and the reaction system maintained within the range of 15°C to 40°C. An aqueous monomer solution with a monomer concentration of 42 parts by weight was obtained, and the 70 mol% acrylic acid portion was neutralized with sodium acrylate. This solution was then added to a 2 liter kettle reactor (manufactured by CHIN LEI MECHANISM CO., LTD., Taiwan).

[0056] Next, 0.9 g of N,N'-methylenebisacrylamide (a radical polymerization reaction crosslinking agent) was added to an aqueous solution of unsaturated monomer. The temperature was maintained at approximately 20°C, and nitrogen gas was injected through piping to perform deoxygenation for 30 minutes.

[0057] Next, 0.3 g of hydrogen peroxide, 3.6 g of sodium bisulfite, 23.4 g of 10% sodium carbonate foaming agent, and 3.6 g of ammonium persulfate were added as polymerization initiators to carry out a radical polymerization reaction. After standing for 30 minutes, a gel was obtained. Example 1

[0058] The gel used in the manufacturing example was sheared by a twisting machine (CT-122 model, manufactured by Chiao Teng Machinery Co., Ltd.). The blades (manufactured by Jinlei Precision) and perforator of the material discharge port of the twisting machine had the following characteristics: the first length R1 was 100 mm, the second length R2 was 200 mm, the ratio R1 / R2 was 0.5, tanθ was 0.330, the hole diameter of the perforator was 16 mm, the pitch between the blades and the perforator was 0.05 mm, and the specific mechanical energy was 25 kWh / t.

[0059] Gels with particle diameters of 2 mm or less were sieved. Next, they were dried at a temperature of 130°C for 2 hours. Furthermore, they were sieved using a fixed particle size screen of 0.1 mm to 0.85 mm to obtain superabsorbent resin particles.

[0060] Next, 100 g of superabsorbent polymer particles were weighed, and an aqueous solution of 5 g of ethylene glycol, 1,4-butanediol (manufactured by Formosa Plastic Group), and methyl alcohol mixed in a 1:1:0.5 ratio was added as a surface crosslinking agent. In addition, a 70 wt% aqueous solution of aluminum lactate was added at a concentration of 0.6 wt% of the superabsorbent polymer particles. Next, the mixture was heat-treated at 200°C for 1 hour. After cooling, the superabsorbent polymer was obtained. Examples 2-11

[0061] The superabsorbent resins of Examples 2-11 were manufactured using the same process steps as in Example 1. They differed in the characteristics of the twisting machine blades and drilling machine, specifically the first length R1, second length R2, ratio R1 / R2, tanθ, hole diameter of the holes in the drilling machine, pitch between the blades and the drilling machine, and specific mechanical energy. The characteristics of the twisting machine blades and drilling machine of Examples 2-11 are shown in Table 1. Comparative Example 1

[0062] According to the method of Chinese Patent CN1206365A, a monomer aqueous solution was prepared by mixing 83.2 parts of acrylic acid, 1662.8 parts of a 37% by weight aqueous solution of sodium acrylate, 5.5 parts of polyethylene glycol diacrylate (with an average total mole count of 8 ethylene oxides (EO)), and 654.5 parts of deionized water. The neutralization rate of acrylic acid in the monomer aqueous solution was 85%, and the monomer concentration was 30%. The temperature of the monomer aqueous solution was maintained at 24°C while blowing nitrogen gas into the monomer aqueous solution to remove dissolved oxygen from it.

[0063] Next, 77 parts of a 10% by weight solution of 2,2'-azobis(2-methylpropionamidine) dihydrochloride were added to the monomer aqueous solution while it was being stirred. Three minutes after the start of stirring, the monomer aqueous solution containing the 2,2'-azobis(2-methylpropionamidine) dihydrochloride solution turned into a white mist, producing a white particulate solid with an average particle size of approximately 9 μm. This particulate solid was 2,2'-azobis(2-methylpropionamidine) diacrylate, which acted as a foaming agent. Five minutes after the start of stirring, under nitrogen gas, 10.8 parts of a 10% by weight aqueous solution of sodium persulfate and 0.5 parts of a 1% by weight aqueous solution of L-ascorbic acid were added as radical polymerization initiators while the monomer aqueous solution was being stirred. After the monomer aqueous solution was thoroughly stirred, it was allowed to stand. The polymerization reaction was started three minutes after the addition of the 10% by weight aqueous solution of sodium persulfate and the 1% by weight aqueous solution of L-ascorbic acid. The polymerization reaction was carried out in a hot water bath, and the temperature of the bath was controlled in accordance with the rise in temperature of the monomer aqueous solution. After 26 minutes following the addition of 10% by weight sodium persulfate aqueous solution to the monomer aqueous solution, the temperature of the monomer aqueous solution reached 97°C. Next, the monomer aqueous solution was allowed to stand for 20 minutes, and its temperature was maintained within the range of 70°C to 90°C to completely carry out the polymerization reaction of the acrylate monomer. A cross-linked hydrogel polymer with bubbles (hereinafter abbreviated as hydrogel (A)) was obtained as a porous cross-linked polymer.

[0064] The obtained hydrogel (A) was continuously pulverized using a rotary mill as shown in Chinese patent CN1206365A. During pulverization, the average residence time, i.e., pulverization time, of hydrogel (A) in the rotary mill 31 was approximately 0.25 minutes. The particle size range of the hydrogel particles obtained by pulverizing hydrogel (A) was approximately 1 to 15 mm. The pulverized hydrogel was dried in a circulating hot air dryer at 160°C for 1 hour. After that, the dried hydrogel was pulverized in a roll mill and sieved using a standard sieve conforming to JIS standards. Particles that passed through the 850 μm sieve but did not pass through the 150 μm sieve pores were obtained as water-absorbent resin particles.

[0065] Next, a surface crosslinking reaction was carried out by applying a secondary crosslinking treatment liquid to obtain a water-absorbent resin. Specifically, 100 parts of water-absorbent resin particles were mixed with a treatment liquid for secondary crosslinking treatment, and then the obtained mixture was heated at 195 °C for 30 minutes to obtain a water-absorbent resin. The secondary crosslinking treatment liquid was 0.05 part of ethylene glycol glycidyl ether (ethylene glycol glycidyl ether) , 0.5 part of lactic acid, 0.02 part of polyoxyethylene sorbitan monostearate, 0.75 part of isopropanol and 3 parts of water were prepared as a composition by mixing. Comparative Example 2

[0066] According to the method of Chinese Patent CN104936989A, water, a 50 wt% sodium hydroxide solution and acrylic acid were continuously mixed to prepare a 42.7 wt% acrylic acid / sodium acrylate solution, and the neutralization degree was 69.0 mol%. After mixing, the monomer solution was cooled to a temperature of 30 °C using a heat exchanger and degassed using nitrogen gas. The polyethylene unsaturated crosslinking agent used was 3-triethoxylated glycerol triacrylate (purity is about 85 wt%), and its usage amount was 0.35 wt% based on the acrylic acid used (based on the acrylic acid; boaa). To initiate the radical polymerization reaction, 0.0008 wt% of hydrogen peroxide in a 2.5 wt% aqueous solution was metered added based on boaa, 0.13 wt% of sodium persulfate in a 15 wt% aqueous solution was metered added based on boaa, and 0.0023 wt% of ascorbic acid in a 0.5 wt% aqueous solution was metered added based on boaa. The flux of the monomer solution was 800 kg / h.

[0067] Each component was continuously metered and added to a List ORP 250 Contikneter continuous series-parallel reactor (LIST AG, Arisdorf, Switzerland). Separately, 26.3 kg / h of a sieved bottom material with a particle size of less than 150 μm was added to the first one-third from the front of the reactor. The feed temperature of the reaction solution was 30 °C. The residence time of the reaction mixture in the reactor was about 15 minutes.

[0068] The polymer gel obtained above was extruded using an SLRE 75 R extruder (SelaMaschinen GmbH; Harbke; Germany). During the extrusion process, the temperature of the polymer gel was 95°C. The perforated plate had 12 holes with a diameter of 8 mm. The thickness of the perforated plate was 16 mm. The ratio of the inner length to the inner diameter (L / D) of the extruder was 4. The specific mechanical energy (SME) of the extrusion was 26 kWh / t. The extruded polymer gel was dispersed onto a metal plate and dried in an air-circulating drying chamber at 175°C for 90 minutes. The polymer gel load on the metal plate was 0.81 g / cm³. 2 That was the case.

[0069] The dried polymer gel was pulverized using a single-roller mill (three pulverization cycles were performed; the gap width for the first pulverization cycle was 1000 μm, for the second pulverization cycle it was 600 μm, and for the third pulverization cycle it was 400 μm). The pulverized and dried polymer gel was then classified, and 600μm~710μm: 10.6% by weight, 500μm~600μm: 27.9% by weight, 300μm~500μm: 42.7% by weight, 200 μm ~ 300 μm: 13.8% by weight, and A synthetic particle size distribution (PSD) having a composition of 150 μm to 200 μm: 5.0% by weight was mixed to obtain raw polymer A (absorbent polymer particles).

[0070] Next, at 23°C and an axial rotation speed of 200 revolutions per minute, 54.6 g of the mixture was coated onto 1.2 kg of the above raw material polymer A using a two-substance nozzle in a plowshaar mixer (Gebr. Maschinenbau GmbH; Paderborn, Germany) equipped with a heating jacket. The mixture consisted of 0.07 wt% N-hydroxyethyl-2-oxazolidinone, 0.07 wt% 1,3-propylene glycol, 0.7 wt% propylene glycol, 2.27 wt% 22 wt% aqueous aluminum lactate solution, 0.448 wt% 0.9 wt% aqueous dehydrated sorbitol monolaurate solution, and 0.992 wt% isopropanol, with each weight percentage based on the raw material polymer A.

[0071] After spraying, the product temperature was raised to 185°C, and the product was maintained at this temperature and with a shaft rotation speed of 50 revolutions per minute for 35 minutes. The resulting product was cooled to ambient temperature and reclassified using a 710 μm screen. Performance analysis was performed on absorbent resins with particle sizes smaller than 710 μm. Comparative Examples 3-10

[0072] The superabsorbent resins of Comparative Examples 3 to 10 were also manufactured using the same process steps as in Example 1. They differed in the characteristics of the twisting machine blades and perforated disc, specifically the first length R1, second length R2, ratio R1 / R2, tanθ, hole diameter of the perforated disc holes, pitch between the blades and the perforated disc, and specific mechanical energy. The characteristics of the twisting machine blades and perforated discs of Comparative Examples 3 to 10 are shown in Table 1. Evaluation format

[0073] To evaluate the properties of the water-absorbing resin of the present invention, its physical properties were analyzed by the following test method. Unless otherwise specified, the following measurement conditions were all carried out at room temperature of 23±2°C and relative air humidity of 45±10%. The water-absorbing resin had to be thoroughly mixed before analysis. holding power

[0074] The centrifuge retention capacity (CRC) was tested according to the test method specified in ERT 241.2(12) by the European Disposables and Nonwovens Association (EDANA). The results of the centrifuge retention capacity tests for the absorbent polymer particles and the absorbent polymer are shown in Tables 2 and 3, respectively. Water purification absorption rate per minute

[0075] The purified water absorption rate per minute was tested according to the test method specified in EDANA's ERT 240.2(12), where saline solution was replaced with deionized water (purified water) and the absorption time was changed from 30 minutes to 1 minute. The test results for the purified water absorption rate per minute of the absorbent polymer particles and the absorbent polymer are shown in Tables 2 and 3, respectively. Surface porosity

[0076] Surface porosity was tested using a mercury porometer (micromeritics AutoPore(R) IV 9520) at a standard filling pressure of approximately 4 kPa. The test results for the water-absorbent polymer particles and the water-absorbent polymer are shown in Tables 2 and 3, respectively. Free swelling rate

[0077] The free swell rate (FSR, unit: g / g / s) was measured and calculated based on the method described in patent no. WO2012 / 174026A1. First, 4 g of superabsorbent polymer was dried at a temperature of 23 ± 2 °C and a pressure of 0.01 torr or less for 48 hours. Then, approximately 1 g was weighed and placed in a beaker, dispersed at the bottom of the beaker. Next, 20 g of a 0.9 wt% sodium chloride aqueous solution was poured in, and the time from when the liquid first came into contact with the superabsorbent polymer until the liquid was completely absorbed by the polymer was measured. The free swell rate was obtained by dividing the amount of liquid by the weight of the superabsorbent polymer and then dividing by the time elapsed. The average results obtained by repeating the process three times for the superabsorbent polymer particles and the superabsorbent polymer are shown in Tables 2 and 3, respectively. Water absorption ratio under pressure

[0078] The absorption rate against pressure (AAP) was tested according to the test method specified in EDANA's ERT 442.3(10). The absorption rate was tested under pressure of 4.9 kPa for 60 minutes with a 0.9% sodium chloride aqueous solution. The test results for the superabsorbent polymer are shown in Table 3. Effective Capacity (EFFC)

[0079] The EFFC value represents the holding power and the water absorption ratio under pressure, and was obtained by summing these two values ​​and dividing by two. The EFFC values ​​of the water-absorbent polymers are shown in Table 3. Water-soluble portion after 1 hour and 16 hours

[0080] The water extractable content at 1 hour and 16 hours was tested according to the test method specified in EDANA's ERT 470.2(02). The test results for the water extractable content of the superabsorbent polymer particles at 1 hour and the water extractable content of the superabsorbent polymer at 16 hours are shown in Tables 2 and 3, respectively. T20 value

[0081] The T20 value (in seconds) was measured and calculated according to the method described in U.S. Patent No. 9,285,302, and represents the time required for 1 gram of this superabsorbent resin to absorb 20 grams of physiological saline and a 0.01 wt% aqueous solution of an alcohol ethoxy compound under a pressure of 0.3 psi, where the alcohol ethoxy compound had 12 to 14 carbon atoms. The average results of testing the superabsorbent resin three times are shown in Table 3. Urine permeability measurement

[0082] Urine permeability measurement (UPM) was performed according to the method described in patent no. WO2012 / 174026A1. The test results for the superabsorbent polymer are shown in Table 3. Fixed height absorption

[0083] Fixed height absorption (FHA) was tested according to the method described in U.S. Patent US7,108,916. The test results for the water-absorbent polymer are shown in Table 3. Free-swelling gel bed permeability

[0084] Free swell gel bed permeability (free swell GBP) was tested according to the method described in U.S. Patent US8,021,998 B2. The test results for the superabsorbent polymer are shown in Table 3.

[0085] [Table 1]

[0086] [Table 2]

[0087] [Table 3]

[0088] According to Tables 2 and 3, the absorption characteristics of the water-absorbing resins obtained in Comparative Examples 1 and 2 of known technologies were inferior to those of Examples 1 to 11, and the water-soluble portion of Comparative Examples 1 and 2 was clearly high. The tanθ of Comparative Example 3 was too large, and the ratio R1 / R2 of Comparative Example 4 was too large; in both cases, it was difficult to form a water-absorbing resin with good absorption characteristics. The pitch between the blade and the perforating plate in Comparative Examples 6 to 8 was too large; in Comparative Example 7, the hole diameter of the perforating plate was too small, and in Comparative Example 8, the hole diameter of the perforating plate was too large; in all cases, the absorption rate and other characteristics of the obtained water-absorbing resins were not good. In Comparative Examples 9 and 10, the first length R1 was equal to the second length R2, and the frictional force between them was insufficient, resulting in low porosity of the water-absorbing resin particles and the surface porosity of the water-absorbing resin, a high water-soluble portion, and poor absorbency.

[0089] According to Table 2, compared to Comparative Examples 1 to 10, the water-absorbing resin particles of Examples 1 to 11 clearly had a lower water-soluble portion and a higher purified water absorption ratio, surface porosity, and free swelling rate per minute.

[0090] According to Table 3, compared to Comparative Examples 1 to 10, the superabsorbent resins of Examples 1 to 11 all had high surface porosity, EFFC value, urine permeability (UPM), fixed-height absorbency (FHA), and free-swell gel bed permeability (GBP), and had low T20 value and water-soluble portion. Therefore, the superabsorbent resins of Examples 1 to 11 readily absorbed liquids in a dry state and also exhibited good liquid permeability and conductivity.

[0091] Therefore, using the method for producing the superabsorbent resin of the present invention, the gel is sheared by a twisting machine having special blades to improve the compactness and surface roughness of the gel, and further improve the surface porosity, absorption rate and liquid conductivity of the obtained superabsorbent resin, while reducing the water-soluble portion.

[0092] Although the present invention has been disclosed in several embodiments as described above, these embodiments are not intended to limit the invention, and those skilled in the art can make various modifications and alterations without departing from the spirit and scope of the invention. Therefore, the scope of protection of the present invention should be based on the claims appended below. [Explanation of symbols]

[0093] 100: Method 110, 120, 130: Operation 200: Blade 210: Cross-section 215: First side length 220: Second side length 225: Adjacent edges R1: First length R2: Second length P1: 1st end point P2: Second end point X: Direction θ: included angle

Claims

1. A method for producing a water-absorbent resin, comprising performing a radical polymerization reaction on a water-absorbent resin composition containing an aqueous solution of an unsaturated monomer, a polymerization initiator, and a radical polymerization crosslinking agent to obtain a gel, The gel is sheared by a twisting machine having a blade with a parallelogram cross-section at the material discharge port and a perforated plate containing multiple holes, thereby obtaining multiple water-absorbing resin particles. The water-absorbing resin is obtained by performing a surface crosslinking reaction on the plurality of water-absorbing resin particles. A method for producing a water-absorbing resin containing water-absorbing resin.

2. The method for producing a water-absorbent resin according to claim 1, wherein the parallelogram has a first side length and a second side length that are parallel to each other in a first direction, the endpoints of the first side length and the second side length on the same side are the first endpoint and the second endpoint, respectively, the first side length is equal to the sum of the first length and the second length, the first length is the distance between the first endpoint of the first side length and the second endpoint of the second side length in the first direction, and the ratio of the first length to the second length is 0.1 to 0.

8.

3. The method for producing a water-absorbent resin according to claim 2, wherein the parallelogram has an adjacent side that intersects the first side length at the first endpoint, and the angle between the first side length and the adjacent side has a tangent value of 0.1 to 0.

9.

4. The method for producing a water-absorbent resin according to claim 2, wherein the first length is 40 mm to 120 mm and the second length is 190 mm to 210 mm.

5. The method for producing a water-absorbent resin according to claim 1, wherein each of the plurality of holes has a pore diameter of 8 mm to 22 mm.

6. The method for producing a water-absorbent resin according to claim 1, wherein the blade and the hole plate are separated by a pitch of 0.01 mm to 0.09 mm.

7. The method for producing a water-absorbent resin according to claim 1, wherein the specific mechanical energy of the twisting machine is 25 kWh / t to 65 kWh / t.

8. Before performing the surface crosslinking reaction, The method for producing a water-absorbent resin according to claim 1, further comprising adding a surface crosslinking agent and an aluminum salt compound to the plurality of water-absorbent resin particles.

9. The method for producing a water-absorbent resin according to claim 8, wherein the amount of the aluminum salt compound added is 0.1 wt% to 1.0 wt% relative to 100 wt% of the water-absorbent resin particles.

10. The method for producing a water-absorbent resin according to claim 8, wherein the aluminum salt compound comprises aluminum sulfate, aluminum lactate, aluminum citrate, or any combination thereof.

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