Water-absorbing resin and method for producing the same

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-absorbing resin and a method for producing the same, and more particularly to a water-absorbing resin produced using a mincer having a variable-diameter orifice plate and a method for producing the same.

Background Art

[0002] A water-absorbing resin (Super Absorbent Polymer; SAP) is a water-insoluble polymer and is mainly applied to various fields such as absorbent articles such as paper diapers and sanitary napkins, water retention agents for agriculture, forestry and horticulture, and water stop agents for industrial use.

[0003] In the production process of water-absorbing resins, it is necessary to use a large amount of monomers and hydrophilic polymers, and polyacrylic acid (salt)-based water-absorbing resins using acrylic acid and / or its salts as monomers are mainly industrially produced. With the improvement of the performance of paper diapers, which are the main application, more functions (such as high cost performance) are required for water-absorbing resins. Specifically, in addition to the water absorption ratio under non-pressure and the water absorption ratio under pressure, which are basic physical properties, various physical properties such as gel strength, water-soluble components, moisture content, water absorption rate, antibacterial property, abrasion resistance, powder fluidity, deodorizing property, color fastness, low dust generation property, and low monomer residual amount are also required for water-absorbing resins. In particular, in the application of sanitary products such as paper diapers, it is desired that the water absorption rate of the water-absorbing resin can be further increased as the product is made thinner.

[0004] Generally, the industrial production method of powdery or granular water-absorbing resins includes a polymerization step, a gel pulverization (atomization) step performed after polymerization or simultaneously with polymerization, a drying step of the atomized gel, a pulverization step of the dried product, a sieving step of the pulverized product, and a surface crosslinking step of the water-absorbing resin powder after classification. Among the currently proposed production methods of water-absorbing resins, there is a production method in which the polymerization step and the gel pulverization step are performed simultaneously using a polymerization apparatus having a pulverizing device. In the case of the above production method, while the liquid monomer is subjected to a polymerization reaction, the generated water-containing gel is pulverized, and the atomized water-containing gel is discharged from the polymerization apparatus.

[0005] However, the size of the gel particles obtained by the above device is approximately several millimeters to several centimeters. In response to the requirement of further improving the water absorption rate, since the size of the above gel particles cannot meet this requirement, it is necessary to add a gel pulverizing device. For example, using a batch kneader and a continuous kneader, the water-absorbing resin can be produced into gel particles having a specific particle size or relatively smaller ones by the wet pulverization method. However, the known gel pulverizing devices are too large in size to be applied to an industrial production line.

[0006] In view of this, in order to pulverize the gel body to have a size as required during the manufacturing process, it has become an urgent task to provide a water-absorbing resin and its manufacturing method.

Summary of the Invention

Means for Solving the Problems

[0007] One aspect of the present invention provides a method for manufacturing a water-absorbing resin, which pulverizes a gel body by a variable-diameter orifice plate of a mincer and further improves the absorption rate and liquid conduction performance of the produced water-absorbing resin.

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

[0009] According to one aspect of the present invention, there is provided a method for manufacturing a water-absorbing resin, including the steps of: subjecting a water-absorbing resin composition containing an acid-based monomer aqueous solution, a polymerization reaction initiator, and a radical polymerization reaction crosslinking agent to a radical polymerization reaction to obtain a gel body; using a mincer having a variable-diameter orifice 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 cut the gel body to obtain a plurality of water-absorbing resin particles; and performing a surface crosslinking reaction on the water-absorbing resin particles to obtain a water-absorbing resin.

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

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

[0012] According to an embodiment of the present invention, the first diameter, the second diameter, and the thickness of the variable-diameter orifice plate have the following relational expression.

Equation

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

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

[0015] According to an embodiment of the present invention, before the step of performing the surface crosslinking reaction, the step further includes adding a surface crosslinking agent and an aluminum salt compound to the water-absorbing resin particles.

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

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

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

Advantages of the Invention

[0019] When the water-absorbing resin and its manufacturing method of the present invention are applied, by crushing the gel body with a mincer having a variable-diameter orifice plate, the density and surface roughness of the gel body are improved, and further the apparent specific gravity, absorption rate, and liquid conduction performance of the produced water-absorbing resin are improved.

Brief Description of the Drawings

[0020] Aspects of the present disclosure can be better understood by reading in conjunction with the drawings with reference to the following detailed description. Note that, as is the case with standard industry practices, many of the features are not drawn to scale. In fact, the sizes of many of the features can be arbitrarily scaled for clarity of consideration.

Figure 1

Figure 2

Modes for Carrying Out the Invention

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

[0022] Hereinafter, the manufacturing and use of the embodiments of the present invention will be examined in detail. However, as can be understood, the embodiments provide many applicable inventive concepts that can be implemented in various specific contexts. The specific embodiments discussed are for illustrative purposes only and are not intended to limit the scope of the present invention.

[0023] As described above, the present invention provides a water-absorbing resin and its manufacturing method. By crushing the gel body with a mincer having a variable-diameter orifice plate, the density and surface roughness of the gel body are improved, and further the apparent specific gravity, absorption rate, and liquid conduction performance of the produced water-absorbing resin are improved.

[0024] Please refer to FIG. 1. FIG. 1 shows a flowchart of a method 100 for manufacturing a water-absorbing resin according to some embodiments of the present invention. First, an operation 110 of subjecting a water-absorbing resin composition to a radical polymerization reaction to obtain a gel body is performed. In some embodiments, the water-absorbing resin composition includes an aqueous acid monomer solution, a polymerization reaction initiator, and a radical polymerization reaction cross-linking agent.

[0025] In some embodiments, the aqueous acid monomer solution in the water-absorbing resin composition includes 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, maleic acid (cis-butenedioic acid), cis-butenyl anhydride, fumaric acid (trans-butenedioic acid), and trans-butenedioic anhydride. The aqueous acid monomer solution may contain one kind of monomer, but is not limited thereto, and two or more kinds of the above monomer aqueous solutions may be selected.

[0026] In some embodiments, based on 100 wt% of the water-absorbing resin composition, the concentration of the aqueous acid monomer solution may be 20 wt% to 55 wt%, but is not limited thereto, and is preferably 30 wt% to 45 wt%. Generally, when the concentration of the aqueous acid monomer solution is 20 wt% to 55 wt%, the viscosity of the product after polymerization is appropriate, machining is easy, and the heat of reaction during the radical polymerization reaction is also 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, dimethylaminoacrylamide, trimethylammonium acrylamide chloride, etc. can be selectively added. However, the addition amount of the above hydrophilic monomer is generally based on the principle of not impairing the physical properties of the water-absorbing resin (such as the centrifugal separation retention capacity and the absorption rate).

[0028] In some embodiments, in order to reduce the manufacturing cost, a water-soluble polymer can be selectively added to the water-absorbing resin composition. The water-soluble polymer may be partially saponified or fully saponified polyvinyl alcohol, polyethylene glycol, polyacrylic acid, polyacrylamide, starch or starch derivatives (such as methyl cellulose, methyl cellulose acrylate, ethyl cellulose), etc. Preferably, starch and partially saponified 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 usage amount of the aqueous acid monomer solution is 100 wt%, the addition amount of the water-soluble polymer is generally 20 wt% or less in principle so as not to deteriorate the physical properties of the water-absorbing resin, preferably 10 wt% or less, and more preferably 5 wt% or less.

[0029] In some embodiments, the aqueous acid monomer solution may be directly subjected to a polymerization reaction, or may be first partially neutralized using a neutralizing agent to make the aqueous acid monomer solution neutral or weakly acidic, and then subjected to a polymerization reaction. In some embodiments, the neutralizing agent includes hydroxides or carbonate compounds of the alkali metal group or alkaline earth metal group (such as 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 acid monomer solution is 45 mol% to 85 mol%, preferably 50 mol% to 75 mol%. When the neutralization concentration is within the above range, the aqueous acid monomer solution can have an appropriate pH value and will not cause harm even if it comes into accidental contact with the human body. It should be noted that the neutralization concentration described in this specification is defined as the ratio of the number of moles of the alkaline solution to the number of moles of the aqueous acid monomer solution, and may also be regarded as the percentage of the acidic groups of the aqueous acid monomer solution being neutralized. In some embodiments, the pH value of the aqueous acid monomer solution is 5.5 to 7.0, preferably 5.5 to 6.5. When the pH value of the aqueous acid monomer solution is 5.5 to 7.0, a large amount of unreacted monomers are less likely to remain in the aqueous solution after polymerization, and the physical properties of the water-absorbing resin produced later are good and the absorption amount is large.

[0030] The preliminary polymerization reaction starts with the decomposition of the polymerization initiator to generate radicals. In some embodiments, based on 100 wt% of the usage amount of the acid-based monomer aqueous solution, the appropriate usage amount of the polymerization initiator is 0.001 wt% to 10 wt%, preferably 0.1 wt% to 5 wt%. When the usage amount of the polymerization initiator is within the above range, the rate of the radical polymerization reaction is appropriate, the economic benefit is good, it is easier to control the reaction heat, and the formation of gel-like solids due to excessive polymerization can be avoided.

[0031] In some embodiments, the polymerization initiator includes thermal decomposition initiators, redox initiators, and combinations thereof. In some embodiments, the thermal decomposition initiators include peroxides such as hydrogen peroxide, di-t-butyl peroxide, peroxide amide, or persulfate (including ammonium salts and alkali metal salts), and azo compounds such as 2,2-azobis(2-amidinopropane) dihydrochloride, 2,2-azobis(N,N-dimethylenebisobutylamidine) dihydrochloride. In some embodiments, the redox initiators include acidic sulfite, ascorbic acid, or ferrous salts. It is preferable to use a combination of a thermal decomposition initiator and a redox initiator. First, the redox initiator is reacted to generate radicals. When the radicals transfer to the monomer, the polymerization reaction is initiated, and the temperature is raised by the large amount of heat released by the polymerization reaction. When a specific temperature is reached, the decomposition of the thermal decomposition initiator can be further initiated to make the polymerization reaction more complete, thus avoiding leaving excessive unreacted monomers.

[0032] The radical polymerization crosslinking agent in the water-absorbent resin composition can impart an appropriate degree of crosslinking to the water-absorbent resin composition and improve the processability of the water-absorbent resin composition after the polymerization reaction. In some embodiments, the radical polymerization crosslinking agent may be selected from, 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, polyoxyethylene glyceryl triacrylate, diethyl polyoxyethylene glyceryl triacrylate, triethylene glycol diacrylate and other compounds containing two or more compounds having unsaturated double bonds. For example, those containing two or more compounds having 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 may also be selected. Two or more radical polymerization crosslinking agents can be used alone or in combination. In some embodiments, based on 100 wt% of the acid monomer aqueous solution, the radical polymerization crosslinking agent is 0.001 wt% to 5 wt%, preferably 0.01 wt% to 3 wt%. When the addition amount of the radical polymerization crosslinking agent is within the above range, the viscosity of the polymer aqueous solution after the reaction is appropriate, machining is easy, and the water absorbency of the water-absorbent resin produced later is good.

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

[0034] Subsequently, an operation 120 of cutting the gel body using a mincer to obtain water-absorbing resin particles is performed. The mincer has a variable-diameter orifice plate. By using the mincer having this variable-diameter orifice plate, the number of times of cutting the gel body can be reduced, and the cut gel body can be aggregated, the obtained water-absorbing resin particles can be made dense, the eluate in the water-absorbing resin particles can be further reduced, and the bulk specific gravity of the water-absorbing resin particles can be improved. Further, since the surface roughness of the gel body can be improved, it contributes to achieving the effects of improving the surface porosity and absorption rate of the water-absorbing resin particles and further improving the liquid conduction performance.

[0035] Refer to FIG. 2. FIG. 2 shows a side view of a material supply end 210 and a material discharge end 220 of a variable-diameter orifice 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, since the first diameter D1 is larger than the second diameter D2, the obtained water-absorbing resin particles have a good adhesion effect.

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

[0037] The variable-diameter orifice plate 200 has a thickness L. In some embodiments, the thickness L is about 20 mm to about 40 mm, preferably 30 mm. When the thickness L is within the above range, the obtained water-absorbing resin particles have a good adhesion effect and an appropriate material discharge rate.

[0038] Moreover, between the first diameter D1, the second diameter D2, and the thickness L of the variable-diameter orifice plate 200, the following relational expression is satisfied.

Equation

[0039] In some embodiments, it is necessary to perform steps such as drying, pulverizing, and screening again on the fine gel body obtained after cutting with a mincer. In the above embodiments, the temperature of the drying step is from about 100°C to about 250°C. By performing the drying process within the above temperature range, the drying time can be effectively controlled, and the degree of crosslinking can be effectively controlled to avoid the remaining of a large amount of unreacted monomers.

[0040] In some embodiments, the screening step is to screen fine gel bodies with an average particle size of about 2.0 mm or less, preferably from about 0.05 mm to about 1.50 mm. It is necessary to send back the gel body with an average particle size larger than 2.0 mm to the mincer and pulverize it again. It is necessary to control the particle size within the above range to avoid the generation of a high amount of fine powder in the subsequent process, and it has good heat conduction properties, and it is possible to avoid the remaining of excessive unreacted monomers and the deterioration of physical properties. Generally, the narrower the particle size distribution of the fine gel body, the better the physical properties, and it contributes to the control of the drying time and temperature.

[0041] In some embodiments, after the screening step, the microgel bodies can be dried again, and the drying process can be selectively performed on the microgel bodies again. In the above embodiments, the drying process is carried out at a temperature of about 100°C to about 180°C. By carrying out the drying process within the above temperature range, the drying time can be effectively controlled, and the degree of crosslinking can be effectively controlled to avoid the remaining of a large amount of unreacted monomers.

[0042] In some embodiments, the particle size of the water-absorbing 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-absorbing resin particles within the above range, the amount of fine powder of the finished product can be reduced, and the absorption performance of the water-absorbing resin can be improved.

[0043] In some embodiments, the produced water-absorbing resin particles have a centrifugal retention capacity of about 34.0 g / g to about 35.0 g / g, a pure water absorption ratio of about 130 g / g to about 160 g / g in 1 minute, a water-soluble part of about 4.7% to about 6.0% in 1 hour, a surface porosity of about 0.033 c.c. / g to about 0.045 c.c. / 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, an operation 130 of performing a surface crosslinking reaction on the water-absorbing resin particles to obtain a water-absorbing resin is carried out. Since the water-absorbing resin is a water-insoluble hydrophilic polymer, there is a uniform crosslinked structure inside the resin. Generally, in order to improve the absorption rate, improve the strength of the gel body, and improve properties such as blocking resistance and liquid permeability, further crosslinking is performed on the surface of the resin. The surface crosslinking reaction is carried out by using a surface crosslinking agent having a functional group capable of reacting with an acid group. In some embodiments, 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. The compound containing an epoxy group may be, for example, sorbitol polyglycidyl ether, polyglycerol polyglycidyl ether, ethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, and 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, and 1,3-dioxepan-2-one. The reaction can be carried out alone or by mixing two or more surface crosslinking agents. Also, based on the selected surface crosslinking agent, the surface crosslinking agent may be added directly, or may be added after first preparing the surface crosslinking agent in an aqueous solution or a hydrophilic organic solution. The hydrophilic organic solvent includes, but is not limited to, methanol, ethanol, propanol, isobutanol, acetone, methyl ether, and ethyl ether, etc.

[0045] In some embodiments, based on 100 wt% of the total solid content of the reactants, the addition amount of the surface crosslinking agent is from about 0.001 wt% to about 10 wt%, preferably from about 0.005 wt% to about 5 wt%. When the addition amount of the surface crosslinking agent is within the above range, a crosslinked structure can be formed on the surface of the water-absorbing resin, and better absorption performance can be achieved.

[0046] In some embodiments, the surface crosslinking reaction further includes adding an aluminum salt compound simultaneously with the addition of the surface crosslinking agent in order to further improve the liquid conduction performance of the water-absorbing resin. In some specific examples, the aluminum salt compound includes aluminum sulfate, aluminum lactate, aluminum citrate, or a combination thereof. In some embodiments, based on 100 wt% of the water-absorbing resin particles, the addition amount of the aluminum salt compound is from 0.1 wt% to 1.0 wt%, preferably from about 0.3 wt% to about 0.7 wt%. By adding the aluminum salt compound in the above range, the water absorption ratio under pressure and the liquid conduction performance of the obtained water-absorbing resin can be improved.

[0047] As described above, the water-absorbing resin produced using the above manufacturing method 100 of the water-absorbing resin has a high bulk specific gravity, a low water-soluble part, and a high surface porosity. In some embodiments, the bulk specific gravity of the water-absorbing resin of the present invention is from about 600 g / L to about 650 g / L, the water-soluble part after 16 hours is from about 5.9% to about 8.6%, and the surface porosity is from about 0.033 c.c. / g to about 0.045 c.c. / g.

[0048] Furthermore, the water-absorbing resin should have good Centrifuge Retention Capacity (CRC) and absorption against pressure (AAP) so that after the water-absorbing resin absorbs liquid, it will not be damaged by the pressure applied to the absorbent from the outside or affect the liquid absorption capacity. In some embodiments, the centrifuge retention capacity of the water-absorbing resin of the present invention is 25 g / g or more, preferably about 28.0 g / g to about 29.0 g / g. In some embodiments, the absorption against pressure of the water-absorbing resin of the present invention is greater than 23 g / g, preferably about 25 g / g to 26 g / g.

[0049] The water-absorbing resin produced by method 100 can have a good absorption rate and can be evaluated using the free swell rate (FSR). The free swell rate of the water-absorbing 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 should be added that a water-absorbing resin with a high free swell rate can quickly absorb liquid without applying pressure.

[0050] The ability of the dried water-absorbing resin to absorb liquid when it first contacts the liquid can be indicated by the T20 value. When the T20 value of the water-absorbing resin is low, it indicates that the dried water-absorbing resin is easy to absorb liquid. The T20 value of the water-absorbing resin of the present invention is about 150 seconds or less, for example, about 100 seconds to about 150 seconds. It should be added that the T20 value is defined as the time required for 1 gram of the water-absorbing resin to absorb 20 grams of physiological saline and an aqueous solution of an alcohol ethoxy compound with 0.01 wt% under a pressure of 0.3 psi, and the alcohol ethoxy compound has 12 to 14 carbon atoms.

[0051] The permeability of the water-absorbing resin can be measured using urine permeability measurement (UPM). UPM usually measures the flow resistance of the pre-swelling layer of the water-absorbing resin. Therefore, when the water-absorbing resin is wet with a liquid, a water-absorbing resin with a high UPM value can exhibit good permeability. The UPM value of the water-absorbing resin of the present invention is about 45×10 -7 cm 3 -s / g to about 65×10 -7 cm 3 -s / g.

[0052] In addition, the liquid conduction properties of the water-absorbing resin can be further measured using fixed height absorption (FHA) and free swell gel bed permeability (free swell GBP). The FHA value measures the amount of fluid absorbed when the water-absorbing resin absorbs the fluid against gravity to a specific height. In some examples, the FHA value of the water-absorbing resin produced using Method 100 is 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 swollen substrate of the water-absorbing resin. As understood, the so-called "free swelling" state means that the swelling of the water-absorbing resin is permitted and there is no swelling restraining load. In some examples, the free swell gel bed permeability of the water-absorbing resin produced using Method 100 is about 22.7×10 -9 cm 2 ~ about 32.5×10 -9 cm 2 .

[0053] Hereinafter, the applications of the present invention will be described using a plurality of examples, but these are not intended to limit the present invention, and those skilled in the technical field of the present invention can make various changes and modifications without departing from the spirit and scope of the present invention. Manufacture of Water-Absorbing Resin Manufacturing Example

[0054] 437.5 g of a 48 wt% aqueous sodium hydroxide solution was slowly added into a 2000 c.c. Erlenmeyer flask containing 540 g of acrylic acid and 583.2 g of water, with the dropping ratio of sodium hydroxide / acrylic acid within the range of 0.85 to 0.95, the dropping time being 2 hours, and the temperature of the neutralization reaction system in the flask being maintained within the range of 15°C to 40°C, to obtain a monomer aqueous solution with a monomer concentration of 42 parts by weight. Here, 70 mol% of acrylic acid was partially neutralized to sodium acrylate and added to a 2-liter tank-type reactor (manufactured by Jinlei Precision Industry Co., Ltd., Taiwan).

[0055] Subsequently, 0.9 g of N,N'-methylenebisacrylamide (radical polymerization cross-linking agent) was added to the acidic monomer aqueous solution. After maintaining the temperature at about 20°C, nitrogen gas was introduced through a pipe, and oxygen removal was carried out for 30 minutes.

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

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

[0058] Gel bodies with a particle size of 2 mm in diameter or less were screened. Subsequently, they were dried at a temperature of 130°C for 2 hours. Screening was carried out using a mesh with a fixed particle size of 0.1 mm to 0.85 mm to obtain water-absorbing resin particles.

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

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

[0061] According to the method in Chinese Patent CN1206365A, 83.2 parts of acrylic acid, 1662.8 parts of 37 wt% aqueous sodium acrylate solution, 5.5 parts of polyethylene glycol diacrylate (average total molar number of ethylene oxide (EO) 8) and 654.5 parts of deionized water were mixed to prepare a monomer aqueous solution. The neutralization rate of acrylic acid in the monomer aqueous solution was 85%, and the monomer concentration was 30%. Nitrogen gas was blown into the monomer aqueous solution to remove dissolved oxygen from the monomer aqueous solution, and at the same time, the temperature of the monomer aqueous solution was maintained at 24 °C.

[0062] Subsequently, 77 parts of a 10 wt% solution of 2,2'-azobis(2-methylpropionamidine) dihydrochloride was added while stirring the aqueous monomer solution. Three minutes after the start of stirring, the aqueous monomer solution containing the 2,2'-azobis(2-methylpropionamidine) dihydrochloride solution became white and cloudy, and white particulate solids with an average particle size of about 9 μm were formed. These particulate solids are 2,2'-azobis(2-methylpropionamidine) diacrylate as a foaming agent. Five minutes after the start of stirring, under nitrogen gas, 10.8 parts of a 10 wt% aqueous sodium persulfate solution and 0.5 part of a 1 wt% aqueous L-ascorbic acid solution as radical polymerization initiators were added while stirring the aqueous monomer solution. After thoroughly stirring the aqueous monomer solution, it was allowed to stand. Polymerization reaction was initiated three minutes after the addition of the 10 wt% aqueous sodium persulfate solution and the 1 wt% aqueous L-ascorbic acid solution. 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. Twenty-six 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 allowed to stand again 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 crosslinked hydrogel polymer having bubbles as a porous crosslinked polymer (hereinafter referred to as hydrogel (A)) was obtained.

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

[0064] Subsequently, a secondary crosslinking treatment liquid was applied to perform a surface crosslinking reaction to produce a water-absorbing resin. Specifically, 100 parts of water-absorbing 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-absorbing resin. The secondary crosslinking treatment liquid was prepared as a composition by mixing 0.05 part of 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. Comparative Examples 2 to 8

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

[0066] To evaluate the properties of the water-absorbing resin of the present invention, its physical properties were analyzed by the following test methods. 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 should be thoroughly mixed before analysis. Centrifuge retention capacity

[0067] The centrifuge retention capacity (CRC) was tested according to the test method of ERT 241.2(12) specified by the European Disposables and Nonwovens Association (EDANA). The test results of the centrifuge retention capacity of the water-absorbing resin particles and the water-absorbing resin are shown in Table 2 and Table 3, respectively. Pure water absorption ratio per minute

[0068] The pure water absorption rate per minute is tested according to the test method of ERT 240.2(12) specified by EDANA, where the saline solution is changed to deionized water (pure water), and the absorption time is changed from 30 minutes to 1 minute. The test results of the pure water absorption rate per minute of the water-absorbing resin particles and the water-absorbing resin are shown in Table 2 and Table 3, respectively. Apparent specific gravity

[0069] The apparent specific gravity (bulk density) is tested according to the test method of ERT 251.0(12) specified by EDANA. The test results of the apparent specific gravity of the water-absorbing resin particles and the water-absorbing resin are shown in Table 2 and Table 3, respectively. Surface porosity

[0070] The surface porosity is tested using a mercury porosimeter (micromeritics AutoPore(R) IV 9520), and its standard filling pressure is about 4 kPa. The test results of the water-absorbing resin particles and the water-absorbing resin are shown in Table 2 and Table 3, respectively. Free swelling rate

[0071] The free swell rate (FSR, unit: g / g / s) is measured and calculated according to the method described in Patent No. WO2012 / 174026A1. First, 4 g of the water-absorbing resin is dried at a temperature of 23 ± 2°C and a pressure of 0.01 torr or less for 48 hours. Subsequently, about 1 g is weighed and placed in a beaker and dispersed at the bottom of the beaker. Next, 20 g of a 0.9 wt% sodium chloride aqueous solution is injected. After the liquid contacts the water-absorbing resin, the elapsed time until the liquid is completely absorbed by the water-absorbing resin is measured. The free swell rate is obtained by dividing the liquid volume by the weight of the water-absorbing resin and then dividing by the elapsed time. The average value results of three repetitions of the water-absorbing resin particles and the water-absorbing resin are shown in Table 2 and Table 3, respectively. Water-soluble part at 1 hour and 16 hours

[0072] The water extractable content at 1 hour and 16 hours is tested according to the test method of ERT 470.2(02) specified by EDANA. The test results of the 1-hour water extractable content of the water-absorbing resin particles and the 16-hour water extractable content of the water-absorbing resin are shown in Table 2 and Table 3, respectively. Absorption against pressure

[0073] The absorption against pressure (AAP) is tested according to the test method of ERT 442.3(10) specified by EDANA. Under a pressure of 4.9 kPa, the absorption against pressure for 60 minutes with respect to a 0.9% sodium chloride aqueous solution is tested. The test results of the water-absorbing resin particles and the water-absorbing resin are shown in Table 2 and Table 3, respectively. T20 value

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

[0075] The urine permeability measurement is tested according to the method described in Patent No. WO2012 / 174026A1. The test results of the water-absorbing resin particles and the water-absorbing resin are shown in Table 2 and Table 3, respectively. Fixed height absorption value

[0076] The fixed height absorption value is tested according to the method described in US Patent US7108916. The test results of the water-absorbing resin particles and the water-absorbing 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-absorbing resin particles and the water-absorbing 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 variable diameter orifice plate was too small, and the gel body could not be discharged smoothly, and the motor of the mincer overheated. Therefore, the water-absorbing resin particles and the water-absorbing resin could not be produced, and various physical properties in Table 2 and Table 3 could not be measured either.

[0082] According to Table 2 and Table 3, in Comparative Example 1 using the prior art, the absorption properties of the produced water-absorbing resin were clearly inferior to those of Examples 1 to 24. In Comparative Example 2, the thickness of the orifice plate was too small and the extrusion path was too short, making it difficult to form a water-absorbing resin with good absorption properties. On the contrary, when the thickness of the orifice plate in Comparative Example 3 was too large, the wear increased and the surface porosity of the water-absorbing resin decreased, so the characteristics such as the absorption rate were good. In Comparative Examples 7 and 8, in both cases, the diameter of the material supply hole was equal to the diameter of the material discharge hole, and due to the insufficient pressing force, the water-soluble part of the water-absorbing resin became high.

[0083] According to Table 2, compared with Comparative Examples 1 to 8, the water-absorbing resin particles of Examples 1 to 24 clearly had a low water-soluble part, and a high pure water absorption ratio per minute, surface porosity, and free swelling rate.

[0084] According to Table 3, compared with Comparative Examples 1 to 8, Examples 1 to 24 all had higher water absorption ratio under pressure, urine permeability (UPM), fixed height absorption value (FHA), and free swelling gel bed permeability (GBP), and lower T20 values. Therefore, the water-absorbing resins of Examples 1 to 24 were easy to absorb liquids in the dry state, and also had good liquid permeability and conduction ability.

[0085] Therefore, by applying the method for manufacturing the water-absorbing resin of the present invention, cutting the gel body with a mincer having a variable-diameter orifice plate, and controlling the diameter of the material supply hole to be larger than the diameter of the material discharge hole, the density and surface roughness of the gel body can be improved, and further the bulk specific gravity, absorption rate, and liquid conduction performance of the manufactured water-absorbing resin can be improved, and the water-soluble part can be reduced.

[0086] Although the present invention is disclosed in a plurality of embodiments as described above, it is not intended to limit the present invention. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention should be based on that defined in the appended patent claims later.

Explanation of Reference Numerals

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

Claims

1. A step of subjecting a water-absorbing resin composition containing an acid monomer aqueous solution, a polymerization reaction initiator, and a radical polymerization reaction crosslinking agent to a radical polymerization reaction to obtain a gel body; A step of cutting the gel body using a mincer having a variable-diameter orifice 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-absorbing resin particles; A step of subjecting the water-absorbing resin particles to a surface crosslinking reaction to obtain the water-absorbing resin; A method for producing a water-absorbing resin, comprising the above steps.

2. The method for producing a water-absorbing resin according to Claim 1, wherein the first diameter is 8 mm to 20 mm, and the second diameter is 6 mm to 18 mm.

3. The method for producing a water-absorbing resin according to Claim 1, wherein the thickness of the variable-diameter orifice plate is 20 mm to 40 mm.

4. The first diameter, the second diameter, and the thickness of the variable-diameter orifice plate have the following relational expression. 【Number 1】 In the above formula, D1 represents the first diameter, D2 represents the second diameter, L represents the thickness of the variable-diameter orifice plate, and the α value is 0.05 to 0.

35. The method for producing a water-absorbing resin according to Claim 3.

5. The step of cutting the gel body The method for producing a water-absorbing resin according to Claim 1, further comprising a step of screening a plurality of micro gel bodies having an average particle diameter of 2.00 mm or less.

6. The method for producing a water-absorbing resin according to Claim 5, wherein the average particle diameter of the water-absorbing resin particles is 0.06 mm to 1.00 mm.

7. Before the step of performing the surface crosslinking reaction, The method for producing a water-absorbing resin according to Claim 1, further comprising a step of adding a surface crosslinking agent and an aluminum salt compound to the water-absorbing resin particles.

8. The method for producing a water-absorbing resin according to Claim 7, wherein the addition amount of the aluminum salt compound is 0.1 wt% to 1.0 wt% based on 100 wt% of the water-absorbing resin particles.

9. The method for producing a water-absorbing resin according to Claim 7, wherein the aluminum salt compound includes aluminum sulfate, aluminum lactate, aluminum citrate, and any combination thereof.

10. A water-absorbing resin produced by the production method according to any one of Claims 1 to 9.

Images