WO2016085294A1

WO2016085294A1 - Superabsorbent polymer having fast absorption rate under load and preparation method therefor

Info

Publication number: WO2016085294A1
Application number: PCT/KR2015/012861
Authority: WO
Inventors: 이상기; 이수진; 남혜미; 황민호
Original assignee: 주식회사 엘지화학
Priority date: 2014-11-27
Filing date: 2015-11-27
Publication date: 2016-06-02

Abstract

The present invention relates to a superabsorbent polymer and a preparation method therefor. According to the present invention, the absorption rate under load of the superabsorbent polymer can be increased without the deterioration of gel strength by using a low temperature foaming agent and a high temperature foaming agent together so as to control the size and distribution of pores inside a superabsorbent polymer.

Description

【Specification】

[Name of invention]

Superabsorbent polymer with high absorption rate under pressure and its preparation method

[Cross Citation with Related Application (s)]

This application is filed with Korean Patent Application No. 10-2014- filed on November 27, 2014.

Claims the benefit of priority based on 0167729 and Korean Patent Application No. 10-2015-0010157, filed Jan. 21, 2015, and all content disclosed in the literature of such Korean patent applications is incorporated as part of this specification.

Technical Field

The present invention relates to a superabsorbent polymer having a high absorption rate under pressure and a method for preparing the same.

Background Art

A super absorbent polymer (SAP) is about its own weight

As a synthetic polymer material capable of absorbing water of about 500 to 1,000 times, it is also called SAMC Super Absorbency Mater Al, AGM (Absorbent Gel Mater Al). Super absorbent resins have been put into practical use as sanitary devices and are now widely used in various materials such as hygiene products such as paper diapers for children, horticultural soil repair agents, civil engineering materials, seedling sheets, and freshness retainers in food distribution. It is used. As a method for producing such a super absorbent polymer, a method by reverse phase suspension polymerization or a solution polymerization is known. Among them, the production of superabsorbent polymers through reverse phase suspension polymerization is disclosed, for example, in Japanese Patent Laid-Open Nos. 56-161408, 57-158209, and 57-198714. In addition, the production of superabsorbent polymers through polymerization of aqueous solution is a thermal polymerization method for polymerizing a hydrogel polymer in a kneader equipped with several shafts while breaking and angled, and polymerizing and drying by irradiating UV light to a high concentration of aqueous solution on a belt. The photopolymerization method etc. which perform simultaneously are known. Meanwhile, the absorption rate, which is one of the important physical properties of the super absorbent polymer, It is associated with the surface dryness of products that come into contact with the skin, such as diapers. In general, this absorption rate can be improved by increasing the surface area of the superabsorbent polymer. For example, a method of forming a porous structure on the particle surface of the super absorbent polymer by using a blowing agent has been applied. However, the general blowing agent has a disadvantage in that the increase in absorption rate is not large because it can form a sufficient amount of porous structure. Methods for forming porous structures on the surface of particles using blowing agents are described in Kabiri, K :, Omidian, H. and Zohur i aan-Mehr, M. (2003), Novel approach to highly porous superabsorbent hydrogels: synergistic effect of porogens on porosity and swelling rate.Polym. Int., 52: 1158 ᅳ 1164). According to the above documents, the selection of the appropriate porogen as a variety of factors for forming the pore, the time and method of injecting the porogen, as well as the gelation time in the polymerization is suggested. Commonly known blowing agents are used to clean carbonate-based materials, and the injection of these blowing agents is suggested as an important factor for forming the pore structure. As another example, there is a method of increasing the surface area by reassembling the fine powder obtained in the manufacturing process of the super absorbent polymer to form porous particles of irregular shape. However, although the absorption rate of the superabsorbent polymer can be improved through this method, there is a limit that the water retention capacity (CRC) and the pressure absorption capacity (AUP) of the resin are relatively lowered. As such, the physical properties such as absorption rate, water holding capacity, and pressure absorbing capacity of the super absorbent polymer are trade-off. Therefore, there is an urgent need for a manufacturing method capable of improving these properties at the same time.

[Content of invention]

[Problem to solve]

The present invention provides high gel strength and a fast rate of absorption under pressure. Eggplant is to provide a super absorbent polymer.

In addition, the present invention is to provide a method for producing the super absorbent polymer.

[Measures of problem]

In order to solve the above problems, the present invention provides the following super absorbent polymers:

A superabsorbent polymer comprising a crosslinked polymer obtained by polymerizing and crosslinking a monomer composition including an acrylic acid monomer having an acidic group and at least a part of the acidic group is neutralized, and a surface crosslinked layer formed on the surface of the crosslinked polymer,

More than 29.5 g / g of centrifugal separation capacity (CRC), more than 18 g / g of pressure absorption capacity (AUU), more than 60 darcy gel permeability (GBP), 18.0 g of gel-AUL for 5 minutes / g or more, super absorbent polymer, which is considered to have important properties such as water retention capacity (CRC), pressure absorption capacity (AUL) and liquid permeability (GBP). In order to increase the absorption rate under pressure, a method of increasing the surface area of the superabsorbent polymer is generally used, and to this end, pores in the superabsorbent resin are conventionally used. It is known to form a large amount of water so that water can be sucked up quickly, or to reduce the particle size of the superabsorbent polymer, etc. However, the particle size of the superabsorbent polymer is enjoyed. In the present invention, there is a disadvantage in that thinning of an article is difficult because the gel strength becomes weak when internal pores are formed in the present invention. And by controlling the distribution, it is possible to increase the absorption rate under pressure without decreasing the gel strength. The pores having an inner diameter of 100 µν to 400 mm 3 are formed, and the pores having a diameter of 5 to 100 in the superabsorbent resin are formed by the high temperature blowing agent. In addition, by adjusting the content of the low-temperature blowing agent and the high-temperature blowing agent, the ratio of the total pore area ratio (A) of the micropores having a diameter of 5 to 100 and the total pore area ratio (Β) of the large pores having a diameter of 100 to 400 (Α) : Regulates Β). The area of the pores can be measured by a conventional method in the art, for example, after taking an accurate photograph (magnification 100 times) of the surface of the absorbent resin with a scanning electron microscope (SEM), a certain area (2 cm X 2 cm In the SEM phenomenon existing within), the area ratio of the pore size can be measured by dividing the number of micropores and macropores present on the surface.

As described above, the ratio of the total pore area ratio (A) of the pores having a diameter of 5 // m to 100 m and the total pore area ratio (B) of the pores having a diameter of 100 m to 400 (A: B) Silver 3: 7-9: 1 are preferable. The pores of the small diameter and the pores of the high diameter are distributed together in the superabsorbent resin in the range as described above, thereby increasing the absorption rate under pressure and preventing the gel strength from being lowered. More preferably, the ratio of A: B is 4: 6 to 8: 2. Such superabsorbent resin may be included in the crosslinked structure of the final resin due to some residual of the low temperature foaming agent and the high temperature foaming agent used to form the pores. Specifically, the super absorbent polymer may further include a low temperature foaming agent and a high temperature foaming agent dispersed in the crosslinked polymer in the surface crosslinking layer. The specific kind of such a low temperature foaming agent and a high temperature foaming agent is explained in full detail below about a manufacturing method. And, in the super absorbent polymer, the acrylic acid monomer is a compound represented by the following formula (1):

[Formula 1]

Ri-COOM ¹ In Chemical Formula 1,

¾ is an alkyl group having 2 to 5 carbon atoms containing an unsaturated bond,

M ¹ is a hydrogen atom, a monovalent or divalent metal, an ammonium group or an organic amine salt. Preferably, the acrylic acid monomer includes at least one member selected from the group consisting of acrylic acid, methacrylic acid and monovalent metal salts thereof, divalent metal salts, ammonium salts and organic amine salts. Here, the acrylic acid monomer may have an acid group and at least a part of the acid group may be neutralized. ^'It may preferably be used which is partially neutralized the monomers with alkali materials such as sodium hydroxide, potassium hydroxide, ammonium hydroxide. In this case, the degree of neutralization of the acrylic acid monomer may be 40 to 95 mol%, or 40 to 80 mol%, or 45 to 75 mol%. The range of neutralization can be adjusted according to the final physical properties. However, when the degree of neutralization is too high, the neutralized monomer may be precipitated and polymerization may be difficult to proceed smoothly. On the contrary, when the degree of neutralization is too low, the absorbency of the polymer may not only be greatly reduced, but may exhibit properties such as elastic rubber that is difficult to handle. have. In addition, the concentration of the acrylic acid monomer in the monomer composition may be appropriately adjusted in consideration of the _evaporation time _ᅵ and reaction conditions, preferably 20 to 90 weight or 40. to 70% by weight. This concentration range may be advantageous to control the grinding efficiency during the grinding of the polymer, which is a subsequent process, while eliminating the need to remove unreacted monomers after polymerization by using the gel phenomenon appearing in the polymerization reaction of the high concentration aqueous solution. However, when the concentration of the monomer is too low, the yield of the super absorbent polymer may be lowered. On the contrary, when the concentration of the monomer is too high, some of the monomers may precipitate or process problems may occur such as when the pulverization efficiency of the polymerized hydrogel polymer is reduced, and the physical properties of the super absorbent polymer may be reduced. On the other hand, the monomer composition includes a crosslinking agent for improving the physical properties of the hydrogel polymer. The crosslinking agent is a first crosslinking agent (internal crosslinking agent) for crosslinking the hydrogel polymer inside, and is used separately from the second crosslinking agent (surface crosslinking agent) for crosslinking the surface of the hydrogel polymer in a subsequent process. Preferably, the crosslinked polymer is Ν, Ν'—methylenebisacrylamide, trimethylolpropane tri (meth) acrylate, ethylene glycol di (meth) acrylate, polyethylene glycol (meth) acrylate, propylene glycol die (meth ) Acrylates, polypropylene glycol (meth) acrylates, butanedidiete (meth) acrylates butyleneglycoldi (meth) acrylates, diethylene glycol di (meth) acrylates, nucleic acid dioldi (meth) acrylates ， Triethylene glycol di (meth) acrylate ， Tripropylene glycol di (meth) acrylate ， Tetraethylene glycol di (meth) acrylate ， Dipentaerythrene pentaacrylate ， Glycerine tri (meth) acrylate ， Pentaeryth Tetraacrylate, triarylamine, ethylene glycol diggle Sidil ether, to an internal cross-linked by one or more selected first cross-linking agent from the group consisting of propylene glycol, glycerin, and ethylene carbonate. In addition, the superabsorbent polymer is preferably a particulate having a particle diameter of 150 to 850. In addition, the centrifugal water retention capacity (CRC) may be represented by Equation 1 below:

[Equation 1]

CRC (g / g) = {[W ₂ (g) ᅳ W ₁ (g)] / W ₀ (g)} ᅳ 1

In Equation 1,

W ₀ (g) is the weight of the absorbent resin (g) ，

Kg) does not use absorbent resin, but using a centrifuge Device weight (g) measured after dehydration at 250G for 3 minutes

W ₂ (g) is the device weight (g) measured after absorbing the absorbent resin in 0.9 mass% of physiological saline for 30 minutes, followed by dehydration at 250 G for 3 minutes using a centrifuge. . In addition, the pressure absorption capacity (AUL) may be represented by the following equation (2):

AUUg / g) = ^: [W ₄ (g) 一 W ₃ (g)] / W ₀ (g)

In Equation 2,

W ₀ (g) is the weight of the absorbent resin (g),

w ₃ ( _g ) is the sum of the weight of the absorbent resin and the weight of the device capable of applying a load to the absorbent resin (g),

W ₄ (g) is the sum of the weight of the water absorbent resin absorbed after absorbing the absorbent resin for 60 minutes under a load (0.9 ps i) and the weight of the device capable of applying a load to the absorbent resin (g )to be. In addition, the 5-minute ge l-AUL may be represented by the following Equation 2-1: Equation 2-1

5 min gel-AUL (g / g) = [W ₄ (g) ᅳ W ₃ (g)] / W ₀ (g)

In Equation 2-1,

W ₀ (g) is the weight of the absorbent resin (g) ，

W ₃ (g) is the sum of the weight of the absorbent resin and the weight of the device capable of applying a load to the absorbent resin (g),

W ₄ (g) is the sum of the weight of the absorbed water absorbed resin after supplying the absorbent resin with water for 5 minutes under load (0.3 ps i) and the weight of the device capable of applying a load to the absorbent resin (g )to be. In addition, the superabsorbent polymer according to the present invention may be prepared by a manufacturing method comprising the following steps.

1) has an acidic group and at least a portion of the acidic group is neutralized Polymerizing and crosslinking a monomer composition comprising an acrylic acid monomer at 25 to 100 ^° C. in the presence of a polymerization initiator, a crab 1 crosslinking agent, a low temperature blowing agent and a high temperature blowing agent to form a hydrous gel polymer,

2) coarsely pulverizing the hydrogel polymer;

3) drying the coarsely pulverized hydrogel polymer at 150 to 250 ^° C.,

4) grinding the dried polymer; and

5) surface modifying the ground polymer with a second crosslinking agent. Hereinafter, the present invention will be described in detail for each step. Formation of hydrogel polymer (step 1)

The acrylic acid monomer having the acidic group and neutralized at least a portion of the acidic group is as defined above, and step 1 is a step of polymerizing the same to prepare a hydrogel polymer. In particular, the present invention is characterized in that the monomer composition comprises a low-temperature blowing agent and a high-temperature blowing agent in addition to the polymerization initiator and the first crosslinking agent. The low temperature foaming agent refers to a foaming agent that is foamed at 60 ^° C or less, since the polymerization and crosslinking temperature of the step 1 is 25 to 100 ^° C, foaming of the low temperature foaming agent occurs during the performance of the step 1. At this time, since the hydrogel polymer prepared is in a state of low viscosity including water, the pores formed by foaming are relatively larger than the pores formed by the high temperature foaming agent to be described below. The low temperature foaming agent is sodium bicarbonate, sodium carbonate, potassium bicarbonate, potassium ^ l "potassium carbonate, calcium bicarbonate (cal cium bicarbonate) ), Calcium carbonate, magnesium bicarbonate, or magnesium bicarbonate Magnesium carbonate can be used. Also, preferably the polymerization and crosslinking temperature is 30 to 90 ^° C. As the high temperature blowing agent, an organic blowing agent capable of forming bubbles by being decomposed from silver may be used. For example, azodicarbonamide (ADDA), dinitrosopenttamethylene tetramine (DPT), ρ, ρ'-oxybisbenzenesulfonylhydrazide (ρ, ρ'-oxyb i sbenzenesu 1 f ony 1 hydr az i de), OBSH), p-luenesulfonyl hydrazide (TSH) Sugar esters. The sugar esters include sucrose stearate, sucrose palmitate, sucrose laurate, and the like. S-970, S-1570, S ᅳ 1670, P 1670 and L-1570. Since the decomposition temperature of the on-foaming agent is more than about 100 ^° C, preferably 120 to 180 ^° C, rather than forming fine pores by decomposition during the polymerization and crosslinking reaction of step 1, decomposition in the drying process of step 3 To form large pores. In addition, by adjusting the increase ratio of the low-temperature foaming agent and the high-temperature foaming agent, the total pore area ratio (A) of the micropores having a diameter of 5 im to 100 in the superabsorbent resin, and the total pore area ratio of the macropores having a diameter of 100 to 400 (B). ) Ratio (A: B), and preferably the weight ratio of the low temperature foaming agent to the high temperature foaming agent is 50: 1 to 2: 1. The polymerization initiator can use the polymerization initiator generally used for manufacture of a super absorbent polymer. As the polymerization initiator, a thermal polymerization initiator or a photopolymerization initiator may be used depending on the polymerization method. However, even by the photopolymerization method, since a certain amount of heat is generated by ultraviolet irradiation or the like, and a certain amount of heat is generated by the progress of the polymerization reaction, which is an exothermic reaction, a thermal polymerization initiator is additionally used even in the case of photopolymerization. Can be. As the photoinitiator, for example, benzoin ether, dialkyl acetophenone, hydroxyl alkylketone, phenylglyoxylate, benzyl dimethyl ketal ( One or more compounds selected from the group consisting of Benzyl Dimethyl Ketal, acyl phosphine, and alpha-aminoketone can be used. As specific examples of the acyl phosphine, commercially available lucirin TP0, that is, 2,4,6-trimethyl-benzoyl-trimethyl phosphine oxide (2,4,6-tr imethyl-benzoyl-tr imethyl phosphine oxide) may be used. Can be. More various photoinitiators are disclosed on page 115 of the Reinhold Schwalm lm "UV Coatings: Basics, Recent Developments and New Appli- cation (Elsevier 2007)". As the initiator, one or more compounds selected from the group consisting of a persulfate initiator, an azo initiator, hydrogen peroxide, and ascorbic acid may be used. Specifically, as the persulfate initiator, sodium persulfate (Na ₂ S). ₂ 0 ₈ ), potassium persulfate (K ₂ S ₂ 0 ₈ ), ammonium persulfate (NH ₄ ) ₂ S ₂ () 8), and the like. Examples of (Azo) -based initiators include 2,2-azobis- (2-amidinopropane) dihydrochloride (2,2-azobis (2-amidinopropane) dihydrochlor ide), 2, 2-azobis (N, Ν— Dimethylene) isobutyramidine dihydrochloride (2, 2-azobi i S- (Ν, Nd i me t hy 1 ene) i sobut yr am idi ne dihydrochlor ide), 2_

(Babamoylazo) isobutyronitrile (2- (carbamoylazo) isobutylonitril), 2,2-azobis [2- (2-imidazoline—2-yl) propane] dihydrochloride (2, 2- azobis [ 2- (2-imidazol in-2-yl) propane] dihydrochlor ide), 4,4 一 azobis— (4-cyanovaleric acid) (4,4-azobis- (4-cyanovaleric acid)) For example. A wider variety of thermal polymerization initiators are disclosed on page 203 of the Odian book "Principle of Polymerization (Wiley, 1981)" and can be referred to this. The polymerization initiator may be added at a concentration of about 0.001 to 1% by weight based on the monomer composition. In other words, when the concentration of the polymerization initiator is too low, the polymerization rate may be slow and a large amount of residual monomer may be extracted in the final product. On the contrary, when the concentration of the polymerization initiator is too high, it is not preferable because the polymer chain constituting the network is shortened, so that the content of the water-soluble component is increased and the pressure absorption capacity is lowered. The first crosslinking agent is as defined above, and is a first crosslinking agent (internal crosslinking agent) for crosslinking the hydrogel polymer, and a second crosslinking agent (surface crosslinking agent) for crosslinking the surface of the hydrogel polymer in a subsequent step. Used separately. The C 1 crosslinking agent may be added at a concentration of about 0.001 to 1% by weight based on the monomer composition. When the concentration of the first crosslinking agent is too low, the absorption rate of the resin may be lowered and the gel strength may be weakened, which is not preferable. On the contrary, when the concentration of the first crosslinking agent is too high, the absorptivity of the resin may be lowered, which may be undesirable as a hop conjugate. In addition, the monomer composition may further include additives such as thickeners, plasticizers, storage stabilizers, antioxidants and the like as necessary. In addition, the monomer composition may be prepared in the form of a solution in which raw materials such as the acrylic acid monomer, a polymerization initiator, a first crosslinking agent, a low temperature blowing agent, and a high temperature blowing agent are dissolved in a solvent. In this case, any solvent that can be used may be used without limitation as long as it can dissolve the above-described raw materials. For example, the solvent includes water, ethanol ethylene glycol, diethylene glycol, triethylene glycol, 1,4-butaneol, propylene glycol, ethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate , Methyl ethyl ketone, acetone, methyl amyl ketone, cyclonucleone, cyclopentanone, diethylene glycol monomethyl ether, diethylene glycol ethyl ether, toluene, xylene, butyrolactone, carby, Methyl cellosolve acetate, Ν, Ν-dimethylacetamide, or a combination thereof may be used. The amount of the solvent may be adjusted to be 1 to 5 times the weight ratio of the acrylic acid monomer content in consideration of polymerization heat control and the like. In addition, when the low temperature foaming agent and the high temperature foaming agent are mixed with water or used by dissolving in acrylic acid, a separate solvent may not be used. On the other hand, the formation of the hydrogel polymer through the polymerization and crosslinking of the monomer composition may be carried out by a conventional polymerization method in the art, the process is not particularly limited. As a non-limiting example, the polymerization method is largely divided into thermal polymerization and photopolymerization according to the type of polymerization energy source, in the case of the thermal polymerization may be carried out in a reactor having a stirring shaft such as kneader, In the case of the addition process can be carried out in a reactor equipped with a movable conveyor belt. For example, a hydrogel polymer may be obtained by adding the monomer composition to a reaction vessel such as a kneader equipped with a stirring shaft, and supplying hot air thereto or by heating and heating the reaction vessel. At this time, the reactor _. The hydrogel polymer discharged to the reactor outlet according to the type of stirring shaft provided is from a few millimeters. It can be obtained in the form of particles of several centimeters. The hydrogel polymer may be obtained in various forms according to the concentration and injection speed of the monomer composition to be injected, and a hydrogel polymer having a weight average particle diameter of 2 kPa to 50 kPa may be obtained. In another example, when photopolymerization of the monomer composition is performed in a reactor equipped with a movable conveyor belt, a sheet-like hydrogel polymer may be obtained. Can be. At this time, the thickness of the sheet may vary depending on the concentration and the injection speed of the monomer composition to be injected, in order to ensure the production rate, while the entire sheet is evenly polymerized, it is usually adjusted to a thickness of 0.5 cm to 5 cm It is preferable. The hydrogel polymer formed by the above method may exhibit a water content of about 40 to 80 weight ¾. It is advantageous in that the water content of the hydrogel polymer falls within the range to optimize the efficiency in the drying step described later. Here, the moisture content is a weight of water in the total weight of the hydrogel polymer, and can be calculated by subtracting the dry polymer weight from the weight of the hydrogel polymer. Specifically, it may be defined as a value calculated by measuring the weight loss due to evaporation of water in the polymer during the process of raising the temperature of the polymer through infrared acid heating. At this time, the drying conditions may be set to 40 minutes, including 5 minutes of the temperature rise step in such a way that the temperature is raised to about 180 ^° C and maintained at 180 ^° C. Coarse grinding of hydrogel polymer (step 2)

The hydrogel polymer obtained through the above steps is subjected to a drying process to impart water absorbency. However, in order to increase the drying efficiency, the step of pulverizing (coarse grinding) the hydrogel polymer before performing the drying process is performed. Non-limiting examples of mills available for the milling include vertical pulverizers, turbo cutters, turbo grinders, rotary cutter mills, and cutting machines. Examples include a cutter mill, a disc mill, a shred crusher, a crusher, a chopper, and a disc cutter. In this case, the coarse grinding may be performed so that the particle diameter of the hydrogel polymer is 2 kPa to 10 kPa. That is, in order to increase the drying efficiency, the hydrous gel polymer is preferably pulverized into particles of 10 mm or less. However, since excessive aggregation may cause intergranular phenomena, the hydrous gel phase polymer is preferably pulverized into particles of 2 mm or more. The coarsely pulverizing step, because the polymer is carried out in a high water content of the polymer may stick to the surface of the grinder may appear. In order to minimize this phenomenon, the coarsely pulverizing step may include steam, water, surfactants, anti-aggregation crabs (for example, cl ay, si li ca, etc.) as necessary; Persulfate initiator, azo initiator, hydrogen peroxide, thermal polymerization initiator, epoxy crosslinking agent, diol crosslinking agent, crosslinking agent including di- or trifunctional or higher polyfunctional acrylate, crosslinking agent of monofunctional group including hydroxyl group And the like can be added. Drying the coarsely hydrated gel polymer (step 3)

Through the above-described steps, the step of drying the coarsely pulverized hydrogel polymer is carried out. The hydrogel polymer is provided to the drying step in the coarsely pulverized state of the particles of 2 mm to 10 mm 3 through the above-described steps, so that drying can be performed with higher efficiency. Drying of the coarsely pulverized hydrogel polymer may be performed at a temperature of 120 to 250 ^° C., preferably 140 to 200 ^° C., more preferably 150 to 190 ^° C. In this case, the drying temperature may be defined as the temperature of the heat medium supplied for drying or the temperature inside the drying reactor including the heat medium and the polymer in the drying process. If the drying temperature is low and the drying time is long, the process efficiency is lowered. In order to prevent this, the drying temperature is preferably 120 ° C or higher. In addition, when the drying temperature is higher than necessary, the surface of the hydrous gel polymer may be excessively dried to increase the generation of fine powder in the subsequent grinding step, and the physical properties of the final resin may be lowered. It is preferable that it is 25 CTC or less. As described above in step 1, in the present invention, a hydrogel polymer was prepared including a hot blowing agent, and thus the hot blowing agent is included in the coarsely pulverized hydrogel polymer. The high temperature foaming agent means a foaming agent that is foamed at 1C C or more, and the above. Since the drying temperature of step 3 is greater than 100 t, foaming of the high silver blowing agent occurs during the performance of step 3 above. At this time, the coarsely pulverized hydrous gel polymer produced is low in water content due to a drying process, and thus has a high viscosity. At this time, the pores formed by the foaming are relatively smaller than the pores formed by the low-temperature blowing agent described above. At this time, the drying time in the drying step is not particularly limited, in consideration of the process efficiency and the physical properties of the resin, it can be adjusted to 20 minutes to 90 minutes under the drying temperature. The drying may be performed using a conventional medium. For example, the drying may be performed by hot air supply, infrared irradiation, microwave irradiation, or ultraviolet irradiation to the coarsely pulverized hydrogel polymer. And such drying is preferably carried out so that the dried polymer has a water content of about 0.1 to 10% by weight. That is, when the moisture content of the dried polymer is less than 0.1% by weight, it is not preferable because an increase in manufacturing cost and degradation of the crosslinked polymer may occur due to excessive drying. In addition, when the moisture content of the dried polymer exceeds 10% by weight, defects may occur in subsequent processes, which is not preferable. Grinding the dried polymer (step 4)

Through the steps described above, a step of pulverizing the dried polymer is performed. The grinding step is to optimize the surface area of the dried polymer, the particle diameter of the pulverized polymer is 150 to 850

May be performed. At this time, the grinder may be a pin mill, a hammer mill, a screw mill, a roll mill, a disc mill, a jog mill, or the like. May be used. In addition, in order to manage the physical properties of the super absorbent polymer to be finalized, the polymer obtained through the grinding step The step of selectively classifying particles having a particle size of 150 to 850 in the particles may be further performed. Surface opening of the pulverized polymer (step 5)

The surface modi fi cat i on the ground polymer with the second crosslinking agent is carried out through the above-mentioned steps. The surface modification is a step of inducing a crosslinking reaction on the surface of the pulverized polymer in the presence of a second crosslinking agent (surface crosslinking agent), thereby forming a superabsorbent resin having improved physical properties. Through such surface modification, a surface modification layer (surface crosslinked layer) is formed on the surface of the pulverized polymer particles. The surface modification may be carried out by a conventional method of increasing the crosslinking density of the polymer particle surface, for example, a method of mixing and crosslinking the pulverized polymer with a solution containing a second crosslinking agent (surface crosslinking agent). It can be performed as. Here, the said 2nd crosslinking agent is a compound which can react with the functional group which the said polymer has, The structure is not specifically limited. However, by way of non-limiting example, the second crosslinking agent is ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerol polyglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycid Dyl ether, ethylene glycol, diethylene glycol, propylene glycol, triethylene glycol, tetraethylene glycol, propane diol, dipropylene glycol, polypropylene glycol, glycerin, polyglycerol, butanediol, heptanedi, nucleic acid ditrimethyl propane, Pentaerythritol, sorbitol, scabbard hydroxide, magnesium hydroxide, aluminum hydroxide, iron hydroxide, calcium chloride, magnesium chloride, aluminum chloride, and iron chloride. 61

At this time, the content of the crab 2 cross-linking agent may be appropriately adjusted according to the type or reaction conditions of the cross-linking agent, and preferably may be adjusted to 0.001 to 5 parts by weight based on 100 parts by weight of the pulverized polymer. If the content of the crab 2 cross-linking agent is too low, the surface modification is not made properly, the physical properties of the final resin may be lowered. On the contrary, if an excessive amount of the second crosslinking agent is used, absorption of the resin may be lowered due to excessive surface crosslinking reaction, which is not preferable. On the other hand, the surface modification step, the method of mixing the second cross-linking agent and the pulverized polymer in the reaction tank, the method of spraying the second cross-linking agent to the pulverized polymer, the pulverized polymer and the second cross-linking agent in a continuously operated mixer It can be carried out by conventional methods, such as the method of supplying continuously and mixing. In addition, water may be additionally added when the second crosslinking agent is added. As such, when the second crosslinking agent and water are added together, even distribution of the second crosslinking agent may be induced, the aggregation of the polymer particles is prevented, and the penetration depth of the second crosslinking agent into the polymer particles may be more optimized. In view of these objects and effects, the amount of water added with the second crosslinking agent may be adjusted to 0.5 to 10 parts by weight based on 100 parts by weight of the pulverized polymer. In addition, the surface modification step may be performed at a temperature of 100 to 25CTC. In addition, the surface modification may be performed for 1 minute to 120 minutes, preferably 1 minute to 100 minutes, more preferably 10 minutes to 60 minutes. That is, in order to induce a minimum surface crosslinking reaction and to prevent excessive semi-aeration polymer particles from being damaged and deteriorating physical properties, the surface modification step may be performed under the above-described conditions.

【Effects of the Invention】

The superabsorbent polymer according to the present invention can be used in combination with a low temperature foaming agent and a high temperature foaming agent to adjust the size and distribution of the internal pores of the superabsorbent polymer, thereby increasing the absorption rate under pressure without decreasing the gel strength. [Brief Description of Drawings]

1 is a schematic diagram showing an example of a device for measuring the pressure absorption rate for the super absorbent polymer according to an embodiment of the present invention.

Figure 2 is a schematic diagram showing an example of a gel bed permeability (GBP, Gel Bed Permeabi li ty) measuring apparatus according to an embodiment of the present invention, Figure 3 and Figure 4 is an example of a gel bed permeability measurement cylinder and mesh arrangement, respectively It is a schematic diagram showing.

[Specific contents to carry out invention]

Hereinafter, preferred embodiments are presented to help understand the invention. However, the following examples are only for illustrating the present invention, and the present invention is not limited thereto. Example 1

In a 2 L glass reactor surrounded by a jacket in which a heat medium pre-cornered at 25 ^° C. was circulated, 11 g of 0.5% IRGACURE 819 initiator (110 ppm for the monomer composition) diluted in 500 g of acrylic acid was mixed and acyl acid 26 g of 5% polyethyleneglycol diacrylate (PEGDA, molecular weight 400) distilled into a mixed solution (A solution) was injected, and trimethylolpropane triacryl containing 9 mol% of 5% ethylene oxide diluted in acrylic acid. A mixed solution (B solution) was added 14 g of Ethoxyl ated-TMPTA, TMP (E0) 9TA, M-3190 Miwon Specialty Chemical Co., Ltd., and 2.8 g of a S ᅳ 1570 solution diluted 0.5% in acrylic acid. Were mixed and 800 g (C solution) of 24% caustic soda solution was slowly added dropwise. As the water-soluble ethylenically unsaturated monomer thus obtained, the degree of acrylic acid neutralization was 70 mol% in sodium acrylate.

After confirming that the silver content of the mixture rises above 72 ^° C by the heat of neutralization when mixing the two solutions, wait for the temperature to rise to 40 ^° C, and then when the reaction temperature reaches 40 ^° C, sodium bicarbonate (sodium bicarbonate) carbonate) was mixed with 2 g of monomer as a solid phase and at the same time 54 g of a 2% sodium persulfate solution diluted in water was injected.

The solution was placed in a vat shaped tray (15 cm x 15 cm) mounted in a square polymerizer with a light irradiator mounted on top and preheated to 80 ^° C. 15 cm), and irradiated with light to start photo. After about 25 seconds after the light irradiation, the gel was generated from the surface and after 50 seconds, the polymerization was confirmed to occur simultaneously with foaming, and then reacted for 3 minutes further, and the polymerized sheet was taken out and cut into a size of 3 cm X 3 cm. Then, the chopper was prepared by using a chopping chopper (meat chopper) to prepare a powder (crump).

The crump was dried in an oven capable of transferring air volume up and down. The hot air of 18 CTC was uniformly dried by flowing from downward to upward for 15 minutes and upward from downward for 15 minutes. After drying, the water content of the dried body was 2% or less.

After drying, the resultant was pulverized with a grinder and classified to prepare a base resin by selecting 150 to 850 sizes. The water solubility of the base resin thus prepared was 36.5 gig, and the water-soluble component content was 12.5 wt%.

Thereafter, 3 g of water, 3 g of methane, 0.4 g of ethylene carbonate, and 0.2 g of aerosol 200 were mixed in a 100 g base resin, followed by a surface crosslinking reaction at 190 ^° C. for 30 minutes. After the grinding, the surface-treated superabsorbent polymer having a particle size of 150 to 850 / im was obtained using sieve. Example 2

In Example 1, except that the addition of sodium bicarbonate when the temperature of the mixture is 45 ^° C, was prepared in the same manner as in Example 1 to obtain a super absorbent resin. Example 3

In Example 1, except that 520g of acrylic acid and 760g of 24.5% caustic soda solution, was prepared in the same manner as in Example 1 to obtain a super absorbent polymer. In this case, unlike Example 1, the sheet was very tough after polymerization, and the pore size of the sheet was smaller when visually observed. Example 4 In Example 1, except that S-1570 instead of 3 g of the TSH solution limped in acrylic acid was prepared in the same manner as in Example 1 to obtain a superabsorbent resin. Comparative Example 1

In Example 1, except for not using sodium bicarbonate (carbonate bicarbonate), was prepared in the same manner as in Example 1 to obtain a water absorbent resin. Comparative Example 2

In Example 1, except that S-1570 was not used, was prepared in the same manner as in Example 1 to obtain a water absorbent resin. Test Example

Physical properties of the resins prepared in Examples 1 to 4 and Comparative Examples 1 and 2 were evaluated in the following manner.

(1) particle size evaluation

The particle size of each resin was measured in accordance with the European Di sposables and Nonwovens Assoc ion (EDANA) standard EDANA WSP 220.2 method.

(2) Centri fuge Retent ion Capacity (CRC) The water-retaining capacity by the unloaded absorption ratio of each resin was measured according to EDANA WSP 241.2. Specifically, the resin W ₀ (g) (about 0.2 g) obtained through Examples and Comparative Examples was evenly placed in a non-woven bag and sealed, and then immersed in physiological saline (0.9 wt%) at room temperature. I was. After 30 minutes have elapsed, the device is drained from the bag for 3 minutes under the conditions of 250G using a centrifugal separator. Mass (g) was measured. Moreover, mass ^ g) at that time was measured after performing the same operation without using resin. Using each mass obtained, CRC (g / g) was computed according to the following formula.

[Equation 1]

CRC (g / g) = i [W ₂ (g)-W! (G)] / W ₀ (g)} ᅳ 1

(3) Pressurized absorption capacity and absorption under pressure

Absorbency under Load (AUL)

The pressure absorption capacity of 0.9 ps i of each resin was measured according to the EDANA method WSP 242.3, and an apparatus for measuring the pressure absorption capacity (AUL) as shown in FIG. 1 was used. Specifically, a stainless steel 400 mesh wire mesh was mounted on the bottom of a plastic cylinder having an inner diameter of 25 mm 3. Piston which can evenly spread the absorbent resin W ₀ (g) (0. 16 g) on the wire mesh under conditions of room temperature and humidity of 50% and impart a more uniform load of 5. 1 kPa (0.9 psi) on it Is slightly smaller than the outer diameter of 25 mm, has no gap with the inner wall of the cylinder, and does not interfere with the vertical movement. At this time, the weight W ₃ (g) of the apparatus was measured.

A 90 mm diameter and 5 mm thick glass filter was placed inside a 150 mm diameter petri dish, and the physiological saline consisting of 0.9 wt% sodium chloride was brought to the same level as the top surface of the glass filter. One sheet of filter paper 90 mm in diameter was loaded thereon. The measuring device was placed on the filter paper and the liquid was absorbed for 1 hour under load. After 1 hour, the measuring device was lifted up and the weight W ₄ (g) was measured.

Using each mass obtained, the pressure absorption capacity (g / g) was computed according to following Formula.

[Equation 2]

AUL (g / g) = [W ₄ (g)-W ₃ (g)] / W ₀ (g)

Absorption rate under pressure Perform the same method as the pressure absorbing capacity, but use 0.3 ps i load instead of 0.9 ps i load, absorb the physiological saline consisting of 0.9% by weight sodium chloride for 5 minutes, then high on the vacuum pressure plate and gel at a vacuum pressure of 5 ps i The brine between and the gel was drained under vacuum for 30 seconds. Since the method of calculating the AUL by measuring the weight is the same as the pressure absorption capacity previously, this was called "5 minutes gel- AUL".

(4) Gel Bed Permeability (GBP)

For each resin, gel bed permeability (GBP, Gel Bed Permeabi 1 i ty) was measured. The GBP measurement method is specified in US Pat. Nos. 7, 7,179 and 851. In particular, the superabsorbent polymer according to the present invention exhibits specific characteristics or characteristics when measuring free swelling gel bed permeability (GBP) and gel bed permeability (0.3GBP) under load. The free swelling gel bed permeability test is a different measurement of the permeability (eg, separation from an absorbent structure) of a swelling bed of superabsorbent material, under specified pressure, after a condition commonly referred to as a "free swelling" state. "Free flow" means that the superabsorbent material swells without absorbing the swelling load upon absorption of the test solution.The gel bed transmittance under load (0.3GBP) is defined as about 0.3 ps i. After bringing it to a pressure state, it means the transmittance of the swelling bed of the gel particles (e.g., the superabsorbent resin of the present invention).

Free Swelling Gel Bed Permeability (GBP) Test

First, a free swelling gel bed permeability (GBP) test is performed on the swelling bed of gel particles (e.g., surface treated absorbent material or absorbent material prior to surface treatment) under conditions commonly referred to as a "free swelling" state. The transmittance is measured. By "free swelling" is meant that the gel particles swell without limiting load upon absorption of the test solution. Suitable apparatus for performing the transmittance test are shown in FIGS. 3 and 4, and generally indicated as 28 in FIG. 3. Test apparatus 28 is a sample container (usually 30 And piston (generally indicated as 36). The piston 36 includes a cylindrical LEXANR shaft 38 having a central cylindrical hole 40 drilled below the longitudinal axis of the shaft. Both ends of the shaft 38 are machined to provide the upper and lower ends (indicated by 42 and 46, respectively). The weight (indicated by 48) is above one end 42 and has a cylindrical hole 48a that is drilled through at least a portion of its center.

The circular piston head 50 is located above the other end 46 and has a central inner ring of seven holes (60 each of which has a diameter of about 0.95 cm) and 14 holes (54 each of which are about 0.95 cm in diameter). Having a central outer ring). The holes 54 and 60 are drilled from the top to the bottom of the piston head 50. The piston head 50 also has a cylindrical hole 62 drilled in its center to receive the end 46 of the shaft 38. The lower portion of the piston head 50 may also be covered with a biaxially stretched 400 mesh stainless steel screen 64.

The sample vessel 30 includes a cylinder 34 and a 400 mesh stainless steel skinned screen 66, which is taut biaxially stretched and attached to the lower end of the cylinder. The superabsorbent polymer sample (designated 68 in FIG. 3) is supported on the screen 66 inside the cylinder 34 during the test.

The cylinder 34 may be perforated with a transparent LEXANR rod or equivalent material or cut into a lexan tube or equivalent material, having an internal diameter of about 6 cm (eg, cross-sectional area of about 28.27 oif) and a wall thickness of about 0.5 cm It is about 10 cm high. A drain hole (not shown) is formed in the side wall of the cylinder 34 at a height of about 7.8 cm above the screen 66 to drain the liquid from the cylinder, and at about 8 cm above the screen 66, the fluid of the sample vessel increases. Maintain the level. The piston head 50 is machined from a lexan rod or equivalent material and has a height of approximately 16 mm and a diameter of a predetermined size so that it still slides freely while fitting it to the minimum wall space inside the cylinder 34. The shaft 38 is machined from a lexan rod or equivalent material and has an outer diameter of about 2.22 cm and an inner diameter of about 0.64 _cm .

The shaft upper end 42 is about 2.54 cm in length and about 1.58 cm in diameter, thereby forming an annular slad 47 to support the weight 48. fantasy The weight 48 is about 1.59 cm in internal diameter, so that it slips over the upper end 42 of the shaft 38 and is present on the annular shoulder 47 formed thereon. The annular weight 48 may be made of stainless steel or of another suitable material that is corrosion resistant in the presence of a test solution that is 0.9 wt% sodium chloride in distilled water. The combined weight of the piston 36 and the annular weight 48 corresponds to approximately 596 g, which means that the pressure applied to the absorbent structure sample 68 is about 0.3 ps i or about 20.7 g / cirf for a sample area of about 28.27 ciif. Corresponds to

When the test solution is flowed into the test apparatus during the test described below, the sample vessel 30 generally resides on a 16 mesh rigid stainless steel support screen (not shown). Alternatively, the sample vessel 30 resides on a support ring (not shown) having a diameter size substantially the same as the cylinder 34 so that the support ring does not restrict flow from the bottom of the vessel.

To perform the gel bed permeability test under “free swelling” conditions, a piston 36 with a weight 48 disposed thereon is placed in the hollow sample vessel 30 and a cylinder 34 from the bottom of the weight 48. The height to the top of is measured with a caliper with suitable measurement accuracy up to 0.01 mm 3. In the case of using multiple test apparatus, it is important to measure the hollow height of each sample vessel 30 and to maintain the contact where the piston 36 and weight 48 are used. The same piston 36 and weight 48 should be used for the measurement when the superabsorbent polymer sample 68 is water swelled after saturation.

The sample tested is made from superabsorbent material particles, which are prescreened through a US standard 30 mesh screen and held on a US standard 50 mesh screen. Thus, the test sample includes particles in the size range of about 300 to about 600. The particles can be prescreened manually or automatically. About 2.0 g of sample is placed in sample vessel 30, and then in the absence of piston 36 and weight 48, the vessel is immersed in the test solution for a period of about 60 minutes to saturate the sample and swell the sample without limiting load. .

At the end of this period, the piston 36 and the weight 48 are placed over the saturated sample 68 in the sample vessel 30, and then the sample vessel 30, the piston 36, the weight 48 and the sample 68 ) Is removed from the solution. The thickness of the saturated sample 68, previously used The same clipper or meter, with the zero point unchanged from the initial height measurement, is determined by measuring the height again from the bottom of the weight 48 to the top of the cylinder 34. The height measurement obtained by the measurement of the hollow sample vessel 30, the piston 36 and the height 48 is subtracted from the height measurement obtained after saturation of the sample 48. The value obtained is the thickness or height ("H") of the swelling sample.

Permeability measurements are initiated by delivering a flow of test solution to a sample vessel 30 having a saturated sample 68, a piston 36, and a weight 48 therein. The flow rate of the test solution into the vessel is adjusted to maintain a fluid height of about 7.8 cm above the bottom of the sample vessel. The amount versus time of solution passing through sample 68 is determined gravimetrically. Data points are collected every second for at least 20 seconds if the fluid level remains stabilized at about 7.8 cm height. The flow rate (Q) through the swelling sample 68 is measured in g / s by a linear minimum drag approximation of fluid (g) versus time (seconds) passing through the sample 68.

The transmittance (darcy) is calculated according to the following formula.

[Equation 3]

K = [QxH xMu] / [A x Rho xP]

In Equation 3, K is the transmittance (citf), Q is the flow rate (g / velocity), H is the height of the sample (cm), Mu is the liquid viscosity (poi se) (test solution used in the test Is approximately 1 cps), A is the cross-sectional area for liquid flow (cm ² ), Rho is the liquid density (g / ciif) (for the test solution used in the test), and P is the hydrostatic pressure (dynes / cuf). (Typically about 3,923 dynes / cuf). The hydrostatic pressure is calculated by the following equation.

[Equation 4]

P = Rho X g x h

In Equation 3 above, Rho is the liquid density (g / crf), g is the increase acceleration, typically 981 cm / sec ² and h is the fluid height (e.g. 7.8 cm for the permeability test described herein). .

Gel bed permeability test Gel bed permeability tests under load (or expressed in GBP at 0.3 psi) are typically used to treat gel particles (eg, surface treated absorbent materials or surface treatments) under conditions that are referred to as "loading" conditions. The transmittance of the swelling bed of the absorbent material before) is measured. The term "under load" means "is to be limited by the load which generally matches the normal working load that the swelling of the particles, applied to the particles by the wearer (e.g., sitting, walking eu bend, ^etc.).

More specifically, the gel bed permeability test under load is substantially the same as the free swelling gel bed permeability test described above, with the following exceptions. About 2.0 g of sample is placed in the sample vessel 30, uniformly dispersed in the lower portion of the sample vessel, the piston 36 and the weight 48 are placed on the sample inside the sample vessel, and then the sample vessel (the piston and weight inside ) Is immersed in the test solution (0.9 weight% NaCl saline) for about 60 minutes. As a result, a 0.3 psi limit load is applied to the sample as the sample saturates and swells. The measurement results are shown in Table 1 below.

Table 1

As shown in Table 1, the superabsorbent polymers of the examples according to the present invention were found to exhibit a high absorption rate under pressure while maintaining a similar water holding capacity compared to the resin of the comparative example. Therefore, when using the super absorbent polymer according to the present invention, it is possible to produce a diaper or the like to which ultra-thin technology is applied more easily.

Claims

【Patent Claims】

【Claim 1】

In a superabsorbent resin consisting of a crosslinked polymer obtained by polymerizing and internally crosslinking a monomer composition containing an acrylic acid-based monomer having an acidic group and at least a portion of the acidic group neutralized, and a surface crosslinking layer formed on the surface of the crosslinked polymer,

The water retention capacity (CRC) is more than 29.5 g/g, the absorbency under pressure (AUL) is more than 18 g/g, the gel bed permeation (GBP) is more than 60 Darcy, and the 5-minute gel_AUL is 18.0 g/g. Lee Sang-in,

Super absorbent resin.

[Claim 2]

In paragraph U,

The ratio (A:B) of the total pore area ratio (A) of pores with a diameter of 5 to 100 卿 and the total pore area ratio (B) of pores with a diameter of 100 to 400 in the superabsorbent polymer is 3:7 to 9: Characterized by 1,

Super absorbent resin.

[Claim 3]

In paragraph 1,

The ratio (A:B) of the total pore area ratio (A) of pores with a diameter of 5 /tn to 100 in the superabsorbent polymer and the total pore area ratio (B) of pores with a diameter of 100 im to 400 is 4:6 to 4:6. Characterized by 8:2,

Super absorbent resin.

【Claim 4】

In clause 1,

Further comprising a low-temperature foaming agent and a high-temperature foaming agent dispersed in the crosslinked polymer,

Super absorbent resin.

[Claim 5]

According to clause 4,

The low-temperature foaming agent is sodium bicarbonate, sodium carbonate, potassium bicarbonate, potassium ^}·bonate, calcium bicarbonate, calcium carbonate ( characterized in that it is calcium bicarbonate), magnesium bicarbonate, or magnesium carbonate,

Super absorbent resin.

【Claim 6】

In paragraph 14,

The high-temperature foaming agent is azodicarbonamide (ADCA), dinitroso pentamethylene tetramine (DPT), ^^-oxybisbenzenesulfonylhydrazide^，^ᅳ

oxyb i sbenzenesu 1 f ony 1 hydr az i de ), OBSH), p-toluenesulfonyl hydrazide (TSH) or sugar ester,

Super absorbent resin.

【Claim 7】

In clause 1,

The acrylic acid-based monomer is characterized in that it is represented by the following formula (1):

Super absorbent polymer:

[Formula 1]

In Formula 1,

¾ is an alkyl group with 2 to 5 carbon atoms containing an unsaturated bond, M ¹ is a hydrogen atom, a monovalent or divalent metal, an ammonium group, or an organic amine salt.

【Claim 8】

In clause U,

The acrylic acid-based monomer is characterized in that it contains at least one member selected from the group consisting of acrylic acid, methacrylic acid, and monovalent metal salts, divalent metal salts, ammonium salts, and organic amine salts thereof.

Super absorbent resin.

【Claim 9】

According to clause 1,

The cross-linked polymer is Ν,Ν'-methylenebisacrylamide, trimethylpropane tri(meth)acrylate, ethylene glycol di(meth)acrylate, polyethylene glycol (meth)acrylate, propylene glycol di(meth)acrylate, poly Propylene glycol (meth)acrylate, butane diol di(meth)acrylate, butylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, nucleic acid diol di(meth)acrylate, triethylene glycol Di(meth)acrylate, tripropylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, dipentaerythry pentaacrylate, glycerin tri(meth)acrylate pentaerythium tetraacrylate, A superabsorbent resin internally crosslinked with one or more ^crosslinking agents selected from the group consisting of triarylamine, ethylene glycol diglycidyl ether, propylene glycol, glycerin, and ethylene carbonate.

[Claim 10]

In clause U,

The superabsorbent polymer is characterized in that it is in the form of particles having a particle size of 150 to 850. highly absorbent water

【Claim 11】

A method for producing the superabsorbent polymer of any one of claims 1 to 10 comprising the following steps: -

1) A monomer composition containing an acrylic acid-based monomer having an acidic group and at least a portion of the acidic group has been neutralized is polymerized and crosslinked at 25 to 100 ^° C in the presence of a polymerization initiator, a first crosslinking agent, a low temperature foaming agent, and a high temperature foaming agent. Step of forming a water-containing gel polymer,

2) Crudely pulverizing the water-containing gel polymer,

3) Drying the coarsely ground hydrogel polymer at 150 to 250 ^° C,

4) pulverizing the dried polymer, and

5) Surface-modifying the pulverized polymer with a second cross-linking agent.

【Claim 12】

In clause 11,

The low-temperature foaming agent is sodium bicarbonate, sodium carbonate, potassium bicarbonate, potassium ^！ "potassium carbonate, and calcium bicarbonate. , Calcium bi carbonate, magnesium bi carbonate, or magnesium carbonate,

Manufacturing method of superabsorbent polymer.

【Claim 13】

In clause 11,

Characterized in that the polymerization and crosslinking temperature in step 1 is 30 to 9 C C,

Method for manufacturing superabsorbent polymer.

[Claim 14]

In clause 11,

The high-temperature foaming agent is azodicarbonamide (ADC A), dinitroso pentamethylene tetramine (DPT), ^—oxybisbenzenesulfonylhydrazide^，^ᅳ

oxyb i sbenzenesu 1 f ony 1 hydr az i de ) , OBSH) , p_toluenesulfonyl hydrazide (TSH) or sugar ester,

Manufacturing method of superabsorbent polymer.

【Claim 15】

In clause 14,

The sugar ester is sucrose stearate, sucrose palmitate, or sucrose laurate.

Manufacturing method of superabsorbent polymer.

[Claim 16]

In clause 11,

Characterized in that the weight ratio of the low-temperature foaming agent and the high-temperature foaming agent is 50:1 to 2:1,

Manufacturing method of superabsorbent polymer. 【Claim 17】

In clause 11,

A method for producing a superabsorbent polymer, characterized in that the drying temperature in step 3 is 150 to 200 ^° C. [Claim 18] In clause 11,

The second crosslinking agent is ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerol polyglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, ethylene glycol, die Ethylene glycol, propylene glycol, triethylene glycol, tetra ethylene glycol, propane diol, dipropylene glycol, polypropylene glycol, glycerin, polyglycerin, butanediol, heptanediol, hexane diol trimethylpropane, pentaerythricol, sorbitol Characterized by at least one selected from the group consisting of calcium hydroxide, magnesium hydroxide, aluminum hydroxide, iron hydroxide, calcium chloride, magnesium chloride, aluminum chloride, and iron chloride,

Manufacturing method of superabsorbent polymer.