A superabsorbent resin, its preparation method and uses

Abstract

This application provides a superabsorbent resin, its preparation method, and its uses. The preparation method includes: Step 1: causing a first polymeric monomer to undergo a first polymerization reaction in an aqueous solution to obtain a prepolymer; Step 2: forming a dispersion of the prepolymer in a nonpolar solvent, adding a second polymeric monomer to the dispersion, and carrying out a second polymerization reaction to obtain an intermediate resin; Step 3: modifying the intermediate resin with a surface crosslinking agent to obtain the superabsorbent resin. This application synthesizes a superabsorbent resin with superior water absorption rate and high liquid permeability through a simple and low-cost process design.

Description

Technical Field

[0001] This application relates to the field of polymers, and more specifically to a superabsorbent resin and a method for preparing the same, as well as products manufactured using the superabsorbent resin. Background Technology

[0002] Superabsorbent polymer (SAP) is a polymer compound with strong water absorption and retention capabilities. It is widely used in hygiene materials such as diapers and sanitary napkins, as well as in water-blocking materials for cables, wastewater treatment materials, and water-retaining agents for agriculture, forestry, and horticulture. With the increasing demand for high-performance diapers, its primary application, there is a growing demand for SAPs to possess more and better functions, especially high absorbency, high absorption speed, high absorbency under pressure, high permeability, low leaching content, and low residual resin content.

[0003] To meet these increasingly stringent requirements, relevant enterprises and research institutes are constantly developing and updating SAP materials and their synthesis processes. For example, many different polymerization reaction processes have been developed for synthesis, and various adjustments have been made to the reaction raw materials, additives, and process conditions to improve the properties of the final SAP material. However, unfortunately, the final results have always been unsatisfactory. For example, the products inevitably have poor water absorption rate and liquid permeability (leakage), and also suffer from one or more of the following defects: excessively high content of leached substances, excessively high content of residual monomers, complex synthesis process, high production cost, long reaction time, excessive waste of catalysts and other raw materials, and environmental pollution caused by waste.

[0004] Therefore, there is an urgent need in the art to develop a novel new technology for preparing SAP materials that can have the superior water absorption rate and liquid flow performance required by the art, preferably while also solving one or more of the other defects mentioned above, and most preferably solving all of the defects mentioned above. Summary of the Invention

[0005] In response to the above problems, the inventors of this application have conducted extensive and in-depth research and unexpectedly developed the method of this invention, which effectively solves a long-standing problem in the prior art.

[0006] The first aspect of this application provides a method for preparing a water-absorbing resin, the method comprising the following steps:

[0007] Step 1: The first monomer undergoes a first polymerization reaction in the aqueous solution phase to obtain the prepolymer;

[0008] Step 2: Form a dispersion of the prepolymer in a non-polar solvent, add the second polymerizable monomer to the dispersion, and carry out a second polymerization reaction to obtain an intermediate resin;

[0009] Step 3: Modify the intermediate resin with a surface crosslinking agent to obtain the water-absorbing resin; and

[0010] The first polymerizing monomer and the second polymerizing monomer are compounds containing at least one carbon-carbon double bond and at least one active group, and the first polymerizing monomer and the second polymerizing monomer may be the same as or different from each other.

[0011] According to one embodiment of the first aspect of this application, the surface crosslinking agent was not used for modification before performing step three.

[0012] According to another embodiment of the first aspect of this application, the surface crosslinking agent is a polyol poly(glycidyl ether).

[0013] According to another embodiment of the first aspect of this application, in step one and / or step two, one or more internal crosslinking agents are optionally used, said internal crosslinking agent being selected from one or more of the following: poly(unsaturated carboxylic acid) polyol esters, polyacrylamide, poly(meth)acrylate carbamate, allylated starch, allylated cellulose, poly(allyl) polycarboxylic acid esters, polyallyl isocyanurate, polyvinyl aromatic compounds, and poly(allyl) polyol ethers.

[0014] According to another embodiment of the first aspect of this application, the first polymeric monomer and the second polymeric monomer may be the same as or different from each other, and each is independently selected from one or more of the following: (meth)acrylic acid, (meth)acrylic acid C1-C12 alkyl ester, (meth)acrylic acid C1-C12 hydroxyalkyl ester, (meth)acryloyl C2-C12 alkyl sulfonate, (meth)acrylamide C2-C12 alkyl sulfonic acid, hydroxyalkyl (meth)acryloyl phosphate, itaconic acid, cinnamic acid, vinyl sulfonic acid, allyl toluene sulfonic acid, vinyl toluene sulfonic acid, styrene sulfonic acid, (meth)acrylamide, N-ethyl (meth)acrylamide, N,N-dimethyl (meth)acrylamide, N,N-dimethylaminoethyl (meth)acrylate, N,N-dimethylaminopropyl (meth)acrylate, N,N-dimethylaminopropyl (meth)acrylamide, mercapto-unsaturated monomer, phenolic hydroxyl-unsaturated monomer, N-vinylpyrrolidone.

[0015] According to another embodiment of the first aspect of this application, the molar ratio of the first polymeric monomer to the second polymeric monomer is 1:10 to 10:1.

[0016] According to another embodiment of the first aspect of this application, after step one and before step two, the prepolymer obtained in step one is crushed and sieved to obtain first primary particles of prepolymer with a median particle size greater than or equal to 10 micrometers and less than 150 micrometers, which are then used in step two.

[0017] According to another embodiment of the first aspect of this application, in steps one and two, one or more of the following may be used: an initiator, a dispersion stabilizer, or an alkaline reagent.

[0018] According to another embodiment of the first aspect of this application, in step two, the nonpolar solvent is selected from one or more of the following: n-hexane, n-heptane, cyclohexane, toluene, and xylene.

[0019] According to another embodiment of the first aspect of this application, an inorganic additive is added during, before, or after one or more of steps one through three.

[0020] According to another embodiment of the first aspect of this application, the water-absorbing resin is in the form of secondary particles formed by the agglomeration of second primary particles, the median particle size of the secondary particles being 250-500 micrometers, and the median particle size of the second primary particles being 15-150 micrometers.

[0021] According to another embodiment of the first aspect of this application, step one is carried out at a temperature of 45-120°C, such that 60-100% of the first polymeric monomer undergoes polymerization.

[0022] According to another embodiment of the first aspect of this application, step two is performed at a temperature of 60-95°C.

[0023] According to another embodiment of the first aspect of this application, step three is carried out at a temperature of 50-100°C, and the amount of the surface crosslinking agent is 0.001-1 by weight, based on 100% by weight of the total weight of the second polymeric monomer.

[0024] A second aspect of this application provides an absorbent product comprising: diapers, sanitary napkins, adult incontinence pads, absorbent paper, napkins, disposable mattress protectors, soil moisturizing materials, leak-sealing materials, wastewater treatment materials, and mud solidification materials; at least a portion of the absorbent product comprises an absorbent resin prepared by the method of this invention.

[0025] In the detailed embodiments section below, the methods, raw materials, process conditions and products of this application will be further described with reference to the accompanying drawings. Attached Figure Description

[0026] Figure 1A and Figure 1B The image shows an SEM image of the SAP particles prepared according to the embodiments of this application. Detailed Implementation

[0027] The “range” disclosed in this document takes the form of a lower limit and an upper limit. It can be one or more lower limits and one or more upper limits, respectively. A given range is defined by selecting a lower limit and an upper limit. The selected lower and upper limits define the boundaries of the particular range. All ranges that can be defined in this way are end values ​​and combinable, meaning that any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is also expected that ranges of 60-110 and 80-120 are also expected. Furthermore, if the minimum range values ​​are listed as 1 and 2, and if the maximum range values ​​are listed as 3, 4, and 5, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5.

[0028] In this application, unless otherwise stated, the numerical range "ab" is a shortened representation of any combination of real numbers from a to b, where a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" have been listed in this document, and "0-5" is simply a shortened representation of these numerical combinations.

[0029] Unless otherwise specified in this application, all embodiments and preferred embodiments mentioned herein can be combined to form new technical solutions.

[0030] Unless otherwise specified, all technical features and preferred features mentioned herein can be combined to form new technical solutions.

[0031] In this application, unless otherwise specified, the term "comprising" as used herein can be either open-ended or closed-ended. For example, "comprising" may mean that it may also include other components not listed, or it may only include the listed components.

[0032] According to one technical solution of this application, the method of this application includes the following steps: Step 1: causing a first polymeric monomer to undergo a first polymerization reaction in an aqueous phase to obtain a prepolymer; Step 2: forming a dispersion of the prepolymer in a non-polar solvent, adding a second polymeric monomer to the dispersion to carry out a second polymerization reaction to obtain an intermediate resin; Step 3: modifying the intermediate resin with a surface crosslinking agent to obtain the water-absorbing resin.

[0033] One of the inventive points of this invention is that it employs a stepwise approach, combining aqueous-phase polymerization and reverse-phase polymerization. In the aqueous-phase polymerization, a first polymeric monomer undergoes a first polymerization reaction to form first primary particles (particles). In the reverse-phase polymerization, a newly added second polymeric monomer polymerizes in the presence of the first primary particles, forming second primary particles, which then agglomerate to ultimately form secondary particles. Figure 1A and 1B As shown, the SAP particles of this application include secondary particles formed by the aggregation of primary particles (secondary primary particles).

[0034] Another aspect of this invention is that the applicant unexpectedly discovered that after reverse polymerization, i.e., after the formation of "secondary particles," surface modification using a surface crosslinking agent can significantly improve the product's water absorption rate and liquid permeability. However, existing technologies often exhibit a bias that surface modification using a surface crosslinking agent should be performed before, rather than after, the formation of secondary particles. Performing the modification after secondary particle formation is considered insufficient to improve performance and may even negatively impact water absorption. This invention overcomes this bias, achieving a completely unexpected technical effect.

[0035] According to one embodiment of this application, in step one and / or step two above, one or more internal crosslinking agents may optionally be used during the polymerization reaction.

[0036] In this invention, the "internal crosslinking agent" refers to a crosslinking agent that exists within the polymerization reaction system during the polymerization process to form first primary particles (for the first step), second primary particles, and secondary particles (for the second step), and crosslinks them while forming polymer chains, thereby promoting the formation of the aforementioned first primary particles and / or second primary particles and / or secondary particles.

[0037] The "surface crosslinking agent" is applied to the secondary particles after they have been formed. In the third step of "modification" using the surface crosslinking agent, the polymerization reaction related to the primary and / or secondary particles does not occur.

[0038] According to one embodiment of this application, the surface crosslinking agent is a polyol poly(glycidyl ether). The polyol refers to a C2-C16 polyol or polymeric polyol containing two or more hydroxyl groups, such as ethylene glycol, polyethylene glycol, propylene glycol, polypropylene glycol, polyethylene oxide glycol, polypropylene oxide glycol, butanediol, polybutylene glycol, glycerol, pentaerythritol, trimethylolpropane, etc. Two or more, for example two, three, four, five, six, or all, carboxyl groups in the polyol are linked to a corresponding number of glycidyl groups via ether bonds, thereby forming the polyol poly(glycidyl ether) of this invention. According to an exemplary embodiment of this application, the surface crosslinking agent includes one or more of the following: ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, polyethylene oxide glycol diglycidyl ether, polypropylene oxide glycol diglycidyl ether, butanediol diglycidyl ether, polybutylene glycol diglycidyl ether, glycerol triglycidyl ether, pentaerythritol tetraglycidyl ether, trimethylolpropane triglycidyl ether, etc. In the third step, the surface crosslinking agent can be directly applied to the slurry obtained in step two, or the surface crosslinking agent and optional other components can be formulated into a solution, such as an aqueous solution, and then added to the slurry obtained in step two.

[0039] According to one embodiment of this application, with the total molar amount of the first and second polymeric monomers being 100 mol%, the amount of the surface crosslinking agent can be 0.001-1 mol%, for example, within the range of any combination of the following two values: 0.001 mol%, 0.002 mol%, 0.005 mol%, 0.006 mol%, 0.008 mol%, 0.01 mol%, 0.02 mol%, 0.05 mol%, 0.06 mol%, 0.08 mol%, 0.1 mol%, 0.3 mol%, 0.5 mol%, 0.6 mol%, 0.8 mol%, 0.9 mol%, 1 mol.

[0040] According to one embodiment of this application, the internal crosslinking agent is used in step one, or in step two, or simultaneously in both steps one and two. The internal crosslinking agent is selected from one or more of the following: poly(unsaturated carboxylic acid) polyol esters, polyacrylamide, poly(meth)acrylate carbamate, allylated starch, allylated cellulose, poly(allyl) polycarboxylic acid esters, polyallyl isocyanurate, polyvinyl aromatic compounds, and polyol poly(allyl) ethers. The polyol refers to a C2-C16 polyol or polymeric polyol containing two or more hydroxyl groups, such as ethylene glycol, polyethylene glycol, propylene glycol, polypropylene glycol, polyethylene oxide glycol, polypropylene oxide glycol, butanediol, polybutylene glycol, glycerol, pentaerythritol, trimethylolpropane, etc. For example, the internal crosslinking agent may be selected from one or more of the following: poly(meth)acrylate, poly(maleic acid)polyol ester, poly(fumaric acid)polyol ester; di(meth)acrylate carbamoyl esters obtained by reacting polyisocyanates such as toluene diisocyanate or hexamethylene diisocyanate with hydroxyethyl methacrylate; allylated starch; allylated cellulose; diallyl phthalate; N,N',N''-triallyl isocyanurate; divinylbenzene; pentaerythritol triallyl ether; polyethyleneimine, etc. Preferably, the internal crosslinking agent is selected from one or more of the following: N,N'-methylenebisacrylamide, polyethylene glycol diacrylate, pentaerythritol triallyl ether.

[0041] According to one embodiment of this application, when an internal crosslinking agent is used in step one, based on a total molar amount of 100 mol% of the first polymerizable monomer, the amount of the internal crosslinking agent used in the first step can be 0.002-1 mol%, for example, it can be within the range of values ​​obtained by combining any two of the following values: 0.002 mol%, 0.005 mol%, 0.006 mol%, 0.008 mol%, 0.01 mol%, 0.02 mol%, 0.05 mol%, 0.06 mol%, 0.08 mol%, 0.1 mol%, 0.3 mol%, 0.5 mol%, 0.6 mol%, 0.8 mol%, 0.9 mol%, 1 mol.

[0042] According to another embodiment of this application, when an internal crosslinking agent is used in step two, based on a total molar amount of the second polymerizing monomer of 100 mol%, the amount of the internal crosslinking agent used in the second step can be 0.002-1 mol%, for example, within the range of values ​​obtained by combining any two of the following values: 0.002 mol%, 0.005 mol%, 0.006 mol%, 0.008 mol%, 0.01 mol%, 0.02 mol%, 0.05 mol%, 0.06 mol%, 0.08 mol%, 0.1 mol%, 0.3 mol%, 0.5 mol%, 0.6 mol%, 0.8 mol%, 0.9 mol%, 1 mol.

[0043] According to one embodiment of this application, the first polymerizing monomer used in step one and the second polymerizing monomer used in step two may be the same or different from each other, each containing at least one carbon-carbon double bond and at least one active group, the active group may be carboxyl, hydroxyl, amino, amide, sulfonic acid, mercapto, etc. For example, the first and second polymerizing monomers may each be independently selected from one or more of the following: (meth)acrylic acid, (meth)acrylic acid C1-C12 alkyl ester, (meth)acrylic acid C1-C12 hydroxyalkyl ester, (meth)acryloyl C2-C12 alkyl sulfonate, (meth)acrylamide C2-C12 alkyl sulfonic acid, hydroxyalkyl (meth)acryloyl phosphate, itaconic acid, cinnamic acid, vinyl sulfonic acid, allyl toluenesulfonic acid, vinyl toluenesulfonic acid, styrene sulfonic acid, (meth)acrylamide, N-ethyl (meth)acrylamide, N,N-dimethyl (meth)acrylamide, N,N-dimethylaminoethyl (meth)acrylate, N,N-dimethylaminopropyl (meth)acrylate, N,N-dimethylaminopropyl (meth)acrylamide, mercapto-unsaturated monomers, phenolic hydroxyl-unsaturated monomers, and N-vinylpyrrolidone. According to an exemplary embodiment, the first and second polymerizing monomers are each independently selected from one or more of the following: (meth)acrylic acid, maleic acid (anhydride), itaconic acid, cinnamic acid, vinyl sulfonic acid, allyl toluenesulfonic acid, vinyl toluenesulfonic acid, styrene sulfonic acid, 2-(meth)acrylamide-2-methylpropanesulfonic acid, 2-(meth)acryloyl ethanesulfonic acid, 2-(meth)acryloyl propanesulfonic acid, 2-hydroxyethyl(meth)acryloyl phosphate, and other acid-containing unsaturated monomers; (meth)acrylamide, N-ethyl(meth)acrylamide, N,N-dimethyl(meth)acrylamide, and other amide-containing unsaturated monomers; N,N-dimethylaminoethyl(meth)acrylate, N,N-dimethylaminopropyl(meth)acrylate, N,N-dimethylaminopropyl(meth)acrylamide, and other amino-containing unsaturated monomers; mercapto-containing unsaturated monomers; phenolic hydroxyl-containing unsaturated monomers; N-vinylpyrrolidone, and other lactam-containing unsaturated monomers.

[0044] According to one embodiment of this application, the weight ratio of the first polymeric monomer and the second polymeric monomer can be from 1:10 to 10:1, for example, within the range of values ​​obtained by combining any two of the following ratios: 1:10, 1:9, 1:8, 1:7, 1:6, 1:5, 1:4, 1:3, 1:2, 1:1, 3:2, 4:3, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1.

[0045] According to a specific embodiment of this application, in step one, an aqueous solution of the first monomer containing a first polymerizing monomer and a first initiation system is prepared, and the aqueous solution of the first polymerizing monomer undergoes an aqueous solution polymerization reaction to obtain a primary polymer.

[0046] According to one embodiment of this application, step one is carried out at a temperature of 45-120°C. For example, the reaction temperature of step one can be within the range of any combination of the following two values: 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, 115°C, 120°C.

[0047] According to another embodiment of this application, in step one, 60-100% of the first polymeric monomer is polymerized, for example, 70-100% of the first polymeric monomer is polymerized, or 80-100% of the first polymeric monomer is polymerized, or 90-100% of the first polymeric monomer is polymerized.

[0048] According to one embodiment of this application, after obtaining the prepolymer, it is dried, pulverized, and classified to obtain first primary particles, which are then used in step two. The first primary particles can be irregularly shaped particles with angular features.

[0049] According to one embodiment of this application, the median particle size of the first primary particle is greater than or equal to 10 micrometers and less than 150 micrometers. For example, the median particle size of the first primary particle can be within the range of values ​​obtained by combining any two of the following values: 15 micrometers, 20 micrometers, 30 micrometers, 40 micrometers, 45 micrometers, 50 micrometers, 60 micrometers, 70 micrometers, 80 micrometers, 90 micrometers, 100 micrometers, 110 micrometers, 120 micrometers, 130 micrometers, 140 micrometers, and 145 micrometers.

[0050] According to one embodiment of this application, in step two, the first primary particles of the above-mentioned primary polymer are dispersed in a non-polar solvent containing a dispersing stabilizer. Simultaneously, an aqueous solution of a second monomer containing a second polymerizing monomer and a second initiation system is prepared. The aqueous solution of the second monomer is then added to the non-polar solvent containing the first primary particles, and a reverse-phase suspension polymerization reaction is performed to obtain an intermediate resin. This intermediate resin contains secondary particles formed by the agglomeration and stacking of the second primary particles.

[0051] Subsequently, in step three, the intermediate resin secondary particles are modified using a surface crosslinking agent to obtain the SAP particles of the present invention. The temperature in step three can be 50-100°C, for example 60-90°C, or 75-85°C.

[0052] According to one embodiment of this application, an inorganic additive, such as silica, talc, zeolite, alumina powder, etc., can be added after step two or after step three. The content of the inorganic additive can be 0.01-5 parts by weight, based on 100 parts by weight of SAP.

[0053] According to one embodiment of this application, the median particle size of the secondary particles obtained by the method is 250-500 micrometers, preferably 300-450 micrometers, and more preferably 350-420 micrometers.

[0054] According to one embodiment of this application, when the first and second monomers used in steps one and two have acidic groups such as carboxyl groups and sulfonic acid groups, it may be necessary to add an alkaline reagent (neutralizing agent) to the polymerization reaction system. For example, alkali metal hydroxides or ammonium hydroxides can be used, such as sodium hydroxide, potassium hydroxide, lithium hydroxide, ammonium hydroxide, etc., or mixtures of two or more of the above-mentioned bases. According to one embodiment of this application, the amount of alkaline reagent added should neutralize 10-100 mol% of the acidic groups in all monomers, for example, 20-90 mol% or 30-80 mol%.

[0055] In steps one and two, initiators, such as free radical initiators, can be added. Examples include persulfates (potassium persulfate, ammonium persulfate, and sodium persulfate, etc.), peroxides (butanone peroxide, methyl isobutyl ketone peroxide, di-tert-butyl peroxide, tert-butyl cumene peroxide, tert-butyl peroxyacetate, tert-butyl peroxyisobutyrate, tert-butyl perpentyl peroxide, and hydrogen peroxide, etc.), and azo compounds (2,2'-azobis[2-(N-phenylamidinyl)propane)). Dihydrochloride, 2,2'-azobis[2-(N-allylamidinyl)propane] Dihydrochloride, 2,2'-azobis{2-[1-(2-hydroxyethyl)-2-imidazolin-2-yl]propane} The free radical polymerization initiator consists of dihydrochloride, 2,2'-azobis{2-methyl-N-[1,1-di(hydroxymethyl)-2-hydroxyethyl]propionamide}, 2,2'-azobis[2-methyl-N-(2-hydroxyethyl)-propionamide], and 4,4'-azobis(4-cyanopentanoic acid). The free radical polymerization initiator can be used alone or in mixtures of two or more. Preferably, the free radical polymerization initiator is selected from one or more of potassium persulfate, ammonium persulfate, and sodium persulfate. The first initiator used in step one and the second initiator used in step two can be the same or different. The above-mentioned free radical polymerization initiator can be combined with sodium sulfite, sodium bisulfite, ferrous sulfate, and / or L-ascorbic acid as a redox polymerization initiator.

[0056] In the first step, with the total molar amount of the first polymerizing monomer being 100 mol%, the amount of the first initiator can be 0.005-1 mol%, for example, it can be within the range of any combination of the following two values: 0.008 mol%, 0.01 mol%, 0.03 mol%, 0.05 mol%, 0.08 mol%, 0.1 mol%, 0.2 mol%, 0.3 mol%, 0.5 mol%, 0.8 mol%, 0.9 mol%, 1 mol.

[0057] In the second step, with the total molar amount of the second polymerizing monomer being 100 mol%, the amount of the second initiator can be 0.005-1 mol%, for example, it can be within the range of any combination of the following two values: 0.008 mol%, 0.01 mol%, 0.03 mol%, 0.05 mol%, 0.08 mol%, 0.1 mol%, 0.2 mol%, 0.3 mol%, 0.5 mol%, 0.8 mol%, 0.9 mol%, 1 mol.

[0058] According to one embodiment of this application, a dispersion stabilizer may be used in the first and / or second steps. The dispersion stabilizer may include a surfactant, preferably a nonionic surfactant. The surfactant may be one or more selected from the group consisting of: sucrose fatty acid esters, polyglycerol fatty acid esters, dehydrated sorbitol fatty acid esters, polyoxyethylene dehydrated sorbitol fatty acid esters, polyoxyethylene glycerol fatty acid esters, sorbitol fatty acid esters, polyoxyethylene sorbitol fatty acid esters, polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene castor oil, polyoxyethylene hardened castor oil, alkylallyl formaldehyde-polyoxyethylene ether condensates, polyoxyethylene polyoxypropylene block copolymers, polyoxyethylene polyoxypropylene alkyl ethers, polyethylene glycol fatty acid esters, alkyl glucosides, N-alkyl glucamides, polyoxyethylene fatty amides, polyoxyethylene alkylamines, phosphate esters of polyoxyethylene alkyl ethers, and phosphate esters of polyoxyethylene alkylallyl ethers. The surfactant used as a dispersion stabilizer may be used alone or in mixtures of two or more. From the viewpoint of dispersion stability in aqueous solutions of monomers, one or more of the following are preferred: sucrose fatty acid ester, polyglycerol fatty acid ester, sorbitol fatty acid ester, dehydrated sorbitol fatty acid ester, polyoxyethylene dehydrated sorbitol fatty acid ester, polyoxyethylene glycerol fatty acid ester, and polyoxyethylene hardened castor oil.

[0059] The dispersion stabilizer may further include a polymeric dispersant, or the polymeric dispersant may be used in conjunction with the aforementioned surfactant. The polymeric dispersant used may be of the following types: maleic anhydride-modified polyethylene, maleic anhydride-modified polypropylene, maleic anhydride-modified ethylene-propylene copolymer, maleic anhydride-modified EPDM (ethylene-propylene-diene terpolymer), maleic anhydride-modified polybutadiene, ethylene-maleic anhydride copolymer, ethylene-propylene-maleic anhydride copolymer, butadiene-maleic anhydride copolymer, oxidized polyethylene, ethylene-acrylic acid copolymer, ethyl cellulose, ethyl hydroxyethyl cellulose, etc. The polymeric dispersant may be used alone or in combination with two or more. Preferably, the polymeric dispersant includes one or more of the following: maleic anhydride-modified polyethylene, maleic anhydride-modified polypropylene, maleic anhydride-modified ethylene-propylene copolymer, oxidized polyethylene, oxidized polypropylene, and ethylene-acrylic acid copolymer.

[0060] According to one embodiment of this application, for the first step, if a dispersing stabilizer is used, the amount of the dispersing stabilizer is 0.01-6 parts by weight, based on a total weight of 100 parts by weight of the first polymeric monomer.

[0061] According to one embodiment of this application, for the second step, if a dispersing stabilizer is used, the amount of the dispersing stabilizer is 0.1-5 parts by weight, preferably 0.5-2 parts by weight, based on a total weight of 100 parts by weight of the second polymeric monomer.

[0062] According to one embodiment of this application, the nonpolar solvent used in step two is also called a hydrophobic solvent. The solvent is preferably a petroleum hydrocarbon solvent, and more preferably selected from one or more of the following: n-hexane, n-heptane, cyclohexane, toluene, and xylene.

[0063] According to another embodiment of this application, step two is carried out at a temperature of 60-95°C. For example, the reaction temperature of step two can be within the range of any combination of the following two values: 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C.

[0064] The following embodiments illustrate the superior effects achievable by the method of this application. Their purpose is to provide a better understanding of the content of this application. It should be understood that these embodiments are merely illustrative and not restrictive. Unless otherwise stated, the reagents used in the embodiments are commercially available. Unless otherwise specified, the methods and conditions used in the embodiments are conventional methods and conditions.

[0065] Example

[0066] All raw materials used in the following examples are commercially available analytical grade raw materials and are used directly without further processing.

[0067] In the following embodiments, the median particle size was measured and controlled, and the performance of the water-absorbing resin products was tested using the following techniques:

[0068] A. Median particle size (micrometers)

[0069] The method for testing the median particle size of the primary particles obtained in step one is as follows:

[0070] Take all the pulverized primary particles and prepare JIS standard sieves (sieve openings 425μm, 250μm, 180μm, 150μm, 106μm, 75μm, 45μm).

[0071] Stack the JIS standard sieves from top to bottom in the following order: sieve openings of 425μm, 250μm, 180μm, 150μm, 106μm, 75μm, and 45μm. Add the above-mentioned water-absorbing resin particles to the top sieve and vibrate for 10 minutes using a rotating tapping vibrating sieve.

[0072] Subsequently, by calculating the percentage of the mass of residual absorbent resin particles on each sieve relative to the total mass, starting with the largest particles, the relationship between the sieve aperture size and the integral value of the percentage of residual absorbent resin particles on the sieve was plotted on logarithmic probability paper. The points on the probability paper were connected by straight lines, and the median particle size of the secondary particles was defined as the particle size corresponding to a cumulative mass percentage of 50%.

[0073] The method for testing the median particle size of the secondary particles obtained in Stage 2 is as follows:

[0074] Take all the dried secondary particles and prepare JIS standard sieves (sieve openings of 850μm, 710μm, 600μm, 500μm, 425μm, 300μm, 180μm, 150μm).

[0075] Stack the JIS standard sieves in order of sieve aperture size: 850μm, 710μm, 600μm, 500μm, 425μm, 300μm, 180μm, 150μm, from top to bottom. Add the above-mentioned water-absorbing resin particles to the top sieve and vibrate for 10 minutes using a rotating tapping vibrating sieve.

[0076] Subsequently, by calculating the percentage of the mass of residual absorbent resin particles on each sieve relative to the total mass, starting with the largest particles, the relationship between the sieve aperture size and the integral value of the percentage of residual absorbent resin particles on the sieve was plotted on logarithmic probability paper. The points on the probability paper were connected by straight lines, and the median particle size of the secondary particles was defined as the particle size corresponding to a cumulative mass percentage of 50%.

[0077] B. Absorption rate of SAP product (seconds)

[0078] Add 0.02 parts by weight of indigo (a food additive) to 1000 parts by weight of a pre-prepared 0.90 wt% NaCl aqueous solution, and adjust the liquid temperature to 25°C. Add 50 g of the blue-colored 0.90 wt% NaCl aqueous solution to a 100 ml beaker. While stirring at 600 rpm with a cylindrical stirrer (20 mm long and 5 mm thick), add 2.0 g of highly absorbent resin. Start timing immediately after the addition is complete. The endpoint is defined as the point where the lowest point of the liquid vortex just covers the stir bar. This time interval t is the water absorption rate. The smaller t is, the faster the brine is absorbed.

[0079] C. Permeability (seconds)

[0080] Weigh 150g of 0.9wt% NaCl solution adjusted to 23℃, add 0.32g of accurately weighed high-absorbency resin test sample, and let it stand for 30min to swell. Fix the percolation tube vertically, with a filter screen and plug at the lower end, and mark the volumetric graduation intervals. The inner diameter of the percolation tube is 30mm, and the length of each graduation interval is 35mm. Record the time required for the 0.9wt% NaCl solution at 23℃ to flow through the graduation interval of the percolation tube as T1. Transfer the prepared hydrogel particles and saline solution together into the percolation tube. When the swollen gel particles sink to the bottom, place a pressure shaft with a circular metal wire mesh with perforations on top, and place a weight at the top of the pressure shaft. Then open the valve at the bottom of the percolation tube and record the time T2 for the saline solution to flow through its graduation interval. The total pressure applied to the swollen gel particles by the pressure shaft and weight is 2.0kPa. The less time it takes for the liquid to pass through the permeation tube, the better the liquid permeability of the superabsorbent resin. The value is calculated as follows: T2-T1.

[0081] D. Amount of pure water absorbed in 1 minute (g / g)

[0082] Weigh 2.0000±0.001g of sample into a 400-mesh nylon mesh bag and record the weight W1. Fill a 5L beaker 2 / 3 full with pure water, maintaining the temperature at 23±0.5℃. Quickly immerse the nylon mesh bag containing the sample into the pure water and start timing. After 1 minute, remove the nylon mesh bag from the pure water and let it stand for a few seconds until no water drips from the bottom. Weigh the water-absorbed nylon mesh bag on a balance and zero it. Clean all the water-absorbed SAP particles from the bag, then weigh the empty bag on the balance and record the weight W2. Calculate the CRC using the following formula.

[0083] Pure water volume absorbed in 1 minute = (W2 - W1) / W1

[0084] E. Centrifugal water retention capacity (g / g)

[0085] The centrifugal water retention capacity (CRC) of the superabsorbent polymer (SAP) was determined according to the EDANA method (ERT 441.2-02). "EDANA" is the abbreviation for the European Nonwovens Industry Association. "ERT" is the abbreviation for the European Standard Method for the Determination of Superabsorbent Polymers. In this invention, unless otherwise specified, the physical properties of the SAP are determined in accordance with the original ERT (2002 revised edition / publicly available literature).

[0086] Specifically, 0.20 g of superabsorbent resin was evenly placed into a tea-sealing bag (60 mm × 85 mm) and heat-sealed. The bag was then immersed in a well-excess (usually about 500 ml) of 0.90 wt% NaCl aqueous solution at 23 (±2) °C. After 30 minutes, the bag was lifted and centrifuged (Kokusan Co., Ltd., Japan, model H-122) at 250 G for 3 minutes to remove water. The weight of the bag, W1 g, was then measured. The same procedure was performed without superabsorbent resin, and the weight, W2 g, was measured. The CRC was then calculated using the following formula.

[0087] CRC = (W1 - W2) / 0.2 - 1

[0088] Example 1

[0089] (a) Aqueous phase polymerization step: In a 2000ml PP beaker, add 174.78g of acrylic acid (purchased from Shanghai Huayi New Materials Co., Ltd.), 148.19g of deionized water, and 69.84g of 50wt% NaOH aqueous solution (purchased from Shanghai Chlor-Alkali Chemical Co., Ltd.). The NaOH solution needs to be added under strong stirring. During the addition of the NaOH solution, precipitates can be observed, but they gradually dissolve to form a transparent, homogeneous solution. The temperature of the material rises to 65°C. o C. This causes the material to cool to 56°C. o C, then add 23.59 g of polyethylene glycol diacrylate 400 (purchased from Chang Hsing Materials Industrial Co., Ltd., Taiwan, as a 4% aqueous solution) as an internal crosslinking agent. Then add 40... o After adding 71.79 g of a 50 wt% NaOH aqueous solution of C, the material temperature rose to 88°C due to the heat of neutralization. o C. Lower the temperature of the reaction solution to 78°C. o C. Add 11.32 g of a 3% sodium persulfate aqueous solution to obtain the monomer aqueous solution from step one, and stir for 2 seconds. Then, while stirring, quickly pour it into 25... Preheat 25cm to 105 o Place the entire stainless steel tray (C) in a 105-meter range. o In an oven at temperature C, the polymerization reaction began after 20-30 seconds. During this reaction, water vapor was generated while the polymer expanded and foamed in all directions, then contracted and collapsed to a size slightly larger than the polymerization tray. Three minutes after the start of the polymerization reaction, the cross-linked polymer containing ribbon-like hydrogel morphology was removed from the polymerization tray. The peak polymerization temperature was 110°C. o C.

[0090] The hydrogel obtained from the above-mentioned aqueous phase polymerization reaction was broken down using a meat grinder (purchased from Zhengyuan Precision Machinery Co., Ltd., model RY-12S, 8mm aperture) to obtain granular hydrogel. During the gel breaking down process, a 90°C spray was continuously and uniformly applied to the gel. o Approximately 90g of deionized water (C).

[0091] The granular hydrogel obtained through the above operations is spread on a stainless steel wire mesh with a mesh size of 850 micrometers, and then heated at 185°C. o The polymer was dried in a forced-air drying oven for 70 minutes. Then, the dried polymer was pulverized using a grinder and sieved using standard sieves with mesh sizes of 45 microns and 150 microns to obtain primary particles with a particle size of 45 microns to 150 microns.

[0092] (b) Reverse suspension polymerization step: Add 124.4 g of acrylic acid to a 500 ml Erlenmeyer flask, and add 189.9 g of 27% sodium hydroxide aqueous solution dropwise under ice-water bath conditions to neutralize 74% of the acrylic acid. Then add 0.192 g of potassium persulfate and 13.9 mg of N,N'-methylenebisacrylamide (product number: 14085E, purchased from Adamas Reagent Co., Ltd.) and dissolve them. Then add 20 g of water to prepare the monomer aqueous solution of step two.

[0093] Prepare a 1000mL five-necked detachable flask. Attach the reflux condenser, nitrogen inlet tube, and stirrer (an 80mm crescent-shaped impeller) to the flask. Place the entire flask in an oil bath and heat to 80°C. o C. Add 408 ml of n-heptane, 1.104 g of sucrose stearate (Mitsubishi Chemical Corporation, Ryoto sucrose ester S-370), and 1.104 g of maleic anhydride-modified ethylene-propylene copolymer (Mitsui Chemicals Corporation, Hi-wax 1105A) to the flask to dissolve the dispersant stabilizer. Adjust the rotation speed to 500 rpm, weigh 110 g of the primary particles obtained from the above aqueous phase polymerization and add them to the flask, then add 100 g of water.

[0094] The water bath temperature was lowered to 20°C, and the monomer aqueous solution from the second stage above was added to the flask. After the addition was completed, the air in the system was replaced with nitrogen for 30 minutes. Then the flask was immersed in a water bath at 70°C for 60 minutes to polymerize, and the slurry from step two was obtained through polymerization.

[0095] (c) Surface modification step: Place the slurry obtained in the above steps at 120°C. oIn an oil bath of C, water and n-heptane were azeotropically reacted. While ensuring reflux of the n-heptane, 230g of water was removed from the system. Then, the oil bath temperature was lowered to 80°C. o C. Add 10.34 g of a 2% aqueous solution of ethylene glycol diglycidyl ether (product number: 38399B, purchased from Adamas Reagent Co., Ltd.) and maintain at 80 °C for 120 min. Dry by evaporating n-heptane, yielding 260.1 g of secondary particles obtained by the method described above. The median particle size of the secondary particles is 402.4 μm, and the particle size distribution is shown in Table 1. Mix 100 parts by weight of this absorbent resin with 0.3 parts by weight of AEROSIL 200 (gas-phase SiO2, Degussa) to obtain the final resin sample. The results of various performance tests are shown in Table 2. Figure 1A and Figure 1B The microstructure of the product at different magnifications is shown, revealing that the product consists of secondary particles formed by the aggregation of a large number of irregularly shaped primary particles.

[0096] Example 2

[0097] (a) Aqueous phase polymerization step: In a 2000ml PP beaker, add 174.78g of acrylic acid (purchased from Shanghai Huayi New Materials Co., Ltd.), 148.19g of deionized water, and 69.84g of 50wt% NaOH aqueous solution (purchased from Shanghai Chlor-Alkali Chemical Co., Ltd.). The NaOH solution needs to be added under strong stirring. During the addition of the NaOH solution, precipitates can be observed, but they gradually dissolve to form a transparent, homogeneous solution. The temperature of the material rises to 65°C. o C. This causes the material to cool to 56°C. o C, then add 23.59 g of polyethylene glycol diacrylate 400 (purchased from Chang Hsing Materials Industrial Co., Ltd., Taiwan, as a 4% aqueous solution) as an internal crosslinking agent. Then add 40... o After adding 71.79 g of a 50 wt% NaOH aqueous solution of C, the material temperature rose to 88°C due to the heat of neutralization. o C. Lower the temperature of the reaction solution to 78°C. o C. Add 11.32 g of a 3% sodium persulfate aqueous solution to obtain the monomer aqueous solution from step one, and stir for 2 seconds. Then, while stirring, quickly pour it into 25... Preheat 25cm to 105 o Place the entire stainless steel tray (C) in a 105-meter range. oIn an oven at temperature C, the polymerization reaction began after 20-30 seconds. During this reaction, water vapor was generated while the polymer expanded and foamed in all directions, then contracted and collapsed to a size slightly larger than the polymerization tray. Three minutes after the start of the polymerization reaction, the cross-linked polymer containing ribbon-like hydrogel morphology was removed from the polymerization tray. The peak polymerization temperature was 110°C. o C.

[0098] The hydrogel obtained from the above-mentioned aqueous phase polymerization reaction was broken down using a meat grinder (purchased from Zhengyuan Precision Machinery Co., Ltd., model RY-12S, 8mm aperture) to obtain granular hydrogel. During the gel breaking down process, a 90°C spray was continuously and uniformly applied to the gel. o Approximately 90g of deionized water (C).

[0099] The granular hydrogel obtained through the above operations is spread on a stainless steel wire mesh with a mesh size of 850 micrometers, and then heated at 185°C. o The polymer was dried in a forced-air drying oven for 70 minutes. Then, the dried polymer was pulverized using a grinder and sieved using standard sieves with mesh sizes of 45 microns and 150 microns to obtain primary particles with a particle size of 45 microns to 150 microns.

[0100] (b) Reverse suspension polymerization step: Add 124.4 g of acrylic acid to a 500 ml Erlenmeyer flask, and add 189.9 g of 27% sodium hydroxide aqueous solution dropwise under ice-water bath conditions to neutralize 74% of the acrylic acid. Then add 0.192 g of potassium persulfate and 13.9 mg of N,N'-methylenebisacrylamide (product number: 14085E, purchased from Adamas Reagent Co., Ltd.) and dissolve them. Then add 20 g of water to prepare the monomer aqueous solution of step two.

[0101] Prepare a 1000mL five-necked detachable flask. Attach the reflux condenser, nitrogen inlet tube, and stirrer (an 80mm crescent-shaped impeller) to the flask. Place the entire flask in an oil bath and heat to 80°C. o C. Add 408 ml of n-heptane, 1.104 g of sucrose stearate (Mitsubishi Chemical Corporation, Ryoto sucrose ester S-370), and 1.104 g of maleic anhydride-modified ethylene-propylene copolymer (Mitsui Chemicals Corporation, Hi-wax 1105A) to the flask to dissolve the dispersant stabilizer. Adjust the rotation speed to 500 rpm, weigh 110 g of the primary particles obtained from the above aqueous phase polymerization and add them to the flask, then add 80 g of water.

[0102] The water bath temperature was lowered to 20°C, and the monomer aqueous solution from the second stage above was added to the flask. After the addition was completed, the air in the system was replaced with nitrogen for 30 minutes. Then the flask was immersed in a water bath at 70°C for 60 minutes to polymerize, and the slurry from step two was obtained through polymerization.

[0103] (c) Surface modification step: Place the slurry obtained in the above steps at 120°C. o In an oil bath of C, water and n-heptane were azeotropically reacted. While ensuring reflux of the n-heptane, 230g of water was removed from the system. Then, the oil bath temperature was lowered to 80°C. o C. Add 10.34 g of a 2% aqueous solution of ethylene glycol diglycidyl ether (product number: 38399B, purchased from Adamas Reagent Co., Ltd.) and maintain at 80 °C for 120 min. Dry by evaporating n-heptane, yielding 259.4 g of secondary particles obtained by the method described above. The median particle size of the secondary particles is 365.0 μm, and the particle size distribution is shown in Table 1. Mix 100 parts by weight of this absorbent resin with 0.3 parts by weight of AEROSIL 200 (gas-phase SiO2, Degussa) to obtain the final resin sample. The results of various performance measurements are shown in Table 2. The SEM image shows that the product comprises secondary particles formed by the agglomeration of numerous irregularly shaped primary particles.

[0104] Example 3

[0105] (a) Aqueous phase polymerization step: In a 2000ml PP beaker, add 174.78g of acrylic acid (purchased from Shanghai Huayi New Materials Co., Ltd.), 148.19g of deionized water, and 69.84g of 50wt% NaOH aqueous solution (purchased from Shanghai Chlor-Alkali Chemical Co., Ltd.). The NaOH solution needs to be added under strong stirring. During the addition of the NaOH solution, precipitates can be observed, but they gradually dissolve to form a transparent, homogeneous solution. The temperature of the material rises to 65°C. o C. This causes the material to cool to 56°C. o C, then add 23.59 g of polyethylene glycol diacrylate 400 (purchased from Chang Hsing Materials Industrial Co., Ltd., Taiwan, as a 4% aqueous solution) as an internal crosslinking agent. Then add 40... o After adding 71.79 g of a 50 wt% NaOH aqueous solution of C, the material temperature rose to 88°C due to the heat of neutralization. o C. Lower the temperature of the reaction solution to 78°C. o C. Add 11.32 g of a 3% sodium persulfate aqueous solution to obtain the monomer aqueous solution from step one, and stir for 2 seconds. Then, while stirring, quickly pour it into 25... Preheat 25cm to 105 oPlace the entire stainless steel tray (C) in a 105-meter range. o In an oven at temperature C, the polymerization reaction began after 20-30 seconds. During this reaction, water vapor was generated while the polymer expanded and foamed in all directions, then contracted and collapsed to a size slightly larger than the polymerization tray. Three minutes after the start of the polymerization reaction, the cross-linked polymer containing ribbon-like hydrogel morphology was removed from the polymerization tray. The peak polymerization temperature was 110°C. o C.

[0106] The hydrogel obtained from the above-mentioned aqueous phase polymerization reaction was broken down using a meat grinder (purchased from Zhengyuan Precision Machinery Co., Ltd., model RY-12S, 8mm aperture) to obtain granular hydrogel. During the gel breaking down process, a 90°C spray was continuously and uniformly applied to the gel. o Approximately 90g of deionized water (C).

[0107] The granular hydrogel obtained through the above operations is spread on a stainless steel wire mesh with a mesh size of 850 micrometers, and then heated at 185°C. o The polymer was dried in a forced-air drying oven for 70 minutes. Then, the dried polymer was pulverized using a grinder and sieved using standard sieves with mesh sizes of 45 microns and 150 microns to obtain primary particles with a particle size of 45 microns to 150 microns.

[0108] (b) Reverse suspension polymerization step: Add 124.4 g of acrylic acid to a 500 ml Erlenmeyer flask, and add 189.9 g of 27% sodium hydroxide aqueous solution dropwise under ice-water bath conditions to neutralize 74% of the acrylic acid. Then add 0.192 g of potassium persulfate and 13.9 mg of N,N'-methylenebisacrylamide (product number: 14085E, purchased from Adamas Reagent Co., Ltd.) and dissolve them. Then add 20 g of water to prepare the monomer aqueous solution of step two.

[0109] Prepare a 1000mL five-necked detachable flask. Attach the reflux condenser, nitrogen inlet tube, and stirrer (an 80mm crescent-shaped impeller) to the flask. Place the entire flask in an oil bath and heat to 80°C. o C. Add 408 ml of n-heptane, 1.104 g of sucrose stearate (Mitsubishi Chemical Corporation, Ryoto sucrose ester S-370), and 1.104 g of maleic anhydride-modified ethylene-propylene copolymer (Mitsui Chemicals Corporation, Hi-wax 1105A) to the flask to dissolve the dispersant stabilizer. Adjust the rotation speed to 500 rpm, weigh 110 g of the primary particles obtained from the above aqueous phase polymerization and add them to the flask, then add 120 g of water.

[0110] The water bath temperature was lowered to 20°C, and the monomer aqueous solution from the second stage above was added to the flask. After the addition was completed, the air in the system was replaced with nitrogen for 30 minutes. Then the flask was immersed in a water bath at 70°C for 60 minutes to polymerize, and the slurry from step two was obtained through polymerization.

[0111] (c) Surface modification step: Place the slurry obtained in the above steps at 120°C. o In an oil bath of C, water and n-heptane were azeotropically reacted. While ensuring reflux of the n-heptane, 230g of water was removed from the system. Then, the oil bath temperature was lowered to 80°C. o C. Add 10.34 g of a 2% aqueous solution of ethylene glycol diglycidyl ether (product number: 38399B, purchased from Adamas Reagent Co., Ltd.) and maintain at 80 °C for 120 min. Dry by evaporating n-heptane, yielding 266.9 g of secondary particles obtained by the method. The median particle size of the secondary particles is 390.7 μm, and the particle size distribution is shown in Table 1. Mix 100 parts by weight of this absorbent resin with 0.3 parts by weight of AEROSIL 200 (gas-phase SiO2, Degussa) to obtain the final resin sample. The results of various performance measurements are shown in Table 2. The SEM image shows that the product comprises secondary particles formed by the agglomeration of numerous irregularly shaped primary particles.

[0112] Example 4

[0113] (a) Aqueous Phase Polymerization Step: The polymerization reaction was carried out in a belt reactor. 154.8 g of acrylic acid (purchased from Shanghai Huayi New Materials Co., Ltd.), 0.62 g of crosslinking agent pentaerythritol triallyl ether (item number: 01140358, purchased from Adamas Reagent Co., Ltd.), and 343 g of deionized water were added and stirred, maintaining the temperature at 3°C. Nitrogen gas was introduced into the mixture to reduce the dissolved oxygen content to below 1 ppm. Then, while maintaining mixing, 0.6 g of 1% hydrogen peroxide aqueous solution, 1 g of 2% ascorbic acid aqueous solution, and 2.3 g of 2% 2,2-azobis[2-(imidazolin-2-yl)propane]dihydrochloride aqueous solution were added to initiate the polymerization reaction. After the mixture reached 90°C, polymerization was carried out at 90±2°C for approximately 5 hours to obtain a hydrogel.

[0114] After the polymerization reaction was completed, the hydrogel was crushed using a meat grinder (Zhengyuan Precision Machinery Co., Ltd., model RY-12S, 8mm pore size), and 108g of 48.5% sodium hydroxide aqueous solution was added for neutralization to obtain a neutralized gel.

[0115] The granular hydrogel obtained through the above operations is spread on a stainless steel wire mesh with a mesh size of 850 micrometers, and then heated at 185°C. oThe polymer was dried in a forced-air drying oven for 70 minutes. Then, the dried polymer was pulverized using a grinder and sieved using standard sieves with mesh sizes of 45 microns and 150 microns to obtain primary particles with particle sizes ranging from 45 microns to 150 microns.

[0116] (b) Reverse suspension polymerization. In this step, 124.4 g of acrylic acid was added to a 500 ml Erlenmeyer flask, and 189.9 g of 27% sodium hydroxide aqueous solution was added dropwise under ice-water bath conditions to neutralize 74% molar of acrylic acid. Then, 0.192 g of potassium persulfate and 13.9 mg of N,N'-methylenebisacrylamide (product number: 14085E, purchased from Adamas Reagent Co., Ltd.) were added and dissolved. Then, 20 g of water was added to prepare the monomer aqueous solution of step two.

[0117] Prepare a 1000mL detachable five-necked flask. Attach the reflux condenser, nitrogen inlet tube, and stirrer (an 80mm crescent-shaped impeller) to the flask. Place the entire flask in an oil bath and heat to 80°C. o C. Add 408 ml of n-heptane, 1.104 g of sucrose stearate (Mitsubishi Chemical Corporation, Ryoto sucrose ester S-370), and 1.104 g of maleic anhydride-modified ethylene-propylene copolymer (Mitsui Chemicals Corporation, Hi-wax 1105A) to the flask, and wait for the dispersant stabilizer to dissolve. Adjust the rotation speed to 500 rpm, weigh 110 g of the primary particles obtained from the polymerization of the aqueous solution in the above steps, add them to the flask, and add 100 g of water.

[0118] The water bath temperature was lowered to 20°C, and the monomer aqueous solution from step two was added to the detachable flask. After the addition was completed, the air in the system was immediately replaced with nitrogen for 30 minutes. Then the flask was immersed in a water bath at 70°C for 60 minutes to obtain the slurry from step two through polymerization.

[0119] (c) Surface modification step: Place the slurry from step two at 120°C. o In an oil bath of C, water and n-heptane were azeotropically reacted. While ensuring reflux of the n-heptane, 230g of water was removed from the system. Then, the oil bath temperature was lowered to 80°C. oC. Add 10.34 g of a 2% aqueous solution of ethylene glycol diglycidyl ether (product number: B38399B, purchased from Adamas Reagent Co., Ltd.) and maintain at 80 °C for 120 min. Then evaporate n-heptane for drying, and 244.1 g of secondary particles are obtained by the method described above. The median particle size of the secondary particles is 415.7 μm, and the particle size distribution is shown in Table 1. Mix 100 parts by weight of this absorbent resin with 0.3 parts by weight of AEROSIL 200 (gas-phase SiO2, Degussa) to obtain the final resin sample. The results of various performance tests are shown in Table 2. The SEM image shows that the product includes secondary particles formed by the agglomeration of a large number of irregularly shaped primary particles.

[0120] Comparative Example 1

[0121] In Comparative Example 1, a polymerization reaction design different from that of the present invention was used. Both polymerization steps were reverse-phase polymerizations using hydrocarbon solvents, and the median particle size and properties of the final polymerization product were characterized. Specifically, the following steps were used in this comparative example:

[0122] Step 1 (Polymerization reaction in nonpolar hydrocarbon solvents): Add 88.88 g of acrylic acid to a 500 ml Erlenmeyer flask. Under ice-water bath conditions, add 164.5 g of a 22% by mass sodium hydroxide aqueous solution dropwise to neutralize 74% molar acrylic acid. Then, add 0.132 g of potassium persulfate and 8.9 mg of N,N'-methylenebisacrylamide (product number: 14085E, purchased from Adamas Reagent Co., Ltd.) to the flask and dissolve them. Finally, add 20 g of water to the flask to prepare the monomer aqueous solution for the first stage.

[0123] Prepare a 1000mL detachable five-necked flask. Attach the reflux condenser, nitrogen inlet tube, and stirrer (an 80mm crescent-shaped impeller) to the flask. Place the entire flask in an oil bath and heat to 80°C. o C. Add 408 ml of n-heptane to the flask, start the stirrer, and adjust the stirring speed to 400 rpm. Add 1.104 g of sucrose stearate and 1.104 g of maleic anhydride-modified ethylene-propylene copolymer (model: Hi-wax1105A, purchased from Mitsui Chemicals Co., Ltd.) to the flask, and wait for the dispersion stabilizer to dissolve. Reduce the oil bath temperature to 50°C. o C. Add the monomer aqueous solution prepared as described above in the first stage to the above-mentioned detachable flask, immediately replace the air in the system with nitrogen, and after the addition is completed, immerse the flask in 70°C water. o The mixture was heated in an oil bath at temperature C to carry out a polymerization reaction for 60 minutes, yielding a first-stage slurry. After the reaction was complete, the oil bath was cooled to 20°C. o C.

[0124] Step 2: Prepare another 500ml Erlenmeyer flask. Add 124.4g of acrylic acid to the flask. Under ice-water bath conditions, add 189.9g of 27% sodium hydroxide aqueous solution dropwise to neutralize 74% of the acrylic acid. Then, add 0.192g of potassium persulfate and 13.9mg of N,N'-methylenebisacrylamide (product number: 14085E, purchased from Adamas Reagent Co., Ltd.) to the flask and dissolve them. Finally, add 20g of water to prepare the monomer aqueous solution for the second stage.

[0125] The monomer aqueous solution from the second stage was added to the detachable flask containing the slurry from the first stage, while simultaneously purging the air in the system with nitrogen. After the addition was complete, the reaction flask was immersed in 70°C water. o The second stage of polymerization was carried out by heating in an oil bath at C for 60 minutes, and a slurry of the second stage was obtained through polymerization.

[0126] Step 3 (Modification Step): Place the polymerized slurry obtained in Step 2 at 120°C. o In an oil bath of C, water and n-heptane are azeotropically mixed. While ensuring reflux of n-heptane, 300g of water is removed from the system, and the oil bath temperature is then lowered to 80°C. o C. Add 10.34 g of a 2% aqueous solution of ethylene glycol diglycidyl ether (product number: B38399B, purchased from Adamas Reagent Co., Ltd.) to a flask and maintain at 80 °C for 120 min. Then evaporate n-heptane for drying, and obtain 180.4 g of secondary particles by the above method. The median particle size of the secondary particles is 384.2 μm, and the particle size distribution is shown in Table 1. Mix 100 parts by weight of this absorbent resin with 0.3 parts by weight of AEROSIL 200 (gas-phase SiO2, Degussa) to obtain the final resin sample. The results of various performance tests are shown in Table 2.

[0127] Comparative Example 2

[0128] In Comparative Example 2, a polymerization reaction design different from that of the present invention was used. The polymerization product was prepared solely through aqueous solution polymerization. Surface modification was performed after the polymerization reaction, and the median particle size and properties of the polymerization product were characterized. Specifically, the following steps were performed in this comparative example:

[0129] In a 2000ml PP beaker, 174.78g of acrylic acid (purchased from Shanghai Huayi New Materials Co., Ltd.), 148.19g of deionized water, and 69.85g of a 50wt% NaOH aqueous solution (Shanghai Chlor-Alkali Chemical Co., Ltd.) were added. The NaOH solution was added under vigorous stirring. During the addition of the NaOH solution, precipitates were observed to form, but these precipitates gradually dissolved to form a transparent, homogeneous solution. The temperature rose to 65°C. o C. This cools the material in the beaker to 56°C. o C, then add 23.59g of a 4% aqueous solution of polyethylene glycol diacrylate 400 (Chang Hsing Materials Industrial Co., Ltd., Taiwan) as an internal crosslinking agent to the beaker. Then add 40... o 71.79 g of a 50 wt% NaOH aqueous solution of C was added. After the addition was complete, the temperature of the material in the beaker was observed to rise to 88°C due to the heat of neutralization. o C. Lower the temperature of the reaction solution in the beaker to 78°C. o C, then add 11.32g of a 3% sodium persulfate aqueous solution to prepare the first-stage monomer aqueous solution. Stir the monomer aqueous solution for 2 seconds, then quickly stir and pour into 25 Preheat 25cm to 105 o The entire tray is placed in a stainless steel tray of size C, at 105°C. o In an oven at temperature C, the polymerization reaction began after 20-30 seconds. During this reaction, water vapor was generated while the polymer expanded and foamed in all directions, then contracted and collapsed to a size slightly larger than the polymerization tray. Three minutes after the start of the polymerization reaction, the cross-linked polymer containing the ribbon-like hydrogel was removed from the polymerization tray. The peak polymerization temperature was 110°C. o C.

[0130] The hydrogel obtained from the above polymerization reaction was broken down using a meat grinder (Zhengyuan Precision Machinery Co., Ltd., model RY-12S, 8mm aperture) to obtain granular hydrogel. During the gel breaking down process, a spray at a temperature of 90°C was continuously sprayed onto the gel. o Approximately 90g of deionized water (C).

[0131] The granular hydrogel obtained through the above operations is spread on a stainless steel wire mesh with a mesh size of 850 micrometers, and then heated at 185°C. o The polymer was dried in a forced-air drying oven for 70 minutes. The dried polymer was then pulverized using a grinder and sieved using standard sieves with mesh sizes of 150 micrometers and 600 micrometers to obtain particles with diameters ranging from 150 micrometers to 600 micrometers.

[0132] 0.6 parts by weight of methanol, 0.06 parts by weight of ethylene glycol diglycidyl ether, and 4 parts by weight of deionized water were mixed to obtain a surface crosslinking solution. 100g of the above-obtained absorbent resin particles were added to a stirred tank at 500 rpm. Then, 4.67g of the surface crosslinking solution was sprayed into the mixer to obtain a coated wet material. The coated wet material was then spread evenly on a tray and placed in an 80°C oven for 60 minutes to perform surface crosslinking, thus obtaining an absorbent resin. 100 parts by weight of this absorbent resin were mixed with 0.3 parts by weight of AEROSIL 200 (vapor-phase SiO2, Degussa) to obtain the final resin sample. The median particle size of the particles obtained by this method was 351.7 μm, and the particle size distribution results are shown in Table 1. The results of various performance measurements are shown in Table 2.

[0133] Comparative Example 3

[0134] In Comparative Example 3, a polymerization reaction design different from that of the present invention was used. The polymerization product was prepared solely through aqueous solution polymerization. Surface modification was performed after the polymerization reaction, and the median particle size and properties of the polymerization product were characterized. Specifically, the following steps were performed in this comparative example:

[0135] 154.8 g of acrylic acid, 0.62 g of crosslinking agent pentaerythritol triallyl ether (product number: 01140358, purchased from Adamas Reagent Co., Ltd.), and 343 g of deionized water were mixed and stirred together, and the temperature of the mixture was maintained at 3°C. o C. Nitrogen gas is introduced into the mixture to reduce the dissolved oxygen content to below 1 ppm. While continuing mixing, 0.6 g of a 1% hydrogen peroxide aqueous solution, 1 g of a 2% ascorbic acid aqueous solution, and 2.3 g of a 2% 2% 2,2-azobis[2-(imidazolin-2-yl)propane]dihydrochloride aqueous solution are added to initiate polymerization. The temperature of the mixture reaches 90°C. o After C, at 90±2 o Polymerization was continued at temperature C for approximately 5 hours to obtain a hydrogel. The hydrogel was then crushed using a meat grinder (Zhengyuan Precision Machinery Co., Ltd., model RY-12S, 8mm pore size), and 108g of a 48.5% sodium hydroxide aqueous solution was added to neutralize it, resulting in a neutralized gel.

[0136] The granular hydrogel obtained through the above operations is spread on a stainless steel wire mesh with a mesh size of 850 micrometers, and then heated at 185°C. o The polymer was dried in a forced-air drying oven for 70 minutes. Then, the dried polymer was pulverized using a grinder and sieved using standard sieves with mesh sizes of 150 micrometers and 600 micrometers to obtain primary particles with particle sizes ranging from 150 micrometers to 600 micrometers.

[0137] 0.6 parts by weight of methanol, 0.06 parts by weight of ethylene glycol diglycidyl ether, and 4 parts by weight of deionized water were mixed to obtain a surface crosslinking solution. 100g of the above-obtained absorbent resin particles were added to a stirred tank at 500 rpm. Then, 4.67g of the surface crosslinking solution was sprayed into the mixer to obtain a coated wet material. The coated wet material was then spread evenly on a tray and placed in an 80°C oven for 60 min to perform surface crosslinking, thus obtaining the absorbent resin. The median particle size of the particles obtained by this method was 368.9 μm, and the particle size distribution is shown in Table 1. 100 parts by weight of the absorbent resin were mixed with 0.3 parts by weight of AEROSIL 200 (vapor-phase SiO2, Degussa) to obtain the final resin sample. The results of various performance tests are shown in Table 2.

[0138] Comparative Example 4

[0139] In this Comparative Example 4, a polymerization reaction design different from that of the present invention was used, and surface modification was performed between the aqueous polymerization step and the reverse suspension polymerization step, as well as after the reverse suspension polymerization reaction.

[0140] (a) Aqueous phase polymerization step: In a 2000ml PP beaker, add 174.78g of acrylic acid (purchased from Shanghai Huayi New Materials Co., Ltd.), 148.19g of deionized water, and 69.84g of 50wt% NaOH aqueous solution (purchased from Shanghai Chlor-Alkali Chemical Co., Ltd.). The NaOH solution needs to be added under strong stirring. During the addition of the NaOH solution, precipitates can be observed, but they gradually dissolve to form a transparent, homogeneous solution. The temperature of the material rises to 65°C. o C. This causes the material to cool to 56°C. o C, then add 23.59 g of polyethylene glycol diacrylate 400 (purchased from Chang Hsing Materials Industrial Co., Ltd., Taiwan, as a 4% aqueous solution) as an internal crosslinking agent. Then add 40... o After adding 71.79 g of a 50 wt% NaOH aqueous solution of C, the material temperature rose to 88°C due to the heat of neutralization. o C. Lower the temperature of the reaction solution to 78°C. o C. Add 11.32 g of a 3% sodium persulfate aqueous solution to obtain the monomer aqueous solution from step one, and stir for 2 seconds. Then, while stirring, quickly pour it into 25... Preheat 25cm to 105 o Place the entire stainless steel tray (C) in a 105-meter range. oIn an oven at temperature C, the polymerization reaction began after 20-30 seconds. During this reaction, water vapor was generated while the polymer expanded and foamed in all directions, then contracted and collapsed to a size slightly larger than the polymerization tray. Three minutes after the start of the polymerization reaction, the cross-linked polymer containing ribbon-like hydrogel morphology was removed from the polymerization tray. The peak polymerization temperature was 110°C. o C.

[0141] The hydrogel obtained from the above-mentioned aqueous phase polymerization reaction was broken down using a meat grinder (purchased from Zhengyuan Precision Machinery Co., Ltd., model RY-12S, 8mm aperture) to obtain granular hydrogel. During the gel breaking down process, a 90°C spray was continuously and uniformly applied to the gel. o Approximately 90g of deionized water (C).

[0142] The granular hydrogel obtained through the above operations is spread on a stainless steel wire mesh with a mesh size of 850 micrometers, and then heated at 185°C. o The polymer was dried in a forced-air drying oven for 70 minutes. Then, the dried polymer was pulverized using a grinder and sieved using standard sieves with mesh sizes of 45 microns and 150 microns to obtain primary particles with a particle size of 45 microns to 150 microns.

[0143] (b) Surface modification steps:

[0144] Prepare five 1000mL detachable flasks and install a reflux condenser, nitrogen inlet tube, and a stirring paddle (80mm diameter crescent-shaped paddle) on the flasks. Add 408mL of n-heptane, 1.104g of sucrose stearate (Mitsubishi Chemical Corporation, Ryoto sucrose ester S-370), and 1.104g of maleic anhydride-modified ethylene-propylene copolymer (Mitsui Chemicals Corporation, Hi-wax 1105A) to the flasks. Immerse the flasks in a water bath and heat to 80°C. Wait for the dispersant stabilizer to dissolve and the solution to become clear. Add 110g of primary particles, set the stirring speed to 400rpm to disperse the particles, add 32.49g of water, and continue dispersing for 15 minutes. 4.36 g of a 2% aqueous solution of ethylene glycol diglycidyl ether (product number: 38399B, purchased from Adamas Reagent Co., Ltd.) was added, and the mixture was kept at this temperature for 120 min. After the reaction was completed, 63.24 g of water was added. The primary particles obtained by this method have completed the surface crosslinking reaction.

[0145] (c) Reverse suspension polymerization step: Add 124.4 g of acrylic acid to a 500 ml Erlenmeyer flask, and add 189.9 g of 27% sodium hydroxide aqueous solution dropwise under ice-water bath conditions to neutralize 74% of the acrylic acid. Then add 0.192 g of potassium persulfate and 13.9 mg of N,N'-methylenebisacrylamide (item number: 14085E, purchased from Adamas Reagent Co., Ltd.) and dissolve them. Then add 20 g of water to prepare the monomer aqueous solution of step (c).

[0146] The water bath temperature of the mixture obtained in step (b) was lowered to 20°C, and the monomer aqueous solution from step (c) described above was added to the flask. After the addition was completed, the air in the system was replaced with nitrogen for 30 minutes. Then the flask was immersed in a water bath at 70°C for 60 minutes.

[0147] (d) Surface modification step: The polymerized slurry obtained in step (c) is placed at 120°C. o In an oil bath of C, water and n-heptane are azeotropically mixed. While ensuring reflux of n-heptane, 300g of water is removed from the system, and the oil bath temperature is then lowered to 80°C. o C. Add 10.34 g of a 2% aqueous solution of ethylene glycol diglycidyl ether (product number: B38399B, purchased from Adamas Reagent Co., Ltd.) to a flask and maintain at 80 °C for 120 min. Then evaporate n-heptane for drying, and 260.4 g of secondary particles are obtained by the above method. The median particle size of the secondary particles is 382.3 μm, and the particle size distribution is shown in Table 1. Mix 100 parts by weight of this absorbent resin with 0.3 parts by weight of AEROSIL 200 (gas-phase SiO2, Degussa) to obtain the final resin sample. The results of various performance tests are shown in Table 2.

[0148] The particle size distribution of the absorbent resins obtained in the above embodiments and comparative embodiments is shown in Table 1, and the properties are shown in Table 2.

[0149] Table 1

[0150]

[0151] Table 2

[0152]

[0153] The SAP particles obtained by the method of this invention are composed of irregularly shaped small particles aggregated together. These irregular small particles are the primary particles obtained from the first stage of polymerization, crushing, and classification. During the second stage of polymerization, the molecular chains formed by the polymerization of the newly added second polymerizing monomer link these primary particles together, forming particles such as... Figure 1A and 1BThe final secondary particle morphology is shown. As can be seen from the comparison of the examples and comparative examples, the method of the present invention can significantly improve both the product's permeability and its brine absorption rate.

Claims

1. A method for preparing a water-absorbing resin, the method comprising the following steps: Step 1: The first monomer undergoes a first polymerization reaction in an aqueous solution to obtain a prepolymer, wherein the first monomer is acrylic acid; in Step 1, an initiator is used, which is a combination of hydrogen peroxide, ascorbic acid, and 2,2-azobis[2-(imidazolin-2-yl)propane]dihydrochloride, and the amount of the initiator is 0.005-1 mol% based on 100 mol% of the total molar amount of the first monomer; an internal crosslinking agent is also used in Step 1, which is pentaerythritol triallyl ether; the amount of the internal crosslinking agent used in Step 1 is 0.002-1 mol% based on 100 mol% of the total molar amount of the first monomer; Step 1 is carried out at a temperature of 85-95°C; an alkaline reagent is added to the polymerization reaction system; After step one and before step two, the prepolymer obtained in step one is crushed and sieved to obtain the first primary particles of prepolymer with a median particle size of greater than or equal to 45 micrometers and less than 150 micrometers, which are then used in step two. Step 2: A dispersion of the prepolymer in a nonpolar solvent is formed. A second polymeric monomer is added to the dispersion to carry out a second polymerization reaction, yielding an intermediate resin. The second polymeric monomer is acrylic acid. In Step 2, a free radical initiator, which is persulfate, is used. In Step 2, based on a total molar amount of the second polymeric monomer of 100 mol%, the amount of the free radical initiator is 0.005-1 mol%. In Step 2, an internal crosslinking agent, N,N'-methylenebisacrylamide, is used. Based on a total molar amount of the second polymeric monomer of 100 mol%, the amount of the internal crosslinking agent used in Step 2 is 0.002-1 mol%. Step 2 is carried out at a temperature of 65-75°C. An alkaline reagent is added to the polymerization reaction system. The alkaline reagent added in steps one and two is an alkali metal hydroxide or ammonium hydroxide; the amount of alkaline reagent added is 30-80 mol% to neutralize the acidic groups in all monomers; The weight ratio of the first polymeric monomer to the second polymeric monomer is 4:3 to 1:1; Step 3: Modify the intermediate resin with a surface crosslinking agent to obtain the water-absorbing resin; the temperature of step 3 is 75-85℃; the surface crosslinking agent is a polyol polyglycidyl ether, and the amount of the surface crosslinking agent is 0.001-1% by weight, based on 100% by weight of the total weight of the second polymerizing monomer. After step three, an inorganic additive is added. This inorganic additive is selected from silica, talc, zeolite, and alumina powder. Based on 100 parts by weight of the absorbent resin, the content of the inorganic additive is 0.01-5 parts by weight. No surface crosslinking agent was used for modification before step three was performed; The water-absorbing resin is in the form of secondary particles formed by the aggregation of second primary particles, wherein the median particle size of the secondary particles is 250-500 micrometers and the median particle size of the second primary particles is 15-150 micrometers.

2. The method as described in claim 1, characterized in that, In steps one and two, a dispersion stabilizer may optionally be used; In step two, the nonpolar solvent is selected from one or more of the following: n-hexane, n-heptane, cyclohexane, toluene, and xylene.

3. The method as described in claim 1, characterized in that, Step one is carried out at a temperature of 85-95°C, so that 60-100% of the first polymerizable monomers are polymerized.

4. An absorbent product, said product comprising: Disposable diapers, sanitary napkins, adult incontinence pads, absorbent paper, paper napkins, disposable mattress pads, soil moisturizing materials, leak sealing materials, water-blocking materials, sewage treatment materials, and mud solidification materials; At least a portion of the absorbent product comprises an absorbent resin prepared by any one of claims 1-3.

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