Superabsorbent resin, and preparation method therefor and use thereof

Abstract

The present application provides a superabsorbent resin, and a preparation method therefor and the use thereof. The preparation method comprises: step 1, subjecting a first polymerizable monomer to a first polymerization reaction in an aqueous solution phase, so as to obtain a prepolymer; step 2, forming a dispersion of the prepolymer in a non-polar solvent, adding a second polymerizable monomer to the dispersion, and performing a second polymerization reaction, so as to obtain an intermediate resin; and step 3, modifying the intermediate resin by using a surface crosslinking agent, so as to obtain the absorbent resin. In the present application, a superabsorbent resin having a higher water absorption rate and high liquid permeability is synthesized by means of a simple and low-cost process design.

Description

Superabsorbent resin, method for producing the same, and use thereof TECHNICAL FIELD

[0001] The present application relates to the field of polymers, and more particularly to a superabsorbent resin, a method for producing the same, and a product manufactured using the superabsorbent resin. BACKGROUND

[0002] Superabsorbent resin (SAP) is a kind of polymer compound with strong water absorption and water retention capacity, which is widely used in the field of sanitary materials such as paper diapers, sanitary napkins, water-blocking materials for cables, sewage treatment materials, and water-retaining agents for agriculture, forestry, and gardening. With the high performance of paper diapers as its main use, people hope that the superabsorbent resin has more excellent functions, especially high water absorption ratio, high water absorption speed, high water absorption ratio under high pressure, high liquid permeability, low content of eluate, and low content of residual monomer.

[0003] In order to meet the above increasingly stringent requirements, relevant enterprises and research institutions are constantly developing new SAP materials and their synthesis processes. For example, many different polymerization processes have been developed in the past to synthesize SAP materials, and various adjustments have been made to the reaction raw materials, additives, and process conditions in an attempt to improve the performance of the final SAP materials. Unfortunately, the final results have always been unsatisfactory, for example, the products always have poor water absorption rate and liquid permeability, and one or more of the following defects: high content of eluate, high content of residual monomer, complex synthesis process, high production cost, long reaction time, waste of catalyst and other raw materials, environmental pollution caused by waste materials, etc.

[0004] Therefore, it is urgent to develop a new technology for preparing SAP materials that can have more excellent water absorption rate and liquid permeability, and preferably can also solve one or more of the other defects described above, and most preferably can solve all the defects described above.

[0005] SUMMARY

[0006] In view of the above problems, the inventors of the present application have conducted extensive and in-depth research and unexpectedly developed the method of the present application, which effectively solves the long-standing problems in the prior art.

[0007] The first aspect of the present application provides a method for preparing a superabsorbent resin, the method comprising the following steps:

[0008] Step 1: causing a first polymerization reaction of a first polymerization monomer in an aqueous solution phase to obtain a prepolymer;

[0009] Step two: forming a dispersion of the prepolymer in a non-polar solvent, adding a second polymerization monomer to the dispersion, and performing a second polymerization reaction to produce an intermediate resin;

[0010] Step three: modifying the intermediate resin with a surface crosslinking agent to produce the water-absorbing resin; and

[0011] The first and second polymerization monomers are each a compound comprising at least one carbon-carbon double bond and at least one active group, and the first and second polymerization monomers are the same or different.

[0012] According to one embodiment of the first aspect of the present application, the intermediate resin is not modified with a surface crosslinking agent prior to performing the step three.

[0013] According to another embodiment of the first aspect of the present application, the surface crosslinking agent is a polyol poly(glycidyl ether).

[0014] According to another embodiment of the first aspect of the present application, one or more internal crosslinking agents are optionally used in the step one and / or step two, and the internal crosslinking agent is selected from one or more of the following: poly(unsaturated carboxylic acid) polyol ester, polyacrylamide, poly(carbamoyl (meth)acrylate), allylated starch, allylated cellulose, polycarboxylic acid poly(allyl ester), isocyanuric acid polyallyl ester, polyvinyl aromatic compound, polyol poly(allyl) ether.

[0015] According to another embodiment of the first aspect of the present application, the first and second polymerization monomers are the same or different from each other, and each is independently selected from one or more of the following: (meth)acrylic acid, C1-C12 alkyl (meth)acrylate, C1-C12 hydroxyalkyl (meth)acrylate, C2-C12 alkylsulfonyl (meth)acrylate, C2-C12 alkylsulfonyl (meth)acrylamide, hydroxyalkyl (meth)acryloyl phosphate, itaconic acid, cinnamic acid, vinylsulfonic 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, thiol-containing unsaturated monomer, phenolic hydroxyl-containing unsaturated monomer, N-vinyl pyrrolidone.

[0016] According to another embodiment of the first aspect of the present application, the molar ratio of the first polymerization monomer to the second polymerization monomer is 1:10 to 10:1.

[0017] According to another embodiment of the first aspect of the present application, the pre-polymer obtained in step one is subjected to pulverization and sieving to obtain a first primary particle of the pre-polymer having a median particle diameter of greater than or equal to 10 micrometers and less than 150 micrometers, which is used in step two, after step one and before step two.

[0018] According to another embodiment of the first aspect of the present application, in said step one and step two, one or more selected from the group consisting of an initiator, a dispersion stabilizer, a basic agent is optionally used.

[0019] According to another embodiment of the first aspect of the present application, in said step two, the non-polar solvent is selected from one or more of the group consisting of n-hexane, n-heptane, cyclohexane, toluene and xylene.

[0020] According to another embodiment of the first aspect of the present application, an inorganic additive is added before, after or during one or more of steps one to three.

[0021] According to another embodiment of the first aspect of the present application, the water-absorbent resin is in the form of secondary particles obtained by agglomeration of second primary particles, the secondary particles having a median particle diameter of 250-500 micrometers, and the second primary particles having a median particle diameter of 15-150 micrometers.

[0022] According to another embodiment of the first aspect of the present application, said step one is performed at a temperature of 45-120°C, so that 60-100% of the first polymerizable monomer is polymerized.

[0023] According to another embodiment of the first aspect of the present application, said step two is performed at a temperature of 60-95°C.

[0024] According to another embodiment of the first aspect of the present application, said step three is performed at a temperature of 50-100°C, and the surface crosslinking agent is used in an amount of 0.001-1% by weight based on 100% by weight of the total amount of the second polymerizable monomer.

[0025] The second aspect of the present application provides a water-absorbent product, which includes: a paper diaper, a sanitary napkin, an adult care pad, an absorbent paper, a paper towel, a disposable bed pad, a soil moisture retaining material, a leak stopping material, a sewage treatment material, a slurry solidifying material; at least a portion of the water-absorbent product contains the water-absorbent resin prepared by the method of the present application.

[0026] In the detailed description of the application hereinafter, the method, raw materials, process conditions and products of the present application are further described in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS

[0027] [Corrected according to Rule 91 on 04.11.2024] FIG. 1A and FIG. 1B show SEM images of SAP particles prepared in accordance with embodiments of the present application. DETAILED DESCRIPTION

[0028] The ranges disclosed herein are presented in terms of "about" a value and "about" a range. When the term "about" is used, it is intended to encompass numbers, which are preciously approximated to the exact value or range in some way. For example, if a range is stated as "about 0-5", it is intended to encompass, for example, a range of 0-5, 0-4, 0-3, 0-2, 0-1, 1-5, 2-5, 3-5, 4-5, 0-1.5, 1.5-5, 3-4, 3.5-4.5, 3.8-4.2, etc.

[0029] In the present application, unless otherwise stated, the numerical range "a-b" represents a shorthand for the full set of real combinations of a to b, wherein a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" have been listed herein, and "0-5" is just a shorthand for these combinations of numbers.

[0030] In the present application, unless otherwise stated, all embodiments and preferred embodiments mentioned herein can be combined with each other to form new technical solutions.

[0031] In the present application, unless otherwise stated, all technical features and preferred features mentioned herein can be combined with each other to form new technical solutions.

[0032] In the present application, unless otherwise stated, "comprising" mentioned herein represents open-ended, and can also be closed. For example, the "comprising" can mean that it can also contain other components not listed, or can only include the listed components.

[0033] According to one technical solution of the present application, the method of the present application comprises the following steps: step one: a first polymerization reaction of a first polymerization monomer occurs in an aqueous solution phase to obtain a prepolymer; step two: a dispersion of the prepolymer in a non-polar solvent is formed, and a second polymerization monomer is added to the dispersion to perform a second polymerization reaction to prepare an intermediate resin; step three: the intermediate resin is modified with a surface crosslinking agent to prepare the water-absorbing resin.

[0034] One of the invention points of the present application is that, in a step-by-step manner, by combining aqueous phase polymerization and reverse phase polymerization, in the aqueous phase polymerization, the first polymerization monomer undergoes a first polymerization reaction to form first primary particles (particles). In the reverse phase polymerization, the newly added second polymerization monomer undergoes polymerization in the presence of the first primary particles to form second primary particles and agglomerate the second primary particles with each other, and finally form secondary particles. As shown in FIGS. 1A and 1B, the SAP particles of the present application include secondary particles formed by agglomeration of primary particles (second primary particles).

[0035] Another aspect point of the present application is that the applicant surprisingly found that, after the reverse phase polymerization, i.e., after the formation of the "secondary particles", using a surface crosslinking agent to perform surface modification on the secondary particles can significantly improve the water absorption rate and liquid permeability of the product. However, in the prior art, there is a technical prejudice that the operation of surface modification using a surface crosslinking agent should be performed before the formation of the secondary particles, and not after the formation of the secondary particles. If it is performed after the formation of the secondary particles, it cannot bring about significant performance improvement, and may even adversely affect the water absorption. The present application is obtained after overcoming the above technical prejudice, and achieves a completely unexpected technical effect.

[0036] According to one embodiment of the present application, in the above-mentioned step one and / or step two, one or more internal crosslinking agents can be optionally used during the polymerization reaction.

[0037] In the present application, the "internal crosslinking agent" refers to a crosslinking agent that exists in the polymerization reaction system during the polymerization to form the first primary particles (for the first step), the second primary particles, and the secondary particles (for the second step), and crosslinks the polymer chains while forming the polymer chains, thereby promoting the formation of the first primary particles and / or the second primary particles and / or the secondary particles.

[0038] The "surface crosslinking agent" is applied to the already formed secondary particles after the formation of the secondary particles, and in the third step of "modification" using the surface crosslinking agent, no polymerization reaction related to the primary particles and / or the secondary particles occurs.

[0039] According to one embodiment of the present application, the surface crosslinking agent is a polyol poly(glycidyl ether). The polyol therein refers to a C2-C16 polyol or a polymeric polyol containing two or more hydroxyl groups, for example, the polyol includes ethylene glycol, polyethylene glycol, propylene glycol, polypropylene glycol, poly(ethylene oxide) glycol, poly(ethylene oxide) glycol, butylene glycol, polybutylene glycol, glycerol, pentaerythritol, trimethylolpropane, and the like. Two or more, for example, two, three, four, five, six, or all of the hydroxyl groups in the polyol are linked to a corresponding number of glycidyl groups via ether bonds, thereby forming the polyol poly(glycidyl ether) of the present application. According to one exemplary embodiment of the present 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, poly(ethylene oxide) glycol diglycidyl ether, poly(ethylene oxide) glycol diglycidyl ether, butylene glycol diglycidyl ether, polybutylene glycol diglycidyl ether, glycerol triglycidyl ether, pentaerythritol tetraglycidyl ether, trimethylolpropane triglycidyl ether, and the like. In the third step, the surface crosslinking agent can be applied directly to the slurry prepared in step two, or the surface crosslinking agent and optional other components can be formulated into a solution, for example, an aqueous solution, and then added to the slurry prepared in step two.

[0040] According to one embodiment of the present application, the amount of the surface crosslinking agent can be 0.001-1 mole %, for example, can be within a range of any two of the following values in combination: 0.001 mole %, 0.002 mole %, 0.005 mole %, 0.006 mole %, 0.008 mole %, 0.01 mole %, 0.02 mole %, 0.05 mole %, 0.06 mole %, 0.08 mole %, 0.1 mole %, 0.3 mole %, 0.5 mole %, 0.6 mole %, 0.8 mole %, 0.9 mole %, 1 mole %, based on 100 mole % of the total moles of the first and second polymerizable monomers.

[0041] According to one embodiment of the present application, the internal crosslinking agent is used in step one, or in step two, or in both step one and step two. The internal crosslinking agent is selected from one or more of the following: poly (unsaturated carboxylic acid) polyol ester, polyacrylamide, poly (carbamoyl (meth) acrylate), allylated starch, allylated cellulose, polycarboxylic acid poly (allyl ester), isocyanuric acid polyallyl ester, polyvinyl aromatic compound, polyol poly (allyl) ether. Wherein polyol means a C2-C16 polyol or polymeric polyol containing two or more hydroxyl groups, for example the polyol includes ethylene glycol, polyethylene glycol, propylene glycol, polypropylene glycol, polyethylene oxide glycol, polypropylene oxide glycol, butylene glycol, polybutylene glycol, glycerol, pentaerythritol, trimethylolpropane, and the like. For example, the internal crosslinking agent can be selected from one or more of the following: poly [(meth) acrylate] polyol ester, poly (maleic acid) polyol ester, poly (fumaric acid) polyol ester; di (carbamoyl (meth) acrylate) s obtained by reacting a polyisocyanate such as toluene diisocyanate or hexamethylene diisocyanate with hydroxyethyl (meth) acrylate; allylated starch; allylated cellulose; diallyl phthalate; N,N',N"-triallylisocyanuric acid; divinylbenzene; pentaerythritol triallyl ether; polyethyleneimine, and the like. Preferably, the internal crosslinking agent is selected from one or more of the following: N,N'-methylenebisacrylamide, polyethylene glycol diacrylate, pentaerythritol triallyl ether.

[0042] According to one embodiment of the present application, when an internal crosslinking agent is used in step one, the amount of the internal crosslinking agent used in the first step can be 0.002-1 mole %, for example, can be within the range of values obtained by combining any two of the following values with each other: 0.002 mole %, 0.005 mole %, 0.006 mole %, 0.008 mole %, 0.01 mole %, 0.02 mole %, 0.05 mole %, 0.06 mole %, 0.08 mole %, 0.1 mole %, 0.3 mole %, 0.5 mole %, 0.6 mole %, 0.8 mole %, 0.9 mole %, 1 mole %, based on 100 mole % of the total moles of the first polymerization monomers.

[0043] According to another embodiment of the present application, when an internal crosslinking agent is used in step two, the amount of the internal crosslinking agent used in the second step can be 0.002-1 mole %, for example, can be within any two of the following values combined: 0.002 mole %, 0.005 mole %, 0.006 mole %, 0.008 mole %, 0.01 mole %, 0.02 mole %, 0.05 mole %, 0.06 mole %, 0.08 mole %, 0.1 mole %, 0.3 mole %, 0.5 mole %, 0.6 mole %, 0.8 mole %, 0.9 mole %, 1 mole %, based on 100 mole % of the total moles of the second polymerization monomers.

[0044] According to one embodiment of the present application, the first polymerization monomers used in step one and the second polymerization monomers used in step two can be the same or different from each other, each comprising at least one carbon-carbon double bond and at least one active group, which can be a carboxyl group, a hydroxyl group, an amino group, an amide group, a sulfonic acid group, a mercapto group, and the like. For example, the first and second polymerization monomers can each independently be selected from one or more of the following: (meth)acrylic acid, C1-C12 alkyl (meth)acrylate, C1-C12 hydroxyalkyl (meth)acrylate, C2-C12 alkyl (meth)acryloyl sulfonate, C2-C12 alkyl sulfonic acid (meth)acrylamide, 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-containing unsaturated monomers, phenolic hydroxyl group-containing unsaturated monomers, N-vinyl pyrrolidone. According to one exemplary embodiment, the first and second polymerization 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 toluene sulfonic acid, vinyl toluene sulfonic acid, styrene sulfonic acid, 2-(meth)acrylamido-2-methylpropane sulfonic acid, 2-(meth)acryloyl ethane sulfonic acid, 2-(meth)acryloyl propane sulfonic acid, 2-hydroxyethyl (meth)acryloyl phosphate, and the like acid group-containing unsaturated monomers; (meth)acrylamide, N-ethyl (meth)acrylamide, N,N-dimethyl (meth)acrylamide, and the like amide group-containing unsaturated monomers; N,N-dimethylaminoethyl (meth)acrylate, N,N-dimethylaminopropyl (meth)acrylate, N,N-dimethylaminopropyl (meth)acrylamide, and the like amino group-containing unsaturated monomers; mercapto-containing unsaturated monomers; phenolic hydroxyl group-containing unsaturated monomers; N-vinyl pyrrolidone and the like lactam group-containing unsaturated monomers.

[0045] According to one embodiment of the present application, the weight ratio of the first polymerization monomer and the second polymerization monomer can be 1:10 to 10:1, for example, can be 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.

[0046] According to one embodiment of the present application, in the step one, a first monomer aqueous solution containing the first polymerization monomer and the first initiation system is prepared, and the aqueous solution of the first polymerization monomer is subjected to an aqueous solution polymerization reaction to obtain a primary polymer.

[0047] According to one embodiment of the present application, the step one is carried out at a temperature of 45-120°C, for example, the reaction temperature of the step one can be within the range of values obtained by combining any two of the following 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.

[0048] According to another embodiment of the present application, in the step one, 60-100% of the first polymerization monomer is subjected to polymerization, for example, 70-100% of the first polymerization monomer is subjected to polymerization, or 80-100% of the first polymerization monomer is subjected to polymerization, or 90-100% of the first polymerization monomer is subjected to polymerization.

[0049] According to one embodiment of the present application, after the preparation of the prepolymer, the prepolymer is dried, crushed and classified to obtain first primary particles, and the first primary particles are used in the step two. The first primary particles can be in the form of irregularly shaped particles with edges and corners.

[0050] According to one embodiment of the present application, the first primary particles have a median particle size of greater than or equal to 10 microns and less than 150 microns, for example, the first primary particles can have a median particle size within the range of values obtained by combining any two of the following values: 15 microns, 20 microns, 30 microns, 40 microns, 45 microns, 50 microns, 60 microns, 70 microns, 80 microns, 90 microns, 100 microns, 110 microns, 120 microns, 130 microns, 140 microns, 145 microns.

[0051] According to one embodiment of the present application, in step two, the first primary particles of the above-mentioned initial polymer are dispersed in a non-polar solvent containing a dispersion stabilizer, while a second monomer aqueous solution containing a second polymerization monomer and a second initiation system is prepared, and then the second monomer aqueous solution is added to the non-polar solvent of the first primary particles, and a reverse phase suspension polymerization reaction is carried out to obtain an intermediate resin. The intermediate resin contains secondary particles formed by agglomeration and stacking of the second primary particles.

[0052] Subsequently, in step three, the secondary particles of the intermediate resin are modified using a surface crosslinking agent to obtain the SAP particles of the present application. The temperature of step three can be 50-100°C, for example 60-90°C, or 75-85°C.

[0053] According to one embodiment of the present application, an inorganic additive such as silica, talc, zeolite, alumina powder, etc. can be added after step two or after step three, and the content of the inorganic additive can be 0.01-5 parts by mass based on 100 parts by mass of the weight of the SAP.

[0054] According to one embodiment of the present application, the secondary particles obtained by the method have a median particle size of 250-500 microns, preferably 300-450 microns, and more preferably 350-420 microns.

[0055] According to one embodiment of the present application, when the first monomer and the second monomer used in step one and step two have acid groups such as carboxyl groups and sulfonic acid groups, it can be necessary to add a basic agent (neutralizing agent) to the polymerization system, and for example, an alkali metal hydroxide or an ammonium hydroxide such as sodium hydroxide, potassium hydroxide, lithium hydroxide, ammonium hydroxide, etc. or a mixture of two or more of the above-mentioned bases can be used. According to one embodiment of the present application, the amount of the basic agent added should neutralize 10-100 mole % of the acid groups in all the monomers, for example 20-90 mole %, or 30-80 mole %.

[0056] In the first and second steps, an initiator such as a radical initiator can be added, examples of which can include persulfates (potassium persulfate, ammonium persulfate, and sodium persulfate, etc.), peroxides (butanone peroxide, methyl isobutyl ketone peroxide, di-t-butyl peroxide, t-butyl hydroperoxide, t-butyl peroxyacetate, t-butyl peroxyisobutyrate, t-butyl peroxyneopentanoate, and hydrogen peroxide, etc.), and azo compounds (2,2'-azobis[2-(N-phenylamidino)propane] dihydrochloride, 2,2'-azobis[2-(N-allylamidino)propane] dihydrochloride, 2,2'-azobis{2-[1-(2-hydroxyethyl)-2-imidazolin-2-yl]propane} dihydrochloride, 2,2'-azobis{2-methyl-N-[1,1-bis(hydroxymethyl)-2-hydroxyethyl]propionamide}, 2,2'-azobis[2-methyl-N-(2-hydroxyethyl)propionamide], and 4,4'-azobis(4-cyanopentanoic acid). The radical polymerization initiator can be used either alone or as a mixture of two or more. Preferably, the radical polymerization initiator is selected from one or more of potassium persulfate, ammonium persulfate, and sodium persulfate. The first initiator used in the first step and the second initiator used in the second step can be the same or different. The above radical polymerization initiator can be used in combination with sodium sulfite, sodium bisulfite, ferrous sulfate, and / or L-ascorbic acid as a redox polymerization initiator.

[0057] In the first step, the amount of the first initiator can be 0.005 to 1 mol% based on 100 mol% of the total moles of the first polymerization monomers, for example, can be within a range of values obtained by combining any two of the following 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%, and 1 mol%.

[0058] In the second step, the amount of the second initiator can be 0.005 to 1 mol% based on 100 mol% of the total moles of the second polymerization monomers, for example, can be within a range of values obtained by combining any two of the following 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%, and 1 mol%.

[0059] According to one embodiment of the present application, a dispersion stabilizer can be used in the first step and / or the second step. The dispersion stabilizer can include a surfactant, preferably a nonionic surfactant. The surfactant can be one or more selected from the group consisting of sucrose fatty acid ester, polyglycerol fatty acid ester, sorbitol fatty acid ester, polyoxyethylene sorbitol fatty acid ester, polyoxyethylene glycerol fatty acid ester, sorbitol fatty acid ester, polyoxyethylene sorbitol fatty acid ester, polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, polyoxyethylene castor oil, polyoxyethylene hardened castor oil, alkyl allyl formaldehyde-polyoxyethylene ether condensate, polyoxyethylene polyoxypropylene block copolymer, polyoxyethylene polyoxypropyl alkyl ether, polyethylene glycol fatty acid ester, alkyl glucoside, N-alkyl glucamide, polyoxyethylene fatty acid amide, polyoxyethylene alkyl amine, phosphate ester of polyoxyethylene alkyl ether, and phosphate ester of polyoxyethylene alkyl allyl ether. The surfactant as the dispersion stabilizer can be used alone or in a mixture of two or more simultaneously. From the viewpoint of dispersion stability of the monomer aqueous solution, one or more of sucrose fatty acid ester, polyglycerol fatty acid ester, sorbitol fatty acid ester, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene glycerol fatty acid ester, and polyoxyethylene hardened castor oil are preferred.

[0060] The dispersion stabilizer can also include a polymeric dispersant, or a polymeric dispersant can be used simultaneously with the above-mentioned surfactant. The polymeric dispersant used can be one of the following kinds: 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, and the like. The polymeric dispersant can be used alone or two or more simultaneously. The polymeric dispersant preferably includes one or more of maleic anhydride-modified polyethylene, maleic anhydride-modified polypropylene, maleic anhydride-modified ethylene-propylene copolymer, oxidized polyethylene, oxidized polypropylene, and ethylene-acrylic acid copolymer.

[0061] According to one embodiment of the present application, for the first step, if a dispersion stabilizer is used, the amount of the dispersion stabilizer is 0.01 to 6 parts by weight, based on 100 parts by weight of the total weight of the first polymerization monomer.

[0062] According to one embodiment of the present application, for the second step, if a dispersion stabilizer is used, the amount of the dispersion stabilizer is 0.1 to 5 parts by weight, preferably 0.5 to 2 parts by weight, based on 100 parts by weight of the total weight of the second polymerization monomer.

[0063] According to one embodiment of the present application, the non-polar solvent used in step two is also referred to as a hydrophobic solvent, which is preferably a petroleum hydrocarbon solvent, more preferably one or more selected from the group consisting of n-hexane, n-heptane, cyclohexane, toluene and xylene.

[0064] According to another embodiment of the present application, the step two is carried out at a temperature of 60-95°C, for example the reaction temperature of step two can be in the range of any two of the following values in combination with each other: 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C.

[0065] In the following examples, the excellent effects that can be achieved by the process of the present application are specifically illustrated. The purpose is to better understand the content of the present application. It should be understood that these examples are merely illustrative and not limiting. The reagents used in the examples are commercially available unless otherwise specified. The methods and conditions used in the examples are conventional methods and conditions unless otherwise specified.

[0066] Examples

[0067] All raw materials used in the following examples are commercially available analytical pure raw materials, which are used directly without further treatment.

[0068] In the following examples, the median particle size measurement and control and the performance test of the water-absorbing resin product are carried out by the following techniques:

[0069] A. Median particle size (microns)

[0070] The test method of the median particle size of the primary particles obtained in step one is as follows:

[0071] Take all the primary particles after crushing, prepare JIS standard sieves (sieve holes 425 μm, 250 μm, 180 μm, 150 μm, 106 μm, 75 μm, 45 μm).

[0072] Stack the JIS standard sieves from the top according to the sieve holes: 425 μm, 250 μm, 180 μm, 150 μm, 106 μm, 75 μm, 45 μm in the order from top to bottom, add the above water-absorbing resin particles to the uppermost sieve, and use a rotary light tapping vibrating sieve to vibrate for 10 minutes.

[0073] Subsequently, by calculating the mass percentage of the water-absorbing resin particles remaining on each sieve relative to the total mass, starting from the particles with large particle size in turn, the relationship between the sieve hole size and the integral value of the mass percentage of the water-absorbing resin particles remaining on the sieve is plotted on a log probability paper. The points on the probability paper are connected by a straight line, and the median particle size of the secondary particles is defined as the particle size corresponding to a cumulative mass percentage of 50%.

[0074] The method for measuring the median particle diameter of the secondary particles obtained in Stage 2 is as follows:

[0075] The entire secondary particles after drying were prepared for JIS standard sieves (sieve openings: 850 μm, 710 μm, 600 μm, 500 μm, 425 μm, 300 μm, 180 μm, 150 μm).

[0076] The JIS standard sieves were stacked in the order of the receiving dishes from the top to the bottom, with the sieve openings: 850 μm, 710 μm, 600 μm, 500 μm, 425 μm, 300 μm, 180 μm, 150 μm, and the water-absorbent resin particles were added to the uppermost sieve. A rotary light tapping type vibration sieve was used to vibrate for 10 minutes.

[0077] Subsequently, the mass percentage of the water-absorbent resin particles remaining on each sieve with respect to the total amount was calculated, and the relationship between the sieve opening size and the integrated value of the mass percentage of the water-absorbent resin particles remaining on the sieve was plotted on a log probability paper, starting from the particles with the largest particle size. The points on the probability paper were connected by a straight line, and the median particle diameter of the secondary particles was defined as the particle size corresponding to the cumulative mass percentage of 50%.

[0078] B. Water absorption rate of SAP product (sec)

[0079] To 1000 parts by weight of a 0.90 wt% NaCl aqueous solution prepared in advance, 0.02 parts by weight of indigo as a food additive was added, and the liquid temperature was adjusted to 25°C. To a 100-ml beaker, 50 g of the 0.90 wt% NaCl aqueous solution colored blue was added, and 2.0 g of the superabsorbent resin was added during stirring at 600 rpm using a cylindrical stirrer having a length of 20 mm and a thickness of 5 mm. The time interval t from the start of the timing at the moment of the addition to the point when the liquid vortex just covered the stirring blade was the water absorption speed. The smaller t was, the faster the water absorption speed was.

[0080] C. Liquid permeability (sec)

[0081] A 150 g sample of 0.9 wt% NaCl solution at 23°C is weighed into a beaker. The sample is then added to the beaker and allowed to swell for 30 minutes. A tube is prepared by attaching a screen and plug to the lower end of the tube and marking the tube with a graduated volume scale. The tube has an internal diameter of 30 mm and the graduated volume scale is 35 mm in length. The time taken for the 0.9 wt% NaCl solution at 23°C to flow through the graduated volume scale of the tube is recorded as Tl. The prepared sample of hydrogel particles and saline are then transferred to the tube. When the swollen gel particles have settled to the lower end of the tube, a pressurised shaft with a wire mesh screen is placed on top of the gel particles and a weight is placed on the top of the shaft. The valve at the bottom of the tube is then opened and the time taken for the saline to flow through the graduated volume scale of the tube is recorded as T2. The total pressure exerted by the pressurised shaft and weight on the swollen gel particles is 2.0 kPa. The lower the time taken for the liquid to pass through the tube, the better the liquid permeability of the superabsorbent resin, which is calculated as T2-Tl.

[0082] D. 1 minute water uptake (g / g)

[0083] A 2.0000 ± 0.001 g sample is weighed into a 400 mesh nylon mesh bag and the weight Wi is recorded. A 5 L beaker is filled with 2 / 3 pure water and the temperature is controlled at 23 ± 0.5°C. The nylon mesh bag containing the sample is quickly immersed in the pure water and the timer is started. After 1 minute, the nylon mesh bag is removed from the pure water and left for a few seconds until no water drips from the bottom. The nylon mesh bag is then weighed on the balance and the weight W2is recorded. The CRC is calculated according to the following formula.

[0084] 1 minute water uptake = (W2- Wi) / Wi

[0085] E. Centrifuge retention capacity (CRC) (g / g)

[0086] The centrifuge retention capacity (CRC) of the superabsorbent resin is determined according to EDANA method (ERT 441.2-02). "EDANA" is an abbreviation for the European Disposables and Nonwoven Association. "ERT" is an abbreviation for the European Standard Test method for superabsorbent resins. In the present invention, unless otherwise specified, the physical properties of the superabsorbent resins are determined according to the ERT original (2002 revision / known literature).

[0087] Specifically, 0.20 g of the high-absorbency resin was uniformly placed in a tea bag (60 mm x 85 mm) and heat-sealed, and then immersed in a far excess amount (usually about 500 ml) of a 0.90 wt% NaCl aqueous solution at 23 (±2) °C. After 30 min, the bag was lifted, and water was removed using a centrifugal separator (manufactured by Kokusan Co., Ltd., Japan, Model H-122) at a centrifugal force of 250 G for 3 min, and the weight Wlg of the bag was measured. In addition, the same operation was performed without using the high-absorbency resin, and the weight W2g at this time was measured, and the CRC was calculated according to the following equation.

[0088] CRC = (W1-W2) / 0.2-1

[0089] Example 1

[0090] (a) Water-phase polymerization step: In a PP beaker with a volume of 2000 ml, 174.78 g of acrylic acid (purchased from Shanghai Huayi New Materials Co., Ltd.), 148.19 g of deionized water, and 69.84 g of a 50 wt% NaOH aqueous solution (purchased from Shanghai Chlor-Alkali Chemical Co., Ltd.) were placed, and the NaOH solution was added under strong stirring. During the addition of the NaOH solution, precipitates were observed, but gradually dissolved to form a transparent and uniform solution, and the temperature of the material rose to 65 °C. The material was allowed to cool to 56 °C, and then 23.59 g of polyethylene glycol diacrylate 400 (purchased from Changxing Material Co., Ltd., Taiwan, as a 4% aqueous solution) was added as an internal crosslinking agent. Then, 71.79 g of a 50 wt% NaOH aqueous solution at 40 °C was added, and after the addition was completed, the temperature of the material rose to 88 °C due to neutralization heat. The temperature of the reaction solution was reduced to 78 °C, and 11.32 g of a 3% sodium persulfate aqueous solution was added thereto, thereby obtaining a monomer aqueous solution of step one, which was stirred for 2 seconds. Then, it was quickly poured into a 25*25 cm stainless steel tray preheated to 105 °C while stirring, and the tray was placed in an oven at 105 °C, and the polymerization reaction was started after 20-30 s. During the polymerization reaction, water vapor was generated and expanded in all directions, and then shrank and collapsed to a size slightly larger than the polymerization tray. After 3 min from the start of the polymerization reaction, the crosslinked polymer containing a strip-shaped hydrogel was taken out of the polymerization tray. The peak temperature during polymerization was 110 °C.

[0091] The hydrogel obtained by the above water-phase polymerization reaction was comminuted using a meat grinder (purchased from Zhengyuan Precision Machinery Co., Ltd., Model RY-12S, aperture 8 mm) to obtain a particulate hydrogel. During the gel comminution, about 90 g of deionized water at a temperature of 90 °C was continuously and uniformly sprayed onto the gel.

[0092] The granular water-containing gel obtained by the above operation was spread on a stainless steel mesh wire having a mesh size of 850 μm, and dried in a blast oven at 185°C for 70 min. Then, the dried polymer obtained by the drying operation was pulverized using a grinder, and classified by sieving using standard sieves having mesh sizes of 45 μm and 150 μm, to obtain primary particles having a particle size of 45 μm to 150 μm.

[0093] (b) Reversed-phase suspension polymerization step: A 500-ml three-necked flask was charged with 124.4 g of acrylic acid, and 189.9 g of a 27% by mass aqueous sodium hydroxide solution was added dropwise under ice water cooling, to neutralize 74% by mole of the acrylic acid. Then, 0.192 g of potassium persulfate and 13.9 mg of N,N'-methylenebisacrylamide (No. 14085E, purchased from Aldrich) were added and dissolved, and 20 g of water was further added, to prepare a monomer aqueous solution for the second step.

[0094] A 1000-ml five-necked flask was prepared, and a reflux condenser, a nitrogen inlet tube, and a stirring blade (crescent blade having a blade diameter of 80 mm) as a stirrer were attached to the flask. The flask was placed in an oil bath and warmed to 80°C, and 408 ml of n-heptane, 1.104 g of sucrose stearate (Ryoto Sucroester S-370, manufactured by Mitsubishi Chemical Corporation), and 1.104 g of maleic anhydride-modified ethylene-propylene copolymer (Hi-wax 1105A, manufactured by Mitsui Chemicals, Inc.) were added to the flask to dissolve the dispersion stabilizer. The rotation speed was adjusted to 500 rpm, and 110 g of the primary particles obtained by the above water-phase polymerization were added to the flask, and 100 g of water was further added.

[0095] The temperature of the water bath was lowered to 20°C, and the monomer aqueous solution for the second step described above was added to the flask. After the addition was completed, the system was replaced with nitrogen for 30 min, and then the flask was immersed in a water bath at 70°C, and the polymerization was carried out for 60 min, to obtain a slurry for the second step.

[0096] (c) surface modification step: the slurry obtained in the above step was placed in an oil bath at 120°C to azeotrope water and n-heptane, and 230 g of water was removed from the system while n-heptane was refluxed. Then the oil bath temperature was lowered to 80°C, and 10.34 g of a 2% aqueous solution of ethyleneglycol diglycidyl ether (No. 38399B, purchased from Aldrich) was added, and the mixture was kept at 80°C for 120 min. The n-heptane was evaporated to dryness, and 260.1 g of secondary particles were obtained from the process. The median particle size of the secondary particles was 402.4 microns, and the particle size distribution is shown in Table 1. 100 parts by weight of the absorbent resin was mixed with 0.3 parts by weight of AEROSIL 200 (fumed Si02, Degussa) to obtain a final resin sample. The results of various property measurements are shown in Table 2. Figures 1A and IB show the micro-morphology of the product at different magnifications, and it can be seen that the product comprises secondary particles formed by agglomeration of a large number of irregularly shaped primary particles.

[0097] Example 2

[0098] (a) aqueous phase polymerization step: in a 2000 ml PP beaker, 174.78 g of acrylic acid (purchased from Shanghai Huayi New Materials Co., Ltd.), 148.19 g of deionized water, and 69.84 g of a 50 wt% NaOH aqueous solution (purchased from Shanghai Chlor-Alkali Chemical Co., Ltd.) were added, and the NaOH solution was added under strong stirring. During the addition of the NaOH solution, precipitates were observed, but gradually dissolved to form a transparent and uniform solution, and the temperature of the material rose to 65°C. The material was cooled to 56°C, and then 23.59 g of polyethylene glycol diacrylate 400 (purchased from Changxing Materials Co., Ltd., Taiwan, as a 4% aqueous solution) was added as an internal crosslinking agent. Then 71.79 g of a 50 wt% NaOH aqueous solution at 40°C was added, and after the addition was completed, the temperature of the material rose to 88°C due to the heat of neutralization. The temperature of the reaction solution was lowered to 78°C, and 11.32 g of a 3% aqueous solution of sodium persulfate was added to obtain a monomer aqueous solution of step one, which was stirred for 2 seconds. Then it was quickly poured into a 25*25 cm stainless steel tray preheated to 105°C while stirring, and the tray was placed in an oven at 105°C, and the polymerization reaction started after 20-30 s. During the polymerization reaction, water vapor was generated and expanded in all directions, and then shrank and collapsed to a size slightly larger than the polymerization tray. After 3 min from the start of the polymerization reaction, the crosslinked polymer in the form of a ribbon-shaped hydrogel was taken out of the polymerization tray. The peak temperature during polymerization was 110°C.

[0099] The water-containing gel obtained by the above water phase polymerization was comminuted using a meat grinder (RY-12S, aperture 8 mm, manufactured by Seibetsu Seimitsu Kikai Co., Ltd.) to obtain a particulate water-containing gel. During the comminution of the gel, deionized water at 90°C was continuously and uniformly sprayed on the gel at about 90 g.

[0100] The particulate water-containing gel obtained by the above operation was spread on a stainless steel mesh having a mesh size of 850 μm, and dried in a blast oven at 185°C for 70 min. Then, the dried polymer obtained by the drying operation was pulverized using a grinder, and classified by sieving using standard sieves having mesh sizes of 45 μm and 150 μm to obtain primary particles having a particle size of 45 μm to 150 μm.

[0101] (b) Reversed-phase suspension polymerization step: A 500-ml three-necked flask was charged with 124.4 g of acrylic acid, and 189.9 g of a 27% by mass aqueous sodium hydroxide solution was added dropwise under ice water cooling to neutralize 74% by mole of the acrylic acid. Then, 0.192 g of potassium persulfate and 13.9 mg of N,N'-methylenebisacrylamide (No. 14085E, manufactured by Wako Pure Chemical Industries, Ltd.) were added and dissolved, and 20 g of water was further added to prepare a monomer aqueous solution for the second step.

[0102] A 1000-ml five-necked separable flask was prepared, and a reflux condenser, a nitrogen inlet tube, and a stirring blade (crescent blade having a blade diameter of 80 mm) as a stirrer were attached to the flask. The flask was placed in an oil bath and warmed to 80°C, and 408 ml of n-heptane, 1.104 g of sucrose stearate (Ryoto Sucroester S-370, manufactured by Mitsubishi Chemical Corporation), and 1.104 g of maleic anhydride-modified ethylene-propylene copolymer (Hi-wax 1105A, manufactured by Mitsui Chemicals, Inc.) were added to the flask to dissolve the dispersion stabilizer. The rotation speed was adjusted to 500 rpm, 110 g of the primary particles obtained by the above water phase polymerization was added to the flask, and 80 g of water was further added.

[0103] The temperature of the water bath was lowered to 20°C, and the monomer aqueous solution for the second step described above was added to the flask. After the addition was completed, the system was replaced with nitrogen for 30 min, and then the flask was immersed in a water bath at 70°C, and the polymerization was carried out for 60 min to obtain a slurry for the second step.

[0104] (c) surface modification step: the slurry obtained in the above step was placed in an oil bath at 120°C to azeotrope water and n-heptane, and 230 g of water was removed from the system while n-heptane was refluxed. Then the oil bath temperature was lowered to 80°C, and 10.34 g of a 2% aqueous solution of ethyleneglycol diglycidyl ether (No. 38399B, purchased from Aldrich) was added, and the mixture was kept at 80°C for 120 min. The n-heptane was evaporated to dryness, and 259.4 g of secondary particles were obtained from the process. The median particle size of the secondary particles was 365.0 microns, and the particle size distribution is shown in Table 1. 100 parts by weight of the absorbent resin was mixed with 0.3 parts by weight of AEROSIL 200 (fumed Si02, Degussa) to obtain a final resin sample. The results of various property measurements are shown in Table 2. The SEM image of the product showed that the product comprised secondary particles formed by agglomeration of a large number of irregularly shaped primary particles.

[0105] Example 3

[0106] (a) aqueous phase polymerization step: in a PP beaker with a volume of 2000 ml, 174.78 g of acrylic acid (purchased from Shanghai Huayi New Material Co., Ltd.), 148.19 g of deionized water, and 69.84 g of a 50 wt% NaOH aqueous solution (purchased from Shanghai Chlor-Alkali Chemical Co., Ltd.) were added, and the NaOH solution was added under strong stirring. During the addition of the NaOH solution, precipitates were observed, but gradually dissolved to form a transparent and uniform solution, and the temperature of the material rose to 65°C. The material was cooled to 56°C, and then 23.59 g of polyethylene glycol diacrylate 400 (purchased from Changxing Material Co., Ltd., Taiwan, as a 4% aqueous solution) was added as an internal crosslinking agent. Then 71.79 g of a 50 wt% NaOH aqueous solution at 40°C was added, and after the addition was completed, the temperature of the material rose to 88°C due to the heat of neutralization. The temperature of the reaction solution was lowered to 78°C, and 11.32 g of a 3% aqueous solution of sodium persulfate was added to obtain a monomer aqueous solution of step one, which was stirred for 2 seconds. Then it was quickly poured into a 25*25 cm stainless steel tray preheated to 105°C while stirring, and the tray was placed in an oven at 105°C, and the polymerization reaction started after 20-30 s. During the polymerization reaction, water vapor was generated and expanded in all directions, and then shrank and collapsed to a size slightly larger than the polymerization tray. After 3 min from the start of the polymerization reaction, the crosslinked polymer in the form of a ribbon-shaped hydrogel was taken out of the polymerization tray. The peak temperature during polymerization was 110°C.

[0107] The water-containing gel obtained by the above water-phase polymerization was comminuted using a meat grinder (RY-12S, aperture 8 mm, manufactured by Seibetsu Seimitsu Kikai Co., Ltd.) to obtain a particulate water-containing gel. During the comminution of the gel, deionized water at 90°C was continuously and uniformly sprayed on the gel at about 90 g.

[0108] The particulate water-containing gel obtained by the above operation was spread on a stainless steel mesh having a mesh size of 850 μm, and dried in a blast oven at 185°C for 70 min. Then, the dried polymer obtained by the above drying operation was pulverized using a grinder, and classified by sieving using standard sieves having mesh sizes of 45 μm and 150 μm to obtain primary particles having a particle size of 45 μm to 150 μm.

[0109] (b) Reversed-phase suspension polymerization step: A 500-ml three-necked flask was charged with 124.4 g of acrylic acid, and 189.9 g of a 27% by mass aqueous sodium hydroxide solution was added dropwise under ice water cooling to neutralize 74% by mole of the acrylic acid. Then, 0.192 g of potassium persulfate and 13.9 mg of N,N'-methylenebisacrylamide (No. 14085E, manufactured by Wako Pure Chemical Industries, Ltd.) were added and dissolved, and 20 g of water was further added to prepare a monomer aqueous solution for the second step.

[0110] A 1000-ml five-necked separable flask was prepared, and a reflux condenser, a nitrogen inlet tube, and a stirring blade (crescent blade having a blade diameter of 80 mm) as a stirrer were attached to the flask. The flask was placed in an oil bath and warmed to 80°C, and 408 ml of n-heptane, 1.104 g of sucrose stearate (Ryoto Sucroester S-370, manufactured by Mitsubishi Chemical Corporation), and 1.104 g of maleic anhydride-modified ethylene-propylene copolymer (Hi-wax 1105A, manufactured by Mitsui Chemicals, Inc.) were added to the flask to dissolve the dispersion stabilizer. The rotation speed was adjusted to 500 rpm, 110 g of the primary particles obtained by the above water-phase polymerization was added to the flask, and 120 g of water was further added.

[0111] The temperature of the water bath was lowered to 20°C and the monomer aqueous solution for the second step described above was added to the flask. After the addition was completed, the system was replaced with nitrogen for 30 min, and then the flask was immersed in a water bath at 70°C. The polymerization was carried out for 60 min to obtain a slurry for the second step.

[0112] (c) surface modification step: the slurry obtained in the above step was placed in an oil bath at 120°C to co-boil water and n-heptane, and 230 g of water was removed from the system while n-heptane was refluxing. The temperature of the oil bath was then lowered to 80°C, and 10.34 g of a 2% aqueous solution of ethyleneglycol diglycidyl ether (No. 38399B, purchased from Aldrich) was added. The mixture was maintained at 80°C for 120 min. The n-heptane was evaporated and the secondary particles were dried. The secondary particles obtained from the process weighed 266.9 g. The median particle size of the secondary particles was 390.7 microns, 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 (fumed Si02, Degussa) to obtain a final resin sample. The results of the various property measurements are shown in Table 2. The SEM image of the product showed that the product comprised secondary particles formed by agglomeration of a large number of irregularly shaped primary particles.

[0113] Example 4

[0114] (a) aqueous phase polymerization step: the polymerization was carried out in a belt reactor. 154.8 g of acrylic acid (purchased from Shanghai Huayi New Material Co., Ltd.), 0.62 g of a crosslinking agent, pentaerythritol triallyl ether (No. 01140358, purchased from Aldrich), and 343 g of deionized water were added, mixed, and maintained at a temperature of 3°C. Nitrogen was flowed into the mixture to reduce the amount of dissolved oxygen in the mixture to 1 ppm or less, and then 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-azobis[2-(imidazolin-2-yl)propane] dihydrochloride aqueous solution were added while the mixture was being stirred, and the polymerization was started. After the temperature of the mixture reached 90°C, the polymerization was carried out at a temperature of 90±2°C for about 5 hours to obtain a hydrogel-containing aqueous solution.

[0115] After the polymerization was completed, the hydrogel-containing aqueous solution was ground with a meat grinder (Zhengyuan Precision Machinery Co., Ltd., Model RY-12S, aperture 8 mm) while adding 108 g of a 48.5% sodium hydroxide aqueous solution to neutralize the solution, and a neutralized gel was obtained.

[0116] The granular hydrogel obtained by the above operation was spread on a stainless steel wire mesh with a mesh size of 850 microns, and dried in a forced air oven at 185°C for 70 min. Next, the dried polymer obtained by the drying operation was pulverized using a grinder, and classified 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.

[0117] (b) Reversed phase suspension polymerization. In this step, 124.4 g of acrylic acid was added to a 500 ml three-necked flask, 189.9 g of 27% by mass aqueous sodium hydroxide solution was added dropwise under the condition of an ice water bath so that 74% by mole of the acrylic acid was neutralized, then 0.192 g of potassium persulfate and 13.9 mg of N,N'-methylenebisacrylamide (No. 14085E, purchased from Aldrich) were added and dissolved, and 20 g of water was further added to prepare the monomer aqueous solution of step 2.

[0118] A 1000 ml detachable five-necked flask was prepared, and a reflux condenser, a nitrogen introduction tube, and a stirring blade (crescent blade with a blade diameter of 80 mm) as a stirrer were attached to the flask. The entire flask was placed in an oil bath and warmed to 80°C, and 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, Inc., Hi-wax 1105A) were added to the flask, and the dispersing stabilizer was allowed to dissolve. The rotational speed was adjusted to 500 rpm, and 110 g of the primary particles obtained by polymerization of the aqueous solution of step 1 above was added to the flask, and 100 g of water was further added.

[0119] The temperature of the water bath was lowered to 20°C, and the monomer aqueous solution of step 2 above was added to the detachable flask, and immediately after the addition was completed, the system was replaced with nitrogen for 30 min, and then the flask was immersed in a water bath at 70°C, and the polymerization was carried out for 60 min to obtain the slurry of step 2.

[0120] (c) Surface modification step: The slurry of step 2 was placed in an oil bath at 120°C to co-boil water and n-heptane, and 230 g of water was removed from the system while n-heptane was refluxed, and then the temperature of the oil bath was lowered to 80°C, and 10.34 g of a 2% aqueous solution of ethyleneglycol diglycidyl ether (No. B38399B, purchased from Aldrich) was added thereto, and the mixture was maintained at 80°C for 120 min. Then, n-heptane was evaporated to dry the product, and 244.1 g of secondary particles were obtained by the process. The median particle diameter of the secondary particles was 415.7 μm, and the particle size distribution results are shown in Table 1. 100 parts by weight of the absorbent resin was mixed with 0.3 parts by weight of AEROSIL 200 (fumed Si02, Degussa), and a final resin sample was obtained. The results of the various property measurements are shown in Table 2. The SEM image of the product showed that the product included secondary particles formed by agglomeration of a large number of irregularly shaped primary particles.

[0121] Comparative Example 1

[0122] In this Comparative Example 1, a different polymerization reaction design was used than the method of the present application, both polymerization steps were reverse phase polymerization 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:

[0123] Step 1 (polymerization reaction in non-polar hydrocarbon solvent): A 500 ml three-necked flask was charged with 88.88 g of acrylic acid, and 164.5 g of a 22 mass% aqueous sodium hydroxide solution was added dropwise to the flask under ice water cooling. After neutralizing 74% of the moles of acrylic acid, 0.132 g of potassium persulfate and 8.9 mg of N,N'-methylenebisacrylamide (No. 14085E, purchased from Aldrich) were added to the flask and dissolved, and 20 g of water was further added to the flask to prepare a monomer aqueous solution for the first stage.

[0124] A 1000 ml detachable five-necked flask was prepared, and a reflux condenser, a nitrogen inlet tube, and a stirring blade (crescent blade with a 80 mm blade diameter) as a stirrer were attached to the flask. The entire flask was placed in an oil bath and warmed to 80°C, 408 ml of n-heptane was added to the flask, the stirrer was started, and the stirring speed was adjusted to 400 rpm. Then, 1.104 g of sucrose stearate and 1.104 g of a maleic anhydride-modified ethylene-propylene copolymer (type: Hi-wax 1105A, purchased from Mitsui Chemicals, Inc.) were added to the flask, and the dispersing stabilizer was allowed to dissolve. The oil bath temperature was lowered to 50°C, the monomer aqueous solution for the first stage prepared as described above was added to the flask, and the inside of the system was immediately replaced with nitrogen gas. After the addition was completed, the flask was immersed in an oil bath at 70°C to warm up, and the polymerization reaction was performed for 60 min to obtain a slurry for the first stage. After the reaction, the oil bath was cooled to 20°C.

[0125] Step 2: Another 500 ml three-necked flask was prepared, and 124.4 g of acrylic acid was added to the flask, and 189.9 g of a 27 mass% aqueous sodium hydroxide solution was added dropwise to the flask under ice water cooling. After neutralizing 74% of the moles of acrylic acid, 0.192 g of potassium persulfate and 13.9 mg of N,N'-methylenebisacrylamide (No. 14085E, purchased from Aldrich) were added to the flask and dissolved, and 20 g of water was further added to the flask to prepare a monomer aqueous solution for the second stage.

[0126] The monomer aqueous solution for the second stage was added to the detachable five-necked flask containing the slurry for the first stage, and the inside of the system was immediately replaced with nitrogen gas. After the addition was completed, the reaction flask was immersed in an oil bath at 70°C to warm up, and the polymerization of the second stage was performed for 60 min to obtain a slurry for the second stage.

[0127] Step three (modification step): The polymerized slurry from step two was placed in an oil bath at 120°C to azeotrope water and n-heptane. While n-heptane was refluxing, 300 g of water was removed from the system. The oil bath temperature was then lowered to 80°C. To the flask was added 10.34 g of a 2% aqueous solution of ethyleneglycol diglycidyl ether (No. B38399B, Aldrich) and the mixture was held at 80°C for 120 minutes. The n-heptane was then evaporated and the product was dried. The secondary particles were 180.4 g. The median particle size of the secondary particles was 384.2 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 (fumed Si02, Degussa) to obtain the final resin sample. The results of the various performance measurements are shown in Table 2.

[0128] Comparative Example 2

[0129] In this comparative example 2, a different polymerization design was used than in the process of the present application. Only aqueous polymerization was used to prepare the polymerization product, surface modification was performed after polymerization, and the median particle size and performance of the polymerization product were characterized. Specifically, the following steps were used in this comparative example:

[0130] In a 2000 ml PP beaker, 174.78 g of acrylic acid (purchased from Shanghai Huayi New Material Co., Ltd.), 148.19 g of deionized water, and 69.85 g of a 50 wt% NaOH aqueous solution (Shanghai Chlor-Alkali Chemical Co., Ltd.) were added. The NaOH solution was added with vigorous stirring. During the addition of the NaOH solution, it was observed that precipitates were formed, but the precipitates gradually dissolved to form a transparent and uniform solution, and the temperature rose to 65°C. The temperature of the material in the beaker was lowered to 56°C, and then 23.59 g of a 4% polyethylene glycol diacrylate 400 aqueous solution (Taiwan Changxing Material Co., Ltd.) was added as an internal crosslinking agent. Then 71.79 g of a 50 wt% NaOH aqueous solution at 40°C was added, and after the addition was completed, it was observed that the temperature of the material in the beaker rose to 88°C due to the heat of neutralization. The temperature of the reaction solution in the beaker was lowered to 78°C, and then 11.32 g of a 3% sodium persulfate aqueous solution was added, thereby preparing a first-stage monomer aqueous solution. The monomer aqueous solution was stirred for 2 seconds, and then quickly poured into a 25*25 cm stainless steel tray preheated to 105°C. The tray was placed in an oven at 105°C, and the polymerization reaction began after 20-30 seconds. During the polymerization reaction, water vapor was generated and expanded in all directions, and then shrank and collapsed to a size slightly larger than the polymerization tray. After 3 minutes from the start of the polymerization, the crosslinked polymer in the form of a strip-shaped hydrogel was removed from the polymerization tray. The peak temperature during polymerization was 110°C.

[0131] The water-containing gel obtained by the above polymerization reaction was comminuted using a meat grinder (RY-12S, aperture 8 mm, Sei-Yu Precision Machinery Co., Ltd.) to obtain a particulate water-containing gel. During the comminution of the gel, deionized water at 90°C was continuously sprayed onto the gel at about 90 g.

[0132] The particulate water-containing gel obtained by the above operation was spread on a stainless steel wire mesh with a mesh size of 850 microns and dried in a forced air oven at 185°C for 70 minutes. Next, the dried polymer obtained by the drying operation was pulverized using a grinder and classified using standard sieves with mesh sizes of 150 microns and 600 microns to obtain particles with diameters of 150 microns to 600 microns.

[0133] A surface crosslinking solution was prepared by mixing 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. 100 g of the absorbent resin particles obtained above were placed in a stirred tank, and the stirring speed was set to 500 rpm. Next, 4.67 g of the surface crosslinking solution was sprayed into the mixer to obtain a coated wet material. Next, the coated wet material was spread on a tray and placed in an oven at 80°C for 60 minutes to perform surface crosslinking, thereby obtaining an absorbent resin. 100 parts by weight of the absorbent resin were mixed with 0.3 parts by weight of AEROSIL 200 (fumed Si02, Degussa) to obtain a final resin sample. The median particle size of the particles obtained by the method was 351.7 microns, and the particle size distribution results are shown in Table 1. The performance measurement results are shown in Table 2.

[0134] Comparative Example 3

[0135] In this comparative example 3, a different polymerization reaction design was used than in the method of the present application, and only aqueous solution polymerization was used to prepare the polymerization product, surface modification was performed after the polymerization reaction, and the median particle size and performance of the polymerization product were characterized. Specifically, the following steps were used in this comparative example:

[0136] A mixture of 154.8 g of acrylic acid, 0.62 g of a crosslinking agent, pentaerythritol triallyl ether (No. 01140358, purchased from Aldrich), and 343 g of deionized water was stirred while maintaining the temperature of the mixture at 3°C. After purging the mixture with nitrogen gas to reduce the dissolved oxygen content in the mixture to 1 ppm or less, 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-azobis[2-(imidazolin-2-yl)propane] dihydrochloride aqueous solution were added to the mixture while continuing to stir, and polymerization was initiated. After the temperature of the mixture reached 90°C, the polymerization was continued at a temperature of 90 ± 2°C for about 5 hours to obtain a hydrogel. Next, the hydrogel was ground with a meat grinder (RY-12S, 8 mm, Sei-Yu Seiki Kogyo Co., Ltd.) while adding 108 g of a 48.5% sodium hydroxide aqueous solution to neutralize the hydrogel, and a neutralized gel was obtained.

[0137] The granular hydrogel obtained by the above procedure was spread on a stainless steel mesh having a mesh size of 850 μm, and dried in a blast oven at 185°C for 70 minutes. Next, the dried polymer obtained by the drying procedure was pulverized using a grinder, and classified using standard sieves having mesh sizes of 150 μm and 600 μm to obtain primary particles having a particle size of 150 μm to 600 μm.

[0138] A surface crosslinking solution was prepared by mixing 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. 100 g of the absorbent resin particles obtained above were placed in a stirred tank, and the stirring speed was set to 500 rpm. Then, 4.67 g of the surface crosslinking solution was sprayed into the tank, and mixed to obtain a coated wet material. Next, the coated wet material was spread on a tray, and placed in an oven at 80°C for 60 minutes to perform surface crosslinking, and an absorbent resin was obtained. The median particle size of the particles obtained by the above procedure was 368.9 μm, and the particle size distribution results are shown in Table 1. 100 parts by weight of the absorbent resin were mixed with 0.3 parts by weight of AEROSIL 200 (fumed Si02, Degussa) to obtain a final resin sample. The results of the various performance measurements are shown in Table 2.

[0139] Comparative Example 4

[0140] In this comparative example 4, a polymerization reaction design different from the method of the present application was used, and surface modification was performed after the water phase polymerization step and the inverse suspension polymerization step, and after the inverse suspension polymerization reaction.

[0141] (a) Water phase polymerization step: In a PP beaker with a volume of 2000 ml, 174.78 g of acrylic acid (purchased from Shanghai Huayi New Material Co., Ltd.), 148.19 g of deionized water and 69.84 g of 50 wt% NaOH aqueous solution (purchased from Shanghai Chlor-Alkali Chemical Co., Ltd.) were put in, in which the NaOH solution was added under strong stirring. During the addition of the NaOH solution, precipitates were observed, but gradually dissolved to form a transparent and uniform solution, and the temperature of the material rose to 65°C. The material was cooled to 56°C, and then 23.59 g of polyethylene glycol diacrylate 400 (purchased from Taiwan Changxing Material Co., Ltd., as a 4% aqueous solution) was added as an internal crosslinking agent. Then 71.79 g of 50 wt% NaOH aqueous solution at 40°C was added, and after the addition was completed, the temperature of the material rose to 88°C due to the heat of neutralization. The temperature of the reaction solution was reduced to 78°C, and 11.32 g of 3% sodium persulfate aqueous solution was added to obtain the monomer aqueous solution of step one, which was stirred for 2 seconds. Then it was quickly poured into a 25*25 cm stainless steel tray preheated to 105°C while stirring, and the tray was placed in a 105°C oven, and the polymerization reaction started after 20-30 s. During the polymerization reaction, water vapor was generated and expanded in all directions, and then shrank and collapsed into a size slightly larger than the polymerization tray. After 3 min from the start of the polymerization reaction, the crosslinked polymer containing a strip-shaped hydrogel was taken out of the polymerization tray. The peak temperature during polymerization was 110°C.

[0142] The hydrogel obtained by the above water phase polymerization reaction was disintegrated using a meat grinder (purchased from Zhengyuan Precision Machinery Co., Ltd., model RY-12S, aperture 8 mm) to obtain a granular hydrogel. During the gel disintegration, about 90 g of deionized water at a temperature of 90°C was continuously and uniformly sprayed onto the gel.

[0143] The granular hydrogel obtained by the above operation was laid on a stainless steel mesh with a mesh size of 850 microns and dried in a blast oven at 185°C for 70 min. Then, the dried polymer obtained by the drying operation was crushed using a grinder, and then sieved and classified using standard sieves with mesh sizes of 45 microns and 150 microns to obtain primary particles with a particle size of 45 microns-150 microns.

[0144] (b) Surface modification step:

[0145] A 1000 mL separable flask was prepared, and a reflux condenser, a nitrogen inlet tube, and a stirring blade (crescent blade with a 80 mm blade width) as a stirrer were attached to the flask. The flask was charged with n-heptane 408 mL, sucrose stearate (Mitsubishi Chemical Corporation, Ryoto sucrose ester S-370) 1.104 g, and maleic anhydride-modified ethylene-propylene copolymer (Mitsui Chemicals, Inc., Hi-wax 1105A) 1.104 g. The flask was immersed in a water bath, and the temperature was raised to 80°C. After the dispersing stabilizer was dissolved, 110 g of the primary particles were added, and the stirring speed was set to 400 rpm. The particles were dispersed, and 32.49 g of water was added. The dispersion was continued for 15 minutes. Then, 4.36 g of a 2% aqueous solution of ethylene glycol diglycidyl ether (No. 38399B, purchased from Aldrich) was added, and the temperature was maintained at 80°C for 120 minutes. After the reaction was completed, 63.24 g of water was further added. The primary particles obtained by this method were subjected to the surface cross-linking reaction.

[0146] (c) Reversed-phase suspension polymerization step: A 500 mL flask was charged with acrylic acid 124.4 g, and 27% by mass of an aqueous sodium hydroxide solution 189.9 g was added dropwise under ice water cooling. After 74% by mole of the acrylic acid was neutralized, potassium persulfate 0.192 g and N,N'-methylenebisacrylamide (No. 14085E, purchased from Aldrich) 13.9 mg were added and dissolved. Then, 20 g of water was added, and a monomer aqueous solution for step (c) was prepared.

[0147] The temperature of the water bath for the mixture obtained in step (b) was lowered to 20°C. The monomer aqueous solution prepared in step (c) was added to the flask. After the addition was completed, the system was replaced with nitrogen for 30 minutes. Then, the flask was immersed in a water bath at 70°C, and the polymerization was continued for 60 minutes.

[0148] (d) Surface modification step: The polymerized slurry prepared in step (c) was placed in an oil bath at 120°C, and the water and n-heptane were azeotroped. While the n-heptane was refluxed, 300 g of water was removed from the system. Then, the temperature of the oil bath was lowered to 80°C, and a 2% aqueous solution of ethylene glycol diglycidyl ether (No. B38399B, purchased from Aldrich) 10.34 g was added. The temperature was maintained at 80°C for 120 minutes. Then, the n-heptane was evaporated, and the secondary particles 260.4 g were obtained. The median particle diameter of the secondary particles was 382.3 μm, and the particle size distribution is shown in Table 1. 100 parts by weight of the absorbent resin was mixed with 0.3 parts by weight of AEROSIL 200 (fumed SiO2, Degussa), and a final resin sample was obtained. The results of the measurement of the properties are shown in Table 2.

[0149] The particle size distribution of the water-absorbent resin obtained in each of the above examples and comparative examples is shown in Table 1, and the properties are shown in Table 2.

[0150] Table 1

[0151] Table 2

[0152] The SAP particles produced by the method of the present application are formed by agglomeration of small irregularly shaped particles, which are the primary particles obtained by the first stage polymerization, fragmentation and classification, and the molecular chains formed by the polymerization of the newly added second polymerization monomer in the second stage polymerization process link the primary particles to each other to form the final secondary particle morphology as shown in Figures 1A and 1B. As can be seen from the comparison of the examples and comparative examples, the method of the present application can simultaneously significantly improve the liquid permeability and the salt water absorption speed of the product.

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 the aqueous solution phase to obtain the prepolymer; 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; Step 3: Modify the intermediate resin with a surface crosslinking agent to obtain the water-absorbing resin; and 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.

2. The method as described in claim 1, characterized in that, No surface crosslinking agent was used for modification before step three was performed.

3. The method as described in claim 1, characterized in that, The surface crosslinking agent is a polyol (glycidyl ether).

4. The method as described in claim 1, characterized in that, In step one and / or step two, one or more internal crosslinking agents may be used, the internal crosslinking agents 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.

5. The method as described in claim 1, characterized in that, The first and second polymerizing monomers 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; The molar ratio of the first polymeric monomer to the second polymeric monomer is 1:10 to 10:

1.

6. The method as described in claim 1, characterized in that, 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 greater than or equal to 10 micrometers and less than 150 micrometers, which are then used in step two.

7. The method as described in claim 1, characterized in that, In steps one and two, one or more of the following may be used: initiator, dispersant stabilizer, alkaline reagent; In step two, the nonpolar solvent is selected from one or more of the following: n-hexane, n-heptane, cyclohexane, toluene, and xylene; Optionally, an inorganic additive may be added during, before, or after one or more of steps one through three.

8. The method as described in claim 1, characterized in that, 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.

9. The method as described in claim 1, characterized in that, Step one is carried out at a temperature of 45-120°C, so that 60-100% of the first polymerizing monomer undergoes polymerization; Step two is performed at a temperature of 60-95℃; 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 polymerizable monomer.

10. 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 1-9.

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