CN111116947A

CN111116947A - Method for producing polyacrylic acid water-absorbent resin

Info

Publication number: CN111116947A
Application number: CN201911413815.1A
Authority: CN
Inventors: 顾子旭; 胡健; 徐亮; 徐科峰; 杭渊
Original assignee: YIXING DANSEN TECHNOLOGY CO LTD
Current assignee: YIXING DANSEN TECHNOLOGY CO LTD
Priority date: 2019-12-31
Filing date: 2019-12-31
Publication date: 2020-05-08

Abstract

A method for producing a polyacrylic acid water-absorbent resin, comprising the steps of: obtaining an aqueous solution containing acrylic monomers and a cross-linking agent; carrying out polymerization reaction on an aqueous solution containing an acrylic monomer and a cross-linking agent to obtain a gel-like cross-linked polymer with the water content of 30-80 wt%; mixing the hydrogel cross-linked polymer with polyacrylic acid water-absorbing resin particles with the number-average particle size of 1-200 microns under the action of high shear and/or extrusion force during or after the polymerization reaction, and crushing the mixture into gel particles with the number-average particle size of 50-1 mm; heating and drying the crushed gel particles by adopting a heating medium with the temperature of 80-170 ℃ to obtain a crosslinked polymer with the water content of 0.1-10 wt%; and (3) carrying out grain refining on the dried crosslinked polymer and screening to prepare the water-absorbent resin particles. A method which can efficiently produce a water-absorbent resin having a low liquid reflux amount and a high liquid-absorbing rate, and a water-absorbent resin having a high liquid-absorbing rate are obtained.

Description

Method for producing polyacrylic acid water-absorbent resin

Technical Field

The present invention relates to a water absorbent resin having a high liquid-absorbing rate and a method for producing the same. It is particularly suitable for absorbent articles such as: paper diapers (disposable diapers), sanitary napkins, incontinence pads, bed pads, pet pads, wound care materials, building materials, soil water retention materials, and the like.

Background

Super Absorbent Polymer (SAP), also known as Super absorbent resin, is a crosslinked polymer that contains strongly hydrophilic groups, is insoluble in water, but can absorb tens, hundreds, or even thousands of times the weight of water. Known examples of the super absorbent resin include crosslinked products obtained by partially neutralizing polyacrylic acid, hydrolysates of starch-acrylic acid graft polymers, saponified products of vinyl acetate-acrylic acid ester copolymers, crosslinked products of acrylonitrile copolymers, crosslinked products of acrylamide copolymers, and crosslinked products of cationic monomers. In the fields of sanitary products such as diapers, incontinence pads, and sanitary napkins, and soil moisturizers, absorbers composed of hydrophilic fibers (e.g., pulp) and super absorbent resins as main raw materials are widely used.

In recent years, the structure of disposable sanitary materials such as diapers and sanitary napkins has been becoming thinner. Therefore, there is a tendency that the content of the water-absorbent resin in each sanitary material is increased and the mass of the water-absorbent resin relative to the whole absorbent structure composed of, for example, the water-absorbent resin and hydrophilic fibers is increased. Specifically, the thickness of the sanitary material is reduced by increasing the ratio of the water absorbing agent in the absorbent body by decreasing the amount of the hydrophilic fiber (having a low bulk density) and increasing the amount of the water absorbing resin (having a large liquid absorption amount and a high bulk density). However, the sanitary material in which the ratio of the hydrophilic fiber is decreased and the ratio of the water absorbent resin is increased in the above-described manner is advantageous from the viewpoint of simply storing the liquid, but problems occur when considering the distribution and diffusion of the liquid in the case of the actual use of the sanitary product.

The water-absorbent resin becomes a soft Gel-like state after swelling upon absorbing water, resulting in a so-called "Gel blocking" phenomenon which significantly hinders the permeation and diffusion of liquid, resulting in a sharp decrease in the permeability of liquid in sanitary materials (expressed as Gel bed permeability, GBP). As a result, in actual use, it is difficult for the liquid to reach the position around the center of the liquid-added body of the sanitary material, so that the water-absorbing agent located far from the center cannot function continuously and effectively, and the effect of increasing the content of the water-absorbing agent cannot be sufficiently exhibited, so that the absorption capacity of the sanitary material in actual use is considerably lower than the theoretical value. In order to avoid such problems and maintain the liquid absorption capacity of the absorbent body, the ratio between the hydrophilic fiber and the water absorbing agent is necessarily limited, and this also limits the thinning of the sanitary material. Therefore, in order to break the limit of the thin sanitary product, the permeability of the water-absorbing agent must be greatly improved.

An essential factor affecting the permeability of the water-absorbent resin is the size of the gaps between the swollen gel particles. When the particle size of the swelling gel particles is larger, the gel packing density is smaller, the particle gaps are large, the liquidity of the liquid among the gel particles is excellent, and the permeability is excellent. However, increasing the liquid permeability by increasing the particle size of the water-absorbing agent leads to a significant decrease in the specific surface area of the water-absorbing agent, which is reflected by a significant deterioration in the speed of absorbing liquid during actual use, and when liquid comes into contact with a sanitary product, a large amount of liquid leaks out of the sanitary product or the amount of liquid that returns to the body of the sanitary product increases due to insufficient Absorption speed (AS, the amount of liquid absorbed per unit mass of the water-absorbing agent per unit time), leading to skin rashes of infants and a series of sanitary problems.

The problem that the liquid absorption speed is not enough can be effectively solved by reducing the particle size of the water-absorbent resin, but the small particles have overlarge stacking density, the gaps among the particles are reduced, and the reduction of the liquid passing performance of the water-soluble liquid passing through the particles is reduced. That is, a so-called gel blocking phenomenon occurs, and the smaller the particle diameter, the more likely the gel blocking phenomenon occurs. Therefore, when using water-absorbing resins, the two conflicting parameters mentioned above are considered simultaneously: water absorption rate and liquid permeability. The traditional resin structure is difficult to simultaneously take the water absorption speed and the liquid permeability into consideration, and how to obtain a product with high water absorption speed and high liquid permeability to meet the requirement of a thin sanitary product becomes a hotspot and difficulty in the present stage.

According to the preliminary research, the water-absorbent resin micro surface structure design is adopted, and the pores or the bulges with specific sizes are accurately controlled and generated on the surface of the water-absorbent resin with larger particle sizes, so that the high liquid absorption speed and the high liquid permeability of the resin can be effectively considered. In the structure, the specific surface area of the resin can be effectively increased by the air holes and the bulges with specific sizes, the effect of increasing the specific surface area cannot be achieved when the sizes are too large, and a closed-cell structure is formed when the sizes are too small, so that the effect is ineffective; meanwhile, the larger particle size of the particles endows the swollen gel with wider pore canal gaps, and the water-absorbent resin with the characteristics is suitable for thin sanitary products.

At present, the techniques for imparting a high specific surface area to a resin without changing the particle size of the resin mainly include three types: (1) preparing a water-absorbing resin with a porous structure by a physical or chemical foaming method (such as EP0295438B, WO1994022502A, EP0644207B, EP0538983B, US20050137546A, CN102225981A, US20120258851A, CN103857714A, CN1668343A, CN1296981A, CN101050244A, CN101143913A, CN101423588A, CN104448155A, CN102311557A, CN104448102A, CN103214616A, CN103476811A, CN103857714A, CN105377921A, CN102317329A and CN 102010560A); (2) preparing an agglomerated particle type water absorbent resin by micropowder granulation (e.g., EP 0591168A); (3) surface treatment agents (e.g., clays, inorganic materials, etc.) are added to increase the imbibition rate of the water-absorbent resin (e.g., US20050239942A, WO 2005120221A). Among them, the more studied and effective method is the foaming polymerization strategy.

Regarding the technology of preparing porous structure water-absorbent resin by foaming polymerization, patent CN1668343A selects 5-12 wt% of ammonium carbonate or azodicarbonammonium carbonate or decarboxylated citric acid foaming agent, 0.1-5 wt% of surfactant, thickener and inorganic filler are added in the polymerization process, and the polymer hydrogel is foamed after polymerization. Although the method obviously improves the absorption speed, a large amount of foaming agent is used in the system, the components of the original water-absorbent resin are changed, and the bulk density of the water-absorbent resin is greatly reduced.

Patent CN104448155A, 2-5 wt% sodium bicarbonate is added to the monomer mixture, polymerization is started after introducing nitrogen to remove oxygen for 20 minutes, initiation is started at 5 ℃, and 1-3 wt% silicon dioxide is added to the polymerIn the combined solution, part of HCO₃ ^-Can be stably existed in weak acid system at low temperature, and when the temperature of the system is increased, it can be reacted with H⁺Carbon dioxide is released in the reaction, the viscosity of the system is increased, and the gas cannot be discharged; the silica forms voids and negative pressure at the contact point with the resin. Also, this technique uses too much blowing agent and, in addition, HCO dissolved in the monomer solution₃ ^-The gas generation process of the components lacks nucleating agent, the bubbles are too large, and the liquid absorption speed is improved to a limited extent.

In the patent CN102311557A, 0.01-10 wt% of the coating foaming agent is added for polymerization reaction; the foaming agent component of the coating treatment is a mixture of alum compounds coated on the surfaces of carbonate compound particles. The alum coats the carbonate compound, so that the carbonate compound does not contact with the monomer aqueous solution immediately, the escape of carbon dioxide is further prevented, the carbonate compound in the foaming agent is slowly released, and the resin with the porous structure is obtained. The method is suitable for a low-temperature initiated polymerization system, and the viscosity of the system is increased and the number of pores is increased along with the increase of heat generated by polymerization.

In patent CN105377921A, 0.07-1 wt% of a particulate blowing agent (carbonate) having a particle size of 10-900 μm and 0.07-1 wt% of a surfactant are added to the monomer solution before the initiator is added. In the presence of the surfactant, the bubbles have a smaller diameter.

Patent CN102317329A discloses that polymerization is carried out in the absence of surfactant or in the presence of less than 300ppm of an aqueous acrylic monomer solution in which a gas is dissolved and/or dispersed, fine bubbles of an inert gas are suspended or dissolved in the aqueous monomer solution, the polymerization process stays in the polymerized gel, and the liquid absorption rate is increased by increasing the specific surface area.

In addition, there are other known pipetting speed increasing techniques.

Patent EP0591168A discloses a method of reacting a surface crosslinking agent with primary particles, small particle size resin agglomeration is carried out simultaneously with surface crosslinking, and by controlling the time at which surface crosslinking starts, surface crosslinking between particles is achieved to increase the liquid absorption rate. When the primary particles of the aggregate are contacted with liquid, the separation of fine particles can not occur due to surface cross-linking between the particles, and the gel blockage is reduced; agglomeration increases the specific surface area and increases the rate of absorption.

Patent US20050239942A discloses the addition of clay to water-absorbent resin particles in a surface crosslinking step for improving the liquid-absorption rate and permeability.

WO2001089591A discloses that hydroxyalkyl amide is used to treat the surface of resin, the treatment temperature is 100-160 ℃, the treatment time is 90-150 minutes, and the absorption rate, the absorption liquid amount and the gel strength are improved.

The foaming technology can effectively solve the problem that the liquid absorption speed of the water-absorbent resin is slow, but the pore size is difficult to control due to the randomness of the size of bubbles, a large number of closed pore structures can be formed in pores inside the resin, so that the bulk density of the water-absorbent resin is excessively reduced, and the packaging and transportation cost is increased. In addition, the thin-wall pore channel structure formed by foaming polymerization is easy to break due to impact in the processes of material conveying, packaging and transportation, so that the physical stability is difficult to ensure, and fine powder formed by impact breaking can cause dust floating and environmental deterioration in the using process. The technique disclosed in said patent improves the liquid-absorbing rate of the water-absorbent resin, but is still insufficient. In addition, if the liquid absorption rate is greatly increased, the resin is deteriorated in liquid absorption properties such as impact resistance, ability to conduct and distribute liquid, liquid retention ability, and absorption capacity under pressure.

Disclosure of Invention

The present invention aims to provide a method for efficiently producing a water-absorbent resin having a low liquid reflux amount and a high liquid-absorbing rate without excessively lowering the bulk density of the resin and without affecting the liquid-absorbing characteristics thereof, and to obtain a water-absorbent resin having a high liquid-absorbing rate.

In order to solve the problems, in the granulation process, the shearing stress and the extrusion acting force on gel are increased to destroy the surface structure of the gel, so that the surface of the gel forms an uneven rough surface, the collapse of the surface structure of the water-absorbent resin caused by the drying process is reduced by controlling the temperature in the drying process, and after crushing and screening, the rough surface of the water-absorbent resin provides a higher specific surface area for the water-absorbent resin, so that the liquid absorption rate of the water-absorbent resin is effectively improved.

In order to achieve the above object, the present invention provides a method for producing a water absorbent resin, comprising the steps of:

(a) a step of obtaining an aqueous solution containing an acrylic monomer and a crosslinking agent,

(b) a step of subjecting an aqueous solution containing an acrylic monomer and a crosslinking agent to a polymerization reaction to obtain a gel-like crosslinked polymer having a water content of 20 to 55 wt%,

(c) a step of crushing the hydrogel-like crosslinked polymer into gel particles with a number average particle diameter of 50 micrometers to 1 millimeter under the action of high shear and/or extrusion force during or after the polymerization reaction,

the high shear force and/or extrusion force is provided by increasing the exit resistance of the mincer baffle and/or increasing the speed and length of the mincer screw and/or multiple granulations,

(d) heating and drying the crushed gel particles by adopting a heating medium with the temperature of 80-170 ℃ to obtain a crosslinked polymer with the water content of 0.1-10 wt%,

(e) and a step of preparing water-absorbent resin particles by finely granulating the dried crosslinked polymer and sieving.

In the method for producing a polyacrylic acid water-absorbent resin, a gel surface tension modifier having a surface tension of 15 to 40mN/m and/or a dynamic surface tension of 18 to 60mN/m is added during the step (a) and/or the step (b) and/or the step (c).

A water-absorbent resin having a high liquid-absorbing rate and a method for producing the same are disclosed, which can stably and efficiently produce a water-absorbent resin having a high liquid-absorbing rate without substantially changing the bulk density and impact crushing strength of the water-absorbent resin.

Detailed Description

The method for producing the polyacrylic acid water-absorbent resin of the present invention will be described in detail below, but the scope of the present invention is not limited to these descriptions.

[1] Method for producing polyacrylic acid water-absorbent resin

The polyacrylic acid water-absorbent resin of the present invention is produced by the following steps.

1.1 monomer solution

A step of obtaining an aqueous solution containing an unsaturated acrylic monomer and a crosslinking agent. The following is a detailed description.

The Monomer (Monomer) used in the present invention is a monoethylenically unsaturated acid group-containing Monomer having an unsaturated double bond and capable of forming a water absorbent resin by radical polymerization, and is not particularly limited, and acrylic acid, methacrylic acid, ethacrylic acid, α -chloroacrylic acid, α -cyanoacrylic acid, β -methacrylic acid (crotonic acid), α -phenylacrylic acid, β -acryloyloxypropionic acid, sorbic acid, α -chlorosorbic acid, 2' -methylisotalonic acid, cinnamic acid, p-chlorocinnamic acid, β -stearic acid, itaconic acid, citraconic acid, mesaconic acid, glutaconic acid, aconic acid, maleic acid, cinnamic acid, fumaric acid, tricarboxyethylene and maleic anhydride can be cited.

Other types of monomers may be used to copolymerize with the carboxyl group-containing monomer. The following may be mentioned: anionic unsaturated monomers and salts thereof such as vinylsulfonic acid, allyltoluenesulfonic acid, vinyltoluenesulfonic acid, styrenesulfonic acid, 2- (meth) acrylamido-2-methylpropanesulfonic acid, 2- (meth) acryloylethanesulfonic acid, 2- (meth) acryloylpropanesulfonic acid, and 2-hydroxyethyl (meth) acryloylphosphate; a mercapto group-containing unsaturated monomer; a phenolic hydroxyl group-containing unsaturated monomer; amide group-containing unsaturated monomers such as (meth) acrylamide, N-ethyl (meth) acrylamide, and N, N-dimethyl (meth) acrylamide; and amino group-containing unsaturated monomers such as N, N-dimethylaminoethyl (meth) acrylate, N-dimethylaminopropyl (meth) acrylate, and N, N-dimethylaminopropyl (meth) acrylamide.

These unsaturated monomers may be used alone or in combination of 2 or more, and acrylic acid-based water-absorbent resins containing acrylic acid and/or a salt thereof (for example, a salt such as a sodium salt, a lithium salt, a potassium salt, an ammonium salt, or an amine) can be preferably used in combination of the performance and cost of the water-absorbent resin powder, and among them, a sodium salt of the acrylic acid-based monomer is more preferable in terms of cost.

The neutralization rate of these unsaturated acid group-containing monomers is not particularly limited, and may be partially or completely neutralized, preferably partially neutralized, and if necessary, the polymerization gel may also be neutralized after polymerization. The unsaturated acid group-containing monomer preferably has a neutralization degree of 25 to 100 mol%, particularly preferably at least 40 to 95 mol%, and more preferably 50 to 90 mol%. The neutralization of the unsaturated acid group-containing monomers can be carried out before or after the polymerization. Neutralization can be carried out using alkali metal hydroxides, alkaline earth metal hydroxides, ammonia, and carbonates and bicarbonates. In addition, any other base that can form a water-soluble salt with the acid can be used. Neutralization can also be carried out using a variety of bases. Neutralization with ammonia or alkali metal hydroxides is preferred, and neutralization with sodium hydroxide or sodium carbonate is particularly preferred.

The amount of acrylic acid and/or a salt thereof used as the polyacrylic acid-based water-absorbent resin powder is usually 60 mol% or more, preferably 75 mol% or more, preferably 90 mol% or more, and more preferably 95 mol% or more, based on the whole monomer component (excluding the crosslinking agent).

The concentration of the monomer is not particularly limited, and the concentration of the aqueous solution of the unsaturated acid group-containing monomer and the crosslinking agent is 15 to 60% by weight, preferably 18 to 55% by weight, and more preferably 20 to 50% by weight. When the monomer concentration is less than 20% by weight, productivity is lowered, and therefore, it is not preferable. When the monomer concentration is higher than 60% by weight, the pulverization load increases, resulting in deterioration of production stability. The solvent for the monomers is water, and a small amount of organic solvent may be used in combination.

The internal crosslinking agent is one or more selected from the group consisting of a compound having a plurality of vinyl groups in a molecule, a compound having at least one vinyl compound and at least one functional group capable of reacting with a carboxyl group of the unsaturated monomer in a molecule, and a compound having a plurality of functional groups capable of reacting with a carboxyl group of the unsaturated monomer in a molecule. Previously well known internal cross-linking agents may be used. Specifically, for example, there may be mentioned: one or more of N, N' -methylenebisacrylamide, trimethylolpropane tri (meth) acrylate, ethylene glycol di (meth) acrylate, polyethylene glycol diacrylate, polyethylene glycol di (meth) acrylate, polyethylene glycol diallyl ether, pentaerythritol tetraacrylate, triarylamine, ethylene glycol diglycidyl ether, ethylene glycol, 1, 2-propanediol, 1, 3-propanediol, 1, 4-butanediol, glycerol, pentaerythritol, polyethylene glycol, and vinyl carbonate, and these internal crosslinking agents may be used in consideration of the reactivity. Among these, one or more of trimethylolpropane tri (meth) acrylate, polyethylene glycol diacrylate, ethylene glycol diglycidyl ether, polyethylene glycol, and 1, 4-butanediol are preferable, and one or more of trimethylolpropane tri (meth) acrylate, polyethylene glycol diacrylate, and ethylene glycol diglycidyl ether are more preferable.

The amount of the internal crosslinking agent to be used is determined in accordance with the physical properties of the water absorbent resin, and is preferably 0.001 to 5 mol%, more preferably 0.005 to 2 mol%, and still more preferably 0.01 to 1 mol% based on the monomer content. If the amount of the internal crosslinking agent used is less than 0.001 mol%, the water-soluble matter content of the resulting water-absorbent resin increases, and the water absorption capacity under pressure cannot be sufficiently ensured. If the amount of the internal crosslinking agent used exceeds 5 mol%, the chemical crosslinking density becomes too high, and the water absorption amount of the resulting water absorbent resin powder becomes insufficient. Further, the internal crosslinking agent may be added to the reaction system at once or may be added to the reaction system in portions.

1.2 polymerization step

The polymerization step is a step of polymerizing the aqueous monomer solution. The polymerization process may be carried out under normal pressure, reduced pressure or increased pressure, and is preferably carried out under normal pressure.

As the polymerization initiator used in the present step, there is no particular limitation, and any initiator which can form radicals under polymerization conditions and is generally used for preparing a water absorbent resin may be used. The polymerization can also be initiated by applying an electron beam to the polymerizable aqueous monomer solution. The polymerization can also be initiated by the action of high-energy radiation in the presence of a photoinitiator. One or more kinds are selected from polymerization initiators generally used in the production of water absorbent resins depending on the kind of monomers to be polymerized, polymerization conditions, and the like.

The polymerization initiator is preferably a peroxide, a hydroperoxide, hydrogen peroxide, a persulfate, and an azo compound. Preferably, a water-soluble initiator is used. Specifically, the following are listed: thermal decomposition type initiators such as persulfates of sodium, potassium, ammonium persulfate and the like; peroxides such as hydrogen peroxide, t-butyl peroxide and methyl ethyl ketone peroxide, azo compounds such as azonitrile compounds, azoamidine compounds, cyclic azoamidine compounds, azoamide compounds, alkyl azo compounds, 2 '-azobis (2-amidinopropane) dihydrochloride and 2, 2' -azobis [2- (2-imidazolin-2-yl) propane ] dihydrochloride; or photodegradable initiators such as benzoin derivatives, benzil derivatives, acetophenone derivatives, benzophenone derivatives, azo compounds, and the like. Among these initiators, from the viewpoint of cost and the ability to reduce residual monomers, a thermal decomposition type initiator is preferable, and a persulfate is more preferable.

In addition, the decomposition of these polymerization initiators can be promoted by using a reducing agent in combination. Therefore, a redox system initiator may be used. The reducing agent is not particularly limited, and may be selected from: sodium metabisulfite, sodium sulfite, sodium bisulfite and other sulfurous acid (salts), L-ascorbic acid (salts), metal salts (such as iron (II) ions or silver ions), amines and the like. In the case of using an oxidative polymerization initiator and a reducing agent as in the case of the redox initiator, they may be separately combined with the monomer solution, or the reducing agent may be mixed in advance with the monomer solution.

In the polymerization, a hydrophilic polymer such as polyethylene glycol, starch, a starch derivative, cellulose, a cellulose derivative, polyvinyl alcohol, polyacrylic acid (salt), or a crosslinked polyacrylic acid (salt) may be added to the reaction system before or during the polymerization, if necessary; or a chain transfer agent such as hypophosphorous acid (salt), a chelating agent, etc. As the hydrophilic polymer, a water-soluble resin or a water-absorbent resin can be preferably used, and the viscosity of the reaction system can be increased. The amount of the hydrophilic polymer used is preferably 0 to 30% by weight, more preferably 0.001 to 20% by weight, and still more preferably 0.01 to 10% by weight, based on the monomer.

The polymerization method used in this step is not particularly limited. Preferred are radical polymerization in the homogeneous phase (e.g., radical polymerization in an aqueous solution), precipitation polymerization from an organic solvent, suspension polymerization, emulsion polymerization, miniemulsion polymerization, or the like. The radical polymerization in a homogeneous system is preferable, and the radical polymerization in an aqueous solution is more preferable. The aqueous solution polymerization method includes a static polymerization method in which an aqueous monomer solution is polymerized in a static state, and a stirring polymerization method in which polymerization is performed in a stirring apparatus. Further, polymerization methods are classified into batch-wise polymerization and continuous polymerization according to continuous productivity. Particularly suitable for solving the problem are aqueous solution polymerizations, especially continuous belt polymerizations or continuous kneader polymerizations.

The apparatus for producing the water-absorbent resin of the present invention is not particularly limited, and a continuous conveyer polymerization apparatus or a continuous stirring polymerization apparatus is preferable.

The polymerization apparatus is preferably an endless belt type continuous static polymerization apparatus, and the belt is made of fluororesin or coated with fluororesin. Further, it is preferable to use a system including a heating device or a heat retaining device and recovering and reusing water and/or vapor of the monomer solution generated during polymerization.

The continuous stirring polymerization apparatus may be a single-shaft stirring apparatus or a stirring apparatus having a plurality of stirring shafts, such as a continuous kneader, and the use of a multi-shaft stirring apparatus is preferable from the viewpoint of productivity.

1.3 granulation step

The step of pulverizing the crosslinked hydrogel polymer obtained as described above may be performed during or after polymerization. A kneader may be used for the pulverization during the polymerization, and a slitter, a meat chopper or the like may be used for the pulverization after the polymerization. The gel particle size after pulverization is preferably 50 μm to 1 mm, and if the gel particles are too small, the equipment required for pulverization is excessively high, which is uneconomical, and if the hydrogel-like polymer is not pulverized or the gel particles are too large, the desired granular product having a high liquid-absorbing rate cannot be obtained.

In order to obtain the effect of the invention, the shear stress and the extrusion acting force on the gel are increased to destroy the surface structure of the gel, so that the surface of the gel forms an uneven rough surface, and after crushing and screening, the rough surface of the water-absorbent resin provides a higher specific surface area for the gel, thereby effectively improving the liquid absorption rate of the gel. The high shearing force and/or the extrusion force are provided by changing the aperture of the baffle plate at the outlet of the meat grinder, the gel strength, the using amount and temperature of granulating water, the rotating speed and length of a screw or granulating for multiple times, and are not particularly limited.

In order to obtain the effect of the present invention, it is necessary to add a surface tension modifier during the preparation of the monomer solution and/or during the polymerization process and/or during the gel mincing process. The gel surface tension modifier is a polymer containing at least one hydrophilic group and at least one hydrophobic group. The hydrophilic group is selected from one or more of carboxylic acid (salt), sulfuric acid (salt), sulfonic acid (salt), benzene sulfonic acid (salt), quaternary ammonium salt, polyethylene oxide and derivatives thereof, hydroxyl-containing compound and amino-containing compound. The hydrophobic group is selected from one or more of a straight chain or branched alkyl chain, polypropylene oxide and derivatives thereof, an aromatic chain or a long fluorine-containing chain.

In order to obtain the effect of the present invention, the surface tension of the gel surface tension modifier is 10 to 60mN/m and/or the dynamic surface tension is 10 to 80mN/m, preferably the surface tension is 12 to 50mN/m and/or the dynamic surface tension is 15 to 70mN/m, more preferably the surface tension is 15 to 40mN/m and/or the dynamic surface tension is 18 to 60 mN/m. The surface tension and dynamic surface tension of the surface tension modifier are the values of the tensions measured in a 0.1 wt% aqueous solution at a temperature of 25 ℃.

The surface tension modifier is prepared into a solution in the using process or added into a system for use by pure components, and the concentration of the surface tension modifier in the solution is 0.1-50 wt%. The surface tension modifier is used in an amount of 0.001 to 10 wt%, preferably 0.005 to 5 wt%, and more preferably 0.01 to 3 wt%, based on the hydrogel-like crosslinked polymer.

In order to better or obtain the effect of the invention, polyacrylic acid water-absorbing resin particles with the number average particle diameter of 1-200 microns are mixed with gel in the process of mincing the gel, the polyacrylic acid water-absorbing resin particles contain a surface tension modifier, and the surface tension of the polyacrylic acid water-absorbing resin particles is 10-60 mN/m and/or the dynamic surface tension is 10-80 mN/m, preferably the surface tension is 12-50 mN/m and/or the dynamic surface tension is 15-70 mN/m, further preferably the surface tension is 15-40 mN/m and/or the dynamic surface tension is 18-60 mN/m. The surface tension modifier is contained in an amount of 0.005 to 30% by weight, more preferably 0.01 to 10% by weight, based on the water absorbent resin particles.

1.4 Heat drying step

The heat drying step is to dry the hydrogel-like crosslinked polymer to form a polymer. The drying is usually carried out at a temperature of 80 to 170 ℃ as a heating medium, preferably 95 to 170 ℃, more preferably 110 to 170 ℃. The drying time depends on the surface area and the moisture content of the polymer and the type of dryer, chosen to obtain the target moisture content (moisture content is measured by the 3 hour loss on drying at 105 ℃).

Some drying temperatures are too high to achieve a significant increase in the absorption rate of the invention. Compared with the water-absorbent resin obtained by drying with a heating medium at 180-210 ℃, the water-absorbent resin obtained by drying the crushed gel particles with a heating medium at 80-170 ℃ has a saline absorption speed change rate delta V of one minute₁3-25%, pure water absorption speed change rate delta V in one minute₂10 to 40 percent.

In the formula,. DELTA.V₁One minute amount of brine (80 to 170 ℃) to one minute amount of brine (180 to 210 ℃)/one minute amount of brine (180 to 210 ℃);

in the formula,. DELTA.V₂Pure water absorption amount of one minute (80-170 ℃) to pure water absorption amount of one minute (180-210 ℃)/pure water absorption amount of one minute (180-210 ℃).

The water content of the water absorbent resin used in the present invention is not particularly limited, and the water content is more preferably 0.2 to 30% by weight, still more preferably 0.3 to 15% by weight, and particularly preferably 0.5 to 10% by weight. Too high a water content not only impairs flowability and thus affects production, but also makes comminution of the water-absorbent resin impossible and may lose control over a particular particle size distribution.

As the drying method used is not particularly limited, various methods may be employed to obtain the target water content, specifically listed are: heat drying, hot air drying, drying under reduced pressure, infrared drying, microwave drying, dehydration by azeotrope with hydrophobic organic solvents and drying with high humidity using high temperature steam.

1.5 Fine granulation and sieving step

In order to obtain a water-absorbent resin having a specific particle size (particle size is adjusted in conjunction with the below-described fine powder granulation process), a step of finely granulating and sieving the dried crosslinked polymer is required.

Machines for obtaining an absorbent resin having an irregular crushed shape and a particle diameter which can be effectively controlled, and for grain refining, include shearing coarse crushers, impact powder crushers, and high-speed rotary powder crushers. And further sieving the resin particles after the grain refining.

The mass median particle diameter (D50) of the water-absorbent resin is preferably adjusted to 200 to 650 microns, more preferably 200 to 550 microns, and still more preferably 200 to 500 microns. The proportion of particles having a diameter of less than 150 μm is controlled to be 0 to 8 wt%, preferably 0 to 5 wt%, more preferably 0 to 3 wt%. In addition, the smaller the proportion of particles having a diameter of more than 850 μm, the better, the more preferably 0 to 8% by weight, preferably 0 to 5% by weight, and more preferably 0 to 2% by weight. In the present invention, the surface crosslinking is preferably carried out under the condition that the proportion of particles of 150 to 850 μm is 95 wt% or more, more preferably 98 wt% or more. Logarithmic standard deviation (σ) of particle size distribution_ζ) Preferably, the amount of the organic solvent is controlled to be 0.20 to 0.40, more preferably 0.20 to 0.38, and still more preferably 0.20 to 0.36.

1.6 Recycling of Fine-grained Water-absorbent resin

In the present invention, the amount of generation of small-particle-diameter fine particles (particles of less than 150 μm) is controlled by reusing the fine-particle water-absorbent resin.

The small-particle-size water-absorbent resin particles (particles smaller than 150 microns) obtained through grain refining and screening can be returned to a monomer solution for repolymerization or mixed with a large amount of hot water for agglomeration (the weight ratio of the small-particle water-absorbent resin to the hot water is 2: 1-1: 2) to recover into a hydrogel-like product again, or the small-particle-size particles are directly mixed with gel and then readjusted into the water-absorbent resin particles with the target particle size through the steps of granulation, drying, grain refining and the like. The amount of waste material can be reduced by recovering and regenerating particles outside the target range.

1.7 surface Cross-linking

The production method of the present invention further comprises a step of forming covalent bonds by surface-treating the vicinity of the surface of the water-absorbent resin after sieving the particle size with a surface-crosslinking agent. The water absorption multiplying power and liquid permeability under the resin pressurization can be effectively improved through the surface crosslinking step of the water absorption resin with the screened particle size. However, the centrifugal water retention capacity (CRC) of the water-absorbent resin used in the invention is reduced to a certain extent after surface crosslinking compared with that before crosslinking, and is 50-95% of the original centrifugal water retention capacity, and is further reduced to 60-90%. The degree of reduction in the centrifuge water retention capacity can be adjusted by the type and amount of the crosslinking agent, the reaction temperature and the reaction time.

The surface crosslinking treatment of the present invention means a process of increasing the density of crosslinking points in the vicinity of the particle surface. More specifically, it is an operation of forming a new crosslink by adding a compound having at least two functional groups capable of reacting with a carboxyl group in a molecule, which can form a bond by reacting with the carboxyl group or a salt thereof contained in the particulate water absorbent resin, to the surface of the particle. The surface-crosslinking agent used in this step is preferably a surface-crosslinking agent capable of forming a covalent bond or an ionic bond with the surface functional group of the water-absorbent resin.

The surface cross-linking agent which can be used in the present step is preferably, for example, a polyhydric alcohol compound, an epoxy compound, a polyamine compound or a condensate thereof with a halogenated epoxy compound, an oxazoline compound, a (mono, di or poly) oxazolidinone compound, an alkylene carbonate compound, specifically, a polyhydric alcohol such as polyethylene glycol, 1, 2-propanediol, 1, 3-propanediol, dipropylene glycol, 2,3, 4-trimethyl-1, 3-pentanediol, polypropylene glycol, glycerin, polyglycerin, 2-butene-1, 4-diol, 1, 4-butanediol, 1, 3-butanediol, 1, 5-pentanediol, 1, 6-hexanediol, 1, 2-cyclohexanedimethanol, etc., an epoxy compound such as ethylene glycol diglycidyl ether, polyethylene glycol glycidyl ether, glycidyl, etc., a polyvalent amine compound such as ethylene diamine, diethylene triamine, triethylene tetramine, tetraethylene pentamine, pentaethylene hexamine, polyethylene imine, etc., a halogenated epoxy compound such as epichlorohydrin, epibromohydrin, α -methyl epoxypropane, etc., a polyvalent amine compound such as ethylene diamine, triethylene tetramine, tetraethylene pentamine, a polyvalent alkylene carbonate compound such as a polyvalent ethyleneurea compound, a polyvalent alkylene carbonate compound having a carbon atom of 2-carbon atom, etc., preferably, and a polyvalent alcohol compound having a carbon atom, can be used alone or in combination.

The amount of the surface crosslinking agent to be used depends on the kind of the crosslinking agent to be used and the combination thereof, and is preferably 0.01 to 10% by weight, more preferably 0.05 to 5% by weight, based on the water absorbent resin.

In the surface crosslinking of the present invention, water is preferably used as a solvent for the surface crosslinking agent. The amount of water used depends on the amount of the surface cross-linking agent active ingredient and the water content of the water absorbent resin, and is preferably 0.2 to 20% by weight, more preferably 0.3 to 15% by weight, and further preferably 0.5 to 10% by weight, based on the water absorbent resin. In addition, a hydrophilic organic solvent may be used in combination with water, and when a hydrophilic organic solvent is used, the amount of the organic solvent is preferably 0 to 10% by weight, more preferably 0 to 8% by weight, and further preferably 0 to 5% by weight, based on the water absorbent resin.

The surface-crosslinking agent is preferably premixed in water and/or a hydrophilic organic solvent, and then the treatment liquid is sprayed or dropped to the water-absorbent resin, more preferably a spraying method. The average particle diameter of the sprayed liquid drops is preferably 0.1-500 micrometers, and more preferably 0.1-200 micrometers.

After the surface cross-linking agent is added to the water absorbent resin, it is preferably subjected to heat treatment. The surface treatment temperature is 100 to 220 ℃, preferably 130 to 210 ℃, further preferably 160 to 200 ℃, and the heating time is preferably 1 minute to 2 hours.

1.8 chelating agents

By adding the chelating agent, time-course decomposition of the water absorbing agent derived from the reaction of components in urine with Fe ions can be suppressed, and also dissolution of the water absorbing agent, decrease in the absorption rate of the water absorbing agent, and decrease in the liquid permeability of the water absorbing agent can be suppressed. The chelating agent is added at one or more of the following times: (1) during the polymerization; (2) after polymerization and before surface crosslinking; (3) during surface cross-linking; (4) during agglomeration.

The chelating agent used in the water absorbing agent of the present invention is preferably a chelating agent having a high blocking ability or chelating ability for Fe or Cu ions, preferably an amino polyvalent carboxylic acid and its salt, and particularly preferably an amino carboxylic acid having not less than 3 carboxyl groups and its salt.

The amount of the amino polyvalent carboxylic acid to be used is 0.00001 to 10% by weight, preferably 0.0001 to 1% by weight, based on the water absorbent resin.

1.9 inorganic powders

The liquid permeability of the water-absorbent resin can be effectively improved by adding the inorganic powder, and the inorganic powder is preferably a silica powder having an average particle diameter of 100 nm or less. The amount of the inorganic powder added is 0.001 to 10% by weight, preferably 0.005 to 1% by weight, and more preferably 0.01 to 0.5% by weight, based on the water absorbent resin.

1.10 other additives

Other additives may be added to the water absorbent resin as required, including: an oxidizing agent, an antioxidant, a reducing agent, a color stabilizer, water, a polyvalent metal compound, a water-insoluble inorganic or organic powder such as a metal soap, a deodorant, an antibacterial agent, pulp, a thermoplastic fiber, or the like.

[2] Physical Properties of polyacrylic acid Water-absorbent resin

The polyacrylic acid-based water absorbing resin of the present invention has a particulate water absorbing agent having an irregular pulverized shape, and specific physical properties are as follows.

2.1 particle size and distribution

Mass median particle diameter (D) of the Water-absorbent resin of the present invention₅₀) Preferably 200 to 650 micrometers, more preferably 200 to 550 micrometers, and still more preferably 200 to 500 micrometers. The proportion of particles having a diameter of less than 150 μm is controlled to be 0 to 8 wt%, preferably 0 to 5 wt%, more preferably 0 to 3 wt%. In addition, the smaller the proportion of particles having a diameter of more than 850 μm, the better, the more preferably 0 to 8% by weight, preferably 0 to 5% by weight, and more preferably 0 to 2% by weight. In the present invention, the surface crosslinking is preferably carried out under the condition that the proportion of particles of 150 to 850 μm is 95 wt% or more, more preferably 98 wt% or more. Logarithmic standard deviation (σ) of particle size distribution_ζ) Preferably, the amount of the organic solvent is controlled to be 0.20 to 0.40, more preferably 0.20 to 0.38, and still more preferably 0.20 to 0.36.

2.2 centrifuge Water holding Capacity (CRC)

The centrifugal water retention capacity (CRC) for a 0.9 wt% sodium chloride aqueous solution is preferably 10 to 60g/g, more preferably 20 to 55g/g, still more preferably 25 to 50g/g, and particularly preferably 25 to 45 g/g. In terms of absorption capacity. The higher the CRC, the better, but in actual use, it is necessary to balance with other physical properties as the case may be.

2.3 absorbency under load (AUP)

The water-absorbent resin was surface-crosslinked to improve its water absorption capacity (pressure water absorption capacity, AUP) against a 0.9 wt% aqueous sodium chloride solution under pressure. The AUP is preferably 15 to 55g/g, more preferably 15 to 50g/g, still more preferably 15 to 45g/g, and particularly preferably 15 to 40g/g under a pressure of 1.9kPa (0.3 psi). The AUP is preferably 10 to 50g/g, more preferably 10 to 45g/g, still more preferably 10 to 40g/g, and particularly preferably 10 to 35g/g under a pressure of 4.8kPa (0.7 psi). The higher the AUP, the better, but in actual use, it is necessary to balance the properties with other physical properties as the case may be.

2.4 vortex absorption Rate

The water-absorbent resin of the present invention has a swirl absorption rate of less than 60sec/g, preferably 1 to 55sec/g, more preferably 10 to 50 sec/g. A water-absorbing agent having an absorption rate of more than 60sec/g may not achieve a sufficient effect.

2.5 one minute amount of saline absorbed

The method adopts the saline absorption per minute to characterize the liquid absorption speed of the water absorbent, and the saline absorption per minute of the water absorbent is 15-50 g/g, preferably 17-45 g/g, and further preferably 19-40 g/g. The water-absorbing agent having a water absorption amount of less than 15g/g per minute may not be able to achieve a sufficient effect.

2.6 minute Water intake

The method further characterizes the liquid absorption speed of the water absorbent by adopting the pure water absorption amount per minute, and the pure water absorption amount per minute of the water absorbent is 50-200 g/g, preferably 60-190 g/g, and further preferably 65-180 g/g. A water-absorbing agent having a pure water absorption amount of less than 50g/g per minute may not be able to achieve a sufficient effect.

2.7 Water content

The water content is a parameter for determining a volatile substance such as water contained in the water absorbent resin. The water content of the water-absorbent resin of the present invention is preferably 1 to 10% by weight, more preferably 2 to 10% by weight.

[3] Use of polyacrylic acid-based water-absorbent resin

The particulate water-absorbent resin of the present invention is not particularly limited in its application, and can be used for absorbent articles such as disposable diapers, sanitary napkins, incontinence pads and the like, preferably for thin absorbent substrates and absorbent articles such as thin absorbent articles.

The absorbent article generally contains other absorbent materials (pulp fibers and the like), and the content of the water-absorbent resin is 30 to 100% by weight, preferably 40 to 100% by weight, more preferably 50 to 100% by weight, and still more preferably 60 to 100% by weight.

[4] Examples of the embodiments

The present invention will be illustrated with the following examples and comparative examples, but the present invention is not limited to the following examples.

Various properties of the water absorbent resin were measured by the following methods. The water absorbing resin, the water absorbing agent and the absorbent article were used under conditions of 25. + -. 2 ℃ and 50% RH (relative humidity), unless otherwise specified. The physiological saline solution used was a 0.90 wt% aqueous sodium chloride solution.

4.1 particle size and distribution

Particle size and distribution were tested by sieving. A quantity of superabsorbent powder is separated into atmospheres of different particle sizes by passing through a series of standard sieves arranged in sequence. The powders for each particle size range were weighed and reported as a percentage of the total weight.

The tray and each empty sieve (to the nearest 0.1 gram) were weighed and recorded. The sieves were placed in the correct order (850 microns, 600 microns, 300 microns, 150 microns, 45 microns) on a shaker (fine bottom, coarse top). 100g (to the nearest 0.1 g) of the sample to be tested are weighed into a beaker₁. The weighed sample was poured into the uppermost sieve. The screen cover is closed as instructed by the manufacturer. The screen oscillator was set as follows: oscillation intensity 70 ± 2% (according to the settings of the Retsch VE1000 oscillator), amplitude 1.0 mm, oscillation time 10 minutes. The shaker was turned on and after 10 minutes each sieve and tray was carefully removed and weighed to the nearest 0.01 grams, m₂. The percentage (w) of each sample was calculated as follows:

the particle diameter corresponding to 50% by weight of R is determined as the mass median particle diameter (D)₅₀). Logarithmic standard deviation (σ)_ζ) Represented by the formula, where σ is the smaller value_ζMeaning a narrower particle size distribution.

σ_ζ＝0.5×ln(X₂/X₁)

Wherein, X1 and X₂Particle sizes of 84.1 wt% and 15.9 wt%, respectively.

4.2 centrifuge Water holding Capacity (CRC)

The Centrifuge Retention Capacity (CRC) represents the water absorption capacity of a 0.90 wt% aqueous sodium chloride solution (also referred to as physiological saline) after absorbing water for 30 minutes without pressure and then centrifuging the solution.

0.20 g of water-absorbent resin is weighed out and the weight is recorded as W₀(g) The cloth bag is put into a cloth bag made of non-woven fabric, sealed and immersed into a physiological saline solution controlled at 25 +/-2 ℃. After 30 minutes the bag containing the water-absorbent resin was removed from the saline solution. Dewatering at 250G for 3 min by centrifuge, and weighing to obtain weight W₂(g) In that respect The weight W of the bag was measured after a similar operation without using any water-absorbing agent₁(g) In that respect The centrifuge retention capacity (g/g) was calculated as follows.

Centrifuge retention capacity (g/g) ((W)₂(g)-W₁(g))/W₀(g))-1

4.3 absorbency under load (AUP)

The weighed sample was laid down on a filter screen, the bottom of a specially made cylinder was covered, a uniform pressure (1.9kPa/0.3psi, 4.8kPa/0.7psi) was initially applied to the test sample, and the cylinder was placed in a petri dish filled with 0.90% by weight sodium chloride solution. After the sample had absorbed for 1 hour, the cylinder was removed and the amount of absorbed liquid was measured as follows:

0.900g of water-absorbent resin is weighed out and the weight is recorded as W₃(g) And spreading the organic glass on a dry organic glass cylindrical filter screen to be uniformly distributed. Placing the piston inOn the cylinder and the entire set of cylinders was weighed and recorded as W₄(g) In that respect The filter plate was placed in a petri dish and 120 ml of sodium chloride solution was added to submerge the liquid surface over the aluminum plate surface. Circular filter paper is put on a filter plate and is completely wetted by sodium chloride solution, so that bubbles on the surface are avoided. The entire set of cylinder devices was placed on the soaked filter paper and after 1 hour of standing, the samples were allowed to absorb the sodium chloride solution well. The complete set of equipment is lifted and the piston is removed and the drum equipment is reweighed, recorded as W₅(g) In that respect The Absorbency Under Pressure (AUP) was calculated by the following equation.

Water absorption capacity under pressure (g/g) (W)₅(g)-W₄(g))/W₃(g)

4.4 vortex absorption Rate

In a 100 ml beaker with a stirrer, 50 ml of sodium chloride solution was added by a pipette, and the beaker was placed on a magnetic stirrer and stirred at a rotation speed of 500. + -. 50r/min, confirming that the liquid surface generated a stable vortex. 2.000 g of the water-absorbent resin was accurately weighed and added to the vortex, and a stopwatch was used to start timing, and when the vortex on the liquid surface disappeared and the liquid surface became horizontal, the end point was set, and the time was recorded.

4.5 one minute amount of saline absorbed

1.000 g of water-absorbent resin are weighed out and the weight recorded is W₀(g) The cloth bag is put into a cloth bag made of non-woven fabric, sealed and immersed into a physiological saline solution controlled at 25 +/-2 ℃. After 1 minute, the bag containing the water-absorbent resin was taken out from the saline solution. Suspended for dehydration for 1 minute, and then weighed to obtain a weight W₂(g) In that respect The weight W of the bag was measured after a similar operation without using any water-absorbing agent₁(g) In that respect The amount of saline absorbed in one minute (g/g) was calculated according to the following formula.

One minute absorbed saline water (g/g) ═ W₂(g)-W₁(g))/W₀(g))-1

4.6 pure water absorption in one minute

1.000 g of water-absorbent resin are weighed out and the weight recorded is W₀(g) Uniformly putting the mixture into a cloth bag made of non-woven fabric, sealing, and immersing into an aqueous solution controlled at 25 +/-2 ℃. After 1 minute, the water-absorbing resin will be containedThe bag is removed from the aqueous solution. Suspended for dehydration for 1 minute, and then weighed to obtain a weight W₂(g) In that respect The weight W of the bag was measured after a similar operation without using any water-absorbing agent₁(g) In that respect The amount of pure water absorbed in one minute (g/g) was calculated according to the following formula.

One minute of pure water absorption (g/g) ((W)₂(g)-W₁(g))/W₀(g))-1

4.7 Water content

The ratio of the volatile component of the particulate water-absorbent resin at 180 ℃ was shown.

The method of measuring the water content was carried out in the following manner.

About 1g of water-absorbent resin (weight W) was weighed₇(g) Put into a weighing bottle (weight W)₆(g) In a dry air dryer at 105 ℃ for 3 hours, and dried. The total weight (W) of the dried weighing flask and the particulate water-absorbent resin was measured₈(g) Calculated according to the following formula.

Water content [ weight%]＝{(W₈-W₆-W₇)/W₇}×100。

Production example 1

An acrylic acid/sodium acrylate mixed monomer solution (acrylic acid/sodium acrylate molar ratio of 2.2/7.8) was transported through the pipeline, the acrylic acid/sodium acrylate monomer concentration was 44.0 wt%, and the monomer solution flow rate was 8689 kg/h. The temperature of the monomer solution is 80-90 ℃. Polyethylene glycol diacrylate (molecular weight 522) having a concentration of 11.3% by weight was fed into the branch of the monomer solution line at a flow rate of 72 kg/h. Further, an aqueous solution of sodium persulfate having a concentration of 4% by weight (flow rate: 60kg/h) was fed to the monomer through the branch opening of the monomer solution pipe by a feed pump to initiate polymerization. The reaction solution is sprayed to the reaction bed to obtain the hydrogel polymer.

Example 1

A fine particle gel was prepared by taking 5000g of the hydrous gel-like polymer (water content: 50% by weight) in production example 1, adding 1250g of water to the surface of the gel, and after the water was completely absorbed by the gel, crushing it twice with a meat chopper (aperture diameter of 4.5 mm, aperture ratio of 34.4%). Adding 100g of 10 wt% sucrose stearate (S-770, Mitsubishi chemical) suspension on the surface of the fine particle gel by atomization, mixing well, and crushing into fine particle gel by a meat grinder (the diameter of the hole plate is 4.5 mm, and the hole rate is 34.4%). And spreading the crushed gel particles on a metal wire mesh for drying at the drying temperature of 140 ℃ for 45 minutes to obtain the cross-linked structure polymer. And (3) adopting a crushing machine to carry out grain refining on the dried crosslinked polymer, and sieving to obtain the water-absorbing resin particles 1 with the particle size of less than 150 micrometers and containing the surface modifier.

A fine particle gel was prepared by taking 5000g of the hydrous gel-like polymer (water content: 50% by weight) in production example 1, adding 1250g of water to the surface of the gel, and after the water was completely absorbed by the gel, crushing it once with a meat chopper (aperture diameter of 4.5 mm, aperture ratio of 34.4%). After the fine particle gel was uniformly mixed with the water absorbent resin particles 1, it was crushed into a fine particle gel by a meat chopper (the diameter of the opening of the orifice plate was 4.5 mm, the opening ratio was 34.4%). Adding 100g of sucrose stearate (S-770, Mitsubishi chemical) solution with the concentration of 10 weight percent on the surface of the fine particle gel in an atomizing way, uniformly mixing, and then crushing the fine particle gel into fine particle gel with the particle size of 10 micrometers-5 millimeters by using a meat grinder (the diameter of an opening hole of a pore plate is 4.5 millimeters, the opening rate is 34.4 percent), wherein the proportion of the particle size particles between 50 micrometers and 1 millimeter is more than 50 weight percent. And spreading the crushed gel particles on a metal wire mesh for drying at the drying temperature of 140 ℃ for 45 minutes to obtain the cross-linked structure polymer. And (3) adopting a crushing machine to carry out grain refining on the dried crosslinked polymer, and sieving to obtain the water-absorbing resin 1-1 with the particle size of 300-425 micrometers, the water content of 3.2 weight percent and the CRC of 46.5 g/g.

The water-absorbent resin 1-2 was obtained by mixing 100 parts by weight of the above water-absorbent resin 1-1 with 3.8 parts by weight of a mixed surface cross-linking agent solution containing 1, 2-propylene glycol, ethylene glycol diglycidyl ether and water (weight ratio 1.2:0.07:2.53) and subjecting to surface treatment at 140 ℃ for 30 minutes.

100 parts by weight of the water-absorbing agent described above were mixed with 1.317 parts by weight of an aluminum sulfate solution having a concentration of 10.3% by weight and 0.184 part by weight of silica (having a particle diameter of less than 100 nm) powder, respectively, to obtain water-absorbing agent 1 having a CRC of 34.5g/g, a saline absorption amount per minute of 28.2g/g, a pure water absorption amount per minute of 128.2g/g, and an apparent density of 0.63 g/ml.

Comparative example 1

The drying temperature of the gel in the example 1 is changed to 180 ℃, the drying time is 30 minutes, other operations are the same as the example 1, and the comparative water-absorbent resin 1-1 is obtained, wherein the particle size is 300-425 micrometers, the moisture content is 2.9 weight percent, and the CRC is 51.2 g/g.

Comparative water-absorbing resin 1-1 was further subjected to the same surface crosslinking and additive addition procedures as in example 1 to obtain comparative water-absorbing agent 1 having CRC of 35.7g/g, saline water absorption per minute of 26.1g/g and pure water absorption per minute of 118.4 g/g.

Example 2

The drying temperature of the gel in the example 1 is changed to 130 ℃, the drying time is 60 minutes, other operations are the same as the example 1, and the water-absorbent resin 2-1 is obtained, wherein the particle size is 300-425 micrometers, the moisture content is 3.5 weight percent, and the CRC is 43.2 g/g.

Water-absorbent resin 2-1 was further subjected to the same surface crosslinking and additive addition procedures as in example 1 to give water-absorbent resin 2 having CRC of 32.3g/g, saline absorption per minute of 28.5g/g and pure water absorption per minute of 130.2 g/g.

Example 3

The drying temperature of the gel in the example 1 is changed to 110 ℃, the drying time is 90 minutes, other operations are the same as the example 1, and the water-absorbent resin 3-1 is obtained, wherein the particle size is 300-425 micrometers, the moisture content is 3.1 weight percent, and the CRC is 38.3 g/g.

Water-absorbent resin 3-1 was further subjected to the same surface crosslinking and additive addition procedures as in example 1 to give water-absorbing agent 3 having CRC of 31.3g/g, saline absorption per minute of 28.8g/g and pure water absorption per minute of 130.4 g/g.

Example 4

The drying temperature of the gel in the example 1 is changed to 160 ℃, the drying time is 35 minutes, other operations are the same as the example 1, and the water-absorbent resin 4-1 is obtained, wherein the particle size is 300-425 micrometers, the moisture content is 2.9 weight percent, and the CRC is 48.6 g/g.

Further, water-absorbent resin 4-1 was subjected to the same surface crosslinking and additive addition procedures as in example 1 to obtain water-absorbing agent 3 having CRC of 35.5g/g, saline absorption amount per minute of 27.2g/g and pure water absorption amount per minute of 127.4 g/g.

Comparative example 2

The drying temperature of the gel in the example 1 was changed to 200 ℃ for 30 minutes, and the other operations were the same as those in the example 1, to obtain a comparative water-absorbent resin 2-1 having a particle size of 300 to 425 μm, a moisture content of 2.2 wt%, and a CRC of 55.1 g/g.

Comparative water-absorbing resin 1-1 was further subjected to the same surface crosslinking and additive addition procedures as in example 1 to obtain comparative water-absorbing agent 1 having CRC of 35.9g/g, one-minute saline absorption of 24.2g/g and one-minute pure water absorption of 108.4 g/g.

Example 5

Water-absorbing agent 5, having a CRC of 35.8g/g, a saline absorption amount per minute of 27.8g/g and a pure water absorption amount per minute of 131.5g/g, was obtained in the same manner as in example 1, except that the sucrose stearate (S-770, Mitsubishi chemical) solution was changed to sucrose stearate (S-970, Mitsubishi chemical).

Comparative example 3

The drying temperature of the gel in the example 5 is changed to 190 ℃, the drying time is 30 minutes, other operations are the same as the example 5, and the contrast water-absorbent resin 3-1 is obtained, the particle size is 300-425 micrometers, the moisture content is 2.4 weight percent, and the CRC is 53.1 g/g.

Comparative water-absorbent resin 3-1 was further subjected to the same surface crosslinking and additive addition procedures as in example 5 to obtain comparative water-absorbing agent 3 having CRC of 36.8g/g, saline water absorption per minute of 23.1g/g and pure water absorption per minute of 103.3 g/g.

Example 6

Water-absorbing agent 6 having CRC of 34.3g/g, 0.7psi AUP of 18.8g/g, 0.7psi of 27.2g/g, one minute of pure water absorption of 118.5g/g was obtained in the same manner as in example 1 except that the sucrose stearate (S-770, Mitsubishi chemical) solution was replaced with a fatty alcohol-polyoxyethylene ether (MULTIISO 13/50, surface tension of 25 to 35mN/m) solution.

Comparative example 4

The drying temperature of the gel in the example 6 was changed to 210 ℃ for 30 minutes, and the other operations were the same as those in the example 6, to obtain a comparative water-absorbent resin 4-1 having a particle size of 300 to 425 μm, a moisture content of 1.8% by weight, and a CRC of 56.7 g/g.

Comparative water-absorbing resin 4-1 was further subjected to the same surface crosslinking and additive addition procedures as in example 6 to obtain comparative water-absorbing agent 4 having CRC of 36.2g/g, saline water absorption per minute of 22.2g/g and pure water absorption per minute of 95.2 g/g.

As can be seen from examples 1 to 6 and comparative examples 1 to 4, the rough surface of the water-absorbent resin can be kept uneven in the drying process by controlling the temperature and time in the drying process, and after being crushed and screened, the rough surface of the water-absorbent resin provides a higher specific surface area for the gel surface, so that the liquid absorption rate of the gel surface is effectively improved.

Accordingly, the present invention aims to provide a method which can efficiently produce a water absorbent resin having a high liquid-absorbing rate without affecting the liquid-absorbing characteristics of the water absorbent resin, and to obtain a water absorbent resin having a high liquid-absorbing rate.

The above description is only an embodiment of the present invention, and not intended to limit the scope of the present invention, and all modifications of equivalent structures and equivalent processes, or direct or indirect applications in other related fields, which are made by the contents of the present specification, are included in the scope of the present invention.

Claims

1. A method for producing a polyacrylic acid-based water-absorbent resin, characterized by comprising the steps of:

2. The method for producing a polyacrylic acid-based water-absorbent resin according to claim 1, wherein the aqueous solution of the unsaturated acrylic monomer and the crosslinking agent is a mixed solution containing acrylic acid and/or a water-soluble salt of acrylic acid as a main component.

3. The method for producing a polyacrylic acid-based water-absorbent resin according to claim 2, wherein the crosslinking agent is one or more selected from the group consisting of a compound having a plurality of vinyl groups in a molecule, a compound having at least one vinyl compound and at least one functional group capable of reacting with a carboxyl group on the unsaturated monomer in a molecule, and a compound having a plurality of functional groups capable of reacting with a carboxyl group on the unsaturated monomer in a molecule.

4. The method for producing a polyacrylic acid-based water-absorbent resin according to claim 3, wherein the crosslinking agent is one or more selected from the group consisting of N, N' -methylenebisacrylamide, trimethylolpropane tri (meth) acrylate, ethylene glycol di (meth) acrylate, polyethylene glycol diacrylate, polyethylene glycol di (meth) acrylate, polyethylene glycol diallyl ether, pentaerythritol tetraacrylate, triarylamine, ethylene glycol diglycidyl ether, ethylene glycol, 1, 2-propanediol, 1, 3-propanediol, 1, 4-butanediol, glycerol, pentaerythritol, polyethylene glycol and vinyl carbonate, preferably one or more selected from the group consisting of trimethylolpropane tri (meth) acrylate, polyethylene glycol diacrylate, ethylene glycol diglycidyl ether, polyethylene glycol and 1, 4-butanediol, further preferred is one or more of trimethylolpropane tri (meth) acrylate, polyethylene glycol diacrylate and ethylene glycol diglycidyl ether.

5. The method for producing a polyacrylic acid-based water-absorbent resin according to claim 1, wherein the high shearing force and/or the pressing force is provided by changing the hole diameter of the exit baffle of the meat chopper, the gel strength, the amount and temperature of the granulating water, the rotation speed and length of the screw, or by performing granulation for a plurality of times.

6. The method for producing a polyacrylic acid-based water-absorbent resin according to claim 1, wherein the gel surface tension modifier is a polymer containing both at least one hydrophilic group and at least one hydrophobic group; the hydrophilic group is selected from one or more of carboxylic acid (salt), sulfuric acid (salt), sulfonic acid (salt), benzene sulfonic acid (salt), quaternary ammonium salt, polyethylene oxide and derivatives thereof, hydroxyl-containing compound and amino-containing compound; the hydrophobic group is selected from one or more of a straight chain or branched alkyl chain, polypropylene oxide and derivatives thereof, an aromatic chain or a long fluorine-containing chain.

7. The method for producing a polyacrylic acid-based water-absorbent resin according to claim 1, wherein the surface tension modifier has a surface tension and a dynamic surface tension which are values measured in an aqueous solution having a concentration of 0.1 wt% at a temperature of 25 ℃.

8. The method for producing a polyacrylic acid-based water-absorbent resin according to claim 1, wherein the water-absorbent resin obtained by drying the crushed gel particles with a heating medium having a temperature of 80 to 170 ℃ has a saline absorption rate Δ V per minute as compared with the water-absorbent resin obtained by drying with a heating medium having a temperature of 180 to 210 ℃₁3 to 25 percent of the total amount of the components, and is sucked in one minuteRate of change of velocity of pure water Δ V₂10 to 40 percent.