WO2021212331A1 - Superabsorbent polymer and preparation method therefor - Google Patents

Abstract

A superabsorbent polymer (SAP) and a preparation method therefor. The preparation method comprises the following steps that: at the temperature of 20°C or below, an ethylenically unsaturated monomer containing carboxyl and/or a salt thereof, an oxidizing agent, a reducing agent, and an internal cross-linking agent containing a double-bond compound are in contact to initiate a polymerization reaction to obtain hydrogel; the hydrogel is crushed and squeezed and then is in contact with a neutralizer for neutralization reaction, so as to obtain colloid particles; and after the colloidal particles are dried, ground, and screened, surface cross-linking treatment is performed by contacting with a surface cross-linking agent to obtain an SAP resin; wherein the surface cross-linking agent at least comprises a gallic acid epoxy resin. The method enhances the surface cross-linking effect of the obtained SAP resin, and can ensure the excellent pressurizing performance and liquid absorption rate of the SAP resin while improving the liquid passing performance of the SAP resin.

Description

[Name of invention established by ISA according to Rule 37.2] 　Super absorbent polymer and its preparation method Technical field

The invention relates to a super absorbent polymer, in particular to a super absorbent polymer with improved properties and a preparation method thereof.

Background technique

Superabsorbent Polymers (SAP, Superabsorbent Polymers) is a synthetic polymer material that can absorb water from about 500 times to about 1000 times its own weight. It can be widely used in sanitary products, such as children’s diapers and feminine hygiene. Supplies, adult diapers, etc. In the future, as the global aging trend further strengthens, its market demand has a large space.

At present, the known materials used for sanitary products are mainly series products of polyacrylic acid and its sodium salt, of which about 95% are prepared by aqueous solution polymerization process, and about 5% are prepared by reverse suspension process. Aqueous polymerization process is divided into two categories: one is a belt process, which is generally initiated by heat during polymerization, and the temperature generated by the neutralization heat is used to initiate the polymerization reaction; the reaction rate is fast, the temperature is high, but the reaction time is short, which will cause SAP The content of residual monomers in the resin is relatively high, the content of extractables is relatively high, and the long-term reverse osmosis performance is poor; the other is the kettle type process, which is initiated by a low-temperature oxidation-reduction initiator at the initial stage of polymerization, and uses the later temperature rise. Thermal initiation with a thermal initiator; although the reaction time used is long, including the holding time, it generally lasts 5-10 hours, but the content of residual monomers is low, the content of extractables is small, and the formed molecular chain skeleton structure is longer, which is suitable for Fields with high requirements for long-term reverse osmosis.

For SAP resin, its water absorption capacity, liquid absorption rate, pressurization, liquid permeability and other performance indicators are mutually restricted. Generally speaking, SAP particles with a fast liquid absorption rate will block the internal pores of the particles, resulting in insufficient liquid absorption capacity in the later stage, and serious gel agglomeration, which reduces the performance of the liquid. In short, to achieve the balance of the various properties of the SAP resin, it is necessary to do further research.

Regarding the aqueous solution polymerization process used to prepare superabsorbent polymers, the prior art selects secondary surface crosslinking or adding inorganic particles to improve its liquid permeability. For example, Nuoer Biotech's patent documents (its publication numbers are CN106987075 A and CN102702656 A) disclose a method for preparing a water-absorbent resin polymerized at low temperature and subjected to multiple surface cross-linking, which can prepare excellent liquid permeability and gel Strong water-absorbent resin.

Patent document CN 107406595 A discloses a method for preparing SAP particles by two surface cross-linking and different cross-linking agents used in the two surface cross-linking. The inventor aims to achieve a multiple shell structure in the polymer through two cross-linking, and to improve the problem of resin agglomeration.

Patent document CN 107428948 A discloses a method for preparing SAP particles by surface crosslinking by different methods. Polyols, polyvalent metal salts, and polyglycidyl ethers can be used as surface crosslinking agents for different surface crosslinking treatments. However, Because the surface cross-linking agents used all contain EO segment structure, the molecular chain is soft and may be degraded during the high-temperature baking reaction stage, resulting in a decrease in the overall performance of SAP.

In the above existing patent documents, multiple surface cross-linking methods are used to improve the liquid permeability of SAP particles, but the process is more complicated and the efficiency is lower.

All in all, the SAP resin for sanitary products requires low monomer residue rate, low long-term reverse osmosis, low extractable content and other properties, such as a combination of water retention, pressurization, and liquid permeability. In order to meet such comprehensive performance, it is necessary to conduct in-depth research on the surface crosslinking agent selected in the crosslinking treatment.

Summary of the invention

The purpose of the present invention is to provide a superabsorbent polymer (SAP) with improved performance and a preparation method thereof in view of the defect that the comprehensive performance cannot meet the requirements in the preparation of superabsorbent polymers in the prior art. The surface cross-linking effect of SAP is enhanced, which can ensure the excellent pressurization performance and liquid absorption rate of SAP resin while improving its liquid permeability.

In order to achieve the above objectives, the technical solutions provided by the present invention are as follows:

In one aspect, a super absorbent polymer is provided, the raw materials of the polymerization reaction include the following components:

a) The concentration of ethylenically unsaturated monomer and/or its salt containing carboxyl group in the polymerization aqueous solution is greater than or equal to 20wt% and less than or equal to 35wt% (for example, 22wt%, 25wt%, 28wt%, 33wt%), preferably greater than Equal to 20wt% and less than or equal to 30wt%;

b) Internal crosslinking agent containing double bond compound, the amount is 0.01wt%-4wt% of the weight of component a) (for example, 0.015wt%, 0.02wt%, 0.05wt%, 0.1wt%, 0.4wt%, 0.8 wt%, 1wt%, 1.5wt%, 3wt%), preferably 0.5wt%-2wt%;

c) Oxidizing agent, the amount used is 0.005wt%-5wt% of the weight of component a) (for example, 0.008wt%, 0.015wt%, 0.03wt%, 0.05wt%, 0.1wt%, 0.4wt%, 0.8wt%, 1wt %, 1.5wt%, 3wt%), preferably 0.01wt%-0.5wt%;

d) reducing agent, in an amount of 0.005% to 5% by weight of component a) (for example, 0.008%, 0.015%, 0.03%, 0.05%, 0.1%, 0.4%, 0.8%, 0.8%) 1wt%, 1.5wt%, 3wt%), preferably 0.01wt%-0.5wt%;

Wherein, after the hydrogel obtained by the polymerization reaction is neutralized, the neutralization degree of carboxylic acid of the polymer in the colloidal particles obtained is 50-80 mol% (for example, 55 mol%, 60 mol%, 70 mol%, 75 mol%); the colloidal particles are transformed Are polymer particles, and the proportion of polymer particles with a particle size of 150-700 microns is greater than or equal to 92 wt% (for example, 93 wt%, 95 wt%, 98 wt%);

And, the surface of the polymer particles adopts the following treatments:

e) Surface cross-linking is carried out by applying a surface cross-linking agent to the surface of the dried polymer particles, the surface cross-linking agent includes at least gallic acid epoxy resin; based on the dried polymer particles, the gallic acid epoxy resin The amount of resin used is 0.005wt%-0.5wt% (for example, 0.008wt%, 0.015wt%, 0.03wt%, 0.05wt%, 0.1wt%, 0.4wt%), preferably 0.01wt%-0.2wt%; and , Optionally

f) Based on the dried polymer particles, 0-2wt% (for example, 0.05wt%, 0.1wt%, 0.5wt%, 1wt%) of insoluble inorganic powder is added after surface crosslinking.

In the present invention, the ethylenically unsaturated monomer containing a carboxyl group and/or its salt means a salt of an ethylenically unsaturated monomer containing a carboxyl group and/or an ethylenically unsaturated monomer containing a carboxyl group. The salt here may be an alkali metal salt (for example, a sodium salt or potassium salt) of an ethylenically unsaturated monomer containing a carboxyl group.

According to the superabsorbent polymer provided by the present invention, in some examples, the ethylenically unsaturated monomer containing a carboxyl group is selected from acrylic acid, methacrylic acid, ethacrylic acid, α-chloroacrylic acid, α-cyanoacrylic acid, β -Methacrylic acid (crotonic acid), α-phenyl acrylic acid, β-acryloxypropionic acid, sorbic acid, α-chlorosorbic acid, 2'-methylisocrotonic acid, cinnamic acid, p-chlorocinnamic acid, One or more of β-stearic acid, itaconic acid, citraconic acid, mesaconic acid, glutaconic acid, aconitic acid, maleic acid, fumaric acid, tricarboxyethylene and maleic anhydride, It is preferably selected from acrylic acid and/or methacrylic acid, more preferably acrylic acid.

In some examples, the internal crosslinking agent containing double bond compounds is selected from the group consisting of ethylene glycol diacrylate, propylene glycol diacrylate, N,N'-methylene bisacrylamide, polyethylene glycol diacrylate, poly Propylene glycol diacrylate, pentaerythritol triallyl ether, ethoxylated glycerol triacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, triallylamine, pentaerythritol tetraacrylate and dipentaerythritol hexaacrylate One or more of esters.

In some examples, the oxidant is peroxide, preferably one or more selected from sodium persulfate, hydrogen peroxide, potassium persulfate and ammonium persulfate, more preferably hydrogen peroxide.

In some examples, the reducing agent is selected from one or more of ascorbic acid, ammonium bisulfite, ammonium thiosulfate, ammonium dithionite, ammonium sulfide, and sodium hydroxymethyl sulfoxylate, preferably ascorbic acid.

In some examples, the insoluble inorganic powder is selected from silicon dioxide, silica, titanium dioxide, aluminum oxide, magnesium oxide, zinc oxide, talc, calcium phosphate, clay, diatomaceous earth, zeolite, bentonite, kaolin, hydrotalcite, and activated clay One or more of them are preferably silica (for example, fumed silica and/or precipitated silica).

In some examples, the surface crosslinking agent further includes one or more of polyol compounds, epoxy compounds, amine compounds, and metal inorganic salts. Based on the dried polymer particles, the content is 0-2wt% (for example, 0.05wt%, 0.15wt%, 0.5wt%, 1.5wt%), preferably 0.1-1wt%.

Preferably, the polyol compound is selected from ethylene glycol, propylene glycol, glycerol, 1,4-butanediol or pentaerythritol.

Preferably, the epoxy compound is selected from (poly)ethylene glycol diglycidyl ether, 1,4-butanediol diglycidyl ether, ethylene carbonate or propylene carbonate.

Preferably, the amine compound is selected from trimethylolaminomethane or carbodiimide.

Preferably, the metal inorganic salt is selected from an inorganic salt of calcium, an inorganic salt of magnesium, an inorganic salt of aluminum, an inorganic salt of iron, an inorganic salt of copper, or an inorganic salt of zinc.

In some examples, the raw materials for the polymerization reaction further include: g) at least one thermal initiator.

In some examples, the thermal initiator is an azo initiator, preferably selected from azobisisobutyronitrile, azobiscyanovaleric acid, azobisdimethylvaleronitrile, 2,2'-azo Bis(2-amidinopropane) dihydrochloride, azobisamidinopropane dihydrochloride, 2,2'-azobis(N,N-dimethylisobutamidine) dihydrochloride, One or more of 2-(carbamoylazo)isobutyronitrile and 4,4-azobis(4-cyanovaleric acid).

In some examples, the thermal initiator is used in an amount of 0.005wt%-1wt% (for example, 0.008wt%, 0.015wt%, 0.03wt%, 0.05wt%, 0.1wt%, 0.4wt% of the weight of component a) , 0.6wt%, 0.8wt%), preferably 0.01wt%-0.2wt%.

According to the super absorbent polymer provided by the present invention, in some examples, the super absorbent polymer has a liquid absorption rate of 60-70 g/g, a centrifugal water retention rate of 33-40 g/g, and a 0.7 psi pressurized liquid absorption rate It is 23-28g/g, the liquid absorption rate is 20-35s, the liquid flow rate (GBP) is greater than or equal to 40 Darcy, the content of residual monomers is less than or equal to 400ppm, and the content of extractables is less than or equal to 5wt%.

In another aspect, a method for preparing a super absorbent polymer is provided, which includes the following steps:

At ≤20°C (for example, 0°C, 5°C, 10°C, 15°C), internal crosslinking of ethylenically unsaturated monomers containing carboxyl groups and/or their salts, oxidizing agents, reducing agents and compounds containing double bonds Contact with the agent to initiate a polymerization reaction to obtain a hydrogel; crush and extrude the hydrogel and then contact with a neutralizer for neutralization reaction to obtain colloidal particles; after the colloidal particles are dried, ground and sieved, they are passed through Contact with the surface cross-linking agent for surface cross-linking treatment to obtain super absorbent polymer resin;

Wherein, the surface crosslinking agent at least includes gallic acid epoxy resin.

Among the surface crosslinking agents, they are selected from gallic acid epoxy resins with tetrafunctionality (the structural formula is shown in the following formula I). Because of the four epoxy groups in its molecular structure, it is cross-linked on the surface. After that, the local cross-linking density of the polymer surface will be high; and the molecular structure of gallic acid epoxy resin contains benzene ring. After the surface cross-linking treatment, the polymer will have a strong surface cross-linking strength, which can ensure that the resin has High pressure absorption rate and liquid flow rate.

During the surface cross-linking treatment, the gallic acid epoxy resin, the polyol and the solvent can be configured into a solution in proportion, and the surface cross-linking can be made more uniform through the dilution process. The polyol here can be 1,2-propanediol, glycerol, 1,3-propanediol, ethylene glycol; the solvent can be water, propylene glycol monomethyl ether, or dipropylene glycol butyl ether.

The preparation method of gallic acid epoxy resin, for example, can be prepared with reference to the method disclosed in the patent document CN 102276788 A.

The flow rate (GBP) mentioned here can also be referred to as gel bed permeability. For details, please refer to patent document CN105392805B.

According to the preparation method provided by the present invention, in some examples, the polymerization reaction is aqueous solution polymerization. For example, the polymerization reaction is an aqueous solution polymerization of an ethylenically unsaturated monomer containing a carboxyl group and/or its salt in the presence of at least one internal crosslinking agent and water. The initial temperature of the aqueous polymerization reaction does not exceed 20°C. After the initial temperature of the system is greater than 25°C, there will be more branching and chain transfer reactions, which may lead to an increase in the content of extracts in the polymerization reaction. In some examples, the system is deoxygenated with nitrogen before the start of the reaction, which is conducive to the initiation of the monomers.

In the preparation method, the carboxyl-containing ethylenically unsaturated monomer and/or the salt of the carboxyl-containing ethylenic unsaturated monomer may participate in the polymerization reaction. When the salt of an ethylenically unsaturated monomer containing a carboxyl group participates in the polymerization reaction, it is necessary to neutralize the ethylenically unsaturated monomer containing a carboxyl group with a basic substance before the polymerization reaction (it can be called a pre-neutralization reaction). ) To obtain a salt of an ethylenically unsaturated monomer containing a carboxyl group, and then proceed with the polymerization reaction. The alkaline substance here may be the same as the neutralizing agent used for neutralizing the hydrogel (which may be called a post-neutralization reaction), for example, it may be sodium hydroxide or potassium hydroxide.

During the polymerization reaction, the concentration of the ethylenically unsaturated monomer containing the carboxyl group and/or its salt in the polymerization aqueous solution can be appropriately controlled, and the concentration is generally 20-35 wt%. When the concentration continues to decrease, the heat of reaction is insufficient and the temperature of the system is not obvious, which may cause insufficient reaction and higher residual monomers. When the concentration of monomers involved in the polymerization in the system is too high, the temperature during the polymerization process will rise and the temperature will exceed the boiling point of water, which is not conducive to the control of the polymerization reaction. In some examples, the concentration of the carboxyl-containing ethylenically unsaturated monomer and/or its salt in the polymerization aqueous solution is greater than or equal to 20 wt% and less than or equal to 35 wt% (for example, 22 wt%, 25 wt%, 28 wt%, 33 wt%) , Preferably greater than or equal to 20 wt% and less than or equal to 30 wt%.

The internal crosslinking agent used in the preparation method should contain at least two double bond structures, so that crosslinking points of the gel can be formed during radical polymerization. In some examples, based on the weight of the carboxyl-containing ethylenically unsaturated monomer and/or its salt, the amount of the internal crosslinking agent containing the double bond compound is 0.01 wt% to 4 wt% (for example, 0.015 wt%, 0.02 wt%, 0.05 wt%, 0.1 wt%, 0.4 wt%, 0.8 wt%, 1 wt%, 1.5 wt%, 3 wt%), preferably 0.5 wt% to 2 wt%.

In the polymerization system, in addition to the monomers participating in the polymerization and the internal crosslinking agent, an oxidation-reduction initiator is also included. In some examples, based on the weight of the ethylenically unsaturated monomer containing a carboxyl group and/or its salt, the amount of the oxidizing agent is 0.005% to 5% by weight (for example, 0.008%, 0.015%, 0.03%, 0.05% by weight). wt%, 0.1 wt%, 0.4 wt%, 0.8 wt%, 1 wt%, 1.5 wt%, 3 wt%), preferably 0.01 wt% to 0.5 wt%.

In some examples, based on the weight of the carboxyl-containing ethylenically unsaturated monomer and/or its salt, the reducing agent is used in an amount of 0.005% to 5% by weight (for example, 0.008% by weight, 0.015% by weight, 0.03% by weight, 0.05wt%, 0.1wt%, 0.4wt%, 0.8wt%, 1wt%, 1.5wt%, 3wt%), preferably 0.01wt%-0.5wt%.

In the preparation method, the polymerization reaction can be understood as: the temperature of the system is increased after the induction period is completed by keeping the temperature in an ice bath at the beginning, and the polymerization starts at this time, and the temperature does not exceed 20°C. The subsequent polymerization reaction exotherms, and the temperature of the system is increased to 70-90°C, and then the temperature is kept at this temperature for several hours to proceed with the reaction.

In order to make the polymer hydrogel obtained by the polymerization reaction have lower residual monomers, the polymer hydrogel can be matured and kept for a period of time after the temperature rise of the polymerization process is finished. In some examples, the temperature for aging and holding is 85-95°C, and the time for aging and holding is 4-8 hours.

After the polymerization reaction is completed, the obtained hydrogel needs to be crushed and extruded and then subjected to neutralization treatment, so that the degree of neutralization of the carboxylic acid of the polymer can be controlled within an appropriate range. The carboxylic acid neutralization of the polymer is too low, which will cause the resulting gel to be sticky, which is not conducive to subsequent processing; the carboxylic acid neutralization of the polymer is too high, which will increase the pH of the SAP resin, which may cause human skin when used Security issues. In some examples, after the hydrogel is subjected to a neutralization reaction, the degree of carboxylic acid neutralization of the polymer in the obtained colloidal particles is 50-80 mol% (for example, 55 mol%, 60 mol%, 70 mol%, 75 mol%).

After the colloidal particles are dried, ground and sieved, super absorbent polymer (SAP) particles can be obtained; then the surface of the colloidal particles is subjected to surface cross-linking treatment. In some examples, based on the dried superabsorbent polymer particles, the gallic acid epoxy resin is used in an amount of 0.005wt%-0.5wt% (for example, 0.008wt%, 0.015wt%, 0.03wt%, 0.05wt% , 0.1wt%, 0.4wt%), preferably 0.01wt%-0.2wt%.

According to the preparation method provided by the present invention, in some examples, the ethylenically unsaturated monomer containing a carboxyl group is selected from acrylic acid, methacrylic acid, ethacrylic acid, α-chloroacrylic acid, α-cyanoacrylic acid, β-methyl Acrylic acid, α-phenyl acrylic acid, β-acryloyloxypropionic acid, sorbic acid, α-chlorosorbic acid, 2'-methylisocrotonic acid, cinnamic acid, p-chlorocinnamic acid, β-stearic acid, coating One or more of canonic acid, citraconic acid, mesaconic acid, glutaconic acid, aconitic acid, maleic acid, fumaric acid, tricarboxyethylene and maleic anhydride, preferably selected from acrylic acid and/or Methacrylic acid, more preferably acrylic acid.

In some examples, the internal crosslinking agent containing double bond compounds is selected from the group consisting of ethylene glycol diacrylate, propylene glycol diacrylate, N,N'-methylene bisacrylamide, polyethylene glycol diacrylate, poly Propylene glycol diacrylate, pentaerythritol triallyl ether, ethoxylated glycerol triacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, triallylamine, pentaerythritol tetraacrylate and dipentaerythritol hexaacrylate One or more of esters.

In some examples, the oxidant is peroxide, preferably one or more selected from sodium persulfate, hydrogen peroxide, potassium persulfate and ammonium persulfate, more preferably hydrogen peroxide.

In some examples, the reducing agent is selected from one or more of ascorbic acid, ammonium bisulfite, ammonium thiosulfate, ammonium dithionite, ammonium sulfide, and sodium hydroxymethyl sulfoxylate, preferably ascorbic acid.

In some examples, the neutralizer is an aqueous solution of a basic compound with a concentration of 30-60% by weight, preferably 40-50% by weight. In a preferred embodiment, the basic compound is selected from one or more of sodium hydroxide, potassium hydroxide, sodium carbonate and potassium carbonate, and more preferably sodium hydroxide.

In addition, if necessary, during the surface cross-linking treatment, in addition to the gallic acid epoxy resin, another surface cross-linking agent can be added for surface cross-linking. In some examples, the surface crosslinking agent further includes one or more of polyol compounds, epoxy compounds, amine compounds, and metal inorganic salts.

For the amount of additional surface crosslinking agent added, in some examples, based on the superabsorbent polymer particles after drying, the content is 0-2wt% (for example, 0.05wt%, 0.3wt%, 0.5wt, 1.5wt %), preferably 0.1-1wt%.

In some examples, the polyol compound is selected from ethylene glycol, propylene glycol, glycerol, 1,4-butanediol, or pentaerythritol.

In some examples, the epoxy compound is selected from (poly)ethylene glycol diglycidyl ether, 1,4-butanediol diglycidyl ether, ethylene carbonate, or propylene carbonate.

In some examples, the amine compound is selected from tris or carbodiimide.

In some examples, the metal inorganic salt is selected from an inorganic salt of calcium, an inorganic salt of magnesium, an inorganic salt of aluminum, an inorganic salt of iron, an inorganic salt of copper, or an inorganic salt of zinc.

After neutralization, the colloidal particles obtained are extruded and crushed to obtain small-sized colloidal particles. Because the water content of the colloidal particles is relatively high, further drying treatment is required before this. According to the preparation method provided by the present invention, in some examples, the temperature at which the colloidal particles are dried is 100-240°C. The drying treatment here can be achieved by using devices or equipment well known in the art, for example, blast drying through an oven.

After the dried rubber particles are further ground and sieved, the size of the obtained SAP particles can be controlled. The size here can be understood as the particle size of the particles.

When sieving, select a sieve of the required size for sieving, and control the proportion of particles that are too large and too small. For example, sieving with a particle size of 150 μm and 700 μm can realize that the size of most SAP particles is in the range of 150-700 μm; among them, super absorbent polymer (SAP) particles with a particle size of less than 150 μm account for The proportion does not exceed 3wt%, and the proportion of superabsorbent polymer (SAP) particles with a particle size greater than 700 microns does not exceed 5wt%. In some examples, after the colloidal particles are dried, the colloidal particles are further ground and sieved to control the size of the superabsorbent polymer particles; wherein the particle size is 150-700 microns (e.g., 180 microns, 250 microns, 400 microns). The proportion of super-absorbent polymer particles (micrometers, 600 micrometers) is greater than or equal to 92wt% (for example, 93wt%, 95wt%, 98wt%).

The SAP particles obtained after sieving can be referred to herein as raw polymer powder. Further, the surface of the super absorbent polymer (SAP) particles obtained by sieving is subjected to surface cross-linking treatment. In some examples, the process conditions of the surface crosslinking treatment include: a reaction temperature of 50-150°C, preferably 80-130°C; and a reaction time of 0.5h-3h, preferably 1h-2h.

In order to improve the fluidity of superabsorbent polymers, some water-insoluble inorganic powders are generally added to prevent adhesion during mass production. Optionally, based on the dried superabsorbent polymer particles, 0-2wt% (for example, 0.05wt%, 0.3wt%, 0.5wt%, 1.5wt%) of insoluble inorganic powder is added after the surface crosslinking treatment. In some examples, the insoluble inorganic powder is selected from silicon dioxide, silica, titanium dioxide, aluminum oxide, magnesium oxide, zinc oxide, talc, calcium phosphate, clay, diatomaceous earth, zeolite, bentonite, kaolin, hydrotalcite, and activated clay One or more of them are preferably silica.

In order to further reduce the residual monomers in the SAP resin, a thermal initiator can also be used in the polymerization process. Adding a thermal initiator to the system can continue to consume the remaining monomers in the system at the later stage of the polymerization temperature rise. According to the preparation method provided by the present invention, in some examples, at least one thermal initiator is added during the polymerization reaction. In some examples, the thermal initiator is an azo initiator, preferably selected from azobisisobutyronitrile, azobiscyanovaleric acid, azobisdimethylvaleronitrile, 2,2'-azo Bis(2-amidinopropane) dihydrochloride, azobisamidinopropane dihydrochloride, 2,2'-azobis(N,N-dimethylisobutamidine) dihydrochloride, One or more of 2-(carbamoylazo)isobutyronitrile and 4,4-azobis(4-cyanovaleric acid).

In some examples, based on the weight of the carboxyl-containing ethylenically unsaturated monomer and/or its salt, the thermal initiator is used in an amount of 0.005 wt% to 1 wt% (for example, 0.008 wt%, 0.015 wt%, 0.03 wt%). wt%, 0.05 wt%, 0.1 wt%, 0.3 wt%, 0.5 wt%, 0.8 wt%), preferably 0.01 wt% to 0.2 wt%.

In the process of preparing superabsorbent polymers, the external surface cross-linking treatment mainly focuses on the improvement of pressurization. The water absorption capacity of the resin under pressure regulation belongs to the state of unsaturated absorption. The amount of voids in the molecular structure of the outer surface and whether it is easy to collapse mainly determines the liquid flow rate and liquid absorption rate of the polymer resin.

The external surface crosslinking agent disclosed in the prior art contains an epoxy structure, which is currently a common technical solution for surface crosslinking of SAP resins to increase the liquid flow rate. However, the currently known technical solutions mostly use bifunctional flexible chain surface crosslinking agents for surface crosslinking, and the performance improvement range has basically reached the upper limit. After long-term research and exploration, this application has specially selected gallic acid epoxy resin, whose molecular structure has the following characteristics:

(1) It has tetrafunctionality, which makes it possible to use a smaller amount of gallic acid epoxy resin in the cross-linking process to achieve local high cross-linking points on the polymer surface, so that the resin has a higher pressure absorption Magnification and higher liquid flow rate;

(2) Its functionality is supported by the benzene ring structure in the middle. Compared with the flexible chain structure, the surface crosslinking strength formed by it is higher; in addition to improving the liquid flow performance, this also greatly promotes the increase in pressurization and absorption rate. .

The ingenuity of the present invention is that a small amount of gallic acid epoxy resin is used as a surface cross-linking agent to achieve a relatively high degree of cross-linking locally, which can well improve and balance the various indexes of super absorbent polymers. , And the benzene ring structure of gallic acid epoxy resin supports its functional group, which can ensure a certain gel strength.

Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

The surface crosslinking of SAP particles is carried out by introducing gallic acid epoxy resin. Under the condition of low dosage, the local crosslinking density is high, and the gallic acid epoxy resin contains benzene ring, which increases the strength of the crosslinking point. SAP resin does not tend to agglomerate, and the liquid penetration rate and penetration depth are significantly improved. While ensuring the higher pressure absorption rate and penetration rate of SAP particles, its liquid absorption rate is also faster.

Detailed ways

In order to be able to understand the technical features and content of the present invention in detail, the preferred embodiments of the present invention will be described in more detail below. Although the preferred embodiments of the present invention are described in the examples, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein.

<Source of raw materials>

Acrylic acid, purchased from Yantai Wanhua Chemical, with a purity of over 99.5%;

Gallic acid epoxy, self-made, and its preparation method refers to the patent document CN 102276788 A (for example, Example 1);

Hydrogen peroxide (H ₂ O ₂ solution), purchased from Sinopharm, a 30% concentration aqueous solution;

Ascorbic acid, purchased from Sigma, with a purity of over 99%;

Aqueous solutions of caustic soda with concentrations of 32wt% and 50wt% were purchased from Yantai Wanhua Chemical;

Pentaerythritol triallyl ether, purchased from Dasso, Japan, with a purity of over 80%;

Polyethylene glycol diacrylate, purchased from Changxing Materials, with a purity of over 95%;

Other reagents used in the embodiments of the present invention are conventional reagents in the field, and their purchase information will not be repeated here.

<Test method>

a) Absorption rate

Weigh 0.2g test sample, accurate to 0.001g, and record the mass as m, pour all the test samples into the tea bag, seal the tea bag, and soak into a beaker containing a sufficient amount of 0.9% normal saline. Soak for 30 minutes. Then take out the tea bag containing the test sample and hang it with a clip. After dripping water for 10 minutes in a static state, weigh the mass of the tea bag containing the test sample and record the mass as m1). Then use the teabag without the test sample to measure the blank value, weigh the mass of the blank test teabag, and record the mass as m2. Then, the liquid absorption rate=(m1-m2)/m.

b) Centrifugal water retention rate

Dehydrate the tea bag containing the test sample for 3 minutes under 250G centrifugal force after the above-mentioned test of the liquid absorption rate, and then weigh the mass of the tea bag containing the test sample, and record the mass as m3. Use the tea bag without the test sample to measure the blank value, weigh the mass of the blank tea bag and record the mass as m4. Then, centrifugal water retention rate=(m3-m4)/m.

c) 0.7psi pressurized liquid suction rate

The equipment used for the test is: (1) A plastic cylinder with an inner diameter of 60mm with openings at both ends, one end of which is fixed with a 200-mesh nylon mesh; (2) A plastic piston with an outer diameter slightly less than 59mm, which can be tightly connected with the above-mentioned plastic cylinder. It can move up and down freely; (3) a round weight with a weight of 1340g; (4) a glass dish with a perforated plate inside, so that the plastic cylinder can be placed on the perforated plate without touching the bottom of the glass dish. It can absorb water freely.

The test method is: place the glass dish on the platform, and then pour the 0.9% normal saline. Weigh 0.9 g of the test sample and evenly sprinkle it into the bottom of the plastic cylinder, then add the plastic piston with weights to the plastic cylinder, measure its mass and mark it as m5. Put the plastic cylinder with the sample on the perforated plate of the glass dish, lift the plastic cylinder out of the glass dish after 60 minutes, and test the quality of the plastic cylinder after the water drops and mark it as m6. Then, the pressurized liquid absorption rate at 0.7 psi = (m6-m5)/0.9.

d) Liquid absorption rate (vortex method)

A 100 ml beaker was used to weigh 50 g of physiological saline at a temperature of 23° C., and then a magnetic rod was added to the beaker, and the beaker was placed on a magnetic stirrer for stirring at a rotation speed of 600 rpm. Accurately weigh 2.0g of the test sample, and pour it all into the vortex at one time. After the input, the timing starts, and the vortex in the middle gradually becomes smaller as the test sample absorbs the physiological saline. Stop timing until the vortex disappears and the liquid surface reaches the level, and the measured time is the liquid absorption rate of the test sample.

e) Liquid flow rate (GBP)

Weigh 0.9g of the test sample and put it into a plexiglass cylinder with an inner diameter of 60mm; put the plexiglass cylinder containing the test sample in 0.9% physiological saline and expand freely for 30 minutes. Take the plexiglass cylinder out of the saline, cover the cylinder cover, put a weight, read the height of the gel layer and mark it as H. Put the plexiglass cylinder on the test equipment, make the liquid level in the cylinder reach the 4cm mark line, and keep the liquid level unchanged. After the liquid flows out stably, start timing and measure the liquid flowing through the gel layer Calculate the flow rate Q of the liquid through the gel layer.

The formula for calculating GBP is:

Among them, Q is the liquid flow rate in g/s;

H is the height of the gel layer in cm;

μ is the liquid viscosity, the unit is P, the viscosity of physiological saline is 1cP=0.01P;

A is the area of the gel layer in cm ² , the inner diameter of the plexiglass cylinder is 6 cm, and the area of the gel layer is 28.27 cm ² ;

P is the hydrostatic pressure, the unit is dyne/cm ² , and P=ρgh, h is the height of the liquid level 4cm, then the hydrostatic pressure is 3924 dyne/cm ² ;

ρ is the density of the liquid in g/cm ³ , and the density of physiological saline is calculated as 1 g/cm ³ .

f) The content of extractables

Measure 200ml 0.9% NaCl solution in a 250ml beaker with a graduated cylinder, weigh 1.0g of the test sample to the nearest 0.005g, add it to the solution, seal the beaker with a sealing film, and place the beaker on a magnetic stirrer Use a Buchner funnel and filter paper to filter the supernatant in the beaker, collect more than 50ml of filtrate, and measure 50ml. The filtrate is subjected to a titration test.

At the same time, prepare a blank sample (200ml 0.9% NaCl solution), titrate the blank solution (100ml 0.9% NaCl aqueous solution), use 0.1mol/l NaOH solution for titration, until PH=10; then use 0.1mol/l Titrate the hydrochloric acid solution until PH=2.7. The blank titers obtained are [bNaOH], [bHCL] (mL).

Add a 0.9% NaCl solution to 100 ml of the 50 ml of the filtrate, and perform the same titration operation as described above to obtain titers of [NaOH], [HCl] (mL), respectively.

The calculation formula of the degree of neutralization is as follows:

DN(%)=100-(([NaOH]-[bNaOH])×c(NaOH)*100)/(([HCl]-[bHCl])×c(HCl));

Average molecular weight Mw=72.06x(1-DN/100)+94.04xDN/100;

Extractable matter content Ex(wt%)=(([HCl]-[bHCl])xc(HCl)×Mwx2)/5.

g) Residual monomer content (ppm)

Weigh 1.000 grams of the test sample, accurate to 0.005 grams, in a clean 250ml beaker, measure 200ml 0.9% NaCl solution into the beaker with a graduated cylinder; add a magnetic stir bar, seal the beaker with a sealing film, and place it on the magnetic stirrer Above, stir the solution for 60 minutes at 500 ± 50 rpm. Stop stirring, after standing for 5 minutes, take 1-2 ml of the upper solution, filter the solution with a 0.45 μm filter, and place it in a special sample bottle for liquid phase, label it for HPLC analysis.

Open the autosampler, fill the numbered sample bottle into the corresponding position, align the position, and close the door. Select the sequence in the software, open the sequence table, edit the sequence table, and click Apply. Click the green switch on button in the menu bar, enter the sample group name independently, and then click "Run" to start the test. At this time, the change of sample signal intensity over time can be seen. Wait for the instrument to stabilize so that the temperature and degassing pressure of the column oven of the host and the temperature and energy of the detector reach the set values, and the test starts automatically at this time.

After the sample is tested, open the LC1260 (offline) software, select "Data Analysis", open the folder, and find the analysis result that needs to be opened. Select the sample to be processed, open the spectrum, select "Integrate the current chromatogram", and read the peak area. Use the calibration curve to calculate the residual monomer content in the test sample in the EXCEL table.

Example 1

Preparation of SAP resin particles:

Mix 550g of acrylic acid solution with a concentration of 60wt%, 640g of deionized water, 0.85g of pentaerythritol triallyl ether, and 1.6g of polyethylene glycol diacrylate in a 2L polymerizer, and cool to 5°C in an ice bath , Use nitrogen to deoxidize for 10 minutes, add 2g H ₂ O ₂ aqueous solution (diluted to a concentration of 2wt%), 2g 2,2'-azobis(N,N-dimethylisobutamidine) two Hydrochloride solution (diluted to a concentration of 4wt%) and 2.5g of an aqueous solution of ascorbic acid with a concentration of 2wt% and mixed (in the polymerization aqueous solution, the monomer concentration is 27.5wt%); after the induction period is over, the temperature begins to rise significantly At that time, the polymerization reaction started, and the temperature reached about 85°C after about 1.5 hours of reaction, and then continued to heat and mature for 5 hours to obtain a hydrogel-like polymer.

The hydrogel-like polymer was crushed and extruded using a pelletizing auger, and then 270g of NaOH solution with a concentration of 50% by weight was added for neutralization treatment, so that about 74 mol% of the carboxyl groups in the polymer of the obtained colloidal particles were neutralized into Carboxylic acid sodium salt; use a blast drying oven (purchased from the high-speed rail company) for drying, set the drying temperature to 180 ℃, blast dry the neutralized colloidal particles, and the drying time lasts for 40 minutes. The colloidal particles are crushed by a pulverizer or a wall breaker (purchased from Midea), and are sieved to a particle size in the range of 150-700 microns using a screen to obtain SAP resin particles. SAP particles without surface crosslinking are defined as polymer raw powder a.

Surface cross-linking treatment of polymer powder a:

Weigh 100g of raw polymer powder a, atomize a mixture of 0.05g gallic acid epoxy resin, 1.4g 1,2-propylene glycol and 6g propylene glycol monomethyl ether, and spray it evenly on the surface of the particles of polymer raw powder a , And the polymer particles are fluidized in the air and continuously mixed. Then, the mixed polymer particles are placed in a high-temperature blast oven and heated at 110° C. for 1 hour for surface cross-linking treatment.

Cool the polymer particle material after surface crosslinking to below 40℃, and then spray 2g of aluminum sulfate aqueous solution with a concentration of 20wt% onto the polymer particles after surface crosslinking treatment. At the same time, the polymer particles Fluidized in air and continuously mixed. The mixed polymer particles are sieved with a standard sieve of the required mesh to obtain a target product with a particle size distribution of 150-700 microns.

Example 2

Preparation of SAP resin particles:

The operation steps refer to the steps for preparing SAP resin particles in Example 1, the difference is:

The mass of deionized water added was 550 g (the monomer concentration in the polymerization aqueous solution was 29.7% by weight).

SAP particles without surface crosslinking are defined as polymer raw powder b.

Surface cross-linking treatment of polymer powder b:

Weigh 100g of polymer powder b, atomize a mixture of 0.1g gallic acid epoxy resin, 2g of 1,2-propylene glycol and 6g of deionized water, and spray it evenly on the surface of the particles of polymer powder b. The polymer particles are fluidized in air and continuously mixed. Then, the mixed polymer particles are placed in a high-temperature blast oven and heated at 150° C. for 1 hour for surface cross-linking treatment.

The polymer particles after surface crosslinking are cooled to below 40°C, and then 2.5g of aluminum sulfate aqueous solution with a concentration of 20wt% is sprayed onto the polymer particles after surface crosslinking treatment, and the polymer particles Fluidized in air and continuously mixed. The mixed polymer particles are sieved with a standard sieve of the required mesh to obtain a target product with a particle size distribution of 150-700 microns.

Example 3

Preparation of SAP resin particles:

The operation steps refer to the steps for preparing SAP resin particles in Example 1, the difference is:

In the polymerization stage, the mass of the added pentaerythritol triallyl ether was replaced with 1.2 g (that is, the degree of internal crosslinking was increased).

SAP particles without surface crosslinking are defined as polymer raw powder c.

Surface cross-linking treatment of polymer powder c:

Weigh 100g of raw polymer powder c, atomize a mixture of 0.2g gallic acid epoxy resin, 3.3g 1,2-propylene glycol and 6g deionized water, and spray it evenly on the surface of the particles of raw polymer powder c. And the polymer particles are fluidized in the air and continuously mixed. Then, the mixed polymer particles are placed in a high-temperature blast oven and heated at 130° C. for 1.5 hours for surface cross-linking treatment.

The polymer particles after surface crosslinking are cooled to below 40°C, and then 2.5g of aluminum sulfate aqueous solution with a concentration of 20wt% is sprayed onto the polymer particles after surface crosslinking treatment, and the polymer particles Fluidized in air and continuously mixed. The mixed polymer particles are sieved with a standard sieve of the required mesh to obtain a target product with a particle size distribution of 150-700 microns.

Example 4

Preparation of SAP resin particles:

The operation steps refer to the steps for preparing SAP resin particles in Example 1, the difference is:

In the polymerization stage, first perform a pre-neutralization reaction of 100 g of NaOH aqueous solution with a concentration of 50% by weight and acrylic acid aqueous solution, and cool down to obtain acrylic acid salt before participating in the polymerization reaction; The gel was subjected to post-neutralization treatment (the degree of neutralization of carboxyl groups in the polymer of the obtained colloidal particles was 79.6 mol%).

SAP particles without surface crosslinking are defined as raw polymer powder d.

Surface cross-linking treatment of polymer powder d:

Weigh 100g of polymer powder d, atomize a mixture of 0.005g gallic acid epoxy resin, 0.05g ethylene glycol diglycidyl ether, 3.3g 1,2-propylene glycol and 6g deionized water, and spray it evenly On the surface of the raw polymer powder d particles, the polymer particles are fluidized in the air and continuously mixed. Then, the mixed polymer particles are placed in a high-temperature blast oven and heated at 130° C. for 1.5 hours for surface cross-linking treatment.

The polymer particles after surface crosslinking are cooled to below 40°C, and then 2.5g of aluminum sulfate aqueous solution with a concentration of 20wt% is sprayed onto the polymer particles after surface crosslinking treatment, and the polymer particles Fluidized in air and continuously mixed. The mixed polymer particles are sieved with a standard sieve of the required mesh to obtain a target product with a particle size distribution of 150-700 microns.

Example 5

Preparation of SAP resin particles:

The operation steps refer to the steps for preparing SAP resin particles in Example 1, the difference is:

In the polymerization stage, in the polymerization kettle, the temperature is lowered to 15°C in an ice bath.

SAP particles without surface crosslinking are defined as polymer powder e.

Surface cross-linking treatment of polymer powder e:

Weigh 100g of raw polymer powder e, atomize a mixture of 0.5g gallic acid epoxy resin, 5.3g 1,2-propylene glycol and 6g deionized water, and spray it evenly on the surface of the particles of raw polymer powder e. And the polymer particles are fluidized in the air and continuously mixed. Then, the mixed polymer particles are placed in a high-temperature blast oven and heated at 120° C. for 1.5 hours for surface cross-linking treatment.

The polymer particles after surface crosslinking are cooled to below 40°C, and then 2g of 20wt% aluminum sulfate aqueous solution is atomized and sprayed onto the polymer particles after surface crosslinking treatment, and the polymer particles are at the same time The air is fluidized and continuously mixed. The mixed polymer particles are sieved with a standard sieve of the required mesh to obtain a target product with a particle size distribution of 150-700 microns.

Example 6

Preparation of SAP resin particles:

The operation steps refer to the steps for preparing SAP resin particles in Example 1, the difference is:

In the polymerization stage, the mass of the added pentaerythritol triallyl ether was replaced with 1.2 g (that is, the degree of internal crosslinking was increased).

SAP particles without surface crosslinking are defined as polymer raw powder c.

Surface cross-linking treatment of polymer powder c:

Weigh 100g of the original polymer powder c, atomize the mixture composed of 0.01g gallic acid epoxy resin, 3g ethylene glycol and 6g deionized water, spray it evenly on the surface of the particles of the original polymer powder c, and polymerize the mixture The particles are fluidized and continuously mixed in the air. Then, the mixed polymer particles are placed in a high-temperature blast oven and heated at 120° C. for 1.5 hours for surface cross-linking treatment.

The surface crosslinked polymer particles were cooled to below 40°C, and 2 g of gas phase silica HDK N20D (WACKER) was added at the same time, and then the polymer particles were fluidized in the air and continuously mixed. The mixed polymer particles are sieved with a standard sieve of the required mesh to obtain a target product with a particle size distribution of 150-700 microns.

Comparative example 1 (without gallic acid epoxy resin)

Preparation of SAP resin particles:

For the operation steps, refer to the step of preparing SAP resin particles in Example 4 to obtain polymer raw powder d.

Surface cross-linking treatment of polymer powder d:

Weigh 100g of the original polymer powder d, atomize the mixture composed of 0.05g ethylene glycol diglycidyl ether, 3.3g 1,2-propylene glycol and 6g deionized water, and spray it evenly on the particles of the original polymer powder d. Surface, and the polymer particles are fluidized in the air and continuously mixed. Then, the mixed polymer particles are placed in a high-temperature blast oven and heated at 130° C. for 1.5 hours for surface cross-linking treatment.

The polymer particles after surface crosslinking are cooled to below 40°C, and then 2.5g of aluminum sulfate aqueous solution with a concentration of 20wt% is sprayed onto the polymer particles after surface crosslinking treatment, and the polymer particles Fluidized in air and continuously mixed. The mixed polymer particles are sieved with a standard sieve of the required mesh to obtain a target product with a particle size distribution of 150-700 microns.

Comparative example 2 (add excess gallic acid epoxy resin)

Preparation of SAP resin particles:

For the operation steps, refer to the step of preparing SAP resin particles in Example 5 to obtain polymer raw powder e.

Surface cross-linking treatment of polymer powder e:

Weigh 100g of raw polymer powder e, atomize a mixture of 2g gallic acid epoxy resin, 5.3g 1,2-propylene glycol and 6g deionized water, and spray it evenly on the surface of the raw polymer powder e particles. The polymer particles are fluidized in air and continuously mixed. Then, the mixed polymer particles are placed in a high-temperature blast oven and heated at 120° C. for 1.5 hours for surface cross-linking treatment.

The polymer particles after surface crosslinking are cooled to below 40°C, and then 2g of 20wt% aluminum sulfate aqueous solution is atomized and sprayed onto the polymer particles after surface crosslinking treatment, and the polymer particles are at the same time The air is fluidized and continuously mixed. The mixed polymer particles are sieved with a standard sieve of the required mesh to obtain a target product with a particle size distribution of 150-700 microns.

The superabsorbent polymers prepared in the foregoing Examples and Comparative Examples were tested using the test methods described above. Unless otherwise specified, the test should be carried out at an ambient temperature of 23±2°C and a relative air humidity of 50±10%, and the absorbent polymer should be mixed evenly before the test. The test results of product performance are shown in Table 1 below:

Table 1 Performance test results of super absorbent polymers

Through the test results in Table 1, it can be found that

In each embodiment, by using a small amount of gallic acid epoxy resin as a surface cross-linking agent for surface cross-linking, the surface cross-linking effect of the obtained SAP resin can be enhanced, while improving its liquid permeability, it can ensure SAP The resin has excellent pressurization performance and liquid absorption rate, and excellent overall performance.

In Comparative Example 1, when the gallic acid epoxy resin is not used as the surface crosslinking agent for surface crosslinking, the pressure absorption rate of SAP resin is lower, the liquid permeability is also low, and the liquid absorption rate is significantly slower. The test data is consistent with the aforementioned explanation of the technical solution.

In Comparative Example 2, when the amount of gallic acid epoxy resin is too high, the cross-linking of the entire SAP particles will be too high. In addition, the strength of the gallic acid epoxy resin is higher, and the centrifugal water retention rate decreases significantly, which is not conducive to The use of super absorbent resin in practical applications. At the same time, its liquid passing rate is also much lower than that of the SAP resin obtained in Example 5.

The embodiments of the present invention have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Without departing from the scope and spirit of the illustrated embodiments, many modifications and changes are obvious to those of ordinary skill in the art.

Claims (13)

1. A super absorbent polymer, characterized in that the raw materials for the polymerization reaction include the following components:

   a) The concentration of ethylenically unsaturated monomers and/or their salts containing carboxyl groups in the polymerization aqueous solution is greater than or equal to 20 wt% and less than or equal to 35 wt%, preferably greater than or equal to 20 wt% and less than or equal to 30 wt%;

   b) Internal crosslinking agent containing double bond compound, the amount is 0.01wt%-4wt% of the weight of component a), preferably 0.5wt%-2wt%;

   c) oxidant, the amount is 0.005wt%-5wt% of the weight of component a), preferably 0.01wt%-0.5wt%;

   d) Reducing agent, in an amount of 0.005% to 5% by weight of the weight of component a), preferably 0.01% to 0.5% by weight;

   Among them, after the hydrogel obtained by the polymerization reaction is neutralized, the neutralization degree of the carboxylic acid of the polymer in the colloidal particles obtained is 50-80 mol%; the colloidal particles are converted into polymer particles with a particle size of 150-700 microns. The proportion of particles is greater than or equal to 92wt%;

   And, the surface of the polymer particles adopts the following treatments:

   e) Surface cross-linking is carried out by applying a surface cross-linking agent to the surface of the dried polymer particles, the surface cross-linking agent includes at least gallic acid epoxy resin; based on the dried polymer particles, the gallic acid epoxy resin The amount of resin used is 0.005wt%-0.5wt%, preferably 0.01wt%-0.2wt%; and, optionally

   f) Based on the dried polymer particles, 0-2wt% of insoluble inorganic powder is added after surface crosslinking.
2. The superabsorbent polymer according to claim 1, wherein the ethylenically unsaturated monomer containing carboxyl group is selected from acrylic acid, methacrylic acid, ethacrylic acid, α-chloroacrylic acid, and α-cyanoacrylic acid. , Β-methacrylic acid, α-phenyl acrylic acid, β-acryloyloxypropionic acid, sorbic acid, α-chlorosorbic acid, 2'-methylisocrotonic acid, cinnamic acid, p-chlorocinnamic acid, β- One or more of stearic acid, itaconic acid, citraconic acid, mesaconic acid, glutaconic acid, aconitic acid, maleic acid, fumaric acid, tricarboxyethylene and maleic anhydride, preferably selected From acrylic acid and/or methacrylic acid, more preferably acrylic acid; and/or

   The internal crosslinking agent containing double bond compound is selected from ethylene glycol diacrylate, propylene glycol diacrylate, N,N'-methylene bisacrylamide, polyethylene glycol diacrylate, polypropylene glycol diacrylate One of pentaerythritol triallyl ether, ethoxylated glycerol triacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, triallylamine, pentaerythritol tetraacrylate and dipentaerythritol hexaacrylate Kind or more; and/or

   The oxidizing agent is a peroxide, preferably one or more selected from sodium persulfate, hydrogen peroxide, potassium persulfate and ammonium persulfate, more preferably hydrogen peroxide; and/or

   The reducing agent is selected from one or more of ascorbic acid, ammonium bisulfite, ammonium thiosulfate, ammonium dithionite, ammonium sulfide and sodium hydroxymethyl sulfoxylate, preferably ascorbic acid; and/or

   The insoluble inorganic powder is selected from one of silicon dioxide, silica, titanium dioxide, aluminum oxide, magnesium oxide, zinc oxide, talc, calcium phosphate, clay, diatomaceous earth, zeolite, bentonite, kaolin, hydrotalcite, and activated clay Or more, preferably silica.
3. The superabsorbent polymer according to claim 1, wherein the surface crosslinking agent further comprises one or more of polyol compounds, epoxy compounds, amine compounds and metal inorganic salts; The content of the dried polymer particles is 0-2wt%, preferably 0.1-1wt%;

   The polyhydric alcohol compound is preferably selected from ethylene glycol, propylene glycol, glycerol, 1,4-butanediol or pentaerythritol;

   The epoxy compound is preferably selected from (poly)ethylene glycol diglycidyl ether, 1,4-butanediol diglycidyl ether, ethylene carbonate or propylene carbonate;

   The amine compound is preferably selected from tris or carbodiimide;

   The metal inorganic salt is preferably selected from an inorganic salt of calcium, an inorganic salt of magnesium, an inorganic salt of aluminum, an inorganic salt of iron, an inorganic salt of copper, or an inorganic salt of zinc.
4. The superabsorbent polymer according to any one of claims 1 to 3, wherein the raw material for the polymerization reaction further comprises: g) at least one thermal initiator, the thermal initiator being an azo initiator , Preferably selected from azobisisobutyronitrile, azobiscyanovaleric acid, azobisdimethylvaleronitrile, 2,2'-azobis(2-amidinopropane) dihydrochloride, azo Bisamidinopropane dihydrochloride, 2,2'-azobis(N,N-dimethylisobutamidine) dihydrochloride, 2-(carbamoylazo)isobutyronitrile and 4, One or more of 4-azobis(4-cyanovaleric acid);

   Preferably, the amount of the thermal initiator is 0.005 wt% to 1 wt% of the weight of component a), more preferably 0.01 wt% to 0.2 wt%.
5. The superabsorbent polymer according to any one of claims 1 to 4, wherein the superabsorbent polymer has a liquid absorption rate of 60-70 g/g, and a centrifugal water retention rate of 33-40 g/g , 0.7psi pressurized liquid absorption rate is 23-28g/g, liquid absorption rate is 20-35s, liquid flow rate (GBP) is greater than or equal to 40 Darcy, the content of residual monomer is less than or equal to 400ppm, and the content of extractables is less than or equal to 5wt %.
6. A preparation method of super absorbent polymer, which is characterized in that it comprises the following steps:

   At ≤20°C, the carboxyl-containing ethylenic unsaturated monomer and/or its salt, oxidizing agent, reducing agent, and internal crosslinking agent containing double bond compounds are contacted to initiate polymerization to obtain a hydrogel; After the gel is crushed and extruded, it is contacted with a neutralizing agent for neutralization reaction to obtain colloidal particles; after drying, grinding and sieving, the colloidal particles are subjected to surface cross-linking treatment by contacting with a surface cross-linking agent to obtain super absorbent Sexual polymer resin;

   Wherein, the surface crosslinking agent at least includes gallic acid epoxy resin.
7. The preparation method according to claim 6, wherein the polymerization reaction is aqueous solution polymerization; preferably, the concentration of the carboxyl-containing ethylenically unsaturated monomer and/or its salt in the polymerization aqueous solution is greater than or equal to 20 wt. % And less than or equal to 35wt%, more preferably greater than or equal to 20wt% and less than or equal to 30wt%; and/or

   Based on the weight of the ethylenically unsaturated monomer containing the carboxyl group and/or its salt, the amount of the internal crosslinking agent containing the double bond compound is 0.01wt%-4wt%, preferably 0.5wt%-2wt%; and/ or

   Based on the weight of the ethylenically unsaturated monomer containing a carboxyl group and/or its salt, the amount of the oxidizing agent is 0.005% to 5% by weight, preferably 0.01% to 0.5% by weight; and/or

   Based on the weight of the ethylenically unsaturated monomer containing a carboxyl group and/or its salt, the amount of the reducing agent is 0.005% to 5% by weight, more preferably 0.01% to 0.5% by weight; and/or

   After neutralizing the hydrogel, the neutralization degree of carboxylic acid of the polymer in the obtained colloidal particles is 50-80 mol%; and/or

   Based on the dried super absorbent polymer particles, the gallic acid epoxy resin is used in an amount of 0.005 wt% to 0.5 wt%, preferably 0.01 wt% to 0.2 wt%.
8. The preparation method according to claim 6 or 7, wherein the ethylenically unsaturated monomer containing a carboxyl group is selected from acrylic acid, methacrylic acid, ethacrylic acid, α-chloroacrylic acid, α-cyanoacrylic acid, β-methacrylic acid, α-phenyl acrylic acid, β-acryloyloxypropionic acid, sorbic acid, α-chlorosorbic acid, 2'-methylisocrotonic acid, cinnamic acid, p-chlorocinnamic acid, β-hard One or more of fatty acid, itaconic acid, citraconic acid, mesaconic acid, glutaconic acid, aconitic acid, maleic acid, fumaric acid, tricarboxyethylene and maleic anhydride, preferably selected from Acrylic acid and/or methacrylic acid, more preferably acrylic acid; and/or

   The internal crosslinking agent containing double bond compound is selected from ethylene glycol diacrylate, propylene glycol diacrylate, N,N'-methylene bisacrylamide, polyethylene glycol diacrylate, polypropylene glycol diacrylate One of pentaerythritol triallyl ether, ethoxylated glycerol triacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, triallylamine, pentaerythritol tetraacrylate and dipentaerythritol hexaacrylate Kind or more; and/or

   The oxidizing agent is a peroxide, preferably one or more selected from sodium persulfate, hydrogen peroxide, potassium persulfate and ammonium persulfate, more preferably hydrogen peroxide; and/or

   The reducing agent is selected from one or more of ascorbic acid, ammonium bisulfite, ammonium thiosulfate, ammonium dithionite, ammonium sulfide and sodium hydroxymethyl sulfoxylate, preferably ascorbic acid; and/or

   The neutralizer is an aqueous solution of an alkaline compound, the concentration of which is 30-60% by weight, preferably 40-50% by weight; the alkaline compound is preferably selected from sodium hydroxide, potassium hydroxide, sodium carbonate and potassium carbonate One or more, more preferably sodium hydroxide.
9. The preparation method according to any one of claims 6-8, wherein the surface crosslinking agent further comprises one or more of polyol compounds, epoxy compounds, amine compounds and metal inorganic salts. Species; based on the dried superabsorbent polymer particles, its content is 0-2wt%, preferably 0.1-1wt%;

   The polyhydric alcohol compound is preferably selected from ethylene glycol, propylene glycol, glycerol, 1,4-butanediol or pentaerythritol;

   The epoxy compound is preferably selected from (poly)ethylene glycol diglycidyl ether, 1,4-butanediol diglycidyl ether, ethylene carbonate or propylene carbonate;

   The amine compound is preferably selected from tris or carbodiimide;

   The metal inorganic salt is preferably selected from an inorganic salt of calcium, an inorganic salt of magnesium, an inorganic salt of aluminum, an inorganic salt of iron, an inorganic salt of copper, or an inorganic salt of zinc.
10. The preparation method according to any one of claims 6-9, wherein the temperature at which the colloidal particles are dried is 100-240°C.
11. The preparation method according to any one of claims 6-10, wherein:

    After the colloidal particles are dried, the colloidal particles are further ground and sieved to control the size of the superabsorbent polymer particles; wherein the proportion of the superabsorbent polymer particles with a particle size of 150-700 microns is greater than or equal to 92wt% .
12. The preparation method according to any one of claims 6-11, wherein the process conditions of the surface crosslinking treatment include: a reaction temperature of 50-150°C, preferably 80-130°C; and a reaction time of 0.5 h-3h, preferably 1h-2h;

    Optionally, based on the dried superabsorbent polymer particles, 0-2wt% of insoluble inorganic powder is added after the surface crosslinking treatment; the insoluble inorganic powder is preferably selected from the group consisting of silica, silica, titania, alumina, One or more of magnesium oxide, zinc oxide, talc, calcium phosphate, clay, diatomaceous earth, zeolite, bentonite, kaolin, hydrotalcite, and activated clay, more preferably silica.
13. The preparation method according to any one of claims 6-12, wherein at least one thermal initiator is added during the polymerization reaction, and the thermal initiator is an azo initiator, preferably selected from azo initiators. Diisobutyronitrile, azobiscyanovaleric acid, azobisdimethylvaleronitrile, 2,2'-azobis(2-amidinopropane) dihydrochloride, azobisamidinopropane di salt Acid salt, 2,2'-azobis(N,N-dimethylisobutamidine) dihydrochloride, 2-(carbamoylazo)isobutyronitrile and 4,4-azobis( One or more of 4-cyanovaleric acid);

    Preferably, based on the weight of the carboxyl-containing ethylenically unsaturated monomer and/or its salt, the thermal initiator is used in an amount of 0.005% to 1% by weight, more preferably 0.01% to 0.2% by weight.