CN109535307B - Reversed phase suspension polymerization preparation process of water-absorbent resin - Google Patents
Reversed phase suspension polymerization preparation process of water-absorbent resin Download PDFInfo
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- C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
- C08F220/00—Copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical or a salt, anhydride ester, amide, imide or nitrile thereof
- C08F220/02—Monocarboxylic acids having less than ten carbon atoms; Derivatives thereof
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- C08F2/32—Polymerisation in water-in-oil emulsions
Abstract
The invention discloses a reverse suspension polymerization preparation process of water-absorbent resin, which comprises the steps of first-stage polymerization, second-stage polymerization, acid-base neutralization, azeotropic dehydration and surface crosslinking, solvent removal and drying. The invention enriches the preparation process of the water-absorbent resin and provides a method for developing the water-absorbent resin with differentiated performance.
Description
Technical Field
The invention belongs to the field of high Polymer materials, relates to a reverse phase suspension polymerization preparation process of a water-Absorbent resin, and particularly relates to a method for preparing a Super Absorbent Polymer (SAP) by adopting a reverse phase suspension polymerization process of polymerization before neutralization.
Background
The super absorbent resin is a lightly crosslinked high molecular polymer, and is widely used in the field of sanitary materials such as paper diapers and sanitary towels, cable water-blocking materials, water-retaining agents for agriculture, forestry and gardening and the like due to the strong water absorption and water retention capacity of the super absorbent resin.
As water-absorbent resins used in sanitary materials, partially neutralized products of polyacrylic acid, neutralized products of starch-acrylic acid graft polymers, hydrolyzed products of starch-acrylonitrile graft polymers, saponified products of vinyl acetate-acrylic ester copolymers, and the like are known.
At present, the water-absorbent resin is mainly prepared by an aqueous solution polymerization method and an inverse suspension (emulsion) polymerization method, about 95 percent of high water-absorbent resin is prepared by the aqueous solution polymerization method, and the manufacturers have Japanese catalysts, BASF, Yingchuanggusai, Sandaya, LG and the like; approximately 5% of the total polymer was prepared by inverse suspension polymerization, representing the manufacturers of Sumitomo refinement and Mitsubishi chemistry.
As the preparation process of the water-absorbent resin, the preparation process of firstly neutralizing and then polymerizing is mostly adopted: that is, acrylic acid monomer and alkali solution such as sodium hydroxide are directly subjected to acid-base neutralization reaction to obtain so-called acrylic acid neutralized solution, then a crosslinking agent and an initiator are added, and then radical polymerization at high temperature is performed to obtain water-absorbent resin, typically Japanese catalysts (e.g., CN102549028A, CN102482433A, CN101177462A, CN1784430A), Sumitomo refinements (e.g., CN1337977A, CN1053796A, CN1175962A), Mitsubishi chemistry (e.g., CN1146997A, CN1197804A), and the like; and a small part of the preparation process adopts the preparation process of polymerization and neutralization: that is, an acrylic acid solution containing an initiator and a crosslinking agent is directly subjected to radical polymerization at a low temperature, and after completion of the polymerization, a part of carboxyl groups in polyacrylic acid is neutralized by adding an alkali solution such as sodium hydroxide, and more typically, water-absorbent resins such as SANYLIC (CN 1589304A, CN106459598A, CN107428948A, CN107406595A) and NOL (CN 106987075A) can be obtained.
The preparation process of polymerization after neutralization and the preparation process of polymerization before neutralization have various advantages, because the polymerization heat of the acrylic acid monomer is higher, the direct polymerization has more strict requirements on reaction conditions, so the polymerization needs to be carried out at low temperature or under the condition of good heat dissipation state, and when the acrylic acid neutralization solution is prepared, the reaction rate constant is reduced, so that the polymerization conditions become mild and controllable.
The production process of firstly polymerizing and then neutralizing in the aqueous solution polymerization method has certain defects, such as the waste of energy sources caused by the removal of a large amount of neutralization heat in the acid-base neutralization process; and the temperature rise in the acid-base neutralization process is obvious, so that the content of acrylic acid dimer in the obtained acrylic acid neutralized liquid is increased sharply, the storage time of the neutralized liquid is limited, and the final product performance of the water-absorbent resin is further influenced.
The reversed phase suspension polymerization is used as a unique preparation process of the water-absorbent resin, the water-absorbent resin with high water absorption rate can be prepared, and the pursuit of the composite core market on the thinness is greatly met. At present, only the resident friend refinement has the capacity of large-scale industrial manufacturing, but the preparation mode also adopts the processes of neutralization first and polymerization later. The application of a process of polymerization before and neutralization to a preparation mode of reverse phase suspension polymerization does not exist in the field.
Disclosure of Invention
The invention aims to improve the defects in various processes for producing water-absorbent resins in the prior art and provide a novel method for preparing differential water-absorbent resins.
In order to solve the above technical problems, in one aspect of the present invention, there is provided a method for preparing a water absorbent resin using a reversed-phase suspension polymerization process of polymerization before neutralization, comprising the steps of:
a. one-stage polymerization: adding a first-stage (methyl) acrylic acid aqueous solution containing a first-stage initiator, a cross-linking agent and a comonomer into a petroleum hydrocarbon solvent dissolved with a dispersant, and carrying out first-stage water-in-oil reversed-phase suspension polymerization to obtain a suspension containing a first-stage poly (methyl) acrylic acid colloidal particle;
b. second-stage polymerization: b, adding a second-stage (meth) acrylic acid aqueous solution containing a surfactant, a second-stage initiator, a cross-linking agent and a comonomer into the suspension containing the first-stage poly (meth) acrylic acid colloidal particles obtained in the step a, enabling (meth) acrylic acid droplets of the second-stage (meth) acrylic acid aqueous solution and the first-stage poly (meth) acrylic acid colloidal particles to adsorb and aggregate with each other, and carrying out second-stage water-in-oil reversed-phase suspension polymerization to obtain a suspension containing the second-stage poly (meth) acrylic acid colloidal particles;
the hydrophilic-lipophilic balance value HLB of the surfactant is more than 7;
c. acid-base neutralization: adding an alkaline solution into the suspension containing the second-stage poly (meth) acrylic acid colloidal particles obtained in the step b, and carrying out acid-base neutralization reaction on the alkaline solution and the second-stage poly (meth) acrylic acid colloidal particles;
d. azeotropic dehydration and surface crosslinking: c, heating the suspension obtained in the step c to the azeotropic point of water and the petroleum hydrocarbon solvent (the azeotropic point T is less than 100 ℃), removing 70-90% of water in the suspension, and adding a surface cross-linking agent for surface cross-linking;
e. solvent removal and drying: removing residual water and petroleum hydrocarbon solvent in the system by adopting a filtering or distilling process, and finally drying to obtain water-absorbent resin;
the (meth) acrylic acid is acrylic acid or methacrylic acid.
In a preferred embodiment, in the above process, the petroleum hydrocarbon solvent in step a is selected from one or more of cyclopentane, cyclohexane, n-heptane, n-hexane and n-octane, preferably n-heptane and/or cyclohexane;
the dispersing agent in the step a is selected from one or more of sucrose fatty acid ester, sorbitan monostearate, sorbitan monooleate, triglycerol monostearate, octadecyl monophosphate and maleic anhydride modified ethylene-propylene copolymer;
the primary initiator in the step a is a thermal initiator and is selected from one or more of sodium persulfate, potassium persulfate, ammonium persulfate, 2 '-azodiisopropyl imidazoline hydrochloride (V-50), 2' -azo (2-methyl-N- (2-hydroxyethyl) propionamide) (VA-086) and 2, 2-aza-bis (2-imidazoline) dihydrochloride (VA-044);
the cross-linking agent in the step a is selected from one or more of ethylene glycol diglycidyl ether, N' -methylene bisacrylamide, polyethylene glycol diacrylate and pentaerythritol triallyl ether;
in the step a, the comonomer is selected from one or more of acrylamide, methacrylamide, glycidyl acrylate, glycidyl methacrylate, hydroxyethyl acrylate, hydroxyethyl methacrylate and vinyl acetate.
In a preferred embodiment, in any one of the above-mentioned methods, the amount of the petroleum hydrocarbon solvent used in step a is 500% by mass, preferably 300% by mass, of the aqueous solution of the one-stage (meth) acrylic acid;
the dosage of the dispersant in the step a is 0.1 to 10 percent of the mass of the petroleum hydrocarbon solvent, and preferably 0.2 to 1 percent;
the dosage of the first-stage initiator in the step a is 0.005-5 percent of the mass of the first-stage (methyl) acrylic acid, and preferably 0.02-2 percent;
the dosage of the cross-linking agent in the step a is 0.001-1%, preferably 0.01-0.5% of the mass of the first section of (methyl) acrylic acid;
the amount of the comonomer in the step a is 0.005-5%, preferably 0.02-2% of the mass of the first-stage (methyl) acrylic acid;
the mass concentration of the first section of (meth) acrylic acid in the first section of (meth) acrylic acid aqueous solution in the step a is 10-60%, preferably 20-40%;
the first section of (meth) acrylic acid is (meth) acrylic acid in the first section of aqueous (meth) acrylic acid solution;
the one-stage water-in-oil reversed-phase suspension polymerization (high-temperature polymerization) in the step a is high-temperature thermal initiation, the polymerization temperature is 40-80 ℃, preferably 60-80 ℃, and the time is 0.5-3h, preferably 0.8-2.5 h.
In a preferred embodiment, in the above method, the surfactant in step b is selected from one or more of alkylphenol ethoxylate (OP-10), sorbitan laurate (Span-20), polyoxyethylene sorbitan monooleate (Tween-80), sucrose fatty acid ester (S-970), polyvinyl alcohol (PVA), and polyoxyethylene lauryl ether phosphate;
the second-stage initiator in the step b is a redox initiator and is selected from one or more of sodium persulfate/sodium sulfite, sodium persulfate/sodium bisulfite, tert-butyl hydroperoxide/ferrous sulfate and hydrogen peroxide/L-ascorbic acid;
the cross-linking agent in the step b is selected from one or more of ethylene glycol diglycidyl ether, N' -methylene bisacrylamide, polyethylene glycol diacrylate and pentaerythritol triallyl ether;
in the step b, the comonomer is selected from one or more of acrylamide, methacrylamide, glycidyl acrylate, glycidyl methacrylate, hydroxyethyl acrylate, hydroxyethyl methacrylate and vinyl acetate.
In a preferred embodiment, in any of the above processes, the amount of the surfactant used in step b is 0.01 to 10%, preferably 0.1 to 1.5%, based on the total mass of (meth) acrylic acid in the primary (meth) acrylic acid and the secondary (meth) acrylic acid;
the dosage of the second-stage initiator in the step b is 0.005-5 percent of the mass of the second-stage (methyl) acrylic acid, and more preferably 0.02-2 percent;
the dosage of the cross-linking agent in the step b is 0.001-1%, preferably 0.01-0.5% of the mass of the second-stage (methyl) acrylic acid;
the amount of the comonomer in the step b is 0.005-5%, preferably 0.02-2% of the mass of the second-stage (methyl) acrylic acid;
the mass concentration of the second-stage (meth) acrylic acid in the second-stage (meth) acrylic acid aqueous solution in the step b is 10-60%, preferably 20-45%;
the first section of (meth) acrylic acid is (meth) acrylic acid in the first section of aqueous (meth) acrylic acid solution; the second-stage (meth) acrylic acid is (meth) acrylic acid in the second-stage (meth) acrylic acid aqueous solution;
in the step b, the two-stage water-in-oil reversed-phase suspension polymerization (low-temperature polymerization) is redox initiation, the polymerization temperature is 20-60 ℃, preferably 30-50 ℃, and the time is 0.5-3h, preferably 0.5-2 h;
in the invention, the stirring is carried out from the beginning of the addition of the dispersant to the end of the polymerization process, and the stirring speed is 200-600 rpm/min.
In a preferred embodiment, in the above method, the alkaline solution in step c is selected from one or more of aqueous solutions of sodium hydroxide, potassium hydroxide, sodium bicarbonate, sodium carbonate, potassium carbonate and ammonium carbonate, preferably one or more of aqueous solutions of sodium hydroxide, potassium hydroxide and sodium bicarbonate.
In a preferred embodiment, in any of the above methods, the concentration of the alkaline solution in step c is 20-55% by mass;
the neutralization degree of the acid-base neutralization reaction in the step c is 60-90%, and preferably 70-80%;
the temperature of the acid-base neutralization reaction in the step c is 30-60 ℃, preferably 40-50 ℃, and the time is 10-90min, preferably 10-30 min.
In a preferred embodiment, in the above method, the surface cross-linking agent in step d is a compound having at least two functional groups capable of reacting with a carboxyl group, preferably one or more of a polyglycidyl compound, a polyhydric alcohol and an alkylene carbonate, more preferably one or more of ethylene glycol diglycidyl ether, glycerol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerol, propylene glycol, ethylene glycol, 1, 4-butanediol, ethylene carbonate and propylene carbonate.
In a preferred embodiment, in any of the above processes, the amount of the surface cross-linking agent used in step d is 0.001 to 15%, preferably 0.01 to 10%, based on the total mass of the primary (meth) acrylic acid and the secondary (meth) acrylic acid;
the first section of (meth) acrylic acid is (meth) acrylic acid in the first section of aqueous (meth) acrylic acid solution; the second-stage (meth) acrylic acid is (meth) acrylic acid in the second-stage (meth) acrylic acid aqueous solution;
the temperature of the surface cross-linking in the step d is 60-100 ℃, preferably 70-90 ℃, and the time is 0.5-3h, preferably 1-2 h;
the distillation temperature in the step e is 100-150 ℃, and the time is 0.2-1 h;
the drying temperature in the step e is 100-180 ℃, and the drying time is 0.5-2 h;
the final water content of the water-absorbent resin is 1 to 10%, preferably 2 to 5%.
In another aspect of the present invention, there is also provided a water-absorbent resin produced by any one of the above-mentioned methods.
Different from the traditional preparation process of the water-absorbent resin with the first neutralization and the second neutralization, the invention adopts the preparation process of the super-absorbent resin with the first polymerization and the second neutralization, which directly carries out the first-stage reversed-phase suspension polymerization (high-temperature thermal initiation) on the acrylic acid aqueous solution, reduces the temperature to be below the decomposition temperature of a water-soluble initiator after the polymerization is finished, then adds the second-stage acrylic acid aqueous solution containing a surfactant to carry out the second-stage reversed-phase suspension polymerization (low-temperature redox initiation), and carries out the second-stage polymerization while carrying out the particle agglomeration; after the polymerization is finished, adding a proper amount of alkaline solution to perform acid-base neutralization reaction with the obtained polyacrylic acid or polymethacrylic acid, and effectively utilizing the temperature and heat in the polymerization process to obtain the water-absorbent resin hydrogel particles. Finally, the obtained hydrogel particles are subjected to azeotropic dehydration, surface crosslinking, distillation, drying and screening to obtain the target super absorbent resin particles. The properties of the final SAP product can be adjusted by the amount of base added at a later time.
The SAP prepared by the invention has good liquid passing rate and 1min pure water absorption capacity, presumably matching of high and low temperature initiation, relatively stable polymerization process and relatively uniform cross-linked network structure, and is caused by increased gel strength of the obtained SAP particles after water absorption.
The invention enriches the preparation process of the water-absorbent resin and provides a thought for the development of the water-absorbent resin with differentiated performance.
Drawings
FIG. 1 is an SEM (scanning electron microscope) image of a water-absorbent resin obtained in example 1 of the present invention.
Detailed Description
Some of the specific steps involved in the experimental procedures used in the examples described below were, unless otherwise specified, routine procedures.
Materials, reagents and the like used in the following examples are commercially available unless otherwise specified.
The present invention will be further described with reference to the following examples. It should be understood that the following examples are illustrative only and are not intended to limit the scope of the present invention.
The basic performance index test method of the super absorbent resin comprises the following steps:
the test method of the liquid absorption rate, the centrifugal water retention and the pressurizing liquid absorption rate is used for executing GB/T22875-2018 and ISO 17190-5-2001 standards, and the rest physical properties are tested according to the following method:
liquid flow rate (g/min)
A liquid permeability measuring device is prepared (a plastic cylinder with the inner diameter of 25mm, the outer diameter of 31mm and the height of 35cm is adopted, and a nylon net with the diameter of 63 mu m is attached to the bottom surface). 0.1g of a super absorbent resin was poured into a 100mL beaker, and 40mL of physiological saline was added thereto to swell the resin. After 30min, the swollen gel was poured into the measuring apparatus (if any residue was in the beaker, the whole was washed with physiological saline). Slowly pressing a 100g weight on the gel in the measuring device, then adding a proper amount of normal saline to a test scale mark (about 28 cm), vertically suspending the measuring device, slowly flowing down the liquid drop at the moment, and measuring the amount of the normal saline which passes through the gel within 1min, namely, the liquid passing rate, wherein the higher the value, the better the diffusion conductivity after the SAP absorbs the liquid.
Extractable content (%)
1.000 +/-0.005 g of SAP is accurately weighed by an analytical balance (precision: 0.0001g), placed in a 250ml beaker, 200ml of physiological saline (mass concentration: 0.9%) is added, the mixture is placed in a magnetic rotor (length: about 3cm), then sealed by a sealing film, placed on a magnetic stirrer to be stirred (the rotating speed is about 500rpm), after 16 hours, the stirring is stopped, the mixture is kept stand for 10 minutes, and the supernatant is filtered by filter paper to obtain 50ml of filtrate.
The filtrate was titrated with 0.1mol/L NaOH solution to pH 10 and the volume of the consumed solution was taken as [ NaOH ], then titrated with 0.1mol/L hydrochloric acid solution to pH 2.7 and the volume of the consumed solution was taken as [ HCl ]. Meanwhile, distilled water is taken for blank experiment, and the volume of the consumed two solutions is recorded as [ bNaOH ], [ bHCl ].
The lower the extractable content, the less the low molecular weight portion of the water-absorbent resin.
1min pure water absorption (g/g)
To a beaker containing 250mL of pure water, 0.5g (to an accuracy of 0.01g) of a dried sample of a super absorbent resin was added, and a stopwatch was started, and at 1min, the sample of a super absorbent resin in the beaker and water were stirred uniformly and immediately introduced into a filter bag, and after dropping off the free water slightly, the weight m of the filter bag was weighed2Taking out the super absorbent resin sample from the filter bag and weighing the weight m of the filter bag1And then: the 1min pure water absorption (g/g) of the super absorbent resin sample is (m)2-m1) 0.5, which reflects the amount of pure water absorbed by the SAP per unit time, higher values indicate a faster rate of water absorption.
Sucrose fatty acid ester (S-370) is a product of mitsubishi chemical (shanghai) ltd, CAS No.: 37318-31-3.
The maleic anhydride-modified ethylene-propylene copolymer (1105A) is a product of mitsui chemical corporation, CAS No.: 31069-12-2.
2,2' -azobisisopropylimidazoline hydrochloride (V-50) was WAKO (Japan and Wako pure chemical Co., Ltd.) under CAS number: 2997-92-4.
Ethylene glycol diglycidyl ether is a product of trades of Shanghai, CAS number: 2224-15-9.
Alkylphenol ethoxylates (OP-10) is a product of Nanjing Cutian chemical Co., Ltd, CAS number: 9036-19-5.
Sorbitan laurate (Span20) is a product of carbofuran technologies ltd, beijing, CAS No.: 1338-39-2.
Sorbitan monostearate (Span60) is a product of national pharmaceutical group chemical agents ltd, CAS No.: 1338-41-6.
The competitive product A is a product of Japan Sanda macromolecule Co., Ltd, and is prepared by an aqueous solution polymerization process: polymerizing and then neutralizing; the competitive product B is a Japanese catalyst product of Kabushiki Kaisha, and is prepared by an aqueous solution polymerization process: firstly neutralizing and then polymerizing; the competitive product C is a product of Sumitomo chemical company, and is prepared by a reversed-phase suspension polymerization process: firstly neutralizing and then polymerizing; the basic raw materials used for the three competitions are shown in table 1.
TABLE 1 basic materials for three contestants
Example 1:
1. one-stage polymerization
240g of n-heptane (155.0% by weight based on the mass of the one-stage aqueous acrylic acid solution) was charged into a 1L four-necked round-bottomed flask equipped with a stirrer, a reflux condenser, a thermometer and a nitrogen inlet pipe. 0.92g of sucrose fatty acid ester (S-370) (0.38 wt% based on the mass of n-heptane) was added thereto, heated to 60 ℃ and uniformly dissolved and dispersed at a stirring speed of 250rpm, and then cooled to 40 ℃. 99.7g of an aqueous solution in which 0.055g of sodium persulfate (0.10% by weight based on the mass of the one-stage acrylic acid), 0.028g of 2,2' -azobisisopropylimidazoline hydrochloride (V-50) (0.05% by weight based on the mass of the one-stage acrylic acid), 0.278g of hydroxyethyl methacrylate (0.5% by weight based on the mass of the one-stage acrylic acid), 22.1mg of ethylene glycol diglycidyl ether (0.04% by weight based on the mass of the one-stage acrylic acid) were dissolved was added to 55.2g of acrylic acid (i.e., one-stage acrylic acid) to obtain an aqueous one-stage acrylic acid solution (the mass concentration of the one-stage acrylic acid was 35.6%). The one-stage acrylic acid aqueous solution was added to the above four-necked round-bottomed flask, and nitrogen gas was introduced while stirring to sufficiently remove oxygen. Then heating to 60 ℃ for reaction for 2h to carry out primary water-in-oil (W/O) reversed-phase suspension polymerization to obtain a suspension containing primary polyacrylic acid colloidal particles.
2. Two stage polymerization
68.8g of an aqueous solution in which 0.055g of sodium persulfate (0.1 wt% based on the mass of the secondary acrylic acid), 0.278g of hydroxyethyl methacrylate (0.5 wt% based on the mass of the secondary acrylic acid), 22.1mg of ethylene glycol diglycidyl ether (0.04 wt% based on the mass of the secondary acrylic acid), and 0.55g of alkylphenol polyoxyethylene ether (OP-10) (HLB of 13.5) (0.5 wt% based on the total mass of the primary and secondary acrylic acids) were dissolved was added to 55.2g of acrylic acid (i.e., secondary acrylic acid), followed by 0.022g of sodium sulfite (0.04 wt% based on the mass of the secondary acrylic acid) to obtain an aqueous solution of the secondary acrylic acid (mass concentration of the secondary acrylic acid is 44.4%). After that, the suspension containing the primary polyacrylic acid colloidal particles obtained in the step 1 is cooled to 40 ℃, a secondary acrylic acid aqueous solution is added, and after nitrogen is sufficiently replaced, the suspension is stirred for 30min at the rotating speed of 350rpm, so that acrylic acid droplets of the secondary acrylic acid aqueous solution and the primary polyacrylic acid colloidal particles are adsorbed and aggregated with each other. Then, carrying out two-stage water-in-oil reversed-phase suspension polymerization while particle agglomeration is generated, and obtaining a suspension containing two-stage polyacrylic acid colloidal particles.
3. Acid-base neutralization
After the second-stage polymerization was completed, 143.8g of an aqueous solution of sodium hydroxide having a mass concentration of 32% was dropped into the suspension containing the second-stage polyacrylic acid colloidal particles obtained in step 2 at a dropping rate of 2 to 3 drops/sec. At the moment, the added alkali liquor and the obtained two-stage polyacrylic acid colloidal particles are subjected to acid-base neutralization reaction, the temperature of the acid-base neutralization reaction is 40 ℃, the time is 15min, the neutralization degree is 75%, and the system is continuously stirred for 15min after the temperature is constant.
4. Azeotropic dehydration and surface crosslinking
The suspension from step 3 was warmed to 100 ℃ for azeotropic dehydration and n-heptane was refluxed, resulting in a total removal of 200g of water (75% water based on a total of 266g of water in the four-necked round-bottomed flask). The system temperature is adjusted to 80 ℃, 9.2g of ethylene glycol diglycidyl ether aqueous solution with the mass concentration of 1% (the dosage of the ethylene glycol diglycidyl ether is 0.08 percent of the total mass of the first-stage acrylic acid and the second-stage acrylic acid) is added into the suspension, and the reaction is carried out for 1 hour at the temperature for surface crosslinking.
5. Solvent removal and drying
The system was warmed to 120 ℃ and distilled for 0.5h to remove the remaining water and n-heptane, at which time it was observed that grape-string-like particles of super absorbent resin (SAP) settled at the bottom of the flask, as shown in fig. 1. Finally, it was dried at 130 ℃ for 1 hour and sieved to obtain a water-absorbent resin product having a desired particle diameter (150-.
Example 2:
the procedure of example 1 was repeated except for replacing 0.55g of alkylphenol polyoxyethylene ether (OP-10, HLB ═ 13.5) used in the two-stage polymerization with 0.45g of sorbitan laurate (Span20, HLB ═ 8.6) (0.4 wt%, based on the total mass of the one-stage and two-stage acrylic acids). The morphology of the finally obtained water-absorbent resin was similar to that of example 1, and the final water content was 3%.
Example 3:
the operation of example 1 was repeated except that 0.92g of sucrose fatty acid ester (S-370) (0.38 wt%, based on the mass of n-heptane) of the dispersant before polymerization was replaced with 0.46g of sorbitan monostearate (Span60, HLB ═ 4.7) (0.19 wt%, based on the mass of n-heptane) and 0.46g of maleic anhydride-modified ethylene-propylene copolymer (1105A) (0.19 wt%, based on the mass of n-heptane), and heated to 80 ℃ and uniformly dissolved and dispersed at a stirring speed of 300rpm, followed by cooling to 40 ℃. The morphology of the finally obtained water-absorbent resin was similar to that of example 1, and the final water content was 4%.
Example 4:
the procedure of example 1 was repeated except that the comonomer hydroxyethyl methacrylate in the first-stage polymerization and the second-stage polymerization was replaced with vinyl acetate, and the amount added in each stage was changed to 0.552g (1.0% by weight based on the mass of acrylic acid in each stage). The morphology of the finally obtained water-absorbent resin was similar to that of example 1, and the final water content was 2%.
Example 5:
the operation of example 1 was repeated except that 143.8g of an aqueous sodium hydroxide solution having a mass concentration of 32% in the acid-base neutralization step was replaced with 197.8g of an aqueous sodium carbonate solution having a mass concentration of 50.5%. The morphology of the finally obtained water-absorbent resin was similar to that of example 1, and the final water content was 5%.
Example 6:
1. one-stage polymerization
240g of n-heptane (155.0% by weight based on the mass of the one-stage aqueous acrylic acid solution) was charged into a 1L four-necked round-bottomed flask equipped with a stirrer, a reflux condenser, a thermometer and a nitrogen inlet pipe. 0.92g of sucrose fatty acid ester (S-370) (0.38 wt% based on the mass of n-heptane) was added thereto, heated to 60 ℃ and uniformly dissolved and dispersed at a stirring speed of 250rpm, and then cooled to 40 ℃. 99.7g of an aqueous solution in which 0.055g of sodium persulfate (0.10% by weight based on the mass of the one-stage acrylic acid), 0.028g of 2,2' -azobisisopropylimidazoline hydrochloride (V-50) (0.05% by weight based on the mass of the one-stage acrylic acid), 0.278g of hydroxyethyl methacrylate (0.5% by weight based on the mass of the one-stage acrylic acid), 22.1mg of ethylene glycol diglycidyl ether (0.04% by weight based on the mass of the one-stage acrylic acid) were dissolved was added to 55.2g of acrylic acid (i.e., one-stage acrylic acid) to obtain an aqueous one-stage acrylic acid solution (the mass concentration of the one-stage acrylic acid was 35.6%). The one-stage acrylic acid aqueous solution was added to the above four-necked round-bottomed flask, and nitrogen gas was introduced while stirring to sufficiently remove oxygen. Then heating to 80 ℃ for reaction for 0.5h to carry out primary water-in-oil (W/O) reversed-phase suspension polymerization to obtain a suspension containing primary polyacrylic acid colloidal particles.
2. Two stage polymerization
0.092g of H with the mass concentration of 30 percent is dissolved2O2(H2O20.05 wt% based on the mass of the secondary acrylic acid), 0.278g of hydroxyethyl methacrylate (0.5 wt% based on the mass of the secondary acrylic acid), 22.1mg of ethylene glycol diglycidyl ether (0.04 wt% based on the mass of the secondary acrylic acid), and 68.8g of an aqueous solution of 0.55g of alkylphenol polyoxyethylene ether (OP-10) (HLB of 13.5) (0.5 wt% based on the total mass of the primary and secondary acrylic acids) were added to 55.2g of acrylic acid (i.e., the secondary acrylic acid), and then 0.011g of ascorbic acid (0.02 wt% based on the mass of the secondary acrylic acid) was added to obtain an aqueous solution of the secondary acrylic acid (mass concentration of the secondary acrylic acid is 44.4%). After that, the suspension containing the primary polyacrylic acid colloidal particles obtained in the step 1 is cooled to 30 ℃, a secondary acrylic acid aqueous solution is added, after nitrogen is sufficiently replaced, the mixture is stirred for 30min at the rotating speed of 350rpm, so that acrylic acid droplets of the secondary acrylic acid aqueous solution and the primary polyacrylic acid colloidal particles are adsorbed and aggregated with each other. Then, carrying out two-stage water-in-oil reversed-phase suspension polymerization while particle agglomeration is generated, and obtaining a suspension containing two-stage polyacrylic acid colloidal particles.
3. Acid-base neutralization
After the second-stage polymerization was completed, 186.7g of an aqueous sodium hydroxide solution having a mass concentration of 23% was dropped into the suspension containing the second-stage polyacrylic acid colloidal particles obtained in step 2 at a dropping rate of 2 to 3 drops/sec. At the moment, the added alkali liquor and the obtained two-stage polyacrylic acid colloidal particles are subjected to acid-base neutralization reaction, the temperature of the acid-base neutralization reaction is 30 ℃, the time is 10min, the neutralization degree is 70%, and the stirring is continued for 15min after the temperature of the system is constant.
4. Azeotropic dehydration and surface crosslinking
The suspension from step 3 was heated to 100 ℃ for azeotropic dehydration and n-heptane was refluxed for a total removal of 220g of water (70% water based on a total of 313g of water in the four-necked round-bottomed flask). The system temperature is adjusted to 80 ℃, 9.2g of ethylene glycol diglycidyl ether aqueous solution with the mass concentration of 1% (the dosage of the ethylene glycol diglycidyl ether is 0.08 percent of the total mass of the first-stage acrylic acid and the second-stage acrylic acid) is added into the suspension, and the reaction is carried out for 1 hour at the temperature for surface crosslinking.
5. Solvent removal and drying
The system was warmed to 120 ℃ and distilled for 0.5h to remove the remaining water and n-heptane, at which time it was observed that grape-string-like particles of super absorbent resin (SAP) settled at the bottom of the flask. Finally, it was dried at 100 ℃ for 1.5 hours and sieved to obtain a water-absorbent resin product having a desired particle diameter (150- & ltSUB & gt 710/& ltSUB & gt, 85% & lt/SUB & gt) and a final water content of 3%.
Comparative test:
the water-absorbent resins prepared in examples 1 to 6 of the present invention were compared with competitors A, B and C for their basic properties, and the results are shown in Table 2.
TABLE 2 comparison of basic Properties of Water-absorbent resins
As can be seen from Table 2, the water-absorbent resin obtained by the present invention (reversed-phase suspension polymerization process of polymerization first and neutralization second) exhibited improvements in the 1-min pure water absorption and extractables, although the flow rate was lowered as compared with the case of preparation A; compared with the competitive product B, the water-absorbent resin of the invention has greatly improved pure water absorption and extractables in 1 min; in contrast, the water-absorbent resin showed a significantly improved flow rate in spite of a decrease in pure water absorption and an increase in extractables at 1min as compared with sample C.
Since the properties of the water-absorbent resin are mutually restricted, the water-absorbent resin prepared by the invention obtains SAP particles with good liquid passing rate and 1min pure water absorption capacity under the condition that the reduction degree of other properties is acceptable (the liquid absorption rate and the centrifugal water retention property need to be improved), but provides a new idea for the development of the water-absorbent resin applied to the ultrathin composite core market at present. The unique reversed phase suspension polymerization process of the invention enriches the manufacturing method of SAP and provides a possibility for preparing SAP with differentiated performance.
Claims (16)
1. A method for preparing water-absorbent resin by adopting a reversed-phase suspension polymerization process of polymerization before neutralization comprises the following steps:
a. one-stage polymerization: adding a first-stage (methyl) acrylic acid aqueous solution containing a first-stage initiator, a cross-linking agent and a comonomer into a petroleum hydrocarbon solvent dissolved with a dispersant, and carrying out first-stage water-in-oil reversed-phase suspension polymerization to obtain a suspension containing a first-stage poly (methyl) acrylic acid colloidal particle;
b. second-stage polymerization: b, adding a second-stage (meth) acrylic acid aqueous solution containing a surfactant, a second-stage initiator, a cross-linking agent and a comonomer into the suspension containing the first-stage poly (meth) acrylic acid colloidal particles obtained in the step a, and carrying out second-stage water-in-oil reversed-phase suspension polymerization to obtain a suspension containing second-stage poly (meth) acrylic acid colloidal particles;
the hydrophilic-lipophilic balance value HLB of the surfactant is more than 7;
c. acid-base neutralization: adding an alkaline solution into the suspension containing the second-stage poly (meth) acrylic acid colloidal particles obtained in the step b, and carrying out acid-base neutralization reaction on the alkaline solution and the second-stage poly (meth) acrylic acid colloidal particles;
d. azeotropic dehydration and surface crosslinking: c, heating the suspension obtained in the step c to the azeotropic point of water and the petroleum hydrocarbon solvent, removing 70-90% of water in the suspension, and adding a surface cross-linking agent for surface cross-linking;
e. solvent removal and drying: removing residual water and petroleum hydrocarbon solvent in the system, and finally drying to obtain the water-absorbent resin;
the (meth) acrylic acid is acrylic acid or methacrylic acid;
the first-stage initiator in the step a is a thermal initiator;
and the second-stage initiator in the step b is a redox initiator.
2. The method of claim 1, wherein: the petroleum hydrocarbon solvent in the step a is one or more selected from cyclopentane, cyclohexane, n-heptane, n-hexane and n-octane;
the dispersing agent in the step a is selected from one or more of sucrose fatty acid ester, sorbitan monostearate, sorbitan monooleate, triglycerol monostearate, octadecyl monophosphate and maleic anhydride modified ethylene-propylene copolymer;
the primary initiator in the step a is one or more selected from sodium persulfate, potassium persulfate, ammonium persulfate, 2 '-azodiisopropyl imidazoline hydrochloride, 2' -azo (2-methyl-N- (2-hydroxyethyl) propionamide) and 2, 2-aza-bis (2-imidazoline) dihydrochloride;
the cross-linking agent in the step a is selected from one or more of ethylene glycol diglycidyl ether, N' -methylene bisacrylamide, polyethylene glycol diacrylate and pentaerythritol triallyl ether;
in the step a, the comonomer is selected from one or more of acrylamide, methacrylamide, glycidyl acrylate, glycidyl methacrylate, hydroxyethyl acrylate, hydroxyethyl methacrylate and vinyl acetate.
3. The method of claim 1, wherein: the using amount of the petroleum hydrocarbon solvent in the step a is 500% of the mass of the one-section (methyl) acrylic acid aqueous solution;
the dosage of the dispersant in the step a is 0.1 to 10 percent of the mass of the petroleum hydrocarbon solvent;
the dosage of the first-stage initiator in the step a is 0.005-5% of the mass of the first-stage (methyl) acrylic acid;
the dosage of the cross-linking agent in the step a is 0.001-1% of the mass of the first section of (methyl) acrylic acid;
the using amount of the comonomer in the step a is 0.005-5% of the mass of the first-stage (methyl) acrylic acid;
the mass concentration of the first section of (meth) acrylic acid in the first section of (meth) acrylic acid aqueous solution in the step a is 10-60%;
the first section of (meth) acrylic acid is (meth) acrylic acid in the first section of aqueous (meth) acrylic acid solution;
the water-in-oil reversed-phase suspension polymerization in the step a is initiated by high-temperature heat, the polymerization temperature is 40-80 ℃, and the time is 0.5-3 h.
4. The method of claim 3, wherein: the using amount of the petroleum hydrocarbon solvent in the step a is 300 percent of the mass of the one-section (methyl) acrylic acid aqueous solution;
the using amount of the dispersing agent in the step a is 0.2-1% of the mass of the petroleum hydrocarbon solvent;
the dosage of the first-stage initiator in the step a is 0.02-2% of the mass of the first-stage (methyl) acrylic acid;
in the step a, the dosage of the cross-linking agent is 0.01-0.5 percent of the mass of the first section of (methyl) acrylic acid;
the using amount of the comonomer in the step a is 0.02-2% of the mass of the first section of (methyl) acrylic acid;
the mass concentration of the first section of (meth) acrylic acid in the first section of (meth) acrylic acid aqueous solution in the step a is 20-40%;
the water-in-oil reversed-phase suspension polymerization in the step a is initiated by high-temperature heat, the polymerization temperature is 60-80 ℃, and the time is 0.8-2.5 h.
5. The method according to any one of claims 1-4, wherein: the surfactant in the step b is selected from one or more of alkylphenol polyoxyethylene, sorbitan laurate, polyoxyethylene sorbitan monooleate, sucrose fatty acid ester, polyvinyl alcohol and polyoxyethylene dodecyl ether phosphate;
the secondary initiator in the step b is one or more selected from sodium persulfate/sodium sulfite, sodium persulfate/sodium bisulfite, tert-butyl hydroperoxide/ferrous sulfate and hydrogen peroxide/L-ascorbic acid;
the cross-linking agent in the step b is selected from one or more of ethylene glycol diglycidyl ether, N' -methylene bisacrylamide, polyethylene glycol diacrylate and pentaerythritol triallyl ether;
in the step b, the comonomer is selected from one or more of acrylamide, methacrylamide, glycidyl acrylate, glycidyl methacrylate, hydroxyethyl acrylate, hydroxyethyl methacrylate and vinyl acetate.
6. The method according to any one of claims 1-4, wherein: the dosage of the surfactant in the step b is 0.01-10% of the total mass of the (methyl) acrylic acid in the first-stage (methyl) acrylic acid and the second-stage (methyl) acrylic acid;
the using amount of the second-stage initiator in the step b is 0.005-5% of the mass of the second-stage (methyl) acrylic acid;
the dosage of the cross-linking agent in the step b is 0.001-1% of the mass of the second-stage (methyl) acrylic acid;
the using amount of the comonomer in the step b is 0.005-5% of the mass of the second-stage (methyl) acrylic acid;
the mass concentration of the second-stage (methyl) acrylic acid in the second-stage (methyl) acrylic acid aqueous solution in the step b is 10-60%;
the first section of (meth) acrylic acid is (meth) acrylic acid in the first section of aqueous (meth) acrylic acid solution; the second-stage (meth) acrylic acid is (meth) acrylic acid in the second-stage (meth) acrylic acid aqueous solution;
in the step b, the two-stage water-in-oil reversed-phase suspension polymerization is redox initiation, the polymerization temperature is 20-60 ℃, and the time is 0.5-3 h.
7. The method of claim 6, wherein: the dosage of the surfactant in the step b is 0.1-1.5% of the total mass of the (methyl) acrylic acid in the first-stage (methyl) acrylic acid and the second-stage (methyl) acrylic acid;
the using amount of the second-stage initiator in the step b is 0.02-2% of the mass of the second-stage (methyl) acrylic acid;
in the step b, the dosage of the cross-linking agent is 0.01-0.5 percent of the mass of the second-stage (methyl) acrylic acid;
the using amount of the comonomer in the step b is 0.02-2% of the mass of the second-stage (methyl) acrylic acid;
the mass concentration of the second-stage (methyl) acrylic acid in the second-stage (methyl) acrylic acid aqueous solution in the step b is 20-45%;
in the step b, the two-stage water-in-oil reversed-phase suspension polymerization is redox initiation, the polymerization temperature is 30-50 ℃, and the time is 0.5-2 h.
8. The method according to any one of claims 1-4, wherein: the alkaline solution in step c is one or more selected from the group consisting of sodium hydroxide, potassium hydroxide, sodium bicarbonate, sodium carbonate, potassium carbonate and ammonium carbonate aqueous solution.
9. The method according to any one of claims 1-4, wherein: the mass concentration of the alkaline solution in the step c is 20-55%;
in the step c, the neutralization degree of the acid-base neutralization reaction is 60-90%;
and c, performing acid-base neutralization reaction at the temperature of 30-60 ℃ for 10-90 min.
10. The method of claim 9, wherein: in the step c, the neutralization degree of the acid-base neutralization reaction is 70-80%;
and c, performing acid-base neutralization reaction at 40-50 ℃ for 10-30 min.
11. The method according to any one of claims 1-4, wherein: the surface cross-linking agent in step d is a compound having at least two functional groups capable of reacting with carboxyl groups.
12. The method of claim 11, wherein: the surface cross-linking agent in step d is one or more of a polyglycidyl compound, a polyhydric alcohol and an alkylene carbonate.
13. The method of claim 12, wherein: in the step d, the surface cross-linking agent is one or more of ethylene glycol diglycidyl ether, glycerol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerol, propylene glycol, ethylene glycol, 1, 4-butanediol, ethylene carbonate and propylene carbonate.
14. The method according to any one of claims 1-4, wherein: the dosage of the surface cross-linking agent in the step d is 0.001-15% of the total mass of the first-stage (methyl) acrylic acid and the second-stage (methyl) acrylic acid;
the first section of (meth) acrylic acid is (meth) acrylic acid in the first section of aqueous (meth) acrylic acid solution; the second-stage (meth) acrylic acid is (meth) acrylic acid in the second-stage (meth) acrylic acid aqueous solution;
the temperature of the surface cross-linking in the step d is 60-100 ℃, and the time is 0.5-3 h;
the final water content of the water-absorbent resin is 1 to 10%.
15. The method of claim 14, wherein: the dosage of the surface cross-linking agent in the step d is 0.01-10% of the total mass of the first-stage (methyl) acrylic acid and the second-stage (methyl) acrylic acid;
the temperature of the surface cross-linking in the step d is 70-90 ℃, and the time is 1-2 h;
the final water content of the water-absorbent resin is 2 to 5%.
16. A water-absorbent resin produced by the method according to any one of claims 1 to 15.
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