WO2018117441A1 - Superabsorbent polymer and method for manufacturing same - Google Patents

Abstract

The present invention relates to a superabsorbent polymer and a method for manufacturing the same. According to the present invention, a superabsorbent polymer having a high water retention capacity and absorption rate can be manufactured by using a specific foam stabilizer.

Description

 [Name of invention]

 Super Absorbent Resin

Technical Field

 Cross citation with related application (s)

 This application claims the benefit of priority based on Korean Patent Application No. 10-2016-0174930 of December 20, 2016 and Korean Patent Application No. 10-2017-0155824 of January 21, 2017, and the Korean Patent Application All content disclosed in these references is included as part of this specification.

 The present invention relates to a super absorbent polymer and a method for preparing the same.

[Technique to become background of invention]

 A super absorbent polymer (SAP) is a synthetic polymer material that can absorb about 500 to 1,000 times its own weight. It is also called SAM (Snper Absorbency Material) or AGM (Absorbent Gel Material). have. Super absorbent resins have been put into practical use as sanitary devices and are now widely used in various materials such as hygiene products such as paper diapers for children, horticultural soil repair agents, civil engineering index materials, seedling sheets, and freshness retainers in food distribution. It is used. As a method for producing such a super absorbent polymer, a method by reverse phase suspension polymerization or a solution polymerization is known. Among them, Japanese Patent Application Laid-Open No. 56-161408, Japanese Patent Application Laid-Open No. 57-158209, for the production of a super absorbent polymer through reverse phase suspension polymerization. And Japanese Patent Application Laid-Open No. 57-198714. In addition, the production of superabsorbent polymers through polymerization of aqueous solution is a thermal polymerization method for polymerizing while breaking and cooling the hydrogel polymer in a kneader equipped with several shafts, and polymerizing and drying by irradiating UV light to a high concentration of aqueous solution on a belt. The photopolymerization method etc. which perform simultaneously are known.

On the other hand, the absorption rate, which is one of the important properties of the superabsorbent polymer, is associated with the surface dryness of the product which comes into contact with the skin such as a diaper. In general, this absorption rate can be improved by increasing the surface area of the superabsorbent polymer. For example, using a blowing agent porous on the surface of the particles of the superabsorbent polymer The method of forming a structure is applied. However, a general blowing agent is not able to form a sufficient amount of porous structure has a disadvantage that the increase in the rate of absorption is not large.

As another example, there is a method of increasing the surface area by reassembling the fine powder obtained in the manufacturing process of the super absorbent polymer to form porous particles of irregular shape. However, although the hop speed of the superabsorbent polymer can be improved through this method, there is a _limit that the water retention capacity (CRC) and the pressure absorption capacity (AUP) of the resin are relatively lowered. As such, physical properties such as absorption rate, water retention capacity, and pressure absorption capacity of the superabsorbent polymer are trade-off. Therefore, there is an urgent need for a manufacturing method capable of improving these properties simultaneously.

 Korean Laid-Open Patent No. 2016-0063956 regulates the size and distribution of internal pores in the preparation of superabsorbent polymers. A method of increasing the rate of absorption under pressure without deterioration has been proposed. However, the method requires control of the photopolymerization temperature in order to control the size and distribution of the pores, which makes the process complicated and does not exhibit sufficient absorption and absorption rates to meet market demand.

[Content of invention]

 Problem to be solved

 Accordingly, the present invention is to provide a super absorbent polymer having a fast absorption rate and absorbent capacity, and having a high bulk density.

 . In addition, the present invention is to provide a method for producing the super absorbent polymer.

[Measures of problem]

According to an aspect of the present invention for solving the above problems, a nonionic bubble stabilizer, a sugar ester having an acidic group and an acrylic acid monomer, polyalkylene oxide (polyalkylene oxide) at least a portion of the acidic group is augmented (sugar esters), internal crosslinkers, and polymerization initiators Polymerizing the monomer composition to form a hydrogel polymer;

 Drying the hydrogel polymer;

 Pulverizing the dried polymer; And

 It provides a method for producing a super absorbent polymer comprising the step of performing a surface crosslinking reaction by mixing the pulverized polymer and the surface crosslinking agent.

 According to another aspect of the present invention,

 A base resin having an acidic group and polymerized and internally crosslinked with a monomer composition comprising an acrylic acid monomer in which at least a portion of the acidic group is neutralized; And a superabsorbent polymer comprising a surface crosslinking layer formed on the surface of the base resin,

 The base resin has a centrifugal water retention (CRC) of 35 g / g or more, an absorption rate of 40 seconds or less, and a bulk density of 0.51, measured according to the EDANA method WSP 241.3. To 0.70 g / mL, which provides a superabsorbent polymer.

【Effects of the Invention】

 The superabsorbent polymer according to the present invention stabilizes bubble generation during the polymerization process by using a combination of a specific nonionic polyalkylene oxide and a sugar ester in a predetermined weight ratio as a bubble stabilizer during polymerization, thereby providing high water retention and volume. Density, and fast absorption rate.

- Carrying out the Invention DETAILED ^';

The terminology used herein is for the purpose of describing exemplary embodiments only and is not intended to be limiting of the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. As used herein, the terms "comprise,""including," or "having" are intended to indicate that there is a feature, step, component, or combination thereof, and one or more other features, steps, or components. It is to be understood that the present invention does not exclude, in advance, the possibility of the presence or the addition of these or any combination thereof. As the invention allows for various changes and numerous modifications, particular embodiments will be illustrated and described in detail below. However, this is not intended to limit the present invention to a specific disclosed form, it should be understood to include all modifications, equivalents, and substitutes included in the spirit and scope of the present invention.

 Hereinafter, a super absorbent polymer and a method for preparing the same according to specific embodiments of the present invention will be described in detail. Superabsorbent polymers are evaluated for their water retention capacity (CRC), pressurized absorption capacity (AUL), and absorption rate as important physical properties. For this purpose, a large amount of pores are formed in the superabsorbent polymer so that water can be quickly sucked or superabsorbent. The method of making particle size of resin small is known. However, there is a limit in reducing the particle size of the superabsorbent polymer, and there is a disadvantage in that thinning of the article is difficult because the gel strength becomes weak when the internal pores are formed. Therefore, a method of increasing the absorption rate by controlling the size and distribution of internal pores in the manufacturing process of the super absorbent polymer by using a low temperature foaming agent and a high temperature foaming agent has been proposed, but it is necessary to control the polymerization temperature to control the size and distribution of the pores. The process is complicated, and it is difficult to prepare a base resin having a water retention capacity (CRC) of 35 g / g or more and a vortex time of 40 seconds or less. The need still exists.

The present inventors have completed the present invention by observing that by using a combination of specific bubble stabilizers in polymerization, a superabsorbent polymer having a more stable and even bubble distribution and consequently having a high water holding capacity and a fast absorption rate can be produced. It was. Hereinafter, the superabsorbent polymer of the present invention and a manufacturing method thereof will be described in detail. For reference, in the specification of the present invention, "polymer", or "polymer" means that the water-soluble ethylenically unsaturated monomer is in a polymerized state, and may cover all water content ranges or particle size ranges. Before drying As a state, a polymer having a moisture content (water content) of about 40% by weight or more may be referred to as a hydrous gel polymer.

 In addition, "base resin" or "base resin powder" is a powder (powder) by drying and grinding the polymer, it means a polymer before performing the surface cross-linking step to be described later.

 In the method for preparing a super absorbent polymer according to an embodiment of the present invention, a nonionic bubble stabilizer including an acrylic acid monomer having a acidic group and at least a portion of the acidic group is neutralized, and a polyalkylene oxide. A monomer composition comprising a crosslinking agent, a sugar ester, and a polymerization initiator is polymerized to form a hydrogel polymer.

The acrylic acid monomer may have an acid group and at least a portion of the acid group may be neutralized. Preferably, those which have been partially neutralized with alkyl materials such as sodium hydroxide, potassium hydroxide, ammonium hydroxide and the like can be used. In this case, the neutralization degree of the acrylic acid-based monomer may be 40 to 95 mole _^0/0, or 40 to 80 mole _^0/0, or 45 to 75 mole ⁰ /. The range of neutralization can be adjusted according to the final physical properties. However, when the degree of neutralization is too high, polymerization of the monomer may be difficult to proceed due to precipitation of the neutralized monomer. On the contrary, when the degree of neutralization is too low, the absorbency of the polymer may not only be greatly reduced, but may exhibit properties such as elastic rubber that is difficult to handle. have. Preferably, the acrylic acid monomer is a compound represented by the following formula (1):

 [Formula 1]

'-COOM ¹

 In Chemical Formula 1,

R ¹ is an alkyl group having 2 to 5 carbon atoms containing an unsaturated bond,

M ¹ is a hydrogen atom, a monovalent or divalent metal, an ammonium group or an organic amine salt. Preferably, the acrylic acid monomer includes at least one member selected from the group consisting of acrylic acid, methacrylic acid and monovalent metal salts, divalent metal salts, ammonium salts and organic amine salts thereof.

In addition, the concentration of the acrylic acid monomer in the monomer composition is polymerization time And it may be appropriately adjusted in consideration of reaction conditions and the like, preferably 20 to 90% by weight, or 40 to 70% by weight ⁰ /. This concentration range may be advantageous in controlling the grinding efficiency during the grinding of the polymer, which is a subsequent process, while eliminating the need for removing the unbanung monomer after polymerization by using the gel phenomenon appearing in the polymerization reaction of the high concentration aqueous solution. However, when the concentration of the monomer is too low, the yield of the super absorbent polymer may be lowered. On the contrary, when the concentration of the monomer is too high, some of the monomer may be precipitated or a process problem may occur such as when the pulverization efficiency of the polymerized hydrogel polymer is pulverized, and the physical properties of the super absorbent polymer may be reduced.

 On the other hand, the monomer composition includes an internal crosslinking agent for improving the physical properties of the hydrogel polymer. The crosslinking agent is a crosslinking agent for crosslinking the inside of the hydrogel polymer, and is used separately from the surface crosslinking agent for crosslinking the surface of the hydrogel polymer in a subsequent process.

Preferably, the internal crosslinking agent is _N , _N methylenebisacrylamide, trimethyl to propane tri (meth) acrylate, ethylene glycol di (meth) acrylate, polyethylene glycol (meth) acrylate, polyethylene glycol di (meth) acryl , Propylene glycol di (meth) acrylate, polypropylene glycol (meth) acrylate, butanediol di (meth) acrylate,. Butylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, nucleic acid diol di (meth) acrylate, triethylene glycol di (meth) acrylate, tripropylene glycol di (meth) acrylate, tetra Ethylene glycol di (meth) acrylate, dipentaerythritol pentaacrylate, glycerin tri (meth) acrylate, pentaeryth tetraacrylate, triarylamine, ethylene glycol diglycidyl ether, propylene glycol, glycerin, And it may be one or more selected from the group consisting of ethylene carbonate.

 More preferably, when the polyethylene glycol diacrylate (PEGDA) is used as the internal crosslinking agent, it may exhibit improved water holding capacity and absorption rate.

The internal crosslinking agent is about 100 parts by weight of the acrylic acid monomer. It may be added at a concentration of 0.001 to 1 parts by weight. When the concentration of the internal crosslinking agent is too low, the absorption rate of the resin may be lowered and the gel strength may be weakened, which is not preferable. On the contrary, when the concentration of the internal crosslinking agent is too high, the absorptivity of the resin may be low, which may be undesirable as an absorber. The acrylic acid monomer having the acidic group and neutralized at least a part of the acidic group is as defined above, and polymerized to prepare a hydrogel polymer.

 In particular, the present invention is characterized in that the monomer composition includes, in addition to the polymerization initiator and the internal crosslinking agent, a nonionic bubble stabilizer containing a polyalkylene oxide and a sugar ester.

 The nonionic bubble stabilizer comprising the polyalkylene oxide serves to form more stable bubbles in the polymerization process with the sugar ester, thereby allowing the hydrogel polymer to be polymerized to have a high water holding capacity and a fast absorption rate. .

 The polyalkylene oxide is not limited thereto, but may be polyethylene oxide (PEO), polypropylene oxide (PPO), polyethylene oxide-polypropylene oxide (PEO-PPO) diblock copolymer, And polyethylene oxide-polypropylene oxide-polyethylene oxide (PEO-PPO-PEO) triblock copolymer, and may be at least one selected from the group consisting of (PEO-PPO-PEO) triblock. ) Copolymers can be used.

According to one embodiment of the present invention, the polyalkylene oxide has a weight average molecular weight of about 500 to about 5,000 g / mol, or about 1,000 to about 4,000 g / md, and the weight of ethylene oxide (EO) in the polyalkylene oxide. It may be more desirable to use PEO-PPO-PEO triblock copolymers having a ratio of 20 to 80 weight ⁰ /., Or 20 to 60 weight ⁰ / o.

The nonionic bubble stabilizer may be added at a concentration of about 0.001 to about 1 part by weight, or about 0.01 to about 0.5 part by weight based on 100 parts by weight of the acrylic acid monomer. When the concentration of the nonionic bubble stabilizer is too low, the role of the bubble stabilizer is insignificant to achieve an absorption rate improvement effect. On the contrary, if the concentration of the nonionic bubble stabilizer is too high, the water holding capacity and the absorption rate may decrease, which may be undesirable.

 The sugar ester used with the nonionic bubble stabilizer comprising the polyalkylene oxide includes sucrose stearate, sucrose palmitate or sucrose laurate. For example, but the present invention is not limited thereto. Preferably sucrose stearate can be used.

 The sugar ester may be added at a concentration of about 0.001 to about 0.08 parts by weight, or about 0.005 to about 0.05 parts by weight, or about 0.01 to about 0.05 parts by weight based on 100 parts by weight of the acrylic acid monomer. When the concentration of the sugar ester is too low, the role as a bubble stabilizer is difficult to achieve the absorption rate improvement effect, on the contrary, when the concentration of the sugar ester is too high, the water holding capacity may decrease rather. In addition, since the color or odor quality of the polymer may be degraded, the weight range is preferable in this respect. In addition, the sugar ester is preferably contained in a ratio of 1 to 30 parts by weight, or 1 to 20 parts by weight, or 1 to 10 parts by weight with respect to 100 parts by weight of the non-unique bubble stabilizer including the polyalkylene oxide. . If the sugar ester is used in an amount less than 1 part by weight relative to the polyalkylene oxide OO increase part, the absorption rate improvement effect may be insignificant, whereas when used in excess of 30 parts by weight, a large amount of foaming occurs in the composition. In addition, the resin may yellow or discolor in the drying process of the polymer. The weight part range is preferable in this respect.

 According to an embodiment of the present invention, the monomer composition is sodium bicarbonate, sodium carbonate, potassium bicarbonate, potassium carbonate, calcium carbonate, calcium bicarbonate, It may further comprise at least one blowing agent selected from the group consisting of calcium carbonate, calcium ratio ^! "Magnesium bicarbonate and magnesium carbonate.

The polymerization initiator is generally used for the production of superabsorbent polymers. A polymerization initiator can be used. As the polymerization initiator, a thermal polymerization initiator or a photopolymerization initiator may be used depending on the polymerization method. However, even with the photopolymerization method, since a certain amount of heat is generated by ultraviolet irradiation or the like, and a certain amount of heat is generated in accordance with the progress of the polymerization reaction, which is an exothermic reaction, a thermal polymerization initiator is additionally used. Can be.

 Examples of the photopolymerization initiator include benzoin ether, dialkyl acetophenone, hydroxyl alkylketone, phenylglyoxylate, and benzyldimethyl ketal (for example, benzoin ether). One or more compounds selected from the group consisting of benzyl dimethyl ketal, acyl phosphine, and alpha-aminoketone can be used. As specific examples of acylphosphine, commercially available ludrin TPO, that is, 2,4,6-trimethyl-benzoyl-trimethyl phosphane oxide can be used. . More various photopolymerization initiators are disclosed on page 1 15 of Reinhold Schwalm, "UV Coatings: Basics, Recent Developments and New Application (Elsevier 2007)".

In addition, as the thermal polymerization initiator, one or more compounds selected from the group consisting of persulfate initiator, azo initiator, hydrogen peroxide, and ascorbic acid may be used. Specifically, as persulfate initiator, sodium persulfate; Na ₂ S ₂ 0 ₈ ), potassium persulfate (K ₂ S ₂ 0 ₈ ), ammonium persulfate (NH ₄ ) ₂ S ₂ 0 ₈ , and the like. In addition, as an azo (Azo) initiator

2,2-azobis (2-amidinopropane) dihydrochloride, 2,2-azobis- (Ν, Ν-dimethylene) isobutyramidine di Hydrochloride (2,2-azobis- (N, N-dimethylene) isobutyramidine

dihydrochloride),

 2- (carbamoyl azo) isobutyronitrile (2- (carbamoylazo) isobutylonitril),

2,2-azobis [2- (2-imidazolin-2-yl) propane]

Dihydrochlorai H (2,2-azobis [2- (2-imidazolin-2-yl) propane] dihydrochloride), 4,4-azobis- (4-cyanovaleric acid) (4,4-azobis -(4-cyanovaleric acid)) Can be. A wider variety of thermal polymerization initiators are disclosed on page 203 of the Odian book "Principle of Polymerization (Wiley, 1981)" and can be referred to this.

 The polymerization initiator may be added at a concentration of about 0.001 to 1 parts by weight based on 100 parts by weight of the acrylic acid monomer. In other words, when the concentration of the polymerization initiator is too low, the polymerization rate may be slow and a large amount of the remaining monomers may be extracted in the final product. On the contrary, when the concentration of the polymerization initiator is too high, it is not preferable because the polymer chain constituting the network is shortened, so that the content of the water-soluble component is increased and the pressure absorption capacity is lowered.

 In addition, the monomer composition may further include additives such as thickeners, plasticizers, storage stabilizers, antioxidants, and the like, as necessary.

In addition, the monomer composition may be prepared in the form of a solution in which raw materials such as the acrylic acid monomer, a polymerization initiator, an internal crosslinking agent, a sugar ester, and a nonionic bubble stabilizer are dissolved in a solvent. In this case, the solvent may be used as long as it can dissolve the above-described raw materials. For example, the solvent may be water, ethanol, ethylene glycol, diethylene glycol, triethylene glycol, 1,4-butanedi, propylene glycol, ethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monomethyl Ether acetate, methyl ethyl ketone, acetone, methyl amyl ketone, cyclonucleanone, cyclopentanone, diethylene glycol monomethyl ether, diethylene glycol ethyl ether, toluene, xylene, butyrolactone, carbitle, methylcello Solvate, Ν, Ν-dimethylacetamide, or a combination thereof. The amount of the solvent may be adjusted to be 1 to 5 times the weight ratio of the acrylic acid monomer containing in consideration of polymerization heat control and the like. On the other hand, the formation of the hydrogel polymer through the polymerization and crosslinking of the monomer composition may be carried out by a conventional polymerization method in the art, the process is not particularly limited. As a non-limiting example, the polymerization method is largely divided into thermal polymerization and photopolymerization according to the type of polymerization energy source, and in the case of the thermal polymerization, the polymerization method has a stirring shaft such as a kneader. It may be carried out in the reactor, in the case of proceeding the light integration may be performed in a semi-unggi equipped with a movable conveyor belt.

In one example, the hydrogel polymer may be obtained by adding the monomer composition to a reaction vessel such as a kneader equipped with a stirring shaft, and supplying hot air thereto or heating and heating the reaction vessel. In this case, the hydrogel polymer discharged to the reactor outlet according to the shape of the stirring shaft provided in the reactor may be obtained in the form of particles of several millimeters to several centimeters. The hydrous gel phase polymer may be obtained in various forms according to the concentration and the injection speed of the monomer composition to be injected _. A hydrogel polymer of 2 mm to 50 mm can be obtained.

 In another example, when the photopolymerization of the monomer composition is carried out in a reaction vessel equipped with a movable conveyor belt, a sheet-like hydrogel polymer may be obtained. At this time, the thickness of the sheet may vary depending on the concentration and the injection speed of the monomer composition to be injected, in order to ensure the production rate, while the entire sheet can be polymerized evenly, it is usually adjusted to a thickness of 5 cm to 5 cm It is desirable to be.

The hydrogel polymer formed by the above method may exhibit a water content of about 40 to 80% by weight. The water content of the hydrogel polymer is in the above range _. Lifting is advantageous in that it optimizes the efficiency in the drying step described below. Here, the moisture content is a weight of water in the total weight of the hydrogel polymer, and may be calculated by subtracting the dry polymer weight from the weight of the hydrogel polymer. Specifically, it may be defined as a value calculated by measuring the weight loss due to evaporation of water in the polymer in the process of raising the temperature of the polymer through infrared heating. At this time, the drying condition is a total drying time may be set to 40 minutes, including 5 minutes of the temperature rise step in such a way that the temperature is raised to about 180 ^° C at room temperature and maintained at 180 ^° C. The hydrogel polymer obtained through the above steps is subjected to a drying process to impart water absorbency. However, in order to increase the efficiency of such drying, the step of pulverizing (coarsely pulverizing) the hydrogel polymer before performing the drying process may be performed. As a non-limiting example, the grinders available for the coarse grinding include a vertical pulverizer, a turbo cutter, a turbo grinder, a rotary cutter mill, a cutting type. Examples include a cutter mill, a disc mill, a shred crusher, a crusher, a chopper, a disc cutter, and the like.

 At this time, the coarse grinding may be performed so that the particle diameter of the hydrogel polymer is 2 mm to 10 mm. That is, in order to increase the drying efficiency, the hydrous gel polymer is preferably pulverized into particles of 10 mm or less. However, since excessive particle grinding may occur, the hydrous gel phase polymer is preferably pulverized into particles of 2 mm or more.

 The coarsely pulverizing step, because the polymer is carried out in a high water content of the polymer may stick to the surface of the mill may appear. In order to minimize this phenomenon, the coarse grinding step may include steam, water, surfactants, anti-fog agents (for example, clay, silica, etc.) as necessary; Persulfate-based initiator, azo-based initiator, hydrogen peroxide, thermal polymerization initiator, epoxy-based crosslinking agent, diol crosslinking agent, crosslinking agent comprising a bifunctional or polyfunctional acrylate of trifunctional group, crosslinking agent of I functional group including hydroxyl group And the like can be added.

 The step of drying the coarsely pulverized hydrogel polymer is carried out through the step of puncture. The hydrogel polymer is provided to the drying step in the coarsely pulverized state of the particles of 2 mm to 10 mm through the above-described step, it can be dried at a higher efficiency.

Drying of the coarsely pulverized hydrogel polymer may be performed at a temperature of 120 to 250 ^° C., preferably 140 to 200 ^° C., more preferably 150 to 19 TC. In this case, the drying temperature may be defined as the temperature of the heat medium supplied for drying or the temperature inside the drying reaction vessel including the heat medium and the polymer in the drying process. If the drying temperature is low and the drying time is long, the process efficiency is lowered. In order to prevent this, the drying temperature is preferably 120 ^° C. or more. In addition, if the dry silver content is higher than necessary, the surface of the hydrogel polymer is excessively dried, so that in the subsequent grinding step The fine powder may increase, and the physical properties of the final resin may be lowered. In order to prevent this, the drying temperature is preferably 250 ^° C. or lower.

 At this time, the drying time in the drying step is not particularly limited, but may be adjusted to 20 to 90 minutes under the drying temperature in consideration of process efficiency and the physical properties of the resin.

 The drying may be performed using a conventional medium. For example, the drying may be performed by hot air supply, infrared irradiation, microwave irradiation, or ultraviolet irradiation to the coarsely pulverized hydrogel polymer.

 And such drying is preferably carried out even if the dried polymer has a water content of about 0.1 to 10% by weight. That is, when the water content of the dried polymerizer is less than 0.1% by weight, it is not preferable because an increase in manufacturing cost and degradation of the crosslinked polymer may occur due to excessive drying. In addition, when the moisture content of the dried polymer exceeds 10% by weight, defects may occur in subsequent processes, which is not preferable.

 Through the steps described above, a step of pulverizing the dried polymer is performed. The milling step is a step for optimizing the surface area of the dried polymer, it may be carried out so that the particle diameter of the milled polymer is 150 to 850.

 At this time, a mill, a pin mill, a hammer mill, a screw mill, a mill, a disc mill, a jog mill, etc., may be used. Can be. In addition, in order to manage the physical properties of the super absorbent polymer to be finalized, the step of selectively classifying particles having a particle size of 150 to 850 from the polymer particles obtained through the grinding step may be further performed.

 The polymer (base resin) polymerized, dried and pulverized by the above-described process of the present invention has a water retention capacity (CRC) of about 35 g / g or more, or about 36 g / g or more, measured according to the EDANA method WSP 241.3. Or about 37 g / g or more and about 50 g / g or less, or about 45 g / g or less, or about 42 g / g or less.

In addition, the base resin has a hop number speed of 40 seconds or less by Vortex method, or _. About 39 seconds or less, or about 38 seconds or less and about 15 seconds or more, or about 20 seconds or more, or about 30 seconds or more. In addition, the base resin has a bulk density of about 0.50 g / mL or more, for example about 51 g / mL or more, or about 0.52 g / mL or more, or about 0.55 g / mL or more, and about 0.70. A high bulk density of up to g / mL, or up to about 0.68 g / mL, or up to about 0.65 g / mL. The greater the bulk density, the more the weight of the resin may be included in the same volume, which is more advantageous in terms of productivity, transportability and the like.

 In sum, the base resin is excellent in physical properties such as water-retaining ability and absorption rate, and at the same time may exhibit high productivity with high bulk density.

 Surface modification of the polymer ground through the above-mentioned steps with a surface crosslinking agent is carried out.

 The surface modification is a step of forming a superabsorbent resin having more improved physical properties by inducing crosslinking reaction on the surface of the ground polymer in the presence of a surface crosslinking agent. Through such surface modification, a surface crosslinking layer is formed on the surface of the pulverized polymer particles.

 The surface modification (surface crosslinking reaction) may be carried out by a conventional method of increasing the crosslinking density of the surface of a polymer particle, for example, a method of mixing and crosslinking the pulverized polymer with a solution containing a surface crosslinking agent. It can be performed as.

 Here, the said surface crosslinking agent is a compound which can react with the functional group which the said polymer has, The structure is not specifically limited. However, by way of non-limiting example, the surface crosslinking agent is ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerol polyglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl Ether, ethylene glycol, diethylene glycol, propylene glycol, triethylene glycol, tetraethylene glycol, propane diol, dipropylene glycol, polypropylene glycol, glycerin, polyglycerol, butanediol, heptanedi, nucleic acid diol trimethyl propane, pentaerythritol, Sorbi may be at least one compound selected from the group consisting of calcium hydroxide, magnesium hydroxide, aluminum hydroxide, iron hydroxide, calcium chloride, magnesium chloride, aluminum chloride, and iron chloride.

At this time, the content of the surface cross-linking agent is the kind of crosslinking agent or reaction conditions It may be appropriately adjusted according to, preferably from 0.001 to 5 parts by weight based on 100 parts by weight of the pulverized polymer. When the content of the surface crosslinking agent is too low, the surface modification is not properly made, the physical properties of the final resin may be lowered. On the contrary, when an excessive amount of surface crosslinking agent is used, absorption of the resin may be lowered due to excessive surface crosslinking reaction, which is not preferable.

On the other hand, the surface modification step, the method of mixing the surface cross-linking agent and the pulverized polymer into the reaction tank, the method of spraying the surface cross-linking agent to the pulverized polymer, the continuous supply of the pulverized polymer and surface crosslinking agent to the mixer to be continuously operated It can be carried out in a conventional manner such as a mixing method. In addition, water may be additionally added when the surface crosslinking agent is added. As such, the surface crosslinking agent and water are added together to induce even dispersion of the surface crosslinking agent, to prevent agglomeration of the polymer particles, and to further optimize the penetration depth of the surface crosslinking agent into the polymer particles. In view of these objects and effects, the amount of water added with the surface crosslinking agent may be adjusted to 0.5 to 10 parts by weight based on 100 parts by weight of the pulverized polymer. In addition, the surface modification step may be performed under a temperature of 100 to 250 ^° C. In addition, the surface modification may be performed for 1 minute to 120 minutes, preferably 1 minute to 100 minutes, more preferably 10 minutes to 60 minutes. That is, the surface modification step may be carried out under the above-described conditions in order to induce a minimum surface crosslinking reaction and to prevent excessive semi-amplification polymer particles from being damaged and deteriorating physical properties.

 According to another embodiment of the present invention, a base resin polymerized and internally crosslinked with a monomer composition including an acrylic acid monomer having an acidic group and at least a portion of the acidic group is neutralized, and a surface crosslinking layer formed on the surface of the base resin. In the super absorbent 'resin, the base resin has a water retention capacity (CRC) of 35 g / g or more, measured according to EDANA WSP 241.3, an absorption rate of 40 seconds or less by a vortex method, and a volume. It provides a super absorbent polymer having a bulk density of 0.51 to 0.70 g / mL.

Therefore, in the present invention, a specific nonionic bubble stabilizer and sugar during polymerization By using the esters together to stabilize the bubbles generated during the preparation of the super absorbent polymer, high water holding capacity, absorption rate and bulk density can be exhibited. Preferably, the acrylic acid monomer is a compound represented by the following formula (1):

 [Formula 1]

R'-COOM ¹

 In Chemical Formula 1,

R ¹ is an alkyl group having 2 to 5 carbon atoms containing a unsaturated bond, and M ¹ is a hydrogen atom, a monovalent or divalent metal, an ammonium group or an organic amine salt. Preferably, the acrylic acid monomer includes at least one member selected from the group consisting of acrylic acid, methacrylic acid and monovalent metal salts, divalent metal salts, ammonium salts and organic amine salts thereof.

Here, the acrylic acid monomer may have an acid group and at least a part of the acid group may be neutralized. Preferably, those which have been partially neutralized with alkyl materials such as sodium hydroxide, potassium hydroxide, ammonium hydroxide and the like can be used. In this case, the neutralization degree of the acrylic acid-based monomer may be 40 to 95 mole ⁰ /., Or 40 to 80 mole _^0/0, or 45 to 75 mole ⁰ /. The range of neutralization can be adjusted according to the final physical properties. However, if the degree of neutralization is too high, the neutralized monomer may be precipitated and polymerization may be difficult to proceed smoothly. On the contrary, if the degree of neutralization is too low, the absorbency of the polymer may not only be greatly reduced, but may exhibit properties such as elastic rubber that is difficult to handle. have.

Preferably, the crosslinked polymer is Ν, Ν'-methylenebisacrylamide, trimethylolpropane tri (meth) acrylate, ethylene glycol di (meth) acrylate, polyethylene glycol (meth) acrylate, polyethylene glycol di (meth) ) acrylic ^Level byte, propylene glycol di (meth) acrylate, polypropylene glycol (meth) acrylate, butanediol di (meth) acrylate, butylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate Latex, nucleic acid diol di (meth) acrylate, triethylene glycol di (meth) acrylate, tripropylene glycol Di (meth) acrylate, tetraethylene glycol di (meth) acrylate, dipentaerythritol pentaacrylate, glycerin tri (meth) acrylate, pentaerythyl tetraacrylate, triarylamine, ethylene glycol diglyci It may be internally crosslinked by at least one internal crosslinker selected from the group consisting of dill ether, propylene glycol, glycerin, and ethylene carbonate. More preferably, it may be internally crosslinked by polyethylene glycol diacrylate (PEGDA).

 In the present invention, the crosslinked polymer may have a centrifugal water retention (CRC) of at least about 35 g / g, or at least about 36 g / g, or at least about 37 g / g, measured according to the EDANA method WSP 241.3. The upper limit of the water retention capacity (CRC) is not particularly limited but may be, for example, about 50 g / g or less, or about 45 g / g or less, or about 42 g / g or less.

 In addition, the crosslinked polymer may have an absorption rate by Vortex of 40 seconds or less, or about 39 seconds or less, or about 38 seconds or less. The lower limit of the absorption rate is specifically. Although not limited, it may be for example about 15 seconds or more, or about 20 seconds or more, or about 30 seconds or more.

 At this time, the water holding capacity and the absorption rate is a base resin which is a crosslinked polymer in a form of powder after drying and pulverizing after polymerization of the monomer composition before forming a surface crosslinked layer on the surface of the crosslinked polymer. Measured for.

 In addition, the base resin has a bulk density of at least 0.51 g / mL, for example at least about 0.51 g / mL, or at least about 0.52 g / mL, or at least about 0.55 g / mL, and at least about 0.70 g. A high bulk density of up to / mL, or up to about 0.68 g / mL, or up to about 0.65 g / mL. The greater the bulk density, the more the weight of the resin may be included in the same volume, which is more advantageous in terms of productivity, transportability and the like.

 In sum, the base resin is excellent in physical properties such as water retention and absorption rate, and at the same time may exhibit high productivity with high bulk density.

Forming a surface crosslinked layer with respect to the base resin generally increases the pressure absorbency (AUP) and improves the absorption rate (vortex time), but the water retention capacity (CRC) Will decrease. Therefore, in consideration of such a tendency to reduce the water retention capacity, it is very important to prepare a base resin having a high water retention ability to secure the physical properties of the final product. The superabsorbent polymer having the surface crosslinked layer formed on the high water-retaining base resin has little concern about a decrease in water-retaining ability, and at the same time, it has an improved pressure-absorbing capacity and absorption rate, thereby obtaining a higher quality resin. . In addition, the super absorbent polymer having the surface crosslinked layer formed on the base ^| resin may further increase in bulk density.

For example, the superabsorbent polymer having the surface crosslinked layer formed on the crosslinked polymer (base resin) having the above water-retaining capacity and absorption rate has a low centrifugal water-retaining capacity (CRC) measured according to the EDANA method WSP 241.3. 30 g / g or more, or about 31 g / g or more, or about 33 g / g or more, about 45 g / g or less, or about 40 g / g or less, or ^' about 38 g / g or less.

 In addition, the superabsorbent polymer having a surface crosslinked layer formed on the base resin has an absorption rate of 34 seconds or less, or about 33 seconds or less, or about 30 seconds or less, about 10 seconds or more, by a vortex method (or About 15 seconds or more, or about 20 seconds or more.

 The centrifugal water retention capacity (CRC) is measured according to the EDANA method WSP 241.3, and may be represented by the following Equation 1:

 [Equation 1]

CRC (g / g) = {[W ₂ (g)-W, (g)] / Wo (g)}-1

 In Equation 1,

W ₀ (g) is the weight of the resin (g),

 W, (g) is the device weight (g) measured after dehydration at 250G for 3 minutes using a centrifuge without using resin,

W ₂ (g) is the device weight (g) measured after the resin was immersed in 0.9 mass% of physiological saline at room temperature for 30 minutes and then dehydrated at 250 G for 3 minutes using a centrifuge.

The measurement of the absorption rate by the vortex method was carried out by putting 50 ml saline with a magnetic stirring bar in a 100 ml beaker, using a stirrer to designate the stirring speed of the magnetic stirring bar at 600 rpm, and then adding 2.0 g of saline to the stirring solution. At the same time the resin is added, the time is measured and the time taken until the vortex disappears in the beaker (unit: seconds) is measured as the vortex time.

 Hereinafter, preferred embodiments are presented to help understand the invention. However, the following examples are only for illustrating the present invention, and the present invention is not limited thereto.

<Example>

 Example 1

 1-1. Preparation of Base Resin

 100 parts by weight of acrylic acid, 83.3 parts by weight of 50% caustic soda (NaOH), 89.8 parts by weight of water, and the following components were mixed to prepare a monomer composition.

 Internal crosslinkers: 0.27 parts by weight (2700 ppmw) polyethylene glycol diacrylate (PEGDA; Mw = 400) and polyethylene glycol diacrylate (PEGDA;

Mw = 200) 0.054 parts by weight (540 ppmw)

Polymerization initiator: hydrogen peroxide (¾0 ₂ ) 0.p2 parts by weight (300 ppmw), ascorbic acid

0.05 parts by weight (500 ppmw), potassium persulfate (KPS) () .2 parts by weight (2000 ppmw)

Bubble stabilizer: 0.016 parts by weight (160 ppmw) of sucrose stearate (S1670), and 0.16 parts by weight (1600 ppmw) of polyalkylene oxide (PEO-PPO-PEO triblock copolymer, Mw: 2550)-thermal with the monomer composition The polymerization reaction was carried out to obtain a polymerized sheet. The polymerized sheet was taken out and cut to a size of 3 cm X 3 cm, and then subjected to a chopping process using a meat chopper to prepare a powder. The powder (cmmb) was dried in an oven capable of transferring air volume up and down. The hot air ^at 180 ^° C. was uniformly dried by flowing 15 minutes downward and upward and 15 minutes upward and downward, and the water content of the dried body was 2% or less after drying. After drying, it was pulverized with a grinder and classified to sort particles having a particle diameter of 150 to 850 to prepare a base resin.

1-2. Preparation of Super Absorbent Resin 4 parts by weight of water, 4 parts by weight of methanol, 0.3 parts by weight of ethyleneglycol diglycidyl ether, 0.06 parts by weight of silica (Aerosil 200), based on 100 parts by weight of the base resin prepared in 1-1. And 0.2 parts by weight of oxalic acid were mixed, followed by reaction at 140 ^° C. for 40 minutes at a surface crosslinking temperature, and a surface treated superabsorbent polymer having a particle size of 150 to 850 μιη was obtained using a sieve after grinding. Example 2

 In Example 1, a super absorbent polymer was obtained in the same manner as in Example 1, except that 0.01 parts by weight of sodium bicarbonate (SBC) was further included as a blowing agent in the monomer composition. Examples 3-7

 Except for changing the components of the monomer composition in Example 1 was prepared in the same manner as in Example 1 to obtain a super absorbent polymer. Comparative Examples 1 to 7

 Except for changing the components of the monomer composition in Example 1 was prepared in the same manner as in Example 1 to obtain a super absorbent polymer. The main components of the monomer composition used in the above Examples and Comparative Examples are summarized in Table 1 as follows.

Table 11

 PEO-PPO-PEO triblock sucrose blowing agent (SBC) copolymer (part by weight) Stearate (part by weight)

 (Parts by weight)

Example 1 0.16 0.016 μs Example 2 0.16 0.016 '0.01

 Example 3 0.16 0.016 0.025

Example 4 0.16 0.016 0.05

Example 5 0.16 0.016 0.2

Example 6 0.28 0.028 Example ₇ 0.32 0.032 Comparative Example 1 0.008 0.1

 Comparative Example 2-0.016 0.1

Comparative Example 3-0.032 0.1

Comparative Example 4-0.04 0.1

Comparative Example 5-0.056 0.1

Comparative Example 6-0.032 0.2

Comparative Example 7-0.032 0.3

Experimental Example

 The physical properties of the superabsorbent polymers prepared in Examples and Comparative Examples were evaluated in the following manner.

 The physical property evaluation was performed for each of the base resin in the state before the surface crosslinking and the superabsorbent polymer after the surface crosslinking in each Example and Comparative Example.

 (1) Centrifuge Retention Capacity (CRC)

 The water holding capacity by the no-load absorption ratio of each resin was measured according to EDANA WSP 241.3.

Specifically, the superabsorbent polymers W ₀ (g) (about 0.2 g) of the Examples and Comparative Examples were uniformly placed in a nonwoven fabric bag and sealed, and then immersed in normal saline (0.9 wt%) at room temperature. After 30 minutes had elapsed, the water was removed from the bag for 3 minutes under the conditions of 250 G using a centrifuge, and the mass W ₂ (g) of the bag was measured. Moreover, mass Wi (g) at that time was measured after performing the same operation | movement without using a base resin. Using each mass obtained, CRC (g / g) was computed according to the following formula. [Equation 1]

CRC (g / g) = {[W ₂ (g)-W g ^ / Woig)}-1

(2) Vortex time

 50 ml saline was placed in a 100 ml beaker with a magnetic bar. The stirring speed was specified at 600 rpm using a stirrer. 2.0 g of superabsorbent polymer was added to the stirred saline solution and the time was measured. The time measurement was terminated when the swirl disappeared in the beaker. (3) Bulk Density

 The bulk density of the base resin before the surface crosslinking was measured by the following method.

The weight of the specific gravity cup (density cup) was measured and recorded as W, and 100 g of the base resin sample was taken in a 250 ml beaker while mixing well so that the particle size was evenly mixed. After filling by filling lightly on the top of the orifice damper, the bottom of the orifice damper was opened to eject the base resin. The base resin sample, which was overflowed onto the specific gravity cup with a spatula, was carefully rolled off using the flat side of the reagent spoon and flattened off. The specific gravity cup containing the base resin was weighed and recorded as W ₂ and the bulk density was calculated according to the following Equation 1.

 [Equation 1]

Apparent density (g / ml) = (W ₂ -W,) / 100

 Wi ： Weight of Density cup (g)

W ₂ ： Density cup + weight of base resin (g)

 100: volume of Density cup (ml) The measurement results are shown in Table 2 below.

Table 2

Base surface crosslinking base resin Superabsorbent superabsorbent polymer resin after base resin after surface crosslinking

Example 1 40.4 35.7 35 25 0.62 Example 2 40.3 36.1 36 22 0.60 Example 3 40.0 37.0 37 25 0.59 Example 4 35.8 31.2 36 27 0.55 Example 5 36.3 31.3 37 26 0.59 Example 6 38.6 31.2 30 22 0.61 Example Ί 39.8 32.0 31 20 0.61 Comparative Example 1 40.7 35.3 55 43 0.56 Comparative Example 2 39.0 33.5 50 42 0.58 Comparative Example 3 39.1 33.0 43 35 0.59 Comparative Example 4 38.7 33.6 41 35 0.57 Comparative Example 5 37.6 31.7 42 36 0.58 Comparative Example 6 38.6 32.1 42 38 0.57 Comparative Example 7 37.0 32.0 44 36 0.55 Referring to Tables 1 and 2, the base resins of Examples 1 to 7 according to the preparation method of the present invention exhibited a high water holding capacity of 35 g / g for 40 seconds. With the following fast absorption rate, it was possible to finally obtain a super absorbent polymer having a very fast absorption rate and high water holding capacity in the 20s. In addition, all of the bulk density of 0.51 g / mL or more due to such a high bulk density can have advantages such as high productivity, easy transport.

 On the other hand, Comparative Example. From 1 to 7, all of the base resins prepared without the nonionic bubble stabilizer of polyalkylene oxide showed an absorption rate exceeding 40 seconds. Therefore, it was shown that the sugar ester and the blowing agent alone could not achieve the absorption rate of 40 seconds or less, and the same result was obtained even when the content of the sugar ester and the blowing agent was increased than in the examples.

Claims

[Claim]

 [Claim 1]

 Monomer composition having an acidic group and comprising at least a portion of the acidic group having a neutralized acrylic acid monomer, a nonionic bubble stabilizer including polyalkylene oxide, a sugar ester, an internal crosslinking agent, and a polymerization initiator Polymerizing to form a hydrogel polymer;

 Drying the hydrogel polymer;

 Pulverizing the dried polymer; And

 Method for producing a super absorbent polymer comprising the step of performing a surface crosslinking reaction by mixing the pulverized polymer and a surface crosslinking agent.

[Claim 2]

 The method of claim 1,

 The polyalkylene oxide (polyalkylene oxide), polyethylene oxide (PEO), polypropylene oxide (polypropylene oxide (PPO), polyethylene oxide-polypropylene oxide (PEO-PPO) diblock copolymer, and Polyethylene oxide-polypropylene oxide-polyethylene oxide (PEO-PPO-PEO) triblock copolymer comprising at least one member selected from the group consisting of, a method for producing a super absorbent polymer.

[Claim 3]

 The method of claim 1,

The sugar ester is sucrose stearate _: Sucrose stearate _: Sucrose palmitate and sucrose laurate (Sucrose laurate), a super absorbent polymer comprising at least one selected from the group consisting of Manufacturing method.

[Claim 4]

 The method of claim 1,

The nonionic bubble based on 100 parts by weight of the acrylic acid monomer A method for producing a super absorbent polymer, comprising from 0.001 to 1 part by weight of a stabilizer.

[Claim 5]

 The method of claim 1,

 The sugar ester based on 100 parts by weight of the acrylic acid monomer

0.001 to 0.08 parts by weight, comprising a super absorbent polymer.

[Claim 6]

 The method of claim 1,

 The sugar ester is contained in 1 to 30 parts by weight with respect to 100 parts by weight of the nonionic bubble stabilizer containing the polyalkylene oxide, a method for producing a super absorbent polymer.

[Claim 7]

 According to claim 1,

 Wherein the pulverized polymer has a bulk density of 0.51 to 0.70 g / mL.

[Claim 8]

 The method of claim L,

 The monomer composition is sodium bicarbonate, sodium carbonate, potassium bicarbonate, potassium carbonate, calcium bicarbonate, calcium bicarbonate, calcium carbonate, magnesium A method for producing a superabsorbent polymer further comprising at least one blowing agent selected from the group consisting of bicarbonate (magnesium bicarbonate) and magnesium carbonate (magnesium carbonate).

[Claim 9]

Acrylic acid type having an acidic group and at least part of the acidic group is increased A superabsorbent polymer comprising a base resin polymerized and internally crosslinked with a monomer composition comprising a monomer, and a surface crosslinking layer formed on the surface of the base resin,

 The base resin has a centrifugal water retention (CRC) of 35 g / g or more, an absorption rate of 40 seconds or less, and a bulk density of 0.51, measured according to the EDANA method WSP 241.3. To 0.70 g / mL,

 Superabsorbent polymer.

[Claim 10]

 The method of claim 9,

 The acrylic acid monomer is represented by Formula 1, super absorbent polymer:

 [Formula 1]

 R'-COOM '

 In Chemical Formula 1,

R ¹ is an alkyl group having 2 to 5 carbon atoms containing an unsaturated bond, and M ¹ is a hydrogen atom, a monovalent or divalent metal, an ammonium or an organic amine.

[Claim 11]

 The method of claim 9,

 The acrylic acid monomer is a super absorbent polymer comprising at least one selected from the group consisting of acrylic acid, methacrylic acid and monovalent metal salts, divalent metal salts, ammonium salts and organic amine salts thereof.

[Claim 12]

 The method of claim 9,

The base resin is Ν, Ν'-methylenebisacrylamide, trimethyl propane tri (meth) acrylate, ethylene glycol di (meth) acrylate, polyethylene glycol (meth) acrylate, polyethylene glycol di (meth) acrylate, propylene Glycol di (meth) acrylate, Polypropylene glycol (meth) acrylate, butanediol di (meth) acrylate, butylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, nucleic acid diol di (meth) acrylate, triethylene glycol di (Meth) acrylate, tripropylene glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate, dipentaerythritol pentaacrylate, glycerin tri (meth) acrylate, pentaeryth tetraacrylate, A superabsorbent polymer that is internally crosslinked by at least one internal crosslinker selected from the group consisting of triarylamine, ethylene glycol diglycidyl ether, propylene glycol, glycerin, and ethylene carbonate.

[Claim 13]

 The method of claim 9,

 The superabsorbent polymer is a superabsorbent polymer having a centrifugal water retention capacity (CRC) of 30 g / g or more and a absorption rate of 34 seconds or less according to a vortex method (Vortex), measured according to EDANA method WSP 24L3.