WO2018147600A1 - Superabsorbent polymer and preparation method therefor - Google Patents

Abstract

The present invention relates to a superabsorbent polymer and a preparation method therefor. According to the present invention, a superabsorbent polymer having a high retention capacity and absorption rate can be prepared by using specific foam stabilizers and polymerization initiators.

Description

 [Name of invention]

 Super Absorbent Resin and Method for Making the Same

Technical Field

 Reciprocal Citation of Related Application (s

 This application claims the benefit of priority based on Korean Patent Application No. 10-2017-0018678 dated February 10, 2017 and Korean Patent Application No. 10-2018-0012910 dated February 1, 2018. All content disclosed in the literature is included as part of this specification. The present invention relates to a super absorbent polymer having a fast absorption rate and a method for producing the same. Background Art

 Super Absorbent Polymer (SAP) is from 500 to 500

It is a synthetic polymer material that can absorb up to 1,000 times of water, and each developer has a different name such as SAM (Super Absorbency Material) and AGM (Absorbent Gel Material). Such super absorbent polymers have been put into practical use as physiological devices, and are currently used in gardening soil repair materials, civil engineering, building index materials, seedling sheets, food freshness maintaining materials in addition to hygiene products such as paper diapers for children, and It is widely used as a material for steaming.

In many cases, such superabsorbent polymers are widely used in the field of hygiene products such as diapers and sanitary napkins. In such sanitary materials, the superabsorbent resin is generally included in the pulp. However, in recent years, efforts have been made to provide sanitary materials such as thinner diapers, and as a part thereof, the content of pulp is reduced, or more so-called pulpless diapers in which no pulp is used at all. Development is underway. As such, in the case of a sanitary material in which the content of the peel is reduced or the pulp is not used, a relatively high absorbent resin is contained in a high proportion, and such superabsorbent Resin particles are inevitably included in a multilayer in the sanitary material. In order for the overall superabsorbent polymer particles contained in the multilayer to absorb the liquid such as urine more efficiently, the superabsorbent resin basically needs to exhibit high absorption performance and absorption rate.

 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 diapers. In general, this absorption rate can be improved by increasing the surface area of the superabsorbent polymer. For example, a method of forming a porous structure on the particle surface of the super absorbent polymer by using a blowing agent has been 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 absorption rate of the super absorbent polymer can be improved through this method, there is a limit that the water retention capacity (CRC) and the pressurized 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. [Detailed Description of the Invention]

 [Technical problem]

 The present invention is to provide a super absorbent polymer having a fast absorption rate.

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

Technical Solution

 The present invention

In the presence of a polymerization initiator, a bubble stabilizer, and an internal crosslinking agent, at least a portion of Crosslinking and polymerizing an acrylic acid monomer having a neutralized acidic group to form a hydrous gel polymer;

 Drying, pulverizing and classifying the hydrogel polymer to form a base resin powder; And

 In the presence of a surface crosslinking liquid, surface crosslinking the base resin powder through heat treatment to form superabsorbent polymer particles,

 The polymerization initiator includes a photoinitiator and a cationic azo initiator, and the bubble stabilizer includes a sucrose ester and a polyalkylene oxide, to provide a method for producing a super absorbent polymer. In addition, the present invention,

A monomer composition comprising an acrylic acid monomer at least partially neutralize the acidic group, and ^"includes a surface cross-linked layer formed on the polymerization and internal crosslinking in which the base resin, and the surface of the base resin, ^■

 A superabsorbent polymer having a centrifugal water retention (CRC) of 30 g / g or more and a absorption rate of 34 seconds or less by the Vortex method is measured according to the EDANA method WSP 241.3.

[Effects of the Invention】

 In the superabsorbent polymer according to the present invention, azo compounds having a specific structure are used as polymerization initiators, and polyalkylene oxides and sucrose esters are used in combination as bubble stabilizers to stably generate bubbles in the polymerization process. Can be adjusted to exhibit high water holding capacity and absorption rate. [Form for implementation of invention]

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. In this specification, terms such as "comprise", "include" or "have" refer to a feature that is implemented, It is to be understood that one or more of the steps, elements, or combinations thereof are intended to be present, but do not preclude the existence or addition of one or more other features or steps, elements, or combinations thereof in advance.

 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 the 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, and for this purpose, conventionally, a lot of pores are formed in the superabsorbent polymer so that water can be sucked up quickly or absorbed into water. The method of making particle size of resin small is known. However, there is a limitation in reducing the particle size of the superabsorbent polymer, and when the internal pores are formed, the gel strength becomes weak, so that the thinning of the article is difficult.

 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 high level of water retention (CRC) and a fast vortex time, and there is still a need for a method of preparing a superabsorbent polymer having improved absorption and absorption rates. exist.

The present inventors use a combination of specific bubble stabilizers in polymerization, and use cationic azo polymerization initiators to produce superabsorbent polymers that exhibit more stable and even bubble distribution, and consequently exhibit high water retention and fast absorption rates. With this in mind, it has been completed the present invention. Hereinafter, the super absorbent polymer of the present invention and a method for producing the same will be described in detail. For reference, in the specification of the present invention, "polymer", or "polymer" means that the acrylic acid monomer is in a polymerized state, and may cover all moisture content ranges or particle size ranges. Among the above polymers, a polymer having a water content (water content) of about 40% by weight or more after being dried before polymerization may be referred to as a hydrous gel polymer.

 In addition, "base resin" or "base resin powder" means that the polymer is dried and ground to form a powder. In the method for preparing a super absorbent polymer according to an embodiment of the present invention, first, an acid group is included, and at least a part of the acid group includes an acrylic acid monomer, a polymerization initiator, a bubble stabilizer, and an internal crosslinking agent. Combined to form 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 an alkali substance 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 mol%, or 45 to 75 mol%. 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]

R'-COOM ¹

 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 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 may be appropriately adjusted in consideration of polymerization time and reaction conditions, preferably about 20 to about 90 weight ⁰ / ^° , or may be about 40 to about 70 weight% have. 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, if the concentration of the monomer is excessively high, a problem may occur in the process, such as the precipitation efficiency of the monomer precipitated or the pulverization of the polymerized hydrogel polymer may be degraded, 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, the surface for crosslinking the surface of the hydrogel polymer in a subsequent process. It is separate from the crosslinking agent.

Preferably, the internal crosslinking agent is Ν, Ν'-methylenebisacrylamide, trimethyl propane tri (meth) acrylate, ethylene glycol di (meth) acrylate, polyethylene glycol (meth) acrylate, polyethylene glycol di (meth) acrylic Propylene glycol di (meth) acrylate, polypropylene glycol (meth) acrylate, butanediol di (meth) acrylate, butylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, hexane Diuldi (meth) acrylate, triethylene glycol di (meth) acrylate, tripropylene glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate, dipentaerythrite pentaacrylate, glycerin tri (meta ) Acrylates, pentaerythres, tetraacrylates, triarylamines, ethylene glycol diglycidyl ethers, Propylene glycol, glycerin _. , And at least one selected from the group consisting of ethylene carbonate. More preferably, when the polyethylene glycol diacrylate (PEGDA) and / or nucleic acid diol diacrylate (HDDA) is used as the internal crosslinking agent, it can exhibit improved water retention 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 about 1 part 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. In addition, in the present invention, in addition to the monomer composition and the internal crosslinking agent, a polymerization initiator includes a cationic azo initiator, and a bubble stabilizer includes a sucrose ester and a polyalkylene oxide.

 The polyalkylene oxide, together with the sucrose ester, serves to form more stable bubbles in the polymerization process, thereby allowing the hydrous gel polymer to be polymerized to have a high water holding capacity and a fast absorption rate.

 The polyalkylene oxide is specifically, for example, 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 ( triblock) copolymer may be used, but is not limited thereto.

According to one embodiment of the invention, the weight average molecular weight of the polyalkylene oxide is at least about 500g / mol, less than about 3,000g / mol, or about 1,000 to about 2,700g / m, ethylene oxide in the polyalkylene oxide It may be more preferable to use PEO-PPO-PEO triblock copolymers having a ratio of (EO) of 20 to 80% by weight ⁰ /., Or 20 to 60% by weight.

Polyalkylene oxide having a weight average molecular weight value in the above range When used, it is possible to improve the properties related to absorption and speed, such as Vortex time. The polyalkylene oxide 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 polyalkylene oxide is too low, the role as a bubble stabilizer is insufficient to achieve the absorption rate improvement effect, on the contrary, when the concentration of the polyalkylene oxide is too high, the water holding capacity and the absorption rate is rather reduced, or the surface tension This lowering problem may occur. The surface tension is related to dryness when the superabsorbent resin ^ᅵ etc. is applied to absorbent articles such as ^diapers.The lower the surface tension of the superabsorbent polymer, the more absorbed the moisture is and the more the absorbent resin is drained out. The amount of will be increased. Examples of the sucrose ester used with the bubble stabilizer including the polyalkylene oxide include sucrose stearate, sucrose isobutylate, and sucrose palmitate. Or sucrose laurate (sucrose laurate) and the like, for example, may be used in combination of one or more, but the present invention is not limited thereto. Preferably sucrose stearate can be used.

 The sucrose ester is about 100 parts by weight of the acrylic acid monomer

It may be added at a concentration of 0.001 to about 0.1 parts by weight, or about 0.005 to about 0.05 parts by weight. '

The character when the concentration of the saccharide ester is too low, the function as bubble stabilizer mimihayeo difficult to achieve the improved rate of absorption effects, whereas the ⁷ i Here preferably the concentration of the saccharide ester is too high, polymerization beam SAT and the absorption rate is rather lowered You can't.

In addition, the sucrose ester is preferably used in a ratio of about 1 to 50 parts by weight, or about 1 to 10 parts by weight with respect to 100 parts by weight of the polyalkylene oxide. In addition, the bubble stabilizer including the polyalkylene oxide and the sucrose ester may be added in an amount of about 0.001 to about 2 parts by weight, or about 0.01 to about 1 part by weight based on 100 parts by weight of the acrylic acid monomer. In addition, when the cationic azo initiator is used together with a sucrose ester and a polyalkylene oxide, it is possible to realize a fast vortex absorption rate in a high CRC region with respect to the superabsorbent polymer to be produced, and at the same time, remains in the polymerization process. It is possible to reduce the monomer content.

 Specifically, when the cationic azo initiator is used together with a sucrose ester and a polyalkylene oxide, the residual monomer content of the base resin is about 450 ppm or less, or about 300 ppm, based on the EDANA method WSP 210.3. It may be from about 450ppm, preferably from about 350ppm to about 400ppm, and based on the surface-treated superabsorbent resin, may be about 350ppm or less, or about 250ppm to about 350ppm, preferably about 250ppm or more It may be 300 ppm or less.

Examples of cationic azo initiators that can be used include azo ^' nitrile initiators (trade name: Wako V-501), azoamide initiators (trade name: Wako VA-086), azo amidine initiators (brand names: Wako VA-057, V -50), and azo imidazoline-based initiators (trade names: Wako VA-061, VA-044) and the like, but the present invention is not necessarily limited thereto.

 A cationic azo initiator can be used together with the polymerization initiator generally used for manufacture of the existing superabsorbent polymer, as follows.

 As the polymerization initiator, a thermal polymerization initiator or a photopolymerization initiator may be used depending on the polymerization method. However, even by 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 as the polymerization reaction, which is an exothermic reaction, a certain amount of heat is generated. Can be.

As the photoinitiator, for example, benzoin ether, dialkyl acetophenone, hydroxyl alkyl ketone (hydroxyl) one or more compounds selected from the group consisting of alkylketone, phenyl glyoxylate, benzyl dimethyl ketal, acyl phosphine, and alpha-aminoketone have. As specific examples of the acylphosphine, commercially available lucirin TPO, that is, 2,4,6-trimethyl-benzoyl-trimethyl phosphine oxide may be used. . More various photoinitiators are disclosed on page 115 of Reinhold Schwalm's book, "UV Coatings: Basics, Recent Developments and New Application (Elsevier 2007)".

In addition, the thermal polymerization initiator may be used at least one compound selected from the group consisting of persulfate initiator, azo initiator, hydrogen peroxide, and ascorbic acid. Specifically, the persulfate-based initiators include 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, azo-based initiators include 2,2-azobis- (2-amidinopropane) dihydrochloride (2,2-azobis (2-amidinopropane) dihydrochloride), 2,2-azobis- (Ν, N-dimethylene) isobutyramidine dihydrochloride (2,2-azobis-

(N, N-dimethylene) isobutyramidine dihydrochloride), 2-

(Carbamoyl-azo) isobutyronitrile nitrile ^(2- (carbamoylazo) isobutylonitril), the ^{2-azobis [2-} (2-imidazolin-2-yl) propane] dihydrochloride (2, ² -azobis ^[2- ( ² -imidazolin- ² -y]) propane] dihydrochloride), 4,4-azobis- (4-cyanovaleric acid) (4,4-azobis- (4-cyanovaleric acid)), and the like. . More various thermal polymerization initiators are disclosed on page 203 of the Odian book "Principle of Polymerization (Wiley, 1981)".

 The polymerization initiator is about 100 parts by weight of the acrylic acid monomer.

It may be added at a concentration of 0.001 to about 1 part by weight. 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, the polymer chain forming the network is shortened. It is not preferable because the physical properties of the resin, such as the content of the water-soluble component is high and the pressure absorption capacity is lowered. According to one embodiment of the invention, the monomer composition is. Sodium bicarbonate, Sodium carbonate, Potassium bicarbonate 1 "Potassium bicarbonate, Potassium ^ l" Potassium carbonate, Calcium bicarbonate, Calcium carbonate bicarbonate), magnesium bicarbonate (magnesium bicarbonate) and magnesium carbonate (magnesium carbonate) may further include at least one blowing agent selected from the group consisting of. In addition, the monomer composition may further include additives such as thickeners, plasticizers, storage stabilizers, and antioxidants, 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 sucrose ester, and a bubble stabilizer are dissolved in a solvent.

In this case, any solvent that can be used may be used without limitation as long as it can dissolve the above-described raw materials. For example, as the solvent, water, ethanol, ethylene glycol, diethylene glycol, triethylene glycol, 1,4-butanediol, propylene glycol, ethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate , Methyl ethyl ketone, acetone, methyl amyl ketone, cyclonucanonone, cyclopentanone, diethylene glycol monomethyl ether, diethylene glycol ethyl ether, toluene, xylene, butyrolactone, carbitle, methyl cellosolve acetate Ν, Ν-dimethylacetamide, or a combination thereof may be used. The amount of the solvent may be adjusted to be 1 to 5 times the weight ratio of the acrylic acid monomer content 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 The method is largely divided into thermal polymerization and photopolymerization according to the type of polymerization energy source, in which the thermal polymerization may be performed in a reaction vessel having a stirring shaft such as a kneader. It can be carried out in a semi-unggi equipped with a movable conveyor belt.

For example, a 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 functional polymer is a gel may be obtained in various forms depending on the concentration and the injection rate of the ^"monomer composition to be injected, it is usually a weight-average particle diameter of 2mm to 50mm of a function gel polymer can be obtained.

 In another example, when the photopolymerization of the monomer composition is performed in a semi-unggi 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 is evenly polymerized, it is usually adjusted to a thickness of about 0.5cm to about 5cm It is preferable to be.

 The hydrogel polymer formed by the above method may exhibit a water content of about 40 to 80% by weight. It is advantageous in that the water content of the hydrogel polymer falls within the range to optimize the efficiency in the drying step described later.

Here, the moisture content is an increase in water occupying 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 conditions 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 and then maintained at 180 ^° C.

The hydrogel polymer obtained through the above-mentioned steps is used for imparting absorbency. It goes through a drying process. By the way, in order to increase the drying efficiency, 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.

In this case, the coarse grinding may be performed such that the particle size of the hydrogel polymer is about 2 mm to about 10 mm. That is, in order to increase the drying efficiency, the hydrous gel polymer is preferably pulverized into particles of about 10 mm or less. However, excessive ^■ To avoid the possibility of ungjip phenomenon between particles during milling, the functional polymer gel is preferably ground to a particle of about 2mm 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-agglomerating agents (eg clay, silica, etc.) as necessary; Persulfate-based initiator, azo-based initiator I, hydrogen peroxide, thermal polymerization initiator, epoxy-based cross-linking agent, diol cross-linking agent, cross-linked body comprising a acrylate of a bifunctional group or a polyfunctional group of at least three functional groups, 1 containing a hydroxyl group A crosslinking agent of a functional group, etc. can be added.

 Through the above-described steps, the step of drying the coarsely pulverized hydrogel polymer is carried out. The hydrogel polymer is provided to the drying step in the coarsely pulverized state of the particles of about 2mm to about 10mm 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 about 120 to about 2501 :, preferably about 140 to about 200 ^° C, more preferably about 150 to about 190 ^° C. 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. Low drying temperature reduces drying time The longer the process, the lower the efficiency, so the drying temperature is about

It is preferable that it is more than 120 ^° C. In addition, when the drying temperature is higher than necessary, the surface of the hydrogel polymer may be excessively dried to increase the generation of fine powder in the subsequent grinding step, and the physical properties of the final resin may be lowered. It is preferred that it is about 250 ^° C or less.

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

The drying may be done using a conventional medium, for example, the hot air supply tank to the grinding function gel polymer, infrared irradiation, microwave irradiation may _be performed through a method such as ultraviolet irradiation or.

And such drying is preferably carried out so that the dried polymer has a water content of about 0.1 to about 10 weight ⁰ /. That is, when the moisture content of the dried polymer is less than about 0.1 weight ⁰ / ^°, it is not preferable because an increase in the 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 about 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 about 150 to about 850 / m.

 At this time, the grinding mill may be a pin mill, a hammer mill, a screw mill, a roll mill, a disc mill, a jog mill, or the like. 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 37 g / g or more, as measured according to the EDANA method WSP 241.3, or About 40 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. Further, the absorption rate by Vortex may be 42 seconds or less, or about 40 seconds or less and about 25 seconds or more, or about 30 seconds or more, or about 35 seconds or more. Subsequently, in the step of modifying the surface of the pulverized polymer through the above-described steps, in the presence of a surface crosslinking solution containing a surface crosslinking agent, surface crosslinking the base resin powder through heat treatment to form superabsorbent polymer particles to be.

 The surface modification is a step of forming a superabsorbent polymer 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 polymer particle surface, 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, polyester ^styrene glycol diglycidyl ether, glycerol polyglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol di Glycidyl ether, ethylene glycol, diethylene glycol, propylene glycol, triethylene glycol, tetraethylene glycol, propane di, dipropylene glycol, polypropylene glycol, glycerin, polyglycerine, butanedi, heptanediol, nucleic acid ditrimethyl, propane, penta EPO recalled, sorbitan beetle, calcium hydroxide, magnesium hydroxide, aluminum hydroxide, iron hydroxide, calcium chloride, magnesium chloride, aluminum chloride, and ^iron, selected from the group consisting of chloride

It may be one or more compounds.

In this case, the content of the surface crosslinking agent may be appropriately adjusted according to the type of crosslinking agent or reaction conditions, and preferably, about 0.001 to about 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, excessive surface crosslinking agents are used The crosslinking reaction may lower the absorptivity of the resin, 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 in 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 cross-linking 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 aggregation 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 together with the surface crosslinking agent may be adjusted to about 0.5 to about 10 parts by weight based on 100 parts by weight of the pulverized polymer.

 In addition, the surface crosslinking may be performed at a temperature of about 175 to about 200 ° C, and may be continuously performed after the drying and grinding steps proceed to a relatively high temperature. More preferably, it may proceed under a temperature of about 180 to about 195 ° C.

 At this time. The surface crosslinking reaction may proceed for about 1 to about 120 minutes, or about 1 to about 100 minutes, or about 10 to about 60 minutes. That is, in order to induce a minimum surface crosslinking reaction and to prevent the polymer particles from being damaged due to excessive reaction and deteriorating physical properties, the above-described surface crosslinking reaction may be performed. 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 polymer consisting of, the base resin is a super absorbent polymer having a water retention capacity (CRC) of 35 g / g or more measured according to the EDANA method WSP 241.3, the absorption rate by the Vortex method (Vortex) of 40 seconds or less to provide.

Therefore, in the present invention, by using a specific bubble stabilizer and sucrose ester together during polymerization, bubbles generated during the preparation of superabsorbent polymers are avoided. By stabilizing, high water holding capacity and absorption rate 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 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.

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 about 40 to about 95 mole ⁰ /., Or from about 40 to about 80 mol%, or from about 45 to about 75 mole _^0/0. The range of neutralization can be adjusted according to the final physical properties. However, when the degree of neutralization is too high, it may be difficult for the polymerization to proceed smoothly due to the precipitation of the thickened monomer. On the contrary, when the degree of neutralization is too low, the absorbency of the polymer may be greatly reduced and may exhibit properties such as elastic rubber, which is difficult to handle. There is

. 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) ) 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, 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) and / or nucleic acid diol diacrylate (HDDA).

In the present invention, the crosslinked polymer is centrifuged as measured according to the EDANA method WSP 241.3 _. The water retention capacity (CRC) may be at least about 35 g / g, or at least about 36 g / g, or at least about 40 g / g. The upper limit of the water holding 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 be less than or equal to the absorption speed by the vortex method (Vortex) not more than 40 seconds, or less than about 39 seconds, or from about ^'37 seconds. The lower limit of the absorption rate is not particularly limited, but 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 retention capacity and the absorption rate is a base resin which is a crosslinked polymer in the 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.

 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 decreases the water retention capacity (CRC). 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. .

For example, the superabsorbent polymer in which the surface crosslinked layer is formed with respect to the crosslinked polymer (base resin) having the above water-retaining capacity and absorption rate is EDANA. The centrifugal water retention (CRC) measured according to method WSP 241.3 is at least about 30 g / g, or at least about 31 g / g, or at least about 34 g / g, at most about 45 g / g, or at most about 40 g / g, or About 36 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 Equation 1 below:

 [Equation 1]

CRC (g / g) = {[W ₂ (g)-\ ν, ( _Ε )] / \ ν ₀ ( _§ )}-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.

 Measurement of the absorption rate by the vortex method, 50ml saline into a 100ml beaker with a magnetic stir bar, using a stirrer to specify a stirring speed of 600rpm and then put 2.0g of resin in the saline stirred Measure the time and measure the time (in seconds) to the point where the swirl disappears in the beaker as the vortex time. In addition, the super absorbent polymer, when swelling with physiological saline, specifically,

Swelled with 0.9% by weight aqueous sodium chloride solution, and the measured surface tension ( _sur f _ace tension) value of at least about 40 mN / m, preferably about 40 to about 70 mN / m, or about 60 to It may be desirable to be about 70 mN / m. This surface tension is measured, for example, at room temperature of 23 ± 2 ^° C. Can be measured. The specific measuring method of surface tension is described in the Example mentioned later.

 . The surface tension of the superabsorbent polymer may be a measure for evaluating urine leakage in a diaper including the superabsorbent polymer as physical properties that are distinguished from water-retaining capacity, pressure-absorbing capacity, liquid permeability, and the like. The surface tension swells the superabsorbent polymer in saline, and means the surface tension measured for the saline, and if the surface tension of the superabsorbent polymer is low, urine leakage is likely to occur in a diaper manufactured by the same. . According to the super absorbent polymer of one embodiment, it is possible to produce a high-quality sanitary article by reducing the possibility of leakage by having a suitable surface tension while maintaining high fluidity and the like. When the surface tension of the superabsorbent polymer is too low, urine leakage, that is, rewet may increase, and when the surface tension is excessively high, the surface crosslinking layer may be unevenly formed, thereby deteriorating physical properties such as liquid permeability. Hereinafter, the operation and effect of the invention will be described in more detail with reference to specific embodiments of the invention. However, these embodiments are only presented as an example of the invention, whereby the scope of the invention is not determined.

<Example>

 Example

 Example 1

 1-1. Preparation of Base Resin

 A monomer composition was prepared by mixing 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.

 Internal crosslinker: 0.27 parts by weight (2700 ppmw) of polyethylene glycol diacrylate (PEGDA; Mw = 400) and 0.054 parts by weight (540 ppmw) of polyethylene glycol diacrylate (PEGDA; Mw = 200)

-Polymerization initiator: 0.1 part by weight (10 ppm) of cationic azo initiator (V50), 0.02 part by weight (300 ppmw) of hydrogen peroxide (H ₂ 0 ₂ ), 0.05 part by weight (500 ppmw) of ascorbic acid, 0.2 parts by weight of potassium persulfate (KPS) Part (2000ppmw) Bubble stabilizer: 0.016 parts (160 ppmw) of sucrose stearate (S 1670), and 0.16 parts (1600 ppmw) of polyalkylene oxide (PEO-PPO-PEO triblock copolymer, Mw: 2550)

Thermal polymerization reaction was carried out with the monomer composition to obtain a polymerized sheet. The polymerized sheet was taken out and cut to a size of 3 cm 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 heated uniformly from 15 minutes downwards to 15 minutes and upwards from downwards to 15 minutes, and dried to have a water content of 2% or less. 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 methane, 0.3 parts by weight of ethyleneglycol diglycidyl ether, and silica (Aer _OS il 200) based on 100 parts by weight of the base resin prepared in 1-1. The mixture was added with 2 parts by weight of oxalic acid, and then mixed. Then, the mixture was reacted at 140 ^° C. for 40 minutes at a surface crosslinking temperature, and the surface treated super absorbent polymer having a particle diameter of 150 to 850 using a sieve. Got.

 Examples 2-7 and Comparative Examples 1-6

 By varying the content of each component, a super absorbent polymer was prepared in the same manner as in Example 1. Examples 8, 9; And Comparative Example 8

 As bubble stabilizer, polyalkylene oxides with different weight average molecular weight values (PEO-

Using a PPO-PEO triblock copolymer), except that the box, the superabsorbent polymer was prepared in the same manner as in Example 1. The content of each component used in Examples and Comparative Examples is shown in Table 1 below. Table 1

Experimental Example: Evaluation of Physical Properties of Super Absorbent Polymer

 The physical properties of the super absorbent polymers prepared in Examples and Comparative Examples were evaluated by the following method.

(1) Absorption Rate (Vortex)

In a 100 11 beaker, 0.9 weight of ⁰ /. NaCl solution 50 was added, and the stirrer was 2 g of superabsorbent polymers prepared in Examples and Comparative Examples were added thereto while stirring at 600 rpm. Then, the time until the vortex of the liquid generated by stirring disappeared and a smooth surface was measured, and the result was expressed as the vortex removal time (absorption rate; vortex).

(2) Centrifuge Retention Capacity (CRC)

According to the European Disposables and Nonwovens Association (EDANA) standard EDANA WSP 241.3, the centrifugal water retention capacity _(CRC) was measured for the superabsorbent polymers of Examples and Comparative Examples by the unloaded absorption ratio.

Specifically, the examples and the comparative example resins W0 (g, about 0.2 g) placed uniformly on the envelope of the nonwoven fabric sealing (seal) one after, immersion in physiological saline is a sodium chloride solution of 0.9 weight ⁰ /. To room temperature I was. After 30 minutes, the bag was centrifuged and drained at 250 G for 3 minutes, and then the mass W2 (g) of the bag was measured. Moreover, after carrying out the same operation without using a super absorbent polymer, the mass W1 (g) at that time was measured. Using each mass thus obtained, CRC (g / g) was calculated according to Equation 1 below.

 [Equation 1]

 CRC (g / g) = {[W2 (g)-Wl (g)-W0 (g)] / W0 (g)}

 In Equation 1,

W0 (g) is the initial weight of superabsorbent resin (g), Wl (g) is absorbed by immersion in physiological saline for 30 minutes without using superabsorbent resin, and then centrifuge at 250G for 3 minutes. The device weight measured after dehydration> W2 (g) is absorbed by immersing the superabsorbent resin in physiological saline for 30 minutes at room temperature, and then dehydrated at 250G for 3 minutes using a centrifuge, and includes the superabsorbent resin. The weight of the device measured by (3) surface tension

All procedures were performed in a constant temperature and humidity room (temperature 23 ± 2 ^° C, relative humidity 45 ± 10%).

150 g of saline solution consisting of 0.9 weight of ⁰ / ^° sodium chloride was placed in a 250 mL beaker and stirred with a magnetic bar. Each l.Og of the superabsorbent polymer prepared in Examples and Comparative Examples was added to the stirring solution, stirred for 3 minutes, and the stirring was stopped and left for at least 15 minutes to allow the swollen superabsorbent resin to sink to the bottom.

 The supernatant (the solution just below the surface) was then pipetted and transferred to another clean cup and measured using a surface tensionmeter Kruss K11 / K100. The said measurement was progressed by the same method also about the base resin manufactured by the manufacture process of an Example and a comparative example. The measurement results are shown in Table 2 below.

Table 2

Comparative Example 1 39.1 48 36.8 38-Comparative Example 2 37.6 45 35.4 36-Comparative Example 3 37.6 47 35.2 36-Comparative Example 4 38.6 44 36.1 35-Comparative Example 5 38.5 39 35.9 31 39.4

 Comparative Example 6 38.0 37 36.4 32 36.1

 Comparative Example 7 38.9 37 36.8 36-Comparative Example 8 37.5. 38 36.2 37-Referring to Table 2, it can be seen that the base resin and the super absorbent polymer prepared according to the present example have a high CRC value and a very high Vortex absorption rate.

 However, the base resin and the super absorbent polymer prepared according to the comparative example, it can be seen that the CRC value is lowered, or the Vortex absorption rate is lowered, in particular, in Comparative Examples 5 and 6, a relatively high content of polyalkyl By using the ethylene oxide-based compound, it can be seen that the surface tension value is very small compared to the superabsorbent polymer according to the embodiment of the present invention.

Claims

[Range of request]

 [Claim 1]

 In the presence of a polymerization initiator, a bubble stabilizer, and an internal crosslinking agent, crosslinking polymerization of an acrylic acid monomer having at least part of a neutralized acid group to form a hydrous gel polymer;

 Drying, pulverizing and classifying the hydrogel polymer to form a base resin powder; And

 In the presence of a surface crosslinking solution, surface crosslinking the base resin powder through heat treatment to form superabsorbent resin particles,

 The polymerization initiator includes a photoinitiator and a cationic azo initiator, the bubble stabilizer comprises a sucrose ester and a polyalkylene oxide,

 Method for producing a super absorbent polymer.

[Claim 2]

 The method of claim 1,

 The sucrose ester is at least one selected from the group consisting of sucrose stearate, sucrose isobutylate, sucrose palmitate and sucrose laurate. The manufacturing method of the superabsorbent polymer containing.

[Claim 3]

 The method of claim 1,

The polyalkylene oxides include polyethylene oxide (PEO), polypropylene oxide (PPO), polyethylene oxide-polypropylene oxide (PEO-PPO) diblock copolymers, and polyethylene oxide—poly Propylene oxide-polyethylene oxide (PEO-PPO-PEO) triblock copolymer comprising one or more selected from the group consisting of Method for producing a super absorbent polymer.

[Claim 4]

 The method of claim 1,

 The sucrose ester is used in 1 to 50 parts by weight based on 100 parts by weight of the polyalkylene oxide,

 Method for producing a super absorbent polymer.

[Claim 5]

 The method of claim 1,

 The bubble stabilizer is used in 0.001 to 2 parts by weight based on 100 parts by weight of the acrylic acid monomer,

 Method for producing a super absorbent polymer.

[Claim 6]

 The method of claim 1,

 The cationic azo initiator comprises at least one compound selected from the group consisting of an azo nitrile initiator, an azo amide initiator, an azo amidine initiator, and an azo imidazoline initiator.

 Super Absorbent .Resin Preparation Method.

[Claim 7]

 The method of claim 1,

 The polymerization initiator is used in 0.001 to 1 part by weight based on 100 parts by weight of the acrylic acid monomer,

 Superabsorbent polymer and manufacturing method.

[Claim 8]

The method of claim 1, The heat treatment temperature is 175 to 200 ° C.,

 Method for producing a super absorbent polymer.

[Claim 9]

 The method of claim 1,

 The crosslinking polymerization is sodium bicarbonate, sodium carbonate, potassium bicarbonate, potassium carbonate, calcium bicarbonate, calcium bicarbonate, calcium carbonate, Further using one or more blowing agents selected from the group consisting of magnesium bicarbonate and magnesium carbonate,

 Method for producing a super absorbent polymer.

[Claim 10]

 A base resin polymerized and internally crosslinked with a monomer composition comprising at least a portion of an acidic group neutralized acrylic acid monomer, and a surface crosslinking layer formed on the surface of the base resin,

 The centrifugal water holding capacity (CRC) measured according to EDANA method WSP 241.3 is 30 g / g or more, and the absorption rate by Vortex method is 34 seconds or less,

 Superabsorbent polymer.

[Claim 1 11]

 The method of claim 10,

 A super absorbent polymer having a surface tension value of 40 mN / m or more upon swelling with physiological saline.