阅读说明：本技术 制备超吸收性聚合物的方法和超吸收性聚合物 (Method for producing superabsorbent polymers and superabsorbent polymers ) 是由 崔用锡 洪连祐 申恩智 安泰彬 于 2019-11-27 设计创作，主要内容包括：提供了超吸收性聚合物及其制备方法。更特别地,提供了包含细粉再组装体的超吸收性聚合物及其制备方法,其中所述超吸收性聚合物表现出优异的吸收性能和吸收速率。(Superabsorbent polymers and methods of making the same are provided. More particularly, a superabsorbent polymer including a fine powder reassembly, wherein the superabsorbent polymer exhibits excellent absorption properties and absorption rate, and a method of preparing the same, are provided.)

1. A method of making a superabsorbent polymer, the method comprising the steps of:

performing thermal polymerization or photopolymerization of a monomer composition comprising a water-soluble ethylenically unsaturated monomer and a polymerization initiator to prepare an aqueous gel polymer;

drying, pulverizing and size sorting the aqueous gel polymer to classify the aqueous gel polymer into a fine powder having a particle size of less than 150 μm and conventional particles having a particle size of 150 to 850 μm;

mixing one or more of fluff pulp and synthetic polymer fibers with the fines and water to produce an aqueous fine powder solution; and

the fine powder aqueous solution was stirred to prepare a fine powder reassembled body.

2. The method of preparing a superabsorbent polymer of claim 1 wherein the aqueous fine powder solution comprises the fiber in an amount of 1 part by weight or more to less than 20 parts by weight with respect to 100 parts by weight of the fine powder.

3. The method of preparing superabsorbent polymer of claim 1 wherein the length of the fibers is from 1mm to 20 mm.

4. The method of preparing superabsorbent polymer of claim 1 wherein the width of the fibers is from 1 μ ι η to 100 μ ι η.

5. The method of preparing a superabsorbent polymer of claim 1 wherein the synthetic polymer fibers are one or more selected from the group consisting of: nylon, polypropylene, polyethylene, polyester, polyacrylonitrile, polyvinyl chloride, polyvinyl alcohol, polyacrylate, and acetate.

6. The method of preparing a superabsorbent polymer of claim 1 wherein the aqueous fine powder solution comprises water in an amount of 50 to 150 parts by weight relative to 100 parts by weight of the fine powder.

7. The method of preparing superabsorbent polymer of claim 1 further comprising the step of drying, pulverizing and size sorting the fine powder reassembled.

8. The method of preparing a superabsorbent polymer of claim 7 further comprising the step of surface cross-linking the comminuted and size-sorted fine powder reassembler.

9. A superabsorbent polymer prepared by the preparation method according to any one of claims 1 to 8.

10. A superabsorbent polymer comprising a fine powder reassembler which is reassembled by mixing fine powder having a particle size of less than 150 μm in a polymer obtained by polymerising a water-soluble ethylenically unsaturated monomer containing at least partially neutralised acidic groups with one or more fibres of fluff pulp and synthetic polymer fibres.

11. The superabsorbent polymer of claim 10 wherein at least a portion of the fibers are incorporated into the interior of the fine powder reassembled particles.

12. The superabsorbent polymer of claim 10 wherein the fine powder reassemble comprises the fibers in an amount of 1 part by weight or more to less than 20 parts by weight relative to 100 parts by weight of the fine powder.

13. The superabsorbent polymer of claim 10 wherein the Centrifuge Retention Capacity (CRC) measured according to EDANA method WSP 241.3 is from 30 to 45 g/g.

14. The superabsorbent polymer of claim 10 wherein the 0.3psi Absorbency Under Load (AUL) measured according to EDANA method WSP 242.3 is from 25g/g to 40 g/g.

15. The superabsorbent polymer of claim 10 wherein the absorption rate (vortex time) is 60 seconds or less.

Technical Field

Cross Reference to Related Applications

The present application is based on and claims priority from korean patent application nos. 10-2018-0158920 and 10-2019-0152657, filed on 11/12/2018 and 25/2019/11/2019, respectively, the disclosures of which are incorporated herein by reference in their entirety.

The present invention relates to superabsorbent polymers and methods of making the same. More particularly, the present invention relates to a superabsorbent polymer comprising a fine powder reassembly, wherein the superabsorbent polymer exhibits excellent absorption characteristics, and a method of preparing the same.

Background

Superabsorbent polymers (SAPs) are synthetic polymeric materials that are capable of absorbing 500 to 1000 times their own weight in water. Since such super absorbent polymers have been put into practical use in sanitary products, they are now widely used not only in sanitary products such as disposable diapers for children, but also in water-retaining soil products for horticulture, water-stopping materials for civil engineering and construction, sheets for growing seedlings, freshness-retaining agents for the field of food distribution, materials for dressings, and the like.

The absorption mechanism of the superabsorbent polymer is controlled by the osmotic pressure due to the difference in electrical attraction force represented by the charge of the polymer electrolyte, the affinity between water and the polymer electrolyte, the molecular expansion due to the repulsive force between the ions of the polymer electrolyte, and the expansion-inhibiting interaction due to cross-linking. In short, the absorption capacity of the absorbent polymer depends on the above-mentioned affinity and molecular swelling, and the absorption rate thereof is greatly influenced by the osmotic pressure of the absorbent polymer itself.

Many studies have been made to improve the absorption rate of superabsorbent polymers. For example, korean patent publication No. 2014-0063457 describes a method for preparing a superabsorbent polymer, which includes a step of preparing a fine powder reassembled body using only fine powder and a base polymer without an additive. However, there are the following problems: the physical properties of the fine powder reassembled body are more deteriorated than those of the base polymer, and the complicated process causes a decrease in efficiency.

[ Prior art documents ]

Patent document 1: korean patent laid-open No. 2014-0063457

Disclosure of Invention

Technical problem

In order to solve the above-mentioned problems of the prior art, the present invention provides a superabsorbent polymer comprising a fine powder reassemble, which has an excellent absorption rate and does not cause deterioration of physical properties such as water retention capacity (CRC) or Absorption Under Pressure (AUP), and a method for preparing the same.

Technical scheme

In order to accomplish the above object, the present invention provides a method of preparing a superabsorbent polymer, the method comprising the steps of:

performing thermal polymerization or photopolymerization of a monomer composition comprising a water-soluble ethylenically unsaturated monomer and a polymerization initiator to prepare an aqueous gel polymer;

drying, pulverizing and size-sorting the aqueous gel polymer to classify the aqueous gel polymer into a fine powder having a particle size of less than 150 μm and conventional particles having a particle size of 150 to 850 μm;

mixing one or more of fluff pulp and synthetic polymer fibers with a fine powder and water to prepare an aqueous fine powder solution; and

the fine powder aqueous solution was stirred to prepare a fine powder reassembled body.

The aqueous fine powder solution may contain the fiber in an amount of 1 part by weight or more to less than 20 parts by weight with respect to 100 parts by weight of the fine powder.

The length of the fibers may be 1mm to 20 mm.

The width of the fibers may be 1 μm to 100 μm.

The synthetic polymer fibers may be one or more selected from the group consisting of: nylon, polypropylene, polyethylene, polyester, polyacrylonitrile, polyvinyl chloride, polyvinyl alcohol, polyacrylate, and acetate.

The fine powder aqueous solution may contain water in an amount of 50 to 150 parts by weight with respect to 100 parts by weight of the fine powder.

The preparation method of the present invention may further comprise the steps of drying, pulverizing and size-sorting the fine powder reassembled body. In addition, the production method of the present invention may further include a step of surface-crosslinking the pulverized and size-sorted fine powder reassembler.

Further, the present invention provides a superabsorbent polymer prepared by the preparation method.

Specifically, the present invention provides a superabsorbent polymer comprising a fine powder reassembler which is reassembled by mixing fine powder having a particle size of less than 150 μm in a polymer obtained by polymerizing a water-soluble ethylenically unsaturated monomer containing an at least partially neutralized acidic group with one or more fibers of fluff pulp and synthetic polymer fibers.

At least a portion of the fibers may be incorporated into the interior of the fine powder reassembled body particles.

The fine powder reassembled body may include the fiber in an amount of 1 part by weight or more to less than 20 parts by weight with respect to 100 parts by weight of the fine powder.

The superabsorbent polymer may have a Centrifuge Retention Capacity (CRC) of from 30g/g to 45g/g as measured according to EDANA method WSP 241.3.

The superabsorbent polymer may have an Absorbency Under Load (AUL) of from 25g/g to 40g/g at 0.3psi as measured according to EDANA method WSP 242.3.

The superabsorbent polymer may have an absorption rate (vortex time) of 60 seconds or less.

Advantageous effects

According to the superabsorbent polymer and the method of preparing the same according to the present invention, it is possible to provide a high quality superabsorbent polymer having excellent basic absorption properties while exhibiting a more improved absorption rate.

Drawings

FIG. 1 is a Scanning Electron Microscope (SEM) image of a superabsorbent polymer prepared in example 3.

Detailed Description

The terms used in the present specification are used only for illustrating exemplary embodiments, and they are not intended to limit the present invention. Unless otherwise indicated in context, singular expressions may include plural expressions. It must be understood that the terms "comprises," "comprising," or "having" in this specification are used merely to specify the presence of stated features, steps, components, or combinations thereof, but do not preclude the presence or addition of one or more other features, steps, components, or combinations thereof.

The present invention is susceptible to various modifications and forms, and specific examples thereof are described in the specification. However, it is not intended to limit the present invention to the specific examples, and it must be understood that the present invention includes each modification, equivalent, or alternative included in the spirit and technical scope of the present invention.

Hereinafter, the superabsorbent polymer and the method of preparing the same will be described in more detail according to embodiments of the present invention.

The method of preparing a superabsorbent polymer according to one embodiment of the present invention may include the steps of: performing thermal polymerization or photopolymerization of a monomer composition comprising a water-soluble ethylenically unsaturated monomer and a polymerization initiator to prepare an aqueous gel polymer; drying, pulverizing and size-sorting the aqueous gel polymer to classify the aqueous gel polymer into a fine powder having a particle size of less than 150 μm and conventional particles having a particle size of 150 to 850 μm; mixing one or more of fluff pulp and synthetic polymer fibers with a fine powder and water to prepare an aqueous fine powder solution; and stirring the fine powder aqueous solution to prepare a fine powder reassembled body.

For reference, as used herein, "polymer" means the polymerized state of water-soluble ethylenically unsaturated monomers, and may encompass all ranges of water content, particle size, surface cross-linked state, or processed state of the polymer. Among the polymers, a polymer having a water content (moisture content) of about 40% by weight or more after polymerization and before drying may be referred to as a water-containing gel polymer.

Further, among the polymers, the polymer having a particle size of less than 150 μm may be referred to as "fine powder". The fine powder may encompass those generated during all processes of the method of preparing the superabsorbent polymer, such as a polymerization process, a drying process, a process of pulverizing the dried polymer, or a surface crosslinking process.

Further, "fine powder reassembled body" means a particle having a particle size of 150 μm or more, or a population of a plurality of particles, in which fine powder is aggregated.

Further, "superabsorbent polymer" means the polymer itself, depending on the context, or is intended to encompass those made suitable for commercialization by additional processes such as surface crosslinking, reassembly of fines, drying, size reduction, size sorting, and the like.

In the method of preparing a superabsorbent polymer of the present invention, thermal polymerization or photopolymerization of a monomer composition including a water-soluble ethylenically unsaturated monomer and a polymerization initiator is first performed to form an aqueous gel polymer.

The monomer composition as a raw material of the superabsorbent polymer includes a water-soluble ethylenically unsaturated monomer and a polymerization initiator.

As the water-soluble ethylenically unsaturated monomer, any monomer generally used for preparing the superabsorbent polymer may be not particularly limited. Here, any one or more monomers selected from the following may be used: anionic monomers and salts thereof, nonionic hydrophilic monomers, and amino group-containing unsaturated monomers and quaternization products thereof.

In particular, one or more selected from the following may be used: anionic monomers such as (meth) acrylic acid, maleic anhydride, fumaric acid, crotonic acid, itaconic acid, 2-acryloylethanesulfonic acid, 2-methacryloylethanesulfonic acid, 2- (meth) acryloylpropanesulfonic acid, or 2- (meth) acrylamide-2-methylpropanesulfonic acid, and salts thereof; a nonionic hydrophilic monomer such as (meth) acrylamide, N-substituted (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, or polyethylene glycol (meth) acrylate; and amino group-containing unsaturated monomers such as (N, N) -dimethylaminoethyl (meth) acrylate or (N, N) -dimethylaminopropyl (meth) acrylamide, and quaternized products thereof.

More preferably, acrylic acid or a salt thereof, for example, acrylic acid or an alkali metal salt thereof such as a sodium salt thereof, may be used. When these monomers are used, a superabsorbent polymer having more excellent physical properties can be prepared. When an alkali metal salt of acrylic acid is used as a monomer, acrylic acid may be used after neutralization with an alkaline compound such as caustic soda (NaOH).

The concentration of the water-soluble ethylenically unsaturated monomer may be about 20% by weight to about 60% by weight, preferably about 40% by weight to about 50% by weight, relative to the monomer composition and the solvent of the raw material containing the superabsorbent polymer, and the concentration may be appropriately controlled by considering polymerization time, reaction conditions, and the like. If the concentration of the monomer is too low, the yield of the superabsorbent polymer may become low and there may be a problem in economic efficiency. Conversely, if the concentration of monomer is too high, the following process problems exist: a part of the monomer precipitates or the pulverization efficiency is reduced when the polymerized aqueous gel polymer is pulverized, and the physical properties of the superabsorbent polymer may be reduced.

As the polymerization initiator used during the polymerization of the method of preparing a superabsorbent polymer of the present invention, a polymerization initiator generally used for preparing a superabsorbent polymer may be used without particular limitation.

Specifically, the polymerization initiator may be a thermal polymerization initiator or a photopolymerization initiator by UV irradiation, depending on the polymerization method. However, even in the case of using the photopolymerization method, since a certain amount of heat is generated by ultraviolet irradiation or the like and a certain degree of heat is generated according to the progress of the exothermic polymerization reaction, a thermal polymerization initiator may be additionally included.

In view of the constitution, the photopolymerization initiator may be used without limitation as long as it is a compound capable of forming radicals by light such as UV rays.

The photopolymerization initiator may include, for example, one or more initiators selected from the group consisting of: benzoin ethers, dialkyl acetophenones, hydroxy alkyl ketones, phenyl glyoxylates, benzyl dimethyl ketals, acyl phosphines and alpha-amino ketones. Meanwhile, specific examples of the acylphosphine may include commercially available lucirin TPO, i.e., 2,4, 6-trimethyl-benzoyl-trimethylphosphine oxide. Further different photopolymerization initiators are well disclosed on page 115 of "UV Coatings: bases, recountdevelopments and New Application (Elsevier, 2007)" written by Reinhold Schwalm, however, the photopolymerization initiators are not limited to the above examples.

The photopolymerization initiator may be included at a concentration of about 0.01 wt% to about 1.0 wt% with respect to the monomer composition. When the concentration of the photopolymerization initiator is too low, the polymerization rate may become low, and when the concentration of the photopolymerization initiator is too high, the molecular weight of the superabsorbent polymer becomes small and the physical properties thereof may become non-uniform.

Further, as the thermal polymerization initiator, one or more initiators selected from the group consisting of: persulfate-based initiators, azo-based initiators, hydrogen peroxide, and ascorbic acid. Specific examples of the persulfate-based initiator may include sodium persulfate (Na)₂S₂O₈) Potassium persulfate (K)₂S₂O₈) Ammonium persulfate ((NH)₄)₂S₂O₈) And the like, examples of the azo-based initiator may include 2, 2-azobis- (2-amidinopropane) dihydrochloride, 2-azobis- (N,n-dimethylene) isobutyramidine dihydrochloride, 2- (carbamoylazo) isobutyronitrile, 2-azobis [2- (2-imidazolin-2-yl) propane]Dihydrochloride, 4-azobis- (4-cyanovaleric acid), and the like. More various thermal Polymerization initiators are well disclosed in "principles of Polymerization (Wiley, 1981)" page 203 written by Odian, however, the thermal Polymerization initiators are not limited to the above examples.

The thermal polymerization initiator may be included at a concentration of about 0.001 wt% to about 0.5 wt% with respect to the monomer composition. When the concentration of the thermal polymerization initiator is too low, additional thermal polymerization hardly occurs, and thus the effect caused by the addition of the thermal polymerization initiator may not be significant, and when the concentration of the thermal polymerization initiator is too high, the molecular weight of the superabsorbent polymer becomes small and the physical properties may become uneven.

According to an embodiment of the present invention, the monomer composition may further include an internal crosslinking agent as a raw material of the superabsorbent polymer. As the internal crosslinking agent, a crosslinking agent having one or more functional groups reactive with the water-soluble substituent group of the water-soluble ethylenically unsaturated monomer and one or more soluble ethylenically unsaturated groups; or a crosslinking agent having two or more functional groups reactive with the water-soluble substituents of the monomer and/or the water-soluble substituents formed by hydrolysis of the monomer.

Specific examples of the internal crosslinking agent may include one or more selected from the group consisting of: bisacrylamide having 8 to 12 carbon atoms, bismethacrylamide, poly (meth) acrylate esters of polyols having 2 to 10 carbon atoms, or poly (meth) allyl ethers of polyols having 2 to 10 carbon atoms. More specific examples thereof may include one or more selected from the group consisting of: n, N' -methylenebis (meth) acrylate, ethyleneoxy (meth) acrylate, polyethyleneoxy (meth) acrylate, propyleneoxy (meth) acrylate, glycerol diacrylate, glycerol triacrylate, trimethyloltriacrylate, triallylamine, triarylcyanurate, triallylisocyanate, polyethylene glycol, diethylene glycol, and propylene glycol.

The internal crosslinking agent may be included at a concentration of about 0.01 wt% to about 0.5 wt% relative to the monomer composition, thereby crosslinking the polymerized polymer.

In the preparation method of the present invention, the monomer composition of the superabsorbent polymer may further include additives such as a thickener, a plasticizer, a preservation stabilizer, an antioxidant, and the like, if necessary.

Raw materials such as the above-mentioned water-soluble ethylenically unsaturated monomer, photopolymerization initiator, thermal polymerization initiator, internal crosslinking agent and additives may be prepared in the form of a solution in which the monomer composition is dissolved in a solvent.

As the usable solvent, any solvent may be used without limitation in view of the constitution as long as it can dissolve the above components, for example, one or more selected from the following may be used in combination: water, ethanol, ethylene glycol, diethylene glycol, triethylene glycol, 1, 4-butanediol, propylene glycol, ethylene glycol monobutyl ether, propylene glycol monomethyl ether acetate, methyl ethyl ketone, acetone, methyl amyl ketone, cyclohexanone, cyclopentanone, diethylene glycol monomethyl ether, diethylene glycol diethyl ether, toluene, xylene, butyrolactone, carbitol, methyl cellosolve acetate, and N, N-dimethylacetamide.

The solvent may be included in a residual amount excluding the above components from the total weight of the monomer composition.

Meanwhile, in view of the constitution, thermal polymerization or photopolymerization of the monomer composition is not particularly limited as long as it is a commonly used polymerization method.

Specifically, polymerization methods are roughly classified into thermal polymerization and photopolymerization according to the polymerization energy source. Thermal polymerization can be generally carried out in a reactor equipped with an agitating shaft (such as a kneader), while photopolymerization can be carried out in a reactor equipped with a movable conveyor belt. The above polymerization method is only an example, and the present invention is not limited to the above polymerization method.

For example, an aqueous gel polymer can be obtained by: the thermal polymerization is carried out while supplying hot air to the above-mentioned reactor equipped with a stirring shaft, such as a kneader or heating the reactor. Depending on the type of stirring shaft provided in the reactor, the aqueous gel polymer may have a size of centimeters or millimeters when it is discharged from the reactor outlet. Specifically, the size of the obtained aqueous gel polymer may vary depending on the concentration of the monomer composition fed thereto, the feeding speed, and the like, and generally an aqueous gel polymer having a weight average particle size of 2mm to 50mm may be obtained.

Further, as described above, when photopolymerization is performed in a reactor equipped with a movable conveyor belt, the obtained water-containing gel polymer may be generally a sheet-like water-containing gel polymer having a width of the belt. In this case, the thickness of the polymer sheet may vary depending on the concentration of the monomer composition fed thereto and the feeding speed. Generally, it is preferable to supply the monomer composition so that a sheet-like polymer having a thickness of about 0.5cm to about 5cm can be obtained. When the monomer composition is supplied to such an extent that the thickness of the sheet-like polymer becomes too thin, it is undesirable due to low production efficiency, and when the thickness of the sheet-like polymer is more than 5cm, the polymerization reaction may not occur uniformly throughout the thickness due to an excessive thickness.

The water content of the aqueous gel polymer obtained by the above method may be about 40% to about 80% by weight. Meanwhile, "water content" as used herein means the weight of water relative to the total weight of the aqueous gel polymer, which may be a value obtained by subtracting the weight of the dried polymer from the weight of the aqueous gel polymer. Specifically, the water content may be defined as a value calculated by measuring weight loss caused by evaporation of water in the polymer during the process of drying by raising the temperature of the polymer by infrared heating. At this time, the water content was measured under the drying conditions determined as follows: the drying temperature was increased from room temperature to about 180 ℃ and then the temperature was maintained at 180 ℃, and the total drying time was set to 20 minutes, including 5 minutes of the temperature increase step.

Subsequently, the aqueous gel polymer is coarsely pulverized.

In this regard, the pulverizer used herein is not limited by its configuration, and specifically, it may include any one selected from the group consisting of: vertical mills, turbo cutters, turbo grinders, rotary shredders (rotary mill), shredders (chopper mill), disc mills, chip breakers, crushers, shredders (choppers), and disc cutters, but are not limited to the above examples.

In this regard, the coarse pulverization step may be performed such that the particle size of the aqueous gel polymer becomes about 2mm to about 20 mm.

Due to the high water content of the aqueous gel polymer, it is technically not easy to coarsely pulverize it to a particle size of less than 2mm, and agglomeration between pulverized particles may occur. Meanwhile, if the polymer is coarsely pulverized to a particle size of more than 20mm, the effect of improving efficiency in a subsequent drying step may not be significant.

Subsequently, the obtained hydrous gel polymer is dried.

The aqueous gel polymer coarsely pulverized as above, or the aqueous gel polymer immediately after polymerization without being subjected to the coarsely pulverizing step is subjected to a drying step. In this regard, the drying temperature of the drying step may be about 150 ℃ to about 250 ℃. If the drying temperature is less than 150 ℃, the drying time becomes too long and the physical properties of the final superabsorbent polymer may deteriorate. If the drying temperature is higher than 250 ℃, only the polymer surface is excessively dried, and thus fine powder may be generated during a subsequent pulverizing process and physical properties of the finally formed superabsorbent polymer may be deteriorated. Thus, drying may be carried out at a temperature of from about 150 ℃ to about 200 ℃, and more preferably at a temperature of from about 160 ℃ to about 180 ℃.

Meanwhile, the drying step may be performed for about 20 minutes to about 90 minutes in consideration of process efficiency, but is not limited thereto.

In the drying step, any drying method may be selected and used without limitation in consideration of the constitution, as long as it is generally used in the process of drying the aqueous gel polymer. Specifically, the drying step may be performed by a method such as hot air supply, infrared irradiation, microwave irradiation, or ultraviolet irradiation. When the drying step is complete as above, the water content of the polymer may be from about 0.1% to about 10% by weight.

Next, the dried mixture obtained by the drying step is pulverized.

The particle size of the polymer powder obtained by the pulverization step may be about 150 μm to about 850 μm. Specific examples of the pulverizer that can be used to achieve the above particle size may include a pin mill, a hammer mill, a screw mill, a roll mill, a disc mill, a jog mill, and the like, but the present invention is not limited thereto.

In order to control the physical properties of the superabsorbent polymer powder finally commercialized after the pulverization step, the polymer powder obtained after the pulverization is generally size-classified according to particle size. Preferably, the polymer powder is selected from the group consisting of polymers having a particle size of less than about 150 μm, polymers having a particle size of from about 150 μm to about 850 μm, and polymers having a particle size of greater than about 850 μm.

In the present invention, fine powder particles having a particle size smaller than a predetermined particle size, i.e., a particle size smaller than about 150 μm, are referred to as superabsorbent polymer fine powder, SAP fine powder, or fine powder (fines). Particles having a particle size of about 150 μm to about 850 μm are referred to as conventional particles. The fine powder may be generated during a polymerization process, a drying process, or a pulverization step of the dried polymer. If fine powder is contained in the final product, it is difficult to handle and physical properties may be deteriorated, for example, a gel blocking phenomenon and the like may occur. Thus, fines are preferably excluded so that the final polymer product does not contain fines or the fines are reused in conventional granules.

In the present invention, the fine powder is agglomerated to the size of conventional particles, thereby forming a fine powder reassemble of the superabsorbent polymer.

More specifically, the fine powder reassembly is performed by: the fine powder reassembled body is prepared by mixing one or more fibers of fluff pulp and synthetic polymer fibers with fine powder and water to prepare an aqueous fine powder solution, and then stirring the prepared aqueous fine powder solution to aggregate the above materials.

At this time, the moisture content of the fine powder may be 40% to 60%. The aggregation strength of the fine powder may increase as the moisture content of the fine powder is higher. However, in the reassembly process, a large reassembled piece or a reassembled piece (colloidal sphere) in a solid aggregated state due to the fine powder partially containing a large amount of moisture may occur, which may cause a problem in the operation of the subsequent pulverization process. In addition, when the moisture content of the fine powder is too low, the reassembly process is easy, but the aggregation strength is low, and thus the polymer is easily broken into fine powder again after the reassembly. Therefore, the water content preferably satisfies the above range.

Fluff pulp is cellulosic fluff pulp and can be, but is not limited to, wood fluff pulp, such as softwood kraft and hardwood kraft pulp. Fluff pulp used in absorbent articles can be used without limitation.

The synthetic polymer fibers may be one or more selected from the group consisting of: nylon, polypropylene, polyethylene, polyester, polyacrylonitrile, polyvinyl chloride, polyvinyl alcohol, polyacrylate, and acetate. Since the synthetic polymer fiber has excellent moisture absorption characteristics and the width or length of the fiber can be easily controlled, the physical properties of the superabsorbent polymer can be easily controlled.

The length of the fibers may preferably be 1mm to 20 mm. Further, the width of the fiber may preferably be 1 μm to 100 μm. If the length of the fiber is too short or the width of the fiber is too narrow, it is difficult to ensure the effect of improving the absorption rate of the fine powder reassembled body. Conversely, if the length of the fiber is too long or the width of the fiber is too wide, it is difficult to introduce the fiber into the fine powder reassembled body.

In this regard, the length of the fibers may preferably be 2mm or more, or 3mm or more, and 15mm or less, or 10mm or less. For example, fibers having an average length of 3mm to 10mm in which the length of each fiber satisfies a range of 1mm to 20mm may be preferably used. Here, the average length of the fibers can be obtained by: 100 fibers were randomly selected, the length of each fiber was measured, and the average thereof was calculated.

Further, the width of the fibers may be 5 μm or more, or 10 μm or more, and 80 μm or less, or 50 μm or less.

In the step of forming the fine powder reassembled body, the content of the fiber in the aqueous fine powder solution may be 1 part by weight or more, 2 parts by weight or more, or 5 parts by weight or more, and less than 20 parts by weight, 15 parts by weight or less, or 10 parts by weight or less, relative to 100 parts by weight of the fine powder. If the content of the fiber is less than 1 part by weight with respect to 100 parts by weight of the fine powder, the effect of improving the absorption rate of the fine powder reassembled body due to the fluff pulp cannot be secured. If the content of the fiber is 20 parts by weight or more with respect to 100 parts by weight of the fine powder, the absorption rate is improved, but basic absorption properties such as water retention capacity, absorption under load, and the like may be lowered.

Meanwhile, the aqueous solution of the fine powder contains water, and the content of water may be 50 parts by weight to 150 parts by weight, or 70 parts by weight to 150 parts by weight, with respect to 100 parts by weight of the fine powder. If the content of water is more than 150 parts by weight with respect to 100 parts by weight of the fine powder, the reassembled block may be too large, or colloidal spheres may appear, as described above. If the content of water is less than 50 parts by weight with respect to 100 parts by weight of the fine powder, the aggregation strength of the prepared reassembled body may be reduced.

In one embodiment, the aqueous fine powder solution may be prepared by: the fines and fibers are first dry-blended before the water is added, then water is added and the mixture is stirred. As noted, when water is added after dry mixing the fines and fibers, it is preferred that the fibers be more uniformly dispersed in the fines reassembled.

Then, the prepared fine powder aqueous solution is mixed to form a fine powder reassembled body. The method of mixing the aqueous solution of the fine powder is not particularly limited, but may be performed, for example, by stirring at a temperature of 25 ℃ to 100 ℃ and a speed of 200rpm to 2000rpm for 5 seconds to 60 seconds.

According to an embodiment of the present invention, the steps of drying, pulverizing and size-sorting the obtained fine powder reassembled body may be further included.

The step of drying the fine powder reassembled body may be performed at a temperature of 150 ℃ to 250 ℃ for 20 minutes to 90 minutes. Further, in view of the constitution, the means for raising the temperature for drying is not particularly limited. Specifically, the heating medium may be supplied or the heating may be directly performed by such as electric, but the present invention is not limited to the above example. Specifically, applicable heat sources may include steam, electricity, ultraviolet rays, infrared rays, etc., and heated thermal fluid, etc., may be used.

The dried fine powder reassembled body may then be pulverized to have a particle size of about 150 μm to about 850 μm. Specific examples of the pulverizer that can be used to achieve the above particle size may include a pin mill, a hammer mill, a screw mill, a roll mill, a disc mill, a jog mill, and the like, but the present invention is not limited to the above examples.

In addition, the fine powder reassembled body obtained after pulverization may be sorted into particles having a particle size of less than about 150 μm, particles having a particle size of about 150 μm to about 850 μm, and particles having a particle size of greater than about 850 μm.

The size-sorted fine powder reassembles can be subjected to a surface cross-linking process either alone or in admixture with other conventional particles (particles having a particle size of 150 μm to 850 μm).

The surface crosslinking step is to increase the crosslink density near the surface of the superabsorbent polymer particles relative to the crosslink density inside the particles. Typically, the surface cross-linking agent is applied to the surface of the superabsorbent polymer particles. Thus, the reaction occurs on the surface of the superabsorbent polymer particles, which improves the crosslinkability on the surface of the particles without substantially affecting the interior of the particles. Thus, surface crosslinked superabsorbent polymer particles have a higher degree of crosslinking near the surface than inside the surface.

Here, in view of the constitution, the surface cross-linking agent is not limited as long as it is a compound capable of reacting with the functional group of the polymer.

Preferably, in order to improve the characteristics of the superabsorbent polymer to be prepared, the surface cross-linking agent may include one or more selected from the group consisting of: a polyol compound; an epoxy compound; a polyamine compound; a halogenated epoxy compound; condensation products of halogenated epoxy compounds;an oxazoline compound; sheet

Oxazolidinone, di

Oxazolidinones or polypeptidesAn oxazolidinone compound; a cyclic urea compound; a polyvalent metal salt; and an alkylene carbonate compound.

Specific examples of the polyol compound may include one or more selected from the group consisting of: monoethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol or polyethylene glycol, monopropylene glycol, 1, 3-propanediol, dipropylene glycol, 2,3, 4-trimethyl-1, 3-pentanediol, polypropylene glycol, glycerol, polyglycerol, 2-butene-1, 4-diol, 1, 4-butanediol, 1, 3-butanediol, 1, 5-pentanediol, 1, 6-hexanediol and 1, 2-cyclohexanedimethanol.

Further, the epoxy compound may be ethylene glycol diglycidyl ether, glycidyl, and the like. The polyamine compound may be one or more selected from the group consisting of: ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, polyethyleneimine and polyamide polyamine.

Further, the halogenated epoxy compounds may be epichlorohydrin, epibromohydrin, and α -methyl epichlorohydrinOxazolidinone, di

Oxazolidinones or polypeptidesExamples of the oxazolidinone compound may include 2-Oxazolidinones, and the like.

Further, examples of the alkylene carbonate compound may include ethylene carbonate and the like. These compounds may be used alone or in combination thereof. Meanwhile, in order to increase the efficiency of the surface crosslinking process, among the surface crosslinking agents, one or more polyol compounds are preferably included, and more preferably, a polyol compound having 2 to 10 carbon atoms.

The content of the surface cross-linking agent to be added may be appropriately selected according to the kind of the surface cross-linking agent to be added or the reaction conditions, but may be generally about 0.001 to 5 parts by weight, preferably about 0.01 to about 3 parts by weight, and more preferably about 0.03 to about 2 parts by weight, relative to 100 parts by weight of the polymer.

If the content of the surface cross-linking agent is too small, the surface cross-linking reaction hardly occurs. If the content of the surface cross-linking agent is more than 5 parts by weight with respect to 100 parts by weight of the polymer, the absorption capacity and physical properties may be deteriorated due to an excessive surface cross-linking reaction.

The surface crosslinking reaction and drying may be simultaneously performed by heating the polymer particles to which the surface crosslinking agent is added.

The means for raising the temperature for the surface crosslinking reaction is not particularly limited. Heating may be performed by providing a heating medium or by directly providing a heat source. In this regard, the kind of the heating medium that may be used may be a hot fluid such as steam, hot air, hot oil, etc., but the present invention is not limited thereto. The temperature of the heating medium to be supplied may be appropriately controlled in consideration of the manner of heating the medium, the heating rate, and the target temperature. Meanwhile, as the heat source to be directly provided, an electric heater or a gas heater may be used, but the present invention is not limited to these examples.

The fine powder reassembled body prepared by the above method contains fibers having excellent moisture absorption characteristics, thereby exhibiting excellent basic absorption characteristics while having a very excellent absorption rate. In other words, according to the present invention, since the fiber having hygroscopic property is mixed with the fine powder during the step of reassembling the fine powder, at least a part of the fiber can be incorporated into the interior of the fine powder reassembling body particle, and compared to a composite in which the fine powder reassembling body and the fiber having hygroscopic property are simply mixed with each other, the fiber thus incorporated rapidly absorbs surrounding moisture and transfers it to the fine powder reassembling body, thereby having a significantly improved absorption rate.

Thus, according to one embodiment of the present invention, there is provided a superabsorbent polymer comprising a fine powder reassembler which is reassembled by mixing fine powder having a particle size of less than 150 μm in a polymer obtained by polymerizing a water-soluble ethylenically unsaturated monomer containing at least partially neutralized acidic groups with one or more fibers of fluff pulp and synthetic polymer fibers.

In the fine powder reassembled body contained in the superabsorbent polymer, at least a portion of the fibers may be incorporated into the interior of the fine powder reassembled body particles. In other words, the fibers are distributed inside and outside the particles of the fine powder reassembler and quickly absorb the surrounding moisture and transfer it to the fine powder reassembler particles, thereby contributing to an improvement in the absorption rate.

The fine powder reassemble may include fibers in an amount of 1 part by weight or greater, 2 parts by weight or greater, or 5 parts by weight or greater, and less than 20 parts by weight, 15 parts by weight or less, or 10 parts by weight or less, relative to 100 parts by weight of the fine powder. When the content of the fibers satisfies the above range, improvement in absorption rate can be ensured while maintaining excellent basic absorption characteristics such as water retention capacity, absorption under load, and the like.

The Centrifuge Retention Capacity (CRC) of the superabsorbent polymer, as measured according to EDANA method WSP 241.3, can be in the range of about 30g/g or more, 32g/g or more, or about 33g/g or more and about 45g/g or less, about 40g/g or less, or about 35g/g or less.

Further, the superabsorbent polymer can have an Absorbency Under Load (AUL) at 0.3psi of 25g/g or greater, or 27g/g or greater, and 40g/g or less, or 30g/g or less, as measured according to EDANA method WSP 242.3.

Further, the absorption rate (vortex time) of the superabsorbent polymer may be 60 seconds or less, or 50 seconds or less, as measured after adding 2g of the superabsorbent polymer to 50mL of physiological saline at 23 ℃ to 24 ℃, stirring a magnetic rod (8 mm in diameter and 31.8mm in length) at 600rpm, and measuring the time (seconds) taken for vortex loss. A lower absorption rate means that the superabsorbent polymer is more excellent. Therefore, the lower limit is not limited, but is, for example, 10 seconds or longer, or 20 seconds or longer.

Hereinafter, the present invention will be described in more detail with reference to examples. However, the following examples are only for illustrating the present invention, and the contents of the present invention are not limited to the following examples. In addition, "%" and "part(s)" representing the contents are "wt%" and "part(s) by weight", respectively, in the following examples and comparative examples, unless otherwise specified.

< example >

Preparation example 1

100g of acrylic acid, 3.0g of polyethylene glycol diacrylate (PEGDA, Mw 523) as a crosslinking agent, 0.008g of phenyl bis (2,4, 6-trimethylbenzoyl) phosphine oxide as a photoinitiator, 0.08g of Sodium Persulfate (SPS) as a thermal initiator, 128g of caustic soda (NaOH) and 63.5g of water were mixed with one another. To the mixture, each fiber in table 1 below was added in an amount of 5 parts by weight with respect to 100 parts by weight of the monomer composition, thereby preparing a monomer composition.

Thereafter, the monomer composition was placed on a continuously moving conveyor belt and irradiated by UV (UV intensity: 2 mW/cm)²) The UV was allowed to polymerize for 2 minutes to obtain an aqueous gel polymer sheet.

The aqueous gel polymer sheet was cut into a size of 3cm × 3cm and minced using a meat chopper (hole size of 16mm, speed of 60Hz) to prepare chips. The chips are dried in an oven that moves the airflow up and down. Specifically, the crumb was uniformly dried by flowing hot air at 185 ℃ for 15 minutes from bottom to top and 15 minutes from top to bottom, so that the moisture content of the dried product was 2% or less.

The dried polymer was pulverized using a pulverizer, and then classified for 10 minutes at an amplitude of 1.5mm (mesh number combination: #20/#30/#50/# 100). Conventional particles having a particle size of 150 to 850 μm and fine powder particles having a particle size of less than 150 μm are obtained.