Composition for producing superabsorbent resin and method for producing superabsorbent resin using the same

Abstract

The present invention provides a composition for producing a superabsorbent polymer and a method for producing a superabsorbent polymer using the same. The composition for producing a superabsorbent polymer of the present invention contains clay, and the clay is uniformly dispersed in the composition, exhibiting a low sedimentation rate and excellent dispersion stability even during long-term storage. Therefore, the composition for producing a superabsorbent polymer can be used to produce a superabsorbent polymer having excellent water absorption properties.

Description

[Technical field]

[0001] [CROSS REFERENCE TO RELATED APPLICATIONS] This application claims the benefit of priority based on Korean Patent Application No. 10-2023-0028618 filed on March 3, 2023 and Korean Patent Application No. 10-2024-0030239 filed on February 29, 2024, and all contents disclosed in the documents of said Korean patent applications are incorporated herein by reference.

[0002] The present invention relates to a composition for producing a superabsorbent resin, which has excellent clay dispersion stability, and a method for producing a superabsorbent resin using the clay dispersion. [Background technology]

[0003] Superabsorbent polymers (SAPs) are synthetic polymeric substances capable of absorbing 500 to 1,000 times their own weight in water. They first came into practical use as sanitary products, and are now widely used in sanitary products such as disposable diapers for babies and sanitary products, as well as in soil water retention agents for horticulture, waterproofing materials for civil engineering and construction, seedling sheets, freshness-preserving agents in the food distribution sector, and materials for compresses.

[0004] Attempts have been made to introduce additives to improve basic physical properties such as centrifuge retention capacity (CRC) and absorption under pressure (AUP) of superabsorbent polymers, and clay is one such additive. However, clay particles have a tendency to aggregate with each other in a solution with a high ion concentration, making it difficult to ensure dispersion stability. Therefore, it is difficult to uniformly disperse clay in a monomer composition for producing superabsorbent polymers, and as a result, the aggregated clay is distributed unevenly in particulate form in the produced superabsorbent polymer, resulting in a problem that it is difficult to obtain the effect of improving the physical properties of the superabsorbent polymer.

[0005] Therefore, there is a demand for the development of a clay dispersion that exhibits excellent dispersibility in a composition for producing a superabsorbent resin and can improve the physical properties of the superabsorbent resin. Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention provides a composition for producing a superabsorbent resin, which contains clay, in which the clay is uniformly dispersed, and which has excellent dispersion stability of the clay even during long-term storage.

[0007] The present invention also provides a method for producing a superabsorbent resin using the composition for producing a superabsorbent resin. [Means for solving the problem]

[0008] According to one embodiment of the present invention, there is provided a composition for producing a superabsorbent resin, comprising: clay; a polymeric dispersant containing two or more functional groups selected from the group consisting of an amine group, a carbonyl group, and a hydroxyl group; a water-soluble ethylenically unsaturated monomer having acidic groups, at least a portion of which has been neutralized; and a polymerization initiator; and the polymeric dispersant is contained in an amount of more than 20 parts by weight to 200 parts by weight or less relative to 100 parts by weight of the clay.

[0009] According to another embodiment of the present invention, there is provided a method for producing a superabsorbent polymer, comprising: irradiating the composition for producing a superabsorbent polymer with heat and / or light to cause a polymerization reaction to produce a hydrogel polymer; drying and pulverizing the hydrogel polymer to produce a base resin; and additionally crosslinking the surface of the base resin in the presence of a surface crosslinking agent to form a surface crosslinked layer.

[0010] According to another embodiment of the present invention, there is provided a highly water-absorbent resin comprising: a crosslinked polymer of a water-soluble ethylenically unsaturated monomer having acidic groups, at least a portion of which has been neutralized; and a clay whose surface has been modified with a polymeric dispersant containing two or more functional groups selected from the group consisting of an amine group, a carbonyl group, and a hydroxyl group; and the polymeric dispersant is contained in an amount of more than 20 parts by weight to 200 parts by weight per 100 parts by weight of the clay. Effect of the Invention

[0011] The composition for producing a superabsorbent polymer of the present invention contains clay, has a slow settling rate of clay particles, and exhibits excellent dispersion stability even during long-term storage. Therefore, the composition for producing a superabsorbent polymer is excellent in water absorption properties such as centrifugal water retention capacity and pressure water absorption capacity, and can be usefully used for producing a superabsorbent polymer having improved gel strength. In addition, the superabsorbent polymer produced using the composition for producing a superabsorbent polymer exhibits excellent color properties without the risk of discoloration. [Brief description of the drawings]

[0012] [Figure 1] 3 shows photographs taken 48 hours after production of compositions for producing superabsorbent resins of Examples 1-1 to 1-3 (respectively referred to as Examples 1 to 3), Comparative Examples 1-3 and 1-4 (respectively referred to as Comparative Examples 3 and 4). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] The terms used in this specification are merely used to describe exemplary embodiments and are not intended to limit the present invention. A singular expression includes a plural expression unless the context clearly indicates otherwise. In this specification, the terms "include", "comprise", "have" and the like are intended to specify the presence of an implemented feature, step, component, or combination thereof, and should be understood not to preclude the possibility of the presence or addition of one or more other features, steps, components, or combinations thereof.

[0014] Although the present invention can be modified in various ways and has various forms, specific embodiments are exemplified and described in detail below. However, it is not intended to limit the present invention to the specific disclosed embodiments, and it should be understood that the present invention includes all modifications, equivalents, and alternatives falling within the spirit and technical scope of the present invention.

[0015] In this specification, the term "clay" is used to encompass both single particles of phyllosilicate minerals and aggregates of a large number of such particles, and the term "clay dispersion" refers to a dispersion in which the clay is dispersed in a solvent.

[0016] In this specification, the term "(meth)acrylate" is used to include both acrylate and methacrylate.

[0017] In this specification, the term "base resin" or "base resin powder" refers to a polymer obtained by drying and pulverizing a polymer obtained by polymerizing a water-soluble ethylenically unsaturated monomer into a particle or powder form, and is not surface-modified or surface-crosslinked.

[0018] The present invention will be described in detail below.

[0019] According to one embodiment of the present invention, there is provided a composition for producing a superabsorbent resin, comprising: clay; a polymeric dispersant containing two or more functional groups selected from the group consisting of an amine group, a carbonyl group, and a hydroxyl group; a water-soluble ethylenically unsaturated monomer having acidic groups, at least a portion of which has been neutralized; and a polymerization initiator; and the polymeric dispersant is contained in an amount of more than 20 parts by weight to 200 parts by weight or less relative to 100 parts by weight of the clay.

[0020] The composition for producing a superabsorbent polymer exhibits the effect of significantly improving the dispersion stability of clay by the polymer dispersant containing two or more functional groups selected from the group consisting of an amine group, a carbonyl group, and a hydroxyl group. Clay has a layered structure in which layers of small silicate plates with a thickness of about 1 nm are stacked on top of each other due to strong van der Waals attractive forces between them, but the polymer dispersant bonds to the surface of the clay and exfoliates the silicate layers (i.e., spreads the interlayer distance to more than 1 nm). Since the clay chemically exfoliated in this way exhibits significantly improved dispersion stability, the clay particles do not aggregate or settle when the clay dispersion is contained in a composition for producing a superabsorbent polymer containing an alkali metal salt or a basic compound, and can be uniformly dispersed in the composition.

[0021] Therefore, the superabsorbent polymer produced using the composition for producing a superabsorbent polymer can have improved water absorption properties such as centrifugal water retention capacity, pressure water absorption capacity, etc. In addition, since the polymer dispersant does not cause discoloration of the superabsorbent polymer, a high-quality superabsorbent polymer having excellent water absorption properties and color characteristics can be produced using the composition for producing a superabsorbent polymer of the present invention.

[0022] The clay may be a swelling or non-swelling clay. The swelling clay is a layered organic material having water absorption ability, and may be montmorillonite, saponite, nontronite, laponite, beidellite, hectorite, vermiculite, magadiite, bentonite, etc., while the non-swelling clay may be kaolin, serpentine, mica, etc. The clay may be used alone or in combination of two or more kinds.

[0023] The clay may have an average particle size (D50) of 0.025 μm or more, or 0.05 μm or more, or 0.1 μm or more, or 1 μm or more and 10 μm or less, or 8 μm or less, or 5 μm or less. If the average particle size (D50) of the clay is less than 0.025 μm, the gel strength of the superabsorbent resin cannot be sufficiently improved. If the average particle size (D50) of the clay exceeds 10 μm, the clay is difficult to disperse uniformly in the water system due to the strong interlayer attraction, and it is difficult to modify the surface of the clay uniformly, which may result in a problem that transparency is not ensured after dispersion.

[0024] Here, "particle size Dn" means the particle size at n% of the cumulative particle number distribution according to the particle size, and D50 is the particle size at 50% of the cumulative particle number distribution according to the particle size. The average particle size (D50) of the clay can be measured by laser diffraction and dynamic light scattering using a particle size analyzer. Specifically, the powder to be measured is dispersed in a dispersion medium and then introduced into a commercially available laser diffraction particle size measuring device (e.g., Malvern's Mastersizer 3000), and when the particles pass through a laser beam, the difference in the diffraction pattern according to the particle size is measured to calculate the particle size distribution. D50 can be measured by calculating the particle size at 50% of the cumulative particle number distribution according to the particle size in the measuring device.

[0025] The polymer dispersant contains two or more functional groups selected from the group consisting of an amine group, a carbonyl group, and a hydroxyl group, and is used in an amount of more than 20 parts by weight to 200 parts by weight based on 100 parts by weight of the clay.

[0026] In this specification, "two or more functional groups selected from the group consisting of amine groups, carbonyl groups, and hydroxyl groups" is used to mean functional groups in which two or more of amine groups, carbonyl groups, and hydroxyl groups are combined, such as amide groups that simultaneously contain amine groups and carbonyl groups, and carboxyl groups that simultaneously contain carbonyl groups and hydroxyl groups. As an example, a "polymer dispersant containing an amine group and a carbonyl group" may be one that contains both an amine group and a carbonyl group in the molecule, or one that contains an amide group that combines an amine group and a carbonyl group.

[0027] The polymer dispersant containing the functional group may be bonded to the surface of clay through the non-shared electrons of nitrogen and oxygen atoms, and may induce charges in the polymer through the resonance phenomenon in a composition for producing a superabsorbent polymer with a high ion concentration. Due to these characteristics, the polymer dispersant can exfoliate the layered structure of clay to improve dispersibility. In addition, the polymer dispersant can be suitably used in the production of a superabsorbent polymer since it does not cause discoloration or deterioration of the physical properties of the superabsorbent polymer.

[0028] From this viewpoint, the polymer dispersant preferably contains an amine group and a carbonyl group; or a carbonyl group and a hydroxyl group. More preferably, the polymer dispersant may contain an amide group and / or a carboxyl group.

[0029] Specific examples of the polymer dispersant include one or more selected from the group consisting of polyvinylpyrrolidone, polyacrylamide, and polyacrylic acid. Preferably, the polymer dispersant is polyvinylpyrrolidone.

[0030] The molecular weight of the polymer dispersant is not particularly limited, but for example, a polymer dispersant having a weight average molecular weight of 2,500 g / mol or more, 5,000 g / mol or more, or 10,000 g / mol or more and 200,000 g / mol or less, 100,000 g / mol or less, or 40,000 g / mol or less can be used. If the weight average molecular weight of the polymer dispersant is less than 2,500 g / mol, when the polymer dispersant is bonded to the surface of the clay, it is difficult to sufficiently expand the interlayer distance of the clay silicate to peel it off, which may cause problems in terms of ensuring dispersibility and long-term stability, and if it exceeds 200,000 g / mol, there are process difficulties and it is not effective in modifying the surface of the clay, so it is preferable to satisfy the above range.

[0031] The weight average molecular weight of the polymeric dispersant can be measured using gel permeation chromatography (GPC) using polystyrene standards.

[0032] As an example, GPC analysis can be performed using a Polymer Laboratories PLgel MIX-B 300 mm long column using a Waters PL-GPC220 instrument under the following conditions:

[0033] Column temperature: 160℃ Solvent: 1,2,4-trichlorobenzene Flow rate: 1mL / min Sample: Prepared to a concentration of 10mg / 10mL and supplied in a volume of 200μL

[0034] Mw and Mn values ​​were derived using a calibration curve generated using polystyrene standards (nine types of standard molecular weights: 2,000 / 10,000 / 30,000 / 70,000 / 200,000 / 700,000 / 2,000,000 / 4,000,000 / 10,000,000).

[0035] In order to ensure the dispersibility of the clay, the polymer dispersant is used in an amount of more than 20 parts by weight to 200 parts by weight or less, relative to 100 parts by weight of clay, and preferably in an amount of 23 parts by weight or more, or 25 parts by weight or more and 150 parts by weight or less, or 100 parts by weight or less.

[0036] If the content of the polymer dispersant is 20 parts by weight or less per 100 parts by weight of clay, the degree of surface modification of the clay is insufficient and the interlayer spacing of the clay cannot be sufficiently expanded. Therefore, the dispersion stability of the clay is insufficient and the clay particles are likely to aggregate. Also, if the content of the polymer dispersant is excessively high, exceeding 200 parts by weight per 100 parts by weight of clay, the polymer dispersant reduces the property improvement effect that the clay can provide, and the physical properties of the superabsorbent resin may be reduced.

[0037] The content of the clay in the composition for producing a superabsorbent resin may be 0.1 parts by weight or more, or 0.2 parts by weight or more, or 0.25 parts by weight or more, and 1 part by weight or less, or 0.7 parts by weight or less, or 0.5 parts by weight or less, based on 100 parts by weight of the water-soluble ethylenically unsaturated monomer.

[0038] The water-soluble ethylenically unsaturated monomer has an acidic group, and at least a part of the acidic group is neutralized by partially neutralizing the water-soluble ethylenically unsaturated monomer with an alkaline substance such as an alkali metal salt or an alkali compound. The alkali metal salt capable of neutralizing the water-soluble ethylenically unsaturated monomer may be sodium acrylate, or the alkali compound may be caustic soda (NaOH), potassium hydroxide, ammonium hydroxide, or the like.

[0039] The degree of neutralization of the water-soluble ethylenically unsaturated monomer is 50 to 95%, preferably 70 to 85%. If the degree of neutralization of the monomer is low, the water absorbency of the produced superabsorbent resin may be low, and if the degree of neutralization is high, the neutralized monomer may precipitate, making the polymerization difficult and making the superabsorbent resin difficult.

[0040] The water-soluble ethylenically unsaturated monomer is not particularly limited as long as it is a monomer that is commonly used in the production of superabsorbent resins, but preferably, any one or more selected from the group consisting of anionic monomers and their salts, nonionic hydrophilic monomers, and amino group-containing unsaturated monomers and their quaternary derivatives can be used. Specific examples of the water-soluble ethylenically unsaturated monomer include one or more selected from the group consisting of anionic monomers of acrylic acid, methacrylic acid, maleic anhydride, fumaric acid, crotonic acid, itaconic acid, 2-acryloylethanesulfonic acid, 2-methacryloylethanesulfonic acid, 2-(meth)acryloylpropanesulfonic acid, and 2-(meth)acrylamido-2-methylpropanesulfonic acid, and their salts; nonionic hydrophilic monomers of (meth)acrylamide, N-substituted (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, and polyethylene glycol (meth)acrylate; and amino group-containing unsaturated monomers of (N,N)-dimethylaminoethyl (meth)acrylate or (N,N)-dimethylaminopropyl (meth)acrylamide, and their quaternized products.

[0041] The concentration of the water-soluble ethylenically unsaturated monomer may be about 20 to 60 parts by weight, preferably 40 to 60 parts by weight, based on 100 parts by weight of the composition for producing a superabsorbent polymer, or may be an appropriate concentration taking into consideration the polymerization time and reaction conditions, etc. If the concentration of the monomer is too low, the yield of the superabsorbent polymer may be low, causing problems in terms of economy, and if the concentration is too high, problems may occur in the process, such as partial precipitation or low grinding efficiency when grinding the polymerized hydrogel polymer, and the physical properties of the superabsorbent polymer may be reduced.

[0042] As the polymerization initiator, a photopolymerization initiator can be used when a photopolymerization method is used, and a thermal polymerization initiator can be used when a thermal polymerization method is used.

[0043] However, even in the photopolymerization method, a certain amount of heat is generated by irradiation with ultraviolet light or the like, and a certain amount of heat is generated by the progress of the polymerization reaction, which is an exothermic reaction, so a thermal polymerization initiator may be additionally used.

[0044] The thermal polymerization initiator is not particularly limited, but preferably, one or more selected from the group consisting of persulfate initiators, azo initiators, hydrogen peroxide, and ascorbic acid can be used. Specifically, examples of persulfate initiators include sodium persulfate (Na 2 S 2 O 8 ), potassium persulfate (K 2 S 2 O 8 ), Ammonium persulfate ((NH 4 ) 2 S 2 O 8 Examples of azo initiators include 2,2-azobis(2-amidinopropane) dihydrochloride, 2,2-azobis-(N,N-dimethylene)isobutyramidine dihydrochloride, 2-(carbamoylazo)isobutylonitrile, 2,2-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride, 4,4-azobis-(4-cyanovaleric acid), Acid)) and the like can be used.

[0045] The photopolymerization initiator is not particularly limited, but preferably, one or more selected from the group consisting of benzoin ether, dialkyl acetophenone, hydroxyl alkylketone, phenyl glyoxylate, benzyl dimethyl ketal, acyl phosphine, and α-aminoketone can be used. On the other hand, a specific example of the acylphosphine is diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide.

[0046] The composition for producing a superabsorbent polymer may contain a solvent. Any solvent may be used without limitation as long as it can dissolve the above-mentioned components. As an example, one or more solvents selected from the group consisting of 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, cyclohexanone, cyclopentanone, diethylene glycol monomethyl ether, diethylene glycol ethyl ether, toluene, xylene, butyrolactone, carbitol, methyl cellosolve acetate, and N,N-dimethylacetamide may be used as the solvent.

[0047] Meanwhile, the composition for producing a superabsorbent polymer may further include a crosslinking agent, which may be a crosslinking agent having one or more functional groups capable of reacting with the water-soluble substituent of the water-soluble ethylenically unsaturated monomer and one or more ethylenically unsaturated groups; or a crosslinking agent having two or more functional groups capable of reacting with the water-soluble substituent of the monomer and / or the water-soluble substituent formed by hydrolysis of the monomer.

[0048] Specific examples of the crosslinking agent include one or more selected from the group consisting of N,N'-methylenebisacrylamide, trimethylolpropane tri(meth)acrylate, ethylene glycol di(meth)acrylate, (meth)acrylate, propylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, polypropylene glycol (meth)acrylate, butanediol di(meth)acrylate, butylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, hexanediol di(meth)acrylate, triethylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, dipentaerythritol pentaacrylate, glycerin tri(meth)acrylate, pentaerythritol tetraacrylate, triallylamine, ethylene glycol diglycidyl ether, propylene glycol, glycerin, and ethylene carbonate.

[0049] The crosslinking agent may be included in an amount of 0.01 parts by weight or more, 0.05 parts by weight or more, 0.1 parts by weight or more, or 0.3 parts by weight or more and 2 parts by weight or less, 1.5 parts by weight or less, or 1 part by weight or less, based on 100 parts by weight of the water-soluble ethylenically unsaturated monomer, to crosslink the polymerized polymer.

[0050] The composition for producing a superabsorbent resin may contain additives such as a foaming agent, a thickener, a plasticizer, a storage stabilizer, and an antioxidant, if necessary.

[0051] As an example, the composition for producing a superabsorbent polymer may include, as a foaming agent, one or more foaming agents selected from the group consisting of sodium bicarbonate, sodium carbonate, potassium bicarbonate, potassium carbonate, calcium bicarbonate, calcium carbonate, magnesium bicarbonate, and magnesium carbonate.

[0052] The foaming agent may be added in an amount of 0.01 parts by weight or more, or 0.05 parts by weight or more, or 0.08 parts by weight or more, and 0.5 parts by weight or less, 0.3 parts by weight or less, or 0.2 parts by weight or less, based on 100 parts by weight of the monomer.

[0053] The method for producing the composition for producing a superabsorbent polymer is not particularly limited, and for example, the composition for producing a superabsorbent polymer can be produced by mixing clay, a polymer dispersant, a water-soluble ethylenically unsaturated monomer, an alkali metal salt or an alkali compound capable of neutralizing the water-soluble ethylenically unsaturated monomer, and a polymerization initiator at once in the presence of a solvent.

[0054] Alternatively, the clay and the polymer dispersant are mixed together with a solvent (a solvent used in the composition for producing a superabsorbent polymer can be used) to produce a clay dispersion, which is then mixed with a water-soluble ethylenically unsaturated monomer; an alkali metal salt or an alkali compound capable of neutralizing the water-soluble ethylenically unsaturated monomer; and a polymerization initiator to produce the composition for producing a superabsorbent polymer.

[0055] The composition for producing a superabsorbent resin contains the clay and the polymer dispersant, so that the clay particles do not aggregate or settle, and maintain excellent dispersion stability in the composition.

[0056] Specifically, the settling velocity of the clay in the composition for producing a superabsorbent polymer may be 100 μm / s or less, and preferably 50 μm / s or less, or 30 μm / s or less, or 10 μm / s or less, and 1 μm / s or more, or 5 μm / s or more. The method for measuring the settling velocity will be described in detail in the following experimental examples.

[0057] The composition for producing a superabsorbent polymer contains clay, and the clay maintains excellent dispersion stability due to a polymer dispersant containing two or more functional groups selected from the group consisting of an amine group, a carbonyl group, and a hydroxyl group, and can be suitably used for producing a superabsorbent polymer that has excellent water absorption performance and is free from the risk of discoloration.

[0058] Therefore, according to another embodiment of the present invention, there is provided a superabsorbent resin using the composition for producing a superabsorbent resin, and a method for producing the same.

[0059] The superabsorbent resin includes a crosslinked polymer of a water-soluble ethylenically unsaturated monomer having acidic groups, at least a portion of which has been neutralized; and a clay whose surface has been modified with a polymer dispersant containing two or more functional groups selected from the group consisting of an amine group, a carbonyl group, and a hydroxyl group. The superabsorbent resin may include more than 20 parts by weight to 200 parts by weight of the polymer dispersant relative to 100 parts by weight of the clay.

[0060] The superabsorbent resin is produced from the composition for producing a superabsorbent resin described above, and has a morphology in which the surface-modified clay described above is uniformly dispersed inside and outside the crosslinked polymer.

[0061] The method for producing the superabsorbent polymer includes the steps of: irradiating the above-mentioned composition for producing a superabsorbent polymer with heat and / or light to cause a polymerization reaction to produce a hydrogel polymer; drying and pulverizing the hydrogel polymer to produce a base resin; and additionally crosslinking the surface of the base resin in the presence of a surface crosslinking agent to form a surface crosslinked layer.

[0062] The polymerization method is largely divided into thermal polymerization and photopolymerization depending on the polymerization energy source. In general, when thermal polymerization is carried out, it may be carried out in a reactor having a stirring shaft such as a kneader, and when photopolymerization is carried out, it may be carried out in a reactor equipped with a movable conveyor belt. However, the above-mentioned polymerization method is merely an example, and the present invention is not limited to the above-mentioned polymerization method.

[0063] For example, the hydrogel polymer obtained by thermal polymerization by supplying hot air to a reactor such as a kneader equipped with an agitator shaft as described above or by heating the reactor may have a hydrogel polymer discharged from the outlet of the reactor in the form of several centimeters to several millimeters depending on the form of the agitator shaft equipped in the reactor. Specifically, the size of the obtained hydrogel polymer may vary depending on the concentration of the monomer composition injected and the injection speed, but a hydrogel polymer having a weight average particle size of about 2 to 50 mm is usually obtained.

[0064] In addition, when photopolymerization is carried out in a reactor equipped with a movable conveyor belt as described above, the form of the obtained hydrogel polymer may be a sheet-like hydrogel polymer having the width of the belt. In this case, the thickness of the polymer sheet varies depending on the concentration and injection speed of the monomer composition to be injected, but it is preferable to supply the monomer composition so that a sheet-like polymer having a thickness of about 0.5 to about 5 cm is obtained. If the monomer composition is supplied so that the thickness of the sheet-like polymer is too thin, the production efficiency is low, which is undesirable, and if the thickness of the sheet-like polymer exceeds 5 cm, the polymerization reaction may not occur uniformly over the entire thickness due to the excessively thick thickness.

[0065] The water content of the hydrogel polymer obtained by this method may be about 40 to about 80% by weight. Meanwhile, throughout this specification, the "water content" refers to the water content relative to the total weight of the hydrogel polymer, and means the weight of the hydrogel polymer minus the weight of the polymer in a dry state. Specifically, it is defined as a value calculated by measuring the weight loss due to evaporation of water in the polymer during the process of drying by increasing the temperature of the polymer by infrared heating. Here, the drying conditions are a method of increasing the temperature from room temperature to about 180°C and then maintaining it at 180°C, and the total drying time is set to 20 minutes, including 5 minutes for the temperature increase step, and the water content is measured.

[0066] After the monomers are cross-linked and polymerized, a base resin powder can be obtained through processes such as drying, pulverization, and classification, and it is appropriate that the base resin powder and the superabsorbent resin obtained therefrom are manufactured and provided so as to have a particle size of about 150 to 850 μm through such processes as pulverization and classification. More specifically, at least about 95% by weight of the base resin powder and the superabsorbent resin obtained therefrom may have a particle size of about 150 to 850 μm, and fine powder having a particle size of less than about 150 μm may account for less than about 3% by weight.

[0067] By adjusting the particle size distribution of the base resin powder and the superabsorbent resin within the preferred range, the final superabsorbent resin can exhibit the above-mentioned physical properties and better liquid permeability.

[0068] Meanwhile, the method of carrying out the drying, pulverization and classification will be described in more detail as follows.

[0069] First, when drying the hydrogel polymer, a step of coarsely pulverizing the polymer before drying may be performed, if necessary, in order to increase the efficiency of the drying step.

[0070] In this case, the crusher used is not limited in configuration, and specifically may include any one selected from the group of crushing equipment consisting of a vertical pulverizer, a turbo cutter, a turbo grinder, a rotary cutter mill, a cutter mill, a disc mill, a shred crusher, a crusher, a chopper, and a disc cutter, but is not limited to the above examples.

[0071] At this time, the coarse pulverization step can be carried out so that the hydrogel polymer has a particle size of about 2 to about 10 mm.

[0072] Grinding to a particle size of less than 2 mm is technically difficult due to the high water content of the hydrogel polymer, and may result in aggregation of the ground particles. On the other hand, grinding to a particle size of more than 10 mm may result in little increase in the efficiency of the subsequent drying step.

[0073] The hydrogel polymer that has been coarsely pulverized as described above or that has not been subjected to the coarse pulverization step is dried immediately after polymerization. At this time, the drying temperature in the drying step may be about 150 to about 250°C. If the drying temperature is less than about 150°C, the drying time may be excessively long, and the physical properties of the superabsorbent polymer that is finally formed may be deteriorated. If the drying temperature exceeds about 250°C, only the surface of the polymer may be excessively dried, and fine powder may be generated in the subsequent pulverization step, and the physical properties of the superabsorbent polymer that is finally formed may be deteriorated. Therefore, the drying may be preferably performed at a temperature of about 150 to about 200°C, more preferably at a temperature of about 160 to about 180°C.

[0074] Meanwhile, the drying time may be about 20 to about 90 minutes in consideration of process efficiency, but is not limited thereto.

[0075] The drying method in the drying step can be selected and used without any limitation on the configuration as long as it is one that is usually used in the drying process of a hydrogel polymer. Specifically, the drying step can be carried out by a method such as hot air supply, infrared radiation, ultrashort wave radiation, or ultraviolet radiation. The water content of the polymer after such a drying step may be about 0.1 to about 10% by weight.

[0076] Next, the dried polymer obtained through such a drying step is subjected to a pulverization step.

[0077] The polymer powder obtained after the pulverization step may have a particle size of about 150 to about 850 μm. Specifically, the pulverizer used for pulverizing to such a particle size may be a pin mill, a hammer mill, a screw mill, a roll mill, a disc mill, a jog mill, or the like, but is not limited to the above examples.

[0078] After the pulverization step, in order to control the physical properties of the superabsorbent resin powder to be manufactured as a final product, a separate process of classifying the polymer powder obtained after pulverization according to particle size can be performed. Preferably, the polymer having a particle size of about 150 to about 850 μm is classified, and only the polymer powder having such a particle size can be manufactured as a product through a surface crosslinking reaction step.

[0079] On the other hand, after the above-mentioned base resin powder formation process has been carried out, the surface of the base resin powder can be additionally crosslinked in the presence of a surface crosslinking agent to form a surface crosslinked layer, thereby producing a highly water-absorbent resin.

[0080] As the surface crosslinking agent, a compound capable of reacting with a functional group of the polymer is used, and examples thereof include polyhydric alcohol compounds, polyfunctional epoxy compounds, polyamine compounds, haloepoxy compounds, condensation products of haloepoxy compounds, oxazoline compounds, and alkylene carbonate compounds.

[0081] Specifically, examples of polyhydric alcohol compounds that can be used include one or more selected from the group consisting of di-, tri-, tetra- or polyethylene 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.

[0082] In addition, examples of the polyfunctional epoxy compound that can be used include ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, and glycidol. Examples of the polyamine compound that can be used include one or more compounds selected from the group consisting of ethylenediamine, diethylenetriamine, triethylenetetraamine, tetraethylenepentamine, pentaethylenehexamine, polyethyleneimine, and polyamidepolyamine.

[0083] As the haloepoxy compound, epichlorohydrin, epibromohydrin, and α-methylepichlorohydrin can be used, while as the mono-, di-, or polyoxazolidinone compound, for example, 2-oxazolidinone can be used.

[0084] As the alkylene carbonate compound, ethylene carbonate or the like can be used.

[0085] The compounds may be used alone or in combination with one another.

[0086] The content of the surface crosslinking agent to be added can be appropriately selected depending on the type of the surface crosslinking agent to be added and the reaction conditions, and usually, 0.001 to 5 parts by weight, preferably 0.01 to 2 parts by weight, and more preferably 0.05 to 3 parts by weight can be used relative to 100 parts by weight of the base resin.

[0087] In addition, there is no limitation on the constitution of the method for adding the surface crosslinking agent to the base resin powder. For example, a method of putting the surface crosslinking agent and the base resin powder in a reaction tank and mixing them, a method of spraying the surface crosslinking agent onto the base resin powder, a method of continuously supplying the base resin powder and the surface crosslinking agent to a continuously operating mixer and mixing them, etc. can be used.

[0088] When the surface crosslinking agent is added, water and methanol may be added together. When water and methanol are added, there is an advantage that the surface crosslinking agent can be uniformly dispersed in the base resin powder. At this time, the content of the added water and methanol may be adjusted and applied in an addition ratio relative to 100 parts by weight of the base resin powder in order to induce uniform dispersion of the surface crosslinking agent and prevent the clumping phenomenon of the base resin powder, while optimizing the surface penetration depth of the crosslinking agent.

[0089] The surface cross-linking reaction may be carried out by heating the base resin powder to which the surface cross-linking agent has been added at about 160° C. or higher for about 20 minutes or more. In particular, in order to produce a superabsorbent resin that more appropriately satisfies the physical properties according to one embodiment, the surface cross-linking process conditions may be a maximum reaction temperature of about 180 to 200° C., and a maintenance time at the maximum reaction temperature of about 20 minutes or more, or about 20 minutes to 1 hour or less. In addition, the temperature rise time from the initial reaction start temperature, for example, about 160° C. or higher, or about 160 to 170° C., to the maximum reaction temperature can be controlled to about 10 minutes or more, or about 10 minutes to 1 hour or less, and it has been confirmed that a superabsorbent resin that appropriately satisfies the physical properties according to one embodiment can be produced by satisfying the above-mentioned surface cross-linking process conditions.

[0090] The temperature raising means for the surface crosslinking reaction is not particularly limited. Heating can be performed by supplying a heat medium or directly supplying a heat source. At this time, the type of heat medium that can be used can be a heated fluid such as steam, hot air, hot oil, etc., but is not limited to these, and the temperature of the heat medium to be supplied can be appropriately selected in consideration of the means of the heat medium, the heating rate, and the target temperature of the heat raising. On the other hand, the heat source to be directly supplied can be an electric heating method or a gas heating method, but is not limited to the above-mentioned examples.

[0091] The superabsorbent resin obtained by the above-mentioned production method can exhibit extremely excellent properties in which various physical properties such as water retention capacity and water absorption capacity under pressure are improved, and therefore can be suitably used in sanitary products such as diapers.

[0092] Below, preferred examples are presented to help understand the present invention. However, the following examples are merely illustrative of the present invention, and it will be apparent to those skilled in the art that various changes and modifications are possible within the scope of the scope and technical ideas of the present invention. It goes without saying that such changes and modifications fall within the scope of the appended claims.

[0093] [Example] <Production of composition for producing superabsorbent resin> Example 1-1 450g of acrylic acid, 3g of polyethylene glycol diacrylate 400, and 0.04g of diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide were mixed, and 580g of 31.5% aqueous sodium hydroxide solution was added to prepare an acrylic acid monomer composition.

[0094] Separately, in a 10 mL vial, add 5 g of ZrO 2Beads were weighed and added. 12 mg of polyvinylpyrrolidone (PVP, Aldrich's PVP10; weight average molecular weight 10,000) was added as a dispersant, and then 24 mg of clay powder (Bentonite, BYK's OPTIGEL CK, particle size range 1-5 μm, average particle size (D50) 3 μm) was added. 4.7 g of the acrylic acid monomer composition was added to this, and the mixture was shaken and mixed at 300 rpm for 4 hours using a Shaker (JEIO TECH, SK-600) to produce a composition for producing a superabsorbent resin.

[0095] Examples 1-2 to 1-3 and Comparative Examples 1-1 to 1-4 Except for changing the type and amount of the dispersant as shown in Table 1 below, compositions for producing a superabsorbent resin of Examples 1-2 to 1-3 and Comparative Examples 1-1 to 1-4 were produced in the same manner as in Example 1-1.

[0096] In Examples 1-5, poly(acrylic acid) having a weight average molecular weight of 25,000 g / mol was used, manufactured by Wako Pure Chemical Co., Ltd., and in Comparative Examples 1-6, poly(ethylene oxide) having a weight average molecular weight of 100,000 g / mol was used, manufactured by Sigma-Aldrich Co., Ltd.

[0097] DISPERBYK-102 (BYK) used in Comparative Example 1-2 is a phosphoric acid ester-based polymer, and Sokalan HP-20 (BASF) used in Comparative Example 1-3 is a polyethyleneimine-based polymer dispersant.

[0098] [Table 1]

[0099] Experimental Example 1: Evaluation of the physical properties of the composition for producing superabsorbent resin The properties of each of the compositions for producing a superabsorbent resin in Examples 1-1 to 1-3 and Comparative Examples 1-1 to 1-4 were evaluated by the following methods. The results are shown in Table 2.

[0100] (1) Sedimentation velocity The settling velocity of the clay particles in each of the compositions of Examples 1-1 to 1-5 and Comparative Examples 1-1 to 1-6 was measured using a LUMiSizer Dispersion & Particle Size Analyzer.

[0101] Specifically, 1.6 mL of the composition for producing a superabsorbent polymer was taken and placed in a 10 mm PC cell, which was then attached to a LUMiSizer, and the transmittance profile was measured at 400 points at 10 second intervals at a temperature of 25°C and 1,500 rpm (~280 G). In the transmittance profile thus measured, a threshold was set to 21%, and the sedimentation velocity was calculated.

[0102] (2) Dispersion stability after 48 hours 4 g of each of the compositions for producing a superabsorbent resin in Examples 1-1 to 1-3 and Comparative Examples 1-1 to 1-4 was placed in a 10 ml vial and left standing in a vial rack at a temperature of 25° C. for 48 hours. Then, whether or not layer separation occurred in the supernatant was observed with the naked eye. If layer separation occurred, the dispersion was evaluated as having no dispersion stability (X), and if layer separation did not occur, the dispersion was evaluated as having dispersion stability (O).

[0103] [Table 2]

[0104] Referring to Table 2, it can be seen that the compositions for producing a superabsorbent resin of Examples 1-1 to 1-3, in which a clay dispersion containing 25 to 50 parts by weight of a PVP dispersant relative to 100 parts by weight of clay, do not easily cause clay sedimentation and have excellent dispersion stability even after 48 hours.

[0105] <Production of superabsorbent resin> Example 2-1 (1) Preparation of 4% clay dispersion Into a flask, 2g of clay (Bentonite, BYK's OPTIGEL CK, particle size range 1-5μm, average particle size 3μm) and 1g (50 parts by weight to 100 parts by weight of clay) of polyvinylpyrrolidone (Aldrich's PVP10, weight average molecular weight 10,000) as a polymer dispersant were added, and water was added so that the total weight of the mixture became 50g. This was stirred with a magnetic stirrer at 500 rpm for 12 hours to produce a 4wt% clay dispersion.

[0106] (2) Manufacturing of superabsorbent polymers In a 3L glass container, 450g of acrylic acid (AA), 3g of polyethylene glycol diacrylate 400 (PEGDA400), and 0.04g of diphenyl(2,4,6-tribenzoyl)-phosphine oxide were added and dissolved, and then 580g of 31.5% aqueous sodium hydroxide solution was added to prepare an acrylic acid monomer composition.

[0107] The 4 wt% clay dispersion prepared in (1) above was added to the monomer composition so that the clay content was 0.5 parts by weight per 100 parts by weight of acrylic acid, and 0.1 parts by weight of sodium bicarbonate (SBC), a carbonate-based foaming agent, was added per 100 parts by weight of acrylic acid to prepare a composition for producing a superabsorbent resin.

[0108] 1000 g of the composition for producing a superabsorbent resin was placed in a stainless steel container measuring 250 mm in width, 250 mm in length, and 30 mm in height, and irradiated with ultraviolet light (irradiation dose 10 mV / cm 2 ) and UV polymerization was carried out for 90 seconds to obtain a hydrogel polymer.

[0109] The sheet-like hydrogel polymer was then fed into a meat chopper to obtain hydrogel particle powder, which was then dried in an oven so that the moisture content of the dried product was 1% or less. The dried particles were pulverized in a pulverizer and then classified to prepare a base resin having a size of 150 to 850 μm.

[0110] 6 g of a surface crosslinking agent aqueous solution containing 3 g of ethylene carbonate was sprayed onto 100 g of the base resin powder, and the mixture was stirred at room temperature to uniformly distribute the surface crosslinking liquid on the base resin powder. Next, the base resin powder mixed with the surface crosslinking liquid was placed in a surface crosslinking reactor, heated to 190° C. for 30 minutes, and the surface crosslinking reaction was carried out at the same temperature for 15 minutes.

[0111] After the surface cross-linking step, the powder was classified using a standard mesh sieve according to ASTM standards to produce a highly water-absorbent resin having a particle size of 150 to 850 μm.

[0112] Examples 2-2 to 2-3 and Comparative Examples 2-1 to 2-3 A clay dispersion was prepared in the same manner as in Example 2-1(1), except that the types and contents of clay and dispersant were adjusted as shown in Table 3. Thereafter, the superabsorbent resins of Examples 2-2 to 2-3 and Comparative Examples 2-1 to 2-3 were prepared in the same manner as in Example 2-1(2).

[0113] [Table 3]

[0114] Experimental Example 2: Evaluation of the physical properties of superabsorbent resin The physical properties of each of the superabsorbent resins of Examples 2-1 to 2-3 and Comparative Examples 2-1 to 2-3 were evaluated by the following methods, and the results are shown in Table 4.

[0115] (1)EFFC(Effective Absorption Capacity) The EFFC value was calculated using the following formula:

[0116] EFFC=1 / 2(CRC+AUP)

[0117] In the above formula, CRC and AUP were measured by the following method.

[0118] a) Measurement of CRC (Centrifuge Retention Capacity) The CRC of the superabsorbent polymer was measured by EDANA WSP241.2.

[0119] Specifically, the resins obtained in the examples and comparative examples were classified using sieves of #30-50 to obtain the highly water-absorbent resin W. 0 (g) (about 0.2 g) was uniformly placed in a nonwoven bag and sealed, and then immersed in physiological saline (0.9 wt%) at room temperature. After 30 minutes, the bag was centrifuged at 250 G for 3 minutes to remove water, and the mass of the bag W 2 The mass W (g) was measured after the same procedure was performed without using the resin. 1 (g) was measured.

[0120] Using the obtained masses, the CRC (g / g) was calculated according to the following formula.

[0121] CRC(g / g) = {[W 2 (g)-W 1 (g)] / W 0 (g)}-1

[0122] b) Measurement of AUP (Absorption Under Pressure)

[0123] The AUP at 0.7 psi of the superabsorbent polymer was measured by EDANA method WSP242.2.

[0124] First, when measuring the pressurized water absorption capacity, the resin-classified powder used in the CRC measurement was used.

[0125] Specifically, a 400-mesh stainless steel wire net was attached to the bottom of a plastic cylinder with an inner diameter of 60 mm. Under conditions of room temperature and humidity of 50%, water-absorbent resin W was placed on the wire net. 0 The piston that can uniformly apply a load of 0.7 psi on the surface is slightly smaller than 60 mm in outer diameter, has no gap with the inner wall of the cylinder, and is designed so that the up and down movement is not hindered. At this time, the weight W 4 (g) was measured.

[0126] A glass filter with a diameter of 90 mm and a thickness of 5 mm was placed inside a petroleum dish with a diameter of 150 mm, and physiological saline containing 0.9% by weight of sodium chloride was placed at the same level as the upper surface of the glass filter. A sheet of filter paper with a diameter of 90 mm was placed on top of the glass filter. The measuring device was placed on the filter paper, and the liquid was absorbed under a load for one hour. After one hour, the measuring device was lifted up and its weight W 5 (g) was measured.

[0127] Using the obtained masses, the AUP (g / g) was calculated according to the following formula.

[0128] AUP(g / g) = [W 5 (g)-W 4 (g)] / W 3 (g)

[0129] (2) Color b The color b value of the superabsorbent polymer was measured according to the ASTM D2985 standard.

[0130] [Table 4]

[0131] Referring to Table 4, it can be seen that Comparative Example 2-1 does not contain a dispersant, and as a result, the dispersion stability of the clay is reduced, resulting in a significant reduction in the EFFC value.

[0132] On the other hand, when comparing Examples 2-1 to 2-3, in which a clay dispersion containing a dispersant together with clay was used, with Comparative Examples 2-2 and 2-3, it can be confirmed that the color b value is higher in Comparative Examples 2-2 and 2-3, in which Sokalan HP-20 was used as a dispersant, than in Examples 2-1 to 2-3, in which PVP was used.

[0133] From the above results, it can be confirmed that the composition for producing a superabsorbent polymer of the present invention has excellent dispersion stability of clay in the composition and can improve the water absorption properties of the produced superabsorbent polymer. In addition, it can be confirmed that the superabsorbent polymer produced from the superabsorbent polymer composition of the present invention has excellent color characteristics without the risk of discoloration due to a dispersant.

Claims

1. clay; A polymeric dispersant containing two or more functional groups selected from the group consisting of an amine group, a carbonyl group, and a hydroxyl group; A water-soluble ethylenically unsaturated monomer having an acidic group, at least a portion of which has been neutralized; and a polymerization initiator; The composition for producing a superabsorbent resin contains the polymer dispersant in an amount of more than 20 parts by weight and not more than 200 parts by weight per 100 parts by weight of clay.

2. 2. The composition for producing a highly water-absorbent resin according to claim 1, wherein the polymer dispersant is contained in an amount of 25 to 100 parts by weight per 100 parts by weight of clay.

3. 2. The composition for producing a superabsorbent resin according to claim 1, wherein the clay is at least one selected from the group consisting of montmorillonite, saponite, nontronite, laponite, beidellite, hectorite, vermiculite, magadiite, bentonite, kaolin, serpentine, and mica.

4. The composition for producing a superabsorbent resin according to claim 1, wherein the clay has an average particle size (D50) of 0.025 μm to 10 μm.

5. 2. The composition for producing a superabsorbent resin according to claim 1, wherein the polymer dispersant contains an amine group and a carbonyl group; or a carbonyl group and a hydroxyl group.

6. 2. The composition for producing a superabsorbent resin according to claim 1, wherein the polymer dispersant is at least one selected from the group consisting of polyvinylpyrrolidone, polyacrylamide, and polyacrylic acid.

7. 2. The composition for producing a superabsorbent resin according to claim 1, wherein the degree of neutralization of the water-soluble ethylenically unsaturated monomer is 50 to 95%.

8. 2. The composition for producing a superabsorbent resin according to claim 1, wherein the sedimentation velocity of the clay is 100 μm / s or less.

9. The water-soluble ethylenically unsaturated monomer is an anionic monomer of acrylic acid, methacrylic acid, maleic anhydride, fumaric acid, crotonic acid, itaconic acid, 2-acryloylethanesulfonic acid, 2-methacryloylethanesulfonic acid, 2-(meth)acryloylpropanesulfonic acid, or 2-(meth)acrylamido-2-methylpropanesulfonic acid, or a salt thereof; nonionic hydrophilic-containing monomers of (meth)acrylamide, N-substituted (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, or polyethylene glycol (meth)acrylate; and The composition for producing a superabsorbent resin according to claim 1, which is at least one selected from the group consisting of amino group-containing unsaturated monomers, such as (N,N)-dimethylaminoethyl (meth)acrylate and (N,N)-dimethylaminopropyl (meth)acrylamide, and quaternary derivatives thereof.

10. The composition for producing a superabsorbent polymer according to any one of claims 1 to 9, wherein the content of the clay in the composition for producing a superabsorbent polymer is 0.1 to 1 part by weight per 100 parts by weight of the ethylenically unsaturated monomer.

11. A step of irradiating the composition for producing a superabsorbent resin according to any one of claims 1 to 10 with heat and / or light to cause a polymerization reaction to produce a hydrogel polymer; drying and grinding the hydrogel polymer to produce a base resin; and A method for producing a superabsorbent resin, comprising the step of additionally crosslinking a surface of the base resin in the presence of a surface crosslinking agent to form a surface crosslinked layer.

12. A crosslinked polymer of a water-soluble ethylenically unsaturated monomer having acidic groups, at least a portion of which has been neutralized; and a clay whose surface has been modified with a polymeric dispersant containing two or more functional groups selected from the group consisting of amine groups, carbonyl groups, and hydroxyl groups; The highly water-absorbent resin contains the polymer dispersant in an amount of more than 20 parts by weight and not more than 200 parts by weight per 100 parts by weight of clay.

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