Composition for producing superabsorbent polymers and method for producing superabsorbent polymers 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 the contents disclosed in the documents of the Korean patent applications are included as part of this specification.

[0002] The present invention relates to a composition for producing a superabsorbent resin having excellent dispersion stability of clay and a method for producing a superabsorbent resin using the clay dispersion.

Background Art

[0003] Superabsorbent polymers (SAPs) are synthetic polymer substances having a function of absorbing about 500 to 1000 times their own weight of water. They began to be put into practical use as sanitary products and are now widely used in various materials such as disposable diapers for children, sanitary materials for menstruation, soil water retention agents for horticulture, water stop materials for civil engineering and construction, seedling - raising sheets, freshness - retaining agents in the food distribution field, and materials for ships.

[0004] Attempts have been made to introduce additives to improve basic physical properties such as the centrifuge retention capacity (CRC) and absorption under pressure (AUP) of superabsorbent resins, and clay is one of them. However, in a solution having a high ion concentration, clay particles tend to aggregate with each other, and it is not easy to ensure dispersion stability. Therefore, it is difficult to uniformly disperse clay in the monomer composition for producing a superabsorbent resin. As a result, the aggregated clay is distributed unevenly in the form of particles in the produced superabsorbent resin, and ultimately, it is difficult to obtain the effect of improving the physical properties of the superabsorbent resin.

[0005] Therefore, there is a need for the development of a clay dispersion that exhibits excellent dispersibility in compositions for producing superabsorbent polymers and can improve the physical properties of the superabsorbent polymers. [Overview of the Initiative] [Problems that the invention aims to solve]

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

[0007] Furthermore, the present invention provides a method for producing a superabsorbent resin using the superabsorbent resin production composition described above. [Means for solving the problem]

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

[0009] Another embodiment of the present invention provides a method for producing a superabsorbent resin, comprising the steps of: producing a water-containing gel polymer by irradiating the superabsorbent resin production composition with heat and / or light to cause a polymerization reaction; producing a base resin by drying and pulverizing the water-containing gel polymer; and forming a surface crosslinked layer by further crosslinking the surface of the base resin in the presence of a surface crosslinking agent.

[0010] According to another embodiment of the present invention, a superabsorbent polymer is provided comprising: a crosslinked polymer of a water-soluble ethylene-based unsaturated monomer having acidic groups, wherein at least a portion of the acidic groups is neutralized; and clay modified with a polymeric dispersant having two or more functional groups selected from the group consisting of amine groups, carbonyl groups, and hydroxyl groups on its surface; wherein the polymeric dispersant is contained in an amount of more than 20 parts by weight and no more than 200 parts by weight per 100 parts by weight of clay. [Effects of the Invention]

[0011] The present invention provides a composition for producing superabsorbent polymers that contains clay, exhibits a slow settling rate of clay particles, and shows excellent dispersion stability even during long-term storage. Therefore, the composition for producing superabsorbent polymers has excellent water absorption properties, such as centrifugal water retention capacity and pressurized water absorption capacity, and can be usefully used to produce superabsorbent polymers with improved gel strength. Furthermore, the superabsorbent polymer produced using the composition for producing superabsorbent polymers exhibits excellent color properties without the risk of discoloration. [Brief explanation of the drawing]

[0012] [Figure 1] These are photographs of the superabsorbent polymer compositions for Examples 1-1 to 1-3 (referred to as Examples 1 to 3, respectively), Comparative Example 1-3, and Comparative Example 1-4 (referred to as Comparative Examples 3 and 4, respectively), 48 hours after production. [Modes for carrying out the invention]

[0013] The terms used herein are used solely to describe exemplary embodiments and are not intended to limit the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this specification, terms such as “includes,” “equip,” or “have” are intended to specify the existence of implemented features, stages, components, or combinations thereof, and should be understood not to preemptively exclude the possibility of the existence or addition of one or more other features, stages, components, or combinations thereof.

[0014] While the present invention can take on various forms through diverse modifications, specific embodiments are described in detail below. However, it should be understood that this is not intended to limit the present invention to any particular disclosure, but rather to include all modifications, equivalents, or substitutions that fall within the spirit and technical scope of the present invention.

[0015] In this specification, "clay" is used to encompass both single particles of phyllosilicate mineral and aggregates of many such particles, and "clay dispersion" means a dispersion in which the clay is dispersed in a solvent.

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

[0017] In this specification, "base resin" or "base resin powder" refers to a polymer obtained by drying and pulverizing a polymer in which water-soluble ethylene-based unsaturated monomers have been polymerized, and which has not undergone surface modification or surface crosslinking.

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

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

[0020] The aforementioned composition for producing superabsorbent polymers exhibits a significant improvement in the dispersion stability of clay due to the use of a polymer dispersant containing two or more functional groups selected from the group consisting of amine groups, carbonyl groups, and hydroxyl groups. The 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 by strong van der Waals forces. The polymer dispersant binds to the surface of the clay and exfoliates the silicate layer (i.e., widens the interlayer distance to more than 1 nm). Since the clay, which has been chemically exfoliated in this way, exhibits significantly improved dispersion stability, the clay dispersion can be uniformly dispersed in the composition without the clay particles agglomerating or settling, even when it is included in a composition for producing superabsorbent polymers containing alkali metal salts or basic compounds.

[0021] Therefore, the superabsorbent polymer produced using the above-mentioned composition for producing superabsorbent polymers can have its water absorption properties, such as centrifugal separation water retention capacity and pressurized water absorption capacity, further improved. Furthermore, since the polymer dispersant does not cause discoloration of the superabsorbent polymer, the composition for producing superabsorbent polymers of the present invention can be used to produce high-quality superabsorbent polymers with excellent water absorption properties and color characteristics.

[0022] The clay can be either a swollen or non-swollen clay. The swollen clay is a layered organic material with water absorption capacity, and can be montmorillonite, saponite, nontronite, laponite, beiderite, hectorite, vermiculite, magadiite, bentonite, etc. The non-swollen clay can be kaolin, serpentine, mica, etc. The clay can be used individually or in mixtures of two or more types.

[0023] The clay can 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. When the average particle size (D50) of the clay is less than 0.025 μm, the effect of improving the gel strength of the superabsorbent resin cannot be sufficiently obtained. When the average particle size (D50) of the clay exceeds 10 μm, it is difficult to achieve uniform dispersion in an aqueous system due to the strong interlayer attraction of the clay, it is difficult to uniformly modify the surface of the clay, and there may be a problem that transparency cannot be ensured after dispersion.

[0024] At this time, "particle size Dn" means the particle size at the n% point of the particle number cumulative distribution according to the particle size, and D50 is the particle size at the 50% point of the particle number cumulative distribution according to the particle size. The average particle size (D50) of the clay can be measured by using a particle size analyzer by the laser diffraction and dynamic light scattering methods. Specifically, after dispersing the measurement target powder in a dispersion medium, it is introduced into a commercially available laser diffraction particle size measuring device (for example, Mastersizer 3000 of Malvern). When the particles pass through the 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 diameter at the point where it becomes 50% of the particle number cumulative 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 at a content of more than 20 parts by weight to 200 parts by weight or less with respect to 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 that combine two or more amine groups, carbonyl groups, and hydroxyl groups, such as amide groups containing both amine and carbonyl groups, and carboxyl groups containing both carbonyl and hydroxyl groups. For example, a "polymeric dispersant containing amine and carbonyl groups" may contain amine and carbonyl groups separately in its molecule, or it may contain an amide group which is a combination of an amine and a carbonyl group.

[0027] The polymeric dispersant containing the functional group may be bonded to the surface of the clay by lone electrons of nitrogen and oxygen atoms, or a charge can be induced within the polymer by resonance in a high-ion-concentration composition for producing superabsorbent polymers. Due to these properties, the polymeric dispersant can exfoliate the layered structure of the clay and improve its dispersibility. Furthermore, since the polymeric dispersant does not cause discoloration or deterioration of the properties of the superabsorbent polymer, it can be suitably used in the production of superabsorbent polymers.

[0028] From this viewpoint, the polymer dispersant is preferably said to contain an amine group and a carbonyl group; or a carbonyl group and a hydroxyl group. More preferably, the polymer dispersant is said to 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, polyvinylpyrrolidone can be used as the polymer dispersant.

[0030] While the molecular weight of the polymeric dispersant is not particularly limited, as an example, dispersants with a weight-average molecular weight of 2,500 g / mol or more, or 5,000 g / mol or more, or 10,000 g / mol or more and 200,000 g / mol or less, or 100,000 g / mol or less, or 40,000 g / mol can be used. If the weight-average molecular weight of the polymeric dispersant is less than 2,500 g / mol, when the polymeric dispersant binds to the surface of the clay, it may not sufficiently widen the interlayer distance of the silicate in the clay, making it difficult to detach, which can cause problems in terms of ensuring dispersibility and long-term stability. If it exceeds 200,000 g / mol, there are process difficulties and it is not effective in surface modification of the clay, so it is preferable to satisfy the above range.

[0031] The weight-average molecular weight of the polymer dispersant can be measured using gel permeation chromatography (GPC) with a polystyrene standard.

[0032] As an example, GPC analysis can be performed using a 300mm long Polymer Laboratories PLgel MIX-B column and 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 10 mg / 10 mL, then supplied in a volume of 200 μL.

[0034] The values ​​of Mw and Mn were derived using test curves formed with polystyrene standards (nine types of standard samples with molecular weights of 2,000 / 10,000 / 30,000 / 70,000 / 200,000 / 700,000 / 2,000,000 / 4,000,000 / 10,000,000).

[0035] The polymer dispersant is used in an amount of more than 20 parts by weight and up to 200 parts by weight per 100 parts by weight of clay to ensure the dispersibility of the clay, 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 amount of polymeric dispersant is 20 parts by weight or less per 100 parts by weight of clay, the degree of surface modification of the clay will be insufficient, and the interlayer spacing of the clay will not be sufficiently widened. Consequently, the dispersion stability of the clay will be insufficient, and the clay particles will be prone to aggregation. Furthermore, if the amount of polymeric dispersant is excessively high, exceeding 200 parts by weight per 100 parts by weight of clay, the polymeric dispersant may reduce the property-improving effect that the clay can provide, potentially leading to a decrease in the properties of the superabsorbent polymer.

[0037] The clay content in the superabsorbent resin manufacturing composition 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 water-soluble ethylene-based unsaturated monomer.

[0038] The aforementioned water-soluble ethylene-based unsaturated monomer has an acidic group, and at least a portion of the acidic group is neutralized, meaning the water-soluble ethylene-based unsaturated monomer is partially neutralized with an alkaline substance such as an alkali metal salt or an alkali compound. Examples of alkali metal salts that can neutralize the water-soluble ethylene-based unsaturated monomer include sodium acrylate, and examples of alkali compounds that can be used include caustic soda (NaOH), potassium hydroxide, and ammonium hydroxide.

[0039] The degree to which the water-soluble ethylene-based unsaturated monomer is neutralized is 50-95%, preferably 70-85%. If the degree of neutralization of the monomer is too low, the water absorption capacity of the superabsorbent polymer produced may be low. If the degree of neutralization is too high, the neutralized monomer may precipitate, hindering polymerization and making it difficult to produce the superabsorbent polymer.

[0040] As the water-soluble ethylene-based unsaturated monomer, there are no special restrictions as long as it is a monomer commonly used in the production of superabsorbent polymers. However, preferably, one or more can be selected from the group consisting of anionic monomers and their salts, nonionic hydrophilic monomers, and amino group-containing unsaturated monomers and their quaternary derivatives. Specific examples of the aforementioned water-soluble ethylene-based unsaturated monomers include one or more selected from the group consisting of anionic monomers and salts 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; nonionic hydrophilic monomers containing (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 and quaternary derivatives of (N,N)-dimethylaminoethyl (meth)acrylate or (N,N)-dimethylaminopropyl (meth)acrylamide.

[0041] The concentration of the water-soluble ethylene-based unsaturated monomer may be about 20 to 60 parts by weight, preferably 40 to 60 parts by weight, per 100 parts by weight of the composition for producing superabsorbent polymer, or it may be an appropriate concentration considering the polymerization time and reaction conditions. If the concentration of the monomer is too low, the yield of the superabsorbent polymer may be low, causing economic problems. If the concentration is too high, some of the monomer may precipitate, or the grinding efficiency may be low when grinding the polymerized water-containing gel-like polymer, causing process problems and potentially degrading the physical properties of the superabsorbent polymer.

[0042] As for the polymerization initiator, if the polymerization method is photopolymerization, a photopolymerization initiator can be used, and if the polymerization method is thermal polymerization, a thermal polymerization initiator or the like can be used.

[0043] However, even with photopolymerization methods, a certain amount of heat is generated by irradiation such as ultraviolet light, and a certain amount of heat is also generated by the progress of the polymerization reaction, which is an exothermic reaction. Therefore, a thermal polymerization initiator may be used in addition.

[0044] The thermal polymerization initiator is not particularly limited, but preferably one or more initiators 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 (Na2S2O8), potassium persulfate (K2S2O8), and ammonium persulfate ((NH4)2S2O8). Examples of azo initiators include 2,2-azobis-(2-amidinopropane)dihydrochloride and 2,2-azobis-(N,N-dimethylene)isobutyramidine dihydrochloride. Examples of dihydrochloride, 2-(carbamoylazo)isobutylonitrile, 2,2-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride, and 4,4-azobis-(4-cyanovaleric acid) can be used.

[0045] There are no particular restrictions on the photopolymerization initiator, but preferably one or more selected from the group consisting of benzoin ether, dialkyl acetophenone, hydroxyl alkyl ketone, phenyl glyoxylate, benzyl dimethyl ketal, acyl phosphine, and α-aminoketone can be used. On the other hand, a specific example of acyl phosphine is diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide.

[0046] The above-mentioned composition for producing superabsorbent polymers may contain a solvent. Any solvent that can dissolve the above-mentioned components is acceptable and is not limited in its composition. For 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 can be used as a solvent.

[0047] On the other hand, the composition for producing the superabsorbent polymer may further contain a crosslinking agent. The crosslinking agent may be a crosslinking agent having one or more functional groups that can react with the water-soluble substituents of the water-soluble ethylene-based unsaturated monomer and one or more ethylenically unsaturated groups; or a crosslinking agent having two or more functional groups that can react with the water-soluble substituents of the monomer and / or water-soluble substituents 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 can 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 per 100 parts by weight of a water-soluble ethylene-based unsaturated monomer, thereby crosslinking the polymerized polymer.

[0050] The aforementioned composition for producing superabsorbent polymers may optionally contain additives such as foaming agents, thickeners, plasticizers, preservatives, and antioxidants.

[0051] As an example, the superabsorbent polymer manufacturing composition may contain 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 per 100 parts by weight of monomer.

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

[0054] Alternatively, a clay dispersion can be produced by mixing clay and a polymer dispersant with a solvent (a solvent used in compositions for producing superabsorbent polymers can be used), and then mixing this dispersion with a water-soluble ethylene-based unsaturated monomer; an alkali metal salt or alkali compound capable of neutralizing the water-soluble ethylene-based unsaturated monomer; and a polymerization initiator to produce a composition for producing superabsorbent polymers.

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

[0056] Specifically, the settling velocity of the clay in the superabsorbent polymer manufacturing composition may be 100 μm / s or less, 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 explained in detail in the following experimental example.

[0057] The aforementioned composition for producing superabsorbent polymers contains clay, and the clay maintains excellent dispersion stability with a polymeric dispersant containing two or more functional groups selected from the group consisting of amine groups, carbonyl groups, and hydroxyl groups. It is suitable for use in producing superabsorbent polymers that have excellent water absorption performance and are free from the risk of discoloration.

[0058] Therefore, according to another embodiment of the present invention, a superabsorbent polymer using the superabsorbent polymer manufacturing composition and a method for manufacturing the same are provided.

[0059] The superabsorbent resin comprises a crosslinked polymer of a water-soluble ethylene-based unsaturated monomer having acidic groups, at least a portion of which are neutralized; and clay modified with a polymeric dispersant whose surface contains two or more functional groups selected from the group consisting of amine groups, carbonyl groups, and hydroxyl groups. The superabsorbent resin may contain the polymeric dispersant in an amount of more than 20 parts by weight and up to 200 parts by weight per 100 parts by weight of clay.

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

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

[0062] The polymerization methods described above can be broadly divided into thermal polymerization and photopolymerization depending on the polymerization energy source. Typically, thermal polymerization may be carried out in a reactor with a stirring shaft such as a kneader, and photopolymerization may be carried out in a reactor equipped with a movable conveyor belt. However, the polymerization methods described above are merely examples, and the present invention is not limited to the polymerization methods described above.

[0063] As an example, the hydrated gel polymer obtained by thermal polymerization by supplying hot air to a reactor such as a kneader equipped with a stirring shaft as described above, or by heating the reactor, may be discharged from the reactor outlet in the form of several centimeters to several millimeters, depending on the configuration of the stirring shaft provided in the reactor. Specifically, the size of the obtained hydrated gel polymer can vary depending on the concentration and injection rate of the monomer composition injected, but typically, a hydrated gel polymer with a weight-average particle size of about 2 to 50 mm is obtained.

[0064] Furthermore, when photopolymerization is carried out in a reactor equipped with a movable conveyor belt as described above, the resulting hydrated gel polymer may typically be in the form of a sheet-like hydrated gel polymer having the width of the belt. In this case, the thickness of the polymer sheet varies depending on the concentration and injection rate of the monomer composition being injected, but it is generally preferable to supply the monomer composition so that a sheet-like polymer with a thickness of about 0.5 to about 5 cm is obtained. If the monomer composition is supplied to such an extent that the thickness of the sheet-like polymer is excessively thin, the production efficiency will be low and undesirable, and if the thickness of the sheet-like polymer exceeds 5 cm, the excessive thickness may prevent the polymerization reaction from occurring uniformly across the entire thickness.

[0065] In this case, the typical water content of the water-containing gel polymer obtained by this method may be about 40 to about 80% by weight. On the other hand, throughout this specification, "water content" refers to the amount of water relative to the total weight of the water-containing gel polymer, and means the value obtained by subtracting the weight of the dry polymer from the weight of the water-containing gel polymer. Specifically, it is defined as the value calculated by measuring the weight loss due to water evaporation in the polymer during the drying process in which the temperature of the polymer is raised by infrared heating. In this case, the drying conditions are set to raise the temperature from room temperature to about 180°C and then maintain it at 180°C, and the total drying time is set to 20 minutes, including the 5 minutes for the temperature rise stage, and the water content is measured.

[0066] After crosslinking polymerization of the monomer, a base resin powder can be obtained through processes such as drying, grinding, and classification. It is appropriate that the base resin powder and the superabsorbent resin obtained therefrom be manufactured and provided so that they have a particle size of approximately 150 to 850 μm through such grinding and classification processes. More specifically, at least approximately 95% by weight of the base resin powder and the superabsorbent resin obtained therefrom may have a particle size of approximately 150 to 850 μm, and fine powder with a particle size of less than approximately 150 μm may account for less than approximately 3% by weight.

[0067] By adjusting the particle size distribution of the base resin powder and the superabsorbent resin to a favorable range, the final manufactured superabsorbent resin can exhibit the aforementioned physical properties and even better liquid permeability.

[0068] On the other hand, the drying, grinding, and classification processes described above can be explained in more detail as follows.

[0069] First, when drying the water-containing gel polymer, if necessary, a step of coarse grinding before drying may be performed to improve the efficiency of the drying step.

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

[0071] At this stage, the coarse grinding process can be performed so that the particle size of the water-containing gel polymer is approximately 2 to 10 mm.

[0072] Grinding the particle size to less than 2 mm is technically difficult due to the high water content of the water-containing gel polymer, and aggregates may occur between the ground particles. On the other hand, grinding to a particle size exceeding 10 mm may only slightly increase the efficiency of the subsequent drying stage.

[0073] As described above, drying is performed on the coarsely ground or the water-containing gel polymer immediately after polymerization without going through the coarse grinding step. 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 will be excessively long, which may cause a decrease in the physical properties of the final superabsorbent resin. If the drying temperature exceeds about 250°C, only the surface of the polymer will be excessively dried, which may cause fine powder to be generated in the subsequent grinding step, which may also cause a decrease in the physical properties of the final superabsorbent resin. Therefore, preferably, the drying may be performed at a temperature of about 150 to about 200°C, and more preferably at a temperature of about 160 to about 180°C.

[0074] On the other hand, the drying time may be approximately 20 to 90 minutes, taking into consideration process efficiency, but it is not limited to this.

[0075] The drying method in the aforementioned drying step can be selected and used without limitation on its configuration, as long as it is one that is commonly used in the drying process of water-containing gel polymers. Specifically, the drying step can be carried out by methods such as supplying hot air, infrared irradiation, ultra-high frequency irradiation, or ultraviolet irradiation. 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 this drying process is pulverized.

[0077] The polymer powder obtained after the grinding step may have a particle size of approximately 150 to 850 μm. The grinders used to achieve this particle size can include, but are not limited to, pin mills, hammer mills, screw mills, roll mills, disc mills, or jog mills.

[0078] Furthermore, after this grinding stage, in order to control the physical properties of the superabsorbent polymer powder that will be commercialized as a final product, the polymer powder obtained after grinding can undergo a separate process of classification according to its particle size. Preferably, polymers with a particle size of about 150 to about 850 μm can be classified, and only polymer powders with such particle sizes can be commercialized by proceeding to the surface crosslinking reaction step.

[0079] On the other hand, after the base resin powder formation process described above has been carried out, the surface of the base resin powder can be further crosslinked in the presence of a surface crosslinking agent to form a surface crosslinked layer, thereby enabling the production of a superabsorbent resin.

[0080] As the surface crosslinking agent, a compound that can react with the functional groups of the polymer can be used. Examples include polyhydric alcohol compounds, polyhydric epoxy compounds, polyamine compounds, haloepoxy compounds, condensation products of haloepoxy compounds, oxazoline compounds, or alkylene carbonate compounds.

[0081] Specifically, examples of polyhydric alcohol compounds 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] Furthermore, as polyvalent epoxy compounds, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, and glycidol can be used, and as polyamine compounds, one or more selected from the group consisting of ethylenediamine, diethylenetriamine, triethylenetetraamine, tetraethylenepentamine, pentaethylenehexamine, polyethyleneimine, and polyamide polyamine can be used.

[0083] Furthermore, epichlorohydrin, epibromohydrin, and α-methylepichlorohydrin can be used as the halo-epoxy compound. On the other hand, as the mono-, di-, or polyoxazolidinone compound, for example, 2-oxazolidinone can be used.

[0084] Furthermore, ethylene carbonate and other similar compounds can be used as alkylene carbonate compounds.

[0085] The aforementioned compounds may be used individually or in combination with each other.

[0086] The content of the added surface crosslinking agent can be appropriately selected depending on the type of surface crosslinking agent added and the reaction conditions, but typically, 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 per 100 parts by weight of the base resin.

[0087] Furthermore, there are no limitations on the configuration of the method for adding the surface crosslinking agent to the base resin powder. For example, methods such as mixing the surface crosslinking agent and the base resin powder in a reaction vessel, spraying the surface crosslinking agent onto the base resin powder, or continuously supplying the base resin powder and the surface crosslinking agent to a continuously operating mixer for mixing can be used.

[0088] When adding the surface crosslinking agent, water and methanol can be added in a mixture. Adding water and methanol has the advantage of allowing the surface crosslinking agent to disperse uniformly in the base resin powder. In this case, the amount of water and methanol added can be adjusted relative to 100 parts by weight of the base resin powder in order to induce uniform dispersion of the surface crosslinking agent, prevent clumping of the base resin powder, and optimize the surface penetration depth of the crosslinking agent.

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

[0090] The means of raising the temperature for the surface crosslinking reaction are not particularly limited. Heating can be achieved by supplying a heat transfer medium or by directly supplying a heat source. In this case, the types of heat transfer mediums that can be used include heated fluids such as steam, hot air, and hot oil, but are not limited to these. Furthermore, the temperature of the supplied heat transfer medium can be appropriately selected considering the type of heat transfer medium, the heating rate, and the target temperature. On the other hand, directly supplied heat sources include electric heating and gas heating methods, but are not limited to the examples described above.

[0091] The superabsorbent polymer obtained by the manufacturing method described above exhibits excellent properties, with improved water retention capacity and pressure-absorbing capacity, and is therefore suitable for use in sanitary products such as diapers.

[0092] The following are preferred embodiments for understanding the present invention. However, these embodiments are merely illustrative of the present invention, and it will be obvious to those skilled in the art that various changes and modifications are possible within the scope of the present invention and the technical concept, and it goes without saying that such changes and modifications fall within the scope of the attached claims.

[0093] [Examples] <Manufacturing of compositions for producing superabsorbent polymers> Example 1-1 An acrylic acid monomer composition was prepared by mixing 450 g of acrylic acid, 3 g of polyethylene glycol diacrylate 400, and 0.04 g of diphenyl (2,4,6-trimethylbenzoyl)phosphine oxide, and then adding 580 g of a 31.5% aqueous sodium hydroxide solution.

[0094] Separately, 5 g of ZrO2 beads were weighed and placed into a 10 mL vial as a grinding medium. To this, 12 mg of polyvinylpyrrolidone (PVP, Aldrich's PVP10; weight-average molecular weight 10,000) was added as a dispersant, followed by 24 mg of clay powder (bentonite, BYK's OPTIGEL CK, particle size range of 1-5 μm, average particle size (D50) 3 μm). 4.7 g of the acrylic acid monomer composition was then added, and the mixture was shaken at 300 rpm for 4 hours using a shaker (JEIO TECH, SK-600) to produce a composition for manufacturing superabsorbent polymers.

[0095] Examples 1-2 to 1-3 and Comparative Examples 1-1 to 1-4 The compositions for producing superabsorbent polymers for 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, except that the type and amount of dispersant were changed as shown in Table 1 below.

[0096] For Examples 1-5, poly(acrylic acid) with a weight-average molecular weight of 25,000 g / mol was used, and for Comparative Examples 1-6, poly(ethylene oxide) with a weight-average molecular weight of 100,000 g / mol was used, a product of Sigma-Aldrich.

[0097] The DISPERBYK-102 (BYK Corporation) used in Comparative Examples 1-2 is a phosphate ester-based polymer, while the Sokalan HP-20 (BASF Corporation) used in Comparative Examples 1-3 is a polyethyleneimine-based polymer dispersant.

[0098] [Table 1]

[0099] Experimental Example 1: Evaluation of physical properties of compositions for manufacturing superabsorbent polymers The physical properties of each superabsorbent polymer manufacturing composition in Examples 1-1 to 1-3 and Comparative Examples 1-1 to 1-4 were evaluated using the method described below, and the results are shown in Table 2.

[0100] (1) Settlement velocity The sedimentation velocity of clay particles in each composition 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 a superabsorbent polymer manufacturing composition was placed in a 10 mm PC cell, then mounted on a LUMiSizer, and the transmittance profile for 400 points was measured at 10-second intervals at a temperature of 25°C and 1,500 rpm (~280 G). The threshold was set to 21% in the transmitted value profile measured in this way, and the sedimentation velocity was calculated.

[0102] (2) Dispersion stability after 48 hours Four g of each superabsorbent polymer manufacturing composition from Examples 1-1 to 1-3 and Comparative Examples 1-1 to 1-4 was placed in a 10 ml vial and left upright in a vial rack at a temperature of 25°C for 48 hours. After that, the supernatant liquid was observed visually to see if layer separation had occurred. If layer separation occurred, the dispersion stability was evaluated as "no" (X), and if layer separation did not occur, the dispersion stability was evaluated as "good" (O).

[0103] [Table 2]

[0104] Referring to Table 2 above, it can be confirmed that the superabsorbent polymer production compositions of Examples 1-1 to 1-3, in which a clay dispersion containing 25 to 50 parts by weight of PVP dispersant relative to 100 parts by weight of clay is added, do not exhibit significant clay sedimentation and maintain excellent dispersion stability even after 48 hours.

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

[0106] (2) Production 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. Then, 580g of a 31.5% aqueous sodium hydroxide solution was added to produce an acrylic acid monomer composition.

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

[0108] 1000g of the aforementioned superabsorbent polymer manufacturing composition was placed in a stainless steel container measuring 250mm wide, 250mm long, and 30mm high, and irradiated with ultraviolet light (irradiation dose 10mV / cm²). 2 The mixture was then subjected to UV polymerization for 90 seconds to obtain a hydrated gel polymer.

[0109] Subsequently, the obtained sheet-like hydrated gel polymer was placed in a meat chopper to obtain hydrated gel particle powder, which was then dried in an oven until the moisture content of the dried material was 1% or less. After the dried particles were crushed in a pulverizer, they were classified to select particles with a size of 150-850 μm to prepare the base resin.

[0110] 100 g of the base resin powder was mixed with 6 g of an aqueous surface crosslinking agent solution containing 3 g of ethylene carbonate by spraying it onto the base resin powder and stirring at room temperature to ensure uniform distribution of the surface crosslinking solution. Next, the base resin powder mixed with the surface crosslinking solution was placed in a surface crosslinking reactor and heated to 190°C for 30 minutes, after which the surface crosslinking reaction was carried out at the same temperature for 15 minutes.

[0111] After the surface crosslinking process, the powder was classified using an ASTM standard sieve to produce a superabsorbent polymer with a particle size of 150 to 850 μm.

[0112] Examples 2-2 to 2-3 and Comparative Examples 2-1 to 2-3 The clay dispersion was prepared in the same manner as in Example 2-1 (1), except that the types and amounts of clay and dispersant were adjusted as shown in Table 3 below. Subsequently, the superabsorbent polymers 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 polymers The physical properties of each superabsorbent resin in Examples 2-1 to 2-3 and Comparative Examples 2-1 to 2-3 were evaluated using the method described below, and the results are shown in Table 4.

[0115] (1)EFFC(Effective Absorption Capacity) The value of EFFC 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 using EDANA WSP241.2.

[0119] Specifically, resins were obtained by classifying the resins obtained in the examples and comparative examples using a #30-50 sieve. Approximately 0.2 g of this superabsorbent resin W0 (g) was uniformly placed in a nonwoven fabric bag and sealed. The bag was then immersed in physiological saline (0.9 wt%) at room temperature. After 30 minutes, the bag was drained for 3 minutes under 250 G conditions using a centrifuge, and the mass of the bag W2 (g) was measured. The same procedure was also performed without the resin, and the mass W1 (g) was measured at that time.

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

[0121] CRC(g / g)={[W2(g)-W1(g)] / W0(g)}-1

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

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

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

[0125] Specifically, a 400-mesh stainless steel wire mesh was attached to the bottom of a 60mm inner diameter plastic cylinder. Under normal temperature and 50% humidity conditions, a water-absorbing resin W0(g) (0.90g) was uniformly scattered on the wire mesh. A piston capable of uniformly applying a load of 0.7 psi was placed on top of it, with an outer diameter slightly smaller than 60mm, and without any gaps between it and the inner wall of the cylinder, so as not to hinder its vertical movement. At this time, the weight W4(g) of the device was measured.

[0126] A glass filter with a diameter of 90 mm and a thickness of 5 mm was placed inside a 150 mm diameter petroleum dish, and physiological saline solution consisting of 0.9 wt% sodium chloride was poured in so that it was level with the top surface of the glass filter. A sheet of filter paper with a diameter of 90 mm was placed on top of that. The measuring device was placed on the filter paper and allowed to absorb the liquid under load for 1 hour. After 1 hour, the measuring device was lifted and its weight W5 (g) was measured.

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

[0128] AUP(g / g)=[W5(g)-W4(g)] / W3(g)

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

[0130] [Table 4]

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

[0132] On the other hand, comparing Examples 2-1 to 2-3, which used a clay dispersion containing a dispersant along with the clay, with Comparative Examples 2-2 and 2-3, it can be confirmed that Comparative Examples 2-2 and 2-3, which used Sokalan HP-20 as a dispersant, had higher color b values ​​compared to Examples 2-1 to 2-3, which used PVP.

[0133] From the above results, it can be confirmed that the superabsorbent polymer composition of the present invention exhibits excellent dispersion stability of clay in the composition, and can improve the water absorption properties of the superabsorbent polymer produced. Furthermore, it can be confirmed that the superabsorbent polymer produced from the superabsorbent polymer composition of the present invention does not risk discoloration due to the dispersant and exhibits excellent color characteristics.

Claims

1. clay; One or more polymeric dispersants selected from the group consisting of polyvinylpyrrolidone and polyacrylic acid; A water-soluble ethylene-based unsaturated monomer having an acidic group, wherein at least a portion of the acidic group is neutralized; and Polymerization initiator; A composition for producing superabsorbent polymers, comprising 25 to 180 parts by weight of the polymer dispersant per 100 parts by weight of clay.

2. The composition for producing superabsorbent resins according to claim 1, comprising 25 to 100 parts by weight of the polymer dispersant per 100 parts by weight of clay.

3. The composition for producing a superabsorbent polymer according to claim 1, wherein the clay is one or more selected from the group consisting of montmorillonite, saponite, nontronite, laponite, byderite, hectorite, vermiculite, magadiite, bentonite, kaolin, serpentine, and mica.

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

5. The composition for producing superabsorbent polymers according to claim 1, wherein the degree of neutralization of the water-soluble ethylene-based unsaturated monomer is 50 to 95%.

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

7. The composition for producing superabsorbent polymers according to claim 1, wherein the water-soluble ethylene-based unsaturated monomer is 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, or 2-(meth)acrylamido-2-methylpropanesulfonic acid and their salts.

8. The composition for producing a superabsorbent resin according to claim 1, wherein the amount of clay in the composition for producing a superabsorbent resin is 0.1 to 1 part by weight per 100 parts by weight of ethylene-based unsaturated monomer.

9. A step of producing a water-containing gel polymer by irradiating a superabsorbent resin production composition according to any one of claims 1 to 8 with heat and / or light to cause a polymerization reaction; A step of drying and pulverizing the water-containing gel polymer to produce a base resin; and A method for producing a superabsorbent resin, comprising the step of further crosslinking the surface of the base resin in the presence of a surface crosslinking agent to form a surface crosslinked layer.

10. A crosslinked polymer of a water-soluble ethylene-based unsaturated monomer having an acidic group, wherein at least a portion of the acidic group is neutralized; and Clay whose surface is modified with one or more polymeric dispersants selected from the group consisting of polyvinylpyrrolidone and polyacrylic acid; A superabsorbent resin comprising 25 to 180 parts by weight of the polymer dispersant per 100 parts by weight of clay.

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