technical field
[One]
Cross-Citation with Related Applications
[2]
This application claims the benefit of priority based on Korean Patent Application No. 10-2019-0123772 on October 07, 2019, and all contents disclosed in the documents of the Korean patent applications are incorporated as a part of this specification.
[3]
[4]
The present invention relates to a method for producing a super absorbent polymer.
[5]
background
[6]
Super Absorbent Polymer (SAP) is a synthetic polymer material that can absorb water 500 to 1,000 times its own weight. Material), etc., are named differently. The superabsorbent polymer as described above has started to be put to practical use as a sanitary tool, and now, in addition to hygiene products such as paper diapers for children, a soil repair agent for gardening, a water-retaining material for civil engineering and construction, a sheet for seedlings, a freshness maintenance agent in the food distribution field, and It is widely used as a material for poultice, etc.
[7]
As a method for producing the superabsorbent polymer as described above, a method by suspension polymerization, aqueous solution polymerization, or gas phase polymerization is known.
[8]
As the method using aqueous solution polymerization, a thermal polymerization method in which the polymerization gel is broken and cooled in a kneader equipped with several axes, and a photopolymerization method in which a high-concentration aqueous solution is irradiated with ultraviolet rays or the like on a belt to perform polymerization and drying simultaneously etc. are known.
[9]
The hydrogel polymer obtained through the polymerization reaction as described above is generally marketed as a powdery product after being pulverized through a drying process.
[10]
In products using superabsorbent polymers, permeability is a measure of the fluidity of absorbed liquids. The transmittance may vary depending on characteristics such as the particle size distribution of the crosslinked resin, the particle shape and the connectivity of the openings between the particles, and the surface modification of the swollen gel. The fluidity of the liquid passing through the swollen particles varies according to the transmittance of the superabsorbent polymer composition. If the transmittance is low, the liquid cannot easily flow through the superabsorbent polymer composition.
[11]
One method of increasing the transmittance of the superabsorbent polymer is a method of performing a surface crosslinking reaction after polymerization of the resin. In this case, a method of adding silica or clay together with a surface crosslinking agent has been used.
[12]
However, as the silica or clay is added, the transmittance is improved, but the water holding capacity or the absorbency under pressure is decreased in proportion to this, and there is a problem in that it is easy to separate from the superabsorbent polymer due to an external physical impact during movement. In particular, when silica or clay is mixed wet or dry, anti-caking properties, etc. can be obtained, but the absorption performance under pressure is significantly lowered and it is difficult to realize fast absorption performance when applied to actual diapers, etc. There are disadvantages.
[13]
In particular, in the case of silica, it is difficult to secure the target anti-caking effect unless dry mixing is performed, and there is a side effect of excessively decreasing absorption performance under pressure even when a small amount is added. In addition, dry mixed silica has a disadvantage in that silica dust separated from the super absorbent polymer is generated during product transfer in the line.
[14]
In addition, in recent years, with the thinning of sanitary materials such as diapers and sanitary napkins, a method for reducing substances harmful to the human body while achieving higher absorption performance for superabsorbent polymers has emerged as an important issue.
[15]
Therefore, research on the development of superabsorbent materials that can realize excellent absorption-related physical properties and exhibit excellent storage stability even in high-temperature and high-humidity environments with excellent anti-caking properties while excluding the use of substances that are controversial in the manufacturing process need.
[16]
DETAILED DESCRIPTION OF THE INVENTION
technical challenge
[17]
This specification does not use an epoxy-based surface cross-linking agent, which is controversial about harm to the human body, but uses a non-epoxy cross-linking agent, but proceeds with surface cross-linking at a relatively lower temperature than before, so that excellent absorption-related physical properties can be maintained and super absorbent polymer An object of the present invention is to provide a method for manufacturing a superabsorbent polymer that can implement anti-caking of particles.
[18]
means of solving the problem
[19]
The present specification provides a method for forming a hydrogel polymer by cross-linking and polymerizing a water-soluble ethylenically unsaturated monomer having an acid group at least partially neutralized in the presence of a polymerization initiator and an internal cross-linking agent; drying, pulverizing, and classifying the hydrogel polymer to obtain a base resin powder; In the presence of a surface crosslinking solution, surface crosslinking the base resin powder at a temperature of 170 ° C. or less to form super absorbent polymer particles, wherein the surface crosslinking is performed while raising the temperature from the initial temperature to the first temperature. An object of the present invention is to provide a method for producing a superabsorbent polymer, including one surface crosslinking and a second surface crosslinking proceeding while lowering the temperature from a first temperature to a second temperature, wherein the second temperature is lower than the first temperature.
[20]
[21]
The initial temperature is a temperature before the surface crosslinking reaction is performed by introducing the base resin to the surface crosslinking process, and may be a temperature of about 0 to about 50 °C, or about 10 to about 30 °C, or room temperature.
[22]
[23]
In this case, the first temperature may be preferably about 165 °C or more and about 170 °C or less.
[24]
[25]
And, the second temperature may be preferably about 160 °C or more and less than about 165 °C.
[26]
[27]
In addition, the first and second surface crosslinking may each independently proceed for about 10 to about 60 minutes, or about 10 to about 40 minutes, or about 10 minutes to about 35 minutes.
[28]
[29]
According to an embodiment of the present invention, the surface crosslinking solution may include a non-epoxy-based surface crosslinking agent, and on the contrary, it may be preferable not to include an epoxy-based surface crosslinking agent.
[30]
That is, it may be preferable that the surface crosslinking solution contains only a non-epoxy surface crosslinking agent.
[31]
[32]
Specifically, the surface crosslinking solution may include a polyhydric alcohol compound, a polyamine compound, an oxazoline compound; It may include at least one selected from the group consisting of mono-, di-, or polyoxazolidinone compounds, cyclic urea compounds, polyvalent metal salts, and alkylene carbonate compounds.
[33]
[34]
The surface crosslinking agent may be used in an amount of about 0.5 to about 10 parts by weight, preferably about 0.5 to about 5 parts by weight, or about 1 to about 3 parts by weight based on 100 parts by weight of the base resin powder.
[35]
And, according to an embodiment of the present invention, after the second surface crosslinking, a third surface crosslinking performed at a constant temperature at the second temperature may be further included.
[36]
The third surface crosslinking may be performed for about 10 to about 60 minutes, or about 10 to about 40 minutes, or about 10 minutes to about 20 minutes.
[37]
[38]
In the present invention, terms such as first, second, etc. are used to describe various components, and the terms are used only for the purpose of distinguishing one component from another.
[39]
In addition, the terminology used herein is used only to describe exemplary embodiments, and is not intended to limit the present invention.
[40]
The singular expression includes the plural expression unless the context clearly dictates otherwise.
[41]
In the present specification, terms such as “comprise”, “comprising” or “have” are used to describe an embodied feature, number, step, component, or combination thereof, and include one or more other features, number, or step. , components, combinations or additions thereof are not excluded.
[42]
Also in this specification, when it is said that each layer or element is formed "on" or "over" each layer or element, it means that each layer or element is formed directly on each layer or element, or other It means that a layer or element may additionally be formed between each layer, on the object, on the substrate.
[43]
Since the present invention may have various changes and may have various forms, specific embodiments will be illustrated and described in detail below. However, this is not intended to limit the present invention to the specific disclosed form, and should be understood to include all modifications, equivalents and substitutes included in the spirit and scope of the present invention.
[44]
[45]
Throughout this specification, physiological saline refers to physiological saline (0.9 wt% NaCl(s)).
[46]
[47]
Hereinafter, the present invention will be described in detail.
[48]
[49]
According to one aspect of the present invention, cross-linking polymerization of a water-soluble ethylenically unsaturated monomer having an acid group at least partially neutralized in the presence of a polymerization initiator and an internal cross-linking agent to form a hydrogel polymer; drying, pulverizing, and classifying the hydrogel polymer to obtain a base resin powder; In the presence of a surface crosslinking solution, surface crosslinking the base resin powder at a temperature of 170 ° C. or less to form super absorbent polymer particles, wherein the surface crosslinking is performed while raising the temperature from the initial temperature to the first temperature. 1 surface crosslinking, and a second surface crosslinking that proceeds while lowering the temperature from the first temperature to the second temperature, wherein the first temperature is higher than the initial temperature, and the second temperature is lower than the first temperature. A method of making a resin is provided.
[50]
[51]
The inventors of the present invention, in the conventional method for producing a superabsorbent polymer that undergoes a surface crosslinking process, limit the component of the surface crosslinking agent to a specific material, excluding the use of an epoxy-based surface crosslinking agent, and crosslinking a plurality of surfaces at different temperatures As the reaction proceeds, in particular, when the progress temperature of each surface crosslinking process is gradually lowered in stages, the excellent absorption-related physical properties of the superabsorbent polymer can be maintained despite the use of a non-epoxy surface crosslinking agent, and the anti-inflammatory properties of the superabsorbent polymer Found that caking can be implemented, and completed the present invention.
[52]
[53]
Hereinafter, the manufacturing method of the superabsorbent polymer of one embodiment Each step of the law will be explained in more detail.
[54]
[55]
For reference, as used herein, "polymer" or "polymer" means a polymerized state of a water-soluble ethylenically unsaturated monomer, and may cover all water content ranges, all particle size ranges, and all surface cross-linked states or processed states. . Among the polymers, a polymer having a water content (moisture content) of about 40% by weight or more in a state before drying after polymerization may be referred to as a hydrogel polymer.
[56]
[57]
In addition, the base resin refers to a particulate resin or powder in the form of drying and pulverizing the hydrogel polymer, and does not undergo additional processes such as surface crosslinking, fine powder reassembly, re-drying, re-grinding, reclassification, etc. it means not
[58]
[59]
In addition, "super absorbent polymer" means the polymer itself, or the base resin, depending on the context, or additional processes for the polymer, such as surface crosslinking, fine powder reassembly, drying, grinding, classification, etc. It can be used to encompass all of those that are in a state suitable for commercialization after passing through, and preferably, it can be used to mean a surface-crosslinked polymer.
[60]
[61]
In the manufacturing method of one embodiment, first, a hydrogel polymer is prepared.
[62]
[63]
The hydrogel polymer may be prepared by polymerizing a monomer mixture including a water-soluble ethylenically unsaturated monomer and a polymerization initiator.
[64]
As the water-soluble ethylenically unsaturated monomer, any monomer commonly used in the preparation of the super absorbent polymer may be used without particular limitation. Here, any one or more monomers selected from the group consisting of anionic monomers and salts thereof, nonionic hydrophilic monomers, amino group-containing unsaturated monomers, and quaternaries thereof may be used.
[65]
Specifically, (meth)acrylic acid, maleic anhydride, fumaric acid, crotonic acid, itaconic acid, 2-(meth)acryloylethanesulfonic acid, 2-(meth)acryloylpropanesulfonic acid or 2-(meth)acrylamide- anionic monomers of 2-methyl propane sulfonic acid and salts thereof; (meth)acrylamide, N-substituted (meth)acrylamide, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, methoxypolyethylene glycol (meth)acrylate or polyethylene glycol ( a nonionic hydrophilic-containing monomer of meth)acrylate; and (N,N)-dimethylaminoethyl (meth)acrylate or (N,N)-dimethylaminopropyl (meth)acrylamide containing an unsaturated monomer containing an amino group and a quaternary product thereof can
[66]
More preferably, acrylic acid or a salt thereof, for example, an alkali metal salt such as acrylic acid or a sodium salt thereof may be used. Using such a monomer, a superabsorbent polymer having better physical properties can be prepared. When the alkali metal salt of acrylic acid is used as a monomer, it may be used by neutralizing the acrylic acid with a basic compound such as caustic soda (NaOH).
[67]
The concentration of the water-soluble ethylenically unsaturated monomer may be from about 20 to about 60% by weight, preferably from about 40 to about 50% by weight, based on the monomer composition including the raw material and the solvent of the superabsorbent polymer. It may be an appropriate concentration in consideration of time and reaction conditions. However, if the concentration of the monomer is too low, the yield of the superabsorbent polymer may be low and economical problems may occur. Conversely, if the concentration is too high, some of the monomers are precipitated or the grinding efficiency is low when the polymerized hydrogel polymer is pulverized. Process problems may occur, and the physical properties of the superabsorbent polymer may be deteriorated.
[68]
[69]
The polymerization initiator used during polymerization in the method for preparing the superabsorbent polymer according to the exemplary embodiment is not particularly limited as long as it is generally used in the manufacture of the superabsorbent polymer.
[70]
Specifically, the polymerization initiator may be a thermal polymerization initiator or a photo polymerization initiator according to UV irradiation according to the polymerization method. However, even by the photopolymerization method, a certain amount of heat is generated by irradiation such as ultraviolet irradiation, and a certain amount of heat is generated according to the progress of the polymerization reaction, which is an exothermic reaction, so a thermal polymerization initiator may be additionally included.
[71]
The photopolymerization initiator may be used without limitation in its composition as long as it is a compound capable of forming radicals by light such as ultraviolet rays.
[72]
The photopolymerization initiator is, for example, benzoin ether (benzoin ether), dialkyl acetophenone (dialkyl acetophenone), hydroxyl alkyl ketone (hydroxyl alkylketone), phenyl glyoxylate (phenyl glyoxylate), benzyl dimethyl ketal (Benzyl) At least one selected from the group consisting of dimethyl ketal), acyl phosphine, and α-aminoketone may be used. On the other hand, as a specific example of the acylphosphine, commercially available lucirin TPO, that is, 2,4,6-trimethyl-benzoyl-trimethyl phosphine oxide (2,4,6-trimethyl-benzoyl-trimethyl phosphine oxide) may be used. . A more diverse photoinitiator is well described in Reinhold Schwalm's book "UV Coatings: Basics, Recent Developments and New Application (Elsevier 2007)" p115, but is not limited to the above-described examples.
[73]
The photopolymerization initiator may be included in a concentration of about 0.01 to about 1.0 wt% based on the monomer mixture. If the concentration of the photopolymerization initiator is too low, the polymerization rate may be slowed, and if the concentration of the photopolymerization initiator is too high, the molecular weight of the superabsorbent polymer may be small and physical properties may be non-uniform.
[74]
In addition, as the thermal polymerization initiator, at least one selected from the group consisting of a persulfate-based initiator, an azo-based initiator, hydrogen peroxide and ascorbic acid may be used. Specifically, examples of the persulfate-based initiator include sodium persulfate (Na 2S 2O 8), potassium persulfate (K 2S 2O 8), ammonium persulfate (Ammonium persulfate; (NH 4) 2S 2O 8) and the like, and examples of the azo-based initiator include 2,2-azobis-(2-amidinopropane)dihydrochloride (2,2-azobis(2-amidinopropane) dihydrochloride), 2,2-azobis- (N,N-dimethylene)isobutyramidine dihydrochloride (2,2-azobis-(N,N-dimethylene)isobutyramidine dihydrochloride), 2-(carbamoylazo)isobutyronitrile (2-(carbamoylazo) isobutylonitril), 2,2-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride (2,2-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride) , 4,4-azobis-(4-cyanovaleric acid) (4,4-azobis-(4-cyanovaleric acid)) and the like. More various thermal polymerization initiators are well specified in Odian's book 'Principle of Polymerization (Wiley, 1981)', p203, and are not limited to the above-described examples.
[75]
The thermal polymerization initiator may be included in a concentration of 0.001 to 0.5 wt% based on the monomer mixture. If the concentration of the thermal polymerization initiator is too low, additional thermal polymerization hardly occurs and the effect of the addition of the thermal polymerization initiator may be insignificant. there is.
[76]
[77]
According to an embodiment, the monomer mixture may further include an internal crosslinking agent as a raw material for the super absorbent polymer. The internal crosslinking agent includes a crosslinking agent having at least one functional group capable of reacting with a water-soluble substituent of the water-soluble ethylenically unsaturated monomer and having at least one ethylenically unsaturated group; Alternatively, a crosslinking agent having at least two functional groups capable of reacting with a water-soluble substituent of the monomer and/or a water-soluble substituent formed by hydrolysis of the monomer may be used.
[78]
Specific examples of the internal crosslinking agent include bisacrylamide having 8 to 12 carbon atoms, bismethacrylamide, poly(meth)acrylate of a polyol having 2 to 10 carbon atoms, or poly(meth)allyl ether of a polyol having 2 to 10 carbon atoms, etc. and more specifically, N,N'-methylenebis(meth)acrylate, ethyleneoxy(meth)acrylate, polyethyleneoxy(meth)acrylate, propyleneoxy(meth)acrylate, glycerin diacrylate , glycerin triacrylate, trimethylol triacrylate, triallylamine, triaryl cyanurate, triallyl isocyanate, polyethylene glycol, diethylene glycol and at least one selected from the group consisting of propylene glycol may be used.
[79]
The internal crosslinking agent may be included in a concentration of 0.01 to 0.5% by weight based on the monomer mixture to crosslink the polymerized polymer.
[80]
[81]
In the manufacturing method according to an embodiment of the present invention, the monomer mixture of the super absorbent polymer may further include additives such as a thickener, a plasticizer, a storage stabilizer, and an antioxidant, if necessary.
[82]
Raw materials such as the above-described water-soluble ethylenically unsaturated monomer, photopolymerization initiator, thermal polymerization initiator, internal crosslinking agent and additives may be prepared in the form of a monomer mixture solution dissolved in a solvent.
[83]
The solvent that can be used at this time can be used without limitation in its composition as long as it can dissolve the above-mentioned components, for example, 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, butyl Lolactone, carbitol, methyl cellosolve acetate, N, N- dimethyl acetamide, etc. may be used in combination of one or more selected from.
[84]
The solvent may be included in the remaining amount excluding the above-mentioned components with respect to the total content of the monomer mixture.
[85]
[86]
On the other hand, as long as the method of polymerizing such a monomer mixture to form a hydrogel polymer is also a commonly used polymerization method, there is no particular limitation on the structure.
[87]
Specifically, 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, Although it may be carried out in a reactor equipped with a movable conveyor belt, the polymerization method described above is an example and is not limited to the polymerization method described above.
[88]
For example, as described above, the hydrogel polymer obtained by thermal polymerization by supplying hot air or heating the reactor to a reactor such as a kneader having a stirring shaft is fed to the reactor outlet according to the shape of the stirring shaft provided in the reactor. The discharged hydrogel polymer may be in the form of several centimeters to several millimeters. Specifically, the size of the hydrogel polymer obtained may vary depending on the concentration and injection rate of the monomer mixture to be injected, and usually, a hydrogel polymer having a weight average particle diameter of 2 to 50 mm can be obtained.
[89]
In addition, as described above, when photopolymerization is performed in a reactor equipped with a movable conveyor belt, the form of the hydrogel polymer obtained may be a hydrogel polymer on a sheet having the width of the belt. At this time, the thickness of the polymer sheet varies depending on the concentration and injection rate of the monomer composition to be injected, but it is preferable to supply the monomer composition so that a polymer sheet having a thickness of about 0.5 to about 5 cm can be obtained. When the monomer composition is supplied so that the thickness of the polymer on the sheet is too thin, the production efficiency is low, which is undesirable. it may not happen
[90]
[91]
Typically, the water content of the hydrogel polymer obtained in this way may be 40 to 80 wt%. Meanwhile, throughout the present specification, "moisture content" refers to a value obtained by subtracting the weight of the polymer in a dry state from the weight of the hydrogel polymer as the amount of moisture occupied with respect to the total weight of the hydrogel polymer. Specifically, it is defined as a value calculated by measuring the weight loss due to evaporation of moisture in the polymer during drying by raising the temperature of the polymer through infrared heating. At this time, the drying condition is set to 20 minutes including 5 minutes of the temperature rise step in such a way that the temperature is raised from room temperature to 180° C. and then maintained at 180° C., and the moisture content is measured.
[92]
[93]
According to one embodiment of the invention, a coarse grinding process may be optionally further performed on the hydrogel polymer obtained above.
[94]
At this time, the pulverizer used in the coarse pulverization process is not limited in configuration, but specifically, 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 selected from the group consisting of a grinding device. It may include any one, but is not limited to the above-described example.
[95]
In this case, in the coarse grinding step, the hydrogel polymer may have a particle diameter of about 2 to 20 mm.
[96]
Coarse pulverization with a particle diameter of less than 2 mm is not technically easy due to the high water content of the hydrogel polymer, and also aggregation between the pulverized particles may occur. On the other hand, when the particle size is coarsely pulverized to more than 20 mm, the effect of increasing the efficiency of the subsequent drying step may be insignificant.
[97]
[98]
Optionally, after the hydrogel polymer is prepared in the method for producing a super absorbent polymer according to an embodiment of the present invention, the hydrogel polymer may be dried and pulverized to classify the hydrogel polymer into fine powder and normal particles.
[99]
The drying process is performed on the hydrogel polymer immediately after polymerization without being coarsely pulverized or subjected to a coarse pulverization step. In this case, the drying temperature of the drying step may be about 150 to about 250 ℃. When the drying temperature is less than 150°C, the drying time becomes excessively long and there is a risk that the physical properties of the superabsorbent polymer finally formed may decrease. fine powder may occur, and there is a risk that the physical properties of the superabsorbent polymer finally formed may be deteriorated. Therefore, preferably, the drying may be carried out at a temperature of about 150 °C to about 200 °C, more preferably at a temperature of about 160 °C to about 180 °C.
[100]
Meanwhile, in the case of drying time, in consideration of process efficiency, etc., the drying time may be performed for about 20 to about 90 minutes, but is not limited thereto.
[101]
If the drying method of the drying step is also commonly used in the drying process of the hydrogel polymer, it may be selected and used without limitation in its configuration. Specifically, the drying step may be performed by a method such as hot air supply, infrared irradiation, microwave irradiation, or ultraviolet irradiation. After the drying step, the moisture content of the polymer may be about 0.1 to about 10% by weight.
[102]
Next, a pulverization process is performed on the dried polymer obtained through such a drying step.
[103]
The polymer powder obtained after the grinding step may have a particle diameter of about 150 to about 850 μm. The grinder used for grinding to such a particle size is specifically, a pin mill, a hammer mill, a screw mill, a roll mill, a disc mill, or a jog. A mill (jog mill) or the like may be used, but the invention is not limited to the above-described examples.
[104]
[105]
In order to manage the physical properties of the super absorbent polymer powder to be finalized after the pulverization step, the polymer powder obtained after pulverization is generally classified according to particle size. Preferably, a step of classifying particles having a particle diameter of 150 μm or less and particles having a particle diameter of more than about 150 μm and 850 μm or less is performed.
[106]
Unless otherwise specified herein, "particle size or particle size" may be measured by a standard sieve analysis method or a laser diffraction method, preferably a standard sieve analysis method, and "average particle diameter or weight average" "Particle diameter" may mean a particle diameter (D50) that is 50% of the weight percentage in a particle size distribution curve obtained through laser diffraction method.
[107]
In addition, in the present specification, fine particles having a particle size of less than or equal to a certain particle size, that is, about 150 μm or less, are referred to as base resin fine powder, super absorbent polymer fine powder, SAP fine powder or fines, and a particle size of 150 μm is referred to as fine powder. Particles larger than 850 μm or less are referred to as normal particles.
[108]
The fine powder may be generated during the polymerization process, the drying process, or the pulverization step of the dried polymer. When the fine powder is included in the final product, it is difficult to handle and may reduce physical properties such as exhibiting a gel blocking phenomenon. Therefore, it is desirable to exclude the fine powder from being included in the final resin product or to reassemble the fine powder to become normal particles.
[109]
As an example, a reassembly process may be performed in which the fine particles are aggregated to have a normal particle size. In general, in the reassembly process, in order to increase cohesive strength, a reassembly process is performed in which the fine particles are agglomerated in a wet state. At this time, the higher the moisture content of the fine powder, the higher the cohesive strength of the fine powder. However, during the reassembly process, an excessively large mass of reassembly may occur, which may cause problems during process operation. After that, it is often crushed into fine powder again (fun differentiation). In addition, the fine powder re-assembled body obtained in this way has lower physical properties such as water holding capacity (CRC) and absorbency under pressure (AUP) than normal particles, leading to a decrease in the quality of the superabsorbent polymer.
[110]
Accordingly, in an exemplary manufacturing method, water and additives are selectively added to the fine powder and re-assembled to obtain a fine powder re-assembly.
[111]
In the manufacturing step of the fine powder reassembly, using a mixing device or mixer capable of adding a shear force, the fine powder and the aqueous additive solution are mixed at a speed of about 10 to about 2000 rpm, about 100 to about 1000 rpm, or about 500 to about 800 rpm It can be mixed by stirring.
[112]
And, as an example, the drying process of the manufacturing step of the fine powder re-assembly may be performed at about 120 to about 220° C. to form a fine powder re-assembly having improved cohesive strength through covalent bonding, and the moisture content of the fine powder re-assembly within an appropriate time can be adjusted to about 1 to about 2% by weight.
[113]
The drying process may be performed using a conventional drying machine, but according to an embodiment of the present invention, it may be performed using a hot air dryer, a paddle-type dryer, or a forced circulation dryer. In addition, as a means for increasing the temperature for drying in the drying process, there is no limitation in the configuration thereof. Specifically, a heating medium may be supplied or the heating medium may be directly heated by means such as electricity, but the present invention is not limited to the above-described examples. Specifically, a heat source that can be used includes steam, electricity, ultraviolet rays, infrared rays, and the like, and a heated thermal fluid may be used.
[114]
[115]
Next, in the method for producing a superabsorbent polymer according to an embodiment of the present invention, the fine powder re-assembly prepared in the above step is pulverized as necessary, and the re-assembled fine powder (hereinafter referred to as 'fine powder') and re-assembly normal particles are used. can proceed step by step all.
[116]
The fine powder re-assembly obtained through the step of preparing the fine powder re-assembly has a high cohesive strength, and the ratio of re-crushing into fine powder after being pulverized, that is, the ratio of re-pulverization is low.
[117]
The pulverization of the fine powder re-assembly may be performed so that the particle diameter of the fine powder re-assembly is about 150 to about 850 μm. The grinder used for grinding to such a particle size is specifically, a pin mill, a hammer mill, a screw mill, a roll mill, a disc mill, or a jog. A mill (jog mill) or the like may be used, but the present invention is not limited to the above-described examples.
[118]
In order to manage the physical properties of the super absorbent polymer powder to be finalized after the pulverization step, the polymer powder obtained after pulverization is generally classified according to particle size. Preferably, the step of classifying into fine flour having a particle diameter of 150 μm or less, and re-assembled normal particles having a particle diameter of greater than 150 μm and 850 μm or less is performed.
[119]
[120]
And, in the method for producing a superabsorbent polymer according to an embodiment of the present invention, in the presence of a surface crosslinking solution, the base resin powder, or optionally the base resin powder including the fine powder re-assembly, is surface cross-linked at a temperature of 170° C. or less. to form superabsorbent polymer particles.
[121]
The surface crosslinking is a step of increasing the crosslinking density near the surface of the superabsorbent polymer particles in relation to the crosslinking density inside the particles. In general, the surface crosslinking agent is applied to the surface of the superabsorbent polymer particles. Accordingly, this reaction occurs on the surface of the superabsorbent polymer particles, which improves cross-linking properties on the surface of the particles without substantially affecting the inside of the particles. Therefore, the surface cross-linked super absorbent polymer particles have a higher degree of cross-linking near the surface than inside.
[122]
[123]
At this time, the surface crosslinking includes a first surface crosslinking that proceeds while raising the temperature from an initial temperature to a first temperature, and a second surface crosslinking that proceeds while lowering the temperature from the first temperature to a second temperature, wherein the second temperature is It is controlled to be lower than the first temperature.
[124]
As in the conventional surface crosslinking process, the first surface crosslinking reaction is performed at a relatively high temperature compared to the case where the surface crosslinking reaction is carried out while the temperature is constantly maintained at a high temperature, or the surface crosslinking reaction is performed while the temperature is increased. When the second surface crosslinking reaction proceeds by lowering the temperature, the excellent absorption-related physical properties of the superabsorbent polymer can be maintained despite the use of a non-epoxy-based surface crosslinking agent, and the anti-caking of the superabsorbent polymer is prevented. can be implemented
[125]
[126]
In this case, the first temperature may be preferably about 165 °C or more and about 170 °C or less.
[127]
And, it may be preferable that the second temperature is greater than or equal to about 160 °C and less than about 165 °C.
[128]
If the surface crosslinking temperature is too high out of the above temperature range, or if the temperature is not lowered in an appropriate time, the CRC value in the superabsorbent polymer to be manufactured may decrease, and if the temperature range is too low, the effective absorption capacity is reduced Problems may arise.
[129]
[130]
In addition, it may be preferable that the first and second surface crosslinking are each independently performed for about 10 to about 60 minutes.
[131]
If the surface crosslinking time is too short, the surface crosslinking layer is not properly formed in the superabsorbent polymer to be produced, which may cause a problem in that the physical properties of the absorbent are lowered. If the surface crosslinking time is too long, the King phenomenon may occur.
[132]
[133]
According to an embodiment of the present invention, the surface cross-linking solution may include a non-epoxy-based surface cross-linking agent, and on the contrary, it may be preferable not to include an epoxy-based surface cross-linking agent, which has recently been controversial about human toxicity.
[134]
In this case, the surface crosslinking agent is a compound capable of reacting with a functional group of the polymer, and if it is a non-epoxy surface crosslinking agent that does not contain an epoxy group in the molecule, there is no limitation in its configuration.
[135]
Preferably, in order to improve the properties of the resulting superabsorbent polymer, a polyhydric alcohol compound as the surface crosslinking agent; polyamine compounds; oxazoline compounds; mono-, di- or polyoxazolidinone compounds; cyclic urea compounds; polyvalent metal salts; And one or more selected from the group consisting of alkylene carbonate compounds may be used.
[136]
Specifically, examples of the polyhydric alcohol compound include mono-, di-, tri-, tetra- or polyethylene glycol, monopropylene glycol, dipropylene glycol, polypropylene glycol, 2,3,4-trimethyl-1,3-pentanediol , glycerol, polyglycerol, 2-butene-1,4-diol, 1,4-butanediol, 1,3-butanediol, 1,5-pentanediol, 1,6-hexanediol, and 1,2-cyclohexanediol At least one selected from the group consisting of methanol may be used.
[137]
In addition, as the alkylene carbonate compound, ethylene carbonate or the like may be used. Each of these may be used alone or in combination with each other. On the other hand, in order to increase the efficiency of the surface crosslinking process, it is preferable to include one or more polyhydric alcohol compounds among these surface crosslinking agents, and more preferably, polyhydric alcohol compounds having 2 to 10 carbon atoms can be used.
[138]
[139]
The content of the added surface crosslinking agent may be appropriately selected depending on the type of the added surface crosslinking agent or reaction conditions, but usually from about 0.5 to about 10 parts by weight, preferably from about 0.5 to about 10 parts by weight, based on 100 parts by weight of the polymer. 5 parts by weight, more preferably about 1 to about 3 parts by weight may be used.
[140]
When the content of the surface crosslinking agent is too small, the surface crosslinking reaction hardly occurs, and when the content of the surface crosslinking agent is too large, the absorption capacity and physical properties may be deteriorated due to the excessive progress of the surface crosslinking reaction.
[141]
[142]
By heating the polymer particles to which the surface crosslinking agent is added, the surface crosslinking reaction and drying can be performed simultaneously.
[143]
The temperature control means for the surface crosslinking reaction is not particularly limited. For example, a heat medium or a heat source may be directly supplied to the reaction system, and the temperature may be decreased or increased by controlling the amount of heat supplied.
[144]
[145]
At this time, as the type of heat medium that can be used, a heated fluid such as steam, hot air, hot oil, or conversely, a cooled fluid such as cold air or oil may be used, but the present invention is not limited thereto, and The temperature of the supplied thermal medium may be appropriately selected in consideration of the means of the heating medium, the rate of temperature increase and decrease, or the target temperature for temperature increase and temperature decrease, and the like. On the other hand, the directly supplied heat source may be a heating method through electricity or a gas heating method, but the present invention is not limited to the above-described example.
[146]
[147]
And, according to an embodiment of the present invention, after the second surface crosslinking, a third surface crosslinking performed at a constant temperature at the second temperature may be further included.
[148]
The third surface crosslinking may be performed for about 10 to about 60 minutes, or about 10 to about 40 minutes, or about 10 minutes to about 20 minutes.
[149]
According to the third surface crosslinking reaction, in the superabsorbent polymer to be prepared, various physical properties related to absorption may be improved, and the anti-caking effect may be more excellently realized.
[150]
[151]
Further, after the surface crosslinking, the surface crosslinked fine powder having a particle size of 150 μm or less, and surface crosslinked normal particles having a particle diameter of more than 150 μm and 850 μm or less, are classified into fine powder, and the surface crosslinked fine powder having a particle size of 150 μm or less is fine powder. It is reintroduced into the process for granulation, and the surface-crosslinked normal particles can be commercialized and used.
[152]
Effects of the Invention
[153]
The superabsorbent polymer manufacturing method according to one aspect of the present invention does not use an epoxy-based surface crosslinking agent, which is controversial about harm to the human body, and uses a non-epoxy crosslinking agent, but proceeds with surface crosslinking at a relatively lower temperature than before, It is possible to implement anti-caking while maintaining excellent absorption-related physical properties of the water absorbent resin particles.
[154]
Modes for carrying out the invention
[155]
Hereinafter, through specific examples of the invention, the operation and effect of the invention will be described in more detail. However, these embodiments are merely presented as an example of the invention, and the scope of the invention is not defined thereby.
[156]
[157]
Preparation of base resin - Examples and Comparative Examples
[158]
A monomer composition was prepared by mixing 100 parts by weight of acrylic acid, 126.8 parts by weight of 31.5% caustic soda (NaOH), 46 parts by weight of water, and the following components.
[159]
- Internal crosslinking agent: 0.2 parts by weight of polyethylene glycol diacrylate (PEGDA; Mw = 400) (2000 ppmw)
[160]
-Polymerization initiator: 0.008 parts by weight (80ppmw) of bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (photoinitiator) and 0.12 parts by weight (1200ppmw) of sodium persulfate (thermal initiator)
[161]
The composition was introduced into the supply part of the polymerization reactor consisting of a conveyor belt moving continuously, and the polymerization reaction was carried out by irradiating ultraviolet rays with a UV irradiation device for 1.5 minutes (about 2 mW/cm 2 ), and a hydrogel polymer was obtained as a product. .
[162]
[163]
The hydrogel polymer was cut through a cutter. Then, the hydrogel polymer was dried in a hot air dryer at 190° C. for 40 minutes, and the dried hydrogel polymer was pulverized with a grinder. Then, a polymer having a particle size (average particle size) of 150 μm to 850 μm was classified using a sieve to obtain fine base resin powder and normal base resin particles.
[164]
The CRC value of the obtained base resin was about 54 g/g.
[165]
[166]
surface crosslinking
[167]
Example 1
[168]
For the base resin prepared above, a standard sieve Using this, a base resin having the following particle size distribution was prepared.
[169]
#20-#30: 22 wt%, #30-#50: 64wt%, #50-#100: 13wt%, #100: 1wt%
[170]
Based on 100 parts by weight of the base resin, about 5.4 parts by weight of water, about 1.8 parts by weight of ethylene carbonate and propylene carbonate (1:1), about 0.58 parts by weight of propylene glycol, and 0.24 parts by weight of aluminum sulfate are mixed in a ratio of, and surface crosslinking solution was prepared.
[171]
With respect to 100 parts by weight of the base resin powder, the surface crosslinking solution was added, and well mixed with stirring at about 1000 rpm for about 30 seconds using a mixer.
[172]
This was put into the reactor, and the surface crosslinking reaction proceeded while the temperature was raised to about 168° C. over about 30 minutes. (first surface crosslinking)
[173]
Thereafter, while the temperature of the reaction system was lowered to about 163° C. over about 15 minutes, the surface crosslinking reaction was carried out. (Second surface crosslinking)
[174]
Thereafter, the temperature of the reaction system was adjusted to about 163° C., and the surface crosslinking reaction was performed while maintaining it for about 15 minutes again. (third surface crosslinking)
[175]
[176]
After the surface crosslinking was completed, the obtained superabsorbent polymer was put into a pulverizer and pulverized, and then a surface-treated superabsorbent polymer having a particle diameter of 150 to 850 μm was obtained using a sieve.
[177]
[178]
Example 2
[179]
For the base resin prepared above, using a standard sieve, a base resin having the following particle size distribution was prepared.
[180]
#20-#30: 22 wt%, #30-#50: 64wt%, #50-#100: 13wt%, #100: 1wt%
[181]
Based on 100 parts by weight of the base resin, about 5.4 parts by weight of water, about 1.8 parts by weight of ethylene carbonate and propylene carbonate (1:1), about 0.58 parts by weight of propylene glycol, and 0.24 parts by weight of aluminum sulfate are mixed in a ratio of, and surface crosslinking solution was prepared.
[182]
With respect to 100 parts by weight of the base resin powder, the surface crosslinking solution was added, and well mixed with stirring at about 1000 rpm for about 30 seconds using a mixer.
[183]
This was put into the reactor, and the surface crosslinking reaction was performed while the temperature was raised to about 170° C. over about 30 minutes. (first surface crosslinking)
[184]
Thereafter, while the temperature of the reaction system was lowered to about 160° C. over about 15 minutes, the surface crosslinking reaction was carried out. (Second surface crosslinking)
[185]
Thereafter, the temperature of the reaction system was adjusted to about 160° C., and the surface crosslinking reaction was carried out while maintaining it again for about 15 minutes. (third surface crosslinking)
[186]
[187]
After the surface crosslinking was completed, the obtained superabsorbent polymer was put into a pulverizer and pulverized, and then a surface-treated superabsorbent polymer having a particle diameter of 150 to 850 μm was obtained using a sieve.
[188]
[189]
Comparative Example 1
[190]
Based on 100 parts by weight of the base resin obtained above, about 3.2 parts by weight of water, about 4.5 parts by weight of methanol, and about 0.132 parts by weight of ethylene glycol were mixed in a ratio to prepare a surface crosslinking solution.
[191]
With respect to 100 parts by weight of the base resin powder, the surface crosslinking solution was added, and well mixed with stirring at about 1000 rpm for about 30 seconds using a mixer.
[192]
Thereafter, it was put into the reactor, and the surface crosslinking reaction was performed while the temperature was raised to about 163° C. over about 30 minutes. (first surface crosslinking)
[193]
Thereafter, the surface crosslinking reaction proceeded while the temperature of the reaction system was raised to about 183° C. over about 15 minutes. (Second surface crosslinking)
[194]
Thereafter, the temperature of the reaction system was adjusted to about 185° C., and the surface crosslinking reaction was performed while maintaining it for about 15 minutes again. (third surface crosslinking)
[195]
After the surface crosslinking was completed, the obtained superabsorbent polymer was put into a pulverizer and pulverized, and then a surface-treated superabsorbent polymer having a particle diameter of 150 to 850 μm was obtained using a sieve.
[196]
[197]
Comparative Example 2
[198]
Based on 100 parts by weight of the base resin obtained above, about 5.4 parts by weight of water, about 1.8 parts by weight of ethylene carbonate and propylene carbonate (ECPC), and about 0.58 parts by weight of propylene glycol were mixed to prepare a surface crosslinking solution.
[199]
With respect to 100 parts by weight of the base resin powder, the surface crosslinking solution was added, and well mixed with stirring at about 1000 rpm for about 30 seconds using a mixer.
[200]
Thereafter, it was put into the reactor, and the surface crosslinking reaction was performed while the temperature was raised to about 163° C. over about 30 minutes. (first surface crosslinking)
[201]
Thereafter, the surface crosslinking reaction proceeded while the temperature of the reaction system was raised to about 183° C. over about 15 minutes. (Second surface crosslinking)
[202]
Thereafter, the temperature of the reaction system was adjusted to about 185° C., and the surface crosslinking reaction was performed while maintaining it for about 15 minutes again. (third surface crosslinking)
[203]
After the surface crosslinking was completed, the obtained superabsorbent polymer was put into a pulverizer and pulverized, and then a surface-treated superabsorbent polymer having a particle diameter of 150 to 850 μm was obtained using a sieve.
[204]
[205]
Comparative Example 3
[206]
Based on 100 parts by weight of the base resin obtained above, about 3.2 parts by weight of water, about 4.5 parts by weight of methanol, and about 0.132 parts by weight of ethylene glycol were mixed in a ratio to prepare a surface crosslinking solution.
[207]
With respect to 100 parts by weight of the base resin powder, the surface crosslinking solution was added, and well mixed with stirring at about 1000 rpm for about 30 seconds using a mixer.
[208]
Thereafter, it was put into the reactor, and the surface crosslinking reaction was performed while the temperature was raised to about 163° C. over about 30 minutes. (first surface crosslinking)
[209]
Thereafter, the surface crosslinking reaction proceeded while the temperature of the reaction system was raised to about 183° C. over about 15 minutes. (Second surface crosslinking)
[210]
Thereafter, the surface crosslinking reaction proceeded while the temperature of the reaction system was raised to about 185° C. over about 15 minutes. (third surface crosslinking)
[211]
With respect to 100 parts by weight of the superabsorbent polymer obtained after the surface crosslinking was completed, about 0.05 parts by weight of a post-added inorganic filler (Aerosil 200, manufactured by Evonik) was added and mixed well.
[212]
After this was put in a grinder and pulverized, a surface-treated superabsorbent polymer having a particle diameter of 150 to 850 μm was obtained using a sieve.
[213]
[214]
Comparative Example 4
[215]
Based on 100 parts by weight of the base resin obtained above, about 3.2 parts by weight of water, about 4.5 parts by weight of methanol, and about 0.132 parts by weight of ethylene glycol were mixed in a ratio to prepare a surface crosslinking solution.
[216]
With respect to 100 parts by weight of the base resin powder, the surface crosslinking solution was added, and well mixed with stirring at about 1000 rpm for about 30 seconds using a mixer.
[217]
Thereafter, it was put into the reactor, and the surface crosslinking reaction was performed while the temperature was raised to about 163° C. over about 30 minutes. (first surface crosslinking)
[218]
Thereafter, the temperature of the reaction system was adjusted to about 163° C., and the surface crosslinking reaction was performed while maintaining it for about 15 minutes again. (Second surface crosslinking)
[219]
Thereafter, the surface crosslinking reaction proceeded while the temperature of the reaction system was raised to about 168° C. over about 15 minutes. (third surface crosslinking)
[220]
After the surface crosslinking was completed, the obtained superabsorbent polymer was put into a pulverizer and pulverized, and then a surface-treated superabsorbent polymer having a particle diameter of 150 to 850 μm was obtained using a sieve.
[221]
[222]
Comparative Example 5
[223]
For the base resin prepared above, using a standard sieve, a base resin having the following particle size distribution was prepared.
[224]
#20-#30: 22 wt%, #30-#50: 64wt%, #50-#100: 13wt%, #100: 1wt%
[225]
Based on 100 parts by weight of the base resin, about 5.4 parts by weight of water, about 1.8 parts by weight of ethylene carbonate and propylene carbonate (1:1), about 0.58 parts by weight of propylene glycol, and 0.24 parts by weight of aluminum sulfate are mixed in a ratio of, and surface crosslinking solution was prepared.
[226]
With respect to 100 parts by weight of the base resin powder, the surface crosslinking solution was added, and well mixed with stirring at about 1000 rpm for about 30 seconds using a mixer.
[227]
This was put into the reactor, and the surface crosslinking reaction was carried out while raising the temperature to about 165° C. over about 30 minutes. (first surface crosslinking)
[228]
Thereafter, the surface crosslinking reaction proceeded while the temperature of the reaction system was lowered to about 150° C. over about 15 minutes. (Second surface crosslinking)
[229]
Thereafter, the temperature of the reaction system was adjusted to about 150° C., and the surface crosslinking reaction was carried out while maintaining it again for about 15 minutes. (third surface crosslinking)
[230]
[231]
After the surface crosslinking was completed, the obtained superabsorbent polymer was put into a pulverizer and pulverized, and then a surface-treated superabsorbent polymer having a particle diameter of 150 to 850 μm was obtained using a sieve.
[232]
[233]
Comparative Example 6
[234]
For the base resin prepared above, using a standard sieve, a base resin having the following particle size distribution was prepared.
[235]
#20-#30: 22 wt%, #30-#50: 64wt%, #50-#100: 13wt%, #100: 1wt%
[236]
Based on 100 parts by weight of the base resin, about 5.4 parts by weight of water, about 1.8 parts by weight of ethylene carbonate and propylene carbonate (1:1), about 0.58 parts by weight of propylene glycol, and 0.24 parts by weight of aluminum sulfate are mixed in a ratio of, and surface crosslinking solution was prepared.
[237]
With respect to 100 parts by weight of the base resin powder, the surface crosslinking solution was added, and well mixed with stirring at about 1000 rpm for about 30 seconds using a mixer.
[238]
This was put into the reactor, and the temperature was raised to about 165° C. over about 30 minutes, while surface crosslinking.The reaction proceeded. (first surface crosslinking)
[239]
Thereafter, the surface crosslinking reaction proceeded while the temperature of the reaction system was lowered to about 60° C. over about 15 minutes. (Second surface crosslinking)
[240]
Thereafter, the temperature of the reaction system was adjusted to about 60° C., and the surface crosslinking reaction was performed while maintaining it for about 15 minutes again. (third surface crosslinking)
[241]
[242]
After the surface crosslinking was completed, the obtained superabsorbent polymer was put into a pulverizer and pulverized, and then a surface-treated superabsorbent polymer having a particle diameter of 150 to 850 μm was obtained using a sieve.
[243]
[244]
Physical property evaluation
[245]
With respect to the surface-treated superabsorbent polymer obtained above, various physical properties related to absorption were measured by the following method.
[246]
[247]
CRC measurement
[248]
The water holding capacity of each resin according to the absorption magnification under no load was measured according to EDANA WSP 241.3.
[249]
Specifically, in each of the superabsorbent polymers obtained in Examples and Comparative Examples, resins classified through a sieve of #30-50 were obtained. This resin W0 (g) (about 0.2 g) was uniformly put in a non-woven bag and sealed, and then immersed in physiological saline (0.9 wt %) at room temperature. After 30 minutes, the bag was drained of water for 3 minutes under the conditions of 250G using a centrifuge, and the mass W2 (g) of the bag was measured. Moreover, after performing the same operation without using resin, the mass W1 (g) at that time was measured. Using each obtained mass, CRC (g/g) was calculated according to the following formula.
[250]
[Equation 1]
[251]
CRC (g/g) = {[W2(g) - W1(g)]/W0(g)} - 1
[252]
[253]
0.7 AUP measurement
[254]
The absorption capacity under pressure of 0.7 psi of each resin was measured according to EDANA method WSP 242.3.
[255]
First, in the measurement of the combined absorption capacity, the fraction of the resin classified at the time of the CRC measurement was used.
[256]
Specifically, a stainless steel 400 mesh wire mesh was mounted on the bottom of a plastic cylinder with an inner diameter of 25 mm. A piston capable of uniformly spreading the absorbent resin W0(g) (0.16 g) on ​​the wire mesh under conditions of room temperature and humidity of 50% and applying a load of 0.7 psi (or 0.3, 0.9 psi) more uniformly thereon It is slightly smaller than the outer diameter of 25 mm, there is no gap with the inner wall of the cylinder, and the vertical movement is not disturbed. At this time, the weight W3 (g) of the device was measured.
[257]
A glass filter having a diameter of 90 mm and a thickness of 5 mm was placed on the inside of a 150 mm diameter petro dish, and physiological saline composed of 0.9 wt% sodium chloride was placed at the same level as the upper surface of the glass filter. One filter paper having a diameter of 90 mm was loaded thereon. The measuring device was placed on the filter paper, and the liquid was absorbed under load for 1 hour. After 1 hour, the measuring device was lifted and the weight W4 (g) was measured.
[258]
Using each obtained mass, absorbency under pressure (g/g) was calculated according to the following equation.
[259]
[Equation 2]
[260]
AUP(g/g) = [W4(g) - W3(g)]/W0(g)
[261]
[262]
The arithmetic mean value of the measured CRC value and 0.7 AUP value was obtained and summarized as effective absorption capacity.
[263]
[264]
Anti-caking property measurement (Anti-caking)
[265]
2 g (W5) of the superabsorbent polymer prepared in Examples and Comparative Examples is evenly applied to a 9 cm diameter Petri dish, and then maintained for 10 minutes in a constant temperature and humidity chamber maintaining a temperature of 40±3° C. and a humidity of 80±3%. After washing, the flask dish was turned over on the filter paper and taped three times, and then the amount of superabsorbent polymer dripping (W6) was measured.
[266]
The caking prevention efficiency was calculated according to the following Equation 2 using the measured weight, and the higher the value, the better the caking prevention efficiency.
[267]
[Equation 3]
[268]
Anti-caking efficiency (%) = [W6(g) / W5(g)] * 100
[269]
In Equation 3, W5(g) is the initial weight (g) of the superabsorbent polymer, and W6(g) is uniformly applied to a flask dish with a diameter of 10 cm, temperature 40±3℃, humidity 80±3% level It is the amount (g) that the superabsorbent polymer falls after holding the flask for 10 minutes in a constant temperature and humidity chamber to be maintained and then taping the flask three times on the filter paper.
[270]
[271]
The measured values ​​are summarized in Table 1 below.
[272]
[273]
[Table 1]
CRC
(g/g) 0.7 AUP
(g/g) effective absorption capacity
(g/g) anti-caking
(%)
Comparative Example 1 36.6 22.7 29.6 0
Comparative Example 2 33.5 22.9 28.2 0
Comparative Example 3 36.3 20.4 28.9 80
Comparative Example 4 41.5 12.5 27.0 0
Comparative Example 5 44.3 11.0 27.8 85
Comparative Example 6 45.5 9.5 27.5 85
Example 1 40.8 20.4 30.6 90
Example 2 41.5 19.1 30.3 90
[274]
Referring to Table 1, the superabsorbent polymer prepared according to an embodiment of the present invention has excellent CRC value and 0.7 AUP value, despite surface cross-linking at a relatively lower temperature than before, excellent effectiveness. It can be seen that the anti-caking efficiency is very high while maintaining the absorption capacity.
Claims
[Claim 1]
cross-linking a water-soluble ethylenically unsaturated monomer having an acid group at least partially neutralized in the presence of a polymerization initiator and an internal crosslinking agent to form a hydrogel polymer; drying, pulverizing, and classifying the hydrogel polymer to obtain a base resin powder; In the presence of a surface crosslinking solution, comprising the step of surface crosslinking the base resin powder at a temperature of 170 ° C. or less to form super absorbent polymer particles, wherein the surface crosslinking is performed while raising the temperature from the initial temperature to the first temperature. 1 surface crosslinking, and a second surface crosslinking that proceeds while lowering the temperature from the first temperature to the second temperature, wherein the first temperature is higher than the initial temperature, and the second temperature is lower than the first temperature. A method for producing a resin.
[Claim 2]
The method of claim 1 , wherein the first temperature is 165° C. or higher and 170° C. or lower.
[Claim 3]
The method of claim 1, wherein the second temperature is 160°C or higher and less than 165°C.
[Claim 4]
The method of claim 1 , wherein the first and second surface crosslinking are each independently performed for 10 to 60 minutes.
[Claim 5]
The method according to claim 1, wherein the surface crosslinking solution contains a non-epoxy surface crosslinking agent.
[Claim 6]
The method according to claim 1, wherein the surface crosslinking solution comprises: a polyhydric alcohol compound, a polyamine compound, an oxazoline compound; A method for producing a superabsorbent polymer, comprising at least one selected from the group consisting of mono-, di-, or polyoxazolidinone compounds, cyclic urea compounds, polyvalent metal salts, and alkylene carbonate compounds.
[Claim 7]
The method of claim 1 , wherein the surface crosslinking agent is used in an amount of 0.5 to 10 parts by weight based on 100 parts by weight of the base resin powder.
[Claim 8]
The method of claim 1 , further comprising a third surface crosslinking performed at a constant temperature at the second temperature after the second surface crosslinking.