[One]Cross-Citation with Related Application(s)
[2]This application claims the benefit of priority based on Korean Patent Application No. 10-2019-0140502 on November 5, 2019 and Korean Patent Application No. 10-2020-0146310 on November 4, 2020, All content disclosed in the literature is incorporated as a part of this specification.
[3]
The present invention relates to a method for producing a super absorbent polymer. More specifically, it is possible to improve the water content of the superabsorbent polymer to prevent changes in surface properties due to external changes, and to reduce the amount of fine powder to improve processability in the manufacture of articles using the superabsorbent polymer. It relates to a manufacturing method.
background
[4]
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 began 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.
[5]
As a method for producing the superabsorbent polymer as described above, a method by reverse-phase suspension polymerization or a method by aqueous solution polymerization is known. Reversed-phase suspension polymerization is disclosed, for example, in Japanese Patent Application Laid-Open No. 56-161408, Japanese Patent Application Laid-Open No. 57-158209, and Japanese Unexamined Patent Application Publication No. 57-198714.
[6]
As the method by aqueous solution polymerization, a thermal polymerization method in which the polymerization gel is broken and cooled while being 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.
[7]
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.
[8]
Meanwhile, in order to obtain a super absorbent polymer having better physical properties, there is a method of performing a surface crosslinking reaction after polymerization of the resin. In general, the surface crosslinking reaction is performed by spraying and stirring a surface crosslinking solution obtained by adding a crosslinking agent to water on the surface of the superabsorbent polymer, followed by heating and reacting.
[9]
However, since the surface crosslinking reaction by heating is usually performed at a high temperature of 140° C. or higher, most of the moisture contained in the superabsorbent polymer is evaporated, and as a result, the moisture content of the superabsorbent polymer finally manufactured is greatly reduced. The superabsorbent polymer having such a low water content is prone to surface damage due to friction between particles generated during movement and storage, which ultimately leads to deterioration of the physical properties of the superabsorbent polymer. In addition, the amount of fine powder generated increases during the commercialization process using the superabsorbent polymer having a low water content, thereby reducing process stability and productivity, resulting in deterioration of product quality.
[10]
Accordingly, a method of increasing the water content of the superabsorbent polymer by performing a hydrolysis process after surface crosslinking has been proposed.
[11]
As a watering method for improving the water content of the superabsorbent polymer, a direct injection method through a line and an injection method using a spray nozzle are mainly used. However, when it is introduced through a line, the size of the droplet is large, so there is a problem in that a mixture of a high moisture content mass and low moisture content general particles agglomerated into large particles is generated. On the other hand, when it is injected through a spray nozzle, the moisture content can be uniformly increased, but flow occurs due to the small droplet size, which causes device contamination and foreign substances.
DETAILED DESCRIPTION OF THE INVENTION
technical challenge
[12]
In order to solve the problems of the prior art as described above, the present invention improves the moisture content of the superabsorbent polymer by uniformly controlling the droplet size used during watering, thereby preventing changes in surface properties due to external changes, and reducing the amount of fine powder generated. An object of the present invention is to provide a method for manufacturing a superabsorbent polymer, which can improve processability such as preventing clogging of a bag filter and preventing caking when manufacturing an article using the superabsorbent polymer, and the superabsorbent polymer prepared thereby.
means of solving the problem
[13]
In order to achieve the above object, the present invention
[14]
forming a hydrogel polymer by performing thermal polymerization or photopolymerization with respect to a monomer composition comprising a water-soluble ethylenically unsaturated monomer and a polymerization initiator;
[15]
drying and pulverizing the hydrogel polymer to prepare a base resin powder;
[16]
preparing a surface-crosslinked base resin powder by adding a surface crosslinking agent to the base resin powder and performing a surface crosslinking reaction; and
[17]
Including; hydrotreating the surface-crosslinked base resin powder by pulse spraying with water;
[18]
It provides a method for producing a super absorbent polymer, wherein the scattering index according to the following Equation 1 of the droplets generated during the pulse spraying is 5 to 10:
[19]
[Equation 1]
[20]
Scattering index = [(Re droplet)/(Re air)] × 100
[21]
In Equation 1, Re droplet is a Reynolds number of a droplet, and Re air is a Reynolds number of air.
Effects of the Invention
[22]
According to the manufacturing method of the superabsorbent polymer of the present invention, it is possible to prepare a superabsorbent polymer having an improved water content and not having a risk of a change in surface properties due to external changes. In addition, the amount of fine powder generated in the superabsorbent polymer is reduced, so that when an absorbent article using the superabsorbent polymer is manufactured, processability such as preventing bag filter clogging and preventing caking can be improved.
Modes for carrying out the invention
[23]
Since the present invention may have various modifications and 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, it should be understood to include all modifications, equivalents and substitutes included in the spirit and scope of the present invention.
[24]
Hereinafter, the method for producing the superabsorbent polymer of the present invention and the superabsorbent polymer prepared thereby will be described in detail.
[25]
In the case of using a general spray nozzle during hydrotreatment to increase the moisture content of the conventional superabsorbent polymer, the smaller the diameter of the nozzle, the smaller the size of droplets generated during spraying. In this case, when the particle size is too small, there is a problem of scattering and causing process contamination. In addition, when the diameter of the nozzle is increased, in addition to this, when the flow rate is small, there is no atomization and large droplets are formed. However, when the size of the droplets increases, it is difficult to provide uniform and sufficient water to the superabsorbent polymer, and the droplets induce aggregation of the surface-crosslinked polymer particles. This causes a large amount of clogging and caking of the bag filter during the process.
[26]
Accordingly, in the present invention, by using a spray nozzle that sprays water according to a pulse during hydrotreatment, the droplet size is uniformly and easily controlled, thereby increasing the moisture content of the superabsorbent polymer to prevent changes in surface properties due to external changes, and , and the amount of fine powder is reduced, so that processability in manufacturing an article using the superabsorbent polymer can be improved.
[27]
Specifically, the method for producing a superabsorbent polymer according to an embodiment of the present invention comprises:
[28]
Forming a hydrogel polymer by thermal polymerization or photopolymerization with respect to a monomer composition comprising a water-soluble ethylenically unsaturated monomer and a polymerization initiator (step 1);
[29]
drying and pulverizing the hydrogel polymer to prepare a base resin powder (step 2);
[30]
To the base resin powder, adding a surface crosslinking agent and performing a surface crosslinking reaction to prepare a surface crosslinked base resin powder (step 3); and
[31]
The surface cross-linked base resin powder is subjected to hydrotreatment by pulse spraying water (step 4);
[32]
At this time, the scattering index according to the following Equation 1 of the droplets generated during the pulse spraying is 5 to 10.
[33]
[Equation 1]
[34]
Scattering index = [(Re droplet)/(Re air)] × 100
[35]
In Equation 1, Re droplet is a Reynolds number of a droplet, and Re air is a Reynolds number of air.
[36]
Conditions during the pulse spraying, for example, orifice diameter, pulse-on ratio, water input flow rate, pulse cycle, etc., affect the size of the droplets, and by controlling these conditions, the size of the generated droplets can be adjusted to high absorbency. It can be optimized within a range that can minimize the improvement of the water content of the resin and the generation of fine particles or coarse particles. In the present invention, the optimum size of the droplet was defined as the scattering index by using the Reynolds number of the droplet because the conditions during the pulse spraying affect the size of the droplet.
[37]
Specifically, in the present invention, the droplets generated during pulse spraying have a scattering index of 5 or more, or 6 or more, or 7 or more, or 7.5 or more, or 7.8 or more, and 10 or less, or 9 or less according to Equation 1 , or 8.8 or less. When the scattering index of the droplets is less than 5 or exceeds 10, the reactor contamination becomes serious due to an increase in fine droplets with a particle size of 300 μm or less, or the content of coarse particles with a particle size of more than 850 μm in the superabsorbent polymer produced is large can increase
[38]
In Equation 1, the Reynolds number is a term representing the ratio of the inertial force and the viscous force of the flow in fluid mechanics, and is proportional to the density of the fluid, the flow rate, and the length of an object placed in the flow, and is proportional to the viscosity of the fluid. inversely proportional
[39]
Specifically, in the present invention, the Reynolds number of the liquid droplet and air may be calculated according to Equation 2 below.
[40]
[Equation 2]
[41]
Reynolds number = [(density of fluid × average flow velocity of fluid × characteristic length of fluid)/ coefficient of viscosity of fluid
[42]
In Equation 2, the fluid is a droplet (water) or air, and literature values ​​may be used for the density and viscosity coefficient of the fluid. Specifically, when the fluid is a droplet (water), the density of the droplet is 1000 kg/m 3 , which is the literature density value of water at 25° C., and the viscosity coefficient is 10 kg/m/sec. In addition, when the fluid is air, the density of air is 1.12 kg/m 3 , which is a literature value at 25° C., and the viscosity coefficient is 0.17 kg/m/sec.
[43]
In addition, in Equation 2, the average flow velocity of the fluid can be predicted through flow analysis. Specifically, the average flow rate of the droplet is the flow rate of the fluid injected into the reactor, that is, the input flow rate of water (m 3 /hr), the area of ​​the cross-sectional shape in the flow direction of the fluid water, the area of ​​the present invention. In this case, since water flows inside the orifice, it can be calculated by dividing by the area of ​​the cut surface of the orifice perpendicular to the flow (or flow) direction of the water. In addition, the average flow rate of the air is the flow rate of the air introduced into the reactor, that is, the sweep air flow rate (m 3 /sec), and the area of ​​the shape of the cross section in the flow direction of the air in the reactor, that is, the flow direction of the air introduced into the reactor. It can be calculated by dividing by the area of ​​the cross section inside the reactor perpendicular to . On the other hand, the shape cross section in the flow direction means a cut surface when cut in a direction perpendicular to the flow direction when the fluid flows.
[44]
In addition, the characteristic length of the fluid means a length that affects the flow characteristics or heat transfer characteristics, and in the case of an external flow, the characteristic length (Lc) of the fluid is the shape cross section in the flow direction The value obtained by dividing the cross-sectional area by the cross-sectional perimeter (Lc = cross-sectional area/cross-sectional perimeter) is used. In consideration of the influence on the flow, the hydraulic diameter (Dh) is used, and the hydraulic diameter is 4 times the cross-sectional area of ​​the flow direction as the wetted perimeter. The divided value (Dh = 4 (cross-sectional area)/wetted perimeter) is used.
[45]
In the present invention, the characteristic length of a droplet is the mean diameter (SMD) of the droplet. In addition, in the case of air, as it passes through the inside of the reactor, the cross section in the flow direction of the air corresponds to the cut surface inside the reactor perpendicular to the flow direction of the air. For example, when the reactor has a shape such as a rectangular duct, the cross section of the shape in the air flow direction becomes a rectangle, and it can be calculated according to Equation 3 below:
[46]
[Equation 3]
[47]
Characteristic length of air = [4 × (horizontal length of reactor cross-section × length of reactor cross-section)] / [2 × (horizontal length of reactor cross-section + vertical length of reactor cross-section)]
[48]
In Equation 3, the transverse and longitudinal lengths of the cross section of the reactor are the transverse and longitudinal lengths at the inner section of the reactor perpendicular to the flow direction of the air.
[49]
Specifically, the Reynolds number of the droplet calculated according to Equation 2 may be 0.2 to 0.35, more specifically 0.2 or more, or 0.22 or more, or 0.23 or more, or 0.24 or more, and 0.35 or less, or 0.3 or less, or 0.28 or less, or 0.27 or less. In addition, the Reynolds number of air calculated according to Equation 2 may be 2 to 5, more specifically 2 or more, or 2.5 or more, or 2.8 or more, or 3 or more, 5 or less, or 4.5 or less, or 4 or less, or 3.5 or less.
[50]
In addition, the droplet may have an average diameter (SMD) of 400 to 600 µm, more specifically 400 µm or more, or 450 µm or more, and 600 µm or less, or 580 µm or less, or 550 µm or less. In addition, the proportion of the droplets having a diameter of 300 μm or less among the generated droplets may be 10 wt% or less, or 9 wt% or less, or 8.5 wt% or less, based on the total weight of the droplets. It is preferable that the content of the fine droplets with a diameter of 300 μm or less is smaller, but when considering the conditions of the manufacturing process, the proportion of droplets having a diameter of 300 μm or less among the generated droplets is at least 3 wt% or more, or 5 wt% or more, or It may be 5.5% by weight or more. Although having a diameter in the above range, as the content of fine droplets with a diameter of 300 μm or less that can generate flow or contaminate the device is reduced, the moisture content of the superabsorbent polymer can be improved while the degree of contamination can be minimized.
[51]
In the present invention, the average diameter (SMD) of the droplets generated during the pulse spraying and the ratio of the droplets having a diameter of 300 μm or less among the droplets can be measured by optical diffraction analysis or laser image analysis, and the specific measurement method is the following test Examples will be described in detail.
[52]
In the manufacturing method according to an embodiment of the present invention, the pulse spraying process may be performed under a controlled condition that satisfies the conditions of the droplets.
[53]
Hereinafter, a method of manufacturing a super absorbent polymer according to an embodiment of the present invention will be described in detail for each step.
[54]
First, in the method for preparing a super absorbent polymer according to an embodiment of the present invention, step 1 is a step of forming a hydrogel polymer by thermal polymerization or photopolymerization on the monomer composition.
[55]
The monomer composition, which is a raw material for the super absorbent polymer, includes a water-soluble ethylenically unsaturated monomer and a polymerization initiator.
[56]
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. 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.
[57]
Specifically, (meth)acrylic acid, maleic anhydride, fumaric acid, crotonic acid, itaconic acid, 2-acryloylethanesulfonic acid, 2-methacryloylethanesulfonic acid, 2-(meth)acryloylpropanesulfonic acid or 2- an anionic monomer of (meth)acrylamide-2-methyl propane sulfonic acid and a salt thereof; (meth) acrylamide, N-substituted (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, methoxy polyethylene 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 amino group-containing unsaturated monomer and a quaternary product thereof can
[58]
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. By 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). In this case, the degree of neutralization may be 40 to 95 mol%, or 40 to 80 mol%, or 45 to 75 mol%. The range of the degree of neutralization may vary depending on the final physical properties, but if the degree of neutralization is too high, the neutralized monomer may be precipitated and it may be difficult for polymerization to proceed smoothly. It can exhibit properties like elastic rubber, which is difficult to handle.
[59]
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, a part of the monomer is 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.
[60]
In addition, the polymerization initiator used in polymerization of the water-soluble ethylenically unsaturated monomer is not particularly limited as long as it is generally used in the production of the super absorbent polymer.
[61]
Specifically, as the polymerization initiator, a thermal polymerization initiator or a photopolymerization initiator according to UV irradiation may be used according to a 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.
[62]
The photopolymerization initiator may be used without limitation as long as it is a compound capable of forming radicals by light such as ultraviolet rays.
[63]
As the photopolymerization initiator, for example, benzoin ether, dialkyl acetophenone, hydroxyl alkylketone, phenyl glyoxylate, benzyl dimethyl ketal Ketal), acyl phosphine, and alpha-aminoketone (α-aminoketone) may be used at least one selected from the group consisting of. On the other hand, as a specific example of the acylphosphine, commercially available lucirin TPO, that is, diphenyl(2,4,6-trimethylbenzoyl)-phosphine oxide may be used. For a more diverse range of photoinitiators, see Reinhold Schwalm, “UV Coatings: Basics, Recent Developments and New Application” (Elsevier 2007), p. 115, and not limited to the above example.
[64]
The photopolymerization initiator may be included in an amount of 0.001 to 1 parts by weight, or 0.005 to 0.1 parts by weight based on 100 parts by weight of the monomer. When the content of the photopolymerization initiator is less than 0.001 part by weight, the polymerization rate may be slowed, and when the content of the photopolymerization initiator exceeds 1 part by weight, the molecular weight of the superabsorbent polymer may be small and the physical properties may be non-uniform.
[65]
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 2 S 2 O 8 ), potassium persulfate (K 2 S 2 O 8 ), ammonium persulfate (Ammonium persulfate; (NH 4 ) 2 S 2 O 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. For more various thermal polymerization initiators, see Odian's book 'Principle of Polymerization (Wiley, 1981)', p. 203, and not limited to the above example.
[66]
The thermal polymerization initiator may be included in an amount of 0.001 to 1 parts by weight, or 0.01 to 0.5 parts by weight based on 100 parts by weight of the monomer. If the content of the thermal polymerization initiator is less than 0.001 parts by weight, additional thermal polymerization hardly occurs, so the effect of adding the thermal polymerization initiator may be insignificant. If the content of the thermal polymerization initiator exceeds 1 part by weight, the molecular weight of the superabsorbent polymer is small and The physical properties may become non-uniform.
[67]
Also, according to one embodiment of the present invention, the monomer composition may further include an internal crosslinking agent as a raw material for the super absorbent polymer. Examples of the internal crosslinking agent include 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.
[68]
Specific examples of the internal crosslinking agent include bisacrylamide having 8 to 12 carbon atoms, bismethacrylamide, poly(meth)acrylate of a polyhydric alcohol compound having 2 to 10 carbon atoms, or poly(meth)acrylate of a polyhydric alcohol compound having 2 to 10 carbon atoms. (meth) allyl ether etc. are mentioned, More specifically, N,N'- methylenebis (meth)acrylate, ethyleneoxy (meth)acrylate, polyethyleneoxy (meth)acrylate, propyleneoxy (meth)acryl Late, glycerin diacrylate, glycerin triacrylate, trimethylol triacrylate, triallylamine, triaryl cyanurate, triallyl isocyanate, polyethylene glycol diacrylate, polyethylene glycol, diethylene glycol and propylene glycol One or more selected from the group may be used.
[69]
The internal crosslinking agent may be included in an amount of 0.01 to 1 part by weight, or 0.1 to 0.5 parts by weight based on 100 parts by weight of the monomer to crosslink the polymerized polymer. When the content of the internal crosslinking agent is less than 0.01 parts by weight, the improvement effect due to crosslinking is insignificant, and when the content of the internal crosslinking agent exceeds 1 part by weight, the absorbency of the superabsorbent polymer may be reduced.
[70]
In addition, in the manufacturing method according to an embodiment of the present invention, the monomer composition may further include one or more additives such as a thickener, a plasticizer, a storage stabilizer, and an antioxidant, if necessary.
[71]
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 composition solution dissolved in a solvent.
[72]
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 At least one selected from ether, toluene, xylene, butyrolactone, carbitol, methyl cellosolve acetate and N, N-dimethylacetamide may be used in combination.
[73]
The solvent may be included in the remaining amount excluding the above-mentioned components with respect to the total content of the monomer composition.
[74]
On the other hand, as long as the method for forming the hydrogel polymer by thermal polymerization or photopolymerization of such a monomer composition is also a commonly used polymerization method, there is no particular limitation on the configuration.
[75]
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 in the case of photopolymerization, movable Although the process may be carried out in a reactor equipped with a conveyor belt, the polymerization method described above is an example, and the present invention is not limited to the polymerization method described above.
[76]
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 obtained hydrogel polymer may vary depending on the concentration and injection rate of the injected monomer composition, and a hydrogel polymer having a weight average particle size of 2 to 50 mm can be obtained.
[77]
In addition, as described above, when photopolymerization is carried out 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 of the injected monomer composition and the injection rate, but it is preferable to supply the monomer composition so that the 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 be
[78]
At this time, the water content of the hydrogel polymer obtained in this way may be about 40 to about 80 wt% based on the total weight of the hydrogel polymer. Meanwhile, throughout the present specification, "moisture content" refers to the amount of moisture occupied with respect to the total weight of the hydrogel polymer, and refers to a value obtained by subtracting the weight of the polymer in the dry state from the 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 conditions are set to 20 minutes including 5 minutes of the temperature rising step in such a way that the temperature is raised from room temperature to about 180° C. and then maintained at 180° C., and the moisture content is measured.
[79]
Meanwhile, after the preparation of the hydrogel polymer, a coarse grinding process of pulverizing the prepared hydrogel polymer before subsequent drying and pulverization processes may be selectively performed.
[80]
The coarse grinding process is a process for increasing the drying efficiency in the subsequent drying process and controlling the particle size of the superabsorbent polymer powder to be manufactured. (Vertical pulverizer), Turbo cutter (Turbo cutter), Turbo grinder (Turbo grinder), Rotary cutter mill, Cutter mill, Disc mill, Shred crusher), a crusher (Crusher), a meat chopper (meat chopper), and may include any one selected from the group consisting of a disc cutter (Disc cutter), but is not limited to the above-described example.
[81]
The coarse grinding process may be performed, for example, so that the particle size of the hydrogel polymer is about 2 to about 10 mm. It is not technically easy to pulverize the hydrogel polymer having a particle size of less than 2 mm due to the high water content of the hydrogel polymer, and a phenomenon of agglomeration between the pulverized particles may occur. On the other hand, when the particle size is pulverized to more than 10 mm, the effect of increasing the efficiency of the subsequent drying step is insignificant.
[82]
Next, step 2 is a step of drying and pulverizing the hydrogel polymer prepared in step 1 above.
[83]
The drying may be performed at a temperature of 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 be generated, 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 to about 200 °C, more preferably at a temperature of about 160 to about 180 °C.
[84]
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.
[85]
In addition, the drying method may be selected and used without limitation in its configuration, as long as it is commonly used in the drying process of the hydrogel polymer. 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 5 to about 10% by weight.
[86]
After the drying process, a grinding process is performed.
[87]
The pulverization process may be performed so that the particle size of the polymer powder, that is, the base resin powder, 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 mill or the like may be used, but the present invention is not limited to the above-described examples.
[88]
In addition, after the pulverization step as described above, in order to manage the physical properties of the superabsorbent polymer powder to be finalized, a process of classifying the pulverized polymer powder according to the particle size may be further performed.
[89]
Preferably, a polymer having a particle size of about 150 to about 850 μm is classified, and only a polymer having such a particle size is used as a base resin powder to be commercialized through a surface crosslinking reaction step.
[90]
Next, in step 3, the base resin powder obtained by drying and pulverizing in step 2 is mixed with a surface crosslinking agent and heated to perform a surface crosslinking reaction.
[91]
The surface crosslinking is a step of increasing the crosslinking density near the surface of the base resin powder with respect to the crosslinking density inside the particles. In general, the surface crosslinking agent is applied to the surface of the base resin powder. Therefore, this reaction takes place on the surface of the base resin powder, which improves the cross-linking property on the surface of the particle without substantially affecting the inside of the particle. Therefore, the surface cross-linked base resin powder has a higher degree of cross-linking near the surface than inside.
[92]
In this case, the surface crosslinking agent is not limited in its composition as long as it is a compound capable of reacting with a functional group of the polymer.
[93]
Preferably, in order to improve the properties of the resulting superabsorbent polymer, a polyhydric alcohol-based compound as the surface crosslinking agent; epoxy compounds; polyamine compounds; haloepoxy compounds; condensation products of haloepoxy compounds; oxazoline compounds; mono-, di- or polyoxazolidinone compounds; cyclic urea compounds; polyvalent metal salts; And at least one selected from the group consisting of alkylene carbonate-based compounds may be used.
[94]
Specifically, examples of the polyhydric alcohol compound include ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, 1,2-hexanediol, 1,3-hexanediol, selected from the group consisting of 2-methyl-1,3-propanediol, 2,5-hexanediol, 2-methyl-1,3-pentanediol, 2-methyl-2,4-pentanediol, tripropylene glycol and glycerol One or more of these may be used.
[95]
In addition, ethylene glycol diglycidyl ether and glycidol can be used as the epoxy compound, and the polyamine compounds include ethylenediamine, diethylenetriamine, triethylenetetraamine, tetraethylenepentamine, and pentaethylenehexamine. , at least one selected from the group consisting of polyethyleneimine and polyamide polyamine may be used.
[96]
And as the haloepoxy compound, epichlorohydrin, epibromohydrin, and α-methylepichlorohydrin may be used. Meanwhile, as the mono-, di- or polyoxazolidinone compound, for example, 2-oxazolidinone may be used.
[97]
As the alkylene carbonate-based compound, an alkylene carbonate having 2 to 6 carbon atoms, such as ethylene carbonate or propylene carbonate, may be used. These may be used individually, or two or more types of alkylene carbonates having different carbon numbers may be mixed and used.
[98]
In addition, as the polyvalent metal salt, specifically, a metal-containing sulfate, such as aluminum, or a carboxylate, etc. may be used, and more specifically, aluminum sulfate, aluminum carboxylate, or a mixture thereof may be used. Among them, aluminum sulfate may be more preferably used.
[99]
Among the above-mentioned surface crosslinking agents, in order to increase the surface crosslinking efficiency, it is preferable to use a mixture of a polyhydric alcohol-based compound, an alkylene carbonate-based compound, and a polyvalent metal salt. More specifically, 0.01 to 2 parts by weight, or 0.1 to 1 part by weight of a polyhydric alcohol-based compound based on 100 parts by weight of the base resin powder; 0.01 to 3 parts by weight of an alkylene carbonate-based compound, or 0.05 to 2 parts by weight, or 0.1 to 1 part by weight; And 0.1 to 1 part by weight of the polyvalent metal salt, or 0.2 to 0.5 parts by weight; may be used in a mixture. In addition, the polyhydric alcohol-based compound, the alkylene carbonate-based compound, and the surface crosslinking agent comprising a polyvalent metal salt, as a polyvalent metal salt, contain aluminum sulfate in an amount of 0.1 to 1 part by weight, or 0.2 to 0.5 parts by weight, based on 100 parts by weight of the base resin powder. may be included as a part.
[100]
In addition, the surface crosslinking agent may further include inorganic particles, specifically, hydrophilic inorganic particles, and the superabsorbent polymer thus prepared may further include hydrophilic inorganic particles in the surface crosslinking layer.
[101]
When the hydrophilic inorganic particles are included in the surface crosslinking agent, the hydrophilic inorganic particles effectively surround the surface crosslinking agent. Accordingly, the surface crosslinking agent is prevented from being rapidly absorbed in only a part of the base resin powder locally, so that it can be uniformly applied over the entire surface of the base resin powder. Physical properties such as liquid permeability can be expressed and maintained for a long period of time.
[102]
The hydrophilic inorganic particles may be silica particles or metal oxide particles surface-treated with a compound having a hydrophilic group. The metal oxide particles may be aluminum oxide particles, titanium oxide particles, or the like. As another example, as the hydrophilic silica particles, commercially available hydrophilic silica particles such as A200 (manufactured by Evonik) may be used.
[103]
Meanwhile, in the present invention, hydrophilicity may be defined as a contact angle of the inorganic particles to water measured on a glass substrate is 0°.
[104]
The hydrophilic inorganic particles may be included in an amount of 0.005 to 0.2 parts by weight, or 0.01 to 0.1 parts by weight based on 100 parts by weight of the base resin powder.
[105]
A method of mixing the surface crosslinking agent with the base resin powder is not limited in its configuration. A method of mixing the surface crosslinking agent and the base resin powder in a reaction tank, spraying the surface crosslinking agent on the base resin powder, or a method of continuously supplying and mixing the base resin powder and the surface crosslinking agent to a continuously operated mixer can be used.
[106]
In addition to the surface crosslinking agent, water and alcohol may be mixed together and added in the form of the surface crosslinking solution. When water and alcohol are added, there is an advantage that the surface crosslinking agent can be uniformly dispersed in the base resin powder. At this time, the content of the added water and alcohol is about 5, based on 100 parts by weight of the polymer, for the purpose of inducing even dispersion of the surface crosslinking agent, preventing agglomeration of the base resin powder, and optimizing the surface penetration depth of the crosslinking agent. It is preferably added in a proportion of from to about 12 parts by weight.
[107]
Surface crosslinking by heating the base resin powder to which the surface crosslinking agent is added at a temperature of about 150 to about 220°C, preferably about 165 to about 210°C, for about 15 to about 100 minutes, preferably about 20 to about 80 minutes A binding reaction may take place. When the crosslinking reaction temperature is less than 150°C, the surface crosslinking reaction may not sufficiently occur, and when it exceeds 220°C, the surface crosslinking reaction may proceed excessively. In addition, if the crosslinking reaction time is too short (less than 15 minutes), sufficient crosslinking reaction cannot be carried out. can
[108]
The means for increasing the temperature for the surface crosslinking reaction is not particularly limited. It can be heated by supplying a heating medium or by directly supplying a heat source. At this time, as the type of heating medium that can be used, a fluid having an elevated temperature such as steam, hot air, or hot oil may be used, but the present invention is not limited thereto. It can be appropriately selected in consideration of the target temperature. On the other hand, the directly supplied heat source may be a heating method through electricity or a heating method through a gas, but the present invention is not limited to the above-described example.
[109]
The total content of the surface crosslinking agent included in the surface crosslinking solution may be appropriately selected depending on the type of the added surface crosslinking agent or reaction conditions, but based on 100 parts by weight of the base resin powder, from about 0.2 to about 2 parts by weight; Preferably, about 0.25 to about 1.5 parts by weight may be used. If the content of the surface crosslinking agent is too small, the surface crosslinking reaction hardly occurs, and when it exceeds 2 parts by weight based on 100 parts by weight of the base resin powder, the absorption capacity and physical properties may deteriorate due to the excessive surface crosslinking reaction proceeding. have.
[110]
The water content of the surface-crosslinked base resin powder obtained by the above method is in the range of about 0.1 to about 0.5% by weight. This very low moisture content is because most of the moisture in the base resin powder is evaporated during the heating at a high temperature in the surface crosslinking reaction. Such an extremely low moisture content causes a problem in that the amount of fine powder generated increases during the movement and storage of the superabsorbent polymer. For example, in the superabsorbent polymer having a moisture content in the above range, fine powder having a particle size of less than 150 μm is generated in an amount of about 1 to about 5 wt %, which ultimately leads to deterioration of the quality of the final product.
[111]
Accordingly, in the present invention, a process of hydrolyzing the surface-crosslinked base resin powder by adding water is performed. By increasing the water content of the final superabsorbent polymer by the above-described hydrotreatment, the amount of dust generated can be reduced, and as a result, process stability can be improved.
[112]
Next, the hydrotreatment of step 4 in the production method according to an embodiment of the present invention is performed by pulse spraying water on the surface cross-linked polymer prepared in step 3 above.
[113]
The pulse spraying is to generate water spray at regular time intervals, and may be performed using a pulse-type spray nozzle in which spraying is turned on/off according to a pulse, such as a pulse jet nozzle.
[114]
The pulse spraying is performed so that the droplets generated as described above satisfy the scattering index condition defined by Equation 1 above.
[115]
Specifically, during the pulse spraying, the size of the sprayed droplets affects the moisture content of the superabsorbent polymer and the amount of coarse particles generated, and the size of the droplets is affected by the orifice diameter. In the present invention, the diameter of the orifice of the spray nozzle is 1 to 2 mm, more specifically, 1 mm or more, or 1.2 mm or more, and 2 mm or less, or 1.7 mm may be used. When it has an orifice diameter in the above range, it is possible to control an appropriate water input flow rate, specifically 0.02 to 0.05 m 3 /hr , in the pulse-on ratio range to be described later , and the generated droplets have an appropriate size, and thus have high water absorption. It is possible to suppress the generation of coarse particles while improving the moisture content of the resin. If the diameter of the orifice is less than 1 mm, the droplet size is too small to cause flow, and device contamination and foreign matter may occur. On the other hand, when the diameter of the orifice exceeds 2 mm, the size of the droplet increases, and as a result, the water content of the superabsorbent polymer increases excessively, so that the absorption capacity may be rather reduced, and there is a concern that the generation of coarse particles having a particle size of more than 850 μm may increase. there is
[116]
In addition, the pulse cycle (Hz) during pulse spraying means the number of on/off per minute, and in the present invention, the pulse cycle during pulse spraying is 1 to 2000 Hz, more specifically 1 Hz or more. , or 10 Hz or more, 2000 Hz or less, or 1000 Hz or less, or 500 Hz or less. When it is within the above range, it is possible to have an appropriate flow rate in the above-mentioned orifice diameter range, and as a result, the size of the droplet is also optimized to improve the moisture content of the superabsorbent polymer while suppressing the generation of fine powder and coarse particles. If the pulse cycle is less than 1 Hz, the pulse effect is weakened and there is a risk of a decrease in the effect due to an increase in the droplet size. Also, if the pulse cycle exceeds 2000 Hz, the on/off switching is not smooth, so flow rate change or droplet size change There is a risk of a decrease in effectiveness.
[117]
In addition, the pulse on ratio during the pulse spraying, that is, the ratio of the time during which spraying is performed according to the application of a pulse during the entire pulse spraying process. In the present invention, the pulse on ratio during the pulse spraying process is a pulse It may be 10 to 50%, more specifically 10% or more, or 20% or more, and 50% or less, or 35% or less with respect to the total time of the spraying process. When the pulse-on ratio is less than 10%, the amount of droplet generation is small, so sufficient watering is difficult. If the pulse-on ratio exceeds 50%, aggregation occurs between the hydrolyzed particles due to excessively high droplet generation, and as a result, the superabsorbent polymer There is a risk that the content of my coarse particles will increase.
[118]
On the other hand, as the water content increases during hydrotreating, the absorption rate of the finally prepared super absorbent polymer may increase. However, when the absorption rate of the superabsorbent polymer exceeds a certain level, the absorption ability is rather reduced, and when the water content is too high, the content of coarse particles in the final manufactured superabsorbent polymer increases by aggregation between the hydrolyzed particles. The water input flow rate can be adjusted by the above-described pulse-on ratio, orifice diameter and flow rate, spray pressure applied to water during pulse spraying, etc., in the present invention, the water input flow rate during pulse spraying is 0.02 to 0.05 m 3 /hr, more specifically 0.02 m 3 /hr or more, or 0.025 m 3 /hr or more, or 0.024 m 3 /hr or more, and 0.05 m 3 /hr or less, or 0.04 m 3 /hr or less, or 0.035 m 3 /hr or less, or 0.03 m 3 /hr or less. If the flow rate is less than 0.02 m 3 /hr, there is a fear that the effect of increasing the water content by water is insignificant, and the flow rate is 0.05 m 3If it exceeds /hr, the size of the droplets increases, and as a result, the water content of the superabsorbent polymer is excessively increased, so that the absorbency may be rather deteriorated, and there is a possibility that the generation of coarse particles having a particle size of more than 850 μm may increase.
[119]
Through the control of the conditions during pulse spraying as described above, the droplets generated through the spray nozzle satisfy the conditions of optimized droplets that can improve the moisture content of the superabsorbent polymer and minimize the generation of fine particles or coarse particles. In the present invention, as the conditions of such droplets are defined as a scattering index, the droplets generated during pulse spraying in the present invention specifically have a scattering index of 5 or more, or 6 or more, or 7.5 or more according to Equation 1 below. , or 7.8 or more, or 10 or less, or 9 or less, or 8.8 or less. As the generated droplets have a scattering index within the above range, fine droplets with a particle size of 300 μm or less can be reduced to minimize reactor contamination, and coarse particles with a particle size of more than 850 μm can be controlled by controlling the moisture content in the superabsorbent polymer to be produced. content can be significantly reduced.
[120]
The superabsorbent polymer according to an embodiment of the present invention prepared through the above-described manufacturing process includes a base resin powder comprising a first crosslinked polymer of a water-soluble ethylenically unsaturated monomer having at least a partially neutralized acidic group; and a surface cross-linking layer formed on the base resin powder and including a second cross-linked polymer in which the first cross-linked polymer is further cross-linked through a surface cross-linking agent. In addition, when the surface crosslinking agent includes hydrophilic inorganic fine particles, the surface crosslinking layer may further include hydrophilic inorganic fine particles derived therefrom.
[121]
The superabsorbent polymer having the above composition and structure has a high water content along with excellent water absorption capacity, and the content of coarse particles having a particle size of more than 850 μm is minimized to minimize dust generation, and as a result, contamination to the reactor can be minimized. Accordingly, according to another embodiment of the present invention, there is provided a super absorbent polymer manufactured by the above-described manufacturing method, and articles such as an absorbent material and a sanitary material including the same.
[122]
Specifically, the superabsorbent polymer is 1 to 5 wt%, more specifically 1 wt% or more, or 1.5 wt% or more, or 1.8 wt% or more, 5 wt% or less, or 3 wt% or less, or 2.5 wt% It has a high moisture content of % or less. As described above, the moisture content of the superabsorbent polymer applied to the product is maintained at an appropriate level, so that the amount of fine powder generated during movement and storage can be reduced, and thus the quality of the final product can be improved. The moisture content of the superabsorbent polymer may be calculated by subtracting the weight of the superabsorbent polymer in a dry state from the weight of the superabsorbent polymer, and a specific measurement method will be described in detail in Test Examples below.
[123]
In addition, the superabsorbent polymer may have a particle size of 150 to 850 μm. More specifically, at least 95% by weight of the superabsorbent polymer has a particle size of 150 to 850 μm, and the content of coarse particles having a particle size of more than 850 μm is 5% by weight or less based on the total weight of the superabsorbent polymer, more Specifically, it is 3 wt% or less, or 2.5 wt% or less, or 2 wt% or less.
[124]
In the present invention, the particle size of the superabsorbent polymer can be measured according to the European Disposables and Nonwovens Association (EDANA) standard EDANA WSP 220.3 method, and the content of coarse particles in the superabsorbent polymer is, was classified on a standard sieve having a scale of 850 μm (20 mesh), 600 μm (30 mesh), 300 μm (50 mesh), and 150 μm (100 mesh), and 850 μm (20 mesh) After measuring the weight of coarse particles having an excessive particle size, the content of coarse particles with respect to the total weight of the superabsorbent polymer is expressed as a percentage, and a specific measuring method thereof will be described in detail in Test Examples below.
[125]
In addition, the content of the superabsorbent polymer adhering to the outer wall of the reactor and the rotating body, that is, the degree of contamination, may be minimized due to the high water content and the minimized coarse particle content in the superabsorbent polymer. Specifically, the weight of the superabsorbent polymer attached to the outer wall of the reactor and the rotating body is separated and the weight is measured, and the weight ratio of the superabsorbent polymer attached to the total weight of the superabsorbent polymer, that is, the degree of contamination is calculated, the value is 2% by weight or less. , or 1.7 wt% or less.
[126]
The superabsorbent polymer obtained according to the above-described manufacturing method can minimize the amount of dust generated during the manufacturing process by increasing the water content and reducing the coarse particle content while maintaining excellent absorption performance such as water holding capacity and absorbency under pressure. Accordingly, a sanitary material such as a diaper, in particular, an ultra-thin sanitary material having a reduced pulp content may be appropriately used.
[127]
[128]
The invention is described in more detail in the following examples. However, the following examples only illustrate the present invention, and the content of the present invention is not limited by the following examples.
[129]
Preparation Example 1
[130]
100 g of acrylic acid, 123.5 g of 32% sodium hydroxide (NaOH), 0.2 g of sodium persulfate as a thermal polymerization initiator, 0.008 g of diphenyl (2,4,6-trimethylbenzoyl)-phosphine oxide as a photoinitiator, polyethylene glycol diacrylate 0.24 g, 0.18 g of laponite, and 55.0 g of water were mixed to prepare a monomer composition having a total solid concentration of 43.8% by weight.
[131]
The monomer composition was fed on a rotary belt having a width of 10 cm and a length of 2 m, rotating at a speed of 50 cm/min, at a feed rate of 500 to 2000 ml/min. At the same time as the supply of the monomer composition, ultraviolet rays having an intensity of 10 mW/cm 2 were irradiated, and the polymerization reaction was carried out for 60 seconds. After the polymerization reaction proceeded, it was cut by a meat chopper method, dried at 185° C. for 40 minutes using an air-flow oven, and pulverized to prepare a base resin powder.
[132]
With respect to 100 g of the base resin powder prepared above, a mixed solution of 6.0 g of ultrapure water, 0.5 g of propylene glycol, 0.4 g of ethylene carbonate, 0.01 g of hydrophilic silica particles (A200™, manufactured by Evonik), and 0.2 g of aluminum sulfate was added, Mix for 1 minute. This was heated at 185° C. for 90 minutes, dried, and classified to obtain a surface-crosslinked base resin powder having a size of 150 to 850 μm.
[133]
[134]
Example 1
[135]
For the surface-crosslinked base resin powder prepared in Preparation Example 1, the superabsorbent polymer was prepared by performing a hydrolysis process using a pulse-type spray nozzle in which water is sprayed only when a pulse is applied, that is, when the pulse is on. .
[136]
Specifically, 10 kg of the surface-crosslinked base resin powder prepared in Preparation Example 1 was put into a rotary reactor equipped with sweep air and maintained at 50°C. Then, under the conditions shown in Table 1 below, air was introduced into the reactor through sweep air, and water of 0.03 m 3 /hr was sprayed onto the surface-crosslinked base resin powder through an orifice in a pulse-type spray nozzle. A superabsorbent polymer was prepared by performing a hydrolysis process for 10 seconds.
[137]
[138]
Examples 2 and 3
[139]
A superabsorbent polymer was prepared in the same manner as in Example 1, except that the hydrolysis process was performed under the conditions shown in Table 1 below.
[140]
[141]
Comparative Example 1
[142]
A superabsorbent polymer was prepared by hydrolyzing according to a conventional method without applying a pulse using a normal type spray nozzle.
[143]
Specifically, 10 kg of the surface-crosslinked base resin powder prepared in Preparation Example 1 was placed in the same rotary reactor equipped with sweep air as in Example 1 and maintained at 50°C. After that, under the conditions shown in Table 1 below, air is introduced into the reactor through sweep air, and 0.106 m 3 /hr of water is introduced through an orifice in a pulse-type spray nozzle to perform a hydrolysis process for 10 seconds. , a super absorbent polymer was prepared.
[144]
[145]
Comparative Examples 2 and 3
[146]
A superabsorbent polymer was prepared in the same manner as in Comparative Example 1, except that the hydrolysis process was performed under the conditions shown in Table 1 below.
[147]
[148]
Comparative Examples 4 and 5
[149]
A superabsorbent polymer was prepared in the same manner as in Example 1, except that the hydrolysis process was performed under the conditions shown in Table 1 below.
[150]
[Table 1]
spray nozzle type Orifice diameter
(mm) Orifice capacity (l/hr) @3bar Input flow rate
of water (m 3 /hr) sweep air flow
(m 3 /sec) Reactor cross-sectional area
(m 2 ) Spray pressure
(bar) Pulse Cycle
(Hz) Pulse On Rate
(%)
Example 1 pulse type 1.4 120 0.03 0.49 0.98 3 500 25
Example 2 pulse type 1.4 120 0.027 0.49 0.98 2.5 500 25
Example 3 pulse type 1.4 120 0.024 0.49 0.98 2 500 25
Comparative Example 1 normal type 1.4 120 0.106 0.49 0.98 2.5 - 100
Comparative Example 2 normal type 1.4 120 0.027 0.49 0.98 2.5 - 100
Comparative Example 3 normal type 0.81 35.4 0.028 0.49 0.98 2.5 - 100
Comparative Example 4 pulse type 1.4 120 0.017 0.49 0.98 2.5 500 5
Comparative Example 5 pulse type 1.4 120 0.063 0.49 0.98 2.5 500 60
[151]
In Table 1, the pulse cycle (Hz) is the number of on/off per minute (Hz), and the pulse-on ratio is the ratio of the spraying time according to the pulse application during the entire pulse spraying process (%) ), the cross-sectional area of ​​the reactor means the area of ​​the cross-section inside the reactor perpendicular to the flow direction of the air in the reactor.
[152]
[153]

[154]
The physical properties of each superabsorbent polymer prepared in Examples and Comparative Examples were measured and evaluated by the following method.
[155]
(1) scattering index
[156]
The scattering index of droplets generated from the spray nozzle during hydrolysis according to Examples and Comparative Examples was calculated according to Equation 1 below.
[157]
[Equation 1]
[158]
Scattering index = [(Re droplet)/(Re air)] × 100
[159]
In Equation 1, Re droplet is a Reynolds number of a droplet, Re air is a Reynolds number of air, and the Reynolds number of the droplet and Reynolds number of air may be calculated according to Equation 2 below.
[160]
[Equation 2]
[161]
Reynolds number = [(density of fluid × average flow velocity of fluid × characteristic length of fluid)/ coefficient of viscosity of fluid]
[162]
In Equation 2, the fluid is a droplet or air.
[163]
Accordingly, when the fluid is a droplet, the density of the droplet is 1000 kg/m 3 , which is the literature value of water at 25°C . In addition, the average flow rate of the droplet is the flow rate of the fluid injected into the reactor, that is, the input flow rate of water (m 3 /hr), and the area of ​​the cross-sectional shape in the flow direction of the fluid, that is, the flow of water ( Or flow) is calculated by dividing by the area of ​​the cut surface of the orifice perpendicular to the direction, and the average flow velocity of the droplets in this experimental example is as shown in Table 1 below. In addition, the characteristic length of the droplet is the average diameter (SMD) of the droplet, and can be measured according to the method described in (2) below, and the specific value is as shown in Table 1 below. In addition, the viscosity coefficient of the said droplet is 10 kg/m/sec which is the literature value of water at 25 degreeC.
[164]
In addition, when the fluid is air, the density of air is 1.12 kg/m 3 , which is a literature value of air at 25°C . In addition, the average flow rate of the air is the flow rate of the air introduced into the reactor, that is, the sweep air flow rate (m 3 /sec), and the area of ​​the shape cross-section in the air flow direction, that is, the inner cut surface of the reactor perpendicular to the air flow direction. was calculated by dividing by the area of ​​, and in this experimental example, the internal cut surface of the reactor was rectangular, and the area was calculated as the horizontal length × vertical length of the cut surface, and as a result, the average flow velocity of the air was 0.5 m/s. In addition, the characteristic length of the air was calculated from the following formula using the conditions of the internal flow, and the characteristic length of the air in this experimental example was 0.933 m.
[165]
[Equation 3]
[166]
Characteristic length of air = [4 × (horizontal length of reactor cross-section × length of reactor cross-section)] / [2 × (horizontal length of reactor cross-section + vertical length of reactor cross-section)]
[167]
In Equation 3, the transverse and longitudinal lengths of the cross section of the reactor are the transverse and longitudinal lengths at the inner section of the reactor perpendicular to the flow direction of the air. In the rotary reactor used in the preparation of the superabsorbent polymer according to Examples and Comparative Examples, the cross section of the reactor was rectangular, and the horizontal length was 1.4 m and the vertical length was 0.7 m.
[168]
In addition, the viscosity coefficient of air is 0.17 kg/m/sec which is the literature value of air at 25 degreeC.
[169]
Table 2 below shows the treatment conditions and the Reynolds number of the droplets and the Reynolds number of water during the hydrolysis treatment in Examples and Comparative Examples, respectively.
[170]
[Table 2]
Droplet density
(kg/m 3 ) Average flow velocity of the droplet
(m/s)
SMD
of the droplet (μm) Droplet viscosity coefficient
(kg/m/sec) Reynolds number of droplet Air density
(kg/m 3 ) Air average flow velocity
(m/s) Characteristic length of air
(m) Air viscosity coefficient
(kg/m/sec) Reynolds number of air
Example 1 1000 5.42 471 10 0.26 1.12 0.5 0.933 0.17 3.07
Example 2 1000 4.87 550 10 0.27 1.12 0.5 0.933 0.17 3.07
Example 3 1000 4.33 530 10 0.24 1.12 0.5 0.933 0.17 3.07
Comparative Example 1 1000 19.14 775 10 1.48 1.12 0.5 0.933 0.17 3.07
Comparative Example 2 1000 4.87 3754 10 1.83 1.12 0.5 0.933 0.17 3.07
Comparative Example 3 1000 15.10 241 10 0.36 1.12 0.5 0.933 0.17 3.07
Comparative Example 4 1000 3.07 273 10 0.08 1.12 0.5 0.933 0.17 3.07
Comparative Example 5 1000 11.37 813 10 0.92 1.12 0.5 0.933 0.17 3.07
[171]
(2) average diameter (SMD) of droplets, and droplet ratio of 300 μm or less in diameter
[172]
A droplet particle size measuring device (Sympatec HELOS/KR, Sympatec GmbH) was used to measure the average diameter (SMD) of droplets generated through the spray nozzle during hydrotreatment according to Examples and Comparative Examples and the ratio of droplets with a diameter of 300 μm or less among the droplets. was measured by optical diffraction analysis. The proportion of droplets having a diameter of 300 μm or less was expressed as a percentage based on the total weight of the generated droplets (% by weight).
[173]
[174]
(3) moisture content
[175]
The superabsorbent polymers obtained in Examples and Comparative Examples were sieved with a scale of 850 μm (20 mesh), 600 μm (30 mesh), 300 μm (50 mesh), and 150 μm (100 mesh). ), and the moisture content of the superabsorbent polymer particles having a particle size of 150 to 850 μm was measured.
[176]
The moisture content is the amount of water (wt%) occupied with respect to the total weight of the superabsorbent polymer, and refers to a value obtained by subtracting the weight of the superabsorbent polymer in a dry state from the weight of the superabsorbent polymer. Specifically, in the process of raising the temperature of the superabsorbent polymer through infrared heating and drying, the weight loss due to evaporation of moisture in the superabsorbent polymer was measured and calculated. The total drying time was set to 20 minutes including 5 minutes of the temperature rise step in such a manner that the temperature was maintained at 180°C.
[177]
[178]
(4) content of coarse particles having a particle size greater than 850 μm
[179]
The superabsorbent polymers obtained in Examples and Comparative Examples were sieved with a scale of 850 μm (20 mesh), 600 μm (30 mesh), 300 μm (50 mesh), and 150 μm (100 mesh). ), and after measuring the weight of coarse particles having a size greater than 850 μm (20 mesh), the content of the coarse particles was expressed as a percentage based on the total weight of the superabsorbent polymer (weight%) ).
[180]
[181]
(5) Pollution degree
[182]
The degree of contamination was calculated from the ratio of the superabsorbent polymer attached to the reactor.
[183]
Specifically, after hydrotreatment according to Examples and Comparative Examples, the superabsorbent polymer (SAP) attached to the outer wall of the reactor and the rotating body is separated and the weight is measured, and then the superabsorbent polymer attached to the reactor is based on the total weight of the superabsorbent polymer. The weight ratio of the resin is expressed as a percentage (% by weight).
[184]
[185]
Each physical property value measured by the above method is summarized in Table 3 below.
[186]
[Table 3]
scattering index Reynolds number of droplet Reynolds number of air SMD
of the droplet (μm) Droplet ratio of 300 μm or less
(wt%) Moisture content
(wt%) Coarse content greater than 850 μm
(% by weight) Pollution degree
(wt%)
Example 1 8.47 0.26 3.07 471 8.4 2.4 1.7 1.4
Example 2 8.79 0.27 3.07 550 5.6 2.3 1.6 1.7
Example 3 7.82 0.24 3.07 530 6.5 1.8 2.4 1.6
Comparative Example 1 48.21 1.48 3.07 775 1.7 9.4 7.2 8.7
Comparative Example 2 59.61 1.83 3.07 3754 0.1 1.3 39.4 0.2
Comparative Example 3 11.73 0.36 3.07 241 48.3 2.3 2.1 17.4
Comparative Example 4 2.61 0.08 3.07 273 29.1 2.7 2.3 13.7
Comparative Example 5 29.97 0.92 3.07 813 1.8 8.8 6.9 4.6
[187]
As a result of the experiment, in the case of Examples 1 to 3, the content of coarse particles was greatly reduced while having an improved moisture content, and the degree of contamination in the reactor was also low.
[188]
On the other hand, in the case of Comparative Example 1 in which the water treatment was performed without applying a pulse using a normal type spray nozzle, it was difficult to apply the watering process by spraying due to an excessive flow rate. As a result, the water content of the prepared superabsorbent polymer was excessively increased, and the content of coarse particles having a particle size of more than 850 μm in the superabsorbent polymer also increased. From this, it can be expected that the absorption capacity of the superabsorbent polymer is reduced.
[189]
In addition, in the case of Comparative Example 2, where the hydrotreatment process was performed in the same manner as in Comparative Example 1, but the input flow rate of water was lowered to the Example level, spraying was difficult due to the small flow rate, and the moisture content of the prepared super absorbent polymer also too low
[190]
Also, in the case of Comparative Example 3, the smallest diameter of the orifice during hydrolysis, the smallest droplet scattering index, and as a result, the most serious reactor contamination.
[191]
On the other hand, in Comparative Examples 4 and 5, which performed pulse spraying through a pulse-type spray nozzle as in the present invention, but did not meet the spraying conditions, the scattering index of the droplets was too low or high, and as a result, the degree of contamination The content of coarse particles greatly increased due to a significant increase in , or an excessive increase in the moisture content in the superabsorbent polymer.

WE CLAIMS

forming a hydrogel polymer by performing thermal polymerization or photopolymerization with respect to a monomer composition comprising a water-soluble ethylenically unsaturated monomer and a polymerization initiator; drying and pulverizing the hydrogel polymer to prepare a base resin powder; preparing a surface-crosslinked base resin powder by adding a surface crosslinking agent to the base resin powder and performing a surface crosslinking reaction; and hydrolyzing the surface-crosslinked base resin powder by pulse-spraying water, wherein the scattering index according to Equation 1 below is 5 to 10 of the droplets generated during the pulse-spraying, superabsorbent polymer Manufacturing method: [Equation 1] scattering index = [(Re droplet) / (Re air)] × 100 In Equation 1, Re droplet is the Reynolds number of the droplet, and Re air is the Reynolds number of the air.
[Claim 2]
The method according to claim 1, wherein the pulse spraying is performed using a pulse-type spray nozzle in which spraying is turned on/off according to a pulse.
[Claim 3]
The method according to claim 2, wherein the orifice diameter of the spray nozzle is 1 to 2 mm.
[Claim 4]
The method according to claim 1, wherein in the pulse spraying, the pulse-on ratio is 10 to 50% with respect to the total pulse spraying time.
[Claim 5]
According to claim 1, When the pulse spraying, the input flow rate of water is 0.02 to 0.05 m 3 /hr, the manufacturing method.
[Claim 6]
The method according to claim 1, wherein, in the pulse spraying, the pulse cycle is 1 to 2000 Hz.
[Claim 7]
The method of claim 1 , wherein the droplet has a Reynolds number of 0.2 to 0.35 and air has a Reynolds number of 2 to 5.
[Claim 8]
The method according to claim 1, wherein the average diameter of the droplets is 400 to 600 µm.
[Claim 9]
The method according to claim 1, wherein a proportion of droplets having a diameter of 300 μm or less among the droplets is 5 to 10 wt% based on the total weight of the generated droplets.
[Claim 10]
The method according to claim 1, wherein the surface crosslinking agent includes a polyhydric alcohol-based compound, an alkylene carbonate-based compound, and a polyvalent metal salt.
[Claim 11]
11. The method of claim 10, wherein the polyhydric alcohol compound is ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, 1,2-hexanediol, 1,3-hexane diol, 2-methyl-1,3-propanediol, 2,5-hexanediol, 2-methyl-1,3-pentanediol, 2-methyl-2,4-pentanediol, tripropylene glycol, or glycerol which is a manufacturing method.
[Claim 12]
The method according to claim 10, wherein the alkylene carbonate-based compound includes ethylene carbonate or propylene carbonate.
[Claim 13]
The method according to claim 10, wherein the polyvalent metal salt comprises aluminum sulfate, aluminum carboxylate, or a mixture thereof.
[Claim 14]
The method according to claim 10, wherein the surface crosslinking agent further comprises hydrophilic inorganic particles.
[Claim 15]
The method of claim 1 , wherein the superabsorbent polymer has a moisture content of 1 to 5% by weight and a content of coarse particles having a particle size of greater than 850 μm of 5% by weight or less based on the total weight of the superabsorbent polymer.