Title of the invention: Super absorbent polymer and its manufacturing method
Technical field
[One]
Cross-reference with related application(s)
[2]
This application claims the benefit of priority based on Korean Patent Application No. 10-2019-0006228 filed January 17, 2019 and Korean Patent Application No. 10-2020-0006215 filed January 16, 2020. All contents disclosed in the literature are included as part of this specification.
[3]
The present invention relates to a super absorbent polymer and a method for producing the same.
[4]
Background
[5]
Super Absorbent Polymer (SAP) is a synthetic polymer material with a function of absorbing moisture of 500 to 1,000 times its own weight, and each developer has a SAM (Super Absorbency Material), AGM (Absorbent Gel). Material) and so on. The super absorbent polymer as described above has begun to be put into practical use as a sanitary tool, and now, in addition to hygiene products such as paper diapers for children, soil repair agents for gardening, water resistant materials for civil engineering and construction, sheets for seedlings, freshness maintaining agents in the field of food distribution, and It is widely used as a material for poultice.
[6]
In most cases, such super absorbent polymers are widely used in the field of sanitary materials such as diapers and sanitary napkins, and for this purpose, it is necessary to exhibit high absorption power for moisture, etc., and moisture absorbed by external pressure must not escape, In addition, it is necessary to exhibit excellent permeability by maintaining the shape well even in the state of volume expansion (swelling) by absorbing water.
[7]
In recent years, as hygiene materials such as diapers and sanitary napkins have become thinner, higher absorption performance is required for super absorbent polymers. Among these, the opposite physical properties, such as improved water holding capacity and pressure absorption capacity, and improved liquid permeability are emerging as important issues.
[8]
In addition, pressure may be applied to sanitary materials such as diapers and sanitary napkins by the weight of the user. In particular, after the super absorbent polymer applied to sanitary materials such as diapers and sanitary napkins absorbs liquid, when pressure by the user's weight is applied thereto, some liquid absorbed by the super absorbent polymer oozes out again. Over and over, leakage of urine may occur.
[9]
To this end, conventional superabsorbent resins use a method of lowering the internal crosslinking degree and increasing the surface crosslinking degree. However, the above method has an aspect of increasing the absorption rate, but after the superabsorbent polymer swells with the absorbed liquid, the liquid exists on the surface of the superabsorbent polymer, reducing the fit and causing a cause of skin rash. do.
[10]
In this way, after the superabsorbent polymer absorbs the liquid, dryness is required so that no liquid exists on the surface, and the degree of drying under several pressures does not impair the absorption performance and absorption rate of the superabsorbent polymer. There is a demand for the development of a super absorbent polymer having excellent water absorption.
[11]
Detailed description of the invention
Technical challenge
[12]
An object of the present invention is to provide a super absorbent polymer having a high absorption rate and maintaining elasticity even in a pressurized environment several times, and thus having excellent dryness characteristics, and a method of manufacturing the same.
[13]
Means of solving the task
[14]
In order to solve the above problem, one aspect of the present invention,
[15]
It provides a super absorbent polymer having a recovery rate of 85% or more, calculated by the following formula 1:
[16]
[Equation 1]
[17]
Recovery rate (%) = 4th resilience value / 1st resilience value * 100
[18]
In Equation 1,
[19]
The first resilience value is that 2 g of a superabsorbent polymer is swelled in 200 mL of physiological saline (0.9 wt% NaCl) for 1 hour under no pressure, and then loaded into a dynamic mechanical analysis (DMA) measuring device at room temperature (25° C.) and 0.72. It is the modulus (unit: Kpa) of the super absorbent polymer measured after pressurizing under psi for 5 minutes, releasing the pressurization, and allowing it to stand for 10 minutes,
[20]
The fourth resilience value is the modulus of the super absorbent polymer, which is measured for the fourth time by repeating the process of measuring the first resilience value and then pressing again to measure the resilience value three more times in the same manner. Kpa).
[21]
Another aspect of the present invention in order to solve the above problem,
[22]
Polymerizing a monomer composition including an acrylic acid-based monomer, a foaming agent, an internal crosslinking agent, and a polymerization initiator having an acidic group at least partially neutralized to form a hydrogel polymer;
[23]
Chopping the hydrogel polymer by passing through a chopper including two or more hole plates arranged in series;
[24]
Drying, pulverizing and classifying the chopped hydrogel polymer to form a base resin; And
[25]
Forming a surface crosslinking layer by further crosslinking the surface of the base resin powder in the presence of a surface crosslinking agent;
[26]
It provides a method for producing a super absorbent polymer comprising a.
[27]
Effects of the Invention
[28]
As described above, according to the superabsorbent polymer of the present invention and a method for producing the same, it is possible to provide a superabsorbent polymer having excellent physical properties because elasticity is maintained even in multiple pressurized environments while having a high absorption rate.
[29]
Accordingly, the super absorbent polymer of the present invention can be preferably used for hygiene materials such as diapers and exhibit excellent performance.
[30]
Brief description of the drawing
[31]
1 is a schematic diagram showing a chopper according to an embodiment of the present invention.
[32]
2 is a schematic diagram showing a chopper according to the prior art.
[33]
3 is a schematic diagram showing a chopper according to the prior art.
[34]
Mode for carrying out the invention
[35]
The present invention will be described in detail below and exemplifying specific embodiments, as various modifications may be made and may have various forms. However, this is not intended to limit the present invention to a specific form disclosed, it should be understood to include all changes, equivalents, and substitutes included in the spirit and scope of the present invention.
[36]
In the specification of the present invention, "polymer", "polymer", or "super absorbent resin" refers to a state in which an acrylic acid-based monomer is polymerized, and may encompass all ranges of moisture content or particle size. Among the above polymers, a polymer having a moisture content (moisture content) of about 40% by weight or more, which is in a state before drying after polymerization, may be referred to as a hydrogel polymer.
[37]
In addition, "base resin" or "base resin powder" refers to a polymer which is dried and pulverized to form a powder, and before performing the surface crosslinking step described below.
[38]
Hereinafter, a super absorbent polymer and a method of manufacturing the same according to an embodiment of the present invention will be described.
[39]
[40]
In order to improve the water absorption performance of the super absorbent polymer, a method of increasing the surface area of ​​the super absorbent polymer is being studied. In order to increase the surface area of ​​the super absorbent polymer, a method of using a foaming agent during polymerization of acrylic acid monomers is known, but excessive use of the foaming agent may cause problems in distribution and storage because the gel strength or density of the super absorbent polymer decreases. As another method, there is a method of reducing the size of the particles through coarse pulverization of the hydrous gel polymer, but if excessive shearing force is applied during coarse pulverization, there is a problem that the physical properties of the super absorbent polymer are deteriorated or the process of coarse pulverization is difficult. have.
[41]
Accordingly, the inventors of the present invention completed the present invention by conceiving that the gel strength of the hydrogel polymer can be maintained and the absorption rate can be improved by controlling the process of the coarse pulverization step after polymerization of the hydrogel polymer resin.
[42]
The super absorbent polymer according to an aspect of the present invention is characterized in that the recovery rate of the super absorbent polymer calculated by Equation 1 below is 85% or more:
[43]
[Equation 1]
[44]
Recovery rate (%) = 4th resilience value / 1st resilience value * 100
[45]
In Equation 1,
[46]
The first resilience value is that 2 g of a superabsorbent polymer is swelled in 200 mL of physiological saline (0.9 wt% NaCl) for 1 hour under no pressure, and then loaded into a dynamic mechanical analysis (DMA) measuring device at room temperature (25° C.) and 0.72. It is the modulus (unit: Kpa) of the super absorbent polymer measured after pressurizing under psi for 5 minutes, releasing the pressurization, and allowing it to stand for 10 minutes,
[47]
The fourth resilience value is the modulus of the super absorbent polymer, which is measured for the fourth time by repeating the process of measuring the first resilience value and then pressing again to measure the resilience value three more times in the same manner. Kpa).
[48]
The recovery rate takes into account the use environment in which pressure is applied according to various posture changes such as sitting and rising, lying or lying down when a product such as a diaper containing a super absorbent polymer is actually used. It was quantified so that the degree of recovery can be quantitatively evaluated.
[49]
The higher the recovery rate, the higher the elasticity of the super absorbent polymer can be maintained even under several pressurizations, and the super absorbent polymer prepared according to the manufacturing method of the present invention includes the recovery rate of the super absorbent polymer calculated by Equation 1 Recovery rate) may be 85% or more, or 88% or more, or 90% or more. The recovery rate is preferably closer to 100%, and may be, for example, 100% or less, or 98% or less, or 95% or less.
[50]
In addition, the super absorbent polymer of the present invention has a primary resilience value of 90 Kpa or more, 92 Kpa or more, or 93 Kpa or more, and 100 Kpa or less, or 99 Kpa or less, or 98 Kpa or less, and has a high initial elastic modulus. Can be indicated.
[51]
In addition, the super absorbent polymer as described above may have an absorption rate of 40 seconds or less measured according to a vortex measurement method. The absorption rate refers to the time when a superabsorbent polymer is added to the physiological saline solution and stirred, and the vortex of the liquid disappears due to rapid absorption, and refers to the rapid absorption ability of the superabsorbent polymer. The specific measurement method thereof is more specific in Examples below. The absorption rate of the super absorbent polymer may be 40 seconds or less, or 35 seconds or less, or 30 seconds or less, or 27 seconds or less, or 25 seconds or less, and 10 seconds or more, or 15 seconds or more, or 20 seconds or more.
[52]
The super absorbent polymer may include: a base resin including a crosslinked polymer of an acrylic acid-based monomer and an internal crosslinking agent having at least partially neutralized acid groups; And a surface crosslinking layer formed on the base resin by further crosslinking the surface of the base resin in the presence of a surface crosslinking agent.
[53]
The super absorbent polymer of the present invention as described above, but is not limited thereto, may be manufactured according to a manufacturing method described later.
[54]
[55]
A method of preparing a super absorbent polymer according to another aspect of the present invention comprises forming a hydrogel polymer by polymerizing a monomer composition including an acrylic acid-based monomer, a foaming agent, an internal crosslinking agent, and a polymerization initiator having an acidic group at least partially neutralized. ; Chopping the hydrogel polymer by passing through a chopper including two or more hole plates arranged in series; Drying, pulverizing and classifying the chopped hydrogel polymer to form a base resin; And forming a surface crosslinking layer by further crosslinking the surface of the base resin powder in the presence of a surface crosslinking agent.
[56]
In the method for producing a super absorbent polymer of the present invention, in the step of coarsely pulverizing the hydrogel polymer after polymerization, by passing through a chopper including two or more hole plates arranged in series and chopping In addition, coarse pulverization is effectively performed without imparting excessive shearing force, thereby maintaining the gel strength of the hydrogel polymer and improving the absorption rate.
[57]
Conventionally, in order to maintain the gel strength of a hydrogel polymer, a technique of pulverizing so that the average particle diameter is 1.0 mm to 2.0 mm when coarsely pulverized by using at least one of a foaming agent or a surfactant during polymerization has been disclosed. .
[58]
However, the above method is a method of forming pores only by chemical foaming.As such, the super absorbent polymer particles including pores formed only by chemical foaming have a problem that the strength of the particles is weakened after drying, so that they are easily broken, and the resilience is not good. There is this. In comparison, the manufacturing method of the present invention solves the above problems by passing through a chopper including two or more hole plates arranged in series and chopping.
[59]
On the other hand, in the production method of the present invention, the use of a foaming agent or a surfactant during polymerization of the hydrogel polymer is not excluded. Can additionally be used.
[60]
[61]
Hereinafter, the above manufacturing method will be described in detail for each step.
[62]
[63]
First, the acrylic acid-based monomer constituting the hydrogel polymer may be any monomer commonly used in the manufacture of a super absorbent polymer. As a non-limiting example, the acrylic acid-based monomer may be a compound represented by the following Formula 1:
[64]
[Formula 1]
[65]
R 1 -COOM 1
[66]
In Chemical Formula 1,
[67]
R 1 is an alkyl group having 2 to 5 carbon atoms containing an unsaturated bond,
[68]
M 1 is a hydrogen atom, a monovalent or divalent metal, an ammonium group, or an organic amine salt.
[69]
Preferably, the acrylic acid-based monomer may include at least one selected from the group consisting of acrylic acid, methacrylic acid, and monovalent metal salts, divalent metal salts, ammonium salts, and organic amine salts thereof.
[70]
Here, the acrylic acid-based monomer may have an acidic group and at least a part of the acidic group is neutralized. Preferably, one obtained by partially neutralizing the acrylic acid-based monomer with an alkyl material such as sodium hydroxide, potassium hydroxide, ammonium hydroxide, or the like may be used. At this time, the degree of neutralization of the acrylic acid-based monomer may be about 40 to about 95 mol%, or about 40 to about 80 mol%, or about 45 to about 75 mol%. The range of the degree of neutralization may be adjusted according to the final physical properties. However, if the degree of neutralization is too high, neutralized monomers may be precipitated and polymerization may be difficult to proceed smoothly, whereas if the degree of neutralization is too low, the absorbency of the polymer is greatly reduced, and it may exhibit properties such as elastic rubber that are difficult to handle. have.
[71]
In addition, the concentration of the acrylic acid monomer in the monomer composition may be appropriately adjusted in consideration of polymerization time and reaction conditions, and may be preferably 20 to 90% by weight, or 40 to 65% by weight. This concentration range may be advantageous in order to control the pulverization efficiency during pulverization of the polymer, which will be described later, while avoiding the need to remove the unreacted monomer after polymerization by using the gel effect phenomenon occurring in the polymerization reaction of the high-concentration aqueous solution. However, if the concentration of the monomer is too low, the yield of the super absorbent polymer may be lowered. Conversely, if the concentration of the monomer is too high, a problem may occur in the process, such as a decrease in pulverization efficiency when a part of the monomer is precipitated or the pulverization efficiency of the polymerized hydrogel polymer is pulverized, and the physical properties of the super absorbent polymer may be deteriorated.
[72]
Any compound may be used as the internal crosslinking agent as long as it allows the introduction of crosslinking bonds during polymerization of the acrylic acid monomer. As a non-limiting example, the internal crosslinking agent is N,N'-methylenebisacrylamide, trimethylolpropane tri(meth)acrylate, ethylene glycol di(meth)acrylate, polyethylene glycol(meth)acrylate, propylene glycol di( Meth)acrylate, polypropylene glycol (meth)acrylate, butanedioldi(meth)acrylate, butylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, hexanedioldi(meth)acrylate )Acrylate, triethylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, dipentaerythritol pentaacrylate, glycerin tri(meth)acrylate, penta A polyfunctional crosslinking agent such as erythritol tetraacrylate, triarylamine, ethylene glycol diglycidyl ether, propylene glycol, glycerin, or ethylene carbonate may be used alone or in combination of two or more, but is not limited thereto.
[73]
This internal crosslinking agent may be added in a concentration of about 0.001 to 1% by weight based on the monomer composition. That is, if the concentration of the internal crosslinking agent is too low, the absorption rate of the resin may be lowered and the gel strength may be weakened, which is not preferable. Conversely, if the concentration of the internal crosslinking agent is too high, the absorbent power of the resin may be lowered, making it undesirable as an absorber.
[74]
The polymerization initiator may include a polymerization initiator generally used in the manufacture of a super absorbent polymer. As a non-limiting example, as the polymerization initiator, a thermal polymerization initiator or a photo polymerization initiator may be used depending on the polymerization method, and in particular, a thermal polymerization initiator may be used. However, even by the photopolymerization method, since a certain amount of heat is generated by ultraviolet irradiation or the like, and a certain amount of heat is generated according to the progress of the polymerization reaction, which is an exothermic reaction, a thermal polymerization initiator may be additionally included.
[75]
As the thermal polymerization initiator, at least one compound selected from the group consisting of a persulfate-based initiator, an azo-based initiator, hydrogen peroxide, and ascorbic acid may be used. Specifically, as a persulfate-based initiator, sodium persulfate (Na 2 S 2 O 8 ), potassium persulfate (Potassium persulfate; K 2 S 2 O 8 ), ammonium persulfate (Ammonium persulfate; (NH 4 ) 2 S 2 O 8) And the like. In addition, as an azo initiator, 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-(carbamoyl azo)isobutyronitrile (2-(carbamoylazo)isobutylonitril), 2,2-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride), 4, Examples include 4-azobis-(4-cyanovaleric acid) (4,4-azobis-(4-cyanovaleric acid)) and the like. More various thermal polymerization initiators are disclosed in Odian's book "Principle of Polymerization (Wiley, 1981)" on page 203, which may be referred to.
[76]
As the photopolymerization initiator, for example, benzoin ether, dialkyl acetophenone, hydroxyl alkylketone, phenyl glyoxylate, benzyl dimethyl ketal ( One or more compounds selected from the group consisting of Benzyl Dimethyl Ketal), acyl phosphine and alpha-aminoketone may be used. Among them, as a specific example of acylphosphine, a 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 wider variety of photopolymerization initiators are disclosed on page 115 of Reinhold Schwalm's book "UV Coatings: Basics, Recent Developments and New Application (Elsevier 2007)", which may be referred to.
[77]
This polymerization initiator may be added in a concentration of about 0.001 to 1% by weight based on the monomer composition. That is, if the concentration of the polymerization initiator is too low, the polymerization rate may be slowed, and a large amount of residual monomer may be extracted in the final product, which is not preferable. On the contrary, when the concentration of the polymerization initiator is higher than the above range, the polymer chain forming the network is shortened, so that the content of the water-soluble component increases and the absorption capacity under pressure may decrease, which is not preferable.
[78]
[79]
According to an embodiment of the present invention, the monomer composition includes a blowing agent.
[80]
The foaming agent serves to increase the surface area by foaming during polymerization to form pores in the hydrogel polymer. The foaming agent may use a carbonate, for example sodium bicarbonate, sodium carbonate, potassium bicarbonate, potassium carbonate, calcium bicarbonate, calcium Carbonate (calcium bicarbonate), magnesium bicarbonate (magnesium bicarbonate) or magnesium carbonate (magnesium carbonate) can be used.
[81]
It is preferable to use the blowing agent in an amount of 500 ppmw or less based on the total weight of the acrylic acid monomer. The less the foaming agent is used, the better the gel strength, and if it is used in excess of 500 ppmw, the gel strength may be weakened, so it is preferable to use it at 500 ppmw or less, for example, 450 ppmw or less, or 400 ppmw or less, or 350 ppmw or less, or 300 ppmw or less can be used. The lower limit of the amount of the foaming agent used is not particularly limited, but for effective presentation, it may be used as, for example, 10 ppmw or more, 50 ppmw or more, or 100 ppmw or more.
[82]
[83]
According to an embodiment of the present invention, the monomer composition may further include a surfactant to further improve the absorption rate by developing a porous structure of the super absorbent polymer, and the surfactant may be an anionic surfactant or a nonionic surfactant. Surfactants can be used.
[84]
Examples of the anionic surfactant include sodium dodecyl sulfate, ammonium lauryl sulfate, sodium laureth sulfate, dioctyl sodium sulfosuccinate, perfluorooctane sulfonate, perfluorobutane sulfonate, alkyl-aryl ether. And one or more selected from the group consisting of phosphate, alkyl ether phosphate, sodium myreth sulfate, and carboxylate salt.
[85]
Examples of the nonionic surfactant include fatty acid esters, sorbitan trioleate, polyethoxylated sorbitan monooleate (product name: TWEEN 80), sorbitan monooleate (product name: SPAN 80), and sugar ester (product name : S-570) is one or more selected from the group consisting of.
[86]
When the monomer composition further includes a surfactant, the total amount of the surfactant including the anionic surfactant and the nonionic surfactant may be included in a concentration of 100 ppmw or less based on the total weight of the acrylic acid monomer. . More specifically, it may be included in a concentration of 100 ppmw or less, or 70 ppmw or less, 1 ppmw or more, 5 ppmw or more, or 10 ppmw or more, or 20 ppmw or more, or 30 ppmw or more. If the concentration of the surfactant is higher than 100 ppmw, other physical properties of the super absorbent polymer such as pressure absorption capacity, gel strength, or surface tension may be deteriorated.If the concentration of the surfactant is too low, the addition of the surfactant Accordingly, the effect of improving the absorption rate may not be sufficient.
[87]
[88]
On the other hand, in the method for producing a superabsorbent polymer according to the present invention, the hydrogel polymer is chopped through a chopper including two or more hole plates arranged in series. Since the strength can be maintained, the absorption rate can be improved while supplementing the disadvantages associated with the use of the surfactant, such as a decrease in surface tension, by including only a small amount of 100 ppmw or less even if the surfactant is not included.
[89]
In addition, additives such as a thickener, a plasticizer, a storage stabilizer, and an antioxidant may be further included in the monomer composition as needed.
[90]
In addition, such a monomer composition may be prepared in the form of a solution in which raw materials such as the above-described monomers are dissolved in a solvent. At this time, the usable solvent may be used without limitation of its configuration as long as it can dissolve the aforementioned raw materials. For example, as the solvent, water, ethanol, ethylene glycol, diethylene glycol, triethylene glycol, 1,4-butanediol, propylene glycol, ethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate , Methyl ethyl ketone, acetone, methyl amyl ketone, cyclohexanone, cyclopentanone, diethylene glycol monomethyl ether, diethylene glycol ethyl ether, toluene, xylene, butyrolactone, carbitol, methyl cellosolve acetate, N,N-dimethylacetamide, or mixtures thereof, and the like may be used.
[91]
[92]
In addition, the formation of the hydrogel polymer through polymerization of the monomer composition may be performed by a conventional polymerization method, and the process is not particularly limited. As a non-limiting example, the polymerization method is largely divided into thermal polymerization and photopolymerization according to the type of polymerization energy source.In the case of performing the thermal polymerization, it can be carried out in a reactor having a stirring axis such as a kneader, and photopolymerization In the case of proceeding, it may be carried out in a reactor equipped with a movable conveyor belt.
[93]
For example, the monomer composition may be added to a reactor such as a kneader equipped with a stirring shaft, and hot air may be supplied thereto, or the reactor may be heated to perform thermal polymerization to obtain a hydrogel polymer. At this time, the hydrogel polymer discharged to the reactor outlet according to the shape of the stirring shaft provided in the reactor may be obtained as particles of several millimeters to several centimeters. Specifically, the resulting hydrogel polymer may be obtained in various forms depending on the concentration and injection speed of the monomer composition to be injected, and a hydrogel polymer having a (weight average) particle diameter of 2 to 50 mm may be obtained.
[94]
And, as another example, when photopolymerization is performed on the monomer composition in a reactor equipped with a movable conveyor belt, a sheet-shaped hydrous gel polymer may be obtained. At this time, the thickness of the sheet may vary depending on the concentration of the monomer composition to be injected and the injection speed.In order to ensure the production speed while ensuring the entire sheet can be evenly polymerized, it is usually adjusted to a thickness of 0.5 to 5 cm desirable.
[95]
At this time, the water content of the hydrogel polymer obtained by this method may be 40 to 80% by weight. Meanwhile, throughout the present specification, "water content" refers to a value obtained by subtracting the weight of the dried polymer from the weight of the hydrogel polymer as the content of moisture occupied by the total weight of the hydrogel polymer. Specifically, it is defined as a calculated value 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 a method of increasing the temperature from room temperature to about 180°C and then maintaining it at 180°C. The total drying time is set to 20 minutes including 5 minutes of the temperature increase step, and the moisture content is measured.
[96]
[97]
Next, the hydrogel polymer is chopped by passing through a chopper including two or more hole plates arranged in series.
[98]
A chopper is a device that performs pulverization by inserting an object, that is, a hydrogel polymer into the inlet, and pushing it through a hole plate in which a number of holes having a certain size are formed. In this case, the extruder used to extrude the hydrogel polymer may be a single or multiple screw type extruder.
[99]
When coarsely pulverized by pushing the hydrogel polymer into a hole plate as described above, a certain pressure is applied to the hydrogel polymer, and this pressure changes the original gel strength and morphology of the hydrogel polymer. Therefore, the physical properties of the polymer after performing the coarse pulverization step may be changed.
[100]
That is, according to the structure and operating principle of the chopper, the super absorbent polymer is compressed at the front end of the hole plate, and the pressure is released while passing through the hole plate, so that the super absorbent polymer, that is, the hydrogel, expands. During the compression and expansion process, the gel strength and morphology of the hydrogel polymer are deformed, so the physical properties of the polymer after performing the coarse pulverization step are changed.
[101]
Accordingly, a method of adjusting the physical properties of the hydrogel polymer by adjusting the diameter or shape of the hole in the hole plate or performing a coarse pulverization step using a plurality of choppers is known. However, there is a limit to improving the physical properties of the hydrogel polymer even by the above method.
[102]
In the manufacturing method of the present invention, continuous chopping is performed while shortening the compression and expansion interval of the hydrogel polymer in the chopping step by connecting the hole plates in series in one chopper, thereby reducing the decrease in gel strength and excellent elasticity. It was confirmed that the absorption rate was maintained so that the superabsorbent polymer could exhibit optimized physical properties.
[103]
That is, according to the method of manufacturing the super absorbent polymer of the present invention, the hydrogel polymer coarsely pulverized through the first hole plate is continuously passed through the next hole plate to repeat the coarse pulverization process. A super absorbent polymer having a resilience and a recovery modulus different from that of the super absorbent polymer particles can be obtained.
[104]
1 is a schematic diagram showing a chopper according to an embodiment of the present invention, and FIG. 2 is a schematic diagram showing a chopper according to the prior art.
[105]
Referring to FIG. 1, a chopper used in the manufacturing method of the present invention includes two or more hole plates 10a, 10b, and 10c, and the two or more hole plates are connected in series. More specifically, the hydrogel polymer is introduced into the chopper through the inlet 20, and is coarsely pulverized while being pushed out to the first hole plate 10a by a screw. The hydrogel polymer that has passed through the first hole plate 10a is continuously pushed out to the second hole plate 10b and is secondarily coarsely pulverized. The hydrogel polymer passing through the second hole plate 10b finally passes through the last hole plate 10c and is discharged to the outside of the chopper.
[106]
Meanwhile, in FIG. 1, the chopper includes three hole plates, but the present invention is not limited thereto, and two or more, for example, two to five, or two to four, or two It may include various numbers of hole plates, such as three to three.
[107]
According to one embodiment of the present invention, when referring to the hole plate closest to the inlet as the first plate in order, it is preferable to make the average diameter of the hole plate smaller as the distance from the inlet becomes. For example, the average diameter of the holes of the first hole plate may be 16 to 18 mm, and the average diameter of the holes of the second hole plate may be smaller than this, and may be 12 to 14 mm. In addition, the average diameter of the hole of the last hole plate for discharging the hydrogel polymer to the outside may be 8 to 10 mm, but the present invention is not limited thereto.
[108]
In comparison, referring to FIG. 2 showing a conventional chopper, the hydrogel polymer injected into the chopper through the inlet 20 passes through the hole plate 10a only once and is discharged to the outside of the chopper to perform the next step. do.
[109]
Referring to FIG. 3 showing another conventional chopper, there is a method of connecting two or more choppers in multiple stages, and in this case, the water-containing gel polymer discharged through the hole plate 10a of the first chopper is again It is re-introduced through the inlet 40 of the chopper and discharged to the outside of the chopper.
[110]
As described above, when the hydrogel polymer passes through two or more hole plates in sequence and coarsely pulverized according to the manufacturing method of the present invention, it is smaller due to continuous chopping than the conventional coarse pulverization step of chopping using only one hole plate. It is possible to form pores of a size, for example, pores having a diameter of 100 μm or less. In addition, when the two choppers are used in the second stage as shown in FIG. 3, since the time to move from the first stage to the second stage is long, there is a problem in that pore formation is not efficiently performed, and the absorption rate decreases. Therefore, the chopping method of the present invention using a chopper including two or more hole plates continuously in the chopper as in the present invention may be more advantageous.
[111]
[112]
According to an embodiment of the present invention, a polycarboxylic acid-based copolymer may be further added in the chopping step to chop together with the hydrogel polymer.
[113]
The polycarboxylic acid-based copolymer lowers the load of the chopper due to the lubricating action to induce uniform pulverization of the polymer, and can suppress the generation of water-soluble components during pulverization. Through this, it is possible to manufacture a super absorbent polymer having a fast absorption rate and high pressure absorption characteristics at the same time.
[114]
For example, the polycarboxylic acid-based copolymer includes an alkoxy polyalkylene glycol mono(meth)acrylic acid ester monomer (a representative example, methoxypolyethylene glycol monomethacrylate (MPEGMAA), etc.) and a (meth)acrylic acid ester monomer ( As a representative example, use of a random copolymer derived from hydrophilic monomers such as (meth)acrylic acid, etc.) may be more advantageous in expressing the above-described effect.
[115]
And, in order to allow the effect of the addition of the polycarboxylic acid-based copolymer to be better expressed, the polycarboxylic acid-based copolymer preferably has a weight average molecular weight (Mw) of 500 to 1,000,000 g/mol. . More preferably, the weight average molecular weight is 1,000 to 500,000 g/mol, 10,000 to 100,000 g/mol, 20,000 to 90,000 g/mol, 30,000 to 80,000 g/mol, or 40,000 to 70,000 g/mol.
[116]
In addition, the content of the polycarboxylic acid-based copolymer may be appropriately adjusted according to the type of the copolymer or reaction conditions. Preferably, the polycarboxylic acid-based copolymer may be mixed in an amount of 0.001 to 5 parts by weight based on 100 parts by weight of the hydrogel polymer. If the content of the polycarboxylic acid-based copolymer is too small, the effect required in the present invention may not be sufficiently expressed. On the contrary, if the polycarboxylic acid-based copolymer is used in an excessive amount, the function of the super absorbent polymer may be deteriorated, resulting in a decrease in absorption properties or a decrease in surface tension and a decrease in powder flowability, which is not preferable.
[117]
[118]
Next, the chopped hydrogel polymer is dried, pulverized and classified to form a base resin.
[119]
The drying temperature may be 50 to 250°C. If the drying temperature is less than 50°C, the drying time may be too long and the physical properties of the finally formed super absorbent polymer may be deteriorated.If the drying temperature exceeds 250°C, only the polymer surface may be excessively dried, resulting in fine powder. In addition, there is a concern that physical properties of the finally formed super absorbent polymer may be deteriorated. More preferably, the drying may be performed at a temperature of 150 to 200°C, more preferably 160 to 190°C. Meanwhile, the drying time may be performed for 20 minutes to 15 hours in consideration of process efficiency, etc., but is not limited thereto.
[120]
As long as it is commonly used in the drying process, it may be selected and used without limitation of its configuration. Specifically, the drying step may be performed by a method such as hot air supply, infrared irradiation, microwave irradiation, or ultraviolet irradiation. The moisture content of the polymer after the drying step proceeds may be 0.05 to 10% by weight.
[121]
[122]
Next, a step of pulverizing the dried polymer obtained through such a drying step is performed.
[123]
The polymer powder obtained after the pulverization step may have a particle diameter of 150 to 850 μm. The pulverizer used to pulverize with such a particle size is specifically, a ball mill, a pin mill, a hammer mill, a screw mill, a roll mill, and a disk. Mill (disc mill) or jog mill (jog mill) may be used, but is not limited to the above-described example.
[124]
In addition, in order to manage the physical properties of the super absorbent polymer powder that is finally commercialized after the pulverization step, a separate process of classifying the polymer powder obtained after pulverization according to the particle size may be performed. Preferably, a polymer having a particle diameter of 150 to 850 µm is classified, and only a polymer powder having such a particle diameter can be commercialized through a surface crosslinking reaction step to be described later.
[125]
[126]
Next, in the presence of a surface crosslinking agent, the surface of the base resin powder is further crosslinked to form a surface crosslinked layer, thereby preparing a superabsorbent polymer.
[127]
More specifically, in the presence of a surface crosslinking liquid containing a surface crosslinking agent, the base resin powder is heat-treated to perform surface crosslinking, thereby preparing a super absorbent polymer.
[128]
Here, the kind of the surface crosslinking agent is not particularly limited. As a non-limiting example, the surface crosslinking agent is ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerol polyglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, ethylene Carbonate, ethylene glycol, diethylene glycol, propylene glycol, triethylene glycol, tetraethylene glycol, propane diol, dipropylene glycol, polypropylene glycol, glycerin, polyglycerin, butanediol, heptanediol, hexanediol trimethylol It may be one or more compounds selected from the group consisting of propane, pentaerythritol, sorbitol, calcium hydroxide, magnesium hydroxide, aluminum hydroxide, iron hydroxide, calcium chloride, magnesium chloride, aluminum chloride, and iron chloride.
[129]
At this time, the content of the surface crosslinking agent may be appropriately adjusted according to the type or reaction conditions thereof, and preferably may be adjusted to 0.001 to 5 parts by weight based on 100 parts by weight of the base resin. If the content of the surface crosslinking agent is too low, the surface crosslinking may not be properly introduced, and the physical properties of the final super absorbent polymer may be deteriorated. On the contrary, if the surface crosslinking agent is used in an excessively large amount, the absorbency of the superabsorbent polymer may be rather lowered due to excessive surface crosslinking reaction, which is not preferable.
[130]
In addition, the surface crosslinking liquid is water, ethanol, ethylene glycol, diethylene glycol, triethylene glycol, 1,4-butanediol, propylene glycol, ethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, Methyl ethyl ketone, acetone, methyl amyl ketone, cyclohexanone, cyclopentanone, diethylene glycol monomethyl ether, diethylene glycol ethyl ether, toluene, xylene, butyrolactone, carbitol, methyl cellosolve acetate and N, It may further include one or more solvents selected from the group consisting of N-dimethylacetamide. The solvent may be included in an amount of 0.5 to 10 parts by weight based on 100 parts by weight of the base resin.
[131]
Meanwhile, in order to perform the surface crosslinking, a method of mixing the surface crosslinking solution and the base resin in a reaction tank, spraying a surface crosslinking solution onto the base resin, and surface crosslinking with the base resin in a continuously operated mixer. A method of continuously supplying and mixing the liquid may be used.
[132]
In addition, the surface crosslinking may be performed under a temperature of 100 to 250°C, and may be continuously performed after the drying and pulverizing step performed at a relatively high temperature. At this time. The surface crosslinking reaction may proceed for 1 to 120 minutes, or 1 to 100 minutes, or 10 to 60 minutes. That is, in order to induce a surface crosslinking reaction of a minimum limit and to prevent physical properties from deteriorating due to damage to the polymer particles during excessive reaction, the above-described surface crosslinking reaction may be performed.
[133]
In addition, in order to manage the physical properties of the super absorbent polymer powder that is finally commercialized after the surface crosslinking step, a separate process of classifying the super absorbent polymer powder according to the particle size using a sieve may be performed. By this classification process, the superabsorbent polymer having a particle diameter of 150 to 850 µm may be 90% by weight or more, or 92% by weight or more, or 95% by weight or more.
[134]
The superabsorbent polymer prepared as described above may exhibit an improved absorption rate, and also maintain excellent properties including gel strength and various physical properties.
[135]
[136]
Hereinafter, preferred embodiments are presented to aid in the understanding of the present invention. However, the following examples are only for illustrating the present invention, and the present invention is not limited thereto.
[137]
[138]

[139]
Example 1
[140]
A solution in which 8.6 g of IRGACURE 819 initiator diluted to 0.5% by weight in acrylic acid (80 ppmw based on the monomer) and 12.3 g of polyethylene glycol diacrylate (PEGDA, Mw=400) diluted in 20% by weight in acrylic acid are mixed (solution A ) Was prepared.
[141]
540 g of acrylic acid and the A solution were injected into a 2L glass reactor surrounded by a jacket through which the heat medium cooled in advance to 25°C was circulated.
[142]
In addition, 832 g of a 25% by weight caustic soda solution (solution B) was gradually added dropwise to the glass reactor, followed by mixing. After confirming that the temperature of the mixed solution rises to about 72° C. or higher by the neutralization heat, the mixed solution waited for cooling. In the thus obtained mixed solution, the degree of neutralization of acrylic acid was about 70 mol%.
[143]
On the other hand, 20 g of a C solution obtained by diluting sodium bicarbonate as a foaming agent to 5% by weight in water was prepared. Then, when the temperature of the neutralized mixed solution was cooled to about 45° C., a C solution prepared in advance was injected into the neutralized mixed solution to be mixed.
[144]
Subsequently, the mixed solution prepared above was poured into a Vat-shaped tray (15 cm x 15 cm in width) installed in a square polymerization reactor equipped with a light irradiation device on the top and preheated to 80°C. Thereafter, the mixed solution was irradiated with light. It was confirmed that the gel was formed from the surface after about 20 seconds from the time of light irradiation, and it was confirmed that the polymerization reaction occurred simultaneously with foaming about 30 seconds after the time of light irradiation. Then, the polymerization reaction was carried out for an additional 2 minutes, and the polymerized sheet was taken out and cut into a size of 3 cm x 3 cm.
[145]
In addition, the cut sheet was prepared as a crumb by chopping using a chopper as shown in FIG. 1 (however, including two hole plates, and the average diameter of the holes of each hole plate is 18mm and 14mm in turn). . The average particle size (diameter) of the prepared crumb was 0.2 mm.
[146]
Subsequently, the crumb was dried in an oven in which the air volume can be adjusted up and down. In order that the moisture content of the dried powder is less than about 2% by weight, hot air at 180° C. is flowed from the bottom to the top for 15 minutes, and then flows from the top to the bottom for 15 minutes to obtain the crumb. It was dried evenly. The dried powder was pulverized with a grinder and classified to obtain a base resin having a size of 150 to 850 μm.
[147]
Then, to 100 g of the prepared base resin, 4.5 g of water, 1 g of ethylene carbonate, 0.05 g of Aerosil 200 (Aerosil 200, Evonik), 0.25 g of a 20% by weight aqueous silica (Snowtex, ST-O) solution were added. After mixing the mixed crosslinking agent solution, a surface crosslinking reaction was performed at 190°C for 30 minutes. Then, the obtained product was pulverized and a surface crosslinked superabsorbent polymer having a particle diameter of 150 to 850 µm was obtained using a sieve. A super absorbent polymer was prepared by additionally mixing 0.1 g of Aerosil 200 to the obtained super absorbent polymer in a dry manner.
[148]
[149]
Example 2
[150]
In Example 1, a super absorbent polymer was prepared in the same manner as in Example 1, except that a chopper including three hole plates (average diameters of the holes of each hole plate were 18mm, 14mm, 12mm in turn).
[151]
[152]
Example 3
[153]
In Example 1, a superabsorbent polymer was prepared in the same manner as in Example 1, except that sodium dodecylsulfate as a surfactant was added to the solution C so as to be 100 ppmw based on the total weight of the acrylic acid.
[154]
[155]
Example 4
[156]
In Example 2, a superabsorbent polymer was prepared in the same manner as in Example 2, except that sodium dodecylsulfate as a surfactant was added to the solution C so as to be 100 ppmw based on the total weight of the acrylic acid.
[157]
[158]
Comparative Example 1
[159]
A solution in which 8.6 g of IRGACURE 819 initiator diluted to 0.5% by weight in acrylic acid (80 ppmw based on the monomer) and 12.3 g of polyethylene glycol diacrylate (PEGDA, Mw=400) diluted in 20% by weight in acrylic acid are mixed (solution A ) Was prepared.
[160]
540 g of acrylic acid and the A solution were injected into a 2L glass reactor surrounded by a jacket through which the heat medium cooled in advance to 25°C was circulated.
[161]
In addition, 832 g of a 25% by weight caustic soda solution (solution B) was gradually added dropwise to the glass reactor, followed by mixing. After confirming that the temperature of the mixed solution rises to about 72° C. or higher by the neutralization heat, the mixed solution waited for cooling. In the thus obtained mixed solution, the degree of neutralization of acrylic acid was about 70 mol%.
[162]
Subsequently, the mixed solution prepared above was poured into a Vat-shaped tray (15 cm x 15 cm in width) installed in a square polymerization reactor equipped with a light irradiation device on the top and preheated to 80°C. Thereafter, the mixed solution was irradiated with light. It was confirmed that the gel was formed from the surface after about 20 seconds from the time of light irradiation, and it was confirmed that the polymerization reaction occurred simultaneously with foaming about 30 seconds after the time of light irradiation. Then, the polymerization reaction was carried out for an additional 2 minutes, and the polymerized sheet was taken out and cut into a size of 3 cm x 3 cm.
[163]
In addition, the cut sheet was prepared as a crumb by chopping using a chopper as shown in FIG. The average particle size (diameter) of the prepared crumb was 0.4 mm.
[164]
Subsequently, the crumb was dried in an oven in which the air volume can be adjusted up and down. In order that the moisture content of the dried powder is less than about 2% by weight, hot air at 180° C. is flowed from the bottom to the top for 15 minutes, and then flows from the top to the bottom for 15 minutes to obtain the crumb. It was dried evenly. The dried powder was pulverized with a grinder and classified to obtain a base resin having a size of 150 to 850 μm.
[165]
Then, to 100 g of the prepared base resin, 4.5 g of water, 1 g of ethylene carbonate, 0.05 g of Aerosil 200 (Aerosil 200, Evonik), 0.25 g of a 20% by weight aqueous silica (Snowtex, ST-O) solution were added. After mixing the mixed crosslinking agent solution, a surface crosslinking reaction was performed at 190°C for 30 minutes. Then, the obtained product was pulverized and a surface crosslinked superabsorbent polymer having a particle diameter of 150 to 850 µm was obtained using a sieve. A super absorbent polymer was prepared by additionally mixing 0.1 g of Aerosil 200 to the obtained super absorbent polymer in a dry manner.
[166]
[167]
Comparative Example 2
[168]
A solution in which 8.6 g of IRGACURE 819 initiator diluted to 0.5% by weight in acrylic acid (80 ppmw based on the monomer) and 12.3 g of polyethylene glycol diacrylate (PEGDA, Mw=400) diluted in 20% by weight in acrylic acid are mixed (solution A ) Was prepared.
[169]
540 g of acrylic acid and the A solution were injected into a 2L glass reactor surrounded by a jacket through which the heat medium cooled in advance to 25°C was circulated.
[170]
In addition, 832 g of a 25% by weight caustic soda solution (solution B) was gradually added dropwise to the glass reactor, followed by mixing. After confirming that the temperature of the mixed solution rises to about 72° C. or higher by the neutralization heat, the mixed solution waited for cooling. In the thus obtained mixed solution, the degree of neutralization of acrylic acid was about 70 mol%.
[171]
On the other hand, 20 g of a C solution obtained by diluting sodium bicarbonate as a foaming agent to 5% by weight in water was prepared. Then, when the temperature of the neutralized mixed solution was cooled to about 45° C., a C solution prepared in advance was injected into the neutralized mixed solution to be mixed.
[172]
Subsequently, the mixed solution prepared above was poured into a Vat-shaped tray (15 cm x 15 cm in width) installed in a square polymerization reactor equipped with a light irradiation device on the top and preheated to 80°C. Thereafter, the mixed solution was irradiated with light. It was confirmed that the gel was formed from the surface after about 20 seconds from the time of light irradiation, and it was confirmed that the polymerization reaction occurred simultaneously with foaming about 30 seconds after the time of light irradiation. Then, the polymerization reaction was carried out for an additional 2 minutes, and the polymerized sheet was taken out and cut into a size of 3 cm x 3 cm.
[173]
In addition, the cut sheet was manufactured into a crumb by chopping using one chopper (the average diameter of the hole of the hole plate is 14 mm) as shown in FIG. 2. The average particle size (diameter) of the prepared crumb was 0.55 mm.
[174]
Other than that, a super absorbent polymer was prepared in the same manner as in Comparative Example 1.
[175]
[176]
Comparative Example 3
[177]
In the chopping step of Comparative Example 2, the cut sheet was chopped using a chopper as shown in FIG. It was prepared as a crumb. The average particle size (diameter) of the prepared crumb was 0.4 mm.
[178]
Other than that, a super absorbent polymer was prepared in the same manner as in Comparative Example 2.
[179]
[180]
Comparative Example 4
[181]
In the chopping step of Comparative Example 2, by chopping using a parallel chopper similar to that shown in FIG. The cut sheet was made into a crumb. The average particle size (diameter) of the prepared crumb was 0.3 mm.
[182]
Other than that, a super absorbent polymer was prepared in the same manner as in Comparative Example 2.
[183]
[184]
Comparative Example 5
[185]
In the chopping step of Comparative Example 1, the cut sheet was powdered by chopping using a chopper similar to that shown in FIG. (crumb) was prepared. The average particle size (diameter) of the prepared crumb was 0.3 mm.
[186]
Other than that, a super absorbent polymer was prepared in the same manner as in Comparative Example 1.
[187]
[188]
Comparative Example 6
[189]
A super absorbent polymer was prepared according to Example 2 of KR Patent Application Publication No. 2018-0076272.
[190]
[191]
The main process conditions of the Examples and Comparative Examples are summarized in Table 1 below.
[192]
[Table 1]
Foaming agent (unit: ppmw)* Surfactant (unit: ppmw)* Chopping method
Example 1 500 0 Chopping with two hole plates arranged in series in the chopper
Example 2 500 0 Chopping with 3 hole plates arranged in series in the chopper
Example 3 500 100 Chopping with two hole plates arranged in series in the chopper
Example 4 500 100 Chopping with 3 hole plates arranged in series in the chopper
Comparative Example 1 0 0 2-stage chopping by connecting 2 choppers
Comparative Example 2 500 0 1-stage chopping
Comparative Example 3 500 0 2-stage chopping by connecting 2 choppers
Comparative Example 4 500 0 3-stage chopping by connecting 3 choppers
Comparative Example 5 0 0 Chopping with two hole plates arranged in series in the chopper
Comparative Example 6 1000 200 1-stage chopping
[193]
* The content of the blowing agent and surfactant was calculated as the content (unit: ppmw) with respect to the total weight of the acrylic acid monomer.
[194]
[195]

[196]
The physical properties of the super absorbent polymer prepared in Examples and Comparative Examples were evaluated by the following method, and the results are shown in Table 1.
[197]
[198]
(1) Recovery rate
[199]
2 g of super absorbent polymer was swelled in 200 mL of physiological saline (0.9 wt% NaCl) for 1 hour under no pressure, and then loaded on a DMA (dynamic mechanical analysis) measuring device (device name: dynamic mechanical analysis Q800, manufacturer: TA instrument) at room temperature. After pressurization under (25° C.) and 0.72 psi for 5 minutes, the pressurization was released and allowed to stand for 10 minutes, and then the modulus (unit: Kpa) of the super absorbent polymer was measured to obtain a first resilience value.
[200]
After measuring the first resilience value, the process of measuring the resilience value by pressing again was repeated three more times in the same manner to measure a total of four times.
[201]
In addition, the recovery rate was measured by substituting the first resilience value and the fourth-order resilience value measured in the following equation 1.
[202]
[Equation 1]
[203]
Recovery rate (%) = 4th resilience value / 1st resilience value * 100
[204]
[205]
(2) absorption rate (Vortex time)
[206]
The absorption rate of the superabsorbent polymers of Examples and Comparative Examples was measured in seconds according to the method described in International Patent Publication No. 1987-003208.
[207]
Specifically, for the absorption rate (or vortex time), 2 g of superabsorbent resin was added to 50 mL of physiological saline at 23°C to 24°C, and a magnetic bar (diameter 8 mm, length 31.8 mm) was stirred at 600 rpm to vortex ( vortex) was calculated by measuring the time until disappearance in seconds.
[208]
[209]
The results measured as described above are shown in Table 2 below.
[210]
[Table 2]
1st resilience value (unit: Kpa) 2nd resilience value (unit: Kpa) 3rd resilience value (unit: Kpa) 4th resilience value (unit: Kpa) Recovery rate (%) Vortex time (seconds)
Example 1 95 94 92 85 89 33
Example 2 93 92 89 79 85 24
Example 3 98 93 90 88 90 30
Example 4 92 90 85 81 88 23
Comparative Example 1 93 88 82 75 81 57
Comparative Example 2 75 67 62 58 77 40
Comparative Example 3 80 65 60 55 69 32
Comparative Example 4 73 63 54 40 55 25
Comparative Example 5 95 92 90 86 91 56
Comparative Example 6 73 70 64 55 75 41
[211]
Referring to Table 1, all of the super absorbent polymers of the present invention exhibited excellent resilience and an excellent absorption rate of 40 seconds or less. Accordingly, it is expected that a super absorbent polymer having excellent dryness characteristics can be provided by maintaining elasticity even in multiple pressurized environments.
[212]
However, in the case of Comparative Examples 1 to 5 in which the chopping method of the present invention was not used, it was found that the resilience was significantly lowered as the pressing was repeated, so that the elasticity was not properly maintained in the pressurized environment.
[213]
[214]
Claims
[Claim 1]
A super absorbent polymer having a recovery rate of 85% or more calculated by the following equation 1: [Equation 1] Recovery rate (%) = 4th resilience value / 1st resilience value ( resilience value) * 100 In Equation 1, the first resilience value is that 2 g of a superabsorbent polymer is swelled in 200 mL of physiological saline (0.9 wt% NaCl) for 1 hour under no pressure, and then used in a DMA (Dynamic Mechanical Analysis) measuring device. Loaded and pressurized at room temperature (25° C.) and 0.72 psi for 5 minutes, release the pressurization and let stand for 10 minutes, and the modulus of the super absorbent polymer is measured, and the 4th resilience value is , After measuring the first resilience value, the process of measuring the resilience value by pressing again is repeated three more times in the same manner, and the modulus (unit: Kpa) of the super absorbent polymer is measured for the fourth time.
[Claim 2]
The super absorbent polymer according to claim 1, wherein the primary resilience value is 90 Kpa or more.
[Claim 3]
The superabsorbent polymer according to claim 1, wherein the absorption rate measured according to the vortex measurement method is 40 seconds or less.
[Claim 4]
Polymerizing a monomer composition including an acrylic acid-based monomer, a foaming agent, an internal crosslinking agent, and a polymerization initiator having an acidic group at least partially neutralized to form a hydrogel polymer; Chopping the hydrogel polymer by passing through a chopper including two or more hole plates arranged in series; Drying, pulverizing and classifying the chopped hydrogel polymer to form a base resin; And forming a surface crosslinked layer by further crosslinking the surface of the base resin powder in the presence of a surface crosslinking agent.
[Claim 5]
The method of claim 4, wherein the average diameter of the hole plate is smaller as the distance from the chopper inlet increases.
[Claim 6]
The method of claim 4, wherein the blowing agent is sodium bicarbonate, sodium carbonate, potassium bicarbonate, potassium carbonate, calcium bicarbonate, calcium carbonate ( calcium bicarbonate), magnesium bicarbonate, and magnesium carbonate (magnesium carbonate) comprising at least one selected from the group consisting of, a method for producing a super absorbent polymer.
[Claim 7]
The method of claim 4, wherein the blowing agent is contained in an amount of 500 ppmw or less based on the total weight of the acrylic acid monomer.
[Claim 8]
The method of claim 4, wherein the monomer composition further comprises a surfactant.
[Claim 9]
The method of claim 8, wherein the surfactant is sodium dodecyl sulfate, ammonium lauryl sulfate, sodium laureth sulfate, dioctyl sodium sulfosuccinate, perfluorooctane sulfonate, perfluorobutane sulfonate, alkyl-aryl A method for producing a super absorbent polymer comprising at least one selected from the group consisting of ether phosphate, alkyl ether phosphate, sodium myreth sulfate and carboxylate salt.
[Claim 10]
The method of claim 4, wherein in the chopping step, a polycarboxylic acid-based copolymer is further added and chopped.
[Claim 11]
The super absorbent polymer according to claim 10, wherein the polycarboxylic acid-based copolymer comprises at least one selected from the group consisting of an alkoxy polyalkylene glycol mono (meth) acrylic acid ester monomer and a (meth) acrylic acid ester monomer. The manufacturing method of.