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. 10-2019-0001977 filed on January 7, 2019, and all contents disclosed in the documents of the Korean patent application are included as part of this specification.
[3]
The present invention relates to a super absorbent polymer and a method for producing the same, which not only has excellent basic absorption performance, but also exhibits an improved absorption rate.
Background
[4]
Super Absorbent Polymer (SAP) is a synthetic polymer material that can absorb moisture of 500 to 1,000 times its own weight. Material) and so on. Since the above-described superabsorbent resin has begun to be put into practical use as a sanitary tool, nowadays, in addition to hygiene products such as paper diapers for children, soil repair agents for horticultural use, water resistant materials for civil engineering and construction, sheets for seedlings, freshness maintenance agents in the food distribution field, and It is widely used as a material for poultice.
[5]
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 a high absorption ability 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.
[6]
In recent years, as the demand for a thin diaper increases, the content of fibrous materials such as pulp in the diaper decreases, and the proportion of the superabsorbent polymer tends to increase relatively. Accordingly, there is a need for a super absorbent polymer to have the performance that was in charge of the diaper fiber material, and for this purpose, it is necessary to exhibit a high absorption capacity as well as a high absorption rate. In particular, as the diaper becomes thinner, the risk of urine leaking out of the diaper increases according to the movement of a baby who is a diaper user.
[7]
On the other hand, in order for the superabsorbent polymer to exhibit a higher absorption rate, it is necessary to exhibit a porous structure having a large surface area and having a large number of fine pores therein. Thus, a super absorbent polymer having such a porous structure has been prepared by applying a foaming agent or a surfactant.
[8]
After pulverization of the super absorbent polymer, a large amount of particles having a small aspect ratio are generated, and these particles have a high risk of uneven shape and the like. For this reason, at the time of surface crosslinking after pulverization or mixing of an additive for improving physical properties, the surface crosslinking is made uneven, or the application of the additive is made uneven in many cases. As a result, in the prior art in which a porous structure or the like is formed to realize a high absorption rate of a super absorbent polymer, other physical properties such as absorption performance are often deteriorated. In addition, in the case of such an existing method, the corresponding particles may be easily broken during the pulverization, classification, or transfer process of the resin particles. In this case, generation of fine powder may increase, and physical properties after surface crosslinking may be deteriorated. In addition, the surface area of ​​the super absorbent polymer may be reduced due to the crushing of the particles during the pulverization, classification, or transport process, and as a result, the absorption rate may be rather lowered.
[9]
Accordingly, there is a continuous demand for the development of a technology capable of providing a super absorbent polymer which simultaneously exhibits a further improved absorption rate while suppressing deterioration in absorption performance by reducing the amount of foaming agent used and reducing the generation of particles having a small aspect ratio.
Detailed description of the invention
Technical challenge
[10]
Accordingly, the present invention is to provide a super absorbent polymer and a method of manufacturing the same, which not only has excellent basic absorption performance, but also exhibits more improved absorption rate and liquid permeability.
Means of solving the task
[11]
The present invention provides a base resin powder comprising a first crosslinked polymer of a water-soluble ethylenically unsaturated monomer having an acidic group at least partially neutralized; And
[12]
A superabsorbent polymer comprising a surface crosslinked layer comprising a second crosslinked polymer formed on the base resin powder, wherein the first crosslinked polymer is further crosslinked via a surface crosslinking agent,
[13]
The superabsorbent polymer contains less than 9.9% by number of superabsorbent polymer particles having an aspect ratio of less than 0.5, which is defined as the shortest diameter / longest diameter of each superabsorbent polymer particle,
[14]
The absorption rate by the vortex method is 5 to 55 seconds,
[15]
It provides a superabsorbent polymer having a surface tension of 50 to 80 mN/m.
[16]
The present invention also provides a step of forming a monomer mixture comprising a water-soluble ethylenically unsaturated monomer and an internal crosslinking agent having at least a partly neutralized acidic group;
[17]
Transferring the monomer mixture to a polymerization reactor along a transfer pipe having a diameter varying depending on the section;
[18]
Crosslinking the monomer mixture transferred to the polymerization reactor to form a hydrogel polymer including the first crosslinked polymer;
[19]
Gel grinding, drying, grinding and classifying the hydrogel polymer to form a base resin comprising less than 9.9% by number of base resin powders having an aspect ratio of less than 0.5, defined as the shortest diameter / longest diameter of each base resin powder. ; And
[20]
In the presence of a surface crosslinking agent, comprising the step of forming a surface crosslinking layer by further crosslinking the surface of the base resin powder,
[21]
In the transfer step of the monomer mixture, the monomer mixture exhibits a maximum transfer rate in the minimum diameter section of the transfer pipe, the monomer mixture exhibits a minimum transfer rate in the maximum diameter section of the transfer tube, and the maximum transfer rate is the It provides a method for producing a super absorbent polymer having 2.5 times or more of the minimum feed rate.
[22]
Hereinafter, a super absorbent polymer and a manufacturing method thereof according to a specific embodiment of the present invention will be described in more detail. However, this is presented as an example of the invention, whereby the scope of the rights of the invention is not limited, and it is obvious to those skilled in the art that various modifications to the embodiments are possible within the scope of the invention.
[23]
Additionally, unless otherwise specified in the specification, the term "comprising" or "containing" refers to including any component (or component) without particular limitation, and the addition of other components (or components) It cannot be construed as excluding.
[24]
According to one embodiment of the invention, at least a part of the base resin powder comprising a first crosslinked polymer of a water-soluble ethylenically unsaturated monomer having a neutralized acidic group; And
[25]
A superabsorbent polymer comprising a surface crosslinked layer comprising a second crosslinked polymer formed on the base resin powder, wherein the first crosslinked polymer is further crosslinked via a surface crosslinking agent,
[26]
The superabsorbent polymer contains less than 9.9% by number of superabsorbent polymer particles having an aspect ratio of less than 0.5, which is defined as the shortest diameter / longest diameter of each superabsorbent polymer particle,
[27]
The absorption rate by the vortex method is 5 to 55 seconds,
[28]
A super absorbent polymer having a surface tension of 50 to 80 mN/m is provided.
[29]
In the process of transferring the monomer mixture to the polymerization reactor, the superabsorbent polymer according to an embodiment of the present invention is controlled to a specific range while changing the transfer rate thereof according to the method described below, and then polymerization, drying, pulverization, classification and surface crosslinking, etc. It can be manufactured through the process of.
[30]
As a result of the continuous research of the present inventors, when the transfer rate of the monomer mixture is changed as described above, physical foaming occurs, reducing or not using a foaming agent, etc., while exhibiting a developed porous structure and excellent absorption rate. It was found that the resin could be prepared and the invention was completed.
[31]
This is predicted to be because the solubility of gases such as oxygen in the monomer mixture decreases as the transfer speed of the monomer mixture changes during the transfer through the transfer pipe and the pressure applied to the monomer mixture changes instantaneously. Accordingly, in the feed rate adjustment step, a large amount of bubbles are generated from the monomer mixture, and foam polymerization may proceed in the crosslinking polymerization step by the generated bubbles. As a result, even if the foaming agent is not used or the amount of the foaming agent is greatly reduced, a super absorbent polymer having a porous structure developed by physical foaming can be manufactured.
[32]
As a result of the large reduction in the amount of blowing agent used, the formation rate of super absorbent polymer particles having a small aspect ratio, that is, the aspect ratio defined as the shortest diameter / longest diameter of the super absorbent polymer particles, is 9.9% by number. It can be significantly reduced to less than, 1 to 9.9 number%, or 3 to 9.7 number%. Accordingly, there is practically no possibility that other physical properties, such as absorption performance, will deteriorate during surface crosslinking or when mixing additives. In addition, as the formation ratio of particles having a small aspect ratio decreases, the risk of deteriorating the final physical properties of the super absorbent polymer may also be greatly reduced due to damage or breakage of the particles during pulverization, classification, or transport of the particles.
[33]
Accordingly, the superabsorbent polymer of one embodiment can exhibit excellent absorption speed while maintaining excellent properties such as absorption performance, and having a porous structure developed by the above-described physical foaming.
[34]
Therefore, the superabsorbent polymer of one embodiment can exhibit a more improved absorption rate and the like while being able to excellently maintain basic absorption performance, unlike the conventional common sense that it is difficult to achieve excellent absorption rate and absorption performance at the same time. It can be preferably applied to sanitary materials such as diapers having a thickness.
[35]
Hereinafter, the super absorbent polymer of one embodiment will be described in more detail.
[36]
In addition, the term "super absorbent polymer" referred to herein refers to a base resin powder comprising a first crosslinked polymer of a water-soluble ethylenically unsaturated monomer having an acidic group at least partially neutralized; And a surface crosslinked layer including a second crosslinked polymer formed on the base resin powder, wherein the first crosslinked polymer is further crosslinked through a surface crosslinking agent.
[37]
The water-soluble ethylenically unsaturated monomer may be any monomer commonly used in the preparation of a super absorbent polymer. As a non-limiting example, the water-soluble ethylenically unsaturated monomer may be a compound represented by the following Formula 1:
[38]
[Formula 1]
[39]

[40]
In Chemical Formula 1,
[41]
R 1 is an alkyl group having 2 to 5 carbon atoms containing an unsaturated bond,
[42]
M 1 is a hydrogen atom, a monovalent or divalent metal, an ammonium group, or an organic amine salt.
[43]
Suitably, the monomer may be one or more selected from the group consisting of acrylic acid, methacrylic acid, and monovalent metal salts, divalent metal salts, ammonium salts and organic amine salts of these acids. As such, when acrylic acid or a salt thereof is used as a water-soluble ethylenically unsaturated monomer, it is advantageous to obtain a super absorbent polymer having improved water absorption. In addition, the monomers include maleic anhydride, fumaric acid, crotonic acid, itaconic acid, 2-acryloylethanesulfonic acid, 2-methacryloylethanesulfonic acid, 2-(meth)acryloylpropanesulfonic acid, or 2-( Anionic monomers of meth)acrylamide-2-methyl propane sulfonic acid and salts thereof; (Meth)acrylamide, N-substituted (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, methoxypolyethylene glycol (meth)acrylate or polyethylene glycol ( Nonionic hydrophilic-containing monomers of meth)acrylate; And (N,N)-dimethylaminoethyl (meth)acrylate or an amino group-containing unsaturated monomer of (N,N)-dimethylaminopropyl (meth)acrylamide and a quaternary product thereof; Can be used.
[44]
Here, the water-soluble ethylenically unsaturated monomer may have an acidic group, and at least a part of the acidic group may be neutralized. Preferably, the monomer partially neutralized with an alkaline substance such as sodium hydroxide, potassium hydroxide, ammonium hydroxide, or the like may be used.
[45]
In this case, the degree of neutralization of the monomer may be 40 to 95 mol%, or 40 to 85 mol%, or 45 to 80 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 precipitate and the polymerization may be difficult to proceed smoothly. It may exhibit properties such as elastic rubber that are difficult to handle.
[46]
The'first crosslinked polymer' means that the water-soluble ethylenically unsaturated monomer is crosslinked and polymerized in the presence of an internal crosslinking agent, and the'base resin powder' means a material containing such a first crosslinked polymer. In addition, the'second crosslinked polymer' means a material in which the first crosslinked polymer is further crosslinked through a surface crosslinking agent, and is thus formed on the base resin powder. The surface crosslinking agent will be described later.
[47]
As described above, the super absorbent polymer of this embodiment is obtained without the use of a foaming agent or in a state where the amount of the foaming agent is minimized, and thus the base resin powder is obtained by physical foaming polymerization. The water absorbent resin particles can minimize the generation rate of particles having a relatively small aspect ratio. More specifically, the super absorbent polymer of one embodiment includes a plurality of super absorbent polymer particles, and based on the total number of these super absorbent polymer particles, for example, defined as the shortest diameter / longest diameter of the super absorbent polymer particles. The super absorbent polymer particles having an aspect ratio of less than 0.5 may be included in a ratio of less than 9.9%, 1 to 9.9%, or 3 to 9.7%.
[48]
At this time, the aspect ratio of the base resin powder and the super absorbent polymer particles is, for example, as shown in Figure 1, each particle is analyzed with an electron microscope to calculate the shortest diameter (a) and the longest diameter (b), And from this, the aspect ratio of each base resin powder and super absorbent polymer particles can be calculated. From the thus calculated aspect ratio data of each particle, the ratio of the number of particles having the aspect ratio less than 0.5 can be calculated. For reference, it is confirmed that the aspect ratios of the base resin powder and the super absorbent polymer particles are equal to each other.
[49]
As described above, since the superabsorbent polymer of one embodiment has a porous structure developed by physical foaming polymerization and contains particles having a small aspect ratio in a very reduced content, the surface crosslinking layer and/or additives are formed on the entire particles. It can be formed uniformly. Accordingly, the superabsorbent polymer of one embodiment may exhibit an improved absorption rate due to the developed porous structure while maintaining excellent absorption performance and/or liquid permeability.
[50]
In addition, as particles having a small aspect ratio are included in a reduced content, it is possible to greatly reduce the phenomenon that the super absorbent polymer particles are crushed or the physical properties are deteriorated due to physical damage during the transfer or product application process of the super absorbent polymer. . Conversely, when a large amount of particles having a small aspect ratio is included, the shape of the super absorbent polymer particles becomes uneven, and a large number of relatively long particles are included, so that the super absorbent polymer particles are physically damaged during the transfer or product application process. , It is easy to deteriorate greatly in physical properties.
[51]
On the other hand, the super absorbent polymer of the above-described embodiment has excellent absorption performance and absorption rate under basic pressure or no pressure, which can be defined by physical properties such as CRC, AUP, absorption, vortex absorption rate, or surface tension. I can.
[52]
Specifically, the superabsorbent polymer of one embodiment may have a centrifugal water retention capacity (CRC) of 25 to 35 g/g, or 26 to 33 g/g for 30 minutes for physiological saline (0.9 wt% sodium chloride aqueous solution). have. This centrifugal water retention capacity (CRC) range may define excellent absorption performance under no pressure that the super absorbent polymer of one embodiment exhibits.
[53]
The centrifugal water retention capacity (CRC) for the physiological saline solution can be calculated by the following calculation formula 1 after the superabsorbent polymer is absorbed in the physiological saline solution over 30 minutes:
[54]
[Calculation 1]
[55]

[56]
In Equation 1 above,
[57]
W 0 (g) is the initial weight (g) of the super absorbent polymer,
[58]
W 1 (g) is the weight measured after impregnating a nonwoven bag without a super absorbent polymer in it in physiological saline for 30 minutes at room temperature, and then dehydrating at 250 G for 3 minutes using a centrifuge,
[59]
W 2 (g) is the weight measured after impregnating a nonwoven bag containing a super absorbent polymer in physiological saline for 30 minutes at room temperature and then dehydrating at 250 G for 3 minutes using a centrifuge.
[60]
In addition, the superabsorbent polymer according to an embodiment has a pressure absorption capacity (AUP) of 22 to 28 g/g, or 23 to 27 g/g for 1 hour under 0.7psi for physiological saline (0.9 wt% sodium chloride aqueous solution). Can be. This pressure absorption capacity (AUP) range may define excellent absorption performance under pressure exhibited by the super absorbent polymer of one embodiment.
[61]
This pressure absorption capacity (AUP) can be calculated according to the following calculation formula 2 after the superabsorbent polymer is absorbed in physiological saline under pressure of 0.7 psi over 1 hour:
[62]
[Calculation Equation 2]
[63]

[64]
In Equation 2 above,
[65]
W 0 (g) is the initial weight (g) of the super absorbent polymer, W 3 (g) is the sum of the weight of the super absorbent polymer and the weight of the device capable of applying a load to the super absorbent polymer, W 4 (g ) Is the sum of the weight of the superabsorbent polymer and the weight of the device capable of imparting a load to the superabsorbent polymer after absorbing physiological saline in the superabsorbent polymer for 1 hour under load (0.7 psi).
[66]
In addition, as the superabsorbent polymer of one embodiment exhibits centrifugation water retention capacity (CRC) and pressure absorption capacity (AUP) in the above-described range, the superabsorbent polymer has an absorbency of 46 to 63 g/g as defined by Equation 1 below. , Or 50 to 60 g/g:
[67]
[Equation 1]
[68]

[69]
In Equation 1 above,
[70]
CRC is the water holding capacity by centrifugation for 30 minutes with respect to the physiological saline solution (0.9 wt% sodium chloride aqueous solution) of the super absorbent polymer, and represents the water holding capacity calculated as in the above calculation formula 1,
[71]
AUP is the absorbency under pressure for 1 hour under 0.7psi of the physiological saline solution (0.9 wt% sodium chloride aqueous solution) of the superabsorbent polymer, and indicates the absorbency under pressure calculated by the above calculation formula 2.
[72]
Accordingly, the superabsorbent polymer of one embodiment exhibits excellent absorption performance, such as basic water absorption and absorption retention under pressure, so that it can be suitably used for various sanitary materials.
[73]
In addition, the superabsorbent polymer of one embodiment may have a surface tension of 50 to 80 mN/m, or 65 to 75 mN/m.
[74]
Such surface tension can be measured using a surface tension meter at room temperature of, for example, 23±2°C. A specific method of measuring such surface tension is described in Examples described later.
[75]
The surface tension of the super absorbent polymer may be a measure capable of evaluating urine leakage from a diaper including the super absorbent polymer as a physical property that is distinguished from water holding capacity and pressure absorption capacity. The surface tension swells the super absorbent polymer in brine and refers to the surface tension measured for the brine.If the surface tension of the super absorbent polymer is low, there is a high possibility that urine leaks in diapers manufactured including the super absorbent polymer. . According to the superabsorbent polymer of one embodiment, it is possible to produce a high-quality hygiene product by reducing the possibility of leakage by having an appropriate range of surface tension along with an excellent absorption rate.
[76]
On the other hand, the superabsorbent polymer of the above-described embodiment may exhibit a characteristic in which the absorption rate by the vortex method is 5 to 55 seconds, or 20 to 50 seconds, which may define an excellent absorption rate of the super absorbent polymer.
[77]
The absorption rate according to the vortex method was determined by adding 2 g of superabsorbent resin to 50 mL of physiological saline at 23°C to 24°C, and stirring a magnetic bar (diameter 8 mm, length 31.8 mm) at 600 rpm to prevent a vortex. It can be calculated by measuring the time until disappearance in seconds.
[78]
As the super absorbent polymer maintains excellent absorption performance and has a developed porous structure, it can simultaneously exhibit an excellent absorption rate defined by the above-described vortex absorption rate range. Therefore, the super absorbent polymer can be preferably used in sanitary materials in which the content of fiber materials such as pulp is reduced.
[79]
Meanwhile, in the super absorbent polymer of the above-described embodiment, the first crosslinked polymer included in the base resin powder is trimethylolpropane tri(meth)acrylate, ethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylic. Rate, propylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, butanediol di(meth)acrylate, butylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, hexane Dioldi(meth)acrylate, triethylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, dipentaerythritol pentaacrylate, glycerin tri(meth) Acrylate, pentaerythritol tetraacrylate, ethyleneglycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerol polyglycidyl ether, propylene glycol diglycidyl ether and polypropylene glycol di In the presence of at least one internal crosslinking agent selected from the group consisting of glycidyl ether, the monomer may be crosslinked and polymerized. In addition, it is of course possible to use various internal crosslinking agents known to be usable in the manufacturing process of the super absorbent polymer.
[80]
Further, in the above-described superabsorbent polymer, the second crosslinked polymer further includes a surface crosslinked layer in which the first crosslinked polymer of the base resin powder is further crosslinked through a surface crosslinking agent. As such a surface crosslinking agent, any functional compound known to be usable in the manufacture of a super absorbent polymer may be used. Examples of such surface crosslinking agents include polyhydric alcohol compounds, polyhydric epoxy compounds, polyamine compounds, and halo At least one selected from the group consisting of an epoxy compound, a condensation product of a haloepoxy compound, an oxazoline compound, and an alkylene carbonate compound. Among these, in consideration of the liquid permeability and/or gel strength of the super absorbent polymer, the surface crosslinking agent is an alkylene carbonate-based compound having 2 to 10 carbon atoms or 2 to 6 carbon atoms, more specifically ethylene carbonate, propylene carbonate, Trimethylene carbonate or glycerol carbonate can be more preferably used.
[81]
The super absorbent polymer of the above-described embodiment may have a particle diameter of 150 to 850 μm. More specifically, at least 95% by weight or more of the base resin powder and the super absorbent polymer including the same has a particle diameter of 150 to 850 μm, and a fine powder having a particle diameter of less than 150 μm is less than 5% by weight, or less than 3% by weight, Or it may be less than 1% by weight. In this case, the particle diameter of the super absorbent polymer may be defined as the longest diameter of the super absorbent polymer particle described above.
[82]
Meanwhile, according to another embodiment of the present invention, a method of manufacturing the super absorbent polymer of the embodiment is provided. This manufacturing method comprises the steps of forming a monomer mixture comprising a water-soluble ethylenically unsaturated monomer and an internal crosslinking agent having at least a partly neutralized acidic group;
[83]
Transferring the monomer mixture to a polymerization reactor along a transfer pipe having a diameter varying depending on the section;
[84]
Crosslinking the monomer mixture transferred to the polymerization reactor to form a hydrogel polymer including the first crosslinked polymer;
[85]
Gel grinding, drying, grinding and classifying the hydrogel polymer to form a base resin comprising less than 9.9% by number of base resin powders having an aspect ratio of less than 0.5, defined as the shortest diameter / longest diameter of each base resin powder. ; And
[86]
In the presence of a surface crosslinking agent, comprising the step of forming a surface crosslinking layer by further crosslinking the surface of the base resin powder,
[87]
In the transfer step of the monomer mixture, the monomer mixture exhibits a maximum transfer rate in the minimum diameter section of the transfer pipe, the monomer mixture exhibits a minimum transfer rate in the maximum diameter section of the transfer tube, and the maximum transfer rate is the It may be more than 2.5 times the minimum feed rate.
[88]
In the manufacturing method of this other embodiment, in the process of transferring the monomer mixture to the polymerization reactor, the maximum transfer rate in the minimum diameter section of the transfer tube while changing the diameter of the transfer tube and the transfer rate thereof is the minimum transfer rate in the maximum diameter section. The speed is controlled to be 2.5 times or more, or 3 times or more, and 5 times or less, or 4 times or less. When the transfer rate of the monomer mixture is changed as described above, the solubility of gases such as oxygen in the monomer mixture may decrease as the pressure applied to the monomer mixture during transfer changes continuously/momentarily. Air bubbles may occur. Therefore, by the generation of such bubbles, foaming polymerization may proceed in the crosslinking polymerization step. Therefore, according to the method of another embodiment, even if the foaming agent is not used or the amount of the foaming agent is greatly reduced, a super absorbent polymer having a porous structure developed by the above-described physical foaming and an improved absorption rate can be produced.
[89]
As a result of the large reduction in the amount of foaming agent used, the base resin powder and super absorbent polymer particles having a small aspect ratio, i.e., the shortest diameter / longest diameter of each particle, when drying, pulverizing and classifying after the crosslinking polymerization are performed. The ratio of the base resin powder and the super absorbent polymer particles having a defined aspect ratio of less than 0.5 may be significantly reduced to less than 9.9% by number, 1 to 9.9% by number, or 3 to 9.7% by number. Accordingly, there is practically no possibility that other physical properties, such as absorption performance, will deteriorate during surface crosslinking or when mixing additives.
[90]
As a result, according to the method of another embodiment, a superabsorbent polymer of one embodiment can be prepared that maintains excellent absorption performance while exhibiting a more improved absorption rate.
[91]
Hereinafter, the manufacturing method for each step will be described in detail.
[92]
First, the manufacturing method of another embodiment includes the step of forming a hydrogel polymer by crosslinking polymerization. Specifically, it is a step of thermally polymerizing or photopolymerizing a monomer mixture including a water-soluble ethylenically unsaturated monomer and a polymerization initiator in the presence of an internal crosslinking agent to form a hydrogel polymer.
[93]
The water-soluble ethylenically unsaturated monomer contained in the monomer mixture is as described above.
[94]
In addition, the monomer mixture 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. 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.
[95]
Here, as the photopolymerization initiator, for example, benzoin ether, dialkyl acetophenone, hydroxyl alkylketone, phenyl glyoxylate, benzyldimethyl 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.
[96]
In addition, 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.
[97]
This polymerization initiator may be added in a concentration of about 0.001 to 1% by weight based on the monomer mixture. 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 too high, 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.
[98]
Meanwhile, the monomer mixture includes a crosslinking agent ("internal crosslinking agent") for improving the physical properties of the resin by polymerization of the water-soluble ethylenically unsaturated monomer. The crosslinking agent is for internally crosslinking the hydrogel polymer, and may be used separately from the "surface crosslinking agent" to be described later. However, since the types of the internal crosslinking agent have already been described above, additional descriptions thereof will be omitted.
[99]
The total content of the internal crosslinking agent may be 0.01 parts by weight to 2 parts by weight, or 0.05 to 1.8 parts by weight based on 100 parts by weight of the monomer mixture including the internal crosslinking agent and the monomer. Depending on the content of the internal cross-linking agent, it is possible to more effectively obtain a super-absorbent resin that satisfies the physical properties of one embodiment by achieving a cross-linking density inside the super-absorbent resin at an appropriate level. However, if the content of the internal crosslinking agent is too large, the basic absorption performance of the super absorbent polymer may be deteriorated.
[100]
On the other hand, the above-described monomer mixture may further include a foaming agent when it is necessary to further improve the absorption rate. However, as already described above, according to the method of another embodiment, a super absorbent polymer that satisfies a highly developed porous structure and water absorption rate can be obtained even when a foaming agent is used in a significantly reduced content than before.
[101]
Such a foaming agent may cause chemical foaming during polymerization, thereby forming more pores in the hydrogel polymer. As the foaming agent, a carbonate salt may be used as a representative example, and examples include sodium bicarbonate, sodium carbonate, potassium bicarbonate, potassium carbonate, and calcium bicarbonate. ), calcium bicarbonate, magnesium bicarbonate or magnesium carbonate can be used.
[102]
In addition, the blowing agent may be added in a concentration of 0 to 1.0 parts by weight, 0 to 0.5 parts by weight, or 0.01 to 0.1 parts by weight based on 100 parts by weight of the acrylic acid-based monomer. When the amount of the foaming agent is increased, the water absorption performance of the super absorbent polymer may decrease.
[103]
In addition, the monomer mixture may further include a surfactant to optimize pore formation. Such a surfactant may play a role of uniformly distributing the air bubbles over the entire polymer region while maintaining the shape of the air bubbles formed in the monomer mixture. Therefore, the absorption rate of the super absorbent polymer may be further improved due to the additional use of such a surfactant.
[104]
As such a surfactant, any component previously used in the foaming polymerization of the super absorbent polymer may be used. For example, a cationic, anionic, or nonionic surfactant may be used.
[105]
The surfactant may be added in a concentration of 0.001 parts by weight to 0.1 parts by weight, or 0.002 parts by weight to 0.03 parts by weight based on 100 parts by weight of the acrylic acid-based monomer. If the concentration of the surfactant is too low, the role of stabilizing the bubbles is insignificant, making it difficult to achieve the effect of improving the absorption rate, and on the contrary, if the concentration is too high. Since the surface tension of the super absorbent resin is lowered, water leakage may occur from the diaper.
[106]
In addition, additives such as a thickener, a plasticizer, a storage stabilizer, and an antioxidant may be further included in the monomer mixture as necessary.
[107]
In addition, such a monomer mixture may be prepared in the form of a solution in which raw materials such as the above-described monomer, polymerization initiator, and internal crosslinking agent are dissolved in a solvent.
[108]
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 a mixture thereof may be used.
[109]
The solvent may be included in a residual amount excluding the above-described components with respect to the total content of the monomer mixture.
[110]
On the other hand, after the above-described components are mixed to form a monomer mixture, the monomer mixture may be transferred to a polymerization reactor through a transfer pipe, and the transfer speed thereof may be changed while controlling. More specifically, in the transfer process of the monomer mixture, the maximum transfer speed in the minimum diameter section of the transfer pipe while changing the diameter of the transfer pipe and the transfer speed of the monomer mixture is 2.5 with respect to the minimum transfer speed in the maximum diameter section. It becomes more than twice, or more than 3 times, and it can be adjusted to be less than 10 times or less than 8 times.
[111]
As already described above, the solubility of gases such as oxygen in the monomer mixture can be reduced by adjusting the pressure applied to the monomer mixture by changing the diameter of the transfer pipe, the transfer speed, etc. during the transfer of the monomer mixture. Accordingly, bubbles are generated from the monomer mixture, and foaming polymerization may proceed in the crosslinking polymerization step by the generated bubbles, and a super absorbent polymer having a porous structure developed by such physical foaming may be prepared.
[112]
If the maximum transfer rate is controlled to be less than 2.5 times the minimum transfer rate, physical foaming and foaming polymerization do not proceed properly, and thus the porous structure and absorption rate of the super absorbent polymer may not be properly expressed. Conversely, if the maximum feed rate is controlled excessively, the additional foaming effect is not large, and the feed rate in the process is not properly controlled, which may cause difficulties in the process.
[113]
Meanwhile, in order to satisfy the relationship between the above-described maximum transfer speed and minimum transfer speed, the transfer speed thereof may be changed by adjusting the diameter of the transfer pipe or the flow rate of the monomer mixture. For example, the monomer mixture is conveyed along a conveying pipe having a diameter that varies according to a section, and specifically, the diameter of the conveying pipe may be reduced according to a conveying path. As a result, the monomer mixture may be controlled to exhibit a maximum conveying speed in the minimum diameter section of the conveying pipe.
[114]
In a more specific example, the transfer pipe has a diameter of 0.002 to 0.01m, or 0.005 to 0.009m in the minimum diameter section, and 0.011 to 0.020m, or 0.012 to 0.016m in the maximum diameter section before the minimum diameter section. I can have it. The diameter of the conveying pipe may be appropriately determined within the above-described range in consideration of the flow rate of the monomer mixture for achieving an appropriate productivity of the super absorbent polymer and the relationship of the above-described conveying speed.
[115]
In addition, in the manufacturing process of a super absorbent polymer, the monomer mixture is usually 100 to 15000 kg/hr, or 100 to 13000 kg/hr, or 110 to 1000 kg/hr, in order to secure appropriate productivity and control the above-described transfer rate relationship. It can be transferred through the transfer pipe at a flow rate. When conveying at such a flow rate, by changing the diameter of the conveying pipe within the above-described range, it is possible to control the conveying speed relationship according to the method of another embodiment. As a result, it is possible to manufacture a super absorbent polymer having a developed porous structure and excellent absorption rate by optimizing the degree of physical foaming.
[116]
Meanwhile, due to the above-described control of the flow rate and the diameter of the conveying pipe, in the minimum diameter section of the conveying pipe, the monomer mixture can be conveyed at a maximum conveying speed of 0.45 to 2.5 m/s, or 0.7 to 2.2 m/s. In the maximum diameter section of the transfer pipe, the monomer mixture may be controlled to be transferred at a minimum transfer speed of 0.1 to 0.5 m/s, or 0.2 to 0.4 m/s.
[117]
On the other hand, while physically foaming the monomer mixture by the above-described method, after transporting the monomer mixture to the polymerization reactor, the monomer mixture may be thermally polymerized or photopolymerized to form a hydrogel polymer. The method/condition for performing such a polymerization step is not particularly limited, and may be followed by a general polymerization condition and method of a super absorbent polymer.
[118]
Specifically, 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, the polymerization method can be performed in a reactor having an agitation axis such as a kneader, and photopolymerization is performed. If so, it can be carried out in a reactor equipped with a movable conveyor belt.
[119]
For example, the monomer mixture may be added to a reactor such as a kneader equipped with a stirring shaft, and hot air is supplied thereto, or the reactor is 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 mixture to be injected, and a hydrogel polymer having a (weight average) particle diameter of 2 to 50 mm may be obtained.
[120]
And, as another example, when photopolymerization is performed on the monomer mixture 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 mixture to be injected and the injection speed.In order to ensure the production speed, etc., while allowing the entire sheet to be evenly polymerized, it is usually adjusted to a thickness of 0.5 to 10 cm. desirable.
[121]
On the other hand, after forming the hydrogel polymer by the above-described crosslinking polymerization, the hydrogel polymer having a controlled moisture content is subjected to gel pulverization.
[122]
In the gel grinding step, the crusher used is not limited in configuration, but specifically, a vertical pulverizer, a turbo cutter, a turbo grinder, and a rotary cutter mill), Cutter mill, Disc mill, Shred crusher, Crusher, Chopper and Disc cutter. Any one may be included, but is not limited to the above-described example.
[123]
Gel grinding of the hydrogel polymer may be performed such that the particle diameter of the hydrogel polymer is 0.01 mm to 50 mm, or 0.01 mm to 30 mm. That is, in order to increase drying efficiency, the hydrogel polymer is preferably pulverized into particles of 50 mm or less. However, since aggregation between particles may occur during excessive pulverization, the hydrogel polymer is preferably gel pulverized into particles of 0.01 mm or more.
[124]
In addition, since the gel pulverization of the hydrous gel polymer is performed in a state where the moisture content is relatively low, a phenomenon in which the hydrogel polymer adheres to the surface of the gel pulverizer may occur. In order to minimize this phenomenon, if necessary, steam, water, surfactants, anti-aggregation agents (eg, clay, silica, etc.); Persulfate-based initiator, azo-based initiator, hydrogen peroxide, thermal polymerization initiator, epoxy-based cross-linking agent, diol-based cross-linking agent, a cross-linking agent containing an acrylate of a polyfunctional group of a bifunctional group or a trifunctional group or more, a crosslinking agent of a monofunctional group containing a hydroxyl group And the like may be added to the hydrogel polymer.
[125]
After the above-described gel pulverization, the hydrogel polymer can be dried. The drying may be performed under a temperature of 120 to 250°C, preferably 140 to 200°C, more preferably 150 to 200°C. In this case, the drying temperature may be defined as the temperature of the thermal medium supplied for drying or the temperature inside the drying reactor including the thermal medium and the polymer in the drying process. If the drying temperature is low and the drying time is long, the process efficiency is lowered, and thus the drying temperature is preferably 120°C or higher to prevent this. In addition, if the drying temperature is higher than necessary, the surface of the hydrous gel polymer may be excessively dried, resulting in increased fine powder generation in the subsequent pulverization step, and the physical properties of the final resin may be degraded.To prevent this, the drying temperature is It is preferably 250°C or less.
[126]
In this case, the drying time in the drying step is not particularly limited, but may be adjusted from 20 minutes to 90 minutes under the drying temperature in consideration of process efficiency and physical properties of the resin.
[127]
The drying may be performed using a conventional medium. For example, it may be performed through a method such as hot air supply, infrared irradiation, microwave irradiation, or ultraviolet irradiation to the pulverized hydrogel polymer.
[128]
And, such drying is preferably carried out so that the dried polymer has a moisture content of 0.1 to 10% by weight. That is, when the moisture content of the dried polymer is less than 0.1% by weight, manufacturing cost may increase due to excessive drying and degradation of the crosslinked polymer may occur, which is not preferable. In addition, if the moisture content of the dried polymer exceeds 10% by weight, the dried polymer may adhere in a subsequent process and may interfere with the transport path, which is not preferable.
[129]
After the drying, the dried polymer can be pulverized, whereby the particle diameter and surface area of ​​the polymer can be adjusted to an appropriate range. The pulverization may be performed so that the pulverized polymer has a particle diameter of 150 to 850 µm. The particle diameter at this time may also be defined as the longest diameter of each polymer particle, and is the same in the following.
[130]
The crusher that can be used at this time is usually a pin mill, a hammer mill, a screw mill, a roll mill, a disc mill, a jog mill, etc. Can be used.
[131]
In addition, in order to manage the physical properties of the super absorbent polymer to be finally commercialized, a step of selectively classifying particles having a particle diameter of 150 to 850 µm from the polymer particles obtained through the pulverization step may be further performed.
[132]
The base resin powder prepared through the classification process, as already described above, has an aspect ratio of less than 0.5, defined as the shortest diameter / longest diameter of each particle, and the formation ratio of the base resin powder is less than 9.9% by number, 1 to 9.9. %, or it can be greatly reduced to 3 to 9.7% by number. Accordingly, there is practically no possibility that other physical properties, such as absorption performance, will deteriorate during surface crosslinking or when mixing additives.
[133]
On the other hand, after preparing the base resin powder through the above-described classification process, the base resin powder may be surface-crosslinked while heat-treating in the presence of a surface crosslinking agent to form super absorbent polymer particles. The surface crosslinking induces a crosslinking reaction on the surface of the base resin powder in the presence of a surface crosslinking agent, and a surface modification layer (surface crosslinking layer) may be formed on the surface of the base resin powder through such surface crosslinking.
[134]
Since the types of the surface crosslinking agent that can be used during the surface crosslinking have already been described above, an additional description thereof will be omitted.
[135]
In addition, the content of the surface crosslinking agent may be appropriately adjusted according to the type of the crosslinking agent or reaction conditions, and preferably 0.001 to 5 parts by weight based on 100 parts by weight of the base resin powder. If the content of the surface crosslinking agent is too low, surface modification may not be performed properly, and physical properties of the final resin may be deteriorated. Conversely, when an excessive amount of the surface crosslinking agent is used, the basic absorption performance of the resin may be rather degraded due to excessive surface crosslinking reaction, which is not preferable.
[136]
In addition, the above-described surface crosslinking step further uses one or more selected from the group consisting of a polyvalent metal salt, for example, an aluminum salt, more specifically aluminum sulfate, potassium salt, ammonium salt, sodium salt, and hydrochloride salt, You can proceed.
[137]
As these polyvalent metal salts are additionally used, the liquid permeability of the super absorbent polymer prepared by the method of one embodiment may be further improved. These polyvalent metal salts may be added to the surface crosslinking solution together with the surface crosslinking agent, and may be used in an amount of 0.01 to 4 parts by weight based on 100 parts by weight of the base resin powder.
[138]
Meanwhile, the surface crosslinking process may be performed using a surface crosslinking solution containing water and/or a hydrophilic organic solvent (eg, alcohol-based polar organic solvent such as methanol) as a liquid medium, together with the above-described surface crosslinking agent. . At this time, the content of water and the hydrophilic organic solvent induces even dispersion of the surface crosslinking solution, prevents agglomeration of the base resin powder, and at the same time optimizes the surface penetration depth of the surface crosslinking agent. It can be applied by adjusting the addition ratio.
[139]
There is also no particular limitation on the configuration of the method of adding the above-described surface crosslinking liquid to the base resin powder. For example, a method of mixing the surface crosslinking liquid and the base resin powder in a reaction tank, or spraying the surface crosslinking liquid onto the base resin powder, and continuously supplying and mixing the base resin powder and the surface crosslinking liquid to a continuously operated mixer. Method, etc. can be used.
[140]
For the base resin powder to which the surface crosslinking solution is added, the surface for 5 minutes to 60 minutes, or 10 minutes to 50 minutes, or 20 minutes to 45 minutes at the maximum reaction temperature of 140°C to 200°C, or 170°C to 195°C The crosslinking reaction can proceed. More specifically, in the surface crosslinking step, the temperature is raised to the highest reaction temperature over 10 minutes or more, or 10 to 30 minutes at an initial temperature of 20°C to 130°C, or 40°C to 120°C, and the maximum temperature is increased. It can be carried out by holding for 5 minutes to 60 minutes and heat treatment.
[141]
By satisfying these surface crosslinking process conditions (especially, a temperature increase condition and a reaction condition at the highest reaction temperature), a super absorbent polymer that satisfies the physical properties of one embodiment can be more effectively prepared.
[142]
The means for increasing the temperature for the surface crosslinking reaction is not particularly limited. It can be heated by supplying a heat medium or by directly supplying a heat source. At this time, as the type of the heat medium that can be used, a heated fluid such as steam, hot air, or hot oil may be used, but the temperature of the heat medium supplied is not limited thereto. It can be appropriately selected in consideration. On the other hand, the heat source directly supplied may include heating through electricity and heating through gas, but is not limited to the above-described example.
[143]
The superabsorbent polymer obtained according to the above-described manufacturing method maintains excellent absorption performance such as water holding capacity and pressure absorption capacity, satisfies a more improved absorption rate, etc., thereby satisfying all physical properties of one embodiment, and hygiene such as diapers. Ash, in particular, an ultra-thin sanitary material with a reduced pulp content can be suitably used.
Effects of the Invention
[144]
The superabsorbent polymer according to the present invention is capable of excellently maintaining basic absorption performance, exhibiting an improved absorption rate, and the like, and can be preferably applied to hygiene materials such as diapers having a thinner thickness.
Brief description of the drawing
[145]
1 is an electron micrograph showing an example of a definition of an aspect ratio of a super absorbent polymer particle and a method of measuring the same in a super absorbent polymer according to an embodiment.
Mode for carrying out the invention
[146]
Hereinafter, preferred embodiments are presented to aid in understanding the invention. However, the following examples are only for illustrating the present invention, and the present invention is not limited thereto.
[147]
Example 1
[148]
As a manufacturing device for super absorbent polymer, a continuous manufacturing device consisting of a polymerization process, a hydrogel grinding process, a drying process, a grinding process, a classification process, a surface crosslinking process, a cooling process, a classification process, and a transport process connecting each process is used. I did.
[149]
100 parts by weight of acrylic acid, 0.4 parts by weight of polyethylene glycol diacrylate (weight average molecular weight: ~ 500 g/mol) as an internal crosslinking agent, 0.01 parts by weight of sodium lauryl sulfate as a surfactant, and Phenylbis (2, as a photoinitiator) A monomer solution was prepared by mixing 0.01 parts by weight of 4,6-trimethylbenzoyl)phosphine oxide. Subsequently, while continuously supplying the monomer solution to a metering pump, 160 parts by weight of a 24% by weight sodium hydroxide aqueous solution was continuously line-mixed to prepare an aqueous monomer solution. Further, 6 parts by weight of a 4% by weight sodium persulfate aqueous solution was continuously line-mixed to prepare a monomer mixture.
[150]
This monomer mixture is firstly fed through a single tube with a diameter of 0.015m (maximum diameter section) at a flow rate of 240kg/h, and then continuously transferred through a single tube (minimum diameter section) that is changed to a diameter of 0.008m. I did. The transfer speed of each section in this transfer process was as summarized in Table 1 below.
[151]
Through this transfer, an aqueous monomer solution was introduced into a polymerization reactor consisting of a moving conveyor belt, and ultraviolet rays were irradiated through a UV irradiation device (irradiation amount: 2mW/cm2) to perform UV polymerization for 2 minutes to prepare a hydrogel polymer .
[152]
After the hydrogel was cut to have an average size of about 300 mm or less, it was put into a grinder (including a porous plate including a plurality of holes having a diameter of 10 mm) and pulverized.
[153]
Subsequently, the pulverized hydrogel was dried in a dryer capable of transferring air volume up and down. The hydrogel was uniformly dried by flowing hot air at 180° C. from the bottom to the top for 15 minutes so that the moisture content of the dried powder was less than about 2%, and flowing from the top to the bottom for another 15 minutes. .
[154]
The dried resin was pulverized with a grinder and then classified to obtain a base resin having a size of 150 to 850 μm.
[155]
Then, to 100 parts by weight of the prepared base resin powder, 6 g of an aqueous surface crosslinking agent solution containing 3 parts by weight of ethylene carbonate was sprayed and stirred at room temperature to evenly distribute the surface crosslinking solution on the base resin powder. Then, the base resin powder mixed with the surface crosslinking solution was put into a surface crosslinking reactor, and a surface crosslinking reaction was performed.
[156]
In this surface crosslinking reactor, it was confirmed that the base resin powder was gradually heated at an initial temperature around 80°C, and the reaction was operated to reach the maximum reaction temperature of 190°C after 30 minutes elapsed. After reaching this reaction maximum temperature, after further reaction for 15 minutes, the final prepared superabsorbent polymer sample was taken. After the surface crosslinking process, the superabsorbent polymer of Example 1 was prepared by classifying it with a standard mesh of ASTM standards and having a particle diameter of 150 µm to 850 µm.
[157]
The base resin and super absorbent polymer obtained by the above method were analyzed by electron micrographs (see Fig. 1, etc.), and the aspect ratio (a/b) of each base resin powder and super absorbent polymer particles was calculated. The ratio (number %) of particles having an aspect ratio of less than 0.5 among the water absorbent resin particles was measured. As a result of the measurement, the ratio of particles having an aspect ratio of less than 0.5 among the base resin powder and the super absorbent polymer particles is shown in Table 1 below.
[158]
Example 2
[159]
In Example 1, Example 1 except that the diameter of the single pipe (transfer pipe) of the minimum diameter section was changed to 0.006 m when transporting the monomer mixture, and the maximum transport speed in the corresponding section was adjusted as shown in Table 1 below. In the same manner as, the super absorbent polymer of Example 2 was prepared.
[160]
Example 3
[161]
In Example 1, the flow rate of the monomer mixture was adjusted to 400 kg/h, and the transfer rate for each section of the monomer mixture was adjusted as shown in Table 1 below. A super absorbent polymer was prepared.
[162]
Example 4
[163]
A super absorbent polymer of Example 4 was prepared in the same manner as in Example 1, except that the surfactant was included in an amount of 0.005 parts by weight in the monomer mixture.
[164]
Example 5
[165]
In Example 1, the monomer mixture was first introduced through a single tube having a diameter of 0.015 m (maximum diameter section) at a flow rate of 240 kg/h, and then a single tube (minimum diameter) changed to a diameter of 0.002 m Section) was carried out in the same manner as in Example 1, except that the continuous transfer was carried out to prepare a super absorbent polymer of Example 5. The transfer speed of each section in this transfer process was as summarized in Table 1 below.
[166]
Comparative Example 1
[167]
In Example 1, Example 1 except that the diameter of the single pipe (transfer pipe) in the minimum diameter section was changed to 0.012 m when the monomer mixture was transferred, and the maximum transfer speed in the section was adjusted as shown in Table 1 below. In the same manner as, the super absorbent polymer of Comparative Example 1 was prepared.
[168]
Comparative Example 2
[169]
In Example 1, Example 1 except that the diameter of the single pipe (transfer pipe) in the minimum diameter section was changed to 0.015 m when the monomer mixture was transferred, and the maximum transfer speed in the corresponding section was adjusted as shown in Table 1 below. In the same manner as, a super absorbent polymer of Comparative Example 2 was prepared.
[170]
Comparative Example 3
[171]
The super absorbent polymer of Comparative Example 3 was prepared in the same manner as in Comparative Example 2, except that the surfactant was included in an amount of 0.02 parts by weight in the monomer mixture, and a blowing agent of 0.1% by weight sodium hydrogen carbonate was further mixed.
[172]
Experimental example
[173]
The physical properties of each superabsorbent polymer prepared in Examples and Comparative Examples, and various physical properties during the manufacturing process were measured and evaluated by the following methods.
[174]
(1) Transfer speed of aqueous monomer solution (m/s)
[175]
The transfer speed of the aqueous monomer solution was calculated from the following equation by obtaining the cross-sectional area from the diameter of the transfer pipe in the transfer section and measuring the flow rate of the monomer mixture in the transfer section:
[176]
Feed rate (m/s) = flow rate (m 3 /hr)/cross-sectional area (m 2 )
[177]
(2) Measurement of aspect ratio and particle distribution of base resin powder and super absorbent polymer particles
[178]
As shown in Figure 1, the shortest diameter (a) and longest diameter (b) of each powder/particles were calculated through an electron microscope, and the aspect ratio of each powder/particles was measured therefrom, and the total powder/particles obtained in each Example/Comparative Example Among the particles, the ratio of the number of powders/particles having an aspect ratio of less than 0.5 (number %) was calculated.
[179]
(3) Centrifuge Retention Capacity (CRC)
[180]
In accordance with the European Disposables and Nonwovens Association (EDANA) standard EDANA WSP 241.3, the centrifugal water retention capacity (CRC) by the absorption rate under no load was measured. The super absorbent polymer W 0 (g, about 0.2 g) was uniformly placed in a nonwoven bag and sealed, and then immersed in physiological saline solution of 0.9 wt% sodium chloride aqueous solution at room temperature. After 30 minutes, the bag was centrifuged and dried at 250 G for 3 minutes, and the mass W 2 (g) of the bag was measured. In addition, after performing the same operation without using a super absorbent polymer, the mass W 1 (g) at that time was measured. Using each of the masses thus obtained, CRC (g/g) was calculated according to the following equation 1 to confirm the water holding capacity.
[181]
[Calculation 1]
[182]

[183]
(4) Absorbing under Pressure (AUP)
[184]
For the superabsorbent polymers of Examples and Comparative Examples, Absorbency under Pressure (AUP) was measured according to the method of EDANA WSP 242.3 of the European Disposables and Nonwovens Association.
[185]
First, a stainless steel 400 mesh wire mesh was mounted on the bottom of a plastic cylinder having an inner diameter of 60 mm. Resin W 0 (g, 0.90 g) obtained in Examples 1 to 6 and Comparative Examples 1 to 4 was evenly sprayed on a wire mesh under conditions of 23±2° C. and 45% relative humidity , and 4.83 kPa (0.7 The piston, which can apply more uniformly the load of psi), has an outer diameter of a little less than 60 mm, and there is no gap with the inner wall of the cylinder, and the vertical movement is not obstructed. At this time, the weight W 3 (g) of the device was measured.
[186]
A glass filter having a diameter of 125 mm and a thickness of 5 mm was placed on the inside of a 150 mm diameter PET dish, and a physiological saline solution composed of 0.90 wt% sodium chloride was at the same level as the upper surface of the glass filter. The measuring device was mounted on a glass filter, and the liquid was absorbed for 1 hour under load. After 1 hour, the measuring device was lifted and the weight W 4 (g) was measured.
[187]
Using each of the masses thus obtained, AUP (g/g) was calculated according to the following calculation formula 2, and the absorbency under pressure was confirmed.
[188]
[Calculation Equation 2]
[189]

[190]
In Equation 2 above,
[191]
W 0 (g) is the initial weight (g) of the super absorbent polymer,
[192]
W 3 (g) is the sum of the weight of the super absorbent polymer and the weight of the device capable of imparting a load to the super absorbent polymer,
[193]
W 4 (g) is the sum of the weight of the super absorbent polymer and the weight of the apparatus capable of applying a load to the super absorbent polymer after absorbing physiological saline in the super absorbent polymer for 1 hour under load (0.7 psi).
[194]
(5) Absorption rate by vortex method (Vortex time)
[195]
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.
[196]
Specifically, the absorption rate (or vortex time) is a vortex ( vortex) was calculated by measuring the time until disappearance in seconds.
[197]
(6) Surface tension of super absorbent polymer
[198]
All processes were carried out in a constant temperature and humidity room (temperature 23±0.5°C, relative humidity 45±0.5%). The surface tension of the superabsorbent polymer was 150 g of physiological saline composed of 0.9 wt% sodium chloride in a 250 mL beaker and stirred with a magnetic bar. 1.0 g of super absorbent polymer was added to the stirring solution and stirred for 3 minutes, then the stirring was stopped and left for 15 minutes or longer so that the swollen super absorbent polymer settled on the floor.
[199]
After that, the supernatant (the solution immediately below the surface) was extracted with a pipette, transferred to another clean cup, and measured using a surface tension meter (surface tensionmeter Kruss K11/K100).
[200]
The physical property values ​​of Examples 1 to 5 and Comparative Examples 1 to 3 measured by the above method are summarized and shown in Table 1 below.
[201]
[Table 1]
[202]
Referring to Table 1, the superabsorbent polymers of Examples 1 to 5, in which the feed rate during the transfer of the aqueous monomer solution was controlled, exhibited a water holding capacity, pressure absorption capacity, and surface tension equal to or higher than those of the comparative example, but improved absorption rate It was confirmed to indicate.
[203]
Comparative Example 3 had a certain degree of absorption rate, but it was confirmed that the absorption rate decreased compared to the Example due to the use of a foaming agent and a surfactant. In addition, in Comparative Example 3, as a large amount of particles having a small aspect ratio are included, crushing of the particles or deterioration of physical properties is likely to be very large in the process of transferring the super absorbent polymer and applying the product.
Claims
[Claim 1]
A base resin powder containing a first crosslinked polymer of a water-soluble ethylenically unsaturated monomer having an acidic group at least partially neutralized; And a surface crosslinking layer formed on the base resin powder, wherein the first crosslinked polymer comprises a second crosslinked polymer further crosslinked through a surface crosslinking agent, wherein the superabsorbent polymer is It contains less than 9.9% by number of super absorbent polymer particles with an aspect ratio of less than 0.5, defined as the shortest diameter / longest diameter of the super absorbent polymer particles, and the absorption rate by the vortex method is 5 to 55 seconds, and the surface tension is 50 to 80 mN/m super absorbent polymer.
[Claim 2]
The superabsorbent polymer according to claim 1, wherein the superabsorbent polymer has a water absorption of 46 to 63 g/g represented by the following formula: [Formula 1] In the formula 1, CRC is a physiological saline solution of the super absorbent polymer (0.9 wt% sodium chloride aqueous solution). ) For 30 minutes by centrifugation, and AUP represents the absorption capacity under pressure for 1 hour under 0.7 psi of physiological saline (0.9% by weight sodium chloride aqueous solution) of the superabsorbent polymer.
[Claim 3]
The super absorbent polymer according to claim 2, wherein the CRC is 25 to 35 g/g.
[Claim 4]
The super absorbent polymer according to claim 2, wherein the AUP is 22 to 28 g/g.
[Claim 5]
The method of claim 1, wherein the surface crosslinking agent is selected from the group consisting of polyhydric alcohol compounds, polyvalent epoxy compounds, polyamine compounds, haloepoxy compounds, condensation products of haloepoxy compounds, oxazoline compounds, and alkylene carbonate compounds. Super absorbent polymer containing more than one species.
[Claim 6]
Forming a monomer mixture comprising a water-soluble ethylenically unsaturated monomer having an acidic group at least partially neutralized and an internal crosslinking agent; Transferring the monomer mixture to a polymerization reactor along a transfer pipe having a diameter varying depending on the section; Crosslinking the monomer mixture transferred to the polymerization reactor to form a hydrogel polymer including the first crosslinked polymer; Gel grinding, drying, grinding and classifying the hydrogel polymer to form a base resin comprising less than 9.9% by number of base resin powders having an aspect ratio of less than 0.5, defined as the shortest diameter / longest diameter of each base resin powder. ; And forming a surface crosslinking layer by further crosslinking the surface of the base resin powder in the presence of a surface crosslinking agent, wherein in the transporting step of the monomer mixture, the monomer mixture in the minimum diameter section of the transport pipe is In the maximum diameter section of the transfer pipe, the monomer mixture exhibits a minimum transfer rate, and the maximum transfer rate is 2.5 times or more of the minimum transfer rate.
[Claim 7]
The method of claim 6, wherein the monomer mixture further comprises a surfactant.
[Claim 8]
The method of claim 6, wherein in the minimum diameter section of the transfer pipe, the monomer mixture is transferred at a speed of 0.45 to 2.5 m/s, and in the maximum diameter section of the transfer pipe, the monomer mixture is 0.1 to 0.4 m/s. A method for producing a super absorbent polymer that is conveyed at a speed.
[Claim 9]
The method of claim 6, wherein the conveying pipe has a diameter of 0.002 to 0.01 m in the minimum diameter section, and a diameter of 0.011 to 0.020 m in the maximum diameter section before the minimum diameter section.
[Claim 10]
The method of claim 6, wherein the monomer mixture is transferred through a transfer pipe at a flow rate of 100 to 15000 kg/hr.
[Claim 11]
The method of claim 6, wherein bubbles are generated in the monomer mixture due to a change in a feed rate during transfer of the monomer mixture, and foam polymerization is performed in the crosslinking polymerization step by the generated bubbles.
[Claim 12]
The method of claim 6, wherein the surface crosslinking agent is selected from the group consisting of polyhydric alcohol compounds, polyvalent epoxy compounds, polyamine compounds, haloepoxy compounds, condensation products of haloepoxy compounds, oxazoline compounds, and alkylene carbonate compounds. A method for producing a super absorbent polymer containing more than one species.
[Claim 13]
The method of claim 6, wherein the surface crosslinking step is heated from an initial temperature of 20°C to 130°C over 10 to 30 minutes to a maximum temperature of 140°C to 200°C, and the maximum temperature is maintained for 5 to 60 minutes. A method for producing a super absorbent polymer that proceeds by performing heat treatment.