Title of the invention: Method for producing super absorbent polymer
Technical field
[One]
Cross-reference with related application(s)
[2]
This application claims the benefit of priority based on Korean Patent Application No. 10-2018-0157082 filed on December 7, 2018, and all contents disclosed in the documents of the Korean patent application are incorporated as part of this specification.
[3]
The present invention relates to a method for producing a super absorbent polymer that enables the production of a super absorbent polymer that exhibits an improved water absorption rate while reducing the amount of the foaming agent used.
Background
[4]
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.
[5]
In most cases, such super absorbent polymers are widely used in the field of sanitary materials such as diapers and sanitary napkins. In such sanitary materials, the super absorbent polymer is generally included in a state of being spread in pulp. However, in recent years, efforts to provide sanitary materials such as diapers having a thinner thickness are continuing, and as part of this, the content of pulp is reduced, and furthermore, so-called pulpless diapers are not used at all. Development is actively progressing.
[6]
In this way, the content of pulp is reduced, or in the case of a sanitary material in which pulp is not used, a relatively high water absorbent resin is included in a high proportion, and such super absorbent polymer particles are inevitably included in multiple layers in the sanitary material. In order for the entire super absorbent polymer particles included in multiple layers to more efficiently absorb liquids such as urine, it is necessary for the super absorbent polymer to basically exhibit high absorption performance and absorption rate.
[7]
Accordingly, in recent years, attempts to manufacture and provide a super absorbent polymer having an improved absorption rate have been continuously made.
[8]
The most common method for increasing the absorption rate is a method of increasing the surface area of ​​the super absorbent polymer by forming a porous structure inside the super absorbent polymer.
[9]
As described above, in order to increase the surface area of ​​the super absorbent polymer, a method of forming a porous structure in the base resin powder was typically applied as crosslinking polymerization was performed using a carbonate-based foaming agent. When such a carbonate-based foaming agent is used, carbon dioxide gas may be generated in the polymerization process to form micropores, so that a super absorbent polymer having a porous structure may be prepared.
[10]
However, in this method, depending on the polymerization temperature and time, the effect of generating carbon dioxide gas is reduced, and as a result, there is a disadvantage in that the physical properties of the superabsorbent polymer may vary. In addition, when chemical foaming with the carbonate-based foaming agent is carried out, a large amount of unwanted fines are generated in the process of drying and pulverization, and other physical properties of the super absorbent polymer are deteriorated, and recycling of fines is required. There were also disadvantages in the process.
[11]
Accordingly, development of a technology that enables the production of a super absorbent polymer having an improved absorption rate by forming an appropriate porous structure while reducing the amount of the foaming agent is continuously requested.
Detailed description of the invention
Technical challenge
[12]
Accordingly, the present invention is to provide a method for producing a super absorbent polymer that enables the production of a super absorbent polymer exhibiting an improved water absorption rate while reducing the amount of the foaming agent used.
Means of solving the task
[13]
Accordingly, the present invention 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;
[14]
While transferring the monomer mixture to the polymerization reactor, controlling the transfer rate thereof to adjust the dynamic pressure applied to the monomer mixture during transfer calculated by the following calculation formula 1 to 140Pa or more;
[15]
Crosslinking the monomer mixture transferred to the polymerization reactor to form a hydrogel polymer;
[16]
Drying, pulverizing and classifying the hydrogel polymer to form a base resin powder; And
[17]
In the presence of a surface crosslinking agent, there is provided a method for producing a super absorbent polymer comprising the step of forming a surface crosslinking layer by further crosslinking the surface of the base resin powder:
[18]
[Calculation 1]
[19]

[20]
In Formula 1, p represents the density of the monomer mixture being transported, and V represents the transport rate of the monomer mixture.
[21]
Hereinafter, a method of manufacturing a super absorbent polymer 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 rights of the invention.
[22]
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.
[23]
According to one embodiment of the invention, forming a monomer mixture comprising a water-soluble ethylenically unsaturated monomer and an internal crosslinking agent having an acidic group at least partially neutralized;
[24]
While transferring the monomer mixture to the polymerization reactor, controlling the transfer rate thereof to adjust the dynamic pressure applied to the monomer mixture during transfer calculated by the following calculation formula 1 to 140Pa or more;
[25]
Crosslinking the monomer mixture transferred to the polymerization reactor to form a hydrogel polymer;
[26]
Drying, pulverizing and classifying the hydrogel polymer to form a base resin powder; And
[27]
In the presence of a surface crosslinking agent, there is provided a method for producing a super absorbent polymer comprising the step of forming a surface crosslinking layer by further crosslinking the surface of the base resin powder:
[28]
[Calculation 1]
[29]

[30]
In Formula 1, p represents the density of the monomer mixture being transported, and V represents the transport rate of the monomer mixture.
[31]
The present inventors continued research to develop a technology for producing a superabsorbent polymer exhibiting a developed porous structure and excellent absorption rate while reducing the amount of the foaming agent used.
[32]
As a result of these inventors' research, in the process of transferring the monomer mixture to the polymerization reactor, by changing the diameter of the transfer pipe or the transfer speed of the monomer mixture through the transfer pipe, the dynamic pressure applied to the monomer mixture in a specific area of ​​the transfer pipe was reduced to 140 Pa. Above, or in the case of adjusting to 150 to 1000 Pa, or 150 to 800 Pa, it was discovered that it was possible to manufacture a super absorbent polymer having a developed porous structure and excellent absorption rate while reducing the amount of carbonate-based foaming agent by physical foaming. Was completed.
[33]
This is predicted because the solubility of gases such as oxygen in the monomer mixture decreases as the pressure applied to the monomer mixture instantaneously changes during transport through the transfer pipe. Therefore, in the dynamic pressure adjustment step, oxygen bubbles are generated from the monomer mixture, and foam polymerization may proceed in the crosslinking polymerization step by the generated bubbles, and as a result, physical foaming even if no blowing agent is used or the amount of use thereof is reduced. A super absorbent polymer having a porous structure developed by can be prepared.
[34]
This super absorbent polymer can exhibit an excellent absorption rate while minimizing the amount of the foaming agent used, and thus can exhibit an excellent absorption rate, and the remaining physical properties can also be excellently maintained by reducing the phenomenon of deterioration of physical properties due to the foaming agent. As a result, according to the method of one embodiment, while reducing the amount of the foaming agent, a super absorbent polymer having excellent water absorption rate and various physical properties can be prepared.
[35]
Hereinafter, the manufacturing method of one embodiment will be described in more detail for each step.
[36]
In the method of manufacturing a super absorbent polymer of one embodiment, first, the monomer mixture, which is a raw material of the super absorbent polymer, has an acidic group and at least a part of the acidic group is neutralized acrylic acid-based monomer, an internal crosslinking agent, and a polymerization initiator, and optionally a foaming agent. The monomer mixture comprising a is polymerized to obtain a hydrogel polymer, which is dried, pulverized, and classified to form a base resin powder.
[37]
This will be described in more detail below.
[38]
The monomer mixture, which is a raw material of the super absorbent polymer, has an acidic group and may include a water-soluble ethylenically unsaturated monomer in which at least part of the acidic group is neutralized, more specifically, an acrylic acid-based monomer and a polymerization initiator.
[39]
The acrylic acid-based monomer is a compound represented by the following formula (1):
[40]
[Formula 1]
[41]

[42]
In Chemical Formula 1,
[43]
R 1 is an alkyl group having 2 to 5 carbon atoms containing an unsaturated bond,
[44]
M 1 is a hydrogen atom, a monovalent or divalent metal, an ammonium group, or an organic amine salt.
[45]
Preferably, the acrylic acid-based monomer includes 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.
[46]
Here, the acrylic acid-based monomer may have an acidic group and at least a part of the acidic group is neutralized. Preferably, the monomer partially neutralized with a basic substance such as sodium hydroxide, potassium hydroxide, ammonium hydroxide, or the like may be used. In this case, the degree of neutralization of the acrylic acid-based monomer may be adjusted to 80 mol% or less, or 40 to 75 mol%, or 50 to 70 mol%.
[47]
However, if the degree of neutralization is too high, the polymerization may be difficult to proceed smoothly due to precipitation of neutralized monomers.Moreover, the effect of additional neutralization after the initiation of surface crosslinking is substantially eliminated, so that the degree of crosslinking of the surface crosslinking layer is optimized. It may not be possible, and the liquid permeability of the super absorbent polymer may not be sufficient. On the contrary, if the degree of neutralization is too low, not only the absorption power of the polymer is greatly reduced, but also it may exhibit properties such as elastic rubber that are difficult to handle.
[48]
The concentration of the monomer may be 20 to 60% by weight, or 30 to 55% by weight, or 40 to 50% by weight based on the monomer mixture including the raw material of the super absorbent polymer and the solvent, and polymerization time and reaction It can be made into an appropriate concentration considering conditions, etc. However, if the concentration of the monomer is too low, the yield of the superabsorbent polymer may be low and economical problems may occur. On the contrary, if the concentration is too high, a part of the monomer is precipitated or the pulverization efficiency is low when the polymerized hydrogel polymer is pulverized. In the process, problems may occur, and the physical properties of the super absorbent polymer may be deteriorated.
[49]
The polymerization initiator used in the polymerization in the method for preparing the super absorbent polymer of the embodiment is not particularly limited as long as it is generally used for preparing the super absorbent polymer.
[50]
Specifically, the polymerization initiator may be a thermal polymerization initiator or a photopolymerization initiator according to UV irradiation depending on the polymerization method. However, even by the photopolymerization method, a certain amount of heat is generated by irradiation such as UV irradiation, and a certain amount of heat is generated according to the progress of the polymerization reaction, which is an exothermic reaction, and thus a thermal polymerization initiator may be additionally included.
[51]
The photopolymerization initiator may be used without limitation of its configuration as long as it is a compound capable of forming radicals by light such as ultraviolet rays.
[52]
Examples of the photopolymerization initiator include benzoin ether, dialkyl acetophenone, hydroxyl alkylketone, phenyl glyoxylate, and benzyl dimethyl ketone. Ketal), acyl phosphine, and alpha-aminoketone (α-aminoketone) may be used at least one selected from the group consisting of. Meanwhile, 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. . More various photoinitiators are well specified in p115 of Reinhold Schwalm's book'UV Coatings: Basics, Recent Developments and New Application (Elsevier 2007)', and are not limited to the above-described examples.
[53]
The photopolymerization initiator may be included in a concentration of 0.01 to 1.0% by weight, or 0.1 to 0.9% by weight, or 0.3 to 0.7% by weight based on the monomer mixture. If the concentration of the photopolymerization initiator is too low, the polymerization rate may be slow, and if the concentration of the photopolymerization initiator is too high, the molecular weight of the superabsorbent polymer may be small and physical properties may become uneven.
[54]
In addition, as the thermal polymerization initiator, at least one selected from the group of initiators consisting of persulfate-based initiators, azo-based initiators, hydrogen peroxide and ascorbic acid may be used. Specifically, examples of persulfate-based initiators include sodium persulfate (Na 2 S 2 O 8 ), potassium persulfate (Potassium persulfate; K 2 S 2 O 8 ), and ammonium persulfate (Ammonium persulfate; (NH 4 )) 2 S 2 O 8), and examples of azo-based initiators include 2,2-azobis-(2-amidinopropane)dihydrochloride (2,2-azobis(2-amidinopropane) dihydrochloride), 2, 2-azobis -(N, N-dimethylene) isobutyramidine dihydrochloride (2,2-azobis-(N, N-dimethylene) isobutyramidine dihydrochloride), 2- (carbamoyl azo) isobutyronitrile (2-(carbamoylazo) )isobutylonitril), 2, 2-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride (2,2-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride ), 4,4-azobis-(4-cyanovaleric acid) (4,4-azobis-(4-cyanovaleric acid)) and the like. More various thermal polymerization initiators are well specified in Odian's'Principle of Polymerization (Wiley, 1981)', p203, and are not limited to the above-described examples.
[55]
According to an embodiment of the present invention, the monomer mixture includes an internal crosslinking agent as a raw material for the super absorbent polymer. This internal crosslinking agent is for crosslinking the interior of a polymer in which an acrylic acid-based monomer is polymerized, that is, a base resin, and is distinguished from a surface crosslinking agent for crosslinking the surface of the polymer.
[56]
The type of the internal crosslinking agent is not particularly limited, and any internal crosslinking agent may be used as it can be used in the manufacture of a super absorbent polymer. Specific examples of such an internal crosslinking agent include a poly(meth)acrylate-based compound of a polyol having 2 to 20 carbon atoms, a polyglycidyl ether-based compound of a polyol having 2 to 20 carbon atoms, or an allyl (meth)acrylate having 2 to 20 carbon atoms. System compounds, etc. are mentioned.
[57]
More specific examples of these internal crosslinking agents include trimethylolpropane tri(meth)acrylate, ethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, and polypropylene glycol di. (Meth)acrylate, butanediol di(meth)acrylate, butylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, hexanediol di(meth)acrylate, triethylene glycol di(meth) Acrylate, tripropylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, dipentaerythritol pentaacrylate, glycerin tri(meth)acrylate, pentaerythritol tetraacrylate, ethylene glycol diglyci Ethyleneglycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerol polyglycidyl ether, propylene glycol diglycidyl ether or polypropylene glycol diglycidyl ether. Can be used as an internal crosslinking agent.
[58]
These internal crosslinking agents are included in a concentration of 0.01 to 1% by weight, or 0.05 to 0.8% by weight, or 0.2 to 0.7% by weight, based on the monomer mixture, to form a crosslinked structure inside the hydrogel polymer and the base resin powder formed therefrom. Can be introduced. When the content of the internal cross-linking agent is too small, the degree of internal cross-linking of the super absorbent polymer is lowered, so that various physical properties such as pressure absorption capacity may be deteriorated.
[59]
On the other hand, the above-described monomer mixture, depending on the degree of absorption rate to be achieved, if necessary, a foaming agent in an amount of 0.01 to 0.3% by weight, or 0.05 to 0.25% by weight, or 0.1 to 0.2% by weight of the total monomer mixture. It can also be included. However, in the method of one embodiment, since it is possible to use a significantly reduced content of the foaming agent to obtain the same level of porosity than previously known, problems such as excessive use of the foaming agent can be minimized.
[60]
As the foaming agent, any foaming agent known to be usable for foaming polymerization of a super absorbent polymer, for example, a carbonate-based foaming agent may be used. Specific examples of such carbonate-based blowing agents include sodium bicarbonate, sodium carbonate, potassium bicarbonate, potassium carbonate, calcium bicarbonate, and calcium carbonate. calcium bicarbonate), magnesium bicarbonate or magnesium carbonate.
[61]
Meanwhile, the above-described monomer mixture may further include additives such as a thickener, a plasticizer, a storage stabilizer, and an antioxidant, if necessary.
[62]
In addition, such a monomer mixture has an acidic group described above, and at least a part of the acidic group is neutralized, and raw materials such as a photopolymerization initiator, a thermal polymerization initiator, an internal crosslinking agent, a selective blowing agent and an additive are dissolved in a solvent. Can be.
[63]
The solvent that can be used at this time can be used without limitation of its composition as long as it can dissolve the above-described components. For example, water, ethanol, ethylene glycol, diethylene glycol, triethylene glycol, 1,4-butanediol, Propylene glycol, ethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, methyl ethyl ketone, acetone, methyl amyl ketone, cyclohexanone, cyclopentanone, diethylene glycol monomethyl ether, diethylene glycol One or more selected from ethyl ether, toluene, xylene, butyrolactone, carbitol, methyl cellosolve acetate, and N,N-dimethylacetamide may be used in combination.
[64]
The solvent may be included in a residual amount excluding the above-described components with respect to the total content of the monomer mixture.
[65]
On the other hand, after forming the monomer mixture by the above-described method, while transferring the monomer mixture to the polymerization reactor through the transfer pipe, the transfer rate thereof is controlled to reduce the dynamic pressure applied to the monomer mixture during transfer calculated by the above calculation formula 1 to 140 Pa. It can be adjusted to the above, or 150 to 1000 Pa, or 150 to 800 Pa.
[66]
As already described above, the solubility of gases such as oxygen in the monomer mixture may be reduced by adjusting the dynamic 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, oxygen 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 developed porous structure may be prepared by such physical foaming.
[67]
If the dynamic pressure is too low, physical foaming and foaming polymerization may not proceed properly, and thus the porous structure and absorption rate of the super absorbent polymer may not be properly expressed. Conversely, when the dynamic pressure is too high, not only does not have a large additional foaming effect, but also the transfer speed during the process is not properly controlled, and thus, it may be difficult to proceed in the process.
[68]
The dynamic pressure can be calculated from the density and transport speed of the monomer mixture, as confirmed in the above calculation formula 1, and the density of the monomer mixture can be easily measured and calculated by a person skilled in the art according to the concentration or type of each component. The density of such a monomer mixture can generally be measured by the method of a pycnometer, a hydrometer or a density layer. The most common method can be measured using a hydrometer.
[69]
Meanwhile, in order to control the dynamic pressure described above, the diameter of the conveying pipe or the conveying speed of the monomer mixture may be changed. 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, and the above-described dynamic pressure may be achieved through a change in the diameter of the conveying pipe or the conveying speed of the monomer mixture.
[70]
In a more specific example, the conveying pipe has a diameter of 0.002 to 0.01 m, or 0.005 to 0.009 m in the minimum diameter section, and a diameter of 0.011 to 0.020 m, or 0.012 to 0.015 m 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 conveying speed for achieving the above-described dynamic pressure.
[71]
In addition, in the minimum diameter section of the transfer pipe, the monomer mixture may be transferred at a speed of 0.45 to 2.5 m/s, or 0.7 to 2.0 m/s, and in the maximum diameter section of the transfer pipe, the monomer mixture is 0.1 To 0.5m/s, or 0.2 to 0.4m/s.
[72]
In general, in the process of manufacturing a super absorbent polymer, it is understood to ensure appropriate productivity, the monomer mixture may be transferred through a transfer pipe at a flow rate of 100 to 15000 kg/hr, or 100 to 13000 kg/hr, or 110 to 1000 kg/hr. . When conveying at such a flow rate, the dynamic pressure applied to the monomer mixture can be controlled within the above-described range by changing the diameter of the conveying pipe and/or the conveying speed of the monomer mixture within the above-described range. 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.
[73]
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.
[74]
Specifically, the polymerization method is largely divided into thermal polymerization and photopolymerization depending on the polymerization energy source, and when thermal polymerization is usually performed, it can be performed in a reactor having an agitation axis such as a kneader, and when photopolymerization is performed, it is possible to move. Although it may be carried out in a reactor equipped with a conveyor belt, the polymerization method described above is an example, and the invention is not limited to the polymerization method described above.
[75]
For example, as described above, the hydrogel polymer obtained by thermal polymerization by supplying hot air or heating the reactor to a reactor such as a kneader equipped with a stirring shaft is transferred to the reactor outlet according to the shape of the stirring shaft provided in the reactor. The discharged hydrogel polymer may be in the form of several centimeters to several millimeters. Specifically, the size of the resulting hydrogel polymer may vary 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, or 3 to 30 mm can be obtained. .
[76]
In addition, when photopolymerization is carried out in a reactor equipped with a movable conveyor belt as described above, the form of the hydrogel polymer usually obtained may be a hydrogel polymer in a sheet form having the width of the belt. At this time, the thickness of the polymer sheet varies depending on the concentration and injection speed of the monomer mixture to be injected, but it is preferable to supply the monomer mixture so that a sheet-like polymer having a thickness of 0.5 to 5 cm or 1 to 3 cm can be obtained. Do. If the monomer mixture is supplied so that the thickness of the polymer on the sheet is too thin, the production efficiency is not preferable, and if the thickness of the polymer on the sheet exceeds 5 cm, the polymerization reaction does not occur evenly over the entire thickness due to the excessively thick thickness. I can't.
[77]
At this time, the water content of the hydrogel polymer obtained by this method may be 40 to 80% by weight, or 50 to 70% by weight. Meanwhile, in the entire 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 water occupied with respect to 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.
[78]
Next, a step of drying the obtained hydrogel polymer is performed.
[79]
In this case, if necessary, a step of coarsely pulverizing before drying may be further performed in order to increase the efficiency of the drying step.
[80]
At this time, the grinder used is not limited in configuration, but specifically, a vertical pulverizer, a turbo cutter, a turbo grinder, a rotary cutter mill, and cutting Cutter mill, disc mill, shred crusher, crusher, chopper, and disc cutter. However, it is not limited to the above-described example.
[81]
At this time, the pulverization step may be pulverized so that the particle diameter of the hydrogel polymer is 2 to 50 mm, or 3 to 30 mm. The particle diameter of the hydrogel polymer may be defined as the longest distance among linear distances connecting arbitrary points on the surface of the hydrogel polymer.
[82]
Grinding with a particle diameter of less than 2 mm is not technically easy due to the high moisture content of the hydrogel polymer, and the pulverized particles may aggregate with each other. On the other hand, when the particle diameter is pulverized to more than 50 mm, the effect of increasing the efficiency of the subsequent drying step is insignificant.
[83]
Drying is performed on the hydrogel polymer immediately after polymerization, which is pulverized as described above or has not undergone a pulverization step. In this case, the drying temperature in the drying step may be 150 to 250°C. When the drying temperature is less than 150°C, the drying time may be too long and the physical properties of the finally formed super absorbent polymer may be deteriorated. When the drying temperature exceeds 250°C, only the polymer surface is excessively dried, resulting in a subsequent pulverization process. Fine powder may be generated in, and there is a concern that the physical properties of the finally formed super absorbent polymer may be deteriorated. Therefore, preferably, the drying may be performed at a temperature of 150 to 200°C, more preferably at 160 to 180°C.
[84]
Meanwhile, in the case of the drying time, it may be performed for 10 to 90 minutes or 20 to 70 minutes in consideration of process efficiency, but is not limited thereto.
[85]
The drying method in the drying step may also be selected and used without limitation of its configuration, as long as it is commonly used as a drying process of the hydrogel polymer. Specifically, the drying step may be performed by a method such as hot air supply, infrared irradiation, microwave irradiation, or ultraviolet irradiation. The moisture content of the polymer after such a drying step may be 0.1 to 10% by weight, or 1 to 8% by weight. If the moisture content after drying is too low, the hydrogel polymer may deteriorate in the drying process and the physical properties of the superabsorbent polymer may be deteriorated.On the contrary, if the moisture content is too high, the water absorption performance may decrease due to a large amount of moisture in the superabsorbent polymer, or the subsequent process Can be difficult to proceed.
[86]
Next, a step of pulverizing the dried polymer obtained through such a drying step is performed.
[87]
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 pin mill, a hammer mill, a screw mill, a roll mill, a disc mill, or a jog. Mill (jog mill) or the like may be used, but the invention is not limited to the above-described examples.
[88]
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, and a certain weight ratio of the polymer powder according to the particle size range. It can be classified so as to be.
[89]
Meanwhile, after the base resin is obtained in powder form through the above-described classification step, the base resin powder is heated in the presence of a surface crosslinking agent to perform surface crosslinking of the base resin powder.
[90]
In a general method for producing a super absorbent polymer, a dried, pulverized and classified polymer, i.e., a surface crosslinking solution containing a surface crosslinking agent is mixed with the base resin powder, and then the mixture is heated to raise the surface of the base resin powder. The crosslinking reaction is carried out.
[91]
The surface crosslinking step is a step of forming a super absorbent polymer having improved physical properties by inducing a crosslinking reaction on the surface of the pulverized polymer in the presence of a surface crosslinking agent. A surface crosslinking layer is formed on the surface of the pulverized and classified base resin powder through such surface crosslinking.
[92]
In general, since the surface crosslinking agent is applied to the surface of the base resin powder, a surface crosslinking reaction occurs on the surface of the base resin powder, which substantially does not affect the inside of the particles and improves the crosslinkability on the surface of the particles. Accordingly, the surface crosslinked superabsorbent polymer particles have a higher degree of crosslinking near the surface than at the inside by further crosslinking the crosslinked polymer on the surface of the base resin powder.
[93]
On the other hand, as the surface crosslinking agent, a compound capable of reacting with a functional group of the base resin is used, for example, a polyhydric alcohol compound, a polyepoxy compound, a polyamine compound, a haloepoxy compound, a condensation product of a haloepoxy compound, and oxazoline compounds. , Or an alkylene carbonate-based compound may be used without any particular limitation.
[94]
Specifically, examples of the polyhydric alcohol-based compound include di-, tri-, tetra- or polyethylene glycol, 1,3-propanediol, dipropylene glycol, 2,3,4-trimethyl-1,3-pentanediol, and polypropylene. Glycol, glycerol, polyglycerol, 2-butene-1,4-diol, 1,4-butanediol, 1,3-butanediol, 1,5-pentanediol, 1,6-hexanediol, and 1,2-cyclohexane One or more selected from the group consisting of dimethanol may be used.
[95]
In addition, ethylene glycol diglycidyl ether and glycidol may be used as polyvalent epoxy compounds, and as polyamine compounds, ethylenediamine, diethylenetriamine, triethylenetetraamine, tetraethylenepentamine, pentaethylenehexa One or more selected from the group consisting of min, polyethyleneimine, and polyamide polyamine may be used.
[96]
And as the haloepoxy compound, epichlorohydrin, epibromohydrin, and α-methylepichlorohydrin may be used. Meanwhile, as the mono-, di-, or polyoxazolidinone compound, for example, 2-oxazolidinone may be used.
[97]
In addition, as the alkylene carbonate-based compound, ethylene carbonate or propylene carbonate may be used. These may be used alone or in combination with each other.
[98]
The content of the surface crosslinking agent added may be appropriately selected depending on the type of the surface crosslinking agent to be added or reaction conditions, but usually 0.001 to 5 parts by weight, or 0.01 to 3 parts by weight, based on 100 parts by weight of the base resin powder, Alternatively, 0.05 to 2 parts by weight may be used.
[99]
If the content of the surface crosslinking agent is too small, the surface crosslinking reaction hardly occurs, and if it exceeds 5 parts by weight based on 100 parts by weight of the polymer, basic absorption properties such as water holding capacity may be deteriorated due to the progress of the excessive surface crosslinking reaction. have.
[100]
When the surface crosslinking agent is added, water may be mixed together and added in the form of a surface crosslinking solution. When water is added, there is an advantage that the surface crosslinking agent can be evenly dispersed in the polymer. At this time, the amount of water added is a ratio of 1 to 10 parts by weight based on 100 parts by weight of the polymer for the purpose of inducing even dispersion of the surface crosslinking agent and preventing agglomeration of the polymer powder and optimizing the surface penetration depth of the surface crosslinking agent. It is preferably added as.
[101]
On the other hand, 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 in addition to the surface crosslinking agent. You can proceed.
[102]
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.
[103]
Meanwhile, a surface modification step is performed on the base resin powder by heating the mixture of the base resin powder and the surface crosslinking solution to increase the temperature.
[104]
The surface crosslinking step may be performed under well-known conditions depending on the type of surface crosslinking agent, for example, it may be performed at a temperature of 100 to 200°C for 20 to 60 minutes. In a more specific example, in the surface crosslinking step, a surface crosslinking agent is added to the base resin powder having an initial temperature of 20°C to 80°C, and the maximum temperature is 140°C to 200°C over 10 to 30 minutes. It can be carried out by raising the temperature and maintaining the maximum temperature for 5 minutes to 60 minutes to heat treatment.
[105]
Depending on the surface crosslinking conditions, basic absorption characteristics such as water holding capacity of the super absorbent polymer, and liquid permeability and/or pressure absorption capacity may be optimized together.
[106]
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. Meanwhile, as a heat source directly supplied, heating through electricity and heating through gas may be mentioned, but the present invention is not limited to the above-described examples.
[107]
The super absorbent polymer prepared by the above-described method may include 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 formed on the base resin powder, wherein the first crosslinked polymer is further crosslinked through a surface crosslinking agent, wherein a plurality of pores are formed in the base resin powder.
[108]
The super absorbent polymer does not substantially contain a foaming agent and may exhibit an excellent absorption rate.
[109]
More specifically, the super absorbent polymer has a T-20 indicating the time required to absorb 20 g of sodium chloride and 20 g of an alcohol ethoxylate aqueous solution having 12 to 14 carbon atoms under pressure of 0.3 psi of 1 g of the resin is 170 seconds or less, or 165 seconds or less. , Or 163 seconds or less, 100 seconds or more, or 110 seconds or more, or 120 seconds or more may exhibit a characteristic. This may reflect the high absorption rate of the super absorbent polymer.
[110]
In addition, the superabsorbent polymer has a water holding capacity (CRC) of 28 g/g or more, or 28.4 g/g or more for physiological saline (0.9 wt% sodium chloride aqueous solution) measured according to the EDANA method WSP 241.3 for 30 minutes. In addition, it may have a range of 40 g/g or less, 36 g/g or less, or 34 g/g or less.
[111]
In addition, the superabsorbent resin has a pressure absorption capacity (AUP) of 0.7psi measured according to the EDANA method WSP 242.3-10, 23 to 27 g/g, or 23.5 to 26.5 g/g, or 24 to 26 g/g. And the absorbency under pressure may reflect the excellent absorbency under pressure of the super absorbent polymer.
[112]
In addition, the superabsorbent polymer of one embodiment has a flow induction property (SFC, 10 -7 cm 3 s/g) of physiological saline (0.685 wt% sodium chloride aqueous solution) of 30 (10 -7 cm 3 s/g) or more. , Or 35 (10 -7 cm 3 s/g) or more, 100 (10 -7 cm 3 s/g) or less, or 70 (10 -7 cm 3 s/g) or less Can be indicated.
[113]
The physiological saline flow induction (SFC) can be measured and calculated according to a method well known to those skilled in the art from before, for example, a method disclosed in columns 54 to 59 of U.S. Patent No. 5562646.
[114]
As described above, the superabsorbent polymer prepared by the method of one embodiment may reduce other physical property degradation due to excessive use of the foaming agent, and thus exhibit excellent water-permeability and water-retaining power, such as excellent water-permeability and water-retaining ability, at the same time.
[115]
In addition, the super absorbent polymer may exhibit a characteristic that the super absorbent polymer has an absorption rate of 5 to 50 seconds, or 10 to 45 seconds by a vortex method, and this also can define an excellent absorption rate of the super absorbent polymer. have.
[116]
As described above, the superabsorbent polymer obtained according to the manufacturing method of the embodiment exhibits an excellent absorption rate, and does not require excessive use of a foaming agent, and other various physical properties can also be excellently maintained. As a result, the super absorbent polymer may be suitably used as a sanitary material such as a diaper, and in particular, an ultra-thin sanitary material having a reduced pulp content.
Effects of the Invention
[117]
As described above, according to the present invention, a super absorbent polymer having a porous structure developed by physical foaming and an excellent absorption rate can be manufactured only with minimal use of a foaming agent.
[118]
Accordingly, the superabsorbent polymer prepared by the above method exhibits an excellent absorption rate, and does not require excessive use of a foaming agent, and other physical properties such as absorption capacity and liquid permeability may also be excellently maintained. As a result, the super absorbent polymer may be suitably used as a sanitary material such as a diaper, particularly, an ultra-thin sanitary material having a reduced pulp content.
Mode for carrying out the invention
[119]
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.
[120]
Example 1
[121]
Acrylic acid, caustic soda, polyethylene glycol diacrylate (Mw = 523; 0.5% by weight based on acrylic acid) as an internal crosslinking agent, and 0.033 g of diphenyl (2,4,6-trimethylbenzoyl)-phosphine oxide as a UV initiator Then, an aqueous monomer solution having an acrylic acid neutralization of 70 mol% and a monomer concentration of 43 wt% was prepared.
[122]
Thereafter, in the monomer aqueous solution, first, 0.3% by weight of a blowing agent solution of 0.17% by weight sodium hydrogencarbonate (based on the aqueous monomer solution) was mixed, and this composition was firstly mixed with a diameter of 0.015 m (maximum diameter) at a flow rate of 110 kg/h. After inputting through a single pipe having a section), it was transferred continuously through a single pipe (minimum diameter section) that was secondarily changed to a diameter of 0.008 m. 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: 2 mW/cm 2 ), and UV polymerization was performed for 2 minutes to prepare a hydrogel polymer. .
[123]
At this time, the dynamic pressure of the monomer aqueous solution composition passing through the final secondary single tube was 152pa.
[124]
After the hydrogel polymer was transferred to a cutter, it was cut to a maximum length of 0.2 cm. At this time, the water content of the cut hydrogel polymer was 52% by weight.
[125]
Subsequently, the hydrogel polymer was dried for 30 minutes in a hot air dryer at a temperature of 190°C, and the dried hydrogel polymer was pulverized with a pin mill. Then, a polymer having a particle diameter of less than 150 μm and a polymer having a particle size of 150 μm to 850 μm were classified using a sieve.
[126]
Thereafter, an aqueous surface crosslinking agent solution containing 1.5 parts by weight of ethylene carbonate was sprayed to 100 parts by weight of the prepared base resin powder to treat the surface of the super absorbent polymer. In addition, in the step of treating the surface, the classified base resin powder was supplied to one surface crosslinking reactor, and the surface crosslinking reaction was performed at a temperature of 190°C or higher for 35 minutes.
[127]
Thereafter, after the surface treatment, the temperature of the super absorbent polymer was cooled to 90° C., and a surface-treated super absorbent polymer having a particle diameter of 150 to 850 μm was obtained using a sieve. The fine powder content of less than 150 μm contained in the super absorbent polymer was less than 2% by weight.
[128]
Example 2
[129]
In Example 1, it was carried out in the same manner as in Example 1, except that the feed rate of the aqueous monomer solution was adjusted as shown in Table 1 below by adjusting the amount of the monomer aqueous solution composition to be 150 kg/h. The dynamic pressure of the aqueous monomer solution passing through the (minimum diameter section) was 282 pa.
[130]
Example 3
[131]
In Example 1, it was carried out in the same manner as in Example 1, except that the feed rate of the aqueous monomer solution was adjusted as shown in Table 1 below by adjusting the input amount of the aqueous monomer solution composition to 242 kg/h. The dynamic pressure of the aqueous monomer solution passing through the (minimum diameter section) was 734pa.
[132]
Comparative Example 1
[133]
In Example 1, it was carried out in the same manner as in Example 1, except that the feed rate of the aqueous monomer solution was adjusted as shown in Table 1 below by adjusting the input amount of the aqueous monomer composition to 90 kg/h. The dynamic pressure of the aqueous monomer solution passing through the (minimum diameter section) was 101pa.
[134]
Comparative Example 2
[135]
In Example 1, it was carried out in the same manner as in Example 1, except that the amount of the monomer aqueous solution composition to be added was adjusted to 242 kg/h, and the aqueous monomer solution was transferred without changing the diameter of the transfer pipe (single tube). The dynamic pressure of the aqueous solution was 59pa.
[136]
Experimental example
[137]
The physical properties of each superabsorbent polymer prepared in Examples and Comparative Examples, and various factors during the manufacturing process were measured and evaluated by the following methods.
[138]
(1) the density of the aqueous monomer solution
[139]
The density of the monomer mixture immediately before being transferred through the transfer pipe was measured by a method using a Mettler Toledo hydrometer. As a result of these measurements, it was confirmed that the aqueous monomer solutions prepared in Examples and Comparative Examples had a density of 1.05 g/cm 3 .
[140]
(2) Transfer speed of aqueous monomer solution (m/s)
[141]
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:
[142]
Feed rate (m/s) = flow rate (m 3 /hr)/cross-sectional area (m 2 )
[143]
(3) Dynamic pressure (Pa)
[144]
By substituting the density and feed rate measured in (1) and (2), respectively, into the formula 1, the dynamic pressure during the transfer of the aqueous monomer solution was calculated.
[145]
(4) Grain size evaluation
[146]
The particle diameters of the base resin powder and superabsorbent polymer used in Examples and Comparative Examples were measured according to the European Disposables and Nonwovens Association (EDANA) standard EDANA WSP 220.3 method.
[147]
(5) Centrifuge Retention Capacity (CRC)
[148]
The centrifugal separation capacity (CRC) was measured according to the European Disposables and Nonwovens Association (EDANA) standard EDANA WSP 241.3. Super absorbent polymer (or base resin powder; the same below) W 0 (g, about 0.2 g) is evenly put in a nonwoven bag and sealed, and then immersed in physiological saline solution of 0.9 wt% sodium chloride aqueous solution at room temperature. Made it. 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, the mass W 1 (g) at that time was measured after performing the same operation without using a super absorbent polymer . Using each of the masses thus obtained, CRC (g/g) was calculated according to the following formula 2 to confirm the water holding capacity.
[149]
[Calculation Equation 2]
[150]

[151]
(6) Absorbing under Pressure (AUP)
[152]
For the superabsorbent polymers of Examples and Comparative Examples, Absorbency under Pressure (AUP) was measured according to the method of the European Disposables and Nonwovens Association standard EDANA WSP 242.3-10.
[153]
First, a stainless steel 400 mesh wire mesh was mounted on the bottom of a plastic cylinder having an inner diameter of 60 mm. The resin W 0 (g, 0.90 g) obtained in Examples and Comparative Examples was evenly sprayed on a wire mesh under a temperature of 23±2℃ and a relative humidity of 45%, and a load of 4.83 kPa (0.7 psi) was uniformly applied thereto. The piston, which can be further imparted, 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.
[154]
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.
[155]
Using each of the masses thus obtained, AUP (g/g) was calculated according to the following calculation formula 3, and the absorbency under pressure was confirmed.
[156]
[Equation 3]
[157]

[158]
In Equation 2 above,
[159]
W 0 (g) is the initial weight (g) of the super absorbent polymer,
[160]
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,
[161]
W 4 (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 after absorbing physiological saline in the super absorbent polymer for 1 hour under load (0.7 psi).
[162]
(7) saline flow conductivity (SFC)
[163]
Measurements and calculations were made according to the method disclosed in column 54 to column 59 of U.S. Patent Registration No. 5622646. It was different from the US patent that only 1.5 g of the super absorbent polymer used in the measurement was used instead of 0.9 g.
[164]
(8) T-20
[165]
An aqueous solution was prepared by dissolving 9 g of sodium chloride and 0.1 g of Lorodac (main component: alcohol ethoxylate having 12 to 14 carbon atoms, CAS# 68439-50-9) in 1 L of distilled water, and under pressure of 0.3 psi, a super absorbent polymer It was calculated and measured as the time required for 1 g to absorb 20 g of this aqueous solution. A specific measurement method of this T-20 is described in detail in US Patent Publication No. 2013-007940.
[166]
(9) Absorption rate (Vortex time)
[167]
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.
[168]
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.
[169]
The above physical property evaluation results are summarized and shown in Table 1 below.
[170]
[Table 1]
[171]
Referring to Table 1, the superabsorbent polymer prepared in Examples 1 to 3 in which the dynamic pressure was applied at 140Pa or higher during the transfer of the aqueous monomer solution exhibited a water holding capacity, pressure absorption capacity, and liquid permeability equal to or higher than that of the comparative example. It was confirmed that it exhibited a more improved absorption rate.
Claims
[Claim 1]
Forming a monomer mixture comprising a water-soluble ethylenically unsaturated monomer having an acidic group at least partially neutralized and an internal crosslinking agent; While transferring the monomer mixture to the polymerization reactor, controlling the transfer rate thereof to adjust the dynamic pressure applied to the monomer mixture during transfer calculated by the following calculation formula 1 to 140Pa or more; Crosslinking the monomer mixture transferred to the polymerization reactor to form a hydrogel polymer; Drying, pulverizing and classifying the hydrogel polymer to form a 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: [Equation 1] In Formula 1, p is the monomer mixture being transferred. It represents the density (g/cm 3 ), and V represents the feed rate (m/s) of the monomer mixture.
[Claim 2]
The method of claim 1, wherein the monomer mixture is conveyed along a conveying pipe having a diameter that varies depending on the section, and in the minimum diameter section of the conveying pipe, the monomer mixture exhibits a maximum conveying speed, and in this maximum conveying speed section, the A method for producing a super absorbent polymer wherein the dynamic pressure applied to the monomer mixture is controlled to 140 Pa or more.
[Claim 3]
The method of claim 2, wherein the conveying pipe has a diameter of 0.002 to 0.01 m in a minimum diameter section, and a diameter of 0.011 to 0.020 m in a maximum diameter section before the minimum diameter section.
[Claim 4]
The method of claim 3, wherein the monomer mixture is transferred through a transfer pipe at a flow rate of 100 to 15000 kg/hr.
[Claim 5]
The method of claim 2, 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 of manufacturing a super absorbent polymer that is conveyed at a speed.
[Claim 6]
The method of claim 1, wherein the monomer mixture further comprises a blowing agent in an amount of 0.01 to 0.3% by weight based on the total mixture.
[Claim 7]
The method of claim 1, wherein in the dynamic pressure adjustment step, oxygen bubbles in the monomer mixture are generated, and foam polymerization is performed in the crosslinking polymerization step by the generated bubbles.
[Claim 8]
The method of claim 1, wherein the super absorbent polymer has a T-20 of 170 seconds or less, indicating a time required to absorb 20 g of sodium chloride and an alcohol ethoxylate aqueous solution having 12 to 14 carbon atoms under pressure of 0.3 psi. Manufacturing method.
[Claim 9]
The method of claim 1, wherein the superabsorbent polymer has a centrifugal water retention capacity (CRC) of 28 g/g or more for physiological saline (0.9 wt% sodium chloride aqueous solution) for 30 minutes.
[Claim 10]
The super absorbent polymer according to claim 1, wherein the super absorbent polymer has a pressure absorption capacity (AUP) of 0.7psi measured according to the EDANA method WSP 242.3-10 from 23 to 27 g/g.
[Claim 11]
The method of claim 1, wherein the superabsorbent polymer has a flow induction property (SFC; 10 -7 cm 3 s/g) of physiological saline (0.685 wt% sodium chloride aqueous solution) of 30 (10 -7 cm 3 s). /g) a method for producing a super absorbent polymer.
[Claim 12]
The method of claim 1, wherein the super absorbent polymer has an absorption rate of 5 to 50 seconds by a vortex method.