Cross-Citation with Related Application(s)
[2]
This application claims the benefit of priority based on Korean Patent Application No. 10-2019-0114795 on September 18, 2019 and Korean Patent Application No. 10-2020-0118534 on September 15, 2020, All content disclosed in the literature is incorporated as a part of this specification.
[3]
The present invention relates to a super absorbent polymer and a method for preparing the same. More particularly, it relates to a superabsorbent polymer having excellent basic absorbency such as water holding capacity and improved rewet properties and liquid permeability, and a method for preparing the same.
[4]
background
[5]
Super Absorbent Polymer (SAP) is a synthetic polymer material that can absorb water 500 to 1,000 times its own weight. Material), etc., are named differently. The superabsorbent polymer as described above began to be put to practical use as a sanitary tool, and now, in addition to sanitary products such as paper diapers for children and sanitary napkins, a soil repair agent for gardening, a water stop material for civil engineering and construction, a sheet for seedlings, and a freshness maintenance agent in the food distribution field. , and is widely used as a material for poultice.
[6]
In most cases, these superabsorbent polymers are widely used in sanitary materials such as diapers and sanitary napkins. In addition, it is necessary to exhibit excellent permeability by absorbing water and maintaining its shape well even in a state of volume expansion (swelling).
[7]
In addition, pressure may be applied to sanitary materials such as diapers or sanitary napkins by the weight of the user. In particular, after the superabsorbent polymer applied to sanitary materials such as diapers or sanitary napkins absorbs liquid, when pressure is applied to it by the user's weight, some of the liquid absorbed in the superabsorbent polymer oozes out again. In addition, urine leakage may occur.
[8]
Therefore, various attempts are being made to suppress this re-wetting phenomenon. However, there is still no concrete way to effectively suppress the re-wetting phenomenon.
[9]
DETAILED DESCRIPTION OF THE INVENTION
technical challenge
[10]
In order to solve the problems of the prior art as described above, it is an object of the present invention to provide a superabsorbent polymer resin in which re-wetting and urine leakage are suppressed, and a method for manufacturing the same.
[11]
means of solving the problem
[12]
In order to achieve the above object, according to one aspect of the present invention,
[13]
preparing a base resin in which an acrylic acid-based monomer having an acidic group and at least a portion of the acidic group neutralized and an internal crosslinking agent are crosslinked; and
[14]
In the presence of a surface crosslinking agent, comprising the step of performing surface modification of the base resin by raising the temperature of the base resin,
[15]
The internal crosslinking agent includes a first epoxy crosslinking agent having an epoxy equivalent of 100 g/eq or more and less than 130 g/eq and a second epoxy crosslinking agent having an epoxy equivalent of 130 g/eq or more.
[16]
In addition, according to another aspect of the present invention,
[17]
In the presence of an internal crosslinking agent comprising a first epoxy crosslinking agent having an epoxy equivalent of 100 g/eq or more and less than 130 g/eq and a second epoxy crosslinking agent having an epoxy equivalent of 130 g/eq or more, at least a portion of the acidic group is neutralized acrylic acid-based a base resin comprising a cross-linked polymer in which a monomer is cross-linked; and
[18]
There is provided a superabsorbent polymer including a surface cross-linking layer formed on the surface of the particles of the base resin and wherein the cross-linked polymer is further cross-linked through a surface cross-linking agent.
[19]
Effects of the Invention
[20]
According to the superabsorbent polymer and its manufacturing method of the present invention, it is possible to provide a superabsorbent polymer having excellent basic absorbent properties while suppressing rewet and urine leakage.
[21]
Modes for carrying out the invention
[22]
Since the present invention may have various changes and may have various forms, specific embodiments will be illustrated and described in detail below. However, this is not intended to limit the present invention to the specific disclosed form, it should be understood to include all modifications, equivalents and substitutes included in the spirit and scope of the present invention.
[23]
Hereinafter, a method for producing a super absorbent polymer according to an embodiment of the present invention will be described in detail.
[24]
[25]
The method for producing a super absorbent polymer according to an embodiment of the present invention comprises:
[26]
preparing a base resin in which an acrylic acid-based monomer having an acidic group and at least a portion of the acidic group neutralized and an internal crosslinking agent are crosslinked; and
[27]
In the presence of a surface crosslinking agent, heating the base resin to perform surface modification of the base resin,
[28]
The internal crosslinking agent includes a first epoxy crosslinking agent having an epoxy equivalent of 100 g/eq or more and less than 130 g/eq and a second epoxy crosslinking agent having an epoxy equivalent of 130 g/eq or more.
[29]
[30]
In the specification of the present invention, "base resin" or "base resin powder" is made by drying and pulverizing a polymer in which a water-soluble ethylenically unsaturated monomer is polymerized to form particles or powder, which will be described later by surface modification or It refers to a polymer in a state in which the surface crosslinking step has not been performed.
[31]
The hydrogel polymer obtained by polymerization of an acrylic acid monomer is marketed as a powdery product, a superabsorbent polymer, through processes such as drying, pulverization, classification, and surface crosslinking.
[32]
Recently, in superabsorbent polymers, not only absorbent properties such as absorbency and liquid permeability but also how much dryness of the surface can be maintained in a situation in which a diaper is actually used has become an important measure of diaper properties.
[33]
The superabsorbent polymer obtained by the manufacturing method according to an embodiment of the present invention has excellent absorbent properties such as water holding capacity, absorbency under pressure, and liquid permeability, and remains dry even after swelling by water and is absorbed into the superabsorbent polymer The present invention has been reached by confirming that it is possible to effectively prevent rewet and urine leakage from which the old urine is leaked again.
[34]
In the method for producing the superabsorbent polymer of the present invention, first, as a raw material for the superabsorbent polymer, a monomer composition comprising an acrylic acid-based monomer having an acidic group and at least a portion of the acidic group neutralized, an internal crosslinking agent, and a polymerization initiator is prepared; This is polymerized to obtain a hydrogel polymer, and then dried, pulverized, and classified to prepare a base resin.
[35]
This will be described in more detail below.
[36]
The monomer composition, which is a raw material for the superabsorbent polymer, includes an acrylic acid-based monomer having an acid group and at least a portion of the acid group neutralized, and a polymerization initiator.
[37]
The acrylic acid-based monomer is a compound represented by the following formula (1):
[38]
[Formula 1]
[39]
R 1 -COOM 1
[40]
In Formula 1,
[41]
R 1 is an alkyl group having 2 to 5 carbon atoms including an unsaturated bond,
[42]
M 1 is a hydrogen atom, a monovalent or divalent metal, an ammonium group, or an organic amine salt.
[43]
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.
[44]
Here, the acrylic acid-based monomer may have an acidic group and at least a portion of the acidic group is neutralized. Preferably, the monomer may be partially neutralized with an alkyl material such as sodium hydroxide, potassium hydroxide, ammonium hydroxide and the like. In this case, the degree of neutralization of the acrylic acid-based monomer may be 40 to 95 mol%, or 40 to 80 mol%, or 45 to 75 mol%. The range of the degree of neutralization may be adjusted according to the final physical properties. However, if the degree of neutralization is too high, the neutralized monomer may be precipitated and polymerization may be difficult to proceed smoothly. have.
[45]
The concentration of the acrylic acid-based monomer may be about 20 to about 60% by weight, preferably about 40 to about 50% by weight, based on the monomer composition including the raw material and solvent of the superabsorbent polymer, and the polymerization time and It may be an appropriate concentration in consideration of the reaction conditions and the like. However, if the concentration of the monomer is too low, the yield of the superabsorbent polymer may be low and economical problems may occur. Conversely, if the concentration is too high, some of the monomer is precipitated or the grinding efficiency is low when the polymerized hydrogel polymer is pulverized. Process problems may occur, and the physical properties of the superabsorbent polymer may be deteriorated.
[46]
The polymerization initiator used during polymerization in the method for preparing the superabsorbent polymer of the present invention is not particularly limited as long as it is generally used in the manufacture of the superabsorbent polymer.
[47]
Specifically, as the polymerization initiator, a thermal polymerization initiator or a photopolymerization initiator according to UV irradiation may be used according to a polymerization method. However, even by the photopolymerization method, a certain amount of heat is generated by irradiation such as ultraviolet irradiation, and a certain amount of heat is generated according to the progress of the polymerization reaction, which is an exothermic reaction, so a thermal polymerization initiator may be additionally included.
[48]
The photopolymerization initiator may be used without limitation in its composition as long as it is a compound capable of forming radicals by light such as ultraviolet rays.
[49]
As the photopolymerization initiator, for example, benzoin ether, dialkyl acetophenone, hydroxyl alkylketone, phenyl glyoxylate, benzyl dimethyl ketal Ketal), acyl phosphine (acyl phosphine) and alpha-aminoketone (α-aminoketone) may be used at least one selected from the group consisting of. On the other hand, as a specific example of acylphosphine, commercially available lucirin TPO, that is, 2,4,6-trimethyl-benzoyl-trimethyl phosphine oxide (2,4,6-trimethyl-benzoyl-trimethyl phosphine oxide) may be used. . A more diverse photoinitiator is well specified in Reinhold Schwalm's book 'UV Coatings: Basics, Recent Developments and New Application' (Elsevier 2007) p115, but is not limited to the above-described example.
[50]
The photopolymerization initiator may be included in a concentration of about 0.01 to about 1.0 wt% based on the monomer composition. If the concentration of the photopolymerization initiator is too low, the polymerization rate may be slowed, and if the concentration of the photopolymerization initiator is too high, the molecular weight of the superabsorbent polymer may be small and physical properties may be non-uniform.
[51]
In addition, as the thermal polymerization initiator, at least one selected from the group consisting of a persulfate-based initiator, an azo-based initiator, hydrogen peroxide, and ascorbic acid may be used. Specifically, examples of the persulfate-based initiator include sodium persulfate (Na 2 S 2 O 8 ), potassium persulfate (K 2 S 2 O 8 ), ammonium persulfate (Ammonium persulfate; (NH 4 ) 2 S 2 O 8) and the like, and examples of the azo-based initiator include 2,2-azobis-(2-amidinopropane)dihydrochloride (2,2-azobis(2-amidinopropane) dihydrochloride), 2,2-azobis -(N,N-dimethylene)isobutyramidine dihydrochloride (2,2-azobis-(N,N-dimethylene)isobutyramidine dihydrochloride), 2-(carbamoylazo)isobutyronitrile (2-(carbamoylazo) )isobutylonitril), 2,2-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride (2,2-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride ), 4,4-azobis-(4-cyanovaleric acid) (4,4-azobis-(4-cyanovaleric acid)) and the like. More various thermal polymerization initiators are well described in Odian's book 'Principle of Polymerization (Wiley, 1981)', p203, and are not limited to the above-described examples.
[52]
According to an embodiment of the present invention, the monomer composition includes an internal crosslinking agent as a raw material for the super absorbent polymer. The internal crosslinking agent is for crosslinking the inside of the polymer in which the acrylic acid-based monomer is polymerized, and is distinguished from the surface crosslinking agent for crosslinking the surface of the polymer.
[53]
In the present invention, an epoxy-based crosslinking agent is included as an internal crosslinking agent, and a first epoxy crosslinking agent having an epoxy equivalent of 100 g/eq or more and less than 130 g/eq and a second epoxy crosslinking agent having an epoxy equivalent of 130 g/eq or more are used simultaneously.
[54]
As such, when internal crosslinking agents having different epoxy equivalents are used at the same time, the two types of crosslinking agents form networks of different structures. can
[55]
That is, as the two types of crosslinking agents are chemically bonded to the polymer main chain, the crosslinked polymer network exhibits different flexibility for each part, and the superabsorbent polymer thus prepared is a gel for external pressure while absorbing water. The degree of shrinkage and the flow characteristics of water are different. Due to this structure, the superabsorbent polymer may exhibit improved rewet properties and liquid permeability.
[56]
In the method for producing the superabsorbent polymer of the present invention, only the first epoxy crosslinking agent and the second epoxy crosslinking agent may be used as the internal crosslinking agent, or a commonly used internal crosslinking agent in addition to the first epoxy crosslinking agent and the second epoxy crosslinking agent may be further used. can However, in order to secure the effect of improving the liquid permeability and rewet properties of the superabsorbent polymer, it may be more preferable to use only the first epoxy crosslinking agent and the second epoxy crosslinking agent.
[57]
As the first and second epoxy internal crosslinking agents, a crosslinking agent having two or more epoxy functional groups capable of reacting with carboxylic acid and carboxylate of an acrylic acid-based monomer may be used.
[58]
The first epoxy crosslinking agent is used for overall internal crosslinking of the polymer in which the acrylic acid-based monomer is polymerized, and has an epoxy equivalent weight of 100 g/eq or more, or 110 g/eq or more, and less than 130 g/eq, or 125 g/eq. eq or less, and those containing two or more, preferably two, epoxy functional groups in the molecule may be used. If the epoxy equivalent of the first epoxy crosslinking agent is less than 100 g/eq, there may be a problem in that the flexibility of the crosslinked polymer network is lowered and the absorption power of the superabsorbent polymer is lowered. There may be a problem that it cannot form.
[59]
Specifically, the first epoxy crosslinking agent may be ethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, or a combination thereof.
[60]
Preferably, the first epoxy crosslinking agent may be ethylene glycol diglycidyl ether or diethylene glycol diglycidyl ether having an epoxy equivalent of 110 to 125 g/eq.
[61]
The second epoxy crosslinking agent uses a higher epoxy equivalent than the first epoxy crosslinking agent to obtain a double crosslinking effect, and specifically, an epoxy equivalent of 130 g/eq or more, 150 g/eq or more, or 180 g/eq or more and 400 g/eq or less, or 380 g/eq or less may be used. If the epoxy equivalent of the second epoxy cross-linking agent is too high, the cross-linked chain length is too long and there may be a problem in gel strength, so it is preferable to satisfy the above range.
[62]
As the second epoxy crosslinking agent, a bifunctional epoxy crosslinking agent may be suitably used, and specifically , poly(ethylene glycol) diglycidyl having 3 to 15 ethylene glycol repeating units (-CH 2 CH- 2 O-) One or more of the ethers may be used. Preferably, the second epoxy crosslinking agent may be poly(ethylene glycol) diglycidyl ether having 4 to 13 ethylene glycol repeating units. Preferably, the second epoxy crosslinking agent may be poly(ethylene glycol) diglycidyl ether having an epoxy equivalent weight of 180 g/eq to 380 g/eq and the number of ethylene glycol repeating units from 4 to 13.
[63]
The internal crosslinking agent may be included in a concentration of 0.001 to 1.0 parts by weight based on 100 parts by weight of the acrylic acid-based monomer to crosslink the polymerized polymer.
[64]
In this case, the first epoxy crosslinking agent and the second epoxy crosslinking agent may each be included in an amount of 0.01 to 0.5 parts by weight based on 100 parts by weight of the acrylic acid-based monomer. Specifically, the first epoxy crosslinking agent may be included in an amount of 0.1 to 0.3 parts by weight based on 100 parts by weight of the acrylic acid-based monomer, and the second epoxy crosslinking agent may be included in an amount of 0.01 to 0.15 parts by weight based on 100 parts by weight of the acrylic acid-based monomer.
[65]
Meanwhile, the content ratio of the first epoxy cross-linking agent and the second epoxy cross-linking agent is not particularly limited, and may be appropriately adjusted according to the type and characteristics of the cross-linking agent used. However, in order to ensure an appropriate degree of crosslinking of the polymer and to secure the flexibility and gel strength effect of the crosslinked polymer network, the weight ratio of the first epoxy crosslinking agent to the second epoxy crosslinking agent is preferably 1:1 to 30:1, or 1.1: 1 to 27:1.
[66]
In the manufacturing method of the present invention, the monomer composition of the superabsorbent polymer may further include additives such as a thickener, a plasticizer, a storage stabilizer, and an antioxidant, if necessary.
[67]
Raw materials such as an acrylic acid-based monomer having the above-described acidic group and at least a part of the acidic group neutralized, a photopolymerization initiator, a thermal polymerization initiator, an internal crosslinking agent, and an additive may be prepared in the form of a monomer composition solution dissolved in a solvent.
[68]
The solvent that can be used at this time can be used without limitation in its composition as long as it can dissolve the above-mentioned components, for example, water, ethanol, ethylene glycol, diethylene glycol, triethylene glycol, 1,4-butanediol, Propylene glycol, ethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, methyl ethyl ketone, acetone, methyl amyl ketone, cyclohexanone, cyclopentanone, diethylene glycol monomethyl ether, diethylene glycol At least one selected from ethyl ether, toluene, xylene, butyrolactone, carbitol, methyl cellosolve acetate and N,N-dimethylacetamide may be used in combination.
[69]
The solvent may be included in the remaining amount excluding the above-mentioned components with respect to the total content of the monomer composition.
[70]
On the other hand, as long as the method for forming the hydrogel polymer by thermal polymerization or photopolymerization of such a monomer composition is also a commonly used polymerization method, there is no particular limitation on the structure.
[71]
Specifically, the polymerization method is largely divided into thermal polymerization and photopolymerization depending on the polymerization energy source. In general, when thermal polymerization is carried out, it may be carried out in a reactor having a stirring shaft such as a kneader. Although the process may be carried out in a reactor equipped with a conveyor belt, the polymerization method described above is an example, and the present invention is not limited to the polymerization method described above.
[72]
For example, as described above, a hydrogel polymer can be obtained by supplying hot air to a reactor such as a kneader having a stirring shaft or heating the reactor to conduct thermal polymerization, and depending on the shape of the stirring shaft provided in the reactor, The hydrogel polymer discharged to the reactor outlet may be in the form of several centimeters to several millimeters. Specifically, the size of the hydrogel polymer obtained may vary depending on the concentration and injection rate of the monomer composition to be injected, and usually, a hydrogel polymer having a weight average particle diameter of 2 to 50 mm can be obtained.
[73]
In addition, as described above, when photopolymerization is performed in a reactor equipped with a movable conveyor belt, the form of the hydrogel polymer obtained may be a sheet-like hydrogel polymer having the width of the belt. At this time, the thickness of the polymer sheet varies depending on the concentration and injection rate of the monomer composition to be injected, but it is preferable to supply the monomer composition so that a polymer sheet having a thickness of usually about 0.5 to about 5 cm can be obtained. When the monomer composition is supplied so that the thickness of the polymer on the sheet is too thin, the production efficiency is low, which is not preferable. When the thickness of the polymer on the sheet exceeds 5 cm, the polymerization reaction occurs evenly over the entire thickness due to the excessive thickness it may not be
[74]
In this case, the typical water content of the hydrogel polymer obtained by this method may be about 40 to about 80 wt%. Meanwhile, in the present specification, "moisture content" refers to the amount of moisture occupied with respect to the total weight of the hydrogel polymer, and refers to a value obtained by subtracting the weight of the polymer in a dry state from the weight of the hydrogel polymer. Specifically, it is defined as a value calculated by measuring the weight loss due to evaporation of moisture in the polymer during drying by raising the temperature of the polymer through infrared heating. At this time, the drying condition is set to 20 minutes including 5 minutes of the temperature rise step in a manner such that the temperature is raised from room temperature to about 180° C. and then maintained at 180° C., and the moisture content is measured.
[75]
Next, a step of drying the obtained hydrogel polymer is performed.
[76]
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.
[77]
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, cutting Including any one selected from the group of crushing devices consisting of a cutter mill, a disc mill, a shred crusher, a crusher, a chopper, and a disc cutter However, it is not limited to the above-described example.
[78]
In this case, in the grinding step, the hydrogel polymer may have a particle diameter of about 2 to about 10 mm.
[79]
Grinding to a particle diameter of less than 2 mm is not technically easy due to the high moisture content of the hydrogel polymer, and also aggregation between the pulverized particles may occur. On the other hand, when the particle diameter exceeds 10 mm, the effect of increasing the efficiency of the subsequent drying step is insignificant.
[80]
Drying is performed on the hydrogel polymer immediately after polymerization that has been pulverized as described above or has not undergone a pulverization step. In this case, the drying temperature of the drying step may be about 150 to about 250 ℃. When the drying temperature is less than 150°C, the drying time becomes excessively long and there is a risk that the physical properties of the superabsorbent polymer finally formed may decrease. fine powder may occur, and there is a fear that the physical properties of the superabsorbent polymer finally formed may be deteriorated. Therefore, preferably, the drying may be carried out at a temperature of about 150 to about 200 °C, more preferably at a temperature of about 160 to about 180 °C.
[81]
Meanwhile, in the case of drying time, in consideration of process efficiency, etc., the drying time may be performed for about 20 to about 90 minutes, but is not limited thereto.
[82]
As long as the drying method of the drying step is also commonly used as a drying process for the hydrogel polymer, it may be selected and used without limitation in its configuration. Specifically, the drying step may be performed by a method such as hot air supply, infrared irradiation, microwave irradiation, or ultraviolet irradiation. After the drying step, the moisture content of the polymer may be about 0.1 to about 10% by weight.
[83]
Next, a step of pulverizing the dried polymer obtained through such a drying step is performed.
[84]
The polymer powder obtained after the grinding step may have a particle diameter of about 150 to about 850 μm. The grinder used for grinding to such a particle size is specifically, a pin mill, a hammer mill, a screw mill, a roll mill, a disc mill, or a jog. A mill (jog mill) or the like may be used, but the present invention is not limited to the above-described examples.
[85]
And, in order to manage the physical properties of the superabsorbent polymer powder to be finalized after the pulverization step, a separate process of classifying the polymer powder obtained after pulverization according to the particle size may be performed, and the polymer powder is mixed in a certain weight ratio according to the particle size range. It can be classified as
[86]
[87]
Next, a surface crosslinking agent is mixed with the dried and pulverized polymer, that is, the base resin.
[88]
In a general method for producing a superabsorbent polymer, a surface crosslinking reaction is performed on the pulverized polymer by mixing a surface crosslinking solution containing a surface crosslinking agent with a dried and pulverized polymer, that is, a base resin, and then heating the mixture to increase the temperature. carry out
[89]
The surface crosslinking step is a step of inducing a crosslinking reaction on the surface of the pulverized polymer in the presence of a surface crosslinking agent, thereby forming a superabsorbent polymer having improved physical properties. Through such surface crosslinking, a surface crosslinking layer (surface modification layer) is formed on the surface of the pulverized polymer particles.
[90]
In general, since the surface crosslinking agent is applied to the surface of the superabsorbent polymer particles, the surface crosslinking reaction occurs on the surface of the superabsorbent polymer particles, which improves crosslinking properties on the surface of the particles without substantially affecting the inside of the particles. Therefore, the surface cross-linked super absorbent polymer particles have a higher degree of cross-linking near the surface than inside.
[91]
On the other hand, as the surface crosslinking agent, a compound capable of reacting with a functional group of the polymer is used, for example, a polyhydric alcohol compound, an epoxy compound, a polyamine compound, a haloepoxy compound, a condensation product of a haloepoxy compound, an oxazoline compound, a polyvalent metal salt, Alternatively, an alkylene carbonate compound or the like may be used.
[92]
Preferably, an epoxy-based surface crosslinking agent may be used so that the absorbency can be further improved without degrading the rewet property of the superabsorbent polymer.
[93]
Examples of epoxy-based surface crosslinking agents that satisfy these conditions include ethylene glycol diglycidyl ether, diethyleneglycol diglycidyl ether, and triethyleneglycol diglycidyl ether. ether), tetraethyleneglycol diglycidyl ether, glycerin polyglycidyl ether, or sorbitol polyglycidyl ether.
[94]
The amount of the epoxy-based surface crosslinking agent added is about 0.005 parts by weight or more, or about 0.01 parts by weight or more, or about 0.02 parts by weight or more, and about 0.2 parts by weight or less, or about 0.1 parts by weight based on 100 parts by weight of the base resin. part or less, or 0.05 part by weight or less.
[95]
If the content of the epoxy-based surface crosslinking agent is too small, the crosslinking density of the surface crosslinking layer is too low, and absorption properties such as absorbency under pressure and liquid permeability are lowered. The rewet properties may be degraded.
[96]
When the epoxy-based surface crosslinking agent is added, water may be additionally 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 uniformly dispersed in the polymer. At this time, the amount of added water is about 1 to about 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 at the same time optimizing the surface penetration depth of the surface crosslinking agent. It is preferably added in a negative ratio.
[97]
On the other hand, in addition to the above-described surface crosslinking agent, a polyvalent metal salt, for example, an aluminum salt, more specifically, aluminum sulfate, potassium salt, ammonium salt, sodium salt, and hydrochloride salt may further include at least one selected from the group consisting of.
[98]
As such a polyvalent metal salt is additionally used, the liquid permeability of the superabsorbent polymer prepared by the method of the embodiment can be further improved. The polyvalent metal salt 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.
[99]
On the other hand, by mixing the surface crosslinking agent with the base resin, the hydrophobic material may be optionally mixed with the base resin before the temperature is raised to perform the surface crosslinking reaction to further improve the rewet properties. In addition, the surface crosslinking efficiency is improved, so that the absorption rate and liquid permeability may be further improved compared to a resin not using a hydrophobic material.
[100]
As the hydrophobic material, a material having an HLB of 0 or more, or 1 or more, or 2 or more as its lower limit and 6 or less, or 5 or less, or 5.5 or less as an upper limit thereof may be used. In addition, since the hydrophobic material must be melted during the surface crosslinking reaction and located in the surface modification layer of the base resin, a material having a melting point equal to or less than the surface crosslinking reaction temperature may be used.
[101]
Hydrophobic materials that can be used include, for example, glyceryl stearate, glycol stearate, magnesium stearate, glyceryl laurate, sorbitan. stearate), sorbitan trioleate, or PEG-4 dilaurate, and preferably glyceryl stearate, or glyceryl laurate may be used, The present invention is not limited thereto.
[102]
The hydrophobic material is distributed in the surface modification layer of the surface of the base resin to prevent the swollen resin particles from agglomeration or agglomeration depending on the increased pressure in the process of the superabsorbent polymer absorbing the liquid and swelling, and to make the surface hydrophobic By providing it, the permeation and diffusion of a liquid can be made more easily. Therefore, it can contribute to improving the rewet property of the superabsorbent polymer.
[103]
The hydrophobic material is about 0.02 parts by weight or more, or about 0.025 parts by weight or more, or about 0.05 parts by weight or more and about 0.5 parts by weight or less, or about 0.3 parts by weight or less, or about 0.1 parts by weight based on 100 parts by weight of the base resin. It can mix so that it may become the following. If the content of the hydrophobic material is too small, less than 0.02 parts by weight, it may be insufficient to improve the rewet property, and if it is included in excess of 0.5 parts by weight, the base resin and the hydrophobic material are separated from each other and there is no effect of improving the rewet or impurities. Since there may be a problem acting as a , the range of parts by weight may be preferable from this point of view.
[104]
The method of mixing the hydrophobic material is not particularly limited as long as it can be mixed evenly with the base resin, and may be appropriately adopted and used.
[105]
For example, the hydrophobic material is mixed in a dry manner before mixing the surface crosslinking solution containing the epoxy-based surface crosslinking agent with the base resin, or dispersed in the surface crosslinking solution with the surface crosslinking agent and mixed with the base resin. can do. Alternatively, separately from the surface crosslinking solution, the hydrophobic material may be heated to a melting point or higher to be mixed in a solution state.
[106]
Next, a surface modification step is performed on the base resin by heating the mixture of the base resin and the epoxy-based surface crosslinking agent to increase the temperature.
[107]
The surface modification step may be performed by heating at a temperature of about 120 to about 190 °C, preferably about 130 to about 180 °C for about 10 to about 90 minutes, preferably about 20 to about 70 minutes. If the crosslinking reaction temperature is less than 120 °C or the reaction time is too short, the surface crosslinking reaction does not occur properly and the transmittance may be lowered.
[108]
The means for increasing the temperature for the surface modification reaction is not particularly limited. It can be heated by supplying a heating medium or by directly supplying a heat source. At this time, as the type of heating medium that can be used, a fluid having an elevated temperature such as steam, hot air, or hot oil may be used, but the present invention is not limited thereto. It can be appropriately selected in consideration of the target temperature. On the other hand, the directly supplied heat source may be a heating method through electricity or a heating method through a gas, but the present invention is not limited to the above-described example.
[109]
By the surface modification step as described above, a surface crosslinking structure formed by reacting an epoxy-based surface crosslinking agent with a functional group of the base resin is formed on the surface of the base resin, and the hydrophobic material is evenly distributed in the surface crosslinking structure. A modified layer may be formed.
[110]
The super absorbent polymer produced by the method of the present invention has a double cross-linked structure due to two types of epoxy-based internal cross-linking agents having different epoxy equivalents, thereby reducing physical properties such as water holding capacity and absorbency under pressure. It is possible to have improved rewet properties and initial absorption rate without dehydration.
[111]
Accordingly, according to another embodiment of the present invention, in the presence of an internal crosslinking agent comprising a first epoxy crosslinking agent having an epoxy equivalent of 100 g/eq or more and less than 130 g/eq and a second epoxy crosslinking agent having an epoxy equivalent of 130 g/eq or more , a base resin comprising a crosslinked polymer in which an acrylic acid-based monomer in which at least a portion of an acidic group is neutralized is crosslinked; and a surface crosslinking layer formed on the surface of the particles of the base resin, wherein the crosslinked polymer is further crosslinked through a surface crosslinking agent.
[112]
A detailed description of the specific manufacturing method and physical properties of the superabsorbent polymer is the same as described above in the manufacturing method of the superabsorbent polymer.
[113]
The superabsorbent polymer has a water holding capacity (CRC) of about 25 g/g or more, or about 29 g/g or more, or about 30 g/g or more, and about 40 g/g or less, as measured according to WSP 241.3 of the EDANA method. , or about 38 g/g or less, or about 35 g/g or less.
[114]
In addition, the superabsorbent polymer may have a permeability (unit: seconds) measured according to Equation 1 below about 35 seconds or less, or about 30 seconds or less. The liquid permeability is better as the value is smaller, so that the theoretical lower limit value is 0 seconds, for example, it may be about 5 seconds or more, or about 10 seconds or more, or about 12 seconds or more.
[115]
[Equation 1]
[116]
Permeability (sec) = T1 - B
[117]
In Equation 1 above,
[118]
For T1, put 0.2 ± 0.0005 g of a classified (300 ~ 600 μm) sample of superabsorbent polymer in a chromatography tube, add brine to make the volume of brine 50 ml, and leave it for 30 minutes, and then increase the liquid level from 40 ml to 20 is the time it takes to decrease to ml, and B is the time it takes for the liquid level to decrease from 40 ml to 20 ml in a chromatography tube filled with brine.
[119]
In addition, the superabsorbent polymer may exhibit improved rewet properties while exhibiting excellent absorption properties.
[120]
More specifically, 4 g of the superabsorbent polymer was immersed in 200 g of tap water to swell for 2 hours, and then the swollen superabsorbent polymer was left on filter paper under a pressure of 0.75 psi for 1 minute, and then the superabsorbent polymer The rewet property (long-term rewetting of pressurized tap water), defined as the weight of the water re-blotted from the filter paper, may be 1.0 g or less, or 0.9 g or less, or 0.8 g or less, or 0.76 g or less. The lower the weight of the water, the better, so the theoretical lower limit is 0 g, but may be, for example, 0.1 g or more, or 0.2 g or more, or 0.3 g or more.
[121]
The tap water used in the evaluation of the rewet properties has an electrical conductivity of 140 to 150 μS/cm. Since the electrical conductivity of tap water has a great influence on the measured properties, it is necessary to measure the properties such as rewet using tap water having an equivalent level of electrical conductivity.
[122]
As described above, the superabsorbent polymer of the present invention has excellent absorbency and can suppress rewetting and urine leakage even when a large amount of urine is absorbed.
[123]
The present invention will be described in more detail in the following examples. However, the following examples only illustrate the present invention, and the content of the present invention is not limited by the following examples.
[124]
[125]

[126]
Preparation of super absorbent polymer
[127]
Example 1
[128]
(1) Preparation of base resin
[129]
518 g of acrylic acid, 1.40 g of ethylene glycol diglycidyl ether (EGDGE, epoxy equivalent 113 g/eq) (0.27 parts by weight based on 100 parts by weight of acrylic acid), ethylene in a 3 L glass container equipped with a stirrer, nitrogen input device and thermometer Poly(ethylene glycol) diglycidyl ether having 4 glycol repeating units (PEGDGE, epoxy equivalent 185 g/eq) 0.052 g (0.01 parts by weight based on 100 parts by weight of acrylic acid), and diphenyl (2,4,6 -Trimethylbenzoyl)-phosphine oxide was dissolved by adding 0.04 g, and then 822.2 g of a 24.5% sodium hydroxide solution was added thereto to prepare a water-soluble unsaturated monomer aqueous solution while continuously adding nitrogen. The aqueous solution of the water-soluble unsaturated monomer was cooled to 40 °C.
[130]
500 g of this aqueous solution was added to a stainless steel container having a width of 250 mm, a length of 250 mm, and a height of 30 mm, and UV polymerization was performed for 90 seconds by irradiating ultraviolet rays (irradiation amount: 10 mV/cm 2 ) to obtain a hydrogel polymer. . After the obtained hydrogel polymer was pulverized to a size of 2 mm * 2 mm, the obtained gel-like resin was spread out to a thickness of about 30 mm on stainless wire gauze having a pore size of 600 μm, and dried in a hot air oven at 180° C. for 30 minutes. The dried polymer thus obtained was pulverized using a pulverizer, and classified through a standard mesh sieve of ASTM standard to obtain a base resin having a particle size of 150 to 850 μm.
[131]
[132]
(2) Preparation of super absorbent polymer
[133]
Spraying and mixing a surface crosslinking solution containing 6.2 parts by weight of water, 0.02 parts by weight of ethylene glycol diglycidyl ether, 0.2 parts by weight of aluminum sulfate, and 0.03 parts by weight of glyceryl stearate (HLB 3.8) to 100 parts by weight of the base resin And it was put into a container consisting of a stirrer and a double jacket, and surface crosslinking reaction was carried out at 140 °C for 35 minutes. Thereafter, the surface-treated powder was classified with a standard mesh sieve of ASTM standard to obtain a superabsorbent polymer powder having a particle size of 150 to 850 μm.
[134]
[135]
Example 2
[136]
In step (1), 0.23 parts by weight of ethylene glycol diglycidyl ether and 0.05 parts by weight of poly(ethylene glycol) diglycidyl ether having 4 ethylene glycol repeating units were used with respect to 100 parts by weight of acrylic acid, except that obtained a superabsorbent polymer powder in the same manner as in Example 1.
[137]
[138]
Example 3
[139]
In step (1), 0.18 parts by weight of ethylene glycol diglycidyl ether and 0.10 parts by weight of poly(ethylene glycol) diglycidyl ether having 4 ethylene glycol repeating units were used with respect to 100 parts by weight of acrylic acid, except that obtained a superabsorbent polymer powder in the same manner as in Example 1.
[140]
[141]
Example 4
[142]
In step (1), 0.15 parts by weight of ethylene glycol diglycidyl ether and 0.13 parts by weight of poly(ethylene glycol) diglycidyl ether having 4 ethylene glycol repeating units were used with respect to 100 parts by weight of acrylic acid, except that obtained a superabsorbent polymer powder in the same manner as in Example 1.
[143]
[144]
Example 5
[145]
In step (1), poly(ethylene glycol) diglycidyl ether having 9 ethylene glycol repeating units instead of poly(ethylene glycol) diglycidyl ether having 4 ethylene glycol repeating units (epoxy equivalent 268 eq/g ) was used, and superabsorbent polymer powder was obtained in the same manner as in Example 2.
[146]
[147]
Example 6
[148]
In step (1), poly(ethylene glycol) diglycidyl ether having 13 ethylene glycol repeating units instead of poly(ethylene glycol) diglycidyl ether having 4 ethylene glycol repeating units (epoxy equivalent 372 eq/g ) was used, and superabsorbent polymer powder was obtained in the same manner as in Example 2.
[149]
[150]
Example 7
[151]
In step (1), a super absorbent polymer powder was prepared in the same manner as in Example 2, except that diethylene glycol diglycidyl ether (DGDGE, epoxy equivalent 122 g/eq) was used instead of ethylene glycol diglycidyl ether. got it
[152]
[153]
Example 8
[154]
In step (1), a super absorbent polymer powder was prepared in the same manner as in Example 3, except that diethylene glycol diglycidyl ether (DGDGE, epoxy equivalent 122 g/eq) was used instead of ethylene glycol diglycidyl ether. got it
[155]
[156]
Example 9
[157]
In step (1), poly(ethylene glycol) diglycidyl ether having 9 ethylene glycol repeating units instead of poly(ethylene glycol) diglycidyl ether having 4 ethylene glycol repeating units (epoxy equivalent 268 eq/g ) was used, and superabsorbent polymer powder was obtained in the same manner as in Example 7.
[158]
[159]
Example 10
[160]
In step (1), poly(ethylene glycol) diglycidyl ether having 13 ethylene glycol repeating units instead of poly(ethylene glycol) diglycidyl ether having 4 ethylene glycol repeating units (epoxy equivalent 372 eq/g ) was used, and superabsorbent polymer powder was obtained in the same manner as in Example 7.
[161]
[162]
Comparative Example 1
[163]
In step (1), as an internal crosslinking agent, poly(ethylene glycol) diglycidyl ether having 4 ethylene glycol repeating units was not included, and only ethylene glycol diglycidyl ether was used in an amount of 0.28 parts by weight based on 100 parts by weight of acrylic acid. A superabsorbent polymer powder was obtained in the same manner as in Example 1, except that.
[164]
[165]
Comparative Example 2
[166]
In step (1), as an internal crosslinking agent, poly(ethylene glycol) diglycidyl ether having 4 ethylene glycol repeating units was not included, and only ethylene glycol diglycidyl ether was used in an amount of 0.32 parts by weight based on 100 parts by weight of acrylic acid. A super absorbent polymer powder was obtained in the same manner as in Example 1, except that.
[167]
[168]
Comparative Example 3
[169]
In step (1), as an internal crosslinking agent, poly(ethylene glycol) diglycidyl ether having 4 ethylene glycol repeating units is not included, and diethylene glycol diglycidyl ether (DGDGE, epoxy equivalent 122 g/eq) A superabsorbent polymer powder was obtained in the same manner as in Example 1, except that only 0.28 parts by weight based on 100 parts by weight of acrylic acid was used.
[170]
[171]
Comparative Example 4
[172]
In step (1), 0.28 parts by weight of only poly(ethylene glycol) diglycidyl ether having 4 ethylene glycol repeating units without containing ethylene glycol diglycidyl ether as an internal crosslinking agent was used in an amount of 0.28 parts by weight based on 100 parts by weight of acrylic acid. A super absorbent polymer powder was obtained in the same manner as in Example 1, except that.
[173]
[174]

[175]
The superabsorbent polymers prepared in Examples and Comparative Examples were evaluated for physical properties in the following manner.
[176]
Unless otherwise indicated, all of the following physical property evaluations were performed at constant temperature and humidity (23±1° C., relative humidity 50±10%), and physiological saline or saline means 0.9 wt% sodium chloride (NaCl) aqueous solution.
[177]
In addition, as for the tap water used in the evaluation of the following rewet properties, when measured using Orion Star A222 (Thermo Scientific), one having an electrical conductivity of 140 to 150 μS/cm was used.
[178]
[179]
(1) Centrifuge Retention Capacity (CRC)
[180]
The water holding capacity of each resin according to the no-load absorption magnification was measured according to EDANA WSP 241.3.
[181]
Specifically, the superabsorbent polymer W 0 (g) (about 0.2 g) was uniformly put in a non-woven bag and sealed, and then immersed in physiological saline (0.9 wt %) at room temperature. After 30 minutes, the bag was drained of water for 3 minutes under the condition of 250 G using a centrifugal separator, and the mass W 2 (g) of the bag was measured. Further, after the same operation without the use of resin, then the mass W of the first to (g) was measured. Using each obtained mass, CRC (g/g) was calculated according to the following equation.
[182]
[Equation 1]
[183]
CRC (g/g) = {[W 2 (g) - W 1 (g)]/W 0 (g)} - 1
[184]
[185]
(2) Permeability
[186]
Lines were marked on the liquid levels of 20 ml and 40 ml in a state in which a piston was placed in a chromatography tube (F20 mm). Thereafter, water was added in reverse to prevent bubbles from forming between the glass filter and the cock at the bottom of the chromatography tube to fill about 10 ml, washed 2-3 times with brine, and filled with 0.9% brine up to 40 ml or more. A piston was placed in the chromatography tube, the lower valve was opened, and the time (B) for the liquid level to decrease from 40 ml to 20 ml was recorded.
[187]
10 ml of brine was left in the chromatography tube, 0.2 ± 0.0005 g of a classified (300 ~ 600 μm) superabsorbent polymer sample was added, brine was added to make the volume of brine 50 ml, and then left for 30 minutes. After that, put an additional piston (0.3 psi = 106.26 g) in the chromatography tube, leave it for 1 minute, open the lower valve of the chromatography tube, and record the time (T1) for the liquid level to decrease from 40 ml to the 20 ml mark, The time (unit: seconds) of T1 - B was calculated.
[188]
[189]
(3) Pressurized tap water long-term rewet (2 hrs)
[190]
① Spread 4 g of superabsorbent resin evenly in a 13 cm diameter petri dish to disperse it, pour 200 g of tap water, and swell for 2 hours.
[191]
② Spread the superabsorbent polymer swollen for 2 hours on 20 pieces of filter paper (manufacturer: whatman, catalog No. 1004-110, pore size 20-25 μm, diameter 11 cm) and put a 11 cm diameter, 5 kg weight (0.75 psi) was pressurized for 1 minute.
[192]
③ After pressurizing for 1 minute, the amount (unit: g) of tap water on the filter paper was measured.
[193]
[194]
The physical property values ​​for the Examples and Comparative Examples are shown in Table 1 below.
[195]
[196]
[Table 1]
Internal crosslinking agent content (parts by weight relative to 100 parts by weight of acrylic acid) super absorbent resin
first crosslinking agent Second crosslinking agent (PEGDGE, n is the number of repeating units) CRC (g/g) Permeability (sec) Pressurized tap water long-term rewet (g)
Example 1 0.27 (EGDGE) 0.01 (n=4) 30.1 29 0.75
Example 2 0.23 (EGDGE) 0.05 (n=4) 30.3 25 0.51
Example 3 0.18 (EGDGE) 0.10 (n=4) 30.9 28 0.65
Example 4 0.15 (EGDGE) 0.13 (n=4) 31.1 29 0.76
Example 5 0.23 (EGDGE) 0.05 (n=9) 30.4 28 0.62
Example 6 0.23 (EGDGE) 0.05 (n=13) 30.4 29 0.65
Example 7 0.23 (DGDGE) 0.05 (n=4) 30.4 26 0.55
Example 8 0.18 (DGDGE) 0.10 (n=4) 30.9 29 0.65
Example 9 0.23 (DGDGE) 0.05 (n=9) 30.6 28 0.62
Example 10 0.23 (DGDGE) 0.05 (n=13) 30.8 29 0.66
Comparative Example 1 0.28 (EGDGE) - 30.1 37 0.84
Comparative Example 2 0.32 (EGDGE) - 28.5 28 1.21
Comparative Example 3 0.28 (DGDGE) - 30.3 37 0.83
Comparative Example 4 - 0.28 (n=4) 31.5 36 0.80
[197]
Referring to Table 1, it can be seen that Examples 1 to 10 have excellent water holding capacity and excellent liquid permeability and rewet properties. However, as in Comparative Examples 1, 3, and 4, when only one of the first and second epoxy-based cross-linking agents was used as the internal cross-linking agent, the liquid permeability and re-wetting properties were significantly improved compared to Examples 1 to 10 using the same amount of the internal cross-linking agent. fell. Also, in Comparative Example 2, in which one type of internal crosslinking agent was used and the content of the crosslinking agent was increased, the liquid permeability was slightly improved, but the water holding capacity and rewet property were inferior.
[198]
From these results, it can be confirmed that, according to the present invention, improved liquid permeability and re-wetting properties can be secured while maintaining excellent basic absorbent properties such as water holding capacity of the superabsorbent polymer.
Claims
[Claim 1]
preparing a base resin in which an acrylic acid-based monomer having an acidic group and at least a portion of the acidic group neutralized and an internal crosslinking agent are crosslinked; and in the presence of a surface crosslinking agent, performing surface modification of the base resin by raising the temperature of the base resin, wherein the internal crosslinking agent has an epoxy equivalent of 100 g/eq or more and less than 130 g/eq of a first epoxy crosslinking agent and a second epoxy crosslinking agent having an epoxy equivalent of 130 g/eq or more.
[Claim 2]
The method of claim 1, wherein the second epoxy crosslinking agent has an epoxy equivalent of 150 g/eq to 400 g/eq.
[Claim 3]
The method of claim 1 , wherein the first epoxy crosslinking agent and the second epoxy crosslinking agent are each included in an amount of 0.01 to 0.5 parts by weight based on 100 parts by weight of the acrylic acid-based monomer.
[Claim 4]
The method of claim 1, wherein the weight ratio of the first epoxy crosslinking agent to the second epoxy crosslinking agent is 1:1 to 30:1.
[Claim 5]
The method of claim 1, wherein the first epoxy crosslinking agent is ethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, or a combination thereof.
[Claim 6]
The method of claim 1 , wherein the second epoxy crosslinking agent is at least one of poly(ethylene glycol) diglycidyl ethers having 3 to 15 ethylene glycol repeating units.
[Claim 7]
The method of claim 1 , wherein the surface modification of the base resin is performed in the presence of a hydrophobic material having an HLB of 0 or more and 6 or less.
[Claim 8]
The method of claim 1, wherein the preparing the base resin comprises an acrylic acid-based monomer having an acidic group and neutralized at least a portion of the acidic group, an internal crosslinking agent comprising a first epoxy crosslinking agent and a second epoxy crosslinking agent, and a polymerization initiator forming a hydrogel polymer by polymerizing the monomer composition comprising the; drying the hydrogel polymer; pulverizing the dried polymer; and classifying the pulverized polymer.
[Claim 9]
In the presence of an internal crosslinking agent comprising a first epoxy crosslinking agent having an epoxy equivalent of 100 g/eq or more and less than 130 g/eq and a second epoxy crosslinking agent having an epoxy equivalent of 130 g/eq or more, at least a portion of the acidic group is neutralized acrylic acid-based a base resin comprising a cross-linked polymer in which a monomer is cross-linked; and a surface crosslinking layer formed on the particle surface of the base resin, wherein the crosslinked polymer is additionally crosslinked through a surface crosslinking agent.
[Claim 10]
The superabsorbent polymer according to claim 9, wherein the superabsorbent polymer has a centrifugation retention capacity (CRC) of 25 g/g or more.
[Claim 11]
The superabsorbent polymer according to claim 9, wherein the superabsorbent polymer has a liquid permeability of 30 seconds or less, measured according to Equation 1 below: [Equation 1] Liquid permeability (sec) = T1 - B In Equation 1, T1 is chromatographic After putting 0.2 ± 0.0005 g of a classified (300 ~ 600 μm) sample of superabsorbent polymer in the graph tube, adding brine to make the volume of brine 50 ml, and leaving it for 30 minutes, the liquid level decreases from 40 ml to 20 ml is the time it takes for the brine to rise, and B is the time it takes for the liquid level to decrease from 40 ml to 20 ml in a chromatography tube filled with brine.
[Claim 12]
10. The method of claim 9, wherein the superabsorbent polymer is, 4 g of the superabsorbent polymer is immersed in 200 g of tap water to swell for 2 hours, and then the swollen superabsorbent polymer is dried on filter paper under a pressure of 0.75 psi for 1 minute. The superabsorbent polymer having a long-term re-wetting of pressurized tap water defined as the weight of water that seeps back from the superabsorbent polymer to the filter paper after standing still is 1.0 g or less.