KR102616889B1 - Method for preparation of super absorbent polymer - Google Patents

Abstract

According to the superabsorbent polymer manufacturing method of the present invention, fine particles present in the manufactured superabsorbent polymer are removed, thereby solving the problem of dispersion of fine particles and inhibition of physical properties of the superabsorbent polymer.

Description

Method for preparing super absorbent polymer}

The present invention relates to a method for producing a superabsorbent polymer, which can solve the problem of dispersing fine particles and inhibiting the physical properties of the superabsorbent polymer.

Super Absorbent Polymer (SAP) is a synthetic polymer material that has the ability to absorb moisture 500 to 1,000 times its own weight. Each developer produces SAM (Super Absorbency Material) and AGM (Absorbent Gel). They are named with different names, such as Material). The above-mentioned superabsorbent resins have begun to be commercialized as sanitary products, and are now used in sanitary products such as children's paper diapers, as well as soil maintenance materials for horticulture, water-stop materials for civil engineering and construction, sheets for seedlings, freshness maintainers in the food distribution field, and It is widely used as a material for poultices, etc.

In most cases, these superabsorbent polymers are widely used in the field of sanitary products such as diapers and sanitary napkins. In these sanitary materials, the superabsorbent resin is generally included in a spread state within the pulp. However, in recent years, efforts have continued to provide sanitary materials such as diapers with a thinner thickness, and as part of this, the content of pulp has been reduced or, furthermore, so-called pulpless diapers in which no pulp is used at all have been developed. Development is actively underway.

Meanwhile, the superabsorbent polymer produced is generally made of particles with a particle diameter of 150 to 850 um, and the optimal physical properties of the superabsorbent polymer are expressed in the above particle size range. In order to manufacture a superabsorbent polymer having such a particle size, grinding and classification steps are inevitably included in the manufacturing process of the superabsorbent polymer.

However, despite the grinding and classification process as described above, due to the nature of the powder, particles with a particle size of less than 150 um are contained to some extent in the superabsorbent resin from which they are manufactured, and as a result, the problem of dispersion of particles as described above occurs during the manufacturing process. This causes various problems in the process, such as problems with the process environment and air filtration devices to remove them during this process. In addition, the above-mentioned particles are also included in super-absorbent polymer products, and when the super-absorbent polymer absorbs moisture, the particles agglomerate, thereby deteriorating the original physical properties of the super-absorbent polymer. do.

For this purpose, a method of removing fine particles by spraying moisture from the superabsorbent polymer being manufactured has been used in the past. However, removing fine particles by dispersing moisture is somewhat effective in removing fine particles, but there was a problem in that the fine particles clumped together and remained in the superabsorbent polymer during the process, which deteriorated various physical properties of the superabsorbent polymer. Shiki is becoming a factor.

Against the above background, the present invention relates to a method of removing fine particles present in a manufactured superabsorbent polymer using salt water in order to solve the problem of dispersing fine particles and inhibiting the physical properties of the superabsorbent polymer.

In order to solve the above problems, the present invention provides a superabsorbent polymer comprising the following steps:

Cross-polymerizing a water-soluble ethylenically unsaturated monomer having at least a partially neutralized acidic group in the presence of an internal cross-linking agent to form a water-soluble gel polymer including a first cross-linking polymer (step 1);

Forming a base resin powder by drying, pulverizing and classifying the water-containing gel polymer (step 2);

In the presence of a surface cross-linking solution, heat treating the base resin powder to surface cross-link it to form superabsorbent resin particles (step 3); and

Comprising the step of adding salt water to the superabsorbent polymer particles (step 4),

The conductivity of the brine is 15 to 55 mS/cm,

Method for producing superabsorbent polymer.

Hereinafter, the present invention will be described in detail step by step.

(Step 1)

Step 1 is a step of cross-polymerizing a water-soluble ethylenically unsaturated monomer having at least a partially neutralized acidic group in the presence of an internal cross-linking agent to form a water-soluble gel polymer including the first cross-linking polymer.

The water-soluble ethylenically unsaturated monomer constituting the first crosslinked polymer may be any monomer commonly used in the production of superabsorbent resin. As a non-limiting example, the water-soluble ethylenically unsaturated monomer may be a compound represented by the following formula (1):

[Formula 1]

R ₁ -COOM ₁

In Formula 1,

R ₁ is an alkyl group having 2 to 5 carbon atoms containing an unsaturated bond,

M ₁ is a hydrogen atom, a monovalent or divalent metal, an ammonium group, or an organic amine salt.

Preferably, the monomer may be 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 of these acids. In this way, when acrylic acid or its salt is used as a water-soluble ethylenically unsaturated monomer, it is advantageous to obtain a superabsorbent polymer with improved water absorption. In addition, the monomers include maleic anhydride, fumaric acid, crotonic acid, itaconic acid, 2-acryloyl ethane sulfonic acid, 2-methacryloyl ethane sulfonic acid, 2-(meth)acryloylpropane sulfonic acid, or 2-(meth) ) Acrylamide-2-methyl propane sulfonic acid, (meth)acrylamide, N-substituted (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, methoxypolyethylene Glycol (meth)acrylate, polyethylene glycol (meth)acrylate, (N,N)-dimethylaminoethyl (meth)acrylate, (N,N)-dimethylaminopropyl (meth)acrylamide, etc. can be used.

Here, the water-soluble ethylenically unsaturated monomer has an acidic group, and at least a portion of the acidic group may be neutralized. Preferably, the monomer partially neutralized with an alkaline substance such as sodium hydroxide, potassium hydroxide, ammonium hydroxide, etc. may be used.

At this time, the degree of neutralization of the 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 vary depending on the final physical properties, but if the degree of neutralization is too high, the neutralized monomer may precipitate, making it difficult for polymerization to proceed smoothly. Conversely, if the degree of neutralization is too low, the absorption capacity of the polymer will be greatly reduced. It can exhibit properties similar to elastic rubber that are difficult to handle.

Additionally, the concentration of the water-soluble ethylenically unsaturated monomer in the monomer composition may be appropriately adjusted considering polymerization time and reaction conditions, and may preferably be 20 to 90% by weight, or 40 to 65% by weight. This concentration range may be advantageous for eliminating the need to remove unreacted monomers after polymerization by utilizing the gel effect phenomenon that appears in the polymerization reaction of a high-concentration aqueous solution, while controlling the pulverization efficiency when pulverizing the polymer, which will be described later. However, if the concentration of the monomer is too low, the yield of the superabsorbent polymer may be lowered. Conversely, if the concentration of the monomer is too high, process problems may occur, such as some of the monomer precipitating or the grinding efficiency may decrease when grinding the polymerized hydrogel polymer, and the physical properties of the superabsorbent polymer may deteriorate.

Additionally, the monomer composition may include a foaming agent, if necessary. The foaming agent acts to increase the surface area by forming pores in the water-containing gel polymer by foaming during polymerization. The foaming agent may be an inorganic foaming agent or an organic foaming agent. Examples of inorganic blowing agents include sodium bicarbonate, sodium carbonate, potassium bicarbonate, potassium carbonate, calcium bicarbonate, and calcium bicarbonate. , magnesium bicarbonate or magnesium carbonate. Additionally, examples of organic blowing agents include 2,2'-Azobis(2-methylpropionamidine) dihydrochloride (AAPH) and azodicarbonamide (ADCA). , dinitroso pentamethylene tetramine (DPT), p,p'-oxybisbenzenesulfonylhydrazide (OBSH), and p-toluenesulfonyl hydrazide ( p-toluenesulfonyl hydrazide, TSH).

In addition, the foaming agent is preferably used in an amount of 1.0% by weight or less based on the weight of the water-soluble ethylenically unsaturated monomer. If the amount of the foaming agent used exceeds 1.0% by weight, the number of pores increases too much, the gel strength of the superabsorbent polymer decreases, and the density decreases, which may cause problems in distribution and storage. In addition, the foaming agent is preferably used in an amount of 0.01% by weight or more based on the weight of the water-soluble ethylenically unsaturated monomer.

Additionally, any compound can be used as the internal cross-linking agent as long as it enables the introduction of cross-linking bonds during polymerization of the water-soluble ethylenically unsaturated monomer. As a non-limiting example, the internal crosslinking agent is N,N'-methylenebisacrylamide, trimethylolpropane tri(meth)acrylate, ethylene glycol di(meth)acrylate, polyethylene glycol (meth)acrylate, propylene glycol di( Meth)acrylate, polypropylene glycol (meth)acrylate, butanediol di(meth)acrylate, butylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, hexanediol di(meth)acrylate ) Acrylate, triethylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, dipentaerythritol pentaacrylate, glycerin tri(meth)acrylate, pentaacrylate Multifunctional crosslinking agents such as erythol tetraacrylate, triarylamine, ethylene glycol diglycidyl ether, propylene glycol, glycerin, or ethylene carbonate may be used alone or in combination of two or more, but are not limited thereto. Preferably, two types of polyethylene glycol diacrylates with different molecular weights are used.

This internal cross-linking agent may be added at a concentration of about 0.001 to 1% by weight based on the monomer composition. That is, if the concentration of the internal cross-linking agent is too low, the absorption rate of the resin may be lowered and the gel strength may be weakened, which is not desirable. Conversely, if the concentration of the internal crosslinking agent is too high, the absorption power of the resin may be lowered, making it undesirable as an absorbent.

Additionally, in Step 1, a thermal polymerization initiator, a photo polymerization initiator, or an oxidation-reduction (redox) initiator commonly used in the production of superabsorbent resin may be included.

As the thermal polymerization initiator, one or more compounds selected from the group consisting of persulfate-based initiator, azo-based initiator, hydrogen peroxide, and ascorbic acid may be used. Specifically, persulfate-based initiators include sodium persulfate (Na ₂ S ₂ O ₈ ), potassium persulfate (K ₂ S ₂ O ₈ ), and ammonium persulfate (NH ₄ ) ₂ S ₂ O ₈ ) and the like can be given as examples. In addition, azo-based initiators include 2,2-azobis(2-amidinopropane) dihydrochloride, 2,2-azobis-(N, 2,2-azobis-(N,N-dimethylene)isobutyramidine dihydrochloride, 2-(carbamoylazo)isobutyronitrile, 2,2-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride (2,2-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride), 4, Examples include 4-azobis-(4-cyanovaleric acid) (4,4-azobis-(4-cyanovaleric acid)). For more information on various thermal polymerization initiators, please refer to page 203 of Odian's book "Principle of Polymerization (Wiley, 1981)."

Examples of the photopolymerization initiator include benzoin ether, dialkyl acetophenone, hydroxyl alkylketone, phenyl glyoxylate, and benzyl dimethyl ketal ( One or more compounds selected from the group consisting of Benzyl Dimethyl Ketal, acyl phosphine, and alpha-aminoketone may be used. Among them, as a specific example of acylphosphine, commercially available lucirin TPO, that is, 2,4,6-trimethyl-benzoyl-trimethyl phosphine oxide (2,4,6-trimethyl-benzoyl-trimethyl phosphine oxide) can be used. . For more information on various photopolymerization initiators, please refer to page 115 of "UV Coatings: Basics, Recent Developments and New Application (Elsevier 2007)" by Reinhold Schwalm.

Additionally, a reducing agent that promotes decomposition of the above-mentioned polymerization initiator can be used in combination, and by combining the two, it can also be used as an oxidation-reduction (redox) initiator. As a reducing agent, sulfites such as sodium sulfite or sodium bisulfite, reducing metals such as ferrous salts, L-ascorbic acid, and amines may be used alone or in combination of two or more types, but are not limited thereto.

This polymerization initiator may be added at a concentration of about 0.001 to 1% by weight based on the monomer composition. That is, if the concentration of the polymerization initiator is too low, the polymerization rate may be slow and a large amount of residual monomer may be extracted into the final product, which is not desirable. Conversely, if the concentration of the polymerization initiator is higher than the above range, the polymer chains forming the network become shorter, which is not preferable because the physical properties of the resin may decrease, such as increasing the content of water-soluble components and lowering the absorbency under pressure.

In addition, the monomer composition may further include additives such as thickeners, plasticizers, storage stabilizers, and antioxidants, if necessary.

In addition, this monomer composition can be prepared in the form of a solution in which raw materials such as the above-mentioned monomers are dissolved in a solvent. At this time, the usable solvent may be used without limitation as long as it can dissolve the above-mentioned raw materials. For example, the solvents include water, ethanol, ethylene glycol, diethylene glycol, triethylene glycol, 1,4-butanediol, propylene glycol, ethylene glycol monobutyl ether, propylene glycol monomethyl ether, and propylene glycol monomethyl ether acetate. , methyl ethyl ketone, acetone, methyl amyl ketone, cyclohexanone, cyclopentanone, diethylene glycol monomethyl ether, diethylene glycol ethyl ether, toluene, xylene, butyrolactone, carbitol, methyl cellosolve acetate, N,N-dimethylacetamide, or mixtures thereof, etc. may be used.

In addition, the monomer composition may further include additives such as thickeners, plasticizers, storage stabilizers, and antioxidants, if necessary.

In addition, this monomer composition can be prepared in the form of a solution in which raw materials such as the above-described monomers are dissolved in a solvent. At this time, the usable solvent may be used without limitation as long as it can dissolve the above-mentioned raw materials. For example, the solvents include water, ethanol, ethylene glycol, diethylene glycol, triethylene glycol, 1,4-butanediol, propylene glycol, ethylene glycol monobutyl ether, propylene glycol monomethyl ether, and propylene glycol monomethyl ether acetate. , methyl ethyl ketone, acetone, methyl amyl ketone, cyclohexanone, cyclopentanone, diethylene glycol monomethyl ether, diethylene glycol ethyl ether, toluene, xylene, butyrolactone, carbitol, methyl cellosolve acetate, N,N-dimethylacetamide, or mixtures thereof, etc. may be used.

Here, the conditions for thermal polymerization or UV polymerization of the monomer composition are not particularly limited, and conventional methods can be used. Specifically, thermal polymerization can be divided into a redox polymerization method in which polymerization is performed at a temperature of 30 to 100 ° C. for 2 minutes to 30 minutes, and a thermal polymerization method in which polymerization is performed for 2 minutes to 30 minutes. Additionally, UV polymerization (light polymerization) can be carried out by irradiating light at a temperature of 30 to 90°C for 10 seconds to 5 minutes. Additionally, upon UV irradiation, the amount of ultraviolet rays may be 0.1 to 30 mW/cm ² . The light source and wavelength range used during UV irradiation can also be well-known in the art.

As an example, the monomer composition is added to a reactor such as a kneader equipped with a stirring shaft, and hot air is supplied thereto or the reactor is heated to perform thermal polymerization, thereby obtaining a water-containing gel polymer. At this time, depending on the type of stirring shaft provided in the reactor, the hydrogel polymer discharged from the reactor outlet can be obtained as particles of several millimeters to several centimeters. Specifically, the resulting hydrous gel polymer can be obtained in various forms depending on the concentration and injection speed of the injected monomer composition, and usually a hydrogel polymer with a (weight average) particle diameter of 2 to 50 mm can be obtained. And, as another example, the formation of the water-containing gel polymer can be performed by a conventional UV-initiated method. In this case, the reaction can proceed by adding the monomer composition into a chamber containing a UV irradiation device and a tray and irradiating UV. Specifically, the resulting water-containing gel polymer can be obtained in various forms depending on the concentration and injection speed of the injected monomer composition, and usually a water-containing gel polymer having a (weight average) particle diameter of 2 to 50 mm can be obtained.

Meanwhile, the normal moisture content of the hydrogel polymer obtained by the above method may be 40 to 80% by weight. Meanwhile, throughout this specification, “moisture content” refers to the content of moisture relative to the total weight of the water-containing gel polymer, which is calculated by subtracting the weight of the polymer in a dry state from the weight of the water-containing gel polymer. Specifically, it is defined as a value calculated by measuring the weight loss due to moisture evaporation from the polymer during the drying process by raising the temperature of the polymer through infrared heating. At this time, the drying conditions are to increase the temperature from room temperature to about 180°C and then maintain it at 180°C. The total drying time is set to 20 minutes, including 5 minutes for the temperature increase step, and the moisture content is measured.

(Step 2)

Step 2 is a step of drying, grinding, and classifying the hydrogel polymer prepared in Step 1 to form a base resin powder, and the base resin powder and the superabsorbent resin obtained therefrom are manufactured to have a particle size of 150 to 850 ㎛. and provided are appropriate. More specifically, at least 95% by weight of the base resin powder and the superabsorbent polymer obtained therefrom may have a particle size of 150 to 850 ㎛, and the fine powder having a particle size of less than 150 ㎛ may be less than 3% by weight. As the particle size distribution of the base resin powder and the superabsorbent polymer is adjusted to a desirable range, the final manufactured superabsorbent polymer can better exhibit the above-mentioned physical properties.

Meanwhile, the drying, grinding, and classification methods will be described in more detail as follows.

First, when drying the hydrogel polymer, if necessary, a coarse grinding step may be further performed before drying to increase the efficiency of the drying step. At this time, the pulverizer used is not limited in composition, but specifically, vertical pulverizer, turbo cutter, turbo grinder, rotary cutter mill, cutting. Includes any one selected from the group of shredding machines consisting of a cutter mill, a disc mill, a shred crusher, a crusher, a chopper, and a disc cutter. It can be done, but it is not limited to the above-described example.

At this time, the coarse grinding step may grind the hydrogel polymer so that the particle size is from about 2 mm to about 10 mm. Grinding to a particle size of less than 2 mm is not technically easy due to the high moisture content of the hydrogel polymer, and agglomeration may occur between the pulverized particles. On the other hand, when pulverizing with a particle diameter exceeding 10 mm, the effect of increasing the efficiency of the subsequent drying step may be minimal.

Drying is performed on the water-containing gel polymer that is coarsely ground as described above or immediately after polymerization without going through the coarse grinding step. At this time, the drying temperature in the drying step may be 50 to 250°C. If the drying temperature is less than 50℃, the drying time becomes too long and there is a risk that the physical properties of the final formed superabsorbent polymer may deteriorate, and if the drying temperature exceeds 250℃, only the polymer surface is dried excessively, resulting in a subsequent grinding process. Fine powder may occur, and there is a risk that the physical properties of the final formed superabsorbent polymer may deteriorate. More preferably, the drying may be carried out at a temperature of 150 to 200°C, more preferably at a temperature of 160 to 190°C. Meanwhile, the drying time may last from 20 minutes to 15 hours, considering process efficiency, etc., but is not limited thereto.

As long as it is commonly used in the drying process, it can be selected and used without limitation in its composition. Specifically, the drying step can be performed by methods such as hot air supply, infrared irradiation, microwave irradiation, or ultraviolet irradiation. The moisture content of the polymer after this drying step may be 0.05 to 10% by weight.

Next, the dried polymer obtained through this drying step is pulverized. The polymer powder obtained after the grinding step may have a particle diameter of 150 to 850 ㎛. The grinders used for grinding to such particle sizes are specifically ball mills, pin mills, hammer mills, screw mills, roll mills, and disks. A mill (disc mill) or jog mill (jog mill) may be used, but it is not limited to the above-mentioned examples.

In addition, in order to manage the physical properties of the superabsorbent polymer powder that is finalized after the grinding step, a separate process may be performed to classify the polymer powder obtained after grinding according to particle size. Preferably, polymers with particle diameters of 150 to 850 ㎛ are classified, and only polymer powders with such particle diameters can be commercialized through a surface cross-linking reaction step to be described later.

(Step 3)

Step 3 is a step of crosslinking the surface of the base resin prepared in Step 2. In the presence of a surface crosslinking solution containing a surface crosslinking agent, the base resin powder is heat treated to surface crosslink to form superabsorbent resin particles. It's a step.

Here, the type of surface cross-linking agent included in the surface cross-linking solution is not particularly limited. As a non-limiting example, the surface cross-linking agent is ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerol polyglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, ethylene Glycol, diethylene glycol, propylene glycol, triethylene glycol, tetra ethylene glycol, propane diol, dipropylene glycol, polypropylene glycol, glycerin, polyglycerin, butanediol, heptanediol, hexanediol, trimethylolpropane, It may be one or more compounds selected from the group consisting of pentaerythritol, sorbitol, calcium hydroxide, magnesium hydroxide, aluminum hydroxide, iron hydroxide, calcium chloride, magnesium chloride, aluminum chloride, and iron chloride.

At this time, the surface cross-linking agent is preferably used in an amount of 0.01 to 5 parts by weight based on 100 parts by weight of the base resin. If the content of the surface cross-linking agent exceeds 5 parts by weight, excessive surface cross-linking occurs, and when the superabsorbent polymer absorbs water, a large amount of moisture is present on the surface, which causes a problem of low dryness.

In addition, the surface cross-linking solution includes water, ethanol, ethylene glycol, diethylene glycol, triethylene glycol, 1,4-butanediol, propylene glycol, ethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, Methyl ethyl ketone, acetone, methyl amyl ketone, cyclohexanone, cyclopentanone, diethylene glycol monomethyl ether, diethylene glycol ethyl ether, toluene, xylene, butyrolactone, carbitol, methyl cellosolve acetate and N, It may further include one or more solvents selected from the group consisting of N-dimethylacetamide. Preferably, it contains water. The solvent can be used in an amount of 0.5 to 10 parts by weight based on 100 parts by weight of the base resin powder.

Additionally, the surface cross-linking solution may contain an inorganic filler. The inorganic filler may include silica, aluminum oxide, or silicate. The inorganic filler may be included in an amount of 0.01 to 0.5 parts by weight based on 100 parts by weight of the base resin powder.

Additionally, the surface cross-linking solution may further include a thickener. By additionally crosslinking the surface of the base resin powder in the presence of a thickener, deterioration in physical properties can be minimized even after grinding. Specifically, the thickener may be one or more selected from polysaccharides and hydroxy-containing polymers. Examples of the polysaccharide include gum-based thickeners and cellulose-based thickeners. Specific examples of the gum-based thickener include xanthan gum, arabic gum, karaya gum, tragacanth gum, ghatti gum, and guar gum. (guar gum), locust bean gum, and psyllium seed gum, etc., and specific examples of the cellulose-based thickener include hydroxypropylmethylcellulose, carboxymethylcellulose, and methylcellulose. , hydroxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, hydroxyethylmethylcellulose, hydroxymethylpropylcellulose, hydroxyethylhydroxypropylcellulose, ethylhydroxyethylcellulose, and methylhydroxypropylcellulose. You can. Meanwhile, specific examples of the hydroxy-containing polymer include polyethylene glycol and polyvinyl alcohol.

Meanwhile, in order to perform the surface cross-linking, a method of mixing the surface cross-linking solution and the base resin in a reaction tank, a method of spraying the surface cross-linking solution on the base resin, and surface cross-linking of the base resin with a continuously operated mixer. A method of continuously supplying and mixing the liquid may be used.

Additionally, the surface modification step may be performed at a temperature of 100 to 250°C, preferably 180 to 250°C. Additionally, the surface modification may be performed for 1 minute to 120 minutes, preferably 1 minute to 100 minutes, and more preferably 10 minutes to 60 minutes. That is, in order to induce a minimum surface crosslinking reaction and prevent polymer particles from being damaged and physical properties deteriorated during excessive reaction, the surface modification step may be performed under the conditions described above.

(Step 4)

Step 4 is a step of adding salt water to the superabsorbent polymer particles prepared previously.

In the superabsorbent polymer prepared in step 3, fine particles with a particle diameter of 150 ㎛ or less inevitably exist due to the nature of the powder, which means that the fine particles are formed during the manufacturing process or when the superabsorbent polymer is used by consumers as a product. It is dispersed in the air, causing process problems or health problems. In addition, during the process of the superabsorbent polymer absorbing moisture, agglomeration of fine particles occurs, which is a factor that impairs the original physical properties of the superabsorbent polymer.

Accordingly, the present invention further includes a step of removing fine particles present in the superabsorbent polymer by adding a hydrolysis process using salt water to the superabsorbent polymer particles prepared above. Through this, it is possible to remove about 50% or more of the fine particles contained in the superabsorbent polymer, thereby suppressing the problem of dispersion of the fine particles and the phenomenon of deterioration of the physical properties of the superabsorbent polymer.

The conductivity of the brine is 15 to 55 mS/cm. If the conductivity of the salt water is less than 15 mS/cm, in addition to fine particles, particles (coarse particles) generated by agglomeration of superabsorbent polymers with relatively large diameters are generated and removed, and there is a risk that the physical properties of the superabsorbent polymer may deteriorate. , In particular, there is a problem of deterioration of CRC properties. In addition, when the conductivity of the salt water is greater than 55 mS/cm, the conductivity of the salt water is too high, which may cause damage to the degree of cross-linking of the superabsorbent polymer, leading to a risk of deterioration in the physical properties of the superabsorbent polymer, and in particular, deterioration of the CRC physical properties. there is a problem.

Preferably, the conductivity of the saline water is at least 20 mS/cm, at least 25 mS/cm, at least 30 mS/cm, at least 35 mS/cm, or at least 40 mS/cm; It is 54 mS/cm or less, 53 mS/cm or less, 52 mS/cm or less, or 51 mS/cm or less. Preferably, the conductivity of the brine is 20 to 55 mS/cm, more preferably 40 to 55 mS/cm.

Meanwhile, the conductivity of the salt water is measured at room temperature (25°C) and normal pressure (1 atm).

Preferably, the brine is an aqueous solution of Na ₂ CO ₃ , NaCl, or Mg(CH ₃ COO) ₂ , and the amount of the material added is determined according to the conductivity described above.

Meanwhile, the salt water treatment can be performed by spraying the salt water on the surface of the superabsorbent polymer particles prepared previously. The salt water treatment amount can be 0.1 to 10% by weight, preferably 0.5 to 5% by weight, or 0.5 to 1.5% by weight, based on the superabsorbent polymer particles.

Meanwhile, step 4 is preferably performed at 10 to 30°C, and room temperature (23°C) is more preferable. In addition, salt water is sprayed on the surface of the superabsorbent polymer prepared in step 3, and at this time, the temperature of the surface of the superabsorbent polymer is about 70 to 100°C. Therefore, cooling of the superabsorbent polymer proceeds naturally, and it is desirable to leave the salt water for 15 to 30 minutes from the time of spraying.

(Superabsorbent polymer)

The superabsorbent polymer manufactured according to the above-described manufacturing method has fine particles removed, thereby suppressing agglomeration when absorbing moisture, etc., and also maintaining the original physical properties of the superabsorbent polymer without being impaired during the moisture absorption process.

Specifically, the superabsorbent polymer according to the present invention includes a crosslinked polymer obtained by polymerizing a water-soluble ethylenically unsaturated monomer having at least a portion of a neutralized acidic group in the presence of an internal crosslinking agent; The cross-linked polymer includes a surface cross-linked layer modified by a surface cross-linking agent; Coarse particle generation rate is less than 2% by weight.

Preferably, the superabsorbent polymer according to the present invention has a CRC (Centrifugal Retention Capacity) of 27.5 g/g or more, more preferably 27.6 g/g or more, 27.7 g/g or more, 27.8 g/g or more, and 27.9 g. /g or more, 28.0 g/g or more. In addition, the higher the CRC value, the better it is, so there is no theoretical limit to its upper limit, but for example, it may be 30.0 g/g or less. Meanwhile, the specific measurement method of the CRC is described in detail in the examples below.

Preferably, the superabsorbent polymer according to the present invention has an AAP (Absorption Against Pressure; 0.7 psi condition) of 24.0 g/g or more, more preferably 24.1 g/g or more, 24.2 g/g or more, and 24.3 g/g. or more, 24.4 g/g or more, or 24.5 g/g or more. In addition, the higher the AAP value, the better it is, so there is no theoretical limit to its upper limit, but for example, it may be 28.0 g/g or less. Meanwhile, the specific measurement method of the AAP is described in detail in the examples below.

Preferably, the superabsorbent polymer according to the present invention has a permeability of 30 mL or more, more preferably 31 mL or more, 32 mL or more, 33 mL or more, 34 mL or more, or 35 mL or more; It is 50 mL or less, 49 mL or less, 48 mL or less, 47 mL or less, 46 mL or less, or 45 mL or less. Meanwhile, specific methods for measuring the liquid permeability are described in detail in the examples below.

Preferably, the superabsorbent polymer according to the present invention has a vortex (absorption rate) of 70 seconds or less, more preferably 65 seconds or less, 64 seconds or less, 63 seconds or less, 62 seconds or less, 61 seconds or less, or 60 seconds or less. seconds or less. Additionally, the smaller the vortex value, the better it is, and examples of its lower limit may be 40 seconds or more, 45 seconds or more, or 50 seconds or more. Meanwhile, the specific measurement method of the vortex is described in detail in the examples below.

According to the superabsorbent polymer manufacturing method of the present invention, fine particles present in the manufactured superabsorbent polymer are removed, thereby solving the problem of dispersion of fine particles and inhibition of physical properties of the superabsorbent polymer.

Hereinafter, the operation and effects of the invention will be described in more detail through specific examples of the invention. However, these examples are merely presented as examples of the invention, and the scope of the invention is not determined by them.

Example 1

The manufacturing equipment for superabsorbent polymers includes a continuous manufacturing equipment consisting of a polymerization process, hydrogel grinding process, drying process, grinding process, classification process, surface cross-linking process, cooling process, classification process, and a transport process connecting each process. used.

(Step 1)

A monomer solution was prepared by mixing 100 parts by weight of acrylic acid, 0.4 parts by weight of polyethylene glycol diacrylate (weight average molecular weight: ~ 500 g/mol) as an internal crosslinking agent, 0.1 part by weight of hexanediol diacrylate, and 0.01 part by weight of IRGACURE 819 as a photoinitiator. was manufactured. Subsequently, the monomer solution was continuously supplied using a metering pump, and at the same time, 160 parts by weight of a 24% by weight aqueous sodium hydroxide solution was continuously line mixed to prepare an aqueous monomer solution. At this time, after confirming that the temperature of the monomer aqueous solution had risen to about 72°C or higher due to the heat of neutralization, we waited for the temperature to cool to 40°C.

When the temperature was cooled to 40°C, 6 parts by weight of solid sodium bicarbonate, a foaming agent, and 6 parts by weight of 2% by weight aqueous sodium persulfate solution were added to the monomer aqueous solution.

The solution was poured into a vat-shaped tray (15 cm wide x 15 cm long) installed in a square polymerization reactor equipped with a light irradiation device on top and the inside preheated to 80°C, and photoinitiated by light irradiation. It was confirmed that a gel was generated from the surface about 25 seconds after light irradiation, and that a polymerization reaction occurred simultaneously with foaming after about 50 seconds. The reaction was continued for an additional 3 minutes to obtain a sheet-like hydrogel polymer.

(Step 2)

Cut the water-containing gel polymer prepared in step 1 into a size of 3 cm chopping).

Next, the pulverized hydrogel polymer was dried in a dryer capable of shifting the air volume up and down. Hot air at 180°C was flowed from downward to upward for 15 minutes so that the water content of the dried powder was about 2% or less, and then flowed from upward to downward for another 15 minutes to uniformly dry the water-containing gel polymer. I ordered it.

The dried polymer was pulverized with a grinder and then classified to obtain base resin powder with a size of 150 to 850 ㎛.

(Step 3)

100 parts by weight of the base resin prepared in step 2 was mixed with a cross-linking agent solution containing 3 parts by weight of water, 3 parts by weight of methanol, and 0.5 parts by weight of ethylene carbonate, and then subjected to surface cross-linking reaction at 180°C for 40 minutes.

(Step 4)

The product obtained in step 3 was cooled to 90°C, and then 1 part by weight of brine (Na ₂ CO ₃ 5% aqueous solution) was added using a dropper based on 100 parts by weight of the product. Afterwards, after maintaining the stirring state and performing additional stirring/cooling for 15 to 25 minutes, surface cross-linked superabsorbent polymer particles with a particle diameter of 150 to 850 ㎛ were obtained. The temperature of the final recovered superabsorbent polymer particles was 40°C.

Example 2

A superabsorbent polymer was prepared in the same manner as in Example 1, except that in step 4 of Example 1, a 2% aqueous NaCl solution was used instead of a 5% aqueous Na ₂ CO ₃ solution.

Example 3

A superabsorbent polymer was prepared in the same manner as in Example 1, except that in step 4 of Example 1, a ₅ % aqueous solution of Mg(CH ₃ COO) 2 was used instead of a 5% aqueous solution of Na ₂ CO ₃ .

Comparative Example 1

A superabsorbent polymer was prepared in the same manner as in Example 1, except that step 4 of Example 1 was omitted.

Comparative Example 2

A superabsorbent polymer was prepared in the same manner as in Example 1, except that distilled water was used instead of the 5% Na ₂ CO ₃ aqueous solution in step 4 of Example 1.

Comparative Example 3

A superabsorbent polymer was prepared in the same manner as in Example 1, except that in step 4 of Example 1, a 0.5% aqueous NaCl solution was used instead of a 5% aqueous Na ₂ CO ₃ solution.

Comparative Example 4

A superabsorbent polymer was prepared in the same manner as in Example 1, except that a 10% Na ₂ CO ₃ aqueous solution was used instead of a 5% Na ₂ CO ₃ aqueous solution in step 4 of Example 1.

Experiment example

For the superabsorbent polymer prepared above, the physical properties were measured according to the following method.

(1) Dust view

30 g of each superabsorbent polymer prepared in Examples and Comparative Examples was prepared, and the dust value was measured and analyzed using Dustview II (manufactured by Palas GmbH), which can measure the dust level of the superabsorbent polymer with a laser. Because small particles and certain substances fall at a slower rate than coarse particles, the dust number was calculated according to Equation 1 below.

[Equation 1]

Dust number = Max value + 30 sec. value

(In Equation 1, Max value represents the maximum dust value, and 30 sec. value is the value measured 30 seconds after reaching the maximum dust value)

(2) Coarse particle generation rate

The superabsorbent polymer particles prepared in Examples and Comparative Examples were mixed with Amp using a 710 ㎛ mesh (manufacturer: Retsch). After classification was carried out for 10 minutes under the condition of 1.0 mm, the proportion (weight ratio) of the residue at the top of the mesh was calculated.

(3) CRC (Centrifugal Retention Capacity)

The water retention capacity of each resin based on the no-load absorption capacity was measured according to EDANA WSP 241.3.

Specifically, from the resins obtained through Examples and Comparative Examples, resins classified through a #30-50 sieve were obtained. This resin W ₀ (g) (about 0.2 g) was uniformly placed in a non-woven bag, sealed, and then immersed in physiological saline solution (0.9% by weight) at room temperature. After 30 minutes, water was removed from the bag for 3 minutes under conditions of 250 G using a centrifuge, and the mass W ₂ (g) of the bag was measured. In addition, after the same operation was performed without using the resin, the mass W ₁ (g) at that time was measured. Using each obtained mass, CRC (g/g) was calculated according to the following equation.

[Equation 1]

CRC (g/g) = {[W ₂ (g) - W ₁ (g)]/W ₀ (g)} - 1

(4) AAP (Absorption Against Pressure)

The absorbency under pressure of 0.7 psi of each resin was measured according to EDANA method WSP 242.3. In addition, when measuring the absorption capacity, the resin classification used for the above CRC measurement was used.

Specifically, a stainless steel 400 mesh wire mesh was mounted on the bottom of a plastic cylinder with an inner diameter of 25 mm. Under the conditions of room temperature and 50% humidity, absorbent resin W ₀ (g) (0.16 g) is uniformly sprayed on the wire mesh, and the piston, which can further uniformly apply a load of 0.7 psi, has an outer diameter slightly smaller than 25 mm. There are no gaps with the inner wall of the cylinder, and the up and down movement is not hindered. At this time, the weight W ₃ (g) of the device was measured. A glass filter with a diameter of 90 mm and a thickness of 5 mm was placed inside a Petro dish with a diameter of 150 mm, and a physiological saline solution consisting of 0.9 wt% sodium chloride was placed at the same level as the upper surface of the glass filter. A sheet of filter paper with a diameter of 90 mm was placed on top of it. The measuring device was placed on filter paper, 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. Using each obtained mass, the absorbency under pressure (g/g) was calculated according to the following equation.

[Equation 2]

AUP(g/g) = [W ₄ (g) - W ₃ (g)]/W ₀ (g)

(5) Permeability (Perm)

The liquid permeability of the superabsorbent polymers prepared according to the above Examples and Comparative Examples was measured using Equation 3 below.

[Equation 3]

Perm = [20 mL/T ₁ (seconds)] × 60 seconds

In Equation 3 above,

Perm is the liquid permeability of superabsorbent polymer,

T ₁ puts 0.2 g of superabsorbent polymer in a cylinder, pours physiological saline (0.9% by weight aqueous sodium chloride solution) so that the superabsorbent polymer is completely submerged, swells the superabsorbent polymer for 30 minutes, and then 20 mL under a pressure of 0.3 psi. This is the time (seconds) it takes for physiological saline solution to pass through the swollen superabsorbent polymer.

Specifically, a cylinder and piston were prepared. The cylinder had an inner diameter of 20 mm and was equipped with a glass filter and a stopcock at the bottom. The piston uses a screen whose outer diameter is slightly smaller than 20 mm, allowing the cylinder to freely move up and down, placed at the bottom, a weight placed at the top, and the screen and the weight connected by a rod. It has been done. A weight was installed on the piston that could apply a pressure of 0.3 psi due to the addition of the piston.

With the stopcock of the cylinder closed, 0.2 g of superabsorbent polymer was added, and an excess amount of physiological saline solution (0.9% by weight sodium chloride aqueous solution) was poured so that the superabsorbent polymer was completely submerged. Then, the superabsorbent polymer was swollen for 30 minutes. Afterwards, a piston was added so that a load of 0.3 psi could be uniformly applied to the swollen superabsorbent polymer.

Next, the stopcock of the cylinder was opened and the time taken for 20 mL of physiological saline to pass through the swollen superabsorbent polymer was measured in seconds. At this time, if you mark the meniscus when the cylinder is filled with 40 mL of physiological saline and mark the meniscus when the cylinder is filled with 20 mL of physiological saline, the level starts at 40 mL and goes up to 20 mL. T1 in Equation 1 above can be easily measured by measuring the time it takes to reach the corresponding level.

(6) Vortex (absorption speed by vortex method)

For the superabsorbent polymers of Examples and Comparative Examples, the absorption rate was measured in seconds according to the method described in International Patent Publication No. 1987-003208.

Specifically, the absorption rate is determined by adding 2 g of superabsorbent polymer to 50 mL of physiological saline at 23°C to 24°C and stirring it with a magnetic bar (8 mm in diameter, 31.8 mm in length) at 600 rpm until the vortex disappears. It was calculated by measuring the time taken in seconds.

The measurement results are summarized in Table 1 below.

unit Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Substance used Na ₂ CO ₃ 5% NaCl 2% Mg(CH ₃ COO) ₂ 5% - H ₂ O NaCl 0.5% Na ₂ CO ₃ 10% conductivity mS/cm 50.5 30.5 20.5 - 0 10.0 83.6 throughput Weight% compared to SAP 1.0 1.0 1.0 - 1.0 1.0 1.0 moisture content weight% 0.95 0.89 0.90 0.25 0.92 0.91 0.92 Dust view - 0.4 0.5 0.6 1.5 0.5 0.5 0.4 Coarse particle generation rate % 1.0 1.3 1.7 0 3.5 2.6 1.2 CRC g/g 28.1 28.2 28.0 28.2 27.4 27.7 27.3 AAP g/g 24.7 24.5 24.6 24.6 24.6 24.4 24.1 CRC+AAP g/g 52.8 52.7 52.6 52.8 52.0 52.1 51.4 Permeability mL 41 40 39 38 40 37 42 Vortex sec 44 42 41 43 45 44 42

As shown in Table 1, Examples 1 to 3 treated with salt water having the conductivity of salt water according to the present invention have a lower dust view compared to Comparative Example 1 without salt water treatment, while retaining the original physical properties of the superabsorbent polymer. was confirmed to be maintained, and this is due to the removal of fine particles without affecting the original properties of the superabsorbent polymer by treatment with the salt water.

On the other hand, in cases where the salt water conductivity was small, such as in Comparative Examples 2 and 3, the dust view could be improved, but it was confirmed that the generation of coarse particles increased and the CRC properties especially deteriorated.

In addition, when the salt water conductivity is high as in Comparative Example 4, it can be seen that the CRC physical properties are reduced even though the production rate of coarse particles is similar to the example according to the present invention, which means that the salt water with high conductivity is highly absorbent. This is due to damage to the cross-linking degree of the resin, resulting in a decrease in CRC properties.

Claims (7)

Cross-polymerizing a water-soluble ethylenically unsaturated monomer having at least a partially neutralized acidic group in the presence of an internal cross-linking agent to form a water-soluble gel polymer including a first cross-linking polymer (step 1);
Forming a base resin powder by drying, pulverizing and classifying the water-containing gel polymer (step 2);
In the presence of a surface cross-linking solution, heat treating the base resin powder to surface cross-link it to form superabsorbent resin particles (step 3); and
Comprising the step of adding salt water to the superabsorbent polymer particles (step 4),
The conductivity of the brine is 15 to 55 mS/cm,
The brine is an aqueous solution of Na ₂ CO ₃ , NaCl, or Mg(CH ₃ COO) ₂ .
Method for producing superabsorbent polymer.
According to paragraph 1,
The water-soluble ethylenically unsaturated monomer is a compound represented by the following formula (1):
Method for producing superabsorbent polymer:
[Formula 1]
R ₁ -COOM ₁
In Formula 1,
R ¹ is an alkyl group having 2 to 5 carbon atoms containing an unsaturated bond,
M ₁ is a hydrogen atom, a monovalent or divalent metal, an ammonium group, or an organic amine salt.
According to paragraph 1,
The internal crosslinking agent is N,N'-methylenebisacrylamide, trimethylolpropane tri(meth)acrylate, ethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, and propylene glycol di(meth)acrylate. Latex, polypropylene glycol di(meth)acrylate, butanediol di(meth)acrylate, butylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, hexanediol di(meth)acrylate, tri. Ethylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, dipentaerythritol pentaacrylate, glycerin tri(meth)acrylate, pentaerythol tetraacrylate Containing at least one selected from the group consisting of triarylamine, ethylene glycol diglycidyl ether, propylene glycol, glycerin, and ethylene carbonate,
Method for producing superabsorbent polymer.
According to paragraph 1,
Step 3 is performed at 180 to 250°C.
Method for producing superabsorbent polymer.
According to paragraph 1,
The conductivity of the brine is 20 to 55 mS/cm,
Method for producing superabsorbent polymer.
delete According to paragraph 1,
The treatment amount of the brine is 0.1 to 10% by weight based on the superabsorbent polymer particles.
Method for producing superabsorbent polymer.