KR20210037450A - Preparation method of super absorbent polymer - Google Patents

Abstract

The present invention relates to a method for producing a super absorbent polymer. More particularly, the present invention relates to a method for producing a super absorbent polymer, which controls the temperature of a neutralizing solution when polymerizing a super absorbent polymer, and exhibits an improved dryness along with a fast absorption rate by adding a reducing agent. Thus, when the super absorbent polymer is applied to a product, the surface thereof can be kept dry, thereby improving a wearer's discomfort and skin rash problems.

Description

Manufacturing method of super absorbent polymer TECHNICAL FIELD [PREPARATION METHOD OF SUPER ABSORBENT POLYMER}

The present invention relates to a method for producing a super absorbent polymer. More specifically, a method of manufacturing a super absorbent polymer that can improve the wearer's discomfort and skin rash problems by showing an improved dryness with a fast absorption rate and maintaining a dry surface when applied to a product. It is about.

Super Absorbent Polymer (SAP) is a synthetic polymer material that has the ability to absorb moisture of 500 to 1,000 times its own weight, and each developer has a SAM (Super Absorbency Material), AGM (Absorbent Gel). Material) and so on. Since the above-described superabsorbent resin has begun to be put into practical use as a sanitary tool, it is now widely used as a material such as a soil repair agent for horticultural, civil engineering, construction water, seedling sheet, freshness maintenance agent and poultice in the food distribution field. .

These super absorbent polymers are mainly widely used in the field of sanitary materials such as diapers and sanitary napkins. In the sanitary material, the super absorbent polymer is generally included in a state of being spread in pulp. However, in recent years, efforts to provide sanitary materials such as diapers with a thinner thickness are continuing, and as part of this, the content of pulp is reduced, and furthermore, so-called pulpless diapers are not used at all. Development is actively progressing.

In this way, the content of the pulp is reduced, or in the case of the sanitary material in which pulp is not used, the super absorbent polymer is contained in a relatively high proportion, so that the super absorbent polymer particles are inevitably included in multiple layers in the sanitary material. In order for the entire super absorbent polymer particles included in multiple layers to more efficiently absorb liquids such as urine, it is necessary for the super absorbent polymer to basically exhibit high absorption performance and absorption rate.

To this end, a method of lowering the internal crosslinking degree of the super absorbent polymer and increasing the surface crosslinking degree has been proposed. However, the above method has an aspect of increasing the absorption rate, but after the superabsorbent polymer swells with the absorbed liquid, the liquid exists on the surface of the superabsorbent polymer, resulting in a reduced fit and a cause of skin rash. do.

As described above, the degree to which liquid does not exist on the surface after the superabsorbent polymer absorbs the liquid is called dryness. Therefore, the high degree of dryness is excellent without impairing the absorption performance and absorption rate of the superabsorbent polymer. Development of a water absorbent resin is required.

Accordingly, the present invention is to provide a method of manufacturing a super absorbent polymer capable of improving the discomfort and skin rash problems of the wearer by maintaining a dry surface condition when applied to a product by showing a fast absorption rate and excellent dryness. will be.

In order to solve the above problem, according to an embodiment of the present invention,

Neutralizing by adding a neutralizing agent to a monomer composition comprising a water-soluble ethylenically unsaturated monomer having an acidic group, an internal crosslinking agent, and a photopolymerization initiator;

Cooling the neutralized monomer composition to 25 to 35°C;

Adding a thermal polymerization initiator to the cooled monomer composition and performing a polymerization reaction in the order of a photopolymerization reaction and a thermal polymerization reaction to prepare a hydrogel polymer;

Adding a reducing agent to the hydrogel polymer, mixing, drying and pulverizing to prepare a base resin powder; And

Including; after mixing the base resin powder with a surface crosslinking agent, performing a surface crosslinking reaction,

The reducing agent comprises at least one selected from the group consisting of bisulfite, sulfinate, and salts thereof, and is added in an amount of 2500 to 5000 ppmw based on the total weight of the hydrogel polymer,

It provides a method for producing a super absorbent polymer.

According to the manufacturing method of the present invention, it is possible to prepare a super absorbent polymer having a good balance of centrifugation water holding capacity (CRC) and pressure absorption capacity (AUP), a high absorption rate (vortex), and improved dryness. I can. When the super absorbent polymer is applied to a product, the surface condition is maintained dry, thereby improving the discomfort of the wearer and the problem of skin rash. Accordingly, it can be particularly preferably used for hygiene materials such as diapers.

The terms used in the present specification are only used to describe exemplary embodiments, and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In the present specification, terms such as "comprise", "include", or "have" are intended to designate the existence of a feature, step, component, or combination of the implemented features, one or more other features or steps, It is to be understood that the possibility of the presence or addition of components, or combinations thereof, is not preliminarily excluded.

The present invention will be described in detail below and exemplify specific embodiments, as various modifications can be made and various forms can be obtained. However, this is not intended to limit the present invention to a specific form disclosed, it should be understood to include all changes, equivalents, and substitutes included in the spirit and scope of the present invention.

The present invention will be described in detail below and exemplify specific embodiments, as various modifications can be made and various forms can be obtained. However, this is not intended to limit the present invention to a specific form disclosed, it should be understood to include all changes, equivalents, and substitutes included in the spirit and scope of the present invention.

The term "polymer" or "polymer" used in the specification of the present invention means that a water-soluble ethylenically unsaturated monomer is polymerized, and may encompass all ranges of moisture content or particle size. Among the above polymers, a polymer having a moisture content (moisture content) of about 40% by weight or more, which is in a state before drying after polymerization, may be referred to as a hydrogel polymer.

In addition, "base resin" or "base resin powder" is made into a particle or powder form by drying and pulverizing a polymer in which a water-soluble ethylenically unsaturated monomer is polymerized, and a surface modification or surface crosslinking step described below is performed. It means a polymer in a state that has not been performed.

In addition, "super absorbent polymer" means the polymer or the base resin itself, depending on the context, or an additional process such as surface crosslinking, fine powder reassembly, drying, grinding, classification, etc. for the polymer or the base resin It is used to cover all items that have been in a state suitable for commercialization after passing through.

Hereinafter, a method of manufacturing a super absorbent polymer according to a specific embodiment of the present invention and a super absorbent polymer prepared according to the method will be described in more detail.

In the conventional method for preparing a super absorbent polymer, the water-soluble ethylenically unsaturated monomer for preparing the super absorbent polymer was reacted with a neutralizing agent to neutralize the acidic group. However, since the neutralization reaction is an exothermic reaction, the temperature of the neutralization liquid rapidly rises to 70°C or higher during the reaction. Accordingly, when the neutralized monomer is used at a high temperature in the polymerization reaction for the production of the hydrogel polymer, it is difficult to control the rate of the polymerization reaction, and as a result, the molecular weight of the polymer increases and the crosslinking density increases, so that the superabsorbent polymer There arises a problem that the initial absorption capacity and absorption rate are slowed down. In addition, after the polymerization reaction is completed, the prepared hydrogel polymer is dried and pulverized to prepare a base resin powder.During the drying process, the water-soluble component in the base resin increases due to the reaction with oxygen. The dryness of the super absorbent polymer is deteriorated .

On the other hand, in the present invention, after neutralizing the monomer composition, by performing a process of cooling the high-temperature monomer composition to a controlled temperature range, the polymerization reaction can be stably performed by slowing the reaction rate during the subsequent polymerization reaction. The molecular weight decreases and the crosslinking density decreases, so that the absorption rate of the superabsorbent polymer may be greatly improved. In addition, the hydrogel polymer obtained after the polymerization reaction is mixed with a reducing agent, followed by a drying process, whereby the reducing agent reacts with oxygen during drying and the content of the water-soluble component in the base resin powder (Extractable contents; 16 hr E/ C) can be reduced, and as a result, the CRC and AUP of the final produced super absorbent polymer can be improved in a good balance, the absorption rate can be increased, and the drying degree can be improved .

Specifically, the method of manufacturing a super absorbent polymer according to an embodiment of the present invention,

Neutralizing by adding a neutralizing agent to a monomer composition comprising a water-soluble ethylenically unsaturated monomer having an acidic group, an internal crosslinking agent, and a photopolymerization initiator (step 1);

Cooling the neutralized monomer composition to 25 to 35° C. (Step 2);

Adding a thermal polymerization initiator to the cooled monomer composition and performing a polymerization reaction in the order of a photopolymerization reaction and a thermal polymerization reaction to prepare a hydrogel polymer (Step 3);

Adding a reducing agent to the hydrogel polymer, mixing, drying and pulverizing to prepare a base resin powder (step 4); And

After mixing the base resin powder with a surface crosslinking agent, performing a surface crosslinking reaction (step 5); and,

The reducing agent includes at least one selected from the group consisting of bisulfite, sulfinate, and salts thereof, and is added in an amount of 2500 to 5000 ppmw based on the total weight of the hydrogel polymer.

Hereinafter, each step will be described in more detail.

In the production method according to an embodiment of the present invention, step 1 is a neutralization step for a monomer composition containing a water-soluble ethylenically unsaturated monomer having an acidic group.

Specifically, it may be carried out by adding a neutralizing agent to the monomer composition to neutralize the acidic group of the water-soluble ethylenically unsaturated monomer contained in the monomer composition.

As the neutralizing agent, a basic substance such as sodium hydroxide (or caustic soda), potassium hydroxide, and ammonium hydroxide capable of neutralizing an acidic group may be used.

The amount of the neutralizing agent added and the neutralization reaction process are not particularly limited, and the degree of neutralization of the water-soluble ethylenically unsaturated monomer, which refers to the degree of neutralization by the neutralizing agent among the acid groups contained in the water-soluble ethylenically unsaturated monomer, is 50 to 90 mol%. , Or, it may be carried out to be 60 to 85 mol%, or 65 to 85 mol%, or 70 to 80 mol%. The range of the degree of neutralization may vary depending on the final physical properties, but if the degree of neutralization is too high, the neutralized monomer may be precipitated and the polymerization may be difficult to proceed smoothly. On the contrary, if the degree of neutralization is too low, the absorption power of the polymer is greatly reduced. It may exhibit properties such as elastic rubber that are difficult to handle.

Meanwhile, the monomer composition specifically includes a water-soluble ethylenically unsaturated monomer having an acidic group, an internal crosslinking agent, and a photopolymerization initiator, and may be prepared by mixing these components.

The water-soluble ethylenically unsaturated monomer included in the monomer composition may be any monomer commonly used in the manufacture of a super absorbent polymer. As a non-limiting example, the water-soluble ethylenically unsaturated monomer may be a compound represented by the following Formula 1:

[Formula 1]

R ₁ -COOM ¹

In Formula 1,

R ₁ is an alkyl having 2 to 5 carbon atoms including 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 (meth)acrylic acid, and monovalent (alkali) metal salts, divalent metal salts, ammonium salts, and organic amine salts of these acids.

As described above, when (meth)acrylic acid and/or a salt thereof are used as a water-soluble ethylenically unsaturated monomer, it is advantageous to obtain a super absorbent polymer having improved water absorption. In addition, the monomers include maleic anhydride, fumaric acid, crotonic acid, itaconic acid, 2-acryloylethane sulfonic acid, 2-methacryloylethanesulfonic acid, 2-(meth)acryloylpropanesulfonic 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, and the like may be used.

In addition, the concentration of the water-soluble ethylenically unsaturated monomer in the monomer composition may be appropriately adjusted in consideration of polymerization time and reaction conditions, and may be preferably 20 to 90% by weight, or 40 to 65% by weight. This concentration range may be advantageous in order to control the pulverization efficiency during pulverization of the polymer, which will be described later, while eliminating the need to remove the unreacted monomer after polymerization by using the gel effect phenomenon occurring in the polymerization reaction of the high concentration aqueous solution. However, if the concentration of the monomer is too low, the yield of the super absorbent polymer may be lowered. Conversely, when the concentration of the monomer is too high, a problem may occur in the process, such as a decrease in pulverization efficiency when a part of the monomer is precipitated or the polymerization hydrogel polymer is pulverized, and the physical properties of the super absorbent polymer may be deteriorated.

Further, in the monomer composition, any compound may be used as the internal crosslinking agent as long as it allows the introduction of crosslinking 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, butanedioldi(meth)acrylate, butylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, hexanedioldi(meth)acrylate Rate, triethylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, dipentaerythritol pentaacrylate, glycerin tri(meth)acrylate, pentaerythritol Polyfunctional crosslinking agents such as 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. Among these, when considering the excellent effect of improving the crosslinking effect and thus improving the absorption ability of the super absorbent polymer, preferably, polyethylene glycol diacrylate may be used, and more specifically, polyethylene glycol having a weight average molecular weight of 500 to 800 g/mol Diacrylate can be used.

This internal crosslinking agent may be used in an amount of 0.01 to 5 parts by weight based on 100 parts by weight of the water-soluble ethylenically unsaturated monomer. That is, when the concentration of the internal crosslinking agent is too low, the absorption rate of the resin may be lowered and the gel strength may be weakened, which is not preferable. Conversely, when the concentration of the internal crosslinking agent is too high, the absorbent power of the superabsorbent polymer may be lowered, making it undesirable as an absorber. More specifically, it may be included in 1 to 5 parts by weight, or 1 to 3 parts by weight.

Meanwhile, the term'internal crosslinking agent' used in the present specification is a term used to distinguish it from a surface crosslinking agent for crosslinking the surface of a base resin to be described later, and serves to crosslink and polymerize the unsaturated bonds of the water-soluble ethylenically unsaturated monomers described above. Do it. The crosslinking in the above step proceeds without distinction between the surface or the interior, but by the surface crosslinking process of the base resin to be described later, the surface of the finally prepared superabsorbent polymer has a structure crosslinked by a surface crosslinking agent, and the interior is the internal crosslinking agent. It is made of a structure that is crosslinked by

A method for producing a super absorbent polymer according to an embodiment of the present invention uses both a photopolymerization initiator and a thermal polymerization initiator as a polymerization initiator. In the case of a conventional method for producing a superabsorbent polymer using these initiators together, it is common to mix and add two initiators together. However, in the present invention, when a neutralizing agent is added to the monomer composition, the thermal polymerization reaction occurs together with the heat of the neutralization reaction, making it difficult to control the degree of polymerization, and as a result, in order to prevent the physical properties of the super absorbent polymer from deteriorating, the photopolymerization initiator is used during polymerization of the monomer mixture. And the thermal polymerization initiator is added before the polymerization reaction after neutralization.

Specifically, in the monomer composition, the photopolymerization initiator may be used without limitation of its configuration as long as it is a compound capable of forming a radical by light such as ultraviolet rays.

Examples of the photopolymerization initiator include benzoin ether, dialkyl acetophenone, hydroxyl alkylketone, phenyl glyoxylate, and benzyl dimethyl ketone. Ketal), acyl phosphine, and alpha-aminoketone (α-aminoketone) may be used at least one selected from the group. On the other hand, specific examples of acylphosphine include diphenyl (2,4,6-trimethylbenzoyl) phosphine oxide, phenylbis (2,4,6-trimethylbenzoyl) phosphine oxide, ethyl (2,4,6- Trimethylbenzoyl)phenylphosphineate and the like. More various photopolymerization initiators are well specified in Reinhold Schwalm's book "UV Coatings: Basics, Recent Developments and New Application (Elsevier 2007)" p115, and are not limited to the above-described examples.

The photopolymerization initiator may be used in an amount of 0.01 to 5 parts by weight, or 0.1 to 4.5 parts by weight based on 100 parts by weight of the water-soluble ethylenically unsaturated monomer. If the concentration of the photopolymerization initiator is too low, the polymerization rate may be slow, and if the concentration of the photopolymerization initiator is too high, the molecular weight of the superabsorbent polymer may be small and physical properties may become uneven.

In addition, the monomer composition may further include one or more additives such as a thickener, a plasticizer, a storage stabilizer, and an antioxidant, if necessary.

And, such a monomer composition, for example, may be prepared in the form of a solution dissolved in a solvent such as water. At this time, the usable solvent may be used without limitation of its configuration as long as it is capable of dissolving the above-described raw materials. For example, as the solvent, water, ethanol, ethylene glycol, diethylene glycol, triethylene glycol, 1,4-butanediol, propylene glycol, ethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate , Methyl ethyl ketone, acetone, methyl amyl ketone, cyclohexanone, cyclopentanone, diethylene glycol monomethyl ether, diethylene glycol ethyl ether, toluene, xylene, butyrolactone, carbitol, methyl cellosolve acetate, N,N-dimethylacetamide, or mixtures thereof, and the like may be used.

In addition, the solid content of the monomer composition in the solution state, that is, the concentration of the monomer, the internal crosslinking agent, and the polymerization initiator may be appropriately adjusted in consideration of the polymerization time and reaction conditions. For example, the solid content in the monomer composition may be 10 to 80% by weight, or 15 to 60% by weight, or 20 to 40% by weight based on the total weight of the monomer composition. When the monomer composition has a solid content in the above range, the gel effect phenomenon occurring in the polymerization reaction of a high concentration aqueous solution is used to prevent the need to remove the unreacted monomer after polymerization, while improving the pulverization efficiency during pulverization of the polymer to be described later. It can be advantageous to control.

The neutralization liquid obtained as a result of the neutralization reaction for the above-described monomer composition, or the neutralized monomer composition, may contain a water-soluble ethylenically unsaturated monomer, an internal crosslinking agent, and a polymerization initiator having an acidic group at least partially neutralized. .

Next, Step 2 is a cooling step for the neutralized monomer composition as a result of the neutralization reaction in Step 1.

As described above, since the neutralization reaction is an exothermic reaction, the neutralized monomer composition after completion of the neutralization reaction exhibits a high temperature of 70°C or higher. For this, a cooling system performs a process of cooling the neutralized monomer composition to a temperature of 25 to 35°C.

If the temperature of the neutralized monomer composition during cooling is lowered to less than 25°C, the reaction is excessively delayed during the subsequent polymerization reaction, and as a result, the molecular weight and crosslinking density of the polymer are greatly lowered, resulting in deterioration of the physical properties of the finally prepared superabsorbent polymer. have. On the other hand, when the cooling temperature of the neutralized monomer composition exceeds 35°C, the effect of delaying the reaction rate in the subsequent polymerization reaction is not sufficient, and as a result, the molecular weight and crosslinking density of the polymer increases, and the absorption rate of the super absorbent polymer Can be slow. More specifically, the cooling temperature of the neutralized monomer composition may be 30 to 35°C.

In addition, the cooling method is not particularly limited, and may be performed using a cooled thermal medium or the like.

Next, step 3 is a step of preparing a hydrogel polymer by introducing a thermal polymerization initiator to the monomer composition cooled in step 2, and performing a polymerization reaction in the order of a photopolymerization reaction and a thermal polymerization reaction.

As the thermal polymerization initiator, at least one selected from the group of initiators consisting of persulfate-based initiators, azo-based initiators, hydrogen peroxide and ascorbic acid may be used. Specifically, examples of 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 ), etc., and examples of azo-based initiators include 2,2-azobis-(2-amidinopropane) dihydrochloride (2,2-azobis(2-amidinopropane) dihydrochloride), 2 ,2-azobis-(N,N-dimethylene)isobutyramidine dihydrochloride (2,2-azobis-(N,N-dimethylene)isobutyramidine dihydrochloride), 2-(carbamoyl azo)isobutyronitrile (2-(carbamoylazo)isobutylonitril), 2,2-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride (2,2-azobis[2-(2-imidazolin-2- yl)propane] dihydrochloride), 4,4-azobis-(4-cyanovaleric acid) (4,4-azobis-(4-cyanovaleric acid)) and the like. More various thermal polymerization initiators are well specified in Odian's'Principle of Polymerization (Wiley, 1981)', p203, and are not limited to the above-described examples.

The thermal polymerization initiator may be used in an amount of 0.01 to 5 parts by weight, or 0.1 to 4 parts by weight based on 100 parts by weight of the monomer. If the concentration of the thermal polymerization initiator is too low, additional thermal polymerization hardly occurs, so the effect of the addition of the thermal polymerization initiator may be insignificant.If the concentration of the thermal polymerization initiator is too high, the molecular weight of the super absorbent polymer may be small and physical properties may become uneven. have. Among the polymerization initiators, the amount of the thermal polymerization initiator to be used affects the physical properties of the base resin prepared in step 4, in particular, the content of the water-soluble component of the base resin. When the number of water-soluble components increases, the physical properties of the prepared super absorbent polymer deteriorate, and in particular, the degree of drying deteriorates. Accordingly, in the present invention, a super absorbent polymer having excellent dryness can be prepared while maintaining excellent absorption performance by using the thermal polymerization initiator of the above content. When the amount of the thermal polymerization initiator exceeds 5 parts by weight, the drying degree of the super absorbent polymer finally produced is lowered. In addition, when the amount of the thermal polymerization initiator is less than 0.01 parts by weight, the efficiency of hydrogel polymerization decreases, and various physical properties of the finally produced superabsorbent polymer are deteriorated.

In addition, the thermal polymerization initiator and the photopolymerization initiator used in the preparation of the super absorbent polymer according to the present invention are under the conditions that satisfy the respective content ranges described above, and the total amount of the polymerization initiator is 0.05 to about 100 parts by weight of the water-soluble ethylenically unsaturated monomer. It is preferably 10 parts by weight, or 0.5 to 8.5 parts by weight, or 1 to 8.5 parts by weight. Accordingly, when each polymerization initiator is used, the content is appropriately adjusted so as to satisfy the above total usage conditions. If the total content of the photopolymerization and thermal polymerization initiator added to the polymerization reaction is less than 0.05 parts by weight, the polymerization rate may be slowed and a large amount of residual monomers may be extracted from the final product, which is not preferable. Conversely, when the concentration of the polymerization initiator is higher than the above range, the polymer chain forming the network is shortened to increase the content of the water-soluble component, thereby increasing the dryness of the superabsorbent resin and lowering the absorption capacity under pressure. This can be degraded, which is not preferable.

In addition, when the thermal polymerization initiator is added, one or more additives capable of improving the physical properties of the super absorbent polymer such as a surfactant and a foaming agent may be additionally added.

The surfactant serves to increase the surface area of the polymer by maintaining the shape of the bubbles formed during polymerization and at the same time uniformly distributing the bubbles over the entire polymer area. Specifically, as the surfactant, a cationic surfactant, an anionic surfactant, or a nonionic surfactant may be used. For example, as the anionic surfactant, a compound represented by the following Formula 2 may be used, and more preferably, sodium dodecyl sulfate may be used.

[Formula 2]

R-SO ₃ Na

In Chemical Formula 2,

R is alkyl having 8 to 16 carbon atoms.

In addition, the surfactant may be added in an amount of 1 to 10 parts by weight, more specifically 3 to 7 parts by weight based on 100 parts by weight of the water-soluble ethylenically unsaturated monomer. If the amount of the surfactant is less than 1 part by weight, there is no substantial improvement effect, and if it exceeds 10 parts by weight, the content of the surfactant in the super absorbent polymer increases, which is not preferable.

In addition, the foaming agent serves to increase the surface area by foaming during polymerization to form pores in the hydrogel polymer. Specifically, an inorganic foaming agent or an organic foaming agent may be used as the 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. In addition, examples of the organic blowing agent include azodicarbonamide (ADCA), dinitroso pentamethylene tetramine (DPT), p,p'-oxybisbenzenesulfonylhydrazide (p,p' -oxybisbenzenesulfonylhydrazide, OBSH), and p-toluenesulfonyl hydrazide (TSH).

In addition, the blowing agent may be added in an amount of 0.05 to 5 parts by weight, more specifically 0.5 to 3 parts by weight, based on 100 parts by weight of the water-soluble ethylenically unsaturated monomer. If the amount of the foaming agent is less than 0.05 parts by weight, the improvement effect according to the injection is insignificant, and if the amount of the foaming agent exceeds 5 parts by weight, the pores are too large to reduce the gel strength and density of the super absorbent polymer, which causes problems in distribution and storage. Can lead to.

Next, a polymerization reaction is carried out on the resulting mixture.

The polymerization reaction is preferably carried out in the order of a photopolymerization reaction through light irradiation such as UV, followed by a thermal polymerization reaction by heating or the like.

For example, the photopolymerization may be carried out in a reactor equipped with a movable conveyor belt, and in this case, the form of the obtained hydrogel polymer may be a sheet-shaped hydrogel polymer having the width of the belt. At this time, the thickness of the polymer sheet varies depending on the concentration and injection speed of the monomer composition to be injected, but it is preferable to supply the monomer composition so that a sheet-like polymer having a thickness of about 0.5 to about 5 cm can be obtained. In the case of supplying the monomer composition to the extent that the thickness of the polymer on the sheet is too thin, the production efficiency is not preferable, and when the thickness of the polymer on the sheet exceeds 5 cm, the polymerization reaction does not occur evenly over the entire thickness due to the excessively thick thickness. I can't.

After completion of the photopolymerization reaction by light irradiation, a thermal polymerization reaction is performed by supplying hot air from a reactor having an agitation shaft such as a kneader or heating the reactor.

For example, as described above, the hydrogel polymer obtained by thermal polymerization by supplying hot air or heating the reactor to a reactor such as a kneader equipped with a stirring shaft may be transferred to the reactor outlet according to the shape of the stirring shaft provided in the reactor. The discharged hydrogel polymer may be in the form of several centimeters to several millimeters. Specifically, the size of the resulting hydrogel polymer may vary depending on the concentration and injection speed of the monomer composition to be injected, and a hydrogel polymer having a weight average particle diameter of 1 to 50 mm, or 2 to 10 mm may be obtained.

The moisture content of the hydrogel polymer prepared through the polymerization reaction may be about 40 to about 80% by weight. In the present specification, the "water content" refers to a value obtained by subtracting the weight of the dried polymer from the weight of the hydrogel polymer as the content of water occupied with respect to the total weight of the hydrogel polymer. Specifically, it is defined as a calculated value by measuring the weight loss due to evaporation of moisture in the polymer during drying by raising the temperature of the polymer through infrared heating. At this time, the drying condition is a method of raising the temperature from room temperature to about 180° C. and then maintaining it at 180° C., and the total drying time is set to 20 minutes including 5 minutes of the temperature increase step, and the moisture content is measured.

Next, step 4 is a step of adding a reducing agent to the hydrogel polymer prepared in step 3, mixing, drying and pulverizing to form a powdery base resin.

In the present invention, by adding and mixing a reducing agent before drying the hydrogel polymer, the reducing agent reacts with oxygen during the drying process to prevent an increase in water-soluble components in the base resin powder. If there are many non-crosslinked water-soluble components in the base resin powder, the super absorbent polymer cannot absorb salt water in a short time, and physical properties may be deteriorated. In addition, when the reducing agent is added during the preparation of the monomer composition, there is a problem in that a reaction occurs due to light to form a solid material.

As the reducing agent, at least one compound selected from the group consisting of bisulfite, sulfinate, and salts thereof may be used. In addition, the salt may be an alkali metal salt or an alkaline earth metal salt, and more specifically, it may be a metal salt containing Li, Na, or K.

The bisulfite or its salt is _{a compound containing HSO 3} ⁻ ions in the molecule, and is used as an oxidation-reduction initiator in the polymerization reaction for the production of a conventional super absorbent polymer, or as a reducing agent that accelerates decomposition of the polymerization initiator. Was used. In the present invention, after completion of the polymerization reaction, bisulfite is mixed and used for the resulting hydrogel polymer, so that the content of the water-soluble component in the base resin powder can be lowered through reaction with oxygen in the air during drying.

Specific examples of the bisulfite or salt _{thereof may include NaHSO 3} , but are not limited thereto.

In addition, the sulfinate or a salt thereof may be a compound specifically represented by the following formula (3).

[Formula 3]

In Formula 3, X is a hydrogen atom, an ammonium cation, or an alkali metal cation,

R is a C 1 to C 20, saturated or unsaturated aliphatic or aromatic hydrocarbon radical, or _{a radical of YOOC-R 1} -, wherein Y is a hydrogen atom, an ammonium cation, or an alkali metal cation, and R ₁ is a C 1 to C. It is an alkylene radical of 8, and at least one of the hydrogen atoms of _{R 1 is substituted with a hydroxy group.}

More specifically, the sulfinate or its salt may be a 2-hydroxy-2-sulfinatoacetic acid disodium salt.

The reducing agent is added in an amount of 2500 to 5000 ppmw based on the total weight of the hydrogel polymer. If the content of the reducing agent is less than 2500 ppmw, the content of the water-soluble component in the base resin powder increases, and as a result, the effect of improving the drying degree of the super absorbent polymer may be reduced. In addition, when the content of the reducing agent exceeds 5000 ppmw, there is a concern that the water-retaining ability and the absorption under pressure of the super absorbent polymer may be lowered. More specifically, it may be added in an amount of 3000 ppmw or more and 5000 ppmw or less, or 4500 ppmw or less, or 4000 ppmw or less.

The mixing of the hydrogel polymer and the reducing agent may be performed according to a conventional mixing process.

Next, when drying the mixture of the hydrogel polymer and the reducing agent, if necessary, a step of coarsely pulverizing before drying in order to increase the efficiency of the drying step may be further performed. At this time, the grinder used is not limited in configuration, and specifically, a vertical pulverizer, a turbo cutter, a turbo grinder, a rotary cutter mill, and cutting Cutter mill, disc mill, shred crusher, crusher, chopper, and disc cutter include any one selected from the group of crushing machines. However, it is not limited to the above-described example.

In this case, the coarse pulverization step may be pulverized so that the particle diameter of the hydrogel polymer is about 2 mm to about 10 mm. Grinding with a particle diameter of less than 2 mm is not technically easy due to the high moisture content of the hydrogel polymer, and a phenomenon of agglomeration between the pulverized particles may occur. On the other hand, when the particle diameter is pulverized to more than 10 mm, the effect of increasing the efficiency of the subsequent drying step may be insignificant.

Drying is performed on the mixture of the hydrogel polymer and the reducing agent that is coarsely pulverized as described above or has not been subjected to the coarse pulverization step.

In this case, the drying temperature in the drying step may be 50 to 250°C. When the drying temperature is less than 50°C, the drying time may be too long and the physical properties of the finally formed super absorbent polymer may be deteriorated, and when the drying temperature exceeds 250°C, only the polymer surface is excessively dried, and a subsequent pulverization process Fine powder may be generated at, and there is a concern that the physical properties of the finally formed super absorbent polymer may be deteriorated. More preferably, the drying may be performed at a temperature of 150 to 200°C, more preferably 160 to 190°C. Meanwhile, in the case of the drying time, it may be performed for 20 minutes to 15 hours in consideration of process efficiency, but is not limited thereto.

As long as the drying method in the drying step is also commonly used as a drying process of the hydrous gel polymer, it may be selected and used without limitation of its configuration. Specifically, the drying step may be performed by a method such as hot air supply, infrared irradiation, microwave irradiation, or ultraviolet irradiation.

The moisture content of the dried polymer after the drying step as described above may be 5% by weight or less, more specifically 0.1 to 3% by weight. When the moisture content of the dried polymer exceeds 5% by weight, an undried resin can be obtained.

Next, a step of pulverizing the dried polymer obtained through such a drying step is performed. The polymer powder obtained after the pulverization step may have a particle diameter of 150 to 850 μm. The pulverizer used to pulverize with such a particle size is specifically, a ball mill, a pin mill, a hammer mill, a screw mill, a roll mill, and a disk mill. (disc mill) or jog mill may be used, but is not limited to the above-described example.

In addition, in order to manage the physical properties of the super absorbent polymer powder that is finally commercialized after the pulverization step, a separate process of classifying the polymer powder obtained after pulverization according to the particle size may be performed. Preferably, a polymer having a particle diameter of 150 to 850 µm is classified, and only a polymer powder having such a particle diameter can be commercialized through a surface crosslinking reaction step to be described later.

It is appropriate that the base resin powder obtained through the above process and the super absorbent polymer obtained therefrom are manufactured and provided so as to have a particle diameter of 150 to 850 µm. More specifically, at least 95% by weight or more of the base resin powder and the super absorbent polymer obtained therefrom may have a particle diameter of 150 to 850 μm, and a fine powder having a particle diameter of less than 150 μm may be less than 3% by weight. As described above, as the particle size distribution of the base resin powder and the super absorbent polymer is adjusted to a preferable range, the finally prepared super absorbent polymer may better express the above-described physical properties.

Next, step 5 performs a step of forming a surface crosslinking layer by further crosslinking the surface of the base resin in the presence of a surface crosslinking agent.

The step is a step of forming a surface crosslinking layer using a surface crosslinking agent to increase the surface crosslinking density of the base resin, so that the unsaturated bonds of the water-soluble ethylenically unsaturated monomer remaining on the surface without crosslinking are crosslinked by the surface crosslinking agent. As a result, a super absorbent polymer having a high surface crosslinking density is formed. The surface crosslinking density, that is, the external crosslinking density, is increased by this heat treatment process, while the internal crosslinking density does not change, so that the superabsorbent polymer having a surface crosslinked layer formed thereon has a structure having a higher crosslinking density on the outside than on the inside.

The surface crosslinking agent is not limited in its constitution as long as it is a compound capable of reacting with a functional group of the polymer.

Preferably, in order to improve the properties of the resulting super absorbent polymer, a polyhydric alcohol-based compound as the surface crosslinking agent; Epoxy compounds; Polyamine compounds; Haloepoxy compounds; Condensation products of haloepoxy compounds; Oxazoline compounds; Mono-, di- or polyoxazolidinone compounds; Cyclic urea compounds; Polyvalent metal salts; And one or more selected from the group consisting of alkylene carbonate-based compounds may be used.

Specifically, examples of the polyhydric alcohol-based compound include ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, 1,2-hexanediol, 1,3-hexanediol, Selected from the group consisting of 2-methyl-1,3-propanediol, 2,5-hexanediol, 2-methyl-1,3-pentanediol, 2-methyl-2,4-pentanediol, tripropylene glycol and glycerol One or more of these can be used.

In addition, ethylene glycol diglycidyl ether and glycidol may be used as the epoxy compound, and as polyamine compounds, ethylenediamine, diethylenetriamine, triethylenetetraamine, tetraethylenepentamine, pentaethylenehexamine , Polyethyleneimine and polyamide polyamine may be used at least one selected from the group consisting of.

And as the haloepoxy compound, epichlorohydrin, epibromohydrin, and α-methylepichlorohydrin may be used. Meanwhile, as the mono-, di-, or polyoxazolidinone compound, for example, 2-oxazolidinone may be used.

As the alkylene carbonate-based compound, an alkylene carbonate having 2 to 6 carbon atoms such as ethylene carbonate or propylene carbonate may be used. Each of these may be used alone, or two or more types of alkylene carbonates having different carbon atoms may be used in combination.

In addition, as the polyvalent metal salt, specifically, a metal-containing sulfate such as aluminum or a carboxylate may be used, and among them, aluminum sulfate may be more preferably used.

Such a surface crosslinking agent may be used in an amount of 0.001 to 5 parts by weight based on 100 parts by weight of the base resin. When the amount of the surface cross-linking agent exceeds 5 parts by weight, excessive surface cross-linking proceeds, and various physical properties of the super absorbent polymer, especially dryness, may deteriorate. In addition, the surface crosslinking agent is preferably used in an amount of 0.01 parts by weight or more based on 100 parts by weight of the base resin. By adjusting the content range of the surface crosslinking agent to the above-described range, a super absorbent polymer having excellent absorption properties can be prepared.

Among the above-described surface crosslinking agents, in order to increase the surface crosslinking efficiency, it is preferable to mix and use a mixture of an epoxy compound such as ethylene glycol diglycidyl ether and a polyvalent metal salt such as aluminum sulfate, and more preferably, a base resin powder. 0.001 to 1 parts by weight, or 0.01 to 0.1 parts by weight of an epoxy compound, and 0.01 to 2 parts by weight of a polyvalent metal salt, or 0.1 to 1 part by weight may be mixed and used based on 100 parts by weight.

In addition, the surface crosslinking agent may further include an inorganic filler. The inorganic filler may include silica, clay, alumina, silica-alumina composite, titania, zinc oxide or silicate. The inorganic filler may be included in an amount of 0.01 to 0.5 parts by weight, or 0.1 to 0.5 parts by weight, based on 100 parts by weight of the base resin powder .

In addition, the surface crosslinking agent may further include a thickener. If the surface of the base resin powder is further crosslinked in the presence of a thickener in this way, degradation of physical properties can be minimized even after pulverization. Specifically, as the thickener, at least one selected from polysaccharides and hydroxy-containing polymers may be used. As the polysaccharide, a gum-based thickener and a cellulose-based thickener may be used. 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. Specific examples of the cellulose-based thickener include hydroxypropylmethylcellulose, carboxymethylcellulose, methylcellulose, hydroxy Hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxyethylmethyl cellulose, hydroxymethylpropyl cellulose, hydroxyethyl hydroxypropyl cellulose, ethyl hydroxyethyl cellulose, and methyl hydroxypropyl cellulose, and the like. . Meanwhile, specific examples of the hydroxy-containing polymer include polyethylene glycol and polyvinyl alcohol.

In addition, there is no limitation on the configuration of the method of mixing the surface crosslinking agent with the base resin. For example, a method of mixing a surface crosslinking agent and a base resin in a reaction tank, spraying a surface crosslinking agent onto the base resin, or a method of continuously supplying and mixing a base resin and a surface crosslinking agent to a continuously operated mixer. .

When mixing the surface crosslinking agent and the base resin, water and methanol may be mixed together and added. When water and methanol are added, there is an advantage that the surface crosslinking agent can be evenly dispersed in the base resin. At this time, the amount of water and methanol added may be appropriately adjusted to induce even dispersion of the surface crosslinking agent, prevent agglomeration of the base resin, and optimize the surface penetration depth of the crosslinking agent. The solvent may be used in an amount of 0.5 to 10 parts by weight based on 100 parts by weight of the base resin powder.

The surface crosslinking process may be performed at a temperature of about 80°C to about 250°C. More specifically, the surface crosslinking process may be performed at a temperature of about 100°C to about 220°C, or about 120°C to about 200°C, for about 20 minutes to about 2 hours, or about 40 minutes to about 80 minutes. . When the above-described surface crosslinking process conditions are satisfied, the surface of the base resin is sufficiently crosslinked, thereby increasing the absorption capacity under pressure.

The means for increasing the temperature for the surface crosslinking reaction is not particularly limited. It can be heated by supplying a heat medium or by directly supplying a heat source. At this time, as the type of the heat medium that can be used, a heated fluid such as steam, hot air, or hot oil may be used, but the temperature of the heat medium supplied is not limited thereto. It can be appropriately selected in consideration. On the other hand, the heat source directly supplied may include heating through electricity and heating through gas, but is not limited to the above-described example.

Meanwhile, the step may further include classifying the base resin on which the surface crosslinking layer is formed.

The physical properties of the super absorbent polymer powder to be finally commercialized may be managed through the step of classifying the base resin on which the surface crosslinking layer is formed according to the particle size. It is appropriate that the superabsorbent polymer obtained therefrom is manufactured and provided so as to have a particle diameter of about 150 to 850 µm through such processes such as pulverization and classification. More specifically, at least about 95% by weight or more of the base resin on which the surface crosslinking layer is formed may have a particle diameter of about 150 to 850 μm, and a fine powder having a particle diameter of less than about 150 μm may be less than about 3% by weight. As the particle diameter distribution of the super absorbent polymer is adjusted to a preferable range, the finally prepared super absorbent polymer may exhibit excellent absorption properties. Accordingly, in the classification step, a polymer having a particle diameter of about 150 to about 850 μm can be classified and commercialized.

While maintaining excellent water absorption performance with high water absorption produced by the manufacturing method of the present invention as described above, it is excellent in dryness.

Specifically, the superabsorbent polymer according to the present invention has a centrifugal water retention capacity (CRC) of 30 g/g or more for physiological saline (0.9 wt% sodium chloride aqueous solution) measured according to the EDANA method WSP 241.3. to be. The measurement method of the centrifugation water holding capacity is more specific in the examples below. Preferably, the centrifugation water holding capacity is 30.5 g/g or more, or 31 g/g or more. In addition, the centrifugation water holding capacity is excellent as the value increases, and thus there is no practical upper limit, but, for example, it is 35 g/g or less, 34 g/g or less, or 33 g/g or less.

In addition, preferably, the super absorbent polymer according to the present invention has a pressure absorption capacity (AUP) of 20 g/g or more, or 21 g/g or more at 0.7 psi, as measured according to the EDANA method WSP 242.3-10. In addition, the pressure absorption capacity is excellent as the value increases, and there is no practical upper limit, but, for example, it is 25 g/g or less, 24 g/g or less, or 23 g/g or less.

In addition, the superabsorbent polymer according to the present invention has an absorption rate of 55 seconds or less measured according to the Vortex measurement method. The absorption rate refers to a time at which a vortex of a liquid disappears due to rapid absorption when a superabsorbent polymer is added to the physiological saline solution and stirred, and may define a rapid absorption rate of the superabsorbent polymer. The measurement method of the Vortex is more specific in the following examples. In addition, the smaller the value, the better, and the lower limit of the absorption rate is theoretically 0 seconds, but for example, it is 10 seconds or more, 20 seconds or more, or 25 seconds or more.

In addition, the super absorbent polymer according to the present invention has a dryness of 0.85 g or less. The degree of drying is determined by swelling the super absorbent polymer with 200 g of tap water at 24° C. for 2 hours, placing a filter paper thereon, pressing for 1 minute at a pressure of 0.75 psi, and then weighing the weight of tap water on the filter paper. It can be obtained by measuring. A specific measurement method is more specific in the following examples. Preferably, the degree of drying is 0.81 g or less, or 0.8 g or less. In addition, the smaller the value, the better, and the lower limit of the degree of drying is 0 g in theory, but, for example, 0.1 g or more, or 0.2 g or more.

Hereinafter, preferred embodiments are presented to aid in understanding the invention. However, the following examples are for illustrative purposes only, and the invention is not limited thereto.

<Production of super absorbent polymer>

Example 1

Acrylic acid mixture was dissolved by adding 12 g of polyethylene glycol diacrylate (PEGDA, Mw=523 g/mol) as an internal crosslinking agent and 20 g of diphenyl (2,4,6-trimethylbenzoyl)-phosphine oxide as a photopolymerization initiator to 480 g of acrylic acid. Was prepared. 640 g of 31.5% caustic soda (NaOH) and 200 g of water were mixed in a separate vessel and stirred for 30 minutes to prepare a caustic soda aqueous solution, and the prepared caustic soda aqueous solution was introduced into a vessel containing the acrylic acid mixture using a pump. Mixed. When the aqueous solution of caustic soda was added, it was confirmed that the temperature of the neutralized solution was increased to 72°C or higher due to the heat of neutralization, and then the temperature of the neutralized solution in the reactor was cooled to 30°C by the cooled thermal medium surrounding the reactor (neutralization degree: 70 mol%).

The resulting mixture is a bottle containing 19.2 g of sodium persulfate (SPS) as a thermal polymerization initiator, 10.1 g of sodium bicarbonate as a blowing agent, and 31.8 g of sodium dodecyl sulfate as a surfactant. Let it drain on.

The resulting mixture was applied 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 60 seconds by irradiation with ultraviolet rays (irradiation amount: 10 mV/cm 2} ) and heat was applied for 120 seconds to obtain a hydrogel polymer. I did. The obtained hydrous gel polymer was pulverized to a size of 2 mm * 2 mm, and the moisture content was measured to be 40.1% by weight.

_{A solution in which 180 g of water and 3000 ppm of NaHSO 3} were dissolved was evenly applied to 1400 g of the pulverized hydrogel polymer, and then passed through a hole plate with a diameter of 11 mm using a meat chopper to obtain a crumb resin. 1000g of this gel-type resin is spread on stainless wire gauze with a hole size of 600㎛ to a thickness of about 30mm, and the powder is used in an oven capable of air volume transfer up and down, and hot air at 185℃ is applied downward for 20 minutes. It was dried uniformly by flowing from the top to the top and the next 20 minutes from the top to the bottom (after drying, the moisture content of the dried body is 2% or less).

After drying, it was pulverized with a grinder, and classified for 10 minutes with Amplitute 1.5 mm to obtain a base resin powder having a particle diameter of about 150 µm to 850 µm.

With respect to 100 parts by weight of the base resin prepared above, the surface crosslinking solution (8 parts by weight of water, 5 parts by weight of methanol, 0.02 parts by weight of ethylene glycol diglycidyl ether (EX-810)), aluminum sulfate 23 hydrate (aluminum sulfate 23) hydrate; Al-S) 0.2 parts by weight, and Aerosol 200 as an inorganic filler (including 0.1 parts by weight of 0.1 parts by weight) were added, and a surface crosslinking reaction was performed at 140° C. for 40 minutes. After completion of the surface crosslinking reaction, a super absorbent polymer having an average particle diameter of 150 to 850 μm was obtained using a sieve.

Examples 2 to 6 and Comparative Examples 1 to 12

A superabsorbent polymer was prepared by performing the same method as in Example 1, except that the conditions described in Table 1 were used.

Test example

In the preparation of the superabsorbent resin according to the above Examples and Comparative Examples, the absorption capacity such as centrifugation water holding capacity (CRC) and vortex for the base resin prepared as an intermediate material and the finally prepared super absorbent polymer was as follows. Each was measured by the method.

(1) Centrifuge Retention Capacity (CRC)

The water holding capacity of each resin according to the absorption ratio under no load was measured according to the European Disposables and Nonwovens Association (EDANA) standard EDANA WSP 241.3.

Specifically, from the resins obtained through the Examples and Comparative Examples, respectively, to obtain a resin classified through a sieve of #30-50. This resin W ₀ (g) (about 0.2 g) was evenly put in a nonwoven bag and sealed, and then immersed in physiological saline (0.9% by weight) at room temperature. After 30 minutes elapsed, water was removed from the bag for 3 minutes under the condition of 250 _{G using a centrifuge, and the mass W 2} (g) of the bag was measured. Moreover, after performing the same operation without using a resin, the mass W ₁ (g) at that time was measured.

Using each obtained mass, CRC (g/g) was calculated according to Equation 1 below.

[Equation 1]

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

(2) Absorption rate by vortex method

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

Specifically, the absorption rate (or vortex time) is 2 g of superabsorbent resin in 50 mL of physiological saline at 23 to 24°C, and a magnetic bar (diameter 8 mm, length 31.8 mm) is stirred at 600 rpm to vortex ( vortex) was calculated by measuring the time until disappearance in seconds.

(3) Content of water-soluble ingredients (Extractable contents; 16 hr E/C (% by weight))

In the same manner as described in the European Disposables and Nonwovens Association standard EDANA method WSP 270.2, the water-soluble component of the base resin was measured during the manufacturing process of the Examples and Comparative Examples.

Specifically, 1.0 g of the base resin was added to 200 g of 0.9 wt% NaCl solution, soaked for 16 hours while stirring at 500 rpm, and the aqueous solution was filtered off with filter paper. The filtered solution was first titrated to pH 10.0 with 0.1 N caustic soda solution, and then reverse titrated to pH 2.7 with 0.1 N hydrogen chloride solution, and the polymer material that was not crosslinked from the amount required at the time of neutralization was calculated and measured as a water-soluble component. I did.

(4) Absorbency under Pressure (AUP)

The absorbency under pressure of 0.7 psi was measured according to the EDANA method WSP 242.3 for the base resin and the super absorbent polymer in Examples and Comparative Examples.

First, in the measurement of the absorbency under pressure, the resin fraction in the CRC measurement was used.

Specifically, a 400 mesh stainless steel mesh was mounted on the bottom of a plastic cylinder having an inner diameter of 25 mm. Under the conditions of room temperature and humidity of 50%, the base resin or super absorbent polymer W ₀ (g) (0.16 g) is evenly sprayed on the wire mesh, and the piston capable of evenly applying an additional 0.7 psi load on the wire has an outer diameter of 25 It is slightly smaller than mm, and there is no gap with the inner wall of the cylinder, and the vertical movement is not disturbed. At this time, the weight W ₃ (g) of the device was measured.

A glass filter having a diameter of 90 mm and a thickness of 5 mm was placed on the inside of a 150 mm diameter PET dish, and a physiological saline solution composed of 0.9 wt% sodium chloride was at the same level as the upper surface of the glass filter. One sheet of filter paper with a diameter of 90 mm was mounted on it. The measuring device was placed on the 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 of the obtained masses, the absorbency under pressure (g/g) was calculated according to Equation 2 below.

[Equation 2]

AUP(g/g) = [W ₄ (g)-W ₃ (g)]/W ₀ (g)

(5) Dryness

4 g of the super absorbent polymer prepared in the above Example or Comparative Example was evenly sprayed on a 13 cm petri-dish, 200 g of tap water at 24° C. was poured, and then swelled for 2 hours. Thereafter, 20 sheets of 11cm diameter filter paper (manufacturer whatman, catalog No. 1004-110) were placed on the swollen super absorbent polymer, and pressed with a diameter of 11cm and a 5kg weight (0.75psi) for 1 minute. After pressurization, the amount of tap water applied to the filter paper was measured and expressed as a dryness (g).

As a result of the experiment, Comparative Examples 1 to 3, Comparative Examples 7 and 12, which did not satisfy the range of the neutralization solution temperature control under the manufacturing conditions of the super absorbent polymer according to the present invention, were final The drying degree of the superabsorbent polymer to be produced was high, and the vertex was increased. In particular, in the case of Comparative Example 7 where the temperature of the neutralization solution was too low, the content of the water-soluble component in the base resin was also increased, and in Comparative Example 12 where the temperature of the neutralization solution was too high, a large decrease in CRC was observed with an increase in dryness. Appeared together.

In addition, in the case of Comparative Examples 4 to 6, which satisfies the temperature control condition of the neutralization solution, but does not satisfy the condition of the reducing agent to be added thereafter, the content of the water-soluble component (16h EC) in the base resin is greatly increased to 9% by weight or more. , Drying of the finally prepared super absorbent polymer also increased to more than 1, and vertex also increased to more than 55 seconds.

In addition, even if the temperature control of the neutralizing solution and the reducing agent conditions are satisfied, when the conditions for the amount of the reducing agent are not satisfied, in particular, Comparative Example 8, where the amount of the reducing agent is too small, showed a high degree of drying, and the amount of the reducing agent was too large. In the case of Comparative Examples 9, 10, and 11, an improved effect was exhibited in terms of dryness, but the water absorption capacity of the superabsorbent polymer was significantly lowered.

From these results, it can be seen that in order to improve the dryness while maintaining the excellent water absorption capacity of the super absorbent polymer, the temperature of the neutralizing solution and the input conditions of the reducing agent must be controlled at the same time.

Claims (11)

Neutralizing by adding a neutralizing agent to a monomer composition comprising a water-soluble ethylenically unsaturated monomer having an acidic group, an internal crosslinking agent, and a photopolymerization initiator;
Cooling the neutralized monomer composition to 25 to 35°C;
Adding a thermal polymerization initiator to the cooled monomer composition and performing a polymerization reaction in the order of a photopolymerization reaction and a thermal polymerization reaction to prepare a hydrogel polymer;
Adding a reducing agent to the hydrogel polymer, mixing, drying and pulverizing to prepare a base resin powder; And
Including; after mixing the base resin powder with a surface crosslinking agent, performing a surface crosslinking reaction,
The reducing agent comprises at least one selected from the group consisting of bisulfite, sulfinate, and salts thereof, and is added in an amount of 2500 to 5000 ppmw based on the total weight of the hydrogel polymer,
Method for producing a super absorbent polymer.
The method of claim 1,
The reducing agent comprises sodium bisulfite, 2-hydroxy-2-sulfinatoacetic acid disodium salt, or a mixture thereof.
The method of claim 1,
The base resin powder has a water-soluble component content of 6 to 9% by weight when measured according to the EDANA method WSP 270.2, a manufacturing method.
The method of claim 1,
The internal crosslinking agent is N,N'-methylenebisacrylamide, trimethylolpropane tri(meth)acrylate, ethylene glycol di(meth)acrylate, polyethylene glycol (meth)acrylate, polyethylene glycol di(meth)acrylate, Propylene glycol di(meth)acrylate, polypropylene glycol(meth)acrylate, polypropylene glycol di(meth)acrylate, butanedioldi(meth)acrylate, butylene glycol di(meth)acrylate, diethylene glycol Di(meth)acrylate, hexanedioldi(meth)acrylate, triethylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, dipentaerythritol penta Including at least one compound selected from the group consisting of acrylate, glycerin tri(meth)acrylate, pentaerythritol tetraacrylate, triarylamine, ethylene glycol diglycidyl ether, propylene glycol, glycerin, and ethylene carbonate That, the manufacturing method.
The method of claim 1,
The photopolymerization initiator and the thermal polymerization initiator are added in an amount of 0.01 to 5 parts by weight, respectively, based on 100 parts by weight of the water-soluble ethylenically unsaturated monomer.
The method of claim 1,
When the thermal polymerization initiator is added, a foaming agent and a surfactant are additionally added.
The method of claim 1,
The neutralizing agent comprises at least one selected from the group consisting of sodium hydroxide, potassium hydroxide and ammonium hydroxide.
The method of claim 1,
The neutralization is carried out such that the degree of neutralization of the water-soluble ethylenically unsaturated monomer is 50 to 90 mol%.
The method of claim 1,
The drying is carried out so that the moisture content of the dried body is 5% by weight or less at a temperature of 50 to 250°C.
The method of claim 1,
The surface crosslinking agent comprises 0.001 to 1 parts by weight of an epoxy compound, 0.01 to 2 parts by weight of a polyvalent metal salt, and 0.01 to 0.5 parts by weight of an inorganic filler based on 100 parts by weight of the base resin powder.
The method of claim 1,
The super absorbent polymer is a manufacturing method that satisfies the following conditions:
(i) Centrifugation water holding capacity (CRC) 30 to 35 g/g measured according to the EDANA method WSP 241.3;
(ii) pressure absorption capacity (AUP) of 0.7psi measured according to the EDANA method WSP 242.3-10 20 to 25 g/g,
(iii) Absorption rate of 55 seconds or less according to the Vortex measurement method
(iv) Dryness (After swelling the superabsorbent polymer with 200 g of tap water at 24° C. for 2 hours, put a filter paper on it, pressurized at a pressure of 0.75 psi for 1 minute, and then Weight measurement) 0.85g or less.