KR100258017B1 - Super absorbent resin - Google Patents

Abstract

PURPOSE: A highly absorptive resin for a composite surface treatment is provided to achieve improved absorptivity, absorption speed, and gel strength when it is applied to water or base solution. CONSTITUTION: The highly absorptive resin is manufactured through a surface treatment on acryl resin for a surface modifier, in which the surface modifier is prepared by co-polymerization of styrene ionomer(formula 1) or acryl ionomer(formula 2) and poly(styrene-ethyleneglycolacrylate), the copolymer of 50-95 mol% of styrene monomer and 5-50 mol% of ethyleneglycolacrylate. The styrene ionomer comprises sulfonated alkali matal ions or alkali earth metal ions by 3-20 mol% of styrene ionomer, and the acryl ionomer comprises acrylated alkali matal ions or alkali earth metal ions by 3-20 mol% of acryl ionomer. In addition, as for the composite surface treatment, the ratio of ionomer: poly(styrene-ethyleneglycolacrylate) is 20-80: 80-20 wt.%.

Description

Superabsorbent polymer

The present invention relates to a super absorbent polymer, and more particularly, by treating a surface of an acrylic resin prepared by crosslinking an acrylic acid monomer with a composite surface treatment agent containing an ionomer and a poly (styrene-ethylene glycol acrylate) copolymer, It not only improves the absorption and absorption rate of water or salt solution, but also synergistically improves the effect of improving gel strength upon absorption, and uses high molecular weight materials as surface treatment agents instead of toxic low molecular weight materials. The present invention relates to a new super absorbent polymer that can create a safe working environment.

Superabsorbent polymers have been widely used in the field of sanitary products such as paper diapers, sanitary napkins, etc., and have a wide range of applications. They are also used for industrial applications such as horticulture, construction, food, etc. It is a substance becoming.

Superabsorbent polymers are mainly produced by cross-linking three-dimensionally with water-soluble polymers such as acrylic acid, starch and methyl cellulose as main components.

The general process of preparing a super absorbent polymer by using acrylic acid as an example is as follows.

First, oxygen is removed while flowing high purity nitrogen (purity 99.99%) for 2 hours at a flow rate of 80 cc / min to a 500 cc reactor equipped with a nitrogen gas inlet, a cooler, and a stirrer. Then, an acrylic acid monomer, distilled water as a solvent, methylene bisacrylamide (MBA) as a crosslinking agent and potassium sulfate (K ₂ S0 ₄ ) as an initiator are quantified and injected into the reactor. Dissolved oxygen is removed while passing the injected reactant through a nitrogen gas, and the cooling water is flowed into the cooler while stirring the temperature of the reactor to 70 ℃ and stirred. At this time, if the reaction rate for 4 hours while lowering the flow rate of nitrogen injected into the reactor to 20cc / min, a gel having a conversion rate of 95% or more based on the acrylic acid monomer. Thereafter, 2N aqueous sodium hydroxide solution is added to neutralize about 70% of acrylic acid, and the neutralized gel is dried in an oven at 120 ° C. for 10 hours to obtain a white powder of acrylic resin.

Next, after dispersing the white powder of the acrylic resin obtained above in a solvent such as methanol, using a low molecular weight material such as hexamethylenediamine (surface treatment agent) to induce crosslinking on the surface and in the oven at 120 ℃ The surface crosslinking reaction is carried out while drying to obtain the desired superabsorbent polymer.

However, the acrylic superabsorbent polymer prepared by the above method has a high absorption of pure water, but has a problem of low absorption for a salt solution similar to an actual physiological solution. This is because the ionized salts included in the salt solution, that is, cations and anions, bind to the superabsorbent resin and then absorb water, thereby increasing the rigidity of the polymer chain and not expanding.

In order to make up for such drawbacks, many studies have been conducted mainly on the method of modifying the surface of the resin by changing the surface treatment agent component used for surface crosslinking of the super absorbent polymer.

As such an example, a method of modifying the surface of a super absorbent polymer using a hydrophobic substance as a secondary crosslinking agent is known (US Pat. No. 4,666,983). However, in this case, the absorption rate of the resin is improved, but the effect of absorption is not obtained. Also, since a toxic low molecular material such as diamine or diol is used as a crosslinking agent for surface treatment, there is a problem that is harmful to the human body. .

In addition, a method of using a single molecule compound such as barium acetate, aluminum acetate or cobalt acetate as a surface treatment cross-linking agent is known. There is no problem with this.

In addition, the present applicant has also filed a patent for a super absorbent polymer using a poly (styrene-ethylene glycol acrylate) copolymer and an ionomer as a surface treatment agent, respectively (Korean Patent Application Nos. 97-022294 and 97-022297). The acrylic resin using ionomer as a surface treatment agent showed a relatively increased absorption amount, and the acrylic resin using a poly (styrene-ethylene glycol acrylate) copolymer as the surface treatment agent exhibited a more improved absorption rate.

Accordingly, the present applicant has tried to develop a surface treatment agent that can improve the absorption amount and the absorption rate at the same time. As a result, when the respective surface treatment agents are used together, the absorption amount and absorption rate are improved at the same time. The present invention has been completed by knowing that it has effects that are typically beyond the predictable extent.

Therefore, the present invention uses a composite surface treatment agent mixed with an ionomer and a poly (styrene-ethylene glycol acrylate) copolymer to simultaneously improve the amount of absorption and the rate of absorption due to synergy of the two components, as well as solution absorption. The purpose of the present invention is to increase the strength of the gel that is formed and to provide a super absorbent polymer that is harmless to the human body.

The present invention is an acrylic resin prepared by crosslinking an acrylic monomer, characterized in that the superabsorbent polymer prepared by surface treatment of the resin surface with a composite surface treatment agent consisting of ionomer and poly (styrene-ethylene glycol acrylate). .

Referring to the present invention in more detail as follows.

The present invention is a composite surface treatment agent in which a poly (styrene-ethylene glycol acrylate) copolymer (hereinafter referred to as a "PSE copolymer") having an excellent effect of improving the absorption rate and an improvement in the absorption rate on the acrylic resin surface is excellent. By showing the unique properties of each component as well as the superabsorbent polymer to exhibit a more improved absorbency and absorption rate improvement effect by the synergy between each other.

The ionomer as a component of the composite surface treatment agent used in the present invention may be used as long as it has a chemical unit structure capable of ionizing. Representative ionomers include styrene-based ionomers represented by the following general formula (1) or acrylic ionomers represented by the general formula (2), all of which are known [US Patent No. 3,870,841].

In the above formulas, M is an alkali metal ion or alkaline earth metal ion; x is a rational number of 3-20.

The styrene-based ionomer represented by the formula (1) is styrene as a main chain and sulfonated metal ions are introduced into the side chain group, and the acrylic ionomer represented by the formula (2) is acrylic acid as the main chain to introduce acrylated metal ions. It has an ion unit structure which can adsorb | suck. The metal cation introduced into the side chain of the ionomer is one containing 3 to 20 mol% based on the total amount of the styrene or acrylic ionomer. In this case, if the content of the metal cation is less than 3 mol%, the effect of increasing the amount of absorption for the purpose of the present invention cannot be expected.

The reason for using these ionomers as a surface treatment agent is that when they are introduced by crosslinking reaction on the surface of the acrylic superabsorbent resin, the amount of the side chains is combined with the anions of the salt solution and immobilized when the salt solution is absorbed by the resin. Therefore, since the ion concentration of the salt solution actually absorbed is lowered, the amount of absorption increases accordingly.

In addition, the present invention uses PSE copolymer as another component of the composite surface treatment agent. PSE copolymer has lipophilic styrene as the backbone, and ethylene glycol acrylate having hydrophilicity is introduced into the pandant group. When the PSE copolymer is introduced on the surface of the acrylic resin, the lipophilic and hydrophilic properties are simultaneously applied to the surface of the resin to improve the absorption rate and the absorption power of the water and the salt solution, and gel blocking due to the lipophilic property of the surface treatment agent. Not only prevents the phenomenon, but also the hydroxyl of the ethylene glycol acrylate of the surface treatment agent and the carboxyl group of the acrylic acid on the surface of the resin react to form a covalent bond, thereby increasing the strength of the gel upon absorption by the surface crosslinking reaction by covalent bonding of the resin. Will have the advantage of increasing the effect.

In order to use such a co-polymer as a surface treatment agent, it is preferable that 50-95 mol%, especially 75-90 mol% of a styrene part is contained, and also 5-50 mol% of ethylene glycol acrylate as a long side chain group, It is preferable to contain 10-25 mol%. If the styrene content of the copolymer is less than 50 mol%, gel blocking occurs and the strength of the gel decreases. On the other hand, if the content exceeds 95 mol%, the surface crosslinking efficiency is poor. . In addition, if the content of ethylene glycol acrylate as the side chain group is less than 5 mol% is difficult to form a covalent bond is not good, crosslinking efficiency is not good, if containing more than 50 mol% there is a problem that the strength of the gel is lowered is also undesirable.

In the present invention, in the PSE copolymer which is a constituent of the composite surface treatment agent, a similar effect can be obtained by polymerizing with alpha styrene, methyl methacrylate or vinyl chloride in addition to the styrene monomer as a lipophilic monomer. have.

The composite surface treatment agent according to the present invention is a solution in which the ionomer and the PSE copolymer are dissolved, and an organic solvent such as tetrahydrofuran, methanol, or toluene is used as a solvent for dissolving these components. In addition, there is a slight difference in the absorption and absorption rate depending on the mixing ratio of the ionomer and the PSE copolymer. In order to obtain the maximum synergy effect according to the mixed use, the ionomer: PSE copolymer is 20 to 80:80 to 20% by weight. To mix.

Referring to the process for producing a super absorbent polymer by crosslinking the surface of the acrylic surface-based composite surface treatment agent as described above in detail as follows.

The first step is a step of synthesizing and drying the acrylic resin by the crosslinking polymerization reaction of the acrylic monomer.

Oxygen is removed while flowing high-purity nitrogen (nitrogen content 99.99%) at a flow rate of 80 cc / min in a 500 cc reactor equipped with a nitrogen gas inlet and a cooler stirrer. An acrylic acid monomer, distilled water as a solvent, methylene bisacrylamide or hexanediol diacrylate as a crosslinking agent, and potassium persulfate (K ₂ (S0 ₄ ) ₂ ) as an initiator are quantified and injected into the reactor. In this case, the content of the crosslinking agent is 0.05 to 1 mol%, more preferably 0.05 to 0.25 mol% based on the acrylic acid monomer. If the content of the crosslinking agent exceeds 1 mol%, there is a problem in that the amount of absorption decreases. If the content is less than 0.05 mol%, the strength of the gel is weak. Thereafter, dissolved oxygen is removed while passing through the nitrogen gas, and the cooling water is flowed through the cooler while raising the temperature of the reactor to 70 ° C. When the flow rate of nitrogen injected into the reactor was lowered to 20cc / min while reacting for 4 hours, the gel acrylic acid polymer having a conversion rate of 95% or more based on the acrylic acid monomer was synthesized.

Then, using 2N aqueous sodium hydroxide solution to neutralize 70% acrylic acid based on the total acrylic acid monomers. At this time, the selection of the neutralization method is important, and the neutralization method that can be applied to the present invention is a method of neutralizing all in the monomer state, a method of neutralizing 35% in the monomer state and 35% after the polymerization, or after the polymerization is completely completed. There is a way to neutralize. In the present invention, all of these polymerization methods can be applied. However, in consideration of the amount of absorption after the production, the method of polymerization after the polymerization is completely completed shows the best water absorption. Therefore, it is preferable to apply this method.

Thereafter, the neutralized gel is dried in an oven at 120 ° C. for 10 hours to obtain an acrylic resin in a white powder state.

The second step is a step of surface-treating the acrylic resin prepared above with a composite surface treatment agent consisting of an ionomer and a PSE copolymer.

First, the composite surface treating agent is a 1-50 w / v% solution in which an ionomer and a PSE copolymer are dissolved in a solvent such as toluene, and the surface crosslinking is obtained by dispersing the acrylic resin prepared in the first step in the composite surface treating agent solution. Let At this time, the surface crosslinking amount of the composite surface treatment agent is preferably in the range of 1 to 10 parts by weight with respect to the acrylic resin. If the amount of surface crosslinking is less than 1 part by weight, the gel strength is lowered. .

Then, when the solvent is volatilized while heating at a temperature of 70 to 120 ° C. for 30 to 100 minutes in a hot stirrer, an acryl-based superabsorbent polymer coated with a composite surface treatment agent consisting of ionomer and PSE copolymer is obtained. Can be.

The carboxyl groups of acrylic acid present on the resin surface in the heating process combine with the hydroxyl group of ethylene glycol acrylate to form a covalent bond, thereby maintaining the bond formed when water or salt solution is absorbed. By improving the strength and introducing a new hydrophilic group on the surface of the resin, not only the amount of water absorption of the resin is increased but also the rate of absorption is improved.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited by Examples.

[Production example]

[Synthesis of Complex Surface Treatment Agent]

(1) Synthesis of Ionomers

A styrene-based ionomer substituted with sodium sulfonate was prepared by a synthesis method as shown in US Pat. No. 3,870,841, and the substitution amount of the ionomer was prepared by changing the ion content within a range of 3 to 20 mol%.

(2) Synthesis of PSE Copolymer

Oxygen was removed while flowing high purity nitrogen (nitrogen content 99.99%) at a flow rate of 80 cc / min in a 500 cc reactor equipped with a nitrogen gas inlet, a cooler, and a stirrer. 80 mol% of styrene as a monomer and 20 mol% of ethylene glycol acrylate and toluene as a reaction medium were added 5 times based on the monomer volume, and 0.005 mol% of azobisbutyronitrile (AIBN) as an initiator was injected into the reactor. It was. Thereafter, dissolved oxygen was removed while passing through nitrogen gas, and cooling water was flowed through the cooler while raising the temperature of the reactor to 70 ° C. When starting the stirring, the flow rate of nitrogen injected into the reactor was lowered to 20 cc / min and reacted for 6 hours to synthesize a PSE copolymer having a copolymerization rate of 55% or more based on the styrene monomer. This was dropped in non-solvent methanol to produce a white precipitate, which was dried in a vacuum oven at 100 ° C. for about 10 hours to obtain a white PSE copolymer powder.

EXAMPLE

[Production of Acrylic Super Absorbent Polymer]

(1) Synthesis and Drying of Acrylic Resin

Oxygen was removed while flowing high purity nitrogen (nitrogen content 99.99%) at a flow rate of 80 cc / min in a 500 cc reactor equipped with a nitrogen gas inlet, a cooler, and a stirrer. 30 g of acrylic acid monomer, 100 ml of distilled water, and 0.1 mol% of crosslinking agent methylene bisacrylamide and 0.05 g of potassium persulfate were quantitatively injected into the reactor. Thereafter, dissolved oxygen was removed while passing through nitrogen gas, and the cooling water was flowed through the cooler while raising the temperature of the reactor to 70 ° C. While starting the stirring, the flow rate of nitrogen injected into the reactor was lowered to 20 cc / min and reacted for 4 hours to synthesize a gel-type acrylic acid polymer having a conversion rate of 95% based on the acrylic acid monomer. After the polymerization was terminated, 70% acrylic acid was neutralized based on the total amount of the acrylic acid monomers added using a 2N aqueous sodium hydroxide solution.

Thereafter, the neutralized gel was dried in an oven at 120 ° C. for 10 hours to obtain an acrylic acid resin in a white powder state.

(2) surface treatment process

The ionomer and PSE copolymer prepared in Preparation Example were dissolved in toluene, an organic solvent, to prepare a composite surface treatment solution. Then, the acrylic resin prepared above was dispersed in this solution.

Then, the solution was heated in a heating stirrer at 100 to 120 ° C. for 10 to 37 minutes to evaporate the solvent, thereby obtaining an acrylic superabsorbent polymer of the present invention coated with a copolymer and an ionomer.

Experimental Example

The absorption rate and absorption amount of the super absorbent polymer were measured by the following method. According to US Pat. No. 4,666,983, 0.2 g of an acrylic superabsorbent resin was placed in the center of a 11 × 11 cm nonwoven fabric, tied with a thread to form a tea bag, and then immersed in 0.9 wt% saline. Absorbance was measured by measuring the amount of absorption after 24 hours had elapsed.

In addition, the absorption rate was measured by standardizing the weight of the salt solution absorbed during the initial 1 minute with the weight of the super absorbent polymer.

Experimental Example 1

Styrene ionomer substituted by 10 mol% sulfonated natrium (Formula 1), poly (styrene-ethylene glycol acrylate) copolymer having a styrene monomer content of 78% mol in the surface treatment process for the acrylic resin in the above embodiment, and Each of the composite surface treatment agents contained in a 50:50 weight ratio was compared to 100 parts by weight of acrylic resin, and the absorption, absorption rate, and gel strength of the surface treated at 0, 1, 2.5, 5, and 10 parts by weight were compared. Shown in

Experimental Example 2

The acrylic ionomer substituted with 10 mol% of barium acrylate in the surface treatment process for the acrylic resin in the above embodiment, the poly (styrene-ethylene glycol acrylate) copolymer having a styrene monomer content of 90% mol, and 50:50 weight ratio Each of the composite surface treatment agents contained in the present invention was shown in Table 2 by comparing and measuring the absorption and absorption rates when surface treatment was performed at 0, 1, 2.5, 5, and 10 parts by weight based on 100 parts by weight of the acrylic resin.

As shown in Table 1 and Table 2, ionomers and poly (styrene-ethylene glycol acrylate) copolymers effective as surface modifiers were treated with a composite surface treatment agent mixed with each other in comparison with the case where they were used alone or It can be seen that there is an effect of improving the gel strength as well as the absorption and absorption rate of each of the salt solution.

Claims (5)

In the super absorbent polymer prepared by surface-treating acrylic resin with a surface modifier, the surface modifier may be a styrene ionomer represented by the following formula (1) or an acrylic ionomer represented by the following formula (2) and a poly (styrene-ethylene glycol acrylate) Superabsorbent polymer, characterized in that the copolymer is a mixed surface treatment agent. [Formula 1]

[Formula 2]

The superabsorbent polymer according to claim 1, wherein the styrene-based ionomer comprises 3 to 20 mol% of sulfonated alkali metal or alkaline earth metal ions with respect to the total amount of the styrene-based ionomer. The superabsorbent polymer according to claim 1, wherein the acrylic ionomer contains 3 to 20 mol% of the acrylic metal ion or alkaline earth metal ion based on the total amount of the acrylic ionomer. The superabsorbent polymer according to claim 1, wherein the composite surface treatment agent is a mixture of ionomer: poly (styrene-ethylene glycol acrylate) copolymer at 20 to 80:80 to 20 wt%. The superabsorbent polymer according to claim 1, wherein the poly (styrene-ethylene glycol acrylate) copolymer is a copolymer of 50 to 95 mol% of a styrene monomer and 5 to 50 mol% of an ethylene glycol acrylate monomer.