KR100212978B1 - Super absorbent acrylate resin coated with poly(styrene-etyleneglycol acrylate) copolymer - Google Patents

Abstract

The present invention relates to an acrylic superabsorbent polymer, and more particularly, a surface of an acrylic resin prepared by crosslinking an acrylic acid monomer is surface treated with a poly (styrene-ethylene glycol acrylate) copolymer to simultaneously introduce hydrophilicity and lipophilic property. In addition, the hydroxyl group 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 improving not only the absorption rate and the absorption rate of water or salt solution, but also the gel strength upon absorption. It relates to a new acrylic superabsorbent resin.

Description

Acrylic Super Absorbent Resin

The present invention relates to an acrylic superabsorbent polymer. More particularly, the surface of an acrylic resin prepared by crosslinking an acrylic acid monomer is surface treated with a poly (styrene-ethylene glycol acrylate) copolymer to simultaneously introduce hydrophilicity and lipophilic property. In addition, the hydroxyl group 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 improving not only the absorption rate and the absorption rate of water or salt solution, but also the gel strength upon absorption. It relates to a new acrylic superabsorbent resin.

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, and are also used for industrial applications such as horticulture, construction, food, etc. It is an expanding substance.

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

The manufacturing process of the super absorbent polymer will be briefly described by taking acrylic acid as an example. First, oxygen is removed while flowing high purity nitrogen (purity 99.99% or more) for 2 hours at a flow rate of 80 cc / min in 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 persulfate (K ₂ S ₂ O ₈ ) 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 20 cc / 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 substance 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.

The acrylic super absorbent polymer prepared by the above method has a large amount of pure water absorbed, but a small amount of absorbed water for a salt solution similar to the actual physiological liquid. 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.

U.S. Patent No. 4,666,983 discloses a method of modifying the surface of a superabsorbent resin using hydrophobic materials as secondary crosslinkers. In this case, the absorption rate of the resin is improved, but the effect of absorption is not obtained. Furthermore, since a toxic low molecular substance such as diamine or diol is used as the crosslinking agent for the surface treatment, it is harmful to the human body.

In addition, U.S. Patent No. 4,043,952 discloses a method of using a single molecule compound such as barium acetate, aluminum acetate or cobalt acetylacetate as a crosslinking agent for surface treatment. In this case, although the absorption rate is improved, there is a variation in the absorption amount. There was no.

MEANS TO SOLVE THE PROBLEM The present inventors apply | coated the surface of acrylic resin using the poly (styrene-ethylene glycol acrylate) (henceforth PSE) copolymer obtained by copolymerizing styrene and ethylene glycol acrylate as a surface treating agent, and the ethylene glycol acrylate terminal The hydroxyl group and the carboxyl groups on the resin surface react to form covalent bonds, thereby greatly improving the absorption rate and absorption amount of water or salt solution and increasing the strength of the gel by surface crosslinking by covalent bonds. Was completed.

Accordingly, an object of the present invention is to provide a new acrylic superabsorbent polymer that can simultaneously improve the absorption rate and the absorption amount using a PSE copolymer and also increase the strength of the gel formed upon solution absorption.

The present invention is an acrylic resin prepared by crosslinking an acrylic monomer, characterized in that an acrylic superabsorbent resin prepared by crosslinking a surface of the acrylic resin with a PSE copolymer.

When explaining the invention in more detail as follows.

According to the present invention, an acrylic resin is prepared by first crosslinking an acrylic acid monomer, and then the resin surface is crosslinked with a PSE copolymer so that the hydroxyl group of acrylic acid and ethylene glycol acrylate on the resin surface forms a covalent bond. The present invention relates to an acryl-based superabsorbent polymer capable of simultaneously improving the absorption rate and the absorbency of the polymer and increasing the strength of the gel formed upon absorption.

That is, the superabsorbent polymer according to the present invention introduces a PSE copolymer on the surface of the acrylic resin to impart lipophilic and hydrophilic properties at the same time, thereby improving the absorption rate and absorption power of water and salt solution due to the hydrophilicity of the surface treatment agent, and the surface Due to the lipophilic properties of the treatment agent, gel blocking is prevented and the strength of the gel is increased when absorbed by the surface crosslinking reaction by covalent bonding of the surface treatment agent and the resin.

In the present invention, the PSE copolymer used as the surface treating agent has styrene having lipophilic backbone and ethylene glycol acrylate having hydrophilicity is introduced into the pandant group. In order to use such a copolymer as a surface treatment agent, the styrene portion contains 50 to 95 mol%, preferably 75 to 90 mol%, and 5-50 mol% of ethylene glycol acrylate as the long side chain group, preferably 10 It is preferable to contain-25 mol%. If the styrene content in the copolymer is less than 50 mol% Gel Blocking (Gel Blocking) phenomenon occurs, the strength of the gel is reduced, if the content exceeds 95 mol% surface cross-linking efficiency is not good.

In the copolymer used as the surface treating agent in the present invention, similar effects can be obtained by using alphamethylstyrene, methyl methacrylate or vinyl chloride in addition to the styrene monomer as the lipophilic monomer.

Referring to the process for producing a super absorbent polymer by crosslinking the copolymer as described above to the acrylic resin surface 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 by flowing high-purity nitrogen (nitrogen content 99.99% or more) at a flow rate of 80 cc / min for 2 hours in a 500cc reactor equipped with a nitrogen gas inlet, a cooler, and a stirrer. An acrylic acid monomer, distilled water as a solvent, methylene bisacrylamide or hexanediol diacrylate as a crosslinking agent, and potassium persulfate (K ₂ S ₂ O ₈ ) as an initiator are quantified and injected into the reactor. At this time, 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 that the absorption amount is reduced, if the content is less than 0.05 mol% there is a problem that the strength of the gel is weak. Thereafter, dissolved oxygen is removed while passing through nitrogen gas, and the cooling water is 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 4 hours to synthesize gel acrylic acid polymer having a conversion rate of 95% or more based on the acrylic acid monomer.

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 for neutralizing all in the monomer state, a method of neutralizing 35% in the monomer state and 35% after the polymerization, or the polymerization is completed There is a way to neutralize later. In the present invention, all of these polymerization methods can be applied. However, in consideration of the amount of absorption after production, the method of polymerization after the polymerization is completely completed shows the best water absorption, and 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 copolymer.

First, the copolymer is dissolved in toluene to form a 1-50 w / v% solution, and the acrylic resin prepared in the first step is dispersed therein to perform surface crosslinking. At this time, the surface crosslinking amount of the copolymer is preferably in the range of 1 to 10 parts by weight with respect to the acrylic resin. If the surface crosslinking amount is less than 1 part by weight, the gel strength is lowered.

Then, when the solvent is volatilized while heating at 70 to 120 ° C. for 30 to 100 minutes in a heating stirrer, an acrylic superabsorbent polymer having a surface substituted with a PSE copolymer can be obtained.

The carboxyl group of acrylic acid present on the resin surface in the heating process combines with the hydroxyl group of ethylene glycol acrylate to form a covalent bond, and thus the strength of the gel formed while the bond is maintained when water or salt solution is actually absorbed. In addition, by introducing a new hydrophilic group on the surface of the resin, the amount of absorption of the resin is increased and at the same time the rate of absorption is improved.

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto.

Preparation Example: Preparation 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 form a white precipitate, which was dried in a vacuum oven at 100 ° C. for about 10 hours to obtain a white copolymer powder.

Example: Preparation of Acrylic Super Absorbent Resin

(1) Manufacturing process 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. Here, 30 g of acrylic acid monomer, 100 ml of distilled water, and 0.05 mol% of methylene bisacrylamide and 0.05 g of potassium persulfate were quantified based on the acrylic monomer and injected into the reactor. 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. While starting the stirring, the flow rate of nitrogen injected into the reactor was reduced 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 resin having a white powder.

(2) surface treatment

The PSE copolymer prepared in Preparation Example was dissolved in toluene to prepare a copolymer solution of 10 w / v%. The acrylic resin prepared above was dispersed in the copolymer solution, and then the solvent was volatilized while heating it at 100 ° C. for 45 minutes in a heating stirrer to obtain an acrylic superabsorbent polymer having a surface substituted with a PSE copolymer.

Experimental Example 1

In order to measure the absorption rate and the amount of absorption of the water absorbent resin according to the styrene monomer and ethylene glycol acrylate monomer content in the PSE copolymer used as the surface treatment agent, 2.5 parts by weight of the PSE copolymer having a different monomer content was surface treated. . The measurement results of the absorption rate and the absorption amount for each of these absorbent resins are shown in Table 1 below.

Measurement of Absorption Rate and Absorption Amount

0.2 g of acrylic superabsorbent polymer was placed in the center of a 11 x 11 cm nonwoven fabric, tied with a thread to form a tea bag, and then absorbed after 24 hours in 0.9 wt% saline. Absorbance was measured by weight. 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.

TABLE 1

Styrene Monomer (mol%) Ethylene glycol acrylate monomer (mol%) Absorption rate (g / g · min) Absorption amount (g / g) 95 5 50.8 73.8 90 10 54.7 74.0 85 15 57.2 74.2 78 23 51.5 72.0

Experimental Example 2

When the acrylic superabsorbent polymer was prepared using a PSE copolymer or a conventional hexamethylenediamine as the surface treating agent in the process of preparing the acrylic superabsorbent polymer of the above embodiment, the absorption rate and the amount of absorption according to the surface treatment were measured and the results are shown in Table 2 below. Indicated.

TABLE 2

Surface treatment agent throughput (parts by weight) Surface Treatment Type PSE copolymer Hexamethylenediamine Absorption rate (g / g · min) Absorption amount (g / g) Absorption rate (g / g · min) Absorption amount (g / g) 0 47.2 70.3 47.2 70.3 One 58.0 74.9 57.2 72.8 2.5 57.6 74.2 56.9 72.2 5 57.1 72.7 56.2 71.9 10 57.1 72.0 55.9 71.5

Experimental Example 3

Prepared in the same manner as in Example 1, the content of the primary crosslinking agent methylene bisacrylamide was prepared in 0.1 mol% based on the acrylic acid monomer to prepare a super absorbent polymer. Then, the absorption rate and the absorption amount were measured and shown in Table 3.

TABLE 3

Surface treatment agent throughput (parts by weight) Surface Treatment Type PSE copolymer Hexamethylenediamine Absorption rate (g / g · min) Absorption amount (g / g) Absorption rate (g / g · min) Absorption amount (g / g) 0 40.6 59.1 40.6 59.1 One 62.7 64.1 54.8 62.1 2.5 63.1 66.4 52.5 61.8 5 63.0 63.7 52.4 59.2 10 63.5 61.4 52.6 58.9

Experimental Example 4

It was prepared in the same manner as in the above example, except that the superabsorbent polymer was prepared based on the content of methylene bisacrylamide used as a crosslinking agent in the acrylic resin manufacturing process at 0.25 mol% based on the acrylic acid monomer. Then, the absorption rate and the absorption amount were measured in the same manner as in Experimental Example 1, and the results are shown in Table 4 below.

TABLE 4

Surface treatment agent throughput (parts by weight) Surface Treatment Type PSE copolymer Hexamethylenediamine Absorption rate (g / g · min) Absorption amount (g / g) Absorption rate (g / g · min) Absorption amount (g / g) 0 37.2 41.4 37.2 41.4 One 50.0 53.4 39.4 45.8 2.5 38.8 49.6 35.9 45.8 5 39.0 44.3 36.0 43.9 10 40.0 42.2 32.3 40.0

As described above, the present invention does not use toxic low-molecular weight diamine compounds or diol compounds as surface treating agents for producing superabsorbent polymers, and thus the manufacturing process thereof is environmentally friendly, and high molecular weight PSE air. The superabsorbent polymer of the present invention, surface-treated with coal, greatly improved the absorption rate and the amount of absorption and the gel strength upon solution absorption.

Claims (3)

An acrylic resin prepared by crosslinking an acrylic monomer, wherein the surface of the acrylic resin is prepared by recrosslinking with a poly (styrene-ethylene glycol acrylate) copolymer. The super absorbent polymer according to claim 1, wherein the poly (styrene-ethylene glycol acrylate) copolymer is a copolymer of 50 to 95 mol% of styrene monomer and 5 to 50 mol% of ethylene glycol acrylate monomer. The superabsorbent polymer according to claim 1, wherein the poly (styrene-ethylene glycol acrylate) copolymer is surface crosslinked to 1 to 10 parts by weight based on the acrylic resin.