KR20230144356A - Super absorbent polymer film and preparation method thereof - Google Patents

Abstract

The present invention relates to a method of manufacturing a superabsorbent polymer film. Specifically, the present invention relates to a superabsorbent polymer film that exhibits excellent absorption performance despite being thin, and particularly improved absorbency under pressure, and a method of manufacturing the same.

Description

Superabsorbent polymer film and manufacturing method thereof {SUPER ABSORBENT POLYMER FILM AND PREPARATION METHOD THEREOF}

The present invention relates to a superabsorbent polymer film and a method of manufacturing the same.

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

In general, sanitary products such as various diapers, sanitary napkins, or incontinence pads include absorbents containing superabsorbent resin particles. These absorbents mainly contain superabsorbent resin particles, and properly fix the superabsorbent resin particles while properly fixing the absorbents and sanitary products. It was common to use fluff pulp to maintain its shape.

However, due to the presence of such fluff pulp, it was difficult to slim and thin the absorber and sanitary product, and there was a problem of poor wearing comfort, such as sweat accumulating between the user's skin and the sanitary product. Moreover, since fluff pulp is mainly obtained from wood, it runs counter to the recent environmental protection trend, and the use of fluff pulp is also one of the main reasons for increasing the manufacturing cost of sanitary products.

In addition, most of the current superabsorbent resins are manufactured and used in powder form. These powdered superabsorbent resins have parts that can scatter or leak when manufacturing sanitary materials or during actual use, and are used as substrates of certain types. Because it must be used together with a substrate, there are limits to its range of use and thinning. In addition, because the absorption performance of the absorbent may vary depending on the content distribution of the superabsorbent polymer particles, it was difficult to uniformly control the absorption characteristics.

Accordingly, in order to solve the above problem, Korean Patent Publication No. 2021-0118762 proposed a film-type superabsorbent polymer. Superabsorbent resin film is a superabsorbent resin in the form of an ultra-thin transparent or translucent film with a thickness of about 0.5 mm or less. It has excellent absorption properties, high elasticity and flexibility, and can be used as an absorber by itself without auxiliaries such as fluff pulp. There are advantages to this. However, due to the flexible and continuous nature of the superabsorbent polymer film, there is a problem in that the absorbency under pressure is lower than that of the existing powdered superabsorbent resin, so improvement is needed.

Korean Public Patent No. 2021-0118762

In order to solve the above problems, the present invention provides a superabsorbent polymer film with improved absorbency under pressure and a method of manufacturing the same.

According to one embodiment of the present invention,

Preparing an acrylic acid-based monomer neutralizing solution by mixing an acrylic acid-based monomer, an alkaline substance, and a solvent;

Preparing a thickened neutralizing liquid by adding and mixing a cellulose-based thickener and colloidal silica containing silica particles surface-modified with epoxy silane to the acrylic acid-based monomer neutralizing liquid;

Preparing a monomer composition by adding and mixing a crosslinking agent, a moisturizing agent, and a polymerization initiator to the thickened neutralization liquid;

Casting the monomer composition onto a substrate to form a monomer composition film;

Forming a water-containing gel polymer film by irradiating heat and/or light while stretching the monomer composition film; and

A method for producing a superabsorbent polymer film is provided, including the step of drying the water-containing gel polymer film.

According to another embodiment of the present invention, an acrylic acid-based monomer having an acidic group and at least a portion of the acidic group is neutralized, colloidal silica including silica particles surface-modified with a crosslinking agent, a cellulose-based thickener, a moisturizing agent, and epoxy silane, and Provided is a superabsorbent resin film comprising a polymer polymerized in the presence of an initiator, and having an absorbency under pressure of 10 to 30 g/g measured according to the method of EDANA method WSP 242.2.

According to the present invention, it is possible to manufacture a superabsorbent polymer film that is thin but has excellent absorption performance, particularly improved absorbency under pressure.

The superabsorbent polymer film manufactured according to the present invention has no risk of scattering or leaking from the product during manufacturing, and does not require auxiliary agents such as fluff pulp, allowing the product to be thinner and reducing the manufacturing process and cost.

The terminology used herein is for the purpose of describing exemplary embodiments only and is not intended to limit the invention. Singular expressions include plural expressions unless the context clearly dictates otherwise. In this specification, terms such as “comprise,” “comprise,” or “have” are intended to designate the presence of implemented features, steps, components, or a combination thereof, and are intended to indicate the presence of one or more other features or steps, It should be understood that the existence or addition possibility of components or combinations thereof is not excluded in advance.

Since the present invention can be subject to various changes and can take various forms, specific embodiments will be illustrated and described in detail below. However, this is not intended to limit the present invention to a specific disclosed form, and should be understood to include all changes, equivalents, and substitutes included in the spirit and technical scope of the present invention.

Hereinafter, the present invention will be described in detail.

According to one embodiment of the present invention,

Preparing an acrylic acid-based monomer neutralizing solution by mixing an acrylic acid-based monomer, an alkaline substance, and a solvent;

Preparing a thickened neutralizing liquid by adding and mixing a cellulose-based thickener and colloidal silica containing silica particles surface-modified with epoxy silane to the acrylic acid-based monomer neutralizing liquid;

Preparing a monomer composition by adding and mixing a crosslinking agent, a moisturizing agent, and a polymerization initiator to the thickened neutralization liquid;

Casting the monomer composition onto a substrate to form a monomer composition film;

Forming a water-containing gel polymer film by irradiating heat and/or light while stretching the monomer composition film; and

A method for producing a superabsorbent polymer film is provided, including the step of drying the water-containing gel polymer film.

The superabsorbent polymer film manufactured according to the present invention has the form of a thin film rather than a powder, so there is no risk of scattering or leaking from the product when handled, and it can be used without additional auxiliaries such as fluff pulp, and has excellent absorption properties on its own. indicates. In particular, the superabsorbent polymer film manufactured according to the present invention contains fewer water-soluble components compared to existing superabsorbent polymer films, and exhibits excellent physical properties with improved gel strength, absorbency under pressure, and absorption speed.

In the present invention, the superabsorbent polymer film refers to a superabsorbent polymer that has a moisture content of 15% by weight or less, or 14% by weight or less, preferably 13% by weight or less, and takes the form of a flexible, thin layer or film. Preferably, the water content of the superabsorbent polymer film is 15% by weight or less, or 14% by weight or less, or 13% by weight or less, or 12% by weight or less, and 1% by weight or more, or 2% by weight or more, or 4% by weight. % or more, or may be 6 weight % or more.

Meanwhile, throughout this specification, “moisture content” is expressed as a percentage of the amount of moisture contained in the sample relative to the weight of the sample before drying. In other words, the water content can be calculated by subtracting the weight after drying the sample from the weight before drying the sample, dividing it by the weight before drying the sample, and then multiplying by 100. At this time, the drying conditions are to increase the temperature from room temperature to about 150 ℃ and then maintain it at 150 ℃, and the total drying time is set to 20 minutes, including 5 minutes for the temperature increase step.

The superabsorbent polymer film manufactured according to one embodiment of the present invention may have a moisture content of 15% or less, be colorless and transparent, have elasticity, and be in the form of a film with excellent flexibility.

The fact that the superabsorbent polymer film is transparent may mean that the total light transmittance for visible light is 88% or more when the thickness satisfies the range of 0.001 to 0.5 mm. The total light transmittance may theoretically be 100%, for example, may be 99% or less.

In addition, the superabsorbent polymer film of the present invention may have a yellow index of 2.6 or less, 2.5 or less, 2.4 or less, 2.3 or less, 1.9 or less, 1.6 or less, or 1.5 or less according to the ASTM D1925 standard in the thickness range of 0.001 to 0.5 mm. there is.

In the manufacturing method of the present invention, the monomer composition, which is the raw material of the superabsorbent polymer film, includes an acrylic acid-based monomer having an acidic group and at least a portion of the acidic group is neutralized, a cellulose-based thickener, a humectant, a polymerization initiator, colloidal silica, and a solvent. do.

The acrylic acid-based monomer is a compound represented by the following formula (1):

[Formula 1]

R ¹ -COOM ¹

In Formula 1,

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

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

Preferably, the acrylic acid-based monomer includes at least one selected from the group consisting of acrylic acid, methacrylic acid, and monovalent metal salts, divalent metal salts, ammonium salts, and organic amine salts thereof.

Here, the acrylic acid-based monomer may have an acidic group and at least a portion of the acidic group may be neutralized. Preferably, the monomer partially neutralized with an alkaline substance such as sodium hydroxide, potassium hydroxide, ammonium hydroxide, etc. may be used. At this time, the degree of neutralization of the acrylic acid-based monomer may be 40 to 95 mol%, or 40 to 80 mol%, or 45 to 75 mol%. The range of the degree of neutralization can be adjusted depending on the final physical properties. If the degree of neutralization is too high, neutralized monomers may precipitate, making it difficult for polymerization to proceed smoothly. Conversely, if the degree of neutralization is too low, the absorption capacity of the polymer may be greatly reduced.

In a preferred embodiment, the alkaline material may be sodium hydroxide (NaOH), potassium hydroxide (KOH), or a combination thereof. In particular, when potassium hydroxide is included as an alkaline material, a superabsorbent polymer film with better flexibility and dimensional stability can be manufactured.

The concentration of the acrylic acid-based monomer may be about 20 to about 60% by weight, preferably about 40 to about 50% by weight, based on the monomer composition including the raw material of the superabsorbent polymer and the solvent, and polymerization time and The concentration can be adjusted to an appropriate level considering reaction conditions, etc. However, if the concentration of the monomer is too low, the yield of the superabsorbent polymer may be low and problems may arise in economic feasibility. Conversely, if the concentration is too high, problems may occur in the process such as part of the monomer being precipitated, and the physical properties of the superabsorbent polymer may occur. This may deteriorate.

Meanwhile, in the present invention, a thickener and a moisturizer are included in the monomer composition so that the monomer composition can be applied in film form through a solution casting method.

By simultaneously containing a thickener and a humectant, the monomer composition of the present invention exhibits a viscosity suitable for casting into a film, can maintain an appropriate moisture content during the polymerization process after film casting, and the produced superabsorbent resin film has high flexibility. can indicate.

In the present invention, a cellulose-based thickener is used as a thickener, and specifically, it is selected from the group consisting of nanocellulose, hydroxyethylcellulose, hydroxypropylcellulose, hydroxyethylmethylcellulose, hydroxypropylmethylcellulose, and sodium carboxymethylcellulose. One or more types may be used. Preferably, nanocellulose, hydroxyethylcellulose, sodium carboxymethylcellulose, or a combination thereof may be used.

The cellulose-based thickener is present in an amount of 0.01 parts by weight or more, 0.1 parts by weight, 0.2 parts by weight, or 0.4 parts by weight or less, and 5 parts by weight or less, 3 parts by weight or less, and 1 part by weight or less, based on 100 parts by weight of solid content in the monomer composition. , or may be included in an amount of 0.9 parts by weight or less.

At this time, solid content in the monomer composition refers to all components of the composition excluding the solvent. That is, the solid content refers to the total content of acrylic acid-based monomer, an alkali substance for neutralizing acrylic acid-based monomer, cellulose-based thickener, moisturizer, cross-linking agent, thermal initiator, photoinitiator, colloidal silica, and other additives.

If the content of the cellulose-based thickener is less than 0.01 parts by weight based on 100 parts by weight of solid content in the monomer composition, sufficient thickening effect cannot be secured, making it difficult to manufacture a monomer composition film. Conversely, if it exceeds 5 parts by weight, the viscosity of the monomer composition may be excessive. The higher the film thickness, the thicker it becomes, and it may be difficult to control the film thickness uniformly.

The moisturizer may be any substance commonly used as a moisturizing ingredient in pharmaceuticals, cosmetics, chemical products, etc., without limitation. Examples of such humectants include at least one selected from the group consisting of polyhydric alcohols containing two or more hydroxy groups in the molecule, citric acid, and citrate salts.

Specifically, the polyhydric alcohol may be a polyhydric alcohol having 3 to 30 carbon atoms and containing 3 to 12 hydroxy groups in the molecule. In one example, the polyhydric alcohol is glycerin; diglycerin; ethylene glycol; propylene glycol; butylene glycol; sorbitol; polyethylene glycol; polyglycerin-3; polyglycerin-6; polyglycerin-10; and a group consisting of ester compounds of polyglycerin-10 and saturated fatty acids having 3 to 18 carbon atoms (e.g., polyglyceryl-10 distearate, polyglyceryl-10 oleate, polyglyceryl-10 laurate, etc.) There may be one or more types selected from the group consisting of glycerin, diglycerin, propylene glycol, and sorbitol, and one or more types selected from the group may be preferably used.

Additionally, citric acid and/or citric acid salts can be used as moisturizers. Examples of citric acid salts include triethyl citrate, methyl citrate, sodium citrate, and trisodium 2-methyl citrate.

The moisturizer is used in an amount of 5 parts by weight or more, 10 parts by weight, 20 parts by weight, or 30 parts by weight, and 70 parts by weight or less, 60 parts by weight, or 50 parts by weight or less, based on 100 parts by weight of acrylic acid-based monomer. It is desirable to be

If the content of the humectant is less than 5 parts by weight based on 100 parts by weight of acrylic acid-based monomer, the moisture content of the monomer composition film is insufficient, and the film may dry out or break during the subsequent polymerization and drying process, and the flexibility of the produced superabsorbent resin film may decrease. There is a problem that cannot be secured. Conversely, if the content of polyhydric alcohol exceeds 70 parts by weight based on 100 parts by weight of acrylic acid-based monomer, there may be a problem of lowering the absorption capacity of the superabsorbent polymer film. Therefore, it is desirable that the content of the humectant satisfies the above range.

The monomer composition includes a crosslinking agent for internal crosslinking of the polymer. The crosslinking agent may be one used in the production of conventional superabsorbent polymers. More specifically, the crosslinking agent includes a crosslinking agent having at least one functional group capable of reacting with the water-soluble substituent of the acrylic acid-based monomer and at least one ethylenically unsaturated group; Alternatively, a crosslinking agent having two or more functional groups that can react with the water-soluble substituent of the monomer and/or the water-soluble substituent formed by hydrolysis of the monomer may be used.

Specific examples of the cross-linking agent include bisacrylamide, bismethacrylamide, poly(meth)acrylate of polyol with 2 to 10 carbon atoms, or poly(meth)allyl ether of polyol with 2 to 10 carbon atoms, etc. Can be mentioned, more specifically, N, N'-methylenebis(meth)acrylate, ethyleneoxy(meth)acrylate, polyethyleneoxy(meth)acrylate, propyleneoxy(meth)acrylate, glycerin diacrylate. , glycerin triacrylate, trimethylene triacrylate, polyethylene glycol diacrylate, triallylamine, triallyl cyanurate, triallyl isocyanate, polyethylene glycol, diethylene glycol, and propylene glycol. You can use it. In one embodiment, polyethylene glycol diacrylate may be used as the crosslinking agent.

The cross-linking agent may be included in a concentration of 3000 ppm or less relative to the monomer composition to cross-link the polymerized polymer. In one embodiment, the cross-linking agent may be included in an amount of 10 ppm or more, 50 ppm or more, or 100 ppm or more, and 3000 ppm or less, 2500 ppm or less, or 2000 ppm or less.

The polymerization initiator used during polymerization in the method for producing a superabsorbent polymer film of the present invention is not particularly limited as long as it is generally used in the production of superabsorbent resin.

Specifically, the polymerization initiator may be a thermal polymerization initiator or a photopolymerization initiator based on UV irradiation depending on the polymerization method. However, even with the photopolymerization method, a certain amount of heat is generated by irradiation such as ultraviolet ray irradiation, and a certain amount of heat is also generated as the polymerization reaction, which is an exothermic reaction, progresses, so a thermal polymerization initiator may be additionally included. According to a preferred embodiment, a photopolymerization initiator and a thermal polymerization initiator may be used simultaneously as the polymerization initiator.

The photopolymerization initiator can be used without limitation in composition as long as it is a compound that can form radicals by light such as ultraviolet rays.

Examples of the photopolymerization initiator include benzoin ether, dialkyl acetophenone, hydroxyl alkylketone, phenyl glyoxylate, and benzyl dimethyl ketal. Ketal), acyl phosphine, and alpha-aminoketone (α-aminoketone) can be used. Meanwhile, specific examples of acylphosphine include commercially available lucirin TPO (2,4,6-Trimethylbenzoyldiphenylphosphine oxide) and Irgacure 819 (Phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide). For more information on photoinitiators, see Reinhold Schwalm's book "UV Coatings: Basics, Recent Developments and New Applications (Elsevier 2007)" p. 115, and is not limited to the examples described above.

The photopolymerization initiator may be included in an amount of 10 ppm or more, 20 ppm or more, or 40 ppm or more, and 2000 ppm or less, 1000 ppm or less, 500 ppm or less, or 100 ppm or less with respect to the monomer composition. 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 the physical properties may become non-uniform.

Additionally, the thermal polymerization initiator may be one or more selected from the group of initiators consisting of persulfate-based initiator, azo-based initiator, hydrogen peroxide, and ascorbic acid. Specifically, examples of persulfate-based initiators include sodium persulfate (Na ₂ S ₂ O ₈ ), potassium persulfate (K ₂ S ₂ O ₈ ), and ammonium persulfate (NH ₄ ). ₂ S ₂ O ₈ ), etc., and examples of azo-based initiators include 2,2-azobis(2-amidinopropane) dihydrochloride, 2 ,2-azobis-(N,N-dimethylene)isobutyramidine dihydrochloride (2,2-azobis-(N,N-dimethylene)isobutyramidine dihydrochloride), 2-(carbamoylazo)isobutyronitrile (2-(carbamoylazo)isobutylonitril), 2,2-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride (2,2-azobis[2-(2-imidazolin-2- yl)propane] dihydrochloride), 4,4-azobis-(4-cyanovaleric acid), etc. For more information on various thermal polymerization initiators, see Odian's book 'Principle of Polymerization (Wiley, 1981)', p. 203, and is not limited to the examples described above.

The thermal polymerization initiator may be included in the monomer composition in an amount of 10 ppm or more, 100 ppm or more, or 500 ppm or more, and 2000 ppm or less, 1500 ppm or less, or 1000 ppm or less. If the concentration of the thermal polymerization initiator is too low, no additional thermal polymerization occurs, so the effect of adding the thermal polymerization initiator may be minimal. If the concentration of the thermal polymerization initiator is too high, the molecular weight of the superabsorbent polymer may be small and the physical properties may become non-uniform. there is.

According to one embodiment of the present invention, colloidal silica containing silica particles surface-modified with epoxy silane is included as an additive in the monomer composition.

The colloidal silica refers to silica in which charged silica particles on the surface are stably dispersed in a solvent without precipitating or agglomerating.

Colloidal silica has the advantage of being more evenly dispersed in a monomer composition with high viscosity compared to silica powder, so colloidal silica is used as an additive in the present invention.

In particular, the colloidal silica used in the present invention includes silica particles whose surface has been modified with epoxy silane, and such colloidal silica has the effect of improving the pressure absorption capacity of the superabsorbent resin film due to additional reaction with acrylic acid. However, when using colloidal silica containing silica particles whose surface has not been modified or silica particles whose surface has been modified with a material other than epoxy silane, the effect of improving absorbency under pressure cannot be obtained.

In one embodiment of the present invention, the colloidal silica may be silica particles surface-modified with epoxy silane dispersed in water. Among the colloidal silicas, the content of silica surface-modified with epoxy silane may be 20% by weight or more, or 30% by weight or more, and 50% by weight or less, or 40% by weight or less.

The colloidal silica having the silica content is 1 part by weight or more, or 3 parts by weight, or 5 parts by weight, and 20 parts by weight or less, or 15 parts by weight or less, or 10 parts by weight, based on 100 parts by weight of acrylic acid-based monomer. It can be used in the following amounts. If the colloidal silica content is less than 1 part by weight based on 100 parts by weight of acrylic acid-based monomer, the effect of improving the absorbency under pressure of the superabsorbent polymer film cannot be sufficiently obtained, and if it exceeds 20 parts by weight, the water retention capacity is reduced or cured during the polymerization step. And there may be problems with not being filmed.

Meanwhile, the silica particles surface-modified with epoxy silane may have an average particle diameter of 1 nm or more, 5 nm or more, or 10 nm or more, and 20 nm or less, or 15 nm or less. If the average particle diameter of the silica particles is too small, the effect of improving absorbency under pressure cannot be obtained, and if it is too large, the average particle size of the silica particles is not evenly dispersed in the monomer composition, so it is preferable that the above range is satisfied.

The average particle size refers to the D50 particle size, that is, the particle size at 50% of the volume cumulative distribution according to the particle size. After the powder to be measured is dispersed in a dispersion medium, a commercially available laser diffraction particle size measurement device (e.g. Mastersizer 3000) is used. It can be measured by calculating the particle size distribution by measuring the difference in diffraction patterns depending on the particle size when the particles pass through the laser beam. Alternatively, the average particle diameter of the silica particles can be confirmed from the analysis data provided by the manufacturer.

In addition, the silica particles surface-modified with the epoxy silane have a BET specific surface area of 100 m ² /g or more, or 120 m ² /g, or 150 m ² /g or more, and 300 m ² /g or less, or 200 m ² It may be less than /g. When the BET specific surface area range is satisfied, it is preferable because the silica particles can be evenly dispersed in the monomer composition. However, if the specific surface area is too small or large, there may be problems in curing the monomer composition film during the polymerization step. The specific surface area can be measured using a BET specific surface area measuring device, or the specific surface area of the silica particles can be confirmed from analysis data provided by the manufacturer.

In the production method of the present invention, additives such as surfactants, plasticizers, storage stabilizers, and antioxidants may be further included as needed when preparing the monomer composition.

The surfactant may be added to further facilitate casting of the monomer composition. A polyether-modified siloxane-based surfactant can be used as the surfactant. When it is included, the monomer composition can be cast with a more uniform thickness, and even when applied to a continuous process such as a roll-to-roll process, it can be used at high speed without a separate process. A high-absorbent polymer film of uniform quality can be manufactured.

The polyether-modified siloxane-based surfactant is a surfactant containing a polyether chain at the end and/or side chain of the polysiloxane main chain. For example, the polyether-modified siloxane-based surfactant may include a polyethylene oxide group and/or a polypropylene oxide group.

These polyether-modified siloxane-based surfactants can be commercially available, for example, BYK-345, BYK-346, BYK-347, BYK-348, BYK-349, BYK-3450, BYK-3455, BYK- One or more types selected from the group consisting of 3456, BYK-3560, BYK-3565, and BYK-3760 can be used.

The content of the polyether-modified siloxane-based surfactant is 0.05 to 0.5 parts by weight based on 100 parts by weight of the monomer composition, or 0.1 part by weight or more, 0.15 parts by weight or more, or 0.2 parts by weight or more, and 0.45 parts by weight or less, 0.4 parts by weight or more. It may be more preferable that it is less than or equal to 0.35 parts by weight.

If the content of the polyether-modified siloxane-based surfactant is less than 0.05 parts by weight based on 100 parts by weight of the monomer composition, the effect of improving the coating properties of the monomer composition described above cannot be secured, and if it exceeds 0.5 parts by weight, the basic effect of the superabsorbent resin film produced Absorption capacity (initial absorption capacity, normal pressure absorption capacity, etc.) physical properties may be impaired. Accordingly, it is preferable that the polyether-modified siloxane-based surfactant is included in the above-mentioned range so as to exhibit excellent coating properties suitable for application to the roll-to-roll process, etc., while not damaging the physical properties of the final manufactured superabsorbent resin film.

The solvent can be used without limitation as long as it can dissolve the above-mentioned components, for example, water, ethanol, ethylene glycol, diethylene glycol, triethylene glycol, 1,4-butanediol, propylene glycol, ethylene glycol. Monobutyl ether, propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, methyl ethyl ketone, acetone, methyl amyl ketone, cyclohexanone, cyclopentanone, diethylene glycol monomethyl ether, diethylene glycol ethyl ether, toluene, One or more types selected from xylene, butyrolactone, carbitol, methylcellosolveacetate, and N,N-dimethylacetamide can be used in combination. For example, water can be used as the solvent.

In the present invention, the monomer composition includes a cellulose-based thickener and a humectant and exhibits a viscosity suitable for solution casting. Specifically, the viscosity of the monomer composition at 25°C is 100 mPa·s or more, 150 mPa·s or more, 200 mPa·s or more, or 300 mPa·s or more, and is 12,000 mPa·s or less, 5,000 mPa·s or less, It may be 3,000 mPa·s or less, 2,000 mPa·s or less, or 1,600 mPa·s or less. The viscosity of the monomer composition can be measured with a viscometer (for example, TV-22 from TOKI) under the conditions of spindle #1 and rotation speed of 1 rpm.

If the viscosity of the monomer composition is less than 100 mPa·s, it may be difficult to cast the monomer composition to a uniform thickness and polymerize it while stretching it. Conversely, if the viscosity of the monomer composition exceeds 12,000 mPa·s, it is difficult to manufacture a uniform monomer composition, the flowability of the monomer composition is low, resulting in poor processability, and it is difficult to defoame, which is not preferable.

In the present invention, so that colloidal silica can be evenly dispersed without agglomerating in a high-viscosity monomer composition, first, a cellulose-based thickener and colloidal silica are added to the acrylic acid-based monomer neutralization liquid to sufficiently disperse, and then the remaining raw materials included in the monomer composition are added. Mix to prepare a monomer composition.

The acrylic acid-based monomer neutralizing liquid can be prepared by mixing an acrylic acid-based monomer, an alkaline substance capable of neutralizing it, and a solvent.

Next, the cellulose-based thickener and the colloidal silica described above are added to the acrylic acid-based monomer neutralization solution and mixed to prepare a thickened neutralization solution in which silica particles are evenly dispersed. When the remaining raw materials are added to the thickened neutralizing liquid prepared in this way to prepare the monomer composition, the dispersibility of silica in the high-viscosity monomer composition is greatly improved compared to the case of mixing the raw materials at once, so the pressurization of the produced superabsorbent resin film The effect of improving absorption capacity can be maximized.

In order to ensure the above effect, mixing in the thickening neutralizing liquid preparation step may be performed using a high shear mixer. The type of high shear mixer that can be used is not particularly limited, and for example, it can be mixed using devices such as an in-line high shear mixer, high shear batch mixer, or homogenizer. It can be done.

When mixing using the high shear mixer, the mixing speed may be 5,000 rpm or more, or 7,000 rpm or more, or 8,000 rpm or more, and 10,000 rpm or less, or 9,000 rpm or less. If the mixing speed is less than 5,000 rpm, it may be difficult to evenly disperse silica particles in a thickened neutralizing liquid with high viscosity, and if it exceeds 10,000 rpm, there may be problems with heat generation and overdispersion.

Meanwhile, under the above conditions, high shear mixing may be performed for 10 minutes or more, or 20 minutes or more, and 50 minutes or less, or 30 minutes or less, but is not limited thereto, and may be mixed depending on the shear mixing conditions and equipment used. Time can be adjusted appropriately.

After obtaining a thickened neutralizing liquid in which colloidal silica is evenly dispersed as described above, a cross-linking agent, a humectant, a polymerization initiator, and other additives are added to the thickening neutralizing liquid and mixed, and finally a monomer composition having the above-mentioned viscosity range is prepared. can do.

Next, the monomer composition is cast on a substrate to prepare a monomer composition film, which is stretched and polymerized to form a water-containing gel polymer film. The casting and polymerization process of this monomer composition can be performed continuously through a roll-to-roll process. In particular, when a modified siloxane-based surfactant is included in the monomer composition, the application of the monomer composition can be more smooth, making it more suitable for continuous processes that proceed at high speed.

The material of the substrate is not particularly limited, but it is preferable to use a material that facilitates the application of the monomer composition and allows the hydrogel polymer film to be easily separated after polymerization.

Specifically, the substrate may be a polyethylene terephthalate (PET) film, which is commonly used as a release film, and has at least one surface hydrophobically treated with silicon or fluorine. For example, the substrate may be a PET film surface-treated with a siloxane-based polymer or polytetrafluoroethylene (Teflon ^® ). However, the material of the base material is not limited to this, and a suitable base material can be selected depending on the composition and properties of the monomer composition.

For example, the PET film whose surface is hydrophobically treated may have a contact angle with water of 105° to 110° and a surface energy of 20 to 25 mN/m. Such hydrophobically treated PET film not only facilitates application of the monomer composition film, but also facilitates peeling of the hydrogel polymer film produced after polymerization, thereby improving the convenience of the manufacturing process. In particular, when the monomer composition includes the above-described polyether-modified siloxane-based surfactant, the affinity with the hydrophobically treated PET film having the above-mentioned contact angle and surface energy characteristics is higher, so that casting with a uniform thickness is possible. Even in a roll-to-roll continuous process, a uniform and thin film can be formed, further improving productivity.

Meanwhile, unlike the general solution casting method of polymers in which the solvent is removed after casting the polymer solution, in the present invention, after the monomer composition is applied to the substrate, stretching and polymerization processes are immediately performed to prevent the moisture content from decreasing.

If the water content of the monomer composition film is too low, components constituting the monomer composition may precipitate before polymerization, and there may be a problem of the film breaking up after polymerization. Accordingly, the moisture content of the monomer composition film preferably satisfies the range of 30% by weight to 60% by weight, and preferably satisfies the range of 30% by weight to 50% by weight, or 30% by weight to 45% by weight.

The thickness of the monomer composition film can be appropriately adjusted depending on the thickness of the desired superabsorbent polymer film. The thickness of the monomer composition film changes little during the polymerization stage, but the thickness may decrease by about 10 to 40% or 15 to 35% as the moisture content decreases during the drying process of the hydrogel polymer film after polymerization. Taking this into account, A monomer composition film is prepared to an appropriate thickness.

For example, the thickness of the monomer composition film may be 0.8 mm or less, 0.6 mm or less, or 0.5 mm or less, and may be 0.001 mm or more, or 0.01 mm or more, but is not limited thereto, and may be used in the composition, polymerization, or drying steps of the monomer composition. It can be appropriately adjusted depending on the specific conditions and the desired thickness of the superabsorbent polymer film.

Next, a polymerization reaction is performed by irradiating heat and/or light while stretching the monomer composition film in the machine direction (MD direction) to form a water-containing gel polymer film. In this way, mechanical properties such as flexibility and strength of the hydrogel polymer film produced by stretching the film during polymerization can be adjusted.

At this time, the tension applied to the monomer composition film is 40 N/m or more, or 45 N/m or more, or 50 N/m or more, or 60 N/m or more and 100 N/m or less, or 90 N/m or less, or It may be less than 80 N/m. If stretching is applied with too much tension, the monomer composition film may break or become too thin, and if the tension is too small, mechanical properties such as flexibility and strength may not be secured.

The temperature during polymerization can be appropriately adjusted depending on the composition of the monomer composition, but is preferably above 40°C or 50°C for smooth reaction progress. Additionally, if the temperature is too high, the solvent may evaporate and components constituting the monomer composition may precipitate, so the polymerization temperature is preferably 90°C or lower, or 80°C or lower.

The water content of the hydrogel polymer film prepared through the polymerization step is about 20% by weight or more, preferably 25% by weight or more, and may be 40% by weight or less, or 35% by weight or less. Accordingly, the water-containing gel polymer film is dried to prepare the final superabsorbent polymer film.

The temperature of the drying step may preferably be in the range of 80 to 150 °C, or 90 to 120 °C.

In addition, by drying within the above temperature range for about 5 to 30 minutes, the moisture content is 15% by weight or less, or 12% by weight or less, or 10% by weight or less, or 9% by weight or less, and 1% by weight or more, or 2% by weight or more. , or 4% by weight or more, or 6% by weight or more, a superabsorbent polymer film can be obtained.

The superabsorbent polymer film of the present invention has a thickness of 0.5 mm or less and does not require separate auxiliaries, so it can create a thinner absorber than existing powder-type superabsorbent resins. Preferably, the thickness of the superabsorbent polymer film is 0.5 mm or less, or 0.4 mm or less, or 0.3 mm or less, or 0.2 mm or less, or 0.1 mm or less, and 0.001 mm or more, or 0.005 mm or more, or 0.01 mm or more, or 0.05 mm or less. It may be more than mm.

The superabsorbent polymer film manufactured according to the present invention exhibits excellent absorption performance despite being thin, and in particular, exhibits excellent absorbency under pressure compared to existing superabsorbent polymer films.

Specifically, the superabsorbent polymer film has an absorbency under pressure (AUP) under 0.7 psi measured according to EDANA method WSP 242.2 of 10 g/g or more, or 12 g/g or more, or 13 g/g or more, and 30 g/g/g/g. It exhibits excellent absorption properties at g or less, or 25 g/g or less, or 20 g/g or less.

The method for measuring the absorbency under pressure of the superabsorbent polymer film can be specified in the examples below.

The superabsorbent polymer film of the present invention not only has excellent absorption performance, but also has excellent flexibility and elasticity, and is used in various applications such as waterproofing and reinforcing materials such as bars, diapers, wires and cables, electrolyte absorbers, flame retardants, wound protectants, food freshness retainers, and soil repair materials. It can be used for various purposes.

The shape of the superabsorbent polymer film is not particularly limited as long as the thickness is 0.5 mm or less. That is, the superabsorbent polymer film may be in the form of a flat film with no irregularities on the surface and a constant thickness, or may have a pattern formed on the surface to improve the flowability of liquid. At this time, the shape of the pattern is not particularly limited, and the pattern can be formed by variously adjusting the length, width, depth, etc. of the recessed portion and the convex portion as needed.

Preferred examples are presented below to aid understanding of the present invention. However, the following examples are merely illustrative of the present invention, and it is clear to those skilled in the art that various changes and modifications can be made within the scope and spirit of the present invention. It is natural that changes and modifications fall within the scope of the attached patent claims.

[Example]

Example 1

A superabsorbent polymer film was prepared using colloidal silica, Levasil CC401 (CAS no. 1239225-81-0) from Nouryon, using the following method. Levasil CC401 is an aqueous dispersion of silica particles surface-modified with epoxy silane. The silica content is 37% by weight, the average particle diameter of the silica particles is 12 nm, and the BET specific surface area of the silica particles is 200 m ² /g.

First, 55 g of acrylic acid, 66.6 g of a 45% by weight solution of potassium hydroxide (KOH), and 55 g of water were mixed to prepare a neutralization solution in which 70 mol% of acrylic acid was neutralized.

Hydroxyethylcellulose (HEC, Ashland's Natrosol 250HR) as a thickener was added to the neutralization liquid in an amount of 0.45 parts by weight based on 100 parts by weight of solid content of the final monomer composition, and the colloidal silica was added in an amount of 5 parts by weight based on 100 parts by weight of acrylic acid. After addition, high shear mixing was performed at 8,000 rpm for 20 minutes using an in-line high shear mixer (verso high shear in-line mixer from Silveron).

Polyethylene glycol diacrylate (PEGDA, MW=400, Aldrich) as a crosslinking agent, glycerin as a moisturizing agent, sodium persulfate as a thermal polymerization initiator, and Irgacure 819 as a photopolymerization initiator were added to the mixed solution so that the solid content (TSC) was 54% by weight. A phosphorus monomer composition was prepared.

When preparing the monomer composition, 40 parts by weight of glycerin was added based on 100 parts by weight of acrylic acid, 1000 ppm of thermal polymerization initiator, 80 ppm of photopolymerization initiator, and 750 ppm of crosslinking agent were added based on the total weight of the monomer composition.

The viscosity of the prepared monomer composition at 25°C was measured using a TOKI viscometer (TV-22) at 1 rpm, spindle #1. As a result, the viscosity of the monomer composition was confirmed to be 700 mPa·s.

Next, the monomer composition was cast on one side of a polyethylene terephthalate (PET) release film (Mitsubishi MRL film) whose surface was hydrophobically treated with a siloxane-based polymer to form a 0.18 mm thick monomer composition film (moisture content: 30%). . A comma coater (Gap 500 ㎛) was used for the casting, and the moving speed of the applicator roll was set at 0.3 m/min.

Then, polymerization was performed on the monomer composition film by irradiating ultraviolet rays of 370 mJ/cm ² to form a water-containing gel polymer film. At this time, the polymerization reaction was carried out by stretching the monomer composition film by applying a tension of 60 N/m in the MD direction. The thickness of the prepared hydrogel polymer film was 0.18 mm, and it was confirmed that there was no significant change compared to the monomer composition, and the moisture content was 30% by weight.

Next, the prepared hydrogel polymer film was dried at a temperature of 110°C for 10 minutes to obtain a moisture content of 10% by weight, A rectangular superabsorbent polymer film (SAP film) with a thickness of 0.13 mm, a width of 300 mm, and a height of 400 mm was manufactured.

Examples 2 to 5 and Comparative Examples 1 to 2

A superabsorbent polymer film was prepared in the same manner as Example 1, except that the colloidal silica content and the thickness of the superabsorbent polymer film were changed as shown in Table 1 below.

In Table 1 below, the content of colloidal silica is expressed as parts by weight based on 100 parts by weight of acrylic acid.

Comparative Example 3

A superabsorbent polymer film was prepared in the same manner as in Example 1, except that Levasil CA316 PDL (Nouryon), an aqueous dispersion of silica particles without surface modification, was used as colloidal silica. The silica content of Levasil CA316 PDL is 30% by weight, and the BET specific surface area of silica particles is 200 m ² /g.

Comparative Example 4

A superabsorbent polymer film was prepared in the same manner as in Example 1, except that Levasil CT16 APL (Nouryon), an aqueous dispersion of silica particles surface-modified with aluminum, was used as colloidal silica. The silica content of Levasil CT16 APL is 30% by weight, and the BET specific surface area of silica particles is 210 m ² /g.

Comparative Example 5

When preparing the monomer composition, the thickener, colloidal silica, crosslinking agent, moisturizer, thermal polymerization initiator, and photopolymerization initiator were added to the neutralization solution at the same time and mixed at 300 rpm using a mechanical mixer to prepare the monomer composition.

Afterwards, a superabsorbent polymer film was prepared in the same manner as Example 1 using the monomer composition.

Experiment example

Hereinafter, the physical properties of the superabsorbent polymer films of Examples and Comparative Examples were measured by the following method.

(1) Thickness of superabsorbent polymer film

Using a film thickness gauge from Mitutoyo, the thickness was measured at three different random positions within the superabsorbent polymer film, and the average value was calculated.

(2) Moisture content

The moisture content was calculated from the weight before drying (a) and the weight after drying (b) of the superabsorbent polymer film. At this time, drying of the specimen was performed by raising the temperature from room temperature (25 ℃) to 150 ℃ over 5 minutes and then maintaining it at 150 ℃ for 15 minutes.

Moisture content (%) = (a-b)/a*100

(3) Water-soluble components (EC, weight%)

Water-soluble components (EC) were measured according to the method of EDANA method WSP 270.2.

Specifically, the superabsorbent polymer film was cut to weigh 1.0 g. 200 g was placed in a 0.9 wt% NaCl solution and soaked for 16 hours while stirring at 500 rpm, and then the aqueous solution was filtered through filter paper. The filtered solution was first titrated to pH 10.0 with a 0.1 N caustic soda solution, then back-titrated to pH 2.7 with a 0.1 N hydrogen chloride solution, and the uncrosslinked polymer material was calculated as a water-soluble component from the amount required for neutralization. Measured.

(4) Centrifugation retention capacity (CRC, g/g)

Centrifugation retention capacity (CRC) was measured according to the EDANA method WSP 241.2. The water content of the superabsorbent polymer films of each Example and Comparative Example to be measured is as shown in Table 1 below, and the water retention capacity was measured by centrifugation without additional water content adjustment.

Specifically, the superabsorbent polymer film was cut to have a weight (W0) of 0.08 to 0.12 g, placed in a non-woven bag, sealed, and submerged in a 0.9% by weight aqueous sodium chloride solution (physiological saline solution) at room temperature. After 30 minutes, water was removed from the bag for 3 minutes under conditions of 250G using a centrifuge, and the mass W2 (g) of the bag was measured. In addition, after the same operation was performed without using the resin, the mass W1 (g) at that time was measured. Using each obtained mass, CRC (g/g) was calculated according to the following equation.

CRC (g/g) = {[W2(g) - W1(g)]/W0(g)} - 1

(5) Absorbency under pressure (AUP, g/g)

The absorbency under pressure (AUP) under 0.7 psi was measured according to the EDANA method WSP 242.2. The water content of the superabsorbent polymer films of each Example and Comparative Example to be measured is as shown in Table 1 below, and the absorbency under pressure was measured without separate moisture content adjustment.

Specifically, a stainless steel 400 mesh wire mesh was mounted on the bottom of a plastic cylinder with an inner diameter of 25 mm. Under the conditions of room temperature and 50% humidity, the absorbent resin film is cut and placed on a wire mesh to a weight (W3) of 0.6 g, and the piston, which can evenly apply a load of 0.7 psi, has an outer diameter of slightly less than 25 mm. It is small and has no gaps with the inner wall of the cylinder, and the up and down movement is not hindered. At this time, the weight W4 (g) of the device was measured.

A glass filter with a diameter of 90 mm and a thickness of 5 mm was placed inside a petro dish with a diameter of 150 mm, and a physiological saline solution consisting of 0.9 wt% sodium chloride was placed at the same level as the upper surface of the glass filter. A sheet of filter paper with a diameter of 90 mm was placed on top of it. The measuring device was placed on filter paper, and the liquid was absorbed for 1 hour under load. After 1 hour, the measuring device was lifted and the weight W5 (g) was measured.

Using each obtained mass, the absorbency under pressure (g/g) was calculated according to the following equation.

AUP(g/g) = [W5(g) - W4(g)]/W3(g)

Colloidal silica content* SAP film thickness (mm) SAP film moisture content (%) EC (%) CRC (g/g) AUP(g/g) Comparative Example 1 0 0.13 10 9.9 30.2 10.7 Example 1 5 0.13 10 9.4 29.6 13.4 Example 2 10 0.13 10 9.1 28.5 13.1 Comparative Example 2 0 0.2 10 21.4 35.0 11.7 Example 3 One 0.2 10 20.6 34.2 12.8 Example 4 5 0.2 10 19.8 30.6 14.4 Example 5 10 0.2 10 19.1 30.4 14.3 Comparative Example 3 5 0.13 10 10.1 28.9 10.9 Comparative Example 4 5 0.13 10 10.5 28.6 11.1 Comparative Example 5 5 0.13 10 10.3 28.3 10.5

* Parts by weight compared to 100 parts by weight of acrylic acid

Referring to Table 1, when the thickness of the superabsorbent polymer film is the same, compared to the case without colloidal silica, the superabsorbent polymer film of the example prepared according to the present invention has a similar level of water-soluble component amount and centrifugal water retention capacity. It can be confirmed that it exhibits excellent pressure absorption capacity of at least 9.4% or more.

This effect of improving absorbency under pressure can be obtained when using colloidal silica containing silica particles surface-modified with epoxy silane, and when using colloidal silica containing silica particles without surface modification or silica particles surface-modified with a material other than epoxy silane, pressurized It can be confirmed from Comparative Examples 3 and 4 that the effect of improving absorption capacity cannot be obtained.

In addition, it can be confirmed through Comparative Example 5 that in the case of the comparative example in which colloidal silica was mixed with other raw materials at once without pre-dispersing it with the thickener, the effect of improving the absorbency under pressure could not be obtained because the silica was not properly dispersed.

Claims (10)

Preparing an acrylic acid-based monomer neutralizing solution by mixing an acrylic acid-based monomer, an alkaline substance, and a solvent;
Preparing a thickened neutralizing liquid by adding and mixing a cellulose-based thickener and colloidal silica containing silica particles surface-modified with epoxy silane to the acrylic acid-based monomer neutralizing liquid;
Preparing a monomer composition by adding and mixing a crosslinking agent, a moisturizing agent, and a polymerization initiator to the thickened neutralization liquid;
Casting the monomer composition onto a substrate to form a monomer composition film;
Forming a water-containing gel polymer film by irradiating heat and/or light while stretching the monomer composition film; and
A method for producing a superabsorbent polymer film comprising drying the water-containing gel polymer film.
According to paragraph 1,
The colloidal silica is a method of producing a superabsorbent polymer film in which the content of silica surface-modified with epoxy silane is 20 to 50% by weight.
According to paragraph 2,
A method of producing a superabsorbent resin film wherein the colloidal silica is contained in an amount of 1 to 20 parts by weight based on 100 parts by weight of acrylic acid-based monomer.
According to paragraph 1,
A method of producing a superabsorbent polymer film in which the silica particles surface-modified with the epoxy silane have an average particle diameter of 1 to 20 nm.
According to paragraph 1,
A method of producing a superabsorbent polymer film in which the silica particles surface-modified with the epoxy silane have a specific surface area of 100 to 300 m ² /g.
According to paragraph 1,
A method of producing a superabsorbent polymer film, wherein mixing in the thickening neutralizing liquid preparation step is performed under conditions of 5,000 to 10,000 rpm using a high shear mixer.
According to paragraph 1,
The cellulose-based thickener is included in an amount of 0.01 to 5 parts by weight based on 100 parts by weight of solid content in the monomer composition,
A method for producing a superabsorbent resin film, wherein the moisturizing agent is included in an amount of 5 to 70 parts by weight based on 100 parts by weight of acrylic acid-based monomer.
According to paragraph 1,
In the step of forming the hydrogel polymer film, the tension applied to the monomer composition film is 40 to 100 N/m.
According to paragraph 1,
A method of producing a superabsorbent polymer film wherein the temperature of the step of forming the hydrogel polymer film is 40 to 90 ℃, and the temperature of the drying step is 80 to 150 ℃.
An acrylic acid-based monomer having an acidic group and at least a portion of the acidic group is neutralized, a crosslinking agent, a cellulose-based thickener, a humectant, colloidal silica including silica particles surface-modified with epoxy silane, and a polymer polymerized in the presence of an initiator. As a superabsorbent resin film,
A superabsorbent polymer film having a pressure absorption capacity of 10 to 30 g/g under 0.7 psi measured according to the method of EDANA method WSP 242.2.