KR102173028B1 - Preparation method for super absorbent polymer - Google Patents

Abstract

The present invention relates to a method for producing a super absorbent polymer. According to the present invention, a super absorbent polymer having an excellent morphology can be manufactured with a simple process and high efficiency.

Description

Manufacturing method of super absorbent polymer TECHNICAL FIELD {PREPARATION METHOD FOR SUPER ABSORBENT POLYMER}

The present invention relates to a method for producing a super absorbent polymer. More specifically, it relates to a method for producing a super absorbent polymer capable of producing a super absorbent polymer having an excellent morphology with a simple process and high efficiency.

Super Absorbent Polymer (SAP) is a synthetic polymer material that can absorb moisture of 500 to 1,000 times its own weight, and each developer has a Super Absorbency Material (SAM), AGM (Absorbent Gel). Material) and so on. Since the above superabsorbent resins have begun to be put into practical use as sanitary tools, nowadays, in addition to hygiene products such as paper diapers for children, soil repair agents for horticultural use, water resistant materials for civil engineering and construction, sheets for seedlings, freshness maintenance agents in the food distribution field, and It is widely used as a material for poultice.

The super absorbent polymer can be prepared by various polymerization methods such as solution polymerization, reverse suspension polymerization, reverse phase emulsion, dispersion polymerization, and photopolymerization. Among them, the solution polymerization method and the reverse phase suspension polymerization method are most commonly used. The hydrogel polymer obtained by solution polymerization generally undergoes drying, pulverization and classification steps.The polymer powder obtained after the final pulverization step has a large size distribution and non-uniform shape with a weight average diameter, and the polymerization heat generated in bulk polymerization can be controlled. Because it is difficult, the physical properties of the super absorbent polymer may be deteriorated.

The reverse phase suspension polymerization method of superabsorbent resin disclosed in Japanese Patent Publication No. 56-161408, Japanese Patent Publication No. 57-158209, and Japanese Patent Publication No. 57-198714 does not have a pulverization screening process, so post-treatment is simple, but the particle diameter is several hundred µm or more. If this is the case, there is a disadvantage in that it is difficult to obtain uniform particles. In addition, a suspending agent is used to stabilize droplets in a thermodynamically unstable state, but the suspending agent is difficult to remove and may cause problems such as causing skin troubles during product use.

As another method for producing a spherical superabsorbent polymer without a grinding process, a method of polymerizing falling monomer droplets in a gas phase is known, for example, in US Patent Nos. 8,529,805 and 7,727,586. However, since the dropping speed of droplets in the gas phase is very fast, the height of the reactor is increased to send a complete polymerization reaction, and evaporation, aggregation and separation of droplets easily occur while droplets are falling, making it difficult to precisely control the size, shape, and structure of the particles. .

In addition, Chinese Laid-Open Patent No. 103360538 discloses a method of preparing a spherical superabsorbent polymer by precipitating a monomer composition in methyl-silicone oil or epoxy soybean oil through a dripper. . However, in the method disclosed in the Chinese Patent Publication, since droplets are generated by simple dripping, the generation frequency per nozzle is too low, making it difficult to produce on a commercial scale. In addition, since the size of the droplets that can be produced is determined according to the size of the nozzle, it is difficult to obtain particles of various sizes from one device, and the diameter of the obtained superabsorbent resin is 1 to 20 mm, which is too large to be applied directly to the product. There are drawbacks.

In order to solve the problems of the prior art as described above, the present invention is polymerized by a polymerization method by oil-phase sedimentation, and the particle size is less than 1 mm, and the uniformity of circularity and particle size distribution is very high, so that a super absorbent polymer having excellent morphology is obtained. It is an object of the present invention to provide a method that can be manufactured with high productivity.

In order to achieve the above object, one aspect of the present invention,

Preparing a monomer composition comprising an acrylic acid-based monomer having an acidic group and at least a part of the acidic group is neutralized;

Generating droplets by applying vibration to the monomer composition;

Polymerizing the droplets of the monomer composition while sedimenting them into an oil phase to form a hydrogel polymer; And

Drying the hydrogel polymer to form a super absorbent polymer having an average particle diameter (d50) of 100 to 900 μm;

It provides a method for producing a super absorbent polymer comprising a.

According to the method of manufacturing a super absorbent polymer of the present invention, a super absorbent polymer having an excellent morphology can be prepared because the particle size is small and the uniformity of circularity and particle size distribution is very high. That is, the superabsorbent polymer obtained according to the method for producing the superabsorbent polymer of the present invention exhibits an almost perfect spherical shape and a uniform particle size distribution, and has high gel strength, so even without surface crosslinking, the water holding capacity (CRC) and pressure absorption capacity (AUL) This can be made to exhibit excellent properties.

In addition, compared to conventional processes such as polymerization, primary pulverization, drying, secondary pulverization, classification, surface cross-linking, and tertiary pulverization during the manufacture of super absorbent polymers, according to the present invention, pulverization, classification and surface cross-linking after polymerization Since the step is not required, the process is simplified, and the polymerization efficiency per hour is high, so it may be suitable for mass production.

1 is a view showing a reaction apparatus for producing a super absorbent polymer according to an embodiment of the present invention.
2 is a photograph showing particles of a super absorbent polymer prepared according to an embodiment of the present invention.
3 is a photograph showing a fracture surface of super absorbent polymer particles prepared according to an embodiment of the present invention.
4 is a photograph showing the super absorbent polymer particles prepared according to Comparative Example 1 of the present invention.
5 is a photograph showing super absorbent polymer particles prepared according to Comparative Example 2 of the present invention.
6 is a photograph showing super absorbent polymer particles prepared according to Comparative Example 3 of the present invention.

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

Hereinafter, a method of manufacturing the super absorbent polymer of the present invention will be described in detail with reference to the drawings.

A method of preparing a super absorbent polymer according to an aspect of the present invention includes preparing a monomer composition comprising an acrylic acid-based monomer having an acidic group and at least a part of the acidic group neutralized; Generating droplets by applying vibration to the monomer composition; Polymerizing the droplets of the monomer composition while sedimenting them into an oil phase to form a hydrogel polymer; And drying the hydrogel polymer to form a super absorbent polymer having an average particle diameter (d50) of 100 to 900 μm.

According to a conventional method for preparing a super absorbent polymer by solution-phase polymerization, the step of polymerizing a monomer composition containing an acrylic acid-based monomer by photopolymerization or thermal polymerization to prepare a hydrogel polymer, in a state in which the hydrogel polymer is easily dried. It was prepared through several steps such as coarse pulverization to make it, drying the coarsely pulverized hydrogel polymer, pulverizing the dried polymer, and classifying the pulverized polymer powder according to the particle size.

In particular, the pulverized polymer powder after drying has a wide particle diameter range, so to exclude polymers having too small or large particle diameters, polymers having a predetermined particle diameter range, for example, about 150 to about 850 μm, are classified. , Only polymer powders having such particle diameters could be commercialized through a surface crosslinking reaction step.

However, according to the manufacturing method of the present invention, since the monomer composition is made into droplets and polymerization proceeds while sedimenting the droplets of the monomer composition into the oil phase at a controlled rate, super absorbent polymer particles having very high uniformity of circularity and particle size distribution Can be made. Therefore, the physical properties of the super absorbent polymer may be improved due to such high circularity and uniform particle size distribution, and particularly excellent gel strength may be exhibited, so that the water holding capacity and absorption capacity under pressure may be excellent without undergoing a surface crosslinking reaction step.

In addition, since the pulverization and classification process after polymerization is not required, the process can be simplified.

Accordingly, in the method for producing a super absorbent polymer according to the present invention, a monomer composition containing an acrylic acid-based monomer having an acidic group and at least partially neutralized with the acidic group is prepared, and vibration is applied to the monomer composition to form droplets ( droplet) is generated, and then polymerized and dried while the droplets of the monomer composition are settled in an oil phase, thereby forming spherical superabsorbent polymer particles having an average particle diameter (d50) of 100 to 900 μm.

The average particle diameter d50 may be measured using, for example, a laser diffraction method, and means a particle diameter in which the cumulative number of particle distributions is 50%.

1 shows a reaction apparatus for preparing a super absorbent polymer according to an embodiment of the present invention.

Referring to FIG. 1, the monomer composition is transferred to a multinozzle using a pressure means such as a pump. Droplets of the monomer composition may be generated by vibrating and spraying the liquid jet of the monomer composition passing through the nozzle from the top of the polymerization reactor filled with an inert gas and downward filled with the oil phase.

The polymerization reactor may be provided with an ultraviolet irradiation device for photopolymerization in the upper portion, and a heating device in order to achieve a high oil temperature for thermal polymerization in the lower portion.

In the upper part of the reactor, photopolymerization of acrylic acid-based monomers initially proceeds through ultraviolet irradiation, and thermal polymerization is secondarily induced by the polymerization reaction heat generated in the photopolymerization and the temperature increase due to heat transferred from the oil phase.

At the bottom of the reactor, the droplets partially polymerized at the top can be substantially completely polymerized by thermal polymerization.

The hydrogel polymer particles formed after polymerization is completed are precipitated on the bottom of the polymerization reactor. By separating the oil from the precipitated hydrogel polymer particles and drying the moisture, spherical superabsorbent polymer particles can be recovered.

The monomer composition, which is a raw material of the super absorbent polymer, includes an acrylic acid-based monomer and a polymerization initiator.

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 part of the acidic group is neutralized. Preferably, the monomer partially neutralized with an alkyl substance such as sodium hydroxide, potassium hydroxide, ammonium hydroxide, or the like may be used. At this time, the degree of neutralization of the acrylic acid-based monomer may be about 40 to about 95 mol%, or about 40 to about 80 mol%, or about 45 to about 75 mol%. The range of the degree of neutralization may be adjusted according to the final physical properties. However, if the degree of neutralization is too high, neutralized monomers may precipitate and polymerization may be difficult to proceed smoothly, whereas if the degree of neutralization is too low, the absorbency of the polymer is greatly reduced and it may exhibit properties such as elastic rubber that are difficult to handle. have.

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 and the solvent of the super absorbent polymer, and the polymerization time and Considering the reaction conditions, etc., it can be at an appropriate concentration. However, if the concentration of the monomer is too low, the yield of the super absorbent polymer may be low and economic problems may occur. On the contrary, if the concentration is too high, there may be problems in the process such as precipitation of a part of the monomer, and the physical properties of the super absorbent polymer This can be degraded.

As the polymerization initiator, a polymerization initiator generally used in the production of a super absorbent polymer may be used. As the polymerization initiator, a thermal polymerization initiator or a photopolymerization initiator may be used depending on the polymerization method. However, rather than using a thermal polymerization initiator or a photopolymerization initiator alone, it may be more preferable in terms of polymerization efficiency to use a mixture of the two. This is because even by the photopolymerization method, a certain amount of heat is generated by ultraviolet irradiation, etc., and a certain amount of heat is generated according to the progress of the polymerization reaction, which is an exothermic reaction, so when the thermal polymerization initiator is included, thermal polymerization can occur simultaneously. Because.

As the photopolymerization initiator, for example, benzoin ether, dialkyl acetophenone, hydroxyl alkylketone, phenyl glyoxylate, benzyl dimethyl ketal Dimethyl Ketal), acyl phosphine (acyl phosphine), and one or more compounds selected from the group consisting of alpha-aminoketone (α-aminoketone) may be used. Among them, as a specific example of acylphosphine, a commercially available lucirin TPO, that is, 2,4,6-trimethyl-benzoyl-trimethyl phosphine oxide (2,4,6-trimethyl-benzoyl-trimethyl phosphine oxide) may be used. . More various photopolymerization initiators are disclosed on page 115 of Reinhold Schwalm's book "UV Coatings: Basics, Recent Developments and New Application (Elsevier 2007)", which may be referred to.

In addition, as the thermal polymerization initiator, at least one compound selected from the group consisting of a persulfate-based initiator, an azo-based initiator, hydrogen peroxide, and ascorbic acid may be used. Specifically, as a persulfate-based initiator, sodium persulfate (Na ₂ S ₂ O ₈ ), potassium persulfate (Potassium persulfate; K ₂ S ₂ O ₈ ), ammonium persulfate (Ammonium persulfate; (NH ₄ ) ₂ S ₂ O ₈ ) and the like may be mentioned. In addition, as an azo-based initiator, 2,2-azobis-(2-amidinopropane) dihydrochloride (2,2-azobis(2-amidinopropane) dihydrochloride), 2,2-azobis-(N, N-dimethylene) isobutyramidine dihydrochloride (2,2-azobis- (N,N-dimethylene) isobutyramidine dihydrochloride), 2- (carbamoyl azo) isobutyronitrile (2- (carbamoylazo) isobutylonitril), 2,2-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride), 4, Examples include 4-azobis-(4-cyanovaleric acid) (4,4-azobis-(4-cyanovaleric acid)) and the like. More various thermal polymerization initiators are disclosed in Odian's book "Principle of Polymerization (Wiley, 1981)" on page 203, which may be referred to.

The polymerization initiator may be added at a concentration of about 0.001 to 1% by weight based on the monomer composition. That is, if the concentration of the polymerization initiator is too low, the polymerization rate may be slowed, and a large amount of residual monomers in the final product may be extracted, which is not preferable. On the contrary, if the concentration of the polymerization initiator is too high, the polymer chain forming the network is shortened, so that the content of the water-soluble component increases and the absorption capacity under pressure may decrease, which is not preferable.

According to an embodiment of the present invention, the monomer composition may further include an internal crosslinking agent as a raw material of the super absorbent polymer. As the internal crosslinking agent, a crosslinking agent having at least one functional group capable of reacting with the water-soluble substituent of the acrylic acid-based monomer and having at least one ethylenically unsaturated group; Alternatively, a crosslinking agent having two or more functional groups capable of reacting with a water-soluble substituent of the monomer and/or a water-soluble substituent formed by hydrolysis of the monomer may be used.

Specific examples of the internal crosslinking agent include bisacrylamide having 8 to 12 carbon atoms, bismethacrylamide, poly(meth)acrylate of polyol having 2 to 10 carbon atoms or poly(meth)allyl ether of polyol having 2 to 10 carbon atoms, etc. And more specifically, N, N'-methylenebis(meth)acrylate, ethyleneoxy(meth)acrylate, polyethyleneoxy(meth)acrylate, propyleneoxy(meth)acrylate, glycerin diacrylate , Glycerin triacrylate, trimethylol triacrylate, triallylamine, triaryl cyanurate, triallyl isocyanate, polyethylene glycol, diethylene glycol, and propylene glycol may be used at least one selected from the group consisting of.

Such an internal crosslinking agent is included in a concentration of about 0.01 to about 0.5% by weight based on the monomer composition, so that the polymerized polymer can be crosslinked.

In the manufacturing method of the present invention, the monomer composition of the super absorbent polymer may further include additives such as a thickener, a plasticizer, a storage stabilizer, and an antioxidant, if necessary.

Raw materials such as the acrylic acid-based monomer, polymerization initiator, internal crosslinking agent, and additives described above may be prepared in the form of a monomer composition solution dissolved in a solvent.

The solvent that can be used at this time can be used without limitation of its composition as long as it can dissolve the above-described 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, xylene, butylrolactone, carbitol, methyl cellosolve acetate, and one or more selected from N, N-dimethylacetamide and the like may be used in combination.

The solvent may be included in a residual amount excluding the above-described components with respect to the total content of the monomer composition.

Next, vibration is applied to the monomer composition to generate droplets of the monomer composition.

As a method for generating droplets, various methods have been reported, such as simple dripping, electrospraying, and vibration technology for liquid jet breakup. Of these, the simple dropping method is difficult to apply to commercial scale production due to a narrow flow rate range capable of generating uniform droplets and low generation frequency. The electrospray method has a disadvantage in that the productivity is low and the risk of electric shock and explosion by using high-pressure direct current electricity is present.

According to an embodiment of the present invention, uniform droplets can be produced at high speed by applying vibrations of an appropriate frequency to a liquid jet of a monomer composition.

In more detail, according to an embodiment of the present invention, it is transferred from a container containing the monomer composition to a multinozzle to which vibration is applied using a pressure means such as a pump. Droplets of the monomer composition may be generated by spraying the liquid jet of the monomer composition passing through the nozzle from the top of the polymerization reactor filled with an inert gas and downward filled with the oil phase.

The size and size distribution of the droplets may vary depending on various variables such as the size of the nozzle, the viscosity of the droplet, the flow rate of the monomer composition, and the vibration frequency. On the other hand, when a large amount of the monomer composition is added for commercial production to generate a large number of droplets at once, the droplets may be agglomerated with each other during the droplet generation process or in the polymerization reactor in the subsequent stage. It is necessary to carefully control the conditions for generating droplets.

In general, since the diameter of the droplet of the monomer composition is about twice the size of the inner diameter of the nozzle, it is possible to generate a droplet having a desired particle diameter by adjusting the inner diameter of the nozzle. Meanwhile, in order to generate smaller droplets, a coaxial inert gas is flowed to surround the liquid jet sprayed from the nozzle outlet, thereby reducing the diameter of the liquid jet and the size of the generated droplet.

According to an embodiment of the present invention, the inner diameter of the nozzle may be about 100 μm or more, or about 130 μm or more, and about 500 μm or less, or about 350 μm or less.

In addition, the flow rate of the monomer composition sprayed from the nozzle may be about 1 mL/min or more, or about 2 mL/min or more, and about 25 mL/min or less, or about 15 mL/min or less per nozzle.

In addition, the vibration frequency for generating the liquid jet sprayed from the nozzle into a uniform droplet may vary depending on the viscosity, surface tension, density, viscosity, and diameter of the liquid jet of the monomer solution, for example, about 40 Hz or more, or about 80 Hz or more, and about 3,000 Hz or less, or about 2,000 Hz or less.

In addition, the tip of the nozzle is preferably chamfered to minimize liquid wetting.

Mass production is possible by increasing the number of nozzles, and for example, it may be about 5 to 1000, but the present invention is not limited thereto.

According to the present invention, by optimizing the conditions in which droplets are generated as described above, the oil phase polymerization reaction can proceed without agglomeration of droplets even during mass production.

The droplets of the monomer composition produced as described above are polymerized while sedimenting into an oil phase to form a hydrogel polymer.

Referring to FIG. 1, a polymerization reaction may proceed while vertically sedimenting droplets of a spherical monomer composition in a polymerization reactor. Alternatively, the polymerization reactor includes a stirrer, and when the polymerization reactor is used to settle, the droplets of the monomer composition may fall while rotating in a spiral.

According to an embodiment of the present invention, the sedimentation velocity in the vertical direction of the droplets of the monomer composition in the oil phase is about 0.1 cm/sec or more, or about 1 cm/sec or more, or 2 cm/sec or more, and about 50 cm/sec or less, or about 40 cm/sec or less, or about 30 cm/sec or less. If the sedimentation rate of the droplets of the monomer composition is too low, productivity may be reduced, and if the rate is too high, polymerization may not be properly performed during sedimentation, so it may be desirable to have the sedimentation rate range from this point of view.

The sedimentation rate of the droplets in the oil phase can be calculated by Equation 1 below.

[Equation 1]

In equation 1,

V _m is the settling velocity of the droplet (cm/sec),

g is the acceleration of gravity (980cm/sec ² ),

ρ _s is the density of the droplet (g/cm ³ ),

ρ _m is the density of the oil (g/cm ³ ),

d is the diameter of the droplet (cm),

η ₀ is the viscosity of the oil (g/cm·sec).

The oil maintains the speed of the sedimenting droplets within an appropriate range, maintains the spherical shape of the droplets during sedimentation, and controls excessive polymerization heat during polymerization.

The oil that can be used at this time is one having a boiling point higher than the polymerization temperature of the monomer composition by 20°C or higher, for example, having a boiling point of 100°C or higher, and is immiscible with the monomer composition to maintain the shape of the droplets of the monomer composition that settle. Any oil that can be used can be used.

According to an embodiment of the present invention, in order to achieve the sedimentation rate of the droplets of the monomer composition described above, the viscosity coefficient of the oil is about 0.01 g/cm·sec or more, or about 0.02 g/cm·sec or more at 25°C, or It may be about 0.03 g/cm·sec or more, about 4.8 g/cm·sec or less, or about 4 g/cm·sec or less, or about 3 g/cm·sec or less. If the viscosity coefficient of the oil is too low, the sedimentation rate is too fast and polymerization may not be performed properly. If the viscosity coefficient is too high, the monomer composition droplets collide and coalesce at the gas-liquid interface, resulting in the There is a problem that the size cannot be kept uniform.

Further, according to an embodiment of the present invention, in order to achieve the sedimentation rate of the droplets of the monomer composition described above, the density of the oil is about 0.6 g/cm ³ or more at 25° C., or about 0.7 g/cm ³ or more, while about 1.2 g/cm ³ or less, or about 1.1 g/cm ³ or less.

In addition, according to an embodiment of the present invention, in order to achieve the sedimentation rate of the droplets of the monomer composition described above, the density of the droplets is about 1 g/cm ³ or more, or about 1.05 g/cm ³ or more at 25°C, and about 1.5 g/cm ³ or less, or about 1.3 g/cm ³ or less.

In addition, according to an embodiment of the present invention, in order to achieve the sedimentation rate of the droplets of the monomer composition described above, the particle diameter of the droplets may be about 150 μm or more, or about 250 μm or more, and about 1,200 μm, or about 1,000 μm or less. have.

In addition, according to an embodiment of the present invention, as an oil that satisfies the above conditions, dimethyl silicone oil, methylphenyl silicone oil, diphenyl silicone oil, methylhydrogen silicone oil, methylhydroxy silicone oil, fluoro silicone oil, poly Silicone oils such as oxyether silicone oil, alkyl-modified silicone oil, amino-modified silicone oil, and epoxy-modified silicone oil; Mineral oils such as paraffinic mineral oil and naphthenic mineral oil; Fluorinated oil; An aliphatic higher hydrocarbon having 10 or more carbon atoms such as decane, dodecane, hexadecane, or mixtures thereof may be used.

By controlling the oil and droplet conditions as described above, the sedimentation speed range of the droplets of the monomer composition described above can be achieved.

The polymerization of the droplets of the monomer composition in the oil phase may be performed by thermal polymerization, photopolymerization, or a combination thereof.

According to an embodiment of the present invention, it is possible to form super absorbent polymer particles by performing both thermal polymerization and photopolymerization, preferably first, photopolymerization and thermal polymerization are performed together, and then only thermal polymerization alone is additionally performed. I can. An ultraviolet irradiation device for photopolymerization may be provided on the upper part, and a heating device such as a heating jacket may be provided at the lower part to achieve a high oil temperature for thermal polymerization.

When the polymerization is carried out in the order of photopolymerization and thermal polymerization inside the reactor as described above, photopolymerization of acrylic acid-based monomers proceeds for several seconds to tens of seconds through ultraviolet irradiation at the top of the reactor, and the heat of polymerization reaction generated in the photopolymerization and transfer in the oil phase Thermal polymerization is induced secondarily by the increase in temperature due to the heat generated.

At the bottom of the reactor, the droplets partially polymerized at the top are substantially completely polymerized by thermal polymerization. The temperature of the oil phase at the bottom of the reactor where thermal polymerization takes place may be about 50°C or more, or about 70°C or more, and about 120°C or less, or about 100°C or less. If the temperature is lower than the above temperature range, the polymerization conversion rate may decrease, and if the temperature is too high, the physical properties of the super absorbent polymer particles may be lowered.

The average particle diameter (d50) of the hydrogel polymer formed by polymerization as described above may be about 150 μm or more, or about 250 μm or more, and may have a range of about 1,200 μm, or about 1,000 μm or less. At this time, the hydrogel polymer is in a state in which most of the water in the droplet remains, and thus the particle diameter of the generated droplet may be substantially the same.

In addition, the moisture content of the obtained hydrogel polymer may be about 30 to about 70% by weight. On the other hand, throughout the present specification, "water content" refers to a value obtained by subtracting the weight of the dried polymer from the weight of the hydrogel polymer as the content of moisture occupied by the total weight of the hydrogel polymer. Specifically, it is defined as a calculated value by measuring the weight loss due to evaporation of moisture in the polymer during drying by raising the temperature of the polymer through infrared heating. At this time, the drying condition is a method in which the temperature is raised from room temperature to about 180°C and then maintained at 180°C. The total drying time is set to 20 minutes including 5 minutes in the temperature raising step, and the moisture content is measured.

The hydrogel polymer particles formed after polymerization is completed while sedimenting in the oil phase inside the polymerization reactor by the above process is precipitated on the bottom of the polymerization reactor. The oil is separated from the precipitated hydrogel polymer particles, and the super absorbent polymer particles are recovered.

In order to remove the oil remaining on the surface of the recovered hydrogel polymer particles, the oil may be removed with a low boiling point washing solvent such as pentane, hexane, cyclopentane, cyclohexane, and acetone.

Next, a drying step for removing moisture from the hydrogel polymer is performed to obtain super absorbent polymer particles. Meanwhile, when a volatile oil is used in the polymerization process, the volatile oil and moisture may be simultaneously removed in the drying step without using a washing solvent.

The drying temperature in the drying step may be about 150 to about 250°C. If the drying temperature is less than 150℃, there is a risk that it may take too long drying time or moisture may remain, and if the drying temperature exceeds 250℃, the physical properties of the super absorbent polymer finally formed by rapid drying decrease. There is a risk of becoming. Therefore, preferably, the drying may be performed at a temperature of about 150 to about 200°C, more preferably about 180 to about 200°C.

On the other hand, in the case of the drying time, the process may be performed for about 20 to about 120 minutes in consideration of process efficiency, but is not limited thereto.

The drying may be performed using a conventional medium, for example, the hot air supply, infrared radiation, microwave radiation, or ultraviolet radiation. The water content of the super absorbent polymer recovered after the drying step is performed may be about 0.1 to about 10% by weight.

By carrying out the polymerization reaction by the above method, the super absorbent polymer prepared according to the present invention can achieve high circularity and uniform particle size distribution compared to the super absorbent polymer polymerized by a conventional aqueous polymerization reaction. .

The average particle diameter (d50) of the super absorbent polymer of the present invention obtained by the above production method may be about 100 μm or more, or about 250 μm or more, and may have a range of about 900 μm or less, or about 850 μm or less.

In addition, the super absorbent polymer particles prepared according to the present invention may be about 0.80 or more, or about 0.85 or more, or about 0.90 or more and exhibit a circularity of 1 or less. The circularity can be measured by the following Equation 2, and in the case of a complete sphere, it becomes 1, and the closer to 1, the closer to the sphere.

[Equation 2]

In Equation 2, A is the projection area of the particle projected in two dimensions,

P is the circumference of the particle projected in two dimensions.

In addition, the coefficient of variation (C.V.) of the particle diameter of the super absorbent polymer particles may represent about 15% or less, or about 10% or less, or about 6% or less.

In a general method for producing a super absorbent polymer, the super absorbent polymer powder obtained after pulverization is classified according to the particle size in order to manage the physical properties of the super absorbent polymer powder to be finally commercialized, and the super absorbent polymer having a particle diameter of about 150 to about 850 µm. It is commercialized only through a surface crosslinking reaction step.

However, the superabsorbent polymer particles obtained according to the production method of the present invention have a very uniform particle size distribution and do not require a classification step. However, it is not excluded that the classification step may be performed for more improved physical property management.

As described above, the super absorbent polymer obtained by the production method of the present invention can be closely packed (close packing), and since both the surface and the cross section of the particles have substantially non-porous characteristics, high gel strength It has excellent characteristics in centrifugal support capacity (CRC) and pressure absorption capacity (AUP) even without surface crosslinking.

For example, the super absorbent polymer obtained by the production method of the present invention may have a CRC of about 24 to about 45 g/g as measured according to EDANA method WSP 241.3.

In addition, the super absorbent polymer obtained by the production method of the present invention may have an AUP (0.9psi) of about 9 to about 29 g/g as measured according to the EDANA method WSP 242.3.

The present invention will be described in more detail in the following examples. However, the following examples are merely illustrative of the present invention, and the contents of the present invention are not limited by the following examples.

<Example>

Example 1

A solution (solution A) was prepared by gradually adding 1.75 kg of caustic soda (NaOH) and 3 kg of water to 4.5 kg (45% by weight in total solution) of acrylic acid. A solution (solution B) in which 4.5 g of IRGACURE 819 as a photoinitiator, 9 g of sodium persulfate as a thermal initiator, and 22.5 g of polyethylene glycol diacrylate (PEGDA, molecular weight 400 g/mol) was dissolved in 715 g of water was gradually added dropwise thereto. . As the acrylic acid-based monomer thus obtained, the neutralization degree of acrylic acid in sodium acrylate was 70 mol%. The content of the photoinitiator, thermal initiator, and crosslinking agent (PEGDA) was injected to be 1000 ppm, 2000 ppm, and 3000 ppm, respectively, with respect to the total acrylic acid contained in the monomer composition.

The monomer composition was transferred from a pressure vessel through a vibration chamber to a multinozzle, and uniform droplets were generated under an inert nitrogen gas atmosphere. The conditions for generating the droplets are as follows:

Nozzle inner diameter: 0.3 mm

Total flow rate of monomer solution sprayed from the nozzle: 40 ml/min

Vibration frequency applied to the liquid jet from the nozzle: 200 Hz

Number of nozzles: 8

The generated droplets are filled with low-viscosity silicone oil (KF-96-10cs, Shin-Etsu), partially cured while passing through the upper part of the reactor equipped with a UV exposure device, and surrounded by a jacket where the heat medium preheated to 75℃ is circulated. It was completely polymerized as it passed the bottom of the reactor. The conditions of the polymerization reaction are as follows:

Viscosity modulus of oil: 0.0935 g/cmsec (at 25℃)

Oil density: 0.935 g/cm ³ (at 25℃)

Drop density: 1.17 g/cm ³ (at 25°C)

Drop diameter (d50): 650 μm

Droplet sedimentation speed: 6.7 cm/sec

Oil was separated from the polymerized hydrogel polymer particles with cyclohexane and dried at 190° C. for 120 minutes to obtain uniform spherical superabsorbent polymer particles.

A scanning electron microscope (SEM) photograph showing the super absorbent polymer particles prepared according to Example 1 is shown in FIG. 2.

Referring to FIG. 2, it can be seen that super absorbent polymer particles having a spherical uniform particle size distribution were formed.

In addition, a scanning electron microscope (SEM) photograph showing a fracture surface of the super absorbent polymer particles prepared according to Example 1 is shown in FIG. 3.

Referring to FIG. 3, it can be seen that the super absorbent polymer particles form a smooth structure in which no pores are observed on the surface and inside.

Example 2

In Example 1, a crosslinking agent (PEGDA) was prepared in the same manner as in Example 1, except that the content of the crosslinking agent (PEGDA) was injected to be 4000 ppm with respect to the total acrylic acid contained in the monomer composition to obtain super absorbent particles.

Example 3

In Example 1, a crosslinking agent (PEGDA) was prepared in the same manner as in Example 1, except that the content of the crosslinking agent (PEGDA) was injected to be 2000 ppm with respect to the total acrylic acid contained in the monomer composition to obtain super absorbent particles.

Comparative Example 1

In Example 1, it was prepared in the same manner as in Example 1, except that the droplets of the monomer composition were generated by a simple dripping method without applying vibration, to obtain super absorbent particles.

A photograph showing the super absorbent polymer particles prepared according to Comparative Example 1 is shown in FIG. 4.

Referring to FIG. 4, as in Comparative Example 2, particles generated by natural splitting of a liquid jet by simply dropping without applying a vibration frequency exhibited a non-uniform size distribution as shown in FIG. 4.

Comparative Example 2

In Example 1, it was prepared in the same manner as in Example 1, except that the conditions of the polymerization reaction were as follows using silicone oil (KF-96-500cs, Shin-Etsu) to obtain super absorbent particles. .

Viscosity modulus of oil: 4.85 g/cm·sec (at 25℃)

Density of oil: 0.97 g/cm ³ (at 25℃)

Drop density: 1.17 g/cm ³ (at 25°C)

Droplet average particle diameter (d50): 1680 ㎛

Droplet sedimentation rate: 0.95 cm/sec

A scanning electron microscope (SEM) photograph showing the super absorbent polymer particles prepared according to Comparative Example 2 is shown in FIG. 5.

Referring to FIG. 5, when high-viscosity oil is used, the droplets generated at high speed collide and merge with each other while passing through the oil interface, resulting in a problem that the average particle diameter of the super absorbent polymer particles increases and the uniformity decreases.

Comparative Example 3

The same monomer composition as in Example 1 was prepared.

The monomer composition was subjected to conventional solution polymerization to obtain super absorbent polymer particles.

More specifically, the monomer composition was poured into a Vat-shaped tray (15cm wide x 15cm long) installed in a square polymerizer with a light irradiation device mounted on the top and preheated to 80°C, and subjected to light irradiation for 4 minutes for light polymerization Was done.

After the polymerized sheet was cut into a size of 3 cm x 3 cm, a chopping process was performed using a meat chopper having a hole diameter of 8 mm to prepare a crumb. crumb) was dried in an oven capable of air volume transfer up and down. 180 ℃ hot air (hot air) was allowed to flow for 40 minutes to dry uniformly, and after drying, the moisture content of the dried body was 2% or less.

After drying, the base resin was prepared by pulverizing with a pulverizer and then classifying and selecting a size of 150 to 850 μm. Thereafter, 4 g of water, 4 g of methanol, and 0.8 g of ethylene carbonate were mixed with 100 g of the base resin, followed by a surface crosslinking reaction at 180°C for 50 minutes, and then pulverized using a sieve. A surface-treated super absorbent polymer having a diameter of 150 to 850 µm was obtained.

A scanning electron microscope (SEM) photograph showing the base resin particles prepared according to Comparative Example 3 is shown in FIG. 6.

6, as in Comparative Example 3, the super absorbent polymer prepared by the conventional solution polymerization method showed an irregular shape and a non-uniform particle state.

<Experimental Example>

For the super absorbent polymer particles prepared in Examples and Comparative Examples, physical properties were evaluated in the following manner.

(1) Centrifuge Retention Capacity (CRC)

In accordance with the European Disposables and Nonwovens Association (EDANA) standard EDANA WSP 241.3, for the superabsorbent polymers of Examples and Comparative Examples, centrifugal water retention capacity (CRC) was measured by absorption ratio under no load.

Specifically, resin W ₀ (g, about 0.2 g) of Examples and Comparative Examples was evenly put in a nonwoven bag and sealed, and then immersed in physiological saline solution of 0.9% by weight sodium chloride aqueous solution at room temperature. After 30 minutes, the bag was centrifuged and dried for 3 minutes with 250G, and the mass W ₂ (g) of the bag was measured. Further, the mass W ₁ (g) at that time was measured after performing the same operation without using a super absorbent polymer.

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

[Equation 1]

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

In Equation 1,

W ₀ (g) is the initial weight (g) of the super absorbent polymer, and W ₁ (g) is absorbed by immersing in physiological saline for 30 minutes without using the super absorbent polymer, and then using a centrifuge to obtain 250 G. It is the weight of the device measured after dehydration for 3 minutes, and W ₂ (g) is absorbed by immersing a superabsorbent resin in physiological saline at room temperature for 30 minutes, and then dehydrating at 250G for 3 minutes using a centrifuge. It is the device weight measured including the resin.

(2) Absorbing under Pressure (AUP)

According to the method of the European Disposables and Nonwovens Association standard EDANA WSP 242.3, the absorbency under pressure (AUP) of the superabsorbent polymers of Examples and Comparative Examples was measured.

Specifically, a 400 mesh stainless steel mesh was mounted on the bottom of a plastic cylinder having an inner diameter of 60 mm. The resin W ₀ (g, 0.90 g) obtained in Examples and Comparative Examples was evenly sprayed on the wire mesh under conditions of 23±2° C. and 45% relative humidity, and a load of 0.7 psi was evenly applied thereon. The possible piston has an outer diameter of a little less than 60 mm and there is no gap with the inner wall of the cylinder, and the vertical movement is not obstructed. At this time, the weight W ₃ (g) of the device was measured.

A glass filter having a diameter of 125 mm and a thickness of 5 mm was placed on the inside of a 150 mm diameter PET dish, and a physiological saline solution composed of 0.90 wt% sodium chloride was at the same level as the upper surface of the glass filter. One sheet of filter paper with a diameter of 120 mm was mounted thereon. The measuring device was placed on a filter paper, and the liquid was absorbed for 1 hour under load. After 1 hour, the measuring device was lifted and the weight W ₄ (g) was measured.

Using each mass thus obtained, AUP (g/g) was calculated according to Equation 2 below.

[Equation 2]

AUP(g/g) = [W ₄ (g)-W ₃ (g)]/ W ₀ (g)

In Equation 2,

W ₀ (g) is the initial weight (g) of the super absorbent polymer, W ₃ (g) is the sum of the weight of the super absorbent polymer and the weight of the device that can apply a load to the super absorbent polymer, W ₄ (g ) Is the sum of the weight of the superabsorbent polymer and the weight of the device capable of imparting a load to the superabsorbent polymer after absorbing physiological saline in the superabsorbent polymer for 1 hour under load (0.9 psi).

Average particle diameter
(㎛) Circularity Coefficient of variation
(CV) CRC
(g/g) 0.9psi AUL
(g/g) Example 1 478 0.93 3.8% 31.1 18.8 Example 2 471 0.94 3.7% 24.9 20.9 Example 3 484 0.91 4.3% 35 9.7 Comparative Example 3
(Before surface crosslinking) - - - 35.4 6.2 Comparative Example 3
(After surface crosslinking) - - - 30.5 20.5

Referring to Table 1, in Examples 1 to 3 of the present invention, a super absorbent polymer having excellent morphology was obtained due to very high uniformity in circularity and particle size distribution. On the other hand, in Comparative Example 3 using the conventional polymerization method, as shown in FIG. 6, it was impossible to measure the average particle diameter, circularity, and coefficient of variation due to the irregular shape and non-uniform particle state.

In terms of water holding capacity and pressure absorption capacity, when comparing Comparative Example 3 and Example 3 before surface crosslinking, it was found that Example 3 had higher absorption capacity under pressure and high gel strength despite using less internal crosslinking agent. .

Comparing Example 1 and Comparative Example 3 using the same monomer composition, Example 1 exhibited similar water holding capacity and pressure absorption capacity as Comparative Example 3, which was polymerized by a solution polymerization method and subjected to surface crosslinking, even though surface crosslinking was not performed. You can see

Claims (11)

Preparing a monomer composition comprising an acrylic acid-based monomer having an acidic group and at least a part of the acidic group is neutralized;
Generating droplets by applying vibration to the monomer composition;
Polymerizing the droplets of the monomer composition while sedimenting them into an oil phase to form a hydrogel polymer; And
Drying the hydrogel polymer to form a spherical superabsorbent polymer having an average particle diameter (d50) of 100 to 900 μm;
As a method for producing a super absorbent polymer comprising a,
The sedimentation rate of the droplets of the monomer composition is 0.02 to 50 cm/sec,
The oil has a viscosity coefficient of 0.01 to 4.8 g/cm·sec at 25° C., a method for producing a super absorbent polymer.
delete delete The method of claim 1, wherein the oil comprises at least one selected from the group consisting of silicone oil, mineral oil, and aliphatic hydrocarbons having 10 or more carbon atoms.
The method of claim 1, wherein the step of polymerizing while sedimenting droplets of the monomer composition into an oil phase to form a hydrogel polymer,
A method for producing a super absorbent polymer, comprising the steps of first performing photopolymerization and thermal polymerization, and then performing thermal polymerization.
The method of claim 1, wherein the step of generating the droplets of the monomer composition is performed by spraying the monomer composition through a multinozzle.
The method of claim 6, wherein the spraying speed of the monomer composition is 1 to 25 mL/min per nozzle.
The method of claim 1, wherein the frequency of vibration applied to the monomer composition is 40 to 3,000 Hz.
The method of claim 1, wherein the superabsorbent polymer has a circularity of 0.8 to 1.
The method of claim 1, wherein the coefficient of variation (CV) of the particle diameter of the super absorbent polymer is 10% or less.
According to claim 1, After the step of polymerizing while sedimenting the droplets of the monomer composition into an oil phase to form a hydrogel polymer,
A method for producing a super absorbent polymer, further comprising the step of separating the oil from the hydrogel polymer.

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