JP2007084656A - Method for producing liquid absorbent resin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To have excellent liquid absorbency even for high-concentration salt-containing solutions such as seawater and calcium chloride deliquescent aqueous solution, have no aggregation of primary particles, and have a volume-based median diameter of 0.5 to 50 μm Thus, the present invention provides a method for producing liquid-absorbent resin fine particles having a particle diameter distribution that is very narrow.
SOLUTION: A hydrophobic organic solvent containing a surfactant, a monomer mixture containing an ethylenically unsaturated monomer having a sulfonic acid group or an alkyl metal salt thereof, and an aqueous solution containing a radical polymerization initiator, A method for producing a liquid-absorbent resin by charging in a polymerization tank having a stirrer and carrying out reverse phase suspension polymerization while stirring with the stirrer, wherein the stirrer has a low speed stirring blade and a high speed stirring blade. The present invention relates to a method for producing a liquid absorbent resin, characterized in that the average particle diameter of liquid absorbent resin particles is controlled using a shaft stirrer.
[Selection figure] None

Description

  The present invention relates to a method for producing a useful liquid-absorbing resin. More specifically, the present invention relates to a method for producing a liquid-absorbing resin for absorbing a high-concentration salt-containing solution such as seawater or calcium chloride deliquescent aqueous solution. The liquid-absorbing material comprising the liquid-absorbing resin obtained by the method of the present invention can be widely used as a liquid-absorbing material for absorbing a high-concentration salt-containing solution and a water-absorbing water material, for civil engineering, agriculture and horticulture. is there.

In recent years, water-absorbing materials are used not only for sanitary materials such as sanitary products and disposable diapers, but also for water-stopping materials, anti-condensation materials, freshness-keeping materials, solvent dehydrating agents, etc., greening applications, agricultural and horticultural applications, etc. It is being put into practical use. However, with conventional water-absorbing materials, the water absorption performance for salt-containing solutions containing polyvalent metal ions such as calcium and magnesium decreases with increasing ion concentration. Below, there was a big problem of hardly absorbing water.
In order to solve such a problem, a water-absorbing material made of sulfoalkyl (meth) acrylate, acrylamide, or the like has been proposed (for example, see Patent Document 1). In addition, salt-resistant swelling agents (for example, see Patent Document 2) and nursery beds (for example, see Patent Document 3) using the same have been proposed. However, these proposed water-absorbing materials form a gel polymer by forming a cross-linked structure by aqueous solution polymerization, and have a low water absorption ratio and have to be pulverized during use.

On the other hand, as a production method by the water-in-oil type reverse phase suspension polymerization method, a sulfonic acid group-containing unsaturated monomer of 20 to 100 mol% and other polymerizable monomers of 0 to 80 mol% are used. A monomer or an aqueous solution thereof in the presence of 0 to 10 parts by weight of a sorbitan fatty acid ester with respect to 100 parts by weight of the monomer or an aqueous solution thereof, and 100 to 400 parts by weight with respect to 100 parts by weight of the monomer or an aqueous solution thereof. A salt-resistant solution, wherein a suspension of polymerizable fine particles having a particle diameter of 50 μm or less is prepared by reverse-phase suspension polymerization in a portion of a hydrophobic organic solvent, and the fine particles are separated from the suspension and dried. Has been proposed (see Patent Document 4, for example).
According to this production method, polymerizable fine particles having a particle diameter of 50 μm or less are obtained without agglomeration, but in order to obtain polymerizable fine particles having a particle diameter of 50 μm or less without causing aggregation of primary particles. In addition, it is necessary to use 100 to 400 parts by weight of a hydrophobic organic solvent with respect to 100 parts by weight of the monomer or an aqueous solution thereof, and it is inevitable that the yield per reaction kettle becomes low. In addition, the optimum stirring blade and stirring speed are not sufficiently described. When scale-up is performed on a commercial reaction kettle exceeding 1 m ³ or when a paddle blade is used as the stirring blade, the primary particles are aggregated. There were limits to avoid. Furthermore, the particle size distribution of the water-absorbing resin particles obtained tends to be widened, and it is difficult to avoid mixing the water-absorbing resin having a large particle size into the product.

As a method for producing water-absorbent resin fine particles, water-in-oil fine dispersion droplets of monomers are formed in advance before polymerization, and the fine dispersion droplets are dropped into an elevated temperature organic solvent to polymerize. A method is disclosed (for example, see Patent Document 5). However, this proposal has a drawback in that the apparatus becomes large because a dispersion apparatus such as a homomixer is required to form water-in-oil type fine dispersion droplets of the monomer in advance before polymerization.
Furthermore, a method for producing a liquid-absorbing resin in a reaction kettle having a multi-shaft stirrer having a low speed stirring blade and a high speed stirring blade is disclosed (for example, see Patent Document 6). According to this production method, the amount of resin adhering to the polymerization tank is greatly reduced and the yield is improved. However, the control range of the particle diameter of the liquid absorbent resin disclosed in this proposal is 80 to 1000 μm, and no particle diameter control method with a particle diameter of 50 μm or less, further 10 μm or less has been disclosed.

JP-A-1-144404 Japanese Examined Patent Publication No. 63-5427 JP-A 64-51025 JP-A-1-249808 JP-A-5-222107 JP 2005-132957 A

  The object of the present invention is to have excellent liquid absorbency even for high-concentration salt-containing solutions such as seawater and calcium chloride deliquescent aqueous solution, there is no aggregation of primary particles, and the volume-based median diameter is 0. An object of the present invention is to provide a method for producing liquid absorbent resin fine particles which can be controlled to have a particle diameter in the range of 5 to 50 μm and have a very narrow particle diameter distribution.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors contain a hydrophobic organic solvent in which a surfactant is dissolved and an ethylenically unsaturated monomer having a sulfonic acid group or an alkyl metal salt thereof. Volume-based by subjecting an aqueous solution containing a monomer mixture and a radical polymerization initiator to a reverse phase suspension polymerization with stirring in a polymerization tank having a multi-shaft stirrer having a low speed stirring blade and a high speed stirring blade. It has been found that polymerizable fine particles whose median diameter is controlled in the range of 0.5 to 50 μm can be obtained without agglomeration of primary particles, and that a liquid-absorbing resin having a very narrow particle size distribution can be produced. It came to complete.

  That is, the present invention relates to a hydrophobic organic solvent containing a surfactant, a monomer mixture containing an ethylenically unsaturated monomer having a sulfonic acid group or an alkyl metal salt thereof, and an aqueous solution containing a radical polymerization initiator. In a polymerization tank having a stirrer, and reverse phase suspension polymerization while stirring with the stirrer to produce a liquid-absorbent resin, wherein the stirrer includes a low speed stirring blade and a high speed stirring blade. The present invention provides a method for producing a liquid absorbent resin, characterized in that the average particle diameter of the liquid absorbent resin particles is controlled using a multiaxial stirrer.

  According to the method for producing a liquid-absorbing resin according to the present invention, an aqueous solution containing a monomer mixture and a radical polymerization initiator by a shearing force of a high-speed stirring blade is used as a surfactant while gently mixing the whole with a low-speed stirring blade. By uniformly and finely dispersing it in a hydrophobic organic solvent in which is dissolved, the particle diameter of the primary particles of the resin produced by polymerization can be controlled to be small, and the particle diameter distribution can be made very narrow.

There is no restriction | limiting in particular in the shape of the polymerization tank used for this invention, The conventional well-known reaction apparatus, a stirring tank, etc. can be used. Further, additional devices such as a heating device and a condenser can be used as appropriate.
Hereinafter, the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a schematic view showing an embodiment of a polymerization tank 1 having an inner diameter D used in the present invention. A pitched paddle blade is used as a low speed stirring blade 2 having a blade diameter dl, and a turbine is used as a high speed stirring blade 3 having a blade diameter dh. A plurality of stirring blades having blades are provided. At least one high-speed stirring blade 3 is arranged, but two or more high-speed stirring blades 2 may be arranged according to the size of the polymerization tank 1 and the type of the low-speed stirring blade 2 (see FIG. 2). You may make it revolve around. Therefore, in order to arrange the low-speed stirring blade 2 so as not to contact the polymerization tank 1 and to arrange the high-speed stirring blade 3 so as not to obstruct the low-speed stirring blade 2, each blade diameter and the inner diameter of the polymerization tank 1 are used. Is 2 · dl <dh <D.

  The rotational speed of the low-speed stirring blade 2 may be such that the solution in the polymerization tank 1 is gently stirred so that the high-speed stirring blade 3 is not exposed from the liquid surface, and no large vortex is generated. In addition, it is possible to prevent the resin from adhering to the inner wall surface of the polymerization tank 1 by the swirling flow generated by this rotation, and also to prevent the resin particles from agglomerating. On the other hand, the high-speed stirring blade 3 has a rotational speed higher than that of the low-speed stirring blade 2, and this rotation causes the single-piece containing an ethylenically unsaturated monomer having a sulfonic acid group or an alkyl metal salt thereof. The aqueous solution containing the monomer mixture and the radical polymerization initiator is uniformly dispersed in the hydrophobic organic solvent, and at the same time, a shear force is applied to the resin produced by the polymerization, and the resin particles are refined and the particle size by adjusting the shear force. You will be responsible for the control.

  The insertion depth of the high-speed stirring blade 3 with respect to the solution may be as long as it is not exposed from the liquid surface as described above. However, in the vicinity of the liquid surface, bubbles are likely to be generated by being rotated at a high speed, or bubbles are easily involved. Therefore, it is preferable to arrange the liquid surface and the center of the low speed stirring blade 2 so as not to be an obstacle to the low speed stirring blade 2. Further, if the rotating shaft of the high-speed stirring blade 3 is inclined and stirred, an upward flow can be generated with respect to the swirling flow by the low-speed stirring blade 2, and the shearing force can be improved and the low-speed stirring blade 3 can be improved. Since the resin adhesion to the rotating shaft of the stirring blade 2 can also be reduced, it is preferable.

  The rotation direction of the low-speed stirring blade 2 and the high-speed stirring blade 3 may be the same rotation direction or the reverse rotation direction. However, from the viewpoint of reducing the load on the high-speed stirring blade 3, the rotation direction is the same. Is preferred.

  Further, from the viewpoint of preventing resin adhesion on the inner wall of the polymerization tank 1 and preventing troubles due to rotational shaking of the low speed stirring blade 2, the relationship between the inner diameter D of the polymerization tank 1 and the blade diameter dl of the low speed stirring blade 2 is 0.95 ≦ It is preferable to satisfy dl / D ≦ 0.99, and it is more preferable to satisfy 0.96 ≦ dl / D ≦ 0.98.

  Moreover, it is preferable to use an anchor blade as the low-speed stirring blade 2 from the viewpoint of improving the stirring efficiency of the solution throughout the polymerization tank 1 and reducing the adhesion of the resin on the inner wall of the polymerization tank 1. When the anchor blade is used, as shown in FIG. 3, it is preferable that 0.05 ≦ wl / D ≦ 0.10 if the blade width of the anchor blade is wl.

  If the anchor blade is used, the stirring efficiency of the solution can be improved over the entire polymerization tank 1 as described above, and the high-speed stirring blade 3 can be disposed between the anchor blade and the stirring shaft. Since a shearing force can be efficiently applied to the resin produced by polymerization, the particle diameter of the resin can be controlled more easily.

  In this case, it is preferable to use a turbine blade as the high-speed stirring blade 3, for example, a disk turbine blade in which a plurality of inclined blades as shown in FIG. A disk turbine blade in which a plurality of blades are arranged substantially vertically can be used. The relationship between the outer diameter dl and blade width wl of the anchor blade as the low-speed stirring blade 2 and the outer diameter dh of the turbine blade prevents interference with the rotating shaft of the low-speed stirring blade 2 and from the viewpoint of stirring efficiency. 0.1 · dl <dh <0.8 (dl / 2−wl) and 0.15 ≦ dh / D ≦ 0.4 in relation to the inner diameter D of the polymerization tank 1 .

Furthermore, as the high-speed stirring blade 3, it is also preferable to use a disper blade whose dimensions are in the above ranges in place of the turbine blade. For example, as shown in FIG. 5 (a), the periphery of the disk protrudes in a sawtooth shape in plan view, and a plurality of blades are alternately arranged in the vertical direction in a perspective state as shown in FIG. 5 (b). The disper blade as described above is suitable for reducing the particle diameter of the resin because a shearing force can be obtained.
The liquid-absorbing resin produced in the present invention is used by mixing with rubber, cement, plastic or the like. For this reason, an average particle diameter is a volume-based median diameter of at least 50 μm or less, and preferably 10 to 20 μm. Furthermore, when the liquid-absorbing resin is mixed with the coating material and used, the particle diameter of the liquid-absorbing resin is preferably about 1 μm because it is used with a coating thickness of 10 μm or less. For this reason, the average particle diameter of the liquid-absorbent resin is preferably 0.5 to 50 μm in order to meet all needs. The average particle diameter of these liquid absorbent resins can be controlled by the production method of the present invention.

  The liquid-absorbent resin of the present invention can maintain the rotational speed of the high-speed stirring blade 3 while maintaining the state where the rotational speed of the low-speed stirring blade 2 is smaller than the rotational speed of the high-speed stirring blade 3 during the polymerization reaction. By controlling and stirring based on the number, the volume-based median diameter of the primary particles of the liquid-absorbent resin can be controlled to 0.5 to 50 μm. The Weber number is a dimensionless number indicating the ratio of the inertial force acting on the interface between bubbles and droplets and the surface tension, and is expressed by the equation (1).

式（１）中、ｎは高速攪拌翼の攪拌速度（ｒｐｍ）、ｄｈは高速撹拌翼３の攪拌翼径（ｍ）、ρは液密度（ｋｇ／ｍ^３）、μは液粘度（Ｐａ・ｓ）、σは界面張力（Ｎ／ｍ）を示すものである。
ウェーバー数を制御する具体的な方法としては、ウェーバー数と高速攪拌翼径に対する吸液性樹脂の１次粒子の平均粒子径（吸液性樹脂の１次粒子の平均粒子径／高速攪拌翼径）の関係を利用する方法が挙げられる。図６は、吸液性樹脂の１次粒子の平均粒子径を高速攪拌翼径で割った数値とウェーバー数の関係を示したグラフである。すなわち、ウェーバー数と高速攪拌翼径に対する吸液性樹脂の１次粒子の平均粒子径（吸水性樹脂の１次粒子の平均粒子径／高速攪拌翼径）の間には式（２）で表される関係が成立する。

In formula (1), n is the stirring speed (rpm) of the high-speed stirring blade, dh is the stirring blade diameter (m) of the high-speed stirring blade 3, ρ is the liquid density (kg / m ³ ), and μ is the liquid viscosity (Pa · s) and σ represent interfacial tension (N / m).
As a specific method of controlling the Weber number, the average particle diameter of the primary particles of the liquid-absorbent resin with respect to the Weber number and the high-speed stirring blade diameter (average particle diameter of primary particles of the liquid-absorbing resin / high-speed stirring blade diameter) ) Is used. FIG. 6 is a graph showing the relationship between the numerical value obtained by dividing the average particle diameter of primary particles of the liquid-absorbent resin by the high-speed stirring blade diameter and the Weber number. That is, the average particle diameter of the primary particles of the liquid-absorbent resin with respect to the Weber number and the high-speed stirring blade diameter (average particle diameter of the primary particles of the water-absorbent resin / high-speed stirring blade diameter) is expressed by the equation (2). Is established.

式（２）中、ｄｈは高速撹拌翼３の攪拌翼径、Ｗｅはウェーバー数、ｋ_１は、図６の直線において、Ｗｅを１としたときの［（吸液性樹脂の１次粒子の平均粒子径）／ｄｈ］の値、すなわち縦軸の切片の値、ｋ_２は、図６の直線の傾きの絶対値を示すものである。ここで、吸液性樹脂の１次粒子の平均粒子径は、レーザー回折・散乱式粒度分布測定装置により測定する方法で求められる値で示され、体積基準で測定されるメジアン径を表すものである。
図６のグラフを利用することにより、所望の吸液性樹脂の１次粒子の体積基準のメジアン径を得ることが可能になる。

Wherein (2), dh is fast agitation stirring blades 3 blade diameter, We is the Weber number, k _1, in a straight line in FIG. 6, when the We and 1 [(the primary particles of absorbent resin The value of (average particle diameter) / dh], that is, the value of the intercept on the vertical axis, k ₂ represents the absolute value of the slope of the straight line in FIG. Here, the average particle diameter of the primary particles of the liquid-absorbent resin is a value obtained by a method of measuring with a laser diffraction / scattering particle size distribution measuring device, and represents a median diameter measured on a volume basis. is there.
By using the graph of FIG. 6, it becomes possible to obtain the volume-based median diameter of the primary particles of the desired liquid-absorbent resin.

A liquid absorbent resin having an average particle diameter of primary particles of 0.5 to 50 μm or less which is actually desired in a commercial scale reaction kettle can be obtained, for example, by performing the following operation.
First, in a small scale reaction kettle having a multi-shaft stirrer similar to a commercial scale reaction kettle assumed for production, the stirring speed of the low speed stirring blade 2 is controlled to be constant, and the stirring speed of the high speed stirring blade 3 is changed. The experiment was repeated several times to prepare liquid-absorbing resins having different primary particle sizes. Next, a numerical value [(average particle diameter of primary particles of liquid-absorbing resin) / dh] obtained by dividing the primary particle diameter of the liquid-absorbing resin by the high-speed stirring blade diameter is log-log plotted against the Weber number, and the formula By expressing (1) as a straight line on the logarithmic table of FIG. 6, a straight line satisfying the relationship of Expression (1) can be obtained. From FIG. 1, k1 and k2 can be determined.
Next, when the stirring speed in the reverse phase suspension polymerization is determined, the Weber number can be derived from the equation (2). When the Weber number is determined, [(average particle diameter of primary particles of liquid-absorbing resin) / dh] can be calculated from FIG. 6, and the average particle diameter of primary particles of liquid-absorbing resin is expected. The From this, by controlling the Weber number so that the average particle diameter of the primary particles of the liquid-absorbent resin is maintained at a constant value based on the formula (1), and stirring while maintaining a high stirring speed, The average particle diameter of the primary particles can be controlled in the range of 0.5 to 50 μm.
Specifically, in order to control the average particle diameter of primary particles to 10 μm, for example, in a commercial scale reaction kettle with an anchor blade having a stirring blade diameter of 0.8 m and a disper blade having a stirring blade diameter of 22.5 cm. The desired primary particles can be controlled to around 10 μm by controlling the Weber number of the disper blade to about 10, that is, by controlling the rotational speed of the disper blade to 400 to 450 rpm.

  Examples of the ethylenically unsaturated monomer having a sulfonic acid group or an alkyl metal salt thereof in the monomer mixture used in the present invention include 2-sulfoethyl acrylate, 2-sulfoethyl methacrylate, 2-acrylamide-2. -Methylpropanesulfonic acid, 2-methacrylamide-2-methylpropanesulfonic acid, 2-sulfopropyl acrylate, 2-sulfopropyl methacrylate, 3-sulfopropyl acrylate, 3-sulfopropyl methacrylate, 2-sulfobutyl acrylate, Examples thereof include sulfonic acid group-containing compounds such as 2-sulfobutyl methacrylate or salts thereof. Examples of the salt of the sulfonic acid group-containing compound include alkali metal salts, alkaline earth metal salts, and ammonium salts. Examples of the alkali metal salt include sodium salt, potassium salt, lithium salt, and rubidium salt, and examples of the alkaline earth metal salt include calcium salt and magnesium salt. Of these, 2-acrylamido-2-methylpropanesulfonic acid or an alkali metal salt thereof is preferable in that the highest liquid absorbability can be obtained.

The ethylenically unsaturated monomer having a sulfonic acid group or an alkali metal salt thereof used in the present invention is 10 to 100 in the monomer mixture in that it can maintain high liquid absorbency with respect to a high concentration salt-containing solution. % By weight is preferable, and 20 to 70% by weight is preferably used.
The ethylenically unsaturated monomer having a sulfonic acid group or an alkali metal salt thereof can be used by mixing with other water-soluble ethylenically unsaturated compounds. Examples of the water-soluble ethylenically unsaturated compound include (meth) acrylic acid and / or its alkali metal salt, ammonium salt, (meth) acrylamide, N, N-dimethylacrylamide, N-isopropylacrylamide, and 2-hydroxyethyl. Examples thereof include amino group-containing unsaturated compounds such as (meth) acrylate, N-methylol (meth) acrylamide, diethylaminoethyl (meth) acrylate, dimethylaminopropyl (meth) acrylate, and quaternized products thereof. One or more selected from the group can be used. Here, the term “(meth) acryl” means both “acryl” and “methacryl”. Of these, (meth) acrylamide, N, N-dimethylacrylamide, and N-isopropylacrylamide are preferable in view of copolymerizability with an ethylenically unsaturated monomer having a sulfonic acid group or an alkali metal salt thereof.

Polymers obtained by polymerizing the monomer mixture may self-crosslink without using the cross-linking agent, but cross-linking with a cross-linking agent is highly liquid-absorbing with excellent liquid absorbency. It is preferable when manufacturing resin.
Examples of the crosslinking agent include a monomer having two or more ethylenically unsaturated bonds and a compound having two or more functional groups that react with the functional group of the monomer in the monomer mixture.
Examples of the monomer having two or more ethylenically unsaturated bonds include di (meth) acrylic acid ester, tri (meth) acrylic acid ester, and bisacrylamide.
Examples of di (meth) acrylic acid esters include ethylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, polypropylene glycol di (meth) acrylate, di (meth) acrylic acid carb Examples include mill esters.
Examples of the tri (meth) acrylic acid ester include trimethylolpropane tri (meth) acrylate and pentaerythritol tri (meth) acrylate.
Examples of bisacrylamide include N, N′-methylenebisacrylamide and N, N′-ethylenebisacrylamide.
Among the monomers having two or more ethylenically unsaturated bonds, ethylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate, polypropylene glycol di (meth) acrylate, N, N′-methylenebis ( It is preferred to use (meth) acrylamide.

  Examples of the compound having two or more functional groups that react with the functional group of the monomer in the monomer mixture include compounds having two or more functional groups that react with the carboxyl group of (meth) acrylic acid. It is done. Specifically, for example, a compound having two or more epoxy groups, a compound having two or more isocyanate groups, and the like are used. Among them, a diglycidyl ether compound is preferably used.

  Examples of the compound having two or more epoxy groups include ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, glycerin diglycidyl ether, and polyglycerin diglycidyl ether. Of these, ethylene glycol diglycidyl ether is preferably used.

Examples of the compound having two or more isocyanate groups include 2,4-tolylene diisocyanate and hexamethylene diisocyanate.
The monomer having two or more ethylenically unsaturated bonds and the compound having two or more functional groups that react with the carboxyl group of the (meth) acrylic acid are based on 100 parts by weight of the monomer mixture. It is preferable to use within the range of 0.01 to 1 part by weight. A range of 0.01 to 0.5 parts by weight is particularly preferable. If it is in the range of 0.01 to 1 part by weight, a sufficient cross-linked structure is obtained, and the liquid absorption performance does not deteriorate.

  Examples of the radical polymerization initiator used in the present invention include peroxides such as hydrogen peroxide, potassium persulfate, sodium persulfate, and ammonium persulfate, and 2,2′-azobis- (2-aminodipropane) 2 hydrochloric acid. Salt, 2,2'-azobis- (N, N'-dimethyleneisobutylamidine) dihydrochloride, 2,2'-azobis {2-methyl-N- [1,1-bis (hydroxymethyl) -2- Azo compounds such as hydroxyethyl] propionamide}, and these may be used alone or in combination of two or more. At this time, a reducing substance such as sulfite and L-ascorbic acid, an amine salt, or the like can be used in combination with the peroxide as a redox initiator. The radical polymerization initiator is preferably used in an amount of 0.1 to 1 part by weight per 100 parts by weight of the monomer mixture.

The monomer mixture and the like can be mixed with water and stirred to prepare an aqueous solution containing the monomer mixture.
In the present invention, an aqueous solution containing this monomer mixture is supplied to a hydrophobic organic solvent containing a surfactant to carry out reverse phase suspension polymerization.

  Any hydrophobic organic solvent may be used as long as it is basically insoluble in water and inert to the polymerization reaction. For example, aliphatic hydrocarbons such as n-pentane, n-hexane, n-heptane and n-octane; alicyclic hydrocarbons such as cyclohexane and methylcyclohexane; aromatic hydrocarbons such as benzene, toluene and xylene Etc. Among these, particularly preferable solvents include n-hexane, n-heptane, cyclohexane and the like.

For supplying the aqueous solution, a method of dropping a part or the whole of the aqueous solution can be adopted.
That is, first, a monomer having two or more ethylenically unsaturated bonds or a monomer mixture thereof in an ethylenically unsaturated monomer aqueous solution containing 10 to 100% by weight of a sulfonic acid group or an alkali metal salt thereof. 0.01 to 1 part by weight of a compound having two or more functional groups that react with the functional group possessed, and further 0.1 to 1 part by weight of a radical polymerization initiator, and if necessary, thiols and thiolic acids Add water-soluble chain transfer agents such as secondary alcohols, amines, hypophosphites, etc. to prepare aqueous solutions containing monomers, etc., and introduce inert gas such as nitrogen to degas Do. On the other hand, in the polymerization apparatus, a surfactant is put into a hydrophobic organic solvent, and if necessary, the surfactant is slightly heated to dissolve the surfactant in the hydrophobic organic solvent, and an inert gas such as nitrogen is introduced to perform deaeration. . A part of the monomer aqueous solution is injected into the hydrophobic organic solvent, and the temperature rise is started with stirring. During this time, the aqueous solution of the reaction system becomes fine droplets and is suspended while being dispersed in the hydrophobic organic solvent. Over time, heat generation occurs and the polymerization starts. After the polymerization is started, the remaining monomer aqueous solution is added dropwise. It is possible to disperse the heat generated by polymerization by dropping a part or the whole amount.

As the surfactant used for the reverse phase suspension polymerization, any surfactant can be used as long as it has solubility or affinity for a hydrophobic organic solvent and basically forms a water-in-oil emulsion system. . As such a surfactant, generally, HLB (Hydrophile-Lipophile-Balance) is preferably in the range of 1 to 9, more preferably in the range of 2 to 7, and / or nonionic surfactant. An anionic surfactant.
Specific examples of such surfactants include sorbitan fatty acid ester, polyoxysorbitan fatty acid ester, sucrose fatty acid ester, polyglycerin fatty acid ester, polyoxyethylene alkylphenyl ether, ethyl cellulose, ethyl hydroxyethyl cellulose, oxidized polyethylene, anhydrous maleated polyethylene , Maleic anhydride polybutadiene, maleic anhydride ethylene / propylene / diene terpolymer, a copolymer of α-olefin and maleic anhydride or a derivative thereof such as polyoxyethylene alkyl ether phosphoric acid. Two or more of these surfactants can be used in combination as appropriate.

Among these surfactants, it is preferable to use sorbitan fatty acid ester or sucrose fatty acid ester in order to control the particle diameter of primary particles in the range of 0.5 to 50 μm. Further, sorbitan fatty acid ester and sucrose fatty acid ester may be mixed and used. Examples of sorbitan fatty acid esters include sorbitan monolaurate, sorbitan monostearate, sorbitan distearate, sorbitan tristearate, sorbitan monopalmitate, sorbitan monooleate, sorbitan dioleate, sorbitan trioleate having an HLB of 4-9. Is mentioned.
Examples of the sucrose fatty acid ester include sucrose stearate, sucrose palmitate, sucrose oleate, sucrose laurate, sucrose myristic ester, sucrose behenate, sucrose erucate Examples include esters. The commercially available sucrose fatty acid ester is a mixture of a diester and a triester having a monoester as a main component. Of these, a sucrose stearate having a monoester as a main component and having an HLB of 1 to 16 depending on the composition of diester and triester is preferable.
The amount of the surfactant used is preferably 0.05 to 10% by weight, more preferably 0.1 to 5% by weight, based on the hydrophobic organic solvent.

The following method is mentioned as a more specific method of the reverse phase suspension polymerization method.
That is, first, an ethylenically unsaturated monomer aqueous solution containing 10 to 100% by weight of a sulfonic acid group or an alkali metal salt thereof is prepared, and the monomer having two or more ethylenically unsaturated bonds or the above-mentioned single monomer is prepared in this aqueous solution. 0.01 to 1 part by weight of a compound having two or more functional groups that react with the functional group of the monomer mixture is mixed, further 0.1 to 1 part by weight of a radical polymerization initiator, and thiols as required. , Thiolic acids, secondary alcohols, amines, hypophosphites and other water-soluble chain transfer agents are added and dissolved to prepare an aqueous solution containing the above monomers, and inert gas such as nitrogen Introduce and deaerate. On the other hand, a surfactant is placed in a hydrophobic organic solvent in the polymerization apparatus, and if necessary, heated and dissolved slightly, and an inert gas such as nitrogen is introduced to perform deaeration. Next, an aqueous solution containing the monomer and the like is poured into this, and the temperature rise is started with stirring. During this time, the aqueous solution of the reaction system becomes fine droplets and is suspended while being dispersed in the hydrophobic organic solvent. Over time, heat generation occurs and the polymerization starts.

  After the start of polymerization, depending on the state of heat generation, cooling or heating is appropriately performed. The polymerization reaction temperature is preferably in the range of 60 to 100 ° C, more preferably 60 to 80 ° C.

In the method for producing a liquid-absorbing resin of the present invention, primary particles are aggregated by adding sucrose fatty acid ester, which is a surfactant having high thermal stability, to the suspension after the reverse phase suspension polymerization. Can be suppressed.
The liquid-absorbent resin obtained by the present invention can control the particle diameter of primary particles to 50 μm or less during polymerization by the reverse phase suspension polymerization method. The particles in the suspension can be separated from the hydrophobic organic solvent by decantation or filtration, and then dried by heating to obtain a powdery resin. In this case, when the suspension is decanted or filtered as it is and dried, the probability that the primary particles aggregate is high. Therefore, the liquid absorbent resin of the present invention is suspended by an azeotropic dehydration operation of a hydrophobic organic solvent and water in a state where the formed polymer is held with stirring after the reverse phase suspension polymerization is completed. It is preferable to remove water from the liquid. By performing this operation, primary particles can be made difficult to aggregate in a decantation or filtration or a subsequent drying process. The amount of azeotropic dehydration is 8 to 20% by weight of water based on the solid content of the liquid absorbent resin to be obtained, and it is preferable to dehydrate to 10 to 15% by weight. When the water content is 8 to 20% by weight, the particles are aggregated and the liquid-absorbing resin can be obtained in a powder state, and the liquid-absorbing characteristics are not deteriorated.

  When the ratio of the aqueous solution in the suspension containing the hydrophobic organic solvent and the entire aqueous solution is large, or when the solid content concentration in the aqueous solution is high, the primary particle diameter is controlled to 50 μm or less. However, there is a risk that primary particles aggregate during azeotropic dehydration and secondary particles that are much larger than that are formed. In particular, this tendency increases when the reaction kettle is scaled up to a commercial scale. Aggregation of primary particles is more likely to occur during azeotropic dehydration than during reverse phase suspension polymerization where particles are formed. By adding the sucrose fatty acid ester after the reverse phase suspension polymerization is completed and before starting the azeotropic dehydration, it is possible to avoid the risk of the aggregation.

Examples of sucrose fatty acid esters include sucrose stearate, sucrose palmitate, sucrose oleate, sucrose laurate, sucrose myristate, sucrose behenate, sucrose erucate, etc. Is mentioned. The commercially available sucrose fatty acid ester is a mixture of a diester and a triester having a monoester as a main component. Of these, a sucrose stearate having a monoester as a main component and having an HLB of 1 to 16 depending on the composition of diester and triester is preferable.
The physical property that the form of sucrose stearate is a powder and the thermal stability is high at a polymerization reaction temperature of 60 to 100 ° C. does not contribute to the effect of avoiding aggregation of primary particles. It is estimated that.
The amount of sucrose fatty acid ester added is preferably 10 to 50% by weight of the amount of surfactant added at the beginning of polymerization.

As a method for adding the sucrose fatty acid ester, the powder may be added as it is, or a powder suspended or dissolved in a hydrophobic organic solvent may be added. When the inside of the reaction vessel is in a slightly pressurized state and it is difficult to add the powder from a manhole or the like, it is preferable to add the powder after suspending or dissolving in a hydrophobic organic solvent.
The addition timing of the sucrose fatty acid ester is preferably after the reverse phase suspension polymerization is completed and before azeotropic dehydration is started. In order to exert the effect of the sucrose fatty acid ester, it is preferable that the water content with respect to the solid content of the liquid-absorbent resin from which the azeotropic dehydration amount is obtained does not reach 25% by weight, preferably 30% by weight.

The hydrophobic organic solvent is in the range of 40 to 200 parts by weight with respect to 100 parts by weight of the aqueous solution, and even when the hydrophobic organic solvent is as low as 40 to 100 parts by weight, a resin powder is obtained without causing aggregation of primary particles. be able to.
The liquid-absorbing material obtained by the production method of the present invention consists of swollen bead-like particles and can be separated from the hydrophobic organic solvent by decantation or filtration. Thereafter, it is dried by heating to obtain a powdery resin.
The liquid absorbent material thus obtained is usually a powder containing true spherical primary particles having an average particle size of 50 μm or less and secondary particles in which they are partially agglomerated. These secondary particles can also be easily pulverized by mechanical force, which has a great advantage in terms of production and use.
The liquid absorbent resin obtained by the production method of the present invention can be applied to all uses of conventionally known liquid absorbent materials. For example, waterproofing materials for optical fiber cables, water-swellable rubber, cement admixture, civil engineering field as waste mud gelling agent, construction field, industrial field; agriculture / horticulture as soil conditioner, water retention agent, etc. Field: Can be used in a wide variety of fields such as diapers and sanitary products such as sanitary products.

  Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples, but the present invention is not limited to these. In the following, all parts and percentages are based on weight unless otherwise specified. Various characteristics of the resin of the present invention were measured by the evaluation methods outlined below.

[Measuring method of average particle size and particle size distribution]
The average particle size and particle size distribution of the liquid absorbent resin were measured using a laser diffraction / scattering type particle size distribution analyzer LA-910 (manufactured by Horiba, Ltd.). The median diameter measured on a volume basis was defined as the average particle diameter.

Example 1
A polymerization tank of a 5 L separable flask with an inner diameter of 165 mm, equipped with an anchor blade with a stirring blade diameter of 150 mm, a disper blade with a stirring blade diameter of 45 mm, a cooling tube, and a thermometer, 1500 g of cyclohexane, Rhedol SP-S10V (sorbitan stearate, Kao Corporation) After the addition of 15.0 g (manufactured by the company), stirring was started at an anchor blade stirring speed of 150 rpm and a disper blade stirring speed of 3,000 rpm. On the other hand, 410 g of TBAS-Q (2-acrylamido-2-methylpropanesulfonic acid, manufactured by MRC Unitech Co., Ltd.) was added to a 2 L disc cup, and hydroxy-tetramethyl-1-piperidineoxyl was reduced to 0. TBAS-Q was neutralized by adding dropwise 800 g of an aqueous sodium hydroxide solution containing 04 g and dissolving 47.6 g of sodium hydroxide.
After 290 g of acrylamide, 0.30 g of N, N′-methylenebisacrylamide, 1.0 g of acrylic acid, and 1.0 g of ammonium persulfate were added to this solution and dissolved, nitrogen gas was blown to drive out dissolved oxygen.
Next, the monomer aqueous solution containing the polymerization initiator and the crosslinking agent obtained as described above was added to the above cyclohexane, and 0.6 g of sodium hydrogen sulfite was added in a powder state, and then the anchor blade was stirred. The speed was set to 150 rpm, the stirring speed of the disperser blade was set to 3000 rpm, and the temperature was raised to 70 ° C. to initiate the polymerization. After the heat generation due to the polymerization had subsided, 3.0 g of DK ester F-90 (sucrose stearate ester, HLB = 9, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) was added. The temperature inside the system was controlled at a temperature of 60 ° C. to 70 ° C. while stirring at an anchor blade stirring speed of 150 rpm and a disper blade stirring speed of 3000 rpm for 1 hour.
At this time, the liquid density was 0.979 kg · m ³ , the interfacial tension was 0.05 N / m, and the Weber number was 4.5. After extracting 300 g of water by azeotropic dehydration, the resin was taken out and dried at 70 ° C. under reduced pressure to obtain liquid absorbent resin A. The volume-based median diameter of the liquid absorbent resin A was 4 μm.

Example 2
Liquid absorbing resin B was obtained by the same operation as in Example 1 except that the stirring speed of the disperser blade was controlled to 2000 rpm. The Weber number was 2.0. The volume-based median diameter of the liquid absorbent resin B was 7 μm.
Example 3
Liquid absorbent resin C was obtained in the same manner as in Example 1 except that the stirring speed of the disper blade was controlled to 1500 rpm. The Weber number was 1.1. The volume-based median diameter of the liquid absorbent resin C was 11 μm.
Example 4
A liquid absorbent resin D was obtained by the same operation as in Example 1 except that the stirring speed of the disper blade was controlled to 1000 rpm. The Weber number was 0.5. The volume-based median diameter of the liquid absorbent resin D was 24 μm.
Example 5
Liquid absorbent resin E was obtained by the same operation as in Example 1 except that the stirring speed of the disper blade was controlled to 800 rpm. The Weber number was 0.3. The volume-based median diameter of the liquid absorbent resin E was 41 μm.

  Based on the results of Examples 1 to 5, the relationship between the Weber number and the primary particle diameter of the water-absorbent resin with respect to the stirring blade diameter (primary particle diameter of the water-absorbent resin / stirring blade diameter) is illustrated in FIG. A straight line graph was obtained.

Example 6
After charging 89.0 kg of cyclohexane and 1.5 kg of Rhedol SP-S10V in a 300 L polymerization tank equipped with an anchor blade with a stirring blade diameter of 800 mm, a disperse blade with a stirring blade diameter of 225 mm, a cooling pipe, and a thermometer, Agitation was started at a blade stirring speed of 500 rpm and a disper blade stirring speed of 35 rpm. On the other hand, TBAS-Q 24.0 kg was added to a 100 L tank, and while cooling from the outside, sodium hydroxide aqueous solution 47 containing 2.4 g of hydroxy-tetramethyl-1-piperidineoxyl and 2.8 kg of sodium hydroxide was dissolved. 6 kg was added dropwise to neutralize TBAS-Q.
After 17.0 kg of acrylamide, 17.8 g of N, N′-methylenebisacrylamide, 180 g of acrylic acid and 57.8 g of ammonium persulfate were added to this solution and dissolved, nitrogen gas was blown to drive out dissolved oxygen.
Next, the monomer aqueous solution containing the polymerization initiator and the crosslinking agent obtained as described above was added to the above-mentioned cyclohexane, and 34.8 g of sodium hydrogen sulfite was added in a powder state. Polymerization was started by raising the temperature. After the exotherm due to polymerization had subsided, 350 g of DK ester F-90 was added. The temperature in the system was controlled to a temperature of 60 ° C. to 70 ° C. while stirring at an anchor blade stirring speed of 35 rpm and a disper blade stirring speed of 500 rpm for 1 hour.

At this time, the liquid density was 0.979 kg · m ³ , the interfacial tension was 0.05 N / m, and the Weber number was 30.1. After 39 kg of water was extracted by azeotropic dehydration, the resin was taken out and dried at 70 ° C. under reduced pressure to obtain liquid absorbent resin F. The volume-based median diameter of the liquid absorbent resin F was 7 μm. The results are also shown in FIG. It can be seen that this result is on the straight line of the Weber number obtained in Examples 1 to 5 and [(average particle diameter of primary particles of liquid absorbent resin) / d]. It was found that the particle size on the large scale can be controlled based on the relationship obtained on the small scale.

<< Comparative Example 1 >>
A polymerization tank of a 2 L separable flask having an inner diameter of 130 mm, equipped with an anchor blade having a stirring blade diameter of 105 mm, a cooling pipe, and a thermometer, was charged with 800 g of cyclohexane and 13.2 g of Rhedol SP-S10V, and then a reflux cooling dehydration pipe and a dropping funnel. And stirring was started at a stirring speed of 450 rpm. Meanwhile, 210 g of TBAS-Q was added to a 2 L disc cup, and 420 g of an aqueous sodium hydroxide solution containing 0.02 g of hydroxy-tetramethyl-1-piperidineoxyl and 23.8 g of sodium hydroxide was added dropwise while cooling from the outside. TBAS-Q was neutralized.
After 146 g of acrylamide, 0.15 g of N, N′-methylenebisacrylamide and 0.5 g of ammonium persulfate were added to this solution and dissolved, nitrogen gas was blown to drive out dissolved oxygen.
Next, the monomer aqueous solution containing the polymerization initiator and the crosslinking agent obtained as described above was added to the above cyclohexane, and 0.4 g of sodium hydrogen sulfite was added in a powder state. As a result of adjusting the stirring speed, it was found that when rotating at 450 rpm or more, the vortex became large and the operation was difficult. Therefore, the stirring speed was set to 450 rpm and the polymerization was started by raising the temperature to 70 ° C. After the exotherm due to polymerization had subsided, the temperature in the system was controlled at a temperature of 60 ° C. to 70 ° C. while stirring for 1 hour at a stirring speed of 450 rpm. At this time, the liquid density was 0.979 kg · m ³ , the interfacial tension was 0.05 N / m, and the Weber number was 1.4. After extracting 300 g of water by azeotropic dehydration, the resin was taken out and dried at 70 ° C. under reduced pressure to obtain a liquid absorbent resin G. The volume-based median diameter of the liquid absorbent resin G was 30 μm.
In order to obtain a liquid-absorbent resin having a smaller particle diameter using an anchor blade, it is necessary to carry out the polymerization at a higher stirring speed, but it has been found to be dangerous because the vortex becomes large. It was found that particle diameter control is limited in this anchor blade.

<< Comparative Example 2 >>
A liquid absorbent resin H was obtained by the same operation as in Comparative Example 1 except that a three-stage pitched paddle blade with a stirring blade diameter of 95 mm was used and the stirring speed was set to 1000 rpm. The volume-based median diameter of the liquid absorbent resin H was 17 μm.
In order to obtain a liquid-absorbent resin with a three-stage pitched paddle blade and a smaller particle size, it is necessary to carry out the polymerization at a stirring speed higher than 1000 rpm. However, it was found that the vortex becomes large and dangerous. . It was found that particle size control is limited in this three-stage pitched paddle blade.

The schematic diagram which shows arrangement | positioning of one Embodiment of the polymerization tank used for the manufacturing method of the water absorbing resin of this invention. The schematic diagram which shows arrangement | positioning of one Embodiment of the polymerization tank used for the manufacturing method of the water absorbing resin of this invention. The schematic diagram which shows arrangement | positioning of one Embodiment of the polymerization tank used for the manufacturing method of the water absorbing resin of this invention. The schematic diagram which shows the example of the disk turbine blade which is a high-speed stirring blade. The schematic diagram which shows an example of the disper blade | wing which is a high-speed stirring blade. It is a graph showing the straight line which shows the relationship between a Weber number and (the average particle diameter of liquid absorbing resin / stirring blade diameter). 6 is a graph showing the relationship line between the Weber number based on the experimental results obtained in Examples 1 to 5 and (average particle diameter of liquid-absorbent resin / stirring blade diameter) and the results of Example 6.

Explanation of symbols

1 Polymerization tank 2 Low speed stirring blade 3 High speed stirring blade

Claims (11)

A hydrophobic organic solvent containing a surfactant, a monomer mixture containing an ethylenically unsaturated monomer having a sulfonic acid group or an alkyl metal salt thereof, and an aqueous solution containing a radical polymerization initiator have a stirrer A method for preparing a liquid-absorbent resin by charging in a polymerization tank and performing reverse phase suspension polymerization while stirring with the stirrer, wherein a multi-shaft stirrer having a low speed stirring blade and a high speed stirring blade is used as the stirrer. A method for producing a liquid-absorbent resin, comprising: controlling an average particle diameter of the liquid-absorbent resin particles. 2. The average particle diameter of the liquid-absorbent resin particles is controlled in the range of 0.5 to 50 μm by controlling the rotation speed of the high-speed stirring blade based on the Weber number represented by the relational expression (1). A method for producing the liquid-absorbent resin as described.

[In relational expression (1), We represents the Weber number, n represents the rotational speed of the high-speed stirring blade, dh represents the blade diameter of the high-speed stirring blade, ρ represents the liquid density, and σ represents the interfacial tension. ] The method for producing a liquid-absorbent resin according to claim 1, wherein the high-speed stirring blade is a turbine blade. The method for producing a liquid-absorbent resin according to claim 1, wherein the rotation speed of the low-speed stirring blade is smaller than the rotation speed of the high-speed stirring blade. The relationship between the inner diameter of the polymerization tank and the blade diameter of the low-speed stirring blade,
0.95 ≦ dl / D ≦ 0.99
[In the above formula, dl and D are the same as described above. ]
The method for producing a liquid-absorbent resin according to any one of claims 1 to 4. The low-speed stirring blade is an anchor blade, and the relationship between the blade width of the anchor blade and the inner diameter of the polymerization tank is 0.05 ≦ wl / D ≦ 0.10.
[In the above formula, wl represents the span of the anchor wing, and D is the same as above. ]
The method for producing a liquid-absorbing resin according to any one of claims 1 to 5. The relationship between the inner diameter of the polymerization tank and the blade diameter of the high-speed stirring blade,
0.15 ≦ dh / D ≦ 0.4
In the above formula, dh and D are the same as described above. ]
The method for producing a liquid-absorbing resin according to any one of claims 1 to 6. The method for producing a liquid-absorbing resin according to any one of claims 1 to 7, wherein the surfactant is a sorbitan fatty acid ester. After the reverse phase suspension polymerization is completed, azeotropic dehydration operation of a hydrophobic organic solvent and water is performed with stirring to remove water from the suspension. Method for producing liquid absorbent resin. The method for producing a liquid-absorbing resin according to claim 9, wherein a sucrose fatty acid ester is added before the azeotropic dehydration operation. The ethylenically unsaturated monomer having the sulfonic acid group or an alkali metal salt thereof is 2-acrylamido-2-methylpropanesulfonic acid or an alkali metal salt thereof. Method for producing liquid absorbent resin.

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