JP5956232B2 - Method for producing water absorbent resin - Google Patents

Description

  The present invention relates to a method for producing a water absorbent resin.

  In recent years, water-absorbing resins have been used in sanitary materials such as sanitary products, disposable diapers, disposable rags, agricultural and horticultural materials such as water retention agents, soil conditioners, sludge coagulants, dew condensation agents for building materials, and oil dehydrants. Useful in various fields such as materials. Among these, water-absorbing resins are widely used especially for sanitary materials such as sanitary goods and disposable diapers.

  As such a water-absorbent resin, the acrylate polymer cross-linked product has a high water-absorbing capacity, and acrylic acid as a raw material is easily available industrially, has a constant quality, can be produced at low cost, and Since it has a number of advantages such as no defects such as rot, it is regarded as a preferred water-absorbent resin.

  Conventionally, as a method for obtaining a crosslinked acrylate polymer as a water-absorbing resin, a method of obtaining acrylic acid or alkali metal acrylate by bulk polymerization, aqueous solution polymerization, reverse phase emulsion polymerization, and reverse phase suspension polymerization, etc. It has been known. Among these, the method of obtaining a water-absorbent resin by bulk polymerization and aqueous solution polymerization is difficult to remove the polymerization heat, and the viscosity of the polymerization solution becomes extremely high, so it is difficult to produce using a general reaction vessel. There are also problems such as difficulty in obtaining powdery products.

  On the other hand, as a method for obtaining a water-absorbent resin by reverse phase emulsion polymerization and reverse phase suspension polymerization, a method for obtaining a powdery polymer from α, β-unsaturated carboxylic acid (salt) is disclosed (Patent Documents). 1, Patent Document 2, Patent Document 3, Patent Document 4, and Patent Document 5).

Japanese Patent Publication No. 34-010644 JP-A-53-046389 Japanese Patent Laid-Open No. 56-026909 JP-A-62-172006 JP 2006-001976 A

  In the reverse phase emulsion polymerization and the reverse phase suspension polymerization using a general reaction vessel disclosed in Patent Document 1 or the like, it is necessary to enlarge the reaction vessel when the production is to be efficiently performed. As the number of tanks increases, removal of polymerization heat may become a problem. Furthermore, when the temperature is raised to the temperature at which the polymerization starts, heating is performed from the outside of the reaction vessel, and energy is consumed to raise the temperature of not only the water-soluble ethylenically unsaturated monomer aqueous solution but also all hydrocarbon solvents. However, there is a problem in terms of energy, for example, heating more than that required for polymerization is required.

  In general, in reverse-phase emulsion polymerization and reverse-phase suspension polymerization, the higher the ratio of water-soluble unsaturated monomer aqueous solution (aqueous phase), the better the productivity. There is a possibility that problems in equipment such as an increase in the concentration of water and difficulty in stirring may occur.

The present invention relates to a method for producing a water absorbent resin as described below.
That is,
Item 1. A method for producing a water-absorbent resin, characterized in that a water-absorbent resin is produced by subjecting a water-soluble ethylenically unsaturated monomer aqueous solution to reverse phase suspension polymerization in a hydrocarbon solvent to produce a water-absorbent resin.
Item 2. Item 2. The water-absorbent resin according to Item 1, wherein the water-soluble ethylenically unsaturated monomer is at least one selected from the group consisting of acrylic acid and alkali metal salts thereof, and methacrylic acid and alkali metal salts thereof. Method.
Item 3. Item 3. The method for producing a water absorbent resin according to Item 1 or 2, wherein the hydrocarbon solvent is at least one selected from the group consisting of n-hexane, n-heptane, cyclohexane, toluene and xylene.
Item 4. Item 4. The method for producing a water absorbent resin according to any one of Items 1 to 3, wherein the polymerization is performed in the presence of a surfactant and / or a polymer protective colloid.
Item 5. The surfactant has sorbitan fatty acid ester, polyglycerin fatty acid ester, sucrose fatty acid ester, sorbitol fatty acid ester, polyoxyethylene alkylphenyl ether, and a hydrophobic group consisting of a dodecyl glycol group at one or both ends and a polyoxyethylene chain Item 5. The method for producing a water-absorbent resin according to Item 4, which is at least one selected from the group consisting of a poly (oxyethylene) glycol / dodecyl glycol block copolymer formed by:

Item 6. The polymer protective colloid is at least one selected from the group consisting of ethyl cellulose, ethyl hydroxyethyl cellulose, oxidation-modified polyethylene, maleic anhydride-modified polyethylene, maleic anhydride-modified polybutadiene, and maleic anhydride-modified ethylene / propylene copolymer. Item 5. A method for producing a water-absorbent resin according to Item 4.
Item 7. Item 7. The method for producing a water absorbent resin according to any one of Items 1 to 6, wherein the polymerization is performed in the presence of a crosslinking agent.
Item 8. The crosslinking agent is selected from the group consisting of ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, ethylene glycol diacrylate, ethylene glycol dimethacrylate, polyethylene glycol diacrylate, polyethylene glycol dimethacrylate, and N, N'-methylenebisacrylamide. Item 8. A method for producing a water absorbent resin according to Item 7, which is at least one selected from the group consisting of:
Item 9. Item 1-8, wherein the mass ratio (W / O ratio) of the water-soluble ethylenically unsaturated monomer aqueous solution (W) to the hydrocarbon solvent (O) is 0.2 to 2.0. A method for producing the water-absorbent resin as described.
Item 10. Item 1 in which a water-absorbent resin is produced by reverse-phase suspension polymerization of a water-soluble ethylenically unsaturated monomer aqueous solution in a hydrocarbon solvent, using a series of reactors arranged in series and / or in parallel. The manufacturing method of the water absorbing resin of any one of -9.
Item 11. Item 11. The method for producing a water absorbent resin according to Item 10, wherein the reactor is a tubular reactor.

  According to the present invention, when water-soluble ethylenically unsaturated monomer aqueous solution is subjected to reverse-phase suspension polymerization in a hydrocarbon solvent, heating is performed by microwave, so that it can be industrially produced from the viewpoint of energy and productivity. An advantageous method for producing a water-absorbent resin can be provided.

  As a result of various studies on the above problems, the present inventors have conducted heating in a method for producing a water-absorbing resin by subjecting a water-soluble ethylenically unsaturated monomer aqueous solution to reverse phase suspension polymerization in a hydrocarbon solvent. It has been found that a method for producing a water-absorbent resin can be provided industrially advantageously from the viewpoints of energy, productivity, and the like, by performing using microwaves.

  The reason why the water-absorbent resin production method according to the present invention can be advantageously produced industrially from the viewpoints of energy and productivity is not clear, but is considered as follows. By heating the reverse-phase suspension polymerization with microwaves, only the water-soluble ethylenically unsaturated monomer aqueous solution is selectively heated without substantially heating hydrocarbon solvents or the like that do not need to be heated. It is thought that it is because it is possible. That is, in the conventional heating method, the reaction tank is heated by heating from a jacket outside the reaction tank, and all the water-soluble unsaturated monomer aqueous solution, hydrocarbon solvent, etc. are heated by heat transfer. However, the method of heating by microwave is excellent in terms of energy because the reaction tank, the hydrocarbon solvent, and the like are hardly heated, and energy required for these heating is not required. Furthermore, compared with the conventional heating method by heat transfer, the polymerization proceeds extremely mildly because the polymerization heat generated in the water-soluble ethylenically unsaturated monomer aqueous solution is deprived by the hard-to-heat hydrocarbon solvent. Also turned out. Utilizing this mild polymerization, polymerization does not occur even if the mass ratio of the water-soluble ethylenically unsaturated monomer aqueous solution and the hydrocarbon solvent is increased, which was difficult with the conventional method using a reaction vessel. Found that is possible.

  Examples of the water-soluble ethylenically unsaturated monomer used in the present invention include (meth) acrylic acid and its alkali metal salts, ammonium salts and the like (in this specification, “acrylic” and “methacrylic” (Meth) acrylic ”. The same applies hereinafter); 2- (meth) acrylamide-2-methylpropanesulfonic acid and its alkali metal salts, ammonium salts, etc .; (meth) acrylamide, N, N-dimethyl (meth) acrylamide Nonionic monomers such as 2-hydroxyethyl (meth) acrylate, N-methylol (meth) acrylamide, polyethylene glycol mono (meth) acrylate; N, N-diethylaminoethyl (meth) acrylate, N, N-diethylamino Such as propyl (meth) acrylate and diethylaminopropyl (meth) acrylamide Examples thereof include an amino group-containing unsaturated monomer and a quaternized product thereof, and these may be used alone or in combination of two or more. Among these, acrylic acid or an alkali metal salt thereof, methacrylic acid or an alkali metal salt thereof is preferably used because it is easily available industrially.

  The water-soluble ethylenically unsaturated monomer is used as an aqueous solution. The concentration of the water-soluble ethylenically unsaturated monomer in the water-soluble ethylenically unsaturated monomer aqueous solution is preferably 25% by mass to a saturated concentration.

  When the water-soluble ethylenically unsaturated monomer contains an acid group, the acid group may be neutralized with an alkali metal salt, an ammonium salt, or the like. From the viewpoint of increasing the osmotic pressure of the resulting water-absorbent resin, increasing the water absorption rate, and preventing the occurrence of safety problems due to the presence of excess alkali metal, etc. It is preferable that it is 10-100 mol% of the acid group of a water-soluble ethylenically unsaturated monomer. As the salt for neutralization, alkali metal salts such as lithium, sodium, and potassium are preferable, and sodium and potassium are particularly preferable.

Examples of the hydrocarbon solvent used in the present invention include aliphatic hydrocarbon solvents, alicyclic hydrocarbon solvents, and aromatic hydrocarbon solvents. Examples of the aliphatic hydrocarbon solvent include n-pentane, n-hexane, n-heptane, and ligroin. Examples of the alicyclic hydrocarbon solvent include cyclopentane, methylcyclopentane, cyclohexane, and methylcyclohexane. Examples of the aromatic hydrocarbon solvent include benzene, toluene and xylene. These hydrocarbon solvents may be used alone or in combination of two or more.
Among these hydrocarbon solvents, n-hexane, n-heptane, cyclohexane, toluene and xylene are preferably used from the viewpoints of industrially constant quality, availability, and low cost. . The hydrocarbon solvent is less likely to be heated when heated by microwaves compared to water or water-soluble ethylenically unsaturated monomers, and is used for reverse phase suspension polymerization using microwaves according to the present invention. It is considered suitable.

  The amount of the hydrocarbon solvent used is such that the mass ratio (W / O ratio) of the water-soluble ethylenically unsaturated monomer aqueous solution (W) and the hydrocarbon solvent (O) is 0.2 to 2.0. The amount is preferable, and more preferably 0.6 to 1.7. Here, W and O indicate the mass of only the water-soluble ethylenically unsaturated monomer aqueous solution and the mass of the hydrocarbon solvent, respectively, which are used as a crosslinking agent, a polymerization initiator, a surfactant, Does not include mass of polymer protective colloids. When the mass ratio (W / O ratio) is less than 0.2, the volumetric efficiency is deteriorated, which may not be economical. In addition, when the mass ratio exceeds 2.0, the suspension state of the water-soluble ethylenically unsaturated monomer aqueous solution and the hydrocarbon solvent may become unstable during polymerization, or aggregation of polymer particles may easily occur. is there.

  As the microwave used in the present invention, a microwave having a generally used wavelength can be used. Specifically, a microwave having a wavelength of 1 m to 100 μm and a frequency of 300 MHz to 3 THz is used. In addition, industrially, microwaves mainly used are those having the same wavelength of 12.2 cm and frequency of 2.45 GHz as those used in microwave ovens, and those of this wavelength are also preferred in the present invention. Can be used. The microwave can be heated at high speed and efficiently, it has thermal responsiveness, that is, it can be instantaneously heated and stopped by turning on / off the power supply, uniformly from the inside rather than from the surface There are characteristics such as being able to be heated and being able to be locally heated.

  The reaction temperature of reversed-phase suspension polymerization when heating is performed by microwave is usually 20 to 110 ° C., although it varies depending on the polymerization initiator used. From the viewpoint of shortening the polymerization time by allowing the polymerization to proceed rapidly, easily removing the heat of polymerization, and performing the reaction smoothly, it is preferably 30 to 110 ° C, more preferably 60 to 80 ° C. is there. The reaction time varies depending on the wavelength and frequency of the microwave, but is usually 0.05 to 10 minutes. In addition, it is preferable to perform the said reaction in nitrogen or argon atmosphere as needed.

  In the method for producing a water-absorbent resin according to the present invention, the polymerization can be carried out in the presence of a surfactant and / or a polymer protective colloid.

  Examples of the surfactant include a nonionic surfactant or a combination of a nonionic surfactant and an anionic surfactant. Among these, sorbitan fatty acid ester, polyglycerin fatty acid ester, sucrose fatty acid ester, sorbitol fatty acid ester, polyoxyethylene alkylphenyl ether, and a hydrophobic group composed of a dodecyl glycol group at one or both ends and a polyoxyethylene chain It is preferably at least one selected from the group consisting of a poly (oxyethylene) glycol / dodecyl glycol block copolymer to be formed. 0.05-5 mass parts is preferable with respect to 100 mass parts of water-soluble ethylenically unsaturated monomer aqueous solution, and, as for the usage-amount of the said surfactant, More preferably, it is 0.1-3 mass parts.

  Examples of the polymer protective colloid include, for example, maleic anhydride modified polyethylene, maleic anhydride modified polypropylene, maleic anhydride modified ethylene / propylene copolymer, maleic anhydride modified polybutadiene, ethylene / maleic anhydride copolymer, ethylene Examples thereof include propylene / maleic anhydride copolymer, butadiene / maleic anhydride copolymer, oxidized polyethylene, ethylene / acrylic acid copolymer, ethyl cellulose, ethyl hydroxyethyl cellulose, and oxidized modified polyethylene. These may be used alone or in combination of two or more. Among these, at least one selected from the group consisting of ethyl cellulose, ethyl hydroxyethyl cellulose, oxidation-modified polyethylene, maleic anhydride-modified polyethylene, maleic anhydride-modified polybutadiene, and maleic anhydride-modified ethylene / propylene copolymer is preferably used. . 0.1-5 mass parts is preferable with respect to 100 mass parts of water-soluble ethylenically unsaturated monomer aqueous solution, and, as for the usage-amount of a polymer protective colloid, More preferably, it is 0.2-3 mass parts.

  In the method for producing a water-absorbent resin according to the present invention, it is preferable to use a crosslinking agent in order to suppress the water-soluble property of the obtained water-absorbent resin and ensure sufficient water absorption performance. When using a crosslinking agent, for example, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, ethylene glycol diacrylate, ethylene glycol dimethacrylate, polyethylene glycol diacrylate, polyethylene glycol dimethacrylate, and N, N′-methylenebisacrylamide Etc. These may be used alone or in combination of two or more. The crosslinking agent is usually used by adding to a water-soluble ethylenically unsaturated monomer, and the amount used is 0.001 to 5 parts by mass with respect to 100 parts by mass of the water-soluble ethylenically unsaturated monomer. Preferably, it is 0.01-2 mass parts.

  In the method for producing the water-absorbent resin according to the present invention, a polymerization initiator is usually used. As the polymerization initiator, a radical polymerization initiator is used, and specifically, a commonly used water-soluble radical polymerization initiator such as potassium persulfate, ammonium persulfate, and sodium persulfate is preferably used. Such radical polymerization initiators can also be used as redox initiators in combination with sulfites and the like.

  As the radical polymerization initiator, an oil-soluble radical polymerization initiator can also be used. However, when an oil-soluble radical polymerization initiator is used, since the polymer to be produced is generally water-soluble, it is preferable to use the above-described crosslinking agent in order to obtain a water-absorbing resin. As the oil-soluble radical polymerization initiator, benzoyl peroxide, azobisisobutyronitrile and the like are preferably used.

  The amount of the polymerization initiator used is usually preferably 0.0001 to 0.1 mol, more preferably 0.0002 to 0.05 mol, relative to 1 mol of the water-soluble ethylenically unsaturated monomer. It is. When the amount is less than 0.0001 mol, a long time is required for the polymerization reaction, and when it exceeds 0.1 mol, an excessively rapid polymerization reaction occurs, which is not preferable.

  In addition, according to the present invention, since the water-soluble ethylenically unsaturated monomer can be selectively heated without substantially heating the hydrocarbon solvent or the like, it is easy to remove the polymerization heat. Since the time is extremely short, it can also be produced by continuous polymerization. The method for continuous polymerization is not particularly limited, but, for example, a reverse phase obtained by mixing a hydrocarbon solvent and a water-soluble ethylenically unsaturated monomer aqueous solution, and optionally a raw material such as a surfactant and / or a polymer protective colloid. After preparing the suspension, a method of continuously polymerizing the reverse phase suspension is used.

  The continuous polymerization reactor may be a tank type or a tube type, and two or more reactors may be arranged in series and / or in parallel. However, when it is difficult to obtain a high monomer conversion rate with a single tank reactor, two or more, more preferably, a tube reactor is connected subsequently or if only a tank reactor is used. Are preferably connected in three or more groups. The method for introducing each raw material in the continuous polymerization is not particularly limited, and can be appropriately set depending on the shape of the reactor used, the mass ratio of each raw material, and the like. When two or more reactors are connected, a part of the water-soluble ethylenically unsaturated monomer aqueous solution is introduced into at least one of the second and subsequent reactors, so that the water-absorbing resin can be more stably added. Sometimes you can get. In the present invention, a tubular reactor is preferred from the viewpoint of easiness of continuous polymerization, ease of design of the reactor, and the like.

  In the case of production using a tubular reactor, for example, a solvent composition comprising a water-soluble ethylenically unsaturated monomer aqueous solution and, if desired, a hydrocarbon solvent in which a surfactant and / or a polymer protective colloid are dissolved. Are prepared separately, mixed in a mixer, and a reverse phase suspension is prepared in advance. On the other hand, continuous polymerization can be carried out by setting a tubular reactor in a microwave reactor, passing a reverse phase suspension prepared by a pump, and irradiating with microwaves.

  In the case of a tubular reactor, a solvent composition comprising a hydrocarbon solvent in which a surfactant and / or a polymer protective colloid is dissolved, and water-soluble ethylene, if desired, other than the above-described continuous polymerization method. It is also possible to carry out continuous polymerization by separately passing aqueous unsaturated monomer solutions. When this method is used, the microwave is consumed to raise the temperature of the water-soluble ethylenically unsaturated monomer aqueous solution to a predetermined temperature at which polymerization starts, but the water-soluble ethylenic water in the reverse phase suspension is used. Since the droplet diameter of the unsaturated monomer aqueous solution is very small, from several μm to several hundred μm, water is transferred to the solvent composition within a short time, and as a result, the water-soluble ethylenically unsaturated monomer that is desired to increase in temperature. There is also a risk of lowering the temperature. In that case, it can manufacture efficiently by raising the temperature of a solvent composition beforehand.

  In the production method according to the present invention, the material of the reactor is not particularly limited as long as it is a material that does not react with microwaves and transmits microwaves. Usually, glass or polytetrafluoroethylene is used.

  According to the method of the present invention, by heating with microwaves, it is possible to polymerize stably even if the mass ratio of the water-soluble ethylenically unsaturated monomer aqueous solution and the hydrocarbon solvent is large, in a very short time. Since the polymerization is possible, the production amount of the water-absorbent resin per unit microwave irradiation energy is 1 to 5 kg / kw · hr, and the water-absorbent resin can be produced very efficiently.

The specific production method will be described in detail with reference to examples, but in the case of a tank reactor, the outline is a microwave reactor (manufactured by Shikoku Keiki Kogyo Co., Ltd.) with a stirrer, thermometer, cooling And a reactor equipped with a nitrogen gas introduction pipe to prepare a solvent composition comprising a hydrocarbon solvent in which a surfactant and / or polymer protective colloid is dissolved, and then, if necessary, a crosslinking agent and a polymerization initiator. after introducing dissolved water-soluble ethylenically unsaturated monomer solution was to give a reverse phase suspension by performing stirring. Next, after performing nitrogen substitution, heating is performed by irradiation with sufficient microwaves. The internal temperature rises to a temperature at which the polymerization reaction starts within a few seconds, and the polymerization is completed soon.

  As the water-absorbent resin widely used in hygiene materials, powdered ones are preferably used, and those having a particle size of about several μm to several hundreds μm are preferably used. Therefore, in the method for producing a water-absorbent resin according to the present invention, it is important to select a hydrocarbon solvent to be used, a water-soluble ethylenically unsaturated monomer, and a surfactant or polymer protective colloid to be used as desired. Furthermore, selection of a crosslinking agent is also important in order to keep the water absorbent resin having various performances.

  Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples. The median particle diameter, physiological saline water absorption capacity, residual monomer content, and water-soluble content of the water absorbent resin obtained in each example were evaluated by the methods shown below.

<Medium particle size>
JIS standard sieve from above, sieve with an opening of 850 μm, sieve with an opening of 600 μm, sieve with an opening of 500 μm, sieve with an opening of 425 μm, sieve with an opening of 300 μm, sieve with an opening of 250 μm, sieve with an opening of 150 μm, and saucer In this order, 50 g of the water-absorbing resin was put into the uppermost sieve combined, and the mixture was classified by shaking for 20 minutes using a low-tap shaker.
After classification, the mass of the water-absorbent resin remaining on each sieve is calculated as a percentage by mass with respect to the total amount, and the mass of the water-absorbent resin remaining on the sieve opening and the sieve is calculated by integrating in order from the larger particle size. The relationship between percentage and integrated value was plotted on a logarithmic probability paper. By connecting the plots on the probability paper with a straight line, the particle diameter corresponding to an integrated mass percentage of 50 mass% was defined as the median particle diameter.

<Saline water absorption capacity>
In a 500 mL beaker, 500 g of 0.9 mass% sodium chloride aqueous solution (physiological saline) was weighed and stirred at 600 rpm, and 2.0 g of the water-absorbing resin was dispersed so as not to generate mako. The mixture was allowed to stand for 60 minutes in a stirred state to sufficiently swell the water absorbent resin. Thereafter, the mass Wa (g) of a standard sieve having an opening of 75 μm is measured in advance, and the content of the beaker is filtered using this, so that the sieve has an inclination angle of about 30 degrees with respect to the horizontal. Excess water was filtered off by standing for 30 minutes in an inclined state. The mass Wb (g) of the sieve containing the water-absorbing gel was measured, and the physiological saline water-absorbing ability was determined by the following formula.
Formula: Saline water absorption capacity (g / g) = [Wb−Wa] (g) / mass of water absorbent resin (g)

<Residual monomer content of water-absorbent resin>
In a 500 mL beaker, 500 g of 0.9 mass% sodium chloride aqueous solution (physiological saline) was weighed, and 2.0 g of water absorbent resin was added thereto, followed by stirring for 60 minutes. The contents of the beaker were filtered with a JIS standard sieve having an opening of 75 μm and further with a filter paper (No. 3 manufactured by ADVANTEC) to separate the water-absorbing gel and the extract. The monomer content dissolved in the obtained extract was measured by high performance liquid chromatography. The measured value was converted to a value per mass of the water-absorbent resin, and was defined as the residual monomer content (ppm).

<Water-soluble component>
In a 500 mL beaker, weigh out 500 ± 0.1 g of 0.9 mass% sodium chloride aqueous solution (physiological saline), put a magnetic stirrer bar (8 mmφ × 30 mm without ring), and add a magnetic stirrer [Iuchi ( Iuchi), product number: HS-30D]. Subsequently, the magnetic stirrer bar was adjusted to rotate at 600 rpm, and the bottom of the vortex generated by the rotation of the magnetic stirrer bar was adjusted to be close to the top of the magnetic stirrer bar.

  Next, 2.0 ± 0.002 g of the water absorbent resin was quickly poured and dispersed between the center of the vortex in the beaker and the side surface of the beaker and stirred for 3 hours. The water-absorbent resin-dispersed water after stirring for 3 hours was filtered through a standard sieve (aperture 75 μm), and the obtained filtrate was further suction filtered using a Kiriyama funnel (filter paper No. 6).

The obtained filtrate was weighed in a 100 mL beaker with a constant weight, 80 ± 0.1 g, dried with a hot air dryer (manufactured by ADVANTEC) at 140 ° C. until it became a constant weight, and the mass Wd of the solid content of the filtrate (G) was measured.
On the other hand, the same procedure as described above was performed without using a water-absorbent resin, and the mass Wet (g) of the solid content of the filtrate was measured, and the formula: dissolved content (mass%) = [[(Wd−We) × (500/80 ] / 2] × 100
Based on the above, the dissolved content was calculated.

Example 1
A 500 ml four-necked flask equipped with a stirrer, a reflux condenser, a thermometer, and a nitrogen gas inlet tube was charged with 92 g (1.03 mol) of an 80% by mass aqueous acrylic acid solution and 2.16 g of ion-exchanged water, While cooling with ice from the outside so that the temperature does not exceed 30 ° C., 104.2 g (0.78 mol) of a 30% by mass aqueous sodium hydroxide solution was gradually added dropwise to neutralize 76 mol% of acrylic acid. Next, 73.6 mg (0.387 mmol) of potassium persulfate as a water-soluble radical polymerization initiator, 10.1 mg (0.058 mmol) of ethylene glycol diglycidyl ether and 37.1 g of ion-exchanged water as a crosslinking agent were added. A water-soluble ethylenically unsaturated monomer aqueous solution was prepared by dissolution.

  Separately, a four-necked flask equipped with a stirrer, reflux condenser, dropping funnel, and nitrogen gas inlet tube in a microwave reactor (trade name: μReactor EX, manufactured by Shikoku Keiki Kogyo Co., Ltd.) Installed in this four-necked flask was 290 g of n-heptane and 0.736 g of maleic anhydride-modified ethylene / propylene copolymer (trade name: High Wax 1105A, manufactured by Mitsui Chemicals) as a polymer protective colloid. As an activator HLB3, 0.736 g of sucrose stearate (trade name: Surf Hope SS-3, manufactured by Mitsubishi Chemical Foods Co., Ltd.) was added and dissolved in n-heptane to prepare a hydrocarbon solvent composition.

Subsequently, the entire amount of the water-soluble ethylenically unsaturated monomer aqueous solution was added to the hydrocarbon solvent composition, and the suspension was kept at 30 ° C. with stirring. At the same time, sufficient nitrogen gas was blown to drive out residual oxygen.
At this time, the mass ratio (W / O ratio) between the water-soluble ethylenically unsaturated monomer aqueous solution and the hydrocarbon solvent was 0.81.

Subsequently, reverse phase suspension polymerization was performed by irradiating a microwave with a frequency of 2.45 GHz with an output of 1 kW using a microwave reactor. Polymerization proceeded promptly and gently, and after 80 seconds of irradiation, microwave irradiation was stopped when the internal temperature reached 70 ° C.
After completion of the polymerization, the flask was taken out from the microwave reactor, and water and n-heptane were distilled off by distillation and dried to obtain 90.9 g of a water-absorbing resin.
The obtained water-absorbent resin had a median particle diameter of 60 μm, a saline water absorption capacity of 54 g / g, a residual monomer content of 207 ppm, and a water-soluble content of 7.6 mass%.

Example 2
In Example 1, the same operation as in Example 1 was performed except that the amount of n-heptane used was changed to 160 g. At this time, the mass ratio (W / O ratio) between the aqueous water-soluble ethylenically unsaturated monomer solution and the hydrocarbon solvent was 1.46.
Polymerization proceeded promptly and gently, and after 69 seconds of irradiation, microwave irradiation was stopped when the internal temperature reached 70 ° C. After completion of the polymerization, the flask was taken out from the microwave reactor, and water and n-heptane were distilled off by distillation and dried to obtain 90.5 g of a water absorbent resin.
The obtained water-absorbent resin had a median particle diameter of 61 μm, a physiological saline water absorption capacity of 64 g / g, a residual monomer content of 220 ppm, and a water-soluble content of 9.6% by mass.

Example 3
A 3 L four-necked flask equipped with a stirrer, a reflux condenser, a thermometer, and a nitrogen gas inlet tube was charged with 920 g (10.3 mol) of an 80% by mass acrylic acid aqueous solution and 21.6 g of ion-exchanged water, While cooling with ice from the outside so that the temperature does not exceed 30 ° C., 1042.3 g (7.8 mol) of a 30% by mass aqueous sodium hydroxide solution was gradually added dropwise to neutralize 76 mol% of acrylic acid. Next, 736 mg (3.87 mmol) of potassium persulfate as a water-soluble radical polymerization initiator, 101 mg (0.58 mmol) of ethylene glycol diglycidyl ether and 371 g of ion-exchanged water as a crosslinking agent were added and dissolved to dissolve in water-soluble ethylenic acid. An unsaturated monomer aqueous solution was prepared.

  Separately, 2900 g of n-heptane and maleic anhydride-modified ethylene / propylene copolymer as a polymer protective colloid in a 7 L four-necked flask equipped with a stirrer, reflux condenser, thermometer, and nitrogen gas introduction tube Combined (Mitsui Chemicals Co., Ltd., trade name: High Wax 1105A) 7.36 g, Surfactant HLB3 as sucrose stearate (Mitsubishi Chemical Foods Co., Ltd., trade name: Surf Hope SS-3) 7. 36 g was added to prepare a hydrocarbon solvent composition.

Subsequently, the hydrocarbon solvent composition was added to the total amount of the water-soluble ethylenically unsaturated monomer aqueous solution, and the mixture was kept at 30 ° C. and suspended under stirring. At the same time, sufficient nitrogen gas was blown to drive out residual oxygen. This mixture was designated as Suspension 1.
At this time, the mass ratio (W / O ratio) between the water-soluble ethylenically unsaturated monomer aqueous solution and the hydrocarbon solvent was 0.81.

A glass U-shaped continuous reaction tube (with a reaction tube volume of 39 ml) having an inner diameter of 10 mm and a length of 50 cm was installed in a microwave reactor (trade name: μReactor EX, manufactured by Shikoku Keiki Kogyo Co., Ltd.). Suspension 1 was passed through the U-shaped continuous reaction tube at a rate of 78 g / min. The residence time of the suspension in the reaction tube is 30 seconds.
Five minutes after passing the solution, microwaves with a frequency of 2.45 GHz were irradiated at an output of 1 kW to perform reverse phase suspension polymerization. The liquid passing through the reaction tube was smooth even after microwave irradiation. A suspension polymerization solution was collected for 10 minutes from 5 minutes after the start of microwave irradiation, and water and n-heptane were distilled off by distillation, followed by drying to obtain 135 g of a water-absorbent resin.
The obtained water-absorbent resin had a median particle diameter of 68 μm, a physiological saline water absorption capacity of 51 g / g, a residual monomer content of 210 ppm, and a water-soluble content of 10.4% by mass.

Example 4
In Example 3, the same operation as in Example 3 was performed except that the amount of n-heptane used was changed to 1600 g. At this time, the mass ratio (W / O ratio) between the aqueous water-soluble ethylenically unsaturated monomer solution and the hydrocarbon solvent was 1.46.
After completion of the polymerization, the flask was taken out from the microwave reactor, and water and n-heptane were distilled off by distillation, followed by drying to obtain 178 g of a water absorbent resin.
The obtained water-absorbent resin had a median particle diameter of 73 μm, a physiological saline water absorption capacity of 52 g / g, a residual monomer content of 220 ppm, and a water-soluble content of 10.9% by mass.

Comparative Example 1
In Example 1, the reverse phase suspension in the flask was heated by heating with a water bath instead of the microwave reactor. When the reversed-phase suspension reached 70 ° C., polymerization occurred rapidly, and the aqueous phase became a gel-like lump, and a particulate water-absorbing resin was not obtained.

Comparative Example 2
In Comparative Example 1, the same operation as in Comparative Example 1 was performed except that the amount of n-heptane used was changed to 160 g. The mass ratio (W / O ratio) between the water-soluble ethylenically unsaturated monomer aqueous solution and the hydrocarbon solvent at this time was 1.46.
When the temperature of the reversed-phase suspension reached 70 ° C., polymerization occurred rapidly, and the aqueous phase became a gel-like lump, and a particulate water-absorbing resin could not be obtained.

Claims (10)

The water-soluble ethylenically unsaturated monomer solution in a hydrocarbon solvent, a process for the preparation of water-absorbent resin by reversed phase suspension polymerization using a radical polymerization initiator, have rows by microwave heating, and, It is characterized by carrying out continuous polymerization using reactors arranged in series and / or in parallel, and the production amount of the water absorbent resin per unit microwave irradiation energy is 1 to 5 kg / kw · hr . Production method.   The water-absorbent resin according to claim 1, wherein the water-soluble ethylenically unsaturated monomer is at least one selected from the group consisting of acrylic acid and alkali metal salts thereof, and methacrylic acid and alkali metal salts thereof. Production method.   The method for producing a water-absorbent resin according to claim 1 or 2, wherein the hydrocarbon solvent is at least one selected from the group consisting of n-hexane, n-heptane, cyclohexane, toluene and xylene.   The method for producing a water-absorbent resin according to any one of claims 1 to 3, wherein polymerization is performed in the presence of a surfactant and / or a polymer protective colloid.   The surfactant has sorbitan fatty acid ester, polyglycerin fatty acid ester, sucrose fatty acid ester, sorbitol fatty acid ester, polyoxyethylene alkylphenyl ether, and a hydrophobic group consisting of a dodecyl glycol group at one or both ends and a polyoxyethylene chain The method for producing a water-absorbent resin according to claim 4, wherein the water-absorbent resin is at least one selected from the group consisting of a poly (oxyethylene) glycol / dodecylglycol block copolymer formed by:   The polymer protective colloid is at least one selected from the group consisting of ethyl cellulose, ethyl hydroxyethyl cellulose, oxidation-modified polyethylene, maleic anhydride-modified polyethylene, maleic anhydride-modified polybutadiene, and maleic anhydride-modified ethylene / propylene copolymer. The manufacturing method of the water absorbing resin of Claim 4 which exists.   The method for producing a water-absorbent resin according to claim 1, wherein polymerization is performed in the presence of a crosslinking agent.   The crosslinking agent is selected from the group consisting of ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, ethylene glycol diacrylate, ethylene glycol dimethacrylate, polyethylene glycol diacrylate, polyethylene glycol dimethacrylate, and N, N'-methylenebisacrylamide. The method for producing a water-absorbent resin according to claim 7, wherein the water-absorbent resin is at least one kind.   The mass ratio (W / O ratio) between the water-soluble ethylenically unsaturated monomer aqueous solution (W) and the hydrocarbon solvent (O) is 0.2 to 2.0. 9. A method for producing a water-absorbent resin as described in 1. above. The method for producing a water-absorbent resin according to claim 1 , wherein the reactor is a tubular reactor.