JP4975536B2 - Method for producing water-absorbing polymer - Google Patents

Description

  The present invention relates to a method for producing a water-absorbing polymer used for sanitary goods and the like.

  Water-absorbing polymers are used in the sanitary products field as water-absorbing substances in absorbent articles such as disposable diapers for infants, adults or incontinent (disposable diapers) or sanitary napkins for women. Currently, polyacrylic acid-based water-absorbing polymers occupy the mainstream as water-absorbing polymers.

The average diameter, particle size distribution, bulk specific gravity and the like of the water-absorbing polymer greatly affect the water-absorbing physical properties of the water-absorbing polymer. For this reason, although the average diameter and particle size distribution are controlled by the polymerization conditions and the like (see Patent Documents 1, 2, 3 and 4), it is still not sufficient.
Japanese Patent Laid-Open No. 3-227301 JP-A-4-348103 JP-A-6-184212 JP-A-6-206929

  An object of the present invention is to provide a method for producing a water-absorbing polymer having a high water-absorbing ability with good reproducibility by controlling the average diameter and particle size distribution, and a method for controlling the particle size of the water-absorbing polymer.

  The present invention is a method for producing a water-absorbing polymer by polymerizing a monomer component containing a water-soluble vinyl monomer, wherein 1 to 30 weights of all monomer components used for polymerization are added to a hydrophobic organic solvent in a reaction vessel. % Of the initially charged monomer component and 0 to 0.005% by weight of the polymerization initiator (hereinafter referred to as polymerization initiator 1) with respect to the initial charged monomer component, and then 0. A method for producing a water-absorbing polymer in which 01 to 10% by weight of a polymerization initiator (hereinafter referred to as polymerization initiator 2) is continuously or intermittently supplied to the reaction vessel, and a weight-based median diameter of the water-absorbing polymer by this production method The method of controlling the particle size of a water-absorbing polymer is provided.

  By the production method and particle size control method of the present invention, the average diameter and particle size distribution of the water-absorbing polymer can be controlled, and a water-absorbing polymer having a high water-absorbing ability can be produced with good reproducibility.

[Monomer component]
The monomer component used in the present invention contains a water-soluble vinyl monomer. The proportion of the water-soluble vinyl monomer in the monomer component of the present invention is preferably 50% by weight or more, and more preferably 70% by weight or more.

  Specific examples of water-soluble vinyl monomers include olefinic unsaturated carboxylic acids or salts thereof, olefinic unsaturated carboxylic acid esters, olefinic unsaturated sulfonic acids or salts thereof, olefinic unsaturated phosphoric acids or salts thereof, Examples thereof include vinyl monomers having a polymerizable unsaturated group such as olefinic unsaturated phosphate ester, olefinic unsaturated amine, olefinic unsaturated ammonium, and olefinic unsaturated amide. Among these, olefinic unsaturated carboxylic acids and salts thereof are preferable, acrylic acid, methacrylic acid, and alkali metal salts and ammonium salts thereof are more preferable, and acrylic acid and alkali metal salts of acrylic acid (sodium salt, potassium salt, etc.) ) And ammonium acrylate salts are particularly preferred. One or more of these monomers can be used.

  The monomer component may also contain a water-insoluble vinyl monomer that can be copolymerized with a water-soluble vinyl monomer. Examples of the water-insoluble vinyl monomer include unsaturated carboxylic acid alkyl ester monomers such as acrylic acid, methacrylic acid, maleic acid and fumaric acid having an alkyl group having 1 to 18 carbon atoms.

[Production method of water-absorbing polymer and particle size control method]
In the method of the present invention, first, a hydrophobic organic solvent is charged into a reaction vessel, and 1-30 wt% of initial charged monomer components and initial charged monomers out of all monomer components used for polymerization are added to this hydrophobic organic solvent. 0 to 0.005% by weight of the polymerization initiator 1 is supplied to the components. Next, 0.01 to 10% by weight of the polymerization initiator 2 with respect to the remaining monomer component and the remaining monomer component is continuously or intermittently supplied to the reaction vessel.

  The larger the amount of monomer supplied to the hydrophobic organic solvent in the reaction vessel in the initial stage, the smaller the average diameter of the water-absorbing polymer after the polymerization is completed, but when it is too much, when the polymerization initiator starts to be added Since the polymerization proceeds rapidly, the weight of the monomer initially supplied to the reaction vessel is 1 to 30% by weight, preferably 2 to 20% by weight, more preferably 3 to 15% by weight based on the total monomer weight used for the polymerization. By setting in the range of%, a water-absorbing polymer having a desired average diameter can be obtained.

  The monomer may be supplied as an aqueous solution, and the concentration of the aqueous monomer solution when the monomer is used as an aqueous solution is preferably 10 to 90% by weight, more preferably 30 to 60% by weight.

  In the present invention, examples of the hydrophobic organic solvent charged in the reaction layer include n-pentane, cyclopentane, n-hexane, cyclohexane, n-heptane, methylcyclohexane and other aliphatic hydrocarbons, benzene, toluene and the like. Examples thereof include aliphatic hydrocarbons having 4 to 6 carbon atoms such as aromatic hydrocarbons, n-butyl alcohol and n-amyl alcohol, aliphatic ketones such as methyl ethyl ketone, and aliphatic esters such as ethyl acetate. One or more of these hydrophobic organic solvents can be used. Moreover, the usage-amount of a hydrophobic organic solvent becomes like this. Preferably it is 50 weight part or more with respect to 100 weight part of all the monomer components, More preferably, it is 100-1000 weight part.

  In addition to the hydrophobic organic solvent, an amphiphilic solvent may be charged into the reaction tank. Examples of the amphiphilic solvent include alcohols such as methanol, ethanol, propanol, and 2-propanol, ketones such as acetone, and ethers such as tetrahydrofuran and dioxane. The amount of the amphiphilic solvent used is preferably a total amount with the hydrophobic organic solvent and up to 500 parts by weight per 100 parts by weight of the monomer.

  Moreover, a dispersing agent can be used when polymerizing a monomer. Examples of the dispersant include cationic and amphoteric surfactants such as sorbitan fatty acid esters such as sorbitan monostearate, sorbitan monolaurate and polyoxymethylene sorbitan monooleate, trimethylstearylammonium chloride and carboxymethyldimethylcetylammonium. Agents, anionic surfactants such as polyoxyethylene dodecyl ether sulfate sodium salt and dodecyl ether sulfate sodium salt, glycoside compounds such as alkyl glucoside, cellulose ethers such as ethyl cellulose and benzyl cellulose, cellulose acetate, cellulose butyrate and Cellulose esters such as cellulose acetate butyrate, maleated polybutadiene, maleated polyethylene, maleated α-o Fin, styrene - dimethylaminoethyl methacrylate quaternary salt and isopropyl methacrylate - can be exemplified a polymer dispersant such as dimethylaminoethyl methacrylate quaternary salt. One or more of these dispersants can be used. The amount of the dispersant used is preferably 0.01 to 5 parts by weight with respect to 100 parts by weight of the monomer. In particular, when reverse phase suspension polymerization of a monomer is performed, it is preferable to use an ionic surfactant as a dispersant for the monomer in terms of preventing aggregation of water-absorbing polymer particles.

  In the present invention, as described above, 1 to 30% by weight of the initial charge monomer component of all the monomer components and 0 to 0.005% by weight of the polymerization initiator 1 with respect to the initial charge monomer component are supplied, and then the rest 0.01 to 10% by weight of the polymerization initiator 2 is continuously or intermittently supplied to the reaction vessel with respect to the monomer component and the remaining monomer components. According to such a method of adding a monomer and a polymerization initiator, it is possible to obtain a water-absorbing polymer having a desired average particle diameter, few coarse particles, and good absorption performance.

In the present invention, the polymerization initiator 2 is supplied to the reaction vessel at a rate such that the addition rate V represented by the following formula (I) is 0.1 × 10 ⁻⁵ to 10 × 10 ⁻⁵ (1 / min). It is preferable to supply the reaction tank at a rate of 0.2 × 10 ^{−5 to} 5 × 10 ⁻⁵ (1 / min).
V = C / T (I)
(Here, C represents the average molar concentration of the polymerization initiator 2, and C = the amount of the polymerization initiator 2 used (mol) / the total amount of monomer components used in the polymerization (mol). T is the polymerization initiator.) 2 indicates the addition time (min).)

  Examples of the polymerization initiator used in the present invention include an azo polymerization initiator and an oxidative polymerization initiator, and an oxidative polymerization initiator is preferred. The polymerization initiator 1 and the polymerization initiator 2 may be the same or different.

  Specific examples of the azo polymerization initiator include those described in JP-A-8-337726, page 4, column 5, lines 4-19. These can use 1 or more types. Among these, 2,2′-azobis (2-amidinopropane) dihydrohalide, 2,2′-azobis [2- (2-imidazolin-2-yl) propane] dihydrohalide and 4,4′-azobis-4 -1 or more types selected from the group which consists of cyanovaleric acid are preferable in order to achieve the objective of this invention. In the above compound, the halide is preferably chloride from the economical viewpoint.

Specific examples of the oxidative polymerization initiator include those described in JP-A-8-337726, page 3, column 4, line 43 to page 4, column 5, line 3, and hydrogen peroxide / Examples thereof include ferrous salts, persulfates / sulfites, cumene hydroperoxide / ferrous salts, redox polymerization initiators such as hydrogen peroxide / L-ascorbic acid, and the like. These can use 1 or more types. Among these, persulfate is preferable for achieving the object of the present invention.
Further, one or more azo polymerization initiators and oxidative polymerization initiators can be used in combination.

  In the present invention, the total amount of the polymerization initiator used is preferably 0.01 to 10 parts by weight, more preferably 0.02 to 5 parts by weight, particularly 0.05 to 2 parts by weight based on 100 parts by weight of the monomer. preferable. When the amount of the polymerization initiator is within this range, it is possible to obtain a water-absorbing polymer in which polymerization proceeds smoothly, has a high water absorption retention ability, and has good stability over time in a water-containing state.

  The amount of the polymerization initiator 1 with respect to 100 parts by weight of the initially charged monomer component is 0.005 parts by weight or less, but the amount of the polymerization initiator may be zero. Moreover, 0.01-10 weight part is preferable with respect to 100 weight part of remaining monomer components remove | excluding the initial charge monomer component from all the monomer components used for superposition | polymerization, and 0.02-5 weight part is more. 0.05 to 2 parts by weight is preferable. When the amount of the polymerization initiator is within this range, it is possible to obtain a water-absorbing polymer in which polymerization proceeds smoothly, has a high water absorption retention ability, and has good stability over time in a water-containing state.

  In the present invention, from the viewpoint of controlling the particle diameter of the resulting water-absorbing polymer, a reverse phase suspension polymerization method in which an aqueous monomer solution is supplied into a dispersion medium containing a hydrophobic organic solvent is preferable, and the polymerization is performed by a batch operation. It is more preferable. Specifically, after supplying the predetermined amount of the monomer aqueous solution to the reaction vessel charged with the hydrophobic organic solvent, the monomer / polymerization initiator mixed aqueous solution obtained by adding the polymerization initiator or the aqueous solution to the remaining monomer aqueous solution is added. What is necessary is just to make and supply to a reaction tank. Alternatively, the monomer aqueous solution and the polymerization initiator or the aqueous solution thereof may be simultaneously added to the reaction vessel in parallel from different lines. When the polymerization initiator is used as an aqueous solution, the concentration of the polymerization initiator aqueous solution is preferably 0.05 to 90% by weight, more preferably 1 to 50% by weight.

  The polymerization temperature for polymerizing the monomer is preferably 20 to 120 ° C, more preferably 40 to 100 ° C. When the polymerization temperature is within this range, a preferable polymerization rate is achieved.

  In the present invention, a crosslinking agent can be added before polymerization, during polymerization, after polymerization, or during drying. Examples of cross-linking agents include polyallyl compounds, polyvinyl compounds, polyglycidyl ethers, haloepoxy compounds, polyaldehydes, polyols, polyamines, hydroxyvinyl compounds, and inorganic salts or organic compounds that produce polyvalent ions such as calcium, magnesium, zinc, and aluminum. A metal salt etc. can be illustrated.

  In addition, after the polymerization of the monomer (preferably reversed phase suspension polymerization) is completed, a desired water-absorbing polymer can be obtained by performing usual post-treatment, for example, azeotropic dehydration, drying, etc., if necessary. .

  According to the method of the present invention, the weight-based median diameter of the water-absorbing polymer can be controlled to 200 to 600 μm.

  In the present invention, the weight-based median diameter of the water-absorbing polymer is determined by classifying the sample using a sieve of 850 μm, 600 μm, 500 μm, 355 μm, and 106 μm, and measuring the weight of the particles remaining on each sieve. It can be determined by measuring the particle size distribution on a weight-based sieve and interpolating the particle size at 50% by weight.

Example 1
After diluting 510.0 g of 80 wt% acrylic acid with 203.8 g of water and neutralizing with 339.7 g of 48 wt% aqueous sodium hydroxide while cooling, the dispersion aid acylated sodium glutamate (Amisoft PS- 11, Ajinomoto Co., Ltd.) 0.18 g and dispersion auxiliary agent polyethylene glycol (K-PEG6000LA, Kao Co., Ltd.) 0.41 g were added to make a uniform solution to prepare a monomer / dispersion aid mixed aqueous solution. Separately, 965 g of normal heptane was charged into a 5-liter reaction vessel (separable flask) equipped with a reflux cooling dehydration tube, a dropping funnel, a nitrogen introduction tube, and an anchor blade (d / D = 0.9) as a stirring blade. Polyoxyethylene dodecyl ether sulfate sodium salt (average number of moles of added ethylene oxide = 1, Emar 170J, manufactured by Kao Corporation) as a dispersant was added at 0.582 g of a 70% by weight aqueous solution and stirred at a rotational speed of 300 r / min. After the inside of the reactor was purged with nitrogen, the temperature was raised to the boiling point, and 0.4 g of water was removed with a reflux condenser. After adjusting the temperature of normal heptane to 90 ° C., the above monomer / dispersion aid mixed aqueous solution is fed into this normal heptane at a constant flow rate for 3 minutes, and 5.0% by weight of all monomers used for polymerization / The dispersion aid mixture was charged into the reaction vessel. Next, a monomer / dispersion aid / polymerization initiator mixed aqueous solution in which 3.49 g of a 4.7% by weight sodium persulfate (NaPS) aqueous solution was added as a polymerization initiator to 45.0% by weight of the monomer / dispersion aid mixed solution, Furthermore, a monomer / dispersion aid / polymerization initiator mixed aqueous solution in which 7.00 g of 4.7% by weight aqueous sodium persulfate solution was added to 50.0% by weight of the remaining monomer / dispersion aid mixed solution was supplied to the reaction tank at a constant flow rate for 57 minutes. (In the following Examples 2 to 5 and Comparative Example 1 as well, the monomer supply time to the reaction vessel was 60 minutes in total). After completion of the monomer reaction tank supply, 284.2 g of water was dehydrated at a reaction tank temperature of 81 to 86 ° C. using a reflux cooling dehydration tube, and a crosslinking agent ethylene glycol diglycidyl ether (Denacol EX-810) at a reaction tank temperature of 86 ° C. , Manufactured by Nagase Chemtech Co., Ltd.) 0.1224 g dissolved in 10 g of ion-exchanged water was added. Thereafter, 125.3 g of dehydration was further performed at a reaction vessel temperature of 86 to 90 ° C., the product was fractionated, and dried under reduced pressure to obtain 501.4 g of acrylic acid (sodium) polymer particles. The obtained polymer particles were granular particles having a weight-based median diameter of 536 μm by a sieving method, and the bulk specific gravity was 0.62.

Example 2
After supplying the monomer / dispersion aid mixed aqueous solution to the reaction vessel to 6 minutes and charging 10.0% by weight of the monomer / dispersion aid mixed solution of all monomers used for polymerization into the reaction vessel, A monomer / dispersion aid / polymerization initiator mixed aqueous solution in which 3.49 g of a 4.7% by weight sodium persulfate aqueous solution as a polymerization initiator was added to 40.0% by weight of the monomer / dispersion aid mixed solution in the reaction vessel at a constant flow rate. The same operation as in Example 1 was performed except that the above was supplied. After drying, 502.1 g of acrylic acid (sodium) polymer particles were obtained. The weight-based median diameter was 372 μm and the bulk specific gravity was 0.71.

Example 3
After supplying the monomer / dispersion aid mixed aqueous solution to the reaction vessel to 9 minutes and charging the reactor with 15.0% by weight of the monomer / dispersion aid mixture of all the monomers used in the polymerization, A monomer / dispersion aid / polymerization initiator mixed aqueous solution in which 3.49 g of a 4.7% by weight sodium persulfate aqueous solution as a polymerization initiator was added to 35.0% by weight of the monomer / dispersion aid mixed solution in the reaction vessel at a constant flow rate. The same operation as in Example 1 was performed except that the above was supplied. After drying, 501.5 g of acrylic acid (sodium) polymer particles were obtained, the weight-based median diameter was 233 μm, and the bulk specific gravity was 0.78.

Example 4
After diluting 51.0 kg of 80 wt% acrylic acid with 20.4 kg of water and neutralizing with 34.0 kg of 48 wt% aqueous sodium hydroxide while cooling, 18 g of acylated sodium glutamate and 41 g of polyethylene glycol In addition, a homogeneous solution was prepared to prepare a monomer / dispersion aid mixed aqueous solution. Separately, 96.5 kg of normal heptane was charged in a 300 liter reaction tank (made of SUS316L) equipped with a condenser and an anchor blade (d / D = 0.9) as a stirring blade, and then polyoxyethylene dodecyl ether as a dispersant. After adding 58.2 g of 70% by weight aqueous solution of sulfate ester sodium salt (average number of moles of added ethylene oxide = 1, Emar 170J, manufactured by Kao Corporation) and stirring at a rotational speed of 120 r / min, the reactor was purged with nitrogen The temperature was raised to the boiling temperature, and 100 g of water was removed by reflux dehydration. After adjusting the temperature of normal heptane to 90 ° C., the aforementioned monomer / dispersion aid mixed aqueous solution is fed into this normal heptane for 6 minutes at a constant flow rate, and 10.0% by weight of the monomers out of all monomers used for polymerization / The dispersion aid mixture was charged into the reaction vessel. Next, a monomer / dispersion assistant / polymerization initiator mixed aqueous solution in which 349 g of a 4.7% by weight sodium persulfate aqueous solution was added as a polymerization initiator to 40.0% by weight of the monomer / dispersion auxiliary mixture was further added to the remaining monomer / A monomer / dispersion agent / polymerization initiator mixed aqueous solution in which 700 g of a 4.7% by weight sodium persulfate aqueous solution was added to 50.0% by weight of the dispersion auxiliary mixed solution was supplied to the reaction vessel at a constant flow rate for 54 minutes. After completion of the monomer supply to the reactor, 28.4 kg dehydration was performed at a reaction vessel temperature of 81 to 86 ° C., and a crosslinking agent ethylene glycol diglycidyl ether (Denacol EX-810, manufactured by Nagase Chemtech Co., Ltd.) at a reaction vessel temperature of 86 ° C. ) A solution of 12.2 g dissolved in 1.0 kg of ion exchange water was added. Then, 12.5 kg dehydration was further carried out at a reaction vessel temperature of 86 to 90 ° C., the product was fractionated, and dried under reduced pressure to obtain 52.3 kg of acrylic acid (sodium) polymer particles. The obtained polymer particles were granular particles having a weight-based median diameter of 274 μm by a sieving method, and the bulk specific gravity was 0.72.

Example 5
After diluting 510.0 g of 80 wt% acrylic acid with 203.8 g of water and neutralizing with 339.7 g of 48 wt% aqueous sodium hydroxide while cooling, the dispersion aid acylated sodium glutamate (Amisoft PS- 11, 0.18 g of Ajinomoto Co., Inc.) was added to make a uniform solution, and a monomer / dispersion aid mixed aqueous solution was prepared. Separately, 965 g of normal heptane was charged into a 5-liter reaction vessel (separable flask) equipped with a reflux cooling dehydration tube, a dropping funnel, a nitrogen introduction tube, and an anchor blade (d / D = 0.9) as a stirring blade. Polyoxyethylene dodecyl ether sulfate sodium salt (average number of moles of ethylene oxide added = 1, Emar 170J, manufactured by Kao Corporation) as a dispersant is added at 0.582 g of a 70% by weight aqueous solution and stirred at a rotational speed of 300 r / min. After the inside of the reactor was purged with nitrogen, the temperature was raised to the boiling point, and 0.4 g of water was removed with a reflux condenser. After adjusting the temperature of normal heptane to 90 ° C., the aforementioned monomer / dispersion aid mixed aqueous solution is fed into this normal heptane for 6 minutes at a constant flow rate, and 10.0% by weight of the monomers out of all monomers used for polymerization / The dispersion aid mixture was charged into the reaction vessel. Subsequently, 0.20 g of a dispersion auxiliary agent polyethylene glycol (K-PEG6000LA, manufactured by Kao Corporation) as a polymerization initiator and 4-50% by weight of the monomer / dispersion auxiliary mixture liquid, W-50 (manufactured by Wako Pure Chemical Industries, Ltd.) ) A monomer / dispersion aid / polymerization initiator mixed aqueous solution in which an aqueous solution prepared by dissolving 41 mg and iron ammonium citrate 0.4 mg in 14 g of water was added for 30 minutes, and the remaining monomer / dispersion aid mixed solution 50.0 A monomer / dispersion aid / polymerization initiator mixed aqueous solution in which 10.5 g of a 4.7% by weight sodium persulfate aqueous solution was added to the weight percent was supplied to the reaction vessel at a constant flow rate for 30 minutes. After completion of the monomer reaction tank supply, 284.2 g of water was dehydrated at a reaction tank temperature of 81 to 86 ° C. using a reflux cooling dehydration tube, and a crosslinking agent ethylene glycol diglycidyl ether (Denacol EX-810) at a reaction tank temperature of 86 ° C. , Manufactured by Nagase Chemtech Co., Ltd.) 0.163 g dissolved in 10 g of ion-exchanged water was added. Thereafter, 125.3 g of dehydration was further carried out at a reaction vessel temperature of 86 to 90 ° C., the product was fractionated, and dried under reduced pressure to obtain 500.4 g of acrylic acid (sodium) polymer particles. The obtained polymer particles were granular particles having a weight-based median diameter of 370 μm by a sieving method, and the bulk specific gravity was 0.74.

Comparative Example 1
Before the polymerization initiator (potassium persulfate aqueous solution) is supplied to the reaction vessel, the monomer is not supplied to the reaction vessel, and after the polymerization initiator is added to the total monomer / dispersion aid mixture used for polymerization, the monomer / dispersion is added. The same operation as in Example 1 was performed except that the supply of the aqueous solution of the auxiliary agent / polymerization initiator mixture to the reaction vessel was started. After drying, 500.8 g of acrylic acid (sodium) polymer particles were obtained, the weight-based median diameter was 645 μm, and the bulk specific gravity was 0.63.

Examples 6-11
A water-absorbing polymer was obtained in the same manner as in Example 1 except that the polymerization composition and conditions were changed as shown in Table 2. Table 2 summarizes the weight-based median diameter and bulk specific gravity of the obtained polymer by the sieving method.

  The water absorption rate of the water absorbing polymer obtained in Examples 1 to 11 and Comparative Example 1 was measured by the following method. These results are shown in Tables 1 and 2.

<Measurement method of water absorption rate>
a) With the water absorption rate measuring device shown in FIG. 1, the cock A of the bullet 1 with a horizontal cock (inner diameter 10.4 mmφ) is opened, the cock B is closed, and the physiological saline 2 is filtered through the filter paper 3 (No. 2: 70 mmφ). Inject until fully wet.

  b) Close cock A and inject physiological saline 2 to the 10 cc mark, close rubber stopper 4 and open cock A.

  c) Next, the cock B is opened, and the surface of the filter paper 3 is aligned with the center line of the cock B so that the liquid does not remain in the pipe of the cock B. Here, 7 is an air hole.

  d) Lightly wipe off excess liquid on the filter paper 3 with tissue paper or the like, and adjust the liquid level of the burette 1 to 20 cc.

  e) The polymer 5 accurately weighed in advance in an amount of 0.3 g is quickly and uniformly spread on the filter paper 3 within the diameter of the glass filter 6. Here, 8 is a plastic cylinder for preventing scattering of the polymer.

  f) When a bubble comes out from the cock B, the stopwatch is operated and the time of the liquid level is measured. At this time, the amount of absorption after 30 seconds is defined as the water absorption rate (cc / 30 sec).

* 1: (Pure amount of total dispersant used for polymerization) / (Pure amount of total acrylic acid used for polymerization) × 100
* 2: (Pure amount of initiator supplied to the reaction vessel at the indicated time) / (Pure amount of acrylic acid supplied to the reaction vessel at the indicated time) × 100
* 3: (Monomer charge amount at the start of initiator addition / total monomer amount used for polymerization) × 100

It is a device for measuring the water absorption rate.

Explanation of symbols

1 Burette with side cock 2 Saline 3 Filter paper 4 Rubber stopper 5 Polymer 6 Glass filter 7 Air hole 8 Plastic cylinder

Claims (7)

  A method for producing a water-absorbing polymer by polymerizing monomer components including a water-soluble vinyl monomer, and initially charging 1 to 30% by weight of all monomer components used for polymerization in a hydrophobic organic solvent in a reaction vessel After supplying 0 to 0.005% by weight of a polymerization initiator (hereinafter referred to as polymerization initiator 1) with respect to the monomer component and the initially charged monomer component, 0.01 to 10% with respect to the remaining monomer component and the remaining monomer component % Polymerization initiator (hereinafter referred to as polymerization initiator 2) is continuously or intermittently supplied to the reaction tank.   The method for producing a water-absorbing polymer according to claim 1, wherein the water-soluble vinyl monomer is an olefinically unsaturated carboxylic acid or a salt thereof.   The method for producing a water-absorbing polymer according to claim 1 or 2, wherein the polymerization initiator is an oxidative polymerization initiator. The polymerization initiator 2 is supplied to the reaction vessel at a rate such that the addition rate V represented by the following formula (I) is 0.1 × 10 ⁻⁵ to 10 × 10 ⁻⁵ (1 / min). 3. A method for producing a water-absorbing polymer according to any one of 3 above.
V = C / T (I)
(Here, C represents the average molar concentration of the polymerization initiator 2, and C = the amount of the polymerization initiator 2 used (mol) / the total amount of monomer components used in the polymerization (mol). T is the polymerization initiator.) 2 indicates the addition time (min).)   The manufacturing method of the water absorbing polymer in any one of Claims 1-4 whose superposition | polymerization is reverse phase suspension polymerization.   The method for producing a water-absorbing polymer according to any one of claims 1 to 5, wherein the polymerization is carried out by batch operation.   A method for controlling the particle size of a water-absorbing polymer, wherein the weight-based median diameter of the water-absorbing polymer is controlled to 200 to 600 μm by the production method according to claim 1.

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