JP3294463B2 - Method for producing superabsorbent polymer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for stably producing a superabsorbent polymer.

[0002]

2. Description of the Related Art The prior art relating to a method for producing a superabsorbent polymer is disclosed, for example, in JP-B-60-25045 and JP-A-57-15.
No. 8210, JP-A-57-21405, JP-A-57-98513, JP-A-61-87702, JP-B-2-19122 and JP-A-4-23.
Japanese Patent Application Laid-Open No. 6203 is known.

[0003] Briefly described in the above publication, JP-B-60-25045 discloses that an aqueous solution of acrylic acid and an alkali acrylate is suspended in an alicyclic or aliphatic hydrocarbon solvent in the presence of a dispersant. And performing suspension polymerization in the presence of a water-soluble radical polymerization initiator.

Japanese Patent Application Laid-Open No. 57-158210 discloses that when an aqueous solution of a water-soluble ethylenically unsaturated monomer containing no cross-linking agent is dispersed in a hydrocarbon for polymerization, a polymerization temperature as a protective colloid is used. It is described that a polymer having a large particle size can be obtained by using an oil-soluble cellulose ester or cellulose ether.

Japanese Patent Application Laid-Open No. 57-21405 discloses that when a monomer aqueous solution is subjected to suspension polymerization using a water-soluble radical polymerization initiator, α, β is added to a low molecular weight monoolefin polymer as a protective colloid. It describes that a polymer having a large particle size can be obtained by using a reaction product obtained by grafting an unsaturated polycarboxylic acid or an anhydride thereof.

Japanese Patent Application Laid-Open No. 57-98513 discloses that an α, β-unsaturated carboxylic acid has an affinity for an organic solvent as a dispersant when it is subjected to water-in-oil reverse phase suspension polymerization. It is described that a polymer having a large particle size can be obtained by using a basic nitrogen-containing polymer.

[0007] Japanese Patent Application Laid-Open No. 61-87702 discloses that when a α, β-unsaturated carboxylic acid is polymerized in a petroleum hydrocarbon solvent using a radical polymerization initiator, a sucrose fatty acid ester is protected with a protective colloid. It is described that a highly water-absorbent resin having high water absorbency, a high water absorption rate, and sufficient gel strength can be obtained by using the resin.

Further, Japanese Patent Publication No. 2-19122 discloses that
An aqueous solution polymerization method in which acrylic acid and an aqueous solution of an alkali metal acrylate are polymerized while being pulverized in, for example, a double-arm kneader is described.

Japanese Patent Application Laid-Open No. Hei 4-236203 discloses that a stationary aqueous solution polymerization is carried out using a redox-based polymerization catalyst comprising a peroxide and a reducing agent, so that the water absorption under normal pressure and the water absorption under pressure can be reduced. It is stated that a highly water-absorbing hydrogel is obtained.

In addition to the techniques described in each of the above publications, an aqueous solution of acrylic acid and an aqueous solution of an alkali alkali acrylate is impregnated in a nonwoven fabric, paper, or the like, and then exposed to an electron beam and / or a redox aqueous solution using a radical polymerization initiator. A polymerization method or a polymerizable monomer such as acrylic acid is gradually added to a boiled hydrophobic reaction medium with vigorous stirring, and a polymerization regulator is added as needed in the presence of an oil-soluble radical catalyst for polymerization. A pearl polymerization method is also known.

However, the method for producing a superabsorbent polymer as described above has the following problems. That is, when the superabsorbent polymer is produced by the above-described method, even if an extremely small amount of metal ions of several ppm is present in the aqueous solution containing the polymerizable monomer, the water absorbing performance of the obtained polymer is deteriorated. . In particular, when a superabsorbent polymer is produced by reversed-phase suspension polymerization, various dispersants or protective colloids are used to stabilize the dispersion of the aqueous monomer solution and prevent aggregation of the produced polymer particles. ,
If metal ions are present in the aqueous monomer solution, the polymerization stability is deteriorated, aggregation occurs, and even if a polymer is obtained, the water absorption performance of the polymer is inferior.

In order to solve the above problems, Japanese Patent Application Laid-Open No.
No. 7903 discloses a proposal in which, when a superabsorbent polymer is produced by suspension polymerization, an attempt was made to suppress aggregation of polymer particles and performance deterioration of the obtained polymer by the presence of a chelate compound as a polymerization stabilizer. It has been done. The method in which the chelate compound is present suppresses stabilization of polymerization and deterioration of the performance of the obtained polymer to some extent. However, the effect was not always sufficient. In order to achieve the effect, it is often necessary to add a large amount of the above chelate compound or to use a chelate compound having a very strong action. Under such circumstances, there is a problem that the original physical properties and functions of the superabsorbent polymer are significantly impaired.

[0013] Accordingly, an object of the present invention is to stably polymerize without polymer aggregation, and to deteriorate the performance of the produced polymer (fluctuation in water absorption, decrease in water absorption rate, decrease in flow rate of physiological saline, The present invention is to provide a method for producing a superabsorbent polymer in which the stability of the polymer and the increase in the soluble portion of the polymer are extremely suppressed.

[0014]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that the above object can be achieved by polymerizing a water-soluble monomer in the presence of a chelate compound having specific physical properties. .

The present invention has been made based on the above-mentioned findings. In a method for producing a superabsorbent polymer by polymerizing a water-soluble vinyl monomer, the polymerization is preferably
The solubility of Cu salt in physiological saline at 25 ° C. is 0.0
The above object has been achieved by providing a method for producing a superabsorbent polymer, which is carried out in the presence of at least one chelate compound of 1% by weight or less.

The superabsorbent polymer obtained by the method of the present invention is used in, for example, cosmetics and food additives containing radical-generating species such as ascorbic acid, depending on the type of superabsorbent polymer used. In particular, it is suitably used as a water-absorbing substance in sanitary articles which tend to cause problems in stability during use.

Hereinafter, the method of the present invention will be described in detail.

In the method of the present invention, a superabsorbent polymer is produced by polymerizing a water-soluble vinyl monomer. In this case, it is preferable to adopt a method of preparing an aqueous solution of the water-soluble vinyl monomer and polymerizing the monomer. The polymerization method is not particularly limited, and a conventionally known method can be appropriately used. For example, various polymerization methods such as an aqueous solution polymerization method, a reversed phase suspension polymerization method, and a pearl polymerization method can be employed. Above all, it is preferable to employ the reversed-phase suspension polymerization method or the aqueous solution polymerization method in view of workability at the time of polymerization and water absorbing properties of the obtained superabsorbent polymer.

Next, the water-soluble vinyl monomer used in the present invention will be described. As the water-soluble vinyl monomer, various vinyl monomers which are water-soluble and have a polymerizable unsaturated group can be used. .
For example, olefinically unsaturated carboxylic acids and salts thereof, olefinically unsaturated sulfonic acids and salts thereof, olefinically unsaturated phosphoric acids and salts thereof, olefinically unsaturated amines,
Examples include, but are not limited to, olefinically unsaturated ammonium and vinyl monomers having polymerizable unsaturated groups such as olefinically unsaturated amides.

The water-soluble vinyl monomers listed above will be described in more detail. Examples of olefinically unsaturated carboxylic acids and salts thereof include acrylic acid, methacrylic acid, maleic acid and fumaric acid, and alkali salts and esters thereof. Is mentioned. As the alkali salt,
For example, alkali metal salts (Na salt, K salt, etc.), alkaline earth metal salts (Ca salt, Mg salt, etc.), ammonium salts and the like can be mentioned. In this case, the degree of neutralization of the olefinically unsaturated carboxylic acid is generally about 0.5 to 0.9 mol per 1 mol of the acidic group. Further, as the ester of the olefinically unsaturated carboxylic acid, for example,
Examples include methoxypolyethylene glycol (meth) acrylate, phenoxypolyethylene glycol (meth) acrylate, and hydroxyethyl (meth) acrylate.

The olefinically unsaturated sulfonic acids and salts thereof include, for example, (meth) acrylamidomethylpropanesulfonic acid and allylsulfonic acid, and alkali salts thereof. In this case, the degree of neutralization of the olefinically unsaturated sulfonic acid is generally about 0.5 to 0.9 mol per 1 mol of the acidic group.

Examples of the olefinically unsaturated phosphoric acid and salts thereof include (meth) acryloyl (poly) oxyethylene phosphate and alkali salts thereof. In this case, the neutralization degree of the olefinically unsaturated phosphoric acid is generally 0.5 to 1 mol of the acidic group.
About 0.9 mol.

The above-mentioned olefinically unsaturated amine includes:
For example, dimethylaminoethyl (meth) acryl methacrylate and the like can be mentioned.

Examples of the olefinically unsaturated ammonium include (meth) acryloyloxyethylenetrimethylammonium halogen salt.

The above-mentioned olefinically unsaturated amide includes:
Examples thereof include (meth) acrylamide derivatives such as (meth) acrylamide, methyl (meth) acrylamide, ethyl (meth) acrylamide, and propyl (meth) acrylamide, and vinyl methylacetamide.

Among the above water-soluble vinyl monomers, olefinically unsaturated carboxylic acids and their alkali salts are particularly preferably used. More preferably, acrylic acid, methacrylic acid and metal salts thereof are used.

In the present invention, it is preferable to use only the above-mentioned water-soluble vinyl monomer and homopolymerize or copolymerize it to produce a superabsorbent polymer. However, the water-insoluble polymer which can be copolymerized with the above-mentioned water-soluble vinyl monomer is preferably used. Monomers, for example acrylic acid having an alkyl group having 1 to 18 carbon atoms,
Unsaturated carboxylic acid ester monomers such as methacrylic acid, maleic acid, and fumaric acid can be used together in an amount of 50% by weight or less of all monomers.

As described above, the water-soluble vinyl monomer is preferably used as an aqueous solution for polymerization. In this case, the concentration of the aqueous solution is preferably 1 to 70% by weight, and 10 to 65% by weight. %, More preferably 30 to 60% by weight.

When polymerizing the water-soluble vinyl monomer, it is preferable to use a polymerization initiator in combination. Less than,
The polymerization initiator will be described.

As the polymerization initiator, a radical initiator is generally used. Examples of such a radical initiator include ketone peroxides such as methyl ethyl ketone peroxide and methyl isobutyl ketone peroxide;
dialkyl peroxides such as tert-butyl peroxide and tert-butyl cumyl peroxide; tert-butyl peracetate, tert-butyl perisobutyrate, tert
Alkyl peresters such as -butyl pivalate; tert
Hydroperoxides such as butyl hydroperoxide and cumene hydroperoxide; persulfates such as hydrogen peroxide, potassium persulfate and ammonium persulfate; perchlorates such as potassium perchlorate and sodium perchlorate; chlorine Halogen salts such as potassium acid and potassium bromate; 2-
(Carbamoylazo) -isobutyronitrile, 2,2-
Azobis (N, N'-dimethyleneisobutylamidine)
Dihydrochloride, 2,2′-azobis (2-amidinopropane) dihydrochloride, 2,2′-azobis (N, N′-dimethyleneisobutylamidine), 4,
4'-azobis (4-cyanopentanoic acid), azobisisobutyronitrile, 2,2'-azobis (4-methoxy-2,4-dimethylvaleronitrile), (1-phenylethyl) azodiphenylmethane,
Dimethyl-2,2'-azobisisobutyrate, 2,
2′-azobis (2-methylbutyronitrile), 1,
1'-azobis (1-cyclohexanecarbonitrile), 2,2'-azobis (2,4,4'-trimethylpentane), 2-phenylazo-2,4-dimethyl-4
-Methoxyvaleronitrile, 2,2'-azobis (2-
Azo compounds such as methylpropane). These radical initiators may be used alone or as a mixture of two or more. Further, sulfites and these radical initiators can be used as a redox initiator system by combining them with a reducing agent such as L-ascorbic acid or ferrous salt. Among these polymerization initiators, it is particularly preferable to use potassium persulfate and 2,2′-azobis (2-amidinopropane) dihydrochloride. The polymerization initiator is preferably used in an amount of 0.01 to 10% by weight, more preferably 0.02 to 5% by weight, based on the water-soluble vinyl monomer. .

The method of adding the polymerization initiator to the reaction system is not particularly limited, but it is generally preferable to add the polymerization initiator to an aqueous solution of the water-soluble vinyl monomer in advance.

In carrying out the method of the present invention, before the polymerization,
A known crosslinking agent can be added to the reaction system during or after the polymerization. Hereinafter, such a crosslinking agent will be described.

Examples of the crosslinking agent include N, N'-
Polyallyl compounds such as diallyl acrylamide, diallylamine, diallyl methacrylamine, diallyl phthalate, diallyl maleate, diallyl terephthalate, triallyl cyanurate, triallyl phosphate; divinylbenzene, N, N-methylenebisacrylamide, ethylene glycol diacrylate, polyethylene Polyvinyl compounds such as glycol diacrylate, ethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, and glycerin trimethacrylate; polyglycidyl ethers such as ethylene glycol glycidyl ether, polyethylene glycol diglycidyl ether and polyglycerin polyglycidyl ether; epichlorohydrin, α-methylchlor Haloepoxidation of hydrin etc. Things; polyamines such as ethylenediamine; polyols such as glycerin; glutaraldehyde, polyaldehydes such as glyoxal 2-
Examples thereof include hydroxyvinyl compounds such as hydroxyethyl methacrylate; inorganic metal salts and organic metal salts capable of generating multivalent ions such as calcium, magnesium, zinc and aluminum. The amount of the crosslinking agent to be added can be appropriately adjusted according to the desired properties of the final produced polymer, but is usually 0.01 to 10% by weight based on the produced polymer.
It is preferable to add them so as to fall within the range.

In carrying out the method of the present invention, a monoglycidyl compound such as phenol polyoxyethylene glycol ether may be used as a modifier in addition to the crosslinking agent. The amount of the modifier added can be in the same range as that of the above-mentioned crosslinking agent.

The polymerization temperature in the method of the present invention depends on the type of polymerization initiator used, but is generally in the range of 2 to 4.
The temperature is preferably from 0 to 120 ° C, more preferably from 40 to 100 ° C. When the polymerization temperature exceeds 120 ° C., the crosslinking becomes extremely high, so that the water absorption capacity of the polymer particles is extremely lowered. When the polymerization temperature is lower than 20 ° C., the polymerization rate is extremely lowered.

As described above, the polymerization method in the method of the present invention is not particularly limited, but generally, the inverse suspension polymerization method is preferably used. Hereinafter, such a reversed-phase suspension polymerization method will be described.

The conditions for the above-mentioned reversed-phase suspension polymerization are not particularly limited. Preferably, the polymerization is carried out in the presence of a dispersant, using a hydrophobic organic solvent inert to the polymerization and an aqueous solution of the above-mentioned water-soluble vinyl monomer. The organic solvent and the dispersant will be described below.

First, the organic solvent will be described.
The organic solvent is preferably a hydrophobic organic solvent inert to polymerization. Such organic solvents include, for example, n-
Aliphatic hydrocarbons such as pentane, cyclopentane, n-hexane, cyclohexane, n-heptane, and methylcyclohexane; aromatic hydrocarbons such as benzene and toluene; and 4- to 4-carbon atoms such as n-butyl alcohol and n-amyl alcohol Aliphatic alcohols such as 6; aliphatic ketones such as methyl ethyl ketone; and aliphatic esters such as ethyl acetate. Such organic solvents can be used alone or as a mixture of two or more.
Such an organic solvent is preferably used in an amount of 50 to 500% by weight based on the aqueous solution of the water-soluble vinyl monomer.

When the above organic solvent is used, an amphiphilic solvent may be added within a range not exceeding the amount (weight) of the organic solvent used. Examples of such amphiphilic solvents include alcohols such as methanol, ethanol, propanol and 2-propanol; ketones such as acetone; and ethers such as tetrahydrofuran and dioxane.

Next, the dispersant used together with the organic solvent will be described. Examples of the dispersant include sorbitan fatty acid esters such as sorbitan monostearate, sorbitan monolaurate and polyoxymethylene sorbitan monooleate; Cationic and amphoteric surfactants such as stearyl ammonium chloride and carboxymethyldimethylcetyl ammonium; anionic surfactants such as sodium polyoxyethylene dodecyl ether sulfate and sodium dodecyl ether sulfate; glycosides such as alkyl glucoside Compounds; Cellulose ethers such as ethylcellulose and benzylcellulose; Cellulose such as cellulose acetate, cellulose butyrate and cellulose acetate butyrate Suesuteru; maleated polybutadiene, maleated polyethylene, maleated α- olefin, styrene - dimethylaminoethyl methacrylate quaternary salt and isopropyl methacrylate - may be mentioned polymeric dispersing agent such as dimethyl aminoethyl methacrylate quaternary salt. These dispersants can be used alone or as a mixture of two or more.

The above-mentioned chelate compound, which is a feature of the present invention, will be described. As described above, in the method of the present invention, the polymerization of the water-soluble vinyl monomer includes:
The solubility of Cu salt in physiological saline at 25 ° C. is 0.0
It is important that the reaction is performed in the presence of at least one chelating compound which is less than 1% by weight.

The "solubility" in the present invention means that the above-mentioned chelate compound Cu salt is added to physiological saline at 25 ° C. and dissolved while stirring for 30 minutes, and then the solution becomes transparent. The concentration (% by weight) obtained by dividing the maximum addition amount (weight) of the Cu salt by the weight of the solution and multiplying by 100 is meant.

The amount of the chelate compound to be added is 0.0 to 100 parts by weight of the produced polymer.
The amount is preferably from 0.01 to 10 parts by weight, more preferably from 0.01 to 5 parts by weight of the chelate compound.
The amount is such that it becomes parts by weight. The above addition amount is 0.001
If the amount is less than part by weight, coagulation may occur during reverse phase suspension polymerization, the amount of water absorbed by the produced polymer may fluctuate, or the performance of the produced polymer may deteriorate. Further, even if the addition amount exceeds 10 parts by weight, the addition effect is not improved,
Moreover, the physical properties of the produced polymer tend to be impaired, so that it is preferable to be within the above range.

The method of adding the chelate compound is not particularly limited. For example, the chelate compound may be added to an aqueous solution of the water-soluble vinyl monomer, or may be added to the organic solvent at the time of suspension polymerization. Alternatively, it may be added to the reaction system together with the aqueous solution of the water-soluble vinyl monomer during suspension polymerization.

The above-mentioned chelate compound preferably has a common logarithmic value (hereinafter, referred to as “pKCu”) of a chelate stability constant with Cu ²⁺ ions of about 3 or more at 25 ° C. If the pKCu is less than this, the performance as a polymerization stabilizer and a performance stabilizer (performance deterioration inhibitor) in the production of a superabsorbent polymer may be insufficient. The above pKCu is more preferably 4 or more, and further preferably 5 or more.

In the present invention, it is particularly preferable that the chelate compound is selected from the following three groups in addition to having the above-mentioned various physical properties. First group: hydrophilic having a hydrophobic part comprising a saturated or unsaturated hydrocarbon group having 6 or more carbon atoms and at least one group selected from the group consisting of a carboxylic acid group, a sulfonic acid group, a hydroxyl group and a phosphoric acid group. And a compound comprising: Group 2: β-diketone derivatives. Group 3: Tropolone derivatives.

In the present invention, at least one compound selected from the group consisting of the first to third groups can be used. Hereinafter, each of these compounds will be described.

First, the chelate compounds belonging to the first group will be described. The chelate compounds belonging to the first group are saturated or unsaturated having 6 or more carbon atoms (preferably 6 to 30, more preferably 12 to 22). It comprises a hydrophobic part comprising a saturated hydrocarbon group and a hydrophilic part having at least one group selected from the group consisting of a carboxylic acid group, a sulfonic acid group, a hydroxyl group and a phosphoric acid group. The saturated hydrocarbon group includes a linear or branched alkyl group or a cycloalkyl group, and the unsaturated hydrocarbon group includes a linear or branched alkenyl group or a phenyl group. Examples of the chelate compound having such a group include organic acid amide derivatives, hydroxycarboxylic acid derivatives, polycarboxylic acid derivatives, iminodiacetic acid derivatives, phosphate ester derivatives, N-acylated amino acid derivatives, and alkali metal salts thereof. And alkaline earth metal salts, but are not limited to these examples.

The chelate compounds listed above will be described in further detail. Examples of the organic acid amide derivatives include monoalkylamide citrate, monoalkenylamide citrate, and salts thereof. Examples of the hydroxycarboxylic acid derivative include monoalkyl citrate and monoalkenyl citrate, and salts thereof. Examples of the polyvalent carboxylic acid derivative include alkylmalonic acid and alkenylmalonic acid, and salts thereof. Examples of the above iminodiacetic acid derivatives include N-alkyl-N′-
Carboxymethyl aspartic acid and N-alkenyl-
N'-carboxymethyl aspartic acid and salts thereof can be mentioned. Examples of the phosphate derivative include monoalkyl phosphates and monoalkenyl phosphates, and salts thereof. Examples of the N-acylated amino acid derivative include N-
Acylated glutamic acid and N-acylated aspartic acid and salts thereof can be mentioned.

Of these, citric acid monoalkylamides and citric acid monoalkenylamides, salts thereof, citric acid monoalkyl esters and citric acid monoalkenyl esters, salts thereof, alkylmalonic acids and alkenylmalonic acids, and salts thereof N-alkyl-N'-carboxymethyl aspartic acid and N-alkenyl-N'-carboxymethyl aspartic acid and salts thereof, monoalkyl phosphates and monoalkenyl phosphates and salts thereof, N-acylated glutamic acid And N-acylated aspartic acid and salts thereof are preferably used as the above-mentioned chelate compound, and particularly, N-acylated glutamic acid and N-acylated aspartic acid and salts thereof (alkali metal salts, ammonium salts, etc.) Amino acid derivatives, more preferable since stabilizing effect of polymerization in performance and manufacture of superabsorbent polymers obtained is high. In particular, the use of N-acylated glutamic acid or a salt thereof as the chelate compound is particularly preferable because the particle size distribution of the produced polymer is further narrowed.

The above citric acid monoalkylamide and citric acid monoalkenylamide and salts thereof are preferably represented by the following general formula (I).

[0052]

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The above citric acid monoalkylamide and citric acid monoalkenylamide and salts thereof can be synthesized by a known method. For example, it can be obtained by hydrolyzing and neutralizing an imine obtained by completely performing dehydration condensation of an amine and citric acid. By properly selecting the number of carbon atoms of R ¹ in the general formula (I), monoalkylamide citrate, monoalkenylamide citrate and salts thereof can be obtained. R ¹
Number of carbon atoms is significantly deteriorated soluble exceeds 30, there is a case where the performance as a stabilizing agent for polymerization in performance and manufacture of the number of carbon atoms of R ¹ is less than 6 superabsorbent polymer falls Therefore, it is preferable to be within the above range. The number of carbon atoms in R ¹ is more preferably 12 to 22.

The above monoalkyl citrate, monoalkenyl citrate and salts thereof are preferably represented by the following general formula (II).

[0055]

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The above monoalkyl citrate and monoalkenyl citrate and salts thereof can be synthesized by a known method. For example, it is obtained by dehydration condensation of alcohol and citric acid. By properly selecting the number of carbon atoms of R ² in the general formula (II), monoalkyl citrate and monoalkenyl citrate and salts thereof can be obtained. When the number of carbon atoms of R ² exceeds 30, the water solubility becomes remarkably deteriorated, and when the number of carbon atoms of R ² is less than 6, the performance of the superabsorbent polymer and the performance as a polymerization stabilizer in the production deteriorate. Therefore, it is preferable to be within the above range. The number of carbon atoms of R ² is more preferably 12 to 22.

The above-mentioned alkylmalonic acid and alkenylmalonic acid and salts thereof are preferably represented by the following general formula (III):
It is represented by

[0058]

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The above-mentioned alkylmalonic acid and alkenylmalonic acid and salts thereof can be synthesized by a known method. For example, an α-olefin is added to methyl malonate or ethyl malonate to obtain methyl alkyl malonate or ethyl alkyl malonate, which is then hydrolyzed and neutralized. R in the general formula (III)
By appropriately selecting the number of carbon atoms of ³ , alkylmalonic acid and alkenylmalonic acid, and their salts, can be obtained. When the number of carbon atoms of R ³ exceeds 30, the water solubility becomes extremely poor, and the number of carbon atoms of R ³ becomes 6
If the amount is less than the above range, the performance of the superabsorbent polymer and the performance as a polymerization stabilizer in the production may be deteriorated. The number of carbon atoms in R ³ is
More preferably, it is 12 to 22.

The above-mentioned N-alkyl-N'-carboxymethylaspartic acid and N-alkenyl-N'-carboxymethylaspartic acid and salts thereof are preferably represented by the following general formula (IV).

[0061]

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The above-mentioned N-alkyl-N'-carboxymethylaspartic acid and N-alkenyl-N'-carboxymethylaspartic acid and salts thereof can be synthesized by known methods. For example, it is obtained by carboxymethylating an alkylaminosuccinic acid obtained by adding an amine to maleic acid with carboxymethyl chloride and neutralizing the alkylaminosuccinic acid. By appropriately selecting the number of carbon atoms of R ⁴ in the general formula (IV), N-alkyl-N′-carboxymethylaspartic acid and N
-Alkenyl-N'-carboxymethylaspartic acid and salts thereof can be obtained. When the number of carbon atoms of R ⁴ exceeds 30, the water solubility becomes remarkably poor, and when the number of carbon atoms of R ⁴ is less than 6, the performance of the superabsorbent polymer and the performance as a stabilizer for polymerization in the production deteriorate. Therefore, it is preferable to be within the above range. The number of carbon atoms of R ⁴ is more preferably 12 to 22.

The above monoalkyl phosphates and monoalkenyl phosphates and salts thereof are preferably represented by the following general formula (V).

[0064]

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The above monoalkyl phosphates and monoalkenyl phosphates and salts thereof can be synthesized by known methods. For example, it can be obtained by phosphorylating an alcohol with phosphorus pentoxide, phosphorus oxychloride, polyphosphoric acid, or the like. By appropriately selecting the number of carbon atoms of R ⁵ in the general formula (V), monoalkyl phosphoric acid esters and monoalkenyl phosphoric acid esters, and salts thereof, can be obtained. R
^{If the} number of carbon atoms of ⁵ exceeds 30, the water solubility will be remarkably deteriorated, and if the number of carbon atoms of R ⁵ is less than 6, the performance of the superabsorbent polymer and the performance as a polymerization stabilizer in the production may decrease. Therefore, it is preferable to be within the above range. The number of carbon atoms in R ⁵ is more preferably 12 to 22.

The above-mentioned N-acylated glutamic acid and a salt thereof are preferably represented by the following general formula (VI).

[0067]

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The above-mentioned N-acylated glutamic acid and salts thereof can be synthesized by known methods, but are also available as commercial products. R ⁶ —CO in the general formula (VI)
By appropriately selecting the number of carbon atoms of-, N-acylated glutamic acid and a salt thereof which are suitable for the purpose can be obtained. When the number of carbon atoms of R ⁶ —CO— exceeds 30, the water solubility becomes extremely poor, and when the number of carbon atoms of R ⁶ —CO— is less than 6, the performance of the superabsorbent polymer and the polymerization stabilizer in production are stabilized. It is preferable that the content be within the above range, since the performance of the device may decrease. The number of carbon atoms of R ⁶ —CO— is more preferably 12 to 22.

The above-mentioned N-acylated aspartic acid and its salt are preferably represented by the following general formula (VII).

[0070]

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The above-mentioned N-acylated aspartic acid and salts thereof can be synthesized by known methods, but are also available as commercial products. R ⁷ -C in the general formula (VII)
By appropriately selecting the number of carbon atoms of O-, N-acylated aspartic acid and a salt thereof can be obtained which are suitable for the purpose. When the number of carbon atoms in R ⁷ —CO— exceeds 30, the water solubility becomes extremely poor, and the number of carbon atoms in R ⁷ —CO—
If the amount is less than the above range, the performance of the superabsorbent polymer and the performance as a polymerization stabilizer in the production may be deteriorated. R ⁷ —CO— more preferably has 12 to 22 carbon atoms.

Next, the chelate compounds belonging to the second group will be described. As described above, the chelate compounds belonging to the second group are β-diketone derivatives, and examples thereof include acetylacetone, benzoylacetone, and dibenzoyl. Methane, furoyl acetone, benzoyl furoyl methane, 4-hydroxybenzoyl acetone, 4-te
rt-butyl-4'-hydroxydibenzoylmethane, 4
-Hydroxybenzoylmethane-tert-butyl ketone,
Examples include compounds such as 4-hydroxy-4'-hydroxydibenzoylmethane, but are not limited to these examples. Of these, acetylacetone, 4-
Hydroxybenzoyl acetone and 4-hydroxybenzoylmethane-tert-butyl ketone are particularly preferably used.

Next, the chelate compounds belonging to the third group will be described. As described above, the chelate compounds belonging to the third group are tropolone derivatives, and examples thereof include tropolone, β-thiaprisin, and γ-thiaprisin. , Β-Drabrin and 6-isopropyltropolone-
Examples include methyl 4-carboxylate and its sodium and potassium salts, but are not limited thereto. Of these, β-thyaprisin and γ-
Tsuyaprisin is particularly preferably used. Particularly, β-tsuyaprisin is preferable because it is added / used as a fragrance such as a nourishing and restoring agent, a toothpaste, a fragrance, an external preparation, a bath agent, a shampoo, and a rinse, and is a compound safe for a living body.

As the above-mentioned tropolone derivative, a synthetic product or a semi-synthetic product may be used, or natural hiba oil or hinoki oil extract containing the above-mentioned tropotone derivative may be used as it is, or these may be purified. May be used.

[0075]

According to the method of the present invention, in producing a superabsorbent polymer, deterioration of the water absorption performance of the polymer caused by the presence of a trace amount of metal ions, particularly iron ions (for example, a decrease in gel strength) , Change in water absorption, increase in the amount of polymer in the soluble part, etc.). In particular, there is an advantage that aggregation of polymer particles caused by the presence of metal ions during production of a polymer by suspension polymerization can be suppressed. Thus, the superabsorbent polymer obtained by the method of the present invention has no deterioration in gel strength and water absorption performance. According to the method of the present invention,
Since the polymerization reaction is also stabilized, the method is industrially excellent. In particular, when N-acylated glutamic acid or a salt thereof is used as the chelate compound, the particle size distribution of the produced polymer is further narrowed, so if a polymer having such a particle size distribution is used for a sanitary article such as a disposable diaper,
In the step of mixing and holding the polymer in pulverized pulp or nonwoven fabric, the polymer is advantageously prevented from falling off, and the processability of the sanitary article is significantly improved.

[0076]

The present invention will be described below in more detail with reference to Examples and Comparative Examples, but the present invention is not limited thereto. Unless otherwise specified, “%” in the following Examples and Comparative Examples represents “% by weight”.

The reagents used in Examples and Comparative Examples are generally commercially available reagents. However, as the N-acylated glutamic acid 2Na salt, Amisoft HS-21 and GS-11 manufactured by Ajinomoto Co., Inc. were used, and β-tsuyaprisin and γ-tsuyaprishi were manufactured by Takasago International Corporation. Acid monoalkylamide 2Na salt, citric acid monoalkyl ester Na salt, citric acid monooleyl ester, alkylmalonic acid, N-alkyl-N'-carboxymethylaspartic acid 3Na salt, monoalkyl phosphate ester, monooleyl phosphate ester As the N-acylated aspartic acid 2Na salt, those synthesized by a known method were used.

Table 1 shows the solubility of the Cu salt and the value of pKCu of the chelate compounds used in Examples and Comparative Examples. In addition, the solubility of pKCu and Cu salt was measured by the following method.

<Method of Measuring pKCu> A Cu ion electrode method (Orion, pH / ion, analyzer, Cu ion electrode) is used, and a 0.1 M triethanolamine-hydrochloric acid (pH 8) buffer solution is used as a solution. First, CuCl
Standard copper ion buffer solution [400 using ₂ · 2H ₂ O,
320, 240, 160, 80 ppm (Cu ²⁺ conversion)]
Is prepared, and a calibration curve is created using a Cu ion electrode. Next, the chelate compound (weighing 0.1 g) is dissolved in a buffer solution (100 ml) using a volumetric flask. This solution was added to a 0.05 M CuCl ₂ .2H ₂ O buffer solution (pH
8) is added dropwise from the burette in an amount of 0.6 ml, and the potential of the Cu ion electrode at that time is read. Titration is 400 ppm
The measurement is performed to the point where the potential exceeds (corresponding to Cu ²⁺ ), and the blank is measured in the same manner. The concentration of free Cu ions is calculated from the potential, and the change in the liquid volume of the system due to titration is corrected to that value. PKCu is calculated from equation (1) assuming that when the equimolar amount of Cu is added to the chelate compound, the chelate compound and the Cu ion form a 1: 1 mole complex.

[0080]

(Equation 1)

<Measurement Method of Solubility of Cu Salt of Chelate Compound>
After adding u salt and dissolving with stirring for 30 minutes,
The maximum addition amount (S ₁ g) of the Cu salt of the chelate compound so that the solution becomes transparent is measured. Assuming that the weight of the aqueous solution at this time is S ₂ g, the solubility of the Cu salt of the chelate compound can be obtained from the following equation (2).

[0082]

(Equation 2)

[0083]

[Table 1]

Before describing the examples and comparative examples, test methods and evaluation methods for the superabsorbent polymers obtained in the examples and comparative examples will be described below.

<Method of measuring water absorption of superabsorbent polymer> 1 g of the superabsorbent polymer was dispersed in a large excess of physiological saline (0.9% saline), and the polymer was equilibrated. After swelling until the solution becomes, the physiological saline is filtered through an 80 mesh wire mesh, the weight (W) of the obtained swollen polymer is measured, and this value is divided by the polymer weight W ₀ before water absorption. The value was taken as the equilibrium swelling water absorption.

<Method of measuring water absorption rate of superabsorbent polymer>
FIG. 1 which is generally known as an apparatus for performing the DW method
Fig. 1 using the equipment (Demand Wettability Tester) shown in
As shown in Fig. 7, the superabsorbent polymer P was placed on a polymer spray table 2 (70 mmφ, a table in which No. 2 filter paper was placed on a glass filter No. 1) in which the liquid surface of the physiological saline W was set at an equal water level. The amount of water absorption at the time when 3 g was sprayed and the superabsorbent polymer was sprayed was set to 0, and the amount of water absorption after 60 seconds (this amount of water absorption is measured by a burette scale indicating the amount of decrease in the level of the physiological saline W). Was measured, and this value was taken as the water absorption rate.

<Measurement Method of Flow Rate of Physiological Saline in Superabsorbent Polymer> Apparatus 10 shown in FIG. 2 (inner diameter 25.6)
A burette consisting of a glass cylinder tube having a length of about 500 mm (cylindrical portion) having a length of about 500 mm is filled with 0.5 g of the superabsorbent polymer, and the superabsorbent polymer is equilibrium-swelled with an excess of physiological saline, and the liquid level is increased. The cock was adjusted to 200 ml from the lower part, and the cock was opened after confirming that the swollen superabsorbent polymer P had sufficiently settled as shown in the figure. 150ml from the bottom
), M (100 ml from the bottom) tube (liquid volume 5
0 cc) was measured, and the liquid volume in the gauge tube was divided by the measurement time to obtain the liquid passing speed.

<Method of Measuring Stability of Superabsorbent Polymer> 1 g of the superabsorbent polymer was swollen with 45 g of a physiological saline solution containing L-ascorbic acid at a concentration of 0.05%, and placed in a screw tube at 40 ° C. And the state of the gel after 3 hours was observed. The following three scales were used for the evaluation of stability. ；: The swollen particles have no fluidity or spinnability and show the same shape. C: Although not dissolved, the swollen particles have fluidity and spinnability, and the shape becomes unclear. X: Partial dissolution occurs, a liquid state is observed, and more than half of the particles do not leave a shape. In this evaluation, ○ or more is a sanitary napkin, disposable diaper,
Suitable as superabsorbent polymer used for adult sheets, tampons, sanitary cotton, etc.

<Method for Measuring Soluble Part of Superabsorbent Polymer>
1 g of the superabsorbent polymer is precisely measured in a 200 ml beaker, 150 ml of physiological saline is added, and occasionally stirred for about 1 hour.
Leave at room temperature for 5 hours to swell the superabsorbent polymer. Thereafter, the filtrate (A) was filtered by filtering the swollen gel slurry.
g) is collected. About 1/5 (Bg) of this filtrate is 100
Transfer to a volumetric flask, dilute with ion-effect water and add
Make it 0 ml. 5 ml of this reagent solution is placed in a 100 ml Erlenmeyer flask, 10 ml of a 0.005 N methyl glycol chitosan solution is added, and the pH is adjusted to about 1 with aqueous ammonia.
After adjusting to 1, add 2-3 drops of toluidine blue solution. 0.0025N excess methyl glycol chitosan
Titrate with polyvinyl potassium sulfate solution until the color of the solution changes from blue to magenta. Separately, a blank test was performed in the same manner, and the calculated value according to the following formula (3) was defined as the amount of soluble part polymer (%).

[0090]

(Equation 3)

Example 1 72.1 g of acrylic acid was added to 1
The solution was diluted with 8.0 g of water, and then, while cooling, 98.9 g of a 30% aqueous sodium hydroxide solution was added to neutralize the solution to prepare an aqueous monomer solution. Then, 10.7 g of a 2.8% aqueous solution of potassium persulfate (polymerization initiator) and an epoxy-based crosslinking agent (polyglycerol polyglycidyl ether, manufactured by Nagase Kasei Co., Ltd., Denacol EX-512)
1 g of 0.36% aqueous solution and N-acylated glutamic acid 2
Na salt (Ajinomoto Co., Ltd., trade name Amisoft HS-2
1) A solution of 0.88 g in 3.1 g of water was added to the above aqueous monomer solution to prepare an aqueous monomer / initiator solution. The concentration of copper ions in the aqueous monomer solution at this time was 0.4 ppm.

Separately, 283 ml of cyclohexane was placed in a 500 ml flask equipped with a reflux condenser, a dropping funnel, a stirrer, and a nitrogen inlet tube, and ethyl cellulose (manufactured by Hercules, trade name: ethyl cellulose N-100).
0.44 g (0.5% of the produced polymer) was added thereto, and the mixture was stirred (300 rpm) and dispersed. After the atmosphere in the flask was replaced with nitrogen, the bath temperature was raised to 75 ° C. The above monomer / initiator aqueous solution was added dropwise thereto over 60 minutes. After the dropping of the monomer / initiator aqueous solution was completed, the mixture was heated and stirred at 75 ° C. for 0.25 hours, and further stirred and polymerized at a bath temperature of 80 ° C.
At this time, only water was continuously removed from the azeotropic reflux liquid of cyclohexane and water to the outside of the reaction system, and the water content of the polymer was adjusted to 30 parts by weight or less based on 100 parts by weight of the polymer. Partially cross-linked acrylic acid (sodium) thus obtained
The polymer was removed and dried. The resulting partially crosslinked acrylic acid (sodium) polymer was separated and dried under reduced pressure to obtain 88.4 g of a superabsorbent polymer.
About the obtained superabsorbent polymer, the water absorption amount, the water absorption rate, the flow rate of physiological saline, the stability in the L-ascorbic acid solution, and the amount of the soluble part polymer were measured.
Table 2 shows the results.

Examples 2 to 12 N-acylated glutamic acid 2Na salt as a chelate compound (manufactured by Ajinomoto Co., Inc.)
A super-water-absorbing polymer was obtained in the same manner as in the method described in Example 1 except that the chelating compounds of the types and amounts shown in Table 2 were used instead of the trade name Amisoft HS-21). About the obtained superabsorbent polymer, the same measurement as Example 1 was performed. Table 2 shows the results.

[0094]

[Table 2]

[Examples 13 to 24] The copper ion concentration was 0.1%.
A method described in Example 1 except that a monomer / initiator aqueous solution having an iron ion concentration of 4 ppm was used in place of the monomer / initiator aqueous solution having a concentration of 4 ppm, and a chelating compound of the type and amount shown in Table 3 was used. A superabsorbent polymer was obtained with the same formulation as in Example 1 (however, the type and amount of the chelate compound in Example 13 were the same as in Example 1). About the obtained superabsorbent polymer, the same measurement as Example 1 was performed. Table 3 shows the results.

Example 25 1.3% 2,2'-azobis (2-amidinopropane) dihydrochloride aqueous solution was used instead of potassium persulfate aqueous solution as a polymerization initiator.
4 g and an iron ion concentration of 4 pm instead of an aqueous monomer / initiator solution having a copper ion concentration of 0.4 ppm
A superabsorbent polymer was obtained in the same manner as in the method described in Example 1 except that the monomer / initiator aqueous solution was used. About the obtained superabsorbent polymer, the same measurement as Example 1 was performed. Table 3 shows the results.

[0097]

[Table 3]

[Example 26] 72.1 g of acrylic acid was added to 1
The solution was diluted with 8.0 g of water, and then, while cooling, 98.9 g of a 30% aqueous sodium hydroxide solution was added to neutralize the solution to prepare an aqueous monomer solution. Subsequently, 10.7 g of a 2.8% aqueous solution of potassium persulfate (polymerization initiator) and an epoxy-based crosslinking agent (polyglycerol polyglycidyl ether, manufactured by Nagase Kasei Co., Ltd., Denacol EX-512)
The above monomer / initiator aqueous solution was prepared by adding 1 g of a 0.36% aqueous solution. At this time, the iron ion concentration in the monomer aqueous solution was 4 ppm.

Separately, 283 ml of cyclohexane was placed in a 500 ml flask equipped with a reflux condenser, a dropping funnel, a stirrer and a nitrogen inlet tube, and ethyl cellulose (manufactured by Hercules, trade name: ethyl cellulose N-100) was added.
A solution prepared by dissolving 0.44 g (0.5% relative to the produced polymer) and 0.88 g of N-acylated glutamic acid 2Na salt (trade name: Amisoft HS-21, manufactured by Ajinomoto Co., Ltd.) in 3.1 g of water is added and stirred. (300 rpm), and after dispersing and replacing the inside of the flask with nitrogen, the bath temperature was raised to 75 ° C.
The above monomer / initiator aqueous solution was added dropwise thereto over 60 minutes. Except for this, a superabsorbent polymer was obtained in the same formulation as in the method described in Example 1. About the obtained superabsorbent polymer, the water absorption amount, the water absorption rate, the flow rate of physiological saline, and the stability in the L-ascorbic acid solution were measured. Table 4 shows the results.

Examples 27 to 37 N-acylated glutamic acid 2Na salt which is a chelate compound (Ajinomoto Co., Inc.)
Example 2 except that chelating compounds of the type and amount shown in Table 4 were used in place of Amisoft HS-21).
According to the same formulation as in the method described in No. 6, a superabsorbent polymer was obtained. About the obtained superabsorbent polymer, the same measurement as Example 26 was performed. Table 4 shows the results.

[0101]

[Table 4]

Example 38 283 ml of cyclohexane was placed in a 500 ml flask equipped with a reflux condenser, a dropping funnel, a stirrer and a nitrogen inlet tube, and sodium polyoxyethylene dodecyl ether sulfate (average number of moles of ethylene oxide added = 2) was added. 0.29 g of a 25% aqueous solution was added, stirred and dispersed (300 rpm), and the inside of the flask was replaced with nitrogen. Then, the bath temperature was raised to 75 ° C. The same monomer / initiator aqueous solution as described in Example 1 except that the iron ion concentration was 4 ppm was added dropwise thereto over 60 minutes. Except for this, a superabsorbent polymer was obtained in the same formulation as in the method described in Example 1. About the obtained superabsorbent polymer, the same measurement as Example 26 was performed. Table 5 shows the results.

[Examples 39 to 49] N-acylated glutamic acid 2Na salt which is a chelate compound (Ajinomoto Co., Inc.)
Example 3 except that chelating compounds of the kind and amount shown in Table 5 were used in place of Amisoft HS-21).
A superabsorbent polymer was obtained in the same manner as in the method described in No. 8. About the obtained superabsorbent polymer, the same measurement as Example 26 was performed. Table 5 shows the results.

Example 50 283 ml of cyclohexane was placed in a 500 ml flask equipped with a reflux condenser, a dropping funnel, a stirrer and a nitrogen inlet tube, and polyoxyethylene dodecyl ether sulfate sodium salt (average number of moles of ethylene oxide added = 2) was added. 0.29 g of a 25% aqueous solution and N-acylated glutamic acid 2Na salt (Ajinomoto Co., Inc.)
0.88 g of Amisoft HS-21) (trade name).
The solution dissolved in 1 g was added, stirred (300 rpm) and dispersed, and the inside of the flask was replaced with nitrogen.
The temperature was raised to ° C. To this, the monomer / initiator aqueous solution described in Example 26 was added dropwise over 60 minutes. Except for this, a superabsorbent polymer was obtained in the same formulation as in the method described in Example 1. About the obtained superabsorbent polymer, Example 2
The same measurement as in Example 6 was performed. Table 5 shows the results.

Example 51 72.1 g of acrylic acid was added to 1
The solution was diluted with 8.0 g of water, and then, while cooling, 98.9 g of a 30% aqueous sodium hydroxide solution was added to neutralize the solution to prepare an aqueous monomer solution. Then, 10.7 g of a 2.8% aqueous solution of potassium persulfate (polymerization initiator) and an epoxy-based crosslinking agent (polyglycerol polyglycidyl ether, manufactured by Nagase Kasei Co., Ltd., Denacol EX-512)
1 g of 0.36% aqueous solution and N-acylated glutamic acid 2
Na salt (Ajinomoto Co., Ltd., trade name Amisoft HS-2
1) A solution of 0.44 g dissolved in 1.55 g of water was added to prepare a monomer / initiator aqueous solution. At this time, the iron ion concentration in the monomer aqueous solution was 4 ppm.

Separately, 283 ml of cyclohexane was placed in a 500 ml flask equipped with a reflux condenser, a dropping funnel, a stirrer and a nitrogen inlet tube, and polyoxyethylene dodecyl ether sulfate sodium salt (average number of moles of ethylene oxide added = 2). 0.29 g of a 25% aqueous solution and N-acylated glutamic acid 2Na salt (Ajinomoto Co., Inc.)
Amisoft HS-21) (0.44 g, water 1.
55 g was dissolved and stirred (300 rpm),
After dispersing and purging the flask with nitrogen, the bath temperature was reduced to 7
The temperature was raised to 5 ° C. The above monomer / initiator aqueous solution was added dropwise thereto over 60 minutes. Except for this, a superabsorbent polymer was obtained in the same formulation as in the method described in Example 1.
About the obtained superabsorbent polymer, the same measurement as Example 26 was performed. Table 5 shows the results.

[0107]

[Table 5]

Comparative Example 1 The same formulation as in Example 1 was used, except that N-acylated glutamic acid 2Na salt (manufactured by Ajinomoto Co., Inc., trade name Amisoft HS-21) was not used. When the polymerization was carried out, aggregation occurred in the polymerization system during the polymerization, and the polymerization could not be continued.

[Comparative Examples 2 to 4] N which is a chelate compound
-A formulation similar to that of the method described in Example 1 except that the chelating compound of the type and amount shown in Table 6 was used instead of the acylated glutamic acid 2Na salt (trade name: Amisoft HS-21, manufactured by Ajinomoto Co., Inc.) Thus, a superabsorbent polymer was obtained. About the obtained superabsorbent polymer, the same measurement as Example 1 was performed. Table 6 shows the results.

Comparative Example 5 The same formulation as in Example 13 was used except that N-acylated glutamic acid 2Na salt (manufactured by Ajinomoto Co., Inc., trade name Amisoft HS-21) was not used. When polymerization was performed at
During the polymerization, agglomeration occurred in the polymerization system, and the polymerization could not be continued.

[Comparative Examples 6 to 8] N as a chelate compound
-A formulation similar to that of the method described in Example 13 except that the chelating compound of the type and amount shown in Table 6 was used instead of the acylated glutamic acid 2Na salt (manufactured by Ajinomoto Co., Inc., trade name: Amisoft HS-21) Thus, a superabsorbent polymer was obtained. About the obtained superabsorbent polymer, the same measurement as Example 1 was performed. Table 6 shows the results.

[Comparative Example 9] A chelate compound, N-acylated glutamic acid 2Na salt (trade name: Amisoft HS-21, manufactured by Ajinomoto Co., Inc.) was not used, and a monomer aqueous solution having an iron ion concentration of 4 ppm was used. When polymerization was carried out in the same manner as in Example 13 except that an aqueous monomer solution having an iron ion concentration of 2 ppm was used, agglomeration occurred in the polymerization system during polymerization, and the polymerization was continued. I couldn't do that.

Comparative Example 10 The chelating compound N-
An acylated glutamic acid 2Na salt (manufactured by Ajinomoto Co., Inc., trade name: Amisoft HS-21) was not used, and a monomer aqueous solution having an iron ion concentration of 0.5 ppm was used instead of the monomer aqueous solution having an iron ion concentration of 4 ppm. except,
A superabsorbent polymer was obtained in the same formulation as in the method described in Example 13. About the obtained superabsorbent polymer, the same measurement as Example 1 was performed. Table 6 shows the results.

Comparative Example 11 N- as a chelate compound
Polymerization was carried out in the same manner as in Example 38 except that acylated glutamic acid 2Na salt (trade name: Amisoft HS-21, manufactured by Ajinomoto Co., Inc.) was not used. Agglomeration occurred and polymerization could not be continued.

[Comparative Examples 12 to 14] N-acylated glutamic acid 2Na salt which is a chelate compound (Ajinomoto Co., Inc.)
Example 3 except that chelating compounds of the type and amount shown in Table 6 were used in place of Amisoft HS-21).
A superabsorbent polymer was obtained in the same formulation as in the method described in Example 8. About the obtained superabsorbent polymer, the same measurement as Example 1 was performed. Table 6 shows the results.

[0116]

[Table 6]

Example 52 72.1 g of acrylic acid was added to 1
The solution was diluted with 8.0 g of water, and then, while cooling, 98.9 g of a 30% aqueous sodium hydroxide solution was added to neutralize the solution to prepare an aqueous monomer solution. Next, 5.4 g of 1.3% aqueous solution of 2,2′-azobis (2-amidinopropane) dihydrochloride (polymerization initiator) and N-acylated glutamic acid 2Na salt (Amisoft HS-, trade name, manufactured by Ajinomoto Co., Inc.) 21) A solution of 0.88 g in 3.1 g of water was added to the above aqueous monomer solution to prepare an aqueous monomer / initiator solution. At this time, the iron ion concentration in the monomer aqueous solution was 4 ppm.

Separately, 283 ml of cyclohexane was placed in a 500 ml flask equipped with a reflux condenser, a dropping funnel, a stirrer, and a nitrogen inlet tube, and polyoxyethylene dodecyl ether sulfate sodium salt (average number of moles of ethylene oxide added = 2). 0.29 g of a 25% aqueous solution was added, and the mixture was stirred (300 rpm) and dispersed. After the inside of the flask was replaced with nitrogen, the bath temperature was raised to 75 ° C. The above monomer / initiator aqueous solution was added dropwise thereto over 60 minutes. After the dropping of the monomer / initiator aqueous solution was completed, the mixture was heated and stirred at 75 ° C. for 0.25 hours, and further stirred and polymerized at a bath temperature of 80 ° C. At this time, only water was continuously removed from the azeotropic reflux liquid of cyclohexane and water to the outside of the reaction system, and the water content of the polymer was adjusted to 30 parts by weight or less based on 100 parts by weight of the polymer. An epoxy-based cross-linking agent (polyglycerol polyglycidyl ether, Nagase Kasei Co., Ltd.) is added to cyclohexane in which the polymer hydrate thus obtained is dispersed.
Denacol EX-512) 1.55% aqueous solution 1.8
g was added dropwise over 5 minutes. Subsequently, the mixture was reacted for 120 minutes to obtain a partially crosslinked acrylic acid (sodium) polymer. The partially crosslinked acrylic acid (sodium) polymer was taken out and dried. The resulting partially crosslinked acrylic acid (sodium) polymer was separated and dried under reduced pressure to obtain 88.4 g of a superabsorbent polymer. About the obtained superabsorbent polymer, the water absorption amount, the water absorption rate, the flow rate of physiological saline, and the stability in the L-ascorbic acid solution were measured. Table 7 shows the results.

[Examples 53 to 63] N-acylated glutamic acid 2Na salt which is a chelate compound (Ajinomoto Co., Inc.)
Example 5 except that chelating compounds of the type and amount shown in Table 7 were used in place of Amisoft HS-21).
A superabsorbent polymer was obtained in the same manner as in the method described in 2. The same measurement as in Example 52 was performed on the obtained superabsorbent polymer. Table 7 shows the results.

Example 64 To the aqueous monomer / initiator solution of Example 52, 0.007 g of an epoxy-based crosslinking agent (polyglycerol polyglycidyl ether, manufactured by Nagase Kasei Co., Ltd., Denacol EX-521) was added, and a homogeneous solution was added. age,
An aqueous monomer / initiator solution was used. Otherwise, Example 5
A superabsorbent polymer was obtained by the same formulation as in the method described in 2. The same measurement as in Example 52 was performed on the obtained superabsorbent polymer. Table 7 shows the results.

Comparative Example 15 N- as a chelate compound
Polymerization was performed in the same manner as in Example 52 except that acylated glutamic acid 2Na salt (trade name: Amisoft HS-21, manufactured by Ajinomoto Co., Inc.) was not used. Agglomeration occurred and polymerization could not be continued.

[Comparative Examples 16 to 18] N-acylated glutamic acid 2Na salt which is a chelate compound (Ajinomoto Co., Inc.)
Example 5 except that chelating compounds of the type and amount shown in Table 7 were used in place of Amisoft HS-21).
A superabsorbent polymer was obtained by the same formulation as in the method described in 2. The same measurement as in Example 52 was performed on the obtained superabsorbent polymer. Table 7 shows the results.

[0123]

[Table 7]

Example 65 288.4 g of acrylic acid was diluted with 72.0 g of water, and then, while cooling, 395.6 g of a 30% aqueous sodium hydroxide solution was added to neutralize the solution, and the monomer aqueous solution was neutralized. Was prepared. Next, an epoxy-based crosslinking agent (polyglycerol polyglycidyl ether, manufactured by Nagase Kasei Co., Ltd., Denacol EX-512)
4 g of 0.36% aqueous solution, N-acylated glutamic acid 2N
a salt (manufactured by Ajinomoto Co., Inc., Amisoft HS-21) 3.5
A solution of 2 g in 12.4 g of water and 337.8 g of ion-exchanged water were added to the above monomer aqueous solution. At this time, the iron ion concentration in the monomer aqueous solution was 4 ppm.

Next, the monomer aqueous solution was charged into a reactor equipped with a jacketed stainless steel double-armed kneader having two sigma-type blades having an inner volume of 2.5 L, and nitrogen gas was blown into the reactor to replace nitrogen. did. Further, while rotating the two sigma-type blades, the jacket was heated to 50 ° C.
2.8 as a polymerization initiator while heating through warm water.
42.8 g of a 5% aqueous potassium persulfate solution was added. One minute after the addition of the polymerization initiator, the polymerization starts, and 10 minutes after the addition of the polymerization initiator, the peak temperature in the reaction system reaches 85 ° C., and the hydrogel polymer is subdivided into a particle diameter of about 5 mm. It had been. The mixture was further stirred for 60 minutes, and the obtained partially crosslinked acrylic acid (sodium) polymer was taken out and dried. With respect to the superabsorbent polymer thus obtained, the water absorption, the water absorption rate, the flow rate of physiological saline, the stability in the L-ascorbic acid solution, and the amount of the polymer in the soluble part were measured. Table 8 shows the results.

[Examples 66 to 76] N-acylated glutamic acid 2Na salt which is a chelate compound (Ajinomoto Co., Inc.)
Example 6 except that chelating compounds of the type and amount shown in Table 8 were used in place of Amisoft HS-21).
A superabsorbent polymer was obtained in the same manner as in the method described in No. 5. The same measurement as in Example 65 was performed for the obtained superabsorbent polymer. Table 8 shows the results.

Comparative Example 19 N- as a chelate compound
A superabsorbent polymer was obtained by the same formulation as in Example 65 except that acylated glutamic acid 2Na salt (manufactured by Ajinomoto Co., Inc., trade name: Amisoft HS-21) was not used. About the obtained superabsorbent polymer, Example 6
The same measurement as in Example 5 was performed. Table 8 shows the results.

[Comparative Examples 20 to 22] N-acylated glutamic acid 2Na salt which is a chelate compound (Ajinomoto Co., Inc.)
Example 6 except that chelating compounds of the type and amount shown in Table 8 were used in place of Amisoft HS-21).
A superabsorbent polymer was obtained in the same manner as in the method described in No. 5. The same measurement as in Example 65 was performed for the obtained superabsorbent polymer. Table 8 shows the results.

[0129]

[Table 8]

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an apparatus for measuring the water absorption rate of a superabsorbent polymer used in Examples and Comparative Examples.

FIG. 2 is a schematic diagram showing a measuring device for measuring the flow rate of physiological saline used in Examples and Comparative Examples.

[Explanation of symbols]

 W Physiological saline P polymer 1 Measuring device for water absorption indicating the water absorption speed of polymer 10 Measuring device for flow rate of physiological saline 2 Polymer spraying table 3 Burette M, L Marked line

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Yasunori Hosokawa 1334 Minato, Wakayama City, Wakayama Prefecture Kao Corporation Laboratory (56) References JP-A-64-75506 (JP, A) (58) Fields investigated (Int. Cl. ^7, DB name) C08F 2/32 C08F 2/44

Claims (10)

(57) [Claims] 1. A method for producing a superabsorbent polymer by polymerizing a water-soluble vinyl monomer, wherein the polymerization comprises a chelate compound having a solubility of Cu salt in physiological saline at 25 ° C. of 0.01% by weight or less. A method for producing a superabsorbent polymer, which is carried out in the presence of at least one of the following. 2. A common logarithmic value (p) of the chelate stability constant of the above chelate compound with Cu ²⁺ ion at 25 ° C.
The method for producing a superabsorbent polymer according to claim 1, wherein KCu) is 3 or more. 3. The chelate compound according to claim 1, wherein the chelate compound is a hydrophobic part comprising a saturated or unsaturated hydrocarbon group having 6 or more carbon atoms and at least one selected from the group consisting of a carboxylic acid group, a sulfonic acid group, a hydroxyl group and a phosphoric acid group. The method for producing a superabsorbent polymer according to claim 1 or 2, comprising a hydrophilic portion having one group. 4. The method according to claim 1, wherein the chelate compound is an organic acid amide derivative, a hydroxycarboxylic acid derivative, a polycarboxylic acid derivative, an iminodiacetic acid derivative, a phosphate ester derivative or an N-acylated amino acid derivative. The method for producing a superabsorbent polymer according to any one of the above. 5. The method for producing a superabsorbent polymer according to claim 4, wherein the chelate compound is an organic acid amide derivative, a hydroxycarboxylic acid derivative, an iminodiacetic acid derivative or an N-acylated amino acid derivative. 6. The method according to claim 5, wherein the chelate compound is an N-acylated amino acid derivative. 7. The method according to claim 7, wherein the N-acylated amino acid derivative is
The method for producing a superabsorbent polymer according to claim 6, which is -acylated glutamic acid or a salt thereof. 8. The method for producing a superabsorbent polymer according to claim 1, wherein the chelate compound is a β-diketone derivative. 9. The method according to claim 1, wherein the chelate compound is a tropolone derivative. 10. The method according to claim 1, wherein the polymerization is carried out by inverse suspension polymerization using a hydrophobic organic solvent inert to the polymerization and an aqueous solution of the water-soluble vinyl monomer in the presence of a dispersant.
10. The method for producing a superabsorbent polymer according to any one of items 9 to 9.