JP4251281B2 - Manufacturing method of superabsorbent resin - Google Patents

Description

The present invention relates to a method for producing a superabsorbent resin, and more particularly to a method for producing a superabsorbent resin by reverse phase suspension polymerization. Since the superabsorbent resin obtained by the method of the present invention has a large average particle size and a high absorption rate, it is suitable for use as an absorbent material such as disposable diapers and sanitary products.

  Conventionally, as a method for producing a superabsorbent (mainly water-absorbing) resin, a water-soluble monomer is directly bulk-polymerized to form a water-containing gel-like polymer, which is then pulverized and then dehydrated and dried. A method of subjecting an aqueous solution of a water-soluble monomer to reverse phase suspension polymerization in a hydrophobic organic solvent is mainly used. Of these, the former bulk polymerization method is difficult to grind and dehydrate / dry after polymerization, and therefore the latter reverse phase suspension polymerization method, which does not require a pulverization step and is easy to dehydrate / dry, is considered preferable. It has been. In this method, water that forms an azeotrope with water is used as the hydrophobic organic solvent, so that water contained in the produced polymer particles is easily removed by azeotropic distillation with the hydrophobic organic solvent. be able to.

One of the problems in the production of a highly water-absorbent resin by the reverse phase suspension polymerization method is that the reverse phase suspension polymerization tends to generate fine particle resin particles that may rise during handling. As an improvement method of this point, it has been proposed to apply oil-soluble cellulose ester or cellulose ether as a dispersant (for example, see Patent Document 1 and Patent Document 2). In addition, a monoalkyl phosphate having a linear alkyl group having 12 to 24 carbon atoms is used as a dispersant (for example, see Patent Document 3), and polyoxyethylene alkyl ether sulfate is used as a dispersant (for example, Patent Document 4). Have been proposed). Further, it has been proposed to use a phosphate ester obtained from an aliphatic alcohol ethylene oxide adduct or a phosphate ester obtained from an alkylphenol ethylene oxide adduct as a dispersant (see, for example, Patent Document 5 and Patent Document 6).
However, although these methods can produce resin particles having a large average particle diameter, there are problems such that the produced resin particles are likely to adhere to the wall of the apparatus and the range of conditions under which stable polymerization can be performed is narrow. . In addition, in absorbent articles such as paper diapers and sanitary products, which are the main uses of superabsorbent resins, the shape of the superabsorbent resins used in the past is often spherical, so that it is used for pulp, etc. There is a problem that it is difficult to be fixed to the substrate and the absorption performance is likely to change.

  In addition, a technique has been proposed in which organic bentonite is used as a suspension stabilizer during reverse phase suspension polymerization of a water-absorbent resin (see, for example, Patent Document 7). However, the spherical particles obtained by this technique are only small particles having an average particle size of 160 μm or less, and those having a large particle size with a structure in which primary particles excellent in blood absorption performance are fused as in the present invention can be obtained. Absent.

JP 57-158210 A Japanese Patent Publication No. 1-17482 JP-A-61-209201 JP-A-6-93008 Japanese Patent Laid-Open No. 11-5808 JP 2001-31704 A JP-A-63-146901

Accordingly, an object of the present invention is to provide a method for stably producing a granular superabsorbent resin having a large average particle diameter and improved resin fixability by a reverse phase suspension polymerization method. In particular, the present invention intends to provide a highly absorbent resin excellent in blood-sucking performance.

As a result of intensive studies to solve the above-mentioned problems, the present inventors have conducted polymerization of water-soluble ethylenically unsaturated monomers with specific hardly soluble fine particles and salt-type anionic surfactants. It has been found that the above-described object can be achieved by carrying out in the presence, and the present invention has been completed.
That is, the present invention provides at least one ethylenically unsaturated double bond in a molecule in a hydrophobic organic solvent containing organic bentonite in the presence of an anionic surfactant represented by the following general formula (1). supplying an aqueous solution containing a water-soluble monomer having a method wherein the high absorbent resin which is characterized in that the reverse-phase suspension polymerization of water-in-oil, R ¹ is, carbon atoms An alkyl group which may be substituted with 8 to 30 phenyl groups or an aryl group which may be substituted with an alkyl group, n represents an integer of 1 to 30, M represents an alkali metal, a quaternary ammonium salt Or a quaternary amine salt, and R ² represents —OM or R ¹ O— (CH ₂ CH ₂ O) n— (wherein R ¹ , M and n represent the same as described above). . ] Is provided.

  It can be seen that the method for producing a superabsorbent resin of the present invention can stably obtain a granular superabsorbent resin having a small amount of sticking to the pot, a large average particle diameter, and improved resin fixability. The obtained superabsorbent resin not only has excellent blood absorption properties, but also has excellent absorbability of protein-containing water, etc., so sanitary napkins, tampons, medical blood absorbent sheets, drip absorbents It can be applied to various uses that require blood and blood absorption characteristics.

Below, the manufacturing method of the superabsorbent resin of this invention is demonstrated in detail.
As a water-soluble monomer having at least one ethylenically unsaturated double bond in the molecule used in the present invention (hereinafter referred to as a water-soluble unsaturated monomer), it is known to give a superabsorbent resin. Any water-soluble unsaturated monomer can be used as a raw material.

  Examples of such water-soluble unsaturated monomers include a) ionic monomers such as (meth) acrylic acid and alkali metal salts and ammonium salts thereof, acrylamide-2-ethylsulfonic acid and alkali metal salts thereof (b) ) Nonionic monomers such as (meth) acrylamide, N, N-dimethylacrylamide, 2-hydroxyethyl (meth) acrylate, N-methylol (meth) acrylamide, etc. (c) amino group-containing monomers and their Quaternized products such as diethylaminoethyl (meth) acrylate, dimethylaminopropyl (meth) acrylate and the like can be mentioned, and these monomers can be used alone or in admixture of two or more.

  Among these, (meth) acrylic acid and its alkali metal salts and ammonium salts, (meth) acrylamide and the like are preferable. As the alkali metal salt, sodium salt, potassium salt, lithium salt, rubidium salt and the like are used, but sodium salt or potassium salt is used from the aspect of the performance, industrial availability, safety, etc. of the obtained superabsorbent resin. Is preferred.

  These water-soluble unsaturated monomers are used so that the monomer concentration in the aqueous solution is usually 20% by weight or more, preferably 25% by weight or more to the saturated concentration. In addition, the ionic monomer, for example, (meth) acrylic acid, acrylamide-2-ethylsulfonic acid, etc. is in a form in which at least a part thereof is neutralized with an alkali metal hydroxide, ammonium hydroxide or the like, that is, It is preferably used in the form of a salt. The degree of neutralization is usually 20 to 100 mol%, preferably 30 to 100 mol%.

  These water-soluble unsaturated monomers, particularly acrylic acid monomers, undergo some degree of self-crosslinking during polymerization without the use of a cross-linking agent, but in order to balance the absorption performance, It is preferable to use a crosslinking agent in combination with the polymerizable unsaturated monomer. As the crosslinking agent, a monomer having two or more ethylenically unsaturated bonds or a compound having two or more functional groups that react with the functional group of the water-soluble unsaturated monomer is used.

  Examples of the monomer having two or more ethylenically unsaturated bonds include (a) di- or tri (meth) acrylic acid esters of polyol, such as ethylene glycol, propylene glycol, trimethylolpropane, glycerin, polyoxy (B) In (a), the unsaturated acid is other than (meth) acrylic acid, for example, maleic acid, fumaric acid, etc., (c) ethylene glycol, polyoxypropylene glycol, polyglycerin, etc. ) Bisacrylamides such as N, N′-methylenebisacrylamide, etc. (d) di- or tri (meth) acrylates obtained by reacting polyepoxide with (meth) acrylic acid, (e) polyisocyanate and ( Di (meth) acrylic acid carbamyl ester obtained by reaction of (meth) acrylic acid hydroxyalkyl ester For example, polyisocyanate is tolylene diisocyanate, hexamethylene diisocyanate, etc., (f) polyvalent allyl compounds, for example allylated starch, allylated cellulose, diallyl phthalate, tetraallyloxyethane, pentaerythritol triallyl ether, trimethylol Examples include propane triallyl ether, diethylene glycol diallyl ether, triallyl trimellitate and the like.

  Among these, ethylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate, polypropylene glycol di (meth) acrylate, N, N′-methylenebis (meth) acrylamide and the like are preferable in the present invention.

Examples of the compound having two or more functional groups that react with the functional group of the water-soluble unsaturated monomer include diglycidyl ether compounds, haloepoxy compounds, and isocyanate compounds. Of these, diglycidyl ether compounds are particularly preferred.
Specific examples of the diglycidyl ether compound include ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, glycerin diglycidyl ether, polyglycerin diglycidyl ether and the like. Among these, ethylene glycol diglycidyl ether is preferable.
Examples of the haloepoxy compound include epichlorohydrin and β-methylepichlorohydrin, and examples of the isocyanate compound include 2,4-tolylene diisocyanate and hexamethylene diisocyanate.
The amount of these crosslinking agents to be used is generally 0 to 10% by weight, preferably 0 to 5% by weight, based on the water-soluble unsaturated monomer.

  In the reverse phase suspension polymerization, a radical polymerization initiator is preferably used, and a conventional water-soluble radical polymerization initiator can be used as the radical polymerization initiator. Some examples are (a) hydrogen peroxide, (b) persulfates such as potassium persulfate, sodium persulfate and ammonium persulfate, (c) azo initiators such as 2,2′-azobis- ( 2-aminodipropane) dihydrochloride, 2,2′-azobis- (N, N′-dimethyleneisobutylamidine) dihydrochloride, 2,2′-azobis {2-methyl-N- [1,1- Bis (hydroxymethyl) -2-hydroxyethyl] propionamide} and the like. These water-soluble radical polymerization initiators can be used alone or in admixture of two or more. Hydrogen peroxide and persulfate can also be used as a redox initiator by combining a reducing substance such as sulfite and L-ascorbic acid and an amine salt. These radical polymerization initiators are suitably used in the range of 0.001 to 5% by weight, particularly 0.01 to 1% by weight, based on the water-soluble unsaturated monomer.

As the hydrophobic organic solvent that is a reaction medium for the reverse phase suspension polymerization, any solvent can be used as long as it is basically insoluble in water and inert to the polymerization. Those that form an azeotrope are preferred. Some examples are (a) aliphatic hydrocarbons such as n-pentane, n-hexane, n-heptane, n-octane, etc., and (b) alicyclic hydrocarbons such as cyclohexane, methylcyclohexane, etc. c) Aromatic hydrocarbons such as benzene, toluene, xylene and the like. Of these, n-hexane, n-heptane, cyclohexane and the like are preferably used.
The hydrophobic organic solvent is usually used in an amount of 0.5 to 10 times by weight with respect to the ethylenically unsaturated monomer aqueous solution, but preferably 0.8 to 3 times by weight. If the ratio of the hydrophobic organic solvent is too small, the resin particles easily aggregate even in the presence of the surfactant, and it becomes difficult to obtain a superabsorbent resin having a desired particle size. On the contrary, if this ratio is too large, the productivity is lowered.

  In the present invention, in reverse phase suspension polymerization, an organic bentonite is contained in a hydrophobic organic solvent as a reaction medium, and an anionic surfactant is contained in an aqueous solution of a water-soluble unsaturated monomer. is there.

The organic bentonite is produced by organizing smectite having a hydrophilic group as an inorganic component with an organic compound containing a long-chain aliphatic hydrocarbon, etc., and is insoluble in water and has an affinity for a hydrophobic organic solvent, In addition, it has a property of incorporating a hydrophobic organic solvent between its own layers, swelling and thickening.
The organic bentonite used in the present invention is obtained by organicizing a clay containing a natural bentonite mainly composed of smectite montmorillonite, hectorite, beidellite, nontronite, saponite, saconite and / or a synthetic product thereof. Manufactured. For example, it is produced by mixing a smectite-containing clay sufficiently swollen in water with a cationic organic compound or the like at 25 to 95 ° C., and exchanging the smectite exchangeable inorganic cation with the cationic organic compound or the like.

  Examples of the cationic organic compound include various sulfonium salt type, ammonium salt type, and phosphonium salt type organic compounds. Specifically, alkyltrimethylammonium salt, dialkyldimethylammonium salt, alkyldimethylbenzylammonium salt, dimethyl Examples thereof include dibenzylammonium salt, polyoxyethylene alkyl monomethylammonium salt, alkylamine salt, alkylpyridinium salt, alkyltri-n-butylphosphonium salt, and alkyldimethylsulfonium salt.

The alkyl group referred to herein is preferably a long chain having 8 or more carbon atoms, and these cationic organic compounds may be used alone or as a mixture of two or more. Furthermore, these may be used in combination with organic compounds such as anionic surfactants, nonionic surfactants, and amphoteric surfactants.
Examples of commercially available organic bentonites treated with these cationic organic compounds include Orben (manufactured by Shiraishi Kogyo), Benton 34, 38, 27 (manufactured by National Red), and Espen (manufactured by Toyoshiro Yoko).

  The amount of organic bentonite used in the hydrophobic organic solvent is 0.01 to 10% by weight, preferably 0.05 to 5% by weight. If it is less than 0.01% by weight, the dispersion stability of the aqueous solution of the water-soluble unsaturated monomer is lowered to produce a lump. Conversely, if it exceeds 10% by weight, the viscosity of the polymerization system becomes too high, There is a concern that organic bentonite remains attached to the surface of the generated resin, which is not preferable.

As an anionic surfactant used in the present invention, it is essential to use a polyoxyethylene phosphate salt represented by the following general formula (1) . Here, as the salt, an alkali metal salt, a quaternary ammonium salt or an amine salt is usually used. [In General Formula (1), R ¹ represents an alkyl group which may be substituted with a phenyl group having 8 to 30 carbon atoms or an aryl group which may be substituted with an alkyl group. Specific examples include octylphenyl group, nonylphenyl group, dinonylphenyl group, dodecylphenyl group, distyrenylphenyl group, 2-ethylhexyl group, lauryl group, tridecyl group, octadecyl group and the like. N represents an integer of 1 to 30, preferably 2 to 15. M represents an alkali metal, quaternary ammonium or amine salt. Examples of the alkali metal include sodium, potassium, lithium, rubidium and the like, and examples of the amine salt include monoethanolamine, diethanolamine, triethanolamine and the like. Further, R ² represents —OM or R ¹ O— (CH ₂ CH ₂ O) n— (wherein M and n are as defined above). In the latter case, two R ¹ O— (CH ₂ CH ₂ O) n— is preferably the same. ]

The phosphoric acid ester salt type anionic surfactant is generally dissolved in various phosphoric acid ester type surfactants which are strongly acidic so as to be equivalent to them calculated from their acid values. It can be easily obtained by adding and mixing into an alkali metal hydroxide aqueous solution, ammonium hydroxide aqueous solution or mono-, di-, or triethanolamine aqueous solution.

In the case of using an alkali metal salt of (meth) acrylic acid as the water-soluble unsaturated monomer used in the present invention, an aqueous solution of an alkali metal hydroxide is mainly used for the alkali metal chlorination. By adding various phosphate ester type surfactants, phosphate ester salt type anionic surfactants can be obtained very easily. As the alkali metal salt, as described above, a sodium salt or a potassium salt is preferably applied in terms of the performance of the obtained superabsorbent resin, industrial availability, safety and the like.

The anionic surfactant to be used in the present invention is usually contained in an aqueous water-soluble unsaturated monomer solution in an amount of 0.01 to 5% by weight, preferably 0.05 to 2% by weight. If it is less than 0.01% by weight, the desired dispersion effect cannot be obtained. Conversely, if it exceeds 5% by weight, the produced resin particles tend to aggregate when dried.

The present invention includes an organic bentonite having an ionic property in a hydrophobic organic solvent as a reaction medium, and an anionic surfactant in an aqueous monomer solution, so that proteins, blood cell components, tissue degradation products, etc. Thus, an absorbent resin with improved absorption characteristics with respect to blood containing water and suppressed repelling and the like can be obtained.

The anionic surfactant used in the present invention is used in combination with an anionic surfactant other than the anionic surfactant for the purpose of controlling the surface structure of the water-absorbent resin particles in a more complex manner as necessary. It is also possible to use a nonionic surfactant in combination.
Examples of such anionic surfactant include sodium dodecene and tetradecene mixed sodium sulfonate, sodium dodecylbenzene sulfonate, sodium lauryl sulfate, sodium polyoxyethylene lauryl ether sulfate, sodium octylphenyl sulfate, sodium polyoxyethylene octylphenyl ether sulfate. And sodium dialkylsulfosuccinate.
Examples of the nonionic surfactant include polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, polyoxyethylene octadecyl ether, polyoxyethylene oleyl ether, polyethylene glycol laurate, polyethylene glycol oleate, polyoxy Examples include ethylene sorbitan monolaurate and polyoxyethylene polyoxypropylene glycol.

  Furthermore, for the purpose of more complex control of the surface structure of the absorbent resin particles, water-soluble hydroxyethyl cellulose, polyacrylic acid or its soda salt, polyvinyl alcohol, etc. in an aqueous solution mainly composed of an ethylenically unsaturated monomer A small amount of a polymer compound may be added.

At the time of reverse phase suspension polymerization, it is preferable to supply a polyacidic amino acid having at least one ethylenically unsaturated bond and / or a polyacidic amino acid not having an ethylenically unsaturated bond in the molecule to the hydrophobic organic solvent. .
By introducing such a polyacidic amino acid into a superabsorbent resin, it is possible to further improve blood sucking performance.

  The polyacidic amino acid having at least one ethylenically unsaturated bond in the molecule is not particularly limited. For example, a hydrolyzate of polysuccinimide having a maleimide end group as a terminal group (a), and Examples thereof include a compound (b) obtained by reacting a polyacidic amino acid with a compound having an ethylenically unsaturated bond and a functional group capable of reacting with the polyacidic amino acid in the molecule.

Such a polysuccinimide having a maleimide terminal group can be obtained, for example, by reacting maleic anhydride, fumaric acid, malic acid or the like with ammonia and heating to maleimide or maleamic acid.
The hydrolyzate (a) of polysuccinimide having a maleimide end group is obtained by hydrolyzing the polysuccinimide obtained above usually with an aqueous alkaline solution. The reaction temperature at this time is preferably in the range of 0 to 100 ° C, more preferably 20 to 95 ° C.

Examples of the alkali compound used in the alkaline aqueous solution include an alkali metal compound and / or an alkaline earth metal compound. Typical examples of the alkali metal compound or alkaline earth metal compound include hydroxides and carbonates, such as LiOH, NaOH, KOH, Mg (OH) ₂ , Ca (OH) ₂ , and Li ₂ CO _3. , Na ₂ CO ₃ , K ₂ CO ₃ , MgCO ₃ , CaCO _{3 and the} like. As these alkali metal compounds or alkaline earth metal compounds, NaOH or KOH is usually used.
The alkaline aqueous solution is preferably a 0.1 to 40% by weight aqueous solution of these compounds. Moreover, it is preferable that the usage-amount of an alkali compound uses 0.4-1.0 mol with respect to one imide ring group.

  Further, the hydrolyzate (a) of polysuccinimide having a maleimide terminal group may be neutralized with a protonic acid such as hydrochloric acid, sulfuric acid, phosphoric acid or the like for the purpose of adjusting pH.

Here, the compound (b) obtained by reacting the polyacidic amino acid with a compound having an ethylenically unsaturated bond and a functional group capable of reacting with the polyacidic amino acid in the molecule will be specifically described.
Examples of the polyacidic amino acid include polyaspartic acid and polyglutamic acid. These compounds may have a linear structure or a branched structure.
Furthermore, the basic skeleton of the polyacidic amino acid may contain an amide bond and amino acid units other than glutamic acid and aspartic acid.

  The polyacidic amino acid used in the present invention includes a salt thereof. Examples of the salt of the polyacidic amino acid include alkali metal salts, alkaline earth metal salts, and ammonium salts of the above polyacidic amino acids. Examples of the alkali metal salt include sodium salt, potassium salt, lithium salt, and rubidium salt. Examples of the alkaline earth metal salt include calcium salt and magnesium salt.

  The compound having a functional group capable of reacting with an ethylenically unsaturated bond and a polyacidic amino acid in the molecule is not particularly limited, but in the present invention, for example, it is a compound represented by the following general formula (2). Is preferred.

(式中、Ｒ^１はアミノ基、エポキシ基、カルボキシル基、カルボジイミド基、オキサゾリン基、イミノ基、イソシアネート基からなる群より選ばれる少なくとも１種類の基を示し、Ｑは炭素原子数が１〜１０のアルキレン基を示し、Ｒ^２は水素原子又は炭素原子数が１〜４のアルキル基を示す。)

(In the formula, R ¹ represents at least one group selected from the group consisting of an amino group, an epoxy group, a carboxyl group, a carbodiimide group, an oxazoline group, an imino group, and an isocyanate group, and Q has 1 to 10 carbon atoms. R ² represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms.)

  Examples of the compound represented by the general formula (2) include glycidyl (meth) acrylate, (meth) acrylic acid, 2-methacryloyloxyethyl isocyanate, and 2-isocyanate methyl acrylate.

  The production method of the compound (b) obtained by reacting a polyacidic amino acid with a compound having an ethylenically unsaturated bond and a functional group capable of reacting with the polyacidic amino acid in the molecule is not particularly limited. Any production method can be used as long as the compound (b) can be reacted with the polyacidic amino acid under conditions where the ethylenically unsaturated bond is protected so as not to cause a change such as polymerization. Also good.

  Examples of the polyacidic amino acid having no ethylenically unsaturated bond include the polyaspartic acid and polyglutamic acid or derivatives thereof, and the like. Although not particularly limited, among these, for example, a terminal group having no ethylenically unsaturated bond A hydrolyzate of polysuccinimide having the following is preferably used.

  The method of supplying the polyacidic amino acid to the hydrophobic organic solvent during the water-in-oil type reverse phase suspension polymerization is not particularly limited, but 1) an aqueous solution of a polyacidic amino acid hydrolyzed in advance. 2) A method of adding an aqueous solution of a polyacidic amino acid simultaneously with an aqueous solution of an ethylenically unsaturated monomer; 3) An ethylenic unsaturated Examples include a method of adding an aqueous solution of a polyacidic amino acid after adding an aqueous solution of a monomer.

  Any of these methods may be used, but the method of 3) is preferable in that the stability of the system can be further maintained. As a method for adding an aqueous solution of a polyacidic amino acid, this aqueous solution is added as it is, or an inert solvent in which a surfactant is dissolved in an aqueous solution of a polyacidic amino acid is added, stirred and dispersed, and then added. The latter addition method is more preferable because the resin particles do not aggregate and the polymerization stability is improved. At this time, the surfactant to be dissolved in the aqueous solution of the polyacidic amino acid is not particularly limited, and one or more of the anionic surfactants used in the reverse phase suspension polymerization method may be mixed. However, another surfactant can also be used.

Next, the method for producing the superabsorbent resin of the present invention will be specifically described.
An aqueous solution containing an anionic surfactant, an ethylenically unsaturated monomer and a crosslinking agent and a radical polymerization initiator, preferably a polyacidic amino acid, are supplied in a hydrophobic organic solvent in which organic bentonite is dispersed. Then, the aqueous solution is dispersed in the form of droplets in the oil, water-in-oil type reverse phase suspension polymerization is performed, and the resulting absorbent resin particles are further subjected to surface cross-linking treatment.

  As a method for supplying the aqueous solution or the like into the hydrophobic organic medium, there are a method for supplying the entire amount of the aqueous solution, a method for sequentially supplying the divided solution, and the like. In the method of starting the polymerization reaction after supplying the entire amount of the aqueous solution, not only the operation range in which granular absorbent resin particles with improved resin fixing property can be produced, but also the exothermic heat removal due to polymerization is difficult. It becomes.

  A specific method of sequential supply is, for example, by supplying a part of an aqueous solution containing an ethylenically unsaturated monomer, usually 1 to 25%, into a hydrophobic organic solvent to start polymerization, After proceeding to some extent, the polymerization is carried out while sequentially supplying the remaining aqueous solution.

  Further, as a method other than the above method, the polymerization is allowed to proceed simultaneously while sequentially supplying an aqueous solution mainly composed of ethylenically unsaturated monomer from the beginning into a hydrophobic organic solvent previously maintained under the polymerization conditions. Also good.

In carrying out these methods, a mixture of an aqueous solution mainly composed of an ethylenically unsaturated monomer and a part of the hydrophobic organic solvent may be supplied into the remaining hydrophobic organic solvent.
The supply of the aqueous solution mainly composed of the ethylenically unsaturated monomer is usually performed over a time of 20% or more, preferably 40% or more of the total polymerization time.

  The supply of the aqueous solution mainly composed of an ethylenically unsaturated monomer is usually performed at a constant rate, but if desired, the supply rate may be changed in the middle, and the supply may be temporarily interrupted in the middle. . This method is preferable because it makes it easier to produce granular particles.

  Although superposition | polymerization temperature is based also on a radical polymerization initiator, it is normally performed at 40-150 degreeC. If the temperature is too high, the self-crosslinking proceeds and the absorbability of the generated resin particles decreases. On the other hand, when the temperature is too low, not only does the polymerization take a long time, but there is a risk of causing sudden polymerization and generating a lump. A suitable polymerization temperature is 60 to 90 ° C., and the polymerization is particularly preferably carried out under reflux conditions of an inert solvent.

  Among the stirring conditions in reversed-phase suspension polymerization, the stirring rotation speed cannot be uniquely indicated because the absolute value varies depending on the type of stirring blade used and the scale of the polymerization reaction tank, but the stirring speed is In order to influence the average particle diameter of the polymer particles and to achieve the object of the present invention, it is preferable that the average particle diameter of the absorbent resin particles is in the range of 100 to 1000 μm. The range is preferable, and the range of 200 to 1000 rpm is particularly preferable. Absorbent resin particles having a structure in which primary particles are fused can be obtained by appropriately selecting the type of stirring blade and the stirring power within the stirring rotation speed within this range.

  By the above-described reverse phase suspension polymerization method, a slurry-like mixture composed of the hydrogel, excess surfactant and hydrophobic organic solvent is produced. This slurry-like mixture can be obtained by a known method, for example, direct dehydration or azeotropic dehydration with a hydrophobic organic solvent, followed by drying, classification with a sieve, and the like to obtain gel-like absorbent resin particles.

  The absorbent resin particles used in the present invention further increase the osmotic pressure with respect to urine, blood, etc. by causing the absorbent resin particles obtained above to undergo a crosslinking reaction in the vicinity of the surface of the particles using a surface crosslinking agent. be able to.

  Examples of such a surface cross-linking agent include compounds having two or more functional groups capable of reacting with functional groups near the surface of the absorbent resin particles. Moreover, since it will remain on the surface of the particles when used in an absorbent article or the like, it is preferable that it is highly safe for the human body.

  Examples of such compounds include compounds having a reactive group capable of reacting with two or more carboxyl groups (carboxylate groups) such as polyamine and polyglycidyl ether, and γ-glycidoxypropyltrimethoxysilane, γ Silane coupling agents such as glycidoxypropylmethyldiethoxysilane, N-β- (aminoethyl) -γ-aminopropyltrimethoxysilane and γ-mercaptopropyltrimethoxysilane, dibutyltin dilaurate which is a silanol condensation catalyst, dibutyltin Examples thereof include ethylenically unsaturated compounds having a reactive group such as diacetate and dibutyltin dioctoate, and these can be used alone or in combination of two or more.

  The surface crosslinking of the absorbent resin particles can be performed by mixing a powdery resin obtained by drying the slurry mixture to a predetermined moisture content and a surface crosslinking agent. At this time, in order to uniformly mix the resin and the surface cross-linking agent, it is preferable to use water and a hydrophilic solvent. In this case, 50 parts by weight or less of water and 60 parts by weight or less of the hydrophilic solvent are used with respect to 100 parts by weight of the resin. Furthermore, in order to improve the surface wettability of the resin, a small amount of a nonionic surfactant or an anionic surfactant having a high HLB may be added to these solvents.

  Examples of the hydrophilic solvent include lower alcohols such as methanol, ethanol, n-propanol, isopropanol, n-butanol, and isobutanol, ketones such as acetone and methyl ethyl ketone, dioxane, tetrahydrofuran, and diethyl ether. And ethers such as N, N-dimethylformamide and amides such as N, N-diethylformamide and sulfoxides such as dimethyl sulfoxide.

The mixing method of the resin and the surface cross-linking agent is not particularly limited, and for example, a known mixing device can be used.
Examples of such known mixing apparatuses include a cylindrical mixer, a double wall conical mixer, a high-speed stirring mixer, a V-shaped mixer, a ribbon mixer, a screw mixer, and a fluid-type furnace rotary desk type. Examples include a mixer, an airflow type mixer, a double arm type kneader, an internal mixer, a pulverizing type kneader, a rotary mixer, a screw type extruder, and the like. In order to mix with these mixing apparatuses, it is preferable to add the surface cross-linking agent while stirring the resin, and it is more preferable to add the surface cross-linking agent while spraying.

  The heating time at the time of surface crosslinking is appropriately selected depending on the heating temperature, but in order to obtain absorbent resin particles having high absorption performance without causing thermal deterioration, the temperature is from 60 ° C. to 300 ° C. for 5 minutes to 100 minutes. It is preferable that it is less than time.

  Although it does not specifically limit as a heating apparatus, Usually, a dryer or a heating furnace can be used. Specifically, for example, a groove type mixer / dryer, a rotary dryer, a disk dryer, a fluidized bed dryer, an airflow dryer, an infrared dryer, a vacuum dryer and the like can be mentioned.

  Since the resin-fixing property of the superabsorbent resin obtained by the present invention is improved, it is firmly fixed to the pulp of the base material of the structure, and absorbs paper diapers and sanitary goods with little change in absorption performance during use. A sex article can be created.

  As an absorbent article, in particular, a blood absorbent article has blood absorption characteristics such as sanitary napkins, tampons, medical blood absorption sheets, drip absorbents, wound protection materials, wound healing materials, surgical waste liquid treatment agents, and the like. The required items are listed. In addition to blood, protein-containing water, such as milk, breast milk, and urine, which shows excellent absorption characteristics, urine, seawater, cement water, soil water, Since it has excellent absorption characteristics for fertilizer-containing water, rainwater, drainage, etc., its application field is wide.

  Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples. In the following, all percentages are by weight unless otherwise specified. Various properties of the absorbent resin were measured by the following methods.

[Measurement method of average particle size]
The absorptive resin particles obtained in the examples described later were sieved with a mesh of 16 mesh (1000 μm), 30 mesh (500 μm), 100 mesh (150 μm), 140 mesh (106 μm), and 235 mesh (63 μm) (JIS-Z8801). ), And in the order of the saucer, about 20 g of resin particles were put in the uppermost sieve and sufficiently shaken. The weight of the resin particles remaining on each sieve was weighed, the total weight was 100%, the particle size distribution was obtained from the weight fraction, and the 50% particle size based on weight was taken as the average particle size.

[Measurement method of blood suction volume]
Absorbent resin particles obtained in Examples described later on 15 sheets of toilet paper (55 mm × 75 mm) soaked in 20 ml of horse defibrillated blood (obtained from Japan Biomaterials Center, Inc.) in a petri dish with an inner diameter of 95 mm After adding 1 g and absorbing for 5 minutes, a resin swelling gel was collected and its weight was measured. The weight of the swollen gel after absorption was divided by the weight of the resin particles before absorption to calculate the blood suction amount (g / g).

[Measurement method of blood absorption rate and affinity for blood]
In a petri dish having an inner diameter of 70 mm, about 0.5 g of the absorbent resin particles obtained in the examples described later are evenly dispersed, and then 2.5 ml of equine defibrinated blood is added to absorb the blood into the resin particles. The time until was taken as the blood absorption rate. In addition, the affinity between the resin particles and the blood at this time is visually observed, and the case where the blood penetrates the entire resin particles is “affinity”. The case where it hardly permeates while on the road was judged as “no affinity”.

Reference Example 1 Production Example of Polysuccinimide 96 g of maleic anhydride and 50 g of ion-exchanged water were added to a 1 L four-necked flask equipped with a stirrer, a thermometer, a reflux apparatus, and a nitrogen gas blowing apparatus. Thereafter, the mixture was heated to 55 ° C. to dissolve maleic anhydride, and then cooled once to obtain a maleic anhydride slurry. The system was heated again, and when the temperature reached 55 ° C., 60.8 g of 28% ammonia water was added. Thereafter, the temperature inside the system was heated to 80 ° C. And after making it react for 3 hours, the obtained aqueous solution was dried and the reaction intermediate body was obtained.
Next, 100 g of this reaction intermediate and 10 g of 85% phosphoric acid were charged into a 2 L eggplant flask and reacted for 4 hours using an evaporator at an oil bath temperature of 200 ° C. and a reduced pressure. The resulting product was washed several times with water and methanol. As a result of measuring the obtained polysuccinimide by GPC, the weight average molecular weight was 3000.

<< Reference Example 2 >> Example of production of introduction of methacryloyl group into polysuccinimide 20.6 g of sodium hydroxide was dissolved in a 500 ml four-necked flask equipped with a stirrer, thermometer, reflux apparatus and nitrogen gas blowing apparatus. After adding 75 g of an aqueous solution, 50 g of the polysuccinimide powder obtained in Reference Example 1 was added to obtain an aqueous solution of polysuccinimide. Next, after raising the temperature to 90 ° C., 5.0 g of glycidyl methacrylate was added and reacted for 1 hour to obtain an aqueous solution containing a hydrolyzate of polysuccinimide having a methacryloyl group introduced.

Example 1
1.68 g of PRISURF A210G (polyoxyethylene octylphenyl ether phosphoric acid, manufactured by Daiichi Kogyo Seiyaku Co., Ltd., acid value of about 100) was dissolved in 77.3 g of an aqueous sodium hydroxide solution in which 8.46 g of sodium hydroxide was dissolved. Sodium salt was used.
Next, this aqueous solution was dropped into a 500 ml Erlenmeyer flask containing 30 g of acrylic acid while cooling from the outside to neutralize 50 mol% of acrylic acid. Further, 0.047 g of N, N′-methylenebisacrylamide and 0.1 g of ammonium persulfate were added to this solution and dissolved.

  Separately from this, 164 g of cyclohexane was added to a 500 ml four-necked flask equipped with a stirrer, a thermometer, a reflux device, and a nitrogen gas blowing device, and Olven (quaternary ammonium salt-modified organic bentonite, Shiroishi Kogyo Co., Ltd.) 0.95 g was added and dispersed while stirring at 500 rpm. Next, after the flask was purged with nitrogen, the temperature was raised to 75 ° C., and the acrylic acid aqueous solution prepared above was added dropwise over 60 minutes. After the dropwise addition, 7.8 g of a polyaspartic acid aqueous solution into which the methacryloyl group obtained in Reference Example 2 was introduced was added all at once. Next, after maintaining at 70 to 75 ° C. for 3 hours, the resin produced by azeotropy with cyclohexane was dehydrated until the water content became 10%. Stirring was performed constantly at a rotation speed of 500 rpm. After completion of the reaction, the cyclohexane phase was separated by decantation, and then water was removed from the obtained water-containing resin particles by drying under reduced pressure to obtain a polymer powder. The amount of resin adhering to the inner wall of the flask and the stirring blade was about 2.1 g.

  30 g of polymer particles obtained in a 500 ml flask were weighed and mixed therewith 1.2 g of acetone, 2.1 g of ion-exchanged water, 0.09 g of glycidyl methacrylate, 0.09 g of ammonium persulfate, and hydrophilic silica (Japan Aerosil Co., Ltd. (200CF) 0.3 g was uniformly sprayed and mixed well. The obtained water-containing resin particles were spread on a metal bat and dried under reduced pressure at 108 ° C. for 1 hour to perform surface crosslinking of the resin particles. When the obtained absorbent resin was observed with a microscope, it had a structure in which fine primary particles were fused. Table 1 shows the results of the characteristic evaluation of the absorbent resin of the present invention. It can be seen that the absorbent resin obtained in Example 1 has a large average particle diameter due to the fused structure, is excellent in blood suction ability (aspiration amount, absorption speed), and has an affinity for blood.

Example 2
Absorbent resin particles were obtained in the same manner as in Example 1 except that the amount of N, N′-methylenebisacrylamide was increased to 0.141 g. The amount of resin adhering to the inner wall of the flask and the stirring blade after the reverse phase suspension polymerization was about 1.6 g. When the microscopic observation of the absorbent resin particles obtained by surface cross-linking was performed, it had a structure in which fine primary particles were fused. The evaluation results of the properties of the absorbent resin of the present invention are shown in Table-1. It can be seen that the absorbent resin obtained in Example 2 has a large average particle diameter due to the fused structure, is excellent in blood suction ability, and has an affinity for blood.

Example 3
Except for dissolving 1.68 g of plysurf A213B (polyoxyethylene lauryl ether phosphoric acid, manufactured by Daiichi Kogyo Seiyaku Co., Ltd., acid value of about 95) instead of plysurf A210G in sodium hydroxide aqueous solution, Absorbent resin was obtained by the same operation as in Example 1. The amount of resin adhering to the inner wall of the flask and the stirring blade after the reverse phase suspension polymerization was about 2.4 g. When the absorptive resin particles obtained by surface cross-linking were observed with a microscope, they had a structure in which primary particles were fused. The evaluation results of the properties of the absorbent resin of the present invention are shown in Table-1. It can be seen that the absorbent resin obtained in Example 3 has a large average particle diameter due to the fused structure, is excellent in blood suction ability, and has an affinity for blood.

Example 4
Instead of the polyaspartic acid aqueous solution introduced with methacryloyl group obtained in Reference Example 2, 7.8 g of an aqueous polyaspartic acid solution in which polysuccinimide powder before introduction of methacryloyl group was dissolved was added all at once. Except that, an absorbent resin was obtained by the same operation as in Example 1. The amount of resin adhering to the inner wall of the flask and the stirring blade after the reverse phase suspension polymerization was about 1.9 g. When the absorptive resin particles obtained by surface cross-linking were observed with a microscope, they had a structure in which primary particles were fused. The evaluation results of the properties of the absorbent resin of the present invention are shown in Table-1. It can be seen that the absorbent resin obtained in Example 4 has a large average particle diameter due to the fused structure, is excellent in blood suction ability, and has an affinity for blood.

Example 5
The same procedure as in Example 1 was performed except that 6.72 g of Emar 20C (25% aqueous solution of polyoxyethylene dodecyl ether sulfate sodium salt, manufactured by Kao) was used in the acrylic acid monomer aqueous solution in place of Prisurf A210G. An absorbent resin was obtained. The amount of the resin adhering to the inner wall of the flask and the stirring blade after the reverse phase suspension polymerization was about 2.5 g. When the absorptive resin particles obtained by surface cross-linking were observed with a microscope, they had a structure in which primary particles were fused. The evaluation results of the properties of the absorbent resin of the present invention are shown in Table-1. Although the absorptive resin obtained in Example 5 has a slightly small average particle diameter, it is understood that the absorptive resin has excellent blood suction ability and affinity for blood.

<< Comparative Example 1 >>
Without adding and dissolving PRISURF A210G in the aqueous sodium hydroxide solution, and after the dropping of the acrylic acid aqueous solution into cyclohexane is completed, do not add the polyaspartic acid aqueous solution introduced with the methacryloyl group obtained in Reference Example 2 Except for this, an absorbent resin was obtained in the same manner as in Example 1. The amount of resin adhering to the inner wall of the flask and the stirring blade after the reverse phase suspension polymerization was about 2.9 g. When the absorptive resin particles obtained by surface cross-linking were observed with a microscope, the primary particles did not have a fused structure, but only fine spherical particles. As shown in Table 1, the average particle size was small, and an excellent blood absorption ability could not be obtained.

<< Comparative Example 2 >>
50 mol in exactly the same manner as in Comparative Example 1 except that 1.68 g of Emulgen 106 (polyoxyethylene lauryl ether, HLB = 10.5, manufactured by Kao) was added and dissolved in a 500 ml Erlenmeyer flask. % Neutralized aqueous acrylic acid solution was prepared.

Thereafter, in exactly the same manner as in Example 1, a cyclohexane dispersion in which olben was dispersed was prepared in a 500 ml four-necked flask, and the flask was purged with nitrogen while stirring at a rotation speed of 500 rpm. The acrylic acid aqueous solution prepared above was added dropwise over 60 minutes, but the polyaspartic acid aqueous solution introduced with methacryloyl group obtained in Reference Example 2 was not added thereafter.

  Subsequently, after hold | maintaining at 70-75 degreeC for 3 hours, the resin particle produced | generated by azeotropy with cyclohexane was dehydrated until the moisture content became 10%. Stirring was performed at a constant rotation speed of 500 rpm. After completion of the reaction, the cyclohexane phase was separated by decantation, and then water was removed from the water-containing resin particles by drying under reduced pressure to obtain a polymer powder. The amount of resin adhering to the inner wall of the flask and the stirring blade was about 3.0 g.

  30 g of polymer particles obtained in a 500 ml flask were weighed and subjected to surface cross-linking treatment by the same operation as in Example 1. When the obtained water-absorbing resin particles were observed with a microscope, the primary particles did not have a fused structure, but only fine spherical particles. As shown in Table 1, the average particle size was small, and an excellent blood absorption ability could not be obtained.

<< Comparative Example 3 >>
A 50 mol% neutralized aqueous acrylic acid solution was prepared in exactly the same manner as in Comparative Example 1, except that 1.68 g of Prisurf A210G was added and dissolved in water in a 500 ml Erlenmeyer flask.

  Separately, 164 g of cyclohexane was added to a 500 ml four-necked flask equipped with a stirrer, a thermometer, a reflux apparatus, and a nitrogen gas blowing apparatus, and 0.41 g of sorbitan monostearate having an HLB of 4.7 was added thereto. It was added and dispersed while stirring at 500 rpm. Next, after the flask was purged with nitrogen, the temperature was raised to 75 ° C., and the acrylic acid aqueous solution prepared above was added dropwise over 60 minutes.

  Subsequently, after hold | maintaining at 70-75 degreeC for 3 hours, it spin-dry | dehydrated until the moisture content of the resin particle produced | generated by azeotropy with a cyclohexane became 10%. Stirring was performed at a constant rotation speed of 500 rpm. After completion of the reaction, the cyclohexane phase was separated by decantation, and then water was removed from the water-containing resin particles by drying under reduced pressure to obtain a polymer powder. The amount of resin adhering to the inner wall of the flask and the stirring blade was about 2.8 g.

  30 g of polymer particles obtained in a 500 ml flask were weighed and subjected to surface cross-linking treatment by the same operation as in Example 1. When the obtained water-absorbent resin particles were observed with a microscope, they had a granular structure in which the primary particles were fused. As shown in Table 1, although the average particle diameter was large, the blood absorption ability was excellent. I could not get.

Claims (2)

Water-soluble monomer having at least one ethylenically unsaturated double bond in the molecule in a hydrophobic organic solvent containing organic bentonite in the presence of an anionic surfactant represented by the following general formula (1) A method for producing a superabsorbent resin, comprising supplying an aqueous solution containing a body and performing water-in-oil type reverse phase suspension polymerization.

[Wherein, R ¹ represents an alkyl group which may be substituted with a phenyl group having 8 to 30 carbon atoms or an aryl group which may be substituted with an alkyl group, and n represents an integer of 1 to 30. , M represents an alkali metal, a quaternary ammonium salt or a quaternary amine salt, and R ² represents —OM or R ¹ O— (CH ₂ CH ₂ O) n— (where R ¹ , M and n Indicates the same as above. ] A polyacidic amino acid containing at least one ethylenically unsaturated double bond in the molecule and / or a polyacidic amino acid not containing an ethylenically unsaturated double bond in the molecule is supplied to the hydrophobic organic solvent. A method for producing the superabsorbent resin according to 1 .