JP5042674B2 - Method for producing polyacrylic acid (salt) water-absorbing resin - Google Patents

Description

  The present invention relates to a method for producing a polyacrylic acid (salt) water-absorbing resin. Specifically, the present invention relates to a method for producing a water-absorbing resin having high physical properties and excellent safety with high productivity.

  In recent years, water-absorbing resins have been developed as crosslinked synthetic polymers having water-absorbing properties, and are widely used in applications such as absorbent articles such as disposable diapers and sanitary napkins, agricultural and horticultural water retention agents, and industrial waterstop materials. Many monomers and hydrophilic polymers have been proposed as raw materials for such a water-absorbent resin. Among these, acrylic acid-based water-absorbing resins using acrylic acid and / or a salt thereof as a monomer are most frequently used industrially because of their high absorption performance.

  In particular, hygiene materials such as diapers have become highly functional and thin, and the amount of water absorption resin used in the sanitary material is increased and the ratio of use (ratio in absorbent articles, mass%) is increased. The thickness is reduced while ensuring the increase of the leakage and leakage prevention. For this reason, advanced physical properties are required for the water-absorbent resin.

  Properties required for the water-absorbent resin include, for example, reduction of an uncrosslinked water-soluble polymer that contradicts the increase in absorption capacity (Patent Document 1), physical properties under pressure such as absorption capacity under pressure and liquid flow rate under pressure. (Patent Document 2).

  Since the water-absorbent resin has a cross-linked structure, preferably inside the polymer, more preferably further on the surface, the cross-linking means greatly affects the physical properties. Therefore, a method using a specific cross-linking agent or specific cross-linking conditions during polymerization and / or surface cross-linking has been proposed.

  For example, as a crosslinking agent and crosslinking conditions at the time of polymerization, a production method using polyoxyalkylene glycol di (meth) acrylate or the like as an internal crosslinking agent (Patent Documents 3 and 4), a production method using a specific trimethylolpropane triacrylate ( Patent Documents 5 and 6), a process using polyallyl ether as an internal cross-linking agent (Patent Documents 7 to 9), a process using polyalkoxylated trimethylolpropane acrylic ester (Patent Documents 10 to 12), A method using a saturated amino alcohol (Patent Document 13) has been proposed.

  In addition, means (Patent Documents 14 to 16) in which a surfactant is used in combination with an internal crosslinking agent during polymerization has also been proposed.

  Furthermore, a method of using a combination of three specific types of crosslinking agents as a crosslinking agent has been proposed (Patent Document 8).

Moreover, the method of using a specific crosslinking agent and specific crosslinking conditions for the physical property improvement of a water absorbing resin is proposed (patent documents 1-13). However, problems such as a decrease in safety and a decrease in surface tension due to the presence of the crosslinking agent, a problem in polymerization delay and an increase in residual monomers, a problem in coloring of the final product, and the like occur, and the physical properties of the water-absorbent resin cannot be said to be sufficient. Moreover, in the method of using a surfactant during polymerization, there are cases where not only the cost of the surfactant is increased, but also a problem of a decrease in surface tension due to the remaining of the surfactant (Patent Documents 14 to 16). Furthermore, a technique in which the improvement of the absorption characteristics of the water-absorbent resin is insufficient from the viewpoint of the affinity with the acrylic acid monomer and the copolymerization characteristics has also been reported (Patent Document 8).
US Pat. No. 4,654,039 US Pat. No. 5,562,646 U.S. Pat. No. 4,351,922 US Pat. No. 5,532,323 US Pat. No. 5,574,121 US Pat. No. 5,506,324 International Publication WO 97/18890 US Pat. No. 5,837,789 International Publication No. WO01 / 29132 International Publication WO2003 / 104302 International Publication No. WO2003 / 104299 International Publication WO2003 / 104300 US Pat. No. 6,087,450 US Pat. No. 4,286,082 US Pat. No. 5,985,944 US Pat. No. 6,251,960

  The object of the present invention is to reduce the residual cross-linking agent and the residual surfactant in the method for producing a water-absorbent resin, to achieve high productivity, and to obtain the physical properties of the resulting water-absorbent resin (for example, absorption capacity, water-soluble content , Powder friction, gel grindability).

  In order to solve the above problems, the present inventors have studied. As a result, a polyfunctional (meth) acrylate-based cross-linking agent having a polyethylene glycol structure is used as an internal cross-linking agent when manufacturing a water-absorbent resin, and further specified for the polyfunctional (meth) acrylate-based cross-linking agent. It has been found that the above problem can be solved by using a mono (meth) acrylate compound having a polyethylene glycol structure in an amount or controlling the molecular weight distribution of the polyfunctional (meth) acrylate-based crosslinking agent to be narrow.

One of the methods for producing the water-absorbent resin of the present invention is:
Including a step of polymerizing an aqueous monomer solution mainly composed of an acrylic acid monomer in the presence of a crosslinking agent, and a step of heat drying.
The cross-linking agent is a polyfunctional (meth) acrylate-based cross-linking agent having a polyethylene glycol structural unit having a total ethylene oxide repeating unit of 6 to 200,
In the monomer aqueous solution, 0.1 to 30% by mass of a mono (meth) acrylate compound having a polyethylene glycol structural unit is allowed to coexist with the polyfunctional (meth) acrylate crosslinking agent.

Another one of the methods for producing the water-absorbent resin of the present invention is:
Including a step of polymerizing an aqueous monomer solution mainly composed of an acrylic acid monomer in the presence of a crosslinking agent, and a step of heat drying.
The cross-linking agent is a polyfunctional (meth) acrylate-based cross-linking agent having a polyethylene glycol structural unit having a total ethylene oxide repeating unit of 6 to 200,
The molecular weight distribution defined by the distribution index of ethylene oxide repeating units of the polyfunctional (meth) acrylate crosslinking agent is 50 to 100%.

  In preferable embodiment, the (meth) acryloyl oxyacrylate type crosslinking agent which has 0.01-30 mass% polyethyleneglycol structural unit with respect to the said polyfunctional (meth) acrylate type crosslinking agent in the said monomer aqueous solution. Coexist.

  In a preferred embodiment, the ratio of the number of polyethylene glycol structural units of the polyfunctional (meth) acrylate-based crosslinking agent to the number of polyethylene glycol structural units of the mono (meth) acrylate-based compound is 0.5-2. A range of zero.

In a preferred embodiment, 1.0 × 10 ^{−5 to} 0.5 mol% of the mono (meth) acrylate compound and the polyfunctional (meth) acrylate crosslinking agent are used with respect to the acrylic acid monomer. It contains 1.0 × 10 ^{−3 to} 1.0 mol%.

  In a preferred embodiment, a surface crosslinking step with heating is included after the drying step.

In a preferred embodiment, the acrylic acid-based monomer contains 1 to 1000 polymerization inert organic compounds having a solubility parameter of 1.0 × 10 ^{4 to} 2.5 × 10 ⁴ (Jm ⁻³ ) ^1/2. Contains mass ppm.

  In preferable embodiment, the said acrylic acid-type monomer contains 0.01-5 mass ppm of iron.

  The method of the present invention can reduce the residual cross-linking agent and the residual surfactant, can easily control the polymerization reaction, and is a physical property of the obtained water-absorbent resin (for example, a fundamental physical property opposite to that of the water-absorbent resin). (Improvement of the relationship between “absorption capacity” and “water-soluble polymer”), and it is possible to produce a water-absorbent resin with good powder characteristics and high productivity without causing a decrease in surface tension. it can.

(1) Water absorbent resin and its monomer

(Water absorbent resin)
In the present specification, the crosslinked water-absorbing resin refers to a water-swellable water-insoluble polymer in which a crosslinked structure is introduced into the polymer. “Water swellability” means that the absorption capacity (GVs) under no pressure with respect to physiological saline is 3 g / g or more, preferably 5 to 200 g / g, more preferably 20 to 100 g / g. Say. “Water-insoluble” means that the water-soluble component in the resin is substantially 0 to 50% by mass, preferably 0 to 25% by mass, more preferably 0 to 15% by mass, and still more preferably 0 to 10% by mass. It is water-insoluble. These measuring methods will be described later.

  Even if the water-absorbent resin contains a small amount of additives (for example, inorganic powder, deodorant, antibacterial agent, hydrophilic polymer or hydrophobic polymer) and the water-absorbent resin is a composition, In the invention, it is generically called a water-absorbing resin.

(Monomer)
In the present invention, the “acrylic monomer” refers to acrylic acid and / or acrylate.

  In the present invention, from the viewpoint of physical properties, a monomer aqueous solution containing an acrylic acid monomer as a main component is used for polymerization. In the total monomers (excluding the crosslinking agent) used for the polymerization, the content of the acrylic monomer is 50 mol% or more, preferably 70 mol% or more, more preferably 90 mol% or more, and still more preferably 95 More than mol%.

  From the viewpoint of physical properties, the acrylate is preferably a monovalent salt of acrylic acid composed of an alkali metal salt, an ammonium salt or an amine salt, more preferably an alkali metal salt, still more preferably a sodium salt, a lithium salt or potassium. Salt. In addition, polyvalent metal salts such as calcium salts and aluminum salts may be used in combination within the range of water swelling.

  In the water absorbent resin obtained in the present invention, it is preferable that acid groups derived from acid group-containing monomers such as acrylic acid are neutralized. The neutralization rate is usually 20 to 100 mol%, preferably 50 to 95 mol%, more preferably 60 to 90 mol%. This neutralization may be performed on the monomer before polymerization, may be performed on the polymer during or after the polymerization, and the neutralization of the monomer and the neutralization of the polymer are used in combination. May be.

  You may use "other monomers" other than an acrylic acid-type monomer in the ratio of 50 mol% or less in the total monomer (except a crosslinking agent) used for superposition | polymerization. Examples of the other monomer include monomers exemplified in the following US patents and European patents. Specifically, for example, methacrylic acid, (anhydrous) maleic acid, fumaric acid, crotonic acid, Itaconic acid, vinylsulfonic acid, 2- (meth) acrylamido-2-methylpropanesulfonic acid, (meth) acryloxyalkanesulfonic acid and its alkali metal salts, ammonium salts, N-vinyl-2-pyrrolidone, N-vinylacetamide , (Meth) acrylamide, N-isopropyl (meth) acrylamide, N, N-dimethyl (meth) acrylamide, 2-hydroxyethyl (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, polyethylene glycol (meth) acrylate, isobutylene, Lauryl (meth) acrelan Etc., water-soluble may be used as a copolymerization component or hydrophobic unsaturated monomers.

  The content of the other monomer is less than 50 mol%, preferably 0 to 30 mol%, more preferably 0 to 10 mol%, particularly preferably in the total monomers (excluding the crosslinking agent) used for polymerization. Is 0 to 1 mol%. By using the other monomer in the above proportion, the absorption characteristics of the obtained water absorbent resin can be further improved, and the water absorbent resin can be obtained at a lower cost.

[Polyfunctional (meth) acrylate crosslinking agent and mono (meth) acrylate compound]
In this invention, the polyfunctional (meth) acrylate type crosslinking agent which has a polyethyleneglycol structural unit whose ethylene oxide repeating unit total is 6-200 is used as an internal crosslinking agent. In one embodiment, a specific amount of a specific mono (meth) acrylate compound is allowed to coexist, and in another embodiment, the molecular weight distribution of the crosslinking agent is controlled. In the present invention, (meth) acrylate is a general term for methacrylate, acrylate, and a mixture thereof. In the present invention, acrylate is preferred.

  Hereinafter, the polyfunctional (meth) acrylate crosslinking agent and mono (meth) acrylate compound having a polyethylene glycol structural unit having a total ethylene oxide repeating unit of 6 to 200 will be described.

  In the present invention, the mono (meth) acrylate compound having a polyethylene glycol structural unit is a compound having a polyethylene glycol chain in the molecule, one end of which is a (meth) acrylic ester, and the other end. Is any suitable substituent. As said substituent, an alkyl group, an allyl group, a phenyl group, and a hydroxyl group are mentioned, for example, Preferably it is a hydroxyl group from the surface of a physical-property improvement.

  In the present invention, the polyfunctional (meth) acrylate-based cross-linking agent having a polyethylene glycol structural unit has a polyethylene glycol chain in the molecule, and a plurality of, preferably 2 to 10, more preferably 2 to 6 ends (meta ) A compound that has become an acrylic ester, and any other suitable substituent such as an alkyl group, an allyl group, or a phenyl group can be employed at the other end.

  As the compound having a polyethylene glycol structural unit, any appropriate compound can be adopted as long as it has a polyethylene glycol structural unit in the molecule. For example, polyethylene glycol, polyethylene glycol derivatives such as propylene glycol, 1,3-propanediol, dipropylene glycol, 2,3,4-trimethyl-1,3-pentanediol, polypropylene glycol, glycerin, polyglycerin, 2-butene- EO of various polyhydric alcohols such as 1,4-diol, 1,4-butanediol, 1,3-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,2-cyclohexanedimethanol ( Examples include mono- or polyfunctional acrylates for (ethylene oxide) adducts. Polyethylene glycol monoacrylate is preferred.

  Examples of the polyfunctional (meth) acrylate-based crosslinking agent include EO-added propylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, EO-added neopentyl glycol di (meth) acrylate, and EO-added trimethylolpropane di ( (Meth) acrylate, EO-added trimethylolpropane tri (meth) acrylate, EO-added glycerol tri (meth) acrylate, EO-added pentaerythritol tetra (meth) acrylate, EO-added pentaerythritol tri (meth) acrylate, EO-added dipentaerythritol hexa (Meth) acrylate, EO-added tripentaerythritol octa (meth) acrylate may be mentioned. In addition, EO addition is a general term for a polyethylene glycol structure, and is not necessarily obtained by EO addition, and can be obtained by any appropriate method.

  The total number of ethylene oxide repeating units in the polyethylene glycol structural unit in the polyfunctional (meth) acrylate crosslinking agent is in the range of 6 to 200, preferably 6.5 to 100, more preferably 7 to 50, even more preferably, per molecule of the crosslinking agent. Is in the range of 8-40. When the total of ethylene oxide repeating units in the polyethylene glycol structural unit in the polyfunctional (meth) acrylate-based crosslinking agent is within the above range, there is little turbidity when the crosslinking agent is used as an aqueous solution, and the transmittance is high.

  When the average addition number of ethylene oxide is less than 5, there is a possibility that the absorption characteristics of the resulting water-absorbent resin may be deteriorated. When the average addition number of ethylene oxide exceeds 200, the heat resistance of the obtained water absorbent resin may be lowered. The total number of ethylene oxide repeating units per molecule of the cross-linking agent is a plurality (for example, three in the former) of EO when having a plurality of polyethylene glycol structures in the same compound (for example, an EO adduct of trimethylolpropane). Calculate the sum of repeat units.

  In the present invention, ethylene oxide is synonymous with polyethylene glycol, and the number of additions is the average value of the number of ethylene oxide units in the internal crosslinking agent molecule. For example, in polyethylene glycol, the average number of ethylene oxide repeats is calculated from the mass average molecular weight measured by gel permeation chromatography (GPC).

  The distribution index of the polyfunctional acrylate crosslinking agent having a polyethylene glycol structural unit indicates the distribution of polyethylene glycol chain length. The distribution index of the polyfunctional acrylate crosslinking agent having a polyethylene glycol structural unit is preferably higher, preferably 50 to 100, more preferably 60 to 100, still more preferably 70 to 100, particularly preferably 80 to 100, most preferably. Preferably it is 90-100. When the distribution index is less than 50, there are many polyfunctional acrylate-based cross-linking agents having polyethylene glycol structural units with different numbers of ethylene oxide additions, which may make it difficult to control polymerization or reduce absorption characteristics.

  From the viewpoint of physical properties, the proportion of ethylene oxide having an average addition number of 4 or less or 300 or more in the polyfunctional acrylate crosslinking agent is preferably 0 to 10% or less, more preferably 5% or less, and further preferably 2%. Hereinafter, it is particularly preferably 0.5% or less.

  Among the polyfunctional acrylate-based cross-linking agents having the above polyethylene glycol structural unit, polyethylene glycol diacrylate is preferable, and polyethylene glycol diacrylate is more preferable, from the viewpoint of the reactivity with acrylic acid or a salt thereof and the properties of the resulting water-absorbent resin. The total number of ethylene oxide repeating units in the structural unit is 8 to 40 polyethylene glycol diacrylate per molecule of the crosslinking agent, and more preferably the total number of ethylene oxide repeating units is 8 to 20 per molecule of the crosslinking agent. A polyethylene glycol diacrylate.

  In the polyfunctional (meth) acrylate-based crosslinking agent having a polyethylene glycol structural unit and the mono (meth) acrylate-based compound having a polyethylene glycol structural unit, the ethylene oxide repeating unit may be the same or different. Preferably, the repeating unit ratio is 0.5 to 2.0, more preferably 0.7 to 1.5, still more preferably 0.8 to 1.3, and particularly preferably 0.9 to 1.1. Used together.

  The mono (meth) acrylate-based compound having the polyethylene glycol structural unit and the polyfunctional (meth) acrylate-based cross-linking agent having the polyethylene glycol structural unit are handled in the actual production process, the fine adjustment of the amount of the cross-linking agent, and the water absorption obtained. From the viewpoint of the physical properties (soluble content, etc.) of the conductive resin, it is preferably used in an aqueous solution. For example, when a 20% by mass aqueous solution is used, it is important that no precipitate or precipitate is generated.

  That is, the mono (meth) acrylate compound having a polyethylene glycol structural unit is known as a water-soluble compound because it has a polyethylene glycol structural unit. In the production of the water-absorbing resin, the mono (meth) acrylate compound is used by adding a very small amount (for example, 0.1% by mass) to the acrylic acid monomer aqueous solution, so that it dissolves uniformly and has a recognition of solubility. It wasn't. However, it has been found that even the same mono (meth) acrylate compound does not dissolve in a 20% by mass aqueous solution. The solubility in the case of such a 20% by mass aqueous solution greatly affects the physical properties of the water absorbent resin. For example, among the above-mentioned compounds that are commercially available as aqueous solutions, there are those that dissolve uniformly in an acrylic acid monomer aqueous solution, but, for example, precipitates and precipitates are generated when the amount is 10 to 50% by mass. A water-absorbent resin produced using such a compound may not have desired physical properties.

  The mono (meth) acrylate-based compound having the polyethylene glycol structural unit is preferably 1 to 50% by mass, more preferably 1 to 20% by mass for the purpose of improving the physical properties and stable production of the water absorbent resin. To the monomer aqueous solution.

  For the above reasons, light at a wavelength of 500 nm when the mono (meth) acrylate compound having the polyethylene glycol structural unit and the polyfunctional (meth) acrylate crosslinking agent having the polyethylene glycol structural unit are made into a 20% by mass aqueous solution. The transmittance is preferably 70 to 100%, more preferably 80 to 100%, still more preferably 90 to 100%, particularly preferably 95 to 100%, and most preferably 98 to 100%.

  In one embodiment of the present invention, 0.1 to 30 mass of the mono (meth) acrylate compound having a polyethylene glycol structural unit is added to the polyfunctional (meth) acrylate crosslinking agent having the polyethylene glycol structural unit. %, Preferably 0.1 to 20% by weight, more preferably 0.5 to 15% by weight, still more preferably 0.5 to 10% by weight, particularly preferably 0.6 to 10% by weight, and most preferably 0.8. It is made to coexist at the time of superposition | polymerization in 7-5 mass%.

  When the proportion of the mono (meth) acrylate compound having a polyethylene glycol structural unit is less than 0.1% by mass, the absorption characteristics may be deteriorated. Moreover, when it exceeds 30 mass%, there exists a possibility that the heat resistance of the water absorbent resin obtained may fall and an absorption characteristic may fall.

In achieving the object of the present invention, the amount of the mono (meth) acrylate compound used is preferably 1.0 × 10 ^{−5 to} 0.5 mol%, more preferably, with respect to the acrylic acid monomer. Preferably it is 0.001-0.5 mol%, More preferably, it is 0.001-0.2 mol%, More preferably, it is 0.005-0.2 mol%, Most preferably, it is 0.005-0.1 mol% It is. Moreover, the usage-amount of this polyfunctional (meth) acrylate type crosslinking agent becomes like this with respect to an acrylic acid monomer, Preferably it is 0.001-1.0 mol%, More preferably, it is 0.001-0.5 mol. %, More preferably 0.001 to 0.2 mol%, particularly preferably 0.005 to 0.2 mol%, and most preferably 0.005 to 0.1 mol%.

  When the usage-amount of the said polyfunctional (meth) acrylate type crosslinking agent or the said mono (meth) acrylate type compound remove | deviates from the said range, there exists a possibility that a desired absorption characteristic may not be obtained.

  The above-mentioned use amounts of the mono (meth) acrylate compound having a polyethylene glycol structural unit and the polyfunctional (meth) acrylate cross-linking agent having the polyethylene glycol structural unit may be appropriately mixed. The conditions for the esterification of glycol and the purification conditions may be appropriately adjusted to form a predetermined mixture.

[Third (meth) acrylate compound]
In the present invention, as the third (meth) acrylate compound, a (meth) acryloyloxyacrylate-based crosslinking agent having a polyethylene glycol structural unit with respect to the polyfunctional (meth) acrylate-based crosslinking agent is preferably 0.00. You may coexist 01-30 mass%, More preferably, it is 0.1-20 mass%, More preferably, you may make 1-10 mass%. The use of a (meth) acryloyloxyacrylate-based crosslinking agent is preferable because the crosslinking point is cut by reverse Michael addition (elimination) by heating after polymerization, and the absorption capacity can be improved.

  The third (meth) acrylate compound can be synthesized by esterification of a polyhydric alcohol having a polyethylene glycol structural unit and acryloyloxypropionic acid. In this synthesis, acrylic acid may coexist or may be used as a solvent. The (meth) acryloyloxyacrylate-based crosslinking agent preferably has one or more acrylate groups and (meth) acryloyloxyacrylate groups.

  Examples of the third (meth) acrylate compound include polyethylene glycol di (β-acryloyloxypropionate), polyethylene glycol monoacrylate mono (β-acryloyloxypropionate), EO-added propylene glycol di ( β-acryloyloxypropionate), EO-added propylene glycol monoacrylate mono (β-acryloyloxypropionate), EO-added neopentyl glycol di (β-acryloyloxypropionate), EO-added neopentyl glycol acrylate Mono (β-acryloyloxypropionate), EO-added trimethylolpropane tri (β-acryloyloxypropionate), EO-added glycerol diacrylate mono (β-acryloylo) (Meth) acryloyloxypropionate-based crosslinking agents such as xylpropionate).

[Other internal cross-linking agents]
In this invention, you may use together other internal crosslinking agents other than the polyfunctional (meth) acrylate type crosslinking agent which has a polyethyleneglycol structural unit.

  Examples of the other internal cross-linking agents include cross-linking agents that polymerize or react with acrylic acid. For example, N, N′-methylenebisacrylamide, (poly) propylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, trimethylolpropane di (meth) acrylate, trimethylolpropane tri (β-acryloyloxypro) Pionate), poly (meth) allyloxyalkane and other polymerizable group-containing crosslinkers, polyethylene glycol diglycidyl ether and other polymerizable group and reactive group-containing crosslinkers, ethylene glycol, polyethylene glycol, glycerin and more Examples thereof include a reactive group-containing crosslinking agent. These may be used alone or in combination of two or more.

  The amount of the other internal crosslinking agent used is preferably 0 to 1.0 mol% or less, more preferably 0 to 0.1 mol%, still more preferably 0 to 0.0 mol% based on the acrylic acid monomer. Further, it is preferably at most 1 mol%, more preferably at most 50 mol%, still more preferably at most 20 mol%, based on the polyfunctional (meth) acrylate crosslinking agent.

[Other components during polymerization]
The monomer used in the present invention may further contain other trace components to improve physical properties and polymerizability. Specific examples of the compound include a polymerization inert organic compound, methoxyphenol, Fe, and acrylic acid dimer. These may coexist on the order of ppm. Hereinafter, the trace component which can be used together is further demonstrated.

[Polymerization inert organic compound]
In the present invention, the solubility parameter is adjusted to 1.0 × 10 ^{4 to} 2.5 × 10 ⁴ (Jm) in order to improve physical properties (improvement of the relationship between the absorption capacity and the soluble content) in the monomer during polymerization. ^-3 ) It is preferable to contain 1-1000 mass ppm of the polymerization inactive organic compound which is ^1/2 in the total monomer used for superposition | polymerization. “Polymerization inert organic compound” means an organic compound having no polymerizable unsaturated bond, and a compound having a saturated bond that is not polymerized by thermal decomposition, radical polymerization by an oxidizing agent / reducing agent, ultraviolet rays, or γ rays. Alternatively, it refers to an organic compound such as an aromatic compound.

  The above-mentioned “solubility parameter” refers to the cohesive energy density. For example, published in publications such as Polymer Handbook 3rd edition (WILLEY SCIENCE, Inc., pages 527-539) and Chemical Handbook Basics (The Chemical Society of Japan). The solubility parameter and δ value described above are applied, and the δ value derived by substituting the Hoy cohesive energy constant described on page 525 into the Small formula described on page 524 of the third edition of the polymer handbook (published by WILLEY SCIENCE). Applies.

  The amount of the polymerization inert organic compound used in the total monomer used for the polymerization is more preferably 0.1 to 500 ppm by mass, further preferably 1 to 300 ppm by mass, further preferably 5 to 300 ppm by mass, Especially preferably, it is 10-300 mass ppm, Most preferably, it is 10-100 mass ppm.

The solubility parameter is preferably 1.0 × 10 ^{4 to} 2.2 × 10 ⁴ (Jm ⁻³ ) ^1/2 , more preferably 1.1 × 10 ^{4 to} 2.0 × 10 ⁴ (Jm ^{− 3} ) ^1/2 , more preferably 1.3 × 10 ^{4 to} 2.0 × 10 ⁴ (Jm ⁻³ ) ^1/2 , and particularly preferably 1.5 × 10 ^{4 to} 1.9 × 10. ⁴ (Jm ⁻³ ) ^1/2 .

  The polymerization inert organic compound is preferably an organic compound containing no halogen from the viewpoint of environmental burden, and more preferably a hydrocarbon composed of only carbon and hydrogen.

  The boiling point of the polymerization inert organic compound is preferably 95 to 300 ° C, more preferably 130 to 260 ° C. Specifically, heptane (boiling point 95 ° C), dimethylcyclohexane (132 ° C), ethylcyclohexane, toluene (110 ° C), ethylbenzene (136 ° C), xylene (138-144 ° C), diethylketone (101) ° C), diisopropyl ketone (124-125 ° C), methyl propyl ketone (102 ° C), methyl isobutyl ketone, methyl-t-butyl ketone, n-propyl acetate (101 ° C), n-butyl acetate (124- 125 ° C.), diphenyl ether (259 ° C.), and diphenyl (255 ° C.) are preferred. An aromatic compound is more preferable, and toluene, diphenyl ether, and diphenyl are particularly preferable from the viewpoints of polymerization characteristics and productivity.

  The polymerization-inert organic compound is preferably contained in the monomer before polymerization and the polyfunctional (meth) acrylate-based crosslinking agent. As the preparation method, the monomer may be added after the preparation or may be added at the time of the monomer preparation. The monomer raw material (acrylic acid, the polyfunctional (meth) acrylic crosslinking agent, water , Alkali compounds, etc.) may be contained in advance or added. Among these, since the polymerization inert organic compound is hydrophobic and generally insoluble in water, it is preferably dissolved or contained in advance in acrylic acid or the polyfunctional (meth) acrylate-based crosslinking agent. .

  In addition, about the said polymerization inert organic compound, it describes in international publication WO2006 / 109845, for example.

[Methoxyphenols]
In the present invention, methoxyphenols are preferably used during polymerization, and more preferably in the range of 10 to 300 ppm in the total monomers used for polymerization. When the content of methoxyphenol exceeds 300 ppm by mass in the total monomer used for polymerization, there may be a problem of coloring (yellowing / yellowing) of the resulting water-absorbent resin. In addition, when the content of methoxyphenol is less than 10 ppm by mass, particularly less than 5 ppm by mass in the total monomer used for polymerization, for example, p-methoxyphenol which is a polymerization inhibitor is purified by purification such as distillation. If it is removed, there is a risk that the polymerization may occur before the polymerization is intentionally started, and the polymerization rate may be slow. Methoxyphenols are preferably used by being dissolved in acrylic acid or a polyfunctional (meth) acrylate-based crosslinking agent in order to be uniformly mixed in the monomer aqueous solution.

  Examples of methoxyphenols include o, m, p-methoxyphenol (ortho, meta, para-methoxyphenol), and further one or more substitutions such as a methyl group, a t-butyl group, and a hydroxyl group. And methoxyphenols having a group. P-methoxyphenol is preferable.

  In addition, about the said methoxyphenol, it describes in international publication WO2003 / 51940, for example.

[Minor components of acrylic acid]
In one preferred embodiment of the method for producing a water-absorbent resin of the present invention, the acrylic monomer preferably contains 1 to 1000 ppm by mass of the polymerization-inert organic compound, preferably β- Contains hydroxypropionic acid and / or acrylic acid dimer in a total amount of 1-1000 mass ppm (unneutralized acrylic acid equivalent mass standard / all the same, preferably 1-500 mass ppm, more preferably 1-300 mass ppm) An acrylic acid monomer containing 10 to 200 ppm of methoxyphenol is used. Such an acrylic acid monomer can be obtained by any appropriate method.

  When the total amount of the polymerization inert organic compound and β-hydroxypropionic acid and / or acrylic acid dimer is less than 1 ppm, it becomes difficult to control the polymerization due to excessive temperature rise of the polymer due to heat generation during polymerization, There is a possibility of causing a decrease in absorption physical properties. When there is too much said total amount, there exists a possibility that the residual monomer (residual acrylic acid) of the water-absorbing resin obtained may increase.

  For the acrylic acid monomer used in the present invention, a polymerization inhibitor other than p-methoxyphenol can be used in the production process. Examples include phenothiazine, hydroquinone, copper salt, and methylene blue. Since these polymerization inhibitors, unlike methoxyphenol, inhibit polymerization, the smaller the amount, the better. In the acrylic monomer, preferably 0 to 0.1 mass ppm, more preferably 0 mass ppm (below the detection limit). is there.

  The content of protoanemonin and / or furfural in the acrylic monomer used in the present invention is preferably 0 to 20 ppm by mass. As the content of protoanemonin and / or furfural increases, the polymerization time (time to polymerization peak temperature) may increase and the residual monomer may increase. Further, although the absorption rate slightly increases, the water-soluble component is greatly increased and the physical properties are often relatively lowered. From the viewpoint of improving the physical properties and properties of the water-absorbent resin, the protoanemonin and / or furfural content in the acrylic acid monomer is more preferably 10 mass ppm or less, and still more preferably 0.01 to 5 mass. ppm, more preferably 0.05-2 mass ppm, particularly preferably 0.1-1 mass ppm.

  The content of aldehyde other than furfural and / or maleic acid in the acrylic acid monomer used in the present invention is preferably 0 to 5 ppm by mass, more preferably 0 to 3 ppm by mass, particularly preferably 0 to 1. Mass ppm, most preferably 0 ppm by mass (below the detection limit). Examples of aldehyde components other than furfural include benzaldehyde, acrolein, and acetaldehyde.

  The content of the saturated carboxylic acid composed of acetic acid and / or propionic acid in the acrylic acid monomer used in the present invention is preferably 1000 ppm by mass or less, more preferably 10 to 800 ppm by mass, and particularly preferably 100 to 500 ppm. Mass ppm. Since such saturated carboxylic acid does not polymerize and has volatility, when it exceeds 1000 ppm by mass, there is a problem of odor. However, addition of a small amount is preferable because it imparts safe antibacterial properties to the water absorbent resin.

[Basic substance]
In the present invention, a basic substance may be used. Examples of the basic substance include carbonate (hydrogen) salt, alkali metal hydroxide, ammonia, and organic amine. In order to obtain a water-absorbing resin having higher physical properties, strong alkali substances, that is, hydroxides of alkali metals such as sodium hydroxide, potassium hydroxide, and lithium hydroxide are preferable, and sodium hydroxide is particularly preferable.

Among basic substances that can be used in the present invention, iron (in terms of Fe ₂ O ₃ ) is preferably 0.001 to 10.0 mass ppm, more preferably 0.01 to 5 based on the solid content of the basic substance. It is contained at 0.0 mass ppm, more preferably 0.03 to 4 mass ppm, more preferably 0.05 to 2 mass ppm, and particularly preferably 0.1 to 1 mass ppm. If the iron content is less than 0.001 ppm by mass, there is a risk that the polymerization will occur before the addition of the polymerization initiator, and there is a possibility that the polymerization will be delayed even if the initiator is added. The iron that can be used in the present invention may be Fe ions, but is preferably trivalent iron, particularly preferably Fe ₂ O ₃ . Incidentally, when adding iron, such as Fe ₂ O _3, may be added to the monomers used in the polymerization, it may be added to the basic compound.

  In addition, about the said basic substance, it describes in international publication WO2006 / 109842, for example.

[Others]
Upon polymerization, water-soluble resin or water-absorbing resin is preferably added in an amount of 0 to 50% by weight, more preferably 0 to 20% by weight, based on the monomers used for the polymerization, and various physical properties of the water-absorbing resin obtained. May be improved. Further, various foaming agents (carbonates, azo compounds, bubbles, etc.), surfactants, chelating agents, chain transfer agents, etc. are preferably added in an amount of 0 to 5% by weight, more preferably 0 to 1% by weight. Various physical properties of the obtained water-absorbent resin may be improved.

(2) Polymerization step When polymerizing the monomer component, from the viewpoint of performance and ease of polymerization control, aqueous solution polymerization or reverse phase suspension polymerization is usually performed using the monomer component as a monomer aqueous solution. It is preferable. These polymerizations may be performed in an air atmosphere or in an inert gas atmosphere such as nitrogen or argon (for example, oxygen 1% or less). Preferably, it is carried out in an inert gas atmosphere. The monomer component is preferably used for polymerization after the dissolved oxygen is sufficiently substituted with an inert gas (for example, less than 1 ppm of oxygen). In the present invention, it is particularly suitable for aqueous solution polymerization having high productivity and high physical properties, and particularly preferred aqueous solution polymerization includes continuous belt polymerization, continuous or batch kneader polymerization.

  The polymerization initiation temperature is preferably 40 ° C. or higher, more preferably 50 ° C. or higher, further preferably 60 ° C. or higher, particularly preferably 70 ° C. or higher, most preferably 80 ° C. or higher, in order to improve the absorption rate, and the upper limit is Preferably it is 150 degrees C or less, More preferably, it is 110 degrees C or less, More preferably, it is 100 degrees C or less. By increasing the polymerization start temperature, it is possible to easily remove dissolved oxygen. If the polymerization start temperature is too low, the absorption rate may not be improved, and if the polymerization start temperature is too high, other physical properties such as absorption capacity and soluble content may be lowered. When the polymerization start temperature is less than 40 ° C., not only the productivity is lowered due to the extension of the induction period and the polymerization time, but the physical properties of the resulting water-absorbent resin are also lowered.

  In the present invention, the polymerization step is preferably carried out by reverse phase suspension polymerization or aqueous solution polymerization, particularly preferably aqueous solution polymerization, from the viewpoint of physical properties.

  Reverse-phase suspension polymerization is a polymerization method in which an aqueous monomer solution is suspended in a hydrophobic organic solvent. For example, U.S. Pat. Nos. 4,093,764, 4,367,323, 4,446,261, 4,683,274, and 5,244,735. Are listed. The aqueous solution polymerization is a method of polymerizing an aqueous monomer solution without using a dispersion solvent. For example, U.S. Pat. Nos. 4,462,001, 4,873,299, 4,286,082, 4,973,632, 4,985,518, 5,124,416, No. 5,250,640, No. 5,264,495, No. 5,145,906 and No. 5,380,808, and European Patent Nos. 081636, 09555086, and 0922717. In the present invention, the monomers, crosslinking agents, polymerization initiators, and other additives described in these can be applied. The monomer during polymerization is used in the form of an aqueous monomer solution, and the concentration of the aqueous solution is preferably 10 to 70% by mass, and more preferably 20 to 60% by mass.

  In the present invention, in order to achieve an improvement in absorption characteristics during polymerization, the total time from neutralization and after monomer preparation to the start of polymerization is preferably as short as possible, preferably within 24 hours, more preferably 12 Within hours, more preferably within 3 hours, particularly preferably within 1 hour.

  Industrially, since a large amount of neutralization and preparation of monomer components are performed in a tank, the residence time usually exceeds 24 hours. It has been found that the longer the time after neutralizing the body, the more the residual monomer increases and the coloring occurs. Therefore, in order to shorten the residence time, it is preferable to perform continuous polymerization or continuous polymerization by performing continuous neutralization and continuous monomer component preparation. More preferably, continuous polymerization is performed.

  When polymerizing the monomer aqueous solution, persulfate such as potassium persulfate, ammonium persulfate, sodium persulfate, t-butyl hydroperoxide, hydrogen peroxide, 2,2′-azobis (2-amidinopropane) Only one polymerization initiator such as dihydrochloride, 2-hydroxy-1-phenyl-propan-1-one, or benzoin methyl ether may be used, or two or more polymerization initiators may be used in combination. Furthermore, a reducing agent that promotes the decomposition of the polymerization initiator can be used in combination, and a redox initiator can be obtained by combining the two. Examples of the reducing agent include (bi) sulfite (salt) such as sodium sulfite and sodium hydrogen sulfite, L-ascorbic acid (salt), reducing metal (salt) such as ferrous salt, and amines. . Preferably, it is a redox polymerization initiator with persulfate and / or peroxide. The amount of these polymerization initiators and reducing agents used is preferably 0.001 to 2 mol%, more preferably 0.01 to 0.5 mol%, based on the total monomers used for the polymerization.

  Among the polymerization initiators, hydrogen peroxide and / or sulfite (hydrogen) salt is preferably used, and hydrogen peroxide is more preferably used. This is because the water absorbent resin obtained in the present invention can achieve high absorption characteristics. In addition to these, other polymerization initiators, particularly azo compounds may be used in combination. The amount of hydrogen peroxide and / or sulfite (hydrogen) salt used is preferably 0.00001 to 0.1 g, more preferably 0.0001 to 0.01 g, based on 1 mol of the total monomer used for polymerization. More preferably, the amount is less than the polymerization initiator used in combination. In addition, although an azo compound has an effect for low coloring, use of an excessive persulfate may cause deterioration of physical properties or coloring.

  Instead of using the polymerization initiator, the polymerization reaction may be carried out by irradiating the reaction system with active energy rays such as radiation, electron beam, and ultraviolet rays, or they may be used in combination with the polymerization initiator.

  The reaction temperature and reaction time in the polymerization reaction may be appropriately determined as appropriate depending on the type of the hydrophilic monomer or polymerization initiator, the reaction temperature, and the like. Preferably, below the boiling point and over 0 and within 3 hours, more preferably within 2 hours, even more preferably within 1 hour, particularly preferably within 0.5 hour, preferably at 150 ° C. or less at the peak temperature, More preferably, it is 90-120 degreeC. Moreover, it is preferable to collect the water and acrylic acid monomer (for example, acrylic acid) which evaporate at the time of superposition | polymerization as needed, and to recycle to the manufacturing process of a water absorbing resin.

  The production method of the present invention is suitable for large-scale production of a certain amount or more per line, and particularly suitable for continuous production. The production method of the present invention can be applied to laboratory-level production, production in pilots and small-scale plants, but large-scale production, particularly 1 When the production amount per line is preferably 300 kg / hour or more, more preferably 500 kg / hour or more, and even more preferably 700 kg / hour or more, a water absorbent resin having sufficiently high physical properties can be obtained by applying the present invention. Can be obtained.

(3) Drying step A hydrogel crosslinked polymer is obtained by the polymerization step. The obtained water-containing gel-like cross-linked polymer is further dried after being subdivided using a gel grinder if necessary.

  Any appropriate temperature can be adopted as the drying temperature. In the drying step, it is preferable to perform heating at a temperature equal to or higher than the boiling point of the polymerization inert organic compound. The drying temperature (specified by the heating medium temperature) is preferably 100 to 300 ° C., more preferably 150 to 250 ° C., and the time is preferably 1 minute to 3 hours, more preferably 10 minutes to 1 hour. . By heat-drying at the above temperature and time, the absorption capacity of the resulting water-absorbent resin can be further improved, and residual acrylic acid and residual crosslinking agent can be reduced.

  Any appropriate method can be adopted as the drying method. For example, heat drying, hot air drying, reduced pressure drying, infrared drying, microwave drying, drum dryer drying, dehydration by azeotropy with a hydrophobic organic solvent, and high humidity drying using high-temperature steam can be mentioned. Heat drying is preferable.

  The water-absorbent resin after drying preferably has a resin solid content determined from loss on drying (1 g of powder or particles heated at 180 ° C. for 3 hours), preferably 80% by mass or more, more preferably 85 to 99% by mass, and still more preferably It is 90-98 mass%, Most preferably, it is 92-97 mass%.

  In the production method of the present invention, the load when the hydrated gel-like crosslinked polymer is subdivided (gel pulverization) is low, so that a decrease in absorbent physical properties during subdivision is suppressed. For example, when the hydrogel crosslinked polymer is subdivided by a screw extrusion pulverizer such as a meat chopper, no kneading state is caused. Therefore, damage to the molecular chain of the hydrogel crosslinked polymer due to shearing force is suppressed. Further, since the gel particle diameter control after pulverization becomes easy, the drying process can be easily controlled and the physical properties can be improved.

  In order to reduce the residual acrylic acid, it is preferable that the time from the completion of the polymerization to the start of drying through a gel pulverization step is shorter as necessary. That is, drying of the hydrogel crosslinked polymer after polymerization is preferably started (introduced into a dryer) within 1 hour, more preferably within 0.5 hour, and even more preferably within 0.1 hour. Moreover, in order to achieve reduction of a residual monomer and low coloring, the temperature of the water-containing gel-like crosslinked polymer from polymerization to the start of drying is preferably controlled to 50 to 80 ° C, more preferably 60 to 70 ° C. In industrial scenes, a large amount of polymerization is carried out, so that the residence time after polymerization usually exceeds 3 hours. However, the longer the time until the start of drying, or the more the temperature deviates from the above temperature, In addition to the increase, coloring becomes significant. Therefore, the residence time is preferably shortened by continuous polymerization and continuous drying.

(4) Surface cross-linking step Next, the surface cross-linking step in the present invention will be described. In the present invention, it is preferable that after drying, pulverization, classification, and granulation are performed as necessary, and the surface cross-linking step is performed under specific temperature conditions. The water-absorbent resin obtained by the production method of the present invention has high physical properties after drying, and the physical properties are further improved through a surface crosslinking step.

  The surface cross-linking of the water-absorbing resin is to provide a portion having a high cross-linking density in the surface layer of the water-absorbing resin (near the surface: usually near several tens of μm or less from the surface in thickness). Since the water-absorbent resin obtained by the production method of the present invention has a low water-soluble content and a high absorption capacity, an excellent surface cross-linking effect is obtained, and even higher physical properties and characteristics are exhibited. AAP) and liquid permeability efficiency under pressure (PPUP) are increased, and odor is also reduced.

  Any appropriate surface crosslinking agent can be adopted as the crosslinking agent for performing the surface crosslinking. From the viewpoint of physical properties, a crosslinking agent capable of reacting with a carboxyl group, generally a polyhydric alcohol compound, an epoxy compound, a polyvalent amine compound or a condensate thereof with a haloepoxy compound, an oxazoline compound, a mono-, di-, or polyoxazolidinone Examples thereof include compounds, polyvalent metal salts, and alkylene carbonate compounds.

  As the surface cross-linking agent, specifically, the surface cross-linking agents described in US Pat. Nos. 6,228,930, 6071976, and 6254990 can be employed. For example, mono, di, tri, tetra or polyethylene glycol, monopropylene glycol, 1,3-propanediol, dipropylene glycol, 2,3,4-trimethyl-1,3-pentanediol, polypropylene glycol, glycerin, polyglycerin , 2-butene-1,4-diol, 1,4-butanediol, 1,3-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,2-cyclohexanedimethanol, etc. Alcohol compounds; epoxy compounds such as ethylene glycol diglycidyl ether and glycidol; ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, polyethyleneimine, polyamide polyamine, etc. Haloepoxy compounds such as epichlorohydrin, epibromhydrin, α-methylepichlorohydrin; condensates of the polyvalent amine compounds and haloepoxy compounds; oxazolidinone compounds such as 2-oxazolidinone; ethylene carbo And alkylene carbonate compounds such as nates. In order to maximize the effect of the present invention, it is preferable to use at least a polyhydric alcohol among these crosslinking agents. More preferably, a polyhydric alcohol having 2 to 10 carbon atoms is used, and more preferably a polyhydric alcohol having 3 to 8 carbon atoms.

  0.001 mass part-10 mass parts are preferable with respect to solid content of 100 mass parts of resin, and, as for the usage-amount of a surface crosslinking agent, 0.01 mass part-5 mass parts are more preferable.

  It is preferable to use water for surface crosslinking. The amount of water used is preferably 0.5 to 20 parts by mass, more preferably 0.5 to 10 parts by mass with respect to 100 parts by mass of the water absorbent resin, although it depends on the water content of the water absorbent resin to be used. is there. In addition to water, a hydrophilic organic solvent may be used. The amount of the hydrophilic organic solvent to be used is preferably 0 to 10 parts by mass, more preferably 0 to 5 parts by mass, and still more preferably 0 to 3 parts by mass with respect to 100 parts by mass of the water absorbent resin. The temperature of the crosslinking agent solution is preferably 0 ° C. to boiling point, more preferably 5 to 50 ° C., and still more preferably 10 to 30 ° C. from the viewpoint of mixing properties and stability. The temperature of the water absorbent resin powder before mixing is preferably 0 to 80 ° C., more preferably 40 to 70 ° C., from the viewpoint of mixing properties.

  In the surface cross-linking step, a method in which water and / or a hydrophilic organic solvent and a surface cross-linking agent are mixed in advance, if necessary, and then the aqueous solution is sprayed or dropped onto the water-absorbent resin is preferable, and the spraying method is more preferable. The average size of the sprayed droplets is preferably 1 to 300 μm, more preferably 10 to 200 μm. In mixing, the water-insoluble fine particle powder and the surfactant may be allowed to coexist in an amount of preferably 0 to 10% by mass or less, more preferably 0 to 5% by mass, and still more preferably 0 to 1% by mass. The description of WO2005 / 077500 can be used for the surfactant used in the surface crosslinking step and the amount of the surfactant used, for example.

  The water-absorbing resin after mixing the surface cross-linking agent is preferably heat-treated. The heating temperature (specified by the heating medium temperature) is preferably a heating temperature equal to or higher than the boiling point of the polymerization inert organic compound. Specifically, it is preferably 120 to 250 ° C., more preferably 150 to 250 ° C., and the heating time is preferably 1 minute to 2 hours. The heat treatment can be performed using a normal dryer or a heating furnace. Examples of the dryer include a groove type mixed dryer, a rotary dryer, a disk dryer, a fluidized bed dryer, an airflow dryer, and an infrared dryer. You may cool the water-absorbing resin after a heating as needed.

  Surface crosslinking methods include European Patent Nos. 0349240, 0605150, 0450923, 0812873, 0450924, 0668080, Japanese Patent Application Laid-Open Nos. 7-242709 and 7-224304, and US Pat. No. 5,409,771. No. 5,597,873, No. 5,385,983, No. 5,610,220, No. 5,633,316, No. 5,674,633, No. 5,462,972, and International Publications WO99 / 42494, WO99 / 43720, and WO99 / 42496 may be incorporated. .

(5) Physical properties and shape of water-absorbent resin [shape]
Arbitrary appropriate shapes can be employ | adopted for the shape of the water absorbing resin obtained by the manufacturing method of this invention. For example, it may be in the form of particles such as irregularly crushed or spherical or powder, gel, sheet, rod, fiber, or film, and may be composited or supported on a fiber substrate. . Usually, when the absorbent article and horticultural greening which are the uses are considered, a particulate form or a powder form is preferable. When the water absorbent resin is in the form of particles or powder, it may be granulated particles or primary particles.

  When the water-absorbent resin is in the form of particles or powder, the mass average particle diameter is preferably 10 to 2000 μm, more preferably 100 to 1000 μm, still more preferably 200 to 600 μm, particularly preferably after surface crosslinking or after surface crosslinking. Is 300-500 μm. Moreover, the ratio of the particle diameter of 850-150 micrometers is preferably 90-100 mass%, More preferably, it is 95-100 mass%, Most preferably, it is 98-100 mass%. When these mass average particle diameters deviate, there is a possibility that the effect particularly when used as an absorbent article such as a disposable diaper is reduced.

[Powder characteristics]
The water-absorbent resin obtained by the production method of the present invention provides good powder characteristics (powder friction characteristics) and powder flowability during moisture absorption without causing a decrease in surface tension even when dispersed in water. Can do.

  The water-absorbent resin obtained by the production method of the present invention has a maximum insertion load (PIL) described later in Examples of powder characteristics, particularly powder friction characteristics, preferably 0 to 5000 g weight, more preferably 0 to 3000 g. Weight, more preferably 10 to 2000 g weight, particularly preferably 20 to 1000 g weight. When the weight exceeds 5000 g, the powder conveyance characteristics are remarkably deteriorated. For example, when an absorbent article such as a diaper is produced using a water absorbent resin, the absorbent physical properties may be lowered. Moreover, when the maximum insertion load (PIL) is too low, there is a possibility that the water-absorbent resin is easily dropped from the hydrophilic fiber when the absorbent body in the diaper is mixed with the hydrophilic fiber such as pulp.

  The surface tension of the water absorbent resin obtained by the production method of the present invention does not substantially decrease. Specifically, the surface tension of the water absorbent resin dispersion obtained by dispersing 0.5 g of the water absorbent resin in 50 ml of physiological saline at 20 ° C. is preferably 55 mN / m or more, more preferably 60 mN / m or more, It is preferably 65 mN / m or more, particularly preferably 68 mN / m or more, and most preferably 70 mN / m or more. The upper limit of the surface tension of the water absorbent resin dispersion is preferably 85 mN / m, more preferably 80 mN / m, and still more preferably 78 mN / m. If the surface tension is lower than 55 mN / m, the liquid diffusibility may be lowered when a water-absorbing resin is used for sanitary materials such as diapers.

[Absorption capacity and soluble content]
Since the water-absorbent resin obtained by the production method of the present invention has an improved relationship between “absorption capacity” and “amount of water-soluble polymer”, which are opposite basic properties of the water-absorbent resin, it has higher physical properties by surface crosslinking. It becomes.

  The above water-absorbent resin has an absorption capacity (GVs) under no pressure, preferably 3 g / g or more, more preferably 5 to 200 g / g, and still more preferably 20 to 100 g / g. The water insolubility is such that the water-soluble content in the resin is preferably 0 to 50% by mass, more preferably 0 to 25% by mass, still more preferably 0 to 15% by mass, and particularly preferably 0 to 10% by mass. It is essentially water-insoluble. Furthermore, the GEX value (specified in the examples) defined by the relationship between the absorption capacity (GVs) and the soluble component is preferably 17 or more, more preferably 18 or more, and particularly preferably 19 or more.

[Other physical properties]
The water-absorbent resin obtained by the production method of the present invention has an absorbency against pressure of physiological saline (4.8 kPa), preferably 15 g / g or more, more preferably 20 g / g or more, and even more preferably 23 g / g or more. Especially preferably, it is 25 g / g or more.

  The water-absorbent resin obtained by the production method of the present invention has an absorption capacity under load (1.9 kPa) with respect to physiological saline, preferably 15 g / g or more, more preferably 20 g / g or more, and even more preferably 25 g / g or more. Particularly preferably, it is 28 g / g or more, and most preferably 32 g / g or more.

  The water-absorbing resin obtained by the production method of the present invention has a water absorption capacity (GVs) under no pressure, preferably 25 g / g or more, more preferably 28 g / g or more, and further preferably 32 g / g or more.

  The upper limit of the absorption capacity under pressure or the absorption capacity without pressure is preferably 60 g / g from the viewpoint of balance with other physical properties and cost.

  The water-absorbent resin obtained by the production method of the present invention has a liquid permeability efficiency under pressure (PPUP) of preferably 20 to 100%, more preferably 30 to 100%, still more preferably 40 to 100%, most preferably 50 to 100%.

  Liquid passing efficiency under pressure (PPUP) is different from the absorption capacity under pressure (AAP), when the water-absorbing resin amount (resin amount per unit area of measurement) is increased from 0.90 g to 5.0 g. It is an index of stability (no decrease) in absorption capacity under pressure (AAP). For example, in diapers, the amount of water-absorbing resin (the amount of resin per unit area of measurement) is partially different, and the change in the absorption capacity under pressure (AAP) due to the change in the amount of resin is the physical property of diapers during actual use. Is the cause of the decline. When the liquid passing efficiency under pressure (PPUP) is very high, any water-absorbing resin amount (concentration) in any diaper stably exhibits high physical properties, indicating high liquid permeability. The liquid passing efficiency under pressure (PPUP) is described in detail in Japanese Patent Application No. 2005-109779 (filed on Apr. 6, 2005), and such description is incorporated herein.

The water-absorbent resin obtained by the production method of the present invention has a liquid permeability of SFC (described in US Patent Publication No. 2004/254553), preferably 1 × 10 ⁻⁷ (cm ³ × sec / g) or more, More preferably, it is 10 × 10 ⁻⁷ (cm ³ × sec / g) or more, and further preferably 50 × 10 ⁻⁷ (cm ³ × sec / g) or more.

  Since the production method of the present invention is excellent in polymerizability, the residual monomer in the obtained water-absorbent resin is small, and the residual monomer amount is preferably 0 to 400 ppm or less, more preferably 0 to 300 ppm or less. Moreover, there are few residual internal crosslinking agents in the water-absorbing resin obtained, and the amount of residual internal crosslinking agents is preferably substantially ND (preferably 1 ppm or less, more preferably 0.1 ppm or less).

[Other additives]
In order to impart various functions to the water-absorbent resin obtained by the production method of the present invention, a chelating agent, an oxidizing agent, a reducing agent such as a sulfurous acid (hydrogen) salt, a chelating agent such as an aminocarboxylic acid, a water-insoluble inorganic or A polyvalent metal salt such as an organic powder, a deodorant, an antibacterial agent, a polymer polyamine, or an aluminum salt is preferably added in an amount of 0 to 10% by mass, more preferably 0 to 1% by mass.

  Multivalent metals and inorganic powders are exemplified in WO 2004/069915, for example. Chelating agents and deodorants are exemplified in US Pat. Nos. 6,599,989 and 6,469,080, for example.

(11) Use According to the production method of the present invention, a water-absorbing resin having good absorption characteristics excellent in the absorption capacity under no pressure (GVs), the absorption capacity under pressure (AAP), and the balance of soluble components. It can be easily manufactured. Such water-absorbing resins are widely used in agriculture, horticulture, rooftop greening and desert greening water retention agents, soil modifiers, industrial water retention agents, waste liquid solidifying agents, hygroscopic agents, dehumidifying agents, building materials, etc. It is particularly preferably used for sanitary materials such as incontinence pads, breast milk pads, sanitary napkins.

  Since the water-absorbent resin obtained by the production method of the present invention has excellent physical properties in a well-balanced manner, the hygienic material has a high concentration of the water-absorbent resin (mass ratio of the water-absorbent resin to the total of the water-absorbent resin and the fiber substrate) (For example, a paper diaper) It can use suitably, Specifically, the density | concentration of water absorbing resin becomes like this. Preferably it is 30-100 mass%, More preferably, it is 40-100 mass%, More preferably, it is 50-95 mass%. .

  Hereinafter, the present invention will be described in accordance with examples, but the present invention is not limited to the examples. Various physical properties described in the present specification were determined according to the following measuring methods. In addition, unless otherwise specified, the electrical equipment used in the examples was used at 200V or 100V. Furthermore, unless otherwise specified, the water-absorbent resin was used under the conditions of 25 ± 2 ° C. and relative humidity 50% RH. The reagents and instruments exemplified in the following measurement methods and examples may be appropriately replaced with equivalent products.

<Absorption capacity under no pressure (GVs / Gel Volume in Saline)>
0.2 g of water-absorbent resin was uniformly put in a non-woven bag (60 mm × 60 mm) for sealing, and immersed in 100 g of a 0.90 mass% sodium chloride aqueous solution. After 60 minutes, the bag was pulled up, drained at 250 G for 3 minutes using a centrifuge, and then the mass W1 of the nonwoven fabric bag was measured. The same operation was carried out without using a water-absorbent resin, the mass W2 at that time was obtained, and the absorption capacity (GVs) under no pressure was calculated by the equation (1).
Formula (1): GVs = (W1-W2) /0.2-1

<Water-soluble polymer amount (sometimes referred to as soluble content or soluble content)>
Weigh out 184.3 g of 0.90% by weight sodium chloride aqueous solution in a plastic container with a lid of 250 ml capacity, add 1.00 g of water-absorbing resin to the aqueous solution, and stir for 16 hours. Extracted. 50.0 g of the filtrate obtained by filtering this extract using one filter paper (ADVANTEC Toyo Co., Ltd., product name: (JIS P 3801, No. 2), thickness 0.26 mm, reserved particle diameter 5 μm) Was measured and used as a measurement solution.

First, the physiological saline alone is titrated to pH 10 with a 0.1N aqueous NaOH solution, and then titrated to a pH 2.7 with a 0.1N aqueous HCl solution (blank titration [[bNaOH] ml, [bHCl] ml). The titration ([NaOH] ml, [HCl] ml) was determined by performing the same titration operation on the measurement solution. For example, in the case of a water-absorbing resin composed of a known amount of acrylic acid and its sodium salt, based on the average molecular weight of the monomer and the titration amount obtained by the above operation, the soluble content in the water-absorbing resin (extracted A water-soluble polymer is a main component) is calculated by the formula (2). In the case of an unknown amount, the average molecular weight of the monomer is calculated using the neutralization rate obtained by titration (formula (3)).
Formula (2):
Soluble content (% by weight) = 0.1 × (average molecular weight) × 184.3 × 100 × ([HCl] − [bHCl]) / 1000 / 1.0 / 50.0
Formula (3):
Neutralization rate (mol%) = (1 − ([NaOH] − [bNaOH]) / ([HCl] − [bHCl])) × 100

<GEX value>
Usually, the higher the absorption ratio (GVs), the more the water-soluble content tends to increase. In the case of a water-absorbent resin, the relationship between the contradictory GVs value and the water-soluble content (x) is important. When x exceeded 1% by mass, the GEX value was evaluated as an index of the relationship. The higher the GEX value, the higher the performance. When the GVs value is represented by y (g / g) and the soluble content is represented by x (mass%), the GEX value was defined by the formula (4).
Formula (4): GEX value = (y) / ln (x)

  In addition, about the GVs value y (g / g) and soluble content x (mass%) required in order to calculate a GEX value, the value measured above is used.

<Residual monomer>
The residual monomer (acrylic acid and its salt) of the water-absorbent resin powder after drying was measured by measuring 184.3 g of a 0.90% by mass sodium chloride aqueous solution in a 250-ml plastic container with a lid, and the water-absorbent resin was put in the aqueous solution. 1.00 g was added, and the filtrate obtained by stirring and filtering for 2 hours was analyzed by UV analysis using liquid chromatography. The residual monomer in the hydrogel before drying was agitated for 16 hours after the finely divided hydrogel containing about 500 mg of resin solid content, and the filtrate was similarly subjected to UV analysis by liquid chromatography to correct the solid content. I asked for it.

<Absorbency Against Pressure (AAP) (Absorption Under Pressure under Pressure of 4.8 kPa with respect to 0.90% by Mass Sodium Chloride Aqueous Solution)>
A water-absorbing resin (or particulate water-absorbing agent) 0 is placed on a metal mesh at the bottom of a plastic support cylinder having an inner diameter of 60 mm in which a 400-mesh stainless steel mesh (mesh size 38 μm) is welded to one side (bottom) of a cylindrical section. .900 g is uniformly dispersed, and a piston (cover plate) on which the outer diameter is slightly smaller than 60 mm is not formed on the wall surface with the support cylinder and the vertical movement is not hindered. The mass W3 (g) of the water absorbent resin and the piston was measured. On this piston, a load adjusted so that a load of 4.9 kPa including the piston can be uniformly applied to the water-absorbing resin was placed, and a complete measuring apparatus was completed. A glass filter having a diameter of 90 mm and a thickness of 5 mm was placed inside a petri dish having a diameter of 150 mm, and physiological saline adjusted to 25 ± 2 ° C. was added so as to be at the same level as the upper surface of the glass filter. On top of that, a sheet of 9 cm diameter filter paper (Toyo Filter Paper Co., Ltd., No. 2) was placed so that the entire surface was wetted, and excess liquid was removed.

The set of measuring devices was placed on the wet filter paper, and the liquid was absorbed under load. When the liquid level dropped from the top of the glass filter, the liquid was added to keep the liquid level constant. One hour later, the set of measuring devices was lifted, and the weight W4 (g) (the weight of the supporting cylinder, the swollen water-absorbing resin and the piston) after removing the load was measured again. And from these masses W3 and W4, the absorption capacity under pressure (g / g) was calculated according to the following formula.
Absorption capacity under pressure (AAP: 0.90 g) (g / g) = (mass W4 (g) −mass W3 (g)) / mass of water absorbent resin (or particulate water absorbing agent) (g)

  The absorption capacity under pressure at the load of 4.9 kPa (water absorbent resin 0.90 g) is referred to as AAP 4.9 kPa, and when the load is changed to 1.9 kPa, it is referred to as AAP 1.9 kPa.

<Liquid flow efficiency under pressure (PPUP: Permeability Potential Under Pressure)>
In the measurement of the absorption capacity under pressure at 4.9 kPa (AAP: 0.90 g), the same operation was performed except that the amount of the water absorbent resin was changed from 0.900 g to 5.000 g, and the absorption capacity under pressure was The value of (AAP: 5.0 g) was determined. At this time, if the absorption capacity under pressure (AAP: 5.0 g) is high, the height of the swollen water-absorbent resin layer may become very high, so the height of the support cylinder to be used is sufficiently large. It is necessary to have. By using the absorption capacity under pressure (AAP: 0.90 g) and (AAP: 5.0 g) obtained by the above operation, the liquid passing efficiency (PPUP) under pressure was calculated by the following formula.
Liquid passing efficiency under pressure (PPUP) (%) = (AAP: 5.0 g (g / g) / AAP: 0.90 g (g / g)) × 100

<Peak time and induction time>
Measure the temperature of the monomer or polymer gel during polymerization with a thermometer, the time (min) from the initiator addition to the temperature rise is the induction time, and the time to the maximum temperature (peak temperature) of the polymerization system Peak time was taken.

<Mass average particle diameter (D50)>
The water-absorbent resin powder is sieved with a JIS standard sieve (JIS Z8801-1 (2000) or equivalent) such as 850 μm, 710 μm, 600 μm, 500 μm, 425 μm, 300 μm, 212 μm, 150 μm, 106 μm, 75 μm, and the residual percentage is determined. Plotted on log probability paper. Thereby, the mass average particle diameter (D50) was read. For sieving, 10 g of water-absorbent resin powder was charged into the above JIS standard sieve (The IIDA TESTING SIEVE: inner diameter 80 mm) under the conditions of room temperature (20 to 25 ° C.) and relative humidity 50 ± 5% RH, and a low-tap sieve shaker ( Classification was carried out for 10 minutes using an ES-65 type sieve shaker manufactured by Iida Seisakusho. Further, a logarithmic standard deviation value (σζ) was calculated in accordance with column 10 (1) of US Pat. No. 5,026,800. The mass average particle diameter (D50) is a particle diameter of a standard sieve corresponding to 50% by mass of the whole particle with a standard sieve having a constant aperture, as described in US Pat. No. 5,026,800.

<High performance liquid chromatography analysis and distribution index>
The distribution index of the polyfunctional (meth) acrylate crosslinking agent having a polyethylene glycol structural unit was measured by high performance liquid chromatography. First, polyfunctional (meth) acrylate crosslinkers having polyethylene glycol structural units with different ethylene oxide repeat units (ethylene oxide addition number) are separated, and the area ratio (area%) of each fraction with different ethylene oxide addition numbers is detected. did. Next, the distribution index was defined as the sum of the area ratio of the number of ethylene oxide additions corresponding to the fraction with the largest area ratio and the area ratio (area%) of the addition number ± 2 fractions corresponding to the largest fraction.

  For example, when the maximum area ratio of the fractions separated by high performance liquid chromatography corresponds to the number of ethylene oxide additions 10, the sum of the area ratios of the fractions corresponding to the numbers of ethylene oxide additions 8, 9, 10, 11, 12 Calculated as distribution index.

  When separating and detecting the above polyfunctional acrylates with different ethylene oxide addition numbers by high-performance liquid chromatography in each fraction, a mixed solution of 1/1 ion-exchanged water and methanol was used as the eluent, and an analyzer (Shimadzu Corporation) was used. 5 μL of sample solution is passed through a column (GL Science's Inertsil / ODS-2) at a flow rate of 0.8 ml / min and kept at 35 ± 0.1 ° C. in UV (wavelength 254 nm). It was detected at. The other conditions were appropriately selected.

  In addition, it analyzed by performing the same operation also about the distribution index of the mono (meth) acrylate compound which has a polyethyleneglycol structural unit.

<Quantification of p (para) -methoxyphenol>
UV analysis was performed using liquid chromatography.

<Protoanemonin amount, furfural amount>
Using a gas chromatograph (manufactured by Shimadzu Corporation, GC-7A type) and a data processing device (manufactured by Shimadzu Corporation, C-R6A type), quantification was performed using a standard sample under the following conditions. analyzed.
Detector: FID
Hydrogen amount: 30 m / min
Air volume: 0.5L / min
Column: Hard glass tube with an inner diameter of 3 mm and a length of 3.1 m Filler: Chromosorb W column temperature chamber temperature: 100 ° C.
Sample introduction part temperature: 150 ° C
Carrier gas flow rate: nitrogen 40mL / min

<Powder characteristic evaluation>
In order to evaluate the powder fluidity of the water-absorbent resin, the maximum insertion load (PIL) was measured in accordance with US Patent Publication No. 2005/0118423, page 17 [0210]. For measurement, a sample obtained by separating particles passing through a JIS standard sieve mesh with a mesh size of 600 μm and remaining on a mesh mesh with a mesh size of 300 μm was used. For PIL measurement, the starting point range was 0 mm to 10 mm (insertion distance). The maximum insertion load within the range of the insertion distance of 0 to 10 mm was measured according to the description except that the measurement was performed at 0 to 10 mm.

<Saline Flow Conductivity (SFC)>
This was performed in accordance with US Patent Publication No. 2004/254553.

<Surface tension>
A well-washed 100 ml beaker was charged with 50 ml of physiological saline adjusted to 20 ° C., and the surface tension of the physiological saline was first measured using a surface tension meter (K11 automatic surface tension meter, KRUSS). . In this measurement, the surface tension value must be in the range of 71 to 75 mN / m. Next, a well-washed 25 mm long fluororesin rotor and 0.5 g of a water-absorbing agent were put into a beaker containing physiological saline after measuring the surface tension adjusted to 20 ° C., under the condition of 500 rpm. Stir for 4 minutes. After 4 minutes, the stirring was stopped and the water-absorbing water-containing agent settled, and then the surface tension of the supernatant was measured again by the same operation. In the present invention, a plate method using a platinum plate was adopted, and the plate was thoroughly washed before each measurement and heated and washed with a burner.

<Transmissivity>
A mono (meth) acrylate compound having a polyethylene glycol structural unit and a polyfunctional (meth) acrylate crosslinking agent having a polyethylene glycol structural unit are dissolved in ion-exchanged water filtered through a cellulose acetate filter having a pore diameter of about 2 mm, and 20 mass % Aqueous solution. The light transmittance (%) of light at 500 nm at 25 ± 1 ° C. was measured for the adjusted aqueous solution using a light meter (U-2010 SPECTROTOPOMETER, manufactured by Hitachi, Ltd.) with the ion-exchanged water as 100% blank.

<Absorber performance evaluation: Evaluation of return amount>
In order to evaluate the performance of the obtained water-absorbent resin as an absorber, an absorber was prepared and the return amount was evaluated.

(How to make an absorber for evaluation)
2 parts by mass of water absorbent resin powder and 2 parts by mass of pulverized wood pulp were dry mixed using a mixer. The obtained mixture was spread on a wire screen formed in 400 mesh (eye size = 38 μm) and molded into a web having a diameter of 90 mmφ. This web was pressed at a pressure of 196.14 kPa (2 kgf / cm ² ) for 1 minute to obtain an evaluation absorbent having a basis weight of about 0.06 g / cm ² .

(Return amount evaluation method)
An absorber for evaluation was placed on the bottom of a SUS petri dish having an inner diameter of 90 mmφ, and a non-woven fabric having a diameter of 90 mmφ was laid thereon. Next, a piston and a weight adjusted so that a load of 4.8 kPa was applied evenly to the absorber were placed. The piston and the weight used were equipped with a liquid inlet having a diameter of 5 mm at the center. Next, 25 ml of physiological saline (0.90 mass% sodium chloride aqueous solution) was poured into the central part of the above-described evaluation absorber to absorb the solution. After 30 minutes, 25 ml of physiological saline (0.90 mass% sodium chloride aqueous solution) was further poured into the center of the above-described evaluation absorber, and the solution was further absorbed for 30 minutes. After 30 minutes, the piston and the weight were removed, and 30 sheets of filter paper (No. 2 made by Toyo Filter Paper Co., Ltd.) having an outer diameter of 90 mmφ whose total weight (W5 (g)) was measured in advance on the absorber for evaluation. Further, a piston and a weight (total mass: 20 kg) were quickly placed on the filter paper so that the absorbent body, the nonwoven fabric, and the filter paper were uniformly loaded with an outer diameter of 90 mmφ. A load was applied for 5 minutes to absorb the liquid returned to the filter paper. Then, the mass (W6 (g)) of 30 filter papers was measured. The return amount was measured from the following formula.
Return amount (g) = W6 (g) -W5 (g)

[Production Example 1]
Supplying commercially available acrylic acid obtained by vapor phase catalytic oxidation (Wako Pure Chemical Industries, reagent special grade: containing 200 ppm of p-methoxyphenol) to the bottom of a high-boiling-point impurity separation tower having 50 plates of non-weired perforated plates, Acrylic acid composition (1) consisting of 99% or more of acrylic acid and a small amount of impurities (mainly water) by distilling with toluene as the azeotropic solvent at a reflux ratio of 1 and further re-distilling (also known as purification) Acrylic acid) was obtained.

  The amount of p-methoxyphenol in the acrylic acid composition (1) is ND (less than 1 mass ppm), the amount of protoanemonin (protoanemonin), the amount of furfural, the amount of β-hydroxypropionic acid, the amount of acrylic acid dimer is ND (1 mass). less than ppm) and the amount of toluene was 1 ppm by mass. The amount of phenothiazine in the acrylic acid composition (1) was 0 ppm, the amount of aldehyde and the amount of maleic acid were 1 ppm or less, the amount of acetic acid and the amount of propionic acid were 200 ppm.

  Furthermore, acrylic acid composition (2) was obtained by adding 90 ppm of p-methoxyphenol to acrylic acid composition (1) (vs. solid content of acrylic acid).

[Production Example 2]
Into a 5 L 5-neck flask equipped with two dropping funnels, a pH meter, a thermometer and a stirring blade, 1598 g of ion-exchanged water was charged. Separately, 1280 g of acrylic acid composition (2) consisting of substantially acrylic acid at room temperature and 1488 g of 48 mass% sodium hydroxide (Fe 0.5 mass ppm / Fe ₂ O ₃ equivalent) aqueous solution at room temperature were each added to two dropping funnels. The 5 L flask was immersed in a water-cooled bath. Next, while maintaining the neutralization reaction system in the 5 L flask at 35 ° C. or lower and stirring, a 48 mass% sodium hydroxide aqueous solution and the acrylic acid composition (2) were simultaneously dropped into the flask. The dropping of the acrylic acid composition (2) was completed in about 35 minutes, and the dropping of the 48 mass% sodium hydroxide aqueous solution was completed in about 45 minutes. After completion of the dropwise addition of the acrylic acid composition (2), the dropping funnel was washed with 100 g of ion exchange water, and all the washing water was put in the flask. Further, after the completion of the dropwise addition of the 48 mass% sodium hydroxide aqueous solution, the dropping funnel was similarly washed with 100 g of ion-exchanged water, and all the washing water was put in the flask.

  After completion of all the dropwise additions, the temperature is adjusted to 20 to 35 ° C. and ripened for 20 minutes. After ripening, a very small amount of acrylic acid composition (2) is dropped to adjust the pH to 10 (± 0.1). Thus, a sodium acrylate aqueous solution (1) having a concentration of 37% by mass and a neutralization rate of 100 mol% was obtained.

[Production Example 3]
Commercially available polyethylene glycol and toluene were charged into a 5 L flask, and a catalyst was added and stirred. Subsequently, a dehydration reaction was performed while sequentially dropping acrylic acid while heating. After completion of the reaction, the reaction solution was washed with excess saturated aqueous sodium sulfate solution, and the saturated aqueous sodium sulfate solution was removed by decantation. After repeating this operation 10 times, 500 mass ppm was added to the polyethylene glycol charged with p-methoxyphenol, and toluene was removed by nitrogen bubbling to obtain polyethylene glycol diacrylate (1). The obtained polyethylene glycol diacrylate (1) had an average ethylene oxide repeating unit number of 8, a distribution index of 72.9, and a transmittance of 99%.

[Production Example 4]
To 90 parts by mass of the polyethylene glycol diacrylate (1) obtained in Production Example 3, 10 parts by mass of polyethylene glycol monoacrylate (average number of ethylene oxide repeating units 9) is mixed to obtain a crosslinking agent composition (1). It was. The transmittance of the crosslinking agent composition (1) was 98%.

[Production Example 5]
2 parts by mass of polyethylene glycol monoacrylate (average number of ethylene oxide repeating units 9) is mixed with 98 parts by mass of the polyethylene glycol diacrylate (1) obtained in Production Example 3 to obtain a crosslinking agent composition (2). It was. The transmittance of the crosslinking agent composition (2) was 98%.

[Production Example 6]
To 99.5 parts by mass of the polyethylene glycol diacrylate (1) obtained in Production Example 3, 0.5 part by mass of polyethylene glycol monoacrylate (average number of ethylene oxide repeating units: 10) is mixed to obtain a crosslinking agent composition ( 3) was obtained. The transmittance of the crosslinking agent composition (3) was 99%.

[Example 1]
As a polymerization vessel, a polypropylene cylindrical container with a 1 L capacity lid was prepared.

  23.0 g of the acrylic acid composition (2) obtained in Production Example 1, 244.0 g of the sodium acrylate aqueous solution (1) obtained in Production Example 2, 95.2 g of ion-exchanged water, and Production Example 4 as an internal crosslinking agent By mixing 0.1 mol% (vs. the total monomers) of the obtained crosslinking agent composition (1) with an aqueous solution, a monomer aqueous solution having a monomer aqueous solution concentration of 33% by mass and a neutralization rate of 75 mol% (1) was obtained.

  Furthermore, the monomer aqueous solution (1) was kept at 25 ° C., charged into the cylindrical container, and nitrogen gas was blown to replace the system with 1 ppm or less of dissolved oxygen. Next, the cylindrical container is kept in an adiabatic state, and sodium persulfate (0.12 g / mol) and L-ascorbic acid (0.001 g / mol) are added to the monomer aqueous solution (1) as a polymerization initiator in an aqueous solution. Then, static polymerization was started. The induction time was 30 seconds, the peak time was 27 minutes, and the peak temperature was 95 ° C. Polymerization was further performed for 30 minutes after reaching the peak temperature to obtain a cylindrical hydrogel crosslinked polymer (1).

  The obtained hydrogel crosslinked polymer (1) was cooled to room temperature and then cut into about 20 mm to 40 mm squares with scissors. (Diameter: 6.2 mm), the gel was pulverized and subdivided to obtain a hydrogel crosslinked polymer (2).

  The hydrogel crosslinked polymer (2) after pulverization had a weak adhesive force, hardly aggregated, and was difficult to adhere to a desktop extruder. The obtained hydrogel crosslinked polymer (2) was spread on a 850 μm wire net and dried with hot air at 180 ° C. and a dew point of 70 ° C. for 90 minutes. Next, the dried product was pulverized with a vibration mill and further classified using a JIS 850 μm standard sieve to obtain a water absorbent resin powder (1) as a passing product.

  Various physical properties of the obtained water absorbent resin powder (1) were measured. The results are shown in Table 1.

[Example 2]
In Example 1, it carried out similarly to Example 1 except having replaced the crosslinking agent composition (1) with the crosslinking agent composition (2) obtained by manufacture example 5, and obtained the water absorbing resin powder (2).

  Various physical properties of the obtained water absorbent resin powder (2) were measured. The results are shown in Table 1.

Example 3
In Example 1, except having replaced the crosslinking agent composition (1) with the crosslinking agent composition (3) obtained in manufacture example 6, it carried out similarly to Example 1 and obtained the water absorbing resin powder (3).

  Various physical properties of the obtained water absorbent resin powder (3) were measured. The results are shown in Table 1.

[Comparative Example 1]
A cylindrical comparative hydrogel crosslinked polymer was carried out in the same manner as in Example 1 except that the crosslinking agent composition (1) was replaced with the polyethylene glycol diacrylate (1) obtained in Production Example 3 in Example 1. (1) was obtained. In the polymerization, the induction time was 35 seconds, the peak time was 31 minutes, and the peak temperature was 93 ° C. The comparative hydrogel crosslinked polymer (1) was cut into about 20 mm to 40 mm squares with scissors in the same manner as in Example 1, and the gel was pulverized and subdivided with a desktop extruder, and the comparative hydrogel crosslinked polymer ( 2) was obtained. Subsequently, the comparative hydrogel polymer was spread on a 850 μm wire net and dried with hot air at 180 ° C. and a dew point of 70 ° C. for 90 minutes. Next, the dried product was pulverized using a vibration mill and further classified using a JIS 850 μm standard sieve to obtain a comparative water absorbent resin powder (1) as a passing product.

  Various physical properties of the obtained comparative water absorbent resin powder (1) were measured. The results are shown in Table 1.

[Comparative Example 2]
23.0 g of the acrylic acid composition (2) obtained in Production Example 1, 244.0 g of the aqueous sodium acrylate solution (1) obtained in Production Example 2, 95.2 g of ion-exchanged water, and Production Example 3 as an internal crosslinking agent 0.1 mol% of polyethylene glycol diacrylate (1) obtained (vs. all monomers), 1.5 mol% of polyethylene glycol monoacrylate (average number of ethylene oxide repeating units: 10) (vs. all monomers) Were mixed with an aqueous solution to obtain a monomer aqueous solution (2) having a neutralization rate of 75 mol%. About monomer aqueous solution (2), operation similar to Example 1 was performed and the comparative water absorbent resin powder (2) was obtained.

  Various physical properties of the obtained comparative water absorbent resin powder (2) were measured. The results are shown in Table 1.

  Moreover, the return amount of the absorber using the comparative water absorbent resin powder (2) was 10 g.

Example 4
20 g of the hydrogel crosslinked polymer (2) is placed in a JIS standard sieve (JIS Z8801-1) having an opening of 5.60 mm, and the sieve is immersed in a bath containing a 20% by mass sodium chloride aqueous solution. The cross-linked polymer was shaken for about 5 minutes so as not to spill from the upper surface, and the amount of gel remaining on the metal mesh having an opening of 5.60 mm was measured. As a result, the residual gel amount was 0.2 g, and the gel grinding property of the hydrogel crosslinked polymer (2) was good.

[Comparative Example 3]
The same operation was performed except that the hydrogel crosslinked polymer (2) was replaced with the comparative hydrogel crosslinked polymer (2) in Example 4. As a result, the amount of gel remaining on the metal mesh having an opening of 5.60 mm was 18 g. The gel pulverization characteristics of the comparative hydrous gel-like crosslinked polymer were remarkably deteriorated.

Example 5
Water absorbent resin powders (1) to (3) 100 parts by mass, 0.4 parts by mass of 1,4-butanediol, 0.6 parts by mass of propylene glycol, 3.0 parts by mass of ion-exchanged water, 0.5 parts by mass of isopropanol The surface cross-linking agent consisting of a part (mass ratio of passing material) was spray mixed and further heat treated at 210 ° C. for 40 minutes to obtain surface-crosslinked water-absorbing resin powders (4) to (6). .

  The PPUP of the water absorbent resin powders (4) to (6) was 66%, 70%, and 73%, respectively.

Moreover, SFC of water-absorbent resin powders (4) to (6) is 30 × 10 ⁻⁷ (cm ³ × sec / g), 42 × 10 ⁻⁷ (cm ³ × sec / g), and 55 × 10 ^{−7, respectively.} (Cm ³ × sec / g).

  Moreover, the return amounts of the absorbent bodies using the water absorbent resin powders (4) to (6) were 5 g, 4 g, and 4 g, respectively.

[Comparative Example 4]
To 10 g of the comparative water absorbent resin powder (1) obtained in Comparative Example 1, 1 g of a 10% by mass aqueous solution of polyoxyethylene sorbitan monostearate was added and mixed, dried with hot air at 120 ° C., and passed through a JIS 850 μm standard sieve. As a result, a comparative water absorbent resin powder (4) was obtained.

  Various physical properties of the obtained comparative water absorbent resin powder (4) were measured. The results are shown in Table 1.

  Moreover, the return amount of the absorber using the comparative water absorbent resin powder (4) was 12 g.

[Summary]
Examples 1 to 5 and Comparative Examples 1 to 3 are all water-absorbing resins obtained by polymerizing acrylic acid monomers using polyethylene glycol diacrylate as an internal cross-linking agent.

  Compared with Comparative Example 1 in which polyethylene glycol monoacrylate was not added, in Examples 2 and 3 in which a specific amount coexists, the water-soluble content is reduced, and the GEX value (relationship between absorption ratio GVs and soluble content) is improved. It can be seen that the PIL value, which is the powder characteristic (friction resistance), is also reduced. Further, in Comparative Example 2 in which the amount of polyethylene glycol monoacrylate added is large, the absorption ratio is greatly reduced and the GEX value (relationship between the absorption ratio GVs and the soluble content) is deteriorated as compared with Examples 1 to 3 in which a specific amount is present. I understand that. A water-absorbent resin with improved powder characteristics (friction resistance) is excellent in transportability and impact resistance. Further, as described in Example 1 and Comparative Example 1, the polymerization time can be shortened by using a specific amount of polyethylene glycol monoacrylate.

  In Example 4 and Comparative Example 3, the gel grinding load was evaluated. Compared with Comparative Example 4 to which polyethylene glycol monoacrylate was not added, in Example 4 in which a very small amount coexists, the gel grinding characteristics were good. Uniform gel pulverization not only has high productivity, but also reduces the subsequent drying load, and further facilitates pulverization after drying and easy particle size control.

  In Example 5, surface cross-linking was further performed, but PPUP was greatly improved in the water absorbent resin of the present application using polyethylene glycol monoacrylate.

  Furthermore, both the powder characteristics and the surface tension reduction prevention characteristics are satisfied in Examples 1 to 3, but are not realized in Comparative Examples 1, 2, and 4.

  Although not shown in the table, all the remaining crosslinking agents were ND, and the residual monomer was 300 ppm or less.

  According to the production method of the present invention, a water-absorbent resin having good absorption characteristics excellent in the absorption capacity under no pressure (GVs), the absorption capacity under pressure (AAP), and the balance of soluble components is easily produced. be able to. Such water-absorbing resins are widely used in agriculture, horticulture, rooftop greening and desert greening water retention agents, soil modifiers, industrial water retention agents, waste liquid solidifying agents, hygroscopic agents, dehumidifying agents, building materials, etc. It is particularly preferably used for sanitary materials such as incontinence pads, breast milk pads, sanitary napkins.

Claims (10)

Including a step of polymerizing an aqueous monomer solution mainly composed of an acrylic acid monomer in the presence of a crosslinking agent, and a step of heat drying.
The cross-linking agent is a polyfunctional (meth) acrylate-based cross-linking agent having a polyethylene glycol structural unit having a total ethylene oxide repeating unit of 6 to 200,
During the monomer aqueous solution, from 0.1 to 30% by weight relative to the polyfunctional (meth) acrylate-based crosslinking agent, allowed to coexist mono (meth) acrylate compound having polyethylene glycol structural units,
The ratio of the number of polyethylene glycol structural units of the polyfunctional (meth) acrylate-based crosslinking agent and the number of polyethylene glycol structural units of the mono (meth) acrylate-based compound is in the range of 0.5 to 2.0.
A method for producing a water-absorbent resin.   The manufacturing method of the water absorbing resin of Claim 1 whose molecular weight distribution prescribed | regulated by the distribution index of the ethylene oxide repeating unit of the said polyfunctional (meth) acrylate type crosslinking agent is 50 to 100%. The relative acrylic monomer, the mono (meth) acrylate compound 1.0 × ¹⁰ -5 to 0.5 mol%, the polyfunctional (meth) acrylate crosslinking agent 1.0 × 10 ^- The production method according to claim 1 or 2 , comprising ^{3 to} 1.0 mol%. The manufacturing method in any one of Claim 1 to 3 including the surface crosslinking process with a heating after a drying process. The acrylic acid-based monomer contains 1-1000 mass ppm of a polymerization inert organic compound having a solubility parameter of 1.0 × 10 ^{4 to} 2.5 × 10 ⁴ (Jm ⁻³ ) ^1/2. The manufacturing method in any one of 1-4 . The manufacturing method in any one of Claim 1-5 in which the said acrylic acid-type monomer contains 0.01-5 mass ppm of iron. The polymerization step is aqueous solution polymerization process according to any one of claims 1 to 6. The production method according to any one of claims 1 to 7 , wherein the total monomer used in the polymerization contains methoxyphenols in a range of 10 to 300 ppm. The production method according to any one of claims 1 to 8 , wherein the acrylic acid monomer contains protoanemonin and / or furfural at 10 ppm by mass or less. The manufacturing method according to any one of claims 1 to 9 , wherein, in the heat drying step, the drying temperature is 150 to 250 ° C, and the drying time is 1 minute to 3 hours.