WO2024009541A1 - Method for producing water-absorbing resin composition - Google Patents

Abstract

The present invention is a method for producing a water-absorbing resin composition which involves a polymerization step for obtaining a water-containing gel which contains a cross-linked polymer (A), and a drying step for drying the water-containing gel in a dryer, said method being characterized in that: the dryer is a rotary dryer for performing a drying treatment inside a tumbling barrel, and has a tumbling barrel capable of rotating around an axis, and a stirring shaft which is capable of rotating, has a stirring rod, and is arranged in the axial direction; and the water-containing gel is lifted while being dried inside the tumbling barrel of the rotary dryer by rotating the tumbling barrel and stirring rod during the drying step. The present invention makes it possible to provide a method for producing a water-absorbing resin composition which makes it possible to contribute to a reduction in environmental burden by reducing the time which the drying step takes, and also to reduce the occurrence of discolored foreign matter and performance degradation caused by the drying step.

Description

Method for producing water absorbent resin composition

The present invention relates to a method for producing a water-absorbing resin composition.

Currently, water-absorbent resin compositions whose main ingredients are hydrophilic fibers such as pulp and acrylic acid (salt) are widely used as absorbents in sanitary materials such as disposable diapers, sanitary napkins, and incontinence pads. . In recent years, the demand for these sanitary materials has increased worldwide, and it can be said that it is necessary to improve productivity in order to meet this demand. In the manufacturing process of a water-absorbing resin composition, it is necessary to dry a large amount of water contained in the water-absorbing resin composition, and this drying process becomes a rate-limiting step, making it difficult to improve productivity.

In order to speed up the drying rate of the water-absorbing resin composition, there is a method of increasing the drying temperature. However, when the drying temperature is raised, the superabsorbent resin composition is thermally degraded, resulting in a decrease in water absorption performance and an increase in soluble content. When water absorption performance decreases, the surface of sanitary materials that come into contact with the skin becomes difficult to dry, leading to rashes. Moreover, even if the soluble content increases, it may cause rashes during use of sanitary materials. Therefore, there is a need for improved drying methods for producing water absorbent resin compositions with less deterioration in performance.

The water-absorbing resin composition can be dried by polymerizing acrylic acid in an aqueous solution, then shredding the resulting hydrogel with a shredder, and drying it in a conveyor dryer, or by polymerizing acrylic acid in an aqueous solution, then A conventionally known method is to neutralize and shred the resulting hydrogel using a shredder, and dry it using a conveyor-type dryer as illustrated in FIG. 3 (for example, Patent Document 1 and Patent Document 2).

However, conveyor-type stationary drying requires layering and drying of hydrogels, which tends to cause uneven drying, resulting in undried matter, which increases equipment load in the crushing and classification processes that are the post-drying processes. Problems such as lower yields and lower yields occur. Therefore, when producing a water absorbent resin composition using a conveyor type dryer, excessive drying is required to suppress the generation of undried materials. Excessive drying requires a large amount of high-temperature gas and consumes a large amount of energy during drying, and there are also problems such as a decrease in the absorption performance of the resulting water-absorbing resin composition and the generation of colored foreign matter.

In addition, methods for drying the water-absorbing resin composition using a dryer other than a conveyor-type dryer include a method in which a water-containing gel is suspended by an air current and dried (Patent Document 3), a method in which a water-containing gel is dried in a rotary dryer (Patent Document 4, 5) has also been proposed.

However, since hydrogels have a high cohesive property, some hydrogels coalesce and remain in the dryer due to decreased fluidity and adhesion to the dryer. Excessive heat exposure caused problems such as deterioration of water absorption performance and generation of colored foreign matter. In addition, when the drying temperature was lowered to avoid thermal deterioration, problems arose in that the production volume per unit time decreased due to a decrease in drying speed, and that undried gel adhered to the dryer, making continuous operation of the equipment difficult.

In order to improve drying performance, a method of adding a surfactant to a hydrogel and drying it has been proposed (Patent Document 6), but a dryer with low drying efficiency requires a large amount of surfactant material to be added. There were problems such as coloring due to thermal deterioration of the surfactant and deterioration of water absorption performance due to the addition of the surfactant.

As a measure to reduce colored foreign matter contained in water-absorbing resin compositions, a method of color-sorting and removing foreign matter (Patent Document 7) has been proposed, but it is difficult to suppress deterioration of water-absorbing performance, and manufacturing This made the process complicated.

Patent No. 3297192 Patent No. 5587384 JP2007-71415 Patent No. 6913107 International patent WO2020/144948 JP2000-143720 Patent No. 5271717

An object of the present invention is to provide a water-absorbing resin composition that can contribute to reducing environmental impact by reducing the time required for the drying process, and can also reduce performance deterioration and generation of colored foreign matter caused by the drying process. An object of the present invention is to provide a manufacturing method.

The present invention provides at least one monomer selected from the group consisting of a water-soluble unsaturated monocarboxylic acid (a1) and its salt, and a monomer (a2) that becomes the water-soluble unsaturated monocarboxylic acid (a1) upon hydrolysis. (A1) and an internal crosslinking agent (b) as structural units to obtain a hydrogel containing a crosslinked polymer (A); and a drying step of drying the hydrogel in a dryer. A method for producing a synthetic resin composition, comprising:
The dryer includes a rotary cylinder that can freely rotate around an axis, and a rotatable stirring shaft that is disposed in the direction of the axis and has a stirring rod, and the dryer has a rotating cylinder that performs a drying process within the rotary cylinder. It is a type dryer,
In the drying step, the water-containing gel is dried in the rotary cylinder of the rotary dryer while being scraped up by rotating the rotary cylinder and the stirring rod. It is.

According to the present invention, a water-absorbing resin composition can contribute to reducing environmental load by reducing the time required for the drying process, and can also reduce performance deterioration and generation of colored foreign matter caused by the drying process. A manufacturing method can be provided.

FIG. 2 is a diagram schematically showing a part of a cross section in the axial direction of a rotary cylinder of a rotary dryer. FIG. 2 is a diagram schematically showing a vertical cross section of the axis of a rotary cylinder of a rotary dryer. FIG. 1 is a diagram schematically showing a cross section of a conventionally used conveyor dryer.

<Method for manufacturing water absorbent resin composition>
The method for producing the water absorbent resin composition of this embodiment is as follows:
One or more monomers (A1) selected from the group consisting of a water-soluble unsaturated monocarboxylic acid (a1) and its salt, and a monomer (a2) that becomes the water-soluble unsaturated monocarboxylic acid (a1) upon hydrolysis; , an internal crosslinking agent (b), and a drying step of drying the hydrogel in a dryer. A method of manufacturing,
The dryer includes a rotary cylinder that can freely rotate around an axis, and a rotatable stirring shaft that is disposed in the direction of the axis and has a stirring rod, and the dryer has a rotating cylinder that performs a drying process within the rotary cylinder. It is a type dryer,
In the drying step, the hydrogel is dried in the rotary cylinder of the rotary dryer while being scraped up by rotating the rotary cylinder and the stirring rod.

According to the method for producing a water-absorbing resin composition of the present embodiment, it is possible to contribute to reducing the environmental load by reducing the time required for the drying process, and also to reduce performance deterioration and generation of colored foreign matter due to the drying process. can be reduced.

[Polymerization process]
The method for producing a water-absorbing resin composition of the present embodiment includes a water-soluble unsaturated monocarboxylic acid (a1) and its salt, and a monomer (a2) that becomes the water-soluble unsaturated monocarboxylic acid (a1) by hydrolysis. The method includes a polymerization step of obtaining a hydrogel containing a crosslinked polymer (A) having as constituent units one or more monomers (A1) selected from the group consisting of one or more monomers (A1) and an internal crosslinking agent (b). In the polymerization step, the hydrogel can be obtained by polymerizing a monomer composition containing the monomer (A1) and the crosslinking agent (b).

[Monomer (A1)]
(Water-soluble unsaturated monocarboxylic acid (a1) and its salt)
The water-soluble unsaturated monocarboxylic acid (a1) can be used without particular limitation as long as it is a water-soluble unsaturated monocarboxylic acid. The water-soluble unsaturated monocarboxylic acid (a1) is preferably at least one selected from the group consisting of acrylic acid, methacrylic acid, and crotonic acid, from the viewpoint of water absorption performance when crosslinked and ease of availability. , acrylic acid, and methacrylic acid are more preferred.

Examples of the salts of the water-soluble unsaturated monocarboxylic acid (a1) include alkali metal (lithium, sodium, potassium, etc.) salts, alkaline earth metal (magnesium, calcium, etc.) salts, and ammonium (NH ₄ ) salts. . Among these salts, from the viewpoint of absorption performance and the like, alkali metal salts and ammonium salts are preferred, alkali metal salts are more preferred, and sodium salts are particularly preferred.

(Monomer (a2))
The monomer (a2) which becomes the water-soluble unsaturated monocarboxylic acid (a1) by hydrolysis can be used together with or instead of the water-soluble unsaturated monocarboxylic acid (a1). The monomer (a2) is not particularly limited, and examples include monomers having one hydrolyzable substituent that becomes a carboxy group upon hydrolysis. The hydrolyzable substituent includes a group containing an acid anhydride (1,3-oxo-1-oxapropylene group, -COO-CO-), a group containing an ester bond (alkyloxycarbonyl, vinyloxycarbonyl, allyl), and a group containing an ester bond (alkyloxycarbonyl, vinyloxycarbonyl, allyl). Examples include oxycarbonyl or propenyloxycarbonyl, -COOR) and cyano group. Note that R is an alkyl group having 1 to 3 carbon atoms (methyl, ethyl, and propyl), vinyl, allyl, and propenyl.

In addition, in this specification, water-soluble means that at least 100g is dissolved in 100g of water at 25°C. Moreover, the hydrolyzability of the monomer (a2) means the property of being hydrolyzed by the action of water and, if necessary, a catalyst (acid, base, etc.) and becoming water-soluble. The monomer (a2) may be hydrolyzed during polymerization, after polymerization, or both, but from the viewpoint of the absorption performance of the resulting water-absorbing resin composition, it is preferably after polymerization.

In addition to the monomer (A1), the monomer composition may contain another vinyl monomer (A2) that is copolymerizable with these monomers. The vinyl monomer (A2) may be used alone or in combination of two or more.

The vinyl monomer (A2) is not particularly limited, and includes known hydrophobic vinyl monomers disclosed in paragraphs 0028 to 0029 of Japanese Patent No. 3648553, paragraph 0025 of Japanese Patent Application Publication No. 2003-165883, and Hydrophobic vinyl monomers such as the vinyl monomers disclosed in paragraph 0058 of Publication No. 2005-75982 can be used, and specifically, for example, the following vinyl monomers (i) to (iii) can be used.
(i) Aromatic ethylenic monomers having 8 to 30 carbon atoms Styrene such as styrene, α-methylstyrene, vinyltoluene and hydroxystyrene, and halogen substituted products of styrene such as vinylnaphthalene and dichlorostyrene.
(ii) Aliphatic ethylenic monomers having 2 to 20 carbon atoms Alkenes (ethylene, propylene, butene, isobutylene, pentene, heptene, diisobutylene, octene, dodecene, octadecene, etc.); and alkadienes (butadiene, isoprene, etc.).
(iii) Alicyclic ethylenic monomers having 5 to 15 carbon atoms, monoethylenically unsaturated monomers (pinene, limonene, indene, etc.); and polyethylenic vinyl monomers [cyclopentadiene, bicyclopentadiene, ethylidene norbornene, etc.].

The amount of the vinyl monomer (A2) in the monomer composition is preferably 0 to 5 parts by mole, more preferably 0 to 5 parts by mole, based on 100 parts by mole of the monomer (A1), from the viewpoint of absorption performance and the like. The amount is 3 mol parts, particularly preferably 0 to 2 mol parts, particularly preferably 0 to 1.5 mol parts, and most preferably 0 mol parts from the viewpoint of absorption performance and the like.

[Internal crosslinking agent (b)]
The internal crosslinking agent (b) is not particularly limited and is known in the art (for example, a crosslinking agent having two or more ethylenically unsaturated groups disclosed in paragraphs 0031 to 0034 of Japanese Patent No. 3648553, a water-soluble substituent and Crosslinking agent having at least one reactive functional group and at least one ethylenically unsaturated group, and crosslinking agent having at least two functional groups capable of reacting with a water-soluble substituent, JP 2003-165883A A crosslinking agent having two or more ethylenically unsaturated groups, a crosslinking agent having an ethylenically unsaturated group and a reactive functional group, and a crosslinking agent having two or more reactive substituents disclosed in paragraphs 0028 to 0031 of the publication Crosslinking agents, crosslinkable vinyl monomers disclosed in paragraph 0059 of JP-A No. 2005-75982 and cross-linkable vinyl monomers disclosed in paragraphs 0015 to 0016 of JP-A No. 2005-95759, etc. Can be used.

The internal crosslinking agent (b) is preferably a crosslinking agent having two or more ethylenically unsaturated groups, and from the viewpoint of reactivity with monomers and water absorption characteristics, a polyvalent (meth) having two or more ethylenically unsaturated groups. ) allyl compounds and acrylamide compounds are preferred; poly(meth)allyl ethers of polyhydric alcohols such as alkylene glycols, trimethylolpropane, glycerin, pentaerythritol and sorbitol; ) Allyl compounds, and one or more selected from the group consisting of polyvalent (meth)acrylamide compounds having two or more (meth)acrylamide groups in one molecule are more preferred. The internal crosslinking agent (b) may be used alone or in combination of two or more. From the viewpoint of reactivity, balance of water retention and absorption under load, it is more preferable to use poly(meth)allyl ether of polyhydric alcohol or polyhydric (meth)acrylamide compound.

From the viewpoint of absorption performance, etc., the amount of the internal crosslinking agent (b) in the monomer composition is 100 mol parts of the monomer (A1), and (A1) when using other vinyl monomers (A2). The amount is preferably 0.001 to 5 mol parts, more preferably 0.005 to 3 mol parts, particularly preferably 0.005 to 1 mol part, based on a total of 100 mol parts of (A2) and (A2).

When performing aqueous solution polymerization, a mixed solvent containing water and an organic solvent can be used. Examples of the organic solvent include methanol, ethanol, acetone, methyl ethyl ketone, N,N-dimethylformamide, dimethyl sulfoxide, and mixtures of two or more thereof.

When carrying out aqueous solution polymerization, the amount (wt%) of the organic solvent used is preferably 40 or less, more preferably 30 or less, based on the weight of water.

When the polymerization method is a suspension polymerization method or a reverse phase suspension polymerization method, the polymerization may be carried out in the presence of a conventionally known dispersant or surfactant, if necessary. Furthermore, in the case of reverse phase suspension polymerization, polymerization can be carried out using conventionally known hydrocarbon solvents such as xylene, n-hexane, and n-heptane.

Among the polymerization methods, the aqueous solution polymerization method is preferable because it does not require the use of organic solvents and is advantageous in terms of production cost. The aqueous adiabatic polymerization method is more preferable because it can be obtained easily and does not require temperature control during polymerization.

The weight percent concentration of the monomer composition containing the monomer (A1) and the internal crosslinking agent (b) during polymerization is preferably 15 to 55% based on the total weight of the polymerization solution at the start of polymerization. If it is lower than this range, productivity may deteriorate, and if it is higher than this range, sufficient gel strength may not be obtained.

In the polymerization of the monomer (A1), a known radical initiator can be used if necessary.

Known radical initiators include azo compounds [azobisisobutyronitrile, azobiscyanovaleric acid and 2,2'-azobis(2-amidinopropane) hydrochloride, 2,2'-azobis[2-methyl-N- (2-hydroxyethyl)propionamide], etc.), inorganic peroxides (hydrogen peroxide, ammonium persulfate, potassium persulfate, sodium persulfate, etc.), organic peroxides [benzoyl peroxide, di-t-butyl peroxide, etc.] , cumene hydroperoxide, succinic acid peroxide and di(2-ethoxyethyl) peroxydicarbonate, etc.], redox catalysts (reduction of alkali metal sulfites or bisulfites, ammonium sulfite, ammonium bisulfite, ascorbic acid, etc.) alkali metal persulfate, ammonium persulfate, hydrogen peroxide, and an oxidizing agent such as an organic peroxide), a photoradical generator [2,4,6-trimethylbenzoyl-diphenyl-phosphine] oxide, 1-hydroxycyclohexyl-phenylketone-hydroxyalkylphenone, α-aminoalkylphenone, etc.]. These radical initiators may be used alone or in combination of two or more thereof.

The amount of the radical initiator used is preferably 0.0005 to 5 parts by mole, more preferably 0.001 to 2 parts by mole, per 100 parts by mole of monomer (A1).

Through the above polymerization step, a polymer gel of the crosslinked polymer (A) having the monomer (A1) and the internal crosslinking agent (b) as constituent units is obtained, and this polymer gel can be shredded if necessary. Can be done. The size of the gel after shredding (longest diameter) is preferably 50 μm to 10 cm, more preferably 100 μm to 2 cm, particularly preferably 1 mm to 1 cm. Within this range, the drying properties in the drying step will be even better.

The hydrous gel can be shredded by a known method, using a shredding device (for example, a Bex mill, a rubber chopper, a Pharma mill, a mincing machine (meat chopper), an impact crusher, a roll crusher), etc. Can be used to shred. Further, if necessary, the polymer gel obtained as described above can be mixed with an alkali to neutralize it.

As the alkali, those known in the art (such as those disclosed in Japanese Patent No. 3205168) can be used. Among these, from the viewpoint of water absorption performance, lithium hydroxide, sodium hydroxide, and potassium hydroxide are preferable, more preferably sodium hydroxide and potassium hydroxide, and particularly preferably sodium hydroxide. From the viewpoint of water absorption performance and handling, the neutralization rate is preferably 20 to 100 mol%, more preferably 50 to 80 mol%. If the degree of neutralization is less than 50 mol%, the resulting hydrogel polymer will have high stickiness, and workability during production and use may deteriorate. Furthermore, the water retention amount of the resulting water absorbent resin may be reduced. On the other hand, if the degree of neutralization exceeds 80%, the pH of the resulting resin may become high and there may be concerns about safety for human skin.

[Hydrophobic substance addition step]
The method for producing a water absorbent resin composition may include a hydrophobic substance addition step of adding a hydrophobic substance (c) before the drying step. The hydrophobic substance (c) can suppress blocking due to aggregation of the hydrogel particles obtained by shredding the hydrogel, and prevents the hydrogel particles from fusing together, resulting in the formation of the hydrogel during drying. Since the surface area of the drying agent is increased, drying performance can be improved. Furthermore, it is possible to prevent the hydrogel from adhering to the interior of the dryer, thereby suppressing deterioration of water absorption performance and generation of colored foreign matter.

The hydrophobic substance (c) includes a hydrophobic substance (c1) containing a hydrocarbon group having 8 to 30 carbon atoms, a hydrophobic substance (c2) which is an organic polysiloxane, and the like.

The hydrophobic substance (c1) includes polyolefin resins, polyolefin resin derivatives, polystyrene resins, polystyrene resin derivatives, waxes, long-chain fatty acid esters, long-chain fatty acids and their salts, long-chain aliphatic alcohols, long-chain aliphatic amides, and Mixtures of two or more of these are included.

The polyolefin resin has a weight of olefin having 2 to 4 carbon atoms {ethylene, propylene, isobutylene, isoprene, etc.} as an essential constituent monomer (olefin content is at least 50% by weight based on the weight of the polyolefin resin). Examples include polymers having an average molecular weight of 1,000 to 1,000,000 {eg, polyethylene, polypropylene, polyisobutylene, poly(ethylene-isobutylene), and isoprene, etc.}.

Examples of polyolefin resin derivatives include polymers with a weight average molecular weight of 1,000 to 1,000,000, which are obtained by introducing carboxyl groups (-COOH), 1,3-oxo-2-oxapropylene (-COOCO-), etc. into polyolefin resins {for example, polyethylene thermal Degraded product, thermally degraded polypropylene, maleic acid-modified polyethylene, chlorinated polyethylene, maleic acid-modified polypropylene, ethylene-acrylic acid copolymer, ethylene-maleic anhydride copolymer, isobutylene-maleic anhydride copolymer, maleated polybutadiene, ethylene-vinyl acetate copolymer, maleated ethylene-vinyl acetate copolymer, etc.).

As the polystyrene resin, a polymer having a weight average molecular weight of 1,000 to 1,000,000 can be used.

The polystyrene resin derivative is a polymer having a weight average molecular weight of 1,000 to 1,000,000 and containing styrene as an essential constituent monomer (styrene content is at least 50% by weight, based on the weight of the polystyrene derivative) {for example, styrene- Maleic anhydride copolymer, styrene-butadiene copolymer, styrene-isobutylene copolymer, etc.}.

Examples of the wax include waxes with a melting point of 50 to 200°C {for example, paraffin wax, beeswax, carnauba wax, beef tallow, etc.}.

Long-chain fatty acid esters include esters of fatty acids with 8 to 30 carbon atoms and alcohols with 1 to 12 carbon atoms {for example, methyl laurate, ethyl laurate, methyl stearate, ethyl stearate, methyl oleate, oleic acid Ethyl, glycerin lauric acid monoester, glycerin stearic acid monoester, glycerin oleic acid monoester, pentaerythritol lauric acid monoester, pentaerythritol stearic acid monoester, pentaerythritol oleic acid monoester, sorbitol lauric acid monoester, Sorbitol stearate monoester, sorbitoleate monoester, sucrose palmitate monoester, sucrose palmitate diester, sucrose palmitate triester, sucrose stearate monoester, sucrose stearate diester, sucrose stearate triester esters, beef tallow, etc.}.

Examples of long-chain fatty acids and their salts include fatty acids having 8 to 30 carbon atoms (for example, lauric acid, palmitic acid, stearic acid, oleic acid, dimer acid, and behenic acid), and examples of their salts include zinc, calcium, Examples include salts with magnesium or aluminum (hereinafter abbreviated as Zn, Ca, Mg, Al, respectively) {for example, Ca palmitate, Al palmitate, Ca stearate, Mg stearate, Al stearate, etc.}.

Examples of long-chain aliphatic alcohols include aliphatic alcohols having 8 to 30 carbon atoms (eg, lauryl alcohol, palmityl alcohol, stearyl alcohol, oleyl alcohol, etc.). From the viewpoint of leakage resistance of the absorbent article, palmityl alcohol, stearyl alcohol, and oleyl alcohol are preferred, and stearyl alcohol is more preferred.

Examples of the long-chain aliphatic amide include an amidation product of a long-chain aliphatic primary amine having 8 to 30 carbon atoms and a carboxylic acid having a hydrocarbon group having 1 to 30 carbon atoms, ammonia, or a primary amine having 1 to 7 carbon atoms. and a long-chain fatty acid having 8 to 30 carbon atoms; amidation products of a long-chain aliphatic secondary amine having at least one aliphatic chain having 8 to 30 carbon atoms and a carboxylic acid having 1 to 30 carbon atoms; and Examples include amidation products of secondary amines having two aliphatic hydrocarbon groups having 1 to 7 carbon atoms and long-chain fatty acids having 8 to 30 carbon atoms.

An amidated product of a long-chain aliphatic primary amine having 8 to 30 carbon atoms and a carboxylic acid having a hydrocarbon group having 1 to 30 carbon atoms includes a product obtained by reacting a primary amine and a carboxylic acid in a 1:1 ratio, and 1 :Divided into 2 reacted substances. Examples of products reacted at a ratio of 1:1 include acetic acid N-octylamide, acetic acid N-hexacosylamide, heptacanoic acid N-octylamide, and heptacanoic acid N-hexacosylamide. Examples of those reacted at a ratio of 1:2 include diacetic acid N-octylamide, diacetic acid N-hexacosylamide, diheptacanoic acid N-octylamide, and diheptacanoic acid N-hexacosylamide. In addition, in the case of a product obtained by reacting a primary amine and a carboxylic acid at a ratio of 1:2, the carboxylic acids used may be the same or different.

As the amidated product of ammonia or a primary amine having 1 to 7 carbon atoms and a long chain fatty acid having 8 to 30 carbon atoms, a 1:1 reaction of ammonia or a primary amine with a carboxylic acid and a 1:2 reaction of ammonia or a primary amine with a carboxylic acid are available. It can be divided into reactants. Products reacted at a ratio of 1:1 include nonanoic acid amide, nonanoic acid methylamide, nonanoic acid N-heptylamide, heptacanoic acid amide, heptacanoic acid N-methylamide, heptacanoic acid N-heptylamide, and heptacosanoic acid N-hexacosylamide. etc. Those reacted at a ratio of 1:2 include dinonanoic acid amide, dinonanoic acid N-methylamide, dinonanoic acid N-heptylamide, dioctadecanoic acid amide, dioctadecanoic acid N-ethylamide, dioctadecanoic acid N-heptylamide, diheptacanoic acid amide , diheptacosanoic acid N-methylamide, diheptacosanoic acid N-heptylamide, diheptacosanoic acid N-hexacosylamide, and the like. In addition, as a product obtained by reacting ammonia or a primary amine with a carboxylic acid at a ratio of 1:2, the carboxylic acids used may be the same or different.

Examples of amidated products of long-chain aliphatic secondary amines having at least one aliphatic chain having 8 to 30 carbon atoms and carboxylic acids having 1 to 30 carbon atoms include acetic acid N-methyloctylamide, acetic acid N-methylhexacylamide, and acetic acid N-methyloctylamide. ruamide, acetic acid N-octylhexacosylamide, acetic acid N-dihexacosylamide, heptacanoic acid N-methyloctylamide, heptacanoic acid N-methylhexacosylamide, heptacanoic acid N-octylhexacosylamide and heptacosane Examples include acid N-dihexacosylamide and the like.

Examples of amidated products of a secondary amine having two aliphatic hydrocarbon groups having 1 to 7 carbon atoms and a long chain fatty acid having 8 to 30 carbon atoms include nonanoic acid N-dimethylamide, nonanoic acid N-methylheptylamide, Examples include nonanoic acid N-diheptylamide, heptacanoic acid N-dimethylamide, heptacanoic acid N-methylheptylamide, and heptacosanoic acid N-diheptylamide.

Examples of the hydrophobic substance (c2) include polydimethylsiloxane, polyether-modified polysiloxane {polyoxyethylene-modified polysiloxane and poly(oxyethylene/oxypropylene)-modified polysiloxane, etc.}, carboxy-modified polysiloxane, and epoxy-modified polysiloxane. , amino-modified polysiloxane, alkoxy-modified polysiloxane, and mixtures thereof.

The HLB value of the hydrophobic substance (c) is preferably 1 to 10, more preferably 2 to 8, particularly preferably 3 to 7. Within this range, the blocking resistance during initial swelling will be even better. The HLB value means the hydrophilic-hydrophobic balance (HLB) value, which is determined by the Oda method (New Introduction to Surfactants, p. 197, Takehiko Fujimoto, published by Sanyo Chemical Industries, Ltd., 1981). .

Among the hydrophobic substances (c), from the viewpoint of anti-blocking property during initial swelling, the hydrophobic substance (c1) is preferable, and more preferably long-chain fatty acid esters, long-chain fatty acids and salts thereof, long-chain aliphatic alcohols and long-chain aliphatic amides, more preferably sorbitol stearate, sucrose stearate, stearic acid, Mg stearate, Ca stearate, Zn stearate and Al stearate, particularly preferably sucrose stearate ester and Mg stearate, most preferably sucrose stearate.

The amount of the hydrophobic substance (c) to be blended is 0.001 to 1.0 parts by weight based on 100 parts by weight of the crosslinked polymer (A) from the viewpoint of absorption performance and blocking resistance during initial swelling. It is preferably 0.005 to 0.5 parts by weight, particularly preferably 0.01 to 0.3 parts by weight.

[Drying process]
The method for producing a water-absorbent resin composition of the present embodiment includes a drying step of drying the hydrogel with a dryer. The dryer has a rotary cylinder that is rotatable around an axis, and a rotatable stirring shaft that is disposed in the direction of the axis and has a stirring rod, and the dryer has a rotating cylinder that performs drying processing within the rotary cylinder. The hydrogel is dried in the rotary cylinder of the rotary dryer while being scraped up by rotating the rotary cylinder and the stirring rod.

In the drying step, the hydrogel is dried by heating the hydrogel within the rotating cylinder. The heating means for the hydrogel is not limited as long as it can apply the amount of heat necessary for drying, and examples include heating means using convection heat transfer, conduction heat transfer, microwaves, infrared rays, etc. From the viewpoint of efficiency, heating by convection electric heating is preferred.

Examples of drying methods using convection heat transfer include a method of introducing a stream of air heated to a high temperature into the dryer. The type of air flow is not limited, but air, nitrogen, etc. are preferable, and air is most preferable. The temperature of the airflow is not limited, but hot air is preferred, and the temperature (°C) of the airflow at the inlet of the dryer is preferably 200 to 500, more preferably 250 to 500, from the viewpoint of drying efficiency, absorption performance, and coloring. 450, most preferably 300-400. The absolute humidity (kg/kg) of the hot air at the dryer inlet is preferably 0.001 to 1.0 from the viewpoint of drying efficiency and coloring, more preferably 0.002 to 0.8, and most preferably 0.005 to 0. .6. The wind speed (m/s) of the airflow is not particularly limited, but from the viewpoint of drying efficiency, absorption performance, and coloring, it is preferably from 1 to 30, more preferably from 1 to 20, and most preferably from 1 to 10.

It is preferable that the moving direction of the hot air in the rotating cylinder is the same as the moving direction of the hydrogel in the rotating cylinder.

An example of the rotary dryer used in the drying process will be described with reference to the drawings.

FIG. 1 is a schematic diagram of the rotary dryer 100. The rotary dryer 100 has a rotary cylinder 1 that is rotatable around an axis. In FIG. 1, a part of the rotary cylinder 1 in the axial direction is shown in a cross-sectional view for explaining the inside of the rotary cylinder 1. As shown in FIG.

The rotary dryer 100 includes a hydrogel inlet 3 for injecting the hydrogel at one end of the rotary cylinder 1, and a hydrogel inlet 3 for injecting hot air above the hydrogel inlet 3 on the same end side. It has a hot air inlet 2. The rotary dryer 100 has a dry polymer discharge port 8 on the other end side of the rotary cylinder 1 for discharging the dried polymer obtained by drying the hydrogel input from the hydrogel input port 3. , and has a hot air outlet 7 above the dry polymer outlet 8 for discharging the hot air input from the hot air inlet 2.

The inner diameter (diameter) of the rotary cylinder 1 is preferably 0.5 to 5.0 m, more preferably 1.0 to 4.0 m, and most preferably 2.0 to 3.5 m from the viewpoint of drying efficiency. Further, the length of the rotary cylinder 1 in the axial direction (long axis direction of the rotary cylinder 1) is preferably 1 to 20 m from the viewpoint of drying efficiency, more preferably 3 to 15 m, still more preferably 5 to 12 m, and most preferably Preferably it is 6 to 10 m.

The rotary cylinder 1 has a lifter 4 on its inner wall for scraping up the hydrogel. A rotatable stirring shaft 6 is disposed inside the rotary cylinder 1 in the axial direction of the rotary cylinder 1, and the stirring shaft 6 has a plurality of stirring rods 5 for stirring up the hydrogel.

FIG. 2 is a diagram schematically showing a cross section of the rotary cylinder 1 in a direction perpendicular to its axis. The lifter 4 extends from the inner wall of the rotary cylinder 1 toward the axis of the rotary cylinder 1 . In the drying step, the rotary cylinder 1 rotates in one direction around its axis to scrape up the hydrogel with the lifter 4, and the stirring shaft 6 rotates to scrape the hydrogel with the stirring rod 5. Stir up. There is no particular restriction on the rotation direction of the rotary cylinder 1 and the stirring shaft 6, but for example, in FIG. It rotates in the stirring shaft rotation direction 9, which is the same direction as the rotation cylinder rotation direction 10. By rotating the rotating cylinder 1 and the rotating shaft 6 in the same direction, the hydrous gel is crushed by the lifter 4 and the stirring rod 5, and the contact efficiency between the hydrous gel and the hot air is increased, and the drying efficiency is improved. do. Further, when the hydrophobic substance (c) is added in the hydrophobic substance addition step, the crushing efficiency of the hydrogel is further improved, and the drying efficiency is further improved.

In the drying step, the water content of the hydrogel charged into the rotary cylinder 1 is preferably 45 to 90%, more preferably 50 to 85%, and most preferably 60 to 80%. If the moisture content is high, drying performance deteriorates, causing problems such as the generation of foreign matter and post-drying processes. On the other hand, if the water content is low, the absorption performance will deteriorate. Note that the water content can be measured by the method described in Examples.

The lifter 4 extends from the inner wall of the rotary cylinder 1 toward the axis of the rotary cylinder 1. There is no particular restriction on the shape of the lifter 4, and it may be a flat lifter, a square lifter, or the like. From the viewpoint of stirring efficiency and drying efficiency, a flat lifter and/or a F-shaped lifter are preferable, and from the viewpoint of drying efficiency, a F-shaped lifter is more preferable. Note that the flat lifter means a flat plate-shaped lifter, and the F-shaped lifter means a flat lifter bent by more than 0° and less than 90°. The lifter 4 in FIG. 2 is a square-shaped lifter. The F-shaped lifter is preferably bent 10° to 60° forward in the rotational direction of the rotary cylinder 1 from the viewpoint of drying efficiency as well as raking efficiency.

In the drying step, the rotation speed (rpm) of the stirring shaft 6 when drying the hydrogel is preferably from 1 to 1000, more preferably from 10 to 500, particularly preferably from 50 to 1000, from the viewpoint of drying efficiency. It is 300.

In the drying step, the rotation speed (rpm) of the rotary cylinder 1 when drying the hydrogel is preferably from 0.1 to 20, more preferably from 0.5 to 15, particularly from the viewpoint of drying efficiency. Preferably it is 1-10.

The water content (weight %) of the hydrogel after drying is preferably 0 to 20, more preferably 1 to 15, particularly preferably 2 to 13, and most preferably 3 to 12. Within this range, quality problems such as poor pulverization can be further reduced in the pulverization process described below.

[Crushing process]
The method for producing a water absorbent resin composition of the present embodiment includes pulverizing the water absorbent resin composition obtained in the drying step to obtain a particulate water absorbent resin composition containing the crosslinked polymer (A). It may also include a pulverization step.

In the pulverizing step, there is no particular limitation on the method of pulverizing the water-absorbing resin composition containing the crosslinked polymer (A), and a pulverizing device (for example, a hammer-type pulverizer, an impact-type pulverizer, a roll-type pulverizer) is used. Machines such as pulverizers and Schette airflow pulverizers can be used. The particle size of the pulverized water-absorbing resin composition can be adjusted by sieving or the like, if necessary.

[Surface crosslinking process]
The method for producing a water absorbent resin composition of the present embodiment may include, after the polymerization step, a surface crosslinking step of crosslinking the surface of the crosslinked polymer (A) with a surface crosslinking agent (d).

The water absorbent resin composition obtained through the surface crosslinking step has a structure in which the surface of the crosslinked polymer (A) is crosslinked with a surface crosslinking agent (d). By crosslinking the surface of the crosslinked polymer (A), the gel strength of the water absorbent resin composition can be improved, and the desired water retention amount and absorption amount under load of the water absorbent resin composition are satisfied. be able to. Furthermore, since blocking on the surface of the water-absorbent resin composition is suppressed and uniform water absorption can be achieved, an improvement in decomposition efficiency can be expected when decomposing with an oxidizing agent.

The surface crosslinking agent (d) can be either an inorganic substance or an organic substance. As the surface crosslinking agent (d), known compounds (such as polyvalent glycidyl compounds, polyvalent amines, polyvalent aziridine compounds, and polyvalent isocyanate compounds described in JP-A-59-189103, JP-A-58-180233) can be used. Polyhydric alcohols described in Japanese Patent Publication No. 61-16903, silane coupling agents described in Japanese Patent Application Publication No. 61-211305 and Japanese Patent Application Publication No. 61-252212, and described in Japanese Patent Publication No. 5-508425. organic surface crosslinking agents such as alkylene carbonates, polyvalent oxazoline compounds described in JP-A No. 11-240959, etc.) can be used. Among these surface crosslinking agents (d), polyhydric glycidyl compounds, polyhydric alcohols, and polyhydric amines are preferred from the viewpoint of economy and absorption characteristics, and polyhydric glycidyl compounds and polyhydric alcohols are more preferred, and polyhydric alcohols are particularly preferred. The preferred are polyglycidyl compounds, most preferably ethylene glycol diglycidyl ether. One type of surface crosslinking agent (d) may be used alone, or two or more types may be used in combination.

The amount (wt%) of the surface crosslinking agent (d) to be used is not particularly limited, as it can be varied depending on the type of surface crosslinking agent, conditions for crosslinking, target performance, etc., but from the viewpoint of absorption characteristics, etc. Based on the weight of the crosslinked polymer (A), it is preferably 0.001 to 3, more preferably 0.005 to 2, particularly preferably 0.01 to 1.5.

The surface crosslinking of the crosslinked polymer (A) can be performed by mixing the crosslinked polymer (A) and the surface crosslinking agent (d) and heating the mixture. The method for mixing the crosslinked polymer (A) and the surface crosslinking agent (d) includes a cylindrical mixer, a screw mixer, a screw extruder, a turbulizer, a Nauta mixer, and a double-arm kneader. The above-mentioned crosslinking is carried out using a mixing device such as a fluid mixer, a V-type mixer, a mincing mixer, a ribbon mixer, a fluid mixer, an air flow mixer, a rotating disk mixer, a conical blender, and a roll mixer. A method of uniformly mixing the polymer (A) and the surface crosslinking agent (d) may be mentioned. At this time, the surface crosslinking agent (d) may be used after being diluted with water and/or any solvent.

The temperature at which the crosslinked polymer (A) and the surface crosslinking agent (d) are mixed is not particularly limited, but is preferably 10 to 150°C, more preferably 20 to 100°C, particularly preferably 25 to 80°C. It is.

After mixing the crosslinked polymer (A) and the surface crosslinking agent (d), a heat treatment is usually performed. The heating temperature is preferably 100 to 180°C, more preferably 110 to 175°C, particularly preferably 120 to 170°C from the viewpoint of breakage resistance of the water absorbent resin composition. Heating at a temperature of 180° C. or lower allows indirect heating using steam and is advantageous in terms of equipment, whereas heating at a temperature of less than 100° C. may result in poor absorption performance. Further, the heating time can be appropriately set depending on the heating temperature, but from the viewpoint of absorption performance, it is preferably 5 to 60 minutes, more preferably 10 to 40 minutes. It is also possible to further surface crosslink the water-absorbing resin composition obtained by surface crosslinking using a surface crosslinking agent of the same type or different from the surface crosslinking agent used initially.

After the surface of the crosslinked polymer (A) is crosslinked with the surface crosslinking agent (d), it is sieved if necessary to adjust the particle size. The average particle diameter of the obtained particles is preferably 100 to 600 μm, more preferably 200 to 500 μm. The content of fine particles is preferably small, the content of particles of 100 μm or less is preferably 3% by weight or less, and the content of particles of 150 μm or less is more preferably 3% by weight or less.

<Water absorbent resin composition>
The water-absorbing resin composition of the present embodiment is selected from the group consisting of a water-soluble unsaturated monocarboxylic acid (a1) and its salt, and a monomer (a2) that becomes the water-soluble unsaturated monocarboxylic acid (a1) by hydrolysis. A water absorbent resin composition containing a crosslinked polymer (A) having one or more selected monomers (A1) and an internal crosslinking agent (b) as constituent units, the water absorbent resin composition comprising 200 g of the water absorbent resin composition. The number of colored foreign substances contained in the product is 50 or less. The water absorbent resin composition can be manufactured by the method for manufacturing the water absorbent resin composition described above.

From the viewpoint of absorption performance, etc., the amount of the vinyl monomer (A2) units in the crosslinked polymer (A) is determined to be 100 in total of the constituent units of the water-soluble unsaturated monocarboxylic acid (a1) and the constituent units of its salt. Based on the mole part, it is preferably 0 to 5 mole parts, more preferably 0 to 3 mole parts, particularly preferably 0 to 2 mole parts, particularly preferably 0 to 1.5 mole parts, and from the viewpoint of absorption performance etc. Therefore, it is most preferable that the content of the vinyl monomer (A2) unit is 0 part by mole.

From the viewpoint of absorption performance, etc., the amount of the internal crosslinking agent (b) in the crosslinked polymer (A) is 100 in total of the constituent units of the water-soluble unsaturated monocarboxylic acid (a1) and the salt thereof. 100 molar parts, when using other vinyl monomers (A2), the total of the structural units of the water-soluble unsaturated monocarboxylic acid (a1) and its salt, and the structural units of the vinyl monomer (A2) 100 The amount is preferably 0.001 to 5 mol parts, more preferably 0.005 to 3 mol parts, particularly preferably 0.005 to 1 mol part.

The amount of the internal crosslinking agent other than the internal crosslinking agent (b) is preferably 0 to 50 parts by mole based on 100 parts by mole of the internal crosslinking agent (b) from the viewpoint of decomposition performance.

The water absorbent resin composition may contain the hydrophobic substance (c). When the water-absorbing resin composition contains the hydrophobic substance (c), the content of the hydrophobic substance (c) in the solid content of the water-absorbing resin composition is determined by the absorption performance and the initial swelling resistance. From the viewpoint of blocking properties, it is preferably 0.001 to 1% by weight, more preferably 0.005 to 0.5% by weight, particularly preferably 0.01 to 0.3% by weight. In this specification, the solid content of the water-absorbing resin composition is determined by measuring 5 g of the water-absorbing resin composition at 150°C for 15 minutes using an infrared moisture meter (manufactured by Kett Scientific Research Institute Co., Ltd., FD-230). It can be determined by the following formula using the moisture content measured by heating and drying.
Solid weight of water-absorbing resin composition (g) = Weight of water-absorbing resin composition (g) x {100-water content (%)}/100

The water absorbent resin composition may contain the silicone compound. When the water-absorbing resin composition contains the silicone compound, the content of the silicone compound in the solid content of the water-absorbing resin composition is determined to prevent adhesion to manufacturing process equipment and piping between the equipment and to prevent breakage. From this point of view, it is preferably 0.0005 to 0.040% by weight, more preferably 0.010 to 0.030% by weight, and still more preferably 0.015 to 0.025% by weight.

The water-absorbing resin composition may contain a certain amount of other components such as a residual solvent and a residual crosslinking component within a range that does not impair its performance.

Other examples of the other ingredients include preservatives, fungicides, antibacterial agents, ultraviolet absorbers, antioxidants, colorants, fragrances, deodorants, liquid permeability improvers, inorganic powders, and organic fibers. Examples include things like these. The amount thereof is usually 5% by weight or less based on the weight of the water absorbent resin composition.

From the viewpoint of water absorption performance, the water absorbent resin composition preferably contains at least one typical element selected from the group consisting of iodine, tellurium, antimony, and bismuth as the other component. When the water-absorbing resin composition contains the typical element, the content of the typical element in the solid content of the water-absorbing resin composition is preferably 0.0005 to 0.1% by weight from the viewpoint of water absorption performance. , more preferably 0.001 to 0.05% by weight.

There is no particular limitation on the shape of the water-absorbing resin composition, and examples thereof include amorphous crushed shapes, flaky shapes, pearl shapes, and rice grain shapes. Among these, amorphous crushed particles are preferable from the viewpoint of good entanglement with fibrous materials for use in disposable diapers, etc., and no fear of falling off from the fibrous materials.

The water retention amount (g/g) of the water absorbent resin composition can be measured by the method described below, and from the viewpoint of absorption amount, it is preferably 28 or more, more preferably 33 or more, and particularly preferably 35 or more. Further, from the viewpoint of stickiness, the upper limit is preferably 60 or less, more preferably 55 or less, and particularly preferably 50 or less. The amount of water retained can be appropriately adjusted by the amounts (wt%) of the internal crosslinking agent (b) and the surface crosslinking agent (d).

The soluble content (wt%) of the water absorbent resin composition can be measured by the method described in Examples, and is preferably 20% based on the water absorbent resin composition from the viewpoint of liquid permeability and water absorption rate. more preferably less than 15%. If the soluble content exceeds 20%, the soluble content will not be eluted during water absorption, resulting in gel blocking, which will adversely affect liquid passing performance and water absorption capacity, which is not preferable. In the present invention, the amount of soluble components is reduced by adjusting the type and amount of the internal crosslinking agent and the amount of water in the surface crosslinking agent.

The number of colored foreign substances contained in 200 g of the water-absorbing resin composition is preferably 50 or less, more preferably 30 or less, particularly preferably 20 from the viewpoint of reducing the foreign body sensation of disposable diapers, sanitary napkins, and incontinence products. less than or equal to The number of colored foreign substances contained in 200 g of the water absorbent resin composition can be measured by the method described in Examples.

The absorption amount under load (g/g) of the water-absorbent resin composition can be measured by the method described below, and is preferably 15 or more from the viewpoint of the absorption amount of a diaper under load, and 20 or more is more preferable. It is preferably 25 or more, particularly preferably 25 or more. It is empirically known that the amount of absorption under load is contradictory to the amount of water retained, and depending on the configuration of the diaper, there are cases where a high amount of water retention is required and cases where an amount of absorption under load is required.

<Absorber>
An absorbent body can be obtained using the water absorbent resin composition. As the absorbent body, the water-absorbing resin composition may be used alone or together with other materials to form an absorbent body. Examples of the other materials include fibrous materials. The structure and manufacturing method of the absorber when used with a fibrous material are the same as those known (Japanese Patent Laid-Open Nos. 2003-225565, 2006-131767, and 2005-097569, etc.). be.

Preferred as the fibrous material are cellulose fibers, organic synthetic fibers, and mixtures of cellulose fibers and organic synthetic fibers.

Examples of cellulose fibers include natural fibers such as fluff pulp, and cellulose chemical fibers such as viscose rayon, acetate, and cupro. The raw materials (softwood, hardwood, etc.), manufacturing method (chemical pulp, semi-chemical pulp, mechanical pulp, CTMP, etc.), bleaching method, etc. of this cellulosic natural fiber are not particularly limited.

Examples of organic synthetic fibers include polypropylene fibers, polyethylene fibers, polyamide fibers, polyacrylonitrile fibers, polyester fibers, polyvinyl alcohol fibers, polyurethane fibers, and heat-fusible composite fibers (the above-mentioned fibers with different melting points). Examples include fibers in which at least two of the above fibers are combined into a sheath-core type, eccentric type, parallel type, etc., fibers in which at least two of the above fibers are blended, and fibers in which the surface layer of the above fibers is modified.

Among these fibrous materials, preferred are cellulose natural fibers, polypropylene fibers, polyethylene fibers, polyester fibers, heat-fusible composite fibers, and mixed fibers thereof, and more preferred are Fluff pulp, heat-fusible conjugate fibers, and mixed fibers thereof are used because they have excellent shape retention properties after water absorption.

The length and thickness of the above-mentioned fibrous material are not particularly limited, and it can be suitably used as long as the length is in the range of 1 to 200 mm and the thickness is in the range of 0.1 to 100 denier. The shape is not particularly limited as long as it is fibrous, and examples thereof include a thin cylinder, a split yarn, a staple, a filament, and a web.

When the water-absorbing resin particles are used as an absorber together with a fibrous material, the weight ratio of the water-absorbing resin particles to the fibers (weight of water-absorbing resin particles/weight of fibrous material) is 40/60 to 90/10. The ratio is preferably 70/30 to 80/20.

<Absorbent article>
An absorbent article can be obtained using the water absorbent resin composition. Specifically, the above absorber is used. Absorbent products include not only sanitary products such as disposable diapers and sanitary napkins, but also anti-condensation agents, water retention agents for agriculture and gardening, residual soil solidification materials, disaster sandbags, waste blood solidification agents, disposable body warmers, ice packs, and alkaline batteries. It can be used for various purposes such as absorbing various aqueous liquids, holding agent, gelling agent, etc. in various industrial fields such as cosmetics, pet sheets, and cat litter. The manufacturing method of the absorbent article is the same as known methods (those described in JP-A No. 2003-225565, JP-A No. 2006-131767, JP-A No. 2005-097569, etc.).

The present invention will be further explained below with reference to Examples and Comparative Examples, but the present invention is not limited thereto. Hereinafter, parts refer to parts by weight, and % refers to % by weight, unless otherwise specified.

<Evaluation method>
The water retention amount, the amount of absorption under load, and the absorption rate measured by the Vortex test method were each measured in a room at 25±2° C. and 50±10% humidity using the following methods. The temperature of the physiological saline used was adjusted in advance to 25°C±2°C.

[Moisture content]
Using an infrared moisture meter (for example, FD-230, manufactured by Kett Scientific Research Institute), 5 g of the measurement sample was heated and dried at 150° C. for 15 minutes, and the weight was calculated from the difference in weight before and after drying.

[Weight ratio of particles having a particle diameter of 1.4 mm or more to the total weight of dry powder]
The weight ratio of particles having a particle size of 1.4 mm or more to the total weight of the dry powder was determined using a low tap test sieve shaker and a standard sieve (JIS Z8801-1:2006) by Perry's Chemical Engineers. It was measured by the method described in Handbook, 6th Edition (McGraw-Hill Book Company, 1984, p. 21). That is, assemble JIS standard sieves in the order of 4.0 mm, 1.4 mm, 0.5 mm and a saucer from the top, put about 50 g of particles to be measured into the top sieve, and shake for 5 minutes with a low tap test sieve shaker. I let it happen. The weight of the particles to be measured on each sieve and saucer was weighed, and the weight fraction of the particles on each sieve was determined with the total as 100% by weight. The total weight fraction of particles having a diameter of 4.0 mm or more and 1.4 mm or more was taken as the weight fraction of particles having a particle diameter of 1.4 mm or more.

[Method for measuring water retention amount for 0.9% by weight physiological saline]
Put 1.00 g of the measurement sample into a tea bag (length 20 cm, width 10 cm) made of nylon mesh with an opening of 63 μm (JIS Z8801-1:2006), and add it to 1,000 ml of physiological saline (salt concentration 0.9%). After being immersed in water for 1 hour without stirring, the sample was taken out and hung for 15 minutes to drain. Thereafter, each tea bag was placed in a centrifuge, centrifuged at 150G for 90 seconds to remove excess physiological saline, the weight (h1) including the tea bag was measured, and the water retention amount was determined from the following formula. Note that the temperature of the physiological saline used and the measurement atmosphere was 25°C±2°C.
Water retention amount (g/g) = (h1) - (h2)
In addition, (h2) is the weight of the tea bag measured by the same operation as above in the case where there is no measurement sample.

[Method for measuring soluble content]
Weigh out 100 g of 0.9% saline in a 300 ml plastic container, add 1.2 g of water-absorbing resin particles to the saline, seal with plastic wrap, and stir for 3 hours by rotating a stirrer at 500 rpm to absorb water. A soluble content extract from which the soluble content of the resin particles was extracted was prepared. Then, this soluble extract was filtered using a filter paper manufactured by ADVANTEC Toyo Co., Ltd. (product name: JIS P 3801, No. 2, thickness 0.26 mm, retained particle size 5 μm). Then, 20 g of the obtained filtrate was weighed out and 30 g of ion-exchanged water was added thereto to obtain a measurement solution.

First, a blank test solution prepared by adding 30 g of ion-exchanged water to 20 g of 0.9% by weight saline was titrated with an N/50 KOH aqueous solution until the pH of the saline became 10. Then, the titration amount ([W _{KOH, b} ] ml) of the N/50 aqueous KOH solution required to adjust the pH of the 0.9 wt % saline to 10 was obtained. Thereafter, a N/10 aqueous HCl solution was titrated until the pH of the saline solution became 2.7. Then, the titration amount ([W _HCl,b ]ml) of the N/10 aqueous HCl solution required to adjust the pH of the 0.9 wt% saline solution to 2.7 was obtained.

Next, the above measurement solution is subjected to the same operation as the above titration operation, and the titration amount of the N/50 KOH aqueous solution ([W _KOH,S ] ml) necessary for the pH of the measurement solution to become 10 is determined. , and a method for obtaining the titration amount ([W _HCl,S ]ml) of the N/10 aqueous HCl solution necessary for the pH of the measurement solution to be 2.7 will be specifically explained.

For example, in the case of water-absorbing resin particles consisting of acrylic acid and its sodium salt, the amount of unneutralized acrylic acid substance n _COOH is:
n _COOH (mol) = (W _{KOH, S} - W _{KOH, b} ) x (1/50)/1000 x 5
In addition, the total amount of acrylic acid substances n _tot is
n _tot (mol) = (W _{HCl, S} - W _{HCl, b} ) x (1/10)/1000 x 5
In addition, the amount of neutralized acrylic acid substance n _COONa is
n _COONa (mol)=n _tot -n _COOH
Furthermore, the unneutralized acrylic acid weight m _COOH is
m _COOH (g)=n _COOH ×72
In addition, the amount of neutralized acrylic acid substance m _COONa is
m _COONa (g)=n _COONa ×94
Based on the above and the water content ([W _H2O ] weight %) of the water-absorbing resin particles used as a sample, the soluble content of the water-absorbing resin particles can be calculated using the following formula.
Soluble content (wt%) = {(m _COOH + m _COONa ) x 100}/{1.2 x (100-W _H2O )}

[Number of colored foreign substances in 200g of water absorbent resin composition]
200 g of the weighed sample was put into a 0.5 L SUS hopper, and 70 g of the sample was fed per minute to an automatic powder inspection device using a vibrating feeder (feeding width 25 mm), and the foreign matter content was measured by image processing. The automatic powder inspection equipment is a CCD line sensor camera (2048 pixels), reflected illumination located parallel to the CCD line sensor camera, and transmitted illumination located on the opposite side of the CCD line sensor camera to inspect the sample supplied to the line. This is a device that can process images. (256-level gray scale, scan rate 75 μs, detection level 65, illuminance 200-255)

[Method of measuring absorption under load]
A cylindrical plastic tube (inner diameter: 25 mm, height: 34 mm) with a nylon mesh with an opening of 63 μm (JIS Z8801-1:2006) attached to the bottom, and a 250 to 500 μm mesh were sieved using a 30 mesh sieve and a 60 mesh sieve. Weigh 0.16 g of the measurement sample that has been sieved into a wide area, arrange the cylindrical plastic tube vertically on the nylon net so that the measurement sample has an approximately uniform thickness, and place a weight (weight: 210.6 g, outer diameter: 24.5 mm) was loaded. After weighing the entire weight (M1) of this cylindrical plastic tube, place the cylindrical plastic tube containing the measurement sample and weight in a petri dish (diameter: 12 cm) containing 60 ml of physiological saline (salt concentration 0.9%). The tube was immersed in an upright vertical position with the nylon mesh side facing down, and left to stand for 60 minutes. After 60 minutes, remove the cylindrical plastic tube from the Petri dish, tilt it diagonally, collect the water that has adhered to the bottom in one place, and let it drip as drops to remove excess water. The weight (M2) of the entire cylindrical plastic tube was measured, and the amount of absorption under load was determined from the following formula. Note that the temperature of the physiological saline used and the measurement atmosphere was 25°C±2°C.
Absorption amount under load (g/g) = {(M2)-(M1)}/0.16

<Example 1>
[Polymerization process]
A monomer aqueous solution was prepared by stirring and mixing 300 parts of acrylic acid (manufactured by Mitsubishi Chemical Corporation), 0.975 parts of pentaerythritol triallyl ether (manufactured by Daiso Corporation) as a crosslinking agent (b), and 691 parts of deionized water. This mixed solution was put into a polymerization tank capable of adiabatic polymerization. By introducing nitrogen gas into the solution, the amount of dissolved oxygen in the solution was set to 0.2 ppm or less, and the solution temperature was set to 5°C. To this polymerization solution, 4.5 parts of 2% 2,2'-azobis[2-methyl-N-(2-hydroxyethyl)propionamide] aqueous solution, 1.2 parts of 1% hydrogen peroxide aqueous solution, and 2% ascorbic acid were added. 2.25 parts of an acid aqueous solution was added and mixed to initiate polymerization. After a temperature rise indicating the start of polymerization was confirmed and reached approximately 90°C, the mixture was further aged for 9 hours to obtain a hydrogel polymer.

[Gel shredding process]
While kneading and shredding the hydrous gel obtained in the polymerization step using a mincer, 247 parts of a 48.5% aqueous sodium hydroxide solution was added and mixed, and the mixture was shredded three times using a mincer to obtain a shredded gel. Subsequently, 0.6 part of gel blocking inhibitor (c-1) {sucrose stearate} was added and mixed, and the mixture was further shredded once with a mincer to obtain hydrogel particles.

[Drying process]
The obtained hydrogel particles were dried using a rotary dryer having a stirring bar having the basic configuration shown in FIGS. 1 and 2. The rotary cylinder of the rotary dryer has an F-shaped lifter on its inner wall. Hydrous gel particles having the water content shown in Table 1 and hot air at 400° C. and an absolute humidity of 0.15 kg/kg were introduced from each inlet. The rotating cylinder was rotated at 5 rpm in the bending direction of the F-shaped lifter, and the rotating shaft was rotated at 200 rpm in the same direction as the rotational direction of the rotating cylinder. Continuous drying was performed with an average residence time of 20 minutes for the hydrogel particles, and the crosslinking weight was removed. A dry powder (1) containing aggregate (A) was obtained.

Subsequently, the dry powder (1) was pulverized with a roll mill (RM-10 type roll pulverizer, Asano Iron Works Co., Ltd.) with a clearance of 0.35 mm, and then sieved to obtain powder with an opening of 710 to 150 μm. The particle size was adjusted to within the range to obtain resin particles (A-1) containing the crosslinked polymer (A).

[Surface crosslinking process]
Next, 100 parts of the obtained resin particles (A-1) were stirred at high speed (high-speed stirring turbulizer manufactured by Hosokawa Micron Co., Ltd.: rotation speed 2000 rpm), and 0% of ethylene glycol diglycidyl ether was added as the surface crosslinking agent (d). 0.05 parts of water, 0.5 parts of propylene glycol, and 1.7 parts of water were added, mixed uniformly, and heated at 140°C for 40 minutes to form particulate water absorbent resin composition (P -1) was obtained.

<Example 2>
A water absorbent resin composition (P-2) was obtained in the same manner as in Example 1, except that the hot air introduction temperature was changed to 250°C.

<Example 3>
A water absorbent resin composition (P-2) was obtained in the same manner as in Example 1, except that the hot air introduction temperature was changed to 450°C.

<Example 4>
In Example 1, a water-absorbing resin composition ( P-4) was obtained.

<Example 5>
In Example 1, a water-absorbing resin composition ( P-5) was obtained.

<Example 6>
[Polymerization process]
A monomer aqueous solution was prepared by stirring and mixing 200 parts of acrylic acid (manufactured by Mitsubishi Chemical Corporation), 0.65 parts of pentaerythritol triallyl ether (manufactured by Daiso Corporation) as a crosslinking agent (b), and 794 parts of deionized water. This mixed solution was put into a polymerization tank capable of adiabatic polymerization. By introducing nitrogen gas into the solution, the amount of dissolved oxygen in the solution was set to 0.2 ppm or less, and the solution temperature was set to 5°C. To this polymerization solution, 3.0 parts of 2% 2,2'-azobis[2-methyl-N-(2-hydroxyethyl)propionamide] aqueous solution, 0.8 part of 1% hydrogen peroxide aqueous solution, and 2% ascorbic acid were added. Polymerization was initiated by adding and mixing 1.50 parts of an acid aqueous solution. After a temperature rise indicating the start of polymerization was confirmed and reached approximately 90°C, the mixture was further aged for 9 hours to obtain a hydrogel polymer.

[Gel shredding process]
While kneading and shredding the hydrous gel obtained in the polymerization step using a mincer, 165 parts of a 48.5% aqueous sodium hydroxide solution was added and mixed, and the mixture was shredded three times using a mincer to obtain a shredded gel. Subsequently, 0.4 part of hydrophobic substance (c-1) {sucrose stearate} was added and mixed, and the mixture was further shredded once with a mincer to obtain hydrogel particles.

[Drying process]
The obtained hydrogel particles were dried using a rotary dryer having a stirring bar having the basic configuration shown in FIGS. 1 and 2. The rotary cylinder of the rotary dryer has an F-shaped lifter on its inner wall. Hydrous gel particles having the water content shown in Table 1 and hot air at 400° C. and an absolute humidity of 0.15 kg/kg were introduced from each inlet. The rotating cylinder was rotated at 5 rpm in the bending direction of the F-shaped lifter, and the rotating shaft was rotated at 200 rpm in the same direction as the rotational direction of the rotating cylinder. Continuous drying was performed with an average residence time of 20 minutes for the hydrogel particles, and the crosslinking weight was removed. A dry powder (2) containing aggregate (A) was obtained.

Subsequently, the dry powder (2) was pulverized with a roll mill (RM-10 type roll pulverizer, Asano Iron Works Co., Ltd.) with a clearance of 0.35 mm, and then sieved to obtain powder with a mesh size of 710 to 150 μm. The particle size was adjusted to within the range to obtain resin particles (A-6) containing the crosslinked polymer (A).

[Surface crosslinking process]
Next, while stirring 100 parts of the resin particles (A-6) at high speed (High speed stirring turbulizer manufactured by Hosokawa Micron Co., Ltd.: rotation speed 2000 rpm), 0.05 part of ethylene glycol diglycidyl ether as the surface crosslinking agent (d) was added. , 0.5 parts of propylene glycol, and 1.7 parts of water were added, mixed uniformly, and heated at 140° C. for 40 minutes to form a particulate water-absorbing resin composition (P-6). I got it.

<Example 7>
[Polymerization process]
To a solution (A) in which 0.975 parts of polyethylene glycol diacrylate (weight average molecular weight 523) (manufactured by TCI) as a crosslinking agent (b) was added to 300 parts of acrylic acid (manufactured by Mitsubishi Chemical), 48% of the solution was added under ice cooling. A mixed solution was prepared by mixing the solution (B) obtained by diluting 247 parts of a 5% aqueous sodium hydroxide solution with 444 parts of deionized water under stirring while controlling the temperature so as not to exceed 40°C. was put into the polymerization tank. By introducing nitrogen gas into the solution, the amount of dissolved oxygen in the solution was set to 0.2 ppm or less, and the solution temperature was set to 10°C. To this polymerization solution, 4.5 parts of 2% 2,2'-azobis[2-methyl-N-(2-hydroxyethyl)propionamide] aqueous solution, 1.20 parts of 1% hydrogen peroxide aqueous solution, and 2% ascorbic acid were added. 2.25 parts of an acid aqueous solution was added and mixed to initiate polymerization. Polymerization was carried out while removing heat, and after the temperature reached approximately 90° C. and no exotherm due to reaction heat was observed, the polymer was further aged for 9 hours to obtain a hydrogel polymer.

[Gel shredding process]
The hydrous gel obtained in the polymerization step was kneaded and shredded using a mincer and shredded three times to obtain shredded gel. Subsequently, 0.6 part of hydrophobic substance (c-1) {sucrose stearate} was added and mixed, and the mixture was further shredded once using a mincer to obtain hydrogel particles.

[Drying process]
The obtained hydrogel particles were dried using a rotary dryer having a stirring bar having the basic configuration shown in FIGS. 1 and 2. The rotary cylinder of the rotary dryer has an F-shaped lifter on its inner wall. Hydrous gel particles having the water content shown in Table 1 and hot air at 400° C. and an absolute humidity of 0.15 kg/kg were introduced from each inlet. The rotating cylinder was rotated at 5 rpm in the bending direction of the F-shaped lifter, and the rotating shaft was rotated at 200 rpm in the same direction as the rotational direction of the rotating cylinder. Continuous drying was performed with an average residence time of 20 minutes for the hydrogel particles, and the crosslinking weight was removed. A dry powder (3) containing aggregate (A) was obtained.

Subsequently, the dry powder (3) was pulverized with a roll mill (RM-10 type roll pulverizer, Asano Iron Works Co., Ltd.) with a clearance of 0.35 mm, and then sieved to obtain powder with a mesh size of 710 to 150 μm. The particle size was adjusted to within the range to obtain resin particles (A-7) containing the crosslinked polymer (A).

[Surface crosslinking process]
Next, while stirring 100 parts of the resin particles (A-7) at high speed (high speed stirring turbulizer manufactured by Hosokawa Micron Co., Ltd.: rotation speed 2000 rpm), 0.05 part of ethylene glycol diglycidyl ether as the surface crosslinking agent (d) was added. , 0.5 parts of propylene glycol, and 1.7 parts of water were added, mixed uniformly, and heated at 140°C for 40 minutes to form a particulate water-absorbing resin composition (P-7). I got it.

<Example 8>
[Polymerization process]
To a solution (A) in which 1.3 parts of polyethylene glycol diacrylate (weight average molecular weight 523) (manufactured by TCI) as a crosslinking agent (b) was added to 400 parts of acrylic acid (manufactured by Mitsubishi Chemical), 48% of the solution was added under ice cooling. A mixed solution was prepared by mixing the solution (B) prepared by diluting 330 parts of a 5% aqueous sodium hydroxide solution with 258 parts of deionized water under stirring while controlling the temperature so as not to exceed 40°C. was put into the polymerization tank. By introducing nitrogen gas into the solution, the amount of dissolved oxygen in the solution was set to 0.2 ppm or less, and the solution temperature was set to 10°C. To this polymerization solution, 6.0 parts of 2% 2,2'-azobis[2-methyl-N-(2-hydroxyethyl)propionamide] aqueous solution, 1.60 parts of 1% hydrogen peroxide aqueous solution, and 2% ascorbic acid were added. Polymerization was started by adding and mixing 3.00 parts of an acid aqueous solution. Polymerization was carried out while removing heat, and after the temperature reached approximately 90° C. and no exotherm due to reaction heat was observed, the polymer was further aged for 9 hours to obtain a hydrogel polymer.

[Gel shredding process]
The hydrous gel obtained in the polymerization step was kneaded and shredded using a mincer and shredded three times to obtain shredded gel. Subsequently, 0.8 part of hydrophobic substance (c-1) {sucrose stearate} was added and mixed, and the mixture was further shredded once with a mincer to obtain hydrogel particles.

[Drying process]
The obtained hydrogel particles were dried using a rotary dryer having a stirring bar having the basic configuration shown in FIGS. 1 and 2. The rotary cylinder of the rotary dryer has an F-shaped lifter on its inner wall. Hydrous gel particles having the water content shown in Table 1 and hot air at 400° C. and an absolute humidity of 0.15 kg/kg were introduced from each inlet. The rotating cylinder was rotated at 5 rpm in the bending direction of the F-shaped lifter, and the rotating shaft was rotated at 200 rpm in the same direction as the rotational direction of the rotating cylinder. Continuous drying was performed with an average residence time of 20 minutes for the hydrogel particles, and the crosslinking weight was removed. A dry powder (4) containing aggregate (A) was obtained.

Subsequently, the dry powder (4) was pulverized with a roll mill (RM-10 type roll pulverizer, Asano Iron Works Co., Ltd.) with a clearance of 0.35 mm, and then sieved to obtain powder with a mesh size of 710 to 150 μm. Resin particles (A-8) containing a crosslinked polymer were obtained by adjusting the particle size within the range.

(Surface crosslinking process)
Next, while stirring 100 parts of the resin particles (A-8) at high speed (high-speed stirring turbulizer manufactured by Hosokawa Micron Co., Ltd.: rotation speed 2000 rpm), 0.05 part of ethylene glycol diglycidyl ether as the surface crosslinking agent (d) was added. , 0.5 parts of propylene glycol, and 1.7 parts of water were added, mixed uniformly, and heated at 140°C for 40 minutes to form a particulate water-absorbing resin composition (P-8). I got it.

<Comparative example 1>
A water absorbent resin composition (R-1) was obtained in the same manner as in Example 1, except that a rotary dryer without a stirring bar was used.

<Comparative example 2>
A water-absorbing resin composition (R-2) was obtained in the same manner as in Example 1, except that drying was performed without rotating the rotary cylinder and stirring rod.

<Comparative example 3>
A water absorbent resin composition (R-3) was obtained in the same manner as in Example 1, except that the conveyor type dryer illustrated in FIG. 3 was used.

The evaluation results of the water absorbent resin compositions (P-1) to (P-8) and (R-1) to (R-3) are shown in Table 1 below.

From the results shown in Table 1, according to the method for producing a water absorbent resin composition of the present invention, the water content after drying is low, troubles are less likely to occur in the pulverization process after the drying process, and the obtained water absorbent resin It can be seen that the composition has few colored foreign substances and has excellent water absorption performance. This is presumably because the manufacturing method of the present invention has high thermal efficiency during drying, and thermal deterioration of the water absorbent resin is suppressed.

1 Rotating tube 2 Hot air inlet 3 Hydrogel inlet 4 Lifter 5 Stirring rod 6 Stirring shaft 7 Hot air outlet 8 Dry polymer outlet 9 Stirring shaft rotation direction 10 Rotating tube rotation direction 11 Venting belt 12 Hydrogel 13 Drying chamber 14 Ventilation direction 15 Movement direction of ventilation belt 16 Dry hydrogel

Claims (8)

1. One or more monomers (A1) selected from the group consisting of a water-soluble unsaturated monocarboxylic acid (a1) and its salt, and a monomer (a2) that becomes the water-soluble unsaturated monocarboxylic acid (a1) upon hydrolysis; , an internal crosslinking agent (b), and a drying step of drying the hydrogel in a dryer. A method of manufacturing,
   The dryer includes a rotary cylinder that can freely rotate around an axis, and a rotatable stirring shaft that is disposed in the direction of the axis and has a stirring rod, and the dryer has a rotating cylinder that performs a drying process within the rotary cylinder. It is a type dryer,
   In the drying step, the water-containing gel is dried in the rotary cylinder of the rotary dryer while being scraped up by rotating the rotary cylinder and the stirring rod. .
2. The rotary dryer has a lifter extending from the inner wall of the rotary cylinder toward the axis of the rotary cylinder,
   2. The method for producing a water-absorbing resin composition according to claim 1, wherein in the drying step, the hydrogel is dried while being rotated by the rotary tube and the hydrogel is scraped up by the lifter.
3. 3. The method for producing a water-absorbing resin composition according to claim 2, wherein the lifter is selected from the group consisting of a flat lifter and a C-shaped lifter to lift up the hydrogel.
4. The method for producing a water-absorbing resin composition according to claim 1, wherein in the drying step, hot air is passed through the rotating cylinder, and the hydrogel is dried by convection heat transfer by the hot air.
5. The method for producing a water-absorbing resin composition according to claim 4, wherein the hot air is supplied at a temperature of 200 to 500°C when the hot air is supplied into the rotating cylinder.
6. The method for producing a water-absorbing resin composition according to any one of claims 1 to 5, comprising a hydrophobic substance addition step of adding a hydrophobic substance (c) to the hydrogel before the drying step.
7. The water absorption according to claim 6, wherein the hydrophobic substance (c) is a hydrophobic substance (c1) containing a hydrocarbon group having 8 to 30 carbon atoms and/or a hydrophobic substance (c2) that is an organic polysiloxane. A method for producing a synthetic resin composition.
8. The manufacturing method according to claim 6, wherein the amount of the hydrophobic substance (c) is 0.001 to 1.0 parts by weight based on 100 parts by weight of the crosslinked polymer (A).
   

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