JP2012031278A - Absorbent resin particle, absorber comprising the same, and absorbent article - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem that conventional methods for reducing a residual monomer amount are inferior in absorbing performance.SOLUTION: The absorbent resin particle comprises a crosslinked polymer particle (A) comprising as an essential constituting unit a water-soluble vinyl monomer (a1) and/or a hydrolyzable vinyl monomer (a2) and an internal crosslinking agent (b) and has a residual monomer content of at most 500 ppm, a water retention for physiological saline of 30-50 g/g and gel strength of 1-3 kN/mafter deteriorated by artificial urine. Preferably the absorbent resin particle contains a hydrazide compound (c) in an amount of 0.001-10 wt.% based on the weight of the crosslinked polymer particle (A).

Description

  The present invention relates to absorbent resin particles, an absorbent body containing the same, and an absorbent article.

  Resins obtained by radical aqueous solution polymerization are used in a wide variety of applications. In any application, a resin having a small residual monomer amount is desired. In particular, regarding water-absorbent resins used in sanitary products such as disposable diapers and sanitary napkins, it is important not only to have excellent absorption performance but also to have a small amount of residual monomer from the viewpoint of safety.

As a method for reducing the amount of residual monomers, for example, an absorbent resin is used for polymerization using a Redox catalyst in which a specific kind of organic peroxide and a reducing substance are combined (Patent Documents 1 and 2). A method of adding a reducing agent after polymerization (Patent Document 3), a method of adding a peroxide or an azo compound after polymerization (Patent Document 4), a polymerization initiator that generates radicals at a temperature of 40 ° C. or less, and 10 hours A polymerization initiator having a relationship of [T-25 <T _1/2 <T (formula-1)] between the half-life temperature and the temperature (T) at which the polymerization rate reaches 95% is used in combination. A method (Patent Document 5) has been proposed.

JP-A-3-37212 Japanese National Patent Publication No. 5-507508 Japanese Patent Laid-Open No. 1-62317 JP-A-1-103644 JP 2000-26510 A

  However, the conventional method of reducing the amount of residual monomer using a large amount of polymerization initiator has a problem that the molecular weight of the resulting resin is low and the absorption performance is low. In addition, the method of adding an additive (reducing agent, oxidizing agent or azo compound) after polymerization is effective to some extent in reducing the amount of residual monomer, but radicals generated by decomposition of the additive are molecular chains of the polymer. There is a problem that the molecular weight is cut to lower the absorption performance. Moreover, although the method using two types of polymerization initiators having different reaction initiation temperatures is effective for reducing the residual monomer, there is a problem that the absorption performance is low because the molecular weight of the polymer does not increase.

The absorbent resin particles of the present invention contain crosslinked polymer particles (A) having water-soluble vinyl monomer (a1) and / or hydrolyzable vinyl monomer (a2) and internal crosslinking agent (b) as essential constituent units. And
The residual monomer is 500 ppm or less,
The water retention amount with respect to physiological saline is 30-50 g / g,
The gist is that the strength of artificial urine degradation gel is 1 to 3 kN / m ² .
The gist of the absorbent body of the present invention is that it contains the absorbent resin particles and a fibrous material.
The gist of the absorbent article of the present invention is that the absorbent article is provided.

  The absorbent resin particles of the present invention have very good absorption performance and a low residual monomer amount.

  The water-soluble vinyl monomer (a1) is not particularly limited and is known {for example, a vinyl monomer disclosed in Japanese Patent No. 3648553, Japanese Patent Laid-Open No. 2003-165883, Japanese Patent Laid-Open No. 2005-75982, Japanese Patent Laid-Open No. 2005-95759}. Etc. can be used.

  The hydrolyzable vinyl monomer (a2) means a vinyl monomer that becomes a water-soluble vinyl monomer (a1) by hydrolysis, and is not particularly limited (for example, Japanese Patent No. 3648553, JP-A No. 2003-165883, The vinyl monomer etc. of Unexamined-Japanese-Patent No. 2005-75982, Unexamined-Japanese-Patent No. 2005-95759} etc. can be used. The water-soluble vinyl monomer means a vinyl monomer having a property of dissolving at least 100 g in 100 g of water at 25 ° C. The term “hydrolyzable” refers to the property of being hydrolyzed by the action of 50 ° C. water and, if necessary, the catalyst (acid or base) to make it water-soluble. Hydrolysis of the hydrolyzable vinyl monomer may be performed either during polymerization, after polymerization, or both of them, but from the viewpoint of the molecular weight of the resulting absorbent resin particles, etc., is preferable.

  Of these, water-soluble vinyl monomers (a1) are preferred from the viewpoint of absorption characteristics, etc., more preferably anionic vinyl monomers, and more preferably carboxy (salt) groups, sulfo (salt) groups, amino groups, carbamoyl groups. Vinyl monomers having an ammonio group or a mono-, di- or tri-alkyl ammonio group, then preferably vinyl monomers having a carboxy (salt) group or a carbamoyl group, particularly preferably (meth) acrylic acid (salt) and (Meth) acrylamide, next particularly preferably (meth) acrylic acid (salt), most preferably acrylic acid (salt).

The “carboxy (salt) group” means “carboxy group” or “carboxylate group”, and the “sulfo (salt) group” means “sulfo group” or “sulfonate group”. Moreover, (meth) acrylic acid (salt) means acrylic acid, acrylate, methacrylic acid or methacrylate, and (meth) acrylamide means acrylamide or methacrylamide. Examples of the salt include an alkali metal (such as lithium, sodium and potassium) salt, an alkaline earth metal (such as magnesium and calcium) salt or an ammonium (NH ₄ ) salt. Among these salts, alkali metal salts and ammonium salts are preferable from the viewpoint of absorption characteristics and the like, more preferably alkali metal salts, and particularly preferably sodium salts.

  When either the water-soluble vinyl monomer (a1) or the hydrolyzable vinyl monomer (a2) is used as a structural unit, each may be used alone as a structural unit, or two or more kinds may be used as a structural unit if necessary. The same applies when the water-soluble vinyl monomer (a1) and the hydrolyzable vinyl monomer (a2) are used as constituent units. Further, when the water-soluble vinyl monomer (a1) and the hydrolyzable vinyl monomer (a2) are used as structural units, the content molar ratio (a1 / a2) is preferably 75/25 to 99/1, more preferably. 85/15 to 95/5, particularly preferably 90/10 to 93/7, and most preferably 91/9 to 92/8. Within this range, the absorption performance is further improved.

  As a structural unit of the absorbent resin particles, in addition to the water-soluble vinyl monomer (a1) and the hydrolyzable vinyl monomer (a2), other vinyl monomers (a3) copolymerizable therewith can be used as the structural unit. .

Other vinyl monomers (a3) that can be copolymerized are not particularly limited and are known {for example, Japanese Patent No. 3648553, Japanese Patent Application Laid-Open No. 2003-165883, Japanese Patent Application Laid-Open No. 2005-75982, Japanese Patent Application Laid-Open No. 2005-95759. } Can be used, and the following vinyl monomers (i) to (iii) can be used.
(I) C8-C30 aromatic ethylenic monomer Styrene such as styrene, α-methylstyrene, vinyltoluene and hydroxystyrene, and halogen substituted products of styrene such as vinylnaphthalene and dichlorostyrene.
(Ii) C2-C20 aliphatic ethylene monomer Alkene [ethylene, propylene, butene, isobutylene, pentene, heptene, diisobutylene, octene, dodecene, octadecene, etc.]; and alkadiene [butadiene, isoprene, etc.], etc.
(Iii) C5-C15 alicyclic ethylene monomer Monoethylenically unsaturated monomer [pinene, limonene, indene and the like]; and polyethylene vinyl polymerizable monomer [cyclopentadiene, bicyclopentadiene, ethylidene norbornene and the like] and the like.

  When the other vinyl monomer (a3) is used as a constituent unit, the content (mol%) of the other vinyl monomer (a3) unit is that of the water-soluble vinyl monomer (a1) unit and the hydrolyzable vinyl monomer (a2) unit. Based on the number of moles, 0.01 to 5 is preferable, more preferably 0.05 to 3, then preferably 0.08 to 2, and particularly preferably 0.1 to 1.5. From the viewpoint of absorption characteristics and the like, the content of other vinyl monomer (a3) units is most preferably 0 mol%.

There are no particular limitations on the crosslinking agent (b), and known crosslinking agents such as those disclosed in known {eg, Japanese Patent No. 3648553, Japanese Patent Laid-Open No. 2003-165883, Japanese Patent Laid-Open No. 2005-75982, Japanese Patent Laid-Open No. 2005-95759}, and the like. Can be used.
Among these, from the viewpoint of absorption characteristics, etc., a crosslinking agent having two or more ethylenically unsaturated groups is preferable, more preferably a poly (meth) allyl ether of a polyol having 2 to 10 carbon atoms, particularly preferably triallylsia. Nurate, triallyl isocyanurate, tetraallyloxyethane and pentaerythritol triallyl ether, most preferably pentaerythritol triallyl ether.

  The content (mol%) of the crosslinking agent (b) unit is preferably 0.001 to 5, more preferably, based on the number of moles of the water-soluble vinyl monomer (a1) unit and the hydrolyzable vinyl monomer (a2) unit. Is 0.005 to 3, particularly preferably 0.01 to 1. Within this range, the absorption characteristics are further improved.

  The crosslinked polymer particles (A) may be one kind or a mixture of two or more kinds.

  The crosslinked polymer particles (A) may be produced by known aqueous solution polymerization (adiabatic polymerization, thin film polymerization, spray polymerization method, etc .; JP-A-55-133413, etc.) or known reverse phase suspension polymerization (JP-B-54-30710). , JP-A 56-26909 and JP-A 1-5808, etc.}. Among the polymerization methods, the solution polymerization method is preferable, and an aqueous solution polymerization method is particularly preferable because it is not necessary to use an organic solvent and is advantageous in terms of production cost.

  Water-containing gel obtained by polymerization {consists of a crosslinked polymer and water. } Can be shredded as necessary. The size (longest diameter) of the gel after chopping is preferably 50 μm to 10 cm, more preferably 100 μm to 2 cm, and particularly preferably 1 mm to 1 cm. Within this range, the drying property in the drying process is further improved.

  Shredding can be performed by a known method, and can be shredded using a normal shredding device {for example, a bex mill, rubber chopper, pharma mill, mincing machine, impact crusher and roll crusher}. .

  When using a solvent (organic solvent, water, etc.) for the polymerization, it is preferable to distill off the solvent after the polymerization. When the solvent contains an organic solvent, the content (% by weight) of the organic solvent after the distillation is preferably 0 to 10, more preferably 0 to 5, particularly preferably 0, based on the weight of the absorbent resin particles. ~ 3, most preferably 0-1. It is. Within this range, the absorption performance (particularly the water retention amount) of the absorbent resin particles is further improved.

  When water is contained in the solvent, the water content (% by weight) after distillation is preferably from 3 to 20, more preferably from 3.5 to 10, particularly preferably from 4 to 9, based on the weight of the crosslinked polymer. Most preferably, it is 4.5-8. Within this range, the absorption performance and the breakability of the absorbent resin particles after drying are further improved.

  In addition, the content and water content of the organic solvent are infrared moisture measuring devices {JE400 manufactured by KETT Co., Ltd .: 120 ± 5 ° C., 30 minutes, atmospheric humidity before heating 50 ± 10% RH, lamp specification 100V, It is calculated | required from the weight loss of the measurement sample before and behind heating when heated by 40W}.

  As a method of distilling off the solvent (including water), a method of distilling (drying) with hot air at a temperature of 80 to 230 ° C, a thin film drying method using a drum dryer heated to 100 to 230 ° C, (heating) Vacuum drying, freeze drying, infrared drying, decantation, filtration, and the like can be applied.

  The crosslinked polymer can be pulverized after drying. The pulverization method is not particularly limited, and a normal pulverizer (for example, a hammer-type pulverizer, an impact-type pulverizer, a roll-type pulverizer, and a shet airflow-type pulverizer) can be used. The pulverized crosslinked polymer can be adjusted in particle size by sieving or the like, if necessary.

  The weight average particle diameter (μm) of the crosslinked polymer particles (A) when screened if necessary is preferably 100 to 800, more preferably 200 to 700, next preferably 250 to 600, particularly preferably 300 to 500. Most preferably, it is 350-450. Within this range, the absorption performance is further improved.

  In addition, the weight average particle diameter was measured using a low-tap test sieve shaker and a standard sieve (JIS Z8801-1: 2006), Perry's Chemical Engineers Handbook, 6th edition (Mac Glow Hill Book, 1984). , Page 21). That is, JIS standard sieves are combined in the order of 1000 μm, 850 μm, 710 μm, 500 μm, 425 μm, 355 μm, 250 μm, 150 μm, 125 μm, 75 μm and 45 μm, and a tray from the top. About 50 g of the measured particles are put in the uppermost screen and shaken for 5 minutes with a low-tap test sieve shaker. Weigh the measured particles on each sieve and the pan, and calculate the weight fraction of the particles on each sieve with the total as 100% by weight. This value is the logarithmic probability paper {the horizontal axis is the sieve aperture (particle size ), The vertical axis is plotted in the weight fraction}, a line connecting the points is drawn, and the particle diameter corresponding to the weight fraction of 50% by weight is obtained, and this is defined as the weight average particle diameter.

  Further, since the absorption performance is better when the content of fine particles is smaller, the content of fine particles of 106 μm or less (preferably 150 μm or less) in the total particles is preferably 3% by weight or less, more preferably 1% by weight or less. It is. The content of the fine particles can be determined using a plot created when determining the above weight average particle diameter.

  The apparent density (g / ml) of the crosslinked polymer particles (A) is preferably 0.54 to 0.70, more preferably 0.56 to 0.65, and particularly preferably 0.58 to 0.60. . Within this range, the absorption performance is further improved. The apparent density is measured at 25 ° C. according to JIS K7365: 1999.

  The shape of the crosslinked polymer particles (A) is not particularly limited, and examples thereof include an irregularly crushed shape, a flake shape, a pearl shape, and a rice grain shape. Among these, from the viewpoint of good entanglement with the fibrous material in the use of paper diapers and the like and no fear of dropping off from the fibrous material, an irregular crushed shape is preferable.

  The cross-linked polymer particles (A) may be surface-crosslinked with a surface cross-linking agent as required. Examples of the surface cross-linking agent include polyvalent glycidyl described in JP-A No. 59-189103, JP-A No. 58- Polyhydric alcohols, polyhydric amines, polyhydric aziridines and polyhydric isocyanates described in JP-A No. 180233 or JP-A No. 61-16903, JP-A No. 61-212305 or JP-A No. 61-252212, etc. And polyvalent metals described in JP-A No. 51-136588 or JP-A No. 61-257235, and the like. Of these surface cross-linking agents, polyvalent glycidyl, polyvalent amine and silane coupling agent are preferable from the viewpoint of absorption characteristics and breakability of absorbent resin particles, more preferably polyvalent glycidyl and silane coupling agent, Polyvalent glycidyl is preferred. Among polyvalent glycidyl, ethylene glycol diglycidyl ether and glycerin diglycidyl ether are preferable, and ethylene glycol diglycidyl ether is particularly preferable.

  The content (% by weight) of the surface cross-linking agent is preferably 0.01 to 0.10, more preferably 0.03 to 0, based on the weight of the cross-linked polymer particles (A) from the viewpoint of absorption performance and the like. .8, particularly preferably 0.05 to 0.06.

  When performing surface crosslinking, the surface crosslinking method may be a known method {for example, the method disclosed in JP-A No. 13-2935, JP-A No. 2003-147005, or JP-A No. 2003-165883}. Can do.

  The surface crosslinking may be performed by repeating the above surface crosslinking twice or more. That is, the absorbent resin particles obtained by surface cross-linking with a surface cross-linking agent can be subjected to additional surface cross-linking with the same or different surface cross-linking agents. The content of the additional surface crosslinking agent, the treatment method, the treatment temperature, the treatment time, etc. are the same as in the above case.

  The absorbent resin particles of the present invention preferably further contain a hydrazide compound (c). The content (% by weight) of the hydrazide compound (c) is preferably 0.001 to 10, more preferably 0.01 to 5, particularly preferably 0.1 based on the weight of the crosslinked polymer particles (A). ~ 2. Within this range, the residual monomer amount of the absorbent resin particles is further reduced.

  The hydrazide compound (c) refers to a compound containing one or more hydrazide groups in one molecule. The hydrazide compound used in the present invention includes a monohydrazide compound having one hydrazide group in one molecule, a dihydrazide compound having two hydrazide groups in one molecule, and three or more hydrazide groups in one molecule. The polyhydrazide compound which has is mentioned.

  Monohydrazide compounds include form hydrazide, acetohydrazide, propionic acid hydrazide, salicylic acid hydrazide, benzoic acid hydrazide, lauric acid hydrazide, naphthoic acid hydrazide, p-hydroxybenzoic acid hydrazide, methyl carbazate, ethyl carbazate and semicarbazide hydrochloride A salt etc. can be mentioned.

  Examples of the dihydrazide compounds include oxalic acid dihydrazide, malonic acid dihydrazide, succinic acid dihydrazide, glutamic acid dihydrazide, adipic acid dihydrazide, pimelic acid dihydrazide, suberic acid dihydrazide, azelaic acid dihydrazide, sebacic acid dihydrazide dihydradide dihydradide Acid dihydrazide tartaric acid dihydrazide, malic acid dihydrazide, iminodiacetic acid dihydrazide, itaconic acid dihydrazide, dodecanedihydrazide, hexadecanedihydrazide, naphthodihydrazide, benzenedihydrazide, pyridinedihydrazide, cyclohexanedihydrazide and pyromellitic dihydride

  Examples of the polyhydrazide compound include citric acid trihydrazide, nitriloacetic acid trihydrazide, cyclohexanetricarboxylic acid trihydrazide, ethylenediaminetetraacetic acid tetrahydrazide, naphthoic acid tetrahydrazide, and polyacrylic acid hydrazide.

  Among the above hydrazide compounds, hydrazide in which oxalic acid dihydrazide, malonic acid dihydrazide, succinic acid dihydrazide, glutamic acid dihydrazide, adipic acid dihydrazide, citric acid trihydrazide, trinitroacetic acid trihydrazide, and naphthoic acid tetrahydrazide react with each other. The amount is large, which is preferable from the viewpoint of the residual monomer amount reducing effect.

  The absorbent resin particles of the present invention preferably contain part or all of the hydrazide compound (c) in the interior of the absorbent resin particles from the viewpoint of reducing the residual monomer amount of the absorbent resin particles. The hydrazide compound (c) may be contained in any manner.

  The structure comprising a part or all of the hydrazide compound (c) inside the absorbent resin particles comprises: (1) a hydrogel of the hydrazide compound (c) and the crosslinked polymer particles (A). It can be produced by a method of mixing and kneading, or (2) a method of polymerizing structural units in the presence of the hydrazide compound (c) to obtain a hydrogel of the crosslinked polymer particles (A).

The mixing method of the crosslinked polymer particles (A) and the hydrazide compound (c) is not limited as long as the hydrazide compound (c) is mixed so as to exist inside the crosslinked polymer particles (A).
However, the hydrazide compound (c)) is preferably mixed with the hydrogel of (A) or the polymerization solution of (A), not the dried product of the crosslinked polymer particles (A), more preferably (A). It is to be mixed with a hydrous gel. In addition, it is preferable to mix uniformly so that mixing may be carried out.
When the crosslinked polymer particles (A) are obtained by the aqueous solution polymerization method, the timing for mixing and kneading the hydrazide compound (c) and (A) is not particularly limited, but during the polymerization process, immediately after the polymerization process, Examples thereof include crushing (minching) and drying of the hydrogel. Among these, from the viewpoint of the polymerization behavior of the absorbent resin particles, it is preferable to be immediately after the polymerization step and during the water-containing gel crushing (mincing) step, more preferably during the water-containing gel crushing (mincing) step.

  When the crosslinked polymer particles (A) are obtained by the reverse phase suspension polymerization method or emulsion polymerization, the timing of mixing the hydrazide compound (c) and (A) is not particularly limited, but during the polymerization step {(c) In the presence of (A)}, immediately after the polymerization step, during the dehydration step (in the step of dehydrating to a water content of about 10% by weight), immediately after the dehydration step, and after the dehydration step, the step of separating and distilling off the organic solvent used in the polymerization For example, during the drying of the hydrogel. Among these, from the viewpoint of the polymerization behavior of the absorbent resin particles, etc., preferably immediately after the polymerization step, during the dehydration step, immediately after the dehydration step, and during the step of separating and distilling off the organic solvent used for the polymerization, more preferably immediately after the polymerization step The dehydration process is in progress.

  In the case of mixing during the hydrogel crushing (minching) step, as a mixing device, usual devices such as a Bex mill, rubber chopper, pharma mill, mincing machine, impact pulverizer, and roll pulverizer can be used. When mixing in the polymerization solution, a device having a relatively high stirring force such as a homomixer or a biomixer can be used. Moreover, when mixing in drying of a hydrogel, kneading apparatuses, such as SV mixer, can also be used.

  The mixing temperature (° C.) is preferably 20 to 100, more preferably 40 to 90, and particularly preferably 50 to 80. Within this range, it becomes easier to mix uniformly, and the effect of reducing the residual monomer amount is further improved.

  In the method for producing the crosslinked polymer particles (A) in the presence of the hydrazide compound (c), the hydrazide compound (c) is dissolved or emulsified (dispersed) in the polymer solution of the crosslinked polymer particles (A). Polymerization of (A) can be performed. The polymerization method is the same as in the case of the crosslinked polymer particles (A) except that the polymerization is performed in the presence of the hydrazide compound (c).

The hydrazide compound (c) can also be used in a form dissolved and / or emulsified in water and / or a volatile solvent (however, no emulsifier is used). The volatile solvent preferably has a vapor pressure (Pa) at 20 ° C. of 0.13 to 5.3, more preferably 0.15 to 4.5, particularly preferably, from the viewpoint of easy removal. Is from 0.23 to 3.8.
Examples of the volatile solvent include alcohols having 1 to 3 carbon atoms (such as methanol, ethanol and isopropyl alcohol), hydrocarbons having 5 to 8 carbon atoms (such as pentane, hexane, cyclohexane and toluene), and ethers having 2 to 4 carbon atoms ( Dimethyl ether, diethyl ether, tetrahydrofuran, etc.), C3-C4 ketones (acetone, methyl ethyl ketone, etc.), C3-C5 esters (ethyl formate, ethyl acetate, isopropyl acetate, diethyl carbonate, etc.) and the like. When using water and / or a volatile solvent, these usage-amount (weight%) is preferable 1-900 based on the weight of a hydrazide compound (c), More preferably, it is 5-700, Most preferably, it is 10 ~ 400. When water and a volatile solvent are used, the amount (% by weight) of water used is preferably from 50 to 98, more preferably from 60 to 95, particularly preferably from 70 to 90, based on the weight of water and the volatile solvent. It is.

The water-containing gel containing the hydrazide compound (c) can be chopped as necessary. The size (longest diameter) of the hydrogel particles after chopping is preferably 50 μm to 10 cm, more preferably 100 μm to 2 cm, and particularly preferably 1 mm to 1 cm. Within this range, the drying property in the drying process is further improved.
As the shredding method, the same method as in the case of the crosslinked polymer particles (A) can be adopted.

In the water-absorbent resin particles of the present invention, an optional step {the cross-linked polymer particle (A) production step, a polymerization step, a crushing step, a drying step, a crushing step, a surface cross-linking step and / or a step of these steps, if necessary. Before and after and after the step of mixing the crosslinked polymer particles (A) and the hydrazide compound (c), etc.}, additives can be added.
As additives, known additives (for example, Japanese Patent Application Laid-Open No. 2003-225565) {preservatives, fungicides, antibacterial agents, antioxidants, ultraviolet absorbers, colorants, fragrances, deodorants, and organic fibers Etc.}, etc., and one or more of these may be used in combination.

  The residual monomer (ppm) of the absorbent resin particles of the present invention is 500 or less, preferably 15 to 450, more preferably 30 to 400, from the viewpoint of anti-fogging property of the absorbent article. The residual monomer of the absorbent resin particles is measured by the following method.

<Method for measuring residual monomer of absorbent resin particles>
1 g of the water-absorbing resin is dispersed in 249 g of physiological saline, and the residual monomer is extracted for 3 hours with stirring at 25 ° C. ± 2 ° C. The solution is filtered and the filtrate is analyzed by liquid chromatography according to known methods. The residual monomer amount is determined by converting the measured monomer content in the filtrate per 1 g of resin.

  The water retention amount (g / g) of the absorbent resin particles of the present invention with respect to physiological saline is 30 to 50, preferably 32 to 48, more preferably 34 to 45, from the viewpoint of anti-fogging property of the absorbent article. It is. The water retention amount of the absorbent resin particles is measured by the following method.

<Measurement method of water retention amount of absorbent resin particles>
1.00 g of a measurement sample is put into a tea bag (20 cm long, 10 cm wide) made of a nylon net having a mesh size of 63 μm (JIS Z8801-1: 2006), and 1,000 ml of physiological saline (saline concentration 0.9% by weight). After soaking for 1 hour without stirring, hang for 15 minutes and drain. Thereafter, each tea bag is placed in a centrifuge, centrifuged at 150 G for 90 seconds to remove excess physiological saline, and the weight (h1) including the tea bag is measured to obtain the water retention amount from the following equation. In addition, the temperature of the physiological saline used and measurement atmosphere shall be 25 degreeC +/- 2 degreeC.
The weight of the tea bag after centrifugal dehydration is measured (h2) in the same manner as above except that no measurement sample is used.

  Water retention amount (g / g) = (h1)-(h2)

The artificial urine deterioration gel strength (kN / m ² ) of the absorbent resin particles of the present invention is 1 to 3, preferably 1.2 to 2.8, from the viewpoint of stability during long-term use of the absorbent article. More preferably, it is 1.5 to 2.6. In addition, the artificial urine deterioration gel strength of the absorbent resin particles is measured by the following method.
<Measurement of artificial urine degradation gel strength>
Artificial urine (0.03% by weight of calcium chloride, 0.08% by weight of magnesium sulfate, 0.8% by weight of sodium chloride, 99.09% by weight of ion-exchanged water) is added to 1 g of a measurement sample having an absorbent resin particle size of 250 μm to 500 μm. ) After adding 39 g and preparing a 40-fold gel, the 40-fold gel is kept in a sealed container at 40 ° C. for 3 hours and then allowed to cool to room temperature. 0.1 g of the cooled gel is weighed and placed flat on a table of a creep meter (manufactured by Yamaden, model RE-3305). Load the gel 40 times at a constant speed (10 mm / min) with a probe having a cross-sectional area of 2 cm ² (0.1 kgf to 10 kgf), measure the continuously changing stress, and measure the stress corresponding to the maximum peak height. As F (g), the gel elastic modulus is calculated from the following equation.

Artificial urine deterioration gel strength (kN / m ² ) = F × 98 / 3.333 / 1000

By applying the water-absorbent resin particles of the present invention to various absorbers, an absorbent article having excellent absorption performance can be produced. The absorber and the absorbent article are manufactured by a known method (for example, Japanese Patent Application Laid-Open No. 2005-186016).
Absorbent articles include sanitary products {paper diapers (children's disposable diapers and adult disposable diapers, etc.), napkins (sanitary napkins, etc.), vomiting absorption etiquette bags, paper towels, pads (incontinence pads and surgical underpads) Etc.) and pet sheets (pet urine absorption sheets, heat insulation sheets, etc.)} and various household and industrial absorption sheets {freshness maintenance sheets, drip absorption sheets, paddy rice seedling sheets, concrete curing sheets and cables, etc. Running prevention sheet, etc.}.
Among these, the water-absorbent resin particles of the present invention are suitable for sanitary goods, and further suitable for paper diapers, pads and sanitary napkins, particularly paper diapers and sanitary napkins.

  Hereinafter, although an example and a comparative example explain the present invention further, the present invention is not limited to these. Unless otherwise specified, “part” means “part by weight” and “%” means “% by weight”. In addition, the residual monomer of the absorbent resin particles, the water retention amount, and the artificial urine deterioration gel strength were measured by the methods described above.

<Example 1>
Water-soluble vinyl monomer (a1) {acrylic acid, manufactured by Mitsubishi Chemical Corporation, purity 100%} 155 parts (2.15 mole parts), crosslinking agent (b) {pentaerythritol triallyl ether, manufactured by Daiso Corporation} 0 6225 parts (0.0024 mole part) and 340.27 parts deionized water were kept at 3 ° C. with stirring and mixing. Nitrogen was introduced into the mixture to reduce the dissolved oxygen amount to 1 ppm or less, and then 0.62 part of 1% aqueous hydrogen peroxide solution and 1.1625 part of 2% ascorbic acid aqueous solution were added and mixed to initiate polymerization. . After the temperature of the mixture reached 90 ° C., a water-containing gel was obtained by polymerization at 90 ± 2 ° C. for about 5 hours.
Next, the hydrated compound (c) was mixed by adding 128.42 parts of 48.5% sodium hydroxide aqueous solution while chopping 502.27 parts of this hydrogel with a mincing machine (12VR-400K manufactured by ROYAL). 1.9 parts of {citric acid hydrazide} were added and mixed to obtain a chopped gel. Further, the chopped gel was dried with a ventilation type band dryer {150 ° C., wind speed 2 m / sec} to obtain a dried product. The dried product was pulverized with a juicer mixer (Osterizer BLENDER manufactured by Oster Co., Ltd.), and then adjusted to a particle size of 150 to 710 μm using a 150 and 710 μm sieve to obtain dried particles. While stirring 100 parts of the dry particles (high-speed stirring turbulizer manufactured by Hosokawa Micron: rotation speed 2000 rpm), a 2% water / methanol mixed solution of ethylene glycol diglycidyl ether (water / methanol weight ratio = 70/30). 5 parts of was added while being sprayed and mixed, and left to stand at 150 ° C. for 30 minutes to crosslink the surface to obtain absorbent resin particles. The absorbent resin particles of the present invention were added by impregnating 100 parts of the absorbent resin particles with high-speed stirring (high-speed stirring turbulizer manufactured by Hosokawa Micron: rotation speed: 2000 rpm) while adding 7 parts of water while spraying. (1) was obtained. The weight average particle diameter of the absorbent resin particles (1) was 395 μm, the apparent density was 0.58 g / ml, and the water content was 6%.

<Example 2>
Except that “hydrazide compound (c) {1.9 parts of citrate hydrazide}” was changed to “hydrazide compound (c) {1.9 parts of succinate dihydrazide}”, in the same manner as in Example 1, Absorbent resin particles (2) were obtained. The weight average particle diameter of the absorbent resin particles (2) was 390 μm, the apparent density was 0.58 g / ml, and the water content was 6%.

<Example 3>
Except that “hydrazide compound (c) {1.9 parts citric acid hydrazide} 1.9 parts” was changed to “hydrazide compound (c) {1.9 parts lauric acid hydrazide}”, in the same manner as in Example 1, Absorbent resin particles (3) were obtained. The weight average particle diameter of the absorbent resin particles (3) was 400 μm, the apparent density was 0.58 g / ml, and the water content was 6%.

<Example 4>
Except for changing “hydrazide compound (c) {1.9 parts of citrate hydrazide} 1.9 parts” to “hydrazide compound (c) {0.5 parts of citrate hydrazide}”, in the same manner as in Example 1, Absorbent resin particles (4) were obtained. The weight average particle diameter of the absorbent resin particles (4) was 395 μm, the apparent density was 0.58 g / ml, and the water content was 6%.

<Example 5>
Except that “hydrazide compound (c) {1.9 parts citric acid hydrazide} 1.9 parts” was changed to “5.7 parts hydrazide compound (c) {citric acid hydrazide}}”, the same as in Example 1 was carried out. Absorbent resin particles (5) were obtained. The weight average particle diameter of the absorbent resin particles (5) was 405 μm, the apparent density was 0.60 g / ml, and the water content was 6%.

<Comparative Example 1>
Water-soluble vinyl monomer (a1) {acrylic acid, manufactured by Mitsubishi Chemical Corporation, purity 100%} 155 parts (2.15 mole parts), crosslinking agent (b) {pentaerythritol triallyl ether, manufactured by Daiso Corporation} 0 6225 parts (0.0024 mole part) and 340.27 parts deionized water were kept at 3 ° C. with stirring and mixing. Nitrogen was introduced into the mixture to reduce the dissolved oxygen amount to 1 ppm or less, and then 0.62 part of 1% aqueous hydrogen peroxide solution, 1.1625 part of 2% aqueous ascorbic acid solution and 2% 2,2′-azobis [ 2.325 parts of 2-methyl-N- (2-hydroxyethyl) -propionamide] aqueous solution was added and mixed to initiate polymerization. After the temperature of the mixture reached 90 ° C., a water-containing gel was obtained by polymerization at 90 ± 2 ° C. for about 5 hours.
Next, 128.42 parts of 48.5% sodium hydroxide aqueous solution was added and mixed while chopping 502.27 parts of this hydrogel with a mincing machine (12VR-400K manufactured by ROYAL) to obtain a chopped gel. . Further, the chopped gel was dried with a ventilation type band dryer {150 ° C., wind speed 2 m / sec} to obtain a dried product. The dried product was pulverized with a juicer mixer (Osterizer BLENDER manufactured by Oster Co., Ltd.), and then adjusted to a particle size of 150 to 710 μm using a 150 and 710 μm sieve to obtain dried particles. While stirring 100 parts of the dry particles (high-speed stirring turbulizer manufactured by Hosokawa Micron: rotation speed 2000 rpm), a 2% water / methanol mixed solution of ethylene glycol diglycidyl ether (water / methanol weight ratio = 70/30). 5 parts of was added while being sprayed and mixed, and left to stand at 150 ° C. for 30 minutes to crosslink the surface to obtain absorbent resin particles. By further impregnating 100 parts of the absorbent resin particles with high-speed stirring (high-speed stirring turbulizer manufactured by Hosokawa Micron: rotation speed: 2000 rpm) while spraying with 7 parts of water, comparative absorbent resin particles ( H1) was obtained. The weight average particle diameter of the absorbent resin particles (H1) was 397 μm, the apparent density was 0.58 g / ml, and the water content was 6%.

<Comparative example 2>
Comparative absorbent resin particles (as in Example 1 except that “1.9 parts of the hydrazide compound (c) {citrate hydrazide}}” were changed to “1.9 parts of a 15.8% aqueous sodium sulfite solution” ( H2) was obtained. The weight average particle diameter of the absorbent resin particles (H2) was 390 μm, the apparent density was 0.58 g / ml, and the water content was 6%.

<Comparative Example 3>
Comparative absorbent resin particles (as in Example 1 except that “1.9 parts of the hydrazide compound (c) {citrate hydrazide}}” were changed to “5.7 parts of a 15.8% aqueous sodium sulfite solution” ( H3) was obtained. The weight average particle diameter of the absorbent resin particles (H3) was 380 μm, the apparent density was 0.59 g / ml, and the water content was 6%.

<Comparative example 4>
Comparative absorptive resin particles (in the same manner as in Example 1, except that “1.9 parts of hydrazide compound (c) {citrate hydrazide}}” was changed to “0.5 part of 15.8% sodium sulfite aqueous solution”. H4) was obtained. The weight average particle diameter of the absorbent resin particles (H4) was 380 μm, the apparent density was 0.59 g / ml, and the water content was 6%.

  About the absorptive resin particles obtained in Examples 1 to 5 and Comparative Examples 1 to 4, measured physical properties {weight average particle diameter, apparent density}, residual monomer and performance evaluation results {water retention amount, artificial urine deterioration gel strength } Is shown in Table 1. In addition,% shows content (weight%) based on the weight of a crosslinked polymer (A).

  From the results of Table 1, the absorbent resin particles (1) to (5) of the present invention obtained in Examples 1 to 5 satisfy all the physical property values of residual monomer, water retention amount and artificial urine deterioration gel strength. In contrast, the comparative absorbent resin particles (H1) to (H4) of Comparative Examples 1 to 4 have a large amount of residual monomer, or the residual monomer is reduced, but the absorption performance is reduced, and absorption A dramatic improvement in both performance and residual monomer is observed.

  The absorbent resin particles of the present invention can be applied to an absorbent body containing absorbent resin particles and a fibrous material, and absorbent articles {paper diapers, sanitary napkins, and medical blood retaining bodies comprising the absorbent body. It is useful for the agent}. In addition, pet urine absorbent, urine gelling agent for portable toilets, freshness preservation agent for fruits and vegetables, drip absorbent for meat and seafood, cooler, disposable warmer, battery gelling agent, water retention agent for plants and soil, dew condensation It can also be used in various applications such as inhibitors, water-stopping agents, packing agents and artificial snow.

Claims (4)

It contains crosslinked polymer particles (A) having water-soluble vinyl monomer (a1) and / or hydrolyzable vinyl monomer (a2) and internal crosslinking agent (b) as essential constituent units,
The residual monomer is 500 ppm or less,
The water retention amount with respect to physiological saline is 30-50 g / g,
Absorbent resin particles having an artificial urine degradation gel strength of 1 to 3 kN / m ² . The absorptive resin particle of Claim 1 formed by containing 0.001-10 weight% of hydrazide compounds (c) based on the weight of a crosslinked polymer particle (A). The absorber formed by containing the absorptive resin particle of Claim 1 or 2, and a fibrous material. An absorbent article comprising the absorbent body according to claim 3.