JP2010094656A - Water absorbing agent prepared by sticking fine particle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a water absorbing agent which is excellent in absorption rate, absorption speed, liquid permeability and deodorization property and maintains the performance for a long period of time. <P>SOLUTION: The water absorbing agent is prepared by sticking organic fine particles and/or inorganic fine particles to the surface of an acid group-containing water absorptive resin particle, wherein an acid group-neutralization rate on the surface of the water absorbing agent is less than the acid group-neutralization rate on the interior of the water absorptive resin particle. Preferably, the water absorbing agent is prepared by treating the surface with treating liquid containing an acid group-containing radically polymerizable compound. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a water-absorbing agent formed by adhering fine particles. More specifically, the present invention relates to a water absorbent and an absorbent article that are suitably used for sanitary materials such as disposable diapers, sanitary napkins, and incontinence pads.

  Conventionally, a water-absorbing resin has been used as a constituent material of sanitary materials that absorb sanitary cotton, disposable diapers, or other body fluids. Examples of such a water-absorbing resin include a hydrolyzate of starch-acrylonitrile graft polymer, a neutralized product of starch-acrylic acid graft polymer, a saponified product of vinyl acetate-acrylic ester copolymer, and an acrylonitrile copolymer. Examples thereof include hydrolysates of polymers or acrylamide copolymers, cross-linked products thereof, and cross-linked products of partially neutralized polyacrylic acid. All of these have an internal crosslinking structure and are insoluble in water.

  Properties desired for such a water-absorbent resin include a high absorption rate, an excellent absorption rate, a deodorizing property, an antibacterial property, and the like.

In order to improve the above-described characteristics, the water-absorbent resin is subjected to various treatments.
For example, the following literature is mentioned as a water-absorbing agent composition excellent in absorption characteristics and deodorizing properties.
In Patent Document 1 (Japanese Patent Laid-Open No. 2004-156010, US Patent Publication No. 20040048955), an extract of semi-fermented tea and / or an extract of fermented tea and the surface portion and / or the vicinity thereof were surface-treated with a crosslinking agent. A water absorbent composition containing a water absorbent resin is disclosed.

In Patent Document 2 (Special Tables 2004-530777, WO2003 / 002623), an acidic highly swellable hydrogel having a pH ≦ 5.7, specifically, based on a polyacrylic acid having a neutralization degree of preferably ≦ 60 mol% A hydrogel is disclosed.
Moreover, the following documents are mentioned as what is excellent in absorption characteristics, such as an absorption rate.

  Patent Document 3 (Japanese Patent Laid-Open No. 11-333292) discloses a water-absorbing agent in which water-absorbing fine particles having an absorption ratio lower than that of the water-absorbing resin particles are fixed to the surface of the water-absorbing resin particles. Yes.

  Patent Document 4 (Japanese Translation of PCT International Publication No. 2008-526502) discloses a granulated product of water-absorbing resin fine powder that exhibits a high water absorption rate, and polyhydric alcohol, polycarboxylic acid, and water are used as a granulating agent. .

  Furthermore, Patent Document 5 (U.S. Pat. No. 7,204,1941), Patent Document 6 (WO 2006/062253), and the like are listed as techniques for performing surface treatment by adding a treatment liquid containing a radical polymerizable compound.

US Patent Publication No. 20040048955 Special Table 2004-530777 JP 11-333292 A Special table 2008-526502 U.S. Pat. International Publication No. 2006/062253 Pamphlet

  An object of the present invention is to provide a water-absorbing agent excellent in absorption capacity, absorption rate, liquid permeability, and deodorizing property. It is another object of the present invention to provide a water-absorbing agent that can maintain the performance for a long time without adhering fine particles adhering to it even if it absorbs water and swells.

In order to solve the above problems, the present inventor has intensively studied. As a result, the following water-absorbing agent and absorbent article could be found.
(1) A water-absorbing agent in which organic fine particles and / or inorganic fine particles are fixed on the surface of acid group-containing water-absorbing resin particles, and the acid group neutralization rate on the surface of the water-absorbing agent is determined in the water-absorbing resin particles. A water-absorbing agent characterized by being less than the acid group neutralization rate.
(2) The water-absorbing agent according to (1), wherein the water-absorbing agent is surface-treated with a treatment liquid containing an acid group-containing radically polymerizable compound.
(3) The water-absorbing agent according to (1) or (2), wherein the acid group neutralization rate inside the water-absorbent resin particles is more than 40 mol% and 90 mol% or less.
(4) The water-absorbing agent according to (2) or (3), wherein the neutralization rate of the acid group-containing radically polymerizable compound contained in the treatment liquid is 0 to 30 mol%.
(5) The water-absorbing agent according to any one of (1) to (4), wherein the water-absorbent resin particles have a mass average particle diameter of 150 μm or more and 850 μm or less.
(6) The water-absorbing agent according to any one of (1) to (5), wherein the fine particles have a mass average particle diameter of less than 150 μm.
(7) An absorbent article comprising the water-absorbing agent according to any one of (1) to (6).

  The water-absorbing agent of the present invention, which has excellent absorption capacity, absorption speed, liquid permeability, and deodorizing property, is firmly fixed on the surface of the water-absorbent resin particles. Performance can be maintained for a long time.

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

  In the present invention, “weight” is treated as a synonym for “mass”, “weight%” is treated as a synonym for “mass%”, and “weight ppm” is treated as a synonym for “mass ppm”.

  The present invention relates to a water-absorbing agent in which organic fine particles and / or inorganic fine particles are fixed to the surface of acid group-containing water-absorbing resin particles, and the acid group neutralization rate on the surface of the water-absorbing agent is determined by the water-absorbing resin particles. It is a water-absorbing agent characterized by being less than the internal acid group neutralization rate.

As the method for producing the water-absorbing agent, the raw materials and production methods disclosed in US Pat. No. 7,204,941 and International Publication No. 2006/062253 may be adopted as appropriate. Preferably, as the surface treatment method of the water absorbent resin, a) Acid group-containing radical polymerizable compound with respect to a mixture of 100 parts by weight of acid group-containing water absorbent resin particles (converted to a solid content of 100% by weight) and fine particles A step of mixing 0.1 to 20 parts by weight and 5 to 20 parts by weight of water, and b) a step of polymerizing the acid group-containing radical polymerizable compound, and neutralizing the acid group-containing radical polymerizable compound The rate is 0 to 30 mol%, and the surface of the water-absorbing agent is lower than the neutralization rate inside the water-absorbent resin particles.
In the preferred embodiment, the acid group-containing water-absorbent resin particles are premixed with organic fine particles and / or inorganic fine particles, and / or the organic fine particles and / or inorganic fine particles contain the acid group-containing radical polymerizable compound and water. By dispersing in the treatment liquid, the water absorbing agent to which the fine particles of the present invention are finally fixed is obtained.

  Hereinafter, the characteristic part of the water-absorbing agent according to the present invention will be described. However, the scope of the present invention is not limited to these descriptions, and changes other than the following examples are made as appropriate without departing from the spirit of the present invention. Can be implemented.

(A) Water absorbent resin (particles)
The water-absorbing resin that can be used in the present invention is a water-swellable, water-insoluble crosslinked polymer that can form a hydrogel. In the present invention, “water swellability” means that the free swelling ratio is essentially 2 g / g or more, preferably 5 to 100 g / g, more preferably 10 in a 0.9 wt% sodium chloride aqueous solution (saline). Those that absorb -60 g / g of physiological saline. The “water-insoluble” is preferably 0 to 50% by weight, more preferably 25% by weight or less, and still more preferably 15% by weight or less of an uncrosslinked water-soluble component (water-soluble polymer) in the water-absorbent resin. Particularly preferably, it means 10% by weight or less. In addition, the free swell ratio and the numerical values of the water-soluble component are determined by the measurement method defined in the examples described later.

  In the present specification, “polymerize an acid group-containing radically polymerizable compound” means that an acid group-containing radically polymerizable compound is polymerized on and / or in the vicinity of a water absorbent resin. "Means any physical or chemical action performed on the water-absorbent resin as a result of polymerization of the acid group-containing radical polymerizable compound, preferably surface cross-linking of the water-absorbent resin, pore formation, hydrophilization, Including “surface treatment” such as hydrophobization, more preferably surface cross-linking of the water-absorbent resin. The “surface-treated water-absorbing resin” is also referred to as “water-absorbing agent”.

  The water-absorbing resin that can be used in the present invention preferably has an acid group, particularly preferably a carboxyl group, and is conventionally known using a monomer component that essentially contains an ethylenically unsaturated monomer. If it can be obtained by polymerization using the above method or the like, there is no particular limitation. In addition to the polymerization of the ethylenically unsaturated monomer, a water-soluble polymer cross-linked product such as a CMC cross-linked product or a polyaspartic acid cross-linked product can also be used as the acid group-containing water-absorbing resin.

  The ethylenically unsaturated monomer is not particularly limited and is preferably a monomer having an unsaturated double bond at the terminal, such as (meth) acrylic acid, 2- (meth) acryloylethanesulfonic acid, 2- Anionic monomers such as (meth) acryloylpropane sulfonic acid, 2- (meth) acrylamide-2-methylpropane sulfonic acid, vinyl sulfonic acid, styrene sulfonic acid and salts thereof; (meth) acrylamide, N-substituted (meta ) Nonionic hydrophilic group-containing monomers such as acrylamide, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate; N, N-dimethylaminoethyl (meth) acrylate, N, N-diethylaminoethyl (Meth) acrylate, N, N-diethylaminopropyl (meth) acrylate, N, N- Methylamino propyl (meth) acrylamide, amino group-containing unsaturated monomers and their quaternized products and the like; or the like can be cited, and may be used alone or two or more selected from these. Preferably, (meth) acrylic acid, 2- (meth) acryloylethanesulfonic acid, 2- (meth) acrylamido-2-methylpropanesulfonic acid, salts thereof, N, N-dimethylaminoethyl (meth) acrylate, N , N-dimethylaminoethyl (meth) acrylate quaternized product, (meth) acrylamide, particularly preferably acrylic acid and / or a salt thereof. The proportion of acrylic acid (salt) is preferably from 50 to 100 mol%, more preferably from 70 to 100 mol%, particularly preferably from 90 to 100 mol%, based on all monomers.

  When acrylate is used as the monomer, a monovalent salt of acrylic acid selected from alkali metal salts, ammonium salts, and amine salts of acrylic acid is preferable from the viewpoint of water absorption performance of the water absorbent resin. More preferred are alkali metal acrylates, and particularly preferred are acrylates selected from sodium salts, lithium salts, and potassium salts.

  When producing the water-absorbent resin, other monomer components other than the above-mentioned monomers can be used within a range not impairing the effects of the present invention. For example, an aromatic ethylenically unsaturated monomer having 8 to 30 carbon atoms, an aliphatic ethylenically unsaturated monomer having 2 to 20 carbon atoms, and an alicyclic ethylenically unsaturated monomer having 5 to 15 carbon atoms And hydrophobic monomers such as alkyl group (meth) acrylic acid alkyl ester having 4 to 50 carbon atoms. Generally the ratio of these hydrophobic monomers is the range of 0-20 weight part with respect to 100 weight part of said ethylenically unsaturated monomers. When the amount of the hydrophobic monomer exceeds 20 parts by weight, the water absorption performance of the resulting water absorbent resin may be deteriorated.

  The water absorbent resin used in the present invention becomes insoluble due to the formation of internal crosslinks. Such internal crosslinking may be a self-crosslinking type that does not use a crosslinking agent, but uses an internal crosslinking agent having two or more polymerizable unsaturated groups and / or two or more reactive functional groups in one molecule. Can be formed.

  Such an internal cross-linking agent is not particularly limited, and preferably, for example, N, N′-methylenebis (meth) acrylamide, N-methylol (meth) acrylamide, glycidyl (meth) acrylate, (poly) ethylene glycol diester (Meth) acrylate, (poly) propylene glycol di (meth) acrylate, glycerin tri (meth) acrylate, glycerin acrylate methacrylate, pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol hexa (meth) Acrylate, (meth) acrylic acid polyvalent metal salt, trimethylolpropane tri (meth) acrylate, trimethylolpropane di (meth) acrylate, glycerin di (meth) acrylate, triary Examples include ruamine, triallyl cyanurate, triallyl isocyanurate, triallyl phosphate, ethylene glycol diglycidyl ether, (poly) glycerol glycidyl ether, polyethylene glycol diglycidyl ether, and the like. Two or more of these internal cross-linking agents may be used in combination. Among these, a polymerizable cross-linking agent having a polymerizability with a monomer, particularly an ethylenically unsaturated monomer is preferable, and (poly) ethylene glycol di (meth) acrylate is preferably used.

  The amount of the internal crosslinking agent used is preferably 0.0001 to 1 mol%, more preferably 0.001 to 0.5 mol%, based on the total amount of monomer components used in producing the water absorbent resin. More preferably, it is 0.005-0.2 mol%. When the amount is less than 0.0001 mol%, internal crosslinking is not introduced into the resin. On the other hand, when the amount exceeds 1 mol%, the gel strength of the water-absorbent resin becomes too high, and the water absorption ratio may be lowered. When a crosslinked structure is introduced into the polymer using the internal cross-linking agent, the internal cross-linking agent is added to the reaction system before, during or after the polymerization of the monomer, or after the polymerization or neutralization. What should I do?

  In order to obtain a water-absorbing resin, the monomer component including the monomer and the internal crosslinking agent may be polymerized in an aqueous solution. In this case, usable polymerization initiators include persulfates such as potassium persulfate, ammonium persulfate and sodium persulfate; potassium peracetate, sodium peracetate, potassium percarbonate, sodium percarbonate, t-butyl hydroperoxide; Hydrogen peroxide; azo compounds such as 2,2′-azobis (2-amidinopropane) dihydrochloride, water-soluble radical polymerization initiators such as 2-hydroxy-2-methyl-1-phenylpropan-1-one There exist photoinitiators, such as. Further, for example, a reducing agent such as sulfite, L-ascorbic acid or ferric salt may be combined with the water-soluble radical polymerization initiator and used as a redox initiator. The amount of the polymerization initiator used is not particularly limited, but is preferably 0.001 to 2 mol%, more preferably 0.01 to 0.5 mol%, based on the total amount of the monomer components. is there. The amount of redox initiator used when using a redox initiator is also not particularly limited, but is preferably 0.0001 to 2 mol%, more preferably 0, based on the total amount of monomer components. 0.001 to 1.5 mol%.

  Although there is no restriction | limiting in particular in the density | concentration of the monomer in the said monomer aqueous solution, Preferably it is 15 to 90 weight%, More preferably, it is 35 to 80 weight%. If it is less than 15% by weight, the resulting hydrogel has a large amount of water, which requires a heat amount and time for drying, which is disadvantageous.

  The polymerization method is not particularly limited, and well-known methods such as aqueous solution polymerization, reverse phase suspension polymerization, precipitation polymerization, bulk polymerization and the like can be employed. Among these methods, aqueous solution polymerization in which a monomer is dissolved in an aqueous solution for polymerization and reverse phase suspension polymerization are preferable from the viewpoint of ease of control of the polymerization reaction and performance of the obtained water-absorbent resin.

  When starting the above polymerization, the above polymerization initiator is used. In addition to the above polymerization initiator, active energy rays such as ultraviolet rays, electron beams and γ rays may be used alone or in combination with a polymerization initiator. The temperature at the start of polymerization depends on the type of polymerization initiator used, but is preferably in the range of 15 to 130 ° C, more preferably in the range of 20 to 120 ° C. If the temperature at the start of polymerization is outside the above range, the residual monomer of the resulting water-absorbent resin may increase, or excessive self-crosslinking reaction may proceed to reduce the water-absorbing performance of the water-absorbent resin. It is not preferable. The polymerization time is not particularly limited, but is preferably 30 seconds to 60 minutes.

  The reverse phase suspension polymerization is a polymerization method in which the monomer aqueous solution is suspended in a hydrophobic organic solvent. For example, U.S. Pat. Nos. 4,093,764, 4,367,323, 4,446,261, U.S. Pat. Nos. 4,683,274 and 5,244,735. Aqueous solution polymerization is a method of polymerizing an aqueous monomer solution without using a dispersion solvent. For example, U.S. Pat. Nos. 4,462,001, 4,873,299, 4,286,682, 4,973,632, 4,985,518, 5,124,416, No. 5,264,495, US Pat. No. 5,145,906, US Pat. No. 5,380,808, and European patents such as European Patent Nos. 081636, 09555086, and 0922717. Monomers and initiators exemplified in these polymerization methods can also be applied in the present invention.

  When polymerization is performed, a partially neutralized product such as acrylic acid is polymerized, or an acid group-containing monomer such as acrylic acid is polymerized, and then the polymer is converted with an alkali compound such as sodium hydroxide or sodium carbonate. It can also be neutralized. Therefore, the water-absorbing resin used in the present invention preferably contains an acid group and has a predetermined neutralization rate (mol% of neutralized acid groups in all acid groups). Under the present circumstances, the neutralization rate (mol% of the neutralized acid group in all the acid groups) of the water absorbing resin obtained becomes like this. Preferably it is the range of 25-100 mol%, More preferably, it is 40-100 mol%. In the range of 40 to 90 mol%, more preferably in the range of 50 to 80 mol%, and most preferably in the range of 50 to 70 mol%.

After polymerization, a hydrogel crosslinked polymer is usually obtained. In the present invention, the hydrogel crosslinked polymer can be used as a water-absorbing resin as it is, but is preferably used after being dried. The drying may be performed, for example, using a dryer such as a hot air dryer, preferably at 100 to 220 ° C, more preferably at 120 to 200 ° C. In addition, when the water-containing gel-like cross-linked polymer obtained by polymerization is a lump, for the purpose of making such a water-containing gel-like cross-linked polymer into particles, the polymer is You may perform the gel granulation process to grind | pulverize. By using a particulate hydrous gel, the surface area of the gel increases, so that the drying process described above can proceed smoothly. The pulverization can be performed by various cutting means such as a roller cutter, a guillotine cutter, a slicer, a roll cutter, a shredder, or a scissor, alone or in combination, and is not particularly limited.
The water-absorbent resin used in the present invention is preferably in the form of powder. More preferably, it is a powdery water-absorbent resin containing 90 to 100% by weight, particularly preferably 95 to 100% by weight of particles having a particle size in the range of 150 to 850 μm (specified by sieve classification). For example, when a water-absorbing resin larger than 850 μm is surface-treated using such a water-absorbing resin for a diaper or the like, the touch may be poor and the top sheet of the diaper may be broken. On the other hand, when the amount of particles smaller than 150 μm exceeds 10% by weight, fine powder may be scattered or clogged at the time of use, and the water absorption performance of the surface-treated water absorbent resin may be lowered. The weight average particle diameter is in the range of 10 to 1,000 μm, preferably 150 to 850 μm, preferably 200 to 600 μm, and more preferably 300 to 500 μm. If the weight average particle size is less than 10 μm, it may be unfavorable for safety and health. On the other hand, if it exceeds 1,000 μm, it may not be used for diapers. The logarithmic standard deviation (σζ) of the particle size distribution is preferably 0.23 to 0.45, and more preferably 0.25 to 0.40. In addition, as the numerical value of the particle size, a value measured by a measurement method of the following particle size distribution [numerical value of logarithmic standard deviation (σζ) of weight average particle size and particle size distribution] is adopted.

[Measuring method of particle size distribution]
10 g of the water-absorbent resin is sieved with a test sieve (made by IIDA Seisakusho) having a diameter of 75 mm and openings of 850 μm, 600 μm, 300 μm, and 150 μm, the respective weights are measured, and the weight% of each particle size is obtained. The sieving is performed by shaking for 5 minutes using a SIEVE SHAKER ES-65 model manufactured by IIDA Corporation. The water-absorbing resin is measured after being dried in advance at 60 ± 5 ° C. under reduced pressure (less than 1 mmHg (133.3 Pa)) for 24 hours. As for the weight average particle diameter, the residual percentage R is plotted on logarithmic probability paper, and the particle diameter corresponding to R = 50% by weight is read as the weight average particle diameter (D50) from this plot.

  Further, when X1 is R = 84.1% by weight and X2 is each particle size when R = 15.9% by weight, the logarithmic standard deviation (σζ) is expressed by the following equation. That is, the smaller the value of σζ, the narrower the particle size distribution.

σζ = 0.5 × ln (X2 / X1) Formula In addition to or instead of the above, the water-absorbent resin used in the present invention preferably has a neutralization rate as described above. At this time, the neutralization rate of the water-absorbing resin may be adjusted by polymerizing a monomer whose neutralization rate has been adjusted in advance. For example, a neutralization method after acid polymerization (for example, US Pat. No. 6,187, 872) and the like, after once producing a polymer having a low neutralization rate, the neutralization rate of the polymer may be adjusted to a desired neutralization rate.
The water content before the surface treatment of the water absorbent resin used in the surface treatment method of the water absorbent resin of the present invention is not particularly limited as long as the water absorbent resin has fluidity. Preferably, the moisture content after drying at 180 ° C. for 3 hours is in the range of 0 to 20 wt%, preferably 0 to 10 wt%, more preferably 0 to 5 wt%.

  The water-absorbent resin used in the present invention is not limited to the one produced by the above method, and may be one prepared by another method. The water-absorbent resin obtained by the above method is usually a water-absorbent resin that is not surface-crosslinked, but the water-absorbent resin used in the surface treatment method of the water-absorbent resin of the present invention is a polyhydric alcohol in advance Further, a water-absorbent resin surface-crosslinked using a polyvalent epoxy compound, an alkylene carbonate, an oxazolidone compound or the like may be used.

(B) Acid group-containing radical polymerizable compound In the present invention, a radical polymerizable compound containing an acid group is essentially used. Among radically polymerizable compounds, a compound containing an acid group is very excellent in terms of water absorption characteristics. Examples of the acid group include a carboxyl group, a sulfone group, and a phosphoric acid group.

  The acid group-containing radical polymerizable compound to be mixed with the water-absorbent resin particles in the present invention is preferably a monomer containing an acid group among the ethylenically unsaturated monomers described above. Specifically, (meth) acrylic acid, 2- (meth) acryloylethanesulfonic acid, 2- (meth) acryloylpropanesulfonic acid, 2- (meth) acrylamido-2-methylpropanesulfonic acid, vinylsulfonic acid, styrene Examples include sulfonic acid and / or a salt thereof. Among these, (meth) acrylic acid and 2- (meth) acrylamido-2-methylpropanesulfonic acid are more preferable, (meth) acrylic acid is even more preferable, and acrylic acid is particularly preferable in terms of water absorption characteristics. The proportion of acrylic acid is preferably 50 to 100 mol%, more preferably 70 to 100 mol%, particularly preferably 90 to 100 mol% of all monomers. The acid group-containing radically polymerizable compound may be used alone or in a mixture of two or more.

  In this invention, the neutralization rate of an acid group containing radically polymerizable compound is 0-60 mol%. When the neutralization rate is in such a range, the reaction rate of polymerization (surface treatment) by active energy ray irradiation and / or heating in the subsequent step b) is improved, and a water-absorbing resin having excellent water absorption characteristics is obtained at a low temperature. It can be obtained in a short time. Conventionally, the neutralization rate was higher than the range of the present invention. This is because there was concern about the odor due to the decrease in water absorption ratio and the radical polymerizable compound remaining after the surface treatment. However, when an acid group-containing radical polymerizable compound having a neutralization rate lower than the neutralization rate of a radical polymerizable compound that has been used in the past is used contrary to conventional concerns, the surface treatment is unexpectedly performed rapidly. In addition, it has been found that the physical properties of the obtained water-absorbent resin are maintained.

  The neutralization rate of the acid group-containing radically polymerizable compound is preferably 0 to 50 mol%, more preferably 0 to 40 mol%, still more preferably 0 to 30 mol%, particularly preferably 0 to 0 mol%. 15 mol%, most particularly preferably 0 to 10 mol%. In the above range, the surface treatment time is several hours, preferably about several minutes, while the conventional surface time is in units of several hours. When large-scale production of / hr (preferably during continuous production), a great economic effect is brought about.

  In the present invention, the neutralization rate of the acid group-containing radically polymerizable compound is lower than the neutralization rate of the water absorbent resin particles as the base polymer. Here, the relationship of the neutralization rate between the acid group-containing radically polymerizable compound and the water absorbent resin is not particularly limited as long as the above relationship is satisfied. Specifically, the neutralization rate of the acid group-containing radical polymerizable compound to be mixed is preferably a numerical ratio of 0 to 80% with respect to the neutralization rate of the water-absorbent resin as the base polymer. % Is more preferable, 0 to 40% is more preferable, 0 to 20% is particularly preferable, and 0 to 10% is most particularly preferable. In the present specification, the “neutralization rate” refers to the ratio of neutralized acid groups to the total acid groups of the acid group-containing radical polymerizable compound. “Total acid groups of acid group-containing radically polymerizable compound” and “neutralized acid groups” are those in each of the acid group-containing radically polymerizable compounds when there are two or more acid group-containing radically polymerizable compounds. Refers to the sum of acid groups and neutralized acid groups. For example, when acrylic acid and sodium acrylate are used in a molar ratio of 1: 1 as the acid group-containing radical polymerizable compound, the neutralization rate of the acid group-containing radical polymerizable compound is 50 mol%.

  When the acid group-containing radically polymerizable compound is neutralized (in the form of a salt), the compound is preferably a monovalent salt selected from alkali metal salts, ammonium salts, and amine salts. More preferred is an alkali metal salt, and particularly preferred is a salt selected from a sodium salt, a lithium salt and a potassium salt.

  The amount of the acid group-containing radically polymerizable compound to be used is in the range of 0.1 to 20 parts by weight with respect to 100 parts by weight of the acid group-containing water absorbent resin. If the amount of the acid group-containing radical polymerizable compound is less than 0.1 parts by weight, the absorption performance under pressure of the water absorbent resin may not be sufficiently improved. On the other hand, when the amount of the acid group-containing radically polymerizable compound is more than 20 parts by weight, the absorption capacity of the obtained surface-treated water-absorbing resin may decrease. Moreover, the amount of the acid group-containing radical polymerizable compound to be used is preferably in the range of 0.5 to 15 parts by weight, more preferably in the range of 1 to 10 parts by weight, and still more preferably with respect to 100 parts by weight of the water absorbent resin. Is in the range of 3-8 parts by weight. When the amount of the acid group-containing radically polymerizable compound is in such a range, the effect of the present invention that the surface treatment time can be shortened appears remarkably.

  In the present invention, a radical polymerizable compound other than the acid group-containing radical polymerizable compound may be contained. As the radical polymerizable compound other than the acid group-containing radical polymerizable compound, the above-mentioned ethylenically unsaturated monomers and crosslinkable unsaturated monomers are preferably used. More preferably, the crosslinkable unsaturated monomer is further mixed in step a).

  Examples of the ethylenically unsaturated monomer include a nonionic hydrophilic group-containing monomer such as (meth) acrylamide, N-substituted (meth) acrylamide, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, etc. N; N-dimethylaminoethyl (meth) acrylate, N, N-diethylaminoethyl (meth) acrylate, N, N-diethylaminopropyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylamide, etc. And amino group-containing unsaturated monomers and their quaternized products. The amount of the ethylenically unsaturated monomer in such a case can be appropriately selected depending on the desired properties, but is preferably 0 to 100% by weight, more preferably 100% by weight with respect to 100% by weight of the acid group-containing radical polymerizable compound. Is 1 to 50% by weight.

  Although it does not restrict | limit especially as a crosslinkable unsaturated monomer, For example, the monomer illustrated as an internal crosslinking agent used by manufacture of a water absorbing resin is mentioned. Of these, polyethylene glycol diacrylate having an average ethylene oxide number of 2 to 50, trimethylolpropane tri (meth) acrylate, N, N′-methylenebis (meth) acrylamide, glycerin acrylate methacrylate, glycerin diacrylate and the like are preferably used. The In order for the crosslinkable unsaturated monomer to efficiently (co) polymerize with the ethylenically unsaturated monomer on the surface of the water absorbent resin, the crosslinkable unsaturated monomer and the ethylenic monomer in the mixing step with the water absorbent resin are used. It is desirable that the diffusion behavior of the unsaturated monomer into the water absorbent resin is similar. For this purpose, it is desirable that the crosslinkable unsaturated monomer is similar to the ethylenically unsaturated monomer used in terms of molecular weight and hydrophilicity. The amount of the crosslinkable unsaturated monomer to be used can be appropriately selected depending on the desired properties, but is preferably 0 to 20% by weight, more preferably 0.1 to 100% by weight of the acid group-containing radical polymerizable compound. -15% by weight, most preferably 0.5-5% by weight. By using a crosslinkable unsaturated monomer in combination, the absorption capacity under pressure can be further improved. The reason why the absorption capacity under pressure is improved by using a crosslinkable unsaturated monomer is not clear, but the water-soluble ethylenically unsaturated monomer is crosslinked by a crosslinkable unsaturated monomer during polymerization. This is presumably because this is introduced into the surface of the water-absorbent resin.

  In the present specification, “ethylenically unsaturated monomer” is a monomer having one vinyl group in one molecule, and “crosslinkable unsaturated monomer” is 2 in one molecule. It is a monomer having the above vinyl group. In the present invention, the ethylenically unsaturated monomer is an essential component, and the crosslinkable unsaturated monomer may be used in combination.

  At this time, the molar composition ratio of the ethylenically unsaturated monomer and the crosslinkable unsaturated monomer as the radical polymerizable compound other than the acid group-containing radical polymerizable compound is the same as that of the water absorbent resin as the base polymer. However, it is preferably different from the composition of the water-absorbent resin as the base polymer. Double the crosslinkable monomer. The amount of the crosslinkable unsaturated monomer used is preferably 0.001 to 100 mol%, more preferably 0.01 to 50 mol%, based on the total amount of the ethylenically unsaturated monomer, Preferably it is 0.05-30 mol%, Especially preferably, it is 0.1-20 mol%, Most preferably, it is 0.5-10 mol%. In particular, it is preferable to use acrylic acid (salt) as a main component as an ethylenically unsaturated monomer and to use a crosslinkable unsaturated monomer in combination with this in view of excellent water absorption characteristics. Instead of the crosslinkable unsaturated monomer, a compound having a polymerizable unsaturated group other than two or more vinyl groups and / or two or more reactive functional groups in one molecule can also be used.

  In addition, by appropriately selecting an acid group-containing radical polymerizable compound to be mixed with the water-absorbent resin, the surface-treated water-absorbent resin particle surface has various properties such as hydrophilicity, hydrophobicity, adhesiveness, and biocompatibility. Can be granted. Examples of the ethylenically unsaturated monomer that imparts hydrophilicity to the surface of the water-absorbent resin particles include hydroxyl group-containing monomers such as 2-hydroxyethyl (meth) acrylate and 2-hydroxypropyl (meth) acrylate, polyethylene glycol (meta Examples thereof include polyethylene glycol-containing monomers such as acrylate and polyethylene glycol methyl ether (meth) acrylate. Examples of ethylenically unsaturated monomers that impart hydrophobicity to the water-absorbent resin particle surface include alkyl (meth) acrylates such as methyl methacrylate and stearyl (meth) acrylate, and aromatic group-containing monomers such as styrene. Examples include fluorine-containing monomers such as 2,2-trifluoroethyl methacrylate. Examples of the ethylenically unsaturated monomer that imparts adhesiveness to the surface of the water-absorbent resin particles include monomers that form a polymer having a glass transition temperature of 25 ° C. or lower, such as butyl acrylate and 2-ethylhexyl acrylate, vinylamine, allylamine, Examples include cationic monomers such as dimethylaminoethyl (meth) acrylate and (meth) acryloyloxyethyltrimethylammonium chloride, and monomers containing a silane group such as 3-methacryloyloxypropyltrimethoxysilane. Among them, a monomer containing a silane group is preferably used because not only the adhesiveness between the water-absorbing resin particles but also the adhesiveness of the water-absorbing resin particles to a substrate such as metal, glass, and pulp can be improved. . Furthermore, when 3-methacryloyloxypropyltrimethoxysilane is added to an aqueous solution containing partially neutralized acrylic acid and persulfate, a water-absorbing resin having excellent liquid permeability can be obtained as compared with the case where it is not added. it can. Examples of the ethylenically unsaturated monomer that imparts biocompatibility to the water-absorbent resin particle surface include monomers having a phospholipid-like structure such as 2-methacryloyloxyethyl phosphorylcholine.

  In order to achieve the object of modifying the properties of the water-absorbent resin particle surface, the acid group-containing radical polymerizable compound is an ethylenically unsaturated compound used to produce the water-absorbent resin described in (a) above. It is desirable to include a compound different from the monomer and the internal crosslinking agent. At this time, the ethylenically unsaturated monomer having a neutralization rate different from that of the ethylenically unsaturated monomer used to produce the water-absorbent resin described in (a) above is described in “(a) above”. It is included in “an acid group-containing radically polymerizable compound different from the ethylenically unsaturated monomer and the internal crosslinking agent” used for producing the water absorbent resin. When the ethylenically unsaturated monomer used to produce the water-absorbent resin described in (a) above is an acid group-containing ethylenically unsaturated monomer, the effects of the present invention are appropriately obtained. As described above to obtain, the neutralization rate of the acid group-containing radical polymerizable compound is more than the neutralization rate of the ethylenically unsaturated monomer used to produce the water absorbent resin described in (a). By lowering, the effect of the present invention is exhibited.

Further, as a compound different from the ethylenically unsaturated monomer and the internal cross-linking agent used for producing the water-absorbent resin described in the above (a), in the acid group-containing radical polymerizable compound, nitrogen, An ethylenically unsaturated monomer containing at least one hetero atom other than oxygen selected from the group consisting of sulfur, phosphorus, silicon, and boron may be used. By using the ethylenically unsaturated monomer, the properties of the water absorbent resin particles can be greatly modified. More preferably, silicon, especially silane group _{(X n Si (OR) 4} -n, Here, R represents methyl, ethyl, phenyl or acetoxy group, n is an integer of 1 to 3, n is 1 Or when it is 2, R may be the same or different, and an ethylenically unsaturated monomer containing phosphorus is used. In addition, when using an ethylenically unsaturated monomer containing a heteroatom other than oxygen as the acid group-containing radical polymerizable compound, the amount of the ethylenically unsaturated monomer containing a heteroatom other than oxygen is as desired. Although it can be appropriately selected depending on the properties, it is 50 parts by weight or less, more preferably 0.01 to 20 parts by weight, and most preferably 0.1 to 10 parts by weight with respect to 100 parts by weight of the total amount of the acid group-containing radical polymerizable compound. Preferably there is.

  Among the above-mentioned ethylenically unsaturated monomers, a compound having low water solubility is dispersed in an aqueous solution containing a radical polymerization initiator and, if necessary, another radical polymerizable compound, or dissolved in a hydrophilic organic solvent. After mixing with the aqueous solution, it may be added to the water absorbent resin. Alternatively, if necessary, it may be dissolved in an organic solvent and added separately from the aqueous solution. At this time, the addition order of the ethylenically unsaturated monomer is not particularly limited, and may be added before or after the aqueous solution.

  The radical polymerizable compound may be used alone or in a mixture of two or more, and the combination in the latter case can be appropriately selected depending on the properties to be imparted and is particularly limited. It is not something.

  The amount of the acid group-containing radical polymerizable compound to be used is preferably in the range of 0.1 to 20 parts by weight, more preferably in the range of 0.5 to 15 parts by weight, based on 100 parts by weight of the acid group-containing water-absorbing resin. Preferably it is the range of 1-10 weight part. When the amount of the radical polymerizable compound is less than 0.1 parts by weight, the absorption performance under pressure of the water absorbent resin may not be sufficiently improved. On the other hand, if the amount of the radical polymerizable compound is more than 20 parts by weight, the absorption capacity of the resulting surface-treated water-absorbing resin may be lowered.

(C) Radical polymerization initiator In a preferred production method of the water-absorbing agent of the present invention, a radical polymerization initiator is preferably used in the step of mixing a) the water-absorbing resin, the acid group-containing radical polymerizable compound and water. Although it does not specifically limit as a radical polymerization initiator, Specifically, a thermally decomposable radical polymerization initiator and a photoinitiator are mentioned.
Although there is no restriction | limiting in the usage-amount of a radical polymerization initiator, In this invention, the range of 0.001-20 weight part is preferable with respect to 100 weight part of acid group containing water-absorbing resin, More preferably, it is 0.05-10 weight. Parts, more preferably 0.1 to 5 parts by weight. If the radical polymerization initiator is in such a range, a water-absorbing resin having excellent water absorption characteristics can be obtained, and the surface treatment reaction rate can be improved, so that productivity is excellent. Moreover, the radical polymerization initiator may be used alone or in combination of two or more.

  The thermally decomposable radical polymerization initiator is a compound that generates radicals by heating, and preferably has a 10-hour half-life temperature of 0 ° C. or higher and 120 ° C. or lower, more preferably 20 ° C. or higher and 100 ° C. or lower, Considering the temperature conditions for irradiating the active energy ray, those of 40 ° C. or more and 80 ° C. or less are particularly preferable. If the 10-hour half-life temperature is less than 0 ° C. (lower limit), it is unstable during storage, and if it exceeds 120 ° C. (upper limit), it may be chemically too stable to lower the reactivity.

The thermal decomposable radical polymerization initiator is relatively inexpensive as compared with a compound marketed as a photopolymerization initiator, and strict light shielding is not always required, so that the manufacturing process and the manufacturing apparatus can be simplified. Typical thermal decomposable radical polymerization initiators include persulfates such as sodium persulfate, ammonium persulfate, and potassium persulfate; hydrogen peroxide; 2,2′-azobis (2-amidinopropane) dihydrochloride, 2 , 2′-azobis [2-2 (-imidazolin-2-yl) propane] dihydrochloride, 2,2′-azobis (2-methylpropionitrile) and the like. Among them, persulfates such as sodium persulfate, ammonium persulfate, potassium persulfate, and the like, and 2,2′-azobis (2-amidinopropane) dihydrochloride having a 10-hour half-life temperature of 40 to 80 ° C., 2, Azo compounds such as 2′-azobis [2-2 (-imidazolin-2-yl) propane] dihydrochloride and 2,2′-azobis (2-methylpropionitrile) are preferred. Among these, the use of persulfate is particularly preferable in terms of excellent absorption capacity under load, liquid permeability, and free swelling capacity. Persulfate can be used in combination of not only one type but also two or more types having different counterions. The thermal decomposable radical polymerization initiator used is preferably 0.001 to 5 parts by weight, more preferably 0.01 to 3 parts by weight, based on 100 parts by weight of the water absorbent resin. More preferably, it is 1-1 weight part.

In the present invention, photopolymerization initiators such as oil-soluble benzoin derivatives, benzyl derivatives, and acetophenone derivatives, oil-soluble ketone peroxides, peroxyketals, hydroperoxides, dialkyl peroxides, peroxyesters, peroxycarbons, and the like. Oil-soluble organic peroxides such as nates may be used. Such a photopolymerization initiator may be a commercially available product, trade names of Ciba Specialty Chemicals: Irgacure (registered trademark) 184 (hydroxycyclohexyl-phenyl ketone), Irgacure (registered trademark) 2959 (1- [4- (2-hydroxyethoxy)) -Phenyl] -2-hydroxy-2-methyl-1-propan-1-one) and the like. The photopolymerization initiator used is preferably 0.001 to 1 part by weight, more preferably 0.005 to 0.5 part by weight with respect to 100 parts by weight of the water absorbent resin. More preferably, it is 01-0.1 weight part.
As the radical polymerization initiator of the present invention, either oil-soluble or water-soluble can be used. Oil-soluble radical polymerization initiators are characterized in that the decomposition rate is less affected by pH and ionic strength than water-soluble radical polymerization initiators. However, since the water-absorbent resin is hydrophilic, it is more preferable to use a water-soluble radical polymerization initiator in consideration of permeability to the water-absorbent resin. In addition, water-soluble means what melt | dissolves 1 weight% or more in water (25 degreeC), Preferably it is 5 weight% or more, More preferably, it melt | dissolves 10 weight% or more.

  The water-soluble radical polymerization initiator preferably includes a radical polymerization initiator selected from a persulfate, hydrogen peroxide, and an azo compound. Specifically, persulfates such as ammonium persulfate, sodium persulfate, and potassium persulfate; hydrogen peroxide; 2,2′-azobis-2-amidinopropane dihydrochloride, 2,2′-azobis [2-2 And water-soluble azo compounds such as (-imidazolin-2-yl) propane] dihydrochloride. Among these, the use of persulfate is particularly preferable in that the absorption capacity under pressure, liquid permeability, and free swelling ratio of the water-absorbent resin after the surface treatment are all excellent.

  In addition to or in place of the above radical polymerization initiator, a percarbonate such as sodium percarbonate; a peracetate such as peracetic acid or sodium peracetate may be further used. .

  When other radical polymerization initiators such as a thermally decomposable radical polymerization initiator and a photopolymerization initiator are used in combination according to the present invention, the latter is used in an amount of 0 to 20 parts by weight with respect to 100 parts by weight of the water-absorbing resin, The amount is preferably 0 to 15 parts by weight, particularly 0 to 10 parts by weight, and the use ratio thereof is less than the thermally decomposable radical polymerization initiator, for example, 1 / weight ratio of the thermally decomposable radical polymerization initiator. 2 or less, further 1/10 or less, particularly 1/50 or less.

(D) Step of mixing water-absorbent resin, radical polymerizable compound, and water a)
As a preferred surface treatment method for a water-absorbent resin of the present invention, in the mixing step a), a) the acid group-containing radically polymerizable compound 0 having a neutralization rate of 0 to 60 mol% with respect to 100 parts by weight of the acid group-containing water-absorbent resin. 0.1 to 20 parts by weight and 5 to 20 parts by weight of water are mixed to obtain a water absorbent resin composition.

  Conventionally, the surface treatment of a water-absorbent resin has been generally performed by blending a surface cross-linking agent. If a surface cross-linking agent is blended, the functional group on the resin surface and the surface cross-linking agent are chemically strongly bonded, and thereby a stable surface cross-linking structure can be introduced on the resin surface. Further, the surface crosslinking distance can be easily adjusted by appropriately selecting the chain length of the surface crosslinking agent, and the crosslinking density can be controlled by adjusting the blending amount. However, in the present invention, the surface treatment (modification) of the water-absorbing resin can be achieved only by using an acid group-containing radical polymerizable compound and, if necessary, a radical polymerization initiator, without blending such a surface crosslinking agent. Specifically, a crosslinked structure can be introduced on the surface of the water absorbent resin. Furthermore, the crosslinked structure can be efficiently introduced on the surface of the water-absorbent resin particles by subjecting the water-absorbent resin composition obtained by mixing water to irradiation treatment with active energy rays and / or heat treatment. In addition, the water absorption characteristics of the surface-treated (modified) water-absorbing resin can be improved. In addition to the above-mentioned advantages, in step b) described later, the water-absorbing property is obtained by using an acid group-containing radical polymerizable compound having a low degree of neutralization in step a) and further adding a relatively large amount of water to the water-absorbing resin. A crosslinked structure can be efficiently introduced on the surface of the resin particles. For this reason, the surface treatment time (specifically, the active energy ray irradiation time or heating time) necessary for improving the saline flow conductivity (SFC) to a desired level is preferably about several tens of minutes. There is also an advantage that it can be shortened to about several minutes. SFC affects the liquid permeability after swelling of the surface-treated water-absorbing resin composition (water-absorbing agent). That is, for example, when the water-absorbent resin composition of the present invention is used as a part of an absorbent body of a paper diaper, the liquid permeability is improved, the liquid is sufficiently distributed to the absorbent body, and the urine or other excretory liquid during use is used. The effect of increasing the amount of absorption and preventing liquid leakage is significantly improved. Properties required for the water-absorbent resin include absorption capacity, absorption speed, gel strength, and suction force. Among these characteristics, in the surface treatment method of the present invention, the surface reaction treatment time required to obtain the desired saline flow conductivity (SFC) is significantly reduced compared to the conventional method. Although the detailed mechanism is unknown, it is considered that the polymerization rate of the radical polymerizable compound has been improved.

  There is no limitation on the order of mixing when the radically polymerizable compound, water, and the radical polymerization initiator added as necessary are mixed with the water absorbent resin. Therefore, each may be mixed alone with the water-absorbent resin, or an aqueous solution containing a radical polymerization initiator and a radical polymerizable compound may be prepared in advance and mixed with the water-absorbent resin. However, in order for both to be uniformly dispersed on the surface of the water-absorbent resin, it is preferable to prepare an aqueous solution containing a radical polymerization initiator and a radical polymerizable compound in advance and mix this with the water-absorbent resin. In addition, after mixing a radical polymerization initiator, a radically polymerizable compound, and a water absorbing resin, you may mix the obtained mixture with water.

  The aqueous solution in which the radical polymerization initiator and the radical polymerizable compound are dissolved may contain, in addition to water, other solvents as long as they do not impair their solubility, but preferably use only water. The radical polymerization initiator and / or the radical polymerizable compound are used in the form of an aqueous solution in the absence of a hydrophobic organic solvent.

  The amount of water mixed with the water-absorbent resin in the mixing step a) is 5 to 20 parts by weight, preferably 6 to 15 parts by weight, based on 100 parts by weight of the water-absorbent resin (converted to a solid content of 100% by weight). Parts, more preferably 7 to 12 parts by weight. When water is mixed in such a range, the speed of the surface treatment reaction by active energy ray irradiation treatment and / or heat treatment increases, and more energy is required in the drying process after active energy ray irradiation treatment and / or heat treatment. It is preferable because the water-absorbent resin is less likely to be decomposed.

When the acid group-containing radically polymerizable compound or the like is mixed in the form of an aqueous solution, the amount of water in the aqueous solution used can be adjusted so that the amount of water in the resulting water-absorbent resin composition is in the above-described range. In addition, the mixing form of the water to a water absorbing resin is not necessarily restricted to the case of mixing with the form of the aqueous solution containing an acid group containing radically polymerizable compound etc. For example, water may be mixed after mixing an acid group-containing radical polymerizable compound, a radical polymerization initiator, and a water-absorbing resin. Therefore, the water-containing gel-like crosslinked polymer (water-absorbent resin) obtained by polymerizing the monomer components is dried until the water content is such that the amount of water in the obtained water-absorbent resin composition is in the above-mentioned range. The water-absorbent resin composition may be obtained by directly mixing the radical polymerizable compound and the radical polymerization initiator into the product.
(E) Organic fine particles and / or inorganic fine particles As the fine particles used in the present invention, fine particles of various solid substances such as organic substances, inorganic substances, and organic-inorganic composite substances can be used. For example, polyacrylic acid (salt) cross-linked product, polyacrylamide and cross-linked product thereof, acrylic acid (salt) -acrylamide copolymer cross-linked product, or N, N-dimethylaminoethyl (meth) acrylate and quaternary salt thereof Monomer and polyacrylamide copolymer cross-linked, organic substances such as cross-linked polycation compounds such as polyethyleneimine, polyvinylamine, polyallylamine, talc, kaolin, fuller earth, bentonite, activated clay, barite, natural asphalt Tam, strontium ore, ilmenite, pearlite and other mineral products; aluminum sulfate 14-18 hydrate (or anhydride), potassium aluminum sulfate 12 hydrate, sodium aluminum sulfate 12 hydrate, aluminum chloride, polyaluminum chloride, aluminum oxide, etc. No al Nitrogen compounds, other polyvalent metal salts; hydrophilic amorphous silica (eg, dry method: Reolosil QS-20, Tokuyama Co., precipitation method: DEGUSSA Sipernat (registered trademark) 22S, Sipernat 2200), silicon oxide, aluminum oxide, Examples include inorganic substances such as magnesium oxide composites (eg, Atgel 1 (registered trademark) # 50 manufactured by ENGELHARD), zeolite, silicon oxide, aluminum oxide, activated carbon and the like. Moreover, the composite body and blend of an organic substance and an inorganic substance are also mentioned.

  The shape of the solid (solid) is not particularly limited and may be fibrous or particulate, but the particulate has a higher surface area and more effectively absorbs and deodorizes. It is preferable because the properties can be improved.

These solids (solids) are usually preferably powdery (fine particle) compounds that are solid at room temperature. As the particle diameter, the mass average particle diameter is preferably 150 μm or less, more preferably 100 μm or less, and particularly preferably 50 μm or less. The lower limit is a few nm, for example 1 nm. If the particle diameter of the fine particles exceeds 150 μm, even if the fine particles are fixed, they do not contribute to an increase in surface area, and the effect of improving the absorption rate and deodorizing property becomes insufficient. In addition, the fixed fine particles are easily detached.
Moreover, it is more preferable that the particle size of substantially all (99.9% by weight or more) particles is in the range of 1 nm to 150 μm, and the particle size of all particles is 5 nm to 100 μm. Most preferably within the range. When the particle diameter of the fine particles is less than 1 nm, dust and the like are generated, and there is a risk that the handleability is lowered.

  The particle size can be measured with a standard sieve (JIS Z8801-1 (2000)) for particles of 38 μm or more, and can be measured with a laser analysis type particle size distribution measuring device for particles of 38 μm or less. .

  In the present invention, organic fine particles are preferably used. Among them, a polyacrylic acid (salt) crosslinked polymer having high water absorption, that is, a polyacrylic acid (salt) water-absorbing resin is preferably used. The organic fine particles are dry fine particles or surface-treated fine particles which are the base polymer of the water absorbent resin.

When a polyacrylic acid (salt) -based water absorbent resin is used, the absorption capacity (GV) is usually 50 g / g or less, preferably 40 g / g or less, more preferably 30 g / g or less, in achieving the present invention. Especially preferably, it is 20 g / g or less. The lower limit is 5 g / g or more, preferably 10 g / g or more from the absorption capacity. The amount of soluble component is preferably 30% or less, more preferably 15% or less, more preferably 10% or less, and particularly preferably 5% or less. That is, in the present invention, preferably, the fine particles are water-absorbent resin fine particles having an absorption ratio (GV) of 5 to 20 g / g with respect to physiological saline.
Such polyacrylic acid (salt) water-absorbing resin may be produced separately or may be fine powder removed for particle size control. That is, after removing fine powder in the manufacturing process of the water absorbent resin, it is possible to recycle by using it as the fine particles of the present invention without discarding them, and when fixed to the water absorbent resin particles, the surface area is improved and is attributed to the fine particles Performance is improved.

  Further, the ratio of the fine particles to the water-absorbent resin particles may be appropriately set according to the target performance, but is usually 0.01% by weight or more, preferably 0.1% by weight or more, based on the water-absorbent resin particles. It is preferably 1% by weight or more, more preferably 3% by weight or more, particularly preferably 5% by weight or more, and most preferably 10% by weight or more. The upper limit is usually 50% by weight or less, preferably 40% by weight or less, more preferably 30% by weight or less, and still more preferably 20% by weight or less. If it is less than 0.01% by weight, the effect of addition is hardly observed, and if it exceeds 50% by weight, a decrease in absorption capacity may be observed.

  The method for mixing fine particles is not particularly limited. For example, the fine particles may be added and dispersed in a surface treatment liquid contained in a container, or continuously using a mixer in the surface treatment liquid flowing continuously. In addition, a method of dispersing in water, a method of mixing a water-absorbing resin and fine particles in advance, or a combination of the above methods can be used. As a result, the fine particles can be uniformly attached to the surface of the water-absorbent resin particles or be present in the vicinity thereof.

In addition, as a method of obtaining a mixture by mixing water-absorbing resin particles and fine particles, an ordinary mixer such as a V-type mixer, a ribbon-type mixer, a screw-type mixer, a rotating disk-type mixer, an airflow type Examples of the mixing method include a mixer, a batch kneader, a continuous kneader, a paddle type mixer, and a vertical mixer.
(F) Step b) of polymerizing the acid group-containing radical polymerizable compound
A preferable production method for obtaining the water-absorbing agent of the present invention is: a) a mixture of 100 parts by weight of acid group-containing water-absorbent resin particles (converted to a solid content of 100% by weight) and organic fine particles and / or inorganic fine particles (base polymer) ), 0.1 to 20 parts by weight of an acid group-containing radically polymerizable compound and 5 to 20 parts by weight of water, and b) a step of polymerizing the acid group-containing radically polymerizable compound. . In step b), an acid group-containing radical polymerizable compound is polymerized to a mixture of water-absorbent resin particles and the above fine particles. Here, the polymerization method of the acid group-containing radically polymerizable compound into the mixed product is not particularly limited. Preferably, step b) includes a step of irradiating the mixture obtained in step a) with active energy rays and / or a step of heating the mixture obtained in step a). Specifically, the acid group-containing radical polymerizable compound mixed with the base polymer is preferably polymerized on the surface of the base polymer mixture and / or in the vicinity thereof by using radical generating means such as irradiation with active energy rays and / or heating. To do.

By the polymerization, the crosslink density in the vicinity of the surface is increased from the inside of the water-absorbent resin particles, and properties desired at the time of actual use of the water-absorbent resin such as absorption capacity under load and liquid permeability are enhanced. Hereinafter, the step of irradiating the mixture of the base polymer and the surface treatment liquid with active energy rays and the step of heating the mixture for obtaining the water-absorbing agent of the present invention to which fine particles are fixed will be described. However, the present invention is not limited to the following forms.
(F-1) Irradiation of active energy rays In the production of a water absorbent resin, it is known to irradiate active energy rays to improve the polymerization rate. For example, an insoluble water-absorbing resin having internal cross-linking can be prepared by blending an internal cross-linking agent and a photopolymerization initiator into a polymerizable monomer component and irradiating active energy rays such as ultraviolet rays, electron beams, and γ rays. it can. On the other hand, as a surface treatment method for a water-absorbent resin, it is also known to use a surface cross-linking agent and promote reaction under heating conditions to form surface cross-linking. As such surface cross-linking of the water-absorbent resin, there are compounds having a plurality of functional groups in one molecule such as polyhydric alcohol, polyhydric glycidyl ether, haloepoxy compound, polyhydric aldehyde and the like. Generally, when heated to 100 to 300 ° C., these functional groups react with carboxyl groups and the like on the surface of the water absorbent resin, and a crosslinked structure is formed on the surface of the water absorbent resin. However, in the present invention, even without such a surface cross-linking agent, the surface treatment of the water-absorbing resin can be carried out by the presence of the polymerizable monomer, the irradiation of the radical polymerization initiator and the active energy ray. By performing the surface treatment with the organic fine particles and / or the inorganic fine particles attached to the water absorbent resin particles, it is possible to obtain a water-absorbing agent in which the organic fine particles and / or the inorganic fine particles are firmly fixed. As a result, it is possible to obtain a water-absorbing agent having excellent water-absorbing characteristics due to the adhered fine particles.

  In the present invention, irradiation with active energy rays may be performed during mixing of the mixture (base polymer), water, the acid group-containing radical polymerizable compound, and, if necessary, the radical polymerization initiator, and two or more of these may be performed. Irradiation may be performed after mixing. However, it is preferable to obtain a mixture composition (base polymer), water, an acid group-containing radical polymerizable compound and a mixed composition containing a radical polymerization initiator if necessary after obtaining a uniform surface treatment. The obtained mixed composition is irradiated with active energy rays.

Examples of active energy rays include one or more of ultraviolet rays, electron beams, and gamma rays. Of these, ultraviolet rays and electron beams are preferable. Considering the influence of the active energy ray on the human body, ultraviolet rays are more preferable, ultraviolet rays having a wavelength of 300 nm or less, particularly preferably 180 to 290 nm are more preferable. Irradiation conditions, when ultraviolet rays are used, preferably, irradiation intensity 3~1000mW / cm ^2, irradiation amount is 100~10000mJ / cm ^2.

Stirring is preferably performed during irradiation with active energy rays. The active energy ray can be uniformly irradiated to the mixture of the radical polymerization initiator and the mixture (base polymer) by stirring. The devices that can stir the base polymer during irradiation with active energy rays include a vibratory mixer, vibratory feeder, ribbon type mixer, conical ribbon type mixer, screw type mixing extruder, airflow type mixer, and batch type. Examples thereof include a kneader, a continuous kneader, a paddle type mixer, a high-speed flow type mixer, and a floating flow type mixer.
The rotation speed is preferably 10 to 1000 rpm, more preferably 15 to 500 rpm, particularly preferably 20 to 300 rpm, and most preferably 30 to 100 rpm. Moreover, 10-100 degreeC is preferable, as for the temperature of the mixture (mixed composition with a process liquid) in that case, 20-80 degreeC is further more preferable, and 30-70 degreeC is especially preferable.
(F-2) Heating As described above, the acid group-containing radical polymerizable compound to be mixed with the mixture (base polymer) can be polymerized by heating. In the case where the polymerization is carried out by heating alone, it is not necessary to separately provide an active energy ray irradiation device, which is excellent in the design of the manufacturing apparatus. In addition, it is possible to improve the water absorption characteristics (particularly the absorption capacity and liquid permeability under pressure) of the surface-treated water-absorbing agent obtained by a low-cost and safe technique.

  What is necessary is just to prepare the mixture obtained at the said a process on the conditions similar to the time of irradiation of the active energy ray mentioned above, and a radical polymerization initiator is not an essential component. It is preferable to mix the acid group-containing radically polymerizable compound, water, and, if necessary, the radical polymerization initiator in a specific amount as described above with respect to the mixture (base polymer). And it is preferable to heat a mixture on specific temperature conditions.

  b) When the step is a step of heating the mixture (mixed composition with the treatment liquid), the mixture obtained in the step a) is generated under the conditions different from those of the above-mentioned active energy ray irradiation to generate radicals. Can be controlled.

Although the heating time at the time of performing heat processing is not restrict | limited, Preferably it is 1 to 90 minutes, More preferably, it is 2 to 60 minutes, More preferably, it is 3 to 30 minutes. If the heating time is 1 minute or longer, a crosslinked structure is introduced on the surface of the base polymer. On the other hand, if the heating time is 90 minutes or shorter, deterioration of the base polymer due to heating can be prevented.
(G) Other treatments After irradiation with active energy rays, the water-absorbing agent may be heat-treated at a temperature of 50 to 250 ° C. as necessary for drying and the like.

  Further, after the active energy ray irradiation, surface cross-linking may be formed by using a conventionally known surface cross-linking agent such as polyhydric alcohol, polyhydric epoxy compound, and alkylene carbonate.

Moreover, you may add a liquid permeability improver to a water absorbing agent after active energy ray irradiation. As such a liquid permeability improver, it is preferable to use the inorganic fine particles described above.
(H) Water-absorbing agent formed by adhering surface-treated organic fine particles and / or inorganic fine particles In the present invention, a surface treatment method is preferably performed by polymerizing an acid group-containing radical polymerizable compound on the surface of water-absorbent resin particles. By using, the fine particles present on the surface of the water-absorbent resin particles are firmly fixed. An image diagram is shown in FIG.

As shown in FIG. 2 and FIG. 3 described later, the water-absorbing agent of the present invention is not a simple granulated particle. That is, strictly controlling the particle size of the fine particles to be fixed to the internal water-absorbent resin particles, the fine particles are preferably fixed in a single layer.
The mass average particle diameter of the internal water-absorbing resin particles is 150 μm or more and 850 μm or less. The fine particles have a smaller particle size than the internal water-absorbent resin particles, and their mass average particle diameter is less than 150 μm. By distinguishing in this way, the surface treatment with the acid group-containing radically polymerizable compound and the surface area control of the water-absorbing agent can be performed smoothly, and the function of the fine particles to be fixed is efficiently expressed.
The acid group neutralization rate on the surface is less than the acid group neutralization rate inside the water-absorbent resin particles. Preferably, the neutralization rate of the acid group-containing radically polymerizable compound in the surface treatment solution is 30 mol% or less, more preferably 10 mol% or less, and most preferably 0%.
In the present invention, the “surface” when the neutralization rate is confirmed by analysis means water-absorbing resin particles that are exposed to the outside air. That is, the size relationship is not confirmed on the surface of the fine particles. In addition, “inside the water-absorbent resin particles” means a portion further toward the center than near the surface of the water-absorbent resin particles. Here, “near the surface of the water-absorbent resin particles” means a portion having a thickness of 1/10 of the particle diameter (short diameter) from the surface of the water-absorbent resin particles. The thickness from the surface of the water absorbent resin particles can be confirmed with a scanning electron microscope (SEM), EPMA or the like. The “acid group (preferably carboxyl group) neutralization rate” can be measured by a micro ATR (Micro Attenuated Total Reflection) method or an EPMA method, which is one of infrared absorption analysis methods. Further, in the microscopic ATR method, the surface of the water-absorbent resin particles may be directly measured by the microscopic ATR method, and the inside of the water-absorbent resin particles may be measured by, for example, an ultramicrotome (manufactured by Reichert, ULTRACUT). By using N), the water-absorbing agent is cleaved to expose the central portion, and then measurement can be performed by the microscopic ATR method. As the measuring device, for example, a known device such as FTS-575 manufactured by Bio-Rad may be used.

In the present invention, the magnitude relationship can be confirmed with high accuracy by the following EPMA measurement method.
The cross section of the water-absorbing agent is measured with EPMA (Electron Probe Microanalyzer; manufactured by Shimadzu Corporation, trade name: EPMA-1610). Measurement is performed by surface analysis (mapping). Measurement conditions are as follows: acceleration voltage: 15 kV, Beam size: 1 μm, Beam Current: 0.05 μA. Measurement of mapping is as follows: Measurement time: 40 msec, Data Point: 200 for both X and Y, Step size: 0.5 μm for both X and Y, Area size: 100 μm, Measurement Type: One-Way, Start Type: Center, Na X-ray (Kα-ray) wavelength: Performed at 11, 8950 angstroms. The element to be measured is Na (spectral crystal: RAP (Rubidium acid phthalate)), and the observation at that time is performed by a backscattered electron image (BEI). For one sample, the above mapping is measured at three places where fine particles are not fixed. Thereafter, analysis is performed.

  Actually, the basic malodor components (for example, ammonia and amines) can be neutralized by the non-neutralized acrylic acid portion on the surface of the fine particles and the surface of the water-absorbent resin particles on which the fine particles are not fixed. Further, it has been found that the surface area is increased by fixing the fine particles, and as a result, the deodorizing effect is greatly improved. Moreover, fine particles are not detached even after water absorption and swelling, and the performance can be maintained for a long time even when used in various environments.

The deodorizing property is increased when the acid group neutralization rate inside the water-absorbent resin particles is preferably in the range of 40 mol% to 60 mol%, and when the fine particles are water-absorbent resin particles, the acid groups Similarly, the neutralization rate is in the range of 40 mol% to 60 mol%. And the neutralization rate of the acid group-containing radical polymerizable compound to be surface-treated is 30 mol% or less, and the neutralization rate of the whole water-absorbing agent is in the range of 40 mol% to 60 mol%, especially the surface is less than the neutralization rate range The effect becomes larger by making it.
The water-absorbing agent according to the present invention can be used for various applications including absorbent articles such as paper diapers in the field of hygiene. As fine particles fixed on the surface, deodorant, antibacterial agent, fragrance, inorganic powder fine particles such as silicon dioxide and titanium oxide, phosphorescent agent, hydrophilic short fiber, plasticizer, fertilizer, thermoplastic resin such as polyethylene and polypropylene, polyester If fine particles such as a thermosetting resin such as a resin or a urea resin are used, various functions are provided, and the performance can be maintained for a long time because the fixed state continues for a long time.

  If the water-absorbing resin fine particles as described above are used as the organic fine particles, the effect of improving the water absorption characteristics such as the absorption rate is increased.

  The surface coverage by the surface treatment with the acid group-containing radical polymerizable compound necessary for fixing is preferably 30% or more, more preferably 50% or more, particularly preferably 70% of the surface of the water-absorbent resin particles inside. Above, most preferably 90% or more. The upper limit is 100%.

  The surface coverage can control the expression of performance depending on various applications. When importance is attached to the function of the fine particles themselves, the coverage can be controlled to, for example, 20% or more and 50% or less. When the acid group of the acid group-containing radically polymerizable compound is emphasized, the deodorizing property is improved by controlling the acid group to 50% or more and 100% or less, for example.

  If the surface coverage exceeds 100%, the effect commensurate with the amount added will not be achieved. Further, the film becomes thick, and even if fine particles are present, the surface area is not increased sufficiently.

The ratio of the organic fine particles and / or inorganic fine particles to the water-absorbing resin particles constituting the water-absorbing agent of the present invention may be appropriately set according to the intended performance, but is 0.01% by weight or more with respect to the water-absorbing resin particles. It is preferably 0.1% by weight or more, more preferably 1% by weight or more, more preferably 3% by weight or more, particularly preferably 5% by weight or more, and most preferably 10% by weight or more. The upper limit is 50% by weight or less, preferably 40% by weight or less, more preferably 30% by weight or less, and still more preferably 20% by weight or less. If it is less than 0.01% by weight, the effect of addition is hardly observed, and if it exceeds 50% by weight, a decrease in absorption capacity may be observed.
As the water absorption characteristics of the water-absorbing agent of the present invention, the absorption capacity under pressure of 4.83 kPa is preferably 8 g / g or more, more preferably 12 g / g or more, still more preferably 15 g / g or more, and particularly preferably 20 g / g or more. Preferably it is 22 g / g or more. In addition, although an upper limit is not ask | required in particular, about 40 g / g may be enough from the cost increase by the difficulty of manufacture. The value measured by the method described in the examples is adopted as the value of water absorption under pressure.

  The free swelling ratio (GV) is preferably 8 g / g or more, more preferably 15 g / g or more, still more preferably 20 g / g or more, and particularly preferably 25 g / g or more. Although an upper limit is not specifically limited, Preferably it is 50 g / g or less, More preferably, it is 40 g / g or less, More preferably, it is 35 g / g or less. When the free swell ratio (GV) is less than 8 g / g, the amount of absorption is too small and it is not suitable for the use of sanitary materials such as diapers. On the other hand, when the free swelling ratio (GV) is larger than 50 g / g, the gel strength is weak and there is a possibility that a water absorbent resin having excellent liquid permeability cannot be obtained. The value measured by the method described in the examples is adopted as the value of the free swelling ratio.

Further, the saline flow conductivity (SFC) is preferably 10 (unit: 10 ⁻⁷ · cm ³ · s · g ⁻¹ ) or more, more preferably 30 (unit: 10 ⁻⁷ × cm ³ × s × g). ⁻¹ ) or more, more preferably 50 (unit: 10 ⁻⁷ × cm ³ × s × g ⁻¹ ) or more. Although an upper limit is not specifically limited, Preferably it is 500 (unit: 10 <^-7> * cm < ^{3 >} * s * g <^-1> ) or less. When the saline flow conductivity (SFC) is less than 10 (unit: 10 ⁻⁷ × cm ³ × s × g ⁻¹ ), the liquid permeability is not sufficient, so that the liquid can be sufficiently distributed to the absorber. In addition, there is a risk of reducing the amount of absorption of excreted liquid such as urine during use. The value measured by the method described in Examples is adopted as the saline flow conductivity value.
The water-absorbing agent of the present invention has a weight average particle diameter (specified by sieve classification) of 10 to 1,000 μm, preferably 200 to 600 μm, preferably 150 to 850 μm in content with respect to the water absorbent resin. 90 to 100% by weight, more preferably 95 to 100% by weight. The logarithmic standard deviation (σζ) of the particle size distribution is preferably 0.23 to 0.45, and more preferably 0.25 to 0.35.
The specific surface area of the water-absorbing agent of the present invention is preferably 0.02 m ² / g or more and 1.0 m ² / g or less.
More preferably not more than 0.03 m ² / g or more 0.5 m ² / g. If it is less than 0.02 m ² / g, the deodorizing property and the absorption rate are insufficient. If it exceeds 1.0 m ² / g, there is a possibility that the performance is lowered due to process damage (damage due to collision between particles or collision between particles and apparatus).
The absorption rate (FSR) of the water-absorbing agent of the present invention exceeds 0.15 and is 2.00 (g / g / sec) or less, preferably 0.17 or more and 1.00 (g / g / sec). Hereinafter, it is more preferably 0.20 or more and 0.90 (g / g / sec) or less, particularly preferably 0.30 or more and 0.80 (g / g / sec) or less. When the FSR is 0.15 or less, the absorption rate is slow, which may cause diaper leakage. Moreover, when FSR exceeds 2.00, there exists a possibility that the liquid diffusion in a diaper may fall.

  Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples, but the present invention is not limited to these. Hereinafter, for convenience, “part by weight” may be simply referred to as “part”, and “liter” may be simply referred to as “L”. Measurement methods and evaluation methods in Examples and Comparative Examples are shown below.

(1) Particle size distribution 10 g of water-absorbing resin particles or water-absorbing agent is sieved with a test sieve (made by IIDA Seisakusho) having a diameter of 75 mm, openings of 850 μm, 600 μm, 300 μm, and 150 μm, the respective masses are measured, and the weight of each particle size %. The sieving was performed by shaking for 5 minutes using a SIEVE SHAKER ES-65 type manufactured by IIDA Seisakusho. The water-absorbent resin was measured after drying at 60 ± 5 ° C. under reduced pressure (less than 1 mmHg (133.3 pa)) for 24 hours.

(2) Measurement of solid content 1 g of water-absorbing resin was uniformly spread on the bottom of the aluminum bag cup in an aluminum cup having a bottom diameter of 4 cm and a height of 2 cm. This was left in a hot air dryer adjusted to 180 ° C. for 3 hours, and the solid content (%) of the water absorbent resin was calculated from the weight loss before and after.

(3) Free swelling ratio (GV)
Put 0.2 g of water-absorbent resin uniformly in a non-woven bag (Nangoku Pulp Industries Co., Ltd., trade name: Heatron paper, model: GSP-22, size: 60 mm × 60 mm), and a large excess (usually 500 mL) of 0.9 wt% aqueous sodium chloride solution (saline) at room temperature (25 ± 2 ° C.). After 30 minutes, the bag was pulled up and drained with a centrifugal force of 250 G for 3 minutes using a centrifuge, and then the mass W ₁ (g) of the bag was measured. Moreover, the same operation was performed without using a water absorbent resin, and the mass W ₂ (g) of the bag at that time was measured. _Then, the W 1, _{W 2,} was calculated free swelling capacity (GV) (g / g) by the following equation.

Free swelling ratio (g / g) = [W ₁ (g) −W ₂ (g) −mass of water absorbent resin (g)] / mass of water absorbent resin (g)
(4) Absorption capacity under pressure (AAP)
A stainless steel 400 mesh wire mesh (aperture size 38 μm) is fused to the bottom of a plastic support cylinder with an inner diameter of 60 mm, and water is absorbed on the wire mesh at room temperature (25 ± 2 ° C.) and humidity 50 RH%. 0.900 g of the water-soluble resin was uniformly sprayed, and the outer diameter was adjusted to be able to uniformly apply a load of 4.83 kPa to the water-absorbent resin. A piston and a load in which no gap was formed between the wall surface and the vertical movement was not hindered were placed in this order, and the mass Wa (g) of this measuring device set was measured.

  A glass filter with a diameter of 90 mm (manufactured by Mutual Riken Glass Co., Ltd., pore diameter: 100 to 120 μm) is placed inside a petri dish with a diameter of 150 mm, and a 0.9 wt% sodium chloride aqueous solution (saline) (20 to 25 ° C.) was added to the same level as the upper surface of the glass filter. On top of that, a sheet of filter paper having a diameter of 90 mm (manufactured by ADVANTEC Toyo Co., Ltd., product name: (JIS P 3801, No. 2), thickness 0.26 mm, retained particle diameter 5 μm) was placed so that the entire surface was wet. Excess liquid was removed.

A set of measuring devices was placed on the wet filter paper, and the liquid was absorbed under load for a predetermined time. This absorption time was calculated from the start of measurement and was 1 hour later. Specifically, after 1 hour, the measuring device set was lifted and its mass W _b (g) was measured. This mass measurement must be performed as quickly as possible and without vibrations. Then, the absorption capacity under pressure (AAP) (g / g) was calculated from W _a and W _b by the following formula.

AAP (g / g) = [W _b (g) −W _a (g)] / mass of water absorbent resin (g)
(5) Saline flow conductivity (SFC)
The saline flow conductivity (SFC) is a value indicating the liquid permeability when the water absorbent resin swells. It shows that it has high liquid permeability, so that the value of SFC is large.

  This was performed according to the saline flow conductivity (SFC) test described in JP-T 9-509591.

  Using the apparatus shown in FIG. 1, a water-absorbent resin (0.900 g) uniformly placed in a container 40 is swollen for 60 minutes in an artificial urine under a pressure of 0.3 psi (2.07 kPa) to form a gel layer of gel 44 Then, under a pressure of 0.3 psi (2.07 kPa), 0.69 wt% saline 33 was passed through the swollen gel layer from the tank 31 at a constant hydrostatic pressure. The SFC test was performed at room temperature (20-25 ° C.). Using a computer and a balance, the amount of liquid passing through the gel layer at 20 second intervals as a function of time was recorded for 10 minutes. The flow rate Fs (T) passing through the swollen gel 44 (mainly between the particles) was determined in units of g / s by dividing the increased mass (g) by the increased time (s). Let Ts be the time at which a constant hydrostatic pressure and a stable flow rate were obtained, use only the data obtained between Ts and 10 minutes for the flow rate calculation, and use the flow rate obtained between Ts and 10 minutes. The value of Fs (T = 0), ie the initial flow rate through the gel layer, was calculated. Fs (T = 0) was calculated by extrapolating the result of the least squares method of Fs (T) versus time to T = 0.

Saline flow conductivity (SFC)
= (Fs (t = 0) × L0) / (ρ × A × ΔP)
= (Fs (t = 0) × L0) / 139506
here,
Fs (t = 0): flow rate expressed in g / s,
L0: height of the gel layer expressed in cm,
ρ: density of NaCl solution (1.003 g / cm ³ ),
A: Area above the gel layer in the cell 41 (28.27 cm ² ),
ΔP: Hydrostatic pressure applied to the gel layer (4920 dyne / cm ² ), and the unit of SFC value is (10 ⁻⁷ · cm ³ · s · g ⁻¹ ).

  In the apparatus shown in FIG. 1, a glass tube 32 is inserted into the tank 31, and the lower end of the glass tube 32 is 5 cm from the bottom of the swollen gel 44 in the cell 41 with 0.69 wt% saline 33. It was arranged so that it could be maintained at the upper height. The 0.69 wt% saline solution 33 in the tank 31 was supplied to the cell 41 through the L-shaped tube 34 with a cock. Under the cell 41, a container 48 for collecting the passed liquid is disposed, and the collection container 48 is installed on an upper pan balance 49. The inner diameter of the cell 41 is 6 cm. A 400 stainless steel wire mesh (aperture 38 μm) 42 was installed. There was a hole 47 sufficient for the liquid to pass through the lower part of the piston 46, and a glass filter 45 with good permeability was attached to the bottom so that the water-absorbing resin or its swelling gel did not enter the hole 47. . The cell 41 was placed on a table on which the cell was placed, and the surface of the table in contact with the cell was placed on a stainless steel wire mesh 43 that did not prevent liquid permeation.

  The artificial urine is composed of 0.25 g of calcium chloride dihydrate, 2.0 g of potassium chloride, 0.50 g of magnesium chloride hexahydrate, 2.0 g of sodium sulfate, 0.85 g of ammonium dihydrogen phosphate, A mixture of 0.15 g of diammonium hydrogen phosphate and 994.25 g of pure water.

(6) Absorption rate (FSR)
1.00 g of water-absorbing resin was put in a 25 ml glass beaker (diameter 32 to 34 mm, height 50 mm). At this time, the upper surface of the water absorbent resin placed in the beaker was made horizontal. (If necessary, the surface of the water-absorbent resin may be leveled by carefully tapping the beaker.) Next, 20 g of physiological saline adjusted to 23 ° C. ± 2 ° C. is added to a 50 ml glass beaker. The total weight (unit: g) of physiological saline and glass beaker was measured (W3). The weighed physiological saline was carefully and quickly poured into a 25 ml beaker containing a water absorbent resin. Time measurement was started at the same time as the poured physiological saline contacted the water-absorbent resin. When the upper surface of the physiological saline solution in the beaker into which the physiological saline has been poured is viewed at an angle of about 20 °, the upper surface that was the surface of the physiological saline solution firstly absorbs the physiological saline. Thus, the time measurement was completed (unit: seconds) (t _S ) when the surface was replaced with the water-absorbent resin surface that had absorbed physiological saline. Next, the weight (unit: g) of a 50 ml glass beaker after pouring physiological saline was measured (W4). The weight of the poured physiological saline (W5, unit: g) was determined by the following formula. The absorption rate (FSR) was calculated by the following equation.
Formula: W5 (g) = W3 (g) -W4 (g)
Formula: FSR (g / g / s) = W5 / (t _S × mass of water absorbent resin (g))
(7) Soluble content
Weigh out 184.3 g of 0.900 wt% sodium chloride aqueous solution in a plastic container with a lid of 250 ml capacity (diameter 6 cm x height 9 cm), add 1.00 g of particulate water-absorbing resin to the aqueous solution, and continue for 16 hours. By using a magnetic stirrer having a diameter of 8 mm and a length of 25 mm and stirring at a rotation speed of 500 rpm, a soluble component in the resin was extracted. 50.0 g of the filtrate obtained by filtering this extract using one filter paper (ADVANTEC Toyo Co., Ltd., product name: JIS P 3801 No. 2, thickness: 0.26 mm, reserved particle diameter 5 μm) A measurement solution was obtained.

  First, only 0.900 wt% sodium chloride aqueous solution was titrated to pH 10 with 0.1N NaOH aqueous solution, and then titrated to pH 2.7 with 0.1N HCl aqueous solution ([bNaOH]). ml, [bHCl] ml).

  The titration ([NaOH] ml, [HCl] ml) was determined by performing the same titration operation on the measurement solution.

  For example, in the case of a water-absorbing resin composed of a known amount of acrylic acid and its sodium salt, based on the average molecular weight of the monomer and the titration amount obtained by the above operation, the soluble content in the water-absorbing resin is expressed by the following equation: Can be calculated. In the case of an unknown amount, the average molecular weight of the monomer was calculated using the neutralization rate obtained by titration.

Soluble content (% by weight) = 0.1 × (average molecular weight) × 184.3 × 100 × ([HCl] − [bHCl]) / 1000 / 1.0 / 50.0
Neutralization rate (mol%) = [1-([NaOH]-[bNaOH]) / ([HCl]-[bHCl])] × 100
(8) Specific surface area The specific surface area of the water-absorbing agent can be determined by “BET (Brunauer-Emmett-Teller) one-point method”. As the measuring apparatus, “specimen fully automatic specific surface area measuring apparatus 4-sorb U-1” (manufactured by Yuasa Ionics Co., Ltd.) is used. First, about 5 g of powder is placed in a microcell (TYPE: QS-400) having an internal volume of about 13 cm ³ , and the microcell containing the sample is heated to 150 ° C. under a nitrogen gas stream to sufficiently degas and dehydrate the sample. Do. Next, the microcell containing the sample is cooled to −200 ° C. under a mixed gas stream composed of helium gas and 0.1% krypton gas, and the mixed gas is adsorbed to the sample until equilibrium is reached. Thereafter, the temperature of the microcell containing the sample is returned to room temperature, desorption from the sample of the mixed gas is performed, and the specific surface area of the water-absorbent resin powder is obtained from the desorption amount of the krypton mixed gas. In addition, the adsorption | suction-desorption process of the microcell containing a sample is performed 3 times, and the specific surface area (m < ² > / g) of a water absorbing agent is calculated | required from the average amount.
(Production example)
5433 g of an aqueous solution of sodium acrylate having a neutralization rate of 70 mol% (monomer) in a reactor formed by attaching a lid to a stainless steel double arm type kneader with an internal volume of 10 L and having two sigma blades Concentration: 43% by weight) was charged, and 12.83 g of polyethylene glycol diacrylate (average number of ethylene oxide units: n = 9) as an internal crosslinking agent was dissolved in the aqueous solution to prepare a reaction solution. Subsequently, this reaction liquid was deaerated under a nitrogen gas atmosphere. Subsequently, 29.43 g of a 10 wt% aqueous solution of sodium persulfate as a polymerization initiator and 24.53 g of a 0.1 wt% aqueous solution of L-ascorbic acid were added to the reaction solution while stirring. As a result, polymerization started after about 1 minute. Then, polymerization was performed at 20 to 95 ° C. while pulverizing the generated gel, and a hydrous gel-like crosslinked polymer was taken out 30 minutes after the polymerization started. The particle size of the obtained hydrogel crosslinked polymer was 5 mm or less. The crushed water-containing gel-like crosslinked polymer was spread on a 50 mesh (mesh opening 300 μm) wire net and dried with hot air at 175 ° C. for 50 minutes. In this way, an agglomerated powdery aggregate that can be easily pulverized was obtained.

The obtained powdery aggregate was pulverized using a roll mill, and further classified using a JIS standard sieve having openings of 300 μm and 600 μm to obtain water-absorbing resin particles (sample A) having a particle size of 300 to 600 μm. . Next, the particles that passed through the sieve having an opening of 300 μm by the above operation were classified using a JIS standard sieve having an opening of 45 μm, and fine particles (sample B) that passed through the sieve having an opening of 45 μm were obtained.
Separately, a base polymer is separately produced as a different fine particle, heated and treated with polyhydric alcohol, classified using a JIS standard sieve having an opening of 45 μm, and passed through a sieve having an opening of 45 μm (sample treated) C) was obtained.
These classified water-absorbing resin particles and fine particles were prepared, and the following comparative experiment was conducted.
Example 1 Sample A (90 wt%) and sample B (10 wt%) were mixed and then subjected to surface treatment by irradiation with ultraviolet rays.
Comparative Example 1 Sample A (90 wt%) and Sample B (10 wt%) were mixed.
Comparative Example 2 Sample A UV surface-treated product (90 wt%) and sample C (10 wt%) were mixed.

The surface treatment was performed by the following method.
(Method of surface treatment by ultraviolet ray irradiation)
Add 30 g of water-absorbent resin particles (mixture of sample A and sample B or sample A alone) as a base polymer to a 500-mL quartz separable flask, stir with a stirring blade, and add 2-hydroxy-3-acryloyloxypropyl methacrylate ( Shin Nakamura Chemical Co., Ltd., NK Ester 701A) 0.03 g, acrylic acid 1.20 g, water 2.10 g, Irgacure 2959 (Ciba Specialty Chemicals Co., Ltd.) 0.003 g, polyethylene glycol monomethyl ether (number average) A treatment liquid in which 0.003 g of a molecular weight of about 2,000) was mixed in advance was added. After stirring for 10 minutes, an irradiation intensity of 65 mW / cm ² (quartz) was used using an ultraviolet irradiation device (UV-152 / 1MNSC3-AA06) equipped with a metal halide lamp (Ushio Electric, UVL-1500M2-N1). Ultraviolet rays were irradiated at room temperature for 1 minute at a position closest to the UV lamp on the wall of the separable flask manufactured by Ushio Electric's UV integrated light meter UIT-150 and light receiving unit UVD-S254. Thereafter, sampling was performed to obtain a surface-treated water-absorbing resin (UV surface-treated product).

The obtained three mixtures were placed on a transparent plate, and 0.9% by weight aqueous sodium chloride solution (physiological saline) was appropriately swelled at room temperature. (Water absorption is about 25 times)
The state after the saturation swelling was observed with an optical microscope. Table 1 shows the observed state.

  Further, as shown in Table 2, the physical properties of the mixture of Example 1 were large in surface area and excellent in absorption characteristics. Moreover, when the optical micrograph of FIG. 3 is seen, it turns out that microparticles | fine-particles have adhered.

  The surface of the mixture obtained in Example 1 of the present invention is surface-treated with acrylic acid (neutralization rate 0%). A basic malodorous component (for example, ammonia, amines) can be neutralized by an acrylic acid moiety that has not been neutralized. Furthermore, the surface area is large. Therefore, the deodorizing property is high.

  Moreover, since fine particles are not detached even after swelling due to water absorption, the performance can be maintained for a long time even when used in various environments.

  The water-absorbing agent of the present invention has excellent water-absorbing characteristics because fine particles firmly fixed are present on the surface and the surface area is large. Therefore, it can be used as a paper diaper and the like, which is industrially useful.

It is the schematic of the measuring apparatus used for the measurement of a saline flow conductivity (SFC). It is an image figure of the water absorbing agent which the microparticles | fine-particles of this invention fixed. 2 is an optical micrograph showing the water-absorbing agent before swelling obtained in Example 1. FIG.

Explanation of symbols

31 tanks,
32 glass tubes,
33 0.69 wt% aqueous sodium chloride solution,
34 L-shaped tube,
35
40 containers,
41 cells,
42, 43 wire mesh,
44 swollen gel,
45 Glass filter,
46 piston,
47 holes,
48 collection containers,
49 Precision balance,

Claims (7)

A water-absorbing agent in which organic fine particles and / or inorganic fine particles are fixed to the surface of acid group-containing water-absorbing resin particles, wherein the acid group neutralization rate on the surface of the water-absorbing agent is determined by the acid groups inside the water-absorbing resin particles. A water-absorbing agent characterized by being less than a neutralization rate. The water-absorbing agent according to claim 1, wherein the water-absorbing agent is surface-treated with a treatment liquid containing an acid group-containing radically polymerizable compound. The water-absorbing agent according to claim 1 or 2, wherein an acid group neutralization rate inside the water-absorbent resin particles is more than 40 mol% and 90 mol% or less. The water-absorbing agent according to claim 2 or 3, wherein the neutralization rate of the acid group-containing radical polymerizable compound contained in the treatment liquid is 0 to 30 mol%. The water-absorbing agent according to any one of claims 1 to 4, wherein the water-absorbent resin particles have a mass average particle diameter of 150 µm or more and 850 µm or less. The water-absorbing agent according to any one of claims 1 to 5, wherein the fine particles have a mass average particle diameter of less than 150 µm. An absorbent article comprising the water-absorbing agent according to any one of claims 1 to 6.

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