JP6029800B2 - Water absorbent resin particles - Google Patents

Description

  The present invention relates to a water absorbent resin and a method for producing the same. More specifically, the present invention relates to a water-absorbent resin having a high absorption rate, which has a controlled particle size distribution, a small amount of fine powder, and excellent impact resistance (powder wear resistance), and a method for producing the same.

  In recent years, water-absorbing resins, which are examples of hydrophilic polymers, have been widely used in various applications such as paper diapers, sanitary napkins, adult incontinence products, soil water retention agents, etc. for mass production and consumption. Has been. In particular, in sanitary products such as paper diapers, sanitary napkins, and incontinence products for adults, the amount of water-absorbing resin used tends to increase and the amount of pulp fiber used tends to decrease in order to make the product thinner. Therefore, a water-absorbing resin having a high absorption capacity under pressure is desired. On the other hand, since the amount of water-absorbing resin used per sanitary product is large, it is desired that the water-absorbing resin can be manufactured at low cost. Therefore, it is desired to reduce the energy consumption in the production line of the water-absorbent resin, reduce the emissions, and establish a rational production method using them.

  Properties desired for water-absorbing resins include high absorption capacity, high compression capacity, high absorption rate, low residual monomer, low (less) water-soluble content, etc. Is one of the basic issues of water-absorbing resins, and many methods have been proposed.

  Since the absorption rate greatly depends on the specific surface area, the method of reducing the particle diameter has a problem that other physical properties such as generation of dust and liquid permeability decrease. Therefore, many speed improvement methods such as foaming and granulation have been proposed. For example, a method in which a solid (solid) is dispersed to perform foam polymerization (Patent Document 1), and a method in which a gas is dispersed to perform foam polymerization (Patent Document 2). ), Foam polymerization with carbonate (Patent Documents 3 and 4), foam polymerization with 0.1 to 20% of surfactant (Patent Documents 5 and 6), extrusion granulation method from aspherical die (Patent Documents) 7) A method of granulating water-absorbent resin fine particles with a polyvalent metal (Patent Document 8), a method of heating with microwaves (Patent Document 9), a method of incorporating a filler (Patent Document 10), etc. are known. .

Also known is a method (Patent Document 11) of foaming polymerization to polymerize a slurry of sodium acrylate fine precipitates containing microbubbles of inert gas.
US Pat. No. 5,985,944 (published November 16, 1999) US Pat. No. 6,107,358 (published August 22, 2000) US Pat. No. 5,721,316 (published January 27, 1998) US Pat. No. 5,462,972 (published October 31, 1995) US Pat. No. 6,136,973 (released October 24, 2000) US Pat. No. 6,174,929 (published January 26, 2001) US Pat. No. 6,133,193 (published October 17, 2000) US Pat. No. 5,002986 (published March 26, 1991) US Pat. No. 6,076,277 (published June 20, 2000) US Pat. No. 6,284,362 (published September 4, 2001) Japanese Patent Laid-Open No. 3-115313 (published on May 16, 1991)

  However, in the method of increasing the absorption speed by increasing the surface area by reducing the particle diameter, other physical properties are reduced as the fine powder increases. In addition, the method of granulating the water-absorbent resin in order to improve the absorption rate is complicated in process, and generally has a problem such as dust and physical property degradation because the granulation strength is weak. In addition, foaming methods not only require new foaming agents and surfactants, but also increase transportation and storage costs due to the decrease in bulk specific gravity due to foaming, and the foamed particles are weak, resulting in generation of fine powders and deterioration of physical properties. There's a problem. Furthermore, foaming polymerization has a problem of an increase in residual monomer and a problem that it is difficult to improve the absorption capacity under pressure (AAP).

  And with conventional water-absorbing resins, it is not only difficult or impossible to control all the physical properties such as water absorption rate, absorption capacity under pressure, particle size, residual monomer amount, etc. to a preferable range, but temporarily these physical properties are Even when a controlled water-absorbing resin is obtained, when a diaper is produced on a large scale, the diaper performance expected in the laboratory may not be exhibited.

  As a result of searching for the above causes, if the water absorption rate is increased (foaming or granulating), the water absorbent resin is damaged when it is transported in a factory line or the like, and fine powder is easily generated. Problems such as lowering the performance of diapers when used in diapers have also been found.

  For this reason, there has been a demand for a water-absorbing resin that improves the performance of the water-absorbing resin capable of maximizing the performance of diapers, specifically, has a high water-absorbing speed and is resistant to damage (it is difficult to generate fine powder).

  The present invention has been made in view of the above problems, and its object is to provide a method for producing a water-absorbing resin with a small amount of fine powder and dust, having a small amount of residual monomers and a high absorption rate with high productivity. It is to provide.

  As a result of intensive studies in view of the above problems, the present inventors have made a monomer aqueous solution contain a solid (solid) in a method for producing a water-absorbing resin in which an aqueous solution of an acid group-containing unsaturated monomer is crosslinked. And it discovered that the said subject could be solved by the high temperature polymerization prescribed | regulated by the high temperature polymerization start or high temperature polymerization peak more than specific temperature, and completed this invention. That is, by high-temperature polymerization at a specific temperature or higher and by crosslinking polymerization of an aqueous monomer solution containing a solid (preferably water-insoluble particles), productivity is high in a simple process, and the absorption rate is improved. It was also found that a water-absorbing resin with reduced residual monomers can be obtained.

  As a result of pursuing the cause of insufficient performance of diapers in actual use for the above water-absorbing resin with high water absorption speed, particle destruction of the water-absorbing resin occurs during transportation and diaper manufacturing process, and it is incorporated into diapers It was found that the physical properties of the water-absorbent resin were greatly reduced. Furthermore, the water-absorbing resin found in the present invention containing fine particles or the water-absorbing resin satisfying specific water-absorbing performance solves the above problems, maintains high performance even in diapers, and provides excellent diapers. Found that you can.

  That is, the method for producing a water-absorbing resin of the present invention is a method for producing a water-absorbing resin in which an aqueous solution of an acid group-containing unsaturated monomer is cross-linked, preferably cross-linked and polymerized. (Preferably a water-insoluble solid), and the polymerization is allowed to stand in the presence of the solid, and the polymerization start temperature is controlled to 40 ° C or higher, or the maximum temperature during polymerization is controlled to 100 ° C or higher. It is characterized by carrying out polymerization.

  In the method for producing a water-absorbent resin of the present invention, the solid is preferably water-insoluble particles.

  In the method for producing a water absorbent resin of the present invention, it is preferable that the standing polymerization is performed by a continuous belt device.

  In the method for producing a water absorbent resin of the present invention, the solid is preferably a dry powder or swollen gel particles of the water absorbent resin.

  In the method for producing a water absorbent resin of the present invention, the content of the solid is 0.1 to 50% by weight with respect to the acid group-containing unsaturated monomer, and 90% by weight or more of the solid is a standard sieve. It is preferable that it is a 5 mm passage.

  In the method for producing a water absorbent resin of the present invention, the monomer preferably contains 70 to 99.999 mol% of acrylic acid (salt) and 0.001 to 5 mol% of a crosslinking agent.

  In the method for producing a water absorbent resin of the present invention, the solid material is preferably a water absorbent resin having an absorption capacity (CRC) of 5 to 20 g / g with respect to physiological saline.

  In the method for producing a water absorbent resin of the present invention, the polymerization time is preferably 10 minutes or less.

  In the method for producing a water absorbent resin of the present invention, the aqueous solution concentration of the monomer is preferably in the range of 40 to 90% by weight.

  The water-absorbing resin particles of the present invention are water-absorbing resin particles having 70 to 99.999 mol% of acrylic acid (salt) and 0.001 to 5 mol% of a cross-linking agent as repeating units. ) To (6) are satisfied.

  (1) Absorption capacity (CRC) is 20-40 g / g.

  (2) Absorption capacity under pressure (AAP) is 20 to 40 g / g.

  (3) Absorption rate (FSR) is 0.25 to 1.0 g / g / sec.

  (4) The bulk specific gravity (JIS K 3362) is 0.50 to 0.80 g / ml.

  (5) The residual monomer is 0 to 400 ppm.

  (6) Particles (JIS Z8801-1) of 850 to 150 μm are 95 to 100% by weight.

  The water-absorbent resin particles of the present invention are obtained by polymerizing an aqueous solution of an acid group-containing unsaturated monomer, and water-insoluble particles 0.1 to 0.1 on the basis of the weight of the acid group-containing unsaturated monomer at the time of polymerization. 50% by weight is preferably contained inside.

  Other objects, features, and advantages of the present invention will be fully understood from the following description. The advantages of the present invention will become apparent from the following description with reference to the accompanying drawings.

  As described above, the method for producing a water-absorbing resin according to the present invention is a method for producing a water-absorbing resin in which an aqueous solution of an acid group-containing unsaturated monomer is crosslinked, preferably crosslinked, and the monomer aqueous solution. The solid content (preferably a water-insoluble solid) is allowed to stand in the presence of the solid, so that the polymerization start temperature is 40 ° C. or higher, or the maximum temperature during polymerization is 100 ° C. or higher. It is characterized by controlled polymerization at rest.

  For this reason, there is an effect that it is possible to provide a method for producing a water-absorbing resin with a small amount of fine powder and dust, a low amount of residual monomer, and a high absorption rate with high productivity.

The water-absorbing resin particles of the present invention are water-absorbing resin particles having 70 to 99.999 mol% of acrylic acid (salt) and 0.001 to 5 mol% of a cross-linking agent as repeating units. ) To (6) are satisfied.
(1) Absorption capacity (CRC) is 20-40 g / g.
(2) Absorption capacity under pressure (AAP) is 20 to 40 g / g.
(3) Absorption rate (FSR) is 0.25 to 1.0 g / g / sec.
(4) The bulk specific gravity (JIS K 3362) is 0.50 to 0.80 g / ml.
(5) The residual monomer is 0 to 400 ppm.
(6) Particles (JIS Z8801-1) of 850 to 150 μm are 95 to 100% by weight.

  For this reason, there is an effect that it is a water-absorbing resin with a small amount of fine powder and dust, a residual monomer is small, and a water-absorbing resin having a high absorption rate can be provided.

  Hereinafter, one embodiment of the present invention will be described in detail. However, the scope of the present invention is not limited to these descriptions, and modifications other than the following examples may be made as appropriate without departing from the spirit of the present invention. Can be implemented.

  In the following description, “weight” is treated as a synonym for “mass”, “weight%” is treated as a synonym for “mass%”, and “main component” is 50 mass% or more (more preferably 60%). (Mass% or more) treated as meaning. In addition, “A to B” indicating a range indicates that the range is A or more and B or less.

  In the present specification, “(meth) acryl”, “(meth) acryloyl”, “(meth) acrylate” and the like are “acryl or methacryl”, “acryloyl or methacryloyl”, and “acrylate or methacrylate”. Each means “acrylic acid (salt)” means “acrylic acid or acrylate”. The “acrylic acid salt” means a monovalent salt.

(Water absorbent resin)
In the present invention, the water-absorbent resin is a water-swellable, water-insoluble crosslinked polymer that can form a hydrogel. The water-swellable crosslinked polymer refers to, for example, a polymer that absorbs 5 times or more, preferably 50 to 1000 times the weight of its own weight in ion-exchanged water. The water-insoluble crosslinked polymer is preferably, for example, an uncrosslinked water-soluble component (water-soluble polymer) in the water absorbent resin, preferably 0 to 50% by mass, more preferably 25% by mass or less, and still more preferably. 20% by mass or less, more preferably 15% by mass or less, particularly preferably 10% by mass or less.

(Monomer)
Examples of monomers used in the present invention to be polymerized to become a water-absorbing resin include acrylic acid, methacrylic acid, maleic acid, maleic anhydride, β-acryloyloxypropionic acid, fumaric acid, crotonic acid, itaconic acid. , Cinnamic acid, vinyl sulfonic acid, allyl toluene sulfonic acid, vinyl toluene sulfonic acid, styrene sulfonic acid, 2- (meth) acrylamide-2-methylpropane sulfonic acid, 2- (meth) acryloylethane sulfonic acid, 2- ( Anionic unsaturated monomers and salts thereof such as (meth) acryloylpropanesulfonic acid, 2-hydroxyethyl (meth) acryloyl phosphate; mercapto group-containing unsaturated monomers; phenolic hydroxyl group-containing unsaturated monomers; (Meth) acrylamide, N-ethyl (meth) acrylamide, N, N-dimethyl Amide group-containing unsaturated monomers such as (meth) acrylamide; N, N-dimethylaminoethyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylamide An amino group-containing unsaturated monomer such as

  These monomers may be used singly or may be used in combination of two or more, but acrylic acid and / or a salt thereof (for example, sodium) from the viewpoint of performance and cost of the resulting water-absorbent resin It is preferable to use a salt of lithium, potassium, ammonium, amines, etc. as a main component.

  The neutralization rate of acrylic acid before or after polymerization is preferably 30 to 100 mol%, more preferably 50 to 85 mol%, more preferably 55 to 80 mol%, and most preferably 60 to 75 mol%.

  Preferably, acrylic acid and / or a salt thereof is 50 to 100 mol%, more preferably 50 mol% or more, still more preferably 80 mol% or more, particularly preferably 80 mol% or more, based on all monomer components (excluding the crosslinking agent). Preferably it is 95 mol% or more.

  The concentration of the monomer is not particularly limited, but is usually 20% by weight or more, preferably 30% by weight or more, more preferably 35% by weight or more, more preferably 40% by weight or more, and particularly preferably 45% by weight or more. Preferably it is 50 weight% or more. The upper limit is the saturation concentration of the monomer, or 80% by weight or less, preferably 70% by weight or less, more preferably 60% by weight or less. If the concentration is less than 20% by weight, the absorption rate may not be improved. Also known is a method for producing a water-absorbing resin in which sodium acrylate is polymerized with a slurry aqueous dispersion exceeding the saturation concentration (JP-A-3-115313). If it exceeds%, the absorption capacity tends to be low. The saturation concentration of the monomer is determined by the type of monomer, temperature, type of solvent, type of auxiliary agent (for example, surfactant), addition amount, and the like.

  In the present invention, as a method for obtaining a water-absorbent resin having a crosslinked structure, polymerization is performed by adding a crosslinking agent to the monomer. In this case, a known crosslinking method for obtaining a water-absorbing resin such as radical self-crosslinking or radiation crosslinking during polymerization may be used in combination.

  The internal cross-linking agent used can be used without limitation as long as it can form a cross-linked structure at the time of polymerization. For example, the cross-linking agent having a plurality of polymerizable unsaturated groups, glycidyl acrylate and the like are not polymerizable. Crosslinker having both a saturated group and a highly reactive group, a sorbitol (see, for example, International Publication No. 2006/319627 pamphlet), a crosslinker having a plurality of highly reactive groups such as (poly) ethylene glycol diglycidyl ether An ionic cross-linking agent such as a polyvalent metal salt such as aluminum chloride, a cross-linking agent having a plurality of hydroxyl groups such as glycerin is exemplified, and the combined use is not limited, but a cross-linking agent having a plurality of polymerizable unsaturated groups Is most preferable in terms of various physical properties. Examples of the crosslinking agent having a plurality of polymerizable unsaturated groups used include N, N′-methylenebisacrylamide, (poly) ethylene glycol di (meth) acrylate, (poly) propylene glycol di (meth) acrylate, and trimethylol. Propane tri (meth) acrylate, trimethylolpropane di (meth) acrylate, trimethylolpropane tri (β-acryloyloxypropionate), polyethylene glycol di (β-acryloyloxypropionate), (meth) allyloxyalkane, One type or two or more types such as glyceryl acrylate methacrylate are exemplified. In addition, although the usage-amount of a crosslinking agent is suitably determined according to the kind of crosslinking agent and the target water absorbing resin, it is 0.001-5 mol% normally with respect to an acid group containing polymerizable monomer, 0. 0.005 to 4 mol%, preferably 0.01 to 1 mol%.

As described above, in the present invention, it is preferable that 70 to 99.999 mol% of acrylic acid (salt) and 0.001 to 5 mol% of a crosslinking agent are included as repeating units.
In addition, a monomer, starch, poval, water-soluble polymer such as PEG and PEO, about 0 to 30% by mass, a chain transfer agent such as hypophosphorous acid (salt), and a chelating agent described later may be added. Good.

(Solid matter)
The compound to be dispersed in the monomer aqueous solution has an aqueous solution temperature of 0 to 40 ° C., more preferably 10 to 30 ° C., particularly 25 ° C. (note that the pressure is normal pressure (1 atm)). In some cases, the compound is insoluble or hardly soluble and dispersible in the aqueous solution. Preferably, the solid (solid) is water-insoluble particles.

  As such a solid material (hereinafter also referred to as a solid or a solid material), various solid materials such as an inorganic material, an organic material, and an organic-inorganic composite material can be used. For example, inorganic substances such as bentonite, zeolite, silicon oxide, aluminum oxide, activated carbon, polyacrylic acid (salt) crosslinked product, polyacrylamide and its crosslinked product, acrylic acid (salt) -acrylamide copolymer crosslinked product, or N, N- Examples include organic substances such as a copolymer crosslinked product of a cationic monomer such as dimethylaminoethyl (meth) acrylate and its quaternary salt and polyacrylamide, and a crosslinked product of a polycation compound such as polyethyleneimine, polyvinylamine, and polyallylamine. . Moreover, the composite body and blend of an organic substance and an inorganic substance are also mentioned. The solid may swell in a monomer aqueous solution to form a gel. In the present invention, even in the form of a gel, the state in which it is not dissolved in the monomer but dispersed is also solid.

  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 promotes foaming more effectively. Is preferable.

  These solids (solids) are usually preferably powdery (particulate) compounds that are solid at room temperature. The particle diameter is preferably 90% by weight or more (up to 100% by weight), preferably 5 mm or less, more preferably 3 mm or less, still more preferably 1 mm or less, and particularly preferably 150 μm or less. When the particle diameter of the powder exceeds 5 mm, the number of bubbles that can be present in the water-absorbent resin is reduced, and it may be necessary to perform pulverization, which is not preferable.

  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 5 mm, and the particle size of all particles is 5 nm to 1 mm. Most preferably within the range. When the particle diameter of the powder is less than 1 nm, it may be difficult to mix uniformly in the monomer aqueous solution.

  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. . Specifically, in the compound to be dispersed, 70% by weight or more of the compound is insoluble in water at normal temperature, more preferably 80% by weight or more, more preferably 90% by weight or more, more preferably 95% by weight or more, Particularly preferred is 98% by weight or more.

  In the present invention, a polyacrylic acid (salt) cross-linked polymer, that is, a polyacrylic acid (salt) water-absorbing resin is preferably used as a solid (solid). The solid is a dry powder or swollen gel particle of a water absorbent resin.

  When a polyacrylic acid (salt) -based water-absorbing resin is used, the absorption capacity (CRC) is preferably as low as possible to achieve the present invention, and is usually 50 g / g or less, preferably 40 g / g or less, more preferably 30 g. / G or less, particularly preferably 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, preferably in the present invention, the solid (solid) is a water-absorbing resin having an absorption capacity (CRC) 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 or coarse particles removed for particle size control. That is, after removing fine powder and coarse particles in the manufacturing process of the water-absorbent resin, they can be used as a solid (solid) of the present invention without discarding them, so that the particle size can be controlled and the absorption rate is improved. .

  The concentration of solid (preferably water-absorbing resin) with respect to the monomer may be appropriately set according to the intended performance, but is usually 0.1% by weight or more, preferably 1% by weight with respect to the monomer. Or more, more preferably 3% by weight or more, more preferably 5% by weight or more, particularly preferably 10% by weight or more, and the upper limit is usually 50% by weight or less, preferably 40% by weight or less, more preferably 30% by weight or less, More preferably, it is 20 weight% or less. If the amount is less than 0.1% by weight, the effect of the addition is hardly observed. If the amount exceeds 50% by weight, a decrease in the absorption capacity may be observed.

  Further, the method for dispersing the solid (solid) is not particularly limited. For example, the solid (solid) is dispersed in a liquid monomer or monomer aqueous solution in a tank or continuously flowing in the liquid. The method of continuously dispersing using a mixer, the method of dispersing in the monomer aqueous solution supplied to the polymerization machine and mixing and dispersing as necessary, and further, after dispersing the solid in the polymerization machine A method may be used in which an aqueous monomer solution is supplied and mixed and dispersed as necessary. Thus, by dispersing the compound, the compound can be uniformly dispersed in the monomer aqueous solution.

  As the dispersion method, when continuous stationary polymerization using an endless belt, which will be described later, is performed, a method of spraying solids on the monomer aqueous solution supplied to the endless belt, or supplying the monomer aqueous solution to the endless belt A method of spraying a solid before the treatment is preferred, and the former is more preferred.

  The above dispersion method is more preferable because a solid matter does not cause trouble due to local deposition, unlike the case where a solid matter is previously charged into the monomer aqueous solution adjustment tank or when line mixing is performed.

  Furthermore, in the above dispersion method, since the solid matter can be dispersed intermittently with or without the solid matter, while the stationary polymerization is continuously performed without stopping the stationary polymerization halfway. The amount of solid matter sprayed can be adjusted as appropriate.

  The timing of spraying the solid in the above method of spraying the solid on the monomer aqueous solution supplied to the endless belt is not particularly limited as long as it is performed before the polymerization of the monomer aqueous solution is completed, but it is more effective. From the viewpoint of carrying out foaming polymerization, it is more preferable to spray the solid matter on the monomer aqueous solution immediately after the start of polymerization (specifically, within 10 seconds from the start of polymerization).

(polymerization)
The polymerization in the present invention is a static aqueous solution polymerization, and it is essential that the polymerization is started at a polymerization start temperature of 40 ° C. or higher or a maximum temperature of 100 ° C. or higher. When it is not stationary polymerization, for example, when it is reverse phase suspension polymerization or aqueous solution stirring polymerization, even if a solid is contained, the resulting water-absorbent resin does not improve the absorption rate. Even when the polymerization starting temperature is 40 ° C. or higher or the maximum temperature is not 100 ° C. or higher, the absorption rate is not improved. In addition, kneader polymerization (US Patent Application Publication No. 2004-110897, US Patent Nos. 670141, 462501, 5250640, etc.) is known as stirring aqueous solution polymerization, and these are obtained because stirring is performed throughout the polymerization. It is inferior in the improvement of the absorption rate of the water-absorbent resin obtained, and is not applied in the present invention.

  The static polymerization is a polymerization method in which a polymerization reaction is allowed to proceed without performing an operation of stirring the monomer aqueous solution with a stirrer or the like. In addition, strictly speaking, in the case where the polymerization initiator is added to the monomer aqueous solution and the stationary polymerization is performed after the monomer aqueous solution is uniformly mixed, an operation of stirring during the polymerization reaction is strictly performed. However, in this specification, even such a form is included in the stationary polymerization.

  That is, the stationary polymerization in the present specification is specifically a polymerization method in which a polymerization reaction proceeds without performing an operation of stirring the monomer aqueous solution at least after 30 seconds from the start of polymerization. Part of stirring or gel pulverization may be performed during the polymerization, but more preferable is a polymerization method in which a polymerization reaction is allowed to proceed without performing any operation of stirring the monomer aqueous solution from the start of polymerization. The embodiment using the endless belt described later is included in the stationary polymerization because it moves the entire monomer aqueous solution and does not perform an operation of stirring the monomer aqueous solution.

  The reverse phase suspension polymerization is a polymerization method in which an aqueous monomer solution is suspended in a hydrophobic organic solvent. For example, U.S. Pat. Nos. 4,093,764, 4,367,323, 4,446,261, 4,683,274, and 5,244,735. Are described in US patents. Aqueous solution polymerization is a method of polymerizing an aqueous monomer solution without using a dispersion solvent. For example, US Pat. Nos. 4,462,001, 4,873,299, 4,286,082, 4,973,632, 4,985,518, 5,124,416, 5,250,640 are used. No. 5,264,495, US Pat. No. 5,145,906 and US Pat. No. 5,380,808, and European patents such as European Patents 081636, 09555086, and 0922717. The monomers, crosslinking agents, polymerization initiators, and other additives described therein can also be applied in the present invention as long as they are used for standing aqueous solution polymerization.

(Polymerization equipment)
The stationary polymerization method can be carried out batchwise, but continuous stationary polymerization using an endless belt (for example, US Patent Application Publication No. 2005-215734) is preferable. The belt is preferably a resin or rubber belt that does not allow the heat of polymerization to escape from the contact surface. In order to improve the absorption rate, it is preferable that an open space exists in the upper part of the polymerization vessel. The charged thickness of the aqueous monomer solution (or gel) when the aqueous monomer solution containing the monomer, polymerization initiator, crosslinking agent and dispersed solid is supplied to the belt is usually preferably 1 to 100 mm, more preferably. Is 3 to 50 mm, most preferably 5 to 30 mm. If the thickness of the monomer aqueous solution is 1 mm or less, it is difficult to adjust the temperature of the monomer aqueous solution, and if it is 100 mm or more, it is difficult to remove the heat of polymerization, which causes the physical properties of the water-absorbent resin to deteriorate. The speed of the endless belt is usually preferably 0.3 to 100 m / min, more preferably 0.5 to 30 m / min, most preferably 1 to 20 m / min, although it depends on the length of the polymerization apparatus. . When the belt speed is slower than 0.3 m / min, the productivity is lowered, and when the belt speed is faster than 100 m / min, the polymerization apparatus becomes undesirably large.

  That is, the polymerization method of the present invention comprises a monomer aqueous solution containing a monomer, a polymerization initiator, a crosslinking agent and a dispersed solid, an endless belt to which the monomer and the produced hydropolymer are conveyed, It is a continuous production method of a water-absorbent resin using a continuous polymerization apparatus having an outlet for the water-containing polymer, and preferably satisfies the following conditions.

  The continuous polymerization apparatus is a method for continuously producing a water-absorbing resin, wherein the side surface and the ceiling surface are covered, and the apparatus porosity defined by the following formula 1 is in the range of 1.2 to 20.

Formula 1. Device porosity = B / A
A (cm ² ): Maximum cross-sectional area of the water-containing polymer during polymerization in the width direction of the endless belt B (cm ² ); between the endless belt of the continuous polymerization apparatus and the ceiling surface of the continuous polymerization apparatus It is preferable that the maximum cross-sectional area of the space with respect to the width direction of the endless belt and the polymerization method of the present invention further satisfy the following conditions.

  The continuous production method of a water-absorbent resin according to claim 1 or 2, wherein the apparatus height ratio defined by the following formula 3 is in the range of 10 to 500 and is a continuous production method.

Formula 3. (Belt ratio) = E / D
D (cm); charging thickness of the aqueous monomer solution E (cm); maximum height from the endless belt to the ceiling surface of the continuous polymerization apparatus In the stationary polymerization method according to the present embodiment, foaming is more Since the polymerization is performed in an increased state, a polymer having a surface area increased by bubbles can be obtained. For this reason, when polymerizing by the endless belt as described above, the obtained polymer does not adhere to the belt, and the obtained polymer can be easily peeled from the belt. This eliminates the need to forcibly scrape off the polymer adhering to the belt, thereby reducing the load on the belt and extending the usable period of the belt.

(Polymerization start temperature)
The polymerization initiation temperature in the present invention is essentially 40 ° C. or higher, preferably 50 ° C. or higher, more preferably 60 ° C. or higher, more preferably 70 ° C. or higher, more preferably 80 ° C. or higher, in order to improve the absorption rate. The upper limit is 150 ° C. or lower, usually 110 ° C. or lower, and further 100 ° C. or lower. When the temperature is low, the absorption rate is not improved, and when the temperature is too high, the absorption capacity is decreased and the soluble content is increased, so that the physical properties of the water-absorbent resin are deteriorated. Moreover, in this invention, it has the advantage that removal of dissolved oxygen becomes easy by making superposition | polymerization start temperature (monomer temperature) high. If the polymerization start temperature is less than 40 ° C., foam polymerization does not occur. Furthermore, not only the productivity is lowered due to the prolonged induction period and polymerization time, but also the physical properties of the water-absorbent resin are lowered.

  The polymerization initiation temperature can be observed by the cloudiness of the aqueous monomer solution, the increase in viscosity, the increase in temperature, and the like. The polymerization start temperature and the maximum polymerization temperature can be measured using a general mercury thermometer, alcohol thermometer, platinum resistance thermometer, contact temperature sensor such as a thermocouple or thermistor, and a radiation thermometer. Active energy rays such as ultraviolet rays, redox polymerization using an oxidizing agent and a reducing agent, and thermal initiation polymerization using an azo initiator generally have a short induction period of about 1 second to 1 minute. You may prescribe | regulate by the temperature of the monomer aqueous solution before irradiation.

(Maximum temperature)
In the present invention, the maximum polymerization temperature is determined by the maximum temperature reached by the polymerization gel or monomer during polymerization. The maximum polymerization temperature is essentially 100 ° C. or higher, preferably 105 ° C. or higher, more preferably 110 ° C. or higher, more preferably 115 ° C. or higher, more preferably 120 ° C. or higher. C. or lower, usually 140 ° C. or lower, and further 130 ° C. or lower. When the temperature is low, the absorption rate is not improved, and when the temperature is too high, the absorption capacity is decreased and the soluble content is increased, so that the physical properties of the water-absorbent resin are deteriorated.

  The polymerization temperature can be measured by using a PC card type data collection system NR-1000 manufactured by Keyence Corporation. Specifically, a thermocouple is placed at the center of the polymerization system, and measurement is performed at a sampling period of 0.1 seconds. The polymerization start temperature and peak temperature (maximum temperature reached) are read from the obtained temperature-time chart.

  In the present invention, the difference ΔT between the polymerization initiation temperature and the highest temperature reached during the polymerization is more than 0 ° C., preferably 70 ° C. or less, more preferably 60 ° C. or less, still more preferably 50 ° C. or less, Preferably it is 40 degrees C or less, More preferably, it is 30 degrees C or less, Most preferably, it is 25 degrees C or less. When ΔT is higher than 70 ° C., the absorption rate of the resulting water-absorbent resin may decrease, which is not preferable. As an example of obtaining a polymerization heat at which the temperature during polymerization is as described above, the monomer concentration is more preferably 30% by weight or more.

(Polymerization initiator)
There is no restriction | limiting in particular as a polymerization initiator used by this invention (For example, persulfate: sodium persulfate, potassium persulfate, ammonium persulfate; peroxide: hydrogen peroxide, t-butyl) Peroxide, methyl ethyl ketone peroxide); azo compound: azonitrile compound, azoamidine compound, cyclic azoamidine compound, azoamide compound, alkylazo compound, 2,2′-azobis (2-amidinopropane) dihydrochloride, 2,2′-azobis [2 -(2-imidazolin-2-yl) propane] dihydrochloride) and photodegradable initiators (for example, benzoin derivatives, benzyl derivatives, acetophenone derivatives, benzophenone derivatives, azo compounds) and the like can be used.

  Persulfate is preferred because of its cost and ability to reduce residual monomer. It is also a preferable method to use a photolytic initiator and ultraviolet rays. More preferably, a photodegradable initiator and a thermal decomposable initiator are used in combination. The amount of the polymerization initiator is usually in the range of 0.001 to 1 mol%, preferably 0.01 to 0.5 mol%, more preferably 0.05 to 0.2 mol% with respect to the monomer.

(Polymerization time)
The polymerization time is not particularly limited, but is usually 15 minutes or less, preferably 10 minutes or less, more preferably 5 minutes or less, more preferably 3 minutes or less, more preferably 2 minutes or less, more preferably 1 minute or less. is there. If it exceeds 15 minutes (especially 5 minutes), not only will the productivity of the resulting polymer (hydropolymer, base polymer, and water-absorbing resin) be reduced, but in some cases the physical properties such as absorption rate will also be reduced. It is not preferable.

  Here, the polymerization time is calculated by the time when the aqueous monomer solution is placed in the polymerization vessel and the conditions for initiating the polymerization are complete (if a photodegradable initiator is used, the photodegradable initiator is When not used, it is obtained by measuring the time from when the aqueous monomer solution and the polymerization initiator are put into the polymerization vessel to the peak temperature. That is, the polymerization time can be calculated by measuring (induction period) + (time from the start of polymerization until reaching the peak temperature).

(Starting temperature adjustment means)
To bring the monomer to 40 ° C or higher, the polymerization vessel itself may be heated, or when the monomer aqueous solution is supplied to the polymerization vessel, it is preheated (for example, heated to 40 ° C or higher in the line). May be. Although the temperature of the monomer may be 40 ° C. or higher by performing such external heating, it is more preferable to preheat the monomer before being supplied to the polymerization vessel. Is preferably used for raising the temperature. The generation of heat of neutralization and / or heat of hydration is preferable because it can be used not only for increasing the temperature of the monomer aqueous solution but also for removing dissolved oxygen and further improving the absorption rate.

  Thus, in order to effectively use the heat of neutralization and / or heat of hydration, it is preferable to perform neutralization in an adiabatic state, and it is more preferable to perform continuous neutralization and continuous polymerization. Therefore, for example, it is desirable to use a container that suppresses heat dissipation as much as possible, and as the material, a resin, rubber, stainless steel non-contact material part covered with a heat insulating material, or the like is preferably used.

(Degassing)
In a preferred embodiment of the present invention, the polymerization is carried out with the dissolved oxygen amount (oxygen concentration) being preferably 4 ppm or less, more preferably 2 ppm or less, and most preferably 1 ppm or less with respect to the monomer aqueous solution.

  As a means for obtaining such an oxygen concentration, it is possible to remove dissolved oxygen that inhibits polymerization by blowing an inert gas or degassing under reduced pressure before adding a polymerization initiator. In view of cost, in a more preferred embodiment of the present invention, the dissolved oxygen is removed by using neutralization heat and / or heat of hydration, raising the temperature of the aqueous monomer solution to volatilize the dissolved oxygen. It can be carried out.

  The amount of dissolved oxygen can be measured, for example, by using a measuring device (DO meter UD-1 type manufactured by Central Science Co., Ltd.). In addition, when the temperature of monomer aqueous solution exceeds 50 degreeC, it may be unable to measure from the heat resistance of a measuring apparatus. The prepared monomer aqueous solution is ice-cooled in a nitrogen atmosphere while gently stirring so as not to entrap bubbles, and the amount of dissolved oxygen is measured when the liquid temperature reaches 50 ° C.

  It is also preferable to partially deoxygenate part or all of acrylic acid, aqueous alkali solution, water, etc., which are raw materials for the monomer aqueous solution, and further deoxygenate by heat of neutralization. In addition, when the acrylic acid and alkali are neutralized by line mixing and the polymerization initiator is further line mixed to start polymerization at a high temperature of 80 ° C. or higher, the raw material acrylic acid is used to prevent the polymerization from starting in the line. In the case of alkaline aqueous solution, water, etc., it is preferable to reduce the amount of deoxygenation beforehand or not deoxygenate.

(Increased solid content)
In the method of the present invention, polymerization is carried out in such a form that the solid content concentration is increased in order to obtain a water-absorbing resin having a high absorption rate.

  According to a preferred example of the polymerization method of the present invention, the temperature of the system rapidly rises after the start of polymerization, and a low polymerization rate, for example, a polymerization rate of 10 to 20 mol% when all monomers are 100 mol%. The boiling point is reached, water vapor is emitted, and the polymerization proceeds while increasing the solid concentration. The polymerization heat is effectively used to increase the solid content concentration. The increase in solid content concentration during polymerization is preferably 1% by weight or more, more preferably 2% by weight or more, and further preferably 3% by weight or more.

  The increase in the solid content is defined by the difference between the solid content concentration of the monomer aqueous solution and the solid content concentration of the obtained hydrogel polymer. The measurement method is one of the hydropolymers taken out from the polymerization vessel. A small amount of the polymer was cut off and quickly cooled, and 5 g of the hydrous polymer quickly segmented with scissors was taken in a petri dish and dried in a 180 ° C. dryer for 24 hours for calculation. The solid content concentration of the particulate hydrous polymer can be calculated by weight loss after taking 5 g of a sample in a petri dish and drying it in a 180 ° C. dryer for 24 hours.

  As an example of a specific means for increasing the solid content concentration in the polymerization of the present invention, for example, in the polymerization under normal pressure, when the polymerization rate is 40 mol%, the temperature is already 100 ° C. or higher, and the polymerization rate is 50 mol%. However, polymerization is also a preferred embodiment at a temperature of 100 ° C. or higher. Polymerization in which the temperature is already 100 ° C. or higher when the polymerization rate is 30 mol% and the temperature is still 100 ° C. or higher even when the polymerization rate is 50 mol% is a more preferable embodiment. The most preferable embodiment is such that the temperature is already 100 ° C. or higher when the polymerization rate is 20 mol%, and the temperature is still 100 ° C. or higher even when the polymerization rate is 50 mol%. In the case of low pressure polymerization, the boiling temperature is already reached when the polymerization rate is 40 mol%, and the boiling temperature is still preferable even when the polymerization rate is 50 mol%. The polymerization is such that the boiling point is already at the boiling point when the polymerization rate is 30 mol%, and the boiling point is still at the boiling point even when the polymerization rate is 50 mol%, and the boiling temperature is already reached when the polymerization rate is 20 mol%. Polymerization that is still at the boiling temperature even at a rate of 50 mol% is the most preferred embodiment.

(Dry)
When the polymer obtained by the polymerization is in a gel form, the gel polymer is dried, preferably 70 to 250 ° C., more preferably 120 to 230 ° C., particularly preferably 150 to 210 ° C., most preferably Can be made into a water-absorbent resin powder having a mass average particle size of about 10 to 1000 μm by drying at 160 to 200 ° C. and, if necessary, pulverizing. When the drying temperature is out of the temperature range, a water absorption rate, a decrease in water absorption magnification, and the like may be observed. Although there is no restriction | limiting in particular in a drying method, The drying method which contacts a hot air and a heat-transfer surface well like moving a material like a stirring drying method, a fluidized-bed drying method, an airflow drying method, etc. is used preferably.

  In addition, although the above-mentioned Patent Document 11 (Japanese Patent Laid-Open No. 3-115313) does not disclose the drying conditions, the drying conditions also affect the physical properties as will be apparent from Examples described later.

  The hydrogel polymer produced by aqueous polymerization of the monomer component that is polymerized to form a water-absorbent resin usually has a particle size in the case of a shape that is difficult to dry as it is, such as a thick plate, block, or sheet. The gel is pulverized to 10 mm or less, further about 3 mm or less, and then dried. For gel pulverization, water, surfactant, and water-soluble polymer are added in an amount of 0 to 30% by mass, and further 0 to 10% by mass (with respect to water-absorbing resin) to improve gel pulverization and improve physical properties. May be.

  Furthermore, after drying, it becomes a water-absorbent resin through steps such as pulverization, classification, and surface treatment as necessary. In the present invention, the fine powder and coarse particles obtained in the classification step are preferably applied to the polymerization as a solid.

(Surface cross-linking)
In the production method of the present invention, the water-absorbing resin after polymerization, particularly the dried and pulverized water-absorbing resin, may be further subjected to surface crosslinking treatment. Absorption capacity under pressure and liquid permeability under pressure can be improved.

  Suitable surface cross-linking agents include oxazoline compounds (US Pat. No. 6,297,319), vinyl ether compounds (US Pat. No. 6,372,852), epoxy compounds (US Pat. No. 6,625,488), oxetane compounds (US Pat. No. 6,809,158), polyhydric alcohol compounds (US Pat. 4734478), polyamide polyamine-epihalo adducts (US Pat. Nos. 4,755,562 and 4,824,901), hydroxyacrylamide compounds (US Pat. No. 6,239,230), oxazolidinone compounds (US Pat. No. 6,559,239), bis or polyoxazolidinone compounds (US Pat. No. 6,472,478). ), 2-oxotetrahydro-1,3-oxazolidine compound (US Pat. No. 6,657,015), alkylene carbonate compound (US Pat. No. 5,672,633), etc. 1 type (s) or 2 or more types are used. In addition, a water-soluble cation such as an aluminum salt (US Pat. No. 6,605,673, US Pat. No. 6,620,899) may be used in combination with such a surface cross-linking agent, an alkali (US Patent Application Publication No. 2004-106745), an organic acid or an inorganic acid. (US Pat. No. 5,610,208) may be used in combination. Moreover, it is good also as surface bridge | crosslinking (US Patent application publication 2005-48221) by superposing | polymerizing a monomer on the surface of a water absorbing resin.

  The cross-linking agent and the cross-linking conditions used in the above patents can be applied to the present invention as appropriate.

  The surface cross-linking agent preferably used is a cross-linking agent capable of reacting with an acid group. For example, (poly) propylene glycol, (poly) ethylene glycol, (poly) glycerin, sorbitol (for example, WO 2005/44915). No. pamphlet), polyhydric alcohol compounds such as 1,3-propanediol and 1,4-butanediol, polyhydric epoxy compounds such as (poly) ethylene glycol diglycidyl ether; polyvalent amines such as (poly) ethyleneimine Compounds; various alkylene carbonate compounds such as 1,3-dioxolan-2-one, 4-methyl-1,3-dioxolan-2-one, 4,6-dimethyl-1,3-dioxan-2-one; aluminum salts Polyvalent metal salts such as Rukoto is preferable.

  These surface crosslinking agents may be used alone or in combination of two or more. In addition, what is necessary is just to make this usage-amount with respect to water absorbing resin into the range of 0.001 to 10 weight% with respect to 100% of water absorbing resin, More preferably, it exists in the range of 0.01 to 5 weight%.

  The method for adding the surface cross-linking agent is not particularly limited, and examples thereof include a method in which the cross-linking agent is dissolved and mixed in a hydrophilic solvent or a hydrophobic solvent, and a method in which the cross-linking agent is mixed without a solvent. Among these, water or a mixture with a water-soluble organic solvent is preferable as the hydrophilic solvent. The amount of the hydrophilic solvent or a mixture thereof is 0 to 50% by weight, preferably 0.5 to 30% by weight, based on 100% of the water absorbent resin, although it depends on the water absorbent resin and the combination with the crosslinking agent. Should be within the range. In mixing, the surface cross-linking agent or the solution thereof can be mixed by dropping or spraying.

  In order to increase the crosslinking density on the surface of the water-absorbent resin, a surface crosslinking agent is added and mixed and then heated. The heating temperature may be appropriately selected according to the desired crosslink density and the like. Usually, the heating temperature is 100 to 250 ° C, more preferably 150 to 250 ° C. Moreover, what is necessary is just to select a heating time suitably according to heating temperature, However, It is preferable to carry out within the range of about 1 minute-2 hours.

(Granularity)
In the present invention, the particle size of the water absorbent resin is preferably adjusted to a specific range by pulverization or classification. By using coarse particles (for example, a particle diameter of 1 mm or more) and fine powders (for example, a particle diameter of 150 μm or less) generated by the pulverization or classification as a solid in the present invention, the particle size can be controlled. Further, a high absorption rate can be achieved without reducing the particle size as in the prior art.

  That is, the water-absorbent resin of the present invention is easy to control the particle size. For example, the mass average particle diameter (D50) is preferably 200 to 710 μm, more preferably 250 to 600 μm, and particularly preferably 300 to 500 μm. And the ratio of particles of 850 μm or more to less than 150 μm is controlled to 0 to 5% by mass, preferably 0 to 3% by mass, more preferably 0 to 2% by mass, and particularly preferably 0 to 1% by mass. . The logarithmic standard deviation (σζ) of the particle size distribution is preferably in the range of 0.20 to 0.50, more preferably 0.45 to 0.25, particularly 0.40 to 0.28. The particle size is measured by standard sieve classification (JIS Z8801-1 (2000) or equivalent) according to US Patent Application Publication No. 2005-118423.

  In the present invention, the bulk specific gravity (specified in JIS K-3362-1998) is preferably in the range of 0.40 g / ml to 0.90 g / ml, more preferably 0.50 g / ml to 0.85 g / ml. Be controlled. Conventionally, the bulk specific gravity, which has been sacrificed by improving the absorption rate, can be maintained high in the present invention. Therefore, not only can the transportation and storage costs of the water-absorbent resin be reduced, but also the impact resistance (paint shaker test described later) is improved.

  The particle shape of the water-absorbent resin is irregularly crushed particles because it undergoes a pulverization step.

(Residual monomer and absorption rate)
In the present invention, as an example of the effect, in addition to the above particle size control, the absorption rate is improved. Although the absorption rate depends on the particle size, in the case of the above particle size, FSR (Free Swell Rate) is 0.20 to 2.00 (g / g / sec), preferably 0.25 to 1.00 (g / g / sec), more preferably 0.27 to 0.90 (g / g / sec), and particularly preferably 0.30 to 0.80 (g / g / sec). If the FSR is less than 0.20, the absorption rate is too slow, causing diaper leakage and the like. Moreover, when FSR exceeds 2.00, there exists a possibility that the liquid diffusion in a diaper may fall.

  In the present invention, as an example of the effect, in addition to the above particle size control, residual monomer can also be reduced. In general, the foaming polymerization for improving the absorption rate has a tendency to increase the residual monomer, but the present invention is preferable because the residual monomer does not increase or decrease even if the absorption rate is improved.

  The residual monomer amount is 0 to 400 ppm, preferably 0 to 300 ppm, and more preferably 0 to 100 ppm.

(Other physical properties)
In the present invention, physical properties are controlled by adjusting the cross-linking according to the purpose, but in the case of sanitary materials such as diapers, the physical properties are controlled as follows. Conventionally, the absorption capacity under pressure, which has been sacrificed by the absorption rate, is preferably high in the present invention because of its high absorption capacity under pressure.

  That is, the water absorption resin of the present invention has an absorption capacity (CRC) of 0.9% by mass physiological saline under no pressure, usually 10 g / g or more, preferably 25 g / g or more, more preferably 30 to 100 g / g, Preferably it is 33-50 g / g, Most preferably, it is the range of 34 g / g-40 g / g.

  The absorption capacity under load (AAP 1.9 kPa) at a load of 1.9 kPa of physiological saline is 20 g / g or more, more preferably 25 g / g to 40 g / g, and particularly preferably 27 to 35 g / g. Further, the absorption capacity under load at a load of 4.9 kPa (AAP 4.9 kPa) is 10 g / g or more, more preferably 22 g / g to 40 g / g, and particularly preferably 24 to 35 g / g.

  The PPUP determined from the absorption capacity under pressure is 40 to 100%, preferably 50 to 100%, more preferably 60 to 100%, and particularly preferably 70 to 100%. The PPUP of the present invention is shown in International Publication No. 2006/109844, and the PPUP is defined below.

PPUP is the absorption capacity under load with 0.9 g of particulate water-absorbing agent (AAP: 0.90 g) at an absorption capacity under pressure of 0.90 mass% sodium chloride aqueous solution under a pressure of 4.8 kPa for 60 minutes, and When the absorption capacity under pressure (AAP: 5.0 g) with 5.0 g of the particulate water-absorbing agent is used, the liquid-passing efficiency under pressure (PPUP) of the particulate water-absorbing agent is defined by the following formula.
PPUP (%) = (AAP: 5.0 g) / (AAP: 0.90 g) × 100
SFC (US Patent Application Publication No. 2004-254553) as liquid permeability is usually 1 × 10 ⁻⁷ (cm ³ × sec / g) or more, preferably 10 × 10 ⁻⁷ (cm ³ × sec / g) or more, More preferably, it is 50 × 10 ⁻⁷ (cm ³ × sec / g) or more.

  The moisture content (specified by the weight loss of 1 g of resin after 180 ° C./3 hours) is preferably 90% by mass or more, more preferably 93% by mass or more and 99.9% by mass or less, particularly preferably 95% by mass or more. It is the range of 99.8 mass% or less.

(Other additives)
In addition to the above steps, the water-absorbent resin used in the present invention may further contain 0 to 10% by mass, preferably 0.001 (10 ppm) of an additive at the time of polymerization or after polymerization (for example, at the time of surface crosslinking, granulation, etc.). ) To about 1 wt% (more preferably 50 ppm to 1 wt%) may be used. Preferably, the physical properties can be further improved by adding a chelating agent.

  In such a step, an additive or a solution thereof, for example, an aqueous solution in which various additive components other than water are dissolved can be added to the water absorbent resin. For example, water-insoluble fine particles, chelating agents (see US Pat. No. 6,599,989) (diethylenetriaminepentaacetic acid salt, triethylenetetraaminehexaacetic acid, cyclohexane-1,2-diaminetetraacetic acid, N-hydroxyethylethylenediaminetriacetic acid, ethylene glycol diethyl ether Diamine tetraacetic acid, etc.), plant components (tannin, tannic acid, pentaploid, gallic acid, gallic acid, etc.), inorganic salts (polyvalent metal salts such as calcium, aluminum, magnesium, zinc, etc.), reducing agents (US Pat. No. 4,97,2019, No. 4863989).

(Water-absorbent resin of the present invention)
That is, in the present invention, a water-absorbing resin having 70 to 99.999 mol% of acrylic acid (salt) and 0.001 to 5 mol% of a cross-linking agent as repeating units, which satisfies the following six conditions Also provide.

Absorption capacity (CRC) of 20-40 g / g
Absorption capacity under pressure (AAP) is 20-40 g / g
Absorption rate (FSR) of 0.25 to 1.0 g / g / sec
Bulk specific gravity (JIS K 3362) is 0.50 to 0.80
0 to 400 ppm of residual monomer
95-100% by weight of particles having a particle size distribution of 850 to 150 μm (JIS Z8801-1)
The “water-absorbing resin having 70 to 99.999 mol% of acrylic acid (salt) and 0.001 to 5 mol% of a crosslinking agent as a repeating unit” refers to acrylic acid (salt) molecules 14 to 999999.9. It means a water-absorbent resin having a structure in which one crosslinker molecule is bonded as a repeating unit.

  The water-absorbent resin is, for example, a method for producing the water-absorbent resin according to the present invention described above, that is, standing polymerization in the presence of a water-insoluble solid, and the polymerization start temperature is 40 ° C. or higher or during polymerization. It can be produced by controlling the maximum temperature to 100 ° C. or higher.

  Such a water-absorbent resin preferably contains 0.1 to 50% by weight of water-insoluble particles (preferably water-absorbent resin powder) based on the mass of the acid group-containing unsaturated monomer during polymerization.

  The above-described six physical properties such as absorption ratio and preferred ranges of the water-absorbing resin powder content are described. In the present invention, by containing a specific amount of water-insoluble particles (preferably water-absorbent resin powder), in general, it has been difficult to improve absorption rate, residual monomer reduction, particle size control, improvement of absorption capacity under pressure, The bulk specific gravity can be controlled.

  In particular, conventional water-absorbing resins with a high water absorption rate require foaming and granulation, and thus have a fatal defect that the impact resistance and bulk specific gravity of powder are low and bulky. It was. In US Pat. No. 6,071,976, US Pat. No. 6,642,214, US Pat. No. 5,837,789, US Pat. No. 6,562,879, etc., which disclose absorptive capacity (AAP) under pressure and deterioration of liquid permeability (SFC) due to impact Compared with the water-absorbing resin described, the water-absorbing resin according to the present invention has drastically improved water absorption rate (FSR) and the like. Therefore, it is possible to provide a novel water-absorbent resin excellent in impact resistance and water absorption speed, which is suitable for actual use in diapers.

  And even if it is a time of incorporating in a diaper, the water absorbing resin which maintains high absorption performance can also be obtained. That is, a water-absorbing resin having a fast absorption rate even in diapers, having a small amount of residual monomer, and obtaining a novel water-absorbing resin that does not cause an increase in transportation cost due to a decrease in bulk specific gravity regardless of the presence or absence of water-insoluble particles. You can also

(Use)
The water-absorbent resin of the present invention absorbs not only water but also various liquids including body fluid, physiological saline, urine, blood, cement water, fertilizer-containing water, disposable diapers, sanitary napkins, incontinence In addition to sanitary materials such as pads, it is also suitably used in various industrial fields such as civil engineering and agriculture and horticulture.

(Mechanism estimation of the present invention)
Although the details of the reason why the absorption rate is improved in the present invention are unclear, the mechanism is estimated as follows. The mechanism does not limit the rights of the present invention.

  As described above, the production method of the present invention is performed by dispersing an insoluble or hardly soluble compound in an aqueous monomer solution in the aqueous monomer solution and starting polymerization at 40 ° C. or higher, preferably foaming. By polymerizing, the added compound plays a role like zeolite, and it is presumed that many bubbles are present in the hydrophilic polymer (for example, water-absorbing resin) by significantly promoting foaming.

  In addition, since the monomer is polymerized with significant foaming, the gel surface area is increased, so that the evaporation of moisture is efficiently performed, so that a so-called heat removal effect can be obtained at the same time. It is possible to produce a water absorbent resin. Furthermore, the evaporation of unpolymerized monomer components and the evaporation of moisture increase, reducing the amount of residual monomer (residual monomer) in the polymer, increasing the solid content of the polymer, and increasing the heat removal efficiency during polymerization. It is estimated that it will be possible.

  According to the method of the present invention, when compared with conventional high-temperature initiation polymerization (without addition of a compound that is insoluble or hardly soluble in an aqueous solution containing a hydrophilic monomer and is dispersible at room temperature and solid), It is possible to significantly accelerate foaming during polymerization (increase the number of foams). Further, in the polymerization of the present invention, vapor is generated (foamed) at the boiling point during the polymerization, thereby causing bubbles (pores) to exist in the hydrophilic polymer. Most of them shrink. That is, the shape of the hydrophilic polymer (for example, a water-absorbent resin) is almost the same as that containing no bubbles, and many latent bubbles can be present in the hydrophilic polymer. These latent bubbles are present again as pores when a hydrophilic polymer (for example, a water-absorbing resin) is immersed in a solvent such as water and swollen.

  According to the method of the present invention, it is possible to produce a water-absorbent resin containing a large amount of the above-described latent bubbles (pores). From this fact, the absorption speed is remarkably improved by increasing the surface area of the bubbles (pores) during swelling of the water absorbent resin.

〔Example〕
Hereinafter, the present invention will be described more specifically based on examples, but the present invention is not limited thereto. Hereinafter, for convenience, “parts by mass” may be simply referred to as “parts”, and “liters” may be simply referred to as “L”. In addition, “mass%” may be described as “wt%”. Furthermore, the water absorbent resin was used (handled) under the conditions of 25 ° C. ± 2 ° C. and relative humidity of about 50% ± 5% RH. Moreover, 0.90 mass% sodium chloride aqueous solution was used as physiological saline.

  In addition, when analyzing a commercial item such as a water-absorbent resin in a diaper, when moisture is absorbed, the measurement may be performed by appropriately drying under reduced pressure and adjusting the water content to about 5%.

<Absorption capacity (CRC)>
After uniformly heat-sealing 0.2 g of the water-absorbent resin in a bag (85 mm × 60 mm) made of a nonwoven fabric (Nangoku Pulp Industries Co., Ltd., trade name: Heaton paper, model: GSP-22), 20 ° C. It was immersed in a large excess (usually about 500 ml) of physiological saline adjusted to -25 ° C. After 30 minutes, the bag was pulled up and drained for 3 minutes with a centrifugal force (250 G) described in edana ABSORBENCY II 441.1-99 using a centrifuge (manufactured by Kokusan Co., Ltd., centrifuge: model H-122). After that, the mass W1 (g) of the bag was measured. Moreover, the same operation was performed without using a water absorbent resin, and the mass W2 (g) at that time was measured. And from these W1 and W2, the absorption capacity | capacitance (g / g) was computed according to following Formula.

Absorption capacity (g / g) = (W1 (g) −W2 (g)) / (mass of water absorbent resin (g)) − 1
<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 (W5, unit: g) of the poured physiological saline was determined by the following formula (a).

  The absorption rate (FSR) was calculated by the following formula (c).

Formula (a): W5 (g) = W3 (g) -W4 (g)
Formula (c): FSR (g / g / s) = W5 / (t _S × mass of water absorbent resin (g))
<Absorption capacity under pressure (AAP)>
A stainless steel 400 mesh wire mesh 101 (mesh size 38 μm) is fused to the bottom of a plastic support cylinder 100 having an inner diameter of 60 mm using the apparatus shown in FIG. 0.900 g of particles having a particle size of 38 μm or more (particularly 99% by weight or more) is uniformly dispersed, and a load of 4.83 kPa (0.7 psi) is uniformly applied to the water absorbent resin. The piston 103 and the load 104, which are adjusted so that the outer diameter is slightly smaller than 60 mm and does not cause a gap with the support cylinder 100 and the vertical movement is not hindered, are placed in this order. The mass W6 (g) of was measured.

  A glass filter 106 having a diameter of 90 mm (manufactured by Mutual Riken Glass Co., Ltd., pore diameter: 100 to 120 μm) is placed inside a petri dish 105 having a diameter of 150 mm, and physiological saline 108 (20 ° C. to 25 ° C.) is placed on the glass filter. It was added so as to be the same level as the top surface. On top of that, a sheet of filter paper 107 having a diameter of 90 mm (ADVANTEC Toyo Co., Ltd., product name: (JIS P 3801, No. 2), thickness 0.26 mm, reserved particle diameter 5 μm) was placed so that the entire surface was wetted. Excess liquid was removed.

  The set of measuring devices was placed on the wet filter paper, and the liquid was absorbed under load. After 1 hour, the measuring device set was lifted and its mass W7 (g) was measured. And the absorption capacity | capacitance under pressure with respect to a pressure (g / g) was computed from W6 and W7 according to the following formula.

Absorption capacity under pressure = (W7 (g) -W6 (g)) / (mass of water absorbent resin (g))
<Soluble content (amount)>
In a 250 ml capacity plastic container with a lid, 184.3 g of physiological saline was weighed, and 1.00 g of a water-absorbing resin was added to the aqueous solution, followed by stirring for 16 hours to extract the soluble component in the resin. 50.0 g of the filtrate obtained by filtering this extract using filter paper (ADVANTEC Toyo Co., Ltd., product name: (JIS P 3801, No. 2), thickness 0.26 mm, retained particle diameter 5 μm) A weighed measurement solution was obtained.

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

<Residual monomer amount (ppm)>
The water-absorbing resin (1.00 g) was dispersed in physiological saline (184.3 g), and the remaining monomer was extracted by stirring for 16 hours with a magnetic stirrer having a length of 25 mm. Then, the swelling gel was filtered using (Toyo Filter Paper Co., Ltd., No. 2, retention particle diameter 5 μm defined in JIS P 3801), and this filtrate was filtered with HPLC sample pretreatment filter chromatodisc 25A (Kurashiki Spinning Co., Ltd.). It was further filtered through a water-based type, a pore size of 0.45 μm) to obtain a residual monomer measurement sample.

  This residual monomer measurement sample was analyzed by high performance liquid chromatography (HPLC). A calibration curve obtained by analyzing a monomer standard solution having a known concentration is used as an external standard, and the water absorbent resin particles or particulates are taken into account by considering the dilution ratio of the water absorbent resin particles or particulate water absorbent to deionized water. The amount of residual monomer in the water-absorbing agent was quantified. The measurement conditions of HPLC are as follows.

Carrier solution: Phosphoric acid aqueous solution in which 3 ml of phosphoric acid (85% by mass, manufactured by Wako Pure Chemical Industries, Ltd., special grade reagent) is diluted with 1000 ml of ultrapure water (specific resistance 15 MΩ · cm or more) Carrier speed: 0.7 ml / min .
Column: SHODEX RSpak DM-614 (Showa Denko KK)
Column temperature: 23 ± 2 ° C
Wavelength: UV205nm
<Bulk specific gravity, flow velocity>
It measured according to JISK3362 using the bulk specific gravity measuring device (made by Kuramochi Scientific Instruments Seisakusho). In order to eliminate unevenness due to the particle size, 100.0 g of a sufficiently mixed water absorbent resin was placed in a funnel with a damper closed, and then the damper was quickly opened, and the water absorbent resin was dropped into a receiver having an internal volume of 100 ml. The time (seconds) from when the water-absorbent resin starts to drop until it drops is taken as the flow-down speed. The water-absorbing resin swelled from the receiver was rubbed off with a glass rod, and the weight of the receiver containing the water-absorbing resin was accurately weighed to 0.1 g, and the bulk specific gravity was calculated by the following equation.

Bulk specific gravity (g / ml) = (weight of the receiver containing the water-absorbing resin (g) −weight of the receiver (g)) / content of the receiver (100 ml)
In addition, the temperature of the environment where the measurement was performed was 25 ± 2 ° C., and the relative humidity was 30 to 50% RH.

<Weight average particle diameter (D50) and logarithmic standard deviation (σζ)>
The water absorbent resin was sieved with JIS standard sieves of 850 μm, 710 μm, 600 μm, 500 μm, 425 μm, 300 μm, 212 μm, 150 μm, 106 μm, 75 μm, 45 μm, and the residual percentage was plotted logarithmically. In addition, according to the particle size of the water-absorbent resin, a sieve is added as necessary and measured. Thereby, the particle diameter corresponding to R = 50 mass% was read as the weight average particle diameter (D50). Further, the logarithmic standard deviation (σζ) of the particle size distribution is expressed by the following equation, and the smaller the value of σζ, the narrower the particle size distribution.

σζ = 0.5 × ln (X2 / X1)
(X1 is R = 84.1%, X2 is each particle size when R = 15.9%)
For sieving, 10.0 g of water-absorbent resin is charged into JIS standard sieves (The IIDA TESTING SIEVE: 80 mm inner diameter) such as 850 μm, 710 μm, 600 μm, 500 μm, 425 μm, 300 μm, 212 μm, 150 μm, 106 μm, 75 μm, 45 μm. Then, it was classified for 5 minutes by a low tap type sieve shaker (manufactured by Iida Seisakusho, ES-65 type sieve shaker).

  The weight average particle diameter (D50) is a particle diameter of a standard sieve corresponding to 50 mass% of the whole particle with a standard sieve having a constant mesh, as described in US Pat. No. 5,051,259.

<Solid content>
1.00 g of the water absorbent resin was weighed into an aluminum cup having a bottom diameter of about 50 mm, and the total mass W8 (g) of the water absorbent resin and the aluminum cup was measured. Then, it was left to stand in an oven with an atmospheric temperature of 180 ° C. for 3 hours and dried. After 3 hours, the water-absorbing resin taken out of the oven and the aluminum cup were sufficiently cooled to room temperature in a desiccator, and then the dried water-absorbing resin and the total mass W9 (g) of the aluminum cup were determined. The solid content was determined.

Solid content (mass%) = 100 − ((W8−W9) / (mass of water absorbent resin (g)) × 100)
<Impact resistance test (also known as paint shaker test)>
The paint shaker test is a glass container having a diameter of 6 cm and a height of 11 cm with 10 g of glass beads having a diameter of 6 mm and 30 g of water-absorbing resin attached to a paint shaker (Toyo Seisakusho Co., Ltd. product No. 488), and 800 cycles / min. The details of the apparatus are disclosed in US Pat. No. 6,071,976 (corresponding Japanese Patent Publication No. 9-235378). The shaking time was 30 minutes.

  After shaking, the glass beads are removed with a JIS standard sieve having an opening of 2 mm, and a damaged water-absorbing resin is obtained.

[Reference Example 1]
In a reactor formed by covering a stainless steel double-armed kneader with a 10 L internal volume and having two sigma-shaped blades with a lid, 530.2 g of acrylic acid, 4364.2 g of 37 mass% sodium acrylate aqueous solution, pure water 553.7 g and 7.7 g of polyethylene glycol diacrylate (molecular weight 523) were dissolved to prepare a reaction solution.

  Next, this reaction solution was degassed for 20 minutes in a nitrogen gas atmosphere while adjusting to 25 ° C. Subsequently, 19.6 g of a 15% by mass aqueous sodium persulfate solution and 24.5 g of a 0.1% by mass L-ascorbic acid aqueous solution were added to the reaction solution with stirring. Polymerization started after about 1 minute. The polymerization initiation temperature at this time was 25.2 ° C.

  And it superposed | polymerized at 25-95 degreeC, grind | pulverizing the produced | generated gel, 30 minutes after superposition | polymerization started, the water-containing gel-like crosslinked polymer was taken out. The obtained hydrogel crosslinked polymer was subdivided to have a diameter of about 5 mm or less.

  This finely divided hydrogel cross-linked polymer is spread on a stainless steel wire mesh having an opening of 850 μm, dried with hot air at 180 ° C. for 40 minutes, and the dried product is roll milled (WML type roll crusher, manufactured by Inoguchi Giken Co., Ltd.). The resulting mixture was pulverized and classified with a JIS standard sieve having an opening of 150 μm to obtain an irregularly crushed water-absorbing resin (A) having a size of 150 μm or less. The water absorption resin (A) had an absorption capacity of 35.3 g / g and a soluble content of 16.5% by mass.

[Example 1]
(polymerization)
293.1 g of acrylic acid, 1.1 g of polyethylene glycol diacrylate (average molecular weight 522) as an internal cross-linking agent, 1.8 g of a 1% by weight diethylenetriaminepentaacetic acid-5 sodium solution as a chelating agent, and IRGACURE (registered trademark) as a polymerization initiator 3.6 g of 184 1.0% by mass acrylic acid solution was mixed in a 1 L polypropylene resin container, and the temperature was adjusted to 50 ° C. with solution (A) and 237.65 g of 48.5% by mass sodium hydroxide aqueous solution. A solution (B) in which 251.82 g of ion-exchanged water was mixed was prepared. Using a magnetic stirrer chip having a length of 50 mm, 500 r. p. m. To the solution (A) stirred in step 54, 54 g of the water-absorbent resin (A) obtained in Reference Example 1 was added, and then the solution (B) was quickly added and mixed to obtain a monomer aqueous solution (C). The aqueous monomer solution (C) rose to 102 ° C. due to heat of neutralization and heat of dissolution.

  Next, when the temperature of the monomer aqueous solution (C) dropped to 97 ° C., immediately after adding 11 g of a 3 mass% sodium persulfate aqueous solution to the monomer aqueous solution (C) and stirring for about 1 second, Stainless steel bat mold with a bottom surface of 250 mm x 250 mm with Teflon (registered trademark) attached to the inner surface, the surface temperature of which was heated by a hot plate (NEO HOTPLATE H1-1000, manufactured by Seiei Inai Co., Ltd.) set to 130 ° C. It was poured into the container in an open system. The stainless bat-shaped container has a bottom surface of 250 mm × 250 mm, a top surface of 640 mm × 640 mm, a height of 50 mm, a central cross section that is trapezoidal, and an upper surface that is open. In addition, the aqueous monomer solution was poured into the stainless steel bat-shaped container and at the same time, an ultraviolet irradiation device (Toscure 401 model name: HC-04131-B lamp: H400L /) installed at a height of 600 mm from the bottom of the stainless bat-shaped container. 2 Irradiated with ultraviolet light by Harrison Toshiba Lighting Co., Ltd.

  Polymerization started shortly after the monomer aqueous solution was poured into the vat, and stationary aqueous solution polymerization proceeded while generating water vapor (polymerization start temperature: 97 ° C.). The polymerization reached a peak temperature within about 1 minute (peak temperature: 106 ° C.). After 3 minutes, the irradiation of ultraviolet rays was stopped, and the water-containing polymer (water-containing gel) was taken out. These series of operations were performed in a system open to the atmosphere.

(Gel subdivision)
The water-containing gel-like crosslinked polymer taken out was cut into strips with a width of 30 mm, and then ion-exchanged water was added at 1.4 g / sec, while a meat chopper (MEAT-CHOPER) was added at a feed rate of about 6 g / sec. TYPE: 12VR-400KSOX Iizuka Kogyo Co., Ltd., die hole diameter: 9.5 mm, hole number: 18, die thickness 8 mm) to obtain a finely divided hydrogel crosslinked polymer.

(Drying, grinding and classification)
The finely divided pulverized gel particles are spread on a wire mesh having an opening of 850 μm, dried with hot air at 180 ° C. for 40 minutes, and the dried product is pulverized using a roll mill (WML type roll pulverizer, manufactured by Inoguchi Giken Co., Ltd.). Furthermore, by classifying and preparing with a JIS 850 μm standard sieve, the proportion of particles having a D50 of 461 μm and a particle size of 600 μm or more and less than 850 μm is 28% by mass, and the proportion of particles having a particle size of less than 150 μm is 2.2% by mass. An irregularly shaped water-absorbing resin having a logarithmic standard deviation (σζ) of 0.364 and a solid content of 96% by mass was obtained.

(Surface cross-linking)
To 100 parts by weight of the obtained water-absorbing resin, uniformly apply a surface treating agent solution composed of a mixed solution of 0.3 parts by weight of 1,4-butanediol, 0.5 parts by weight of propylene glycol and 2.7 parts by weight of pure water. Mixed. The water-absorbent resin mixed with the surface cross-linking agent solution was heat-treated for any time with a jacketed heating device equipped with a stirring blade (jacket temperature: 210 ° C.). After the heat treatment, the obtained water absorbent resin was passed through a JIS 850 μm standard sieve to obtain a particulate water absorbent resin (1) having a crosslinked surface. Various physical properties of the particulate water-absorbing resin (1) are shown in Table 1. Moreover, although it classified with the JIS standard sieve after the paint shaker test of this particulate water-absorbing resin, the ratio which passed 150 micrometers of openings accounted for 6.2 mass% of this particle | grain total amount.

[Example 2]
In this example, the procedure was carried out except that the polyethylene glycol diacrylate (average molecular weight 522) used in Example 1 was 0.75 g, and the water absorbent resin (A) obtained in Reference Example 1 to be added was 72 g. A particulate water-absorbing resin (2) was obtained in the same manner as in Example 1. Various physical properties of the particulate water-absorbing resin (2) are shown in Table 1.

Example 3
In this example, the water-absorbent resin (A) used in Example 1 was used in place of synthetic zeolite (Tosoh Co., Ltd., Zeorum A-4, 100 mesh pass powder) (18 g used), A particulate water-absorbing resin (3) was obtained in the same manner as in Example 1. Various physical properties of the particulate water-absorbing resin (3) are shown in Table 1.

Example 4
(polymerization)
A solution (D) prepared by mixing 202.7 g of acrylic acid, 1776.5 g of a 37 mass% sodium acrylate aqueous solution and 3.8 g of polyethylene glycol diacrylate (average molecular weight 522) as an internal cross-linking agent was adjusted to 15 ° C. Deoxygenation was performed by blowing nitrogen gas at a flow rate of 2 L / min for 30 minutes while warming. The deoxygenated solution (D) is poured into a 300 mm × 220 mm × 60 mm deep stainless steel container coated with Teflon (registered trademark), and the upper opening is covered with a polyethylene film, so that the solution (D) does not get oxygen. Thus, nitrogen gas was continuously blown at a flow rate of 2 L / min, and the space was maintained in a nitrogen gas atmosphere. Next, 7.8 g of a 15% by mass aqueous sodium persulfate solution as a polymerization initiator and 9.1 g of a 2% by mass L-ascorbic acid aqueous solution were added, and a magnetic stirrer chip having a length of 50 mm was added to 300 r. p. m. After stirring and mixing uniformly, 129 g of the water absorbent resin (A) obtained in Reference Example 1 was added. The polymerization start (white turbidity) was confirmed 2.4 minutes after charging the initiator, and the stainless steel container was immersed 10 mm in a water tank adjusted to 10 ° C. The temperature of the solution when the polymerization was started was 16 ° C. The polymerization temperature reached a peak at 5.9 minutes after charging the initiator. The peak temperature at this time was 103 ° C. After 12 minutes from the start of the initiator (6.1 minutes after the polymerization peak), the stainless steel container was transferred to a water bath at 80 ° C. and soaked 10 mm as before (soaked in a water bath at 10 ° C.). The stainless steel container was pulled up from the water tank 12 minutes after being immersed in the 80 ° C. water tank, and the water-containing polymer (hydrated gel) was taken out from the stainless steel container.

  Gel fragmentation, drying / pulverization and classification are the same as in Example 1. The proportion of particles having a D50 of 434 μm and a particle size of 600 μm or more and less than 850 μm is 24% by mass, and the proportion of particles having a particle size of less than 150 μm An amorphous crushed water-absorbing resin having a solid content of 3.6% by mass and a solid content of 95% by mass was obtained.

  Surface crosslinking was performed in the same manner as in Example 1 to obtain a particulate water-absorbing resin (4) having a crosslinked surface. Various physical properties of the particulate water-absorbing resin (4) are shown in Table 1.

[Comparative Example 1]
In this comparative example, a comparative particulate water-absorbing resin (1) was obtained by performing polymerization in the same manner as in Example 1 except that the water-absorbing resin (A) used in Example 1 was not added. Table 1 shows properties of the comparative particulate water-absorbing resin (1).

[Comparative Example 2]
In this comparative example, comparative particles were polymerized by the same method as in Reference Example 1 except that 321 g of the water absorbent resin (A) obtained in Reference Example 1 was added to the reaction solution after degassing in Reference Example 1. A water-absorbing resin (2) was obtained. Table 1 shows properties of the comparative particulate water-absorbing resin (2).

[Comparative Example 3]
In this comparative example, with reference to US Pat. No. 6,187,358 (Example 2 of JP-A-10-251310), foam polymerization was performed as a conventional method for improving the absorption rate.

  360 g of acrylic acid, 3240 g of 37% by weight sodium acrylate aqueous solution, 8.8 g of polyethylene glycol diacrylate (average molecular weight 522), 0.3 g of polyoxyethylene sorbitan monostearate (trade name: Rheodor TW-S120, manufactured by Kao Corporation) Then, 1420 g of ion-exchanged water and 10 g of 10 mass% sodium persulfate aqueous solution were mixed to prepare a monomer aqueous solution.

  Using the whip auto Z manufactured by Aikosha Co., Ltd., the aqueous solution and nitrogen were dispersed in nitrogen gas bubbles in the aqueous solution and immediately placed in a container, 10 g of 10% by mass aqueous sodium hydrogen sulfite solution was immediately added, and polymerization was performed immediately. I started it. The polymerization initiation temperature at this time was 26.2 ° C. The solution was allowed to stand in the container for 1 hour, and polymerized in a standing aqueous solution to obtain a sponge-like hydrogel crosslinked polymer containing a large amount of bubbles (peak temperature: 98 ° C.). The water-containing gel-like crosslinked polymer is cut into a 10-30 mm square shape and spread on a 20-mesh wire mesh. Thereafter, various physical properties of the comparative particulate water-absorbing resin (3) are obtained in the same manner as in Example 1. Are shown in Table 1.

[Comparative Example 4]
The same operation as in Example 1 was performed except that the stirring polymerization, that is, the continuous kneader polymerization used in US Patent Application Publication No. 2004-110897 was performed. As a polymerization vessel having a biaxial stirring blade, after continuous polymerization with a continuous kneader (CKDJS-40 manufactured by Dalton Co., Ltd.) used in the examples of the US patent, drying and pulverization surface cross-linking are performed in the same manner. The absorption rate was not improved. As described above, stirring polymerization such as US Patent Application Publication No. 2004-110897, US Patent Nos. 670141, 462001, and 5250640 is not preferable.

[Comparative Example 5]
In this comparative example, a slurry of sodium acrylate having a monomer aqueous solution (slurry) concentration of 56% and a neutralization rate of 75 mol% was prepared as in Example 1 described in JP-A-3-115313. Next, this monomer slurry (aqueous dispersion of monomer) was cooled to 35 ° C., then sodium persulfate was added as an initiator, and polymerization was carried out in a layered form having a thickness of 15 mm. The same operation as in Example 1 was performed.

  As in Example 1 of JP-A-3-115313, gelation (peak temperature: 105 ° C.) was observed in about 20 minutes, the bottom of the polymerization vessel was further heated to 100 ° C., and the water-containing polymer was polymerized after 15 minutes. Removed from container. The peak temperature at this time was 171 ° C. Further, for comparison with Example 1 of the present application, the number of moles of the polymerization initiator and the crosslinking agent was adjusted to that of Example 1 of the present application.

  About the obtained water-containing polymer, similarly to Example 1 of this application, the gel was subdivided, dried, pulverized, and classified to obtain a comparative particulate water-absorbing resin (5). Table 1 shows properties of the comparative particulate water-absorbing resin (5).

[Comparative Example 6]
In this comparative example, according to Example 2 of JP-A-3-115313, 1% by weight (solid content of monomer) of fine-particle silica (trade name: Aerosil, average particle size: 0.02 μm). A slurry of sodium acrylate containing 57 wt% and neutralization rate of 73 mol% was prepared, and the same operation as in Example 1 of the present application was performed except that polymerization was performed in the same manner as in Comparative Example 5. The peak temperature of the polymerization was 168 ° C.

  For the obtained hydrous polymer, the gel was subdivided, dried, pulverized and classified in the same manner as in Example 1 of the present application to obtain a comparative particulate water-absorbing resin (6). Table 1 shows properties of the comparative particulate water-absorbing resin (6).

[Comparative Example 7]
Except not adding water-absorbing resin (A), operation similar to Example 4 was performed and the comparative particulate water-absorbing resin (7) was obtained. Table 1 shows properties of the comparative particulate water-absorbing resin (7).

[Comparative Example 8]
The amount of pure water was changed from 553.7 g to 504.6 g, and a 10% by mass 2,2′-azobis (2-amidinopropane) dihydrochloride (V-50, manufactured by Wako Pure Chemical Industries, Ltd.) aqueous solution 49. The same operation as in Reference Example 1 was carried out except that 1 g was added simultaneously with a 15% by mass sodium persulfate aqueous solution and a 0.1% by mass L-ascorbic acid aqueous solution to obtain a finely divided hydrogel crosslinked polymer. It was.

  Then, the obtained finely divided hydrogel crosslinked polymer was dried, pulverized, classified and surface-crosslinked by the same method as in Example 1 to obtain a comparative particulate water-absorbing resin (8). Table 1 shows properties of the comparative particulate water-absorbing resin (8).

[Comparative Example 9]
A comparative particulate water-absorbing resin (9) was obtained according to EXAMPLE1 of US Pat. No. 6,562,879.

  Specifically, sodium acrylate having a neutralization rate of 75 mol% in a reactor formed by attaching a lid to a stainless steel double-armed kneader with a volume of 10 liters and having two sigma type blades. When 2.4 g of ammonium persulfate and 0.12 g of L-ascorbic acid were added to a reaction solution in which 2.50 g of polyethylene glycol diacrylate was dissolved in 5500 g of an aqueous solution (monomer concentration: 33% by weight), approximately 1 minute. Polymerization started later. And it superposed | polymerized at 30-80 degreeC, grind | pulverizing the produced | generated gel, and the water-containing gel-like crosslinked polymer was taken out 60 minutes after superposition | polymerization started.

  The obtained hydrogel crosslinked polymer was subdivided to have a diameter of about 5 mm or less. This finely divided hydrogel crosslinked polymer was spread on a 50 mesh (mesh opening 300 μm) wire mesh and dried with hot air at 150 ° C. for 90 minutes to obtain a water absorbent resin as a crosslinked polymer.

  The water-absorbent resin was pulverized with a hammer mill (rooster: hole diameter: 3 mm), and 150 g of the water-absorbent resin was placed in a homogenizer (manufactured by Nippon Seiki Co., Ltd., high-speed homogenizer, Model: MX-7), and about 1 at a rotation speed of 6000 rpm. Polished for hours. The obtained water-absorbent resin was sieved with a JIS standard sieve (aperture 850, 212 μm) and classified to a particle size of 850 to 212 μm.

  Table 1 shows properties of the comparative particulate water-absorbing resin (9).

Example 5
A particulate water-absorbing resin (5) was obtained in the same manner as in Example 1 except that the drying temperature of the hydrous polymer (hydrous gel) was changed from 180 ° C to 100 ° C. Table 1 shows properties of the particulate water absorbent resin (5).

  In addition, this invention is not limited to each structure demonstrated above, A various change is possible in the range shown to the claim.

(Explanation of the table)
In standing aqueous solution polymerization at the same polymerization temperature, compared to Comparative Example 1 in which no solid was added, Example 1 (added about 15% by weight of water absorbent resin), Example 2 (added about 20% by weight of water absorbent resin) In Example 3 (addition of about 5% by mass of zeolite), the absorption rate (FSR) is improved about twice, and the residual monomer is also reduced by 100 ppm or more. Furthermore, other physical properties (absorption capacity, absorption capacity under pressure, soluble content (amount), etc.) tend to be improved.

  Compared to Comparative Example 3 which is conventional foam polymerization, Example 1 (added about 15% by weight of water-absorbing resin), Example 2 (added about 20% by weight of water-absorbing resin), Example 3 (zeolite was added) In the case of about 5% by mass addition, the residual monomer is reduced by about 500 ppm, the absorption capacity under pressure (AAP) is improved by 2 to 5 g / g, and the impact resistance of the water absorbent resin powder is also improved. Furthermore, in the present invention, the bulk specific gravity also increases from 1.2 to 1.4 times, so that transportation and storage costs can be greatly reduced.

  In addition, the water-absorbing resin containing fine particles or the water-absorbing resin satisfying specific water-absorbing performance obtained in the above example is resistant to damage during transportation, and fine powder and dust are reduced. Furthermore, even in a diaper, high performance can be maintained and an excellent diaper can be provided.

  In Comparative Examples 5 and 6 of this application according to Japanese Patent Laid-Open No. 3-115313 (slurry polymerization of sodium acrylate fine precipitation), since the monomer is polymerized in a slurry state or the polymerization start temperature is as low as 35 ° C. Compared with Example 1, the absorption capacity and water absorption rate of the water-absorbing resin obtained are low. In addition, even if it is the same monomer concentration (56-57 weight%) as the comparative examples 4 and 5, the solubility of a monomer changes with solvent temperature, and it becomes a slurry or a solution, A slurry is obtained at a temperature of 35 ° C.

  Regarding the influence of the drying temperature, in Example 5 where the drying temperature is 100 ° C., compared to Example 1 where the drying temperature is 180 ° C., the water absorption ratio and the water absorption rate of the obtained water absorbent resin tend to decrease. The residual monomer tended to increase, but the impact resistance tended to improve.

  The effect of adding the water-absorbent resin (A), which is a water-insoluble solid, could be confirmed by comparing Example 4 and Comparative Example 7. That is, the water-absorbent resin obtained in Example 4 was superior to the water-absorbent resin obtained in Comparative Example 7 in terms of residual monomer amount, impact resistance, and absorption rate.

  Furthermore, the water-absorbent resin obtained in Comparative Example 8 using 2,2'-azobis (2-amidinopropane) dihydrochloride as an initiator has a high absorption rate but a reduced impact resistance.

  According to the method for producing a water-absorbent resin of the present invention, the productivity is not impaired as compared with the conventional production method, it is very advantageous in terms of cost, and further there is little decrease in physical properties due to powdering, etc. However, it is possible to produce a water-absorbing resin that is significantly improved. There is no need for foam polymerization, the manufacturing process can be simplified, and the cost can be reduced.

  In addition, the water-absorbing resin containing fine particles or the water-absorbing resin satisfying specific water-absorbing performance obtained by the production method of the present invention is resistant to damage during transportation and reduces fine powder and dust. Furthermore, even in a diaper, high performance can be maintained and an excellent diaper can be provided.

  In the present invention, by including a specific amount of water-absorbing resin, in general, it has been difficult to improve absorption rate, residual monomer reduction, particle size control, improvement of absorption capacity under pressure, control of bulk specific gravity, impact resistance. Improvements are possible.

  The specific embodiments or examples made in the detailed description section of the invention are merely to clarify the technical contents of the present invention, and are limited to such specific examples and are interpreted in a narrow sense. It should be understood that various modifications may be made within the spirit of the invention and the scope of the following claims.

FIG. 1 is a view showing an apparatus for measuring the absorption capacity under pressure (AAP) in the measurement of physical properties of a water absorbent resin in an example of the present invention.

Claims (2)

A water-absorbent resin particle having 70 to 99.999 mol% of acrylic acid (salt) and 0.001 to 5 mol% of a crosslinking agent as repeating units, and by polymerizing an aqueous solution of an acid group-containing unsaturated monomer The obtained water-insoluble particles are contained in an amount of 0.1 to 50% by weight based on the weight of the acid group-containing unsaturated monomer at the time of polymerization, and the water-insoluble particles are a water-absorbent resin or a synthetic zeolite. Water-absorbent resin particles satisfying 1) to (7).
(1) Absorption capacity (CRC) is 25-40 g / g.
(2) Absorption capacity under pressure (AAP 4.9 kPa) is 22.2 to 25.6 g / g.
(3) Absorption rate (FSR) is 0.25 to 1.0 g / g / sec.
(4) The bulk specific gravity (JIS K 3362) is 0.50 to 0.80 g / ml.
(5) The residual monomer is 0 to 400 ppm.
(6) Particles (JIS Z8801-1) of 850 to 150 μm are 95 to 100% by weight.
(7) Amorphous crushed particles. Water-absorbent resin particles according to claim 1, wherein the water-soluble component is not more than 25 wt%.