JP3135878B2 - Water absorbing agent and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a water-absorbing agent which is obtained by press-molding a powder containing fine particles of a water-absorbing resin and has excellent absorption performance and absorption speed, and a method for producing the same.

[0002]

2. Description of the Related Art In the process of producing a water-absorbent resin, a method of adjusting the particle size by a sieve operation is usually employed in order to control the particle size of the obtained water-absorbent resin powder to an appropriate range. In particular, recently, there has been a demand for minimizing the content of fine particles as much as possible from the viewpoint of preventing scattering of fine particles in the process of handling the powdery water-absorbent resin and improving worker safety by reducing the chance of inhaling fine particles. strong. In order to satisfy this demand, fine particles are usually removed by a sieving operation, but the removed fine particles are often discarded because of their poor utility value. For this reason, the production cost is increased due to a decrease in the yield and a disposal cost of the fine particles.

[0003] From the above background, it has become important how to effectively use the fine particles removed by adjusting the particle size. For example, the following methods have been proposed as methods for effectively utilizing fine particles. A method in which the fine particles are recycled during the process of producing the water-absorbent resin (polymerization liquid or hydrogel polymer) and reused (JP-A-4-41532, JP-A-4-22770)
No. 5, JP-A-4-348103) A method of fixing fine particles or a particle aggregate containing the fine particles using a binder, and granulating the particles into large particles (Japanese Patent Application Laid-Open No. 62-132936, JP-A-2-284
927, JP-A-2-227435, JP-A-3-137129, JP-A-4-214736, etc.)

[0004]

However, in this method,
Since the recycle-added fine particles pass through the process of drying and pulverizing again, there is a problem that the absorption performance of the obtained water-absorbent resin decreases as the amount of the recycle-added fine particles increases. In the method of (1), the mechanical strength of the granulated material is not sufficient, and the granulated material is subjected to external force such as mechanical shock, frictional force, vibration during transportation, etc. Is a problem that occurs again.
When the amount of the binder added is increased or the fixing force is increased by using a crosslinking agent in combination, another problem occurs in that the absorption rate of the obtained water-absorbent resin is reduced.

[0005]

SUMMARY OF THE INVENTION In view of these problems, the present inventors have manufactured a powder containing fine particles of a water-absorbent resin, have excellent absorption performance and absorption speed, and have a mechanical shock and frictional force. The present inventors have conducted intensive studies with the aim of providing a water-absorbing agent that does not regenerate fine particles even when an external force such as vibration during transportation is applied, and a method for producing the same.

That is, according to the present invention, the water-absorbent resin (A) powder containing 30% by mass or more of fine particles having a particle size of 150 μm or less is mixed with water in an amount of 0.003 to 5% by mass based on (A).
Crosslinking agent having two or more functional groups capable of reacting with (A)
In the presence of (C) , it is molded under pressure at a surface pressure of 50 kg / cm ² or more or a linear pressure of 25 kg / cm or more, and if necessary, dried or dried and pulverized.
Water-absorbing agent of 1000 μm; powder of water- absorbent resin (A) containing fine particles having a particle size of 150 μm or less is converted into (A) together with water.
0.003 to 5% by mass of a functional group capable of reacting with (A)
Obtained by pressure molding in the presence of a cross-linking agent (C) having two or more particles having an average particle size of 200 to 1000 μm and a density of 0.4
１1.6 g / cm ³ , absorption under normal pressure in physiological saline is 40 g / g or more, absorption under pressure of 20 g / cm ² is 2
0 g / g or more of a water-absorbing agent; and a water-absorbent resin (A) powder containing 30% by mass or more of fine particles having a particle size of 150 μm or less, together with water , in an amount of 0.003 to 5% by mass based on (A).
Crosslinking agent having two or more functional groups capable of reacting with (A)
(C) Surface pressure of 50 kg / cm ² or more or 2 in the presence of
After pressure molding at a linear pressure of 5 kg / cm or more, if necessary, dry or dry and pulverize.
m is a method for producing a water absorbing agent.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, examples of the water-absorbent resin (A) include a crosslinked product of a starch-acrylate copolymer, a crosslinked polyacrylate, a self-crosslinked polyacrylate, and acrylic acid. Saponified ester / vinyl acetate copolymer crosslinked product, isobutylene / maleic anhydride crosslinked product, polysulfonate crosslinked product, acrylate / sulfonate crosslinked copolymer, acrylic acid / acrylamide crosslinked copolymer And water-absorbent resins in the form of powder such as acrylamide cross-linked polymers and partial hydrolysates thereof, and modified cellulose derivatives. These can be used in combination of two or more.

The method for producing (A) is not particularly limited, and includes, for example, a method of polymerizing an aqueous solution in the presence of a crosslinking agent, a method of reverse phase suspension polymerization in the presence or absence of a crosslinking agent, radiation or light. Examples thereof include a method of polymerizing and a method of post-crosslinking a water-soluble resin. Preferred as (A) are acrylic acid and acrylate, which can absorb and hold a large amount of liquid by ionic osmotic pressure and have little water separation even when a load or an external force is applied, as a main constituent monomer unit of the polymer. It is a water-insoluble water-absorbent resin (A1), particularly a water-absorbent resin that has been subjected to aqueous solution polymerization in the presence of a crosslinking agent.

The ratio of acrylic acid to the total of acrylic acid and acrylate as constituent units of the water-absorbent resin (A1) is usually 20 to 50 mol%, preferably 20 to 40 mol%. When the acrylic acid content is less than 20 mol%, the pH when water is absorbed becomes alkaline, which may cause a problem in terms of skin safety. On the other hand, when the content of acrylic acid exceeds 50 mol%, not only does the absorption performance decrease, but also the pH at the time of absorbing water becomes acidic, which is also undesirable in terms of skin safety. The type of salt in the acrylate is not particularly limited, but is usually an alkali metal salt such as sodium or potassium, and may be an ammonium salt or an amine salt if necessary. In the vicinity of the surface of the particles of the water-absorbing resin exemplified above, for example, a polyglycidyl ether compound, a polyol compound, a polyamine compound, a cross-linking agent such as a polyvalent metal compound, the resin further surface cross-linked by a normal method is also a water-absorbing resin. (A) can be suitably used in the present invention.

In the present invention, the powder of the water-absorbent resin (A) containing fine particles (hereinafter referred to as fine particle-containing powder) is
Usually, a powder containing 30% by mass or more of fine particles having a particle size of 150 μm or less. The content of the fine particles having a particle size of 150 μm or less in the fine particle-containing powder is preferably 50% by mass or more, particularly 7% by mass.
0 mass% or more. When the content of the fine particles having a particle size of 150 μm or less is less than 30% by mass, problems such as abrasion of the pressure molding device, an increase in pressure fluctuation during molding, and a decrease in the yield of molded products may occur.

The method for obtaining the fine particle-containing powder is not particularly limited, and examples thereof include the following. The fine particle-containing powder does not need to have a single composition, and may be a mixture of two or more kinds. Production of water-absorbent resin Fine-particle-containing powder generated in a process of producing a water-absorbent resin (for example, a sieving process for particle size adjustment), production of a water-absorbent resin Fine particle-containing powder obtained by collecting fine particles generated in the step or the step of using a water-absorbent resin with a bag filter or the like, fine-particle-containing powder obtained by mixing the above fine particles with a normal water-absorbent resin

The shape of the fine particle-containing powder is not particularly limited, and examples thereof include powder, scaly, granular, pearl and the like, and these may be mixed. It is preferably in powder form. The water content in the fine particle-containing powder is also not particularly limited, and is usually 0.1 to 10% by mass, preferably 1 to 8% by mass. As the absorption performance of the fine particle-containing powder, the absorption amount under normal pressure with respect to physiological saline is 40 g.
/ G or more, absorption under pressure of 20 g / cm ² is 20 g / g
The above is preferred. More preferably, the absorption amount under normal pressure is 45 to 75 g / g, and the absorption amount under pressure is 22 to 55 g / g.
g, and particularly preferably, the absorption amount under normal pressure is 48 to 70.
g / g, and the absorption amount under pressure is 25 to 50 g / g. still,
The absorption amount under normal pressure and the absorption amount under pressure are values measured by a method described later.

If one or more kinds of inorganic fine powders (P), such as hydrophilic or hydrophobic silicon dioxide, titanium oxide and aluminum oxide, are previously mixed with the fine particle-containing powder, and then water is added, mamako is formed. However, it is preferable because water can be uniformly present in the fine particle-containing powder. The average particle size of the primary particles of the inorganic fine powder (P) is preferably 10
0 μm or less, particularly 5 to 50 μm, and the specific surface area by the BET method is preferably 50 to 500 m ² / g, particularly 8
0 to 450 m ² / g. The amount of the inorganic fine powder (P) to be added is preferably not more than 5% by mass, more preferably 0.05 to 2% by mass, and particularly preferably 0.
1 to 1% by mass.

The water-absorbing agent of the present invention must be molded under pressure in the presence of water. It is preferable to use water alone without using an organic solvent in terms of safety and cost in handling.However, an aqueous solution in which a hydrophilic organic solvent (methanol, ethanol, ethylene glycol, propylene glycol, glycerin, etc.) is mixed with water. Liquid can be used if necessary. When the aqueous liquid is used, the amount of the hydrophilic organic solvent is 40% or less, preferably 30% or less by mass based on the entire aqueous liquid.
It is as follows. The amount of water with respect to the fine particle-containing powder is 2 to 80%, preferably 3 to 60%, and more preferably 5 to 50% on a mass basis. If the amount of water exceeds 80%, the fine particle-containing powder absorbs water and becomes swollen, so that even if the pressure during pressure molding is increased, the shapeability during molding is lacking. On the other hand, if it is less than 2%, the fixability of the fine particle-containing powder is poor, and the pressure moldability is reduced. Note that "in the presence of water" does not necessarily mean that water is added to the fine particle-containing powder, but the present invention also includes the use of fine particles containing water.

In the present invention, a water-soluble resin and / or a water-soluble resin may be used together with water for the purpose of increasing the strength of the press-formed product.
Alternatively, pressure molding can be performed in the presence of the water-dispersed resin (B). Since (B) is a resin that dissolves or disperses in water, it can be in the presence of an aqueous solution or dispersion of (B). In (B), the water-soluble resin may be any of a natural polymer and a synthetic polymer. Examples of the natural polymer include starches (solubilized starch, pregelatinized starch, amylose, etc.), and cellulose derivatives (carboxymethylcellulose). Sodium, hydroxyethylcellulose), sodium alginate, guar gum, xanthan gum,
Gum arabic, locust bean gum, carrageenan,
Mannan, gluten, chitosan and the like.

Examples of synthetic polymers include polyvinyl alcohol, polyvinyl pyrrolidone, polyethylene oxide, polyethylene glycol, sodium polyacrylate,
And polyvinyl ether compounds. Examples of the aqueous dispersion resin in (B) include, for example, aqueous dispersions such as synthetic resin emulsions (eg, acrylic emulsions, polyolefin resin emulsions, polyurethane resin emulsions), natural or synthetic wax emulsions, and natural or synthetic rubber emulsions. State. These water-soluble resins and / or water-dispersible resins (B) can be used alone or in combination of two or more. When using the water absorbing agent of the present invention (B)
In order not to elute, (B) preferably has a weight average molecular weight of at least 2,000 or more. The upper limit of the molecular weight of (B) is not particularly limited, and preferably has a molecular weight in which (B) is dissolved or dispersed in water and has a viscosity that does not hinder mixing with the powder of (A).

The amount of (B) to the fine particle-containing powder is preferably 0.01 to 20 on a mass basis per solid content.
%, Preferably 0.1 to 10%. By setting the amount of (B) within this range, it is preferable that the water-absorbing agent obtained has a small decrease in water-absorbing performance. As an embodiment in which (B) is present, (B) may be dissolved and / or dispersed in water in advance, or (B) may be contained in fine particle-containing powder, and water may be added thereto. Then, (B) may move to the water side, and a part may be dissolved and / or dispersed.

In the present invention, together with water, a fine particle-containing powder is used together with water for the purpose of increasing the strength of the obtained press-formed product and improving the shape retention and surface dryness of the gel after absorbing water. Pressure molding is performed in the presence of a crosslinking agent (C) having two or more functional groups capable of reacting with a group (for example, a carboxyl group). Examples of the crosslinking agent (C) include conventionally known polyglycidyl compounds (for example, polyethylene glycol diglycidyl ether, glycerol diglycidyl ether, glycerol triglycidyl ether,
Ethylene glycol diglycidyl ether, polyglycerol polyglycidyl ether, etc.), polyhydric amine compounds (eg, ethylene diamine, polyamide polyamine epichlorohydrin resin, etc.), polyhydric alcohols (eg, glycerin, ethylene glycol, etc.), polyhydric isocyanates, aziridine compounds, Alkylene carbonate (for example, ethylene carbonate and the like), and a mixture of two or more thereof are exemplified. The crosslinking agent (C) is preferably soluble in water or an aqueous liquid, and more preferably a polyglycidyl compound, particularly ethylene glycol diglycidyl ether, because it can be reacted at a relatively low temperature. The amount of the crosslinking agent (C) used with respect to the fine particle-containing powder is usually 0.003 to 5%, preferably 0.005 to 2%, particularly 0.01 to 1% on a mass basis.

When the pressure molding is carried out in the presence of (C) together with water, the pressure molding after the pressure molding is carried out for the purpose of enhancing the reactivity between the fine particle-containing powder and (C) or shortening the reaction time. It is preferable to perform the heat treatment at such a stage. The temperature of this heat treatment can be variously changed depending on the type of (C) contained in water. For example, when an aziridine compound is used as (C), the temperature is usually from room temperature to 60 ° C, preferably 30 to 50 ° C, and when a polyglycidyl compound is used as (C), the temperature is usually from 80 to 160.
C., preferably 100 to 150 ° C., and when using a polyhydric alcohol or alkylene carbonate as (C), usually 160 to 230 ° C., preferably 180 to 220 ° C.
° C.

Examples of industrial equipment used for adding water to the fine particle-containing powder include conical blenders, Nauter mixers, double-arm kneaders, V-type mixers, and the like.
Examples include a mechanical mixing device such as a fluidized bed mixer, a turbulizer, a screw type line blending device, a ribbon mixer, and a mortar mixer. However, the device is not limited to the above as long as the device can uniformly mix.

The following methods may be used for molding the fine particle-containing powder under pressure in the presence of water. After mixing the fine-particle-containing powder and water, press-molding in a mold having a desired shape and size.The fine-particle-containing powder and water are mixed, and once in a sheet form,
After pressure-molding into a bar or block shape, a method of pulverizing and adjusting the particle size to obtain a desired particle size Heating the fine particle-containing powder containing water, under conditions where the water in the fine particle-containing powder evaporates Pressure molding method

Examples of the industrial apparatus for press forming include a roll press forming machine (such as a briquette machine and a roller compactor), a press press forming machine, and a perforated extrusion press forming machine (such as a disk pelleter). ), A piston-type press molding machine, and the like, but are not limited thereto.

The pressure at the time of pressure molding is determined by the type of the fine particle-containing powder, the content of the fine particles, the properties (such as breaking strength and gel strength), the amount of water or aqueous liquid added, (B) and / or Alternatively, it can be appropriately changed according to the presence or absence of (C) and the content thereof, but is usually a surface pressure of 50 kg / cm ² or more or a linear pressure of 25 kg / cm or more. Preferably 50 kg / cm ^{2 to} 10 ton / cm ^{2 for} surface pressure, 25 kg / cm to 5 ton / c for linear pressure
m, especially 100 kg / cm ^{2 to} 6 ton / cm ^{2 for} surface pressure and 50 kg / cm to 3 ton / c for linear pressure.
m. When the surface pressure is less than 50 kg / cm ² or the linear pressure is less than 25 kg / cm, the press-molded product has poor shapeability, and the obtained molded product is easily broken by external force or shear force. A preferable surface pressure is 50 kg / c.
m ² to 10 ton / cm ² , and the linear pressure was 25 kg / cm to 5 ton / cm, when the surface pressure exceeded 10 ton / cm ² or the linear pressure exceeded 5 ton / cm. This is because the shapeability and stability against external force are further improved, but a large-sized apparatus is required, and the absorption speed of the obtained molded product tends to be slow.

The temperature at the time of pressure molding is not particularly limited, and it is usually carried out at room temperature. If necessary, the pressure molding is carried out while heating (for example, 30 to 200 ° C., preferably 80 to 150 ° C.). Is also good. In particular, when pressure molding is performed while heating to 80 ° C. or higher, the water normally contained in the fine particle-containing powder evaporates, and since this water acts as a binder, water is added to the fine particle-containing powder. Operation is not always necessary. When the water used contains the crosslinking agent (C), the temperature is not limited to the above-mentioned temperature, and the above-mentioned temperature necessary for the reaction of (C) can be selected.

The shape of the water-absorbing agent obtained by pressure molding is not particularly limited, and may be any shape such as, for example, granules, spheres, beans, dice, polyhedrons, plates, sheets, rods or blocks. No. The density of the water-absorbing agent formed by pressure is usually 0.3 g / cm ³ or more, preferably 0.4 to 1.6 g / cm ³ , more preferably 0.5 to 1.6 g / cm ^3.
1.5 g / cm ³ . By setting the density to 0.3 g / cm ³ or more, even if an external force such as mechanical shock, frictional force, or vibration during transportation is applied to the molded product, the molded water-absorbing agent is broken and fine particles are regenerated. It is not preferable because it does not cause any problems.

According to the amount of water to be present at the time of pressure molding,
If necessary, a drying operation can be added after the pressure molding to adjust the moisture content of the molded product. Usually, when the amount of water to be present is 2 to 9% by mass, the drying operation can be omitted,
When the amount of water exceeds 9% by mass, it is preferable to perform a drying operation. Preferred methods for obtaining a pressure-formed water-absorbing agent include a method of directly pressing into granules, granules, and beans, a method of shredding a bar-shaped press, and pressing into a sheet or flat plate. This is a method of pulverizing a molded product.
The thickness when pressure-molding into a flat plate or a sheet is usually 1 to 10 mm, preferably 2 to 8 mm.

The pressed product is dried if necessary as described above, and is then pulverized by a usual method, if necessary, to adjust the particle size to an average particle size of 200 to 1000 μm to obtain the water absorbing agent of the present invention. . Preferred average particle size is 250 to 90
0 μm, more preferably 280-800 μm.
If the average particle size exceeds 1000 μm, the surface area becomes too small, and the absorption rate may be reduced. On the other hand, if the average particle size is less than 200 μm, the particles become too fine, and the effects of preventing scattering and reducing the opportunity for inhalation by workers are poor, which is not preferable. Here, the average particle size is 16 mesh, 20 mesh, 26 mesh, 30 mesh,
Using JIS standard sieve of 42 mesh, 50 mesh, 60 mesh, 100 mesh, 140 mesh,
The particle size distribution (percentage by mass) measured by the sieving method was plotted on a log-normal probability paper, and the cumulative percentage of particles passing through the opening of each sieve was plotted on a log-normal probability paper. The particle size.

In particular, sanitary articles (eg, disposable disposable diapers, sanitary napkins, incontinent pads, breast milk pads, surgical underpads, etc.) and sheets (pet sheets, drip absorbing sheets, dew condensation preventing sheets, etc.), etc. The preferred particle size when applied to an absorbent article is from 100 to
90% by mass or more, preferably 95% by mass or more, particularly preferably 150 to 850 μm, of particles having a size of 850 μm.
Is 95% by mass or more.

The thus obtained granular material after pressure molding can be used as it is as the water-absorbing agent of the present invention, but the ordinary water-absorbent resin (A ') which has not been pressure-molded can be used.
(Preferably 90% by mass or more having a particle size of 100 to 850 μm) to obtain the water absorbing agent of the present invention. A pressure-absorbing water-absorbing agent for mixing,
The mixing ratio with (A ') can be arbitrarily selected, but (A') is usually not more than 90% of the whole, preferably 10 to 90%, more preferably 20 to 8 on a mass basis.
0%.

The water-absorbing agent of the present invention may be one further subjected to surface cross-linking by a usual method, and the surface cross-linking can be carried out during or after pressure molding. Further, the surface can be cross-linked after being mixed with a normal water-absorbent resin (A ′) that has not been press-molded.

In any step before or after pressure molding, silica, zeolite, antioxidants, surfactants, various silicone oils, chelating agents may be used as additives and extenders, if necessary. Fungicides, antibacterial agents, deodorants, fragrances, fibrous materials (pulp, synthetic fibers, etc.) and the like.

The water-absorbing agent of the present invention preferably has an absorption under normal pressure to physiological saline of 40 g / g or more, and an absorption under pressure of 20 g / cm 2 of 20 g / g or more. Preferably, the absorption amount under normal pressure is 45 to 70 g / g, and the absorption amount under pressure is 22 to 50 g / g. 40 g / g absorption under normal pressure
When the absorption amount under pressure is less than 20 g / g, the absorption performance is inferior to that of a conventional water-absorbent resin, so that it must be added in a large amount to be applied to sanitary articles and absorbent articles. Absent. The absorption under normal pressure and the absorption under pressure are values measured by the method described below.

[0033]

The present invention will be further described with reference to the following examples and comparative examples, but the present invention is not limited to these examples. Hereinafter, unless otherwise specified,% indicates mass%. Absorption amount under normal pressure, absorption amount under pressure, absorption speed,
The mechanical strength and the shape retention of the gel after water absorption were measured by the following methods.

Absorbency under normal pressure: 1.00 g of a water-absorbing agent was placed in a 10 × 20 cm tea bag made of a 250-mesh nylon cloth, and excess saline (0.9 g) was added.
% Sodium chloride aqueous solution) for 30 minutes, then suspend the tea bag vertically and drain it for 15 minutes to determine the increased mass. This value was taken as the absorption amount under normal pressure.

Absorption under pressure: cylindrical plastic cylinder (inner diameter 28 m) with a 250 mesh nylon cloth adhered to the bottom surface
m, height 50 mm) and uniformly spread 0.100 g of a water absorbing agent. A weight having an outer diameter of 28 mm is placed on this so as to give a load of 20 g / cm ² . This is immersed in a Petri dish (diameter 11 cm) containing 25 ml of physiological saline with the nylon cloth side facing down. The tenfold value of the increased weight after immersion for 30 minutes was defined as the absorption under pressure.

Absorption speed: 50 g of physiological saline and a magnetic stirrer piece (30 mm in length) are placed in a 100 ml beaker, and 2.0 g of a water-absorbing agent is quickly added while stirring at 600 rpm using a magnetic stirrer. The time from the completion of the introduction of the water-absorbing agent to the point at which the water-absorbing agent absorbed the physiological saline and gelled, the eddy disappeared, and the liquid surface became flat was measured in seconds to determine the absorption rate.

Mechanical strength: 100 g of a water-absorbing agent whose particle size distribution was measured in advance, and a ceramic ball (diameter 18 mm) 15
And placed in a 400 ml ball mill,
The mechanical strength test is performed by rotating at 10 m for 10 minutes. The particle size distribution after the test was measured to measure the increase amount of the fine particles having a size of 100 μm or less (rounded off to the decimal point) and evaluated according to the following criteria. ：: The increase amount of the fine particles of 100 μm or less is less than 3% by mass. ○: The increase amount of the fine particles of 100 μm or less is 3% to less than 5% by mass. Δ: The increase amount of the fine particles of 100 μm or less is 5% by mass to 10%.
Less than mass% ×: The amount of increase of fine particles of 100 μm or less is 10 mass% or more.

Gel shape retention after water absorption: The beaker containing the gel whose absorption rate has been measured is placed in a plastic bag, sealed, and stored at 40 ° C. for 1 hour. Thereafter, the water-absorbing gel was taken out, spread on a vinyl sheet, and a force was applied to the gel by pressing it with the palm, and the state of the gel was evaluated in four steps according to the following criteria. ◎: The gel shape at the time of water absorption is maintained even when force is applied, and the dry feeling is good. ：: Some gel returns to fine particles when force is applied, and the dry feeling is good. : Paste-like, poor dry feeling ×: Most of the gel becomes paste-like when force is applied, and there is no dry feeling

Reference Example 1 A commercially available water-absorbent resin (“Sunwet IM-6320”;
(A crosslinked product of surface crosslinked polyacrylate manufactured by Sanyo Chemical Industries; water content: 1.2%) was sieved with a 100-mesh JIS standard sieve (aperture: 150 μm), and fine particles (a) passed through the sieve were collected. . Using a small turbulizer (manufactured by Hosokawa Micron Corporation), 20% water was added to (a) and mixed, and at room temperature, a surface pressure of 2 ton / cm ² and a diameter of about 1 mm were obtained using a briquetting machine. It was pressed into granules and dried to a water content of 5% to obtain a water absorbing agent (1). The water-absorbing agent (1) has an average particle size of 910 μm and a density of 0.1 μm.
It was 93 g / cm ³ . Table 2 shows the performance measurement results of the water absorbing agent (1).

REFERENCE EXAMPLE 2 In the same apparatus as in Reference Example 1, 20% water was added to the fine particles (a), and a sheet was formed at room temperature using a roller compacting machine (manufactured by Nakata Seisakusho) at a linear pressure of 1 ton / cm. Was press molded. This pressed product is dried to a moisture content of 5%,
After grinding with a roll mill, adjust the particle size to 100 to 850 µm
Water-absorbing agent (2) having a particle size of The water-absorbing agent (2) had an average particle size of 440 μm and a density of 0.92 g / cm ³ . Table 2 shows the performance measurement results of the water absorbing agent (2).

[0041] In Reference Example 3-6 Reference Example 2, the amount of water added, except that the line pressure during pressure molding were varied as shown in Table 1 in the same manner as in Reference Example 2, the water-absorbing agent (3) To (6) were obtained. Their average particle size,
The results of measuring the density are also shown in Table 1. Table 2 shows the performance measurement results of the obtained water absorbing agents (3) to (6).

Reference Example 7 In Reference Example 2, sodium alginate 10% was used instead of water.
Reference Example 2 except that the same amount of the aqueous solution was used (the amount of sodium alginate was 2% and the amount of water was 18% based on the fine particles (a)).
In the same manner as in the above, a water absorbing agent (7) was obtained. The water-absorbing agent (7) had an average particle size of 460 μm and a density of 0.90 g / cm ³ . Table 2 shows the performance measurement results of the water absorbing agent (7).

Reference Example 8 A commercially available water-absorbent resin ("Sunwet IM-5000")
D "; a crosslinked product of polyacrylate, manufactured by Sanyo Chemical Industries, Ltd .; water content: 5.6%) was sieved with a 100-mesh JIS standard sieve (mesh size: 150 μm), and fine particles (b) passed through the sieve were collected. Using a small turbulator,
(B) contains finely divided hydrophilic silica (“Aerosil 20”).
0 "(manufactured by Nippon Aerosil Co., Ltd.) 0.1%, followed by addition and mixing of 20% water. The mixture was rolled at room temperature using a roller compacting machine at a line pressure of 1
It was press-formed into a sheet at ton / cm. The pressed product was dried to a moisture content of 5%, pulverized by a roll mill, and adjusted for particle size to obtain a water absorbing agent (8) having a particle size of 100 to 850 µm. The water absorbing agent (8) has an average particle size of 430 μm and a density of 0.3.
It was 83 g / cm ³ . Table 2 shows the performance measurement results of the water absorbing agent (8).

REFERENCE EXAMPLE 9 The fine particles (b) obtained in Reference Example 8 were subjected to a linear pressure of 3 tons /
cm in sheet form. Emission of water vapor was observed during the pressing, and the water content of the obtained pressed product was 1.
It had dropped to 4%. This was pulverized with a roll mill, and the particle size was adjusted to obtain a water absorbing agent (9) having a particle size of 100 to 850 μm. The water-absorbing agent (9) has an average particle size of 380 μm and a density of 0.3.
It was 93 g / cm ³ . Table 2 shows the performance measurement results of the water absorbing agent (9).

[0045] In Example 1 Reference Example 8, the amount of ethylene glycol diglycidyl ether 0.2% ethylene glycol diglycidyl ether in place of the water to the same amount of [fine particle (b) is 0.04%, the amount of water The water absorbing agent (10) was obtained in the same manner as in Reference Example 8 except for using 19.06%. Water-absorbing agent (1
0) has an average particle size of 420 μm and a density of 0.84 g / cm
^{Was 3} . Table 2 shows the performance measurement results of the water absorbing agent (10).
Shown in

REFERENCE EXAMPLE 10 40 parts of the water-absorbing agent (5) obtained in Reference Example 5 and 60 parts of a water-absorbing resin "Sunwet IM-6320" were uniformly mixed with a V-type mixer, and the water-absorbing agent (11) was added. Obtained. The water-absorbing agent (11) had an average particle size of 390 μm and a density of 0.77 g / cm ³ . Table 2 shows the performance measurement results of the water absorbing agent (11).

Comparative Examples 1 and 2 The water-absorbent resin "Sunwet IM-6320" of Reference Example 1
(Absorption amount under normal pressure 54 g / g, absorption amount under pressure 31 g / g,
The fine particles (a) obtained from the absorption speed of 35 seconds) were used as comparative water-absorbing agents (1 ′), and the water-absorbing resin “Sunwet IM-5000D” of Reference Example 8 (absorption under normal pressure: 50 g / g, absorption under pressure) The fine particles (b) obtained from 30 g / g at an absorption rate of 28 seconds) were used as comparative water-absorbing agents (2 ′), and the performance measurement results are shown in Table 2.

Comparative Example 3 The water-absorbent resin “Sunwet IM-6320” was sieved with a 50-mesh JIS standard sieve (mesh size: 300 μm), and fine particles (c) passed through the sieve were collected. When this particle size distribution was measured, the content of fine particles having a size of 150 μm or less was 28%. Using a small turbulizer, 20% water was added to (c) and mixed, and at room temperature, a surface pressure of 2 ton / cm ² using a briquetting machine.
Was compression molded into granules having a diameter of about 1 mm and dried to a water content of 5% to obtain a comparative water-absorbing agent (3 ′). Comparative water-absorbing agent (3 ')
Had an average particle size of 860 μm and a density of 0.85 g / cm ³ . Table 2 shows the performance measurement results of the comparative water absorbing agent (3 ′).
Shown in

Comparative Example 4 In Reference Example 1, the surface pressure during pressure molding was 40 kg / c.
A comparative water-absorbing agent (4 ') was obtained in the same manner as in Reference Example 1 except that m2 was used. The average particle size of the comparative water absorbing agent (4 ′) is 88.
It was 0 μm and the density was 0.82 / cm ³ . Table 2 shows the performance measurement results of the comparative water absorbing agent (4 ′).

Comparative Example 5 Using the fine particles (a) obtained in Reference Example 1,
A granulated product was obtained by operating according to Example 12 of JP-A-32936. That is, 50 g of the fine particles (a) was placed in a 500 ml four-necked round bottom flask equipped with a stirrer, a water separator, a dropping funnel, and a nitrogen gas inlet tube, and 600 ml of normal heptane and 2.5 g of sorbitan monolaurate were added. Underneath, slowly add 45.5 g of water with a dropping funnel. After adding 0.68 g of fine powder silica to this suspension, water and normal heptane are removed by distillation under stirring, and further dried to obtain a granulated product. By adjusting the particle size of the granulated product, a comparative water-absorbing agent (5 ′) having a particle size of 100 to 850 μm was obtained. The average particle size of the comparative water-absorbing agent (5 ′) was 450 μm, and the density was 0.62 g / cm ³ . Table 2 shows the performance measurement results of the comparative water absorbing agent (5 ′).

[0051]

[Table 1]

[0052]

[Table 2]

[0053]

The water absorbing agent of the present invention obtained by the production method of the present invention has the following features and effects. As with the conventional powdery water-absorbent resin, it has excellent absorption performance under normal pressure and under pressure. Despite the use of fine particles as a starting material, there is no generation of mamako upon water absorption, and the absorption rate is excellent. It is superior in mechanical strength to a granulated product obtained by a conventionally proposed granulation method, and has almost the same mechanical strength as a conventional water-absorbent resin that has not been subjected to pressure molding. Therefore, it can be handled by the same operation and device as the conventional water-absorbing resin. Since the scattering of the fine particles is small, the chance of inhaling the fine particles is small, and the worker is safe. By containing a water-soluble or water-dispersible resin in the water to be used, or by including a crosslinking agent, the mechanical strength is further improved, and the shape retention of the water-absorbing gel is further improved. The dry feeling is further improved.

Because of the above effects, the water-absorbing agent of the present invention can be used for sanitary articles (eg, disposable children's and adult paper diapers, sanitary napkins, incontinent pads, surgical underpads, breast milk pads, puerperium mats) Etc.). Other sheet-like absorbent articles (for example, pet sheet, freshness retaining sheet, drip absorbing sheet, dew condensation preventing sheet, paddy rice seedling seedling sheet, concrete curing sheet, etc.), soil water retention agent, chemical warmer, cold insulator, sludge solidification, various types It can be suitably used for most applications to which conventional water-absorbing resins are applied, such as gelling agents for solutions and body fluids and artificial snow.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kenji Tanaka 11-1-1, Hitotsubashi-Honcho, Higashiyama-ku, Kyoto Examiner at Sanyo Kasei Kogyo Co., Ltd. Eiichi Yoshi ▼ (56) References JP-A-60-99339 (JP, A) Japanese Patent Application Laid-Open No. Hei 10-113557 (JP, A) Japanese Translation of International Patent Application No. Hei 5-506263 (JP, A) International Publication No. 96/13542 (WO, A1) (58) Fields investigated (Int. Cl. ⁷ , (DB name) C08J 3/00-3/28 C08L 1/00-101/16

Claims (6)

(57) [Claims] 1. A water absorbent resin (A) powder containing 30% by mass or more of fine particles having a particle size of 150 μm or less, together with water.
Reacts with 0.003 to 5% by mass of (A) based on (A)
50 in the presence of a crosslinking agent (C) having two or more functional groups
A water-absorbing agent having an average particle diameter of 200 to 1000 μm obtained by pressure molding at a surface pressure of not less than kg / cm ² or a linear pressure of not less than 25 kg / cm and, if necessary, drying or drying and pulverizing. 2. The powder of (A) contains at least one inorganic fine powder (P) selected from silicon dioxide, titanium oxide and aluminum oxide not exceeding 5% by mass based on the powder of (A). The water-absorbing agent according to claim 1, which is obtained by press-molding a mixture obtained by pressure-mixing in the presence of water. 3. The water-absorbing agent according to claim 1, wherein the amount of water with respect to the powder of (A) at the time of press molding is 3 to 60% by mass. 4. It is obtained by pressure molding in the presence of a water-soluble resin and / or a water-dispersible resin (B) together with water,
The amount of (B) with respect to the powder of (A) is 0.0
The water-absorbing agent according to any one of claims 1 to 3, which is 1 to 20% by mass. 5. A powder of water- absorbent resin (A) containing fine particles having a particle size of 150 μm or less, together with water , is added to water (A) in an amount of 0.
Two or more functional groups capable of reacting with 003 to 5% by mass of (A)
It is obtained by pressure molding in the presence of the cross-linking agent (C), having an average particle size of 200 to 1000 μm and a density of 0.4 to 1.6.
g / cm ³ , absorption amount under normal pressure to physiological saline is 40 g
/ G or more, absorption under pressure of 20 g / cm ² is 20 g / g
Above is a water absorbing agent. 6. A water-absorbent resin (A) powder containing 30% by mass or more of fine particles having a particle size of 150 μm or less, together with water.
Reacts with 0.003 to 5% by mass of (A) based on (A)
50 in the presence of a crosslinking agent (C) having two or more functional groups
A method for producing a water-absorbing agent having an average particle diameter of 200 to 1000 μm, which is formed by pressing under a surface pressure of not less than kg / cm ² or a linear pressure of not less than 25 kg / cm and then drying or drying and pulverizing as necessary.