JPH06107800A - Production of granular hydrous gel-like polymer and water-absorbing resin - Google Patents

Abstract

PURPOSE:To accomplish classification for obtaining granular hydrous gel-like polymer excellent in uniformity and useful as a sanitary absorbent etc., by feeding a hydrous gel-like polymer to a feed port provided close to one end of a channel having specified penetrating holes on its wall surface to efficiently eliminate the coarse particles contained in the polymer. CONSTITUTION:A hydrous gel-like polymer is fed to a feed port 6 provided close to one end of a channel 3 having penetrating holes 2 2-15mm in at least one-way length on its wall surface, and allowed to move toward a discharge port 7 provided close to the other end of the channel 3. During the process, the hydrous gel-like polymer granules passing through the penetrating holes are recovered, while the coarse particles having been existed in the original polymer and impassable through the holes are discharged through the discharge port 7, thus accomplishing the objective classification of the hydrous gel-like polymer. The polymer passed through the penetrating holes and classified is then dried to obtain the other objective water-absorbing resin.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a particulate hydrogel polymer and a water absorbent resin. More specifically, the present invention efficiently removes coarse particles contained in a hydrogel polymer, and a classification method for recovering a hydrogel polymer having a desired particle size, as well as a drying operation using such a classification operation. The present invention relates to a method for producing a water absorbent resin which is in a uniform state and has no deterioration in performance.

[0002]

2. Description of the Related Art Water absorbent resins include crosslinked polyacrylic acid salts, saponified acrylic acid ester-vinyl acetate copolymers, crosslinked polyvinyl alcohol modified products, crosslinked isobutylene-maleic anhydride copolymers, starch-acrylic acid. BACKGROUND ART Graft polymers and the like are known and are widely applied to sanitary napkins, sanitary absorbents such as paper diapers, and a wide range of applications such as water retention agents and dehydrating agents in the fields of agriculture and horticulture and the field of civil engineering.

As a method for producing these water-absorbent resins, a reverse-phase suspension polymerization method is disclosed, for example, in JP-A-56-161,408.
No. 57-94,011, 57-158,209
And 57-198,714 are known, and as an aqueous solution polymerization method, for example, JP-A-57 / 1982
-34,101, Japanese Patent Publication No. 48-42,466, JP-A No. 58-49,714, Japanese Patent Publication No. 59-37,003.
The methods described in US Pat. No. 4,286,082 and US Pat. No. 4,625,001 are known.

The hydrogel polymer obtained by these methods is generally dried and pulverized into a product, but since the hydrogel polymer immediately after the polymerization contains coarse particles, it remains as it is. It is difficult to obtain a dry and stable product. That is, in a condition suitable for drying a hydrogel polymer having a smaller particle size, an undried product is mixed in the product, and conversely, a condition suitable for drying coarse particles has a smaller particle size. Excessive heat energy is added to the water-containing gel-like polymer, resulting in deterioration of product performance. In order to eliminate such inconvenience, several methods of adjusting the particle diameter of the hydrogel polymer have been proposed. For example, a method of extruding a hydrous gel polymer from a porous plate and crushing it (Japanese Patent Publication No. 54-3).
No. 2,176, JP-A No. 50-136,348, etc.) is known, but in the conventionally known method, the hydrogel polymer extruded finely and extruded is redeposited to form a string. However, a particulate hydrogel polymer could not be obtained. Further, when the hydrogel polymer is extruded from a porous plate and crushed, a method of adding an additive such as a lubricant for the purpose of preventing redeposition of the hydrogel polymer (JP-A-59-30,
No. 826 and JP-A-59-119,172) are known, but additives remaining in the polymer sometimes adversely affect the performance of the product.

Further, in order to remove coarse particles contained in the water-containing gel polymer by classification, it is possible to use a vibrating sieve which is generally used in powder classification, but it is possible to use water on a sieve plate during operation. The classification operation was difficult because the gelled polymer tends to aggregate to increase the particle size.

[0006]

As described above, a particulate hydrogel having a high absorption capacity and a low water-soluble content can be obtained by drying a particulate hydrogel polymer with a conventional simple process and high productivity. A method for producing a polymer and a water absorbent resin has not been established.

Accordingly, the present invention provides a hydrogel polymer for efficiently removing coarse particles from the hydrogel polymer to recover a hydrogel polymer having a desired particle size without adversely affecting the final product. The purpose is to provide a classification method of. Another object of the present invention is to provide a method for producing a particulate hydrogel polymer and a water-absorbent resin which have good drying efficiency, a high water absorption capacity and a low water-soluble content. A further object of the present invention is to provide a method for producing a water-absorbent resin which has a uniform dry state and is free from deterioration of performance.

[0008]

[Means for Solving the Problems]
What is claimed is: 1. A method for classifying a hydrogel polymer, comprising removing coarse particles from a hydrogel polymer containing coarse particles to recover a hydrogel polymer having a uniform particle size, wherein the wall surface has a length of at least one direction. Is supplied to the supply port provided in the vicinity of one end of the passage having a through hole of 2 to 15 mm,
The hydrous gel polymer particles passing through the through hole of the wall surface of the passage are recovered from the hydrous gel polymer moving toward the outlet provided near the other end of the passage, and passed through the through hole. It is achieved by a method for classifying a water-containing gel polymer, which comprises discharging non-coarse coarse particles from the outlet.

The above-mentioned objects are also a method for producing a water-absorbent resin, which comprises classifying a hydrogel polymer containing coarse particles, crushing and / or crushing and then drying the polymer, wherein at least 1 The hydrogel polymer is supplied to a supply port provided in the vicinity of one end of a passage having a through hole having a length in the direction of 2 to 15 mm, and toward the discharge port provided in the vicinity of the other end of the passage. Hydrous gel polymer particles that pass through the through-hole of the wall surface of the passage are recovered from the moving hydro-gel polymer, and coarse particles that do not pass through the through-hole are crushed and / or crushed to recover the water-containing polymer. It can also be achieved by a method for producing a water-absorbent resin by mixing with gel polymer particles and drying the mixture.

[0010]

The hydrogel polymer used in the present invention is obtained by forming a crosslinked structure by aqueous solution polymerization and polymerizing a monomer component to be the hydrogel polymer. That is, it is essential that the hydrogel polymer used in the present invention has a crosslinked structure.

Such a hydrous gel polymer is, for example,
Japanese Patent Publication No. 61-36,763, Japanese Patent Publication No. 2-19,122
Monomer composition containing at least one monomer selected from the group consisting of (meth) acrylic acid, an alkali metal or ammonium salt thereof and (meth) acrylamide as disclosed in (I). ), The crosslinkable monomer (II) having two or more polymerizable double bonds in the molecule is 0.001 to 50 mol% relative to the monomer composition (I),
Preferably, there is a hydrogel polymer having a crosslinked structure formed by polymerizing monomer components blended in a proportion of 0.01 to 10 mol%.

The water content of the hydrogel polymer used in the present invention is not particularly limited as long as it is in the hydrogel state, but is usually 40 to 90% by weight, preferably 50 to 80% by weight. %. In the present specification, the water content of the hydrous gel polymer means the content of water in the total weight of the hydrous gel polymer expressed in% by weight.

The shape of the hydrogel polymer may be any size and shape that can be supplied to the classifier described later. In one embodiment of the present invention, the hydrogel polymer as described above has a spiral stirring blade 4 along a central axis of a cylindrical or semi-cylindrical passage 3 having a through hole 2 on a wall surface as shown in FIG.
Is supplied to a supply port 6 provided in the vicinity of one end of the passage 3 of the classifier 1 in which a rotating shaft 5 around which is wound is installed.

The shape of the through-hole 2 provided in the cylindrical or semi-cylindrical passage 3 of the classifier 1 is shown in FIGS.
Various types such as a slit type as shown in (c), a mesh type as shown in FIG. 2 (d), or a porous type as shown in FIG. 2 (e) may be used. ,
Of these, a slit-like one is preferable from the viewpoint of classification ability.
The through hole 2 may be provided at least on the side wall surface of the lower end portion of the cylindrical or semi-cylindrical passage 3, but is usually 10 to 300 ° to the left and right in the circumferential direction around the lowermost end portion, preferably 60 to 200. It is installed on the wall at an angle of °.

The slit-shaped through hole 2 is shown in FIG.
As shown in FIG. 2A, one opened along the axial direction of the cylindrical or semi-cylindrical passage 3, one opened along the circumferential direction as shown in FIG. As shown in c), it is considered as a preferable embodiment that the spiral stirring blade 4 is opened corresponding to the spiral. The slit-shaped through holes 2 do not necessarily have to be provided at equal intervals, but it is desirable that they be provided at a predetermined interval. Further, the width of this slit is usually 2 to 15 mm in at least one direction, preferably 5 to 12 mm.
It is desirable that the thickness is about mm. If the slit width is less than 2 mm, the classification efficiency of the hydrogel polymer may be extremely poor, and the function of the classifier may not be fulfilled substantially. On the other hand, if the slit width is more than 15 mm, it may be classified. This is because the coarse gel that is present may pass through the slit and may not function as a classifier.
Further, even when the through hole 2 has a shape other than the slit shape, it is desirable that the size thereof be similar to that in the case of the slit shape.

Further, the transport mechanism of the hydrogel polymer in the classifier 1 is, as described above, a spiral stirring blade wound around a rotary shaft installed along the central axis of the cylindrical or semicylindrical passage 3. As the stirring blade 4, a standard screw-shaped or ribbon screw-shaped blade or the like is used. When a transport mechanism having standard screw-shaped or ribbon screw-shaped blades is arranged in a classifier, the clearance (distance) between the blades and the wall surface of the cylindrical or semi-cylindrical passage is not particularly limited. 0.1
It is desirable that it is about 10 mm, more preferably about 1 to 5 mm. If this clearance is less than 0.1 mm, there is a great risk that the hydrogel polymer will be clogged between the blade and the wall surface of the passage during operation, while if the clearance exceeds 10 mm, efficient classification or There is a great risk that transportation will not be possible.

Further, the rotary shaft 5 may be installed along the central axis of the cylindrical or semi-cylindrical passage 3, and if it has the spiral stirring blades 4 rotating in this passage, it may be a single shaft. But it may be multi-axis.

In the present invention, when the hydrogel polymer is fed to such a classifier, the temperature of the hydrogel polymer is
It is preferably in the range of 30 to 90 ° C. When supplied at a temperature of less than 30 ° C, the hydrous gel polymer adheres to the classifier, and there is a high possibility that the through holes will be clogged and sufficient classification cannot be performed. It is not preferable because it causes deterioration of the physical properties of the polymer.

In the present invention, the water-containing gel-like polymer supplied from the supply port 6 of the classifier 1 having the above-mentioned structure is supplied from the supply port 6 to the passage by the spiral stirring blade 4 rotating about the rotating shaft 5. 3 is conveyed toward an outlet 7 provided in the vicinity of the other end of the gel 3, and during that time, hydrogel polymer particles having a particle size not larger than a specified particle pass through a through hole 2 on the wall surface of the passage 3 to the outside. On the other hand, coarse particles larger than the specified particle size that do not pass through the through-hole are discharged from the discharge port 7. The classification operation can be achieved by collecting the hydrogel polymer particles having a particle size not larger than the specified particle size, which have been taken out through the through holes 2 to the outside.

In the present invention, the hydrogel polymer particles can be efficiently classified by performing the classification operation having the above-mentioned constitution.
For example, it is also possible to perform desired classification by tilting the classifier itself and adjusting the classification efficiency and the transportation speed. Further, in the present invention, the shape of the passage having a through hole having a length of 2 to 15 mm in at least one direction on the wall surface as the classifying mechanism does not necessarily have to be a cylinder or a semi-cylindrical shape as shown in FIG. As the transportation mechanism of the water-containing gel polymer on such a passage, other than the spiral stirring blade as shown in FIG. 1, any other transporting mechanism can be used.

In the method for producing a water-absorbent resin of the present invention, the water-containing gel polymer particles having a particle size equal to or less than the specified particle size which are recovered by passing through the through holes 2 in the classification operation as described above are discharged without passing through the through holes 2. Coarse particles of the hydrogel polymer discharged from the outlet 7 are crushed and / or crushed, then mixed, dried, and further crushed and / or crushed if necessary after drying. .

In the method for producing the water absorbent resin of the present invention,
Examples of means for crushing and / or crushing coarse particles of the water-containing gel polymer include a screw type extruder having a perforated plate such as meat chopper, a coarse crusher such as a shredder, an edge runner, and a middle crusher such as a cutter mill. Used.

The drying can be carried out by a conventionally known means. For example, a box dryer, an aeration box dryer, an aeration band dryer, an aeration vertical dryer, a rotary dryer and the like can be mentioned. The drying temperature for drying the hydrogel polymer may be a conventionally known temperature, but is in the range of 80 to 250 ° C, preferably 100 to 200 ° C. If the temperature exceeds 250 ° C, the polymer may be deteriorated or decomposed. The time required for drying is significantly shorter in the production method of the present invention than in the conventional production methods, regardless of which of the above means is adopted.

A particularly advantageous embodiment of the production method of the present invention is to carry out the drying method described in JP-A No. 64-26604. This method is a suitable method for obtaining a polymer having a low residual monomer, but when achieving a low level of residual monomer, there is a problem that its drying efficiency (productivity) becomes low. there were. By using the particulate hydrogel polymer that has undergone the classification step as described above, the drying efficiency is significantly improved, and the water absorption ratio targeted by the present invention is high,
In addition to satisfying that the water-soluble content is small, it is possible to obtain a water-absorbent resin having a significantly small amount of residual monomer with high productivity.

In the present invention, the powdery water-absorbent resin can be obtained by the above-mentioned drying treatment and then pulverization, and conventionally known pulverization means can be used. For example, high-speed rotary crusher (pin mill,
Hammer mill etc.), screw mill (coffee mill), roll mill and the like. Among them, since the dried product of the particulate hydrogel polymer obtained by the production method of the present invention is a uniform dried product, without undergoing a step such as removal of the undried portion, pulverization (crushing) with a roll mill By doing so, a water absorbent resin having a small content of fine powder can be obtained.

The water-absorbent resin obtained by the production method of the present invention may be subjected to a conventionally known surface treatment method. For example, water absorption obtained by polymerizing and reacting a water-absorbent resin and a crosslinking agent having at least two functional groups capable of reacting with the functional group of the water-absorbent resin to increase the crosslink density near the surface of the water-absorbent resin. There is a method of modifying the functional resin. The water-absorbent resin obtained by the production method of the present invention or the water-absorbent resin subjected to the above surface treatment may be subjected to a conventionally known granulation method.

[0027]

EXAMPLES The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples.

The absorption capacity, water-soluble content and average particle size in the examples were measured by the following methods.

Absorption ratio of dry pulverized product Approximately 0.2 g of dry pulverized product of hydrous gel polymer classified according to JIS standard sieve mesh from 10 mesh to 100 mesh
Accurately weighed, and made of non-woven tea bag type bag (40mm × 1
50 mm) and then soak in 0.9% saline 60
The weight after the minutes was measured, and the absorption capacity was calculated according to the following mathematical formula 1.

[0030]

[Equation 1]

Water-soluble content of dry pulverized product Approximately 0.5 g of dry pulverized product of hydrogel polymer classified according to JIS standard sieve mesh from 10 mesh to 100 mesh
Was dispersed in 1000 ml of deionized water, stirred for 16 hours, and then filtered with a paper filter (TOYO # 6) for at least 100
g of filtrate was obtained. Exactly 100 g of the filtrate was concentrated to about 2 to 3 ml with a rotary evaporator, deionized water was added, and the mixture was transferred to a petri dish (W ₀ g). This was dried at 120 ° C. (W ₁ g). The water-soluble content was determined according to the following mathematical formula 2.

[0032]

[Equation 2]

Average Particle Diameter of Particulate Hydrous Gel Polymer 25 g of the sampled particulate hydrogel polymer (solid content α% by weight) is 20% by weight aqueous sodium chloride solution 120
It was put into 0 g and the stirrer chip was rotated at 300 rpm and stirred for 60 minutes. After stirring, sieve (opening 9.5 mm, 2.0 mm, 0.85 mm, 0.6 mm,
0.3 mm, 0.075 mm) into the dispersion,
From above, 6000 g of a 20 wt% sodium chloride aqueous solution was slowly poured, and the hydrogel polymer was classified. The classified water-containing gel polymer on each sieve was thoroughly drained and then weighed. The sieve opening was converted to a sieve opening R (α) corresponding to the solid content α% by weight of the hydrogel polymer according to the following mathematical formula 3. Solid content α weight% on log probability paper
The particle size distribution of the corresponding particulate hydrous gel polymer was plotted. The particle diameter corresponding to 50% by weight on the integrated sieve in the plot was defined as the average particle diameter of the sample.

[0034]

[Equation 3]

R (α): sieve opening (mm) when converted to a water-containing gel polymer having a solid content of α% by weight W: total weight (g) γ of the water-containing gel polymer after classification and draining : Opening of a sieve (m in which a hydrogel polymer swollen in a 20 wt% sodium chloride aqueous solution is classified)
m) Example 1 A stainless steel kneader with a jacket having a double-armed sigma blade with an internal volume of 10 liters and equipped with a thermometer, 75 mol% sodium acrylate and 25 mo acrylic acid.
5500 g of an aqueous solution containing 1% of a monomer component (38% by weight of the monomer component) and 3.49 g of trimethylolpropane triacrylate (0.05 mol% with respect to the monomer component) as a crosslinking agent were added, and nitrogen was added. A gas was blown in to replace the inside of the reaction system with nitrogen. Next, use the two kneader blades 40r
Rotate at pm and heat the jacket with warm water of 35 ° C. while heating it with sodium persulfate 2.8.
g and 0.14 g of L-ascorbic acid were added. Polymerization started 3 minutes after the addition of the polymerization initiator, and after 15 minutes 86
A polymerization peak temperature of ° C was reached. Further, stirring was continued at 40 rpm, and 30 minutes after the initiation of the polymerization, a hydrogel polymer was obtained. At this time, about 12% by weight of the hydrogel polymer was a hydrogel polymer having a size of 10 mm or more. The amount of the hydrogel polymer having a size of 10 mm or more is
This is a sample in which 500 g of the hydrogel polymer was sampled, and the hydrogel polymer having a size of 10 mm or more was visually selected, and this was expressed in% by weight.

Next, the hydrogel polymer was slit to a width of 8
mm, a semi-cylindrical passage with a pipe diameter of 150 mm, and a classifier (length 1500 mm) consisting of screw-shaped blades with a pitch-to-pipe diameter ratio (P / D) of 1, 120 kg / of hydrogel polymer at 50 ° C. It was supplied at a rate of hr and the screw blade was rotated at a rate of 15 rpm to measure the transport amount of the hydrogel polymer, the amount passing through the slit, and the average particle diameter.
The results are shown in Table 1.

Further, the hydrogel polymer discharged from the outlet without passing through the slit of the classifier was pulverized by using a pulverizer (Chopper made by Hiraga Machinery Co., Ltd.) and mixed with the hydrogel polymer passed through the slit. Thus, a particulate hydrogel polymer was obtained. The amount of the hydrous gel polymer having a size of 10 mm or more in this particulate hydrous gel polymer was 0%. 1000 g of this water-containing gel polymer is added to 200 mm × 280 mm × 8
When placed in a 0 mm wire net and dried with hot air at 160 ° C. using a batch-type aerated flow box dryer (manufactured by Satake Kagaku Kikai Kogyo Co., Ltd.), as shown in Table 1, the time when the water content becomes 6% is 36 minutes. It was The obtained dried product was pulverized with a roll mill (manufactured by Meiji Machinery Co., Ltd.) to obtain a dry pulverized product having 1.7 millipass (JIS standard sieve 10 mesh pass), that is, a water absorbent resin powder. The water absorption capacity and water-soluble content of this product were measured, and the results are shown in Table 2. As can be seen from each table, it was found that the drying time was considerably shortened and the physical properties were improved as compared with the case where classification and pulverization were not performed.

Examples 2 to 4 Polymerization was carried out in the same manner as in Example 1 to obtain a hydrogel polymer, which was fed to a classifier in the same manner as in Example 1 and the rotational speed of the screw blades was changed to give a hydrogel gel. The transport amount of the coalescence, the slit passing amount and the average particle size were measured. Further, the hydrogel polymer discharged from the outlet without passing through the classifier slit was pulverized in the same manner as in Example 1, and the drying time and the physical properties when mixed with the hydrogel polymer passed through the slit and dried. The value was measured. The results are shown in Tables 1 and 2.

Examples 5 to 8 Polymerization was carried out in the same manner as in Example 1 to obtain a hydrogel polymer, which was supplied to the classifier in the same manner as in Example 1, and the slit width of the classifier was set to 10 mm, and the screw blades were used. The transport amount, the slit passage amount, and the average particle size of the hydrogel polymer when the number of rotations was changed were measured. Further, the hydrogel polymer discharged from the outlet without passing through the classifier slit was pulverized in the same manner as in Example 1, and the drying time and the physical properties when mixed with the hydrogel polymer passed through the slit and dried. The value was measured. The results are shown in Tables 1 and 2.

Examples 9 to 12 Polymerization was carried out in the same manner as in Example 1 to obtain a water-containing gel-like polymer, and this water-containing gel-like polymer was supplied at a rate of 240 kg / hr. And the slit width of the classifier was set to 10 mm, and the transport amount, the slit passage amount, and the average particle diameter of the hydrogel polymer when the rotation speed of the screw blade was changed were measured. Further, the hydrogel polymer discharged from the outlet without passing through the classifier slit was pulverized in the same manner as in Example 1, and the drying time and the physical properties when mixed with the hydrogel polymer passed through the slit and dried. The value was measured. The results are shown in Tables 1 and 2.

Comparative Example 1 Polymerization was carried out in the same manner as in Example 1 to measure the average particle size of the hydrogel polymer, and the drying time was measured when the polymer was dried as it was. The results are shown in Table 1. Further, the dried product was pulverized in the same manner as in Example 1, and the absorption capacity and the water-soluble content were measured. The absorption capacity was 45 times and the water-soluble content was 11 times.
%Met.

Comparative Examples 2 to 4 Polymerization was carried out in the same manner as in Example 1 to obtain a hydrogel polymer, which was supplied to the classifier in the same manner as in Example 1, and the slit width of the classifier was set to 30 mm and the screw blades were used. The transport amount, the slit passage amount, and the average particle size of the hydrogel polymer when the number of rotations was changed were measured. Further, the hydrogel polymer discharged from the outlet without passing through the classifier slit was pulverized in the same manner as in Example 1, and the drying time and the physical properties when mixed with the hydrogel polymer passing through the slit and dried. The value was measured. The results are shown in Tables 1 and 2. As is clear from the table, most of the hydrous gel polymer passed through the slits and did not substantially function as a classifier.

Comparative Examples 5 to 8 Polymerization was carried out in the same manner as in Example 1 to obtain a hydrogel polymer, which was supplied to the classifier in the same manner as in Example 1, and the slit width of the classifier was set to 1 mm, and the screw blade was formed. The transport amount, the slit passage amount, and the average particle size of the hydrogel polymer when the number of rotations was changed were measured. Further, the hydrogel polymer discharged from the outlet without passing through the classifier slit was pulverized in the same manner as in Example 1, and the drying time and the physical properties when mixed with the hydrogel polymer passing through the slit and dried. The value was measured. The results are shown in Tables 1 and 2. As is clear from the table, most of the hydrogel polymer was transported and did not substantially function as a classifier.

Comparative Example 9 Polymerization was carried out in the same manner as in Example 1 to obtain a hydrogel polymer, and in order to screen spherical gels having a size of 10 mm or more, plate-shaped slits (400 m in width of 8 mm) were prepared.
It was attempted to screen the hydrogel polymer by vibrating (m × 700 mm × 3 mm). 4 kg of hydrous gel polymer was supplied on the plate slit, and 1200 minutes per minute.
When classification was attempted for 5 minutes while giving vibrations once, the proportion of the gel that passed through the slit was 45% by weight, and the hydrous gel on the slit tended to aggregate, and sufficient classification could not be performed.

[0045]

[Table 1]

[0046]

[Table 2]

[0047]

As described above, according to the present invention, the rotary shaft around which the spiral stirring blade is wound is installed along the central axis of the cylindrical or semi-cylindrical passage having the through hole in the wall surface. A hydrogel polymer is supplied to a supply port provided in the vicinity of one end of the passage of the classifier, and is discharged from the supply port in the vicinity of the other end of the passage by the rotational movement of the spiral stirring blade. The water-containing gel-like polymer particles that pass through the through-hole of the wall surface of the passage are collected from the water-containing gel-like polymer that moves toward the outlet, and coarse particles that do not pass through the through-hole are discharged from the outlet. By a simple operation, coarse particles can be efficiently removed from the hydrogel polymer without adversely affecting the final product, and the hydrogel polymer having a desired particle size can be recovered. . Furthermore, after carrying out classification in this way, coarse particles that have been separated are pulverized and mixed with the particulate hydrogel polymer that has passed through the through holes, and the water absorbent resin is produced by drying. In addition, the water absorbent resin has good drying efficiency, and the obtained water absorbent resin has a high absorption capacity and a low water-soluble content.

[Brief description of drawings]

FIG. 1 is a perspective view showing the configuration of an embodiment of a classifier used in the method for classifying a hydrogel polymer according to the present invention,

2 (a) to (e) are perspective views each showing an example of the shape of a through hole in a tubular passage of a classifier used in the method for classifying a hydrogel polymer according to the present invention.

[Explanation of symbols]

1 ... Classifier, 2 ... Through hole, 3 ... Cylindrical or semi-cylindrical passage, 4 ... Helical rotor, 5 ... Rotating shaft, 6 ... Supply port, 7 ... Discharge port.

Front page continuation (72) Inventor Kazufumi Hirata 992-1 Nishioki, Okihama, Aboshi-ku, Himeji-shi, Hyogo Nippon Shokubai Co., Ltd. Himeji Factory (72) Akito Yano, Nishiki, Okihama, Aboshi-ku, Himeji-shi, Hyogo 992-1 Nippon Shokubai Co., Ltd. Inside the Himeji Plant (72) Inventor Yoshihiko Masuda Inside the Nippon Shokubai Himeji Research Laboratories 992-1 Nishioki, Okihama, Aboshi Ward, Himeji City, Hyogo Prefecture

Claims (7)

[Claims] 1. A method for classifying a hydrogel polymer, comprising removing coarse particles from a hydrogel polymer containing coarse particles to recover a hydrogel polymer having a uniform particle size, comprising:
A hydrogel polymer is supplied to a supply port provided near one end of a passage having a through hole having a length of at least one direction of 2 to 15 mm, and is supplied to an outlet provided near the other end of the passage. Water-containing gel-like polymer particles that pass through the through-hole of the wall surface of the passage from the water-containing gel-like polymer that is moved toward, and coarse particles that do not pass through the through-hole are discharged from the discharge port. Method for classifying gel polymer. 2. The classification method according to claim 1, wherein the passage has a cylindrical or semi-cylindrical shape. 3. The method according to claim 2, wherein the water-containing gel polymer is moved by the rotational movement of the rotating shaft of the spiral stirring blade installed along the central axis of the cylindrical or semi-cylindrical passage. Classification method described. 4. The classification method according to claim 1, wherein the through holes have a slit shape. 5. A method for producing a water-absorbent resin, which comprises classifying a hydrogel polymer containing coarse particles, crushing and / or crushing and then drying, wherein at least one wall surface is coated with at least 1.
The hydrogel polymer is supplied to a supply port provided in the vicinity of one end of a passage having a through hole having a length in the direction of 2 to 15 mm, and toward the discharge port provided in the vicinity of the other end of the passage. Hydrous gel polymer particles that pass through the through-hole of the wall surface of the passage are recovered from the moving hydro-gel polymer, and coarse particles that do not pass through the through-hole are crushed and / or crushed to recover the water-containing polymer. A method for producing a water absorbent resin, which comprises mixing with gel polymer particles and drying the mixture. 6. The production method according to claim 5, which further comprises crushing and / or crushing after drying. 7. The production method according to claim 5, wherein the crushing and / or crushing after drying is performed by a roll rotary crusher.