JPH06313042A - Production of resin having high water absorption property - Google Patents

Abstract

PURPOSE:To provide the production method of a resin having high water absorption property, capable of efficiently producing a water absorbing resin having high water absorption rate or highly water absorbing ability. CONSTITUTION:Base polymer particles having water absorbing property are granulated into granules having prescribed particle diameters while being fluidized with an air flow and being sprayed with a binder and a cross-linking agent and the surface of the granules is cross-linked to produce a resin having high water absorption property.

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 highly water-absorbent resin, and more specifically, to water absorption in a wide range of fields such as sanitary products, sanitary products such as disposable diapers, medical products, soil water retention agents and the like. The present invention relates to a method for producing a highly water-absorbent resin, which can be used for applications requiring retention of the liquid.

[0002]

2. Description of the Related Art Water-absorbent resins have hitherto been used in a wide variety of fields including sanitary napkins, sanitary articles such as disposable paper diapers. Among them, when using the water-absorbent resin in hygiene products,
A large water absorption capacity, a large water absorption rate, a liquid permeability, and a large gel strength are required to avoid problems such as urine leakage that cause discomfort, but it is very difficult to satisfy these characteristics at the same time.

For example, as means for increasing the water absorption speed,
Examples include a method of reducing the particle size of the water absorbent resin, a method of increasing the crosslink density of the surface of the water absorbent resin, and a method of increasing the surface area of the water absorbent resin. However, in general, when the particle size is reduced, the water absorbing resin is likely to cause the "mamako" phenomenon and gel blocking due to contact with the urine, so that the water absorbing rate is reduced. Further, a method of increasing the surface cross-linking density of the water-absorbent resin has been proposed as a technique for increasing the water-absorption rate without reducing the water-absorption capacity (the ratio of the weight of the absorbent resin to the weight of the absorbent resin). However, since most of the water-absorbent resins produced by this technique contain a large amount of fine powder, floating of the fine powder occurs and the working environment is adversely affected. In addition, when water is absorbed, there is a problem that a mamako phenomenon is likely to occur and the water absorption performance is deteriorated. A possible solution to this problem is to remove the fine powder by classification, but this is uneconomical and is not preferred.

On the other hand, as a method for increasing the surface area of the water absorbent resin, granulation can be mentioned. The method relating to the granulation of the water-absorbent resin is described in JP-B-4-3411 and JP-B-4-3.
No. 412 is disclosed. The method described in the publication uses a special mixer such as a high-speed rotating blade type mixer or an air flow type mixer to uniformly mix the water-absorbing resin and the aqueous liquid, and crush and granulate the obtained mixture. Is the way. However, the granulated product obtained by the above method, although the handling as a powder is improved, the granulated product disperses into the original small particles before granulation during water absorption, causing a mamako phenomenon, and Causes gel blocking, and thus has a problem that the water absorption performance decreases.

The method for granulating the water-absorbent resin is as follows:
It is also disclosed in JP-A-2-227435. The method described in the publication discloses a liquid-absorbent base polymer having a normal pressure-absorbing capacity of 30 ml / g or more, containing no particles larger than 300 μm, and having a particle size distribution of 40% by weight or more and 150 μm or less. The solution is introduced into the mixing zone, the surface of the base polymer is brought into uniform contact with the aqueous solution of the cross-linking agent, and these are mixed at high speed to granulate an absorbent polymer composition having an absorption rate of 20 seconds or less. In the above-mentioned granulation method, 1 to 20% by weight of an aqueous solution of a crosslinking agent is used with respect to the liquid-absorbent base polymer, and each liquid-absorbent base polymer is granulated by the action of water in this aqueous solution. However, since no binder is used in the above-mentioned granulation method, the above-mentioned water alone causes insufficient granulation, resulting in various problems.
Eventually, the resulting granulated product has low mechanical strength, and for example, particles granulated and crosslinked during granulation are broken by a granulator and the uncrosslinked part is exposed, or There is a problem that the physical properties of water absorption are not always satisfactory, because the substances are likely to decompose into the original primary particles when absorbing water.

[0006] Therefore, an object of the present invention is to provide a method for producing a highly water-absorbent resin capable of efficiently producing a water-absorbent resin having a high water-absorption rate and / or a high water-absorption capacity.

[0007]

Means for Solving the Problems As a result of intensive studies to develop a method for producing a water absorbent resin, the present inventors have found that
It has been found that the above object can be achieved by fluidizing the base polymer particles and spraying the binder and the cross-linking agent onto the base polymer particles to crosslink the surface of the granulated product, thereby completing the present invention. Came to do.

That is, according to the present invention, the base polymer particles having a predetermined particle size are formed by fluidizing the water-absorbent base polymer particles with an air stream and spraying the binder and the crosslinking agent onto the base polymer particles. The present invention provides a method for producing a highly water-absorbent resin, which comprises granulating and granulating the surface of the granulated material.

The method for producing the super absorbent polymer of the present invention will be described in detail below. Preferred examples of the base polymer particles that can be used in the present invention include particles made of a known polymer that absorbs a large amount of water in water and swells to form a hydrogel.
As the polymer, a polymer having a carboxyl group is preferable, and examples thereof include a hydrolyzate of a starch-acrylonitrile graft copolymer, a (partial) neutralized product of a starch-acrylic acid ester copolymer, and a vinyl acetate-acrylic acid ester copolymer. Saponified polymer, hydrolyzate of acrylonitrile copolymer or acrylamide copolymer, polyvinyl alcohol modified product, partially neutralized polyacrylic acid salt, isobutylene-maleic anhydride copolymer and the like. They can be used alone or as a mixture of two or more.

The base polymer particles may have a cross-linking structure by a cross-linking agent, but preferably a polymer not having a cross-linking structure by the cross-linking agent is desirable. If the cross-linking density of the polymer is high, granulation is possible, but the mechanical strength of the granulated product is weak, and it becomes easy for the granules to come into contact with water or urine, which is not preferable.

The base polymer particles can be obtained by various known polymerization methods. For example, it may be produced by synthesizing a polymer by a method such as reverse phase suspension polymerization, reverse phase emulsion polymerization, aqueous solution polymerization, etc., or by drying it as it is,
Alternatively, it is dried and then pulverized, but the method for producing the base polymer particles is not limited to these methods.

The particle size of the above-mentioned base polymer particles is not particularly limited, but preferably the particle size is 150 μm or less, more preferably the particle size of 70 μm or less is 60% by weight or more of the total fine particles. It is desirable to have a diameter. When the above particle size exceeds 150 μm, the surface area is small, so there are few contacts between the base polymers, making it difficult to granulate, and the granulated product is likely to collapse.
Since the surface area is small, it is difficult to obtain a high water absorption rate, which is not preferable.

Examples of the binder that can be used in the present invention include water, a mixed liquid of a hydrophilic organic solvent and water, a water-soluble polymer, and the like. A water-soluble polymer solution in which a water-soluble polymer is dissolved in water or the above-mentioned mixed solution is preferable because the strength is increased. The concentration of the water-soluble polymer in the water-soluble polymer solution is preferably 10% by weight or less. When the concentration of the water-soluble polymer exceeds 10% by weight, the viscosity of the binder becomes high and it becomes difficult to adjust and spray the binder, which is not preferable.

Examples of the hydrophilic organic solvent include lower alcohols such as methanol, ethanol and propanol, lower glycols such as ethylene glycol and propylene glycol, monoethers of lower glycols and lower alcohols, glycerin and acetone.

Examples of the water-soluble polymer include polyacrylic acid, polyacrylic acid metal salt, carboxymethyl cellulose, hydroxyethyl cellulose, polyethylene glycol, polyvinyl alcohol and the like.

In the present invention, the amount of the binder used is not particularly limited, but when the binder is water, the mixed solution or the water-soluble polymer solution, the amount of water used is 100 parts by weight of the base polymer particles. Against
The amount is preferably 20 to 500 parts by weight, more preferably 40 to 200 parts by weight. If the amount used is less than 20 parts by weight, the granulation may be insufficient and the base polymer may remain in a large amount without being granulated. If the amount used exceeds 500 parts by weight, it takes a long time to dry. Not preferable.

When the water-soluble polymer or the water-soluble polymer solution is used as the binder, the amount of the water-soluble polymer added is 0.001 to 10 parts by weight based on 100 parts by weight of the base polymer particles. Parts is preferred, and more preferably 0.005 to 5 parts by weight. Usage is 0.
If the amount is less than 001 parts by weight, the granulation may be insufficient and the base polymer particles may remain in a large amount without being granulated.
On the other hand, if the amount exceeds 10 parts by weight, the water-soluble polymer impairs the water absorption performance, which is not preferable.

The cross-linking agent which can be used in the present invention is not particularly limited and includes, for example, the following compounds, and one or more cross-linking agents which do not react with each other from the group consisting of the following compounds. Can be selected and used.

(Poly) ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, (poly) glycerin, propylene glycol, diethanolamine, triethanolamine, polyoxypropylene, oxyethylene-oxypropylene block copolymer, pentaerythritol and sorbitol. Polyhydric alcohols; (poly) ethylene glycol diglycidyl ether, (poly) glycerin polyglycidyl ether, diglycerin polyglycidyl ether, sorbitol polyglycidyl ether, pentaerythritol polyglycidyl ether, propylene glycol diglycidyl ether and polypropylene glycol diglycidyl ether Polyglycidyl ether compounds such as ethers; 2,2-bi Hydroxymethyl butanol - tris [3- (1-aziridinyl) propionate], 1,
Polyaziridine compounds such as 6-hexamethylenediethyleneurea and diphenylmethane-bis-4,4'-N, N'-diethyleneurea; epichlorohydrin and α-
Haloepoxy compounds such as methylfluorohydrin; polyamine compounds such as ethylenediamine, diethylenediamine, triethylenetetraamine, tetraethylenepentamine, pentaethylenehexamine and polyethyleneimine; polyamines such as 2,4-toluylene diisocyanate and hexamethylene diisocyanate Isocyanate compound; an inorganic salt or an organic metal salt that produces multivalent ions such as zinc, calcium, magnesium and aluminum.

Among the above compounds, compounds having two functional groups are particularly preferable, and specifically, diethylene glycol, triethylene glycol, polyethylene glycol, glycerin, polyglycerin, propylene glycol, diethanolamine, triethanol are particularly preferable. One or more compounds selected from the group consisting of amine, polyoxypropylene, oxyethylene-oxypropylene block copolymer, pentaerythritol and sorbitol are preferably used.

The amount of the above cross-linking agent used is the amount of the base polymer 1
0.01 to 30 parts by weight is preferable with respect to 00 parts by weight,
0.1 to 10 parts by weight is more preferable. Crosslinking agent amount is 0.0
If it is less than 1 part by weight, the cross-linking density of the obtained granule becomes small and the water absorption rate is lowered due to gel blocking. If the amount of the cross-linking agent exceeds 30 parts by weight, the cross-linking density becomes too high and the water absorption rate and water absorption amount are Is decreased, which is not preferable.

When the above-mentioned crosslinking agent is used,
It can be used as a solution dissolved or diluted in a solvent such as water. The concentration of the cross-linking agent in the solution is 1 to
It is preferably in the range of 30% by weight. When water is used as the solvent, the water also acts as a binder.

Thus, the method for producing a superabsorbent resin of the present invention comprises the steps of fluidizing the base polymer particles with an air stream and spraying the binder and the cross-linking agent onto the base polymer particles. It is characterized in that the particles are granulated into a granulated product having a predetermined particle size and the surface of the granulated product is cross-linked.

The fluidization of the above base polymer particles by an air flow can be suitably carried out by a known method. Specifically, there is a method in which the particles in the cylinder are fed from the lower part of the packed bed through a rectifying plate using a fluidized bed apparatus which is an apparatus for flowing a group of particles. Here, the fluidization refers to a state in which the powdery particles are blown up by the air flow and suspended in the gas phase. The gas used as the air flow is a known gas, and examples thereof include air and nitrogen.

The binder and the cross-linking agent can be sprayed by a known method, for example, a rotating disk method, a pressure nozzle method, a two-fluid nozzle method, or the like.
It is preferable to use the two-fluid nozzle method because the droplet diameter can be easily adjusted, the high-viscosity binder can be atomized, and the atomization can be performed at low pressure. Further, the binder and the cross-linking agent may be sprayed individually or may be uniformly mixed and sprayed together.

The above-mentioned fluidization and spraying are preferably carried out in the same device, and as the device, for example, a fluidized bed granulating device, a rolling fluidized bed granulating device or the like can be used.
The fluidized bed granulating device refers to a device for attaching a nozzle for atomizing a binder to the fluidized bed device, and granulating by bringing spray droplets of the binder into contact with the fluidized powder or granules, for example, " WSG / WSG "(manufactured by Powrec Co., Ltd.)," powder coater GPCG "[manufactured by Powrec Co., Ltd.]," Glowmax "[manufactured by Fuji Paudal Co., Ltd.] and the like. The tumbling fluidized bed granulator is an apparatus incorporating the functions of centrifugal tumbling granulation and stirring granulation in a fluidized bed granulator, for example, "multiplex" (manufactured by Paulec Co., Ltd.), Examples thereof include "New Marmelizer" [manufactured by Fuji Paudal Co., Ltd.].

The above-mentioned base polymer particles are granulated by the above-mentioned fluidization and spraying, and a plurality of the above-mentioned base polymer particles are aggregated by the action of the binder to form a granulated product. At this time, the surface of the granulated product is crosslinked simultaneously with the granulation. The cross-linking is not limited to the surface of the granulated product, and for example, the surface of each of the base polymer particles may be cross-linked. The temperature and time at the time of granulation / crosslinking can be appropriately selected depending on the types of the base polymer, binder, and crosslinking agent used, but are usually 25 to
It is in the range of 250 ° C, and more preferably in the range of 40 to 90 ° C. The time is preferably 10 to 120 minutes.

The granulated product obtained as described above is an aggregate of particles formed by collecting a plurality of the base polymer particles, and the surface of the granulated product is crosslinked and has a predetermined particle size. It can be used as a super water-absorbent resin as it is or after being dried if necessary. The above predetermined particle size is preferably 70 to 1500 μ
m, more preferably 100 to 1000 μm. 70
If it is less than μm, the mamako phenomenon is likely to occur and 1500μ
When it exceeds m, it is not preferable because it is easily restricted by the particle size when used for various purposes.

The highly water-absorbent resin obtained by the production method of the present invention has excellent water-absorbing properties, and for example, the parallel-swelling water absorption amount is preferably 30 to 70 (g / g) according to the following measuring methods. g), the initial water absorption rate is preferably 5 to 15 (ml / 30 sec), and the liquid passing rate is preferably 20 to 150 (ml / min).

[Equilibrium Swelling Water Absorption Measurement Method] 1 g of the polymer was dispersed in 200 g of physiological saline (0.9% saline), and the polymer was swollen until the water absorption reached an equilibrium state. It is obtained by filtering a mixed solution of a polymer and physiological saline with a wire mesh of 80 mesh, measuring the weight (W) of the obtained swollen polymer, and dividing this value by the weight of the polymer before water absorption (W0). The value, that is, the value of W / W0 was taken as the equilibrium swelling water absorption (g / g).

[Measurement Method of Initial Water Absorption Rate] As shown in FIG. 1, the apparatus Demand Wettability Tester, which is generally known as an apparatus for measuring the initial water absorption rate, is used to measure the physiological saline solution W. On a polymer spraying table (70 mmφ, No.2 filter paper placed on the glass filter No.1) with the liquid surface set to the same water level, 0.
The amount of water absorption at the time of spraying 3 g of the polymer was set to 0, and the amount of water absorption after 30 seconds (this amount of water absorption is measured by a burette scale indicating the amount of decrease in the water level of the physiological saline W).
Was measured to determine the initial water absorption rate (ml / 30 sec).

[Measuring Method of Liquid Flow Rate] The apparatus 10 shown in FIG. 2 (inner diameter 25.6 mm, length about 500 mm)
(Cylindrical part) (glass cylinder filter with a cock) was filled with 0.5 g of polymer, the polymer was swollen with an excess of physiological saline, and the cock was closed by adjusting the liquid level to 200 ml from the bottom, and the swollen polymer Make sure that P has fully settled as shown in the figure, open the cock, and put the saline W between the two marked lines L (150 ml point from the bottom) and M (100 ml point from the bottom) (liquid) shown in the figure. 50 ml)
Was measured, and the liquid volume (ml) between the marked lines was divided by the measurement time (min) to obtain the liquid flow rate (ml / min).

[0033]

The present invention will be described in detail below with reference to Examples and Comparative Examples, but the present invention is not limited to these.

The measuring methods used in Examples and Comparative Examples are as described above and below. [Measurement method of particle size distribution and average particle size] 100 g of the polymer was classified by using JIS sieve, and the particle size distribution and the average particle size were obtained from the weight fraction of each fraction.

[Production Example 1] 1600 ml of cyclohexane and sorbitan monostearate ["Reodol SP-S10", manufactured by Kao Corporation, were placed in a 5-liter four-necked round bottom flask equipped with a stirrer, a reflux condenser and a nitrogen inlet tube. ] 5 g was charged, dispersed, and after nitrogen substitution, the temperature was raised to 75 ° C. Further, in another container, 510 g of 80% by weight acrylic acid aqueous solution was added to 30% by weight caustic soda aqueous solution 560.
After neutralization with g, 0.4 g of potassium persulfate as an initiator was added together with 30 g of ion-exchanged water to prepare a polymerizable aqueous solution. Then, the polymerizable aqueous solution was dropped into the above-mentioned four-necked round bottom flask over 1.5 hours, polymerization was carried out under stirring, and then the temperature was kept at 70 to 75 ° C. for 0.5 hours to complete the polymerization. The obtained sodium polyacrylate polymer particles were dried, and the particle size distribution and the average particle size were measured. As a result, 85% by weight of fine particles of sodium polyacrylate were particles having a particle size of 70 μm or less. The water content in the finely divided sodium polyacrylate particles was 0.6% by weight. The equilibrium swelling water absorption amount, the initial water absorption rate, and the liquid passing rate were measured for the obtained fine-grained sodium polyacrylate particles (base polymer particles). The results are shown in [Table 1].

Example 1 1000 g of finely divided sodium polyacrylate particles having 85% by weight of particles having a particle size of 70 μm or less obtained by the method of Production Example 1 were used as base polymer particles, and a fluidized bed granulation having a volume of 10 liters was carried out. 80 ℃ for the equipment
By flowing the air into the apparatus, the flow of the finely particulate sodium polyacrylate was started. Next, 500 g of water as a binder and "Denacol EX81 as a cross-linking agent.
0 "[manufactured by Nagase Kasei Kogyo Co., Ltd.] 10.0 g was sprayed into the system for about 30 minutes. Next, the temperature of the supplied air was raised to 85 ° C. and dried for 30 minutes to obtain a granulated product. With respect to the obtained granulated product, the particle size distribution and the average particle size were measured using a shaking sieve as described above, and the equilibrium swelling water absorption amount, the initial water absorption speed and the liquid passing speed were measured. The results are shown in [Table 1]. As is clear from the results shown in [Table 1], the obtained granulated product has almost no fine powder or coarse particles, and it is understood that the production method of the present invention is a method excellent in granulation property.

[Example 2] Fluidized bed granulation with a volume of 10 liters using 1000 g of finely divided sodium polyacrylate particles having a particle size of 70 µm or less obtained by the method of Production Example 1 and 85% by weight as base polymer particles. 80 ℃ for the equipment
The air of the above was introduced into the apparatus to start the flow of the finely divided sodium polyacrylate particles. Next, as a binder, 0.03% by weight aqueous solution of sodium polyacrylate 500
g and 5.0 g of "Denacol EX810" (manufactured by Nagase Kasei Kogyo Co., Ltd.) as a crosslinking agent dissolved in 10 g of ion-exchanged water were separately sprayed into the system over 30 minutes. Next, the temperature of the supplied air was raised to 85 ° C. and dried for 30 minutes to obtain a granulated product. About the obtained granulated product,
The same measurement as in Example 1 was performed. The results are shown in [Table 1]. As is clear from the results shown in [Table 1], the obtained granulated product had almost no fine powder or coarse particles,
It can be seen that the production method of the present invention is a method excellent in granulation property.

Example 3 500 g of finely divided sodium polyacrylate particles having a particle size of 70 μm or less obtained by the method of Production Example 1 and 85% by weight were used as a base polymer.
Into a liter capacity of "Multiplex" (manufactured by Powrex Co., Ltd.), air at 80 ° C. was fed into the apparatus and stirring was performed by a stirring blade to flow and stir and mix the finely divided sodium polyacrylate particles. Started. next,
0.6 g of sodium polyacrylate and "Denacol EX810" (manufactured by Nagase Chemical Industry Co., Ltd.) as a cross-linking agent 5.0
A solution of g and 1000 g in ion-exchanged water was started to be sprayed into the system, and the spraying of the binder was completed in about 40 minutes. Then, it was dried with air at 85 ° C. for 30 minutes and then cooled to obtain a granulated product. The same measurement as in Example 1 was performed on the obtained granulated product. The results are shown in [Table 1]. As is clear from the results shown in [Table 1], the obtained granulated product has almost no fine powder or coarse particles, and it is understood that the production method of the present invention is a method excellent in granulation property.

Comparative Example 1 A granulated product was obtained in the same manner as in Example 1 except that the crosslinking agent was not used. Then, the same measurement as in Example 1 was performed on the obtained granulated product. The results are shown in [Table 1]. As is clear from the results shown in [Table 1], the water absorption performance of the obtained granules was low.

[0040]

[Table 1]

[0041]

EFFECTS OF THE INVENTION According to the present invention, there is provided a method for producing a highly water-absorbent resin capable of efficiently producing a water-absorbent resin having a high water-absorption rate or a high water-absorption capacity. Since the base polymer particles having water absorbability are granulated without applying any force or shearing force, it is possible to obtain a porous and irregular shaped granule, that is, a water absorbent resin having a large surface area. Thus, a highly water-absorbent resin having a significantly improved liquid passing rate can be obtained. Furthermore, it is possible to simplify the process by simultaneously advancing granulation and crosslinking, and since the base polymers are crosslinked, the granulated product does not collapse even when contacted with water. A highly water-absorbent resin that does not cause gel blocking can be obtained. Therefore, the super absorbent polymer obtained by the production method of the present invention,
It can be used in a wide range of fields including hygiene products such as disposable diapers and sanitary napkins.

[Brief description of drawings]

FIG. 1 is a schematic view showing an apparatus for measuring an initial water absorption rate used in Examples and Comparative Examples.

FIG. 2 is a schematic view showing a device for measuring a liquid flow rate used in Examples and Comparative Examples.

[Explanation of symbols]

 W Physiological saline solution P Polymer 1 Measuring device for initial water absorption rate of polymer 2 Polymer spraying table 3 Burette 10 Measuring device for polymer passage rate M, L Mark lines

Claims (2)

[Claims] 1. A base polymer particle having a predetermined particle size is granulated while fluidizing a water-absorbent base polymer particle with an air stream and spraying a binder and a crosslinking agent onto the base polymer particle. A method for producing a highly water-absorbent resin, which comprises cross-linking the surface of the granulated product together. 2. The method for producing a highly water-absorbent resin according to claim 1, wherein the granulation is performed using a fluidized bed granulator.