JPH10113557A - Production of granular water-absorptive resin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently produce firm granules of highly water-absorptive resin having particle size within a desiring range by compression-molding a water- absorptive resin powder dampened by adding an aqueous liquid into a sheet-like shape and then pulverizing and granulating the sheet-like molded product. SOLUTION: Water-absorptive resin, for example a hydrolyzed product of starch-acrylonitrile graft copolymer is dampened by adding an aqueous liquid containing an aqueous solution of water soluble polymer and the dampened water-absorptive resin powder is compression-molded into a sheet-like product, and after that, the sheet-like product is pulverized and granulated. That is, the water-absorptive resin powder surface is provided with wettability and stickiness during the process of bringing the water-absorptive resin powder into contact with an aqueous liquid, so that the resin powder particles are brought into contact with one another through the liquid drops in such conditions and granular bodies are produced by sticking and granulating the resin powder particles. In this case, after the aqueous liquid is added and preferably before the wettability of the resin powder surface is lowered and the stickiness is decreased, in other words the surface is still in dampened state, the sheet-like molded product is produced by compression-molding.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a water-absorbent resin powder,
Particularly, the present invention relates to a method for producing a granular water-absorbent resin in which a fine powder of a water-absorbent resin is granulated, and the particle size is adjusted or the particle size is within a certain range, and belongs to a water-absorbent resin production technique. is there.

[0002]

2. Description of the Related Art Water-absorbent resins include sanitary products such as sanitary products, disposable diapers, disposable rags, agricultural and horticultural products such as water retention agents, soil modifiers, solidification of sludge, prevention of dew condensation on building materials, and dehydration in oils and fats. It is widely used in various fields such as. Polymers used in these water-absorbing resins include, specifically, cross-linked acrylate polymer, starch-acrylic acid graft copolymer, starch-acrylonitrile graft copolymer hydrolyzate, polyoxyethylene Crosslinked products, carboxymethylcellulose crosslinked products and the like.

[0003] These polymers are generally synthesized by a method such as reverse phase suspension polymerization, reverse phase emulsion polymerization, aqueous solution polymerization, etc., and are dried as they are or dried and then pulverized to be used as a basic material of a water-absorbing resin. Can be In addition, a post-treatment is performed to increase the cross-linking density of the polymer particles obtained in this way, and furthermore, an anti-blocking agent is added to suppress the moisture-absorbing blocking property of the granular material and used as a water-absorbing resin. Can be

[0004]

However, the water-absorbent resin produced by these methods generally contains a considerable proportion of fine powder that passes through a 100-mesh standard sieve. This causes a problem of scattering. Therefore, in general, a product obtained by removing fine powder contained in a water-absorbent resin with a sieve is used as a product. Together with the problem of treating the fine powder removed by the sieve.

Therefore, various granulation methods have been studied in order to make the fine powder into a product having a particle size within a desired range. For example, Japanese Patent Application Laid-Open Nos. 62-132936 and 2-3
As disclosed in JP 08820, a method of granulating fine powder using a binder has been proposed. In this method, as the binder, powdered inorganic substance silicon dioxide, water-soluble polymer polyvinyl alcohol, sodium polyacrylate, starch, cellulose and the like are exemplified.
These methods not only have a danger of ignition in the drying process after granulation because they are used in combination with organic solvents or petroleum solvents, but also have a problem in biological safety due to the residual organic solvents. Yes, if an aqueous solution is used instead of an organic solvent as a binder, the above-mentioned problem does not occur.However, the water-absorbent resin powder to be caking-granulated rapidly absorbs the aqueous solution and forms a large dense mass. The problem is that it is difficult to obtain a uniform and easily granulated product.

As a method for solving these problems, Japanese Patent Application Laid-Open No. 61-97333 and Japanese Patent Application Laid-Open No. 61-101536
Japanese Patent Application Laid-Open Publication No. Hei 7 (1995) -175, proposes a method of mixing and granulating a superabsorbent resin powder and an aqueous liquid by using a specific mixer such as a high-speed rotary paddle type mixer or an airflow type mixer. -62
No. 073 proposes a method in which a resin powder dispersed by an air flow and an aqueous liquid are brought into contact in a co-current state to granulate. However, in any of the above methods, the granulation effect is small, and the recovery rate of the granulated material is extremely low. Therefore, in order to enhance the granulation effect, a fine powder and a resin powder having a product particle size are mixed at a specific ratio, and granulation is attempted. As a result, granulation is substantially impossible only when the proportion of the fine powder is 50% or less. They are,
This is a major problem from the viewpoint of efficient processing of fine powder.

On the other hand, Japanese Patent Application Laid-Open No. Hei 7-290446 proposes a method for granulating a polymer compound, in which polymer particles are compression-molded into a plate using a dry granulator and then crushed by a crusher. The apparatus of the dry granulator and the crusher is disclosed. These apparatuses are effective dry granulators for foamed fine particles of methylene chloride of polyester, methyl ethyl ketone solution of organic dye, and other raw materials having high adhesiveness. However, the water-absorbing resin powder is generally added with an anti-blocking agent to reduce the adhesiveness of the powder, and since the anti-blocking agent is usually fine particles of 100 μm or less, the water-absorbing resin powder contains After passing through the sieve for removing the fine powder, the fine powder removed by the sieve contains a large amount of the antiblocking agent.
Therefore, the fine powder of such a water-absorbent resin has extremely low adhesiveness, and a plate-like molded product is not obtained at all even when compressed using the dry granulator. Will be discharged. Therefore, it was difficult to granulate the water-absorbent resin powder by the dry granulation method. Therefore, in view of the current state of the prior art, the present inventors have intensively studied a method for firmly and efficiently granulating fine powder contained in a water-absorbent resin and separated and removed by a sieve. It was done.

[0008]

Means for Solving the Problems The present inventors have found that the adhesiveness of a water-absorbent resin fine powder is such that when an aqueous liquid is added to the fine powder,
A phenomenon was found that increased temporarily immediately after addition, and then decreased remarkably, and it was found that the above problem could be solved by using this phenomenon. That is, by adding an aqueous liquid to the fine powder, the adhesiveness is increased, the fine powder particles are firmly adhered to each other, and then compression-molded to form a sheet-like molded product. By disintegrating, the above-mentioned problems can be solved, and a strong granulated product of a superabsorbent resin having a high quality and a particle size within a desired range can be efficiently obtained from the fine powder at a high recovery rate. Thus, the present invention was completed. That is, the present invention provides a method for producing a granular water-absorbent resin, which is characterized in that after the water-absorbent resin powder that has absorbed moisture by the addition of an aqueous liquid is compression-molded into a sheet, the sheet-like molded product is granulated by crushing. The present invention relates to a production method, and further uses a water-absorbent resin powder whose surface is in a wet state with an aqueous liquid, compresses it into a sheet, and then granulates by crushing the sheet-like molded product. The present invention relates to a method for producing a granular water-absorbent resin.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The water-absorbing resin applicable to the present invention includes, for example, a hydrolyzate of a starch-acrylonitrile graft copolymer (JP-B-49-43395) and a starch-acrylic acid graft polymer. Japanese products (JP-B-53-46199, JP-B-55-210)
No. 41), saponified acrylate-vinyl acetate copolymer (JP-B-53-13495, JP-B-55-19243), cross-linked polyvinyl alcohol modified product (JP-A-54-20093) Crosslinked products of partially neutralized polyacrylate (JP-A-55-84304, JP-A-56-93716, JP-A-56-16)
1408, JP-A-58-71907) and a crosslinked isobutylene-maleic anhydride copolymer (JP-A-56-71907).
JP-A-36504) and the like. And even if these water-absorbent resins have uniform crosslinking,
Alternatively, JP-A-58-180233, JP-A-58-180233
As disclosed in JP-A-117222 and JP-A-58-42602, any of those subjected to a surface cross-linking treatment can be used.

As the aqueous liquid in the present invention, water alone or an aqueous solution of a water-soluble polymer is used. Specific examples of the water-soluble polymer include polyacrylic acid and its salts, polyvinyl alcohol and its derivatives, polyethylene glycol and its derivatives, starch and its derivatives, and cellulose and its derivatives. The amount of the aqueous liquid used cannot be determined unconditionally because it differs depending on the type of the water-absorbent resin powder, the particle diameter, etc., but usually 1 to 50 parts by weight, more preferably 1 to 50 parts by weight, based on 100 parts by weight of the water-absorbent resin powder. What is necessary is just 5-20 weight part. If the amount used is less than 1 part by weight, granulation may be insufficient. On the other hand, if the amount exceeds 50 parts by weight, granules having a large particle diameter are easily formed, and excessive drying is required, which is preferable. Absent. The amount of the water-soluble polymer to be added is preferably 0.5 to 25 parts by weight based on 100 parts by weight of the water-absorbent resin powder. Also, if the concentration of the water-soluble polymer is too high, the viscosity of the aqueous liquid becomes too high to prepare and transfer the aqueous liquid, so that the concentration of the water-soluble polymer aqueous solution is usually 50% by weight or less, more preferably 20% by weight or less. % By weight or less.

According to the present invention, in the process of bringing the aqueous liquid into contact with the water-absorbent resin powder, the surface of the water-absorbent resin powder becomes wet and tacky. In this state, the resin powders come into contact with each other via the droplets, and are caustic-granulated to form granules. The binding force of the powder in such a granulated body is not strong, and if left for a certain period of time, the wettability of the surface is reduced, the tackiness is reduced, the granulated body is collapsed, and a water-absorbent resin having a desired particle size is obtained. It is difficult to efficiently recover the wastewater. Therefore, a compression molding machine such as Pharmapactor (manufactured by Hosokawa Micron Corporation) is preferably used after the aqueous liquid is added, preferably before the wettability of the resin powder surface is reduced and the adhesive strength is reduced, that is, while the surface is wet. Into a sheet-like molded product. A crusher for adjusting the particle size of the sheet-like molded product,
For example, it is crushed to an appropriate size with a flake crusher (manufactured by Hosokawa Micron Co., Ltd.) to obtain a water-absorbent resin granule. In addition, usually, in order to obtain a desired particle diameter, a screen of a desired size is sieved with a two-stage sieve, and only particles of a desired size are taken out to obtain a product. The coarse particles can be crushed again by a crusher, and the fine powder can be compression-molded again with the raw resin powder to obtain a product. The time from the addition of the aqueous liquid to the end of the compression molding is preferably within 3 hours, more preferably within 1 hour. If the time exceeds 3 hours, the wettability of the surface of the water-absorbent resin is reduced, the adhesive strength is significantly reduced, and it becomes difficult to obtain a sheet-shaped molded product even by using a compression molding machine, or The recovery rate is reduced, making it difficult to efficiently granulate the water absorbent resin. As described above, the present invention is suitable for the granulation of water-absorbent resin fine powder, and is excellent as a method for producing a water-absorbent resin having an adjusted particle size.However, the present invention is not applied only to granulation of fine powder. Instead, it can also be used to adjust the particle size of the water absorbent resin to a predetermined one.

[0012]

The following examples and reference examples are provided to explain the present invention more specifically. The water absorption capacity, particle size distribution, and binding property of the sheet-like molded product were measured according to the following methods.倍率 Water absorption capacity About 0.5 g of the water-absorbing resin was placed in a 250-mesh nylon tea bag bag (5 cm × 15 cm), immersed in 0.9% saline, and weighed after 30 minutes. The water absorption capacity was calculated according to the following equation using the weight of the liquid absorption of only the tea bag bag as a blank. 粒度 Particle size distribution A standard sieve with a mesh size of 18 mesh, 50 mesh, 100 mesh and a 70 mm diameter sieve and a classifying dish of a saucer are stacked, 30 g of the water-absorbent resin powder is put thereon, and the mixture is shaken with a classifier for 10 minutes, and then classified. The items were weighed and indicated in% by weight.結 Binding property of sheet-shaped molded product The sheet-shaped molded product was rubbed with the fingers of a hand and evaluated as to whether or not it was easily powdered as follows. ◎ Passed without collapse at all ○ Passed slightly collapsed but passed △ Easily collapsed and failed × Sheeting not possible

<Example 1> The particle size was 100 mesh (150 mesh).
water) with respect to 100 parts by weight of water-absorbent resin powder
Parts by weight were sprayed to bring the resin powder into contact with water. Water addition 5
After a minute, the obtained resin powder is compressed by a roll-type compression molding machine (Pharmabacta, model L200 / 50P) having two rolls having a diameter of 200 mm, a width of 50 mm, and a rotation speed of 3 rpm, having irregularities of 0.3 mm on the surface. A sheet-shaped compression-molded product was produced by applying a force of 8 KN. A crusher (flake crusher) that presses the raw material against a surrounding 1.7 mm screen with a rotary rotor rotating at 70 rpm with a diameter of 150 mm, a length of 200 mm and five fixed teeth. (Type FC200) to obtain granules of a water-absorbent resin powder. <Example 2> Processing was performed in the same manner as in Example 1, except that the time from the addition of water to the compression molding was 60 minutes. <Example 3> The procedure of Example 1 was repeated, except that the aqueous liquid was a 3% aqueous polyvinyl alcohol solution. <Example 4> Processing was performed in the same manner as in Example 1, except that the amount of water to be sprayed was changed to 5 parts by weight. <Example 5> Processing was performed in the same manner as in Example 1, except that the time from water addition to compression molding was changed to 6 hours. <Example 6> In Example 1, the amount of water was changed to 40 parts by weight.
By drying at 0 ° C. for 30 minutes, a granulated body of the water-absorbent resin powder was obtained. <Comparative Example 1> The procedure of Example 1 was repeated, except that no water was added. <Comparative Example 2> The procedure of Example 1 was repeated, except that the compression molding machine was not used. The water absorption ratio, the particle size distribution, and the binding property of the sheet-like molded product of the water-absorbent resin powder obtained in the above Examples and Comparative Examples were measured by the methods described above. Table 1 shows the results.

[0014]

[Table 1]

As shown in Table 1 above, in the granulation method of the present invention, an aqueous liquid is added to a water-absorbent resin powder, compression molding is performed quickly, and the molded product is pulverized extremely efficiently.
It can be seen that a granulated product having a large particle size and good binding properties can be obtained without lowering the water absorption capacity.

[0016]

According to the present invention, the fine powder of the water-absorbent resin powder can be efficiently formed into a granulated product having relatively uniform grains without deteriorating the physical properties, and the obtained granulated product can be obtained. Eliminates dust during handling, which can contribute to improvement of the working environment. In addition, utilizing the fact that the water-absorbent resin obtained by the present invention is a granulated product, sanitary products, disposable diapers, sanitary products such as disposable rags and water retention agents, agricultural and horticultural products such as soil modifying agents. Initially, it can be used in various fields such as solidification of sludge, prevention of dew condensation on building materials, and dehydration in fats and oils.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Minoru Atsuchi 1 at Funamicho, Minato-ku, Nagoya-shi, Aichi, Japan

Claims (2)

[Claims] 1. A method for producing a granular water-absorbent resin, comprising compressing a water-absorbent resin powder, which has been absorbed by the addition of an aqueous liquid, into a sheet, and pulverizing the sheet-like molded product to granulate. Method. 2. The method for producing a granular water-absorbing resin according to claim 1, wherein a water-absorbing resin powder whose surface is in a wet state with an aqueous liquid is used.