JPS5986657A - Highly absorptive resin composition - Google Patents

Abstract

PURPOSE:To provide a highly absorptive resin compsn. which is suitable for use as a water retaining agent in agriculture and horiticulature can retain high absorptivity and is excellent in handling, by wetting a finely divided cellulose powder with an aq. soln., mixing it with a highly absorptive resin powder and granulating the mixture. CONSTITUTION:2-10pts.wt. powdered cellulose which has an average fiber length of 400mu or below and such particle size distribution that at least 90wt% of particles passes through a 100-mesh standard sieve, is wetted with 1-10pts.wt. aq. soln. such as a mixture of water and methyl alcohol. The wetted powdered, cellulose is mixed with a highly absorptive resin powder having such a particle size distribution that all particles pass through a 20-mesh standard sieve and 90wt% or less of particles pass through a 200-mesh stardard sieve. The mixture is granulated to obtain the desired highly absorptive resin compsn. having a bulk density of 0.25-0.6g/cc. Examples of the highly absorptive resin powders are crosslinked polyacrylate salt and crosslinked modified polyvinyl alcohol.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a superabsorbent resin composition with improved handling properties as a powder.

In recent years, superabsorbent resins have come to be used in a variety of fields, including sanitary products such as sanitary cotton and water retention agents for agriculture and horticulture.

1- However, many of the conventionally used superabsorbent resins often contain a large amount of imitation wood that passes through a 100-mesh standard sieve, or have a relatively large bulk specific gravity. There are the following problems when using such a powdery cylinder absorbent resin.

1. Dust is likely to be generated.

2゜Poor mixability and dispersibility.

In the production of sanitary products, cotton-like pulp is sometimes mixed with pulp, but in this case, if the difference in specific gravity between the KM-like barb and the superabsorbent resin powder is large, the mixing tends to be uneven. When mixed with soil or sand in the field of agriculture and horticulture, especially when they are moist, hygroscopic lumps of superabsorbent resin tend to form.
Once a clump forms, even if you water it later, it will become 60cm thick and its water retention capacity will decrease.

Methods for determining the crystallization of these materials include a method of crushing the superabsorbent resin under conditions that increase the particle size to reduce the amount of fine powder, and a method of pulverizing the superabsorbent resin powder with a binder such as water. A possible method is to attach the particles using a powder and granulate the particles. However, the former method is not preferred because the absorption rate becomes low. In addition, the latter method requires a large amount of binder, and it is difficult to disperse the binder uniformly, resulting in a wide particle size distribution and relatively high density agglomerates, resulting in high-speed absorption. It is undesirable because it inhibits sex. In particular, when an aqueous liquid is used as a binder, because the granulated material has high water absorption, it is difficult to uniformly disperse the aqueous liquid by using only a small amount of the aqueous liquid, resulting in large, high-density clumps. It is difficult to obtain homogeneous granules.

In view of the current situation, the inventors of the present invention conducted intensive studies to obtain a superabsorbent resin composition that maintains high-speed absorption and is also easy to handle as a powder. A superabsorbent resin composition obtained by moistening a small amount of powdered extremely fine specific cellulose l# fibers, mixing it with a specific superabsorbent resin powder, and granulating it solves the above problems at once. They have found a solution to this problem and have completed the present invention.

Therefore, an object of the present invention is to provide a superabsorbent resin composition that is easily handled as a powder by an extremely simple manufacturing method.

That is, in the present invention, the average fiber length is 400μ or less and
After wetting 2 to 10 parts by weight of powdered cellulose (4) with 1 to 10 parts by weight of aqueous liquid (B), the entire amount passes through a standard sieve of 20 mesh. And those that pass through a standard sieve of 200 mesh are 9
The granulated bulk specific gravity obtained by mixing with 0.00 parts by weight or less of superabsorbent resin powder (0.1100 parts by weight) has a bulk specific gravity of 0.25 to 0.00 parts by weight.
The present invention relates to a superabsorbent resin composition of 65'/σ.

The superabsorbent resin used in the present invention is one that does not substantially dissolve in water, absorbs water and swells, and has an absorption capacity of 10 times or more.

Such high absorbency resins include, for example, polyacrylate crosslinked products, starch-acrylate graft crosslinked products,
Examples include polyvinyl alcohol-modified crosslinked products and maleic acid copolymer crosslinked products. These superabsorbent resins can be used regardless of whether they have a uniform crosslinking density or have undergone surface crosslinking treatment, and are not particularly limited. The particle size of the superabsorbent resin powder 0 is such that it passes through a 20-mesh standard sieve, and 900 parts by weight or less passes through a 200-mesh standard sieve. Those containing particles larger than this are not preferred because of their low absorption rate. In addition, if a particle size smaller than this is used, it is necessary to use an aqueous liquid containing more than 10 parts by weight of K in order to obtain a granulated product with a small amount of fine powder of 100 mesh or less. This is not preferable because it tends to produce particles with a relatively large particle size and requires a drying step.

The powdered cellulose (6) used in the present invention has an average fiber length of 40
It has a particle size of 0μ or less and 900 parts by weight or more of it passes through a 100-mesh standard sieve. In other words, if the average fiber length is larger than this or if the particle size is large, flocs may exist in some parts due to entanglement between cellulose, and it is difficult to uniformly disperse the fibers even when wetted with an aqueous liquid. is undesirable because it causes relatively dense lumps in the resulting composition.

An example of the powdered cellulose (4) used in the present invention is commercially available from Sanyo Kokusaku Valve Co., Ltd. KC flock ow
-] Oo, W-300 and pulp flock ■W-1, W-
4, W-s, etc.

Powdered cellulose (5) is used in a ratio of 2 to 10 parts by weight per 100 parts by weight of superabsorbent resin powder.

The optimal value for the amount used should be determined appropriately depending on the type and particle size of the superabsorbent resin powder (01), but if the ratio is less than 2 parts by weight, it will not be very effective, and on the contrary, if the ratio exceeds 10 parts by weight In this case, the bulk specific gravity of the resulting composition becomes too small and a part of the powdered fiber predisposition remains in a free state, which is not preferable.

As the aqueous liquid, water alone, a mixture of water and an organic solvent miscible with water, or an aqueous solution in which a water-soluble polymer is dissolved in water or a mixture thereof can be used. Examples of organic solvents that are miscible with water include lower alcohols, lower glycols, monoethers of ethylene glycol and lower alcohols, glycerin, and acetone.

Examples of water-soluble polymers include polyacrylic acid, alkali metal salts of polyacrylic acid, carboxymethyl cellulose, polyethylene glycol, and polyvinyl alcohol. When using a water-soluble polymer, if the concentration is too high, the viscosity of the aqueous liquid will increase, resulting in powdered cellulose (
This is not preferable since it becomes difficult to mix 5) with the aqueous liquid 03). The concentration of the water-soluble polymer is usually 10% by weight or less.

The amount of aqueous liquid) used is superabsorbent resin powder (C) lo.

The ratio ranges from 1 to 10 parts by weight. The optimal value for the amount used must be determined appropriately depending on the type and particle size of the superabsorbent resin (Q) and the amount of powdered cellulose (8) used. )
This is insufficient for adhering and granulating superabsorbent resin 0, and conversely, if the ratio exceeds 10 parts by weight, granules with large particle sizes tend to be produced, which is not preferable.

In order to wet the powdered cellulose (5) with the aqueous liquid in the present invention, both may be placed in a suitable mixer and mixed.

As such a mixer, a mixer commonly used for mixing, kneading, and cross-mixing of solids can be used.

Examples of such mixers include rotating cylindrical mixers, V-type mixers, double-arm kneaders, continuous injection mixers, high-speed mixers, and the like. A mixing time of 30 minutes or less is usually sufficient, but a longer time may be used.

To granulate powdered cellulose (5) by wetting it with an aqueous liquid (13) and then mixing it with a superabsorbent resin powder (Q), when wetting the powdered cellulose (5) with an aqueous liquid (B), The mixer mentioned above can be used.Then, after wetting the powdered fiber element with an aqueous liquid, the superabsorbent resin powder (Q) may be added and mixed and granulated. Alternatively, the powdered cellulose (4) may be wetted with an aqueous liquid in advance, and then put into a separate mixer together with the superabsorbent resin powder (Q) and mixed to form granules.

By mixing the powdered fiber element (4) moistened with the aqueous liquid (B) and the superabsorbent resin powder (Q) in the specified ratio, the powdered cellulose (4) moistened with the aqueous liquid (B) and The superabsorbent resin powder (Q) is granulated.The superabsorbent resin composition of the present invention has a bulk specific gravity of 0.25.
~0.6f/CC.

If the bulk specific gravity is less than 0.25 f/cc, the granules will become too bulky and will be difficult to handle;
If it exceeds 20%, it is not preferable because the mixability and dispersibility are low.

Although the superabsorbent resin composition of the present invention obtained in this way contains a small amount of water, there is no need for a drying process and it can be handled as a powder as it is, and the original superabsorbent resin composition can be treated as a powder. Polymer resin powder (compared to Q, the bulk specific gravity is lower, and there are fewer fine powders of 100 mesh or less, which solves all the problems of conventional powdered superabsorbent resins at once.The drying process is Although it is not necessary, it is of course possible to perform drying if necessary.

When the superabsorbent resin composition of the present invention is observed under a microscope, it can be seen that a plurality of superabsorbent resin particles (Q) are granulated through a small amount of powdered fiber element, and the resulting granules are The surface of the object was hardly covered with powdered cellulose (5).This indicates that a single hydrogel particle disclosed in JP-A-51-35685 was covered with a large amount of relatively long fibers. Furthermore, according to Japanese Patent Application Laid-Open No. 51-35685, a drying process is necessary because a large amount of water is used for the hydrogel in order to attach the fibers and the hydrogel. However, in the present invention, a very small amount of aqueous liquid is sufficient, so a drying step is unnecessary.

In addition, with the present invention, by simply using a small amount of fine powdered cellulose, most of which passes through a standard sieve of 100 mesh, it is possible to significantly reduce the bulk specific gravity and reduce the amount of fine powder of 100 mesh or less. It's amazing what happened.

The superabsorbent resin composition of the present invention has excellent handling properties as a powder as it is, but in order to further improve the fluidity of the powder, a fluidity improver such as finely powdered silica may be added. You can also use

EXAMPLES The present invention will be specifically described below with reference to Examples, but the scope of the present invention is not limited to these Examples.

The water absorption capacity of the absorbent resin is calculated by placing the absorbent resin powder evenly in a tea bag made of non-woven fabric, immersing it in pure water, measuring the weight after 10 minutes, and using the following formula: did.

Example l Sodium acrylate 74.9 mol, acrylic acid 25
Molarity and trimethylolpropane triacrylate 0
．． 14,000 parts of a 43% aqueous solution of an acrylate monomer having a 1 molar ratio of 55 to 100 parts was mixed with 0.6 parts of ammonium persulfate and 0.2 parts of sodium bisulfite in a nitrogen atmosphere.
Stationary polymerization was performed at 80° C. to obtain a gel-like hydropolymer. This gel-like water-containing polymer was dried in a hot air dryer at 180°C and then ground in a vibrating grinder to form a powder of cross-linked polyacrylate (a
) was obtained. The water absorption capacity of this powder (a) was 350 times.

KC flock ■W-100 in a V-type blender with a capacity of 4 tons
[Manufactured by Sanyo Kokusaku Valve Co., Ltd. (100 mesh passes, 90 layers or more)] 100 g and 40 liters of water were added and mixed well until a uniform wet powder was obtained.

Powder (a) 1 000 P was added to this and mixed with stirring for 30 minutes to obtain a buffy coat aggregate of granules. The soft film aggregate of the granules was easily loosened to obtain a powder (1) of a superabsorbent resin composition having a small bulk specific gravity.

Table 1 shows the particle size distribution and bulk specific gravity of this powder (1) and powder (a).

Example 2 Sodium acrylate 74.95 mol, acrylic acid 2
4000 parts of a 43% aqueous solution of an acrylate monomer consisting of 5 moles of trimethylolpropane triacrylate and 0.05 moles of trimethylolpropane triacrylate was heated in a nitrogen atmosphere using 0.6 parts of ammonium persulfate and 0.2 parts of sodium bisulfite. 5th year middle school
Stationary polymerization was carried out at 5 to 80°C to obtain a gel-like hydropolymer. After drying this gel-like hydrous polymer in a hot air dryer at 180°C,
It was ground with a vibrating grinder to obtain a material passing through 60 meshes.

0.3 parts of glycerin was added to 100 parts of this powder and mixed in a screw type mixer, and the resulting mixture was heat-treated in a disk dryer. That is, the above mixture was placed on a disk heated with a heating medium at 220°C to a thickness of 1 cnr, and heated for 15 minutes while stirring with a scraper to obtain a powder (b) of crosslinked polyacrylate. . The water absorption capacity of this powder (1)) was 500 times.

Pulp flock ■W-5 [manufactured by Sanyo Kokusaku Pulp Co., Ltd. (100 mesh pass 60 weight factor or more)] AZR was put into a double-arm kneading machine with a total capacity of 2.5 tons, and the molecular weight was about 20.0.
4 by adding 2% aqueous solution 322 of polyacrylic acid 00.
Mixed for 0 minutes. Add 400f of powder (b) to this,
After mixing for 20 minutes, a buffy coat mass of granules was obtained. The buffy coat aggregate of this granule was easily loosened to obtain a powder (2) of a superabsorbent resin composition.

The particle size distribution and bulk specific gravity of this powder (2) and powder (b) are shown in Table 1.

Example 3 Same as Example 2, except that the gel-like hydrous polymer was dry-pulverized and had a different particle size as the powder.
Powder (e) of crosslinked polyacrylate was obtained in the same manner as above. The absorption capacity of this powder (e) in water was 500 times.

24 r of pulp floc 0W-1 (manufactured by Sanyo Kokusaku Pulp Co., Ltd. (100 mesh pass 90 weight ratio or more)) was placed in a narrator-type mixer with a total capacity of 2.5 t, and 12 f of water was added and stirred for 10 minutes. Powder (400 f) was added to this and mixed for 5 minutes to obtain a powder (3) of a superabsorbent resin composition which is a granulated product. The particle size distribution and bulk specific gravity are shown in Table 1.

Example 4 1 pulp flock ■W-4 [manufactured by Sanyo Kokusaku Pulp Co., Ltd. (400 mesh pass 90 weight FKQB or more)] 25 or was placed in a lipon blender with a total capacity of 30 tons, and polyethylene glycol with an average molecular weight of 20,000 was added while stirring. 5
Aqueous solution 2502 was added dropwise over 5 minutes. After mixing for 30 minutes, powder (c) 5.00 OS' of the same polyacrylate crosslinked product used in Example 3 was added, and the mixture was stirred and mixed for 20 minutes to form a superabsorbent resin composition as a granulated product. powder (4
) was obtained. The particle size distribution and bulk specific gravity of this powder (4) are shown in Table 1.

Example 5 50 parts of corn starch, 200 parts of water, and 1,000 parts of methanol were placed in a reaction vessel equipped with a stirring rod, a nitrogen blowing tube, and a thermometer, stirred at 50°C for 1 hour under a nitrogen stream, and then cooled to 30°C. Then, 25 parts of acrylic acid, 75 parts of sodium acrylate, 0.5 parts of methylenebisacrylamide, 0.1 part of ammonosulfate as a polymerization catalyst, and 0.1 part of sodium bisulfite as a promoter were added. When the mixture was reacted at 60° C. for 4 hours, a white suspension was obtained.

The powder obtained by filtering this white suspension was washed with a water-methanol mixed solution (water:methanol weight ratio: 2:10), dried under reduced pressure at 60°C for 3 hours, and then ground to obtain starch-methanol. A powder (d) of acrylic #salt graft crosslinked product was obtained. The water absorption capacity of this powder (d) was 250 times.

Powder (d) 300 f was placed in a 2.5 ton Nigu, and the average molecular weight was 6. KC floc oW-300 [manufactured by Demikokusaku Pulp Co., Ltd. (300
mesh pass 90 weight ratio or more): Add 9r, 10
The mixture was mixed and granulated for minutes to obtain a powder (5) of a superabsorbent resin composition.

The particle size distribution and bulk specific gravity of this powder (5) and powder (d) are shown in Table 1.

Example 6 300 parts of n-hexane was placed in a reactor, and 0.7 part of sorbitan monostearate was dissolved therein. Then in this
After dissolving 30 parts of acrylic acid in 40 parts of water, it was neutralized with 12.5 parts of caustic soda, and then an aqueous monomer solution containing 0.05 part of potassium peroxide was added and dispersed, and the mixture was kept at 65°C under a nitrogen stream. Polymerization was carried out for 5 hours. After polymerization,
A powder was obtained by drying under reduced pressure. 1 part of polyethylene glycol 300 was added to 100 parts of this powder and mixed in a V-type mixer. The resulting mixture was placed on a belt conveyor and passed through an infrared dryer for heat treatment to obtain a crosslinked polyacrylate powder (e). The average heating time was 4 minutes, and the material temperature at the dryer outlet was 23
It was 0°C. The absorption capacity of this powder (e) in water is 40
It was 0 times.

In Example I, a powder (6) of a superabsorbent resin composition was obtained in the same manner as in Example 1, except that powder (e) was used instead of powder (a).

Table 1 shows the particle size and bulk specific gravity of the powder (6) and powder (e).

Comparative Example 1 Comparative powder (1) was obtained in the same manner as in Example 1, except that cotton-like pulp with an average fiber length of 500 μm was used in place of KC Flock ■W-100. Comparative powder (
There were hard-to-disassemble lumps of superabsorbent resin adhering to the surface and inside of entangled pulp fiber flocks. Table 1 shows the particle size distribution and bulk specific gravity of this comparative powder (1) excluding lumps.

Comparative Example 2 Two of the powders (a) were used instead of powder (a) in Example 1.
Bakashi (powder (f)) that passes through a 00 mesh sieve
Comparative powder (2) was obtained in the same manner as in Example 1, except that t, o o o y and water were used.

Comparative powder (2) contained large, highly dense lumps. Comparative powder (2) with lumps removed and powder (f
) are shown in Table 1.

Comparative example 3 KC flock ■W-100 in a V-type blender with a capacity of 4 tons
24002 and 400f of powder (a) used in Example 1 were added and mixed for 10 minutes. Then, while stirring,
40 f of water was added over 0 minutes. Stirring was continued for another 10 minutes to obtain comparative powder (3).

Comparative powder (3) contained a mixture of large-density lumps, and the powder fiber predisposition was caused by moistening with a superabsorbent resin composition (an aqueous liquid before mixing with Q). I know it won't happen. Table 1 shows the particle size distribution and bulk specific gravity of the comparative powder (3) from which lumps were removed.

Claims (1)

[Claims] Powdered cellulose (A
) 2 to 10 parts by weight of aqueous liquid (B) 1 to 10 parts by weight
After being allowed to dry, it passes through a 20-mesh standard sieve, and those that pass the 200-mesh standard rating are under 90 weight board. Highly absorbent! # Granulated bulk specific gravity obtained by mixing with 100 parts by weight of fat powder 0.25 to 0.6 f/c
The superabsorbent resin composition of c.