JPS6153386B2 - - Google Patents

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. However, many of the conventionally used superabsorbent resins often contain a large amount of fine powder that can pass through a 100-mesh standard sieve, or have a relatively large bulk specific gravity. There are the following problems when using such powdered superabsorbent resins. 1 Dust is likely to be generated. 2 Poor mixability and dispersibility. In the production of sanitary products, cotton-like pulp is sometimes mixed, but in this case, if the difference in specific gravity between the cotton-like pulp and the superabsorbent resin powder is large, uneven mixing is likely to occur. In addition, when mixed with soil or sand in the field of agriculture and horticulture, especially when they are damp, moisture-absorbed lumps of superabsorbent resin tend to form, and once a lump forms, it will not be able to absorb water even after irrigation. As a result, the water retention capacity decreases. Solutions to these problems include reducing the amount of fine powder by crushing the superabsorbent resin under conditions that increase the particle size, and using a binder such as water to bind the superabsorbent resin powder together. A possible method is to make the particles adhere to each other and granulate them. 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 because it is difficult to uniformly disperse the binder, the particle size distribution becomes wide and relatively dense agglomerates occur, resulting in high-speed absorption. This is not preferable because it inhibits 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 specific extremely fine cellulose fibers in powder form, mixing them with specific superabsorbent resin powder, and granulating them solves the above problems at once. They have discovered that this is the case and have completed the present invention. Therefore, an object of the present invention is to provide a superabsorbent resin composition that is easy to handle as a powder and can be produced by an extremely simple method. That is, in the present invention, 2 to 10 parts by weight of powdered cellulose (A), which has an average fiber length of 400 μ or less and 90% by weight or more of which passes through a standard sieve of 100 mesh, is mixed with 1 to 10 parts by weight of an aqueous liquid (B).
Highly absorbent resin powder (C) that passes through a 20-mesh standard sieve and 90% by weight or less passes through a 200-mesh standard sieve after being moistened with parts by weight.
Granulated bulk specific gravity obtained by mixing with 100 parts by weight
This relates to a superabsorbent resin composition of 0.25 to 0.6 g/cc. 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 in water. Examples of such superabsorbent resins include polyacrylate crosslinked products, starch-acrylate graft crosslinked products, 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 these superabsorbent resin powders (C) is such that it can pass through a standard sieve of 20 mesh, and the amount that can pass through a standard sieve of 200 mesh is 90% by weight or less. Those containing particles larger than this are
Not preferred due to low absorption rate. In addition, if a particle size smaller than this is used, it is necessary to use more than 10 parts by weight of an aqueous liquid in order to obtain a granulated product with a small amount of fine powder of 100 mesh or less, and in that case, This is not preferable because it tends to produce particles with a relatively large particle size and requires a drying step. The powdered cellulose (A) used in the present invention has an average fiber length of
400μ or less and 90% by weight or more of it passes through a 100-mesh standard sieve. In other words, those with a larger average fiber length or larger particle size,
Some flocs are present due to intertwining between the fiber elements, and it is difficult to uniformly disperse them even when wetted with an aqueous liquid, resulting in relatively dense lumps in the resulting composition. Undesirable. An example of the powdered cellulose (A) used in the present invention is commercially available from Sanyo Kokusaku Pulp Co., Ltd. KC Flock W-100, W-300 and Pulp Flock W-
1, W-4, W-5, etc. Powdered cellulose (A) is used in a ratio of 2 to 10 parts by weight based on 100 parts by weight of superabsorbent resin powder (C). The optimal value for the amount used needs to be determined appropriately depending on the type and particle size of the superabsorbent resin powder (C), but if the ratio is less than 2 parts by weight, it will not be very effective; If the ratio exceeds the above ratio, the bulk specific gravity of the resulting composition will become too small or a part of the powdered cellulose (A) will remain in a free state, which is not preferable. As the aqueous liquid (B), 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,
Examples include polyethylene glycol and polyvinyl alcohol. When using these water-soluble polymers, if the concentration is too high, the viscosity of the aqueous liquid will increase, making it difficult to mix the powdered cellulose (A) with the aqueous liquid (B) to wet it, which is not preferable. The concentration of water-soluble polymer is usually 10% by weight or less. The amount of aqueous liquid (B) used is 100% of superabsorbent resin powder (C).
The ratio ranges from 1 to 10 parts by weight. The optimal value for the amount to be used must be determined appropriately depending on the type and particle size of the superabsorbent resin (C) and the amount of powdered cellulose (A) used, but if the ratio is less than 1 part by weight, it will be mixed with powdered cellulose (A). This is insufficient for adhering the superabsorbent resin (C) and granulating it, 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 (A) with the aqueous liquid (B) in the present invention, both may be placed in a suitable mixer and mixed. As such a mixer, a mixer commonly used for mixing, summing, and kneading solids can be used. Examples of such mixers include rotating cylindrical mixers, V-type mixers, double-arm mixers, continuous injection mixers, high-speed mixers, and the like. A mixing time of 30 minutes or less is usually sufficient, but may be longer. To wet powdered cellulose (A) with aqueous liquid (B) and then mix it with superabsorbent resin powder (C) for granulation, wet powdered cellulose (A) with aqueous liquid (B). The mixers listed as being available may be used. Then, after the powdered cellulose (A) is moistened with the aqueous liquid (B), the superabsorbent resin powder (C) may be added subsequently to mix and granulate, or the powdered cellulose (A) may be mixed and granulated in advance. ) may be moistened with the aqueous liquid (B) and then placed in a separate mixer together with the superabsorbent resin powder (C) and mixed to form granules. Powdered cellulose (A) moistened with aqueous liquid (B) is obtained by mixing powdered cellulose (A) moistened with aqueous liquid (B) and superabsorbent resin powder (C) in the above-mentioned specific ratio. and some superabsorbent resin powder (C) are granulated. The superabsorbent resin composition of the present invention is granulated in this manner and has a bulk specific gravity of 0.25 to 0.6 g/cc. If the bulk specific gravity is less than 0.25 g/cc, the granules will become too bulky and become difficult to handle, and the bulk specific gravity will be less than 0.6 g/cc.
If it exceeds cc, it is undesirable because of poor mixability and dispersibility. 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. It has a smaller bulk specific gravity than the polyester resin powder (C), and contains fewer fine powders of 100 mesh or less, which solves all the problems of conventional powdered superabsorbent resins at once. Although a drying step 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 is found that a plurality of superabsorbent resin particles (C) are granulated through a small amount of powdered cellulose (A). The surface of the granulated powder was hardly covered with powdered cellulose (A). This is completely different from the one disclosed in JP-A-51-35685 in which a single hydrogel particle is 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, but in the present invention, a very small amount of aqueous liquid is required. A drying step is not necessary as it is sufficient. In addition, in the present invention, the bulk specific gravity can be greatly reduced by using a small amount of fine powdered cellulose, most of which passes through a standard sieve of 100 mesh.
It is surprising that it has become possible to reduce the amount of fine powder below mesh size. The superabsorbent resin composition of the present invention has excellent handling properties as a powder, but in order to further improve its fluidity as a powder, it may be added with a fluidity improver such as finely powdered silica. You can also use EXAMPLES Hereinafter, the present invention will be specifically explained with reference to Examples, but the scope of the present invention is not limited only to these Examples. The water absorption capacity of the absorbent resin is determined by uniformly placing the absorbent resin powder in a non-woven T-bag type bag, immersing it in pure water, and measuring the weight after 10 minutes, according to the following formula. Calculated. Absorption capacity = Weight after absorption (g) - Weight before absorption (g) / Weight of powder (g) Example 1 Sodium acrylate 74.9 mol%, acrylic acid
4000 parts of a 43% aqueous solution of acrylate monomers consisting of 25 mol% and 0.1 mol% of trimethylolpropane triacrylate were mixed with 0.6 mol% of ammonium persulfate.
1 part and 0.2 parts of sodium bisulfite were allowed to stand at 55 to 80° C. in a nitrogen atmosphere to obtain a gel-like hydrated polymer. This gel-like hydrous polymer was dried in a hot air dryer at 180° C. and then ground in a vibrating grinder to obtain a powder (a) of a crosslinked polyacrylate. The absorption capacity of this powder (a) in water was 350 times. KC Flock W in a V-type blender with a capacity of 4
−100 [Manufactured by Sanyo Kokusaku Pulp Co., Ltd. (100 mesh pass 90
% by weight or more)] and 40 g of water were mixed well until a uniform wet powder was obtained. Powder (a)
After adding 1000 g and stirring and mixing for 30 minutes, soft aggregates of granules were obtained. The soft aggregates of the granules were easily loosened to obtain a powder (1) of a superabsorbent resin composition with a low bulk specific gravity. Table 1 shows the particle size distribution and bulk specific gravity of this powder (1) and powder (a). Example 2 4000 parts of a 43% aqueous solution of acrylate monomers consisting of 74.95 mol% sodium acrylate, 25 mol% acrylic acid and 0.05 mol% trimethylolpropane triacrylate was added to ammonium persulfate.
Using 0.6 parts and 0.2 parts of sodium bisulfite, standing polymerization was carried out at 55 to 80°C in a nitrogen atmosphere 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 obtain 60 meshes. 0.3 parts of glycerin was added to 100 parts of this powder and mixed using a screw type mixer, and the resulting mixture was heat-treated using 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 cm, and heated for 15 minutes while stirring with a scraper to obtain a crosslinked polyacrylate powder (b). The absorption capacity of this powder (b) in water is
It was 500 times hotter. Put 32 g of Pulp Flock W-5 [manufactured by Sanyo Kokusaku Pulp Co., Ltd. (100 mesh passes 60% by weight or more)] into a double-armed machine with a total capacity of 2.5, and the molecular weight is approximately 20,000.
Add 32 g of a 2% aqueous solution of polyacrylic acid to 40
Mixed for a minute. Add 400g of powder (b) to this and
After mixing for a minute, a soft agglomerate of granules was obtained.
The soft aggregates of the granules were easily loosened to obtain a powder (2) of the 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 In Example 2, a powder (c) of a crosslinked polyacrylate was prepared in the same manner as in Example 2, in which powders having different particle sizes were obtained by drying and pulverizing a gel-like hydrous polymer. Obtained. The absorption capacity of this powder (c) in water was 500 times. Put 24 g of Pulp Flock W-1 [manufactured by Sanyo Kokusaku Pulp Co., Ltd. (100 mesh pass 90% by weight or more)] into a Nauta type mixer with a total capacity of 2.5, and add 12 g of water.
was added and stirred for 10 minutes. 400 g of powder (c) 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 of this powder (3) and powder (c) are shown in Table 1. Example 4 Put 250 g of Pulp Flock W-4 (manufactured by Sanyo Kokusaku Pulp Co., Ltd. (400 mesh pass 90% by weight or more) into a ribbon blender with a total capacity of 30 mm, and add 250 g of a 5% aqueous solution of polyethylene glycol with an average molecular weight of 20,000 while stirring. was added dropwise over 5 minutes. After mixing for 30 minutes, 5000 g of the same polyacrylate crosslinked powder (c) as used in Example 3 was added, and the mixture was stirred and mixed for 20 minutes. ) 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 1000 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. 25 parts acrylic acid, 75 parts sodium acrylate, 0.5 parts methylenebisacrylamide, as polymerization catalyst
0.1 part of ammonium persulfate and 0.1 part of sodium bisulfite were added as a promoter, and the mixture was reacted at 60° C. for 4 hours to obtain a white suspension. The powder obtained by filtering this white suspension was mixed with water.
It was washed with a methanol mixed solution (water:methanol weight ratio: 2:10), dried under reduced pressure at 60°C for 3 hours, and then ground to obtain a powder (d) of starch-acrylate graft crosslinked product. The absorption capacity of this powder (d) in water was 250 times. 300 g of powder (d) was placed in a kneader with a capacity of 2.5 and pre-wetted with 12 g of a 3% aqueous solution of polyethylene glycol with an average molecular weight of 6000. above)] was added and mixed and granulated for 10 minutes to obtain a powder (5) of a superabsorbent resin composition. Table 1 shows the particle size distribution and bulk specific gravity of the powder (5) and powder (d). Example 6 300 parts of n-hexane was placed in a reactor, and 0.7 part of sorbitan monostearate was dissolved therein. Next, in this, 30 parts of acrylic acid was dissolved in 40 parts of water, and then
The mixture was neutralized with 12.5 parts of caustic soda, and an aqueous monomer solution containing 0.05 part of potassium persulfate was added to disperse the mixture, followed by polymerization at 65° C. under a nitrogen stream for 5 hours. After the polymerization was completed, the mixture was dried under reduced pressure to obtain a powder. Add 1 part of polyethylene glycol 300 to 100 parts of this powder.
1 part and mixing was carried out using a V-type mixer. The resulting mixture was thinly 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 is 4 minutes, and the material temperature at the dryer outlet is 230℃.
It was hot. The absorption capacity of this powder (e) in water was 400 times. 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 flocculent pulp with an average fiber length of 500 μm was used instead of KC Flock W-100. Comparative powder (1) contained hard-to-dissolve lumps of superabsorbent resin adhering to the surface and inside of entangled pulp fiber flocs. Table 1 shows the particle size distribution and bulk specific gravity of this comparative powder (1) excluding lumps. Comparative Example 2 In Example 1, powder (a) was replaced with powder (a).
Only those that pass through a 200 mesh sieve (powder)
(f)) Except that 1000g was used and 100g of water was used.
Comparative powder (2) was obtained in the same manner as in Example 1. Comparative powder (2) contained large, high-density lumps. Comparison powder (2) with lumps removed and powder (f)
The particle size distribution and bulk specific gravity are shown in Table 1. Comparative example 3 KC floc W in a V-type blender with a capacity of 4
-400g of -100 and 400g of powder (a) used in Example 1
and mixed for 10 minutes. Then 40 g of water was added over 10 minutes with stirring. moreover
Stirring was continued for 10 minutes to obtain comparative powder (3). The comparative powder (3) contains large-density lumps, and the powdered cellulose (A) was wetted with an aqueous liquid (B) before being mixed with the superabsorbent resin composition (C). I know what I have to keep. Table 1 shows the particle size distribution and bulk specific gravity of the comparative powder (3) from which lumps were removed.

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Claims (1)

[Claims] 1 Average fiber length is 400μ or less and 90% by weight
After moistening 2 to 10 parts by weight of powdered cellulose (A) with 1 to 10 parts by weight of an aqueous liquid (B), which passes through a standard sieve of 100 mesh, the entire cellulose passes through a standard sieve of 20 mesh, and Granulated bulk specific gravity 0.25-0.6 g/
cc super absorbent resin composition.