JPH04372636A - Water-absorbing resin composition - Google Patents

Abstract

PURPOSE:To prepare a compsn. which is in the form of beads and has a high water absorption capacity and a moderate water absorption rate. CONSTITUTION:This compsn. comprises a composite consisting of 40-95wt.% polyethylene or polypropylene resin having a number-average mol.wt. of 1,000-5,000 and 5-60wt.% water-absorbing resin and is in the form of beads having a diameter of 2-10mm.

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary of the Invention] [Industrial Field of Application] The present invention relates to a bead-shaped water-absorbing resin composition. Since the water-absorbing resin composition according to the present invention has a bead-like shape with a diameter of 2 to 10 mm, it has excellent handling workability, high water-absorbing ability, and moderate water-absorbing speed. Specific applications include, for example, water stop agents, lubricants, anti-sludge agents used in civil engineering work, and soil water retention agents for agriculture and horticulture. [0002] Conventionally, water-absorbing resins have been widely used as particulate water-absorbing materials, mainly in disposable diapers and sanitary products. Recently, these resins have been widely developed for use as soil water retention agents, lubricants or water absorption agents for civil engineering works, gels for cold storage agents, and the like. [0003] Examples of water-absorbing resin include starch.
Acrylate graft copolymers, acrylic acid (salt) polymers, modified cellulose derivatives, vinyl alcohol-acrylic acid (salt) copolymers, modified polyethylene oxide, and the like are generally known. These water-absorbing resins absorb water several tens to 1000 times their own weight, and swell and gel. Commercially available water absorbent resins are generally in powder form with a particle size of about 0.05 to 1 mm. [0004] The water absorption rate of these water-absorbing resins is designed to be extremely fast because the water-absorbing resins are mainly used for disposable diapers and sanitary products. For example, the time required for the resin to come into contact with water and reach near the saturated water absorption amount is approximately 10 seconds to 10 minutes. [0005] Therefore, in order to widely use these water-absorbent resins for purposes other than disposable diapers, etc., the above-mentioned too small particle size and too fast water absorption rate are often inconvenient due to handling work, purpose of use, and situation. there were. For example, when handled outdoors for civil engineering, agricultural purposes, etc., there are problems such as being easily dispersed by wind and absorbing moisture excessively or prematurely. [0006] For this reason, many composites (mixed dispersions of water-absorbing resins) of water-absorbing resins and general thermoplastic resins (polyethylene, polypropylene, polyvinyl acetate, etc.) or rubber, etc. have recently been proposed. ing(
JP-A No. 51-75747, JP-A No. 56-33032, JP-A No. 57-14515, and JP-A No. 2-242858). [0007] The above-mentioned composite material can be granulated and molded, and therefore has improved handling efficiency. However, since the thermoplastic resins and rubbers used in these products are ordinary high-molecular weight materials (with molecular weights of several thousand or more), the resulting composites do not have the inherent water absorption capacity of the composite water-absorbing resins. (Water absorption capacity) is significantly reduced. Therefore, the water absorption rate becomes extremely slow. For example, the time it takes to reach near saturated water absorption after coming into contact with water is from several hours to more than 24 hours in most cases. [Means for Solving the Problems] [Summary of the Invention] <Summary
> As a result of consideration in view of the above-mentioned problems, the present inventors found that
We have found a bead-shaped water-absorbing resin composition that has a high water-absorbing capacity, an appropriate water-absorbing speed that is neither too fast nor too slow, and has excellent handling properties. Therefore, the water absorbent resin composition according to the present invention is a polyethylene resin or a polypropylene resin having a number average molecular weight in the range of 1,000 to 5,000.
bead-shaped with a diameter of 2 mm to 10 mm;
It is characterized by: <Effect> The bead-shaped water-absorbing resin composition according to the present invention does not impair the water-absorbing ability of the water-absorbing resin, compared to conventional composites of water-absorbing resin and thermoplastic resin or rubber. It has high water absorption capacity and moderate water absorption rate. The degree of speed can be controlled by appropriately changing the type and proportion of the water-absorbing resin used, or the type and molecular weight of the polyethylene resin. Usually 30 minutes to 18
Those having a water absorption rate of about 0 minutes are practical for each of the above-mentioned uses. [0011] The composition according to the present invention absorbs water and swells when used, but after swelling it does not exhibit its original bead-like form, and the water-absorbing resin portion becomes a discontinuous gel-like substance. In addition, the polyethylene resin and the like are mixed in the gel-like material in the form of fine powder or threads. [0012] This is thought to be because the polyethylene resin or the like as a binder is shredded by the volumetric expansion force of the water-absorbing resin when it absorbs water. Such properties are not found in conventional composites. [Detailed description of the invention] <Polyethylene resin etc.> The polyethylene resin or polypropylene resin used in the present invention has a number average molecular weight of 1000 to 5000, preferably 2000 to 40.
00, the polyethylene resin or polypropylene resin used in the present invention has a significantly low molecular weight. Here, "polyethylene resin" and "polypropylene resin" mean polymers (homopolymers and copolymers) whose main components are ethylene and propylene, respectively. In the case of a copolymer, the comonomer may be of any type as long as it can be copolymerized with the main monomer, and the copolymerization form may be random, block, graft, or any other suitable form. It can be. Those having a number average molecular weight of less than 1,000 are unsuitable because they become liquid at room temperature and do not become bead-like even when composited. Generally, most commonly used numbers are 10,000 or more. [0015] Various types of water-absorbing resins can be used in the present invention. In the present invention, for example, (a)
Starch-acrylate-graft polymer crosslinked product, (b) polyacrylate crosslinked product, (c) acrylate-acrylic ester copolymer crosslinked product, (d) acrylic ester, vinyl acetate copolymer One or more selected from the group consisting of saponified products of crosslinked products, (e) crosslinked acrylate-acrylamide copolymer products, and (f) hydrolyzed products of crosslinked polyacrylonitrile products can be used. The above-mentioned water-absorbing resin has a water-absorbing capacity of 5 times its own weight.
It is about 0 to 1000 times larger. Also, its shape is
It is in the form of fine particles of about 0.01 to 1 mm. 1
Particles having a size of mm or more are not preferred because they cannot be formed well when they are blended with polyethylene resin or polypropylene resin and then granulated into beads. The shape may be either spherical particles or irregularly shaped particles. <Blending ratio> In the present invention, the blending ratio of polyethylene resin, polypropylene resin, etc. and water-absorbing resin is 40 to 95% by weight of the former and 5 to 60% by weight of the latter.
It is. Preferably the former is 50-80% by weight, the latter 20-80% by weight.
It is 50% by weight. <Production of bead-shaped water-absorbing resin composition> The water-absorbing resin composition according to the present invention is first a composite of a specific polyolefin and a water-absorbing resin. Here, the "complex" typically refers to a form in which one of these components is dispersed in a matrix of the other. Since the water absorbent resin is obtained by the so-called "reverse phase suspension polymerization method",
Considering that it is powder itself and has a higher melting point than a low molecular weight polyolefin, a typical form is one in which a water absorbent resin is dispersed in a polyolefin matrix. The water-absorbing resin composition according to the present invention is made of such a composite in the form of beads with a diameter of 2 mm to 10 mm. Such a material is preferable in terms of product usage and processing precision into bead-like objects. Although any method can be used to obtain such a bead-like water-absorbing resin composition, one particularly preferred method in the present invention is, for example, the following method. First, a water-absorbing resin is mixed and dispersed in a molten resin liquid that has been melted at a temperature higher than the melting point of the polyethylene resin, etc. to be used, and then this molten liquid is pumped into a cylindrical tank with a large number of holes. The molten mixture of extruded droplets is dropped onto a metal belt cooler at a temperature below the melting point of polyethylene or the like. The falling molten material is granulated into beads by surface tension, cooled, and solidified. In addition, the size of the target composition can be arbitrarily determined by changing the diameter of the hole (nozzle) made in the cylindrical tank. In the present invention, in addition to the polyethylene resin and the water-absorbing resin, other additives include inorganic substances (earth, sand, bentonite, activated carbon, carbon, etc.), antioxidants, ultraviolet absorbers, and fungicides. , fragrances, coloring agents, other industrial chemicals, agricultural chemicals, etc. can also be added in small amounts. [Example] The methods for measuring and calculating the saturated water absorption amount and water absorption rate in Examples and Comparative Examples are shown below. [0024] Saturated water absorption: 1 g of the water absorbing agent was sealed in a 250 mesh nylon tea bag, and the bag was immersed in 2000 ml of large excess water (ion-exchanged water, pH 6.5-7.0) for 24 hours. After that, the tea bag was pulled up and drained for 20 minutes, and the weight (g) of the swollen sample was taken as the saturated water absorption amount (g). Water absorption rate In the same operation as the saturated water absorption measurement method, the tea bag soaked in water is taken out at an arbitrary time, the weight of the swollen sample at that time is measured, and the weight is calculated using the following formula. <Example 1> Ethylene polymer was synthesized using a stirring autoclave type continuous reactor with an internal volume of 1 liter (number average molecular weight: 4500, melting point: 110°C)
. After melting 60 parts by weight of this ethylene polymer at a temperature of 110°C or higher and liquefying it, commercially available water absorbent resin A (sodium polyacrylate crosslinked product, average particle size 60-100
μ) 40 parts by weight were added and mixed to obtain a molten dispersion. Next, this molten dispersion was passed through a special nozzle of a granulator (Rotoformer manufactured by Sandvik) and dropped onto a metal belt-type cooler pre-cooled to 15 to 30°C. A resin composition (1) was obtained (particle size: 5 mm, white beads). The saturated water absorption amount and water absorption rate of this product were as follows. <Example 2> A propylene polymer (number average molecular weight: 4700, melting point: 168°C) was synthesized using the same apparatus instead of using the ethylene polymer of Example 1.
A water-absorbing resin composition (2) was obtained in the same manner except that the following procedure was used (particle size: 5 mm, white bead shape). The saturated water absorption amount and water absorption rate of this product were as follows. <Comparative Example 1> Ethylene polymer (number average molecular weight: 11000, melting point: 110°C) synthesized using the same apparatus instead of using the ethylene polymer of Example 1
Comparative material (1) was obtained in the same manner except that . The saturated water absorption amount and water absorption rate of this product were as follows. <Comparative Example 2> The saturated water absorption amount and water absorption rate of water absorbent resin A used in Example 1 alone were measured. [Test results] Water absorption rate test Contact time with water (minutes)
0 10 30 60 9
0 120 150 180
Composition (1) 0 7
25 55 80 95
100 Composition (2) 0
0 15 40 65 8
5 95 100 Comparison (1)
0 0 0
5 8 12 16
20 Water absorbent resin A 0 100
(%) [0031] Compositions (1) and (2) after saturated water absorption: The compositions did not exhibit the original bead shape, but became discontinuous gel-like as a whole. The binder (polyethylene, etc.) is mixed in the gel-like material in the form of fine powder or threads. Comparative example (1
) It shows the original bead shape, which swells to a particle size of about 10
mm (twice) in size. Effects of the Invention: The bead-shaped water-absorbing resin composition according to the present invention has a high water-absorbing capacity and an appropriate water-absorbing rate, as described above in the section ``Means for Solving the Problems.'' By the way.

Claims (1)

[Claims] Claim 1: Polyethylene resin or polypropylene resin 40 having a number average molecular weight in the range of 1000 to 5000.
A water-absorbing resin composition, which is a composite consisting of ~95% by weight of a water-absorbing resin and 5-60% by weight of a water-absorbing resin, and is bead-shaped with a diameter of 2 mm to 10 mm.