JP3043465B2 - Water-absorbing resin composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[Summary of the Invention]

The present invention relates to a bead-shaped water-absorbing resin composition. Since the water-absorbent resin composition according to the present invention has a bead shape having a diameter of 2 to 10 mm, it has excellent handling workability, and has a high water-absorbing ability and an appropriate water-absorbing speed. Specific applications include, for example, water-blocking agents, lubricants, anti-sludge agents, and soil water retention agents for agricultural and horticultural use used in civil engineering works.

[0002]

2. Description of the Related Art Conventionally, water-absorbing resins have been widely used as powdery and granular water-absorbing materials, mainly for use in disposable diapers and sanitary products. Recently, these resins have been widely developed for use as soil water retention agents, lubricants or water absorbing agents for civil engineering work, gels for cold storage agents, and the like.

[0003] As the water absorbing resin, for example, starch-
An acrylate graft copolymer, an acrylic acid (salt) polymer, a modified cellulose derivative, a vinyl alcohol-acrylic acid (salt) copolymer, a modified polyethylene oxide, and the like are generally known. These water-absorbing resins absorb water of several tens to 1000 times their own weight, and swell and gel. Commercially available water-absorbent resins are generally in the form of powder having a particle size of about 0.05 to 1 mm.

[0004] The water absorbing rate of these water absorbing resins is designed to be extremely high, since the main uses of the water absorbing resin are disposable diapers and sanitary products. For example, the time required for the resin to come into contact with water and reach near saturated water absorption is about 10
It is about 10 seconds to 10 minutes.

Therefore, in order to widely use these water-absorbing resins in applications other than disposable diapers and the like, the above-mentioned too small particle diameter and too fast water absorption rate are often inconvenient depending on handling work, use purpose and circumstances. there were. For example, when handled outdoors for civil engineering applications, agricultural applications, etc., there are problems such as easy diffusion by wind and excessive or premature moisture absorption.

[0006] For these reasons, many composites (mixed dispersions of water-absorbent resins) of a water-absorbent resin and a general thermoplastic resin (polyethylene, polypropylene, polyvinyl acetate, etc.) or rubber have recently been proposed. (JP-A-51-75747, JP-A-56-33032,
Nos. 57-14515 and JP-A-2-242858).

[0007]

Since the above-mentioned composite can be granulated and molded, its handling workability is improved. However, since the thermoplastic resins and rubbers used for them use ordinary high molecular weight substances (thousands of thousands or more in molecular weight), the resulting composites have the inherent water absorbing capacity of the composite water absorbent resin. (Water absorption ratio) is significantly reduced. Therefore, the water absorption speed becomes extremely slow. For example, most of the time when it comes into contact with water and reaches near saturated water absorption is several hours to 24 hours or more.

[0008]

Means for Solving the Problems [Summary of the Invention] <Summary> As a result of investigations in view of the above-mentioned problems, the present inventors have found that a moderate water absorption capacity, not too fast and not too slow. A bead-shaped water-absorbent resin composition having a water absorption rate and excellent in handleability was found.

Accordingly, the water-absorbent resin composition according to the present invention has a number average molecular weight in the range of 1,000 to 5,000 polyethylene resin or polypropylene resin 40 to 95.
A composite comprising 5% by weight and 5 to 60% by weight of a water-absorbent resin, characterized in that it is in the form of beads having a diameter of 2 mm to 10 mm.

<Effect> The bead-shaped water-absorbent resin composition of the present invention does not impair the original water-absorbing ability of the water-absorbent resin as compared with a conventional composite of a water-absorbent resin and a thermoplastic resin or rubber. Has high water absorption capacity and moderate water absorption speed.
The degree of the 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 or the like. Usually 30 to 18 minutes
Those having a water absorption rate of about 0 minutes are practical in the above-mentioned respective applications.

The composition according to the present invention absorbs water when used and swells. However, after swelling, the composition does not show the original bead-like form, and the water-absorbent resin portion is a discontinuous gel-like substance. In addition, the portion of the polyethylene resin or the like is in a state of being mixed in the gel-like material in the form of fine powder or thread (spiral).

It is considered that this is because the polyethylene resin or the like as a binder is cut by the volume expansion force of the water-absorbent resin when absorbing water. Such properties are not found in conventional composites.

[Specific description of the invention] <Polyethylene resin and the like> 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.
Therefore, the polyethylene resin or the polypropylene resin used in the present invention is significantly low molecular weight. Here, "polyethylene resin" and "polypropylene resin" mean polymers (homopolymers and copolymers) containing ethylene and propylene as main components, respectively. In the case of a copolymer, the comonomer can be any as long as it can be copolymerized with the main monomer, and the copolymer form is also random, block, graft, or any other suitable purpose. It can be.

Those having a number average molecular weight of less than 1000 are unsuitable because they become liquid at room temperature and do not become beads even if they are compounded. In general, most commonly used ones are 10,000 or more.

Various water-absorbent resins can be used in the present invention. In the present invention, for example, (a)
Starch-acrylate-graft polymer crosslinked product,
(B) cross-linked polyacrylate, (c) acrylate-
Acrylic ester copolymer crosslinked product, (d) Acrylic ester, saponified product of vinyl acetate copolymer crosslinked product,
One or two or more selected from the group consisting of a crosslinked product of (e) an acrylate-acrylamide copolymer and a hydrolyzate of (f) a crosslinked polyacrylonitrile can be used.

The above water-absorbent resin has a water absorption capacity of 5% of its own weight.
It is about 0 to 1000 times. Also, its shape is
It is a fine powder of about 0.01 to 1 mm. 1mm
Particles having the above sizes are not preferable because they cannot be molded well when granulated into beads after blending with a polyethylene resin or a polypropylene resin. The shape may be either spherical particles or irregular particles.

<Blending Ratio> In the present invention, the blending ratio of the polyethylene resin or polypropylene resin and the 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 to 80% by weight, and the latter is 20 to 80% by weight.
50% by weight.

<Production of Bead-shaped Water-absorbing Resin Composition> The water-absorbing resin composition according to the present invention is a composite of a specific polyolefin and a water-absorbing resin. Here, the “composite” typically has a form in which one of these components is dispersed in one matrix. From where the water-absorbent resin is obtained by the so-called "reverse phase suspension polymerization method",
Considering that it is powdery and has a higher melting point than a low-molecular-weight polyolefin, a form in which a water-absorbing resin is dispersed in a polyolefin matrix is typical.

The water-absorbent resin composition according to the present invention is in the form of beads having a diameter of 2 mm to 10 mm of such a composite. Such a product is preferable in terms of the use of the product, the processing accuracy into a bead, and the like.

The method for obtaining such a bead-shaped water-absorbent resin composition is optional, but one of the particularly preferred methods in the present invention is, for example, the following.

First, a water-absorbing resin is mixed and dispersed in a molten resin liquid melted at a temperature not lower than the melting point of the polyethylene resin or the like to be used, and then this molten liquid is pressure-fed to a cylindrical tank having a large number of holes. The molten mixture of the extruded droplets is dropped on a metal belt cooler having a temperature equal to or lower than the melting point of polyethylene or the like. The dropped melt is granulated into a bead form by surface tension, cooled, and solidified. The size of the target composition can be arbitrarily determined by changing the diameter of the hole (nozzle) formed in the cylindrical tank.

In the present invention, in addition to the polyethylene resin and the water-absorbing resin, other additives such as inorganic substances (soil, sand, bentonite, activated carbon, carbon, etc.) or antioxidants, ultraviolet absorbers, and fungicides , Fragrances, coloring agents, other industrial chemicals, agricultural chemicals and the like can also be added in small amounts.

[0023]

EXAMPLES The methods for measuring and calculating the saturated water absorption and the water absorption in Examples and Comparative Examples are described below.

Saturated water absorption 1 g of a water- absorbing agent is sealed in a 250-mesh nylon tea bag and immersed in 2000 ml of a large excess of water (ion-exchanged water, pH 6.5 to 7.0) for 24 hours. Then, the weight (g) of the swollen sample after the tea bag is pulled up and drained for 20 minutes is defined as a saturated water absorption (g). At water absorption saturation water absorption measurement method and the same operation, the tea bag was immersed in water extraction at any time, to measure the weight of the swollen sample at that time is calculated by the following equation.

Example 1 An ethylene polymer was synthesized using a stirring-type autoclave type continuous reactor having 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 more and liquefaction, a commercially available water-absorbing resin A
(Crosslinked sodium polyacrylate, average particle size 60-1
00μ) 40 parts by weight were added and mixed to obtain a molten dispersion. Next, the molten dispersion was passed through a dedicated nozzle of a granulator (Rotoformer of Sandvik), and was previously heated to 15 to 30 ° C.
Was dropped onto a cooled metal belt cooler to obtain the desired water-absorbent resin composition (1) of the present invention (particle size: 5 m).
m, white beads). Its saturated water absorption and water absorption rate were as follows.

Example 2 Instead of using the ethylene polymer of Example 1, a propylene polymer synthesized using the same apparatus (number average molecular weight: 4700, melting point: 168 ° C.)
Was used to obtain a water-absorbent resin composition (2) (particle size: 5 mm, white beads). Its saturated water absorption and water absorption rate were as follows.

Comparative Example 1 Instead of using the ethylene polymer of Example 1, an ethylene polymer synthesized using the same apparatus (number average molecular weight: 11000, melting point: 110 ° C.)
Was used in the same manner as in Comparative Example 1 except that was used. Its saturated water absorption and water absorption rate were as follows.

Comparative Example 2 The water absorption and the water absorption rate of the water-absorbent resin A used in Example 1 alone were measured.

[Test Result] Water absorption speed Test time of contact with water (min) 0 10 30 60 90 120 150 180 Composition (1) 0 7 25 55 80 95 100 Composition (2) 0 0 15 40 65 85 95 100 Comparative (1) 0 0 0 5 8 12 16 20 Water absorbent resin A 0 100 (%)

[0030]

State after Saturated Water Absorption Compositions (1) and (2) The whole was in the form of a discontinuous gel without showing the original beads. The binder (polyethylene or the like) is present in the gel-like material in the form of fine powder or thread (spirit). Comparative Example (1) The original beads were swelled and formed into a water-absorbent material having a particle size of about 10 mm (twice).

[0032]

The bead-shaped water-absorbing resin composition according to the present invention has a high water-absorbing ability and an appropriate water-absorbing speed, as described above in the section of "Means for Solving the Problems".

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-3-95211 (JP, A) JP-A-2-242858 (JP, A) JP-A-1-252669 (JP, A) JP-A-63- 305170 (JP, A) JP-A-63-48337 (JP, A) JP-A-62-190239 (JP, A) JP-A-57-145151 (JP, A) (58) Fields investigated (Int. ⁷ , DB name) C08L 101/14 C08L 23/04 C08L 23/10 C08J 3/12

Claims (1)

(57) [Claims] 1. A polyethylene resin or polypropylene resin 40 having a number average molecular weight in the range of 1,000 to 5,000.
A water-absorbent resin composition, which is a composite consisting of up to 95% by weight and 5 to 60% by weight of a water-absorbent resin, which is in the form of beads having a diameter of 2 to 10 mm.