JPH0710903B2 - Water absorbent material - Google Patents

Description

TECHNICAL FIELD The present invention relates to a water-absorbent material composed of a water-absorbent resin, and more specifically, it has a water absorption rate equivalent to that of a conventional water-absorbent resin in the form of powder or granules. However, since it retains a film-like or fibrous form and is porous, it has excellent secondary processability unlike a water absorbent resin in the form of granules, and compared to the case where a non-porous substrate is used. The present invention relates to a water-absorbent material having a high grafting rate per unit time and thus having high productivity during manufacturing.

[Problems to be Solved by Conventional Techniques and Inventions] Conventionally, various materials such as starch-acrylonitrile graft copolymers and acrylic acid polymers have been used as water-absorbent resins. However, it has been pointed out that all of them are powdery and inferior in secondary workability. That is, it is necessary to mix the powdery particles of the water-absorbent resin with other fibrous substances or to sandwich them between other fibrous sheets before use. That is, when a water absorbent material is manufactured using a conventional water absorbent resin in the form of powder or granules, there is a problem in that secondary processing is required to add extra labor and time in the processing step.

If there exists a film-like or fibrous material of a water-absorbent resin that can be easily subjected to secondary processing, the secondary processing becomes extremely easy when manufacturing a water-absorbing material as a product from these materials.

An object of the present invention is to solve the above-mentioned problems and to provide a novel water absorbent material having a water absorption rate equivalent to that of a conventional water absorbent resin in the form of powder or granules.

[Means for Solving the Problems] As a result of intensive studies to achieve the above object, the present inventors have found that a polyolefin base material having a specific pore diameter is graft-copolymerized with a certain amount or more of acrylic acid. The material is
The fact that the water absorbing property is remarkably improved was found, and the water absorbing material of the present invention was developed.

That is, the water absorbent material of the present invention has an average pore diameter of 0.005 to 2
Acrylic acid is graft-copolymerized with a polyolefin substrate having fine pores of 0 μm and maintaining the form of a film or fiber, and the graft ratio is 50% by weight or more.

The polyolefin substrate according to the present invention, 0.005 ~ 2
Those having an average pore diameter of 0 μm are used. This is because if the average pore diameter exceeds 20 μm, the mechanical strength of the grafted product is lowered, and if it is less than 0.005 μm, the reaction rate is lowered and the grafting reaction takes time. It is preferably 0.01 to 5 μm.

Further, the polyolefin substrate according to the present invention has a porosity
It is preferably 20 to 80%. If the porosity exceeds 80%, the reaction rate will be improved, but the mechanical strength of the product will be decreased, and if it is less than 20%, the reaction rate of the grafting reaction will be decreased, which is not preferable. . More preferably, it is 30 to 50%.

The porous polyolefin substrate according to the present invention can be manufactured, for example, as follows.

First, a polyolefin powder is mixed with a predetermined amount of a powder of a water-soluble salt having a predetermined particle diameter and then kneaded.

Next, the kneaded product is molded and processed, and the molded product thus obtained is immersed in water to dissolve the salt, so that the portions where the salt exists remain as fine pores. The average pore diameter and porosity of the polyolefin base material can be appropriately changed depending on the average particle diameter and the amount of the salt used. The average pore diameter can be appropriately changed by subjecting such a porous film to a stretching treatment while changing the stretching ratio.

Examples of the material of the polyolefin substrate according to the present invention include polyethylene, polypropylene, ethylene propylene copolymer, ethylene vinyl acetate copolymer, polytetrafluoroethylene, poly-4-methylpentene-
1, Polyvinyl chloride can be used, and polyethylene and polypropylene are particularly preferable.

Examples of the usage form of the polyolefin substrate according to the present invention include forms such as a film, a fiber, a knitted fabric, a woven fabric, and a laminated film.

Next, the acrylic acid to be graft-copolymerized with the above-mentioned polyolefin base material needs to be graft-copolymerized in an amount of 50% by weight or more based on the weight of the base material polyolefin. This is because if it is less than 50% by weight, a water absorption rate equal to that of a water absorbing material using a conventional water absorbing resin cannot be obtained. It is preferably 100 to 400% by weight.

Examples of the method of graft-copolymerizing acrylic acid on the polyolefin substrate in the present invention include a method of photo-irradiating graft copolymerization in the liquid phase or in the gas phase in the presence of a photosensitizer. In addition to this, a method of graft copolymerization by irradiation of radiation, irradiation of electron beam, or the like can also be used.

Light irradiation graft copolymerization which is a suitable method for the present invention will be described. First, for example, the concentration of the photosensitizer in the solvent described below is 0.01 to 2% by weight, preferably 0.1 to 1% by weight.
And then immersing the polyolefin substrate in this solution for several seconds, and then 0 to 60 ° C., preferably 20 to
Dry at 30 ° C. for 10 to 120 minutes, preferably 15 to 30 minutes.
Alternatively, the polyolefin substrate may be spray coated with this solution. The drying conditions are the same as those for dipping. The solvent used at this time is not particularly limited as long as it dissolves the photosensitizer such as acetone, methyl ethyl ketone, tetrahydrofuran, chloroform, benzene, and toluene, does not damage the substrate, and is easy to handle. Further, as the photosensitizer, for example, benzophenone, azobisisobutyronitor, benzoyl peroxide, 2
-Azobispropane, azomethane, azobiscyclohexanecarbonitrile can be mentioned.

Then, light irradiation graft copolymerization is performed on the polyolefin base material treated with the photosensitizer in a liquid phase or a gas phase. First, when performing light irradiation graft copolymerization in the liquid phase,
The polyolefin substrate is immersed in an aqueous solution of acrylic acid of 5 to 80% by weight, preferably 20 to 40% by weight, to obtain 20 to 120% by weight.
Ultraviolet irradiation with a high-pressure mercury lamp at 5 ° C, preferably 50 to 90 ° C, is performed for 5 to 180 minutes, preferably 20 to 60 minutes.
Further, when the light irradiation graft copolymerization is carried out in the gas phase, the polyolefin base material is kept in the upper space of acrylic acid or a solution of acrylic acid, and UV irradiation is carried out by a high pressure mercury lamp under an inert gas atmosphere or under vacuum. For 5 to 20 minutes.

Finally, the obtained graft-copolymerized polyolefin substrate is left for 24 hours in a solvent reflux atmosphere such that it is a good solvent for the above-mentioned acrylic acid polymer, and a single acrylic acid monomer not graft-copolymerized. It is removed by extraction, washed with the same solvent and acetone, and then dried to obtain the water-absorbing material of the present invention, which is a porous polyolefin-based material having a graft ratio of 50% by weight or more.

[Examples] Examples 1 to 3 Low-density polyethylene powder was mixed with 20 wt% of sodium chloride powder and kneaded. This kneaded product was press-molded and then immersed in water to dissolve sodium chloride. The low density polyethylene film obtained has an average pore size.
The thickness was 10 μm, the porosity was 30%, and the thickness was 100 μm.

This polyethylene film contains 1% by weight of benzophenone
After immersing it in a concentrated acetone solution and applying benzophenone to the polyethylene film surface and pore inner wall surface,
It was dried under reduced pressure for 20 minutes. Put the obtained film in a reaction vessel, add an aqueous solution of acrylic acid with a concentration of 15% by weight, and irradiate it with ultraviolet light (400 nm) from a 400 W high-pressure mercury lamp. And processed. The obtained film was washed with hot water and acetone and then dried to measure the graft ratio from the amount of increase in weight after graft copolymerization. Then, this film at 25 ℃
Was immersed in water for 5 hours to absorb water, and the water absorption rate was measured from the amount of increase in weight after water absorption. The results are shown in the table.

Examples 4 to 6 As a polyolefin base material, a stretching treatment of 0.
Has 02 × 0.2μm oblong pores, porosity 50%, thickness 50μ
m except that polypropylene film was used,
Graft copolymerization was carried out in the same manner as in Example 1, and the graft ratio and water absorption were measured. The results are shown in the table.

Example 7 A polyolefin base material having an average pore diameter of 5 μm and a porosity of 20
%, Graft copolymerization was performed in the same manner as in Example 1 except that polypropylene fiber having a yarn diameter of 0.5 mm was used, and the graft ratio and water absorption were measured. The results are shown in the table.

Comparative Examples 1 to 3 Graft copolymerization was carried out in the same manner as in Example 1 except that a low-density polyethylene film having no pores was used as the polyolefin substrate, and the graft ratio and water absorption were measured. The results are shown in the table.

Comparative Examples 4 to 6 Graft copolymerization was performed in the same manner as in Example 1 except that a polypropylene film having no pores was used as the polyolefin substrate, and the graft ratio and water absorption were measured. The results are shown in the table.

Comparative Example 7 Using sodium acrylate as the polar vinyl compound,
This was subjected to reverse phase emulsification in a water-n-heptane system, and then 1% by weight of raw material sodium acrylate, benzoyl peroxide, was added for graft copolymerization.

The water absorption rate of the obtained granular polymer was measured in the same manner as in Example 1. The results are shown in the table.

[Effects of the Invention] As is clear from the above description, the water-absorbent material of the present invention has a water absorption rate equivalent to that of the conventional powdery granular water-absorbent resin,
Further, since it is excellent in that it retains a film-like or fibrous form, secondary processing becomes easy. In addition, since a porous substrate is used, the graft rate per unit time is large and the productivity at the time of production is high as compared with a non-porous substrate. Therefore, it is useful as a material for dehydrating materials, sanitary materials, and agricultural / horticultural materials.

Claims (1)

[Claims] 1. A polyolefin base material having fine pores having an average pore diameter of 0.005 to 20 μm and having a film or fiber morphology is graft-copolymerized with acrylic acid, and the graft ratio is 50% by weight or more. A water-absorbent material characterized in that