JPS61127710A - Water-absorbing and water-retaining material - Google Patents

Abstract

PURPOSE:To carry out polymerization reaction smoothly without causing an abnormal reaction, and to obtain easily the titled material containing a highly water-absorbing resin, by impregnating a porous granular material with an acrylic acid aqueous stock solution, and heating the impregnated material so that the monomer component in the aqueous solution is polymerized. CONSTITUTION:An aqueous stock solution comprising acrylic acid as a main component, forming a highly water-absorbing resin by a radical polymerization reaction, is impregnated into a porous granular material (e.g., granular pumice, etc.), and the impregnated material is heated to polymerize a monomer component in the aqueous stock solution. The polymer is further dried to give the aimed material. The aqueous stock solution is preferably prepared by blending acrylic acid as a main component with a water-soluble copolymerizable monomer such as methacrylic acid, etc., a polyfunctional monomer such as N,N'- methylenebisacrylamide, etc., and a small amount component selected from water-soluble polymers such as CMC, etc. to become a graft main polymer of acrylic acid, and a water-soluble radical initiator such as potassium persulfate, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a material containing a super absorbent resin and having excellent water absorption and water retention properties.

Super absorbent resins absorb several hundred times their own weight in water and have excellent water retention properties, and in recent years have been used to make sanitary napkins and disposable diapers by taking advantage of this property.

It is also known that super absorbent resin is mixed into soil and applied to plant cultivation by utilizing water absorbing and water retaining properties. Various other materials are known that are characterized by water absorption and water retention properties and are made by mixing super absorbent resin powder.

The skeleton of superabsorbent resin made with acrylic acid as the main component is polyacrylic acid partially alkali gold yAi, which is made insoluble in water by introducing a moderate amount of framework. It is a substantially neutral polymer electrolyte consisting of

The key point in the production of polyacrylic acid-based superabsorbent resins is the introduction of a suitable framework; if the framework density is too low, it will partially dissolve in water, and if it is too high, the water absorption capacity will decrease. It is important to control the crosslink density, which is insoluble in water and provides high water absorption capacity. The crosslinking density is adjusted by the monomer concentration and the crosslinking agent.

The concentration of neutral acrylic acid partial alkali metal salt aqueous solution is 40
% or more, self-crosslinking effectively occurs throughout the radical polymerization. The crosslinking density is adjusted by adding a crosslinking agent as necessary. In this case, controlling the polymerization reaction of acrylic acid becomes a manufacturing problem. The polymerization reaction progresses in a short period of time, and it is difficult to remove the reaction heat, resulting in runaway and explosive reactions. As a polymerization method currently practiced industrially, there is a reverse-phase suspension polymerization method, which is a method in which an aqueous stock solution is dispersed in the form of fine water droplets in an oil phase for polymerization. Although this method is excellent in terms of reaction control, it is costly in terms of processing a large amount of organic solvent.

The feature of the present invention is that by impregnating porous granules with an acrylic acid-based aqueous stock solution and polymerizing the impregnated material, reaction heat is effectively removed and the polymerization reaction is completed in a short time without running out of control. The point is that it can be done. The impregnated material not only absorbs heat by itself, but also contacts the space over a wide area, and the water vapor generated by the heat of the polymerization reaction is easily dissipated out of the system. That is, since the heat of reaction is effectively removed as the heat of vaporization of water, the temperature of the polymerization system is substantially 100°C.
It can be kept below.

The porous granules used in the present invention may be either mineral or organic materials. Mineral materials include granular pumice, granular coal, and porous granular glass, and organic materials include rice husk, buckwheat, and wood chips (sawdust). These porous granules must not contain substances that inhibit the degree of polymerization of the aqueous stock solution, 11iC'. In such a case, the granules are purified in advance by removing polymerization inhibitors by washing with water and boiling.

The aqueous stock solution, which is applied to the present invention and which has acrylic acid as a main component and produces a superabsorbent resin through a radical polymerization reaction, is prepared as follows.

The main component is acrylic acid, and a water-soluble copolymer monomer,
One or more components selected from a crosslinkable monomer and a small amount of a water-soluble polymer that becomes the grafted backbone polymer of acrylic acid are added.

60 to 8 degrees of carboxyl groups contained in these components are neutralized as an alkali metal salt, and a water-soluble radical initiator is added to an aqueous solution having a concentration of 30 degrees or more to prepare a raw material. Examples of water-soluble copolymer components include methacrylic acid, maleic anhydride, and acrylamide. Crosslinkable monomers are added for the purpose of adjusting crosslink density, and react with polyfunctional monomers such as N,N'-methylenebisacrylamide and functional groups of polymers such as N-methylolacrylamide to form crosslinks. A monomer is used. In addition, starch,
Examples include cellulose derivatives such as CMC. These minor components are selectively added as needed. The aqueous solution consisting of the above component Kanakura is neutralized with caustic alkali to become a potash metal salt containing 60 to 80% of carboxyl groups. The water fB solution preferably has a high concentration from the viewpoint of self-crosslinking formation and economical efficiency, and is prepared to a concentration of 30 to 60%. Persulfates such as potassium persulfate are usually used as water-soluble radical polymerization initiators.

Another preferred aqueous stock solution is a system in which a water-soluble radical initiator is added to an aqueous solution of a partial alkali metal salt of acrylic acid to which the above-mentioned minor components are not added. The neutral point (pH = 7) when acrylic acid is neutralized with caustic soda is the point at which about 70% of the carboxyl groups have become sodium salts, and 60 to 80 of the carboxyl groups have become neutral as a substantially neutral aqueous solution. The summed range is used. In this case, raw a:! Since the crosslinking density of the composite is adjusted by self-crosslinking of polyacrylic acid, the concentration is 40% or more. Although the upper limit of the concentration is not particularly set, it is actually 70% or less because it is limited by the solubility of the polymerization component in water.

The proportion of the aqueous concentrate with which the porous granules are impregnated is selected depending on the purpose. Since the feature of the present invention is the control and smooth progress of the polymerization reaction, the reaction control is limited to a possible range. The proportion varies depending on the specific gravity and shape of the porous granules, but
Usually, the amount of aqueous stock solution is not more than twice that of the granular material. Since the polymerization reaction is inhibited by acid accumulation, it is preferably carried out in an inert atmosphere such as nitrogen. With persulfate total initiators, polymerization is initiated at temperatures of 70-80°C and completed within minutes.

The water-absorbing/water-retaining material containing the superabsorbent resin of the present invention is usually in the form of granules, but it can also be made into a sheet by pressing the reaction product before drying. The water-absorbing/water-retaining material has various uses, for example, when mixed with soil, it becomes a water-retaining material for plant culture.

Example 1 A stock solution was prepared by adding 0.2 parts of potassium persulfate to an aqueous solution consisting of 43 parts of acrylic acid, 45 parts of water, and 17 parts of caustic soda. This is a neutral aqueous solution in which acrylic acid 701 is neutralized with caustic soda and has a concentration of 50%.

Add 80 parts of the above aqueous stock solution to 100 parts of granular pumice with an average particle size of 3fi.
Spray the impregnated material uniformly and soak the impregnated material at 90°C with nitrogen gas.
Polymerization was carried out at a temperature of 5 minutes. During this time, the temperature of the impregnated material was kept below 100°C, and about half of the water evaporated. When the product is produced and dried, it shows a high degree of water absorption and water retention.

To measure the water absorption capacity, the dry granules were ground into a fine powder.
Part 1. ! i'? It was added to 500 g of water, left to stand for 3 hours while stirring, and then strained through an 80-mesh wire mesh.The weight of the water gel was 160 g. Resin contained in granules 1y
The water absorption capacity of this product is 560g. Example 2: 43 parts of acrylic acid, 56 parts of water, 17 parts of caustic soda, N
, 0.2 part of potassium persulfate was added to an aqueous solution consisting of 0.01 part of N'-methylenebisacrylamide to prepare a stock solution. This is a neutral aqueous solution in which 70% of the acrylic acid is neutralized with caustic soda and has a concentration of 45%.

100 parts of rice cake that has been boiled and washed with water and dried is added to the above 5. *
100 parts of the stock solution was uniformly sprayed to impregnate the sample, and the impregnated product was polymerized at a temperature of 90° C. for 5 minutes in a nitrogen atmosphere. The dried product exhibits a high degree of water absorption and water retention.

Water absorption capacity was measured in the same manner as in Example 1. 1716 (l) of water was absorbed per part of the sample, which is 500 l per resin II.
It corresponds to the water absorption capacity of g.

Example 3: Adding persulfuric acid to an aqueous solution consisting of 43 parts of acrylic acid, 49 parts of water, 17 parts of caustic soda and 4 parts of soluble starch
, 2 parts were added to prepare a stock solution. This is a neutral aqueous solution in which 70% of the acrylic acid is neutralized with caustic soda and has an RA of 50 degrees.

100 parts of sawdust that had been boiled with a 3% aqueous solution of caustic soda, neutralized with hydrochloric acid, washed with water and dried was uniformly sprayed with 140 parts of the above water-based raw material FL to impregnate it, and the impregnated product was mixed with 100 parts of sawdust in a nitrogen atmosphere.
Polymerization treatment was carried out by heating to a temperature of .degree. C. for 5 minutes. The dried product exhibits a high degree of water absorption and water retention.

1 g of the product was added to 500 g of water, opened at 10 o'clock, and then filtered through an 80-mesh wire mesh, resulting in a water gel weighing 140 g.

Claims (3)

[Claims] (1) A porous particulate material is impregnated with an aqueous stock solution containing acrylic acid as the main component and producing a superabsorbent resin through a radical polymerization reaction, and the impregnated material is heated to polymerize the monomer components contained in the aqueous stock solution. A water-absorbing and water-retaining material produced by drying. (2) The aqueous stock solution contains acrylic acid as a main component, and one or two components selected from a water-soluble copolymerizable monomer, a crosslinkable monomer, and a small amount of a water-soluble polymer that becomes a graft backbone polymer of acrylic acid. A water-soluble radical initiator is added to an aqueous solution in which 60 to 80% of the carboxyl groups contained in the component is neutralized as an alkali metal salt and the concentration is 30% by weight or more. A water-absorbing/water-retaining material according to claim 1. (3) The aqueous stock solution is obtained by adding a water-soluble radical initiator to an acrylic acid aqueous solution having a concentration of 40% by weight or more in which 60 to 80% of the carboxyl groups are neutralized as an alkali metal salt. Water-absorbing and water-retaining materials listed in scope 1.