JP2554872B2 - Method for manufacturing water-absorbing starch - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a water-absorbing starch using a starch graft copolymer having an alkali functional graft chain as a raw material.

The water-absorbent starch according to the present invention is laminated on a pulp fiber laminate in the form of dry starch or film, and is used as a napkin for absorbing menstrual blood, a tampon, a urine absorbing diaper, an auxiliary agent for enhancing performance such as bed pad, and further potted. It can be used for applications such as water retention agents and water blocking agents for civil engineering work.

(Prior Art) As a highly water-absorbent material that can be used for the above-mentioned applications,
Crosslinkable sodium polyacrylate, crosslinkable carboxymethyl cellulose, crosslinkable carboxymethyl starch, crosslinkable polyethylene oxide, alkali saponified starch-polyacrylonitrile graft copolymer, etc. are known, and particularly starch-polyacrylonitrile graft copolymer The combined alkali-saponified product exhibits high water absorption and is a highly practical substance.

The alkali-saponified product of this starch-polyacrylonitrile graft copolymer is prepared by graft-polymerizing 1.5 to 9 mol of acrylonitrile in an aqueous medium with 1 mol of starch using a ceric salt as an initiator and then saponifying with an alkali base. It is obtained as a powder and has a gelling ability of absorbing 300 times or more of water (Japanese Patent Publication No. 54-14157).

On the other hand, according to Japanese Examined Patent Publication No. 54-14157, after saponifying a starch-polyacrylonitrile graft copolymer with an alkali, the saponified product is once adjusted to have a pH of about 3 with a suitable acid to obtain a water-insoluble acid. A saponified product of starch-polyacrylonitrile copolymer is precipitated, which is isolated, washed, and again
It is disclosed to prepare the water-absorbing agent by suspending in water and readjusting to PH of about 4 to 12 by any suitable means and performing drying.

(Problems to be Solved by the Invention) A complicated production process as described above is required because after saponification, a large amount of a basic substance is contained in a solution of a saponified starch-polyacrylonitrile graft copolymer. This is because the quality of the final product, particularly the water absorption capacity, is significantly reduced unless it remains and is not removed.

After saponification, isolation and washing with water are performed to remove the residual basic substance.In this method, the saponified product of the water-insoluble acid-type starch-polyacrylonitrile graft copolymer is treated with a considerable amount of water. It exhibits swelling property, absorbs a large amount of washing water and swells, and a great amount of fuel consumption is required to remove this water, which is not preferable in terms of cost. Further, even if centrifugal dehydration or the like is performed, there is a problem in industrial production due to extremely poor filterability.

By further washing with water, impurities remaining in the saponified product of the water-insoluble acidic starch-polyacrylonitrile graft copolymer are removed, but at the same time, the graft copolymer itself is washed away during the process, and about 10% is usually collected. The rate decreases. For this reason, the production efficiency may be significantly reduced, and further, such a graft polymer may flow out into the waste water to cause a problem in environmental measures.

Such a problem is not limited to the case where the starch-polyacrylonitrile graft copolymer is used as a raw material, but the same problem occurs in other starch graft copolymers having an alkali functional graft chain. .

(Means for Solving Problems) As a result of earnest research to solve such problems, the inventors of the present invention acted a basic aqueous solution on a starch graft copolymer having an alkali functional graft chain, After introducing a hydrophilic group into the graft copolymer, the ethylenically unsaturated acid is allowed to act on the basic substance remaining in the aqueous solution containing the hydrophilic polymer for neutralization, and then a polymerization initiator is added to the hydrophilic group. The present inventors have found that a water-absorbing starch can be produced by simultaneously polymerizing and drying a mixed solution containing a water-soluble polymer at a temperature of 100 ° C. or higher, and the above problems can be solved, thus completing the present invention.

The monomer used in the present invention for performing graft polymerization on starch is not limited to acrylonitrile, but has a functional group capable of being converted into a hydrophilic group by being hydrolyzed by a base, such as acrylamide and methacrylamide. Examples thereof include those having an amide group and monomers having an ester group such as methyl acrylate, ethyl acrylate, methyl methacrylate, and ethyl methacrylate. A raw material is obtained by graft-polymerizing one or more of these monomers with starch.

A preferable polymerization initiator for performing graft polymerization on starch is a dicerium ammonium nitrate-nitric acid system, but the present invention is not limited thereto and other preferable initiators can be used by those skilled in the art.

Starch and alkali-functional monomer are in a weight ratio of 1: 0.1-
Graft polymerization is preferred at a ratio of 1: 6.

The type of starch used in the present invention is not particularly limited, and in addition to general starch such as wheat starch, corn starch, potato starch, tapioca starch, sweet potato starch, etc., etherified starch, esterified starch, crosslinked starch, oxidized starch Modified starches such as starches, acid-treated starches, dextrins and pregelatinized starches may be used, and when used, it is desirable that they be sufficiently swelled or moistened with water prior to the operation of the graft copolymer to be gelatinized.

The starch graft copolymer thus obtained is saponified with an alkali under heating in water or an aqueous solvent containing water as a main component. As the alkali to be used, hydroxides of alkali metals such as lithium hydroxide, sodium hydroxide, potassium hydroxide and the like are suitable, and the amount of the alkali to be used is 1 mol of the monomer of the side chain grafted on the starch. ,
0.3 to 2.0 mol is preferable. The amount of alkali used is 0.3
When the amount is less than the molar amount, the time required for saponification becomes long, moreover, sufficient saponification cannot be performed, and the water absorption capacity of the final product is lowered, which is not preferable. On the other hand, when the amount is 2 mol or more, the saponification time is shortened, but a large amount of alkali remains in the reaction system, and as a result, a large amount of ethylenically unsaturated acid is required, which is not preferable.

Suitably the saponification is carried out at a temperature of 70-100 ° C. for 1-5 hours.

Examples of the ethylenically unsaturated acid that acts on the residual alkali after the saponification reaction include acrylic acid, methacrylic acid, itaconic acid, and styrenesulfonic acid, but are not particularly limited thereto. The amount of these ethylenically unsaturated acids is 1.0 with respect to the number of moles of residual alkali.
~ 2.0 moles are preferred. If it is 1.0 mol or less, sufficient neutralization is not carried out, and a basic substance remains, which is not preferable. Also, 2.
If it is 0 mol or more, the pH of the water-absorbing agent becomes too low and the water-absorbing ability is lowered, which is not preferable.

The initiator to be added after saponification may be a commonly used one, and examples thereof include potassium persulfate, ammonium persulfate, hydrogen peroxide, and t-butyl peroxide. The addition amount is preferably 0.1 to 10.0% by weight based on the ethylenically unsaturated acid.
Polymerization and drying of the thus obtained mixture is carried out simultaneously on the surface of at least one roller at a temperature of 100 to 200 ° C.

(Operation) The water-absorbing agent obtained by the present invention can be produced in a very short process and has extremely high production efficiency as compared with the conventional methods. The water absorption capacity is almost the same as the conventional product, and it has a high water absorption capacity. Utilizing this property, it is used for napkins for absorbing blood, tampons, diapers for absorbing urine, sweat absorbents, bed pads, and the like.

(Examples and effects) Examples 1 to 5 25 g (anhydrous weight) of corn starch was suspended in 400 ml of water, heated to 75 ° C and maintained at this temperature for 30 minutes, and then 30
Cool to 0 ° C and add the amount of monomer shown in Table 1 to 30
Stir for 1 minute, 1N cerium ammonium nitrate nitric acid solution 15g
Was added and the reaction was carried out by stirring at 35 ° C. for 3 hours. The starch graft copolymer was separated and purified by filtration, and the graft ratio after drying is shown in Table 1.

Examples 6 to 10 The starch graft copolymers obtained in Examples 1 to 5 are suspended in water to prepare 13.0% slurry liquids. Example 6 uses the one obtained in Example 1, and
The materials obtained in Examples 2, 3, 4, and 5 are used as 8, 9, and 10, respectively. To this, a predetermined amount of alkali shown in Table 2 was added, saponification was performed at 90 ° C. for 2 hours, and then cooled to room temperature. Then, it was neutralized with the ethylenically unsaturated acid shown in the table.

The amount required for neutralization is shown in Table 3, and the type and amount of the initiator are also shown in Table 3. These were directly supplied to a double drum dryer having a surface temperature of 138 to 145 ° C to obtain a light yellow brittle film. Table 4 shows these water absorption amounts and residual monomer amounts.

As a comparative example, the water absorptivity and the amount of residual alkali of only those obtained by alkali saponifying the ones obtained in Examples 1 to 5 are shown.
Compare with the example. It is better to add the numerical value of the residual alkali amount to the examples.

Comparative Examples 1 to 5 Table 5 shows the water absorption amount and the residual alkali amount when the product was not neutralized with the ethylenically unsaturated acid and dried with a drum dryer as it is after being saponified in Examples 6 to 10.

Front Page Continuation (72) Inventor Tokushige Ogura Yumiko Isshiki Examiner, 3-329 Mitsuya Kita, Yodogawa-ku, Osaka

Claims (1)

(57) [Claims] 1. A basic aqueous solution is allowed to act on a starch graft copolymer having an alkali functional graft chain to introduce a hydrophilic group into the graft copolymer, and then an ethylenically unsaturated acid is added to the hydrophilic polymer. The hydrophilic polymer mixed solution obtained by acting on the basic substance remaining in the coalescence-containing aqueous solution to neutralize it and further adding a polymerization initiator, is characterized by simultaneously polymerizing and drying at a temperature of 100 ° C. or higher. A method for producing a water-absorbing starch.