JPH0368889B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a polymer having an excellent ability to absorb particularly body fluids (urine, sweat, menstrual blood, etc.).

In recent years, superabsorbent polymers have been used for a variety of purposes, including sanitary products such as sanitary products and diapers, agriculture and horticulture as water-retaining agents, and other applications that utilize water absorption and water-retention properties, and their usefulness is generally recognized. It's summery.

Under these circumstances, various types of superabsorbent polymers such as cellulose-based, starch-based, polyacrylate-based, and modified polyvinyl alcohol-based polymers are currently being developed. Although it exhibits a water absorption capacity of about 500 to 1000 times its own weight, the water absorption capacity in ionic aqueous solutions is significantly reduced. However, since most of these water-absorbing polymers are used in conjunction with ionic aqueous solutions, improving the water-absorbing ability in ionic aqueous solutions has become a major challenge in the technical field. The technical problem that the present inventors attempted to solve in the present invention lies precisely in this point, and as a result of intensive study on polymers that have a sufficient ability to absorb body fluids, the following production method was developed. The present invention was completed based on the discovery that the resulting polymer has superior absorbency to body fluids than existing superabsorbent polymers.

That is, the present invention involves graft polymerizing water-soluble monomers at a temperature of 60°C or lower in an aqueous solution containing natural polysaccharides xanthan gum (hereinafter referred to as XG) and locust bean gum (hereinafter referred to as LG),
The present invention relates to a method for producing a superabsorbent polymer, which comprises heating the polymerization system to 60° C. and then allowing it to cool, and is characterized as a method for producing a polymer having particularly excellent absorbency for body fluids.

The superabsorbent polymer of the present invention can be used in many fields such as sanitary products, diapers, and water retaining agents for agriculture and horticulture by utilizing its high absorbency and high water retention properties.

Conventionally, it has been known that the viscosity of an aqueous solution containing XG and LG mixed at a ratio of 6:4 to 4:6 is significantly higher than the viscosity of an aqueous solution of each of them alone. When heated and allowed to cool, a highly elastic gel is formed. Although this gel exhibits an absorption capacity for ion-exchanged water comparable to that of the existing superabsorbent polymers, its absorption capacity for ionic aqueous solutions is significantly reduced.

However, in an aqueous solution containing XG and LG, at 60℃
When a water-soluble monomer was graft-polymerized at the following temperature, and the polymerized system was then heated to 60°C or higher and allowed to cool, a polymer with better absorption ability in ionic aqueous solutions than existing superabsorbent polymers was obtained. Obtained. This graft polymer of a water-soluble monomer to a mixture of XG and LG is a new polymer, and its production method is also new.

The aqueous solution monomer used to obtain the polymer of the present invention is, for example, a monomer having a carboxyl group such as (meth)acrylic acid (acrylic acid or methacrylic acid; the same applies hereinafter), maleic anhydride; (meth)acrylic acid Sodium salt, (meth)
Monomers having a carboxyl group in the form of salts such as acrylic acid trimethylamine salt, (meth)acrylic acid triethanolamine salt, sodium maleate salt, methylamine maleate salt; vinylsulfonic acid, vinyltoluenesulfonic acid, (meth)acrylic acid A monomer having a sulfonic acid group such as sulfopropyl acid; vinyl sulfonic acid sodium salt,
Monomers containing sulfonic acid salts such as vinylsulfonic acid methylamine salt, (meth)acrylic acid sulfopropyl sodium salt, (meth)acrylic acid sulfopropyl diethanolamine salt; hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate Monomers with hydroxyl groups such as ethylene glycol monomethyl ether (meth)acrylate, monomers with ether groups such as trioxyethylene glycol (meth)acrylate; dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate Monomers having an amino group such as (meth)acrylamide, N-hexylacrylamide, N-vinylpyrrolidone, N-methylolated acrylamide, N-methylacrylamide, N,N-dimethylacrylamide; monomers having an amide group such as N, N,N-trimethyl-N-(meth)acryloyloxyethylammonium chloride,
4 such as N,N,N-triethyl-N-(meth)acryloyloxyethylammonium chloride
Examples include monomers having a class ammonium base.

As the water-soluble monomer, a mixture of two or more of the above monomers can be used, and a hydrophobic monomer can also be used in combination within a range that does not impair the water solubility of the polymer.

The polymerization method of the present invention is an aqueous solution polymerization at 60°C.
It is characterized in that graft polymerization is carried out at the following temperature, and then the temperature of the polymerization system is raised to 60°C or higher.

The polymerization initiator used may be any initiator that initiates polymerization at a temperature of 60°C or lower, but especially the second polymerization initiator.
A cerium salt-based initiator is preferred because it improves the graft polymerization rate and provides a polymer with high absorption capacity.

Further, during graft polymerization, it reacts with the water-soluble monomer to form a crosslinked structure. For example, if a compound having two or more vinyl groups in one molecule such as methylenebisacrylamide is used in combination, XG or LG
Homopolymers that are not grafted onto the gel also form a three-dimensional crosslinked structure, and this gel structure itself also contributes to absorption capacity, which is preferable.

The reason why the polymer of the present invention exhibits high absorption capacity is because
In addition to improving hydrophilicity due to the water-soluble polymer obtained by polymerizing water-soluble monomers, the linear mannose of LG is
When reacting with the helical structure of XG to adopt a conformation that is favorable for producing a type of crosslinking, the crosslinked structure is disturbed due to the water-soluble polymer grafted to XG and LG. This is thought to be due to the formation of a looser gel structure than in the case without the graft.

Hereinafter, the present invention will be explained with reference to Examples. However, since the gist of the present invention is a method for producing a superabsorbent polymer according to the claims based on the above technical idea, the present invention is based on the description of these Examples. The scope is not limited in any way by this.

Absorption capacity (ml/g) in Examples was evaluated by the following method. That is, the polymer solid content d
%) about 0.5g (xg) and put it into the test solution 1 under stirring. After stirring for 10 minutes, let it stand for 1 hour, and then
Pour the mixture onto a 100 mesh wire mesh, measure the excess liquid volume (yml), and calculate using the formula 1000-y/xd/100.

Example 1 In a separable flask equipped with a stirrer, thermometer, reflux condenser and nitrogen inlet tube,
Dissolve 2.5 g of LG in 495 ml of ion-exchanged water and replace with nitrogen.

Separately, 5 g of acrylic acid was neutralized with an equivalent amount of aqueous sodium hydroxide solution, 0.01 g of methylenebisacrylamide was added and dissolved therein, and this was added to the aqueous solution of the mixture of XG and LG, and the mixture was further replaced with nitrogen.

Next, ceric ammonium nitrate solution (1N
After adding 1.5 ml of 0.1 mol cerium ion in nitric acid and stopping nitrogen substitution, polymerization was carried out at 40 to 45°C for 2.5 hours. Thereafter, the temperature of the polymerization system was raised to 80°C, stirred for 1 hour, and then allowed to cool.

The polymer was precipitated with a large amount of isopropyl alcohol, dried under vacuum, and then ground to obtain a powdered polymer. The resulting polymer in saline (0.9
The absorption capacity for sodium chloride (wt% aqueous solution) was 150 ml/g, which was far superior to the absorption capacity of existing superabsorbent polymers (approximately 100 ml/g).

As a result of infrared spectroscopy, the produced polymer has a 1000
Characteristic absorptions of polysaccharides up to ~600 cm ^-1 and absorptions of 1420 cm ^-1 and 1560 cm ^-1 based on ionized carboxyls were observed.

On the other hand, absorption at 1420 cm ^-1 was observed in XG used for polymerization, but no absorption at 1560 cm ^-1 was observed.

Example 2 A polymer obtained by the same procedure as Example 1 except that acrylamide was used instead of a neutralized product of acrylic acid (sodium acrylate) had an absorption capacity of 134 ml/g for physiological saline. Ta.

Reference Example 1 2.5 g of XG and 2.5 g of LG were dissolved in 495 ml of ion-exchanged water, heated to 80°C, stirred for 1 hour, and then allowed to cool. The polymer was precipitated with a large amount of isopropyl alcohol, dried under vacuum, and then ground to obtain a powdered polymer. The obtained polymer had an absorption capacity of 949 ml/g for ion-exchanged water and 68 ml/g for physiological saline.

Claims (1)

[Claims] 1. A method for producing a superabsorbent polymer, which comprises graft polymerizing a water-soluble monomer at a temperature of 60°C or lower in an aqueous solution containing xanthan gum and locust bean gum, and then heating the polymerized system to 60°C or higher and allowing it to cool. .