JPS63165402A - Production of light-fast and water absorbing resin - Google Patents

Abstract

PURPOSE:To obtain a resin, having excellent water absorbing property and providing a gel extremely stable even when exposed to light, by carrying out a water-in-oil type reversed phase suspension polymerization method in the presence of a benzophenone based ultraviolet ray absorber in polymerizing an acrylic acid monomer. CONSTITUTION:An acrylic acid monomer consisting essentially of (meth)acrylic acid and alkali metal or ammonium salts thereof is polymerized by using a water-soluble radical initiator, e.g. hydrogen peroxide, tert-butyl hydroperoxide, etc., in an amount of normally 0.1-2wt.% based on the acrylic monomer. In the process, polymerization is carried out in the presence of a benzophenone based ultraviolet ray absorber, e.g. 2,4-dihydroxybenzophenone, etc., by a water- in-oil type reversed phase suspension polymerizaion method to afford the aimed resin. The above-mentioned resin absorbs a large amount of water to swell, but is insoluble in water.

Description

[Detailed Description of the Invention] [Background of the Invention] [Industrial Field of Application] The present invention relates to a method for producing a water-absorbing resin that has excellent water absorption and is extremely stable even when the absorbed gel is exposed to light. .

The light-resistant water-absorbing resin of the present invention absorbs a large amount of water and swells, but is water-insoluble and the absorbed gel is extremely stable against light. It can be advantageously used in the production of various materials that are used in a swollen state.

[Prior art]

In recent years, various highly water-absorbent polymeric materials that absorb water tens to hundreds of times their own weight have been proposed.

For example, starch graft polymer (Japanese Patent Publication No. 53-46199
Publications, etc.), cellulose-modified materials (JP-A-50-8037)
6, etc.), crosslinked products of water-soluble polymers (Japanese Patent Publication No. 43-2)
3462, etc.), self-crosslinking type acrylic acid alkali metal salt polymers (Japanese Patent Publication No. 54-30710, etc.), and these are used as absorbents for sanitary products, disposable diapers, etc., or for agricultural and horticultural purposes. It is being developed for use as a water retention agent, sludge coagulant, dew condensation prevention agent for building materials, water stop agent for civil engineering, desiccant, etc.

However, although these superabsorbent polymer materials have an excellent ability to absorb a large amount of water and excellent stability over time when dry, they have extremely poor stability when water is absorbed. For example, if a gel-like material that absorbs water is exposed to sunlight, it will deteriorate and become fluid in just a few hours.
It becomes impossible to maintain the form of the gel-like product, which is a major problem especially when the above-mentioned superabsorbent resins are used in water retention agents for agriculture and horticulture, water stop agents for civil engineering, and the like.

As a method to improve such light resistance, there is a method of mixing carbon black or activated carbon with super absorbent resin (Japanese Patent Laid-Open No. 59-1999).
-38271) and a water-insoluble water absorbent resin obtained by polymerizing an acrylic acid monomer with a sulfoalkyl (meth)acrylate monomer as a comonomer together with a crosslinking agent (Japanese Patent Application Laid-Open No. 61-36309). Although it has been proposed that the method is effective, the effect is small and still insufficient, which poses a problem in practice.

[Summary of the invention]

[Problems to be Solved by the Invention] The present invention provides a water-retaining agent which improves the above-mentioned drawbacks and significantly improves photostability upon absorption of water while retaining water-absorbing properties.

[Means for solving problems]

As a result of various studies to solve the above-mentioned problems, the present invention was developed by polymerizing an acrylic acid monomer in the presence of a benzophenone ultraviolet absorber by a water-in-oil reverse phase suspension polymerization method. In addition, the present invention was completed based on the discovery that a superabsorbent resin whose gelatinized product upon absorption of water is extremely stable against light can be obtained.

That is, in the method for producing a light-resistant water-absorbing resin according to the present invention, a water-absorbing resin is produced by polymerizing acrylic acid and/or methacrylic acid and their alkali metal salts or ammonium salts using a water-soluble radical initiator. The present invention is characterized in that the polymerization is carried out in the presence of a benzophenone ultraviolet absorber by a water-in-oil reverse phase suspension polymerization method.

〔Effect of the invention〕

As is clear from Examples 5 and 6, the light-resistant water-absorbing resin obtained by the method of the present invention is extremely stable against ultraviolet rays. - Therefore, the water-absorbing resin obtained in the present invention can be advantageously used particularly as a soil conditioner, a water retention agent for agriculture and horticulture, a water stopper for civil engineering, etc. by taking advantage of its excellent light resistance.

[Detailed description of the invention]

Monomer 1 The monomer used in the polymerization reaction of the present invention is mainly composed of acrylic acid and/or methacrylic acid and their alkali metal salts or ammonium salts. A specific example of such an acrylic acid monomer is one in which 20% or more, preferably 50% or more of the total carboxyl groups are neutralized with an alkali metal salt or an ammonium salt. If the degree of neutralization in this case becomes too low, the amount of water absorbed will drop significantly and the strength of the resulting water-absorbing gel will also be extremely low.

The upper limit of the degree of neutralization is about 90%.

Alkali metal hydroxides, bicarbonates, etc. can be used as alkaline agents for neutralizing acid monomers into alkali metal salts, but alkali metal hydroxides are preferable, and specific examples include hydroxides, bicarbonates, etc. Sodium oxide, potassium hydroxide,
and lithium hydroxide. Sodium hydroxide is most preferred in terms of industrial availability, price, and safety.

In addition, in the present invention, as seven polymers other than the above, (a) itaconic acid, maleic acid, fumaric acid, 2-acrylamido-2-methylpropanesulfonic acid, 2-acryloylethanesulfonic acid, 2-acryloylpropanesulfonic acid, and its salts, (b) alkyl or alkoxy esters of dicarboxylic acids such as itaconic acid, maleic acid, and fumaric acid, (c) (meth)acrylamide, (d) vinyl sulfonic acid, (v) acrylic acid methyl ester, acrylic acid Ethyl ester, etc., (meth)acrylic acid hydroxyethyl ester, (meth)acrylic acid hydroxypropyl ester, (g)polyethylene glycol mono(meth)acrylate, N-methylol (meth)acrylamide, glycidyl (meth)acrylate, etc. Monomers having a copolymerizable double bond in the molecule such as, other crosslinking agents such as N,N'-methylenebis(meth)acrylamide, polyethylene glycol di(meth)acrylate, polybrobylene glycol di(meth)acrylate,
Those having two or more copolymerizable double bonds in the molecule such as glycerin tri(meth)acrylate, etc., or ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, di- or polyhydric alcohols, etc. A functional group in an acrylic acid monomer such as glycidyl ether, for example, a functional group that reacts with a carboxyl group during polymerization or during drying after polymerization.
It is also possible to use compounds having more than one compound.

Ultraviolet absorber The ultraviolet absorber used in the present invention is a benzophenone compound, examples of which include 2,4-dihydroxybenzophenone, 2-hydroxy-4-methoxybenzophenone, and 2-hydroxy-4-octoxybenzophenone. , 2-hydroxy-4-dodecyloxybenzophenone, 2,2'-dihydroxy-4,4'-dimethoxybenzophenone, 2-hydroxy-4-methoxy-5-
Examples include sulfobenzophenone, 2-hydroxy-9-glycidoxybenzophenone, 2-hydroxy-4-methacryloxybenzophenone, and the like. Among these, 2,4-dihydroxybenzophenone is particularly preferred.

The amount of these ultraviolet absorbers added is preferably 0.1 to 10% by weight based on the acrylic acid monomer.

If it is less than 0.1% by weight, the effect of addition is small, and if it exceeds 10% by weight, no noticeable effect of addition is observed, and it is not advantageous in terms of cost.

These UV absorbers can be added to the polymerization system by adding them into an aqueous solution of acrylic acid monomers, by adding them into an inert solvent together with a protective colloid (details will be described later), or by adding an aqueous solution of acrylic acid monomers into an aqueous solution of an acrylic acid monomer in the presence of a protective colloid. This can be carried out by, for example, adding the substance to a suspension in an inert solvent. Generally, it is preferable to add the protective colloid to an inert solvent, then add an acrylic acid monomer, and polymerize.

Water-in-oil type reverse-phase suspension polymerization The polymerization method used in the present invention is a water-in-oil type reverse-phase suspension polymerization method, in which an aqueous solution of the monomers and polymerization initiator (details will be described later) as described above is used during the polymerization reaction. This can be carried out using a protective colloid and an inert solvent that can form a stable water-in-oil dispersion.

To give a specific example, (1) using a copolymer of α-olefin and α,β-unsaturated polycarboxylic acid anhydride or a derivative thereof as a protective colloid, and using a hydrocarbon solvent in the presence of hydroxyethyl cellulose; Method of use (Special application 1986)
0-234878 and Japanese Patent Application No. 60-234877), (2) A method using a sorbitan aliphatic acid ester with an HLB of 3 to 6 as a protective colloid and a petroleum-based aliphatic hydrocarbon solvent (Japanese Patent Publication No. 1983- Publication No. 30710),
(3) A method using an oil-soluble cellulose ester or cellulose ether as a protective colloid and a hydrocarbon solvent (JP-A-58-32607); (4) A nonionic surfactant with an HLB of 6 to 9 as a protective colloid. method using a hydrocarbon solvent (Japanese Patent Application Laid-Open No. 57-1
67302), (5) HLB as a protective colloid
8 to 12 nonionic surfactants and an alicyclic or aliphatic hydrocarbon solvent; (6) a basic nitrogen-containing polymer as a protective colloid and a hydrocarbon solvent (especially Publication No. 57-98513), (7
) A method using a carboxyl group-containing polymer as a protective colloid and a hydrocarbon solvent (JP-A-57-9401)
1), (8) A method using sucrose fatty acid ester as a protective colloid and a hydrophobic organic solvent (Japanese Unexamined Patent Publication No. 6
1-43606, JP-A-61-87702), (9) as a protective colloid (A) 50 to 97 mol% of styrene and/or its alkyl-substituted derivative, (B) dialkylaminoalkyl-acrylate or -methacrylate and/or using a copolymer consisting of 3 to 50 mol% of dialkylaminoalkyl-acrylamide or methacrylamide and 0 to 30 mol% of an unsaturated monomer that can be copolymerized with (C), (A) and (B). , a method using a hydrophobic organic solvent (JP-A-61-40309),
(10) Sorbitan fatty acid ester and/or sucrose fatty acid ester as a protective colloid, and (A) 50 to 97 mol% of styrene and/or its alkyl-substituted derivative;
(B) dialkylaminoalkyl-acrylate or -methacrylate and/or dialkylaminoalkyl-acrylamide or monomethacrylamide 3-5
A method using a hydrophobic organic solvent using a copolymer consisting of 0 mol % and (C) 0 to 30 mol % of an unsaturated monomer copolymerizable with the above (A) and (B) (Japanese Patent Laid-Open No. 61 -5330
(11) HLB3-9 as a protective colloid
using a mixture of sorbitan fatty acid ester and polyoxyalkylene monoether type nonionic surfactant,
Examples include a method using a hydrophobic solvent (Japanese Unexamined Patent Publication No. 61-97301). Among these, the method (1) using a copolymer of α-olefin and α,β-unsaturated polycarboxylic acid or a derivative thereof as the protective colloid and using a hydrocarbon solvent in the presence of hydroxyethylcellulose (especially Application No. 60-234878, Special Application No. 60-23
4877) is mentioned as a suitable polymerization method.

In addition, the water-soluble radical initiators used in the present invention include hydrogen peroxide, persulfates such as ammonium persulfate and potassium persulfate, hydroperoxides such as t-butyl hydroperoxide and cumene hydroperoxide, and azoisoisomers. Azo initiators such as butyronitrile and 2,2'-azobis(2-amidinopropane) dihydrochloride are used. These water-soluble radical polymerization initiators may also be used as a redox type initiator in combination with reducing substances such as sodium bisulfite, amines, and the like. The amount of these water-soluble radical initiators used is 0.01 to 10% by weight, preferably 0.1 to 10% by weight based on the acrylic acid monomer.
211i amount%.

An example of a preferred specific embodiment of the manufacturing method of the present invention is as follows. That is, acrylic acid and/or
Alternatively, methacrylic acid is neutralized to form an aqueous alkali metal salt solution or an aqueous ammonium salt solution, and a crosslinking agent, a radical polymerization initiator, etc. are added thereto to obtain an aqueous acrylic acid monomer solution.

Separately, a protective colloid and a benzophenone compound are added and dissolved in an inert solvent. The above acrylic acid monomer aqueous solution is added to this and polymerized. The polymer after polymerization is obtained in a wet state as a slurry in an inert solvent, and after separation from the inert solvent by decantation, evaporation, etc., it can be dried to obtain a powder.

EXPERIMENTAL EXAMPLES The present invention will be further explained in detail with reference to Examples and Comparative Examples.

Example 1 375 g of cyclohexane was placed in a 1 liter round bottom flask equipped with a stirrer, reflux condenser, thermometer and nitrogen gas inlet tube, and 4.5 g of cyclohexane was added.
3.3 g of 2,4-dihydroxybenzophenone was added thereto, and dissolved oxygen was expelled by blowing in nitrogen gas.

Separately, in a flask with a capacity of 500 ml, acrylic acid 75
31.2 g of caustic soda dissolved in 201 g of water was added to the 74 g of carboxyl group while cooling with water externally.
．． Neutralized 9%. Next, 0.05% of N,N'-methylenebisacrylamide was added to this. After adding and dissolving 0.26 g of potassium persulfate, nitrogen gas was blown in to drive out dissolved oxygen.

The contents of this 500 ml flask were added to the contents of the four-bottle flask described above, and the contents were heated at 65-72°C for 3 hours with stirring.
Polymerized for hours.

When stirring was stopped after 3 hours of reaction, the wet polymer particles settled to the bottom of the flask and could be easily separated from the cyclohexane phase by decantation. The separated wet polymer was transferred to a vacuum dryer and heated to 80-90°C.
Remove adhering cyclohexane and water and apply water retaining agent (1
) was obtained.

Example 2 Acrylic acid 70 instead of acrylic acid in Example 1
．． Using a mixture of
) was obtained.

Example 3 185 g of cyclohexane was placed in a 500 ml four-day round bottom flask equipped with a stirrer, reflux condenser, thermometer, and nitrogen gas inlet tube, and α-olefin-maleic anhydride copolymer (Mitsubishi Chemical Co., Ltd.) was added to the flask. 1.8 g (molecular weight: about 10.000) and 1.0 g of 2,4-dihydroxybenzophenone were added, and the internal temperature was brought to 65° C. under a nitrogen gas atmosphere.

Separately, in a conical flask with a capacity of 200 m1, 30 g of acrylic acid was added to 63.1 g of water while cooling from the outside. 12.9. of caustic soda was added to neutralize 77.4% of the carboxyl groups.

Next, 0.0% of N,N'-methylenebisacrylamide was added to this. 015 tr, hydroxyethyl cellulose (
Degree of etherification -1, number of moles of EO added -2) 9 g of O and 0.1 g of potassium persulfate were added and dissolved.

Add this 200ml to the contents of the four-day round bottom flask.
The contents of the flask were added, and polymerization was carried out at 65 to 70° C. for about 1 hour while stirring.

When stirring was stopped after 1 hour of reaction, the wet polymer particles settled to the bottom of the flask and could be easily separated from the cyclohexane phase by decantation. The separated wet polymer was transferred to a vacuum dryer and heated at 80 to 90°C to remove the attached cyclohexane and water, forming a water retention agent (3).
I got it.

Example 4 Water retention agent (4) was obtained by polymerizing in the same manner as in Example 3 except that 2-hydroxy-4-methacryloxybenzophenone was used instead of 2,4-dihydroxybenzophenone.

Comparative Examples 1 to 3 Water retention agents (5) to (7) were obtained by polymerizing in the same manner as in Examples 1 to 3, except that the benzophenone compound was not added.

Example 5 Water retention agent (1) obtained in Examples 1 to 4 and Comparative Examples 1 to 3
Take 1g of ~(7) and add 100g of water to each.
It was swollen with. 20 g of each of the obtained gels was placed in graduated bottles and irradiated with light using a lamp (400 W).

Table 1 shows the polymerization ratio of the remaining gel after 8 hours of irradiation.

Example 6 The same gel as shown in Example 5 was left outdoors for about 2 days at the same time.

Table 2 shows the weight percentage of the remaining gel at that time.

It should be noted that the weather was clear for the two days the plant was left unattended.

Table 1 Table 2

Claims (1)

[Claims] 1. Acrylic acid and/or
Alternatively, when producing a water-absorbing resin by polymerizing acrylic acid monomers whose main components are methacrylic acid and their alkali metal salts or ammonium salts, the polymerization is carried out in the presence of a benzophenone ultraviolet absorber using a water-in-oil reverse phase method. A method for producing a light-resistant water-absorbing resin, which is carried out by a suspension polymerization method. 2. The production method according to claim 1, wherein the acrylic acid monomer has 20% or more of its total carboxyl groups neutralized with an alkali metal salt or an ammonium salt. 3. The ultraviolet absorber is 2,4-dihydroxybenzophenone, and a copolymer of α-olefin and α,β-unsaturated polycarboxylic acid anhydride or Claims 1 to 1 are carried out using the derivative in the presence of hydroxyethyl cellulose.
The manufacturing method according to any one of Section 2.