JPH0656933A - Water-absorbing resin and its production - Google Patents

Abstract

PURPOSE:To provide a water-absorbing resin which can absorb a large amt. of water even from a water soln. contg. a salt or an org. solvent in a high concn. and is easily decomposable when it is disposed after the use. CONSTITUTION:A water-absorbing resin is prepd. by polymerizing a hydrophilic unsatd. monomer component contg. 30-100wt.% acidic monomer of the general formula (1) (wherein n is an integer of at least 1; and X is at least one group selected from the group consisting of H, a monovalent metal, NH4, NH3R1, and NH2R1R2 provided that R1 and R2 are each a group which forms the same or different primary or secondary amine) and crosslinking the resulting polymer.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a water absorbent resin and a method for producing the same. More specifically, the present invention relates to a water absorbent resin which exhibits a high water absorption capacity even for an aqueous liquid containing a large amount of salts or organic solvents, and is also excellent in decomposability upon disposal after use, and a method for producing the same. is there.

[0002]

2. Description of the Related Art In recent years, a water-absorbent resin that absorbs a large amount of water and gels has been developed as a kind of synthetic polymer, and is used in the field of sanitary materials such as paper diapers and sanitary napkins, the field of agriculture and forestry, and the field of civil engineering. Widely used.

Examples of such water-absorbent resins include crosslinked polyacrylic acid partially neutralized products, hydrolyzates of starch-acrylonitrile graft polymers, neutralized products of starch-acrylic acid graft polymers, and vinyl acetate-acrylic acid. Saponified product of ester copolymer, hydrolyzate of acrylonitrile copolymer or acrylamide copolymer, cross-linked product of cationic monomer, cross-linked product of 2-acrylamido-2-methylpropanesulfonic acid and acrylic acid, 2 -Many known are cross-linked products of sulfoethyl methacrylate, in particular,
Acrylic acid-based water-absorbent resins using acrylic acid as the main component of the monomer have become the mainstream due to the ease of availability of raw materials and their excellent water absorption properties.

Generally, these water absorbent resins can absorb pure water several hundred times their own weight or more, but their water absorption capacity is strongly influenced by the metal salts and organic solvents present in the liquid to be absorbed, and Urine and soil water containing a lot of salt, regenerator aqueous solution containing a lot of organic solvent and industrial / medical wastewater have a drawback that the water absorption coefficient is significantly reduced. I even didn't show it.

Therefore, a method using a nonionic monomer such as acrylamide or ethylene oxide as a water absorbent resin having a high water absorption capacity even with an aqueous liquid containing a large amount of salts or organic solvents (JP-A-56). -22378
No.), a method using a strongly acidic monomer such as sulfonic acid (JP-A-56-161412, JP-A-62-144748).
No.), a method using a cationic monomer such as a quaternary ammonium salt (JP-A-64-15130, JP-A-2-11).
9934, JP-A-2-242809) and the like have been reported.

However, the nonionic water-absorbent resin has a slow water absorption rate and requires several hours to several tens of hours to reach the saturated water absorption capacity. Further, the water-absorbent resin obtained from a strongly acidic monomer or a cationic monomer is unsuitable in the disposable field such as sanitary materials because the monomer itself is extremely expensive.
Since the polymerizability of the monomer is also poor, there are problems in safety and productivity.

In addition to the above-mentioned problem of water absorption capacity, much attention has recently been paid to the degradability of the water absorbent resin after use.

Recently, as one of the environmental problems, attention has been paid to the influence of the synthetic polymer on the environment after disposal and its degradability, but most of the water-absorbent resin is used in the disposable field and is equivalent to every year. Although the amount of the water-absorbent resin is discarded, the degradability of these water-absorbent resins is generally low, and it is the reality that they remain in the environment for a long time after the disposal. Known methods for decomposing the water-absorbent resin include irradiation with ultraviolet rays (JP-A-1-231983) and addition of an oxidant (JP-A-1-284507). However, these methods involve complicated steps. At present, it is necessary and the decomposition rate is low. Therefore,
Biodegradable water-absorbent resin that decomposes naturally after disposal
No. 291292) has been proposed, but not only its biodegradation rate is low, but also it is expensive and inferior in various physical properties as compared with the water-absorbent resins currently used.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and therefore an object of the present invention is to exhibit a high water absorption capacity even for an aqueous liquid containing a large amount of salts or organic solvents. It is to provide a water absorbent resin.

Another object of the present invention is to provide a water absorbent resin which can be easily decomposed at the time of disposal after use.

[0011]

Means and Actions for Solving the Problems As a result of intensive investigations by the present inventors to solve the above problems, the water-absorbent resin having a functional group of a specific structure contains a large amount of salts and organic solvents. High water absorption capacity for aqueous liquids, and
The present invention was found to be easily decomposed into a low molecular weight compound by heating after use, and the present invention has been completed.

That is, the present invention provides a "general formula (1)" as a first invention.

[0013]

[Chemical 3]

The acid group-containing monomer represented by
A method for producing a water-absorbent resin, which comprises polymerizing a hydrophilic unsaturated monomer contained in a weight percentage. And a second invention is “general formula (2)

[0015]

[Chemical 4]

A water absorbent resin in which the total amount of the components derived from the structural unit represented by is 30 to 100% by weight. It is about ". Hereinafter, the present invention will be described in more detail.

The acid group-containing monomer represented by the general formula (1) (hereinafter simply referred to as an acrylic acid oligomer (salt)), which is essential in the present invention, is an acrylic acid oligomer or an acrylic acid oligomer salt. , Β-acryloyloxypropionic acid (salt) in which n = 1, and n
Is a mixture or a single product composed of oligomeric acids (salts) which are multimers of 2 or more.

The amount of the acrylic acid oligomer (salt) used in the present invention is 30 to 100% by weight, preferably 40 to 100% by weight based on the total amount of the hydrophilic unsaturated monomer used for the polymerization.
%, More preferably 50 to 100% by weight, further preferably 70 to 100% by weight. When the amount of the acrylic acid oligomer (salt) used is less than 30% by weight, the ability to absorb water into a high salt concentration aqueous solution and the decomposability due to heating are low and insufficient,
Further, it does not show any improvement effect by absorption with respect to the aqueous solution of organic solvent.

Incidentally, in recent years, in order to prevent phase separation at the time of polymerization when producing an acrylic acid-based water-absorbing resin, a technique in which a small amount of the second monomer is present in an amount of about 5 to 20% by weight (Japanese Patent Laid-Open No. No. 165610) is proposed, and β-acryloyloxypropionic acid is exemplified as one kind of the second monomer in that case. However, the use of such a small amount of β-acryloyloxypropionic acid cannot achieve the desired effects of the present invention.

The acrylic acid oligomer (salt) that is essential to the present invention is represented by the general formula (1) as described above, and the number of n in the formula is usually about 1 to 10, preferably 1. Although a mixture of 5 to 5 or a pure product is used, when the main purpose is to absorb water or urine, it is more preferable to use an acrylic acid oligomer (salt) in which the ratio of n = 1 is 50 to 100 mol%. At this time, the acrylic acid oligomer (salt) may contain a small amount of an acid with n = 0, that is, acrylic acid, but the permissible content is acrylic acid as a copolymerization component which is appropriately used depending on the purpose. The amount should be determined according to the amount used, for example, when 70% by weight of acrylic acid is used as the copolymerization component, the acrylic acid oligomer (salt) contains 70% by weight or less of the total amount of acrylic acid. You can stay. Of course, if the content does not reach the amount used as the copolymerization component, acrylic acid which is insufficient may be added.

The acrylic acid oligomer is synthesized by known means, for example, (I) a Michael addition reaction of acrylic acid itself, (II) an esterification reaction of acrylic acid or acrylic acid chloride with 3-hydroxypropionic acid, (III) It is synthesized by a ring-opening reaction of β-propiolactone with acrylic acid, among which (I)
Is preferred. Further, if a method of separating and refining a by-product acrylic acid oligomer in the production of acrylic acid is used as a method of obtaining the acrylic acid oligomer, it is possible to produce it in a large amount at a very low cost.

The acrylic acid oligomer (salt) used in the present invention is an inexpensive raw material and, at the same time, has a higher boiling point and is less likely to volatilize than acrylic acid, which is often used as a monomer of the water-absorbent resin. And excellent in safety. Furthermore, since the acrylic acid oligomer (salt) has a structure similar to that of acrylic acid (salt), acrylic acid (salt), which is currently the mainstream, is used.
Using the manufacturing equipment and manufacturing process of the water-based water absorbent resin,
The water absorbent resin of the present invention can also be produced.

In the present invention, the above-mentioned acrylic acid oligomer (salt) is used as an essential component as the hydrophilic unsaturated monomer, but a hydrophilic monomer other than the acrylic acid oligomer (salt) may be used depending on the purpose. A monomer and / or a hydrophobic monomer may be used together as the second monomer.

The second monomer used in the present invention is not particularly limited as long as it can be copolymerized with the acrylic acid oligomer (salt), and the hydrophilic monomer is, for example, acrylic acid. , Methacrylic acid, maleic acid, maleic anhydride, fumaric acid, crotonic acid, itaconic acid, vinylsulfonic acid, styrenesulfonic acid, 2- (meth) acrylamido-2-methylpropanesulfonic acid, 2- (meth) acryloylethanesulfone Acid groups, hydrophilic monomers containing an acid group such as 2- (meth) acryloylpropanesulfonic acid, sulfoethoxypolyethylene glycol mono (meth) acrylate and salts thereof; acrylamide, methacrylamide, N-ethyl (meth) acrylamide,
N-n-propyl (meth) acrylamide, N-isopropyl (meth) acrylamide, N, N-methyl (meth) acrylamide, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, methoxy polyethylene glycol ( (Meth) acrylate, polyethylene glycol mono (meth) acrylate, vinylpyridine, N-vinylpyrrolidone, N-acryloylpiperidine, N-acryloylpyrrolidine and other nonionic hydrophilic monomers; N, N-dimethylaminoethyl (meth) Cationic agents such as acrylate, N, N-diethylaminoethyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylamide and quaternary salts thereof. Can be exemplified such as an aqueous monomer can be used alone or in combination of two or more selected from these groups. In addition, as a hydrophilic monomer, methyl (meth)
You may use the hydrophilic unsaturated monomer which forms a water absorbent resin by hydrolysis of the functional group after a polymer like acrylate, ethyl (meth) acrylate, vinyl acetate. Among these exemplified hydrophilic monomers, acrylic acid (salt), methacrylic acid (salt), 2- and the like from the viewpoint of copolymerizability with acrylic acid oligomer (salt) and various physical properties of the resulting water absorbent resin. (Meth) acryloylethanesulfonic acid (salt), 2- (meth) acrylamido-2-methylpropanesulfonic acid (salt), methoxypolyethylene glycol (meth) acrylate, N, N-dimethylaminoethyl (meth) acrylate, acrylamide Preferably
Acrylic acid (salt) is more preferable.

As the hydrophobic monomer used, styrene, vinyl chloride, butadiene, isobutene, ethylene,
Propylene, stearyl (meth) acrylate, lauryl (meth) acrylate, etc. are mentioned.

When these second monomers are used, in order not to deviate from the object of the present invention, the amount of the hydrophilic unsaturated monomer is 0 to 70% by weight, preferably 0 to 30% by weight. Good to use. In particular, when a hydrophobic monomer is used, attention should be paid to the water absorption capacity of the water absorbent resin obtained.

From the viewpoint of water absorption capacity and water absorption rate of the resulting water-absorbent resin, the acrylic acid oligomer, which is essential in the present invention, and other acid group-containing hydrophilic monomers, which are used as necessary, are used. It is preferable to use a part or all of the salt. Neutralization can be performed before or after polymerization, but it is usually preferable to neutralize before polymerization. When the main purpose is to absorb water or urine, the neutralization rate of acid groups is usually 30 to 10.
It is 0 mol%, preferably 40 to 95 mol%, and more preferably 50 to 90 mol%.

In the case of neutralizing the acid group, in order to further enhance the effect of the present invention, a neutralization method in which an acidic substance is gradually added to an excessively strong base substance, which is usually carried out industrially, is used. Instead, neutralization in an acidic region or a weakly basic region is preferable so that the acrylic acid oligomer and its polymer are not exposed to the strongly basic condition. As a method of neutralizing with acid, a neutralizing method of gradually adding a basic substance such as caustic soda to excess acrylic acid oligomer or its polymer is exemplified, and neutralization with weak acidity is also performed. Examples of the method include a neutralization method using a weak base such as carbonic acid (hydrogen) salt, ammonia, primary amine, and secondary amine.

In the present invention, a hydrophilic unsaturated monomer containing an acrylic acid oligomer (salt) as a main component is polymerized and crosslinked to obtain a water absorbent resin.

The cross-linking method used is not particularly limited. For example, after obtaining the water-soluble resin by polymerizing the hydrophilic unsaturated monomer of the present invention, a cross-linking agent is added during or after the polymerization. Post-crosslinking, radical crosslinking with a radical polymerization initiator, radiation crosslinking with an electron beam, etc. may be mentioned. However, in order to obtain a water absorbent resin having excellent performance with high productivity, a predetermined amount of the crosslinking agent is previously used. It is preferable to carry out the polymerization by adding it to the hydrophilic unsaturated monomer and carry out a crosslinking reaction simultaneously with or after the polymerization.

As the crosslinking agent used in the method of adding a predetermined amount of the crosslinking agent to the hydrophilic unsaturated monomer in advance and carrying out the polymerization reaction simultaneously with or after the polymerization, N, N
′ -Methylenebisacrylamide, (poly) ethylene glycol di (meth) acrylate, (poly) propylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, trimethylolpropane di (meth) acrylate, (poly) ethylene Glycoldi (β-acryloyloxypropionate), trimethylolpropane tri (β-acryloyloxypropionate), poly (meth) allyloxyalkane,
(Poly) ethylene glycol diglycidyl ether, ethylene glycol, polyethylene glycol, glycerin, pentaerythritol, ethylenediamine, polyethyleneimine, etc. are exemplified. The amount used is usually 0.005 to 5 mol% and more preferably 0.01 to 1 mol% with respect to the hydrophilic unsaturated monomer. Even among these cross-linking agents, due to the durability and water absorption properties of the resulting water-absorbent resin, and the handleability of the hydrogel at the time of production, the polymerizability of having two or more polymerizable unsaturated groups in the molecule It is preferable to essentially use a crosslinking agent.

When the above-mentioned hydrophilic unsaturated monomer is polymerized in the present invention, it is possible to carry out bulk polymerization or precipitation polymerization, but the hydrophilic unsaturated monomer is used because of its performance and easy control of polymerization. It is preferable to carry out the polymerization by using the monomer as a solution. The polymerization solvent is not particularly limited as long as it is a liquid in which a hydrophilic unsaturated monomer is dissolved, and examples thereof include water, methanol, ethanol, acetone, dimethylformamide, and dimethyl sulfoxide, but water or an aqueous liquid is particularly preferable. preferable. The concentration of the hydrophilic unsaturated monomer may be higher than the saturated concentration, but is usually preferably in the range of 20% by weight to the saturated concentration.

During polymerization, a water-soluble chain transfer agent such as hypophosphite, thiols and thiolic acids is used in combination to improve various properties of the water absorbent resin and further improve decomposability. Is also good. It should be noted that the presence of a synthetic or natural hydrophilic polymer such as starch, cellulose, polyvinyl alcohol, polyacrylic acid, polyacrylic acid salt cross-linked product in the polymerization does not change the gist of the present invention.

Examples of the method for polymerizing the hydrophilic unsaturated monomer in the present invention include polymerization with a radical polymerization initiator, radiation polymerization, electron beam polymerization, and ultraviolet polymerization with a photosensitizer. In order to obtain a water absorbent resin having excellent performance, polymerization with a radical polymerization initiator is preferable. Examples of the radical polymerization method include casting polymerization performed in a mold, polymerization on a belt conveyor,
Various aqueous solution polymerizations such as polymerization while subdividing a hydrous gel polymer, reverse phase suspension polymerization, reverse phase emulsion polymerization, precipitation polymerization,
Known polymerization methods such as bulk polymerization can be exemplified, but reverse phase suspension polymerization or aqueous solution polymerization is particularly preferable. In the polymerization, continuous polymerization, palindrome polymerization, and reduced pressure, increased pressure, and normal pressure are not particularly limited, and a fibrous base material may coexist during the polymerization to form a water-absorbent composite. Further, except for the initial stage of the polymerization, it is preferable that the polymerization temperature is kept substantially in the range of 0 to 130 ° C, preferably 30 to 100 ° C.

The radical polymerization initiator used for the polymerization is, for example, potassium persulfate, ammonium persulfate,
Persulfates such as sodium persulfate; Organic peroxides such as t-butyl hydroperoxide and cumene hydroperoxide; Hydrogen peroxide; Azo compounds such as 2,2′-azobis (2-amidinopropane) dihydrochloride Other examples include known initiators such as chlorite, hypochlorite, cerium salt, and permanganate. Among these, among these,
One or more selected from the group consisting of persulfates, hydrogen peroxide and azo compounds are preferable. When an oxidizing radical polymerization initiator is used, a reducing agent such as a sulfurous acid (hydrogen) salt or L-ascorbic acid may be used in combination, and when an azo polymerization initiator is used, ultraviolet rays may be used in combination. Good. In addition, these radical polymerization initiators may be added to the polymerization system all at once or may be added sequentially, but the amount used is usually 0.001 to 2 mol% relative to the hydrophilic unsaturated monomer. , And more preferably 0.01 to 1 mol%.

The gelled polymer after the polymerization is optionally dried depending on the use and the solid content after the polymerization. The drying method used includes known drying methods such as hot air drying, azeotropic dehydration in a hydrophobic organic solvent, and dehydration by adding a solvent such as methanol, and is not particularly limited.

The drying temperature in the present invention is room temperature to 150 ° C.
Is preferable, and more preferably 60 to 130 ° C. In the conventional water absorbent resin, high temperature drying at 150 to 250 ° C. is preferably used in order to improve productivity and water absorption characteristics. However, in the case of the water-absorbent resin obtained by the present invention, such high temperature drying may reduce the water-absorbing ability for an organic solvent aqueous solution or an aqueous solution having a high salt concentration and the decomposability at the time of disposal after use. It costs.

Further, in the present invention, not only the drying temperature but also the polymerization temperature and the heating temperature after the polymerization are more than 150 ° C., which is not preferable for the same reason. Therefore, the production of the water-absorbent resin in the present invention is substantially 0 to 150 ° C. when the heating operation is performed in all steps from the polymerization to the final product.
It is preferably carried out at 30 to 130 ° C. It should be noted that the temperature of the monomer at the start of the polymerization or at the very initial stage, and the temperature in the intermediate conveying step and the like may be 0 ° C. or lower, which does not matter.

The water-absorbent resin obtained as described above may be pulverized or granulated to adjust the particle size. For example, when a powder is intended, the average particle size is 10 to 2000 μm,
The thickness is more preferably 100 to 1000 μm, most preferably 300 to 600 μm. Further, the surface of the resulting water-absorbent resin is further cross-linked, or by adding a reducing agent such as a sulfite (hydrogen) salt to the water-absorbent resin before or after drying, an inert inorganic substance, or a surfactant. Its physical properties may be improved.

Further, the present invention also provides a novel water absorbent resin. That is, in the water absorbent resin of the present invention, the total amount of components derived from the structural unit represented by the general formula (2) is 30.
A novel water-absorbent resin having a proportion of ˜100% by weight,
It is a water-absorbent resin that has an unprecedented property that it has an excellent ability to absorb a certain liquid and that it is easily decomposed into a low-molecular substance when heated.

That is, the water-absorbent resin of the present invention exhibits high durability at about room temperature when it is actually used, but it easily decomposes into a low-molecular substance when left for a long time in a heated or water-containing state. The decomposition rate into low-molecular substances is greatly accelerated by heating, and 130 ° C or higher is preferable for decomposing in a short time. For example, when heated at 150 ° C for 60 minutes, 8% by weight or more decomposes into low-molecular substances. To do. Therefore, the water-absorbent resin of the present invention can be easily thermally decomposed into a low-molecular substance when discarded after use,
It is suitable for landfill processing and compost processing leading to compost. It should be noted that the combined use of an oxidizing agent, a reducing agent, ultraviolet rays, and the like when decomposing does not change the gist of the present invention.

[0042]

The water absorbent resin of the present invention and the method for producing the same have the following advantages.

(1) A water absorption capacity is dramatically higher than that of a conventional water-absorbent resin even for a high-concentration organic solvent aqueous solution.

(2) It has excellent salt resistance and shows a high water absorption capacity even in a concentrated salt concentration solution.

(3) It has high durability at room temperature, but easily decomposes into a low molecular weight compound by heating. Therefore, it is suitable for disposal after use, such as landfill processing and compost processing leading to compost.

(4) The monomer to be used can be easily produced, is inexpensive, exhibits high polymerizability and productivity, and has a high boiling point and low volatility as compared with acrylic acid.

(5) Since the monomer is an acrylic acid derivative, the conventionally widely used method for producing an acrylic acid-based water absorbent resin can be applied as it is.

[0048]

EXAMPLES The present invention will be described below with reference to examples.
The scope of the invention is not limited to only these examples. The various physical properties of the water absorbent resin described in the examples are values measured by the following test methods.

(1) Water absorption ratio As the aqueous solution to be absorbed, (a) 50% by weight isopropyl alcohol aqueous solution of organic solvent, (b) 0.9% sodium chloride aqueous solution, and high salt concentration aqueous solution ( c) 5% sodium chloride aqueous solution, (d) 10%
The water absorption capacity was measured for each of five types of aqueous sodium chloride solution and (e) 20% aqueous sodium chloride solution.

As a measuring method, a non-woven tea bag type bag (40 * 150 m) containing 0.2 g of a water absorbent resin is used.
m) was dipped in the predetermined aqueous solution of (a) to (e) for 2 hours, the tea bag bag was drained, the weight was measured, and the water absorption capacity was calculated by the following formula.

[0051]

[Equation 1]

(2) Degradability The obtained water-absorbent resin is heated at 150 ° C. for 1 hour, and the low-molecular compound decomposed and generated is quantified to obtain a low-molecular compound which is a phenomenon peculiar to the water-absorbent resin of the present invention. Was used as an index of degradability (% by weight). For reference, the amount of residual monomers in the water absorbent resin before decomposition was also measured, but all were 0.1% by weight or less. As a method for quantifying the generated low molecular weight compound, 0.5 g of the water absorbent resin is 1000 m
After stirring in 1 l of deionized water for 2 hours, the filtrate was analyzed by liquid chromatography.

[0053]

Example 1 A water absorbent resin was obtained by using β-acryloyloxypropionic acid as the acid group-containing monomer represented by the general formula (1).

That is, after dissolving the acid group-containing monomer consisting of 29.81 g of β-acryloyloxypropionic acid and 9.06 g of acrylic acid in 51.62 g of water, a 48% by weight aqueous solution of sodium hydroxide was added while cooling with ice. 19.41g
Was gradually added to neutralize the acid groups so that the pH was always acidic. Next, 0.01 mol% (relative to all monomers) of polyethylene glycol diacrylate (n = 8) was dissolved as a crosslinking agent in the neutralized solution. Thus, a hydrophilic unsaturated monomer aqueous solution containing 75% by weight of the monomer represented by the general formula (1) and having a concentration of 40% and a neutralization ratio of 70% was obtained.

Separately, 500 ml of 4 equipped with a stirrer, a reflux condenser, a thermometer, a nitrogen gas introducing pipe and a dropping funnel.
A two-necked separable flask was prepared as a reaction vessel, and 200 ml of cyclohexane and 1.0 g of sorbitan monostearate (HLB4.7) were put therein, and the atmosphere was replaced with nitrogen.

Next, after substituting the hydrophilic unsaturated monomer with nitrogen, 0.05 mol of sodium persulfate (relative to the monomer) was dissolved, added to the separable flask and dispersed with stirring. Then, by heating the cyclohexane phase to 60 ° C., the polymerization of the hydrophilic unsaturated monomer is started, and the polymerization is further continued for 2 hours, and then the obtained hydrous gel is azeotropically dehydrated. Further, it was dried under reduced pressure at 60 ° C. Table 1 shows the physical properties of the water absorbent resin 1 thus obtained.

[0057]

Example 2 Instead of the hydrophilic unsaturated monomer in Example 1, 23.85 g of β-acryloyloxypropionic acid and 14.50 acrylic acid were added to 50.25 g of water.
After dissolving g, 48 wt% caustic soda aqueous solution 2
Neutralize with 1.41 g, and 0.01 mol% polyethylene glycol diacrylate (n = 8) as a crosslinking agent.
(Vs total monomer) Dissolved to contain 60% by weight of the monomer represented by the general formula (1), concentration 40%, neutralization rate 7
0% of hydrophilic unsaturated monomer was obtained.

Thereafter, polymerization was carried out in the same manner as in Example 1, followed by azeotropic dehydration and vacuum drying to obtain a water absorbent resin 2. The results are shown in Table 1.

[0059]

Example 3 Instead of the hydrophilic unsaturated monomer in Example 1, 15.90 g of β-acryloyloxypropionic acid and 21.75 acrylic acid were added to 48.33 g of water.
After dissolving g, 48 wt% caustic soda aqueous solution 2
Neutralization with 4.06 g, 0.01 mol% polyethylene glycol diacrylate (n = 8) as a crosslinking agent
(To all monomers) By dissolving, 40% by weight of the monomer represented by the general formula (1) is contained at a concentration of 40% and a neutralization rate of 7
0% of hydrophilic unsaturated monomer was obtained.

Thereafter, polymerization was carried out in the same manner as in Example 1, followed by azeotropic dehydration and vacuum drying to obtain a water absorbent resin 3. The results are shown in Table 1.

[0061]

Example 4 Instead of the hydrophilic unsaturated monomer in Example 1, 25.39 g of β-acryloyloxypropionic acid and 8.56 g of acrylic acid were added to 58.83 g of water.
After being dissolved, a 48 wt% caustic soda aqueous solution 17.
It was neutralized with 22 g, and polyethylene glycol di (β-acryloyloxypropionate) (n
= 7) is dissolved by 0.05 mol% (relative to the monomer) to contain 73 wt% of the monomer represented by the general formula (1) at a concentration of 35% and a neutralization rate of 70%. A monomer was obtained.

Polymerization was carried out in the same manner as in Example 1 except that the above monomers were used and the dispersant was changed from sorbitan monostearate to ethyl cellulose.
Further, water-absorbent resin 4 was obtained by azeotropic dehydration and vacuum drying. The results are shown in Table 1.

[0063]

Comparative Example 1 A water absorbent resin was obtained by using acrylic acid without using the acid group-containing monomer represented by the general formula (1).

That is, in the preparation of the hydrophilic unsaturated monomer of Example 1, 36.25 g of acrylic acid was added to 44.38 g of water.
After being dissolved in water, a 48 wt% caustic soda aqueous solution 29.
Neutralization with 37 g and 0.01 mol% of polyethylene glycol diacrylate (n = 8) as a cross-linking agent (relative to monomer) were dissolved to obtain a hydrophilic hydrophilic acrylate salt having a concentration of 40% and a neutralization rate of 70%. Aqueous unsaturated monomer aqueous solution was obtained.

Thereafter, polymerization was carried out in the same manner as in Example 1, followed by azeotropic dehydration and vacuum drying to obtain comparative water absorbent resin 1. The results are shown in Table 1.

[0066]

Comparative Example 2 A water absorbent resin was obtained from a hydrophilic unsaturated monomer having a small amount of acid group-containing monomer represented by the general formula (1).

That is, in the preparation of the hydrophilic unsaturated monomer of Example 1, 7.95 g of β-acryloyloxypropionic acid and 29.00 of acrylic acid were added to 46.33 g of water.
After dissolving g, 48 wt% caustic soda aqueous solution 2
Neutralize with 6.71 g, and 0.01 mol% polyethylene glycol diacrylate (n = 8) as a crosslinking agent.
(To Monomer) By being dissolved, the concentration of the monomer represented by the general formula (1) is 20% by weight, the concentration is 40%, and the neutralization rate is 70.
% Hydrophilically unsaturated monomer was obtained.

Thereafter, polymerization was carried out in the same manner as in Example 1, followed by azeotropic dehydration and vacuum drying to obtain comparative water absorbent resin 2. The results are shown in Table 1.

[0069]

Comparative Example 3 A water absorbent resin was obtained from a sulfonic acid group-containing acid group-containing monomer.

That is, in the preparation of the hydrophilic unsaturated monomer of Example 1, 110 g of a sulfoethyl methacrylate sodium salt aqueous solution having a neutralization rate of 75% and a concentration of 40% was further added with polyethylene glycol diacrylate (n
= 8) was dissolved in 0.01 mol% (relative to the monomer) to obtain a hydrophilic unsaturated monomer.

Thereafter, polymerization was carried out in the same manner as in Example 1, followed by azeotropic dehydration and drying under reduced pressure to obtain a comparative water absorbent resin 3. The results are shown in Table 1.

[0072]

[Table 1]

As is clear from Table 1, the water-absorbent resin of the present invention has a high ability to absorb physiological saline, and moreover, (1) 50 compared with the comparative water-absorbent resin which is a conventional water-absorbent resin. %
It has a high water absorption capacity even for aqueous solutions containing a large amount of salts and organic solvents such as isopropanol aqueous solution and (2) 20% sodium chloride aqueous solution, and (3) easily decomposes into low molecular weight compounds by heating. .

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshihiko Masuda 1 992, Nishioki, Okihama, Aboshi-ku, Himeji-shi, Hyogo 1

Claims (5)

[Claims] 1. A general formula (1): A method for producing a water-absorbent resin, comprising polymerizing a hydrophilic unsaturated monomer containing the acid group-containing monomer represented by the above in a proportion of 30 to 100% by weight. 2. The production method according to claim 1, wherein a polymerizable crosslinking agent is allowed to coexist during the polymerization. 3. The production method according to claim 1, wherein the polymerization is carried out under a temperature condition of substantially 30 to 100 ° C. 4. The production method according to claim 1, wherein the polymerization is carried out by reverse phase suspension polymerization or aqueous solution polymerization. 5. A general formula (2): The total amount of components derived from the structural unit represented by
Water-absorbent resin in a proportion of 0% by weight.