JP2002302513A - Acrylate-based polymer and sanitary material using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an acrylate-based polymer which scarcely contains residual monomers and hardly produces or increases the residual monomers even under various use conditions. SOLUTION: This acrylate-based polymer has a residual monomer content of <=160 ppm, comprises 50 to 100 mol % of the repeating units of an acrylate and 0 to 50 mol % of the repeating units of a hydrophilic unsaturated monomer and/or a hydrophobic unsaturated monomer, has a neutralization rate of 30 to 100 mol %, is a water-absorbable resin having a cross-linked structure, has a further cross-linked area in the vicinity of the surface, and contains β- hydroxypropionic acid and its salt in a total content of <=1,000 ppm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an acrylate polymer and a sanitary material using the same. More specifically, the present invention relates to a partially neutralized or completely neutralized acrylate polymer in which the amount of residual monomer is small and little generation or increase of the residual monomer is observed even under various use conditions, and a sanitary material using the same. Things.

The acrylate-based polymer of the present invention can be easily and inexpensively produced, and has excellent performance and safety, so that it can be used in a wide range of fields as a water-absorbing resin or a water-soluble resin.

[0003]

2. Description of the Related Art Hydrophilic resins are generally classified into two types, water-soluble resins and water-absorbent resins, depending on their solubility in water.

A water-soluble resin is a hydrophilic resin that dissolves in water and is used as a coagulant for water treatment, an oil drilling additive, a food additive, a thickener, and the like. For example, sodium polyacrylate (Japanese Patent Publication No. Sho 48) -42466, Japanese Patent Publication No. 42-9656
No.), polyacrylic acid, polyacrylamide (JP-A-5
4-145782, JP-A-57-18652), 2
-Acrylamide-2-methylpropanesulfonic acid polymer (JP-A-2-173108), polyacrylamide partial hydrolyzate (JP-A-52-137483), acrylic acid-acrylamide copolymer (JP-A-59-1983) Fifteen
No. 417), (meth) acrylic acid-itaconic acid copolymer (JP-A-58-91709), polyvinyl alcohol and the like are known.

[0005] The water-absorbing resin is a water-insoluble hydrophilic resin that gels upon absorbing water, and is widely used in the field of sanitary materials such as disposable diapers and sanitary napkins, as well as in the fields of agriculture, forestry and civil engineering. For example, a crosslinked product of partially neutralized polyacrylic acid (JP-A-55-84304, JP-A-55-84304)
-108407, JP-A-55-133413), a hydrolyzate of a starch-acrylonitrile graft polymer (JP-A-46-43995), and a neutralized product of a starch-acrylic acid graft polymer (JP-A-51-413) No. 125468), a saponified product of a vinyl acetate-acrylic acid ester copolymer (JP-A-52-14689), a hydrolyzed product of an acrylonitrile copolymer or an acrylamide copolymer (JP-A-5353)
No. 15959), cross-linked products thereof, and cross-linked products of cationic monomers (JP-A-58-154709 and JP-A-58-154710).

As described above, many monomers have been proposed as monomers for obtaining these hydrophilic resins. However, from the viewpoint of performance and cost, acrylates that are partially or completely neutralized (hereinafter, referred to as "neutralized acrylates") have been proposed. Acrylate) is the mainstream, and acrylate-based polymers containing acrylate as a main component are produced today in large quantities in both water-absorbent resins and water-soluble resins. It is widely used in sanitary materials and foods. However, in these acrylate-based polymers, residual monomers such as unpolymerized acrylic acid (salt) usually remain in the order of 500 to 3000 ppm, and it is presently required to reduce the residual monomers. Further, among these hydrophilic resins, the water-absorbing resin is used for sanitary materials and the like. Therefore, it is particularly required to reduce the residual monomer, and in recent years, it has been required to reduce the residual monomer to 100 ppm or less. However, since the water-absorbing resin has an essential crosslinked structure, it is difficult to perform uniform polymerization or uniform mixing of additives and organic solvents for reducing residual monomers after polymerization, and acrylates have a medium pH. As you approach sex,
Since the polymerization rate is slow, it has been particularly difficult to reduce residual monomers among water-absorbent resins that require a neutral or crosslinked structure among these hydrophilic resins.

Conventionally, attempts to reduce the residual monomer of the hydrophilic resin have been studied for a long time in the field of polymer flocculants and the like. With respect to hydrophilic resins, studies have been made to reduce residual monomers.

[0008] These known techniques include the following (a) to
(F) It is roughly classified into six types.

(A) As a method for improving the polymerization rate of the polymer itself and reducing the residual monomer, for example, increasing the amount of a polymerization initiator and using a composite initiator (JP-A-50-96689)
No.), increase in reaction temperature, increase in polymerization concentration, extension of polymerization time, and specification of aging conditions (JP-A-53-145895).
No.), two-stage addition of a polymerization initiator (JP-A-56-72005).
No.), irradiation with radiation after polymerization (JP-A-63-43930)
No.), UV irradiation after polymerization (JP-A-63-260906)
No.) and the like.

(B) As a method of adding an additive for reducing residual monomers after polymerization, for example, a method of post-adding a primary or secondary amine (JP-A-50-40689)
No.), a method of post-adding sulfur dioxide (USP-3780)
No. 006) and a method of post-adding an alkali metabisulfite (JP-A-55-135110).

(C) As a method of extracting the residual monomer, for example, a method of extracting with a hydrophilic organic solvent (Japanese Patent Laid-Open No.
No. 292003), and a method of performing supercritical extraction using carbon dioxide.

(D) As a method of adding a microorganism that degrades the residual monomer, for example, a method of decomposing the residual acrylamide by the microorganism (Japanese Patent Publication No. 60-29523)
And the like.

(E) As a method of volatilizing the residual monomer at a high temperature, for example, a method of volatilizing the residual acrylonitrile at a high temperature (JP-A-54-119588) can be mentioned.

(F) A method focusing on the water-soluble unsaturated monomer before polymerization has been proposed in recent years. For example, a method of polymerizing using an acrylate obtained by a specific neutralization method (Japanese Patent Laid-Open No. No. 2-209906) and a method of polymerizing using a monomer having a small amount of heavy metal (JP-A-3-31306).

However, in the method (a), the effect of reducing the residual monomer is insufficient. Generally, not only 0.03% or more remains but also self-crosslinking of the hydrophilic resin due to severe polymerization or post-treatment conditions. Inevitably, a decrease in the basic molecular weight, an increase in the water-soluble content of the water-absorbent resin, a decrease in the gel strength, etc.
It was a fact that the physical properties of the desired hydrophilic resin were reduced. Moreover, the addition of the polymerization initiator in two stages or the use of a large amount of the polymerization initiator may leave the polymerization initiator, which is not preferable in terms of safety.

In the methods (b) and (c), the possibility of reducing the residual monomer to 0.03% or less is also described, but the process is complicated and the additives and organic compounds to be used are reduced. Solvents and the like may remain in the hydrophilic resin. Moreover, since the acrylate does not dissolve in an organic solvent such as methanol, the effect of reducing the residual monomer by the method (c) is limited.

Furthermore, the method (d) is not only industrially difficult because of the use of microorganisms, but it is not safe to use such microorganisms. In the method (e), various physical properties may be reduced due to high temperatures, and the acrylate does not volatilize even at high temperatures, so that the effect of reducing residual monomers can hardly be expected. Was. Furthermore, even when the method (f) was used, the effect of reducing the residual monomer was still insufficient.

As described above, even if these methods are used, the effects are not only insufficient, but also complicated steps are required, and it is actually accompanied by a decrease in productivity and various physical properties and a significant increase in cost. Met. Moreover, even with these methods, the residual monomers of the acrylate-based polymer are merely reduced apparently, and it has never been possible to suppress the increase in the residual monomers after the polymerization described below.

That is, the inventors of the present invention have observed that during the production process of the acrylate polymer or during use thereafter, several tens to several thousand ppm of residual monomers are generated and increased in the acrylate polymer. Was found. That is, in the conventional acrylate-based polymer, it was also found that a large amount of the residual monomer actually increases with time even if the residual monomer is apparently reduced to about several hundred ppm. This increase over time is significant when heat is applied. Therefore, in these conventional acrylate-based polymers, even if the residual monomer is at least, for example, when a further heating step is required, or when used for a long time in agriculture and horticulture or at a high temperature such as hot water, etc. Needless to say, this is not preferable in terms of safety because the amount of residual monomers increases.

Regarding the production of the acrylate polymer, crosslinking in the vicinity of the surface of the acrylate polymer is widely performed in order to further improve various physical properties after the polymerization. As an improvement,
At present, many improvements are still being proposed.

For example, as a surface cross-linking method using a specific surface cross-linking agent, a method using a polyhydric alcohol (Japanese Unexamined Patent Publication No.
0-17328, JP-A-61-16903), a method using an alkylene carbonate (DE-402078).
0C), using glyoxal (JP-A-52-1)
17393), a method using a polyvalent metal (Japanese Patent Laid-Open No.
JP-A-136588, JP-A-61-257235, JP-A-62-7745), a method using a silane coupling agent (JP-A-61-211305, JP-A-61-252).
No. 212, JP-A-61-264006) and the like. As a method of surface cross-linking under specific reaction conditions, for example, a method of cross-linking by dispersing a water-absorbent resin in a mixed solvent of water and a hydrophilic organic solvent (JP-A-57-44627)
), A method of crosslinking by dispersing a water-absorbing resin in an inert solvent in the presence of a specific amount of water (JP-A-58-117222).
No.), a method in which inorganic powder and water coexist and crosslink (USP-
4587308) and a method of irradiating electromagnetic radiation (Japanese Patent Application Laid-Open No. 63-43930) are known.

However, in the course of studying the improvement of the surface cross-linking of the acrylate-based polymer, the present inventors discovered that the residual monomer in the acrylate-based polymer, which had not been known at all, was subjected to surface cross-linking. From 10 to 100
ppm, and found that the increase in residual monomer due to such surface crosslinking accounts for a large proportion of the residual monomer in the final product.

[0023]

SUMMARY OF THE INVENTION The present invention has been made in view of the above situation. Therefore, an object of the present invention is to reduce residual monomers, and even after polymerization,
In the acrylate-based polymer, which was found to have a peculiar phenomenon that the residual monomer is further generated and increased during the manufacturing process and use, it shows excellent physical properties, the residual monomer is small, and the generation and increase of the residual monomer are almost An object of the present invention is to provide an acrylate-based polymer that cannot be seen and a sanitary material using the same. Another object of the present invention is to improve various physical properties by cross-linking the surface of the acrylate-based polymer, exhibit excellent physical properties, reduce the amount of residual monomers, and furthermore, hardly generate or increase residual monomers. An object of the present invention is to provide a crosslinked acrylate polymer and a sanitary material using the same.

[0024]

As a result of diligent studies to achieve the above object, the present inventors have found that the conventional acrylate-based polymer having a large amount of residual monomer and a large amount of the residual monomer are increased. In conventional acrylate-based polymers, β-hydroxypropionic acid (salt) contains a few thousand ppm to 1% as a minor component other than the residual monomer.
The fact was found before and after, and the fact that there was a correlation between the content of β-hydroxypropionic acid (salt) and the residual monomer.

Therefore, the inventors of the present invention, as a means for solving the above-mentioned problems, consider the importance of β-hydroxypropionic acid (salt) contained in a small amount in an acrylate-based monomer, which has not received much attention. And solved the above problem by controlling the content thereof, thereby completing the present invention.

That is, the present invention relates to (1) an "acrylate polymer having a residual monomer content of 160 ppm or less, wherein 50 to 100 mol% of acrylate and 0 to 50 mol% of other A water-absorbent resin having a neutralization ratio of 30 to 100 mol% and having a repeating unit of a hydrophilic unsaturated monomer and / or a hydrophobic unsaturated monomer, wherein the polymer is a water-absorbing resin having a crosslinked structure. Yes,
The vicinity of the surface of the polymer is further crosslinked, and the total content of β-hydroxypropionic acid and its salt is 1,000.
An acrylate-based polymer having a content of not more than ppm. It is about.

According to the present invention, (2) the residual monomer amount is 1
An acrylate polymer having a content of not more than 60 ppm, wherein 50 to 100 mol% of an acrylate and 0 to 50 mol% of another hydrophilic unsaturated monomer and / or a hydrophobic unsaturated monomer in the polymer. Is an acrylate polymer having a neutralization ratio of 30 to 100 mol% having a repeating unit of
The polymer is a water-absorbent resin having a crosslinked structure, the surface of the polymer is further crosslinked, and the resulting acrylate polymer is further heated at 180 ° C. for 3 hours. 30 ppm of residual monomer
The present invention relates to an acrylate polymer characterized by the following.

[0028]

(Equation 2)

The present invention relates to (3) the acrylate-based polymer according to the above (1) or (2), wherein the vicinity of the surface of the polymer is crosslinked with a polyhydric alcohol.

According to the present invention, (4) the residual monomer amount is 1
An acrylic acid-based polymer having a content of 60 pppm or less, and 50 to 100 mol% of an acrylate and 0 to 50 mol% of another hydrophilic unsaturated monomer and / or a hydrophobic unsaturated monomer in the polymer Is a acrylate-based polymer having a neutralization ratio of 30 to 100 mol% having a repeating unit of a body, wherein the polymer is a dried water-absorbent resin having a crosslinked structure and having an average particle diameter of 100 to 1000 μm, and near the surface of the polymer. Is further crosslinked with a polyhydric alcohol, and the total content of β-hydroxypropionic acid and its salt is 10
The present invention relates to an acrylate-based polymer of not more than 00 ppm.

The present invention provides (5) the acrylic acid according to any one of the above (1) to (4), wherein the acrylate is a sodium acrylate or a potassium acrylate. It relates to a salt-based polymer.

The invention of the present application is characterized in that (6) the water-absorbent resin is a powder having an average particle diameter of 300 to 600 μm.
It relates to the polymer according to any one of (5).

The present invention provides (7) the above (1) to (6)
The present invention relates to a sanitary material using the acrylate polymer according to any one of the above.

The present invention provides (8) a neutralization ratio of 30 to 100.
When preparing a water-soluble unsaturated monomer containing 50 to 100 mol% of an acrylate salt and then polymerizing to prepare an acrylate polymer, the total of β-hydroxypropionic acid and its salt is 1, The present invention relates to a method for producing an acrylate polymer, which comprises using a water-soluble unsaturated monomer containing 000 ppm or less.

The present invention provides (9) a neutralization ratio of 30 to 100.
After preparing a water-soluble unsaturated monomer containing 50 to 100 mol% of an acrylate of 50 mol%, it is polymerized and cross-linked in the vicinity of the surface of the obtained acrylate-based polymer to form a cross-linked acrylic in the vicinity of the surface. In producing the acid salt polymer, β-
The total of hydroxypropionic acid and its salts is
The present invention relates to a method for producing a crosslinked acrylate-based polymer near the surface, characterized by using an acrylate-based polymer obtained by preparing and then polymerizing a water-soluble unsaturated monomer containing 0 ppm or less. is there.

The present invention relates to (10) the method of (10) wherein the crosslink near the surface is a polyhydric alcohol, a polyhydric epoxy compound, a polyvalent amine compound, a polyvalent aziridine compound, an alkylene carbonate compound, a polyhydric aldehyde, a polyvalent isocyanate compound, (9) The method for producing an acrylate polymer according to the above (9), wherein at least one type of a surface cross-linking agent selected from the group consisting of a oxazoline compound, a haloepoxy compound, and a polyvalent metal salt is used. It is about.

The present invention relates to (11) the above (9) or (1), wherein the polymer is a water-absorbing resin having a crosslinked structure.
0) A method for producing the polymer described in the above.

The present invention relates to (12) the water-absorbent resin,
The above (1) which is a powder having an average particle size of 300 to 600 μm.
The present invention relates to a method for producing a polymer described in 1).

The present invention provides (13) the acrylate-based polymer according to any one of the above (8) to (12), wherein the acrylate-based polymer or a dried product thereof is heat-treated. And a method for producing the same.

The present invention relates to (14) the method for producing an acrylate polymer according to the above (10), wherein the surface crosslinking agent is a polyhydric alcohol.

According to the present invention, (15) the heat treatment temperature is 1
The method according to the above (13), wherein the temperature is from 00 to 300 ° C.

The present invention provides the production of the acrylate polymer according to any one of the above (8) to (15), wherein (16) the total content of β-hydroxypropionic acid and a salt thereof is 100 ppm or less. It is about the method.

The present invention relates to (17) the method for producing an acrylate polymer according to any one of the above (8) to (16), wherein the acrylate is a sodium acrylate or a potassium acrylate. Things.

The present invention is characterized in that (18) the water-soluble unsaturated monomer is polymerized within 24 hours after preparation.
The present invention relates to the production method according to any one of the above (8) to (17).

The invention of the present application is characterized in that (19) acrylic acid is used for neutralization or preparation of a water-soluble unsaturated monomer within 24 hours after purification by distillation. The present invention relates to any one of the manufacturing methods.

In the present invention, (20) in the neutralization step of acrylic acid, the neutralization rate is at least 100 mol% for at least one time.
(8)-
(19) The method according to any one of (19).

The present invention relates to (21) the production method according to any one of the above (8) to (20), wherein the acrylate polymer after polymerization is further dried at 130 ° C. or higher. It is.

The present invention provides (22) a neutralization ratio of 30 to 10
After preparing a water-soluble unsaturated monomer containing 50 to 100 mol% of acrylate of 0 mol%, polymerization was carried out, and the vicinity of the surface of the obtained acrylate polymer was cross-linked to thereby cross-link the vicinity of the surface. In producing an acrylate polymer, the obtained polymer is a water-absorbing resin having a crosslinked structure, and a water-soluble unsaturated monomer containing a total content of β-hydroxypropionic acid and a salt thereof of 1,000 ppm or less. Is used for polymerization and dried after polymerization to obtain an average particle diameter of 100 to 1
Acrylic acid salt obtained by obtaining a water-absorbent resin having a crosslinked structure of 000 μm, further adding a polyhydric alcohol as a surface cross-linking agent near the surface of the water-absorbent resin, and performing heat treatment at 100 to 300 ° C The present invention relates to a method for producing a polymer.

According to the present invention, (23) the heating temperature is 150
The present invention relates to the method for producing an acrylate polymer according to the above (22), wherein the temperature is up to 230 ° C.

Hereinafter, the present invention will be described in more detail.

In the present invention, the proportion of the acrylate in the water-soluble unsaturated monomer used for the polymerization is from 50 to 100.
Mole% is essential. (Note that the acrylate in the present invention refers to the sum of unneutralized acrylic acid and neutralized acrylate (that is, partially neutralized or completely neutralized acrylate)). In the present invention, since the residual monomer reduction effect is exhibited more, the ratio of the acrylate salt of the present invention is more preferably 70 to 100 mol%, furthermore 90 to 100 mol%.
Mol%. When the content of the acrylate is less than 50 mol%, not only the performance is lowered and the cost is increased,
The effect of the present invention is hardly exhibited, and in some cases, the residual monomer may be increased, which is not preferable.

The neutralization rate of the acrylate used for the water-soluble unsaturated monomer is essential to be 30 to 100 mol%. If the neutralization ratio is out of this range, there may be cases where various physical properties are reduced and residual monomers are increased. (Note that the neutralization rate of the acrylate in the present invention may be the neutralization rate of the acrylate used for the preparation of the water-soluble unsaturated monomer, or may be mixed with another monomer if necessary. After neutralization of acrylate in water-soluble unsaturated monomer). Furthermore, when the water-soluble unsaturated monomer of the present invention is used, the residual monomer is more remarkably reduced as compared with the conventional method, so that a more preferable neutralization ratio is 40 to 95 mol%, furthermore 50 to 80 mol%. It is.

The water-soluble unsaturated monomer used in the present invention is prepared by converting an acrylate having a neutralization ratio of 30 to 100 mol% to 50 to 100 mol%.
100 mol%, but other 0-50 mol%
The hydrophilic unsaturated monomer and / or the hydrophobic unsaturated monomer may be used.

As the hydrophilic unsaturated monomer which can be used in the range of 0 to 50 mol% if necessary, for example, methacrylic acid, maleic acid, maleic anhydride, fumaric acid,
Acids such as crotonic acid, itaconic acid, vinylsulfonic acid, styrenesulfonic acid, 2- (meth) acrylamido-2-methylpropanesulfonic acid, 2- (meth) acryloylethanesulfonic acid, and 2- (meth) acryloylpropanesulfonic acid Group-containing hydrophilic unsaturated monomers and salts thereof; acrylamide, methacrylamide, N
-Ethyl (meth) acrylamide, Nn-propyl (meth) acrylamide, N-isopropyl (meth) acrylamide, N, N-dimethyl (meth) acrylamide, 2-hydroxyethyl (meth) acrylate, 2-
Nonionic hydrophilic unsaturated monomers such as hydroxypropyl (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, polyethylene glycol mono (meth) acrylate, vinylpyridine, N-vinylpyrrolidone, N-acryloylpiperidine, and N-acryloylpyrrolidine N, N-dimethylaminoethyl (meth) acrylate, N, N-diethylaminoethyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylamide and Examples thereof include cationic hydrophilic unsaturated monomers such as quaternary salts thereof, and one or more kinds selected from these groups can be used. Further, as the hydrophilic unsaturated monomer, methyl (meth) acrylate, ethyl (meth) acrylate,
An unsaturated monomer that forms a hydrophilic resin by hydrolysis of a functional group, such as vinyl acetate, may be used.

Among these, methacrylic acid (salt), 2- (meth) acryloylethanesulfonic acid (salt), 2- (meth) as the hydrophilic unsaturated monomer used in the present invention at 0 to 50 mol%. Acrylamide-2-methylpropanesulfonic acid (salt), methoxypolyethylene glycol (meth) acrylate, N, N-dimethylaminoethyl (meth) acrylate, and acrylamide are preferred.

The hydrophobic unsaturated monomer which can be used in the range of 0 to 50 mol% if necessary includes, for example, styrene, vinyl chloride, butadiene, isobutene,
Examples include ethylene, propylene, stearyl (meth) acrylate, and lauryl (meth) acrylate.
These hydrophobic unsaturated monomers have a content of 0 to 50 in all the monomers.
Mol%, preferably 0 to 20 mol%, more preferably 0 mol%.
-10 mol% are used.

The neutralization of a water-soluble unsaturated monomer containing 50 to 100 mol% of an acrylate having a neutralization ratio of 30 to 100 mol% is performed only when preparing the water-soluble unsaturated monomer. It may be further neutralized during or after the polymerization of the water-soluble monomer adjusted to the above range.

In the present invention, the neutralization ratio as described above is 30 to
In preparing a water-soluble unsaturated monomer containing 50 to 100 mol% of an acrylate salt of 100 mol%, β-hydroxypropionic acid and its salt per water-soluble unsaturated monomer (hereinafter, both are combined) , Simply referred to as β-hydroxypropionic acid.) Is essential to prepare a water-soluble unsaturated monomer having a content of 1000 ppm or less.

In the present invention, the content of β-hydroxypropionic acid in the water-soluble unsaturated monomer is essential to be not more than 1000 ppm per solid, preferably not more than 500 ppm, more preferably not more than 300 ppm. Most preferably, it is 100 ppm or less. When the content of β-hydroxypropionic acid exceeds 1000 ppm, the obtained acrylate-based polymer has a large amount of residual monomers, and further residual monomers are generated in a subsequent manufacturing process, at a high temperature, or for a long time. In addition to the phenomenon of increase, the physical properties of the acrylate polymer may be insufficient, which is not preferable.

In the present invention, the content of β-hydroxypropionic acid in the water-soluble unsaturated monomer used for the polymerization is 100%.
The amount may be limited to 0 ppm or less, and the means for preparing such a water-soluble unsaturated monomer is not particularly limited, but one example of a preferred specific embodiment is as follows.

Acrylic acid is used for neutralization and preparation of a water-soluble unsaturated monomer within as short a time as possible after distillation purification, for example, within 24 hours, preferably 12 hours, more preferably within 6 hours. In the neutralization step, a state where the neutralization ratio exceeds 100 mol% is passed at least for one period. Next, a water-soluble unsaturated monomer is prepared using the acrylic acid, the obtained acrylate, and other monomers as required.
Finally, the obtained water-soluble unsaturated monomer is as short as possible, for example, 24 hours after the completion of the preparation of the water-soluble unsaturated monomer,
The polymerization may be carried out preferably within 12 hours, more preferably within 6 hours, particularly preferably within 2 hours. Further, it is preferable that the acrylic acid after distillation purification is kept at a temperature as low as possible, for example, 30 ° C. or lower, preferably a freezing point to 25 ° C., until it is used for neutralization or preparation of a water-soluble unsaturated monomer. The neutralization step is preferably performed at low temperature for a short time, preferably within 4 hours. If acrylic acid after distillation is kept for a relatively long time, it is preferable to keep it in a non-aqueous state. Further, the water-soluble unsaturated monomer after completion of the preparation should be stored at a temperature from its freezing point to 40 ° C or lower, preferably 0 to 30 ° C.
If these conditions are not satisfied, β-hydroxypropionic acid and residual monomers tend to increase, and thus care must be taken.

Acrylic acid is stored and shipped after the final distillation at the acrylic acid plant, so it takes 4 to 5 days, usually several tens to several months, before it is actually used industrially by the user. It is the present situation. In addition, since water-soluble unsaturated monomers are prepared and stored in large quantities at factories,
An average of 3 days or more elapses from the end of the preparation to the actual use, and several hours are required for the deaeration time of the water-soluble unsaturated monomer and the temperature adjustment time during the polymerization. Is the actual situation. However, the present inventor believes that the longer the time after the acrylic acid distillation purification and the longer the time from the completion of the preparation of the water-soluble unsaturated monomer to the time of polymerization, the β-hydroxypropionic acid and the residual monomer Is found to increase, and therefore, in the present invention, the polymerization is preferably performed in a short time.

Examples of the basic substance used for neutralizing acrylic acid include known ones such as carbonic acid (hydrogen) salt, alkali metal hydroxide, ammonia, and organic amine. It doesn't matter. However, among these basic substances, in order to obtain an acrylate polymer having excellent physical properties and a reduced residual monomer, it is necessary to use at least a strong basic substance such as sodium hydroxide or potassium hydroxide. Is preferred, and sodium hydroxide is particularly preferred.

At least during the neutralization step, the simplest method of neutralizing acrylic acid under conditions where the neutralization rate of acrylic acid exceeds 100 mol% is (1) a neutralization reaction system. There is a method in which acrylic acid is gradually added to a certain amount of a basic substance while cooling. Further, as another method, disclosed in Japanese Patent Application Laid-Open No. 2-209906,
(2) After the neutralization rate of the acrylate in the neutralization system is maintained at less than 100 mol% from the start of neutralization, and after the neutralization rate exceeds 100 mol% during the neutralization, And a method of finally adjusting the neutralization ratio to 30 to 100 mol%.

The temperature of the acrylate solution in these neutralization steps is preferably kept at 0 to 50 ° C. by cooling.
In order to obtain an acrylate having a low content of β-hydroxypropionic acid, the neutralization method (1) is preferably carried out at a lower temperature than the conventional method, preferably at a temperature of 10 ° C. or lower. This leads to a decrease in sex. However, in the neutralization method (2), as long as the above-mentioned acrylic acid is used, the content of β-hydroxypropionic acid can be rapidly reduced to a high level of 100 ppm or less quickly.

In the present invention, it is preferable that the content of β-hydroxypropionic acid is small, but if the content is reduced to 100 ppm or less, the acrylate polymer desired by the present invention can be sufficiently obtained. Is obtained,
Even if the content is reduced to less than 10 ppm, particularly to about 1 ppm, no remarkable influence on various physical properties such as residual monomers is observed. In addition, in order to make the content of β-hydroxypropionic acid less than 1 ppm or undetectable, extremely difficult purification and production steps are required, which is generally uneconomical. The content is not harmful.

In the present invention, it is essential to use the water-soluble unsaturated monomer having a low content of β-hydroxypropionic acid obtained as described above. It can be a water-absorbing resin. For water-absorbent resins where it is difficult to reduce residual monomers,
The method for producing an acrylate polymer of the present invention is suitably used.

The crosslinking method used is not particularly limited. For example, (A) a water-soluble resin is obtained by polymerizing the water-soluble unsaturated monomer of the present invention, and then during or after polymerization. And (B) radical crosslinking with a radical polymerization initiator, (C) radiation crosslinking with an electron beam, etc., to obtain a water absorbent resin having excellent performance with good productivity. Preferably, (D) a predetermined amount of an internal crosslinking agent is added to a water-soluble unsaturated monomer in advance to carry out polymerization, and a crosslinking reaction is carried out simultaneously with or after the polymerization.

Examples of the internal crosslinking agent used in the method (D) include 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 glycol di (β-acryloyloxypropionate), trimethylolpropane tri (β-acryloyloxypropionate), poly ( (Meth) allyloxyalkane, (poly) ethylene glycol diglycidyl ether, ethylene glycol, polyethylene glycol, glycerin, pentaerythritol,
One or more internal crosslinking agents such as ethylenediamine and polyethyleneimine are used, and the amount thereof is usually 0.005 to 5 mol%, more preferably 0.1 to 5 mol%, based on the water-soluble unsaturated monomer. 01 to 1 mol%. In addition,
Among these internal cross-linking agents, polymerizable internal cross-linking having two or more polymerizable unsaturated groups in the molecule due to the durability and water absorption properties of the resulting water-absorbing resin, and the handling properties of the hydrogel during production. It is preferable to use an agent indispensably.

In the polymerization, the water-soluble unsaturated monomer of the present invention may be subjected to bulk polymerization or precipitation polymerization as it is, but it is preferable to perform polymerization as a solution from the viewpoint of performance and easy control of polymerization. . The polymerization solvent is not particularly limited as long as it is a liquid in which the water-soluble unsaturated monomer is dissolved, and examples thereof include water, methanol, ethanol, acetone, dimethylformamide, and dimethylsulfoxide. Is particularly preferred. When the water-soluble unsaturated monomer is polymerized as a solution, the concentration thereof is not particularly limited and may be higher than the saturation concentration. concentration,
Preferably it is in the range of 25 to 50% by weight. In addition, at the time of polymerization, water-soluble unsaturated monomers may be added to water-soluble chain transfer agents such as hypophosphorous acid (salt), thiols, thiolic acid (salt), starch, cellulose and derivatives thereof, polyvinyl alcohol, A hydrophilic polymer such as polyacrylic acid or a crosslinked polyacrylate may be added. Their usage is usually less than 5 parts by weight for the former and less than 50 parts by weight for the latter.

The water-soluble unsaturated monomer having a β-hydroxypropionic acid content of 1000 ppm or less obtained above is then polymerized. In the present invention, as described above, the water-soluble unsaturated monomer after completion of the preparation is preferably polymerized in as short a time as possible.

Examples of the polymerization method used in the present invention include (a) polymerization with a radical polymerization initiator, (b) radiation polymerization, (c) electron beam polymerization, and (d) ultraviolet polymerization with a photosensitizer. Although known methods can be mentioned, in order to obtain an acrylate-based polymer having excellent performance,
(A) Polymerization with a radical polymerization initiator is preferred.

As the polymerization method (a), for example, casting polymerization performed in a mold (Japanese Patent Publication No. Sho 48-42466),
Polymerization on a belt conveyor (JP-A-58-49714)
), Polymerization carried out while subdividing a hydrogel polymer (JP-A-57-34101), polymerization under pressure (JP-A No.
-129207), reversed-phase suspension polymerization (JP-B-59-37003), reverse-phase emulsion polymerization (JP-A-63-90510, JP-A-63-90537),
Precipitation polymerization (JP-A-58-84819, JP-A-1-17)
No. 10, JP-A-1-204910) and known polymerization methods such as bulk polymerization, but reversed-phase suspension polymerization or aqueous solution polymerization is particularly preferred. During the polymerization, continuous polymerization,
The distinction between semi-batch polymerization, batch polymerization, and decompression, pressurization, and normal pressure is not particularly limited. Further, a fiber base material and the like may coexist at the time of polymerization to form a water-absorbing composite (JP-A-2-242).
975).

Examples of the radical polymerization initiator used in the polymerization include persulfates such as potassium persulfate, ammonium persulfate and sodium persulfate; organic peroxides such as t-butyl hydroperoxide and cumene hydroperoxide. Hydrogen peroxide; 2,2′-azobis (2
Azo compounds such as -amidinopropane) dihydrochloride; and other known polymerization initiators such as chlorite, hypochlorite, ceric salt, and permanganate. One or two or more selected from the group consisting of sulfates, hydrogen peroxide and azo compounds are preferred. Also,
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 or the like is used, ultraviolet light may be used in combination. Incidentally, these radical polymerization initiators and the like may be added to the polymerization system all at once, or may be added sequentially,
The amount used is usually 0.0
It is from 0.01 to 2 mol%, preferably from 0.01 to 1 mol%. In addition, by using the water-soluble unsaturated monomer of the present invention, the amount of the residual monomer can be reduced even with the use amount of the radical polymerization initiator smaller than usual, so that the polymerization can be easily controlled and the obtained acrylate-based polymer can be obtained. Are also preferable because the various physical properties of the above are further improved.

When the polymerization is carried out using a water-soluble unsaturated monomer as a solution, the acrylate-based polymer after polymerization may be used as it is, but it is preferable to dry it in order to improve the handleability and reduce the residual monomer. .

The drying method used in the present invention includes known means. For example, a method in which polymerization is carried out at a high concentration and drying and polymerization are carried out simultaneously by heat of polymerization (Japanese Patent Application Laid-Open No. 58-71907, (Japanese Unexamined Patent Publication No. 2-34607), or the obtained gel polymer may be further dried depending on the solid content after polymerization. In the case of further drying, for example, drying under high humidity conditions (Japanese Patent Laid-Open No. 1-2660)
No. 4), azeotropic dehydration in an organic solvent, microwave drying, belt or drum dryer heated to a predetermined temperature, drying in a cylinder equipped with a high-speed rotor (JP-A-2-240112), and others. Forced ventilator, infrared,
Drying can be performed using a vacuum dryer or the like.

The drying temperature in the present invention is usually from 70 to 2
It is in the range of 30C, preferably 110-220C, more preferably 150-210C. When the temperature is out of this range, the effect of using the water-soluble unsaturated monomer of the present invention is difficult to appear, and in some cases, the residual monomer may increase, and various physical properties and productivity may decrease. The drying time depends on the water content and particle size of the gel polymer, the drying temperature, etc.
It is determined as appropriate.

As described above, the present inventors have found an increase in residual monomers during drying, and it has been found that the use of the water-soluble unsaturated monomer of the present invention makes it possible to obtain residual monomers for any polymerization method, drying temperature and drying time for the first time. An acrylate-based polymer having excellent physical properties and containing few monomers can be obtained.

The acrylate polymer of the present invention thus obtained may be used as it is.
Further, the particle size may be adjusted by pulverization or granulation. The target particle size varies depending on the type and purpose of use of the acrylate polymer, but in the case of a powdery water-absorbing resin, usually,
Average particle size 10 to 2000 μm, more preferably 100
１０００1000 μm, most preferably about 300-600 μm. Further, various inorganic powders, oxidizing agents, reducing agents, fragrances, fertilizers, binders, water and the like may be further added to the obtained acrylate polymer.

Further, the method of the present invention for producing an acrylate polymer having a crosslinked surface is provided by crosslinking the vicinity of the surface of the acrylate polymer obtained by the above method.

As an acrylate polymer that crosslinks near the surface, the content of β-hydroxypropionic acid is 10%.
When an acrylate-based polymer obtained from a water-soluble unsaturated monomer exceeding 00 ppm is used, the residual monomer increases due to surface cross-linking, not only adversely affecting safety but also deteriorating various physical properties. Is not preferred.

As the water content of the acrylate polymer used, the acrylate polymer after polymerization may be used as it is. However, from the viewpoint of the surface crosslinking effect, the water content is usually 40% or less, more preferably the water content. An acrylate polymer dried to a water content of 30% or less, more preferably 10% or less, is preferred. Further, as the particle size of the acrylate polymer used, the average particle size is 10 to 200
It is about 0 μm, more preferably about 100 to 1000 μm, and most preferably about 300 to 600 μm, and its particle size distribution is preferably narrow. The acrylate polymer used may be a water-soluble resin, but the effect of improving various physical properties by surface cross-linking is more clearly exhibited with respect to the acrylate water-absorbent resin.

In the present invention, the cross-linking in the vicinity of the surface of the acrylate polymer may be carried out by radiation or the like, but it is usually carried out by adding a surface cross-linking agent in the vicinity of the surface.
As the surface cross-linking agent to be used, known ones are exemplified without particular limitation, for example, ethylene glycol, propylene glycol, polyethylene glycol, propylene glycol, glycerin, polyglycerin, 1,6-hexanediol, trimethylolpropane, diethanolamine, Various polyhydric alcohols such as triethanolamine, polyoxypropylene, oxyethyleneoxypropylene block copolymer, pentaerythritol, sorbitol; various polyhydric epoxy compounds such as ethylene glycol diglycidyl ether and polyethylene glycol diglycidyl ether; ethylene diamine; Various polyamine compounds such as polyethyleneimine; 2,2-
Bishydroxymethylbutanol-tris (3- (1-
Polyvalent aziridine compounds such as aziridinyl) propionate; 1,3-dioxolan-2-one, 4-methyl1.3-dioxolan-2-one, 4,6-dimethyl-1,3-dioxan-2-one Various polyalkylene aldehyde compounds such as glyoxal; polyvalent isocyanate compounds such as 2,4-tolylene diisocyanate; polyvalent oxazoline compounds such as 1,2-ethylenebisoxazoline; epichlorohydrin Haloepoxy compound; aluminum,
Polyhydric metal salts such as hydroxides and chlorides such as iron and zirconium; and compounds having a combination of these functional groups can also be exemplified.

In the present invention, among these surface cross-linking agents, one selected from the group consisting of polyhydric alcohols, polyglycidyl compounds, polyamines, and alkylene carbonates is used.
It is more preferable to use one or more kinds, and in the effect of the present invention, a polyhydric alcohol is most preferable. The amount of the surface cross-linking agent varies depending on the cross-linking conditions to be used and the like. The range is 10 parts by weight.

Known methods are used for adding a surface cross-linking agent to the acrylate polymer, for example, a method of directly adding the surface cross-linking agent to the acrylate polymer, or a method of dispersing the acrylate in a solvent. A method of adding a surface cross-linking agent to the system polymer is exemplified. In the former case,
In this case, an inorganic compound (USP-4587308) such as silicon oxide fine powder or a surfactant may be further used in combination for uniform addition of a surface cross-linking agent. It may be performed as steam (Japanese Patent Laid-Open No. 1-297430). As the latter method, there are a method of dispersing an acrylate polymer in a hydrophilic organic solvent (JP-A-57-44627) and a method of dispersing an acrylate polymer in a hydrophobic solvent (JP-A-59-44659). -62665) and the like, and in this case,
It is preferred that a specific amount of water coexist.
117222).

When the surface cross-linking agent is added to the acrylate polymer, the surface cross-linking agent may be added as a solution or a dispersion. As the solvent to be used, for example, hydrophilic organic solvents such as methyl alcohol, ethyl alcohol, n-propyl alcohol, iso-propyl alcohol, acetone, and tetrahydrofuran, and water are preferable. The amount used is generally in the range of 0 to 20 parts by weight, preferably 0 to 8 parts by weight, based on 100 parts by weight of the solid content of the acrylate polymer.

In performing surface cross-linking in the present invention, the presence of water is preferred from the viewpoint of the surface treatment effect.
When using a substantially dried acrylate polymer, it is preferable to add water. The addition of water may be performed simultaneously with the surface crosslinking agent or may be performed separately, but the amount thereof is based on 100 parts by weight of the solid content of the acrylate polymer.
Usually, it is 20 parts by weight or less, preferably 0.5 to 10 parts by weight.

After mixing the acrylate polymer and the surface cross-linking agent according to the above-mentioned method, the surface cross-linking method of the present invention is preferably subjected to a heat treatment in view of various physical properties and residual monomers.

When the acrylate polymer of the present invention is used, the heat treatment temperature is usually 75 ° C. or higher, preferably 1 ° C.
The temperature is in the range of 00 to 300 ° C, more preferably 120 to 250 ° C, and still more preferably 150 to 230 ° C. When the temperature is out of the above range, various physical properties are deteriorated, and the effect of using the acrylate-based polymer of the present invention may not be easily exhibited. The heating time is appropriately determined depending on the intended surface crosslinking effect, heating temperature, and the like, but is usually in the range of 1 minute to 10 hours.

In the present invention, as the method of performing the heat treatment, any known means can be used without limitation. For example, (1) a surface cross-linking agent or a solution thereof is directly added to an acrylate polymer and then heat-treated as it is. Examples of the method include (2) a method of adding a surface cross-linking agent to a acrylate-based polymer dispersed in a solvent and then performing a heat treatment while keeping the dispersion, and (3) a method of performing a heat treatment by filtering from a dispersion medium. But
Because of the ease of heating, safety, cost and productivity,
The method (1) is preferred. In addition, there is no restriction | limiting in particular about a heat processing apparatus, A well-known apparatus, such as a hot-air dryer, a fluidized-bed dryer, and a Nauter type dryer, is used.

As described above, this time, the present inventors have found an increase in residual monomers due to surface cross-linking, and for the first time by using the acrylate polymer of the present invention, an acrylic resin having excellent physical properties with little residual monomers is obtained by any surface cross-linking method. An acid salt polymer was obtained.

The acrylate polymer of the present invention obtained before or after surface crosslinking obtained as described above has not only a low residual monomer content of 100 ppm or less, but also a β-
It is a novel acrylate polymer having a reduced content of hydroxypropionic acid. The content of β-hydroxypropionic acid of the present invention is 1 to 1000 ppm, preferably 1 to 500 ppm, and more preferably 1 to 100 ppm.

That is, the acrylate-based polymer of the present invention not only has a small amount of residual monomer but also has a low content of β-hydroxypropionic acid, so that there is almost no generation or increase of residual monomer, and it is very safe to use acrylic acid. It is a salt polymer. In conventional acrylate-based polymers, even with low residual monomers, a significant increase in the generation of residual monomers was observed due to heating and aging, but this problem was solved for the first time in the acrylate-based polymers of the present invention. Was.

It is unknown how β-hydroxypropionic acid in the water-soluble unsaturated monomer or the acrylate polymer leads to an increase or generation of residual monomers. It is presumed that the acrylate polymer is heated,
Melting point of sodium β-hydroxypropionate (142
C)), the remaining monomer increases or is generated even after heating, so that β-hydroxypropionic acid is extremely easily decomposed in the acrylic acid-based polymer, or
It is also presumed that hydroxypropionic acid promotes the depolymerization of the acrylate polymer. Further, it is also presumed that various physical properties of the acrylate-based polymer were reduced due to the generation and increase of the residual monomer and the depolymerization of the polymer.

[0095]

Hereinafter, the present invention will be described with reference to Examples.
The scope of the present invention is not limited only to these examples. The physical properties of the acrylate polymers described in the examples are values measured by the following test methods.

The term "potential residual monomer" as used herein means a residual monomer which is generated or increased in a long-time use or at a high temperature, in addition to the residual monomer usually measured at room temperature in an acrylate polymer. . Even if the apparent residual monomer is small, if this potential residual monomer is large,
Needless to say, it is not preferable for safety.

(1) Water Absorption Ratio 0.2 g of an acrylate polymer was uniformly placed in a nonwoven fabric bag (40 × 150 mm) and immersed in a 0.9% by weight aqueous sodium chloride solution. Thirty minutes later, the tea bag type bag was pulled up and drained for a certain period of time, then the weight of the tea bag type bag was measured, and the water absorption capacity was calculated by the following equation.

[0098]

(Equation 3)

(2) Residual monomer 0.5 g of acrylate polymer was added to 1000 parts of deionized water.
After stirring for 2 hours in ml, filtration was performed, and the residual monomer in the filtrate was measured using high performance liquid chromatography.

(3) Potential Residual Monomer In order to simplify the analysis of the potential residual monomer, the obtained acrylate polymer was further heated at 180 ° C. for 3 hours, and the residual monomer was removed by the method of (2). The residual monomer measured and increased by heating was defined as potential residual monomer.

[0101]

(Equation 4)

(5) Suction force An artificial urine (composition: urea, NaCl, CaCl ₂ , MgSO ₄ was 1.9% by weight, 0.9% by weight, 0.1% by weight, 0% by weight, respectively) was placed on a dish on which tissue paper was placed. .1% by weight)
After pouring 0 ml, an additional 1 g of the acrylate-based polymer having a crosslinked surface is dropped on the center of the Petri dish, and artificial urine is absorbed through tissue paper. After a lapse of 10 minutes, the weight of the swollen gel is measured and used as the suction force of the acrylate polymer.

(Acrylate used) The acrylate used in Examples and Comparative Examples is an acrylate obtained by the following method. In addition, the content of β-hydroxypropionic acid is a value per solid content determined by liquid chromatography.

The acrylic acid after distillation purification was stored in a dark room at a constant temperature of 20 to 40 ° C. assuming normal temperature until used for neutralization. Normally, acrylic acid used at the manufacturing site is several tens of
It is the fact that 0 days have passed. In addition, in a manufacturing site, it is often handled and stored as an aqueous 80% acrylic acid solution having a high freezing point and not freezing.

(Production Example 1) Acrylic acid obtained from an acrylic acid production site was purified by distillation. The acrylic acid after the distillation purification was stored at a temperature of 30 ° C. for 3 hours, and the acrylic acid was neutralized according to the method of Example 1 of JP-A-2-209906 shown below. 2744 g of ion-exchanged water was charged into a distillation flask equipped with a stirrer. While maintaining the temperature of the neutralization reaction system in the flask at 20 to 40 ° C., 1390 g of acrylic acid
And 1480 g of 48% by weight sodium hydroxide were simultaneously dropped into the flask over a period of 100 minutes at a dropping ratio of sodium hydroxide / acrylic acid of 0.9 to 0.95. After the completion of the dropwise addition, 160 g of a 48% by weight aqueous sodium hydroxide solution was further supplied to make the neutralization rate of the neutralization reaction system in the flask 102 mol%. Then, the temperature of the neutralization reaction system was adjusted to 40 ° C., and aging was performed for 30 minutes. After aging, 499 g of acrylic acid was supplied to the neutralization reaction system over 10 minutes to obtain an acrylate (I) having a neutralization rate of 75 mol% and a concentration of 37%. The content of β-hydroxypropionic acid per solid content in the acrylic salt (I) is 40 p.
pm.

(Production Examples 2 and 3) In Production Example 1, except that acrylic acid used for neutralization was stored at a temperature of 30 ° C. after distillation and purification, and the storage time was changed to 10 hours and 24 hours. Acrylates (II) and (III) were obtained in the same manner as in Production Example 1. Acrylic salt (I
The contents of β-hydroxypropionic acid per solid content in I) and (III) are 90 ppm and 190 ppm, respectively.
Met.

(Production Example 4) In the same manner as in Production Example 1, except that acrylic acid used for neutralization was stored at a temperature of 25 ° C. after distillation purification and the storage time was set to 24 hours, and acrylic acid used for neutralization was used. The acrylate (I
V). Β- per solid in acrylic salt (IV)
The content of hydroxypropionic acid was 100 ppm.

(Preparation Examples 5 to 7) In Preparation Example 1, acrylic acid used for neutralization was stored at a temperature of 20 ° C. after distillation and purification, and the storage time was set to 10, 24, and 48 hours. Acrylates (V) to (VII) were obtained in the same manner except that they were used. Acrylic salt (V) ~
The content of β-hydroxypropionic acid per solid content in (VII) is 50 ppm, 80 ppm, and 13 ppm, respectively.
It was 0 ppm.

(Production Example 8) A commercially available production of acrylic acid (special grade of Wako Pure Chemical Industries) was purified by distillation. The acrylic acid after the distillation purification was stored at a temperature of 30 ° C. for 3 hours, and the acrylic acid was neutralized according to the method of Comparative Example 2 of JP-A-2-209906 shown below.

In a distillation flask equipped with a stirrer, 2744 g of ion-exchanged water and 164% by weight of sodium hydroxide 164 were added.
0 g was charged. Next, the temperature of the neutralization reaction system is set to 20 to 4
While maintaining the temperature at 0 ° C., 1889 g of acrylic acid was added to the flask.
Was supplied over 120 minutes to obtain acrylate (VIII) having a neutralization rate of 75 mol% and a concentration of 37%. The content of β-hydroxypropionic acid per solid content in the acrylic salt (VIII) was 230 ppm.

(Production Examples 9 and 10) In Production Example 8, the acrylic acid used for neutralization was 30 ° C. after distillation and purification.
And using the same procedure as in Production Example 8 except that acrylic acid was used for which the storage time was 10 hours and 24 hours.
Acrylates (IX) and (X) were obtained. Acrylic salt (I
The contents of β-hydroxypropionic acid per solid content in X) and (X) are 290 ppm and 390 ppm, respectively.
Met.

(Production Example 11) A commercially available acrylic acid production (special grade of Wako Pure Chemical Industries) was purified by distillation. The acrylic acid after the distillation purification was converted into an 80% aqueous solution having a high freezing point and easy to handle, then stored at 30 ° C. for 3 hours, and neutralized according to the following method similar to that of Production Example 8.

In a distillation flask equipped with a stirrer, 2272 g of ion-exchanged water and 164% of 48% by weight sodium hydroxide were added.
0 g was charged. Next, the temperature of the neutralization reaction system is set to 20 to 4
While maintaining the temperature at 0 ° C., 2361 g of an 80% aqueous solution of acrylic acid was supplied to the flask over 120 minutes to obtain an acrylate (XI) having a neutralization rate of 75 mol% and a concentration of 37%. The content of β-hydroxypropionic acid per solid content in the acrylic salt (XI) was 290 ppm.

(Production Example 12) Neutralization was carried out in the same manner as in Production Example 8, except that the neutralization temperature was lowered to 10 ° C, to obtain an acrylate (XII). However, since the neutralization temperature was lowered, the time required for the neutralization was 6 times, which is three times that of Production Example 8.
The content of β-hydroxypropionic acid with solids in the acrylic salt (XII) was 70 ppm.

(Production Example 13) Production Example 13 was the same as Production Example 1, except that the amount of acrylic acid added to the neutralization reaction system was changed from 499 g of acrylic acid to 1446 g after aging at a neutralization ratio of 102 mol%. In the same manner as in Example 1, acrylate (XIII) having a neutralization ratio of 50 mol% and a concentration of 45% was obtained. The content of β-hydroxypropionic acid per solid content in the acrylic salt (XIII) was 30 ppm.

(Production Example 14) Production Example 14 was the same as Production Example 1, except that the amount of acrylic acid added to the neutralization reaction system was changed from 499 g of acrylic acid to 184 g after aging at a neutralization rate of 102 mol%. Performed in the same manner as in Example 1, with a neutralization ratio of 90 mol%
Gave an acrylate (XIV) with a concentration of 34%. The content of β-hydroxypropionic acid per solid content in the acrylic salt (XIV) was 50 ppm.

(Production Example 15) In Production Example 8, the amount of water was changed from 2774 g to 1942 g, and the amount of acrylic acid suitable for the neutralization reaction system was changed from 1889 g to 1418 g.
g, except that the neutralization rate was 10 g.
Acrylate (XV) having a concentration of 37% was obtained at 0 mol%. The content of β-hydroxypropionic acid per solid content in the acrylic salt (XV) was 290 ppm.

(Comparative Production Example 1) In Production Example 1, the acrylic acid used for neutralization was 20
A comparative acrylate (I) was obtained in the same manner as in Production Example 1 except that acrylic acid stored for one day was used. The content of β-hydroxypropionic acid per solid content in the comparative acrylic salt (I) was 2500 ppm.

(Comparative Production Example 2) The same procedure as in Production Example 1 was carried out except that the commercially available acrylic acid (Kanto Chemical, special grade) was used as the acrylic acid for neutralization without purification by distillation. To obtain a comparative acrylate (II). The content of β-hydroxypropionic acid per solid content in the comparative acrylic salt (II) was 4,200 ppm.

(Comparative Production Example 3) In Production Example 1, the same procedure as in Production Example 1 was carried out except that commercially available acrylic acid (Wako Pure Chemicals, special grade) was used as the acrylic acid for neutralization without distillation and purification. Done and compare acrylates (III)
I got Β per solid in comparative acrylic salt (III)
-The content of hydroxypropionic acid is 8200 ppm
Met.

(Comparative Production Examples 4 and 5)
The same procedure as in Production Example 1 was carried out except that acrylic acid stored for 120 hours and 240 hours after distillation purification was used as the acrylic acid used for neutralization.
(V) was obtained. The content of β-hydroxypropionic acid per solid content in the comparative acrylic salts (IV) and (V) was 1100 ppm and 1900 ppm, respectively.

(Comparative Production Example 6) Production Example 1 was carried out in the same manner as in Production Example 1 except that acrylic acid used for neutralization was stored at a temperature of 40 ° C after distillation purification and the storage time was 48 hours. By carrying out similarly, comparative acrylate (VI) was obtained. The content of β-hydroxypropionic acid per solid content in the comparative acrylic salt (VI) was 1300.
ppm.

(Comparative Production Examples 7 and 8)
The same procedure as in Production Example 1 was carried out except that acrylic acid stored for 120 hours and 240 hours after distillation purification was used as the acrylic acid used for neutralization.
(VIII) was obtained. The content of β-hydroxypropionic acid per solid content in the comparative acrylic salts (VII) and (VIII) was 1300 ppm and 2100 ppm, respectively.

(Comparative Production Examples 9 and 10) Production Example 11 was carried out in the same manner as in Production Example 1 except that the 80% aqueous acrylic acid solution used for neutralization was an aqueous acrylic acid solution preserved for 240 hours and 480 hours after distillation and purification. As a result, comparative acrylates (IX) and (X) were obtained. Comparative acrylic salt (I
The contents of β-hydroxypropionic acid per solid content in X) and (X) were 3300 ppm and 6700 p, respectively.
pm.

(Comparative Production Example 11) In Production Example 8, the temperature of the neutralization system was raised from 20 to 40 ° C to 50 to 60 ° C in order to shorten the neutralization time. 1
It was reduced from 20 minutes to 40 minutes. However, the content of β-hydroxypropionic acid in the obtained acrylate is
It increased significantly to 2100 ppm. Hereinafter, this acrylate is referred to as comparative acrylate (XI).

(Comparative Production Example 12)
Performed in the same manner as in Production Example 13 except that the acrylic acid used in Comparative Production Example 1 was used as the acrylic acid used for neutralization,
Comparative acrylate having a neutralization rate of 50 mol% and a concentration of 45% (hydroxypropionic acid content of 1800 ppm) (XI
I) got.

(Comparative Production Example 13)
Performed in the same manner as in Production Example 15 except that acrylic acid used in Comparative Production Example 1 was used as the acrylic acid used for neutralization,
A comparative acrylate (XIII) having a hydroxypropylionic acid content of 3200 ppm and a neutralization ratio of 100 mol% was obtained.

(Experimental Example 1) N, N'- as an internal crosslinking agent was added to 5500 g of the acrylate (I) obtained in Production Example 1.
By dissolving 1.8 g of methylenebisacrylamide, the content of β-hydroxypropionic acid is reduced to 40 ppm.
Of a water-soluble unsaturated monomer (I). (Concentration: 37%, neutralization rate: 75 mol%) Stainless steel double-armed cutter with a jacket and two sigma-type blades with an internal volume of 10 L and a water-soluble unsaturated monomer degassed with nitrogen gas for 30 minutes. (Kneader) The reactor was supplied with a lid, and the water-soluble unsaturated monomer (I) was kept at a temperature of 30 ° C. and the reaction system was placed in nitrogen. Next, while being heated through warm water at 35 ° C., 0.3 mol% of ammonium sulfate and 0.03 mol% of sodium bisulfite were added as polymerization initiators. In addition, after preparing the water-soluble unsaturated monomer (I) by the above operation,
It took 2 hours until the polymerization initiator was charged and the polymerization was started.

One minute after the addition of the polymerization initiator, polymerization starts, and after 16 minutes, the hydrogel polymer is subdivided into a diameter of about 5 mm, and stirring is continued to start polymerization. The polymer was removed. Next, the obtained granulated product of the hydrogel polymer was spread on a 50-mesh wire mesh,
Hot air drying was performed at 0 ° C. for 90 minutes. The dried product was pulverized using a vibration mill, and further classified with 20 mesh to obtain an acrylic acid salt water-absorbent resin (1).

(Experimental Examples 2 to 4) In Experimental Example 1, the water-soluble unsaturated monomer (I) was allowed to stand for a predetermined time so that the time from preparation to the start of polymerization was 6, 12 hours, 24 hours.
By repeating the same operation as in Experimental Example 1 except that the time was extended, acrylate water-absorbing resins (2) to (4) were obtained.

(Experimental Examples 5 to 7) In Experimental Example 1, acrylate (II) was used instead of acrylate (I) as the acrylate used for preparing the water-soluble unsaturated monomer.
-(IV), except that the content of β-hydroxypropionic acid was 90 ppm and 19 ppm, respectively.
0 ppm, 100 ppm of water-soluble unsaturated monomer (II)
(IV) was obtained. Next, these water-soluble unsaturated monomers (I
For I) to (IV), polymerization was performed in the same manner as in Experimental Example 1 two hours after preparation, and the same operation as in Experimental Example 1 was repeated to thereby obtain the acrylate-based water-absorbing resins (5) to (7). ) Got.

(Experimental Example 8) In Experimental Example 1, the acrylate used for preparing the water-soluble unsaturated monomer was changed to acrylate (V) instead of acrylate (I). Simultaneously with Experimental Example 1 except that the internal crosslinking agent was replaced with 2.2 g (0.02 mol%, based on monomer) of polyethylene glycol diacrylate (average n is 8) instead of N, N'-methylenebisacrylamide. Thus, a water-soluble unsaturated monomer (V) having a β-hydroxypropionic acid content of 50 ppm was obtained.

Then, the water-soluble unsaturated monomer (V) was polymerized 6 hours after the preparation in the same manner as in Experimental Example 1. The gel polymer thus obtained was dried at 150 ° C. for 75 minutes, and thereafter, crushed and classified in the same manner as in Experimental Example 1.
An acrylate-based water-absorbing resin (8) was obtained.

(Experimental Examples 9 and 10) In Experimental Example 8, acrylate (V) was used instead of acrylate (V) as the acrylate used for preparing the water-soluble unsaturated monomer.
Except for I) and (VII), β-
The content of hydroxypropionic acid is 80 pp each
m, 130 ppm of a water-soluble unsaturated monomer (VI), (VI
I) got. Next, these water-soluble unsaturated monomers (V
About I) and (VII), by performing in the same manner as in Experimental example 8,
Acrylate-based water-absorbing resins (9) and (10) were obtained.

(Experimental Example 11) In Experimental Example 1, the acrylate used for the preparation of the water-soluble unsaturated monomer was:
13.6 g of trimethylolpropane triacrylate (0.2 mol%) was replaced with acrylate (VIII) instead of acrylate (I), and the internal crosslinking agent was replaced with N, N'-methylenebisacrylamide. , With respect to the monomer), to obtain a water-soluble unsaturated monomer (VIII) having a β-hydroxypropionic acid content of 230 ppm in the same manner as in Experimental Example 1.

Thereafter, the water-soluble unsaturated monomer (VIII) was polymerized 2 hours after preparation in the same manner as in Experimental Example 1, and the obtained gel polymer was dried at 180 ° C. for 60 minutes.
An acrylate-based water-absorbent resin (11) was obtained in the same manner as in Experimental Example 1.

(Experimental Examples 12 and 13) In Experimental Example 11, acrylates (IX) and (IX) were used in place of acrylates (VIII) as acrylates used for preparing a water-soluble unsaturated monomer. X) except that the content of β-hydroxypropionic acid was 290 ppm and 39 ppm, respectively.
0 ppm of water-soluble unsaturated monomers (IX) and (X) were obtained.
Next, these water-soluble unsaturated monomers (IX) and (X) were treated in the same manner as in Experimental Example 11 to obtain acrylate-based water-absorbing resins (12) and (13).

(Experimental Example 14) A stirring rod, a nitrogen blowing tube,
In a reaction vessel equipped with a thermometer, 30 g of corn starch are dissolved in 600 g of water, and 718 g (3 mol) of acrylate (XI) and acrylamide 71 are added.
g (1 mol), 0.12 g of trimethylolpropane triacrylate as an internal cross-linking agent (by dissolving 0.01 mol% of the monomer in an aqueous starch solution, the content of β-hydroxypropionic acid is 230 ppm, and the water-soluble unsaturated Monomer (XI) was prepared.

Next, the water-soluble unsaturated monomer (XI) was added to 30
After maintaining at 2 ° C. for 2 hours, nitrogen gas was blown for 1 hour to drive off dissolved oxygen. Furthermore, to this water-soluble unsaturated monomer,
0.1 mol% of sodium persulfate as a polymerization initiator, L-
0.05 mol% of ascorbic acid was added, and the obtained hydrogel was polymerized for 3 hours. Further, the gel polymer was dried with a double drum dryer having a surface temperature of 150 ° C. and then pulverized to obtain an acrylate-based water-absorbent resin (14) having passed through 20 mesh.

(Experimental example 15) Acrylate (XII) 10
Then, 3.4 g (0.1 mol%, relative to the monomer) of tetraelene glycol diacrylate as an internal crosslinking agent was added to and dissolved in 00 g of a water-soluble unsaturated monomer (XII) having a β-hydroxypropionic acid content of 70 ppm. ) Was prepared.

After the adjustment of the water-soluble unsaturated monomer (XII) was completed, the temperature was maintained at 50 ° C., and nitrogen gas was blown in to expel dissolved oxygen. Then, the water-soluble unsaturated monomer is layered and flow-extended to a thickness of 5 mm under a nitrogen atmosphere, and then 0.2 mol% of 2,2′-azobis (2-amidinopropane) dihydrochloride is used as a polymerization initiator. Was added. It should be noted that it takes 2 hours from the preparation of the water-soluble unsaturated monomer to the start of polymerization.
Polymerization was started immediately, and after 10 minutes, the gel polymer was taken out, fragmented, and dried at 150 ° C. for 60 minutes. Next, the dried product was ground and classified in the same manner as in Experimental Example 1 to obtain an acrylate-based water-absorbent resin (15).

(Experimental Examples 16 and 17) In Experimental Example 15, except that polymerization was carried out using a water-soluble unsaturated monomer (XII) stored at 30 ° C. for 12 hours and 24 hours after completion of the preparation.
Acrylate-based water-absorbing resins (16) and (17) were obtained in the same manner as in Experimental Example 1.

Experimental Example 18 Acrylate (XII) 8
3.4 g and 0.004 g of N, N′-methylenebisacrylamide as an internal crosslinking agent (based on the monomer 0.00
Using 65 mol% and 17.77 g of ion-exchanged water, a water-soluble unsaturated monomer (XII ′) having a concentration of 35% and a β-hydroxypropionic acid content of 70 ppm having a neutralization rate of 75% was prepared. Four hours after the completion of the preparation of the aqueous unsaturated monomer (XII), nitrogen gas was blown for one hour to expel dissolved oxygen.

Separately, a reaction vessel was equipped with a stirrer, a reflux condenser, a thermometer, a nitrogen gas inlet tube and a dropping funnel.
250 ml of cyclohexane was placed in a 00 ml four-neck separable flask, and 2.0 g of sorbitan monostearate (HLB4.7) was added and dissolved as a dispersant, and dissolved oxygen was expelled by blowing nitrogen gas. After degassing for 1 hour, 0.06 mol% of potassium persulfate was added as a polymerization initiator to the water-soluble unsaturated monomer, and the bath temperature was raised to 60 ° C. to start the polymerization reaction. It takes 4 hours from the preparation of the water-soluble unsaturated monomer to the polymerization. 2
After polymerization for an hour, azeotropic dehydration is performed to obtain a water content of 1
After filtering to 0% or less, the mixture was filtered and further dried in an oven at 130 ° C., whereby the acrylate-based water-absorbing resin (1
8) was obtained.

(Experimental Example 19) In Experimental Example 1, the acrylate used for preparing the water-soluble unsaturated monomer was as follows:
By replacing the acrylate (I) with the acrylate (XIII), a water-soluble unsaturated monomer having a β-hydroxypropionic acid content of 30 ppm, a neutralization ratio of 50% and a concentration of 45% (XIII) was obtained.

Next, this water-soluble unsaturated monomer (XIII)
About 4 hours after the preparation, the polymerization was started in the same manner as in Experimental Example 1, and the same operation as in Experimental Example 1 was repeated.
An acrylate-based water-absorbing resin (19) was obtained.

(Experimental Example 20) In Experimental Example 1, the acrylate used for preparing the water-soluble unsaturated monomer was as follows:
By replacing the acrylate (I) with the acrylate (XIV), a water-soluble unsaturated monomer having a β-hydroxypropionic acid content of 50 ppm, a neutralization ratio of 90% and a concentration of 34% (XIV) was obtained.

Next, this water-soluble unsaturated monomer (XIV)
, Polymerization was started in the same manner as in Experimental Example 1 24 hours after preparation, and the same operation as in Experimental Example 1 was repeated to obtain an acrylate-based water-absorbent resin (20).

Experimental Example 21 Acrylate (XV) 400
0 g as a water-soluble unsaturated monomer (XV) having a content of β-hydroxypropionic acid of 290 ppm,
SUS31 with inner surface lined with tetrafluoroethylene resin
6 and placed in an openable / closable polymerization apparatus having an internal volume of 300 mm x 300 mm x 50 mm, and purged with nitrogen.
C. in a water bath.

Further, 24 hours after the completion of the preparation, 0.05 mol% of ammonium persulfate and 0.02 mol% of sodium bisulfite were added to carry out polymerization, and 5 hours after the start of polymerization, a hydrogel was added from a casting polymerization apparatus. After taking out the polymer in the form of a string using a meat chopper, the polymer was dried and pulverized in the same manner as in Experimental Example 1 to obtain a water-soluble acrylate resin (2).
1) was obtained.

Example 1 100 parts of the water-absorbent resin (1) obtained in Experimental Example 1 was mixed with 1 part of glycerin, 2 parts of water and 2 parts of ethyl alcohol.
Heat treatment was performed at 20 ° C. for 20 minutes to obtain a water-absorbent resin (22) in which the vicinity of the surface was crosslinked.

(Example 2) 0.1 part of ethylene glycol diglycidyl ether was added to 100 parts by weight of the water absorbent resin (5).
After mixing 1 part of water, 5 parts of water and 1 part of isopropyl alcohol, the resulting mixture was subjected to a heat treatment at 180 ° C. for 30 minutes to obtain a water-absorbent resin (23) having a crosslinked surface.

Example 3 0.5 part of diethylene glycol, 2 parts of water and 1 part of isopropyl alcohol were mixed with 100 parts of the water-absorbent resin (6), and the resulting mixture was mixed with 1 part.
By performing a heat treatment at 50 ° C. for 3 hours, a water-absorbent resin (24) having a cross-linked surface was obtained.

Example 4 100 parts by weight of the water-absorbent resin (8) was dispersed in a mixed solvent consisting of 300 parts of methanol and 30 parts of water, and 0.1 part of ethylene glycol diglycidyl ether was further mixed. 160 ° C
For 1 hour and evaporated to dryness to obtain a water-absorbent resin (25) having a cross-linked surface.

Example 5 2.5 parts of ethylene carbonate, 2.5 parts of water and 2.5 parts of acetone were added to 100 parts of the water-absorbent resin (9), followed by heat treatment at 180 ° C. for 1 hour. The water-absorbent resin (26) having a cross-linked surface area
I got

Example 6 One part by weight of silicon inorganic fine powder (Aerosil) was added to 100 parts by weight of the water absorbent resin (11), and 0.1 part of ethylene glycol diglydyl ether and 10 parts of water were mixed. The resulting mixture was heat-treated at 150 ° C. for 1 hour to obtain a water-absorbent resin (27) having a cross-linked surface.

Example 7 One part of aluminum sulfate, one part of glycerin and eight parts of water were mixed with 100 parts by weight of the water-absorbent resin (12), and the resulting mixture was heated at 180 ° C. for 30 minutes. Thus, a water-absorbent resin (28) having a cross-linked surface was obtained.

Example 8 The water absorbing resin (18) was dispersed in 250 ml of cyclohexane. Separately, 50 g of cyclohexane is placed in a flask and sorbitan monolaurate (Rhodol SP-1 manufactured by Kao Corporation) is used as a surfactant.
0, HLB = 8.6) 0.5 g was dissolved therein, and 0.04 g of ethylene glycol diglycidyl ether was added thereto and water 2 was added.
The aqueous solution dissolved in ml was added with vigorous stirring to obtain a dispersion of ethylene glycol diglycidyl ether (average droplet diameter 3 microns). Next, this dispersion is mixed with the suspension of the water-absorbent resin (18) under stirring, the system temperature is maintained at 75 ° C. for 3 hours, and further filtration and drying under reduced pressure are performed to crosslink the surface vicinity. Water absorbent resin (29) was obtained.

(Comparative Examples 1 to 3) In the experimental example 1, the acrylate used in the preparation of the water-soluble unsaturated monomer was changed from the comparative acrylate (I) to the acrylate (I). Except for using (III), in the same manner as in Experimental Example 1,
The content of β-hydroxypropionic acid is 250
0 ppm, 4200 ppm, and 8200 ppm of comparative water-soluble unsaturated monomers (I) to (III) were obtained. Next, the comparative acrylate-based water-absorbent resins (1) to (3) are repeated for the comparative water-soluble unsaturated monomers (I) to (III) by repeating the same operation as in Experimental Example 1. I got

(Comparative Examples 4 to 6) In Comparative Example 1, except that the time from the completion of preparation of the comparative water-soluble unsaturated monomer (I) to the start of polymerization was extended to 12, 24 and 240 hours. By repeating the same operation as in Comparative Example 1, the comparative acrylate-based water-absorbent resins (4) to (6) were obtained.

(Comparative Examples 7 to 9) In Experimental Example 8, the comparative acrylate (I) was used in place of the acrylate (V) as the acrylate used for preparing the water-soluble unsaturated monomer.
Except that V) to (VI), the content of β-hydroxypropionic acid was 1100 p in the same manner as in Experimental Example 8.
pm, 1900 ppm and 1300 ppm of comparative water-soluble unsaturated monomers (IV) to (VI) were obtained. Next, the comparative acrylate-based water-absorbent resins (7) to (9) are repeated for these comparative water-soluble unsaturated monomers (IV) to (VI) by repeating the same operation as in Experimental Example 8. ) Got.

(Comparative Examples 10 to 12) In Experimental Example 11, the acrylate used for preparing the water-soluble unsaturated monomer was changed from Comparative acrylate (VII) to acrylate (VIII). Except for (IX), in the same manner as in Experimental Example 8, the content of β-hydroxypropinic acid was 1
300 ppm, 2100 ppm and 3300 ppm of comparative water-soluble unsaturated monomers (VII) to (IX) were obtained. Then
By repeating the same operation as in Experimental Example 11 for these comparative water-soluble unsaturated monomers (VII) to (IX), the comparative acrylate-based water-absorbent resins (10) to (1)
2) was obtained.

Comparative Example 13 The procedure of Example 14 was repeated except that the acrylate used in the preparation of the water-soluble unsaturated monomer was the comparative acrylate (X) instead of the acrylate (XI). In the same manner as in Experimental Example 14, a comparative water-soluble unsaturated monomer (X) containing 6700 ppm of β-hydroxypropionic acid was obtained. Next, the same operation as in Experimental Example 14 was repeated for this comparative water-soluble unsaturated monomer (X) to obtain a comparative acrylic salt-based water-absorbent resin (13).

(Comparative Example 14) In Example 15, the comparative acrylate (XI) was used instead of the acrylate (XII) as the acrylate used for preparing the water-soluble unsaturated monomer. In the same manner as in Experimental Example 15, a comparative water-soluble unsaturated monomer (XI) having a β-hydroxypropionic acid content of 2100 ppm was obtained. Then, the same operation as in Experimental Example 15 was repeated for the comparative water-soluble unsaturated monomer (XI) to obtain a comparative acrylate-based water-absorbent resin (14).

(Comparative Examples 15 and 16) Experimental Example 1 was carried out in the same manner as in Comparative Example 14, except that polymerization was carried out using a water-soluble unsaturated monomer stored at 30 ° C. for 24 hours and 120 hours after completion of preparation.
By performing in the same manner as in 3, the acrylate-based water-absorbing resin (1
5) and (16) were obtained.

(Comparative Example 17) In Experimental Example 19, the acrylate used in the preparation of the water-soluble unsaturated monomer was changed to the comparative acrylate (XII) instead of the acrylate (XIII). By comparison, the content of β-hydroxypropionic acid is 1800 ppm,
(XII) was obtained. Next, the water-soluble unsaturated monomer (XII)
Thereafter, the same operation as in Experimental Example 19 was repeated to obtain a comparative acrylate-based water-absorbent resin (17).

(Comparative Example 18) In Experimental Example 21, the acrylate used for the preparation of the water-soluble unsaturated monomer was changed to the comparative acrylate (XIII) instead of the acrylate (XV). As a result, a water-soluble unsaturated monomer (XIII) having a β-hydroxypropionic acid content of 3200 ppm was obtained. Then, the water-soluble unsaturated monomer (XI
For II), the same operation as in Experimental Example 21 was repeated to obtain a comparative acrylate-based water-soluble resin (18).

(Comparative Example 19) In Experimental Example 21, β-hydroxypropionic acid was added separately to the acrylate (XV).
By adding 590 ppm, the content of β-hydroxypropionic acid was 2800 ppm to obtain a comparative water-soluble water-soluble unsaturated monomer (XIV). Subsequently, the same operation as in Experimental Example 21 was repeated for this comparative water-soluble unsaturated monomer (XIV) to obtain a comparative acrylate-based water-soluble resin (19).

(Comparative Examples 20 to 22) In Examples 1 to 3, the comparative water-absorbent resin was used in place of the water-absorbent resins (1), (5) and (6) as the water-absorbent resin whose surface was crosslinked. Except for (1) to (3), the same procedure was performed to obtain comparative water absorbent resins (20) to (22).

(Comparative Examples 23 and 24) In Examples 4 and 5, instead of the water absorbent resins (8) and (9), the comparative water absorbent resins (7) and (9)
Except for (8), the procedure was exactly the same to obtain comparative water-absorbent resins (23) and (24) in which the vicinity of the surface was crosslinked.

(Comparative Examples 25 and 26) In Examples 6 and 7, instead of the water absorbent resins (11) and (12), the comparative water absorbent resin (1
1) The procedure was exactly the same except for (12) to obtain comparative water-absorbent resins (25) and (26) in which the vicinity of the surface was crosslinked.

The analysis results of the acrylate polymers of Experimental Examples 1 to 21 and Comparative Examples 1 to 29 are shown in Tables 1 and 2, respectively. Examples 1 to 8 and Comparative Examples 20 to 2
Table 3 shows the analysis results of the acrylate polymer in which the vicinity of the surface of No. 6 was crosslinked.

The β-hydroxypropionic acid in the acrylate polymer obtained in the examples was 500
In the case of those obtained from the water-soluble unsaturated monomers having a content of β-hydroxypropionic acid of 100 ppm or less, in particular, those obtained from the water-soluble unsaturated monomers were less than 100 ppm, whereas those of the comparative examples exceeded 1000 ppm.

[0174]

[Table 1]

[0175]

[Table 2]

[0176]

[Table 3]

[0177]

According to the production method of the present invention, the following (1) to (5)
It has excellent features such as: The excellent acrylate polymer can be widely used in fields such as sanitary materials, food, civil engineering, and agriculture.

(1) Conventionally, the residual monomer, which has been reduced by sacrificing the performance, productivity, cost and safety of the acrylate polymer through a complicated process such as addition of an additive, can be obtained in an advanced and simple manner. Can be reduced.

(2) Even when a high temperature is used in the production process, the production can be performed with high productivity because the increase in the residual monomer during the production is small. In addition, since the reaction can be performed at a high temperature, various excellent physical properties can be improved.

(3) Since the amount of residual monomer generated and increased during subsequent use at high temperature or for a long time is extremely small, it is used for a long time such as agricultural and horticultural use or use under high temperature using hot water. High safety under any use conditions.

(4) In addition to improving the polymerizability, the residual monomer can be reduced even with a small amount of a polymerization initiator or mild polymerization conditions.
In addition, an acrylate polymer having excellent physical properties can be obtained.

(5) Almost no increase in residual monomer during surface crosslinking is observed, and the surface treatment effect is improved.

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(Equation 1)

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[0026] That is, the present invention provides (1) the residual presence monomer amount is a salt of acrylic acid-based polymer is less than 160 ppm, the polymer in our partial neutralization or complete neutralization of the acrylate 50 to 100 mol% And a acrylate-based polymer having a neutralization ratio of 30 to 100 mol% and having a repeating unit of 0 to 50 mol% of a hydrophilic unsaturated monomer and / or a hydrophobic unsaturated monomer, wherein the polymer is a water absorbent resin having a crosslinked structure, crosslinked near the surface of the polymer further total content of β- hydroxy acid and its salt is relates to acrylate-based polymer over or less 1,000ppm .

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According to the present invention, (2) the residual monomer amount is 1
An acrylate polymer having a content of not more than 60 ppm, wherein 50 to 100 mol% of partially or completely neutralized acrylate and another 0 to 50 mol% of a hydrophilic unsaturated monomer and / or Or a acrylate-based polymer having a neutralization ratio of 30 to 100 mol% having a repeating unit of a hydrophobic unsaturated monomer, wherein the polymer is a water-absorbing resin having a crosslinked structure, and the vicinity of the surface of the polymer is further reduced. crosslinked, to a salt of acrylic acid-based polymer characterized by potential residual monomer amount defined or one under following formula is 30ppm or less.

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(Equation 2)

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According to the present invention, (4) the residual monomer amount is 1
An acrylate-based polymer having a content of not more than 60 ppm and partially or completely neutralized acrylate in the polymer of 50 to 100 mol% and other 0 to 50 mol% of a hydrophilic unsaturated monomer; A water-absorbent resin having a neutralization ratio of 30 to 100 mol% and having a repeating unit of a hydrophobic unsaturated monomer and having a crosslinked structure and a dried average particle diameter of 100 to 1000 μm. The present invention relates to an acrylate polymer in which the vicinity of the surface of the polymer is further crosslinked with a polyhydric alcohol, and the total content of β-hydroxypropionic acid and a salt thereof is 1000 ppm or less.

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The invention of the present application is characterized in that (6) the water-absorbent resin is a powder having an average particle diameter of 300 to 600 μm.
The present invention relates to the acrylate-based polymer according to any one of (5).

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 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Kunihiko Ishizaki, Inventor Kunihiko Ishizaki, Himeji-shi, Hyogo 992-Nishioki, Okihama-shi 1 Nippon Shokubai Co., Ltd. F-term (reference) 4J100 AA02R AA03R AA06R AB02R AB07R AC03R AE71S AG04R AJ01R AJ02Q AJ02R AJR AJR AK08P AK13P AK32R AL03R AL05R AL08R AL09R AL63S AL66S AL67S AM15R AM17R AM21R AM24S AP01R AQ08R AQ12R AS02R BA03R BA03S BA05R BA08R BA08S BA15H BA31R BA56R BC65R CA01 CA33 HC37 HC37 JA37 HC37 JA37 HC37 HA37

Claims (7)

[Claims] 1. An acrylate-based polymer having a residual monomer content of 160 ppm or less, wherein the acrylate is 50 to 100 mol% and the other 0 to 50 mol% in the polymer.
Is a acrylate-based polymer having a repeating unit of a hydrophilic unsaturated monomer and / or a hydrophobic unsaturated monomer having a neutralization ratio of 30 to 100 mol%, wherein the polymer has a crosslinked structure An acrylate polymer in which the vicinity of the surface of the polymer is further crosslinked and the total content of β-hydroxypropionic acid and a salt thereof is 1,000 ppm or less. 2. An acrylate polymer having a residual monomer content of 160 ppm or less, wherein 50 to 100 mol% of acrylate and 0 to 50 mol% of others in the polymer.
Is a acrylate-based polymer having a repeating unit of a hydrophilic unsaturated monomer and / or a hydrophobic unsaturated monomer having a neutralization ratio of 30 to 100 mol%, wherein the polymer has a crosslinked structure Wherein the vicinity of the surface of the polymer is further crosslinked, and the amount of the latent residual monomer defined by the following formula after the obtained acrylate polymer is further heated at 180 ° C. for 3 hours is 30 ppm or less. Characterized acrylate polymer. (Equation 1) 3. The acrylate polymer according to claim 1, wherein the vicinity of the surface of the polymer is crosslinked with a polyhydric alcohol. 4. An acrylate polymer having a residual monomer content of 160 pppm or less, and 50 to 100 mol% of acrylate and other 0 to 50 mol% in the polymer.
An acrylic acid-based polymer having a neutralization ratio of 30 to 100 mol% and having a repeating unit of a hydrophilic unsaturated monomer and / or a hydrophobic unsaturated monomer in an amount of 30% by mol, wherein the polymer has a crosslinked structure. Average particle diameter 100-1000μ
m. a water-absorbent resin, wherein the surface vicinity of the polymer is further crosslinked with a polyhydric alcohol, and the total content of β-hydroxypropionic acid and salts thereof is 1000 ppm or less. 5. The acrylate-based polymer according to claim 1, wherein the acrylate is a sodium acrylate or a potassium acrylate. 6. The water-absorbent resin has an average particle size of 300 to 600.
The polymer according to claim 1, which is a μm powder. 7. A sanitary material using the acrylate polymer according to any one of claims 1 to 6.