JPH06256414A - Production of (meth)acrylic acid (salt) polymer - Google Patents

Abstract

PURPOSE:To obtain a polymer excellent in water solubility and storage stability by placing a water-contg. substance comprising a (meth)acrylic acid (salt) polymer having a specified degree of neutralization in a specified thickness on a sheet, thermally drying and cooling the substance, and separating it from the sheet. CONSTITUTION:This (meth)acrylic acid (salt) polymer is produced by polymerizing a (meth)acrylic acid (salt) monomer in an aqueous soln., neutralizing the polymn. product so that up to 50mol% of acid groups in the product are neutralized, placing the product in a thickness of 0.5-10mm on a sheet, thermally drying the product at 80-230 deg.C to remove water, cooling the resulting polymer to 60 deg.C or lower, and separating the polymer from the sheet. The obtd. polymer is excellent in water solubility and storage stability, giving, even when dissolved in water after storage, a soln. which does not undergo decrease in thickening effect.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a (meth) acrylic acid (salt) -based polymer having a low degree of neutralization. The present invention relates to a method for producing a (meth) acrylic acid (salt) -based polymer by efficiently drying and removing water from the obtained polymerization product.

[0002]

2. Description of the Related Art (Meth) acrylic acid (salt) -based polymers have excellent tackiness, thickening, water absorption and cohesive action, and by taking advantage of their performances, thickeners and adhesives for poultices It is widely used as a paper strengthening agent, hardening agent, flocculant, dehydrating agent and soil conditioner. Above all, a low-neutralization (meth) acrylic acid (salt) -based polymer composed of poly (meth) acrylic acid or a (meth) acrylic acid salt having a neutralization degree of 50 mol% or less has particularly excellent performance for the above-mentioned applications. Demonstrate. When the (meth) acrylic acid (salt) -based polymer is used in the above-mentioned applications, it should be supplied in powder or granular form in consideration of ease of blending, handling, convenience of transportation and the like. There are many.

Examples of the method for producing a (meth) acrylic acid (salt) polymer include a bulk polymerization method, a suspension polymerization method, an emulsion polymerization method, a slurry polymerization method and an aqueous solution polymerization method. The aqueous solution polymerization method and the slurry polymerization method are widely used.

According to the slurry polymerization method, a solution in which a polymerizable monomer mainly composed of (meth) acrylic acid (salt) and a radical polymerization initiator are added and dissolved in an organic solvent which is a poor solvent for the polymerization product is polymerized. By doing so, a (meth) acrylic acid (salt) polymer is obtained as a precipitate. On the other hand, according to the aqueous solution polymerization method, when a radical initiator is added to an aqueous solution of a polymerizable monomer mainly composed of (meth) acrylic acid (salt) and the polymerization reaction is carried out by appropriately heating as necessary, (meth ) An acrylic acid (salt) polymer is obtained as a water-containing substance having tackiness and viscosity.

[0005]

The (meth) acrylic acid (salt) type polymer precipitate obtained by slurry polymerization can be obtained as a powdery polymer by drying under reduced pressure or the like. There were problems such as the need for capital investment for recovery and explosion proof, and the safety of the organic solvent remaining in the polymer. Moreover, a polymer having an arbitrary molecular weight could be obtained only in a relatively narrow range.

On the other hand, in the case of a water-containing (meth) acrylic acid (salt) polymer obtained by aqueous solution polymerization, a highly neutralized one having a neutralization degree of more than 50 mol% has small tackiness and film-forming property. Since it is small, it is possible to obtain a powdery polymer by relatively easily removing water with a well-known drum dryer, a ventilated hot air dryer or the like.

However, a low-neutralization degree (meth) acrylic acid (salt) polymer hydrate having a degree of neutralization of 50 mol% or less has a very high tackiness, and therefore the polymer after drying is dried. It was difficult to remove the moisture remaining inside because it was difficult to peel off because of the film-forming property, or because only the surface layer portion, which is the evaporation surface of moisture, was dried and became skin-tight. When attempting to remove the water content inside and crushing during drying to increase the surface area, crushing was not easy because the glass transition temperature of the polymer was low. Further, if the drying temperature is excessively increased, the surface layer portion becomes overheated and a branching reaction or a cross-linking reaction occurs, so that the redissolvability in water is lowered and a water-insoluble matter is generated, or the decomposition reaction occurs. However, there is a problem that the thickening effect after re-dissolution decreases due to storage, which adversely affects storage stability.

The present invention has been made by paying attention to the above circumstances, and its object is to provide a water-containing substance of a (meth) acrylic acid (salt) polymer having a low degree of neutralization obtained by aqueous solution polymerization. Dried efficiently without adversely affecting the re-solubility in water after drying, and has excellent storage stability for thickening action (meta)
It is to provide an acrylic acid (salt) -based polymer.

[0009]

The structure of the production method according to the present invention, which has been capable of solving the above-mentioned problems, is (meth) acrylic acid or a salt thereof (meth) acrylic acid (salt).
When a (meth) acrylic acid (salt) -based polymer is produced by removing water from the polymerization product after aqueous polymerization of the system monomer, the neutralization rate of the acid group contained in the polymerization product is adjusted to 50%. After adjusting the amount to be less than mol%, the polymerization product is placed on the sheet in an amount of 0.5 to 1
The product is loaded with a thickness of 0 mm, heated and dried at 80 to 230 ° C to separate and remove water, and the resulting (meth) acrylic acid (salt) polymer having a neutralization rate of 50 mol% or less is cooled to 60 ° C or less. The point is that the subsequent peeling from the sheet is carried out sequentially.

[0010]

The manufacturing method according to the present invention has a neutralization degree of 5 as described above.
Aqueous solution polymerization for (meth) acrylic acid (salt) -based polymer of 0 mol% or less is performed, and further reduction of re-solubility in water and change of viscosity increase due to crosslinking reaction in the drying step are prevented. In addition, the present invention provides a technique for efficiently producing a polymer having excellent storage stability, thereby succeeding in enhancing the performance as a pressure-sensitive adhesive, a thickener, a coagulant and the like.

The main monomers constituting the (meth) acrylic acid (salt) polymer according to the present invention are acrylic acid, methacrylic acid and salts thereof (hereinafter referred to as (meth) acrylic acid (salt)). 70 mol% or more, more preferably 90 mol% or more, of the monomers constituting the polymer consist of (meth) acrylic acid (salt). The salt in the (meth) acrylic acid (salt) polymer means a monovalent salt such as an alkali metal salt such as sodium, potassium and lithium, or an ammonium salt, for example, a salt such as calcium or aluminum. Polyvalent or trivalent or higher polyvalent metal salts lack water solubility and are therefore excluded from the salts of the present invention.

Other copolymerizable monomers optionally contained include carboxyl group-containing monomers such as maleic acid, fumaric acid and itaconic acid; vinyl sulfonic acid, methallyl sulfonic acid, allyl sulfonic acid, 3- (Meth) allyloxy
Sulfonic acid group-containing monomers such as 2-hydroxypropanesulfonic acid; amide-based monomers such as (meth) acrylamide and tertiary butyl (meth) acrylamide; allyl ether-based monomers such as glycerol mono (meth) allyl ether Polymer; 2-hydroxyethyl (meth) acrylate, allyl alcohol, 3-methyl-3-buten-1-ol (isoprenol), hydroxyl group-containing monomer such as glycerol mono (meth) acrylate; (meth) acrylonitrile, etc. Nitrile type monomer; methyl (meth) acrylate,
(Meth) acrylic acid ester-based monomers such as ethyl (meth) acrylate, propyl (meth) acrylate, and butyl (meth) acrylate; vinyl-based monomers such as vinyl acetate; styrene, α-methylstyrene, Examples thereof include styrene-based monomers such as styrene sulfonic acid, and if necessary, one kind or two or more kinds can be used by copolymerizing with (meth) acrylic acid (salt).

However, among these copolymerizable monomers, the hydrophobic monomer tends to impair the water solubility of the resulting polymer, so that a hydrophilic monomer is preferably used as the copolymerization component. Good to do. Particularly preferred as the copolymerization component are carboxyl group-containing monomers such as maleic acid, fumaric acid and itaconic acid.

Therefore, in order to obtain a polymer having a high level of water solubility, the amount of (meth) acrylic acid (salt) in all monomers is set to 70 mol% or more and other copolymerizable monomers are used. It is preferable to keep the amount to 30 mol% or less.

Further, in the present invention, the degree of neutralization of the (meth) acrylic acid (salt) type polymer is required to be 50 mol% or less, and the (meth) acrylic acid (salt) to be subjected to aqueous solution polymerization is used.
The neutralization degree of the system monomer is set to 50 mol% or less, or the acid group contained in the polymerization product obtained by the aqueous solution polymerization is neutralized to a degree of 50 mol% or less. I will go. A high degree of neutralization (meta) with a degree of neutralization exceeding 50 mol%
With the water-containing material of acrylic acid (salt) polymer, only a polymer having inferior performance as a pressure-sensitive adhesive can be obtained as compared with the polymer having a low degree of neutralization obtained in the present invention. Further, since the film-forming property is also small, the water can be easily removed to obtain a polymer without adopting the production method specified in the present invention, and therefore the meaning of adopting the present invention becomes small.

Above all, the degree of neutralization is 30 mol% or less, and further 1
Polymers of 0 mol% or less, more preferably 0% are preferably applicable by this method.

(Meth) acrylic acid (salt) in the present invention
The system polymer is obtained by aqueous solution polymerization. Aqueous solution polymerization is carried out by mixing a water-soluble radical polymerization initiator into an aqueous solution of a (meth) acrylic acid (salt) -based monomer, and appropriately heating the mixture to perform polymerization. Depending on the molecular weight of the polymer, a viscous aqueous solution or a hydrogel polymerization product can be obtained. By using the aqueous solution polymerization, it is possible to reduce the burden such as removal of the organic solvent and safety in the slurry polymerization method, and it is possible to obtain a polymer having an arbitrary molecular weight in a wide range. Further, a small amount of a water-soluble organic solvent such as ethanol or methanol may be added to the aqueous solution as long as the effect of the present invention is not impaired.

The water-soluble radical polymerization initiator used in the present invention is not particularly limited as long as it dissolves in water to generate radicals by heat or light, and examples thereof include azobis-
Azo compounds such as 2-amidinopropane dihydrochloride and azobis-2-methyl-propionamide dihydrate; persulfates such as ammonium persulfate and sodium persulfate; represented by peroxides, sulfites and amines And a redox initiator in combination with a reducing agent. Among them, the azo compound is preferable because a (meth) acrylic acid (salt) polymer excellent in storage stability can be obtained.

As described above, the polymerization product obtained by the aqueous solution polymerization has the neutralization ratio of the acid groups contained in the polymerization product reduced to 50 mol% or less, and is then placed on a sheet to remove moisture by heating and drying. By doing so, a target (meth) acrylic acid (salt) polymer having a low degree of neutralization is obtained.

The sheet used in the present invention is obtained by processing a resin having water repellency such as polytetrafluoroethylene, polytrifluoroethylene, polypropylene and polycarbonate into a sheet shape, a film shape and an endless belt shape. Can be used, side plates may be provided as necessary to prevent the polymerized product from flowing out or falling off,
The point is that any material may be used as long as it can support the polymerization product above it. The sheet may be made of only the above resin, but may be a sheet of metal material such as stainless steel coated with a resin that imparts water repellency, or a glass fiber cloth impregnated with a water repellent resin. It is sufficient that the sheet has a water-repellent surface to the extent that the polymerization product does not adhere strongly.

The resin used for this sheet may have heat resistance such that it does not melt and plasticize under drying conditions, but is preferably 130 ° C. or higher, more preferably 250.
It is preferably one having a heat resistance of not less than 0 ° C., and specific examples thereof include polytetrafluoroethylene (Teflon). The higher the heat resistance of the sheet, the higher the heating temperature during drying and the higher the drying efficiency.

In the present invention, the polymerization product is loaded on the sheet so as to have a thickness of 0.5 to 10 mm, preferably 1 to 5 mm. Loading thickness is 0.5m
When it is less than m, problems such as skinning due to water evaporation of the surface layer part are eliminated, but not only is it difficult to load, but the sheet contact area per unit weight of the polymer obtained by drying becomes too large. Peeling of the polymer becomes difficult.
On the other hand, when it exceeds 10 mm, the surface layer portion becomes skinned, and the drying efficiency of the loaded polymerization products is significantly reduced. Further, if water is forcibly removed, a polymer having poor resolubility in water and poor storage stability will be obtained.

The heating temperature during drying in the present invention is 80 to
It is carried out in the range of 230 ° C, preferably 130 to 2
It is in the range of 30 ° C. If the temperature is lower than 80 ° C., the problem of skinning is unlikely to occur, but the time required for drying is long and the drying efficiency is reduced, which is not preferable. If the temperature is higher than 230 ° C., the drying efficiency will be high, but a branching reaction or a cross-linking reaction will occur, so that an insoluble matter in water will be produced and the storage stability of the polymer will be deteriorated.

The heating method includes any one of a method of directly heating the polymerization product stacked on the sheet from above, a method of heating the sheet from below to heat the polymerization product by conduction heat transfer, and a method of using both of them together. Although the above method may be used, it is preferable that the method of heating from below is essential. The reason for this is that when heated from below, the water vaporizes while sequentially moving from the lower side (sheet side) of the polymerization product to the surface side, so that skin is unlikely to skin. As heating means, hot air from above,
Non-contact type heating methods such as infrared rays, far infrared rays, and microwaves can be applied, and plate heaters that use heat sources such as heat medium, steam, and electricity, and hot air, infrared rays, far infrared rays, and microwaves can be used for heating from below. It is applicable regardless of contact type such as waves or non-contact type.

When the polymerization product is stacked on the sheet according to the present invention, the stacking thickness of the polymerization product is as described above, but the stacking area on the sheet is arbitrary, and the entire surface of the sheet is stacked. Alternatively, the sheets may not be stacked on a part of the sheet and may be stacked with a gap. However, in view of the drying efficiency and the re-solubility of the obtained polymer, the polymerization product is formed on the sheet so that the loading area of the polymerization product is 80% or less of the effective drying area, preferably 50 to 80%. It is preferable to provide the parts where the objects are not loaded as uniformly as possible. The method of loading the polymer product is arbitrary, but it is preferable to load the polymer product in a streak shape in order to provide a portion where the polymer product is not loaded on the sheet as uniformly as possible. Specifically, a loading method using a single or a plurality of swing nozzles or a plurality of fixed nozzles can be applied.

The dry effective area in the present invention indicates an area heated on the sheet per unit drying time. For example, when the sheet is heated by the plate heater, a portion not in contact with the plate heater corresponds to the dry effective area. do not do. If the polymerization products are stacked on the sheet without leaving a gap, the polymerization products swelled during the drying process are dried in an overlapping state, so that the drying efficiency is reduced. Such swelling is not a problem when the heating temperature is relatively low, but tends to occur as the heating temperature becomes higher. Therefore, when the heating temperature is 160 ° C. or higher, the loading area of the polymerization product is set to 80% or less of the effective drying area. Preferably. Further, it is preferable to make the thickness of the loading portion as uniform as possible in order to improve the drying efficiency.

The polymer obtained by the above heat drying has a low glass transition temperature and is plasticized at the drying temperature. If it is left as it is, peeling and handling will be significantly hindered. Need to be peeled off. As a cooling method, cooling by contact of a cooling plate using cold water or the like, cooling by cold air, etc. are used, and contact type or non-contact type and cooling from above or below or both can be freely performed.

In the present invention, it is possible to dry by arbitrarily combining the above conditions, but in view of productivity, drying should be carried out at a drying efficiency of 100 (g / m ² · hr) or more. Is preferred, and further 300 (g / m ² · h
It is more preferable that the condition is r) or more. The water content in the polymer obtained after drying is preferably 10% by weight or less, more preferably 5% by weight or less. If the water content is 10% by weight or more, the drying is insufficient and the adhesiveness is high, so that it is difficult to peel it from the sheet, and it is difficult to crush and powder it in a later step.

The polymer obtained by peeling from the sheet is obtained in the form of a line, a sheet or a film, which can be cut into an appropriate size as it is depending on the intended use to produce a product. In order to enhance the re-dissolvability in the above, they can be crushed into powders, and if necessary, classified to be commercialized.

[0030]

EXAMPLES The present invention will now be specifically described with reference to examples, but the present invention is not limited to the following examples. The physical property testing methods adopted in the following examples are as follows.

Ratio of loading area to effective drying area (abbreviated as loading area ratio) (%): {(A) / (B * C * 0.1
* D)} * 100 (where A is the weight of the polymer-containing solution (g / hr),
B is the effective dry area (cm ² / hr), C is the coating thickness (m
m) and D are the specific gravities of the polymerized products) Drying efficiency (g / m ² · hr): Dry effective weight of the dried polymer per 1 m ² * 1 hr of effective drying area Water content (wt%) in the polymer: About 1 g of the powder obtained by pulverizing the dried polymer was loaded on a Petri dish so that the thickness was about 1 mm or less, dried at 105 ° C. for 180 minutes, and the water content was determined by weight reduction.

Storage stability of polymer: Viscosity (A) of 10% by weight aqueous solution when polymer powder immediately after drying is redissolved,
The polymer powder is stored at 60 ° C. for 30 days and then redissolved in a 10 wt% aqueous solution viscosity (B) is measured to evaluate the storage stability from B / A. (The closer the value is to 1, the better) Solubility of the polymer in water: The solubility is evaluated based on the presence or absence of insoluble matter when a 10 wt% aqueous solution is left at room temperature for 3 hours.

[0033]

Polymerization Example 1 A four-necked flask having a capacity of 5 liters equipped with a thermometer, a nitrogen introducing tube, a stirrer and a reflux condenser was charged with 11 parts of water.
94 g was charged and the temperature was raised to 100 ° C. Then 1% by weight
70 g of 2,2'-azobis-2-amidinopropane dihydrochloride aqueous solution and 2666 g of 30% by weight acrylic acid aqueous solution were continuously added dropwise at normal temperature and boiling temperature over 60 minutes to carry out polymerization reaction with stirring. 1% by weight 2,
70 g of 2'-azobis-2-amidinopropane dihydrochloride aqueous solution was continuously added dropwise at a boiling point temperature under normal pressure for 60 minutes, and after completion of the addition, the polymerization reaction was completed by stirring for 30 minutes at the boiling point of the system, An aqueous polyacrylic acid solution (polymerization product P1) having a solid content of 20% by weight was obtained.

[0034]

Polymerization Example 2 A four-necked flask having a capacity of 5 liters equipped with a thermometer, a nitrogen inlet tube, a stirrer and a reflux condenser was charged with 20 parts of water.
34 g was charged and the temperature was raised to 100 ° C. Next, 70 g of 10% by weight 2,2′-azobis-2-amidinopropane dihydrochloride aqueous solution and 1600 g of 80% by weight aqueous acrylic acid solution.
Was continuously added dropwise at a boiling point temperature over 120 minutes at normal temperature to carry out a polymerization reaction. Further, 296 g of 48 wt% sodium hydroxide aqueous solution is continuously added dropwise at a boiling point temperature under normal pressure for 20 minutes, and after completion of the dropping, further 3 points are added at a boiling point temperature of the system.
The mixture was stirred for 0 minute to complete the polymerization reaction, and an aqueous polyacrylate solution (polymerization product P2) having a solid content of 34% by weight and a neutralization ratio of 30 mol% was obtained.

[0035]

Polymerization Example 3 A four-necked flask having a capacity of 5 liters equipped with a thermometer, a nitrogen inlet tube, a stirrer and a reflux condenser was filled with water.
0 g and maleic anhydride 466 g were charged and the temperature was raised to 100 ° C. Next, 500 g of a 10% by weight 2,2′-azobis-2-amidinopropane dihydrochloride aqueous solution and 1714 g of an 80% by weight acrylic acid aqueous solution were continuously added dropwise at a boiling temperature under atmospheric pressure for 120 minutes to carry out a polymerization reaction. It was After completion of the dropping, the polymerization reaction was completed by further stirring for 30 minutes at the boiling temperature of the system to obtain a polyacrylic acid-maleic acid copolymer aqueous solution (polymerization product P3) having a solid content of 56% by weight.

[0036]

Polymerization Example 4 A four-necked flask having a capacity of 5 liters equipped with a thermometer, a nitrogen inlet tube, a stirrer and a reflux condenser was charged with 12 parts of water.
24 g was charged and the temperature was raised to 100 ° C. Then 2% by weight
40 g of sodium persulfate aqueous solution and 2666 g of 30 wt% acrylic acid aqueous solution were continuously added dropwise at normal temperature at boiling temperature over 60 minutes to carry out polymerization reaction. Further, 70 g of a 2 wt% sodium persulfate aqueous solution is added under normal pressure for 15 minutes
Continuously add dropwise at the boiling point temperature, and after completion of the addition, stir for an additional 30 minutes at the boiling point temperature of the system to complete the polymerization reaction, and to obtain a solid content of 2
A 0% by weight aqueous solution of polyacrylic acid (polymerization product P4) was obtained.

[0037]

Polymerization Example 5 A separable flask having a capacity of 1 liter, equipped with a thermometer, a nitrogen introducing tube, a stirrer and a reflux condenser, was used.
After charging 00 g of methacrylic acid and 780 g of water and blowing nitrogen gas with stirring to remove oxygen dissolved in the aqueous solution, 20% by weight of 2,2′-azobis-2-
20 g of amidinopropane dihydrochloride was added and immersed in a constant temperature bath at 60 ° C. The aqueous solution started to thicken after 5 minutes and showed a maximum temperature of 79 ° C. 15 minutes after the initiation of polymerization. After 3 hours, an aqueous polymethacrylic acid solution having a solid content of 20% by weight (polymerization product P5) was obtained.

[0038]

Examples 1 to 11 and Comparative Examples 1 to 3 Polymerization products A1 to A5 obtained in the above-mentioned Polymerization Examples 1 to 5 were loaded with the polymerization products by the methods shown in the following drying methods 1 to 3. Drying is performed by changing the area ratio, heating conditions and cooling conditions variously.
The physical properties of the obtained polymers were evaluated. The results are shown in Table 1 to Table 3.
It is shown collectively.

Drying Method 1 A pair of rollers 2 such as the rotary dryer shown in FIG.
A drying method of heat transfer heating with a heating plate 4 and heat transfer cooling with a cooling plate 5 from below the endless belt 1 made by impregnating Teflon into a glass fiber cloth having a heat resistant temperature of 260 ° C. and rotating by a and 2b was adopted. . The heating conditions and the cooling conditions were changed as shown in Tables 1 to 3 to perform drying. Length of heating plate is 100 cm, length of cooling plate is 20 c
m. Each of the polymerization products P on this belt is shown in Tables 1 to 3
In order to obtain the thickness and the loading area ratio shown in (3), the polymerization product is supplied by using a swing nozzle provided at the lower end of the supply unit 3.
It was dried continuously. After drying, each polymer was obtained by peeling with a scraper 6.

Drying Method 2 A hot air dryer of the type in which hot air is blown in the transverse direction is used, and the polymerization product P is shown in Table 1 on a Teflon sheet having a heat resistant temperature of 260 ° C. on a wire mesh. After being applied at a thickness and a loading area ratio, it was placed, and hot air drying and cold air cooling were performed under the conditions shown in Table 1. After cooling, the sheet was peeled off to obtain a polymer.

Drying Method 3 The same operation as in Drying Method 2 was performed except that the Teflon sheet used in Drying Method 2 was changed to a polycarbonate sheet having a heat resistant temperature of 135 ° C. and the heating / cooling conditions were as shown in Table 1.

[0042]

[Table 1]

[0043]

[Table 2]

[0044]

[Table 3]

As is clear from Tables 1 to 3, the polymers obtained by the method of the present invention are excellent in storage stability and re-dissolvability in water and do not yellow, and are exfoliated with high drying efficiency. There was no problem in sex.

[0046]

INDUSTRIAL APPLICABILITY According to the present invention, a (meth) acrylic acid (salt) -based polymer, which is extremely excellent in all of redissolvability in water, storage stability of thickening effect after redissolution, etc., can be efficiently prepared. It can be manufactured. The polymer obtained in the present invention can be widely used as a thickener, a pressure-sensitive adhesive, a water absorbing agent, a coagulant, etc. by utilizing its excellent thickening action.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a drying method 1 used in Examples.

[Explanation of symbols]

 1 Belt 2a, 2b Roller 3 Polymerization Product Supply Section 4 Heating Plate 5 Cooling Plate 6 Scraper P Polymerization Product

Claims (3)

[Claims] 1. A (meth) acrylic acid (salt) -based monomer obtained by polymerizing a (meth) acrylic acid (salt) -based monomer comprising (meth) acrylic acid or a salt thereof in an aqueous solution and then removing water from the polymerization product. In producing the polymer, the neutralization ratio of the acid groups contained in the polymerization product is set to 50 mol% or less, and then the polymerization product is stacked on a sheet with a thickness of 0.5 to 10 mm.
The resulting (meth) acrylic acid (salt) -based polymer having a neutralization rate of 50 mol% or less is cooled to 60 ° C. or less, and then peeled from the sheet. A method for producing a (meth) acrylic acid (salt) polymer, which is characterized in that 2. The method for producing a (meth) acrylic acid (salt) polymer according to claim 1, wherein a water-soluble azo compound is used as a radical polymerization initiator during aqueous solution polymerization. 3. The (meth) acrylic acid according to claim 1, wherein a portion where the polymerization product is not loaded is provided on the sheet so that the loading area of the polymerization product is 80% or less of the effective drying area. Method for producing (salt) -based polymer.