JP2567453B2 - Method for producing water-soluble polymer and water-swellable polymer - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a water-soluble polymer and a water-swellable polymer. More specifically, the present invention relates to a method for producing a water-soluble polymer or water-swellable polymer having a low residual monomer content from a hydrogel polymer.

(Problems to be Solved by the Related Art and Invention) Examples of the water-soluble polymer that forms an aqueous gel-like polymer by polymerizing monomers in an aqueous solution include sodium polyacrylate,
There are polyacrylamide, polyacrylamide partial hydrolyzate, polyvinyl alcohol, etc., and these water-soluble polymers are used as coagulants for water treatment, mud additives for petroleum debris removal, food additives, thickeners, etc. .

Examples of the water-swellable polymer that forms a hydrogel polymer by polymerizing a monomer in an aqueous solution include, for example, crosslinked polyacrylic acid salt, ken compound of acrylic acid ester-vinyl acetate copolymer, and crosslinked polyvinyl alcohol modified. Products, partially neutralized polyacrylate cross-linked products, cross-linked isobutylene-maleic anhydride copolymers, starch-acrylic acid graft polymers, etc., sanitary absorbents, sanitary absorbents such as paper diapers, or agricultural and forestry, gardening, and greening. It is used as a water retention agent for foods, food freshness retention film, etc. In these applications, the polymer may come into contact with human skin or be absorbed into the body, and there is a risk that it will be mixed into drinking water and the like again after it has flowed out into the environment due to disposal, and thus it will be contained in the polymer. In recent years, the demand for reduction of residual monomers has been increasing.

Generally, as a method for reducing the residual monomer of a hydrogel polymer, addition of ammonia and amine (Japanese Patent Publication No. 33-2646, Japanese Patent Publication No. 50-40689) and addition of sulfite and hydrogen sulfite (USP
2960486, JP-A-55-135110), a method of adding these compounds to a residual monomer to reduce it, and a combination of a low-temperature decomposition type catalyst and a high-temperature decomposition type catalyst (JP-B-50-44280, JP-A-59-133).
205, JP-A-53-141388) or a combined use of a redox catalyst and an azo initiator (JP-A-50-96689, JP-B-47-26430), a method for polymerizing and reducing the residual monomer, and decomposition by a microorganism. A method of reducing the amount (Japanese Patent Publication No. 60-29523) has been proposed.

However, although the addition of ammonia, amines, sulfites, and bisulfites is quite effective in reducing residual monomers, a small amount of these compounds is not effective,
Further, there is a problem that the added compound itself is toxic.
In addition, the method in which a catalyst is used in combination does not have a sufficient effect in reducing the residual monomer, and the method using a microorganism is currently industrially difficult.

On the other hand, in order to obtain a water-soluble or water-swellable polymer by drying the hydrogel polymer, a conduction heat transfer type dryer, a radiation heat transfer type dryer, a hot air heat transfer type dryer or the like can be used. But,
Due to the speed of drying, a hot air heat transfer type dryer (hereinafter referred to as a hot air dryer) is often used. However, with such a method, the water content in the hydrogel polymer can be efficiently removed, but the residual monomer cannot be sufficiently reduced.

Furthermore, when a water-soluble polymer is produced by polymerizing a 40-80 wt% aqueous solution of acrylamide or a mixture of acrylamide and another vinyl monomer, the relative humidity of the polymerization atmosphere is set to 60% or more in an atmosphere. A method of polymerizing an aqueous solution by holding it in a thin film on a solid support (JP-A-54-15).
5296) has also been proposed. However, such a method can be applied only to a polymer obtained by a specific polymerization method, and it is difficult to achieve a high level of residual monomer reduction of, for example, 200 ppm or less.

Therefore, an object of the present invention is to provide a novel method for producing a hydrophilic polymer.

Another object of the present invention is to provide a water-soluble or water-swellable polymer having a low residual monomer content and a method for producing the polymer from a hydrogel polymer.

(Means and Actions for Solving the Problems) The inventors of the present invention have conducted extensive studies to solve the above-mentioned problems, and as a result, the amount of residual monomer is remarkably increased by drying the hydrogel polymer under specific conditions. It was found that the number decreased, and the present invention was completed.

That is, the present invention provides at least one selected from the group consisting of (meth) acrylic acid, a metal or ammonium salt of (meth) acrylic acid, acrylamide, 2-hydroxyethyl (meth) acrylate and acrylonitrile.
A water-containing gel polymer having a water content of 40 to 80% by weight obtained by polymerizing a monomer component containing 10% by weight or more of a seed monomer.
At a temperature of 80-250 ℃, containing at least water vapor and 50
Drying at least one kind selected from the group consisting of a conductive heat transfer dryer, a radiant heat transfer dryer, a hot air heat transfer dryer and a dielectric heating dryer while contacting with a gas having a dew point of -100 ° C. The present invention relates to a method for producing a hydrophilic polymer selected from the group consisting of a water-soluble polymer and a water-swellable polymer having a low residual monomer content, which is characterized in that it is dried at the dew point using a machine.

The hydrogel polymer in the present invention is a hydrogel of a water-soluble or water-swellable polymer obtained by polymerizing an aqueous solution of a monomer, and contains an unreacted monomer, The gel polymer is subdivided so as to have a surface area sufficient to be dried by the above gas.

Such a water-containing gel polymer is a water-containing gel polymer obtained by polymerizing a monomer in a mold as described in, for example, JP-B-48-42466. , Those which have been subdivided by cutting with an extruder, kneader, etc. Polymerization in a kneader, etc. with stirring blades capable of subdividing the hydrous gel polymer as described in JP-A-57-34101 Subdivision of water-containing gel-like polymer A water-containing gel-like polymer polymerized on a belt conveyor as described in JP-A-58-49714 is optionally subdivided by a meat cheater, an extruder, a kneader, etc. JP-B-59 And a pearl-like hydrogel polymer obtained by reverse phase suspension polymerization as described in -37003.

Examples of the monomer necessary for obtaining the hydrogel polymer in the present invention include (meth) acrylic acid or a metal salt or ammonium salt thereof, (meth) acrylamide, acrylonitrile, maleic acid, fumaric acid, or these Half-esterified product of saturated dibasic acid or metal salt or ammonium salt of these dibasic acid or half-esterified product, 2-acrylamido-2-methylpropanesulfonic acid, 2- (meth) acryloylethanesulfonic acid or metal salt thereof or Ammonium salt, 2-
Examples thereof include hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate,
These 1 type, or 2 or more types of mixtures can be used. In addition, for example, methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, vinyl acetate, vinyl propionate, etc. can be obtained in an amount that does not extremely impair the hydrophilicity of the hydrogel polymer that can obtain monomers. You may use. Furthermore, when obtaining a water-containing gel-like polymer of a water-swellable polymer, for example, ethylene glycol diacrylate, ethylene glycol dimethacrylate, diethylene glycol diacrylate, diethylene glycol dimethacrylate, triethylene glycol diacrylate, triethylene glycol dimethacrylate, polyethylene Glycol diacrylate, polyethylene glycol dimethacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, pentaerythritol triacrylate, pentaerythritol trimethacrylate, N, N'-methylenebisacrylamide, triallyl isocyanurate, pentaerythritol diacrylate, penta Crosslinking agent such as erythritol dimethacrylate Serial may be used in combination to the monomer.

Among these monomers, acrylic acid, a metal salt of acrylic acid and an ammonium salt, acrylamide, 2-hydroxyethyl (meth) acrylate, and acrylonitrile are more toxic than the monomer group. The method of the present invention is applied to a hydrogel polymer obtained by polymerizing a monomer component containing 10% by weight or more of at least one selected monomer, and an alkali metal acrylate and / Or ammonium salt and acrylic acid 0-100 / 10
It is particularly preferably applied to a hydrogel polymer which is a (co) polymer crosslinked product obtained by using a ratio of 0 to 0, more preferably 20 to 100/80 to 0, and most preferably 50 to 85/50 to 15. To be done.

Polymerization to obtain a water-containing gel polymer is a monomer component,
After degassing an aqueous monomer solution prepared by dissolving a polymerization initiator and a cross-linking agent used as necessary in water with an inert gas such as nitrogen gas, for example, in a mold as described in JP-B-48-42466. Polymerization by casting in a container, JP-A-58-4971
4, a method of polymerizing on a belt conveyor, as described in JP-A-57-34101 polymerization in a kneader or the like having a stirring blade capable of subdividing the hydrous gel polymer inside How to do it, and Japanese Patent Publication Sho 59-37003
The reverse phase turbidity polymerization and the like as described in 1.

The polymerization initiator is not particularly limited and may be used, for example, ammonium persulfate, potassium persulfate, hydrogen peroxide, V-50.
(2,2′-azobis (2-amidinopropane) hydrochloride manufactured by Wako Pure Chemical Industries, Ltd.) and the like, and these, sodium bisulfite, L-ascorbic acid, first
A redox type initiator or the like obtained by combining with a reducing agent such as an iron salt is used, but it is preferable to use a persulfate in combination with a reducing agent if necessary.

The water content of the water-containing gel polymer is 40 to 80% by weight.
The amount of the polymerization initiator used is 0.0001 to 0.5% by weight, preferably 0.0002 to 0.1% by weight, and 0.01 to 2% by weight, preferably 0.05, for the water-swellable polymer in the case of a water-soluble polymer.
~ 1% by weight.

In carrying out the present invention, it is preferable that the residual monomer of the hydrogel polymer is small, but usually the residual amount of the monomer is 0.1 to 10% by weight, and a large amount of the residual monomer is always the residual monomer according to the method of the present invention. A hydrophilic polymer which is a low water-soluble or water-swellable polymer is obtained. The hydrogel polymer obtained by the polymerization may be already crushed in some cases, but in many cases, it is preferable to make it into a form that can be dried by subdividing. As a method of subdividing,
For example, there is disintegration using a meat chiyosper, extruder, kneader or the like.

The gas used for drying the hydrogel polymer in the present invention and simultaneously reducing the residual monomer is not particularly limited as long as it contains at least water vapor and has a dew point of 50 to 100 ° C. Preferred are steam-air mixed gas and / or steam-inert gas or steam. Further, the dew point of the gas is preferably in the range of 60 to 100 ° C. from the effect of reducing the amount of residual monomer. Drying temperature is 80-250
Although the temperature is 0 ° C, it is preferably 100 to 180 ° C because of the effect of drying, the effect of reducing the amount of residual monomers and the prevention of deterioration of the polymer. The drying temperature here means the temperature of at least one of the gas used and the hydrogel polymer to be dried. Examples of the inert gas include nitrogen, carbon dioxide, helium and the like.

Examples of the drying device used in the present invention include a conductive heat transfer type dryer, a radiant heat transfer type dryer, a hot air heat transfer type dryer, and a dielectric heating dryer. (Hereinafter, referred to as a hot air dryer) is preferable. Examples of the hot air dryer include a ventilation band type, a ventilation circuit type, a ventilation vertical type, a parallel flow band type, a ventilation tunnel type, a ventilation groove type stirring type, a fluidized bed type, an air flow type, and a spray type drying device. Therefore, when a hot air dryer is used, the most preferable method is to supply hot air containing at least water vapor and having a dew point of 50 to 100 ° C and a temperature of 80 to 250 ° C to the drying zone for drying. Radiation heat transfer type devices include infrared rays and far infrared ray dryers, and conduction heat transfer type devices include paddle dryers,
Examples thereof include a drum dryer.

To carry out the method of the present invention, the hydrogel polymer may be dried under the conditions specified by the method of the present invention until the drying is completed, but in some cases, Only the first stage is dried under the conditions specified by the method of the present invention,
Then, it may be dried by a completely different method other than the present invention such as drying by contact with a gas having a dew point of less than 50 ° C. or vacuum drying. However, in the case of drying by this method, the solid content of the hydrogel polymer is 60% by weight or more, preferably 80% by weight or more, more preferably 90% by weight or more conditions defined by the method of the present invention It is preferable to dry down. Furthermore, the water-soluble or water-swellable polymer obtained by drying the hydrogel polymer after polymerization under conditions other than the conditions specified by the method of the present invention is again used as the hydrogel polymer. It may be dried under the conditions defined by the method of the invention.

The temperature of the gas and / or water-containing gel polymer in the dryer at the time of drying is 80 to 250 ° C, preferably 100 to 180 ° C. If the temperature is lower than 80 ° C, the effect of reducing the residual monomer is not sufficient, and the drying efficiency is poor, which is not practical. Further, at a temperature of 250 ° C. or higher, deterioration of the polymer may occur to deteriorate the quality, which is not practical. The dew point of the mixed gas is in the range of 50 to 100 ° C., preferably 60 to 100 ° C., but if it is less than 50 ° C., the effect of reducing the residual monomer is small, which is not practical.

The hydrophilic polymer thus obtained, the residual monomer is significantly reduced, for example, in the water-soluble polymer is 0.
3% by weight or less, particularly 0.05% by weight or less in a water-swellable polymer that requires a high level of residual monomer reduction,
It is reduced to 0.02% by weight or less.

(Effect of the Invention) According to the method of the present invention, a hydrophilic polymer which is a water-soluble or water-swellable polymer having a significantly small amount of residual monomers can be obtained. Moreover, in a dryer that also circulates hot air, the water vapor that evaporates from the hydrous gel polymer can be used as it is to obtain a high dew point, and therefore, the amount of fresh air can be reduced, so the amount decreased. It is possible to save energy for the amount of heat that heats the fresh air. Furthermore, for example, in a ventilated band dryer,
When drying with hot air having a low dew point, there is a phenomenon that the physical properties of the thick material are uneven on the upper side, the middle side, and the lower side. However, the unevenness is alleviated by the method of the present invention.

Therefore, the hydrophilic polymer, which is a water-soluble or water-swellable polymer obtained by applying the method of the present invention, has no adverse effects on the human body, the environment, etc., and is a coagulant for water treatment, oil drilling mud. It is preferably used for applications such as additives, food additives, absorbents for sanitary materials, water retention agents, and food freshness keeping films.

(Examples) Hereinafter, the present invention will be described in detail with reference to Examples, but the scope of the present invention is not limited to these Examples.

Examples 1 to 10 Inner volume 10 openings 220 mm × 260 mm, depth 240 mm Blades with a rotating diameter of 120 mm Two sigma type blades with two jackets made of stainless steel with a lid attached to a kneader (kneader) with a lid,
Into this kneader, 5500 g of an aqueous solution of an acrylate monomer consisting of 75 mol% of sodium acrylate and 25 mol% of acrylic acid (40% of monomer concentration) and 2.2 g of methylenebisacrylamide were charged, and a nitrogen gas was blown into the reaction system. The inside was replaced with nitrogen. Then, two sigma type blades were rotated at speeds of 67 and 56 rpm, respectively, and 2.5 g of ammonium persulfate and 2.5 g of sodium bisulfite as polymerization initiators were added while heating the jacket with hot water at 35 ° C. The polymerization reaction started 5 minutes after the addition of the polymerization initiator. Twenty minutes after the addition of the polymerization initiator, the temperature in the reaction system reached 83 ° C, the gel polymer was subdivided into fine particles with a diameter of about 5 mm, and stirring was continued for 60 minutes after the start of the polymerization reaction. Then, the hydrogel polymer was taken out. In this hydrogel polymer,
1000 unreacted acrylic acid and sodium acrylate combined
0ppm Atsuta.

This hydrogel polymer 1 was spread in a hot air dryer (Okawara Seisakusho, aeration dryer, see FIG. 1) 8 to a thickness of 40 mm. Then, the gas from the fresh air introducing pipe 2 and the steam introducing pipe 3 is introduced into the heat exchanger 6 and heated by the heat transfer medium introduced from the heat medium introducing pipe 7 to a temperature of 100 to 180 ° C. and a dew point of 60 to 100. Hot air consisting of steam-air mixed gas, steam-inert gas mixed gas, or steam at 0 ° C was blown at a wind speed of 1.0 m / sec and dried to a water content of 10% by weight or less to obtain a water-swellable polymer. A part of the gas was exhausted through the exhaust pipe 4 and then circulated to the heat exchanger 6 by the blower 5. The amount of residual monomers and absorption capacity of the water-swellable polymer obtained by pulverizing this water-swellable polymer were measured by the following methods. The amount of residual monomer was 0.5 g of powder dispersed in 1000 ml of ion-exchanged water and stirred for 2 hours, followed by Whatman's paper GF / F (particle retention capacity).
0.7 micron) and then measured by liquid chromatography.

As for the absorption capacity, 0.2 g of powder was uniformly put in a non-woven Taibagu type bag (40 mm × 150 mm) and immersed in 0.9 wt% saline, and after 30 minutes, the weight was measured and the absorption capacity was calculated according to the following formula. It was

The results are shown in Table 1.

Comparative Examples 1 to 5, except that hot air having a temperature of 120 to 180 ° C. and a dew point of 5 ° C. was used instead of the hot air composed of the steam / air mixed gas, the steam / inert gas mixed gas or steam in Example 1.
The same operation as in Example 1 was repeated to obtain a water-swellable polymer for comparison. Example 1 using this comparative water-swellable polymer
The results of the same tests as in Table 1 are shown in Table 1.

As shown in Table 1, the dew point of the hot air at the inlet of the hot air dryer is 60,
Water-swellable polymers dried at 80 and 100 ° C have dew points of 5 and 2
The residual monomer amount was significantly reduced as compared with the comparative water-swellable polymer dried with hot air at 0 and 40 ° C.

Example 11 The hydrogel polymer obtained by polymerizing in Example 1 was heated in the same apparatus as in Example 1 with hot air consisting of a steam / air mixed gas at a temperature of 120 ° C. and a dew point of 80 ° C. at a wind speed of 1.0 m / sec. Spray and dry to a solid content of 80%, and further dry it with hot air with a dew point of 5 ° C and a wind speed of 1.0 m / sec and a non-humidified water content of 10% by weight.
It was dried to the following, pulverized, and the residual monomer and absorption capacity were measured by the same method as in Example 1. The results are shown in Table 2.

As shown in Table 2, a water-swellable polymer obtained by partially drying with hot air consisting of a steam / air mixed gas and then drying with hot air that was not humidified, and the steam / air mixture until the end in Examples. Comparing the obtained water-swellable polymers dried with hot air consisting of gas, there was almost no difference.

Examples 12 to 13 Powders of the hydrogel polymer (12 and 13) were obtained by repeating the same procedure as in Example 1 except that the monomer components used in Example 1 had the compositions shown in Table 3. Obtained. These hydrogel polymers (12 and 13) were dried and pulverized by the same procedure as in Example 1 (however, the hot air used was a steam / air mixed gas having a temperature of 120 ° C. and a dew point of 80 ° C.) to swell with water. A powder of water-soluble and water-soluble polymer was obtained. Using these powders, the amount of residual monomer was measured under the same conditions as in Example 1, and the results are shown in Table 4.
It was shown to.

Comparative Examples 6 to 7 In Examples 12 to 13, a temperature of 120 ° C. and a dew point of 80 ° C. were used instead of the hot air composed of a steam / air mixed gas.
The same procedure was repeated except that hot air having a dew point of 5 ° C. and a dew point of 5 ° C. was used to obtain a powder of a comparative water-swellable and comparative water-soluble polymer. Using these powders, the amount of residual monomer was measured under the same conditions as in Example 1, and the results are shown in Table 4.

As shown in Table 4, the temperature of 120 ° C and the dew point of 80 ° C, which was dried with hot air composed of steam / air mixed gas, was 12 ° C.
The amount of residual monomer was smaller than that of the product dried with hot air having a dew point of 5 ° C. at 0 ° C.

Example 14 Apparatus as shown in FIGS. 2 and 3, that is, two stainless steel plates having fluorine resin coating 16 on the inside.
Insert the rubber packing 15 between 17 and the bolt 13 and nut.
Casting polymerizer fixed and sealed with 18 (internal volume 1.6,
(Length 230 mm x width 230 mm x width 30 mm) 2000 g of sodium acrylate aqueous solution with a concentration of 40% by weight, which was previously replaced with nitrogen.
Ammonium persulfate 0.04g and sodium bisulfite
0.02 g was introduced through the raw material inlet 12 and air was exhausted through the air outlet 14. This cast polymerization apparatus was placed in a water bath equipped with a stirrer and a temperature controller, the temperature of the water bath was maintained at 30 ° C., and polymerization was performed while removing reaction heat. Five hours after the initiation of the polymerization, the hydrogel polymer was taken out from the casting polymerization apparatus, made into a string with a meat cheater and dried and pulverized by the same procedure as in Examples 12 and 13 to obtain a water-soluble polymer. A powder was obtained. The amount of residual monomer in the obtained powder was measured by the bromine addition method, and 0.2 g of the powder was added to water.
The viscosity of an aqueous solution dissolved in 100 g at 25 ° C. was measured with a Brutsk Field viscometer. The results are shown in Table 5.

Comparative Example 8 A water-soluble polymer for comparison was obtained by repeating the same operation as in Example 14 except that hot air having a temperature of 120 ° C. and a dew point of 5 ° C. was used instead of the hot air composed of the steam / air mixed gas in Example 14. It was The results of the same test as in Example 14 using this comparative water-soluble polymer are shown in Table 5.

As shown in Table 5, steam with a temperature of 120 ° C and a dew point of 80 ° C
Drying with hot air consisting of an air-mixed gas has a dew point of 5 ° C.
The amount of residual monomer was smaller than that dried with hot air.

Examples 15 to 16 The same operation as in Example 14 was repeated, except that a monomer component consisting of 480 g of acrylamide and 320 g of sodium acrylate was used in place of sodium allylate (800 g) in Example 14, to give elasticity. A water-containing gel polymer was obtained.
This was formed into a string in the same manner as in Example 14, and the temperature was 120 ° C. and 150 ° C. in a rotary aeration dryer (PTA-30 manufactured by Okawara Seisakusho).
C., hot air consisting of a mixed gas of steam and air having a dew point of 80.degree. C. was blown to dry the mixture to a water content of 10% by weight or less, and further pulverized to obtain a water-soluble polymer powder. The residual monomer amount of this powder was measured by the same method as in Example 14. The results are shown in Table 6.

Comparative Examples 9 to 10 The same operations as in Examples 15 to 16 were performed, except that hot air having a temperature of 120 ° C., 150 ° C. and a dew point of 5 ° C. was used instead of the hot air composed of the steam / air mixed gas in Examples 15 to 16. Repeat,
A comparative water-soluble polymer powder was obtained. The residual monomer amount of this powder was measured by the same method as in Example 14, and the results are shown in Table 6.

As shown in Table 6, the amount of residual monomer was significantly reduced in the case where the steam / air mixed gas at the inlet of the hot air dryer was dried with hot air having a dew point of 80 ° C, compared with the case where it was dried with hot air with a dew point of 5 ° C. .

Example 17 5000 ml with a reflux condenser whose system was previously replaced with nitrogen
A flask was charged with 1930 g of sorbitan monolaurate of HLB8.6 and 2130 g of cyclohexane, and the surfactant was dissolved at room temperature under stirring. Then, 1200 g of an aqueous solution of 25 mol% acrylic acid and 75 mol% sodium acrylate (concentration 40 wt% ) Was added dropwise with an aqueous monomer solution containing 1.3 g of potassium persulfate and suspended. After the system was sufficiently replaced with nitrogen again, the temperature was raised and the bath temperature was kept at 55 to 60 ° C. to carry out a polymerization reaction for 3 hours. The polymer obtained by passing the generated polymerization liquid was heated at a temperature of 120 ° C. in a fluidized bed dryer (FCS-1 manufactured by Okawara Seisakusho).
Moisture content with hot air consisting of a steam / air mixture with a dew point of 80 ° C
The amount of residual monomers in the powder of the water-swellable polymer obtained by pulverizing this after drying to 10% by weight or less was measured by the same method as in Example 1. The results are shown in Table 7.

Comparative Example 11 The same operation as in Example 17 was repeated except that hot air having a temperature of 120 ° C. and a dew point of 5 ° C. was used in place of the hot air composed of the steam / air mixed gas in Example 17, and the comparative water-swellable polymer was obtained. Powder was obtained. The residual monomer amount of this powder was measured by the same method as in Example 17, and the results are shown in Table 7.

As shown in Table 7, the amount of residual monomer was significantly reduced in the one dried with hot air in which the dew point of the steam / air mixed gas at the inlet of the hot air dryer was 80 ° C, compared with the one dried by other methods.

Example 18 Example 1 A far-infrared radiation ceramic heater (Jard Co., Ltd.) in which the water-containing gel-like polymer obtained was previously aerated with an air / steam mixed gas to adjust the atmosphere to a dew point of 80 ° C.
Box type dryer (6 with SF type Infrajet 2000W)
(00 x 600 x 600 mm) to a thickness of 20 mm, heat with a far infrared radiation ceramic heater, water content 10 in 30 minutes
% Or less to obtain a water-swellable polymer. At this time, the temperature of the gas just above the gel was 120 ° C. The water-swellable polymer was pulverized, and the residual monomer and absorption capacity were measured in the same manner as in Example 1. The results are shown in Table 8.

Comparative Example 12 A water-swellable polymer for comparison was obtained by repeating the same operation as in Example 18 except that the air was previously ventilated and the atmosphere was adjusted to 20 ° C. or lower. At this time, the temperature of the gas just above the gel was 120 ° C. The water-swellable polymer for comparison was pulverized, and the residual monomer and absorption capacity were measured by the same method as in Example 1. The results are shown in Table 8.

As shown in Table 8, the amount of residual monomer was remarkably reduced in the sample dried in an atmosphere having a dew point of 80 ° C as compared with those having a dew point of 20 ° C or lower.

Example 19 The hydrogel polymer obtained in Example 1 was preliminarily aerated with an air / steam mixed gas to form an atmosphere having a dew point of 80 ° C. and a temperature of
JP-B-55-21041 installed under the condition adjusted to 120 ℃
Using a double-drum dryer with a scraping blade (effective drum area 1.0 m ² ) as described in, conditions under which the drum surface temperature is 140 ° C, the rotation speed is 1 rpm, and the film thickness of the dried product is 1 mm. After being dried to the ground, it was pulverized to obtain a water-swellable polymer. The residual monomer and absorption capacity of this water-swellable polymer were measured in the same manner as in Example 1. The results are shown in Table 9.

Comparative Example 13 A comparative water-swellable polymer was obtained by repeating the same operation as in Example 19, except that the atmosphere was adjusted to 20 ° C. or lower and the temperature was 120 ° C. by passing air through. The residual monomer and absorption capacity of this comparative water-swellable polymer were measured in the same manner as in Example 1. The results are shown in Table 9.

As shown in Table 9, those dried in an atmosphere with a dew point of 80 ° C. had less residual monomers than those with a dew point of 20 ° C. or lower.

Comparative Example 14 The procedure of Example 1 was repeated, except that hot water of 95 ° C. was passed through the jacket immediately after the temperature in the reaction system reached 83 ° C. for 5 hours to repeat the polymerization operation for a long time. The amount of residual monomer in the hydrogel polymer was measured by sampling every hour after the initiation of the polymerization reaction. Table 10 shows the results.

As is clear from Table 10, even if the atmosphere during the polymerization in which the solid content of the water-containing gel polymer is almost constant is the same as the conditions specified in the present invention, the high level of residue as obtained in Example 1 remains. No monomer reduction is achieved, and a high level of residual monomer reduction is achieved only by setting the atmosphere to the conditions specified in the present invention in the drying process in which the solid content of the hydrogel polymer rises with time.

[Brief description of drawings]

FIG. 1 is a schematic explanatory view of a drying apparatus used in Examples 1 to 13 and Comparative Examples 1 to 7 of the present invention, and FIG. 2 is a polymerization used in Examples 14 to 16 and Comparative Examples 8 to 10 of the present invention. 3 is a schematic front view of the apparatus, and FIG. 3 is a schematic sectional view taken along the line III-III in FIG. 1: Water-containing gel polymer, 2: Fresh Air introduction pipe 3: Water vapor introduction pipe, 4: Exhaust discharge pipe 5: Blower, 6: Heat exchanger 7: Heat medium introduction pipe, 11: Casting polymerization device 12: Raw material Input port, 13: Bolt 14: Air exhaust port, 15: Rubber packing 16: Fluorocarbon resin coating, 17: Stainless steel plate 19: Nut

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kaoru Iwasaki Kaoru Iwasaki 992 No. 1 Nishioki Okihama, Aboshi-ku, Himeji-shi, Hyogo Prefecture Nihon Catalysis & Chemicals Co., Ltd. Himeji Laboratory (72) Inventor Akiraaki Fujiwara Nishioki-oki 952, Aboshi-ku, Himeji-shi, Hyogo Prefecture Address 1 Nihon Catalytic Chemical Industry Co., Ltd., Himeji Laboratory (72) Inventor Takumi Hatta 5-8 Nishimitabicho Suita City, Osaka Prefecture Central Research Laboratory, Nippon Catalysis Chemical Co., Ltd. (72) Inventor Tadashi Shimomura Osaka Prefecture Central Research Laboratory, Nippon Catalysis Chemical Co., Ltd. 5-8 Nishiomitabicho, Suita-shi (56) Reference JP-A-51-112893 (JP, A) JP-A-57-177009 (JP, A)

Claims (10)

(57) [Claims] 1. (Meth) acrylic acid, a metal or ammonium salt of (meth) acrylic acid, acrylamide, 2-
Water-containing gel-like polymer having a water content of 40-80% by weight obtained by polymerizing a monomer component containing 10% by weight or more of at least one monomer selected from the group consisting of hydroxyethyl (meth) acrylate and acrylonitrile. 80-250 coalescing
At a temperature of ℃, containing at least water vapor and 50 ~ 100 ℃
Using at least one dryer selected from the group consisting of a conductive heat transfer dryer, a radiant heat transfer dryer, a hot air heat transfer dryer, and a dielectric heating dryer while contacting with a gas having a dew point of A method for producing a hydrophilic polymer selected from the group consisting of a water-soluble polymer and a water-swellable polymer, which has a low residual monomer content and is characterized by being dried at the dew point. 2. The method according to claim 1, wherein the gas containing at least steam is at least one selected from the group consisting of steam-air mixed gas, steam-inert gas mixed gas and steam. 3. A gas containing at least steam of 60 to 10
The method of claim 2 having a dew point of 0 ° C. 4. The method according to claim 1, wherein the solid content of the hydrophilic polymer is 90% by weight or more. 5. The method according to claim 1, wherein the drying temperature is 100 to 180 ° C. 6. The dryer is a hot air heat transfer type dryer.
The method described in. 7. The hydrogel polymer according to claim 1, which is a cross-linked copolymer of acrylic acid and at least one salt selected from the group consisting of alkali metal acrylates and ammonium acrylates. Method. 8. The method according to claim 7, wherein the hydrogel polymer is obtained by using a persulfate and, if necessary, a reducing agent as an initiator during polymerization. 9. A hydrogel polymer is dried while contacting with a gas containing at least water vapor at a temperature of 80 to 250 ° C. and having a dew point of 50 to 100 ° C. until the solid content of the hydrogel polymer is 60% by weight or more, The method according to claim 1, which is then dried by another method. 10. The method according to claim 9, wherein the hydrogel polymer is contacted with the gas until the solid content is 80% by weight or more.