JP2008013748A - Method for producing (meth) acrylic acid (salt) type water-soluble polymer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a (meth)acrylic acid (salt) type water-soluble polymer capable of producing, at high productivity, a high molecular weight (meth)acrylic acid (salt) type water-soluble polymer wherein insolubles are satisfactorily reduced. <P>SOLUTION: A method of producing a (meth)acrylic acid (salt) type water-soluble polymer comprises drying an aqueous gel containing a (meth)acrylic acid (salt) type water-soluble polymer by passing a hot gas at 160-230°C having a dew-point of 70°C or lower through spaces in the aqueous gel at a linear speed of 0.1 m/s or more. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to a method for producing a (meth) acrylic acid (salt) -based water-soluble polymer. More specifically, the present invention relates to a method for producing a (meth) acrylic acid (salt) -based water-soluble polymer that is widely used in various fields such as medicine, paints, production processes, civil engineering and construction.

(Meth) acrylic acid (salt) -based water-soluble polymers are known to exhibit properties such as cohesion and thickening. For example, in the pharmaceutical field, adhesives and water retention of poultices and poultices It is used as an additive and hydrophilic ointment base material for the purpose of improving adhesiveness. In the paint field, it is used as a thickener for carpet compounds, as a thickener and adhesive for paints, and as an adhesive improver. . In the field of production processes, it is frequently used as a red mud settling agent during alumina production and a flocculant for salt water purification in the soda industry. Furthermore, in the civil engineering and construction fields, it is used as a drilling soil treatment agent, dredged soil treatment agent, and a mud additive, and in other general industrial fields, it is also used as a moisture absorbent, desiccant, surface modifier, and various thickeners. Has been. As described above, (meth) acrylic acid (salt) -based water-soluble polymers are widely used in various fields.

In the production of such a (meth) acrylic acid (salt) -based water-soluble polymer, the water content is usually obtained by drying a hydrogel polymer (hereinafter simply referred to as a hydrogel) prepared by aqueous solution polymerization. However, if the hydrogel is pulverized, the hydrogel is made porous or refined, the drying property is improved, and the production efficiency and product quality are improved. Become. As a method for crushing the (meth) acrylic acid (salt) -based water-soluble polymer-containing gel, it is generally performed by an extruder, and the (meth) acrylic acid (salt) -based water-soluble polymer is: For example, it is manufactured through a polymerization process, a crushing process, a drying process, and the like.

As a conventional method for producing a (meth) acrylic acid (salt) -based water-soluble polymer, monomer components such as (meth) acrylamide and (meth) acrylic acid (salt) are polymerized under specific conditions, and water is contained. A method for producing a high molecular weight water-soluble polymer is described in which a hydrous rubber-like polymer having a rate of less than 60% by weight is obtained, coarsely pulverized, dried, and pulverized at a moisture content of 18% by weight or more (for example, Patent Document 1). Although pulverization is performed in a high water content region having a water content of 18% by weight or more, quality deterioration associated with pulverization can be prevented and generation of fine powder can be prevented. However, the amide system used is not focused on drying conditions. Since the polymer is hydrolyzed, it cannot be dried at a high temperature, and there is room for devising to sufficiently reduce the insoluble content of the high molecular weight water-soluble polymer.

In addition, cationic system that photopolymerizes an aqueous solution consisting of a cationic vinyl monomer alone or a mixture with other water-soluble vinyl monomers using ultraviolet rays under specific conditions, and makes the particles fine and dry. A method for producing a water-soluble polymer is described (for example, see Patent Document 2). Although various excellent effects are exhibited by such a production method, the production method is a production method of a cationic water-soluble polymer, and is suitable for producing an anionic polymer in terms of quality. There was room for ingenuity. In addition, since cationic water-soluble polymers cannot be dried at high temperatures because hydrolysis occurs, the productivity is low. When producing an anionic polymer, the drying conditions are also devised from the viewpoint of productivity. There was room.

Furthermore, a method for producing a hydrophilic polymer is described, which comprises drying a hydrogel polymer in contact with a gas containing water vapor under specific conditions and drying (high-humidity drying) (for example, patent document). 3). The technique disclosed here is to reduce the residual monomer content by bringing a hydrogel polymer into contact with a gas containing water vapor under specific conditions and drying. In the present technology, since the hydrogel is dried under high humidity, the hydrophilic polymer is steamed as a result, and the crosslinking is promoted. Therefore, when the hydrophilic polymer as a production target is a crosslinked polymer, there is no problem because the crosslinked polymer itself is insoluble, but in the case of a water-soluble polymer, a water-soluble polymer with a small amount of insoluble matter is used. It was necessary to devise to get.

A method for producing a hydrophilic crosslinked polymer through a specific drying and crushing process after polymerizing an aqueous solution containing a hydrophilic monomer and a crosslinking agent to obtain a hydrous crosslinked polymer is described. (For example, see Patent Document 4). The technique disclosed here is useful in terms of being able to perform uniform and efficient drying and less deterioration during drying (increase in soluble content), but production of a crosslinked polymer. Is the method. That is, it is not intended to reduce insoluble matter. In other words, the technique of Patent Document 4 is intended to obtain a polymer having a low soluble content (in other words, a high amount of insoluble content), and is the completely opposite purpose of the present application.
JP 58-52310 A (pages 1 to 5) JP 62-235305 A (1st, 2nd, 5th pages) JP-A 64-26604 (page 1-4) Japanese Patent Laid-Open No. 11-240914 (page 1-4)

This invention is made | formed in view of the said present condition, and can obtain the high molecular weight (meth) acrylic acid (salt) type | system | group water-soluble polymer by which the insoluble content was fully reduced with high productivity ( An object of the present invention is to provide a method for producing a (meth) acrylic acid (salt) -based water-soluble polymer.

The inventor conducted various studies on the production method of the (meth) acrylic acid (salt) water-soluble polymer, and the quality of the obtained (meth) acrylic acid (salt) water-soluble polymer was determined in the drying step. Focusing on the cause, the inventors have conceived that the above-mentioned problems can be solved brilliantly by performing drying under specific conditions. Specifically, not a plate-like hydrogel but a hydrogel having a gap through which hot air can pass (for example, extruded gel (granular, string-like, etc.), finely crushed gel, finely cut gel, etc.) When the hot air having a dew point of 70 ° C. or lower and a temperature of 160 to 230 ° C. passes through the hydrogel gap at a linear velocity of 0.1 m / s or higher and is dried, the insoluble matter is reduced, It has been found that a high molecular weight (meth) acrylic acid (salt) -based water-soluble polymer can be obtained with high productivity. In such a drying process, the linear velocity of hot air is set to 0.5 to 3.0 m / s, the (meth) acrylic acid (salt) -based water-soluble polymer hydrated gel is used as an extruded gel, or (meth) acrylic. If an acid (salt) -based water-soluble polymer hydrogel is made into a polymer hydrogel obtained by polymerizing a monomer component containing 60 mol% or more of a (meth) acrylic acid (salt) monomer, it is more inconvenient. It has been found that a polymer having a reduced dissolved content can be produced with high productivity. Further, this is also the case with the step of drying by controlling the drying speed so that the time for the solid content concentration of the (meth) acrylic acid (salt) -based water-soluble polymer-containing gel to reach 97% by mass is within 100 minutes. It has been found that it is possible to obtain a (meth) acrylic acid (salt) -based water-soluble polymer with reduced insoluble content, and the present invention has been achieved.

That is, the present invention is a method for producing a (meth) acrylic acid (salt) water-soluble polymer by drying a (meth) acrylic acid (salt) water-soluble polymer hydrogel, A (meth) acrylic acid (salt) system comprising a step of drying such that hot air having a dew point of 70 ° C. or less and a temperature of 160 to 230 ° C. passes through the hydrogel gap at a linear velocity of 0.1 m / s or more. It is a manufacturing method of a water-soluble polymer.
In addition, when the present inventors dried a (meth) acrylic acid (salt) -based water-soluble polymer water-containing gel, they found that the insoluble matter after drying is related to the porosity of the water-containing gel. That is, when comparing a porous gel (surface area increased) and a non-porous gel, the former gel was found to have less insoluble matter.
The degree of porosity can be expressed in terms of how much specific power is applied to the gel (the power applied when it is extruded to form the gel), or the surface area per unit volume of the gel. A preferred range of specific power is 0.06 kWh / kg or more, and a preferred range of surface area is 9 cm ² / cm ³ or more. When extruded with a high specific power, the surface area of the gel increases, and the specific power affects the drying performance.
In the present invention, a gel extruded with a specific power that is not so large, such as a gel obtained using a meat chopper as an extruder to form the gel, or a gel having a surface area of less than 9 cm ² / cm ³ is also used. Yes (ie within the scope of the present invention).
Further, even the above-mentioned meat chopper becomes a porous gel which is a preferable form of the gel in the drying step of the present invention depending on conditions. In this case, the surface area of the obtained gel is 9 cm ² / cm ³ or more, and can be preferably applied to the drying step of the present invention. That is, when the gel becomes porous, its surface area is increased and drying properties are improved.
That is, even when extruded under normal conditions with a meat chopper, it can be used as a gel of the present invention, can be applied to the drying process of the present invention, and can be a porous gel depending on the extrusion conditions, It is possible to obtain a gel form preferable for the present invention (a gel form having good drying properties), that is, a gel having a large surface area.
In the present invention, as described above, extrusion is performed at a high specific power (0.06 kWh / kg or more, the upper limit is not limited, and the maximum specific power that can be applied when the gel is extruded by an extruder is the upper limit). High-surface area (9 cm ² / cm ³ or more, the upper limit is not limited, the maximum surface area possible in the technology that can make the gel high surface area is the upper limit) Although it can be said to be an optimal embodiment in terms of obtaining quality (low insoluble content), the upper limit of the specific power is 0 in terms of equipment and inadvertently applying excessive specific power unnecessarily to the gel. 0.6 kWh / kg is preferable, and 0.2 kWh / kg is more preferable.
In summary, if the gel is porous (porous), the drying property is improved. When the porous gel is dried, the porous gel is quickly dried, and the amount of insoluble matter can be controlled to be small. In order to dry a water-soluble hydrogel, the conditions of the extruder (specific power) when molding before drying, such that the gel becomes porous, or the surface area per unit volume of the gel is increased. It is preferable to adopt a simple gel preparation method from the viewpoint that the insoluble matter is controlled to be small and higher quality (low insoluble matter) is obtained. In order to control the amount of insoluble matter to be small, it has been found that the specific power when forming a gel is one point.
The present invention is described in detail below.

In the method for producing a (meth) acrylic acid (salt) -based water-soluble polymer of the present invention, a (meth) acrylic acid (salt) -based water-soluble polymer hydrated gel (hereinafter also simply referred to as “hydrated gel”) is dried. Then, a method for producing a (meth) acrylic acid (salt) water-soluble polymer, in which the hot air having a dew point of 70 ° C. or less and a temperature of 160 to 230 ° C. It includes a step of drying so as to pass at a linear speed of 0.1 m / s or more.
In the present invention, the (meth) acrylic acid (salt) -based water-soluble polymer means a (meth) acrylic acid-based water-soluble polymer or a (meth) acrylate-based water-soluble polymer.
The dew point can be measured using a dew point meter. Although it does not specifically limit as a dew point meter, For example, the specular cooling dew point meter (UHQ-4P) for a high dew point measurement by Toyo Technica Co., Ltd. is mentioned.
The linear velocity is an average value of the entire air flow in the dryer, and can be measured, for example, by inserting a sensor part of the anemometer from the side wall of the dryer, and can also be calculated from the blower exhaust capacity. .
Although it does not specifically limit as an anemometer, For example, the Anemo master anemometer (model 6162) by KANOMAX company is mentioned.

As a drying method, it is particularly preferable to carry out aeration band drying on a hydrogel having a gap through which hot air can pass. The aeration band dryer is characterized by its simple structure and easy maintenance compared to other dryers, but it can be obtained when it is used to dry (meth) acrylic acid (salt) polymer hydrogel ( There is a drawback that the insoluble content in the (meth) acrylic acid (salt) -based polymer tends to increase. The present application has successfully overcome this problem. The hydrogel having a gap may be a hydrogel having a gap through which hot air passes. When the hot air passes through the water-containing gel gap, the hot air is uniformly supplied to the surface of the water-containing gel.
In the method for producing a (meth) acrylic acid (salt) -based water-soluble polymer of the present invention, the water-containing gel having the gap is a granular or string-like extruded gel, a finely crushed gel, or a finely cut gel. Preferably there is.
Extruded gel refers to a gel that is extruded so as to be easily dried by extruding a polymer gel obtained in a polymerization step using an extruder.
In the case of a granular extruded gel, a plurality of granular extruded gels are loaded in a dryer, and hot air passes through the gap between one granular extruded gel and the other granular extruded gel to contain water. Hot air is uniformly supplied to the gel surface.
In the case of a string-like extruded gel, a plurality of string-like extruded gels are stacked in a dryer, and hot air passes through a gap between one string-like extruded gel and another string-like extruded gel. The hot air is uniformly supplied to the surface of the hydrogel.
Bubbles existing inside the gel may become a hot air path.
The finely pulverized gel refers to a fine gel obtained by pulverizing a polymer gel-like material obtained in a polymerization step with a crusher or the like.
The finely cut gel refers to a fine gel obtained by cutting a polymer gel-like product obtained in a polymerization step with a cutting machine or the like.
Similarly, in the case of finely crushed gel, finely cut gel, etc., multiple hydrogels are loaded in the dryer, and hot air passes through the gaps between the multiple hydrogels to supply hot air evenly to the surface of the hydrogel. Will be.
Extruded gel is particularly preferable because drying is sufficiently promoted into the hydrous gel. That is, the (meth) acrylic acid (salt) -based water-soluble polymer-containing gel is preferably an extruded gel.

The drying process of this invention should just be performed so that a hot air may pass through the water-containing gel gap | interval with the linear velocity mentioned above within a dryer. Further, the direction in which the hot air blows and the direction in which the hot air is blown are not particularly limited, but may be appropriately set so that the hot air passes through the gap between the hydrogels at various linear speeds in various dryers. .
The drying step can be performed using an aeration dryer.
Examples of the aeration dryer include an aeration band dryer, a fluidized bed dryer, and a vibrating fluidized bed dryer. The agitation dryer is a drier equipped with a stirring blade such as a kneader, a paddle dryer, or a CD dryer, and is a type of dryer in which the water-containing gel is dried while being kneaded with such a stirring blade. It is difficult to set an operation in which hot air passes through the gel gap at a specified linear velocity, and it may not be possible to satisfy the linear velocity condition in the production method of the present invention.
In the ventilation band dryer, the material to be dried itself is dried without moving on the drying plate. In the vibration fluidized bed dryer described later, the material to be dried moves on the drying plate. It will be dried.
The effect of the present invention is most remarkable when a ventilation band dryer, which is a dryer in which gels tend to adhere to each other and hot air tends to deteriorate, is used.
Further, in the case of a vibrating fluidized bed dryer, since the adhesion between gels is relatively strong, the effect of the present invention appears strongly.
When using an aeration band dryer in the present invention, it is particularly preferable to supply and dry the gel so that the layer height of the gel is about 3 to 200 mm so that the gel is fully dried as a whole. .
A more preferable gel layer height is 10 to 150 mm, and most preferably 20 to 120 mm.
In the case of using a vibrating fluidized bed dryer in the present invention, the gel is supplied so that the entire gel is sufficiently dried, and the gel layer height during drying is about 3 to 100 mm so that vibration is sufficiently transmitted. And drying. A more preferable gel layer height is 5 to 80 mm, and most preferably 10 to 60 mm.

In addition to excellent drying performance, the hot air having a dew point of 70 ° C. or less and a temperature of 160 to 230 ° C. passes through the hydrogel gap at a linear velocity of 0.1 m / s or more. It is possible to obtain a hot air property suitable for the production method of the present invention in which drying is sufficiently promoted into the hydrogel and the insoluble content of the hydrogel is reduced without causing thermal decomposition of the polymer. .
By drying the hot air so that it passes through the hydrogel gap at a linear velocity of 0.1 m / s or more, the hot air can be uniformly supplied to the gel surface, and the drying performance of the entire hydrogel can be improved. . As a result, it is possible to produce a (meth) acrylic acid (salt) -based water-soluble polymer with a sufficiently reduced insoluble content, as supported by the examples described later. The reason why a (meth) acrylic acid (salt) -based water-soluble polymer having a sufficiently reduced insoluble content is obtained is that the drying of the water-containing gel is sufficiently accelerated, so that the water-containing gel having a low solid content can be obtained. It is inferred that the time during which the polymer is steamed is shortened as a result, and the crosslinking reaction due to heat is suppressed. In other words, when the drying property of the gel subjected to drying is improved, the insoluble matter is reduced. In contrast, for example, in an oven-type dryer, the hydrogel is placed on a drying plate, and hot air is usually circulated on the upper surface side or lower surface side of the hydrogel, and the hot air passing through the hydrogel gap is not The linear velocity is less than 0.1 m / s. In this case, since the hot air does not sufficiently pass through the gap between the hydrated gels, the drying of the upper surface portion and the lower surface portion of the hydrated gel placed on the drying plate is promoted, but the drying is sufficiently promoted into the hydrated gel. Never happen.
When the linear velocity is less than 0.1 m / s, the drying performance is not sufficient, and the drying is not sufficiently promoted into the hydrous gel. The lower limit is preferably 0.3 m / s or more, and more preferably 0.5 m / s or more. The upper limit is preferably 3.0 m / s or less. That is, the linear velocity of hot air in the drying step is preferably 0.5 to 3.0 m / s.
When the linear velocity is higher than 3.0 m / s, there is a possibility that a part of the dried product is scattered along with the air current during drying, as is supported in Examples described later.

By setting the dew point in the hot air to 70 ° C. or lower and the drying temperature to 160 ° C. or higher, the difference between the dew point and the drying temperature increases, and the hot air that has been sufficiently dried dries at a high temperature into the hydrogel. As a result, the drying time can be shortened, and the water-containing gel is steamed in the drying step and the crosslinking reaction can be sufficiently suppressed. Therefore, the insoluble matter can be reduced as supported by the examples described later. The dew point is preferably 60 ° C. or lower, and more preferably 50 ° C. or lower. The temperature is preferably 170 ° C. or higher, and more preferably 180 ° C. or higher.
Moreover, it can prevent that the polymer which is a drying object raise | generates thermal decomposition by making the temperature of the said hot air into 230 degrees C or less. The temperature is preferably 220 ° C. or lower, and more preferably 210 ° C. or lower.
The drying time is preferably within 100 minutes.

The (meth) acrylic acid (salt) -based water-soluble polymer-containing gel used in the drying step is a (meth) acrylic acid (salt) simple substance composed of (meth) acrylic acid and / or (meth) acrylate. It is a gel-like product containing water, which is formed from a polymer obtained by polymerizing a monomer component having an essential monomer. A preferred form of such a water-containing gel is formed by a polymer obtained by polymerizing a monomer component containing a (meth) acrylic acid (salt) monomer, and the (meth) acrylic It is preferable that an acid (salt) monomer is 60 mol% or more with respect to 100 mol% of all monomer components. That is, as a preferred embodiment of the present invention, the above (meth) acrylic acid (salt) -based water-soluble polymer-containing gel contains a monomer component containing 60 mol% or more of (meth) acrylic acid (salt) monomer. The form which is the water-containing gel of the polymer obtained by polymerizing is mentioned. The hydrated gel becomes a hydrated gel containing a polymer obtained by polymerization using such a monomer. The higher the ratio of (meth) acrylic acid (salt) monomer, the more remarkable the effect of the present invention. More preferably, it is 70 mol% or more.
The polymer may be an acid type polymer having an acid group or a salt type polymer having no acid group. When a salt type polymer is produced, a salt type single unit in which the acid portion is neutralized from the beginning is used. A mer may be used.

The above (meth) acrylic acid (salt) water-soluble polymer hydrated gel preferably has a solid content of 20 to 60% by mass. By making solid content into such a range, it can be set as a preferable form when suiting the drying method of this case. Even if the solid content is less than 20% by mass or exceeds 60% by mass, the quality such as a decrease in molecular weight or an increase in insoluble content may be deteriorated. A more preferred lower limit is 25% by mass and an upper limit is 55% by mass, a still more preferred lower limit is 30% by mass, and an upper limit is 50% by mass.
Usually, the hydrogel having a solid content of 20 to 60% by mass contains 80 to 40% by mass of water.
Here, solid content can be calculated | required as follows.
Moreover, by drying the hydrated gel under the conditions of the present invention, it can be dried more efficiently and without increasing the insoluble matter in a short time.

The (meth) acrylic acid (salt) water-soluble polymer-containing gel preferably has a surface area per unit volume of 9 cm ² / cm ³ or more.
In the production method of the present invention, a gel having a high surface area (9 cm ² / cm ³ or more, the upper limit is not limited, and the maximum surface area possible in the technology capable of making the gel a high surface area is the upper limit) is dried. Drying improves by providing. Thereby, a high-quality (low insoluble matter) (meth) acrylic acid (salt) -based water-soluble polymer can be obtained.

(Measurement method of solid content)
In the case of a gel that cannot be crushed, use a scissor to cut the gel so that the particle size is about 3 mm. (Hereinafter also referred to as scissors-treated product A.) About 2 g of the gel was added to an aluminum petri dish No. 1072 (Miyano Medical Co., Ltd.) was precisely weighed, and the remaining amount after drying for 1 hour with a hot air circulation dryer (Yamato, Constant Temperature Oven, DN600 type) pre-adjusted to 200 ° C. Weigh. Let the ratio of the mass of the residual amount after drying with respect to the mass before drying be solid content (mass%).
In the case of a water-containing polymer that can be pulverized, the polymer is pulverized with a desktop pulverizer (Osterizer) and classified so as to have a 20 mesh pass. (Hereinafter referred to as “Classified product B”) About 1 g of the classified product B is precisely weighed in an aluminum wheel container, and is preliminarily adjusted to 200 ° C. with a hot air circulation dryer (manufactured by Yamato, Constant Temperature Oven, DN600 type). Weigh the remaining amount after drying for 1 hour. Let the ratio of the mass of the residual amount after drying with respect to the mass before drying be solid content (mass%).
That is, as described above, depending on the dry state of the hydrated gel, for example, when the water content is high, the gel can be cut with scissors. When the drying state further progresses and the water content decreases, it becomes impossible to cut with scissors, and it becomes a water-containing polymer that can be pulverized. The two kinds of methods for measuring the solid content can be appropriately used as long as the solid content of the polymer can be measured.

The (meth) acrylic acid (salt) -based water-soluble polymer obtained through the production method of the present invention preferably has a solution viscosity of 100 mPa · S or more when the polymer is a salt type. More preferably, it is 200 mPa * S or more, More preferably, it is 300 mPa * S or more.
Moreover, when a polymer is an acid type, it is suitable that solution viscosity is 5 mPa * S or more. More preferably, it is 10 mPa * S or more, More preferably, it is 15 mPa * S or more. Solution viscosity means the B-type viscosity at 30 ° C. of an aqueous solution containing 0.2% by mass of a (meth) acrylic acid (salt) -based water-soluble polymer. Those that become highly viscous when dissolved in water are suitably used as thickeners, mud additives, fluidity reducing agents for soil discharge, and the like.
The solution viscosity can be determined as follows.

(Measurement method of solution viscosity)
After adding 20 ml of methanol to a beaker having a capacity of 500 ml, 1 g of the above polymer powder (for example, the above-mentioned classified product B) whose solid content is dried to 97% by mass or more is added as a pure content. While adding 500 ml of ion exchange water while stirring with a magnetic stirrer, using a jar tester, stirring and dissolving at 100 rpm for 50 minutes, adjusting the temperature to 30 ° C. and using a B-type viscometer (manufactured by Tokyo Keiki Co., Ltd.) Measure (30 rpm).

Further, the insoluble content of the (meth) acrylic acid (salt) -based water-soluble polymer is preferably 3% by mass or less. This makes it possible to sufficiently exert the action and effect of the (meth) acrylic acid (salt) -based water-soluble polymer with a small amount of use. For example, when used as a poultice, a more homogeneous plaster can be obtained. Will be obtained. On the other hand, if the insoluble content exceeds 3% by mass, the active ingredient of the (meth) acrylic acid (salt) -based water-soluble polymer may be reduced. In addition, a large amount of insoluble matter (gel) accumulates in the strainer attached to the tank for dissolving the water-soluble polymer, frequently necessitating cleaning, and may cause clogging of the liquid transfer pipe. is there. Preferably, it is 2 mass% or less, More preferably, it is 1 mass% or less, More preferably, it is 0.7 mass% or less, Most preferably, it is 0.5 mass% or less. That is, the (meth) acrylic acid (salt) -based water-soluble polymer obtained by the drying step preferably has an insoluble content of 0.5% by mass or less. The insoluble matter can be determined as follows.

(Measurement method of insoluble matter)
After adding 20 ml of methanol to a beaker having a capacity of 500 ml, 1 g of the above polymer powder (for example, the above-mentioned classified product B) whose solid content is dried to 97% by mass or more is added as a pure content. While adding 500 ml of ion-exchanged water while stirring with a magnetic stirrer, using a jar tester, stirring and dissolving at 100 rpm for 50 minutes, and then filtering using a 32 mesh filter, water-containing insoluble matter is removed. Take out. And it measures quickly so that this insoluble matter may not dry, and calculates an insoluble content based on the following formula (1). The filtration and weighing are performed at 25 ° C. and a relative humidity of 60%.
Insoluble matter (mass%) = {mass of insoluble matter (g) / 500 (g)} × 100 (1)

Furthermore, the weight average molecular weight of the (meth) acrylic acid (salt) -based water-soluble polymer is preferably 500,000 to 10,000,000. With this molecular weight range, the (meth) acrylic acid (salt) -based water-soluble polymer can exhibit sufficient cohesive force and thickening, and can stably possess these physical properties. More preferably, it is 1 million to 7 million, More preferably, it is 2 million to 6 million, Most preferably, it is 3 million to 5 million.
The measuring method of the said weight average molecular weight is measured on condition of the following using a dynamic light scattering photometer.
Apparatus: Dynamic light scattering photometer (trade name: DSL-700, manufactured by Otsuka Electronics Co., Ltd.)
Solvent: 0.16M NaCl aqueous solution Sample concentration: 0.05-2 mg / ml
Sample pH: 10 (at 25 ° C)
Measurement temperature: 25 ° C

The method for producing the (meth) acrylic acid (salt) -based water-soluble polymer of the present invention may include a step of drying so that hot air passes through the water-containing gel gap under the above specific conditions, It is preferable to further include an extrusion step of extruding the (meth) acrylic acid (salt) -based water-soluble polymer-containing gel, and as the treatment step, as shown in FIG. 1, polymerization, extrusion, drying, pulverization, and classification are performed in this order. These steps are preferably included. Here, the polymerization step is a step of polymerizing a monomer component mainly composed of (meth) acrylic acid (salt), and the extrusion step extrudes a polymer gel-like material obtained in the polymerization step. It is the process of crushing so that it may dry easily. The pulverization step is a step of pulverizing the dried product into a certain size (particle size), and it is preferable to classify the thus obtained powder particles in the subsequent classification step. By passing through such a process, a (meth) acrylic acid (salt) -based water-soluble polymer that can be suitably used in various fields is obtained.

The polymerization step, extrusion step, drying step, pulverization step and classification step in the production method of the present invention will be further described below.
(Polymerization process)
In the polymerization step, as described above, polymerizing a monomer component essentially comprising a (meth) acrylic acid (salt) monomer composed of (meth) acrylic acid and / or (meth) acrylate; Become. The (meth) acrylic acid (salt) -based water-soluble polymer hydrogel is a gel-like product containing water as a polymerization solvent, formed by the polymer thus obtained. ) As acrylates, neutralized products obtained by neutralizing (meth) acrylic acid with monovalent metals, divalent metals, ammonia, organic amines, etc., that is, sodium (meth) acrylate, potassium (meth) acrylate , Magnesium (meth) acrylate, calcium (meth) acrylate, ammonium (meth) acrylate, and the like are suitable. These may be used alone or in combination of two or more. Among these, sodium (meth) acrylate is preferable. More preferably, it is sodium acrylate.

The monomer component may contain an acid monomer other than the (meth) acrylic acid (salt) monomer and other monomers, and the (meth) acrylic acid (salt) monomer. Examples of acid monomers other than those include unsaturated monocarboxylic acid monomers such as α-hydroxyacrylic acid and crotonic acid; unsaturated dicarboxylic acid monomers such as maleic acid, fumaric acid, itaconic acid and citraconic acid Body; vinyl sulfonic acid, allyl sulfonic acid, methallyl sulfonic acid, styrene sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid, 3-allyloxy-2-hydroxypropane sulfonic acid, sulfoethyl (meth) acrylate, sulfopropyl ( Unsaturated sulfonic acid monomers such as (meth) acrylate, 2-hydroxysulfopropyl (meth) acrylate, sulfoethylmaleimide; Unsaturated phosphonic acid monomers such as chloramidomethanephosphonic acid, 2- (meth) acrylamide-2-methylpropanephosphonic acid, and these acid-type monomers are monovalent metals, divalent metals, ammonia, organic amines, etc. Neutralized products obtained by neutralization with are suitable. These may be used alone or in combination of two or more.

Examples of the other monomers include acrylamide monomers such as (meth) acrylamide and t-butyl (meth) acrylamide; hydrophobic monomers such as (meth) acrylic acid ester, styrene, 2-methylstyrene, and vinyl acetate. 3-mer-2-buten-1-ol (prenol), 3-methyl-3-buten-1-ol (isoprenol), 2-methyl-3-buten-2-ol (isoprene alcohol), 2 -Hydroxyethyl (meth) acrylate, polyethylene glycol mono (meth) acrylate, polypropylene glycol mono (meth) acrylate, polyethylene glycol monoisoprenol ether, polypropylene glycol monoisoprenol ether, polyethylene glycol monoallyl ether, polypropylene glycol Unsaturated monomers having hydroxyl groups such as dimethyl monoethyl ether, glycerol monoallyl ether, N-methylol (meth) acrylamide, glycerol mono (meth) acrylate, vinyl alcohol; dimethylaminoethyl (meth) acrylate, dimethylaminopropyl (meth) ) Cationic monomers such as acrylates; Nitrile monomers such as (meth) acrylonitrile are suitable. These may be used alone or in combination of two or more.
In the polymerization of the above (meth) acrylic acid (salt) -based water-soluble polymer-containing gel, especially acrylamide monomers are not sufficiently polymerized and are likely to remain. The amount of acrylamide monomer used as the other monomer is 30 mol% with respect to 100 mol% of all monomers used. The following is preferable. More preferably, it is 20 to 0 mol%, More preferably, it is 10 to 0 mol%, Most preferably, it is in the range of 5 to 0 mol%.

As a manufacturing method (polymerization method) of the (meth) acrylic acid (salt) -based water-soluble polymer-containing gel, a solution polymerization method is preferable. More preferably, it is a method of polymerizing by standing polymerization in an aqueous solution, and such a method is preferable because it has a small insoluble content and can easily produce a high-molecular-weight water-soluble polymer. Moreover, as a polymerization form, a cast polymerization method or a belt polymerization method can be employed. The monomer concentration during the polymerization is preferably 20 to 60% by mass. More preferably, it is 25-55 mass%, More preferably, it is 30-50 mass%.

As the polymerization method, either thermal polymerization or photopolymerization can be used.
In thermal polymerization, photopolymerization, etc., the polymerization temperature, polymerization time, and in the case of photopolymerization, the polymerization conditions such as light intensity and wavelength, etc. What is necessary is just to set suitably on the conditions normally performed when polymerizing a body component and preparing a (meth) acrylic acid (salt) type water-soluble polymer. That is, using the raw materials disclosed in this specification and other raw materials that can be used, a monomer component that essentially contains an acrylic acid (salt) monomer is polymerized to obtain the desired molecular weight and polymerization rate. The polymerization conditions may be appropriately set so that the (meth) acrylic acid (salt) -based water-soluble polymer is prepared.
The thermal polymerization is preferably a static polymerization method in which a monomer is polymerized in the presence of a thermal polymerization initiator. When performing a static polymerization method, when preparing a (meth) acrylic acid type polymer, it is preferable to carry out in the presence of amines, and when preparing a (meth) acrylate type polymer, polyvalent It is preferable to carry out in the presence of alcohol and amines.

Specific examples of the polyhydric alcohol include, for example, ethylene glycol, diethylene glycol, polyethylene glycol, propylene glycol, polypropylene glycol, propanediol, butanediol, butanetriol, glycerin, neopentyl glycol, hexylene glycol, pentaerythritol, Trimethylolethane, trimethylolpropane, sorbitol and the like can be mentioned, but are not particularly limited. These polyhydric alcohols may be used alone or in combination of two or more. Of the above exemplified compounds, glycerin is more preferred.

The amount of the polyhydric alcohol added to the monomer component is not particularly limited, but is preferably in the range of 0.01 to 20% by mass, and more preferably in the range of 0.1 to 10% by mass. . Thereby, the polymerization degree of the (meth) acrylate water-soluble polymer can be further increased. When the addition amount of polyhydric alcohol is less than 0.01% by mass, or when the addition amount of polyhydric alcohol exceeds 20% by mass, (meth) acrylic acid having ultra high molecular weight and excellent water solubility It may be difficult to efficiently produce a salt-based water-soluble polymer.

Examples of the amines include monoethanolamine, diethanolamine, triethanolamine, ethylamine, diethylamine, propylamine, butylamine, ethylenediamine, trimethylenediamine, tetramethylenediamine, hexamethylenediamine, methylethanolamine, dimethylethanolamine, diethyl Examples include ethanolamine, methyldiethanolamine, 3-amino-1-propanol, ethylhexylamine, ethoxypropylamine, dimethyllaurylamine, polyethyleneimine, pyridine, aminobenzoic acid, aminophenol, aniline, dimethylaniline, and the like. It is not something. Only one kind of these amines may be used, or two or more kinds may be used in combination. Of the compounds exemplified above, triethanolamine is more preferred.

Although the addition amount with respect to 1 mol of monomer components of the said amines is not specifically limited, The inside of the range of 1 * 10 ^{< -5} > ^-1 * 10 ^<-2> mol is preferable, and 1 * 10 < ^-4 > ^-3 * More preferably in the range of 10 ⁻³ mol. Thereby, the polymerization degree of the (meth) acrylic acid (salt) -based water-soluble polymer can be further increased. When the addition amount of amines is less than 1 × 10 ⁻⁵ mol, the progress of the polymerization is slow. When the addition amount of amines exceeds 1 × 10 ⁻² mol, it is difficult to efficiently produce a (meth) acrylic acid (salt) water-soluble polymer having an ultrahigh molecular weight and excellent water solubility. There is a risk of becoming.

Examples of the polymerization initiator in the case of the thermal polymerization include hydrogen peroxide; persulfates such as sodium persulfate, potassium persulfate, and ammonium persulfate; 2,2′-azobis- (2-amidinopropane) dihydrochloride. Water-soluble radical polymerization initiators such as azo compounds such as 2,2′-azobis- [2- (2-imidazolin) -2-yl] propane] dihydrochloride, and the like. Can be used. Among these thermal polymerization initiators, persulfate is particularly preferable. The amount of the thermal polymerization initiator used is preferably in the range of 0.0001 to 0.05 g with respect to 1 mol of the monomer component. As a polymerization start temperature at the time of thermal polymerization, 15 to 50 ° C. is preferable. It is preferable to control the polymerization so that the maximum temperature of the reaction solution during polymerization is 150 ° C. or lower, preferably 120 ° C. or lower, more preferably 110 ° C. or lower.

As the polymerization initiator in the case of the photopolymerization, the following compounds can be used.
2,2'-azobis (2-amidinopropane), 2,2'-azobis (N, N'-dimethyleneisobutylamidine), 2,2'-azobis [2- (5-methyl-2-imidazoline-2 -Yl) propane], 1,1'-azobis (1-amidino-1-cyclopropylethane), 2,2'-azobis (2-amidino-4-methylpentane), 2,2'-azobis (2- N-phenylaminoamidinopropane), 2,2′-azobis (1-imino-1-ethylamino-2-methylpropane), 2,2′-azobis (1-allylamino-1-imino-2-methylbutane), 2,2'-azobis (2-N-cyclohexylamidinopropane), 2,2'-azobis (2-N-benzylamidinopropane) and its hydrochloric acid, sulfuric acid, acetate, etc., 4,4'-azo (4-cyanovaleric acid) and its alkali metal salts, ammonium salts, amine salts, 2- (carbamoylazo) isobutyronitrile, 2,2'-azobis (isobutyramide), 2,2'-azobis [2 -Methyl-N- (2-hydroxyethyl) propionamide], 2,2'-azobis [2-methyl-N- (1,1'-bis (hydroxymethyl) ethyl) propionamide], 2,2'- An azo photopolymerization initiator such as azobis [2-methyl-N-1,1′-bis (hydroxyethyl) propionamide].

2,2-dimethoxy-1,2-diphenylethane-1-one, 1-hydroxy-cyclohexyl-phenyl-ketone, 2-hydroxy-2-methyl-1-phenyl-propan-1-one, 1-hydroxy-cyclohexyl A eutectic mixture of phenyl-ketone (Irgacure 184) and benzophenone, 1- [4- (2-hydroxyethoxy) -phenyl] -2-hydroxy-2-methyl-1-propan-1-one, 2-methyl -1 [4- (methylthio) phenyl] -2-morpholinopropan-1-one, 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butanone-1, 2-benzyl-2- Dimethylamino-1- (4-morpholinophenyl) -butanone-1 (Irgacure 369) and 2,2-dimethoxy-1,2 3: 7 mixture with diphenylethane-1-one (Irgacure 651), bis (2,4,6-trimethylbenzoyl) -phenylphosphine oxide, bis (2,6-dimethoxybenzoyl) -2,4,4 -1: 3 mixture of trimethyl-pentylphosphine oxide (CGI403) and 2-hydroxy-2-methyl-1-phenyl-propan-1-one (Darocur 1173), bis (2,6-dimethoxybenzoyl)- A 1: 3 mixture of 2,4,4-trimethyl-pentylphosphine oxide (CGI 403) and 1-hydroxy-cyclohexyl-phenyl-ketone (Irgacure 184), bis (2,6-dimethoxybenzoyl) -2,4 , 4-trimethyl-pentylphosphine oxide (CGI403) and 1: 1 mixture with -hydroxy-cyclohexyl-phenyl-ketone (Irgacure 184), 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide and 2-hydroxy-2-methyl-1-phenyl-propane-1 -1: 1 liquid mixture with ONE (Darocur 1173), bis (η ⁵ -2,4-cyclopentadien-1-yl) -bis (2,6-difluoro-3- (1H-pyrrol-1-yl) ) -Phenyl) titanium, oligo [2-hydroxy-2-methyl-1- [4- (1-methylvinyl) phenyl] propanone], eutectic mixture of 2,4,6-trimethylbenzophenone and 4-methylbenzophenone Liquid mixture of 4-methylbenzophenone and benzophenone, 2,4,6-trimethylbenzoyldiphenyl O scan fins oxide and oligo [2-hydroxy-2-methyl-1- [4- (1-methylvinyl) phenyl] propanone] and the liquid mixture of methyl benzophenone derivatives.

1- [4- (4-Benzoylphenylsulfanyl) phenyl] -2-methyl-2- (4-methylphenylsulfanyl) propan-1-one, benzyldimethyl ketal, 2-hydroxy-2-methyl-1-phenyl- 1-propanone, α-hydroxycyclohexyl-phenyl ketone, ethyl 4-dimethylaminobenzoate, acrylated amine synergist, benzoin (iso- and n-) butyl ester, acrylic sulfonium (mono, di) hexafluorophosphate, 2 -Isopropylthioxanthone, 4-benzoyl-4'-methyldiphenyl sulfide, 2-butoxyethyl 4- (dimethylamino) benzoate, ethyl 4- (dimethylamino) benzoate, benzoin, benzoin alkyl ether, benzoin hydroxy Ruki ether, diacetyl and its derivatives, anthraquinone and its derivatives, diphenyl disulfide and its derivatives, benzophenone and its derivatives, benzyl and its derivatives.

The amount of the photopolymerization initiator used is preferably 0.0001 g or more and more preferably 1 g or less with respect to 1 mol of the monomer component used for polymerization. Thereby, the weight average molecular weight and the polymerization rate of the (meth) acrylic acid (salt) -based water-soluble polymer can be made sufficiently high. More preferably, it is 0.001 g or more and 0.5 g or less. The polymerization initiation temperature for photopolymerization is preferably 0 to 30 ° C. The polymerization is preferably controlled so that the maximum temperature of the reaction solution during the polymerization is 150 ° C. or lower, preferably 120 ° C., more preferably 110 ° C. or lower.

When carrying out the photopolymerization, it is preferable to irradiate the reaction solution or the like with near ultraviolet rays. For example, a high-pressure mercury lamp, a low-pressure mercury lamp, a metal halide lamp, a fluorescent chemical lamp, or a fluorescent blue lamp is suitable as a device that irradiates near ultraviolet rays. Further, the wavelength region of near ultraviolet rays is preferably 300 nm or more, and preferably 500 nm or less. By irradiating the reaction liquid or the like with ultraviolet rays having a wavelength in this range, photopolymerization starts and the polymerization reaction proceeds at an appropriate rate. Moreover, when performing photopolymerization, it is preferable to superpose | polymerize by irradiating near ultraviolet rays with the intensity | strength of 0.1-100 W / m < ² >, and, thereby, an insoluble part can be decreased more.

In the polymerization method, it is preferable to use a chain transfer agent together with the polymerization initiator. By using an appropriate amount of chain transfer agent, it is possible to produce a polymer having a higher weight average molecular weight and less insoluble content of the (meth) acrylic acid (salt) -based water-soluble polymer. As a result, the effects of the present invention can be more fully exhibited.
Examples of the chain transfer agent include sulfur-containing compounds such as thioglycolic acid, thioacetic acid, and mercaptoethanol; phosphorous compounds such as phosphorous acid and sodium phosphite; hypophosphorous acid such as hypophosphorous acid and sodium hypophosphite Preferred compounds are alcohols such as methyl alcohol, ethyl alcohol, isopropyl alcohol and n-butyl alcohol. Among these, hypophosphorous acid compounds are preferable. More preferred is sodium hypophosphite. The amount of the chain transfer agent used may be appropriately set depending on the polymerization concentration, a combination with a photopolymerization initiator, and the like, but is preferably 0.0001 g or more with respect to 1 mol of the monomer component used for the polymerization. Moreover, 0.2 g or less is preferable. Further, it is more preferably 0.001 g or more and 0.15 g or less, and particularly preferably 0.005 g or more and 0.10 g or less.

(Extrusion process)
In the extrusion process, the hydrogel obtained in the polymerization process is formed by extrusion. The extruded gel obtained in this way can increase the surface area of the gel, and when extruded at a high pressure, it is made porous by containing air in the extruder, so that the drying performance is improved. In other words, if the gel is porous, the drying property is improved. If the drying property of the gel is improved, the insoluble content is reduced as described above. That is, when the porous gel is dried, it can be quickly dried and the amount of insoluble matter can be controlled to be small. Therefore, the form which dries a porous gel in the manufacturing method of this invention is especially preferable. Moreover, since such an extruded gel is reduced in weight when dried, it is advantageous for transportation and storage.
Although it does not specifically limit as a form of the said extrusion gel, For example, a granular form, string shape, etc. are suitable, and it is preferable that it was extruded using the extruder whose die diameter is 0.5-20 mm. By extruding with a die diameter of 3 mm or less, the hydrated gel appropriately contains air and becomes porous. However, when the die diameter is less than 0.5 mm, the discharge pressure during extrusion becomes abnormally high, and the gel may not be extruded well. Moreover, when it exceeds 20 mm, drying efficiency may fall. It is more preferably 15 mm or less, and further preferably 8 mm or less.
The longest diameter when the extruded gel is granular is preferably 0.5 to 20 mm. The upper limit is more preferably 15 mm, and still more preferably 8 mm.
Moreover, when the said extrusion gel is string shape, it is preferable that a diameter is 15 mm or less and length is 50 cm or less. More preferably, the diameter is 10 mm or less and the length is 40 cm or less, and particularly preferably the diameter is 8 mm or less and the length is 30 cm or less.
For example, the surface area per unit volume of the extruded gel can be adjusted to 9 cm ² / cm ³ or more by an extrusion process. By setting it as such a surface area, drying property improves as mentioned above, and the insoluble content of the water-soluble polymer manufactured by the manufacturing method of this invention can be reduced.
The size and shape of the extruded gel can vary depending on conditions such as the die diameter and extrusion speed.
In order to dry the (meth) acrylic acid (salt) water-soluble polymer-containing gel, it is preferable to apply the conditions of the extruder such that the gel becomes porous.

In the production method of the present invention, it is preferable to extrude while applying a high specific power in the extrusion step. The specific power is obtained by dividing the power applied to the hydrogel by the unit treatment amount, that is, the power applied to 1 kg per unit time, and can be obtained as follows. By adjusting the specific power to a specific preferred range, the hydrogel becomes porous and the drying property is improved, and the insoluble content of the water-soluble polymer produced by the production method of the present invention is reduced. Can do.
FIG. 2 schematically shows the flow of power when extruding using an extruder.
In FIG. 2, P0 (kW) is three-phase AC power (motor input), and the following formula (2);
P0 (kW) = √3 × voltage [V] × current [A] × power factor cos θ (0.85) / 1000 (2)
Is required.
P1 (kW) is a three-phase AC output (motor output), and is the power obtained by removing the loss in the motor from P0. The following formula (3);
P1 (kW) = P0 × motor efficiency ηm (0.78)
= √3 × Voltage [V] × Current [A] × Power factor cos θ (0.85) × Motor efficiency ηm (0.78) / 1000 (3)
Is required.

P2 (kW) is a reduction gear exit power, and is a power obtained by removing a loss in the reduction gear from P1, and the following formula (4);
P2 (kW) = P1 × Speed reducer efficiency ηc (0.8)
= √3 × voltage [V] × current [A] × power factor cos θ (0.85) × motor efficiency ηm (0.78) × reduction gear efficiency ηc (0.8) / 1000
= √3 × voltage [V] × current [A] × total efficiency η (0.53) / 1000 (4)
Is required.
In the above formula (4), the total efficiency is a value in consideration of the power factor, motor efficiency, and reduction gear efficiency, and reduction gear outlet power = shaft power.
From the above, the specific power ESP [kWh / kg] is expressed by the following formula (5);
Specific power ESP [kWh / kg] = Speed reducer outlet power P2 (kW) / Processing amount [kg / h] (5)
It can ask for.
The numerical values described as the power factor cos θ, the motor efficiency ηm, the speed reducer efficiency ηc, and the total efficiency η are only preferable examples, and are not limited thereto, and may be set as appropriate according to the extruder. .

In the extrusion step, it is appropriate that the specific power (kWh / kg) thus determined is 0.06 kWh / kg or more. By setting it as such a specific power, a hydrogel is made porous and it comes to dry rapidly, and it can control by causing less insoluble matter resulting from it. If it is less than 0.06 kWh / kg, the insoluble content may not be sufficiently reduced. When the specific power is low, the water-containing gel is not sufficiently porous, so that it is difficult to dry it quickly. Further, when the specific power is low, it is also conceivable that the cross-linked portion in the polymer is not sufficiently cut and the insoluble matter is not sheared to such an extent that it can be dissolved in water.
The specific power (kWh / kg) is more preferably 0.07 kWh / kg or more. More preferably, it is 0.08 kWh / kg or more.
Although the upper limit of the specific power is not limited, when the gel is extruded with an extremely high specific power exceeding 0.6 kWh / kg, the molecular chain of the gel may be cut, resulting in a low molecular weight. 0.2 kWh / kg or less is more preferable.
The treatment amount (kg / h) of the acrylate-based water-soluble polymer-containing gel may be appropriately determined in consideration of specific power, the screw rotation number described later, and the like.

As the extrusion step, it is preferable to use a screw extruder. Thereby, a hydrogel can be extruded efficiently and it becomes possible to improve processing efficiency.
The screw extruder used in the present invention is, for example, a single screw extruder, a 2 (multi) -shaft co-rotating screw extruder, a 2 (multi) -shaft counter-rotating screw extruder, a two-stage extruder (single screw / Although not particularly limited, such as single axis, single axis / 2 axis, 2 axis / 2 axis), a single screw extruder or a two-stage extruder (single axis / single axis) is preferable. The reason for this is that the internal structure is simple and the gel flow is uniform, so that there is no variation in product quality. On the contrary, the more complicated the structure, the more locally the stagnant portion, the more complicated the flow path, and the like, and there is a possibility that the quality may vary due to slight pressure and temperature changes.
In addition, as a structure of a screw extruder, what is used by embodiment (Example 19) mentioned later can be illustrated, for example. Such an extruder employs a method of increasing the kneading effect by adding a squeeze to the extrusion part, which is composed of a fixed cylinder (cylinder) and a rotating screw.
Moreover, what is necessary is just to set suitably as the rotation speed of a screw according to a processing amount, For example, it is preferable that it is 30-110 rpm, and such a form is also one of the suitable forms of this invention. In this form, the hydrogel can be made more porous, the insoluble matter can be sufficiently reduced, and a high molecular weight acrylate-based water-soluble polymer can be obtained more efficiently. More preferably, it is 40-100 rpm.

As said extrusion process, before supplying a hydrogel to an extruder, it is suitable to cut | disconnect a (meth) acrylic-acid (salt) type water-soluble polymer hydrogel in a strip shape. Thereby, a hydrogel can be extruded efficiently.
Although it does not specifically limit as said extruder, For example, a meat chopper, a single screw extruder, a plunger extruder, a twin screw extruder, a twin screw single screw extruder etc. can be used conveniently.

(Drying process)
In the drying step, as described above, the hydrogel is dried so that hot air having a dew point of 70 ° C. or lower and a temperature of 160 to 230 ° C. passes through the hydrogel gap at a linear velocity of 0.1 m / s or higher. It will be.
The hydrous gel is preferably a granular or string-like extruded gel made through an extrusion process.
(Crushing process)
In the pulverization step, the dried product dried in the drying step is crushed into a certain size (particle size), but the pulverization step is not particularly limited, and a commonly performed method is employed.
(Classification process)
In the classification step, the particle size of the granular material crushed in the pulverization step is prepared, and the classification method is not particularly limited, and a commonly performed method is adopted.

In the method for producing a (meth) acrylic acid (salt) -based water-soluble polymer of the present invention, drying is performed by controlling the drying rate so that the time for the solid content concentration of the hydrogel to reach 97% by mass is within 100 minutes. It is preferable to include a process.

The above-mentioned “drying by controlling the drying speed so that the time until the solid content concentration of the hydrous gel reaches 97% by mass is within 100 minutes” means a drying speed (solid content of 97 It means that the hydrogel is dried under a drying condition such that the time to reach mass% is within 100 minutes, and the hot air properties (hot air temperature, dew point, air volume, wind speed, etc.) What is necessary is just to set conditions, such as the shape of a gel used for drying, and a layer height suitably, and to dry until a gel fully dries. Actually, it is not necessary to dry until the solid content concentration of the hydrogel reaches 97% by mass, but it is preferable to dry until the solid content concentration becomes 90% by mass or more, and it is possible to dry until the solid content concentration becomes 95% by mass or more. More preferably, it is more preferable to dry until it becomes 97 mass% or more. The drying time is preferably within 100 minutes, more preferably 5 minutes or more. When the drying time is less than 5 minutes, inconveniences such as an increase in the size of the dryer may occur. More preferably, it is 10 minutes or more, More preferably, it is 20 minutes or more.
The lower limit of the drying temperature is preferably 170 ° C, and more preferably 180 ° C. The upper limit is preferably 220 ° C, and more preferably 210 ° C. Moreover, what is necessary is just to select an air volume suitably so that a hot air may make the gel gap | interval linear velocity 0.1m / s (preferably 0.5-3.0m / s). Setting the drying temperature and the air volume within the above ranges is a preferable condition for increasing the drying speed.

(How to determine the drying rate (time to reach a solid content of 97% by mass))
Sampling is performed at regular intervals in the drying step, and the solid content (mass%) of the sample is determined according to the above-described (Solid content measurement method) for each of the gel that cannot be pulverized and the water-containing polymer that can be pulverized. Measure.
The drying time is plotted on the horizontal axis and the solid content at that time is plotted on the vertical axis, and the drying rate (time to reach 97 mass% solid content) is determined by a drawing method.

By drying by controlling the drying speed so that the time for the solid content concentration of the hydrogel to reach 97% by mass is within 100 minutes, as shown in the examples described later, A reduced (meth) acrylic acid (salt) -based water-soluble polymer can be produced. The reason for obtaining a (meth) acrylic acid (salt) -based water-soluble polymer with sufficiently reduced insoluble content is that the polymer is steamed in a hydrous gel with a low solid content by drying at a high drying rate. As a result, it is assumed that this is because the crosslinking time due to heat is suppressed.
In the above production method, the water-containing gel having the gap is preferably a granular or string-like extruded gel, a finely crushed gel, or a finely cut gel, and more preferably an extruded gel.

Although it does not limit as said drying process, What is necessary is just to introduce and dry inert gas, such as air and nitrogen which is heated and low humidity enough. For example, aeration band drying, vibrating fluidized bed drying, fluidized bed drying and the like can be mentioned.
The hot air introduction conditions of the present invention can be preferably applied to the above-described dryer.
Among the above drying methods, aeration band drying and vibrating fluidized bed drying, which exhibit the effects of the present application most, are preferable. In particular, aeration band drying is preferred.
The ventilation band drying is as described above.

The vibrating fluidized bed drying is performed by using a vibrating fluidized bed dryer to cause the material to flow while vibrating.
Examples of the vibrating fluidized bed dryer include a Q unit (continuous type and batch type) manufactured by Mitsubishi Materials Techno Corporation. For example, when a vibrating fluidized bed dryer having a frequency of around 1000 cpm is used, the vibrating fluidized bed is set so that the gel layer height during drying is about 3 to 100 mm so that the gel is fully dried as a whole. It is preferable to supply to a dryer and dry.
In the case of using a vibrating fluidized bed dryer, the vibrating stroke or the like may be set to a vibrating stroke (2 to 20 mm) normally performed in the vibrating fluidized bed dryer.

Examples of the fluidized bed dryer include a horizontal fluidized bed dryer (FBA type) manufactured by Okawara Seisakusho Co., Ltd.
The drying step of the present invention is preferably performed using the aeration band dryer or the vibrating fluidized bed dryer.

Although the manufacturing method of the (meth) acrylic acid (salt) -based water-soluble polymer of the present invention may include a step of drying by controlling the specific drying rate, (meth) acrylic acid (salt) It is preferable to further include an extrusion step of extruding the water-based polymer-containing water-containing gel. As described above, the treatment step preferably includes these steps in the order of polymerization, extrusion, drying, pulverization, and classification. Here, the polymerization process, the extrusion process, the pulverization process, and the classification process are as described above. By passing through such a process, a (meth) acrylic acid (salt) -based water-soluble polymer that can be suitably used in various fields is obtained.

Since the method for producing a (meth) acrylic acid (salt) -based water-soluble polymer of the present invention has the above-described configuration, it is excellent in water solubility and has a high molecular weight (meth) acrylic acid with sufficiently reduced insoluble matter. (Salt) water-soluble polymers can be obtained with high productivity, additives for poultices and poultices, hydrophilic ointment bases, thickeners for carpet compounds, thickeners and adhesives for paints And adhesion improver, red mud settling agent during alumina production, flocculant for salt water purification in soda industry, excavation soil treatment agent, dredged soil treatment agent and mud preparation agent, moisture absorbent, desiccant, surface modifier, various It can be suitably used for a thickener or the like. Among them, polyacrylic acid (salt) is suitable as a food additive and feed additive.

The present invention will be described in more detail with reference to the following examples. However, the present invention is not limited to these examples. Unless otherwise specified, “part” means “part by mass” and “%” means “% by mass”.

Synthesis example 1 (neutralization degree 100 mol%, thermal polymerization)
A beaker with a capacity of 5 L was charged with 4865 parts of a 37% by weight aqueous solution of sodium acrylate, 36 parts of glycerin and 0.111 part of sodium persulfate as a polymerization initiator, and these were uniformly dissolved. The pH of the aqueous solution was adjusted to 12.0 by adding a small amount of sodium hydroxide to the aqueous solution. Thereafter, 5000 parts of a reaction solution was prepared by adding ion exchange water to the aqueous solution. Further, dissolved oxygen contained in the reaction solution was removed by bubbling nitrogen gas. The concentration of sodium acrylate in the reaction solution was 36% by mass. And the addition amount of glycerol with respect to sodium acrylate was 2.0 mass%, and the addition amount of sodium persulfate with respect to 1 mol of sodium acrylate was 0.0058g (2.5 * 10 < ^-5 > mol).

After 5000 parts of the reaction solution was charged into the polymerization vessel shown in FIGS. 3 and 4, the inside of the polymerization vessel was sealed by closing the glass cock and inserting a thermometer.
This polymerization container was immersed in a constant temperature water bath (heating device) adjusted in advance to 35 ° C. to initiate polymerization (stationary polymerization). Therefore, the water bath temperature (heating temperature) at the start of polymerization is 35 ° C.

After immersing the polymerization vessel in a thermostatic water bath, the polymerization temperature reached a peak and reached 82 ° C. (peak temperature) 3.6 hours after the point of time when the polymerization gradually proceeded and immersed. During this time, the water bath temperature was maintained at 35 ° C. And after superposition | polymerization temperature reached peak temperature, the water bath temperature was hold | maintained at 35 degreeC for further 0.5 hour. Next, the water bath temperature was continuously raised from 35 ° C. to 75 ° C. over 0.5 hours. Then, the temperature (heating temperature) was maintained for 2.0 hours to complete the polymerization. After completion of the polymerization, the polymerization vessel was cooled, the bolts and nuts were loosened, the mold was opened, and the contents were taken out. The content obtained was a transparent plate-like gel. The solid content was 37% by mass.

Synthesis example 2 (neutralization degree 100 mol%, thermal polymerization)
In a 5 L beaker, 1929 parts of a 37% by weight aqueous solution of sodium acrylate, 846.2 parts of 2-acrylamido-2-methylpropanesulfonic acid, 1820 parts of ion-exchanged water and 41.3 parts of glycerin were dissolved. The pH of the solution was adjusted to 12.8 by adding about 340 parts of a 48% by weight aqueous solution of sodium hydroxide to the solution. Furthermore, after adding 0.117 parts of sodium persulfate as a polymerization initiator and stirring and dissolving, a small amount of ion-exchanged water was added to prepare 5000 parts of a reaction solution. Dissolved oxygen contained in the reaction solution was removed by bubbling nitrogen gas. The concentration of the monomer consisting of sodium acrylate and sodium 2-acrylamido-2-methylpropanesulfonate in the reaction solution was 33% by mass. And the addition amount of glycerol with respect to a monomer was 2.5 mass%, and the addition amount of sodium persulfate with respect to 1 mol of monomers was 0.010g.

After 5000 parts of the reaction solution was charged into the same polymerization vessel as used in Synthesis Example 1, the glass cock was closed and a thermometer was inserted to seal the inside of the polymerization vessel.
This polymerization container was immersed in a constant temperature water bath (heating device) adjusted in advance to 38 ° C. to initiate polymerization (stationary polymerization). Therefore, the water bath temperature (heating temperature) at the start of polymerization is 38 ° C.

After immersing the polymerization vessel in a constant temperature water bath, the polymerization temperature reached a peak and reached 62 ° C. (peak temperature) 3.3 hours after the polymerization gradually proceeded and immersed. During this time, the water bath temperature was maintained at 38 ° C. And after superposition | polymerization temperature reached peak temperature, the water tank temperature was hold | maintained at 38 degreeC for further 0.5 hour. Subsequently, the water bath temperature was continuously raised from 38 ° C. to 75 ° C. over 0.5 hours. Then, the temperature (heating temperature) was maintained for 2.0 hours to complete the polymerization. After completion of the polymerization, the polymerization vessel was cooled, the bolts and nuts were loosened, the mold was opened, and the contents were taken out. The obtained content is a transparent plate gel made of a polymer having a constitutional unit ratio derived from a monomer of sodium acrylate / 2-acrylamido-2-methylpropanesulfonate = 65/35 (molar ratio) Met. The solid content was 34% by mass.

Synthesis example 3 (neutralization degree 100 mol%, thermal polymerization)
A beaker having a capacity of 5 L was charged with 1490 parts of a 37% by weight aqueous solution of sodium acrylate, 993.2 parts of 2-acrylamido-2-methylpropanesulfonic acid, 2070 parts of ion-exchanged water, and 41.3 parts of glycerin. The pH of the solution was adjusted to 12.8 by adding about 400 parts of a 48% by weight aqueous solution of sodium hydroxide to the solution. Furthermore, after adding 0.106 part of sodium persulfate as a polymerization initiator and stirring and dissolving, a small amount of ion-exchanged water was added to prepare 5000 parts of a reaction solution. Dissolved oxygen contained in the reaction solution was removed by bubbling nitrogen gas. The concentration of the monomer consisting of sodium acrylate and sodium 2-acrylamido-2-methylpropanesulfonate in the reaction solution was 33% by mass. And the addition amount of glycerol with respect to a monomer was 2.5 mass%, and the addition amount of sodium persulfate with respect to 1 mol of monomers was 0.010g.

After 5000 parts of the reaction solution was charged into the same polymerization vessel as used in Synthesis Example 1, the glass cock was closed and a thermometer was inserted to seal the inside of the polymerization vessel.
This polymerization container was immersed in a constant temperature water bath (heating device) adjusted in advance to 38 ° C. to initiate polymerization (stationary polymerization). Therefore, the water bath temperature (heating temperature) at the start of polymerization is 38 ° C.

After immersing the polymerization vessel in a constant temperature water bath, the polymerization temperature reached a peak and reached 60 ° C. (peak temperature) 3.6 hours after the point where the polymerization gradually proceeded and immersed. During this time, the water bath temperature was maintained at 38 ° C. And after superposition | polymerization temperature reached peak temperature, the water tank temperature was hold | maintained at 38 degreeC for further 0.5 hour. Subsequently, the water bath temperature was continuously raised from 38 ° C. to 75 ° C. over 0.5 hours. Then, the temperature (heating temperature) was maintained for 2.0 hours to complete the polymerization. After completion of the polymerization, the polymerization vessel was cooled, the bolts and nuts were loosened, the mold was opened, and the contents were taken out. The obtained content is a transparent plate gel made of a polymer having a constitutional unit ratio derived from a monomer of sodium acrylate / 2-acrylamido-2-methylpropanesulfonate = 55/45 (molar ratio). Met. The solid content was 34% by mass.

Synthesis example 4 (neutralization degree 60 mol%, photopolymerization)
In a beaker having a capacity of 500 ml, 76.1 g of acrylic acid, 402.6 g of 37% aqueous solution of sodium acrylate, 16.58 g of ion-exchanged water, 5% of 2,2 ′-(2-amidinopropane) dihydrochloride as a photopolymerization initiator 2.13 g of aqueous solution and 2.64 g of 1% aqueous sodium hypophosphite solution were added.
The concentration of the monomer consisting of acrylic acid and sodium acrylate in the reaction solution was 50%, and the degree of neutralization was 60 mol%. The amount of 2,2 '-(2-amidinopropane) dihydrochloride used was 0.04 g per mole of monomer. Moreover, the usage-amount of sodium hypophosphite was the ratio of 0.01g with respect to 1 mol of monomers. After stirring and mixing the polymerization solution, a Teflon (registered trademark) film having a thickness of 0.08 mm (adhesive is a silicone system having a thickness of 0.05 mm) is attached to the bottom surface shown in FIG. Was led to a polymerization vessel made of SUS304 in which water adjusted to a temperature of 35 ° C. was circulated.
After covering the polymerization vessel with Saran Wrap (registered trademark), dissolved oxygen in the reaction solution was removed by bubbling nitrogen.

Next, as shown in FIG. 6, a black light mercury lamp (H100BL-L, manufactured by Toshiba Lighting & Technology Co., Ltd.) was irradiated from the top having a height of 35 cm. The light intensity is 3.7 W / m ² at the upper surface position of the reaction solution. For the light intensity, the above-mentioned light meter (UV meter (model UVA-365) manufactured by Custom Inc.) was used.
As soon as the light irradiation was started, the polymerization started and reached the primary peak temperature of 73 ° C. after 16 minutes.
Then, after standing for 3 minutes, polymerization was performed by irradiating with a black light mercury lamp (Refer to Toshiba Lighting & Technology Co., Ltd., H400BL-L) for 7 minutes. Was completed. The light intensity is 17 W / m ² at the upper surface position of the reaction solution.
When the gel polymer thus obtained was taken out from the polymerization vessel, it was easily released without any polymer remaining attached to the vessel. A polymer comprising a partially neutralized polyacrylic acid was obtained. The solid content was 52% by mass.

Among the following examples and comparative examples, the granular gel, string-like gel and cut gel used in Examples 1-18 and Comparative Examples 1-5 have a specific power of 0.06 kWh / kg applied during extrusion. The surface area was less than 9 cm ² / cm ³ .
Example 1 (Example of ventilation band dryer)
After the plate-like gel obtained in Synthesis Example 1 is cut into strips, it is supplied to a meat chopper (Hiraga Kogyo Co., No. 32 type, die diameter 4.5 mmΦ), and is an extrudate (granular) extruded gel. Got.
Next, using the hot air dryer (Okawara Seisakusho, ventilated dryer) shown in FIG. 8, hot air (air) having a temperature of 200 ° C. and a dew point of 50 ° C. is used as the air volume in the circulation system. The aeration was carried out so that the linear velocity of 1.0 m / s.
The drying container in which the gel is placed is made of stainless steel having a width of 40 cm, a length of 40 cm, and a height of 20 cm, and a 20-mesh wire mesh is stretched at the bottom. The side is a stainless steel plate, so no wind flows out of the side. All the hot air enters from the bottom of the drying container, and the periphery of the shelf of the dryer is glazed.
The extruded gel was loaded in a drying container so that the gel layer thickness was 50 mm, and drying was started by introducing it into the dryer. Sampling was performed at regular time intervals, and the drying rate, insoluble matter and solution viscosity were measured. The results are shown in Table 1.

Examples 2 to 13 (Examples of aeration band dryer)
The hot air having the properties shown in Table 1 was used, and drying was carried out in the same manner as in Example 1 except that the gel layer height was changed to the value shown in Table 1, and the drying rate, insoluble matter and The solution viscosity was measured and the results are shown in Table 1. In Example 13, during drying, the dried product was scattered with a little airflow.

Example 14 (Example of ventilation band dryer)
The plate-like gel obtained in Synthesis Example 1 was dried in the same manner as in Example 1 except that the gel was cut into a width of about 10 mm, a length of about 50 mm, and a thickness of about 2 mm. The drying rate, insoluble matter and solution viscosity were measured, and the results are shown in Table 1.

Example 15 (Example of ventilation band dryer)
After the plate-like gel obtained in Synthesis Example 2 is cut into strips, it is supplied to a meat chopper (Hiraga Kogyo Co., No. 32 type, die diameter: 4.5 mmΦ), and it is an extrudate (granular) extruded gel. Got.
Drying was performed in the same manner as in Example 1 except that the extruded gel was used and hot air having the properties shown in Table 1 was used, and the gel layer height was changed to the value shown in Table 1. The speed, insoluble content and solution viscosity were measured and the results are shown in Table 1.

Example 16 (Example of ventilation band dryer)
The plate-like gel obtained in Synthesis Example 3 was cut into strips, and then supplied to a meat chopper (Hiraga Kakujo Co., No. 32 type, die diameter 4.5 mmΦ) to obtain a salmon-like (granular) extruded gel. Got.
Drying was performed in the same manner as in Example 1 except that the extruded gel was used and hot air having the properties shown in Table 1 was used, and the gel layer height during drying was changed to the values shown in Table 1. The drying rate, insoluble matter and solution viscosity were measured and the results are shown in Table 1.

Example 17 (Example of ventilation band dryer)
The plate-like gel obtained in Synthesis Example 4 was cut into strips, and then supplied to a meat chopper (Hiraga Kakusho, No. 32 type, die diameter 4.5 mmΦ) to obtain an extrudate (granular) extruded gel. Got.
Drying was performed in the same manner as in Example 1 except that the extruded gel was used and hot air having the properties shown in Table 1 was used, and the gel layer height during drying was changed to the values shown in Table 1. The drying rate, insoluble matter and solution viscosity were measured and the results are shown in Table 1.

Example 18 (Example of Vibrating Fluidized Bed Dryer)
After the plate-like gel obtained in Synthesis Example 1 is cut into strips, it is supplied to a meat chopper (Hiraga Kogyo Co., No. 32 type, die diameter 4.5 mmΦ), and is an extrudate (granular) extruded gel. Got.
The above-mentioned salmon gel was supplied to a vibrating fluidized bed dryer (Mitsubishi Materials Techno Co., Ltd., QAD, batch type stroke 5 mm) so as to have a layer height of 20 mm, and drying was started. During the drying period, the hot air velocity was 1.0 m / S, the hot air dew point was 30 ° C., and the hot air temperature was 200 ° C.
The drying rate, insoluble matter and solution viscosity were measured in the same manner as in Example 1, and the results are shown in Table 1.

Example 19 (Example of ventilation band dryer)
After the plate-like gel obtained in Synthesis Example 1 is cut into strips, it is extruded from a nozzle with a diameter of 1 mmφ using a screw type extruder with a screw diameter of 30 mm, L / D = 17, and a screw speed of 45 rpm, and a string shape with a diameter of 3 mmφ. A gel was obtained. The string-like gel was porous and white in color because air was entrained in the gel. The surface area per unit volume was 13 cm ² / cm ³ .
It dried like Example 1 except having used this string-like gel. Moreover, it sampled for every fixed time similarly to Example 1, and measured the drying rate, the insoluble matter, and the solution viscosity. The drying rate (time to reach a solid content of 97%) was 62 minutes, the insoluble content was 0.01%, and the solution viscosity was 670 mPa · S. The drying rate was fast, the insoluble content was very small, and the quality was good. The results are shown in Table 1.

Example 20 (Example of ventilation band dryer)
First, the belt polymerization machine used in FIGS. 9 and 10 will be described in detail.
The belt has a weir 31 (edge rope) having a height of 50 mm in a form adjacent to the upper portion thereof, a width of 300 mm, and a material is SUS301. The space on the belt is continuously supplied with nitrogen so that the oxygen concentration is 4% by volume. Also, six near-ultraviolet lamps 26 (trade name: Black Light Mercury Lamp H250BL-L, manufactured by Toshiba Lighting & Technology Co., Ltd.) are mounted and lit on the upper part of the belt.
Note that up to four blacklights counted from the polymerization solution supply port have a light reducing plate 27 (punching metal, aperture ratio 10.7 so that the light intensity at the upper surface position of the polymerization solution is about 3.7 W / m ^2. %). Further, 5 to 6 black lights counted from the supply port of the polymerization solution are reduced by a light reducing plate 28 (punching metal, opening ratio 51%) so that the light intensity at the upper surface position of the polymerization solution is about 17 W / m ^2. It is fading. The belt moves continuously at a speed of 10.9 cm / min. In order to remove the polymerization heat, water having a temperature of 35 ° C. is sprayed from the spray nozzle 30 from below the belt. A scraper 29 is attached to the belt polymerization machine outlet, and the hydrogel is discharged without remaining on the belt surface. The spray nozzle 30 has a structure in which water is sprayed onto the upper belt from below, and the temperature of the upper belt can be adjusted. Normally, the upper belt is heated by the polymerization reaction, and the belt surface is cooled by water sprayed from the spray nozzle 30. The sprayed water is collected from the lower part of the belt.

On the other hand, the polymerization solution was prepared as follows. 525.4 parts of a 37% aqueous solution of sodium acrylate and 4.86 parts of glycerin were charged into a 200 L drum made of SUS316. After stirring the solution, the pH was adjusted to 10.0 with dilute aqueous sodium hydroxide. Next, a small amount of ion exchange water was added to make the total amount 536 parts, and then deaerated until the dissolved oxygen became 4 ppm by bubbling nitrogen.

2,2'-azobis- (2-aminodipropane) dihydrochloride as a photopolymerization initiator (trade name V-50, manufactured by Wako Pure Chemical Industries, Ltd.) 2% as a photopolymerization initiator with respect to 536 parts of the monomer aqueous solution 4.14 parts of the aqueous solution was mixed with a line mixer provided immediately before being supplied to the belt polymerization machine, so as to be supplied to the belt polymerization machine as one polymerization liquid.
The monomer (sodium acrylate) concentration in the polymerization solution was 36%. The amount of glycerin added was 2.5% with respect to the monomer. Moreover, the addition amount of V-50 was 0.04g with respect to 1 mol of monomers. The temperature of the polymerization solution is adjusted to 20 ° C. before being supplied to the belt polymerization machine.
The polymerization solution was supplied by adjusting the flow rate so that the thickness on the belt was 15 mm.
The polymerization solution was first reacted at a light intensity of 3.7 W / m ² for about 17 minutes and then at an intensity of 17 W / m ² for about 8 minutes for a total of 25 minutes. A sodium polyacrylate hydrogel having a thickness of about 14 mm was continuously discharged from the belt outlet.
The hydrogel was roughly crushed with a crusher (10 type, manufactured by Nippon Spindle Co., Ltd.).
Next, the crushed gel was extruded by applying a specific power of 0.12 kWh / kg shear to an extruder (special two-stage 130 wear extruder manufactured by Osaka Seiki Co., Ltd.) shown in FIG.
It was dried in the same manner as in Example 1 except that the gel was used. Moreover, it sampled for every fixed time similarly to Example 1, and measured the drying rate, the insoluble matter, and the solution viscosity.
The drying rate (time to reach a solid content of 97%) was 59 minutes, the insoluble content was 0.00%, and the solution viscosity was 660 mPa · S. The drying rate was fast, the insoluble content was very small, and the quality was good. The results are shown in Table 1.
In the column of “Dryer” in the following Tables 1 to 3, A represents an aeration band dryer, B represents a vibrating fluidized bed dryer, and C represents a hot air circulation dryer.

Comparative Example 1 (Comparative example of a hot air circulation dryer)
After the plate-like gel obtained in Synthesis Example 1 is cut into strips, it is supplied to a meat chopper (Hiraga Kogyo Co., No. 32 type, die diameter 4.5 mmΦ), and is an extrudate (granular) extruded gel. Got.
The extruded gel was uniformly loaded so that the layer height was about 9.0 mm (that is, two layers) on a cage (width 30 cm × length 30 cm × height 7 cm) made of a 20 mesh stainless steel wire mesh. Then, it dried by putting in the hot-air circulation type dryer (The Yamato Kagaku company make, Constant Temperature Oven, model DN600) by which the temperature was previously adjusted to 200 degreeC.
The drying rate, insoluble matter and solution viscosity in the drying experiment were measured in the same manner as in Example 1, and the results are shown in Table 2.

Comparative Example 2 (Comparative example of a hot air circulation dryer)
The plate-like gel obtained in Synthesis Example 1 is cut into strips, and then supplied to a meat chopper (manufactured by Hiraga Works, No. 32 type, dice diameter 9.5 mmΦ), and is an extrudate (granular) extruded gel. Got.
Using this extruded gel, the drying rate, solution viscosity and insoluble content were measured in the same manner as in Example 1 except that the gel layer height was as shown in Table 2. The results are shown in Table 2.

Comparative Examples 3 to 4 (Comparative example of a hot air circulation dryer)
The drying rate, solution viscosity, and insoluble matter were measured in the same manner as in Example 1 except that the drying rate was as shown in Table 2. The results are shown in Table 2.

Comparative Example 5 (Comparative example of a hot air circulation dryer)
The plate-like gel obtained in Synthesis Example 1 was cut with scissors into a width of 10 mm, a length of 50 mm, and a thickness of 5 mm. The drying rate, solution viscosity and insoluble content were measured in the same manner as in Example 1 except that the gel was used and the gel layer was 5 mm. The results are shown in Table 2.

Comparative Examples 6 to 10 (Comparative example of a ventilation band dryer)
Using hot air having the properties shown in Table 3, except that the gel layer height was changed to the value shown in Table 3, drying was performed in the same manner as in Example 1, and the drying speed, insoluble matter and solution viscosity were measured. The results are shown in Table 3.
Comparative Example 11 (Comparative example of a ventilation band dryer)
Drying was performed in the same manner as in Example 15 except that hot air having a dew point of 80 ° C. was used, and the drying rate, insoluble matter, and solution viscosity were measured. The results are shown in Table 3.

From the examples and comparative examples described above, it was found that the critical significance of the numerical range of the present invention can be said as follows. That is, the hot air having a dew point of 70 ° C. or lower and a temperature of 160 to 230 ° C. is dried so as to pass through the hydrogel gap at a linear velocity of 0.1 m / s or higher, so that the insoluble content of the polymer is reduced. It has been found that it exerts an advantageous effect and is remarkable.

Regarding the technical significance of the upper limit of the numerical range of the dew point, when comparing Examples 1 to 4 and Comparative Example 6, Example 3 is the upper limit at 70 ° C., and Examples 1, 2 and 4 (30 to 60 ° C.) is lower than the upper limit value, which is apparent when compared with Comparative Example 6 (80 ° C.) exceeding the upper limit value. In Example 3, the insoluble content is 0.45% by mass, and Examples 1, 2, and 4 are 0.06% by mass or less. On the other hand, in Comparative Example 6, the insoluble content is 1.7% by mass, and the advantageous effects of the present invention are remarkably exhibited in the Examples. In Examples 1 to 4, the product of the (meth) acrylic acid (salt) -based water-soluble polymer composition is at a level that can be used in various applications because the insoluble content is sufficiently reduced. Although it is useful in applications of additives and feed additives, Comparative Example 6 is not useful in such various applications. Such an effect, that is, the effect that the product of the (meth) acrylic acid (salt) -based water-soluble polymer composition can be industrially produced and used suitably for various uses is said to be outstanding. Needless to say.

Regarding the technical significance of the lower limit of the numerical range of hot air temperature, when Examples 9 and 12 and Comparative Example 7 are compared, Example 9 and Example 12 are the lower limit at 160 ° C. and are lower than the lower limit. It is clear when compared with Comparative Example 7. In Example 9 and Example 12, the insoluble content is 0.73% by mass and 0.92% by mass, respectively, whereas in Comparative Example 7, the insoluble content is 2.2% by mass, In the embodiment, the advantageous effects of the present invention are remarkably exhibited. In Example 9 and Example 12, the product of the (meth) acrylic acid (salt) -based water-soluble polymer composition can be used in various applications, and particularly useful in food additives and feed additives. However, Comparative Example 7 is not usable for such various applications. Such an effect, that is, the effect that the product of the (meth) acrylic acid (salt) -based water-soluble polymer composition can be industrially produced and used suitably for various uses is said to be outstanding. Needless to say. In the examples other than Example 9 and Example 12, the hot air temperature is set to 180, 200 ° C., or 210 ° C., but in these examples, the effect of the present invention is further remarkably exhibited in this respect.

The technical significance of the upper limit of the numerical range of the hot air temperature is apparent when comparing Example 7 or 10 in which the hot air temperature is 210 ° C. with Comparative Example 9 that exceeds the upper limit of the hot air temperature. In Example 7 or 10, the insoluble content is 0.36% by mass or 0.42% by mass, respectively, whereas Comparative Example 9 is 5.8% by mass. The advantageous effect will be noticeable. In Example 7 or 10, the (meth) acrylic acid (salt) -based water-soluble polymer composition can be used industrially in various applications, and is particularly useful for food additives and feed additives. However, Comparative Example 9 is not usable for such various applications. Such an effect, that is, the effect that the product of the (meth) acrylic acid (salt) -based water-soluble polymer composition can be industrially produced and used suitably for various uses is said to be outstanding. Needless to say.

Furthermore, focusing on “drying by controlling the drying speed so that the time for the solid content concentration of the hydrogel to reach 97% by mass is within 100 minutes”, a specific comparison was made for the examples. By setting the time for the solid content concentration of the hydrogel to reach 97% by mass within 100 minutes, the insoluble content is from 0.92 to 0.95% by mass (Examples 11 and 12) to 0.03 to 0.73. It reduced to mass% (Examples 1-10, 13-18).

In the above-described embodiment, an aeration band dryer and a vibrating fluidized bed dryer are used as the dryer. However, “(meth) acrylic acid (salt) -based water-soluble polymer hydrogel is dried (meta ) A method for producing a water-soluble acrylic acid (salt) -based polymer, in which the hot air having a dew point of 70 ° C. or less and a temperature of 160 to 230 ° C. passes through the water-containing gel gap at a linear velocity of 0 The mechanism of action that produces the effect of the present invention is the same as long as it includes a step of “drying by passing at a rate of 1 m / s or more”. That is, in the method for producing a (meth) acrylic acid (salt) -based water-soluble polymer, there is an essential feature of the present invention in which at least the above drying conditions are essential, and these drying conditions have the same characteristics. Thus, the effects as shown in this embodiment can be obtained. Therefore, even if it is dryers other than a ventilation band dryer and a vibration fluidized bed dryer, the effect (performance) of this invention can be exhibited. For example, even when a fluidized bed dryer or the like is used, the advantageous effects of the present invention can be exhibited if the drying conditions are essential in the present invention. At least in the case of using an aeration band dryer or a vibrating fluidized bed dryer, the advantageous effects of the present invention are sufficiently demonstrated by the above-described examples and comparative examples, and the technical significance of the present invention is supported. .

Since the (meth) acrylic acid (salt) -based water-soluble polymer produced by the production method of the present invention has an insoluble content reduced by the effect of the present invention, it is an additive for poultices and poultices. And hydrophilic ointment bases, carpet compound thickeners, paint thickeners and adhesives and tackifiers, red mud settling during alumina production, flocculants for salt refining in soda industry, drilling soil treatment It can be suitably used for agents, clay treatment agents, mud adjusters, hygroscopic agents, desiccants, surface modifiers, various thickeners and the like. Among them, polyacrylic acid (salt) is suitable as a food additive and feed additive.
The above-described examples and comparative examples clearly demonstrate the advantageous effects of the present invention, and support the technical significance of the present invention.

It is process drawing which shows the suitable form of the manufacturing method of this invention. In the manufacturing method of this invention, it is a flowchart of motive power in the case of extruding using an extruder. BRIEF DESCRIPTION OF THE DRAWINGS It is an example of the reactor suitably used in order to manufacture the (meth) acrylic acid (salt) type water-soluble polymer of this invention, and is a schematic front view of this reactor (polymerization container). FIG. 4 is a schematic cross-sectional view of the reaction apparatus of FIG. 3. It is a figure which shows one form of the superposition | polymerization apparatus which manufactures the (meth) acrylic acid (salt) type | system | group water-soluble polymer of this invention. It is a figure which shows one Embodiment of the first photopolymerization process in the manufacturing method of the (meth) acrylic acid (salt) type water-soluble polymer of this invention. It is a figure which shows one Embodiment of the photopolymerization process of the 2nd step in the manufacturing method of the (meth) acrylic acid (salt) type water-soluble polymer of this invention. It is the schematic of the drying apparatus used in Examples 1-17 of this invention, 19, 20, and Comparative Examples 6-11. BRIEF DESCRIPTION OF THE DRAWINGS It is a side surface conceptual diagram which shows one form of the superposition | polymerization apparatus which manufactures the (meth) acrylic acid (salt) type water-soluble polymer of this invention. It is a perspective conceptual diagram which shows one form of the superposition | polymerization apparatus which manufactures the (meth) acrylic acid (salt) type | system | group water-soluble polymer of this invention. FIG. 20 is a schematic view showing the structure of an extruder used in Example 19.

Explanation of symbols

1: Mold 2: Reaction liquid injection port 3: Reaction liquid purge port 4: Packing 5: Thermometer 6: Polymerization part 7: Release material 8: Heat transfer base material 9: Saran wrap (registered trademark) (manufactured by Asahi Kasei Kogyo Co., Ltd.) )
10: Thermometer 11: Water (cooling water)
12: Water inlet 13: Water outlet 14: Blacklight mercury lamp (H100BL-L), Toshiba Lighting & Technology Corporation 15: Lamp holder, Toshiba Lighting & Technology Corporation 16: Blacklight mercury lamp (H400BL-L), Toshiba Lighting & Technology Corporation Company 17: Reflection shade (SN-4057T), Toshiba Lighting & Technology Corporation 18: Hydrogel polymer 19: Fresh air introduction pipe 20: Steam introduction pipe 21: Exhaust discharge pipe 22: Blower 23: Heat exchanger 24: Heat medium introduction pipe 25: Ventilation band dryer 26: Black light mercury lamp (H250BL-L), manufactured by Toshiba Lighting & Technology Co., Ltd. 27: Light reduction plate (opening ratio 10.7%, punching metal)
28: Light-reducing plate (aperture ratio 51%, punching metal)
29: Scraper 30: Spray nozzle 31: Weir (edge rope)
32: Acrylate-based water-soluble polymer hydrogel 33: Supply port 34: Screw 35: Cylinder 36: Breaker plate 37: Reduction gear 38: Jacket

Claims (8)

A method for producing a (meth) acrylic acid (salt) -based water-soluble polymer by drying a (meth) acrylic acid (salt) -based water-soluble polymer hydrogel,
The production method includes a step of drying such that hot air having a dew point of 70 ° C. or less and a temperature of 160 to 230 ° C. passes through the hydrogel gap at a linear velocity of 0.1 m / s or more. A method for producing a (meth) acrylic acid (salt) -based water-soluble polymer. The method for producing a (meth) acrylic acid (salt) water-soluble polymer according to claim 1, wherein a linear velocity of the hot air in the drying step is 0.5 to 3.0 m / s. The (meth) acrylic acid (salt) water-soluble polymer-containing water-containing gel is an extruded gel, and the (meth) acrylic acid (salt) -based water-soluble polymer according to claim 1 or 2, Method. The (meth) acrylic acid (salt) water-soluble polymer hydrated gel is a polymer hydrated gel obtained by polymerizing a monomer component containing 60 mol% or more of a (meth) acrylic acid (salt) monomer. The method for producing a (meth) acrylic acid (salt) -based water-soluble polymer according to any one of claims 1 to 3. The (meth) acrylic acid (salt) -based water-soluble polymer obtained by the drying step has an insoluble content of 0.5% by mass or less. A method for producing a (meth) acrylic acid (salt) -based water-soluble polymer. 6. The production of a (meth) acrylic acid (salt) -based water-soluble polymer according to any one of claims 1 to 5, wherein the drying step is performed using an aeration band dryer or a vibrating fluidized bed dryer. Method. 2. The method according to claim 1, wherein the production method includes a step of drying by controlling a drying rate so that a time for the solid content concentration of the hydrogel to reach 97 mass% is within 100 minutes. A method for producing a (meth) acrylic acid (salt) -based water-soluble polymer. The (meth) acrylic acid (salt) -based water-soluble polymer water-containing gel has a solid content of 20 to 60% by mass (meth) acrylic acid ( Salt) A method for producing a water-soluble polymer.

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