JP3145155B2 - Spray polymerization method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for spray-polymerizing a monomer solution containing an organic unsaturated carboxylic acid or a salt thereof as a main component using a redox polymerization initiator, and particularly to a method for producing a superabsorbent resin. It is about a suitable method.

[0002]

2. Description of the Related Art As a method for producing a superabsorbent resin from a monomer containing an organic unsaturated carboxylic acid or a salt thereof as a main component, a reversed-phase suspension method is mainly used, and a solution polymerization method is also used in some cases. I have. These methods require post-processes such as drying and pulverization, and the reverse phase suspension method also generates fine particles having a particle size of 100 μm or less, so that there are also problems in homogenization and handling of the product.

Japanese Patent Publication No. 32-10196 discloses an aqueous solution of a monomer comprising a water-soluble salt such as acrylic acid, methacrylic acid, itaconic acid or the like in the presence of an alkali metal persulfate or an ammonium persulfate catalyst.
(82.degree. C.) are sprayed into a gaseous medium heated to 82.degree. C.). Examples of the spraying method include a spray gun and a rotating disk, and a method in which a monomer aqueous solution and a catalyst are mixed in advance and then supplied to the rotating disk, or a method in which the monomer aqueous solution and the initiator solution are mixed immediately before and supplied to the rotating disk. Is also mentioned.

JP-A-49-105889 discloses that an organic unsaturated carboxylic acid or a salt thereof is formed by using a redox polymerization initiator comprising an organic hydroperoxide and a reducing agent to form an insoluble component in water. The spray polymerization method without the method is described, and there are a rotating disk type, a pressure nozzle type, a two-fluid nozzle type, etc. as the sprayer, but from a long-term operation, the monomer and the polymerization initiator solution are separated from each other by a separate conduit. It is preferable that the liquid supplied from a plurality of conduits be mixed in the disk in a short time, such as a rotating disk.

JP-A-2-64106 discloses a solution containing a water-soluble ethylenically unsaturated monomer as a main component in a gas phase obtained by mixing water vapor or a gas substantially inactive with at least one kind of polymerization with water vapor. And a method of producing a water-absorbent resin which is polymerized in the gas phase. Japanese Patent Application Laid-Open No. 2-138306 discloses a method in which a solution having a monomer concentration of at least 20% by weight is supplied to the gas phase. Relative humidity 30
%, A method for producing a water-absorbent resin that is polymerized under the conditions of not less than
By spraying into a gas phase at 40 to 180 ° C. using an atomizer and a spray nozzle (pressure nozzle), a particulate superabsorbent resin having an average particle size of about 100 to 400 μm is obtained.

[0006] In the case where the polymerizable monomer and the polymerization initiator are mixed before spraying, there is a danger that polymerization is started inside the nozzle in principle. In particular, when operating for a long time, the residence time distribution always occurs, and there is a high risk that the polymerization reaction proceeds in the nozzle. Further, since the polymerization reaction is an exothermic reaction, if the reaction starts to occur even a little, it proceeds in a runaway manner and causes nozzle blockage. In addition, both the method of spraying with a spray and the method of using a rotating disk tend to broaden the particle size distribution, and it is difficult to control the particle size of the resin to a desired value.

[0007]

The present invention relates to a method for spray-polymerizing a monomer solution containing an organic unsaturated carboxylic acid or a salt thereof as a main component by using a redox polymerization initiator. It is intended to provide a method for facilitating the operation.

[0008]

SUMMARY OF THE INVENTION The spray polymerization method according to the present invention is a method for spray-polymerizing a monomer solution containing an organic unsaturated carboxylic acid or a salt thereof as a main component using a redox polymerization initiator. One of the oxidizing agent and the reducing agent constituting the polymerization initiator added to the monomer solution is supplied to one nozzle, and the other is supplied from another nozzle with or without addition of the monomer solution. It is characterized in that the two jetted at the outlet are mixed, and the polymerization reaction is carried out in the gas phase as droplets having a controlled particle diameter by vibrating both nozzles.

As a monomer solution for producing a superabsorbent resin, acrylic acid, methacrylic acid, maleic acid,
An aqueous solution or a mixed aqueous solution of an organic unsaturated carboxylic acid or a salt thereof such as itaconic acid or a salt thereof is used. Particularly preferred is acrylic acid or a salt thereof. Salts of organic unsaturated carboxylic acids include ammonium salts, alkali metal salts and alkaline earth metal salts, especially sodium, potassium and ammonium acrylates or methacrylates. Further, a copolymerizable monomer such as acrylamide, methacrylamide, or acrylate may be allowed to coexist. The total concentration of the organic unsaturated carboxylic acid or salt thereof in the aqueous solution is at least 20% by weight, preferably at least 25% by weight. In order to improve water absorption performance, a crosslinking agent may be added in an amount of 0.5% by weight or less based on the weight of the monomer.

As the polymerization initiator, a redox type is used because the polymerization reaction time is short. As the combination of the oxidizing agent and the reducing agent constituting the redox-based polymerization initiator, those which are generally well known can be used. For example combination of H ₂ O ₂ and l- ascorbic acid or amine and the like.

As the gaseous phase gas which is polymerized while the sprayed droplets fall, it is preferable to use nitrogen, helium, carbon dioxide or the like which is inert to the polymerization, but it may be air. In addition, there is no particular limitation on the humidity in the gas including the case of only steam.
The temperature condition of the gas is not lower than room temperature and not higher than 200 ° C., preferably not higher than 150 ° C. The flow direction of the gas may be either countercurrent or cocurrent, but if the residence time needs to be increased, the countercurrent (anti-gravity direction) is preferred.

The outer diameter of the tip portion of the nozzle is preferably 1 mm or less in order to reduce the surface tension acting on the droplet and to easily shake off the droplet by vibration. The inner diameter is not particularly limited. Further, it is desirable that the two nozzles are arranged such that their tip positions are aligned. The linear velocity of the aqueous monomer solution at the nozzle outlet is preferably 1 to 20 cm / sec. The total flow rate of the liquid is 0.4 μl / sec (1.44 m
1 / hr) or more.

One example of the arrangement of the nozzles and a method of oscillating the nozzles will be described with reference to FIG. 1. Two nozzles 1 and 2 which are installed side by side and the tip positions of both nozzles are aligned.
The nozzles 1 and 2 are vibrated by the tip of a wire 5 attached to the vibrator (cone paper) 4 of the speaker 3. In order to vibrate the nozzle, the nozzle may be hit with the tip of the wire 5 as shown in FIG. 1, or the tip of the wire 5 may be brought into close contact with the nozzle and synchronized. The frequency and amplitude of the nozzle are determined by the frequency and voltage of the signal applied to the speaker. Since the droplets 6 are shaken off at every periodic oscillation, the droplets have a substantially uniform diameter. FIG. 2 is a cross-sectional view of the nozzle tip XX, showing a state where the nozzles 1 and 2 are arranged side by side.

The total flow rate of the liquid from the nozzle is represented by Q (μl / s
ec), assuming that the nozzle frequency is f (Hz), the average droplet diameter ( _DL : μm) is theoretically D = (6Q / π · f)
It is expressed by the formula of ^1/3 . Since the droplets are dried and dehydrated during the polymerization, if the monomer content in the liquid is C (%), the average diameter of the resin (D _R : μm) is theoretically D = (6 CQ /
100π · f) ^1/3 Therefore, in order to obtain resin particles having a desired diameter, the total flow rate of the liquid and the nozzle frequency may be controlled according to the monomer concentration in the monomer solution.

FIG. 3 shows another type of nozzle arrangement, in which one nozzle 1A is inserted into the other nozzle 2A, and the tip positions of both nozzles are aligned. is there. FIG. 4 is a sectional view of the nozzle tip YY. The method of vibrating the double tube nozzle is the same as that described with reference to FIG.

Another example of a method of vibrating the nozzle will be described with reference to FIG. 5. A pair of nozzles 1 and 2 are installed in close contact with an electrostrictive element (unimorph, bimorph type) 7, and both of them vibrate. I do. As a method of vibrating the nozzle, the nozzle may be struck using an electrostrictive element instead of the speaker shown in FIG. The frequency of the nozzle is determined by the resonance frequency when the electrostrictive element is set together with the nozzle. This resonance frequency can be adjusted by the length and the total weight of the electrostrictive element.

As a method of vibrating the two nozzles,
Appropriate means can be adopted without being limited to the ceramic vibrator such as the speaker, the electrostrictive element, and the piezoelectric element.
The vibration cycle of the nozzle is preferably set to 150 hertz (Hz) or less in order to provide stable vibration to the nozzle.

Hereinafter, the present invention will be described specifically with reference to examples, but the present invention is not limited to the following examples.

[0019]

[Preparation Example 1 of Monomer Solution] 125 parts by weight of an aqueous solution of 80% by weight of acrylic acid, 65.1 parts by weight of an aqueous solution of 42.6% by weight of sodium hydroxide and 0.14 part by weight of a crosslinking agent (N, N'-methylenebisacrylamide) And 2.8 parts by weight of a 30% by weight aqueous hydrogen peroxide solution as an oxidizing agent were added to prepare solution A. Solution A had a monomer concentration of 60% by weight and a degree of neutralization of 50 mol%.

[0020]

Preparation Example 2 of Monomer Solution 125 parts by weight of an 80% by weight aqueous solution of acrylic acid, 67.1 parts by weight of a 41.4% by weight aqueous solution of sodium hydroxide and 0.14 part by weight of a crosslinking agent (N, N'-methylenebisacrylamide) And 0.34 parts by weight of 1-ascorbic acid or 0.67 parts by weight as a reducing agent.
The solutions added in parts by weight were prepared as solutions B1 and B2, respectively. The monomer concentrations and the degrees of neutralization of the solutions B1 and B2 were the same as those of the solution A.

[0021]

Example 1 In polymerization of an acrylic acid (salt) monomer aqueous solution using a redox polymerization initiator, a monomer aqueous solution containing an oxidizing agent and a monomer aqueous solution containing a reducing agent were arranged side by side as shown in FIG. It was supplied by another nozzle. Solution A on the oxidizing agent side, Solution B on the reducing agent side
1 each at 9.24 ml / hr, total (Q) 18.4
At 8 ml / hr, the solution was supplied to two nozzles having an outer diameter of 0.6 mm and an inner diameter of 0.35 mm at the tip. The two nozzles were united and vibrated at a frequency of 60 Hz by a blow using vibration of a speaker. The droplets ejected from the nozzles were dropped in an ascending flow of N ₂ at 55 ° C. and 12 cm / sec, and collected 4.5 m below. When the collected resin was observed with a scanning electron micrograph, the particle size distribution was 100 to 50.
0 μm spherical resin was obtained, and the average particle size was 440 μm.
m. At this time, the calculated value of the average particle size is 461 μm.
And the measured values are in good agreement. Further, the resin had a water absorption of deionized water of 294 g / g resin. Table 1 summarizes the test conditions and test results.

[Table 1]

[0022]

Examples 2 to 9 The same tests as in Example 1 were carried out by changing the type of monomer solution, the supply speed, the air flow speed for drying, the nozzle diameter, the vibration method and the like as shown in Table 1. In Example 6, only a 15% aqueous hydrogen peroxide solution was used as the solution on the oxidizing agent side. Table 1 shows the test results of Examples 2 to 9.
In each case, a spherical resin was obtained. In particular, when the outer diameter of the tip portion of the nozzle was 1 mm or less, the calculated value and the measured value coincided with an error of 10% or less. On the other hand, when the outer diameter of the nozzle tip portion was 1.1 mm, the measured value of the average resin particle diameter was 2,500 μm when the same procedure as in Example 9 was performed except that no vibration was applied to the nozzle. In Example 9, the average particle diameter was controlled to 850 μm by applying vibration. However, the difference between the calculated value and the measured value was larger than when the outer diameter of the nozzle tip was 1 mm or less. When the frequency was 170 Hz, the frequency was high and the stability of the vibration was poor, and adhesion of the polymer to the tip of the nozzle was observed about 20 minutes after the start of operation.

[0022]

By changing the supply speed of the monomer solution and the frequency of the nozzle, the average droplet diameter is changed.
A resin having an arbitrary average particle size can be obtained. In addition, since the polymerization initiator acts after the droplets are formed, there is no possibility that the nozzle for supplying the monomer solution is clogged with the polymer, and the operation can be performed for a long time.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of a configuration of an apparatus for implementing the present invention.

FIG. 2 is a sectional view of the nozzle shown in FIG.

FIG. 3 is a diagram showing another example of the configuration of the device for carrying out the present invention.

FIG. 4 is a sectional view of the nozzle shown in FIG. 3;

FIG. 5 is a diagram showing another example of the configuration of the device for implementing the present invention.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Fujio Tsuchiya 2 110 Saki-cho, Handa-shi, Aichi Prefecture JGC Co., Ltd. Inside Kinuura Research Laboratories (58) Field surveyed (Int. Cl. ⁷ , DB name) C08F 2/01

Claims (4)

(57) [Claims] When a monomer solution containing an organic unsaturated carboxylic acid or a salt thereof as a main component is spray-polymerized using a redox-based polymerization initiator, an oxidizing agent and a reducing agent constituting the redox-based polymerization initiator are used. One is added to the monomer solution and supplied to one nozzle, and the other is supplied from another nozzle with or without addition of the monomer solution so that the two ejected at the nozzle outlet are mixed, and both are added. A spray polymerization method wherein a polymerization reaction is performed in a gas phase as droplets having a controlled particle size by vibrating a nozzle. 2. The vibration cycle of the nozzle is set to 150 Hz (H
The spray polymerization method according to claim 1, wherein z) is as follows. 3. The spray polymerization method according to claim 1, wherein two nozzles are arranged side by side, each nozzle has an outer diameter of 1 mm or less, and both nozzles have the same tip positions. 4. The spray polymerization method according to claim 1, wherein one nozzle is housed inside the other nozzle, and a double tube type nozzle is used in which both nozzles have the same tip positions.