JPH0971609A - Recovery of polymer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for recovering efficiently polymer particles of a narrow range of particle size distribution from a polymer latex by making the polymer latex contact with an aqueous solution of a coagulant in a piston- flow path and flow through the path in condition of a laminar flow to obtain coagulated slurry, and stirring the slurry at a specific temperature. SOLUTION: This method makes a polymer latex obtained by emulsion polymerization (e.g. latex of polybutadiene, butadiene-styrene copolymer, etc.) contact with an aqueous solution of a coagulant such as an inorganic or organic acid (salt) in a path that causes a piston flow in coagulating equipment, and the mixture flow through the path in the coagulating equipment in laminar flow condition of Reynolds number of <=1000 to form coagulated slurry, and then agitates the slurry in an agitating vessel at a temperature higher than the coagulating temperature in the coagulating equipment.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for recovering a polymer, and more particularly to a method for recovering polymer particles by coagulating / aggregating a polymer latex obtained by emulsion polymerization.

[0002]

As a method for recovering a polymer from a polymer latex obtained by emulsion polymerization, an electrolyte such as an acid or a salt is added to a latex in a stable state, or vice versa. A method of obtaining a powdery resin by performing an operation to solidify the polymer, followed by dehydration and drying is commonly used.

The important thing required for this solidification process is
It is intended to prevent polymer particles from accumulating and clogging in the steps after solidification, and to produce polymer particles having excellent powder characteristics which enable stable industrial production.

As a method for obtaining polymer particles having excellent powder characteristics, for example, a method of taking out polymer latex as spherical particles by slow coagulation (Japanese Patent Publication No. 3-51728, Japanese Patent Application Laid-Open No. 5-320221), and A method of obtaining polymer particles by adding an organic liquid which is insoluble in the dispersion medium and which is a poor solvent for the polymer, and stirring the mixture (JP-A-62-14972).
6 and JP-A-62-115032).

These new techniques have made it possible to obtain polymer particles having a narrow particle size distribution and improved powder characteristics. However, the polymer obtained by the former method has a low rubber content and a high minimum film-forming temperature. Comparing the agglomerated particles of a polymer with a high rubber content and a low minimum film forming temperature, the agglomerated particles of a polymer with a low rubber content and a high minimum film forming temperature have a low bulk specific gravity and a high moisture content of wet powder. On the other hand, in the latter method, in contrast to the former method, when a polymer having a high rubber content and a low minimum film forming temperature is used, the organic liquid penetrates into the rubber portion of the polymer,
There is a disadvantage that polymer particles having excellent powder characteristics cannot be obtained unless a large amount of organic liquid is used. For this reason, in the above-mentioned technique, depending on the type of polymer latex, a sufficient coagulation effect cannot be obtained, and the use of this method is currently limited.

Further, as a conventional coagulation technique, polymer latex and a coagulant or an aqueous solution thereof are mixed in one or more coagulation tanks equipped with stirring blades to accelerate the aggregation of polymer particles and thereby Although a method of collecting coalesced particles is used (Japanese Patent Laid-Open No. 60-26006), in this method, coagulation and destruction proceed at the same time in the coagulation tank, and the coagulation rate,
That is, there is a drawback that it is extremely difficult to control the particle size. On the other hand, in contrast to this method, a method of using an apparatus consisting of a double tube to control the residence time has also been proposed (Japanese Patent Laid-Open No. 58-174401), but an aggregate having a uniform particle size is obtained. There is a drawback that it is hard to be caught.

[0007]

Means for Solving the Problems As a result of intensive studies in view of the above situation, the present inventors have found that Brownian agglomeration and turbulent agglomeration are predominant in the initial stage of agglomeration of the polymer latex, and the agglomeration in the middle stage. After that, it was clarified that shear fracture became dominant, and there, the early and middle stages of aggregation were separated,
It has been found that, by controlling independently, all kinds of polymer latexes obtained by emulsion polymerization can be aggregated into polymer particles having the same particle size distribution, and the present invention has been completed.

That is, according to the present invention, after a polymer latex obtained by emulsion polymerization and an aqueous solution of a coagulant are brought into contact with each other in a flow path in a coagulation device for producing a piston flow, a laminar flow having a Reynolds number of 1000 or less is obtained. In this state, a flow path in the coagulation device is flowed to form a coagulation slurry, and the coagulation slurry is then stirred in a stirring tank at a temperature higher than the coagulation temperature in the coagulation device. There is a method for recovering the polymer.

[0009]

DETAILED DESCRIPTION OF THE INVENTION A detailed description will be given below. A feature of the present invention is that in a coagulation device that causes a piston flow, in order to reduce the influence of shear, by keeping the polymer latex and the coagulant in contact with each other while keeping the laminar flow in the coagulation device,
The polymer latex is coagulated, and then the obtained coagulated slurry is broken and solidified by shearing in a stirring tank, and the particle size is controlled by stirring to obtain polymer particles having a narrow particle size distribution. is there. By using this method, polymer particles having a narrow particle size distribution can be continuously obtained from all polymer latexes obtained by emulsion polymerization.

The polymer latex used in the present invention is not particularly limited, and those obtained by emulsion polymerization can be used. Examples thereof include polybutadiene, butadiene-styrene copolymer, butadiene-acrylonitrile copolymer, acrylonitrile-butadiene-styrene copolymer (ABS resin), methyl methacrylate-butadiene-styrene copolymer (MBS resin), acrylic acid. Ester-acrylonitrile-styrene copolymer (A
AS resin), latex such as multi-stage polymer of methyl methacrylate-butyl acrylate / styrene-methyl methacrylate, but not limited thereto.

The coagulant used in the present invention is not particularly limited, and known ones can be used. Examples of the coagulant include inorganic acids such as hydrochloric acid, sulfuric acid and nitric acid, organic acids such as formic acid and acetic acid, inorganic salts such as calcium chloride, magnesium sulfate and aluminum sulfate, and organic acid salts such as calcium acetate and aluminum acetate. can give.

The method for recovering the polymer of the present invention is carried out by using the above-mentioned polymer latex and the coagulant aqueous solution.
The polymer latex is brought into contact with the coagulant aqueous solution in the coagulation device. The coagulation device used is one that causes a piston flow, for example, a tubular coagulation device consisting of a double tube of a polymer latex supply pipe and a coagulant aqueous solution supply pipe, and a large number immersed in a coagulant aqueous solution flow. Nozzle coagulation device for discharging the polymer latex from the thin tube nozzle.

When the polymer latex is coagulated by the coagulation device, the Reynolds number in the flow path inside the coagulation device is 100.
It is important that the polymer latex and the aqueous coagulant solution are brought into contact with each other in a laminar flow of 0 or less. Reynolds number is 1
If the polymer latex and the aqueous solution of the coagulant are brought into contact with each other in a state of exceeding 000, turbulent flow aggregation occurs in the coagulation device, and it becomes difficult to recover the polymer particles having a narrow particle size distribution.

The Reynolds number of the present invention is defined by the following formula: Re = D <v> ρ / μ (where Re is the Reynolds number, D is the diameter of the circular tube, and <v>
Is the average velocity of the cross section, ρ is the density of the fluid, and μ is the viscosity of the fluid. In the present invention, a Reynolds number of 1000 or less was used as a laminar flow state.

The supply rate of the polymer latex and the aqueous solution of the coagulant supplied to the coagulation device cannot be unconditionally determined because it depends on the type and concentration of the polymer latex, but the polymer latex is the coagulation device. Inside the polymer latex supply port (flow rate of the polymer latex), flow rate of the aqueous coagulant solution in the coagulation device (flow rate of the coagulant aqueous solution), and coagulation after the polymer latex and the coagulant aqueous solution are mixed. The velocities of the slurries flowing in the coagulation device (coagulated slurry flow rates) are preferably equal to each other.

The coagulation temperature in the coagulation device cannot be generally determined depending on the type and concentration of the polymer latex, but
It is 0 to 90 ° C., and the coagulation time is 2 seconds to 10 minutes.

The coagulated slurry thus exiting the coagulator is sent to a stirring tank. The stirring tank used is not particularly limited, but two or more continuous type mixing tanks having stirring means such as a turbine, a propeller, and an anchor in the tank are often used, but in addition to this, there are two or more chambers. It may be a cylindrical container or the like that is fractionated into each chamber and is equipped with a stirring device in each chamber. Alternatively, a batch type mixing tank may be used in which one coagulation tank is used and the second and subsequent steps are performed after the completion of the first step.

In the stirring tank, the coagulated slurry obtained by the coagulation apparatus is stirred by a stirrer, and the shearing force generated by stirring is used to break and control the particle size to form polymer particles having a narrow particle size distribution. Let

In this case, the temperature in the stirring tank must be higher than the coagulation temperature in the coagulation device. When the temperature of the stirring tank is lower than the coagulation temperature of the coagulation device, it becomes difficult to recover polymer particles having a narrow particle size distribution, which is the object of the present invention.

By the above operation, 90% of the dry particles can be obtained regardless of the type of polymer latex obtained by emulsion polymerization.
Polymer particles having the above particle size in the range of 0.1 to 1.0 mm can be obtained.

[0021]

EXAMPLES The present invention will now be described in detail with reference to examples, but the present invention is not limited to these examples.
In addition,% in an Example shows weight%.

[Example 1] Inner diameter 3 cmφ, length 50 cm
A 25 ° C coagulant aqueous solution (sulfuric acid concentration 0.004
%) At a flow rate of 1.0 cm / sec. On the other hand, a polymer latex (copolymer of butadiene and styrene obtained by graft-polymerizing a mixture of methyl methacrylate and styrene with a copolymer of butadiene and styrene at a temperature of 25 ° C. in parallel with this coagulant aqueous solution was used.
%, Styrene 30% and methyl methacrylate 13%
A polymer latex containing. Solid content concentration 27.4
%. ) Was discharged from the nozzle having a pore diameter of 0.5 mmφ into the coagulant aqueous solution at a latex outflow rate of 1.0 cm / sec (the number of Rey nozzles in a circular tube = 1.28).

Then, the obtained coagulated slurry was transferred to a first continuous stirring tank (5 liters) equipped with a turbine blade having a blade diameter of 7 cm × 6 sheets (5 liters), operating temperature 75 ° C., rotation speed 20.
Agitation was performed by stirring at 0 rpm. Then, the polymer slurry, which has been allowed to aggregate in the first continuous stirring tank, is supplied to a second continuous stirring tank equipped with the same type of turbine blade as that installed in the first continuous stirring tank, and an operating temperature of 85 ° C. Stirring speed 2
Aggregation was completed at 00 rpm.

The slurry that has left the second continuous stirring tank is washed with water and then dehydrated by a centrifuge to obtain wet powder (moisture content: 25.7%). Got united. Table 1 shows the measurement results of the particle size distribution of this polymer.

The measurement of the particle size distribution in the examples is as follows.
The test was performed using a standard test sieve defined by Japanese Industrial Standards (JIS No. 408). As the sample, 2 g of the dried polymer was used, and the sieving time was 10 minutes.

[0026]

[Table 1]

[Example 2] Inner diameter 3 cmφ, length 50 cm
A 25 ° C coagulant solution (magnesium sulfate,
(Concentration 0.064%) at a flow rate of 1.0 cm / sec.
On the other hand, the polymer latex at 25 ° C. was co-flowed with this aqueous solution of coagulant (butyl methacrylate and styrene were copolymerized with methyl methacrylate, and then methyl methacrylate was graft-polymerized thereon, butyl acrylate 3
0%, styrene 25% and methyl methacrylate 45
% Polymer latex. Solid content concentration 12%. )
Was discharged from the nozzle having a hole diameter of 0.5 mmφ into the aqueous coagulant solution at a latex outflow rate of 1.0 cm / sec (the number of Rey nozzles in the circular tube = 1.30).

Then, the obtained coagulated slurry was transferred to a first continuous stirring tank (5 liters) equipped with a turbine blade having a blade diameter of 7 cm × 6 sheets (5 liters), an operating temperature of 85 ° C., and a rotation speed of 20.
Agitation was performed by stirring at 0 rpm. Next, the polymer slurry, which has been allowed to undergo aggregation in the first continuous stirring tank, is supplied to a second continuous stirring tank equipped with the same type of turbine blade as that installed in the first continuous stirring tank, and the operating temperature is 90 ° C. Stirring speed 2
Aggregation was completed at 00 rpm.

The slurry that has left the second continuous stirring tank is washed with water, dehydrated by a centrifuge to obtain wet powder (water content 34.6%), and the wet powder is dried by a dryer to obtain a powdery weight. Got united. Table 2 shows the measurement results of the particle size distribution of this polymer.

[0030]

[Table 2]

[0031]

According to the present invention, polymer particles having a narrow particle size distribution can be efficiently recovered from various polymer latexes.

Claims (1)

[Claims] 1. A polymer latex obtained by emulsion polymerization is brought into contact with an aqueous solution of a coagulant in a flow path in a coagulation device that causes a piston flow, and then the coagulation is performed in a laminar flow state with a Reynolds number of 1000 or less. A polymer characterized in that a coagulation slurry is formed by flowing through a flow path in the coagulation device and then the coagulation slurry is stirred in a stirring tank at a temperature higher than the coagulation temperature in the coagulation device. Recovery method.