JPH07233214A - Recovery of polymer - Google Patents

Abstract

PURPOSE:To obtain polymer particles excellent in powder properties by adding a spray of a polymer latex into a coagulation tank within a specific range of coagulation temp. and within a specific range of peripheral speed of agitating blades to coagulate the polymer latex. CONSTITUTION:A vinyl copolymer latex such as a styrene-acrylonitrile copolymer latex and/or a rubber-modified vinyl polymer latex such as an ABS latex is sprayed in the form of droplets of 75mum to 2mm in size through a spray nozzle into a coagulation tank with an agitator wherein agitation is effected under conditions: (Tv-40) <= coagulation temp. ( deg.C) <= (Tv+20) [wherein Tv is a Vicat softening point ( deg.C) of the polymer] and 100 <= peripheral speed (cm/s) of agitating blades <=800, and into which a coagulant such as an aqueous soln. of sulfuric acid having a concn. of about 1% is dropwise added, whereby a coagulated slurry is prepd. The coagulated slurry is heat-treated under conditions: Tv <= treatment temp. ( deg.C) <=(Tv+80) and 5min <= treatment time <=180min, then dehydrated with a centrifugal dehydrator or the like, and washed, followed by separation of coagulated polymer particles, which are then dried with a flash dryer or the like to obtain polymer particles excellent in powder properties.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for recovering a polymer from a polymer latex obtained by emulsion polymerization or the like, and more specifically to a polymer for obtaining polymer particles having excellent powder characteristics. Regarding collection method.

2. Description of the Related Art Generally, in order to recover a powdery polymer from a polymer latex produced by an emulsion polymerization method, it is necessary to add a coagulating liquid to the polymer latex to coagulate the polymer latex. As the most general method for coagulating such a polymer latex, there is known a method in which the polymer latex and a coagulation liquid are continuously supplied to a coagulation tank for coagulation and aggregation. However, this method can obtain only those having a wide particle size distribution, low bulk density, and low fluidity. As a second method, there is a method in which a coagulant is sprayed into a coagulation chamber in the form of gas or mist, and then brought into contact with droplets of the polymer latex in space to coagulate (JP-A-58-87).
No. 102). However, in this method, it is necessary to coagulate the latex in the gas phase until the hardness becomes sufficient within a short time when the latex droplets drop, so that the tower height is high in order to obtain a relatively large particle size. Coagulation tower is required, equipment cost is high, and it is not economical.

The present invention has been made in the background of the above-mentioned prior art, and an object thereof is to provide a method for recovering a polymer capable of recovering polymer particles having excellent powder characteristics.

[0002]

Means for Solving the Problems As a result of intensive studies for solving the above-mentioned problems, the present inventors have found that the coagulation temperature, stirring conditions and latex addition method in the coagulation step are limited to a specific range. The inventors have found that the solution to the problem can be achieved and arrived at the present invention. The present invention is a method for recovering a polymer, which comprises coagulating a polymer latex under the following conditions (a), (b) and (c). (A) Solidification temperature (° C) (Tv-40) ≤ solidification temperature ≤ (Tv + 20) However, Tv; Vicat softening point (° C) of the recovered polymer (b) Mixing and stirring are performed in the solidification tank The peripheral speed of the tip of the blade is 100 ≦ peripheral speed ≦ 800 (cm / s) (c) The spray addition of the polymer latex is provided to the coagulation tank which is mixed and stirred.

The present invention will be described in detail below. A method of obtaining the softening point (Tv) shown in (A) of the present invention will be described first. The softening point (Tv) is obtained by previously collecting the polymer from the polymer latex used for coagulation,
Using the dried polymer, the Vicat softening point is measured according to the method of JIS K7206, and this value is taken as the softening point (Tv) of the present invention. The polymer latex of the present invention comprises a vinyl-based polymer latex and / or a rubber-modified vinyl-based polymer latex, and these vinyl-based polymer latexes usually obtained by emulsion polymerization are vinyl-based monomers shown below. Alternatively, it can be obtained by polymerizing a monomer copolymerizable therewith. The rubber-modified vinyl polymer latex is obtained by polymerizing a vinyl monomer shown below or a monomer copolymerizable therewith under the rubber polymer shown below.

The vinyl-based monomer is not particularly limited, but examples thereof include (meth) acrylic acid such as acrylic acid and methacrylic acid; alkyl acrylate-based monomers such as methyl acrylate, ethyl acrylate and butyl acrylate; Methacrylic acid alkyl ester type monomers such as methyl methacrylate and ethyl methacrylate; vinyl cyan type monomers such as acrylonitrile and methacrylonitrile; aromatic vinyl type monomers such as styrene and α-methylstyrene; vinyl chloride, odor Various monomers such as vinyl halide-based monomers such as vinyl chloride may be mentioned, and these may be used in combination of two or more kinds. Examples of preferable vinyl monomers include (meth) acrylic acid alkyl esters, vinyl cyan monomers, and aromatic vinyl monomers.

Examples of other copolymerizable monomers include maleimide monomers such as maleimide, N-methylmaleimide, N-phenylmaleimide and N-cyclohexylmaleimide. When a maleimide-based monomer is used, heat resistance is improved and a polymer having excellent heat resistance can be obtained.

As the rubber-like polymer, polybutadiene,
Styrene-butadiene copolymer (styrene content 5-6
0% by weight is preferred. ), Styrene-isoprene-based copolymer, acrylonitrile-butadiene-based copolymer, ethylene-α-olefin-based copolymer, acrylic rubber, butadiene-acrylic-based copolymer, polyisoprene, styrene-butadiene block copolymer , Hydrogenated butadiene-based polymers, ethylene-based ionomers, and silicone-based rubbers. These rubber-like polymers may be one or two.
Used in seeds and above. As a preferable rubber-like polymer,
Examples thereof include polybutadiene, styrene-butadiene copolymer, acrylic rubber, and silicon rubber (particularly preferably unsaturated group-containing silicon rubber).

The rubber-like polymer used in the production of the rubber-modified vinyl polymer is in the form of latex. Examples of the polymer of the polymer latex (A) include acrylic resins, polystyrene, styrene-acrylonitrile copolymers, (α-methyl) styrene- (acrylonitrile) -maleimide monomer-based copolymers, and ABS resins, Examples thereof include resinous polymers such as rubber-modified vinyl polymers such as MBS resin, AES resin, and AAS resin. The rubber-like polymer content in the polymer latex is
It is preferably 50% by weight or more, more preferably 60% by weight or more, and the use of those within this range will further exert the objects and effects of the present invention.

As the coagulant of the present invention, those commonly used for coagulating latex can be used. Examples thereof include inorganic acids such as hydrochloric acid and sulfuric acid, organic acids such as acetic acid and formic acid, and metal salts of these acids. In addition, a polymer flocculant and the like can be used in combination. Examples of the above metal salts include calcium chloride, calcium nitrate, aluminum chloride, aluminum sulfate, magnesium sulfate and the like. In the present invention, polyvalent metal salts and inorganic acids are preferred. More preferred are calcium chloride, magnesium sulfate and sulfuric acid. Examples of the polymer flocculant include polyacrylamide.
Further, the salt and the acid can be used in combination. The coagulant may be added to the coagulation tank by piping, or may be sprayed with a spray nozzle and brought into contact with the latex. The polymer latex used in the present invention is sprayed and added to the coagulation tank in the form of droplets, and the droplet diameter is preferably in the range of 75 μm to 2 mm, more preferably 100 to 100.
0 μm, particularly preferably 70% by weight or more of all the liquid droplets. 30% by weight of fine droplets of less than 75 μm
If the particle size distribution exceeds, the bulk density and flow properties are deteriorated. On the other hand, if it exceeds 2 mm, the spherical particles are deformed and destroyed when spray-added to the coagulation tank, and those having excellent powder characteristics cannot be recovered, which is not preferable. When the dispersed latex droplets enter the coagulation tank, they coagulate from the surface of the droplets. If the polymer is heat-treated before it completely solidifies to the inside, the inside of the particles becomes porous,
The bulk density of the resulting product is reduced. For this reason, it is preferable to previously add a coagulant having a coagulation value of 1/4 or more to less than the coagulation value in the latex sprayed from the spray nozzle. If it is less than 1/4 of the coagulation value, the effect of increasing the bulk density is insufficient, and if it exceeds the coagulation value, solidification occurs and atomization becomes difficult. The coagulation value is determined by using the polymer latex used for coagulation and the coagulant used for coagulation,
It was determined by the method shown below. The polymer latex is diluted with water to a concentration of 0.20%. 10 cc of this polymer latex was placed in a test tube, 10 cc of coagulant aqueous solution of various concentrations was added, mixed well, and allowed to stand in a constant temperature bath at 30 ° C. The presence or absence of formation of a precipitation tank after 1 hour was examined, and the lowest concentration at which precipitation occurred (mmol / l after mixing) was taken as the coagulation value. The solidification temperature of (a) is (Tv-40 ° C) ≤ solidification temperature ≤ (Tm + 20 ° C), and preferably (Tv-35).
° C) ≤ solidification temperature ≤ Tm. At a temperature lower than the temperature of (Tv-40 ° C.), the particle size distribution becomes wide and the target particles cannot be obtained. At a temperature higher than (Tv + 20 ° C.), solidified particles are likely to be fused and coarse particles are generated,
Moreover, the solidified slurry concentration cannot be increased. The stirring condition (b) is that the peripheral speed at the tip of the stirring blade is 100 ≦ peripheral speed ≦ 800.
(Cm / s), preferably 150 ≦ peripheral speed ≦ 750 (cm
/ S) and the peripheral speed is less than 100 cm / s, a large lump is generated. Further, when the peripheral speed exceeds 800 cm / s, fine powder is generated and particles having excellent powder characteristics cannot be obtained. The polymer latex is atomized and added to the coagulation tank. A spraying device for spraying the polymer latex includes a two-fluid nozzle, a high-pressure nozzle, an ultrasonic nozzle, a high-frequency nozzle, a rotating disk, and the like. The sprayed latex is preferably added by spraying to the upper part of the coagulation tank, which is being stirred and mixed, and dispersed. Further, in order to improve powder properties such as mechanical strength and bulk density of the solidified particles, it is preferable to heat-treat the solidified particles.
This preferable heat treatment condition is Tv ≦ treatment temperature ≦ Tv +
80, more preferably Tv + 10 ≦ treatment temperature ≦ Tv +
70. If it is lower than Tv, the effect of the heat treatment becomes small, and the effect of increasing the bulk density and reducing the water content in the recovered coagulated particles does not appear. If the temperature exceeds Tv + 80 ° C., the solidified particles are fused with each other to form a mass, which makes stable operation impossible. Also, the slurry concentration cannot be increased. The heat treatment time is 5 minutes ≦ treatment time ≦ 180 minutes. If it is shorter than 5 minutes, the effect of the heat treatment is small, and the effects of increasing the bulk density and reducing the water content in the recovered coagulated particles do not appear. If it exceeds 180 minutes, the physical properties such as the hue of the resin will be impaired, and the equipment will be large, which is not economical. The shape of the stirring blade used for this stirring is not particularly limited, and generally used blades such as a paddle blade, a turbine blade, a propeller blade, and a gate type blade can be used. In the present invention, the above-mentioned aggregated polymer particles in the coagulated slurry can be separated, washed with water and dried if necessary to obtain dried polymer particles. Examples of the separation method include the following methods. That is, it can be dehydrated, washed and separated by a horizontal belt filter, a centrifugal dehydrator and the like. Further, it can be dried by a flash dryer or a fluid dryer and collected as dried polymer particles. Further, the coagulated slurry can be dried as it is or after being dehydrated with a horizontal belt filter, a centrifugal dehydrator or the like, and then dried with a twin-screw extruder with a dehydration slit. Since the agglomerated polymer particles according to the present invention have few fine powder particles, there are problems that usually occur in the above-mentioned method, namely, horizontal belt filter, clogging of filter cloth of centrifugal dehydrator, and biting at the inlet of a twin-screw extruder. It is possible to perform dehydration and drying without causing a low discharge rate due to defects and without causing leakage of agglomerated particles from the dehydration slit of the twin-screw extruder.

[0009]

EXAMPLES The method of the present invention will be specifically described below with reference to examples, but these do not limit the scope of the present invention. Powder property measuring method Bulk density: Measured according to JIS K6721.
(Unit: g / ml) Average particle size; Up to a particle size of 1000 μm, the particle size distribution is determined by a laser diffraction / scattering type particle size distribution measuring device (manufactured by Horiba Ltd.) For those exceeding 1000 μm, it is determined by image analysis. The average particle diameter d ₅₀ is the particle diameter of 50% cumulative value obtained from the cumulative distribution curve of this particle size distribution. Liquidity is defined as the liquidity index (chemical Enginee
ring. Jan. 18, (1965)).

Example 1 20 parts by weight of styrene and 20 parts by weight of methymethacrylate were added in the presence of 60 parts by weight (in terms of solid content) of a styrene / butadiene copolymer latex having a styrene / butadiene weight ratio of 24/76. Graft polymerization was carried out in an aqueous emulsion state to obtain a rubber-modified polymer latex. The solid content concentration of this rubber-modified polymer latex was 20% by weight, and the coagulation value measured using an aqueous solution of sulfuric acid (coagulant) was 2 mmo.
The L / l and Vicat softening point were 72 ° C. In a coagulation tank with an internal volume of 2 liters equipped with a stirrer (two-stage inclined paddle blades, blade diameter 7.5 cm, tip peripheral speed 275 cm / s, stirring and mixing)
A two-fluid nozzle (air pressure 0.3
(75 kg / cm ² G) by spraying at 75 ml / min, while 1% sulfuric acid aqueous solution was added dropwise at a rate of 39.2 ml / min, and ion-exchanged water was added dropwise at a rate of 85.8 ml / min to the coagulation tank. . An aqueous solution of sulfuric acid was previously added to the polymer latex so that the concentration of sulfuric acid in the latex would be 1.8 mmol / l. The temperature of the coagulation tank is controlled to 45 ° C by heating the jacket, and the coagulation is continuously performed at 40
The solidified slurry was collected when it was stabilized after being carried out for a minute. After heat-treating this slurry at 110 ° C. for 40 minutes, a polymer was separated using a centrifuge, washed with water, and dehydrated to obtain a wet powder. The wet powder was dried to obtain polymer dry particles. The results are shown in Table 1.

[0011]

[Table 1]

Example 2 Example 1 was repeated except that sulfuric acid was not added to the latex in advance. Example 3 The solidification temperature was 70 ° C., and the tip speed of the stirring blade was 470 cm / s.
The same procedure as in Example 1 was carried out except that Examples 1 to 3 are examples carried out within the scope of the present invention, and have excellent powder characteristics, and the object of the present invention has been achieved.

Comparative Examples 1 to 5 Polymers were recovered in the same manner as in Example 1 except that the coagulation conditions were changed as shown in Table 1. Comparative Example 1 has a solidification temperature below the range of the present invention and contains a large amount of fine powder. In Comparative Example 2, the solidification temperature exceeds the range of the present invention, the fusion of the polymer particles is vigorous, and the operation is impossible. In Comparative Example 3, the peripheral speed of the stirring blade is less than the range of the present invention, and a large lump is generated. In Comparative Example 4, the peripheral speed of the stirring blade exceeds the range of the present invention, and fine powder is generated. Comparative Example 5 is an example in which the polymer latex was added without spraying.

[0014]

Industrial Applicability The recovery method of the present invention comprises adding a polymer latex in a spray form to a coagulation tank having a coagulation temperature and a stirring blade tip speed in a specific range and coagulating the polymer to obtain a polymer having excellent powder characteristics. The particles can be recovered from the polymer latex.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Teizo Fukuda 2-11-24 Tsukiji, Chuo-ku, Tokyo Japan Synthetic Rubber Co., Ltd.

Claims (1)

[Claims] 1. A polymer latex according to the following (a) (b)
A method for recovering a polymer, wherein the polymer is solidified under the condition (c). (A) Solidification temperature (° C) (Tv-40) ≤ solidification temperature ≤ (Tv + 20) However, Tv; Vicat softening point (° C) of the recovered polymer (b) Mixing and stirring are performed in the solidification tank The peripheral speed of the tip of the blade is 100 ≦ peripheral speed ≦ 800 (cm / s) (c) Spray addition of the polymer latex to the coagulation tank with mixing and stirring.