JPH0596538A - Recovery of polymer powder - Google Patents

Abstract

(57) [Summary] [Structure] A process of adding a coagulant to a polymer latex to obtain a slurry, a process of recovering a polymer cake from the slurry using a vacuum suction type dehydrator, and a screw type The cake obtained in the previous step is supplied to a squeezing dehydrator to obtain a water content of 5
A method for recovering a polymer powder, which comprises a step of obtaining a powder of 35% by weight and a step of drying the powder of the previous step using a hot air dryer to obtain a powder having a water content of 3% by weight or less. [Effects] The method for recovering the polymer powder of the present invention consumes less drying energy and is excellent in the quality of the recovered polymer as compared with the conventional general method.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for recovering polymer powder from a polymer latex. The method of the present invention is
It is executed by a device that combines a vacuum suction type dehydrator and a screw type squeezing dehydrator. Therefore, the drying energy is small and the operability and productivity are excellent.
Further, the recovered polymer powder is excellent in color tone and other physical properties.

[0002]

2. Description of the Related Art Polystyrene, AS resin, ABS resin,
The PVC resin or the like is polymerized by an emulsion polymerization method to obtain a polymer latex. As a method for recovering a polymer component from these polymer latexes, for example, the following method is performed.

(1) Method Using Centrifugal Dewatering Machine A slurry obtained by adding a coagulant to polymer latex and coagulating it is washed and dehydrated with a centrifugal dewatering machine, and further obtained from the centrifugal dewatering machine. The wet powder to be dried with hot air,
This is a method of obtaining dry powder.

In the above method, it is difficult to reduce the water content of the wet powder obtained from the centrifugal dehydrator to 30% by weight or less due to the functional restriction of the centrifugal dehydrator, and generally 30 to 45% by weight. A high water content of about%. Therefore, a large amount of drying energy is required in the next drying process. Further, in the above method, an emulsifier used during emulsion polymerization,
Residues such as other polymerization chemicals cannot be removed sufficiently.
For this reason, the collected powder, the pellets of the powder, or the molded product processed using them are likely to be colored or have other physical properties deteriorated. In addition, in many applications of molded articles using the above powder as a molding material, the color tone is often emphasized, and the above coloring is a fatal drawback. Further, in the above method, the washing / dehydrating step carried out by the centrifugal dehydrator includes respective steps of supplying a slurry to the centrifugal dehydrator, dewatering, washing, dehydrating, and removing wet powder. Therefore, operability and productivity are extremely poor.

(2) Method using a screw type squeezing dehydrator Japanese Patent Publication No. 50-17227 discloses a method for recovering a polymer powder which consumes less drying energy than the method (1). It is disclosed. This is a method using a screw type squeezing dehydrator. In the method of Japanese Patent Publication No. 50-17227, first, the polymer latex and the coagulant are separated,
Alternatively, they are mixed and continuously supplied to the cylinder of the dehydrator. The supplied material is compressed while being mixed by the rotation of the screw in a relatively low temperature portion of the cylinder (= portion near the supply port). This allows
Most of the water is discharged from the grooves, holes, and gaps in the portion near the supply port. Then, the polymer is melted in the high temperature region of the cylinder, the residual water and other volatile substances are removed from the exhaust hole of the high temperature portion, and the polymer is taken out in a molten state from the die portion at the tip of the cylinder.

[0006] However, according to this method, as described in the publication, the resin is melted by high shearing when it is squeezed and dehydrated. Therefore, even if the resin is taken out and dried, it is dried normally. The machine is very difficult to dry it. Therefore, after squeezing and dewatering, the product is extruded to the screw tip without being taken out from the screw, and the remaining water that cannot be fully squeezed is evaporated from the vent port at the tip of the screw and then extruded from the die at the tip to produce a product as pellets I was taking it out. For this reason, expensive electric energy is required for drying, and a vent extruder, which is expensive in equipment, is also required. That is, the cost problem is large. Also,
In the above method, since the resin is melted during dehydration, it becomes extremely difficult to wash the resin. Therefore, there is also a problem that impurities such as an emulsifier in the residual water that cannot be squeezed remain in the resin to deteriorate the physical properties of the resin. Further, in the above method, since the resin is obtained in the form of pellets, it cannot be applied to the case where a powdery product is desired. Further, since it is in the form of pellets, it is difficult to mix it uniformly when powdered additives, pigments, etc. are added in the next step, and deviation occurs between the pellets and the above powder, resulting in uneven color of the product. There is also a problem that it is easy to cause such as.

[0007]

DISCLOSURE OF THE INVENTION The present invention has a low consumption of dry energy, is excellent in operability and productivity, and is excellent in the color tone of recovered powder and other physical properties. Another object of the present invention is to provide a method for recovering polymer powder.

[0008]

Means for Solving the Problems The present invention includes the following (a)-
The present invention provides a method for recovering a polymer powder, which sequentially carries out the three steps of (C). That is, (a) the step of supplying the slurry obtained by coagulating the polymer latex to a vacuum suction type dehydrator to recover the cake, and (b) the step of recovering the cake in the above step (a). -Ki is supplied to a screw type squeezing dehydrator having a drainage function, and the water content is 5 to
A step of continuously dehydrating to 35% by weight to obtain a powder, and (c) a step of drying the powder collected in the step (b) with a dryer to obtain a powder having a water content of 3% by weight or less. , Of 3
The steps are performed sequentially.

The present invention will be described in detail below. [1] Outline of the Invention In the method of the present invention, first, a coagulant is added to a polymer latex obtained by an emulsion polymerization method to coagulate a polymer component to obtain a slurry. In this coagulation step, if it is necessary to increase the particle size of the polymer component in the slurry, it may be heated. Next, the slurry is supplied to a vacuum suction type dehydrator to be dehydrated, or washed with water and dehydrated to obtain a polymer cake (= cake-like polymer component) from the slurry. Are continuously collected. Next, the cake is supplied to a screw type dehydrator having a drainage function or a drainage function and a cleaning function, and the water content becomes 5 to 35% by weight without melting the polymer component. Until it is squeezed, dehydrated and discharged. At this time, cleaning may be performed simultaneously. Since the discharged powder is squeezed out of water due to a large compressive force inside the screw, it may be obtained as a cake in which the powders are firmly fixed to each other. In such a case, disintegrate. Next, the powder is supplied to the dryer. Drying is performed using heated gas or by combining heated gas with heating from a jacket or a heat transfer tube until the water content becomes 3% by weight or less. In this way, the polymer powder of the present invention is obtained.

[2] Polymer Latex The polymer latex is preferably a resin latex. As a preferable resin latex, a homopolymer latex of an aromatic vinyl monomer, a copolymer of an aromatic vinyl monomer and another monomer, and an aromatic vinyl monomer in the presence of a rubbery polymer. It is an aromatic vinyl polymer latex such as a graft copolymer latex obtained by polymerizing a monomer mixture of a monomer or an aromatic vinyl monomer and another monomer.

Examples of the aromatic vinyl-based polymer include ABS resin latex, MBS resin latex and A resin latex.
S resin latex, α-methylstyrene-acrylonitrile copolymer latex, α-methylstyrene-methyl methacrylate copolymer latex, α-methylstyrene-acrylonitrile-methyl methacrylate copolymer latex, styrene-butadiene copolymer Examples thereof include polymer (high styrene rubber) latex, polystyrene latex, styrene-maleside copolymer latex, and HIPS resin latex.

A particularly preferred polymer latex is
It is the above graft copolymer latex, and its improvement effect is remarkably exhibited as compared with the conventional recovery method. Others, styrene-butadiene copolymer rubber latex, acrylonitrile-butadiene copolymer rubber latex,
Examples thereof include polybutadiene rubber latex and vinyl chloride polymer latex.

[3] Production of Slurry Production of a slurry from a polymer latex is carried out by adding a coagulant to the polymer latex. That is, the polymer component is precipitated by the addition of the coagulant and becomes a slurry. At this time, if the particle size of the precipitated polymer component is 100 μm to 1 mm, the operability, productivity, processing capacity and the like in the subsequent steps are improved. Therefore, in general,
An operation of adjusting the particle size to an optimum value by heating the slurry is performed. As the coagulant, a commonly used one can be used. Examples thereof include inorganic acids such as sulfuric acid / hydrochloric acid / nitric acid, organic acids such as acetic acid, and electrolytes such as calcium chloride / sodium chloride / magnesium chloride.
These are used alone or in combination of two or more.

[4] Vacuum suction type dehydrator A vacuum suction type dehydrator is a slurry supplied on a filter cloth.
Is suctioned from the back side of the filter cloth by negative pressure, and the filtrate and the washing water used for washing are removed by filtration, whereby a cake-like polymer is formed on the filter cloth. The components are separated. For example, the device shown in FIGS. 1 and 2, and
Devices with similar functions can be used. The material of the filter cloth is, for example, fiber, metal, paper, plastic, ceramic or the like.

The water content of the cake polymer component left on the filter cloth of the vacuum suction type dehydrator is preferably 30 to 50% by weight. In the present specification, the “water content” is a value displayed as a wet base percentage.

[5] Screw-type squeezing dewatering A screw-type squeezing dewatering machine is a device that conveys and compresses the above-mentioned polymer components by means of a screw arranged in a cylinder (= barrel). Yes, it has a drainage function or a drainage function and a cleaning function. Further, it may have a heating function. Further, the whole or a part of the barrel is provided with a punch plate or slit for drainage, and the compression ratio is 1.0 to 5.0 and the length is the screw diameter.
It is desirable to have a screw of 3 to 15 times. Further, it is preferable to provide a water supply hole for injecting cleaning water into the barrel.

The water content of the polymer component obtained by the above-mentioned screw type dehydrator is 5% by weight to 35% by weight,
It is preferably 10% to 30% by weight, more preferably 10% to 25% by weight. When the water content is less than 5% by weight,
The polymer component is easily melted, and stable operation becomes difficult. If it exceeds 35% by weight, much energy is required for drying in the next step.

The above-mentioned polymer component obtained by the above-mentioned screw type dehydrator may be in the form of powder or hard cake. In that case, for example, a powder (powder) having good dryability can be easily obtained by giving an impact with a hammer-shaped crusher or the like.
Can be returned to.

[6] The dried powdery polymer component is then dried using a known dryer using hot air, and has a water content of 3% by weight or less, preferably 2% by weight. % Or less, and more preferably 1.5% by weight or less of the polymer powder. Here, examples of the dryer using hot air include a tunnel dryer, an aeration band dryer, a fluidized dryer, and a flash dryer. The dryer is used alone or in combination of two or more.

[0020]

EXAMPLES The present invention is not limited to the following examples. Examples of the present invention are described below. [1] Mechanism and action of vacuum suction type dehydrator [2] Mechanism and action of screw type dehydrator [3] Dehydration of polymer latex by the method of the present invention [4] The dehydration of the polymer latex by the conventional method will be described in order.

[1] Mechanism and Action of Vacuum Suction Type Dehydrator First, the mechanism and action of the vacuum suction type dehydrator used in the embodiment will be described. The polymer latex slurry is, for example,
It is dehydrated using the horizontal vacuum suction dehydrator 1 shown in FIG. 1 or the drum vacuum suction dehydrator 3 shown in FIG. 2 to obtain a cake-like polymer component.

In the dehydrator 1 shown in FIG. 1, the filter cloth 13 is
The driving roller 14 and the driven roller 15 are endlessly supported in a tensioned state. The filter cloth 13 is driven in the direction of arrow a by the drive roller 14 driven by a motor (not shown). This allows
The slurry of polymer latex supplied from above via the slurry supply pipe 11 is conveyed to the right in the figure. Further, not only the above-mentioned slurry but also the washing water is supplied from above the filter cloth 13 through the washing water supply pipe 12 at a position downstream thereof.

Further, under the inner surface of the filter cloth 13, a suction force due to a negative pressure of the vacuum pump 19 is exerted via the knockout drum 18 and the intake pipe 17, so that
The slurry on the filter cloth 13 and the washing water are sucked downward on the inner surface side. As a result, the water content (= filtrate) filtered by the filter cloth 13 is collected on the tray 16 and then discharged through the intake pipe 17 and the knockout drum 18. In this way, the slurry on the filter cloth 13 is transported to the right while being gradually dehydrated, and the wet powder (case) having a water content of 30 to 50% by weight.
G) Collected as 100. After the cake 100 is peeled off, the filter cloth 13 is washed by a washing device (not shown) and then sent to the slurry supply position again.

On the other hand, unlike the dehydrator 1 shown in FIG. 1, in the dehydrator 3 shown in FIG. 2, the filter cloth 13 is supported on the surface of a drum 34 in which a large number of pores are formed. Is rotated in the direction of arrow b by being driven by a motor (not shown). In the dehydrator 3 shown in FIG. 2, the slurry of polymer latex is supplied to the filter cloth 13 from the slurry tank 31 arranged below the drum 34. That is, as shown in the drawing, the lower side of the drum 34 is the slurry in the slurry tank 31.
The drum is soaked in the drum, and the soaked portion continuously changes as the drum 34 rotates. Therefore, the slurries are successively deposited on the filter cloth 13 supported by the drum 34.

The slurry thus attached to the filter cloth 13 is
The cleaning water supplied from above via the cleaning water supply pipe 12 is sucked into the inside of the drum 34 by the suction force by the negative pressure of the vacuum pump 19. As a result, the filtrate is collected in the lower portion inside the drum 34, and the filtrate is discharged through the intake pipe 17 and the knockout drum 18. Thus, filter cloth
The slurry on 13 is gradually dehydrated and conveyed to the right, and is collected as a wet powder (cake) 100 having a water content of 30 to 50% by weight, as in the case of FIG.

In the apparatus shown in FIGS. 1 and 2, the amount of washing water supplied, the amount of slurry supplied, the moving speed of the filter cloth 13, the degree of vacuum by the vacuum pump 19, and the like are the target cakes. It is appropriately adjusted according to the water content of 100 or the like. Also, in the above,
The slurry is produced by coagulating a polymer latex produced by emulsion polymerization by a usual method. The temperature of the slurry is preferably not higher than the temperature obtained by adding 10.0 ° C. to the heat distortion temperature of the polymer. In general, when the polymer latex is coagulated, it is often heated to 80 to 90 ° C. Therefore, unless the polymer particles are fused, it is efficient to supply at the same temperature. Here, "heat distortion temperature" is a temperature measured according to ASTM D648 (1/2 in, 66 psi).

[2] Mechanism and Operation of Screw Type Dewatering Machine Next, the mechanism and operation of the screw type dewatering machine used in the embodiment will be described. The wet powder (cake) obtained by the vacuum suction type dehydrator (the dehydrator shown in FIGS. 1 and 2)
100 is then supplied to the screw type dehydrator 5 in FIG. 3 and further dehydrated by the dehydrator 5 to obtain a water content of 5 to 35.
Weight% powder.

The dehydrator 5 shown in FIG. 3 has the above-mentioned wet powder (case).
G) 100 is taken in through the feed port 53 and the dehydration barrel 51
This is a device for compressing and squeezing out water while being conveyed leftward in the figure by a screw 52 disposed inside, and then discharging it from a discharge port 54.

Therefore, the dehydrator 5 uses the above-mentioned wet powder (case).
G) A feed port 53 for supplying 100, a dehydration barrel 51 integrally connected to the feed port 53, a discharge port 54 arranged at the tip side of the dehydration barrel 51, Dehydration barrel
And a screw 52 disposed in the axial direction of the motor 51.The screw 52 is configured to be driven at a desired speed by a motor 60 via a transmission 59. There is.
The peripheral speed of the screw 52 is preferably 20 cm / sec or less. Above 20 cm / sec, the above-mentioned wet powder (cake) 10
This is because an excessive shearing force is applied to 0 to facilitate melting and it becomes difficult to obtain a powdery product.

The lower part of the feed port 53 and a part or the whole of the dehydrating barrel 51 are punching plates, so that the water squeezed out by the compression action of the screw 52 can be quickly discharged. Alternatively, it has a slit structure. In addition, the tip end side of the screw 52 (=
It is desirable that the portion having a high internal pressure) has a slit structure in terms of strength. Hole diameter of the above punching plate,
And, the opening of the above slit is about 0.1 to 2.0 mm,
Desirably, it is about 0.3 to 1.0 mm. From the viewpoint of not leaking the resin particles, it is preferable that the particle size is small, but if it is too small, the drainage capacity decreases, and it becomes difficult to dehydrate to a region having a low water content.

The groove bottom 52a of the screw 52 is configured so as to gradually become shallower from the feed port 53 side toward the discharge port 54 side, whereby the wet powder (case) is formed.
G) 100 is gradually compressed as it is conveyed by the screw 52. Further, a resistor 57 is provided at the discharge port 54, which allows the wet powder (cake) 10 to be formed.
In addition to the compressive force of the screw 52, the compressive force of the resistor 57 is applied to 0, so that the squeezing of water becomes more effective. Here, the resistor 57
Is a mechanism for adjusting the degree of throttling by urging a spring (not shown) or hydraulically driving the gap between the screw 52 and the tip portion of the screw 52. In place of the resistor 57, the tip portion is constituted by a die, and the compressed polymer component is extruded from a hole or groove having a desired size and cut into an appropriate size by a cutter. You may do it.

The compression ratio of the screw 52 (the volume of the groove portion corresponding to the screw-1 pitch at the inlet / the groove portion volume corresponding to the screw-1 pitch at the outlet) is preferably 1.0 to 5.0, more preferably 1.2 to 2.5. is there. When the compression ratio is 1.0 or less,
Since the volume increases toward the screw tip side, the wet powder (cake) 100 cannot be compressed, and if the compression ratio is 5.0 or more, the resin tends to melt and dehydration in powder state becomes difficult. This is because.

The length of the screw 52 is preferably 3 to 15 times the diameter of the screw. If the length is less than 3 times the screw diameter, it is difficult to dehydrate to a sufficiently low water content, and even if it is attempted to reduce the water content to a low water content by constructing a high compression ratio, The feed ability of-is reduced, so the objective cannot be achieved. On the other hand, even if the length is configured to be 15 times the screw diameter or more, the achievable water content is about the same, which is disadvantageous in terms of cost.

The screw shaft may be a single shaft or a plurality of shafts. However, if it is a single axis, the structure is simple and
It is also advantageous in terms of cost. In addition, the shaft of the screw is processed into a hollow structure so that a heat medium can pass through the hollow shaft, and the shaft of the screw is heated or cooled to a desired temperature as required. May be. Further, by utilizing the above-mentioned hollow portion, a preferable number of holes are opened at the inlet portion of the screw 52, flush water is flown through the screw 52 to wash the cake, and then drained from the barrel 51. The method is also an effective method when more cleaning effect is desired.

The flight of the screw may be either a single flight or a double flight. However, by constructing about one pitch on the screw exit side into a double flight, the uneven load on the screw is alleviated, and the screw and the barrel are relaxed. It is desirable to have a structure that does not contact with.

When the low water content polymer component obtained by the dehydrator 5 shown in FIG. 3 is in the form of a hard cake,
Although only the surface in contact with the screw and barrel may be melted by friction, most of the part is only solidified by pressing, and the shape of individual particles is left as it is. For this reason, it is possible to easily return the powder to the original powder shape by giving an impact with a hammer type crusher.

[3] Dehydration of Polymer Latex by the Method of the Present Invention Next, a specific example in which the slurry of the polymer latex is dehydrated by the method of the present invention using the above-mentioned two types of dehydrators will be described. In addition, in the following description, "moisture content" is the moisture content percentage, and other "parts" or "%" are respectively
Parts by weight,% by weight.

* First step: Production of polymer latex In the presence of 40% (solid content) of polybutadiene latex,
A monomer composed of 45% styrene and 15% acrylonitrile is polymerized by an emulsion polymerization method to obtain an ABS resin latex (heat distortion temperature of resin: 91 ° C.).

* Second step: manufacture of slurry 100 parts of ABS resin latex (solid content) and 20 parts of 10% sulfuric acid aqueous solution were put into a coagulation tank, and the residence time was 90 to 95 ° C.
Under the condition of 30 minutes, 25% of water slurry, 300kg (solid content) / Hr
I took it out.

* Third step: Dehydration by vacuum suction type dehydrator The above water slurry is supplied onto the filter cloth 13 through the slurry supply pipe 11 of the vacuum suction type dehydrator 1 of FIG. Under conditions, a cake-like polymer component with a water content of 40% was continuously added,
It was taken out at 300 kg (solid content) / Hr. Amount of 25% water slurry supplied: 300 kg (solid content) / Hr Amount of washing water: 300 kg per 100 kg solid content Vacuum degree: -400 mmHg

* Fourth step: Dehydration with a screw type dehydrator and disintegration with a disintegrator The above-mentioned cake-like polymer component is fed into the feed port 53 of the screw type dehydrator 5 in FIG. Then, operating under the following conditions, the powder of the polymer component with a water content of 10% was continuously
It was taken out at 0 kg (solid content) / Hr. Screw diameter: 200 mm Screw length: 1000 mm (5 times the screw diameter) Screw compression ratio: 1.6 Barrel: Lower 0.5 mmφ punching plate (opening ratio 20%) Drainage barrel Whole area slit screen (Gap 0.3 mm) Operating conditions of screw-dewatering machine 5: Screw-rotation speed: 6 rpm (screw-outer peripheral speed: 6.3 cm /
sec) Key feed amount: 300 kg (solid content) / Hr

In this way, after being hardened into a cake,
It is roughly crushed by the resistor 57 and screw type dehydrator 5
The block-shaped ABS resin discharged from the discharge port 54 was crushed using a crusher (Hosokawa Micron Feather Mill FM-1 type) to obtain a powder.

* Fifth Step: Drying with a Fluid Dryer The above powder having a water content of 10% was dried using a fluid dryer under the following operating conditions to obtain a powder having a water content of 1%. The time required for drying was 60 minutes, and the color tone of the molded product molded using the powder after drying was white without yellowing. Feed amount to fluidized dryer: 300 (solid content) kg / Hr Hot air temperature: 90 ° C Hot air flow rate: 50m ³ / min

[4] Dehydration of Polymer Latex by Conventional Method Next, for comparison with the above method [3], the polymer latex was dehydrated by the conventional method as follows.

[4-1] Comparative Example 1 In the method of [3], the third step was omitted. That is, the water slurry obtained in the second step is directly supplied to the screw type dehydrator 5 in the fourth step,
The operation was performed under the following conditions to obtain a powder having a water content of 10%. After that, it is dried in the same manner as in the above [3], and the water content is 1%.
To obtain powder. The time required for drying was 60 minutes, and a slight yellowing occurred in the color tone of the molded product molded from the powder after drying. Screw diameter: 200 mm Screw length: 1000 mm (5 times the screw diameter) Screw compression ratio: 1.6 Barrel: Lower 0.5 mmφ punching plate (opening ratio 20%) Drainage barrel Whole area slit screen (Gap 0.3 mm) Operating conditions of screw-dewatering machine 5: Screw-rotation speed: 6 rpm (screw-outer diameter peripheral speed: 6.
3cm / sec) Slurry feed temperature: 85-90 ℃ Slurry feed amount: 300kg (solid content) / Hr

[4-2] Comparative Example 2 In the method of [3] above, the third and fourth steps were omitted, and a centrifuge was used instead of them. That is, the water slurry obtained in the second step was supplied to a centrifuge and operated under the following conditions to obtain a powder having a water content of 35%. Thereafter, it was dried in the same manner as in the above [3] to obtain a powder having a water content of 1%. The time required for drying was 90 minutes, and a slight yellowing occurred in the color tone of the molded product molded using the powder after drying. Centrifuge rotation speed: 1700 rpm Washing water volume: 300 kg per 100 kg of solids Operating conditions: Dehydration time: 600 seconds Water washing time: 60 seconds Dehydration time: 600 seconds

Comparing the above method [3] with the above method [4], the method for recovering the polymer powder of the present invention is as follows.
The drying time is short and the color tone is good as compared with the conventional method.

[0048]

The method of the present invention consumes less energy in the drying process (= the most energy consuming process) than the conventional method. Further, as is clear from the evaluation of the color tone of the molded product, the residual amount of impurities is small and a polymer of excellent quality can be obtained. Thus, the method of the present invention has extremely high industrial value.

[Brief description of drawings]

FIG. 1 is an explanatory view schematically showing a mechanism of a horizontal vacuum suction type dehydrator.

FIG. 2 is an explanatory view schematically showing the mechanism of a drum type vacuum suction type dehydrator.

FIG. 3 is an explanatory view schematically showing the mechanism of a screw type squeezing dehydrator.

[Explanation of symbols]

1 vacuum suction type dehydrator, 3 vacuum suction type dehydrator,
5 screw type squeezing dehydrator,

Claims (1)

[Claims] 1. A method for recovering a polymer powder, which comprises the following steps (a), (b) and (c): (A) Slurry obtained by coagulating polymer latex
To a vacuum suction type dehydrator to recover the cake, and (b) the cake collected in the above step (a) to a screw type squeezing dehydrator having a drainage function. The step of supplying and continuously dehydrating until the water content becomes 5 to 35% by weight to obtain a powder. (C) The powder recovered in the above step (B) is dried by a dryer to obtain a water content. Obtaining 3% by weight or less of powder.