JP2002226595A - Method for producing diene-based graft copolymer powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing diene-based graft copolymer powder, with which a fear of ignition by autoxidation of a diene-based graft copolymer in a dryer, etc., is removed and the diene-based graft copolymer powder is obtained from a latex of the diene-based graft copolymer by spray drying. SOLUTION: This method for producing the diene-based graft copolymer powder comprises spraying the latex of the diene-based graft copolymer having 10 mass % to 85 mass % of a butadiene unit in the polymer in the dryer, sending superheated steam as a heated gas for drying from the inlet part of the dryer to the dryer, drying the latex to give the diene-based graft copolymer powder and recovering the powder from the outlet part of the dryer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a diene-based graft polymer powder, and more particularly, to a method for producing a thermoplastic resin containing a diene-based polymer as a main component, a latex produced by an emulsion polymerization process. And a method for recovering powder by spray drying.

[0002]

2. Description of the Related Art A diene-based graft polymer represented by MBS (methyl methacrylate / butadiene / styrene) resin and ABS (acrylonitrile / butadiene / styrene) resin is excellent in impact resistance, rigidity and fluidity, and is used for various plastics. Widely used for impact strength modifiers. These diene-based graft polymers are usually produced by emulsion polymerization, but for melt-kneading with other resins,
Finally, it is necessary to recover a latex from the latex obtained by emulsion polymerization. From the latex obtained by such emulsion polymerization, as a method of recovering a polymer as a dry powder, a coagulation method of adding a coagulant to the latex and aggregating the polymer particles in the latex, or the latex directly in hot air A spray drying method of spray drying and the like can be mentioned.

However, in the above coagulation method,
Since the polymer particles are usually coagulated in water, a process such as a coagulation process, a coagulant washing process, a dehydration process, and a drying process is required before the polymer is recovered as a dry powder. There are many problems from the viewpoint of. On the other hand, in the spray drying method, a dry powder of a polymer can be obtained at a stroke from the latex after emulsion polymerization, and the production process can be simplified. This is a superior method.

[0004]

However, when such a spray-drying method is used for recovering a powder of a diene-based graft polymer, there are the following problems. In general, a diene polymer has a property of causing a reaction such as autoxidation in the presence of oxygen and heat to ignite. In the spray drying method, it is common to use air containing oxygen as a heating gas for drying used to dry the latex, and when spray drying the diene-based graft polymer under such an environment, The diene-based graft polymer may cause a reaction such as autoxidation to cause ignition or explosion. In particular, when the spray drier is continuously operated, a considerable amount of accumulated diene-based graft polymer accumulates in the drier, which increases the danger. In order to avoid such a situation, it is necessary to shorten the residence time of the residue of the diene-based graft polymer, and therefore it is necessary to frequently wash the inside of the dryer to remove the residue. The operation significantly reduces productivity. The biggest problem in spray-drying a diene-based graft polymer in this way is prevention of ignition by autoxidation of the diene-based polymer in the trunk polymer portion.

Therefore, as a method for industrially spray-drying a diene-based graft polymer latex, Japanese Patent Application Laid-Open No. 2000-02000
No. 72882 proposes a method for preventing autoxidation for a long time by adding a hindered phenol-based stabilizer and a thioether-based stabilizer to a graft-polymerized latex and spray drying. According to this method, the safety of spray-drying the latex of the diene-based graft polymer has been remarkably improved, but the cost of the stabilizer has been increased, so that there remains a slight problem in economy. As described above, a method of spray-drying the diene-based graft polymer latex without any trouble has been reported yet.

The present invention has been made in view of the above circumstances, and eliminates the possibility of ignition due to autoxidation of a diene-based graft polymer in a dryer, and is economical for a long period of time without hindrance. An object of the present invention is to obtain a method for obtaining a diene-based graft polymer powder from a latex of a graft polymer by spray drying. It is another object of the present invention to appropriately perform industrial production without affecting the quality aspect (powder characteristics) of the product and without reducing the productivity of the diene-based graft polymer powder in the spray drying method.

[0007]

The present inventors have studied a method for preventing the autoxidation of a diene-based graft polymer during spray drying, and have found that superheated steam is used as a drying heating gas during spray drying. By doing so, it was possible to prevent autoxidation without lowering the quality and productivity, and it was found that the diene-based graft polymer latex can be spray-dried for a long period of time. That is, in the method for producing a diene-based graft polymer powder of the present invention, a diene-based graft polymer latex in which the butadiene unit in the polymer is from 10% by mass to 85% by mass is sprayed into a drier, and Superheated steam is sent from the inlet as a heating gas for drying, and the latex is dried to obtain a diene-based graft polymer powder, which is recovered from the outlet. In the method for producing a diene-based graft polymer powder, the partial pressure of steam near the outlet of the dryer is set to be equal to or less than the saturated steam pressure at the temperature near the outlet of the dryer (hereinafter, referred to as “outlet temperature”), Further, it is preferable that the outlet temperature be equal to or lower than a temperature obtained by adding 100 ° C. to the minimum film forming temperature of the diene-based graft polymer latex.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. The method for producing a diene-based graft polymer powder of the present invention comprises spraying a latex of the diene-based graft polymer into a dryer and sending a heating gas for drying from an inlet portion of the dryer to dry the latex. In this method, superheated steam is used as the heating gas for drying, and the powder is recovered from the outlet of the dryer.

The superheated steam is steam heated at a certain pressure to a temperature equal to or higher than the boiling point of water at that pressure. If such superheated steam is used as a heating gas for drying, oxygen is not contained in the superheated steam, so that oxidation of the diene-based graft polymer and further its retentate in the spray dryer can be prevented. Continuous operation of drying becomes possible. In addition, there is no reactivity with the diene-based graft polymer, and the quality of the obtained diene-based graft polymer powder is not affected. Further, by using the heated steam, it is possible to recirculate the steam used for the drying, which has the effect of saving energy.

It is also possible to use a mixture of the above-mentioned superheated steam with another gas containing no oxygen such as nitrogen. When using superheated steam and another gas in this way, in order to prevent condensation of steam in the superheated steam, the gas to be mixed is preheated in advance so that the steam in the superheated steam does not condense. It is preferable to adjust the temperature to about the same. In addition, the method of mixing superheated steam and another gas can be mixed at any point in the piping, in the nozzle, or in the dryer, and a dedicated mixing tank and device are provided in the piping to the dryer. Is also good.

In the method for spray-drying a diene-based graft polymer, it is preferable that the partial pressure of steam near the outlet, which is the powder recovery section of the dryer, is lower than the saturated vapor pressure at the outlet temperature at that time. .

When the partial pressure of the water vapor near the outlet of the dryer exceeds the saturated vapor pressure at the outlet temperature at that time, the superheated water vapor near the outlet condenses and the undried diene graft polymer is obtained. May occur or condensation may occur in the dryer. When using a heating gas in which another gas is mixed with the superheated steam, the mixing ratio of the heating gas and the system in the system are adjusted so that the partial pressure of the steam near the outlet of the dryer is equal to or lower than the saturated steam pressure at the outlet temperature. Adjust the total pressure of. The partial pressure of steam near the outlet of such a dryer is determined by the temperature of the outlet, the flow rate of superheated steam flowing from the inlet, and the temperature near the inlet (hereinafter referred to as “inlet temperature”).
) Can be appropriately adjusted. In this case, since the superheated steam does not agglomerate in the dryer, dew condensation does not occur in the dryer, and undried diene-based graft polymer does not occur.

Further, in addition to the conditions of the partial pressure of steam near the outlet of the dryer, the outlet temperature is increased by adding 100 ° C. to the minimum film forming temperature of the diene-based graft polymer latex (hereinafter referred to as “MFT”). It is preferable that the temperature is not higher than the temperature. More preferably, the temperature is set to 80 ° C. or lower. When the outlet temperature exceeds the temperature obtained by adding 100 ° C. or more to the MFT, the fusion of the surface portion of the diene-based graft polymer powder proceeds, and a problem that redispersibility at the time of melt-kneading deteriorates occurs, which is not preferable.
The outlet temperature is preferably not less than the boiling point of water at that pressure, more preferably not less than 100 ° C. If the outlet temperature is lower than the boiling point of water at that pressure, the water vapor will condense and form condensation. If the outlet temperature is lower than 100 ° C., the pressure of the superheated steam near the outlet needs to be equal to or lower than the normal pressure so that the steam does not agglomerate. Thus, for example, MF
In the case of latex having T of 60 ° C, it is preferable to operate the dryer at an outlet temperature of 100 to 140 ° C under normal pressure.

The outlet temperature of such a dryer can be controlled by adjusting the inlet temperature. The inlet temperature can be appropriately set according to the flow rate of the superheated steam flowing into the dryer and the amount of the material to be dried (the spray amount of the diene-based graft polymer latex) so that the dryer outlet temperature falls within the above range.

Here, the MFT of the latex is a minimum temperature at which a transparent continuous film can be formed when a film is formed from the latex. That is, it is a value representing the glass transition temperature (hereinafter referred to as “Tg”) of the latex particle surface. The MFT of the latex can be determined by the following measurement method. First, by providing heating and cooling devices at both ends of a horizontally installed aluminum plate, the aluminum plate is given a temperature gradient. Next, the latex is spread uniformly and thinly on an aluminum plate having a temperature gradient. Then, measure the minimum temperature of the aluminum plate where the spread latex forms a transparent continuous film,
This is called MFT.

As described above, in the method for producing a diene-based graft polymer powder, by setting the outlet temperature condition of the dryer using MFT, the diene-based graft polymer having good powder characteristics without surface fusion is obtained. It becomes possible to obtain a polymer powder. When a powder is obtained from a polymer latex by spray drying, a method has been proposed in which the outlet temperature is defined in consideration of the glass transition temperature (Tg) of the polymer.
In the case of a graft polymer having a multilayer structure such as a diene-based graft polymer, it is not possible to simply specify the temperature condition at which the powder is fused by Tg. Therefore, in the case of such a diene-based graft polymer, it is effective to set the temperature conditions using MFT, and the present invention sets the air temperature at the dryer outlet based on this MFT. It is a feature.

The diene-based graft polymer used in the method for producing the diene-based graft polymer powder is obtained by graft-polymerizing a hard resin component monomer unit which is polymerizable with a butadiene-based polymer as a trunk polymer. There is no particular limitation as long as it forms a polymer. Here, the butadiene-based polymer is polybutadiene, or butadiene-styrene copolymer, butadiene-butyl acrylate copolymer,
Butadiene-acrylonitrile copolymer and the like. The hard resin component monomer constituting the branch polymer is not particularly limited as long as it is a polymerizable monomer that can be used for emulsion polymerization, and any monomer can be used. Preferably, the monomer constituting the branch polymer is mainly composed of methyl methacrylate, styrene, acrylonitrile, or the like, and these are preferably used alone or in combination of two or more.

In the diene-based graft polymer, butadiene units are contained in the polymer in an amount of 10% by mass to 85% by mass.
It is preferable that the content is contained by mass%. The above method for producing a polymer powder using superheated steam can perform spray drying safely and with good productivity even when used for a diene-based graft polymer in which autoxidation is likely to occur. Therefore, the above-described production method is most effective in a diene-based graft polymer having a butadiene unit of 10% by mass or more. If the butadiene unit is 85% by mass or more, adhesion to the inner wall of the drying chamber during spray drying becomes remarkable, and continuous operation may be difficult. More preferably, the butadiene unit of the diene-based graft polymer is from 20% by mass to
80% by mass.

The diene-based graft polymer latex is produced by emulsion polymerization. The emulsion polymerization method and emulsion polymerization conditions at that time are not particularly limited, and can be produced by conventionally known methods and conditions. Preferably, from the viewpoint of latex stability at the time of spray drying, first, polybutadiene or butadiene-styrene copolymer, butadiene-butyl acrylate copolymer, butadiene-acrylonitrile copolymer latex to be a core is polymerized, and the core is polymerized. It is preferable to carry out graft polymerization in one stage or two or more stages with methyl methacrylate or styrene, or methyl methacrylate and styrene, or acrylonitrile and styrene.

The latex of the diene-based graft polymer preferably has an MFT of 20 ° C. to 120 ° C. When the MFT is lower than 20 ° C., the outlet temperature is set to 1
It is necessary to keep the temperature at 00 ° C or lower, and the equipment becomes large-scale such as reducing the pressure inside the system to normal pressure or less to prevent dew condensation. In addition, the drying speed is slow and uneconomical. When the temperature is higher than 120 ° C., the powder recovered by spray drying is easily crushed, the particle size distribution is wide, and the powder performance such as blocking resistance tends to deteriorate, which is not preferable.

The diene-based graft polymer latex may be used alone, or may be a mixture of a plurality of latexes. Further, blocking during spray drying, in order to improve the powder properties such as bulk specific gravity silica, talc, inorganic fillers such as calcium carbonate, polyacrylate,
Spray drying can also be performed by adding polyvinyl alcohol, polyacrylamide, or the like. Further, a suitable antioxidant, an additive and the like can be added to the latex to be sprayed and spray dried.

In the method for producing the diene-based graft polymer powder, the spray-drying apparatus, latex spraying method, spray-drying conditions and the like are particularly limited except that superheated steam is used as the heating gas for drying. Not something.
For example, as a method of generating droplets, a rotating disk type,
Any type such as a pressure nozzle type, a two-fluid nozzle type, and a pressurized two-fluid nozzle type can be used. The capacity of the dryer is not particularly limited, and it can be used in any scale from a small scale used in a laboratory to a large scale used industrially. The position of the inlet, which is the supply of the heating gas for drying in the dryer, and the outlet, which is the outlet for the heating gas for drying and the dry powder, are also the same as those of a commonly used spray-drying apparatus, and are not particularly limited. Not something.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on embodiments. In Examples and Comparative Examples, “parts” and “%” are “parts by mass” and “% by mass”, respectively, unless otherwise specified.
Is represented. Various evaluations in Examples and Comparative Examples were performed by the following methods. 1) Evaluation of continuous operation of spray drying Spray drying was performed using a small spray dryer (NIRO JA).
The following diene-based graft polymer latex was spray-dried under normal pressure using a straight body part height of 0.8 m, a straight body part inner diameter of 1.5 m, and a rotating disk atomizer (manufactured by PAN Corporation). 2) Measurement of minimum film formation temperature Measurement was performed using a minimum film formation temperature measurement device manufactured by Takabayashi Rika Co., Ltd. The measurement temperature was measured under the conditions of a low temperature side = 20 ° C. and a high temperature side = 180 ° C.

Examples 1-4 Comparative Example 1 (1) Synthesis of butadiene polymer latex (A-1) 25 parts of styrene, 0.3 parts of paramenthane hydroperoxide, 0 parts of sodium pyrophosphate (anhydrous) 15 parts, potassium tallow fatty acid 1.5 parts, Na pyrophosphate (anhydrous) 0.1
5 parts, deionized water (hereinafter simply referred to as water) 14
After 0 parts were charged into an autoclave (practical withstand pressure: 0.6 MpaG) and subjected to nitrogen substitution, 75 parts of 1,3 butadiene was charged therein. Then, the obtained mixture was heated while stirring, and when the temperature reached 45 ° C., a mixture of 0.003 part of ferrous sulfate heptahydrate, 0.2 part of hydrous dextrose and 10 parts of water was reacted. It was charged in a vessel and heated to 60 ° C. as it was. Next, the polymerization was terminated when the polymerization conversion in the above solution reached 97%. The solid content of the obtained butadiene rubber polymer latex (A-1) was 40%.

(2) Graft polymer latex (A-
Synthesis of 2) Butadiene rubber polymer latex (A-1) 583
Parts (233 parts as solid content), 85 parts of water, and 5.0 parts of potassium tallow fatty acid were charged into a reactor, and after purging with nitrogen, 0.3 parts of sodium formaldehyde sulfoxylate dihydrate was added, and the mixture was heated at an internal temperature. Was heated to 70 ° C. Then
28 parts of methyl methacrylate, 7 ethyl acrylate
, And a mixture of 0.15 parts of cumene hydroperoxide were continuously added over 30 minutes and maintained for 100 minutes. Then, a mixture of 55 parts of styrene and 0.20 parts of cumene hydroperoxide was continuously added over 100 minutes,
Hold for 0 minutes. Then, 10 parts of methyl methacrylate,
A mixture of 0.05 parts of cumine hydroperoxide was continuously added over 30 minutes and maintained for 120 minutes to complete the polymerization. The obtained graft polymer latex (A-2) was evaluated for continuous spray-drying operation. Tables 1 and 2 show the observation results of the retained matter in the spray dryer after the continuous operation.

Example 5 Comparative Example 2 (1) Synthesis of butadiene polymer latex (B-1) 150 parts of water, 1 part of potassium rosinate, 1 part of potassium oleate, sodium formaldehyde sulfoxylate dihydrate 0.4 parts of sodium chloride, 0.1 part of sodium sulfate, 0.3 part of t-dodecyl mercaptan, 0.5 part of diisopropylpropylbenzene hydroperoxide, 1,3-butadiene 2
6.2 parts and 1.4 parts of styrene were charged into an autoclave (practical pressure resistance: 0.6 MpaG), and the temperature was raised to 57 ° C. During heating, sodium pyrophosphate (decahydrate) 0.
Two parts and 0.003 part of ferrous sulfate heptahydrate were added to initiate polymerization. Next, when the polymerization temperature reached 57 ° C,
A monomer composed of 68.8 parts of 1,3-butadiene and 3.6 parts of styrene was continuously dropped. Then, when the polymerization conversion reached 40%, n-octyl mercaptan 0.3
And the polymerization was continued. 8 hours remaining 1,3
-Butadiene was removed to terminate the polymerization. The solid content of the obtained butadiene polymer latex was 40.2%, and the polymerization conversion was 97%.

(2) Acid-containing polymer latex (B-
Preparation of 2) 3000 parts of water, 30 parts of potassium oleate, 15 parts of sodium dioctylsulfosuccinate and 4.5 parts of sodium formaldehyde sulfoxylate were charged into a reactor, and the temperature was raised to 60 ° C. After continuously dropping a mixture consisting of 1275 parts of butyl, 225 parts of methacrylic acid and 6.0 parts of cumene hydroperoxide over 120 minutes, the mixture was further aged for 2 hours,
The polymerization conversion is 98% and the mass average particle diameter is 0.08 μm
The acid group-containing polymer latex (B-1) was obtained.

(3) Rubbery polymer latex (B-3)
The butadiene polymer latex (B-1) 2
489 parts (1000 parts as a rubbery polymer) were added, and then the above acid-containing polymer latex (B-
2) After adding 61 parts (20 parts as a solid content), stirring was continued for 30 minutes, and the mass average particle diameter was 0.28 μm,
An enlarged rubbery polymer latex (B-3) having a solid content of 40.7% was obtained.

(4) Graft polymer latex (B-
Synthesis of 4) 1500 parts of water and the above rubbery polymer latex (B-
3) 2500 parts (1000 parts as a rubbery polymer), 6.0 parts of dextrose, sodium pyrophosphate (anhydrous)
1.0 part and ferrous sulfate heptahydrate 0.1 part were charged into a reactor, and after purging with nitrogen, the temperature was raised to 60 ° C., 300 parts of acrylonitrile, 700 parts of styrene, 12.0 parts of t-dodecyl mercaptan and A monomer mixture consisting of 3.0 parts of cumine hydroperoxide was added dropwise over 200 minutes, during which the internal temperature was controlled to 65 ° C. After completion of the dropping, cumine hydroperoxide 1.2
And further kept at 70 ° C. for 1 hour, and an antioxidant (Antage W-400, manufactured by Kawaguchi Chemical Industry Co., Ltd.) 10
After adding parts, the mixture was cooled. The polymerization conversion was 97%. The obtained graft polymer latex (B-4) was evaluated for continuous spray-drying operation. Table 1 shows the results of observation of the residue in the spray dryer after the continuous operation.

Example 6 Comparative Example 3 (1) Production of butadiene polymer latex (C-1)
140 parts of water, 1.0 part of tallow fatty acid potassium, 0.5 part of lauroyl sarcosine sodium, and 0.15 part of sodium pyrophosphate (anhydrous) were autoclaved (with a practical pressure of 0.6 MPa).
aG), and after purging with nitrogen, 1,3 butadiene 5
0 parts, 50 parts of butyl acrylate, and 0.24 parts of diisopropylbenzene hydroperoxide were charged, and the temperature was raised to 50 ° C. while stirring. Next, a mixture of 0.003 part of ferrous sulfate heptahydrate, 0.2 part of hydrous crystalline dextrose, and 10 parts of water was charged into the reactor, and the temperature was directly raised to 60 ° C. Next, when the polymerization conversion reached 98%, the polymerization was terminated. The solid content of the obtained butadiene polymer latex was 40.5%.

(2) Acid group-containing polymer latex (C-
Preparation of 2) 200 parts of water, 2 parts of potassium oleate, 1 part of sodium dioctylsulfosuccinate and 0.3 part of sodium formaldehyde sulfoxylate were charged into a reactor,
The temperature was raised to 0 ° C, and from that point on, 85-butyl acrylate was added.
, A mixture consisting of 15 parts of methacrylic acid and 0.4 part of cumene hydroperoxide was continuously dropped over 120 minutes, and then aged for 2 hours to obtain an acid group-containing polymer having a polymerization conversion of 98%. Latex (C-2) was obtained.

(3) Rubbery polymer latex (C-3)
A butadiene polymer latex (C-1) 2
48.9 parts (100 parts as a rubbery polymer) were added, and then the above acid-containing polymer latex (C-
2) After adding 6.1 parts (2.0 parts as solid content),
Subsequently, the mixture was stirred for 30 minutes to obtain an enlarged rubbery polymer latex (C-3) having a solid content of 40.7%.

(4) Production of graft polymer (C-4) 1500 parts of water and the above-mentioned rubbery polymer latex (C-
3) 2500 parts (1000 parts as a rubber-like polymer), 6.0 parts of dextrose, 1.0 part of sodium pyrophosphate, and 0.1 part of ferrous sulfate heptahydrate were charged into a reactor, and purged with nitrogen. The temperature was raised to 60 ° C and methyl methacrylate 3
A monomer mixture consisting of 80 parts, 20 parts of methyl acrylate, 0.25 part of t-dodecyl mercaptan and 0.075 part of cumene hydroperoxide was added dropwise over 200 minutes, during which the internal temperature was 65 ° C. Was controlled. After the completion of the dropwise addition, the mixture was kept at 70 ° C. for 1 hour, and an antioxidant (Antage W-40 manufactured by Kawaguchi Chemical Industry Co., Ltd.)
0) After adding 1 part, the mixture was cooled. 98% polymerization conversion
Met. The obtained graft polymer latex (C-
4) was evaluated for continuous spray-drying operation. Table 1 shows the results of observation of the residue in the spray dryer after the continuous operation.

[0034]

[Table 1]

[0035]

[Table 2]

From the results shown in Tables 1 and 2, it was found that in the examples of the present invention, autoxidation of the retentate of the diene-based graft polymer was not observed. On the other hand, in the comparative example, autoxidation was observed in the retentate.

[0037]

As described above, according to the method for producing a diene-based graft polymer powder of the present invention, the auto-oxidation of the diene-based graft polymer in a dryer can be performed without adding a stabilizer or the like to the latex. Can be prevented, and a diene-based graft polymer powder can be obtained from the latex of the diene-based graft polymer by spray drying economically without any trouble. In addition, since there is little danger of autoxidation of the residue of the diene-based graft polymer, continuous operation is possible, and the productivity of the diene-based graft polymer powder can be improved.

In the present invention, by adjusting the steam pressure in the vicinity of the outlet of the dryer, which is the recovery unit for the diene-based graft polymer powder, even if steam is used as the heating gas for drying, the steam is generated in the dryer. The powder can be obtained by drying the diene-based graft polymer latex without causing aggregation and condensation. At the same time, by adjusting the temperature of the outlet portion with reference to the MFT of the diene-based graft polymer, a diene-based graft polymer powder having excellent powder properties can be obtained without fusing the powder surface. .

Claims (2)

[Claims] 1. A diene-grafted polymer latex in which a butadiene unit in a polymer is 10% by mass to 85% by mass is sprayed into a dryer and heated steam is fed from an inlet of the dryer. A method for producing a diene-based graft polymer powder, comprising drying to obtain a diene-based graft polymer powder, and collecting the powder from an outlet of a dryer. 2. The partial pressure of steam near the outlet of the dryer is equal to or lower than the saturated steam pressure at the temperature near the outlet of the dryer, and the temperature near the outlet of the dryer is lower than that of the diene-based graft polymer latex. The method for producing a diene-based graft polymer powder according to claim 1, wherein the temperature is not higher than a temperature obtained by adding 100 ° C to the minimum film forming temperature.