JP5236892B2 - Method for producing polymer powder - Google Patents

Description

  The present invention is a process for producing a polymer powder in which a polymer latex obtained by emulsion polymerization is spray-dried by a circulation type spray dryer equipped with a condenser, and the polymer in the polymer latex is recovered as a powder. It is about the method.

  Examples of a method for recovering the polymer as a powder from the polymer latex include a method of spray-drying the polymer latex. Spray drying is an industrially advantageous process from the standpoint of equipment cost and operation management because it can directly obtain a dry powder of the polymer from the polymer latex. As the spray dryer, a non-circulating spray dryer or a circulating spray dryer is used.

  In the non-circulating spray dryer, after the polymer is recovered from the polymer latex as a powder, the drying gas used for drying the polymer latex is discharged into the atmosphere. Since high-temperature drying gas is discharged into the atmosphere, energy use efficiency is low. On the other hand, in the circulation type spray dryer, the drying gas used for drying the polymer latex is heated again and returned to the dryer as the drying gas, so that the fuel used for heating the drying gas can be saved and the energy can be saved. High usage efficiency. For example, Patent Document 1 proposes a method for recovering polymer powder using a circulation spray dryer equipped with a condenser.

  By the way, in the method in which polymer latex is spray-dried and the polymer is recovered as a powder, components such as emulsifiers, catalysts, polymerization initiators, and their decomposition products used in emulsion polymerization (hereinafter referred to as “residual components”). Will remain in the recovered polymer powder. For this reason, there exists a problem that the thermal stability of the obtained polymer powder falls. Patent Document 2 proposes reducing residual components in the recovered polymer powder by selecting a polymerization initiator used for emulsion polymerization using a non-circulating spray dryer.

When a circulation type spray dryer is used, the amount of residual components in the polymer powder to be recovered increases as compared with the case where a non-circulation type spray dryer is used. For this reason, even when the polymerization initiator used in the examples of Patent Document 2 is used, when a continuous operation is performed for a long time with a circulation type spray dryer, the polymer powder is gradually mixed with time. There is a problem in that the amount of residual components increases, and the odor considered to be the cause is strongly felt.
Japanese Patent No. 3643051 Japanese Patent No. 3822816

  The present invention aims to reduce the residual components in the recovered polymer powder when the polymer latex obtained by emulsion polymerization is spray-dried by a circulating spray dryer equipped with a condenser. Yes.

  As a result of intensive studies, the inventors of the present invention have an influence on the quality of the polymer powder. Among the residual components in the polymer powder, in particular, the polymerization initiator used in the emulsion polymerization and a decomposition product thereof (hereinafter referred to as the decomposition product) , And referred to as “polymerization initiator-derived component”). Furthermore, when a polymerization initiator having high solubility in water is used, the polymerization initiator is dissolved in the condensed water and discharged out of the system in the condenser provided in the circulation spray dryer, and the polymerization initiator-derived component is the polymer. It was found that it was difficult to remain in the powder.

  That is, the present invention includes a step of obtaining a polymer latex by emulsion polymerization, and spray-drying the polymer latex with a circulation spray dryer equipped with a condenser, so that the polymer in the polymer latex is powdered. A method of producing a polymer powder having a step of recovering, wherein in the emulsion polymerization, only a polymerization initiator having a solubility in water at 20 ° C. of 2% by mass or more is used, whereby a component derived from a polymerization initiator remaining. A polymer powder having a reduced amount of is provided.

  According to the present invention, when the polymer powder is recovered using a circulating spray dryer equipped with a condenser, the polymerization initiator used for the emulsion polymerization is discharged out of the system, so that it can be continuously for a long time. Even if the operation is performed, a polymer powder in which the amount of the polymerization initiator-derived component is reduced can be obtained without increasing the amount of the polymerization initiator-derived component in the polymer powder. This is advantageous in terms of the quality of the polymer powder and safety in using the polymer powder.

  In the present specification, (meth) acrylate means acrylate or methacrylate. The polymer of the present invention is preferably a graft copolymer or an acrylic copolymer.

  The graft copolymer of the present invention is a polymer obtained by graft polymerization of a vinyl monomer in the presence of a rubbery polymer (trunk polymer) latex. As the rubbery polymer constituting the graft copolymer, those having a glass transition temperature (Tg) of 20 ° C. or less are preferable. Examples of the rubbery polymer include acrylic rubbery polymers mainly composed of n-butyl acrylate, 2-ethylhexyl acrylate, etc .; diene rubbery polymers mainly composed of butadiene, isoprene, etc .; organosiloxanes, etc. And silicone-based rubbery polymers containing as the main component. Moreover, the composite rubber which compounded 2 or more types of these rubber-like polymers may be sufficient. Further, it may be a rubbery polymer containing a glassy polymer in the core.

  Examples of the vinyl monomer used for the graft polymerization include methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, acrylonitrile, and styrene. These vinyl monomers may be used alone or in combination of two or more.

  The amount of the rubber polymer used relative to the entire graft copolymer (100% by mass) is preferably 40 to 90% by mass. If the amount of the rubbery polymer used is 40% by mass or more with respect to the entire graft copolymer (100% by mass), the impact resistance of the resulting molded product can be improved when the graft copolymer is blended with a thermoplastic resin. Can be improved. When the amount of the rubbery polymer used is 90% by mass or less based on the entire graft copolymer (100% by mass), the handleability of the graft copolymer becomes good.

  As for the usage-amount of the vinyl monomer with respect to the whole graft copolymer (100 mass%), 10-60 mass% is preferable. When the amount of vinyl monomer used is 10% by mass or more based on the graft copolymer (100% by mass), the handleability of the graft copolymer is improved. If the amount of vinyl monomer used relative to the graft copolymer (100% by mass) is 60% by mass or less, the impact resistance of the resulting molded product will be improved when the graft copolymer is blended with a thermoplastic resin. Can be made.

  The acrylic copolymer of the present invention is a polymer obtained by copolymerizing methyl methacrylate and other vinyl monomers.

  The methyl methacrylate unit contained in the acrylic copolymer (100% by mass) is preferably 50 to 90% by mass. If the methyl methacrylate unit contained in the acrylic copolymer (100% by mass) is 50% by mass or more, the handleability of the acrylic copolymer will be good. If the methyl methacrylate unit contained in the acrylic copolymer (100% by mass) is 90% by mass or less, the processability of the thermoplastic resin is improved when the acrylic copolymer is blended with the thermoplastic resin. be able to.

  The other vinyl monomer unit contained in the acrylic copolymer (100% by mass) is preferably 10 to 50% by mass. If the other vinyl monomer unit contained in the acrylic copolymer (100% by mass) is 10% by mass or more, when the acrylic copolymer is blended with the thermoplastic resin, Workability can be improved. If the other vinyl monomer unit contained in the acrylic copolymer (100% by mass) is 50% by mass or less, the handleability of the acrylic copolymer will be good.

  In the present invention, first, a polymer latex containing the polymer is obtained by emulsion polymerization. That is, a monomer for forming the polymer and an emulsifier are mixed in water, and emulsion polymerization is performed using a polymerization initiator.

  As the emulsifier used in the present invention, anionic emulsifiers such as alkyl benzene sulfonate, alkyl sulfate ester salt and alkyl phosphate ester salt are preferable. As the alkylbenzene sulfonate, sodium dodecylbenzenesulfonate is preferable. As the alkyl sulfate ester salt, sodium lauryl sulfate is preferable. Examples of the alkyl phosphate ester salts include alkali metal salts of linear alkyloxypolyoxyethylene phosphates such as mono-n-decyloxytetraoxyethylene phosphate and di-n-decyloxytetraoxyethylene phosphate; mono-isotridecyloxyhexa Examples thereof include alkali metal salts of branched alkyloxypolyoxyethylene phosphoric acid such as oxyethylene phosphoric acid and di-isotridecyloxyhexaoxyethylene phosphoric acid. These emulsifiers may be used individually by 1 type, and may use 2 or more types together.

  The amount of the emulsifier used is preferably 0.5 to 5 parts by mass with respect to 100 parts by mass of the monomer constituting the polymer. If the usage-amount of the emulsifier with respect to 100 mass parts of monomers which comprise a polymer is 0.5 mass part or more, stability of polymer latex will improve. As for the usage-amount of the emulsifier with respect to 100 mass parts of monomers which comprise a polymer, 1 mass part or more is more preferable. If the usage-amount of the emulsifier with respect to 100 mass parts of monomers which comprise a polymer is 5 mass parts or less, foaming at the time of emulsion polymerization will reduce and productivity will improve. As for the usage-amount of the emulsifier with respect to 100 mass parts of monomers which comprise a polymer, 4 mass parts or less are more preferable.

  In the case of using the above-mentioned emulsifier, an emulsifying dispersant can be used in combination in order to improve the stability of the polymer latex. Examples of the emulsifying dispersant include alkyl naphthalene sulfonate, alkyl diphenyl ether disulfonate, polyoxyethylene alkyl sulfate ester salt, salt of naphthalene sulfonic acid formalin condensate, and the like. The amount of the emulsifying dispersant used is preferably 0 to 30 parts by mass with respect to 100 parts by mass of the emulsifier.

  In the present invention, in the step of obtaining a polymer latex by emulsion polymerization, only a polymerization initiator having a solubility in water at 20 ° C. of 2% by mass or more is used. When the polymer is a graft copolymer, the solubility in water at 20 ° C. is 2 in the polymerization step of the rubbery polymer and the step of graft polymerization of the vinyl monomer in the presence of the rubbery polymer latex. Only a polymerization initiator of mass% or more is used. When emulsion polymerization is performed in multiple stages, only a polymerization initiator having a solubility in water at 20 ° C. of 2% by mass or more is used in all polymerization steps.

  The polymerization initiator used in the present invention is a polymerization initiator having a solubility in water of 20 ° C. of 2% by mass or more. If the solubility of the polymerization initiator in water at 20 ° C. is 2% by mass or more, the polymerization initiator is dissolved in the condensed water and discharged out of the system by the condenser provided in the circulation type spray dryer. It is difficult for the initiator-derived component to remain in the polymer powder. The solubility of the polymerization initiator in water at 20 ° C. is preferably 3% by mass or more, and more preferably 5% by mass or more.

  Examples of the polymerization initiator having a solubility in water of 20 ° C. of 2% by mass or more include potassium persulfate (solubility in water at 20 ° C .: 5.2% by mass), sodium persulfate (solubility in water at 20 ° C .: 55 .6 mass%), ammonium persulfate (solubility in water at 20 ° C .: 58.2 mass%), t-butyl hydroperoxide (solubility in water at 20 ° C .: 15.7 mass%), 2,2′-azobis (2-Amidinopropane) dihydrochloride (solubility in water at 20 ° C .: 23.2% by mass) and the like. Among these, potassium persulfate and t-butyl hydroperoxide are preferable. These polymerization initiators may be used alone or in combination of two or more.

  As for the usage-amount of a polymerization initiator, 0.01-5 mass parts is preferable with respect to 100 mass parts of monomers which comprise a polymer. If the amount of the polymerization initiator used relative to 100 parts by mass of the monomer constituting the polymer is 0.01 parts by mass or more, the polymerization initiator can function sufficiently and reduce unreacted vinyl monomers. it can. If the usage-amount of the polymerization initiator with respect to 100 mass parts of monomers which comprise a polymer is 5 mass parts or less, a polymerization initiator origin component will become difficult to remain in polymer powder. As for the usage-amount of the polymerization initiator with respect to 100 mass parts of monomers which comprise a polymer, 3 mass parts or less are more preferable, and 2 mass parts or less are more preferable.

  As a polymerization initiator, a reducing agent such as sodium bisulfite or amines may be used as a redox polymerization initiator in combination with a persulfate or an organic peroxide. Also about the said reducing agent, it is preferable that the solubility with respect to 20 degreeC water is 2 mass% or more.

  In the present invention, the polymer latex thus obtained is spray-dried by a spray dryer, and the polymer in the polymer latex is recovered as a powder. The spray dryer used in the present invention is a circulation type spray dryer having a condenser.

  Circulating spray dryers can be used from small-scale equipment used in laboratories to large-scale equipment used industrially. The circulation type spray dryer is characterized in that the drying gas used for drying the polymer latex is heated again and returned to the dryer as a drying gas. Since the drying gas is heated again and returned to the dryer, it may be referred to as a circulating gas. As a device for spraying the polymer latex in the dryer, any device such as a rotating disk type, a pressure nozzle type, a two-fluid nozzle type, a pressurized two-fluid nozzle type, etc. can be used.

  The condenser provided in the circulation type spray dryer is for condensing the moisture in the circulating gas increased by drying the polymer latex by cooling below the dew point of the circulating gas, and taking out the condensed moisture. . Examples of the condenser include an indirect heat exchanger typified by a multi-tube heat exchanger and a heat exchanger with multi-tube fins; a direct heat exchanger typified by a wet scrubber and the like.

  The inlet temperature of the drying gas (hot air inlet temperature) is preferably 120 to 200 ° C. If the inlet temperature of the drying gas is 120 ° C. or higher, the polymer latex can be sufficiently dried. If the inlet temperature of the drying gas is 200 ° C. or lower, the polymer is not altered by heat in the spray drying process. The inlet temperature of the drying gas is more preferably 180 ° C or lower.

  The polymer latex to be spray dried may be a single polymer latex or a mixture of a plurality of polymer latexes.

  In order to prevent blocking during spray drying, adjust the bulk specific gravity of the resulting polymer powder, etc., inorganic fillers such as silica, talc, or calcium carbonate, polyacrylate, polyvinyl alcohol, polyacrylamide, etc. It can also be added and spray dried. Moreover, it is also possible to add a phenol-based, sulfur-based, phosphorus-based antioxidant or the like to the polymer latex and spray-dry it.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited thereto. “Part” and “%” represent “part by mass” and “% by mass”, respectively, unless otherwise specified. Various evaluations in Examples and Comparative Examples were performed by the following methods.

(A) Solid content of polymer latex About 10 g of polymer latex was sampled and heated at 180 ° C. for 30 minutes. The solid content of the polymer latex was determined from the amount of polymer latex collected and the mass of the heating residue.

(B) Polymer polymerization rate The solid content of the polymer latex determined in the evaluation of item (a) was divided by the solid content at the time of preparation to determine the polymerization rate of the polymer.

(C) Evaluation of volatile content of powder Using a head space autosampler and a gas chromatograph mass spectrometer (GC-MS), the amount of volatile content present in the polymer powder was measured under the following conditions. Evaluation was performed using the total area value of peaks detected by GC-MS. The measurement was performed 3 times and the average value was obtained.
(apparatus)
Headspace autosampler: Tekmar 7000 (trade name, manufactured by Tekmar)
GC-MS: QP-5000 (trade name, manufactured by Shimadzu Corporation)
(Head space condition)
Sample amount: 0.02 g
Heating temperature: 180 ° C
Heating time: 10 minutes (GC-MS conditions)
Column: HP-5 (trade name, manufactured by Agilent Technology)
Length: 50m
Liquid phase: 0.25 μm
Inner diameter: 0.32 mm
Carrier gas: He
Column pressure: 0.098 MPa
(D) Odor evaluation of powder 500 g of polymer powder recovered by spray drying was placed in a plastic bag, and the odor was evaluated. The degree of odor was determined according to the following criteria.

◎: Do not feel odor ○: Feel odor slightly △: Feel odor ×: Feel odor strongly (Example 1)
(1) Manufacture of graft copolymer (A2) powder (1-1) Manufacture of rubbery polymer (A1) Latex A reactor equipped with a thermometer, a nitrogen inlet tube and a stirrer (withstand pressure of 30 MPa) was charged with the following components: The inside of the reactor was purged with nitrogen and stirred.

Sodium dodecylbenzenesulfonate 2.33 parts Sodium pyrophosphate anhydrous 0.2 parts 1,3-butadiene 78 parts Styrene 22 parts Divinylbenzene 0.5 parts t-butyl hydroperoxide (purity: 69%) 0.12 parts ( Perbutyl H-69: Product name manufactured by NOF Corporation
181 parts of deionized water After raising the internal temperature of the reactor to 70 ° C., the following reducing agent aqueous solution was added to initiate polymerization.

Reducing agent aqueous solution:
Ferrous sulfate heptahydrate 0.0003 parts Disodium ethylenediaminetetraacetate 0.0009 parts Sodium formaldehyde sulfoxylate 0.17 parts Deionized water 4 parts After holding for 5 hours, the following polymerization initiator was added, and Hold for 4 hours.

t-Butyl hydroperoxide 0.09 part By the above polymerization reaction, rubber polymer (A1) latex was obtained. The resulting rubbery polymer (A1) latex had a solid content of 35.1%, and the polymerization rate of the rubbery polymer was 98.0%.

(1-2) Production of Graft Copolymer (A2) Latex The following rubber polymer latex was charged into a reactor equipped with a thermometer, a cooling tube, a nitrogen introduction tube, and a stirrer.

208 parts of latex polymer (A1) latex
(Solid content: 73 parts)
After substituting the inside of the reaction apparatus with nitrogen, the following reducing agent was added and stirred to raise the internal temperature of the reaction apparatus to 70 ° C.

Sodium formaldehyde sulfoxylate 0.3 part Then, the following 1st monomer mixture was dripped over 50 minutes, Then, it hold | maintained for 60 minutes.

First monomer mixture:
Methyl methacrylate 9 parts Butyl acrylate 1 part t-Butyl hydroperoxide 0.0375 parts Next, the following second monomer mixture was added dropwise over 60 minutes, and then held for 120 minutes.

Second monomer mixture:
Styrene 14.3 parts t-butyl hydroperoxide 0.0536 parts Next, the following third monomer mixture was added dropwise over 20 minutes, and then held for 90 minutes.

Third monomer mixture:
Methyl methacrylate 2.7 parts t-butyl hydroperoxide 0.0101 parts Graft copolymer (A2) latex was obtained by the polymerization reaction described above.

  The following two types of antioxidants were added to the obtained graft copolymer (A2) latex. The addition amount of the antioxidant is an amount relative to 100 parts of the solid content of the graft copolymer (A2).

Emulsified and dispersed triethylene glycol-bis [3- (3-tertiarybutyl-5-methyl-4-hydroxyphenyl) propionate]
(IRGANOX245: trade name manufactured by Ciba Specialty Chemicals Co., Ltd.)
0.21 parts Dilauryl-3,3′-thiodipropionate emulsified and dispersed (IRGANOXPS800: trade name, manufactured by Ciba Specialty Chemicals)
0.63 parts (1-3) Production of Graft Copolymer (A2) Powder Using CL-8 (trade name, manufactured by Okawara Chemical Co., Ltd.), which is a circulating spray dryer equipped with a condenser, The graft copolymer (A2) latex after the addition of the antioxidant was spray-dried. Spray drying was performed continuously for 120 minutes to obtain a graft copolymer (A2) powder. The operating conditions were as follows.

Drying gas inlet temperature 155 ° C
Drying gas outlet temperature 70 ° C
Condenser temperature 10 ° C
Spraying device (rotating disk type) 25,000 rpm
A polymer powder collected 20 minutes after the start of spray drying and a polymer powder collected 120 minutes later were used as samples for evaluation. For evaluation of the volatile content of the powder, polymer powder collected after 20 minutes and polymer powder collected after 120 minutes were used. For the odor evaluation of the powder, polymer powder collected after 120 minutes was used. The evaluation results are shown in Table 1.

(Example 2)
(2) Manufacture of graft copolymer (B2) powder (2-1) Manufacture of rubbery polymer (B1) Latex A reactor equipped with a thermometer, a nitrogen inlet tube and a stirrer (withstand pressure of 30 MPa) was charged with the following components: The inside of the reactor was purged with nitrogen and stirred.

Sodium dodecylbenzenesulfonate 2.33 parts Sodium pyrophosphate anhydrous 0.2 parts 1,3-butadiene 78 parts Styrene 22 parts Divinylbenzene 0.5 parts Deionized water 181 parts The internal temperature of the reactor was raised to 80 ° C . Next, the following polymerization initiator aqueous solution was added to initiate polymerization. In order to control the inside of the system during the polymerization reaction to pH 9, sodium hydroxide was added together.

Polymerization initiator aqueous solution:
Potassium persulfate 0.26 parts Sodium hydroxide 0.03 parts Deionized water 4 parts After holding for 4 hours, the following polymerization initiator was added and held for another 4 hours.

Potassium persulfate 0.2 parts A rubbery polymer (B1) latex was obtained by the polymerization reaction. The resulting rubbery polymer (B1) latex had a solid content of 34.5%, and the polymerization rate of the rubbery polymer was 95.5%.

(2-2) Production of Graft Copolymer (B2) Latex The following rubber polymer latex was charged into a reactor equipped with a thermometer, a cooling tube, a nitrogen introduction tube, and a stirrer.

Rubber polymer (B1) latex 212 parts
(Solid content: 73 parts)
After substituting the inside of the reaction apparatus with nitrogen, the following reducing agent aqueous solution was added and stirred to raise the internal temperature of the reaction apparatus to 70 ° C.

Reducing agent aqueous solution:
Ferrous sulfate heptahydrate 0.0002 parts Disodium ethylenediaminetetraacetate 0.0006 parts Sodium formaldehyde sulfoxylate 0.3 parts Deionized water 4 parts Then, the following first monomer mixture is added dropwise over 50 minutes. And then held for 60 minutes.

First monomer mixture:
Methyl methacrylate 9 parts Butyl acrylate 1 part t-Butyl hydroperoxide 0.0375 parts Next, the following second monomer mixture was added dropwise over 60 minutes, and then held for 120 minutes.

Second monomer mixture:
Styrene 14.3 parts t-butyl hydroperoxide 0.0536 parts Next, the following third monomer mixture was added dropwise over 20 minutes, and then held for 90 minutes.

Third monomer mixture:
Methyl methacrylate 2.7 parts t-butyl hydroperoxide 0.0101 parts Graft copolymer (B2) latex was obtained by the polymerization reaction described above. In the same manner as in Example 1, an antioxidant was added to the obtained graft copolymer (B2) latex.

(2-3) Production of Graft Copolymer (B2) Powder Spray drying was performed in the same manner as in Example 1 to obtain a graft copolymer (B2) powder.

  A polymer powder collected 20 minutes after the start of spray drying and a polymer powder collected 120 minutes later were used as samples for evaluation. The evaluation results are shown in Table 1.

(Comparative Example 1)
(3) Manufacture of graft copolymer (C2) powder (3-1) Manufacture of rubbery polymer (C1) Latex A reactor equipped with a thermometer, a nitrogen inlet tube and a stirrer (withstand pressure of 30 MPa) was charged with the following components: The inside of the reactor was purged with nitrogen and stirred.

Sodium dodecylbenzenesulfonate 2.33 parts Sodium pyrophosphate anhydrous 0.2 parts 1,3-butadiene 78 parts Styrene 22 parts Divinylbenzene 0.5 parts Diisopropylbenzene hydroperoxide (purity: 50%)
(Park Mill P: Product name manufactured by NOF Corporation) 0.36 parts Deionized water 181 parts The solubility of diisopropylbenzene hydroperoxide used here in water at 20 ° C is 1.7%.

  After raising the internal temperature of the reactor to 70 ° C., the following reducing agent aqueous solution was added to initiate polymerization.

Reducing agent aqueous solution:
Ferrous sulfate heptahydrate 0.0003 parts Disodium ethylenediaminetetraacetate 0.0009 parts Sodium formaldehyde sulfoxylate 0.17 parts Deionized water 4 parts After holding for 5 hours, the following polymerization initiator was added, and Hold for 4 hours.

Diisopropylbenzene hydroperoxide 0.27 parts A rubbery polymer (C1) latex was obtained by the polymerization reaction described above.

  The resulting rubbery polymer (C1) latex had a solid content of 34.8%, and the polymerization rate of the rubbery polymer was 97.0%.

(3-2) Manufacture of Graft Copolymer (C2) Latex 208 parts of rubber polymer (A1) latex (solid content: 73 parts) used in the manufacture of graft copolymer (A2) latex was added to rubber weight A graft copolymer (C2) latex was obtained in the same manner as in Example 1 except that the blend (C1) latex was changed to 210 parts (solid content: 73 parts).

  In the same manner as in Example 1, an antioxidant was added to the obtained graft copolymer (C2) latex.

(3-3) Production of Graft Copolymer (C2) Powder Spray drying was performed in the same manner as in Example 1 to obtain a graft copolymer (C2) powder.

  A polymer powder collected 20 minutes after the start of spray drying and a polymer powder collected 120 minutes later were used as samples for evaluation. The evaluation results are shown in Table 1.

  As shown in Table 1, in Examples 1 and 2, only a polymerization initiator having a solubility in water at 20 ° C. of 2% or more is used, and a continuous operation with a circulation spray dryer having a condenser for a long time. Even when the process was performed, the increase in the amount of volatile components present in the polymer powder was small. Further, the odor of the polymer powder collected 120 minutes after the start of spray drying was not felt in Example 1, but was slightly felt in Example 2.

  In Comparative Example 1, a polymerization initiator having a solubility in water at 20 ° C. of 1.7% was used in the polymerization step of the rubbery polymer, and the continuous operation was continued for a long time with a circulating spray dryer equipped with a condenser. In the case of the above, an increase in the amount of volatile components present in the polymer powder was observed. Further, the odor of the polymer powder collected 120 minutes after the start of spray drying was strongly felt.

  Thus, in Examples 1 and 2, the polymerization initiator present in the polymer powder when Comparative Example 1 was continuously operated for a long time with a circulating spray dryer provided with a condenser. It is observed that the amount of derived components is reduced.

  In Examples 1 and 2, it is possible to perform continuous operation for a long time with a circulation type spray dryer provided with a condenser.

Claims (1)

A step of obtaining a polymer latex by emulsion polymerization, and a step of spray-drying the polymer latex by a circulating spray dryer equipped with a condenser and recovering the polymer in the polymer latex as a powder. A method for producing a polymer powder, comprising:
In the emulsion polymerization, only a polymerization initiator having a solubility in water of 20 ° C. of 2% by mass or more is used.