JP2003137923A - Method for drying polymer powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for drying by which impurities such as residual monomers, organic solvents or malodorous components contained in a polymer powder are extremely efficiently and highly separated and removed without causing decomposition or discoloration in polymer particles and without deteriorating fluidity of the powder. SOLUTION: This wet polymer powder is subjected to drying in a first stage under a reduced pressure of atmospheric pressure, if necessary, while being stirred and then subjected to drying by contact with steam while being fluidized under a reduced pressure of 50-500 mmHg in a second stage.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to volatile impurities such as residual monomers, organic solvents and odorous components contained in polymer powder, without causing decomposition or coloring of vinyl polymer particles, impairing fluidity of the powder. The present invention relates to a drying method that removes extremely efficiently.

[0002]

2. Description of the Related Art Vinyl polymer powder is used as an additive for various products because of its characteristics such as transparency, light weight and smoothness. When it is used in pharmaceuticals, cosmetics, etc. It is required that impurities such as odorous components are removed to 50 ppm or less, preferably 10 ppm or less. Therefore, the polymer powder from the polymer slurry obtained by the radical polymerization reaction is dried in a usual drying process until the water content becomes 20 to 40%, and then the residual monomer and the residual solvent are left at a considerably high temperature under normal pressure or reduced pressure. And impurities such as odorous components are dried and removed, but the removal rate decreases as the amount of impurities attached to or adsorbed in the powder particles and absorbed in the powder particles decreases, so it is extremely difficult to reduce impurities to 10 ppm or less. Took a long time.
Also, unlike normal spherical powders, the porous particles require a longer time. Moreover, if the powder is heated and stirred for a long time, the fluidity of the powder deteriorates due to the influence of static electricity that is generated, making the classification and sieving processes that are performed later difficult or impossible. There was a problem. If the drying temperature is raised, the removal rate will be increased, but in that case, fusion between the polymers may occur, depolymerization of the polymer may occur, or the polymer may be colored pale yellow.

Therefore, in order to increase the removal rate of trace impurities in the polymer powder, a method has been proposed in which dry air or nitrogen as an inert gas is passed through the powder. However, in the case of nitrogen, the economic burden of using a large amount of expensive gas is not negligible. Furthermore, a large-capacity vacuum pump is required to maintain the reduced pressure, which is not preferable as an industrial production method. Further, when air is used, the polymer powder may be colored, and dust explosion may occur.

[0004]

According to the present invention, volatile impurities such as residual monomers, residual solvents and odorous components contained in a dry polymer powder are dried to 10 ppm or less in a short time without impairing the physical properties of the polymer powder, It is to provide a method of removing.

[0005]

Means for Solving the Problems As a result of various investigations by the present inventors, the wet polymer powder was subjected to normal drying (first step) under reduced pressure or normal pressure, and then the powder was flowed under reduced pressure. The above problem was solved by carrying out drying (second step) by contacting with water vapor. That is, the present invention is
(1) After the first step of drying the wet polymer powder obtained by the dispersion polymerization of the radically polymerizable vinyl monomer under reduced pressure or normal pressure, under reduced pressure of 50 to 500 mmHg,
A method for drying a polymer powder, in which a second step of drying is performed in which steam is supplied while fluidizing the polymer powder to bring the particles into contact with steam, and (2) the polymer of the radical-polymerizable vinyl monomer is an alkyl (meth) acrylate-based monomer. The drying method according to (1), which is a polymer, a polymer of a styrene-based monomer or a copolymer of these monomers, (3) the first-stage drying and the second-stage drying are performed at 40 to 120 ° C. (1) or (2). ), And (4) after the second-stage drying, the supply of steam is stopped and the pressure is reduced under normal pressure or 40
The drying method according to any one of (1) to (3), wherein the third stage drying is performed at ˜120 ° C.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION A wet polymer powder obtained by a mechanical solid-liquid separation method such as centrifugation or filtration of a polymer slurry obtained by dispersion polymerization including suspension polymerization and emulsion polymerization for the drying of the present invention. Can be used. Wet polymer powder according to the present invention refers to a polymer powder containing 10-40% by weight of water. Monomers for synthesizing the polymer of the polymer powder are monofunctional and / or polyfunctional vinyl monomers, and include, for example, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, and (meth) acrylic. Butyl acid, (meth)
(Meth) acrylic acid ester-based monomers such as n-octyl acrylate and 2-ethylhexyl (meth) acrylate, and aromatic vinyls such as styrene, α-methylstyrene, chlorostyrene, and chloromethylstyrene. -Based monomers, vinyl cyanide-based monomers typified by acrylonitrile, methacrylonitrile, ethacrylonitrile, etc., monomers consisting of one or more selected from vinyl acetate, vinyl chloride, vinyl chloride, and the like, and ( Allyl (meth) acrylate, diallyl phthalate, ethylene glycol di (meth) acrylate,
Having two or more polymerizable unsaturated groups in the molecule represented by 1,3-butylene glycol di (meth) acrylate, diallyl itaconate, divinylbenzene, triallyl cyanurate, triallyl isocyanurate, etc. A polymerizable monomer composed of a polyfunctional vinyl monomer is preferably used.

For example, in order to obtain an acrylic polymer powder by suspension polymerization, if necessary, a polymerizable monomer such as a polyfunctional vinyl monomer is appropriately mixed with the above-mentioned (meth) acrylic acid ester-based monomer, and a dispersant is added thereto. , The oily radical polymerization initiator and water are charged into a dispersion container to disperse into desired monomer droplets, and then charged into a polymerization container and reacted to form particles. By using a polyfunctional vinyl monomer, it is possible to improve the heat resistance and durability of the copolymer particles.

The weight average particle size and weight particle size distribution of the particles constituting the vinyl polymer powder are mainly determined by the number of revolutions of the disperser and the dispersion time at the time of dispersing the monomer droplets prior to the initiation of the polymerization reaction. In order to obtain a powder having a narrow particle size distribution, it is necessary to select the type of disperser and the structure of the dispersion tank so that the shearing force applied to the dispersion becomes uniform. As a disperser, a homodisper or a colloid mill type is preferable.
In addition, it is necessary to make an appropriate selection because it is affected by the type and amount of dispersant used.

Examples of the dispersant include gelatin,
Water-soluble polymers such as methyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, carboxymethyl cellulose, polyethylene glycol, polyoxyethylene-polyoxypropylene block copolymer, polyacrylamide, polyacrylic acid, polyacrylic acid salt, sodium alginate, and polyvinyl alcohol; phosphorus Examples include inorganic substances such as tricalcium acid and calcium carbonate. Among these dispersants, hydroxyethyl cellulose, hydroxypropyl cellulose, polyvinyl alcohol, tricalcium phosphate and the like are preferably used. These dispersants may be used either individually or in combination of two or more. The amount of the dispersant used is, for example, 0.1 to 30% by weight, preferably 0.5 to 10% by weight, based on the whole monomer mixture.

Further, if necessary, a surfactant for stabilizing the dispersion of monomer droplets (for example, anionic surfactants such as sodium dodecylbenzenesulfonate and sodium lauryl sulfate, nonionic surfactants, etc.) ), A water-soluble mercamptan compound or an inhibitor of aqueous phase polymerization such as sodium nitrite may be added. Also,
A monomer dispersion liquid can be obtained even by directly charging the above-mentioned monomer component into a polymerization vessel and performing dispersion by vigorous stirring.

Examples of the oil-soluble radical polymerization initiator include organic peroxides such as benzoyl peroxide, o-methoxybenzoyl peroxide, o-chlorobenzoyl peroxide, lauroyl peroxide and cumene hydroperoxide; 2,2 Examples thereof include azo compounds such as'-azobisisobutyronitrile and 2,2'-azobis (2,4-dimethylvaleronitrile).
Of these radical polymerization initiators, benzoyl peroxide, lauroyl peroxide, and 2,2′-azobisisobutyronitrile are often used. The radical polymerization initiator may be used alone or in combination of two or more, and the amount thereof is 0.01 to 5% by weight based on the whole monomer mixture,
It is preferably about 0.1 to 2% by weight. By recovering the polymer particles from the suspension produced by suspension polymerization, powdery polymer particles can be obtained. The powdery polymer particles are dehydrated by, for example, a centrifuge or a filter press to obtain a polymer powder having a water content of 10 to 40% by weight. This powder usually contains 5000 ppm or more of residual monomer.

The moist polymer powder is subjected to a first stage of drying under reduced pressure. As the drying device (3), for example, a drum-type or conical vacuum dryer having a heating jacket (4) on the outside is conveniently used. Heating is performed by circulating hot water or steam through the jacket. It is preferable to have a stirrer (5) inside to enhance the drying efficiency. This first-stage drying is performed under reduced pressure or atmospheric pressure, preferably 1 to 150 mmHg, more preferably 5 to 100 mmHg
Under reduced pressure of mmHg, 40 to 120 ° C., preferably 50 to 120 ° C.
It is carried out at 110 ° C., optionally with stirring. Usually 1-5
After drying for 3 hours, the water content is less than 3% and the residual monomer is 300
It becomes 0 ppm or less.

After the first-stage drying, the second-stage drying is carried out to obtain residual monomers attached to or contained in the polymer powder, lower and higher alcohols added during the polymerization depending on the purpose, aromatic solvents, and ketone-based compounds. A solvent and an odorous component such as an aliphatic or aromatic sulfur compound added to adjust the molecular weight of the polymer powder obtained by dispersion polymerization such as suspension polymerization or emulsion polymerization and to improve the centrifugal separation property are added to
It is removed to 0 ppm or less, preferably 10 ppm or less.

Also in the second stage drying, it is convenient to use the dryer used for the first stage drying. In this second-stage drying, the steam generated by the steam generator (1) is introduced into the dryer (3) from one or a plurality of gas inlets (2) provided at the bottom of the dryer. Then
The polymer powder and steam are brought into contact with each other while the particles are fluidized by the steam introduction pressure or by the stirrer (5), and the residual volatile impurities are guided to the outside of the dryer together with the steam to be removed. The degree of vacuum in the dryer is 50 to 500 mmHg, preferably 100 to 450 mmHg, so that the vacuum pump (9) sucks. The temperature in the dryer is 40 to 120.
C., preferably 50 to 110.degree. Speaking of the relationship between the temperature and the pressure inside the dryer, when drying is performed at a higher temperature of 90 to 120 ° C., the atmospheric pressure is 300 to 400 mmHg.
40-60 ° C due to the low softening point of the polymer
When drying at a lower temperature of 50 to 100 mm
It is better to increase Hg and the degree of reduced pressure.

The steam is preferably introduced after the temperature of the polymer powder in the dryer is close to the steam saturation temperature of the operating pressure so as not to be condensed in the dryer. In addition, it is desirable that steam or warm water be caused to flow through a heating jacket (4) attached to the outside of the dryer to prevent heat loss to the outside and prevent condensation of water vapor. The amount of steam introduced is determined by the physical properties of the polymer powder and the amount of the target residual monomer. The introduction rate is determined in consideration of the operation time and the characteristics of the apparatus, but usually 50 to 250 Kg / hour, preferably 100 to 250 kg for drying the polymer powder 1000 kg.
120 Kg / h of steam is introduced. Water vapor and impurities that have exited the dryer via the bag filter (6) are condensed and removed by a condenser (7) set between the dryer and a vacuum pump, and then passed through a condensed water receiver (8) to the pump ( It is discharged by 10). Due to the condensation of the water vapor, the load of the vacuum pump is only the amount of leakage of the apparatus and the exhaust of pulse air used for the bag filter, which is far more efficient and economical than the drying by air or an inert gas.

According to the drying method of the present invention, 1000 Kg
About 5 to 12 hours is sufficient to dry the wet polymer particles until the residual monomer content is 10 ppm or less. This is ⅕ or less of the drying time of 30 to 60 hours required for drying without using steam.

After the second-stage drying, the supply of new steam is stopped, and the pressure is reduced or at normal pressure, preferably 1 to 150 mm.
By suppressing the agglomeration of the polymer powder by adding a third drying step of drying under a reduced pressure of Hg, more preferably under a reduced pressure of 5 to 100 mmHg with stirring, if necessary.
Impurities such as residual monomers are almost completely removed (for example, 5 ppm
Hereinafter, preferably 1 ppm or less) can be removed. The temperature of this step is 40 to 120 ° C., preferably 50.
˜110 ° C. is preferable, and the drying time may be relatively short, such as 15 minutes to 1 hour.

[0018]

EXAMPLES The present invention will be specifically described below with reference to Examples and Comparative Examples. Example 1 A polymethylmethacrylate slurry having an average particle size of 6 μm obtained by suspension polymerization of methylmethacrylate was dehydrated by centrifugation and washed with ion-exchanged water by showering to obtain a wet cake of polymethylmethacrylate. The water content was 25% and the residual methyl methacrylate was 5000 ppm. The wet 1000 Kg cake was charged from the upper gut opening of a 2000 L capacity Nauter type vacuum dryer (3), heated under a reduced pressure of 10 mmHg from a jacket (4) of hot water at 95 ° C., and stirred by a rotary blade. (20 rp
m), normal drying was completed over 3 hours. At this time, the residual methyl methacrylate in the dry powder of polymethyl methacrylate in the dryer was 3000 ppm. Subsequently, 100 ° C. steam was introduced through three nozzles at the bottom of the dryer at a rate of 100 Kg / hour, and the product temperature was heated to 95 to 100 ° C. under reduced pressure of 400 mmHg to remove the residual monomer. A polymer powder having a water content of 1% and residual methyl methacrylate of 10 ppm or less was obtained by the drying process for 5 hours. Further, the introduction of water vapor is stopped, and the mixture is stirred for 10
Drying is performed at 95-100 ° C for 30 minutes under a pressure of -30 mmHg to obtain a moisture content of 0.2% and residual methyl methacrylate 1
A polymethylmethacrylate powder of ppm or less was obtained. It was a polymethylmethacrylate powder with good fluidity without light yellow coloring or fusion between particles.

Example 2 Instead of the polymethylmethacrylate of Example 1, a reaction slurry of porous polystyrene having an average particle size of 8μ prepared from styrene, divinylbenzene and a solvent methyl isobutyl ketone (MIBK) was treated in the same manner and wetted. A porous polystyrene was obtained. This slurry had a water content of 20%, residual styrene of 10000 ppm and residual MIBK of 2%. The same drying and removal steps as in Example 1 were carried out to obtain porous polystyrene having good fluidity, in which residual styrene and solvent MIBK were removed to 10 ppm or less.

COMPARATIVE EXAMPLE 1 In the drying step of Example 1 in which the residual methyl methacrylate was removed, water vapor was not introduced, and the normal vacuum drying step was continued.
It took 50 hours to remove to below ppm. The resulting polymethylmethacrylate powder has very poor fluidity,
The subsequent sieving process was difficult.

COMPARATIVE EXAMPLE 2 In the step of removing residual styrene and solvent MIBK in the drying step of Example 2, steam was not introduced and the normal reduced pressure drying step was continued. As a result, residual styrene and solvent MIBK were added at 10 pp.
It took 60 hours to remove to m or less.

[0022]

According to the method of the present invention, volatile impurities such as residual monomers, organic solvents and odorous components contained in polymer powder can be removed efficiently and almost completely. Also, by using steam, coloring of the powder during the drying process,
Deterioration agglomeration does not occur and the resulting powder has very good greenhouse fluidity.

[Brief description of drawings]

FIG. 1 Polymer powder drying flowchart

[Explanation of symbols]

1. Steam generator 2. Steam injection tube 3. Nauta type vacuum dryer 4. Heating jacket 5. mixer 6. Bag filter 7. condenser 8. Condensate receiver 9. Vacuum pump 10. pump

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI Theme Coat (reference) F26B 21/00 F26B 21/00 P (72) Inventor Adachi Shigeaki 960 Shimokokura, Kashiwara-cho, Hyogo Prefecture Gantz formation Incorporated (72) Inventor Nobuhisa Kata 960 Shimogokura, Kashiwara-cho, Hikami-gun, Hyogo Prefecture Gantz Kasei Co., Ltd. F-term (reference) 3L113 AA01 AB04 AB05 AC04 AC05 AC24 AC45 AC46 AC58 AC60 AC67 BA02 4D076 AA12 AA16 AA22 BA01 BA09 CD03 CD12 DA10 DA25 EA12Z EA14Z HA11 4J100 AB02P AB03P AB08P AC03P AG04P AL03P AL04P AL05P AL59P AM02P CA01 CA04 EA05 EA06 FA20 FA21 GB03 GB12 GC25 GC26 GC29 GD02 JA50 JA57 JA61

Claims (4)

[Claims] 1. A wet polymer powder obtained by dispersion polymerization of a radical-polymerizable vinyl monomer is first-stage dried under reduced pressure or normal pressure, and then the polymer powder is made to flow under reduced pressure of 50 to 500 mmHg. While drying the polymer powder, the second stage of drying is performed by supplying water vapor to bring the polymer particles into contact with water vapor. 2. A polymer of a radically polymerizable vinyl monomer is a polymer of an alkyl (meth) acrylate-based monomer,
The drying method according to claim 1, which is a polymer of a styrenic monomer or a copolymer of these monomers. 3. The first-stage drying and the second-stage drying are 40 to
The drying method according to claim 1 or 2, which is performed at 120 ° C. 4. The drying according to claim 1, wherein after the second-stage drying, the supply of new steam is stopped and the third-stage drying is performed at 40 to 120 ° C. under reduced pressure or normal pressure. Law.