JPS6254801B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the production of thermoplastic polymer particles with little impurities such as residual additives, and more specifically to the production of thermoplastic polymer particles containing little impurities such as residual additives, and more specifically to the addition of dispersants, dispersion aids, etc. in an aqueous medium in a polymerization tank equipped with a stirrer. When carrying out suspension polymerization in the presence of an agent,
This invention relates to a method for producing thermoplastic polymer particles with less impurities by employing specific stirring conditions.

In a polymerization tank equipped with a stirrer, a polymerizable monomer is subjected to suspension polymerization in a system in which additives such as a dispersant and a dispersion aid are dissolved or dispersed in an aqueous medium to obtain polymer particles. It is more widely practiced than before. Examples of dispersants include sparingly soluble inorganic compounds such as tribasic calcium phosphate, magnesium phosphate, calcium carbonate, sodium phosphate, calcium chloride, or a combination thereof, polyvinyl alcohol,
A water-soluble polymer compound such as carboxymethyl cellulose is used. Furthermore, when a poorly soluble inorganic compound is used as a dispersant, anionic surfactants such as sodium lauryl sulfate, polyoxyethylene, nonylphenol ether,
It is also known to use a nonionic surfactant such as polyoxyethylene sorbitan monolaurate. Furthermore, many combinations of dispersants and dispersion aids have been announced, such as the combination of the above-mentioned sparingly soluble inorganic compounds and water-soluble polymers.

Such suspension polymerization has conventionally been carried out in a stirring tank equipped with a multi-blade stirrer and a finger baffle. However, such conventional suspension polymerization using a stirring tank was not always satisfactory. In other words, the finger blades provided in conventional stirring tanks of this type are inserted deeply into the liquid, or in tanks with a large ratio H/D of liquid depth H to tank diameter D, stirring blades are installed in two stages, upper and lower. However, in such agitating tanks, the buffling significantly obstructs the upward flow of liquid in the tank, or separates the tank into two layers, upper and lower, causing suspended particles to It was difficult to avoid settling or flotation, or uneven mixing between the upper and lower layers. In order to avoid these drawbacks, the stirring speed was unnecessarily increased, but since the power consumption for stirring is generally proportional to the cube of the stirring speed, it required a very large amount of power. This caused huge economic losses.

Solving the drawbacks of conventional stirring tanks as mentioned above,
As a result of conducting research to obtain a uniform mixing state in the tank using a small stirring power, the present inventors have already found that
We have discovered that the position occupied by the finger buttful in the tank and the length of the fingers have a large effect on the mixing condition in the tank, and have developed a stirring device. The stirring device is a cylindrical reactor equipped with a bladed stirrer at the bottom, and the ratio of the horizontal length of the fingers to the diameter of the stirring device is
It is characterized by having a fingered buttful of 0.15 to 0.38 on the inner wall surface within 1/2 from the top of the cylindrical part (Patent Application No. 1982).
No. 54924).

The present invention aims to provide an improved method for suspension polymerization carried out using the above-mentioned stirring device. That is, although the above-mentioned improved stirring device or stirring tank has an excellent stirring effect, there is one problem when applying this to suspension polymerization.

When carrying out suspension polymerization, it is not advisable to suspend the particles using only mechanical stirring power, as this only unnecessarily increases the stirring power. For this reason, as mentioned above, it is customary to use a dispersant or a dispersion aid and carry out the stirring polymerization in the presence of the dispersant or dispersion aid. These dispersants and dispersion aids are generally removed from polymer particles by post-treatments such as dehydration and water washing after polymerization, but these post-treatments are only effective on the surface of polymer particles. , it has almost no effect on dispersants and dispersion aids taken into the inside of the polymer particles, and additives taken into the inside of the polymer particles,
As a result, it remains in the product as it is after undergoing various post-processing steps.

Therefore, compared to polymers obtained by bulk polymerization, polymers obtained by suspension polymerization are less transparent when using poorly soluble inorganic compounds as dispersants. Moreover, when a water-soluble polymer is used as a dispersant, the hue deteriorates significantly due to thermal deterioration of the water-soluble polymer.

Further, suspension polymerization is a method in which a liquid polymerizable monomer is dispersed in droplets in an aqueous medium, and a polymerization reaction proceeds in the droplets. During the reaction, the droplets are constantly dispersed and coalesced by mechanical stirring, and during this process, it can be said that impurities such as dispersants and dispensing aids have the opportunity to be incorporated into the particles. . As the polymerization reaction progresses, the viscosity of the droplets increases and the frequency of coalescence increases, but during this process, impurities are incorporated into the particles and are immobilized to a greater degree. Due to these factors, it is widely known that polymer particles obtained by suspension polymerization contain a large amount of impurities, and it is generally believed that this is an unavoidable phenomenon. No attempt was made to reduce contaminants in a targeted manner.

Problems caused by contaminants typified by additives associated with suspension polymerization mixed into polymer particles are also found when using the above-mentioned improved stirring tank. However, as a result of further research by the present inventors, when using the improved stirring tank described above, the ratio of the circumferential velocity U [mm/sec] of the tip of the stirring blade to the circulation time θ _c [sec] of the fluid in the tank is U/θ. _c
It has been found that there is a correlation between [mm/sec ² ] and the amount of impurities, especially residual additives, incorporated into the polymer particles. Therefore, this value U/θ
The present invention was completed based on the discovery that by controlling _c in the range of 20 to 80 mm/sec ² , it is possible to significantly reduce the amount of impurities remaining in the polymer particles while maintaining a uniform stirring effect. Here, to explain the engineering meaning of U/θ _c in more detail, U is the speed at which the fluid discharged by the rotation of the stirring blade flows in the circumferential direction of the circle drawn by the stirring blade at the tip of the stirring blade,
This value represents the horizontal flow of fluid in the tank. On the other hand, θ _c is the time required for the fluid discharged by the rotation of the stirring blade to rise in the direction of the liquid level in the tank, turn around at the liquid level, descend, and return to the stirring blade again. This value is representative of directional flow. That is, to define U/θ _c is to define the ratio of the reciprocal of the horizontal flow and the vertical flow of the fluid in the tank, and in the present invention, it is possible to control this ratio within a certain range to reduce suspended particles. This is based on the knowledge that it is necessary to ensure uniform dispersion of polymer particles while minimizing the amount of contaminants mixed into the polymer particles. Therefore, the method for producing thermoplastic polymer particles with less impurities according to the present invention has a generally cylindrical overall shape, a stirring blade is provided at the bottom, and the height is 1/2 from the top of the liquid level of the cylindrical portion. When carrying out suspension polymerization in a polymerization tank that does not have a perforated plate below the liquid level,
The ratio U/θ c of the circumferential speed U [mm/sec] at the tip of the stirring blade and the circulation time θ _c [sec _] of the fluid in the tank is 20 to 80 mm/
It is characterized in that the polymerization is carried out under stirring conditions in the range of sec ² .

The present invention will be explained in more detail below.

A preferred example of the polymerization tank used in the present invention has a cross-sectional structure as shown in the attached drawings. That is, in this example, the Foudler-type three-blade stirring blade 1 is provided at the bottom of the tank, and the height H of the liquid level in the cylindrical part of the tank is 1/1.
Two fingered buffles 2 having fingers 3 having a finger length a including the buffle shaft diameter are installed symmetrically in the radial direction on the side closer to the upper liquid level than the buffles 2. Here, the tip of the finger is the static liquid level 4 and the liquid level when the stirring blade is stirred by a drive device such as a motor (hereinafter referred to as the liquid level during stirring) 5.
Instead, always install a buttful with fingers at the bottom. Furthermore, the fingers are prepared and attached so that the ratio (a/D) between the finger length (more precisely, the horizontal length) a and the tank diameter D is 0.15 to 0.38. In the present invention, it is not preferable to install a perforated plate that inhibits flow within the tank.

Ideally, the buttful should be attached directly to the tank wall, but since this makes manufacturing the tank difficult, the buttful shaft is generally inserted from the top of the tank. In this case, with respect to the tank diameter D, the distance between the center of the baffle axis and the tank wall is preferably within a range of 0.15D or less. If it is larger than 0.15D, a dead space will be created between the buttful shaft and the tank wall, which will impair the flow in the tank, which is not preferable. The angle between the finger and the buttful axis is not particularly limited, and although it is shown as an acute angle in the drawing, it may be a right angle, or even an obtuse angle pointing downwards into the finger tank.
In the case of inserting two fingers with fingers into the tank, the fingers may be oriented in the same direction or may be oriented in different directions. The fingers may also be curved or twisted. Further, the number of fingers of the finger-equipped buttful may be one or more as shown in the drawings, and this is synonymous with the fact that the width of the fingers is not particularly limited. Further, although it is preferable that the finger is provided at an angle of 0° to the center of the tank, it is also possible to swing the finger at an angle α of α≦30°. In that case a×
The effects of the present invention cannot be obtained unless the value of cosα is in the range of 0.15 to 0.38.

Next, the ratio of finger length a to tank diameter D is (a/
When D) is less than 0.15, the mixing at the center of the liquid surface is not sufficiently homogeneous, and when it is greater than 0.38, there is a strong tendency for complex vortices to appear on the liquid surface, and on the contrary,
This is undesirable as it results in a lack of uniformity within the tank.

The stirring blade used in the present invention is not particularly limited, provided that it is placed near the bottom of the stirring tank, and other than Foudler blades, for example, paddle-type blades can be used.

In the present invention, when carrying out suspension polymerization using such an apparatus, the U/θ _c value is controlled within the range of 20 to 80. If the U/θ _c value is less than 20, the suspended particles will not be uniformly dispersed and the polymer will become agglomerated. Moreover, if it exceeds 80, the effect of reducing impurities in the polymer particles is poor, so the effect of improving transparency cannot be expected.
The quality is unsatisfactory. To obtain the U/θ _c value, the circumferential speed of the tip of the stirring blade [mm・sec ^-1 ] and the circulation time of the fluid in the tank [sec] are obtained from "Agitator" published by Kagaku Kogyo Co., Ltd. (November 1, 1970). Publication) Formulas described by Yamamoto on pages 21 to 25 and Table 18 on page 1314 of "Chemical Engineering Handbook" edited by the Chemical Engineering Society, published by Maruzen Co., Ltd. (October 25, 1978)
It can be calculated using the following formulas obtained from constants calculated based on 1.

U=1000・d・N θ _c =V/qc qc=N _qc・N・d ³ N _qc =N _qd・[1+0.16 {(D/d) ² −1}] For example, in the case of a Foudler type wing, N _qd = 0.29・(d/D/0.5 ^{) -2.5 ・}(b/D/0
．． 05) In the case of a 4-paddle type wing, N _qd = 0.246・( ^{d/D/0.5) -2.5 ・}(b/D/
0.1) Each symbol here has the following meaning.

V: Tank content capacity [m ³ ] d: Stirring blade diameter [m] N: Rotation speed [sec ^-1 ] qc: Circulation flow rate [m ³・sec ^-1 ] D: Tank diameter [m] b: Stirring blade Width [m] N _qc : Circulation flow rate [-] N _qd : Discharge flow rate [-] n _p : Number of blades [-] When controlling the U/θ _c ratio, for example, set the U/θ _c value to 80 or less. In order to achieve this, any of the following methods may be taken: (1) reducing the rotation speed N, (2) increasing the diameter d of the stirring blades, and (3) increasing the width b of the stirring blades.

Examples of polymerizable monomers that can undergo the suspension polymerization reaction in the present invention include styrene monomers such as styrene, α-methylstyrene, and divinylbenzene, vinyl chloride, acrylonitrile, methyl methacrylate, and vinyl acetate. Their homopolymerization or their copolymerization can be carried out.

Furthermore, the polymerization initiator, suspension stabilizing dispersant, and dispersion aid are not particularly limited, and those suitable for each polymerizable monomer can be selected and used, and plasticizers, molecular weight regulators, etc. There is no problem in using other auxiliaries.

As described above, according to the present invention, it is possible to reduce the amount of impurities mixed into polymer particles while maintaining stable dispersion, and it is possible to obtain polymer particles with excellent transparency and yellowness. . In addition, if the polymer particles obtained in this way, for example polystyrene particles, are impregnated with a blowing agent or a blowing agent is added during polymerization to form expanded styrene beads, the molded product obtained from this will have a smooth and beautiful surface. Become something.

Next, the present invention will be explained using Examples, but the present invention is not limited to the scope of the Examples.

Example 1 A Foudler-type three-blade stirring blade with a stirring blade diameter d of 2000 mm and a blade width b of 200 mm was installed at the bottom of the can, and the horizontal length a of the finger including the full shaft diameter was
The tank diameter D is 2850 mm, and the charging capacity is 2850 mm, in which two fingered buttfuls are inserted radially symmetrically, each having one finger at an angle of 60° with the buttful axis and 0° with respect to the center of the tank. 12,500 liters of pure water and tertiary calcium phosphate in a polymerization can with a V of 25 m ³
Add 62.5Kg and 0.5Kg of sodium lauryl sulfate.
Stirring was carried out at a rotational speed of N33 r.pm. 12,400 liters of styrene and a polymerization initiator were added thereto, and a suspension polymerization reaction was carried out by a conventional method. After the polymerization was completed, the mixture was dehydrated, washed with water, and dried to obtain polystyrene particles.

During this polymerization reaction, U is 1100 mm/sec, θ _c
was 28 sec, and the U/θ _c value was 39 mm/sec ² .

When the amount of calcium contained as a contaminant in the obtained polystyrene particles was treated with hydrochloric acid and a strontium chloride solution and measured by atomic absorption spectrometry at 4227 Å, the amount was found to be extremely small at 6 ppm. After making these polystyrene particles into pellets by a conventional method,
A test piece was prepared by injection molding, and its haze was measured according to JIS K 6714, and it showed excellent transparency of 0.2%.

In addition, the obtained polystyrene particles were sieved and 0.5
After aligning the particles to ~0.8 mm, mix the particles with liquefied propane and liquefied butane at a mixing ratio of 1/1 according to the usual method.
impregnated with liquefied gas. These impregnated polystyrene particles were heated with steam to obtain pre-expanded particles with a bulk factor of approximately 60 times, then filled into a 200 x 120 x 120 mm mold and heated for 1 minute at a steam pressure of 0.7 Kg/cm ² G. A foamed polystyrene molded product was obtained. The surface of this molded product was beautiful with almost no irregularities or voids.

Example 2 Polystyrene particles were obtained in the same manner as in Example 1, except that the stirring blade d was changed to a Foudler-type three-blade with a blade width of 1500 mm and a blade width b of 150 mm, and the rotational speed N was set to 60 rpm.

During this reaction, U is 1500 mm/sec, and θ _c is
19.5 sec, and the U/θ _c value was 77 mm/sec ² .

Calcium content in polystyrene particles is 11ppm
A test piece obtained from these particles in the same manner as in Example 1 had a haze of 0.3% and exhibited excellent transparency.

Comparative Example 1 In Example 1, the rotation speed was N60r.pm, and U
= 2000mm/sec, θ _c = 15.4 sec, U/θ _c value is 130
Polystyrene particles were obtained by carrying out polymerization in the same manner as in Example 1, except that the polymerization reaction was carried out in the following state. The amount of calcium in this item is 22ppm, and the haze level is 0.6%.
The transparency was so poor that even the naked eye could feel it being slightly cloudy.

In addition, when the obtained polystyrene particles were processed in the same manner as in Example 1 to obtain a foamed polystyrene molded product, the surface of this molded product had some particles that were shaped like fish scales and had many irregularities and voids. .

Comparative Example 2 In Example 2, the rotation speed was N90r.pm, and U
Polystyrene particles were obtained by carrying out polymerization in the same manner as in Example ² , except that the polymerization reaction was carried out in a state where θ _{c =2250, θ c} =13 sec, and a U/θ _c value of 173 mm/sec 2 . The amount of calcium in this item is 28 ppm, and the haze level is 0.6%.
As in Comparative Example 1, the molded test piece was perceived to be cloudy even to the naked eye.

Example 3 Polystyrene particles were obtained by polymerization in the same manner as in Example 1, except that 20 kg of polyvinyl alcohol was used as a dispersant instead of tertiary calcium phosphate and sodium lauryl sulfate.

The amount of residual polyvinyl alcohol contained in these polystyrene particles was measured by color development using a boric acid solution and iodine using visible spectrum absorption at 660 nm.
The amount was extremely small at 2 ppm.

After making these polystyrene particles into pellets using a conventional method, test pieces were prepared by injection molding, and JIS
When the yellowness was measured using a color difference meter according to K 7103, it was 1.1, and the yellowness was hardly perceptible to the naked eye.

Comparative Example 3 In Example 3, the rotation speed is 65 r.pm, and U = 2170
mm/sec, θ _c = 14.2 sec, U/θ _c value 153 mm/sec ²
Polystyrene particles were obtained in the same manner except that the polymerization reaction was carried out in the following conditions. When the amount of residual polyvinyl alcohol in this product was measured, it was 40 ppm. The yellowness of the injection molded test piece was 2.5, which gave it a bright yellow tint to the naked eye.

Example 4 A tank with a diameter of 1400 mm, equipped with a paddle-type 4-blade stirring blade with a stirring blade diameter of d800 mm and a blade width of 120 mm at the bottom of the can.
Put 2700 liters of pure water, 1300 liters of methyl methacrylate monomer, 13.5 kg of tribasic calcium phosphate, and 80 g of sodium dodecylbenzenesulfonate into a polymerization can with a charging capacity of 4 m ³ , then add a polymerization initiator and suspend using the usual method. A polymerization reaction was carried out to obtain polymethyl methacrylate particles. During polymerization, the blade stirs at 50 rpm, at which time U is 1200 mm/sec, θ _c is 26 sec, and U/
The θ _c value was 51.5 mm/sec ² .

When the amount of calcium contained in polymethyl methacrylate particles was measured in the same manner as in Example 1,
The amount was extremely small at 8 ppm. An injection molded test piece was prepared in the same manner as in Example 1, and the degree of haze was measured, and it was found to have excellent transparency of 0.2%.

Comparative Example 4 In Example 4, the rotation speed is N90r.pm, and U=2270
Polymethyl methacrylate particles were obtained by carrying out the same procedure except that the polymerization reaction was carried out in mm/sec, θ _c =13.7 sec, and U/θ _c value of 167. The amount of calcium contained in this material was 28 ppm, and the degree of haze was 0.7%, so that it was slightly cloudy even to the naked eye, and its transparency was poor.

Comparative Example 5 In Example 1, the rotation speed N is 20r.pm, and U=
Polymerization was carried out in the same manner except that the conditions were 670 mm/sec, θ _c = 46 sec, and U/θ _c of 14.5, but when the polymerization rate reached approximately 45%, the dispersion disappeared and the polymer has become a baby boom.

Example 5 In Example 1, the rotation speed was N25r.pm, and U
Polystyrene particles were obtained by carrying out polymerization in the same manner as in Example 1, except that the polymerization was carried out under the conditions of =830 mm/sec, θ _c =37 sec, and U/θ _c =22. The amount of calcium in this product was 8 ppm, and the degree of haze was 0.3%, showing extremely excellent transparency.

Furthermore, when the obtained polystyrene particles were treated in the same manner as in Example 1 to obtain a foamed polystyrene molded product, the surface of the molded product was beautiful with almost no irregularities or voids.

Comparative Example 6 In Example 1, the rotation speed was N50r.pm, and U
Polystyrene particles were obtained by carrying out polymerization in the same manner as in Example 1, except that the polymerization was carried out under the conditions of =1670 mm/sec, θ _c =18.5 sec, and U/θ _c =90. The amount of calcium in this product was 20 ppm, and the degree of haze was 0.5%, making it slightly cloudy to the naked eye.

Further, when the obtained polystyrene particles were treated in the same manner as in Example 1 to obtain a foamed polystyrene molded product, the surface of this molded product had many irregularities and voids, although no fish scale-like shiny particles were observed.

Example 6 A Foudler-type three-blade stirring blade with a stirring blade diameter d of 450 mm and a blade width b of 50 mm was installed at the bottom of the can, and the horizontal length a of the finger including the full shaft diameter was 17 mm.
The tank diameter D is 600 mm and the charging capacity V is a tank in which two fingered buttfuls each having one finger at an angle of 60° with the buttful axis and 0° with respect to the center of the tank are inserted symmetrically in the radial direction. into a 0.2 m ³ polymerization can, 103 liters of pure water, and tribasic calcium phosphate.
500 g of sodium dodecylbenzenesulfonate and 2 g of sodium dodecylbenzenesulfonate were added thereto, and the mixture was stirred at a rotation speed of N80 rpm. Here is 49.5Kg of methyl methacrylate and 40.5Kg of styrene.
(total of 97 liters) and a polymerization initiator were added, and a suspension polymerization reaction was carried out according to a conventional method. After the polymerization was completed, the mixture was dehydrated, washed with water, and dried to obtain MS resin particles.

During this reaction, U is 600 mm/sec, and θ _c is
8.3sec, and the U/ _θc value was 72mm/ ^sec2 .

When the amount of calcium contained as a contaminant in the obtained MS resin particles was measured in the same manner as in Example 1, it was found to be an extremely small amount of 9 ppm. In addition, the pellets were formed into pellets using a conventional method and then molded, and the degree of haze was measured in the same manner as in Example 1.
It showed extremely high transparency at 0.2%.

Comparative Example 7 MS resin particles were obtained in the same manner as in Example 6 except that the rotation speed was N100 r.pm.

During this reaction, U is 750 mm/sec, and θ _c is
6.7sec, and the U/ _θc value was 112mm/ ^sec2 . The amount of calcium in the particles was 27 ppm, and the degree of haze was 0.6%, which was visible to the naked eye, and the industrial value of the particles was lost.

Comparative Example 8 In Example 1, two fingers with horizontal finger length a of 360 mm, an angle of 60° with the buttful axis, and 6 fingers with an angle of 0° with respect to the tank center were inserted symmetrically in the radial direction. Polystyrene particles were obtained by carrying out polymerization in the same manner except for the above. The U/θ _c value is the same as in Example 1.

The amount of calcium as a contaminant was 35 ppm, and the degree of haze was 0.6%, showing white turbidity. Further, when a foamed polystyrene molded product was obtained in the same manner as in Example 1, the surface of the molded product had many particles that shone in a fish scale shape, and had many irregularities and voids.

[Brief explanation of the drawing]

The drawing is a cross-sectional view of a stirring tank suitable for implementing the present invention. 1... Stirring blade, 2... Batsuful with fingers,
3...Finger, 4...Static liquid level, 5...Liquid level during stirring, D...Tank diameter, H...Liquid level in tank height of cylindrical part, a...Finger length.

Claims (1)

[Claims] 1. A finger whose overall shape is approximately cylindrical, has a stirring blade at its bottom, and has one finger at a height within 1/2 from the top of the liquid level of the cylindrical portion. When carrying out suspension polymerization in a polymerization tank that is equipped with a perforated plate and does not have a perforated plate below the liquid surface, the circumferential speed of the stirring blade tip U [mm/sec] and the circulation time of the fluid in the tank θ _c [ sec] ratio U/θ _c is 20 to 80
A method for producing thermoplastic polymer particles with less impurities, characterized by carrying out polymerization under stirring conditions in the range of mm/sec ² .