JPH09155174A - Liquid stirring apparatus and production of polycarbonate using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a stirring apparatus preventing the vent-up in the vicinity of a vacuum suction port and having self-cleaning properties and to continuously advance melt polymerization. SOLUTION: A stirring apparatus having self-cleaning properties is equipped with a plurality of rotary shafts rotationally driven in synchronous relation to a vacuum container having a cocoon-shaped cross section and a plurality of the stirring rotors fixed to the respective rotary shafts and the respective stirring rotors are attached so as to leave an interval in an axial direction. In this case, the inner diameter of the vacuum suction port formed to the vacuum container is set to 115-250% of the dimension of each stirring rotor looked from the vacuum suction port when one stirring rotor passes (1) and the position of the vacuum suction port is selected within a range of 45 deg. left and right from the part just above left-hand rotation on the left-hand cylindrical shell of the container when rotation is counterclockwise looking from the mirror plate on the liquid supply side of the vacuum container.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a novel stirring device. More specifically, the present invention relates to a stirring device for a liquid material having a self-cleaning function, which prevents venting up which is a problem in stirring under reduced pressure in a conventional device.
The present invention also relates to a method for efficiently producing an aromatic polycarbonate by using this stirring device.

[0002]

2. Description of the Related Art Generally, as a synthetic polymer production apparatus, for example, a melt polymerization apparatus, high mixing performance and heat transfer performance,
Further, a stirring device having a function of positively preventing polymer retention, that is, a self-cleaning function is often desired.

Particularly, in order to produce an aromatic polycarbonate which is often used in optical applications, a self-cleaning mechanism in a stirring device is extremely important in terms of polymer quality.

Therefore, conventionally, a stirring device having a self-cleaning function has been proposed for treating a viscous substance having a particularly strong adhesive property, for example, an aromatic polycarbonate melt.

The stirring device having such a self-cleaning function is provided with two or more rotating shafts in the container, and the stirring rotors attached to them and the stirring rotor and the inner wall of the container are relatively moved while maintaining a slight gap. This is a device that mechanically attempts to prevent the formation of deposits on the inner wall of the container as much as possible, and as a specific device,
For example, a stirrer described in JP-A-63-232828 is known.

That is, the publication discloses a plurality of rotating shafts disposed in a container and driven to rotate in synchronization with each other, and a plurality of stirring rotors (paddles) fixed to the rotating shafts and performing stirring action. In a stirrer provided, the stirring rotors (paddles) are attached at intervals in the axial direction, and a scraper having a length substantially corresponding to the spacings is attached to the rotating shaft at the tip of the stirring rotor (paddle). Those mounted in parallel are disclosed.

The stirring device having such a self-cleaning mechanism is extremely important in terms of polymer quality, especially in melt polymerization of aromatic polycarbonate which is often used for optical applications.

[0008]

In the conventional stirring device of this kind, as a part of the self-cleaning function,
The operation includes applying the liquid held by the stirring rotor to the inner wall surface of the container. However, in the conventional stirring device, when a vacuum suction port is provided in the container and stirring is performed under reduced pressure, the liquid (for example, the polymerization reaction liquid) rises from the vacuum suction port and the vacuum suction port part Because a phenomenon called "vent up" occurs, such as clogging or a film of liquid being formed at the vacuum suction port and the pressure inside the decompression container fluctuates temporarily,
It was not possible to use a highly reactive stirred rotor.

Therefore, in the conventional apparatus, since the stirring rotor having a relatively low stirring ability with almost no possibility of venting up is used, the self-cleaning function has a problem and the reactivity is poor, and therefore the self-cleaning is performed. When compared with a stirring rotor that is rich in properties, a sufficient reaction rate could not be obtained, leading to an increase in the size of an apparatus for manufacturing products and an increase in cost.

The main object of the present invention is to solve the problems such as vent-up in the conventional device, and prevent the vent-up by selecting the inner diameter and position of the vacuum suction port within a specific range. However, it is an object of the present invention to provide an apparatus capable of continuously producing polycarbonate or the like efficiently and at low operating cost while maintaining product quality, and another object of the present invention is to maintain aromatic polycarbonate in its quality. It is an object of the present invention to provide a method for efficiently producing a high-quality polycarbonate by promoting polymerization while continuously melting under the circumstances.

[0011]

The device of the present invention achieves the above-mentioned object. (1) A cylinder having a cross-sectional shape of preferably two cylinders is provided in a decompression container installed substantially horizontally. In a cocoon-type decompression container in which side surfaces are connected to each other, a plurality of rotating shafts that are driven to rotate in synchronization and a plurality of stirring rotors that are fixed to each rotating shaft and perform stirring action are provided, and each stirring rotor is A liquid body having a self-cleaning property is attached to the rotary shaft at intervals in the axial direction thereof, and a scraper having a dimension substantially corresponding to the space is attached to the tip of each stirring rotor in parallel with the rotary shaft. In the stirring device, the inside diameter of the vacuum suction port provided in the decompression container is 115 to 250%, preferably 12 to 250% of the dimension of the stirring rotor seen from above the vacuum suction port when one stirring rotor passes through.
Agitating device for liquid material to prevent venting up by selecting the range of 0 to 225%, (2) Synchronously rotating in a decompression container with a cocoon-shaped cross section installed substantially horizontally. A plurality of driven rotating shafts and a plurality of agitating rotors fixed to the rotating shafts to perform a stirring action are provided, and the agitating rotors are attached to the rotating shafts at intervals in the axial direction thereof. In a stirring device for a liquid material having self-cleaning property, in which a scraper having a length substantially corresponding to the interval is attached in parallel to the rotating shaft at the tip of the vacuum container, the position of the vacuum suction port provided in the vacuum container is set to the vacuum container. When viewed from the end plate of the liquid material supply side of, when the rotation is counterclockwise, the rotation is clockwise on the cylindrical shell on the left side of the container and within the range of 45 ° to the left and right from right above the rotation on the left side. Is On the right side cylindrical shell of the cocoon-shaped container and by selecting within a range of 45 ° from right above the rotation axis on the right side to prevent venting up, a liquid stirring device, and ( 3) A device combining the above (1) and (2), that is, the size of the stirring rotor that is visible from above the vacuum suction port when one stirring rotor passes through the inner diameter of the vacuum suction port.
%, Preferably in the range of 120 to 225%, and when the position of the vacuum suction port is viewed from the end plate of the liquid supply side of the decompression container, when the rotation is counterclockwise, on the cylindrical shell on the left side of the container. And 45 ° to the left and right from right above the left rotation
Vent up is more effective within the range of 45 ° on the right side cylindrical shell of the cocoon container when the rotation is clockwise and right above the right rotation axis. It is a stirrer designed to prevent

In these devices, it is preferable that the liquid supply port to the decompression container is provided on one end plate of the container, and the vacuum suction port is provided on the cylindrical shell on the low viscosity side of the liquid in the decompression container. Those provided in the above are preferable.

Further, in the method of the present invention, a polycarbonate obtained by melt-polymerizing an aromatic dihydroxy compound and a carbonic acid diester is supplied in a molten state to the above-mentioned stirring apparatus of the present invention, and under the reduced pressure in the apparatus. In addition, the method for producing a polycarbonate is characterized in that the polymerization reaction is further carried out by stirring under a reduced pressure of 0.1 to 10 Torr.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION A specific example of a stirring device for a liquid material (hereinafter, simply referred to as "liquid") according to the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a sectional view showing an example of the stirring device of the present invention, FIG. 2 is an enlarged view of the vicinity of the vacuum gas suction port in the device of FIG. 1, seen from directly above, and FIG. 3 is an example of the shape of the stirring rotor. FIG. 4 is a horizontal cross-sectional view showing an example of the stirring device of the present invention seen from a liquid inlet side end plate, and FIGS. 5 and 6 are horizontal cross-sectional views of the stirring device outside the range specified in the present invention. .

In the figure, the decompression container 1 is installed substantially horizontally, and the inner wall of the container 1 has a shape in which two cylindrical walls centering on the rotating shaft 2 and the rotating shaft 3 are connected by a side surface. It has a cocoon-shaped cross section.

Inside the decompression container 1, two rotary shafts 2 and 3 extending substantially horizontally in the lengthwise direction of the container are provided.
These two rotary shafts 2 and 3 are supported by bearings parallel to each other, and each rotary shaft 2 and 3 is driven by a drive source (not shown).
As indicated by arrows in the figure, they are rotationally driven in the same rotational direction and at the same rotational speed in synchronization with each other.

A plurality of stirring rotors are fixed to each of the rotating shafts 2 and 3 at predetermined intervals along a plane orthogonal to the rotating shaft. As shown in FIG. 3, each stirring rotor is formed in a thick plate shape having a spindle-shaped cross section with a bulged central portion and sharpened both ends, and a scraper is provided at its tip, but the shape can be appropriately selected. Further, the number of stirring rotors fixed to each rotating shaft can be appropriately selected, but it is suitable to dispose the stirring rotors substantially uniformly over the entire rotating shafts.

As shown in FIG. 1, the agitating rotors fixed to the respective rotating shafts are separated from each other by a slight gap in accordance with the rotational angle position thereof, and are adjacent to the inner wall of the cylinder of the decompression container 1 or adjacent thereto. Its dimensions are chosen so that it can face a stirring rotor fixed to the rotating shaft.

That is, one rotating shaft 2 is provided with a plurality of stirring rotors 4a, 4b, 4c, ... 5h at predetermined intervals.
Has been fixed. These stirring rotors are attached to the rotating shaft 2 along a plane orthogonal to the rotating shaft 2.
Further, the dimensions of these stirring rotors are selected so that they can face a corresponding stirring rotor fixed to the cylindrical wall of the container 1 or the other rotating shaft 3 with a slight gap depending on the rotational angular position. Has been done.

On the other hand, a plurality of stirring rotors 5a, 5b, 5c, ... 5h are similarly fixed to the rotary shaft 3. Each agitating rotor is located at the same axial position as the agitating rotor corresponding to the corresponding agitating rotor 2, and is attached to the agitating rotor 3 in a phase shifted by 90 degrees with respect to the agitating rotor. Has been.

In each of the stirring rotors, each tip of the stirring rotor can face a cylindrical inner wall of the container 1 or a corresponding stirring rotor with a slight gap depending on the rotational angle position. Furthermore, the side faces are respectively opposed to adjacent stirring rotors with a slight gap in the axial direction. The stirring rotor fixed to the rotating shaft 2 and the stirring rotor fixed to the rotating shaft 3 are located at the same axial position as the counterpart stirring rotor,
Further, they are attached to the rotating shaft in such a manner that their phases are shifted by 90 degrees with respect to the corresponding stirring rotor. Further, the side surfaces of the respective stirring rotors are adjacent to and face the corresponding stirring rotors with a slight gap in the axial direction.

A scraper is provided at the tip of each stirring rotor. The scraper preferably has a horizontal bar portion as shown in FIG. 4 and has a high scraping efficiency, but other shapes are also acceptable.

In the stirrer of FIG. 1, the liquid supply port 8 to the decompression container 1 is provided on one end plate 6. On the other hand, although the liquid outlet 9 is provided in the end plate 7 on the opposite side of the container 1 in FIG. 2, the position is not limited to this position.

In the stirring device of the present invention, the end plate 6 is provided with the liquid supply port 8
In providing the above, it is preferable to specify the position of the liquid supply port 8 within the area projected onto the end plate 6 in a range where both the stirring rotors fixed to both rotation shafts pass through the end plate 6. Here, "the area projected by the range where both the agitating rotors of both rotating shafts pass" means the range where both the agitating rotor of the rotating shaft 2 and the agitating rotor of the rotating shaft 3 pass when viewed from the end plate 6 direction. The area projected on the mirror plate.

By the way, in the conventional stirring device, when a vacuum suction port is provided to reduce the pressure inside the container, if the stirring rotor is configured as an efficient stirring rotor as shown in FIGS. The liquid (molten polymer) scraped up by the horizontal bar portion of the scraper shown in 4 in the figure rises to the vacuum suction port, and the vacuum suction port is clogged.
Alternatively, there is concern about a phenomenon called vent up in which a liquid (polymer) forms a film on the vacuum suction port and the degree of vacuum inside the stirring device fluctuates temporarily, and there is a possibility of such vent up in the past. When the stirrer was used, venting up was suppressed by installing a relatively low efficiency stirring rotor without a scraper (horizontal bar).

In the stirring device of the present invention, the size (inner diameter) of the vacuum suction port 10 and its mounting position are selected as follows,
The greatest feature of this is to prevent venting up, and it is also possible to use it in a stirring rotor having a horizontal bar 13 shown in FIGS.

(A) Dimensions of Vacuum Suction Port (Inner Diameter) 115 to 250% of the dimensions of the stirring rotor seen from above the vacuum suction port when one stirring rotor passes through the inner diameter of the vacuum suction port 10 of the decompression container 1. , Preferably 120-22
5%. Here, the "dimension of the stirring rotor seen from above the vacuum suction port" means the dimension y of the rotor (including scraper) in the direction of the rotation axis of the portion of the stirring rotor seen from directly above the vacuum suction port, as shown in FIG. In the present invention, the inner diameter x of the vacuum suction port is 115 with respect to the dimension y.
To 250%, preferably 120 to 225%. In this way, by selecting the ratio (x / y) of the dimensions of the inner diameter of the vacuum suction port and the stirring rotor located under the vacuum suction port within the above specific range, vent up can be prevented.

That is, if the inner diameter of the vacuum suction port in FIG. 2 is x and the size of the horizontal bar seen from the vacuum suction port is y, then when y = 1.00, x ≧ 1.15 If designed, vent up hardly occurs and x <
In the case of 1.15, vent up is likely to occur.

(B) Position of vacuum suction port When the position of the vacuum suction port 10 of the decompression container 1 is viewed from the end plate 6 of the liquid supply side of the decompression container having a cocoon-shaped cross section, the rotation is counterclockwise. On the cylindrical shell on the left side of the container and within the range of 45 ° from right above the rotary shaft on the left side, when the rotation is clockwise, on the cylindrical shell on the right side of the cocoon-shaped container and on the rotary shaft on the right side. Within 45 ° from right above to the left and right.

FIG. 4 shows this state. When the rotating shaft and the stirring rotor rotate in the clockwise direction, it is on the right cylindrical shell of the cocoon-shaped container and right and left from right above the right rotating shaft. The vacuum suction port 10 is opened in the range of, preferably right above.

That is, when viewed from the end plate on the supply side of the container, the cylinder on the left side of the cocoon-shaped container when the rotation is counterclockwise and the cylinder on the right side of the cocoon-shaped container when the rotation is clockwise are Since the amount of retained polymer is small, the amount of polymer retained on the horizontal bar of the stirring rotor is also small.
As shown in FIG. 4, the position of the vacuum suction port 10 is such that when the rotation is counterclockwise as viewed from the end plate on the liquid supply side of the container, the rotation on the left side is on the cylindrical shell 12 on the left side of the cocoon-shaped container. Within 45 ° from right above the axis to 45 ° to the left and right from the right rotation axis on the cylindrical shell 11 on the right side of the cocoon container when the rotation is clockwise. Attaching is an effective means for preventing vent-up.

On the other hand, as shown in FIG. 5, when the vacuum suction port is rotated clockwise as viewed from the end plate on the liquid supply side of the container, the vacuum suction port is on the left cylindrical shell of the cocoon-shaped container and on the left side. When it is installed right above the rotation axis, there is a large amount of polymer retention, which causes vent up, and as shown in FIG. 6, the rotation is clockwise when viewed from the end plate on the liquid supply side of the container. When the cocoon-shaped container is installed on the right cylindrical shell and on the vertical tangent extension of the right cylindrical shell, the reaction liquid adheres to the edge of the nozzle of the vacuum suction port although the possibility of venting up is low. Therefore, it was confirmed that a deteriorated product such as a polymer is generated and the product quality is deteriorated.

(C) Combination of both In the stirrer of the present invention, it is preferable that both of the above (A) and (B) are satisfied, and by combination of both, vent up is almost completely prevented. It becomes possible.

The fact that vent up is reduced by selecting the position and the inner diameter of the vacuum suction port provided in the decompression container in a specific range is not known at all in the past, and was found for the first time by the present inventor. This is new knowledge.

The present invention includes a method for producing a polycarbonate, characterized in that the polycarbonate obtained by melt-polymerizing an aromatic dihydroxy compound and a carbonic acid diester is melt-polymerized under reduced pressure with the above stirring device. .

Examples of the aromatic dihydroxy compound include 2,2-bis (4-hydroxyphenyl) propane, 2,2-bis (4-hydroxyphenyl) butane,
2,2-bis (4-hydroxyphenyl) octane, bis (4-hydroxyphenyl) phenylmethane, 2,2
Bis (hydroxyaryl) alkanes such as -bis (4-hydroxy-3-methylphenyl) propane and 1,1-bis (4-hydroxy-t-butylphenyl) propane, 1,1-bis (4-hydroxyphenyl) ) Cyclopentane, bis (hydroxyaryl) cycloalkanes such as 1,1-bis (hydroxyphenyl) cyclohexane, dihydroxyaryl ethers such as 4,4′-dihydroxydiphenyl ether, 4,4′-dihydroxydiphenyl sulfide, etc. Dihydroxyaryl sulfides, dihydroxyaryl sulfoxides such as 4,4′-dihydroxydiphenyl sulfoxide, 4,
Dihydroxyaryl sulfones such as 4′-dihydroxydiphenyl sulfone are used. Among them, 2-
Bis (4-hydroxyphenyl) propane [commonly called bisphenol A] is preferable.

On the other hand, examples of the carbonic acid diester include optionally substituted esters such as aryl groups having 6 to 10 carbon atoms and aralkyl groups. Specific examples include diphenyl carbonate, ditolyl carbonate, bis (chlorophenyl) carbonate, m-cresyl carbonate, dinaphthyl carbonate, bis (diphenyl) carbonate and the like.

The melt polymerization reaction of an aromatic dihydroxy compound and a carbonic acid diester is carried out by distilling an aromatic monohydroxy compound produced by stirring while heating in an inert gas atmosphere as is conventionally known. Be seen. The reaction temperature is usually in the range of 120 to 350 ° C., and in the latter stage of the reaction, the degree of vacuum of the system is increased to 0.1 to 10 Torr to facilitate the distilling of the aromatic monohydroxy compound produced, and the intrinsic viscosity [η ] Of about 0.2 to 0.35 is obtained. Here, the intrinsic viscosity [η] is 0.7 g / dl
Was measured with a Ubbelohde viscometer.

In the method of the present invention, the intrinsic viscosity [η], which is a melt viscosity of about several thousand poise, is 0.2 to
About 0.35 of polycarbonate is supplied to the above stirring device in a molten state, and stirring and mixing are further continued in the device to continuously advance the polymerization reaction to obtain 20,000 to 3
The degree of polymerization is increased to a melt viscosity of 10,000 poise, and an aromatic polycarbonate having a good optical property [η] of about 0.3 to 0.7 is produced.

In this latter polymerization step, the reaction temperature (set temperature in the stirring container) is 120 to 350 ° C., preferably 17
The temperature is 0 to 300 ° C., the pressure is 0.1 to 10 Torr, preferably 0.1 to 1 Torr, and the reaction time (residence time in the apparatus) is preferably about 30 to 120 minutes.

[0042]

As described above in detail, according to the stirring device of the present invention, it is possible to efficiently self-clean the entire container, and there is a problem with the stirring device having the conventional self-cleaning property. It is possible to effectively prevent the up-venting. Therefore, there is a remarkable effect that the polymer or the like can be continuously and stably manufactured while maintaining the quality without increasing the operating cost.

The stirring apparatus of the present invention is particularly useful when an aromatic polycarbonate is produced by a melt polymerization method and is suitable for use in the latter stage of the polymerization, but polyethylene terephthalate, polyethylene-2,6-naphthalate, etc. It can also be used for melt polymerization of other polymers.

[0044]

EXAMPLES Next, an example of producing a polycarbonate by the melt polymerization method using the apparatus of the present invention will be described in detail.

Example 1 Polycarbonate having an intrinsic viscosity [η] of 0.35 obtained by melt-polymerizing bisphenol A and diphenyl carbonate was agitated in a molten state with a stirring rotor diameter of 230 mmφ shown in FIG. Supplied to the device. In this device, as shown in FIG.
A liquid supply port 8 is installed at the midpoint of a line connecting the axes of the rotary shafts 2 and 3, and the molten polycarbonate is continuously fed into the stirring device from here, and the pressure is 1 Torr and the temperature is 270.
The latter-stage melt polymerization reaction was allowed to proceed under the conditions of ° C and a residence time of 1 hour.

At this time, the vacuum suction port 10 was provided at the position shown in FIG. 4, the inner diameter (x) was 125 mmφ, and the dimension (y) of the stirring rotor under the vacuum suction port was 100 mmφ (hence x / y = 125%).

Then, the polymer liquid after the completion of the reaction was continuously taken out from the liquid outlet 9 provided on the mirror plate 7 on the opposite side to carry out the late polymerization reaction, and the final intrinsic viscosity [η] was 0.5. It was possible to stably and continuously produce a polycarbonate having a good hue for about 700 hours without venting up.

After the completion of the above experiment, the inside of the container of the stirring apparatus was disassembled and inspected, and the stirring rotor was confirmed. It was also confirmed that there was no stain such as polymer deterioration and that a good self-cleaning function was maintained. .

[Brief description of the drawings]

FIG. 1 is a vertical cross-sectional view showing a specific example of a stirring device of the present invention.

FIG. 2 is an enlarged view of the vicinity of a vacuum suction port of the stirring device of the present invention.

FIG. 3 is a schematic view showing an example of a stirring rotor of the stirring device of the present invention.

FIG. 4 is a transverse cross-sectional view of the stirring device according to the present invention as viewed from the direction of the liquid supply port side end plate.

FIG. 5 is a cross-sectional view of a stirring device outside the scope of the present invention (comparative example).

FIG. 6 is a cross-sectional view of a stirring device outside the scope of the present invention (comparative example).

[Explanation of symbols]

 1: Decompression container 2,3: Rotating shafts 4a to 4h: Agitation rotor fixed to the rotating shaft 2 5a to 5h: Agitation rotor fixed to the rotating shaft 3,6: End plate of the decompression container 8: Liquid supply to the decompression container Port 9: Liquid outlet from decompression container 10: Vacuum suction port 11: Cylindrical shell on stirring shaft rotation direction side 12: Cylindrical shell on the opposite side of stirring shaft rotation direction 13: Horizontal bar x: Vacuum suction port inner diameter y: Vacuum Dimensions of stirring rotor visible from the suction port

Claims (8)

[Claims] 1. A decompression container that is installed substantially horizontally is provided with a plurality of rotating shafts that are rotationally driven in synchronization and a plurality of stirring rotors that are fixed to the respective rotating shafts and that perform stirring action.
Also, each stirring rotor is attached to the rotating shaft at intervals in the axial direction thereof, and a scraper having a dimension substantially equivalent to the spacing is attached to the tip of each stirring rotor in parallel with the rotating shaft. In a liquid stirring device having a vacuum suction port provided in the decompression container, the inner diameter of the vacuum suction port is 115 to 250, which is the size of the stirring rotor seen from the vacuum suction port when one stirring rotor passes through.
A stirrer for liquid material that prevents venting up by setting the range to%. 2. The stirring device according to claim 1, wherein the cross-sectional shape of the decompression container is a cocoon type in which two cylinders are connected by side surfaces. 3. A plurality of rotating shafts that are rotationally driven in synchronization with each other and a plurality of stirring rotors that are fixed to the rotating shafts and perform stirring action in a decompression container having a cocoon-shaped cross section that is installed substantially horizontally. And each of the stirring rotors is attached to the rotating shaft at intervals in the axial direction thereof, and a scraper having a length substantially corresponding to the spacing is attached to the tip of each stirring rotor in parallel with the rotating shaft. In the liquid material agitator having self-cleaning property, the position of the vacuum suction port provided in the decompression container is viewed from the end plate on the liquid material supply side of the decompression container, and when the rotation is counterclockwise, the cylinder on the left side of the container Within the range of 45 ° to the left and right of the shell on the left side of the rotation, and on the right side of the cocoon-shaped container on the cylindrical shell when the rotation is clockwise, to the left and right of the rotation axis of the right side.
An agitator for a liquid material that prevents venting up by setting it within the range of 5 °. 4. A plurality of rotating shafts that are rotationally driven in synchronization with each other and a plurality of stirring rotors that are fixed to the rotating shafts and perform stirring action in a decompression container having a cocoon-shaped cross section that is installed substantially horizontally. And each of the stirring rotors is attached to the rotating shaft at intervals in the axial direction thereof, and a scraper having a length substantially corresponding to the spacing is attached to the tip of each stirring rotor in parallel with the rotating shaft. In the stirrer having self-cleaning property, the position of the vacuum suction port provided in the decompression container is seen from the end plate of the liquid supply side of the decompression container having a cocoon-shaped cross section, and the rotation of the container is counterclockwise when the rotation is counterclockwise. 4 on the left cylindrical shell and right to left from just above the left rotation
Within the range of 5 °, on the cylindrical shell on the right side of the cocoon-shaped container when the rotation is clockwise, and within the range of 45 ° to the left and right from right above the rotary shaft on the right side, the vacuum suction port 115% to 250% of the size of the stirring rotor seen from the vacuum suction port when one stirring rotor passes through the inner diameter.
A stirring device for a liquid material that prevents venting up by setting the range to. 5. The liquid material stirring apparatus according to claim 1, wherein the liquid material supply port is provided on one end plate of the decompression container. . 6. The liquid material stirring apparatus according to claim 5, wherein a vacuum suction port is provided on the cylindrical shell on the liquid material supply side. 7. A polycarbonate obtained by melt-polymerizing an aromatic dihydroxy compound and a carbonic acid diester is supplied to the stirring device according to any one of claims 1 to 6, and under reduced pressure in the device. A method for producing a polycarbonate, which comprises carrying out a polymerization reaction with stirring. 8. A polycarbonate obtained by melt-polymerizing an aromatic dihydroxy compound and a carbonic acid diester is supplied to the stirring device according to claim 1, and 120 to 350 are supplied in the stirring device. A method for producing a polycarbonate, which comprises stirring at a temperature of ° C under reduced pressure to carry out a polymerization reaction.