JPS62156116A - Production of oxymethylene polymer - Google Patents

Abstract

PURPOSE:To enable continuous production of the titled polymer in high conversion and efficiency, by polymerizing trioxane under a specific condition using a reactor having a cross-section consisting of a pair of mutually overlapped eccentric circles having the same diameter and containing a pair of stirring shafts and elliptical paddles fixed to the shafts. CONSTITUTION:A heating or cooling jacket 4 is attached to the outer wall of a barrel 5 of a reactor having a cross-section consisting of a pair of mutually overlapped eccentric circles having the same diameter. A raw material feeding port 1 and a product delivery port 2 are attached to both ends of the barrel. A pair of horizontal stirring shafts 3 are inserted in the barrel and paddles 6 having elliptical cross-sections are fixed to the shafts.One of the paddles is placed opposite to one of the other row of paddles and is shaped to be rotatable keeping a small clearance between the tip end of the paddle and the inner wall of the barrel and the opposite paddle. The longitudinal arrangement of the paddles on the stirring shaft is selected to give >=10% filling ratio of retaining polymer when a liquid mixture containing <=50mol% trioxane is continuously supplied through the raw material feeding port 1 and (co)polymerizied. Trioxane is polymerized in the above reactor.

Description

Detailed Description of the Invention a. Industrial Field of Application The present invention involves the production of polyacetal polymers or copolymers by homopolymerizing or copolymerizing trioxane by a continuous polymerization method, more specifically a so-called bulk polymerization method. Regarding the method.

b. Prior Art Several methods and apparatuses have been proposed for bulk continuous polymerization of trioxane. For example, Japanese Patent Publication No. 47-629 has a pair of parallel shafts inside the case, each of which has a number of mutually interlocking oval paddles, and the long axis end of each paddle is connected to the corresponding shaft. It has been proposed to use a twin-screw reactor with flattened ends that interlock with the surface of the paddle.

In the above method, if the paddle arrangement is inappropriate, for example, if the amount of polymer retained in the reactor is small, the polymerization conversion rate will hardly increase, or if the amount of retained polymer is excessive, the reactor will torque out. However, the stirring shaft inside the reactor became unable to rotate due to overload.

In order to overcome this defect, in Japanese Patent Publication No. 57-44690, two or more reactors are connected in series, and a polymerization product with a polymerization conversion rate of 40 to 60% is pumped into powder from the outlet of the first reactor. A method has been proposed in which the polymerization conversion rate is further increased by taking out the polymer as a body and using a subsequent reactor.

However, the above method requires two or more reactors, and from an industrial perspective, it is desirable to obtain a polymer with a sufficient polymerization conversion rate using one reactor, which poses a practical problem. .

C8 Problems to be Solved by the Invention The purpose of the present invention is to increase the amount of polymer retained in the reactor, maintain a high final polymerization conversion rate, and prevent the reactor from torque-out.
For example, the object of the present invention is to provide a method that can produce an oxymethylene polymer or copolymer even in one reactor without causing the stirring shaft in the reactor to become unrotatable due to load.

A means for solving the d0 problem, that is, the present invention, has a heating or cooling jacket on the outside of the reactor body, the cross section of which has the shape of two overlapping eccentric concentric circles, and the reactor side Each end is equipped with a raw material supply port and a polymerization product discharge port, and inside thereof is a pair of horizontal stirring shafts and a plurality of paddles fixed to the stirring shafts, and the paddles are arranged in the longitudinal direction of the stirring shafts. is elliptical in cross-section in the direction perpendicular to the , one paddle faces one of the other paddles fixed to the other stirring shaft, and one paddle has its tip slightly connected to the inner surface of the barrel and the opposing paddle. The paddles have a shape that rotates while maintaining a sufficient clearance, and the arrangement of the paddles in the longitudinal direction of the stirring shaft is at least 5 points from the raw material supply port.
Each paddle is combined so that when a liquid raw material mixture containing 0 mol% or more of trioxane is added and continuously polymerized or copolymerized, the filling rate of the polymer product that stays inside the reactor is 10% or more. The present invention provides a method for producing an oxymethylene polymer, which is characterized by using a continuous stirring reactor comprising:

In the bulk polymerization of trioxane, the present invention uses a suitable combination of paddles to increase the filling rate of the polymer product in the reactor and to distribute the polymer product as uniformly as possible in the reactor, thereby achieving a relatively low L This is a method in which an oxymethylene polymer or copolymer can be obtained at a sufficient polymerization conversion rate even with a reactor having a small /D and without torque-out.

In other words, in the bulk polymerization of trioxane, when a catalyst is added to molten trioxane, or trioxane containing a comonomer in some cases, the polymer product precipitates out extremely quickly with heat generation and turns into a slurry. solidifies. Even at this solidified stage, the polymerization conversion rate is 30~
In order to obtain an oxymethylene polymer or copolymer with a polymerization conversion of about 60% and 90% or more, it is necessary to further continue the polymerization in a solid state. Therefore, it is necessary to retain as much of the polymer product as possible in the reactor and react at a high filling rate.

However, even at a high filling rate, there is a risk of torque-out of the reactor if the polymer is significantly unevenly distributed in one part. Therefore, it is preferable not only to simply increase the retention amount, but also to distribute the reaction mixture as uniformly within the reactor as possible.

Bulk polymerization of trioxane is a relatively fast polymerization reaction, but requires a residence time of at least 10 minutes to carry out the polymerization at a sufficiently high polymerization conversion rate. When the flow rate of the reaction mixture is constant, the residence time increases in proportion to the amount of polymer retained in the reactor. Therefore, by performing polymerization at a high filling rate, an oxymethylene polymer or copolymer with a high polymerization conversion rate and a high molecular weight can be obtained.

-IilQ The residence time of the polymer mixture in the reactor is the value obtained by dividing the weight of the polymer mixture staying in the reactor by the flow rate of the reaction mixture. Therefore, if the flow rate is constant,
The filling factor increases and the residence time increases proportionately.

That is, when the flow rate is constant, a polymer can be obtained at a high polymerization conversion rate by increasing the filling rate within a range that does not cause torque-out and performing polymerization with a long residence time.

Furthermore, even if the combination of paddles in the reactor is constant, as the flow rate of the reaction mixture increases, the filling rate increases, but in this case, the residence time does not necessarily increase.

At a higher flow rate, polymerization can be carried out at a high polymerization conversion rate by carrying out the polymerization using a combination of paddles that can provide a sufficient residence time at a higher filling rate. However, depending on the paddle combination, the increase in flow rate can cause significant uneven retention of polymer, leading to reactor torque-out.

Therefore, there is a favorable combination of conditions among the residence time of the polymer mixture in the reactor, polymerization conversion rate, and filling rate, and when these three conditions are satisfied, a uniform polymer can be efficiently produced. be able to. As for this preferred condition, the residence time of the polymer mixture is preferably 5 minutes or more, more preferably 8 to 30 minutes, particularly preferably 1
It is 0 to 25 minutes. Further, the polymerization conversion rate is preferably 80
% or more, more preferably 85-99%, particularly preferably 90-99%, and the filling rate of the polymer mixture in the reactor is 10% (volume) or more, preferably 15-40%, even more preferably 20-99%. It is 40%.

The combination of paddles that satisfies the above conditions should be one with the lowest possible feeding capacity, and the combination of feeding paddles and reverse feeding paddles should be such that the polymer product is concentrated in one part of the paddle. Combinations should be avoided as much as possible.

In order to avoid uneven retention of the polymer and obtain a uniform retention distribution, it is preferable to arrange the paddles in the reactor using a combination of paddles shifted by 90° and having a small feeding capacity. Furthermore, if polymerization is to be carried out at a high filling rate while maintaining a uniform retention distribution, the combination of the paddles shifted by 90° as described above and the paddles shifted by 45° to mainly exhibit reverse feed capability is recommended.
Preferably, a combination of offset paddles is arranged.

In particular, a paddle configuration in which paddles are alternately arranged in combinations offset by 90° and combinations offset by 45° is particularly preferred in order to achieve a high filling rate while maintaining a uniform retention distribution.

The reactor in the present invention will be explained with reference to FIGS. 1 and 2.

FIG. 1 shows a longitudinal sectional view of one side of the two-wheel continuous stirring reactor used in the present invention, the other side appearing symmetrically with FIG. In the figure, 1 is a supply port, 2 is a discharge port, 3 is a stirring shaft, and 4
5 is a jacket, 5 is a reactor body, 6 is a paddle fixed to the stirring shaft 3, and 7 is a screw formed on the stirring shaft 3 near the supply port 1 and the discharge port 2.

FIG. 2 shows a schematic cross-sectional view of the inside of the reactor and shows the combination of paddles 6. In Fig. 1, when viewed from the discharge port of the reactor, the combination of paddles adjacent to the supply port side in the longitudinal direction of the stirring shaft is different from the combination shown in Fig. 2 (8). (B) Or, as shown in Figure 2 (D), use a combination in which the stirring shaft is shifted by 45 degrees in the rotating direction or in the opposite direction, and a combination in which it is shifted by 90 degrees as shown in Figure 2 (C). be able to. Among these, the combination of Fig. 2 (A) and (B) is
The combination of (D) and (D) results in reverse feeding. On the other hand, the combination of FIGS. 2('A) and 2(C) shifted by 90' has almost no feeding capacity.

In addition, Figure 3 shows the arrangement of the paddle combinations shown in Figure 2. In the figure, Sc is a screw, and symbols a to d correspond to (^) to (D) in Figure 2, respectively. A set of four paddles can be divided into five or more parts.

Figure 3 (I) shows the sequential combination of abcd.
This is a combination of feed paddles with each paddle offset by 45 degrees. FIG. 3 (II) shows an example in which dcba reverse feed paddles are incorporated in two locations. Also, Figure 3 (III)
Figure 3 (IV) shows a combination of AC paddles shifted by 90° in the second half, and Fig. 3 (IV) shows a combination of AC paddles and alternately short reverse feed consisting of two paddles BA and DC. It is something.

In the present invention, the combinations of the respective paddles shown in FIG. 3 can be used to obtain a sufficient filling rate. At even higher reaction mixture flow rates, the lower feed capacity shown in Figure 3 (I It is preferable to use a reactor combined with paddles. In order to further increase the filling rate, conversion rate and molecular weight, it is necessary to
It is preferable to use the reactor shown in V).

In the present invention, preferred combinations of paddles include the following (1) and/or (2).

■ One or more of the above reverse feed units (4 paddles or more),
More preferably, the paddles have 2 to 3 units (for example, Fig. 3 (■)); (2) The combination of paddles shifted by 90 degrees accounts for 20 to 100% of the total paddles (excluding the screw part), and more preferably 3 units;
0 to 60% (e.g., Figure 3 (III) (■)
) In the present invention, the filling rate is the ratio of the volume of the polymer staying inside the reactor to the total volume of the voids inside the reactor (
(% by volume).

Here, the total volume of the void inside the reactor can be specifically determined by subtracting the volumes of the paddles and screws (including the shaft) from the internal volume of the reactor body.

In addition, the volume of the polymer staying inside the reactor is determined by supplying the raw material at a constant flow rate, performing continuous polymerization, and determining the volume of the polymer remaining in the reactor at steady state B (the total amount of the supplied material and the total amount of the material discharged). It can be determined as the total volume of the polymer remaining in the reactor when the same condition is reached.

As mentioned above, the filling rate is 10% (volume) or more,
Preferably 15-40% (volume), more preferably 2
0 to 40% (volume).

As mentioned above, if the filling rate exceeds 40% or if the polymer is unevenly distributed in a part, there is a risk that the reactor will torque out, while if the filling rate is less than 10%, the polymerization conversion rate will decrease. The reaction mixture is discharged from the reactor while the temperature remains low, and in extreme cases, it flows out in the form of a slurry, making it difficult to efficiently produce an oxymethylene polymer or copolymer using a single reactor.

In order to obtain an oxymethylene polymer or copolymer with a polymerization conversion rate of 90% or more, a reactor having an L/D of 5 to 30, preferably 6 to 10 is used.

Further, it is desirable that the wall thickness of the elliptical paddle that can be used in the present invention be approximately 1720 to 175 times the diameter of the circumscribed circle of the paddle. Furthermore, it is also possible to use a helical type paddle in which each side surface of the tip of the paddle is twisted symmetrically and the side surfaces are rotationally symmetrical about the stirring axis. In other words, a twisted helical type whose side surface pushes the contents to the discharge port by the rotation of the stirring shaft has a greater feeding effect than a normal flat type, and a helical type whose side is twisted in the opposite direction has a large reverse feeding effect. show.

The tip of the paddle may have a circumferential surface, be flat, or have an acute angle, or may be provided with a sharp scraper.

The screws provided at the supply port and the discharge port of the reactor used in the present invention are of a type that engages with each other, and there is a space between the discharge port and the front end of the reactor in order to efficiently extrude the polymer product. A feeding screw may also be provided.

The polymerization reaction temperature is 64 to 150°C, preferably 70 to 8°C.
Control at 0°C.

The present invention is used for homopolymerization or copolymerization of trioxane.

A Lewis acid is used as a polymerization catalyst. Lewis acid is
For example, boron fluoride and boron fluoride diethyl ether complex, boron fluoride organic coordination compounds such as boron fluoride dibutyl ether complex, antimony trichloride, boron trichloride, aluminum trichloride, tin tetrachloride, tin tetrabromide, Titanium chloride, phosphorus pentafluoride, perchloric acid, trifluoromethanesulfonic acid and its anhydride, triphenylmethylhexafluoroantimonate, allyldiazonium hexafluorophosphate, triethyloxonium tetrafluoroborate, molybdenum oxide acetylacetonate, etc. Among these, boron fluoride coordination compounds are preferred, and boron fluoride diethyl ether complexes and boron fluoride dibutyl ether complexes are particularly preferred.

These Lewis acids have a ratio of 1.0% to trioxane in the total feedstock. OXl0-3.1. They are mixed at a ratio of OXl0-' mol % and supplied to the polymerization reactor from the supply port.

The trioxane copolymer used in the present invention contains 0.4 to 40 mol%, preferably 0.4 to 10 mol%, of oxyalkylene units having 2 or more carbon atoms based on trioxane in the oxymethylene main chain. It is something that The cyclic ether or cyclic acetal providing the oxyalkylene unit is, for example, one represented by the following general formula (1).

R+ R2-C-(R5), 1 The cyclic acetal or cyclic ether represented by the above general formula (1) is preferably ethylene oxide, 1,3-dioxolane, diglycol formal, epichlorohydrin, styrene oxide, etc. 1
．． Cyclic formals such as 4-butanediol formal and 1,6-hexanediol formal are preferred. Among these, ethylene oxide and 1,4-butanediol formal are particularly preferred.

The cyclic ether or cyclic acetal is mixed in a proportion of 0.4 to 40 mol%, preferably 0.4 to 10 mol%, based on trioxane.

Further, in the present invention, the molecular weight of polyoxymethylene can also be controlled using a molecular weight regulator such as methylal or orthoformate.

In the present invention, since the heat of polymerization can be efficiently removed and rapid temperature rise can be suppressed, there is no need to use a large amount of polymerization solvent.
It can be used in the following proportions.

Polymerization solvents that can be used in the present invention include aliphatic hydrocarbons such as pentane, hexane, heptane, octane, and cyclohexane, aromatic hydrocarbons such as benzene and toluene, and chlorinated carbonates such as methylene chloride, chloroform, and ethylene dichloride. There is hydrogen.

A polymerization terminator is immediately added to the polymerization product discharged from the discharge port of the polymerization reactor to deactivate the polymerization catalyst.

Polymerization terminators that can be used in the present invention include aqueous solutions containing hydroxides of alkali metals and alkaline earth metals;
Ammonia, amine compounds, quaternary ammonium salts, and tertiary phosphine compounds can be used.

As the above-mentioned amine compound, primary, secondary, and tertiary aliphatic amines, aromatic amines, and petrocyclic amines can be used.

For example, ethylamine, diethylamine, triethylamine, n-butylamine, di-n-butylamine, tri-n-butylamine, aniline, diphenylamine, pyridine, etc. are suitable.

As the tertiary phosphine compound, tri-n-butylphosphine, triethylphosphine, n-butyldiphenylphosphine, triphenylphosphine, etc. can be used.

The polymerization terminator can also be used as a solution in an organic solvent.

After the neutralization treatment, an antioxidant, a heat stabilizer, a lubricant, etc. are added to the polymer, and then stabilization is performed by melt-kneading the polymer at 200° C. using a melt-kneader.

By using the continuous polymerization method of the present invention detailed above,
High quality polyoxymethylene with excellent thermal stability can be efficiently produced.

e. Example The present invention will be explained in detail using the following examples.

In addition, the measured values in Examples and Comparative Examples were based on the following measuring method.

Reduced viscosity: p-chlorophenol/l containing 2% by weight of α-pinene, 1,2.2-tetrachloroethane (1:
1 weight ratio) in solution, polymer concentration 0.5 g/d1.60
Measured at °C.

RV (50): 220°C, 50 minutes under vacuum,
Weight residual rate when a polymerization product is heated. The higher the RV(50), the better the thermal stability of the polymer product. (In the present invention, the target is 99.4% or more) Example 1 Using a reactor having a barrel inner diameter of 200 mm, an L/D of 10, and the paddle combination shown in Fig. 3(n), 3.5 kg/hour of trioxane containing 4 mol% of ethylene oxide and 0.055 mol of boron fluoride di-n
- Butyl ether complex dissolved in 1,2-dichloroethane? The solution was added at a rate of 0.06 mmJ per mole of trioxane. The temperature of the reactor jacket is 70°C
was controlled by. A polymer product with a polymerization conversion rate of 81% was obtained as a powder from the discharge port. This polymer was supplied to a single screw extruder directly connected to the discharge port of the reactor. This -axial extruder has a polymer supply port at one end, a discharge port at the other end, and a polymerization terminator supply port located between the supply port and the discharge port. The outer circumference of the body has a jacket, and the inside is equipped with a single shaft.The shaft is equipped with screws near the supply and discharge ports, and a stirring blade in the middle where the polymerization terminator is added. The rotation of the shaft moves the polymer from the supply port to the discharge port while being stirred. - From the polymerization terminator supply port of the shaft extruder, 10% by weight of tri-n-butylamine in 1,2-dichloroethane? Yong Nya added.

-The reduced viscosity of the polymer discharged from the axial extruder is 2.1a
/g, RV (50) was 96.2 to 96.4%, the polymerization conversion was 90%, and the results were stable for about 5 hours. The amount of polymer that remained in the reactor during polymerization was 1420 g, the bulk specific gravity of the resulting polymer product was 0.8, and the total volume of voids in the reactor was 17 I! The estimated filling rate was 10%.

The polymer thus obtained was heated at 80 to 90°C for 20
m1)g for 30 minutes under reduced pressure to remove unreacted substances.

After adding a stabilizer, the obtained polymer was supplied to a vented twin-screw extruder and stabilized by melt-kneading at 200° C. for about 2 minutes. The reduced viscosity of the stabilized polymer is 2.1a/g
, RV(50) was 99.5%.

Comparative Example 1 Using a reactor having the same size as in Example 1 and having the paddle combination shown in FIG. supplied. The reactor jacket temperature was controlled at 70''C.

A polymer product with a polymerization conversion rate of 67% was obtained from the discharge port, but the powder was in a wet state due to unreacted substances. This polymer was immediately fed to a single screw extruder connected directly to the reactor. However, about 2 hours after the start of polymerization, the polymer polymerized in the single-screw extruder solidified, and the -screw extruder became inoperable.

The reduced viscosity of the polymer discharged from the reactor during 2 hours after the start of polymerization was 0.9-L, and the 3dl/gSRV (50) was 9.
0.3-96.2% T: Unstable tear. Furthermore, after the polymerization was terminated, the amount of polymer 1 that had remained in the reactor was measured and found to be 1360 g, with a filling rate of 8%.

Example 2 Using the same reactor as in Example 1, 9 kg of trioxane containing 4 mol % of ethylene oxide and 0.25 mmol of methylal per 1 mol of trioxane were supplied per hour from the feed port of the reactor at a concentration of 0.2 mol. boron fluoride di-n
A solution of the -butyl ether complex in 1,2-dichloroethane was added in an amount of O,Q6/IJ-T-1 per mole of trioxane. The jacket temperature of the reactor was controlled at 70°C. A polymer with a polymerization conversion rate of 90% was obtained from the discharge port. This polymer was immediately fed into a single screw extruder, stirred and a polymerization terminator was added.

The polymer discharged from the single screw extruder has a reduced viscosity of 1.8 d.
l/g, RV<50) was 96.2 to 96.4%, the polymerization conversion rate was 95%, and it was stably obtained for about 5 hours. The amount of polymer remaining in the reactor during polymerization was 2080 g, and the filling rate was 15%.

The thus obtained polymer was stabilized by removing unreacted substances in the same manner as in Example 1, adding a stabilizer, and melt-kneading it in a twin-screw extruder. The stabilized polymer had a reduced viscosity of 1.3 d1/g and an RV(50) of 99.6%.

Comparative Example 2 Using the same reactor as in Comparative Example 1, the polymerization raw material was supplied from the supply port in the same manner as in Example 2. A slurry-like mixture of polymer and unreacted substances with a polymerization conversion rate of 40% or less flowed out from the discharge port of the reactor. The filling rate was 3%.

Example 3 The same reactor as in Example 1.2 was used, and the paddles were as shown in Figure 3 (I
Using the combination shown in V), 20 kg of trioxane containing 4 mol% of ethylene oxide was supplied per hour from the feed port of the reactor, and boron fluoride di-n at a concentration of 0.2 mol was added.
A solution of the -butyl ether complex in 1,2-dichloroethane was added at a concentration of 0.06 mmol per mole of trioxane. The reactor jacket temperature was controlled at 70°C. A polymer with a polymerization conversion rate of 90% was obtained from the discharge port. This polymer was immediately added to a single screw extruder, stirred and a polymerization terminator was added.

The polymer discharged from the single screw extruder has a reduced viscosity of 2.6 d.
i/g, RV(50) of 96.0 to 96.4%, and a polymerization conversion of 95%, stably obtained for about 5 hours. The amount of polymer remaining in the reactor during polymerization was 3160 g, with a filling rate of 23%. The polymer thus obtained was stabilized by the same treatment as described above, and had a reduced viscosity of 2.6 dl/g, l
? V(50) was 99.6%.

Comparative Example 3 A reactor of the same size as Comparative Example 1.2 was used, the paddles were of the combination shown in Figure 3(n), and the filling rate was 45.
%, trioxane containing 4 mol% of ethylene oxide was supplied from the feed port of the reactor at a rate of 20 kg per hour.
A molar solution of boron fluoride di-n-butyl ether complex in 1,2-dichloroethane was added at a concentration of 0.06 mmol per mole of trioxane. The jacket temperature of the reactor was controlled at 70°C. However, 20 minutes after the start of polymerization, the polymer solidified inside the reactor, and the reactor was torqued out and stopped.

10 Effects of the Invention The present invention provides a continuous polymerization reactor for polyoxymethylene polymers or copolymers, which uses a specific combination of paddles to increase the filling rate of the polymer in the reactor and uniformly distribute the polymer. The polymer can be efficiently and continuously produced at a higher polymerization conversion rate than conventional methods.

[Brief explanation of drawings]

FIG. 1 is a schematic vertical cross-sectional view of a biaxial continuous stirring reactor used in the present invention, and FIG. 2 is a schematic cross-sectional view of the interior of the biaxial continuous stirring reactor. Figures 3 (1) to (IV) are schematic diagrams showing the arrangement of paddle combinations in the reactor, and S
c indicates a screw, and the symbol a % d is (
This corresponds to the paddle combinations A) to (D). 1... Supply port, 2... Discharge port, 3...
- Stirring shaft, 4... Jacket, 5... Reaction body, 6... Paddle, 7... Screw. Figure 3

Claims (5)

[Claims] (1) The reactor has a heating or cooling jacket on the outside of the body, and its cross section has the shape of two overlapping eccentric circles with the same diameter, and there is a raw material supply port and a polymerization product inlet at both ends of the reactor, respectively. The discharge port has a pair of horizontal stirring shafts and a plurality of paddles fixed to the stirring shafts, and the paddles have an elliptical cross section in a direction perpendicular to the longitudinal direction of the stirring shafts, One paddle faces one of the other paddles fixed to the other stirring shaft, and one paddle has a shape that rotates at its tip with a slight clearance between the inner surface of the barrel and the opposing paddle, The arrangement of the stirring shafts of the paddles in the longitudinal direction is such that when a liquid raw material mixture containing at least 50 mol% trioxane is added from the raw material supply port and continuously polymerized or copolymerized, the A method for producing an oxymethylene polymer, comprising using a continuous stirring reactor in which paddles are combined so that the filling rate of the combined product is 10% or more. (2) Claim (1) using a reactor in which paddles are combined so that the filling rate of the polymer staying inside the reactor is 40% to 15% among the combinations of paddles in the reactor. The method described in section. (3) The method according to claim (1), wherein in the reactor, paddles adjacent to each other in the longitudinal direction of the stirring shaft are offset by 90 degrees with respect to the rotational direction of the stirring shaft. (4) In the above reactor, paddles adjacent to each other in the longitudinal direction of the stirring shaft are arranged in combinations in which the paddles are shifted by 90 degrees and in combinations in which the paddles are shifted by 45 degrees with respect to the rotating direction of the stirring shaft. The method described in section. (5) In the above reactor, [1] it has one or more reverse feeding units made up of four paddles shifted by 45 degrees, and/or [2] the combination of paddles shifted by 90 degrees is a combination of all paddles (the screw part is The method according to claim 1, using a reactor having a reaction rate of 20 to 100% of