JPS6356254B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a continuous process for producing polyester. Specifically, the present invention relates to a method for continuously producing a high molecular weight polyester containing alkylene terephthalate units as a main component using a so-called wet wall column that is not equipped with a stirring mechanism or a similar mechanism. Polyesters whose main constituents are alkylene terephthalate units such as ethylene terephthalate and butylene terephthalate are typical polyesters that have a wide range of uses as fibers and molded products. Such polyesters are typically produced by esterifying or transesterifying terephthalic acid or dimethyl terephthalate with ethylene glycol or 1,4-butanediol to obtain bishydroxyalkyl terephthalate or its lower polymer, followed by ethylene glycol or 1,4-butanediol. ,4
- Manufactured by polycondensation reaction that eliminates butanediol until it reaches an intrinsic viscosity depending on the intended use. In addition to terephthalic acid and ethylene glycol or 1,4-butanediol, a third component is sometimes used to improve the dyeability, moisture absorption, flame resistance, etc. of polyester fiber products, and to improve the properties of polyester as a molded product. This is to improve moldability, crystallinity, etc. Therefore, it is necessary to use such a third component within a range that does not impair the original properties of the polyester, and for this purpose, the content of ethylene terephthalate units or butylene terephthalate units in the polyester must not be less than 80 mol%. It is necessary to use it in As is well known, the polycondensation reaction is carried out in the presence of a catalyst at a temperature equal to or higher than the melting point of the polyester. Since the polycondensation reaction is an equilibrium reaction, it is important to promptly remove the generated glycol component from the reaction system. For this purpose, it is customary to carry out polycondensation under reduced pressure with vigorous stirring of the reactants. Industrially, polycondensation reactions are carried out either batchwise or continuously; however, the batchwise method is used for the production of special products and small-scale production, and the continuous method is used for large-scale production. The continuous method is extremely advantageous in terms of the quality and cost of the polyester obtained. Horizontal stirring reactors are widely used as continuous polycondensation reactors around the world. It is said that horizontal stirring reactors require less polycondensation time because they can increase the gas-liquid contact surface compared to vertical stirring tanks used in batchwise systems, but it is still difficult to achieve polycondensation to a specified degree of polymerization. It usually takes 1 to 2 hours. However, since the polycondensation reaction is carried out at a high temperature, many foreign substances are produced due to side reactions, and therefore it is preferable to shorten the reaction time as much as possible. In order to solve this problem, various improvements have been made to the structure of the stirring mechanism, but satisfactory results have not always been obtained. Furthermore, in a horizontal stirring reactor, it is extremely difficult to perform effective stirring to obtain a polyester with a high degree of polymerization and an intrinsic viscosity of 0.8% or more. On the other hand, recently, the following polycondensation method using a vertical stirring device has been attracting attention. That is, this is a method in which the reaction liquid is caused to flow down on the wall surface by gravity, and the surface of the reaction liquid is polycondensed while being renewed by a stirring blade that slides along the wall surface or moves with a small gap between it and the wall surface. In this method, the reaction solution is applied to the wall surface using a stirring blade to form a thin film, so that the glycol component is quickly removed. As a result, a product having a predetermined degree of polymerization can be obtained by polycondensation in a short period of about several minutes to 30 minutes. However, this method also has the following drawbacks. One of them is
The heat generated by stirring is large, and the temperature rises locally, especially at the tip of the stirring blade near the wall, which adversely affects the quality of the polyester product. The other problem is that the reaction liquid droplets generated by stirring remain in the reaction system for a long time while adhering to the stirring shaft, the top of the reaction vessel, etc., and these droplets grow into foreign substances that have a negative impact on the quality of polyester, and then become a product. It is caused by falling into the polyester. It is important that the polyester product has good color tone, but it is also important that it does not contain foreign substances. This is because foreign matter prevents clogging of the filter, reduces operability, and causes frequent breakage of single filaments during drawing. In addition, this is because it causes the formation of fish eyes during film production. Of course, the above-mentioned contamination of foreign substances can be avoided by frequently cleaning the vertical stirring reactor, but this does not come without significantly sacrificing high productivity, which is one of the advantages of this polycondensation method. No. Of course, the above-mentioned problems are not limited to vertical stirring reaction apparatuses, but are unavoidable problems in reaction apparatuses having a stirring mechanism. On the other hand, a method is known in which bishydroxyalkyl terephthalate or a low polymer thereof is supplied to a vertical reactor not equipped with a stirring mechanism, a so-called wet wall column, and allowed to flow down along the wall surface for polycondensation under reduced pressure. (U.S. Patent No. 3192184, Special Publication No. 1973-
(No. 17558, Japanese Patent Publication No. 43-13238) Since there is no stirring mechanism in such a method, it is presumed that the above-mentioned problems do not occur. Furthermore, since this method naturally does not require the energy required for stirring, it can be said to be an advantageous method in this respect as well. However, there are no examples of producing polyester with an intrinsic viscosity higher than 0.5 using this method. For example, US Pat. No. 3,192,184 has an intrinsic viscosity of
The purpose is to produce polyester with an intrinsic viscosity of 0.4 or less, but in reality it has an intrinsic viscosity of 0.09 to 0.32.
The company only manufactures polyester. In addition, the intrinsic viscosity of Tokuko No. 48-17558 is 0.20.
Polyesters up to ~0.40 are produced in this way,
The subsequent polycondensation reaction is not carried out by this method, but is carried out using a horizontal stirring reactor. and Tokko Akira
In No. 43-13238, a polyester with a degree of polymerization of 5 to 50 (a degree of polymerization of 50 corresponds to an intrinsic viscosity of 0.4 to 0.45) was produced by the method described above, and the subsequent polycondensation was carried out by a stirring reaction that facilitated surface renewal. This is done using a device. That is, such a method requires an intrinsic viscosity of 0.5
It was common knowledge that it was effective only in the case of initial polycondensation (prepolycondensation) to produce a so-called prepolymer with a lower concentration. It is presumed that the main reason for this was the fear that as the intrinsic viscosity increases, the melt viscosity also increases, as described in the above patent, resulting in a decrease in operability and surface renewal. The present inventors used a cylindrical wetted wall tower to improve the intrinsic viscosity.
After intensive research in order to industrially advantageously produce high-quality polyester with a value higher than 0.5, it was discovered that polyester polyester can be polycondensed by supplying the raw material polyester to a wet wall tower at a flow rate per specific immersed side length. The invention has been achieved. That is, the gist of the present invention is the general formula () with an intrinsic viscosity of 0.15 to 1.0. (In the formula, R represents an ethylene group or a butylene group) A polymerizable liquid material whose main component is an ester polymer containing 80 mol% or more of units represented by the formula (200≧F≧A×10 ^{- 3} × IV ^- 〓 ...() [In the formula, F indicates the flow rate per immersion length (Kg/m・hr), IV indicates the intrinsic viscosity of the ester polymer in the polymerizable liquid material, A and β are 4.2 and β, respectively, when R is an ethylene group in the general formula ().
5.1 and 2.7 and 4.5 respectively when R is a butylene group] is supplied to a non-stirring cylindrical wetted wall column at a flow rate per soaked side length that satisfies the following numbers: A method for continuous production of polyester, characterized in that the polyester is polycondensed under reduced pressure by flowing the polyester into a polyester having an intrinsic viscosity of more than 0.5. The present invention will be explained in detail below. In the method of the present invention, a polymerizable liquid material whose main component is an ester polymer containing 80 mol% or more of ethylene terephthalate units or butylene terephthalate units with an intrinsic viscosity of 0.15 to 0.8 (hereinafter simply referred to as raw material polyester) is used as a raw material. do. When the intrinsic viscosity is lower than 0.15, the thickness of the film formed on the wall surface is too thin to maintain the film for the time required for the reaction. In addition, a stable fluid state cannot be obtained because the liquid may run out on the wall or some parts may fall. As a result, foreign matter gets mixed into the polyester, making it impossible to obtain high quality polyester. In the present invention, the intrinsic viscosity is measured at 20° C. by dissolving polyester in a mixed solvent of phenol and tetrachloroethane (weight ratio 1:1) according to a conventional method. The raw material polyester can be produced according to a known method, for example, esterification or transesterification of terephthalic acid or dimethyl terephthalate and ethylene glycol or 1,4-butanediol, followed by polycondensation according to a known method if necessary. It can be manufactured by In addition to the above components, polyhydric alcohols such as diethylene glycol and neopentyl glycol; polycarboxylic acids such as isophthalic acid, p-oxybenzoic acid, 5-sodium sulfoisophthalic acid, and trimellitic acid can be used as copolymerization components; The component is the general formula () in the raw material polyester.
It is necessary to use the unit in such a way that the content of the units represented by is not lower than 80 mol%. Also,
In the method of the present invention, the intrinsic viscosity of the raw material polyester may be quite high.
The method of the present invention can also be applied to further increase the intrinsic viscosity of polyester from 0.55 to 0.7. The above-mentioned polyester-based polymerizable materials differ depending on the degree of polymerization of the raw material polyester, but in the case of raw material polyester containing 80 mol% or more of ethylene terephthalate units, butylene is generally produced at 250°C or higher, particularly at 260°C or higher. The unit of terephthalate is
Normally 220 for raw polyester containing 80 mol% or more
It melts and remains in a liquid state at temperatures above ℃ or above, especially above 230℃. Of course, the polymerizable liquid material may contain well-known polycondensation catalysts and additives such as titanium oxide. In the method of the present invention, it is necessary to supply a polymerizable liquid material containing raw material polyester as a main component to the wet wall tower at a flow rate per immersion side length that satisfies the above formula (). The preferred flow rate per immersion length is 200≧F≧5.3×10 ^-3 ×IV ^-5.1 for raw polyester containing 80 mol% or more of ethylene terephthalate units: In the case of polyester, the range satisfies the following: 200≧F≧3.4×10 ⁻³ ×IV ^−4.5 () (wherein F and IV are both synonymous with formula ()). Even if the intrinsic viscosity is 0.15 or more, the effects of the present invention will not be exhibited unless the immersion length flow rate satisfies the above formula (). In other words, if the immersion length flow rate is less than the lower limit of the range shown in () above, the film thickness will be too thin and there will be parts that are not sufficiently wetted by the reaction liquid, resulting in abnormal retention, which may lead to the generation of foreign matter, which is undesirable. . on the other hand,
If the immersion length flow rate exceeds the upper limit (200 Kg/m・hr) of the range shown in () above, the polymerization reaction will not proceed suitably, and it will be difficult to raise the intrinsic viscosity of the obtained polymer to a level exceeding 0.5. It is. In this way, if the flow rate is set to a certain range of immersed side length according to the intrinsic viscosity as shown by the formula (), polyester having a predetermined intrinsic viscosity can be manufactured with good productivity without generating foreign matter. Of course, considering the reaction rate, even within the scope of the present invention, it is more advantageous for the reaction to occur in a region where the immersion length flow rate is relatively small, especially when the prepolymer has a large intrinsic viscosity. However, the present invention focuses on producing high-quality polyester with few foreign substances, and rather excludes areas where the immersion length and flow rate are too small, and from the viewpoint of maximizing the reaction rate. This is based on common knowledge of known technical ideas or common sense regarding operating conditions, that is, "the thinner the film thickness, the better", a technical idea unrelated to the field. Any known method can be used to supply the polymerizable liquid to the wet wall column, such as overflowing the polymerizable liquid from an overflow wall, or supplying it from a distributor, etc. Ru. Here, the flow rate per immersion length is the supply rate (Kg/hr) of the polymerizable liquid divided by the immersion length (m). In addition, the immersed side length is the length of the side of the solid wall in contact with the fluid. For example, in the case of a circular pipe, the immersed side length is πD (D
indicates the inner diameter (m). The polymerizable liquid material supplied to the wet wall column is caused to flow down in a film form along the wall surface, and is polycondensed under reduced pressure. The structure of the wet wall column does not need to be special, and it may be a wet wall column used for operations such as distillation or gas absorption, or a cylindrical vertical reaction type without a stirring mechanism used for the above-mentioned initial polycondensation of polyester. Any equipment can be used. Wetted wall towers with a plurality of wetted wall tubes are commonly used. In the case of a wet wall pipe, its inner diameter will vary depending on the intrinsic viscosity of the raw material polyester and the flow rate per immersed side length, but it is usually sufficient to have an inner diameter of 3 cm or more, especially 5 cm or more. Also,
Wet walls do not need to have smooth surfaces;
It may have a roughened surface, a surface with grooves of a specific shape, or a wire mesh shape. The preferred one is one with a smooth surface. As long as the polymerizable liquid supplied to the wet wall tower is supplied at a flow rate per immersion length that satisfies the above formula (), it flows down in a film form along the wall surface, and the inside of the wet wall tower is under reduced pressure. Then the polycondensation reaction will proceed. The degree of pressure reduction is the same as in normal polycondensation.
200 mmHg or less, preferably 20 mmHg or less, optimally 5 mmHg or less. The polycondensation temperature is also the same as in normal polycondensation, and is 250 for raw polyester containing 80 mol% or more of ethylene terephthalate units.
-320°C, especially 260-300°C, and in the case of raw polyester containing 80 mol% or more of butylene terephthalate units, the temperature is usually in the range of 220-300°C, especially 230-260°C. According to the method of the present invention, polyester can be produced with high productivity even when the polycondensation temperature is low.
In the case of the above raw material polyester, it is advantageous because it can be used industrially even at temperatures in the range of 260 to 290°C. In the method of the present invention, the intrinsic viscosity is higher than 0.5, preferably 0.55 to 1.2, by the method described above.
Optimally, a polyester of 0.6 to 1.0 is produced. Polyester with an intrinsic viscosity higher than 0.5 is generally used in products,
For example, they are provided for use in fibers and molded products. Therefore, the method of the present invention is advantageously applied, for example, to polycondensation of a raw material polyester having an intrinsic viscosity of 0.5 or less to an intrinsic viscosity that is effective as a product. On the other hand, according to the method of the present invention, it is also possible to produce polyesters having a high intrinsic viscosity, for example, 0.8 or more, which were conventionally produced by solid phase polymerization. In this case, the intrinsic viscosity
It is also possible to apply the process according to the invention following a polycondensation step which already provides a product of 0.5 to 0.75. Of course, if there is a large difference in intrinsic viscosity between the raw material polyester and the target polyester, and if this is carried out in a single-stage wet wall tower, the tower length will be significantly long.
It can be suitably multi-staged, for example, 2 to 5 stages, particularly 2 to 3 stages. The method of the present invention will be explained below with reference to the drawings. 1st
The figure is a schematic diagram of an example of a wetted wall column used in the method of the invention. First, a polymerizable liquid material containing raw material polyester as a main component is supplied from the supply nozzle 4 to the distribution supply section 3 at a flow rate per immersed side length that satisfies the above formula (). The distributed liquid flows down along the wall surface of the wet wall tube 1 in the form of a film. In the case shown in the figure, it is a multi-pipe wetted wall tower with a plurality of wetted wall pipes.
Since the inside of the wet wall tower is under reduced pressure, polycondensation of the polymerizable liquid material flowing down in a film along the wall surface progresses. Gases such as glycol components generated at this time are removed from the exhaust pipe 5. The generated intrinsic viscosity is
Polyester higher than 0.5 is discharged from a discharge pipe 7 via a gear pump 6. Heating within the wet wall tower is carried out by a jacket 2. The heating medium is supplied and discharged from the jacket 2 through a nozzle 8. The method of the present invention has been described in detail above, and the method of the present invention has the following advantages. (1) Since the polycondensation is carried out in a cylindrical wet wall tower without a stirring mechanism, the above-mentioned problems do not occur and high quality polyester can be produced. (2) Since there is no stirring mechanism, the polycondensation apparatus can be made smaller. Therefore, construction costs will be lower. (3) High productivity. (4) It is an energy-saving method because no energy is required for stirring. (5) It is possible to manufacture stable polyester with good operability. (6) It is easy to produce polyester with a high intrinsic viscosity, for example, 0.8% or more. (7) Polycondensation can be carried out at lower temperatures than in vertical stirring reactors. Next, the present invention will be explained in more detail with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist thereof. Example 1 Raw material polyester is immersed into a single pipe wetted wall column with an inner diameter of 0.15 mφ and a length of 5.0 m, and the jacket is heated to 260°C. Flow rate per length is 100 Kg/m・hr
The polycondensation reaction was carried out under reduced pressure of 0.5 mmHg.
The raw material polyester was produced by esterification reaction of terephthalic acid and ethylene glycol, followed by the addition of 2 x 10 ^-4 mol of antimony trioxide per 1 mol of terephthalic acid as a catalyst, and the process was carried out in a two-stage complete mixing tank reactor. A material prepolycondensed to an intrinsic viscosity of 0.38 was used. The evaluation results of the produced polyester are shown in Table 1, and it was found that the polyester had a good color tone and an intrinsic viscosity of 0.55, making it suitable for fiber production. Example 2 A raw material polyester with an intrinsic viscosity of 0.47 obtained in the same manner as in Example 1 was put into the wet wall column used in Example 1, in which the jacket was heated to 280°C, at a flow rate of 100 Kg/m・hr per immersion side length. When the polyester was supplied under reduced pressure of 0.5 mmHg and polycondensed, a polyester with an intrinsic viscosity of 0.69 and a good color tone suitable for fiber production was obtained. The variation in intrinsic viscosity of the polyester obtained by carrying out this reaction continuously for 20 days was ±0.008. 20
After 100 days of operation, the polyester remains in a molten state.
When the mixture was flowed at a flow rate of 1,000 mesh wire mesh through an overlayer with an area of 50 cm ² , the pressure increase over time was as good as 1.1 Kg/cm ² ·Day.
Furthermore, when the polymer was formed into a sheet with a thickness of 0.3 cm and the number of foreign particles in the sheet was detected with the naked eye, the number of foreign particles in the sheet was as low as 4 particles/100 cm ² and it was a good polyester. This means that according to the method of the present invention, the entire reaction wall is wetted by the reaction liquid and no abnormal stagnation occurs, so that there are parts of the reaction wall that are not wetted by the reaction liquid as shown in Comparative Example 1. This shows that the number of foreign substances after long-term operation is lower than that of polyester obtained from a horizontal reactor, indicating that polyester of superior quality can be obtained. Comparative Example 1 A raw material polyester having an intrinsic viscosity of 0.46 obtained in the same manner as in Example 1 was prepared using a polyester having an inner diameter of 0.3 and having a disk blade.
The mixture was fed at a rate of 20 Kg/hr to a horizontal stirring reaction tank having a length of 0.7 m and a jacket heated to 280°C, and a polycondensation reaction was carried out under a reduced pressure of 0.5 mmHg. The obtained polyester had an intrinsic viscosity of 0.68 and a slightly yellowish color tone. The number of foreign objects was measured using a 0.3cm thick polyester sheet after 10 days of continuous operation.
43 pieces/100cm ² . When this was filtered in a molten state in the same manner as in Example 2, the pressure increase was 3.2 Kg/cm ² ·Day. This fact indicates that the quality is poorer than that of the polyester produced in Example 2. Example 3 When the molten polyester obtained in Example 2 with an intrinsic viscosity of 0.69 was polycondensed under the same conditions as in Example 2 except that the flow rate per immersion side length was 60 Kg/m・hr, a high intrinsic viscosity of 1.17 was obtained. A polyester with a high degree of polymerization was obtained. This shows that the method of the present invention is also suitable for polycondensation of polyesters with a high degree of polymerization. Example 4 A raw material polyester with an intrinsic viscosity of 0.15 obtained in the same manner as in Example 1 was wetted with a wall tube having an inner diameter of 0.15 mφ and a length of 20
A flow rate of 200 kg/m hr per immersed side length is supplied to a single-tube wet wall tower whose jacket is heated to 280°C.
Polycondensation reaction was carried out under reduced pressure of 0.5 mmHg. The obtained polyester has a good color tone and an intrinsic viscosity of 0.56, and can be used to produce fibers. After 10 days of continuous operation, the number of foreign particles in the sheet was measured with the naked eye using a 0.3 cm thick sheet.
It was good at ^100cm2 . Comparative Example 2 A raw material polyester with an intrinsic viscosity of 0.10 obtained in the same manner as in Example 1 was subjected to a polycondensation reaction under the same conditions as in Example 4, but the amount of distilled ethylene glycol was large and the degree of vacuum reached only 2.0 mmHg. The intrinsic viscosity of the obtained polyester was as low as 0.40. Furthermore, after 5 days of continuous operation, the polyester sheet was made into a 0.3 cm thick sheet, and when the number of foreign particles in the sheet was measured with the naked eye, it was as large as 19 particles/100 cm ² . This fact indicates that if the product is produced under conditions outside the scope of the present invention, a large number of foreign substances will be present, which is undesirable, probably because a part of the reaction wall is not wetted by the reaction liquid and abnormal retention occurs. Example 5 Raw material polyester with an intrinsic viscosity of 0.21 obtained in the same manner as in Example 1 was heated at a flow rate of 40 kg/m per immersion side length.
When the polycondensation reaction was carried out under the same conditions as in Example 2, a polyester having a good color tone and an intrinsic viscosity of 0.59 and capable of producing fibers was obtained. After 10 days of continuous operation, the number of foreign particles was measured with the naked eye using a 0.3 cm thick sheet of polyester, and the number was good at 5 particles/100 cm ² . Comparative Example 3 When a raw material polyester with an intrinsic viscosity of 0.10 obtained in the same manner as in Example 1 was reacted under the same conditions as in Example 5, the degree of vacuum reached only 2.0 mmHg, and the intrinsic viscosity of the obtained polyester was It was as low as 0.29. In addition, the thickness of polyester after 5 days of continuous operation
When the number of foreign particles in the sheet was measured as a 0.3 cm sheet, it was found to be 32 particles/100 cm ² . This fact indicates that production under conditions outside the scope of the present invention is undesirable due to the large number of foreign particles. Example 6 A raw material polyester having an intrinsic viscosity of 0.33 obtained in the same manner as in Example 1 was immersed in a single-tube wet-wall tower with an inner diameter of 0.15 mφ, a length of 1.0 m, and a jacket heated to 280°C. It was supplied at a flow rate of 10 kg/m·hr per side length, and the reaction was carried out under reduced pressure of 0.5 mmHg. The obtained polyester had an intrinsic viscosity of 0.66, and after 5 days of continuous operation, the number of foreign particles in the sheet was measured using a 0.3 cm thick sheet of polyester, which was 7 particles/100 cm ²
It was good. Comparative Example 4 When a polycondensation reaction was carried out under the same conditions as in Example 6 using a raw material polyester with an intrinsic viscosity of 0.20 obtained in the same manner as in Example 1, the obtained polyester had a low intrinsic viscosity of 0.45. Ta. In addition, after 5 days of continuous operation, the number of foreign particles in the polyester sheet with a thickness of 0.3 cm was measured, and 35 particles/
It was large at ^100cm2 . Example 7 Using raw material polyester with an intrinsic viscosity of 0.33 obtained in the same manner as in Example 1, the flow rate per immersed side length was determined.
When the reaction was carried out in the same manner as in Example 1 except that the supply was carried out at a rate of 3.0 Kg/m・hr, the obtained polyester had an intrinsic viscosity of 0.85, and the number of foreign substances in the sheet was 7.
The number of pieces/ ^100cm2 was good. Comparative Example 5 Using raw material polyester with an intrinsic viscosity of 0.30 obtained in the same manner as in Example 1, the flow rate per immersed side length was
When the reaction was carried out in the same manner as in Example 1 except that the supply was carried out at a rate of 1.2 Kg/m・hr, the obtained polyester had an intrinsic viscosity of 0.87, but the number of foreign substances in the sheet was as large as 69 pieces/100 cm ² . It was. Comparative Example 6 A polycondensation reaction was carried out in the same manner as in Example 4 except that the flow rate per immersion side length was 300 Kg/m・hr. Although there was no foreign matter in the sheet, the intrinsic viscosity of the polyester produced was It was low at 0.41.

【table】

[Table] Example 8 A raw material polyester having an intrinsic viscosity of 0.44 was obtained by esterification of terephthalic acid and 1,4-butanediol, followed by preliminary polycondensation. As catalysts, tetra-n-butyl titanate was used as titanium in an amount of 3.5 x 10 ^-4 mol based on terephthalic acid, and phosphoric acid was used as titanium in an amount of 6.8 x 10 ^-4 mol based on terephthalic acid. This raw material polyester was supplied to the wet wall column used in Example 1 at a flow rate of 100 Kg/m・hr per soaked side length.
Polycondensation reaction was carried out under reduced pressure of mmHg. At that time, the jacket was heated to 235°C. In this way, high quality polybutylene terephthalate with an intrinsic viscosity of 0.64 was obtained. Even after 10 days of continuous operation, high quality polyethylene terephthalate was still obtained.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an example of a wetted wall column used in the method of the invention. In the figure, 1 is a wet wall pipe, 2 is a jacket for heating the wet wall column, 3 is a raw material polyester distribution and supply section, 4 is a raw material polyester supply nozzle, 5 is a produced gas exhaust pipe, 6 is a gear pump for discharging product polyester, and 7 is a The produced polyester discharge pipe 8 is a heating medium supply and discharge nozzle. Figure 2 shows the critical meaning of formula () in the present invention.
FIG. 3 is a diagram plotting the results of Examples and Comparative Examples, with the vertical axis representing the immersion length flow rate and the horizontal axis representing the intrinsic viscosity of the raw material polyester. The curve is a curve representing equation (). The shaded area indicates the scope of the present invention.

Claims (1)

[Claims] 1 General formula () with an intrinsic viscosity of 0.15 to 1.0 (In the formula, R represents an ethylene group or a butylene group) A polymerizable liquid material whose main component is an ester polymer containing 80 mol% or more of units represented by the formula (200≧F≧A×10 ^{- 3} × IV ^- 〓 ...() [In the formula, F indicates the flow rate per immersion length (Kg/m・hr), IV indicates the intrinsic viscosity of the ester polymer in the polymerizable liquid material, A and β are 4.2 and β, respectively, when R is an ethylene group in the general formula ().
5.1 and 2.7 and 4.5 respectively when R is a butylene group] is supplied to a non-stirring cylindrical wetted wall column at a flow rate per soaked side length that satisfies the following numbers: 1. A method for continuously producing polyester, which is characterized by polycondensation under reduced pressure by flowing the polyester into a polyester having an intrinsic viscosity higher than 0.5. 2. In the method for continuous production of polyester according to claim 1, R is an ethylene group, and the flow rate (F) per immersed side length is expressed by the formula () 200≧F≧5.3×10 ^-3 ×IV ^-5.1 ...() (In the formula, IV indicates the intrinsic viscosity of the ester polymer in the polymerizable liquid material.) A method that satisfies the following. 3. In the method for continuously producing polyester according to claim 1, R is a butylene group, and the flow rate (F) per immersion side length is expressed by the formula (200≧F≧3.4×10 ^-3 ×IV ^-4.5 ...() (In the formula, IV indicates the intrinsic viscosity of the ester polymer in the polymerizable liquid material.) A method that satisfies the following. 4. A method for continuously producing polyester according to any one of claims 1 to 3, wherein the polyester obtained by polycondensation has an intrinsic viscosity of 0.55 to 1.2.