JP5751604B2 - Method for producing polybutylene terephthalate resin - Google Patents

Description

  The present invention efficiently and continuously produces a polybutylene terephthalate resin and a polybutylene terephthalate resin having good moldability and post-molding quality with reduced filtration pressure increase rate, amount of foreign matter derived from titanium carbonylate, and haze. It is about how to do.

  Since polybutylene terephthalate resin has excellent physical and chemical properties, it is widely used in various applications such as fibers, films, and other molded articles. In addition, since it is excellent in mechanical properties such as strength and elastic modulus, heat resistance and the like, it is widely used particularly as an engineering plastic.

  As one method for producing such a polybutylene terephthalate resin, an esterification step of obtaining bishydroxybutyl terephthalate and its low polymer by esterification of terephthalic acid and 1,4-butanediol, and bishydroxybutyl terephthalate and its It consists of a polycondensation step to obtain a high degree of polymerization polybutylene terephthalate while distilling excess 1,4-butanediol under high temperature and high vacuum, and as a catalyst, titanium compounds, tin compounds, etc. A phosphorus compound or the like is used as a decomposition inhibitor.

  However, when a tin compound is used, the recent environmental point of view and the reactivity are high. Therefore, the decomposition reaction is also fast, which is preferable in terms of quality such as an increase in gelation rate, haze, and b value. Absent.

  Further, when only the titanium compound is used, it is advantageous in terms of quality as compared with the case where the tin compound or the phosphorus compound is used in combination, but the titanium compound is used to promote the reaction, while depending on the reaction conditions. Is partly foreign, causing pressure, gelation rate and haze increase when the polybutylene terephthalate composition is filtered. This may cause an increase in surface foreign matter.

  On the other hand, from the viewpoint of reducing tetrahydrofuran produced as a by-product by decomposition of 1,4-butanediol as a raw material and producing a high-viscosity product, the addition amount of the titanium compound is increased or the addition method is devised. It is desired to carry out the polymerization efficiently and to shorten the reaction time as much as possible.

  Here, first, regarding the problem of foreign matter generation, Patent Document 1 describes that a filter is installed in a transfer pipe between reaction tanks. However, if the aperture of the filter is made smaller, there is a problem that the filtration pressure increases quickly, the clogging frequency increases, and the filter replacement frequency increases. In addition, the polybutylene terephthalate gel foreign matter generated by the reaction has a three-dimensional structure and is relatively soft, and thus has a problem that it partially passes through the filter.

  Further, as a method for suppressing the generation of foreign matter, Patent Document 2 discloses a method for suppressing the generation of a foreign matter derived from a titanium compound by increasing the stirring power of an esterification reaction tank and making the inside of the tank as uniform as possible to suppress abnormal residence. However, depending on the method of adding the catalyst and the reaction conditions, foreign matters are generated, and there still remain problems such as an increase in filtration pressure and haze. In particular, when polymerizing a high-viscosity product, in order to increase the amount of the titanium compound or lengthen the reaction time, the tendency is more prominent, and it is necessary to have a formulation that suppresses the formation of foreign matter.

However, only the foreign matter countermeasures described above are still insufficient with respect to the foreign matter, gel foreign matter, etc. of the titanium carboxylate of polybutylene terephthalate.
JP 2000-336162 A JP 2005-29581 A

  The present invention is suitable for use in a molded article having excellent mechanical strength and a film having little foreign matter on the surface because the pressure rise upon filtration, foreign matter derived from titanium compounds and gel foreign matter are few, and haze is low. An object of the present invention is to provide a polybutylene terephthalate resin that can be used.

As a result of intensive studies to achieve the above object, the present inventors have reached the present invention.
That is, in the present invention, a titanium compound is added as a catalyst to an esterification reaction tank having an esterification reaction rate of 95 to 98%, and then added to a preliminary polycondensation reaction tank, so that terephthalic acid is a main component. A polybutylene terephthalate resin is continuously produced from a diol mainly composed of dicarboxylic acid and 1,4-butanediol, wherein the titanium compound is diluted to 1,4-butanediol to 20% by weight or less. The solution is added at a flow rate of 0.3 m / s or more and 1.0 m / s or less , and the process is performed under reduced pressure and heating until the solution reaches a liquid phase containing bishydroxybutyl terephthalate and its low polymer. The volatilization rate of 1,4-butanediol at 80% by weight or less ,
The titanium compound is converted into Ti atoms in the esterification reaction tank and the prepolycondensation reaction tank, respectively.
The polybutylene terephthalate resin is produced by adding 25 to 75 ppm based on the total weight of the polymer .

  The polybutylene terephthalate resin of the present invention can be manufactured with less replacement frequency of the polymer filter installed during the process because the pressure rise when filtering is low, and moreover, the titanium compound-derived foreign matter and gel foreign matter are few, so tensile breakage It is possible to obtain a molded article having a high elongation or the like and excellent mechanical strength, or a film having very little surface foreign matter. Moreover, since there are few foreign materials also about a hue, the final product with high whiteness is obtained.

  Hereinafter, the present invention will be described in detail.

  The polybutylene terephthalate resin produced in the present invention is a high molecular weight thermoplastic polyester having an ester bond in the main chain using terephthalic acid as an acid component and 1,4-butanediol as a diol component. As acid component, aromatic dicarboxylic acids such as isophthalic acid, orthophthalic acid, naphthalenedicarboxylic acid, diphenyldicarboxylic acid, sodium sulfoisophthalic acid, cycloaliphatic dicarboxylic acid such as decalin dicarboxylic acid, oxalic acid, malonic acid, succinic acid Acid, sebacic acid, adipic acid, aliphatic dicarboxylic acid such as dodecanedioic acid, etc., and other diol components specifically include, for example, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol Cole, neopentyl glycol, 1,6-hexanediol, polypropylene glycol, aliphatic diol such as polytetramethylene glycol, alicyclic diol such as 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, 2,2 -Aromatic diols such as -bis (4'-hydroxyphenyl) propane can also be used in part. These copolymer components are each preferably 40 mol% or less based on terephthalic acid or 1,4-butanediol.

  The polybutylene terephthalate resin of the present invention is preferably produced by continuous polymerization using a series continuous tank reactor. Specifically, a raw material mainly composed of a diol component and a dicarboxylic acid component is prepared as a slurry, the slurry is supplied to an esterification reaction tank, an esterification reaction is performed, and an oligomer as an esterification reaction product obtained is preliminarily prepared. The polycondensation reaction can be carried out through the polycondensation reaction tank and the final polymerization machine. The obtained polybutylene terephthalate is preferably extracted in the form of a strand from the bottom of the final polymerization machine through a die, water-cooled with cooling water, and then cut with a pelletizer to form pellets or other granular materials.

  As a preferable form of the present invention, the charged molar ratio of the diol component to the dicarboxylic acid component is preferably 1.4 to 2.0, and more preferably 1.6 to 1.8.

  The type of the esterification reaction tank used in the present invention is not particularly limited.For example, a vertical stirring complete mixing tank, a vertical heat convection mixing tank, a shelf-type reaction tank, and the like can be used. When a plurality of reaction vessels are used, a plurality of vessels of the same kind or different types can be used in series. In the present invention, a vertical stirring complete mixing tank is preferable.

  It is preferable to attach a rectification column at the distillation outlet of the esterification reaction tank, and water, tetrahydrofuran and 1,4-butanediol in the distillate can be separated by the rectification column. A distillate containing water and tetrahydrofuran as main components is distilled from the top of the rectification column, condensed in a condenser, and sent to a recovery step. The distillate containing 1,4-butanediol as the main component is condensed at the bottom of the rectifying tower and returned to the esterification reaction tank. At that time, in order to adjust the molar ratio in the esterification reaction tank, a part of 1,4-butanediol returned to the esterification reaction tank may be distilled out of the system. In this case, the distillate containing 1,4-butanediol distilled as a main component can be used again as a raw material and may be used after rectification or may be used as it is.

An organic titanium compound is used for the esterification reaction catalyst used in the present invention. The organic titanium compound preferably used in the present invention is
(R ₁ O) nTi (OR ₂ ) _4-n
(Wherein R ₁ and R ₂ are aliphatic, alicyclic or aromatic hydrocarbon groups having 1 to 10 carbon atoms, and n is a number of 0 to 4 (including decimal numbers)). Represented by esters and condensates.

  Specifically, the organic titanium compound used in the present invention includes titanic acid methyl ester, tetra-n-propyl ester, tetraisopropyl ester, tetra-n-butyl ester, tetraisobutyl ester, tetra-tert-butyl ester, tetra- Examples include 2-ethylhexyl ester, tetraoctyl ester, phenyl ester, benzyl ester, tolyl ester, and mixed esters thereof. Among these, tetra-n-propyl ester (tetra-n-propyl titanate), tetraisopropyl ester (tetra-isopropyl titanate), and tetra-n-butyl ester (tetra-n-butyl titanate) of titanic acid are available at low cost. The tetra-n-butyl ester of titanic acid (tetra-n-butyl titanate) is particularly preferably used. These organic titanium compounds may use only 1 type and can use 2 or more types together. Further, the same species may be used during the esterification reaction and polycondensation, or different organic titanium compounds may be used.

  The organic titanium compound is added together with an organic solvent. Examples of the organic solvent in this case include isopropanol, n-butanol, isobutanol, ethylene glycol, propylene glycol, and 1,4-butanediol. In consideration of the influence on quality, etc., 1,4-butanediol is preferable. Used.

  The concentration of the organic titanium compound in the organic solvent needs to be 20% by weight or less, preferably 15% by weight or less, and more preferably 10% by weight or less. If it is higher than 20% by weight, not only can the viscosity increase and stable addition, but when adding an organic titanium compound / 1,4-butanediol, it reacts due to the heat load of the process in the addition line, etc. It is not preferable because there is a possibility that the The lower limit of the concentration of the organic titanium compound is 3% by weight or more. If the amount is less than 3% by weight, the amount added may increase and the temperature of the reaction vessel may decrease.

  The addition amount of the organic titanium compound is preferably 25 to 75 ppm, more preferably 30 to 70 ppm, based on the total weight of the polymer in terms of Ti atom, as the addition amount to the esterification reaction tank. If the addition amount is less than 25 ppm, the esterification rate may be slow, and the secondary property of tetrahydrofuran may increase. If it exceeds 75 ppm, problems such as an increase in the haze of the polymer may occur.

  In addition, when producing a high-viscosity product, it is necessary to add an organotitanium compound to the prepolycondensation reaction tank in order to increase the polymerization efficiency, and the addition amount may be 25 to 75 ppm additionally as in the esterification. Preferably, 30 to 70 ppm is more preferable. When the amount of the organotitanium compound is increased in the esterification reaction tank and added all at once, the haze and filtration pressure increase rate may increase.

  The organic titanium compound solution needs to be added at a flow rate of 0.3 m / s or more, and preferably 0.4 m / s or more. If the flow rate is less than 0.3 m / s, the inside of the addition pipe is not full and the addition speed is slow, which is not preferable due to heat load in the addition pipe. Furthermore, the volatility of 1,4-butanediol at the time of addition is undesirably high. The upper limit of the flow velocity is not particularly limited, but in the present invention, it is 1.0 m / s or less. If it is faster than 1.0 m / s, it is necessary to make the additive nozzle very thin, and it may be easily clogged with foreign substances.

  Moreover, the addition method of the organic titanium compound is not particularly limited, but the gas phase may be added to the reaction vessel from the upper part or the liquid phase may be added from the lower part. Similarly, the liquid phase may be added to the transfer pipe between the reaction tanks, but the liquid phase addition is preferable in order to suppress the volatilization of 1,4-butanediol diluting the catalyst.

  In addition, the addition of the organic titanium compound / organic solvent is such that the volatilization rate of the organic solvent is 80% by weight or less after reaching the bishydroxyterephthalate and its low polymer after the addition in the process under reduced pressure and heating atmosphere. It is necessary, and it is preferably 50% by weight or less, more preferably 20% by weight or less. When it is higher than 80% by weight, the organotitanium compound and the 1,4-butanediol solution are liable to react, and when the reaction product is added to bishydroxyterephthalate and its low polymer, it is not preferable. The lower limit of the volatility of the organic solvent is not particularly limited, but in the present invention, it is 0.1% by weight or more. There are two main addition methods, vapor phase addition and liquid phase addition, and liquid phase addition with a low volatility of the organic solvent is preferable.

  Moreover, when adding an organic titanium compound, it is necessary to add to the esterification reaction tank by the esterification reaction rate of 95-98% of a dicarboxylic acid component, Preferably it is 96-97%. Further, it is preferable to add an organic titanium compound to the preliminary polycondensation reaction tank. When added to the esterification reaction vessel, if the polymerization rate of the dicarboxylic acid component is less than 95% and a polymerization catalyst is added, a large amount of terephthalic acid remains, and if added at 98% or more, terephthalic acid remains and organic titanium. Problems such as an increase in the solution haze of the polymer due to the reaction of the compound are undesirable.

  In the esterification reaction in the present invention, the reaction temperature is preferably 210 to 260 ° C, more preferably 220 to 250 ° C, and the pressure is preferably 13.3 to 93 kPa, more preferably 20 to 20 in the presence of an organic titanium compound. It is mentioned as preferable conditions to carry out under reduced pressure of 87 kPa.

  The type of the preliminary polycondensation reaction tank used in the present invention is not particularly limited. For example, a vertical stirring polymerization tank, a horizontal stirring polymerization tank, a thin film evaporation polymerization tank, and the like can be used.

  The preliminary polycondensation reaction tank may be a single tank or a plurality of tanks in which a plurality of tanks of the same kind or different kinds are connected in series. The reaction temperature of the preliminary polycondensation reaction is preferably 210 to 270 ° C., more preferably 220 to 260 ° C., and the pressure is preferably 7 kPa or less, more preferably 1 to 6 kPa.

  In the present invention, when the final polymerization machine is used, the type thereof is not particularly limited. For example, a horizontal single-axis reactor, a horizontal twin-axis reactor, or the like can be used.

  The reaction temperature of the final polymerization machine is preferably 220 to 260 ° C., more preferably 230 to 250 ° C., and the pressure is preferably 1.3 kPa or less, more preferably 0.67 kPa or less. .

  The polybutylene terephthalate obtained by polymerization needs to have a haze of 10% or less, preferably 8% or less, more preferably 6% or less. When the haze is higher than 10%, it means that there are many foreign substances in the polymer, and when it is formed into a molded product or film, there is a problem in strength and surface properties. Although there is no limitation in particular about the minimum of haze, in this invention, it is 0.1% or more. Further, similarly to the above, the total light transmittance is preferably 92% or more, and more preferably 95% or more. If the haze is low but the total light transmittance is lower than 92%, it means that there are many very small foreign substances. The upper limit of the total light transmittance is not particularly limited, but is 99% or less in the present invention.

The filtration pressure increase rate is preferably 2.0 kg / cm ² / hr or less, and more preferably 1.0 kg / cm ² / hr or less. In the case of 2.0 kg or more, the filtration pressure of the polymer filter in the process increases rapidly, so the replacement frequency is high, and the quality becomes unstable during replacement, which causes problems in both operation and quality. Sometimes.

  The gelation rate of the polybutylene terephthalate resin is preferably 0.5% or less, and more preferably 0.3% or less. When the gelation rate is higher than 0.5%, there are many polymer gels, which may cause insufficient strength and deterioration of surface properties when formed into final products such as molded products and films.

Usually, as the foreign matter generated in the production process of polybutylene terephthalate resin, black foreign matter such as scale and carbide generated in the reaction tank, white gray foreign matter such as high melting point, etc. are generally known, In addition to this, it was found that the catalyst was converted to foreign matter depending on the reaction conditions and addition method. The foreign matter here refers to a polymer adhering to the sintered fiber filter when the solution is filtered under the condition of a 10 μm sintered fiber filter having a filtration area of 2.0 cm ² and a discharge rate of 6.8 g / min. After heating and dissolving, the solution is filtered through a 50 μm membrane filter, and the filtrate is further collected by filtration through a 5 μm membrane filter. When the filter residue was measured by infrared spectroscopy, specific absorption (1400 cm ⁻¹ and 1525 cm ⁻¹ ) derived from the metal salt carboxylate was observed, and titanium element was detected by a scanning electron microscope. From this, it was found that the foreign matter contains titanium carboxylate derived from the titanium catalyst. Moreover, as a distribution of the size of the foreign matter containing the titanium carboxylate, 5 to 20 μm or 50 to 150 μm is collected. The reason for having two distributions is not clear, but 5 to 20 μm foreign matter is generated due to abnormal stagnation of the catalyst in the reaction tank, and 50 to 150 μm foreign matter is the gas phase part during catalyst addition. It is considered that the product that has been heated and concentrated by the method described above and added to the polymer is added. In the present invention, the content of foreign matter including titanium carboxylate recovered by filtering the solution of polybutylene terephthalate resin is preferably 20 ppm or less, more preferably 10 ppm, based on the polymer to be produced. . If it exceeds 20 ppm, the rate of increase in filtration pressure and haze increase, and the final product may deteriorate in quality.

  The present invention will be described more specifically with reference to the following examples. However, the present invention is not limited to the following examples. In the examples, each measured value was determined as follows.

(1) Color tone (color coordinate b value)
The color coordinate b value of Hunter's color difference formula in the Lab color system described in Reference 1 of JIS Z 8730 was measured by a reflection method using a color tester SC-3-CH type manufactured by Suga Test Instruments Co., Ltd. The measurement is allowed to stand for 4 hours or more after the power is turned on, and after sufficiently stabilizing the apparatus in advance, the sample pellet is filled to the cut-off position in a measurement cell having an inner diameter of 60 mm, a depth of 30 mm, and a light receiving portion made of quartz glass. Measurements were made by changing the direction by 90 degrees in four directions, and the average value was taken as the value.

(2) Intrinsic Viscosity Using a Ubbelohde viscometer and o-chlorophenol, the solution viscosities of polybutylene terephthalate concentrations of 1.0 g / dl, 0.5 g / dl and 0.25 g / dl were measured at 25 ° C., The viscosity number was extrapolated to a concentration of 0.

(3) Filtration pressure increase rate After the chip is dried at 150 ° C. for 4 hours, a 10 μm sintered fiber filter having a temperature of 255 ° C. to 265 ° C. and a filtration area of 2.0 cm ^{2 using} a Fujimelt spinning tester (MST-C400) manufactured by Fuji Filter, Measurement was performed under the condition of a discharge rate of 6.8 g / min, the rate of increase in filtration pressure for 4 hours was measured, and the rate was converted to the rate of increase in pressure per hour.

(4) Haze, total light transmittance 5.4 g of the sample polymer was dissolved in 40 ml of a mixed solvent of phenol / ethane tetrachloride (60:40 wt%) by heating at 100 ° C. for 2 hours, and this solution was put into a cell having an optical path length of 30 mm. Then, haze and total light transmittance were measured with an integral haze meter (Suga Test Instruments: HZ-2).

(5) Oligomerization esterification reaction rate It calculated by reaction rate (%) = (saponification value-acid value) / saponification value x100. Regarding the acid value, 0.4 g of an oligomer was added with 50 ml of an o-cresol / chloroform (3: 2) solution, dissolved at 90 ° C. for 1 hour, and then allowed to cool for 30 minutes. Thereafter, 30 ml of chloroform was added, 5 ml of a 13% lithium chloride methanol solution was further added, and titration was performed with N / 25 ethanolic sodium hydroxide solution using COM-450 manufactured by Hiranuma. The saponification value is obtained by subjecting 0.4 g of oligomer to alkali hydrolysis with 20 ml of N / 2 potassium hydroxide, heating to reflux at 100 ° C. for 1 hour, and back-titration with an N / 2 sulfuric acid solution using an indicator. It was.

(6) Content of foreign matter The sintered fiber filter to which the polymer after the filtration test was attached was taken out, stirred and dissolved at 20 ml of O-chlorophenol at 100 ° C. for 2 hours, and it was 50 μm Teflon (registered trademark) manufactured by Millipore. It filtered with the membrane filter. Further, the filtrate was re-filtered with a 5 μm Millipore Teflon (registered trademark) membrane filter, dried in vacuo at 50 ° C. overnight, weighed, and the weight of the filtered material was filtered. The foreign matter content was calculated by dividing by. Regarding the size of the foreign matter, the isolated foreign matter is observed using a SEM (VE-8800) manufactured by Keyence, and the obtained image is subjected to image processing using an image analyzer, and the particle size distribution of the foreign matter. Was measured.

(7) Infrared spectroscopy (IR)
The isolated foreign matter was observed for the specific absorption wavelength of the foreign matter by a transmission method using an infrared spectrometer with the KBr tablet method.

(8) Terminal carbonyl group concentration (COOH)
To 2.0 g of the chip, 50 ml of an o-cresol / chloroform (3: 2) solution was added and dissolved at 90 ° C. for 1 hour, and then allowed to cool for 30 minutes. Thereafter, 30 ml of chloroform was added, 5 ml of a 13% lithium chloride methanol solution was further added, and titration was performed with N / 25 ethanolic sodium hydroxide solution using COM-450 manufactured by Hiranuma.

(9) Gelation rate 1 g of a chip is heated at 300 ° C. for 2.5 hours in the atmosphere, dissolved in 50 ml of OCP at 150 ° C. for 1 hour, filtered through a 3G3 glass filter, and the filtered product is washed with methylene chloride. . After line drawing, the filter was dried in a vacuum dryer overnight at 50 ° C. and then weighed, and the weight ratio of the amount of filter residue in 1 g of chip was defined as the gelation rate.

(10) Tetrahydrofuran production amount About the amount of tetrahydrofuran produced as a by-product, the production amount (g) of tetrahydrofuran per hour generated from each step was measured using a Shimadzu gas chromatograph GC-17A, and the unit was measured. It was determined by dividing by the amount of polymer produced per hour (kg).

Example 1
A molar ratio of 1,4-butanediol to terephthalic acid is 1.8 in a fully mixed tank type esterification reactor filled with PBT oligomer having a reaction rate of 96% in advance. Thus, the slurry was continuously supplied. At the same time, tetrabutoxy titanate was diluted with 1,4-butanediol to a concentration of 10%, and 0.04 wt% (Ti: 56 ppm) was added to the polymer (PBT) produced at a flow rate of 0.43 m / s. did. The volatility of 1,4-butanediol used for diluting the catalyst was 5%. The esterification reactor was subjected to an esterification reaction at a temperature of 230 ° C., a pressure of 79 kPa, and a reaction time (average residence time) of 2 hours to obtain a PBT oligomer having a reaction rate of 96%. The amount of tetrahydrofuran (THF) generated during the esterification reaction was 95 g / kg polymer. The PBT oligomer obtained in the esterification reactor was continuously taken out and supplied to a pre-polycondensation reactor filled with a PBT oligomer having a reaction rate of 98% in advance. The prepolycondensation reactor is a reaction temperature of 240 ° C., reaction time (average residence time) of 2 hours, and a reaction at a vacuum of 2.7 kPa. , 4-butanediol was diluted, and 0.04 wt% (Ti: 56 ppm) was added to the polymer (PBT) produced at a flow rate of 0.43 m / s. The volatility of 1,4-butanediol used for diluting the catalyst was 10%. Thereafter, the solution was continuously fed to the final polymerization vessel, and a polymerization reaction was carried out at a polymerization temperature of 240 ° C., a reaction time of 1.5 hours, and a vacuum degree of 0.3 kPa to obtain PBT. The obtained PBT has an intrinsic viscosity of 1.0 dl / g, a terminal carboxyl group concentration of 10 eq / t, a haze of 3%, a total light transmittance of 95%, a b value of 5, and a foreign substance containing a titanium carboxylate (particle size: 10 μm, It was a polymer suitable for molded products and films, having a content of 5 ppm (having a peak at 100 μm), a filtration pressure increase rate of 0.5 kg / cm ² / hr, and a gelation rate of 0.2%. The results are shown in Table 1.

Example 2
The same procedure as in Example 1 was performed except that the catalyst addition concentration was changed to 20 wt%. As a result of increasing the catalyst concentration, the volatility of the catalyst dilution solvent was increased, and the amount of foreign matter was slightly increased, but it was within the usable range. The results are shown in Table 1.

Example 3
The same procedure as in Example 1 was performed except that the catalyst addition flow rate was changed to 0.3 m / s. As a result of slowing down the catalyst addition flow rate, the volatility of the catalyst dilution solvent increased and the filtration pressure increase rate increased, but it was within the usable range. The results are shown in Table 1.

Comparative Example 1
The same procedure as in Example 1 was performed except that the catalyst addition flow rate was slowed to 0.1 m / s. As a result of slowing the catalyst addition flow rate, the volatility of 1,4-butanediol for diluting the catalyst was remarkably increased to 90, 96%. As a result, the organotitanium compound became foreign, and haze, filtration pressure increase rate, gelation rate Equal quality has been significantly deteriorated. The results are shown in Table 1.

Comparative Example 2
The same procedure as in Example 1 was performed except that the catalyst concentration was 80%. As a result of increasing the catalyst concentration, a reaction with 1,4-butanediol was caused by the heat load in the addition pipe, and as a result of forming a foreign substance, the quality was deteriorated. The results are shown in Table 1.

Comparative Example 3
The same procedure as in Example 1 was performed except that the esterification reaction time was increased to 3 hours. As a result of increasing the esterification reaction time, the esterification reaction rate was increased, and as a result, the haze was increased. The results are shown in Table 1.

Comparative Example 4
The same procedure as in Example 1 was performed except that the amount of catalyst added was 0.01 wt% (Ti: 14 ppm). As a result of reducing the amount of the catalyst added, the esterification reaction time and the polymerization time became longer, and the polymer stayed at a high temperature for a long time, so that the gelation rate etc. increased and the quality deteriorated. The results are shown in Table 1.

  When PBT is produced by this production method, there are fewer foreign materials and gels derived from the titanium compound than when produced by the conventional method, and the rate of increase in the filtration pressure of the filter is low, so that stable production can be achieved. PBT having excellent strength and surface properties when formed into a film can be obtained. Since the PBT obtained by the present invention is excellent in quality, it can be usefully used for various automobile parts, electrical / electronic parts, films and the like.

Claims (1)

As a catalyst, a titanium compound is added to an esterification reaction tank having an esterification reaction rate of 95 to 98%, and then added to a preliminary polycondensation reaction tank to obtain a dicarboxylic acid containing terephthalic acid as a main component and 1 , 4-Butanediol as a main component, a method for continuously producing a polybutylene terephthalate resin, in which a solution obtained by diluting a titanium compound in 1,4-butanediol to 20% by weight or less is 0.3 m. It was added at / s or 1.0 m / s or less flow rate, until the solution reaches a liquid phase comprising a bis-hydroxybutyl terephthalate and its low polymers, vacuum, 1,4-butane in the step of heating under Setting the diol volatility to 80% by weight or less ,
The titanium compound is converted into Ti atoms in the esterification reaction tank and the prepolycondensation reaction tank, respectively.
The method for producing a polybutylene terephthalate resin, comprising adding 25 to 75 ppm based on the total weight of the polymer .