JP2013240902A - Method for manufacturing polybutylene terephthalate pellet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a polybutylene terephthalate pellet capable of reducing a generation amount of fine powder at pelletizing polybutylene terephthalate having a low polymerization degree.SOLUTION: In a method of manufacturing polybutylene terephthalate pellet, molten polybutylene terephthalate is discharged in a strand shape through an esterification reaction of a dicarboxylic acid component based on terephthalic acid or an ester forming derivative thereof with diol based on 1,4-butanediol and/or an esterification process for performing an ester exchange reaction and a polycondensation process for performing the polycondensation reaction of the oligomer obtained by the esterification process, and after the strand is solidified, it is cut to manufacture the pellet. In this case, the molten polybutylene terephthalate with a polymerization degree of 20-60 is solidified by cooling water of 20-60°C.

Description

  The present invention relates to a method for producing pellets of polybutylene terephthalate having a low polymerization degree.

  Polybutylene terephthalate (hereinafter sometimes referred to as PBT) has excellent mechanical properties, heat resistance, moldability and recyclability, and has high mechanical strength and chemical resistance. It is widely used for films, fibers and the like, and in particular, it is widely used as a material for industrial molded products such as connectors, relays and switches for automobiles and electrical / electronic devices.

  PBT usually forms an oligomer which is a polyester precursor by direct esterification reaction between terephthalic acid and 1,4-butanediol (hereinafter sometimes referred to as 1,4-BG), and then the oligomer is subjected to atmospheric pressure or A method of producing by polycondensation reaction under reduced pressure, or an ester exchange reaction between an ester-forming derivative of terephthalic acid and 1,4-BG to form an oligomer which is a polyester precursor, and then the oligomer is subjected to atmospheric pressure or It is produced by a method of producing by polycondensation reaction under reduced pressure. At this time, it is well known that a titanium compound is used as a reaction catalyst.

On the other hand, in recent years, there has been an increasing demand for miniaturization and weight reduction of industrial molded products, and it is desired to improve the fluidity at the time of melt molding. Further, it is necessary to efficiently manufacture such PBT. It was desired.
Generally, in order to improve fluidity, it is effective to lower the degree of polymerization. However, when such PBT is pelletized, there is a problem that a large amount of fine powder is generated.

Conventionally, a production method with a small amount of fine (fine powder) when pelletizing polyester has been proposed (see Patent Document 1).
Moreover, the preferable pelletization conditions when PBT is used have been proposed (see Patent Document 2).

JP 2001-246622 A JP 2004-306339 A

  However, within the scope of the technique disclosed in Patent Document 1, when PBT is used, the amount of fine powder may increase. Moreover, in the range of the technique currently disclosed by patent document 2, when pelletizing low-polymerization degree PBT, there existed a case where sufficient effect for suppression of the amount of fine powder was not acquired. In view of these problems, an object of the present invention is to provide a method for producing pellets of polybutylene terephthalate that generates a small amount of fine powder when pelletizing PBT having a low polymerization degree.

As a result of intensive studies on the above problems, the present inventors, in a method for producing a low-polymerization degree PBT, solidify the molten PBT at a desired cooling water temperature, thereby discharging the molten PBT in a strand shape. After solidification, the inventors have found that the amount of fine powder when cutting to produce pellets can be suppressed, and the present invention has been achieved.
That is, the gist of the present invention resides in [1] below.
[1] An esterification step in which an esterification reaction and / or a transesterification reaction between a dicarboxylic acid component having terephthalic acid or an ester-forming derivative thereof as a main component and a diol having 1,4 butanediol as a main component, and Through a polycondensation step in which the oligomer obtained in the esterification step undergoes a polycondensation reaction, molten polybutylene terephthalate is discharged in the form of strands, solidified, then cut to produce pellets, and a polymerization degree of 20 to 60 is melted. A method for producing polybutylene terephthalate pellets, characterized in that polybutylene terephthalate is solidified with cooling water at 20 to 60 ° C. and then cut.

  According to the present invention, molten PBT having a degree of polymerization of 20 to 60 is discharged in the form of strands in cooling water, cooled in the range of 20 to 60 ° C., and then cut to reduce the amount of fine powder generated, and high flow. PBT pellets having properties can be produced.

Hereinafter, the present invention will be described in detail. However, the description of each constituent element described below is a representative example of the embodiment of the present invention, and the present invention is not limited thereto.
In the present specification, a numerical range expressed using “to” means a range including numerical values described before and after “to” as a lower limit value and an upper limit value. Moreover, the lower limit value or the upper limit value in this specification means a range including the numerical value of the lower limit value or the upper limit value.

<Production raw materials>
The PBT of the present invention comprises an esterification reaction and / or a transesterification reaction between a dicarboxylic acid component containing terephthalic acid or an ester-forming derivative thereof as a main component and a diol containing 1,4 butanediol as a main component. Obtained by a condensation reaction.
The dicarboxylic acid component mainly comprising terephthalic acid or an ester-forming derivative thereof used in the present invention means that terephthalic acid or an ester-forming derivative thereof in the dicarboxylic acid is usually 80 mol% or more. Preferably it is 90 mol% or more, More preferably, it is 95 mol% or more. Examples of other dicarboxylic acids include isophthalic acid, 2,6-naphthalene dicarboxylic acid, adipic acid, sebacic acid, succinic acid, oxalic acid, cyclohexanedicarboxylic acid, and ester-forming derivatives thereof. These may be used alone or in combination of two or more.

  The diol mainly composed of 1,4 butanediol used in the present invention means that 1,4 butanediol in the diol is usually 80 mol% or more. Preferably it is 90 mol% or more, More preferably, it is 95 mol% or more. Other diols include alkylene glycols such as ethylene glycol, propylene glycol, neopentyl glycol, hexamethylene glycol, decamethylene glycol, cyclohexanedimethanol, poly (oxy) ethylene glycol, polytetramethylene glycol, and polymethylene glycol. These may be used alone or in combination of two or more, and can be arbitrarily selected according to the purpose.

  The ester-forming derivative used in the present invention is an ester-forming derivative that can form an ester as a diol in the resin production process, and is a lower alkyl ester of terephthalic acid or other dicarboxylic acid, specifically methyl ester, ethyl ester, propyl. Examples include esters and butyl esters. One or two or more of these may be mixed, and can be arbitrarily selected depending on the purpose.

<Manufacturing method>
Hereinafter, a method for manufacturing PBT will be described.
Known methods for producing PBT include a so-called direct polymerization method using terephthalic acid and 1,4-BG as main raw materials, and a transesterification method using terephthalic acid dialkyl ester and 1,4-BG as main raw materials.

  In the present invention, a conventionally known method, that is, an esterification reaction and / or a transesterification reaction of a dicarboxylic acid component containing terephthalic acid or its ester-forming derivative as a main component and a diol containing 1,4 butanediol as a main component. Can be carried out by a method of obtaining PBT through an esterification step of performing polycondensation and a polycondensation step of polycondensation reaction of the oligomer obtained by the esterification step. These steps can be carried out either batchwise or continuously.

In the present invention, an oligomer is a precursor of PBT having a number average molecular weight of 500 to 4,000.
In the present invention, the reaction system is an esterification step or a polycondensation step. The esterification step includes an esterification reaction tank and an apparatus connected to the esterification reaction tank by piping, and the polycondensation process includes a polycondensation reaction tank and an apparatus connected to the polycondensation reaction tank by piping.

The esterification step is optional as long as the esterification reaction and / or transesterification reaction can proceed, and the temperature is 120 ° C. or higher, preferably 150 ° C. or higher, while 245 ° C. or lower, preferably 230 ° C. or lower. It is. The reaction time is 2 to 8 hours, preferably 2 to 6 hours, and more preferably 2 to 4 hours.
The esterification step produces an oligomer in which a diol having 1,4 butanediol as a main component and a dicarboxylic acid component having terephthalic acid or an ester-forming derivative thereof as a main component are reacted. And in the polycondensation process mentioned later, this oligomer polycondensation reaction is performed.

  In the polycondensation process, the oligomer obtained in the esterification process is subjected to a polycondensation reaction. The polycondensation reaction is usually performed by a melt polycondensation reaction. The conditions in the polycondensation step are arbitrary as long as the polycondensation reaction can proceed. The reaction temperature (internal temperature) during the polycondensation reaction is preferably 245 ° C. or lower, more preferably 240 ° C. or lower, on the other hand, preferably 230 ° C. or higher, more preferably 235 ° C. or higher. If the reaction temperature exceeds the upper limit, there is a high possibility of thickening during production, and the color tone tends to deteriorate. If the reaction temperature is less than the lower limit, the polycondensation reactivity tends to deteriorate.

  Further, the pressure in the polycondensation step is preferably reduced pressure. Specifically, it is 10 Torr or less, preferably 3 Torr or less. Furthermore, the polycondensation reaction time is preferably 2 to 8 hours. By the polycondensation step, PBT obtained by polycondensation reaction of a diol having 1,4 butanediol as a main component and a dicarboxylic acid component having terephthalic acid or an ester-forming derivative thereof as a main component can be obtained.

A molten PBT having a polymerization degree of 20 to 60 can be obtained as long as it is within the reaction temperature, pressure, and polycondensation reaction time during the polycondensation reaction.
The obtained PBT is extracted as a strand from the bottom of the polycondensation reaction tank, submerged in cooling water and solidified, then the strand is cut with a cutter, and a pellet-like PBT is obtained via a dehydrator.

At this time, the lower limit of the temperature of the cooling water is 20 ° C. or higher, preferably 35 ° C. or higher, more preferably 40 ° C. or higher, and particularly preferably 42 ° C. or higher. On the other hand, the upper limit is 60 ° C. or less, preferably 58 ° C. or less, more preferably 55 ° C. or less, and particularly preferably 50 ° C. or less. If the temperature is less than the lower limit, the amount of fine powder increases, which is not preferable. Furthermore, the amount of moisture attached increases, and the drying efficiency in the subsequent process decreases. On the other hand, if the temperature exceeds the upper limit value, the cooling efficiency is poor and there is a problem in handling, which is not practical.
As a method of controlling the temperature of the cooling water within the above temperature range, a method using a boiler, a heat exchanger, etc., a method of mixing and adjusting high-temperature steam in a cooling water storage tank, or a combination of these methods It can be carried out.

  In producing the PBT in the present invention, a reaction catalyst is preferably used. Examples of reaction catalysts that can be used in this case include antimony compounds such as diantimony trioxide, germanium compounds such as germanium dioxide and germanium tetroxide, titanium alcoholates such as tetramethyl titanate, tetraisopropyl titanate, and tetrabutyl titanate, and tetraphenyl. Titanium compounds such as titanium phenolate such as titanate, dibutyltin oxide, methylphenyltin oxide, tetraethyltin oxide, hexaethylditin oxide, cyclohexahexylditin oxide, didodecyltin oxide, triethyltin hydroxide, triphenyltin Hydroxide, triisobutyltin acetate, dibutyltin diacetate, diphenyltin dilaurate, monobutyltin trichlora , Tributyltin chloride, dibutyltin sulfide, butylhydroxytin oxide, tin stannic acid, ethyl stannic acid, butyl stannic acid, and the like. Among them, titanium compounds are preferred from the viewpoint of catalytic activity. In particular, tetrabutyl titanate and tetraisopropyl titanate are preferable. In addition, a titanium compound may be used individually by 1 type, and may use 2 or more types together by arbitrary combinations and a ratio.

The titanium compound used as a reaction catalyst may be added at the beginning of the esterification reaction or transesterification reaction, during the esterification reaction or transesterification reaction, after the esterification reaction or transesterification reaction, or during the polycondensation reaction. It is preferable to divide and add at the start of the esterification reaction or transesterification reaction and before the polycondensation reaction.
The addition amount of the titanium compound is preferably 20 ppm by weight or more, more preferably 30 ppm by weight or more, on the other hand, preferably 100 ppm by weight or less, more preferably 70 ppm by weight or less as titanium atoms with respect to the PBT to be obtained. If the upper limit is exceeded, not only the color tone and thermal stability tend to deteriorate, but also the solution haze and foreign matter tend to increase due to the deactivation of the titanium catalyst. Moreover, polycondensation reactivity will deteriorate that it is less than a lower limit.
The content of titanium atoms in PBT is measured by ICP (Inductively Coupled Plasma) -MS (Mass Spectrometer) method after recovering the metal in the polymer by wet ashing.

Furthermore, a group 2 metal compound of the periodic table can also be used as a promoter. In the present invention, the Group 2 metal of the periodic table refers to a Group 2 element in the long-period periodic table presented in Nomenclature of Inorganic Chemistry IUPAC Recommendations 2005. Periodic table group 2 metal compounds may be added at the start of esterification or transesterification, during esterification or transesterification, after esterification or transesterification, or during polycondensation However, it is preferable in terms of polycondensation and color tone to be added after the transesterification reaction and before the start of polymerization.

Examples of the metal atom of the Group 2 metal compound used in the present invention include beryllium, magnesium, calcium, strontium, and barium. Of these, magnesium and calcium compounds are preferred from the viewpoints of handling and availability, and the effect as a promoter. Examples of the magnesium compound include magnesium acetate and hydrates thereof, magnesium hydroxide, magnesium carbonate, magnesium oxide, magnesium alkoxide, magnesium hydrogen phosphate, and the like. As calcium compounds, calcium acetate and hydrates thereof,
Examples thereof include calcium hydroxide and calcium carbonate. Of these, magnesium acetate and hydrates thereof are particularly preferred. In addition, the compound of a periodic table group 2 metal may be used individually by 1 type, and may use 2 or more types together by arbitrary combinations and a ratio.

The amount of the Group 2 metal compound added is preferably 5 ppm by weight or more, more preferably 20 ppm by weight or more, on the other hand, 100 ppm by weight or less, more preferably 70 ppm by weight or less, as a metal atom with respect to the obtained PBT. It is. If it is less than the lower limit, the improvement in the polycondensation reaction rate tends to be small, the terminal carboxyl group concentration also increases, and the hydrolysis resistance and color tone tend to deteriorate. If the upper limit is exceeded, the polycondensation reaction rate decreases, and hydrolysis resistance and color tone tend to deteriorate.
In addition, content of the metal atom of the compound of a periodic table group 2 metal in PBT can be measured like the measuring method of content of a titanium atom.

In the present invention, a heat stabilizer can be added to the reaction system. Although there is no restriction | limiting in particular in the heat stabilizer to be used, A hindered phenol type heat stabilizer is preferable. Examples of the hindered phenol heat stabilizer include pentaerythritol tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], 1,3,5-trimethyl-2,4, Examples include 6-tris- (3,5-di-t-butyl-4-hydroxybenzyl) benzene. Among these, pentaerythritol tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] is more preferable in terms of thermal stability during melt residence. In addition, a hindered phenol-based heat stabilizer may be used alone, or 2
You may use a seed | species or more together by arbitrary combinations and ratios.

  The lower limit of the degree of polymerization of the PBT of the present invention is 20 or more, preferably 35 or more, from the viewpoints of pelletization stability, mechanical properties, and fluidity. On the other hand, the upper limit is 60 or less, preferably 50 or less. When the degree of polymerization is less than the lower limit, the fluidity is improved, but the pelletization becomes unstable, and it tends to be difficult to obtain good mechanical properties as quality. If the degree of polymerization exceeds the upper limit, sufficient fluidity cannot be obtained. The degree of polymerization of PBT in the present invention refers to the number average molecular weight relative to the molecular weight of one unit of PBT, and can be measured by a generally known measuring method. It can be measured by the method described.

  The terminal carboxyl group concentration of the PBT of the present invention is not particularly limited, but the lower limit is preferably 1 equivalent / ton, more preferably 2 equivalent / ton, and particularly preferably 3 equivalent / ton. Most preferably, it is 5 equivalents / ton, and the upper limit is preferably 50 equivalents / ton, more preferably 40 equivalents / ton, particularly preferably 30 equivalents / ton, and 25 equivalents / ton. Most preferably. When the terminal carboxyl group concentration of PBT is not more than the upper limit value, the hydrolysis resistance of PBT tends to be good, and when it is more than the lower limit value, polycondensation reactivity tends to be good.

EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to a following example at all unless the summary is exceeded. In addition, the measurement method of the physical property and evaluation item which were employ | adopted in the following examples is as follows.
<Intrinsic viscosity (IV) dL / g>
It calculated | required in the following way using the Ubbelohde type viscometer. That is, using a mixed solvent of phenol / tetrachloroethane (weight ratio 1/1), the number of seconds falling of only the polymer solution having a concentration of 1.0 g / dL and the solvent at 30 ° C. was measured, and the following formula (1) Asked.
IV = ((1 + 4K _H η _sp ) ^0.5 −1) / (2K _H C) (1)
(Where η _SP = η / η ₀ −1, η is the polymer solution dropping seconds, η ₀ is the solvent dropping seconds,
C is the polymer solution concentration (g / dL), and K _H is the Huggins constant. K _H adopted the 0.33. )

<Terminal carboxyl group concentration (AV) equivalent / ton>
After pulverizing the sample, it was dried at 140 ° C. for 15 minutes in a hot air dryer, and 0.1 g was accurately weighed from the sample cooled to room temperature in a desiccator, taken into a test tube, 3 ml of benzyl alcohol was added, The solution was dissolved at 195 ° C. for 3 minutes while blowing dry nitrogen gas, and then 5 ml of chloroform was gradually added and cooled to room temperature. One to two drops of phenol red indicator were added to this solution, and titrated with a 0.1N sodium hydroxide benzyl alcohol solution with stirring while blowing dry nitrogen gas, and the procedure was terminated when the color changed from yellow to red. Moreover, the same operation was implemented as a blank, without melt | dissolving a sample, and the terminal carboxyl group density | concentration (acid value) was computed by the following formula | equation (2).

Terminal carboxyl concentration (equivalent / ton) = (ab) × 0.1 × f / w (2)
(Where a is the amount of 0.1N sodium hydroxide in benzyl alcohol solution required for titration (μl), b is the amount of 0.1N sodium hydroxide in benzyl alcohol solution required for titration with a blank. The amount (μl), w is the amount of the polyester resin sample (g), and f is the titer of 0.1N sodium hydroxide in benzyl alcohol.)
In addition, the titer (f) of the benzyl alcohol solution of 0.1N sodium hydroxide was calculated | required with the following method. Collect 5 ml of methanol in a test tube, add 1-2 drops as an indicator of an ethanol solution of phenol red, Titrate with 0.4 ml of 1N sodium hydroxide in benzyl alcohol to the color change point, then add 0.2 ml of 0.1N aqueous hydrochloric acid solution with known titer as a standard solution, and add 0.1N hydroxide again. The solution was titrated with a sodium benzyl alcohol solution to the discoloration point (the above operation was performed under dry nitrogen gas blowing). The titer (f) was calculated by the following formula (3).

Titer (f) = Titer of 0.1N aqueous hydrochloric acid × Amount of collected 0.1N aqueous hydrochloric acid (μl) / Titration of 0.1N sodium hydroxide in benzyl alcohol (μl) (3)
<Calculation of degree of polymerization>
About 20 mg of the sample was dissolved in 0.75 ml of a deuterated chloroform / heavy hexafluoroisopropanol (volume ratio 7/3) mixed solvent, 25 μl of heavy pyridine was added, and the sample was transferred to an NMR sample tube having an outer diameter of 5 mm. 1H NMR spectra were measured at room temperature using a Bruker AVANCE400 spectrometer. As a standard for chemical shift, the signal of TMS (trimethylsilane) was set to 0.00 ppm. The amount of terminal OH group (equivalent / ton) and the amount of terminal vinyl group (equivalent / ton) are calculated from the signal intensity corresponding to the terminal OH group and terminal vinyl group derived from 1,4 butanediol. The sum of the amount (equivalent / ton) was taken as the total terminal group amount (equivalent / ton).

Subsequently, the number average molecular weight (Mn) was calculated by the following formula (4).
Mn = (2 / total amount of terminal groups) × 1000000 (4)
Furthermore, the degree of polymerization was determined by the following formula (5).
Degree of polymerization = molecular weight of Mn / PBT1 unit (5)
(The molecular weight of one unit of PBT was 220.)

<Pellet color tone (b value)>
Reference Example 1 of JIS Z8730 was prepared by filling pellet-shaped PBT into a cylindrical powder measurement cell having an inner diameter of 30 mm and a depth of 12 mm, and using a colorimetric color difference meter Z300A (manufactured by Nippon Denshoku Industries Co., Ltd.). The b value by the color coordinate of Hunter's color difference formula in the Lab display system described in the above was obtained as a simple average value of four values measured by rotating the measurement cell by 90 degrees by the reflection method.

<Melt viscosity Pa · sec>
Measurement of melt viscosity, using a Toyo Seiki Capillograph (Capillograph 1B), the melt viscosity was measured under the conditions of a temperature of 245 ° C., a shear rate of 10 to 10,000 / sec, a capillary length of 10 mm, and a capillary diameter of 1 mm. In Examples and Comparative Examples, the melt viscosity value is typically 1000 / sec.

<Fine powder ppm>
A plain weave wire mesh (40 mesh, wire diameter 0.2 mm) was installed at the outlet of the dehydrator, and fine powder generated from the start to the end of strand cutting was collected. The fine powder collected on the filter was dried at 120 ° C. for 6 hours and cooled at room temperature, and then the weight of the fine powder was measured. A value obtained by dividing the weight of the fine powder by the weight of the obtained PBT pellet was determined as the amount of fine powder.

[Example 1]
In a reaction vessel equipped with a stirrer, a nitrogen inlet, a heating device, a thermometer, a distilling tube, and a vacuum outlet, 150.9 parts by weight of terephthalic acid, 245.5 parts by weight of 1,4-butanediol and a catalyst 0.95 parts by weight of 1,4-butanediol solution (40 ppm by weight as titanium atoms with respect to the obtained PBT) prepared by dissolving 6% by weight of tetrabutyl titanate in advance was charged, and the system was placed under a nitrogen atmosphere by nitrogen-vacuum substitution. did.

The system was heated to 150 ° C. while stirring, and then reacted for 4 hours while distilling off the water produced by the esterification reaction while raising the temperature to 220 ° C. to obtain an oligomer.
Subsequently, 1.76 parts by weight of a 1,4-butanediol solution in which 1% by weight of magnesium acetate tetrahydrate had been dissolved in advance (10 ppm by weight as Mg atoms relative to the obtained PBT) was charged.

  Next, the temperature was raised to 245 ° C. over 0.5 hours, and the polycondensation reaction was performed by reducing the pressure to 1 torr over 1.5 hours. Thereafter, the reaction system was returned to normal pressure to complete the polycondensation reaction. The obtained PBT was extracted as a strand from the bottom of the reaction vessel and submerged in cooling water at 40 ° C., then the strand was cut with a cutter, and a pellet-like PBT was obtained via a dehydrator. The water temperature of the cooling water was adjusted using a heat exchanger.

  The obtained PBT had an intrinsic viscosity (IV) of 0.61 dL / g, a polymerization degree of 45, and a terminal carboxyl group concentration (AV) of 18 equivalents / ton. The melt viscosity was 35 Pa · sec. The polycondensation time was defined as the time from the start of pressure reduction to the end of the polycondensation reaction, and the polycondensation reaction rate was defined as the intrinsic viscosity / polycondensation reaction time. The polycondensation reaction rate was 0.38 dL / g / h. The amount of fine powder was 56 ppm. The results are shown in Table 1.

[Example 2]
A PBT pellet was obtained in the same manner as in Example 1 except that the cooling water temperature was set to 60 ° C. in Example 1. Various analysis results are shown in Table 1.
[Example 3]
A PBT pellet was obtained in the same manner as in Example 1 except that the cooling water temperature was 20 ° C. in Example 1. Various analysis results are shown in Table 1.

[Example 4]
PBT pellets were obtained in the same manner as in Example 1 except that the pressure was reduced to 1 Torr over 1.5 hours in Example 1 and the polycondensation reaction was then performed at the same degree of vacuum for 0.5 hours. Various analysis results are shown in Table 1.
[Comparative Example 1]
A PBT pellet was obtained in the same manner as in Example 1 except that the cooling water temperature was 10 ° C. in Example 1. Various analysis results are shown in Table 1.

[Comparative Example 2]
PBT pellets were obtained in the same manner as in Example 1 except that the pressure was reduced to 1 torr over 1.5 hours and then the polycondensation reaction was performed at the same reduced pressure for 1.0 hour. Various analysis results are shown in Table 1. Since the degree of polymerization was high, the amount of fine powder generated was small. However, since the melt viscosity was high, the fluidity during molding was low.

  According to the present invention, polybutylene terephthalate having improved fluidity during melt molding can be efficiently produced. In particular, it is effective for injection molded products having a complicated structure such as electrical / electronic parts and precision equipment parts.

Claims (1)

  Esterification step for performing esterification reaction and / or transesterification reaction of dicarboxylic acid component having terephthalic acid or its ester-forming derivative as a main component and diol having 1,4 butanediol as a main component, and esterification step In the polycondensation step of polycondensation reaction of the oligomer obtained by the above, the molten polybutylene terephthalate is discharged in the form of a strand, solidified and then cut to produce pellets. Is solidified with cooling water at 20 to 60 ° C. and then cut, and a method for producing polybutylene terephthalate pellets.