JP2005350659A - Method for producing polybutylene terephthalate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a polybutylene terephthalate (PBT) having excellent color, transparency and quality stability and decreased foreign material content while preventing the loss of the raw materials. <P>SOLUTION: The production method is carried out by using a one-stage or multiple-stage esterification reactor to continuously esterify terephthalic acid with 1,4-butanediol in the presence of a titanium compound catalyst and successively conducting polycondensation reaction, wherein the esterification reaction of terephthalic acid with 1,4-butanediol is conducted in the presence of the titanium compound catalyst having a specific concentration under a specific pressure at a specific molar ratio of the raw materials. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for producing polybutylene terephthalate, and more specifically, in the continuous esterification reaction using terephthalic acid as a raw material, side reactions are suppressed to minimize the loss of the raw material, and the color tone, transparency The present invention relates to a method for producing polybutylene terephthalate with excellent foreign matter and reduced foreign matter.

  Polybutylene terephthalate, a representative engineering plastic among thermoplastic polyester resins, is easy to process, mechanical properties, heat resistance, chemical resistance, fragrance retention, and other physical and chemical properties. Therefore, it is widely used in injection-molded products such as automobile parts, electrical / electronic parts, and precision equipment parts. In recent years, taking advantage of its excellent properties, it has been widely used in fields such as films, sheets, monofilaments and fibers.

  By the way, normally, terephthalic acid or dimethyl terephthalate and 1,4-butanediol are used as raw materials for the production of polybutylene terephthalate. In recent years, the direct polymerization method using terephthalic acid and 1,4-butanediol, among them, the stability of product quality, the miniaturization of production equipment, the energy efficiency, In view of the advantages and the like, a direct continuous polymerization method in which raw materials are continuously supplied and products are continuously obtained has attracted attention.

  In the direct polymerization method, generally, terephthalic acid is esterified with excess 1,4-butanediol to oligomerize, and then generated by excess 1,4-butanediol incorporated in the oligomer molecule and condensation. Polybutylene terephthalate is produced through a polycondensation step in which the water to be removed is removed under reduced pressure to increase the molecular weight. In many cases, however, the initial esterification reaction is promoted and the generation of tetrahydrofuran due to side reactions is suppressed. In addition, a titanium compound is used as a catalyst (for example, Patent Document 1).

  However, it is known that a part of the titanium compound is deactivated during the esterification reaction, and foreign matter is generated or the transparency of the product is deteriorated (for example, Patent Document 2). This is remarkable in the continuous method (for example, Patent Document 3).

  Furthermore, since the titanium compound deactivated in the esterification reaction stage remains deactivated in the polycondensation stage, when polybutylene terephthalate having a desired molecular weight is obtained, as a result, the temperature is increased or the pressure is increased. The reaction conditions for polycondensation must be severed by lowering the temperature, but high temperatures lead to deterioration of the color tone of the polymer and increase of the terminal carboxyl group concentration, and excessive equipment is required to achieve low pressure. There are problems such as. On the other hand, if more titanium compounds are used to compensate for the deactivated titanium compounds, the number of deactivated titanium compounds also increases accordingly, and this leads to a dilemma that promotes the above problems.

  On the other hand, in the esterification reaction stage of the direct polymerization method, it is also important to suppress side reactions in which tetrahydrofuran is produced from 1,4-butanediol in order not to waste 1,4-butanediol as a raw material. . The reaction in which tetrahydrofuran is produced from 1,4-butanediol easily occurs in the presence of an acid catalyst. Therefore, in a direct continuous esterification reaction in which terephthalic acid is always present, terephthalic acid, which is a positive reaction, and 1,4-butanediol are present. How to increase the rate of the esterification reaction with butanediol is a problem, and as a means for solving the problem, it is said that addition of a titanium compound is effective (for example, Non-Patent Document 1). In addition, it is thought that the suppression of the byproduct of tetrahydrofuran in this case is due to the fact that the added titanium compound does not suppress the conversion of 1,4-butanediol to tetrahydrofuran, but promotes the positive reaction.

  On the other hand, since the byproduct rate of tetrahydrofuran depends on the concentration of 1,4-butanediol, an attempt to reduce the amount of byproduct tetrahydrofuran by lowering the concentration of 1,4-butanediol in the esterification reaction system is also available. (For example, Patent Documents 2 and 3).

  However, a decrease in the 1,4-butanediol concentration in the esterification reaction system also causes a decrease in the esterification reaction rate of terephthalic acid, which is a positive reaction, and as described above, tetrahydrofuran is produced from 1,4-butanediol. Since the reaction easily occurs in the presence of an acid catalyst, the amount of tetrahydrofuran by-product cannot be reduced as expected if the esterification reaction, which is a positive reaction, is promoted until the desired conversion rate (esterification rate) is reached. In addition, the solution haze due to catalyst deactivation remains high.

  On the other hand, in the esterification reaction, there is also an attempt to reduce the amount of by-product tetrahydrofuran while promoting a positive reaction at a high titanium compound concentration and maintaining a relatively high 1,4-butanediol concentration (for example, Patent Document 4). .

  However, the deactivation of the titanium compound is considered to be caused by the high molecular weight of the titanium compound due to the action of water or terephthalic acid, and this reaction is promoted as the titanium compound concentration increases, and is proposed above. With such a high titanium compound concentration, there is a problem that the deactivation reaction cannot be avoided, and the generation of foreign matter and the deterioration of transparency cannot be solved. Further, in the production of polybutylene terephthalate, the catalyst is not usually removed, and all of the catalyst is mixed in the product, so that there is a problem that coloring due to the catalyst residue and a decrease in thermal stability are inevitably increased.

  Further, the amount of the organotitanium compound to be added in the production of polybutylene terephthalate is specified, and a method in which the organotin compound is allowed to coexist in the initial esterification reaction stage (for example, Patent Documents 2 and 5), terephthalic acid and 1, The reaction of continuously esterifying 4-butanediol is divided into two stages. In the first stage esterification reaction, only an organotin compound is added, and in the second stage esterification reaction, an organotitanium compound is added. A method of reducing catalyst-derived foreign matter and haze has been proposed (for example, Patent Document 6).

  However, even in the above method, the problem of foreign matter and haze is not solved, and there is a further problem that the color tone of polybutylene terephthalate is deteriorated due to the addition of a tin compound.

  As described above, in the direct continuous production method of polybutylene terephthalate, it is difficult to reduce the amount of tetrahydrofuran produced as a by-product while preventing the deactivation of the titanium compound in the initial esterification reaction stage.

JP 48-47594 A JP 2002-284868 A JP 2002-284870 A Japanese Patent Laid-Open No. 62-195017 Japanese Patent Laid-Open No. 10-330469 Japanese Patent Laid-Open No. 10-330468 Textile Society Journal, 43, No. 1, P.I. 35

  The present invention has been made in view of the above circumstances, and its purpose is to provide a method for producing polybutylene terephthalate having excellent color tone, transparency, and quality stability and reduced foreign matter while preventing loss of raw materials. There is to do.

  As a result of intensive studies to solve the above problems, the present inventors have identified the relationship between the titanium compound concentration in the esterification reaction, the reaction pressure, and the molar ratio of terephthalic acid to 1,4-butanediol. By making it into the range, the deactivation amount of the titanium compound catalyst can be remarkably reduced, and it has been found that the above problems can be easily solved, and the present invention has been completed.

  The present invention has been completed based on the above findings, and the gist of the present invention is that terephthalic acid and 1,4-butanediol are used in the presence of a titanium compound catalyst using a single-stage or multi-stage esterification reactor. In a method for producing polybutylene terephthalate by continuously esterifying and subsequently polycondensating, a method for producing polybutylene terephthalate characterized by satisfying the following conditions (A) to (C): Exist.

(A) The pressure (P) in at least one esterification reaction tank is 20 to 90 kPa.
(B) The density | concentration of the titanium compound catalyst used by esterification reaction is 90 ppm or less as a weight concentration ((alpha)) of the titanium atom with respect to the polybutylene terephthalate finally obtained.
(C) TM is the number of moles of terephthalic acid supplied per unit time, BM is the number of moles of all 1,4-butanediol supplied to each esterification reaction tank per unit time, and titanium is used in the esterification reaction. When the concentration of the compound catalyst is α (weight concentration of titanium atoms with respect to the finally obtained PBT) and the pressure in the esterification reaction tank is P, the following formulas (I) and (II) are established.

  According to the present invention, PBT that can be suitably used for films, monofilaments, fibers, electrical and electronic parts, automobile parts, etc. with excellent color tone and transparency and reduced foreign matter while suppressing side reactions. Is provided.

  Hereinafter, the present invention will be described in detail. However, the description of the constituent elements described below is a representative example of embodiments of the present invention, and the present invention is not limited to these contents.

  The polybutylene terephthalate (hereinafter abbreviated as PBT) of the present invention has a structure in which a terephthalic acid unit and a 1,4-butanediol unit are ester-bonded, and 50 mol% or more of dicarboxylic acid units are composed of terephthalic acid units. The polyester which 50 mol% or more of a diol component consists of a 1, 4- butanediol unit. The proportion of terephthalic acid units in all dicarboxylic acid units is preferably 70 mol% or more, more preferably 80 mol% or more, particularly preferably 95 mol% or more, and 1,4-butanediol unit in all diol units. The ratio is preferably 70 mol% or more, more preferably 80 mol% or more, and particularly preferably 95 mol% or more. When the amount of terephthalic acid units or 1,4-butanediol units is less than 50 mol%, the crystallization rate of PBT is lowered, and the moldability is deteriorated.

  In the present invention, the dicarboxylic acid component other than terephthalic acid is not particularly limited. For example, phthalic acid, isophthalic acid, 4,4′-diphenyldicarboxylic acid, 4,4′-diphenyletherdicarboxylic acid, 4,4′-benzophenone Aromatic dicarboxylic acids such as dicarboxylic acid, 4,4′-diphenoxyethanedicarboxylic acid, 4,4′-diphenylsulfone dicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,2-cyclohexanedicarboxylic acid, 1,3- Aliphatic dicarboxylic acids such as cyclohexanedicarboxylic acid and 1,4-cyclohexanedicarboxylic acid, aliphatic dicarboxylic acids such as malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid and sebacic acid I can list them. These dicarboxylic acid components can be introduced into the polymer skeleton as a dicarboxylic acid or a dicarboxylic acid derivative such as a dicarboxylic acid ester or a dicarboxylic acid halide as a raw material.

  In the present invention, the diol component other than 1,4-butanediol is not particularly limited. For example, ethylene glycol, diethylene glycol, polyethylene glycol, 1,2-propanediol, 1,3-propanediol, polypropylene glycol, polytetra Methylene glycol, dibutylene glycol, 1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, aliphatic diols such as 1,8-octanediol, 1,2-cyclohexanediol, 1,4-cyclohexanediol , 1,1-cyclohexanedimethylol, 1,4-cyclohexanedimethylol and other alicyclic diols, xylylene glycol, 4,4′-dihydroxybiphenyl, 2,2-bis (4-hydroxyphenyl) propane, bis ( 4- And aromatic diols such as hydroxyphenyl) sulfone.

  In the present invention, hydroxycarboxylic acids such as lactic acid, glycolic acid, m-hydroxybenzoic acid, p-hydroxybenzoic acid, 6-hydroxy-2-naphthalenecarboxylic acid, p-β-hydroxyethoxybenzoic acid, and alkoxycarboxylic acids. Monofunctional components such as acid, stearyl alcohol, benzyl alcohol, stearic acid, benzoic acid, t-butylbenzoic acid, benzoylbenzoic acid, tricarbaric acid, trimellitic acid, trimesic acid, pyromellitic acid, gallic acid, trimethylolethane Trifunctional or polyfunctional components such as trimethylolpropane, glycerol and pentaerythritol can be used as the copolymerization component.

  In the present invention, terephthalic acid and 1,4-butanediol as main raw materials are continuously esterified in the presence of a titanium compound catalyst to obtain an oligomer, followed by polycondensation to obtain PBT.

  Specific examples of titanium compounds used as catalysts include inorganic titanium compounds such as titanium oxide and titanium tetrachloride, titanium alcoholates such as tetramethyl titanate, tetraisopropyl titanate, and tetrabutyl titanate, titanium phenolates such as tetraphenyl titanate, etc. Among them, tetraalkyl titanate is preferable, and tetrabutyl titanate is particularly preferable.

  In addition to the titanium compound, a tin compound may be used as a catalyst. Specific examples include dibutyltin oxide, methylphenyltin oxide, tetraethyltin, hexaethylditin oxide, cyclohexahexylditin oxide, didodecyltin oxide, triethyltin hydroxide, triphenyltin hydroxide, triisobutyltin acetate. , Dibutyltin diacetate, diphenyltin dilaurate, monobutyltin trichloride, tributyltin chloride, dibutyltin sulfide, butylhydroxytin oxide, methylstannic acid, ethylstannic acid, butylstannic acid and the like.

  Since tin deteriorates the color tone of PBT, its addition amount is usually 200 ppm or less, preferably 100 ppm or less, more preferably 10 ppm or less, and preferably not added as tin atoms.

  In addition to titanium compounds, magnesium compounds such as magnesium acetate, magnesium hydroxide, magnesium carbonate, magnesium oxide, magnesium alkoxide, magnesium hydrogen phosphate, calcium acetate, calcium hydroxide, calcium carbonate, calcium oxide, calcium alkoxide Side, calcium compounds such as calcium hydrogen phosphate, antimony compounds such as antimony trioxide, germanium compounds such as germanium dioxide and germanium tetroxide, manganese compounds, zinc compounds, zirconium compounds, cobalt compounds, orthophosphoric acid, phosphorous acid, Phosphorous acid, polyphosphoric acid, phosphorus compounds such as esters and metal salts thereof, and reaction aids such as sodium hydroxide and sodium benzoate may be used.

  The concentration of the titanium compound used in the esterification reaction of the present invention needs to be 90 ppm or less as the weight (α) of titanium atoms with respect to the finally obtained PBT.

In the present invention, the lower limit of the titanium content (α) is usually 20 ppm, preferably 25 ppm, more preferably 30 ppm, particularly preferably 35 ppm, and the upper limit is preferably 80 ppm, more preferably 60 ppm, particularly preferably. 50 ppm, especially 40 ppm is optimal.
If the concentration of the titanium compound is too high, it will be deactivated by the esterification reaction, leading to deterioration in color tone and haze, and an increase in foreign matter. If it is too low, the amount of by-product tetrahydrofuran (hereinafter sometimes abbreviated as THF) And increase in polycondensation reactivity.

  The content of titanium atoms and the like can be measured using a method such as atomic emission, atomic absorption, ICP (Inductively Coupled Plasma) after recovering the metal in the polymer by a method such as wet ashing.

  The esterification reaction in the present invention can be carried out in a single stage or a plurality of stages of reaction tanks, and it is preferable to carry out in one stage of one tank in order to prevent the equipment from becoming excessive. The esterification reaction tank is preferably a reaction tank having a stirrer. Specific examples thereof include a vertical stirring complete mixing tank, a vertical heat convection mixing tank, and a tower-type continuous reaction tank. A model is mentioned. A well-known stirrer can be used. In addition to the normal type consisting of a power unit, bearing, shaft, and stirring blade, a high-speed rotating type such as a turbine stator type high-speed rotating stirrer, disk mill type stirrer, rotor mill type stirrer, etc. Can also be used.

  There is no limitation on the form of stirring. Besides the usual stirring method in which the reaction liquid in the esterification reaction tank is directly stirred from the top, bottom, side, etc. of the reaction tank, a part of the reaction liquid is placed outside the reactor. A method of circulating the reaction solution by taking it out with piping or the like and stirring it with a line mixer or the like can be used.

  Known types of stirring blades can also be selected, and specific examples include propeller blades, screw blades, turbine blades, fan turbine blades, disk turbine blades, fiddler blades, full zone blades, and Max blend blades.

  In the present invention, the esterification reaction tank and the polycondensation reaction tank are distinguished from each other when the esterification rate of the oligomer represented by the following formula (III) is 90% or less at the inlet of the reactor. If it exceeds%, the polycondensation reaction tank is used.

  The pressure of the esterification reaction in the present invention needs to be 20 to 90 kPa (absolute pressure, hereinafter the same) in at least one esterification reaction tank, preferably 30 to 75 kPa, more preferably 35 to 70 kPa, and still more preferably. Is 40 to 70 kPa, particularly preferably 50 to 70 kPa.

  If the esterification reaction pressure is less than 20 kPa, the concentration of 1,4-butanediol in the reaction system tends to decrease and the deactivation of the titanium compound catalyst tends to increase. If it exceeds 90 kPa, 1,4-butanediol In addition to an increase in the amount of by-produced THF, the concentration of water in the system also increases, so that deactivation of the titanium compound is unavoidable.

  In the present invention, TM is the number of moles of terephthalic acid supplied per unit time, TM is the number of moles of all 1,4-butanediol supplied to each esterification reaction tank per unit time, and BM is used in the esterification reaction. When the concentration of the titanium compound catalyst is α (weight concentration of titanium atoms with respect to the finally obtained PBT) and the pressure of the esterification reaction tank is P, the following formulas (I) and (II) may be satisfied. is important.

  Formulas (I) and (II) prevent the deactivation of the titanium compound catalyst in the esterification reaction in the method of producing PBT by continuously esterifying terephthalic acid and 1,4-butanediol as raw materials. Shows the optimum conditions for the esterification reaction to minimize the amount of THF produced as a by-product, and the deactivation of the titanium compound catalyst indicates that the lower the titanium compound concentration in the esterification reaction, This is based on the discovery that the higher the 4-butanediol concentration and the lower the water concentration, the lower the concentration.

  The number of moles of terephthalic acid supplied per unit time (TM) here refers to the number of moles of terephthalic acid normally supplied as a mixed slurry with 1,4-butanediol as a raw material. It is an amount proportional to the production amount per unit time.

  On the other hand, the number of moles (BM) of all 1,4-butanediol supplied to each esterification reaction tank per unit time is 1,4-butanediol supplied together with terephthalic acid as a raw slurry. 1,4-butanediol supplied independently, 1,4-butanediol used as a solvent for the catalyst, etc., and the total of 1,4-butanediol entering the reaction tank from the outside of the esterification reaction tank, When there are a plurality of esterification reaction tanks, all of the 1,4-butanediol entering from the outside is added to each reaction tank, and direct reaction of terephthalic acid with excess 1,4-butanediol is performed. In the polymerization method, basically, it can be controlled independently of the production amount.

  The pressure (P) of the esterification reaction tank is the pressure of the reaction tank when there is one esterification reaction tank, and there are a plurality of esterification reaction tanks, and a plurality of esterification reaction tanks therein. When the pressure of 20 to 90 kPa is satisfied, the pressure of the lower reaction tank, when there are a plurality of esterification reaction tanks, and when only one esterification reaction tank satisfies 20 to 90 kPa, To do.

  The value of β is 4.0 or more and 7.0 or less, preferably 4.5 to 6.5, and more preferably 5.0 to 6.0. If the value of β is less than 4.0, the deactivation of the titanium compound tends to increase, and if it is more than 7.0, the amount of THF by-product increases, and further 1,4-butane in the esterification reaction tank Since the amount of diol evaporation increases, it is disadvantageous in terms of energy.

  Among them, the lower limit of the BM / TM value is preferably 2.1, more preferably 2.5, particularly preferably 3.1, and most preferably 3.3. On the other hand, the upper limit is preferably 6.5, more preferably 6.0, particularly preferably 5.5, and most preferably 5.0. If the value of BM / TM is too low, the deactivation of the titanium compound tends to increase. If it is too high, the amount of by-product THF increases, which tends to be disadvantageous in terms of energy.

  The esterification reaction is preferably performed at a temperature equal to or higher than the boiling point of 1,4-butanediol in order to shorten the reaction time in at least one esterification reaction tank. The boiling point of 1,4-butanediol depends on the pressure of the reaction, but is 205 ° C. at 50 kPa.

  Among them, the temperature of the esterification reaction for maintaining the reaction rate and suppressing coloring and side reactions is usually 180 to 260 ° C., preferably 200 to 240 ° C., particularly preferably 210 to 235 ° C., and the esterification reaction tank Is more preferably 210 to 235 ° C. in at least one reaction vessel.

  There is no limitation on the time for the esterification reaction, but if it is too long, by-product THF increases and coloring and deterioration of the oligomer proceed, so that the average residence time based on the terephthalic acid unit in the esterification reaction tank is usually 0. 5 to 12 hours, preferably 1 to 8 hours, particularly preferably 2 to 6 hours.

  The number average degree of polymerization of the oligomer obtained by the production method of the present invention is preferably a pentamer or less, more preferably, when a unit consisting of terephthalic acid and one molecule of 1,4-butanediol is defined as a monomer. Tetramer or less, particularly preferably trimer or less. When the 1,4-butanediol concentration in the reaction system is low, the number average degree of polymerization of the oligomer tends to increase. However, under such conditions, the titanium compound tends to be deactivated as described above. When trying to obtain an oligomer having an esterification rate, the amount of by-product THF tends to increase, and the polycondensation reaction rate in the polycondensation step following the esterification reaction step is reduced.

  The number average degree of polymerization of the oligomer obtained by the esterification reaction can be determined by vapor osmometer, end group titration, end group determination by NMR, and the like.

  In the present invention, preferably, in the esterification reaction tank, at least a portion of 1,4-butanediol is supplied to the esterification reaction tank independently of terephthalic acid in the presence of a titanium compound catalyst, And a step of continuously esterifying 1,4-butanediol.

  That is, in the present invention, haze and foreign matters derived from the catalyst are reduced, and the catalytic activity is not lowered. Therefore, in addition to 1,4-butanediol supplied together with terephthalic acid as a raw slurry or solution, It is preferable to supply 1,4-butanediol to the esterification reaction tank independently of the acid. Hereinafter, the 1,4-butanediol may be referred to as “separately supplied 1,4-butanediol”.

  The “separately supplied 1,4-butanediol” can be applied with fresh 1,4-butanediol independent of the process. In addition, “separately supplied 1,4-butanediol” collects 1,4-butanediol distilled from the esterification reaction tank with a condenser or the like and holds it in the reaction tank as it is or in a temporary tank. It can also be refluxed, or can be supplied as 1,4-butanediol with increased purity by separating and purifying impurities. Hereinafter, “separately supplied 1,4-butanediol” composed of 1,4-butanediol collected by a condenser or the like may be referred to as “recycled 1,4-butanediol”. From the viewpoint of effective utilization of resources and simplicity of equipment, it is preferable to apply “recycled 1,4-butanediol” to “separately supplied 1,4-butanediol”.

  Usually, 1,4-butanediol distilled from the esterification reaction tank contains components such as water, THF, alcohol and the like in addition to the 1,4-butanediol component. Therefore, it is preferable that the 1,4-butanediol obtained by the distillation is separated and purified from these components after being collected by a condenser or the like or collected, and returned to the esterification reaction tank.

  In the present invention, it is preferable to return 10% by weight or more of “separately supplied 1,4-butanediol” directly to the reaction liquid phase part. Here, the reaction liquid phase part indicates the liquid phase side of the gas-liquid interface of the esterification reaction tank, and returning directly to the reaction liquid phase part means “separate supply 1, 4- This means that “butanediol” is supplied directly to the liquid phase part without going through the gas phase part. The ratio of returning directly to the liquid phase part of the reaction liquid is preferably 30% by weight or more, more preferably 50% by weight or more, particularly preferably 80% by weight or more, and most preferably 90% by weight or more. When there is little "separately supplied 1,4-butanediol" returned directly to the reaction liquid phase part, the titanium compound catalyst tends to be deactivated.

  The temperature of “separately supplied 1,4-butanediol” when returning to the reactor is usually 50 to 220 ° C., preferably 100 to 200 ° C., more preferably 150 to 190 ° C. When the temperature of “separately supplied 1,4-butanediol” is too high, the amount of THF by-product tends to increase, and when it is too low, the heat load tends to increase, leading to energy loss.

  In the present invention, in order to prevent deactivation of the catalyst, 10% by weight or more of the titanium compound catalyst used in the esterification reaction may be directly supplied to the reaction liquid phase part independently of terephthalic acid. preferable. Here, the reaction liquid phase part indicates the liquid phase side of the gas-liquid interface in the esterification reaction tank, and the direct supply to the reaction liquid phase part uses piping or the like, and the titanium compound catalyst is in the gas phase. This means that it is directly supplied to the liquid phase part without going through the part. The proportion of the titanium compound catalyst added directly to the reaction liquid phase is preferably 30% by weight or more, more preferably 50% by weight or more, particularly preferably 80% by weight or more, and most preferably 90% by weight or more.

  If the titanium compound catalyst supplied directly to the reaction liquid phase part is less than 30% by weight, it not only causes deactivation and coloring, but also vapor phase part of the esterification reaction vessel due to evaporation, sublimation and entrainment of the titanium compound. Foreign matter is easily generated on the surface, causing various troubles.

  The above titanium compound catalyst can be directly supplied to the reaction liquid phase part of the esterification reaction tank or the transesterification reaction tank with or without being dissolved in a solvent, etc. In order to reduce adverse effects such as heat denaturation from the heat medium jacket of the vessel, it is preferable to dilute with a solvent such as 1,4-butanediol. The concentration at this time is usually 0.01 to 20% by weight, preferably 0.05 to 10% by weight, more preferably 0.08 to 8% by weight, as the concentration of the titanium compound catalyst with respect to the entire solution. Further, in order not to increase foreign matter and haze, the water concentration in the solution is preferably 0.05 to 1.0% by weight, more preferably 0.1 to 0.5% by weight. The temperature for preparing the solution is usually 20 to 150 ° C., preferably 30 to 100 ° C., more preferably 40 to 80 ° C. from the viewpoint of preventing deactivation and aggregation of the titanium compound. Moreover, it is preferable to mix this catalyst solution with a separate supply 1, 4- butanediol by piping etc. and supply to an esterification reaction tank from the point of deterioration prevention, precipitation prevention, deactivation prevention, and stable supply.

  In the production of PBT by the direct polymerization method, a polycondensation reaction is usually carried out following the initial esterification reaction. In the present invention, from the viewpoint of productivity, stability of product quality, and improvement effect of the present invention. The so-called continuous method is preferred in which the esterification reaction is continuously carried out and then the subsequent polycondensation reaction is continuously carried out.

  The PBT polycondensation reaction step may use a single reaction vessel or a plurality of reaction vessels, but preferably uses a plurality of reaction vessels. When continuously performing the polycondensation step, it is preferable to use a plurality of reaction tanks and use 2 to 5 polycondensation reaction tanks arranged in series with different pressure settings.

  The form of the reaction tank may be any type such as a vertical stirring complete mixing tank, a vertical heat convection mixing tank, a tower type continuous reaction tank, or the like. Among them, a reaction tank having a stirring device is preferable, and as a stirring device, a turbine stator type high-speed rotating stirrer, a disk mill type stirrer, a rotor mill type stirrer in addition to a normal type including a power unit, a bearing, a shaft, and a stirring blade. A type that rotates at high speeds can also be used.

  The form of stirring is not particularly limited, and in addition to the usual stirring method in which the reaction solution in the reaction tank is directly stirred from the top, bottom, side, etc. of the reaction tank, a part of the reaction solution is connected to the reactor by piping or the like. A method of circulating the reaction solution by taking it outside and stirring it with a line mixer or the like can also be employed. In particular, at least one of the polycondensation reaction tanks is recommended to use a horizontal reactor having a surface renewal having a rotating shaft in the horizontal direction and excellent in self-cleaning property and plug flow property.

  Further, in order to suppress coloring and deterioration and to suppress an increase in the end of vinyl group or the like, in at least one reaction tank, a high vacuum of usually 1.3 kPa or less, preferably 0.5 kPa or less, more preferably 0.3 kPa or less. The temperature is usually 225 to 255 ° C, preferably 230 to 250 ° C, more preferably 233 to 245 ° C. Moreover, the average residence time converted by PBT obtained is normally 0.5 to 12 hours, preferably 1 to 8 hours, and particularly preferably 2 to 6 hours.

  Further, in the PBT polycondensation reaction step, once a PBT having a relatively small molecular weight, for example, an intrinsic viscosity of about 0.1 to 1.0 dL / g, is produced by melt polycondensation, the PBT is subsequently melted at a melting point of PBT or less. Solid state polycondensation (solid phase polymerization) can also be performed at a temperature.

  The PBT obtained by the production method of the present invention has excellent quality without removing the foreign matters because the foreign matters derived from the catalyst are drastically reduced. By installing a filter in the flow path, PBT with further excellent quality can be obtained. In the present invention, for the reasons described above, when a filter having the same opening as that used in a conventional PBT manufacturing facility is used, it is possible to extend the life until the replacement. Further, if the life until replacement is set to be the same, a filter with a smaller opening can be installed.

  If the filter is installed too far upstream of the manufacturing process, foreign matter generated downstream cannot be removed, and the pressure loss of the filter increases and the flow rate is maintained where the downstream viscosity is high. It is necessary to increase the opening of the filter, to increase the filter filtration area and piping, etc., and to receive high shear when passing through the fluid, so it is inevitable that PBT deteriorates due to shear heat generation. . Therefore, the filter installation position is such that the intrinsic viscosity of PBT or its precursor is usually 0.1 to 1.2 dL / g, preferably 0.2 to 1.0 dL / g, more preferably 0.5 to 0.9 dL. The position / g is selected.

  The filter medium constituting the filter may be any of a metal wind, a laminated metal mesh, a metal nonwoven fabric, a porous metal plate, etc., but from the viewpoint of filtration accuracy, a laminated metal mesh or a metal nonwoven fabric is preferable, and in particular, the mesh opening is large. Those fixed by a sintering process are preferred. The shape of the filter may be any type such as basket type, disc type, leaf disc type, tube type, flat cylindrical type, pleated cylindrical type, and the like. In order not to affect the operation, it is preferable to install a plurality of filters so that they can be switched and used, or to install an auto screen changer.

  The absolute filtration accuracy of the filter is not particularly limited, but is usually 0.5 to 200 μm, preferably 1 to 100 μm, more preferably 5 to 50 μm, and particularly preferably 10 to 30 μm. If the absolute filtration accuracy is too large, the effect of reducing foreign matters in the product is lost, and if it is too small, productivity is lowered and filter replacement frequency is increased. The absolute filtration accuracy indicates a minimum particle size when the filter is completely removed by filtration when a filtration test is performed using a standard particle size product such as glass beads having a known and uniform particle size.

  During the polycondensation reaction, the catalyst added during the esterification reaction is usually used as the polycondensation reaction catalyst. However, a new catalyst or cocatalyst may be added at the end of the esterification reaction or during the polycondensation reaction. The catalyst and cocatalyst added to may be the same as or different from those used in the esterification reaction.

  There is no limit to the amount of catalyst or co-catalyst added, but if it is too much, the color tone of the product PBT will deteriorate, the thermal stability will decrease, the terminal carboxyl group will increase, etc. , Preferably 100 ppm or less, more preferably 50 ppm or less, particularly preferably 20 ppm or less.

  The intrinsic viscosity of the PBT obtained by the production method of the present invention is usually 0.60 to 2.00 dL / g, preferably 0.65 to 1.50 dL / g, more preferably 0.68 to 1.30 dL / g. is there. When the intrinsic viscosity is less than 0.60 dL / g, the mechanical strength of the molded product becomes insufficient, and when it exceeds 2.00 dL / g, the melt viscosity becomes high, the fluidity deteriorates, and the moldability deteriorates. There is a tendency. The intrinsic viscosity is a value measured at 30 ° C. using a mixed solution of phenol / tetrachloroethane (weight ratio 1/1) as a solvent.

  The terminal carboxyl group concentration of PBT obtained by the production method of the present invention is usually 0.1 to 50 μeq / g, preferably 1 to 40 μeq / g, more preferably 1 to 30 μeq / g, and particularly preferably 1 to 25 μeq / g. It is. When the terminal carboxyl group concentration is too high, the hydrolysis resistance of PBT deteriorates.

  The temperature-falling crystallization temperature of PBT obtained by the production method of the present invention is usually 170 to 190 ° C, preferably 172 to 185 ° C, more preferably 175 to 180 ° C. The temperature drop crystallization temperature in the present invention is the temperature of an exothermic peak due to crystallization that appears when the resin is melted using a differential scanning calorimeter at a temperature drop rate of 20 ° C./min. The temperature-falling crystallization temperature corresponds to the crystallization speed, and the higher the temperature-falling crystallization temperature, the faster the crystallization speed. Therefore, the cooling time can be shortened and the productivity can be increased during injection molding. When the temperature-falling crystallization temperature is low, crystallization takes time during injection molding, and the cooling time after injection molding has to be lengthened, and the molding cycle tends to increase and productivity tends to decrease.

  The solution haze of PBT obtained by the production method of the present invention is the solution turbidity when 2.7 g of PBT is dissolved in 20 mL of a phenol / tetrachloroethane mixed solvent (weight ratio 3/2) and measured at an optical path length of 10 mm. Usually, it is 3% or less, preferably 2% or less, more preferably 1% or less, and particularly preferably 0.5% or less. The solution haze depends on the deactivation amount of the titanium compound catalyst, and tends to increase when the deactivation is large. If the value exceeds 3%, it accumulates in the poorly fluid part of the process due to long-term operation. Eventually, it aggregates and grows into foreign matter. This foreign substance becomes a causative substance of fish eye when PBT is formed into a film or sheet, or a causative substance of yarn breakage when it is formed into a filament or fiber.

  Hereinafter, preferred embodiments of a method for producing PBT will be described with reference to the accompanying drawings. FIG. 1 is an explanatory diagram of an example of an esterification reaction step employed in the present invention, FIGS. 2 and 3 are explanatory diagrams of another example of an esterification reaction step employed in the present invention, and FIG. 4 is an illustration of the present invention. Explanatory drawing of an example of the polycondensation process employ | adopted, FIGS. 5-7 are explanatory drawings of another example of the polycondensation process employ | adopted by this invention.

  In FIG. 1, terephthalic acid as a raw material is usually mixed with 1,4-butanediol in a raw material mixing tank (not shown), and supplied to the reaction tank (A) in the form of slurry from the raw material supply line (1). The On the other hand, the titanium compound catalyst is preferably supplied from the catalyst supply line (3) after being made into a solution of 1,4-butanediol in a catalyst adjustment tank (not shown). FIG. 1 shows a mode in which a catalyst supply line (3) is connected to a recycle line (2) for recycle 1,4-butanediol, and both are mixed and then supplied to the liquid phase part of the reaction tank (A). It was.

  The gas distilled from the reaction tank (A) is separated into a high-boiling component and a low-boiling component in the rectifying column (C) through the distillation line (5). Usually, the main component of the high boiling component is 1,4-butanediol, and the main components of the low boiling component are water and THF.

  The high-boiling components separated in the rectification column (C) are extracted from the extraction line (6) and partly circulated from the recirculation line (2) to the reaction tank (A) via the pump (D). , Part is returned from the circulation line (7) to the rectification column (C). Further, the surplus is extracted outside from the extraction line (8). When 1,4-butanediol needs to be supplied to the reaction tank (A), 1,4-butanediol is supplied using an additional supply or recovery line (15). On the other hand, the light boiling components separated in the rectification column (C) are extracted from the gas extraction line (9), condensed in the condenser (G), and temporarily passed through the condensate line (10) to the tank (F). Accumulated. A part of the light boiling components collected in the tank (F) is returned to the rectification column (C) through the extraction line (11), the pump (E) and the circulation line (12), and the remainder is extracted. It is extracted outside through the line (13). The condenser (G) is connected to an exhaust device (not shown) via a vent line (14). The oligomer produced | generated within the reaction tank (A) is extracted through an extraction pump (B) and an extraction line (4).

  In the process shown in FIG. 1, the catalyst supply line (3) is connected to the recirculation line (2), but both may be independent. Moreover, the raw material supply line (1) may be connected to the liquid phase part of the reaction vessel (A).

  The process shown in FIG. 2 differs from the process shown in FIG. 1 in that the rectifier (C) is equipped with a reboiler (H). Installation of the reboiler (H) facilitates operation control of the rectification tower (C).

  The process shown in FIG. 3 differs from the process shown in FIG. 1 in that a bypass line (16) branched from the circulation line (7) is connected to the gas phase portion of the reaction vessel (A). Therefore, in the case of the process shown in FIG. 3, a part of the recycled 1,4-butanediol returns to the reaction solution via the gas phase part of the reaction tank (A).

  In FIG. 4, the oligomer supplied from the extraction line (4) shown in FIGS. 1 to 3 is subjected to polycondensation under reduced pressure in the first polycondensation reaction tank (a) to become a prepolymer, It is supplied to the second polycondensation reaction tank (d) through the extraction gear pump (c) and the extraction line (L1). In the second polycondensation reaction tank (d), polycondensation usually proceeds at a lower pressure than that of the first polycondensation reaction tank (a) to become a polymer. The obtained polymer is extracted in the form of a melted strand from the die head (g) through the extraction gear pump (e) and the extraction line (L3), cooled with water, and then rotated with a rotary cutter ( It is cut into a pellet in h). Reference numeral (L2) is a vent line of the first polycondensation reaction tank (a), and reference numeral (L4) is a vent line of the second polycondensation reaction tank (d).

  The process shown in FIG. 5 differs from the process shown in FIG. 4 in that a filter (f) is provided in the flow path of the extraction line (L3).

  The process shown in FIG. 6 differs from the process shown in FIG. 4 in that the third polycondensation reaction tank (k) is provided after the second polycondensation reaction tank (d). The third polycondensation reaction tank (k) is a horizontal reaction tank composed of a plurality of stirring blade blocks and equipped with a biaxial self-cleaning type stirring blade. The polymer introduced into the third polycondensation reaction tank (k) from the second polycondensation reaction tank (d) through the extraction line (L3) is further subjected to polycondensation here, and then the extraction gear pump (m ) And the extraction line (L5), and is extracted from the die head (g) in the form of a melted strand, cooled with water, and then cut with a rotary cutter (h) to form pellets. Symbol (L6) is a vent line of the third polycondensation reaction tank (k).

  Compared with the process shown in FIG. 6, the process shown in FIG. 7 includes a filter (L3) in the middle of the extraction line (L3) between the second polycondensation reaction tank (d) and the third polycondensation reaction tank (k). The difference is that f) is equipped.

  PBT obtained by the production method of the present invention includes 2,6-di-t-butyl-4-octylphenol, pentaerythrityl-tetrakis [3- (3 ′, 5′-t-butyl-4′-hydroxyphenyl). ) Propionate] and the like, dilauryl-3,3′-thiodipropionate, thioether compounds such as pentaerythrityl-tetrakis (3-laurylthiodipropionate), triphenyl phosphite, tris (nonylphenyl) phos Antioxidants such as phosphorus compounds such as phyto and tris (2,4-di-t-butylphenyl) phosphite, paraffin wax, microcrystalline wax, polyethylene wax, long chain fatty acids represented by montanic acid and montanic acid ester And mold release agents such as esters and silicone oils. May be.

  A reinforcing filler can be blended in the PBT obtained by the production method of the present invention. The reinforcing filler is not particularly limited, but examples thereof include glass fibers, carbon fibers, silica / alumina fibers, zirconia fibers, boron fibers, boron nitride fibers, silicon nitride potassium titanate fibers, metal fibers and other inorganic fibers, aromatics Examples thereof include organic fibers such as polyamide fibers and fluororesin fibers. These reinforcing fillers can be used in combination of two or more. Among the above reinforcing fillers, inorganic fillers, particularly glass fibers, are preferably used.

  When the reinforcing filler is an inorganic fiber or an organic fiber, the average fiber diameter is not particularly limited, but is usually 1 to 100 μm, preferably 2 to 50 μm, more preferably 3 to 30 μm, and particularly preferably 5 to 20 μm. . The average fiber length is not particularly limited, but is usually 0.1 to 20 mm, preferably 1 to 10 mm.

  The reinforcing filler is preferably used after being surface-treated with a sizing agent or a surface treatment agent in order to improve the interfacial adhesion with the PBT. Examples of the sizing agent or surface treatment agent include functional compounds such as epoxy compounds, acrylic compounds, isocyanate compounds, silane compounds, and titanate compounds. The reinforcing filler can be surface-treated with a sizing agent or a surface treatment agent in advance, or can be surface-treated by adding a sizing agent or a surface treatment agent during the preparation of the PBT composition. The addition amount of the reinforcing filler is usually 150 parts by weight or less, preferably 5 to 100 parts by weight with respect to 100 parts by weight of the PBT resin.

  In the PBT obtained by the production method of the present invention, other fillers can be blended together with the reinforcing filler. Other fillers to be added include, for example, plate-like inorganic fillers, ceramic beads, asbestos, wollastonite, talc, clay, mica, zeolite, kaolin, potassium titanate, barium sulfate, titanium oxide, silicon oxide, oxidation Aluminum, magnesium hydroxide, etc. are mentioned. By blending the plate-like inorganic filler, the anisotropy and warpage of the molded product can be reduced. Examples of the plate-like inorganic filler include glass flakes, mica, and metal foil. Among these, glass flakes are preferably used.

  A flame retardant can be blended with the PBT obtained by the production method of the present invention in order to impart flame retardancy. The flame retardant is not particularly limited, and examples thereof include organic halogen compounds, antimony compounds, phosphorus compounds, other organic flame retardants, and inorganic flame retardants. Examples of the organic halogen compound include brominated polycarbonate, brominated epoxy resin, brominated phenoxy resin, brominated polyphenylene ether resin, brominated polystyrene resin, brominated bisphenol A, and polypentabromobenzyl acrylate. Examples of the antimony compound include antimony trioxide, antimony pentoxide, sodium antimonate, and the like. As a phosphorus compound, phosphate ester, polyphosphoric acid, ammonium polyphosphate, red phosphorus etc. are mentioned, for example. Examples of other organic flame retardants include nitrogen compounds such as melamine and cyanuric acid. Examples of other inorganic flame retardants include aluminum hydroxide, magnesium hydroxide, silicon compound, and boron compound.

  Conventional additives and the like can be blended with the PBT obtained by the production method of the present invention, if necessary. Such additives are not particularly limited and include, for example, stabilizers such as antioxidants and heat stabilizers, lubricants, mold release agents, catalyst deactivators, crystal nucleating agents, crystallization accelerators, and the like. It is done. These additives can be added during or after the polymerization. In addition, in order to give PBT the desired performance, UV absorbers, stabilizers such as weather resistance stabilizers, colorants such as dyes and pigments, antistatic agents, foaming agents, plasticizers, impact resistance improvers, etc. I can do it.

  The PBT obtained by the production method of the present invention includes polyethylene, polypropylene, polystyrene, polyacrylonitrile, polymethacrylic acid ester, ABS resin, polycarbonate, polyamide, polyphenylene sulfide, polyethylene terephthalate, liquid crystal polyester, polyacetal, polyphenylene as necessary. Thermosetting resins such as thermoplastic resins such as oxide, phenol resins, melamine resins, silicone resins, and epoxy resins can be blended. These thermoplastic resins and thermosetting resins can be used in combination of two or more.

  The blending method of the various additives and resins is not particularly limited, but a method of using a uniaxial or biaxial extruder having equipment capable of devolatilization from the vent port as a kneader is preferable. Each component including an additional component can be supplied to the kneader in a lump or can be supplied sequentially. In addition, two or more kinds of components selected from each component including an additional component can be mixed in advance.

  The PBT molding method obtained by the production method of the present invention is not particularly limited, and molding methods generally used for thermoplastic resins, that is, molding methods such as injection molding, hollow molding, extrusion molding, and press molding are used. It can be applied.

  PBT obtained by the production method of the present invention is excellent in color tone, thermal stability, transparency, quality stability, and reduced foreign matter, so that injection molded parts such as electrical, electronic parts, automotive parts, films, The improvement effect is remarkable in applications such as monofilament and fiber.

  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.

(1) Esterification rate:
The acid value and saponification value were calculated from the following calculation formula (IV). The acid value was determined by titration using a 0.1 N KOH / methanol solution after dissolving the oligomer in dimethylformamide. The saponification value was determined by hydrolyzing the oligomer with a 0.5N KOH / ethanol solution and titrating with 0.5N hydrochloric acid.

(2) Number average degree of polymerization of oligomer:
About 20 mg of oligomer was dissolved in 1 mL of a mixed solvent of deuterated chloroform / hexafluoroisopropanol = 7/3 (volume ratio), and ¹ H-NMR spectrum was measured at room temperature using a spectrometer (“UnityPlus 400” manufactured by Varian). The β-methylene signal of 1,4-butanediol units appearing in the vicinity of 1.6 to 2.2 ppm (however, the amount derived from unreacted 1,4-butanediol is α-appearing in the vicinity of 3.7 ppm). Quantified and subtracted by the signal of methylene) and the signal ratio of the terephthalic acid unit appearing in the vicinity of 8 ppm.

(3) THF by-product amount:
The amount was determined by gas chromatography, and the product amount (mole) per unit time was divided by the supply amount (mole) of terephthalic acid per unit time. The lower the value, the less THF produced as a by-product.

(4) Calculation of β:
It calculated using Formula (I) from BM / TM, catalyst concentration, and pressure.

(5) Intrinsic viscosity (IV):
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) and measuring the number of seconds of dropping only the polymer solution having a concentration of 1.0 g / dL and the solvent at 30 ° C., the following formula (V) I asked more.

(6) Terminal carboxyl group concentration:
0.5 g of PBT or oligomer was dissolved in 25 mL of benzyl alcohol and titrated using a 0.01 mol / L benzyl alcohol solution of sodium hydroxide.

(7) Titanium concentration in PBT:
PBT was wet-decomposed with high-purity sulfuric acid and nitric acid for electronic industry, and measurement was performed using a high-resolution ICP (Inductively Coupled Plasma) -MS (MassSpectrometer) (manufactured by ThermoQuest).

(8) Terminal vinyl group concentration:
About 100 mg of PBT was dissolved in 1 mL of a mixed solvent of deuterated chloroform / hexafluoroisopropanol = 7/3 (volume ratio), 36 μL of deuterated pyridine was added, and ¹ H-NMR was measured and determined at 50 ° C. “Α-400” or “AL-400” manufactured by JEOL Ltd. was used for the NMR apparatus.

(9) Solution haze:
After dissolving 2.70 g of PBT in 20 mL of a mixed solvent of phenol / tetrachloroethane = 3/2 (weight ratio) at 110 ° C. for 30 minutes, it was cooled in a constant temperature water bath at 30 ° C. for 15 minutes, and made by Nippon Denshoku Co., Ltd. A turbidity measured with a cell length of 10 mm was used as a solution haze by using a photometer (NDH-300A). It shows that transparency is so favorable that a value is low.

(10) Pellet color tone:
A color difference meter (Z-300A type) manufactured by Nippon Denshoku Co., Ltd. was used, and the b value in the L, a, b color system was evaluated. A lower value indicates less yellowing and a better color tone.

(11) Number of fisheye:
The PBT pellets were dried at 120 ° C. for 8 hours under a nitrogen atmosphere, and a film having a thickness of 50 μm was obtained using a film molding machine (model ME-20 / 26V2) manufactured by Optical Control Systems. The cylinder and die temperatures were 250 ° C. The number of fish eyes exceeding 200 μm per 1 m ^{2 of the} film was measured using the Film Quality Testing System [Optical Control Systems, Inc., Type FS-5], and evaluated according to the following three criteria.

Example 1:
Through the esterification reaction step shown in FIG. 1 and the polycondensation reaction step shown in FIG. 4, PBT was produced in the following manner. First, a 60 ° C. slurry mixed at a ratio of 1.80 moles of 1,4-butanediol with respect to 1.00 moles of terephthalic acid is passed through a raw material supply line (1) from a slurry preparation tank in advance with an esterification rate of 99. % Was continuously fed to a reaction vessel (A) for esterification having a stirrer filled with PBT oligomer at 41.0 kg / h. At the same time, 1,4-butanediol having a purity of 98% by weight or more was supplied from the recirculation line (2) at 17.2 kg / h, and 3.0% of tetrabutyl titanate at 65 ° C. was used as a catalyst from the catalyst supply line (3). A weight% 1,4-butanediol solution was fed at 194 g / h (30 ppm relative to the theoretical polymer yield). The water content in this solution was 0.20% by weight.

  The internal temperature of the reaction vessel (A) is 228 ° C., the pressure is 65 kPa, and the produced water, THF, and excess 1,4-butanediol are distilled from the distillation line (5), and the rectification column (C) It separated into a high boiling component and a low boiling component. The high-boiling component at the bottom of the column after the system is stabilized is 98% by weight or more of 1,4-butanediol, and the extraction line (8) so that the liquid level of the rectifying column (C) is constant. The flow rate of 1,4-butanediol in the additional supply line (15) was adjusted. On the other hand, the low boiling point component was extracted from the top of the column in the form of gas, condensed by the condenser (G), and extracted from the extraction line (13) to the outside so that the liquid level of the tank (F) was constant. The main components of this distillate were water and THF, and the content of THF was measured using gas chromatography to determine the amount of THF distilled per unit time.

  A certain amount of the oligomer generated in the reaction tank (A) was extracted from the extraction line (4) using the pump (B), and after the system was stabilized, the esterification rate of the oligomer was 96.5 to 97. The residence time was controlled to be 0% (in this case, the average residence time of the liquid in the reaction tank (A) was 3.3 hr). In this case, the number average degree of polymerization of the oligomer was 2.9. The oligomer extracted from the extraction line 4 was continuously supplied to the first polycondensation reaction tank (a).

  The internal temperature of the first polycondensation reaction tank (a) was 241 ° C., the pressure was 2.1 kPa, and the liquid level was controlled so that the residence time was 120 minutes. An initial polycondensation reaction was performed while extracting water, THF, and 1,4-butanediol from a vent line (L2) connected to a decompressor (not shown). The extracted reaction liquid was continuously supplied to the second polycondensation reaction tank (d).

  The internal temperature of the second polycondensation reaction tank (d) is 243 ° C., the pressure is 130 Pa, the liquid level is controlled so that the residence time is 80 minutes, and a vent line (L4) connected to a decompressor (not shown). ), Polycondensation reaction was further carried out while extracting water, THF and 1,4-butanediol. The obtained polymer was continuously extracted in a strand form from the die head (g), and was cut with a rotary cutter (h). The obtained PBT had an IV of 0.80, a terminal carboxyl group concentration of 12 μeq / g, a small amount of THF by-product, excellent color tone and transparency, and PBT with less fish eye. The analytical values are summarized in Table 2.

Example 2:
In Example 1, the catalyst solution was supplied at 260 g / h, the internal temperature of the second polycondensation reaction tank (d) was 242 ° C., the pressure was 140 Pa, and the residence time was 60 minutes. Went to. A PBT with a small amount of THF by-product, excellent color tone and transparency, and little fish eye was obtained. The analytical values are summarized in Table 2.

Example 3:
In Example 1, the catalyst solution was supplied at 520 g / h, and the supply amount of 1,4-butanediol from the recirculation line (2) was supplied to be 30.0 kg / h. The same procedure as in Example 1 was performed except that the internal temperature of the tank (d) was 241 ° C., the pressure was 180 Pa, and the residence time was 60 minutes. A PBT with a small amount of THF by-product, excellent color tone and transparency, and little fish eye was obtained. The analytical values are summarized in Table 2.

Example 4:
In Example 2, it carried out similarly to Example 2 except having made the pressure of esterification reaction into 88 kPa. A PBT with a small amount of THF by-product, excellent color tone and transparency, and little fish eye was obtained. The analytical values are summarized in Table 2.

Comparative Example 1:
In Example 3, except that the bottom component from the recirculation line (2) was supplied at 17.2 kg / h and the internal temperature of the second polycondensation reaction tank (d) was 246 ° C. The same was done. The polymer color tone and solution haze deteriorated, and the fish eye increased. The analytical values are summarized in Table 3.

Comparative Example 2:
In Example 3, the same procedure as in Example 3 was performed except that the catalyst solution was supplied at 650 g / h, the internal temperature of the second polycondensation reaction tank (d) was 244 ° C., and the pressure was 170 Pa. The polymer color tone and solution haze deteriorated, and the fish eye increased. The analytical values are summarized in Table 3.

Comparative Example 3:
The same procedure as in Example 2 was performed except that the esterification reaction pressure in Example 2 was 15 kPa, the internal temperature of the second polycondensation reaction tank (d) was 250 ° C., the pressure was 130 Pa, and the residence time was 90 minutes. It was. The polymer color tone and solution haze deteriorated, and the fish eye increased. The analytical values are summarized in Table 3.

Comparative Example 4:
In Example 2, it carried out similarly to Example 2 except having supplied so that the supply amount from a recirculation line (2) might be 43 kg / h. The amount of THF by-product was large, and the color tone of the polymer deteriorated.

Explanatory drawing of an example of the esterification reaction process employ | adopted by this invention Explanatory drawing of another example of the esterification reaction step employed in the present invention Explanatory drawing of another example of the esterification reaction step employed in the present invention Explanatory drawing of an example of the polycondensation step employed in the present invention Explanatory drawing of another example of the polycondensation step employed in the present invention Explanatory drawing of another example of the polycondensation step employed in the present invention Explanatory drawing of another example of the polycondensation step employed in the present invention

Explanation of symbols

1: Raw material supply line 2: Recirculation line 3: Catalyst supply line 4: Extraction line 5: Distillation line 6: Extraction line 7: Circulation line 8: Extraction line 9: Gas extraction line 10: Condensate line 11: Extraction line 12: Circulation line 13: Extraction line 14: Vent line 15: Additional supply or recovery line 16: Bypass line A: Reaction tank B: Extraction pump C: Rectification tower D, E: Pump F: Tank G: Condenser H: Reboiler L1: Extraction line L3, L5: Extraction lines L2, L4, L6: Vent line a: First polycondensation reaction tank d: Second polycondensation reaction tank k: Third polycondensation reaction Tanks c, e, m: extraction gear pump f: filter g: dice head h: rotary cutter

Claims (15)

Using a single-stage or multi-stage esterification reactor, terephthalic acid and 1,4-butanediol are continuously esterified in the presence of a titanium compound catalyst, followed by polycondensation reaction to produce polybutylene terephthalate. A method for producing polybutylene terephthalate, wherein the following conditions (A) to (C) are satisfied.
(A) The pressure (P) in at least one esterification reaction tank is 20 to 90 kPa.
(B) The density | concentration of the titanium compound catalyst used by esterification reaction is 90 ppm or less as a weight concentration ((alpha)) of the titanium atom with respect to the polybutylene terephthalate finally obtained.
(C) TM is the number of moles of terephthalic acid supplied per unit time, BM is the number of moles of all 1,4-butanediol supplied to each esterification reaction tank per unit time, and titanium is used in the esterification reaction. When the concentration of the compound catalyst is α (weight concentration of titanium atoms with respect to the finally obtained PBT) and the pressure in the esterification reaction tank is P, the following formulas (I) and (II) are established.

  The production method according to claim 1, wherein the pressure (P) in the at least one esterification reaction tank is 75 kPa or less.   The production method according to claim 1 or 2, wherein BM / TM in the formula (I) is 3.1 or more.   The production method according to claim 1, wherein β in the formula (I I) is 5.0 to 6.0.   The manufacturing method according to claim 1, wherein the weight concentration (α) of titanium atoms is 50 ppm or less.   The production method according to claim 1, wherein the pressure (P) in the esterification reaction tank is 50 to 70 kPa.   The method according to any one of claims 1 to 6, wherein the solution haze is 3% or less when 2.7 g of polybutylene terephthalate is dissolved in 20 mL of a phenol / tetrachloroethane mixed solvent (weight ratio 3/2). .   In the esterification reaction tank, while supplying a part of 1,4-butanediol to the esterification reaction tank independently of terephthalic acid in the presence of a titanium compound catalyst, terephthalic acid and 1,4-butanediol were mixed. In the step of continuously esterifying, 10% by weight or more of the titanium compound catalyst used in the esterification reaction is directly supplied to the liquid phase of the reaction liquid independently of terephthalic acid, and independently of terephthalic acid. The production method according to any one of claims 1 to 7, wherein 10% by weight or more of 1,4-butanediol to be supplied is directly supplied to the reaction liquid phase part.   (1) Step of continuously esterifying terephthalic acid and 1,4-butanediol in the presence of a titanium compound catalyst in an esterification reaction tank, (2) Esterification reaction in a condenser A step of condensing 1,4-butanediol distilled from the inside of the tank, and (3) a polybutylene terephthalate having a recycling step of returning the condensed 1,4-butanediol to the esterification reaction tank independently of terephthalic acid. In the production method of (4), 10% by weight or more of the titanium compound catalyst used in the esterification reaction is directly supplied to the reaction liquid phase part independently of terephthalic acid, and (5) in the recirculation step The production method according to any one of claims 1 to 7, wherein 10% by weight or more of 1,4-butanediol returned to the esterification reaction tank is directly returned to the reaction liquid phase part.   The production method according to claim 1, wherein the titanium compound catalyst is supplied as a 0.01 to 20 wt% 1,4-butanediol solution.   The production method according to claim 10, wherein the water concentration of the titanium compound catalyst in the 1,4-butanediol solution is 0.05 to 1.0% by weight.   The production method according to any one of claims 1 to 11, wherein the reaction temperature in the esterification reaction step is equal to or higher than the boiling point of 1,4-butanediol at the reaction pressure (P).   The titanium compound catalyst used in the esterification reaction and 1,4-butanediol returned to the esterification reaction tank in the recirculation step are then mixed and then supplied to the esterification reaction tank. The manufacturing method of crab.   The production method according to any one of claims 1 to 13, wherein the temperature of 1,4-butanediol supplied independently of terephthalic acid is in the range of 150 to 190 ° C.   The production method according to claim 1, wherein the esterification reaction tank has one stage.

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