Method for producing polybutylene adipate terephthalate and polybutylene adipate terephthalate

Abstract

The present invention relates to a method for producing polybutylene adipate terephthalate and polybutylene adipate terephthalate.

Description

[Technical Field]

[0001] [CROSS-REFERENCE TO RELATED APPLICATIONS] This application claims the benefit of priority based on Korean Patent Application No. 10-2023-0023776, filed February 22, 2023, and Korean Patent Application No. 10-2024-0024326, filed February 20, 2024, and all contents disclosed in the documents of said Korean patent applications are incorporated herein by reference.

[0002] The present invention relates to a method for producing polybutylene adipate terephthalate and polybutylene adipate terephthalate. [Background technology]

[0003] Polyester resins have excellent mechanical and chemical properties and are used in a wide range of applications, including drinking water containers, medical applications, food packaging paper, food containers, sheets, films, and automotive molded parts.

[0004] Among them, polybutylene adipate terephthalate (PBAT) is a soft polyester that can be biodegraded, and has been attracting attention as an alternative material to polyolefin polymers, which are mainly used in films for food packaging and other purposes due to recent environmental regulations.

[0005] Polybutylene adipate terephthalate is processed into films and the like by extrusion or injection molding, but if the acid value of polybutylene adipate terephthalate is excessively high, the mechanical strength will be insufficient, and problems with product quality may occur during processing steps such as extrusion or injection.

[0006] Furthermore, polybutylene adipate terephthalate is mainly used for transparent films, but the produced films tend to discolor to red or yellow, which can degrade the appearance of the product.

[0007] As described above, the acid value and color properties of polybutylene adipate terephthalate are very important. However, since the acid value and color properties of polybutylene adipate terephthalate are somewhat in a trade-off relationship, there is a need to develop a polybutylene adipate terephthalate that has an appropriate acid value, does not cause discoloration, and can simultaneously satisfy excellent mechanical properties and appearance properties. Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention provides a polybutylene adipate terephthalate having an acid value within a specific range, mechanical properties sufficient to prevent problems during processing, and excellent appearance properties such as color.

[0009] The present specification also seeks to provide a method for producing such polybutylene adipate terephthalate. [Means for solving the problem]

[0010]

number

[0011] According to one embodiment of the present invention, in the preparation method, the 1,4-butanediol may be included in an amount of about 100 to about 250 parts by weight based on 100 parts by weight of the adipic acid.

[0012] According to another embodiment of the present invention, in the method, the terephthalic acid may be contained in an amount of about 50 to about 150 parts by weight based on 100 parts by weight of the adipic acid.

[0013] According to another embodiment of the present invention, in the method, the titanium (Ti)-based polymerization catalyst may be included in an amount of about 0.001 to about 10 parts by weight based on 100 parts by weight of the adipic acid.

[0014] According to another embodiment of the present invention, in the method, the titanium (Ti)-based polymerization catalyst may be at least one selected from the group consisting of titanium methoxide, titanium ethoxide, titanium propoxide, titanium isopropoxide, titanium butoxide, titanium isobutoxide, and titanium citrate.

[0015] According to another embodiment of the present invention, in the method, the titanium (Ti)-based polycondensation catalyst may be the same as or different from the titanium (Ti)-based polymerization catalyst.

[0016] According to another embodiment of the present invention, in the method, the titanium (Ti)-based polycondensation catalyst may be included in an amount of about 0.001 to about 0.5 parts by weight based on 100 parts by weight of the polybutylene adipate terephthalate prepolymer.

[0017] According to another embodiment of the present invention, in the manufacturing method, the phosphorus (P)-based heat stabilizer may include at least one selected from the group consisting of phosphoric acid, phosphorous acid, trialkyl phosphate, and trialkyl phosphonoacetate.

[0018] According to another embodiment of the present invention, in the manufacturing method, the phosphorus (P)-based heat stabilizer may be included in an amount of about 0.001 to about 0.1 parts by weight based on 100 parts by weight of the polybutylene adipate terephthalate prepolymer.

[0019] According to another embodiment of the present invention, the weight average molecular weight of the polybutylene adipate terephthalate polymer may be about 70,000 to about 200,000 g / mol.

[0020] According to another embodiment of the present invention, the polybutylene adipate terephthalate polymer may have an acid value (mmol / kg) of about 5 to about 30.

[0021] According to another embodiment of the present invention, the polybutylene adipate terephthalate polymer may have a b* color index value of about 0 to about 30.

[0022] According to another embodiment of the present invention, the polybutylene adipate terephthalate polymer may satisfy the following mathematical formula 1:

number

[0023] In Equation 1, acid number is the acid number (mmol / kg) of the polybutylene adipate terephthalate polymer, and b* is the b* color index value of the polybutylene adipate terephthalate polymer.

[0024] The present specification also provides polybutylene adipate terephthalate having a weight average molecular weight of 70,000 to 200,000 g / mol and satisfying the following mathematical formula 1:

number

[0025] In Equation 1, acid number is the acid number (mmol / kg) of the polybutylene adipate terephthalate polymer, and b* is the b* color index value of the polybutylene adipate terephthalate polymer.

[0026] In the present invention, terms such as first and second are used to describe various components, and the terms are used only to distinguish one component from another.

[0027] Furthermore, the terms used in this specification are merely used to describe exemplary embodiments and are not intended to limit the present invention.

[0028] The singular expression includes the plural expression unless the context clearly indicates otherwise.

[0029] As used herein, terms such as "comprises," "comprises," or "having" are intended to describe one or more other features, numbers, steps, components, or combinations thereof that may be implemented, but do not exclude the possibility of one or more other features, numbers, steps, components, combinations, or additional features.

[0030] Additionally, in this specification, when a layer or element is referred to as being formed "on" or "on" another layer or element, it means that the layer or element is formed directly on the layer or element, or that other layers or elements can be additionally formed between layers, on the object, or on the substrate.

[0031] Since the present invention can be modified in various ways and can have various forms, specific examples are exemplified and described in detail below, but it should be understood that this is not intended to limit the invention to the particular disclosed form, and that the invention also encompasses any modifications, equivalents, or alternatives falling within the spirit and technical scope of the invention.

[0032] The present invention will be described in detail below.

[0033] According to one embodiment of the present invention, there is provided a method for preparing polybutylene adipate terephthalate, comprising: a first step of polymerizing butanediol, adipic acid, and terephthalic acid in the presence of a titanium (Ti)-based polymerization catalyst to prepare a polybutylene adipate terephthalate prepolymer; and a second step of polycondensing the polybutylene adipate terephthalate prepolymer in the presence of a titanium (Ti)-based polycondensation catalyst and a phosphorus (P)-based heat stabilizer to prepare a polybutylene adipate terephthalate polymer, wherein the molar ratio of phosphorus to titanium used in the first and second steps satisfies the condition of the following formula 1:

number

[0034] The present inventors have discovered that in a method for producing a polybutylene adipate terephthalate polymer by polymerizing butanediol, adipic acid, and terephthalic acid to produce a polybutylene adipate terephthalate prepolymer and then polycondensing the prepolymer, when the ratio of phosphorus to titanium used in the polycondensation step is adjusted within a specific range, it is possible to produce a polybutylene adipate terephthalate polymer that has an appropriate acid value and is free from discoloration, thereby simultaneously satisfying excellent mechanical properties and appearance characteristics, and have completed the present invention.

[0035] Polyesters are generally produced by producing a prepolymer by esterifying a diol compound and a dicarboxylic acid compound in the presence of a catalyst to form an ester bond, and then transferring the produced prepolymer to a separate reactor or the like and adding a polycondensation catalyst to carry out a polycondensation reaction to produce a high molecular weight polyester.

[0036] Prepolymer production A prepolymer is a polymer with a relatively low degree of polymerization, which is produced by stopping the polymerization reaction at an intermediate stage.

[0037] In one embodiment, the prepolymer refers to a polymer with a relatively low degree of polymerization obtained by esterifying a monomer mixture containing 1,4-butanediol, adipic acid, and terephthalic acid in the presence of a titanium (Ti)-based polymerization catalyst.

[0038] In this prepolymer formation process, an initial polymer chain can be formed around the catalyst.

[0039] According to one embodiment of the present invention, in the preparation method, the 1,4-butanediol may be included in an amount of about 100 to about 250 parts by weight based on 100 parts by weight of the adipic acid.

[0040] This is the total amount of 1,4-butanediol required for PBAT synthesis. 1,4-butanediol is not only a reactant, but also functions as a solvent or dispersant to disperse catalysts, etc. In existing methods, only a portion of the 1,4-butanediol to be reacted is supplied during the polymerization process to ensure uniformity and stability of the catalyst, and the remaining amount is supplied in a later reaction.

[0041] In this regard, the 1,4-butanediol may be included in an amount of about 150 to about 250 parts by weight, or about 180 to 220 parts by weight, per 100 parts by weight of adipic acid in the monomer mixture.

[0042] According to another embodiment of the present invention, in the method, the terephthalic acid may be contained in an amount of about 50 to about 150 parts by weight, or about 80 to about 120 parts by weight, based on 100 parts by weight of the adipic acid.

[0043] Terephthalic acid may affect the crystallinity of the polymer due to its aromatic ring structure, but polymers produced within the above range of addition can achieve both excellent mechanical properties and biodegradability.

[0044] According to another embodiment of the present invention, in the method, the titanium (Ti)-based polymerization catalyst may be included in an amount of about 0.001 to about 10 parts by weight based on 100 parts by weight of the adipic acid.

[0045] Within this range, the esterification reaction of the monomer mixture can be appropriately mediated.

[0046] If the catalyst amount is too small, the polymerization time will be long and productivity will decrease. If the catalyst amount is too large, the polymerization time may be short, but the final PBAT may become discolored more easily. Therefore, the amount of heat stabilizer must be increased in proportion to the catalyst amount, which increases the production cost.

[0047] Taking this tendency into consideration, the amount of catalyst in the catalyst mixture can be adjusted. For example, the catalyst in the catalyst mixture can be used in an amount of 0.001 parts by weight or more, 0.005 parts by weight or more, or 0.01 parts by weight or more, and 10 parts by weight or less, 5 parts by weight or less, or 0.1 parts by weight or less, based on 100 parts by weight of adipic acid in the monomer mixture.

[0048] According to another embodiment of the present invention, in the method, the titanium (Ti)-based polymerization catalyst may be at least one selected from the group consisting of titanium methoxide, titanium ethoxide, titanium propoxide, titanium isopropoxide, titanium butoxide, titanium isobutoxide, and titanium citrate.

[0049] The step of preparing the prepolymer may be carried out at a temperature ranging from about 150 to about 350° C. for a time period ranging from about 10 to about 240 minutes.

[0050] For example, the step of preparing the prepolymer may be carried out at a temperature of about 150° C. or more, or about 170° C. or more, or about 190° C. or more, or about 210° C. or more, and about 350° C. or less, or about 320° C. or less, or about 290° C. or less, or about 250° C. or less, and for a time period of 10 minutes or more, 15 minutes or more, 20 minutes or more, or 25 minutes or more, and about 240 minutes or less, or about 120 minutes or more, or about 90 minutes or less, or about 60 minutes or less, or about 40 minutes or less.

[0051] In the step of producing the prepolymer, nitrogen gas may be injected into the reactor. Specifically, by quickly removing water generated as a by-product during nitrogen gas injection, reverse reactions caused by water can be suppressed, and the polymerization conversion rate of the monomers can be improved, thereby increasing the molecular weight of the polymer.

[0052] For example, nitrogen gas can be injected at about 0.001 ml / min or more, or about 0.01 ml / min or more, or 0.02 ml / min or more, or about 0.05 ml / min or more, and at about 100 ml / min or less, or about 50 ml / min or less, or about 10 ml / min or less, or about 5 ml / min or less.

[0053] In the step of preparing the prepolymer, about 0.1 to about 1 part by weight of a crosslinking or branching agent may be added based on 100 parts by weight of adipic acid in the monomer mixture.

[0054] When a crosslinking agent is added to perform an esterification reaction, an internally crosslinked prepolymer can be produced, and after polycondensation, the mechanical properties of the final polymer PBAT can be improved.

[0055] The crosslinking agent is a low molecular weight compound containing three or more hydroxy groups or three or more carboxy groups in the molecule, and examples of the crosslinking agent that can be used include erythritol-based compounds, glycerol-based compounds, and citric acid.

[0056] Polycondensation Next, the polybutylene adipate terephthalate prepolymer prepared in the above process is polycondensed to prepare a polybutylene adipate terephthalate polymer.

[0057] In continuous production, polybutylene adipate terephthalate prepolymer may be transferred to a separate polycondensation reactor, etc., and then polycondensation may be carried out. In batch production, the produced polybutylene adipate terephthalate prepolymer may be transferred to another location, or polycondensation may be carried out in the original reactor by adjusting only the reaction conditions, etc.

[0058] According to another embodiment of the present invention, in the method, the titanium (Ti)-based polycondensation catalyst may be the same as or different from the titanium (Ti)-based polymerization catalyst.

[0059] In the polycondensation reaction, the polymer chains are linked by an esterification reaction between the hydroxyl and carboxyl groups at the terminals of the polybutylene adipate terephthalate prepolymer. Therefore, the catalyst used in the polycondensation process, i.e., the titanium (Ti)-based polycondensation catalyst, may be the same as or different from the catalyst used in the esterification reaction to produce the prepolymer, i.e., the titanium (Ti)-based polymerization catalyst described above.

[0060] However, even if the same type of catalyst is used, an additional catalyst is added in the polycondensation reaction of the prepolymer in addition to the amount of catalyst used in the step of producing the prepolymer.

[0061] The first catalyst, i.e., the titanium (Ti)-based polymerization catalyst, is likely to lose activity during the prepolymer production step. For example, titanium, the central metal component of the catalyst, may react with water, a by-product of the esterification reaction, to form titanium oxide, or other functional groups may be substituted for the alkoxide moiety of the titanium alkoxide.

[0062] Therefore, during the polycondensation reaction, a separate catalyst must be added immediately before the polycondensation reaction.

[0063] According to another embodiment of the present invention, in the method, the titanium (Ti)-based polycondensation catalyst may be included in an amount of about 0.001 to about 0.5 parts by weight based on 100 parts by weight of the polybutylene adipate terephthalate prepolymer.

[0064] Next, a heat stabilizer is added separately from the addition of the polycondensation catalyst. The heat stabilizer is used to prevent discoloration of the final polybutylene adipate terephthalate polymer, and may be added simultaneously with the polycondensation catalyst or before or after the addition of the polycondensation catalyst.

[0065] According to another embodiment of the present invention, in the manufacturing method, the phosphorus (P)-based heat stabilizer may include at least one selected from the group consisting of phosphoric acid, phosphorous acid, trialkyl phosphate, and trialkyl phosphonoacetate.

[0066] According to another embodiment of the present invention, in the manufacturing method, the phosphorus (P)-based heat stabilizer may be included in an amount of about 0.001 to about 0.1 parts by weight based on 100 parts by weight of the polybutylene adipate terephthalate prepolymer.

[0067] The polycondensation reaction may include the steps of: increasing the temperature of a reactor containing the prepolymer to a polycondensation reaction temperature, specifically, increasing the temperature until the temperature reaches a range of about 150 to about 350°C; reducing the pressure of the reactor after the temperature increase until the pressure reaches 0.1 to 0.00001 atm; and maintaining the pressure and temperature after the reduction in pressure, checking the degree of polycondensation, and terminating the reaction.

[0068] For example, the temperature of the reactor containing the prepolymer can be increased to a temperature range of about 150°C or more, about 170°C or more, about 190°C or more, or about 210°C or more, and about 350°C or less, about 320°C or less, about 290°C or less, or about 250°C or less.

[0069] About 1 to about 10 minutes after the temperature reaches the above range, the pressure in the reactor is reduced until the pressure reaches a range of about 0.00001 atm or more, about 0.00005 atm or more, about 0.0001 atm or more, or about 0.0002 atm or more, and about 0.1 atm or less, about 0.05 atm or less, about 0.03 atm or less, or about 0.01 atm or less.

[0070] After the pressure reduction, the reaction is continued while maintaining the pressure and temperature, and the reaction can be terminated when it is confirmed that the desired molecular weight is reached depending on the degree of the polycondensation reaction.

[0071] The molecular weight can be determined by sampling the resultant product from the reactor, but generally can be determined by measuring the torque load of the agitator installed in the reactor.

[0072] The reaction time is not particularly limited, but the reaction can be terminated after about 2 hours or more, about 2.2 hours or more, about 2.4 hours or more, or about 3 hours or more, and about 8 hours or less, about 7.5 hours or less, about 7 hours or less, or 6 hours have elapsed since the start of the reaction.

[0073] According to another embodiment of the present invention, the weight average molecular weight of the polybutylene adipate terephthalate polymer produced by the method of one embodiment of the present invention may be from about 70,000 to about 200,000 g / mol, preferably about 70,000 or more, or about 80,000 g / mol or more, or about 200,000 g / mol or less, or about 150,000 g / mol or less.

[0074] According to another embodiment of the present invention, the acid value (mmol / kg) of the polybutylene adipate terephthalate polymer produced by the method of one embodiment of the present invention may be about 5 to about 30, preferably about 5 or more, or about 7 or more, and may be about 30 or less, or about 25 or less, or about 20 or less.

[0075] The acid value refers to the fact that some acid functional groups do not react during the reaction of forming an ester bond between a dicarboxylic acid and a diol and remain in the polymer chain as free acid groups. If the acid value is too high, the free acid groups may accelerate hydrolysis over time, causing various problems such as a decrease in the molecular weight of the polymer or a deterioration in the mechanical properties of the polymer.

[0076] According to another embodiment of the present invention, the polybutylene adipate terephthalate polymer prepared by the method of one embodiment of the present invention has a b* color index value of about 0 to about 30, preferably about 0 or more, or more than about 0, or about 3 or more, or about 5 or more, and about 30 or less, or about 25 or less, or about 20 or less, and thus exhibits little discoloration and excellent optical properties.

[0077] If the b* color index value is too high, the polymer will exhibit a yellow color, making it difficult to use in applications requiring excellent optical properties.

[0078] According to another embodiment of the present invention, the polybutylene adipate terephthalate polymer may satisfy the following mathematical formula 1:

number

[0079] In Equation 1, acid number is the acid number (mmol / kg) of the polybutylene adipate terephthalate polymer, and b* is the b* color index value of the polybutylene adipate terephthalate polymer.

[0080] As described above, the acid value and color properties of polybutylene adipate terephthalate are very important. However, since the acid value and color properties of polybutylene adipate terephthalate are somewhat in a trade-off relationship, it is very difficult to obtain polybutylene adipate terephthalate that has an appropriate acid value to ensure processability and that does not become colored or discolored.

[0081] However, according to one embodiment of the present invention, when the ratio of the titanium (Ti)-based polycondensation catalyst and the phosphorus (P)-based heat stabilizer added during the polycondensation process is maintained within a P / Ti molar ratio of 0.65 to 1, polybutylene adipate terephthalate can be obtained that has an appropriate acid value, does not color or discolor, and has a low b* color index, i.e., has excellent mechanical properties and appearance properties at the same time.

[0082] Meanwhile, according to another embodiment of the present invention, there is provided a polybutylene adipate terephthalate having a weight average molecular weight of 70,000 to 200,000 g / mol and satisfying the following mathematical formula 1:

number

[0083] In Equation 1, acid number is the acid number (mmol / kg) of the polybutylene adipate terephthalate polymer, and b* is the b* color index value of the polybutylene adipate terephthalate polymer. [Effects of the Invention]

[0084] The production method of the present invention can provide polybutylene adipate terephthalate that has an appropriate acid value, does not color or discolor, and has a low b* color index, i.e., that simultaneously satisfies excellent mechanical properties and appearance characteristics. DETAILED DESCRIPTION OF THE INVENTION

[0085] The functions and effects of the present invention will be described in more detail below through specific examples of the present invention, however, these examples are presented only as examples of the present invention and do not limit the scope of the invention.

[0086] <Example> Example 1 Prepolymer production A polymerization reactor was charged with 2,372 g of 1,4-butanediol, 1,538 g of adipic acid, and 1,614 g of terephthalic acid as monomers, 0.741 g of pentaerythritol as a crosslinking agent, and 2.601 g of titanium citrate (Ti content 4.9 wt%) as a titanium (Ti)-based polymerization catalyst, and the temperature was raised to approximately 230°C. After that, the polymerization reaction (esterification reaction) was carried out for approximately 2 hours under a pressure of 400 mbar while maintaining the temperature, to obtain a polybutylene adipate terephthalate prepolymer. (Prepolymer molecular weight: 3,700 g / mol)

[0087] Polycondensation reaction To the reactor in which the polybutylene adipate terephthalate prepolymer was obtained, 4.595 g of titanium citrate (Ti content 4.9 wt%), which was the same as the polymerization catalyst, was further added as a titanium (Ti)-based polycondensation catalyst, and 1.076 g of triethylphosphonoacetate (approximately 35 ppm based on the phosphorus atom content of the resulting PBAT polymer) as a phosphorus (P)-based heat stabilizer, and the mixture was stirred at 60 rpm for approximately 10 minutes.

[0088] After stirring, the temperature of the reactor was raised to about 240°C. When the temperature of the reactor reached about 240°C, the pressure was reduced so that the internal pressure of the reactor reached about 1 mbar about 5 minutes after the temperature reached 240°C. While maintaining the reduced pressure, polycondensation was carried out by continuing stirring at about 60 rpm.

[0089] When the torque value of the stirrer reached about 0.5 Ampere, the reaction was stopped to obtain a polybutylene adipate terephthalate polymer.

[0090] Examples 2 to 4 and Comparative Examples 1 to 6 The same procedure as in Example 1 was carried out to obtain polybutylene adipate terephthalate polymers, except that the amounts of titanium (Ti)-based polycondensation catalyst and phosphorus (P)-based heat stabilizer added in the polycondensation reaction step were varied, and the P / Ti ratio was changed.

[0091] The reaction conditions are summarized in Table 1 below. [Table 1]

[0092] The physical properties of the polybutylene adipate terephthalate polymers obtained in the above examples and comparative examples were measured by the following methods.

[0093] Measurement of weight average molecular weight The sample was dissolved in chloroform at a concentration of 1 mg / ml, and the solution was then loaded into a gel permeation chromatography (GPC) instrument (PL GPC220, Agilent Technologies) to measure the molecular weight. Polystyrene was used as the standard polymer.

[0094] Acid value measurement The sample was dissolved in a 1:1 weight ratio O-cresol:chloroform mixed solution, and 1-2 drops of an aqueous solution containing 0.1 wt % phenol red was used as an indicator.

[0095] Using a micropipette, a 0.1N potassium hydroxide (KOH) / ethanol (ethanol) solution was titrated to measure the acid value according to the following formula 1. [Formula 1] Acid value (mgKOH / g)=(V-V0)×M×F×1000 / W V: Volume (mL) of KOH / ethanol solution consumed in titrating the sample V0: Volume (mL) of KOH / ethanol solution consumed in the titration of the blank test M: Molar concentration of KOH / ethanol solution (0.1M / L) W: mass of sample (g) F: Potency of KOH / ethanol solution

[0096] Acid value is the number of mg of KOH required to neutralize the free fatty acids contained in 1 g of food: RCOOH + KOH → RCOOK + HO. In other words, acid value measures the amount of free fatty acids that are not bound in the form of glycerides.

[0097] In particular, in the esterification reaction, it is a measure of the degree of reaction and refers to the amount of KOH required to neutralize the carboxyl group contained in 1 g of polymer, and a larger value indicates a lower reaction rate.

[0098] b* color index measurement The pelletized PBAT was placed in a cylindrical transparent glass sample bottle with a diameter of 60 mm and a height of 50 mm, and the Color L* / a* / b* / YI values ​​were measured using a spectrophotometer (device product name: ColorFlex EZ) in accordance with the CIE 15:2004 standard.

[0099] The measurement results are summarized in Table 2 below. [Table 2]

[0100] Referring to Table 2 above, it can be seen that Comparative Examples 1 and 2 have excessively high b* color indices, resulting in poor appearance characteristics, while Comparative Examples 3 and 4 have molecular weights that are less than half that of the Examples, resulting in improper polycondensation or molecular weight increase reactions and excessively high acid values. Furthermore, Comparative Example 5 has a low molecular weight and high acid value compared to the Examples, and Comparative Example 6 has an excessively high b* color index, resulting in poor appearance characteristics.

[0101] However, it can be clearly seen that the polybutylene adipate terephthalate prepared according to one embodiment of the present invention has a relatively low acidity value and a low b* color index value, and thus can have excellent mechanical properties and durability, as well as excellent optical properties.

Claims

1. a first step of polymerizing butanediol, adipic acid, and terephthalic acid in the presence of a titanium (Ti)-based polymerization catalyst to produce a polybutylene adipate terephthalate prepolymer; a second step of polycondensing the polybutylene adipate terephthalate prepolymer in the presence of a titanium (Ti)-based polycondensation catalyst and a phosphorus (P)-based heat stabilizer to produce a polybutylene adipate terephthalate polymer; The method for producing polybutylene adipate terephthalate, wherein the molar ratio of phosphorus to titanium used in the first and second steps satisfies the condition of the following formula 1: [Equation 1]

2. The butanediol is contained in an amount of 100 to 250 parts by weight based on 100 parts by weight of the adipic acid. The method for producing polybutylene adipate terephthalate according to claim 1.

3. The terephthalic acid is contained in an amount of 50 to 150 parts by weight based on 100 parts by weight of the adipic acid. The method for producing polybutylene adipate terephthalate according to claim 1.

4. The titanium (Ti)-based polymerization catalyst is included in an amount of 0.001 to 10 parts by weight based on 100 parts by weight of the adipic acid. The method for producing polybutylene adipate terephthalate according to claim 1.

5. The titanium (Ti)-based polymerization catalyst is at least one selected from the group consisting of titanium methoxide, titanium ethoxide, titanium propoxide, titanium isopropoxide, titanium butoxide, titanium isobutoxide, and titanium citrate; The method for producing polybutylene adipate terephthalate according to claim 1.

6. The titanium (Ti)-based polycondensation catalyst may be the same as or different from the titanium (Ti)-based polymerization catalyst; The method for producing polybutylene adipate terephthalate according to claim 1.

7. The titanium (Ti)-based polycondensation catalyst is included in an amount of 0.001 to 0.5 parts by weight based on 100 parts by weight of the polybutylene adipate terephthalate prepolymer. The method for producing polybutylene adipate terephthalate according to claim 1.

8. 2. The method for producing polybutylene adipate terephthalate according to claim 1, wherein the phosphorus (P)-based heat stabilizer comprises at least one selected from the group consisting of phosphoric acid, phosphorous acid, trialkyl phosphate, and trialkyl phosphonoacetate.

9. The phosphorus (P)-based heat stabilizer is included in an amount of 0.001 to 0.1 parts by weight based on 100 parts by weight of the polybutylene adipate terephthalate prepolymer. The method for producing polybutylene adipate terephthalate according to claim 1.

10. The weight average molecular weight of the polybutylene adipate terephthalate polymer is 70,000 to 200,000 g / mol; The method for producing polybutylene adipate terephthalate according to claim 1.

11. The acid value (mmol / kg) of the polybutylene adipate terephthalate polymer is 5 to 30; The method for producing polybutylene adipate terephthalate according to claim 1.

12. The polybutylene adipate terephthalate polymer has a b* color index value of 0 to 30. The method for producing polybutylene adipate terephthalate according to claim 1.

13. The polybutylene adipate terephthalate polymer satisfies the following mathematical formula 1: The method for producing polybutylene adipate terephthalate according to claim 1 [Equation 2] (In Equation 1 above, acid number is the acid number (mmol / kg) of the polybutylene adipate terephthalate polymer, and b* is the b* color index value of the polybutylene adipate terephthalate polymer).

14. The weight average molecular weight is 70,000 to 200,000 g / mol; Polybutylene adipate terephthalate that satisfies the following formula 1 [Equation 3] (In Equation 1 above, acid number is the acid number (mmol / kg) of the polybutylene adipate terephthalate polymer, and b* is the b* color index value of the polybutylene adipate terephthalate polymer).

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