CN111433262A - Polyester resin composition and biaxially stretched polyester film comprising same - Google Patents

Abstract

The present invention provides a polyester resin composition comprising a polyester resin, and a biaxially stretched polyester film comprising the polyester resin composition, the polyester resin comprising terephthalic acid and isophthalic acid A polycondensate of a dicarboxylic acid component and a diol component containing cyclohexanedimethanol.

Description

Polyester resin composition and biaxially stretched polymer comprising the same Ester film

Background of the Invention

(A) Field of Invention

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Korean Patent Application No. 10-2017-0156747, filed with the Korean Intellectual Property Office on Nov. 22, 2017, the disclosure of which is incorporated herein by reference in its entirety.

The present invention relates to a polyester resin composition and a biaxially stretched polyester film comprising the polyester resin composition.

(b) Description of the relevant field

Recently, metal materials have been replaced by plastic materials in order to reduce the weight of automobiles, but the plastic materials used for such automobile parts need to have high heat resistance, and in order to reduce the volume, they need to be made thin. Among the electrical device parts of these automobile parts, FFC (Flexible Flat Cable) is a connecting cable for connecting between PCB (Printed Circuit Board) or PBA (Printed Board Assembly), and has relatively more Small and thinner features. Furthermore, since the FFC is flexible and thus foldable, it is often used as a connecting connector inside electronic devices such as mobile phones.

Generally, a PET (polyethylene terephthalate) stretched film is used to produce FFC, but the PET stretched film has a heat resistance of about 130° C., and therefore, the FFC of the PET stretched film is used It cannot be applied to main parts such as automotive powertrains and engine control parts that require high heat resistance. Therefore, attempts have been made to improve heat resistance through a technique of coating/laminating a PET stretched film, but it is difficult to make the PET stretched film have high heat resistance to withstand a high temperature of 150° C. or higher.

On the other hand, polyimide films having high heat resistance are also used for FFC applications, but polyimide films are thermosetting resins, and thus have the disadvantage of being difficult to reuse in the future.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a polyester resin composition excellent in high heat resistance and high moisture resistance, and a biaxially stretched polyester film comprising the polyester resin composition.

According to one embodiment of the present invention, a polyester resin composition including a polyester resin including a dicarboxylic acid component containing terephthalic acid and isophthalic acid and a cyclohexanedicarboxylic acid component may be provided A polycondensate of a diol component of methanol, wherein the polyester resin has a melting temperature of 250°C or higher, the polyester resin has a melting temperature (Tm) and a melt crystallization temperature (Tmc) of 45°C or higher ), and the polyester resin has a difference (Tcc-Tg) between cold crystallization temperature (Tcc) and glass transition temperature (Tg) of 40°C or more.

According to another embodiment of the present invention, a biaxially stretched polyester film formed using the polyester resin composition can be provided.

The polyester resin composition according to the specific embodiment of the present invention and the biaxially stretched polyester film for flexible flat cable comprising the polyester resin composition will be described in more detail below.

The present inventors have found through experiments that a polyester resin comprising a polycondensate of a dicarboxylic acid component containing terephthalic acid and isophthalic acid and a diol component containing cyclohexanedimethanol has a temperature of 250°C or higher The melting temperature, the difference (Tm-Tmc) between the melting temperature (Tm) and the melt crystallization temperature (Tmc) at 45°C or higher, and the cold crystallization temperature (Tcc) and vitrification at 40°C or higher The difference between transition temperatures (Tg) (Tcc-Tg), which can result in unstretched sheets having a thickness of 1.0 mm or more, which can be used to increase the stretch ratio when producing stretched films , and improved heat resistance and hygroscopicity, thereby completing the present invention.

Specifically, the biaxially stretched polyester film of one embodiment comprises a polyester resin comprising a dicarboxylic acid component containing terephthalic acid and isophthalic acid and a cyclohexanedimethanol-containing Polycondensates of diol components. In addition, the melting temperature of the polyester resin may be 250°C or higher, 250°C to 350°C, or 253°C to 340°C. When the melting temperature of the polyester resin is lower than 250°C, there is a problem that the polyester resin has low heat resistance and thus cannot be applied to parts requiring high heat resistance.

The polyester resin may have a difference (Tm-Tmc) between the melting temperature (Tm) and the melt crystallization temperature (Tmc) of 45°C or higher, 45°C to 120°C, or 50°C to 115°C. When the difference between the melting temperature and the melt crystallization temperature of the polyester resin is less than 45°C, the polyester resin is cooled to a melt crystallization state (around Tmc) in the molten state (around Tm) after the T-die At the same time, it crystallizes rapidly so as to have a thickness of 1.0 mm or more, and at the same time, there is a problem that it is difficult to form an unstretched sheet in a stretchable transparent state.

In addition, the polyester resin may have a difference (Tcc-Tg) between cold crystallization temperature (Tcc) and glass transition temperature (Tg) of 40°C or higher, 40°C to 100°C, or 43°C to 90°C. When the difference between the cold crystallization temperature and the glass transition temperature of the polyester resin is less than 40°C, when the temperature is raised (heated) to perform the step of stretching the unstretched sheet, the glass transition state (Tg ) the section reaching the cold crystallization state (Tcc) becomes shorter, and thus crystallizes rapidly, which makes it difficult to set drawing processing conditions, and thus drawing may become difficult.

That is, since the melting temperature of the polyester resin is 250° C. or higher, it can exhibit high heat resistance. Furthermore, since the difference between the melting temperature and the melt crystallization temperature is 45°C or more, and the difference between the cold crystallization temperature and the glass transition temperature is 40°C or more, the moldability and tensile properties can be excellent.

The content of isophthalic acid contained in the polyester resin may be 3 mol % to 20 mol %, 5 mol % to 20 mol %, 6 mol % to 18 mol %, 8 mol % to 16 mol % and 10 mol % to 14 mol % based on the total dicarboxylic acid component %. When the content of isophthalic acid exceeds 20 mol %, the thermal shrinkage rate at a high temperature of 150° C. or higher is high, and thus, heat resistance may be deteriorated. When the content of isophthalic acid is less than 3 mol %, the thickness of the transparent unstretched sheet is considerably limited to about 0.1 mm, and the stretching ratio is also limited. Therefore, when a stretched film is produced, the stretch ratio is lowered, and thus desired mechanical properties and heat resistance cannot be obtained.

The dicarboxylic acid component and the diol component contained in the polyester resin may have a molar ratio of 1:1 to 2, or 1:1.2 to 1.8. When the molar ratio of the dicarboxylic acid component and the diol component is less than 1:1, the melting temperature may be lowered, and the heat resistance may be deteriorated. When the molar ratio exceeds 1:2, there is a problem that moldability is greatly deteriorated and thus desired mechanical properties cannot be obtained.

In addition to terephthalic acid and isophthalic acid, the dicarboxylic acid component may also include at least one other dicarboxylic acid component selected from the group consisting of: 2,6-naphthalenedicarboxylic acid, dimethyl-meta- Phthalic acid and dimethyl 2,6-naphthalenedicarboxylic acid, but not limited thereto. The content of the other dicarboxylic acid components may be 20 mol % or less, 0.1 mol % to 20 mol %, and 5 mol % to 15 mol % based on the total dicarboxylic acid components.

In addition, the diol component may also include aliphatic diols having 2 to 20 carbon atoms. For example, the diol component may also include at least one other diol component selected from the group consisting of ethylene glycol, diethylene glycol, 1,4-butanediol, 1,3-propanediol, and neopentyl Diols, but not limited thereto. The content of the other diol components may be 20 mol % or less, 0.1 mol % to 20 mol %, and 5 mol % to 15 mol % based on the total diol components.

The polyester resin may have an intrinsic viscosity (IV) of 0.4 dl/g to 1.2 dl/g, 0.5 dl/g to 1.0 dl/g, or 0.7 dl/g to 0.9 dl/g. When the intrinsic viscosity is less than 0.4 dl/g, the melting temperature may decrease, and thus the heat resistance may decrease. When the intrinsic viscosity is more than 1.2 dl/g, moldability is greatly deteriorated, and thus desired mechanical properties cannot be obtained.

The polyester resin may have a number average molecular weight of 15,000 g/mol to 50,000 g/mol, 20,000 g/mol to 45,000 g/mol, or 25,000 g/mol to 40,000 g/mol. When the number average molecular weight is less than 15,000 g/mol, the melting temperature may decrease, and thus the heat resistance may decrease. When the number average molecular weight is more than 50,000 g/mol, moldability is greatly deteriorated, and thus desired mechanical properties cannot be obtained.

In addition, the polyester resin may have a weight average molecular weight of 50,000 g/mol to 150,000 g/mol, 60,000 g/mol to 140,000 g/mol, or 70,000 g/mol to 130,000 g/mol. When the weight average molecular weight is less than 50,000 g/mol, the melting temperature may decrease, and thus the heat resistance may decrease. When the weight average molecular weight is more than 150,000 g/mol, moldability is greatly deteriorated, and thus desired mechanical properties cannot be obtained.

The polyester resin preferably has a melt crystallization temperature of 150°C to 230°C. When the melt crystallization temperature of the polyester resin is lower than 150°C, the heat-setting effect decreases during the post-processing process or during use of the actually stretched film, and thus it may be difficult to impart dimensional stability to the final stretched film. Specifically, high shrinkage rates may occur. When the melt crystallization temperature is higher than 230°C, it may be difficult to produce a transparent unstretched sheet during film extrusion.

According to another embodiment of the present invention, a biaxially stretched polyester film formed using the polyester resin composition can be provided. The biaxially stretched polyester film exhibits heat resistance at a high temperature of 150°C to 200°C, and thus can be applied to overall safety parts such as automotive powertrains, engine controls, and steering devices. In particular, the biaxially stretched polyester film can be used as a material for a flexible flat cable (FFC) requiring excellent heat resistance, moisture resistance and electrical insulating properties.

Typically, as a material for a flexible flat cable, a PET film capable of controlling the thickness of the film up to 1.2 mm when unstretched is used, but the PET film has heat resistance of about 130° C. and thus has a heat-susceptible question. Therefore, attempts have been made to apply to parts requiring heat resistance by using polyethylene terephthalate (PCT) films, but conventional PCT films have high glass transition temperature (Tg) and melting temperature (Tm ).

However, the conventional PCT film also has a high melt crystallization temperature (Tmc), and therefore, immediately after extrusion using a T-die, crystallization proceeds rapidly, and the thickness of the transparent unstretched sheet is considerably reduced by The limit is about 0.1mm, which is problematic. When the thickness of the transparent unstretched sheet is as thin as about 0.1 mm, the stretching ratio may decrease during the stretching process. Meanwhile, since the conventional PCT film has a low cold crystallization temperature (Tcc), when the temperature is raised (heated) to perform the process of stretching the unstretched sheet, the glass transition state (Tg) reaches the cold temperature The section of the crystalline state (Tcc) becomes short and crystallizes rapidly, which makes it difficult to set drawing processing conditions, and thus drawing may become difficult.

However, the polyester resin according to one embodiment has a difference (Tm-Tmc) between the melting temperature (Tm) and the melt crystallization temperature (Tmc) of 45°C or more, and the polyester resin has 40°C or more Higher difference between cold crystallization temperature (Tcc) and glass transition temperature (Tg) (Tcc-Tg), therefore, the crystallization rate can be slowed down shortly after extrusion, resulting in a transparent unstretched sheet The maximum thickness of the PET film can be controlled to be about 1.2 mm, which is a similar level to the thickness of a transparent unstretched sheet of PET film. In addition, since the crystallization rate can be slowed down in the stretching step, the stretching of the unstretched sheet can be promoted, and the heat resistance of the polyester film can be improved.

The biaxially stretched polyester film according to other embodiments may be a multi-layered film or a laminated (thermally bonded) film having two or more layers in which the above polyester resin composition is coextruded.

Specifically, after two or more of the polyester resin compositions are melted in different extruders, the melted resins are sent to a die to be laminated into two or more layers, and then, The non-stretched multilayer film (or laminated film) can be provided by methods such as blowing or casting. The corresponding layers contained in the unstretched multilayer film are transparent and may have a thickness of about 1.2 mm or more. At this time, the two or more polyester resin compositions may be the same composition, or different compositions having different components or contents. Meanwhile, the unstretched multilayer film is biaxially stretched in the machine direction and the transverse direction to obtain a biaxially stretched polyester film excellent in heat resistance and the like.

The biaxially stretched polyester film may have a thermal shrinkage at 150°C for 30 minutes of less than 0.5%, 0.01% to 0.4%, or 0.01% to 0.3%, and less than 1.0%, 0.01% to 0.9%, or 0.01% to 0.8% thermal shrinkage at 200°C for 30 minutes. Since the thermal shrinkage rate of the biaxially stretched polyester film at a temperature of 150°C to 200°C is very low, it can be confirmed that it is excellent in heat resistance.

In addition, the biaxially stretched polyester film has excellent moisture resistance, specifically, when the temperature is 85° C. and the relative humidity is 85%, the moisture absorption rate may be 1% or less, 0.01% to 0.9%, or 0.01% % to 0.8%.

Meanwhile, the method for producing the biaxially stretched polyester film is not limited thereto, but for example, the polyester resin composition may be vacuum-dried to sufficiently remove moisture, and then supplied to an extruder at 200° C. to 300° C. The temperature was melt extruded at a temperature of °C and molded into a sheet form from a T-shaped spinneret. The sheet-like product thus obtained can be cooled and fixed on a mirror-like cooling drum to obtain an unstretched sheet. At this time, in order to improve adhesion to the cast drum, it is preferable to use an electrostatic application method. Thereafter, the obtained unstretched sheet is stretched in the longitudinal direction (machine direction, MD). Preferably, longitudinal direction stretching reduces crystal orientation and promotes thermal crystallization. After stretching in the longitudinal direction, stretching was performed in the transverse direction (width direction, TD; trans-machine direction), and subjected to heat treatment, thereby obtaining a biaxially stretched film.

At this time, the stretching ratio may be 2 times to 5 times, preferably 2.5 times to 5 times, more preferably 2.5 times to 4.0 times in the longitudinal direction, and 2.5 times to 5 times in the transverse direction, preferably 3 times to 4.5 times, more preferably 3.2 times to 4.2 times.

The stretching temperature may be in the range of the glass transition temperature (Tg) of the polyester resin+5°C to Tg+50°C, or in the range of Tg+10°C to Tg+40°C. At this time, tensile properties are improved as Tg decreases, but cracking may occur. In particular, when the stretching temperature is in the range of Tg+10°C to Tg+40°C, the brittleness of the resulting film can be improved.

Further, the stretching speed in the longitudinal direction may be 22 m/min to 500 m/min, 25 m/min to 400 m/min, or 25 m/min to 200 m/min. In this case, when the longitudinal stretching speed is 22 m/min or more, it is advantageous to maintain the orientation properties expected in the present invention, and crystallinity is imparted according to the longitudinal stretching speed, and thus the stretching ratio, transverse stretching The stretching speed may vary depending on the longitudinal stretching conditions.

According to the present invention, a polyester resin composition excellent in high heat resistance and high moisture resistance, and a polyester film containing the polyester resin composition can be provided.

Brief Description of Drawings

FIG. 1 is a graph showing the measurement results of the moisture absorption rate of the films of Example 1 (PCT) and Comparative Example 1 (PET).

2 is a graph showing the measurement results of the hydrolysis resistance ratio (high viscosity retention ratio) of the films of Example 1 (PCT) and Comparative Example 1 (PET).

3 is a photograph of the film surface taken when evaluating the hydrolysis resistance (high viscosity retention rate) of the films of Example 1 (PCT) and Comparative Example 1 (PET).

Figure 4 is a photograph of the film surface taken before and after the oligomer evaluation of Example 1 (PCT) and Comparative Example 1 (PET).

Implementation details

The present invention is described in more detail in the following examples. However, these examples are for illustrative purposes only, and the content of the present invention is not limited thereto.

Example 1

1) Preparation of polyester resin composition

2.0 kg of 1,4-cyclohexanedimethanol, 1.8 kg of dicarboxylic acid containing terephthalic acid and isophthalic acid in a molar ratio of 95 mol %:5 mol %, 0.4 g of triethyl phosphate, 0.2 g of titanium oxide based catalyst (Hombifast PC from Sachtleben, 15 wt% Ti atomic content in the catalyst) and 0.2 g of antimony trioxide (83.5 wt% antimony atomic content in the catalyst) were charged into the reactor. Then, the temperature was raised to 280° C. for 3 hours under normal pressure to perform an esterification reaction. Then, the esterification reaction product was heated to a temperature of 295° C. under a pressure of 0.5 Torr to 1 Torr for 150 minutes, and subjected to polycondensation to produce a polyester resin, and then the polyester resin was processed into chips.

2) Preparation of biaxially stretched polyester film

The polyester resin chips were melt extruded in an extruder, molded into sheets, and cooled. The obtained sheet was stretched 3.6 times in the machine direction (MD) and then 3.8 times in the transverse direction (TD). The stretched film was heat-set at 238°C to obtain a biaxially stretched polyester film.

Example 2 and Example 3

A biaxially stretched polyester film was obtained in the same manner as in the production method of Example 1 except that the content of isophthalic acid was used in the molar ratio shown in Table 1 below.

Comparative Example 1

1.2 kg of terephthalic acid and 1.2 kg of ethylene glycol were charged into a reaction tank, and subjected to normal polymerization at 258° C. to produce polyethylene terephthalate (PET) polymer, and then the polyethylene terephthalate (PET) polymer was The ethylene terephthalate polymer is processed into chips. It was melt extruded in an extruder, molded into a sheet, cooled, stretched 3.7 times in the machine direction (MD), and then stretched 4.0 times in the transverse direction (TD) to produce polyparaphenylene Ethylene glycol diformate membrane.

Comparative Example 2 to Comparative Example 4

A biaxially stretched polyester film was obtained in the same manner as in the production method of Example 1 except that the content of isophthalic acid was used in the molar ratio shown in Table 1 below,

Evaluate

1. Measurement of glass transition temperature, etc. by DSC analysis

The polyester resins of Examples 1 to 3 and Comparative Examples 1 to 5 were analyzed by DSC (Differential Scanning Calorimeter), and glass transition temperature (Tg), cold crystallization temperature (Tcc) were measured , melting temperature (Tm) and melting crystallization temperature (Tmc). Specifically, using DSC, the polyester resin was heated from 30°C to 320°C at a heating rate of 10°C/min, then held for 5 minutes, quenched to 30°C, and then held for 5 minutes. Subsequently, while increasing the temperature from 30°C to 320°C at a heating rate of 10°C/min, glass transition temperature (Tg), cold crystallization temperature (Tcc) and melting temperature (Tm) were measured. After being held at 320°C for 5 minutes, while cooling to 30°C at a cooling rate of 10°C/min, the melt crystallization temperature (Tmc) was measured, and the results are shown in Table 1 below.

2. Maximum thickness measurement of transparent unstretched sheets

The polyester resins of Examples 1 to 3 and Comparative Examples 1 to 5 were melt extruded in an extruder, and the transparent state was measured before stretching in the machine direction (MD) and transverse direction (TD) The maximum thickness of the unstretched sheet, and the results are shown in Table 1 below.

3. Measurement of the maximum stretch ratio

The unstretched sheets of Examples 1 to 3 and Comparative Examples 1 to 5 were biaxially stretched in both the machine and transverse directions, the maximum stretch ratio was measured, and the results are as follows shown in Table 1.

4. Measurement of area thermal shrinkage

The films of Examples 1 to 3 and Comparative Examples 1 to 5 were cut so that one edge was parallel to the machine direction (longitudinal direction) and the other edge was perpendicular to the machine direction (transverse direction) to prepare 10 cm x 10 cm square film sample. The films were kept at 150°C for 30 minutes in an oven in which air was circulated, and then samples were taken and the length changes in the machine and transverse directions were measured at room temperature. The thermal shrinkage rates in the machine direction and the transverse direction were calculated according to Equation 1 below. The film was kept in an oven at 200°C for 30 minutes in the same manner, and then the thermal shrinkage was calculated, and the results are shown in Table 1 below.

[Equation 1]

Thermal shrinkage (%)=[(L ₀ -L)/L ₀ ]×100

In the equation, L ₀ is the length before heat treatment, and L is the length after heat treatment.

5. Evaluation of Tensile Elongation Retention

The films of Example 1 (PCT) and Comparative Example 1 (PET) were maintained at a temperature of 121° C., a relative humidity of 100% and an atmospheric pressure of 2 atm for 48 hours and 60 hours (Pressure Cooker Test), and The tensile elongation retention was then measured, and the results are shown in Table 1 below.

6. Evaluation of moisture absorption resistance

The films of Example 1 (PCT) and Comparative Example 1 (PET) were maintained at a temperature of 85° C. and a relative humidity of 85% for 5000 hours, and the weight gain was then measured and plotted in FIG. 1 . Furthermore, the moisture absorption rate after 5000 hours was calculated, and the results are shown in Table 1 below.

7. Evaluation of hydrolysis resistance

(1) Measurement of intrinsic viscosity

After dissolving the films of Example 1 and Comparative Example 1 in o-chlorophenol at a concentration of 1.2 g/dl, the intrinsic viscosity was measured at 35°C using an Ubbelodhe viscometer.

(2) Measurement of hydrolysis resistance rate (unique viscosity retention rate)

The films of Example 1 and Comparative Example 1 were maintained at a temperature of 85° C. and a relative humidity of 85% for 5000 hours, and then the degree of intrinsic viscosity retention was measured, and the results are shown in the graph of FIG. 2 . In addition, the hydrolysis resistance rate (high viscosity retention rate) after 5000 hours is shown in Table 1 below. In addition, the surfaces of Example 1 (PCT) and Comparative Example 1 (PET) after 5000 hours were photographed and shown in FIG. 3 .

8. Oligomer Assessment

To investigate the elution of oligomers in the films of Example 1 and Comparative Example 1, they were subjected to heat treatment in an oven at 150°C for about 60 minutes, and measurements were made by observing changes using a hazemeter. The results are shown in Table 1 below.

Haze meter: NIPPON DENSHOKU NDH-7000 type

9. Evaluation of Dielectric Breakdown Voltage

Using the films of Example 1 and Comparative Example 1 to produce flexible flat cables, AC 1,000V was applied to the adjacent conductors for 60 seconds to read the voltage when the films were ruptured and shorted, and the results are in Table 1 below Shows.

【Table 1】

-IPA*: isophthalic acid (IPA) content relative to 100 mol% of the dicarboxylic acid component contained in the polyester resin

-P.C.T**: Known as Pressure Cooker Test (P.C.T) or Autoclave Test, a test to assess whether a product can withstand a high temperature/high humidity environment. Tests were performed at a temperature of 121°C, a relative humidity of 100% and an atmospheric pressure of 2 atm.

According to Table 1, it was confirmed that, compared with the PET film of Comparative Example 1, the PCT films of Examples 1 to 3 had a low thermal shrinkage rate and thus had excellent heat resistance, and were excellent in moisture absorption resistance, hydrolysis resistance It is excellent in terms of efficiency and electrical characteristics.

Furthermore, it was confirmed that the PCT films of Examples 1 to 3 had higher maximum stretch ratios and lower thermal shrinkage rates than the PCT films of Comparative Examples 2 to 5. Furthermore, it was confirmed that the PCT films of Examples 1 to 3 can control the thickness of the unstretched sheet to be thicker than the PCT films of Comparative Example 2 and Comparative Example 3.

Claims (16)

1. A polyester resin composition comprising a polyester resin comprising a polycondensate of a dicarboxylic acid component comprising terephthalic acid and isophthalic acid and a diol component comprising cyclohexanedimethanol,

wherein the polyester resin has a melting temperature of 250 ℃ or more,

the polyester resin has a difference (Tm-Tmc) between a melting temperature (Tm) and a melt crystallization temperature (Tmc) of 45 ℃ or more, and

the polyester resin has a difference (Tcc-Tg) between a cold crystallization temperature (Tcc) and a glass transition temperature (Tg) of 40 ℃ or higher.

2. The polyester resin composition according to claim 1,

wherein the content of the isophthalic acid is 3 to 20 mol% based on the total dicarboxylic acid component.

3. The polyester resin composition according to claim 1,

wherein the dicarboxylic acid component further comprises at least one other dicarboxylic acid component selected from the group consisting of: 2, 6-naphthalenedicarboxylic acid, dimethylisophthalic acid and dimethyl 2, 6-naphthalenedicarboxylic acid, and

the content of the other dicarboxylic acid component is 20 mol% or less based on the total dicarboxylic acid component.

4. The polyester resin composition according to claim 1,

wherein the diol component further comprises at least one other diol component selected from the group consisting of: ethylene glycol, diethylene glycol, 1, 4-butanediol, 1, 3-propanediol and neopentyl glycol, and

the content of the other diol component is 20 mol% or less based on the total diol component.

5. The polyester resin composition according to claim 1,

wherein the dicarboxylic acid component and the diol component have a molar ratio of 1:1 to 2.

6. The polyester resin composition according to claim 1,

wherein the polyester resin has an Intrinsic Viscosity (IV) of 0.4dl/g to 1.2 dl/g.

7. The polyester resin composition according to claim 1,

wherein the polyester resin has a number average molecular weight of 15,000 to 50,000 g/mol.

8. The polyester resin composition according to claim 1,

wherein the polyester resin has a weight average molecular weight of 50,000g/mol to 150,000 g/mol.

9. The polyester resin composition according to claim 1,

wherein the polyester resin has a melt crystallization temperature of 150 ℃ to 230 ℃.

10. A biaxially stretched polyester film formed using the polyester resin composition according to any one of claims 1 to 9.

11. A biaxially stretched polyester film according to claim 10,

the polyester film is a multilayer film or a laminated film having two or more layers, in which the polyester resin composition is coextruded.

12. A biaxially stretched polyester film according to claim 10,

wherein the biaxially stretched polyester film is used for a flexible flat cable.

13. A biaxially stretched polyester film according to claim 10,

wherein the biaxially stretched polyester film has a thermal shrinkage at 150 ℃ for 30 minutes of less than 0.5%, and a thermal shrinkage at 200 ℃ for 30 minutes of less than 1.0%.

14. A biaxially stretched polyester film according to claim 10,

wherein the biaxially stretched polyester film is stretched 2 to 5 times in a Machine Direction (MD) and 2 to 5 times in a Transverse Direction (TD).

15. A biaxially stretched polyester film according to claim 10,

wherein the biaxially stretched polyester film has a tensile elongation retention of 50% or more after the lapse of 48 hours and a tensile elongation retention of 30% or more after the lapse of 60 hours in a pressure cooker test at a temperature of 121 ℃, a relative humidity of 100% and an atmospheric pressure of 2 atm.

16. A biaxially stretched polyester film according to claim 10,

wherein the biaxially stretched polyester film has a moisture absorption resistance of 1% or less when the temperature is 85 ℃ and the relative humidity is 85%.

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