Biaxially oriented polyester film and method for manufacturing the same

Abstract

The present invention provides a biaxially oriented polyester film and a method for manufacturing the same, which can achieve excellent productivity ratings while possessing superior physical properties, thereby enabling a strong product competitiveness. [Solution] A biaxially oriented polyester film is manufactured from a polyester resin mixture, wherein the polyester resin mixture includes a polyester material, a metal catalyst material, and a crystallization inhibitor. The biaxially oriented polyester film is analyzed by differential scanning calorimetry and, when cooled from a molten state at cooling rates of 20°C / min and 40°C / min, respectively, the difference between the observed first recrystallization temperature and the second recrystallization temperature is greater than 15°C and less than or equal to 23°C. A method for manufacturing a biaxially oriented polyester film is also provided.

Description

[Technical Field]

[0001] The present invention relates to a biaxially stretched polyester film and a method for producing the same. [Background Art]

[0002] In the production of biaxially stretched polyester films, balancing crystallinity and physical properties is an important issue. For example, when the difference between the two recrystallization temperatures observed when a biaxially stretched polyester film is cooled from a molten state at cooling rates of 20°C / min and 40°C / min respectively is less than 15°C, the crystallinity is too high, and film breakage is prone to occur during the production process. On the other hand, when crystallinity is reduced, physical properties may not meet expectations. Furthermore, as environmental issues are gradually attracting more attention, how to design a biaxially stretched polyester film with product competitiveness has become an important challenge. [Summary of the Invention] [Problem to be Solved by the Invention]

[0003] In the production of biaxially stretched polyester films, balancing crystallinity and physical properties is an important issue. For example, when the difference between the two recrystallization temperatures observed when a biaxially stretched polyester film is cooled from a molten state at cooling rates of 20°C / min and 40°C / min respectively is less than 15°C, the crystallinity is too high, and film breakage is prone to occur during the production process. On the other hand, when crystallinity is reduced, physical properties may not meet expectations. Furthermore, environmental issues are also gradually attracting attention. [Means for Solving the Problem]

[0004] The present invention provides a biaxially stretched polyester film that achieves excellent productivity evaluation while having excellent physical properties, thereby enabling good product competitiveness, and a method for producing the same.

[0005] In the biaxially oriented polyester film produced from the polyester resin mixture of the present invention, the polyester resin mixture includes a polyester material, a metal catalyst material, and a crystallization inhibitor. As a result, when the biaxially oriented polyester film is analyzed by differential scanning calorimetry, the difference between the first recrystallization temperature and the second recrystallization temperature observed when the film is cooled from a molten state at cooling rates of 20°C / min and 40°C / min, respectively, is greater than 15°C and less than or equal to 23°C. If the difference is less than 15°C, the crystallinity is too high, leading to serious film breakage, and if it exceeds 23°C, the crystallinity is too low, causing the film's physical properties to fail to meet the requirements.

[0006] In one embodiment of the present invention, the content of the metal catalyst material is 0.3 to 40 ppm / mol% relative to the molar concentration of the crystal suppressing material, and the crystal suppressing material accounts for 2 to 8 mol% of the molar concentration of the polyester resin mixture. Furthermore, if the ratio of the metal catalyst material content to the molar concentration of the crystal suppressing material is too low, the crystallinity becomes too small, and mechanical strength tends to be insufficient. If the ratio is too high, the crystallinity becomes too high, and the crystallinity before stretching becomes too high, making film breakage more likely during stretching. On the other hand, if the crystal suppressing material is outside the aforementioned range, the variation in stretching conditions for each batch becomes large, making production control difficult and affecting film properties. If it exceeds the upper limit, the crystallinity becomes too small, and structural strength tends to decrease. If it is below the lower limit, the crystallinity becomes too high, and film breakage is more likely to occur during the stretching process. However, the present invention is not limited thereto, and these values ​​can be determined based on actual product design requirements.

[0007] In one embodiment of the present invention, the above-mentioned metal catalyst material includes antimony, germanium, titanium, cobalt, and Group 1A / Group 2A elements such as magnesium, lithium, sodium, and potassium, or combinations thereof.

[0008] In one embodiment of the present invention, the crystal suppression material includes isophthalic acid, neopentyl glycol, diethylene glycol, 1,4-cyclohexanedimethanol, or a combination thereof.

[0009] In one embodiment of the present invention, the polyester material includes recycled polyester material, virgin polyester material, or a combination thereof.

[0010] In one embodiment of the present invention, the above-mentioned first recrystallization temperature is greater than 170°C.

[0011] In one embodiment of the present invention, the above-mentioned second recrystallization temperature is 150 to 175°C.

[0012] In one embodiment of the present invention, the thickness of the biaxially oriented polyester film is greater than 10 micrometers.

[0013] The present invention provides a method for producing a biaxially oriented polyester film, comprising the following steps: 1. Melting and extruding one or more polyester pellets to produce an unstretched thick sheet, wherein the polyester pellets include at least chemically recycled polyester pellets, and the chemically recycled polyester pellets have a higher content of metal catalyst material and crystallization inhibitor than the physically recycled polyester pellets; in other words, in the step of melting and extruding polyester pellets to produce an unstretched thick sheet, the molten polyester pellets are a polyester resin mixture. 2. Biaxially stretching the thick sheet to form the biaxially oriented polyester film, wherein the biaxially oriented polyester film is analyzed by differential scanning calorimetry, and when cooled from a molten state at cooling rates of 20°C / min and 40°C / min, respectively, the difference between the observed first recrystallization temperature and the second recrystallization temperature is greater than 15°C and less than or equal to 23°C.

[0014] In one embodiment of the present invention, the polyester pellets further comprise either or both virgin polyester pellets and physically recycled polyester pellets. [Effects of the Invention]

[0015] Based on the above, the present invention introduces a metal catalyst material and a crystal-inhibiting material into a polyester resin mixture. By having the two materials exert a synergistic effect through their different effects on film properties, the crystallinity of biaxially oriented polyester films is improved, leading to better productivity evaluations. At the same time, the films possess superior physical properties in terms of multiaxial breaking strength and other aspects, resulting in better product competitiveness. For example, if physically recycled polyester pellets contain only metal catalysts such as antimony, germanium, titanium, and cobalt, the adhesion required during film formation is insufficient (insufficient adhesion between the cooling roller and the polyester resin mixture causes uneven film thickness). Therefore, when preparing chemically recycled polyester pellets, antimony, germanium, titanium, cobalt, and / or other Group 1A / 2A elements are added. However, if only the catalyst is added and no crystal-inhibiting material is added, the crystallinity of the polyester resin mixture is significantly improved, leading to serious film tearing during stretching. In some situations, the recycled material itself may contain a small amount of crystal-inhibiting material, but the content is extremely small and still insufficient to overcome the problem. Therefore, in addition to adding the above-mentioned metal catalyst when preparing chemically recycled polyester pellets, the present invention further introduces a crystal-suppressing material to improve productivity and thickness uniformity, and to further enhance physical properties. [Brief explanation of the drawing]

[0016] [Figure 1] This is a flowchart of a method for producing a biaxially oriented polyester film according to one embodiment of the present invention. [Modes for carrying out the invention]

[0017] In the following detailed description, exemplary embodiments that reveal certain details are given for illustrative purposes only, and not limiting, to provide a clear understanding of the various principles of the invention. However, as will be apparent to those skilled in the art, the invention can be practiced in other embodiments that benefit from this disclosure and deviate from the specific details disclosed herein. Furthermore, in order to avoid obscuring the explanation of the various principles of the invention, descriptions of well-known apparatus, methods, and materials may be omitted.

[0018] In this text, a range can be expressed as "approximately" from one specific value to "approximately" another specific value, or directly as "to one specific value and / or another specific value." When expressing such a range, another embodiment includes "from one specific value and / or another specific value." Similarly, when a value is expressed as an approximation using the antecedent "approximately," it is understood that the specific value forms another embodiment. Furthermore, it is understood whether the endpoints of each range are clearly related to or independent of other endpoints.

[0019] In this text, non-restrictive terms (e.g., possible, can, for example, or other similar terms) mean non-essential or optional implementation, inclusion, addition, or presence.

[0020] Unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as those commonly understood by those skilled in the art. Furthermore, terms (as defined in commonly used dictionaries) are to be interpreted as having the meaning consistent with their meaning in the relevant technical context, and should not be interpreted in an idealized or overly formal sense unless expressly defined otherwise.

[0021] Figure 1 is a flowchart of a method for manufacturing a biaxially oriented polyester film according to one embodiment of the present invention. Referring to Figure 1, in step S101, polyester pellets are provided, which consist of at least recycled polyester material and may further include virgin polyester material. Furthermore, the recycled polyester material may include a metal catalyst material and a crystal suppressing material. In step S102, the polyester pellets are melted (also referred to as a polyester resin mixture) and extruded to produce an unstretched thick sheet. In step S103, the thick sheet is biaxially stretched to form the biaxially oriented polyester film. When this biaxially oriented polyester film is analyzed by differential scanning calorimetry (DSC), the difference between the two recrystallization temperatures observed when cooled from a molten state at cooling rates of 20°C / min and 40°C / min is greater than 15°C and less than or equal to 23°C (for example, 16°C, 17°C, 18°C, 19°C, 20°C, 21°C, 22°C, 23°C, or any appropriate value within the range of greater than 15°C and less than or equal to 23°C). Thus, the present invention introduces a metal catalyst material and a crystallization inhibitor into a polyester resin mixture, and the two materials exert a synergistic effect due to the different effects they have on the film properties. In this way, the crystallinity of the biaxially oriented polyester film is improved, a better productivity evaluation is obtained, and at the same time, it is possible to have more reliably superior physical properties in terms of multiaxial breaking strength, thereby providing a good product competitiveness. Here, the recrystallization temperatures observed when cooled from a molten state at cooling rates of 20°C / min and 40°C / min are the first recrystallization temperature and the second recrystallization temperature, respectively.

[0022] In some embodiments, the virgin polyester material accounts for 0 to 50 wt% of the polyester resin mixture by weight (for example, 0 wt%, 5 wt%, 10 wt%, 20 wt%, 45 wt%, 50 wt%, or any suitable value between 0 and 50 wt%), and the recycled polyester material accounts for 50 to 100 wt% of the polyester resin mixture by weight (for example, 55 wt%, 60 wt%, 70 wt%, 80 wt%, 95 wt%, 100 wt%, or any suitable value between 50 and 100 wt%), thereby meeting the requirements of environmental protection. On the other hand, recycled polyester materials generally contain impurities that act as nucleating agents (especially when the content of chemically recycled polyester pellets exceeds 10 wt%), so the crystallinity of the thick sheet before stretching tends to be high, which is likely to cause film breakage during the stretching process. In the present invention, by introducing a metal catalyst material and a crystallization inhibiting material, excellent productivity and physical properties can be achieved while using a high content of recycled polyester material.

[0023] In some embodiments, the metal catalyst material comprises group 1A / group 2A elements selected from antimony, germanium, titanium, cobalt, magnesium, lithium, sodium, potassium, or combinations thereof, and the crystallization inhibiting material comprises isophthalic acid (IPA, CAS No: 121-91-5), neopentyl glycol (NPG, CAS No: 126-30-7), diethylene glycol (DEG, CAS No: 111-46-6), 1,4-cyclohexanedimethanol (CHDM, CAS No: 105-08-8), or combinations thereof.

[0024] In some embodiments, the content of the metal catalyst material is 0.3 to 40 ppm / mol% (concentration of the metal catalyst material (ppm) / molar percentage concentration of the crystal inhibition material in the subsequently formed polyester resin mixture), relative to the molar percentage concentration of the crystal inhibition material (for example, 0.3 ppm / mol%, 0.7 ppm / mol%, 5 ppm / mol%, 10 ppm / mol%, 20 ppm / mol%, 31 ppm / mol%, 35 ppm / mol%, 40 ppm / mol%, or any suitable value between 0.3 and 40 ppm / mol%). In addition, the crystal inhibition material accounts for 2 to 8 mol% of the molar percentage concentration of the polyester resin mixture (for example, 2 mol%, 3 mol%, 4 mol%, 5 mol%, 6 mol%, 7 mol%, 8 mol%, or any suitable value between 2 and 8 mol%). Too little crystal inhibition material may adversely affect the subsequent manufacturing process. If the content exceeds the above upper limit, the crystallinity will become too low and the structural strength tends to decrease. If the content is below the above lower limit, the crystallinity will be too high, which tends to cause film breakage during the stretching process. On the other hand, the metal catalyst material has an effect similar to a nucleating agent, and an appropriate content is conducive to maintaining physical properties. Therefore, when the ratio of the two is within a certain range, better effects can be obtained. Accordingly, within the above ratio range, the synergistic effect can be better exerted, and the competitiveness of the product can be further improved.

[0025] In some embodiments, the polyester resin mixture is composed of a polyester material, a metal catalyst material, and a crystal inhibition material. That is, the total weight of the polyester material, the metal catalyst material, and the crystal inhibition material constitutes 100 wt% of the polyester resin mixture. However, the present invention is not limited thereto, and the polyester resin mixture may also contain other additives. For example, it is a polyester resin mixture in which the total weight of the polyester material, the metal catalyst material, the crystal inhibition material, and other additives (such as a lubricant) constitutes 100 wt%.

[0026] In some embodiments, the first recrystallization temperature is above 170°C. Preferably, it is between 170 and 190°C, and may also exceed 175°C. In some embodiments, the second recrystallization temperature is between 150 and 175°C. Preferably, it is between 155 and 175°C, and may also be between 165 and 175°C. In the present invention, by introducing at least a crystal-inhibiting material, good stretchability can be achieved in the manufacturing process even when the recrystallization temperature is in the higher temperature range mentioned above.

[0027] In some examples, the melting point of the biaxially oriented polyester film is between 243 and 253°C (for example, 243°C, 245°C, 247°C, 249°C, 251°C, 253°C, or any appropriate value between 243 and 253°C).

[0028] In some embodiments, the thickness of the biaxially oriented polyester film is 8 to 350 μm, more preferably 10 to 350 μm, and may also be 50 to 350 μm, which provides superior structural strength, but the present invention is not limited thereto.

[0029] In some embodiments, the polyester resin mixture further contains a lubricant, which accounts for 0.05 to 2 wt% by weight of the polyester resin mixture (e.g., 0.05 wt%, 1 wt%, 1.5 wt%, 2 wt%, or any suitable value between 0.05 and 2 wt%), and has a particle size of 0.05 to 5 μm (e.g., 0.05 μm, 0.3 μm, 0.35 μm, 0.4 μm, 0.5 μm, or any suitable value between 0.05 and 5 μm). The lubricant may be granular. For example, the lubricant may include silicon dioxide particles, calcium carbonate particles, barium sulfate particles, polystyrene particles, silica gel particles, acrylic particles, or a combination thereof.

[0030] In some embodiments, the biaxially oriented polyester film may have a single-layer structure, or it may have a multilayer structure design of a skin layer / base layer / skin layer, where both the base layer and the skin layer can be formed from the polyester resin mixture described above, and in this multilayer structure design, the thickness of the skin layer can account for 2 to 30% of the total thickness of the biaxially oriented polyester film (for example, 2%, 3%, 4%, 10%, 15%, 20%, 30%, or any appropriate value between 2% and 30%).

[0031] The following provides a detailed explanation of the specific steps described above, but these details are for illustrative purposes only and are not intended to limit the invention. Those skilled in the art can make appropriate adjustments and improvements based on these details.

[0032] [Recycled polyester material] A method for recycling polyester materials includes, for example, collecting each type of waste polyester material. The waste polyester material may be classified according to its type, color, and / or intended use. The classified waste polyester material may then be compressed and packaged. The packaged waste polyester material may then be transported to a waste treatment plant. The waste polyester material may include, for example, recycled PET bottles. However, the present invention is not limited thereto.

[0033] A method for recycling polyester material may further include: removing objects (e.g., bottle caps, labels, and / or adhesives) from the waste polyester material; then physically and mechanically crushing the aforementioned waste polyester material; then separating the crushed polyester material using an appropriate method (e.g., flotation); and finally drying the crushed and separated waste polyester material to obtain processed recycled polyester material.

[0034] In one embodiment, the recycled polyester material can be obtained by further recycling a biaxially oriented polyester film formed by the method described later (for example, recycling of the ear portion material after cutting).

[0035] It is necessary to clarify that the terms "polyester" and "polyester material" in the text refer to any type of polyester, and in particular to aromatic polyesters, and here specifically to polyesters derived from purified terephthalic acid (PTA) and ethylene glycol (EG) (i.e., polyethylene terephthalate (PET)).

[0036] Furthermore, the polyester in this text may be, for example, polypropylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, or a combination of the above. In this embodiment, the polyester is preferably polyethylene terephthalate, polypropylene terephthalate, or a combination of the above. Moreover, copolymers may be used, which in particular refer to copolymers obtained by using two or more dicarboxylic acids and / or two or more diol components.

[0037] In some embodiments, the recycled polyester material obtained by the following methods (chemically recycled polyester pellets, physically recycled polyester pellets) can be used to further form recycled polyester pellets and carry out subsequent thin film manufacturing processes.

[0038] [Method for producing chemically recycled polyester pellets] (May include metal catalyst material and crystallization inhibitor material)

[0039] First, the recycled polyester material is chemically depolymerized. For example, the recycled polyester material and a depolymerization solution can be placed in a suitable depolymerization tank to perform chemical depolymerization. This chemical depolymerization solution essentially breaks the chains of polyester molecules in the recycled polyester material, thereby achieving the depolymerization effect. Furthermore, a polyester composition with shorter molecular chains and / or ester monomers consisting of one diacid unit and two diol units (e.g., bis(2-Hydroxyethyl)terephthalate (BHET)) can be obtained. That is, the average molecular weight of the mixture after chemical depolymerization is basically smaller than the average molecular weight of the recycled polyester material. Moreover, the present invention does not limit the type of depolymerization solution. For example, hydrolysis can be performed with water. Alternatively, alcohol decomposition can be performed with alcohols (e.g., methanol, ethanol, ethylene glycol, diethylene glycol, or a mixture of the above). In one example, alcohols are more preferred as the depolymerization solution. A more suitable alcohol hydrolysate is ethylene glycol, partly because ethylene glycol can act as a reaction monomer for virgin polyester pellets (virgin PET chips).

[0040] Next, the product after the chemical depolymerization reaction described above is subjected to an esterification reaction. It should be noted that the present invention does not limit the requirement that all polyester materials be completely depolymerized. For example, the product after the chemical depolymerization reaction described above can be transferred to a suitable esterification tank for esterification. In one embodiment, before transferring the product after the chemical depolymerization reaction described above to the esterification tank, the material can be filtered to remove at least some impurities in the recycled polyester material, thereby reducing the concentration of non-polyester impurities. However, small particles (e.g., metal impurities) may still be present in trace amounts. In one embodiment, the pore size of the filter may be 1 to 10 μm. In some embodiments, after the esterification reaction described above has been carried out for a certain period of time, other additives, such as metal catalysts, crystal inhibitors, lubricants, and stabilizers, can be further added to the esterification tank.

[0041] Next, the product after the esterification reaction is polymerized. For example, the product after the esterification reaction can be transferred to a suitable polymerization tank and polymerized. Finally, polyester pellets are formed. For example, the polymerization reaction is allowed to proceed until the material in the tank has a corresponding intrinsic viscosity (IV). Then, the material in the tank is extruded and / or cut using a granulation method commonly used for general polymer particles to form polyester pellets. In this embodiment, the intrinsic viscosity of the polyester pellets formed by the chemical recycling process described above is typically 0.5 to 0.8 dL / g, for example, 0.6 to 0.78 dL / g.

[0042] In one embodiment, the polyester pellets formed by the aforementioned chemical recycling process can be referred to as chemically recycled polyester chips having a high content of catalyst material and crystal-inhibiting material. By adding chemically recycled polyester pellets during film formation, the crystallinity of the polyester mixture during film formation can be reduced, preventing film breakage during the production process, improving adhesion during film formation, and enhancing the uniformity of the film thickness. Therefore, the polyester pellets for forming a biaxially oriented polyester film include at least chemically recycled polyester pellets.

[0043] [Method for manufacturing physically remote polyester pellets] In this embodiment, the recycled polyester material can be melted to a molten state. Next, the molten recycled polyester material can be filtered to remove solid impurities from the recycled polyester material. Then, the filtered recycled polyester material can be extruded and granulated using an extruder (e.g., a commercially available single-screw extruder (SSE), twin-screw extruder (TSE), or other similar screw extruder, but not limited to these) to form physically recycled, environmentally friendly polyester pellets. In one embodiment, the recycled polyester material can be physically and mechanically crushed before melting to reduce the time and / or energy consumption required for melting the recycled polyester material. On the other hand, the above-described method reshapes the recycled polyester material through the steps of cutting, melting, filtering, and extrusion. That is, physically recycled, environmentally friendly polyester pellets basically do not go through the step of repolymerization after depolymerization, and the manufacturing process consists only of melting, filtering, and granulation.

[0044] In this embodiment, the recycled polyester material undergoes only the melting, filtering, and granulation steps in the aforementioned physical reprocessing process. Therefore, components originally present in the recycled polyester material (e.g., metal impurities) remain present in the physically recycled polyester pellets. That is, some properties of the physically recycled polyester pellets may be identical or similar to some properties of the recycled polyester material originally used. In one embodiment, the average molecular weight of the recycled polyester material in the physical reprocessing process may not change significantly (compared to chemically recycled polyester pellets). That is, the recycled polyester material may have a relatively high viscosity in the molten state (i.e., low fluidity). Therefore, using a filter with too small a pore size may reduce filtration efficiency. In one embodiment, the pore size of the mesh is preferably between 10 and 100 μm, but the present invention is not limited thereto.

[0045] The physically recycled polyester pellets produced by the aforementioned physical reprocessing operations typically have a higher intrinsic viscosity. In this embodiment, the intrinsic viscosity of the physically recycled polyester pellets may be 0.5 to 0.8 dL / g, for example, 0.6 to 0.78 dL / g.

[0046] In one embodiment, the polyester pellets formed by the aforementioned physical reprocessing work can be referred to as physically recycled polyester chips.

[0047] [Method for producing virgin polyester pellets] The method can be the same as or similar to the method described above for producing chemically recycled polyester pellets, the difference being that phthalic acid and ethylene glycol can be directly added to the esterification tank to carry out the esterification reaction. In this embodiment, the intrinsic viscosity of the polyester pellets formed by the above method may be typically 0.5 to 0.8 dL / g, for example, 0.6 to 0.78 dL / g.

[0048] In one embodiment, the polyester pellets formed by the above-described method can be referred to as virgin polyester pellets (virgin polyester chips).

[0049] [Method for manufacturing biaxially oriented polyester film] In this embodiment, at least two of the above-mentioned polyester pellets (for example, one or two of the above-mentioned chemically recycled polyester pellets, virgin polyester pellets, and physically recycled polyester pellets) can be used directly or mixed in appropriate ratios based on the design requirements.

[0050] In one embodiment, polyester pellets can be dried by heating and / or low-pressure standing. For example, polyester pellets can be vacuum-dried at approximately 120-180°C for approximately 3-8 hours.

[0051] Subsequently, the polyester pellets (which may be dried polyester pellets, but are not limited to them) are heated, melted, and extruded. For example, the polyester pellets can be melted in an extruder (e.g., a commercially available single-screw extruder, but are not limited to it) at a temperature of approximately 200-290°C, and the molten polyester can be extruded and molded to produce a thick, unstretched sheet.

[0052] Subsequently, the corresponding biaxial stretching step can be performed on the thick sheet using a method commonly used for general biaxially oriented polyester films. For example, an unstretched thick sheet can be introduced into a longitudinal stretcher and stretched longitudinally to form a corresponding thin film (i.e., a thick sheet stretched longitudinally). Then, the thin film can be drawn into a transverse stretcher and stretched transversely to form a biaxially oriented polyester film (i.e., a thin film stretched transversely).

[0053] In detail, for example, a thick sheet is stretched longitudinally by 2 to 6 times in the length direction (also called the MD) parallel to its transport direction at approximately 70 to 145°C, and then stretched longitudinally by 2 to 6 times in the width direction of the thin film (i.e., another direction perpendicular to the length direction, the transverse direction; also called the TD) at approximately 90 to 160°C. That is, the longitudinal stretching and transverse stretching are performed sequentially, but the present invention is not limited thereto. In other embodiments, the longitudinal stretching and transverse stretching can be carried out simultaneously at approximately 70 to 160°C with a stretching ratio of 2 to 6 times. Furthermore, in some embodiments, the biaxially oriented polyester film may also be subjected to transverse and / or longitudinal pre-shrinkage.

[0054] The steps described above largely complete the manufacturing of the biaxially oriented polyester film of this embodiment. In one embodiment, after transverse stretching, a portion of the film can be cut off (e.g., selvage material) based on design requirements. The biaxially oriented polyester film can be stored by winding; or it can be further sold and / or used.

[0055] [Examples and Comparative Examples] The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not fundamentally limited to the following examples.

[0056] Each example and comparative example can form the corresponding biaxially oriented polyester film using the method described above. The difference lies in adjusting the ratio of polyester pellets, metal catalyst material, and crystal suppressing material used. The metal catalyst material is a group 1A / 2A element such as antimony, germanium, titanium, cobalt, magnesium, lithium, sodium, or potassium, while the crystal suppressing material is a combination of isophthalic acid and diethylene glycol.

[0057] Tests were conducted on the biaxially oriented polyester films [Example 1] to [Example 9] and [Comparative Example 1] to [Comparative Example 4] in Table 1. The results show that by introducing metal catalyst materials and crystallization inhibitors, the crystallinity of the biaxially oriented polyester films is indeed improved, leading to better productivity evaluations, while simultaneously demonstrating superior physical properties such as multiaxial breaking strength. The test items included the film rupture rate of the biaxially oriented polyester film (shown as "film rupture rate (times / 24 hours)" in Table 1), the recrystallization temperature of the biaxially oriented polyester film under different conditions (shown as "recrystallization temperature Tc(20)(°C)" and "recrystallization temperature Tc(40)(°C)" in Table 1) and their difference (shown as "difference value △Tc(°C)" in Table 1), and the physical properties of the biaxially oriented polyester film (shown as "longitudinal breaking strength (kgf / mm²)" in Table 1). 2 )", "Young's modulus in the longitudinal direction (kgf / mm 2 )", "Transverse breaking strength (kgf / mm 2 ) and "Young's modulus in the transverse direction (kgf / mm²) 2 It includes the display as ")".

[0058] A sample of 1.000 ± 0.0003 g containing the crystal-inhibiting material in a polyester resin mixture is precisely weighed and placed in a steel container with 30 ± 0.1 ml of 0.1% triethylene glycol (TEG) / methanol solution. The mixture is heated at 225°C for 2.5 hours, then cooled in cold water and allowed to stand. The lid of the steel container is opened, and the clear upper layer of solution is drawn into a glass bottle. After centrifuging the solution in the glass bottle, the clear upper layer of solution is taken, and the composition of the non-crystal-inhibiting material is analyzed by gas chromatography (GC), and its content is calculated.

[0059] Metal catalyst material content (ppm): Analyzed using X-ray fluorescence spectroscopy (XRF).

[0060] The film rupture rate may be the number of film ruptures per unit time under the same stretching conditions (including the longitudinal or transverse stretching described above).

[0061] Productivity evaluation: ○: No adjustment of stretching conditions, and the number of membrane ruptures per 24 hours is 3 or less. △: No adjustment of stretching conditions, and the number of membrane ruptures per 24 hours is between 4 and 6; or adjustment of stretching conditions is necessary, but the number of membrane ruptures per 24 hours is 3 or less. ×: Without adjusting the stretching conditions, the number of membrane ruptures per 24 hours is 7 or more; or adjustment of the stretching conditions is necessary, and the number of membrane ruptures per 24 hours is 4 or more.

[0062] Recrystallization temperature Tc(20)(°C): After accurately weighing 8±1 mg of the sample, DSC analysis is performed. The temperature is raised from 25°C to 300°C at a heating rate of 20°C / min, and then the temperature is lowered at 20°C / min to analyze the crystal peak.

[0063] Recrystallization temperature Tc(40)(°C): After accurately weighing 8±1 mg of the sample, DSC analysis is performed. The temperature is raised from 25°C to 300°C at a heating rate of 20°C / min, and then cooled at 40°C / min to analyze the crystal peak.

[0064] Breaking strength / Young's modulus: Testing is performed according to ASTM D882. The dimensions of the measurement sample are 15 mm in width, 100 mm in length, and a tensile speed of 200 mm / second.

[0065] [Table 1]

[0066] As described above, the present invention introduces a metal catalyst material and a crystal-inhibiting material into a polyester resin mixture, and these two materials exert a synergistic effect through their different effects on the film properties. As a result, it is possible to improve the crystallinity of biaxially oriented polyester films, obtain better productivity evaluations, and simultaneously possess superior physical properties such as multiaxial breaking strength, thereby providing even greater product competitiveness. [Industrial applicability]

[0067] The bidirectionally oriented polyester film and its manufacturing method of the present invention can be applied to the field of biaxially oriented polyester films. [Explanation of symbols]

[0068] S101, S102, S103: Step

Claims

1. A biaxially oriented polyester film manufactured from a polyester resin mixture, The polyester resin mixture comprises a polyester material, a metal catalyst material, and a crystal suppression material. The biaxially oriented polyester film is analyzed by differential scanning calorimetry and, when cooled from a molten state at cooling rates of 20°C / min and 40°C / min, respectively, the difference between the observed first recrystallization temperature and the second recrystallization temperature is greater than 15°C and less than or equal to 23°C, the content of the metal catalyst material is 0.3 to 40 ppm / mol% relative to the molar percentage concentration of the crystal suppressing material, and the crystal suppressing material accounts for 2 to 8 mol% of the molar percentage concentration of the polyester resin mixture, the metal catalyst material includes antimony, germanium, titanium, cobalt, magnesium, lithium, sodium, potassium, or a combination thereof, the crystal suppressing material includes isophthalic acid, neopentyl glycol, diethylene glycol, 1,4-cyclohexanedimethanol, or a combination thereof, and the polyester resin mixture includes chemically recycled polyester pellets.

2. The biaxially oriented polyester film according to claim 1, wherein the polyester material includes recycled polyester material, virgin polyester material, or a combination thereof.

3. The biaxially oriented polyester film according to claim 1, wherein the first recrystallization temperature exceeds 170°C.

4. The biaxially oriented polyester film according to claim 1, wherein the second recrystallization temperature is between 150°C and 175°C.

5. The biaxially oriented polyester film according to claim 1, wherein the thickness of the biaxially oriented polyester film exceeds 10 micrometers.

6. A method for manufacturing a biaxially oriented polyester film, To provide polyester pellets, The process involves melting and extruding polyester pellets to produce a polyester resin mixture, This includes biaxial stretching of a polyester resin mixture to form a biaxially oriented polyester film. The polyester pellets include at least chemically recycled polyester pellets, and the chemically recycled polyester pellets have a metal catalyst material and a crystal suppression material. A method for producing a biaxially oriented polyester film, wherein the biaxially oriented polyester film is analyzed by differential scanning calorimetry, and when cooled from a molten state at cooling rates of 20°C / min and 40°C / min, the difference between the observed first recrystallization temperature and the second recrystallization temperature is greater than 15°C and less than or equal to 23°C, the content of the metal catalyst material is 0.3 to 40 ppm / mol% relative to the molar percentage concentration of the crystal suppressing material, and the crystal suppressing material accounts for 2 to 8 mol% of the molar percentage concentration of the polyester resin mixture, the metal catalyst material includes antimony, germanium, titanium, cobalt, magnesium, lithium, sodium, potassium, or a combination thereof, and the crystal suppressing material includes isophthalic acid, neopentyl glycol, diethylene glycol, 1,4-cyclohexanedimethanol, or a combination thereof.

7. The method for producing a biaxially oriented polyester film according to claim 6, wherein the polyester pellets further comprise one or both of virgin polyester pellets and physically recycled polyester pellets.

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