Polyester film and its manufacturing method

Abstract

The present invention provides a polyester film containing a polycyclohexylene dimethylene terephthalate resin, which has a machine direction tensile strength (MDTS) of 25 measured at 25°C, a machine direction tensile strength (MDTS) of 200 measured after 24 hours in a container at 200°C, and a machine direction tensile strength reduction rate (MDTS) of 43.5% or less, calculated as {(MDTS25-MDTS200) / MDTS25} x 100%. The present invention also provides a method for manufacturing the same.

Description

[Technical Field]

[0001] The embodiment relates to a polyester film and a method for manufacturing the same. [Background technology]

[0002] In vehicles with internal combustion engines, the waste heat from the engine can be used for heating by blowing air. However, in electric vehicles such as electric cars, it is difficult to use the waste heat from the engine for heating, which can result in a slight decrease in heating energy efficiency and a slight decrease in driving distance depending on the season.

[0003] To enhance the heating efficiency of such electric vehicles, various heat radiation parts and components are built in and are covered with protective films. Materials such as polyethylene terephthalate (PET) and polyimide (PI), which have low elongation, do not have good formability or adhesive strength for application to the curved surfaces of heat radiation parts, making it difficult to maintain efficient heat transfer and heat generation performance.

[0004] Therefore, there is a need to devise an improved film that has excellent formability and can meet the stringent reliability requirements for application in electromobility means.

[0005] The above-mentioned background art is technical information that the inventor possessed for the purpose of deriving the embodiments or that he acquired in the process of deriving the embodiments, and is not necessarily publicly known art that was disclosed to the general public prior to the filing of the present invention.

[0006] Related prior art includes "Biaxially oriented polyester film and manufacturing method thereof" disclosed in Korean Patent Publication No. 10-2021-0088586 and "Biaxially oriented polyester film for molding" disclosed in Korean Patent Publication No. 10-2014-0113664. Summary of the Invention [Problem to be solved by the invention]

[0007] The purpose of this embodiment is to provide a polyester film that is suitable for use as a film for heat-resistant and heat-dissipating parts such as electrical transfer devices because it has excellent formability and does not show significant changes in physical properties even after being left under harsh conditions of high temperature and high pressure for a long period of time.

[0008] Another object of the present embodiment is to provide a method for producing a polyester film that prevents the difference in physical properties from increasing under severe conditions through a low-temperature stretching process. [Means for solving the problem]

[0009] To achieve the above object, the polyester film according to the embodiment includes a polycyclohexylene dimethylene terephthalate resin.

[0010] The polyester film may have a machine direction tensile strength of MDTS25 measured at a temperature of 25°C, a machine direction tensile strength of MDTS200 measured after being left in a container at a temperature of 200°C for 24 hours, and a reduction in machine direction tensile strength expressed as {(MDTS25-MDTS200) / MDTS25}×100% of 43.5% or less.

[0011] In one embodiment, the polyester film may have a width direction tensile strength of TDTS25 measured at a temperature of 25°C, a width direction tensile strength of TDTS200 measured at a temperature of 200°C, and a reduction rate of the width direction tensile strength, expressed as {(TDTS25-TDTS200) / TDTS25}×100%, of 29% or less.

[0012] In one embodiment, the polyester film may have a machine direction elongation of MDE25 measured at a temperature of 25°C and a machine direction elongation of MDE200 measured at a temperature of 200°C, and the rate of change in machine direction elongation, expressed as (|MDE25-MDE200| / MDE25) x 100%, may be 50% or less.

[0013] In one embodiment, the polyester film may have a width direction elongation of TDE25 measured at a temperature of 25°C, a width direction elongation of TDE200 measured at a temperature of 200°C, and a change in width direction elongation, expressed as (|TDE25-TDE200| / TDE25) x 100%, of 15% or less.

[0014] In one embodiment, the polyester film may have a machine direction elongation of 35% or more measured at a temperature of 200°C, and a cross direction elongation of 50% or more measured at a temperature of 200°C.

[0015] In one embodiment, the polyester film may be used as a film for heat-resistant components of an electromotive device.

[0016] In one embodiment, the polycyclohexylene dimethylene terephthalate resin includes a repeating unit derived from a dicarboxylic acid compound and a repeating unit derived from a diol compound.

[0017] The repeating units derived from the dicarboxylic acid compound may contain 80 mol % to 100 mol % of terephthalic acid residues and 0 mol % to 20 mol % of isophthalic acid residues.

[0018] The repeating units derived from the diol compound may contain 85 mol % to 100 mol % of cyclohexanedimethanol residues.

[0019] To achieve the above object, a method for producing a polyester film according to an embodiment includes a sheet-forming step of melting and extruding a film-producing composition containing a polycyclohexylene dimethylene terephthalate resin to form a sheet, and a stretching step of stretching the sheet formed in the sheet-forming step in the machine direction and width direction and heat-setting the stretched sheet to produce a polyester film.

[0020] The stretching step may include an MD stretching step of stretching in the machine direction and a TD stretching step of stretching in the width direction, in that order.

[0021] The MD stretching step may include a preheating process of preheating the sheet formed in the sheet forming step, and an MD stretching process of stretching the preheated sheet in the machine direction.

[0022] The temperature in the preheating step may be 80°C to 86.5°C, the temperature in the MD stretching step may be 80°C to 89°C, and the stretching temperature in the width direction in the TD stretching step may be 100°C to 118°C.

[0023] The polyester film may have a machine direction tensile strength of MDTS25 measured at 25°C, a machine direction tensile strength of MDTS200 measured after being left in a container at a temperature of 200°C for 24 hours, and a reduction in machine direction tensile strength expressed as {(MDTS25-MDTS200) / MDTS25}×100% of 43.5% or less.

[0024] In one embodiment, the TD stretching step includes a first preheating process for primarily preheating the sheet stretched in the MD stretching step, a second preheating process for secondarily preheating the sheet that has undergone the first preheating process, and a TD stretching process for stretching the sheet that has undergone the second preheating process in the width direction.

[0025] The temperature in the first preheating process may be 90°C to 103°C, and the temperature in the second preheating process may be 90°C to 108°C.

[0026] The TD stretching step may be a step of stretching the sheet by 2.5 to 3.5 times.

[0027] The MD stretching step may be a step of stretching the sheet by 3.3 to 4.5 times. [Effects of the Invention]

[0028] The polyester film according to the embodiment is manufactured by a unique low-temperature drawing process, and therefore has properties suitable for heat-resistant and heat-dissipating parts of electromotive devices. [Brief explanation of the drawings]

[0029] [Figure 1] 1 is a graph showing the results of the machine direction tensile strength (MDTS25) at 25°C and the machine direction tensile strength (MDTS200) after a high temperature test at 200°C for samples of Examples 1 and 2 (E1, E2) and Comparative Examples 1 to 3 (CE1 to CE3). [Figure 2] 1 is a graph showing the results of the width direction tensile strength (TDTS25) at 25°C and the width direction tensile strength (TDTS200) after a high temperature test at 200°C for samples of Examples 1 and 2 (E1, E2) and Comparative Examples 1 to 3 (CE1 to CE3). [Figure 3] 1 is a graph showing the results of the machine direction elongation (MDE25) at 25°C and the machine direction elongation (MDE200) after a high temperature test at 200°C for samples of Examples 1 and 2 (E1, E2) and Comparative Examples 1 to 3 (CE1 to CE3). [Figure 4] 1 is a graph showing the results of the widthwise elongation at 25°C (TDE25) and the widthwise elongation after a high temperature test at 200°C (TDE200) of samples of Examples 1 and 2 (E1, E2) and Comparative Examples 1 to 3 (CE1 to CE3). [Figure 5] 1 is a graph showing the results of the machine direction tensile strength reduction rate (MDTS_R) and the width direction tensile strength reduction rate (TDTS_R) of samples of Examples 1 and 2 (E1, E2) and Comparative Examples 1 to 3 (CE1 to CE3). [Figure 6] 1 is a graph showing the results of the rate of change in machine direction elongation (MDTS_R) and rate of change in width direction elongation (TDTS_R) for samples of Examples 1 and 2 (E1, E2) and Comparative Examples 1 to 3 (CE1 to CE3). BEST MODE FOR CARRYING OUT THE INVENTION

[0030] DETAILED DESCRIPTION OF THE INVENTION One or more exemplary embodiments will now be described in detail with reference to the accompanying drawings so as to be readily understood by those skilled in the art. However, the exemplary embodiments may be embodied in many different forms and are not limited to the embodiments set forth herein. Like reference numerals are used throughout the specification to refer to like parts.

[0031] In this specification, when a certain configuration "includes" another configuration, this does not mean that it excludes the other configurations, and that it may further include the other configurations, unless otherwise specified.

[0032] In this specification, when a certain component is said to be "connected" to another component, this includes not only the case where the components are "directly connected" but also the case where the components are "connected via another component between them."

[0033] In this specification, the term "B is located on A" means that B is located on A in direct contact with A, or that B is located on A with another layer located therebetween, and is not to be interpreted as being limited to B being located in contact with the surface of A.

[0034] As used herein, the term "combinations thereof" contained in a Markush expression means a mixture or combination of one or more elements selected from the group of elements set forth in the Markush expression, and means including one or more elements selected from the group of elements.

[0035] In this specification, the expression "A and / or B" means "A, B, or A and B."

[0036] In this specification, terms such as "first", "second" or "A", "B" are used to distinguish identical terms from each other unless otherwise specified.

[0037] In this specification, unless otherwise specified, the singular expression is to be construed as including the singular or plural as the context requires.

[0038] Polyester film To achieve the above object, the polyester film according to the embodiment includes a polycyclohexylene dimethylene terephthalate resin.

[0039] The machine direction tensile strength measured at a temperature of 25°C is MDTS25.

[0040] The tensile strength in the machine direction measured after leaving it in a container at a temperature of 200°C for 24 hours is MDTS200.

[0041] The reduction rate of tensile strength in the machine direction MDTS_R is expressed as {(MDTS25-MDTS200) / MDTS25}×100%.

[0042] The polyester film may have an MDTS_R of 43.5% or less.

[0043] The polycyclohexylenedimethylene terephthalate (PCT) resin of the polyester film may be a copolymer of a dicarboxylic acid compound and a diol compound, and may contain residues and repeating units derived therefrom.

[0044] The polycyclohexylene dimethylene terephthalate resin may contain 80 mol% or more, or 90 mol% or more, or 100 mol% or less of terephthalic acid residues, and may contain 20 mol% or less, or 10 mol% or less, or 0 mol% or more, 1 mol% or more, or 2 mol% or more of isophthalic acid residues, based on 100 mol% of all repeating units derived from dicarboxylic acid compounds.

[0045] The polycyclohexylene dimethylene terephthalate resin may contain cyclohexanedimethanol residues in an amount of 70 mol% or more, 80 mol% or more, or 90 mol% or more to 100 mol% or less, based on 100 mol% of all repeating units derived from diol compounds.

[0046] When the repeating units derived from the dicarboxylic acid compound contain terephthalic acid residues and isophthalic acid residues in the above amounts, the polymer may have a relatively high melting point and low crystallization properties.

[0047] The repeating unit derived from the diol compound may include repeating units derived from the following compounds other than the repeating unit derived from cyclohexanedimethanol: Exemplary repeating units include ethylene glycol, 1,3-propanediol, 1,2-octanediol, 1,3-octanediol, 2,3-butanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 2,2-dimethyl-1,3-propanediol (neopentyl glycol), 2-butyl-2-ethyl-1,3-propanediol, 2,2-diethyl-1,5-pentanediol, 2,4-diethyl-1,5-pentanediol, 3-methyl-1,5-pentanediol, 1,1-dimethyl-1,5-pentanediol, and residues derived therefrom.

[0048] The polycyclohexylene dimethylene terephthalate resin may have a weight average molecular weight (Mw) of 30,000 g / mol to 50,000 g / mol, or 30,000 g / mol to 40,000 g / mol.

[0049] The polycyclohexylene dimethylene terephthalate resin may be catalyst-applied to improve the efficiency of the polymerization reaction.

[0050] The catalyst may be contained in an amount of 0.1 ppm to 500 ppm, or 0.5 ppm to 100 ppm, based on 100 parts by weight of polycyclohexylene dimethylene terephthalate.

[0051] The catalyst may be a titanium-based compound, an antimony-based compound, a germanium-based compound, an aluminum-based compound, or a mixture thereof. Exemplary, the catalyst may be a titanium-based compound. The titanium-based compound may include titanium tetraisopropoxide.

[0052] An antioxidant may be added to the polymerization of the polycyclohexylene dimethylene terephthalate resin. The antioxidant may be added as needed to suppress thermal oxidation at the temperature at which the esterification reaction proceeds. However, the antioxidant is generally added in an appropriate amount. Adding an excessive amount of antioxidant during polymerization may slow the reaction and may also cause a decrease in the intrinsic viscosity of the produced resin. Antioxidants that affect the polymerization of the resin are consumed during the polymerization process and are therefore distinct from antioxidants added during the subsequent film production.

[0053] The antioxidant may include a phenol-based antioxidant, a phosphorus-based antioxidant, a sulfur-based antioxidant, and the like.

[0054] The antioxidant may be contained in an amount of 0.01 to 1 part by weight based on 100 parts by weight of the polycyclohexylene dimethylene terephthalate.

[0055] When producing a film from the polycyclohexylene dimethylene terephthalate resin, an electrostatic agent may be applied. The electrostatic agent may be an alkali metal salt, an alkaline earth metal salt, a magnesium-based compound, or a calcium-based compound, and examples thereof include magnesium acetate and calcium acetate.

[0056] The content of metal or metal ions in the static electricity applying agent may be 300 ppm to 1000 ppm based on 100 parts by weight of the polycyclohexylene dimethylene terephthalate resin.

[0057] In the polyester film, the machine direction (MD) is the longitudinal direction parallel to the direction of movement during the film production process, and the transverse direction (TD) is the direction perpendicular to the machine direction.

[0058] The polyester film has a good property retention rate after the severe conditions of the pressure vessel test, and has properties suitable for a heat-resistant and heat-dissipating film.

[0059] The tensile strength in the machine direction measured at a temperature of 25°C is MDTS25, and the tensile strength in the machine direction measured at a temperature of 200°C is MDTS200.

[0060] The polyester film may have a machine direction tensile strength reduction ratio (MDTS_R) of 43.5% or less, expressed as {(MDTS25-MDTS200) / MDTS25}×100%. The machine direction tensile strength reduction ratio may be 42.6% or less, 41.6% or less, or 30% or less. The machine direction tensile strength reduction ratio may be 10% or more.

[0061] The tensile strength in the width direction measured at a temperature of 25°C is TDTS25, and the tensile strength in the width direction measured under the temperature condition of 200°C is TDTS200.

[0062] The polyester film may have a width direction tensile strength reduction rate (TDTS_R) of 29% or less, expressed as {(TDTS25-TDTS200) / TDTS25} x 100%. The width direction tensile strength reduction rate may be 27.7% or less, 21.4% or less, or 18% or less. The width direction tensile strength reduction rate may be 5% or more.

[0063] The polyester film has such a reduction rate of tensile strength in the machine direction and the width direction, so that it can maintain good durability under harsh conditions and can be effective in maintaining the protective function of heat-resistant and heat-dissipating components.

[0064] The polyester film has an MDTS25 of 12 kgf / mm 2 ~20kgf / mm 2 , 14kgf / mm 2 ~19kgf / mm 2 , or 15 kgf / mm 2 ~18kgf / mm 2 may be.

[0065] The polyester film has an MDTS200 of 5 kgf / mm 2 ~15kgf / mm 2 , 6kgf / mm 2 ~14kgf / mm 2 , or 8.6 kgf / mm 2 ~13kgf / mm 2 may be.

[0066] The polyester film has a TDTS25 of 12 kgf / mm 2 ~25kgf / mm 2 , 15kgf / mm 2 ~24kgf / mm 2 , or 16 kgf / mm 2 ~23kgf / mm 2 may be.

[0067] The polyester film has a TDTS200 of 8 kgf / mm 2 ~18kgf / mm 2 , 9kgf / mm 2 ~17kgf / mm 2 , or 11 kgf / mm 2 ~16kgf / mm 2 may be.

[0068] By having such a range of MDTS25, MDTS200, TDTS25, and / or TDTS200, the polyester film can maintain good durability and be effective in maintaining the protective function of heat-resistant and heat-dissipating components since a drastic difference in physical properties does not occur between normal room temperature and severe conditions.

[0069] The elongation in the machine direction measured at a temperature of 25°C is MDE25, and the elongation in the machine direction measured at a temperature of 200°C is MDE200.

[0070] The polyester film may have a machine direction elongation change ratio MDE_D, expressed as (|MDE25-MDE200| / MDE25) x 100%, of 50% or less. The machine direction elongation change ratio may be 40% or less, 35.3% or less, 20% or less, or 2.4% or less. The machine direction elongation change ratio may be 0.1% or more. In the above formula for the machine direction elongation change ratio and the following formulas, || denotes an absolute value symbol.

[0071] The elongation in the width direction measured at a temperature of 25°C is TDE25, and the elongation in the width direction measured at a temperature condition of 200°C is TDE200.

[0072] The polyester film may have a transverse elongation change rate (TDE_D) of 15% or less, expressed as (|TDE25-TDE200| / TDE25) x 100%. The transverse elongation change rate may be 12% or less, 9.4% or less, or 7.2% or less. The transverse elongation change rate may be 0.1% or more.

[0073] The polyester film having such a change rate of elongation in the machine direction and the width direction can maintain good durability under harsh conditions and can be effective in maintaining the heat-resistant and heat-dissipating component protection function.

[0074] The polyester film may have an MDE25 of 40% to 110%, 45% to 105%, or 55% to 100%.

[0075] The polyester film may have an MDE200 of 25% to 90%, 35% to 85%, or 40% to 80%.

[0076] The polyester film may have a TDE25 of 45% to 90%, 47% to 80%, or 50% to 75%.

[0077] The polyester film may have a TDE200 of 45% to 90%, 47% to 80%, or 55% to 80%.

[0078] By having the MDES25, MDE200, TDES25, and / or TDES200 ranges, the polyester film can maintain good durability and be effective in maintaining the protective function of heat-resistant and heat-dissipating components since a drastic difference in physical properties does not occur between normal room temperature and harsh conditions.

[0079] Here, the elongation percentage means the ratio of the length elongated until the film breaks to the initial length of the film, and can be calculated as follows.

[0080] Elongation rate = {(stretched length - initial length) / initial length} x 100%

[0081] The physical properties related to the tensile strength and elongation can be measured in accordance with ASTM D882, using an Instron Model 4206-0010 apparatus as described in the experimental examples below.

[0082] The thickness of the polyester film may be 1 μm to 1000 μm, or 10 μm to 500 μm.

[0083] The polyester film is produced by a specific low-temperature stretching process in the production method described below, and thus has properties suitable for heat-resistant and heat-dissipating parts of electromotive means.

[0084] To achieve the above object, the heat radiation member for an electromotive means according to an embodiment may include the polyester film described above.

[0085] The heat radiation member may include a carbon-based material, such as graphite, carbon nanotubes, carbon fibers, graphene, diamond, or fullerene.

[0086] Polyester film manufacturing method To achieve the above object, a method for producing a polyester film according to an embodiment includes a sheet-forming step of melting and extruding a film-producing composition containing a polycyclohexylene dimethylene terephthalate resin to form a sheet, and a stretching step of stretching the sheet formed in the sheet-forming step in the machine direction and width direction and heat-setting the stretched sheet to produce a polyester film.

[0087] The stretching step may include an MD stretching step in which the sheet formed in the sheet forming step is stretched in the machine direction, and a TD stretching step in which the sheet stretched in the MD stretching step is stretched in the width direction and heat-set to produce a polyester film.

[0088] The MD stretching step includes a preheating process of preheating the sheet formed in the sheet forming step, and an MD stretching process of stretching the preheated sheet in the machine direction.

[0089] The temperature in the preheating process may be 80°C to 86.5°C.

[0090] The temperature during the MD stretching process may be 80°C to 89°C.

[0091] The stretching temperature in the width direction in the TD stretching step may be 100°C to 118°C.

[0092] The machine direction tensile strength measured at 25°C is MDTS25, and the machine direction tensile strength measured under pressure vessel test conditions is MDTS200.

[0093] The pressure cooker test is carried out by leaving the sample in an oven at a temperature of 200° C., a pressure of 1.4 atm, and a relative humidity of 100% for 24 hours.

[0094] The polyester film has the above-described properties, configuration, etc. of the polyester film. Exemplarily, the polyester film may have a machine direction tensile strength reduction rate (MDTS_R) of 43.5% or less, expressed as {(MDTS25-MDTS200) / MDTS25}×100%.

[0095] The composition for producing the film may include a polycyclohexylene dimethylene terephthalate resin, an antioxidant, an electrostatic agent, etc., and may be melt-extruded during film production. The antioxidant and the electrostatic agent are the same as those described above, so a repeated description will be omitted.

[0096] The film-making composition may be dried before being melted.

[0097] The drying may be carried out at a temperature of 150°C or less, or may be carried out at a temperature of 70°C to 148°C.

[0098] The film-making composition may be dried so that the total moisture content is 100 ppm or less, or 50 ppm or less. If the drying process is performed at a temperature higher than 150°C, an unintended color change may occur in the resin itself.

[0099] The composition for film production may be in the form of chips, pellets, plates, etc., and may be in a form that allows easy addition and effective mixing in the film production process.

[0100] The polycyclohexylene dimethylene terephthalate resin of the film-producing composition can be produced by a conventional polymerization method, and for example, a resin obtained by polymerization in the presence of a catalyst containing a metal such as titanium or antimony may be used.

[0101] As described above, the polycyclohexylene dimethylene terephthalate resin of the film-producing composition may be a copolymer of a dicarboxylic acid compound and a diol compound, and may contain repeating units derived therefrom.

[0102] The extrusion in the sheet-forming step may be carried out at a temperature of 230°C to 300°C, or at a temperature of 250°C to 290°C.

[0103] In the preheating process of the MD stretching step, the sheet may be heat-treated at a temperature of 80°C to 86.5°C for 10 seconds to 1 minute, or may be heat-treated at a temperature of 83°C to 86°C for the same time as above.

[0104] In the MD stretching process of the MD stretching step, the sheet that has been preheated can be stretched in the machine direction by 2.5 to 3.5 times at a temperature of 80 to 89° C. Alternatively, in the MD stretching process, the sheet that has been preheated can be stretched in the machine direction by the same stretching ratio as above at a temperature of 85 to 89° C. or 87 to 89° C.

[0105] The MD stretching step may include a process of heat-treating the preheated unstretched sheet using an infrared heater positioned 30 mm to 200 mm away from the top and / or bottom of the preheated unstretched sheet, and the surface temperature of the infrared heater may be 500°C to 800°C.

[0106] The MD stretching step allows the film to have the desired elongation and strength properties under severe conditions through the preheating and MD stretching processes.

[0107] The TD stretching step may include a primary preheating process for primarily preheating the sheet stretched in the MD stretching step, a secondary preheating process for secondarily preheating the sheet that has undergone the primary preheating process, and a TD stretching process for stretching the sheet that has undergone the secondary preheating process in the width direction.

[0108] The first preheating process may be performed at a temperature of 90°C to 103°C for 10 to 60 seconds, or at a temperature of 95°C to 103°C or 98°C to 102°C for the same period of time.

[0109] The second preheating process may be performed at a temperature of 90°C to 108°C for 10 to 60 seconds, or at a temperature of 97°C to 105°C or 100°C to 105°C for the same period of time.

[0110] In the TD stretching process, the sheet that has been subjected to the second preheating process may be stretched in the width direction by 3.3 to 4.5 times at a temperature of 100° C. to 118° C. Alternatively, in the TD stretching process, the sheet that has been subjected to the second preheating process may be stretched in the width direction by the same stretching ratio as above at a temperature of 105° C. to 115° C. or 107° C. to 113° C.

[0111] The heat setting in the TD stretching step can be carried out for 5 to 600 seconds at a temperature of 200 to 250° C. Alternatively, the heat setting in the TD stretching step can be carried out for 10 to 200 seconds.

[0112] The TD stretching step allows the film to have the desired elongation and strength properties under severe conditions through the preheating and TD stretching processes.

[0113] The film that has been subjected to the TD stretching step may be subjected to a predetermined relaxation treatment in the longitudinal direction and / or the width direction. The temperature during the relaxation may be 150° C. to 250° C. The relaxation rate during the relaxation may be 1% to 10%, or 3% to 7%.

[0114] The present invention will be described in more detail with reference to the following specific examples. The following examples are merely illustrative examples to aid in understanding the present invention, and are not intended to limit the scope of the present invention.

[0115] Example 1 - Preparation of low-temperature stretched PCT film 1 A monomer mixture of 100 mol% cyclohexanedimethanol (CHDM) as a diol compound and 96 mol% terephthalic acid (TPA) and 4 mol% isophthalic acid (IPA) as dicarboxylic acid compounds was added to a mixer, and a titanium catalyst was added in an amount of 1 ppm based on 100 parts by weight of the mixture, followed by a transesterification reaction at 275°C.

[0116] The transesterified material was transferred to a separate reactor equipped with a vacuum facility and polymerized at 285°C for 160 minutes to obtain polycyclohexylene dimethylene terephthalate (PCT) resin.

[0117] The PCT resin was processed into masterbatch chips together with an antioxidant, an electrostatic agent, etc., and dried at a temperature of 140° C. The raw material was then fed into an extruder, extruded into a sheet at a temperature of about 295° C., and cast onto a casting roll.

[0118] The extruded sheet was preheated at 83°C for 30 seconds and then stretched 3 times in the machine direction (MD) at 85°C. During machine direction stretching, an additional heating process was performed using infrared heaters installed at the top and bottom of the film, each 80 mm apart. The surface temperature of the upper heater was 600°C, and the surface temperature of the lower heater was 500°C. Next, the sheet was preheated for 10 seconds at 95°C, preheated for 30 seconds at 100°C, and stretched 3.5 times in the transverse direction (TD) at 110°C. The stretched sheet was then heat-set and relaxed at 240°C for approximately 30 seconds to produce a 50 μm thick PCT film.

[0119] Example 2 - Preparation of low-temperature stretched PCT film 2 A PCT film was produced in Example 1, except that the extruded sheet was preheated at 85° C. and stretched 3.2 times in the machine direction.

[0120] Comparative Example 1 - PCT Film Production 1 In Example 1, a PCT film was produced by changing the preheating temperature before stretching in the machine direction (MD) to 87°C, the temperature during stretching in the machine direction to 90°C, the primary preheating temperature before stretching in the transverse direction (TD) to 105°C, the secondary preheating temperature to 110°C, the temperature during stretching in the transverse direction to 120°C, and the heat setting temperature to 230°C.

[0121] Comparative Example 2 - PCT Film Production 2 In Example 1, a PCT film was produced by changing the preheating temperature before stretching in the machine direction (MD) to 92°C, the temperature during stretching in the machine direction to 95°C, the primary preheating temperature before stretching in the transverse direction (TD) to 115°C, the secondary preheating temperature to 115°C, and the temperature during stretching in the transverse direction to 120°C, and by setting the surface temperatures of the upper heater to 600°C and the lower heater to 500°C.

[0122] Comparative Example 3 - PCT Film Production 3 In Comparative Example 2, the process of heating using the infrared heater was omitted to prepare a PCT film.

[0123] The examples and comparative examples are summarized in Table 1 below (temperature units: °C).

[0124] [Table 1]

[0125] Experimental example - Measurement of tensile strength and elongation before and after high temperature test at 200℃ The tensile strength and elongation of the PCT films prepared in Examples 1 and 2 and Comparative Examples 1 to 3 were measured as follows.

[0126] Each film of the Examples and Comparative Examples was cut into a 100 mm x 15 mm sample, and subjected to tensile tests five times each in the machine direction (MD) and transverse direction (TD) in accordance with ASTM D882 using an Instron 4206-001 device at room temperature of 25°C and a speed of 50 mm / min. The average values ​​of the measured tensile strength in the machine direction (MDTS25), tensile strength in the transverse direction (TDTS25), elongation in the machine direction (MDE25), and elongation in the transverse direction (TDE25) were calculated.

[0127] Each film of the Examples and Comparative Examples was then processed into a sample again using the same method, and after leaving it in an oven at 200°C for 24 hours, the tensile test was carried out using the same method as above, and the machine direction tensile strength (MDTS200), width direction tensile strength (TDTS200), machine direction elongation (MDE200), and width direction elongation (TDE200) after the high temperature test were calculated.

[0128] The results of the tensile strength, elongation, reduction rate, and change rate of the samples before and after the high-temperature test are shown in Tables 2 and 3 and Figures 1 to 5. In Figures 1 to 5, E means the Example, CE means the Comparative Example, MDTS_R means the reduction rate of tensile strength in the machine direction, TDTS_R means the reduction rate of tensile strength in the width direction, MDE_D means the change rate of elongation in the machine direction, and TDE_D means the change rate of elongation in the width direction.

[0129] [Table 2] Tensile strength unit: kgf / mm 2 , elongation rate unit: %

[0130] [Table 3]

[0131] 1-4, the Examples, which underwent low-temperature stretching in the machine direction and the width direction, showed better reduction in tensile strength in the machine direction (MDTS_R), reduction in tensile strength in the width direction (TDTS_R), change in elongation in the machine direction (MDE_D), and change in elongation in the width direction (TDE_D) than the Comparative Examples, which did not. The change in physical properties after long-term exposure to high temperature and pressure was not significant compared to the Comparative Examples, suggesting that the Examples are suitable for use as heat-resistant and heat-dissipating films for electromotive devices.

[0132] Although the preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements made by those skilled in the art using the basic concept of the present invention defined in the appended claims also fall within the scope of the present invention.

Claims

1. Contains polycyclohexylene dimethylene terephthalate resin, The tensile strength in the machine direction measured at a temperature of 25°C is MDTS 25; The tensile strength in the machine direction measured after leaving it in a container at a temperature of 200°C for 24 hours is MDTS 200, A polyester film having a reduction rate of tensile strength in the machine direction, expressed as {(MDTS25-MDTS200) / MDTS25} x 100%, of 43.5% or less.

2. The cross direction is perpendicular to the machine direction, The tensile strength in the width direction measured at a temperature of 25°C is TDTS25, The tensile strength in the width direction measured at a temperature condition of 200°C is TDTS200, 2. The polyester film according to claim 1, wherein a reduction rate of tensile strength in the width direction, expressed as {(TDTS25-TDTS200) / TDTS25}×100%, is 29% or less.

3. The elongation in the machine direction measured at a temperature of 25°C is MDE 25, The elongation in the machine direction measured at a temperature condition of 200°C is MDE 200, 2. The polyester film according to claim 1, wherein the change in elongation in the machine direction, expressed as (|MDE25-MDE200| / MDE25) x 100%, is 50% or less.

4. The cross direction is perpendicular to the machine direction, The transverse elongation measured at a temperature of 25°C is TDE 25, The elongation in the width direction measured at a temperature condition of 200°C is TDE 200, 2. The polyester film according to claim 1, wherein the change in elongation in the width direction, expressed as (|TDE25-TDE200| / TDE25) x 100%, is 15% or less.

5. The elongation in the machine direction measured at a temperature condition of 200°C is 35% or more, 2. The polyester film according to claim 1, wherein the elongation in the width direction measured at a temperature of 200°C is 50% or more.

6. 10. The polyester film of claim 1, which is used as a film for heat-resistant parts of electrotransport means.

7. The polycyclohexylene dimethylene terephthalate resin contains a repeating unit derived from a dicarboxylic acid compound and a repeating unit derived from a diol compound, the repeating units derived from the dicarboxylic acid compound contain 80 mol % to 100 mol % of terephthalic acid residues and 0 mol % to 20 mol % of isophthalic acid residues, 2. The polyester film according to claim 1, wherein the repeating units derived from the diol compound contain 85 mol % to 100 mol % of cyclohexanedimethanol residues.

8. a sheet-forming step of melting and extruding a film-making composition containing a polycyclohexylene dimethylene terephthalate resin to form a sheet; an MD stretching step of stretching the sheet formed in the sheet forming step in a machine direction; and a TD stretching step in which the sheet stretched in the MD stretching step is stretched in the width direction and heat-set to produce a polyester film, The MD stretching step includes a preheating process of preheating the sheet formed in the sheet forming step, and an MD stretching process of stretching the sheet that has been preheated in the machine direction, The temperature during the preheating process is 80°C to 86.5°C, The temperature during the MD stretching process is 80°C to 89°C, The stretching temperature in the width direction in the TD stretching step is 100°C to 118°C, The polyester film is The machine direction tensile strength measured at 25°C is MDTS 25, The tensile strength in the machine direction measured after leaving it in a container at a temperature of 200°C for 24 hours is MDTS 200, A method for producing a polyester film, wherein the reduction rate of tensile strength in the machine direction, expressed as {(MDTS25-MDTS200) / MDTS25} x 100%, is 43.5% or less.

9. The TD stretching step a primary preheating step of primarily preheating the sheet stretched in the MD stretching step; a second preheating step of secondarily preheating the sheet that has undergone the first preheating step; and a TD stretching step of stretching the sheet in the width direction after the second preheating step, The temperature of the first preheating process is 90°C to 103°C, The method for producing a polyester film according to claim 8, wherein the temperature in the second preheating process is 90°C to 108°C.

10. The TD stretching step stretches the sheet by 2.5 to 3.5 times, The method for producing a polyester film according to claim 8, wherein the MD stretching step stretches the sheet by 3.3 to 4.5 times.

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