Polyester film and method for manufacturing the same

Abstract

The present application discloses a polyester film and a manufacturing method thereof. The polyester film comprises a heat-resistant layer, and the heat-resistant layer comprises a high-temperature-resistant resin material and a polyester resin material. The high-temperature-resistant resin material and the polyester resin material are melted and mixed with each other by a double-screw granulator. The double-screw temperature of the double-screw granulator is between 250 DEG C and 320 DEG C, and the double-screw rotating speed of the double-screw granulator is between 300 rpm and 800 rpm, so that the high-temperature-resistant resin material can be dispersed in the polyester resin material with a particle size between 50 nm and 200 nm. Therefore, the finally manufactured polyester film can have good high-temperature resistance and bending resistance without sacrificing transparency, and is particularly suitable for application to a protective film of a folding mobile phone or a protective film for high-temperature manufacturing of a printed circuit board.

Description

Technical Field

[0001] This invention relates to a polyester film, and more particularly to a transparent polyester film that is resistant to high temperatures and bending. Background Technology

[0002] Polyester film is a type of polymer plastic film that is increasingly favored by consumers due to its excellent overall performance. However, existing polyester films still perform poorly in certain physicochemical properties (such as high temperature resistance and bending resistance), making them unsuitable for some special applications (such as protective films for foldable mobile phones).

[0003] For example, Taiwan Patent Application No. 104137871 discloses a biaxially aligned polyester film. This polyester film is a blend of PET and PEN, resulting in a crystallization parameter (Tcg) that falls approximately between 40 and 80°C. This polyester film exhibits excellent heat resistance and resistance to damp heat; however, its glass transition temperature (Tg) is only around 80°C. Therefore, this polyester film is still limited in certain applications requiring high-temperature resistance.

[0004] The polyester film disclosed in Chinese Patent Application No. 99118718.0 is a blend of PET and PEI. Although the glass transition temperature (Tg) of this polyester film can be increased to about 139°C, the amount of PEI added must be above 40wt%, which will cause uneven thickness (about 11%) due to the large difference in the coefficients of thermal expansion between PET and PEI. Furthermore, this patent does not mention the heat resistance characteristics of its polyester film when used at a high temperature of around 230°C.

[0005] The polyester film disclosed in Chinese Patent Application No. 201080031380.5 is a dimensionally stable film material obtained by blending PET with high-temperature resistant resins such as PSU, PEEK, and PAI. However, this patent does not mention the heat resistance, glass transition temperature, or transparency of the blended film material.

[0006] Therefore, the inventor felt that the above-mentioned defects could be improved, so he devoted himself to research and applied scientific principles, and finally proposed an invention that is reasonably designed and effectively improves the above-mentioned defects. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a polyester film and a method for manufacturing the same, addressing the shortcomings of the prior art.

[0008] To solve the above-mentioned technical problems, one of the technical solutions adopted by the present invention is to provide a method for manufacturing polyester film, comprising: implementing a resin alloy masterbatch preparation step, including: using a twin-screw granulator to melt and mix a high-temperature resistant resin material and a polyester resin material, thereby forming a plurality of resin alloy masterbatches; wherein, in the resin alloy masterbatch preparation step, the twin-screw temperature of the twin-screw granulator is between 250°C and 320°C, and the twin-screw speed of the twin-screw granulator is between 300 rpm and 800 rpm. The rpm is such that the high-temperature resistant resin material is dispersed in the polyester resin material with a particle size between 50 nm and 200 nm in a plurality of resin alloy masterbatches; and a film forming step is performed, comprising: melting and extruding a plurality of resin alloy masterbatches in a film extruder to form a polyester film; wherein the polyester film includes a heat-resistant layer, and the heat-resistant layer is formed by a plurality of resin alloy masterbatches such that the heat-resistant layer includes the high-temperature resistant resin material and the polyester resin material.

[0009] Preferably, the high-temperature resistant resin material is at least one material selected from the group consisting of polyetherimide (PEI), polysulfone (PSU), liquid crystal polymer (LCP), polyetheretherketone (PEEK), and polyamide-imide (PAI).

[0010] Preferably, the high-temperature resistant resin material is a crystalline resin material, a semi-crystalline resin material, or a non-crystalline resin material, and the high-temperature resistant resin material has a glass transition temperature, a melting point, or a heat distortion temperature between 180°C and 400°C.

[0011] Preferably, the film forming step further includes: co-extruding a plurality of the resin alloy masterbatches and another polyester resin material using the film extruder, so that the polyester film includes the heat-resistant layer and a polyester resin base layer; wherein the heat-resistant layer is formed on one side surface of the polyester resin base layer.

[0012] Preferably, the film forming step further includes: forming another heat-resistant layer on the other side surface of the polyester resin base layer, such that the polyester resin base layer is sandwiched between the heat-resistant layer and the other heat-resistant layer; wherein the other heat-resistant layer also includes the high-temperature resistant resin material and the polyester resin material.

[0013] Preferably, the content of the high-temperature resistant resin material in the heat-resistant layer is between 10 wt% and 80 wt%, and the content of the polyester resin material in the heat-resistant layer is between 20 wt% and 90 wt%.

[0014] To solve the above-mentioned technical problems, another technical solution adopted by the present invention is to provide a polyester film, comprising: a heat-resistant layer, comprising a high-temperature resistant resin material and a polyester resin material, wherein the high-temperature resistant resin material is dispersed in the polyester resin material with a particle size between 50 nanometers and 200 nanometers; wherein the content of the high-temperature resistant resin material in the heat-resistant layer is between 10 wt% and 80 wt%.

[0015] Preferably, the high-temperature resistant resin material is melted and compounded with the polyester resin material using a twin-screw granulator; wherein the twin-screw temperature of the twin-screw granulator is between 250°C and 320°C, and the twin-screw rotation speed of the twin-screw granulator is between 300 rpm and 500 rpm, so that the high-temperature resistant resin material can be dispersed in the polyester resin material with a particle size between 50 nanometers and 200 nanometers.

[0016] Preferably, the high-temperature resistant resin material is at least one material selected from the group consisting of polyetherimide (PEI), polysulfone (PSU), liquid crystal polymer (LCP), polyetheretherketone (PEEK), and polyamide-imide (PAI).

[0017] Preferably, the high-temperature resistant resin material is a crystalline resin material, a semi-crystalline resin material, or a non-crystalline resin material, and the high-temperature resistant resin material has a glass transition temperature, a melting point, or a heat distortion temperature between 180°C and 400°C.

[0018] Preferably, the polyester film further comprises: a polyester resin base layer, and the heat-resistant layer is formed on one side surface of the polyester resin base layer.

[0019] Preferably, the polyester film further comprises: another heat-resistant layer, and the other heat-resistant layer is formed on the other side surface of the polyester resin base layer such that the polyester resin base layer is sandwiched between the heat-resistant layer and the other heat-resistant layer; wherein the other heat-resistant layer also comprises the high-temperature resistant resin material and the polyester resin material; wherein the polyester resin base layer has a thickness between 15 micrometers and 350 micrometers, the heat-resistant layer has a thickness between 0.5 micrometers and 70 micrometers, and the other heat-resistant layer has a thickness between 0.5 micrometers and 70 micrometers.

[0020] Preferably, the polyester film has a glass transition temperature between 110°C and 150°C, a transparency of not less than 80%, and a haze of not more than 5%.

[0021] Preferably, the polyester film meets the following conditions: (1) after a hot-press test or a heat resistance test, the polyester film has a warpage of no more than 3 mm and does not crack; wherein the hot-press test includes: placing the polyester film in a temperature environment of 220°C to 240°C; then applying a load of 40 kg to 50 kg to the polyester film for 2.5 hours to 3.5 hours; wherein the heat resistance test includes: heating the polyester film in a temperature environment of 220°C to 240°C; then cooling the polyester film in a room temperature environment; and the above heating and cooling steps are repeated five times; and (2) after a bending test, the polyester film does not crack; wherein the bending test includes: continuously bending the polyester film 25,000 to 30,000 times using a bending tester.

[0022] Preferably, the polyester film is a single-layer film structure containing only one heat-resistant layer, and the heat-resistant layer has a thickness between 15 micrometers and 350 micrometers.

[0023] Preferably, the polyester film further comprises: a compatibilizer mixed into the high-temperature resistant resin material and the polyester resin material 1, and the compatibilizer is at least one of polycarbonate and polyphenylene ether resin.

[0024] One of the beneficial effects of the present invention is that the polyester film and its manufacturing method provided by the present invention can achieve the following through the technical solutions: "the high-temperature resistant resin material is dispersed in the polyester resin material with a particle size between 50 nanometers and 200 nanometers" and "in the resin alloy masterbatch preparation step, the twin-screw temperature of the twin-screw granulator is between 250°C and 320°C, and the twin-screw speed of the twin-screw granulator is between 300 rpm and 800 rpm, so that the high-temperature resistant resin material can be dispersed in the polyester resin material with a particle size between 50 nanometers and 200 nanometers". This results in a polyester film that has good high-temperature resistance and bending resistance without sacrificing transparency, making it particularly suitable for use as a protective film for foldable mobile phones or for high-temperature manufacturing of printed circuit boards.

[0025] To further understand the features and technical content of the present invention, please refer to the following detailed description and drawings of the present invention. However, the drawings provided are for reference and illustration only and are not intended to limit the present invention. Attached Figure Description

[0026] Figure 1 This is a flowchart illustrating the manufacturing method of polyester film according to an embodiment of the present invention.

[0027] Figure 2 This is a schematic diagram of a polyester film according to an embodiment of the present invention.

[0028] Figure 3 This is a schematic diagram of a polyester film according to a variation of the present invention.

[0029] Figure 4 This is a schematic diagram of a polyester film according to another variation of the present invention.

[0030] Figure 5 This is a schematic diagram of a polyester film, which is another variation of the present invention.

[0031] Figure 6 This is a schematic diagram of a polyester film, representing another variation of the present invention. Detailed Implementation

[0032] The following specific embodiments illustrate the implementation methods disclosed in this invention. Those skilled in the art can understand the advantages and effects of this invention from the content disclosed in this specification. This invention can be implemented or applied through other different specific embodiments, and various details in this specification can also be modified and changed based on different viewpoints and applications without departing from the concept of this invention. Furthermore, the accompanying drawings of this invention are for simple illustrative purposes only and are not depictions of actual dimensions; this is stated beforehand. The following embodiments will further describe the relevant technical content of this invention in detail, but the disclosed content is not intended to limit the scope of protection of this invention.

[0033] [Manufacturing method of polyester film]

[0034] like Figure 1 and Figure 2 As shown, this embodiment discloses a method for manufacturing a polyester film. The method for manufacturing the polyester film includes steps S110, S120, S130, and S140. It should be noted that the order of the steps and the actual operation method described in this embodiment can be adjusted according to needs and are not limited to those described in this embodiment.

[0035] Step S110 is to perform a material selection step. The material selection step includes: providing a high-temperature resistant resin material 11 and a polyester resin material 12.

[0036] In order to make the final manufactured polyester film 100 have the properties of high temperature resistance and bending resistance, the high temperature resistant resin material 11 is selected from at least one of the materials group consisting of polyetherimide (PEI), polysulfone (PSU), liquid crystal polymer (LCP), polyetheretherketone (PEEK), and polyamide-imide (PAI).

[0037] In the aforementioned high-temperature resistant resin material 11, polyetherimide is a non-crystalline resin material with a glass transition temperature of approximately 215°C. Polysulfone is a non-crystalline resin material with a glass transition temperature of approximately 185°C and a melting point of approximately 280°C. Liquid crystal polymer is a crystalline resin material with a heat distortion temperature approximately between 180°C and 260°C. Polyetheretherketone is a semi-crystalline resin material with a glass transition temperature of approximately 340°C. Polyamideimide is a non-crystalline resin material with a glass transition temperature approximately between 280°C and 290°C.

[0038] In other words, the high-temperature resistant resin material 11 mentioned above can be, for example, a crystalline resin material, a semi-crystalline resin material, or a non-crystalline resin material, and these high-temperature resistant resin materials 11 can, for example, have a glass transition temperature, a melting point, or a heat distortion temperature between 180°C and 400°C.

[0039] Furthermore, the polyester resin material 12 is a high molecular weight polymer obtained by condensation polymerization of a diacid and a diol or its derivative. Preferably, the polyester resin material 12 is polyethylene terephthalate (PET) or polyethylene naphthalate (PEN), but the present invention is not limited thereto.

[0040] It is worth mentioning that the raw material dicarboxylic acid in the above-mentioned polyester resin material 12 is at least one of terephthalic acid, isophthalic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, biphenylcarboxylic acid, diphenylethanedicarboxylic acid, diphenylsulfonedicarboxylic acid, anthracene-2,6-dicarboxylic acid, 1,3-cyclopentanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, malonic acid, dimethylmalonic acid, succinic acid, diethyl 3,3-succinate, glutaric acid, 2,2-dimethylglutaric acid, adipic acid, 2-methyl adipic acid, trimethyl adipic acid, pimelic acid, azelaic acid, sebacic acid, octanoic acid, and dodecanoic acid. Furthermore, the raw material diol used to form the polyester resin material 12 is at least one of ethylene glycol, propylene glycol, hexamethylene glycol, neopentyl glycol, 1,2-cyclohexanediol, 1,4-cyclohexanediol, 1,10-decanediol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, and 2,2-bis(4-hydroxyphenyl)propane or bis(4-hydroxyphenyl)sulfone.

[0041] Step S120 involves preparing a resin alloy masterbatch. The resin alloy masterbatch preparation step includes: using a twin-screw granulator, melting and mixing the high-temperature resistant resin material 11 and polyester resin material 12 according to a predetermined weight ratio range, thereby forming multiple resin alloy master batches.

[0042] In the resin alloy masterbatch preparation step, the amount of the high-temperature resistant resin material 11 is preferably between 10 parts by weight and 90 parts by weight, and the amount of the polyester resin material 12 is preferably between 10 parts by weight and 90 parts by weight. Furthermore, the amount of the high-temperature resistant resin material 11 is particularly preferably between 5 parts by weight and 60 parts by weight, and the amount of the polyester resin material 12 is particularly preferably between 40 parts by weight and 95 parts by weight. The total amount of the above components is 100 parts by weight.

[0043] Furthermore, in order to ensure that the final manufactured polyester film 100 has good high temperature resistance and bending resistance, in this embodiment, the high temperature resistant resin material 11 is dispersed in the polyester resin material 12 at a nanoscale size.

[0044] To achieve the above objectives, in the resin alloy masterbatch preparation step, the twin-screw temperature of the twin-screw granulator is between 250°C and 320°C, and preferably between 280°C and 300°C, and the twin-screw rotation speed of the twin-screw granulator is between 300 rpm and 800 rpm, and preferably between 400 rpm and 600 rpm, so that in the plurality of resin alloy masterbatches, the high-temperature resistant resin material 11 can be dispersed in the polyester resin material 12 with a particle size between 50 nanometers and 200 nanometers.

[0045] In other words, the high-temperature resistant resin material 11 is dispersed in the polyester resin material 12 at nanoscale sizes primarily through the aforementioned twin-screw temperature and twin-screw speed process conditions. Therefore, the high-temperature resistant resin material 11 not only exerts its material properties in the polyester film 100 but also allows the polyester film 100 to maintain its required transparency.

[0046] Furthermore, it is worth mentioning that, in order to increase the compatibility between the high-temperature resistant resin material 11 (e.g., PEI, PSU, LCP, PEEK, PAI) and the polyester resin material 12 (e.g., PET, PEN), the resin alloy masterbatch preparation step (step S120) of this embodiment may further include mixing a compatibilizer into the high-temperature resistant resin material 11 and the polyester resin material 12, and melting and kneading them together. The compatibilizer may be, for example, at least one of polycarbonate and polyphenylene ether resin, and the amount of the compatibilizer in the resin alloy masterbatch is between 0.01 parts by weight and 1 part by weight.

[0047] Step S130 involves performing a film forming step. The film forming step includes: melting and extruding multiple resin alloy masterbatches using a film extruder (or film extruder) to form a heat-resistant layer 1 (e.g., ...). Figure 2 (As shown). Since the heat-resistant layer 1 is formed from multiple resin alloy masterbatches, the heat-resistant layer 1 includes the aforementioned high-temperature resistant resin material 11 and polyester resin material 12. The high-temperature resistant resin material 11 is dispersed in the polyester resin material 12 in a multiple particulate manner, and the particle size of the high-temperature resistant resin material 11 in the heat-resistant layer 1 is between 50 nanometers and 200 nanometers.

[0048] In one embodiment of the present invention, the plurality of resin alloy masterbatches are preferably melted and extruded by the film extruder at an operating temperature range of 280°C to 300°C to form the heat-resistant layer 1.

[0049] Furthermore, it is worth mentioning that the heat-resistant layer 1 in this embodiment is formed by directly melting and extruding multiple resin alloy masterbatches, but the present invention is not limited thereto. For example, if the content of the high-temperature resistant resin material 11 in the resin alloy masterbatch is low (e.g., less than 40 wt%), then these resin alloy masterbatches can be directly melted and extruded as in the above embodiment to form the heat-resistant layer 1.

[0050] However, if the content of the high-temperature resistant resin material 11 in the resin alloy masterbatch is high (e.g., higher than 50 wt%), the resin alloy masterbatch needs to be melted and extruded together with additional polyester resin material 12 to form the heat-resistant layer 1, thereby reducing the concentration of the high-temperature resistant resin material 11 in the heat-resistant layer 1. In this way, the high-temperature resistant resin material 11 can have a suitable content range in the heat-resistant layer 1, so that the finally manufactured polyester film 100 can have good high-temperature resistance and bending resistance without sacrificing transparency.

[0051] To achieve the above objectives, in one embodiment of the present invention, the content of the high-temperature resistant resin material 11 in the heat-resistant layer 1 is preferably between 10 wt% and 80 wt%, and more preferably between 15 wt% and 70 wt%, and the content of the polyester resin material 12 in the heat-resistant layer 1 is preferably between 20 wt% and 90 wt%, and more preferably between 30 wt% and 85 wt%.

[0052] More specifically, in this embodiment, the film forming step S130 is as follows: multiple resin alloy masterbatches and another polyester resin material 21 (e.g., PET, PEN) are co-extruded using the film extruder via co-extrusion technology to simultaneously form two heat-resistant layers 1, 1' and a polyester resin base layer 2. The two heat-resistant layers 1, 1' are respectively formed on two opposite surfaces of the polyester resin base layer 2, such that the polyester resin base layer 2 is sandwiched between the two heat-resistant layers 1, 1'.

[0053] The two heat-resistant layers 1 and 1' are each formed from a plurality of resin alloy masterbatches, while the polyester resin base layer 2 is formed solely from another polyester resin material 21 (e.g., Figure 2 and Figure 3 Alternatively, it can be formed from multiple of the aforementioned resin alloy masterbatches (e.g. Figure 5 and Figure 6 ).

[0054] The types and content ranges of the high-temperature resistant resin material 11 and the polyester resin material 12 of the two heat-resistant layers 1 and 1' can be exactly the same or different, and the types of the polyester resin materials of the two heat-resistant layers 1 and 1' and the polyester resin base layer 2 can also be exactly the same or different. This invention does not impose any restrictions.

[0055] like Figure 2 As shown, according to the manufacturing method described above in this embodiment, the polyester film 100 finally manufactured in this embodiment has a three-layer structure having a heat-resistant layer 1, a polyester resin base layer 2, and another heat-resistant layer 1' stacked sequentially from top to bottom.

[0056] Furthermore, after the polyester film 100 is extruded by the film extruder, it can be rapidly cooled by a cooling drum (e.g., a drum cooled to 15°C to 50°C), but the present invention is not limited thereto.

[0057] Step S140 is to perform a biaxial stretching step. The biaxial stretching step includes: biaxially stretching the above-mentioned polyester film 100 with a three-layer structure to form a biaxially stretched polyester film 100.

[0058] The biaxial stretching method described above can be, for example, a longitudinal single-axis stretching method, a transverse single-axis stretching method, a longitudinal sequential biaxial stretching method, or a longitudinal simultaneous biaxial stretching method, and the present invention is not limited thereto. Furthermore, the biaxial stretching method described above can, for example, involve preheating the unstretched polyester film 100 at a stretching temperature of 50°C to 150°C, and applying a stretching process of 2.0 to 5.0 times, preferably 3.0 to 4.5 times, in the width direction (or longitudinal direction, MD) of the unstretched polyester film 100 according to different stretching ratios, and further applying a stretching process of 2.0 to 5.0 times, preferably 3.0 to 4.5 times, in the length direction (or transverse direction, TD) of the polyester film 100.

[0059] [Polyester film]

[0060] like Figure 2 As shown, this embodiment also discloses a polyester film 100. The polyester film 100 can be obtained by the above-described polyester film manufacturing method, but the present invention is not limited thereto.

[0061] Specifically, the polyester film 100 includes a polyester resin base layer 2 and two heat-resistant layers 1 and 1'. The polyester resin base layer 2 is primarily made of polyester resin material 21 (e.g., ...). Figure 2 and Figure 3 However, it can also be selectively mixed with high-temperature resistant resin materials 11 (such as...). Figure 5 and Figure 6 The two heat-resistant layers 1 and 1' are respectively formed on two opposite surfaces of the polyester resin base layer 2, such that the polyester resin base layer 2 is sandwiched between the two heat-resistant layers 1 and 1'. Each of the two heat-resistant layers 1 and 1' comprises a high-temperature resistant resin material 11 and a polyester resin material 12, and the high-temperature resistant resin material 11 is dispersed in the polyester resin material 12 with a particle size between 50 nanometers and 200 nanometers. The content of the high-temperature resistant resin material 11 in the heat-resistant layers 1 and 1' ranges from 10 wt% to 80 wt%. It should be noted that when the polyester resin base layer 2 is also mixed with the high-temperature resistant resin material 11 (e.g....), Figure 5 and Figure 6 The content of high-temperature resistant resin material 11 in the polyester resin base layer 2 ranges from 5 to 50 wt%, while the content of high-temperature resistant resin material 11 in the heat-resistant layers 1 and 1' ranges from 5 to 80 wt%.

[0062] Please continue reading. Figure 1 As shown, in this embodiment, to ensure that the polyester film 100 has good high-temperature resistance and bending resistance while maintaining good transparency, each layer of the polyester film 100 has a preferred thickness range. Specifically, the polyester resin base layer 2 has a thickness D1 between 15 micrometers and 350 micrometers, the heat-resistant layer 1 has a thickness D2 between 0.5 micrometers and 70 micrometers, and another heat-resistant layer 1 has a thickness D3 between 0.5 micrometers and 70 micrometers.

[0063] In other words, the polyester film 100 has a thickness between 15 micrometers and 350 micrometers, and the thickness ratio of the heat-resistant layer 1, the polyester resin base layer 2, and the other heat-resistant layer 1' is preferably between 1:98:1 and 20:60:20.

[0064] According to the above configuration, the polyester film 100 of this embodiment has good high temperature resistance and bending resistance, while maintaining good transparency. Specifically, the polyester film 100 of this embodiment has a glass transition temperature between 110°C and 150°C, a transparency of not less than 80%, and a haze of not more than 5%. Preferably, the glass transition temperature of the polyester film 100 is between 120°C and 140°C, the transparency of the polyester film 100 is not less than 88%, and the haze of the polyester film 100 is not more than 3%.

[0065] Furthermore, the polyester film 100 of this embodiment meets the following test conditions: (1) After undergoing a hot-press test or a heat resistance test, the warpage of the polyester film 100 at an A4 size is no greater than 3 mm, and the polyester film 100 does not crack (no cracking means the film surface is intact and does not produce cracks); wherein, the hot-press test includes: placing the polyester film 100 in a temperature environment of 220°C to 240°C; then, applying a load of 40 kg to 50 kg to the polyester film 100 for 2.5 hours. Up to 3.5 hours; wherein, the heat resistance test includes: placing the polyester film 100 in a temperature environment of 220°C to 240°C for heating; then, placing the polyester film 100 in a room temperature environment for cooling; and, the above heating step and cooling step are repeated five times; and (2) after a bending resistance test, the polyester film 100 does not crack; wherein, the bending resistance test includes: continuously bending the polyester film 100 25,000 to 30,000 times with a bending resistance testing machine.

[0066] It is worth mentioning that, after the above-mentioned hot pressing test or heat resistance test, the color difference ΔE (or color difference) of the polyester film 100 in this embodiment is not less than 2.

[0067] Regarding mechanical properties, the polyester film 100 of this embodiment was tested according to the international standard test method ASTM D882, and the tensile strength in the longitudinal direction (MD) of the film was found to be not less than 20 kgf / mm. 2 The tensile strength (TD) of the film in the width direction is not less than 25 kgf / mm. 2 The elongation of the film in the length direction (MD) is not less than 230%, and the elongation of the film in the width direction (TD) is not less than 160%.

[0068] The polyester film 100 of this embodiment was tested according to the international standard test method ASTM D1204. The shrinkage rate of the film in the longitudinal direction (MD) at room temperature is between 0.35% and 0.4%, and the shrinkage rate of the film in the transverse direction (TD) at room temperature is between 0.05% and 0.15%. Furthermore, the shrinkage rate of the film in the longitudinal direction (MD) at a temperature environment of 220°C to 240°C is not greater than 2.5%, and the shrinkage rate of the film in the transverse direction (TD) at a temperature environment of 220°C to 240°C is not greater than 4.5%.

[0069] Because the polyester film 100 of this embodiment has good high temperature resistance and bending resistance, as well as good transparency, the polyester film 100 of this embodiment is particularly suitable for use as a protective film for foldable mobile phones or as a protective film for high-temperature manufacturing of printed circuit boards.

[0070] It is worth mentioning that although this embodiment is illustrated using a polyester film 100 with a three-layer structure (comprising a polyester resin base layer 2 and two heat-resistant layers 1), the present invention is not limited thereto.

[0071] For example, such as Figure 3 As shown, in a variant embodiment of the present invention, the polyester film 100' may also be a polyester film 100' with a double-layer structure (comprising a polyester resin base layer 2 and a heat-resistant layer 1 formed on one side surface of the polyester resin base layer 2).

[0072] Or, such as Figure 4 As shown, in another variant embodiment of the present invention, the polyester film 100" may also be a polyester film 100" having only a single-layer structure. That is, the polyester film 100" contains only one heat-resistant layer 1, and the heat-resistant layer 1 has a thickness between 15 micrometers and 350 micrometers. Thereby, the polyester film 100" can still have good high-temperature resistance and bending resistance, and maintain a certain degree of transparency even when it is a single-layer structure.

[0073] Furthermore, such as Figure 5 and Figure 6 The polyester films 100”' and 100”' with three-layer and two-layer structures shown may also contain high-temperature resistant resin material 11. The content of high-temperature resistant resin material 11 in the polyester resin base layer 2 ranges from 5 to 50 wt%, while the content of high-temperature resistant resin material 11 in the heat-resistant layers 1 and 1' ranges from 5 to 80 wt%.

[0074] [Experimental Data Testing]

[0075] The present invention will now be described in detail with reference to Exemplary Examples 1 to 3 and Comparative Examples 1 to 3. However, the following examples are provided only to help understand the present invention, and the scope of the present invention is not limited to these examples.

[0076] Example 1: 50 parts by weight of high-temperature resistant resin material PEI (purchased from Sabic, product name UltemXH6050-1000) and 50 parts by weight of polyester material PET (provided by Nan Ya Plastics) were mixed in a twin-screw granulator with a screw length to screw diameter ratio of 48. The twin-screw temperature of the twin-screw granulator was between 250°C and 320°C, and the twin-screw speed was between 300 rpm and 800 rpm, thereby obtaining a high-temperature resistant resin alloy masterbatch with a PEI-PET mixing ratio of 50 / 50. The masterbatch was then crystallized and dried at 140°C for 240 minutes.

[0077] Polyester resin and the aforementioned high-temperature resistant resin alloy masterbatch are mixed in different proportions and then co-extruded in three layers (A / B / A). The A layer contains 30 wt% PEI, the B layer contains 30 wt% PEI, and the thickness ratio of the A / B / A layers is 10 / 80 / 10. In the biaxial stretching step, the preheating temperature for longitudinal stretching is 95°C, and the longitudinal stretching ratio is 3.0; the preheating temperature for transverse stretching is 120°C, and the transverse stretching ratio is 4.5; the heat setting temperature is 235°C, thereby obtaining a high-temperature resistant and flexurally resistant transparent polyester film.

[0078] Example 2: 50 parts by weight of high-temperature resistant resin material PSU (purchased from Solvay, product name P-3900) and 50 parts by weight of polyester material PET (provided by Nan Ya Plastics) were mixed in a twin-screw granulator with a screw length to screw diameter ratio of 48. The twin-screw temperature of the twin-screw granulator was between 250°C and 320°C, and the twin-screw speed was between 300 rpm and 800 rpm, thereby obtaining a high-temperature resistant resin alloy masterbatch with a PSU-PET mixing ratio of 50 / 50. The masterbatch was then crystallized and dried at 140°C for 240 minutes.

[0079] Example 3: 50 parts by weight of high-temperature resistant resin material PAI (purchased from Solvay, product name Toron4000T) and 50 parts by weight of polyester material PET (provided by Nan Ya Plastics) were mixed in a twin-screw granulator with a screw length-to-screw diameter ratio of 48. The twin-screw temperature of the twin-screw granulator was between 250°C and 320°C, and the twin-screw speed was between 300 rpm and 800 rpm, thereby obtaining a high-temperature resistant resin alloy masterbatch with a PAI-PET mixing ratio of 50 / 50. The masterbatch was then crystallized and dried at 140°C for 240 minutes. The preparation conditions for biaxial elongation in Examples 2 and 3 were the same as in Example 1 and will not be repeated here.

[0080] Comparative Example 1: The polyester film was prepared in the same way as in Exemplary Example 1, except that the twin screw speed in Comparative Example 1 was 200 rpm.

[0081] Comparative Example 2: The polyester film was prepared in the same way as in Exemplary Example 1, except that in the A / B / A layer of Comparative Example 2, the PEI content of layer A was 5%, and the PEI content of layer B was also 5%.

[0082] Comparative Example 3: The polyester film was prepared in the same way as in Exemplary Example 1, except that the overall thickness of the A / B / A layer in Comparative Example 3 was thinner (not more than 15 micrometers).

[0083] The process parameters for each component are summarized in Table 1 below.

[0084] Next, the polyester films prepared in Examples 1 to 3 and Comparative Examples 1 to 3 were subjected to physicochemical property tests to obtain the physicochemical properties of these polyester films, such as glass transition temperature (°C), transparency (%), and haze (%). The relevant test methods are described below, and the relevant test results are summarized in Table 1.

[0085] Glass transfer temperature test: The enthalpy of the substrate's first melting was measured using a differential scanning calorimeter (DSC) TA Q20.

[0086] Transparency and haze testing: The transparency (or light transmittance) and haze value of the polyester films in the following examples were tested using a Tokyo Denshoku Haze Meter (model TC-HⅢ), and the method complied with JIS K7705.

[0087] Warpage deformation test after baking: The polyester film was placed at 220℃ for 1 hour and cycled 10 times. The warpage deformation (mm) was observed using an A4-sized film.

[0088] Thin film cracking test (heat resistance): The polyester film was subjected to a hot-pressing test at 220℃ with a load of 45Kg for 3 hours. Evaluation indicators: smooth film surface without deterioration is rated as ◎, and film surface cracking is rated as ×.

[0089] [Table 1: Process conditions and physical-chemical property tests for exemplary and comparative examples]

[0090]

[0091]

[0092] [Discussion of Test Results]

[0093] In Examples 1 to 3, the various physicochemical properties of the polyester film met the requirements. In Comparative Example 1, the screw speed was too low, making it impossible to achieve uniform dispersion of the high-temperature resistant resin material. In Comparative Example 2, the amount of high-temperature resistant resin material added was too small, resulting in insufficient overall heat resistance of the polyester film and high warpage deformation after baking. In Comparative Example 3, the overall film thickness was too thin, resulting in poor film degradation test results.

[0094] [Beneficial Effects of the Examples]

[0095] One of the beneficial effects of the present invention is that the polyester film and its manufacturing method provided by the present invention can disperse the high-temperature resistant resin material 11 in the polyester resin material 12 with a particle size between 50 nanometers and 200 nanometers and in the resin alloy masterbatch preparation step, the twin-screw temperature of the twin-screw granulator is between 250°C and 320°C, and the twin-screw speed of the twin-screw granulator is between 300 rpm and 500 rpm, so that the high-temperature resistant resin material 11 can be dispersed in the polyester resin material 12 with a particle size between 50 nanometers and 200 nanometers. This makes the final polyester film 100 have good high-temperature resistance and bending resistance without sacrificing transparency, and is therefore particularly suitable for use as a protective film for foldable mobile phones or a protective film for high-temperature manufacturing of printed circuit boards.

[0096] The content disclosed above is only a preferred and feasible embodiment of the present invention, and is not intended to limit the scope of the patent application of the present invention. Therefore, all equivalent technical changes made using the contents of the present invention specification and drawings are included in the scope of the patent application of the present invention.

Claims

1. A method for manufacturing a polyester film, characterized in that, The polyester film is suitable for use as a protective film for foldable mobile phones, and the manufacturing method of the polyester film includes: A resin alloy masterbatch preparation step includes: melting and mixing a high-temperature resistant resin material and a polyester resin material using a twin-screw granulator to form multiple resin alloy masterbatches; wherein, in the resin alloy masterbatch preparation step, the twin-screw temperature of the twin-screw granulator is between 250 °C and 320 °C, and the twin-screw rotation speed of the twin-screw granulator is between 300 rpm and 800 rpm, so that in the multiple resin alloy masterbatches, the high-temperature resistant resin material can be dispersed in the polyester resin material with a particle size between 50 nm and 79 nm; wherein, the high-temperature resistant resin material has a glass transition temperature, a melting point, or a heat distortion temperature between 180 °C and 400 °C; and A film forming step includes: melting and extruding a plurality of the resin alloy masterbatches using a film extruder to form a polyester film; wherein the polyester film includes a heat-resistant layer, and the heat-resistant layer is formed from the plurality of the resin alloy masterbatches such that the heat-resistant layer includes the high-temperature resistant resin material and the polyester resin material; wherein the polyester film as a whole has a glass transition temperature between 110°C and 150°C, a transparency between 88% and 90%, and a haze between 1.5% and 2.0%.

2. The method for manufacturing polyester film according to claim 1, characterized in that, The high-temperature resistant resin material is selected from at least one material in the group consisting of polyetherimide (PEI), polysulfone (PSU), liquid crystal polymer (LCP), polyetheretherketone (PEEK), and polyamide-imide (PAI).

3. The method for manufacturing polyester film according to claim 1, characterized in that, The high-temperature resistant resin material is a crystalline resin material, a semi-crystalline resin material, or a non-crystalline resin material.

4. The method for manufacturing polyester film according to claim 1, characterized in that, The film forming step further includes: co-extruding a plurality of the resin alloy masterbatches and another polyester resin material using the film extruder, so that the polyester film includes the heat-resistant layer and a polyester resin base layer; wherein the heat-resistant layer is formed on one side surface of the polyester resin base layer.

5. The method for manufacturing polyester film according to claim 4, characterized in that, The film forming step further includes: forming another heat-resistant layer on the other side surface of the polyester resin base layer, such that the polyester resin base layer is sandwiched between the heat-resistant layer and the other heat-resistant layer; wherein the other heat-resistant layer also includes the high-temperature resistant resin material and the polyester resin material.

6. The method for manufacturing polyester film according to claim 5, characterized in that, The content of the high-temperature resistant resin material in the heat-resistant layer is between 10 wt% and 80 wt%, and the content of the polyester resin material in the heat-resistant layer is between 20 wt% and 90 wt%.

7. A polyester film, characterized in that, The polyester film is suitable for use as a protective film for foldable mobile phones, and the polyester film comprises: A heat-resistant layer comprises a high-temperature resistant resin material and a polyester resin material, wherein the high-temperature resistant resin material is dispersed in the polyester resin material with a particle size between 50 nanometers and 79 nanometers; wherein the content of the high-temperature resistant resin material in the heat-resistant layer is between 10 wt% and 80 wt%; wherein the high-temperature resistant resin material has a glass transition temperature, a melting point or a heat distortion temperature between 180 °C and 400 °C, and the polyester film as a whole has a glass transition temperature between 110 °C and 150 °C, a transparency between 88% and 90%, and a haze between 1.5% and 2.0%.

8. The polyester film according to claim 7, characterized in that, The high-temperature resistant resin material is melted and compounded with the polyester resin material using a twin-screw granulator; wherein the twin-screw temperature of the twin-screw granulator is between 250°C and 320°C, and the twin-screw speed of the twin-screw granulator is between 300 rpm and 500 rpm, so that the high-temperature resistant resin material can be dispersed in the polyester resin material with a particle size between 50 nanometers and 200 nanometers.

9. The polyester film according to claim 7, characterized in that, The high-temperature resistant resin material is selected from at least one material in the group consisting of polyetherimide (PEI), polysulfone (PSU), liquid crystal polymer (LCP), polyetheretherketone (PEEK), and polyamide-imide (PAI).

10. The polyester film according to claim 7, characterized in that, The high-temperature resistant resin material is a crystalline resin material, a semi-crystalline resin material, or a non-crystalline resin material.

11. The polyester film according to claim 7, characterized in that, The polyester film further comprises: a polyester resin base layer, and the heat-resistant layer is formed on one side surface of the polyester resin base layer.

12. The polyester film according to claim 11, characterized in that, The polyester film further includes: another heat-resistant layer, and the other heat-resistant layer is formed on the other side surface of the polyester resin base layer such that the polyester resin base layer is sandwiched between the heat-resistant layer and the other heat-resistant layer; wherein the other heat-resistant layer also comprises the high-temperature resistant resin material and the polyester resin material; wherein the polyester resin base layer has a thickness between 15 micrometers and 350 micrometers, the heat-resistant layer has a thickness between 0.5 micrometers and 70 micrometers, and the other heat-resistant layer has a thickness between 0.5 micrometers and 70 micrometers.

13. The polyester film according to claim 12, characterized in that, The polyester film meets the following conditions: (1) After undergoing a hot-press test or a heat resistance test, the polyester film exhibits a warpage deformation of no more than 3 mm and does not crack; wherein the hot-press test comprises: placing the polyester film in a temperature environment of 220°C to 240°C; then applying a load of 40 kg to 50 kg to the polyester film for 2.5 hours to 3.5 hours; wherein the heat resistance test comprises: heating the polyester film in a temperature environment of 220°C to 240°C; then cooling the polyester film in a room temperature environment; and the above heating and cooling steps are repeated five times; and (2) The polyester film does not crack after undergoing a bending resistance test; wherein the bending resistance test includes: continuously bending the polyester film 25,000 to 30,000 times using a bending resistance testing machine.

14. The polyester film according to claim 7, characterized in that, The polyester film is a single-layer film structure containing only one heat-resistant layer, and the heat-resistant layer has a thickness between 15 micrometers and 350 micrometers.

15. The polyester film according to claim 7, characterized in that, The polyester film further comprises: a compatibilizer mixed into the high-temperature resistant resin material and the polyester resin material 1, wherein the compatibilizer is at least one of polycarbonate and polyphenylene ether resin.

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