A long-term heat-oxidation-resistant polyester film and a preparation method thereof

Abstract

The application relates to the technical field of polyester films, in particular to a long-term heat-oxygen aging resistant polyester film and a preparation method thereof. The polyester film is obtained by blending phthalonitrile and polyester molecules, the thickness of the polyester film is 0.036mm-0.35mm, the longitudinal stretching multiple is 2.5-4.5 times, and the transverse stretching multiple is 2.5-4.5 times. In the application, phthalonitrile and terminal carboxyl groups in the polyester film occur thermal polymerization reaction at a certain temperature, so that polyphthalonitrile is introduced at the end of the polyester molecular chain. The polyphthalonitrile molecular structure contains multiple benzene rings, the conjugate effect of the whole polyester molecular chain is enhanced, the rigidity of the molecular chain is improved, the molecular chain vibration rupture caused by temperature rise can be reduced, the heat-oxygen aging resistance of the polyester film is effectively improved, and the thermal decomposition temperature is increased by 5-20 DEG C compared with that of common polyester films.

Description

Technical Field

[0001] This application relates to the field of polyester film technology, and in particular to a long-term heat- and oxygen-resistant polyester film and its preparation method. Background Technology

[0002] Polyester film, due to its excellent mechanical stability, electrical insulation properties, water vapor barrier properties, and resistance to environmental aging, has been widely used in the backsheet material industry for photovoltaic module encapsulation. Photovoltaic modules are used in areas such as plateaus, deserts, Gobi, water surfaces, and building rooftops, where they are exposed to the outdoors for extended periods. In such environments, ordinary polyester materials are easily affected by heat and oxygen, leading to degradation within the polyester molecules, resulting in decreased mechanical properties. This significantly shortens the lifespan of photovoltaic modules, reduces power generation efficiency, and increases power generation costs, hindering green, low-carbon, and circular development, and impeding the promotion of energy-saving and low-carbon buildings and facilities. Therefore, improving the heat and oxygen aging resistance of ordinary polyester materials is crucial.

[0003] Currently, domestic companies mainly improve the thermo-oxidative aging performance of polyester materials by adding small molecule stabilizers or inhibitors.

[0004] Chinese patent application CN202110862886.0 discloses a polycarbonate / polyester alloy composition resistant to long-term thermo-oxidative aging and its preparation method. The method uses octadecenoate stabilizers and transesterification inhibitors to passivate the active molecular chain ends of polycarbonate and polyester, thus slowing down aging degradation caused by thermo-oxidative effects. However, transesterification inhibitors (such as sodium dihydrogen phosphate) are low-molecular-weight compounds with poor heat resistance; they decompose due to excessively high temperatures during film processing. Furthermore, small-molecule transesterification inhibitors are prone to migration and precipitation during use, reducing their ability to improve the material's thermo-oxidative aging performance. Chinese patent application CN202110945501.7 discloses a polycarbonate / polyester alloy composition with long-term thermo-oxidative stability, its preparation method, and its applications. The method slows down the thermo-oxidative aging of the polycarbonate / polyester alloy by adding antimony-containing compounds and antioxidants. However, antimony is a harmful heavy metal element, detrimental to human health and environmental protection. Summary of the Invention

[0005] This application provides a long-term heat- and oxygen-resistant polyester film to solve the technical problem of how to greenly improve the heat- and oxygen-resistant aging performance of polyester films in the prior art.

[0006] In a first aspect, this application provides a long-term heat- and oxygen-resistant polyester film, wherein the polyester film is obtained by blending phthalonitrile and polyester molecules, and the thickness of the polyester film is 0.036 mm to 0.35 mm, the longitudinal stretch ratio is 2.5 to 4.5 times, and the transverse stretch ratio is 2.5 to 4.5 times.

[0007] Optionally, the amount of phthalonitrile added is 0.1%-10% of the total mass.

[0008] Optionally, the phthalonitrile is any one or more of o-phthalonitrile, 3-nitrophthalonitrile, 4-nitrophthalonitrile, 4-aminophthalonitrile, and 3,6-dihydroxyphthalonitrile.

[0009] Optionally, the phthalonitrile is phthalonitrile and 3-nitrophthalonitrile.

[0010] Secondly, this application provides a method for preparing a long-term heat- and oxygen-resistant polyester film, comprising the following steps:

[0011] S1. Mix 0.1% to 10% phthalonitrile with 90% to 99.9% ordinary polyester chips evenly and then dry at 100℃ to 160℃ for 4 to 8 hours.

[0012] S2. Extrude the dried mixture into granules to obtain heat-resistant and oxygen-aging-resistant polyester chips.

[0013] S3. Extrude the heat-resistant and oxygen-aging-resistant polyester chips to obtain polyester sheets with a thickness of 0.2 mm to 0.8 mm;

[0014] S4. Simultaneously biaxially stretch the polyester sheet, with a longitudinal stretching ratio of 2.5 to 4.5 times and a transverse stretching ratio of 2.5 to 4.5 times.

[0015] S5. Heat set the biaxially stretched film.

[0016] Optionally, the extrusion temperature in step S2 is 260–290°C.

[0017] Optionally, the extrusion temperature in step S3 is 260℃~300℃.

[0018] Optionally, the stretching temperature in step S4 is 100℃~130℃.

[0019] Optionally, step S5 involves heat setting at 160℃ to 320℃ for 0.1 to 0.5 minutes.

[0020] The technical solutions provided in this application have the following advantages compared with the prior art:

[0021] This application provides a long-term heat- and oxygen-resistant polyester film and its preparation method. By introducing polyphthalonitrile at the end of the polyester molecular chain, the heat- and oxygen-resistant properties of the polyester film are effectively improved, and its thermal decomposition temperature is increased by 5 to 20°C compared with that of ordinary polyester film. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0023] In one embodiment of this application, a long-term heat- and oxygen-resistant polyester film is provided. The polyester film is obtained by blending phthalonitrile and polyester molecules. The thickness of the polyester film is 0.036 mm to 0.35 mm, the longitudinal stretch ratio is 2.5 to 4.5 times, and the transverse stretch ratio is 2.5 to 4.5 times.

[0024] In this application, besides moisture and ultraviolet radiation, heat and oxygen are among the main factors affecting the aging of polyester films. Polyester films exposed to high temperatures and oxygen-rich environments for extended periods are prone to molecular chain breakage, leading to a decrease in molecular weight and a decline in the physical properties of the polyester material (such as tensile strength and elongation at break). Therefore, introducing heat-resistant molecular structures into the polyester molecular chain improves its resistance to heat and oxygen aging, effectively reducing the heat and oxygen aging behavior of the polyester film. In this invention, phthalonitrile undergoes a thermal polymerization reaction with the polyester film, thereby introducing heat-resistant molecular structures into the polyester molecular chain, thus effectively improving the heat and oxygen aging resistance of the polyester film.

[0025] As one possible embodiment, the amount of phthalonitrile added is 0.1%-10% of the total mass.

[0026] In this application, experimental verification showed that phthalonitrile accounts for 0.1% to 10% of the total mass. When the phthalonitrile content is less than 0.1%, the improvement on the heat and oxygen aging resistance of the polyester film is not significant; when the phthalonitrile content is greater than 10%, the processability of the polyester chips decreases, which is not conducive to film formation. The reaction formula between phthalonitrile and polyester film is as follows:

[0027]

[0028] As one possible embodiment, the phthalonitrile is any one or more of o-phthalonitrile, 3-nitrophthalonitrile, 4-nitrophthalonitrile, 4-aminophthalonitrile, and 3,6-dihydroxyphthalonitrile.

[0029] In this application, phthalonitrile can undergo a thermal polymerization reaction with the terminal carboxyl groups in the polyester molecular chain to reduce the concentration of terminal carboxyl groups, and at the same time generate heat-resistant molecular structure polyphthalonitrile. The polyphthalonitrile molecular structure contains multiple benzene rings, which enhances the conjugation effect on the entire polyester molecular chain and increases the rigidity of the molecular chain. This can reduce the molecular chain vibration and breakage caused by temperature rise, thereby improving the heat and oxygen aging resistance of the polyester film.

[0030] As one possible embodiment, the phthalonitrile is phthalonitrile and 3-nitrophthalonitrile.

[0031] In this application, the phthalonitrile and 3-nitrophthalonitrile react with the polyester molecules to further improve the heat and oxygen aging resistance of the polyester film.

[0032] In one embodiment of this application, a method for preparing a long-term heat- and oxygen-resistant polyester film is provided, comprising the following steps:

[0033] S1. Mix 0.1% to 10% phthalonitrile with 90% to 99.9% ordinary polyester chips evenly and then dry at 100℃ to 160℃ for 4 to 8 hours.

[0034] S2. The dried mixture is extruded and granulated at 260-290℃ to obtain heat-resistant and oxygen-aging resistant polyester chips.

[0035] S3. Extrude the heat-resistant and oxygen-aging-resistant polyester chips at 260℃~300℃ to obtain polyester sheets with a thickness of 0.2mm~0.8mm;

[0036] S4. Simultaneous biaxial stretching of the polyester sheet at 100℃~130℃, with a longitudinal stretching ratio of 2.5~4.5 and a transverse stretching ratio of 2.5~4.5.

[0037] S5. Heat-set the biaxially stretched film at 160℃~320℃ for 0.1~0.5min.

[0038] In this application, phthalonitrile and polyester molecules are reacted under certain conditions, then extruded into a film of a certain thickness, and then stretched to obtain a thin film. Throughout the process, each process parameter is strictly controlled to ensure the smooth progress of the thermal polymerization reaction and to guarantee the thermal aging performance of the obtained film.

[0039] Example 1

[0040] A method for preparing a long-term heat- and oxygen-resistant polyester film includes the following steps:

[0041] S1. Mix 1% phthalonitrile with 99% ordinary polyester chips evenly and then dry at 150°C for 4 hours.

[0042] S2. The dried mixture is extruded at 280°C to obtain heat-resistant and oxygen-aging resistant polyester chips.

[0043] S3. The heat-resistant and oxygen-aging-resistant polyester chips are dried at 150°C for 4 hours, then extruded at 280°C, and then cold-drummed at 40°C to form 0.5mm thick polyester sheets.

[0044] S4. The polyester sheet is simultaneously biaxially stretched at 120°C, with a longitudinal stretching ratio of 2.5 and a transverse stretching ratio of 2.5, to obtain a 0.08 mm film.

[0045] S5. The biaxially stretched film is heat-set at 200°C for 0.5 min and then cooled to room temperature to obtain a heat-resistant and oxygen-aging-resistant polyester film.

[0046] Example 2

[0047] A method for preparing a long-term heat- and oxygen-resistant polyester film includes the following steps:

[0048] S1. Mix 5% phthalonitrile with 95% ordinary polyester chips evenly and then dry at 150°C for 4 hours.

[0049] S2. The dried mixture is extruded and granulated at 280°C to obtain heat-resistant and oxygen-aging resistant polyester chips.

[0050] S3. The heat-resistant and oxygen-aging-resistant polyester chips are dried at 150°C for 4 hours, then extruded at 280°C, and then cold-drummed at 40°C to form 0.5mm thick polyester sheets.

[0051] S4. The polyester sheet is simultaneously biaxially stretched at 120°C, with a longitudinal stretching ratio of 2.5 and a transverse stretching ratio of 2.5, to obtain a 0.08 mm film.

[0052] S5. The biaxially stretched film is heat-set at 200°C for 0.5 min and then cooled to room temperature to obtain a heat-resistant and oxygen-aging-resistant polyester film.

[0053] Example 3

[0054] A method for preparing a long-term heat- and oxygen-resistant polyester film includes the following steps:

[0055] S1. Mix 5% 3-nitrophthalonitrile with 95% ordinary polyester chips evenly and then dry at 150°C for 4 hours.

[0056] S2. The dried mixture is extruded and granulated at 280°C to obtain heat-resistant and oxygen-aging resistant polyester chips.

[0057] S3. After drying the heat-resistant and oxygen-aging-resistant polyester chips at 150°C for 4 hours, they are extruded at 260°C to 300°C to obtain polyester sheets with a thickness of 0.5 mm.

[0058] S4. The polyester sheet is simultaneously biaxially stretched at 120°C, with a longitudinal stretching ratio of 2.5 and a transverse stretching ratio of 2.5, to obtain a 0.08 mm film.

[0059] S5. The biaxially stretched film is heat-set at 200°C for 0.5 min and then cooled to room temperature to obtain a heat-resistant and oxygen-aging-resistant polyester film.

[0060] Example 4

[0061] A method for preparing a long-term heat- and oxygen-resistant polyester film includes the following steps:

[0062] S1. Mix 5% 3-nitrophthalonitrile with 95% ordinary polyester chips evenly and then dry at 150°C for 4 hours.

[0063] S2. The dried mixture is extruded and granulated at 285°C to obtain heat-resistant and oxygen-aging resistant polyester chips.

[0064] S3. After drying the heat-resistant oxygen-aging polyester chips at 150°C for 4 hours, they are extruded at 285°C and then cold-drummed at 40°C to form polyester sheets with a thickness of 0.7 mm.

[0065] S4. Simultaneous biaxial stretching of the polyester sheet at 120℃, with a longitudinal stretching ratio of 3.5 and a transverse stretching ratio of 3.5.

[0066] S5. The biaxially stretched film is heat-set at 220°C for 0.5 min and then cooled to room temperature to obtain a heat-resistant and oxygen-aging-resistant polyester film.

[0067] Example 5

[0068] A method for preparing a long-term heat- and oxygen-resistant polyester film includes the following steps:

[0069] S1. Mix 5% 4-aminophthalonitrile with 95% ordinary polyester chips evenly and then dry at 150°C for 4 hours.

[0070] S2. The dried mixture is extruded and granulated at 285°C to obtain heat-resistant and oxygen-aging resistant polyester chips.

[0071] S3. After drying the heat-resistant oxygen-aging polyester chips at 150°C for 4 hours, they are extruded at 285°C and then cold-drummed at 40°C to form polyester sheets with a thickness of 0.7 mm.

[0072] S4. Simultaneous biaxial stretching of the polyester sheet at 120℃, with a longitudinal stretching ratio of 3.5 and a transverse stretching ratio of 3.5.

[0073] S5. The biaxially stretched film is heat-set at 220°C for 0.5 min and then cooled to room temperature to obtain a heat-resistant and oxygen-aging-resistant polyester film.

[0074] Example 6

[0075] A method for preparing a long-term heat- and oxygen-resistant polyester film includes the following steps:

[0076] S1. Mix 5% of 3,6-dihydroxyphthalonitrile with 95% of ordinary polyester chips evenly and then dry at 150°C for 4 hours.

[0077] S2. The dried mixture is extruded and granulated at 285°C to obtain heat-resistant and oxygen-aging resistant polyester chips.

[0078] S3. After drying the heat-resistant oxygen-aging polyester chips at 150°C for 4 hours, they are extruded at 285°C and then cold-drummed at 40°C to form polyester sheets with a thickness of 0.7 mm.

[0079] S4. Simultaneous biaxial stretching of the polyester sheet at 120℃, with a longitudinal stretching ratio of 3.5 and a transverse stretching ratio of 3.5.

[0080] S5. The biaxially stretched film is heat-set at 220°C for 0.5 min and then cooled to room temperature to obtain a heat-resistant and oxygen-aging-resistant polyester film.

[0081] Example 7

[0082] A method for preparing a long-term heat- and oxygen-resistant polyester film includes the following steps:

[0083] S1. Mix 5% phthalonitrile and 3-nitrophthalonitrile with 95% ordinary polyester chips evenly and dry at 150°C for 4 hours; the mass ratio of phthalonitrile and 3-nitrophthalonitrile is 1:1.

[0084] S2. The dried mixture is extruded and granulated at 285°C to obtain heat-resistant and oxygen-aging resistant polyester chips.

[0085] S3. After drying the heat-resistant oxygen-aging polyester chips at 150°C for 4 hours, they are extruded at 285°C and then cold-drummed at 40°C to form polyester sheets with a thickness of 0.7 mm.

[0086] S4. Simultaneous biaxial stretching of the polyester sheet at 120℃, with a longitudinal stretching ratio of 3.5 and a transverse stretching ratio of 3.5.

[0087] S5. The biaxially stretched film is heat-set at 220°C for 0.5 min and then cooled to room temperature to obtain a heat-resistant and oxygen-aging-resistant polyester film.

[0088] Comparative Example 1

[0089] A method for preparing a long-term heat- and oxygen-resistant polyester film includes the following steps:

[0090] S1. Mix the ordinary polyester chips evenly and then dry them at 150℃ for 4 hours;

[0091] S2. The dried mixture is extruded and granulated at 280°C to obtain heat-resistant and oxygen-aging resistant polyester chips.

[0092] S3. After drying the heat-resistant oxygen-aging polyester chips at 150°C for 4 hours, they are extruded at 280°C and then cold-drummed at 40°C to form polyester sheets with a thickness of 0.5 mm.

[0093] S4. The polyester sheet is simultaneously biaxially stretched at 120°C, with a longitudinal stretching ratio of 2.5 and a transverse stretching ratio of 2.5, to obtain a 0.08 mm film.

[0094] S5. The biaxially stretched film is heat-set at 200°C for 0.5 min and then cooled to room temperature to obtain a heat-resistant and oxygen-aging-resistant polyester film.

[0095] Comparative Example 2

[0096] A method for preparing a long-term heat- and oxygen-resistant polyester film includes the following steps:

[0097] S1. Mix 12% phthalonitrile with 88% ordinary polyester chips evenly and then dry at 150°C for 4 hours.

[0098] S2. The dried mixture is extruded and granulated at 285°C to obtain heat-resistant and oxygen-aging resistant polyester chips.

[0099] S3. After drying the heat-resistant oxygen-aging polyester chips at 150°C for 4 hours, they are extruded at 285°C and then cold-drummed at 40°C to form polyester sheets with a thickness of 0.7 mm.

[0100] S4. Simultaneous biaxial stretching of the polyester sheet at 120℃, with a longitudinal stretching ratio of 3.5 and a transverse stretching ratio of 3.5.

[0101] S5. The biaxially stretched film is heat-set at 220°C for 0.5 min and then cooled to room temperature to obtain a heat-resistant and oxygen-aging-resistant polyester film.

[0102] Comparative Example 3

[0103] A method for preparing a long-term heat- and oxygen-resistant polyester film includes the following steps:

[0104] S1. Mix 3% phthalonitrile with 97% ordinary polyester chips evenly and dry at 150°C for 4 hours; S2. Extrude and granulate the dried mixture at 300°C to obtain heat-resistant and oxygen-aging resistant polyester chips.

[0105] S3. After drying the heat-resistant oxygen-aging polyester chips at 150°C for 4 hours, they are extruded at 310°C and then cold-drummed at 40°C to form polyester sheets with a thickness of 0.7 mm.

[0106] S4. Simultaneous biaxial stretching of the polyester sheet at 120℃, with a longitudinal stretching ratio of 3.5 and a transverse stretching ratio of 3.5.

[0107] S5. The biaxially stretched film is heat-set at 340°C for 0.2 min and then cooled to room temperature to obtain a heat-resistant and oxygen-aging-resistant polyester film.

[0108] Related experiments:

[0109] The polyester films prepared in the examples and comparative examples were collected, and their heat resistance oxidation properties were tested. The results are shown in Table 1.

[0110] Table 1

[0111]

[0112] As shown in Table 1, the terminal carboxyl group concentration of the polyester film prepared by the present invention is greatly reduced, and the thermal decomposition temperature is increased by 5.3 to 13.3℃, ​​which greatly improves the oxidation resistance. The heat-resistant and oxygen-aging-resistant polyester film prepared by the present invention is suitable for photovoltaic module backsheets, building materials, furniture and packaging materials, etc.

Claims

1. A polyester film with long-term resistance to heat and oxygen aging, characterized in that: The polyester film is obtained by blending phthalonitrile and polyester molecules, and the thickness of the polyester film is 0.036 mm to 0.35 mm; the amount of phthalonitrile added is 0.1% to 10% of the total mass. The method for preparing the polyester film includes the following steps: S1. Mix 0.1% to 10% phthalonitrile with 90% to 99.9% ordinary polyester chips evenly and then dry at 100℃ to 160℃ for 4 to 8 hours. S2. Extrude the dried mixture into granules to obtain heat-resistant and oxygen-aging-resistant polyester chips. S3. Extrude the heat-resistant and oxygen-aging-resistant polyester chips to obtain polyester sheets with a thickness of 0.2 mm to 0.8 mm; S4. Simultaneously biaxially stretch the polyester sheet, with a longitudinal stretching ratio of 2.5 to 4.5 times and a transverse stretching ratio of 2.5 to 4.5 times. S5. Heat set the biaxially stretched film; In step S2, the extrusion temperature is 260–290°C. The extrusion temperature in step S3 is 260℃~300℃; The stretching temperature in step S4 is 100℃~130℃; Step S5 involves heat setting at 160℃~320℃ for 0.1~0.5 min.

2. The polyester film according to claim 1, characterized in that: The phthalonitrile is any one or more of phthalonitrile, 3-nitrophthalonitrile, 4-nitrophthalonitrile, 4-aminophthalonitrile, and 3,6-dihydroxyphthalonitrile.

3. The polyester film according to claim 2, characterized in that: The phthalonitrile is phthalonitrile and 3-nitrophthalonitrile.

4. A method for preparing a long-term heat- and oxygen-resistant polyester film, characterized in that, Includes the following steps: S1. Mix 0.1% to 10% phthalonitrile with 90% to 99.9% ordinary polyester chips evenly and then dry at 100℃ to 160℃ for 4 to 8 hours. S2. Extrude the dried mixture into granules to obtain heat-resistant and oxygen-aging-resistant polyester chips. S3. Extrude the heat-resistant and oxygen-aging-resistant polyester chips to obtain polyester sheets with a thickness of 0.2 mm to 0.8 mm; S4. Simultaneously biaxially stretch the polyester sheet, with a longitudinal stretching ratio of 2.5 to 4.5 times and a transverse stretching ratio of 2.5 to 4.5 times. S5. Heat set the biaxially stretched film; In step S2, the extrusion temperature is 260–290°C. The extrusion temperature in step S3 is 260℃~300℃; The stretching temperature in step S4 is 100℃~130℃; Step S5 involves heat setting at 160℃~320℃ for 0.1~0.5 min.

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