Degradable polyester plastic film and method for preparing the same

Abstract

The application discloses a degradable polyester plastic film and a preparation method thereof, which comprises the following raw materials and weight parts: PBAT resin 60-75 parts, polylactic acid 37-50 parts, PBS resin 14-23 parts, polycaprolactone 10-15 parts, glycidyl methacrylate grafted polylactic acid copolymer 5-10 parts, inorganic filler 5-10 parts, tributyl citrate 2-4 parts, chain extending compatibilizer ADR 1-2 parts, composite coupling agent 0.3-0.7 parts, dispersant 0.5-1 part and antioxidant 0.5-1 part. The degradable polyester plastic film has excellent toughness, strength and barrier property, and can be well applied in the field of packaging materials.

Description

TECHNICAL FIELD

[0001] The application relates to a degradable polyester plastic film and a preparation method thereof, and belongs to the technical field of plastic film materials. BACKGROUND

[0002] Traditional plastic films such as polyethylene and polypropylene cause serious environmental hazards due to waste plastics, and with people's high concern for environmental protection, degradable plastic film materials are derived. In the natural environment, the degradable plastic film is gradually decomposed through the action of microorganisms or physical and chemical processes such as photooxidation and hydrolysis, and finally converted into harmless substances such as carbon dioxide, water and biomass, which is an environmentally friendly material.

[0003] Polybutylene succinate (PBS), polybutylene terephthalate-adipate (PBAT) and polylactic acid (PLA) are common degradable polyester plastic materials and are recognized as environmentally friendly materials. The existing polyester material prepared plastic film usually has the defects of low toughness and strength, poor barrier property and the like. For example, the material prepared by using PBAT has poor barrier stability, and the material prepared by using PLA has the problems of high brittleness and poor flexibility. SUMMARY

[0004] At least in view of the above-mentioned problems of the prior art, the application provides a degradable polyester plastic film and a preparation method thereof. The degradable polyester plastic film has excellent toughness, strength and barrier properties, and can be well applied in the field of packaging materials.

[0005] In order to achieve the above-mentioned purpose, the application adopts the following technical scheme: a degradable polyester plastic film comprises the following raw materials and their weight parts: 60-75 parts of PBAT resin, 37-50 parts of polylactic acid, 14-23 parts of PBS resin, 10-15 parts of polycaprolactone, 5-10 parts of glycidyl methacrylate grafted polylactic acid copolymer, 5-10 parts of inorganic filler, 2-4 parts of tributyl citrate, 1-2 parts of chain extending compatibilizer ADR, 0.3-0.7 parts of composite coupling agent, 0.5-1 part of dispersant and 0.5-1 part of antioxidant.

[0006] Preferably, the mass ratio of the PBS resin to the polylactic acid is 40-45%.

[0007] Preferably, the mass ratio of the polycaprolactone to the glycidyl methacrylate grafted polylactic acid copolymer is 1.5-2:1.

[0008] Preferably, the inorganic filler is a mixture of calcium carbonate whiskers and nano-silicon dioxide.

[0009] Preferably, the mass ratio of the inorganic filler to tributyl citrate is 2~3:1.

[0010] Preferably, the inorganic filler is a mixture of calcium carbonate whiskers and nano-silica in a mass ratio of 2 to 3:2.

[0011] Preferably, the composite coupling agent is a mixture of titanate coupling agent and silane coupling agent.

[0012] Preferably, the composite coupling agent is a mixture of titanate coupling agent and silane coupling agent in a mass ratio of 1 to 2:2.

[0013] Preferably, the titanate coupling agent is n-butyl titanate.

[0014] Preferably, the silane coupling agent is KH-550.

[0015] Preferably, the dispersant is either zinc stearate or calcium stearate.

[0016] Preferably, the antioxidant is one or both of antioxidant 1010 and antioxidant 168.

[0017] This invention also provides a method for preparing a biodegradable polyester plastic film, comprising the following steps:

[0018] (1) Mix the inorganic filler and composite coupling agent in the above weight parts evenly, then grind at 100~200 rpm for 10~20 min, and then mix evenly with the above weight parts of PBAT resin, polylactic acid, PBS resin, polycaprolactone, glycidyl methacrylate grafted polylactic acid copolymer, tributyl citrate, chain extender compatibilizer ADR, dispersant and antioxidant to obtain a mixture;

[0019] (2) The mixture is fed into a twin-screw extruder, heated and melted, then extruded by a twin-screw extruder. The extruded melt is then cast in a casting machine and cooled to obtain a sheet.

[0020] (3) The sheet is biaxially stretched and then heat-set to obtain a biodegradable polyester plastic film.

[0021] Preferably, in step (2), the heating and melting temperature is 185~205℃, the extrusion temperature is 185~205℃, and the casting temperature is 185~205℃.

[0022] Preferably, in step (3), the bidirectional stretching is performed first in the longitudinal direction and then in the transverse direction. The longitudinal stretching temperature is 90~100℃ and the stretching ratio is 3~5. The transverse stretching temperature is 95~105℃ and the stretching ratio is 3~4. The heat setting temperature is 115~125℃.

[0023] The beneficial effects of this invention are as follows: This invention uses a system with a suitable ratio of PBAT resin, polylactic acid, PBS resin, polycaprolactone, and glycidyl methacrylate-grafted polylactic acid copolymer to prepare a biodegradable polyester plastic film. This film possesses excellent toughness, strength, and barrier properties, making it well-suited for use in packaging materials. The inorganic filler of this invention consists of calcium carbonate whiskers and nano-silica. Through treatment with a composite coupling agent, it exhibits excellent compatibility and bonding ability with the PBAT resin, polylactic acid, and PBS resin matrix, enhancing the toughness and strength of the biodegradable polyester plastic film. This invention effectively blocks water and oxygen while promoting the degradation of polyester plastic films. By controlling the ratio of polylactic acid (PLA) and PBS resin, the toughness of the biodegradable polyester plastic film is further optimized, ensuring its strength. By controlling the ratio of polycaprolactone (PVC) and glycidyl methacrylate (GMA)-grafted PLA copolymer, this invention further enhances the bonding between the PBAT resin, PLA, and PBS resin matrices, optimizes the interfacial bonding strength and tightness, improves barrier properties, enhances mechanical properties, and also improves melt flow uniformity and thermal stability, thus optimizing processing performance. Detailed Implementation

[0024] The following is a clear and complete description of the technical solutions in the implementation of this invention. The described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents, instruments, or components used that do not specify the manufacturer are all conventional products that can be purchased commercially.

[0025] Example 1

[0026] A biodegradable polyester plastic film and its preparation method are disclosed below.

[0027] (1) Mix 5 parts of inorganic filler consisting of calcium carbonate whiskers and nano-silica in a mass ratio of 2.5:2, and 0.3 parts of composite coupling agent consisting of tetrabutyl titanate and KH-550 in a mass ratio of 1.5:2. Grind the mixture at 100 rpm for 20 min. Then mix the mixture with 60 parts of PBAT resin, 37 parts of polylactic acid, 14 parts of PBS resin, 10 parts of polycaprolactone, 5 parts of glycidyl methacrylate-grafted polylactic acid copolymer, 2 parts of tributyl citrate, 1 part of chain extender compatibilizer ADR-4468, 0.5 parts of zinc stearate and 0.5 parts of antioxidant 1010 to obtain a mixture.

[0028] (2) The mixture is fed into a twin-screw extruder, heated and melted at 195°C, and then extruded by a twin-screw extruder at 195°C. The extruded melt is then cast in a casting machine at 195°C and cooled to obtain a sheet.

[0029] (3) The sheet is stretched biaxially, first longitudinally and then transversely. The longitudinal stretching temperature is 95℃ and the stretching ratio is 3. The transverse stretching temperature is 100℃ and the stretching ratio is 3. Then it is heat-set at 120℃ to obtain a biodegradable polyester plastic film.

[0030] Example 2

[0031] A biodegradable polyester plastic film and its preparation method are different from Example 1 in that: 5 parts inorganic filler, 0.3 parts composite coupling agent, 60 parts PBAT resin, 37 parts polylactic acid, 15 parts PBS resin, 10 parts polycaprolactone, 10 parts glycidyl methacrylate-grafted polylactic acid copolymer, 2 parts tributyl citrate, 1 part chain extender compatibilizer ADR-4468, 0.5 parts zinc stearate, and 0.5 parts antioxidant 1010; the rest are the same.

[0032] Example 3

[0033] A biodegradable polyester plastic film and its preparation method are disclosed. The difference between Example 1 and Example 2 is that: 5 parts inorganic filler, 0.3 parts composite coupling agent, 60 parts PBAT resin, 37 parts polylactic acid, 15 parts PBS resin, 11 parts polycaprolactone, 5.5 parts glycidyl methacrylate-grafted polylactic acid copolymer, 2 parts tributyl citrate, 1 part chain extender and compatibilizer ADR-4468, 0.5 parts zinc stearate, and 0.5 parts antioxidant 1010 are included; the rest are the same.

[0034] Example 4

[0035] A biodegradable polyester plastic film and its preparation method are different from Example 1 in that: 8 parts of inorganic filler, 0.5 parts of composite coupling agent, 68 parts of PBAT resin, 44 parts of polylactic acid, 18 parts of PBS resin, 12.5 parts of polycaprolactone, 7.5 parts of glycidyl methacrylate-grafted polylactic acid copolymer, 4 parts of tributyl citrate, 1.5 parts of chain extender and compatibilizer ADR-4468, 0.7 parts of calcium stearate, and 0.7 parts of antioxidant 168; the rest are the same.

[0036] Example 5

[0037] A biodegradable polyester plastic film and its preparation method are different from Example 1 in that: 8 parts of inorganic filler, 0.5 parts of composite coupling agent, 68 parts of PBAT resin, 44 parts of polylactic acid, 16 parts of PBS resin, 12 parts of polycaprolactone, 7 parts of glycidyl methacrylate-grafted polylactic acid copolymer, 4 parts of tributyl citrate, 1.5 parts of chain extender compatibilizer ADR-4468, 0.7 parts of calcium stearate, and 0.7 parts of antioxidant 168; the rest are the same.

[0038] Example 6

[0039] A biodegradable polyester plastic film and its preparation method are different from Example 1 in that: 8 parts of inorganic filler, 0.5 parts of composite coupling agent, 68 parts of PBAT resin, 44 parts of polylactic acid, 20 parts of PBS resin, 13 parts of polycaprolactone, 10 parts of glycidyl methacrylate-grafted polylactic acid copolymer, 4 parts of tributyl citrate, 1.5 parts of chain extender and compatibilizer ADR-4468, 0.7 parts of calcium stearate, and 0.7 parts of antioxidant 1010; the rest are the same.

[0040] Example 7

[0041] A biodegradable polyester plastic film and its preparation method are different from Example 1 in that: 10 parts of inorganic filler, 0.7 parts of composite coupling agent, 75 parts of PBAT resin, 50 parts of polylactic acid, 23 parts of PBS resin, 13 parts of polycaprolactone, 8 parts of glycidyl methacrylate-grafted polylactic acid copolymer, 3 parts of tributyl citrate, 2 parts of chain extender compatibilizer ADR-4468, 1 part of calcium stearate, and 1 part of antioxidant 168; the rest are the same.

[0042] Example 8

[0043] A biodegradable polyester plastic film and its preparation method are disclosed. The difference between Example 1 and Example 2 is that: 10 parts inorganic filler, 0.7 parts composite coupling agent, 75 parts PBAT resin, 50 parts polylactic acid, 22.5 parts PBS resin, 15 parts polycaprolactone, 7.5 parts glycidyl methacrylate-grafted polylactic acid copolymer, 3.4 parts tributyl citrate, 2 parts chain extender compatibilizer ADR-4468, 1 part zinc stearate, and 1 part antioxidant 168 are included; the rest are the same.

[0044] Example 9

[0045] A biodegradable polyester plastic film and its preparation method are different from Example 1 in that: 10 parts of inorganic filler, 0.7 parts of composite coupling agent, 75 parts of PBAT resin, 50 parts of polylactic acid, 23 parts of PBS resin, 15 parts of polycaprolactone, 6.5 parts of glycidyl methacrylate-grafted polylactic acid copolymer, 3.4 parts of tributyl citrate, 2 parts of chain extender and compatibilizer ADR-4468, 1 part of calcium stearate, and 1 part of antioxidant 1010; the rest are the same.

[0046] Example 10

[0047] A biodegradable polyester plastic film and its preparation method are different from Example 1 in that: 8 parts of inorganic filler, 0.7 parts of composite coupling agent, 72 parts of PBAT resin, 39 parts of polylactic acid, 16.5 parts of PBS resin, 13 parts of polycaprolactone, 7.5 parts of glycidyl methacrylate-grafted polylactic acid copolymer, 2 parts of tributyl citrate, 1 part of chain extender and compatibilizer ADR-4468, 0.5 parts of calcium stearate, and 1 part of antioxidant 1010; the rest are the same.

[0048] Example 11

[0049] A biodegradable polyester plastic film and its preparation method are disclosed. The difference between Example 1 and Example 2 is that: 6 parts inorganic filler, 0.4 parts composite coupling agent, 62 parts PBAT resin, 50 parts polylactic acid, 20 parts PBS resin, 11 parts polycaprolactone, 6 parts glycidyl methacrylate-grafted polylactic acid copolymer, 4 parts tributyl citrate, 1 part chain extender and compatibilizer ADR-4468, 0.5 parts calcium stearate, and 1 part antioxidant 1010 are included; the rest are the same.

[0050] Example 12

[0051] A biodegradable polyester plastic film and its preparation method are different from Example 1 in that: 9 parts inorganic filler, 0.6 parts composite coupling agent, 70 parts PBAT resin, 48 parts polylactic acid, 20 parts PBS resin, 12 parts polycaprolactone, 7 parts glycidyl methacrylate-grafted polylactic acid copolymer, 3 parts tributyl citrate, 1 part chain extender compatibilizer ADR-4468, 0.5 parts calcium stearate, and 1 part antioxidant 1010; the rest are the same.

[0052] Example 13

[0053] A biodegradable polyester plastic film and its preparation method are disclosed below.

[0054] (1) Mix 9 parts of inorganic filler consisting of calcium carbonate whiskers and nano-silica in a mass ratio of 2:2, and 0.4 parts of composite coupling agent consisting of tetrabutyl titanate and KH-550 in a mass ratio of 1:2. Grind the mixture at 150 rpm for 15 min. Then mix it with 75 parts of PBAT resin, 43 parts of polylactic acid, 18 parts of PBS resin, 12 parts of polycaprolactone, 6 parts of glycidyl methacrylate-grafted polylactic acid copolymer, 3 parts of tributyl citrate, 1 part of chain extender compatibilizer ADR-4468, 0.5 parts of zinc stearate and 0.5 parts of antioxidant 1010 to obtain a mixture.

[0055] (2) The mixture is fed into a twin-screw extruder, heated and melted at 205°C, and then extruded by a twin-screw extruder at 205°C. The extruded melt is then cast in a casting machine at 205°C and cooled to obtain a sheet.

[0056] (3) The sheet is stretched biaxially, first longitudinally and then transversely. The longitudinal stretching temperature is 100℃ and the stretching ratio is 4. The transverse stretching temperature is 105℃ and the stretching ratio is 4. Then it is heat-set at 125℃ to obtain a biodegradable polyester plastic film.

[0057] Example 14

[0058] A biodegradable polyester plastic film and its preparation method are disclosed below.

[0059] (1) Mix 6 parts of inorganic filler consisting of calcium carbonate whiskers and nano-silica in a mass ratio of 3:2, and 0.7 parts of composite coupling agent consisting of tetrabutyl titanate and KH-550 in a mass ratio of 2:2. Grind the mixture at 150 rpm for 15 min. Then mix the mixture with 65 parts of PBAT resin, 40 parts of polylactic acid, 17.5 parts of PBS resin, 14 parts of polycaprolactone, 8 parts of glycidyl methacrylate-grafted polylactic acid copolymer, 3 parts of tributyl citrate, 1.5 parts of chain extender compatibilizer ADR-4468, 0.6 parts of zinc stearate and 0.8 parts of antioxidant 1010 to obtain a mixture.

[0060] (2) The mixture is fed into a twin-screw extruder, heated and melted at 185°C, and then extruded by a twin-screw extruder at 185°C. The extruded melt is then cast in a casting machine at 185°C and cooled to obtain a sheet.

[0061] (3) The sheet is biaxially stretched, first longitudinally stretched and then transversely stretched. The longitudinal stretching temperature is 90℃ and the stretching ratio is 5. The transverse stretching temperature is 95℃ and the stretching ratio is 4. Then it is heat-set at 115℃ to obtain a biodegradable polyester plastic film.

[0062] Comparative Example 1

[0063] A biodegradable polyester plastic film and its preparation method are disclosed. The preparation process is as follows: Example 1 differs in that: 5 parts inorganic filler, 0.3 parts composite coupling agent, 60 parts PBAT resin, 21 parts polylactic acid, 30 parts PBS resin, 10 parts polycaprolactone, 5 parts glycidyl methacrylate-grafted polylactic acid copolymer, 2 parts tributyl citrate, 1 part chain extender compatibilizer ADR-4468, 0.5 parts calcium stearate, and 0.5 parts antioxidant 1010 are used; the rest are the same.

[0064] Comparative Example 2

[0065] A biodegradable polyester plastic film and its preparation method are disclosed. The preparation process is as follows: Example 1 differs in that: 5 parts inorganic filler, 0.3 parts composite coupling agent, 60 parts PBAT resin, 37 parts polylactic acid, 14 parts PBS resin, 15 parts polycaprolactone, 0 parts glycidyl methacrylate-grafted polylactic acid copolymer, 2 parts tributyl citrate, 1 part chain extender compatibilizer ADR-4468, 0.5 parts calcium stearate, and 0.5 parts antioxidant 1010 are the same as above.

[0066] Comparative Example 3

[0067] A biodegradable polyester plastic film and its preparation method are disclosed. The preparation process is as follows: Example 1 differs in that: 5 parts inorganic filler, 0.3 parts composite coupling agent, 60 parts PBAT resin, 37 parts polylactic acid, 14 parts PBS resin, 0 parts polycaprolactone, 15 parts glycidyl methacrylate-grafted polylactic acid copolymer, 2 parts tributyl citrate, 1 part chain extender compatibilizer ADR-4468, 0.5 parts calcium stearate, and 0.5 parts antioxidant 1010 are the same as above.

[0068] Comparative Example 4

[0069] A biodegradable polyester plastic film and its preparation method are disclosed. The preparation process is as follows: Example 1 differs in that 5 parts of calcium carbonate whiskers are used instead of 5 parts of inorganic filler, and 0.3 parts of tetrabutyl titanate are used instead of 0.3 parts of composite coupling agent.

[0070] Comparative Example 5

[0071] A biodegradable polyester plastic film and its preparation method are disclosed. The preparation process is as follows: The difference in Example 1 is that 5 parts of nano-silica are used instead of 5 parts of inorganic filler, and 0.3 parts of KH-550 are used instead of 0.3 parts of composite coupling agent.

[0072] Comparative Example 6

[0073] A biodegradable polyester plastic film and its preparation method are disclosed. The preparation process is as follows: Example 1 differs in that 0.3 parts of KH-550 are used instead of 0.3 parts of composite coupling agent.

[0074] Test case

[0075] 1. The toughness and strength properties of the biodegradable polyester plastic films prepared in Examples 1-14 and Comparative Examples 1-6 were tested. The test method was in accordance with GB / T1040.3-2006. The test results are shown in Table 1.

[0076] 2. The water vapor barrier properties of the biodegradable polyester plastic films prepared in Examples 1-14 and Comparative Examples 1-6 were tested. The test method was in accordance with GB1037-2021. The test results are shown in Table 1.

[0077]

[0078] As can be seen from the test results in Table 1, the biodegradable polyester plastic film prepared in this application embodiment has excellent toughness, strength and barrier properties, and can be well applied in the field of packaging materials. Compared to Comparative Example 1, Example 1 used a higher amount of polylactic acid than PBS resin, which is beneficial for improving the mechanical properties of the biodegradable polyester film and optimizing its barrier properties. Compared to Comparative Examples 2 and 3, Example 1 lacked either polycaprolactone or glycidyl methacrylate-grafted polylactic acid copolymer, which would reduce the toughness, strength, and barrier properties of the biodegradable polyester film. Compared to Comparative Examples 4 and 5, Example 1 used an inorganic filler composed of calcium carbonate whiskers and nano-silica, which effectively promoted the improvement of the toughness and strength of the biodegradable polyester film and also provided effective barrier properties against water and oxygen. Compared to Comparative Example 6, Example 1 used a composite coupling agent composed of titanate coupling agent and silane coupling agent to treat the inorganic material, which better promoted the compatibility with PBAT resin, polylactic acid, and PBS resin matrix, improved the bonding performance, optimized the toughness and strength of the biodegradable polyester film, and further improved the barrier properties. Furthermore, this invention controls the mass percentage of PBS resin in polylactic acid to be 40-45% and the mass ratio of polycaprolactone to glycidyl methacrylate-grafted polylactic acid copolymer to be 1.5-2:1, further optimizing the bonding and structural system between PBAT resin, polylactic acid, and PBS resin matrix, and significantly improving the toughness, strength, and barrier properties of the biodegradable polyester plastic film.

[0079] In summary, the biodegradable polyester plastic film of the present invention has excellent toughness, strength and barrier properties, and can be well applied in the field of packaging materials.

[0080] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit and essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

[0081] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A biodegradable polyester plastic film, characterized in that, The product comprises the following raw materials and their weight parts: 60-75 parts PBAT resin, 37-50 parts polylactic acid, 14-23 parts PBS resin, 10-15 parts polycaprolactone, 5-10 parts glycidyl methacrylate-grafted polylactic acid copolymer, 5-10 parts inorganic filler, 2-4 parts tributyl citrate, 1-2 parts chain extender and compatibilizer ADR, 0.3-0.7 parts composite coupling agent, 0.5-1 part dispersant, and 0.5-1 part antioxidant; The inorganic filler is composed of a mixture of calcium carbonate whiskers and nano-silica; the composite coupling agent is composed of a mixture of titanate coupling agent and silane coupling agent.

2. The biodegradable polyester plastic film according to claim 1, characterized in that, The PBS resin accounts for 40-45% of the mass of polylactic acid.

3. The biodegradable polyester plastic film according to claim 2, characterized in that, The mass ratio of polycaprolactone to glycidyl methacrylate-grafted polylactic acid copolymer is 1.5~2:

1.

4. The biodegradable polyester plastic film according to claim 3, characterized in that, The mass ratio of the inorganic filler to tributyl citrate is 2~3:

1.

5. The biodegradable polyester plastic film according to claim 1, characterized in that, The titanate coupling agent is n-butyl titanate; the silane coupling agent is KH-550.

6. The biodegradable polyester plastic film according to claim 1, characterized in that, The dispersant is either zinc stearate or calcium stearate; the antioxidant is either antioxidant 1010 or antioxidant 168.

7. A method for preparing a biodegradable polyester plastic film according to any one of claims 1 to 6, characterized in that, Includes the following steps: (1) Mix the inorganic filler and composite coupling agent in the above weight parts evenly, then grind at 100~200 rpm for 10~20 min, and then mix evenly with the above weight parts of PBAT resin, polylactic acid, PBS resin, polycaprolactone, glycidyl methacrylate grafted polylactic acid copolymer, tributyl citrate, chain extender compatibilizer ADR, dispersant and antioxidant to obtain a mixture; (2) The mixture is fed into a twin-screw extruder, heated and melted, then extruded by a twin-screw extruder. The extruded melt is then cast in a casting machine and cooled to obtain a sheet. (3) The sheet is biaxially stretched and then heat-set to obtain a biodegradable polyester plastic film.

8. The method for preparing a biodegradable polyester plastic film according to claim 7, characterized in that, In step (2), the heating and melting temperature is 185~205℃, the extrusion temperature is 185~205℃, and the casting temperature is 185~205℃.

9. The method for preparing a biodegradable polyester plastic film according to claim 7, characterized in that, In step (3), bidirectional stretching is performed first in the longitudinal direction and then in the transverse direction. The temperature for longitudinal stretching is 90~100℃ and the stretching ratio is 3~5. The temperature for transverse stretching is 95~105℃ and the stretching ratio is 3~4. The heat setting temperature is 115~125℃.

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