A biaxially oriented polyester film for VCM coated board and its preparation method

Abstract

The present invention discloses a biaxially oriented polyester film for VCM coated board, which is successively composed of an adhesive layer, a core layer and an anti-adhesive layer; wherein the adhesive layer is made of the following raw materials: copolyester and anti-adhesive masterbatch A, and the copolyester is obtained by polycondensation of terephthalic acid, phthalic acid, ethylene glycol and 1,2-butanediol under the action of a catalyst; the core layer is made of the following raw materials: homopolyester, POE grafted maleic anhydride and LLDPE. The present invention also discloses a preparation method of the biaxially oriented polyester film for VCM coated board. The biaxially oriented polyester film for VCM coated board of the present invention has good dimensional stability, thermal adhesiveness and ductility, and can be directly thermocompounded with a metal plate without gluing.

Description

Technical Field

[0001] The present invention relates to the technical field of polyester films, and in particular to a biaxially oriented polyester film for VCM laminated boards and a preparation method thereof. Background Art

[0002] The biaxially oriented polyester film is a packaging film with relatively comprehensive properties. It has the characteristics of good transparency, high gloss, high tensile strength, high stiffness, appropriate elongation at break, and good dimensional stability, and has properties such as heat resistance, cold resistance, and good chemical resistance, and is widely used in various fields such as printing, packaging, aluminizing, etc. However, with the rapid development of the plastic film field, people's requirements for the performance of the film are getting higher and higher. At present, the market for ordinary biaxially oriented polyester films for packaging has a supply surplus, but high-end products in some special fields are still relatively lacking, such as the biaxially oriented polyester film for thermal lamination in the VCM laminated board field. That is, by covering a dense PET plastic film on the surface of a metal plate, the laminated board has the good strength and processing performance of the metal material, and at the same time also has the excellent decorative performance, corrosion resistance, weather resistance, pollution resistance, etc. of the polymer film. The traditional lamination process is to coat glue between the PET film and the metal plate for lamination. Although this method can attach the PET film to the metal plate, there are some drawbacks such as chemical glue migration, cumbersome process, safety and environmental protection. In addition, the PET film used for metal plate lamination also needs to have excellent ductility and dimensional stability to meet the requirements of the metal plate processing technology. Summary of the Invention

[0003] Based on the technical problems existing in the background art, the present invention proposes a biaxially oriented polyester film for VCM laminated boards and a preparation method thereof. The prepared biaxially oriented polyester film for VCM laminated boards has good dimensional stability, thermal adhesiveness, and ductility, and can be directly thermally laminated with the metal plate without applying glue.

[0004] A biaxially oriented polyester film for VCM laminated boards proposed by the present invention is successively composed of an adhesive layer, a core layer, and an anti-adhesive layer;

[0005] The adhesive layer is made of raw materials with the following mass percentages: 50-80% of copolyester, 20-50% of anti-adhesive masterbatch A; the anti-adhesive masterbatch A is composed of components with the following mass percentages: 95-99% of copolyester, 1-5% of organosilica; the copolyester is obtained by polycondensation of terephthalic acid, phthalic acid, ethylene glycol, and 1,2-butanediol under the action of a catalyst;

[0006] The core layer is made of raw materials with the following mass percentages: 30-50% of homopolyester, 10-30% of POE grafted maleic anhydride, 20-40% of LLDPE;

[0007] The anti-blocking layer is made of raw materials with the following mass percentages: homopolyester 30-50%, anti-blocking masterbatch B 50-70%; the anti-blocking masterbatch B is composed of components with the following mass percentages: homopolyester 95-99%, inorganic calcium carbonate 1-5%.

[0008] Preferably, the mass ratio of terephthalic acid to phthalic acid is (2.5-7):1, the mass ratio of ethylene glycol to 1,2-butanediol is (2-6):1, and the ratio of the sum of the moles of terephthalic acid and phthalic acid to the sum of the moles of ethylene glycol and 1,2-butanediol is 1:(1.2-1.5), that is: [n(terephthalic acid) + n(phthalic acid)]:[n(ethylene glycol) + n(1,2-butanediol)] = 1:(1.2-1.5); the catalyst is titanium dioxide, and the dosage of the catalyst is 30-90 ppm.

[0009] Preferably, the preparation method of the copolyester is: adding terephthalic acid, phthalic acid, ethylene glycol, 1,2-butanediol and titanium dioxide into a reaction kettle, and reacting for 3-5 h under the conditions of a vacuum degree of 30-80 Pa and a reaction temperature of 220-260 °C, then obtaining it.

[0010] Preferably, in the anti-blocking masterbatch A, the particle size of the organosilica is 2-4 μm.

[0011] Preferably, the grafting rate of the POE-grafted maleic anhydride is 2-6%.

[0012] Preferably, the preparation method of the POE-grafted maleic anhydride is:

[0013] Adding POE, maleic anhydride and an initiator into a twin-screw extruder, and melt-extruding at 170-200 °C, then obtaining it, wherein the mass ratio of POE, maleic anhydride and the initiator is (96-99):(0.95-3.75):(0.05-0.25).

[0014] Preferably, the thickness of the biaxially oriented polyester film for VCM laminating board is 15-30 μm; the thickness of the adhesive layer accounts for 5-10% of the total thickness of the biaxially oriented polyester film for VCM laminating board, the thickness of the core layer accounts for 80-90% of the total thickness of the biaxially oriented polyester film for VCM laminating board, and the thickness of the anti-blocking layer accounts for 5-15% of the total thickness of the biaxially oriented polyester film for VCM laminating board.

[0015] A preparation method of the biaxially oriented polyester film for VCM laminating board as described above includes the following steps:

[0016] S1. Add the raw materials of the core layer into the main extruder for melt extrusion, filter through a filter screen to obtain the core layer melt; add the raw materials of the adhesive layer into the first auxiliary extruder for melt extrusion, filter through a filter screen to obtain the adhesive layer melt; add the raw materials of the anti-blocking layer into the second auxiliary extruder for melt extrusion, filter through a filter screen to obtain the anti-blocking layer melt.

[0017] S2. Converge and extrude the core layer melt, the adhesive layer melt, and the anti-blocking layer melt in sequence at the die lip of a three-layer structure extruder to obtain a film; use high-voltage static electricity to attach the film to a chill roll for rapid cooling to form a cast sheet.

[0018] S3. After preheating the cast sheet, perform longitudinal stretching to form a thick film.

[0019] S4. After preheating the thick film, perform transverse stretching, then undergo heat setting and cooling to obtain a biaxially oriented polyester film for VCM coated board.

[0020] Preferably, in S1, the melt extrusion temperature of the main extruder is 260 - 290 °C, the melt extrusion temperature of the first auxiliary extruder is 220 - 260 °C, and the melt extrusion temperature of the second auxiliary extruder is 270 - 290 °C.

[0021] Preferably, in S3, after preheating the cast sheet at 60 - 120 °C, perform longitudinal stretching at 100 - 120 °C by 4.0 - 4.8 times to obtain a thick film.

[0022] Preferably, in S4, after preheating the thick film at 100 - 120 °C, perform transverse stretching at 110 - 130 °C by 4 - 5 times, then perform heat setting at 230 - 250 °C, and then cool at 80 - 110 °C to obtain a biaxially oriented polyester film for VCM coated board.

[0023] The beneficial effects of the present invention are as follows:

[0024] (1) In the present invention, copolyester is added to the raw materials of the adhesive layer, so that the adhesive layer of the film has heat-sealing performance, can be directly heat-compounded with a metal plate without coating glue, the production process is simpler and more environmentally friendly, and at the same time, the bonding strength between the film adhesive layer and the metal plate can reach more than 3.5 N / 15 mm, with good effects.

[0025] (2) In the present invention, POE grafted maleic anhydride and LLDPE are added to the core layer, effectively improving the toughness of the film. The nominal strain at break of the film can reach more than 160%, so that the film will not crack when heat-compounded with metal plates of different shapes. Specific Embodiments

[0026] Below, the technical solutions of the present invention will be described in detail through specific examples.

[0027] In the following examples and comparative examples, POE grafted maleic anhydride was purchased from Coase Chemical Co., Ltd. with a brand name of W1A; LLDPE was purchased from Formosa Plastics Group in Taiwan, China with a brand name of 3470; and homopolymer polyester was purchased from Yizheng Chemical Fiber with a brand name of FG620.

[0028] Example 1

[0029] A biaxially oriented polyester film for a VCM laminated board, which is composed of an adhesive layer, a core layer, and an anti-sticking layer in sequence;

[0030] The adhesive layer is made of the following raw materials in mass percentage: 50% of copolyester and 50% of anti-sticking masterbatch A; the anti-sticking masterbatch A is composed of the following components in mass percentage: 95% of copolyester and 5% of organic silicon dioxide with a particle size of 2 μm; the preparation method of the copolyester is as follows: terephthalic acid, phthalic acid, ethylene glycol, 1,2-butanediol and titanium dioxide are added into a reaction kettle, and reacted for 3 hours under the conditions of vacuum degree of 40 Pa and reaction temperature of 220° C., wherein the mass ratio of terephthalic acid to phthalic acid is 3:1, the mass ratio of ethylene glycol to 1,2-butanediol is 2:1, the ratio of the sum of the molar numbers of terephthalic acid and phthalic acid to the sum of the molar numbers of ethylene glycol and 1,2-butanediol is 1:1.4, and the amount of titanium dioxide used is 40 ppm;

[0031] The core layer is made of the following raw materials in percentage by weight: 30% homopolyester, 30% POE grafted maleic anhydride, and 40% LLDPE;

[0032] The preparation method of POE grafted maleic anhydride is as follows: POE, maleic anhydride and initiator are added into a twin-screw extruder, and melt-extruded at 170° C. to obtain POE, maleic anhydride and initiator in a mass ratio of 96:3.75:0.25.

[0033] The anti-adhesive layer is made of the following raw materials in mass percentage: 30% homopolyester and 70% anti-adhesive masterbatch B; the anti-adhesive masterbatch B is composed of the following components in mass percentage: 95% homopolyester and 5% inorganic calcium carbonate with a particle size of 2.5 μm.

[0034] The thickness of the above-mentioned biaxially oriented polyester film for VCM coated board is 15 μm, of which the thickness of the adhesive layer accounts for 5% of the total thickness of the biaxially oriented polyester film for VCM coated board, the thickness of the core layer accounts for 80% of the total thickness of the biaxially oriented polyester film for VCM coated board, and the thickness of the anti-sticking layer accounts for 15% of the total thickness of the biaxially oriented polyester film for VCM coated board.

[0035] The method for preparing the biaxially oriented polyester film for the VCM coated plate comprises the following steps:

[0036] S1. Add the raw materials of the core layer into the main extruder for melt extrusion, filter through a filter screen to obtain the core layer melt; add the raw materials of the adhesive layer into the first auxiliary extruder for melt extrusion, filter through a filter screen to obtain the adhesive layer melt; add the raw materials of the anti-adhesion layer into the second auxiliary extruder for melt extrusion, filter through a filter screen to obtain the anti-adhesion layer melt. The melt extrusion temperature of the main extruder is 260 °C, the melt extrusion temperature of the first auxiliary extruder is 220 °C, and the melt extrusion temperature of the second auxiliary extruder is 270 °C;

[0037] S2. Converge and extrude the core layer melt, the adhesive layer melt, and the anti-adhesion layer melt in sequence at the die lip of a three-layer structure extruder to obtain a film sheet; use high-voltage static electricity to attach the film sheet to a chill roll for rapid cooling to form a cast sheet;

[0038] S3. After preheating the cast sheet through 14 Teflon rollers at 70 °C, longitudinally stretch it 4 times at 105 °C on a tungsten carbide roll through a speed difference to obtain a thick film;

[0039] S4. After preheating the thick film in a high-temperature oven at 100 °C, transversely stretch it 4 times at 110 °C using a clamping device, then perform heat setting at 230 °C, and then cool it at 80 °C to obtain a biaxially oriented polyester film for VCM coated board.

[0040] Example 2

[0041] A biaxially oriented polyester film for VCM coated board is successively composed of an adhesive layer, a core layer, and an anti-adhesion layer;

[0042] The adhesive layer is made of raw materials with the following mass percentages: 60% of copolyester, 40% of anti-adhesion masterbatch A; the anti-adhesion masterbatch A is composed of components with the following mass percentages: 96% of copolyester, 4% of organosilica with a particle size of 2.5 μm; the preparation method of the copolyester is: add terephthalic acid, phthalic acid, ethylene glycol, 1,2-butanediol, and titanium dioxide into a reaction kettle, react under a vacuum of 30 - 80 Pa and a reaction temperature of 230 °C for 4 h to obtain it. The mass ratio of terephthalic acid to phthalic acid is 3.5:1, the mass ratio of ethylene glycol to 1,2-butanediol is 3:1, the ratio of the sum of the moles of terephthalic acid and phthalic acid to the sum of the moles of ethylene glycol and 1,2-butanediol is 1:1.2, and the dosage of titanium dioxide is 50 ppm;

[0043] The core layer is made of raw materials with the following mass percentages: 40% of homopolyester, 30% of POE grafted maleic anhydride, 30% of LLDPE;

[0044] The preparation method of POE grafted maleic anhydride is as follows: Add POE, maleic anhydride and initiator into a twin-screw extruder, and melt-extrude at 190 °C to obtain it. The mass ratio of POE, maleic anhydride and initiator is 97:2.8:0.2.

[0045] The anti-adhesion layer is made of raw materials with the following mass percentages: homopolyester 30%, anti-adhesion masterbatch B 70%; The anti-adhesion masterbatch B is composed of components with the following mass percentages: homopolyester 95%, inorganic calcium carbonate with a particle size of 3 μm 5%.

[0046] The thickness of the above-mentioned biaxially oriented polyester film for VCM-coated board is 20 μm. Among them, the thickness of the adhesive layer accounts for 7% of the total thickness of the biaxially oriented polyester film for VCM-coated board, the thickness of the core layer accounts for 83% of the total thickness of the biaxially oriented polyester film for VCM-coated board, and the thickness of the anti-adhesion layer accounts for 10% of the total thickness of the biaxially oriented polyester film for VCM-coated board.

[0047] The preparation method of the above-mentioned biaxially oriented polyester film for VCM-coated board is the same as that in Example 1.

[0048] Example 3

[0049] A biaxially oriented polyester film for VCM-coated board is successively composed of an adhesive layer, a core layer and an anti-adhesion layer;

[0050] The adhesive layer is made of raw materials with the following mass percentages: copolyester 70%, anti-adhesion masterbatch A 30%; The anti-adhesion masterbatch A is composed of components with the following mass percentages: copolyester 97%, organic silica with a particle size of 3 μm 3%; The preparation method of the copolyester is as follows: Add terephthalic acid, phthalic acid, ethylene glycol, 1,2-butanediol and titanium dioxide into a reaction kettle, and react for 4 h under the conditions of a vacuum degree of 50 Pa and a reaction temperature of 240 °C to obtain it. The mass ratio of terephthalic acid to phthalic acid is 4.5:1, the mass ratio of ethylene glycol to 1,2-butanediol is 3.5:1, the ratio of the sum of the molar numbers of terephthalic acid and phthalic acid to the sum of the molar numbers of ethylene glycol and 1,2-butanediol is 1:1.5, and the dosage of titanium dioxide is 50 ppm;

[0051] The core layer is made of raw materials with the following mass percentages: homopolyester 50%, POE grafted maleic anhydride 30%, LLDPE 20%;

[0052] The preparation method of POE grafted maleic anhydride is as follows: Add POE, maleic anhydride and initiator into a twin-screw extruder, and melt-extrude at 200 °C to obtain it. The mass ratio of POE, maleic anhydride and initiator is 98:1.85:0.15.

[0053] The anti - adhesion layer is made of raw materials with the following mass percentages: homopolyester 50%, anti - adhesion masterbatch B 50%; the anti - adhesion masterbatch B consists of components with the following mass percentages: homopolyester 97%, inorganic calcium carbonate with a particle size of 3μm 3%.

[0054] The thickness of the biaxially oriented polyester film for VCM coated panel is 25μm. Among them, the thickness of the adhesive layer accounts for 5% of the total thickness of the biaxially oriented polyester film for VCM coated panel, the thickness of the core layer accounts for 80% of the total thickness of the biaxially oriented polyester film for VCM coated panel, and the thickness of the anti - adhesion layer accounts for 15% of the total thickness of the biaxially oriented polyester film for VCM coated panel.

[0055] The preparation method of the biaxially oriented polyester film for VCM coated panel is the same as that in Example 1.

[0056] Example 4

[0057] A biaxially oriented polyester film for VCM coated panel is successively composed of an adhesive layer, a core layer, and an anti - adhesion layer;

[0058] The adhesive layer is made of raw materials with the following mass percentages: copolyester 70%, anti - adhesion masterbatch A 30%; the anti - adhesion masterbatch A consists of components with the following mass percentages: copolyester 98%, organic silica with a particle size of 4μm 2%; the preparation method of the copolyester is: adding terephthalic acid, phthalic acid, ethylene glycol, 1,2 - butanediol, and titanium dioxide into a reaction kettle, reacting under the conditions of a vacuum degree of 70Pa and a reaction temperature of 260°C for 5h to obtain it, where the mass ratio of terephthalic acid to phthalic acid is 6:1, the mass ratio of ethylene glycol to 1,2 - butanediol is 5:1, the ratio of the sum of the moles of terephthalic acid and phthalic acid to the sum of the moles of ethylene glycol and 1,2 - butanediol is 1:1.5, and the dosage of titanium dioxide is 70ppm;

[0059] The core layer is made of raw materials with the following mass percentages: homopolyester 40%, POE grafted maleic anhydride 20%, LLDPE 40%;

[0060] The preparation method of POE grafted maleic anhydride is: adding POE, maleic anhydride, and an initiator into a twin - screw extruder, and melt - extruding at 200°C to obtain it, where the mass ratio of POE, maleic anhydride, and the initiator is 99:0.95:0.05.

[0061] The anti - adhesion layer is made of raw materials with the following mass percentages: homopolyester 40%, anti - adhesion masterbatch B 60%; the anti - adhesion masterbatch B consists of components with the following mass percentages: homopolyester 98%, inorganic calcium carbonate with a particle size of 3.5μm 2%.

[0062] The biaxially oriented polyester film for VCM coated board mentioned above has a thickness of 30 μm, wherein the thickness of the adhesive layer accounts for 10% of the total thickness of the biaxially oriented polyester film for VCM coated board, the thickness of the core layer accounts for 80% of the total thickness of the biaxially oriented polyester film for VCM coated board, and the thickness of the anti-sticking layer accounts for 10% of the total thickness of the biaxially oriented polyester film for VCM coated board.

[0063] The preparation method of the biaxially oriented polyester film for VCM coated board mentioned above is the same as that in Example 1.

[0064] Comparative Example 1

[0065] Compared with Example 1, the difference in Comparative Example 1 is only that: the adhesive layer is composed of 100% anti-sticking masterbatch; the rest are the same.

[0066] Comparative Example 2

[0067] Compared with Example 1, the difference in Comparative Example 2 is only that: the core layer is made of raw materials with the following mass percentages: 80% homopolyester, 10% POE grafted maleic anhydride, 10% LLDPE; the rest are the same.

[0068] Comparative Example 3

[0069] Compared with Example 1, the difference in Comparative Example 3 is only that: the preparation method of the copolyester is: adding terephthalic acid, ethylene glycol, 1,2-butanediol and titanium dioxide into a reaction kettle, reacting at a vacuum degree of 40 Pa and a reaction temperature of 220 °C for 3 h to obtain it, wherein the mass ratio of ethylene glycol to 1,2-butanediol is 2:1, the molar ratio of terephthalic acid to the sum of the molar numbers of ethylene glycol and 1,2-butanediol is 1:1.4 (i.e., n(terephthalic acid):[n(ethylene glycol)+n(1,2-butanediol)] = 1:1.4), and the dosage of titanium dioxide is 40 ppm; the rest are the same.

[0070] Comparative Example 4

[0071] Compared with Example 1, the difference in Comparative Example 4 is only that: the preparation method of the copolyester is: adding terephthalic acid, phthalic acid, ethylene glycol and titanium dioxide into a reaction kettle, reacting at a vacuum degree of 40 Pa and a reaction temperature of 220 °C for 3 h to obtain it, wherein the mass ratio of terephthalic acid to phthalic acid is 3:1, the molar ratio of the sum of the molar numbers of terephthalic acid and phthalic acid to ethylene glycol is 1:1.4 (i.e., [n(terephthalic acid)+n(phthalic acid)]:n(ethylene glycol) = 1:1.4), and the dosage of titanium dioxide is 40 ppm; the rest are the same.

[0072] Test Example

[0073] The performance tests were carried out on the biaxially oriented polyester films prepared in Examples 1-4 and Comparative Examples 1-4, and the test results are shown in Table 1:

[0074] Table 1 Performance test results of biaxially oriented polyester films in examples and comparative examples

[0075]

[0076] The test method for the heat seal strength between the film and the metal plate is as follows: 5 specimens are uniformly cut in the width direction of the film roll, with the specimen length being 150 mm and the width being (15 ± 0.1) mm. Also, 5 metal plates with the same length and width as the film are taken. During the test, the film and the metal plate are aligned in the length and width directions and placed on the welding surface of the heat sealer for heat sealing. The heat sealing temperature is 125 °C, the heat sealing pressure is 0.18 MPa, and the heat sealing time is 2 s. With the heat-sealed part as the center line of the specimen, the two ends of the specimen are respectively clamped on the two fixtures of the testing machine, making the longitudinal axis of the specimen coincide with the center line connecting the upper and lower fixtures, and the fixtures are tightened appropriately. The fixture spacing is 100 mm. The test speed is (100 ± 10) mm / min, and the maximum load at the moment of specimen fracture is read. The test result takes the arithmetic mean of 5 specimens as the heat seal strength of the tested sample, expressed in N / 15 mm.

[0077] As can be seen from Table 1, the biaxially oriented polyester films for VCM-coated boards prepared in Examples 1-4 of the present invention can all be successfully heat-compounded onto the surface of the metal plate, and have good heat seal strength, indicating that they have good heat seal performance for the metal plate substrate, and have good fracture nominal strain and good ductility.

[0078] The above is only the preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, makes equivalent substitutions or changes, and should be covered within the protection scope of the present invention.

Claims

1. A biaxially oriented polyester film for VCM coated board, characterized in that It is successively composed of an adhesive layer, a core layer, and an anti-adhesive layer; The adhesive layer is made of raw materials with the following mass percentages: 50-80% of copolyester, and 20-50% of anti-adhesive masterbatch A; the anti-adhesive masterbatch A is composed of components with the following mass percentages: 95-99% of copolyester, and 1-5% of organosilica; the copolyester is obtained by polycondensation of terephthalic acid, phthalic acid, ethylene glycol, and 1,2-butanediol under the action of a catalyst; the mass ratio of terephthalic acid to phthalic acid is (2.5-7):1, the mass ratio of ethylene glycol to 1,2-butanediol is (2-6):1, and the ratio of the sum of the moles of terephthalic acid and phthalic acid to the sum of the moles of ethylene glycol and 1,2-butanediol is 1:(1.2-1.5); the catalyst is titanium dioxide, and the dosage of the catalyst is 30-90 ppm; The core layer is made of raw materials with the following mass percentages: 30-50% of homopolyester, 10-30% of POE grafted maleic anhydride, and 20-40% of LLDPE; the grafting rate of the POE grafted maleic anhydride is 2-6%; The anti-adhesive layer is made of raw materials with the following mass percentages: 30-50% of homopolyester, and 50-70% of anti-adhesive masterbatch B; the anti-adhesive masterbatch B is composed of components with the following mass percentages: 95-99% of homopolyester, and 1-5% of inorganic calcium carbonate.

2. The biaxially oriented polyester film for VCM coated board according to claim 1, wherein The preparation method of the copolyester is: adding terephthalic acid, phthalic acid, ethylene glycol, 1,2-butanediol, and titanium dioxide into a reaction kettle, and reacting for 3-5 h under the conditions of a vacuum degree of 30-80 Pa and a reaction temperature of 220-260 °C to obtain it.

3. The biaxially oriented polyester film for VCM coated board according to claim 1, wherein In the anti-adhesive masterbatch A, the particle size of the organosilica is 2-4 μm.

4. The biaxially oriented polyester film for VCM coated board according to claim 1, characterized in that, The thickness of the biaxially oriented polyester film for VCM laminating board is 15-30 μm; the thickness of the adhesive layer accounts for 5-10% of the total thickness of the biaxially oriented polyester film for VCM laminating board, the thickness of the core layer accounts for 80-90% of the total thickness of the biaxially oriented polyester film for VCM laminating board, and the thickness of the anti-adhesive layer accounts for 5-15% of the total thickness of the biaxially oriented polyester film for VCM laminating board.

5. A method for preparing a biaxially oriented polyester film for a VCM coated board according to any one of claims 1-4, characterized in that, It includes the following steps: S1. Adding the raw materials of the core layer into a main extruder for melt extrusion, filtering through a filter screen to obtain a core layer melt; adding the raw materials of the adhesive layer into a first auxiliary extruder for melt extrusion, filtering through a filter screen to obtain an adhesive layer melt; adding the raw materials of the anti-adhesive layer into a second auxiliary extruder for melt extrusion, filtering through a filter screen to obtain an anti-adhesive layer melt; S2. Making the core layer melt, the adhesive layer melt, and the anti-adhesive layer melt converge and extrude at the die lip of a three-layer structure extruder in sequence to obtain a film sheet; using high-voltage static electricity to attach the film sheet to a chill roll for rapid cooling to form a cast sheet; S3. After preheating the cast sheet, performing longitudinal stretching to form a thick film; S4. After preheating the thick film, performing transverse stretching, and then passing through heat setting and cooling to obtain the biaxially oriented polyester film for VCM laminating board.

6. The preparation method of the biaxially oriented polyester film for VCM coated board according to claim 5, characterized in that, In S1, the melting and extrusion temperature of the main extruder is 260 - 290 °C, the melting and extrusion temperature of the first auxiliary extruder is 220 - 260 °C, and the melting and extrusion temperature of the second auxiliary extruder is 270 - 290 °C.

7. The preparation method of the biaxially oriented polyester film for VCM coated board according to claim 5, characterized in that, In S3, after preheating the cast film at 60 - 120 °C, it is longitudinally stretched 4.0 - 4.8 times at 100 - 120 °C to obtain a thick film.

8. The preparation method of the biaxially oriented polyester film for VCM coated board according to claim 5, characterized in that, In S4, after preheating the thick film at 100 - 120 °C, it is transversely stretched 4 - 5 times at 110 - 130 °C, then heat-set at 230 - 250 °C, and then cooled at 80 - 110 °C to obtain a biaxially oriented polyester film for VCM coated board.

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