A pet-based film and applications thereof

Abstract

A PET base film, the base film comprises a base material layer, a use side coating layer and a non-use side coating layer coated on both sides of the base material layer respectively, the coating thickness of the use side coating layer and the non-use side coating layer is 40-50 nm, the coating refractive index is 1.40-1.50, and the surface roughness is 0.03-0.05 mu m; the water contact angle of the use side coating layer is 85-95 degrees, the water contact angle of the non-use side coating layer is 83-91 degrees, the water contact angle of the use side coating layer is greater than that of the non-use side coating layer, the surface free energy of the use side coating layer is 35-41 mN / m, and the surface free energy of the non-use side coating layer is 36-46 mN / m. The water-based polyurethane modified acrylic resin emulsion used in the application is coated on the PET base material, which shows good adhesion with the aluminum plating layer and the aluminum oxide plating layer, and is suitable for food packaging.

Description

Technical Field

[0001] This invention relates to a PET-based film, and more particularly to a PET-based film for use with polyester aluminum films. Background Technology

[0002] In daily life, we often see various kinds of food packaging bags. These bags generally have high barrier properties, blocking water and oxygen, thus extending the shelf life of food. With increasing environmental and safety awareness, the requirements for food packaging films are becoming higher and higher. Low-VOC base films are currently the main development trend. Previously, pure aluminum film was the primary material used for food packaging, but aluminum film lacks sufficient toughness, requiring extra caution when packaging food. Currently, thin films have been developed to replace aluminum film, such as CPP and PET base films for aluminized or alumina coatings. PET, being a semi-crystalline material, has excellent high-temperature resistance and water resistance.

[0003] From the perspectives of cost, environmental protection, and safety, the coating of PET base film is generally applied online, and the coatings used are usually water-based. Currently, there is limited research on the formulation of coatings for PET films using polyester aluminum foil. If the aluminum layer peels off or decomposes upon heating when packaging food with polyester aluminum foil, it will affect food safety. Summary of the Invention

[0004] To overcome the shortcomings of existing technologies, this invention provides a PET base film in which an aqueous polyurethane modified acrylic resin emulsion is coated on a PET substrate layer, exhibiting good adhesion to the aluminum plating layer and the alumina plating layer, making it suitable for food packaging.

[0005] The technical solution adopted by this invention to solve its technical problem is:

[0006] A PET base film includes a substrate layer and a service coating and a non-service coating respectively coated on both sides of the substrate layer. The coating thickness of both the service coating and the non-service coating is 40-50 nm, the refractive index of both coatings is 1.40-1.50, and the surface roughness of both coatings is 0.03-0.05 μm. The water contact angle of the service coating is 85-95°, and the water contact angle of the non-service coating is 83-91°. The water contact angle of the service coating is greater than that of the non-service coating. The surface free energy of the service coating is 35-41 mN / m, and the surface free energy of the non-service coating is 38-46 mN / m.

[0007] The aforementioned PET base film uses a water-based polyurethane-modified acrylic resin system as the base coat for the topcoat. This system has a solid content of 6% and comprises the following components by mass percentage: 3.75%-4.8% water-based polyurethane-modified water-based acrylic resin, 0.3% nano-inorganic particles, 0.5%-1.0% silane coupling agent, 0.2%-0.8% curing agent, 0.2%-0.5% thickener, and the remainder is water. The percentages are by mass fraction of the coating liquid. The water-based polyurethane-modified water... The weight ratio of waterborne polyurethane resin to waterborne acrylic resin in the acrylic resin is 1:9; the primer liquid used for non-topcoat layers is a waterborne acrylic resin system with a solid content of 6%, comprising the following components by mass percentage: waterborne acrylic resin 3.85%-4.8%, nano-inorganic particles 0.3%, silane coupling agent 0.5%-1.0%, curing agent 0.2%-0.8%, thickener 0.2%-0.5%, and the remainder is water. The above percentages are mass fractions of the coating liquid.

[0008] The aforementioned PET base film, wherein the waterborne polyurethane is one of aliphatic waterborne polyurethane, aromatic waterborne polyurethane, araliphatic waterborne polyurethane, and alicyclic waterborne polyurethane.

[0009] The aforementioned PET base film contains an alicyclic aqueous polyurethane, which is an uncapped polyurethane with a number-average molecular weight of 30,000 g / mol and a PDI of 1.85. The aqueous polyurethane is synthesized from polyester polyol and dicyclohexylmethane diisocyanate. The polyester polyol is synthesized from ethylene glycol and phthalic anhydride, and has a number-average molecular weight of 500 g / mol.

[0010] The aqueous acrylic resin in the primer of the aforementioned PET base film is a hydroxyl acrylic resin, specifically selected from FS-2050 aqueous hydroxyl acrylic resin.

[0011] The aqueous acrylic resin in the non-topcoat primer of the aforementioned PET base film is Japanese POLYSOLAP-4690 aqueous polyurethane.

[0012] The aforementioned PET base film contains nano-inorganic particles in the double-sided coating primer, which are one or a mixture of two of nano-silica and nano-calcium carbonate; the silane coupling agent is one of aminosilane, epoxysilane, mercaptosilane, methacryloxysilane, and isocyanate-based silane, with isocyanate-based silane coupling agent KH901 preferred for use in the top coating and epoxysilane coupling agent KH570 preferred for use in the non-top coating; the curing agent is one of melamine, isocyanate, and carbodiimide; and the thickener is 7610 produced by BYK.

[0013] The aforementioned PET base film contains nano-inorganic particles that are a mixture of nano-silica and nano-calcium carbonate in a weight ratio of 1:1. The nano-particles are spherical and regular, with a particle size of 50-100 nm.

[0014] The aforementioned PET base film has an ABA three-layer structure, wherein the A layer resin contains inorganic particles, the B layer is pure PET resin, and the thickness ratio of the ABA three layers is 1:15:1.

[0015] An application of a PET base film, wherein the PET base film is used as a base film for a polyester aluminum film, and a 40nm thick aluminum oxide layer or aluminum layer is deposited on the surface coating to form a polyester aluminum film for food packaging.

[0016] The beneficial effects of this invention are:

[0017] The base film coating of this invention uses a waterborne polyurethane-modified acrylic emulsion. The waterborne polyurethane is an alicyclic type, and being uncapped, it can be used on PET substrates. The coating exhibits good adhesion to the aluminized or alumina-plated layer, does not detach even after high-temperature boiling, and shows good surface adhesion after wiping with ethyl acetate, making it suitable for food packaging. The coating formulation of this invention is suitable for online coating, reducing costs. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the PET base film layer structure of the present invention.

[0019] In the diagram, 1 is the substrate layer, which has an ABA three-layer structure; 2 is the surface coating layer; and 3 is the non-surface coating layer. Detailed Implementation

[0020] This invention uses a waterborne polyurethane-modified waterborne acrylic resin as the primer for the topcoat, and limits the addition ratio of waterborne polyurethane to waterborne acrylic resin to 1:9. Waterborne polyurethane-modified waterborne acrylic resin can improve the mechanical properties of the coating and prevent the coating from cracking due to insufficient toughness during the use of the polyester aluminum film. The ratio of the two needs to be strictly controlled because if too much waterborne polyurethane is added, the water resistance will deteriorate due to the ester groups in the polyurethane; if too little polyurethane is added, the mechanical properties of the acrylic resin cannot be improved.

[0021] The waterborne polyurethane of this invention is preferably an alicyclic waterborne polyurethane, specifically an uncapped polyurethane, synthesized from a polyester polyol and dicyclohexylmethane diisocyanate. The polyester polyol is synthesized from ethylene glycol and phthalic anhydride, and its number-average molecular weight is 500 g / mol. Alicyclic waterborne polyurethanes do not contain benzene rings, which are easily oxidized. Alicyclic polyurethanes do not contain double bonds or benzene rings, thus exhibiting good aging resistance and yellowing resistance. Furthermore, the presence of non-benzene ring structures enhances the non-polarity of the polyurethane, improving its resistance to polar solvents. The uncapped alicyclic waterborne polyurethane is used to modify the acrylic resin. The uncapped isocyanate group (-NCO) of the alicyclic waterborne polyurethane reacts with the hydroxyl group (-OH) in the waterborne acrylic resin, forming numerous hydrogen bonds between the molecules. This results in a dense network structure that effectively prevents moisture penetration.

[0022] Furthermore, the surface free energy of the topcoat used in this invention is 35-41 mN / m, while the surface free energy of the non-topcoat is 36-46 mN / m, and the surface free energy of the PET film is 38-40 mN / m. The surface tension of the coating has a high degree of compatibility with PET, resulting in good adhesion.

[0023] The coating of this invention adds a silane coupling agent at a dosage of 0.5-1% to control the water contact angle of the coating surface to be 85-95°.

[0024] In this invention, nano-inorganic particles are added to the primer of both coating layers to prevent sticking and enhance the abrasion resistance of the coating. The amount of inorganic particles added is 0.3%. Too few inorganic particles will not provide the anti-sticking effect and will affect winding, while too many inorganic particles will result in excessive surface roughness, reducing the water-blocking performance of the film. The surface roughness of both the coating and the non-coating of the PET base film of this invention is 0.03–0.05 μm.

[0025] The primer of the two-layer coating of this invention also contains a curing agent and a thickener. The curing agent is selected from melamine, isocyanate, and carbodiimide, preferably carbodiimide, and the addition amount is 0.2-0.8%. The proportion of coating curing agent should not be too low, otherwise it will affect the film drying speed. When the film undergoes transverse stretching heat treatment, the curing will not be complete, and the coating surface will be sticky. If the content of coating curing agent is too high, the cross-linking speed of the coating will be too fast, which will easily form defects such as gel particles and crystal point impurities on the film surface.

[0026] The pH value of the coating needs to be maintained at around 8.5, which needs to be adjusted by adding ammonia. The ammonia will evaporate after transverse heat treatment, so it is not included in the solid content of the primer.

[0027] The substrate layer of this invention has an ABA three-layer structure. Layer B is the substrate resin layer, which is made of polyethylene terephthalate (PET). Inorganic silica particles, irregularly shaped spheres with a particle size distribution of 2-4 μm, are added to the polyester in layer A. The silica is specifically selected from silica masterbatch FG610 produced by Sinopec, and its amount accounts for 50% of the weight of layer A. The thickness ratio of the ABA three-layer substrate layer is 1:15:1.

[0028] The method for preparing the PET base film of the present invention includes the following steps:

[0029] (1) Casting: A three-layer co-extrusion process is adopted; PET polyester chips and silica masterbatch in layer A are melted and extruded, filtered and then introduced into the T-die; at the same time, PET polyester chips in layer B are melted and extruded, filtered and then introduced into the T-die; after ABA three-layer lamination in the die, they are co-extruded and then cast onto a cold roller to obtain a casting;

[0030] (2) Stretching to form film: The cast sheet obtained in step (1) is first stretched longitudinally by 3.5 times, cooled and corona-treated, and then introduced into the coating roller through the guide roller. The primer liquid with the top coating layer and the primer liquid without the top coating layer are coated online. The thickness of both coatings is 40-50nm. After being stretched transversely by 3.6 times and heat-set, it is wound up and slit to obtain a PET base film with a total thickness of 10-23μm.

[0031] (3) The finished base film obtained by online coating is applied downstream by depositing a 40nm aluminum oxide or aluminum layer on the surface coating to obtain a polyester aluminum film.

[0032] The present invention will be further described below with reference to the embodiments.

[0033] In the following examples and comparative examples, the waterborne acrylic resin used in the topcoat was FS-2050 waterborne hydroxyl acrylic resin, and the waterborne acrylic resin used in the primer (not using the topcoat) was Japanese POLYSOL AP-4690 waterborne polyurethane. The waterborne polyurethane used in the topcoat was selected from alicyclic waterborne polyurethane, which is an uncapped polyurethane with a number average molecular weight of 30,000 g / mol and a polymer PDI of 1.85. The waterborne polyurethane was synthesized from polyester polyol and dicyclohexylmethane diisocyanate, wherein the polyester polyol was synthesized from ethylene glycol and phthalic anhydride and had a number average molecular weight of 500 g / mol.

[0034] Example 1

[0035] The base film for the polyester aluminum film has a topcoat with a solid content of 6% and water of 94%, wherein the weight ratio of waterborne polyurethane resin to waterborne acrylic resin is 1:9, with an addition amount of 4.8%, curing agent 0.2%, thickener 0.2%, silane coupling agent 0.5%, and inorganic particles 0.3%. These percentages are by weight fraction of the coating liquid. The non-topcoat layer of the base film has a solid content of 6% and water of 94%, wherein the waterborne acrylic resin content is 4.8%, curing agent 0.2%, thickener 0.2%, silane coupling agent 0.5%, and inorganic particles 0.3%. These percentages are by weight fraction of the coating liquid. The substrate A layer of the base film contains 50% silica masterbatch and 50% polyester PET chips. These percentages are by weight fraction of layer A. Layer B is 100% PET polyester chips. These percentages are by weight fraction of layer B. The base film prepared from the above formulation has a thickness of 12 μm, and the relevant properties are shown in Tables 1 and 2.

[0036] Example 2

[0037] The high-barrier polyester aluminum film base film provided in Example 1, wherein:

[0038] The base film for the polyester aluminum film has a surface coating with a solid content of 6%, comprising a waterborne polyurethane resin to waterborne acrylic resin weight ratio of 1:9, an addition amount of 4.7%, and a thickener of 0.3%. The non-use surface coating of the base film has a solid content of 6%, comprising a waterborne acrylic resin content of 4.7% and a thickener of 0.3%. The addition amounts of the remaining components are consistent with those in Example 1. The film thickness obtained from the above formulation is 12 μm, and the relevant properties are shown in Tables 1 and 2.

[0039] Example 3

[0040] The high-barrier polyester aluminum film base film provided in Example 1, wherein:

[0041] The base film for the polyester aluminum film has a surface coating with a solid content of 6%, comprising a waterborne polyurethane resin to waterborne acrylic resin weight ratio of 1:9, an addition amount of 4.6%, and a thickener of 0.4%. The non-use surface coating of the base film has a solid content of 6%, comprising a waterborne acrylic resin content of 4.6% and a thickener of 0.4%. The addition amounts of the remaining components are consistent with those in Example 1. The film thickness obtained from the above formulation is 12 μm, and the relevant properties are shown in Tables 1 and 2.

[0042] Example 4

[0043] The high-barrier polyester aluminum film base film provided in Example 1, wherein:

[0044] The base film for the polyester aluminum film has a surface coating with a solid content of 6%, comprising a waterborne polyurethane resin to waterborne acrylic resin weight ratio of 1:9, an addition amount of 4.5%, and a thickener of 0.5%. The non-use surface coating of the base film has a solid content of 6%, comprising a waterborne acrylic resin content of 4.5% and a thickener of 0.5%. The addition amounts of the remaining components are consistent with those in Example 1. The film thickness obtained from the above formulation is 12 μm, and the relevant properties are shown in Tables 1 and 2.

[0045] Example 5

[0046] The high-barrier polyester aluminum film base film provided in Example 1, wherein:

[0047] The base film for the polyester aluminum film has a surface coating with a solid content of 6%, comprising: 4.35% waterborne polyurethane resin and 0.2% waterborne acrylic resin (by weight ratio of 1:9), 0.2% curing agent, 0.4% thickener, 0.75% silane coupling agent, and 0.3% inorganic particles. These percentages represent the mass fraction of the coating liquid. The non-use surface coating of the base film also has a solid content of 6%, comprising: 4.45% waterborne acrylic resin, 0.2% curing agent, 0.3% thickener, 0.75% silane coupling agent, and 0.3% inorganic particles. These percentages also represent the mass fraction of the coating liquid. The substrate layer formulation of the base film is consistent with that of Example 1. The film thickness obtained from the above formulation is 12 μm, and the relevant properties are shown in Tables 1 and 2.

[0048] Example 6

[0049] The high-barrier polyester aluminum film base film provided in Example 5, wherein:

[0050] The base film for the polyester aluminum film has a surface coating with a solid content of 6%, comprising a waterborne polyurethane resin to waterborne acrylic resin weight ratio of 1:9, an addition amount of 4.10%, and a silane coupling agent of 1.0%. The non-use surface coating of the base film has a solid content of 6%, comprising a waterborne acrylic resin content of 4.20% and a silane coupling agent of 1.0%. The addition amounts of the remaining components are consistent with those in Example 5. The film thickness obtained from the above formulation is 12 μm, and the relevant properties are shown in Tables 1 and 2.

[0051] Example 7

[0052] The high-barrier polyester aluminum film base film provided in Example 5, wherein:

[0053] The base film for the polyester aluminum film has a surface coating with a solid content of 6%, wherein the weight ratio of waterborne polyurethane resin to waterborne acrylic resin is 1:9, the addition amount is 4.15%, and the curing agent content is 0.4%. The non-use coating of the base film has a surface solid content of 6%, wherein the waterborne acrylic resin content is 4.25%, and the curing agent content is 0.4%. The addition amounts of the remaining components are the same as in Example 5. The film thickness obtained from the above formulation is 12 μm, and the relevant properties are shown in Tables 1 and 2.

[0054] Example 8

[0055] The high-barrier polyester aluminum film base film provided in Example 5, wherein:

[0056] The base film for the polyester aluminum film has a surface coating with a solid content of 6%, wherein the weight ratio of waterborne polyurethane resin to waterborne acrylic resin is 1:9, the addition amount is 3.95%, and the curing agent content is 0.6%. The non-use surface coating of the base film has a solid content of 6%, wherein the waterborne acrylic resin content is 4.05%, and the curing agent content is 0.6%. The addition amounts of the remaining components are the same as in Example 5. The film thickness obtained from the above formulation is 12 μm, and the relevant properties are shown in Tables 1 and 2.

[0057] Example 9

[0058] The high-barrier polyester aluminum film base film provided in Example 5, wherein:

[0059] The base film for the polyester aluminum film has a surface coating with a solid content of 6%, wherein the weight ratio of waterborne polyurethane resin to waterborne acrylic resin is 1:9, the addition amount is 3.75%, and the curing agent content is 0.8%. The non-use surface coating of the base film has a solid content of 6%, wherein the waterborne acrylic resin content is 3.85%, and the curing agent content is 0.8%. The addition amounts of the remaining components are the same as in Example 5. The film thickness obtained from the above formulation is 12 μm, and the relevant properties are shown in Tables 1 and 2.

[0060] Comparative Example 1

[0061] The high-barrier polyester aluminum film base film provided in Example 4, wherein:

[0062] The base film for the polyester aluminum film uses a topcoat with a solid content of 6%, wherein the coating formulation does not contain waterborne polyurethane, the waterborne acrylic resin content is 4.5%, and the contents of the remaining components are the same as in Example 4. The film thickness obtained from the above formulation is 12 μm, and the relevant properties are shown in Tables 1 and 2.

[0063] The high-barrier polyester aluminum film base film prepared by this invention was tested according to the following method:

[0064] Roughness Sa: The surface roughness was measured using a Keyence VX-160K 3D laser microscope with a magnification of 1000x. Five points were taken from each film and averaged to obtain the average value as the surface roughness, which was then recorded as Sa.

[0065] Contact angle & surface free energy calculation: The test was conducted using a Krüger DSA-25 instrument. Five points were taken from each membrane to measure the water droplet angle, and the average value was taken as the water contact angle. The surface free energy calculation required two solutions, a polar solvent and a non-polar solvent, to measure the contact angle of the membrane surface. Water was chosen as the polar solvent, and diiodomethane was chosen as the non-polar solvent. Five points were tested on each membrane. Then, the surface free energy was calculated according to the OWRK model, and the data were recorded.

[0066] Coating thickness & refractive index: JAW2000 was used for testing, with 5 points taken for each sample. After testing, the coating thickness and refractive index were obtained by fitting the Cauchy model.

[0067] Cross-cut test: Performed according to ISO 2409 standard, the membrane is placed on a smooth marble surface, and a cross-cut pattern is drawn on the coating using a cross-cut tool. 3M-610 tape is then applied to the cuts and pulled off. The membrane is placed under a 3D laser microscope at 200x magnification to observe coating peeling. No peeling at the edges of the cross-cut is defined as 5B; small pieces peeling at the intersections of the cuts, with actual damage to the marked area not exceeding 5%, is defined as 4B; peeling at the edges and / or intersections of the cuts, with an area greater than 5% but less than 15%, is defined as 3B; partial or complete peeling at the edges of the cuts, and / or complete peeling of some squares, with a peeled area exceeding 15% but less than 35%, is defined as 2B; large areas of peeling at the edges of the cuts and / or partial or complete peeling of some squares, with an area greater than 35% but not exceeding 65% of the marked area, is defined as 1B.

[0068] The adhesion test for the aluminum-plated layer or aluminum oxide-plated layer is the same as the test for the base film.

[0069] Ethyl acetate test: Moisten a clean cloth with ethyl acetate and wipe the coating on both sides back and forth 30 times. Observe the coating peeling off. If the coating peels off, it is considered a defective product (NG); if the coating does not peel off, it is a good product (OK).

[0070] Curing time test: Place the coated sample in a 120℃ oven for 1 minute for pre-baking, and then bake at 235℃ until the surface is no longer sticky. Record the baking time required for each sample at 235℃.

[0071] Table 1. Performance test results of the polyester aluminum films provided in Examples 1-9 and Comparative Example 1

[0072]

[0073]

[0074] Table 2 shows the performance test results of the polyester aluminum films provided in Examples 1-9 and Comparative Example 1.

[0075]

[0076]

[0077] As shown in Tables 1 and 2, the waterborne polyurethane-modified waterborne acrylic resin coatings all exhibit good overall performance. In Comparative Example 1, the coating without waterborne polyurethane modification was observed to have a small portion of the coating peeling off during a cross-cut adhesion test. In Examples 1-9, considering energy savings, shorter curing times are preferable. Example 9 exhibits the shortest curing time. However, a short curing time implies an excessively fast production line speed; therefore, the formulations in Examples 1-9 need to be matched to the actual production line speed.

[0078] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. All equivalent variations and modifications made based on the content of the present invention are covered within the patent scope of the present invention.

Claims

1. A PET-based film, characterized in that: The base film includes a substrate layer (1), a working surface coating (2) and a non-working surface coating (3) respectively coated on both sides of the substrate layer. The thickness of both the working surface coating (2) and the non-working surface coating (3) is 40~50nm, the refractive index of both is 1.40~1.50, and the surface roughness of both is 0.03~0.05μm. The water contact angle of the working surface coating is 85~95°, and the water contact angle of the non-working surface coating is 83~91°. The water contact angle of the working surface coating is greater than that of the non-working surface coating. The surface free energy of the working surface coating is 35~41mN / m, and the surface free energy of the non-working surface coating is 36~46mN / m. The primer used for the topcoat is a waterborne polyurethane-modified acrylic resin system with a solid content of 6%, comprising the following components by mass percentage: 3.75%~4.8% waterborne polyurethane-modified waterborne acrylic resin, 0.3% nano-inorganic particles, 0.5%~1.0% silane coupling agent, 0.2%~0.8% curing agent, 0.2%~0.5% thickener, and the remainder being water. The above percentages are mass fractions relative to the weight of the coating liquid, wherein the weight ratio of waterborne polyurethane resin to waterborne acrylic resin in the waterborne polyurethane-modified waterborne acrylic resin is 1:

9. The waterborne polyurethane resin is an uncapped polyurethane; the waterborne acrylic resin is a hydroxyl acrylic resin.

2. The PET base film according to claim 1, characterized in that: The primer liquid used for non-topcoat layers is an aqueous acrylic resin system with a solid content of 6%, comprising the following components by mass percentage: aqueous acrylic resin 3.85%~4.8%, nano-inorganic particles 0.3%, silane coupling agent 0.5%~1.0%, curing agent 0.2%~0.8%, thickener 0.2%~0.5%, and the remainder being water. The above percentages are mass fractions of the coating liquid.

3. The PET base film according to claim 2, characterized in that: The waterborne polyurethane is one of aliphatic waterborne polyurethane, aromatic waterborne polyurethane, araliphatic waterborne polyurethane, and alicyclic waterborne polyurethane.

4. The PET base film according to claim 3, characterized in that: The waterborne polyurethane is an alicyclic waterborne polyurethane with a number-average molecular weight of 30,000 g / mol and a PDI of 1.85; the waterborne polyurethane is synthesized from polyester polyol and dicyclohexylmethane diisocyanate; the polyester polyol is synthesized from ethylene glycol and phthalic anhydride with a number-average molecular weight of 500 g / mol.

5. The PET base film according to claim 2, characterized in that: The water-based acrylic resin in the primer liquid used for non-topcoat layers is Japanese POLYSOL AP-4690 water-based polyurethane.

6. The PET base film according to claim 2, characterized in that: The nano-inorganic particles in the double-sided coating primer are one or a mixture of two of nano-silica and nano-calcium carbonate; the silane coupling agent is one of aminosilane, epoxysilane, mercaptosilane, methacryloxysilane, and isocyanate-based silane; the curing agent is one of melamine, isocyanate, and carbodiimide; and the thickener is 7610 produced by BYK.

7. The PET base film according to claim 2, characterized in that: The nano-inorganic particles are a mixture of nano-silica and nano-calcium carbonate in a weight ratio of 1:

1. The nanoparticles are spherical and regular, with a particle size of 50-100 nm.

8. The PET base film according to claim 1, characterized in that: The substrate layer has an ABA three-layer structure, wherein the A layer resin contains inorganic particles, the B layer is pure PET resin, and the thickness ratio of the ABA three layers is 1:15:

1.

9. An application of the PET base film as described in any one of claims 1-8, characterized in that: The PET base film is used as the base film for the polyester aluminum film. A 40nm thick aluminum oxide layer or aluminum layer is deposited on the surface coating to form a polyester aluminum film for food packaging.

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