PET (Polyethylene Terephthalate) base film and application thereof

Abstract

The PET base film comprises a base material layer, a use surface coating and a non-use surface coating, the two sides of the base material layer are coated with the use surface coating and the non-use surface coating respectively, the coating thickness of the use surface coating and the non-use surface coating 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 used surface coating is 85-95 degrees, the water contact angle of the non-used surface coating is 83-91 degrees, the water contact angle of the used surface coating is larger than the water contact angle of the non-used surface coating, the surface free energy of the used surface coating is 35-41 mN / m, and the surface free energy of the non-used surface coating is 36-46 mN / m. The waterborne polyurethane modified acrylic resin emulsion is coated on the PET base material, shows good adhesive force with an aluminum-plated layer and an aluminum oxide-plated layer, and is suitable for food packaging.

Description

Technical Field

[0001] The invention relates to a PET base film, in particular to a PET base film for a polyester aluminum film. Background Art

[0002] In daily life, we often see all kinds of food packaging bags, which generally have high barrier properties, water and oxygen barrier, thus extending the shelf life of food. With the enhancement of people's awareness of environmental protection and life safety, the requirements for food packaging films are getting higher and higher. Low-VOC base film is the main development trend at present. In the past, the market was basically used for food packaging. Pure aluminum film, but aluminum film is not tough enough, so it needs to be particularly cautious when packaging food. At present, the market has developed a film to replace aluminum film, such as CPP and PET substrate for aluminum plating or aluminum oxide. Among them, PET is a semi-crystalline material with excellent high temperature resistance and water barrier properties.

[0003] Considering cost, environmental protection and safety, the coating of PET base film is generally applied online, and the coating used is generally a water-based coating. At present, there is little research on the formulation of coating for polyester aluminum film PET. If the aluminum layer falls off or produces harmful substances when the polyester aluminum film is used to package food, it will affect food safety. Summary of the invention

[0004] The present invention overcomes the drawbacks of the prior art and provides a PET base film, wherein the waterborne polyurethane modified acrylic resin emulsion is coated on the PET substrate layer, has good adhesion to the aluminum-plated layer and the aluminum oxide-plated layer, and is suitable for food packaging.

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

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

[0007] The above-mentioned PET base film, the primer liquid of the top coating is a water-based polyurethane modified acrylic resin system, the solid content of which is 6%, including the following components in mass percentage: 3.75%-4.8% of water-based polyurethane modified water-based acrylic resin, 0.3% of nano inorganic particles, 0.5%-1.0% of silane coupling agent, 0.2%-0.8% of curing agent, 0.2%-0.5% of thickener, and the rest is water. The above percentages are the mass fractions of the weight of the coating liquid, wherein the water-based polyurethane modified water The weight ratio of the waterborne polyurethane resin to the waterborne acrylic resin in the waterborne acrylic resin is 1:9; the primer liquid for the non-top coating is a waterborne acrylic resin system with a solid content of 6%, including the following components in mass percentage: 3.85%-4.8% of waterborne acrylic resin, 0.3% of nano inorganic particles, 0.5%-1.0% of silane coupling agent, 0.2%-0.8% of curing agent, 0.2%-0.5% of thickener, and the rest is water. The above percentages are mass fractions of the weight of the coating liquid.

[0008] In the above-mentioned PET base film, the waterborne polyurethane is one of aliphatic waterborne polyurethane, aromatic waterborne polyurethane, aromatic aliphatic waterborne polyurethane and alicyclic waterborne polyurethane.

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

[0010] For the above-mentioned PET base film, the water-based acrylic resin in the primer solution of the top coating layer is a hydroxy acrylic resin, specifically selected from FS-2050 water-based hydroxy acrylic resin.

[0011] For the above-mentioned PET base film, the water-based acrylic resin in the primer solution of the non-top coating layer is Japanese POLYSOLAP-4690 water-based polyurethane.

[0012] For the above-mentioned PET base film, the nano inorganic particles in the double-sided coating primer are one of nano silicon dioxide and nano calcium carbonate or a mixture of the two; the silane coupling agent is one of aminosilane, epoxysilane, mercaptosilane, methacryloxysilane and isocyanate silane, the silane coupling agent in the top coating is preferably isocyanate silane coupling agent KH901, and the silane coupling agent in the non-top coating is preferably epoxy silane coupling agent KH570; the curing agent is one of melamine, isocyanate and carbodiimide; the thickener is 7610 produced by BYK.

[0013] In the above-mentioned PET base film, the nano inorganic particles are a mixture of nano silicon dioxide and nano calcium carbonate, with a weight ratio of 1:1, and the nano particles are spherical regular particles with a particle size of 50-100nm.

[0014] The above-mentioned PET base film, the substrate layer is 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] The invention discloses an application of a PET base film, wherein the PET base film is used as a base film of a polyester aluminum film, and a 40nm thick aluminum oxide layer or aluminum layer is plated on the surface coating to form a polyester aluminum film for food packaging.

[0016] The beneficial effects of the present invention are:

[0017] The surface coating of the base film of the present invention adopts water-based polyurethane modified acrylic emulsion, the water-based polyurethane is alicyclic water-based polyurethane, which is an uncapped polyurethane and can be used for PET substrates. The coating has good adhesion with the aluminum-plated layer or the aluminum oxide-plated layer, does not fall off after high-temperature boiling, and has good surface coating after wiping with ethyl acetate, which is suitable for food packaging. The coating formula of the present invention is suitable for online coating, which reduces costs. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0019] In the figure, 1. Base material layer, which is an ABA three-layer structure; 2. Use of top coating; 3. No top coating. DETAILED DESCRIPTION

[0020] The primer of the top coating used in the present invention is water-based polyurethane modified water-based acrylic resin, and the addition ratio of water-based polyurethane to water-based acrylic resin is limited to 1:9. Water-based polyurethane modified water-based acrylic resin can improve the mechanical properties of the coating and prevent the coating from breaking due to insufficient toughness during the use of the polyester aluminum film. The ratio of the two needs to be strictly controlled, because if the amount of water-based polyurethane added is too much, the water resistance will deteriorate due to the ester group contained in the polyurethane; if the amount of polyurethane added is too little, the mechanical properties of the acrylic resin cannot be improved.

[0021] The waterborne polyurethane of the present invention is preferably an alicyclic waterborne polyurethane, specifically an uncapped polyurethane, which is synthesized from polyester polyol and dicyclohexylmethane diisocyanate, and the polyester polyol is synthesized from ethylene glycol and phthalic anhydride, and its number average molecular weight is 500g / mol. The alicyclic waterborne polyurethane does not contain a benzene ring, which is easily oxidized, and the alicyclic does not contain a double bond or a benzene ring, so it is resistant to aging and yellowing; and it contains a non-benzene ring cyclic structure, the non-polar part is improved, and the resistance to polar solvents is improved. The uncapped alicyclic waterborne polyurethane is selected to modify the acrylic resin, and the uncapped isocyanate (-NCO) of the alicyclic waterborne polyurethane reacts with the hydroxyl (-OH) in the waterborne acrylic resin, and a large number of hydrogen bonds are formed between the molecules of the two, and a network structure is formed between the molecules, and the structure is dense, which can prevent water from entering.

[0022] In addition, the surface free energy of the top coating used in the present invention is 35-41 mN / m, the surface free energy of the non-top coating is 36-46 mN / m, the surface free energy of the PET film is 38-40 mN / m, the surface tension of the coating is highly consistent with PET, and the adhesion is good.

[0023] The coating of the present invention adds a silane coupling agent in an amount of 0.5-1%, thereby adjusting the water contact angle of the coating surface to 85-95 degrees.

[0024] Nano inorganic particles are added to the primer of the two layers of coating of the present invention, which play an anti-sticking role and can enhance the wear resistance of the coating. The addition amount of inorganic particles is 0.3%. Too little inorganic particles will not play an anti-sticking role and affect the winding. Too much inorganic particles will lead to too large surface roughness, which will reduce the water barrier performance of the film. The surface roughness of the used surface coating and the non-used surface coating of the PET base film of the present invention is 0.03-0.05 μm.

[0025] The primer of the two-layer coating of the present invention also contains a curing agent and a thickener. The curing agent is selected from one of melamine, isocyanate and carbodiimide, preferably carbodiimide, and the addition amount is 0.2-0.8%; the proportion of the coating curing agent cannot be too low, which will affect the film drying speed. When the film is subjected to horizontal stretching heat treatment, the curing is not complete and the coating surface will be sticky; if the content of the coating curing agent is too high, the coating cross-linking speed is too fast, and it is easy to form gel particles, crystal point magazines and other defects on the film surface.

[0026] The pH value of the coating needs to be maintained at around 8.5 and needs to be adjusted by adding ammonia water. Ammonia water will evaporate after horizontal heat treatment and is therefore not included in the solid content of the primer liquid.

[0027] The substrate layer of the present invention is an ABA three-layer structure, the B layer is a substrate resin layer, polyethylene terephthalate (PET) is selected, the polyester of the A layer is added with inorganic particles of silicon dioxide, the shape is an irregular sphere, the particle size distribution is 2-4 μm, the silicon dioxide is specifically selected from the silicon dioxide masterbatch FG610 produced by Sinopec, and the amount thereof accounts for 50% of the weight of the A layer. The thickness ratio of the three layers of the substrate layer ABA is 1:15:1.

[0028] The preparation method of the PET base film of the present invention comprises the following steps:

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

[0030] (2) Stretching to form a film: The cast sheet obtained in step (1) is first longitudinally stretched 3.5 times, cooled and corona treated, and then introduced into a coating roller via a guide roller, and coated online with a primer liquid for a top coating layer and a primer liquid for a non-top coating layer, the thickness of both coatings being 40 to 50 nm. After being transversely stretched 3.6 times and heat-set, it is rolled up and slit to obtain a PET base film with a total thickness of 10 to 23 μm.

[0031] (3) The finished base film obtained by online coating is used in downstream applications, and a 40nm aluminum oxide or aluminum layer is plated on the top coating to obtain a polyester aluminum film.

[0032] The present invention will be further described below in conjunction with the embodiments.

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

[0034] Example 1

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

[0036] Example 2

[0037] As provided in Example 1, the base film for high barrier polyester aluminum film, wherein:

[0038] The polyester aluminum film base film has a topcoat solid content of 6%, wherein the weight ratio of waterborne polyurethane resin to waterborne acrylic resin is 1:9, the addition amount is 4.7%, and the thickener is 0.3%; the non-topcoat solid content of the base film is 6%, wherein the waterborne acrylic resin content is 4.7%, and the thickener is 0.3%; the addition amounts of the remaining components are consistent with those in Example 1. The film prepared by the above formula has a thickness of 12 μm, and the relevant properties are shown in Tables 1 and 2.

[0039] Example 3

[0040] As provided in Example 1, the base film for high barrier polyester aluminum film, wherein:

[0041] The polyester aluminum film base film has a topcoat solid content of 6%, wherein the weight ratio of waterborne polyurethane resin to waterborne acrylic resin is 1:9, the addition amount is 4.6%, and the thickener is 0.4%; the non-topcoat solid content of the base film is 6%, wherein the waterborne acrylic resin content is 4.6%, and the thickener is 0.4%; the addition amounts of the remaining components are consistent with those in Example 1. The film thickness prepared by the above formula is 12 μm, and the relevant properties are shown in Tables 1 and 2.

[0042] Example 4

[0043] As provided in Example 1, the base film for high barrier polyester aluminum film, wherein:

[0044] The polyester aluminum film base film has a topcoat solid content of 6%, wherein the weight ratio of waterborne polyurethane resin to waterborne acrylic resin is 1:9, the addition amount is 4.5%, and the thickener is 0.5%; the non-topcoat solid content of the base film is 6%, wherein the waterborne acrylic resin content is 4.5%, and the thickener is 0.5%; the addition amounts of the remaining components are consistent with those in Example 1. The film thickness prepared by the above formula is 12 μm, and the relevant properties are shown in Tables 1 and 2.

[0045] Example 5

[0046] As provided in Example 1, the base film for high barrier polyester aluminum film, wherein:

[0047] The polyester aluminum film base film has a topcoat solid content of 6%, wherein the weight ratio of waterborne polyurethane resin to waterborne acrylic resin is 1:9, the addition amount is 4.35%, the curing agent is 0.2%, the thickener is 0.4%, the silane coupling agent is 0.75%, and the inorganic particles are 0.3%, and the above percentages are the mass fractions of the weight of the coating liquid; the non-topcoat solid content of the base film is 6%, wherein the waterborne acrylic resin content is 4.45%, the curing agent is 0.2%, the thickener is 0.3%, the silane coupling agent is 0.75%, and the inorganic particles are 0.3%, and the above percentages are the mass fractions of the weight of the coating liquid; the base material layer formula of the base film is consistent with that of Example 1. The film thickness prepared by the above formula is 12 μm, and the relevant properties are shown in Tables 1 and 2.

[0048] Example 6

[0049] As provided in Example 5, the base film for high barrier polyester aluminum film, wherein:

[0050] The polyester aluminum film base film has a topcoat solid content of 6%, wherein the weight ratio of waterborne polyurethane resin to waterborne acrylic resin is 1:9, the addition amount is 4.10%, and the silane coupling agent is 1.0%; the non-topcoat solid content of the base film is 6%, wherein the waterborne acrylic resin content is 4.20%, and the silane coupling agent is 1.0%; the addition amounts of the remaining components are consistent with those in Example 5. The film prepared by the above formula has a thickness of 12 μm, and the relevant properties are shown in Tables 1 and 2.

[0051] Example 7

[0052] As provided in Example 5, the base film for high barrier polyester aluminum film, wherein:

[0053] The polyester aluminum film base film has a solid content of 6% on the surface coating, 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 surface solid content of the base film is 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 consistent with those in Example 5. The film prepared by the above formula has a thickness of 12 μm, and the relevant properties are shown in Tables 1 and 2.

[0054] Example 8

[0055] As provided in Example 5, the base film for high barrier polyester aluminum film, wherein:

[0056] The polyester aluminum film base film has a topcoat 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-topcoat solid content of the base film is 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 consistent with those in Example 5. The film thickness prepared by the above formula is 12 μm, and the relevant properties are shown in Tables 1 and 2.

[0057] Example 9

[0058] As provided in Example 5, the base film for high barrier polyester aluminum film, wherein:

[0059] The polyester aluminum film base film has a topcoat 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-topcoat solid content of the base film is 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 consistent with those in Example 5. The film prepared by the above formula has a thickness of 12 μm, and the relevant properties are shown in Tables 1 and 2.

[0060] Comparative Example 1

[0061] As provided in Example 4, the base film for high barrier polyester aluminum film, wherein:

[0062] The polyester aluminum film base film has a topcoat solid content of 6%, wherein the coating formula does not contain waterborne polyurethane, the waterborne acrylic resin content is 4.5%, and the contents of the remaining components are consistent with those in Example 4. The film thickness prepared by the above formula 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 the present invention is tested according to the following method:

[0064] Roughness Sa: A KEYENCE VX-160K 3D laser microscope with a magnification of 1000 times was used for testing. Five points were averaged for each film, and the average value was taken as the surface roughness and recorded as Sa.

[0065] Contact angle & surface free energy calculation: Krüperz DSA-25 instrument was used for testing. Five points were taken for water drop angle test on each membrane, and the average value was the water contact angle. The calculation of surface free energy required the use of two solutions, polar solvent and non-polar solvent, to test the contact angle of the membrane surface. Water was selected as the polar solvent and diiodomethane was selected as the non-polar solvent. Five points were tested on each membrane, and then the surface free energy was calculated according to the OWRK model and the data was recorded.

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

[0067] Grid test: According to ISO 2409 standard, the film is placed on smooth marble, a grid pattern is cut on the coating with a grid knife, 3M-610 tape is stuck on the cut and pulled apart, and the film is placed under a 3D laser microscope to observe the coating peeling at 200 times. 5B is defined as no peeling at the edge of the cross grid cut; 4B is defined as small pieces peeling at the intersection of the cut, and the actual damage of the grid area does not exceed 5%; 3B is defined as peeling at the edge and / or intersection of the cut, and the area is greater than 5% but less than 15%; 2B is defined as partial peeling or whole peeling at the edge of the cut, and / or some grids are peeled off in whole, and the peeled area is greater than 15% but less than 35%; 1B is defined as large pieces of peeling at the edge of the cut and / or some squares are partially or completely peeled off, and the area is greater than 35% of the grid area but not more than 65%.

[0068] The adhesion test of the aluminum coating or aluminum oxide coating is the same as the test of the base film.

[0069] Double ethyl acetate resistance: Wet the dust-free cloth with ethyl acetate, wipe the front and back coatings back and forth 30 times, and observe the coating shedding. If the coating shedding, it is considered a defective product, NG; if the coating does not shear off, it is a good product, OK.

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

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

[0072]

[0073]

[0074] Table 2 Performance test results of polyester aluminum films provided by Examples 1-9 and Comparative Example 1

[0075]

[0076]

[0077] It can be seen from Table 1 and Table 2 that the waterborne acrylic resin coating modified by waterborne polyurethane has good comprehensive performance; the coating modified by waterborne polyurethane is not added to the surface of the comparative example 1, and a small part of the coating surface is observed to fall off in the 100-grid experiment. In Examples 1-9, the shorter the curing time, the better from the perspective of energy saving cost. Example 9 shows the shortest curing time, but the short curing time means that the production line speed is too fast, so the formula of Examples 1-9 needs to be matched according to the actual speed of the production line in the production line.

[0078] The above is only a preferred embodiment of the present invention and is not intended to limit the protection scope of the present invention. All equivalent changes and modifications made according to the content of the present invention are included in the patent scope of the present invention.

Claims

1. A PET base film, characterized in that: The base film comprises a substrate layer (1), a usable surface coating (2) and a non-usable surface coating (3) respectively coated on both sides of the substrate layer, the coating thickness of the usable surface coating (2) and the non-usable surface coating (3) are both 40-50 nm, the coating refractive index is both 1.40-1.50, and the surface roughness is both 0.03-0.05 μm; the water contact angle of the usable surface coating is 85-95°, and the water contact angle of the non-usable surface coating is 83-91°, the water contact angle of the usable surface coating is greater than the water contact angle of the non-usable surface coating, the surface free energy of the usable surface coating is 35-41 mN / m, and the surface free energy of the non-usable surface coating is 36-46 mN / m.

2. The PET base film according to claim 1, characterized in that: The primer of the topcoat is a waterborne polyurethane modified acrylic resin system, with a solid content of 6%, including the following components in percentage by mass: 3.75% to 4.8% of waterborne polyurethane modified waterborne acrylic resin, 0.3% of nano inorganic particles, 0.5% to 1.0% of silane coupling agent, 0.2% to 0.8% of curing agent, 0.2% to 0.5% of thickener, and the rest is water. The above percentages are the mass fractions of the weight of the coating liquid, wherein the waterborne polyurethane modified waterborne acrylic resin is 3.75% to 4.8%, the nano inorganic particles are 0.3%, the silane coupling agent is 0.5% to 1.0%, the curing agent is 0.2% to 0.8%, the thickener is 0.2% to 0.5%, and the rest is water. The weight ratio of waterborne polyurethane resin to waterborne acrylic resin in the resin is 1:9; the primer solution for the non-topcoat layer is a waterborne acrylic resin system with a solid content of 6%, including the following components in percentage by mass: 3.85% to 4.8% waterborne acrylic resin, 0.3% nano inorganic particles, 0.5% to 1.0% silane coupling agent, 0.2% to 0.8% curing agent, 0.2% to 0.5% thickener, and the rest is water, and the above percentages are the mass fractions of the weight of the coating solution.

3. The PET base film according to claim 2, characterized in that: The waterborne polyurethane is one of aliphatic waterborne polyurethane, aromatic waterborne polyurethane, aromatic aliphatic 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 solution of the top coating layer is a hydroxy acrylic resin.

6. The PET base film according to claim 2, characterized in that: The water-based acrylic resin in the primer solution for the non-top coating is Japanese POLYSOL AP-4690 water-based polyurethane.

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

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

1. The nano particles are spherical regular particles with a particle size of 50-100nm.

9. The PET base film according to claim 1, characterized in that: The substrate layer is 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.

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

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