Scratch-resistant ethylene-vinyl acetate copolymer composite film and method of making same

Abstract

The embodiment of the present application provides a kind of scratch-resistant ethylene-vinyl acetate copolymer composite film and its preparation method, composite film includes sequentially stacked substrate layer, connecting layer and polyurethane scratch-resistant layer;The thickness of composite film is 0.05-0.80mm;The thickness of connecting layer accounts for 5-25% of the total thickness of composite film;The thickness of polyurethane scratch-resistant layer accounts for 10-30% of the total thickness of composite film;Substrate layer is ethylene-vinyl acetate copolymer film layer, ethylene-vinyl acetate copolymer film layer is composed of one or more ethylene-vinyl acetate copolymer resin mixture, the mass fraction range of vinyl acetate of ethylene-vinyl acetate copolymer resin is 10-40%.A kind of composite film is disclosed, the tightness of connection between film layers is improved by setting connecting layer, the high scratch resistance of composite film is improved by setting polyurethane scratch-resistant layer, while ensuring that composite film has high transparency, can solve the technical problems existing in the EVA film in the existing packaging material.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high molecular functional film materials, and particularly relates to a scratch-resistant ethylene-vinyl acetate copolymer composite film and a preparation method thereof. BACKGROUND

[0002] Ethylene-vinyl acetate copolymer (EVA) is an environmentally friendly thermoplastic material, which has the advantages of clear and transparent appearance, soft hand feeling, good flexibility, low temperature resistance, colorless and odorless, good heat sealing property, and is suitable for use as high-grade packaging material. However, EVA itself is not scratch-resistant and is easy to form surface scratches under external force, which is more obvious for transparent EVA film. These scratches affect the appearance and aesthetics of the EVA film, thereby limiting its application in the packaging industry.

[0003] There are many ways to improve the scratch resistance of EVA, and blending modification is one of them. For example, patent CN110387078A discloses a high-strength scratch-resistant polymer EVA protective film and a production process thereof, which uses EVA with a VA content of 9%-15% and PP and ACR resin to blend the film to achieve the purpose. The technical solution needs to use low-VA-content EVA as raw material, which will cause the softness of the product to decrease; in addition, the introduction of PP and ACR resin will inevitably affect the transparency of EVA, and therefore is not suitable for transparent EVA packaging material. Patent CN111662495B adopts a technical solution of adding modified silicone and erucic amide lubricant to EVA, and a lubricating layer is formed on the surface of EVA by the migration and precipitation of the lubricant, which reduces the friction coefficient and improves the scratch resistance. However, the silicone lubricating layer on the surface of EVA will affect the printing of packaging labels or patterns, and in addition, experiments show that the introduction of silicone will significantly increase the haze of EVA film, and this solution is also not suitable for EVA film for packaging.

[0004] Surface treatment is a means that can change the properties of the surface of a material, and in theory, it is also effective for improving the scratch resistance of EVA. For example, the technical solution disclosed in patent CN111593574A is to coat a layer of polyurethane slurry on the surface of EVA to achieve the purpose. Due to the large difference in structure and properties between polyurethane and EVA, they are not compatible, and the adhesion is insufficient when directly coated, and the coating layer is easy to fall off. Therefore, an additional surface grafting treatment agent needs to be coated between polyurethane and EVA in the above technical solution to improve the bonding force between them. This solution needs to be coated twice, which is low in production efficiency; in addition, the surface grafting treatment agent needs to be heated for pre-crosslinking, which is easy to cause shrinkage / deformation of the EVA film at high temperature. Obviously, this solution also fails to solve the problems in the prior art. SUMMARY

[0005] This invention provides a scratch-resistant ethylene-vinyl acetate copolymer composite film and its preparation method, aiming to solve the problem that existing methods cannot simultaneously achieve high scratch resistance and high transparency in the film.

[0006] In a first aspect, embodiments of the present invention provide a scratch-resistant ethylene-vinyl acetate copolymer composite film, wherein the composite film comprises a substrate layer, a connecting layer, and a polyurethane scratch-resistant layer stacked sequentially;

[0007] The thickness of the composite film is 0.05-0.80 mm; the thickness of the connecting layer accounts for 5-25% of the total thickness of the composite film; the thickness of the polyurethane scratch-resistant layer accounts for 10-30% of the total thickness of the composite film.

[0008] The substrate layer is an ethylene-vinyl acetate copolymer film layer, which is composed of one or more ethylene-vinyl acetate copolymer resins, wherein the mass fraction of vinyl acetate in the ethylene-vinyl acetate copolymer resin ranges from 10% to 40%.

[0009] The scratch-resistant ethylene-vinyl acetate copolymer composite film, wherein the connecting layer is an ethylene-acrylic acid copolymer film layer;

[0010] The ethylene-acrylic acid copolymer film is made of a mixture of one or more ethylene-acrylic acid copolymer resins; or the ethylene-acrylic acid copolymer film is made of a mixture of one or more ethylene-methacrylic acid copolymer resins.

[0011] The scratch-resistant ethylene-vinyl acetate copolymer composite film, wherein the ethylene-acrylic acid copolymer resin has an acrylic acid mass fraction ranging from 5-25%; and the ethylene-methacrylic acid copolymer resin has a methacrylic acid mass fraction ranging from 5-25%.

[0012] The scratch-resistant ethylene-vinyl acetate copolymer composite film, wherein the melt index of the ethylene-vinyl acetate copolymer resin, the ethylene-acrylic acid copolymer resin and the ethylene-methacrylic acid copolymer resin are all in the range of 1-30 g / 10 min under the conditions of 190°C and 2.16 kg.

[0013] The scratch-resistant ethylene-vinyl acetate copolymer composite film, wherein the polyurethane scratch-resistant layer is obtained by mixing an aqueous polyurethane dispersion, a film-forming agent, an antifoaming agent and a crosslinking agent in a mass ratio of 100:2-8:0.1-1:4-12.

[0014] The scratch-resistant ethylene-vinyl acetate copolymer composite film, wherein the film-forming agent is obtained by one or more combinations of ethylene glycol methyl ether, ethylene glycol butyl ether, diethylene glycol methyl ether, diethylene glycol butyl ether, and propylene glycol methyl ether; the defoamer is an organosilicon defoamer; and the crosslinking agent is obtained by one or more combinations of trimethylolpropane-tris[3-(2-methylaziridinyl)]propionate, trimethylolpropane-tris(3-aziridinyl)propionate, and pentaerythritol tris(3-aziridinyl)propionate.

[0015] The scratch-resistant ethylene-vinyl acetate copolymer composite film, wherein the aqueous polyurethane dispersion is polymerized from the following monomers: 60-80 parts of polydiol, 30-50 parts of hydroxyl-terminated polysiloxane, 20-40 parts of self-emulsifying monomer, 40-60 parts of aliphatic diisocyanate, and 0.1-0.5 parts of catalyst;

[0016] The method for preparing the aqueous polyurethane dispersion is as follows:

[0017] The polydiol, hydroxyl-terminated polysiloxane and self-emulsifying monomer in the above proportions are mixed and placed in a reaction vessel, and dehydrated under vacuum at 100-120℃ for 0.5-1h.

[0018] Then cool down to 60-80℃, add acetone, and add catalyst in the above proportions.

[0019] Aliphatic diisocyanate was slowly added dropwise through a constant pressure funnel under nitrogen protection, and the reaction was carried out for 2-4 hours.

[0020] After the reaction is complete, triethylamine is added for neutralization, and the temperature is lowered to 30-45°C. Deionized water is added and the mixture is rapidly stirred and emulsified for 0.5-1 h. Acetone is then evaporated under reduced pressure to obtain the aqueous polyurethane dispersion.

[0021] The scratch-resistant ethylene-vinyl acetate copolymer composite film, wherein the molecular weight of the polydiol is 500-4000 g / mol, and the molecular weight of the hydroxyl-terminated polysiloxane is 5000-30000 g / mol.

[0022] The scratch-resistant ethylene-vinyl acetate copolymer composite film, wherein the polydiol is obtained from one or more combinations of polyethylene glycol, polypropylene glycol, polytetrahydrofuran ether glycol, polycarbonate glycol, polyethylene adipate glycol, polyethylene adipate glycol, polyethylene terephthalate glycol, polybutylene terephthalate glycol, and polyethylene terephthalate glycol.

[0023] The self-emulsifying monomer is obtained from one or more combinations of dimethylolpropionic acid, dimethylolbutyric acid, and sodium 1,2-dihydroxy-3-propanesulfonate.

[0024] The aliphatic diisocyanate is obtained from one or more combinations of hexamethylene diisocyanate, isoflurone diisocyanate, dicyclohexylmethane diisocyanate, and pentamethylene diisocyanate;

[0025] The catalyst is dibutyltin dilaurate and / or stannous octoate.

[0026] Secondly, embodiments of the present invention also provide a method for preparing a scratch-resistant ethylene-vinyl acetate copolymer composite film, the method being used to prepare the scratch-resistant ethylene-vinyl acetate copolymer composite film as described in the first aspect above, the method comprising:

[0027] S1: The raw materials for the substrate layer and the connecting layer are fed into different channels of the double-layer melt co-extrusion casting equipment for co-extrusion casting to obtain a double-layer composite film in one step, which is then cooled and wound up for later use; the thickness of each layer in the obtained double-layer composite film is adjusted by controlling the feeding speed of the two materials; the casting and melting temperature of the double-layer melt co-extrusion casting equipment is set to 100-220℃, and the cooling temperature is set to 0-10℃;

[0028] S2: The raw materials for the polyurethane scratch-resistant layer are dispersed in a mixed solution of deionized water and ethanol to prepare an aqueous polyurethane coating liquid with a solid content of 25-35%, wherein the weight ratio of deionized water to ethanol in the mixed solution is 3:1; the aqueous polyurethane coating liquid is applied to the surface of the connecting layer of the double-layer composite film obtained in S1 using a coating equipment, and the thickness of the polyurethane scratch-resistant layer is controlled by the coating line speed; the coating film is dried with hot air at 60-80℃ to remove the solvent, and then cured at 45-55℃ for 48-72 hours to obtain the scratch-resistant ethylene-vinyl acetate copolymer composite film.

[0029] This invention provides a scratch-resistant ethylene-vinyl acetate copolymer composite film and its preparation method. The composite film includes a substrate layer, a connecting layer, and a polyurethane scratch-resistant layer stacked sequentially. The thickness of the composite film is 0.05-0.80 mm. The thickness of the connecting layer accounts for 5-25% of the total thickness of the composite film. The thickness of the polyurethane scratch-resistant layer accounts for 10-30% of the total thickness of the composite film. The substrate layer is an ethylene-vinyl acetate copolymer film layer, which is composed of one or more ethylene-vinyl acetate copolymer resins, with the vinyl acetate mass fraction of the ethylene-vinyl acetate copolymer resin ranging from 10-40%. The polyurethane scratch-resistant layer is a polyurethane scratch-resistant layer. This invention discloses a composite film that improves the tightness of the connection between film layers by setting a connecting layer and improves the high scratch resistance of the composite film by setting a polyurethane scratch-resistant layer. At the same time, the composite film has high transparency, which can solve the technical problems existing in EVA films in existing packaging materials, and has high production efficiency, adapting to existing mainstream production methods. Attached Figure Description

[0030] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 This is a schematic cross-sectional view of the scratch-resistant ethylene-vinyl acetate copolymer composite film provided in an embodiment of the present invention.

[0032] Figure 2 A flowchart illustrating the method for preparing a scratch-resistant ethylene-vinyl acetate copolymer composite film according to an embodiment of the present invention;

[0033] Figure 3 This is a cross-sectional view of the scratch-resistant ethylene-vinyl acetate copolymer composite film provided in Embodiment 1 of the present invention.

[0034] Reference numerals: 1. Substrate layer; 2. Connecting layer; 3. Polyurethane scratch-resistant layer. Detailed Implementation

[0035] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] It should be understood that, when used in this specification and the appended claims, the terms "comprising" and "including" indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0037] It should also be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0038] It should also be further understood that the term "and / or" as used in this specification and the appended claims refers to any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0039] Please seeFigure 1 , Figure 1 This is a cross-sectional structural diagram of the method for preparing the composite thin film provided in an embodiment of the present invention. Figure 1 As shown, the composite film includes a substrate layer 1, a connecting layer 2, and a polyurethane scratch-resistant layer 3, which are stacked sequentially. The thickness of the composite film is 0.05-0.80 mm. The thickness of the connecting layer 2 accounts for 5-25% of the total thickness of the composite film. The thickness of the polyurethane scratch-resistant layer 3 accounts for 10-30% of the total thickness of the composite film. The substrate layer 1 is an ethylene-vinyl acetate copolymer film layer, which is composed of one or more ethylene-vinyl acetate copolymer resins (hereinafter referred to as EVA resins), and the mass fraction of vinyl acetate in the ethylene-vinyl acetate copolymer resin ranges from 10-40%.

[0040] like Figure 1 As shown, the composite film has a three-layer structure, consisting of an EVA (ethylene-vinyl acetate copolymer) substrate layer, an EAA (ethylene-acrylic acid copolymer) binding layer, and a polyurethane scratch-resistant layer.

[0041] In a more specific embodiment, the connecting layer is an ethylene-acrylic acid copolymer film layer; the ethylene-acrylic acid copolymer film layer is composed of one or more ethylene-acrylic acid copolymer resins (hereinafter referred to as EAA resins); or the ethylene-acrylic acid copolymer film layer is composed of one or more ethylene-methacrylic acid copolymer resins (hereinafter referred to as EMAA resins).

[0042] Furthermore, the acrylic acid mass fraction of the ethylene-acrylic acid copolymer resin ranges from 5-25%; the methacrylic acid mass fraction of the ethylene-methacrylic acid copolymer resin ranges from 5-25%. Specifically, the melt index range of the ethylene-vinyl acetate copolymer resin, the ethylene-acrylic acid copolymer resin, and the ethylene-methacrylic acid copolymer resin at 190°C and 2.16 kg is 1-30 g / 10 min.

[0043] In a more specific embodiment, the polyurethane scratch-resistant layer is obtained by mixing an aqueous polyurethane dispersion, a film-forming agent, a defoamer, and a crosslinking agent in a mass ratio of 100:2-8:0.1-1:4-12. Specifically, the film-forming agent is obtained by one or more combinations of ethylene glycol methyl ether, ethylene glycol butyl ether, diethylene glycol methyl ether, diethylene glycol butyl ether, and propylene glycol methyl ether; the defoamer is an organosilicon defoamer; and the crosslinking agent is obtained by one or more combinations of trimethylolpropane-tris[3-(2-methylaziridinyl)]propionate, trimethylolpropane-tris(3-aziridinyl)propionate, and pentaerythritol tris(3-aziridinyl)propionate. The aqueous polyurethane dispersion is polymerized from the following monomers: 60-80 parts of polydiol, 30-50 parts of hydroxyl-terminated polysiloxane, 20-40 parts of self-emulsifying monomer, 40-60 parts of aliphatic diisocyanate, and 0.1-0.5 parts of catalyst.

[0044] More specifically, the preparation method of the waterborne polyurethane dispersion is as follows: Polydiol, hydroxyl-terminated polysiloxane, and self-emulsifying monomer are mixed in the above-mentioned proportions and placed in a reaction vessel. The mixture is then dehydrated under vacuum at 100-120°C for 0.5-1 h. Subsequently, the temperature is lowered to 60-80°C, acetone is added, and a catalyst is added simultaneously in the above-mentioned proportions. Aliphatic diisocyanate is slowly added dropwise through a constant-pressure funnel under nitrogen protection, and the reaction is carried out for 2-4 h. After the reaction is complete, triethylamine is added for neutralization, and the temperature is lowered to 30-45°C. Deionized water is added and rapidly stirred to emulsify for 0.5-1 h. The acetone is then evaporated under reduced pressure to obtain the waterborne polyurethane dispersion.

[0045] In a more specific embodiment, the molecular weight of the polydiol is 500-4000 g / mol, and the molecular weight of the hydroxyl-terminated polysiloxane is 5000-30000 g / mol. Furthermore, the polydiol is obtained from one or more combinations of polyethylene glycol, polypropylene glycol, polytetrahydrofuran ether glycol, polycarbonate glycol, polyethylene adipate glycol, polyethylene adipate glycol, polyethylene terephthalate glycol, polybutylene terephthalate glycol, and polyethylene terephthalate glycol; the self-emulsifying monomer is obtained from one or more combinations of dimethylolpropionic acid, dimethylolbutyric acid, and sodium 1,2-dihydroxy-3-propanesulfonate; the aliphatic diisocyanate is obtained from one or more combinations of hexamethylene diisocyanate, isoflurane diisocyanate, dicyclohexylmethane diisocyanate, and pentamethylene diisocyanate; and the catalyst is dibutyltin dilaurate and / or stannous octoate.

[0046] The total thickness of the composite film is 0.05-0.80 mm, preferably 0.10-0.60 mm. If the thickness of the composite film is too small, the overall strength of the film is too low, and it has no practical application value; if the thickness of the composite film is too large, its flexibility is affected, and it is not suitable for use as a packaging film material.

[0047] The substrate layer serves as the mechanical support and structural foundation of the composite film. It is composed of one or more EVA resins, which are the raw materials for the substrate layer. The melt flow index of the EVA resin ranges from 1 to 30 g / 10 min (190°C, 2.16 kg), preferably 5 to 20 g / 10 min; EVA resin within this range exhibits good processing performance and suitable mechanical strength. The vinyl acetate (VA) mass fraction of the EVA resin ranges from 10 to 40%, preferably 15 to 35%; EVA resin within this range exhibits good processing performance, softness, and transparency. The EVA resin can be in granular, powdered, or flake form, and can be manufactured using conventional and known techniques. Unless otherwise specified, it can be obtained from the market through general procurement channels.

[0048] The bonding layer serves to connect the substrate layer and the polyurethane scratch-resistant layer, improving the adhesion between them to prevent delamination. The thickness of the bonding layer accounts for 5-25% of the total thickness of the composite film. If the thickness is too thin, it will not provide the necessary bonding; if the thickness is too large, it will lead to unnecessary cost increases and affect processing performance. The bonding layer is composed of a mixture of one or more ethylene-acrylic acid copolymer (EAA) resins, or a mixture of one or more ethylene-methacrylic acid copolymer (EMAA) resins.

[0049] The melt flow index of EAA or EMAA resin ranges from 1 to 30 g / 10 min (190°C, 2.16 kg), preferably 5 to 20 g / 10 min. Resins within this range exhibit good processability and compatibility with EVA substrates. The mass fraction of acrylic acid in EAA resin ranges from 5 to 25%, preferably 8 to 20%; the mass fraction of methacrylic acid in EMAA resin ranges from 5 to 25%, preferably 8 to 20%. EAA (or EMAA) resins within this mass fraction range produce EAA bonding layers that exhibit good adhesion to both the substrate layer and the polyurethane scratch-resistant layer.

[0050] The function of the polyurethane scratch-resistant layer is to provide surface scratch resistance. The thickness of the polyurethane scratch-resistant layer accounts for 10-30% of the total thickness of the composite film. If the thickness is too thin, it cannot provide the corresponding scratch resistance; if the thickness is too thick, it will make the EVA film feel too hard and affect its softness. The polyurethane scratch-resistant layer is composed of the components shown in Table 1.

[0051] Table 1

[0052]

[0053] Furthermore, the aqueous polyurethane dispersion is polymerized from the following monomers: 60-80 parts of polydiol (molecular weight 500-4000 g / mol), 30-50 parts of hydroxyl-terminated polysiloxane (molecular weight 5000-30000 g / mol), 20-40 parts of self-emulsifying monomer, 40-60 parts of aliphatic diisocyanate, and 0.1-0.5 parts of catalyst. Specifically, the polydiol is selected from one or more of polyethylene glycol, polypropylene glycol, polytetrahydrofuran ether glycol, polycarbonate glycol, polyethylene adipate glycol, polyethylene adipate glycol, polyethylene terephthalate glycol, polybutylene terephthalate glycol, and polyethylene terephthalate glycol. Specifically, the self-emulsifying monomer is selected from one or more of dimethylolpropionic acid, dimethylolbutyric acid, and sodium 1,2-dihydroxy-3-propanesulfonate. The aliphatic diisocyanate is specifically selected from one or more of hexamethylene diisocyanate, isoflurane diisocyanate, dicyclohexylmethane diisocyanate, and pentamethylene diisocyanate. The catalyst is dibutyltin dilaurate and / or stannous octoate.

[0054] The aqueous polyurethane dispersion can be synthesized by the following method: A measured amount of polydiol, hydroxyl-terminated polysiloxane, and self-emulsifying monomer are mixed in a reaction vessel and dehydrated under vacuum at 100-120°C for 0.5-1 h. The temperature is then lowered to 60-80°C, and an appropriate amount of acetone is added to reduce viscosity, along with a measured amount of catalyst. Aliphatic diisocyanate is slowly added dropwise through a constant-pressure funnel under nitrogen protection, and the reaction is carried out for 2-4 h. After the reaction is complete, triethylamine is added for neutralization, and the temperature is lowered to 30-45°C. Deionized water is added, and the mixture is rapidly stirred and emulsified for 0.5-1 h. The acetone is then evaporated under reduced pressure to obtain the aqueous polyurethane dispersion.

[0055] Furthermore, the film-forming agent is specifically selected from one or more of ethylene glycol methyl ether, ethylene glycol butyl ether, diethylene glycol methyl ether, diethylene glycol butyl ether, and propylene glycol methyl ether. The defoamer is specifically selected from silicone defoamers. The crosslinking agent is a multifunctional aziridinium crosslinking agent, specifically selected from one or more of trimethylolpropane-tris[3-(2-methylaziridinyl)]propionate, trimethylolpropane-tris(3-aziridinyl)propionate, and pentaerythritol tris(3-aziridinyl)propionate.

[0056] This application also provides a method for preparing a scratch-resistant ethylene-vinyl acetate copolymer composite film, the method being used to prepare the scratch-resistant ethylene-vinyl acetate copolymer composite film described in the above embodiments. Figure 2 As shown, the method includes steps S1 and S2.

[0057] S1: The raw materials for the substrate layer and the connecting layer are fed into different channels of the double-layer melt co-extrusion casting equipment for co-extrusion casting to obtain a double-layer composite film in one step, which is then cooled and wound up for later use; the thickness of each layer in the obtained double-layer composite film is adjusted by controlling the feeding speed of the two materials; the casting and melting temperature of the double-layer melt co-extrusion casting equipment is set to 100-220℃, and the cooling temperature is set to 0-10℃.

[0058] Specifically, the raw materials for the EVA substrate layer and the EAA binder layer can be fed into different channels of a double-layer melt co-extrusion casting equipment for co-extrusion casting to obtain an EVA / EAA composite film in one step, which is then cooled and wound up for later use. The thickness of the composite film is controlled by adjusting the feeding speed of the two materials. Based on the material properties, the casting melting temperature is set to 100-220℃, and the cooling temperature is set to 0-10℃.

[0059] S2: The raw materials for the polyurethane scratch-resistant layer are dispersed in a mixed solution of deionized water and ethanol to prepare an aqueous polyurethane coating liquid with a solid content of 25-35%, wherein the weight ratio of deionized water to ethanol in the mixed solution is 3:1; the aqueous polyurethane coating liquid is applied to the surface of the connecting layer of the double-layer composite film obtained in S1 using a coating equipment, and the thickness of the polyurethane scratch-resistant layer is controlled by the coating line speed; the coating film is dried with hot air at 60-80℃ to remove the solvent, and then cured at 45-55℃ for 48-72 hours to obtain the scratch-resistant ethylene-vinyl acetate copolymer composite film.

[0060] Specifically, the raw materials for the polyurethane scratch-resistant layer are dispersed in a mixed solution of deionized water and ethanol (the weight ratio of deionized water to ethanol is 3:1) to prepare an aqueous polyurethane coating solution with a solid content of 25-35%. Using precision coating equipment, the above-mentioned aqueous polyurethane coating solution is applied to the EAA side of the EVA / EAA composite film obtained in S1, and the thickness of the polyurethane scratch-resistant layer is controlled by the coating line speed. The coated film is dried with hot air at 60-80℃ to remove the solvent, and then cured at 45-55℃ for 48-72 hours to obtain the scratch-resistant EVA composite film.

[0061] Compared with the prior art, the beneficial effects and specific progress brought about by this invention are reflected in:

[0062] 1. EVA and EAA / EMAA resins have good compatibility. EVA / EAA composite films with carboxyl functional groups on the surface can be obtained in one step through melt co-extrusion process, avoiding the need for secondary surface treatment in existing technologies. It has the characteristics of being green and environmentally friendly, having high production efficiency, and controllable cost.

[0063] 2. A polyurethane scratch-resistant layer is coated onto the surface of the composite film using water-based coating technology. This polyurethane scratch-resistant layer contains silicone resin, which helps improve surface hardness and smoothness. Simultaneously, a polyfunctional aziridine compound reacts with and crosslinks the carboxyl groups in the polyurethane (reaction formula shown below), further increasing the surface resin density and thus enhancing surface scratch resistance. The coating exhibits flexibility and high transparency, without affecting the overall feel and aesthetics of the film.

[0064]

[0065] 3. An aqueous polyurethane coating solution is applied to the EAA surface. During medium-to-high temperature drying and curing, the crosslinking agent reacts simultaneously with the carboxyl groups in both the polyurethane and EAA layers, bonding the polyurethane coating and the EAA layer through chemical bonds. Introducing the EAA connecting layer overcomes the poor compatibility between polyurethane and EVA, resulting in a transparent and flexible EVA composite film with excellent surface scratch resistance and interlayer adhesion. Furthermore, this preparation method is low-cost, highly efficient, and offers advantages such as good product performance and environmentally friendly processing.

[0066] The following comparison of multiple embodiments illustrates the specific implementation process and beneficial effects of the solution.

[0067] Example 1

[0068] A scratch-resistant EVA composite film has a three-layer structure, consisting of an EVA substrate layer, an EAA binder layer, and a polyurethane scratch-resistant layer in sequence. The EVA substrate layer uses EVA resin with a melt index of 8.0 g / 10 min (190°C, 2.16 kg) and a VA content of 18%. The EAA binder layer uses EAA resin with a melt index of 10.0 g / 10 min (190°C, 2.16 kg) and an acrylic acid content of 9.5%. The polyurethane scratch-resistant layer is composed of the components shown in Table 2.

[0069] Table 2

[0070]

[0071]

[0072] The scratch-resistant EVA composite film described in this embodiment is prepared by the following method:

[0073] Step 1: The raw materials for the EVA substrate layer and the EAA binder layer are fed into different channels of a two-layer melt co-extrusion casting equipment for co-extrusion casting to obtain an EVA / EAA composite film in one step. The film is then cooled and wound up for later use. The casting melt temperature is set to 190℃, and the cooling temperature is set to 4℃.

[0074] Step 2: Take 60 parts of polytetrahydrofuran ether diol (molecular weight 2000 g / mol), 40 parts of hydroxyl-terminated polysiloxane (molecular weight 8000 g / mol), 30 parts of dimethylolpropionic acid, 40 parts of isoflurane diisocyanate and 0.2 parts of dibutyltin dilaurate to synthesize the aqueous polyurethane dispersion of this embodiment.

[0075] Step 3: Disperse the raw materials of the polyurethane scratch-resistant layer in a mixed solution of deionized water and ethanol (weight ratio of deionized water to ethanol is 3:1) to prepare an aqueous polyurethane coating solution with a solid content of 30%. Apply the above aqueous polyurethane coating solution to the EAA side of the EVA / EAA composite film obtained in Step 1 using a precision coating device. Dry the coated film with hot air at 80°C to remove the solvent, and then cure it at 55°C for 72 hours to obtain the scratch-resistant EVA composite film of this embodiment.

[0076] According to the test, the total thickness of the scratch-resistant EVA film in this embodiment is 0.30 mm, of which the thickness of the EAA bonding layer is 0.054 mm and the thickness of the polyurethane scratch-resistant layer is 0.045 mm. Figure 3 This is a cross-sectional view of the scratch-resistant EVA film in this embodiment under an optical microscope.

[0077] Example 2

[0078] A scratch-resistant EVA composite film has a three-layer structure, consisting of an EVA substrate layer, an EAA binder layer, and a polyurethane scratch-resistant layer in sequence. The EVA substrate layer uses EVA resin with a melt index of 25.0 g / 10 min (190°C, 2.16 kg) and a VA content of 28%. The EAA binder layer uses EMAA resin with a melt index of 25.0 g / 10 min (190°C, 2.16 kg) and a methacrylic acid content of 15%. The polyurethane scratch-resistant layer is composed of the components shown in Table 3.

[0079] Table 3

[0080]

[0081]

[0082] The scratch-resistant EVA composite film described in this embodiment is prepared by the following method:

[0083] Step 1: The raw materials for the EVA substrate layer and the EAA binder layer are fed into different channels of a two-layer melt co-extrusion casting equipment for co-extrusion casting to obtain an EVA / EAA composite film in one step. The film is then cooled and wound up for later use. The casting melt temperature is set to 130℃, and the cooling temperature is set to 10℃.

[0084] Step 2: Take 30 parts of polypropylene glycol (molecular weight 2000 g / mol), 38 parts of polycarbonate glycol (molecular weight 1200 g / mol), 30 parts of hydroxyl-terminated polysiloxane (molecular weight 10000 g / mol), 20 parts of dimethylolbutyric acid, 50 parts of hexamethylene diisocyanate and 0.4 parts of dibutyltin dilaurate to synthesize the aqueous polyurethane dispersion of this embodiment.

[0085] Step 3: Disperse the raw materials for the polyurethane scratch-resistant layer in a mixed solution of deionized water and ethanol (weight ratio of deionized water to ethanol is 3:1) to prepare an aqueous polyurethane coating solution with a solid content of 25%. Apply the above aqueous polyurethane coating solution to the EAA side of the EVA / EAA composite film obtained in Step 1 using a precision coating device. Dry the coated film with hot air at 75°C to remove the solvent, and then cure it at 50°C for 55 hours to obtain the scratch-resistant EVA composite film of this embodiment.

[0086] According to the test, the total thickness of the scratch-resistant EVA film in this embodiment is 0.18 mm, of which the thickness of the EAA bonding layer is 0.010 mm and the thickness of the polyurethane scratch-resistant layer is 0.032 mm.

[0087] Example 3

[0088] A scratch-resistant EVA composite film has a three-layer structure, consisting of an EVA substrate layer, an EAA binder layer, and a polyurethane scratch-resistant layer in sequence. The EVA substrate layer uses EVA resin with a melt index of 19.0 g / 10 min (190°C, 2.16 kg) and a VA content of 25%. The EAA binder layer uses EAA resin with a melt index of 14.0 g / 10 min (190°C, 2.16 kg) and an acrylic acid content of 11%. The polyurethane scratch-resistant layer is composed of the components shown in Table 4.

[0089] Table 4

[0090]

[0091]

[0092] The scratch-resistant EVA composite film described in this embodiment is prepared by the following method:

[0093] Step 1: The raw materials for the EVA substrate layer and the EAA binder layer are fed into different channels of a two-layer melt co-extrusion casting equipment for co-extrusion casting to obtain an EVA / EAA composite film in one step. The film is then cooled and wound up for later use. The casting melt temperature is set to 150℃, and the cooling temperature is set to 2℃.

[0094] Step 2: Take 54 parts of polyethylene adipate diol (molecular weight 3800 g / mol), 45 parts of hydroxyl-terminated polysiloxane (molecular weight 25000 g / mol), 33 parts of sodium 1,2-dihydroxy-3-propanesulfonate, 55 parts of isoflurane diisocyanate and 0.2 parts of stannous octoate to synthesize the aqueous polyurethane dispersion of this embodiment.

[0095] Step 3: Disperse the raw materials for the polyurethane scratch-resistant layer in a mixed solution of deionized water and ethanol (weight ratio of deionized water to ethanol is 3:1) to prepare an aqueous polyurethane coating solution with a solid content of 35%. Apply the above aqueous polyurethane coating solution to the EAA side of the EVA / EAA composite film obtained in Step 1 using a precision coating device. Dry the coated film with hot air at 65°C to remove the solvent, and then cure it at 45°C for 70 hours to obtain the scratch-resistant EVA composite film of this embodiment.

[0096] According to the test, the total thickness of the scratch-resistant EVA film in this embodiment is 0.44 mm, of which the thickness of the EAA bonding layer is 0.085 mm and the thickness of the polyurethane scratch-resistant layer is 0.130 mm.

[0097] Example 4

[0098] A scratch-resistant EVA composite film has a three-layer structure, consisting of an EVA substrate layer, an EAA binder layer, and a polyurethane scratch-resistant layer in sequence. The EVA substrate layer uses EVA resin with a melt index of 18.0 g / 10 min (190°C, 2.16 kg) and a VA content of 34%. The EAA binder layer uses EMAA resin with a melt index of 6.0 g / 10 min (190°C, 2.16 kg) and a methacrylic acid content of 21.5%. The polyurethane scratch-resistant layer is composed of the components shown in Table 5.

[0099] Table 5

[0100]

[0101] The scratch-resistant EVA composite film described in this embodiment is prepared by the following method:

[0102] Step 1: The raw materials for the EVA substrate layer and the EAA binder layer are fed into different channels of a two-layer melt co-extrusion casting equipment for co-extrusion casting to obtain an EVA / EAA composite film in one step. The film is then cooled and wound up for later use. The casting melt temperature is set to 175℃, and the cooling temperature is set to 6℃.

[0103] Step 2: Take 46 parts of polyethylene glycol (molecular weight 800 g / mol), 30 parts of polybutylene terephthalate diol (molecular weight 500 g / mol), 44 parts of hydroxyl-terminated polysiloxane (molecular weight 6000 g / mol), 40 parts of dimethylolpropionic acid, 60 parts of dicyclohexylmethane diisocyanate and 0.1 parts of dibutyltin dilaurate to synthesize the aqueous polyurethane dispersion of this embodiment.

[0104] Step 3: Disperse the raw materials for the polyurethane scratch-resistant layer in a mixed solution of deionized water and ethanol (weight ratio of deionized water to ethanol is 3:1) to prepare an aqueous polyurethane coating solution with a solid content of 32%. Apply the above aqueous polyurethane coating solution to the EAA side of the EVA / EAA composite film obtained in Step 1 using a precision coating device. Dry the coated film with hot air at 60°C to remove the solvent, and then cure it at 55°C for 48 hours to obtain the scratch-resistant EVA composite film of this embodiment.

[0105] According to the test, the total thickness of the scratch-resistant EVA film in this embodiment is 0.24 mm, of which the thickness of the EAA bonding layer is 0.035 mm and the thickness of the polyurethane scratch-resistant layer is 0.035 mm.

[0106] Example 5

[0107] A scratch-resistant EVA composite film has a three-layer structure, consisting of an EVA substrate layer, an EAA binder layer, and a polyurethane scratch-resistant layer in sequence. The EVA substrate layer uses EVA resin with a melt index of 3.0 g / 10 min (190°C, 2.16 kg) and a VA content of 40%. The EAA binder layer uses EAA resin with a melt index of 14.0 g / 10 min (190°C, 2.16 kg) and an acrylic acid content of 9.0%. The polyurethane scratch-resistant layer is composed of the components shown in Table 6.

[0108] Table 6

[0109]

[0110] The scratch-resistant EVA composite film described in this embodiment is prepared by the following method:

[0111] Step 1: The raw materials for the EVA substrate layer and the EAA binder layer are fed into different channels of a two-layer melt co-extrusion casting equipment for co-extrusion casting to obtain an EVA / EAA composite film in one step. The film is then cooled and wound up for later use. The casting melt temperature is set to 220℃, and the cooling temperature is set to 0℃.

[0112] Step 2: Take 80 parts of polytetrahydrofuran ether diol (molecular weight 4000 g / mol), 50 parts of hydroxyl-terminated polysiloxane (molecular weight 30000 g / mol), 40 parts of dimethylolbutyric acid, 40 parts of isoflurane diisocyanate, 20 parts of hexamethylene diisocyanate and 0.5 parts of dibutyltin dilaurate to synthesize the aqueous polyurethane dispersion of this embodiment.

[0113] Step 3: Disperse the raw materials of the polyurethane scratch-resistant layer in a mixed solution of deionized water and ethanol (weight ratio of deionized water to ethanol is 3:1) to prepare an aqueous polyurethane coating solution with a solid content of 25%. Apply the above aqueous polyurethane coating solution to the EAA side of the EVA / EAA composite film obtained in Step 1 using a precision coating device. Dry the coated film with hot air at 80°C to remove the solvent, and then cure it at 50°C for 60 hours to obtain the scratch-resistant EVA composite film of this embodiment.

[0114] According to the test, the total thickness of the scratch-resistant EVA film in this embodiment is 0.56 mm, of which the thickness of the EAA bonding layer is 0.140 mm and the thickness of the polyurethane scratch-resistant layer is 0.060 mm.

[0115] Comparative Example 1

[0116] The composition and preparation method are the same as in Example 1. The only difference is that the aqueous polyurethane coating liquid is coated on the EVA surface, and after drying and curing, the EVA film of this comparative example is obtained.

[0117] Comparative Example 2

[0118] The preparation method is the same as in Example 1, except that the polyurethane scratch-resistant layer does not contain aziridine crosslinking agent. The rest of the composition is the same as in Example 1. The EVA film of this comparative example was obtained according to the preparation method of Example 1.

[0119] Comparative Example 3

[0120] The preparation method is the same as in Example 1, except that the aqueous polyurethane dispersion in the polyurethane scratch-resistant layer does not contain hydroxyl-terminated polysiloxane. The rest of the composition is the same as in Example 1. The EVA film of this comparative example was obtained according to the preparation method of Example 1.

[0121] Comparative Example 4

[0122] Referring to the method of patent CN111662495B, 100 parts of EVA resin (melt index of 8.0 g / 10 min (190℃, 2.16 kg), VA content of 18%), 3 parts of silicone masterbatch and 0.2 parts of erucamide were mixed evenly and then the EVA film of this comparative example was prepared by melt casting.

[0123] Test case

[0124] The light transmittance, coating adhesion, and scratch resistance of the sample films from Examples 1-5 and Comparative Examples 1-4 were tested respectively.

[0125] The transmittance test method is as follows: Samples are prepared according to the requirements of national standard GB / T 2410, and the transmittance of the samples is tested using a spectrophotometer. Different areas of each sample are randomly selected and tested repeatedly 5 times, and the average value is recorded.

[0126] The testing method for coating adhesion is as follows: The cross-cut adhesion test is conducted according to the national standard GB / T 9286. Adhesion grades are divided into six levels from 0 to 5, from best to worst. At least five areas of the same sample are randomly selected for testing, and the lowest adhesion grade is recorded as the test result.

[0127] The test method for scratch resistance is as follows: the sample film is cut into 50×50mm sizes and evaluated using a reciprocating friction test. Specific test parameters are: friction stroke 20mm, abrasive #000 grade steel wool, load 68g, and 50 reciprocating cycles. After the test, the scratch resistance is visually rated on a scale of 1-5, with the following standards: no visible scratches under auxiliary side lighting (5 points); minor visible scratches under auxiliary side lighting (4 points); slight scratches under auxiliary side lighting (3 points); slight scratches without auxiliary lighting (2 points); and obvious scratches without auxiliary lighting (1 point). At least 5 areas of the same sample are randomly selected for testing, and the lowest score is recorded as the test result.

[0128] The test results of Examples 1-5 and Comparative Examples 1-4 are shown in Table 7.

[0129] Table 7

[0130]

[0131]

[0132] As shown in Table 1, Comparative Example 1, due to the direct coating of the polyurethane scratch-resistant layer onto the EVA surface, exhibits poor compatibility between the two, resulting in poor coating adhesion and consequently poor scratch resistance compared to Examples 1-5. In Comparative Example 2, the scratch-resistant layer lacks a crosslinking agent, preventing the formation of chemical bonds with the EAA bonding layer compared to Examples 1-5, leading to poor coating adhesion and low strength, further contributing to poor scratch resistance. In Comparative Example 3, the polyurethane composition of the scratch-resistant layer does not contain polysiloxane, lacking the silicone component that improves wear resistance compared to Examples 1-5, resulting in slightly insufficient scratch resistance. Comparative Example 4, employing a silicone and erucamide lubricant solution, exhibits lower light transmittance and less desirable scratch resistance compared to Examples 1-5.

[0133] In summary, compared with Comparative Examples 1-4, the composite films prepared in Examples 1-5 have higher light transmittance, coating adhesion, and scratch resistance, which can meet the application requirements of transparent and scratch-resistant high-end EVA packaging materials.

[0134] The scratch-resistant ethylene-vinyl acetate copolymer composite film and its preparation method provided in this invention embodiment include a substrate layer, a connecting layer, and a polyurethane scratch-resistant layer stacked sequentially. The thickness of the composite film is 0.05-0.80 mm; the thickness of the connecting layer accounts for 5-25% of the total thickness of the composite film; the thickness of the polyurethane scratch-resistant layer accounts for 10-30% of the total thickness of the composite film; the substrate layer is an ethylene-vinyl acetate copolymer film layer, which is composed of one or more ethylene-vinyl acetate copolymer resins, with the vinyl acetate mass fraction of the ethylene-vinyl acetate copolymer resin ranging from 10-40%; the polyurethane scratch-resistant layer is a polyurethane scratch-resistant layer. This invention discloses a composite film that improves the tightness of the connection between film layers by setting a connecting layer, improves the high scratch resistance of the composite film by setting a polyurethane scratch-resistant layer, and ensures that the composite film has high transparency. It can solve the technical problems existing in EVA films in current packaging materials, and has high production efficiency, adapting to existing mainstream production methods.

[0135] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and these modifications or substitutions should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A scratch resistant ethylene-vinyl acetate copolymer composite film, characterized by, The composite film comprises a substrate layer, a connecting layer and a polyurethane scratch-resistant layer arranged in sequence; The thickness of the composite film is 0.05-0.80mm; the thickness of the connecting layer accounts for 5-25% of the total thickness of the composite film; the thickness of the polyurethane scratch-resistant layer accounts for 10-30% of the total thickness of the composite film; The substrate layer is an ethylene-vinyl acetate copolymer film layer composed of one or more ethylene-vinyl acetate copolymer resins, and the mass fraction of vinyl acetate in the ethylene-vinyl acetate copolymer resins ranges from 10% to 40%; The connecting layer is an ethylene-acrylic acid copolymer film layer; The ethylene-acrylic acid copolymer film layer is composed of one or more ethylene-acrylic acid copolymer resins or one or more ethylene-methyl acrylic acid copolymer resins; The polyurethane scratch-resistant layer is obtained by mixing water-based polyurethane dispersion, film-forming agent, defoaming agent and cross-linking agent in a mass ratio of 100:2-8:0.1-1:4-12; The film-forming agent is obtained by combining one or more of ethylene glycol methyl ether, ethylene glycol butyl ether, diethylene glycol methyl ether, diethylene glycol butyl ether and propylene glycol methyl ether; the defoaming agent is silicone-based defoaming agent; and the cross-linking agent is obtained by combining one or more of trimethylolpropane-tris[3-(2-methylaziridinyl)] propionate, trimethylolpropane-tris(3-aziridinyl) propionate and pentaerythritol tri(3-aziridinyl) propionate.

2. The scratch resistant ethylene vinyl acetate copolymer composite film according to claim 1, characterized in that, The mass fraction of acrylic acid in the ethylene-acrylic acid copolymer resins ranges from 5% to 25%, and the mass fraction of methyl acrylic acid in the ethylene-methyl acrylic acid copolymer resins ranges from 5% to 25%.

3. The scratch resistant ethylene-vinyl acetate copolymer composite film according to claim 1 or 2, characterized in that, The melt index of the ethylene-vinyl acetate copolymer resins, the ethylene-acrylic acid copolymer resins and the ethylene-methyl acrylic acid copolymer resins all ranges from 1g / 10min to 30g / 10min under the condition of 190℃ and 2.16kg.

4. The scratch resistant ethylene vinyl acetate copolymer composite film according to claim 1, characterized in that, The water-based polyurethane dispersion is obtained by polymerization of the following monomers: polyhydric alcohol 60-80 parts, hydroxyl-terminated polysiloxane 30-50 parts, self-emulsifying monomer 20-40 parts, aliphatic diisocyanate 40-60 parts and catalyst 0.1-0.5 parts; The preparation method of the water-based polyurethane dispersion is as follows: Mix the polyhydric alcohol, hydroxyl-terminated polysiloxane and self-emulsifying monomer in the above-mentioned parts ratio in a reaction container, and dehydrate at 100-120℃ under vacuum for 0.5-1h; Then, cool to 60-80℃, add acetone, and add the catalyst in the above-mentioned parts ratio; Slowly add the aliphatic diisocyanate through a constant-pressure funnel under the protection of nitrogen, and react for 2-4h; After the reaction is completed, add triethylamine for neutralization, cool to 30-45℃, add deionized water, emulsify quickly by stirring for 0.5-1h, and evaporate the acetone under reduced pressure to obtain the water-based polyurethane dispersion.

5. The scratch resistant ethylene vinyl acetate copolymer composite film according to claim 4, characterized in that, The molecular weight of the polyhydric alcohol is 500-4000g / mol, and the molecular weight of the hydroxyl-terminated polysiloxane is 5000-30000g / mol.

6. The scratch resistant ethylene vinyl acetate copolymer composite film according to claim 5, wherein, The polyhydric alcohol is obtained from one or more of polyethylene glycol, polypropylene glycol, polytetrahydrofuran ether glycol, polycarbonate glycol, polyethylene adipate glycol, polyhexylene adipate glycol, polyethylene terephthalate glycol, polybutylene terephthalate glycol, polyhexylene terephthalate glycol in combination; The self-emulsifying monomer is obtained from one or more of dimethylol propanoic acid, dimethylol butanoic acid, 1,2-dihydroxy-3-propane sulfonic acid sodium in combination; The aliphatic diisocyanate is obtained from one or more of hexamethylene diisocyanate, isophorone diisocyanate, dicyclohexyl methane diisocyanate, penta-methylene diisocyanate in combination; The catalyst is dibutyl tin dilaurate and / or stannous octoate.

7. A method for producing a scratch-resistant ethylene-vinyl acetate copolymer composite film, characterized by, The preparation method is used for preparing the scratch-resistant ethylene-vinyl acetate copolymer composite film according to any one of claims 1-6, and the method comprises: S1: raw materials of the substrate layer and raw materials of the connecting layer are respectively fed into different flow channels of a double-layer melt co-extrusion casting device for co-extrusion casting molding, and a double-layer composite film is obtained in one step, and the obtained double-layer composite film is cooled and rolled for standby; the thickness of each film layer in the obtained double-layer composite film is adjusted by controlling the feeding speed of the two materials; the casting melt temperature of the double-layer melt co-extrusion casting device is set to 100-220℃, and the cooling temperature is set to 0-10℃; S2: the raw materials of the polyurethane scratch-resistant layer are dispersed in a mixed solution of deionized water and ethanol to prepare a water-based polyurethane coating solution with a solid content of 25-35%, and the weight ratio of deionized water to ethanol in the mixed solution is 3:1; the connecting layer surface of the double-layer composite film obtained in S1 is coated with the above water-based polyurethane coating solution by using a coating device, and the thickness of the polyurethane scratch-resistant layer is controlled by the coating line speed; the coated film is dried by hot air at 60-80℃ to remove the solvent, and then aged at 45-55℃ for 48-72h to obtain the scratch-resistant ethylene-vinyl acetate copolymer composite film. S1: raw materials of the substrate layer and raw materials of the connecting layer are respectively fed into different flow channels of a double-layer melt co-extrusion casting device for co-extrusion casting molding, and a double-layer composite film is obtained in one step, and the obtained double-layer composite film is cooled and rolled for standby; the thickness of each film layer in the obtained double-layer composite film is adjusted by controlling the feeding speed of the two materials; the casting melt temperature of the double-layer melt co-extrusion casting device is set to 100-220℃, and the cooling temperature is set to 0-10℃; S2: the raw materials of the polyurethane scratch-resistant layer are dispersed in a mixed solution of deionized water and ethanol to prepare a water-based polyurethane coating solution with a solid content of 25-35%, and the weight ratio of deionized water to ethanol in the mixed solution is 3:1; the connecting layer surface of the double-layer composite film obtained in S1 is coated with the above water-based polyurethane coating solution by using a coating device, and the thickness of the polyurethane scratch-resistant layer is controlled by the coating line speed; the coated film is dried by hot air at 60-80℃ to remove the solvent, and then aged at 45-55℃ for 48-72h to obtain the scratch-resistant ethylene-vinyl acetate copolymer composite film.

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