Metallized polyester composite sheet and preparation method thereof

Abstract

The invention provides a metallized polyester composite sheet. The metallized polyester composite sheet is composed of an outer polyolefin film, double bonding layers, a gradient aluminized polyester layer and a heat sealing layer. Wherein the aluminized layer adopts a three-layer gradient structure base material interface area, an aluminum-peroxide-containing middle transition area and a low-roughness surface area, plasma treatment is combined, and meanwhile, the mechanical and optical properties of the aluminized layer are improved by doping an aluminum-peroxide element. And the outer polyolefin film contains titanium dioxide and a slipping agent. The water and oxygen barrier property of the metallized polyester composite sheet reaches the food grade. The preparation process comprises the steps of biaxial stretching of the PET base film, plasma treatment, magnetron sputtering gradient aluminizing and dry compounding, and the finished product is suitable for various printing processes such as gravure, UV flexographic printing, silk-screen printing and offset printing, has high brightness and durability and can be widely applied to the field of high-end packaging.

Description

Technical Field

[0001] This invention relates to the field of composite sheet technology, specifically to a metal-plated polyester composite sheet, and more particularly to a composite sheet with high gloss and easy printing, as well as a method for preparing such a sheet. Background Technology

[0002] Metallized polyester composite sheets, as important packaging materials, offer excellent barrier properties due to their dense interlayer structure, and are widely used in the packaging of food, pharmaceuticals, and daily chemical products. Conventional metallized polyester materials typically employ a vacuum evaporation process to deposit a 25-60nm thick aluminum layer onto a PET substrate of a certain thickness. Traditionally, the thickness of the metallized layer is positively correlated with gloss, but cracking issues arise when the thickness exceeds 60nm.

[0003] Secondly, traditional sheet materials often lack sufficient gloss to meet the design requirements of multi-color patterns, making them unsuitable for multi-color overlays, light-screen designs, flexographic printing, and other similar printing methods. Specifically, the gloss level of these composite sheets at a 60° angle is typically only 60-70 GU. Surface diffuse reflectance is >25%, significantly impacting the color rendering of printed patterns. Furthermore, the surface tension of conventional aluminized layers is between 38-40 mN / m, resulting in insufficient ink adhesion and a tape peeling rate >15%. The contact thixotropic angle is >120°.

[0004] Therefore, there is an urgent need to develop a new type of metal-plated polyester composite sheet to solve the above-mentioned technical problems. Summary of the Invention

[0005] The purpose of this invention is to provide a metal-plated polyester composite sheet that has good gloss, low cracking problem of the aluminum plating layer, and is suitable for a variety of different printing methods and achieves good color development.

[0006] To achieve the above objectives, the technical solution provided by the present invention is as follows: In a first aspect, the present invention provides a metal-plated polyester composite sheet, characterized in that it comprises sequentially stacked: The outer polyolefin film is a composite structure selected from one or more materials among MDPE (uniaxially oriented polyethylene), HDPE (high-density polyethylene), LLDPE (linear low-density polyethylene), and LDPE (low-density polyethylene). The first adhesive layer has a dry coating weight of 2.5-3.5 g / m². 2 Polyether or polyurethane adhesives; The metallized polyester film layer has a thixotropic angle of 55-65° after plasma treatment, and the aluminum coating layer has a thickness of 45-100nm. The second adhesive layer has a dry coating amount of 2.0-5.0 g / m².2 Acrylic-polyurethane composite adhesive is composed of water. The heat-sealing layer comprises at least one layer of LLDPE / MDPE / HDPE blend material.

[0007] In the above technical solution, the outer polyolefin film contains titanium dioxide and a slip agent to provide whiteness of the base color and processing fluidity; the double adhesive layers are matched with the high modulus of the aluminum-plated layer and the flexibility of the heat-sealing layer to ensure interlayer bonding strength.

[0008] Plasma treatment mainly refers to Ar / O2 mixed gas treatment, where the O2 content is controlled at 20-30%. O2 increases surface energy by oxidizing the PET surface to generate polar groups (-COOH, -OH, -CHO, COCH3); Ar ion bombardment controls roughness. The coating amounts of the first and second adhesive layers differ significantly because the first layer is thinner to match the high modulus characteristics of the aluminized layer, while the second layer is thicker (containing acrylic-polyurethane composite adhesive) to buffer the flexible deformation of the heat-sealing layer (MDPE / HDPE).

[0009] The Al-OC chemical bond between high-purity aluminum and the PET base film enhances interfacial bonding energy and reduces the risk of coating peeling, forming a dense structure and inhibiting cracking. It also alleviates stress concentration caused by differences in thermal expansion coefficients, reducing coating defects.

[0010] In a preferred embodiment, the aluminum plating layer of the metallized polyester film layer has a gradient structure, comprising, from the inside out, a substrate interface region with a thickness of 5-10 nm and an aluminum purity ≥99.6%; and a substrate interface region with a thickness of 30-60 nm and containing 2-5 wt% alumina (Al₂O₃). x The intermediate transition region of the element; the surface region with a thickness of 10-30 nm and a surface roughness Ra≤0.15 μm.

[0011] Adding high-purity aluminum is to ensure its adhesion to the PET base film interface. Here, the purity of aluminum is affected by impurities in the sputtered aluminum element during the process, or by the unavoidable bombardment of some air molecules during sputtering, thus preventing the aluminum purity from reaching 100%. Alumina doping is used to form an aluminum solid solution containing aluminum oxide to improve hardness.

[0012] The aluminum oxide element refers to aluminum oxide that is directly vapor-deposited onto the surface of the PET base film. Specifically, in the magnetron sputtering process, aluminum oxide is directly selected as the target material, rather than sputtered aluminum that oxidizes during the deposition process.

[0013] In a preferred embodiment, the metallized polyester film layer has a reflectivity of ≥85% in the 380-780nm visible light band and a gloss of ≥90GU at a 60° angle.

[0014] In a preferred embodiment, the outer polyolefin film comprises 0.5-1.5 wt% titanium dioxide and 0.3-0.8 wt% siloxane slip agent, and the thickness of the outer polyolefin film is 15-25 μm.

[0015] In a preferred embodiment, the melt flow index of the heat-sealing layer is 5-8 g / 10 min to balance flowability and molecular chain entanglement, thereby achieving a heat-sealing strength ≥8 N / 15 mm. The preferred blending ratio of LLDPE:MDPE:HDPE is 2:7:1. The blended resin balances melt flowability and molecular chain entanglement, expanding the heat-sealing window width while avoiding damage to the aluminum plating layer from the high temperature of heat sealing.

[0016] In a preferred embodiment, the water vapor transmission rate of the composite sheet is ≤0.5 g / m². 2 • Oxygen permeability ≤1.0 cm over 24 hours 3 / m 2 • 24h·atm. The double adhesive layer and the aluminum plating layer form a dense barrier, meeting the requirements for food-grade barrier properties. The gradient aluminum plating layer suppresses pinhole defects, giving it good water and oxygen barrier properties even under relatively thin conditions.

[0017] Secondly, the present invention also provides a method for preparing a high-brightness metallized polyester composite sheet having at least one of the above-mentioned technical features, comprising the following steps: S1. Base film preparation: PET base films with a thickness of 12-25μm are prepared using a biaxial stretching process, with a longitudinal stretching ratio of 3.2-3.8 and a transverse stretching ratio of 3.5-4.0; S2. Plasma treatment: under a vacuum of 10... -2 -10 -3 Under Pa conditions, Ar / O2 mixed gas plasma treatment was used with a power density of 3-5 W / cm². 2 Processing time is 60-120 milliseconds; S3. Vacuum metallization: A magnetron sputtering process is used on the surface of the PET base film to first deposit the substrate interface layer at a rate of 0.8-1.2 Å / s, and then deposit the intermediate transition zone and surface zone at a rate of 2.5-3.5 Å / s. S4. Dry lamination: After coating the first adhesive layer and the second adhesive layer on both sides of the coated PET base film, the outer polyolefin film and the heat-sealing layer are laminated to form a metallized polyester composite sheet, which is then cured at 50-60℃ for 24-48 hours. S5. Slitting and winding: The metal-plated polyester composite sheet is slit under tension control of 20-30N, and the hardness of the rolled material is controlled at 70-80 Shore hardness after winding.

[0018] In a preferred embodiment, the surface energy of the PET base film after plasma treatment in step S2 is 52-56 mN / m, and the water droplet contact angle is 60±3°.

[0019] In a preferred embodiment, in step S3: a pulse bias voltage of 20-50kHz is applied during magnetron sputtering, with a duty cycle of 30-40%; the base film temperature is controlled in the range of 40-50℃ during the aluminum plating process to maintain the PET crystallinity above 50% to avoid shrinkage.

[0020] As a preferred embodiment, step S5 also includes post-processing: after aluminum plating is completed, the temperature is first raised to 80°C at a rate of 5-8°C / min and held for 30 min, and then raised to 120°C at a rate of 3-5°C / min and held for 10 min.

[0021] The advantages and beneficial effects of this invention are as follows: 1. The metallized polyester film layer in this invention has a thixotropic angle of 55-65° after plasma treatment. Through the three-layer structure of the substrate interface area, intermediate transition area and surface area, it gives the material a high brightness and gloss texture. The intermediate transition area contains alumina elements to enhance the bonding force of the aluminum-plated layer, while alleviating the stress concentration caused by the difference in thermal expansion coefficient. Its deposition forms a highly reflective surface to help improve gloss and balance the bonding force and optical performance.

[0022] 2. The balanced design of surface energy of 52-56mN / m and water droplet contact angle of 60±3° enables ink adhesion to reach ISO2409 level 0, which is suitable for various processes such as gravure printing, UV flexographic printing, screen printing, offset printing, and UV flexographic printing.

[0023] 3. The outer polyolefin film and the metallized PET layer form a dense barrier through a double adhesive layer, meeting food-grade barrier requirements. The heat-sealing layer includes an LLDPE / MDPE / HDPE blend, which has suitable strength at a heat-sealing temperature of 130-150℃ and a heat-sealing window width of 15℃, preventing damage to the metallized layer from the high temperature of heat sealing. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the structure of the metal-plated polyester composite sheet shown in this invention; Figure 2 This is an enlarged structural schematic diagram of point A in the present invention; Figure 3 This is a process flow diagram of the preparation process of the metal-plated polyester composite sheet of the present invention; In the figure: 1-outer polyolefin film; 2-first adhesive layer; 3-metallized polyester film layer; 31-surface area; 32-intermediate transition area; 33-substrate interface area; 4-second adhesive layer; 5-heat seal layer. Detailed Implementation

[0025] This invention provides a metallized polyester composite sheet, comprising, sequentially arranged, an outer polyolefin film 1, a first adhesive layer 2, a metallized polyester film layer 3, a second adhesive layer 4, and a heat-sealing layer 5. The metallized polyester film layer 3 includes, from the outside in, a surface region 31, an intermediate transition region 32, and a substrate interface region 33. The substrate interface region forms a dense structure through slow deposition (0.8-1.2 Å / s) to ensure chemical bonding with the PET base film; the intermediate transition region is mixed with 2-5 wt% alumina elements during vacuum evaporation; and the surface region forms an equiaxed crystal structure through rapid deposition.

[0026] The metallized polyester composite sheet of this invention adopts a three-layer gradient aluminum plating structure. The high-purity aluminum layer at the substrate interface ensures good bonding with the PET base film. Specifically, it uses ultra-low speed deposition, enabling aluminum atoms to acquire a surface migration energy of approximately 0.45 eV, forming Al-OC chemical bonds. The interfacial bonding energy is significantly higher than that of conventional processes (5.6 J / m). 2 Increased by approximately 2.6 J / m 2 .

[0027] The intermediate transition zone is formed by incorporating 2-5 wt% of alumina elements to form an Al-Cr solid solution. The alumina elements exist in the form of substitution solid solution, forming an Al(Cr) supersaturated solid solution, which not only improves the hardness of the coating but also alleviates the stress problem caused by the difference in thermal expansion coefficients.

[0028] The ultra-low surface roughness treatment significantly improves optical reflectivity. Rapid deposition forms a (111) plane with preferred orientation and a texture factor TC=3.2. This gradient structure, combined with plasma treatment, enables the aluminum plating layer to achieve ≥85% visible light reflectivity and ≥90GU gloss within a thickness range of 45-100nm, breaking through the traditional contradiction between aluminum plating layer thickness and cracking problem.

[0029] In terms of the preparation process, the ideal molecular orientation and crystallinity are obtained by controlling the stretching ratio of 3.2-4.0 in the biaxially oriented PET base film stage, laying the foundation for subsequent coating. During magnetron sputtering aluminum deposition, differentiated deposition rates are adopted: slow deposition in the interface region ensures compactness, while rapid deposition in the surface region inhibits excessive grain growth.

[0030] It is worth noting that the plasma treatment process, using an Ar / O2 mixed gas at 10 -2 -10 -3 Processing under Pa vacuum not only introduces polar groups to enhance surface energy through oxygen plasma, but also uses Ar ion bombardment to regulate surface morphology, so that the contact angle is precisely controlled within the optimal printability range of 60±3°.

[0031] The addition of 0.5-1.5 wt% titanium dioxide to the outer polyolefin film improves the whiteness of the base color, while a siloxane slip agent ensures processing fluidity. The heat-sealing layer uses a blend of LLDPE / MDPE / HDPE in a 2:7:1 ratio, which ensures both heat-sealing strength and expands the heat-sealing window width. The dual-adhesive layer design cleverly balances the modulus differences between the different layers. The first adhesive layer uses high-modulus polyurethane matched with an aluminized layer, while the second adhesive layer uses a flexible acrylic-polyurethane composite adhesive to buffer the stress of the heat-sealing layer.

[0032] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings and examples. The following examples are only used to more clearly illustrate the technical solutions of the present invention and should not be construed as limiting the scope of protection of the present invention.

[0033] Example 1 A metallized polyester composite sheet, comprising the following components arranged sequentially: The outer polyolefin film is made of MDPE material, with a thickness of 15μm and a melt index of 2.0g / 10min. It contains 0.8wt% TiO2 and 0.5wt% erucamide slip agent, which account for 0.8wt% of the total weight of the outer polyolefin film.

[0034] The first adhesive layer is coated with 3.2 g / m² using a 150-line microgravure process. 2 Polyurethane adhesive is laminated to the metal surface of an aluminized polyester layer.

[0035] The metallized polyester film layer comprises an 18 μm polyester substrate and a 60 nm metal layer. The substrate interface region is composed of 6 nm thick Al with a purity of 99.7%; the intermediate transition region is composed of 40 nm thick Al containing 4.0 wt% AlO. x The surface region has a thickness of 14 nm and a surface roughness Ra = 0.13 μm when it is connected to the second adhesive layer.

[0036] The second adhesive layer uses a dry-based coating with a coverage of 4.0 g / m². 2 The acrylic-polyurethane composite adhesive (ethylene content 23%) has a coating precision of ±0.3 g / m². 2 .

[0037] The heat-sealing layer is made of a blend of LLDPE / MDPE / HDPE = 2:7:1 (mass ratio) with a melt index of 6.5 g / 10 min.

[0038] The preparation method of this metal-plated polyester composite sheet includes: S1, Base film preparation: 18μm PET base film was prepared using a biaxial stretching machine with a preheating temperature of 85℃, a stretching temperature of 105℃, a longitudinal stretching ratio of 3.5:1, a transverse stretching ratio of 3.8:1, and then shaped. S2, Plasma treatment, evacuate the vacuum chamber of the plasma treatment machine to 5×10 -3 Pa, a mixed gas of Ar / O2 = 4:1 was introduced, the RF power was set to 4kW, the electrode spacing was 80mm, the processing time was 90ms, and the water droplet contact angle on the substrate surface after processing was 61±2°. S3, magnetron sputtering aluminum deposition, aluminum target purity 99.99%, base film temperature 45℃, first depositing an 8nm interface layer at a rate of 1.0Å / s, then switching to a rate of 3.0Å / s to deposit a 45nm transition layer, while simultaneously sputtering AlO. x Add aluminum oxide to the target material.

[0039] S4, dry lamination, involves coating the first adhesive layer onto the metal side of the polyester substrate and laminating it with the outer polyolefin film, and then coating the second adhesive layer onto the side of the polyester substrate away from the metal and laminating it with the heat-sealing layer.

[0040] S5, Curing and Slitting: The composite sheet is cured at 55°C for 36 hours in a curing chamber, then slit to the required specifications using a slitting machine with a slitting tension of 25N, and wound up with a Shore hardness of 75.

[0041] Example 2 A metallized polyester composite sheet differs from Example 1 in that its structure includes the following sequentially arranged components: Outer polyolefin film: LLDPE material, 20μm thick, melt index 2.5g / 10min, with 1.2wt% TiO2 and 0.6wt% siloxane slip agent added to the total weight of the film.

[0042] First adhesive layer: dry base coating with a coverage of 2.8 g / m 2 The polyether adhesive has a coating precision of ±0.2g / m. 2 .

[0043] Metallized polyester film layer: comprising a 15μm PET substrate and a gradient aluminum layer with a total thickness of 45nm. The substrate interface region has a thickness of 5nm and an aluminum purity of 99.8%; the intermediate transition region has a thickness of 30nm and contains 2.0wt% AlO₂. x The thickness of the surface region is 10 nm, and the surface roughness Ra = 0.10 μm.

[0044] Second adhesive layer: dry base coating with a coverage of 3.5 g / m 2 Acrylic-polyurethane composite adhesive (ethylene content 20%).

[0045] Heat-sealing layer: made of a blend of LLDPE / MDPE / HDPE = 2:7:1 (mass ratio), with a melt index of 5.5 g / 10 min.

[0046] Preparation method: S1. Base film preparation: 15μm PET base film was prepared by biaxial stretching process with a longitudinal stretching ratio of 3.2:1 and a transverse stretching ratio of 3.5:1. The preheating temperature was 80℃ and the stretching temperature was 100℃.

[0047] S2. Plasma treatment: Vacuum degree 8×10 -3 Pa, Ar / O2 = 3:1 mixed gas, power density 3.5 W / cm³ 2 The processing time is 70 milliseconds, and the surface contact angle after processing is 58±2°.

[0048] S3. Vacuum aluminum deposition: base film temperature 40℃, interface layer deposition rate 0.8 Å / s (thickness 5 nm), transition layer deposition rate 2.5 Å / s (thickness 30 nm), simultaneous sputtering of AlO x Add aluminum oxide to the target material.

[0049] S4. Dry compounding: curing temperature 50℃, curing time 30 hours.

[0050] S5. Slitting and winding: tension control 22N, winding hardness 72 Shore hardness.

[0051] Example 3 A metallized polyester composite sheet differs from Example 1 in that its structure includes the following sequentially arranged components: Outer polyolefin film: HDPE material, 25μm thick, melt index 3.0g / 10min, with 1.5wt% TiO2 and 0.8wt% siloxane slip agent added to the total weight of the film.

[0052] First adhesive layer: dry base coating with a coverage of 3.5 g / m² 2 The polyurethane adhesive has a coating accuracy of ±0.3g / m². 2 .

[0053] Metallized polyester film layer: comprising a 25μm PET substrate and a gradient aluminum plating layer with a total thickness of 100nm. Specifically: the substrate interface region has a thickness of 10nm and an aluminum purity of 99.6%; the intermediate transition region has a thickness of 60nm and contains 5.0wt% AlO₂. x The surface region thickness is 30 nm, and the surface roughness Ra = 0.12 μm.

[0054] Second adhesive layer: dry base coating with a coverage of 5.0 g / m 2 Acrylic-polyurethane composite adhesive (ethylene content 25%).

[0055] Heat-sealing layer: made of a blend of LLDPE / MDPE / HDPE (mass ratio = 2:7:1) with a melt index of 8.0 g / 10 min.

[0056] Preparation method: S1. Base film preparation: 25μm PET base film was prepared by biaxial stretching process with a longitudinal stretching ratio of 3.8:1 and a transverse stretching ratio of 4.0:1. The preheating temperature was 90℃ and the stretching temperature was 110℃.

[0057] S2. Plasma treatment: Vacuum degree 1×10 -2 Pa, Ar / O2 = 5:1 mixed gas, power density 5.0 W / cm³ 2 The processing time is 120 milliseconds, and the surface contact angle after processing is 74±2°.

[0058] S3. Vacuum aluminum deposition: base film temperature 50℃, interface layer deposition rate 1.2 Å / s (thickness 10 nm), transition layer deposition rate 3.5 Å / s (thickness 60 nm), simultaneous sputtering of AlO x Add aluminum oxide to the target material.

[0059] S4. Dry compounding: curing temperature 60℃, curing time 48 hours.

[0060] S5. Slitting and winding: tension control 30N, winding hardness 80 Shore hardness.

[0061] Example 4 A metallized polyester composite sheet, comprising the following components arranged sequentially: Outer polyolefin film: LDPE material, 18μm thick, melt index 2.2g / 10min, with 0.5wt% TiO2 and 0.3wt% siloxane slip agent added according to the total weight of the film.

[0062] First adhesive layer: dry base coating with a coverage of 2.5 g / m 2 The polyether adhesive has a coating precision of ±0.1g / m². 2 .

[0063] Metallized polyester film layer: comprising a 12μm PET substrate and a gradient aluminum plating layer with a total thickness of 80nm. Specifically: the substrate interface region is 8nm thick with 99.9% aluminum purity; the intermediate transition region is 50nm thick and contains 3.5wt% AlO₂. x The surface region thickness is 22 nm, and the surface roughness Ra = 0.14 μm.

[0064] Second adhesive layer: dry coating with a coverage of 2.0 g / m² 2 Acrylic-polyurethane composite adhesive (ethylene content 18%).

[0065] Heat-sealing layer: made of a blend of LLDPE / MDPE / HDPE = 2:7:1 (mass ratio), with a melt flow index of 7.0 g / 10 min.

[0066] Preparation method: S1. Base film preparation: 12μm PET base film was prepared by biaxial stretching process with a longitudinal stretching ratio of 3.3:1 and a transverse stretching ratio of 3.6:1. The preheating temperature was 82℃ and the stretching temperature was 102℃.

[0067] S2. Plasma treatment: Vacuum degree 3×10⁻³ Pa, Ar / O₂=2:1 mixed gas, power density 4.0W / cm³ 2 The processing time is 100 milliseconds, and the surface contact angle after processing is 83±2°.

[0068] S3. Vacuum aluminum deposition: base film temperature 42℃, interface layer deposition rate 1.0 Å / s (thickness 8 nm), transition layer deposition rate 3.0 Å / s (thickness 50 nm), simultaneous sputtering of AlO x Add alumina to the target material.

[0069] S4. Dry compounding: curing temperature 55℃, curing time 40 hours.

[0070] S5. Slitting and winding: tension control 10N, winding hardness 78 Shore hardness.

[0071] Comparative Example The difference from Example 1 is that the metallized polyester film layer is an aluminum layer composed of a 20μm polyester substrate and a 60nm adhesive.

[0072] For the above embodiments and comparative examples, the water vapor transmission rate was tested at 38°C and 90%RH according to GB / T 1037-2021; the oxygen transmission rate was determined at 23°C and 50%RH according to GB / T 19789-2021; the 60° gloss was measured using a multi-angle gloss meter according to ASTM D2457-21; the ink adhesion was tested according to the cross-cut test (1mm spacing, 3M tape peel) according to ISO 2409:2020; and the peel strength, i.e., the heat seal strength, was measured using a tensile testing machine under the heat sealing conditions of 150°C, 0.2MPa, and 1s, according to GB / T 23510-2021.

[0073] Among them, ink adhesion grade 0 indicates no peeling. The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A metal-plated polyester composite sheet, characterized in that, Including those stacked in sequence: Outer polyolefin film (1); The first adhesive layer (2) has a dry coating amount of 2.5-3.5 g / m². 2 Polyether or polyurethane adhesives; The metallized polyester film layer (3) has a thixotropic angle of 55-85° after plasma treatment and an aluminum coating thickness of 45-100nm. The second adhesive layer (4) has a dry coating amount of 2.0-5.0 g / m². 2 Composition of acrylic-polyurethane composite adhesive; The heat-sealing layer (5) comprises a film material made of blended polyethylene.

2. The composite sheet according to claim 1, characterized in that, The aluminum plating layer of the metallized polyester film layer (3) has a gradient structure, comprising layers stacked sequentially from the inside out: Substrate interface region (33): thickness 5-10nm, aluminum purity ≥99.6%; Intermediate transition region (32): 30-60 nm thick, containing 2-5 wt% alumina; Surface region (31): thickness 10-30nm, surface roughness Ra≤0.15μm.

3. The composite sheet according to claim 2, characterized in that, The metallized polyester film layer (3) has a reflectivity of ≥85% in the visible light band of 380-780nm and a gloss of ≥90GU at a 60° angle.

4. The composite sheet according to claim 1, characterized in that, The outer polyolefin film (1) contains 0.5-1.5 wt% titanium dioxide and 0.3-0.8 wt% siloxane slip agent, and the film thickness is 15-25 μm.

5. The composite sheet according to claim 1, characterized in that, The melt flow index of the heat-sealing layer (5) is 5-8 g / 10 min, and the heat-sealing strength is ≥8 N / 15 mm.

6. The composite sheet according to any one of claims 1-5, characterized in that, The water vapor transmission rate of the composite sheet is ≤0.5 g / m². 2 • Oxygen permeability ≤1.0 cm over 24 hours 3 / m 2 24h atm.

7. The method for preparing the high-brightness metallized polyester composite sheet according to any one of claims 1-5, characterized in that, Includes the following steps: S1. Base film preparation: PET base films with a thickness of 12-25μm are prepared using a biaxial stretching process, with a longitudinal stretching ratio of 3.2-3.8 and a transverse stretching ratio of 3.5-4.0; S2. Plasma treatment: under a vacuum of 10... -2 -10 -3 Under Pa conditions, Ar / O2 mixed gas plasma treatment was used with a power density of 3-5 W / cm². 2 Processing time: 60-120ms; S3. Vacuum metallization: A magnetron sputtering process is used on the surface of the PET base film to first deposit the substrate interface layer at a rate of 0.8-1.2 Å / s, and then deposit the intermediate transition zone and surface zone at a rate of 2.5-3.5 Å / s. S4. Dry lamination: After coating the first adhesive layer (2) and the second adhesive layer (4) on both sides of the coated PET base film, the outer polyolefin film (1) and the heat-sealing layer (5) are laminated to form a metallized polyester composite sheet, which is then cured at 50-60℃ for 24-48h. S5. Slitting and winding: The metallized polyester film is slit under tension control of 10-30N, and the hardness of the wound material is controlled at 70-80 Shore hardness after winding.

8. The preparation method according to claim 7, characterized in that, The surface energy of the PET base film after plasma treatment in step S2 is 52-56 mN / m, and the water droplet contact angle is 60±3°.

9. The preparation method according to claim 7, characterized in that, In step S3: During magnetron sputtering, a pulse bias voltage of 20-50 kHz is applied, with a duty cycle of 30-40%. During the aluminum plating process, the temperature of the base film is controlled within the range of 40-50℃.

10. The preparation method according to claim 7, characterized in that, It also includes post-processing steps: after aluminum plating is completed, the temperature is first raised to 80℃ at a rate of 5-8℃ / min and held for 30min, and then raised to 120℃ at a rate of 3-5℃ / min and held for 10min.

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