Preparation method of high-barrier transparent aluminum oxide film and prepared high-barrier transparent aluminum oxide film

Abstract

According to the preparation method of the high-barrier transparent aluminum oxide film and the prepared high-barrier transparent aluminum oxide film, based on in-situ interface chemical bonding and gradient barrier structure design, an aluminum oxide layer and a base material are connected through forming a transition layer which takes Al-O-C bonding as a main part, has the proportion of more than or equal to 50% and has the thickness of 5-10 nm; therefore, the bonding force between the aluminum oxide layer and the substrate is good, and the aluminum oxide film is ensured to have excellent water resistance and oxygen resistance.

Description

Technical Field

[0001] This invention relates to barrier materials, and more particularly to a method for preparing a high-barrier transparent alumina film and the prepared high-barrier transparent alumina film. Background Technology

[0002] High-barrier film materials are core materials in high-end packaging fields such as food, pharmaceuticals, and electronics, and their performance directly determines the product's shelf life, safety, and functionality. Traditional barrier materials are mainly aluminum foil and aluminized film. Although they possess good barrier properties, they suffer from significant technical bottlenecks: First, there are energy consumption and pollution issues. Aluminum foil production requires electrolytic aluminum (energy consumption reaches 13,000-15,000 kWh / ton) and the melting temperature exceeds 1200℃, generating large amounts of CO2 and fluoride emissions. Although aluminized film reduces energy consumption through vacuum evaporation (1100-1200℃), the aluminum wire utilization rate is only 60-70%, and waste recycling is difficult. Second, traditional barrier materials have functional limitations. Aluminum foil is opaque and cannot be microwave-heated, while aluminized film has low mechanical strength (tensile strength <50 MPa) and is prone to micropores due to creases, leading to barrier failure. In addition, the adhesion between the traditional aluminized layer and the substrate is weak (peel strength <30 N / 15mm), resulting in poor adaptability to composite processing and limiting its application in high-end packaging.

[0003] In recent years, technological advancements have created higher demands: after 2010, the EU's REACH regulation restricted the use of chlorine-containing materials (such as PVDC), driving the development of halogen-free, microwave-safe barrier materials. Alumina coatings, due to their high transparency (transmittance >90%) and high-temperature resistance (>120℃), have become a viable alternative. Researchers have attempted to improve barrier performance through multilayer composite structures, such as alumina-PET composite films or silicon oxide coatings. However, early processes suffered from poor coating uniformity (thickness deviation ±20%) and insufficient adhesion. Industry technological advancements have also driven innovation in coating processes, evolving from electrolytic aluminum evaporation (in the 1980s) to physical vapor deposition (PVD) and chemical vapor deposition (CVD). For example, Germany's 100kW electron gun technology (early 2000s) improved aluminum plating efficiency, but the equipment cost was high; while chemical vapor deposition (CVD) can prepare nanoscale oxide layers (5-10 nm thick), the process is complex and raw material costs are high. Breakthroughs have also been made in composite membrane technology: multilayer co-extruded membranes (such as 9-layer EVOH / PET structures) improve performance by stacking barrier layers, but the increase in the number of layers leads to an increase in thickness (>50 μm) and a decrease in flexibility. Furthermore, the barrier properties of EVOH are significantly reduced in high humidity environments (water vapor permeability increases from 0.8 to 2.5 g / m²·day).

[0004] While the above-mentioned technical and formulation improvements for high-barrier alumina films have achieved certain results, problems such as coating uniformity, barrier performance, and adhesion remain unresolved. Summary of the Invention

[0005] To address the problems of uneven coating, insufficient adhesion, and the need to improve barrier performance in existing high-barrier alumina films, this invention proposes a method for preparing a high-barrier transparent alumina film and the prepared high-barrier transparent alumina film.

[0006] The core of this invention lies in using a PET substrate with specific thermal properties (melting point 240-260℃, with a high-temperature phase content >60% and a low-temperature phase content <20%), and precisely controlling the process parameters during physical vapor deposition (PVD), including substrate running speed, oxygen flow rate, and evaporation temperature. This allows for limited activation of the PET substrate surface under controlled thermal radiation during deposition. This promotes the preferential reaction of evaporated aluminum atoms with broken chemical bonds on the substrate surface, forming an in-situ transition layer with a thickness of 5-10 nm, primarily composed of Al-OC chemical bonds (≥50%). AlOx, formed by the continued reaction of aluminum vapor with oxygen, is then deposited on top, forming a dense inorganic vapor-deposited layer. The presence of this transition layer enhances the adhesion between the coating and the substrate.

[0007] By employing the aforementioned technical solution based on in-situ interfacial chemical bonding and gradient barrier structure design, this invention aims to address the insufficient barrier properties of traditional aluminized films. The key advantage of the high-barrier transparent alumina film prepared by this method lies in its significantly improved barrier performance against water vapor and oxygen, thus providing a high-performance barrier material solution for high-end packaging fields such as food and pharmaceuticals.

[0008] The objective of this invention is achieved by providing a method for preparing a high-barrier transparent alumina film. (1) Select PET with a melting point of 240-260℃, a high-temperature phase content of >60%, and a low-temperature phase content of <20% as the substrate, wherein the low-temperature phase peak position is 120-175°C, the medium-high temperature phase peak position is 180-235°C, and the high-temperature phase peak position is >240°C. (2) The substrate is pretreated by corona treatment, chemical treatment or flame treatment; (3) Preparation of transition layer and inorganic vapor deposition layer The pretreated PET substrate is placed on a physical vapor deposition (PVD) machine reel, the chamber door is closed, and a vacuum chamber is evacuated until the vacuum level reaches 2×10⁻⁶. -4When the temperature reaches MBA or above, start the evaporation boat. Once the evaporation boat is heated to above 1400℃, continuously feed aluminum wire with a purity of 99.9% or higher onto the evaporation boat. After the aluminum wire melts and the evaporation state stabilizes, continuously rotate the substrate at a speed of 530m / min-650m / min while introducing oxygen at a flow rate of 360-450sccm. When the substrate passes over the area above the evaporation boat, the temperature of the contact surface of the substrate is 250-300℃. After removing the substrate from the machine, place it in a drying oven at 50-60℃ for 2-3 days to remove surface moisture, forming a transition layer with a thickness of 5-10 nm and an inorganic vapor-deposited layer with a thickness of 5-30 nm. The transition layer is mainly composed of Al-OC bonding, with a proportion greater than or equal to 50%. The inorganic vapor-deposited layer is an AlOx coating. (4) Preparation of protective coating Weigh isopropanol and water as solvents, stir evenly, add at least one of hydroxyl polymer, metal alkoxide, silane coupling agent or their hydrolysis products, hydrolyze for more than 30 min, add resin polymer, stir for 10-20 min, mix evenly to obtain protective coating solution, the pH value of the coating solution is between 7 and 9. The coating liquid is evenly applied to the surface of the inorganic vapor-deposited layer, and then the coated film is dried to obtain the protective coating.

[0009] In step (3), the substrate first passes through the plasma pretreatment zone and then through the area above the evaporation boat, with a plasma power of 2-5 kW.

[0010] Plasma treatment is performed at a high vacuum of 10... -3 -10 -4 Ar / O2 mixed gas plasma treatment under Pa conditions; Ar / O2 ratio is 80% / 20%.

[0011] After drying, the protective coating has a basis weight of 0.01–3 g / m³. 2 ; The thickness of the PET substrate is 5–200 μm; The thickness of the inorganic vapor-deposited layer is 10-20 nm; The O / Al ratio in the inorganic vapor-deposited layer is between 1.2 and 2.0; After drying, the thickness of the protective coating is 0.1–10 μm.

[0012] After drying, the protective coating has a basis weight of 0.03–1 g / m³. 2 ; The thickness of the PET substrate is 6–30 μm; The O / Al ratio in the inorganic vapor-deposited layer is between 1.2 and 1.8; After drying, the thickness of the protective coating is 0.1–5 μm.

[0013] After drying, the protective coating has a basis weight of 0.24-0.6 g / m³. 2 ; The thickness of the PET substrate is 10–15 μm; The O / Al ratio in the inorganic vapor-deposited layer is between 1.3 and 1.5; After drying, the thickness of the protective coating is 0.2–1 μm.

[0014] In step (4), the drying temperature is 50-150℃ and the time is 30 seconds to 2 minutes.

[0015] The resin polymer is at least one of polyacrylic acid resin, polyvinyl alcohol resin, polyurethane resin, carboxymethyl cellulose, and sodium alginate; The silane coupling agent is at least one of vinyltrimethoxysilane, γ-chloropropylmethyldimethoxysilane, γ-chloropropyltrimethoxysilane, epoxypropyltrimethoxysilane, γ-methacryloyloxypropyltrimethoxysilane, γ-methacryloyloxypropylmethyldimethoxysilane, or polymers of the above substances.

[0016] The protective coating liquid, by mass percentage, comprises 3.6-7.2% polyurethane resin, 0.4-0.8% silane coupling agent, 8-15% isopropanol, and the remainder is deionized water.

[0017] The high-barrier transparent alumina film prepared by the aforementioned preparation method.

[0018] Compared with the prior art, the present invention proposes a method for preparing a high-barrier transparent alumina film and the prepared high-barrier transparent alumina film. Based on in-situ interfacial chemical bonding and gradient barrier structure design, a transition layer with Al-OC bonding as the main component, a proportion greater than or equal to 50%, and a thickness of 5-10 nm is formed to connect the alumina layer and the substrate, so that the alumina layer and the substrate have good bonding force, ensuring that the alumina film has excellent water and oxygen barrier properties. Attached Figure Description

[0019] Figure 1 This is a cross-sectional schematic diagram of the high-barrier membrane involved in the present invention.

[0020] 1 is the PET substrate; 2 is the transition layer; 3 is the inorganic vapor deposition layer; 4 is the protective coating.

[0021] Figure 2 These are the DSC curves of the PET substrate used in the embodiments and comparative examples of this invention. Detailed Implementation

[0022] like Figure 1As shown, a high-barrier transparent alumina film includes, from top to bottom, a substrate layer 1, an intermediate transition layer 2 connecting the substrate and the inorganic vapor deposition layer, an inorganic vapor deposition layer 3, and a protective coating 4.

[0023] The substrate layer primarily provides support, while the transition layer connects the substrate to the inorganic vapor-deposited layer, strengthening their adhesion and providing good barrier properties. The oxide coating and protective coating mainly provide barrier properties against water vapor or oxygen.

[0024] 1) Substrate layer The substrate layer is made of PET substrate, which provides both oxygen and water vapor barrier properties.

[0025] In the PET film that forms the substrate layer, various additives such as flame retardants, slip agents, anti-blocking agents, antioxidants, light stabilizers, tackifiers, and antistatic agents can be added without affecting the mechanical and thermal properties of the main material.

[0026] For the PET film constituting the substrate layer, its preparation process can be either stretching or unstretching. Given that biaxially oriented PET films possess superior mechanical strength, heat resistance, water resistance, and dimensional stability, the present invention preferably uses biaxially oriented PET films.

[0027] There is no particular limitation on the thickness of the PET film used as the substrate layer. For example, the thickness can be set to 5–200 μm or 6–30 μm. Depending on the actual application and required characteristics, such as the need for the substrate to have excellent heat resistance, impact resistance and gas barrier properties, a PET film with a thickness of 10–15 μm is preferred.

[0028] For the PET substrate layer, to improve its surface energy and ensure good printability of the resulting high-barrier film material, at least one of several pretreatment methods, such as chemical treatment, corona treatment, plasma treatment, or flame treatment, can be applied to the substrate surface without compromising its barrier properties. Plasma treatment is preferred, performed under high vacuum (10⁻⁶ ppm). -3 -10 - 4 Under the conditions of Pa), Ar / O2 mixed gas plasma treatment is used, with an Ar / O2 ratio of 80% / 20% and a power of 2-5kW.

[0029] The thermal properties of the substrate were determined by DSC. There is no specific limitation on the melting point of the substrate; it can be above 240°C and below 260°C, or above 250°C and below 260°C. The melting point of the substrate layer can be adjusted by crystallinity, molecular weight, and the proportion of copolymers. The melting point of the substrate was determined using a differential scanning calorimeter at a heating rate of 10°C / min. The melting point (melting peak temperature) determined by DSC can exceed 240°C and can exceed 250°C. A substrate melting point exceeding 240°C allows it to withstand temperatures above 250°C for a short time on a high-speed rotating cooling roller. Simultaneously, the substrate must contain >60% high-temperature phase and <20% low-temperature phase. When testing the DSC curve of the substrate, the results were normalized by peak separation. The peak positions of the low-temperature phase were 120-175°C, the peak positions of the medium- and high-temperature phases were 180-235°C, and the peak positions of the high-temperature phase were >240°C. Using a PET substrate that meets this requirement for PVD alumina deposition ensures that only the surface 5-10 nm of the structural layer is activated and decomposed when subjected to thermal radiation from the high temperature of the evaporation boat. This facilitates the rebonding of aluminum vapor and broken carbon-oxygen double bonds without damaging the overall substrate performance, thus achieving the function of a transition layer that provides chemical connection between the substrate and the inorganic oxide barrier layer.

[0030] 2) Inorganic vapor deposition layer The inorganic vapor-deposited layer is an aluminum oxide layer. The very thin aluminum oxide layer has transparency and good barrier properties.

[0031] For alumina layers, vacuum deposition can be used. Vacuum deposition methods can employ physical vapor deposition (PVD) or chemical vapor deposition (CVD). PVD includes, but is not limited to, vacuum thermal evaporation, magnetron sputtering, and ion plating. CVD includes, but is not limited to, thermal CVD, plasma CVD, and photochemical CVD.

[0032] Among the aforementioned vacuum film deposition methods, resistance heating vacuum evaporation, electron beam evaporation (EB), and plasma-enhanced chemical vapor deposition (PECVD) are preferred. Considering processing costs and production efficiency, resistance heating vacuum evaporation is the optimal choice.

[0033] The alumina thin film prepared by vacuum thermal evaporation is preferably 5 nm to 30 nm thick. A film thickness of around 10 nm provides excellent barrier properties against water vapor and oxygen. When the film thickness is below 30 nm, the internal stress is insufficient to cause deformation or cracking, preventing a decrease in the film's water vapor barrier effect. However, when the film thickness exceeds 30 nm, deformation and cracking are more likely to occur. Furthermore, from an economic perspective, excessively thick films require increased material usage and film formation time, leading to increased costs. Considering both cost and performance, a film thickness of 10 nm to 20 nm is more preferable for the alumina layer.

[0034] 3) Transition layer By limiting the properties of the substrate, when preparing the alumina layer using vacuum evaporation, the substrate is subjected to thermal radiation from the evaporation boat when it rotates to the area above the evaporation boat. The temperature of the substrate contact surface is 250-300℃, which causes the carbon-oxygen double bonds in the activated 5-10nm structural layer on the PET substrate surface to break. Since the bond energy of the Al-OC covalent bond (~200 kJ / mol) is much lower than that of the AlOx covalent bond (~500 kJ / mol), Before the alumina coating is deposited, aluminum vapor preferentially rebonds with the thermally decomposed substrate to form an Al-OC structure, accompanied by the formation of a small amount of AlOx structure, resulting in a transition layer with a thickness of 5-10 nm, which is mainly composed of Al-OC structure and accompanied by a small amount of AlOx structure. After the transition layer structure stabilizes, the aluminum vapor continues to react with oxygen to form alumina, which is then deposited on the transition layer. After the surface cools, a bright alumina layer is formed.

[0035] The O / Al ratio of the alumina layer is preferably between 1.2 and 2.0, at which point the alumina layer easily achieves good transparency. Furthermore, the O / Al ratio is preferably below 2.0, which prevents the alumina layer from becoming too hard due to increased AlOx crystallinity and suppresses the formation of cracks in the alumina layer that would reduce its barrier properties. To better achieve these effects, the O / Al ratio of the alumina layer is preferably 1.2-1.8, more preferably 1.3-1.5.

[0036] The transition layer connecting the alumina layer and the substrate can be characterized using XPS. By etching away 10-20 nm of the coating on the surface with argon ions, the elemental valence distribution at this location was tested, confirming that the transition layer structure is mainly Al-OC, with a small amount of AlOx. The ratio of these two structures can be obtained after XPS peak separation. The O / Al ratio in the inorganic oxide layer can also be determined using XPS. Based on the test results, the spectra were analyzed by peak separation. During quantitative analysis, the relative sensitivity factors for O1s and Al2p were 0.19 and 0.78, respectively.

[0037] 4) Protective coating The protective coating is a top coating applied to the inorganic vapor-deposited layer to protect it and prevent it from cracking and deteriorating in performance.

[0038] In addition, the protective coating is a barrier coating that, through its synergistic effect with the inorganic vapor-deposited layer, enables the high-barrier film to exhibit excellent overall barrier performance.

[0039] The protective coating can be applied using a coating solution with water or a water / alcohol mixture as the solvent. The coating solution contains at least one of a hydroxyl polymer, a metal alkoxide, a silane coupling agent, or a hydrolysis product thereof, preferably at least a silane coupling agent or a hydrolysis product thereof. For example, the silane coupling agent can be added directly to an aqueous (water or water / alcohol mixture) solvent, pre-treated by hydrolysis, etc., before mixing with the main resin material.

[0040] As a silane coupling agent, the following substances can be selected: vinyltrimethoxysilane, γ-chloropropylmethyldimethoxysilane, γ-chloropropyltrimethoxysilane, glycidoxypropyltrimethoxysilane, γ-methacryloyloxypropyltrimethoxysilane, γ-methacryloyloxypropylmethyldimethoxysilane, etc., or polymers of the above substances can also be used as silane coupling agents.

[0041] Examples of resin polymers used in coating solutions include: polyacrylic acid resin, polyvinyl alcohol resin, polyurethane resin, carboxymethyl cellulose, sodium alginate, etc. Among these polymers, polyester-based polyurethane resin (PU) is preferred for protective coatings in terms of heat resistance and interlayer adhesion. This resin has excellent barrier properties and good compatibility with inorganic oxides.

[0042] The protective coating liquid, by mass percentage, comprises 3.6-7.2% polyurethane resin, 0.4-0.8% silane coupling agent, 8-15% isopropanol, and the remainder is deionized water.

[0043] The thickness of the protective coating is preferably more than 10 times the thickness of the inorganic oxide layer. Within this thickness range, the inorganic oxide layer can be better prevented from cracking, and the overall barrier performance of the high-barrier film can be further improved. In addition, considering the processing adaptability of the high-barrier film, film flexibility, and cost, the thickness of the protective coating is preferably less than 50 times the thickness of the inorganic oxide layer.

[0044] The thickness of the protective coating is preferably 0.1–10 μm, more preferably 0.1–5 μm, and even more preferably 0.2–1 μm. By controlling its thickness within the above range, it is possible to protect against the cracking of inorganic oxides while further improving the barrier properties.

[0045] For protective coatings applied over inorganic oxide layers, there are no particular limitations on the coating method. Various methods can be used, including roller coating, dip coating, gravure coating, air knife coating, and spray coating. Roller coating is preferred, and a suitable coating roller should be selected based on the liquid-to-solid content of the coating.

[0046] There are no particular limitations on the drying method for the coating film formed by the coating liquid. For example, the coating film can be dried by hot roller drying, hot air drying, infrared irradiation, UV irradiation, high frequency irradiation, or a combination of the above methods.

[0047] The drying method for the coated film is selected based on actual conditions. The drying conditions can be appropriately chosen according to the selected drying method. For example, when using an oven drying method, the drying temperature can be set between 50 and 150°C, preferably between 80 and 130°C. The drying time is preferably set between 30 seconds and 2 minutes. By controlling the drying temperature within this range, cracks in the inorganic oxide layer and the protective coating covering it can be further suppressed, resulting in a high-barrier film material exhibiting excellent barrier properties.

[0048] The coating amount for the protective coating is preferably 0.01–3 g per square meter, more preferably 0.03–1 g, and even more preferably 0.24–0.6 g, after the coating solution dries. When the mass per square meter of the coated film formed by the coating solution is within the above range after drying, the film formation is more complete, the drying is more thorough, and solvent residue is less likely to remain. This results in a high-barrier membrane material with uniform, stable, and good performance.

[0049] The solid content of polyurethane resin is 24-32%.

[0050] The total basis weight of the high-barrier transparent alumina film is 55-70 g / m³. 2 .

[0051] A method for preparing a high-barrier transparent alumina film includes the following steps: (1) Select PET with a melting point of 240-260℃, a high-temperature phase content of >60%, and a low-temperature phase content of <20% as the substrate, wherein the low-temperature phase peak position is 120-175°C, the medium-high temperature phase peak position is 180-235°C, and the high-temperature phase peak position is >240°C. (2) The substrate is pretreated by corona treatment, chemical treatment or flame treatment; (3) Preparation of transition layer and inorganic vapor deposition layer The pretreated PET substrate is placed on a physical vapor deposition (PVD) machine (referring to a machine for vacuum evaporation of alumina film) onto a reel. The chamber door is closed, and a vacuum chamber is evacuated until the vacuum level reaches 2×10⁻⁶. -4When the temperature reaches MBA or above, start the evaporation boat. Once the evaporation boat is heated to above 1400℃, continuously feed aluminum wire with a purity of 99.9% or higher onto the evaporation boat. After the aluminum wire melts and the evaporation state stabilizes, continuously rotate the substrate at a speed of 530m / min-650m / min while introducing oxygen at a flow rate of 360-450sccm. When the substrate passes over the area above the evaporation boat, the temperature of the contact surface of the substrate is 250-300℃. After removing the substrate from the machine, place the resulting roll in a drying oven at 50-60℃ for 2-3 days to remove surface moisture. This forms a transition layer with a thickness of 5-10 nm and an inorganic vapor-deposited layer with a thickness of 5-30 nm. The transition layer is mainly composed of Al-OC bonding, with a proportion greater than or equal to 50%. The inorganic vapor-deposited layer is an AlOx coating. (4) Preparation of protective coating Weigh isopropanol and water as solvents, stir evenly, add at least one of hydroxyl polymer, metal alkoxide, silane coupling agent or their hydrolysis products, hydrolyze for more than 30 min, add resin polymer, stir for 10-20 min, mix evenly to obtain protective coating solution, the pH value of the coating solution is between 7 and 9. The coating liquid is evenly applied to the surface of the inorganic vapor-deposited layer, and then the coated film is dried to obtain the protective coating.

[0052] In step (3), the substrate is first pretreated by plasma and then passes through the area above the evaporation boat with a plasma power of 2-5 kW. At this time, the rapidly rotating substrate surface is first pretreated by plasma, and functional chemical groups (such as -OH, -COOH) are actually formed on the surface. When the substrate rotates to the area above the evaporation boat, it is subjected to thermal radiation from the evaporation boat, and the temperature of the contact surface is 250-300℃. Therefore, the carbon-oxygen double bonds on the activated PET substrate surface will break. Since the bond energy of the Al-OC covalent bond (~200 kJ / mol) is much lower than that of the AlOx covalent bond (~500 kJ / mol), aluminum vapor preferentially rebonds with it to form an Al-OC structure, accompanied by the formation of a small amount of AlOx structure. After the transition layer structure is stable, aluminum vapor continues to react with oxygen to form aluminum oxide, which is deposited on the transition layer. After the surface cools, a bright aluminum oxide coating is formed with a thickness of 10-20 nm. After the roll is removed from the machine, it is placed in a drying room at 50-60℃ for 2-3 days to remove surface moisture and allow the alumina coating to react more fully, resulting in a dense alumina film.

[0053] The present invention will now be described in detail with reference to specific embodiments. It should be noted that these embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Those skilled in the art can make some non-essential improvements and adjustments based on the above description of the present invention.

[0054] Preparation of coating liquid for protective coating Raw material sources: Silane coupling agent—γ-glycidyl etheroxypropyltrimethoxysilane, trade name: Silquest™ A-187 Silane, solids content >98%, manufactured by MomentivePerformance Materials Inc.; polyurethane resin, trade name: TAKELAC TM WPB-341, solid content: 30%, Mitsui Chemicals Co., Ltd.

[0055] Coating liquid 1 The coating solution had a solid content of 3%, with isopropanol comprising 15% and deionized water 82%. The solids contained 10% silane coupling agent and 90% polyurethane resin. First, isopropanol and deionized water were mixed thoroughly. Then, γ-glycidyl etheroxypropyltrimethoxysilane, used as the silane coupling agent, was added and hydrolyzed for 30 minutes. Next, polyurethane resin was added, and the mixture was stirred until homogeneous, yielding a coating solution with a pH of approximately 8.

[0056] Coating liquid 2 The coating solution had a solid content of 4%, with isopropanol comprising 15% and deionized water 81%. The solids contained 10% silane coupling agent and 90% polyurethane resin. First, isopropanol and deionized water were mixed thoroughly. Then, γ-glycidyl etheroxypropyltrimethoxysilane, used as the silane coupling agent, was added and hydrolyzed for 30 minutes. Next, polyurethane resin was added and the mixture was stirred until homogeneous, yielding the coating solution with a pH of approximately 8.

[0057] Coating liquid 3 The coating solution had a solid content of 5%, with isopropanol comprising 15% and deionized water 80%. The solids contained 10% silane coupling agent and 90% polyurethane resin. First, isopropanol and deionized water were mixed thoroughly. Then, γ-glycidyl etheroxypropyltrimethoxysilane, used as the silane coupling agent, was added and hydrolyzed for 30 minutes. Next, polyurethane resin was added and stirred until homogeneous, yielding the coating solution with a pH of approximately 8.

[0058] Coating liquid 4 The coating solution had a solid content of 6%, with isopropanol comprising 15% and deionized water 79%. The solids contained 10% silane coupling agent and 90% polyurethane resin. First, isopropanol and deionized water were mixed thoroughly. Then, γ-glycidyl etheroxypropyltrimethoxysilane, used as the silane coupling agent, was added and hydrolyzed for 30 minutes. Next, polyurethane resin was added and the mixture was stirred until homogeneous, yielding a coating solution with a pH of approximately 8.

[0059] Coating liquid 5 The coating solution had a solid content of 7%, with isopropanol comprising 15% and deionized water 78%. The solids contained 10% silane coupling agent and 90% polyurethane resin. First, isopropanol and deionized water were mixed thoroughly. Then, γ-glycidyl etheroxypropyltrimethoxysilane, used as the silane coupling agent, was added and hydrolyzed for 30 minutes. Next, polyurethane resin was added and stirred until homogeneous, yielding the coating solution with a pH of approximately 8.

[0060] Coating liquid 6 The coating solution had a solid content of 8%, with isopropanol comprising 15% and deionized water 77%. The solids contained 10% silane coupling agent and 90% polyurethane resin. First, isopropanol and deionized water were mixed thoroughly. Then, γ-glycidyl etheroxypropyltrimethoxysilane, used as the silane coupling agent, was added and hydrolyzed for 30 minutes. Next, polyurethane resin was added and the mixture was stirred until homogeneous, yielding the coating solution with a pH of approximately 8.

[0061] Example 1 PET substrate First, a 12μm thick biaxially oriented PET substrate was prepared as the substrate, and its thermal properties were evaluated using DSC. The test results are as follows. Figure 2 As shown, the red curve is the overall fitted curve, not a peak-splitting curve. Therefore, in the peak-splitting curve, the peak at 143℃ corresponds to the low-temperature phase, the peak at 200℃ corresponds to the medium-high temperature phase, and the two peaks above 240℃ both correspond to the high-temperature phase. After normalizing the peak areas of the DSC curve, the proportions of each phase are obtained: low-temperature phase, medium-high temperature phase, and high-temperature phase are 19%, 11%, and 70%, respectively. Furthermore, the DSC test results show that the melting point of this substrate is 255℃. This meets the requirements for PET substrates in this application and can be used as a substrate. In addition, the PET substrates used in other embodiments and comparative examples of this application are the same as those in Example 1.

[0062] Preparation of transition layer and inorganic vapor deposition layer An alumina film is deposited on the corona-treated surface of a biaxially oriented PET substrate, which serves as a support layer. Using resistance thermal evaporation, a transition layer and a transparent alumina coating (i.e., an inorganic evaporation layer) with thicknesses of 8 nm and 12 nm are grown sequentially on the PET substrate under vacuum. The PET substrate is placed on the unwinding shaft of a PVD (vacuum evaporation alumina film deposition) device, the chamber door is closed, and a vacuum chamber is evacuated until the vacuum level reaches 2 × 10⁻⁶. -4During the MBA process, the evaporation boat is activated, with its power set to 5kW. Once the evaporation boat temperature rises above 1400℃ and is maintained at this level, the aluminum wire feeding program is initiated, continuously feeding aluminum wire with a purity of 99.9% or higher onto the evaporation boat. This allows the aluminum wire to continuously melt, spread, and evaporate on the evaporation boat. The adjustment of this process is crucial for the uniformity of the inorganic coating deposition. After the aluminum wire melting and evaporation state stabilizes, the web is activated, allowing the PET substrate to run at a speed of 550m / min. Oxygen is introduced, with the oxygen flow rate set to 380sccm. At this point, the substrate path first passes through the plasma treatment area. This plasma is a low-temperature non-equilibrium plasma, generated under high vacuum by an Ar / O2 mixed gas with an Ar / O2 ratio of 80% / 20% and a power set to 3kW. This only activates the substrate surface to generate polar groups such as -OH and -COOH without causing the polymer substrate's internal chain breakage or mechanical property deterioration. The substrate body temperature remains within a safe range, preventing thermal deformation. When the substrate passes over the area above the evaporation boat, the temperature of the contact surface of the substrate is 250-300℃, which further activates the surface layer within 5-10nm of the substrate surface and preferentially bonds with the evaporated aluminum atoms to form an Al-OC transition layer. Then, the evaporated aluminum atoms continue to react with oxygen to form aluminum oxide, which is deposited on the transition layer to form an inorganic vapor deposition layer. The optical density value of the aluminum oxide coating is set to 0.10, and finally a barrier film sample with the structure of substrate / transition layer / transparent aluminum oxide coating (i.e., inorganic vapor deposition layer) is obtained. The thicknesses of the transition layer and the inorganic vapor deposition layer are 8nm and 12nm, respectively, and the O / Al ratio in the AlOx of the inorganic vapor deposition layer is 1.4.

[0063] Example 2 Except for the plasma treatment being turned off, the alumina barrier film was prepared in the same manner and with the same parameters as in Example 1, resulting in a barrier film sample with a transition layer and a transparent alumina coating (i.e., an inorganic vapor deposition layer) thicknesses of approximately 8 nm and 12 nm, respectively.

[0064] Comparative Example 1 An alumina film was deposited on the corona-treated surface of a biaxially oriented PET substrate, serving as a support layer. Using resistance thermal evaporation, a transition layer and a transparent alumina coating (i.e., an inorganic vapor deposition layer) with thicknesses of 5 nm and 10 nm, respectively, were grown on the PET substrate under vacuum. The transition layer and inorganic vapor deposition layer were prepared according to the steps of Example 1, with the following parameters modified: plasma power 3 kW, vehicle speed 650 m / min, and oxygen flow rate 450 sccm. This resulted in a transition layer primarily composed of an Al-OC structure and an inorganic vapor deposition layer with an O / Al ratio of 2.0. This yielded a barrier film sample with a structure of substrate / transition layer / transparent alumina coating (i.e., inorganic vapor deposition layer).

[0065] (1) XPS analysis of samples with a structure of substrate / transition layer / inorganic alumina coating barrier film XPS tests were performed on the samples prepared in Examples 1, 2, and Comparative Example 1, and depth profile data were collected for the surface and after etching away the inorganic coating. According to the test results, in Example 1, the transition layer mainly consisted of Al-OC bonding, accounting for approximately 90%, with AlOx structures accounting for approximately 10%. The surface inorganic vapor-deposited Al layer exhibited Al-O-Al bonding, with an O / Al ratio of approximately 1.4. In Example 2, the transition layer was still dominated by Al-OC, accounting for approximately 88%, with AlOx structures accounting for approximately 12%. The surface inorganic vapor-deposited Al layer also exhibited Al-O-Al bonding, with an O / Al ratio of approximately 1.4. In Comparative Example 1, the transition layer element distribution showed that Al-OC and AlOx structures were almost equally distributed, and the surface inorganic coating Al still existed as AlOx, with an O / Al ratio of approximately 2.0. This indicates that during alumina deposition, the PET substrate surface is subjected to a certain degree of thermal radiation, causing partial breakage of the carbon-oxygen double bonds on the surface. Under low oxygen flow conditions, evaporated Al atoms preferentially form bonds with these bonds, forming a transition layer dominated by the Al-OC structure. Under higher oxygen flow conditions, the ratio of broken bonds in the Al vapor and PET to bonded bonds in the oxygen is similar, constituting the transition layer structure. After the transition layer structure stabilizes, the evaporated Al atoms continue to react with oxygen to form an AlOx coating on top of the transition layer. The role of plasma is mainly to oxidize the PET to increase its surface energy, which facilitates subsequent topcoat application and improves printability during use.

[0066] (2) Characterization of coating uniformity Scanning electron microscopy (SEM) images were taken from three positions (left, center, and right) across the entire width of the samples obtained in Examples 1, 2, and Comparative Example 1 to observe the surface morphology of the coating layer. The test results showed that the morphology distribution at the three different positions of each sample was consistent, and the overall morphology was uniform and stable.

[0067] Example 3 A 12μm thick biaxially oriented PET substrate was selected as the support layer material.

[0068] Preparation of transition layer and inorganic vapor deposition layer An alumina film was deposited on the corona-treated surface of a biaxially oriented PET substrate, which served as a support layer. Using a resistance thermal evaporation heating method, an Al-OC transition layer and a transparent alumina coating with thicknesses of approximately 8 nm and 12 nm, respectively, were grown on the PET substrate under vacuum. An inorganic vapor-deposited layer with an O / Al ratio of 1.4 was formed according to the method and parameters of Example 1. This yielded a barrier film sample with a structure of substrate / transition layer / transparent alumina coating (i.e., inorganic vapor-deposited layer).

[0069] Preparation of protective coating The coating liquid 1 is applied onto the substrate using a wire rod coating method and dried at 100°C to form a protective coating with a thickness of approximately 150 nm. This results in a high-barrier material with a structure of substrate layer / transition layer / transparent alumina coating (i.e., inorganic vapor deposition layer) / protective coating.

[0070] Example 4 A 12μm thick biaxially oriented PET substrate was selected as the support layer material.

[0071] Preparation of transition layer and inorganic vapor deposition layer An alumina film was deposited on the corona-treated surface of a biaxially oriented PET substrate, which served as a support layer. Using a resistance thermal evaporation heating method, an Al-OC transition layer and a transparent alumina coating (i.e., an inorganic vapor-deposited layer) with thicknesses of approximately 8 nm and 12 nm, respectively, were grown on the PET substrate under vacuum. Following the method and parameters of Example 1, an inorganic vapor-deposited layer with an O / Al ratio of 1.4 was formed. This yielded a barrier film sample with a structure of substrate / transition layer / transparent alumina coating (i.e., an inorganic vapor-deposited layer).

[0072] Preparation of protective coating On the aforementioned alumina coating, coating liquid 2 is applied using a wire rod coating method and dried at 100°C to form a protective coating with a thickness of approximately 200 nm. This results in a high-barrier material with a structure of substrate layer / transition layer / transparent alumina coating (i.e., inorganic vapor deposition layer) / protective coating.

[0073] Example 5 A 12μm thick biaxially oriented PET substrate was selected as the support layer material.

[0074] Preparation of transition layer and inorganic vapor deposition layer An alumina film was deposited on the corona-treated surface of a biaxially oriented PET substrate, which served as a support layer. Using a resistance thermal evaporation heating method, an Al-OC transition layer and a transparent alumina coating (i.e., an inorganic vapor-deposited layer) with thicknesses of approximately 8 nm and 12 nm, respectively, were grown on the PET substrate under vacuum. Modified to: an inorganic vapor-deposited layer with an O / Al ratio of 1.4 was formed according to the method and parameters of Example 1. This yielded a barrier film sample with a structure of substrate / transition layer / transparent alumina coating (i.e., an inorganic vapor-deposited layer).

[0075] Preparation of protective coating On the aforementioned alumina coating, coating liquid 3 is applied using a wire rod coating method and dried at 100°C to form a protective coating with a thickness of approximately 250 nm. This results in a high-barrier material with a structure of substrate layer / transition layer / transparent alumina coating (i.e., inorganic vapor deposition layer) / protective coating.

[0076] Example 6 A 12μm thick biaxially oriented PET substrate was selected as the support layer material.

[0077] Preparation of transition layer and inorganic vapor deposition layer An alumina film was deposited on the corona-treated surface of a biaxially oriented PET substrate, which served as a support layer. Using a resistance thermal evaporation heating method, an Al-OC transition layer and a transparent alumina coating (i.e., an inorganic vapor-deposited layer) with thicknesses of approximately 8 nm and 12 nm, respectively, were grown on the PET substrate under vacuum. Following the method and parameters of Example 1, an inorganic vapor-deposited layer with an O / Al ratio of 1.4 was formed. This yielded a barrier film sample with a structure of substrate / transition layer / transparent alumina coating (i.e., an inorganic vapor-deposited layer).

[0078] Preparation of protective coating On the aforementioned alumina coating, coating liquid 4 is applied using a wire rod coating method and dried at 100°C to form a protective coating with a thickness of approximately 300 nm. This results in a high-barrier material with a structure of substrate layer / transition layer / transparent alumina coating (i.e., inorganic vapor deposition layer) / protective coating.

[0079] Example 7 A 12μm thick biaxially oriented PET substrate was selected as the support layer material.

[0080] Preparation of transition layer and inorganic vapor deposition layer An alumina film was deposited on the corona-treated surface of a biaxially oriented PET substrate, which served as a support layer. Using a resistance thermal evaporation heating method, an Al-OC transition layer and a transparent alumina coating (i.e., an inorganic vapor-deposited layer) with thicknesses of approximately 8 nm and 12 nm, respectively, were grown on the PET substrate under vacuum. Following the method and parameters of Example 1, an inorganic vapor-deposited layer with an O / Al ratio of 1.4 was formed. This yielded a barrier film sample with a structure of substrate / transition layer / transparent alumina coating (i.e., an inorganic vapor-deposited layer).

[0081] Preparation of protective coating On the aforementioned alumina coating, coating liquid 5 is applied using a wire rod coating method and dried at 100°C to form a protective coating with a thickness of approximately 360 nm. This results in a high-barrier material with a structure of substrate layer / transition layer / transparent alumina coating (i.e., inorganic vapor deposition layer) / protective coating.

[0082] Example 8 A 12μm thick biaxially oriented PET substrate was selected as the support layer material.

[0083] Preparation of transition layer and inorganic vapor deposition layer An alumina film was deposited on the corona-treated surface of a biaxially oriented PET substrate, which served as a support layer. Using a resistance thermal evaporation heating method, an Al-OC transition layer and a transparent alumina coating (i.e., an inorganic vapor-deposited layer) with thicknesses of approximately 8 nm and 12 nm, respectively, were grown on the PET substrate under vacuum. Following the method and parameters of Example 1, an inorganic vapor-deposited layer with an O / Al ratio of 1.4 was formed. This yielded a barrier film sample with a structure of substrate / transition layer / transparent alumina coating (i.e., an inorganic vapor-deposited layer).

[0084] Preparation of protective coating On the aforementioned alumina coating, coating liquid 6 is applied using a wire rod coating method and dried at 100°C to form a protective coating with a thickness of approximately 420 nm. This results in a high-barrier material with a structure of substrate layer / transition layer / transparent alumina coating (i.e., inorganic vapor deposition layer) / protective coating.

[0085] Comparative Example 2 A 12μm thick biaxially oriented PET substrate was selected as the support layer material.

[0086] A protective coating is directly applied to the corona-treated surface of a biaxially oriented PET substrate, which serves as the support layer. Coating liquid 4 is applied using a wire rod coating method and dried at 100°C to form a protective coating approximately 300 nm thick. This yields a barrier material with a substrate layer / protective coating structure.

[0087] [Performance Testing] Oxygen permeability (OTR) The oxygen permeability of the prepared barrier membrane was tested using the following method. Samples were cut to specified sizes and shapes, and the oxygen permeability was measured at 23°C and 50% relative humidity (GB / T 19789-2005). The measurement was performed using an oxygen permeability measuring apparatus (MOCON, model: OX-TRAN2 / 22). The unit of measurement is [cc / m]. 2 [day]. The results are shown in Table 1.

[0088] Water vapor transmission rate (WVTR) The samples were cut to the specified size and shape, and the water vapor transmission rate was measured at 38°C and 90% relative humidity (GB / T 26253-2010). The measurement was performed using a water vapor transmission rate measuring apparatus (MOCON, model: PERMATRAN-W3 / 61). The unit of measurement is [g / m³]. 2 [day]. The results are shown in Table 1.

[0089] Light transmittance The samples were cut to the specified size, and their transmittance was measured at 23℃ and 50% relative humidity (GB / T 2410-2008). A transmittance / haze meter (Shanghai Shenguang Instrument Co., Ltd., model WGT-S) was used, and the measured values ​​were percentages. The results are shown in Table 1.

[0090] Ink adhesion According to the "Ink Adhesion Test Method" GB / T 13217.7-2023, ink adhesion is tested using the cross-cut method. A standardized cutting tool is used to cut an orthogonal grid with a 1mm spacing on the ink coating surface. After removing the grid with 3M tape, the percentage of the area that has peeled off is evaluated. The grading system uses a 0-5 system, corresponding to 5B (best adhesion) to 0B (complete peeling) in the ISO / ASTM standards.

[0091] Table 1 In Example 1, where the O / Al ratio in the inorganic oxide coating is 1.4, both water vapor and oxygen permeability are lower than in Comparative Example 1 (O / Al ratio 2.0), indicating a higher gas barrier effect. This suggests that under relatively low vehicle speed and low oxygen flow, the substrate undergoes good surface activation after being subjected to thermal radiation from the evaporation boat during rapid rotation, forming a transition layer mainly composed of Al-OC bonds, resulting in a good bond between the substrate and the alumina coating. However, under excessively high vehicle speed and high oxygen flow, the substrate rotates too quickly, and the atmosphere with a high oxygen concentration is more conducive to alumina formation. The resulting transition layer has a similar Al-OC and AlOx ratio, and the coating thickness is relatively thin, thus the barrier properties of the sample are slightly worse.

[0092] In Example 2, the plasma treatment was turned off during the preparation of the alumina barrier film, and the performance was not significantly different from that of the barrier film in Example 1. XPS testing showed that even without plasma treatment, the substrate, under the thermal radiation of the evaporation boat during the PVD process, still forms a surface activation layer on its surface. Aluminum vapor rebonds with the broken carbon-oxygen double bonds to form a transition layer, and an oxide coating is deposited on this transition layer to obtain a barrier film material with a structure of substrate / transition layer / oxide coating.

[0093] In Examples 3-8, the barrier properties of the samples gradually improved as the solid content of the coating liquid increased. However, considering cost and processing convenience, the coating liquid formulation used in Example 6 was selected after comprehensive evaluation.

[0094] Performance testing revealed that Examples 3-8, with a barrier film structure of substrate / transition layer / inorganic oxide coating / protective coating, exhibited lower water vapor and oxygen permeability than the three / two-layer barrier films of Examples 1, Comparative Example 1 (substrate / transition layer / alumina structure), and Comparative Example 2 (substrate / coating structure). This demonstrates that the four-layer high-barrier film provided by the present invention possesses excellent barrier performance. All samples exhibited excellent light transmittance. Except for Comparative Example 2, the other samples demonstrated excellent ink adhesion. Ink adhesion testing is crucial for ensuring printing quality, especially in food packaging and other fields with high safety requirements. Through standardized testing methods, printing companies can effectively control product quality and reduce the generation of defective products.

[0095] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. It should be noted that for those skilled in the art and any person skilled in the art, any equivalent substitutions or changes made to the technical solution and inventive concept of the present invention without departing from the overall concept of the present invention, as well as any changes and improvements made, should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a high-barrier transparent alumina film, characterized in that: (1) PET with a melting point of 240-260°C, a high-temperature phase substance content of >60%, and a low-temperature phase substance content of <20% is selected as a base material, wherein the low-temperature phase substance peak position is 120-175°C, the medium-high-temperature phase substance peak position is 180-235°C, and the high-temperature phase substance peak position is >240°C; (2) the base material is pretreated by corona treatment, chemical treatment, or flame treatment; (3) a transition layer and an inorganic vapor deposition layer are prepared; and (4) a protective coating is prepared; the isopropanol and water are weighed as solvents, at least one of a hydroxyl high-molecular compound, a metal alkoxide, a silane coupling agent, or a hydrolysis product thereof is added after stirring, and the mixture is stirred for 30 min or more, a resin high-molecular compound is added, and the mixture is stirred for 10-20 min, and the protective coating coating solution is obtained after mixing, wherein the pH value of the coating solution is 7-9; the coating solution is uniformly coated on the surface of the inorganic vapor deposition layer, and then the film after coating is dried to obtain the protective coating. In the step (3), the base material first passes through a plasma pretreatment zone and then passes through an evaporation boat area above, and the plasma power is 2-5 kW.

4. The method for preparing a high-barrier transparent alumina film according to claim 1, characterized in that: the thickness of the PET base material is 5-200 μm; the thickness of the inorganic vapor deposition layer is 10-20 nm; the O / Al ratio in the inorganic vapor deposition layer is 1.2-2.0; and the thickness of the protective coating after drying is 0.1-10 μm.

5. The method for preparing a high-barrier transparent alumina film according to claim 4, characterized in that: the thickness of the PET base material is 6-30 μm; the O / Al ratio in the inorganic vapor deposition layer is 1.2-1.8; and the thickness of the protective coating after drying is 0.1-5 μm. The pretreated PET substrate is placed on a physical vapor deposition (PVD) equipment roll shaft, the door is closed to vacuumize the vacuum chamber, when the vacuum degree reaches 2x10 -4 mba or above, the evaporation boat is opened, when the evaporation boat is warmed to 1400℃ or above, the aluminum wire with purity of 99.9% or above is continuously sent to the evaporation boat, when the aluminum wire is in a state of melting and evaporation, the substrate is continuously rotated at a speed of 530m / min-650m / min, oxygen is introduced, the oxygen flow is 360-450sccm, when the substrate passes through the area above the evaporation boat, the temperature of the contact surface of the substrate is 250-300℃; after the machine is turned off, the obtained roll material is dried in a 50-60℃ drying room for 2-3 days to remove the surface water vapor, forming a transition layer with a thickness of 5-10nm and an inorganic evaporation layer with a thickness of 5-30nm; the Al-O-C bond is mainly formed in the transition layer, the proportion is greater than or equal to 50%; the inorganic evaporation layer is an AlOx plating layer; 6. The method for preparing a high-barrier transparent alumina film according to claim 5, characterized in that: the thickness of the PET base material is 10-15 μm; the O / Al ratio in the inorganic vapor deposition layer is 1.3-1.5; and the thickness of the protective coating after drying is 0.2-1 μm.

7. The method for preparing a high-barrier transparent alumina film according to claim 1, characterized in that: in the step (4), the drying temperature is 50-150°C, and the drying time is 30 s-2 min; the resin high-molecular compound is at least one of a polyacrylic acid resin, a polyvinyl alcohol resin, a polyurethane resin, carboxymethyl cellulose, and sodium alginate; and the silane coupling agent is at least one of vinyltrimethoxysilane, γ-chloropropylmethyldimethoxysilane, γ-chloropropyltrimethoxysilane, epoxypropoxypropyltrimethoxysilane, γ-methacryloyloxypropyltrimethoxysilane, γ-methacryloyloxypropylmethyldimethoxysilane, and a polymer of the above-mentioned substances. The protective coating coating solution comprises, by mass percentage, 3.6-7.2% of a polyurethane resin, 0.4-0.8% of a silane coupling agent, 8-15% of isopropanol, and the rest is deionized water.

2. The method of claim 1, wherein: ​ 3. The method of claim 2, wherein the method further comprises: The plasma treatment is: plasma treatment in high vacuum 10 -3 -10 -4 Ar / O2 mixture plasma treatment under Pa conditions; Ar / O2 ratio 80% / 20%. ​ After drying, the protective coating has a coat weight of 0.01 to 3 g / m 2 ; ​ ​ ​ ​ ​ After drying, the protective coating has a coat weight of 0.03 to 1 g / m 2 ; ​ ​ ​ ​ After drying, the protective coating has a coat weight of 0.24-0.6 g / m 2 ; ​ ​ ​ ​ ​ 8. The method of claim 1, wherein: ​ ​ 9. The method of claim 8, wherein the method further comprises: ​ 10. A high barrier transparent alumina film prepared according to the method of any one of claims 1 to 9.

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