How does high-barrier aluminized PET film achieve excellent barrier properties and multifunctional applications?

1. Analysis of the structure and barrier mechanism of high barrier metallized PET film

In the field of modern packaging materials, high barrier metallized PET film stands out with its excellent performance and has become the preferred material for many industries. To deeply understand why it can achieve excellent barrier properties and multifunctional applications, we must first explore its unique structure and barrier mechanism.

PET (polyethylene terephthalate) film itself has certain barrier properties. Its molecular chain structure is regular and closely arranged, which can block the penetration of gas and moisture to a certain extent. However, in order to meet higher barrier requirements, the aluminizing process is applied to PET film, thus forming a high barrier aluminized PET film.

High barrier aluminized PET film usually consists of a multi-layer structure. The most basic is the PET base layer, which provides good mechanical properties and processing properties for the entire film. The thickness of the PET base layer is generally between 12 and 50 microns, and different thicknesses are suitable for different application scenarios. For example, in the field of food packaging, a thinner PET base layer (12-25 microns) can both ensure a certain strength and reduce costs; while in some industrial packaging with higher requirements for mechanical strength, a thicker PET base layer (25-50 microns) will be used.

On top of the PET base layer is the aluminum coating. The aluminum coating is a key part to achieve high barrier properties. Its thickness is extremely thin, usually between 30 and 100 nanometers. The aluminum coating process generally uses vacuum evaporation. In a high vacuum environment, the aluminum wire is heated to a vaporized state, and the aluminum vapor is deposited on the surface of the PET film to form a continuous and dense metal aluminum layer. This aluminum coating is like a solid barrier that can effectively block the penetration of gases and liquids such as oxygen and water vapor. Aluminum atoms are closely arranged with almost no pores, making it difficult for gas molecules and water molecules to pass through.

In order to protect the aluminum coating and prevent it from being damaged during subsequent processing and use, a protective layer is usually applied on top of the aluminum coating. The protective layer is generally composed of transparent polymer materials, such as acrylic resin, polyester resin, etc., and its thickness is between 0.5 and 2 microns. This protective layer can not only prevent the aluminum coating from being scratched and worn, but also improve the chemical stability of the film and enhance its weather resistance.

From the perspective of barrier mechanism, high barrier metallized PET film mainly achieves high barrier performance through physical barrier and chemical action. In terms of physical barrier, the presence of the aluminized layer greatly increases the path length for gas and liquid molecules to penetrate. When gas or liquid molecules try to pass through the film, they need to bypass the countless aluminum atoms in the aluminized layer, which makes the penetration process extremely difficult. In addition, due to the density of the aluminized layer, gas and liquid molecules can hardly pass directly and can only penetrate through defects in the aluminized layer (such as pinholes, cracks, etc.). In actual production, by strictly controlling the aluminized process, the number and size of these defects can be controlled within a very small range, thereby further improving the barrier performance.

In terms of chemical reaction, aluminum is an active metal. When it comes into contact with oxygen, a very thin layer of aluminum oxide (Al2O3) film will quickly form on the surface. This aluminum oxide film has good chemical stability and barrier properties, which can further prevent the penetration of oxygen. At the same time, for some corrosive gases or liquids, the aluminum oxide film can also play a certain protective role, protecting the aluminum coating from corrosion, thereby maintaining the barrier properties of the film.

In addition, the molecular structure of the PET base layer also contributes to the barrier properties. The ester group (-COO-) in the PET molecular chain is polar and can interact with some polar molecules (such as water molecules) to hinder the diffusion of water molecules. Moreover, the van der Waals force and hydrogen bonding between the PET molecular chains make the molecular chains more closely arranged, further reducing the permeation rate of gas and liquid molecules.

The multi-layer structure design and unique barrier mechanism of high barrier metallized PET film enable it to play an important role in many fields. Whether it is food packaging, pharmaceutical packaging, or electronics, daily chemicals and other industries, they all benefit from the excellent barrier properties of this material, providing reliable protection for the storage and transportation of products.

2. Key performance indicators: water and oxygen barrier, mechanical strength and weather resistance

The reason why high-barrier metallized PET film is so popular in the market is closely related to its outstanding key performance indicators, among which water and oxygen barrier properties, mechanical strength and weather resistance are particularly important. These performance indicators directly determine the applicability and reliability of the film in different application scenarios.

• Water and oxygen barrier is one of the core properties of high barrier aluminized PET film. In the field of food packaging, the presence of oxygen will cause the oil in the food to oxidize and become rancid, causing the food to produce odor and deteriorate, shortening the shelf life of the food; while the penetration of water vapor will make the food damp, affecting its taste and quality. For pharmaceutical packaging, the intrusion of oxygen and moisture may trigger chemical reactions in the medicine, causing the medicine to fail or even produce harmful substances. High barrier aluminized PET film can effectively block the penetration of oxygen and water vapor due to its special structure. The density of the aluminized layer makes it difficult for oxygen and water vapor to pass directly. Its barrier performance for oxygen can usually reach 0.1 - 1.0 cm³/(m²・24h・1MPa), and its barrier performance for water vapor can reach 0.1 - 1.5 g/(m²・24h). This excellent water and oxygen barrier performance can provide good protection for the products in the package, extend the shelf life of the products, and maintain the quality and safety of the products.
• Mechanical strength is also an important indicator for measuring the performance of high-barrier aluminized PET film. During the production, processing and use of the film, it needs to withstand various external forces such as stretching, extrusion, and friction. If the mechanical strength of the film is insufficient, it is easy to break, tear, and other problems, thus affecting the packaging effect and product quality. The PET base provides a good mechanical performance foundation for the film, which has high tensile strength and elongation at break. Generally speaking, the tensile strength of high-barrier aluminized PET film can reach 100-250 MPa, and the elongation at break is between 100-300%. The higher tensile strength makes the film less likely to break during the stretching process and can meet the requirements of various packaging processes; while the larger elongation at break ensures that the film has a certain flexibility when stretched by external forces and is not prone to brittle cracking. In addition, the puncture resistance of the film is also very critical, especially when packaging some sharp objects. Good puncture resistance can prevent the film from being punctured and avoid product leakage or contamination. Through reasonable structural design and material selection, high-barrier aluminized PET film can have good puncture resistance to meet the packaging needs of different products.
• Weather resistance refers to the ability of high-barrier aluminized PET film to maintain stable performance under various climatic conditions, such as temperature changes, light, humidity and other environmental factors. In actual applications, the film may face different environmental conditions such as high temperature, low temperature, humidity, and direct sunlight. If the film has poor weather resistance, it may soften and deform in a high temperature environment, affecting the sealing of the package; it may become brittle and crack in a low temperature environment; and the aluminized layer may oxidize and fall off after long-term exposure to sunlight, resulting in a decrease in barrier performance. In order to improve the weather resistance of the film, in addition to selecting PET materials and aluminized processes with good weather resistance, some special additives such as UV absorbers and antioxidants will be added to the protective layer. UV absorbers can absorb ultraviolet rays to prevent them from damaging the film; antioxidants can inhibit the oxidation of the aluminized layer and extend the service life of the film. The optimized high-barrier aluminized PET film can maintain good performance in the temperature range of -40℃ to 80℃, and can still maintain its barrier performance and mechanical strength stability under long-term light and humid environments.

The three key performance indicators of water and oxygen barrier, mechanical strength and weather resistance are interrelated and mutually influential, and jointly determine the comprehensive performance of high barrier aluminized PET film. In different application fields, according to the characteristics of the product and the use environment, the requirements for these three performance indicators are also different. Only by fully understanding and mastering these key performance indicators can we better play the advantages of high barrier aluminized PET film and meet the market's increasingly diversified demand for packaging materials.

3. Effect of Aluminum Plating Process on Barrier Properties of PET Film

Aluminum plating process is one of the key factors that determine the barrier properties of high-barrier aluminum-plated PET film. Different aluminum plating process parameters and methods will have a significant impact on the structure and properties of the film. In-depth research on the relationship between aluminum plating process and barrier properties is of great significance for improving film quality and meeting market demand.

At present, the most commonly used process for aluminum plating of PET film is vacuum evaporation. During the vacuum evaporation process, there are several key parameters that will affect the quality of the aluminum plating layer and the barrier properties of the film, including vacuum degree, evaporation temperature, aluminum plating rate, film running speed, etc.

• Vacuum degree is one of the important factors affecting the quality of aluminum plating. During the vacuum evaporation process, the pressure in the coating chamber needs to be reduced to an extremely low level, and the vacuum degree is generally required to reach 10⁻³ - 10⁻⁴ Pa. In such a high vacuum environment, the average free path of aluminum vapor molecules is longer, and they can move more freely and deposit on the surface of the PET film to form a uniform and dense aluminum coating layer. If the vacuum degree is insufficient, the gas molecules remaining in the coating chamber will collide with the aluminum vapor molecules, hindering the movement of the aluminum vapor molecules, resulting in uneven distribution of the aluminum vapor molecules during the deposition process, and defects such as pinholes and cracks will appear in the aluminum coating layer, thereby reducing the barrier properties of the film. Studies have shown that when the vacuum degree increases from 10⁻³ Pa to 10⁻² Pa, the number of pinholes in the aluminum coating layer will increase significantly, and the film's barrier properties to oxygen will decrease by about 30%.
• The evaporation temperature directly affects the vaporization rate of aluminum and the energy of vapor molecules. The melting point of aluminum is 660°C. During the vacuum evaporation process, the temperature of the evaporation source is usually controlled at 1200-1400°C. When the evaporation temperature is too low, the vaporization rate of aluminum is slow, and the amount of aluminum vapor evaporated per unit time is insufficient, making it difficult to form a continuous and dense aluminum coating layer; while if the evaporation temperature is too high, the energy of the aluminum vapor molecules will be too high, and when deposited on the surface of the PET film, it may damage the film and affect the performance of the film. In addition, too high an evaporation temperature will also increase energy consumption and production costs. The appropriate evaporation temperature can ensure that aluminum vapor is deposited on the surface of the PET film at an appropriate rate and energy to form a uniform and dense aluminum coating layer, thereby improving the barrier properties of the film.
• The match between the aluminizing rate and the film running speed is also crucial. The aluminizing rate refers to the mass of aluminum deposited on the surface of the PET film per unit time, and the film running speed refers to the speed at which the PET film moves in the coating chamber. If the aluminizing rate is too fast and the film running speed is too slow, aluminum vapor will accumulate excessively on the surface of the film, forming a thick and uneven aluminizing layer, and even aluminum layer peeling may occur; conversely, if the aluminizing rate is too slow and the film running speed is too fast, the aluminizing layer will be too thin and unable to form an effective barrier, and the barrier performance of the film will be significantly reduced. Therefore, it is necessary to accurately adjust the aluminizing rate and the film running speed according to the specific production equipment and process requirements to achieve the best matching state in order to obtain the ideal thickness and quality of the aluminizing layer.

In addition to the vacuum evaporation process parameters, the performance and structure of the aluminum plating equipment will also affect the aluminum plating effect. For example, the type and design of the evaporation source will affect the uniformity and stability of aluminum evaporation; the shape and size of the coating chamber will affect the distribution of vacuum and the diffusion of aluminum vapor; the accuracy and stability of the film transmission system will affect the tension and operating state of the film during the aluminum plating process. Advanced aluminum plating equipment can better control the aluminum plating process parameters, ensure the stability and consistency of the aluminum plating process, and thus produce high-barrier aluminum-plated PET films with higher quality and better barrier properties.

The aluminizing process has a crucial impact on the barrier properties of PET film. By optimizing the vacuum evaporation process parameters, selecting appropriate aluminizing equipment, and accurately controlling each link in the aluminizing process, the quality of the aluminizing layer can be effectively improved, the barrier properties of the film can be enhanced, and the needs of different industries for high-barrier aluminized PET film can be met.

4. Application fields and future development trends of high barrier metallized PET films

High barrier aluminized PET film has been widely used in many fields due to its excellent barrier properties, good mechanical strength and excellent weather resistance. With the continuous development of science and technology and changes in market demand, its future development trend has also attracted much attention.

• In the field of food packaging, high-barrier aluminized PET film is the most widely used. It can effectively block oxygen, water vapor and light, prevent food from oxidation, moisture and deterioration, and extend the shelf life of food. For example, in the packaging of puffed foods such as potato chips and biscuits, high-barrier aluminized PET film can maintain the crisp taste of food and prevent oil oxidation and rancidity; in the packaging of cooked food such as meat and fish, it can block oxygen, inhibit bacterial growth, and ensure the freshness and safety of food. In addition, high-barrier aluminized PET film also has good printability, and can be used to produce exquisite packaging patterns through color printing to attract consumers' attention and enhance the market competitiveness of products.
• Pharmaceutical packaging has extremely high requirements for material safety and barrier properties, and high-barrier aluminized PET film just meets these requirements. It can prevent drugs from contacting with oxygen, moisture, light, etc. in the external environment, and avoid chemical reactions that cause drugs to become ineffective. In the blister packaging of tablets, capsules and other drugs, high-barrier aluminized PET film is used in combination with aluminum foil, PVC and other materials to form a multi-layer packaging structure, providing all-round protection for drugs. At the same time, its good sealing can effectively prevent drugs from being contaminated during transportation and storage, ensuring the safety of patients' medication.
• In the electronics industry, high-barrier aluminized PET film is mainly used for moisture-proof and anti-oxidation packaging of lithium batteries and electronic products. During the production and use of lithium batteries, they are very sensitive to environmental humidity and oxygen content. High-barrier aluminized PET film can effectively block the intrusion of moisture and oxygen, prevent short circuits or chemical reactions inside lithium batteries, and improve the safety and service life of lithium batteries. For some precision electronic components, such as integrated circuits and sensors, high-barrier aluminized PET film can be used as a moisture-proof and anti-oxidation packaging material to protect electronic components from environmental factors during transportation and storage, ensuring their stable performance.
• High-barrier aluminized PET film is increasingly being used in the packaging of daily chemical products. Perfumes, shampoos, cosmetics and other daily chemical products are prone to volatilization and deterioration. High-barrier aluminized PET film can effectively prevent the active ingredients in the products from volatilizing and oxidizing when in contact with air, thus maintaining the quality and aroma of the products. In addition, its beautiful appearance and good printing effect also help to enhance the brand image of daily chemical products.

The development trend of high-barrier metallized PET film is mainly reflected in the following aspects. With the continuous improvement of environmental awareness, the development of green and environmentally friendly high-barrier aluminized PET film will become an important direction. On the one hand, research on degradable PET materials to reduce pollution to the environment; on the other hand, optimize the aluminizing process to reduce energy consumption and waste emissions in the production process. Secondly, in order to meet the market demand for multifunctional packaging materials, high-barrier aluminized PET film will develop in the direction of multifunctional composite. For example, composite with antibacterial materials to give the film antibacterial properties, applied to food and drug packaging, further extending the shelf life of the product; composite with smart materials to give the film sensing functions such as temperature and humidity, and monitor the environmental status inside the package in real time. Furthermore, with the continuous development of nanotechnology, nano-coating technology will be applied to the production of high-barrier aluminized PET film. By coating nano-level barrier materials on the surface of the film, the barrier properties of the film can be further improved, while reducing the thickness of the film, reducing the amount of materials used, and reducing costs.

High barrier aluminized PET film has played an important role in many fields at present and has broad development prospects in the future. Through continuous innovation and technological progress, it will meet the needs of more fields and bring more convenience and value to people's lives and industrial production.