Development and application of vacuum aluminized film
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Vacuum aluminizing film is a process of forming composite film by adhesion on the surface of the film substrate. Mainly used for flavor food, daily necessities, agricultural products, drugs, cosmetics and cigarette packaging.
Vacuum aluminizing thin film is a process of forming composite thin film on the surface of thin film substrate by melting and evaporating aluminum under high vacuum condition by means of resistance, high frequency or electron beam heating. In the plastic film or paper surface coated with a very thin layer of metal aluminum is aluminum coated film or paper.
The vacuum aluminized film used for packaging has the characteristics of less aluminum material consumption, high folding resistance, high barrier performance, anti-static, etc., which makes the aluminized film become a new type of composite film with excellent performance, economic and beautiful appearance, and has replaced the aluminum foil composite material in many aspects. Mainly used for flavor food, daily necessities, agricultural products, drugs, cosmetics and cigarette packaging.
China began to introduce foreign equipment for vacuum aluminum coating film production in the 1990s. After more than 20 years of development, the production capacity of aluminum coating film has reached 400,000 tons, becoming the world's largest vacuum aluminum coating production base.
With the development of substrate film, vacuum evaporation technology and post-treatment technology, the functions and varieties of vacuum aluminized film are continuously expanded and its applications are more extensive. Typical technological developments include:
1. Application of plasma pretreatment technology in vacuum aluminum coating
Plasma is an ionized gas. It is composed of electrons, ions and neutral particles, of which the total charge of electrons and ions is basically equal, so the whole is electrically neutral. Before aluminizing the substrate film, the ionized plasma electrons or ions are hit to the surface of the substrate film by the plasma treatment device. On the one hand, the long molecular chain of the material can be opened and high-energy groups can appear. On the other hand, the film surface by the impact of small sag, but also can make the surface impurities dissociation, resolution. When ionizing ozone has strong oxidation, the attached impurities are oxidized and removed, so as to improve the surface free energy of aluminized substrate film, to achieve the purpose of improving the adhesion fastness of aluminized layer.
Plasma pretreatment technology has different names in different companies, such as Bobst UK and Leybold Optic Germany, which call it plasma pretreatment; Applied Material UK, which calls it glow discharge; and Rexam UK, which registered its trademark as Camplus technology. In addition, the composition of process gas used by different companies varies. Most companies use a combination of oxygen and argon, while a few companies use nitrogen or a combination of oxygen and nitrogen. It has been proved that the adhesion fastness of aluminized film can be improved by 30-50% after plasma treatment, and the improvement of non-polar material is higher than that of polar material.
2. Application of oxide coating technology
In recent years, the rapid development of microwave heating technology has put forward new requirements for microwave food packaging and packaging of a class of goods requiring microwave sterilization, that is, packaging materials should not only have excellent barrier performance, but also high temperature resistance, microwave permeability and other characteristics, traditional packaging materials are difficult to have these characteristics. Therefore, in recent years, Japan, Germany, the United Kingdom, Italy, Canada, the United States and other industrial developed countries have invested a lot of manpower and material resources in the research and development of new high-barrier packaging materials -- SiOX and other metal oxide coating composite materials. This kind of material in addition to the blocking performance can be comparable to those outside the aluminum-plastic composite materials, but also has good microwave permeability, high temperature resistant, transparent, and the advantages of small affected by environmental temperature humidity, especially in terms of goods confirmed incense, effect like glass bottle packaging, long-term storage, or after high temperature treatment, won't produce peculiar smell, therefore, also known as transparent coating. It can be widely used in food, drugs, cosmetics, medical devices and other packaging safety and health performance requirements, shelf life of a class of goods packaging, especially suitable for microwave heating technology applications of a class of goods packaging materials.
SiOX and SiO2 can be used as raw materials for non-metallic coating, and other oxides such as Al2O3, MgO, Y 2O3, TiO2 and Gd 2O3 can also be used, among which SiOX and AlOx are the most commonly used. Oxide coating resistance type and two kinds of electron beam evaporation source, resistance type evaporation source in heating evaporation materials by the principle of heat resistance, the highest temperature can reach 1700 ℃. Electron beam evaporation source using accelerated electron collision deposition materials and the evaporation, the evaporation source is equipped with a gun, accelerated with magnetic field or electric field and electron beam, the beam focused on the local position of evaporation materials and form the heating beam spot, beam spot temperature can reach 3000 ~ 3000 ℃, the highest energy density of 20 kw/cm2.
When non-metallic coating, higher gasification temperature and evaporation of evaporation raw materials can lead to higher temperature of evaporation area in the evaporation process. A large amount of radiant heat makes the substrate absorb excessive heat energy and the temperature increases. At the same time, gasification molecules, ions and other particles in the substrate surface condensation film when the heat released causes the substrate temperature is too high and serious thermal deformation. Heat deformation of the substrate wrinkling, resulting in uneven or broken coating film, can not achieve the effect of improving the barrier performance, therefore, softening point and melting point of the lower plastic film evaporation effect is poor. Experiments show that only PP, PET, PA and other materials can be more suitable for oxide coating processing.
3. Application of coating technology in vacuum aluminum coating film
Combining coating technology with vacuum aluminum plating technology, coating functional layer on the substrate film or aluminum coating film can improve the adhesion fastness, water resistance, barrier performance, decorative performance and other properties of aluminum coating layer, so as to meet the requirements of different application fields.
1) although plasma-pretreated vacuum aluminized film has significantly improved the fastness of aluminized layer, for some aluminum coating adhesion fastness requirements are higher, or need to be used for boiling sterilization conditions still can not meet the requirements. In order to meet the above requirements, by coating the surface of the substrate film with a layer of acrylic acid chemical coating, the coating not only has excellent adhesion to the aluminum coating layer, but also can meet the following conditions of boiling sterilization. For example, the BOPET film of dupont hongji model M121 can be used for the packaging of jellies, pickled vegetables and other products that need to be boiled and sterilized after vacuum aluminum plating. It can meet the requirements of pasteurization and its aluminum coating will not be oxidized due to boiling.
2) in order to further improve the barrier performance of aluminized film, and at the same time protect the aluminized layer from damage in subsequent printing, composite and other processing processes, it can be achieved by coating the aluminized layer with a layer of high-barrier nano-coating or polymer coating. For example, the online coating of Freshure Topcoat, jointly developed by applied materials of Germany and DSM of the Netherlands, can further improve the oxygen barrier performance of aluminized film and maintain the surface tension of more than 50 dyne/cm for 6 to 12 months. Products are mainly used in the oxygen barrier requirements of food, drug packaging, such as nuts, potato chips and so on.
3) In order to improve the decorative properties of the aluminum coating film, before or after the aluminum coating of the substrate film for a variety of colors, or aluminum coating after molding, so that the aluminum coating film has a colorful color or laser effect. This kind of products can be divided into three types: packaging film, decorative film, marking film. It is mainly used for decoration or anti-counterfeiting packaging of gifts and gift boxes, such as outer packaging of food, medicine, toys and anti-counterfeiting packaging of cigarettes and wine.