Aluminum foil overview

Aluminum foil is widely used in food, beverage, cigarette, pharmaceutical, photographic base, household daily necessities, etc. due to its excellent performance, and is commonly used as its packaging material; electrolytic capacitor material; insulation materials for buildings, vehicles, ships, houses, etc. As a decorative gold and silver wire, wallpaper and all kinds of stationery printed matter and light industrial products decorative trademark. In the various applications described above, the most effective performance of aluminum foil is as a packaging material. Aluminum foil is a soft metal film that not only has moisture, air, shading, abrasion resistance, freshness, non-toxic and tasteless, but also has an elegant silver-white luster. It is easy to handle beautiful patterns of various colors and patterns, so it is more susceptible to people’s influence. In particular, after the aluminum foil is combined with plastic and paper, the shielding properties of the aluminum foil are combined with the strength of the paper and the heat sealing property of the plastic, thereby further improving the shielding performance of water vapor and air, and the ultraviolet rays and bacteria necessary as packaging materials. , greatly expanded the application market of aluminum foil. Since the packaged articles are sufficiently isolated from external light, moisture, gas, etc., the package is well protected. Especially for the packaging of retort foods, the use of such a composite aluminum foil material at least ensures that the food does not deteriorate for more than one year. In addition, heating and unpacking are very convenient and very popular among consumers.

With the improvement of people’s living standards and the development of tourism, the demand for beverages and canned foods such as beer and soda is increasing. These require modern packaging and decoration to promote competition in the international market. In order to meet market demand, packaging materials such as plastic film and spray foil have been developed, but their overall performance is not as good as overcoating and lamination. Therefore, it can be said that aluminum foil is a packaging material having various excellent properties and perfection, and has fully demonstrated its wide application prospect in many fields.

In order to improve the rolling efficiency and quality of aluminum foil products, modern aluminum foil rolling mills are developing in four directions: large volume, wide width, high speed and automation. The roll width of the modern aluminum foil rolling mill reaches 2200mm or more, the rolling speed reaches 2000m / min or more, and the coil weight reaches 20t or more. The corresponding level of mill automation has also been greatly improved, the thickness control system (AGC) is generally installed, and most are equipped with a shape meter (AFC). The aluminum foil industry is facing a period of rapid development.

Classification

thickness
Aluminum foil can be divided into thick foil, single zero foil and double zero foil according to the thickness difference.
1 thick foil (“heavy gaugefoil”): a foil having a thickness of 0.1 to 0.2 mm.
2 “medium gauge foil”: a foil having a thickness of 0.01 mm and less than 0.1 mm/.
3 “light gauge foil”: The so-called double-zero foil is a foil with two zeros after the decimal point in its thickness, usually aluminum foil with a thickness less than 0.01, ie 0.005~0.009mm aluminum foil . In foreign countries, an aluminum foil having a thickness of ≤ 40 ltm is sometimes referred to as a “light gauge foil”, and an aluminum foil having a thickness of > 40 btm is collectively referred to as a “heavy gauge foil”.
shape
The aluminum foil can be divided into a rolled aluminum foil and a sheet aluminum foil according to the shape. Most of the aluminum foil deep-processing wool is supplied in rolls, and only a few hand-made industrial packaging uses sheet-like aluminum foil.
Aluminum foil can be classified into hard foil, semi-hard foil and soft foil according to the state.
1 Hard foil: Aluminum foil that has not been softened (annealed) after rolling, and has no residue on the surface without degreasing. Therefore, the hard foil must be degreased before printing, lamination, coating, and can be used directly if it is used for forming.
2 semi-hard foil: aluminum foil hardness (or strength) between the hard foil and the soft foil, usually used for forming.
3 soft foil: aluminum foil which is softened after being fully annealed after rolling, the material is soft and there is no residual oil on the surface. Soft foils are used in most applications, such as packaging, composites, and electrical materials.
surface condition
The aluminum foil can be divided into a light aluminum foil and a double-sided aluminum foil according to the surface state.

1 Single-sided aluminum foil: Double-rolled aluminum foil, which is bright after splitting, and the surface is black. Such aluminum foil is called a light aluminum foil. The thickness of a side of a light aluminum foil usually does not exceed 0.025 mm.
2 double-sided aluminum foil: single-rolled aluminum foil, the two sides are in contact with the rolls. The two sides of the aluminum foil are divided into mirror two-sided aluminum foil and ordinary two-sided aluminum foil due to the different surface roughness of the rolls. The thickness of the two-sided aluminum foil is generally not less than 0.01 mm.
Processing status
Aluminum foil can be divided into plain foil, embossed foil, composite foil, coated foil, colored aluminum foil and printed aluminum foil according to the processing state.
1 plain foil: aluminum foil without any other processing after rolling, also called light foil.
2 embossed foil: aluminum foil with various patterns on the surface.
3 composite foil: a composite aluminum foil formed by laminating aluminum foil and paper, plastic film and cardboard.
4 coated foil: aluminum foil coated with various types of resin or lacquer on the surface.
5 color aluminum foil: the surface is coated with a single color of aluminum foil. 6 Printing aluminum foil: Aluminum foil which is formed by printing various patterns, patterns, characters or pictures on the surface, which can be one color, up to 12 colors.
The soft aluminum foil can be further pressed into a four-zero foil for high-end decoration.

Characteristics

The aluminum foil has a clean, hygienic and shiny appearance. It can be integrated with many other packaging materials, and the surface of the aluminum foil is better than other materials. In addition, the aluminum foil has the following characteristics:
(1) The surface of the aluminum foil is extremely clean and hygienic, and no bacteria or microorganisms can grow on its surface.
(2) Aluminum foil is a non-toxic packaging material that can be in direct contact with food without any concern that may endanger human health.
(3) Aluminum foil is an odorless and odorless packaging material that does not impart any odor to the packaged food.
(4) If the aluminum foil itself is not volatile, it itself and the packaged food will never dry or shrink.
(5) There is no oil penetration of the aluminum foil at high temperatures or at low temperatures.
(6) Aluminum foil is an opaque packaging material, so it is a good packaging material for products exposed to sunlight, such as margarine.
(7) Aluminum foil has good plasticity, so it can be used to package products of various shapes. It can also be used to create containers of various shapes.
(8) The aluminum foil has a large hardness and a large tensile strength, but its tear strength is small, so that it is easily torn.
(9) The aluminum foil itself cannot be heat-sealed and must be coated with a heat-sensitive material such as pe to be heat-sealed.
(10) When aluminum foil is in contact with other heavy metals or heavy metals, there may be adverse reactions.

Rolling

Particularity of aluminum foil rolling
In the production of double-sheet foil, the rolling process of aluminum foil is divided into three processes: rough rolling, medium rolling and finishing rolling. From the perspective of process, it can be roughly divided from the thickness of the rolling outlet. The general method is that the outlet thickness is greater than Or equal to 0.05mm for rough rolling, the outlet thickness is between 0.013 and 0.05 for medium rolling, and the outlet for thickness of less than 0.013 mm and the double-rolled finished product are finish rolling. The rough rolling is similar to the rolling characteristics of the aluminum strip. The thickness control mainly depends on the rolling force and the back tension. The rough rolling processing rate is very small. The rolling characteristics are completely different from the rolling of the aluminum strip and the aluminum foil rolling. The particularity of its characteristics mainly includes the following aspects:
(1) Aluminum strip rolling. In order to make the aluminum strip thinner mainly depends on the rolling force, the automatic thickness control method is the control method of the constant roll joint as the main body of the AGC. Even if the rolling force changes, the roll gap can be adjusted at any time to maintain a certain value of the roll gap. Consistent plate strip. Since aluminum foil is rolled to medium finish rolling, since the thickness of the aluminum foil is extremely thin, the rolling force is increased during rolling, and the elastic deformation of the roll is easier than the plastic deformation of the material to be rolled, and the elastic flattening of the roll cannot be performed. Neglected, the rolling and flattening of the roll determines that the rolling force does not function as a rolled sheet in aluminum foil rolling. The aluminum foil rolling is generally roll-free rolling under constant pressure conditions, and the thickness of the aluminum foil is adjusted. Mainly depends on the adjusted tension and rolling speed.
(2) Rolling. For an extremely thin aluminum foil having a thickness of less than 0.012 mm (the thickness is related to the diameter of the work roll), since the roll is elastically flattened, it is very difficult to use a single-rolling method, so the double-rolling method is adopted, that is, A method of adding lubricating oil to the middle of two aluminum foils and then rolling them together (also called rolling). The lamination rolling can not only roll out extremely thin aluminum foil which cannot be produced by single rolling, but also reduce the number of broken strips and improve labor productivity. This method can mass produce single-sided aluminum foil of 0.006 mm to 0.03 mm.
(3) Speed ​​effect. In the aluminum foil rolling process, the phenomenon that the thickness of the foil becomes thinner with the degree of rolling degree is called the velocity effect. The explanation of the mechanism of velocity effect still needs to be studied in depth. The reasons for the speed effect are generally considered to have the following three aspects:
1) The friction state between the work roll and the rolled material changes, and as the rolling speed increases, the amount of the lubricating oil is increased, so that the lubrication state between the roll and the rolled material changes. The coefficient of friction is reduced, the oil film becomes thicker, and the thickness of the aluminum foil is reduced.
2) The change of the rolling mill itself. In a rolling mill with a cylindrical bearing, as the rolling speed increases, the roll neck floats in the bearing, so that the two interacting loaded rolls will move in a mutually abutting direction.
3) The processing softens when the material is deformed by rolling. The rolling speed of the high-speed aluminum foil rolling mill is very high. As the rolling speed increases, the temperature of the rolling deformation zone increases. According to the calculation, the metal temperature of the deformation zone can rise to 200 ° C, which is equivalent to an intermediate recovery annealing. Process softening of rolled materials.
Formulate the principle of aluminum foil rolling process
1 Determination of the total processing rate The total processing rate refers to the total degree of deformation of the foil after the recrystallization annealing to the finished product. In general, the total processing rate of the 1 series can reach more than 99%, and some 8 series products can also reach this value, but the total processing rate of the aluminum alloy foil is generally below 90%.
Determination of the pass rate of 2 passes The determination of the pass rate is the core of the rolling process. The pure aluminum series products can achieve a pass rate of 65%, and the first pass after the blank is annealed. The processing rate is generally about 50%.
Rolling thickness
Thickness measurement methods for aluminum foil rolling mainly include eddy current thickness measurement, isotope ray thickness measurement and X-ray thickness measurement. X-ray thickness measurement is one of the most common thickness measurement methods used in current aluminum foil production, especially in high speed aluminum foil rolling mills. Thickness control method for aluminum foil rolling: rolling force control, tension control, rolling speed control, tension/speed, speed/tension control

Antiseptic

The main cause of corrosion is mainly due to moisture or water in the production process and during the circulation process. Therefore, controlling the generation of corrosive waste is mainly to prevent the aluminum foil from coming into contact with water.
Anti-corrosion measures:
1 Strengthen the management of the air dryer to ensure that there is no moisture in the compressed air.
2 Strengthen the management of rolling oil, and its water content is controlled below 400×0.000001.
3 Aluminum foil rolls should be packaged in a sealed package, and an appropriate amount of desiccant should be placed in each roll.
4 The humidity of the wooden shaft and the box board of the package is not more than 18%, and the temperature of the packaged aluminum coil is not more than 45 degrees Celsius.
5 From the low temperature area to the area with high temperature and high humidity, do not open the sealed package immediately. 6 The workshop and warehouse roofs are exposed to rain and snow. Aluminum foil rolls should not be placed.
7 When transporting aluminum foil from a low temperature zone to a high temperature zone, it is necessary to strengthen the sealing of the package and, if necessary, add a desiccant.
8 When packaging aluminum foil products in the rainy season, it is necessary to strengthen the sealed packaging and add desiccant.

Prospects

(1) air conditioning foil
The air-conditioning foil is a special material for manufacturing heat exchanger fins for air conditioners, and the air-conditioning foil used in the early days is a plain foil. In order to improve the surface properties of the plain foil, an anti-corrosive inorganic coating and a hydrophilic organic coating are applied before forming to form a hydrophilic foil. The hydrophilic foil accounts for 50% of the total amount of the air-conditioning foil, and its use ratio is further increased. There is also a water-repellent foil that provides a hydrophobic effect on the surface of the fins to prevent condensation from adhering. The technique for improving the surface defrosting property of the water-repellent foil is for further study, and actual production is rare.
The thickness of the air-conditioning foil is from 0.1 mm to 0.15 mm. With the development of technology, air-conditioning foils have a tendency to further reduce the thickness of Japan’s leading products of 0.09mm. In an extremely thin state, the aluminum foil should have good formability, its structure and properties must be uniform, metallurgical defects are small, anisotropy is small, and strength is required, ductility is good, thickness is uniform, and flatness is good. The specifications and alloys of air-conditioning foils are relatively simple and suitable for large-scale production, but their market is seasonal. For professional manufacturers of air-conditioning foils, it is difficult to solve the contradiction between the shortage in the peak season and the almost no demand in the off-season.
Due to the strong market demand, the production capacity and technical level of air-conditioning foils in China have been continuously improved in recent years. Nowadays, large, medium, small, high, medium and low production air-conditioning foils have been formed. Some large enterprises such as Huabei Aluminum and Bohai Aluminum have basic product quality. Has reached the international advanced level. Due to the overcapacity in the domestic market, the market competition is extremely fierce.
(2) Cigarette packaging foil
China is the world’s largest cigarette production and consumption country. At present, there are 146 large-scale cigarette factories in China, with an annual output of 34 million large cigarettes, basically using cigarette foil packaging, of which 30% use spray foil and 70% use calender Aluminum foil, calendered aluminum foil consumption of 35,000 tons, with the increase in people’s health awareness and the impact of foreign imports of cigarettes, the growth of demand for tobacco foil has slowed significantly, is expected to increase slightly in recent years. China’s cigarette packaging foil accounts for 70% of the total volume of double-zero foil. At present, there are two or three companies in China that can produce high-quality cigarette foil. The technical level is equivalent to the international level, but the overall quality of domestic cigarette foil has a certain gap with international standards.
(3) Decorative foil
The decorative foil is a decorative material applied in the form of aluminum-plastic composite, and utilizes the characteristics of good coloration of aluminum foil and high reflectance of light and heat. Mainly used for decoration of buildings, furniture and some gift boxes. The application of decorative foil in China’s construction industry began in the 1990s. It has spread rapidly from central cities such as Shanghai, Beijing and Guangzhou to the whole country. In recent years, the demand has increased sharply, generally as the decoration material for the inner wall of the building and the interior furniture. It is also widely used in the facades and interiors of commercial establishments.
The decorative foil has the advantages of heat insulation, moisture proof, sound insulation, fire prevention and easy cleaning, and the appearance is luxurious, the processing is convenient, and the construction and installation speed is fast. At present, China’s construction and home improvement industry has formed an application boom for decorative foils. With the rapid development of China’s construction industry and the increasing popularity of decorative foil applications, the demand for decorative foils will increase substantially. In addition, the use of decorative foil packaging gifts is very popular in foreign countries. In recent years, the development speed in China is very fast, and it is expected that there will be better prospects.
(four) cable foil
The cable foil is an aluminum-plastic composite foil which is formed by applying a film on one or both sides by using the sealing property and shielding property of the aluminum foil, and is used as a shield for the cable. Cable foil requires less oil on the surface, no holes, high mechanical properties, and low overall quality requirements, but the length requirements are extremely strict.
Domestic advanced cold rolling mills, rolling mills and aluminum foil roughing mills can all be produced, but the market growth is poor. The domestic demand is about 25,000 tons per year.