The characteristics of aluminum foil for flexible packaging
Aluminum foil because of its special performance and low cost in the flexible packaging has a wide range of applications, this paper mainly discusses the characteristics of aluminum foil and the relationship between the quality of flexible packaging.
1, the classification of aluminum foil for flexible packaging
Flexible packaging aluminum foil is mainly used in aluminum foil metallic luster, light barrier, gas barrier and a certain strength, ductility. According to the use of different emphasis on the performance is different, according to the use of flexible packaging with aluminum foil can be divided into three categories:
The first category, food and drug packaging, mainly to seal, mainly stressed gas barrier, light barrier, non-toxic. Such aluminum foil includes: pharmaceutical, quasi-pharmaceutical (pharmaceutical equipment, medical supplies) packaging, 0.02 micron, 0.015 micron, 0.009 micron, 0.007 micron.
Food, quasi-food (toothpaste) packaging, 0.015,0.012,0.009,0.007 microns.
The second category, decorative class, mainly to the main, mainly to emphasize the surface gloss uniform. This type of aluminum foil includes: a variety of printed packaging, advertising category.
The third category, between one or two categories, it is necessary to have a certain degree of sealing and a certain aesthetic. Mainly cigarettes, wine, food packaging.
2, the main technical indicators of different aluminum foil
The characteristics required for different uses of aluminum foil are not the same.
The first type of aluminum foil
The pinhole is the most important indicator, especially for the foil of 0.02,0.015 microns, because the aluminum foil as the main packaging material, no or very little composite layer, requires no pinholes. And 0.009, 0.007 micron aluminum foil is usually used as one of the composite layer, pinholes control in 30 / m2, aluminum foil played a major sealing effect, and the composite layer played a supporting role. Had the theory that the hole diameter of less than 0.005mm will not be permeable and permeable, but the practice has proved that the hole will be breathable and permeable. Just breathable permeability of the size of the problem. No pinhole aluminum foil can be considered breathable permeability of zero, a square meter per square meter φ0.3mm pinhole accounted for the total area of 100 million, 30 pinholes accounted for three parts per million of the total area, that is, Aluminum foil composite ventilation permeability than the raw materials by more than one million times lower, usually the diameter of the pinhole in the 0.05mm-0.3mm or so, so you can determine the relationship between the number of pinhole and air permeability. The area of the pinhole is proportional to the square of the diameter, so the pinhole area of 0.03 mm is 100 times worse than the pinhole area of 0.3 mm. Can be said to add aluminum foil and aluminum foil is not a different grade of packaging, breathable permeability difference of more than one million times, the shading of aluminum foil can also be described in a similar way. The above description is suitable for statistical significance, for specific packaging due to pinhole distribution of nonuniformity, for example: 10mm * 10mm packaging if there is a pinhole, then its sealing effect can only increase 1000-10000 times. Comparison of the air permeability and shading of aluminum foil with other materials is shown in the table below.
The data in this form comes from the "Aluminum Handbook" 20 years ago test, and now aluminum foil can do 0.013mm no pinhole, so 0.013mm above the thickness of aluminum foil moisture permeability is zero. And 0.009mm aluminum foil pinhole only a few. Here only as a reference data, it shows that the permeability of aluminum foil is much smaller than a variety of films.
The data from the Swiss company thickness gauge data, we can see that the role of aluminum foil on the radiation barrier is far greater than the film and paper. For visible light, no pinhole aluminum foil is completely opaque.
Non-toxic non-polluting is one of the main requirements of this aluminum foil, the surface clean and oil-free, aluminum foil composition in line with food packaging standards. At present, the main use of flexible packaging aluminum foil 1235,1145,1100 and other industrial pure aluminum series. Production of such aluminum foil rolling oil and related media can not be toxic, in line with food hygiene standards (low aromatics 1%, low sulfur 5ppm). Surface tension to meet the requirements. To ensure that the composite bonding strength.
Mechanical performance requirements are one of the characteristics of such aluminum foil, because this type of aluminum foil to do the heat seal deformation, the appropriate plasticity becomes very important, otherwise, when the heat seal is easy to crack. Similarly, this type of aluminum foil is not too thin, the thickness is generally greater than 0.007mm. Thickness is too thin to break easily.
Type II aluminum foil
Surface clean, uniform is the most important requirements of this aluminum foil. With the further refinement of printing, the requirements for such aluminum foil are further improved. Surface brightness requirements in the ± 2 (Minolta colorimeter with L value), and can not have vibration, lines, highlights. The simple decorative foil is being replaced by a vacuum-plated aluminum foil. However, the real second type of use of aluminum foil is very small.
The third category of aluminum foil
The third category of aluminum foil is now the main purpose of aluminum foil, it is necessary to seal, but also beautiful decorative. Most of the foil is used to make moisture, shading, and used to do decoration. This type of aluminum foil is mainly combined with paper, aluminum foil in the outermost, or under the transparent layer, aluminum foil metallic luster is the symbol of this packaging. As mentioned earlier, aluminum foil shading, moisture resistance of the packaging can also increase the order of several orders of magnitude. But this kind of aluminum foil moisture and shading is not the most important indicators. Therefore, the thickness of aluminum foil can be thinner, the current thinnest to 0.006mm. As the thickness decreases, the pinholes increase. 0.006mm pinhole can reach 2000 / m2, according to the diameter of 0.1mm hole, the total area of 20m m2, the total area of two hundred thousandths. Even to reach 20,000 / m2, pinhole area is only two ten thousandths. Therefore, the aluminum foil composite layer, the permeability of breathable permeability of less than aluminum foil packaging to reduce the minimum of ten thousand times. It is not enough to ask for a high packing. Pinhole damage is mainly caused in the composite through plastic.
In such aluminum foils, the uniformity of the surface is particularly important. Glossy uniform, no lines, no vibration marks is the basic requirements.
The aluminum foil combined with the cardboard requires the same plasticity as the first type of aluminum foil.
3, the common requirements of flexible packaging aluminum foil
The common requirements for flexible packaging aluminum foil are flat (less than 20 I);
● Uniform surface;
● Consistent thickness (3% tolerance);
● good start (less than three meters);
● clean surface;
● fewer pinholes;
● less secure joints (less than 20%);
Suitable mechanical properties.
4, flexible packaging aluminum foil a few questions
Flexible packaging aluminum foil There are several problems to be solved.
● The uniformity of the surface condition of the flexible packaging aluminum foil is too high and requires a good surface, and the production cost will increase substantially. There is no good way to date.
● Aluminum foil as a limit to the thickness of the product, it almost exhausted all the plasticity. The re-processing of flexible packaging aluminum foil is not high, despite the use of new alloys and processes (eg 8011, 8079). Plastic or no good way to greatly improve. The flexible packaging compound bag processing method to consider this less, so that often burst phenomenon.
● measure the index of aluminum foil plastic is not scientific, can not really show the plasticity of aluminum foil. The performance of flexible packaging aluminum foil is still in the trial stage. There is no scientific measure to measure, production inspection can not be carried out.
● Scientific choice of thickness, reasonable composite process, supporting the material and aluminum foil itself as important as the performance. Reasonable support not only can make the product quality and can reduce the cost.