Discussion on the influence factors of the barrier property of aluminum foil composite soft package
2016/7/2 17:16:56
Aluminum foil as a metal material, non-toxic, odorless, has excellent conductivity and light-shielding, high moisture resistance, gas barrier properties, the barrier properties of any other polymer materials and the deposition film can not match and can not be replaced of. Perhaps it is because the metal foil is completely different from the plastic material, and its performance characteristics are not many people know, and even a lot of misunderstanding. One view is that the barrier properties such as aluminum foil and plastic composite of the simple sum equal to the barrier properties of pure aluminum foil barrier properties of plastic film, this is wrong, because of the simple superposition principle is a prerequisite, each two layers of material microstructure uniformity, concentration diffusion material on the uniform interface diffusion along the interface direction does not exist. Aluminum composite material does not meet these conditions, aluminum composite diffusion pinhole position was significantly higher than other locations. There is also another point of view permeability foil composite material is equal to the air permeability of plastic material multiplied by the ratio of the area of aluminum foil pinhole, the same is wrong, because it is not simply a part of the nearby aluminum foil pinhole breathable plastic, aluminum foil pinhole plastic is also involved in air. Some people think aluminum composite material to increase the thickness of the plastic - times, doubling its barrier properties, of course, this idea is wrong, in fact, when the thickness of the aluminum foil and plastic pinhole size sufficiently smaller than the increase in the thickness of the plastic basically no impact on the overall barrier performance of the composite material. Some people think that as long as the barrier properties of the composite high sealing performance with a package it must be made good. In fact, as a package, factors that affect the sealing performance has a positive penetration, side penetration and leakage, high barrier materials can only say that there is a very low penetration, it does not mean that there is a very low side penetration and leakage. And aluminum foil composite packaging materials in the molding, filling, sealing and other packaging processes and packaging products sterilization, transportation and sales process, the aluminum foil layer may wear pressure, pressure off, fracture, and the overall package sealing performance is affected.
Pinhole aluminum foil after calendering is made of aluminum foil, aluminum foil completely perfect barrier gas, water vapor and light. In fact, since the production of aluminum foil and many other factors, aluminum foil, especially aluminum foil thickness of 20μm or less inevitable pinhole defects. It is due to the presence of pinholes, so that the aluminum foil oxygen permeability and water vapor permeability is not zero. The size and number of aluminum foil and aluminum foil pinhole composites moisture barrier and light-shielding gas has a decisive influence.
National standard GB3198-1996 "industrial pure aluminum foil" pinhole made specific provisions "foil surface allows visible light with the pinhole, but dense pinhole can not make the trip, medicinal aluminum foil pinhole diameter of not more than 0.3mm and not more than 5 / m2. other industrial pure aluminum foil pinhole maximum size should not exceed 0.5mm. number of pinholes can not be too much. ", Appendix B in the standard test methods is also given pinholes and pinholes The number of standards.
Because the pinhole is an important indicator of aluminum foil, many foreign technical information are made of aluminum foil pinhole provisions (see Table 1). US ASTM B-479 "barrier flexible packaging with aluminum foil and alloy foil annealing technology standards" for aluminum foil pinhole makes provision, but also for the relationship between the thickness of aluminum and its water vapor transmission rate. Japanese Industrial Standards JIS Z1520-1990 "aluminum foil standard" also gives the composite with aluminum foil water vapor transmission of reference data.
The number of pinhole aluminum foil aluminum foil thickness is related with the increase of the thickness of the aluminum foil, which rapidly reduce the number of pinholes, the number of pinholes on the number of aluminum foil substantially proportional to its thickness (a), when it reaches a thickness of 20 m, an aluminum foil You can completely free of pinholes. The quality level of domestic aluminum foil with a wide gap between foreign countries, mainly on the performance on the number and size of pinholes. Foreign predetermined thickness greater than 0.020mm aluminum foil should be free of pinholes, and our standards can no pinhole foil thickness greater than 0.050mm; foreign standard does not allow more than 0.1mm pinhole, pinhole aperture typically 0.015mm, and our standard pinhole sizes up to 0.5mm, according to national standard GB3198, pinhole test is not factory inspection items. Although in recent years the quality of our aluminum foil has increased, but the quality of domestic aluminum foil remains stable, fluctuating at pinholes. Improve the quality of aluminum foil, aluminum foil pinhole reduce the number and size, it is the current domestic aluminum foil plant urgent problems.