Aluminum foil material quality and its testing method
Medicinal aluminum foil pinhole and its detection: Metal aluminum has a highly dense metal crystal structure, and theoretically perfect aluminum foil can completely block any gas, water vapor and light. But in fact, due to the influence of many factors such as the rolling process used in the production of aluminum foil, the quality of rolling oil, the condition of the surface of the rolling roll, the process operation technology and the environment of the production site, various defects inevitably appear in the aluminum foil, especially the thin aluminum foil. Pinholes are one of the most important ones.
The size and number of pinholes are one of the important metrics to measure the quality level of aluminum foil products. It is precisely because of the existence of pinholes that the permeation of oxygen and water vapor to the aluminum foil is not zero.
The size and number of aluminum foil pinholes have a decisive influence on the moisture resistance, gas barrier properties and light shading properties of aluminum foil and its composite materials. my country’s national standard GB3198-1996 makes the following provisions on pinholes: “The surface of aluminum foil is allowed to have pinholes visible to the naked eye, but the pinholes shall not be densely arranged, and the diameter of the pinholes of medicinal aluminum foil shall not be greater than 0.3 mm, and shall not exceed 0.3 mm. 5 pcs/m². The pinhole size of other industrial pure aluminum foil shall not exceed 0.5 mm.
Because pinholes are an important indicator for detecting aluminum foils, many foreign technical materials stipulate the pinholes of aluminum foils or the water vapor transmission of aluminum foils. American Society for Testing and Materials standard ASTMB-479-85 “Technical Standard for Annealed Aluminum Foil and Alloy Aluminum Foil for Barrier Flexible Packaging” stipulates: “There should not be too many pinholes, and aluminum foil with a thickness greater than 0.5 mm should be free of pinholes.” Japanese Industrial Standard JISZ1520 -1975 “Standard for Composite Aluminum Foil” gives the data of water vapor transmission of composite aluminum foil.
At present, there is a big gap between the quality level of domestic aluminum foil and foreign countries, which is mainly reflected in the number and size of pinholes. Some foreign standards stipulate that there are no pinholes when the thickness of aluminum foil is greater than 0.025 mm, while domestic standards stipulate that there is no pinhole when the thickness of aluminum foil is greater than 0.05 mm. For pinholes, foreign standards stipulate that pinholes larger than 0.1 mm are not allowed, while domestic standards stipulate that the maximum size of pinholes can reach 0.5 mm.
Improving the quality of aluminum foil and reducing the number and size of pinholes in aluminum foil are problems that domestic aluminum foil manufacturers urgently need to solve. HWPFP has always put more effort into this aspect to ensure the quality of medicinal aluminum foil.
Inspection of pinhole degree of finished medicinal aluminum foil: Pinhole inspection table: use a wooden box of 800 mm x 600 mm x 300 mm or an appropriate volume, install a 30W fluorescent lamp in the wooden box, put a glass plate on the wooden box, and the glass plate is lined with black paper and Leave a 400mm x 250mm space for inspection of specimen pinholes. Take 20 samples with a length of 400 mm and a width of 250 mm from the finished aluminum foil, put them on the pinhole inspection table one by one, and check their pinholes in the dark.
The requirements for pinholes are that there should be no dense, continuous, periodic pinholes, no pinholes with a diameter greater than 0.3 mm, and no more than 1 pinhole per square meter with a diameter of 0.1-0.3 mm .
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