For aluminum foil pharmaceutical packaging, the quality of the product is largely reflected in the heat seal strength of the product. Therefore, several factors that affect the heat-sealing strength of aluminum foil bags for medicines have become the key to improving the quality of product packaging.
1. Raw and auxiliary materials
The original aluminum foil is the carrier of the adhesive layer, and its quality has a great influence on the heat seal strength of the product.
On the one hand, oil stains on the surface of the original aluminum foil will weaken the adhesion between the adhesive and the original aluminum foil. If the surface of the original aluminum foil has oil stains and the surface tension is lower than 31×10-3μm, it is difficult to achieve the ideal heat seal strength. On the other hand, the metal composition and insufficient surface brightness of the original aluminum foil affect the strength of the heat seal, and the quality of the original aluminum foil must be strictly controlled.
2. In terms of adhesives
Adhesive is a special substance containing solvent. It is coated on the dark side (or smooth side) of the original aluminum foil under certain process conditions, and dried in a drying tunnel to form an adhesive layer, which plays a decisive role in the heat seal strength of the product
At present, most domestic manufacturers use imported raw materials to prepare adhesives, and the products can achieve higher heat sealing strength. However, the price of imported raw materials is too expensive. In order to obtain high profits for the products, some manufacturers with strong scientific research capabilities have begun to research and develop similar domestic raw materials.
3. Production process
Under the control of certain process parameters, the adhesive is coated on the surface of the original aluminum foil to form a film, and the quality of the finished composite film will directly affect the heat seal strength of the product. Among the more important parameters include the coating speed, the segmented temperature of the drying tunnel, the shape, depth, number of lines, and the position and angle of the blade of the coating roller.
The coating speed determines the drying time of the coating in the drying tunnel. If the coating speed is too fast and the drying tunnel temperature is too high, the solvent on the surface of the coating film will evaporate too quickly, resulting in residual solvent in the film, and the coating film will not be sufficiently dried, and it will be difficult to form a dry, strong and strong adhesive layer. Affect the heat seal strength of the product and cause adhesion between product layers.
The anilox shape, depth, number of lines and the position and angle of the doctor blade determine the thickness and uniformity of the coating film. If the selection or adjustment is inappropriate, the adhesive will not be evenly coated on the surface of the original aluminum foil, resulting in uneven film formation, the heat sealing effect of the product will not be good, and the strength will also be affected.
4. Heat sealing temperature
The heat-sealing temperature is an important factor that affects the strength of the heat-sealing. If the temperature is too low, the adhesive layer cannot be heat-sealed with the PVC film well, and the bond between the adhesive layer and the PVC film is not strong. If the temperature is too high, the medicine will be affected. Therefore, a reasonable heat sealing temperature is usually between 150°C and 160°C.
5. Heat sealing pressure
To achieve the ideal heat sealing strength, a certain heat sealing pressure must be set. If the pressure is insufficient, not only the adhesive layer of the product and the PVC film cannot be fully bonded and heat-sealed, but also air bubbles can be left between the two, and a good heat-sealing effect cannot be achieved. Therefore, the national standard stipulates that the heat sealing pressure is 0.2mPa.
6. Heat sealing time
The heat-sealing time will also affect the heat-sealing strength of the product. Under normal circumstances, under the same heat sealing temperature and pressure, a longer heat sealing time can make the heat-sealed part be sealed more firmly and perfect, and can better achieve the expected heat-sealing strength. However, the technological conditions of modern high-speed pharmaceutical packaging machines cannot provide a long time for heat sealing. If the heat sealing time is too short, the heat sealing between the adhesive layer and the PVC film will be insufficient. For this reason, the national standard stipulates that the scientific heat sealing time is 1s.