1. Field of the Invention
The invention relates to the technical field of packaging, and more particularly to a method and device of packaging by heat sealing.
2. Description of the Related Art
At present, the method of packaging by heat sealing for plastic films has been widely used for packaging food, medicine, and cosmetics, with the advantages of low cost, high packaging efficiency, moisture resistance, seepage prevention, etc. There are several concrete application methods: (1) continuous liquid packaging, the film raw material adopts a double-layer long film packaging tape, and its two side edges are sealed. During the packaging process, the packaging tape is filled with packaging materials, and then two ends of the packaging tape are transversely sealed and cut off, so as to finish packaging; (2) single packaging, packaging materials are put into a plastic bag or a single cavity with an opening at one end, and then the opening of the plastic bag or the single cavity is sealed with a heat sealing device; (3) a concave cavity for allowing the packaging materials to be placed in is formed on at least one layer of film in two layers of films, a heat sealing cutting die of the heat sealing device is manufactured into the shape consistent with that of a required packaging line, then the two layers of films are sealed at the packaging line, the packaging method can adopt an individual packaging method or a multipack packaging method, and a packaging line is arranged between every two packaging materials, so that the packaging materials are separated from each other. The fundamental principle of the method of packaging by heat sealing is as follows: a heat sealing cutting die is arranged on the heat sealing device and has the same shape as the packaging line, the heat sealing device is used for heating the heat sealing cutting die through a heating device, the heat sealing cutting die is maintained at a set temperature, close to and pressed against the films, the films are mutually bonded after being molten by heat, the heat sealing cutting die is reset, and then the films are cooled and packaged. Although the film for packaging has no harm to human body, it is molten at a high temperature to generate a small amount of toxic decomposition gas during the packaging process, the decomposition gas enters a packaging cavity and packaged food or medicine, thus the secondary pollution to the packaging materials is caused. The prolonged intake of light polluted food or medicine may negatively affect the human health. Currently, some more advanced heat sealing machines are provided, such as a high-frequency heat sealing machine, an ultrasonic heat sealing machine and a heat sealing machine using laser technology, and the heat sealing packaging quality and the heat sealing packaging efficiency are remarkably improved, but the heat-sealed films are bonded together by melting, thus the secondary pollution to the packaging materials cannot be avoided. Even for the normally used plastic bags, the odor left in the plastic bags during the melting and decomposing process can be often smelled when the plastic bags are used in an opened manner.
For example, an upper film and a lower film are placed on a middle die seat and a lower die seat respectively, the lower film is infused with fluid, a vacuum cavity where the middle die seat and the lower die seat are positioned is closed through a valve, the gas in the vacuum cavity can be extracted through a vacuum pump unit, so as to form a state close to the vacuum, a vertically butted sealing seat formed by the middle die seat and the lower die seat is used for heat sealing, the circumferences of the upper film and the lower film are sealed at one time in the state close to the vacuum state to cause the fluid to be enveloped, and no bubbles remain in the fluid. During the packaging process, the packaging cavity is vacuumized, so as to extend the shelf life of packaging materials, but the secondary pollution of trace decomposition gas to the packaging materials cannot be avoided.