Leave Your Message

Exploring Surface Properties and Treatment of Plastic Films


Plastic film is widely used in the field of packaging. Plastic films can be used in food packaging, electrical product packaging, daily necessities packaging, clothing packaging, and so on. They have one thing in common, that is, the plastic film must be printed in color, and as food packaging, it also needs to carry out multi-layer lamination or vacuum aluminization and other process operations. Therefore, the surface free energy of the plastic film is required to be high and the wet tension is large, so as to facilitate the firm adhesion of printing inks, adhesives or aluminized layers to the plastic film; In the process of plastic film production, coiling and high-speed packaging, the surface of the film is required to have a certain friction property to prevent the film from sticking or slipping; When used in the packaging of electrical appliances and electronic products, the film is required to have certain anti-static properties and so on.


Surface tension of plastic films


The surface tension of the plastic film depends on the free energy of the plastic film, which in turn depends on the molecular structure of the film material itself. Most plastic films such as polyolefin films (LDPE, HDPE, LLDPE, PP) are non-polar polymers with low surface free energy and low surface wet tension, generally about 30 dynes/cm. Theoretically, if the surface tension of the object is less than 33 dynes/cm, ordinary inks or adhesives will not adhere firmly and must therefore be treated. Polyesters (PET, PBT, PEN, PETG) are polar polymers with high surface free energy and a surface wet tension of more than 40 dynes/cm. However, for high-speed color printing or to increase the adhesion between the vacuum aluminized layer and the surface of the BOPET film, the surface treatment of the BOPET film is also required to further improve its surface wet tension.


The methods of surface treatment of plastic film are: corona treatment, chemical treatment, mechanical hairing, coating, etc., among which the corona treatment method is often used.


The basic principle of the corona treatment method is that by applying a high-frequency, high-voltage power supply between the metal electrode and the corona treatment roller (generally a high-temperature, ozone-resistant, and highly insulating silicone rubber roller) to produce a discharge, so that the air is ionized and a large amount of ozone is formed. At the same time, a high-energy electrical spark strikes the surface of the film. Under their joint action, the surface of the plastic film is made to live and the surface energy is increased. The wet tension of the polyolefin film can be increased to 38 dynes/cm by corona treatment; The surface wet tension of polyester film can reach more than 52-56 dynes/cm. The amount of wet tension on the surface of the corona treated plastic film is related to the voltage applied to the electrode, the distance between the electrode and the corona treatment roller, and other factors. Of course, corona treatment should be moderate, not the higher the intensity of corona treatment, the better. It is worth noting here that air should not be trapped between the plastic film and the corona treatment roller, otherwise the reverse side of the film may also be treated by corona. The consequences of reverse corona are: 1. It is possible to produce the anti-adhesion phenomenon of ink printing; 2. The transfer of the aluminized layer will occur during aluminization, and the transfer of the gluing layer will occur during gluing. The main measure to prevent the corona on the reverse side of the film is to adjust the pressure of the rubber