Why do PET protective films need Corona treatment?
When the PET protective film is not treated by its appearance, its appearance tension is above 40mN/m, but in order to further improve the binding force between printing ink or vacuum aluminizing layer and the appearance of PET protective film, adhesion fastness is added, it is often necessary to treat the appearance of PET protective film.
The methods of plastic film surface treatment include Corona treatment, chemical treatment, mechanical roughing, coating, flame, etc. Among them, Corona treatment is the most commonly used method.
The basic principle of Corona treatment method is: through the metal electrode and Corona treatment roller (
It is usually a silicon rubber roller with high temperature resistance, ozone resistance and high insulation)
High-frequency and high-voltage power supply is applied between them to make them discharge, so the air is ionized and a lot of ozone is formed. At the same time, high energy electric spark impacts the appearance of the film.
Under the combined effect of them, the plastic film surface can be activated and the appearance can be added.
Corona treatment can make the external wet tension of PET protective film reach 52 ~ Above 56 mN/m, or even higher.
The fineness of the wet tension on the surface of the Corona-treated plastic film is related to such factors as the voltage concave-convex applied to the electrode and the interval between the electrode and the Corona-treated roller.
Of course, Corona treatment should be moderate, not the higher the corona treatment intensity, the better.
It is worth mentioning here that air should be avoided between PET protective film and Corona treatment roller. If air is sandwiched between them, it may cause the film to be Corona treated.
The result of discordant corona formation is: ① There may be an anti-sticking scene of ink printing;
(2) when the aluminum is plated, the aluminum layer will be transported, and when the glue is coated, the glue layer will be transported. These are the last things we expect to have.
The main way to avoid film discord with Corona is to adjust the pressure of the rubber compaction roller in front of the corona treatment roller. The pressure at both ends of the compaction roller should be common and the pressure should be huge and fine and appropriate.
In addition, it is necessary to carry out severe dynamic balance tests on Corona roller and compression roller, and the radial runout request is less than 0.
05mm, the intention is to ensure that the PET protective film enters the Corona roller smoothly, to avoid the air, and then to avoid the occurrence of the scene of the corona.
Corona treatment has the question of aging, which is well known to us.
Especially in the summer of high temperature and high humidity, the appearance of the plastic film after the corona treatment of the wet tension attenuation contrast fierce.
Therefore, the plastic film is printed or aluminized in time after Corona treatment.
If the PET protective film is placed too long after Corona treatment, the external wet tension will gradually decrease, and even because the external wet tension of the printed surface and the non-printed surface tends to be the same, after the surface of the printed film is rolled up, it is easy for the ink to be anti-stuck to the non-printing surface, which is the so-called 'anti-stick' scene.
In order to avoid 'anti-sticking', on the one hand, it is necessary to completely dry the ink when printing the film;
On the other hand, it is necessary to ensure that the printed surface has a satisfactory external wet tension, so that the larger the difference between the external wet tension of the printed surface and the non-printed surface, the better.
Coating method is also another effective way to improve the appearance function of PET protective film.
The so-called coating method is to coat a certain polymer solution on the surface of the film, such as polyacrylate, modified polyester and other polymer solution coatings.
For PET protective film, the coating technology is: in longitudinal direction (MDO)With the horizontal pulling machine (TDO)
Between, equipped with an on-line coating machine, through the longitudinal stretching of the PET protective film immediately through the on-line coating machine for polymer solution coating, and then into the TDO for transverse stretching, after the solvent of the polymer solution in the horizontal puller is dry and evaporated, a layer of coated polymer is left on the surface of the PET protective film.
The test shows that after the surface of PET protective film is coated with modified polyester coating, the wet tension of the surface of the film can be added to more than 58 mN/m.
Moreover, one of the advantages of the coating method is that the wet tension of the film surface will not be attenuated due to the high temperature and high humidity climate conditions, and the water resistance and solvent resistance are excellent.
After aluminizing on the coating of the coated film, the adhesive force is strong, and the phenomenon of aluminum plating layer delamation will not occur due to touching the aqueous solution at high temperature.