Factors affecting the performance of evaporated silicon oxide barrier packaging films

I. Factors affecting the performance of vapour-deposited silicon oxide barrier packaging films

Evaporation base film, evaporation method, evaporation conditions, as well as the composition of the evaporation coating, the thickness of the evaporation layer, etc., may have a great impact on the performance of evaporation-type silicon oxide barrier packaging film.

1. Selectivity of the substrate

As mentioned earlier, the barrier properties of evaporated silicon oxide barrier packaging films depend on the SiOx coating, so the coating cannot be destroyed during the evaporation process. Steam-coated silicon oxide barrier packaging film is usually laminated with other films to create a steaming film, the selection of the steaming substrate should pay attention to the following issues.

(1) Type of plastic film

Evaporation of silicon oxide film and plastic film adhesive fastness between the plastic base film type has a greater relationship between the PET, PVC and other polar film and silicon oxide between the adhesion is better, while the non-polar film, and the adhesion between the silicon oxide is worse.

(2)Surface state of plastic film

The barrier property of evaporated silicon oxide barrier packaging film is not only affected by the thickness of the evaporated layer, but also determined by the uniformity of the silicon oxide coating to a greater extent. Cracks, pinholes and other defects, will lead to evaporation type silicon oxide barrier packaging film barrier significantly reduced, the formation of defects in addition to the evaporation of the chemical composition and structure of the layer itself, the use of the base film surface smoothness, is also an important factor, the greater the roughness, the more likely to cause defects in the evaporation, but the right amount of roughness will make the evaporation layer and the surface of the base film between the formation of a physical anchor to improve the adhesion of the interlayer.

(3) Surface pretreatment condition of plastic film

In order to obtain high-quality vapour-deposited films, moderate surface corona treatment of the base film is essential. Plastic film after surface corona treatment, can form an oxide layer on its surface (through cross-linking, ozonation, carboxylation, nitration and other complex chemical reactions, such as oxygen, nitrogen and other atoms and atomic groups introduced to the surface of the plastic film), increasing the base film and vapour plating coating bonding force between the coating. In the case of certain pretreatment equipment, if the pretreatment time is insufficient, the surface modification is not sufficient, will lead to the base film and the coating between the combination of fastness decreased; pretreatment time is too long, may cause the base film deeper level of interfacial weakening, produce the base film's own weak interfacial layer, but also caused by the surface of the substrate and vapour plating layer between the bonding force decreased.

2. The effect of vapour deposition process conditions on the performance of vapour-deposited silicon oxide barrier packaging film

Whether using physical or chemical vapour deposition, vapour deposition process conditions may have a significant impact on the performance of vapour-deposited silicon oxide barrier packaging film, so it should be used as far as possible to improve the barrier properties of vapour-deposited film process conditions.

(1) When physical vapour deposition is used.

The level of vacuum, the temperature of the substrate film, the power of the electron gun, the shape of the raw material SiO2 evaporation, the speed of oxygen introduction in the vacuum chamber, the thickness of the evaporation coating (determined by the evaporation time and evaporation power) will affect the performance of the final product.

① The higher the vacuum degree during evaporation, the more favourable to the evaporation of SiO2, and the higher the quality of the evaporation coating.

② evaporation of the plastic base film temperature is high, is conducive to the evaporation of SiO, in the plastic base film deposition, the formation of dense coatings and is conducive to improving the adhesion between the evaporation layer and the plastic base film, so appropriate to raise the temperature of the plastic base film, is conducive to improving the quality of evaporation of thin films.

③ using electron gun bombardment, evaporation of SiO2, it is appropriate to use a block of SiO2, because the powdered SiO2 bombarded by the electron gun, easy to produce powder sputtering phenomenon, affecting the quality of the evaporation of the film, and powdered SiO2 is conducive to the resistance heating and evaporation.

④ The introduction rate of oxygen affects the composition of the evaporation layer, i.e., the ratio of the number of Si atoms to the number of 0 atoms in SiOx. The larger the amount of oxygen is, i.e., the larger the value of x is, the evaporation layer moves in the direction of improved transparency, but the barrier tends to decrease. When x is equal to 2, the barrier performance is poor, colourless transparent vapour coating layer, usually x control between 1.5 ~ 1.8 to obtain both high barrier and good transparency of the vapour coating silicon oxide film.

The thickness of the vapour deposition layer increases, the barrier property of the vapour deposition film increases, but when the thickness of the vapour deposition layer exceeds 50nm, the thickness of the vapour deposition layer is further increased, the barrier property of the vapour deposition film basically remains unchanged, so we cannot expect to rely on the reduction of the production line's line speed (increase the vapour deposition time), increase the thickness of the vapour layer method, to unlimitedly improve the barrier property of the vapour deposition film.

(2) chemical vapour plating, high-frequency electromagnetic wave or microwave frequency selection, should be ionized with the ionization of the atmosphere in the ionization energy and the energy required for the ionization of vapour-plated materials to match, high-frequency electromagnetic wave is generally 13.56MHz, microwave is generally 2.45MHz, the vacuum in the 10-2Pa or so can be obtained excellent vapour plating effect, and physical vapour plating requires a higher vacuum, that is, 10-2 ~ 10-3Pa, the vacuum is higher. 10-2~10-3Pa or higher vacuum.

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