What are the factors that affect the attenuation of the dyne value after the film is corona treated?

Tue Apr 19 2022 Klara

After corona machine treatment, the effect is slowly attenuated. Generally speaking, it is mainly affected by the following aspects: additives, environment, and the natural attenuation of the material itself.

There will be additives in the film, and each film, or produced by different manufacturers, even the same film additives will be different, and each manufacturer has its process. After the film is corona treated, the organic and inorganic contaminants are removed from the surface, activating the surface and increasing its surface energy, which can significantly improve the dyne value of the material surface, but over time, the additives in the material will migrate to the material.

Influence of Additive Processing Strength

When the additive is at 200PPM, the corona strength is relatively low. The more additives, the more difficult the corona strength is.

The effectiveness of corona treatment also depends on the corona strength of the specific material treated. Materials have different characteristics, and different amounts of slip agents and additives will affect the effect of corona treatment. There is no limit to how many different materials can be corona treated. However, the required treatment level intensity requirements (W/min/m) may vary significantly, and the corona level is defined as the corona intensity.

The environment where the corona machine is located is also very important. The environment where the corona machine is located should not have a lot of dust, high humidity, and high temperature, which will also affect the effect of corona treatment of materials.

The material itself will also lead to the decline of the effect. Most materials can be kept for 3 days after corona treatment in theory, but different materials will be different. In short, the longer the corona treatment is from the next process, the better the effect. No, so everyone's common practice is to go directly to the next process after corona's treatment

Of course, the material can not only focus on the decline after treatment, the degree of treatment is also very important.

For different materials, the greater the power of the corona, the dyne value will increase in a straight line, of course, it is not an infinite value increase, no matter what material there is always an upper limit. Taking pet as an example, when the corona intensity is 5W, it corresponds to about 52, and it reaches the limit when it is increased by 15KW.

For most materials, the bonding dyne value should reach 33, the printing dyne value should be greater than 38, and the composite dyne value should be greater than 46.

Corona machine intensity formula Corona intensity = corona machine power / (material width m * processing speed m/min)

Over time, the dyne level (in mN/m) obtained will decrease, and if silkscreen or bonding steps are to be performed, the material needs to be corona treated again before the next treatment. If a material contains a slip agent, the dyne level drops faster, while thicker, older films are more difficult to handle because the slip agent may have passed to the surface.

Corona decay is affected by temperature and humidity under material storage conditions. In general, if the material is difficult to handle, it is likely to decay faster over time. It has been confirmed that films with high slip additives above 1200ppm can be completely offset and printed within 24 hours after treatment, so the best way is to go directly to the next process after corona treatment

Materials that have not been corona-treated are difficult to handle after extrusion. Therefore, it is recommended to treat the film immediately after extrusion, and then perform a supplementary corona treatment before the next process, two treatments to increase the dyne value level.