ABC's of CORONA
Corona treating is a way to improve poor adhesion of inks to the substrate, which is caused by the low surface tension of many plastic materials.
First off, what is corona? According to the dictionary it is;"A faintly colored luminous ring appearing to surround a celestial body visible through a haze or thin cloud, especially such a ring around the moon or sun, caused by diffraction of light from suspended matter in the intervening medium."
According to our definition corona is; A high-voltage electrical discharge - that appears visibly as a blue arc. The corona treatment is applied directly to the surface of virtually any material with a low surface tension. When the materials are pre-treated with corona the surface tension will increase, yielding better ink adhesion or wettability.
The surface tension is measured in dynes/cm. To obtain optimum adhesion the dyne level of the material surface has to exceed the dyne level of the inks surface tension by at least 2 dynes. In order to increase the surface energy, the molecular structure of the surface has to be changed. As an example, let's look at polypropylene (PP) or polyethylene (PE) which has a surface tension of approx. 30 dynes and conventional inks typically have a surface tension of approx. 36 to 38 dynes. In order to get quality adhesion to PP or PE you need to raise the dyne level of that material to at least 38 to 40 dynes. Typically with a SICATECH corona treating system you can raise the dyne level of PP and PE to 72 dynes or above, ensuring excellent ink adhesion to the substrate.
To dig a little deeper, the corona discharge field is made up of a collision of neutral molecules and electrically loaded molecules. This rapid collision causes the neutral molecules to become electrically loaded. The electrons created in this field have a charged energy that is 2 to 3 times greater than the energy needed to break the molecular bond of most materials.
When the molecular bond of the substrates surface breaks into an atomic form, free radicals will react with the electrically loaded electrons in the corona field and there by change the energy (surface tension) of the substrates surface. It is important to note that only the surface of the substrate is molecularly changed.
To find out more about how SICATECH Corona treating systems can help improve your ink adhesion problems, please contact your local Deco Tech sales representative or contact our customer service department at (800) 300-DECO.