Materials with low surface energies like polymers and metals are not wettable by printing ink and adhesives. These materials require some treatment to match the surface tension of adhesives. The procedure of using chemicals, plasma or radiations for increasing the surface tension of non-polar materials is called as surface activation.
Although every method of activation has its own pros and cons, choice of the treatment method depends on the nature of the material being treated. For example, plasma treatment is commonly used to activate the polymer surfaces, while for metal surfaces UV radiations are used.
Surface activation is not only used for energizing the surface molecules of a material, but this technique can also modify the following surface properties:
Conductivity of metals can be increased by increasing the number of free electrons or loosely bonded electrons. This can be achieved by treating metals with highly ionized particles like plasma or exposing metals to intense radiations. This technique is frequently used in IC (Integrated Chips) fabrication for improving the conductivity of semi-conductors.
2. Low Carbon Adhesion
Treated surfaces are suitable for printing ink or paint adhesion but surface activation prevents dust or carbon from adhering to activated surfaces, thus improving the quality of the material.
This technique is also used to cover plastic surfaces with a metal coat. Metalized polymers can easily replace metals like copper and aluminum in electric appliances, thus reducing the risk of rusting.
4. Reduced Fogging
Polymers are composed of long chains of hydrocarbons. These hydrocarbons can trap water molecules present in the atmosphere which makes the polymer surface foggy. During surface treatment, polymers are treated with chemicals which form different functional groups on the surface of the material and reduce the probability of fogging.
Surface activation increases the surface energy of plastic and metals and enables the bonding of water and oil based adhesives with these materials.
6. Diffusion Barrier
There are a number of gases present in the atmosphere which can penetrate the surface of polymers and change their properties. Surface treatment changes the atomic structure of polymers and prevent the diffusion of gases like methane, nitrogen etc.
There are three commercial methods of surface activation; chemical activation, plasma treatment and exposure to UV radiations. Choosing the right method depends on the following factors:
- Nature of treated material- every material has its own physical and chemical properties. For example, polymers have lower heat tolerance than metal and flame activation can deform polymer surfaces. Similarly, metals are more reactive than plastics and non-volatile by-products formed during chemical activation can permanently change the properties of metals.
- Reason of treatment- if a material is being treated for cleaning the surface, chemical activation is the most suitable option but if a material is being treated for improving the surface adhesion, plasma activation is a better than other options.
- Budget- although it is not recommended to compromise quality over cost, the selected method of surface activation should be affordable. For example, a small scale company cannot afford high-tech UV treatment plants.