Surface preparation of plastics.

The main objective of the preparation of plastic surfaces is to improve the wetting properties and adhesion of the plastic surface.

Plastics are materials composed of polymers with a defined structure and composition, which provide various chemical, mechanical and physical features that are classified as thermoplastics, thermosets or elastomers materials.

The main characteristics of plastic materials are that they are composed of polymers, which provide the wetting and adhesion properties of the surface.

The main factors that affect the right adhesion of the adhesive on a plastic material are:

• Interactions between plastic polymers and polymers of the adhesive - compatibility.

• Type of plastic (thermoplastic, thermoset or elastomer)

• Surface tension of the plastic, which is directly related to the disposition of the dipoles and polar or non polar behavior.

• Contamination or adsorbed layers that are place prior to the plastic base.

On the surface of a plastic we can find can the following layers:

• Layer of contaminants.

• Adsorbed layer.

• Injection moulding skin.

• Plastic base.

To clean the contaminants found on the surface of the plastic, we can use organic solvents or aqueous agents, it is important to identify the appropriate cleaner to avoid stress-cracking of the plastic surface.

If you need to remove the adsorbed layer and / or Injection moulding skin of plastics prior to adhesive application, you can use the following techniques or processes such as pretreatment of surfaces:

Mechanical processes:

• Sanding

• Blasting

• Peel Ply

Chemical Processes:

• Fluoridation

• Etching

Physical processes:

• Flame Treatment

• Treatment by plasma (high pressure or low pressure)

• Laser Treatment.

The use of blasting and sanding like surface preparation process is not recommended in plastic, due it can easily cause stress-cracking or break the material.

The peel ply technique is used during the manufacture of fiber reinforced plastics, which is placed a film that can be started after keeping intact the plastic surface, not requiring any additional surface preparation.

The chemical processes of surface preparation aimed at the creation of dipoles to activate the surface of the plastic, creating a surface with good wetting properties to adhesion.

The plasma treatment and laser surface preparation of plastics, are techniques that provide superior surface qualities compared with other techniques. Both techniques clean and modify the surface energy and surface structure of plastics increasing wetting and adhesion properties.

After making the correct pretreatment on the plastic surface, this surface produces active sites that react with the environment becoming inactive surface, to avoid such effects activators and primers used prior to adhesive application.

Generally the adhesive manufacturer is indicated in the technical data sheet the surface preparation recommended for each type of plastic