Лако-красочные материалы — производство

Surface finish and surface preparation are both key factors in the success of an adhesively bonded joint and, in many applications, roughening the plastic surface can be beneficial to the overall bond strength and the durability. If the adhesive is injection moulded, it is often possible to spark erode the mould tool to give a slightly rougher surface finish at the bond line thus improving the mechanical keying of the adhesive to the surface. A surface finish of between 1 and 2 Ra will invariably improve the adhesion performance of cyanoacrylates to thermoplastics.

In many non-structural applications, adhesives are used to bond engineering plastics without the need for any surface preparation and indeed this brings out the benefit of using the adhesive, especially when bonding dissimilar materials (where ultrasonic welding or other joining methods may not be possible).

However, surface contaminants such as oil and grease or the presence of mould — release agents will inhibit the substrate adhesion and thus compromise the long-term performance of the bonded joint. Internal and external mould-release agents are used to guarantee easy release of moulded plastic or rubber parts and can sometimes be transferred from the mould tool onto the surface of the plastic. The most common method of cleaning is a solvent wipe but the solvent selected should not craze or soften the plastic [2]. Mould-release agents are described as internal if they are already mixed with the granules and take effect during the processing of the plastic or rubber. These mould release agents may be distributed throughout the whole material so that even mechanical abrasion may not be effective.

Some plastics with a low surface energy will require a surface treatment process prior to bonding and this is covered in more detail in Section 6.3.