Plasma powder activation
Furthermore, hydrophilic PE powder can increase the bonding strength between metal and plastic. This hydrophilization is made possible by low-pressure plasma treatment. The treatment parameters strongly depend on the particle size of the powder. Plasma treatment can take between 5 minutes and several hours. Thermal damage to the powder is excluded since the process temperature remains low the whole treatment time. Likewise, basic properties of the powder such as melting temperature, degree of crystallisation and molar weight are not affected.Via a wide range of variable process parameters, many different coat properties can be achieved.
"20.11.2012 New developments in plasma technology have now made industrial-scale modification of plastic powders and granulates possible. The Ebhausen-based manufacturer Diener plasma GmbH + Co. KG developed a low-pressure plasma system which can for example turn functional hydrophobic additives permanently hydrophilic, improving their product properties for a number of innovative applications.
Since polyethylene is naturally hydrophobic, it cannot absorb moisture. For this reason, the material is not suited for all types of applications. The chemical bond between the plastic granulate and the additive is often missing, for example. To remedy this problem, Diener plasma developed a plasma system that can hydrophilize the powder. Controlled via PC, the system can treat 25 kg of powder per batch by the addition of oxygen, nitrogen or argon as process gases.
Before, plasma treatment of bulk goods such as powder was limited to laboratory-scale volumes of up to 1 kg. With this system, Diener made plasma treatment of powders on an industrial scale possible. During the entire process, the powder is continuously mixed in a drum-shaped vacuum chamber to ensure even treatment. At low process temperatures of approximately 30 °C, thermal damage to the powder and thus any modification of its basic properties is excluded. By means of varying the process parameters, the desired surface properties can be set directly.
Plastic processing companies can look into new innovative applications thanks to the oxygen groups acting in the plasma. The surface energy of polyethylene powder, for example, can be increased tenfold in a matter of several minutes. With these additives, plastic processing companies can for example develop rubbers with higher tear propagation strength or manufacture porous filter elements in a sintering process.”