Joint Project: Optimizing adhesion of waterborne coating systems for plastic moldings by innovative surface modification techniques

Sponsor:
Federal Ministry for Economic Affairs and Energy via AiF within the Industrial Collective Research (IGF) program
 - IGF project 387 ZBG of research consortium Forschungsgesellschaft für Pigmente und Lacke e.V. (FPL), Stuttgart

Funded project partners:
- Fraunhofer-Institut für Produktionstechnik und Automatisierung (IPA), Stuttgart
- Forschungsinstitut für Leder und Kunststoffbahnen Freiberg gGmbH (FILK), Freiberg/Sachsen
- Leibniz-Institut für Polymerforschung Dresden e. V. (IPF), Dresden

Associated project partners:
Plasmatreat GmbH, Rehau AG Co., Kunststoff Christel, Karl Wörwag Lack- und Farbenfabrik GmbH  Co. KG, HEYtex Neugersdorf GmbH, Daimler AG, Asis GmbH, Ahlbrandt System GmbH

Contact persons:
Dr. Karina Grundke
Kathrin Estel
Anne Marschner

Duration:
2011 - 2014

Abstract
In the automotive industry, large-scale plastic parts are increasingly used to contribute to weight reduction and, hence, to saving of energy. Materials based on polypropylene are the most commonly applied plastic types beside polycarbonate blends. Problems arise when thermoplastic polyolefin materials (TPO) have to be coated because of their low surface free energy and the lack of polar functional surface groups. In industrial applications, 3-D automotive parts, such as bumpers, have been flame-treated for many years to obtain good paint adhesion. Despite this surface modification problems with the paintability of the TPO parts cannot be avoided up to now, especially, when waterborne paint systems are used and the plastic parts are exposed to extreme mechanical and thermal conditions after aging. To solve these problems, innovative surface modification techniques are of great interest.

It was the aim of this project, coordinated by the Fraunhofer-Institut für Produktionstechnik und Automatisierung IPA, to compare the commonly used flame treatment of TPO parts with an atmospheric plasma pretreatment technique and with gas phase fluorination.

In IPF, we used complementary surface characterization techniques (contact angle and zeta potential measurements, X-ray photoelectron spectroscopy, scanning force microscopy, confocal light microscopy) to study the modification effects of the three gas phase methods with regard to the chemical composition of the TPO surface region, their surface energetic and acid-base properties as well as their surface roughness. In the focus of this study was the better understanding of the interplay between the surface properties of the treated TPO and the adhesion of waterborne coating systems on these materials.

The surface modification of different commercially available TPO materials and the optimization of the pretreatment techniques were carried out in FILK. For comparison, additional flame treatments were performed by industry partners. The coating of the TPO materials using waterborne paints and the estimation of paint adhesion (vapor jet test DIN 55662) were carried out in IPA.