Resumen de Perceived quality characterization of micro-textured injection moulded components for automotive interior applications
The present PhD thesis is framed within a collaborative project in which institutions such as the Universitat Politècnica de Catalunya Barcelona-Tech, the Centre Català del Plàstic and SEAT S.A have participated. The main objective of this research is to improve the surface quality of the textured injection moulded components of the car interior. To this end, a methodology that allows assessing the appearance objectively using three-dimensional characterization techniques is proposed.
The texture replication ratio of a mould cavity was first investigated. Squared samples of Polypropylene (PP) were injection moulded. It was found that the holding pressure was the most significant parameter for improving the texture replication ratio. In addition, using three-dimensional characterization techniques, it was demonstrated that the multi-scale methodology was a suitable technique to quantify the replication ratio and effectively separate the main surface components namely, roughness, waviness and form either at the macro- or the micro-scale.
Four texture types were utilized to measure the surface appearance. The first one was a leather texture, the second and the third types were obtained by applying a mould treatment on the previous original leather texture. The fourth one was obtained through a painting process. The appearance was measured using a new Total Appearance Measurement (TAM) apparatus. A relationship between topographic features such as roughness, functional height distribution (FHD), texture slope (TS) and texture aperture angle (TAA) and surface appearance properties such as gloss and reflectivity contrast was established.
Finally, the surface performance was studied by means of both scratch and mar resistance tests. The texture influence on the scratch hardness and the scratch visibility resistance was evaluated and quantified using three dimensional techniques. Topographic characteristics such as peak-to-valley symmetry and the number of micro-asperities were analysed. The results showed that surfaces with higher symmetry in their functional height distributions yield lower lightness variations (L*) between the scratch pattern and its residual background height (RBH). On the other hand, topographies with a smaller number of micro-asperities on top of the texture provided an enhanced mar resistance. In these cases, deformation mechanisms such as ironing are minimized, resulting in a lower gloss variation and lower contrast between the damaged area and its surroundings.
