Etude de la stabilite dimensionnelle du TPO lors du traitement de surface pour l'application d'un revetement

The main goal of this experimental work is the study of the dimensional instability of painted and unpainted injection moulded TPO (thermoplastic polyolefin) plaques. The application of paint coating followed by a period of baking at 120°C for 30 minutes on TPO has revealed that excessive deformation other the one generated by TPO aging occurs on the part surface after paint baking. These defects are generated from two different sources; the first one is due to the heat treatment. The second one, however, is generated by paint shrinkage. The combination of these two effects has conducted us to look at a mean to study them separately.; To proceed, a series if one mm thick TPO plaques were injection moulded. Three injection moulding parameters were considered. The first one is the packing pressure, the second one is the injection speed and the third one is the material temperature. The processing window for these three parameters and their central points were as recommended by the material supplier. First the injection speed was set at 80 mm/s, the material temperature at 220°C and the packing pressure was varied, then the packing pressure was set at 45 MPa, the material temperature at 220°C and the injection speed was varied. Finally, the injection speed was set at 80 mm/s, the packing pressure was set at 45 MPa and the material speed was varied.; Relatively to the objectives of this work, this study includes two major parts.; First, the heat effect on the material by baking unpainted TPO plaques in a conventional oven at 120°C during a period of time of 30 minutes was studied. Then the effects of time and temperature were carried. The annealing time effect was studied by fixing the annealing temperature at 120°C and varying the annealing time from 5 to 10 and finally to 30 minutes. In others experiments, the annealing temperature effect was investigated by fixing the annealing time to 30 minutes and varying the annealing temperature from 120 to 130 and finally 140°C.; Deformation measurements were conducted using a laser beam profilograme on as-molded unpainted TPO plaques and just after being heat treated. The results allowed us to measure the deformation generated by heat effect.; In the first part, the study was completed by the material characterisation before and after annealing using three different techniques: DSC (Differential Scanning Calorimeter), PVT (pressure, volume and temperature) and finally by mechanical tensile tests. Many cases related to annealing time effect and annealing temperature effect were studied using DSC technique. The goal of these tests is to simulate in the DSC apparatus heat effect on TPO plaques in a conventional oven.; In the second part of this work, the deformation generated by the paint itself was studied: deformation measurements by the laser beam machine were conducted on painted TPO plaques. The injection parameters were taken in consideration in these tests.; After analyses of the results, we concluded that the deformation of TPO painted plaques has two different sources. The first source is the heat effect and the second one is the paint effect. The deformation due the heat effect is due to relaxation of stress induced during the moulding process and the post-crystallization of some potential chains in the polymer. The deformation due to paint shrinkage is generated by the stress induced during paint solidification. The solvent evaporation induces volume shrinkage in the paint coating. With the strong links between the former and the substrate, a stress at the interface bends the material consequently.