Study of the thermal stability of pigments in the injection molding of Polyamide-12

The aim of this thesis, developed during a six-month internship at EssilorLuxottica, is to analyze the thermal stability of pigments used for polyamide in the injection molding process. The topic is of primary interest for the company, as the stability of the process is crucial for guaranteeing a homogeneous an repeatable output for big volumes of finished products. Moreover, in the fashion and design industries in which the company operates, a continuous and fast development of new colors is required. Then the final goal is to define a catalogue of pigments that will be used for both new colors development and production. A future further improvement would be to have a software able to support this development that currently is very expensive in terms of both base material and labor. In the first part, this work aims to give a theoretical overview on many topics, like the injection molding process, the nature of color and how it can be measured in the colorimetric space, which are fundamental concepts necessary to understand the outputs of this work. Then how polymeric materials can be pigmented, and the different techniques used to achieve that are discussed, looking at the different nature and forms of colorants. In the Second part of this thesis the proper work done during the working experience is reported. At first, the molding procedure defined to produce the samples to be measured is described; this comes from the know-how of the company with some changes aimed to guarantee a stable and repeatable process for all the tested pigments. The produced samples are then analyzed, and the collected data discussed, clustering all the encountered defects. Of course, what the company wants to obtain with this analysis is to avoid the use of the most problematic colorants and ensure that the range of in-house pigments is able to cover the entire colorimetric space. This will ensure the wider flexibility in terms of colors development.