Cross linked sheets for highly stressed thermoforming applications

在之前的项目中，以聚酰胺12（PA 12）为例，收集了关于大分子部分交联对半结晶热塑性塑料热成型性影响的基本知识。与无定形热塑性塑料相比，半结晶热塑性塑料通常不太适合于热成型，这是由于它们的刚度随着结晶熔融而急剧下降，并且熔体的拉伸流变性能不足。因此，迄今为止，满足热成型工艺要求的半结晶工业热塑性塑料的可用性非常有限。这阻碍了技术热成型部件的发展。结果表明，高能辐照使大分子发生部分交联，改变了PA12的熔体刚度和拉伸流变性能，对热成型过程有重要影响。增加的熔体刚度防止片材在加热期间过度下垂，而熔体的主要弹性行为减少了结网的机会。因此，加工温度范围大大增加。此外，交联导致材料的应变硬化行为，从而获得更均匀的壁厚，特别是对于具有高拉伸比的几何形状。该转移项目的目的是增强前一项目的知识，并通过演示器将其转移到应用中，演示器是一种可重复使用的电动驱动组件托盘。大面积托盘通常是用于热成型的合适几何形状。然而，现有的无定形热成型材料并不能满足技术托盘的所有要求，例如，当从注塑工艺中取出零件时，它们需要高耐热性。此外，还需要良好的耐磨性以确保可重复使用性。用于金属部件的托盘通常需要对油和油脂具有额外的耐化学性。应使用交联半结晶热塑性塑料满足这些要求。除了验证工业生产规模的结果外，还出现了其他基本问题。首先，必须研究PA12的结果是否也适用于其他材料，如不同的聚酰胺、聚烯烃或聚酯。此外，还必须研究交联助剂、稳定剂或颜料等添加剂与高能辐照之间可能的相互作用，这些相互作用会影响板材性能以及加工性能和最终的部件性能。此外，必须测量板材加工对热成形性的影响以及热成形条件对零件性能的影响。在这里，研究的性能范围应扩大到包括半结晶热塑性塑料的一些相关应用优势，如磨损行为或耐化学性。

Basic knowledge about the effects of a partial cross linking of macromolecules on the thermoformability of semi-crystalline thermoplastics was gathered in the preceding project using the example of polyamide 12 (PA12). Semi-crystalline thermoplastics are generally less suitable for thermoforming compared to amorphous thermoplastics due to their sharp drop in stiffness with crystalline melting and the melts insufficient elongational rheological properties. Thus the availability of semi-crystalline technical thermoplastics, which meet the requirements of the thermoforming process, is highly limited up to now. This hinders the development of technical thermoforming parts. It could be shown that partial cross linking of the macromolecules by high energy irradiation changes melt stiffness and elongational rheological properties of PA12, which has significant impact on the thermoforming process. The increased melt stiffness prevents excessive sagging of the sheet during heating, while the mainly elastic behavior of the melt reduces the chance of webbing. As a result the processing temperature window is greatly increased.Furthermore cross linking leads to strain hardening material behavior and thus to more homogenous wall thicknesses, especially for geometries with high draw ratios. It is the aim of the transfer project to enhance the knowledge from the preceding project and to transfer it into application by means of a demonstrator, which is a reusable tray for electric drive components. Large-area trays are generally suitable geometries for thermoforming. However available amorphous thermoforming materials do not meet all requirements of technical trays, e.g. they need a high heat resistance when taking up parts from an injection molding process.Furthermore a good wear resistance is needed to ensure reusability. Trays for metal parts often need additional chemical resistance against oils and greases. These requirements shall be met by using cross linked semi-crystalline thermoplastics. Besides verifying the results for the industrial production scale, additional fundamental questions arise. First of all it has to be investigated whether the results from PA12 are also valid for other materials like different polyamides, polyolefines or polyesters. Moreover possible interactions of additives like cross linking aids, stabilizers or pigments and high energy irradiation influencing the sheet properties as well as their processability and resulting part properties have to be investigated. Furthermore effects of sheet processing on thermoformability as well as effects of thermoforming conditions on part properties have to be measured. Here the range of investigated properties shall be expanded to include some of the relevant advantages of semi-crystalline thermoplastics for applications, like wear behavior or chemical resistance.