Cross linked sheets for highly stressed thermoforming applications

在前面的项目中，使用聚酰胺12(PA12)的例子收集了关于大分子的部分交联性对半结晶热塑性塑料热成形能力的影响的基本知识。与无定形热塑性塑料相比，半结晶热塑性塑料一般不太适合热成型，这是因为它们的硬度随着结晶熔化而急剧下降，并且熔体没有足够的拉伸流变性能。因此，到目前为止，满足热成形工艺要求的半结晶工业热塑性塑料的可获得性非常有限。这阻碍了技术热成型零件的发展。结果表明，高能辐照使大分子的部分交联化改变了PA12的熔体硬度和拉伸流变性能，这对PA12的热成形过程有重要影响。增加的熔体硬度可以防止板材在加热过程中过度下垂，而熔体的主要弹性行为减少了卷曲的机会。因此，加工温度窗口大大增加。此外，交联会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深比的几何形状。转让项目的目的是加强前一个项目的知识，并通过演示器将其转化为应用，演示器是电动部件的可重复使用的托盘。大面积托盘通常适合热成型的几何形状。然而，现有的非晶热成型材料并不能满足技术托盘的所有要求，例如，当从注塑成型过程中取出零件时，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。金属部件的托盘通常需要额外的耐油和耐油化学性能。应使用交联型半结晶热塑性塑料来满足这些要求。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，还必须研究交联剂、稳定剂或颜料等添加剂和高能照射对板材性能的可能相互作用，以及它们的加工性和由此产生的部件性能。此外，还必须测量板材加工对热成形性能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在应用中的一些相关优点，如耐磨性或耐化学性。

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.