Bonding mechanism during welding of radiation cross-linked thermoplastic polymers

如果塑料部件由于其复杂性而无法在单个制造步骤中制造，或者如果出于经济原因而不应将其作为目标（例如），则必须使用连接技术。焊接产生材料锁定和介质密封接头的优点，其允许高载荷传递而不使用任何焊接填充材料。塑料完全熔化所需的热量可以以不同的方式输入到接合区。例如，这是利用对流、辐射、热传导或摩擦来进行的。振动焊接是一种利用外摩擦加热原理的焊接工艺，界面处分子间相互扩散缠结是焊接接头高强度的主要原因。二次价键传递的力太小，不能解释焊接接头中的键合机制。对于塑料的焊接，在界面上形成新的价键是未知的。因此，由于在塑料焊接过程中的结合机制仅仅是相互扩散，因此大多数焊接接头由相同类型的塑料制成。在产品中的智能材料组合方面，由不同成分制成的接头，以及根据当地具体要求调整的塑料，也特别令人感兴趣。这种接头，例如由高性能工程热塑性塑料和低成本聚烯烃制成的接头，目前在振动焊接工艺中是不可制造的或仅有限可制造的。对于不同应用中的塑料，对其性能的要求越来越高，而这些要求通常无法直接在生产中实现或通过填料和添加剂实现。以有针对性的方式影响热塑性塑料性能的一种潜在可能性是通过高能辐射交联材料提供的。在自己对辐射交联热塑性塑料振动焊接的研究中，可以表明，焊接过程的温度影响可能导致焊接区域界面上的热致交联。因此，一个额外的粘接机制将在焊接过程中的塑料。该项目的目的是制定出辐射交联热塑性塑料焊接的粘接机制的材料和工艺相关的影响的基础知识。重点是在焊接过程中焊接区域的热致交联。基于对热致交联的基本机制的理解，要导出连接策略，以促进交联作为一种额外的键合机制，以有针对性的方式。这提供了生产混合材料接头的可能性，其目前在普通焊接工艺中是不可制造的或仅是有限的。

If plastic components cannot be manufactured in a single fabrication step because of their com-plexity or if this should not be an objective (for example) for economic reasons, it becomes neces-sary to utilize joining technologies. Welding yields the advantages of a material-locking and media-tight joint which permits a high load transmission without using any welding filler materials. The heat needed for the complete melting of the plastic can be input into the joining zone in different ways. For example, this is carried out using convection, radiation, heat conduction or friction. Vibration welding constitutes one process which makes use of the principle of heating by means of external friction.The entanglement of molecules at the interface by interdiffusion is recognized as the main cause for the high strength of weld joints. The forces transmitted by secondary valence bonds are too low to explain the bonding mechanisms in weld joints. The formation of new valence bonds across the interface is unknown for the welding of plastics. Accordingly, since as a bonding mechanism during welding of plastics merely an interdiffusion comes into question, most weld joints are made of plas-tics from the same type. In terms of a smart material mix in products joints made of different com-ponents, with locally to the specific requirements adapted plastics, are also of particular interest. Such joints, e.g. made of high-performance engineering thermoplastics and low cost polyolefins, are currently not or only limited fabricable in the vibration welding process.For plastics in different applications, increasingly higher requirements are placed on their properties, which often cannot be implemented directly in the production or by fillers and additives. One potential possibility of influencing the properties of thermoplastics in a targeted way is provided by the cross linking of the materials with high energy irradiation. In own studies on vibration welding of radiation cross linkable thermoplastics it could be shown, that the temperature influence of the welding process can possibly lead to a thermally induced cross linking across the interface in the weld area. Thus an additional bonding mechanism would be available during welding of plastics.The aim of the project is to work out fundamental knowledge about material and process related influences on the bonding mechanisms in welding of radiation cross linked thermoplastics. The focus is on the thermally induced cross linking in the weld area during the joining process. Based on the understanding of the fundamental mechanisms of thermally induced cross linking, joining strategies are to be derived in order to promote cross linking as an additional bonding mechanism in a targeted way. This gives the possibility to produce mixed material joints, which are currently not or only limited fabricable in a common welding process.