Inkjet printing of 3D overhanging microstructures

Abstract

Freeform overhanging microstructures are used for various applications, for example in micro metamaterials. To create these structures industry uses a variety of manufacturing methods. There is a gap in manufacturing methods that can produce a microstructure at a high resolution and use multiple materials at individual locations. Inkjet printing can fill this research gap because multiple materials can be printed at individual points in structures by using multiple ink reservoirs. The goal of the research is to develop a method to produce overhanging microstructures using inkjet printing.

Using inkjet printing structures are produced bottom-up therefore a (sacrificial) support material is needed to support building material during the production. This material is later removed resulting in an overhanging structure. To allow removal of the sacrificial material both materials must cure differently. After considering different candidate materials, one building material (mr¬UVCur26SF) and one sacrificial material (KL5315) were used during the manufacturing process. The sacrificial material is a positive photoresist and can be removed in a NaOH (1w%) solution after UV curing as opposed to the building material that solidifies after UV curing.

Two methods were used to increase the height of inkjet-printed structures. The first method is to print multiple layers of material on top of each other while curing the material between each layer, this is used to print the building material. This first method led to poor alignment between layers of sacrificial support material, therefore a new method is proposed to print the sacrificial material. Using the second method multiple lines of sacrificial material are printed next to each other without intermediate curing using a high cross-scan resolution of 4800[dpi] increasing the height of the structure.

Printing both materials close to each other to create an overhanging structure led to a loss of shape because the materials were attracted to each other. To solve this issue a new method is proposed using sacrificial dikes to prevent the building material from losing its shape. The first step of this method is to print and cure a grid of sacrificial support material. After that, the building material is printed in the free space between and on top of the dikes resulting in a microbridge once the sacrificial support material is removed. Using this method a microbridge with an overhanging part of approximately 50 micrometers is created.