A new method for analyzing the refill process and fabrication of a piezoelectric inkjet printing head for LCD color filter manufacturing

摘要

This paper presents a method for analyzing the refill process of a piezoelectric inkjet printing head with a high firing frequency for color filter manufacturing. Theoretical and experimental studies on the equivalent length (L{sub}(eq)) versus jetting characteristics were performed. The new model has shown quantitatively the same result compared with a commercialized simulation code. Also it is identified that the refill time increases with the equivalent liquid length (L{sub}(eq)) because the viscous force increases. The inkjet printing head has been designed with a lumped model analysis and fabricated with a silicon wafer (100) by a MEMS process. To investigate how the equivalent length (L{sub}(eq)) influences the firing frequency, an experiment was conducted using a stroboscope. In the case of colorant ink, it is possible to eject an ink droplet up to 5 kHz with a 40 pl drop volume. On the other hand, the firing frequency calculated with the new model is about 3 kHz under the condition of the equivalent liquid length (L{sub}(eq)), 250 μm. The difference between the new model and experiment may be a result of a mismatch of initial meniscus position due to the meniscus oscillation. Experimentally the meniscus oscillation is observed through an optical measurement with a visualization apparatus and a transparent nozzle. Hence the efficiency of the new model may be enhanced in a high viscosity range. The methods for increasing the firing frequency are to reduce the equivalent length (L{sub}(eq)) and to modify the ink property. Because the former tends to decrease a viscous loss and the latter tends to increase a viscous damping, two parameters should be combined adequately within an allowable drop volume.