Simulation of a Hemispherical Chamber for Thermal Inkjet Printing

Abstract

It is crucial to improve printing frequency and ink droplet quality in thermal inkjet printing. This paper proposed a hemispherical chamber, and we used the CFD (computational fluid dynamics model) to simulate the inkjet process. During the whole simulation process, we first researched the hemispherical chamber's inkjet state equipped with straight, conical shrinkage, and conical diffusion nozzles. Based on the broken time and volume of the liquid column, the nozzle geometry of the hemispherical chamber was determined to be a conical shrinkage nozzle with a specific size of 15 µm in height and 15 µm in diameter at the top, and 20 µm in diameter at the bottom. Next, we researched the inkjet performance of the square chamber, the round chamber, and the trapezoidal chamber. The round chamber showed the best inkjet performance using 1.8 µs as the driving time and 10 MPa as the maximum bubble pressure. After that, we compared the existing thermal inkjet printing heads. The results showed that the hemispherical chamber inkjet head had the best performance, achieving 30 KHz high-frequency printing and having the most significant volume ratio of droplet to the chamber, reaching 14.9%. As opposed to the current 15 KHz printing frequency of the thermal inkjet heads, the hemispherical chamber inkjet head has higher inkjet performance, and the volume ratio between the droplet and the chamber meets the range standard of 10-15%. The hemispherical chamber structure can be applied to thermal inkjet printing, office printing, 3D printing, and bio-printing.

Keywords: Inkjet printing; droplet; fluid; hemispherical chamber.

Figure 1

The working process of thermal inkjet head. (a) The structure of thermal inkjet head; (b) By heating the TaN film, the liquid in the chamber is vaporized to form a vapor bubble, which pushes the liquid out of the nozzle.

Figure 2

Analyzing the fluid flow in different pipes. (a) Analyzing the fluid flow in an abruptly reduced tube; (b) Analyzing the fluid flow in a gradually reduced tube.

Figure 3

The structural parameters of the hemispherical chamber inkjet head. (a) The three-dimensional structure of the hemispherical chamber; (b) The side view of the hemispherical chamber; (c) The back view of the hemispherical chamber.

Figure 4

Mesh model of the hemispherical chamber. (a) The hemispherical chamber is divided into 952,384 units; (b) Enlarged view of nozzle and air domain connection.

Figure 5

Fracture state of liquid column at different contact angles. (a) The contact angle is 30°; (b) The contact angle is 50°; (c) The contact angle is 70°; (d) The contact angle is 90°; (e) The contact angle is 110°; (f) The contact angle is 130°.

Figure 6

Inkjet heads with different nozzles and the contact angle of the SU-8 chamber. (a) Inkjet head equipped with conical shrinkage nozzle; (b) Inkjet head equipped with straight nozzle; (c) Inkjet head equipped with conical diffusion nozzle; (d) The contact angle of the SU-8 chamber.

Figure 7

Under different nozzles, the liquid column’s maximum velocity and the droplet’s volume change. (a) The liquid column’s velocity and the droplet’s volume change for the straight nozzle; (b) The liquid column’s velocity and the droplet’s volume change for the conical shrinkage nozzle; (c) When the bottom diameter of the conical diffusion nozzle is 10 μm, the liquid column’s velocity and the droplet’s volume change in conical diffusion nozzle; (d) When the bottom diameter of the conical diffusion nozzle is 15 μm, the liquid column’s velocity and the droplet’s volume change in conical diffusion nozzle.

Figure 8

The broken state of the liquid column under different nozzles. (a) The broken state of the liquid column in the straight nozzle; (b) The broken state of the liquid column in the conical shrinkage nozzle; (c) The liquid column was broken when the conical diffusion nozzle’s bottom diameter was 10 μm; (d) The liquid column was broken when the conical diffusion nozzle’s bottom diameter was 15 μm.

Figure 9

The liquid column’s maximum velocity and the droplet’s volume change for straight and conical shrinkage nozzles. (a) Under the different widths of the straight nozzles, the liquid column’s velocity and the droplet’s volume change; (b) Under the different heights of the straight nozzles, the liquid column’s velocity and the droplet’s volume change; (c) Under the different widths of the conical shrinkage nozzles, the liquid column’s velocity and the droplet’s volume change; (d) Under the different heights of the conical shrinkage nozzles, the liquid column’s velocity and the droplet’s volume change.

Figure 10

Inkjet process with the straight nozzle. (a) At 1 μs, the nozzle began to squeeze out the liquid; (b) At 4 μs, the liquid column formed; (c) At 6 μs, the liquid column was broken, and the droplet was formed; (d) At 8 μs, the droplet flew out from the air domain; (e) At 20 μs, the bubble disappeared in the chamber; (f) At 46 μs, the chamber was already filled.

Figure 11

Inkjet process with the conical shrinkage nozzle. (a) At 1 μs, the nozzle began to squeeze out the liquid; (b) At 3 μs, the liquid column formed; (c) At 4 μs, the liquid column was broken, and the droplet was formed; (d) At 7 μs, the droplet flew out from the air domain; (e) At 15 μs, the bubble disappeared in the chamber; (f) At 33 μs, the chamber was filled already.

Figure 12

Inkjet head parameters for different chambers. (a) Structural parameters of the trapezoidal inkjet head; (b) Structural parameters of the square inkjet head; (c) Structural parameters of round the inkjet head; (d) Structural parameters of the hemispherical inkjet head.

Figure 13

The volume of droplets under different inkjet heads. (a) For the square inkjet head, the droplet volume is 8.8 pL; (b) For the trapezoidal inkjet head, the droplet volume is 9.0 pL; (c) For the round inkjet head, the droplet volume is 9.2 pL; (d) For the hemispherical inkjet head, the droplet volume is 10.7 pL.