Inkjet Printing

Question 1

What is inkjet printing?

Answer 1

• A direct to substrate technology that uses digital data to control streams of very fine droplets of ink or dye to produce patterns directly on paper or other substrates
• A non-impact printing technology that deposits ink in the familiar patterned array known as the dot matrix.
• Controlled ejection of fluid drops from a small aperture directly to a pre-specified position

Question 2

What are the fluid ink/requirments for piezoelctric inkjet printing and how is the drop formation controlled?

Answer 2

Requirements for a fluid in a piezoelectric demand-mode inkjet device are:

1. viscosity: 0.5-40 mPa s
2. Surface Tension: 0.02-0.07 N/m

Drop formation controlled by:

1. Rheology (study of fluid under stresss and strain)
2. Surface Tension (tendency of a liquid to shrink to the min surface areas)
3. Viscoelasticity: (viscous+elastic characteristics)

Question 3

Why is surface tension important?

Answer 3

1. Surface tension of ink relative to surface energy of substrate controls behaviour of ink drops on substrate
2. Printed features are built drop-by-drop
3. Ability to fine tune morphology of printed features by adjusting ink properties.

Question 4

What are the main three types of ink used in inkjet technology?

Answer 4

1. Aqueous inks (water based) - Based on a mixture of water, glycol, and dyes or pigments, can survive high temperatures without affecting chemical makeup of ink.
2. Solvent inks (volatile compund based) - High volatile organic compounds (VOC’s), carrier is evaporated or is driven off after printing.
3. UV-curable inks: Inks that are forced onto the substrate , then subjected to UV light to be polymerised (Lack VOC’s)

Question 5

What are satellite drops and how are they controlled?

Answer 5

Small droplets formed using jetting the ink, may cause print quality issues.

If carrier speed is higher or the print gap is larger, the effects tend to be worse (“overspray effect”)

Question 6

What are the fluid ink/requirments for inkjet printing

Answer 6

1. no chemical reaction with the print head - ink should not damage print head
2. Combatable with print head - Viscocity and surface tension should be in correct range.
3. Mixture stability - Ink should be stable in the print head, make sure pigment particles dont block nozzle and binder does not dry.
4. Ink should not exhibit print latency - ink must be able to jet normally after inactive period.
   - fast drying solvents can cause increase in viscocity at the nozzle.

Question 7

What is continuous inkjet printing?

Answer 7

High pressure pump directs liquid ink from a reservoir through a gun body and a microscopic nozzle, creating continous streams of ink.

Electrodes impart a charge onto the drops, they pass through a delflection plate, some drops are selected using a electrostatic filed, other drops are collected and returned for re-use

Question 8

Whats the difference between thermal and piezoelectric drop on demand inkjet printing?

Answer 8

Thermal - To eject the ink, pulse of current is passed through the heating element causing a rapid vaporization of the ink in the chamber to form a bubble, which causes a large pressure, propelling a droplet of ink onto the substrate

Piezoelectric - When voltage applied, the piezoelectric material changes shape, generating a pressure pulse in the fluid forcing a droplet of ink from the nozzle