Performance and Testing of Inkjet Inks

Performance and Testing of Inkjet Inks

Table of content.

Basic Performance Indicators of Inkjet Inks

Ink Properties vs. Printing Technologies

Ink Property

Binary Deflection

Multi Deflection

Piezoelectric (Type 1)

Piezoelectric (Type 2)

Bubble Jet

Viscosity (mPa·s)

1–5

3–8

5–12

3

3

Surface Tension (×10⁻³ N/m)

> 35

25–40

> 30

> 30

> 30

Particle Size (nm)

1000

3000

1000

500

200

Conductivity

> 500

> 1000

None

None

None

Other Common Issues

Jetting deflection, dispersion, foaming

Jetting deflection, dispersion, foaming

Pigment settling, foaming

Foaming

Foaming


Performance Testing of Inkjet Inks

Measuring Ink Viscosity with a Viscometer

If the viscosity of the ink is too high, it will negatively affect ink flowability, making it difficult to form droplets and eject them smoothly from the nozzle. This can lead to clogging and reduce the service life of the printhead. In addition, excessively high viscosity makes it harder for the solvent to penetrate, evaporate, and be absorbed quickly, resulting in longer drying times and reduced image resolution.

If the viscosity is too low, the colorant may not adhere properly to the substrate, leading to decolorization or fading, which also affects image quality and durability. Therefore, it is essential to maintain ink viscosity within an appropriate range.

 

 

Determination of Drying Time

Drying time refers to the time required for inkjet droplets to penetrate, evaporate, or be absorbed into substrates such as paper until they are fully dry. The shorter the drying time, the more beneficial it is for improving image quality.

“Fully dry” means that when pressed with a finger for approximately half a second, no smudging or staining occurs. This method is typically used to evaluate drying performance on the substrate.

 

 

Testing Surface Tension with a Surface Tension Analyzer

Ink with appropriate surface tension enables better contact, wetting, and penetration between the solvent and the substrate surface.

In thermal inkjet printing, proper surface tension also facilitates bubble formation, thereby improving printing speed and reducing drying time.

 

 

Measuring Particle Size Using PCS (Photon Correlation Spectroscopy)

In continuous inkjet digital printing, this method can be employed.

With the development of inkjet printing technology, there is a growing trend toward using ultra-fine colorant particles, allowing the ink to flow freely within the printing system. This not only enhances ink stability but also improves image resolution and gloss.

 

 

Determining Dye Decomposition Temperature with a Thermal Analyzer

Under normal conditions, dyes dissolve in water in molecular form. However, in thermal inkjet printing, the surface temperature of the heating element can reach approximately 300°C. Most dyes tend to decompose at temperatures between 250–300°C, producing insoluble substances that deposit on the heating element surface and clog the nozzles, leading to printing issues.

By using a thermal analyzer, more suitable dyes can be selected, effectively addressing this problem.

 

 

In addition, machine testing (on-press testing) is the most important method for evaluating inkjet inks. By examining performance indicators such as image color, diffusion, water resistance, cold resistance, light resistance (optical density), and other properties, the overall quality of the printed image can be assessed. These factors serve as key criteria for determining ink quality.

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