High shear rate characterization of ceramic inks with Fluidicam RheoLUIDICAM RHEO

FluidicamRheo2Introduction

Depending on printing process, the transfer method will vary and thus different pressures will be applied. Offset printing will require a viscous and thick ink layer (40-100cP, >0.5µm) while in the case of an inkjet printer the ink is very liquid and thin (1-5cP, <0.5µm).

Understanding the behavior of the ink is a guarantee of high quality results and avoiding process issues such as bleeding or clogging the printing head with a too viscous ink. We have focused in this paper on studying rheological behavior of ceramic inks. These inks contain ceramic particles (metal oxide pigments) and require a melt carrier that will melt and stick the metal oxides to the body in a glass. Each system will have its own properties and behavior making it essential to be able to predict the behavior of every ink formulation.

Reminder on the technique

FLUIDICAM RHEO uses a co-flow microfluidic principle to measure viscosity of various products. A sample and viscosity standard are introduced together in the microfluidic channel (typically 2.2mm X 150µm) where they undergo strong confinement. Applied shear rate is adjusted by a computer-controlled syringe pump. Under these conditions, the interface position between the two fluids is related to the viscosity ratio between them. Images of the resulting laminar flow are acquired with to an integrated camera and the viscosity of the sample is automatically calculated as a function of shear rate and plotted directly in the software giving a resulting viscosity curve.
                                      microfluidics             

Experimental results

Using FLUIDICAM RHEO, we have measured the viscosity of 3 ceramic inks (A, B, C) of a dark brown color and unknown composition. The analysis took 4 minutes and less than 4mL of sample for a high shear rate analysis (1000 – 15000 s-1).

FLUIDCAM RHEO works with a visual acquisition system and allows observation of the product directly during the measurement. Below, a representative image (ink C) is presented. The sample is a thick liquid which makes it completely opaque and appear black to the camera.

ink

 

Precise viscosity measurements with good repeatability.
Inks were first tested from 1000 to 5000s-1 in 3 replicas and less than 1.5% relative standard deviation was obtained.

It can be noticed that Ink C and B have similar viscosities, while Ink A is slightly more liquid. In this range of shear rate, all inks seem to have a Newtonian behavior.

 

Sample

Viscosity
(cP)

Standard
Dev.

RSD
%

Ink A 20.79 0.18  0.85
Ink B 21.94 0.22 0.99
Ink C 21.86 0.26 1.20
   

High shear rate analysis compared to a rotational rheometer

Resulting flow curves allow to distinguish three different behaviors. Inks B and C have similar viscosities and shear thinning properties while Ink A presents a lower viscosity at low shear rate but tends to same values at higher shear. 

Conclusion

FLUIDICAM RHEO is an innovative rheological instrument for visual flow tests at wide shear rate ranges. It allows to identify and distinguish products even with low viscosity differences. It lets fast and precise analysis with less than 1mL of sample consumption and visual control of the sample behavior in the chip.