Bauer, W.

Binder, J.R.

Friederich, A.

English

Binder, J. R.

KITopen

Rheological control of the coffee stain effect for inkjet printing of ceramics A. Friederich, J. R. Binder, W. Bauer Institute for Applied Materials – Material Process Technology Hermann-von-Helmoltz-Platz 1 76344 Eggenstein-Leopoldshafen Germany KIT – University of the State of Baden-Wuerttemberg and National Research Center of the Helmholtz Association Introduction Characterisation of dried structures Ink preparation and ink properties Conclusion Coffee staining is a general problem of inkjet printing ceramic suspensions. It is caused by a flow of liquid from the centre to the edge of a drying drop and leads to a non-uniform deposition of particles. Conventional thick-film preparation methods such as screen printing do not show coffee staining due to the high viscosity of the printing medium. The approaches to prevent coffee staining that are reported in the literature make use of various physical phenomena such as the Marangoni flow or electro-wetting to obtain homogeneous films. We present a new approach, which follows a simple consideration: Coffee staining can be suppressed by a sufficiently fast increase of viscosity after deposition. However, the ink viscosity during printing is usually restricted to very low values due to the small diameter of the print-head nozzles. Hence, inks with tailored viscosity need to be developed. + 0–1.25 vol.% ethyl cellulose (EC) + 0–50 vol.% isopropy alcohol (IPA) Ink properties:   Long time stable  (no sedimentation observable)  Particle size:   d50 ≈ 150 nm, d100 < 1 µm  Surface tension:  γ = 24–30 mN/m  Viscosity:   η = 5–43 mPa·s   0.09 < Oh < 0.71   all inks well printable The investigations show that the use of a fast drying solvent in the inks is not suitable to prevent coffee staining, if the viscosity is also lowered. When adding a binder to the inks, the viscosity exceeds the boundaries for printing before it is high enough to prevent coffee staining. However, a combination of binder and fast drying solvent is suitable to prevent coffee staining. This is due to a sufficiently low viscosity during printing and a rapid increase of viscosity after deposition, which leads to a considerable improvement in film topography. Initial ink η = 8.4 mPas Combination of IPA and EC: Viscosity:    η = 22.7 mPas Drying time: t / t0= 55% A decrease of drying time is not suitable to prevent coffee staining, if the viscosity is also lowered. Isopropyl alcohol (IPA) content 0 vol.% 25 vol.% 50 vol.% 8.4 5.9 4.6 Viscosity η / mPas 100% 80% 55% Drying time t / t0 Ethyl cellulose (EC) content 0 vol.% 0.62 vol.% 1.25 vol.% 8.4 21.6 42.6 Viscosity η / mPas 100% 100% 100% Drying time t / t0 An increase of viscosity within the boundaries of printability is not suitable to prevent coffee staining Severe coffee staining for all drop sizes and drying temperatures The fast evaporation of the IPA leads to a rapid increase of viscosity  after deposition and prevents coffee  staining at low drying temperatures Thermogravimetric experiment:  IPA evaporates approximately 50 times faster than the residual solvent Rheology measurements:  The viscosity of the ink with EC and IPA rises about 1 order of magnitude in a very short time span dilution to 5 vol.% 10 vol.% + dispersant spray drying Material:  Ba0.6Sr0.4TiO3 Solvent:  butyl diglycol T = 60°C Figures:  Surface topography measurements of drops printed with different inks and dried at different substrate temperatures.  printing + drying 

Rheological control of the coffee stain effect for inkjet printing of ceramics

https://publikationen.bibliothek.kit.edu/220090513/3816247

Rheological control of the coffee stain effect for inkjet printing of ceramics

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