Ink Characterisation for Screen Printing: Understanding Viscosity, Shear Thinning and Thixotropic Recovery
Introduction
Developing new inks for screen-printed electrodes and biosensors involves far more than selecting conductive materials and binders. The ability of an ink to print consistently, produce clean feature definition, and maintain reproducible performance is heavily influenced by its rheological properties.
For organisations developing custom inks, understanding viscosity behaviour under printing conditions is often the difference between a successful manufacturing process and poor print quality. Before a new ink is introduced into production, its flow characteristics should be carefully characterised to determine whether it is suitable for screen printing applications.
For organisations seeking ready-to-use screen-printed electrodes, Zimmer & Peacock offers a range of established electrode platforms through its Screen Printed Electrodes Collection.
Supporting Video
Why Ink Characterisation Matters
Screen printing is a dynamic process in which ink experiences substantial changes in mechanical stress.
During printing:
- Ink is deposited onto the screen.
- A squeegee moves across the screen surface.
- The ink is forced through a patterned mesh.
- The printed design forms on the substrate beneath.
Throughout this process, the ink transitions through dramatically different shear conditions. As a result, its viscosity must change in a controlled and predictable manner.
An ink that behaves appropriately under these conditions can deliver:
✅ Sharp electrode geometries
✅ Consistent print thickness
✅ High manufacturing reproducibility
✅ Reduced defects and waste
The Role of Shear Rate During Screen Printing
One of the most important concepts in ink characterisation is shear rate.
When the ink is stationary in front of the squeegee, it experiences relatively low shear rates, typically in the region of:
| Printing Condition | Approximate Shear Rate |
|---|---|
| Stationary Ink | 0.01 to 0.1 s⁻¹ |
| Active Printing | 5,000 to 20,000 s⁻¹ |
As the squeegee moves, the shear rate rises dramatically. Under these conditions, the ink must flow easily through the screen mesh while still maintaining pattern fidelity.
This behaviour is characteristic of non-Newtonian fluids, where viscosity changes as a function of shear rate.
Shear Thinning: A Key Requirement for Printable Inks
Most screen-printable functional inks are designed to exhibit shear-thinning behaviour.
This means:
- High viscosity when stationary
- Lower viscosity during printing
- Easier passage through screen apertures
- Improved ink transfer onto the substrate
Without sufficient shear thinning, the ink may resist movement through the mesh, resulting in incomplete prints, poor edge quality, and inconsistent deposition.
The relationship between viscosity and shear rate is typically represented using a viscosity flow curve, one of the most important tools used to evaluate printability.
🔬 A viscosity flow curve allows engineers to predict how an ink will behave under real manufacturing conditions before committing to production trials.
Understanding Thixotropic Recovery
While shear thinning is essential, it is only one part of the story. Once the ink has been deposited onto the substrate, it must recover its viscosity at an appropriate rate.
This process is known as thixotropic recovery.
Immediately after printing, an ink may display slightly rough or uneven edges. Ideally, the ink undergoes a brief period of controlled levelling before regaining its original viscosity.
The result is:
- Smoother printed features
- Improved edge definition
- Better electrode appearance
- Enhanced dimensional accuracy
A well-balanced thixotropic response is critical for producing high-quality screen-printed electrodes and biosensors.
When Recovery Happens Too Quickly
An ink can recover viscosity too rapidly.
In this situation:
- The ink effectively freezes immediately after deposition.
- Levelling is restricted.
- Rough print edges remain visible.
- Surface quality may suffer.
The printed structure loses the benefit of the slight flow that normally smooths features and improves pattern definition.
⚙️ Excessively rapid recovery can therefore reduce print quality, even if the ink initially appears stable.
When Recovery Happens Too Slowly
The opposite issue can also occur.
If the ink takes minutes, rather than seconds, to recover its viscosity:
- Excessive spreading may occur.
- Edge definition deteriorates.
- Printed lines become wider than intended.
- Adjacent conductive tracks may merge.
- Electrical shorts can develop.
For fine-feature sensor manufacturing, this behaviour can be particularly problematic.
Achieving the correct balance between levelling and recovery is therefore essential.
Why Rheology Data Is Required
When a custom ink is submitted for screen-printing evaluation, one of the first datasets that should be provided is its rheological profile.
This enables engineers to assess:
- Low-shear viscosity behaviour
- High-shear printing performance
- Degree of shear thinning
- Recovery characteristics
- Overall printability
Rather than relying solely on trial-and-error printing experiments, rheological characterisation provides a scientific method for evaluating suitability before manufacturing begins.
📌 In many cases, a viscosity flow curve can quickly reveal whether an ink is likely to print successfully.
The Importance of the Viscosity Flow Curve
A viscosity flow curve captures how viscosity changes across different shear rates.
For screen-printing applications, this information helps engineers understand:
- How the ink behaves while stationary
- How much it thins during printing
- Whether sufficient flow will occur through the mesh
- How the material is likely to recover after deposition
Because screen printing exposes the ink to a wide range of shear conditions, this information is invaluable when assessing process suitability.
Temperature Considerations
Rheological measurements should be generated under controlled temperature conditions.
For screen-printing assessment, testing should typically be performed at approximately:
20°C
Using a consistent temperature allows meaningful comparison between formulations and ensures that viscosity measurements reflect realistic production conditions.
Practical Takeaways
Key Insights for Ink Developers
✅ Screen-printing inks experience shear rates ranging from approximately 0.01 s⁻¹ up to 20,000 s⁻¹.
✅ Most successful screen-printing inks exhibit strong shear-thinning behaviour.
✅ Thixotropic recovery determines how well printed features level and retain their shape.
✅ Recovery that is too fast can result in rough, poorly levelled prints.
✅ Recovery that is too slow can lead to spreading, bleeding, and electrical shorts.
✅ A viscosity flow curve is one of the most valuable datasets for evaluating printability.
✅ Rheological testing should be performed under controlled conditions, typically around 20°C.
What This Means in Practice
For researchers and manufacturers developing new conductive inks, carbon inks, biosensor inks, or printed electronic materials, rheological characterisation should be considered an essential part of formulation development.
Understanding how viscosity changes during printing enables informed decisions before investing in production runs, helping reduce development time and improve manufacturing success rates.
By supplying viscosity flow curve data alongside a custom ink formulation, developers can significantly improve the likelihood of successful screen-printing outcomes.
Conclusion
The performance of a screen-printing ink is determined not only by its chemistry but also by its rheology. Understanding how viscosity changes across different shear rates, how materials shear thin during printing, and how quickly they recover afterwards is fundamental to achieving precision, reproducibility, and high-quality printed sensor structures.
Whether developing custom conductive formulations, biosensor inks, or next-generation printed electronics, robust rheological characterisation provides the foundation for reliable manufacturing and scalable production.
To discuss custom screen-printing projects, electrode development, or ink suitability assessments, please contact the Zimmer & Peacock team through the Contact Page.
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#ScreenPrinting #PrintedElectronics #Electrochemistry #Biosensors #Rheology #SensorDevelopment #ResearchAndDevelopment #EngineeringInnovation
