For manual screen printing, selecting a silicone ink with appropriate viscosity and thixotropy is crucial to achieve optimal performance. Here are the key considerations and recommendations:
Viscosity
Definition: Viscosity refers to the thickness or flowability of the ink. For manual screen printing, the ink should not be too runny or too thick.
Optimal Range: Silicone inks with medium viscosity (typically 3000 - 10,000 cP) work best for manual printing.
Too high viscosity can make it difficult to push the ink through the screen.
Too low viscosity can cause smudging or uneven prints.
Thixotropy
Definition: Thixotropy is the property of the ink to flow when subjected to shear (e.g., when pushed with a squeegee) and regain its viscosity when at rest. This prevents the ink from flowing uncontrollably but allows smooth application during printing.
Requirements: Silicone inks for screen printing should exhibit moderate thixotropic behavior:
Low thixotropy may cause dripping or ink spreading.
High thixotropy can lead to inconsistent prints and difficulty in manual squeegee strokes.
Recommendations for Silicone Screen Printing Inks
Here are some high-quality silicone inks with suitable viscosity and thixotropy for manual screen printing:
1. ELASTOSIL® Screen Printing Inks (Wacker Chemie AG)
Viscosity: Medium to high viscosity inks available.
Thixotropy: Specifically designed for screen printing; good balance for manual and automatic printing.
Features:
Highly durable.
Excellent adhesion to textiles and other substrates.
Heat-cured for long-lasting results.
Applications: Apparel printing, high-stretch fabrics.
2. Silicone Ink Series by Anysil
Viscosity: Around 4000-8000 cP, ideal for manual screen printing.
Thixotropy: High thixotropic control for better handling during manual strokes.
Features:
Eco-friendly and flexible for fabric applications.
High opacity and vibrant colors.
Applications: Ideal for high-stretch athletic wear.
3. SilForce™ Coatings (Momentive Performance Materials)
Viscosity: Customizable formulations for different screen types.
Thixotropy: Balanced for manual applications.
Features:
Cure at moderate temperatures.
High durability and chemical resistance.
Applications: Industrial and specialty printing.
Tips for Manual Screen Printing with Silicone Inks
Screen Mesh Size:
Use a mesh count between 86 - 160 for smooth ink flow and proper ink deposit.
Lower mesh counts work for thick, opaque designs; higher counts for fine details.
Mixing:
Stir the ink thoroughly before use to ensure consistent viscosity and thixotropy.
Avoid introducing too much air during mixing.
Additives:
Use viscosity reducers or thinners if the ink feels too thick for manual printing.
Add retarders to extend open time and prevent the ink from drying on the screen.
Curing:
Silicone inks typically require heat curing (e.g., 120-150°C for 2-5 minutes).
Ensure proper curing for adhesion and durability.
Squeegee:
Use a medium to soft durometer squeegee (around 60-75).
Maintain consistent pressure and angle for even ink application.
Final Notes
It's essential to test the ink on your specific substrate and printing setup before full-scale production. Most silicone ink manufacturers, like Wacker, Anysil, offer technical support to help you choose the right product for your needs. If you're working with specialty fabrics or designs, consult with the supplier for custom formulations.