Why do lines spread when print pastes have equal viscosity?
Screen printing shears the paste. Equal viscosity at rest does not imply equal flow through the screen. Hydration and printing pressure can also alter edges.
Recheck line width at matched screen and pressure
Print on the same screen, pattern and fabric under the same pressure. Save images of line width and edges. Prepare a soft-water paste to inspect gel particles and record viscosity test conditions.
Why are gel particles present in the stock paste?
Check wetting, hydration and hardness ions. Retest with a soft-water control. Reactive printing: With the same fabric and screen, test print edge definition, bleeding and paste stability. Fine-line printing: At the actual screen mesh and machine speed, check screen passage, trailing and handle after washing.
Checking Viscosity at specified concentration and Filter or sieve residue
Viscosity at specified concentration (mPa·s): Specify concentration, temperature, spindle and hydration time. Filter or sieve residue (Mass or grade): Keep sieve aperture, water quality for paste preparation and standing time constant. Residual paste after washing (Mass or rating): Use the actual fabric and washing procedure.
What to record
- Paste water quality
- Viscosity method
- Screen
- Printing pressure
- Change in line width
Technical references
Products and processes
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