ITW Trans Tech: Troubleshooting Guide: Screen dots are visible

Transfer Pad Printing
Troubleshooting Guide
PROBLEM:
Screen dots are visible.

	Cause	Solution
Ink	Ink is too thick.	Add thinner.
Ink	Thinner is too fast.	Use slower thinner.
Pad	Angle is too sharp.	Use a flatter pad.
Pad	Pad is too soft.	Use harder pad.
Cliché (plate)	Etch is too shallow.	Use same cliché; re-etch deeper.
Cliché (plate)	Wrong screen used. finest screen with steel cliché is 150 line. Finest screen with plastic cliché is 300 line.	The finer the screen, the less visible the dots become.
Material (substrate)	Print surface is contaminated.	Clean parts.
Material (substrate)	Parts have texture.	Check if the product surface texture is visible, not the screen dots.

NOTE: Line screen film is not only used to control etch depth, but may be used for large, bold images. The dot pattern that is created in the image by incorporating the line screen film in the etch process acts to support the doctor blade as it travels over the open area of ink. An improperly supported blade will dip into the image and drag ink out.

Halftone films may be used in all types of pad printing plates, including: Express, Hydro-Foil, Polymer and Steel clichés.

A halftone screen contains a series of dots (see illustrations at right). A 300-line, 85% halftone film equals 300 dots per square inch. 85% refers to the tint (opaque area) of the screen therefore, a higher level of tint results in greater ink laydown.

200 Line, 85% Screen

200 Line, 90% Screen

300 Line, 85% Screen

300 Line, 95% Screen

Examples of the same image with and without a screen added to the cliché plate.