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A guide to exposure determination and the impact of artworkWilliam ShorterCPS Technical Sales Executive/Product Manager
Objective of this screen printing workshop
Factors to consider with exposure systems
• The quality of the UV light.– Wave length:
• Diazo• Photopolymer
– Avoid Infra Red• The power of the
light.– Distance
Factors to consider with exposure systems
• The power of the light.– Distance
1.2m
Factors to consider with exposure systems
• Distance from the stencil.– 1m = 30 seconds.– 2m = 900 seconds.
• Angle of the light.– Diagonal of the
screen.Increase in exposure time
Factors to consider with exposure systems
• Mesh Colour
White Mesh Yellow Meshvs
Faster Slower
Factors to consider with exposure systems
• Vacuum– Good seal– Don’t use white card at
the back
• Integrator or time?
Factors to consider with your artwork
• Quite simply, you can produce bad prints from good artwork, but you cannot produce good prints from bad artwork.
Factors to consider with your artwork
• Opaqueness of ink jet media.
• Must absorb UV light in the region of 350-420 nanometers.
• Don’t overload ink jet positives with ink.
• The smallest dot or line you can print is controlled by the mesh thread width.
Factors that affect durability
• Optimum Exposure– An Exposure
Calculator or step wedge is an important calibration tool.
– Full exposure is when all the diazo has cross linked.
• Indicated by colour change.
– Brown to purple– Green to blue
Factors that affect durability on the press
25%Optimum Exposure
50% Optimum Exposure
75% Optimum Exposure
100% Optimum Exposure
• Masks and positives with poor masking ability will result in you needing to under expose the stencil film or emulsion, compromising the durability and finished print quality.
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