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SCREEN Ink
Take care not to overheat prints as the
substrate may shrink or distort.
Opting for UV inks
UV curing inks also come with their own
limitations. Despite the fact that additives
make up only three per cent of the basic
constituents of UV curing inks, take great care
when using them, as their incorrect use can
destroy the properties of the ink.
Adhesion promoters, for example, improve
the adhesion of the ink yet they can also affect
the usable life of the ink. Gloss/matte thinners
can adjust the colour and reduce cure time, but
they may also reduce ink adhesion. Cured UV
ink is normally a hard film which, if bent will
crack. Flexibility additives provide additional
elasticity, but may also reduce adhesion.
Water based UV ink was produced by ink
manufactures specifically to overcome the ink
build problem that can occur with conventional
Comparison of ink builds UV. This is an issue when printing fine four
colour halftones where skipping can occur. The
result is that much of the third and forth
withstand the destined environment. Also possible to create inks for every printable colours do not get printed onto the substrate.
consider whether it is suitable for use in your substrate as well as mirror gloss inks, inks Water based UV ink addresses this issue
printing machine. that react to light and heat, inks with with its 45 per cent water content. When the
To solve this problem, ink suppliers produce electrical properties and photoluminescent ink is printed the water starts to evaporate
many different ink types. Ink suppliers often inks. and this can be accelerated by applying infra
provide charts that show which of their ink Any application that requires light fast red energy or hot air. The heat drives off the
systems are suitable for a particular colour that sticks well to a substrate water leaving a dried and cured thin film. The
application. Technical data sheets will give and withstands abrasion and chemical build is still slightly more than solvent based
information but for a new substrate, it is attack is likely to be met with a solvent based systems, but low enough to reduce the
worth sending a sample for ink trials. ink. skipping problem.
Once the inks are mixed, the solvents will Another solution is to use a low build stencil
Sourcing solvent inks start to evaporate unless they are kept in a that gives an emulsion over mesh (EOM) of
Solvent based inks are very versatile, but can closed container. As the solvents evaporate, three microns. When used correctly, fine line
present some production issues. From the the ink thickens and flow through the mesh rulings can be printed with conventional UV
printers perspective, maintaining stability of alters, resulting in colour variation. It is curing inks without the skipping problem.
the mixed ink on the screen is challenging, but possible to slow evaporation by using retarder, During ink selection, remember that all
the effects and characteristics that can be but this results in longer drying time. It may be elements of the screen printing process are
achieved are exciting. The inks work by necessary to introduce more drying racks, or a linked together. The successful printer
suspending pigments in resins dissolved in a longer conveyor dryer to run more slowly at a understands how they interact to can make a
combination of solvents, which makes it higher temperature or with higher airflow. profitable technology choice. llll
A low build stencil such as Macdermid Autotype's Capillex CP can eliminate skipping Skipping with conventional stencil
Visit us at www.spdi-online.com January 2010 l SCREEN PROCESS AND DIGITAL IMAGING 11
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