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Photoemulsions for Computer to Screen |
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Solutions from Kissel + Wolf GmbH to the problem of selecting a suitable emulsion for Computer to Screen (CTS) applications.
As to the question of the most suitable emulsion for CTS, this is not an easy one to answer. This is because of the typical requirement profiles for screenprinting, e.g. small, medium or large format, mesh fineness and colour, coating technique, type of ink etc. After clarification of the requirement profile, the special to type demands of the exposure unit have to be considered.
Currently in the market, there are exposure units in DMD (Digital Mirror Device) technology and UV light sources (metal halide lamps) with different performance and construction (e.g. the KIWO ScreenSetter, the StencilMaster from Signtronic and the Digital Light Engraver from CST).
There are also units which digitally expose coated stencils with LED UV lasers, using a wavelength of 405-410 nm (e.g. the Sefar LDS and the Lüscher JetScreen DX).
If we focus on screen quality, the quantity of screens to be made each day and workflow, then the selection criteria of emulsion are reduced to a minimum.
The maximum absorption of diazo-sensitised photoemulsions lies at 370-375 nm and are therefore generally able to be properly cured with powerful DMD units. .From the range of KISSEL + WOLF photoemulsions, AZOCOL POLY-PLUS S and the specially developed AZOCOL Z 110 CTS Violet have proved particularly suitable. AZOCOL Z 110 CTS Violet has been adjusted to minimise and even eliminate problems of light scatter or banding. Added to this, it is also solvent and water resistant and thus has a more universal application.
Single component SBQ-based photoemulsions have a maximum absorption up to of only 340 nm, compensate by having a continuous absorption range up to approx. 450 nm, so that despite the short wave maximum, are decidedly more reactive than diazo-sensitised products. Basically SBQ sensitised products harmonise particularly well with LED UV laser-based units, with their emission maximum at 405-410 nm. This has been proven for example by the excellent results using the SBQ emulsion POLYCOL S 266 Violet.
Unfortunately, it is difficult to formulate water resistant SBQ-based photoemulsions for very high runs; this however is unproblematic for the more powerful versions of LED UV units, for today, they are also able to expose and cure a universal photoemulsion like AZOCOL Z 110 CTS Violet.
For the numerous screen printing applications and the variable adjustment possibilities of most types of exposure unit, a variety of other emulsions can also be used. However the “CTS Photoemulsions” described above represent the first choice. It must however be pointed out, that due to specific features on some units, only high quality emulsion materials should be used and exact processing in the production of the printing stencil observed. Especially important are dimensionally-stable frames, maintaining correct tension values and a clean coating with good Rz values, as the exposure unit is often guided by spacing radar.
The development of further digital UV exposure units for screenprinting with even higher performance characteristics will continue and photoemulsions will be adapted to this growing market. As a participant in this market development, KISSEL + WOLF also optimise emulsion formulations for use on new machine technology.
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