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Optical Brightener

60.055 Development of methods to compensate the differences between proofing and production stock

Nickname: OBA
Fogra-Nr. 35.003
Project leader: Dr. Uwe Berthold; Dr. A. Kraushaar;

Period: 1.7.2010 until 31.12.2012

Funding: Programme of the Federal Ministry of Economics and Technology for the support of “Industrielle Gemeinschaftsforschung [IGF]” via the German Federation of Industrial Research Associations [AiF]

Aim:

Together with the PTS (The paper technology specialist) this project is aiming for easy to use means allowing for a visual and instrumental match of OBA poor proofing paper and OBA rich production stock - for ISO 3664:2009 compliant viewing conditions. This should be materialized by providing concerted recommendations for proof paper selection, measurement modes and ICC-profiles that can be streamlined into the current standardization concept. In addition, the light fastness of proofing substrates containing OBA should be assessed objectively to provide guidance in cases such proofing stock is required for a prescribed match.

Summary:

In this project optical brightener agents (OBA) of typical printing substrates were subject for testing their influence on established graphic art processes such as colour measurement, proof creation, image appraisal or light fastness. First, a method to assess the UV-amount of practical light sources has been developed. It is based on the visual impact of a typical OBA material. Here the OBA-effect only occurs when the OBA in the substrate is excited by the incoming light. Two measures of identifying the OBA-amount have been evaluated, namely ∆B and ∆CIEb*.

In addition more than 100 substrates have been characterized with respect to their colour and fluorescence. The findings were used to identify centroid positions for important paper types. They are the basis for the developed set of characterization data (FOGRA51beta and FOGRA52beta) that reflect the recently revised ISO 12647-2 for sheet-fed printing conditions. The psychophysical experiments backup an outstanding visual and instrumental proof to print match. The quality of the match closely correlates with the agreement of the used light source (D50) for measurements and appraisal. Hence a stringent use of M1 (defined in ISO 13655) and ISO 3664-2009 conforming viewing cabinet is the basis for reliable colour communication with OBA-rich substrates. In order to match the colour gamut of prints on OBA-rich substrates proofing substrates also have to contain OBA. The light fastness tests clearly showed that light fast proofing stocks are available but the light fastness evaluation needs to be done on the nature of ink on paper rather than on paper alone. A modified method for proofing stock has been proposed and already used for the revision of ISO 12647-7.



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