Spectrophotometers & Measuring OBAs (Optical Brightener Additives)


Year: 2018
Pages: 21


In recent years, several printing paper manufacturers have started adding optical brighteners (OBAs) to their papers, as an economical way of making the paper appear brighter and whiter. These brighteners respond to ultra violet (UV) light, and re-emit this energy as visible light, in the 'blue' part of the spectrum (approx. 430 - 460 nm) (Giordano 2000). This results in 'bluer' colors, which we (the end users) actually perceive as being 'whiter' (or less yellow) (Schroeder 2014).

There are a variety of different standards and specifications that apply throughout the 'color managed' stages of a print production workflow. A key part of this overall process is working with clients and print buyers to manage their expectations of the final visual appearance of the product. Through utilizing standards and specifications, color can be accurately predicted, and contract color proofs can be produced that will closely resemble the final printed project, allowing for a 'Print-to-Proof' match (P2P).

These proofs can be used for iterative content and color approvals prior to final production, as well as during the manufacturing run. They are compared to the press sheets to help verify reproduction and provide information on how to adjust the process, to help achieve the desired results (ex. make it more 'red', or less 'green'...). These comparisons are normally done under controlled, standardized, viewing conditions a viewing 'booth' that has neutral gray walls and standardized bulbs that produce a uniform color temperature of light, known as 'D50' (Idealliance 2015).

The process itself has many inherent variables that can interact to impact the overall effectiveness of the P2P match; substrates, colorants, printing technologies, screening algorithms, fountain solution, speeds, relative humidity, colors and layout of the content, and many others.

Supporting this scenario requires that the standards be communicated effectively, that measurement devices which accurately capture characteristics and behaviors be used, and quality control measures are implemented and adhered to, in order to ensure conformity to the standard or specification (Chung 2014).

This project focuses on the 'accuracy' and level of 'precision' of the different commercial spectrophotometers with regards to measuring fluorescence in the approx. 430 nm - 460 nm part of the spectrum, where OBAs re-emit UV energy. It also analyzes and compares the devices behavior for M2 (UV Cut) measurement condition, as a reference for the M1 (D50, UV Included) measurement condition.