Addressing the Challenges of Optical Brightening Agents in Paper Color Measurement

optical brightening agents
Optical brightening agents present special challenges for accurate color measurement in paper products.
Image Source: Pexels user Karolina Grabowska

For decades, spectrophotometric color measurement has played an integral part in the development and production of paper products that meet the diverse needs of consumers in a competitive and growing marketplace. The high level of accuracy, precise quantification of spectral data, non-destructive nature, and versatility of spectrophotometers have made them central to color quality management for paper manufacturers around the globe. However, the increasing popularity of optical brightening agents is posing considerable challenges for spectrophotometers unequipped to handle these unique color enhancers. As the use of these chemical compounds continues to expand, choosing an instrument that allows you to precisely analyze treated papers is more critical than ever before to satisfy the demand for the bright, aesthetically pleasing papers consumers have come to expect.

optical brightening agents
Consumer expectations of exceptionally bright whites have led paper manufacturers to increasingly turn to optical brightening agents as an effective and economical option for creating stark white hues.
Image Source: Flickr user Emilian Robert Vicol

The Effects of Optical Brightening Agents

Traditionally, white paper was created by bleaching processes that removed residual color by chemically modifying the raw materials themselves. However, bleaching alone cannot adequately or economically create the bright whites desired in today’s paper products. As such, manufacturers of all types of paper products – from high-end fine art papers to household tissue – have turned to optical brightening agents (OBAs) that use fluorescence to compensate for yellow paper hues, allowing even lower quality raw materials to produce clean, beautiful papers.1 OBAs work by absorbing non-visible UV light below 400nm and emitting visible light in the 400-480nm range to give paper a slightly bluish appearance that we perceive as bright white. While OBAs are extraordinarily useful for paper manufacturers, they also present special challenges for both visual color assessment and spectrophotometric color measurement. UV-dependent chemistry can cause dramatic differences in appearance based on light conditions and make papers highly vulnerable to metamerism; visual evaluation of OBA-treated papers is then extraordinarily unreliable and spectrophotometric assessment requires careful, controlled illumination for accurate and consistent measurement across the supply chain. As Quality Mag notes:

Defining and controlling the emitted UV component of the measuring device’s illumination is essential to defining standard ways to measure and manage color printed on OBA-enhanced materials. This requires the use of spectrophotometers that use calibrated UV light to measure OBAs with a level of confidence in the color data acquired when measuring OBA-enhanced materials—regardless of where or when the measurements are collected.2

Additionally, the unique spectral phenomenon of fluorescence can also cause spectral reflectance in the 400-480nm range to exceed 100% when fluorescence and ordinary reflectance of radiation combine, leading to potential instrumental confusion. As such, spectrophotometers with features that allow you to account for UV-excitability and modulate light conditions are critical to precise analysis of OBA-treated materials.

optical brightening agents
Controlling and calibrating illuminant conditions is critical to producing accurate and repeatable color measurement in OBA-treated papers.
Image Source: reynermedia

Overcoming Color Measurement Challenges

HunterLab’s innovative range of spectrophotometric instruments comes equipped with automated UV controls that help you overcome the challenges posed by OBAs and give you customizable options for obtaining accurate color measurements in optically brightened papers. Sophisticated UV calibration and control is made possible through motorized, automated UV control filters and fluorescent standards that give you maximum flexibility for analyzing OBA-treated products according to your specific needs. You may also select to exclude UV energy from your measurements entirely by using the filter to completely eliminate UV light. HunterLab’s sophisticated and versatile spectrophotometers allow you to fully examine your products in a range of conditions to evaluate formulations and processing methods, maintain consistency, and ensure accurate color matching. Through hitch standardization, you can ensure that measurements are consistent across instruments and locations to optimize quality control throughout the supply chain, regardless of location.

HunterLab Ingenuity

HunterLab has been a pioneer in the field of color measurement for over 60 years. We are committed to providing the most scientifically advanced, user-friendly spectrophotometric instruments available on the market to help our customers respond to changing market conditions. As such, we have developed and continuously refined our products to provide solutions to the challenges presented by evolving materials, technologies, and industry practices. Contact us to learn more about our diverse range of spectrophotometers, advanced software packages, and extraordinary customer support services.

  1. “Adding Optical Brightening Agents to High-Yield Pulp at the Pulp Mill,” March 2009, http://www.pulpandpapercanada.com/paptac/PDFs/OctNov09/optial-brightening-agents.pdf
  2. “Making the Invisible Visible: Managing the Effects of Optical Brighteners in Plastics,” November 5, 2015, http://www.qualitymag.com/articles/92954-making-the-invisible-visible

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