Making the Invisible Visible

Companies are increasingly using optical brightening agents (OBAs) to achieve a “whiter-than-white” effect on a range of materials, including plastics, paints and coatings and paper. Adding these optical brighteners gives products a brighter, whiter appearance and compensates for the yellowing that can happen over time with white products.

The challenge for manufacturers using OBAs is accurately measuring and maintaining color consistency across their production processes. While adding OBAs makes for a brighter product, the addition of these brighteners fundamentally alters the way the color is perceived in the production process.

How can businesses reap the benefits that whiteness brings to their products while maintaining color consistency throughout the production process?

To start, let’s look at what OBAs are and how they affect the colors we see.

OBAs operate through the process of fluorescence. They absorb invisible ultraviolet (UV) radiation at wavelengths below 400 nanometers (nm) and, through an electro physical change, emit light mostly in the blue end of the visible spectrum at about 400 – 450 nm.

When this light is emitted from products that have used brightening agents, they are perceived as having a color that is “whiter-than-white,” since the observed light from the brightened material is the total of the reflected and emitted light due to the fluorescence.

Under an ultraviolet light source, such as a “black” light, you can clearly detect visible color differences in products that contain various amounts of OBAs. Products that contain more OBAs will appear lighter, while products with less OBAs will be darker.

The challenge, however, is that you need to have a consistent amount of UV light to be able to quantify the amount of OBAs in a given product. This means that when there is little or no UV light, the color differences may be invisible. But when UV light is present, the color differences become quite visible.

So while materials and fabrics that use OBAs may appear similar in production, those same products may look quite different under varied lighting conditions, such as in a retail store, in daylight, or in household light.

As a result, using OBAs can create serious color matching challenges for any industry using them to create a brighter-than-white look for their products, including paper, textiles, plastics, paints, or cosmetics. If the lighting condition is not correct, the whites— and any color that gets applied to the material or fabric—will not be consistent and will fail to meet expectations.

For example, say you are a consumer electronics manufacturer that produces phones, computers, and accessories that are white. Each of these products use OBAs to achieve their whiteness level. However, each product uses varying amounts of OBAs, and these amounts cannot be quantified without calibrated UV light. These products may look fine in the light of the production facility, but when they reach the retail store or consumer’s home, the accessories, computers and phones can all be a different shade of white that don’t match each other.

New illumination sources, including light emitting diodes (LEDs), now allow handheld color measurement instruments to measure with well-defined and controlled UV illumination components. To ensure consistency, new illumination sources and materials containing OBAs required new instrument and measurement standards for defining and measuring the relative UV content, and thus the degree of fluorescence in plastics containing OBAs. Further, companies found that they needed to apply standards to the UV component in the illumination of lighting systems that they used for the visual assessment of color to ensure correlation among various facilities across the supply chain. 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.

Based on this background information, it is clear that the only way to bring color consistency to products that use OBAs is to give stakeholders across the supply chain the tools to accurately measure the amount of OBAs in products. 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.

To understand how this works, let’s go back to the example of a consumer electronics manufacturer.

As we said before, this manufacturer produces a range of devices and accessories in white, and makes use of OBAs to achieve the desired level of whiteness. These devices and accessories are designed to work together, so color consistency is critical to the optimum user experience.

But producing this type of color consistency with consumer electronics is very challenging; the color of the plastics used to produce the devices can vary according to the material supplier and process conditions. For a supplier producing white products, the problem is made even more challenging when OBAs are used in the process.

But by introducing an appropriate spectrophotometer into the production process, the manufacturer can control color consistency of all plastics used in production—from raw material through to the finished product, monitoring all of the color impact of shifts in process variables, including levels of OBAs.

Accompanying quality control software can then store color data that can be shared across the supply chain to ensure color accuracy at all points in the production process.

Given positive consumer response to whiter-than-white products, OBAs will be part of the manufacturing process for a long time to come. And as long as manufacturers are using these brighteners, companies will continue to provide the best instruments and software to measure, manage and control color despite these agents, keeping color consistent with the end result meeting expectations of consumers, brand owners and other key constituents.

Felix Schmollgruber, EMEA technical applications manager, X-Rite. Schmollgruber manages the applications engineering and technical support team for X-Rite in Europe. For more information, call (888) 800-9580 or visit www.xrite.com.