Challenges in Color Measurement
As never before, quality control and assurance professionals are faced with new challenges to provide reliable data on difficult-to-measure colors of paints and coatings and to detect out-of-spec color variations in products at the earliest possible stages during manufacture. But new measurement technologies have kept pace with these challenges, giving quality professionals toolboxes that are both deep and wide when it comes to solid, objective data on the colors of paints and coatings.
Henry Ford’s comment that customers can have a choice of color “so long as it’s black” has gone the way of the Model T. Consumers are demanding a variety of colors in passenger vehicles, office furniture and just about any item found in the home or business. Never has that revolution been more striking than in the automotive industry, which has introduced a bewildering array of metallic flake, pearlescent and other effect paints to differentiate products.
Effect paints have become hugely popular with the public and are now a central selling point for all major automotive manufacturers. For instance, experts say the most popular automotive color worldwide for at least seven years has been silver with effect variations.
But these paints with eye-catching sparkle have created headaches for quality control professionals. Technicians on the production line may observe that a body panel and bumper fascia don’t match properly, but they can’t back up their human perception with data that indicates why the mismatch is occurring.
New instrumentation and software packages can help solve these problems. Handheld spectrophotometers designed for regular use on the factory floor can save manufacturers considerable time and money in applying metallic flake and other effect paints. Using new technology, companies can now speed introduction of new effect paints by designers and paint manufacturers, improve the first-time quality of products being coated with the paints and reduce the time and effort of troubleshooting manufacturing problems that occur on the factory floor.
The key to cracking the effect paint problem was the introduction of twice the number of illumination angles and sensors in advanced hand-held spectrophotometers, compared with prior technologies. Sophisticated software then uses mathematical algorithms to generate graphs that show unique characteristics of an effect paint.
Using this latest generation of technology can help manufacturers obtain reliable and consistent data to:
Laboratory Sampling No MoreInstrument manufacturers also have developed relatively low cost, non-contact in-line devices that measure traditional paints and coatings so companies can now afford to continually monitor processes at a particular piece of equipment on the factory floor, rather than relying only on occasional sampling in the laboratory. Manufacturers that use lab-confined spectrophotometers often will take samples only at the beginning, middle and end of the production runs, simply because of the effort and expense involved in the measurement process. Newer in-line 45/0° geometry spectrophotometers can accurately control the quality of color by measuring a wide range of wet and dry samples without touching test surfaces.
For quality professionals that have dealt with the challenge of measuring test surfaces of materials such as powders, liquids, pastes and leathers, in their natural, unaltered states to yield better "truer" results, 45/0° geometry spectrophotometers, allow the sample to be measured accurately from a distance of about 38mm (1.5 inches). Prior technology relied on pressing glass or clear plastic over test surfaces to protect the instruments from being contaminated by the test samples-altering the test data.
In addition to targeting samples precisely, the latest generation of spectrophotometers have advanced optics and sensors that accurately measure gloss as well as colors. Using computer software, the instrument can compensate for the difference in appearance between dry and wet samples.
Instrument makers have battle hardened spectrophotometers to withstand fluctuating temperatures, vibration, high humidity and variable lighting conditions found on the factory floor through the use of light emitting diodes (LEDS) and other technologies. By using LEDs, the instrument can also detect and ignore ambient light such as incandescent, fluorescent or sodium vapor illumination that can greatly affect results.
When programmed to take regular and frequent measurements, the instruments can markedly reduce scrap and rework because they provide an immediate signal when a process is making parts outside of specifications. Software packages can analyze and correlate the instrument’s measurements with process data such as gloss, film thickness, temperature and other process parameters to improve statistical process control and first-time quality.
Some new instruments even offer a solution to incorrect data due to measurements being taken in the wrong sample area. One type of instrument now available on the market projects an illuminated ring on to the sample to target the desired measurement area, making it easy for technicians to see that they are measuring the right spot on the test sample.
Beyond the SpectrophotometerBut spectrophotometers certainly aren’t the answer for every color measurement application. In cases where precise color measurement is not required, other families of instruments can represent the most cost effective solution for the control of color quality. For instance, colorimeters are simpler and less expensive instruments that use red, green and blue filters that emulate the response of the human eye to light and color. These instruments are used effectively for sorting and quick in-line checks for less exacting jobs.
A good visual analogy to compare the scale of resolution of a colorimeter with a spectrophotometer is this: if a colorimeter measures on the scale of inches, a spectrophotometer will measure on the scale of 1/16th of an inch. There are many applications in everyday manufacturing where a colorimeter is perfectly adequate to the task and a spectrophotometer would be considered overkill.
To help select the right instrument, a company should ask: What exactly is the specification that my customer wants, or more appropriately, what is he willing to pay for?
To get a practical answer to this question, manufacturers need to make sure they employ the same standards as their customers on how color is measured. Going back to the measurement analogy, are you roughing in a house where an inch is acceptable in the trusses or building kitchen cabinets where the difference of a 1/16th inch means the doors don’t fit properly? This may seem obvious, but many companies speed past this basic step, only to find they don’t have the right equipment to perform quality control functions properly.
Here are a few considerations that can get a manufacturer on the road to determining the best equipment for the job: