Formulators Forum—Achieving Color and Gloss Consistency

Color and gloss are two of the most important visual aspects of any powder coating formulation. They can have a big impact on the final appearance of the product and can also affect the overall quality impression of the coating.

The right formulation can make all the difference in achieving the desired color and gloss. The right amount of pigment and binder, along with accurate cure temperature, will result in the perfect color. Impact color, meaning color that can withstand the impacts of daily use, is driven by the right mix of pigments. When it comes to gloss, it is all about quality. A high-quality gloss powder coating will have a higher level of shine. With careful formulation and consistency in your processes, you can create a powder coating that is both beautiful and durable.

There are a few key things to keep in mind when striving for color and gloss consistency. Variables such as material type, part size, and cure temperature can all affect the final color of a part. In addition, it’s important to have a well-controlled process as variations in your finishing line can cause color variation in powder coating applications. This means keeping close tabs on things like cure temperature, conveyor speed, and powder application thickness. By closely monitoring your process, you can better control color and gloss of your finished product from batch to batch. It is also important to use quality ingredients and powders to ensure your powder coating has uniform color and gloss across all applications. Finally, regular testing and calibration of your equipment will confirm your powder coating system is running at peak efficiency and producing consistent results.

There are a few different ways to measure color to ensure you are meeting customer specifications, but the most common method is with a spectrophotometer. This device measures the intensity of light at different wavelengths, which allows for accurate color measurement. Additionally, many powder coating manufacturers use color standards to ensure that their products meet specific color requirements. These standards are used to provide applicators a target for consistency in color and gloss from batch to batch. A spectrophotometer will also provide data to support whether the sample is in (or out of) tolerance with the standard. It is important to note color and gloss are not always correlated.

A powder coating can have a high gloss without being very colorful, or it can be very colorful without having a high gloss. As such, it is important to measure both color and gloss when evaluating the quality of a powder coating.

Gloss is the measure of how light reflects off the surface of a sample; in this case, a powder coated part. A high gloss finish is very shiny, while a low gloss finish has more of a matte appearance. Gloss can be affected by the type and quality of powder used, as well as process variables like cure temperature, conveyor speed, and overspray.

While a spectrophotometer is used to measure color, a glossmeter is used to measure gloss. Sometimes these devices are built into one instrument. To use these instruments, follow these steps (or manufacturer recommendations):

• Calibrate the glossmeter on the certified/traceable tile.
• Calibrate the spectrophotometer on the certified/ traceable tile.
• Best practice is to have an additional color tile that can be used to verify the calibration. If using the spectrophotometer with QC software, it is recommended to store that color check tile as a standard and make trial measurements daily.
• Establish a measurement routine that will provide the best data to be gathered on each part and within a production run. If using a spectrophotometer with a built in glossmeter one will likely be able to gather twice the data in the same amount of time or decrease the measurement time by 50%.
• If using QC software, download the measurements following the routine established above and compare the color and gloss results to the powder manufacturer color standards to ensure that the color and gloss is within tolerance.

While it is important to maintain powder coating equipment, it is equally important to maintain the instrumentation used to measure color and gloss, so that one can have confidence in the data taken. Since spectrophotometers and glossmeters are optical instruments, regular visual inspection is required to check for any contamination from dust, dirt, or foreign material. Follow manufacturer’s recommendation for regular calibration and annual certification.

Maintaining color and gloss uniformity will add value to any powder coating application and will result in higher quality and better-looking products. Long term it should also drive down costs and increase throughput throughout the production process.

John Kowalski is head of marketing with BYK-Gardner USA & Paul N. Gardner Co.