Formulators Forum—Color Matching in Powder Coatings
Posted on Tuesday, April 25, 2023
What does the process of color matching entail when it comes to powder coatings and what are some of the challenges and details to keep in mind when attempting a match? Achieving a perfect color match and finish in powder coatings can often be a challenge due to the complexity of the process involved.
Basics of Color
Before we get into color matching, let’s explore the basics of how color is created. When light hits an object, some wavelengths of light are absorbed while others are reflected back. These reflected rays enter the eye and are absorbed by specialized cells called cones in the retina. There are three types of cone cells, with each type capable of detecting a different range of light wavelengths. The cone cells in turn send electrical signals to the brain which are processed and interpreted as color.
Pigments used to achieve a color contain various elements and compounds, with each component contributing towards a particular color shade. For example, titanium dioxide is used to create whites as well as pastel colors; iron oxides are used for red, yellow, brown, and black; while cobalt is a common component of blue pigments. Additionally, effect pigments and metallic pigments are used to give an ever- expanding range of finishes.
The Process of Matching Colors
Various techniques are utilized for developing a color match to the target color sample in the laboratory before a large production batch can be scheduled.
A color sample, usually in the form of a coated panel, is used as a standard reference to develop the color. The panel can be scanned with a spectrophotometer to get the process started. A spectrophotometer provides precise, measurable color data that can be used along with a color matching software. The software analyzes the data and uses a color library to generate a color formulation that suggests the amount of each pigment to be added to the base to achieve a particular color.
At this stage, it is vital to select the appropriate pigmentation level so that the powder coating is opaque enough to provide adequate hiding of the substrate while preserving the desired finish. Characteristics like gloss and surface finish (texture, wrinkle, hammertone, etc.) each require different additives and adjustments to the total formulation.
The next step in the process involves making a small batch of powder based on this initial formulation. A sample from this batch is then sprayed on test panels and cured in an oven at the designated curing temperature. The sample panels are then compared against the standard reference panel visually, as well as using a spectrophotometer. If the sprayed trial sample is not a close match, adjustments are made to the formulation and a new trial batch is produced. The changes made to the formulation need to be carefully documented. The trials are repeated with additional adjustments until the target color and finish are achieved.
The samples should be compared under different light sources and corrected accordingly to minimize metamerism, a phenomenon where colors appear identical under one light source but different under another light source. Along with the desired color and finish, the sample formulation also needs to be tested for performance parameters such as adhesion, curing, hardness, etc.
Considerations When Matching Powder Coating Colors
The process of matching powder coatings can be short or quite extensive, depending upon the color and finish desired. Sometimes a visual match is necessary instead of one using a spectrophotometer. In this case, the sample panels are compared visually, and adjustments are made as necessary. This method necessitates experience and a trained eye of the person doing the match and can often be subjective, as the perceived color might differ from person to person.
Ideally, a coated panel or a part offers the best standard for matching but often times a situation might warrant a color to be matched from a different substrate, like a paper sample, or at a different gloss level, finish, etc. This can add to the complexity of the process and expectations must be managed, as the same color can often appear significantly different visually at varying gloss levels or in a different texture.
Color matching is a critical step in powder coating production and calls for experience, knowledge about color theory, attention to detail, and patience. By using tools like spectrophotometers, software, and the right techniques, formulators can design powder coatings that are accurately matched to the target color and with consistently high quality.
Troy Sukhadia is president of Spectro Coats.