Plastic material colorants or concentrates overview

Plastics material colorants can sometimes cause nearly as many issues as the materials they are mixed with. It is important to have a solid understanding what potential molding issues to look for when issues such as color swirls, contamination or other potential colorant related issues arrise. Having a solid knowledge of the characteristics that are relevant can sometimes save alot of headache. This is an overview of colorants..their properties, usage and potential defects.

We must first define colorant. Colorants are materials that are almost always made with the the same base as the natural materials they are mixed with. There are several colorant types, the primary categories being pellet, liquid and powder forms. Pellet being the concentrate most commonly used, this article will primarily be aimed towards this method of developing a colorized material.

Pelletized colorants are often called concentrates due to their purpose. Initially the colors themselves start as pigments. These pigments of various colors are often blended together to become a particular color. For instance...a blue pigment can be combined with a yellow pigment to develop a shade of green. This color may require a lighter or darker pigment to become a particular shade of green. When the desired shade has been achieved, this concentrate is blended with a natural powdered base, such as nylon or polypropylene. This completed blend is then extruded and pelletized to be used with natural pellets to mold a specific color. I will describe the process in greater detail in the future... for now, I'll stick with the basics so I can concentrate more on areas that can lead to defects.

Each colorant has a specific ratio. These ratios are often established by the extrusion facility, but these are generally recommendations and there are times when less or more than the recommended ratio is used for cost savings, or better color content. The important thing to remember here is the cost of using too much colorant...as well as the cost of scrap generated by lack of colorant. Best practice dictates that the manufacturer's mixtures be followed. Quite often, this ratio is affixed to the label on the barrel, as well as documented on the Material Safety Data Sheet. The general formula is a virgin-to-concentrate number (in ex: "25:1" is twenty-five pounds of virgin with one pound of color added to it).

Newer age equipment (such as Maguire blenders) do a fantastic job of producing consistent blends. Some of the older equipment, however can be a bit more tricky. The digital equipment is harder to establish just what the proper setpoint should be when first setting up a job. The best method here is to use the manufacturer's color chip in comparison. Readings are taken from parts (NOTE: make sure the press was properly purged and the barrel has had time to heat soak while running several cycles prior to color testing) and compared to the color of the color chip using a McBeth Spectrometer, or similar piece of equipment. This analysis will help you determine if the colorant content is to dark or too light. Once a good read has been established, blender setpoints should be recorded for use in future runs.

Now we'll focus on the key issues regarding color concentrates. I will point out the most common first, then give some rare but equally as aggravating situations to watch for:

One of the first keys to success in molding with colorant is tracking lots. This is often overlooked, but treat colorant with the same precautions as your materials. Some examples of what can happen during an extrusion lot change are as noted:


-Contaminated pellets(poor screw cleaning at extrusion line changeover)

-pellet longs (pellet sizes inconsistent due to end/ beginning of run conditions, or poorly adjusted pelletizers)

-change in pellet size(pellet size changed in diameter or length at changeover

-wrong base material used

-lamination(poor screw clean at changeover while changing base materials)

-change in color (poor blend or improper pigment configuration)

-viscosity changes(too high or low heats, base powder lot change)

Knowing how and when to inspect your concentrates for these conditions is crucial to profitable use of colorant in comparison to precolored materials. Failure to consider these potential factors can lead to an improper diagnosis of a change in molding conditions. One pokayoke that your company should consider is requiring the concentrate supplier to provide a color chip molded from every lot with every new shipment.These chips should be verified for proper color content and visual aesthetics.

Colorant usage can have a profitability factor... but only as long as they are used and analyzed properly.