Flying Colors

In today’s competitive marketplace, consumer goods need strong, repeatable color now more than ever, and that need continues to drive processors toward the apparent contradiction of higher color quality at lower cost. A little knowledge of the fundamentals, and a service-driven color supplier, however, will give most molders and extruders all the tools they’ll need for low-maintenance coloring.

AVOID METAMERISM

In a sense, color is more about what the eye doesn’t see than what it does. Light can be considered a wave, with a characteristic wavelength, a measurement which forms the basis for testing instruments such as spectrophotometers. Objects absorb some wavelengths of incoming or “incident” light, while reflecting others. The reflected waves are the “color” the human eye perceives. The important science that processors need to know is that for a successful match, the same set of incident wavelengths need to strike the part at both the processor’s shop and at the customer’s facility. A perfect match as-molded, for example, may be visibly off in the customer’s quality lab. The phenomenon is called “metamerism”, and the solution is simple: don’t agree on a color match under ambient lighting. Use a light box (with lamps of the correct color “temperature”) and/or instrumentation.

RUNNING COLOR

Other factors to consider include machine age and screw design. While let-down ratios have reached levels which were impossible a generation ago, many extruders and presses are still in production after twenty years or more. Can your mature machine handle extreme let-down ratios? Processors sourcing a new masterbatch should provide extensive equipment data and be prepared to experiment, especially where wear and non-optimal screw designs may compromise efficient distribution.

While it is possible to compensate for sub-optimal distribution by altering running parameters, the complex inter-relationship between resin properties and machine settings can make running changes a costly way to tune coloring. Often, a slightly richer let-down is the simplest solution. Some typical problem areas are described by Rick Malson, technical manager for, Spartech Canada Inc. (Stratford, Ont.,100): “Variations in thickness, letdown ratio, resin color, regrind, and others can all cause differences in appearance. In thin applications especially, the exact same concentrate can produce what you would swear are two different colors, just by changing the thickness.”

Processors with less sophisticated process control or older equipment generally factor in these variables when costing a job. “That’s where the sophistication comes in their feed systems”, says Peter Allan, general manager of Meyers Colour Compounds Ltd. (Oakville, Ont.,102). “With some systems it’s difficult to get good distribution. Distribution is the issue, not dispersion. Dispersion is our job.”

Even regrind composition can have an effect. Rick Malson advises: “Understanding the limitations of certain regrind sources will reduce problems. For example, if your concentrate for a certain application contains little or no titanium dioxide, care should be taken to ensure that a mixed regrind stream containing TiO2 is not used. It will be extremely difficult to obtain the desired color intensity and you will probably be adding an excessive amount of concentrate to cover it up. In such situations it can often be more cost effective to not use regrind at all. Regrind may also require additional stabilization.”

Specialty products are another factor, often requiring special attention. In fluorescents, for example, there are some differences compared to “conventional” color. “There are some metal ions which must be avoided because they kill the color; there are (also) certain waxes and products which will improve the plate-out performance which should be added to the masterbatch. Otherwise they’re very easy to work with,” notes Peter Olley, vice-president, marketing at Day-Glo Color Corporation ( in Canada, A.R. Monteith (77) Ltd., Mississauga, Ont.,103). Day-Glo products, for example are “fully melt-in colorants which dissolve completely in the polymer”, adds Olley.

Additive packages in custom or special effects colorants should be considered when coloring a new resin. Most special effects products can be run successfully with standard equipment and experience, but processors new to the “specials” should work especially closely with their supplier.

Christopher Bain, vice president of Microcolor Dispersions Ltd. (Toronto,105), suggests that tight process control is a good starting point for lowering the cost of coloring. Bain recommends thorough knowledge of base resin specifications, right down to the particle size. “We sometimes have to adjust on a batch-to-batch basis to compensate for (issues) in their production process.” Microcolor uses quick turnaround to courier small quantities of masterbatch to processors who need to fine tune color. Since the fine tuning process costs time and money, the earlier in the production cycle that coloring can be calculated, the better. Optimally, the coloring system should be considered while the part is still “on the drawing board”.

MASTERBATCH IS MORE THAN JUST PIGMENT

Another running consideration for the processor involves the masterbatch composition. While it’s traditional to think of masterbatch coloring products as simply pigment in a carrier, many products use the carrier vehicle to deliver more than just color. Since “color” is in fact a wavelength or combination of wavelengths of light, it’s possible to think of “color” as a property which extends beyond what the human eye can see. In agricultural films, for example, the ultimate end-user is a plant, and the ultraviolet or infra-red “color” needed may not be a property the processor can check at a glance. UV stabilizers, anti-oxidants, and combinations of process aids form the hidden component of the carrier.

Do UV/IR packages radically change processing parameters? “From a processing perspective, no”, says Terry Elliot, director of sales and marketing at Ampacet Canada (Kitchener, Ont.), “but you need to know where your target market is.” Elliot stresses the need for the processor to know the climate conditions at the end use location for proper product formulation: “One year in Arizona or California is very different from one year in Northern Ontario, so they need to know the conditions so they (the masterbatch supplier) can formulate a UV package. Ampacet’s Thermic Brown IR/UV polyethylene masterbatch products (107) are an example where color is used to regulate soil temperatures.

Holland Colours Canada (Don Mills, Ont.), for example, has launched a new carrier for it’s Holcobatch PET products called the “42” carrier system (109). The new system allows faster cycle times with reduced purging and does not require predrying. Holcobatch “42” has no lubricity, eliminating blistering and delamination, and features tight particle size distribution for enhanced consistency when used with volumetric feeders.

For high volume, highly competitive markets such as packaging, agriculture and automotive, tight process control, modern testing equipment and procedures, and a good working relationship with the masterbatch supplier are even more important for consistency at the lowest overall cost.

WHERE TO?

What’s the future of resin coloring? Liquid color has definite advantages, such as excellent dispersion and the absence of a prior heat history, but in the near and medium term, concentrates as masterbatch will continue to dominate.

Processors will continue to enjoy higher let-down ratios and enhanced customer service. Ivan Garneau, sales manager for the Clariant Masterbatches division of Clariant Canada (Mississauga, Ont.,110) describes the situation at Clariant, but he could just as well be describing the industry as a whole: “(We are) reducing let-down ratios in conjunction with micropellets; we’re working on ratios of below one percent. It’s definitely cost-driven. We color-match in three days with production in five days. (It’s about)
faster turnaround on both matching and production.”

Smaller concentrate pellets improve dispersion by better surface-to-volume ratios, and in the extreme, the carrier resin will trend to zero, leaving essentially dry color, but in a hopper-ready, surface-modified form. “You’ll be dealing with no resin carrier as we understand it today,” relates Meyer’s Peter Allan: “That’s the direction we’re going; 100 percent pure.”

Is it technically possible? Yes, but metering equipment and screw designs will need to evolve to take advantage of ultra-concentrates, a process which will take time given the large installed processor base. In the here and now, however, faster turnaround, higher let-down ratios, and improved carrier/additive formulations will keep costs down and the color industry busy. CPL