Choosing Polymer Colorants
Selecting the right polymer colorants can have an impact all along the value chain, from brand recognition to competitive differentiation and consumer perception.
Color is one of the most powerful tools for differentiating products, communicating brand impact, and enhancing value—and even safety—of appliances. To make smart decisions about polymer colorants in your appliance design, it helps to understand the options and identify the most appropriate technology for your material, process and end application.
This article explores the attributes of polymer colorants—including properties, equipment, processing and special effects—and explains how both liquid and solid colorants can play an important role when designing and manufacturing plastic products.
The Business Case for Color
The majority of consumers are strongly influenced by color. One study by a researcher at the University of Winnipeg in Canada found that up to 90% of first impressions about products are based on color alone. (Satyendra Singh, (2006). “Impact of color on marketing”, Management Decision, Vol. 44 Issue: 6, pp.783-789. http/www.emeraldinsight.com/doi/full/10.1108/00251740610673332)
Color can influence people’s moods and feelings, and affect their conscious and unconscious buying preferences and decisions. In addition, effective use of color has many other benefits:
- Colors help a product stand out from competitors
- Colors can reinforce—or even embody—brand identity (think Tiffany & Co.’s robin’s egg blue)
- Colors and effects can create perceived value, such as using green to indicate sustainability or a metallic bronze to suggest luxury
- Certain “safety” colors, such as fire engine red, school bus yellow, or hunters’ neon orange, attract attention or give a warning
- Part identification may depend on standard colors, as in HVAC electrical components
Within different industries, effective color usage presents specific challenges. In the case of major appliances, which typically bring together a variety of polymers for various components, it can be tricky to ensure color consistency across multiple materials, which may include polycarbonate (PC), acrylonitrile-butadiene-styrene (ABS), polypropylene (PP) and thermoplastic elastomers (TPEs). Effective color matching capability is essential in these cases.
In the HVAC sector, colorants must work together with additives that help polymer materials used in housings and hoses to withstand environmental impacts such as UV light exposure, weathering and abrasion. Similarly, colorants for reusable medical equipment and devices may be subjected to harsh disinfectants and high-temperature sterilization, which can cause fading or color shifting. They also usually need to be certified biocompatible under USP Class VI and ISO 10993 standards.
When choosing colors for consumer products such as electronics, it is critical to consider the target demographic and current style trends. Consumer preferences regarding color can vary based on age, geography, ethnicity and gender.
Comparing Polymer Colorants and Pre-colored Resins
A fundamental decision that designers must make is whether to use a pre-colored plastic resin or add colorant to a natural resin. The advantages of pre-colored materials include simplicity, consistency and time savings from avoiding setup in production runs.
Liquid and solid colorants each have their own unique advantages and usage parameters.
A global appliance manufacturer selected a metal pre-colored, rigid vinyl for laundry machine consoles to meet consumer demand for clean lines and bold, metallic colors while controlling costs and minimizing environmental impacts. The manufacturer also evaluated painted or chrome-plated plastic, but found it required costly secondary operations involving volatile organic compound (VOC) emissions.
Using pre-colored rigid vinyl instead of secondary painting saved the company $500,000 a year in manufacturing costs and $10,000 a year in scrap reduction. Additional savings are expected from fewer appliance returns due to surface scratches and mars. The molded-in color extends through the console walls, helping to maintain appearance during shipping, handling and normal use. Molded-in color also avoided the environmental impact of VOC emissions.
The obvious downsides to using pre-colored materials are limited color choices and design options. If you need a custom color or want to match an existing shade, using masterbatch colorants with natural resin may be the best choice. Sophisticated color-matching technologies available today help to drive precision, and suppliers can reliably suggest the best colorant for a specific resin.
In some cases, it may also be more cost-effective to purchase a large quantity of natural resin and small amounts of colorants instead of pre-colored resin. The natural resin can be used across different applications or different versions of the same product, simply by making a color change. Adding colorant during manufacturing avoids the risk of being stuck with a large amount of pre-colored resin that has become obsolete.
Liquid and Solid Colorants
Within the umbrella category of polymer colorants, liquids and solids (masterbatches) are among the most popular choices. Each type lends itself to different use cases.
A solid masterbatch consists of concentrated pigment dispersed in a carrier resin for optimal incorporation in the resin matrix. These masterbatches are supplied as pellets of various sizes for clean handling and precise dosing. A wide range of carrier resins are available, making it easy to find a color masterbatch that is compatible with your chosen plastic.
Liquid colorants are suitable for a wide range of applications, especially those requiring low letdown ratios and highly accurate dispensing. They can be metered more precisely than a pelletized mixture, resulting in high color consistency. Also, liquid colorants can be processed at lower temperatures than masterbatches, which may reduce cycle times. These lower temperatures also allow them to be used with heat-sensitive materials such as polyethylene (PE), polypropylene (PP) or co-polyesters, which can undergo color shifting at high temperatures.
Liquid colorants may have a cost advantage because they can be used at lower loadings than masterbatches. On the other hand, special equipment is required to meter and pump the liquid colorant from its storage container for mixing with the resin during processing. Also, colorant manufacturers offer super-concentrated solid or liquid masterbatches that allow smaller quantities to deliver the same color quality as traditional masterbatches.
Solid colorants are often used for opaque parts, including thin-gauge applications to prevent see-through or to give a saturated effect. Translucent or semi-transparent colors can be achieved with either type of colorant, but liquids are preferable for tints as they can be metered more precisely.
Liquid colorants and masterbatches should be viewed as complementary solutions that can expand design possibilities and broaden the scope of polymers to be considered for an application. For example, packaging producers often use both types of colorants so that they can achieve a clear tint on bottles using liquid and a cost-effective opaque effects on bottle caps using solid masterbatch.
In addition to colorant type, designers and manufacturers can select from many special effects that further differentiate products and appeal to specific audiences. These effects can add value to electronics and appliances. Like colorants, these special effects can be delivered in either a solid or liquid form, depending on the application.
Types of special effects include pearlescent, iridescent, metallic/chrome, edge glow, neon/fluorescent, sparkle/glitter, wood grain, marble, granite, light diffusion, and camouflage. Don’t be shy about asking your colorant supplier for more options, even a tortoise shell look is possible using the right combination of colorants.
Another argument for being open to both liquid and solid colorants is that their measuring and dispensing equipment—while different—can be used in the same manufacturing facility or even on the same processing line.
Masterbatches can be dispensed at the molding machine, or pre-mixed with natural resin in a blender. When coloring at the machine, manufacturers need to ensure that they are delivering the correct ratio of colorant to resin. It is also important to thoroughly clean the machine when changing over from one colorant to another.
- Volumetric feeders: Many manufacturers use a color feeder that is installed at the base of the resin hopper, and an auger screw to add the masterbatch to the resin. These volumetric feeders are calibrated based on the volume of colorant passing through each turn of the screw. Volumetric feeders are highly accurate, but require time-consuming setup, calibration and re-calibration.
- Weight-based, or gravimetric, feeders: These feeders use a load cell that continually registers the loss in weight of the colorant hopper and adjusts the feed rate accordingly. Unlike volumetric feeders, these devices do not require manual calibration and regulation.
Liquid colorants are suitable for a wide range of applications, especially those requiring low letdown ratios and highly accurate dispensing.
Multiple solid feeders can be added to processing machinery, allowing several additive and/or color streams to be fed simultaneously.
When it is time to change colorant, machine operators must disassemble and clean the feeder and remove residual masterbatch pellets, then refill and recalibrate the machine for the next application. Ease of disassembly is a factor to consider in the total system cost of a masterbatch feeder.
Liquid colorants use different types of pumps for dosing during the melt stage of plastic processing. The pumps are connected to a liquid colorant delivery vessel (a drum or container) by a pickup wand.
A global appliance manufacturer selected a metal pre-colored, rigid vinyl for laundry machine consoles to meet consumer demand for clean lines and bold, metallic colors while controlling costs and minimizing environmental impacts.
- Peristaltic (roller) pumps are used for small production runs with frequent color changes. They work best with lower-viscosity colorants. These versatile pumps can operate at low or high speeds, and accommodate a range of flow rates.
- Progressive cavity pumps are recommended for consistent accuracy in longer production runs. They are typically used for pumping at high rates, and are suitable for high-viscosity colorants such as liquid white.
Benefits and Boundaries
Liquid and solid colorants each have their own unique advantages and usage parameters. Liquid colorants may work best for tinting clear parts such as refrigerator touch panels and shelving, while a solid colorant may be the answer when creating highly opaque blender housings. The type of resin and processing method, desired shade, target audience and attributes of the end application all influence the choice of colorant.
Color selection is a critical design factor for most plastic applications. To derive the greatest value from the chosen color, whether that means greater shelf appeal, premium pricing or a competitive advantage, it is important to consider different colorant strategies. Finding the best solution for your application—whether it is pre-colored resin or a colorant—depends on variables including resin type, processing parameters, desired effect and interactions with other additives. While pre-colored resins offer simplicity, solid and liquid colorants provide greater choice, nuance and flexibility. Further, their complementary attributes can often solve colorant challenges within a single product or across a portfolio.