Products that sell are the ones that stand out from the competition. Manufacturers looking for an edge in the marketplace often turn to color – and specifically, special effects – to move items from the shelf to the buyer’s shopping bag.
Pearlescence and iridescence are particularly effective at catching people’s attention because, to consumers, sparkle signifies elegance, luxury, fashion and fun.
For most of human history pearlescent and iridescent items were found only in nature – in pearls and certain gemstones such as opals, or in creatures like iridescent insects, fish and birds. Eventually, people figured out how to create the effects themselves by heat-treating metals or adding flecks of shiny minerals to paints – and later to polymer resins.
As additives for resins, iridescence and pearlescence can be used in almost every type of thermoplastic, including opaque ones. Their effects, however, are most intese in polystyrenes, polypropylene, polyethylene, PVC and silicone.
As a result, shimmer and glimmer can be found in an astounding array of markets and products, including:
The terms pearlescence and iridescence refer to the way the surfaces of some objects appear to change hue depending on the angle at which they are viewed. The science behind the shine comes down to two properties of light: reflection, particularly the reflection of different pigments through translucent surfaces, and diffraction, which can be seen in prisms and rainbows or on the surfaces of CDs and DVDs.
These phase shifts in light are partially responsible for both pearlescence and iridescence. Light waves reflecting, or bouncing off of, a surface return back the way they came. A surface with a high refraction index returns a half-wavelength phase shift back to the viewer’s eye, which perceives a change in color.
Interference occurs when two light waves meet, resulting in a single pulse of light waves passing through each other. The human eye interprets the result as changing colors. Pearlescence is like iridescence except that one of the colors reflected back to the eye is white.
Creating sparkly special effects in plastics has been a process of trial and error. In early attempts, some additives would dissolve a little – or a lot – into the polymer matrix when heated. Aesthetically, this effect resembled bleeding and “blooming” colors, sometimes bad enough to prevent iridescence altogether.
Scientists and researchers eventually discovered how to ensure that special effects could maintain their intensity indefinitely, even during the molding process when plastics take the form of high-temperature liquids.
The most popular ingredient is mica flakes. Mica is a sheet silicate mineral that demonstrates fantastic basal cleavage – that is, it breaks into flat sheets and flakes.
Heat-treating mica coated with iron oxide or titanium dioxide boosts and balances its iridescent effect, and can be done before, during or after the mica is ground. The treatment method and coating determine the final color properties of an end product’s iridescence or pearlescence.
The process of creating pearlescent effects starts with coating mica in bismuth oxychloride and heating it to a high temperature, which produces crystalline layers with a frosted quality.
Mica flakes must then be oriented in the same direction and parallel to the translucent surface of the plastic matrix, an effect achieved hot-pressing the polymer melt flow through a narrow channel. Small flakes deliver a soft sheen in the final product while larger flakes look more glittery, especially when mixed with aluminum flakes. Mixing flakes with other materials can create different color levels and opacities.
Mica intended for iridescence generally looks like dust or powder and arrives at the lab in bottles. The powder is mixed into a masterbatch or liquid color before being added to the resin.
The surface to which flakes are attached can affect color changes as well. A white background can allow weaker-transmission colors to shine through the transparent plastic while a darker background absorbs all but the pigment’s color.
Plastics Color Corporation offers a full catalog of functional and special effect additives for use in plastics. Iridescent and pearlescent additives join metallic, glow-in-the-dark, and glitter special effects choices.
In addition to aesthetic additives and masterbatches, liquid colors and pre-mixed compounds, PCC also offers scented, flame retardant, antimicrobial, optical brightening and matting agent additives to meet customer needs.
Contact PCC today to speak to your account specialist about your custom plastics needs.