additives feature | Special effect pigments
Silberline’s Tufflake
Premier Silvet E1 metallic
effect pigments improve colour retention in high-shear processing
The supplier says Platalux pigments are not only
ideally suited for packaging and decorative applications for the cosmetics and luxury goods industry, but also for high-quality, artificial leathers. The company emphasizes strong hiding power and excellent tem- perature stability of more than 300°C. Eckart also offers Energysafe pigments, designed to
and blow mouldings, film, sheet and profile extrusions. The products are supplied in a low-VOC, low-dust
carrier system. Silberline says that this feature allows the processor a safer means of incorporation over mineral spirits-based pastes or dry powders. “In addition, these carrier types allow formulators the ability to use aluminium flake in a wide range of polymers, easier handling and storage, and reduced clean-up time,” the company notes. Platalux is Eckart’s new generation of effect pigments for plastics applications. These are silver- coated pigments based on glass. Eckart says the “extraordinary inherent sparkle combined with a champagne-coloured shade leads to pronounced glitter effects in pure colours or in combination with transpar- ent colour pigments and dyes.” The sparkle intensity exceeds that of Eckart’s existing Luxan pigments.
substantially increase the solar reflectance properties of plastics across a colour space that includes black, white, silver, and many other shades. Plastics comprising Energysafe pigments may reflect more than 60 % of incident solar energy. The pigments reflect near infrared radiation and
ultraviolet, as well as visible light. They can be used with any thermoplastic. Eckart says that the cooling effect provided by
Energysafe pigments may be useful for outdoor usage as well as for automotive applications such as vehicle dashboards or other plastics interior parts strongly exposed to sunlight. One Energysafe grade, Lignum Brown, has been
tailored for wood-plastic composite (WPC) applications such as outdoor decking. It can be used as the principal colour-giving pigment, providing a total solar reflec- tance (TSR) of 20 %. When decking is exposed to strong sunlight, there may be a significant temperature difference between the top and bottom of the profiles, especially in hollow types, due to the low thermal conductivity of plastics. This can
Special pigmentation effects made simple
The primary types of pearlescent pigments are based on mica flakes coated with titanium dioxide. As the coating thickness increases, the colour varies from silvery white to yellow, red, blue, and green. Different colours can be achieved by adding a second coating of iron oxide (gold and beige) or chrome oxide (green); and a range of metallic colours (bronze and copper) is achieved by replacing the titanium dioxide with iron oxide. The pearl-like appearance can be tuned by adjusting the size of the flakes, notes Scott Sabreen at The Sabreen Group, an expert on special effect pigments. Small flakes (about 5 microns) give rise to a satiny appearance with good opacity. Larger flakes (about 25 microns) give a lustrous effect with lower hiding power. Different particle sizes are often
24 COMPOUNDING WORLD | March 2015
blended together to achieve a desired combination of lustre and opacity. Colour stylists typically combine pearlescent pigments with transparent pigments and dyes to add lustre to the base colour. Because the size and shape of these
particles are so important to the resulting appearance, special care has to be taken when processing the pigments in plastics. High shear forces can fracture the flakes and reduce the lustre effect. While the surface of the pearlescent
flakes reflects light, the edges scatter the light in all directions and are compara- tively darker. This can lead to an unde- sired effect in injection moulded parts. When flow fronts come together they may form a weld line. If pearlescent pigments are used, the flakes tend to flop over at the weld line exposing their edges. The
result is a dark line accentuating the weld. Proper mould design places the gates in such a way that the weld lines are in less visible locations. Metallic pigments are made from
copper alloys and aluminium. The copper versions vary in colour from bright greenish gold to red gold. Aluminium versions are silver and silver-grey in colour. Originally, the vast majority of offerings were in flake form to maximize lustre. As with pearlescents, the plastics
processor has to take care to minimize shear forces to preserve the particle shape, and typically the colourist blends pigments of different particle size to impart the desired balance of lustre and opacity. Smaller particles provide opacity; larger particles provide lustre. ❙
www.sabreen.com
www.compoundingworld.com
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