Guidelines For Coloring Dynaflex™ TPE and Kraton Compounds
Dynaflex™ TPE and Kraton® TPR compounds can be easily colored by a variety of techniques to achieve:
- Conventional Opaque Colors
- High Visibility Fluorescent Bright Colors
- Transparent, Translucent, or Pearlescent Colors
- Thermochromatic Colors
The type and technique for coloring may vary for different grades. Dynaflex™ and Kraton® thermoplastic elastomer compounds are based on two Kraton rubber polymer families manufactured by KRATON Polymers U.S. LLC. Both polymer families have distinctly different chemical make- ups and properties.
One family is called ‘G’ polymers. They contain a block structure of Styrene-Ethylene/Butylene-Styrene (SEBS). The other family of compounds is referred to as the ‘D’series of polymers. They have a block structure of Styrene-Butadiene-Styrene (SBS).
Color Concentrates
SEBS compounds are extremely compatible with polypropylene (PP). As a result, color concentrates using polypropylene as the color carrier in a 20 or 25-to-1 ratio is the best choice for coloring SEBS compounds.
Polypropylene has a tendency to harden the compound slightly. The effect is more pronounced in the low hardness products. The usual effect is a rise of about 5- 8 durometer points. The addition of polypropylene concentrates may make the compound flow a bit easier in the mold.
If you want to minimize the effect, use a high concentration color in a 50-to-1 let down ratio. You will need to have good mixing in the machine, or use a static mixer in the nozzle to achieve the most uniform color.
For coloring TPE compounds, GLS recommends that you use high screw speeds (100-200 rpm), high back pressure (100psi), and a higher degree of ramping of the temperatures in the barrel. Please see the GLS Technical Datasheet for suggested starting conditions for each compound.
EVA based concentrate have also been successfully used for ‘G’ compounds. It has a lesser effect on hardness, but lowers that compound’s temperature resistance slightly. Polyethylene and polystyrene-based color concentrates can work. However, high molecular weight polystyrenes may not mix well with the smaller molecular weights of the Kraton® Polymer endblocks in the compound. As a result, we recommend the use of polypropylene or EVA based concentrates.
The SBS ‘D’ compounds are most compatible with polystyrene. Color concentrates using lower molecular weight polystyrene as a color carrier are the best choice. Concentrate let-down ratios as low as 10-to-1 and as high as 100-to-1 are possible depending on the process and desired result. However, anything over a 25-to-1 ratio requires special attention and handling.
| Compound Type | Color Concentrate Carrier |
|---|---|
Dynaflex™ G, Kraton® G |
Polypropylene Ethylene Vinyl Acetate Paraffinic Oil (liquid carrier) |
| Dynaflex™ D, Kraton® D (SBS) |
Polystyrene Ethylene Vinyl Acetate Paraffinic Oil (liquid carrier) |
Dry Powders or Pre-Dispersed Colors
Dry powders are not generally recommended by GLS due to lack consistency and dispersion. Although they can be utilized, powders tend to separate from the pellets in the hopper or during transportation. This sifting effect is characteristic of a dry color master-batch which usually contains dispersive lubricants that can coat the feed section of the screw and cause uneven feeding or short shots.
Liquid colorants
Liquid colorants can be used successfully if the carriers are compatible with (SEBS) or (SBS) based compounds. Mineral oil carriers work well with most of the Dynaflex and Kraton TPE’s. Paraffin oil carriers are compatible, but they have a slight plasticizing effect and can soften the compounds. Aromatic carriers cannot be used because they will attack the materials styrene end blocks.
Bright, High Visibility or Fluorescent Colors
Bright, neon, fluorescent, or other high visibility colors can be achieved with Kraton and Dynaflex compounds. Material grades described as translucent or clear transparent are the best candidates to provide a deep, rich, or even transparent color effect. It should be noted that pigments and dyes used to make these colors are organic and have a tendency to lighten with exposure to the sun. In all cases the use of color concentrates will need to be fully tested and qualified in the actual application.
For specific recommendations regarding the coloring of other TPE’s from GLS, please contact your GLS Representative.
