Solvent dyes are the preferred colourant for transparent and translucent plastics. Unlike pigments, which scatter light and create opacity, solvent dyes dissolve completely in the polymer matrix — delivering brilliant, transparent colour that showcases the clarity of the plastic substrate.
But not every solvent dye performs equally in every plastic application. Choosing the wrong grade can result in colour fading during processing, migration of colour to adjacent surfaces, or incompatibility with your polymer system. This guide explains what to look for.
Why Solvent Dyes for Plastics?
Solvent dyes offer three advantages that make them the right choice for plastics colouring:
- Transparency: They dissolve completely in the polymer matrix — no scattering, no opacity. Essential for polycarbonate, acrylic, and PET applications.
- Compatibility: Non-ionic chemistry means they are compatible with a wide range of resin systems without ionic interactions.
- Processing convenience: They can be pre-dissolved in a carrier solvent or masterbatch and added directly to the polymer melt.
The Four Key Properties to Evaluate
1. Heat Stability
Thermoplastics are processed at high temperatures — injection moulding, extrusion, and blow moulding can expose the dye to temperatures of 180–300°C. If the dye is not thermally stable at your processing temperature, it will degrade, causing colour shift, fading, or discolouration.
| Plastic Type | Processing Temp. | Required Dye Stability |
|---|---|---|
| Polystyrene (PS) | 190–240°C | Stable to 200°C |
| ABS | 200–260°C | Stable to 220°C |
| Acrylic (PMMA) | 180–250°C | Stable to 200°C |
| Polycarbonate (PC) | 260–310°C | Stable to 280°C+ |
| PET | 260–290°C | Stable to 280°C+ |
| Wax / Candles | 60–90°C | Stable to 100°C |
2. Migration Resistance
Migration is the tendency of a dye molecule to diffuse from the coloured plastic into adjacent materials — packaging contents, clothing, skin, or other plastic components in contact. Low-migration grades have larger molecular structures that cannot diffuse through the polymer matrix.
When migration matters:
- Food and cosmetic packaging — dye must not migrate into the product
- Plastic toys — contact with skin and saliva
- Automotive interiors — contact with textiles and skin
- Multi-component assemblies — adjacent plastic parts must not stain each other
3. Polymer Compatibility
Different solvent dyes have different compatibility profiles across polymer types. A dye that dissolves perfectly in polystyrene may have poor solubility in polycarbonate. Always verify compatibility with your specific resin before production.
| YOBISOL Grade | Good Compatibility | Notes |
|---|---|---|
| YOBISOL BLACK RE (Solvent Black 27) | PS, ABS, acrylic, cellulosics | Premetallized — good lightfastness |
| YOBISOL YELLOW 2GL (Solvent Yellow 146) | PS, ABS, PC, PMMA | High heat stability — engineering plastics |
| YOBISOL ORANGE RLSE (Solvent Orange 62) | PS, ABS, PC | High lightfastness for outdoor use |
| YOBISOL FIRE RED BL (Solvent Red 160) | PS, ABS, PMMA, coatings | Good heat stability and transparency |
| YOBISOL BLUE RGLN (Solvent Blue 48) | PS, ABS, acrylic | Bright transparent blue |
4. Lightfastness
For outdoor plastic applications — garden furniture, automotive components, signage — lightfastness is critical. Standard solvent dyes may fade after UV exposure. Choose grades with lightfastness ratings of 6+ (on an 8-point scale) for outdoor applications.
- High lightfastness (6–7): Solvent Yellow 146, Solvent Orange 62, Solvent Black 27
- Medium lightfastness (4–5): Solvent Red 160, Solvent Blue 48, Solvent Yellow 82
- Lower lightfastness (3–4): Solvent Red 127 — for indoor/non-UV applications only
Application Methods for Plastics
- Masterbatch: The dye is pre-dispersed in a carrier polymer at high concentration. The masterbatch is then blended with the base resin at the processing stage. This is the most common industrial method.
- Compound incorporation: The dye is added directly to the polymer compound during compounding. Requires thorough mixing to ensure even dispersion.
- Solvent pre-dissolution: For laboratory or small-scale work, dissolve the dye in a compatible solvent first, then add to the resin.
Requesting Samples from Yobai Industries
For plastics applications, we recommend requesting a 1–5 kg trial quantity to test shade, migration, and heat stability in your specific polymer and processing conditions before placing a bulk order. Our team can advise on grade selection based on your polymer type and processing temperature.
- MOQ: 10 kg · Sample orders 1–5 kg dispatched in 24 hours
- TDS: Available on request — includes solubility and compatibility data
- Export: India + Worldwide