Pigment Pastes for Solid Surface Manufacturing
Pigment pastes are responsible for providing the final colour to solid surface products. In the manufacturing of solid surfaces and composite sanitaryware, achieving a uniform and batch-to-batch repeatable coloration is one of the most critical industrial challenges. Using high-grade pigment pastes is essential to produce premium solid surface products. Compared to powder pigments (which tend to lump, slow down cycle mixing times, and reduce color yield), liquid pigment dispersions facilitate rapid, clean dispersion, guaranteeing flawless colour distribution without disrupting resin catalysis. At AITANACHEM, we supply high-concentration reactive pigment pastes specifically engineered for solid surface production, and we provide technical assistance on the most delicate aspect of the process: colour.
What Is a Pigment Paste?
A pigment paste is a stable dispersion containing a high concentration of solid pigments (organic or inorganic) suspended in a liquid carrier (a resin) compatible with the target polyester matrix. Compared to solid powder pigments, paste integrates far better into the mixture (yielding homogeneous coloration) and offers higher tinting strength. When this carrier resin is chemically compatible and reactive with the polymer matrix, it is classified as a reactive pigment paste: the colour becomes an integral part of the cured matrix without interfering with polymerization. Although primarily an aesthetic component, the pigment paste also influences catalysis, exotherm reactivity, and slurry viscosity.
Key Technical Factors in Selecting Pigment Pastes
Achieving consistent colour is one of the major technical hurdles in solid surface casting. At AITANACHEM, we formulate and supply pigment pastes adhering to strict technical specifications to guarantee maximum end-product quality:
- High Tinting Strength and Hide Power: Formulated with an elevated pigment concentration (at least 70%) to reach the desired saturation level using the lowest possible paste ratio in the formulation.
- Catalysis System Compatibility: Free of unreacted substances or cheap extender fillers (such as uncontrolled carbonates) that can unpredictably inhibit or accelerate polymerization and alter gel times. Extender fillers accompany the pigment to adjust properties or lower costs, sometimes accounting for 30–50% of the paste’s composition. Due to rising TiO₂ (titanium dioxide) prices, substituting it with cheaper carbonates or ultra-white marble dust is common; while this maintains price points, it can weaken the finished part against household acids.
- Free of Styrene and Harmful Additives: Formulated without styrene or additives that impair catalyst breakdown or slurry reactivity.
- Chemical and Thermal Resistance: Selected pigments withstand high peak exotherms during curing and resist continuous contact with household cleaners, detergents, mild acids, and alkalis.
- UV Stability (Anti-Yellowing): Doped with thermal and light stabilizers to prevent colour degradation and premature aging when exposed to natural or artificial light.
- Single-Pigment Formulations: We recommend selecting single-pigment shades whenever feasible, significantly reducing the risk of colour separation caused by fluid dynamics during mould filling.
How to Prevent Color Separation and Marbling in the Mould
During open mould filling or pressure injection, the moving mixture stream contacts the mould walls and intersecting flow fronts. Variations in particle size and migration velocity between different pigments can trigger chromatic separation, causing unwanted streaking, veining, or marbling effects. To eliminate these processing defects, we assist you with:
- Determining the Color Saturation Curve: We conduct laboratory testing to establish the exact addition percentage (typically 4% to 6% based on pure resin weight) where minor pump dosing fluctuations do not alter the finished shade.
- Stabilizing Poly-Pigment Dispersions: We incorporate specialized surfactants and wetting agents to keep heavy pigments (such as titanium dioxide or hematite) suspended alongside lighter pigments (like carbon black).
- Preventing Mould Contamination: Proper application of composite release agents prevents ghosting or wax residue transfer onto the coloured surface.
- Mitigating Yellowing and Gloss Loss Over Time: UV radiation degrades the polymer matrix (polyester naturally yellows), while moisture ingress can cause surface whitening. This is countered using light-stabilized pigments, ISO-NPG resins, and free-radical scavengers.
AITANACHEM: Custom Colour Matching and On-Site Factory Support
At AITANACHEM, we offer comprehensive colour development and on-site factory support for sanitaryware and furniture manufacturers:
- Custom Colour Development: We formulate bespoke shades upon request based on international colour standards (RAL, NCS) or by colour-matching physical samples.
- Spectrophotometry Testing: We perform batch-to-batch colour tolerance testing (ΔΕ) to guarantee no eye-visible colour variations occur between production lots.
- Dosing Pump Calibration: We adjust paste viscosity and thixotropy to match your plant’s mixing or injection equipment, preventing filter clogging or pump cavitation.
Frequently Asked Questions (FAQ) About Pigment Pastes
Why are pigment pastes preferred over dry powder pigments?
Powder pigments are difficult to disperse uniformly in high-viscosity slurries, resulting in colour specks (mottling), dry powder pockets, and extended mixing cycles that can prematurely trigger gelling. Liquid pigment pastes ensure fast, clean dispersion throughout the mixture, guaranteeing perfect colour distribution without disturbing polymerization.
What percentage of pigment paste should be added to solid surface formulations?
The optimal ratio typically ranges between 4% and 6% based on pure resin weight (approximately 1.5% to 2% of total mixture weight). Working within the saturation zone of the colour curve ensures that minor pump dosing variations will not alter the final shade. This percentage varies significantly depending on the colour shade, being considerably lower for dark colours such as black.
Do pigment pastes affect gel time or resin curing?
If correctly formulated, the paste will not alter curing kinetics. However, low-grade pastes containing non-reactive carriers or cheap extenders can retard catalysis (leaving soft parts) or accelerate it uncontrollably, causing high exotherms and cracking.
How do you prevent white scratch marks on dark-coloured solid surface parts?
White scratching in composites is caused by light refraction off micro-edges created in the scratched polyester matrix. To mitigate this in dark shades (black, charcoal, navy), we formulate pastes with controlled particle sizes and recommend modifying the ISO-NPG resin with MMA to increase elasticity and surface toughness.
What pigment concentration should a high-grade paste have?
It should contain at least a 70% pigment concentration with high tinting strength, reaching saturation with minimal paste volume.
Why do colours separate or show streaks in my cast parts?
This is caused by pigment separation: in multi-pigment shades, each pigment migrates at different speeds as the fluid flows. This issue is avoided by using single-pigment formulations, working with expert colour formulators, and incorporating proper stabilizing additives.
Why do finished parts yellow or lose surface gloss over time?
This is caused by UV radiation (which yellow polyester) and moisture exposure (which causes surface hazing). It is mitigated using light-stabilized pigments, high-grade ISO-NPG resins, and free-radical scavengers.
Can you supply pigment pastes based on the RAL color chart?
Yes. We match shades based on the RAL color chart and provide technical guidance on selecting the optimal paste dispersion for your formulation.
Need to Develop a Custom Colour or Solve Pigmentation Issues?
At AITANACHEM, we combine the supply of high-concentration pigment pastes with expert technical guidance backed by years of field experience. If you want to eliminate shade variations, calibrate machine dosing pumps, or request paste samples for trial casting, contact our technical team. We will recommend the best paste for your formulation and color requirements.
To review the entire casting process or explore other raw materials, visit our master guide on solid surface raw materials and technical support.