Overview
Pigment sedimentation, sag on vertical surfaces, and shelf-life failures all trace back to the same root cause: insufficient low-shear network strength. East Materials supplies hydrophilic and hydrophobic HJSIL® fumed silica that builds the 3D hydrogen-bonded network coating, ink and adhesive formulators rely on for anti-settling and thixotropic performance — replacing organobentonite, castor wax, and polyamide-wax thixotropes in solvent-based and waterborne systems.
Anti-Settling vs Thixotropic — Two Behaviors, One Mechanism
Procurement specs often treat anti-settling agent and thixotropic agent as two SKUs. Chemically they describe two faces of the same rheology: a particulate network that holds the liquid phase rigid at rest and yields under shear.
| Behavior | State | What the formulator measures | End-user benefit |
|---|---|---|---|
| Anti-settling | Static (storage, transport) | Brookfield viscosity at 0.5 rpm; 30-day pigment-layer test | No hard-sediment after 6+ months; consistent shade at point of use |
| Thixotropic | Dynamic (spray, brush, mixing) | Thixotropic index (η_low / η_high); recovery time post-shear | No sag on vertical surfaces; clean spray atomization; brush leveling |
Fumed silica delivers both because the hydrogen-bonded aggregate network reforms within seconds of shear ceasing — fast enough to stop pigment drop in cans, slow enough to allow application leveling. A single grade addresses both spec lines.
Where the Network Matters
Any liquid formulation carrying dense or settle-prone particles benefits from a fumed-silica network. Seven application clusters cover the bulk of industrial demand:
- Industrial & Protective Coatings — Sag-resistant epoxy and PU topcoats on vertical steel structures, anti-corrosive primers for marine and bridges. Loading 1.0–2.0%.
- Architectural & Decorative Paint — Pigment anti-settling in TiO₂-loaded waterborne emulsion paints; controlled drip in roller and brush application.
- Automotive Refinish — Thixotropic flow control in 2K spray basecoats, metallic flake orientation, sag prevention on body panels and door frames.
- Printing Inks — Solvent-based gravure and flexo inks — pigment dispersion stability and short-set rheology for high-speed web presses.
- RTV Silicone Sealants — One- and two-component RTV — extrusion-quality flow under cartridge pressure, slump-free tooling after application.
- Adhesives & Mastics — Epoxy, polyurethane and MS-polymer adhesives — controlled bead profile, no flow on vertical substrates.
- Unsaturated Polyester & Vinyl Ester — Gel coat and laminating resin — fiber wet-out without resin drain on vertical mould surfaces; pigment anti-settling in pre-coloured gel coat.
Why HJSIL Fumed Silica Outperforms Organic Thixotropes
Organic anti-settling agents — hydrogenated castor-oil wax (HCO), polyamide wax, organobentonite, organic urea derivatives — all build a network through aggregation or swelling. Each carries a process or performance limitation that fumed silica avoids.
| Property | HJSIL fumed silica | HCO castor wax | Organobentonite | Polyamide wax |
|---|---|---|---|---|
| Activation | Cold dispersion + high-shear mill | Hot dissolution 50–65 °C | Pre-gel with polar activator | Hot grind > 80 °C |
| Solvent compatibility | Solvent + waterborne (grade-dependent) | Solvent only | Solvent only | Solvent + selected waterborne |
| Clarity in clear coats | Transparent | Slight haze | Opaque tint | Slight haze |
| Thermal stability | Stable to ≥ 600 °C | Soft > 70 °C | Stable | Soft > 70 °C |
| UV / yellowing | Inorganic, no yellowing | Possible | Stable | Possible |
| pH sensitivity | Hydrophobic grades pH-independent | Low | Sensitive in waterborne | Low |
BYK / TEGO / Disparlon organobentonite and polyamide-wax thixotropes require pre-activation and hot processing. Fumed silica disperses cold in the existing pigment-grind step.
Recommended HJSIL Grades
Match the surface chemistry of the silica to the polarity of the binder system. Hydrophilic grades for polar solvent and waterborne; hydrophobic grades for solvent-borne and clear coats requiring water resistance.
| Grade | BET (m²/g) | Surface | Primary use |
|---|---|---|---|
| HJSIL-200 | 200 ± 25 | Hydrophilic (silanol) | Standard waterborne paint, polar-solvent inks, gel coat anti-settling |
| HJSIL-300 | 300 ± 30 | Hydrophilic (silanol) | High-thixotropy demand; sealants, adhesives, sag-critical coatings |
| HJSIL-380 | 380 ± 30 | Hydrophilic (silanol) | Maximum thixotropy; cable gel, ink anti-settling, high-PVC paint |
| HJSIL-R272 | 110 ± 20 | Hydrophobic (PDMS-treated) | Solvent-based industrial coatings, water-resistant clear topcoats |
| HJSIL-R274 | 170 ± 20 | Hydrophobic (HMDS-treated) | High-performance solvent coatings, automotive 2K basecoat |
| HJSIL-R110 | 100 ± 20 | Hydrophobic (DCDMS-treated) | Anti-corrosion epoxy primers; outdoor durability |
| HJSIL-R620 | 180 ± 25 | Hydrophobic (octyl-treated) | Aggressive solvent systems, RTV silicone, high-temperature applications |
All grades sourced from a Chinese fumed silica plant, REACH-registered, ISO 9001 + ISO 14001 manufactured. Sample quantities (500 g) ship from China within 5 working days.
Dosage & Processing — Practical Formulation Guidance
Typical loading
- Architectural emulsion paint: 0.3–0.8% on total formulation weight
- Industrial solvent-based coatings: 0.8–1.5%
- RTV sealants and adhesives: 5–12% (acts as both reinforcing filler and thixotrope)
- Unsaturated polyester gel coat: 1.5–2.5%
- Printing inks: 0.5–1.5%
Dispersion requirements
- Peripheral disc speed 10–15 m/s minimum to break primary aggregates — without it, thickening efficiency drops by 40–60% and visible seeds appear in clear systems
- Add silica to the resin / vehicle before pigment grind — silica wets best in low-viscosity polar fluid
- For waterborne systems, pre-wet hydrophobic grades in a co-solvent (glycol ether) before water-phase addition
- Avoid prolonged high-shear post-grind — over-shearing breaks the aggregate skeleton and reduces low-shear viscosity
Order of addition
- Charge resin and solvent to mixer
- Add HJSIL fumed silica slowly under increasing shear (avoid dusting)
- Disperse 15–20 min at 10–15 m/s peripheral speed
- Add pigment, extenders, additives
- Let down to final viscosity
Related East Materials Products
- HJSIL® Fumed Silica Hub — full 8-grade portfolio, BET values, packaging, CoA
- HMMAT® Matting Agents — for high-PVC anti-settling matting paints (matting silica also provides secondary anti-settling)
- Silicone Leveling Agents — pair anti-settling silica with silicone leveling for balanced sag + flow
- Coatings Application Hub — broader coating formulation context
Inquiry
Contact the East Materials technical team for HJSIL grade selection, anti-settling formulation guidance, 500 g samples, TDS, and MSDS via the inquiry form.
Request a quote, COA, or sample
Fill in the form. Our application chemists respond within 24 hours with full COA / MSDS and a sample plan.