Correct glass flake specification requires matching the physical geometry to your coating's Dry Film Thickness (DFT), and matching the chemical treatment to your resin matrix. Failing to align the particle size with the DFT results in surface protrusion; failing to match the silane treatment guarantees premature coating failure.
To achieve an impenetrable barrier, glass flakes must overlap horizontally within the cured film to form a tortuous diffusion path. This guide provides the definitive rules for specifying the right flake grade (size) and surface treatment (coupling agent) based on your system parameters.
1. Specifying for Epoxy Matrices
All amine- or polyamide-cured epoxy systems require the E-grade surface treatment. These flakes are functionalized with KH-550 (3-Aminopropyltriethoxysilane), which chemically bonds the glass to the epoxy's oxirane rings. Do not use untreated flakes in epoxy coatings intended for chemical or marine service.
Thick-Film Linings & Flooring (> 500 μm DFT)
Specification: C-28E (RCF-600)
For heavy-duty concrete flooring, primary containment, and thick-film structural protection, use C-28E. The massive 300–1700 μm platelets deliver the highest aspect ratio available, completely stalling moisture and chemical permeation. Rule: Only use C-28E if your film thickness comfortably exceeds 500 μm.
Mid-Build Primers & Sealers (200–500 μm DFT)
Specification: C-90E (RCF-160T)
For marine superstructures, standard concrete sealers, and intermediate primers, specify C-90E. With a D50 of ≈ 160 μm, these flakes lay perfectly flat within mid-tier film builds without causing surface roughness or roller drag.
2. Specifying for Vinyl-Ester & Polyester Matrices
Vinyl-ester and unsaturated polyester systems require the V-grade surface treatment. Functionalized with KH-560 (3-Glycidoxypropyltrimethoxysilane), the methacrylate groups co-react with the free-radical curing matrix. This prevents thermal shock detachment in high-heat chemical environments.
FGD Absorbers & Extreme Duty (500 μm – 2 mm DFT)
Specification: C-28V (RCF-600)
Flue-gas desulphurisation (FGD) units and hot-acid bulk storage tanks mandate C-28V applied via trowel or plural-spray. The extreme macro-flake geometry is the only structure capable of withstanding prolonged blistering under severe thermal and acidic gradients.
Standard Process Equipment (200–500 μm DFT)
Specification: C-90V (RCF-160)
For standard chemical piping, secondary containment, and localized FRP repairs, specify C-90V. It provides excellent chemical impedance while allowing for a smoother, easily cleanable surface finish than macro-flakes.
3. Specifying for Airless Spray & Thin Films (< 200 μm DFT)
High-solids coatings applied via standard airless-spray equipment require tightly controlled, fine particle geometries to prevent tip occlusion and surface tearing.
- For Anti-Corrosive Primers (< 200 μm DFT): Specify C-150E. This is the industry standard for external pipeline networks, railcars, and structural steel exposed to atmospheric corrosion.
- For Gloss Topcoats & Aerosols (< 150 μm DFT): Specify C-400N. The 15 μm micronic profile ensures flawless atomization and a perfectly smooth aesthetic finish without compromising splash/spill protection.
4. Pigment Substrates & Cosmetic Applications
When glass flake is used purely for its optical properties—as an extender, a pearlescent substrate, or a metallic effect carrier—barrier properties take a back seat to absolute planar smoothness.
- Industrial Effect Pigments: Specify C-150N or C-400N. The untreated (N) surface provides the perfect foundation for controlled metal-oxide vapor deposition (CVD/PVD) used in automotive and aerospace finishes.
- Cosmetics & Personal Care: You must explicitly specify C-400N (Arsenic-Free). Trace heavy metals in standard industrial melts violate dermal-contact regulations. The low-heavy-metal C-400N variant is mandatory for all compliant cosmetics, nail lacquers, and body lotions.
5. Master Engineering Selection Matrix
Use the following matrix to lock in your specification based on matrix chemistry and required film build.
| Resin / Matrix | Typical Profile | Target DFT | Specified Grade | Required Treatment |
|---|---|---|---|---|
| Epoxy | Heavy-duty flooring, thick-film immersion lining | > 500 μm | C-28E | KH-550 (Epoxy) |
| Epoxy | Mid-DFT marine primer, monolithic concrete sealer | 200–500 μm | C-90E | KH-550 (Epoxy) |
| Vinyl-Ester | FGD absorber internals, severe chemical service | 500 μm – 2 mm | C-28V | KH-560 (Methacrylate) |
| Vinyl-Ester | Chemical process piping, medium-DFT tank lining | 200–500 μm | C-90V | KH-560 (Methacrylate) |
| Epoxy | Airless-spray applied pipeline/railcar primer | < 200 μm | C-150E | KH-550 (Epoxy) |
| Thin-Film | High-gloss topcoat, industrial aerosol primer | < 150 μm | C-400N | None |
| Pigment Base | Effect pigment substrate, architectural extender | N/A | C-150N / C-400N | None |
| Cosmetic | Epidermal-contact pigment (Low heavy metal req.) | N/A | C-400N (As < 10 ppm) | None |
Operational FAQs
Why does Dry Film Thickness (DFT) dictate the glass flake grade?+
Glass flakes must align parallel to the substrate to create a tortuous diffusion path. If the flake diameter exceeds the film thickness, the platelets will stand on edge, protrude through the surface, and create porous pathways that accelerate coating failure. Rule of thumb: The targeted DFT must be at least 3× the nominal diameter of the selected glass flake to allow proper parallel stacking.
What happens if I use an untreated (N-grade) flake in an epoxy or vinyl-ester?+
Without silane coupling agents (E-grade or V-grade), the polymer matrix cannot chemically bond to the siliceous surface of the glass. Over time, physical stress, thermal cycling, or chemical permeation will cause interfacial detachment (filler pull-out). This leads to microcracking and a complete collapse of the coating’s barrier properties. Always use E for epoxies and V for vinyl-esters.
How do I specify glass flake for skin-contact cosmetics?+
You must specify C-400N (Arsenic-Free). Standard industrial glass melts contain trace heavy metals (arsenic, lead) that are perfectly safe in industrial coatings but exceed strict dermatological limits for cosmetics. The cosmetic grade C-400N ensures arsenic levels below 10 ppm while providing the micronic 15 μm profile required for smooth, non-abrasive pearlescent pigment substrates.
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