Composite rock flakes (also called artificial rock sheets or colored composite flakes) are manufactured from inorganic materials, polymer resins, non-ionic additives, and surfactants. The goal is to produce soft, elastic, irregular flakes of about 0.3mm thickness that mimic the colored grains inside natural granite. There are two dominant production methods: the spray method (most common) and the scraping method.
This is the industry-standard process, especially in China's Hebei mining region where most composite flakes are produced.
Raw material formula (typical ratio):
Water-based resin: 60–65 parts | Film-forming agent: 5–8 parts | Natural mineral powder: 30–35 parts
Step 1 — Mixing and Dispersing
All raw materials are added to a mixing bucket in the prescribed order. They are stirred at high speed until a homogeneous blend is achieved. The mixture is then filtered to remove any lumps or impurities.
Step 2 — Spraying and First Drying
The filtered slurry is fed into a spraying machine, which atomizes it into thin, continuous sheets on a conveyor or release surface. These wet sheets immediately enter a drying tunnel. The first drying temperature is controlled between 50°C and 120°C. This step removes most of the water and solidifies the sheet into a semi-rigid film.
Step 3 — Solvent Soaking and Second Drying
The dried sheets are immersed in a solvent for at least 5 minutes (some processes use 80°C for 4 hours). This soaking step is critical — it allows the solvent to penetrate the film, making it pliable and preparing it for the crushing stage. After soaking, the sheets undergo a second drying at 50°C–120°C. The double-drying cycle ensures the flakes have the right balance of flexibility and structural integrity.
Step 4 — Crushing and Screening
The dried sheets are fed into a crusher (hammer mill or similar), which breaks them into irregular fragments of the target sizes: 1–3mm, 1–5mm, 1–8mm, 1–10mm, or 1–12mm. The crushed material is then passed through a screening machine to sort by size. The final product is either wet flakes (flakes suspended in a preservative liquid) or dry flakes (loose irregular flakes with no liquid).
This method is used when higher precision or different resin systems are required.
Raw material formula (typical ratio):
High-elasticity low-tack resin: 25–40 parts | Filler powder: 50–60 parts | Dispersant: 0.1–0.5 parts | Wetting agent: 0.1–0.5 parts | Coupling agent: 0.02–0.1 parts | Release agent: 0.05–5 parts | Anti-stick agent: 0.01–0.1 parts | Thickener: 0.1–1 parts | Water-based color paste: 0.1–2 parts | Water: 5–15 parts
Process:
The fully dispersed slurry is evenly scraped onto a moving base belt using a blade coater. The belt carries the wet film through a hot-air circulation drying oven. Once dried, a brush roller peels the film off the belt. The dried film is then fed into a crusher to break it into irregular pieces, followed by screening to sort by size.
The key advantage of this method is better thickness control and suitability for resins that cannot be easily sprayed.
Some manufacturers, particularly those serving export markets, use an extrusion-based process:
Raw materials (polymer + additives) are selected based on the desired final properties. They are mixed in a high-speed mixer, then fed into an extruder where they are heated and melted. The molten polymer is forced through a die to form a continuous sheet. The sheet is cooled, then cut into flakes of the desired size. Flake size and shape are controlled during the cutting stage. Smaller flakes deliver a smooth finish; larger flakes provide a more textured appearance.
This method offers tighter control over temperature, pressure, and flake dimensions, but it is less common in the Chinese domestic market where spray and scraping dominate.
Double-drying temperature (50°C–120°C): Too low and the flakes stay brittle; too high and the resin degrades. The two-stage drying is what gives composite flakes their signature flexibility.
Solvent soaking time (minimum 5 minutes): This is the step that separates good flakes from bad ones. Insufficient soaking produces flakes that crack during crushing or fail to bond with paint. The optimal absorption rate is 100%–300% (meaning 1g of dry flake absorbs 1–4g of solvent).
Screening precision: Granite imitation requires a three-tier grading system — coarse (10–20 mesh) for the skeleton, medium (20–70 mesh) for the body, fine (80–120 mesh) for the skin. The screening stage must be precise, or the final coating will look flat or chaotic.
The spray method is the dominant production process: mix, spray, dry, soak, dry again, crush, screen. The double-drying and solvent-soaking steps are what make composite flakes soft, elastic, and paintable — qualities that brittle natural rock flakes simply cannot match. The scraping method is a viable alternative for specialty resins, while extrusion is used by some international producers for tighter dimensional control. Regardless of method, the final product must pass physical and chemical tests (strength, hardness, UV resistance, VOC content) before it is released for sale.