Uniform modifier coating is critical for consistent quality of surface‑activated ATH powder. Poor coating causes mixed hydrophilic/hydrophobic particles, inconsistent composite mechanical properties, localized blooming and unstable electrical performance for cable-grade ATH. With JSGX continuous vortex modification mill, uniform coating relies on stable feed, full de‑agglomeration, precise modifier atomization, controlled residence time and temperature management.
1. Fully de-agglomerate incoming fine ATH powder before modification
Ultrafine ATH easily forms micro‑agglomerates via hydrogen bonding. If agglomerates enter the modification chamber, modifier only coats the outer surface of clusters while inner particles remain unmodified.
- Keep upstream air classification stable to avoid oversized agglomerates.
- Maintain dryer outlet free moisture at 0.2–0.5%. Higher moisture increases re-agglomeration.
- Use the high-shear first stage rotor of JSGX mill to break micro-clusters before modifier injection.
- Ensure no large lumps from storage or conveying enter the modification system.
2. Precise, interlocked feeding of ATH powder and modifier
Fixed weight ratio between ATH and modifier is the foundation of even coating. Typical dosage: silane 0.4–1.0 wt%, stearic acid 0.6–1.2 wt%.
- Use variable-frequency screw feeder with loss-in-weight control for ATH to eliminate feed fluctuation.
- Meter modifier by precision metering pump, interlocked with powder feed rate. Modifier flow automatically adjusts when ATH feed changes.
- Avoid manual batch dosing, which creates inconsistent local coating.
3. Fine atomization of modifier before mixing with ATH
Large modifier droplets lead to over-coated particle spots and bare particles.
- Heat stearic acid to fully melt before atomization.
- Use fine spray nozzles to turn liquid modifier into tiny mist, injected directly into the high-turbulence vortex zone.
- Periodically inspect and clean nozzles to prevent blockage, which causes uneven spray distribution.
4. Optimize multi-stage vortex shear and particle residence time
JSGX multi-rotor design creates repeated particle collision and turbulent mixing to spread modifier into thin film on each ATH particle.
- Set proper rotor tip speed: too low, insufficient shear and poor dispersion; too high, excessive friction heat risking ATH dehydration.
- Maintain stable negative pressure inside modification chamber to avoid powder short-circuit flow (some powder passes too fast without coating reaction).
- Multi-chamber sequential treatment gives particles repeated mixing opportunities, eliminating under-coated fractions.
5. Strict temperature control during modification
Reaction temperature must stay between 80–110°C and never exceed 110°C.
- This temperature window provides mild energy for bonding between modifier and ATH surface hydroxyl groups, without decomposing ATH crystal water.
- Install temperature sensors in each chamber with interlock alarm. If temperature rises above threshold, reduce feed rate or adjust auxiliary cooling airflow.
- Hot spots inside the mill cause local modifier degradation and uneven coating.
6. Post-process powder cooling and gentle conveying
Right after modification, ATH powder still carries residual heat. Hot powder may trigger modifier migration and uneven redistribution during storage.
- Add a cooling section after modification mill to lower powder temperature before cyclone and bag filter collection.
- Avoid strong secondary shear after coating, which may strip the modifier layer from ATH particle surface.
7. Regular quality monitoring
Use quick on-site and lab tests to verify coating uniformity:
- Water float test: spot check batches to detect uncoated ATH particles.
- Contact angle test: sample different positions of finished powder to check consistency.
- FTIR analysis: confirm uniform chemical bonding of silane on ATH surface.
- Downstream compound test: check tensile, elongation and dielectric properties of polymer blends.
Common mistakes that ruin coating uniformity
- Wet ATH entering modification mill → persistent agglomerates
- Unstable powder feed → variable modifier-to-powder ratio
- Clogged spray nozzles → large modifier droplets
- Too short residence time → incomplete coating reaction
- Local overheating → modifier decomposition and ATH crystal water loss
Uniform coating on ATH particles is achieved by removing micro-agglomerates first, using synchronized loss-in-weight powder feeding and atomized modifier dosing, applying multi-stage high-shear vortex mixing, controlling temperature and residence time inside the JSGX modification mill, plus post-cooling and routine quality checks. This workflow ensures every ATH particle receives consistent modifier coverage, delivering stable hydrophobicity, dispersion and end-product performance for LSZH cables or general plastic fillers.
