Pigment Dispersion: 7 Common Mistakes and How to Fix Them
📅 Updated: May 20, 2015 |
⏱️ Reading time: 9 min |
🏭 By HENGMEI Engineering Team
Poor pigment dispersion is the #1 cause of bad paint quality. It leads to color streaks, low hiding power, rough finish, and paint that settles in the can. In this guide, we'll cover the 7 most common pigment dispersion mistakes and exactly how to fix them.
💡 Quick Tip:
90% of pigment dispersion problems are not about the machine — they're about wrong technique, wrong order of adding materials, or not enough dispersant.
7. Mistake #1: Not Enough Dispersant
❌ The Problem:
You're using too little dispersant. Pigment particles stick back together (re-agglomeration) immediately after dispersion. The paint looks good on the day you make it, but after a week in the can, it's separated and chunky.
✅ The Fix:
Use 2-5% dispersant (based on pigment weight). For difficult pigments like carbon black, you might need up to 8%. Always add the dispersant to the water phase BEFORE adding the pigment.
6. Mistake #2: Adding Pigment Too Fast
❌ The Problem:
You dump all the pigment in at once. It piles up on top of the liquid, doesn't get wetted properly, and you get lumps and poor dispersion.
✅ The Fix:
Add pigment slowly, a little at a time, while the disperser runs at LOW speed (300-500 RPM). Let each batch get fully wetted and incorporated before adding more. This is called "dusting in."
5. Mistake #3: Wrong Speed
❌ The Problem:
You're mixing at too low speed (no dispersion happening) OR too high speed (creating tons of foam and not actually shearing the pigment). The disc just spins on top of the material without creating a proper vortex.
✅ The Fix:
The disperser disc should be at about 1/3 of the liquid depth. Run at 1200-1500 RPM — you should see a good vortex that pulls material down into the disc. If there's no vortex, you either have too much material or not enough power.
4. Mistake #4: Not Enough Mixing Time
❌ The Problem:
You stop mixing as soon as it "looks" mixed. But pigment dispersion takes time — the agglomerates need 15-30 minutes of high-speed shear to break down properly.
✅ The Fix:
Mix for 20-30 minutes at high speed. Then check the fineness with a Hegman gauge. If it's not at your target (usually Hegman 4-5 for regular paint, 7+ for high-quality), keep mixing.
3. Mistake #5: Wrong Order of Adding Materials
❌ The Problem:
You add pigment and resin at the same time, or you add the thickener too early. The order of adding materials is critical for good dispersion.
✅ The Fix:
Always follow this order: water → additives (dispersant, preservative, pH adjuster) → pigment and filler → high-speed dispersion → resin/emulsion → remaining additives (defoamer, thickener, etc.).
2. Mistake #6: Pigment Not Dispersible in Your System
❌ The Problem:
You're using a pigment that's designed for solvent-based systems, but you're making water-based paint. It just won't disperse no matter how long you mix.
✅ The Fix:
Always buy pigments that are recommended for your system (water-based or solvent-based). Ask your pigment supplier for a recommendation. Don't try to save money by buying the cheapest pigment — it'll cost you more in lost batches.
1. Mistake #7: Not Checking the Fineness
❌ The Problem:
You "eyeball" the paint and assume it's done. But you can't tell the difference between 30 microns and 10 microns just by looking. Your finish quality is suffering and you don't know why.
✅ The Fix:
Buy a Hegman gauge (it costs just $20-$50). Every batch, check the fineness. This 5-second check will save you countless bad batches.
Conclusion
Good pigment dispersion isn't magic — it's following the right process. Use enough dispersant, add pigment slowly at low speed, mix long enough at the right speed, follow the correct order of addition, and always check the fineness with a gauge.
Still having dispersion problems? Send us a sample of your material and we'll help you figure out what's going wrong.
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