Aluminium Paste Stability: Leafing Vs Non-Leafing Sedimentation Behavior

In metallic coatings and printing inks, aluminium paste plays a critical role in delivering brightness, reflectivity, and metallic texture. However, one common concern among formulators is sedimentation performance during storage.

A frequently asked technical question is:

Does leafing aluminium paste sediment differently from non-leafing aluminium paste?

The answer lies in surface treatment chemistry, compatibility with resin systems, and flake orientation behavior.

This article explains the structural differences, sedimentation mechanisms, and practical solutions to improve stability.

First: Structural Difference Between Leafing and Non-Leafing Aluminium Paste

Leafing Aluminium Paste

Leafing aluminium paste is treated with hydrophobic fatty acids. During film formation, the aluminium flakes migrate toward the coating surface and align parallel to form a reflective metallic layer.

Characteristics:

• Strong mirror-like metallic effect

• High brightness and opacity

• Hydrophobic surface chemistry

• Limited compatibility with polar systems

Non-Leafing Aluminium Paste

Non-leafing aluminium paste undergoes surface treatment that enhances compatibility with resin systems. The aluminium flakes distribute uniformly throughout the coating film instead of floating to the surface.

Characteristics:

• Uniform metallic effect

• Better intercoat adhesion

• Suitable for automotive and industrial coatings

• Improved compatibility with water-based systems

Second: Why Sedimentation Occurs in Aluminium Paste Systems

Sedimentation is primarily governed by Stokes’ Law:

Sedimentation rate ∝ (particle size² × density difference) / system viscosity

Since aluminium has a density of approximately 2.7 g/cm³, much higher than most resin systems (1.0–1.3 g/cm³), gravitational settling is inevitable without proper rheological support.

Key influencing factors:

1. Particle size (D50)

2. Surface treatment chemistry

3. System viscosity

4. Resin polarity

5. Storage conditions

Third: Sedimentation Behavior Comparison

1. Leafing Aluminium Paste Sedimentation

Leafing aluminium paste often shows:

• Faster bottom sediment formation

• Harder sediment layer over time

• More noticeable separation in low-viscosity systems

Why?

Because hydrophobic treatment reduces interaction between aluminium flakes and the resin matrix. Weak bonding increases the likelihood of particle aggregation and dense sediment formation.

In solvent-based systems, this effect is manageable with proper rheology modifiers. However, in low-viscosity industrial coatings, sedimentation may be more visible.

2. Non-Leafing Aluminium Paste Sedimentation

Non-leafing aluminium paste generally demonstrates:

• Slower sedimentation rate

• Softer sediment layer

• Better re-dispersibility

The reason lies in improved compatibility with binders. The surface-treated aluminium flakes interact more effectively with resin molecules, forming a semi-stable dispersion structure.

Especially in automotive OEM coatings and waterborne systems, non-leafing aluminium paste typically provides superior storage stability.

Fourth: Impact of Application Type

Sedimentation performance varies depending on the coating system.

For water-based aluminium paste systems, non-leafing grades with inorganic passivation treatment are strongly preferred.

Fifth: Practical Solutions to Improve Sedimentation Stability

Regardless of leafing or non-leafing type, the following measures can significantly reduce sedimentation:

Step One: Optimize Viscosity Structure

Introduce thixotropic agents to create a three-dimensional network that suspends aluminium flakes.

Step Two: Select Appropriate Particle Size

Smaller D50 grades reduce sedimentation speed according to Stokes’ Law.

Step Three: Improve Dispersion Process

Avoid high-shear mixing that damages flake structure. Use low-speed incorporation after base resin preparation.

Step Four: Use Surface-Treated Aluminium Paste

Advanced inorganic coating or double-passivation technology improves compatibility and long-term stability.

Sixth: Which Type Should You Choose?

Choose leafing aluminium paste if:

• Maximum brightness and mirror effect are required

• Surface metallic reflection is the main objective

• Solvent-based system is used

Choose non-leafing aluminium paste if:

• Long-term storage stability is critical

• Waterborne coating is used

• Automotive or multi-layer coating systems are involved

• Intercoat adhesion is important

Supply Stability and Manufacturing Capability Matter

Sedimentation behavior is not determined solely by formulation. Manufacturing consistency plays a major role.

High-quality aluminium paste manufacturers ensure:

• Narrow particle size distribution

• Controlled flake thickness

• Stable non-volatile content

• Consistent surface treatment

With large-scale production facilities and strict quality control, stable batch-to-batch performance can be maintained across global supply chains.

Conclusion

In terms of sedimentation performance:

• Leafing aluminium paste may show faster and denser sediment formation due to hydrophobic treatment.

• Non-leafing aluminium paste generally offers better compatibility and softer sediment with improved re-dispersibility.

The final choice should be based on application requirements, coating system type, and desired metallic effect.

Understanding these differences helps coating formulators reduce storage issues, improve metallic appearance consistency, and optimize production efficiency.

If you are evaluating leafing aluminium paste or non-leafing aluminium paste for your next project, our technical team can assist with:

• Grade selection

• Stability testing

• Application trials

• Bulk supply solutions

Contact us today to receive technical data sheets and sample support.