FAQ

Introduction

Powder coatings have become the preferred method for surface treatment of building materials due to their environmental friendliness, high efficiency, and excellent durability. However, achieving consistent results with powder spraying depends largely on the powder’s flowability. This article explores the key factors influencing powder spray flowability and provides practical recommendations for optimizing the spraying process.

Understanding Powder Flowability

Flowability refers to the ease with which powder particles move and fluidize under air pressure. In powder coatings, flowability directly impacts spray performance and coating quality. Key indicators include:

Angle of repose: The smaller the angle of repose, the better the flowability.

Flow rate (Celiel test): This measures the time it takes for a powder to flow through a funnel.

Key Factors Affecting Flowability

1. Resin Selection

The glass transition temperature (Tg) of the resin is crucial. For powder coatings, the ideal Tg range is 50-65°C. Resins with too high a Tg will reduce flowability due to increased melt viscosity, while resins with too low a Tg will affect powder stability. Resins with a molecular weight between 2.000 and 5.000 offer a balance between performance and processability.

2. Particle Shape and Size

Shape: Irregular or angular particles generally flow better than fibrous or spherical particles.

Size Distribution: The ideal particle size for electrostatic spraying is between 20 and 80 microns. Oversized particles (>90 microns) are prone to surface defects, while ultrafine particles (<10 microns) have poor flow and are susceptible to charging.

3. Fluidized Bed Air Quality

Air pressure and cleanliness significantly affect powder flow. Optimal conditions include:

Air pressure: 0.01–0.1 MPa

Air flow rate: 4–5 m³/h

Humidity Control: Compressed air should be dehumidified to below 15 mg/L to prevent moisture absorption.

Proper air management ensures stable powder flow and prevents defects during extrusion coating.

4. Ambient Humidity

Powder coatings are hygroscopic. Excessive humidity can weaken electrostatics, leading to clumping or clogging, which can cause pinholes and poor adhesion. Maintaining the paint booth’s ambient humidity around 60% and using a dehumidifier can alleviate these problems.

5. Flow Additives

Fumed silica is commonly used to enhance flow and reduce agglomeration (0.1%-0.4%). It coats powder particles, forming a buffer layer that minimizes friction and improves dispersion. However, excessive addition can affect the coating’s appearance and mechanical properties.

Conclusion

With the growing demand for environmentally friendly and aesthetically pleasing aluminum products, optimizing the flow properties of powder coatings has become more important than ever. Continued innovation in material formulation and application technology will drive future developments in this field.