Powder coating

External Mixing and Internal Extrusion: Exploring Two Production Methods for Texture Powder Coatings

Abstract:

Texture powder coatings are among the more complex categories of powder coatings, including common types such as wrinkle, artistic, hammered, sand, and soft textures. Compared to flat powders, texture powders are more challenging to produce. The texture agent (CAB) is a critical raw material, while equipment, formulation, processing techniques, and operator experience also play a significant role in the final effect. This article provides an in-depth analysis of texture powder design, production methods, and reference formulations, and discusses the advantages and limitations of external mixing and internal extrusion to help optimize production and improve coating performance.

1. Design Concept for Wrinkle Powder

Wrinkle powder, also called orange peel, is a widely distributed and abundant type among texture powders. It was originally used on electrical cabinets and instruments to reduce glare by scattering light, protecting the viewer’s eyes. Later, its use expanded to filing cabinets and security doors. The key requirements for wrinkle powder include strong three-dimensional effect, uniform texture distribution, and thin coatings without exposing the substrate. Texture size varies according to client requirements. Large wrinkle textures are difficult to spray evenly: thin coats reveal the substrate, while thick coats flatten the texture. Medium and small wrinkle textures are easier to spray uniformly.

For large wrinkles, minimal filler is used, combined with coarse particle floaters. Coarse particles create prominent texture, while fine particles reduce exposure and eliminate small holes. Special floaters can also be used. Small wrinkles can be produced using either higher filler content, sometimes over 50% including light calcium carbonate to reduce cost, or lower filler content with additional promotors and fine external floaters. The latter approach increases sprayable area and ensures mechanical performance suitable for pre-coated panels that will be stamped or formed after spraying.

2. External Mixing and Internal Extrusion Methods

Wrinkle powder can be produced via external mixing or internal extrusion. External mixing, also called post-mixing or post-addition, involves adding floaters after extrusion. This method allows flexible adjustment of texture and produces strong three-dimensional effects, making it the predominant method in domestic production. However, the drawback is that recycled powder may have inconsistent texture.

Internal extrusion mixes the texture agent with other raw materials during the extrusion process. This method provides more consistent texture even for recycled powders, though the three-dimensional effect is slightly less pronounced than external mixing. Internal extrusion is also more challenging to perform, requiring precise control over equipment and process parameters.

Other factors in the formulation, such as promotors, organic bentonite, and light calcium carbonate (not recommended for outdoor use), can significantly affect wrinkle powder texture. Using high-softening-point epoxy or polyester resin improves texture formation. Screw design in extrusion equipment is crucial, especially for internal extrusion, with some manufacturers providing dedicated texture screws. Extrusion temperatures can be set 10 degrees lower than for flat powders, and powders may be slightly coarser with a slower secondary milling speed, passing through a 140-mesh screen for optimal texture.

3. Reference Formulations for Wrinkle Powder

Wrinkle powder formulations can include 0.05% 2-methylimidazole as a promotor to enhance the three-dimensional effect and improve cold-spray texture formation. Large-texture base powders with additional floaters can achieve finer wrinkle textures, whereas small-texture base powders are harder to adjust for large wrinkles. For thick workpieces, such as castings, 104B special floaters are recommended, particularly for matte wrinkle powders to ensure clear and uniform texture.

4. Artistic Texture Powder

Artistic texture powders create decorative effects using color or metallic pigments. Common pigments include silver and copper powders, with fewer options for colored pigments. Base powder preparation is similar to wrinkle powders, and both external mixing and internal extrusion can be used. Final pigments are usually added via external mixing to achieve the desired appearance.

Black-base silver-flake powders are common, with either fine strands or large, connected block patterns resembling cracks (sometimes called turtle or fissure textures). Black-base gold-flake powders, using copper-gold powders, include variants like yellow brass, red-bronze, or mixed tones. Red or red-bronze powders may oxidize and darken under high temperature or prolonged exposure, potentially causing quality complaints. In such cases, pearl pigments are often used instead of copper-gold powders. Green-bronze powders are more stable and can be applied directly. Depending on formulation and spraying technique, textures can appear as small sesame-like dots or fine strands.

5. Summary

The production of texture powders involves careful formulation design, raw material selection, equipment control, and operator skill. The quality and consistency of wrinkle powders and artistic texture powders depend on the production method—external mixing or internal extrusion—the selection of floaters, filler ratios, and precise control of processing parameters. Using promotors, light fillers, and special floaters can optimize cost while maintaining decorative and mechanical performance. External mixing offers flexibility and strong three-dimensional effects, suitable for most applications. Internal extrusion provides consistency, especially for thick or large workpieces, though it is more technically challenging. By optimizing formulation, equipment, and process control, manufacturers can produce texture powders with superior decorative quality, stability, and performance to meet diverse client and market demands.

Texture Type	Production Method	Key Ingredients / Additives	Advantages	Limitations / Considerations	Application Notes
Wrinkle Powder (Large)	External Mixing	Coarse floaters, minimal filler	Strong 3D effect, adjustable texture	Recycled powder may show texture variation	Thin coat may reveal substrate; thick coat may flatten texture
Wrinkle Powder (Small)	External Mixing	Fine floaters, promotors, optional filler	Easier to spray thinly, better mechanical performance	Texture less pronounced than large wrinkles	Suitable for pre-coated panels that will be stamped or bent
Wrinkle Powder (Large)	Internal Extrusion	Texture agent mixed with base powder and resin	Stable texture even for recycled powders	Slightly lower 3D effect, more complex production	Better consistency for thick or large workpieces
Wrinkle Powder (Small)	Internal Extrusion	Fine floaters, texture agent, promotors	Consistent small texture, good mechanical properties	Texture not as prominent as external mixing	Requires precise screw design and extrusion control
Artistic Texture Powder	External Mixing	Color pigments, metallic pigments, floaters	Flexible design, high decorative effect	Spray stability can vary; large artistic patterns harder to achieve	Post-mix pigments after base powder preparation
Artistic Texture Powder	Internal Extrusion	Texture agent, base powder, resin, pigments	More consistent texture for large batches	3D effect slightly weaker than external mixing	Suitable for large, thick parts or specialized applications

1. What are the two main production methods for texture powder coatings?

Texture powder coatings can be produced using external mixing, where the texturing agent is added after extrusion, and internal extrusion, where all ingredients, including the texture agent, are mixed before extrusion.

2. What are the advantages of external mixing?

External mixing allows flexible adjustment of texture, creates a strong three-dimensional effect, and is easier to control for decorative patterns. However, the texture of recycled powder may vary.

3. What are the benefits of internal extrusion?

Internal extrusion provides more consistent texture, especially for large batches or thick workpieces. It reduces variation caused by recycled powders but the three-dimensional effect is slightly less pronounced compared to external mixing.

4. How does texture size affect powder formulation?

Large wrinkles require coarse floaters and minimal filler to create prominent textures, while small wrinkles use fine floaters, promotors, and sometimes additional fillers to achieve uniform, consistent textures with good mechanical performance.

5. How are artistic texture powders made and applied?

Artistic powders include color or metallic pigments in addition to the base powder. They can be produced via external mixing or internal extrusion, with pigments often added in the external mixing stage for final decorative effect. Proper control of ingredients and processing ensures stable and visually appealing coatings.

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