Powder coating

Development and Application of Low-Gloss Bending Transfer Powder Coating

Abstract:

The market for low-gloss, highly flexible bending transfer powder coatings is relatively niche, especially in the development of products that achieve a gloss range of 5%-15% while maintaining bending performance. This paper analyzes factors such as powder system composition, resin selection, and the ratio of matting agents, exploring how to develop low-gloss, highly flexible bending transfer powder coatings.

1. Introduction

With the rapid development of the real estate industry in China, powder coatings applied in construction materials have gradually become an important industry segment, especially due to their weather resistance and decorative properties. Hot stamping technology has become the mainstream process in surface treatment of construction materials. However, in practical applications, products such as security doors often have uneven surfaces, making traditional transfer methods (such as vacuum or adhesive transfer) difficult to achieve perfect coverage in patterned areas and increasing labor costs.

To solve these problems, bending transfer powder coatings were developed. This technology integrates spraying and transfer processes before forming, reducing the impact of forces such as shearing, bending, and extrusion during post-processing. Bending transfer powder coatings require good flexibility and adhesion after transfer. Although mature products such as high-gloss, textured, and low-temperature fast-curing powders are available in the market, low-gloss, highly flexible bending powders are still rare. This paper focuses on how to develop powder coatings with low gloss and high flexibility through powder system composition, resin selection, and matting agent choices.

For more insights on different powder coating types, you can explore Powder Coating Selection, Application Techniques, and Material Overview.

2. Experiment

The ACM system determines the shaping curve of the powder. The tip speed of the main mill affects the number and energy of impacts: excessively high speed leads to overall finer particles and a temperature rise; excessively low speed results in coarser particles and increased resistance.

In the classification zone, the gap and speed of the classifier wheel are the direct regulators of the “cut point”: narrowing the gap or increasing the speed both increase the proportion of fine powder and narrow the distribution; widening the gap or reducing the speed allows more coarse particles to pass.

Feed rate needs to be linked with airflow volume to keep the mill load and temperature stable. If feeding is too fast, fineness is dominated more by the main mill, and the distribution depends more heavily on the classifier’s cut.

In the gas–solid separation stage, the sealing of the cyclone and rotary airlock is critical to fine-particle back-mixing and separation efficiency. Once air leakage occurs, fine powder rises significantly and the distribution broadens. Excessive airflow commonly causes more coarse particles to be carried over; insufficient airflow leads to fine-particle accumulation and a temperature rise. On site, damper opening and motor current can be combined to judge system conditions.

To obtain more rounded particle morphology and higher sieving efficiency, it is recommended to cool flakes to below 30 °C before grinding, so as to avoid “saw-tooth edges,” overload, and morphology deterioration. Readers who are focused on flow behavior on aluminum profiles may also refer to Optimizing Flowability in Powder Coating for Aluminum Profiles as a complementary process guide.

3. Results and Discussion

3.1 Selection of Matting Pathways

To achieve low-gloss powder, epoxy acrylate matting resin was selected as the matting agent. This resin effectively mattes the coating while providing a higher Tg, avoiding the appearance issues caused by dry-mix matting agents or wax-based agents. Epoxy acrylate matting resin not only achieves a lower gloss but also ensures the coating’s fineness and leveling properties.

For more on how matting agents affect the coating’s finish, check out Powder Coating Color Measurement and Difference Control.

3.2 Selection of Polyester Resin

The acid value, functionality, and degree of curing of polyester resins directly influence transfer effects. Polyester resins with higher acid values have stronger reactivity, greater crosslinking density, and better transfer effects. We found that polyester A, with a higher acid value, has a greater crosslinking density but can cause cracking during bending. Polyester C, with a lower acid value, combined with epoxy acrylate matting resin, improved crosslinking density and compactness, keeping the transfer process free of sticking to paper, with excellent leveling and smooth surface.

4. Conclusion

Through a comparison of different matting pathways, we ultimately selected epoxy acrylate matting resin and combined it with appropriate polyester resins and aliphatic glycol ester to successfully develop a low-gloss, highly flexible bending transfer powder coating. This powder coating offers excellent appearance, transfer effects, and flexibility, effectively meeting the market demand for low-gloss, highly flexible transfer powder coatings.

Section	Factor	Effect on Powder Coating	Mechanism	Practical Recommendation
Introduction	Gloss Level	Low-gloss, highly flexible bending transfer coating	Gloss level is reduced to 5%-15% with good bending performance	Optimize powder system to balance gloss and flexibility while reducing fines
Materials	Polyester Resin	Resin reactivity and acid value affect transfer quality	High acid value leads to higher reactivity and better transfer but can cause cracking	Choose polyester with higher acid value and adjust for better bending resistance
Materials	Epoxy Acrylate Matting Resin	Reduces gloss and improves leveling	Forms a rough surface for matting, but high styrene can reduce weather resistance	Select moderate styrene content for better matting without compromising durability
Materials	Aliphatic Glycol Ester	Increases coating flexibility	Improves bending performance and overall coating flexibility	Optimize the amount to improve flexibility without increasing gloss
Experiment	Hot Transfer Process	Temperature and time affect transfer quality	Improper temperature or transfer time can lead to poor transfer or sticking	Use optimal conditions of 200°C for 180 seconds for best transfer quality
Results & Discussion	Transfer Bending Performance	Improved by resin and matting agent combination	Resins with proper reactivity and matting agents lead to better bending without cracking	Adjust resin ratio and matting agents to enhance bending and surface smoothness
Conclusion	Final Powder Formulation	Successfully balances gloss, flexibility, and bending performance	Combines epoxy acrylate resin with polyester for a balanced formula	Formulate with the appropriate resin and glycol ester combination to meet flexibility and gloss requirements

1. How does Powder coating gloss affect its bending performance?

Powder coating's gloss level doesn't directly determine its bending performance; instead, the powder's inherent flexibility, determined by its chemistry, is the main factor. However, achieving a low-gloss or matte finish often requires additives that can improve flexibility, making low-gloss powders better for bending applications. In contrast, high-gloss finishes may be associated with coatings that can be less flexible and more prone to cracking, particularly if the gloss is achieved through fillers that increase rigidity.

2. What role does resin selection play in Powder coating bending performance?

Resin selection is crucial for powder coating bending performance because the resin is the primary binder that determines the final coating's flexibility, toughness, and durability. Different resins offer varying properties; for example, specially modified polyesters can achieve excellent flexibility for applications like coil coatings, while more rigid resins like epoxy provide superior chemical resistance but are not as flexible. Choosing a flexible resin formulation is key to preventing cracking or failure when the coated part is bent.

3. How does the choice of matting agent affect the appearance and performance of Powder coating?

Matting agents, such as epoxy acrylate resins, are used in Powder coating to reduce gloss and enhance texture. These resins provide a rougher surface, helping achieve low-gloss finishes while maintaining a smooth and fine coating. The balance of styrene content in the matting resin is crucial, as too much styrene can compromise the coating’s weather resistance.

4. How does Powder coating resin flexibility contribute to bending transfer performance?

Powder coating resin flexibility is crucial for bending transfer performance because it allows the coating to withstand the bending and compressive forces of post-forming processes without cracking or failing. A flexible resin can elongate and deform with the metal substrate, maintaining adhesion and preventing defects like cracking, crazing, or flaking, which is essential for a coating system where the part is formed after being coated.

5. What is the significance of curing conditions in the Powder coating transfer process?

Curing conditions are significant because they ensure proper chemical bonding, resulting in a durable, high-performance, and visually appealing finish. The right temperature and time trigger the powder to melt, flow, and cross-link into a continuous film, but incorrect conditions can lead to a variety of failures like peeling, cracking, and poor adhesion.

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