FAQ

Powder coatings have long been acclaimed for their environmental friendliness, durability, and efficiency. However, as powder coatings have become increasingly popular, challenges have become increasingly prominent. One of the main challenges is the high curing temperature of traditional powder coatings.

With the continuous advancement of resin chemistry research in global materials science and continuous innovation and breakthroughs in curing technology, low-temperature curing powder coatings have emerged. They are reshaping the development landscape of the powder coatings industry and bringing new vitality to the industry.

1. Key Advantages of Lowering the Curing Temperature of Powder Coatings:

1.1 Energy Saving and Cost Reduction

In the production and curing process of powder coatings, energy consumption accounts for a significant portion of production costs. Extensive industry practice and statistical analysis have shown that a 10°C reduction in curing temperature can reduce energy consumption by approximately 10% throughout the curing process. This data represents enormous energy and cost savings. For large-scale powder coating manufacturers, given the enormous daily curing workload, the energy savings achieved by lowering the curing temperature are considerable. Long-term adherence to low-temperature curing technology can help companies significantly reduce energy procurement costs and improve their economic benefits, while also contributing significantly to alleviating global energy pressures.

1.2 Expanding Substrate Range and Exploiting Market Potential

Traditional high-temperature curing powder coatings, due to temperature limitations, cannot be applied to heat-sensitive materials such as medium-density fiberboard, plastics, and composites. The emergence of low-temperature curing powder coatings has completely overcome this limitation. Medium-density fiberboard, a common material in the furniture manufacturing industry, offers advantages such as uniform texture and excellent processability. The successful application of low-temperature curing powder coatings on this surface provides a higher-quality, more environmentally friendly option for furniture surface treatment, enhancing the quality and competitiveness of furniture products. In the plastics sector, low-temperature curing powder coatings are perfectly suited for applications ranging from everyday plastic appliance housings to plastic automotive parts, resolving the issues of poor adhesion and flaking associated with traditional coatings on plastic substrates. In the composites sector, the application of low-temperature curing powder coatings has also opened up new avenues for surface protection and decoration of composite products, further tapping the market potential of powder coatings in multiple emerging sectors.

1.3 Accelerating Production and Improving Efficiency

Curing time is one of the key factors affecting powder coating production efficiency. Low-temperature curing powder coatings often reduce curing time while lowering curing temperatures. This shortened curing time means that production equipment can cure more batches of product within the same timeframe, directly increasing product output. For companies, increased production can better meet market demand, shorten order lead times, and improve customer satisfaction. Furthermore, increased production efficiency reduces production time and equipment depreciation costs per unit of product, further strengthening the company’s competitive advantage in the market.

1.4 Practicing Sustainable Development and Reducing Environmental Impact

With the increasing global emphasis on environmental protection and the promotion of sustainable development, reducing energy use has become a key responsibility across all industries. Low-temperature curing powder coatings reduce energy consumption by lowering curing temperatures. This reduction in energy consumption directly translates to lower carbon emissions, effectively reducing a company’s carbon footprint. This not only complies with national environmental protection policies and helps companies avoid penalties for environmental violations, but also enhances their social image and brand reputation, placing them in a favorable position in the wave of green development.

2. Key Technologies

2.1 Highly Reactive Resin

As the primary film-forming component of powder coatings, the properties of resin directly determine the coating’s curing characteristics and final coating performance. To achieve low-temperature curing, researchers have developed a variety of highly reactive resins, including modified polyester resins, epoxy resins, and hybrid systems. These highly reactive resins, through molecular structure modification and optimization, possess superior flow and curing properties. They rapidly crosslink at lower temperatures, forming uniform, dense coatings. For example, modified polyester resins incorporate specialized functional groups to enhance their reactivity, enabling efficient curing within a temperature range of 120-150°C while maintaining excellent flexibility, impact resistance, and chemical resistance. Epoxy resins, with their high adhesion and excellent mechanical properties, also find significant application in low-temperature curing. By appropriately combining and modifying different epoxy resins, they can meet the diverse coating performance requirements of various industries.

2.2 Advanced Catalysts

Catalysts play a crucial role as boosters in low-temperature curing powder coatings. They significantly reduce the activation energy of the resin curing reaction, accelerating the curing reaction and ensuring sufficient curing even at low temperatures. Currently, commonly used advanced catalysts primarily include latent hardeners and accelerators, such as imidazole compounds and organotin compounds. Latent hardeners exhibit excellent stability at room temperature and avoid premature reaction with the resin, ensuring the stability of powder coatings during storage and transportation. However, when the temperature rises to a certain level (i.e., the curing temperature), the latent hardener rapidly activates and reacts vigorously with the resin, resulting in rapid curing of the coating. Organotin compounds, as highly effective accelerators, can synergize with the resin and hardener to further accelerate the curing reaction rate and shorten the curing time. They can also improve the coating’s appearance and performance and reduce the occurrence of coating defects.

2.3 UV and IR Curing

In addition to achieving low-temperature curing through optimized resins and catalysts, innovative curing methods are also important approaches, with ultraviolet (UV) and infrared (IR) curing technologies demonstrating particular strength. UV curing utilizes the energy of ultraviolet radiation to induce a rapid chemical reaction between the photosensitive resin and photoinitiator in the coating, resulting in rapid curing of the coating. This curing method eliminates the need to heat the entire workpiece at high temperatures; instead, it irradiates the coating surface with ultraviolet light, significantly reducing energy consumption. It is particularly suitable for heat-sensitive substrates such as medium-density fiberboard and plastics. Infrared curing technology utilizes the thermal effect of infrared radiation to rapidly and evenly heat the coating from the surface to the interior, reaching the curing temperature and completing the cure. Infrared radiation offers advantages such as strong penetration, rapid heating, and uniform temperature distribution. This effectively shortens curing time, improves production efficiency, and reduces thermal damage to the substrate, expanding the application range of powder coatings.

2.4 Optimizing Polymer Architecture

Optimizing polymer architecture is crucial for improving the performance of low-temperature curing powder coatings. Researchers have designed and synthesized semi-crystalline and hyperbranched polymer systems to effectively improve the coating’s melt flow and crosslinking properties at low temperatures. Semi-crystalline polymers form a crystalline structure at a certain temperature. This crystalline structure provides strength and stability at low temperatures, while the amorphous regions possess good fluidity, facilitating leveling and spreading of the coating on the substrate surface, resulting in a smooth, even coating. Hyperbranched polymers have a highly branched molecular structure, resulting in weak intermolecular forces and excellent fluidity. At low temperatures, they can diffuse rapidly and cross-link with other resin molecules to form a three-dimensional network, thereby improving coating properties such as hardness, adhesion, and chemical resistance.

3. Current Achievements and Limitations

3.1 Current Achievements

3.1.1 Epoxy Resin Systems

Significant progress has been made in the low-temperature curing of epoxy resin systems. For example, the curing temperature for textured paint can be reduced to 130°C, with a curing time of just 15 minutes; the curing temperature for high-gloss paint is 140°C, also in 15 minutes. This achievement enables epoxy powder coatings to achieve rapid, low-temperature curing in applications with varying coating appearance requirements, such as certain metal parts and furniture accessories, significantly reducing production energy consumption and costs. However, this system also has significant drawbacks. Its weather resistance is poor. In outdoor environments, exposed to natural factors such as sun, rain, and alternating heat and cold, the coating is prone to discoloration, chalking, and cracking. This limits its widespread use in outdoor products such as outdoor furniture and outdoor building materials.

3.1.2 Polyester/Epoxy Hybrid System

The polyester/epoxy hybrid system combines the advantages of polyester and epoxy resins, offering excellent low-temperature curing performance. Its curing temperature range is between 135°C and 150°C, meeting the requirements of most heat-sensitive substrates. Furthermore, compared to pure epoxy resin systems, the polyester/epoxy hybrid system offers better color retention and yellowing resistance. Over long-term use, the coating maintains its original color and gloss, resisting discoloration or yellowing due to factors such as light and heat. This makes this system promising for applications requiring high color stability, such as appliance housings and automotive interiors.​

3.1.3 Pure Polyester Systems

Pure polyester systems have also achieved some success in low-temperature curing technology. Their curing temperatures can be controlled between 140°C and 160°C, and they exhibit excellent weather resistance, chemical resistance, and mechanical properties, making them valuable for applications in outdoor products, medical devices, and other fields. However, this system still presents challenges in producing low-gloss, flat-finish coatings. Low-gloss coatings require extremely high resin flowability and matting agent dispersibility. Low-temperature curing conditions result in relatively poor resin flowability, making it difficult for the matting agent to disperse evenly. This can lead to surface defects such as uneven gloss, orange peel, and pinholes, compromising the coating’s appearance.

3.2 Limitations

Despite the significant progress achieved with low-temperature curing powder coatings, some limitations remain in practical application, hindering their further promotion and development.

3.2.1 Storage Stability Affected by Reactivity

To achieve low-temperature curing, the resins and catalysts in powder coatings often possess high reactivity. However, this high reactivity also presents storage stability challenges. During room-temperature storage, highly reactive powder coatings are prone to premature crosslinking, leading to powder agglomeration, decreased fluidity, and even loss of curing properties, rendering them unusable. This places higher demands on powder coating storage conditions, requiring them to be stored in a cool, dry, and light-proof environment. This increases storage costs and management difficulties for manufacturers, shortens the shelf life of powder coatings, and creates inconveniences in production planning and inventory management.

3.2.2 Challenges in Surface Leveling

During the low-temperature curing process, the melt viscosity of the powder coating after melting is relatively high due to the low temperature. This high melt viscosity reduces the coating’s ability to flow and spread on the substrate surface, making it difficult to form a smooth, even coating surface. This can lead to poor leveling, such as orange peel texture, pinholes, and craters. These defects not only affect the coating’s appearance but also reduce its protective properties, such as corrosion and impact resistance, impacting the overall quality and service life of the product.

3.2.3 Limited Additive Effectiveness

Additives play a crucial role in powder coatings. For example, matting agents reduce the gloss of the coating to meet various appearance requirements; degassing agents eliminate bubbles generated during the curing process, ensuring the coating’s density. However, under low-temperature curing conditions, the effectiveness of many additives is limited. For matting agents, the high melt viscosity at low temperatures makes it difficult for matting agent particles to disperse and migrate evenly within the coating, hindering their ability to effectively perform their matting function and making it difficult to control the coating’s gloss within the desired range. Furthermore, during low-temperature curing, gases trapped within the coating cannot escape quickly, inhibiting the degassing agent’s activity to a certain extent. This prevents bubbles from being eliminated promptly, leading to defects such as pinholes in the coating and compromising coating performance.

4. Conclusion

Low-temperature curing powder coatings have revolutionized the powder coating industry by significantly reducing curing temperatures without compromising coating performance. They represent a significant step forward in sustainable and efficient surface treatment technology.