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When you need a surface finish to be applied to metal or plastic components of your project, you face a choice between two organic (non plated, non oxide based and non converting) surface finish options, each with sub-options that should be considered.
In terms of cosmetic and environmental protective finishing of products, especially in the outdoor equipment, manufacturing and automotive sectors, selecting the right method is important in terms of both performance and aesthetics. Two of the technically simpler and more widely used options are powder coating and paint. Each offers benefits and disadvantages, making them suitable for different applications and environments.
Our presentation here is a comprehensive guide that delves into the similarities and differences between powder coating and paint, examining their application procedures, strengths, limitations, and application-specific suitabilities.
Introducing powder coating and paint
Before detailed discussion of the specifics of these closely related processes, it’s worthwhile to illustrate the core principles that powder coating and painting entail.
Powder coat
Powder coating is a dry finishing process wherein powdered material is applied onto a metal or sometimes plastic surface. This powder consists of fine particles of pigment and resin that are electrostatically charged and sprayed onto the surface. With the surface appropriately covered to an equal thickness with powder, the coated part is heated sufficiently for the powder to melt and form a smooth, durable coating. Powder coating is widely known for its strength, resistance to chipping, and environmental friendliness since it emits fewer volatile organic compounds (VOCs) compared to traditional liquid paints.
Paint
Painting, in contrast, is a liquid-based application of finishing materials that dry (by evaporation) or cure (by polymerization) without any further process. Paint consists of pigments suspended in a solvent or two-part polymerization agent that is applied to the surface using brushes, rollers, or spray. Once the paint is applied, the solvent evaporates or the polymer reacts with its catalysts, leaving a thin, robust and bonded colored film on the surface. Paint can be formulated for different finishes such as matte, satin, or glossy, and it is extremely widely used due to its versatility and ease of application, particularly over large areas that cannot be oven-cured or moved to a paint-booth or controlled environment.
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Application process
The profound differences between powder coating and paint lies in their respective chemical basis, their physical condition at application, their application methods and their post-application processing requirements.
Powder coating process
- Before powder coating, the surface must be effectively cleaned and prepped to be ready for the applied coating to key to the bare surface. This involves degreasing, sandblasting, or applying chemical etchants to remove contaminants/oxides and create a high-energy surface for the powder to adhere.
- The powder is sprayed onto the surface using a spray gun that applies an electrostatic charge to the powder as it is dispensed. The powder particles have a negative charge imposed, while the receiving object is grounded, creating an electrical potential between the powder and part that creates attraction between the two.
- Since most polymers are not conductive, a conductive pre-coat is applied to induce the electrical differential for adhesion in powder coating plastic parts. Alternatively, the parts are heated to make the powder adhere as it is applied.
- After the powder is applied to a metal part, the component is placed in a curing oven at high temperatures (around 350°F to 450°F) for 10 to 30 minutes. The heat causes the powder to melt and flow, forming a continuous film that solidifies into a durable coating as it cools.
- Considerations for powder coating of plastics differ in cure temperature – typically 130°C, limiting the materials that can be coated.
Paint application process
- Similar to powder coating, for painting the surface needs to be cleaned and prepped to allow the paint to adhere with a strong chemical and/or mechanical key. This typically includes sanding, grit blasting, degreasing, and often priming with an etchant paint coat that offers better adhesion for the top-coats.
- Paint is applied using brushes, rollers, or by spraying. Multiple layers may be needed to achieve the desired finish, and inter-coat conditions must be carefully met to ensure intra-coat coupling is maximized.
- After application, the solvent in the paint evaporates or the two-part reactive polymer component polymerizes, leaving a thin, colored film. In most cases this stage is referred to as curing or drying, irrespective of paint chemistry. Depending on the type of paint, this stage can take anywhere from a few hours to several days. Some two-part and even some solvent based paints may require additional curing processes, such as UV or heat treatments, to improve durability.
Durability and performance
Durability of powder coating
Powder coating is highly regarded for its durability. The baked-on finish is generally considered highly resistant to chipping, scratching, fading, and abrasive wear. This makes it a preferred choice for components exposed to harsh environments – outdoor furniture, automotive parts, and industrial equipment.
- The corrosion resistance of powder coatings results from a well-integrated protective barrier action that excludes water and Oxygen, preventing corrosion.
- The UV resistance of powder coatings is typically very high, making them less likely to fade or deteriorate when exposed to sunlight for prolonged periods.
Durability of paint
While paint can also offer a durable finish, it is generally less resistant to flaking and abrasion than powder coatings. The application process and cure toughening of paint makes it more prone to chipping, scratching, and wear. Also the lower temperature process results in less chemically stable material, making it more prone to fading and chemical degradation over time, in harsher conditions.
- The corrosion resistance of paint is good, especially when applied with an etchant primer, but it typically requires more maintenance than powder coatings due to its lower chemical and mechanical resilience.
- The UV resistance is highly variable, as some paints are formulated with UV inhibitors to protect against fading, others are very color and chemistry-vulnerable to UV. Any protection will typically diminish over time as the antioxidant is consumed or the reflective agents lose their capability, requiring repainting or touch-ups.
Environmental impact
The environmental impact of finishing processes is an increasingly important factor in today’s manufacturing landscape. All forms of surface finishing rely on either complex chemistries, aggressive solvents, oil-derived polymers etc so all types carry environmental burdens.
Environmental impact of powder coating
Powder coating is generally considered more environmentally friendly than traditional painting methods:
- Low or zero use of solvents results in low volatile organic compounds (VOCs) being released. Unlike liquid paint, powder coating does not contain solvents, which makes it a cleaner process – however, not all powder coat materials are VOC free.
- The electrostatic aspect of application results in minimal waste and overspray. Overspray that does occur can be collected and reused as uncured and essentially fresh material, further reducing waste.
- While powder coating requires curing at high temperatures, modern ovens are typically energy-efficient, minimizing the energy consumption of the process.
Environmental impact of paint
Traditional liquid paints are often criticized for their negative environmental impact, for a range of reasons:
- Most paints contain solvents that release VOCs during the application and curing. These contribute to air pollution and are typically toxic to the people applying them.
- Two-part paints and moisture cured paints that polymerize at the surface typically contain low to zero VOC, but represent a greater hazard to the persons applying them, as they contain highly reactive chemicals that can have serious health effects.
- Liquid paint is often applied with considerable overspray, and leftover paint – particularly mixed two-pack materials – cannot be reused. Excess paint ends up as waste, contributing to environmental pollution.
- Some paints – particularly the low VOC chemically reactive and polymerizing types – may require additional energy-intensive curing processes – heat curing or UV light.
Aesthetic considerations
Powder coating finishes
Powder coatings can achieve a wide range of textures and finishes, from smooth and glossy to matte or heavily 3D profiled surfaces. The electrostatic application allows for uniform coating, and powder coatings are formulated in any PANTONE color.
- Powder coatings can be formulated to achieve specific aesthetic effects, including metallic, textured, or multi-colored finishes.
- Since powder coating is applied electrostatically, it tends to be more consistent in application thickness, providing a more uniform and smoother finish, when correctly handled.
Paint finishes
Liquid paint also offers a variety of finishes, including matte, satin, and high-gloss options – though typically not the textured surfaces except when a very high solids content is used. Achieving a high quality and uniform finish with paint requires greater operator skill than does powder coating.
- Paint provides a greater variety of finish types, including glossy, pearlescent, color changing, heat reactive and metallic finishes that are more customizable per application.
- A significant advantage of paint is the ability to retouch areas where the finish may have chipped or worn away, which is more difficult with powder coating.
Cost considerations
Powder coating costs
While powder coating is typically more expensive in upfront costs, due to the need for specialized equipment and curing ovens, higher durability and lower application skill make it more cost-effective in total cost of ownership.
- Powder coating typically requires less time and skill in labor, as it involves a single application process, whereas paint may require multiple coats and touch-ups.
- The long service life of powder coatings reduces the need for maintenance, delivering cost savings over the product lifecycle.
Paint costs
Painting requires lower investment upfront, especially for small projects that don’t require specialized equipment or facilities. The long-term maintenance and potential need for touch-ups or repainting can drive up cost of ownership over a product life.
- Painting typically requires more labor-intensive and skilled processes, since multiple coats are needed and attention to process detail requires skill and time. It is particularly costly where intricate surfaces are involved, requiring great care that powder coating largely side-steps.
- Depending on the quality and fundamental chemistry of the paint, material costs vary widely. High-performance paints designed for corrosion resistance or UV protection carry a high price burden.
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Suitability for various applications
Powder coating applications
Powder coating is particularly well-suited for applications where durability and corrosion resistance are central requirements. It is commonly used in industries such as:
- Automotive: Powder coating is used on car frames, wheels, and engine parts due to its ability to withstand harsh conditions.
- Outdoor use: The UV and corrosion resistance of powder coating renders it effective for outdoor furniture and equipment.
- Appliances: Many household appliances, such as refrigerators and washing machines, are powder coated to provide a durable aesthetics that endure through teh entire product life.
Paint applications
Paint remains the go-to choice for applications on large parts/surfaces and where color complexity is required as joined surfaces are differentially treated. The adaptability results from flexibility in finishes. Common paint applications include:
- Home decor: From walls to furniture, paint is the primary finishing method for interior and exterior home projects, particularly as oven cure would be impossible.
- Small-scale work: For smaller items or projects where high-end durability is not required, paint is the more cost-effective and adaptive solution.
- Detail: In applications where fine details or intricate color patterns are required, paint offers great flexibility, allowing layering and complexity in design options.
Maintenance and repair
Powder coating maintenance
Powder-coated surfaces require very little maintenance – and are essentially not amenable to repair other than by complete strip and recoat. These finishes are resistant to most forms of wear, and film integrity/toughness prevents chipping. Good chemical keying is necessary to prevent peeling and spalling. If a powder-coated surface is damaged, it can be difficult to repair, often requiring a full recoat.
Paint maintenance
Painted surfaces require more frequent maintenance, especially in harsh environments or more aggressive treatment, where they are more susceptible to fading, chipping, or peeling. Retouch can be easily applied, but extensive damage may require sanding and repainting of the affected area
Conclusion
Choosing between powder coating and paint for your needs depends on a spectrum of considerations, including the nature of the intended application, the long-term durability requirements, aggressive environmental consideration, and materials/labor budget. Powder coating is the preferred choice for projects requiring a tough, long-lasting, and lower environmental impact finishes, particularly for metal components that are suitable for oven processing. However, paint remains a versatile and cost-effective option for applications where customization and intricate application details are necessary.
Understanding the strengths and weaknesses of each method will serve to ensure that you select the right finishing solution, leading to better performance in your project, aesthetics, and longevity of the final product.
