Paint plays a crucial role in the post-processing of wood doors, directly influencing the final appearance and quality of the product. Additionally, paint costs represent one of the largest expenses in the production of wooden doors. There are several types of paints available, including phenolic, alkyd, polyurethane (PU), nitrocellulose, polyester (PE), and others. Among these, phenolic and alkyd paints are largely outdated due to their poor film texture and adhesion. Instead, nitrocellulose, polyester, and PU paints are widely used in the industry.
Nitrocellulose lacquer is popular among hand-decorated wood products because of its ease of application and suitability for manual work. However, it tends to produce thin paint films, which may not provide a smooth finish or satisfactory tactile experience. PU paint, on the other hand, is easy to sand and can save time during the finishing process. Its downside is that the paint film is softer, making it more prone to white shadow dents from minor impacts. Adding at least one layer of PE paint significantly reduces this risk.
PE paint offers a hard film with strong coverage, good transparency, and an excellent ability to showcase the natural grain of the wood. However, it is difficult to polish and requires more time and effort during application. As a result, many manufacturers avoid using PE paint. Currently, about 90% of wooden doors on the market use polyester paint, while only a few manufacturers opt for PU paint.
Both polyester and PU paints typically go through six main processes: color matching, three coats of primer, and two topcoats. Some brands add additional steps like curing and waxing. The cost varies significantly between the types: nitrocellulose lacquer ranges from 8 to 15 yuan per kg, polyester paint from 18 to 28 yuan, and PU paint from 43 to 65 yuan. Due to cost, processing methods, and equipment limitations, polyester paint remains the most commonly used option in the industry.
When choosing paint, there are eight key factors to consider:
1. **Physical Properties**: PU open paint has a thinner film, so its physical properties—such as impact resistance, hardness, and flexibility—are often overlooked. A flexible paint film can withstand temperature changes without cracking. Poor-quality materials may lead to issues like cracking or damage after minor impacts.
2. **Drying Performance**: Open products require multiple steps, so faster drying times are preferable. While it's easier to improve dryness for regular open paint, achieving both fast drying and yellowing resistance—especially for top coatings—is more challenging.
3. **Yellowing Resistance**: For light-colored, natural, or white products, yellowing-resistant paint is essential. Top yellowing-resistant paints are rare due to the difficulty in balancing dryness and resistance.
4. **Clarity**: Transparent products require high clarity to highlight the wood grain. This refers to the compatibility of the paint’s raw materials, not just the visual transparency after application.
5. **Permeability**: Open paint needs to penetrate evenly into the wood surface and internal pores. Poor wettability can cause paint to accumulate around the grain, resulting in an unsatisfactory open effect.
6. **Construction**: High-quality open paint should be applied using standard spraying techniques without requiring special adjustments. If rework is needed, it should not leave visible marks.
7. **Grace**: Grace is an auxiliary product used to enhance wood grain visibility and adjust the depth of the finish. Using mismatched Grace products can lead to peeling or mold. PU open paint should be paired with compatible PU Grace, which requires advanced technology and is only available from a few manufacturers.
8. **Color Accuracy**: Colorants are commonly used, but incorrect formulations can lead to environmental concerns, such as excessive heavy metal content, or poor lightfastness. Some colors may fade over time, causing noticeable color differences from the standard board. It’s best to choose colorants from reputable manufacturers.
By paying attention to these eight aspects, you can ensure the best performance and aesthetics for your wooden door finishes.
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