The wooden door surface is treated through various coating processes. The design principle involves selecting the appropriate coating type based on the customer's product requirements and standards, determining the painting process and equipment configuration. From the perspective of surface finish, wooden doors can be categorized into fully sealed and semi-open effects, as well as transparent and solid color finishes.
In the market, most wooden doors feature a fully sealed transparent or colored finish, with polyurethane (PU) paint being the primary choice. This article will focus on the PU-based fully sealed transparent colored finish, discussing its process, advantages, and disadvantages in detail.
The basic process described here is commonly used by most wooden door manufacturers. However, each factory may adjust the process according to their product positioning and materials, leading to many variations. Below, we will explore these derivative processes in more depth.
**1. One-Base Coat (One Side)**
Process: White blank sanding → Water ash filling → Sanding → Spray transparent primer → Sanding → Spray colored transparent topcoat.
Positioning: Low-end products.
Advantages: Simple process, low cost. It covers wood defects effectively when using dark-colored transparent topcoats.
Disadvantages: No permeability, no natural wood texture visible. Poor filling and anti-sag properties, leading to uneven film and reduced aesthetics. Water ash filling is time-consuming, labor-intensive, and dusty.
**2. Two-Base Coats (Including Water Ash Type)**
Process: White blank sanding → Water ash filling → Sanding → Spray transparent primer → Sanding → Spray transparent primer → Sanding → Spray colored transparent topcoat.
Positioning: Low-end products.
Advantages: Slightly better filling and anti-sag properties than one-base coat.
Disadvantages: Still limited permeability and layering. Water ash grinding is difficult and generates a lot of dust.
Suggestion: Replace water ash with colored filler and use color repair oil for minor touch-ups before applying clear topcoat, which improves permeability and texture visibility without significant cost increase.
**3. Three-Base Coats**
Process: White blank polishing → Spray transparent primer → Sanding → Spray transparent primer → Sanding → Spray transparent primer → Sanding → Repair → Light sanding → Spray clear topcoat.
Positioning: High-end products.
Advantages: Excellent permeability, showing natural wood texture clearly. Eliminates water ash application, reducing grinding effort.
Disadvantages: Higher cost, complex process. For deep wood grain, three primers may not fully fill. Fine textures may not show much improvement.
Suggestion: If the material is dark, apply the second primer wet-on-wet. Alternatively, replace spraying with scraping to reduce cost and improve quality.
**4. Base Coloring, Face Repair**
Process: White blank sanding → Seal with solid base coat → Sanding → Rub PU Gres → Spray transparent primer → Sanding → Spray transparent primer → Sanding → Spray transparent primer → Sanding → Color correction → Light sanding → Spray clear topcoat.
Positioning: High-end products.
Advantages: Excellent permeability and 3D effect. Even if the wood texture isn't clear, it can be enhanced through this process.
Disadvantages: High cost and long working time.
Suggestion: If the wood has a beautiful texture, skip the base coloring (e.g., Sapele veneer). Use lighter face color after base coloring to enhance layering and transparency.
From the above analysis, each process has its own strengths and weaknesses. Choosing the right one depends on the actual needs and conditions. A poor choice can lead to wasted costs and unsatisfactory results.
With the growing popularity of the wooden door industry, competition has become fiercer, and profit margins are shrinking. Controlling costs, improving quality, and boosting efficiency have become critical for every manufacturer. While some believe that higher quality means higher costs, this isn’t always true.
Some want the look of the "base coloring, face repair" process but at a lower cost. This is achievable. Some factories now use new materials instead of traditional water ash, offering good filling and performance while achieving a similar effect. These innovations help optimize processes, reduce costs, and increase efficiency.
Initially, brushing was the main method, but spraying improved both efficiency and quality. Yet, other techniques like scraping are also gaining popularity—offering cost savings, better efficiency, and improved results.
Painting, as a science, is constantly evolving. There is always room for improvement and innovation. As technology advances, so does our understanding of how to achieve the best finishes.
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