The UV roller coating machine primarily consists of a frame, workbench, lifting base, roller wheels, paint supply system, paint return system, and control system. When the rubber roller and steel roller are tightly aligned parallel to each other, a V-shaped space forms between them. As the rollers rotate inward at a constant speed, UV paint within this V-shaped space adheres to the roller surfaces. When furniture workpieces are conveyed forward at a uniform speed on the conveyor belt and make appropriate contact with the rubber roller, the UV paint on the roller is evenly applied to the workpiece surface.
Based on roller rotation direction, roller coating machines are categorized into co-rotating and counter-rotating types. In co-rotating machines, the coating roller rotates in the same direction as the workpiece's advancement. The roller applies pressure to the furniture piece, causing the UV coating to spread under compression. This results in minimal coating volume and a thin finish. Common roller coating methods include: putty rollers, primer rollers, silicone soft primer rollers, and laser rollers for base/topcoats.
Reverse roller coating machines operate with the coating roller rotating in the opposite direction to the substrate's movement. The substrate surface experiences no roller pressure, allowing the coating to spread freely. This method achieves high coating volume and produces thicker layers. Common roller coating methods include: putty roller steel roller sections, primer reverse rollers, etc.
UV Coating Process
The UV roller coating process and equipment layout are determined by the paint finish requirements and desired effect. Common UV roller coating processes include “one color coat, two putty coats, three primer coats, two topcoats” or “one color coat, one putty coat, two primer coats, one color-correcting coat, one topcoat.” Roller coating primarily involves the following six major processes:
1. Sanding of Unfinished Boards
Using a sanding machine to grind and smooth the surface of unfinished wood flooring before coating, eliminating pits and protruding burrs.
2. Application of UV Water-Based Tinting Primer
Applying a water-based coloring primer enhances adhesion strength between subsequent coatings and the board surface while sealing wood oils and deepening grain patterns. Application volume should be controlled between 10–20g/㎡. An automatic rotating brush then evenly distributes the water-based coloring agent into the channel grooves, removing excess to ensure clearer wood grain definition post-coloring. Moisture is removed through 45 seconds of drying in an 80°C hot-air tunnel, followed by final curing in a dual-lamp UV dryer operating at full intensity. After the water-based primer dries, a deburring machine may be added to eliminate raised burrs on the board surface post-drying, thereby improving putty filling effectiveness.
3. UV Putty Application
UV putty is applied via roller coating using a putty machine, involving rubber rollers for application and steel rollers to remove excess putty while pressing it into the wood surface pores. Select filler putty with appropriate viscosity and filling properties based on the board's pore size, along with the number of filling passes, to ensure thorough filling and a smooth coating effect. This reduces primer and topcoat consumption, lowering production costs. Typical application rates range from 30 to 40 g/m?. Curing energy is controlled at 100-150 mJ/cm?, achieving a non-tacky finish with distinct scratch marks. This facilitates sanding while ensuring optimal adhesion for subsequent primer coats.
4. UV Primer Application
Primer application volume is determined by overall film thickness requirements, typically involving 2–3 primer coats at 10–20 g/m? per coat. A leveling device may be added after the final primer coat to enhance surface flatness and reduce sanding volume. For curing between transparent primer coats, use a single-lamp UV dryer with curing energy of 60–80 mJ/cm?. After the final primer coat, employ a dual-lamp UV dryer with curing energy of 100–120 mJ/cm?. For tinting base coats, employ iodine-gallium lamps with enhanced penetration. Cure between coats using a single Ga lamp at 150 mJ/cm?, and for the final coat, use a dual lamp (Ga+Hg) at 450 mJ/cm?.
5. Sanding Primer Application
Sanding primer application levels the aforementioned coatings. This also provides comprehensive treatment for residual imperfections like pinholes in the preceding layers. Sanding ensures surface leveling, while the wear-resistant primer maintains coating integrity. A dual-belt sanding machine with 320-grit and 400-grit belts is recommended. For UV primer + PU topcoat processes, the coating line can proceed directly to automatic PU topcoat spraying after primer application.
6. UV Topcoat Application
The first topcoat layer typically serves for color correction, applied at 7–8 g/m?. To enhance film fullness, achieve roller coating results comparable to spraying, and prevent wrinkling defects at high application rates, a laser roller can be used for the second topcoat application. The laser roller's surface features micro-grooves that disrupt the paint's surface tension. Combined with subsequent leveling equipment, this produces a perfectly smooth coating film. Laser roller application rate: 18–25 g/m?. Curing between topcoats typically employs a single-lamp UV dryer for semi-curing at 80–120 mJ/cm?. Final topcoat undergoes full curing with a triple-lamp UV dryer (Ga+2Hg) at 330–400 mJ/cm?. When the topcoat is white, typically only one roll coat is required at 18–25 g/m?. After infrared leveling, complete curing is achieved using a UV three-lamp dryer (Ga+2Hg) with a curing energy of 330–400 mJ/cm?.