Overview
Phosphor films and quantum dot coatings are key functional layers in modern optoelectronics and display technology. Its performance is highly dependent on the uniformity of the coating, the control of thickness, and the density of the film layer. Precision coating by coating machine is the core process to achieve large-area, high-efficiency, and repeatable preparation. This technology is widely used in solid-state lighting, display backlighting, sensors, and anti-counterfeiting fields, and its process optimization requires comprehensive consideration of material properties, fluid dynamics, and equipment parameters.
Coating process principle
The coating machine spreads a slurry containing phosphor or quantum dots evenly across the surface of the substrate, which is then dried or cured to form a solid film. The uniformity is mainly controlled by the following factors: slurry viscosity (η), surface tension (γ), coating speed (v), clearance between the substrate and the coating head (h), and drying conditions. For Newtonian fluids, in slit extrusion coating, the wet film thickness (hf) can be approximately derived from the conservation of flow:
hf ≈ (Q / v) × k
where Q is the slurry flow rate per unit width, and k is the correction coefficient related to the geometry of the coating head. Quantum dot coatings also need to be strictly isolated from oxygen and water vapor, and are often applied in an inert atmosphere.
Coating machine types and adaptability
According to different coating needs, the coating machine is mainly divided into the following types, and its choice depends on the material properties, substrate type and production scale.
| Coating method | Typical applications and characteristics |
| Slit extrusion coating | It is suitable for high-viscosity slurries, with precise film thickness control, and is often used for large-area uniform film preparation. |
| Scraper coating | It is suitable for rigid substrates or high-solids slurries, and the equipment structure is relatively simple. |
| Rotational coating | It is suitable for small sample areas or R&D stages, with uniform film thickness but low material utilization. |
| Spraying | Suitable for irregular surfaces or flexible substrates, where atomization parameters need to be finely controlled to prevent aggregation. |
Key points of process control that affect coating uniformity
Achieving uniform coating is a systematic project that requires comprehensive control of the front, middle, and back processes.
| Control link | Core considerations |
| Slurry preparation | Particle dispersion, viscosity stability, solvent volatilization rate, defoaming. |
| Coating process | Substrate flatness, tension control, coating head cleanliness, and environmental cleanliness. |
| Dry/cured | Temperature gradient, time, atmosphere control to avoid coffee ring effect or cracking. |
For quantum dot coatings, attention should also be paid to photooxidation and thermal quenching during the coating process, and the process window is usually more stringent.
Performance characterization
The coated film needs to be systematically characterized to evaluate the process effect. Key indicators include film thickness uniformity, surface roughness, fluorescence spectral consistency, and luminescence efficiency. Common problems such as uneven thickness, pinholes, orange peel or fluorescence quenching often stem from slurry agglomeration, rapid drying, or equipment vibration. Real-time feedback through online film thickness monitoring and image analysis system can effectively improve process stability.
Summary
The uniform coating technology of phosphor film and quantum dot coating is a bridge connecting material properties and terminal device performance. With the increasing requirements for display color gamut, lighting efficiency and device life, coating processes are moving towards higher precision, higher efficiency and integration with roll-to-roll flexible manufacturing. A deep understanding of material rheology and process dynamics is the key to achieving industrialization.