In liquid crystal display (LCD) and flat panel display (FPD) manufacturing, surface cleanliness is not merely a quality target—it is a fundamental production requirement. A single particle of dust, a residual droplet of cleaning solution, or an uncontrolled electrostatic charge on a glass substrate can propagate defects through photolithography, orientation layer coating, and cell assembly, resulting in dead pixels, uneven illumination, or complete panel failure.
The cleaning and drying stages of LCD glass substrate processing are among the most technically demanding in the production line. Air knife systems have become a critical technology at multiple points in this process, offering the precision, cleanliness, and non-contact performance that LCD manufacturing demands.
This guide explains where and why air knives are used in LCD cleaning lines, what performance characteristics matter most in this application, and how to specify the right air knife system for flat panel display production environments.
LCD panels use glass. The glass is the base. The glass has an ITO coating. This coating carries electricity. The glass goes through many steps. These steps include coating, etching, and printing. The glass also goes through assembly and lamination.
The glass must be very clean at every step. The glass must have no water. The glass must have no oil. The glass must have no dust. The glass must have no static.
If the glass is wet before coating, the parts will not stick. This causes defects like floating resist and blurring. If the glass has dust before assembly, the gaps in the LCD will be wrong. This makes the screen look bad. Every step needs clean glass to work.
Because LCD panels are produced in cleanroom environments, any drying or blow-off method used within the process must itself be compatible with cleanroom contamination control standards—introducing no particles, no chemical residues, and no uncontrolled airflow that might disturb the laminar HEPA-filtered cleanroom environment.
A typical LCD glass substrate cleaning line includes the following stages, with air knife systems integrated at multiple critical points:
Stage 1: Initial Substrate Unpack and Pre-Inspection
Air Knife Function: Particle blow-off from substrate surfaces prior to inspection
ITO glass substrates are unpacked and inspected for surface defects before entering the production process. At this stage, an air knife blow-off removes loose particulates—including glass dust generated during cutting and handling—from both surfaces of the substrate. This initial cleaning reduces the particle load entering subsequent wet cleaning stages and protects sensitive inspection optics from contamination.
Stage 2: Wet Chemical Cleaning and Deionized Water Rinsing
Air Knife Function: Not applicable during wet stages — air knife deployed at wet-to-dry transition
Substrates are cleaned using ultrasonic baths, chemical washing solutions (deionized water, alkaline solutions, and organic solvents as appropriate), and thorough deionized water rinsing. The wet cleaning stages remove organic residues, oils, and ionic contaminants from the ITO surface. Air knives are not active during immersion or spray wash stages but are positioned immediately at the exit of the final rinse section.
Stage 3: Post-Rinse Air Knife Drying
Air Knife Function: Primary drying — complete removal of deionized water from ITO glass surfaces
This is the most critical air knife application in the LCD cleaning line. As the glass substrate exits the final deionized water rinse, it carries a thin film of water across both the ITO coating surface and the underside of the glass. If this moisture is not completely removed before the substrate enters the photoresist coating or orientation agent printing stage, it causes coating defects that propagate through multiple downstream processes. Air knives mounted above and below the conveyor deliver high-velocity laminar airflow across the full substrate width, peeling the water film from both glass surfaces in a single pass. The impingement angle is typically set at 15°–45° from the substrate plane in the direction of conveyor travel, allowing the airstream to shear the water film toward the trailing edge of the glass rather than driving it back across the surface. For large-format glass substrates (Generation 6 and above, used for television panel production), multiple air knives may be arranged in sequence to ensure complete drying across the full substrate length. Precision airflow uniformity across the slot length is essential at this stage: any variation produces dry stripes and wet stripes on the substrate, which appear as coating thickness non-uniformity in the subsequent photoresist step.
Stage 4: Static Elimination Combined with Air Knife Drying
Air Knife Function: Ionized air knife — simultaneous drying and electrostatic charge neutralization
Glass and ITO-coated glass are electrically insulating materials that readily accumulate electrostatic charge during handling, conveyance, and the mechanical action of cleaning brushes. In cleanroom environments, electrostatically charged glass surfaces attract and hold sub-micron airborne particles that would otherwise remain suspended in the HEPA-filtered laminar airflow—particles that are essentially impossible to remove once electrostatically bonded to the substrate surface. Ionizing bars integrated with the air knife discharge stream neutralize the electrostatic charge on the glass surface simultaneously with the drying action. The ionized airstream delivers positive and negative ions to the substrate surface, neutralizing accumulated charge before the glass enters particle-sensitive downstream processes. This combined drying-and-static-elimination function makes ionized air knives a standard component of high-yield LCD cleaning lines.
Stage 5: Inter-Process Blow-Off Before Coating and Printing Stages
Air Knife Function: Particle removal and surface preparation before photoresist, PI, and spacer processes
Before each coating or printing stage—photoresist application, polyimide (PI) orientation layer printing, and spacer spraying—the substrate receives a final air knife blow-off to remove any particles that may have settled on the surface during transport between process stations. These inter-process blow-off steps are typically shorter in duration than the post-rinse drying stage, but are equally important for yield: a single 1 µm particle on the substrate surface at the photoresist stage can produce a pattern defect that fails the panel at end-of-line inspection.
LCD manufacturing imposes more demanding performance requirements on air knife systems than most general industrial applications. The following characteristics are essential:
Airflow Uniformity Across the Full Slot Length
Substrate width in modern LCD production ranges from 600 mm for small-panel generations to over 3,000 mm for Generation 10.5 (used for 65-inch and larger television panels). The air knife must deliver consistent airflow velocity and pressure across the full substrate width—with no velocity variation exceeding a few percent from center to end of the slot. Non-uniformity produces differential drying rates that appear as coating defects in the photolithography process.
Particle-Free Airstream
The airstream exiting the air knife must be free of particles. In cleanroom LCD production, the blower supplying the air knife must be equipped with HEPA or ULPA filtration at the inlet, and the air knife body and internal plenum must be cleaned and validated as particle-free before installation. Any contamination introduced by the air knife system itself negates the purpose of the cleaning line.
Non-Contact Operation
ITO coatings are thin, electrically conductive, and mechanically fragile. Any physical contact with the substrate surface during drying risks micro-scratches that disrupt current flow and create permanent panel defects. Air knife drying is inherently non-contact, making it the only viable high-throughput drying method for coated glass substrates in inline production.
Corrosion Resistance and Chemical Compatibility
LCD cleaning lines use water and chemicals. They use alkaline solutions and solvents. Air knives must not rust from these vapors. Stainless steel is the standard for wet areas. Use Grade 304 or Grade 316. Aluminum air knives work in dry spots. Use aluminum only where chemical exposure is low.
Cleanroom Compatibility
Cleanrooms must stay very clean. Air knife systems must not make dust. They must not shake. They must not shed particles. Blowers must have smooth surfaces. All pipe connections must be sealed. This stops dirty air from getting into the system.
Recommended Air Knife Types for LCD Cleaning
Stainless Steel Air Knives (304/316): These are for drying after rinsing. They do not rust. They work well in cleanrooms. They fit very long glass production lines.
Aluminum Alloy Air Knives: These have a hard coating. Use them to blow off dust in dry zones. They are light. They are easy to mount overhead. Do not use them near chemicals.
Ionized Air Knife Systems: These use a stainless steel body. They have an ion bar attached. They dry the glass and remove static at the same time. This is important for coated glass substrates.
Dual-Sided Configurations: These use two air knives. One is above the conveyor. One is below the conveyor. They dry both sides of the glass in one pass. This makes the production line faster.
Tornado Air Knives: These make spinning air. Use them for the edges of the glass. Use them for parts with complex shapes. They clean spots that flat air cannot reach.
QXY Machinery (Shenzhen Qixingyuan Machinery Equipment Co., Ltd.) is a Shenzhen-based high-tech enterprise integrating R&D, design, production, and sales, with over 10 years of specialized expertise in air knife systems for drying, dust removal, and water-blowing applications across precision manufacturing industries.
QXY Machinery has independently developed a comprehensive range of air knife products—spanning aluminum alloy, stainless steel, titanium alloy, PVC, and water jet variants—in diverse structural configurations and full size specifications. Our products serve both standard production line requirements and custom-engineered solutions for demanding applications including LCD and flat panel display manufacturing, PCB cleaning lines, pharmaceutical production, and food processing.
For LCD and FPD manufacturing engineers specifying air knife systems for glass substrate cleaning lines, QXY Machinery provides precise technical consultation—covering air knife type and material selection, slot gap and impingement angle recommendations, blower sizing, ionization integration, and cleanroom compatibility review—to ensure your cleaning line meets the surface quality requirements of high-yield panel production.
→ Contact QXY Machinery to discuss the right air knife configuration for your LCD cleaning line.
Q: Why is air knife drying better for LCD glass?
A: Spin drying is for small glass. Large glass panels are too heavy to spin. IR drying uses heat. Heat can stress or bend the glass. IR does not remove dust. Air knives do not touch the glass. They fit any width. They work on a conveyor. They remove water and dust at the same time.
Q: What air knife slot gap is best for LCD glass?
A: Use a gap between 0.5 mm and 1.5 mm. A small gap makes the air move faster. Faster air dries the glass better. The gap must be the same across the whole knife. This keeps the drying even. You should check the gap along the whole length to avoid wet spots.
Q: Can one air knife dry both sides of the glass?
A: No. One air knife dries one side. You need two knives to dry both sides. Put one knife above the glass. Put one knife below the glass. This is a dual-sided setup. It dries both sides in one pass. It is the standard for fast production lines.
Q: How does ionization help with LCD glass?
A: Glass gets static electricity very easily. Static pulls dust from the cleanroom air. You cannot blow this dust off with air alone. Ion bars solve this. They remove the static charge. Then the dust does not stick to the glass. The glass stays clean for the next coating step.
Q: What causes watermarks on the glass?
A: Watermarks happen if the air is too slow. They happen if the air is not even. They happen if the air knife is too far from the glass. The water stays on the glass and leaves mineral spots. Use clean water for the final rinse. Fix the gap and the mounting angle to stop watermarks.
Q: Does the air knife material affect the glass surface?
A: The air knife does not touch the glass. But the material still matters. A rusty knife blows dust onto the glass. Stainless steel stays clean. It does not shed particles. High-quality, smooth knives keep the glass safe. Corroded aluminum can cause contamination.
Q: Can air knives handle Gen 10.5 large glass?
A: Yes. We make air knives longer than 3000 mm. These fit Gen 10.5 glass lines. These big knives need big blowers. The design keeps the air even across the whole length. Many factories use several knives in a row for high-speed drying.
Shenzhen Qixingyuan Machinery Equipment Co., LTD.
+86 188 0268 5954
info@airknifecn.com
Building 8, Wanfeng Third Industrial Zone, Xinqiao Street, Bao'an,Shenzhen，Guangdong China
