Surface Seal® Coated Glass

Surface Seal coated glass is PPG's durable, transparent, water-repellent coated glass that enables windshields to shed rain without the need for windshield wipers. The hydrophobic coated glass is available on PPG glass-faced windshields, providing pilots with enhanced vision during rain conditions. Surface Seal coating system kits have been developed for first-time windshield application or reapplication on the aircraft.

Although plastic surfaces shed water better than untreated glass, glass remains the ideal facing material for aircraft windshields because of its unique characteristics. Glass provides high optical clarity and readily resists abrasion and chemical attack. It's an excellent carrier for conductive films for de-fogging, deicing and antistatic protection; and, in fact, the vast majority of forward-facing aircraft windshields that provide electrically heated anti-icing capability are glass-faced.

But due to the wetting nature of glass, rain removal systems are generally necessary, and prior to the introduction of Surface Seal coated glass, no available system has been optimal. Windshield wipers, usually required during heavy rain conditions, can scratch and damage glass-faced windshields if not properly maintained or if operated on a dry surface. Temporary rain repellent systems are expensive, require periodic maintenance and contents replacement, and add significant weight to the aircraft.

Surface Seal coated glass eliminates these problems. The Surface Seal Coating System changes the wetting and friction characteristics of glass through a molecular bonding of PPG's proprietary coating. Pilot vision is maintained due to the cohesive nature of water and a decreased attraction to the glass surface. Because water beads and rolls off the surface, a large portion of the windshield remains water-free, allowing clear vision through cockpit windows.

Application of the ultra-thin, water-repellent coating not only inhibits surface wetting, but also decreases soil and ice retention without affecting scratch resistance, hardness, strength, color, light reflectance and light transmission.

Once applied, the coating cannot be visibly scratched, and will not crack, craze, peel, or become hazy. Other materials such as sealants will not adhere to its surface.

Water droplets bead and roll off Surface Seal coated glass, above, for enhanced visibility during rain conditions compared with uncoated glass, right.

Performance

Windshield wipers and/or rain repellent systems are generally employed on all critical vision glass-faced windshields because of the basic character of the glass surface itself.

In a rainstorm, raindrops striking the glass flatten out and combine with other droplets to form a nearly continuous film of varying thickness. This non-uniformity causes a viewing distortion by creating a series of constantly changing lenses. Wipers remove these rain-created lenses, restoring the uniform thickness of the windshield necessary for distortion-free vision.

Glass "wetting" from rain is characterized by contact angle, using a precise measurement of how water "beads up" on a surface. When comparing clean, untreated glass, plastic surfaces, and glass treated with a temporary rain repellent, it becomes obvious that clean, uncoated glass exhibits the lowest contact angle. Water does not bead, and does not shed well on uncoated glass.

Plastic surfaces, such as acrylics used for aircraft transparencies, do not wet as much as glass. The contact angle is larger, water tends to bead, and is more easily shed by wind than water drops on uncoated glass. With a contact angle in the range of 50 to 75 degrees, however, plastic surfaces cannot approximate the rain-shedding performance of temporary rain repellents.

Methyl silicone, representative of most commercially available rain repellents, increases the contact angle to approximately 95 degrees, temporarily providing effective water shedding. But such treatments are not durable and must be replaced often.

Surface Seal coated glass exhibits a contact angle of 115 degrees which is greater than any of the other surfaces, demonstrating its highly effective water-shedding capability. In addition, the coating is extremely durable. The glass surface itself has been modified by a chemically bonded molecular layer which is unsurpassed in efficiency and durability.