MIL-PRF-85285 Performance Specifications - Coating: Polyurethane, Aircraft and Support Equipment.

The “MIL-PRF-85285 Performance Specifications - Coatings: Polyurethane, Aircraft and Support Equipment” standard, developed by the United States Department of Defense, covers the requirements for polyurethane coatings containing maximum volatile organic compounds (VOCs). The coating is supplied as a kit.

This specification covers the requirements for a high-solids, aliphatic polyurethane coating with the maximum volatile organic compound (VOC) content specified herein. The coating is assembled as a kit.

The coating must have the following characteristics:

• Type I - Aircraft application (maximum VOC content of 420 grams/liter)
• Type II - Ground support equipment application (maximum VOC content of 340 grams/liter)

Coatings completed under this specification must be products authorized by the qualification activity to be listed in the valid qualified products list prior to contract signing. Any change to the formulation of a qualified product, other than those permitted herein, will require re-qualification of the product.

The materials used in the production of these coatings are not limited, provided that the resulting coatings comply with the requirements of this specification.

Where necessary, the manufacturer shall confirm that the coatings supplied under this specification do not have an adverse effect on the health of personnel when used for their intended purposes and under the precautions listed herein, and a material safety data sheet shall be prepared. Questions regarding the effects of these coatings on the health of personnel using them shall be referred by the procurement activity to the relevant health service acting as a consultant.

The polyurethane coating supplied under this specification shall be a kit consisting of Component A, which contains pigmented polyester resins and solvents, and Component B, which contains clear aliphatic isocyanate resins and solvents. Component B shall act as a hardener or curing agent for Component A. The volume mix ratio shall be as specified by the manufacturer.

The coating kit must be supplied in such a way that the mixed coating consists of the minimum volume specified by the supply activity. The total free isocyanate in the mixed coating must not exceed 1,0 percent by weight when tested according to ASTM-D3432. When tested according to ASTM-D3335, no component of the coating must contain cadmium, cadmium compounds, or lead metal or lead compounds in excess of 0,06 percent by weight. When tested according to ASTM-D3718, the coating must not contain chromium.

Looking at all modern US military aircraft, the visible final protective and cosmetic layer is most likely a coating that meets the MIL-PRF-85285 standard. This coating is the US Department of Defense's performance specification for a high-solids, aliphatic polyurethane chemical-resistant coating and is commonly referred to as Type I, II, IV, and now Type VII polyurethane topcoat.

The MIL-PRF-85285 standard is a performance specification that defines a two-component, high-solids (at least 60 percent by volume), chemically cured polyurethane topcoat paint designed primarily for the exterior surfaces of aircraft. The basic requirements of this standard are defined as follows:

• Solid content by volume: At least 60% (some high-quality products exceed 70%).
• Volatile organic compound (VOC) limit: Maximum 340 g/L (Type I and IV) or 420 g/L (older formulations are now largely obsolete).
• Excellent brightness and color retention.
• Fluid resistance (hydraulic fluid bubbling, fuels, oils, de-icing fluids).
• Flexibility (exceeds 3,18 mm mandrel bend even after aging).
• Chemical-resistant coating properties (resistant to penetration and easily decontaminated after exposure to chemical warfare agents).
• It conforms to federal standard 595 colors (most commonly 36320 dark ghost gray, 36375 light ghost gray, 36231 dark gull gray, 35237 medium gray).

The available types are:

• Type I: Standard chemical-resistant polyurethane coating. Primary application: standard exterior aircraft finish. Gloss level: low (maximum 8 GU).
• Type II: A brighter version of Type I. Its primary use was rare today. Brightness level is half brightness.
• Type IV: A low IR (infrared) reflector version of Type I. Primary use is for stealth/low-visibility aircraft (F-35, B-21). Brightness level: very low.
• Type VII: The latest generation, with improved flexibility and durability. Primary application: new programs (NGAD, some helicopter propellers). Brightness level: low brightness.

The latest revision of the MIL-PRF-85285 standard presents the following:

• 40-50% lower volatile organic compound emissions.
• Better flow and spreading (fewer orange peel defects)
• Superior long-lasting gloss retention in harsh UV environments.
• Easier repairs and touch-ups.
• Better resistance to hydraulic fluid bubbling.

Consequently, the MIL-PRF-85285 standard remains the dominant exterior finish paint for nearly all fixed-wing and rotary-wing aircraft in the U.S. military. Its combination of environmental compatibility, durability, chemical resistance, and repairability makes it difficult to replace with another product, even as new nano-coatings and ceramic varnishes appear on the horizon.

For many years, our organization, with its competent and experienced staff, has been understanding the needs of its clients, providing the advanced testing services they require, and assisting in the establishment, implementation, and improvement of management systems. Within this framework, we also provide testing services to businesses in accordance with the "MIL-PRF-85285 Performance characteristics - Coatings: polyurethane, aircraft and support equipment" standard.