MIL-DTL-81772C Detailed Specification: Thinner, Aircraft Coating

A military standard developed by the United States Department of Defense, “MIL-DTL-81772C Detailed specifications: Thinner, aircraft coating”, describes the requirements for four types of thinners to be used in thinning aircraft coatings.

Aircraft coating thinners are available in the following types:

• Type I Polyurethane thinner
• Type II Epoxy thinner
• Type III Acrylic and alkyd thinner
• Type IV Polyurethane and epoxy thinner (low volatile organic compound (VOC) and hazardous air pollutant (HAP) free)

The requirements in this standard are described as follows:

• Materials shall be of the highest quality commercially available and shall be fully suitable for the intended purpose under normal conditions of use. Materials shall not contain chlorinated hydrocarbons or other toxic solvents. Type I and Type IV materials shall be free of water and alcohols which may adversely affect the performance of polyurethane coatings. The use of recycled thinner is prohibited. For prohibited materials (Type IV only), thinner shall not contain hazardous air contaminants.
• The composition must comply with the volume percentages specified in the table given in the standard.
• The thinner must meet the quantitative requirements specified in the table provided in the standard.
• In terms of qualitative requirements, the appearance of the thinner should be clear and free from suspended matter when examined by transmitted light. The odor should be characteristic of the components and should not be noticeable after drying through the filter paper. When spot testing, the thinner should not leave an oily spot or stain on the filter paper.

In terms of verification,

• The conformity audit is carried out for each batch of thinner submitted for audit and consists of testing the thinner properties.
• When sampling for compliance inspection, an inspection lot of finer material consists of a production run produced by a manufacturer under the same processing conditions, without change in the contents or batches of contents, and simultaneously submitted for delivery. In the case of a batch operation, each batch constitutes a batch. Two full containers are randomly selected for each inspection lot. If more than one batch is represented in the shipment, each represented lot is treated as a separate shipment for sampling purposes. The contents of each full container randomly selected for sampling are thoroughly mixed immediately prior to sampling. Each sample is tested to determine compliance with this specification. The selected samples are subjected individually to the tests specified below. If any sample fails one or more of these tests, the lot is rejected.
• Test procedures are provided in the table provided in the standard. Thinner is tested according to this table. The alcohols present and their concentrations are determined according to ASTM D2804-22. Alcohol content is determined by summing the percentages of all alcohols typically present in the individual components, including diacetone alcohol, methyl amyl carbinol, methyl isoamyl carbinol, 1-methoxy-2-propanol, and the alcohols referenced in ASTM D2804-22.

The test procedures are listed in the table provided in the standard as follows:

• Composition
• Water content (Fischer titration) (ASTM D1364-02 Standard test method for water in volatile solvents - Karl Fischer reagent titration method)
• alcohol content
• Nonvolatile content (ASTM D1353-13 Standard test method for nonvolatile matter in volatile solvents for use in paints, lacquers, lakes, and related products)
• Flash point (Setaflash) (ASTM D3278-21 Standard test methods for flash point of liquids using small-scale closed-cup apparatus)
• Appearance (FED-STD-141 Test method 4261 Paint, varnish, lacquer and related materials: inspection, sampling and test methods)
• Odor (ASTM D1296-01 Standard test method for odor of volatile solvents and diluents)
• Spot test (FED-STD-141 Test method 4491 Paint, varnish, lacquer and related materials: inspection, sampling and test methods)
• Volatile organic compounds
• Acidity (ASTM D1613-06 Standard test method for acidity in volatile solvents and chemical intermediates used in paints, varnishes, lacquers, and related products)
• Compound vapor pressure (ASTM D2879-18 Standard test method for vapor pressure-temperature relationship and initial decomposition temperature of liquids by isoteniscope)
• Platinum-Cobalt scale color (ASTM D1209-05 Standard test method for color of clear liquids, platinum-cobalt scale)

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