ASTM D2370 Standard Test Method for Tensile Properties of Organic Coatings

Get Certified ASTM D2370 Testing for Organic Coatings and Compliance 

Mechanical stress, substrate movement, and environmental degradation can occur during the service life of organic coatings. Low tensile characteristics may lead to early cracking, checking, or delamination of the film. ASTM D2370 outlines the standard test methods for measuring tensile strength, elongation, and elastic modulus of free coating films. These tests can be used to ensure material qualities meet engineering requirements, to optimize coating formulations, and to detect performance risks in manufacturing. 

The scope of ASTM D2370 includes:

•  Material type: Organic coatings – tested in free film condition.
• Samples: Coatings for study of coating behavior under environmental stresses.
• Properties evaluated: Elongation at break, Tensile strength, and Stiffness (Modulus of elasticity)
• Testing Method: Tensile testing of free film with a universal testing machine with controlled thickness of the specimen, gage length, and rate of applied load.
• Result: Elongation, tensile strength, and stiffness (modulus of elasticity) in SI units.
• Limitations of tests: Tests may be affected by specimen thickness, specimen preparation method, gage length, rate of loading, response of the tensile testing machine, and type of grips used. These factors need to be carefully controlled to obtain precise comparative results.
• Use Conditions: Tested at a controlled temperature and humidity. The temperature is usually 23°C, and the relative humidity is 50%.
• Applications: Environmental stress behavior of coatings, aging & weathering studies, quality control, choice of materials for protective or decorative coatings.

What are the Uses of ASTM D2370 Testing?

ASTM D2370 testing assists laboratories in evaluating the tensile properties of organic coatings when tested as free films. Results are used in manufacturing, engineering, or quality control applications to characterize material properties, measure durability, or ensure quality. This standard—

• Measures growth, tensile properties, and stiffness of organic coatings
• Understands behavior of coatings under environmental stresses, including aging and weathering.
• Assesses the durability of the coating for protective and decorative purposes.
• Assists with quality control in coating production methods.
• Allows comparison of different coating formulations for specific applications.
• Helps with the choice of materials for mechanical stress coatings.
• Supplies data for research and development of better coating systems.

What Materials Can Be Tested Under ASTM D2370?

ASTM D2370 covers organic coatings that technicians can cast and remove as uniform free films. Tested materials include automotive coatings, industrial maintenance paints, architectural latex coatings, varnishes, lacquers, epoxies, polyurethanes, and flexible polymeric topcoats.  

Why is ASTM D2370 Important?

Thermal changes and structural loads cause natural substrate expansion, contraction, and flex. Insufficient tensile strength or elongation in an applied coating results in internal stresses that cause microcracking, checking, and delamination. ASTM D2370 offers uniform test data for comparing coating toughness and elasticity to determine which coating system to use in the field.  

ASTM D2370 Testing Process and Data Collection

Technicians apply liquid coating formulations to suitable release panels and let the coatings cure completely. The technician gently removes the dried coating as a free film and cuts it into identical rectangular test strips. The technician uses a micrometer to measure thickness along the gauge length. The technician clamps the strip in the grips of a universal tensile testing machine. The system measures the force as a function of the extension with the crosshead moving at a fixed strain rate until the rupture occurs. Technicians throw away specimens that slip or break at the grip jaws. 

Common Challenges and Troubleshooting

Care needs to be taken with sharp dies and specimen handling during die-cutting, as this creates nicks or edge tears, resulting in prematurely low strength values. Line-contact grips with protective gaskets will eliminate jaw breaks, which are common with thin organic films in standard metallic jaws. The viscoelastic behavior is highly sensitive to the ambient humidity; careful environmental control is required in the laboratory. 

• The laboratory reports the value for elongation at break as a percentage, meaning what amount of strain is required for the specimen to break. This property is related to the deformation and flexibility of the coating.
• The tensile strength is the maximum tensile stress that the coating can endure; the laboratory reports this. The higher they are, the more load they can bear.
• The laboratory reports the stiffness (modulus of elasticity), and it is a measure of the resistance the coating offers to elastic deformation. The higher the value, the stiffer the product is.
• Technicians take the thickness of specimens, method of preparation, gage length, rate of load application, and type of grip all into account. These factors need to be carefully controlled to obtain accurate comparative results.
• The laboratory will compare the report to the applicable product specification and/or design requirements, and will include identification of whether or not the coating(s) tested are capable of meeting the applicable criteria.
• Technicians compare the tensile property results with applicable product properties to determine suitability of the coating for the intended use.

Technicians perform the test in a universal testing machine equipped with proper grips, a thickness measuring device, and a temperature-controlled room. The typical crosshead speed is 25 mm/min.

What is the significance of ASTM D2370 testing? 

Technicians measure tensile properties using this technique, and these properties are useful in the study of the response of coatings to environmental stresses, including aging and weathering.

Link to ASTM D2370