Internal stress paint films

D.Y. Perera, Internal stress and film formation in emulsion paints, J. Oil Colour Chem. As. 68 (1985)... 

The quench is necessary for all basis materials, conversion coatings, and paint formulations. A coil that is rewound when too warm will develop internal and external stresses, causing a possible degradation of the appearance of the paint film and of the forming properties of the coil. The volume of water used in the quench often has the largest flow rate of all of the coil-coating processes. However, the water is often circulated to a cooling tower for heat dissipation and reuse. 

Paint service properties and adhesion includes a discussion of internal stress in paint films. 

The pull-off method has been standardized internationally. This test utilizes stress patterns caused by loads acting either normal or parallel to the plane of contact. A stud, normally made of steel, is glued with the coating and is subjected to axial tension until separation of the paint film occurs. This determines the maximum tensile stress that is possible at the interface. 

The protective ability of a coating is also dependent upon its thickness. Thicker coatings provide improved protection. However, single thick paint films tend to crack due to internal stress. When long term protection is required, multilayer paint coating systems are applied. 

Fillers are very important in polyester coatings because these resins are unnsually prone to build up of internal stresses. The stresses in cured paint films arise for two reasons shrinkage during cure and a high coefficient of thermal expansion. 

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