Organic coatings adhesion tests

Organic coatings are commonly evaluated using salt water immersion, salt fog or spray, modified salt exposure tests (e.g., salt fog with added SO2), and various cyclic exposure tests. Humidity exposure and water immersion, and, for many applications, physical resistance tests (adhesion, impact resistance, etc.) are widely used preliminary tests. Standard methods for most of these tests are given in compilations of standard tests such as the Annual Book of ASTM Standards (16). Test methods have been extensively reviewed (e.g., 17-23). 

Goals of Testing and Classification of Test Methods Nonelectrochemical Methods Electrochemical and Electrical Methods Barrier Characteristics of Coatings Adhesion of Organic Coatings Transport Properties of Coatings Other Film Properties Corrosion Resistance of Painted Metals... 

In cathodic delamination, the delamination rate of an organic coating under a cathodic potential depends upon the applied potential, electrolyte solution, and metal substrate (22,25). Cathodic delamination tests were conducted for all three commercial paints. As an example, Figure 5 shows the cathodic delamination plots of control alkyd enamel and water-reducible ISPC coated on bare CRS coupons. Curves Sa and 5b represent delamination area for the control alkyd enamel and the water-reducible ISPC formulation, respectively curves 5c and 5d are the respective plots of delamination current for the two formulations. The delamination test was conducted in a 3% NaCI solution the alkyd coated CRS coupon served as a cathode and was polarized at -I.IV versus a saturated calomel electrode. A significantly slower delamination rate was obtained for the ISPC formula (curve 5b) as compared to the control alkyd enamel (curve 5a). At 44 hours of delamination time, the entire painted area of the working electrode (almost 20 cm x 20 cm) for the control alkyd paint had been delaminated, whereas the delamination area of the water-reducible ISPC was only as little as 1 cm indicating a remarkable coating adhesion improvement for the alkyd ISPC painted on bare CRS coupon. 

Values of work of adhesion for organic coated surfaces from acUieshm tests ... 

Though organic coatings have been long employed to protect metals from corrosion, there are still many unsolved problems in corrosion mechanisms, adhesion, and practical testing. 

Interfacial fracture toughness can be estimated using a number of qualitative methods such as the adhesion tape test, or scratch test. In addition to DCB tests, more quantitative measurements can be made using indentation delamination tests, blister tests, or various interfacial fracture specimens (Section 4). It is important to note that, in the case of organic (viscoelastic) coatings, the tests should be performed at the proper ambient conditions and strain rate. 

As mentioned before, adhesion is one of the major properties of a protective coating. Testing of adhesion seems dierefore of prime importance for the characterization of organic coatings. In practice it is, however, rather difficult to measures the adhesion of organic coatings. 

D 2197-86 Test Method for Adhesion of Organic Coatings by Scrape Adhesion. 

This is a standard test used on most organic coatings. In the case of two piece cans, the coated can is pasteurised in a water bath at 82°C for 30 minutes, to simulate the pasteurisation of beer. The can is cooled, dried and then crosshatched and an adhesive tape is applied to the crosshatched area to confirm that the cured film adheres to the body and base of the can. 

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