Determination of flexibility of coating and putty films
1 Scope
This standard specifies the determination of flexibility of coating and putty films by using a flexibility tester, and the flexibility of coating and putty films is expressed by the minimum shaft diameter at which the coating and putty films will not be damaged.
This standard is applicable to the determination of flexibility of coating and putty films.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
GB/T 3186 Paints, varnishes and raw materials for paints and varnishes - Sampling
GB/T 9271 Paints and varnishes - Standard panels for testing
GB/T 9278 Temperatures and humidities for conditioning and testing of paint specimens
GB/T 13452.2 Paints and varnishes - Determination of film thickness
GB/T 20777 Paints and varnishes - Examination and preparation of samples for testing
GB/T 37356 Paints and varnishes - Lighting and procedure for visual assessments of coatings
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
flexibility
capability of coating or putty films to deform along with its substrate without damage
4 Determination of flexibility of coating
4.1 Apparatus
4.1.1 Coating flexibility tester
The coating flexibility tester consists of seven shafts with different diameters or curvature radii, which are fixed on the base. The schematic diagram is shown in Figure 1, and the sectional views of shafts 5, 6 and 7 of the coating flexibility tester are shown in Figure 2. The dimensions of each shaft are as follows:
——Shaft 1: about 35mm in length and mm in diameter φ;
——Shaft 2: about 35mm in length and mm in diameter φ;
——Shaft 3: about 35mm in length and mm in diameter φ;
——Shaft 4: about 35mm in length and mm in diameter φ;
——Shaft 5: about 35mm in length, about 10mm in height, 3mm in thickness and (1.5±0.1)mm in curvature radius R (3mm in diameter φ);
——Shaft 6: about 35mm in length, about 10mm in height, 2mm in thickness and (1.0±0.1)mm in curvature radius R (2mm in diameter φ);
——Shaft 7: about 35mm in length, about 10mm in height, 1mm in thickness and (0.5±0.1)mm in curvature radius R (1mm in diameter φ).
After the coating flexibility tester is assembled, the perpendicularity tolerance between each shaft and the installation plane shall not be greater than 0.1mm.
Key
1——Shaft 1
2——Shaft 2
3——Shaft 3
4——Shaft 4
5——Shaft 5
6——Shaft 6
7——Shaft 7
Figure 1 Schematic diagram for coating flexibility tester
Dimensions in millimeters
Key
1——Sectional view of shaft 5
2——Sectional view of shaft 6
3——Sectional view of shaft 7
Figure 2 Schematic diagram for shafts 5, 6 and 7 of coating flexibility tester
4.1.2 Magnifying glass
4X magnifying glass
4.2 Sample
Take a representative sample of the product to be tested (or of each product in the case of a multi-coat system) as described in GB/T 3186.
Examine and prepare each sample for testing, as described in GB/T 20777.
4.3 Test panels
4.3.1 Substrate
Unless otherwise specified, the substrate is tinplate. The tinplate shall meet the technical requirements of GB/T 9271, and its dimension shall be 120mm× 25mm× (0.20mm ~ 0.30mm).
4.3.2 Treatment of substrate and coating of test panel
Unless otherwise specified, treat each test panel in accordance with GB/T 9271 and then coat the product or system to be tested by the specified method.
4.3.3 Drying and conditioning
Dry (or stove) and cure each coated test panel for the specified time under the specified conditions. Test panels that are not cured under the conditions specified in GB/T 9278, when drying, shall be adjusted for at least 16h under the conditions specified in GB/T 9278 before testing.
4.3.4 Thickness of coating
The thickness of coating shall be specified or agreed. The thickness of coating shall be determined according to one of the determination methods for dry film thickness specified in GB/T 13452.2 and expressed in micrometers (μm) or millimeters (mm).
4.4 Test procedures
4.4.1 Number of tests
Carry out three tests on the same shaft.
4.4.2 Test environment
Unless otherwise specified, test shall be carried out under the test environment specified in GB/T 9278.
4.4.3 Testing
Press the test panel tightly on the shaft of coating flexibility tester (4.1.1) with specified diameter with both hands by keeping the paint film of the test panel facing upwards, and bend the test panel with two thumbs around the shaft at a steady speed within 2s ~ 3s. After bending, the two thumbs shall be symmetrical to the center line of the shaft. Observe the paint film for reticulation, cracks and peeling under natural sunlight or artificial sunlight specified in GB/T 37356. If necessary, use a 4x magnifying glass (4.1.2) for observation. In case of reticulation, crack and peeling within 2mm of the edge of the test panel, it will not be included in the test results.
If the paint film is free from reticulation, crack and peeling upon observation, it will be bent with a shaft of smaller diameter, otherwise, it will be bent with a shaft of larger diameter.
4.5 Expression of results
The results are expressed as the minimum shaft diameter (mm) where no reticulation, crack and peeling are observed in at least two tests.
Foreword i
1 Scope
2 Normative references
3 Terms and definitions
4 Determination of flexibility of coating
5 Determination of flexibility of putty films
6 Test report
