The flexibility of the coating film, also known as elasticity or bendability, refers to the maximum degree of bending that the coating film coated on a specified metal plate can withstand, that is, the performance of the coating film without damage after being bent with a certain radius of curvature. (mm) said.
Destruction phenomena after bending include peeling, tearing, brittleness, etc. Therefore, the softness of the coating film is not only related to its elasticity, but also related to the adhesion of the coating film, which can also indirectly reflect the adhesion of the coating film.
At present, there are three methods for testing the flexibility of the coating film, namely, the shaft rod Tester, the cylindrical shaft bending Tester and the cone bending Tester.
1) National Standard GB1731-93 "Determination of Coating Film Softness"
It belongs to the shaft rod measuring instrument, and the test regulations are as follows:
General provisions:
(1) Materials and equipment
①Tinplate used to prepare coating samples: 25mmx120mmx(0.2~0.3)m;
②A 4x magnifying glass used to observe the damage degree of the coating film;
③ Flexibility Tester, as shown in Figure 8-11. It is composed of six steel shaft rods (1-6) with different groups and sizes, and is fixed on the base.
(2) Dimensions of shaft rods The length of each shaft rod is 35mm; shaft rod 1: a casing with a diameter of 10mm and an outer diameter of 15mm; shaft rod 2: a cross-sectional area of 5mmx10mm and a radius of curvature of 2.5mm; shaft rod 3 : Cross-sectional area is 4mrnx10mm, radius of curvature is 2.0mm; Shaft 4: Cross-sectional area is 3mmx10mm, radius of curvature is 1.5mm; Shaft 5: Cross-sectional area is 2mmX10mm, radius of curvature is 1.0mm; Shaft 6: Cross-sectional area is 1mmx10mm , The radius of curvature is 0.5mm.
test methods:
First prepare the coating film on the tin plate according to the specifications specified by the product. After the coating film is completely dry, under the condition of constant temperature and humidity, put the coating film face up (the coating film cannot be in contact with the rod shaft), and tighten the sample plate with both hands. Press on the shaft rod with a diameter specified in the product standard, and bend it around the rod axis. After bending, the thumbs of both hands are symmetrical to the center line of the shaft rod. The action should be fast, and it needs to be completed within 2~3 seconds. Each template can be bent 3~4 parts around the shaft rod. After that, use a magnifying glass to observe the damage of the coating film. If there is no reticulation, cracks and peeling, the product index is considered to be qualified. Usually expressed as the diameter of the shaft (mm).
2) Cylindrical shaft bending Tester test
The national standard GB6742-86 "Paint Film Bending Test (Cylindrical Shaft)" specifies the use of the cylindrical shaft bending test method to test the flexibility of the paint film. It is suitable for detecting samples with substrate thickness less than 0.3mm. The dimensions of the cylindrical shafts are 2mm, 3mm, 4mm, 5mm, 6mm, 8mm, 10mm, 12mm, l6mm, 20mm, 25mm and 32mm. Figures 8-12 are the cylindrical shaft bending Tester for paint film.
During the test, insert the model with the paint film facing upwards, close the instrument smoothly, bend the model on the shaft by 180°, and observe whether the paint film is cracked or peeled off. The flexibility of the paint film is expressed by the diameter (mm) of the cylindrical axis.
3) Cone deflection Tester detection method
The national standard GB1l185-89 "Paint film bending test (cone method)" specifies the use of a cone bending Tester. The paint film cone flexometer is shown in Figure 8_13. Its central axis is a cone with a length of 203 mm, a large diameter of 38 mm, and a small diameter of 3.2 mm.
During the test, after inserting and fixing the test sample, turn the upper handle to make the test plate deflect close to the surface of the cone shaft, and observe the minimum diameter (mm) that causes paint film damage, which represents the flexibility of the paint film. The feature of this instrument is that it can use the whole plate test, and there is continuity between the diameters (diameter range 3.2~203mm), which overcomes the disadvantages of discontinuity in the first two methods (need to change the diameter of the test shaft/rod).
