Determination of film resistance to liquid medium performance
The liquid medium resistance of the coating film can be measured according to the method in the national standard GB/T9274-88 "Determination of the resistance of paints and varnishes to liquid medium". This standard is equivalent to the international standard ISO2812-1974 "Paints and varnishes - Determination of resistance to liquid media." This standard specifies the paint film (single coating or composite coating) or paint removal test piece The test methods for resistance to liquid action are divided into three test methods: immersion method, absorbent medium method and drip method. The choice of method will be determined by the requirements of the test material and the resistance of the coating.
(1) Test piece
①Unless otherwise specified or agreed, the test plate shall be tinplate plate (GB252o): 50mrmX120mmX(0.2~0.3)mm, steel plate (GB912) ordinary carbon cold-rolled steel plate: 50mmX120mm>((0.45~0.55)mm, aluminum plate (GB3880LY12 ):50mm><120mmX(1~2)mm.
②Test rod: only applicable to soaking method. One end of the test bar shall be ground back to a radius close to the radius of the bar itself, and the other end shall have a hole or ring. Unless otherwise specified, the bar shall be of steel or aluminum and measure 15 mm x 150 mm.
③Treatment and coating: For the test panel, unless otherwise specified or agreed, it should be carried out in accordance with the provisions of GB/T9271. It is usually better to coat the back of the test panel with an appropriate protective stripper or test paint, and the edges of the test panel should be sealed by a suitable method. For test rods, unless otherwise specified and agreed upon, it shall be carried out in accordance with the provisions of GB/T1727.
(2) Test procedure of method A (soaking method)
① Test liquid material: connect to the test liquid specified in the product standard.
②Test temperature: Unless otherwise specified, the test should be carried out at 23°C to 1-2°C.
③Test Precautions
a. It is better to use the method of immersing a single test piece in the test solution tank, because when using a test solution with high conductivity, there may be an electrolytic effect, which is more necessary.
b. It may be more convenient to immerse the whole piece in the test solution, but the test piece should be of the same nature, so as to ensure that the test solution is not affected by the test piece.
c. The immersed test piece is at least 30mm away from the inner wall of the tank. If several test pieces are immersed in the same tank, the distance between them should be at least 30mm. The test piece is well insulated from its rack.
④ Use a single-phase liquid
Pour a sufficient amount of test solution into an appropriate container to fully or partially (2/3) immerse the specified test piece (the test rod becomes a test plate), and use a suitable support to immerse the test piece in a nearly vertical position. .
b. In order to reduce the loss of the test solution due to evaporation or precipitation, the container should be added
c If air is required to agitate or circulate the liquid, it shall be aerated with a slow stream of degreased air. If there is such a requirement, the test solution should be added at the appropriate time; into distilled water to compensate for the loss of the liquid, the purpose is to maintain the original volume or concentration.
d. When the end of the specified immersion period is reached, if an aqueous solution is used, effectively rinse the test piece with water. If it is a non-aqueous test liquid, use a solvent known to be harmless to the coating to wash it down, use a suitable moisture-absorbing paper or cloth to mark the surface of the test piece, remove the residual liquid, and check the test coating immediately The change of the test piece can be compared with the unsoaked type. If there is a recovery period specified, this inspection and comparison should be repeated after the specified recovery period.
e. If it is necessary to check the corrosion phenomenon of the J-horse material, remove the coating by the specified method.
⑤ Using two-phase liquid
a. The painted test piece is placed on a suitable support so that it can be placed in a suitable container in a nearly vertical orientation. For the test panel, its bottom edge is in a horizontal orientation.
b. Prepare each test solution immediately before use.
c Unless otherwise specified, slowly pour the dense liquid from the inner wall of the container until the test piece (rod or plate) is immersed to a depth of 60 mm. Be careful not to contaminate the test piece above this level.
d. Unless otherwise specified, add the second liquid slowly along the inner wall of the container in the same way until the test piece is completely submerged. Cover the container and let it sit without stirring.
e. After reaching the specified immersion period, take out the test piece from the test solution, gently wipe off the test solution on the surface of the test piece with an appropriate moisture-absorbing paper or cloth, and immediately check the contact parts of the test piece coating and each liquid phase changes. If necessary, compare with similarly prepared unsoaked specimens. If there is a recovery period specified, then after the specified recovery period, repeat the inspection and comparison.
f. During the midway inspection of the test piece, the bar plate does not need to be taken out, otherwise it should be cleaned immediately and the soaking operation should be repeated.
g. If it is necessary to check the corrosion phenomenon of the substrate, remove the coating by the specified method.
(3) Test procedure of method B (using absorbent medium)
① Test material
Hygroscopic plate: It should not be affected by the test solution. In general, laminated cardboard with a thickness of 1.25mm and a diameter of about 25mm can be used.
b. Test solution specified in product standard
c watch glass of appropriate size
②Test temperature: Unless otherwise specified, the test should be carried out at 23°C ± 2°C.
③Procedure: Soak the moisture-absorbing disk into an appropriate amount of test solution, then let the excess liquid drip dry, and place the disk on the test board, so that the disk is evenly distributed, and at least 12mm away from the edge of the test board. Cover the plate with a watch glass with a diameter of about 40 mm and whose curvature does not touch the disc, so that the test plate is properly placed in a windless environment during the test period (the test period should not exceed 7 days). If volatile liquids are used, it may be necessary to replace them with freshly soaked discs (such tests should be recorded in the report).
After the specified test period is reached, remove the plate. If the test liquid is an aqueous solution, it should be cleaned effectively with water. If it is a non-aqueous liquid, it should be cleaned effectively with a known solvent that will not damage the paint film. Absorb the residual liquid with an appropriate absorbent paper or cloth, and check the coating change of the test panel immediately. If there is a recovery period specified, the inspection and comparison should be repeated after the recovery period is reached.
If it is necessary to check the corrosion phenomenon of the substrate, remove the coating according to the prescribed method.
(4) Test procedure of method C (drop method)
①Test material: test liquid according to the product standard.
②Test temperature: Unless otherwise specified, the test should be carried out at 23°C ± 2°C.
③Procedure: place the test plate in a horizontal position, and drop a few drops of test solution on the coating, each drop has a volume of about 0.1mL, and the centers of the drops are at least 20mm apart, and at least 12mm away from the edge of the test plate.
Unless otherwise specified or agreed, the temperature shall be maintained at 23°C ± 2°C, and the test panel shall not be disturbed and fully exposed to the air within the specified time. If specified, cover the test site in this way to prevent excessive filling of the test solution.
After the specified period is reached, if it is an aqueous solution, it should be effectively washed with water, if it is a non-aqueous solution, it should be effectively rinsed with a solution that will not damage the coating, and the change of the coating should be checked immediately.
If it is necessary to check the corrosion phenomenon of the substrate, remove the coating by the specified method.
