Apply at least two coats of the sample on an iron plate with dimensions 90x120 mm or 50x100 mm. After the second layer is dry, coat the edge of the board with paraffin wax, and after 5 days and nights (for air dry samples), immerse the test board in a common acid solution or alkaline solution. After a certain period of time, remove the test plate wells from the solution and rinse them properly with water. The quality of the coating film can be determined according to the appearance of the coating film and mechanical tests.
It is most convenient to carry out the tests not on iron plates but on metal rods in the shape of a wrapper. Depending on the requirements put forward, the test can be carried out at room temperature or at a higher temperature. In the latter case, instead of paraffin, the edges of the panels are coated with Mendeleev's putty or a mixture of high-point bitumen and rosin.
Determination of acid resistance of coating films on wood and plaster
The acid resistance of certain paint materials (such as acid-resistant enamel) has to be tested on wood or plaster.
Experiment on a plank
Apply two layers of the tested color paint (by brush) on a wooden board with a size of 50x100 mm that has been sanded with sandpaper. The drying time between the layers is subject to the technical conditions. After 43 hours after the removal of the second layer, half of the test panel was immersed in sulfuric acid (specific gravity 125,) for storage battery. Dip the edge of the plate into 3~4 minutes of gold in paraffin wax, so that the edge of the plate is pre-coated with paraffin. After soaking in acid for 48 hours, remove the test panel, rinse the wells with water and dry in air. (Related instrument: paint film drying time Tester)
When inspecting the part of the test plate immersed in acid, there should be no damage such as blistering, peeling, cracking and twisting.
The test was repeated by immersing the painted wooden board in sulfuric acid for battery use at 40°C for 8 hours.
experiment on stucco
The wooden boards measuring 300x100 mm were pre-applied with plaster with a composition of 1 volume of lime, 25 volumes of fine sand and 3 volumes of alabaster. Dry the plastered boards at 18~20°C for at least 20 days and nights, and then apply two layers of the tested color paint, the method is the same as the previous section (test on wooden boards). 48 hours after the second coat of paint is applied to the board, spread some small drops of sulfuric acid on the wine cloth. After the 8-hour test, there should be no signs of damage on the coating film. (Related instrument: drying time Recorder)
It is 1 volume lime, 25 volumes fine sand and 3 volumes alabaster. Dry the plastered boards at 18~20°C for at least 20 days and nights, and then apply two layers of the tested color paint, the method is the same as the previous section (test on wooden boards). 48 hours after the second coat of paint is applied to the board, spread some small drops of sulfuric acid on the wine cloth. After the 8-hour test, there should be no signs of damage on the coating film.
Determination of acid resistance of coating film by comprehensive method
This method is better used to test the acid resistance of the coating film of the battery and the like.
Coat an iron plate of a certain size (90>(120mm, 40x120mm)) with two layers of sample; if the coating film is composed of several different materials, first apply the primer and then the finish paint.
After the last layer has dried, the test panels are sequentially immersed in the following test solutions for 24 hours to test:
1) In sulfuric acid for batteries (specific gravity 1,25);
2) in milk of lime
3) In the mixture of seawater (3% gasification passivation solution) and sulfuric acid for batteries;
4) In transformer oil.
Determination of Acid Resistance and Alkali Resistance of Electric Green Coating Film
In the determination of the stability of the green varnish against acid and alkali, a copper rod with a diameter of about 65 mm and a length of 150 mm must be used. One end of the rod was bent into a ring shape, while the straight part of the rod was first polished, washed with ethanol to dry it, and then immersed in the varnish to be tested.
After the varnish dries, the twisted end of the rod is coated with paraffin. When applying paraffin, not only the ring at the end of the rod is covered with paraffin, but also the copper rod itself is removed by about 20 mm. Hang the varnished copper rod with the ring at the rod end in a magnetic dish filled with 25% sulfuric acid solution (the specific gravity of sulfuric acid is about 114). (Related instrument: drying time Tester)
A millivolt meter with a scale of 1,5 volts is connected with one pole to the zinc post on which the copper rod is suspended, and the other pole is connected in turn to the painted but not paraffin-coated part of the copper rod. If the pointer of the millivolt meter is tilted at this time, the copper rod should be removed from the test, because the tilt of the millivolt meter indicates that the stability of the coating film is poor.
After the copper rod was immersed, the inclination of the pointer of the millivoltmeter was checked on each test piece once in 1 hour, and then checked every longer time.
The determination of the alkali resistance of the absolute green paint is the same as that of the acid resistance, except that a 10% copper hydroxide (specific gravity is about 113) solution is used instead of acid. When these measurements are carried out, changes in the surface of the paint film caused by the action of the corresponding reagents can also be seen.
