1. Water resistance determination
Coating products are often in contact with humid air or moisture in the process of use, and the coating film has a certain degree of water permeability, and with the water permeability of the coating film, swelling, blistering, falling off and other serious adhesion declines The damage phenomenon directly affects the service life of the product. Therefore, the water resistance of the coating film needs to be tested. The detection methods include room temperature method, boiling water method and accelerated water resistance method.
(1) According to the provisions of the national standard GB1733-93 "Determination of water resistance of color paint and varnish - room temperature method", the prepared coating film sample is immersed in water at 40 °C for 240 hours and then taken out, and the surface changes of the coating are observed, and then the adhesion is measured by the grid method, and the water resistance of the coating film is evaluated by the adhesion size. The room temperature immersion method is widely used.
(2) Boiling water method: It is to immerse 2/3 of the coating film sample in boiling distilled water, and after reaching the specified time of the product, take it out to observe the changes on the surface of the coating film and check the adhesion of the coating.
(3) Accelerated water resistance method The advantage of this method is that the measurement time is short, there is no need to wait for a long time (the results can generally be seen on the same day), and the national standard GB5209-85 "color paint, varnish - water resistance determination - water immersion method" is clearly stipulated.
2. Salt spray resistance determination
The coating film is susceptible to swelling by salt spray immersion, and at the same time, it is subject to the penetration of chloride ions and causes corrosion damage. Therefore, a salt spray resistance test is performed on the coating film to determine the corrosion resistance of the coating film.
(1) The national standard GB177l-1991 "Determination of neutral salt spray resistance of color coat and varnish" stipulates that the conditions for the salt spray resistance test of coatings are:
3.5% brine concentration
pH value 6.5~7.2 (related instrument: PH meter)
The temperature inside the chamber is (40±2)°C
Spray salt spray every 45min for 15min, and the humidity in the box is more than 95% when the spraying is stopped
The sedimentation of salt spray was (0.4~1)g/80cm2·h.
At the end of the test, the coating film is rated according to its discoloration, blistering, rusting, and peeling.
(2) Adopt or equivalently adopt IS07253-1984 salt spray resistance test standard or ASTMB-117. (ASTM (ASTM), i.e., continuous spray test method.
Because modern automobiles generally use electrophoretic coating film as an anti-corrosion coating, it has good salt spray resistance. In order to compare the salt spray resistance of the coating film, domestic manufacturers are also using the continuous test method.
The test conditions are: solution pH: 6.5~7.2
Brine concentration: 5%±0.5%
Temperature in the chamber: (35±l)°C
Salt spray sedimentation: (2±l) mLL/80cm2·h; Spray salt spray continuously.
At the end of the test, the coating surface was evaluated according to the blistering, rusting, peeling off and the width of the engraving line.
(3) GM9504P/B method
According to the research of the American Society of Automotive Engineers and the Committee on Protection (SAEACAP) and the American Iron and Steel Institute (AISI), the GM9504P/B method is a better cyclic corrosion test method for automobile exterior corrosion testing. GM9504P/B exposure conditions are:
(4) VDA cycle test
Some car factories in Germany stipulate the following methods:
Electrolyte solution: NaCl = 5%.
Solution acidity: neutral.
The exposure cycle is:
Spray salt spray (NaC1=5%, 35°C) for 4 h.
After 4 hours, the test plate was taken out of the salt spray box, placed in indoor air, and the damp heat test (40 °C, RH>95%) was carried out for l6 hours. Typical exposure time: Repeat the above test for 30 cycles, but when the test plate is closed on Saturday and Sunday, the test plate is placed in an environment of (18~28) °C and RH (40%~60%).
Evaluations will be performed at the end of the test. The erosion at the engraving line is < 2mm (unilateral), and there is no blistering, no rust and no cracking outside the engraving line.
(5) CCT-4 method
Studies by the Society of Automotive Engineers (SAE) and the American Iron and Steel Institute (AISI) suggest that cCT-4 exposure tests correlate better with actual vehicle corrosion. The CCT-4 exposure test conditions are as follows:
Solution: NaCl=5%; The acidity of the solution is not specified. The exposure cycle test is:
Repeat the above test for 50 cycles (1200h). After the test, check the erosion width at the engraving line, the bubbles outside the engraving line, and the corrosion.
3. Resistance to petroleum products
In the process of use, the car will inevitably adhere to the asphalt, leaking gasoline, lubricating oil, grease and brake fluid and other petroleum products on the road, which have a certain dissolving and corrosive effect on the body coating. The gasoline resistance assay is commonly used to determine this performance.
The national standard GBl734-93 "Determination of Gasoline Resistance of Paint Film" stipulates that the gasoline resistance of the coating film can be determined by the gasoline immersion method and the gasoline pouring method. The specific measurement methods are:
(1) Materials and instruments
Tinplate: 50X120X(0.2~0.3)mm;
Weight: 500g, diameter 45±1mm, flat bottom; Rubber solvent gasoline, SY1027-77;
No. 75 aviation gasoline: SY1001-77;
Glass tank for gasoline: Figure 8-33 shows.
(2) Measurement method
(1) Gasoline immersion method: according to GB1727-79 "general preparation method of paint film", the paint film is prepared on three tinplate plates. After the paint film is dry, 2/3 of the area of the paint sample is immersed in gasoline at a temperature of 25±l°C according to the standard. After reaching the soaking requirements of the product standard, take out the sample, blot it with filter paper, and check the surface of the paint film under the condition of constant temperature and humidity, such as wrinkles, blistering, peeling, softening, discoloration, and loss of light. Whether it is qualified or not is qualified according to the product standard, and no less than two samples meet the product standard requirements; However, the part with a width of 5mn on or below the immersion boundary is not judged as the end point.
(2) pouring gasoline method: the same method as the previous method to prepare paint film on three tinplate plates. After the paint film is dry, under the condition of constant temperature and humidity, the painted sample is poured with 5mL of gasoline according to the product standard, and immediately makes it full of the sample, and the sample is placed at a 45 ° angle for 30min and then flattened, two layers of gauze are placed on the paint film, and then a 500g weight is placed to keep it for 1min and then removed, the gauze should not stick to the paint film, and then tap a few times with your fingers on the back of the sample, and the gauze should be able to fall freely.
Note: (1) For each test, the gasoline should be replaced again.
(2) The organic red paint sample and the light paint sample should be separated during the test.
(3) Vehicle gasoline (after the resteaming hall should comply with the provisions of rubber solvent oil Sn027-77, the appearance is colorless and transparent) can replace rubber solvent gasoline.
4. Acid rain resistance test of coating film
With the development of industry and the increase in the number of automobiles, the acid gases emitted into the air have increased significantly, and they are easy to combine with the moisture in the air to form acid rain, so the body surface coating needs to be tested for acid rain. The acid rain cycle test proposed by the Japan Automotive Standardization Organization (JAS0) is as follows:
Solution composition: NaCl=5%; HNO3:0.12%; H2S04:0.17%; NaOH:0.228%。
Solution pH: 3.5.
Exposure cycle: spray at 35°C for 2h; Dry at 60°C, humidity < 30% for 4h, humidity at 50°C, humidity > 95% for 2h.
The conversion time of different test cycles: spraying salt spray to drying within 30min; Dry to moisture within 15min; Wet to spray salt spray within 30min.
5. Chemical resistance test of coating film
In the process of use, the coating film is often damaged by the "dry corrosion" of industrial chemicals such as acids, alkalis, salts and organic solvents, and the ability to resist this "dry corrosion" is chemical resistance.
The specific testing methods can be tested according to GBl763-79 (confirmed in 1989) "Determination of chemical resistance of paint film", GB9274-88 "Determination of liquid medium resistance of color paint and varnish" and other standards.
