The various chemicals that may be generated by the coating film are as follows:
(1) Industrial chemicals
Acids, alkalis, salts, and organic solvents are industrial chemicals. Acids, alkalis, salts and other chemicals can directly cause "dry corrosion" to the metal coated object to corrode the metal, so the resistance of the coating film to the corrosion of these industrial chemicals is very important. It is customary in our country to refer to the prevention of corrosion due to industrial media such as acid, alkali, and salt as anti-corrosion, and to prevent corrosion of natural media (water, sea water, atmosphere, and soil, etc.) corrosion. The anti-corrosion performance of the coating film can be judged by measuring the resistance of the coating film to these industrial media. Organic solvents have a certain erosive effect on the coating film, and the solvent resistance of the coating film can indicate the mechanical strength of the coating film, so it is also an important testing item.
(2) Household chemicals
There are many varieties belonging to this category. According to international habits, it includes water, detergent or soap liquid, soy sauce, cool, oil, alcohol, beverages (such as coffee, tea), fruit juices, condiments (such as mustard, ketchup, etc.) ), cosmetics (such as lipstick), inks and inks, lubricants, pharmaceuticals (such as tincture of iodine), and others. If the coating film meets these items, if it is stained and left traces, or is corroded, it will affect the decoration and protection. Today's household appliances, furniture, etc. pay special attention to the detection of resistance to these chemicals.
Several representative detection methods are introduced below
(1) Acid and alkali resistance
Generally, the test methods for acid resistance and alkali resistance of coating films are basically the same, as stipulated in the national standard GB/T1763-79(89) "Determination of Chemical Resistance of Paint Films", dipping or coating with ordinary low carbon steel rods Brush the tested paint, measure the thickness after drying for 7 days, immerse 2/3 of the area of the test rod in the acid (or alkali) specified in the product standard, and soak at a temperature of 25 °C ± 1 °C. Regularly observe and check the condition of the coating film, and judge the result according to the product standard. In order to speed up, the method of agitation can also be used to make the acid (or alkali) medium flow at a certain speed and increase the temperature at the same time. Or put the test rod in the acid, alkali medium and in the air alternately, because when the test rod is placed in the air, the oxygen can pass through the wet paint film more quickly and penetrate into the test rod to promote the destruction of the paint film.
The national standard GB/T9274-88 "Determination of resistance to liquid media of paints and varnishes" stipulates that in addition to steel rods and aluminum rods, cold-rolled steel plates can also be used, and the test temperature of the immersion method is set at 23 °C ± 2 °C.
The alkali resistance test of architectural coatings is specified in the national standard GB/T9265-88 "Determination of Alkali Resistance of Architectural Coatings". Check the results.
(2) Solvent resistance
Unless otherwise specified by the product, it is usually carried out according to the soaking method in the national standard GB/T9274-88, and soaked at 23°C±2°C for the time specified in the product standard.
In recent years, a method of wiping back and forth with A and B West has been suggested internationally, which can not only measure the strength of the coating film’s resistance to organic solvents, but also judge the mechanical strength of the coating film. For cross-linked coatings, the approximate cross-linking density can be inspected. Condition. The general method is to use a hollow tubular container with a felt tip to wipe one back and forth on the coating film per second, calculate the number of times of back and forth wiping by time, and calculate the exposure of the substrate after wiping off a certain thickness of coating The number of times of wiping back and forth required, for example, 200 or 300 times of wiping back and forth, and the coating film is still not exposed, can indicate that the result is 200+ or 300+.
(3) Resistance to household chemicals
Also known as pollution test. The point picking method in the national standard GB/T9274 is usually used for inspection. It is divided into covering method and open method. Put the test liquid on the surface of the coating film of the prepared test sample, about 0.1mL per sample, cover the liquid with a watch glass, and open the method without covering. At the specified temperature of 23°C ± 2°C, the sample shall not be disturbed within the specified time. After reaching the specified time of the product standard, if it is an aqueous solution, wash it with water, if it is a non-aqueous solution, use a solvent that will not damage the coating film to effectively rinse, and immediately check the change of the coating film. Generally, the grade standard is divided according to the changing situation. Some countries are divided into 11 grades, 10 grades are better, and 0 grades are the worst.
