Introduction to the variety of weather resistance powder coatings

3.2.7 fluorocarbon powder coatings

Although thermoplastic fluorocarbon resin coating (PVdF) has a very good weather resistance, but the production process of pigment dispersion, coating surface gloss is low, must be high temperature baking, so that the application is limited.

In recent years, the existing manufacturers have made of fluorine resin solvent based coatings for high-rise building materials (ie, is now the prevalence of fluorocarbon paint).

The main film forming material of the industrial thermosetting fluorine resin powder is the hydroxyl containing fluorine resin and the blocking isocyanate curing agent, which can be made into transparent powder and has good storage property. Has a good comprehensive mechanical properties, acid rain, ozone, UV, etc.. Outdoor service life long, up to 30 years.

Factors affecting the weather resistance of powder coatings

Powder coating is a new type of material based on petroleum and chemical industry, which is composed of low molecular weight resin, auxiliary agent, pigment and filler, and has certain appearance, luster, color after curing under certain conditions. When an object, such as air conditioner casing, building material by powder coating in the outdoor environment, the film inevitably influenced by various factors such as intrusion, sunlight, rain erosion, after a period of time, the film will be a series of changes, can be expressed as gloss drops, color dim, the rust or crack surface, slightly powder...... .

Once the powder coating is solidified, the low molecular resin is turned into a super high molecular weight polymer by chemical crosslinking, so that it has a series of properties such as elasticity, toughness, chemical resistance and so on.

From a microscopic point of view, the film is like a three-dimensional cross network structure, the main framework is the formation of polymer cross-linking resin, in the middle of the frame is filled with such as pigment, filler particles and other coatings. After a long period of time, the coating surface will be "spot corrosion", gradually "powder". Studies show that the powder coating of the powder mainly from the beginning of the pigment particles, especially in the place where the pigment into the group, which is a photochemical process.

Under the action of heat, oxygen and light, the polymer is aging by free radical process. The network polymer in the coating is connected by a variety of chemical bonds through a variety of molecular chain, these chemical bonds, some of the hydrogen, oxygen, double bond, etc., they are very lively, easy to lose hydrogen, the formation of free radicals. Free radicals and oxygen into a radical, and then react with other molecules into a hydrogen peroxide, making the polymer chain rupture, paint that is the beginning of aging, and the emergence of gloss, powder, and so on.

There are many factors that affect the service life of coating, and almost have: the ultraviolet (especially the wavelength is close to 313nm), humidity, ozone, high temperature, acid rain, industrial waste gas, etc..

How to test the weather resistance of powder coatings

Weather resistance test and evaluation of paint, there must be a sufficient basis, not created.

Now the international popularization of two kinds of methods: natural exposure and artificial accelerated aging test, and stressed that the two kinds of test methods should be combined, comprehensive consideration, to draw more reliable conclusions.

In the U.S. state of Florida natural exposure exposure as the standard, the southernmost tip of the state in the United States, the surrounding sea, year-round sunshine and strong, moisture and salt content is very high in the air, relative to other places on earth, except a few out of extreme weather events, the natural conditions for paint is very harsh the environment.

The standard template prepared, insert the exposure frame, south of 5 degrees or 45 degrees, periodic testing of film gloss and color change, and record. In general, the curve of the coating gloss and color change can be drawn after the test is finished.

Natural exposure is direct and accurate, credible data, but the test cycle is too long, can not guide the scientific research and production quickly, so most of the weathering test are used to complete the artificial accelerated aging.

Artificial accelerated aging test is to simulate the natural conditions, such as the control of certain temperature, humidity and rainfall cycle, and the light of different wavelengths (simulated sunlight), short test period, usually only 200~1000h, will soon be able to draw a conclusion.

Artificial accelerated aging test using a variety of light sources, a common xenon arc solar light and fluorescent UV, carbon arc lamp etc..

Chinese GB for two standard coating aging test: GB/T1865-1997 "artificial weathering and exposure to artificial radiation (xenon arc radiation filtration)" (see Appendix A) and GB/T16585-1996 "vulcanized rubber artificial weathering (Fluorescent UV lamp) test method". These two methods can detect the durability of powder coatings, xenon arc lamp radiation light moderate, more suitable for paints, plastics, long test cycle. The fluorescent UV lamp has good acceleration, it is suitable for rapid detection and wide selection of ultraviolet wavelength, which can meet the requirements of various detection.

It also speeds up the natural exposure test, such as the EMMAQUA test (in Arizona), to strengthen the use of solar light reflector special, and combined with the spray cycle and temperature control. According to the observation, the law and Florida exposure correlated well with the aging speed of 5~6 times.

It should be noted that any accelerated aging test can only be used as a reference, can not be superstitious test results. These tests are only simulated natural conditions, and the actual conditions are different, the results of the aging test and the actual use of the results are very different. So the weather resistance of powder coatings must be based on the actual use of the effect of.

Appendix 1: paint film aging (manual acceleration) method (1865-1997 GB/T)

This standard applies to the weather resistance of the coating. Artificial accelerated weathering test box is used.

2 test conditions

2.1 temperature

Studio air temperature 45 + 2 degrees C.

2.2 relative humidity

Studio air relative humidity 65%-75%.

2.3 rainfall cycle

For 12 min/h.

3 test procedure

3.1 according to the product standards, the selection of primer and matching primer < < heat resistance, salt spray, aging paint film preparation method > > (GB/T 1765) preparation of sample.

3.2 test two samples of each variety, before the test, record the original state.

3.3 the sample into the test plate clamp frame, inserted into the chamber on a drum, start the machine according to the operating rules, test.

3.4 start every 48h down check sample, 192h after every 96h check every time, every time the model, the next position swap.

4 sample inspection and rating

Take out, with a towel on the back of the water heads in test bench to dry, immediately press < film aging test rating method "(GB/T 1766) examination, assessment level.

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