Experimental formula of modified epoxy heavy-duty anticorrosive powder coating (2 of 3)

2 results and discussion

In the discussion of the experimental formula of pulverizing, it is found that the selection of different resins, the amount of catalyst, the variety and amount of filler, baking temperature and baking time have a great impact on the pulverizing function. The thickness of powder coating film with the same formula and the physical and mechanical functions are also quite different when sprayed on the surface of different substrates.

2.1 influence of selection of different resins on Coatings

Due to many benzene rings, ether bonds and hydroxyl structures in the molecular structure, epoxy resin has excellent adhesion, heat resistance and chemical corrosion resistance to the substrate, especially the metal substrate. The coating has excellent mechanical strength, such as hardness, cold and hot shock resistance and mechanical shock resistance.

At present, the epoxy resin selected for heavy-duty anti-corrosion powder coating is mainly bisphenol A epoxy resin and phenolic epoxy resin with medium molecular weight.

Considering the requirements of coating anti-corrosion and adhesion, it is required that the softening point is high and the epoxy value should not be too low, so as to ensure that the coating not only has good flexibility and resistance, but also has a certain degree of crosslinking, so as to ensure the adhesion and appearance hardness of the film.

However, pure bisphenol A epoxy resin only has epoxy groups at both ends of the molecular structure. In order to obtain good resistance and high softening point, only the resin with low epoxy value can be selected, but the crosslinking density of its cured product is low. As a result, the chemical resistance and heat resistance are not good enough, and the coating hardness, wear resistance and adhesion are not good enough.

There can be multiple epoxy groups in the molecular structure of phenolic epoxy resin, the crosslinking density and aromatic density of the cured product are relatively high, and the hardness, heat resistance, wear resistance, chemical corrosion resistance and adhesion to the substrate of the film are relatively good.

Therefore, phenolic epoxy resin or modified phenolic epoxy resin are often selected in the design of heavy-duty anti-corrosion powder coatings abroad.

Although phenolic epoxy resin has good anti-corrosion function, all phenolic epoxy resins are selected. Especially when the epoxy value of phenolic epoxy resin is high, it may lead to high brittleness of cured products, poor low-temperature zigzag and impact function. Both have their own advantages and disadvantages.

Therefore, the addition of some bisphenol A epoxy resin in phenolic epoxy resin will help to improve its low-temperature bending and impact resistance. The mixing ratio of phenolic epoxy / bisphenol A epoxy is 80 / 20 ~ 20 / 80.

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