Look at paint adhesion like this

Adhesion is one of the important indicators for evaluating the performance of powder coating film.

The powder coating adheres to the surface of the substrate after melting, and forms a film after three stages of aggregation, leveling, and solidification

Adhesion test method

Generally, there are cross-cut method, circle method, and open method

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Factors affecting adhesion

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The material of the substrate has an important influence on adhesion

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• When the alkalinity of the degreasing agent is too high, the surface iron atoms react with the alkali to change the surface structure of the iron substrate, which makes it difficult to apply the film on the pre-treatment film; when the substrate is aluminum or aluminum alloy, the degreasing agent is too alkaline to interact with the substrate The surface metal reacts to generate alkaline partial metal salts.
  When it encounters acidic phosphating solution, it immediately generates metal hydroxides.
  After drying, oxides are formed instead of uniform phosphating films, which is the so-called "white spots".
  After spraying powder coating on "white spots", a bulge will be formed if it is too thick for a period of time, and the entire paint film will fall off
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• The calcium ion and magnesium ion in the process water exceed the standard, which seriously affects the effect of the degreasing agent.
  The anions in the water will also adhere to the phosphate film and affect the adhesion of the final coating
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• When there is no anti-rust component in the degreasing agent, the phenomenon of "flash rust" is prone to occur between the work piece from the degreasing process to the phosphating process or other pre-treatment processes
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  Once the workpiece is rusted, poor adhesion will easily occur at the rusted place
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• If qualified pure water is not used for the water washing process or has not been replaced for a long time, the anions and the large amount of residual liquid will be adsorbed on the pretreatment film, and the adhesion to the coating will be poor
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• In the last drying process of the pretreatment process, if the drying temperature is too low or the time is too short, it is difficult to remove the residual moisture and part of the crystal water on the surface of the pretreatment film.
  After spraying and forming the film, the water vapor is in the pretreatment film and coating.
  Accumulate between, resulting in loss of adhesion
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  The drying temperature is too high or the time is too long may cause the pretreatment film to pulverize, and after spraying and curing, it will fall off the substrate together with the coating
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Third, the powder coating itself and curing conditions

• Too low resin content in powder coatings will result in incomplete cross-linking of the overall coating, brittleness of the overall coating, decreased adhesion, and deviation in impact performance
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• Improper use of additives (leveling agents, wetting promoters, etc.
  ) or improper additions will result in poor wetting of the powder coating, and there will be gaps between the coating and the substrate, resulting in poor adhesion
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• Excessive distribution of the resin amount of the resin will cause it to be unable to melt at the same time in a narrow melting temperature range, which greatly affects the crosslinking density of the overall coating and leads to poor adhesion
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• Ensuring sufficient curing time and temperature can ensure good leveling and mechanical properties, but over-baking will cause adverse effects such as yellowing, and it is necessary to reasonably control the chain speed, furnace temperature and other variables
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• In addition, moisture in the powder, water and oil in the compressed air, and large dust in the construction environment may cause adhesion problems
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  Some spraying manufacturers use direct gas baking furnaces to burn small molecules such as sulfides to adhere to the surface of the coating, making the secondary adhesion seriously poor during rework
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There are many factors that affect the adhesion of powder coatings.
In addition to the above introduction, some factors are also a check and balance relationship.
We often need to combine the actual production conditions and environment on site to reach the final conclusion
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In actual production, we need not explore, develop an ideal formula system to optimize process parameters, and match construction conditions to meet the ever-increasing market demand
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