Coating and paint failure guide

The application of paints or coatings is a very common treatment in the production processes of any material or product. These paints, or coatings, are one of the most suitable methods to decorate, protect or give a new functionality to the products where they are applied. A clear example is the front of buildings, where paintings not only act as an aesthetic element, but also have an important protective task or coatings for metal parts in which they generally seek to protect from corrosion.Despite its clear benefits, the application of paints or coatings can cause adhesion failures on the substrate or material where they are applied. These adhesion failures, in turn, can lead to other types of failures such as, for example: aesthetic failures, loss of functionality or even more serious problems such as the lack of protection of a critical area. For this reason, detecting the type of adhesion failure that has occurred is essential to correct it and avoid possible more serious future problems.Within our area of failure analysis, the characterization and resolution of adherence failures is one of the most common topics. For this reason, in today’s blog we tell you the most common types of adherence failures, reasons why they are generated and how to solve them.

What is a coating and paint failure and how is it generated?

In general, paints or coatings are multi-component products that contain resins, plasticizers, pigments or additives among others. All of these components, once applied and cured, form a film that adheres to the surface of the material. Normally, the adhesion problem occurs at this stage, where it is essential to achieve the highest possible adhesion between the film and the material to be coated.

Reasons why failure in coatings and paints may occur

Adhesion failures can appear shortly after applying the paint or after a certain time. The origin of these failures can be due to many causes of different nature. Here are some typical examples:

• Incorrect selection of paint or coating. It may be the case that there is not a good compatibility between the paint or coating selected and the material where they are to be applied.
• Poor cleaning of the surface. Before applying any layer of paint or coating, it is necessary to clean the surface perfectly to get a correct adhesion of the film with the material. In many cases it is necessary to use specific cleaning compounds

• Contamination. Despite cleaning the surface properly, during the manufacturing process it is possible that contamination of the surface occurs before applying paint or just after applying it. This can lead to significant adhesion failures. A clear example is contamination by silicone, we leave you a link to a project where we had to solve this problem.
• Need for activation. On many occasions, to achieve good adhesion between the paint or coating, with the material, it is necessary to activate the surface. For this, different techniques can be used, among which the flame, plasma or primers stand out.

• Incorrect application. The method of applying the coating or paint can be one of the most critical points in achieving a good adhesion or finish. Therefore, it is very important to define the application parameters well.
• Low resistance to external agents. The resistance of the paint or coating to the external agents that it will face is key when it comes to maintaining good adhesion during its useful life. For this reason, it is essential to take it into account before selecting one type or another. We leave you a link of a success case where we had to find the specific external agent that degraded the paint in order to solve the problem.

What types of coatings and paints failures are there?

Adhesion failures can occur in many different ways. Characterizing the failure and determining the type is key when determining the origin and solving it. Here are some of the most common:

• Ampoules or “blisters”. Appearance of small blisters on the entire surface of the paint or coating. This adhesion failure may be due to the use of a very thick paint. Another reason can be the rapid evaporation of the solvent, which can be caused by the use of very high temperatures during the curing process or by the high volatility of the solvent present in the paint. To solve this problem there are 3 possible actions: replace the paint, modify the solution or reduce the curing temperature.

• Bubbles or holes. Small holes or bubbles appear at specific points in the paint or coating. This failure may be due to excessive agitation in the paint, which results in the appearance of foam. Another reason may be the rapid pumping of the paint or rapid evaporation of the solvent, as in the previous case. To solve the problem, you can reduce agitation, work with less volatile solvents, or reduce the curing temperature slightly.

• Spider web. The appearance of strands similar to those of a spider web is one of the most common adhesion failures during the application of coatings. This failure is usually caused by the rapid drying of the coating during its application or even before its application. To avoid the appearance of the defect, you can reduce the amount of air, change the solvent for one that takes longer to dry or reduce the viscosity of the mixture.

• Orange peel. This failure, known as orange peel because of its roughness, usually occurs when the coating loses solvent during the spraying process. To solve the problem, it is necessary to reduce the coating application distance or increase the coating / air ratio.

• Eruptions. Random paint or coating eruptions are a very common bond failure. This defect can be caused by small cavities that contain air, erupting during curing and giving rise to the defect. A good solution to this problem is to force the cavities to erupt before applying the last coat. Another option is to select a low curing temperature coating to avoid eruption during this stage.

• Fisheye. This bond failure appears as a crater that penetrates down to the material. Its cause may be the presence of a contaminant that prevents the material from getting wet during the application stage. A clear example is fingerprints or some oil. To avoid its appearance, the piece must be perfectly cleaned. It is also advisable to control the use of other incompatible products near the application stage.

• Cracks (mud effect). The appearance of small cracks, similar to those of a dried mud, is usually caused when the coating is very thick, especially in paints or water-based coatings. To solve this adhesion failure, the viscosity must be reduced, or thinner films must be applied.

• Opacity or loss of gloss. The loss of gloss of the coating or paint can be due to the presence of moisture during the curing process, since it leaves the surface slightly rough until it loses its shine. It can also be caused by oven fouling or very small film thickness. A good solution is to speed up the cooling ramp by increasing the temperature / time ratio.

• Pollution by particles. Particulate contamination can lead to major bond failures. This defect usually occurs due to the presence of particles in the environment if working in shared spaces, here is an example of a project of these characteristics. It can also be produced in the curing oven. A possible solution to this problem is to ensure the cleanliness of the surfaces and to isolate the areas of application of the coating and curing.

• Drip. The dripping effect on the surface may be due to the low viscosity of the coating or paint. It can also be due to the use of the wrong diluent. A good method to overcome this adhesion failure is to use solvents with higher evaporation rates or apply thinner coats. Additionally, the part can be preheated to avoid this problem.

These are some of the most common adhesion failures, however there are many more types. In many cases, the appearance of the failure is not enough to determine the specific type, so each case must always be studied separately. In this way, the best possible solution can be proposed. In the next section we explain how to carry out a project to solve an adhesion failure.

How to carry out a project to solve coatings and paints failure

At ATRIA we have experience in solving this type of adherence failure. As we anticipated, each failure must be studied separately, since this is the best way to find the origin and propose the most appropriate solution. Here are the steps we follow to carry out this type of project:

1. Characterization of the adherence failure. Many of the adhesion failures can be aesthetically very similar to each other, making it difficult to differentiate them with the naked eye. If necessary, we have characterization equipment that allow us to identify the type of failure in order to provide a correct solution.
2. Proposal for improvement. Once the adherence failure has been determined, is possible to propose a series of improvements to solve it. These improvements, which must be applied taking into account the failure that occurs, can be applied to the process or the product. Some examples are:
   1. Replace or modify the paint or coating.
   2. Vary the temperature or cure time.
   3. Modify the paint or coating application parameters (application distance, ratios, times or any other variable).
   4. Change the solvent for a more or less volatile one.
   5. Vary the viscosity or density of paints or coatings.
   6. Apply films of different density.
   7. Preheat the pieces.
   8. Modify the type of cleaning and previous activation that is carried out.
   9. And many more!
3. Proof of concept and optimization. Before taking the solution to industrial scale, it will be tested on a laboratory scale to verify that it works correctly and to optimize it. Once optimized, it will carry over to the actual process.
4. Industrial scaling. Finally, the solution will be adapted to the industrial production process until the desired results for each client are obtained.

Do you want to apply coatings and paint failure analysis in any of your Projects? Contact us!