Paints and Coatings Defects

Paints and Coatings Defects Paints and coatings defects present a serious problem for manufacturers. Paints and coatings are usually made up of a complex combination of raw materials and for this reason, application must be flawless to achieve the best result. For paints and coatings to perform well, users must prepare and apply the paint correctly, and then ensure it dries and cures according to specifications. Additionally, it is important to prepare the substrate carefully so that the paint performs at maximum capacity. When applied in accordance with application rules, paint will provide good adhesion and create the specified protection against elements. However, if an error is made in application, paints and coatings defects can compromise the integrity of the paint and reduce its quality. Paints and coatings defects can occur in different ways and may happen several times during the lifetime of the coating. Identifying the causes of paint or coating defects is difficult because there may be multiple factors that need to be analyzed. To fully determine the cause of a paint or coating defect, the paint and surface must be examined in detail. First, the paint temperature must be adjusted and stored under appropriate conditions. For several hours after application, it is important to maintain the paint and coating at recommended temperatures, and also to prevent adhesion errors resulting from temperature or humidity changes. Additionally, since paint is a two-component product, the pigment and other solids must be mixed into the paint. Improper application techniques such as not maintaining the appropriate distance during spraying, thus spraying too close to or too far from the surface, and incorrect adjustment of spraying equipment can also damage the quality of the paint and coating. When it comes to surface, detailed preparation is required to prevent contamination. A contaminated surface is usually associated with dust, dirt or grease and adversely affects paint adhesion. To prepare the substrate properly for painting and coating, chemical pretreatment and surface roughening must be performed. Since the causes of paints and coatings defects have been explained in basic terms, we can examine the details of this multi-faceted problem. Abrasion, which can be described as a process of scratching or wear through friction, is among the most common causes of paints and coatings defects. Abrasion usually occurs as a result of exposure to abrasive materials such as dirt, sand, chains and metal chips and adversely affects the durability of the paint and coating. There are several factors that determine durability. Roughness is one of these factors: the rougher the surface of the coating, the more susceptible it is to abrasion. Hardness is another factor that determines durability: if a coating is not sufficiently hard, even small external impacts can lead to fracture of the entire coating system, including the substrate. Balancing hardness is also important, as high hardness levels can weaken flexibility. To strengthen these types of mechanical properties and reduce friction, abrasion-resistant coatings can be used. Application of abrasion-resistant coating on surfaces ensures that the material does not have adverse reactions to chemicals and does not experience wear and tear from friction. The most commonly used type of abrasion-resistant coating is polymers. They are used in numerous applications such as pipes, valves, screens, mixers and stirrers. Some special coatings such as PTFE have non-stick properties. It provides faster surface cleaning and minimizes costs. PTFE can also extend machine life and improve the overall quality of the machine. Alligatoring occurs when a surface cannot prevent water and other abrasive materials from penetrating the substrate. It is distinguished by a crack surface pattern resembling alligator skin. Alligatoring usually starts with small cracks, deepens and expands over time. Alligatoring can occur for various reasons, such as applying a hard coating over a more flexible coating, loss of elasticity of the paint film due to temperature fluctuations, or applying another coat without waiting for the previous coat to fully dry. In this case, the best solution is to prime the surface with quality latex and then allow it to dry. Surface shrinkage resulting from internal stress can also cause alligatoring. If alligatoring results from excessive paint application, a chemical paint stripper can be used to scrape the paint to obtain a clean surface again. Blistering refers to the formation of bubble-like spots within a coating. Blistering is usually a result of pressure caused by moisture accumulation at certain points in the coating film and blisters are produced through gas and vapor pressures within the coating film or substrate. Blisters are generally divided into two main categories: osmotic and non-osmotic blistering. Osmotic blistering occurs when moisture in the warmer part condenses in the cooler part of the coated film as a result of thermal gradients, while non-osmotic blistering is usually associated with the substrate or environmental conditions as part of the painting process. Coating application can only be done in many regions during periods when climate conditions are favorable, such as summer and early autumn. However, sometimes environmentally favorable conditions may have disadvantages. For example, applying a coating directly under sunlight to a surface or applying the coating thicker than recommended can cause blistering. Blisters form as the heat from the sun causes the surface of the applied coating to dry faster than the coating film body. This rapid surface drying process produces a hard surface layer that prevents solvent escape from lower levels of the film. The solvent in the substrates located at the lower levels expands as it heats up and creates vapor pressure inside the coating film, causing blisters to form. To prevent blistering and accompanying foaming, it is important to ensure that the surface and ambient conditions are not affected by contamination and excessive moisture during the coating process. As mentioned above, blistering can result from temperature fluctuations, so applying a paint system with higher tolerance to thermal gradients will minimize the risk of defects. If blisters reach the substrate, establishing a ventilation hole can help eliminate the moisture source and reduce blistering. Peeling is a common paint and coating defect that can be described as paint loss, usually as a result of poor adhesion. Possible causes include improper drying, moisture seepage from unsealed joints, worn or leaking caulk on walls, moisture escape from outer walls, insufficient surface preparation, use of low-quality paint and application of oil-based paint to wet surfaces. Due to loss of adhesion, soft and flexible coatings can be easily removed or fall off the substrate on their own. The effects of surface coating or paint peeling can be significantly reduced by using a coating material with strong adhesion properties through proper surface preparation before application and use of a preventive primer on the substrate before top coating. Using high-quality acrylic latex exterior paint for strong adhesion and water resistance can also prevent peeling. Color bleeding is a coating defect that occurs as a result of diffusion of pigments from the lower layer of the coating film to the top coating due to excessive solvent use. Bleeding usually occurs when strong solvents are used in top coats. Coating bituminous or tar-based products, where tar or bitumen is soluble, with top coat paint can cause color deterioration in the top coat. The best way to prevent color bleeding is to use compatible materials and apply a proper blocking coat to remove the stained layer. In conclusion, paints and coatings defects still present a problem for manufacturers. However, as long as the coating surface is properly prepared and compatible materials are used under favorable conditions, the risk of paint and coating deterioration can be minimized. Even when paints and coatings defects do occur, these defects can be easily corrected through the use of certain materials such as primer or applications such as scraping and sanding. Prepared by: Murat Soygür

Sources

• https://www.pro-techpainting.com/single-post/2017/09/14/common-paint-failures-and-their-solutions • https://www.rust.co.uk/paint-failure-guide • https://www.ppcoatings.co.uk/wp-content/uploads/2016/06/Coating-Failure-Defects.pdf • https://www.dunnedwards.com/explore/how-to/paint-problem-solver/alligatoring/ •https://www.corrosionpedia.com/definition/165/bleeding#:~:text=Bleeding%20is%20a%20coating%20defect,of%20solvents%20 (sometimes%20resins). •https://www.corrosionpedia.com/definition/2274/peeling#:~:text=Peeling%20refers%20to%20the%20formation,uniformly%20across%20an%20object's%20surface. • Image: https://pixabay.com/