The type of vehicle, the appearance to be achieved and the application system are the factors to take into account when selecting the automotive finish. The three-layer finishes are still the least used but they are beginning to gain ground.
By Alejandra García Vélez
Finishes are the key point to make a car have a perfect appearance and an optimal level of protection. So it's no coincidence that as the automotive industry bets on more modern car models, finishes evolve to meet the expectations of manufacturers and users.
First of all, to select the finish of a vehicle, the color and the effects that are expected to be achieved, the application system to be used, the facilities where it will be carried out and the equipment that is available must be taken into account.
These factors include the implementation system. Automotive finishes can be classified according to the number of layers of color and gloss that are applied: monolayer, bilayer and three-layer. The most used today are bilayers, either metallic or pearly, for the visual effects that can be obtained with them. Ruben Moreno, car manager of the company Cesvi Mexico, says that currently for more than 65% of cars this system is used.
The monolayers, although still in force, are in a much smaller percentage; since its application is mainly limited to work vehicles, due to the speed of its application and its low cost. The trilayer, on the other hand, being a higher cost finish is not so common.
"The three-layer finish has a very good aesthetic appearance, but as it requires the application of three layers of product its cost increases. Although its use is increasing, currently several models bring from the assembly plant this finish. Mainly high-end models," Moreno said.
Starting from the base
Digging a little deeper into this classification, the fact that the first type, monolayer, involves the application of paint on one hand stands out; that is, with a single product it is possible to obtain color and brightness in the final layer through a finish composed of resins and pigments (see figures).
In the case of bilayer finishes, we are talking about a two-phase application; the first provides the color, which can be metallic or pearly, and in the second the varnish is applied for protection and final shine.
Finally, the three-layer application, as the name implies, consists of three phases: the first provides a flat color base, the second generates the pearl effect and the third is responsible for protection and brightness.
The differences between the types of finish basically depend on the application process, the visual effects they generate and the durability. "Monolayer colors generate direct shine after application thanks to the characteristic of the resin. For the same reason, with this finish only flat or solid colors can be applied, since they are directly exposed to atmospheric phenomena and sunlight, the main agent of color degradation. " Said Nicolás Merlano, Engineer of Cesvi Colombia.
In this sense, it is essential to know the type of technology to be used during the painting process. "It is important because depending on whether a single-component or two-component technology is used, durability will be defined according to the base resin. In the same way, regarding the covering capacity, it must be known if it is of high or low covering power; as this defines the amount of paint to be applied and on how many hands," Merlano explained.
Of paintings and effects
For his part, Ligia Ovalles, Technical Manager of the company Acabados Automotrices S.A., stressed that to select the finish, the type of vehicle, cost and quality must be taken into account. "The most important thing, whatever finish is chosen, is to make sure we acquire the product from a brand recognized for its quality in the market. There are many products that have a lower cost, but do not have the necessary quality, it is preferable to pay more, but make sure that in the end we will get the desired result, "he says.
Ovalles, highlighted the great variety of types of paint offered by the market for use in the automotive field. These range from acrylic and nitrocellulosic lacquers, alkyd paints, acrylic enamels and urethanes.
In the case of acrylic lacquers and nitrocellulosics, it should be noted that they are lower in cost, and still have a great use in several countries in Latin America, especially in those where there are still many old cars in which it is ideal to use this type of products. On the other hand, those based on alkyd resins offer greater resistance, ideal for cargo and work vehicles, explained Ovalles.
Finally, those of the acrylic and urethane enamel type, are those that are currently used in vehicles that require greater resistance and offer an elegant finish to luxury vehicles.
It is essential to keep in mind that acrylic lacquers, nitrocellulosic and alkyd finishes are more economical, but offer less durability and resistance. While acrylic enamels and urethanes will have high strength and beauty, but will be the most expensive. "However, these types of finishes also have high coverage and performance, so less will be needed to cover the same amount of substrate," Ovalles said.
Finally, a topic that the guests of this article repeatedly touched on was the issue of ecological paintings. They recommend exploring alternatives with water-based paints, rather than solvent-based, as they are the first to be more environmentally friendly.
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How to identify the type of finish
Engineer Nicolás Merlano, from Cesvi Colombia, offered some tips for identifying the type of finish a car has. According to him, monolayer colors are easily identified since they do not generate any kind of visual effect. "That's why they're known as flat or solid colors, and they're usually white, yellow and red tones," he explained.
Another way to identify them is by performing a very smooth sanding process, with a P800 or P1000 grain abrasive on the surface of a piece to later verify if the color of the material is released. "That is, if the abrasive shows material of the same color of the body," he said.
For bilayer finishes the same sanding procedure can be applied but the end result will be a transparent sanding powder. "The quickest and easiest way to differentiate a pearl paint from a metallic one is to see the vehicle in natural daylight and at different angles. Usually the pearl color generates different visos, according to its pigmentation, while the metallic ones generate a single type of viso and varies according to the size of the aluminum particles, "he said.
In the case of trilayers, they can be recognized because they have the ability to generate a "chameleon" type finish in which several effects and colors can be seen on the same piece depending on the angle of view.
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