Os adjunto un artículo que explica qué son las pinturas metalizadas, las efecto perla, etc...
What are Metallic Finishes? Metallic finishes for cars have been described by many names, such as METALLIC, POLYCHROMATIC, METALLESCENT, OPALESCENT, STARMIST AND STARFIRE. Of all these names Metallic is probably the best since it tells the refinisher that the paint contains metallic particles or pigments. Nowadays a large proportion of vehicles requiring repair are painted with metallics owing to their increasing popularity and usage on new motor cars. These finishes cause more problems for the refinisher in the form of application and color matching than any other finish in current use. The main reason for this is that they are both greatly affected by different application techniques. The following information will help in understanding the problems and minimising the time spent in refinishing metallics. FORMULATION A straight color contains only finely dispersed pigments of color matter, usually in sufficient quantity to give complete opacity within the normal thickness of the paint (50 - 70 microns = 2 - 3 Mil, depending on color). Light is reflected from the paint surface in a normal manner (as from a mirror) and usually does not penetrate the paint film beyond 25 microns = 1 Mil. On the other hand a metallic paint usually contains less colored pigment than a straight color, and without the presence of aluminium particles the light would penetrate right through to the undercoat; in other words, the opacity or covering power would be inadequate without these aluminium particles. The aluminium particles reflect the light rays before they reach the primer, but the light will be reflected at different angles. For this reason, metallic colors have to be matched for both top and bottom tones.
TOP AND BOTTOM TONES The color of a metallic finish changes depending upon the angle at which it is viewed.- · Top Tone (face tone, direct view).The top tone is the color seen when viewed at 90° to the panel surface i.e. directly above a bonnet. · Bottom Tone (side tone, flip tone, oblique view)The bottom tone is the color seen when viewed at an acute angle to the panel surface i.e. down the side of the car. Using Metallic Paints Before using a metallic finish it is important to understand the color change that occurs with different methods of application.
WET APPLICATION When a metallic paint is applied very wet it takes a long time to "flash-off". The aluminium flakes tend to settle to the bottom of the layer of paint and assume an upright position before it dries. The light which penetrates the paint is reflected back from the aluminium flakes through the translucent part of the paint film and therefore gives the color a deeper top tone and paler bottom tone.
DRY APPLICATION When a metallic paint is applied dry it "flashes off" very quickly. The aluminium flakes have no time to settle and remain fairly flat in the paint film. The light is reflected from the flakes, as in a wet application, but, as they have not had the time to settle to the bottom or become upright, less of the translucent part of the paint film is seen and, therefore a paler greyer top tone and deeper bottom tone is produced.
What are Pearlescent Finishes The automotive industry, working closely with the paint industry, is constantly seeking new color shades and new color effects with which to attract new car buyers. Typical of this development is the growing use of Pearlescent Finishes. These finishes have a particularly attractive optical effect, which is obtained by using pearlescent pigments. These pigments are transparent mica flakes whose surfaces are covered with a thin metallic oxide coating. The flakes change color depending on the angle they are viewed from, because the metallic oxide coatings have the ability to reflect or suppress specific wave- lengths of incident light. Which wavelengths - blue, red, or yellow - are reflected or suppressed depends on the thickness of the metallic oxide coatings. There are two types of Pearlescent Finish, depending on the opacity of the pearlescent pigment. The majority of Pearlescent Finishes are based on the two stage process, in which pearlescent pigments with good opacity are included in the basecoat which is followed by clear coat - in a similar way to the two-stage Metallic System (Clear over Base). However three stage Pearlescent Finishes are growing in use; in this system the pearlescent pigments are relatively transparent. The first coat or ground coat gives the system its opacity and is a specific color, often white. This is followed by basecoat containing transparent or semi-transparent pearlescent pigments. The system is then completed by the application of clear coat. Tinting of Pearlescent Finishes The procedures to be followed are very similar to those for two-stage Metallic Colors (COB). However the color and optical effect of a Pearlescent Finish is critically dependent on the choice of pearlescent tinting base and the application process. It is therefore imperative that the paint manufacturers instructions are closely followed with respect to the color bases and the application process to be used.