Special Delivery

Jan. 1, 2020
Each year automobile manufacturers, in an effort to have a more attractive, marketable vehicle, search for paint and special effect colors that will make their vehicles stand out. Old stand-bys such as metallic colors are refined by changing the size

Painters today must understand specialty paints to know how to get the best finish for each vehicle.

Each year automobile manufacturers, in an effort to have a more attractive, marketable vehicle, search for paint and special effect colors that will make their vehicles stand out. Old stand-bys such as metallic colors are refined by changing the size or shape of the flake; pearl paints are offered in additional colors; prismatic paints are used more; and new products such as self-healing and scratch-resistant clears continue to be introduced to the market.

Painters must keep up with this ever-changing technology because old techniques for repairing paint change as new and different specialty paints are introduced. We can better understand why techniques must be modified if we understand what is in these paints and how they work. What makes this task difficult is that the details of how new products work are often proprietary, and it may take a painter years to get this information.

Often manufacturers of new product will provide repair techniques and procedures or provide training for new products. However, not all painters have this information before they encounter the need to repair specialty paint. A paint jobber might get a call from a shop that has a new vehicle in their paint department that they are not able to match. That may be when the painter finds out a new specialty paint requires modification of the application technique.

What are specialty paints and how do they work?

To achieve desired paint colors, paint manufacturers experiment with different pigments. Paints are composed of four major ingredients: solvents, rosins (or binders), additives and pigments.

Solvents thin the other ingredients so that the paint can pass through a spray gun and be applied to a vehicle. These thinners or reducers are often referred to as "the vehicle" (for transport). Paints that come from the manufacturer have a regulated amount of solvent in them, and painters further "reduce" paint, making it thin enough to pass through a spray gun, transporting it to the vehicle. There the solvents evaporate as the paint cures.

Rosins, sometimes referred to as binders, are the primary chemical-binding substance in paint. They provide the holding power; they also provide durability and curing characteristics. Rosins were first harvested from naturally occurring products such as pine rosins. In the 1930s alkyd rosins were derived from glycerin processed from animal and vegetable fats. Alkyd rosins represented the early stages of the modern method of paint production. Though only small advances in paint rosins occurred during World War II, this early development paved the way for today's modern rosins. Now rosins are primarily based on high-quality acrylic urethane rosins, though other rosins that can be used are epoxy, polyester and vinyl.

Additives provide a variety of important jobs in paint, such as anti-foaming, anti-blistering, filling, anti-gelling and more.

Pigments are the powdered substances that provide the coating color. When automotive paint was first developed, the pigments available were simple colors and were applied with a brush one coat at a time; the brush marks were sanded out between coats. This made the painting process labor-intensive and time-consuming.

In the 1920s, nitrocellulose paints were introduced, and for the first time paint could be applied with a spray gun. This innovation did provide a much speedier, less labor-intense application, and paved the way for specialty paint pigments that could be suspended in the paint film, which brush application could not provide.

With the introduction of lacquers after World War II, pigments took a leap forward. By the '60s, metallics had been introduced, and shortly thereafter pearls became available. Basecoat-clearcoat paint arrived in the '80s, and change in paint types or application has continued nearly every year since.

Metallics are made from finely ground metal, usually aluminum. They affect the appearance of the paint in relation to how they are orientated in the paint film. If the flakes are closer to the top of the paint, they will reflect their silver color and make the paint appear "glittery." If they lie deeper in the finish, they will appear darker and the color of the dominant pigment will be reflected more.

The size of the metallic flake also determines the amount of light reflection that will be seen, while the shape of the flake also will affect the appearance of the color. Metallic flake product comes in standard irregular shaped flakes and round, lens-like shapes. Round flakes are generally larger and tend not to break up into small pieces during application as the standard flakes do. Round flakes are generally brighter, cleaner and more consistent than standard flakes.

Mica, or pearl, is a substance that was first added to paint to give it the shimmering appearance of a pearl. It was later found that this mined substance, titanium dioxide (TiO2), could have color attached to it, which allows mica to take on varying shades of color. The substance is now marketed in more than 25 shades or colors.

Mica, unlike metallic, does not just reflect light back as colors; when light is shined on mica flake, which is a semi-translucent substance, some light reflects back off it and some passes through the flake. The light that passes through the flake reflects as background color and the light that reflects off provides highlight. Mica can be used as an additive to enhance color or as a mid-coat in a multi-stage paint system, thus adding background and highlights.

Prismatic paint, or color shifting paint, is made possible using a multi-layered pigment flake, which when viewed from different angles reflects different hues. Seven standard colors are currently available: red/gold shifts from red through orange and yellow into green; silver/green shifts from silver through green into purplish blue; gold/silver shifts from gold to blue-silver; green/purple shifts from green through blue and red into orange; cyan/purple shifts from cyan through purple into red-orange; blue/red shifts from blue through purple to warm red; and magenta/gold shifts from magenta through red, orange and gold into yellow.

These ultra-thin, multi-layered interference flakes of magnesium fluoride and aluminum form micro-size flakes. Unlike other specialty additives, they are opaque, thin, flat and highly specular (mirror-like). To produce a tight color tolerance, the layer thickness must be controlled to within a few atoms. The flakes produced have both refractive and diffractive qualities. The diffractive effect (when light waves bend around an obstruction) changes the surface from having a metallic appearance in low illumination to a vivid, multi-rainbow effect when the light hits it.

Application techniques

Metallic flake appearance can be affected by the choice of reducer, hardener, gun set-up, spray technique and air pressure. Painters should be very careful when preparing to paint and should follow all of the paint manufacturer's recommendations.

To choose the correct reducers and hardeners, a painter should consider all the factors in their spray environment conditions, such as temperature, humidity and airflow. Though the temperature in the spray area may be as recommended for the reducer being used, if the humidity is high the reducer will not evaporate as quickly as indicated. (In paint recommendations, standard humidity is considered 50 percent. Therefore, if the humidity is higher, the painter should adjust the reducer.) If the airflow is very high, the reducer will evaporate faster, so the painter should adjust the reducer accordingly.

Paint gun setup

When choosing a paint gun setup, painters often err on the side of choosing too large. When they read the paint manufacturer's gun setup and see a range of 1.2 to 1.4, they generally choose the larger. Remember, though, that the larger the tip size the more air pressure is required to atomize the paint. A better way to choose the appropriate tip size is to know the tip size for the gun being used and the type of paint being sprayed. Many paint manufacturers list the specific tip size for their product by gun make and model. If this information is not available, the painter should choose the smaller of the tip sizes.

Additionally, having separate guns set up for basecoat, clearcoat and sealer will assure that the total application will proceed with more precision and fewer problems that eat away at cycle time.

Spraying mica

Gun set-up and adjustment are also critical when spraying mica. If tip size is incorrect, air pressure is wrong, or if distance and travel are incorrect, the paint film can take on a mottled look. If the mottling occurs in paint containing mica, the mica appears inconsistent in its flow or has a random, unsmooth appearance. The film may look uneven, blotchy or cloudy. The cause of the mottling is poor atomization and/or application technique. To avoid this defect and others, proper paint technique is critical.

Proper spray techniques — distance, holding the gun perpendicular to the surface, proper overlap and rate of travel — are standard practices painters need to develop and use consistently. Most gun control components have not changed over the years. They have just become more critical as specialty paints continue to be introduced.

One change a painter must consider when spraying paint that contains large amounts of mica is overlap. With non-specialty paint, the standard 50/50 overlap will suffice. When spraying paint that has a large amount of mica (and some silver metallic paints), a 70/30 overlap will help avoid both mottling and striping that occurs. If the gun is not adjusted properly and the painter is not careful with overlap, paint that contains large amounts of metallic and/or mica will have streaks and mottling.

Fanning the gun at the end of a blend can cause poor metallic and mica orientation. At lower pressures, the paint will be drier and lighter (the metallic and mica closer to the surface of the paint). When a paint gun is fanned at the end of a stroke, the gun is waved further away from the surface to be painted, thus reducing the pressure as the paint hits the vehicle. By letting the trigger off at the end of the stroke while keeping the same distance, the metallic and mica are more likely to be placed at the proper depth and thus have a closer match.

Standard blending, in which each slightly larger coat is placed on top of the preceding one, can also cause poor metallic and mica lie. To avoid this, the painter is wise to use reverse blending where he applies the largest coat first, with each consecutive coat applied on the previous coat, but applied to cover a slightly smaller area. This procedure allows the metallic to fall on wet paint and thus have better metallic and mica orientation.

For difficult colors such as silver, bronze and copper, the blending method that uses a blending clear first (sometimes referred to as "wet-bedding" blending) will have the metallic and mica hitting a wet surface and thus orientating better than when it hits a dry surface.

Multi-stage paint

Painting with a base or ground coat, a mid–coat and with clear over them all is the traditional tri-coat paint system. These paint colors were first developed for very special high-end vehicles. The mid-coat was normally a clear or nearly clearcoat with large amounts of mica suspended in it. Now we are seeing such paints on standard production vehicles, and the mid-coat could be a coat with color along with mica in it. These vehicles pose a special problem to painters. The only way to know exactly how many mid-coats will be needed to achieve an undetectable repair is by making a letdown panel with several coats of mid-coat applied.

A let down panel is made by applying the base or ground coat to hiding, then masking off a panel so that four to five layers of mid-coat can be applied. After making the letdown panel, the painter can compare the panel to the vehicle and choose the proper number of coats to apply.

When the letdown panel is compared to the vehicle, the painter may find that none of the sections matches the vehicle color. It may appear that the vehicle lies between 3- and 4-coat panels, for example. This would indicate that to get an invisible match, the painter would need to spray three and one-half coats of mid-coat. To do this, the painter must spray three coats at normal strength, then take the reduced mid-coat and mix it 1-to-1 with blending clear to achieve a half strength coat, thus giving the needed three and one-half coats of mid-coat color.

Blending a multi-stage color can be difficult due to all the different coats that one must apply. The painter needs to keep in mind that it is easy for a multi-stage repair area to become very large as the process progresses, and that each additional coat should not be extended any larger than is necessary

In the multi-stage process, the painter should apply the ground coat using a reverse blend method, keeping the repair as small as possible. Next, the mid-coat should be applied using the number of coats determined by the letdown panel.

A multi-stage repair should not be rushed. If flash time is not observed and the repaired area becomes overly wet, the micas may migrate and a halo will become visible around the repair area. That halo, however, may not become visible until the clear is applied. To avoid defects and extra correction steps, the painter should let each coat flash properly before applying the next. Finally, the clearcoat should be applied to the entire panel as is normally done, and then cured, according to the product manufacturer's recommendations.

Prismatic paint application

With most new specialty paints, because of the need to have a precise orientation and position in the paint film, spray techniques have become more exacting and critical. It is a welcome exception to report that prismatic paints do not require any special care to apply, due to their randomness and refractive nature.

As the angle of the light source changes in relation to the person viewing it, the color shifts; thus, the repairs do not become visible. That's not to say that the painter doesn't need to take care with the application of prismatic paints, though. Good gun control and proper set-up are still critical, but no special precautions beyond those for any successful paint application are necessary for these high quality paints.

Specialty paints have developed and changed significantly over the last 37 years. Likewise, shop technicians can look forward to more changes ahead in specialty paints, such as glow-in-the-dark paint, larger metallic flake and more use of prismatic paints. The one constant in automotive refinishing is that change is inevitable, and innovative painters must continue to learn as each change occurs.

About the Author

Al Thomas

Alfred Thomas is associate professor and department head of Collision Repair at Pennsylvania College of Technology. His technical experiences include 15 years in the collision industry as a technician and shop manager, 12 years as a secondary vocational instructor, and the past eight years as lead instructor at Penn College.

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