All About Paint

By SRT-Tom · Mar 23, 2019 ·
  1. SRT-Tom
    In the early days of the automobile industry, painting was a slow process. It was applied manually and dried for weeks at room temperature by solvent evaporation.

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    1930 Packard Factory

    As mass production of cars made the process untenable, paint began to be dried in ovens. Nowadays, two-component (catalyzed) paint is usually applied by robotic arms and cures in just a few hours either at room temperature or in heated booths. (Note- That is why car paint can be waxed as soon as the new owner takes delivery).

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    Robotic Paint Sprayers

    Until several decades ago lead, chromium and other heavy metals were used in automotive paint. Environmental laws have prohibited this, which has resulted in a move to water-based paints. Up to 85% of lacquer paint can evaporate into the air, polluting the atmosphere. Enamel paint is better for the environment and replaced lacquer paint in the late 20th century. Water-based acrylic polyurethane enamels are now almost universally used as the basecoat with a clearcoat.

    Here are the four basic steps of the painting process:

    Pre-Treatment

    High-pressure water spray jets are directed to the body. Without proper pretreatment, premature failure of the finish system can almost be guaranteed. A phosphate coat is necessary to protect the body against corrosion effects and prepares the surface for the E-Coat.

    The body is dipped into the Electro-Coat Paint Operation (ELPO/E-Coat) and high voltage is applied. The body works as a cathode and the paint as an anode sticking on the body surface. It is an eco-friendly painting process. In E-Coat, also called CED paint, utilization is approximately 99.9% and has great salt spray life compared to other painting processes.

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    Electro-Coat Paint Operation

    Primer

    The primer is the first coat to be applied. The primer serves several purposes.
    • It serves as a leveler, which is important since the cab often has marks and other forms of surface defect after being manufactured in the body shop. A smoother surface is created by leveling out these defects and therefore a better final product.
    • It protects the vehicle from corrosion, heat differences, bumps, stone-chips, UV-light, etc.
    • It improves ease of application by making it easier for paints to stick to the surface. Using a primer, a more varied range of paints can be used.
    Base Coat

    Modern automobile paint is applied in several base coat layers, with a total thickness of around 0.1mm. It is applied after the primer coat. This coat contains the visual properties of color and effects, and is usually the one referred to as the paint. Over the years, Dodge has offered exciting “high impact” paint colors such as Hemi-Orange, Yellow Jacket, Plum Crazy, etc. (for further information, see Challengerforum “High Impact Paint” article, published Jan. 18, 2019). Base coat used in automotive applications is commonly divided into three categories: solid, metallic, and pearlescent pigments.

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    • Solid paints have no sparkle effects except the color. This is the easiest type of paint to apply, and the most common type of paint for heavy transportation vehicles, construction equipment and aircraft. It is also widely used on cars, trucks, and motorcycles. Clear coat was not used on solid colors until the early 1990s.
    • Metallic paints contain aluminum flakes to create a sparkling and grainy effect, generally referred to as a metallic look. This paint is harder to manage than solid paints because of the extra dimensions to consider. It must be applied evenly to ensure a consistent looking finish without light and dark spots which are often called "mottling".
    • Pearlescent paints contain special iridescent pigments commonly referred to as "pearls."Pearl pigments impart a colored sparkle to the finish which works to create depth of color. Pearlescent paints can be two-stage in nature (pearl base color + clear) or 3-stage in nature (basecoat + pearl mid-coat + clear-coat). Dodge achieved much publicity when it introduced the 2006 Challenger Concept in classic Hemi-orange paint that “was kicked up a notch” with a dazzling pearlescent paint job complete with embedded mica chips.
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    Trevor Creed introducing the Hemi-orange 2006 Challenger Concept

    Clearcoat

    Usually sprayed on top of a colored basecoat, clearcoat is a glossy and transparent coating that gives the illusion of multiple thick layers of paint. It forms the final interface with the environment. For this reason, clearcoat must be durable enough to resist abrasion and chemically stable enough to withstand UV light. Clearcoat can be either solvent or water-borne.

    One part and two part formulations are often referred to as 1k and 2k respectively. OEM clear coats applied to the metal bodies of cars are normally 1K systems since they can be heated to around 284 degrees F to effect cure. The clear coats applied to the plastic components like the bumpers and side mirrors, however, are 2K systems since they can normally only accept temperatures up to about 194 degrees F. These 2 K systems are normally applied "off line" with the coated plastic parts fixed to the painted metallic body.

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    Painting of Plastic Components

    The entire Challenger painting process can be viewed on the informative YouTube video, MegaFactories (15:25 minute mark). See link below:

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