Automotive paint

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Robotic arm applying paint on car parts. P-50iA.jpg
Robotic arm applying paint on car parts.

Automotive paint is paint used on automobiles for both protective and decorative purposes. [1] [2] Water-based acrylic polyurethane enamel paint is currently the most widely used paint for reasons including reducing paint's environmental impact.

Contents

Modern automobile paint is applied in several layers, with a total thickness of around 100 μm (0.1mm). Paint application requires preparation and primer steps to ensure proper application. A basecoat is applied after the primer paint is applied. Following this, a clearcoat of paint may be applied that forms a glossy and transparent coating. The clearcoat layer must be able to withstand UV light.

History

In the early days of the automobile industry, paint was applied manually and dried for weeks at room temperature because it was a single component paint that dried by solvent evaporation. 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.

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. [1] Water-based acrylic polyurethane enamels are now almost universally used as the basecoat with a clearcoat. [3]

Processes and coatings

Preparation

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), then a 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, use is approximately 99.9% and provides superior salt spray resistance compared to other painting processes. [4]

Paint sanded down to the metal:
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Paint sanded down to the metal:
  metal
  primer
  filling / spackling
  color paint

Primer

The primer is the first coat to be applied. The primer serves several purposes.

Base coat

The base coat 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. Base coat used in automotive applications is commonly divided into three categories: solid, metallic, and pearlescent pigments. With the help of best paint sprayer for cars, [5] automotive painters expertly apply the base coat, showcasing its visual prowess with a seamless fusion of colors and effects. From solid hues to captivating metallic and pearlescent pigments, the paint sprayer brings life and brilliance to the vehicle's surface.


Clearcoat

Usually sprayed on top of a colored basecoat, clearcoat is a glossy and transparent coating that 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. [7]

One part and two part formulations are often referred to as "1K" and "2K" respectively. [8] Car manufacturer (OEM) clear coats applied to the metal bodies of cars are normally 1K systems since they can be heated to around 140 °C to effect cure. The clear coats applied to the plastic components like the bumpers and wing mirrors however are 2K systems since they can normally only accept temperatures up to about 90 °C. These 2K systems are normally applied "off line" with the coated plastic parts fixed to the painted metallic body. Owing to the difference in formulation of the 1K and 2K systems and the fact they are coated in different locations they have a different effect on the "redissolving" of the metallic base coat. This is most easily seen in the light metallic paints like the silver and light blue or green shades where the "flop" difference is most marked.

Terminology

The terminology for automotive paints has been driven by the progression of technologies and by the desire to both distinguish new technologies and relate to previous technologies for the same purpose. Modern car paints are nearly always an acrylic polyurethane "enamel" with a pigmented basecoat and a clear topcoat. It may be described as "acrylic", "acrylic enamel", "urethane", etc. and the clearcoat in particular may be described as a lacquer. True lacquers and acrylic lacquers are obsolete, and plain acrylic enamels have largely been superseded by better-performing paints. [9] True enamel is not an automotive paint. The term is common for any tough glossy paint but its use in the automotive industry is often restricted to older paints before the introduction of polyurethane hardeners. [10]

Chemistry

Modern car paint is typically made from acrylic-polyurethane hybrid dispersions, which are a combination of two different plastics. [11] They were developed during the 1970's and 80's as a water-soluble replacement for enamel paints, following health concerns over their high VOC content. Acrylic is less expensive and can hold more pigment, but has poor scratch resistance, whereas polyurethanes are harder but more costly. Combining both types gives a material which can contain a lot of color and be hard-wearing. Simply mixing the materials is not sufficient, as this give heterogeneous coating with separate acrylic and polyurethane domains. Instead, the starting chemicals for each plastic (monomers) are combined and partially polymerized to give an interpenetrating polymer network. Within this the polymer-chains are not chemically bonded to one another, but instead become entangled and interwoven and as they form. This is possible because they polymerize in different ways, which are incompatible with each other. Polyurethane is formed by step growth polymerization involving polycondensation, whereas acrylic is formed by chain growth polymerization featuring free radicals. The resulting product is homogeneous and tough, with superior properties to the individual plastics.

Types and form

Innovations are taking place in paint industry as well. These days, automotive paints come in liquid form, spray form, and powder forms:-

Types of automotive paints

See also

Related Research Articles

<span class="mw-page-title-main">Acrylic paint</span> Water resistant paint type meant for canvases

Acrylic paint is a fast-drying paint made of pigment suspended in acrylic polymer emulsion and plasticizers, silicone oils, defoamers, stabilizers, or metal soaps. Most acrylic paints are water-based, but become water-resistant when dry. Depending on how much the paint is diluted with water, or modified with acrylic gels, mediums, or pastes, the finished acrylic painting can resemble a watercolor, a gouache, or an oil painting, or it may have its own unique characteristics not attainable with other media.

<span class="mw-page-title-main">Paint</span> Pigment applied over a surface that dries as a solid film

Paint is a liquid pigment that, after applied to a solid material and allowed to dry, adds a film-like layer. As art, this is used to create an image, known as a painting. Paint can be made in many colors and types. Most paints are either oil-based or water-based, and each has distinct characteristics.

<span class="mw-page-title-main">Varnish</span> Transparent hard protective finish or film

Varnish is a clear transparent hard protective coating or film. It is not to be confused with wood stain. It usually has a yellowish shade due to the manufacturing process and materials used, but it may also be pigmented as desired. It is sold commercially in various shades.

<span class="mw-page-title-main">Lacquer</span> Liquid or powder coating material which is applied thinly to objects to form a hard finish

Lacquer is a type of hard and usually shiny coating or finish applied to materials such as wood or metal. It is most often made from resin extracted from trees and waxes and has been in use since antiquity.

<span class="mw-page-title-main">Enamel paint</span> Paint with a glossy finish that dries hard.

Enamel paint is paint that air-dries to a hard, usually glossy, finish, used for coating surfaces that are outdoors or otherwise subject to hard wear or variations in temperature; it should not be confused with decorated objects in "painted enamel", where vitreous enamel is applied with brushes and fired in a kiln. The name is something of a misnomer, as in reality, most commercially available enamel paints are significantly softer than either vitreous enamel or stoved synthetic resins, and are totally different in composition; vitreous enamel is applied as a powder or paste and then fired at high temperature. There is no generally accepted definition or standard for use of the term "enamel paint", and not all enamel-type paints may use it.

<span class="mw-page-title-main">Spray painting</span> Painting technique in which a device sprays coating material through the air onto a surface

Spray painting is a painting technique in which a device sprays coating material through the air onto a surface. The most common types employ compressed gas—usually air—to atomize and direct the paint particles.

<span class="mw-page-title-main">Aerosol paint</span> Paint stored in and administered by the use of pressurized containers

Aerosol paint is paint that comes in a sealed, pressurized container and is released in an aerosol spray when a valve button is depressed. The propellant is what the container of pressurized gas is called. When the pressure holding the gas is released through the valve, the aerosol paint releases as a fine spray. Aerosol painting is one form of spray painting; it leaves a smooth, even coat, unlike many traditional rolled and brushed paints. Aerosol primer can be applied directly to bare metal and many plastics.

<span class="mw-page-title-main">Primer (paint)</span> Preparatory coating put on materials before painting

A primer or undercoat is a preparatory coating put on materials before painting. Priming ensures better adhesion of paint to the surface, increases paint durability, and provides additional protection for the material being painted.

<span class="mw-page-title-main">ChromaFlair</span>

ChromaFlair is a pigment used in paint systems, primarily for automobiles. When the paint is applied, it changes color depending on the light source and viewing angle. It was created at Optical Coating Laboratory, Inc. (OCLI) [later JDS Uniphase and Viavi Solutions] in 1979 and is used by DuPont and PPG.

<span class="mw-page-title-main">Rustproofing</span> Prevention of rusting of iron and steel objects

Rustproofing is the prevention or delay of rusting of iron and steel objects, or the permanent protection against corrosion. Typically, the protection is achieved by a process of surface finishing or treatment. Depending on mechanical wear or environmental conditions, the degradation may not be stopped completely, unless the process is periodically repeated. The term is particularly used in the automobile industry.

<span class="mw-page-title-main">Metallic paint</span> Type of paint used on cars

Metallic paint, which may also called metal flake, is a type of paint that is most common on new automobiles, but is also used for other purposes. Metallic paint can reveal the contours of bodywork more than non-metallic, or "solid" paint. Close-up, the small metal flakes included in the paint create a sparkling effect mimicking a metal surface.

Candy apple red is the name code used by manufacturing companies to define a shade of red similar to the red sugar coating on candied apples. The typical method for producing a candy apple finish is to apply a metallic base-coat, followed by a translucent color coat. A final clear coat adds additional gloss.

<span class="mw-page-title-main">Cement render</span> Mortar mix of sand and cement for wall application

Cement render or cement plaster is the application of a mortar mix of sand and cement, and water to brick, concrete, stone, or mud brick. It is often textured, colored, or painted after application. It is generally used on exterior walls but can be used to feature an interior wall. Depending on the 'look' required, rendering can be fine or coarse, textured or smooth, natural or colored, pigmented or painted.

An anti-graffiti coating is a coating that prevents graffiti paint from bonding to surfaces.

Polyaspartic ester chemistry was first introduced in the early 1990s making it a relatively new technology. The patents were issued to Bayer in Germany and Miles Corporation in the United States. It utilizes the aza-Michael addition reaction. These products are then used in coatings, adhesives, sealants and elastomers. Pure polyurea reacts extremely quickly making them almost unusable without plural component spray equipment. Polyaspartic technology utilizes a partially blocked amine to react more slowly with the isocyanates and thus produce a modified polyurea. The amine/diamine or even triamine functional coreactant for aliphatic polyisocyanate is typically reacted with a maleate. Polyaspartic esters (PAE) initially found use in conventional solvent-borne two-component polyurethane coatings.

An alumina effect pigment is a pearlescent pigment based on alumina. It is used for decorative purposes on paints and plastics, giving them a matte, metal-like appearance.

Paint has four major components: pigments, binders, solvents, and additives. Pigments serve to give paint its color, texture, toughness, as well as determining if a paint is opaque or not. Common white pigments include titanium dioxide and zinc oxide. Binders are the film forming component of a paint as it dries and affects the durability, gloss, and flexibility of the coating. Polyurethanes, polyesters, and acrylics are all examples of common binders. The solvent is the medium in which all other components of the paint are dissolved and evaporates away as the paint dries and cures. The solvent also modifies the curing rate and viscosity of the paint in its liquid state. There are two types of paint: solvent-borne and water-borne paints. Solvent-borne paints use organic solvents as the primary vehicle carrying the solid components in a paint formulation, whereas water-borne paints use water as the continuous medium. The additives that are incorporated into paints are a wide range of things which impart important effects on the properties of the paint and the final coating. Common paint additives are catalysts, thickeners, stabilizers, emulsifiers, texturizers, biocides to fight bacterial growth, etc.

<span class="mw-page-title-main">Conservation and restoration of paintings</span> Preservation of heritage collections

The conservation and restoration of paintings is carried out by professional painting conservators. Paintings cover a wide range of various mediums, materials, and their supports. Painting types include fine art to decorative and functional objects spanning from acrylics, frescoes, and oil paint on various surfaces, egg tempera on panels and canvas, lacquer painting, water color and more. Knowing the materials of any given painting and its support allows for the proper restoration and conservation practices. All components of a painting will react to its environment differently, and impact the artwork as a whole. These material components along with collections care will determine the longevity of a painting. The first steps to conservation and restoration is preventive conservation followed by active restoration with the artist's intent in mind.

Waterborne resins are sometimes called water-based resins. They are resins or polymeric resins that use water as the carrying medium as opposed to solvent or solvent-less. Resins are used in the production of coatings, adhesives, sealants, elastomers and composite materials. When the phrase waterborne resin is used, it usually describes all resins which have water as the main carrying solvent. The resin could be water-soluble, water reducible or water dispersed.

<span class="mw-page-title-main">Chalk paint</span> Water-based paint made with chalk

Chalk paint is a water-based, decorative paint invented by Annie Sloan which may be applied over almost any surface. It requires very little preparation and needs a topcoat to avoid flaking. Chalk paints are also used by utility companies to mark road surfaces.

References

  1. 1 2 John Pfanstiehl (1998). Automotive Paint Handbook: Paint Technology for Auto Enthusiasts & Body Shop Professionals. Penguin. ISBN   978-1-55788-291-2.
  2. Kimio Toda; Abraham Salazar; Kozo Saito (21 December 2012). Automotive Painting Technology: A Monozukuri-Hitozukuri Perspective. Springer Science & Business Media. ISBN   978-94-007-5095-1.
  3. Chris Petris (2012). How to Restore Your Corvette, 1963–1967. CarTech Inc. pp. 63–. ISBN   978-1-934709-76-4.
  4. "A Guide to Seals in the AUTOMOTIVE INDUSTRY, PRE-TREATMENT & PAINT PLANTS" (PDF). arthomson.com. p. 4. Archived from the original (PDF) on 19 February 2018. Retrieved 2 September 2017.
  5. "Best Paint Sprayer for Cars 2023 (Automotive Paint Gun)". 22 September 2021.
  6. "Car Paint Colors | Auto Paint Colors from TheCoatingStore". THECOATINGSTORE.
  7. "DuPont Automotive: Paint & Coatings for Metal Exterior". Archived from the original on 5 September 2013. Retrieved 17 June 2012.
  8. "1K Coating vs 2K Coatings". www.eastwood.com.
  9. Daniel Burrill; Jeffery Zurschmeide (2012). How to Fabricate Automotive Fiberglass & Carbon Fiber Parts. CarTech Inc. pp. 155–. ISBN   978-1-934709-98-6.
  10. Dennis Parks (17 June 2013). How to Paint Your Car: Revised & Updated. Motorbooks. pp. 7–. ISBN   978-0-7603-4388-3.
  11. Hegedus, Charles R; Kloiber, Kristen A. (1996). "Aqueous acrylic-polyurethane hybrid dispersions and their use in industrial coatings" (PDF). Journal of Coatings Technology. 68 (860): 39–48.