What is a surface coating?

A surface coating is a blend of film-forming materials, pigments, solvents, and additives that, once applied to a surface, dries or cures into a thin, functional, and often decorative film. These coatings, commonly paints, varnishes, and synthetic clear coats, primarily protect an object's surface from the environment while enhancing its aesthetic appeal by accentuating or concealing features. Most industrial and consumer surface coatings rely on synthetic polymers, large molecules that create durable, flexible, adhesive films. Other components include pigments for color, solvents for a liquid application medium, and additives for special properties. These coatings can offer chemical and corrosion resistance, crucial for maintaining the integrity of items like cars, appliances, and infrastructure. They can be applied through spraying, brushing, or other industrial processes and then cured to form a solid film.

Why are surface coatings used in everyday life?

Surface coatings play a crucial role in everyday life by protecting objects from environmental factors and enhancing their aesthetic appeal. Many materials lack inherent chemical or corrosion resistance, so protective coatings are necessary. Coatings protect items like cars, appliances, bridges and pipelines from corrosion and aggressive chemicals, extending their lifespan. These coatings often consist of synthetic polymers, pigments, solvents, and additives. The use of organic solvents in coatings is increasingly restricted due to air pollution concerns.

What are the main types of surface coatings?

Surface coatings are mixtures of film-forming materials, pigments, solvents, and additives that yield a thin, functional, often decorative film when applied to a surface. Coatings based on polymers rely on molecular weight, glass transition temperature, and structure for key properties. The three major types of film processes are: * Evaporation of solvent or carrier liquid * Cross-linking of low-molecular-weight polymer precursors * Coalescence of small particles Varnishes, which can be natural or synthetic, form films through solvent evaporation and cross-linking reactions. Lacquers are colored varnishes applied to metal or wood. Optical properties of coatings include opacity, color, and gloss.

How are surface coatings applied to materials?

Surface coatings, such as paints, are applied to protect an object's surface from the environment and enhance its appearance. These coatings consist of film-forming materials, pigments, solvents, and additives. Application methods include spraying and brushing. Following application, film formation occurs through solvent evaporation, cross-linking of polymer precursors, or particle coalescence. For instance, in thermal spray coating, molten metal is sprayed onto a surface. Another method, chemical vapor deposition, involves depositing a thin solid layer onto a surface through vapor-phase chemical reactions.

What chemicals are commonly found in surface coatings?

Surface coatings typically consist of film-forming materials, pigments, solvents, and additives. The film-forming materials are often synthetic polymers that provide adhesion, chemical resistance, and flexibility. Pigments, such as carbon black, iron oxide, and titanium dioxide, provide color, opacity, and gloss control. Solvents, including hexane, toluene, and water, act as carrier liquids for the polymers. Additives like wetting agents, also known as surfactants, are used in small amounts to modify surface properties.

How do surface coatings protect materials from damage, like rust or scratches?

Surface coatings protect materials from damage through different methods. Coatings provide chemical and corrosion resistance, which is key to maintaining the integrity and performance of many items, such as cars and appliances, in environments that contain chemicals or induce corrosion. These coatings act as impermeable barriers , isolating the metal from water and preventing corrosion. For example, enamel coatings on appliances protect the steel underneath from corrosion while also providing an attractive appearance. Similarly, paints, polymers, and thin lacquer films serve as protective barriers for applications near room temperature. Coatings can also provide exterior durability , protecting from solar radiation, which can degrade many natural and synthetic polymers. This is achieved through light absorption and scattering by pigments, as well as the use of ultraviolet absorbers and free-radical quenchers.

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Figure 1: Three common polymer structures. The linear, branched, and network architectures are represented (from top), respectively, by high-density polyethylene (HDPE), low-density polyethylene (LDPE), and phenol formaldehyde (PF). The chemical structure and molecular structure of highlighted regions are also shown.

A three-stage diagram shows the emulsion-polymerization process: monomer droplets, free-radical initiators, and surfactant molecules are added to a water bath; surfactants form micelles around monomers before polymerization; and, after polymerization, latex particles are suspended in the water. Labels identify key components and the transformation from monomer to latex particle.

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Top Questions

What is a surface coating?
A surface coating is a blend of film-forming materials, pigments, solvents, and additives that, once applied to a surface, dries or cures into a thin, functional, and often decorative film. These coatings, commonly paints, varnishes, and synthetic clear coats, primarily protect an object's surface from the environment while enhancing its aesthetic appeal by accentuating or concealing features.

Most industrial and consumer surface coatings rely on synthetic polymers, large molecules that create durable, flexible, adhesive films. Other components include pigments for color, solvents for a liquid application medium, and additives for special properties. These coatings can offer chemical and corrosion resistance, crucial for maintaining the integrity of items like cars, appliances, and infrastructure. They can be applied through spraying, brushing, or other industrial processes and then cured to form a solid film.
2 Britannica Sources
1. metallurgy: Barrier protection
2. surface coating
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
Why are surface coatings used in everyday life?
Surface coatings play a crucial role in everyday life by protecting objects from environmental factors and enhancing their aesthetic appeal. Many materials lack inherent chemical or corrosion resistance, so protective coatings are necessary. Coatings protect items like cars, appliances, bridges and pipelines from corrosion and aggressive chemicals, extending their lifespan. These coatings often consist of synthetic polymers, pigments, solvents, and additives. The use of organic solvents in coatings is increasingly restricted due to air pollution concerns.
2 Britannica Sources
1. metallurgy: Barrier protection
2. surface coating: Chemical- and corrosion-resistance properties
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
What are the main types of surface coatings?
Surface coatings are mixtures of film-forming materials, pigments, solvents, and additives that yield a thin, functional, often decorative film when applied to a surface. Coatings based on polymers rely on molecular weight, glass transition temperature, and structure for key properties.

The three major types of film processes are:
* Evaporation of solvent or carrier liquid
* Cross-linking of low-molecular-weight polymer precursors
* Coalescence of small particles

Varnishes, which can be natural or synthetic, form films through solvent evaporation and cross-linking reactions. Lacquers are colored varnishes applied to metal or wood. Optical properties of coatings include opacity, color, and gloss.
4 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
How are surface coatings applied to materials?
Surface coatings, such as paints, are applied to protect an object's surface from the environment and enhance its appearance. These coatings consist of film-forming materials, pigments, solvents, and additives. Application methods include spraying and brushing. Following application, film formation occurs through solvent evaporation, cross-linking of polymer precursors, or particle coalescence. For instance, in thermal spray coating, molten metal is sprayed onto a surface. Another method, chemical vapor deposition, involves depositing a thin solid layer onto a surface through vapor-phase chemical reactions.
5 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
What chemicals are commonly found in surface coatings?
Surface coatings typically consist of film-forming materials, pigments, solvents, and additives. The film-forming materials are often synthetic polymers that provide adhesion, chemical resistance, and flexibility.

Pigments, such as carbon black, iron oxide, and titanium dioxide, provide color, opacity, and gloss control. Solvents, including hexane, toluene, and water, act as carrier liquids for the polymers. Additives like wetting agents, also known as surfactants, are used in small amounts to modify surface properties.
2 Britannica Sources
1. paint
2. surface coating
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
How do surface coatings protect materials from damage, like rust or scratches?
Surface coatings protect materials from damage through different methods. Coatings provide chemical and corrosion resistance, which is key to maintaining the integrity and performance of many items, such as cars and appliances, in environments that contain chemicals or induce corrosion.

These coatings act as impermeable barriers, isolating the metal from water and preventing corrosion. For example, enamel coatings on appliances protect the steel underneath from corrosion while also providing an attractive appearance. Similarly, paints, polymers, and thin lacquer films serve as protective barriers for applications near room temperature.

Coatings can also provide exterior durability, protecting from solar radiation, which can degrade many natural and synthetic polymers. This is achieved through light absorption and scattering by pigments, as well as the use of ultraviolet absorbers and free-radical quenchers.
3 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

surface coating, any mixture of film-forming materials plus pigments, solvents, and other additives, which, when applied to a surface and cured or dried, yields a thin film that is functional and often decorative. Surface coatings include paints, drying oils and varnishes, synthetic clear coatings, and other products whose primary function is to protect the surface of an object from the environment. These products can also enhance the aesthetic appeal of an object by accentuating its surface features or even by concealing them from view.

Most surface coatings employed in industry and by consumers are based on synthetic polymers—that is, industrially produced substances composed of extremely large, often interconnected molecules that form tough, flexible, adhesive films when applied to surfaces. The other component materials of surface coatings are pigments, which provide colour, opacity, gloss, and other properties; solvents or carrier liquids, which provide a liquid medium for applying the film-forming ingredients; and additives, which provide a number of special properties. This article reviews the composition and film-forming properties of polymer-based surface coatings, beginning with the polymer ingredients and continuing through the pigments, liquids, and additives. The emphasis is on paints (by far the most common type of coating), though occasional reference is made to other types of coatings such as drying oils and varnishes. For a fuller understanding of polymeric compounds, which form the basis of surface coatings, the reader is advised to begin with the article industrial polymers, chemistry of. For an overview of the position of surface coatings within the broader field of industrial polymers, see Industrial Polymers: Outline of Coverage.

Polymers for surface coatings

Polymer-based surface coatings can be considered to be two-phase composite materials consisting of pigment particles and other additives dispersed in a continuous matrix of polymer. Polymers provide the coating film its capacity to adhere to the substrate, most of its chemical resistance, and flexibility. In addition, the continuity of the film, much of its durability in the presence of environmental stresses, its gloss properties, most of its mechanical and thermal properties, and most of any chemical reactivity that the film will exhibit are dependent on polymers as well.

The key properties of the coating polymer are molecular weight, molecular weight distribution, glass transition temperature (T_g), and solubility. Also important are the reactive molecular groups making up the polymer and the kinetics and mechanism by which the polymer is formed—that is, whether it is formed by step-growth polymerization or chain-growth polymerization. (These two polymerization reactions are described in detail in the article industrial polymers, chemistry of). Another key attribute of the polymer is its structure. Polymers can have linear, branched, or network architectures (see Figures 1A, 1B, and 1C of industrial polymers, chemistry of). The latter type of structure, consisting of polymer chains bonded covalently at several sites to form a three-dimensionally cross-linked network, is often formed in the coating film during its curing.

Step-growth and chain-growth polymers

Step-growth polymers include polyesters, epoxies, polyurethanes, polyamides, melamine, and phenolic resins. They are formed most often by reactions between two dissimilar monomers—acids and alcohols in the case of polyesters. This general class of polymers is used widely in the field of organic coatings. Chain-growth polymers are built up by the opening of carbon-carbon double (or sometimes triple) bonds within the monomers and the successive addition of similar monomers onto the ends of a growing chain. Prominent chain-growth polymers in the area of coatings are polyethylene, polystyrene, polymethyl methacrylate, and polyvinyl chloride.

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When used in nonreactive form, chain-growth polymers are usually thermoplastic, high-molecular-weight materials. In some cases, however, carboxylic acid, alcohol, epoxy, amine, amino, and other reactive groups can be incorporated into chain-growth polymers. With such reactive functionality on the polymer chain, these materials can be used in low-molecular-weight form as coreactants in cross-linking systems.

For coatings use, one specific chain-growth polymerization method is utilized extensively—the latex, or emulsion, process. In its simplest form (as shown in Figure 1), the emulsion process involves stabilizing large droplets of a monomer (or monomers) in water using a soap as a surface-acting agent, or surfactant. A water-soluble free-radical initiator is added, forming the latex particles by polymerization within small aggregates, called micelles, that are formed by the surfactant. Because latex coatings are applied as aqueous dispersions of polymer, their use is largely solvent-free, and they are very attractive for retail because they can be cleaned up with soap and water, are very easy to apply, and are durable. Latex polymers form films by particle-particle coalescence processes, discussed below.

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Polymers for surface coatings

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Step-growth and chain-growth polymers