Polymer Coatings and Paints

What are polymer coatings and paints?

Polymer coatings and paints are liquid phases or powder products that are applied to a surface by various methods in a larger of a given thickness. Paints and coatings have a range of applications in various industries. Some of them are,

• As a protective layer.
  • E.g., anticorrosive layer for metal.
• To obtain desired surface properties such as hydrophobic, and oleophobic properties
• For decorative purposes.

There are many ways that can apply a polymer coating to a surface.

Ways of applying polymer coatings are,

• Applying with a brush
• Spray coatings
• Dip coatings
• Spin coating
• Using machinery

Types of paints

Paints and coatings can be classified in different ways like the levels of layers, specific application, emission of volatile components, etc.

1. Classification by the level of a specific layer of the paint.
   • Primers, sealants, and topcoats

2. Classification by the sector to which it is intended to apply.
   • e.g. paints for the automotive industry, paints for construction

3. Classification by the degree of emission of volatile compounds.
   • Powder paints – do not contain any solvent
   • Solvent-based paints – contain a high amount of solvent
   • Water-based paints – solvent is water

4. Classification by the polymeric resin in the paint
   • Epoxy paints
   • Polyurethane paints
   • Acrylic paints
   • Silicon paints

Different layers of a paint coating

Primer

A primer is a paint applied directly to a bare substrate. Mostly applied on metal substrates. Primers protect metal substrates from corrosion by preventing the penetration of moisture and air to the metal surface. 

They also provide good adhesion for the subsequently applied layer. Primer penetrates the pores of the substrate and makes a uniform coating. 

Sealer

Sealers also have a similar function as a primer, but sealers are mostly applied to wood or cement substrates. Sealers seal off surface pores. They protect the undercoat by preventing the migration of materials from the substrate to the undercoat.

Texture

Texture gives a distinct 3D appearance. This is applied over the sealer or primer.

Undercoat

An undercoat is applied to hide minor irregularities on the surface. The undercoat should be compatible with the topcoat and primer or sealer.

Topcoat

Topcoat gives the final appearance in terms of color and finish. Decorative, protective, and other specific functions will be fulfilled by the topcoat. The top layer has hiding power. In other words, the top layer has the ability to hide the substrate. Topcoat protects inner layers from radiation and microorganisms.

Composition of a paint

Every painting has three major components. These are solvent, film-forming material (binder), and pigments with other additives. The solvent is a volatile component, and it will be evaporated after the paint is applied.

Solvents are used in paints to carry the pigments, binder, and additives. The most common solvent used in paints is water. Water is the major component in emulsion paints. Here, it is used water alone or with some amount of alcohol or ether.

The most common solvents used in paints are.

• Water
• Aliphatic hydrocarbon mixtures
• Aromatic hydrocarbons
• Terpenes
• Alcohols
• Esters
• Ketones
• Esters

Film-forming material, pigments, and additives are non-volatile components. After applying and drying the paint only non-volatile components are remaining. Film forming material or a binder is a polymer. The main function of a binder in paint is to bind together particles and hold them on the substrate. Pigments have both decorative and protective properties. Other additives which are added to the paint are as follows.

• Extenders
• Plasticizers
• Antifoaming agents
• Thickening agents
• Wetting agents
• Surfactants
• Film preservatives
• Anti-skinning agents

Pigments, additives, and binders will be discussed in detail in separate articles.