Paint Chemistry

Components of a paint

• solvent
• Pigments
• Binder/ Resin
• Additives

Solvent:

Solvent disperse the different component of the paint and making the desired consistency of the paint. It is adjusting the curing properties and the viscosity of the paint. Solvent is volatile and once the paint applied the solvent evaporates and allow pigments and binder to produce a film coating and gradually drying. Also it controls flow and application of the paint.  Depend on the solvent used paint can be categorizes as,

• Water based – Emulsion paint: Main diluent is the water in this paint
• Solvent based – Enamel paint: Main diluent is the solvent that used as a base.(Primary solvent)

Pigments:

Pigment is a fine powder which provide a colour to a paint by reflecting or transmitting the light. Pigments are insoluble and it suspended in a liquid solvent vehicle to become the colouring material of the paint.  There are two types of pigments used in paint industry as,

• Primary pigments – Provide the primary colour to a paint
• Extender pigments -  These pigments are providing a filling property to a paint. Also these extenders are provide the covering capacity, durability, scrubbing and the colour retention of the paint.

Primary pigments and extenders can be Inorganic or organic pigments  which provide various characteristics to a paint.

Binder/ Resin:

Technically known as a vehicle. It is imparts the adhesion, binds the pigments together. Basically binder/ resin is the film forming component of the paint. Also it influence the gloss, exterior durability, flexibility and the toughness of the paint.

Binders can be categorised according to drying (solvent evaporation) or curing (polymerization) mechanism.

• Solvent evaporation
• Oxidative cross linking
• Catelized polymerisation
• Coalescence

Once the solvent evaporates a solid film form.  It provides the adhesion on to a surface .

Additives:

A paint can have various types of additives  but use them in small quantity. Additives have ability to control the various properties of the paint. Some properties are viscosity, drying time, dispersion of pigments,  pigment stability, gelling properties, foaming, skinning etc.

Classification of paint

Paint can be classified in to several categories as stated in the below.

• Solvent and the binder -  Binder is an important component of paint. Certain types of binders  as well as solvents are used to manufacture paint depend on it's expected properties.

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  Water base (Emulsion) - Acrylic, Vinyl Acrylic and PVC binders are used in water base paints. Generally these are known as Acrylic paints and PVAs.  These are large complex polymers disperse in water. And the micro particles of  the polymers are non soluble and they make 'plastic ' layers in the water medium. When the paint applies water evaporates and these 'plastic' individuals are coalescence  and binding to the substrate to the other particles and make the continuous film.  These paints are known as latex paints or emulsions.

• Solvent base/ Alkyd  (Enamel) - These paints used synthetic binders called alkyds. But classical binders were vegetable oil such as linseed oil and soya oil were common. These are water in-soluble and they have high volatile organic compounds. Also they contain high absorbable organic halides. Therefore they have negative environmental and health  impacts. Also these paints are easily become yellow as it contains alkyd resins. 
• Application
• Decorative paints- for architectural paints used for decorative purposes both interior and exterior. Most of them are water base.Common architectural paints are,
• Primers and bonding liquids- use as a preparatory coat before applying the top coat. This is used to cover stains, enhance the covering capacity of the paints, alkali resistance, cover the uneven surfaces. Also it smooth the rough surfaces and provide a better finish But depending on the substrate primers are use for many requirements. For an example wood primers are use for penetration and stain resistance while metal primers are use for corrosive resistance. 
• Interior paints- The properties are more proven to higher stain resistance.(sometimes wash ability without any damage to paint ) and most commonly preferable with more sheen.
• Exterior paints- Both Interior and exterior paints have same properties. But exterior paints have more protective function such as  resistance to harsh weather conditions( UV light, rain, dust).Also they have higher  resistance to micro biological properties such as fungi, mould, bacteria, etc

•  Roof paint

• Industrial paints- includes wide varieties of specialised paints such as,
• Automotive paints
• Road markings
• Metallic paints
• Marine paints

They are basically solvent based. But rapidly moving to water base as it is more eco friendly

What is paint

Technically  paint is used to cover a surface for it’s protection and for the attraction.It can found in liquids, semi liquids or in powder form. These forms adhere on to a surface of the substrate and making a film. This can be occur chemically or physically. 

• Liquids – Evaporation the solvent part and drying the pigments on to the surface.
• Powders- Melting processing.
• Semi liquids- can be Physically by drying the liquid component and then  solid component chemically forming the film on the surface.

There are certain properties expected from a paint such as protection against corrosion, various weather conditions, mechanical abrasions. Also as for attraction i.e decorative purposes it can be used in house hold applications, automotive and furniture. More over it can be used for source of information provider. Example  road marking, traffic signs, banner markings etc.