Paint can be defined as the pigmented liquid with a liquefiable nature that substrates into a thin layer and converts to a solid film upon application. The primary objective of paint is to protect, impart colour and provide texture to the surface where it is applied. In other words, paint can be understood as the substance that is commonly used as the final finish to the surfaces of the structures for protecting or decorating the surface. The base, vehicle, thinner and pigments are main components of paint.
Paint is basically a pigmented opaque material i.e. it can hide the surface to which it is applied. A wide variety of paints with various formulae are used all over the world. The most common types of paint formulae available in the market are the oil-based formulae and the water-based formulae.
Paint is also available in a wide variety of colours. It is basically stored and applied as a liquid but eventually dries into a solid after application. It is a combination of pigments with appropriate thinners or oil. It is usually applied to the surface by spraying or brushing. It is used as a protective covering to prevent corrosion, chemical attacks and other weathering effects. It is also used to enhance the aesthetic appearance of the structure. All paints are not suitable for all conditions. For different conditions, different types of paints are desirable. The characteristic of good paint can be listed as follows:
a. Paint should have high coverage and durability.
b. It must be able to form an elastic, tough and a hard film upon drying.
c. The paint must have a good hiding power and must impart the required colour.
d. It must not crack upon drying.
e. It must be able to resist the weathering effects as well as corrosion.
f. The paint must dry quickly.
g. The colour imparted by the paint should not fade away within a short period of time.
h. It must be resistive to blistering, cracking and moisture.
i. The brush marks should not appear after application.
j. The paint must provide a long-lasting pleasing appearance.
Components of Paint
There are 7 major components of paint. They are:
1. Base/ Body
The base is one of the main components of paint and is also commonly referred to as the body of paint. It can be defined as the solid substance in a fine state which forms the body of the paint.
The base makes the paint opaque, harder and elastic in nature. It also prevents the paint from cracking particularly the shrinkage cracking. White lead, red lead, zinc oxide, zinc white, iron oxide, titanium white, aluminium powder, lithophone, etc. are examples of the base. Some of them are explained below.
a. White Lead:
White Lead is used extensively for the painting works of the building and woodworks. It is available in the market in a variety of forms commonly powder form and stiff paste form. It is mostly used as an undercoat. The stiff-paste form is made by mixing the white lead with linseed oil.
White lead is dense and water-proof in nature. It can be applied easily and has excellent covering powder. However, it is not suitable for metal works. It must always be kept covered as it is prone to discolouration under exposure to the air.
b. Red Lead:
Red Lead is bright red in colour. The bright red colour is imparted by the presence of the oxide of lead. It is also available in the market in two forms i.e. powder form or the paste form.
Red lead as paint base dries quickly, is durable and has a fresh appearance. It is commonly used for the painting of ironworks and also as a priming coat on wooden surfaces. It can also be used as a drier as it solidifies quickly when mixed with the linseed oil. The disadvantage of red lead is that it is poisonous in nature and must not be used when fresh.
c. Zinc Oxide:
Zinc Oxide is also called Zinc White. It is basically an oxide of zinc and constitutes the base for almost all the zinc paints. It essentially consists of white powder and is also available in paste form by grinding with linseed oil.
Zinc oxide is smooth and transparent in nature. It is highly desirable because it is non-poisonous and resistive to corrosion as well as sulphur attacks. The limitation of zinc oxide is that it is costly, less durable and less workable. After hardening, it is prone to surface cracking.
d. Titanium White:
Titanium white is highly opaque in nature. It consists of chemically inert pigment and is non-poisonous in nature.
Titanium white is not affected by factors such as light, heat as well as acids. Due to its high refractive index titanium white possesses excellent hiding power and generally used as an undercoat in all types of exterior and interior organic coating.
e. Iron Oxide:
Iron oxide forms the base of all sorts of iron paints. It is usually obtained from the haematite ore. It is extensively used as the protective coating for rusting and as a prime coat for the structural steel and iron surfaces.
The vehicle is basically composed of an oily liquid in which both the base and the pigment are soluble. The primary objective of the vehicle is to allow the paint to spread over the surface to which it is applied.
Vehicle mostly adjusts the viscosity of the paint. It is quite volatile in nature due to which it does not necessarily become a part of the paint. Water is used as the vehicle in case of the water-based paints. On the other hand, various types of solvent are used as a vehicle in case of the oil-based paints.
Some of the common examples of vehicles can be listed as follows:
a. Linseed Oil
b. Dehydrated Castor Oil
c. Bleached Oil
d. Fish Oil
e. Soya Bean Oil
f. Petroleum Distillate
h. Ketones and Esters
i. Glycol Ethers
The pigment is responsible for imparting the colour to the paint. The primary function of the pigment is to hide the surface to which it is applied. It also makes the surface opaque and glossy in nature.
The pigment can be commonly classified into two types namely the extender(inert) pigment and the prime pigment. The most common types of pigment used are zinc oxide and titanium oxide.
Some of the common examples of pigments are:
a. In white colour paints: White Lead, Titanium White, Lithophone are used as a pigment.
b. In Yellow Color: Chrome Yellow, Zinc Chromate, Yellow Ochres are used as a pigment.
c. In Red Color: Red Lead, Venetian Red, Chrome Red, Natural Red Oxides of Iron are used as a pigment.
d. In Blue Color: Prussian Blue, Paris Blue, Ultramarine, Cobalt Blue are used as a pigment.
e. In Brown Color: Oxides of Iron are used as a pigment.
Thinner is also called a solvent. It is added to the paints with the objective of making the application of the paints easy, uniform and smooth. It is also used to adjust the viscosity of the paint. The main functions of the thinner can be listed as follows:
a. Increase the fluidity of paints.
b. Making the application of paint easier and smoother.
c. Facilitating the penetration of paint into the porous surfaces.
Some of the examples of the paint thinners are:
a. Turpentine (obtained from the distillation of gums from Pine trees)
d. Coal tar and other hydrocarbons
The extender is also referred to as the fillers. As the name itself implies, the filler is added to the paints to increase or extend the volume of the paint without disturbing other essential properties. The chief characteristic of the extender is that it is chemically inert to other components of paint. Some of the common examples of the extenders are as follows:
d. Silica and Magnesium Silicate
The dryer is usually added to the paint to accelerate the drying of the vehicle of the paint. The primary function of the dryer is to increase the oxidation and hardening of the vehicle. Some of the common examples of the dryer are the organic salts of lead, iron, zinc, manganese, calcium etc.
The additive is added in a small amount to the paint. It is added to the paints to improve the properties of paint such as opacity, colour, dispersion of pigment, anti-freezing properties, corrosion-resistant properties etc.
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