Firstly, we must know the four main components of paints.

Paints are composed of

  1. Solvent
  2. Binder
  3. Pigment
  4. Additives

1. Why does Paint dry on walls but not in sealed tin?

A Solvent is a reason why paint dry on the wall. As the name suggests, it’s something that dissolves something else in it. This helps paint components to dissolve to become a homogeneous mixture. The main feature to make the paint less viscous and thinner. Once spread on a surface its job is to evaporate and leave a thin layer of solid coating. When the paint is applied on the surface you get a nasty smell persisting for a few days until the solvent is evaporated from the wall.

The basic mechanism by which paints dry 

Water-Based Paints: Nowadays modern paints are mostly water-based & note water promptly evaporates. Note that the rate of evaporation of any liquid depends on its vapour pressure above the surface. When the paint is airtight sealed in a tin, vapour pressure is quickly established where won’t evaporate because of the small headspace in the tin. Compared to the Sealed Paint Tin there is no build-up of water vapour pressure in a confined space. So after painting on the wall, the water will promptly evaporate to leave a dried solid film of paint.

Oil-based paints: Oil does not evaporate, unlike water. Oil-based paints dry in a different way. The smaller oil molecules chemically react with oxygen from the air to form larger molecules (i.e polymers) which are in solid-state. As unavailability of oxygen in sealed tin drying of oil-based paint not possible, and the oil remains in the original liquid state. Oil-based solvents have a powerful smell that lingers for several days after painting. Alkyd Based paints also dry the same way as Oil-based paints. Different Solvent gives in various types of surface finishes.

2. Why does paint stick on the wall?

Binder is liquid substances (natural oils such as linseed oil and even synthetic plastics such as polyurethane, epoxy, acrylic or silicone resins) which hold pigments and additive mixture on the wall/ surface after the solvent is evaporated. These make the pigment particles to evenly stick on the wall, and provide a protective layer to it so they don’t wash off when water is added to it. It provides many of the necessary paint film properties such as abrasion resistance, flexibility,  gloss level, adhesion, hardness, speed of drying and durability.

3. Why does paint have various colors?

Pigments is a component is paint that provides different colours based on its composition. Generally, metal compounds are used to provide various colours i.e Titanium dioxide is used to make white, iron oxide gives yellow, brown, red, or orange to the paint & chromium oxide gives a green colour to paint. It is very small particles and is suspended in a solvent – binder system. Pigments are not soluble in the solvent and the binder holds them together to form a thin film on the surface. Different colour pigments can be mixed to achieve a desirable paint.

4.  Why are additives are added to paint?

Additives are added in small quantities to a paint composition. To improve various paint properties such as production and storage properties of the liquid paint products as well as application and other performance properties of the paint film. So, additives are used as plasticizers, driers, UV absorbers, corrosion inhibitors, and various other things to improve the performance of the paints. And also to make the paint surface resistant to marking and scratching Silicone is used.

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