paints and varnish

1. PAINTS

2. PAINTS
Paint is a mechanical dispersion mixture of one or more pigments in vehicle
(drying oil).
metallic and wooden articles to protect them from corrosion and to give better
surface appearance.
When paint is applied to a metal surface, the thinner evaporates while the
drying oil slowly oxidizes forming of pigmented film.

3. Following Characteristics of Good paints are
 It should be resist to atmospheric condition.
 It should have high covering power.
 Its film should be washable.
 Its film should form uniform non porous.
 Its film should be resist to corrosion
 Its film should be reflect light.
Characteristics of Good paints

4. The important constituents of paint are as follows.
1. Pigments
2. Vehicle or drying oils or medium
3. Thinners
4. Driers
5. Fillers or extenders
6. Plasticizers
7. Antiskinning agents
Components of paints and their functions

5. Pigments

6. 1. Pigment:
A pigment is a solid and colour-producing substance which gives desired colour to the
paint.
Example:
Pigments:
1 White pigments Titanium oxide, Zinc oxide.
2 Black pigments Graphite, Carbon black.
3 Red pigments Red Lead, Indian red (Fe2O3).
4 Blue pigments Cobalt blue

7. Functions:
The following are the functions of the pigment:
• A pigment gives opacity and color to the film.
• Give an aesthetical appeal
• It covers the manufacturing defects.
• A pigment gives strength to the film.
• It protects the film by reflecting the destructive ultraviolet rays.

8. 2. Vehicle or drying oils or medium:
The liquid portion in which the pigment is dispersed is called a medium or vehicle. It is film
forming constitute of paint.
Example:
Linseed oil,
soybean oil
fish oil.
dehydrated castor oil,

9. Functions:
Vehicles hold the pigment particles together on the metal surface.
They form the protective film by evaporation or by oxidation and
polymerization of the unsaturated constituents of the oil.
Vehicles give better adhesion to the metal surface.
They impart water repellency, durability and toughness to the film.

10. 3. Thinner:
Thinners are added to paints to reduce the viscosity of the paints in order to make it easy to
apply on the metal surface.

11. Thinner:
Ex: Turpentine, kerosene and petroleum sprit.
Functions: Thinners reduce the viscosity of the paint to render it easy to handle and
apply to the metal surface.
They dissolve the oil, pigments etc. and produce a homogeneous mixture.
Thinners evaporate rapidly and help the drying of the film.
They increase the elasticity of the film.

12. 4.Driers: are oxygen carrier catalyst.
Driers are used to speed up the drying process and accelerate the drying of the oil film by
oxidation, polymerization and condensation.
Example: heavy metallic soaps such as Naphthentates and Resinates of lead, cobalt and
manganese.
Functions: Driers act as oxygen carrier catalysts which help the absorption of oxygen and
catalyze the drying of the oil film by oxidation, polymerization and condensation.

13. 5. Fillers or extenders:
Fillers are used to increase the volume of the paint and to reduce the cost. It increases
the durability of the paint,.
Example: Asbestos, talc, china clay, calcium sulphate and calcium carbonate.
Functions: Fillers serve to fill the voids in the film.
They reduce the cracking of the paints.
Fillers increase the durability of the paints.
They reduce the cost of the paint.

14. 6 Plasticizers:
Plasticizers are chemicals added to increase elasticity of the film and to prevent cracking of
the film.
Example: Tertiary amyl alcohol, triphenyl phosphate,triglyceryl phosphate.
7. Antiskinning agents:
They are chemicals added to the paint to prevent skinning of the paint.
Example: Polyhydroxy phenols, guaiacol, etc.

15. VARNISHES

16. Varnish is a homogenous, transparent viscous liquid of natural or synthetic resin in
oil or spirit medium.
It is prepared by dissolving resins in oils or thinners or both.
If the medium is oil it is known as oil varnishes.
If the medium is spirit it is known as spirit varnishes.
It is used as a protective and decorative coating to the wooden surfaces. It
provides a hard, transparent, glossy appearance and durable film to the coated
surface.

17. TYPES OF VARNISH
• Types of varnishes depends on solvent used;
• Oil varnishes : Amber, Copal in linseed oil
• Spirit varnishes: Lac, Shellac etc.
• Turpentine varnish: Rosin, Gum dammar, Mastic in turpentine
• Water varnish : Shellac in hot water [ with borox,potash or soda added ] to
dissolve the shellac

18. There are two main types of varnishes
1. Oil Varnish : It is prepared by dissolving natural or synthetic resins in oils .
It required long period for drying.
Ex Copal varnish (Copal is a name given to tree resin, particularly the aromatic resins
from the copal tree)
2. Spirit varnish: It is prepared by dissolving natural or synthetic resins in Spirit .
It required Short period for drying.