Engineering Chemistry S Datta

PAINTS 475
A typical composition of an emulsion paint
Constituents
Parts by weight
Titanium dioxide 270
Clay 76.8
Tetrasodium pyrophosphate 1.8
Deionised water 16.5
Casein solution 764
Sodium penta chlorophenate solution 17.4
Pine oil 4.2
Tributyl phosphate 13.2
Copolymer latex 466
Distempers
Distempers are water paints comprising pigments, extenders, binders, and water as a
dispersing medium. The distempers have:
(i) Good covering power
(ii) Ease of application
(iii) Durability
Disadvantage of distemper is that it is not moisture-proof.
Cement paints
Cement paint contains:
(i) White cement,
(ii) Colouring or pigments,
(iii) Hydrated limes, and
(iv) Fine sands as inert filler.
The dispersion medium is water or an oil. In case of brick structure the dispersion medium
is water. In case of metal surface the dispersion medium is boiled linseed oil. Before applying
cement paint a primer coat of a dilute solution of sodium silicate and zinc sulphate is necessary.
Cement paint has marked water-proofing capacity and gives a stable and decorative film.
Varnishes
Varnishes are organic compounds used as protective coating similar to paints. But only
difference is that varnishes do not contain colouring substances, i.e., pigments.
Varnishes are classified under two heads:
• Oleoresinous varnishes and
• Spirit varnishes.
Oleoresinous varnishes are the solutions of one or more than one natural or synthetic
resins in a drying oil and a volatile solvent. While the spirit varnishes are solutions of resins in
volatile solvents only, generally methanol and ethanol. For the oleoresinous varnishes the
formation of the film is due to the polymerisation of the oil and in case of spirit varnishes the
film formation is due to only solvent evaporation.
Oleoresinous varnishes are also classified as:
(i) ‘long oil’ varnishes have high proportions of drying oil
(ii) ‘short oil’ type contains a lower proportion of drying oil