Constituents Of Paint

Constituents of paint explained in detail: Pigment, Solvent, Resin (Binder), Extender and other additives.

Before reading about the constituents of paint, you may like to read:


1. Pigments
Pigments are various inorganic or organic insoluble substances which are widely used in surface coatings. The most important properties of pigments are opacity, good covering power, mixing ability with oil, chemical inertness, non toxicity or low toxicity, high hiding power, high tinting strength and reasonable cost. They protect the film by reflecting the destructive ultra violet light, to strengthen the film.
Pigments are classified as follows:
a) Natural or mineral pigments: e.g. talc mica, chalk, clays, iron ores, barytes, diatomaceous earth etc.
b) Synthetic or chemical pigments: e.g. white lead, zinc oxide, lithopone, titanium oxide, and many other organic and inorganic colours
c) Reactive pigments: Those pigments which react with drying oils or their fatty acids and form soaps are called reactive pigments. e.g. zinc oxide, red lead, titanium dioxide etc
d) Organic dyes: Toners (insoluble organic dyes) used directly as pigments because of their durability and colouring power. Lakes, which are organic dyes on an inorganic adsorbent (such as clay), have also been used in many colours. Para red, toluidine toner, Hansa yellow G (lemon yellow) etc. are important lakes. Clay, barite, aluminum hydroxide etc. are well known inorganic adsorbents. Both toners and lakes are ground in oil or applied like any other pigment.
Various pigments used for making paints are
> White: White lead, titanium dioxide, zinc oxide, lithopone.
> Red: Red lead, iron oxides, cadmium reds, rouge etc.
> Blue: Ultramarine, cobalt blues, iron blues etc.
> Chromium oxide: Chromium oxide, chrome green, phthalocyanine green.
> Yellow: Litharge, lead or zinc cnromates, ochre etc.
> Black: Carbon black, lamp black, furnace black etc.
> Orange: Basic lead ·chromate, cadmium orange etc.
> Brown: Burnt umber, burnt sienna etc.
> Metallics: Copper powder, zinc dust, aluminium etc.
> Metal protective pigments: Red lead, blue lead, zinc and basic lead etc.

2. Extenders or Fillers
They are used for decreasing the cost of paint and to supplement the
pigment in increasing the covering and weathering power of the film. Extenders
improve consistency, levelling and setting of the paint. E.g. Talc, china clay, gypsum,
silica, barite, glass flakes, asbestos and anhydrite etc.

3. Film forming materials
The vehicle or film forming materials plays dual role as carriers for the pigments
and as formers of protective films. Reactive oils containing olefinic unsaturation are
used as vehicles. These are usually called drying and semidrying oils, depending on
degree of unsaturation. E.g. Linseed oil, soyabean oil, tung oil, talc oil, castor oil,
varnishes, casein, fish oil etc. These oils form a protective film through oxidation and
polymerization of the unsaturated constituents of the drying oil.
Drying oil is thus a film forming component which upon exposure to oxygen has
the property of drying to hard, firm, non-sticky film through oxidation involving
organic peroxides as the chain initiators.
The various properties of drying oil which are used to decide the grade of
paints are
> Specific gravity: It lies between 0.93 to 0.97
> Refractive index: It lies between 1.48 to 1.51
> Saponification value: It lies between 183 to 187
> Iodine value: For common drying oils close to 90 – 120, while semi drying oils
have the value close to 90
Linseed oil is light yellow in colour but becomes colourless after oxidative
purification. After drying it sets to a hard glossy film.
Linseed oil is used in four different grades by paint and pigment manufacturers.
> Refined oil
> Boiled linseed oil
> Heat bodied linseed oil (stand oil)
> Blown linseed oil

4. Driers
Initially PbO was used as a drier, but the modern driers are Co, Mn, Pb, Zn, resinoleate, linoleate and naphthenates etc. They dissolve in the hot oil and the drying time has been much reduced. They are usually mixed with hot boiled linseed oil. Too rapid drying is not desirable because of some unwanted effects, e.g, the film suffers from wrinkling.
The drier acts as catalyst and promotes the oxidation polymerization process which accelerates drying of the film. The unsaturated drying oils polymerize by reaction mechanism which involves a peroxide intermediate.

5. Thinners or Diluents
In order to dissolve film forming material and to thin concentrated paints for better handling as well as brushing thinner is added. It is also used to suspended pigments. Diluents or thinners may include aliphatic or aromatic naphtha fractions or many contain turpentine. Solvent such as turpentine in spite of its low volatility, maintains the fluidity of the freshly applied film for reasonable period of time.

6. Lacquer
Lacquer is a liquid coating composition containing the basic film forming ingredients cellulose esters or ethers and plasticizers, without or with resin. Lacquers employ aliphatic chemicals, such as ethers, esters, ketones and alcohols to provide the desired controlled volatility. By virtue of evaporation of solvent, they are also called non-convertible coating. When a pigment is added to a clear lacquer, it is called lacquer enamel or pigmented lacquer.

7. Anti-skinning agent
Certain anti-skinning agents are also added to the paint in order to prevent gelling and skinning of the finished product before application of the paint by brushing, spraying or dipping. e.g. Polyhydroxyphenols.

8. Plasticizers
Plasticizers, low melting solids or liquids of low volatility which provide elasticity to the film and thus prevent cracking of the paint. Chemically, plasticizers are mostly esters. Triphenyl phosphate, dibutylphthalate and castor oil etc are used as plasticizers.

9. Resins
Resins are required for water base paints contain no oils and depend on vinyl acetate, acrylic or butadiene styrene polymer resin as the film forming materials.
Varnishes are also, used in the form of natural or synthetic resins. Examples of natural resins are copal or rosin, while that of synthetic resins are urea formaldehyde, acrylate, vinyl or silicone resins. Laquers also contain nitrocellulose as the resin constituent.

10. Binders
Binders act to fix the paint on the coated surface and provide tough, tenacious and glossy film on the surface being painted.
Binders may be of following types.
(a) Oil modified alkyd resins or polymers forming vehicle with the drying oil
These may be oxidizing alkyd resin (used for house paints, interior paints, air drying under coats etc.) alkyd and cellulose resins (used for making low temperature backing under coats) and alkyd and silicon resins (used for superior chemical and heat resistant coats).
(b) Resin acting as vehicle and not containing any drying oil or alkyd resin
Examples are phenoplast (used for making thermosetting under coats), Polyesters (used for making chemical and discolouration resistant glossy film) and acrylonitrile copolymers, butadiene copolymers etc. (used for making emulsion paints, fire resistant as well as corrosion resistant coats and interior decoration paints etc.)

11. Extenders
Extenders such as clay, talc, barytes etc are added to the paint mix in order to prevent the cracking of the film when dry.

12. Other Compounds
Water based paints also require dispersing agents (e.g. casein), antifoam agent (e.g. pine oil) and preservative (e.g. chlorophenol).
(Source: Internet)



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Youth Voice: Constituents Of Paint
Constituents Of Paint
Constituents of paint explained in detail: Pigment, Solvent, Resin (Binder), Extender and other additives.
Youth Voice
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