What Is Paint?
Paint can be defined as the mixture of homogeneous ingredients namely Binder, Pigment, VOC & additives, which when applied on the surface as a thin layer that forms a solid dry adherent film after oxidation/evaporation/polymerization.
Paint also can be defined as the diffused item in a particular binder, dissolved in a particular solvent.
*Adhesion: is defined as the extent of attachment between film & the substrate.
Properties of Paint
- It should available in the required color with high hiding power.
- It should be able to resist the atmospheric conditions in which it will be put
- The films produced should be washable
- It should resist corrosion
- It should have sufficient consistency (property to resist permanent change of shape) for a particular purpose for which the paint is to be used.
- The paint film covering any surface should give a gloss appearance.
All necessary requirements of purpose can be added to paint by properly choosing the proper pigments, extenders, binders, and their quantities. There are no set methods for doing so.
Purpose of Paint
- To restrict the corrosion of paint.
- The paint should provide resistance against the corrosive effect of sun, wind, rain, frost, atmospheric pollution & other natural elements, heat, moisture, gases, etc.
- It provides delays in rusting.
- It Provides an Aesthetic look to materials & A smooth surface for easy cleaning.
The following are major Painting Components
- Filler/ Extender
- Volatile organic compound (Thinner)
- Additives (Anti skinning agents, Anti settling agents, Plasticizers, fire retardants, etc
“Binders are generally consisted of resins or oils but can be of inorganic compounds”
- It is the major film-forming component & absolutely required ingredient of any paint
- It consists of a resin and a solvent thinner.
- Binder is a component of paint that gets solidified to form the dry paint film when the solvent evaporates.
- The Alkyd resin types are widely used binders to form dry film simply by volatilization as well as by oxidation in the presence of air.
- The Epoxy & PU type of resin binders mainly dry through chemical reactions.
Purpose of Binder
- Binds pigment, fillers & additives together
- Imparts adhesion & strongly influences:
Binders include resins:-
- Alkyds, Polyurethanes (PU), Epoxy, Polyesters
“Pigments are mainly formed from finely ground inorganic or organic powders of higher RI (> 1.5)
- It becomes more the light is bent & greater the opacity due to higher RI.
- As it offers good opacity and has good lighting absorbing & /or scattering properties
- Its particle’s average diameter ranges from 0.01 to 5μ.
Properties of pigment:
- The pigment should be opaque so that it may have good covering power.
- It is because when the pigment is opaque the pigment particles scatter &/or absorb light sufficiently to prevent it from reaching the substrate
- Generally, the Opacity of any substance depends on two characteristic properties.
i) Refractive Index (RI)
In case the particles of pigment do not have a high RI, less the bending of light traveling & thus insufficient hiding of the substrate.
ii) Particle size
The particle size of any pigment has also an effect on the effectiveness of the pigment. It observed that as the particle size decreases, opacifying ability increases.
- The pigment should have non-toxic so that they have no bad effect on the health of the painter & inhabitants.
Purpose of pigment
The pigment is a major constituent in the paint to serve the following properties,
- It offers color opacity, film cohesion, and sometimes corrosion inhibition
- It offers a good aesthetic look to the paint
- Eliminate the substrate and previous color on the substrate if any
- protects the film by reflecting the destructive UV light
Widely used pigments
The majorly used pigment Titanium Dioxide, Red Oxide, Carbon Black, Prussian Blue, Zinc Oxide, Chrome Yellow, White Lead Aluminum powder, etc.
* [Titanium dioxide is majorly used as a pigment as it has good covering power).
Titanium is an excellent reflector of infrared].
The extender or filler is a non-expensive cheaper organic compound added to the paint in order to increase its volume. (RI <1.5)
Extenders are majorly had inorganic nature substances & do not provide color to the paint but are added to improve adhesion, ease of sanding, and film strength.
- As their cost is less compared to prime pigments, they reduce the overall cost of the paints.
- Average dia: up to 50μ
- t does not provide color to paint.
- It has Poor optical properties (reflectance, opacity, etc)
- It helps in improving the adhesion properties of paint.
- If needle-shaped or flaked shape extender is added to paint the settling may be very little.
- To provide a better thickness of the film.
- To Increases volume, paint film thickness
- To reduces the cost of the paint
- It offers better toughness, abrasion resistance & texture
- It helps in consistency control
Widely used fillers
Gypsum, Ground silica, Barytes, Slate powder, French chalk, Calcium carbonate, china clay, asbestos, silica, mica, whiting, etc.
VOC or thinner is a liquid component of paint used for viscosity adjustment and correct application”
- It is mainly used to dissolve binders and to facilitate the application of paint. Solvents are generally organic liquids or water.
- If Excessive thinner is used it may dull the color & gloss.
- It can prove to be hazardous due to its toxicity & flammability
- As the solvent in the paint gets evaporated, the remaining paint is fixed onto the surface.
- Control flow and application properties
- Act as a carrier for binders & pigments
- Help penetration into porous surfaces
- It can be used to clean brushes & other painting tools
Widely used thinner
- Turpentine oil (distilled pine tree sap): the most commonly used thinner
- Benzene & Naphtha: as a substitute.
- Mineral spirit, acetone, carbon tetrachloride, ethyl alcohol
As the drying process of paint depends on the solvent and film thickness, it may take as long as several hours.
The length will be the drying time as the thickness of the film increases. If the process of drying paint is artificially accelerated, there may be problems with adhesion between the protective film and the metal surface.
Its main function is to accelerate the drying process.
Cobalt octane, Litharge, Red lead, Lead acetate, Lead acetate, Manganese octane, Manganese dioxide, Zinc sulfate, etc.
A compound added to a paint which prevents corrosion by forming a metal oxide layer
- To protect the substrate from corrosion
Commonly used corrosion inhibitors:
- Sodium molybdate
- Zinc molybdate
Additives are the small quantity of chemical substance added to a paint to improve or modify the paint properties
- It amounts in paint generally in a range of 0.001% to ≤ 5% & have a profound influence on the physical & chemical properties of the paint
- It helps to Prevent clustering of pigments
- The addictive substance such as polyoxyethylene ethers of dodecyl alcohol is added to attain compatibility of different material in the paint system
- Driers accelerate the process of paint drying (hardening) by catalyzing the oxidation of the binder.
- Plasticizers additives added to a paint to increase the paints flexibility, durability, compatibility & minimize film cracking
- Fungicides, Biocides and Insecticides types of additives prevent growth and attack of fungi, bacteria, and insects.
- Flow control agents in the paint to improve flow properties.
- Defoamers type of additives helps to prevent the formation of air bubbles entrapped in the coatings.
- Emulsifiers is known as wetting agents increasing the colloidal stability of the paints in the liquid state.
- UV stabilizers are offered better stability of the paints under ultra-violet light.
- Anti-skinning agents in paint prevent the formation of skin in the can.
- Adhesion promoters help to improve the adhesion of the coating to the substrate.
- Corrosion inhibitors help to reduce the corrosion rate of the substrate.
- Texturizers in paint impart textures to the coatings.
- Antifreeze helps to withstand exposure
- Pigment stabilizers improve pigment stability
- Fire retardant properties
- Anti settling
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