The Chemistry of Paint

Introduction

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Color has been around for more than 20,000 years and was widely used by the ancient Egyptians and considered to have magical and healing properties. It was between 600 BC-AD 400 that the Greeks and Romans then introduced varnishes to help along the process of what we know today as paint. Paint is made of a pigment, a binder, and appropriate thinners. 5,000 years ago Blue Frit was the first synthetic pigment being produced by the Egyptians from ground down bluegrass. By 1,000 B.C. development of paints and varnishes based on the gum of the acacia tree aka the gum arabic had been developed. In 1856 the first real synthetic dye, 'Mauveine', was discovered, and that a great many dyes could be made synthetically and cheaply. The reason I chose the chemistry of paint is for one simple reason... because I love to paint! My life is affected by paint in numerous ways. First and foremost because I am an avid painter but paint affects all of us in different ways but mostly its just always around us. Paint brings color to our everyday life and I for one am glad that there is always color.

Composition of ...

Pigments: give paint its color and hiding power./Pigments are water-and oil-insoluble natural and synthetic products that impart color to materials such as paper and plastics.



Vehicle: is the combination of synthetic resins and oils that surrounds the pigment particles.

It determines cohesiveness (providing the strength for the dried paint film) as well as adhesiveness.


Carrier: thins the syrupy resins so the paint will flow on; it evaporates first as the paint dries, and it allows for varying consistencies thicker or thinner.

Water is the carrier for latex paints, petroleum distillates for alkyd paints.


Paint: is any liquid, liquefiable, or mastic composition which, after application to a substrate in a thin layer, is converted to a solid film. It is most commonly used to protect, color or provide texture to objects.

Main Chemicals, Compounds, Components

Activator:

ethyl acetate C4H8O2

toluene C7H8

aliphatic polyisocyanate  C6H5CH(CH3)NCO

hexamethylene diisocyanate OCN(CH2)6NCO


Clearcoats:

methyl ethyl ketone C2H5COCH3

toluene C7H8

mixed dibasic esters CH3O2C(CH2)nCO2CH3 (n=2,3,4)

petroleum naphtha C4H10


Thinners:

butyl acetate CH3COO(CH2)3CH3

ethylbenzene C6H5C2H5

toluene/xylene C7H8/ C6H4(CH3)2

methyl ethyl ketone C2H5COCH3


Basecoats:

methyl ethyl ketone C2H5COCH3

titanium dioxide TiO2

metallic pigments

xylene C6H4(CH3)2


Primers:

barium sulfate BaSO4

resins and fillers

toluene/xylene C7H8/ C6H4(CH3)2

isocyanates (often added)  C9H9NO3

Chemistry's Role

The pigment for paint is both man-made and natural it is made by crushing minerals into a fine powder-like texture. It is meant to be mixed with water, oil, or another base along with solvents, additives, and resins to for the paste needed to create what is known as paint. However in the end paint is man-made by default.

How Paint is Made

Making the paste

Pigment manufacturers send bags of fine grain pigments to paint plants. There, the pigment is premixed with resin, one or more solvents, and additives to form a paste.


Dispersing the pigment

The paste mixture for most industrial and some consumer paints is now routed into a sand mill, a large cylinder that agitates tiny particles of sand or silica to grind the pigment particles, making them smaller and dispersing them throughout the mixture. The mixture is then filtered to remove the sand particles.


Up to 90 percent of the water-based latex paints are processed in a high-speed dispersion tank. There, the premixed paste is subjected to high-speed agitation by a circular, toothed blade attached to a rotating shaft. This process blends the pigment into the solvent.


Thinning the paste

Whether created by a sand mill or a dispersion tank, the paste must now be thinned to produce the final product. Transferred to large kettles, it is agitated with the proper amount of solvent for the type of paint desired.

How Paint Works

A chemical can be sprayed along with the paint to dissolve together on the surface of the object being painted.

Some chemical reactions in paint involve the orientation of the paint molecules.


  • A solvent evaporated and leaves the binder with pigment behind-Lacquer


  • An emulsion cures by water evaporating and crosslinking of polymers-water based acrylics


  • A solvent evaporates, leaving a pigmented drying oil behind to oxidize and form a resinous film-Oil based paint


  • A monomer in a solvent are mixed with a hardening catalyst to create a very hard paint film-Automotive polyurethanes, and epoxies



Resources


About the Author
Erin Sears is a junior at Billings Senior High School. She paints, sings, rock climbs, and loves to white water raft. Erin hopes to go to MSU (Montana State University) for college and major in anthropology.She enjoys painting as a more relaxing activity.
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