THE CHEMISTRY OF DYES AND PAINTS
ABSTRACT
The Chemistry of Dyes and Paints
The
existence of man depends on his ability to react to the natural substances that
he is surrounded with and makes use of chemicals of various kinds available to
him to maintain his socio – cultural existence.
This
process include dyeing in ancient time and making of paints in the present day
of modern technology.
Paints
are gradually modifying the existence of man.
In areas of beauty, prevention and preservation of economy.
Today,
colour is no more limited to the seven primary colours that is, Red, Orange, Yellow, Green,
Blue, Indigo and Violet. Any desirable
colour can be made out of these seven primary colours.
TABLE OF CONTENT
Title page
Approval page
Dedication
Acknowledgement
Abstract
Table of content
CHAPTER ONE
1.1
Introduction
1.2
Historical
Survey of Dyes and Paints
1.3
Different
Kinds of Dyes and Paints
CHAPTER TWO
SYNTHESIS
2.1
Mechanism
of Diazotization
2.2
Coupling
Method
2.3
Principles
of Formation and Production of Paints
2.4
Method
of Film Formation
CHAPTER THREE
APPLICATION OF DYES AND PAINTS
3.1
Methods
of Dyeing
3.2
Chemical
Forces Responsible for Dyeing
3.3
Principles
of Dyeing
3.4
Method
of Painting
3.5
Defects
in Paints
CHAPTER FOUR
USES OF DYES AND PAINTS
4.1
Utilization
of Dyes
4.2
Different
Kinds of Dye and Their Uses
4.3
Different
Types of Paint and their Uses
4.4
General
Uses of Paints
4.5
Discussion
4.6
Conclusion
REFERENCES
CHAPTER ONE
1.1
Introduction
Dyes are substances that are used to
colour materials especially fabrics such as wool and cotton. Dye is either a natural or a synthetic
intensely coloured organic substance having the property of imparting more or
less a permanent colour to other substances. (1)
Dyes can be made from chemicals that
occurs in natural object such as plants, wood, shellfish, rocks, or soils.
Nowadays most modern dyes are coloured substances synthesized from certain
chemical compounds called benzonoid hydrocarbons obtained from either coal tar
or petroleum.
A dye is useful if we can affix it to
the substance that is to be coloured and it must also retain its colour on
prolong exposure to light, water and soap treatment, a property referred to as
fastness of dye. The colour of dye is due to the interaction of visible light
with the electron system of the dye molecules (2).
Paint can be defined as a pigmented
liquid composition which is converted to an opaque solid film after application
as thin layer. A pigment is fine solid particles used in preparing paints and
is essentially insoluble in vehicle whilt. Vehicle is the entire liquid portion
of a paint and it includes pigment binder volati9le solvent.(Ref. 3).
1.2
Historical Survey Of Dyes and Paints
Dyes used earliest were natural dye
stuffs derived from plants. These include indigo and alizarin which were
obtained from tintoria and madder roots respectively. With the advent of the
synthetic dye which are far more varied in shades and properties and generally
more brilliant, the production of the
natural dyes has decreased to a very small portion of the total market. Their
greatest uses now are in the dyeing of leather.
Synthetic dyes are not new, chemists
started the synthetic dyes as far back as 1771 when the first synthetic dyes 2,
4, 6 – trini trophenol was prepared by Woulfe and in 1834 Runge prepared
Rosolic acid by oxidation of crude carboxylic acid. It was William who ushered
in the era of commercial synthetic organic dyes when he discovered mauveine
from aniline in 1856. (3)
The discoveries by Peter Griess, a
German chemist of the diazotization reaction of diazorium compound together
with the elucidation by Kekunle in 1865 of the structure of benzene laid the
basis for the next phase of the development of dye industries.
The product obtained by Griess
contained two nitrogen atoms for the one in the amino group.using old name
(azote) for nitrogen, Griess called these new substance diazo compounds (Ref.
3)
R. Clavel discovered disperse dyes
for the dyeing of acetate fibres and vat dyes containing azo groups were
developed by E. Honold and M.Schnbert in 1921.
reactive dyes procion for cellulose were discovered by I. D. Ratte and W.E.
Stephen in 1956 (Ref. 4).
In 1863 C. Martins synthesized
Bismark Brown III. This dye contains three moles of dirphenylene diamine. In
1870 A Kekule coupled diazotized aniline to phenol thus, preparing the first
hydroxyl azodye. The first synthstic azo dye for wool chrysodine Y (basic
orange) was prepared by H.Caro and O.N. Witt.
Very much
familiar with diazotization, Heinrich Caro who happened to be in England when
Griess was there found out that Rosaline could be diazotized. With youthful
exaggeration Carl Graebe and Lieberman made a more intimate research and they
did not only prepare alizarin but they held nitrogen atoms responsible for the
physical properties of colour. This was in 1968.
TYPICAL DYES MENTIONED
OH
NO2 NO2
I II C
N+
(CH3)2 C1-
No 2
Picric
Acid
2,
4, 6 - N (CH3I2 Malachite
Green
Trinitorphenol
BISMARK BROWN III
NH2 NH2
H2N O N=N O N=N O NH2
III
NaO3S O N=N O
O O
IV
FAST RED A
NaO3S
O N=N O OH
O
ORANGE I
NH2
O O N=N O O
O O
SO3Na
So 3N
CONGO RED
DIRECT RED 28
Because of the advancement in
technology there was a shiff from the crude laboratory preparation of pigments
to industrial preparation of pigments for paints.
Today, science can make colour in
ways different from the ancient period. For example, many colours are made from
coal tar and can also be synthesized from other materials.
Taking the international paint of
West Africa for example, who specialized in marine coating, industrial
coatings, powder coatings, packaging coatings and decorative paints, etc has
its strength lying in its association with its technical partner that is the
international paints company (I.P.C) who was one of the earliest established
paint manufacturing company which started about 100 years age.
The need for paint manufacturing
arose when the world first factory made special marine composition to protect
steel ships from corrosion and the damaging effects of marine life was built
near Newcastle, in Northern
England. This small factory
was the fore runner of I.P.C who have retained their position as the dead in
the manufacture, and marketing of marine paints, supplying increasingly
advanced high technology coatings to over one third of the world’s shipping. International paints company has established
two modern factories situated at Ikeja and Oregun backed up by sophicated
laboratories skilled and qualifies chemist.
International paint of West African
manufactures advanced coatings required by Modern industry. I.P.W.A. supplies various marine paints used
in maintenance of vessels that call at Nigerian ports. It also supply paints to the Nigerian Navy,
local ship yards and the dydock at snake Island Apapa.
The increasing demand for the use of
paints and the ability of paint industries to meet this demand is as a result
of advancement in technology, qualified paint technologist and chemist. Research and expansion programme are
intensified by various industries on how to improve and maintain high quality
of paints. (Ref 5).
1.3
Different Kinds of Dyes and Paints
Dyes are classified into various ways
which include:
1)
Acid Dyes: These are salt of organic acids
(sulphoric and oxylic) and are usually marketed as the sodium salts. The acid groups confer water solubility on
the dye stuff molecule. When dissolved,
the dye ionizes with the dye structure in the anionic and carrying the negative
charge part. These dyes are used principally
for wool, natural suk, synthetic fibres of poly acrylic nature, leather and
paper.
2)
Basic Dyes: Basic dyes exhibit generally good
fastness to light and washing when dyed on acylic fibres. They have wide utility for colouring wool suk
leather and paper.
3)
Mordant Dyes: the most common mordants are chrone
deying processes often the chromium compound is applied during the dyeing,
along with the dye or it can be applied after the dyeing, these are called
respectively meta, mono, or auto chroming and after or top chroming operations.
4)
Azoic Dyes: These are water insoluble Azo
compound which have been formed cotthin the substrate by chemical reaction of
the intermediate components. Generally,
the dyeing operation proceeds by dipping the cloth into a solution of one of
the component drying the cloth without rising, and then treating it with a
solution of the other components (usually a diazo component which must be kept
cold to prevent decomposition). Because
the product of the reaction which then be deposited throughout the fibres is a
water insoluble colour, it is actually a pigment instead of a dye stuff. These colours are used for cotton and rayon
in great quantity in printing.
5)
Oxidation Dyes: These are produced directly in the
fibre of other substrates by a chemical oxidation following the impregnation of
the substrate with certain aromatic amine.
The final product is probably a pigment instead of a dye stuff. They are used for the dyeing of hair and fur.
6)
Vat Dyes: This class of colours is
distinguished by the species method of application needed a vating operation,
where in the water – insoluble colour is made soluble by a chemical – reduction
of the chromophore.
This vat solution, which is often a
different colour from the original insoluble material has affinity for cotton,
dyeing it with air or oxidizing agents.
The variety of paints available is
now extremely wide and only a small selection will be given here:
1)
Red Lead metal primer: This is used mainly for iron and
steel. It provides very good protection,
especially where steel has to stand for long periods before further paint is
applied.
Chromate
based metal primers are also widely used and are claimed to be similar in
performance to red lead metal primers.
Additionally they may be used for priming aluminum and its alloys.
2)
Calcium plumbate: This is designed for direct
application to new galvanized iron. It
may also be used for priming wood.
3)
Aluminum Paint: It contains aluminum powder and
gives good heat resistance. It is used
on wood or metal.
4)
Wood Primer: This is normally of a consistency
to suit soft wood. For hard wood it may
need to be thinned to assist penetration.
5)
Alkali: Resisting primer – is for use on
plaster, concrete, asbestos, cement, it is particularly suitable for cement
rendering, especially when painting has been completed.
6)
Glass paint: It is very widely used and
obtainable in many varieties and colours.
Some brands require a double coat of gloss finish for maximum
durability. It provides shiny surfaces
and washable. Mainly used in living room
and bath room and also in the kitchen.
7)
Under coat: Is applied after primer and also to
receive the top coat.
8)
Emuision paints: They are now widely used throughout
the world. They may be applied to brick
work, plaster, cement, wall – board, plaster board, over old paint after proper
preparation or even wall paper. They are
not suitable for direct application to wood surfaces.
9)
Rubber paint and chlorinated rubber
paints: They have
very good chemical resistant and hence are used where other paints would be
considered in appropriate, for instance in chemical works and breweries.
10)
Lacquer: They are used extensively in
industry.
11)
Bituminous paint: Contains tarry base and gives good
water resistance (used where water is to be resisted).
12)
Fungicidal/pesticidal
paint: They contain appropriate pesticide or insecticide – DDT.
Varnish: It is made by mixing oil, resin and driers. Pale colour medium oil varnish is very
suitable for interior work not exposed to sunlight. It is used in floors and furniture works. 
