THE CHEMISTRY OF DYES AND PAINTS
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
Table of content
1.2 Historical Survey of Dyes and Paints
1.3 Different Kinds of Dyes and Paints
2.1 Mechanism of Diazotization
2.2 Coupling Method
2.3 Principles of Formation and Production of Paints
2.4 Method of Film Formation
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
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
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
I II C N+ (CH3)2 C1-
2, 4, 6 - N (CH3I2 Malachite Green
BISMARK BROWN III
H2N O N=N O N=N O NH2
NaO3S O N=N O
FAST RED A
NaO3S O N=N O OH
O O N=N O O
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.