Classification of paint can come in various ways such as; A colouring substance spread or for spreading on a surface. A material made by incorporating a spreading into a convertible coating for both protective and decorative functions. A product applied as a liquid in a thin film either to decorate or protect a surface. A clear or pigmented liquid that imparts decorative as well as protective properties onto a surface after application. A product containing pigments in liquid or powder form, which when applied to a substance (substrate), forms after a time an adherent opaque film having protective, decorative or specific technical properties.
From these definitions it can be deduced that for a substance to act as paint, certain conditions must be fulfilled in the classification of paint. These include:
1. Must be able to provide protective, decorative, and some other desired properties on a substrate after application.
2. Relative strong adhesion to the substrate after application.
3. Suitable colour.
4. Fastness and other desired post application properties.
5. Safe to handle and apply.
6. Affordability should be obtainable from cheap and available materials so as to not only be affordable but also compete favourably in the market.
Paints are used for coating the surface of materials like metals, woods, plastics, and concrete walls. Paints provide protection on materials from corrosion and decay and thereby save replacement cost in addition to providing aesthetic beauty.
Surface coating technology
1.2 CLASSIFICATION
On a broader note, classification of paint can come as Non-convertible coating and Convertible Coating
Paints no matter its nature must be applied in the form of a solution or emulsion. Some films formers like bitumen and cellulose nitrate after being deposited from a solution dry to give a film which can be re-dissolved in the solvent from which it was originally deposited. Such materials are said to be Non-Convertible.
In some cases, the film forming materials behave differently, the film deposited after evaporation of the solvent changes comparatively quickly into a form which is quite unlike the original film-forming material, and moreover it is insoluble in the solvent from which it was deposited, this transformation which is irreversible may be affected by various means oxidation, heating, and catalytically. By whichever means insoluble films are produced and these coatings are thus described as Convertible.
It is pertinent to mention that the distinction between the two classes depends on whether the film is soluble in the solvent used for original solution. It’s solubility in a different solvent is irrelevant.
In this book emphasis will be laid on convertible coatings.
More closely paints can be classified either according to function or to composition. Classification according to functions subdivided paints into Primers, Sealers, Stoppers, Filters, Undercoats and Topcoats of which the following is a brief description.
Primer: this is the first coat to be applied to a surface. Its functions are to provide the adhesion of the total coating system to the surface to assist in the protection of that surface and provide a satisfactory surface for the subsequent coats.
Sealers: This is applied to porous surfaces in order to overcome capillarity effects, i.e. to seal the pores and so prevent absorption of the medium from subsequent coats of paint (such absorption can give rise to varieties of defects). When the sealer is applied to a virgin surface such as unpainted plaster, it is also the primer, but when applied over a sealer, its sole function is that of sealing and providing a suitable surface for subsequent coats.
Stoppers: this is formulated to dry hard in thick layers, it is used to fill or stop holes, cracks and deep indentation in surfaces to be painted. It is usually applied with a palette knife
Filler: this is applied in thick films to fill any unevenness in a surface but not such deep indentation as would require a stopper. It is subsequently flatted down to give a perfectly smooth surface to receive subsequent coats. It can be applied by brush, knife or spray.
Under Coat: This is usually applied next to primer or sealer and is intended to provide opacity and build that is to give a uniform colour by hiding any variations in colour of the surface painted and to provide a non-absorbent surface which will not reduce the gloss of the finishing coats. By “build” it is meant the production of a film of adequate thickness which obliterates minor physical imperfection in the underlying surface.
Top Coat (Finishing coat): As the name implies, is the final coat, it provide the decoration namely colour and sheen, and contribute to the protective value of the painting scheme as a whole. Since they come into direct contact with the atmosphere and elements. They must be formulated to withstand the conditions the conditions of their environment. They vary considerably both in colour and sheen and include high gloss, semi gloss and flat paint, as well a textured paint in which the surfaces is uneven either by virtue of the inclusion of coarse material in the paint or by the texturing of the surface after application.
An alternative method of classification of paints is by the nature of the medium used since this very largely controls the characteristics of the paint. The simplest types are known as oil paint and are based on raw or refined linseed oil. These are easy to brush but slow drying and have relatively low gloss and poor flow and whilst they can be formulated to give reasonably good durability, they are not of the highest quality either for decoration or protection. Varnish paints in which some or all the oil is replaced by varnish show improved
Brushing in ease of application and many cases durability compass with oil paints. This group includes enamels in which the medium is a stand oil. An important group is comprised of alkyd paints or enamels in which he medium is an alkyd resin which impacts to the finish the properties of quick drying and excellent durability. In the water paints group in which the medium is either and excellent durability. In the water paints, group in which the medium is either an aqueous solution or emulsion the solution type includes the cheapest of all paint materials both in price and quality, while emulsions include distempers and latex paints. Latex paints being a high quality water paint.
Classification of paint can also come in three main group;
1. Primers
2. Decorative
3. Industrial and Specialty Coatings
Primers: This group includes all pre-top coatings in both oil-based and water-based paints.
Decoratives: This group of paint include all top coats that are primarily intended for decorative purpose though along the line also provide protective purposes. This is that most common type of paint being used in house, windows and door railings. It can be further sub-divided into water-based and Oil-based decorative coatings. The water-based consists of emulsion and textured paints commonly available in the market. The Oil-based consist of the gloss paints in the decorative group.
Classification of paint can also come in Industrial and Specialty Coatings: though also to a large-extent oil based, this group of coatings are the most technical and sensitive to formulate owing to specificity of the desired properties of the end product. They include; Automotive paints, Marine paints, Radiator and electrode position paints, Agricultural Machinery Coatings, Heavy Duty coatings, Stoving paints, Washing Machines Paints, Industrial Maintenance Paints Chlorinated Rubber Paints
