RED OXIDE PRIMER & ALUMINUM PAINT

Colour has fascinated culture throughout history, every age and every region hasproduced dyes and pigment depending on the available resources. Colour has beenwith us for more than 20,000 years. The evidence can be found in the cave paintings.The tradition of painting in Indian subcontinent grew and developed overtime,resulting in a hilly developed and finest style, incorporating the culture and faith ofthe region and religion. The history ofIndian Paint Industry is as old as the history ofthe Indian people. Indian paints always embrace rich colours and clear symbolism,using specific iconography to make religious figures clearly recognizable.

The Indian paint industry has recently completed lOOyears of manufacturing.Manufacturing of Indian paints started around 1902. The Indian paint industry hasseen a gradual shift in the preferences of people from the traditional white wash tohigher quality paints like emulsions and enamel paints. Growing popularity of newvariants providing improved finishing and textures, increasing per capita income ofpeople and efforts on the part of manufacturers to introduce improved versions likeeco-friendly, odour free and dust and water resistant paints, have propelled the growthof the paint market in India. Efforts on the part of the manufacturers to introduceinnovative technologies in the paint market have led to a growth in demand for paints in India. Paint manufacturers are giving due attention to consumer’s colourpreferences. The market is witnessing introduction of breakthrough technologies to improve the paint quality. Paint companies are also increasingly investing in their R&D, to carve out a differentiated product in the market. For instance, paints, which use water in place ofsolvent, have been introduced in the market. They are better in performance and not harmful for health as it emits little or no Volatile Organic Compounds (VOC).

The industry has also seen the introduction of solar reflectivecoating, which is a roof surface coating that lowers the surface temperatures of theroof resulting into greater comfort inside the building. New technologies in the paint market would lead to better performance, cost reduction and wider applications of paints in India.

The terms ‘paint’ and ‘surface coating’ are often used interchangeably. Surface coating is the more general description of any material that may be applied as a thin continuous layer to a surface. Purists regard the term ‘surface coating’ as tautological. However, it has been used widely in the UK and in North America to distinguish painting from other forms of surface treatment, such as electroplating, anodizing, and the lamination of polymer film onto a surface. Paint was traditionally used to describe pigmented materials as distinct from clear films which are more properly called lacquers or varnishes.

We shall be most concerned with paint in the context of this book; but, as we shall see, modern painting processes may include composite systems in which a total paint system comprises several thin films, some, but not all, of which may be pigmented. We shall use both terms as appropriate to the context in which specific paint compositions are being discussed. The purpose of paints and surface coatings is two-fold. They may be required to provide the solution to aesthetic or protective problems, or both. For example, in painting the motor car the paint will be expected to enhance the appearance of the car body in terms of colour and gloss, and if the body is fabricated out of mild steel it will be required to give protection against corrosion. If the body is formed from glass fibre reinforced plastic the paint will only be required for aesthetic purposes. There are obviously very sound economic reasons why it is attractive to colour only the outer surface of articles that might otherwise be self-coloured by using materials of fabrication, e.g. plastics that are pigmented, particularly if a wide choice of coloured effects is required.

This topic will be developed in the chapters on paints for specific markets In considering the nature of paints it will become abundantly clear that the relationship between the coating and the substrate is extremely important. The requirements for a paint that is to be applied to wood are different from those of a paintto be applied to a metal substrate.

Moreover, the method by which the paint isapplied and cured (or dried) is likely to be very different. In formulating a paint for a particular purpose it will be essential for the formulator to know the use to whichthe painted article is to be put, and physical or mechanical requirements are likelyto be called for. He will also have to know how it is to be applied and cured. Thus,a paint for an item made from cast iron may call for good resistance to damage byimpact (e.g. chipping), whilst a coating on a beer can will call for a high degree of flexibility.

It has long been recognized that it is difficult, if not impossible, to meet therequirements of many painting processes by the use of a single coat of paint. If onelists the requirements of a typical paint system it is easy to see why. Many, if not all,of the following are likely to be required: opacity (obliteration); color; sheen(gloss); smoothness (or texture); adhesion to substrate; specific mechanical or physical properties; chemical resistance; corrosion protection; and the all-embracingterm ‘durability’. Durability is an important area that we shall return to in manycontexts. The number of different layers that comprise the paint system will depend on the type of substrate and in what context the coated object is used.
A typicalarchitectural (gloss) paint system might consist of a ‘primer’, an ‘undercoat’, and a‘topcoat’. All three are likely to be pigmented compositions, and it is probable thatthere will be more than one coat (or layer) of each of these paints. An architect may well specify one coat of primer, two coats of undercoat, and two coats of topcoat.

The purpose of these individual layers and hence their composition is likely to be very different. The primer is designed largely to seal the substrate and provide a means of achieving good adhesion between substrate and undercoat. It may contribute to opacity, but this will not be its main purpose. The undercoat will be used for two purposes: to contribute significantly to the obliteration of the substrate and to provide a smooth surface upon which to apply the topcoat. The smooth surface is obtained by abrading the dried undercoat (after each coat has dried) with fine tungsten carbide paper.

The topcoat is then applied to complete the process of obliteration and to provide the appropriate aesthetic effect (i.e. colour and sheen). The system as a whole would be required to give protection to the wood or metal substrate to which it is applied.

The interrelationship between these multilayers is worth considering. The mechanical and physical properties of the individual coatings will often be very different. The function of the primer in promoting adhesion has already been mentioned. It may also be required to relieve stresses that are built up within the coating system as a result of hardening and ultimately embrittlement of the topcoat (andundercoat) as a result of ageing, or to accommodate stresses imposed by the differential movement of the substrate. The softwoods used in the construction of window frames are known to expand and contract between the dry (summer) andwet (winter) conditions by at least 10% across the grain, but much smaller changesare observed in the direction of the grain. The undercoat will be formulated in acolour close to that of the topcoat, but it may serve this purpose to several closelyrelated topcoat colors. It will normally be highly pigmented, in contrast to thetopcoat which will not.

The reason for the latter is the need, for example, to maximize gloss and extensibility. The use of the type and concentration of pigmentary material in the undercoat would not be conducive to maximizing these properties in the topcoat.

The primer will frequently be required to contribute to corrosion protection. Those formulated for use on steel are likely therefore to incorporate a chemically active anti-corrosive pigment. Corrosion protection may be achieved by yet another means, the chemical treatment of the substrate. Thus many industrial coating processes involve a chemical pretreatment of metal, mainly aluminum or ferrous substrates. The latter is most frequently treated with a phosphate solution that produces a crystalline phosphate layer. Subsequent paint application, i.e. priming, is therefore to a crystalline inorganic layer and not directly to an (uncoated) pure metal surface.

Surfaces are seldom what they seem. With the exception of the noble metals almost all surfaces that will be commonly regarded as ‘metal’ surfaces will present to the paint a surface that is not a metal but an oxide layer. Even so the purity or cleanliness of the surface may well be an unknown quantity. Since this surface will have an important effect on such properties as the adhesive performance of the paint system it is important to appreciate this point. Just as most surfaces will be ‘dirty’ and thus be ill-defined, it is necessary to produce paint systems that can accommodate the contamination and general variability of surfaces.

These types ofsystem must be ‘tolerant’ to all but excessive contamination and are often describedas ‘robust’ if the required degree of tolerance can be achieved. This is not to say that industrial coating processes do not require certain pretreatments such as degreasing, and may involve the chemical pretreatments indicated above.

The deterioration of paints which occurs in many situations is largely due to changes in the chemical nature of the film former with consequent changes in its mechanical properties, and research continues unabated to formulate polymers and resins to improve the performance of paints in use. The development of new improved pigments may contribute to improvements in durability, but in most cases the weakest link in the system is the film former. One consequence of this is the development of systems for specific end uses. Such approaches are adopted when it is practicable to avoid the compromises that are otherwise likely to be required for a general-purpose product. For economic and marketing reasons the best productmay not be available for a specific end use, and a compromise of cost and performance may be required. Indeed the cost-effectiveness of a particular coating composition will usually dominate other considerations particularly in the industrialpaint markets.

The application of paints to various substrates (e.g., metals,wood, plastics, and concrete) is the most widely used method of protecting materials against corrosion and degradation. It is also used to obtain properties that include gloss, color, completely smooth or textured surfaces, abrasion resistance, mar resistance, chemical resistance, and weather resistance. Normally, a combination of properties is required. Paint systems are therefore applied that generally consist of a primer, an intermediate coat, and a topcoat. These coats of paint together with the substrate surface and surface layers resulting from substrate preparation and pretreatment form the coating system.

Only this complete coating system can provide the combination of properties required for the wide range of uses of organic coatings. Most paints are supplied as liquids that are applied by different methods, using various types of equipment.