Coatings, paintings or finishing; whatever the term is used have been around for thousands of years and used for decoration, protection and combinations of both. Our research revolved around the use of water-base/aqueous paints and it’s significance to the study of Colloidal Science. The most significant development in the protective coatings field since World War II has been the rapid growth of water-base paints. During this period it was the development of new synthetic latices that made this possible. Water base latex paints became popular because of the ease of application and other desirable properties. They are practically odorless during application and dry rapidly.¹ Also the wall finish is tough and washable. The water base paint industry also became popular based on the do it yourself market. Equipment such as the paintbrush, paint roller made applications easier. Spills were easily cleaned up with soap and water. The water base paints were then introduced to industrial applications because of the reduced fire hazard and reduction in the amount of solvent released in the environment. Water base paints/coatings have properties superior to those of the solvent paints they replace.

Water-base paints were the earliest types of paint and go back to the dawn of history. From the caveman to the Egyptians, then later to the colonial days of whitewash, water base paintings were used to paint walls etc for decoration. Improvements were then made to paints as time went by, but it was not until the 1940’s and 1950’s with the introduction of latex that there were major developments in water base paints to improve quality and use. The 1970’s introduced semigloss latex paints. These paints incorporated smaller size particle latices along with better-coalescing solvents. Later paints were further improved with the addition of epoxies and acrylics to the latex base paints over the last 30 years. In the late 1970’s and early 1980’s paint specialist evolved and evaluated the historic paints for improvement.² Technological advancement provided sophisticated instruments and procedures such as field sampling, cross-section analysis, and fluorescent and chemical staining to learn about the components of historic paints. In addition, they utilized written documentation, verbal research, and visual information about paints in conjunction with field findings. Many compounds, such as lead and other heavy metal compounds found in water paints were determined environmentally hazardous. Modern water-base paint formulations eliminated such hazardous material.²

The water base paints we used in the past is undeniably part of a technological and commercial record. Paints colors are simply, direct expression of the time, and of taste, values and mood. Water base or aqueous coatings can be divided roughly into three types, water-soluble, water-dispersible, and water-reducible. These can be simplified into solution types and dispersion types. The use of the term solution allows us to involve the term’s colloids and suspensions, due to the fact that the terms are considered arbitrary. They are considered as follows: Solutions are less than 0.001 microns in diameter, Colloids are between 0.001 to 0.2 microns in diameter, and Suspensions are greater than 0.2 microns in diameter.³ With Colloids we are concerned with two-phase systems and with interface between theses phases. With solid, liquid and gases several combinations of interfaces exist. In Water-soluble coatings/paintings the vehicle or binder is dissolved in water. Since the binder is soluble in water, it will remain water sensitive unless converted to an insoluble form by some means such as polymerization. Water-soluble coatings have several properties in terms of advantages and disadvantages. Some advantages are

1. simple formulas-pigment, vehicle, and water with which catalyst and defoamers are necessary
2. Ease of manufacture-can be handled the same as conventional solvent type paints with pigment being ground directly into the vehicle
3. Good film continuity- continuos film similar to conventional solvent systems
4. High pigment binding and gloss- approach that of conventional systems. High gloss can be obtained with pigment/binder ratios of 1:1 or greater
5. Good stability- coatings based on water-soluble systems can be pumped in all types of equipment. There is a minimum of tendency toward skinning or clogging of the dip tank or spray equipment after extended use. Paints can be frozen and thawed repeatedly without adverse effects on the liquid paint.
6. Gloss- possible to produce coatings of high gloss

Some disadvantages are

1. Limited number of materials- only a few materials of this type are available
2. Poor water resistance- most air drying type water-soluble materials have poor resistance
3. Require heat- most water-soluble systems require heat to convert to water-soluble state

The second group of water/aqueous paints, the water-dispersible also have advantages and disadvantages. In this type of coatings the vehicle consist of small particles in a water medium. The size of these particles ranges from 0.1 to10 microns. Some advantages are as follows

1. High molecular weight- it is possible to use high molecular weight polymers with outstanding properties such as color retention, water resistance, chemical resistance, and good mechanical
2. Air drying- superior coatings are obtained on air drying
3. Good holdout- on all types of surfaces including porous substrates

Some disadvantages are as follows:

1. Complicated- since dispersion systems are heterogeneous systems, they are complicated in makeup and contain pigment, latex, thickeners, defoamers, and numerous other materials
2. Special Manufacture- more conventional than for conventional coatings
3. Stability- the mechanical stability of emulsions is only fair. Excessive handling may break an emulsion. Alternate freezing and thawing will produce a break
4. Heterogeneous- since an emulsion coating contains water-soluble thickeners and surfactants which are water-soluble, an emulsion film is not a truly continuous film and is, to a certain extent, permeable
5. Gloss- it is difficult to produce coatings of high gloss from dispersion systems

The third groups of aqueous coatings are water-reducible coatings. These materials can be produced in which conventional solvent materials are used along with some surfactant. For application these can then be reduced with water. Properties are somewhat intermediate between solvent and water-base paints. If enough water is present, the liquid paint will not burn if exposed to a flame even though it contains some inflammable solvents.³

These three groups of water based coatings are used extensively, but water-soluble paints are the most common or popular. Water base coatings are very popular due to the unusual physical properties of water and many other advantages including nominal cost, non inflammability, true odorlessness, and nontoxicity. Along with these advantages there are also some disadvantages, such as it is difficult to adjust wetting, flow and drying³.

These materials are intended to improve resistance to rain peretration with minimal effect on appearance. They function by inhibiting direct capillary absorption, but do not normally provide a continuous surface film. Properties of interest include resistance to water penetration, water vapor transmission rate (permeability), resistance to efflorescence, and longevity of the effect. Such treatments will not necessarily decrease water uptake through cracks, which may, in fact, increase as the treatment causes more water to run across the surface.

In general all coatings for brush application are air-drying, with the most common application areas in the home and building construction industries.

Brush application is one of the oldest methods of applying paint and, although with today’s need for higher production rates using minimum labor, a very large proportion of paints applied by brush will still be found.

Brushes are designed with more air spaces between the bristles at the tip of the brush than at the stock and will therefore hold more paint in the lower portion of the brush. They are generally made from horse hair and recently from special nylon fibers, although the best brushes are made from Chinese hog bristles. These brushes have splayed or split ends, allowing a far greater contact of the brush with the surface and producing a more even spread of the paint.

In painting structural steel one very important advantage of applying a protective primer by brush is that any slight surface contamination by oil and rust will be dispersed by the brushing spray-applied coatings over these surfaces.

The main advantages of brush application are:

1. Versatility;
2. Suitabiliy for use under variable conditions;
3. The operator has full control of the quantity of paint being applied;
4. Low wastage of paint;
5. Little conamination of nearby areas.

The main disadvantages are that it is relatively slow and more costly in labor than many of the other methods of wet-paint application.

The spray gun was first used about 1907 by furniture manufacturers and later used by the automobile industry. Spray application was expanded with the development of nitrocellulose lacquers in the early 1920s.

The basic principle of spray application is atomise the paint into a fine spray and to direct the spray onto the object to be coated. Supplementary equipment such as a source of compressed air, flow control valves, filtration units for the removal of dirt, oil and water from the air supply, and containers for the paint supply are also neede. Paint supply containers vary in size from the 250ml cups attached to the gun to remote 500-liter pressure pots at some distance from the spray guns.

Conventional hand spray guns are still the most common form of industrial paint application in Australia, with major uses in the automobile and furniture industries.

The main advantages of conventional spray guns are:

1. the speed of application;
2. the degree of control the operators have over the film thickness and nature of the finish deposited. This is typified in furniture finishing, where skilled spray operators can allow for both color and grain variations of the timber substrate by varying the quantity of coating deposited on the substrate.

Pulling back the trigger first opens the air valve to allow "dusting" air. As the trigger is further retracted, it unseats the needle valve in the fluid nozzle and allows paint to leave the gun and be mixed with compressed air in a tubular stream. This is called ‘first-stage atomisation’ and takes place immediately outside the nozzle.

Second-stage atomisation follows within 10mm of travel, and it is here that the paint is converted from a tubular stream to a flat spray pattern, by means of blast of compressed air from each side of the air nozzle horns.

1. Gun body
2. Trigger
3. Air valve
4. Needle valve
5. Fluid nozzle
6. Air nozzle
7. Fan control knob
8. Fluid control knob
9. Needle packing

Flow coating is, in principe, the same process as quick dip coating. It is used mainly of objects which are too heavy or unwieldy for normal dipping, or where a series of products is made which vary so much is size and shape that an economical dipping tank cannot be designed. Instead of dipping the object, paint is squirted at it either from a series of suitably disposed or the job may be done by hand, using one or more hosepipes. Hand coating of certain awkward places may be necessary even where the major part of the job is done automatically. The excess paint drains off into a trough and is recirculated.

The technical requirements for paints for flow coating are the same as those for dipping paints.

Curtain coating is a special form of flow coating suited to the treatment of flat surfaces in large numbers. The paint is fed continuously to a thin horizontal slot and falls as a curtain on the surface to be painted. The latter is moved forward under the curtain by belt conveyors, and the amount of paint applied is adjusted by varying the slot width and the speed of traverse of the object being painted. The speed may be as high as 120 m/min. When the end of the object is reached, the curtain passes between the ends of the belt conveyors into a receiving trough whence it is recycled. Curtain coaters have found considerable use in the application of two-component finishes, in particular, polyester finishes in the furniture industry. In the case of using two single-curtain coatings machines or more usually by using a machine fitted with two slots, one for each component. The components first mix on the surface, which is being coated.

Film formation from dispersions is more complex than for a solution. Polymer dispersion, in contrast, consists of a separate polymers phase in the form of individual spheres dispersed in a liquid medium. Such a system is not homogenous on a macular basis. As the water evaporates or is absorbed into the porous substrate, the spherical polymer particle come closer and closer together until they touch. Then, in order to obtain a continuous polymer film, free of voids, deformation of the spheres is necessary. This requires the existence of a driving force for sufficient magnitude to overcome resistance of the polymer spheres to this change in shape. Hard polymers will resist the deformation very strongly under imposed stress, whereas rubbery polymers will deform more readily. The potentiality for film formation of a dispersed polymer is related to this de formability. If the polymer is so rigid that deformation does not occur, film formation is not accomplished, and a powdery or spongy structure remains after water evaporate. The capillary pressure of the water exerts forces that pull the dispersed particles together. This pressure is similar to the pressure that arises when two plates of glass are separated by a thin layer of water. Comparable forces exist when two or more spheres are wet by the intervening aqueous phase. As the water evaporates and the spheres come together, this pressures increases. When the spheres touch, the evaporation of the water exerts pressure deforming the spheres. This results in film formation.

A list of factors affecting the film formation may be environmental, physical, or compositional. Another such factor affecting film formation is time. An adequate amount of time is required to allow the film to form properly. The control of evaporation of water will control the coalescence of the emulsion film. The relative humidity control the evaporation rate and the porosity of the substrate also affects the rapidity with which the water leaves the film. One of the environmental ( physical ) condition that affects the formation of the film is temperature. The temperature of application of the coating is important in film formation. The temperature affects hardness, of the polymer that in turn affects the fusibility. The ultimate limit is that the temperature can not be below the freezing temperature of water. For the physical influence that affects the film formation the physical state of the emulsion has an important influence on the film formation. Normally, the finer the particle size the easier it is to get good film formation. For example, emulsions have a tendency, at certain flocculated condition, to trap water, leaving voids in the film. The chemical composition and molecular weight of the polymer affect the fusion temperature, hence film formation. If the polymer is too hard to fuse together at the application temperature, plasticizers or solvents may be added to soften the resin and aid fusion.

A surfactant is a chemical compound that affects forces off a liquid or a solid in relation to other liquids, gases or solids. The surfactant generally consists of a molecule in which one end is hydrophilic (water loving) and the other is hydrophilic (oil loving). The surface acting agents (surfactant) which include wetting agents, detergents, dispersants, foaming agents, penetrating agents and spreaders, have multiple uses in aqueous coatings. First, a surfactant is used as a dispersant in the grinding of the pigment. It provides a better wetting of the pigment particles. It is used as an agent to promote the suspension of fine particles of solid in a liquid. Secondly, surfactants are required as emulsifiers either in the emulsion polymerization or post emulsification of the vehicle. The emulsifier produce stable interface between the oil or other material and water. The relationship is a liquid, liquid one, for emulsifiers. The third function of the surfactant is to impart certain physical properties to the aqueous coating such as better wetting to the surface on which it is being applied better flow, and more.

Water-soluble hydrophilic colloids include material such as gum arabic, gum tragacanth, starch, sodium alginate, methyl cellulose and many more. These materials produce high viscosity solutions at low concentration. As little as one tenth to one per cent of the protective colloids is usually sufficient. A large portion of the protective colloids incorporated in the grind aids in the dispersion process. By thickening the mix, high shearing action is obtained insuring good mixing. The pigment particle is completely coated with the protective colloid that improves the stability of the paint.a protective colloid is added to an emulsion vehicle or latex in the manufacture. The protective colloid, because of the increased viscosity it imparts to the water phase, reduces pigment settling tendency of the dispersed particles to stick together if subjected to stresses by mechanical means, freezing and more. The water soluble resin, when used as a thickener, produces the correct viscosity for application. The type of protective colloid used will affect the flow and leveling of the coating. For many reasons, including economy, it is advantageous to keep the amount of protective colloid to a minimum. Protective colloids are relatively high in price as compared to other ingredients used in the paint. Once the film is applied and dried, the protective colloid serves no useful purpose and may actually distract from the performance of the coating. Being water soluble, these materials make the coating more water sensitive. The protective colloids are usually not compatible with the vehicle or the latex, so that, when the film dries, there is a tiny network of water sensitive resin throughout the film