LITERATURE REVIEW

Historical review of surface coating (paint) industry.

The surface coating industry is indeed an ancient one. The origin of paints dates back to prelistoric time when the early inhabitants of the earth recorded their activities in colors on the walls of their caves. These crud painted probably consisted of colored earths or clays suspended in water.

The Egyptians, starting very early, developed the art of painting and by 1500 B.C. had a large number and wide variety of colors.

About 1000 B.C. they discovered the fore number of our present day varnishes, usually naturally occurring resins or beeswax were the film forming ingredient. Ping outlined the manufacture of white lead from lead and vinegar, and it is probable that Old Dutch process. Lacquers were used to paint buildings in China about 200BC. Protective coating or painting began, in Europe, about 1200AD. Linseed oil and white lead, a white pigment, find their way into paint industry in 15thand 17th centuries respectively paints (relatively opaque solid normally applied thin layers, whose film were usually formed by polymerization of a poly unsaturated oil), varnished ( clear coatings ), enamels (pigmented varnishes), lacquers (film formed by evaporation only ), printing inks, polishes etc. These classification have been most useful in the past but introduction of plastic resins into the industry has made such classification relatively meaningless.

Although water thinned paints date back to antiquity, they were commercially important until casein- based paints were developed about 1925. Their phenomenal growth is indicated by the large increase in the world production.

Resin- emulsion paints have been widely used since World War 1, but latex based paints introduction commer4cially in 1948, have had spectacular growth, more than 70 percent of interior paint sales this types. This types of paint was developed to meet demands for greater easer of application, low odor, easy clearing, great durability, and impermeability to dirt.

2.2 OUTLINE OF PAINT TECHNOLOGY

Paint

Paint is a mixture composed basically of solid colouring matter (the pigment) and liquid (the vehicle). It is applied as a coating to various types of surfaces, bridges, slips, and storage tanks. The purpose of coating may be decorative, as in beautifying of objects and provision of aesthetic; protective, as in preservation against weather, moisture, solar radiation, chemicals, and mechanical change; or functional, as in communication of an impression. By obliterating the surface over which it is applied paint serves the purpose of its use.

It may be a water based paint (emulsion) or an oil-based paint (gloss).

The vehicle consists of the nonvolatile and volatile liquids. The nonvolatile portion is mostly a resinous ort resin-forming compound called the binder. The types of resin are oils, alkyds, celluloses, acrylics, vinyl, phenulics, epoxies, polyurethanes, silicones, amino resins cureas and moleuins), later form, styrene- butadiene, polyvinyl, and acetates. The volatile portion is used to lower the viscosity of the paint composition to achieve case of application and good leveling. At times thinner is added to thin down the viscosity. This portion consists of hydrocarbon solvents, water, ketones or esters.

The pigments are insoluable powders of very fine particle size. They impart colour and opacity to the paint. Colourants may also be added. Paint also contains extenders which are certain materials that add little to the opacity of, and impart other desirable properties to, the paint. Depending on the colour wated for the paint, the pigments, colourants and extender pigments may be titanium dioxide, calcium carovate, maynesium silicate, clay, inorganic colours, barium sulphate mica, zinc oxide, red lead, metallic (principally aluminum), carbon blacks, organic colours, and white lead.

2.3 PAINT TYPES

Paint, as a widely used chemical product in the society, appears in several forms with varied formulations. These types of paints include:

EMULSION OR WATER PAINT

This is a water based paint. The pigment is dispersed in the aqueous phase so that both polymer and pigment form distinct dispersed phases and should coalesce only in the film when the water evaporates.

LATEX PAINT

The term latex denotes a suspension of polymer particles in water. Emulsion paints consist basically of a combination of pigment and latex, hence it is called latex paint.

Water paints other than latex include white wash, casein paint, cement paint and linseed emulsion paint.

WHITE WASH

This may be made by mixing unslaked line with water and allowing it to stand for a few days before use, or starting with calcium hydroxide in the first place. The applied coating converts to calcium carbonate. Certain additions, like glue, have been used for their cheapness.

CASEIN PAINT

This is usually supplied as a powder to be mixed by the user. Casein is about 10-12% of the composition, together with some line to convert it to insoluble calcium caseinate after application. The balance is pigments plus preservatives.

CEMENT PAINT

This is used to a limited extent to mansory. It is supplied as a powder containing Portland cement and white or alkali-resistant coloured pigments. It is mixed for application.

LINSEED EMULSION PAINT

This may be prepared from linseed oil emulsified by a combination of lipophilic and hydrophilic emulsifiers. The emulsified linseed oil is made into paint by formulaic similar to those used for latex paints, except that addition of metallic driers is necessary.

GLOSS OR OIL PAINT

This is the oil-based paint. It is shiny in appearance. It is an alkyd resin based paint containing from 35% to 80% linseed, Soya or other oil ground without extenders but with other auxiliary ingredients such as solvents, driers etc. They are generally used for maintenance work, where protection is more important than the appearance, and also for interior use.

ENAMEL

The word enamel strictly means a glass like substance fused on to metal surfaces. Besides the glossy wall paints which may be called enamels, (there is no sharp division) practically all trade sales lines include a large selection of bright strong colours and black, for use on comparatively small areas such as lawn furniture, cabinet doors, and similar surfaces. These have a low pigment volume, and are pigmented with such colourant as toluidene red, phythalocyanine blue, hansa yellow, and titanium dioxide and lampblacks for grays. Specifications on these products call for a high degree of pigment dispersion to produce the maximum is smoothness and leveling out.

TRAFFIC PAINTS

High pigment volume, the use of fast-drying vehicles such as low oil content resin combinations or oil. Free synthetic resins, and low-binding solvents such as petroleum fractions with distillation ranges from 100 to 1500c are three factors responsible for the fast-drying characterizes of the road-stripping paints. Resin solutions like politicized chlorinated rubber or styrene but butadiene may be used. Some aromatic hydrocarbon solvent has to be included in these vehicles to maintain solubility.

MARINE PAINTS

Antifouling paints for ship bottoms are formulated with copper and mercury compounds as positions for marine growth, using binders which are not too permanent so that gradual breakdown of the film and release of position can take place tributyltin compounds are used as the toxic materials. A typical formulation calls for zinc oxide ferric oxide, magnesium silicate, cuprous oxide, mercuric oxide, rosin, oil, coal tar, and solvent.

SPECIALTIES

FIRE RETARDATION PAINTS

These contain compounds which intumesce when the temperature is raised beyond a certain point. Urea and acid phosphate esters, pentacrythroil, and others are types of materials used.

AEROSOL COLOURS

These are alkyd compositions. The two components are paint thinned out to low viscosity so that it will atomize, and a gaseous propellant which is liquid under pressure. The host usual the propellant is dichlorodifluoromethane which has a boiling point of 300c. Other halogenated hydrocarbons may be used as modifiers.

INSECTICIDAL PAINT

This paint is meant for protection of substrate against insects. It has various colours in both enamel and emulsion. During drying of the insectidal paint, movement of particles take place throughout the paint film. These particles are carried to the surface by the normal evaporation of the solvents in the coating and crystalize to form the insect repelling layer.

PAINT COMPOSITION AND FORMULATION

Aside from the three basic components of paint pigment, volatile vehicle and non-volatile vehicle there are numerous other additives used in paint mostly as an integral part of the formular, but sometimes for corrective purposes. These include metallic driers; pigment dispensing agents; antiflooding compounds; antisettling agents, e.g. metallic stearates or lecitin, antiskinning agents for oxidizing type paints these may be considered mild antioxidants while they are in the container, but dissipate by evaporation when the film is applied; gelling agents for non drip agents; mildewcides and fungicides; viscosity stabilizers; deodorants these are usually perfumes used in fractional percentages to mask odours during the drying period; ultraviolet absorbers a typical use is in daylight fluorescent paint to delay fading of the pigment; stablizers, e.g. materials which absorb cl or Hcl as possible decomposition products from chlorinated resins, or similar applications.

The modern paint constituents can be outlined as:

RESINS (FILM FORMERS)

SYNTHETIC: Alkyds, acrylics, vinyls, cellulosics, rosin esters, epories, urea melamines, wrethanes, styrenes, phenolics, hydrocarbons, and polyesters.

NATURAL: Shellac, rosin etc.

SOLVENTS

Ketones, aromatics, aliphatics, alcohols, glycol ethers, glycol ether esters, glycols, glycol esters, chlorinated products, terpenes, etc.

DRYING OILS AND FATTY ACIDS

Linseed oil, soyabean oil, fatty acids, tall oil, castor oil, tung oil, safflower oil, fish/marine oil, cocoanut oil, oiticica oil.

PIGMENTS AND EXTENDERS

Titanium dioxide, calcium carbonate, magnesium silicate, clay, inorganic colours, barium sulphate, mica, zinc oxide, zinc dust, red lead, metallics (principally aluminum), carbon blacks, organic colours, white lead.

Driers:

Cobalt, manganese, lead and zinc, naphthenates, resonates, linoleates, 2 ethylhexoates, tallates.

Plasticizers

Octyl, decyl, 2-ethylhexyl and similar easters of phthalic, sebacic, adipic, azelaic, and similar acids.

Further outline on pigments and extenders are ad follows:

Pigments:

This is use to protect the film reflecting the destructure ultraviolet light to strengthen the film, and to impart an aesthetic appeal. Pigments should possess the following properties: opacity and good covering power, wet ability by oil, chemical inertness, nontoxcity or toxicity, reasonable cost. Some of the pigments are:

White

Titanium dioxide, zinc oxide, lithopone, zinc sulphide, antimony oxide.

Black

Carbon black, lampblack, graphite, iron black.

Blue

Ultramarine, copper phthalocyanime, iron blues.

Red

Red lead, iron oxides, corlmium reds, tones and lakes.

Metallics

Aluminum, zinc dust, bronze powder.

Yellow

Litharges, ocher, lead or zinc chromate, hansa yellows, ferric yellows cadium lithopone.

Orange: Basic lead chromate, cadmium orange, molybdeniium orange. Green chromium oxide, chrome green, hydrated chromium oxide, phthalocyanine green, permansa greens (phthalocyanine blue plus zinc chromate). Brown: burnt sienna, burnt umber, Vandyke brown.

Metal protective: red load, blue lead, zinc, basic lead, and barium potassium chromates.

Extenders or inerts or fillers

They are use to reduce the pigment cost and in many cases to increase the covering and in weathering power of pigments by complementing pigment particle size, this improving consistency , leveling and settling .they include , china clay , talc, Asbestos, ( short fibers ) silica, whiting , metal stearates, gypsum, mica , barite, Blancfixe.

EXTERIOR BULDING PAINTS_ FORMULATION

The most important type of protective coating for most surfaces is what is commonly known as house paint .this can be either oil paint (Linseed oil _ based paint) or latex emulsion ( water - based ) paint .

The advantages of latex pa and presertive and presertiveints over oil paints are fast drying, absence of odour, ease of cleanup, and excellent colour retention. Some examples of material used are dispersion agents for pigments, protection colloid and thickeners to thicken the water phase and reduce setting, defoamers, coalescing agent, freeze thaw, additives (glycols), mildewcides and preservatives (mercurial, copper and phenolic compounds), and PH controller (ammonium hydroxide used for adjustment).

A typical formulation for an exterior latex paint is given below.