Application of Paints Supervised by : Dr/ El-Sayed Mansour Presented by : Ahmed Abdullah Balbaa Introduction • Paint can be thought of a pigmented liquid which protects and beautifies substrates. • Paint any liquid, which after application to a substrate in a thin layer is converted to an opaque solid film • Various raw materials are utilized to make this pigmented liquid. Composition of Paints A paint is formulated as a mixture of three ingredients: • Binder • Solvent • Pigment Besides the three ingredients, paint can have a wide variety of : • Additives • Extenders or Fillers 1- Binder • Binder is the main ingredient of paints. • Binders are polymers (resins) forming a continuous film on the substrate surface. • Binders are responsible for good adhesion of the coating to the substrate. The binder holds the pigment particles distributed throughout the coating. The binder is dispersed in a carrier (water or organic solvent) either in molecular form (the solution) or as colloidal dispersions (emulsions) • Binder also known as non-volatile vehicle • Binder can be classified according to drying or curing into four mechanisms : - Simple solvent evaporation. - Oxidative cross linking. - Catalyzed polymerization. - Coalescence. 2- Solvent • Solvent (water or organic solvent) is a medium where the binder, pigment and additives are dispersed in molecular form or colloidal form. • Solvent (thinners) are also used for modification of the paint viscosity required for the application methods :brush, roller, spray…. • The solid coating is formed due to evaporation of solvent therefore the evaporation rate is one of the important properties of solvents. • Other important properties are the ability to dissolve the paint ingredients and toxicity. 3- Pigment • Pigment is a solid substance dispersed throughout the coating to import it a colour opacity (hide the substrate surface). • Pigment may protect the substrate from UV light. • Pigment change the paint appearance (gloss level) • Pigment increase hardness and decrease ductility • Pigment may be natural, synthetic, inorganic or organic. 4- Additives • Additives are small amounts of substances modifying the paints properties. • Examples of additives: dryers, plasticizers, fungicides, flow control agents, defoamers, emulsifiers, UV stabilizer, anti skinning agents, adhesion promoters, corrosion inhibitors and texturizers. 5- Extenders or Fillers • Filler serve to thicken the film, support its structure and simply increase the volume of the paint. Not all paints include fillers. Pigments that also function as fillers are called simply pigments. • Fillers are generally colour-neutral and opaque. The Application of Paints Which can be classified into 3 terms Type Solid• Gas• liquid• Purpose Decoration• Protective layer• Ease of cleaning• Technique Brush• Roller• Air spray• Airless spray• Electrostatic spray• Rotating disc or • bell 1st Term : Types of Paints • As a solid usually used in industrial and automotive applications, the paint is applied as a very fine powder, then backed at a high temperature . This melts the powder and cause it to adhere (stick) to the surface. • As a gas or gaseous suspension, the paint is suspended in solid or liquid form in a gas that is sprayed on an object, The paint stick to the object. • As a liquid application, paint can be applied by direct application using brushes, roller, blades, other instrument, or body parts. 2nd Term : Purpose of Painting • Decoration to interiors and exteriors of a building, they are used to enhance a building by adding pigments, lightness or darkness. Reflective surfaces can be also obtained. • Protective layer paint are also used to protect the outer surfaces of a building or metals to protect them against : sunlight, dust, corrosion and weathering. • Ease of cleaning : - to provide easily cleaning surfaces. - to keep the substrate clean and tidy. 3rd Term : Paints Techniques - Paint is applied onto a substrate surface which has been previously treated by the methods of enhancement of adhesion (surface preparation ): cleaning, surface roughening, primers, adhesion promoters, plasma treatment. - The following techniques are used for application of paints: • Brush : - Brush application is used decorative coating of relatively small and complex areas. - Brush painting is a slow application method but it provide good penetration of the paint. - Brush application prevents paint losses. • Roller : - Roller technique is applied for coating large flat surfaces, this method is faster than brush application. - In contrast to brush method roller paint is not suitable for applying high film build. • Air spray : - In the air spray application method the paint in form of atomized droplets is delivered by a stream of compressed air. - Spray application is a simple and inexpensive method which is capable to coat objects of various shapes and dimensions. - High quality coatings are achieved if the paint composition provides the required level of viscosity and drying rate. - The disadvantages of the air spray application is unavoidable over spray (paint losses) and expensive organic solvents and thinners. The method requires additional investments in safety equipments in order to protect the workers exposed to the hazardous solvent vapors. Air spray technique • Airless spray : - In the airless spray (in contrast to the air spray) the paint is not mixed with air. The liquid paint is delivered to the gun by hydraulic pump producing a high pressure (300-7000 psi). - Using a high pressure pump and preheated paints allow to apply high viscosity paints having a decreased amount of solvent and thinners (lower solvent content). • Electrostatic spray : - Electrostatic spray application is based on the electrostatic attraction of electrically charged atomized (either dry powder or liquid paint droplets) to the grounded (having earth potential) work piece. - The charged particles coming out from the gun hit the whole surface of the object including the back surface. - Electrostatic spray is characterized by very low over spray. The method utilizes at least 95% of the paint. Electrostatic Spray • Rotating Disc or Bell : - In the rotating disc/bell application technique the liquid is pumped to the center of the disc/bell rotating at high speed (at least 10000 rpm) - The centrifugal force drives the liquid to the edge where it is atomized and spun off. - Rotating disc/bell method is used for automatic application of high viscosity paints (e.g. high solid paints). Rotating Disc or Bell painting References: - Paints, Dr. El-Sayed Mansour - Civil engineering Portal , http://www.aboutcivil.org. - California paints is a division of California products corporation. - SubsTech for Substances & Technologies httb://www.substech.com (Application of Paints, Dr. Dmitri Kopeliovich)
