application of paint

8/20/2019 Application of Paint

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PAINT APPLICATION

(Surface treatment procedure)


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Basic composition of paint

Solvents (Liquids)

PigmentsAdditives

Resin (Binder)


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Typical paint composition

• Component Weight %• Binder 30

• Organic solvent 27• Water 10• Pigments 19

• Extenders 12• Additives 2


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RESIN

•Types: Latex, Alkyd, Epoxy, Polyurethane• Binds or glues ingredients (pigments and additives) of paint together• Resin provides adhesion to the substrate• Resin provides durability & resistance properties:

U-V resistanceMoisture resistanceChemical resistanceStain resistanceFade resistanceChalk resistanceBlock resistance


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Drying stages – Alkyd paint

• Physical drying – solvent evaporates / film formed• Chemical drying – also called ―oxidative‖ drying

Four overlapping phases during drying process :1. Induction period2. Hydroperoxide formation3. Hydroperoxide decomposition into free radicals

4. Polymerisation / crosslinking


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The methods of pretreatment

• Method Result• Blast cleaning Ideal• Mechanical wire-brushing Acceptable

• Mechanical disc-sanding Acceptable• Needle chipping Fair• Mechanical scraping Fair• Hand brushing Poor• Hand scrapping Poor

• Water jet cleaning Acceptable


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• While Alkyd thinner is MTO-145, thethinner used in PU paint is Xylene which istoxic (Isocyanate).

• Ford cup No. 4 – 80 to 120 seconds• As per IS 8662


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• For Alkyd – DFT ranges between 120 to 150 microns• 2 coats of primer – 50 micron• 2 coats of surfacer (undercoat) – 50 micron

• 15 + 15 micron – finish – 25 microns• Total – around 125 microns.• For PU , DFT ranges between 200 to 250 microns• (PU primer is expoxy based – 60 microns)


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Gloss / Sheen levels• Gloss or Sheen of paint refers to reflectivity of the dry paint

film.• There is lack of standards and confusion in the paint

industry related to gloss or sheen levels.

• Gloss is measured at 60°

for flat to gloss ranges.• Sheen is measures at 85 ° between flat to eggshell • Some paint manufacturers use different terms to define

products between flat and semi-gloss: silk, suede, satin,velvet, eggshell, low sheen, low luster, pearl, etc.


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Gloss Sheen levels

• Term Gloss @ 60 ° Sheen @ 85• Flat 0-5 0-5• Velvet/Low Luster 5-10 5-15• Eggshell 10-20 15-25• Low Sheen 20-30• Semi-Gloss 55-70

• Gloss 75+


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Alkyd Resin Technology

• ALKYD (Oil-Based)

« A synthetic resin made by reaction between alcoholsand fatty acids

« Soya bean & linseed oil commonly used« Benefits of alkyds:

Superior brushing characteristics Abrasion resistanceExcellent flow and levelingGood adhesion

Used in rust preventative paint


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Factors Affecting Coating Performance

• Structural Design• Coating Selection• Surface Preparation

Protection


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PAINT DEFECTS (Exterior):• Poor Gloss Retention:

Deterioration of the paint film, resulting in excessive or rapid loss ofluster of the top coat.

• Possible Causes: • Use of an interior paint outdoors.• Use of a lower quality paint.• Use of a gloss alkyd/oil-based paint in areas of direct sunlight.

• Solution: • Direct sunshine can degrade the binder and pigment of a paint,

causing it to chalk and lose its gloss. While all types of paint will losesome degree of luster over time, lower quality paints will generallylose gloss much earlier that better grades. The binder in top qualityacrylic latex paint is especially resistant to UV radiation, while oil &alkyd binders actually absorb the radiation, causing the binders tobreak down. Surface preparation for a coating showing poor glossretention should be similar to that used in chalking surfaces.


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Enamel , synthetic exterior• Alkyd — polyester polymers used to form solvent-based coatings; coating formulations also

contain ‗drying oils‘ derived from plant or vegetable oils • Antifouling paints — coatings designed to prevent the growth of barnacles and other marine

organisms on ships‘ bottoms. • Anti-microbial — a substance that kills or inhibits the growth of microorganisms. • Curing agent — chemical used to cause a reaction necessary for formation of the finished

coating after the coating formulation has been applied to the surface • Electrostatic deposition — a technique for moving and charging a powder coating so that it is

deposited on a grounded substrate or surface • Enamel — a smooth, hard, highly glossy coating; can be based on polyester or other types of

polymers; initially referred only to solvent or oil-based paints, but now some waterborne coatingshave adopted the term

• Epoxy — polymers containing numerous carbon and oxygen linkages; the structure provideschemical and temperature resistance, weatherabilty and other high performance properties;initially only available in solvent formulations, but water-based versions are being developed

• High solids — coatings dissolved in solvents where the content of the solids in the solvent is very

high (usually 80% or higher) • Inorganic zinc — coatings made from zinc-rich silicate materials that contain no carbon; they areoften used asa base coat over steel to protect the surface in high temperature applications


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Electrocoating• THE MANUFACTURING PROCESS

Auto bodies are coated with paint in a five stepprocess. The steps are as follows:

• precleaning (to remove dirt and grease)• phosphating (to provide a better surface for the

paint and for additional corrosionprotection)• electrocoating (the actual application of the

paint)• rinsing (to remove the "cream coat" of paint that

hasn't bonded to the metal surface)• baking (to crosslink the polymeric coating)


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• Polyurethane — polymers made from isocyanates, organic compoundsthat contain nitrogen; also contain carbon and oxygen groups; often used asprotective coatings; initially developed as solventborne formulations, butwater dispersions are now available

• Polymerization — chemical reaction in which two or more small molecules(monomers) combine to form large molecules (polymers, macromolecules)that contain repeating structural units of the original molecules and reflectthe percentage composition of the original molecules

• Post-cure — the period after curing of a coating is complete but before thecoating is completely finishedPowder coating — dry coating formulation that exists in a powder form;applied using electrostatic attractive forces created between the surface andthe coating

• Pre-treatment — a step required to prepare a metal surface before coating;involves surface cleaning and corrosion protection • Resin — polymer that forms the paint or coating film on a surface; also

referred to as the binder


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• Since polyurethanes are hard and glossy, theywill show every surface imperfection, so startingwith a very clean, smooth surface is essential,

as is sanding between each coat. Follow labeldirections for application methods and dryingtime.

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Gloss

• Gloss is the measure of reflection of lightthat is reflected into specu;lar direction.


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• Gloss Range with 60 ° GlossMeterMeasure With: If Semi Gloss - 10 to70 GU60 °If High Gloss > 70 GU20 °If LowGloss < 10 GU85 °


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Gloss measurement


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• Some of the most common paint failuresare:

• • cracking• blistering

• poor adhesion• corrosion


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• The following application methods are dealt with:• • pneumatic spraying (conventional air spraying);

• airless spraying;• airmix spraying;• hot spraying;• electrostatic spraying;

• two-component spraying;• HVLP spraying;• roller and brush.


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Adhesion (determination) The checkerboard incision test: adhesion is determined with the help of a ruler anda Stanley knife with a straight knife edge. A pattern of lines is cut into the surfacewhereby 6 parallel lines are first cut, followed by a second set of 6 parallel linesperpendicular to the first set. Tape with the required characteristics (adhesive

strength 10N, 25 mm wide) is then lightly pressed onto the surface. Finally, the tapeis pulled away from the surface in one smooth motion at an angle of 60 °.

The extent to which the paint squares in between the lines are pulled off the surfaceis a measure of the adhesion.

Sellotape type 1112 or 1401 or Scotch tape 828.

Method: ISO2409:1992(E)


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Classification Class Loss ofadhesion

Illustration

-very good Gt0 0% -

-good Gt1 < 5%

-mediocre Gt2 5 - 15%

-poor Gt3 15 - 35%

-very poor Gt4 35 - 65%

-total loss ofadhesion

Gt5 65 - 100% -


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Depending upon the film thickness, the distance between the lines isas follows;

0-60 micron dry film thickness 1 mm interval60-120 micron dry film thickness 2 mm interval120-250 micron dry film thickness 3 mm interval

>250 micro St Andrew's cross cut test or Elcometer test (ISO-4624)

If the paint coating may be subjected to mechanical forces, theadhesion of the paint system should be class GT0/GT1 or better. If nomechanical loading factors are present, it should be GT2 or better


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Gloss

Gloss is the visual impression created by the light-reflectingproperties of a surface and depends upon the incidence of light and

observation.

Method: ISO2813-1978(E), measurement angle: 60 °

Classification:

Classification: Gloss %

Mat 0-10%

Eggshell 10-20%

Silky gloss 20-45%

Semigloss 45-75%

Full gloss 75-100%


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Amount of paint consumed

A rough estimate of the paint loss percentages associated with various sprayingmethods is indicated below:

Application method Application loss

%

Viscosity

DIN-cup 4 Pneumatic spraying 30-40 18-35

Airless spraying 20-40 30-60

Air-assisted spraying 20-40 30-60

Hot spraying 20-40 30-60*

Electrostatic spraying 10-20 18-30

Two-component spraying 20-40 30-60

HVLP spraying 5-10 20-35

Roller and brush 4-6 80-120


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• Airmix spraying • • Airmix spraying is, in principle, the same as airless spraying. The

only difference is that airmix spraying also makes use ofcompressed air, which is why it is also referred to as air-supportingspraying. In this method, an airless pump applies a pressure of circa50 bar to the paint. During the application stage, an additional 1 – 1.5 bar of compressed air is added to achieve an improved spraypattern. The application information for this spraying method is alsoincluded on the product data sheet. The layer thickness that can berealized in one paint run using this method is less than with airlessspraying. This application method is more effective when it comes to

obtaining optimum results with the application of polyurethanepaints.


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• Airless spraying • • Airless spraying was developed to make it possible to cover large

areas with thicker paint coatings in a single run. In airless spraying,the paint is converted into a fine spray mist as it is forced throughthe spray opening under high pressure (150 - 250 bar). Many of theproducts supplied by Baril Coatings can be applied using thismethod. Every product data sheet specifies the viscosity to whichthe paint must be adjusted for airless spraying under the header"application information." Polyurethane paints can be applied viaairless spraying, but extra attention must be paid to the layerthickness in that case. If a layer is applied in one run which is too

thick, it will result in blistering (trapped air) and foam formation aswell as a somewhat matt paint finish, thereby reducing theglossiness of the coating.

•


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• Alkyd paint • • This group of paints is often referred to synthetic paint or alkyd paint. They

are one of the most popular types, and hardening of the paint film is theresult of oxygen absorption. Alkyd paints are used practically everywhere,as they are extremely versatile. They are used in the house painting sector,

construction sector and for ship coatings.• • Generally speaking, alkyd paints have the following characteristics:• • durable• good flow characteristics

• fast drying• good gloss retention• good elasticity• reasonably good corrosion control


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• Polyurethane paint • • Polyurethane paints are mostly two-component products, whereby the primary

component is mixed together with a curing agent shortly before use. There are twoimportant types of polyurethane paints, the aliphatic and aromatic polyurethanepaints. The most important difference between these two types is that the aromatictype is subject to yellowing over time whereas the aliphatic type is not. Besides the

two-component versions, there are also single-component polyurethane paints, theso-called moisture-curing polyurethane paints which use moisture for the curing orhardening process.

• There are many possibilities for formulating polyurethane paints, which is why thereare many types on the market, which can also differ markedly in characteristics.

• • Some important characteristics of these paints are:• • hardness and wear-resistance• resistance to water and chemicals• excellent overall adhesion• fast drying


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Glossmeter

• Medium or Semi Gloss - 60 ° - The UniversalMeasurement AngleOne must remember that allgloss levels can be measured using the

standard measurement angle of 60 °. This 60degree angle is used as the reference angle forall products. So why choose some other anotherangle? Because for extreme gloss, one obtains

better measurements with the complimentaryangles of 85 ° or 20 ° often used for low and highgloss levels respectively.


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• AIRLESS SPRAY PAINTING• Fluid injection hazard: General Safety• Airless spray equipment generates very high fluid pressure. Spray from the gun,

leaks, or ruptured• components can inject fluid through the skin and into your body and cause extremely

serious bodily• injury, including the need for amputation. Also, fluid or splashed into the eyes or onto

the skin can cause• serious damage.• Never point the spray gun at anyone or at any part of the body. NEVER put hand or

fingers over the• spray tip.• Always have the tip guard in place on the spray gun when spraying.• Always follow the pressure relief procedure before cleaning or removing the spray tip

or servicing any• system equipment.• Never try to stop or deflect leaks with your hand or body.• Be sure equipment safety devices are operating properly before each us


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