Automotive Paint Part I

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[: any liquid, liquefiable, or mastic composition which after application to a substrate in a thin layer is converted to an opaque solid film] [1].





Urethane paint was first created in the mid-1960s, utilizing the newly-developed plastics technology of that era, to be superior to enamel paint in terms of durability. It also has the advantage of being a surface that can be applied over enamel if the enamel-painted surface is prepared first. A urethane painted surfaces is minimally affected by ultraviolet rays, making the paint a good choice for outdoor surfaces.



It is widely used in the automotive industry because of its durability. Inexpensive urethane paint might contain less than10 percent polyurethane. High-quality polyurethane paint has a higher percentage of the expensive polyurethane ingredient. A urethane-painted surface can be expected to contract and shrink over time.



Among the inorganic pigments, TiO2white is, by far, the most important one. The photo catalytic activity of TiO2leads to a rapid degradation of the organic binder matrix, so the surface of the TiO2 particles has to be covered by an inorganic coating to prevent the matrix from being photo oxidized. This is done by applying layers of SiO2and Al2O3



Basecoat / Colour Coat Formula



• Petroleum –Based Solvents - 40-60%

• Resins and Binders - 30-50%

• Pigments & Colorants - 5-10%

• Silicone Polymers & Other Additives (Catalysts, etc) - 1-2%



Clear coat 2K Formula



• Petroleum –Based Solvents - 20-40%

• Resins and Binders - 50-70%

• UV Absorbers - 1-2%

• Silicone Polymers & Other Additives (Catalysts, etc) - 1-2%

• Isocyanate hardener and catalyst: 0 -2%



Typical OEM Paint Thickness



• E-Coat 33 µ (1.3 Mil) - an anticorrosion coat applied to both sides of the steel to prevent corrosion



• Primer 18 µ (0.7 mil) - Initial protection layer with texture to assist the pigment layer in bonding to the metal beneath



• Base Coat 15 µ (0.6 mil) - The basecoat is usually 0.5 to 1 mil thick



• Clear Coat 48 µ (1.9 mil) - The clear coat provides gloss plus physical protection from the elements, including ultraviolet rays



All paint has three major components: a pigment for colour and hiding powder; a binder that holds the pigment to the surface; and a carrier to maintain the pigment and binder in liquid form.



1. Primer - the coating layer that joins a corrosion-protected substrate to the topcoat. It functions to smooth out surface irregularities, improve stone-chip performance, and helps to protect the substrate from visible and UV light.



2. Basecoat - the coating layer that provides colour and aesthetic effects. Basecoat must provide uniform appearance initially and for many years without fading. Modern requirements for appealing vehicles often require micas, aluminium flakes and other effect pigmentation. These can be incorporated in one basecoat layer or in a separate layer



3. Clear coat - the coating layer that forms the last interface to the environment. It carries the biggest part of the technological performance and must be able to resist environmental etch, bird droppings, car wash machines and other outside influences. To improve performance against all these influences, OEM coating systems move from colour topcoats to basecoat/clear coat systems.



Base Coat Clear Coat – two stage paint; base (colour) coat and clear coat were adopted as an automotive industry standard in 19982, clear coat paint was originally used to protect metallic paints and provide depth of colour. They are applied over the primer surface and covered by the clear coat layer to protect it from the environment.



There exist three main base coat systems in the paint shops of the automotive industry worldwide: medium solids (MS) high Solids (HS) Water-based (waterborne) (W paints are essentially low solids paints (up to 60% waterborne solvent), but they are legal because de-ionized water is used as the solvent, as opposed to volatile organic compounds (VOC). North America predominantly uses HS, whereas water-based clear coat is the preferred technology in Europe



The clear coat in combination with the basecoat forms the automotive topcoat, which gives the vehicle its appearance. One and two component clear coats (1K and 2K) are applied over both solvent and water-based basecoats.

Modern automotive paint systems of whatever density pose unique challenges to the detailer, to determine the correct polish/and pad combination, machine methodology. This requires a ‘test panel’ to see how the selected polish set-up responses to the paint, and wither it will remove the surface scratches



Select a ‘typical’ 18 x 18 – inch area -one that represents the type of defects that you want to remove and starting with the least abrasive polish and / pad combination and then proceed until the defects are removed. This is the polish / pad combination you’ll need to use. Selecting the correct pad / polish combination for the vehicles paint / defects can take just as long as the paint correction process



Temperature affect on Paint Thickness



A dark colour paint surface can be subjected to temperature swings of 50.OF +/- 10.OF. With an ambient temperature of 80.OF a dark colour horizontal surface can reach a temperature of 160.OFThe urethane used for automobile paint is classified as a semi-solid, micro structured permeable membrane, due to its micro-fissures, or pores’, being a thermosetting polymer it remains flexible, whilst retaining its tensile strength, to enable it to expand and contract to follow temperature fluctuations (elongation). So be cognizant that paint thickness readings will vary in accordance with ambient temperature.



Measure paint thickness on a horizontal surface at temperatures below 50 degrees, and then measure the same spot at mid-day at temperatures above 80.OF. After an hour measure the same spot, you will then obtain a thicker paint surface reading. Conversely with colder ambient temperatures you will then obtain a thinner paint surface reading. There are variables that will affect the paint readings, i.e. instrument sensitivity, humidity, paint surface colour, etc.



Environmental Damage



Environmental damage to paint comes in a varied range of threats; acid rain, road salt, tree sap, hydrazine an extremely active acid that is found in jet fuel, industrial fallout, ultra violet radiation (UV-A and and other airborne contaminants are very detrimental to a vehicles paint film surface.



They are all forms of environmental contamination and given the right catalyst; reactivity (heat) plus moisture, they will become acidic. During this process the metal absorbs oxygen from the water and forms iron oxide (rust). Given the porosity of paint they permeate the paint matrix down to body metal.



Bibliography



1. An Examination of What Paint Is, How It Degrades and What to Do When It Does -By William Rice Evolution

2. Automotive Paint and Protectant Technology, Gene Praschan and David Ghodoussi

3. Auto Painting: Basic of Basics - "Basic of Basics" How do I paint my car myself?

4. Automotive Paint Handbook: Paint Technology for Auto Enthusiasts and Body Shop Professionals - John Pfanstiehl



Information resource



1. Wikipedia Encyclopaedia - Paint - Wikipedia, the free encyclopedia

2. PPG website on paint problems- http://bit.ly/4JAaVa

3. Akzonoble Paints - Welcome to AkzoNobel

4. DuPontâ„¢ Automotive Coatings

5. Glasurit, Advice on Paint and Paintwork Defects - Request Rejected

6. PPG Automotive Refinish Product Catalogue - http://bit.ly/4wMYuH

7. Automotive Body Repair News (ABRN) - http://www.abrn.com/abrn/

8. Benjamin Moore Paints-http://www.benjaminmoore.com/

9. A new perspective on paint defect return - Jason Rose from Meguiar’s

10. PCI Paint & Coating Industry Newsletters





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2. “Clear Coat Thickness and UV Protection Removed by Polishing� - http://www.autopia.org/forum/car-det...-removal.html#

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[Marj]

Thanks, that was very informative, good info. for future reference.