- First a bit of history:
Paint is probably as old as humanity itself, but the oldest rock art paints recently discovered are only 30,000 years old, already demonstrating a certain ingenuity in their method of application. Nevertheless the progress of “homo pictor” was slow and determined by the progress made in other areas. For this reason the industrial revolution of the nineteenth century initially did hardly anything to change the habits of the prisoner painter in terms of the techniques of applying oil paint and the application of paint with a brush.
It took until 1908 when Henry Ford to manufacture cars on a production line, for things finally to get moving. Because of their slow drying, the paints with an overprint varnish base of the time were not compatible with mass production, and a product with a faster drying time had to be found. Remember that aircraft manufacturers were using cellulose varnish to stiffen and waterproof aircraft canvas. This was a solution of nitrocellulose in butyl acetate. Carbon black was added as a pigment and castor oil as a plasticiser. This was the first industrial paint for car bodies, the drying of the new paint being too fast to enable painters to continue using brushes for paint application. Fortunately the air gun had been invented in 1907 by DE WILBISS, and the paint shops in the FORD factories replaced brush coating with gun spraying.
- Let's talk a little about paints:
The good old days when we asked the painter to “make it look pretty" are long gone, and his work, which was essentially an “art”, rapidly developed into an increasingly sophisticated technical process. Brains and common sense were no longer sufficient to navigate the tangled web of formulae of all kinds developed by chemists. To avoid making mistakes, it is now necessary to become familiar with the properties of the product to be applied. Therefore we shall now examine the main points which the painter must consider to ensure that his work is satisfactory.
- Technical criteria for selecting paint
Dry film property:
You do not choose a paint because it is cheaper or because it has been produced by XYZ . A paint is selected for its properties and hence its ability not only to meet the requirements of the person who is to apply but also the requirements of the person who will later use the painted object.
These properties are very different and they are therefore also classified as follows:
- Physical properties
- Mechanical properties
- Chemical properties
- Biological properties
a) Physical properties
Colours, brilliant, satin or mat finish, degree of opacity (for paints and lacquers) or transparency (for varnishes and glazes). Smooth film or a film having a fairly accentuated relief, various decorative effects (metallised, hammered, pearly, etc.), level of impermeability or permeability, resistance to heat, cold, etc..
b) Mechanical properties
Although mechanics are part of physics, these properties are so important that they are considered separately and often examined as a priority. They include: adherence to one or more different surfaces, hardness, flexibility, resistant to impact, scratching, stamping, folding, abrasion, chipping, etc..
c) Chemical properties
This refers to the overall behaviour of the paint film when brought into contact with substances of any kind: water, salt solutions, fuels, acids, corrosive vapours, etc. Resistance to a saline mist is often used to evaluate the degree of corrosion protection of the film.
d) Biological properties
Two special categories of paintings must have properties of this kind, even though they are radically opposed to each other:
Biocidal paints designed to kill living organisms: fungicidal paints, bactericidal paints, insecticidal and acaricidal paints, antifouling marine paints.
- The so-called "food" paints which are absolutely non-toxic, designed to come into contact with food or beverages, without altering the flavour or aroma.
- Application and examples of anti-corrosion coating
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APPLICATIONS |
TYPE OF COATINGS |
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Normal outdoor exposure: - building, bridges, maintenance - decoration, finishing of metal structures - automotive, metal buildings, aluminium profiles - office furniture - finishing of cars (maintenance) |
- oil paint, alkyd, chlorinated rubber - alkyds, acrylics, polyurethanes, vinyls - alkyd-melamines - nitrocellulose, acrylic, polyester, powder - acrylic, nitrocellulose |
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Marine atmosphere: - Installations and superstructures in a marine area - marine paints, cars |
- alkyd, chlorinated rubber, phenolics, vinyls - alkyds-vinyls, polyurethanes |
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IMMERSION in water: - boat hulls - boat hulls, bunkers - boat hulls, pools, swimming pools - marine paints - pipes, tanks |
- phenolics - vinyl - chlorinated rubber - polyurethanes - epoxy pitches |
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Exposure to chemical vapours: - chemical equipment |
- epoxy, chlorinated rubber, vinyl, polyurethane |
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Intense sun exposure: - metal building - car finishing - equipment for the petrochemical industry |
- vinyls - acrylics - alkyd - silicones |
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Humidity: - refrigerators, washing machines - air conditioning - chemical equipment, maintenance |
- alkyd - melamines, acrylics, polyester, powder - epoxies - hardening epoxies, chlorinated rubber, phenolics |
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High temperature: - engine block up to 95 ° C - dryers, kilns, accessories up to 95 ° C - engines, pipes up to 280 ° C - dryers, kilns, roasters up to 300 ° C - ditto up to 600 ° C |
- alkyd - modified alkyds - amines - epoxies - modified silicones - silicone - aluminium |
