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Prepainted
Advantages and Benefits
U.S. Steel prepainted steel sheet is manufactured by a continuous coating process, which involves
cleaning, pretreating, painting and curing (by baking) in coil form. Coils are generally
painted with two-coat paint systems consisting of a primer and a finish color coating on the
side intended for exterior exposure and a primer and a topcoat on the reverse side. The
prepainting process is designed to produce highly uniform, high-quality paint coatings. The
combination of quality steel (galvanized, GALVALUME®-coated or cold rolled) and
coil-coater-applied, high-quality paint results in the significant advantages and benefits
noted on the previous pages.
Numerous options may be specified:
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Metallic coating thickness, substrate
thickness and strength combinations: Galvanized or
GALVALUME® Coated Sheet corrosion-resistant coatings in a range of
thicknesses and base steel sheet.
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Types of
Top-Coatings: polyurethanes, polyesters, silicone-polyesters, acrylics, alkyds, vinyls, fluorocarbons, plastisols, and other coatings. New paints and coatings continue to be developed. These coatings are available in various degrees of glossiness (ranging from flat to very high gloss), hardness and resistance to chalking and fading.
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Colors:
a multiplicity of standard colors and an unlimited range of specially designed hues and tints may be selected. Specific colors can be formulated to coordinate with other components for aesthetic effect.
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Treatments
and Primers: specified pre-treatments and primer coatings work beneath the colored top coat to ensure maximum adhesion to the base metal and resistance to undercutting corrosion (peeling). Chemical pre-treatments prepare the base steel for receiving the coatings. These pre-treatments are applied after extensive degreasing (alkaline cleaning) to put an adherent, anti-corrosion film on the base steel. Primers are high-performance coatings designed to contribute adherence, corrosion resistance, durability and smoothness to the total coating system. Various primers (e.g. epoxy, urethane, etc.) can be selected to help to create a coating system that maximizes the performance of the product for special end-use applications. |
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Prepainted steel sheet for
exterior use consists of:
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| 1. |
Top coat, which provides color, pleasing
appearance and a barrier film to enhance long-term
durability |
| 2. |
Primer coat to prevent undercutting of
paint and enhance corrosion resistance |
| 3. |
Pre-treatment layer applied for good
adhesion |
| 4. |
Galvanized or GALVALUME® Coated Sheet
coating for added corrosion resistance |
| 5. |
Base steel sheet |
Specifications:
These are the important segments of a prepainted sheet
specification. Each one of these segments is critical to
ensure that the product will meet a customer's desired requirements.
When planning to use prepainted steel sheet, consider the
following major factors:
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Dimensions - thickness, width of sheet |
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Steel designation - forming steel, structural steel, etc. |
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Metal coating type - Galvanized or GALVALUME® (if needed for the application)
and coating-layer thickness |
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Pre-treatment (generally chosen on the basis of the type of steel and
paint system) |
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Primer type (e.g. epoxy, urethane, etc.) and thickness |
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Top coat type (e.g. plastisol, polyester, silicone-polyester, etc.),
color and thickness
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Other considerations:
It is possible to specify prepainted steel sheet product by performance attributes,
which are verified by quantitative standard tests. Such a specification may include these attributes: paint
hardness, overall corrosion resistance, paint flexibility, paint adhesion, chalk and fade resistance, color
match, gloss, solvent resistance, detergent resistance, abrasion resistance, and water resistance. When these
items are clearly identified, a well-designed and engineered paint system can be applied to provide excellent
performance in many applications.
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