Major Resin Types
The resin component in the formulation will largely determine the processing and
end-use performance properties of powder coatings. A summary of the characteristics
and applications for the most common thermosetting and thermoplastic powder coatings
may be found in the following sections (click on resin for summary).
There are other powder coating resins that are in commercial use, but not included
here because they are either used less frequently.
There are two main classifications for powder coatings: thermoplastic and thermoset.
A thermoplastic powder coating melts and flows when heat is applied, but continues
to have the same chemical composition once it cools to a solid coating. Thermosetting
powder coatings also melt when exposed to heat. However, after they flow to form
a continuous film, they chemically crosslink on additional heating. The final coating
has a different chemical structure than the applied powder. Table 1 and 2 provide
properties of thermosetting and thermoplastic powders respectively.
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Epoxy
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Epoxy Hybrids
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Urethane Polyester
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TGIC Polyester
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Acrylic
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Hardness (Pencil)
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HB-7H
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HB-2H
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HB-4H
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HB-4H
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H-4H
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Impact Resistance (in-lbs)
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60-160
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60-160
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60-160
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60-160
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40-100
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Gloss (60 deg. meter)
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3-100+
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10-100+
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15-95
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20-90
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10-90
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Color
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Al colors, clear, textures
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Al colors, clear, textures
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Al colors, clear, textures
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Al colors, clear, textures
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Al colors, clear, textures
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Salt Spray
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1000 hrs
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1000 hrs min
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1000 hrs
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1000 hrs min
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1000 hrs min
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Condensing Humidity
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1000 hrs
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1000 hrs min
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1000 hrs
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1000 hrs min
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1000 hrs min
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Cure Range*
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3 min at 232°C to 25 min at 121°C
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10 min at 204°C to 25 min at 149°C
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10 min at 204°C to 25 min at 149°C
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10 min at 204°C to 25 min at 149°C
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10 min at 204°C to 25 min at 177°C
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* Typical 2 mil (50 µm) film – time at metal temperature
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Table 1: Comparison of Properties Between Thermosetting Powder Coating Resins
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Vinyl
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Nylon
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Polyester
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Primer Required
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Yes
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Yes
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No
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Melting Point, °C
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130-150
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186
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160-170
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Typical Pre/Post Heat, °C
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284 / 230
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310 / 250
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300 / 250
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Adhesion
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G-E
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E
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E
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Surface Appearance
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Smooth
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Smooth
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Slight Peel
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Gloss, 60 deg
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40-90
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20-95
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60-95
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Pencil Hardness
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HB-2H
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B
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B-H
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Impact Resistance
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E
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E
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G-E
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Salt Spray Resistance
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G
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E
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G
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Weathering
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G
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G
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E
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Humidity
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E
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E
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G
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Acid Resistance
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E
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F
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G
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Alkali Resistance
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E
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E
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G
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Solvent Resistance
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F
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E
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F
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E = Excellent, G = Good, F = Fair
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Table 2: Physical and Coating Properties of Thermoplastic Powders
Once cured, thermosetting powders are heat stable and, unlike thermoplastic powder
coatings, will not revert back to the molten stage when reheated. Thermosetting
powders are also tougher, have better adhesion to metal substrates, and are more
resistant to solvents and chemicals than thermoplastic coatings. Thermosetting powders
account for about 95% of all powder coatings.
Thermoplastic powders are typically high molecular weight materials that require
high temperatures to melt and flow. The primary advantage of thermoplastic coatings
is that they form a smoother finish and require less energy. They are commonly applied
by fluidized bed application, and the parts are both preheated and postheated. Most
of the thermoplastic powder coatings have marginal adhesion so that the substrate
must be pretreated and sometimes primed prior to coating application.
