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Thermosetting powders are much more widely used than thermoplastics.

They are primarily composed of relatively high molecular weight
solid resins and a crosslinker.

Thermoset powders are used for a wide variety of decorative and protective applications. They are applied by the electrostatic spray process, heated to the necessary temperature
and cured.

The primary resins used in the formulation of thermosetting powders
• Epoxy
• Polyester
• Acrylic

These primary resins are used with different crosslinkers to produce a variety of powder materials. Many crosslinkers, or cure agents, are used in powder coatings, including amines, anhydrides, melamines, and blocked or non-blocked isocyanates.

Some materials also use more than one resin in hybrid formulas.

When a thermoset powder is applied and subjected to heat it will melt, flow and chemically crosslink to form a finished film.

The chemical reaction in the cure cycle creates a polymer network that provides excellent resistance to coating breakdown. A thermoset powder that has cured and crosslinked will not melt and flow again if subjected to heat a second time.

Epoxy powders were the first commercially available thermoset materials and they are the most commonly used of the thermosetting powders today.

They are available in a wide range of formulations for thick film functional applications and thin film decorative applications.
They provide excellent toughness, chemical resistance, corrosion resistance and flexibility.

The primary drawback with epoxies is that they will chalk when subjected to UV radiation. For this reason they are rarely used for outdoor applications.

Functional Epoxy Powder Applications
Functional epoxies are commonly used for electrical insulation and
corrosion protection.

Some typical applications for functional epoxies
are electric motors, alternators and electrical control junction boxes, taking advantage of its insulating properties.

Because functional epoxies also have very good chemical resistance, they are used in a variety of applications where corrosion resistance is required, such as piping, under the hood automobile components and concrete ”rebar.“

Decorative Epoxy Powder Applications
Epoxies are often used for decorative applications. They can be formulated to provide a variety of glosses, colors and textures and applied in relatively thin films of 0.5 to 3 mil, still providing the toughness and durability of the functional coatings.

Typical applications include metal office furniture, shelving, interior car parts, and toys.

Epoxy Polyester Hybrids
Epoxy-Polyester ”Hybrids“, like the name implies, combine epoxy
resins with polyester resins to form a powder with most of the same properties as epoxies.

Although some hybrids are less resistant to chemicals and solvents, they are tough, flexible and competitively priced.

Hybrids are likely to be used in many of the same applications as
epoxies. In addition to the slight improvement in weatherability, the polyester resin sometimes provides some improvement in charging characteristics for electrostatic application.

Polyester Powder
Polyester resins are used to formulate urethane polyesters and polyester triglycidyl isocyanurate (TGIC) materials.

Urethane Polyesters
Urethane cured polyester powders have excellent resistance to outdoor environments, toughness and very good appearance characteristics at 1 to 2 mil film thickness.

A smooth, thin film that resists weathering and physical abuse makes the urethane polyesters a popular finish for high quality products.

It is common to block the crosslinker in urethane polyesters with ecaprolactam.

To begin the crosslinking process, the material must reach
a temperature above the blocking agent threshold. With e-caprolactam, unblocking occurs at approximately 360 °F (182 °C). Therefore, temperatures must be higher than 360 °F to start the melt phase of the cure cycle.

Powders containing e-cap are usually sensitive to films thicker than 3 mils. Thicker films with these urethanes may lose some of their mechanical properties and they may exhibit outgassing effects due to ecaprolactam evolution.

They are used for exterior applications such as patio furniture, automotive wheels and trim, lawnmowers and a wide range of other products requiring high quality, decorative finishes comparable to wet coatings.

Polyester TGIC
Polyester TGIC coatings use the epoxy functional crosslinker triglycidyl isocyanurate (TGIC).

TGIC’s have very good adhesion characteristics, corrosion resistance and exterior durability. They can typically be cured
at lower temperatures than urethanes and/or have shorter cure cycles.

In the cure cycle, they have good overbake characteristics and
they are less sensitive to outgassing. They also provide good edge
coverage and tough, thick films (3–5 mil/75–100 m) due to the inherent higher melt viscosity of the non-blocked TGIC crosslinker. They have equal corrosion resistance to urethane polyesters but they are somewhat less resistant to chemicals.

Some typical applications are automotive wheels, air conditioners,
lawn furniture, and air conditioner cabinets.

Acrylic Powders
Like the polyesters, acrylics give excellent exterior durability.

Common acrylic-based materials include urethane acrylics (hydroxyl functional resins), acrylic hybrids (acid functional resins) and glycidyl methacrylate acrylics (GMA) (epoxy functional resins).

Urethane acrylics require cure temperatures of 360 °F (182 °C). Like urethane polyesters, they may exhibit problems with outgassing at thicker films (3 mils/75 m). They offer excellent thin film appearance, good chemical resistance and hard films. Flexibility and impact resistance is usually poor.

GMA acrylics can be cured in less time or lower temperatures than the urethane acrylics and they also can provide superior weathering characteristics. They make excellent clear coats over brass or chrome due to their exceptional clarity.

Like the urethane acrylics, flexibility is somewhat
limited. They can be applied in films greater than 3 mils (75 m)
without the risk of outgassing that is characteristic with the urethanes. GMA acrylics are typically not compatible with other resins and are run in systems that are isolated from other powders.

Acrylic hybrids combine the acrylic resin with an epoxy binder.

They are somewhat better than a polyester/epoxy hybrid but still not considered acceptable for outdoor use. The mechanical properties that are characteristic in epoxies are a benefit of these materials and theyhave much better flexibility than other acrylics.

Because of their good appearance, tough surface, exceptional weatherability, and excellent electrostatic application characteristics, acrylics are frequently used for applications on products that have very high quality standards.

Appliances, automobiles and other products that require durability and long life in a harsh environment are good candidates
for acrylic powder coatings. Typical applications include automotive wheels, plumbing fixtures and vending machines.

Research has been conducted to determine the suitability of acrylic powder coating as a clear coat on automotive bodies. While the United States automobile manufacturers continue to evaluate this application, one European manufacturer is using it in production.


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abrasive blasting   adhesion problems  caps and plugs

chemical cleaning  cure ovens  defects  fluidized bed

infrared oven  masking  outgassing  powder formulations

pretreatment  quality    powder selection

powder vs. liquid  racking  spray booth  spray gun  substrates

hi-temp tapes  types of powder  troubleshooting


August 2, 2006