Radiation Curable Coatings Information
Radiation curable coatings are liquid coatings that are cured by exposure to radiation.
Applications for radiation curable coatings include coatings for:
These coatings are cured by ultraviolet (UV) radiation or electron beam (EB) radiation, both of which supply fast cure times.
There are two types of radiation curable coatings:
UV curable coatings contain large oligomers, monomers, and photo initiators. The photo initiator is the catalyst for the curing process when it is exposed to UV light source, typically with 180nm to 380nm wavelength. UV lamps require less power in comparison to heaters and ovens for standard coatings. Curing time is anywhere from less than a second to hours depending on the formulation. UV coatings are suitable for three-dimensional objects but coatings cannot have too much pigmentation as this prevents UV from reaching photo initiator additives.
EB curable coatings contain the same components as UV coatings minus the photo initiator; instead high energy electrons delivered by an electron accelerator initiate the curing process. This equipment is more expensive and cannot flood a surface with electrons, meaning 3D coatings are not possible. For EB coatings to work an inert nitrogen blanket is needed. EB coatings create a uniform protective layer and can have more pigmentation than UV coatings.
Radiation curable coatings consist of several components:
Oligomers are the main component of the coating. They are a relatively low-molecular-weight substance that polymerizes to form the coating and gives the coating the majority of its physical properties. Common oligomers are epoxy acrylate, urethane acrylate, polyester acrylate, polyether acrylate, acrylic acrylate, and silicone acrylate with epoxy acrylate.
Monomers are added to the coating formulation to reduce the viscosity of the coating because of their low molecular weight. They also may participate in the polymerization of the oligomers in some formulations.
Photo initiators are only found in UV-curable coatings. They are photo-reactive molecules that absorb UV energy and initiate the polymerization reaction in the oligomers. This is accomplished by releasing cations for cationic photo-initiated coatings or free radicals for free radical-polymerized coatings.
- Coverage: The theoretical area that a coating can cover at a given thickness, usually given in feet squared (ft.²).
- Wetthickness: The layer thickness or range of thicknesses by which a coating can be applied.
- Cure/dry temperature: The minimum temperature at which coatings cure.
- Operating temperature: Temperature range that a coating can be used at or exposed to without degrading structural or other required end-use properties.
- Resistivity: A measurement of the coating's resistance to the flow of electrical current. This is important for surfaces with the potential to be exposed to electrical components.
- Dielectric strength: Maximum voltage that a dielectric material can withstand under specified rupturing. It is usually expressed as volts per unit thickness and is also called disruptive gradient or electric strength.
Lifespan: The average life of the coating after its application. When coatings degrade, they require reapplication or touch up to remain functional.
- Temperature sensitivity: Surfaces of wood, plastic, or other materials may not allow for certain application processes that require high curing temperatures.
- Surface texture: Some coatings are more compatible on rough surfaces than others. Rough surfaces have more surface area and may require more coating than smooth surfaces. Some surface preparation may be required before coatings can be applied.
- Contamination: Surfaces often must be clean of all surface contaminants (e.g. oil, grease, oxides).
Chemical compatibility: Exposure between reactive materials can diminish the effectiveness of radiation-curable coatings or even damage the substrate.
The main purpose of radiation-curable coatings is to enhance material properties. Features pertaining to coatings include:
Anti-static/ESD control: Minimizes static electricity in sensitive environments.
- Chemical resistant: Resistance to acids, alkalis, oils, and general chemicals.
- Conductive: Forms an electrically-conductive layer.
- Dielectric: Nonconducting materials create a dielectric layer used in optical applications. High-reflection coatings consist of a stack of alternating layers of high- and low-refractive-index materials. Each layer in the stack has an optical thickness of a quarter-wave at the design wavelength.
- Corrosion inhibiting: Prevents moisture from reaching the metal or underlying substrate, or provides a sacrificial layer.
- EMI/RFI shielding: Provides shielding from electromagnetic interference (EMI) or radio frequency interference (RFI).
- Flame retardant: Coatings are flame-retardant in accordance to Underwriters Laboratories, Inc. (UL) Flame Class 94V-0, or other equivalent ISO standards. These materials reduce the spread of flame or resist ignition when exposed to high temperatures. They also insulate the substrate and delay damage to the substrate.
- Heat resistant: Resists damage from heat or is formulated for use in high-temperature environments.
- Protective: Protects substrates and surfaces from scratches and abrasion.
- Touch-up: Repairs and matches the original coating where it has been damaged. The touch-up coating material should have good adhesion to damaged, undamaged and prepped substrate surfaces.
- Waterproof/water repellant: Coatings are clear, exterior finishes that cause water to bead on the surface and minimizes moisture penetration.
- Wear resistant: Resistant to wear or erosion. Wear is caused by a sliding action between two or more components. Erosion is surface damage or material removal caused by the impact of particles or slurries.
Weather resistant: Coatings are weather-resistant or protect against damage from UV radiation.
9986165 - Anti-corrosion coating for frames.
ASTM D6577 - Standard guide for testing industrial protective coatings.
DELPHI DX550013 - Corrosion protective coatings - phosphate/organic/oil type.
FORD WSA-M2P170-A1 - Paint performance, corrosion/heat resistant coating, 150 °C, max ***to be used with Ford WSS-M99P1111-A***.