High Solids
High-solids coatings are solvent-based and have a high resin concentration. Solids content typically falls in the 50 to 70 percent range, although some formulations are higher.
- Advantages
- Reduced VOC and HAP emissions
- Reduced solvent usage
- Reduced inventory
- Reduced fire hazards
- Reduced number of spray applications to achieve a given film thickness
- Improved abrasion and mar resistance
- Disadvantages
- Generally require high cure temperatures
- Sensitive to inadequate cleaning of substrate
- Extremely sensitive to temperature and humidity
- Difficult to control film thickness
- Tacky overspray difficult to clean
- May require paint heater in system
- Difficult to control sagging
- Narrow "time-temperature-cure" window
- Cannot use dip or flow coating
- Difficult to repair
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Waterborne Coatings
In waterborne coatings, water, alone or in conjunction with an organic solvent, acts as the carrying medium. Most waterborne coatings contain an organic co-solvent (usually 2 to 30 percent) that is added to dissolve the resin.
- Advantages
- Reduced VOC and HAP emissions
- Conventional application processes can be used
- Reduced toxicity and odor result in improved worker safety and comfort
- Good storage life
- Easy cleanup
- Reduced fire hazard
- Disposal of hazardous waste minimized or even eliminated
- Disadvantages
- May cause grain raising in wood
- Tendency to foam
- Rubbing requires effort
- Surface must be free of oil and dust
- Longer drying times or increased oven temperatures required
- High gloss finish difficult to obtain
- Clean-up difficult once coating is cured
- Great susceptibility to pick up dirt
- Most of these coatings cost more per gallon on an equivalent solids basis
- Not many resins available for waterborne formulations
- Converting solvent-borne coating line may be complex, i.e., stainless steel or plastic lines, valves, etc., are needed
- Problems with atomization, i.e., reduced paint transfer efficiencies
- Increased runs and sags
- Needs good temperature/humidity control
- Storage area requires enclosure and heating
- Refinishing is difficult
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Powder Coatings
Powder coatings contain 100 percent resin in dry powdered form and a built in curing agent.
- Advantages
- Cost savings due to:
- No solvent flash required
- No coatings mix room needed
- Minimal oven length required
- Low ventilation requirement
- Floor space economy, i.e., system requires two thirds to three quarters of wet paint systems
- VOC and HAP compliance, i.e., no solvents
- Quality finish
- Durable finish
- Good corrosion resistance
- Coating utilization efficiencies can reach 95 to 99 percent
- Energy savings
- Little operator expertise required
- Quick "packagebility"
- Variety of resins available
- No hazardous overspray, waste sludge, or contaminated water
- Reduced worker exposure to solvent vapors
- Disadvantages
- Heat requirement restricts powder to metal finishing
- Powder manufacturing limitations
- Difficult to make small amounts
- Control of texture size and distribution limited
- Metallic powder coatings not as attractive as wet metallic finishes
- Recirculating system creates negative pressure in booth
- Need gentle air stream to apply powder
- Enhanced Faraday cage effect
- Difficult to achieve thin films below 1.0 to 1.5 mils
- Powder clumping
- Difficult to change colors
- Needs cool, dry storage area
- Powder coatings difficult to match for repair with liquid paint and hard to strip
- Pretreatment of substrate is critical
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UNICARB™ Spray System
In the UNICARB™ system, supercritical carbon dioxide replaces a substantial amount of the conventional solvents used to spray-apply industrial coatings.
- Advantages
- High quality finish
- Fewer coating applications needed
- Reduced VOCs and HAPs
- Reduced operating costs
- Easy to retrofit
- High transfer efficiency
- May reduce sanding requirements for wood furniture
- Reduced worker exposure to solvent vapors
- Disadvantages
- Limited experience
- Lower fluid delivery rates than airless or air spray guns
- Gun and supply tubing is bulky
- Royalty costs
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Radiation-Cured Coatings
For radiation-cured coatings (ultraviolet (UV), electron beam (EB), and infrared (IR)), electromagnetic radiation is used to alter the physical and chemical properties of a coating such that the organic substrate develops cross-linked or solvent-insoluble network structures.
- Advantages
- UV and EB technologies use coatings with lower VOC and HAP content than conventional coatings
- IR ovens oxidize various VOC's, thus reducing potential emissions
- Increased production rates because of short curing periods
- Low energy costs
- Consistent performance
- Small ovens required
- Low air movement reduces dust and dirt contamination
- Easily installed/retrofitted
- Reduced fire and explosion hazard
- Disadvantages
- Interference of photocure by pigments
- Higher capital investment than conventional ovens
- Higher costs for EB and UV coatings
- Potential problems with acrylate toxicity
- Shrinkage and adhesion problems with acrylate
- Not applicable to all finish types because it produces a specific "look"
- Dermatitis
- Curing sensitive to shape of part
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Two-Component Reactive Liquid Coatings
In a two-component reactive liquid coating system, two low-viscosity liquids are mixed just before they enter into the application system. One liquid contains reactive resins, and the other contains an activator or catalyst that promotes polymerization of the resins.
- Advantages
- Low-temperature processing
- Disadvantages
- Limited experience
- Uncured resin may be harmful
- Highly complex process
- High level of operator skill required
- High capital cost
- Limited pot life
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Vapor Permeation of Injection-Cured Coatings
After a reactive resin is applied as a liquid, curing is induced by exposing the liquid to a vapor containing a compound that initiates polymerization. One example is polyol-isocycanate coatings cured by tertiary amine vapor injection.
- Advantages
- Eliminates or reduces solvent
- Low temperature processing
- Unreacted overspray can be collected for reuse
- Can be used on heat-sensitive substrates
- Disadvantages
- Limited experience
- Highly complex process
- High level of operator skill required
- High capital cost
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