UV-curable coatings provide energy savings—operational bonuses
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With natural gas and electricity prices at or near all-time highs, efficient use of these energy resources is a vital component of business success for finishers today. Efficient use of energy can directly impact the bottom line by lowering production costs, conserving scarce or limited resources and increasing productivity.
In addition to the positive impacts on business results, energy conservation is also beneficial to the environment. The United States Environmental Protection Agency (EPA) promotes energy efficiency with good reason: Reductions in fuel use translate directly into fewer emissions of criteria pollutants such as sulfur oxides, nitrogen oxides, and particulates, as well as greenhouse gases. In short, energy conservation positively impacts the bottom line for both industry and the environment, increasing margins as well as the longevity of the earth’s natural resources.
There is currently a high level of awareness about the continued and intensifying world energy crisis. Scarcity of energy supplies and the energy imbalance between nations threaten prosperity and even national security. The oil-hungry economies of the world’s developed nations compete for dwindling supplies of hydrocarbons.
And experts say the competition for fossil fuels will only increase. Global oil production is apparently nearing its peak, with current estimates converging on some point between 2010 and 2020.
When you couple rising demand with stagnant or dwindling supply, plus greater concentration of resources in the hands of a few, limited spare capacity, and the environmental impacts of energy use, then bad things are bound to happen. Shortages, high prices and more manufacturing moved to economies outside the U.S. are just a few examples.The United States is currently the largest consumer of energy, followed closely by the booming economies of China and India. If US manufacturers cannot find innovative ways to compete in the current market, work will continue to move to foreign economies.
Energy management is especially challenging for the industrial finishing sector because of the complexity and variety of processes used. Although industrial finishers cannot simply lower the heat in their buildings or reduce energy consumption needed for critical processes, there are certainly ways they can make incremental improvements in energy efficiency by assessing their current systems and processes for conservation opportunities. Simple examples include adding insulation, improving controls on burners and fans to use less fuel, and installing mechanisms to capture and reclaim waste heat. However, finishers are still faced with tightening margins and the threat of continued offshoring of jobs as energy costs continue to rise.
In most paint or powder coating operations, one of the largest users of energy is the curing oven. An increasingly viable solution to this problem is a complete change in coating material and process. One such potential change involves use of ultraviolet-curable coatings. UV-curable coatings are 100% solids materials that can be pigmented or clear, liquid or powder, waterborne or non-waterborne. Considered a “green” technology, they are safe for both workers and the environment with little or no volatile organic compounds (VOCs), air pollutants, or flammability. UV-curable coatings also provide lower energy costs, which translate into greater efficiencies for the industrial finisher.
UV-cured coatings convert from liquid to solid instantly upon exposure to UV light. Photoinitiators in the coating material lie dormant until exposed to UV light, at which time the photoinitiator molecules break down into radical and/or ionic species that start the polymerization process. This results in a chemically crosslinked coating that is resistant to both moisture and other various chemicals.
A broad range of performance attributes and film properties can be reached with UV-curable coatings. In some cases, UV-curable materials provide performance advantages over traditional chemistries in hardness and gloss and resistance to scratching, abrasion and chemicals. Coatings can be used on virtually any substrate, including wood, paper, glass, fibers, metal, plastic, concrete, composites. Like conventional paint materials, they can be applied in various ways—dipping, rolling, brushing or spraying. They are used in varied markets such as aerospace, medical, automotive, industrial finishing, metal protection, appliance, fiber optics, inks, adhesives, and many more.
Unlike conventional coatings, which contain higher-molecular-weight resins and solvents, a typical UV coating is comprised of oligomers and monomers and is free of solvents. Oligomer choice will determine overall coating properties, molecular weight is typically in a range of 1,000 to 10,000 g/mole.
Reactive monomers act as diluents and lower the viscosity of the uncured material. These monomers play the role of solvent in a conventional coatings to facilitate application. Photoinitiators absorb UV light, produce reactive species and cause the coating to cure. As with other coatings, additives are used to impart specific properties that give the coating additional or enhanced performance characteristics.
The two key elements of a successful UV curing system are the coating plus the lamps and their support systems. Properties of the finished coating are dictated by the initial chemical composition of the coating, the match of the UV lamp’s spectral output, intensity and dose with that chemistry, and the optimal physical siting of the UV lamps.
How do UV-curable coatings conserve energy?
Energy conservation facilitates the replacement of non-renewable resources with renewable energy. Conservation is often the most economical solution to energy shortages. It is a more environmentally benign alternative to increased energy production. Conservation acknowledges that it’s better to save more rather than to simply make more.
|Table 1: Components of UV-Curable Coatings|
Concentration range, %
|Oligomers||Control final cured film properties||
|Reactive diluents/monomers||Reduce coating viscosity; contribute to coating performance and cure speed||
|Photoinitiators||Absorb UV light and initiate polymerization||
A closer examination of UV curing and total cost indicates additional ways the technology can conserve energy and increase overall profits. These include lower overall operating costs, fast on/off, essentially instantaneous curing and fast cycle times and higher throughput.
Use of UV-curable coatings eliminates the need for costly thermal drying and curing systems. Simply put, there are no ovens involved in the process.
In a liquid UV system, a small cluster of lamps replaces large curing ovens. The cost of installing these lamps is about half the cost of installing a large-capacity thermal dryer. Yearly cost of operation is also dramatically lower. No natural gas is needed, and less electricity is used versus a thermal system.
In a conventional curing system, oven shutdown and startup consume an enormous amount of energy without producing any finished parts. UV lamps, on the other hand, start and stop much faster than ovens, some literally with the flick of a switch.
|Table 2: UV Curing by the Numbers|
|0||Amount of solvents, HAPs, VOC in a 100%-solids UV coating|
|1/10||Floorspace requirement of a UV lamp system versus a conventional thermal oven|
|1/2||Cost of lamp typical lamp installation versus a large-capacity thermal oven system|
|10–100||Times faster in line speed|
Cure time with a conventional coating in a thermal system can take up to an hour, depending on part size and mass. UV-curable coatings dry in seconds, cutting cycle time dramatically.
In addition to instant curing, UV curing also drastically reduces or eliminates cooling time. UV curing raises the temperature of parts no more than 10°F. Parts can be coated, packaged and handled immediately. This contributes to faster service time to customers and can create a competitive advantage.
In addition to energy conservation, UV-curable coatings provide multiple productivity advantages in industrial finishing operations. These include the ability to coat heat-sensitive substrates, faster corrective action of finishing problems for reduced scrap and rework, higher throughput and reduced work in process and simplified reclaim procedures.
UV curing is an enabling technology because it allows finishers to coat a wider variety of substrate materials than thermal curing. Because there are no high-temperature ovens, heat-sensitive part materials such as plastic, paper and wood can be easily coated. Thick metal components can also be processed more efficiently because the parts do not have to consume energy to reach curing temperature.
Dust, dirt and other contaminants often found in finishing shops can find their way onto wet films during curing. The UV process eliminates flash-off time and minimizes exposure of the wet coating to the plant environment. This nearly eliminates the possibility for defects that occur during this part of the painting process.
UV technology also allows rapid detection of coating defects that cannot be found until after curing. Instantaneous curing lets technicians perform quality checks more quickly than conventional processes, enabling fast identification and resolution of problems.
Implementation of UV curing technology also results in significant throughput increases. First, there is a sizable increase in line speed—most often by a factor of 10 to 100 over conventional systems. The lower cycle times of the UV process allow a move toward lean manufacturing and just-in-time (JIT) processing. Work in process and waiting time are both decreased due to faster cycle time and line speeds.
Because UV-curable paints stay liquid until they receive UV light, clean-up is easier. The system eliminates dry paint on the applicator and allows reclaim and reuse of overspray without additional solvents.
The list of ancillary benefits goes on. UV-curing lamp systems typically require only one-tenth the floor space of a conventional thermal oven. A smaller equipment footprint enables finishers to increase production capacity without costly building additions. A smaller system footprint means the length of the conveyor system can be reduced to conserve energy and reduce wear and maintenance requirements.
Insurance, disposal and reporting costs are reduced by elimination of solvent in 100%-solids systems. Such coating materials contain no VOCs or hazardous air pollutants (HAPs), and in many jurisdictions they can be disposed of as ordinary solid waste. The result can be a significant savings in hazardous waste incineration and/or removal.
Reduced reportables are another result of fewer VOCs and HAPs in coating systems. There is simply less expense in managing reportables because of the reduced emissions UV technology can provide.
UV curing technology also eliminates secondary potential adverse impacts associated with some conventional paint systems. These include greenhouse gases, combustion contaminants and hazardous wastes. Reduced fire and explosion hazards should result in lower insurance costs, and 100%-solids UV-curable coatings eliminate employees’ exposure to solvents.
Like any other coating system, UV-curables require that potential users review all the benefits of a particular chemistry to ensure the right fit for their application. UV is not the best solution for every situation; however, results can be spectacular when the right fit is identified and executed.