Advances in Adhesive Dispensing Technology Move Packaging to Greater Sustainability
The world is changing. Resources once considered endless are becoming both limited and costly. For example, adhesives are produced using petroleum, energy and water. Recent adhesive cost increases of 10-25%, along with a decrease in the availability of petroleum-based resin (a key component), have put a significant strain on packaging manufacturers. The once-prevalent practice of placing any amount of adhesive on a package to ensure a strong seal or bond is no longer economically or environmentally feasible. As a result, packagers now require new options that will overcome these challenges while preserving the integrity of their processes and bottom lines.
Why is Packaging Important?Despite calls by extremists to eliminate packaging, primary and secondary packaging perform many critical functions - from allowing for easier goods movement and efficient processing between manufacturers and distributors to providing brand recognition and serving as an information source for consumers.
Increasing resource costs and environmental concerns are spurring efforts to create packaging that effectively achieves shipping and commercial objectives while also being “green.”
But what is green? According to the Sustainable Packaging Coalition, a green product or process must achieve one or more of the following:
- Be beneficial, safe, and healthy for individuals and communities throughout its lifecycle.
- Meet the market’s performance and cost criteria.
- Be sourced, manufactured, transported and recycled using renewable energy.
- Maximize the use of renewable or recycled source materials.
- Be manufactured using clean production technologies and best practices.
- Be made from materials healthy in all probable end-of-life scenarios.
- Be physically designed to optimize materials and energy.
- Be effectively recovered and used in biological and/or industrial cradle-to-cradle cycles.
Adhesives, Oil and WaterThe mathematics of adhesive production and consumption are relatively simple and demonstrate the dramatic conservation - or “greening” - that adhesive reduction can deliver.
Adhesive production and processing requires two very limited resources: oil and water. It takes 1 lb. of oil to make 1 lb. of adhesive. So, for every 315 lbs of adhesive saved, 1 barrel of oil and 7,560 gal of water are conserved.
Manufacturers who minimize adhesive usage will not only conserve vital resources, they will also find that their processes are more efficient, more cost-effective, and, ultimately, more profitable.
Adhesive Evolution - Sticking to Sustainability GoalsAdhesive manufacturers are doing their part by providing improvements and alternatives to existing hot-melt materials. Smaller adhesive forms, metallocene-based adhesives and low-temperature adhesives all offer sustainable benefits.
Smaller Adhesive Forms
Advanced adhesive extrusion technology has given rise to more efficient and smaller adhesive forms. New techniques, such as underwater extrusion, allow adhesives to be cut into shapes, which are easier for packagers to process. These improved manufacturing techniques also use less energy, making shapes (such as pellets) less costly to manufacture. Smaller adhesive forms are also easier to melt and are more efficiently transported by automatic filling systems, whose sustainability and costs savings benefits will be discussed later in this article.
Because of their availability, low cost and excellent bonding characteristics, ethylene vinyl acetate (EVA) adhesives have been the material of choice for packagers for the past 40 years. Metallocene adhesives, introduced in the early 1990s, offer improved performance, less density and reduced adhesive use - but at a higher cost.
New lower-temperature adhesives also promise energy savings. Applied at 200-250°F, low-temperature adhesives can reduce energy costs to operate a single adhesive melter at an average of $0.03/hr.
While their sharp viscosity curve makes precise temperature control of lower-temperature adhesives necessary and makes them more susceptible to substrate and ambient temperature effects, these adhesives can lessen char formation and reduce operator exposure to higher-temperature materials, surfaces, and components.
Advancing Green, Reducing Costs and Staying in the BlackEnvironmental responsibility, sustainability and the movement to greener packaging are all important; however, these goals must be balanced with business objectives.
The bottom line is that there must be a cost benefit to packagers if sustainability and “going green” are to gain momentum and advance. Equipment manufacturers must provide innovation and technology solutions that enable packagers to achieve sustainability, improve efficiency, and maintain or reduce costs.
Following are some examples.
Automatic Filling Systems
When the tank on an adhesive melter runs low, a number of problems can occur. Adding a large amount of adhesive to a melter all at once causes the adhesive temperature to dramatically decrease and requires time for the melter to melt the influx of new adhesive and return to its set operating temperature. This scenario, commonly called “thermal shock,” cuts into productivity while the line waits for the melter to return to its correct temperature; it also causes a spike in energy use. In addition, if adhesive is applied at less than optimal temperature during this cycle, it will not bond properly, creating product rejects and wasted adhesive.
Automatic fill systems maintain optimal tank levels and adhesive temperatures at all times, relieving operators of the filling and monitoring task, and improving both efficiency and bonding quality. These systems save adhesive by eliminating waste associated with manual overfilling and spillage, preventing thermal shock, and reducing the volume of char-producing contaminants entering the tank. As a result, packagers also benefit from fewer missed adhesive beads, bad bonds and reject packages.
Closed Label-Application Systems
Traditional wheel-pot labeling systems are open to the air and have poor insulation, requiring more energy to keep the adhesive temperature at optimal application levels. In addition, the open design allows debris to enter the molten adhesive container or pot. To maintain adequate application temperature, constant reheating of the adhesive is required. This increases adhesive charring and negatively impacts adhesive viscosity, eventually rendering the material in the wheel pot unusable. Contaminants that collect in the open wheel pot also increase charring and can end up applied to the product, causing poor bonding or unsightly product rejects. As a result, open systems require constant cleaning and maintenance, during which unusable adhesive must be removed and disposed of, costing labelers time and money.
Open wheel-pot systems also have numerous moving parts that wear with age and contribute to label application issues, such as wrinkling and folded-back labels. The parts require additional maintenance and upkeep costs.
New closed systems prevent heat from dissipating into the ambient air, reducing energy use and operational costs. Precise application of adhesive, using fiberized spray or slot gun technology, eliminates the imprecise deposition and adhesive slinging associated with open systems. Precision dispensing provides a stable, consistent bond while minimizing the amount of adhesive needed on each label.
Consistent, accurate adhesive application makes label removal easier during the recycling process. The Association of Postconsumer Plastic Recyclers recommends that adhesive usage and surface area covered be minimized to the greatest extent possible to maximize polyethylene terephthalate (PET) yield.
In a typical1 labeling operation, a closed system will produce an average savings of 0.24 g/bottle of adhesive, 12,936 kWh and $1,035 per year.
In a typical2 packaging application, reducing nozzle orifice size just 1/64” can save 25% in adhesive volume, which can reduce adhesive usage by up to 2,400 lbs/year. Conversely, a too-large nozzle or inconsistent adhesive flow is costly. A bead doubled from 1/16” to 1/8” (1.58 to 3.175mm) consumes four times more adhesive.
Today, manufacturers are using smaller package sizes to better meet sustainability and source reduction targets and consumer demand for smaller or individual servings. These smaller packages require improved process control and adhesive dispensing accuracy.
Quality nozzles manufactured to strict tolerances produce quick return on investment through adhesive savings and reduced scrap. Strict quality control also minimizes the occurrence of burrs or other imperfections than contribute to nozzle clogging and increased downtime. Using precision-manufactured nozzles that deliver consistent, shot-to-shot accuracy can reduce adhesive use and waste in a typical3 packaging application by 3,172 lbs/year.
Better Energy Efficiency
It’s a relatively common practice to leave adhesive-application equipment turned on around the clock so that the temperature remains optimal. However, most new adhesive melters have a seven-day clock function that allows manufacturers to program their adhesive application equipment to turn on and off, ensuring that it will be heated and ready when needed. Without the seven-day clock, a typical3 single melter can waste $270 of electricity each year.
Innovative Application Techniques for Cost SavingsA number of new application methods, including the use of both hot and cold adhesives for dual gluing, as well as adhesive foaming and the intermittent stitching of adhesive, offer manufacturers creative means of reducing adhesive costs with minimal equipment investment.
Dual gluing uses both cold-glue and hot-melt adhesives. Cold glue provides a cost-effective, secure seal with excellent fiber tear properties. However, it has longer open and cure times, which can slow production processes. Applying a small amount of hot-melt adhesive keeps the package closed until the cold glue penetrates the board stock and dries, or “sets.” Although dual gluing requires additional equipment, it enables significant savings, reducing hot melt use by more than 50%.
Hot-melt adhesive foaming is accomplished by injecting and mixing inert gas into the adhesive, which expands to produce a closed-cell foam with reduced density.
First introduced in the 1980s, foaming systems used to require a complete stand-alone melting system and significant capital expense to realize a reduction in adhesive use. Now, new compact systems can be retrofitted to existing adhesive melters already in operation. In case-sealing applications, foaming can deliver a 30-40% decrease in density, adhesive use and cost. In addition to its bonding and sealing properties, foaming also provides excellent gap filling, making it ideal for warped board surfaces.
Most packaging applications use pattern controls, which tell the system when to open and close valves in the dispensing guns to deliver specified lengths of adhesive beads to meet individual package requirements. Most pattern controls that have been commercially available for the past 10+ years are capable of being programmed to apply short, small beads of adhesive instead of long, continuous beads. Because the strength of the individual adhesive bond is strongest at the beginning and the end points of the adhesive bead, using shorter, intermittent beads delivers the same tight sealing, bond strength, and fiber tear as longer, continuous beads of adhesive. This simple yet effective concept can, with proper management, reduce adhesive consumption in many applications by up to 50%.
The Ripple EffectThink of adhesive application on the package, container or label as the stone that makes a splash in the water. Reducing adhesive use and costs during the packaging process are only one aspect of achieving packaging sustainability. As the ripples expand, we can see how the entire process is affected, both before and after the adhesive is applied.
Reducing adhesive use reduces the demand for oil, water and energy used in its production. In addition, shipping of raw materials, packaging, handling and transportation of adhesives is also reduced.
Reduced adhesive use improves the recyclability of PET and paperboard stocks while reducing how much adhesive and non-recyclable material ends up in landfills.
Packaging machinery and equipment manufacturers can act as catalysts in the packaging industry’s mandate for sustainability. Even small changes can result in substantial savings; multiple changes produce compounded savings and can revolutionize entire operations.
Once just an industry buzzword, sustainability has come of age as packagers learn that wise investment - in new technology and processes - and simple upgrades to existing processes can produce a positive economic and environmental return on investment.
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- “Typical” labeling operation = 16hrs/day, 6 days/week, 50 weeks/year
- “Typical” packaging operation = 16hrs/day, 6 days/week, 50 weeks/year, 20 packages/min.
- “Typical” single melter = 16hrs/day, 6 days/week, 50 weeks/year, 0.08/KWh