By Cassandra Balentine
The ability to stick to difficult surfaces and withstand challenging conditions as well as dirt, grime, and pollutants is an essential feature for many pressure-sensitive, self-adhesive media options. Properties of the installation location, intended lifecycle, the media itself, the adhesive, and the decision of whether or not use an overlaminate all play into the success of a graphic on a challenging surface.
Above: Drytac Polar Street FX is a PVC-free, aluminum print media for outdoor floor and wall graphics that does not require lamination.
When deciding on the right media for any job, particularly those intended for low-energy surfaces or vulnerable to outside elements, Jay Kroll, product manager for cut, transit, and wall solutions, General Formulations, stresses the importance of compatibility. In other words, it is essential to properly pair the adhesive and film, as well as overlaminate to create the right solution.
When making preparations for all surfaces, both indoor and out, Dennis Leblanc, senior business development manager, North America, Drytac, points out that the adhesive is only as good as what it’s sticking to.
Knowing the environmental factors involved helps with a successful installation. Is the graphic close to a road where it will be subjected to exhaust, road salt, etc., and will a specialized laminate be required? What about exposure to people and graffiti? Is it a high moisture environment? Is the application surface textured, has a low surface energy, or is it dimensionally stable? “Understanding these details ultimately ensures the correct adhesive decision—and of course the lifespan of the installation,” comments Leblanc.
Elements like dirt and grime won’t typically affect adhesion. However, René Bourgeois, VP Sales North America, ASLAN Selbstklebefolien GmbH, is concerned with chemical spills and fumes—i.e. gas from petrol pumps, cars, or motor cross. “They have the ability to attack adhesives,” he cautions.
Solvent-based adhesives typically fare better in outdoor applications as they are less susceptible to heat and moisture that can weaken or breakdown the bond with the surface. “The film should be a higher quality polymeric vinyl that is durable and will resist shrink, to lessen the chance of edge lift where dirt and pollutants could creep in and cause failures,” explains Kroll.
If the surface is flat and heavily textured, Jodi Sawyer, strategic business unit manager, retail, FLEXcon, feels the use of a heavy coat weight, solvent-based adhesive with a calendered or cast vinyl film ensures the best adhesive contact to the surface.
Amanda Smith, marketing and communication manager, Mactac, agrees, adding that it takes a special high coat weight adhesive to adhere to challenging surfaces like brick, rough cement block, and concrete, which may be placed in conditions with dirt, grime, and pollutants.
If the surface is smooth and flat and the graphic is vertical in an area where tampering is not a factor, a calendered vinyl film with a standard coat weight of adhesive applied with uniform pressure to the surface provides good resistance to abrasion, grime, and other environmental conditions. “The important factor is ensuring that the adhesive makes good contact with the surface, especially at the edges, to ensure moisture does not get under the graphic and disrupt the bond to the surface,” continues Sawyer.
For smooth surfaces with complex curves, a cast vinyl film with a standard coat weight of adhesive will lead to better adhesive contact of the product to the surface as compared to a calendared vinyl product. Sawyer says this is because cast can stretch in all directions and install with the use of heat to ensure that the adhesive makes excellent contact with the surface. “Cast vinyls offer excellent conformability as well as five to seven years outdoor durability, making them ideal for vehicle wraps and long-term outdoor applications where they may see extreme weather conditions and UV exposure.”
She says in general, calendered vinyls offer excellent abrasion resistance, but they are rather thick and, therefore, only conformable to moderate curves. “Furthermore, their durability outdoors is limited to about two years.”
An effective laminate is one of the most common ways to protect prints from external conditions.
“It is very important to have a laminate that can withstand the elements, provide the durability or functionality needed for the application, and enhance the aesthetic and longevity of the installation,” stresses Kroll.
If a graphic will be placed horizontally, UV and exposure to moisture and contaminants can present additional challenges for the self-adhesive vinyl to withstand. “The use of an overlaminate with UV resistant film and/or adhesive will extend the life of the graphic and offer resistance to yellowing and degradation of the product,” shares Sawyer.
Sticking to It
Achieving a successful install on a challenging surface requires special attention to the adhesives. However, surface preparation is a critical step that can’t be overlooked.
When confronted with a difficult surface, Joe Leddy, director of sales, U.S. and LATAM, Continental Grafix USA, Inc., says to first ensure the surface is clean of any dirt/debris to maximize the bond strength with the adhesive on the media. “I know this seems obvious, but you would be surprised how many people do not take this step.”
“Eliminating dirt and debris before it can get behind the film and ruin the installation is critical to a successful install,” comments Kroll.
Beyond surface preparation, the adhesive is an essential player in getting vinyl to adhere to hard-to-stick-to surfaces. “The heavy coat weight of a permanent adhesive with high initial tack is used to attach to surfaces like plastic, low volatile organic compound paints, and powered coated metals. Once it’s installed, you will know that it will stay in place,” shares Smith.
“Hard-to-stick-to surfaces, such as powder-coated surfaces or low-energy substrates, pose a problem for print shops on a regular basis,” admits Leddy. “When traditional media fails to bond well to a stubborn surface, many suppliers offer products with specially formulated adhesive that offer a more aggressive bond and/or a thicker coat weight that will assist in making a stronger bond to the surface.”
Bourgeois points out that powder coatings often contain ingredients that work actively against adhesion. “For those, a classic vinyl and even some high-tack products aren’t enough,” he comments.
“It is better to put self-adhesive vinyl on products that do not have powder coatings. If there is a powder coating, it would be best to clean it off if possible, as it will be challenging to get a good bond no matter what adhesive is used,” shares Ashlee Haney, brand manager, Griff Paper and Film.
Molly Waters, senior technical specialist, Avery Dennison Graphics Solutions, notes its the adhesive that allows a pressure-sensitive product to adhere to low-energy surfaces, like powder-coat paints and plastics. “These adhesives are often referred to as high tack and are very aggressive so they will adhere to most surfaces.”
Kroll agrees. “Substrates like plastic that have low surface energy, or rough, porous materials that don’t provide a smooth contact area for the adhesive require a higher initial tack adhesive than a high energy surface, a smooth surface like glass, or a high-gloss paint. “High-tack adhesives provide an immediate bite into the surface, gripping so that the adhesive bond can build over time on that substrate that really doesn’t like things sticking to it.”
Leblanc feels that the entire construction does come into play here, but the mechanical bond of the media to the surface is paramount. “High-tack adhesive formulations as well as coat weight are predominant factors to consider based on the surface being applied to. Utilizing a removable adhesive on powder coated metals will certainly not yield the same results as a high coat weight, high-tack adhesive engineered for that application.”
In addition to choosing the appropriate adhesive, some surfaces may require the use of a heavier adhesive coat weight to provide extra bond strength. “Even more aggressive adhesives may be necessary if the surface is textured, or if acrylic paint has been replaced with powder-coated paint to improve the durability and scratch resistance of the painted surface,” says Sawyer.
“The key component for vinyl to stick to challenging surfaces is a thick coat of an aggressive adhesive,” says Haney. She notes that rubber-based adhesives stick better to low-energy surfaces, such as polypropylene or polyethylene, but acrylic adhesives also work well.
Further into Adhesive
Continuous media and adhesive evolution helps make them suitable for more environments and surfaces. Adhesive selection is determined by the type of surface to which it is being applied and the required performance characteristics of the finished graphic.
Adhesive is critical in the selection process of determining the right media for the job at hand. “For graphics exposed to tough conditions, permanent, high-performance acrylic pressure-sensitive adhesives are typically employed because of inherent resistance to chemicals, solvents, and high temperatures,” says Sawyer.
The physical characteristics used to measure adhesive performance are sheer, tack, and peel.
Sheer measures the internal strength of an adhesive. “Adhesives chosen for durable applications must have a sheer property low enough to allow the adhesive flow required for proper adhesion but not so low that the adhesive may ooze or cause the graphic to slide or move from its intended position,” comments Sawyer.
Tack calculates the ability of an adhesive to form an instantaneous bond. It is not reflective of the overall adhesive strength or bond to the surface. “For some applications, such as transit posters where the surfaces can be a painted wall or stainless steel, and the environmental and temperature conditions can be extreme, a high-tack adhesive will provide a good initial bond to the surface. For applications such as removable window and wall graphics, medium- to low-tack adhesives are good options, especially if reapplying or repositioning is necessary,” explains Sawyer.
Peel is a measurement of ultimate adhesion to an application surface.
Several components go into making adhesives. Kroll says the science behind those formulations include a range of cross-linkers, tackifiers, and stabilizers designed to adhere to specific materials; with the right ratio of cohesive strength and grip.
While exact adhesive formulations are proprietary to the manufacturers that develop them, Leblanc stresses that rigorous testing is done at the coating stage to ensure that the final product marriage of media and adhesive/adhesive coat weight does the intended job for the intended surface. “A multitude of different formulations through acrylic polymers and additives achieve the desired result from ultra low tack to removable to permanently peelable to permanent and then to high tack and just about everything in between.”
Waters adds that adhesives are developed and tested on a variety of substrates and modified to ensure they will stick. High-tack adhesives are designed for substrates that normal permanent adhesives won’t adhere to. These adhesives are then coated onto the coordinating films and products are tested for performance.
Smith points out Mactac’s cast vinyl solution is designed to conform to rough surfaces this sort of application demands. “Strength, elongation, heat stability—the ability to be heated and conformed without the film burning and tearing, and ultimately, its ability to thermal set so it holds to the rough texture of the walls when the application is complete.”
Haney shares that Griff Paper and Film has a removable/repositionable adhesive that allows the user to remove the film with little to no residue and no damage to the application surface. It can then be placed on another surface or back where it was with close to the same amount of hold as before. Haney adds that its permanent adhesive can be removed, but there is a chance for residue to be left behind.
What comes up, must—typically—come down, as alluded to in the last section of this piece.
“It is a constant balancing act in short-to-medium and even long-term applications between the need for the material to be securely adhered, but be easily removable and not leave residue. Every surface is different, which makes it impossible to guarantee clean removal in every situation,” says Leddy. “Education is vital. The speed and angle at which graphics are removed can have a significant impact on the amount of adhesive residue left behind.”
Waters points out that for an adhesive to work well on difficult surfaces it is typically very aggressive, which means it won’t be removable. “If you attempt to remove it the film is likely to come off in pieces and leave residue.”
Kroll agrees, adding that most high-tack products are not designed for removal, so they will behave like a security label and leave significant evidence of their existence with residue or come off in pieces even with the use of heat. “High-tack, removable adhesives are unique in their ability to stick and stay, yet cleanly remove.”
Smith shares that when planning to remove a high-tack adhesive, it is best to use an overlaminate paired with the vinyl. “It will help the removable process by allowing the vinyl to pull off the surface, intact in strips and sometimes whole. It is also best to re-heat small sections of the graphic to help with the removal process.”
Leblanc feels that while the adhesive directly affects the removability, this is relative to client expectations and application surfaces. “Shorter term applications may not require an aggressive solution, which lends to cleaner removability whereas longer term applications will require more aggressive adhesives that ultimately result in less removability and possible adhesive residue,” he explains.
There are processes that can be utilized during the removal process to limit this like using heat to soften the bond and cutting the material with a specialized blade to create smaller strips to be removed. “When adhesive residue is unavoidable, a citrus degreaser is effective,” recommends Leblanc.
If you’re dealing with a very smooth surface, a less aggressive adhesive and/or lower coat weight can do the job without fear of damage upon removal. “More challenging surfaces such as brick or concrete may require a heavier coat weight of adhesive, which carries a greater chance of damage, especially if said surface was in poor condition prior to installation,” continues Sawyer.
When the surface type requires a heavier coat weight of an aggressive adhesive to stay bonded for five to seven years, Sawyer says ensuring a good bond to the surface will take priority over clean removability or risk of damage.
Ready for Anything
Pressure-sensitive, adhesive-backed media is utilized for a variety of applications. However, surfaces aren’t always ideal for smooth installation, either textures, low surface energy, or locations subject to dirt, grime, and other pollutants. It is important to consider all factors when choosing the right combination of film, adhesive, and laminate.
Jan2023, Digital Output