Metallized Special Effects Films
Metallized special effects films have always been popular for decorating race cars, billboards, and short-term promotional signage. Some sign makers shied away from specialty films because older generations of these products lacked long-term durability and were difficult to cut and apply. The good news is that the newer generations of films feature several remarkable improvements which should provide wary buyers with reason enough to give these products a second look. Better colorants and UV inhibitors extend the outdoor life of a growing number of films, improved release liners greatly minimize tunneling during plotter cutting, and more forgiving adhesives make repositioning during graphics application much easier. This article covers which special effects films might best suit your signage needs, how they are made, and how you might use these eye-catching films in future signage projects.
She Couldn’t Believe Her Eyes!
At a trade show I watched a woman repeatedly stroke her hand over the smooth surface of a metallized specialty film, which appeared to be a rugged hunk of metal diamond plate. The amazement on her face revealed that she couldn’t believe her eyes! The three-dimensional illusions, which specialty films create, can certainly make many ponder the mysteries of how these special effects are created. The actual process of manufacturing these films is rather commonplace. Basic production steps are not too dissimilar to those in making other types of films: compounding, color matching, extruding, metallizing, and slitting. And, like any other adhesive coated material, metallized films consist of a sandwich of layers: a plastic film, a very thin layer of metal, adhesive, and a siliconized release liner.
Several different plastic films, including acrylics, polycarbonates and polypropylenes, are metallized for a variety of everyday applications, from plastic potato chip bags and gift wrapping to solar window film. In the sign industry, two of the most popular types of metallized films are polyester and vinyl. Each film is a very different type of plastic with its own unique set of physical properties, performance characteristics and applications.
Vinyl, along with acrylic, polycarbonate, polyethylene and polypropylene, are thermoplastics. These plastics are solids that can be heated and extruded into a film and embossed with an engraved roller.
Metallized specialty vinyl is quickly becoming a popular alternative to polyesters. Its softness makes vinyl easier to plotter cut and thermal die cut, and a more receptive printing substrate for thermal transfer printing, vinyl inks and some solvent-based ink jet inks and air brush paints.
Polyesters are a different type of plastic called thermosets. These plastics start out as liquids and cure with heat. Once they’re cured, they can’t be reheated, reformed or thermal die cut. Compared to vinyl, polyester is a very hard, durable film, which can resist chemical spillage. The toughness of polyester is both its strength and its weakness, because the hardness of the facestock makes it more difficult to plotter cut than vinyl films. Still, metallized polyester films are a staple offering in most every sign supply catalog. For labels, nameplates and short-term signage, which must simulate the look and texture of metal, they are well suited and cost-effective.
Extruding and Embossing
With metallized vinyl or other metallized thermoplastic films, the colorant is an integral component of the film, which extends the fade resistance of the product. Since the color is in the film, it’s protected from sticks and stones encountered in normal driving, harsh cleaning chemicals, and abrading car wash brushes. In contrast, polyesters are surface-dyed, which subjects the colorant to everyday wear and tear and the bleaching effects of the sun.
Prior to extruding a vinyl film, the colorant is blended with the resin in the extruder’s hopper, to evenly disperse the ingredients. This creates color consistency throughout the entire web of the roll. The mixture is then melted and extruded through a slotted die in a process similar to extruding acrylic or polycarbonate sheet.
When the film is hot and malleable, the second surface or underside of the vinyl is micro-embossed or “coined”, creating a textured pattern in the film. Prior to adhesive coating, you can actually feel the embossing on the underside of the film. The top surface, though, is as smooth as glass, which is critical for printing without imperfections.
To create the micro-embossed texture, a pattern is etched into a flat metal mold or shim. This flat plate is then wrapped around a cylinder, which serves as the stamping die. The advantage of hot embossing is that the resulting impression is a deeper and more impressive. Not all films are hot embossed. Polyesters, in contrast, are cold embossed after the film has already been metallized.
Patterns fall into one of two classes. The first class consists of smooth and textured metallized films. Some patterns are relatively simple, duplicating the appearance of brushed or leaf metals. The second class of patterns is the diffraction films. Diffraction patterns are embossed with tiny prisms at varying angles and configurations to create 3-Dimensional illusions or to scatter light into a rainbow of colors.
To improve the bond of the metal layer to the plastic facestock, the films typically require pretreatment, such as corona treatment, prior to metallization.
Corona treating increases the surface energy of the plastic. This makes it easier for the aluminum to wet out and form a uniform layer of metal, so the metal can better adhere to the film.
A good bond is necessary between each layer of the sandwich of the film, the metallized layer and the adhesive layer. This is important in the application process when repositioning the graphic material. A good bond ensures that the adhesive does not delaminate from the metal and the metal layer should not separate from the film.
After the second surface of the film is microembossed, the pattern is coated with a thin layer of metal, which acts like a mirror in reflecting light and creating special illusionary effects. In metallizing films, one process frequently used is called vacuum metallization. It’s not the only way to metallize, but it’s the preferred method in coating a uniform and thin layer of metal.
Vacuum metallizing a film is a two-step process of evaporating a metal, such as aluminum or gold, in a vacuum chamber and then having the metal vapor condense on the film. While several different metals are use in metallizing, approximately 90% of plastic films are coated with aluminum.
Before the metallizing process begins, the atmosphere within the chamber must be pumped out to create as nearly as perfect of a vacuum as possible. Any gases, which are not pumped out will collide with the metal vapor and inhibit the metallization process. In addition, if the aluminum were melted under normal atmospheric conditions, the molten aluminum would just form a pool of melted metal at the bottom of the chamber.
The aluminum turns into a vapor when it comes in contact with a heating element called a boat or crucible. The temperature of the boat gets extremely hot, about 3000 degrees Fahrenheit. The extreme temperatures turn the aluminum wire from a solid to a vapor, as wire contacts the boat.
As the metal vaporizes, a coil of aluminum wire continually feeds into the vacuum chamber, replacing the metal that has evaporated. To maintain consistency in the thickness of the metal layer, the manufacturing processes are tightly controlled from the rate at which the wire is fed, to the pressure of the chamber, to the temperature of the heating element.
Positioned directly above the area where the vaporization occurs is the cooling drum. As vacuum metallization begins, the roll of film is fed into the chamber where it travels around the main cooling drum. The vapor formed rises straight up to the cooling drum, where it condenses on the textured second surface of the film. The process of evaporation and condensation is similar to the hot steam from your shower, fogging up the cooler surface of your bathroom mirror.
How much metal is deposited on the film depends on several variables, such as the temperature of the aluminum in the melting process, the speed of the film as it travels through the metallization chamber and the atmospheric pressure within the chamber.
The aluminum, which condenses on the second surface of the film, is ultra-thin, about one to three millionths of an inch. The thin layer of aluminum acts a reflector to create special effects.
Because the metallization layer is so thin, it’s susceptible to abrasion, oxidation and corrosion. In making special effects films for the sign market, this thin layer of metal is protected, because it is sandwiched between the transparent plastic film and the adhesive coating. Unsupported material, which is film without adhesive, usually needs a protective coating over the metallized surface.
Where To Use Specialty Films
Many sign people, with whom I have spoken, find the look of the specialty films fascinating, but they are at a loss when it comes to where to use it. While it can make some nice looking race car numbers, there are several other places where it can be used.
A little will go a long way when it comes to using special effects films. Used along with opaque vinyl films, air brushing and hand lettering, specialty films are an excellent choice for lettering and logos. I have watched friends create some interesting effects by air brushing with transparent paints on a silvered hammered leaf vinyl.
Drop shadows and white contours can provide contrast between the lettering and the backgrounds. If you are using some older constructions of films with rubber-based adhesive, try overlaying the film on top of a cast vinyl. This is especially important when decorating a banner. The cast film will act as a barrier protecting the rubber-based adhesive from the plasticizers in the banner. Using the cast film as a base layer can also aid in the removal of the metallized film, when it comes time for it.
Darker colored specialty films and some of the textured metallized films can make an eye-catching background for signage or tradeshow booth headers. Try using specialty materials for automotive striping or decorative sign borders. Consider some of the silver smooth or textured patterns as a print media.
Some of the specialty films are printable. Some are not. You should do some careful shopping before selecting a film as a print media. And you also need to follow the manufacturer's recommendations with respect to fabrication. And above all, before going into production, test don’t guess.
If you decide to airbrush on a specialty film, check to see if it is compatible with the paint system. Polyesters typically require a special top coating, whereas vinyl does not. Before you get started, wipe down the film to clean any oils or other contaminates. That’s also good advice before printing on these films. Between coats, use a hair dryer to dry the paint. After airbrushing, protect your work by spraying it with clear coat.
If printed graphics are subjected to gasoline spillage or abrasion, protect your work with an overlaminate.
After you complete your application, always protect the edges by edge sealing. As added protection, clear coating the entire graphics is added insurance.
When all else fails, read the product information bulletin and application instructions provided by the film manufacturer, which will cover things that you should know, such as the application surfaces to which the film will work and not work, substrate preparation and minimum application temperature.
This article was written by Jim Hingst, Business Development Manager-Technology for RTape Corp. and posted on Hingst Sign Post.