Consumers continue to place more requirements on OEMs as they demand higher levels of product differentiation while also expecting low prices. OEMs in turn expect their plastic component suppliers to provide them with innovative methods of meeting customer expectations, while under intense cost pressures and operating in “lean” environments. And if this wasn’t challenging enough, now plastic component suppliers have a new buzzword to deal with: Sustainability. But sustainability is more than just a buzzword; major corporations are adopting sustainability policies, and major U.S. universities are creating entire curriculums around the sustainability concept.
So how do plastic product manufacturers meet the needs of their customers and stand out from their ever-increasing competition while being good stewards of their environment? One way is to use decorative film laminates instead of more traditional plastic coating methods. This paper covers how film laminates are made, how to use them, and the benefits that can be reaped from financial bottom-line improvements (thanks to lower start-up costs and lower piece price costs) to environmental bottom-line improvements (VOC reductions of 98% compared to spray painting and chrome plating).
Decorative Film LaminatesAs the name implies, decorative film laminates are plastic films made of multiple layers, laminated together to provide various types of decoration – from wood grain to chrome appearances. Sometimes called “foils,” the various materials carry the same basic makeup: a cap, or clear layer, decorative layers, and a substrate layer.
How They Are MadeMost decorative film laminates begin with a clear coat, which is either extruded, or more commonly, cast to achieve a lower-stress final product. This clear is most often high gloss, but matte and textured finishes are also available. Almost all of the clear coats used today are some sort of alloy of PMMA (Acrylic), PVDF (Fluoropolymer) or PU (urethane). Each supplier uses a different, proprietary blend of these materials and additives to achieve the weathering and physical characteristics they desire.
Next, some form of decoration is attached to the back of the clear coat so that it is protected from the environment by the clear. For patterns, this is typically done using gravure printing, and nearly any pattern can be duplicated, including wood grains, technical finishes, brushed and distressed metals, and organic patterns like marble. Continuous coats can also be created that perfectly match spray paints, including pearlescent and metallic colors, with the latest development being an actual stretchable chrome appearance. This chrome appearance material can also be coupled with tinted clear coats to produce effects such as “black chrome,” and finishes that mimic copper, brass and gold.
The decoration layer is then sandwiched between the clear and a substrate layer, protecting it from contact. The substrate layer is typically much thicker than the other layers and gives the laminate its strength, which makes it easier to handle and use. The most common substrate material is ABS, with TPO close behind, and PC (polycarbonate) a distant third. The substrate polymer type and thickness are determined by the needs of the next phase in the manufacturing process and will be described in more detail in the next section. Some substrates may also require the addition of primer layers to ensure complete laminate adhesion.
Use of Decorative Film LaminatesPressure-Sensitive Decals
Decorative film laminates are often used in the creation of large pressure-sensitive decals. In this case, the substrate layer is replaced with a pressure-sensitive adhesive and backing. Decals are precision trimmed from the flat laminate, the backing is removed and the decal is applied to an existing component. Pressure is imparted during the application, activating the adhesive system. Common uses include automotive striping and “blackouts” such as b-pillars.
In this application, the clear, decorative and any adhesive layers are brought into intimate contact with the substrate as it exits the die in an extrusion process, laminating them together. This method is becoming an increasingly popular way to decorate profile extrusions, such as automotive roof strips and window seal trim, that are very difficult to mask and paint, and nearly impossible to selectively chrome plate.
In-Mold Decorating (IMD), sometimes called In-Mold Foil (IMF), is another popular method for using decorative film laminates. In this process, laminate with a very thin substrate is placed into, or stretched over, an injection mold cavity. The mold is then closed and molten plastic is injected behind the film, creating a melt bond between the laminate and the molten resin. When the mold opens, the part exits with the decoration permanently attached. In cases where the film is stretched over the entire mold, the excess must be trimmed away after molding. This is performed both mechanically and by using lasers, depending upon the preference of the molder. This method is commonly used where it is not necessary to have the decoration wrap past the parting line and where part geometry is fairly gentle since the film must be stretched by the molten resin, such as for cell phone cases.
For thermoforming, the substrate layer is generally much thicker than the previously described processes as it provides the structure for the completed part. In this process the decorative film laminate is heated to just beyond its glass transition temperature so that it becomes pliable, but not molten. The soft laminate is then draped over a mold to take its shape either through drawing vacuum through the mold (vacuum forming), using pressurized air to force the sheet against the mold (pressure forming), or a combination of both. This process is used to produce parts like casings for exercise equipment, and chrome bumpers for the heavy truck industry.
Insert Injection Molding
Insert injection molding combines the thermoforming of decorative film laminates with injection molding. In this process, laminates are first thermoformed into complex shapes and trimmed to match a complex injection mold cavity. These thermoformed inserts are then placed into the injection mold, and processed similar to IMD/IMF. The advantage of insert injection molding over IMD/IMF is that greater draw lengths and wrapping of decoration past the parting line become possible. This process is used to make a wide variety of products, from computer housings to automotive-body side moldings.
Laminate UsersThe largest user of decorative film laminates is the automotive industry. As consumers have demanded higher and higher levels of decoration, especially in vehicle exterior and interior trim, automotive OEMs have had to find ways to meet that demand without increasing cost. Decorative film laminates have provided an opportunity for them to achieve the high-end appearance of wood, metal and carbon fiber without the high cost of using the real thing. On the exterior, it has given them the opportunity to use suppliers who specialize in certain parts, such as body side moldings or rocker panels, without having to worry about paint match since different suppliers can use the same paint film.
Having proven themselves from decades of use in automobiles, computers and cell phones, decorative film laminates are primed to be used in a myriad of applications including furniture, consumer goods, medical devices, recreational products and, in fact, any industry that uses painting, plating, or hydrographics.
Why Laminates are UsedEconomic Benefits
If manufacturers consider adding the capability to provide differentiated plastic products, they are essentially looking at three options. The first is adding coating capability, and whether we are talking about adding a paint line, adding a chrome plating line or adding a hydrographic line, we are talking about a very high capital expenditure. We are also talking about a large floor space commitment that often becomes the plant’s bottleneck, and compliance costs for emissions that are getting higher all the time.
The second option is to outsource coating. This high-piece cost option involves sending good manufactured parts out to a company who specializes in a coating process, and hoping that they send enough good, coated parts back to allow you to fill your orders. This can result in having to carry “just-in-case” inventory instead of just-in-time as well as increased shipping costs from sending parts back and forth.
The third option is to use decorative film laminates. Using pressure-sensitive decals adds only the cost of the decals. For injection molders, adding IMD/IMF requires only a small amount of capital, and thermoformed inserts can be purchased from suppliers for insert injection molding. For thermoformers, using decorative laminates requires only a dedication to cleanliness, and a small learning curve to get used to processing them. In addition, decorative film laminates are almost completely thermoplastic, allowing them to be reground in most cases, whereas most coatings are thermoset and are often not able to be put back into the stream.
Never before has the condition of our environment been more a part of our collective conscience. One can scarcely watch a TV news program or read a newspaper without being exposed to terms like “Carbon Footprint” and “Sustainability.” Politicians and scientists debate about environmental issues, while corporations and universities race to adopt sustainability programs. With no sign of this trend waning, this is another area where decorative film laminates can help plastic part manufacturers be successful.
According to a study performed by environmental consulting firm MM & A, LLC on automotive exterior painting options, paint film produces at least 95% less VOCs than the spray paint systems (see Table 1). The numbers given for water-based spray painting systems carry an asterisk because, as of the time of this study, they were not capable of matching the full palette of automotive OEM colors. Since paint films can use the same pigments as spray painting, they can match the same colors exactly.
For patterns, the competing process is Hydrographics, and while they don’t publish specific data, the fact that many of their inks are solventborne and have to be sprayed with a protective clear coat after “dipping” implies they would end up in the middle of this table.
Chrome plating is an even bigger environmental concern because of the release of heavy metals (primarily hexavalent chromium) during the plating process. The California Air Resource Board tested several chrome plating companies from 2004 to 2006 and the average hexavalent chromium emissions they found are shown in Table 2.
The latest OSHA exposure requirement is less than 5 micrograms per cubic meter in 8 hours. This means the plating lines are subject to very high compliance costs both from capturing the chromium, and from the regular air testing necessary to ensure they are in compliance, not to mention the potential negative environmental impact from accidents and machinery failures. While the popular solution seems to be to send plating operations to countries with lower environmental restrictions, it is only a matter of time before those countries catch up. Chrome-appearing decorative film laminates provide the look of plated chrome without using heavy metals in their production.
Decorative film laminates also offer a waste reduction potential. Paints produced for use in paint film can be economically run until it is used up. Extra paint mixed up for spray painting is waste if parts to paint run out before the paint does. For the “dipping” processes of hydrographics and chrome plating, processors must take care of what’s left in the tank – laminates do not have that problem.
Finally, when using decorative film laminates to replace much heavier real wood, or real metal parts in vehicles, the overall weight savings result in a reduction in fuel usage and the resultant emissions. For example, a metal chrome bumper for a heavy truck weighs 100 lbs, but its thermoformed chrome film counterpart weighs just 30 lbs and will never rust.
What to WatchLarge volumes are often necessary to achieve the best pricing due to the batch processes involved. There are also some geometry limitations - you can only stretch a wood grain film so far before it distorts the pattern too much to be acceptable. And finally, it is a disruptive technology. It is a very tough decision for companies with paint lines to consider moth-balling that capital equipment, even if it is better for their customers or the environment. However, when done properly, decorative film laminates can truly be a cost-effective and environmentally friendlier alternative to traditional plastics coating methods.
This paper was presented at the International Coatings for Plastics Symposium, June 2007, Chicago, IL. For further information see www.paintfilm.com.