In-mold decorating is a technique for decorating plastics that utilizes a printed and formed plastic film, often called an appliqué, which is permanently fused to a plastic part during the injection molding process. Traditionally, this process has been utilized for its supreme durability, vivid graphics and ability to eliminate secondary operations performed post molding. As new materials and manufacturing technologies have evolved, a whole new array of appearances can be accomplished with in-mold decorating.
Achieving metal appearances with in-mold decorated plastics
Although in-mold decorating is not a new technology, there are now new ways to obtain metal appearances by utilizing this process. For many years, engineers have utilized metal-to-plastic part conversions as a means of reducing cost, eliminating parts, decreasing weight and avoiding the corrosion issues related to metal materials. In addition, shifting from metal to plastic can have a large impact on mitigating the cost increases due to commodity and tariff fluctuations associated with metals. Because of this, many manufacturers are utilizing this same metal-to-plastic conversion strategy when decorating plastics. Knobs, emblems and trim are commonly made from metal that is brushed, plated or painted to give a desired appearance. Many of those appearances now can be produced with current printing technologies and implemented using the in-mold decorating process.
One example of this metal-to-plastic conversion technique is used in the manufacturing of control knobs. In the past, a knob typically was manufactured using a chrome-plated, painted or brushed metal cap that was placed onto an injection-molded dial. By replacing the metal part with an in-mold decorated plastic part, the chrome appearance is accomplished at a lower cost while providing a wider range of plastic resin materials that can be used, some of which traditionally have not been compatible with electrodeposition or vacuum metallizing.
Additionally, this eliminates the environmental and health-related impacts of materials associated with chrome plating or painting. Since the printing process is more efficient from a material usage standpoint and requires less waste water than plating or painting, many companies are seizing this as a potential opportunity to meet corporate environmental sustainability goals for their supply chain.
Another benefit is the flexibility of the appearances achieved with the same infrastructure. By utilizing in-mold decorating, the graphics on the part can be changed quickly by loading a different set of appliqués into the mold without incurring significant downtime related to tooling changeover. This allows manufacturers to be ultra-responsive to the fluctuating demand of their segmented product platforms. The appearance of chrome, brushed stainless steel, high-gloss colors, wood grain and carbon fiber all can be achieved with this process and can be changed over in minutes as opposed to replacing tooling or setting up other equipment.
Using traditional methods would require significant infrastructure from many different suppliers. Plating lines, metal finishing equipment and paint booths are no longer needed, thus allowing manufacturers to accomplish the same outcome with a less complicated supplier base. Along with greater flexibility, this process also allows for a combination of appearances on a single part with one simplified process.
For example, a manufacturer could produce a dial that has a reflective chrome background, a multicolored logo, alpha-numeric setting indicators and a glow-in-the dark trim around the circumference – all with a single process. This process also is effective in producing logo emblems and nameplates that utilize a metallic, painted or carbon fiber background with a multicolored logo and 3D geometry.
To accomplish these applications with traditional means would require multiple process steps and equipment in addition to extensive non-value-added handling and logistics. With several different steps in the process, the probability of defects also increases. For example, plated parts are pad printed to add a logo or indicator. This leads to multiple steps and risk of registration errors due to misalignment of several pad impressions. If there is a mistake, the entire part is scrapped. Conversely, with in-mold decorating, potential errors are caught much earlier in the value stream when less labor and cost has been applied, thus reducing scrap expense.
Using texture to enhance plastics with in-mold decorating
Along with the new types of visual appearances available using in-mold decorating, one should also consider the role that new texture technology can play in decorating and enhancing plastics. Textures can be created with in-mold decorating by utilizing pre-texturized films or through selectively printed textures. Smooth “piano black” gloss, velvet, brushed metal and even rubberized soft-touch can all be incorporated into the design. The textures complement vivid graphics by providing an added dimension and additional sensory effect to the product.
This sense of touch is especially important in the consumer market where cellphone cases, keyboards, smart home products, computers, automotive interiors, appliances and pretty much any gadget that has a user interface can or is being enhanced by adding textures. When using texturized film for in-mold decorating, graphics are reverse printed on the non-textured side. The user looks through the clear, textured material to see the graphics. This provides a vivid graphic while protecting the ink from wear or damage. This is a common approach for designers who want to mimic a surface for their entire part, such as soft-touch or brushed metal. If not utilizing in-mold decorating, the alternative method for adding graphics to a brushed metal appearance is to print over an actual brushed metal part, which is much costlier.
For a rubberized surface, manufacturers would need to coat the plastic with a sprayable soft-touch material or utilize a silicone over-mold process. Although both methods produce a soft-feel surface, they lack the design flexibility of printing and often require a secondary operation to add graphics. One specific example involves a product many can’t live without.
The Defender Series mobile phone cases produced by OtterBox utilizes a material that gives it a soft-touch or rubberized feel that also provides enough friction to prevent it from sliding off a table or dashboard. For solid color models, OtterBox relies on the pigmented injection molding resin to provide both the color appearance and the rubberized texture. However, for their models that utilize graphics, such as camouflage or multicolored designs, this is not possible.
Traditional, non-texturized, in-mold decorating films would not have resulted in the same feel and texture as the elastomeric case and would have lacked a consistent appearance. By utilizing a soft-touch IMD film, OtterBox was able to achieve high-resolution graphics and the soft-feel texture required to match the rest of its molded case.
James Prestien, senior mechanical engineer for OtterBox, explained it best. “The soft-touch film has enabled us to achieve an IMD solution that has a cohesive look and feel with the rest of the case,” he stated. “This resulted in a premium product with a very durable graphic.”
By developing a solution using in-mold decorating, Otterbox can produce many different parts using the same mold and injection molding machine. This is especially important when producing cases for a multitude of graphics ranging from sports teams to movie characters to graphic designs – all within the same physical case geometry. Add in the ability to enhance the feel of the product using IMD texturing, and the product now adds another degree of possible appearances.
In addition to using texturized films, selective texturing can be accomplished by screen printing a texturized material, such as a hard coat. This is very common for customers who want to add a texture to a keypad, logo, button or specific area while maintaining a different appearance for the overall product. Selectively printed textures also are used to create custom raised surface patterns not currently available in texturized films, such as herringbone, polka dot or diamond plate. These options for utilizing both graphics and textures provide designers with an extensive tool box full of ways to enhance their products.
Things to consider with in-mold decorating
Although the options now available through in-mold decorating provide numerous opportunities, the process is not without challenges. While it is possible to accomplish a wide range of appearances, it is important to design the product from the start with this process in mind. Leveraging experienced suppliers early in the process is valuable for ensuring the many moving pieces and variables are accounted for to design a robust process capable of high-volume production.
Things like injection molding tool design and material selection are all important in ensuring the process works well in production. Proper gating design and location can make the difference between success and failure and is not easy to fix once production starts. Compatibility among materials is important, as the resin and appliqué materials must not only meet the physical and chemical requirements of the end user but also be compatible from an inter-material adhesion standpoint. Often this is accomplished only by utilizing surface treatments, adhesion promoters, tie coats and laminates in the correct combinations.
In addition to material compatibility, adhesion properties and chemical resistance, the materials must also be formable to the desired geometry. It can become a challenging puzzle to find the right materials and process that meet all the different requirements. Optimization of temperature, flow, pressure and cooling within the injection molding process is important. How those variables are adjusted during the cycle to account for how the appliqué and injected resin will interact during molding is also a key factor in success.
For instance, sometimes it is required to have a high initial flow to “pin” the appliqué to the mold cavity wall and then ease the material in for the remaining injection cycle. There is a balance, of course, because too much velocity or too high temperature can cause movement of the graphics or ink wash with second surface molding.
Graphic design also plays a key part in a well-executed in-mold decorated part, especially with highly cosmetic appearances like high-gloss, chrome and brushed metal. Designing the right artwork to realistically simulate these appearances and reliably produce them at high volumes combines science and art. Fine details can be susceptible to ink dry-in but can be designed to account for that issue – all while maintaining proper registration. Graphics also must be designed with forming in mind. The transition from 2D to 3D can cause the ink and graphics to stretch or compress. This also must be factored into the printed artwork package. When using many different types of inks, compatibility between individual inks is important. How those materials are layered on top of each other also can have implications in how the appliqué will form and hold its shape. Areas with high amounts of ink thickness located near areas of low ink thickness can cause appliqué curl, which may affect the appliqué’s ability to be reliably placed in the mold.
As highlighted in the previous examples, there are many factors to navigate when producing what appears to be a very simple product. However, extensive design, engineering and process development is required to be successful.
A new world of applications
With the different appearances and textures available with in-mold decorating, the opportunities for applications are nearly endless. Nearly every user interface can benefit from the customization and enhancing nature of these options. Knobs, dials, buttons, brand emblems, controls, accent trim and display bezels are just a few of the components that can utilize this technology. In the era of the Internet of Things, these components can be found in many different end products, such as automotive dashboards, smart home products, appliances, medical devices, industrial controls, outdoor power tools and many consumer electronics. All can benefit from the environmentally friendly, cost-saving, weight-reducing, supply chain-simplifying benefits of the appearances and textures available with in-mold decorating.
Nick Strauss is director of corporate development for Inno-Flex Corporation. Inno-Flex is a manufacturer of custom in-mold decorating, printed electronics, decorative/functional overlays and membrane switches. For nearly 50 years, Inno-Flex has been developing solutions and delivering high-quality products for the medical, appliance, automotive, consumer and industrial markets. To learn more, visit www.innoflexcorp.com.