The Real World of IMDThe Real World of IMD

Loren Johansen,co-owner of custom molder Profile Plastics Inc. (Chanhassen, MN),told the Molding 2000 audience in New Orleans earlier this yearthat his company has focused on a specific type of inmold decorating(IMD) for the last five years. Profile Plastics inserts predecoratedrigid plastic overlays into the mold. Johansen calls this typeof IMD "appliqué molding."

Mike Terlizzi, senior vp of appliqué-IMD solutions providerSerigraph, teamed up with Johansen to discuss technical details.In his presentation, Terlizzi compared the technology to foilIMD, in which graphic inks are transferred from a carrier filmonto a part in the mold; and to traditional decorating methods,such as spray paint/laser etching, pad printing, dip coating,and the use of pressure-sensitive overlays. Excellent opacity,no tacky edge, no VOC emissions, lower costs, recyclability, and,unlike skin-insert/low-pressure IMD, the ability to back-lightmolded-in decorations were among the advantages of appliquéIMD covered by Terlizzi.

Johansen discussed appliqué IMD from an experiencedmolder's point of view. Does this type of IMD makes sense in thereal world of custom molding? Johansen answers yes, but he cautionsus that, like conventional molding, appliqué IMD can bepretty complicated.

Part Design
The first thing molders have to ask themselves is, Does the partdesign fit the appliqué-IMD process? "The appliquémolding process allows a great deal of design freedom in termsof colors, graphics, and textures, but there are limitations relativeto structure," Johansen says. At most, appliqués usuallycover only half the part. If it shows, the appliqué's edgeoften has to be hidden.

Part thickness must be considered. If the part's total wallsection is 1 mm and the appliqué is .75 mm, there's notenough room for the resin. Johansen also cautions that the parthas to be gated on the side opposite the appliqué, whichmay require some recalculation of part geometry. Ejectors, partinglines, and insert lines also have to be on the flip side of thepart.

Then there's the question of warp. A thin, flat part with anappliqué covering the entire front surface will tend towarp. Offsetting A- and B-half mold temperatures may help compensatesomewhat, but this may not always be enough. Rather, Johansenrecommends adding structure or compound curvature to the part,or using a glass-filled resin to reduce the shrink differentialbetween the appliqué and the resin.

He also recommends that molders consider the impact of partdesign on the molding process. Appliqué thickness affectsthe resulting flow channel thickness. Ribs should be 65 to 70percent of the main wall thickness to avoid sink. Though mostsurface defects like blush and knitlines are masked, sink is oftenexaggerated by appliqués.

Substrate and Appliqué Selection
Though similar to choosing property-specific resins in more conventionalmolding, appliqué-IMD resin selection offers the mix-and-matchoption. For example, a molder can choose PC for dimensional stabilityand impact strength, and an acrylic appliqué for solventresistance. An appliqué also can mask the surface appearanceof a glass-filled material. Johansen says bond results are bestwhen the appliqué resin matches the substrate resin. Closematches, like PC to PC/
ABS, also work. Adhesives can be used to match dissimilar materials,but the bond is not as strong.

Appliqué type, thickness, and coating considerationsmust be taken into account early on. A flat appliqué shouldwork if the area of the part to be decorated is relatively flatand if the appliqué need not wrap around the part's edge.Johansen recommends trialing it first if it's questionable. Flatappliqués cost less. If the appliqué needs forming,cold metal dies or thermal forming of some sort can be used, dependingon the required draw depth. Regardless, Johansen cautions thatthe forming process can play a role in graphic design.

"The forming process will distort the graphics if thegraphic feature is located in an area where the appliquésheet stock stretches excessively," he says. "The stretchingresults in graphic distortion and graphic registration concerns.If there is significant distortion the process may not be capable.Some distortion can often be overcome by several iterations ofthe shape and position of the printed graphic."

As appliqué thickness increases, appliqué stockcosts increase. If the appliqué is fully supported by thesubstrate in a part design, then a thinner .2- to .5-mm appliquéwill work. In unsupported areas, thicker appliqués shouldbe used. When determining thickness, ease of handling has to beexamined.

Johansen says molders should ask themselves what the coatingswill look like and to what side of the appliqué the coatingwill be applied. Inks often are blown away in the gate area insecond-surface decorations, he warns. Second-surface decorationsare those wherein the ink is at the interface between the appliquéand the substrate. Still, he says that the coatings and inks availabletoday provide tremendous creativity for decorating everythingfrom parts using dead fronts or a white daylight graphic and acolored back-lit graphic; parts incorporating a lens; or partswith hard-coated, textured, or soft-touch surfaces.

Mold Design
Gate placement is paramount. High shear and temperatures at thegate may wipe off the appliqué's ink and possibly someresin when it is the second surface that's decorated. Johansenalso says to remember that an appliqué is not as durableas tool steel-lower-than-normal cavity pressures between the gateand the last place to fill are required in appliqué IMD,but much more aggressive venting is needed, since appliquésare more sensitive to the higher temperatures of trapped gases

He adds, "It is much more risky to opt for soft productiontooling when molding appliqués-the chance of damage toshutoffs and parting lines is obviously much greater when thereis an appliqué in the cavity as the mold clamps up."

Careful thought also needs to be given to how to hold the appliquéin the cavity. "In most cases the part design will allowone to slip the appliqué over core pins or nest the appliquéinto the cavity with an external press fit. If these two optionsare not available, one must tap into the creativity pool. Remember,a vacuum port on the front surface will probably be visible onthe finished part."

Costing Structure
Johansen laments the fact that process concepts are less wellknown in appliqué IMD than in conventional molding-whichitself has tons of details. The result is a considerably longerto-do list for the project manager. He says this fact has to beconsidered when estimating product development costs and leadtimes.

Even in the most simple cases, expect 5 to 25 percent toolingcost increases to cover equipment to cut the appliqué,the mold, and the appliqué loading tool modifications thatmay be required. Costs of the appliqué material, cutting,loading, and labor could add anywhere from 25 to 150 percent topart costs.

The lion's share of the cost increases are in appliquémanufacturing tooling and its development. Screen-printing, forming,and cutting tooling; plus the several iterations mitigated bygraphics distortion and resolution, color matching, and attemptsto compensate for hot spots in back-lit areas all add to costs.Also, the heightened restrictions on parting line, gating, venting,and finish add to basic mold costs. And since these types of partsgenerally involve higher volumes, custom EOAT for appliquéloading is a possible factor.

Whether robot or manual appliqué loading scenarios areentertained, Johansen says molders must consider the fact thatappliqué IMD also adds to production costs vs. conventionalmolding. But he reminds molders that appliqué-IMD partsare decorated in the mold. It's really an apples-to-oranges comparison.He believes that the added costs involved can be justified byadded-value margin enrichment.

Cost Justification
Johansen admits that, bottom line, appliqué-IMD toolingand production is significantly more costly than conventionalmolding. If the volume is less than 50,000 parts/year, cost-justifyingformed appliqué IMD is challenging, to say the least. Butthis is not to say that projects less than 50,000 parts/year won'tfly with a formed appliqué.

Profile Plastics does several each year. Appearance quality,durability, or paint/VOC elimination often are the primary driversused to justify the switch to IMD. If a part is currently beingpad printed or hot stamped, and the appearance and durabilityare acceptable, Johansen says appliqué molding probablywill not be cost effective.

When, then? "If a button is first molded, then paintedseveral different colors, then is laser etched, and volumes aregreater than 100,000/year, appliqué molding has a goodshot at being justified based on cost."

He continues, "If a part has a 3-D surface to be decoratedwith multiple colors, textured and hard-coated with some graphics,then back-lit, appliqué molding is probably the only manufacturingprocess that is feasible."

Terlizzi says sales of at least $200,000 generally are neededto recover development costs from appliqué IMD.