by Renée Varella
In a recent survey of molding companies involved in in-mold labeling, nearly 86 percent said that their involvement with IML applications consist of being responsible for bringing productivity solutions to my company. The respondents also indicated that the issues they face in IML range from misaligned labels (82.4 percent) to high-voltage arcing when the label is charged inside the cavity (23.5 percent) and everything in between. Here, Plastics Decorating tapped the expertise of five sources with broad IML experience willing to share their top tips.
Accurate IML Placement
Companies decorating with IML use several methods to hold a label securely in place inside the mold, including vacuum ports and electrostatic charging. To ensure accurate label placement, Butch Kaplan Jr., general manager at Central Decal Company, Inc. in Burr Ridge, Ill., noted that the robotics, end-of-arm tooling (EOAT), and decal magazines must be appropriate for the job. “The selection of an automation supplier is the key to success you want someone who has experience in the IML process,” he said. “All too often, a molder selects a source that doesn’t understand the intricacies of the process, which prolongs the startup and subsequent production.”
Matt Davidson, president of Xten Industries in Kenosha, Wis., agreed that automation and a well-designed EOAT make the difference in IML. “Automatic (robotic) placement ensures repeatability, and good EOAT design ensures accurate placement in the cavity,” he said.
“The label magazine or dispenser must be designed and constructed to provide consistent, accurate picking of the label by the robot’s EOAT and, in turn, the automation system and EOAT must be able to maintain consistent accuracy picking the label from a magazine and placing it in the proper position on the surface of the mold tool,” said Scott Shelton, who retired in 2009 as North American sales manager for ITW/Simco Company after over 30 years in the field of electrostatics and IML. “The entire mechanics of the label handling system must be rigid and vibration-free for consistent results.”
To hold graphics in place, Chicago Decal Company in Burr Ridge, Ill., uses static and vacuum systems-and sometimes both-in its applications. “A static charge is preferred, because you don’t have to make a permanent change to the tool, but a vacuum port is best for accuracy because it ensures no movement,” said Dave O’Neill, company sales manager. “Accuracy has a lot to do with flow, speed, and temperature.” To determine the ideal placement of vacuum ports,” he said, you must figure out where the flow is coming together: “If the flow comes in from the left and the right, they’re going to meet in the middle, so four vacuum ports in the corners or three across can fill the void.”
Once an IML job has been properly set up, make sure that the magazine is supplied with labels. “The bulk of the label supply should be properly stored in a temperature- and humidity-controlled environment, and only enough labels should be brought out on the molding floor for about a half day of molding,” Shelton said. “Most labels subjected to high humidity will not charge sufficiently and will lose the charge as soon as the label comes into contact with a conductive surface.” O’Neill agreed: “The moment you stop charging, the charge starts to dissipate and the longer the gap, the higher the likelihood of the graphic moving on you.”
With products running cooler mold tool surface temperatures during the humid summer months, be aware of open doors near the press, Shelton added. “When the press is open, condensation may form on the mold surface and will cause the static charge to bleed off the label so the label will not stick to the mold.” In addition, when set-up is underway or a label is charged for experimentation but not molded, do not attempt to recharge the label and use it again, because overcharging or recharging an already-charged label can result in loss of electrostatic adhesion.
“Qualifying labels for electrostatic IML is the necessary step when designing the process, said Mark Blitshteyn, acting R&D director of Ion Systems, Alameda, Calif. “To avoid expensive label-related problems, we recommend that you put in place an inspection process for testing incoming labels from a label supplier.”
If you do notice a label placement issue, Kaplan added, check the mold surface to make sure there is no residue buildup, double-check the magazines to make sure they are properly locked in place, and double-check the static-charger setting to make sure it is set at the proper kilovolts.
Overcoming Other IML Issues
Here’s an overview of some of the most common issues that come up in IML applications:
Resin selection. Some resins required to mold the part are more user-friendly than others, Kaplan noted. “For example, polycarbonate and nylon resins present challenges because the melt-point temperatures are higher,” he said. “On the other hand, polypropylene and polyethylene applications are much easier to handle due to their reduced melt points.” While there are IML decals for such applications, testing prior to production is a must. “It is important for the end user, the molder, and the decal supplier to agree on the resin to be used before the process is initiated,” Kaplan said. “In some cases and, depending on the size of the part, it may be wise to build a prototype tool for testing of the resin and IML compatibility.”
Durability. Another obvious challenge of IML on the decorating side, O’Neill noted, is achieving the appropriate degree of chemical or environmental resistance-which also requires thorough testing. “For example, floor graphics have to be walked on,” O’Neill said, “and the fuel cans in auto racing must be resistant to chemicals.”
Tool cleanliness. Dust and particulate matter in the IML process must be avoided at all costs, Davidson said, noting that labels must be supplied to the molding station clean, which starts with the label manufacturer. Shelton added that the mold surface where the label is located also should be cleaned periodically with a degreasing solvent.
Label construction. Shelton said that labels for IML must be constructed using substrates, inks, and coatings that will accept and maintain a static charge as well as hold up to the temperatures and pressures of the melt flow. “Labels with foils or metallic inks should be avoided because they will not adequately maintain a static charge, and they also can arc to the mold surface and result in pitting.” He added that many start-up projects have failed simply due to incorrect label construction.
EOAT design. Shelton noted that one method of electrostatic charging the label utilizes ionizing emitters (pin electrodes) or an isolated semi-conductive pad on the EOAT behind the label and connected to a high-voltage power source. “The label is charged as it comes into contact with the surface of the mold,” he said. “The use of ionizing emitters is usually the preferred method for thicker labels as used in the molding of durable goods.” Another method, known as the ‘Simplified Method,’ charges the label outside the press: “This method is popular in molding packaging products that typically use thinner label substrates,” Shelton said.
Label over-molding. With electrostatic IML, low overall charging of the label and an insufficient pinning force can allow molten plastic to flow under the label, Blitshteyn said. Over-molding also can occur when the EOAT design has the suction cups and ionizing electrodes competing for the same areas. To minimize such problems, Ion Systems has developed a patent-pending method of pinning the entire label surface, including the location of the suction cups holding the label.
High-voltage arcing. Preventing high-voltage arcing in electrostatic IML is crucial as well. “The user may not even be aware that the arcing occurs inside the cavity, only to observe unexplained product defects,” Blitshteyn noted. “Whether that is arcing from the ionizing electrodes to the wall of the mold cavity or the brush discharge from the label when its surface is overcharged, both types of arcing are detrimental to the label pinning process, potentially causing label misalignment or over-molding.” To prevent this, he said, non-arcing ionizing electrodes should be used for IML applications. To prevent the brush discharge, the duration of optimal charging should be determined before programming the controls.
Misaligned labels. Misaligned labels may be caused by inadequate design/construction of the label magazine or inaccuracies picking the label by the robot, Shelton said. “Vibration on a long stroke extension of a top- or side-entry robot or worn bearing surfaces can affect accuracy of label placement,” he added. Misaligned labels also may result from inadequate charging of the label, where the label is pushed out of position by the melt flow. “Labels from the label supplier, which already have static charge, may skew on the EOAT when they are picked at the magazine, so a static-neutralizing device may be needed at the magazine to ensure the labels are neutral when picked by the EOAT.”
Shelton added that some molders also attempt to ‘blow’ the label onto the mold surface by cutting the vacuum on the EOAT and applying positive pressure through the suction cups/ports in the EOAT as it approaches the mold. “This helps with release of the label from the EOAT after it has been placed in contact with the mold surface,” he said,”but air pressure should not be used to blow the label across an air gap to the mold, as that usually results in inconsistent placement of the label.”
Davidson recommends gating behind and to the center of the label whenever possible to keep the label edges away from the direct flow of material “and make sure they are charged sufficiently to stay in place on the tool,” he said.
Issues of speed. Acknowledging that putting a graphic in the tool does take some time, O’Neill said you can reduce the penalty in three ways: “First, minimize the vertical movement of the robot by placing the magazine at the same height as the drop-off point for the finished part. Second, orient the magazine to the position of the robot to eliminate or reduce any twisting and turning of the end of the arm. The third idea is to have dual magazines so that the operator is never loading a ‘live’ magazine.”
Time-consuming job set-ups. “Initial set-up on a new IML project, or start-up of an IML project by a molder not experienced in IML, can be extremely time-consuming,”Shelton said, “and may require assistance from an IML label expert, the automation supplier, or an expert in electrostatics – and sometimes all three.”
Blitshteyn said it can be challenging to troubleshoot the electrostatic IML process because you cannot see what is happening inside the mold cavity, and it often turns into a frustrating trial-and-error exercise: “It’s a good idea to use charging generators capable of the constant current mode of operation and capable of displaying and monitoring charging current values with high precision.” He added that, unlike many aspects of IML projects, such as the molding machines, mold design, or automation/robotics which are difficult to change once in place the electrostatic system can be introduced later in the project, modified after installation, or even replaced if not performing to the expectations of the user.
Designed correctly, the IML process should add only about 4 to 6 seconds to the normal cycle time of the press, Kaplan said. “Again, if the EOAT, including the magazine table, are designed correctly, job set-ups should be relatively simple and not time-consuming. Setting up the IML process should take no longer than changing the mold in the tool.”
Davidson agreed that setting up jobs should not be time-intensive if the pick-and-placement program has been stored in the robot and the cycle is stored in the molding machine. “Equipment location should be marked and bolted to the floor, if necessary, to ensure repeatable set-ups,” he added.
Applications best suited for IML. Kaplan noted that the shape of the decal as well as the laminar flow and gate location have a big influence on the success of in-mold labels. “IML applications work best on flat part surfaces or on large radii,” he said. “Long narrow strips with pointed corners do not necessarily work well, because the force of the laminar flow wants to move the decal out of position during molding. The smaller the decal surface, the lesser amount of gripping power there is to hold to the mold surface using static electricity.”
In general, a flat label on a flat mold surface is the easiest to work with, Shelton said. “If you are lucky enough to have the gate positioned behind the label, it is even easier because the high-pressure melt flow does not impact the label from an edge so it is easier to hold the label in place – a scenario suitable for the Simplified Method or the direct method, where the emitters are on the EOAT behind the label. “The big advantage of the Simplified Method is that the EOAT can be very simple and lightweight because the charging applicators are not mounted on the EOAT and high-voltage cables are eliminated on the robot,” Shelton said.
What works for one application may not work in another similar application, Kaplan pointed out. “Once a potential application is identified, it is recommended that the molder, the IML supplier, and the robotic automation source get together and review the project,” he said. “That is the best time to identify any possible conflicts that could cause problems in tooling design, resin/decal materials to be used, and EOAT.”
Communication Is Key
For all of the sources interviewed here, a successful IML program depends on good communication. “At project inception, all parties should get together to review the IML application and stay connected through the initial startup,” Kaplan said. “When this doesn’t happen, confusion and delays usually occur.”
O’Neill concurred: “To ensure success, the supplier must be intimately involved with every aspect of process development, tool design, processing parameters, robotic automation, and end-product performance criteria,” he said. It’s clear that using a qualified label provider, working with companies experienced in robotic or electrostatic systems, and conducting strategic planning before a trial make for a winning combination in IML.