by Jonathan Lim, Avery Dennison Industrial Products Division
In-mold labeling. Although the concept has been around for many years (primarily in blow molding applications), the adoption of in-mold labeling in injection molding has not been as widespread in the United States as it has been in Europe. Factors that seem to deter the adoption of in-mold labeling for injection molded parts are the need to make a change in the manufacturing process and the investment associated with such change, as well as the absence of direct piece price comparisons to other decorating technologies such as pad printing or hot stamping.
When evaluating in-mold labeling, it is important to consider the total applied cost of the manufacturing and decorating processes, and not just the in-mold labeling portion. Advantages that can be achieved include the following:
- Elimination of Secondary Processes the plastic part ejects from the mold complete with decoration
- Reduction in WIP no need for extra handling and storage of molded part while waiting to be decorated
- Reduction in Scrap Rates repeatability and decorating in one step significantly reduces scrap rates
These cost savings must be weighed against the necessary investment in robotic or end-of-arm equipment to determine whether the payback timeframe is acceptable. In-mold labeling, by no means, can completely replace secondary decorating, but there are many applications where it can be a feasible option for injection molding operations.
Once it has been determined that in-mold labeling is the best choice as a decorating option, there are several specific factors to look at before in-mold labeling can be added to an existing injection molding process.
One of the first things that will be required is automation to insert the label into the mold. Injection molding machines with existing robots can have their end-of-arm tool modified to insert a label and remove the finished part upon each insertion into the mold cavity. With larger parts and longer molding times, the percent impact on total cycle time is minimal. Manually inserting the label into the mold may be feasible, but will not have the repeatability, accuracy and precision of automation, and will have a greater penalty on cycle time.
Presenting the label to the robot end-of-arm is another factor that needs to be considered. A common method used today is to have the labels sheeted, then stacked in a magazine. The robot end-of-arm then picks up the individual labels utilizing suction cups. An inherent problem with this process is that static may start to build up between the labels, thus causing the labels to stick together, at times resulting in more than one label being picked up by the robot end-of-arm. Anti-static equipment may be installed to alleviate the issue, or an extra resource may be stationed at the label stack to continually make sure the labels do not stick together. Both of these can be costly solutions. To eliminate this problem altogether, in-mold labels are available that can be supplied in rolls, and presented to the robot end-of-arm on a label dispenser.
Another consideration is temporarily adhering the label to the mold prior to plastic injection. Current methods include modifying the mold to have a vacuum effect or installing a static charger to the robot end-of-arm to apply a static charge, allowing the label to adhere to the mold surface. Products such as Avery Dennison®s Accu-PlaceIML does not require either of these options because of a proprietary surface coating which allows the label to temporarily adhere to the mold before plastic injection. This eliminates the need to modify the mold and also eliminates the disadvantages of using static; namely, labels slipping in humid conditions, inability to use static near electronic equipment, as well as personnel safety issues. Todays molders typically utilize several plastic resins. It is necessary to make sure that the in-mold label supplier offers a wide range of label materials that will mold well to almost any resin, from polypropylene to polycarbonate. The correct label construction plays an important role in creating a permanent bond with the plastic part.
No matter what the label material, the concept remains the same get the label into the mold, temporarily adhere the label to the mold, inject the plastic and form a permanent bond between the label and the part. With the use of the proper automation and the proper label materials, in-mold labeling can become a permanent addition to an injection molding operation.
In-mold labeling may seem like a large undertaking initially; however, todays competitive environment offers a significant advantage to those that make the investment. Once one molding line is up and running with IML, the technology is readily transferable to other lines, providing an opportunity for in-mold labeling to become a vital part of any continuous improvement program.
Avery Dennison Corporation is a worldwide manufacturer of pressure-sensitive adhesives and materials and consumer and converted products. The Industrial & Automotive Product Division of Avery Dennison offers a breadth of label products, including pressure sensitive, functional, heat seal, and in-mold labels and can be contacted at (440) 878-7358 or visit: www.iapna.averydennison.com.