Custom molders are always looking for the competitive advantages that can establish their value to their OEM customers and open the door to new business opportunities, and technology is an optimum way to do this. With the advances being made in in-mold decorating for durable goods, molders can provide their customers with creative solutions, often at reduced costs-to-manufacture, and expand opportunities with customers for greater value-add.
   
Mark Dirr, director of research and development for Xten Industries, a custom injection molding company in Kehosha, WI (www.xtenindustries.com), recently provided insight into how that company has created opportunities for new business and provided solutions to customers’ complex decorating requirements using in-mold decorating (IMD). Dirr gave his presentation at the recent IML/IMDCON, sponsored by AWA Alexander Watson Associates, in Rosemont, IL.
   
It’s key to understand what IMD brings to the table and the cost of that. There are a number of cost/benefit considerations:

Educating the customer on the benefits, costs, and complexity of the product using IML/IMD can be challenging. Some of the issues surrounding IMD include choosing the right kind of IMD and optimum substrate materials are the beginning. “We had a project that used a 30% GF high-temp material, and glass prevents good adhesion of the label,” Dirr explained. “One of the problems we ran into is that the insert in the part acts as an insulator between the label and the part, and we don’t have control over how much glass comes to the surface. So we have to run hotter than normal to achieve a quality surface and good adhesion of the label.”

Dirr also suggested that choosing a supplier with expertise in IML/IMD and that can deliver the product on time is critical to the success of the project. The label is just as important as the plastic substrate material, so making sure that the label supplier has the type of equipment necessary to provide the labels is also important.

“Not all label suppliers are doing both IML and T-IML labels,” Dirr noted. “Supplier expertise is important, as is the type of equipment they have. For example, digital printing provides more flexibility, and enhances the speed at which you can change over because the label supplier simply prints a different art file each time. Unfortunately, there are no UV inks used in digital IML printing at this time so if you need UV resistance and digital printing you have to coat the labels after the fact—lamination or a secondary coating. That adds cost.”

Designing a product specifically for IMD is critical. “If the product has ribs under an IML, using the 60% wall thickness ratio rule might not be good enough,” said Dirr. “The in-mold label takes away wall thickness so you subtract the IML thickness from the wall,” he advised.

If a really glossy in-mold label is being used, Dirr suggested that a different wall thickness ratio might have to be used. “In our experience, sink marks show up easier with glossy labels so it’s best to take the ratio down to a lower percentage. I’ve used 40% and it works great. That’s subject to change depending on other factors, but that’s a good rule of thumb.”

Performing a material flow analysis prior to the mold build is critical for successful IML/IMD. “Gate location and material shear can be a problem,” said Dirr. “You need to know how the material is flowing into the mold so that the label or decorative film stays in place." Xten sub-contracts the analysis to “good suppliers” of that service, and does this analysis on all but the simplest projects.

“You want to make sure you’re gating in the center of the label so the material flows to the edges to get a uniform lay-down of the label,” Dirr said. “We can’t always do that, which means we have to get into some tricks—which we developed as a proprietary process—to achieve what we need. 

"We typically do an analysis on a part to detect any problems. Once we determined we can fill it, we looked for areas of high shear that could burn the label and result in cosmetic issues, gas traps, etc. All the things that you’d be looking for normally are that much more critical in IML. Venting is very critical. Poor venting can lead to burn marks and degradation of the label and adhesion layers.”

Gating is important as well. “If you use multiple gates you can get a crease in the IML part.  Then you may have to use sequential gating in a hot runner system for good IML/IMD results,” Dirr advised. “So far we’ve been able to do all of our parts with a single gate.”