Our industrial equipment and graphic overlay product lines have a Lexan® material option. Because artwork is printed underneath this polycarbonate material, rather than on top, there is no adhesive on the labels or control panels at the time of printing. We add it after the label artwork and graphics is complete. This gives you a lot of flexibility.
First off, it means you can choose your adhesive. Your options are an 2-mil LSE adhesive (covered in Stick to It #2), and 3M numbers 467 (2-mil thick) and 3M 468 (5-mil thick). You may also leave your label without an adhesive, if you want to apply your own at a later time.
If you choose to add an adhesive to your Lexan® labels, the adhesive you select is applied after the artwork is complete. This creates a sandwich, with Lexan® as the top layer, artwork (colors, graphics, cutouts, etc.) as the middle layer, and then the adhesive layer. The more usual label construction has artwork on top of the label material. When the adhesive is added after the artwork, the adhesive layer is called a “laminating” adhesive.
This method of applying adhesive also allows for adhesive-free areas on the label or graphic overlay. This is the second example of the flexibility this process can give you. In the examples below, note the adhesive-free areas. In cases where you are going to place the label over buttons, say in an instrument panel, you don’t want the label to adhere to the buttons. Rather than having a cutout, with laminating adhesives, you can specify that you want that area adhesive-free. You can also add transparent window colors in these adhesive-free zones.
What’s a Dead Front?
Another cool option that is available with adhesive-free areas on our graphic overlays or control panels is “dead front black.” As shown in the image below, we can make adhesive-free locations in our Lexan® labels that appear to be solid black until a light shines behind them. As you can see, once you place a light behind this label, four icons appear in the “dead-front indicators” box, and another (the small battery) appears in the next row down, at the end of the green and red lights.
This can technically be done on labels with adhesives, but the icons will not appear as clearly because the adhesive disperses some of the light. We highly recommend Lexan® with an adhesive-free area for your dead-front applications.
Less Can Be More
When choosing a laminating adhesive to put on a heavy-duty Lexan® control panel, most people would intuitively choose the thicker adhesive over the thinner. After all, if one is good, two must be better, right?
But in the case of laminating adhesives, thicker is not necessarily better. Indeed, for the most part, the thicker the adhesive, the less effective the bond. The adhesive link from surface to surface is strong. But adding more links in between surfaces by increasing the adhesive thickness makes it weaker. This is why a thick adhesive can actually weaken a bond, compared to a thin layer of adhesive.
Highly textured surfaces are the exception to this rule. This is simply a matter of contact area. If there is not enough adhesive to “flow” into the depths of the “valleys” between the high points of the textured surface and cover them, there is less surface area to bond to. In that case, you want a thicker adhesive to flow into those valleys, and form a more complete bond.
We offer two thicknesses of general-purpose laminating adhesive for Lexan® control panels or industrial equipment labels. 3M 467MP is the standard for the control panel industry; it is 2 mils thick, and is your best choice for almost any application with a reasonably smooth surface (including powder coated surfaces). 3M 468MP is the exact same adhesive as 467MP, but in a 5 mil version. It will flow into roughly textured surfaces that might be found in rarer applications.
The third adhesive option is our LSE adhesive, a specialized 2-mil adhesive for adhering to LSE plastic surfaces, covered in part two of this series.
Features of 3M 467/468 Adhesives
- Excellent high temperature performance
- Resistant to humidity and hot/cold cycles
- Shear strength – minimizes edges lifting / slipping
- Resistant to solvents, salt water, cleaning solutions, disinfectants, oils, other substances
- When bonding to plastic, it allows for slight position corrections if initially placed out of alignment (this does not work on metal).