How to print in-mold labels
May 1, 2012
In In-mold labeling (IML) the label, of paper or of a similar material to the molded container, is an integral part of the product placed during the manufacturing of storage units. The making of the container and the label placement can be performed with different techniques: blow molding, injection molding or thermoforming. The choice of the technique strictly depends on the shape of the final product. For example, in injection molding, plastic material is injected into a cavity (mold) that forms the shape of the container in which a label is properly positioned prior to the injection of the plastic. The label is handled by vacuum, air compressed or electrostatic charge so that it shapes properly and holds firmly on the mold.
Multi-color flexo, screen printing and offset are the technologies of choice when producing in-mold labels given their higher graphical performance and remarkable results on pre-treated substrates as those used in in-mold labeling. The decoration is printed on the back side of a clear substrate, typically plastic films such as polypropylene, polycarbonate, or polyethylene. Cavitated (multi-layer substrate having a spongy layer bonded between two very thin solid layers) or laminated material are also often used. Their thickness range varies generally from 15 to 40 micrometers. First, a layer of heat seal coating is applied. This layer is coupled to the substrate, which will receive the heat-resistant ink. A heat-resistant layer of lacquer is finally applied. The substrate, which is heat sensitive in itself, can be printed using a machine fitted with control systems that ensure material stability. With OMET rotary flexo presses, the chill drums control the heat and consequent quality of the finished product, and there are devices to eliminate the build up of static. It is essential that the correct varnishes are used to reduce negative static both in the die cutting phase and in the inmoulding one. OMET has all the technology needed to process the IML label IN A SINGLE PASS thanks to the integration of an inline rotary die cutting system, which is complemented by a unit that delivers the finished label. This method has obvious advantages, especially where short runs are concerned. Final delivery of the printed products is particularly difficult but it can be solved by using vacuum delivery systems, available also in OMET range. The injection plastic into the mold is made on the ink side of the film. After cooling, the label becomes an integral part of the container and the decoration is thoroughly protected against scratching or abrasion.
The world demand for labels is expected to grow over 5 percent per year to 51.6 billion square meters in 2015. Pressure-sensitive labels continue to be the largest label type; above-average demand growth is also expected in other label segments such as stretch sleeve, shrink sleeve and in-mold labels, though gains in these relatively newer label technologies will stem from small bases (source: Freedonia 2011).
**Thanks to Multi-Color Corporation www.mcclabel.com/index.html for the use of the picture