What is IML Converting?
IML is the abbreviation for inmould labels. Inmould labels are mainly used for the decoration of product surfaces. The name inmould indicates that the label is placed in a form or a tool - mould.
How are IML produced?
The raw material for inmould labels is plastic granulate, heated up and extruded in form of a continuous film. After a cooling the film is wound up on a reel. The most common materials for extrusion are polypropylene granules, which are oriented accordingly to the film web. In addition to polypropylene, further materials are used. However, because of the adhesion, these materials should show similarities when bonding the inmould label to the final product.
The material roll is unwound in the further converting processes and cut into separate sheets. Often the sheets are printed, cut into shape and stacked in the same processing step. Usually the products cut into shape are connected to the remaining sheet. After stacking the sheets, the waste matrix is removed in an additional step either manually or automatically and the shape cut products are stacked in individual piles.
Instead of the inline-sheet cutting and printing, this can also be achieved in separate processing steps. The printed sheets are either die cut with rotary tools or punched with a flat-bed punching unit, either with flatbed die cutting tools against a hardened surface or in a traditional punching process with punches and dies. Often the cut sheets are cut into separate packages which are then pressed through a punching knife.
Considerably less process steps are needed when using a roll printing press, since the raw material roll doesn't need to be cut into sheets. This process is notably suited for the converting of thin foils with thickness of less than 60 µm. In a roll printing press, the material is printed rotative and subsequently wound up. After a recommended rest period, the printed roll is fed into a roll cutting machine and cut to the individual product shape with rotating tools. The cut labels are separated directly after the cutting process and the waste matrix is removed. The separate products can be stacked and counted subsequently after being cut to shape – all in the same converting process.
How are the IML processed?
Inmould labels are inserted into the magazines of an injection moulding machine as batches. The handling system of the machine takes individual labels out of the magazine and feeds them into the injection mould. Retrieving the labels from the magazine can be a challenge, since the labels must not be loaded with electrostatic charges, but need to have on the other hand the ability to be destacked / taken up by using means of electrostatics . If they are loaded with statics, they tend to stick to the adjacent label(s) and cannot be retrieved separately. In consequence a batch of labels will be inserted into the injection mould and generate a defective final product. Therefore it is essential to generate as few electrostatic charges as possible in the printing and die cutting processes.
After the labels are placed into the injection mold, the mold is closed and the liquid plastic is injected into the mold. After cooling the bonded product is ejected. The label and the injection moulded part form a unit. Since the label usually consists of the same material as the product, these two form an inseparable bond.
Differentiation to other decorating techniques
Inmould labels are preferably used where direct printing on the formed products is difficult. This is often the case for rectangular cups or for complex print layouts. An alternative to inmould labels is the use of self-adhesive labels or wet glue labels; however these techniques are not suitable for humid environments.
The use of inmould labels allows the recycling of the product, because only one type of material is used and no further glue or bonding media is necessary.
Besides inmould labels that are placed in injection molds, there are also labels that are used in thermoform tools. These labels are abbreviated as IMT. In blow molding machines BML labels are converted. BML labels are slightly thicker than the previously mentioned labels.
What products are decorated with inmould labels?
Food packaging like butter, margarine and yoghurt cups and lids, ice cream tubs, paint buckets, beer crates, storage cases, plastic furniture, vehicle parts, ...
Advantages of the different processes
The offset sheet printing process is advantageous for large inmould labels with a high grammage as well as for the printing of nested product arrangements. Sheets of thin foils are difficult to transport and are more suitable for reel processing. In the past, nested product arrangements could only be printed in rotogravure printing presses. In the meantime seamless printing plates are available for web-offset and for roll flexographic printing, which allows a continuous printed motif on a web. Especially for thin materials (<80µm), a precise die cutting unit is necessary, since an irregular cutting clearance can lead to products getting stuck in the waste matrix or to blunt cutting tools, which subsequently leads to dust formation. Formation of dust affects the converting process negatively, especially when converting food packaging. To achieve constant die cutting results, high precision die cutting modules with gap control systems are used. As a result, dust formation and waste production can be lowered to a minimum; furthermore, the process reliability and the service life of the cutting tools are increased.
By now, even long or nested products that were produced in a roll printing press can be stacked efficiently, for example by a high speed robot with an optional inspection system.