In-mould labelling
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In-mould labelling is a technology used to decorate plastic products during manufacture. Combining the decoration process with the moulding process cuts the total cost, but can increase the manufacturing time.
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[edit] Component functions
[edit] Upstream Automation
A typical scenario: An injection moulding machine will have a label-placing robot near to it - sometimes called 'upstream' automation - which supplies either pre-cut labels or automatically cuts the labels from a roll (a 'web').
For a 'typical' product, with a machine cycle time of 5 to 15 seconds, the upstream automation can add 1 or 2 seconds, so it is important to accelerate the process, and get clever with placing movements, to minimize delay.
[edit] Labelling
Vacuum and compressed air is generally used to handle the labels, although static electricity can be used. Static 'guns' charge a label while it is being transferred to the moulding machine, so that when the label is placed on the tool and released by the labelling robot, it will wrap itself onto the tool.
Labels may be paper or a similar material to the moulded product. Polypropylene or Polystyrene is commonly used as label material, with a thickness of 15 to 40 micrometres.
Cavitated label material is also used. This is a sandwich material, having a 'spongy' layer bonded between two very thin solid layers. An advantage of cavitated film is better conformance to small-radius curves on a product.
Laminated film can be used to decorate products, yielding high wear-resistance. This type of film has the printed surface protected by a second layer of film, with a thickness of 30 or 40 micrometres. Products using this type of label might include picnic-ware, mouse-mats, or internal automotive components.
In-mould labelling is also a popular method of decorating injection molded parts for consumer electronics. Notebook computer and cellphone manufacturers are adopting IML technology for greater wear resistance than spray painting or pad-printing. IML can provide greater decorating options than other methods. Multi-color screen printed and offset lithography printed graphics are used to produce products with higher quality graphics than available with other decorating methods. Most applications in this area use second surface graphics. The decoration is printed on the back side of a clear substrate, typically polycarbonate or acrylic 0.125mm to 0.375mm thick. The injection plastic is on the ink side of the film. This encapsulates the decoration between the film layer and the injected plastic resulting in a decoration that can't be abraded during use.
[edit] Downstream automation
Downstream automation performs any of these tasks: product removal, trimming, inspection or stacking. The mechanics to do these jobs can be incorporated into the upstream automation, so that while a label is placed on one side of a tool, the robot can be removing moulded parts from the other side. Because the labelling operation is simultaneous with the part removal operation, the overhead on cycle time is almost eliminated.
Vision systems can check for accurate label positioning, and can validate label correctness.
