In-mould labelling
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In-mould labelling is a technology to decorate plastic products during their manufacture. Combining the decoration process with the moulding process cuts the total cost, but can add overheads to the manufacturing time.
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[edit] Component functions
[edit] Upstream Automation
Taking 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 very important to speed things up, and get clever with the label placing movements, to keep this overhead to a minimum.
[edit] Labelling
Vacuum and compressed air is generally used to handle the labels, although static electricity is frequently 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 and the thickness can be 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 make labels which are to decorate products with a high wear-resistance. This type of film has the printed surface protected by a second layer of film; the total thickness may be 30 or 40 micrometres. Products using this type of label might include picnic-ware, mouse-mats, or internal automotive components, for instance.
In-mould labelling is also becoming a popular method of decorating injection molded parts for the consumer electronics industries. Computer notebooks and cellphone manufacturers are adopting IML technology to provide greater wear resistance than spray painting or pad-printing. IML can also provide greater decorating options than other decorating methods. Multi-color screen printed and offset lithography printed graphics are being used to produce products with higher quality graphics than available with other decorating methods. Most applications in this product area are using 2nd surface type graphics. This means the decoration is printed on 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 does not flake, rub or scratch off during daily use.
[edit] Downstream automation
Downstream automation is used to perform any or all of the jobs of: 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 be used to check for accurate label positioning, and can also validate label correctness.
