Writing with light

It’s Saturday night in the disco. The beats are blasting out, the floor is heaving, and a laser beam carves shapes in the darkness. For the people on the dance floor, the pulsating light is all part of the show, a transient moment in a night full of fleeting impressions. Few would pause to think, for example, that the plastic bottles of water on sale at the bar might also have something to do with lasers — for example, to inscribe the sell-by date directly onto the plastic or to weld together various plastic components. In reality, however, laser technology has long become a firmly established fact of our everyday lives — both inside and outside the disco.

  
Indeed, lasers are now even used down on the farm. Without the use of ear tags, it would be difficult for anyone to identify the cows in the meadow. Marked with a number and a barcode applied by laser, these plastic labels are in effect a license plate for the cattle, serving to identify each animal at any time. “Laser marking provides a permanent and forgery-proof method of inscribing plastics,” says Oliver Piening, Marketing Manager at Merck. Two different types of pigment are used for this purpose: Lazerflair® and Micabs® pigments. Both produce high-speed, high-contrast, and high-definition markings. To date, the main use for Micabs is for the laser marking of animal ear tags. “The pigment enables high-speed marking and is resistant to UV radiation and manure,” Piening adds. The pigments are a clever combination of chemicals and various polymers. “They consist of tiny spheres in a polymer matrix.” Piening explains. “When this is irradiated with a laser, it triggers a direct reaction that produces the desired coloration.”

The laser egg, a new demo tool from Merck, shows how the pigments look in real life. The egg shows a collection of plastic chips, each of which has been made from differently colored polymers and then inscribed with a different laser setting. This enables customers to inspect individual pigment applications. “It’s a great service for our customers,” says Piening. “In the past, we could only answer their questions theoretically or we had to go into the time-consuming production of a concrete sample. Now, we’ve got actual examples.”

In the majority of laser-marking applications, a dark-colored marking is set against a light background. Laser light penetrates most types of plastic, but it is only when it comes into contact with laser-marking pigments, such as Lazerflair® from Merck, which have been mixed into the plastic in low concentrations, that it generates clearly defined areas of contrast in the polymer. In this case, the laser light passes through the plastic and only if it comes into contact with the pigment is the light converted into heat, which rapidly increases the temperature of the pigment particles. This causes a change in color — not of the pigment itself, but rather its immediate surroundings. The quality of the marking depends on the absorption properties of the polymer matrix. This means that each polymer formulation requires its very own laser-marking solution for the best results. “With Lazerflair® pigments, we have to set up the formulation for the specific type of plastic being inscribed, although this does give us much more flexibility in terms of end applications. It means, for example, that we can produce light-colored markings on a dark background. These are created by the plastic frothing as a result of gas formation,” Piening explains.