Lasers are used to drill tiny holes at high speed in webs of thin paper and plastic. The purpose of these perforations is generally to create weaknesses to allow packages to open is a predefined way (‘Easy Open’) or to make the material porous to allow air or steam to move through the barrier in a controlled way.
For such organic materials Rofin’s sealed CO2 lasers in the range or 100W to a few kW are ideal. These lasers can be switched on and off very rapidly and have very good stability which makes them ideal for processing a web of material between winders, moving at up to 700m/min.
Perforation of cigarette tipping paper
By producing an array of holes in the range of 50µm to 100µm in tipping paper, cigarette manufacturers reduce the tar inhaled by the smoker as cool air is drawn into the filter which encourages the tar vapour to condense inside the filter, rather than being inhaled into the lungs.
A kilowatt CO2 laser is split into multiple beams and delivered to the paper by means of stationary microfocusing heads. In the most rapid winding systems, such dedicated systems are capable of perforating at approaching 500,000 holes per second!
Laser perforation of modified atmosphere packaging
As cut fruit and vegetables continues to respire within plastic packaging, the shelf life of produce can be extended by making the packaging ‘breathable’ – i.e. permeable to oxygen and carbon dioxide. Laser drilled holes are reliably create the correct size and density of holes to facilitate this without drying out the produce.
Fewer holes are required to be drilled in the web of printed polymer than for tipping paper, even at high web speeds and consequently of order of a 100 – 200W source is sufficient.
‘Easy open’ packaging
Lasers can scribe or perforate material which will subsequently be used to package confectionary, snacks, coffee, pharmaceuticals and drinks to make the product easier to access. Tear lines can be created by scribing or making a linear perforation to weaken the packaging where it is required. The CO2 laser is well absorbed by organic materials by not by foil barriers used in peanut and crisp packs meaning that the contents remain sealed from atmosphere.
Similarly, entry holes for drinking straws and exit areas for blister packs can be made so much easier to use by selective package weakening. Creating such structure on a web of material whilst it moves between rollers can require high speed movement of the laser spot across the web. Generally these applications therefore require ‘galvo’ optics which deflect the laser at very high speed using rotating pairs of mirrors.
Anti-forgery ticket and passport perforation
Passports can have the number cut through all the pages by steering the laser to create alphanumerics made from a matrix of circles. World cup tickets have been finished with intricate tear-off perforations which can be very difficult for forgers to emulate.