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Top marks - Laser coding and marking systems

Packaging Professional magazine
,
1 Jan 2008
Laser marking on glass

Ask people what impression they have of lasers and they may recall the 1964 James Bond film Goldfinger. Many think of lasers as powerful high energy light beams. And they can be – engineers have developed a laser with a power of just one kilowatt that can cut plate steel. However, most applications are at a lower power.

We are surrounded by lasers. In entertainment and computing, CD and DVD drives use the high precision and non-contact properties of low power lasers to read and write digital data – the binary code that represents the music and pictures. Applications for low power lasers also include skin surgery for removing moles or tattoos.

The word ‘laser’ is an acronym of ‘light amplification by stimulated emission of radiation’. Light comprises sub-atomic particles called photons, which are given off by atoms in a stimulated state. This state is reached by exposure to a radiant source of energy, including light and radio waves. Amplification is achieved by containing this process of photon emissions so that stray photons strike adjoining atoms, stimulating them and causing them to emit further photons in a kind of chain reaction. This creates an intense source of light.

Marking up

In coding and marking, two laser technologies are in common use, the CO2 laser and the fibre laser. The former is similar to a pinhole camera in reverse – instead of absorbing a spot of light into a dark box, it emits a fine stream of photons in a concentrated beam. This is characteristic of lasers – they emit photons in a tight pattern that has identical colour frequencies.

The photon chain reaction in a CO2 laser is started by a pulse of radio energy. Mirrors within the box prevent photons escaping so that they bounce around inside, stimulating the emission of more photons. A small lens in one of the mirrors allows some photons to escape in a beam of light.

The fibre laser operates on the same principle. It uses a diode as the primary photon source. This introduces light into a specially coated length of optical fibre through a device, known as a grating, that has similar properties to a mirror. A grating at the opposite end of the fibre serves the same purpose as in the CO2 laser, preventing photons escaping unless they are of a specific frequency.

The laser advantage

Lasers overcome many of the problems associated with continuous ink jet (CIJ) marking. They are solid-state devices and have long-life light sources. Euromark Coding and Marking’s Vespalase machines have a projected tube life of 30,000 hours for the CO2 model. This rises to 100,000 hours for the fibre version. There are no servicing requirements or consumable costs. Other advantages are:
• Solvent fumes are not released into the working area, tainting delicate foods.
• Ink/solvent spillage is avoided.
• Lasers will mark most substrates – plastic pots, foil caps, glass or ceramic containers, steel, aluminium, printed or painted foils or films, card, paper and board.
• The devices can mark up to 2,000 characters per second.
• The marks cannot be removed chemically or mechanically without leaving evidence.
• Lasers have no auto-cleaning cycles.
• Crisp, clear imprints are produced of date marks, user instructions, and conventional and 2D matrix bar codes.
• The tool can also produce both Vector and Windows quality graphics and logos with up to 300 lines of information.
• The long life and high volume capability of lasers mean cost per print is lower than any other method.
• The equipment is simple to set up.
• Power consumption is low.

The initial cost of a laser system maybe higher than ink jet. But by taking into account the absence of consumables, servicing costs and operational advantages, there are potentially major lifetime savings. Payback on a laser installation is usually two to three years. Given the lifespan of this equipment, the accumulated savings can be considerable.

 

Further information:

Ian Luck, Euromark Coding and Marking, Unit 5, Croftwood Square, Martland Mill Industrial Estate, Wigan, WN5 0LG, UK. Tel: +44 (0)1942 228882. Fax: +44 (0)1942 228802. Email: info@euromark-coding.co.uk.