Information to be printed

Amount of information

Small (a few lines of text with basic production information) If the information is to change infrequently (daily) you might consider using thermal transfer might be used. Thermal transfer has the added advantage of being able to print while the material is stationary (intermittent) or on the move (continuous). Both these technologies are contact printing technologies and exert pressure in order to make a print. If the text is to be printed directly onto a filled pack or onto a product coming down a production line, you may wish to consider using a non-contact technology such as thermal inkjet or laser.

Large (more complex format possibly including barcodes) Printing this type of information requires using a ‘programmable’ technology such as thermal transfer or thermal inkjet. Again, because of the coding force, thermal transfer can print only on flexible materials such as films, labels and cartons whereas inket can print on just about any surface.

Where the information is being used to customise a generic or blank pack (particularly on a carton, sleeve, pouch or bag) an offline overprinting system might be most appropriate. Depending on the application, this could have the added advantage of being able to feed several lines at once.

Type of information

Simple user input (lot code, manufacturing date, expiry date) With a limited amount of information the information can be changed on the line by an operator/supervisor. In the case of hot foil this will mean changing the engraved type digits. For thermal transfer and thermal inkjet, the new information will simply be keyed into the controller.

Simple auto input (date, time, sequential number, etc.) Not an option with hot foil, but easily achieved with both thermal transfer and thermal inkjet. The "code" that instructs the printer is embedded in the format and needs no further operator intervention.

Barcode (1-D, 2-D, Datamatrix) Due to their high resolutions of at least 300 dots per inch, both thermal transfer and thermal inkjet are idealy suited for printing bar codes. Fixed codes can be embedded in the format, whereas variable codes can either be input by the operator via either keyboard or scanner. Datamatrix codes often print a machine readable version of the Lot and Expriy date and can be linked to these fields.

Complex (list of ingredients, product description, instructions for use, diagrams and logos) Where a more complex format is to be printed it is usual to use a software package on a neighbouring PC to design, modify and preview the print.

Continuous or intermittent printing

Intermittent printing (the machine stops and starts as it packs) gives some flexibility in the choice of technology, but it might mean slower line speeds. Intermittent printing lends itself to hot foil or thermal transfer.

Continuous printing (the machine runs without stopping) also gives some flexibility in the choice of technology. At lower speeds, the technology is dictated by the amount of information to be printed and hot foil may be an option. If a large amount of information is to be printed on a flexible material, then a large area format thermal transfer would be more appropriate. Thermal inkjet is another alternative and is ideally suited for printing most materials online it also has the ability to reach speeds of almost 230m/min.

Line (printing) speeds

Using an intermittent machine As a starting point it is good to know the number of packs per minute that wil be produced. Coupled with the amount of information to be printed, this will give an idea of which technologies to consider. As the print is made during the stop portion of the machine cycle, the time for which the material is actually at rest will have to be calculated / estimated / trialled with a print, but prints per minute is a good starting point.

Using an continuous machine
The line speed is easy to calculate if the following are known: length of the pack, gap between packs, if any, and the number of packs per minute. Multiplying the pack length plus the gap by the number of packs per minute will give the linear line speed at which the printer needs to operate.

Online or offline printing

Online printing has the great advantage of knowing that what is going down that line is packed in material that is printed on that same line.

Offline printing has the advantage of one offline printing station being able to serve several production lines, especially if the final packing is carried out by hand. It also allows the late customisation of packs with information that may be too complicated to be added online.

Operational environment

The environment in which a unit is to operate can affect which technology you choose. You need to know, for example, whether the equipment will be subjected to:

• extremes of temperature (below 5C or above 35C)
• condensation or wash down conditions
• dust
• excessive vibration