Marking and coding product packaging may not be high on your list of priorities . . . until you get a project that uses new packaging materials or has new customer requirements: the customer needs permanent codes; the packaging has changed from a paper box to a plastic bag; the marks need to be highly readable. Then it becomes crucial to know all your options before choosing the right technology.

Careful analysis can make the difference between a successful, efficient operation and one that experiences needless downtime, resulting in unhappy customers. Key factors to consider include:

• Types of materials or substrates you'll be marking
  
• Desired speed of application or throughput
  
• Print quality -- permanence and readability
  
• Up-front investment your company is willing to make
  
• Total cost of operation, including cost of service and consumables such as inks and ribbons
  
• Whether variable data, graphics, and bar codes are needed.

Once you know these factors, it will be easier to choose which marking and coding technology is best for your application. Laser coding, thermal transfer overprinting (TTO), and continuous inkjet (CIJ) printing are all options that have benefits for different applications. Here is how each technology fits into the increasingly diverse industry of package marking and coding.

Laser Coding

Industrial laser marking started in the early 1970s and since then has developed into a well-established technology. Today, laser marking/coding is used in thousands of production lines throughout the world. It can be used for marking numerical codes, 2D-matrix and bar codes, logos, and symbols onto labels, sleeves, glass and plastic bottles, cans, kegs, tubes, blisters, cardboards, tubular films, and caps.

Lasers do not require inks, stamps, or ribbons to generate a code. In modern sealed-off CO2 laser coders, such as Videojet's 3320 or 3120, the infrared laser light is generated via radio frequency discharge in a carbon dioxide gas mixture. The CO2 laser systems code thermally by changing the surface color (e.g. PVC packages), melting, foaming (e.g. PET bottles), or removing the material surface (e.g. printed labels, cardboards, cans, tubes).

The advantages of laser coding are numerous, including speed, versatility, code permanence, noncontact operation, clean and dry process, maintenance-free operation over thousands of hours, extremely low operating costs, and adaptability to a fully automated line. Lasers also offer unsurpassed reliability in "no code/no run" operations where mandatory package coding prior to distribution means that production will stop if a product is coded incorrectly. Halting production is a very expensive process, and most companies will do everything to avoid downtime. The unequaled uptime of a laser coder and its extreme productivity result in cost savings for a variety of applications.

Thermal Transfer Overprinting

Thermal transfer overprinting (TTO) involves a thermal transfer printhead and ribbon that make contact with a flexible substrate, such as synthetic films and labels. Miniature print elements under a glass coating heat small areas of the ribbon and transfer ink to the target substrate. Print elements are program-controlled to create real-time images, including clean, high-resolution bar codes, text, and graphics. TTO systems can address applications in both continuous (moving) and intermittent (stop-print-start) environments.

Maximizing production uptime and ribbon utilization are the keys to success with TTO, and some methods of doing so are more effective than others. For example, the Videojet DataFlex Plus features a solid state, clutchless ribbon drive system that uses bidirectional stepper motors. The system continuously monitors ribbon tension to avoid ribbon-related faults, such as real or false ribbon breaks, which can interfere with production. This system also more precisely controls the ribbon, leaving only a millimeter of space between prints for better ribbon utilization. TTO systems that use clutch-based ribbon drives cannot as effectively accommodate fluctuations in ribbon tension on control spacing between prints. As a result, clutch-based systems use more ribbon and experience more ribbon-related faults, translating to increased downtime and higher operating costs.

Typical applications for TTO are within the snack, bakery, meats, and frozen food industries, where flexible packaging is common. There are also special applications, such as in the coffee and confectionery industries, where generic packaging is used across a wide product range and all product branding and specifications have been added using TTO. This saves companies substantial cost through reduced waste and inventory.

Continuous Inkjet

Perhaps the best known method of noncontact marking and coding is continuous ink jet (CIJ). CIJ has become one of the most versatile and durable options for food manufacturers. Small-character CIJ printers create lot codes, expiration dates, bar codes, and graphics on packaging, while large-character CIJ printers do the same for secondary packaging such as cartons and corrugated boxes.

For example, food packaging requires readable, high-quality codes to ensure accuracy in the tracking and tracing of those products. Small-character CIJ delivers this by applying a stream of ink drops via a printhead to the package. This allows codes to be applied in a variety of fonts, lines, and direction and at a range of throughput speeds -- up to 1,000 fpm and with code heights ranging from 1/32 in. to more than ½ in.

Development of related technologies -- such as software that monitors and controls ink viscosity and automatic flush systems that eliminate daily printhead cleaning -- have helped reduce downtime. Also key is that many small-character CIJ printers are portable and can be moved from line to line as needs arise.

Making the Choice

Careful consideration of the application -- materials to be marked, permanence and readability requirements, anticipated line speeds and operating costs -- is the first and most important step toward determining the right marking and coding technology for your company's needs. From there, supplier representatives can assist in taking the next step in examining the features and costs of specific laser coders, thermal transfer overprinters, and continuous inkjet printers. Once all these issues are factored in, actually choosing a marking and coding system becomes the easiest step of all.