Barcode Printing Technology

ADC Nordic distribute three types of barcode printing technology: Dot Matrix,  Direct Thermal and Thermal Transfer. In this text we focus on Direct Termal and Thermal Transfer.

Every label and ticket printer needs labels or tickets to print. To guarantee optimal performance when printing labels or tickets, specific label material, and sometimes ribbon, is required. The label usage and application are other factors to keep in mind.

Which print technique is the best?

Direct Thermal printing

The choice of print technology is determined almost exclusively by the application. Direct thermal is used when you want the label to last up to 12 months, indoors, and with normal use. Direct thermal labels should not be exposed to daylight during a longer period of time, since this gradually worsens the labels print quality. Also, as heat blackens the label at 80°C, it should not be used in applications with excessive heat. A premium label, however, can be stored many years under ideal circumstances (no direct sunlight, +20°C and 60% relative humidity). When printing using the direct thermal technology, the print head has direct contact with a heat sensitive paper. When the heated print head touches the paper, the heat sensitive top layer of the paper turns black.

Thermal Transfer printing

The thermal transfer print technology is used for producing labels that are supposed to last a long time, for labels with a small, fine text, as well as for graphics. The method gives a high print contrast and is best used for compact barcodes. It also offers the opportunity to print the barcodes in other colors than black, and on other types of material such as plastic, textile or metallic foil.

In thermal transfer printing, a ribbon is used to transfer ink to the label. When the ribbon passes between the heated print head and the label or ticket, ink is released to the surface of the label upon which it adheres.

Comparison between Direct Thermal and Thermal Transfer

Is the barcode to be printed “ladder” or “fence”?

When a barcode label is designed it is important to keep in mind in which direction the barcode shall be positioned. To explain this the terms “ladder” and “fence” are used.
The meaning of the words helps to understand the concept. A ladder is vertical, while a fence is horizontal. All “seen” from the printer’s perspective when it prints the barcode onto the label.

The optimal is for the printer to print in the picket fence direction. When the barcode is printed, the dots are heated in the print head and they stay heated until the entire barcode is printed.

When printing in the ladder direction, the print head dots constantly are turned on and off for every new bar it prints in the barcode.

Consequences
To be able to achieve optimal barcode print quality, the contrast, in other words the sharpness of every line, is very important. When you print picket fence, sharp edges are created for every line because the dots on the print head “draws” a line. When you print ladder, the edges aren’t as sharp and therefore the contrast isn’t as high. Neither is it possible to print as fast as in picket fence mode.

Note that this is a very general rule. In many applications where the barcode doesn’t need to be small and compact, or if the correct receiving material/ribbon is used, you can position the bars in the direction of your choice.

Label Materials & Ribbons

Remember to always test the label material and applicable ribbon before you recommend it to your customers.

Direct Thermal Labels or Tickets

Economy Labels
A paper label which is a good choice for applications in dry in-door environments and when the barcodes are printed in the “picket fence” direction.

Premium Labels
Paper labels, which have a protecting top surface and a “barrier” between the glue (the adhesive) and the label itself. This is so that the label shall be able to resist dampness, wear and tear.

Thermal Transfer Labels/ Tickets and Ribbons

Vellum Labels (paper) & Wax Ribbons
These labels are made from “wood-free” paper and it is the most economical choice for less demanding labels applications and for larger print volumes. Should be used together with ADC´s Standard or Premium ribbons, which give excellent blackness even at higher print speed. The Standard ribbon works well in print speeds up to 300 mm/second. The Premium ribbon has a thicker ink layer, which gives better blackness when printing large black areas, but at the same time it reduces the print speed to 250 mm/second.

Matte Labels and Wax / Resin Ribbons
On this label there’s a special coating for thermal transfer printing. This label is a good choice for environments where the label can be exposed to friction and wear. It offers high print quality for complicated barcodes, and therefore satisfies many industry- and authority standards. ADC recommends Standard and Premium Wax/ Resin Ribbons to be used. This ribbon quality is sometimes called hybrid ribbons because of its chemical mixture.

Semi Gloss Labels & Wax / Resin Ribbons
Coated labels are a good choice when you wish for very compact barcodes on a glossy label to give an exclusive look. ADC Standard or Premium Wax/Resin ribbons should be used.

Synthetic- or Plastic Labels & Resin Ribbons
Synthetic labels are made of synthetic plastic materials, specially treated to have a print friendly surface. Synthetic labels are excellent when used in exposed environments and have a perfect tack on curved surfaces. Together with ADC’s Premium Ribbon they offer optimal print quality as well as ink adherence. Resin ribbons have a very high resistance against mechanical wear and high temperatures, as well as towards chemicals, alcohol, oils and many solvents. ADC also offers an especially heat resistant resin ribbons that resists temperatures up to 200°C. But, also ADC’s Premium wax/resin ribbon functions well with many synthetic materials, and can therefore give a lower total cost.

By choosing a synthetic label in the same material as the packing film, the entire packaging can be recycled.

General about Adhesives

The purpose of the adhesive is to attach the label onto the base material. The adhesives are divided into two groups; rubber based and acrylic based adhesives.

Rubber Adhesives
This type of adhesive is melted onto the back of the label substrate, like a thin emulsion. Thus the term “hot melt” sometimes is used. The rubber-based adhesive often offers good qualities when it comes to initial adherence, often called “tack”, and is available as both permanent and removable. There is also rubber-based adhesives that can endure freezing temperature as well as stick to plastics with softeners. The UV-tolerance is often the time limiting factor if the label long-term is exposed to UV light.

Acrylic Adhesives
This type of adhesive can be made to dissolve in water, potentially demanded in applications where both the label and the packaging are recycled. It can be made very UV-resistant and lasts for many years. Adheres perfectly to plastic materials, but doesn’t have the immediate tack of the rubber based adhesive.

The Application and the Adhesive

The choice of adhesive depends on:
• The surface material where the label is to adhere
• The surface materials form and temperature
• Manual label application or using an applicator
• The environment which the label will be exposed to
• Should the label be able to be removed or not?