Thermal transfer vs. direct thermal printing

First, let’s talk about the similarities: Both label printing methods each require a thermal print head that applies heat to the surface being marked. The print head consists of tiny heating elements (dots) that heat up in selected areas to produce the desired print image. Therefore, the rather general term thermal printer may be used for direct thermal label printers as well as for thermal transfer printers. Their printing resolution is determined by the size, number and arrangement of heating elements, specified in dots per inch (dpi). It is usually 203, 300 or 600 dpi. The higher the number, the higher the print resolution and quality.

The actual difference between the two methods is in the surface that is heated by the print head: Thermal transfer printing uses a wax- or resin-based ribbon that transfers ink onto the label when heated. Direct thermal printing, on the other hand, uses heat-sensitive labels which blacken where they are heated directly.

In thermal transfer printing, the heating elements of the print head apply punctual heat to the passing ribbon, causing it to melt onto the label and form the print image.

The label absorbs the ink so that it becomes part of the media. The ribbon and label stock (material and adhesive) must be carefully matched to each other and to the specific application, in order to receive optimum quality and durability.

Thermal label printers in general are great to produce barcode labels, because they create high-quality images with excellent edge definition, which is required for barcode scanners to capture data successfully. For more information on this topic, check out our 6 tips for better barcode quality and our quick guide on how to check barcodes without a scanner.

We would also like to add that you can print both linear and two-dimensional barcodes such as data matrix codes or QR codes with either thermal printing method. The same goes for text and graphics, of course.

Let’s compare each method’s performance in different categories:

Tip: How to tell the difference using the fingernail test

You can easily determine whether a label is a thermal transfer label or a direct thermal label yourself. Simply perform the fingernail test: scratch the surface of the label with your fingernail. If a black mark appears, it is a direct thermal label.

Thermal transfer printing requires, in addition to the printer and labels, a ribbon (also known as thermal transfer ribbon or foil). The labels used can be standard paper labels or coated labels.

The required ribbons are available in three different grades, designed for various materials and applications:

• Wax thermal transfer ribbon
  For standard and semi-matte paper labels

• Wax/resin thermal transfer ribbon
  For all glossy paper labels and synthetic top materials

• Resin thermal transfer ribbon
  For printing on nameplates, solvent-resistant and heat-resistant labels, washable textile labels, and other specialized applications

Weber Marking also offers the solvent-free SolFree® wax ribbon, which combines numerous benefits for people, the environment, and thermal transfer printers.

In thermal transfer printing, the heating elements of the print head apply punctual heat to the passing ribbon, causing it to melt onto the label and form the print image. The label absorbs the ink so that it becomes part of the media. The ribbon and label stock (material and adhesive) must be carefully matched to each other and to the specific application, in order to receive optimum quality and durability.

Thermal transfer printers are available with different print heads up to 600 dpi resolution. Although a resolution of 203 dpi is sufficient for many applications and the prints are easily legible, some areas—such as the pharmaceutical industry—require particularly sharp prints. A label printer with a resolution of up to 600 dpi prints even small details with high contrast and sharpness. This printing technology is therefore also ideal for printing barcode labels. Poor print quality can otherwise quickly lead to incorrect barcode scans.

Since thermal transfer printing causes the label to absorb the color of the ribbon, the prints are particularly durable and resistant. The right combination of ribbon quality and paper can achieve high resistance to heat, cold, light, moisture, and abrasion. This opens up many possible uses, including applications in outdoor areas.

Another advantage is that the technology is robust and low-maintenance.

One disadvantage of thermal transfer printing technology is that it can usually only print in monochrome and halftone. This means that it is not possible to reproduce photos in full color with high detail. However, there are ways to print at least two-color elements (e.g., pictograms).

Compared to direct thermal printing, thermal transfer printing is slightly slower because the ink must first be melted from the ribbon.

In addition, since two different consumables—paper and ink ribbon—are used, thermal transfer printing is somewhat more expensive and generates more waste than direct thermal printing.

This also makes handling the printer a little more complicated: because the various consumables have to be refilled regularly, downtime occurs more frequently.

Areas of application for thermal transfer printing

Thermal transfer printers are used wherever product labeling needs to be as durable as possible: for example, when it comes to consumer safety and protection or product liability. Here are a few typical areas of application:

• Device labeling: Type plates and warning labels in the electronics industry
• Labels for product identification and traceability
• Food labeling: Labels with ingredients, but also cold storage labels
• Quality labeling: Labels on components and devices
• Labeling in the laboratory area: Laboratory labels and, in this context, cold storage labels
• Logistics labeling: e.g., shipping labels or transport labels for pallets

As with thermal transfer printing, direct thermal printing also involves heating the heating elements in the print head of the label printer. The roll of heat-sensitive labels passes over the heating elements in the print head, causing a kind of color change on the paper. This is due to the special label material, as direct thermal labels have a heat-sensitive coating. The heated elements in the print head trigger a chemical color reaction, thus producing the print image.

Since direct thermal printers do not require ink ribbons, printing is more cost-effective than with thermal transfer printing.

They can also print faster than thermal transfer printers because the ink does not first have to be melted from an ink ribbon.

One disadvantage is the durability of direct thermal prints. They are much more sensitive and not as durable as thermal transfer prints. We are all familiar with direct thermal printing from receipts in our everyday lives. Have you ever kept a receipt and been annoyed a year later that the print is no longer visible? One reason for this is that the paper reacts to heat, abrasion, and light.

Since direct thermal labels do not have a very long shelf life due to the heat-sensitive paper, they are suitable for simple applications that do not require high print resistance and where there is a high label throughput. Classic areas of application for direct thermal printing labels are:

• Address labels for letters and newspapers
• Shipping labels for parcels
• Cash register receipts
• Parking tickets
• Tickets
• Admission tickets

Special label software such as Loftware (formerly NiceLabel) is available for creating and printing labels. This software allows you to quickly and easily design label layouts with text information, barcodes, data matrix codes, or logos and transfer them to the printer.