Thermal Transfer Labels Guide

Archive for the ‘Printer Types’ Category

Flexography printing is also referred to as surface printing and for a long time was the preferred method of printing for packaging. With flexography, a mirrored 3D master plate is created of the image out of a rubber or polymer material. Using an anilox roll, ink is then dispensed in measured amount onto the surface of the printing cylinder. The print surface rotates, and transfers the ink as it comes in contact with the print material.

Flexography was named due to its originally uses as a method for printing the uneven surface of corrugated cardboard. The flexible printing plate remains in contact with the surface during the entire print process, producing a smooth and even finish. When this process was first used, it had a very low print quality. However, great advancements have been made in the last few decades in improving the plate material and the method of which the plate is created. Today, photographic exposure is used which is then followed by chemical etch. However, some manufactures also use direct laser engraving. Because of these advancements, full color printing is now possible.

Flexographic printing is still the most widely used printing method for flexible packaging. However, with the major advancements of thermal-transfer printing an increasing number of companies are switching from flexographic printing to thermal transfer printing. One reason for this is the growing global market and the increasing number of languages and internationally understood symbols, which are required on packages. In addition, in order to comply with European and United States market and FDA regulations, packages must clearly display lot codes/ numbers and expiration dates. This had made the use of flexographic printing plates, which now require constant updating very expensive.

In order to comply with packaging regulations an increasing number of manufactures have turned to thermal-transfer printing. This simple programmable technology is not bound by the limitations of having to physically create a printing plate, but instead can program the needed information directly into the a database, which the microprocessor translates and makes the needed changes to the graphic image.

However, flexographic printing does have its loyal followers. With new and improved inks and plate materials being developed, flexography is still an appealing option. This is especially true for companies who are requested by, their clients to print unvarying information and provide preprinted packaging materials. Therefore, what we are seen in the in-house packaging printing market is a union between flexography and thermal-transfer printing.

Flexography VS Thermal Transfer Printing

Approximately 70% of the films used for packaging are printed on using flexography due to its versatility and its inexpensive operating cost. Another reason why flexographic printing is still used is that it is more suitable for printing on foil, films, and DuPont’s Tyvek brand spunbonded olefin than thermal transfer printing is is. In addition, flexographic technology also produces excellent print quality at high speeds, with flexographic printers having the ability to print hundreds of feet per minute. This makes it even more appealing and economical for large volume print jobs. Flexography ability to print on much wider webs at faster speeds does not harm print quality in fact; many supporters of flexography find it produces finer lines and logos.

However, the main disadvantage of flexography is its inability to compare to the ease of thermal-transfer printing when it comes changing text content. With flexographic printing when any part of the text or codes requires updating the users must change printing plates. Many times this means creating new print plates that can cost as much as $500 each. However, with thermal transfer printing, the user simply enters the changes into the system with a few keystrokes and the change have been made and sent to the printer, costing the company only the time needed to enter the new data.

Packagers routinely faced the problem of frequently having to make print changes due to the market demand for bar codes, lot numbers, and expiration dates as well as the need to print in multiple languages. This need for frequent changes can cost a company an estimated $150,000 to $250,000 per year on printing plates for multiple languages as well as ever changing expiration dates and lot numbers.

Still, many manufactures feel the over all cost of thermal transfer printing is too expensive when compared to flexographic printing despite the drawback of having to create new print plates.

Thermal transfer printers are mostly used for printing bar codes on thermal transfer labels. However, this technology can be used to produce color graphics and images by using colored wax-based ink. Just as with monochrome printers, color thermal transfer printers use the same technology. In unison the paper and ribbon traverse beneath the thermal print head, the colored wax-based ink that is on the ribbon melts onto the paper. Monochrome printers use a black panel for every page that is be printed, whereas color printers will use three or four color panels for each page, with a panel for each color used. For three-color printing the panels are Cyan-Magenta-Yellow (CMY), and for four-color printing the panels are Cyan-Magenta-Yellow-Black (CMYK).

Color thermal transfer printers cannot vary the dot intensity and the images must be dithered. Dithering refers to a technique used in computer graphics, which creates an illusion of color depth using a limited color palette. When the precise color is not available in the palette a diffusion of colored pixels from the available palette are used. The human eye however perceives this effect as the actual color. Often when enlarged, dithered images can be distinguished by a characteristic graininess.

Color thermal transfer printers cannot compare to today’s thermal dye transfer or dye sublimation printers, inkjet printers, or color laser printers. Color thermal transfer printers are commonly used for industrial label printing because of its water resistance and speed. In addition, because of their limited number of moving parts, these printers are considered highly reliable.

Solid-Ink Printers

Tektronix was the first to develop the Solid-Ink or Phaser printers. In 1999, Tektronix’s printing operations were sold to *Xerox. Phaser printers use wax blocks, which are melted then transferred onto the paper using a piezo inkjet head, similar to the process of the inkjet printers. The Phaser printers can be configured so that they produce extremely high-quality images. They are also more economical than the traditional color thermal transfer printers, as the only wax used is that for the printout, instead of consuming an entire ribbon panel. Operational expenses including upkeep and ink are comparable to color laser printers.

*Xerox is a registered trademark and not a verb to be used when referring to copying a document. The Xerox Corporation is concerned about this ongoing practice of using its corporate name as a verb, for this places its trademark in danger of being declared a generic word by the courts. To combat this problem the company has engaged in an ongoing campaign to convince the public that Xerox is not a verb.

Thermal transfer printers are classified as non-impact printers, meaning that the printer head uses heat to register an impression on paper instead of striking the paper to create the image. The print head of the thermal transfer printer contains several small resistive heating pins. When these heating pins come in contact with the print media, they heat, melting the wax-based ink onto ordinary paper. Microprocessors determine precisely which heating pins are heated to produce the desired printed image. The size of the print head has to span the entire width of the print media, therefore if your thermal printer is used to print 3x 5 inch images, it cannot be used to print 1x 2 inch images, nor can a 1 x 2 inch size printer be used to print 3 x 5 inch.

The thermal transfer ribbon consists of three layers, a base layer, the wax ink layer, and the third lay is a coating. The coating and base material prevent the ink from adhering to the print head and causing poor print quality. However, there are several different types of thermal transfer ribbons available, each with their own specific characteristics. The least expensive and possible the most common is the wax ribbon. This type of ribbon is used for transfer labels for inventory control, shipping, hangtags, and basically general-purpose use. The next type of ribbon is the wax/resin ribbon and is used on paper as well as synthetic labels, or on tags when the need for water resistance and smudge resistance is needed for items such as pharmaceutical labels, frozen products, drums, pallets, mattress and pillow labels, etc.

Resin ribbons are used for printing on synthetics and for items were there is a high risk of extreme heat, abrasion, oils, and chemical solvents. The most common application for this type of thermal transfer labels would be outdoor labeling, UL/CSA applications, Dry-cleaning labels etc.

We’ve all heard a salesperson say, “Maximum printing speed of this thermal printer is…? However, they’ve never told you that print speeds have several limitations, including a repeat period of time where the thermal printer prints a line, then moves the media in order to print the next line. This is referred to as the cycle time or pulse cycle, which is the amount of time for the electrical current to flow through the heater element, pluse the time required for it to cool, before it can print the next line. When printers have shorter cycle times, they also have higher printing speed.

One method of increasing print speed is by shorting the pulse width. When a higher power is applied to the thermal printhead this creates a shorter pulse width that has enough energy to darken the media. This shorter pulse width will support a shorter cycle time, thus increase print speed. However, a shorter cooling time is also needed to achieve a higher printing speed.

When the heater does not cool quickly enough, the next pulse will be applied before the temperature has reached the optimal base level resulting in poor quality print and, can shorten the life of the printhead. For this reason many manufactures are using thin film printheads, which have a better heat response than thick film printheads.

Yet, even this can pose problems. Even when using thin film printheads the use of history control is needed, which is the use of a shorter pulse width to print a dot when the same heater retains heat from printing a previous line. Thin glaze increases the limit of when history control is needed. The reason for this is because thin glaze more efficiently disperses heat enabling the heater surface to return to the base level quicker, with out an accumulation of heat after 5 pulses.

Printing speed is also directly related to media sensitivity. High sensitivity media uses less energy therefore prints faster than low sensitivity media. The reason for this is higher sensitivity media also reduces pulse width and cycle time.

Thermal transfer printers are classified as non-impact printers, meaning that the printer head does not strike the paper in order to create the image. They use heat to transfer an image onto paper. The printer heads of thermal transfer printers contain several tiny resistive heating pins. In many modern thermal transfer printers, microprocessors communicate to the printer precisely which individual heating pins are heated in order to melt the wax-based ink, producing the desired image onto paper. The size of the printer head will determine the size of the labels or paper that can be used, this is due to the fact that the print head spans the entire width of the medium that is to be used for printing. Thermal transfer printers are used for printing bar codes, labels, price tags, and other specialty print jobs, such as bumper stickers, large graphics, and even clothing. There are two forms of thermal transfer printers; direct thermal printers and thermal wax transfer printers.

Early fax machines used direct thermal printers, which produce an image by using a heated printer head. As the print head moves over paper that has been chemical treated, the paper changed colors, usually black or blue to produce the image. Direct thermal printers do not use ribbons. However, the thermal paper is extremely sensitive to temperature, light, and chemical vapors and therefore does not have a very long print life.

Thermal wax transfer printers use a ribbon containing wax-based ink. When heat is applied to the ribbon by the thermal print head, the wax melts that transferring the ink to the paper where it becomes permanent once it cools. Generally, the thermal transfer ribbons are made up of three layers, the first being the base material, the second layer is the wax-based ink, and the final layer is a coating. The coating and base material prevent the ink from adhering to the print head. A tremendous benefit over direct thermal printers is that with thermal transfer prints, monochrome and color ribbons are available. However, each time a print ribbon is changed or replaced, it is strongly recommended that the print head be cleaned, using a cotton swab and isopropyl alcohol.

The primary use of thermal transfer labels is in the printing of bar code labels. This is accomplished with the use of bar code printers, which are available in fixed sizes of 4, 6, or 8 inches in width. The main function of these printers is in the production of barcode labels for product identification and or shipping purposes. Barcode printers generally employ either direct thermal printing or thermal transfer printing.

Direct thermal printers use a heated printhead, which creates a thermal chemical on paper that has been treated; causing the paper to turn color, usually black creating the desired image. Labels produced by direct thermal printers must be protected from exposure to heat, direct sunlight, and chemical vapors.

Thermal transfer barcode printers, press the thermal print head onto the label and over the platen, which is a rubber roller. Sandwiched between the print head and the label is the thermal transfer ribbon. This is a polyester film that has been coated with a waxy ink resin. As the label and ribbon are pressed beneath the printhead, tiny pixels located across the printhead are heated, melting the ink resin, and transferring it from the polyester film onto the label. Once the ink has been transferred to the label, the pixels are cooled. The total amount of time for this process to occur is approximately 203 dots per inch or 300 dpi. However, because technology is ever improving, there are several manufacturers that now have printers as faster as 600 dpi.

The demand for high print speeds has created very sophisticated label printers, many of which are equipped with larger memories and very powerful processors, allowing them to produce labels at the same speed as the print mechanism. In order to achieve speeds such as this, the thermal label printers must use an internal description language, which permits the label to be planned and designed in the printers’ memory prior to the actual printing.

Each barcode printer manufacturer has its own unique and often complex language. An example of this language would be the controlling computer transmits a series of codes to the printer. These codes are the requested barcode’s specifications, including size and location of placement on the label, as well as the data to be printed as a barcode. Then using pre-defined algorithms, the printer constructs the barcodes. Barcodes have very stringent rules for accurate printing, which ensures its readability under a variety of circumstances.