Section 7: Media Selection

Direct Thermal Labels
Direct thermal printing is one of the most cost effective ways to produce high quality bar code labels. While they cannot be used in all applications because of their sensitivity to heat and sunlight, they do offer some significant advantages not available when other printing technologies are used. In particular, it is the only technology that does not depend upon a secondary substance transfer for formation of the image. There are no ribbons, ink rollers or other marking agents that must be transferred to the surface of the label. Instead, the image is formed in a heat sensitive layer that is placed on the surface with a thin protective layer placed over it. The image developed by applying heat lies beneath the protective coating, with nothing exposed on the surface. For this reason, direct thermal labels are very resistant to smudging, scratches or abrasion. They are ideal for use in labeling foodstuffs because they are unaffected by moisture or even complete submersion in water. At the same time, foodstuffs are also not tolerant of heat and sunlight, so the two match quite well.

• SENSITIVITY
  Thermally sensitive paper is classified by the amount of energy required to form the image. A high speed uncoated paper, such as that commonly used in fax machines, requires less heat to print, but also is more sensitive to ambient heat than "slower" paper. Labeling media is a compromise between "fast" and "slow." Direct thermal printers generally are capable of producing a more controlled and precise dot than the typical thermal fax machine, but at a slightly lower print speed. Because each different type of printer can represent a different set of tradeoffs, it is important that the printer be carefully matched to the labels used. If not, poorly printed bar codes that are either under-developed or have significant blooming at the bar edges will result.
  
  The thermal coatings have two different sensitivity ratings. The first is the dynamic sensitivity, which is the temperature at which a dot is formed by a print element. Static sensitivity is the ambient temperature at which the label background begins to change. Thermal label coatings are a compromise between these two. On one hand, the highest static temperature possible is desirable, since this is the limiting factor in using thermal labels at high ambient temperatures. Conversely, a coating with a low dynamic temperature will result in faster print speeds since the heat element does not have to reach as high a temperature to form a dot. While these two ratings are not independent of each other, they can be tuned to give us the best coating for a particular application.
  

  LABEL ROLL	M-5900	M-5900L	M-8400RV	CL Series	CX200	XL Series
  Max. Outside Diameter	6.0 in	6.0 In.	8.6 in.	8.6 in.	5.0 in.	9.8 in.
  Core Inside Diameter	3.0 in.	3.0 in.	3.0 in.	3.0 in.	1.5 in.	3.0 in.
  Typical Roll Length	250 ft.	450 ft.	650 ft.	650 ft.	165 ft.	510 ft 10 PT tag) .
  Min.Gap Between Labels	0.125 in.	N/A	0.125 in.	0.125 in.	0.125 in.	0.125 in.
  Max. Label Width	5.0 in.	5.0 in.	5.0 in.	5.0 in.	4.65 in.	4.0 in.
  Wind Direction	Face-In	Face-Out	Face-In	Face-In	Face-In	Face-In

  Label Roll Specifications
  
  
• TEMPERATURE
  SATO recommends three different types of thermal label material for use in the M-5900 and thermal transfer printers running in the direct thermal mode. The first is for general purpose use. It is usable at ambient temperatures up to about 1400F and can be exposed to direct sunlight for several weeks before the bar code contrast ratio drops below acceptable levels. For high ambient temperatures, a different coating is recommended that can withstand temperatures up to 2120F before it becomes non-usable. A special UL filter coating is recommended if exposure to sunlight exceeds several weeks. It filters out most of the harmful ultraviolet rays that cause the background color change and extends the direct sunlight exposure time to several months.
  
  
• RECOMMENDATIONS
  All of the direct thermal labels recommended by SATO are matched to the requirements of the SATO printers. While they can be successfully used with other printers, there is no guarantee they will be compatible. Conversely, only the recommended media can be guaranteed to be compatible with the SATO printers. Media from other suppliers may work just as well, but must be first tested with the printer. When testing the labels, it is important to use a print quality verifier with a visible light wand, since what the eye sees is different from that seen by the scanner.
  
  Synthetic material can be coated with any of the thermally sensitive coatings used for paper labels, resulting in a label that is very tough and of excellent print quality. However, because the coating does not migrate into the surface of the synthetic material like it does for paper labels, the developed image will deteriorate due to ultraviolet light exposure more quickly than the corresponding paper labels.
  
  
• VISIBLE VS. INFRARED
  There are two types of direct thermal labels. The first are used with visible light scanners and employ a thermal sensitive dye that responds quite well to the visible light source used by these scanners. The other type uses a different dye technology that responds to both visible and infrared light. The infrared responding material is more expensive, and for this reason, the standard visible labels are preferred in applications where it is known that infrared scanners will not be used.
  
  
• LINERLESS LABELS
  One of the latest innovations in label media is the new linerless technology. By coating the surface of the labels, the silicone impregnated liner can be eliminated. The coating prevents the adhesive from sticking to the surface of the labels as they are wound on a roll. Direct thermal labels are ideal for this since the image forming layer is generally under a protective coating anyway. The SATO M-5900L is a special version of the M-5900 direct thermal printer that has specially treated internal components that can be used with the linerless media.
  
  Linerless labels have some unique advantages, such as:
  • Elimination of the liner results in more labels in the same diameter roll.
  • There is no liner to rewind or dispose of.
  • Lower total label cost.

Thermal Transfer Labels & Ribbons
Thermal transfer printing is a cross between direct thermal and hot stamp printing. The mechanism is mechanically similar to that of a direct thermal printer except a ribbon consisting of a wax or resin based ink coated on a thin mylar backing is interposed between the print head and the label. The heat from the print element melts the ink and is transferred to the surface of the label material. Most thermal transfer printers can be used for printing on direct thermal label stock, but it is not a common practice. First, the thermal transfer printer is more costly because it must also contain the ribbon mechanism. Second, it requires more energy to print using thermally sensitive paper than is required to release the ink from ribbon. This requires that the head power drive and print speed be adjusted to meet the new heat requirement. And last, the head wear from abrasion is greater when the ribbon is removed.

The major disadvantage of the thermal transfer process is the cost of the ribbon. There is a 1:1 ratio between ribbon usage and labels. If 100 feet of labels are printed, it requires 100 feet of ribbon. Sometimes it is possible to use a "ribbon saver," which lifts the ribbon over un-printed areas to minimize ribbon usage. However, most labels are designed to be the appropriate size and incorporate very little white space since that also means valuable label material is being wasted.

High quality bar code labels can be produced without the major disadvantages of the direct thermal process, namely the sensitivity to heat and sunlight. However, it requires a careful match between the ribbon, the label surface and the printer to consistently get good quality labels. Any variation in one of these can be disastrous.

While the label material itself is not heat sensitive, the ink coating on the ribbon must be released from the mylar backing by the application of heat. The composition of this ink determines the melt point and must be matched to the heat generated by the individual heat elements.

• PERMANENCE
  As the ink that is released from the ribbon must adhere to the label material, there must be a match between the composition of the ink and that of the label. A wax based ink that flows readily when melted will fill a rough surface better than a resin based ink. However, it is more susceptible to smudging when handled or when contact scanners are used, especially at elevated temperatures when the ink becomes soft. Resin based ink, on the other hand, requires a smoother surface for proper adherence. The addition of a plasticizer to the resin can result in an almost indestructible bond between the ink and a synthetic media. But wax based ribbons are much cheaper than resin based ones, and paper labels less expensive than ones made with synthetic materials.
  

SATO Thermal Ribbon Selection Chart

• VISIBLE VS. INFRARED
  The coloring agent in the inks used for the ribbons described in this section are all compatible with infrared or visible light scanners. They respond to either equally well.
• COMPATIBILITY
  The labels and ribbons listed in this section have been carefully chosen to match the characteristics of the SATO thermal transfer printers. While other combinations may work well, there is no guarantee that they will be satisfactory. On the other hand, labels and ribbons presented here may work well with other printers, but again compatibility is not guaranteed.

Adhesives
Attachment is a very important part of bar code labeling. A perfectly printed label lying on the floor is as useless as an unreadable one on the item. A method must be used to secure the label to the item. In many cases, the retail industry for example, the label must stay attached to the item throughout its useful life, and then be easily removed, somewhat of a contradiction. The most popular method of attachment is adhesives applied to the back of the label. These come in two general classifications; permanent and removable.

The most popular adhesive, as you might guess, is permanent. It is suitable for the majority of bar code applications, from industrial marking to grocery tags. As the names imply, they are each designed for a particular type of usage. Other formulations have been prepared for specific applications, but are available only on a special order basis.

The permanent adhesives offer a high initial tack with strong adhesion to a variety of surfaces, such as painted and stainless steel, plastics and paper. It is virtually impossible to remove a label attached with permanent adhesive without destroying it, especially if it has "security cuts" (small cuts into the label surface). This type of adhesive is used in special applications where removal is not wanted, such as postage meter strips. It generally has an apply temperature range starting around 35�F.

Adhesive Selection Chart

Permanent cold temperature adhesives were developed for usage by the grocery industry and have high initial tack and good adhesion to plastic wrap with an apply temperature ranging down to 200F. While it is not impossible to remove the label without destroying it, it is difficult, requiring great care.

The removable adhesives were developed for applications where the label is temporary and must be removed without leaving parts of the label or any residue. They are commonly used as price tags on expensive consumer goods, where the tag must be removed without damaging the item. The apply temperature is higher than that for either of the permanent adhesives, starting around 40�F.

TAG MEDIA
Tag printing is much like label printing, except the media is thicker and there is no liner backing to contend with. The standard tag thickness in the U.S. is 10 pt. (0.10') and occasionally 12 pt. The thicker tag stock makes "curl" more pronounced, especially on the inner layers of the wind. For this reason, a 4-diameter core is sometimes specified. It is also common to print long and narrow tags in a rotated orientation so that any "curl" is across the short direction.

Tag stock is generally supplied on continuous rolls. Since there is no label gap for detecting the beginning of a label, holes, notches or non-reflective sense marks must be used. The preferred methods are round-corner notches or small hang holes. Tags with rounded corners are aesthetically nicer looking in appearance and have no sharp corners to snag on clothing or other parts of the labeled product. By designing the notch properly, it can be used both for sensing and to provide rounded tag corners. Holes are used as attachment points for hanging tags and are typically at the center top of the tag, which can be in the center of the tag roll or, if they are printed in a rotated orientation, along the outside edge of the roll.

The other method of sensing labels is with a preprinted Eye-mark on the bottom of the tag, which is detected, using a reflective sensor. Printing the mark however adds another operation to the process, thereby increasing the overall cost per tag. It also leaves a visible mark on the tag which is objectionable is some applications. Because the tags are most often supplied on continuous rolls, some method must be provided to separate them after they are printed. A heavy duty cutter is needed to reliably cut the thicker stock. The printer must supply some method of adjusting the cut location to accurately position it at the proper cut point. After the tags are cut, they can be collected in a "cb unit" (cardboard box) or placed in a neat stack using a label stacker. A means of inserting "batch separators," by either varying the cut length or placing a visible mark on the edge of a tag, allows the print jobs to be easily separated.

Tags can be printed with standard tabletop label printers but sometimes the stiffness and curl of the tag stock causes feed problems. For heavy duty tag printing, it is best to use a printer, such as the SATO XL Series, designed specifically to handle the heavier tag material. These printers have specially designed cutter and stacker options for handling the tags after they are printed.

Copyright � 1998
Sato America, Inc.

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