Section 5: SATO Thermal Printers

Thermal Printing
Thermal printing has been around for many years. It was originally developed in the early part of this century to produce analog strip chart recordings using a heated stylus moved over the surface of heat sensitive paper. In 1953, a thermally sensitive paper was developed that led to the introduction of the 3M Thermofax office copier. In fact, thermal printers held 30% of the office copier market in 1960, but were quickly replaced by the newly emerging xerographic process during the next decade. Thermal printing thrived however in other applications spurred by three key developments; 1) the introduction by NCR of a thermal color-developing method giving a vastly improved print image, 2) the development of silicon-mesa thick film print heads in the early 1970's and the thin film heads in the late 1970's resulted in print elements with high resolution, and 3) the development of thermal transfer printing in the early 1980's. The technology was divided into two major directions with the introduction of transfer printing; the direct thermal imaging printers that use thermally sensitive paper, and the transfer printers that use a ribbon and untreated paper. Both technologies have their major advantages. Direct printing requires the use of a special thermal sensitive paper, but gives excellent dot formation with a simpler mechanism. Transfer printing uses uncoated paper that is not sensitive to heat or ultraviolet light, but depends upon a secondary substance transfer and a more complicated mechanism.

SATO was a pioneer in the development of thermal transfer printing for bar code applications with the introduction of the Model 5323, the world's first thermal transfer bar code printer, in 1980. The permanence of the image was the overriding factor in the technology selection at that time since the environmental limitations of direct thermal printing did not match well to the industrial market. However, the development of new high temperature papers and ultraviolet coatings have removed many of these limitations. Many industrial uses, such as shipping labels, which were previously marginal applications are now easily covered using the new thermal label materials. Direct thermal now offers a low cost alternative for many industrial tasks that were previously reserved for thermal transfer printers.

Thermal printing was chosen by SATO for all of their bar code printers. Thermal technology has many characteristics that fit quite nicely with bar code printing requirements. The technology is capable of printing high quality bar codes, it is easily adaptable to demand label printing and last, but certainly not least, a reliable and rugged printer can be manufactured within reasonable cost constraints without adversely impacting the first two goals.

• PRINT QUALITY
  Thermal print heads make a very precise and well defined mark on the media. The essentially square dots produced by the heat elements make it possible to form bars with high edge definition without the need for overlapping dots. Round dots on the other hand must be overlapped by at least 50% to produce an acceptable bar edge, and even then result in poor edge definition. Thermal printing allows the shape of the dot to be controlled by the shape of the heat element used. While there is a small amount of "edge blooming" that results from the heat gradient across the element, it can be tuned to produce a substantially square print dot.
  
  The criteria for acceptable bar code symbols includes the bar edge definition, the voids within the bar elements and the contrast ratio between the bar and the media upon which it is printed. Since the primary usage of the SATO printer line is for the printing of high quality bar code symbols, the ability to produce a well defined bar edge (when printing either horizontally or vertically) is an absolute requirement.
  
  
• DEMAND LABEL APPLICATIONS
  A great majority of bar code printing applications involve demand label printing, or the printing of a label on site as it is needed. This implies that the label must be immediately available to the user as soon as it is printed. The print line for thermal printers can be located very close to the label ejection point because of the physical geometry of the print head. They are long and flat and can be easily fitted into a constrained space. The result is that, as soon as a label has finished printing, it is immediately available for usage. Typical dot matrix printers are fitted with pin feed tractor assemblies that trap the last printed label, making it necessary to waste a number of unprinted labels before the last printed one is clear of the tractors. Similarly, a page oriented printer like a laser printer prints a page at a time. If you only need one label, you must waste the remainder of the page to get it.
  
  
• COST
  Cost of ownership can be divided into two categories. The first is the cost connected with the original purchase of the printer and the associated installation. The other is the recurring cost related to consumables purchasing and maintenance.
  
  A quality thermal bar code printer is more cost effective from a manufacturing view point than any of the competing technologies. The typical label width is around 4", making the print head costs reasonable. The paper movement mechanism is relatively simple and even the addition of a ribbon mechanism for thermal transfer printing does not overly complicate the design. The compact design of the printing assembly makes it easy to accommodate options such as label cutters, dispensers and supply take up reels.
  
  The recurring costs associated with the maintenance of the printer and the purchase of consumables is generally more than the initial cost of the unit when accumulated over its lifetime. It is obvious that the more simply a printer can be manufactured, the fewer things there are to go wrong. The inherent simplicity of thermal print mechanisms results in a substantial maintenance advantage, both in the frequency of maintenance, cost of replacement parts and operator training.
  
  The only significant item in a thermal printer that is subject to a meaningful level of wear is the print head. Critical to the rate of wear is the abrasion characteristics of the material that comes into contact with the head. With thermal transfer ribbons, the ribbon backing provides a smooth surface for the head to rub against. With direct thermal printing, it is a different situation. The surface of the label material rubs directly on the head and therefore must present a non-abrasive surface. This can be provided by applying a coating over the surface of the label. In addition, the construction of the new direct thermal print heads used by SATO is such that the resistive elements are not raised on the surface, reducing their exposure to wear. These new heads can significantly increase the wear lifetime, by as much as four times in typical applications.
  
  The other item affecting the head lifetime is "dot transitions" ( i.e. the number of times a print element is exercised). This process exists in all technologies since some type of energy transition is required to form a dot. The transitions may be mechanical (as in a dot matrix print head) which introduces frictional wear. The major factor in wear is how many transitions must be made to form a symbol, a few transitions by a lot of elements or a lot of transitions by a few elements (e.g. a line printer versus a serial character printer). The line printer has a higher lifetime since each element has to make fewer transitions to print a given amount of data. Other types of energy transitions, such as electrical to heat, are subject to different types of "wear," or thermal stress. The SATO printers are line printers that do not use mechanical energy transitions and therefore have the lifetime advantages associated with both line printers and non-mechanical dot formation.
  
  Consumable costs are directly related to the volume of labels printed and the type of supplies required. Direct thermal printing requires paper that has been coated with a thermally activated layer and most people do not consider it to be "plain" paper. However, the definition of "plain" paper is very nebulous, especially when your primary consideration is print quality. Thermal transfer printers print on "plain" paper, but in reality they have difficulty printing acceptable quality bar code symbols on papers with a rough surface, such as rag bond. Therefore, it is important to carefully specify the label stock to be used to ensure good print quality. This is true of all bar code printing technologies that depend upon a secondary material transference. Hence, "plain" paper does not mean "readily available'' or "cheap".
  
  Since we are primarily concerned with demand label printers, another factor comes into consideration. No matter what type of paper is chosen for the label stock, it must be coated with an adhesive, applied to a release liner stock and the labels die-cut. When all of these costs are taken into consideration, the cost of the primary paper stock becomes only a small part of the overall conversion cost. Therefore, when quality of the labels is taken into consideration, the cost of a label produced using thermally coated paper is only slightly greater than labels produced using "plain" paper. Offsetting this is the cost of the secondary transfer media. This can range from the toner/drum cost for a laser printer to the ribbon cost for a thermal transfer printer. Thermal transfer ribbon costs for a demand label printer can be significant since the ribbon must be at least as wide as the print field and if only one dot is printed on a line, the rest of the ribbon is wasted.
  
  
• USER FRIENDLY
  "User Friendly" is a highly subjective term used to describe a user's frustration level. As you might imagine, this level can vary greatly between users. The guiding criteria is to make the printer as simple and easy as possible for the operator to use and maintain, while staying within the range of economic feasibility. A good example of this process is the impact ribbon printers. When they were first introduced, a reel-to-reel spool ribbon was common. However, the frustration of the user in trying to thread the ribbon into the printer resulted in the development and almost exclusive usage of ribbon cartridges even though they are more expensive. The direct thermal printer has a distinct advantage because of the absence of any type of ribbon and any associated loading problems.
  
  Thermal transfer printers are more susceptible in this area than direct thermal printers because of the addition of the ribbon mechanism. The thin transfer ribbon must be loaded into the printer at periodic intervals by the operator. It can be difficult to route and handle, especially for the ribbons used on the wider platen printers.

Direct Thermal vs. Thermal Transfer

There are three primary areas in which these two technologies differ. The first, and most pronounced, is the expected life of the label, followed by the inherent difference in print speed and finally the cost of ownership.

• LABEL LIFE
  Two permanence factors are important to bar code printers; the ability of the bar to remain as printed, and the ability of the media background to remain constant. However, the label life requirements are mostly overlooked in the rhetoric of the arguments. As long as the label lasts as long as its useful life, anything else is unnecessary, and may even be wasting money. If a container is to be stored outside for months in the sunlight or subjected to elevated temperatures above 212� F, then direct thermal labels would be inappropriate. However, these conditions are not typical for most applications.
  
  In direct thermal printing, a heat source activates a dye that changes the reflectance of the coating. The label resulting from this process is therefore highly resistant to mechanical forms of surface abuse, such as scratching, scuffing or fluid dilution. For this reason, thermally produced labels work well when contact scanners are used. Technologies that rely on secondary transference to produce the bar must depend upon a good bond between the media and the transferred ink to prevent damage to the printed areas.
  
  The permanence of the media background is a separate story. While most non-coated media will age with exposure to the atmosphere, the basic properties of the thermal coating present a different problem for a direct thermal label. Since the label is heat activated, exposure to heat above the color formation threshold will result in the entire label changing color. This limits the use of direct thermal labels to temperatures that do not go above the color formation temperature. By judicious selection of the proper paper, this can be extended to around 2120 F. In addition, exposure to ultraviolet light will also change the background color, but at a much slower rate than heat. Tests with some of the newer papers with ultraviolet coatings has shown that labels can stand months of exposure to direct sunlight before the contrast ratio falls below the 75% minimum.
  
  Thermal transfer printing is less susceptible to heat, even though the ink is melted onto the surface of the label by heat. If low temperature paraffin based ribbons are used, high temperatures can cause the ink to soften and become susceptible to smudging. The higher release temperature of the resin based ribbons reduces this susceptibility substantially. The resin based ribbons can also react chemically with certain synthetic materials, producing a label durability comparable to that obtained by laminating the label with a protective material.

  LABEL TYPE	TYPICAL COST/LABEL (10K QTY)
  General Purpose Thermal	$0.055
  High Temp Thermal	$0.062
  Transfer with Standard Ribbon	$0.058
  Transfer with Premier II Ribbon	$0.065
  Transfer with Premier I Ribbon	$0.073

  
  
  
• SPEED
  As pointed out in the Technology Description section, less energy is required to release the ink from a thermal transfer ribbon than it requires to develop a dot in a thermally sensitive coating. The result is that the thermal transfer printer can print faster than its direct thermal cousin, even if the same head and printer is used. While the amount of energy put into a thermal print element can be increased to make it reach the correct temperature more quickly, there is no way to cool it down any faster. The paper must stay stationary underneath the head until the element temperature drops below the dot formation temperature or else a "tail" will be produced as the paper is stepped to the next print position. If you are printing in a horizontal mode (the bars parallel to the paper movement direction), some smearing can be tolerated as it just runs into the next dot forming the bar. But when printing vertically it is a disaster. The smeared bar will encroach on the area reserved for a space in the bar code while at the same time losing the precise bar edge definition so necessary for bar code printing. This problem is present in all thermal printers, even thermal transfer, but it's much more pronounced in direct thermal.
  
  The only alternative is to slow the print speed of the direct thermal printer down to match the thermal inertia of the heat elements. As a general rule, a direct thermal printer, when optimized for the paper sensitivity, will run at approximately 50% of the speed of a comparable thermal transfer printer.
  
  The axiom in racing circles is "Speed costs money." Unless you are involved in bar code printer racing, it is probably not very cost effective to buy more speed than necessary. After all, speed is relative. It is only one of the important considerations in determining how fast something can be done. A high speed automobile is of little use if it has to stop each block for a traffic light. To use the speed other factors must be taken into consideration, such as taking the freeway where there are no traffic lights. It is the same with printers. When a limited amount of time is available to produce a job, a high speed printer may help, but often it is not the complete answer, and in some cases, it may be a waste of money.
  
  Printing labels is perhaps more demanding upon the complete print system than other types of print jobs. Questions must be answered, such as the label size, the resolution of the character symbols, the amount and type of data to be printed and whether or not they can be batch printed or must be printed one at a time. These factors can sometimes control the actual "speed" at which a label can be printed more than the maximum print speed of the printer.

Print and Apply
Print/apply describes a process where labels are printed and then mechanically applied to the product. Label apply machinery places some unique demands on printers. They must be able to print labels fast enough to keep up with the conveyor system and present it so that the applicator mechanism can easily and accurately apply it. The placement of the label on the item must be accurate to within 1/16th of an inch. Any variance in the position of the label will cause the position of the applied label to vary.

Since a print/apply unit does not sit on a table top, it must be easily mounted in a variety of configurations. The majority of label apply applications require a side mounted printer so that the label can be applied to the side of a carton. This keeps the "throw" distance of the apply mechanism consistent for range of carton sizes, since the conveyor can force the carton to one side. The mechanism must be easily accessible in all configurations for changing media or removing label jams. Information display panels should be viewable from any angle so that the operator can easily determine the status of the printer.

Reliability is of utmost importance since production line downtime must be kept to an absolute minimum. Media supply capacity and reloading is also critical for the same reason.

Another consideration is the ability to synchronize the label printing with the applicator. If a label is printed before the applicator is ready to accept it, it may get in the way of the application process or even jam the mechanism. A separate port for interfacing to the applicator and controlling the print cycle is needed.

While it is possible to adapt a standard label printer to meet some print and apply applications, it is much more desirable to use a printer that is designed for such applications, such as the SATO "5" model printers. These printers are designed to be mounted in application machinery and provide reliable service. SATO "5" printers are the printers of choice for these print/apply applications.

SATO BAR CODE LABEL PRINTER SUMMARY

Specifications subject to change without notice.

SATO BAR CODE LABEL PRINTER SUMMARY (cont'd)

(1) User changeable Interface Cards. Either Serial or Parallel specified at time of order Specifications subject to change without notice.

SATO BAR CODE LABEL PRINTER SUMMARY (cont'd)

Specifications subject to change without notice.

Copyright � 1998
Sato America, Inc.

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