Thermal Transfer vs. Direct Thermal
Dots Per Inch (DPI)
Thermal Transfer vs. Direct Thermal
Thermal Transfer (TT):
Thermal Transfer printing is when the heat from the printhead is applied to the ribbon. The material on the ribbon is then transferred to the label media. As you'll read later, this method is easier on the printhead, as the back of the ribbon is very smooth and protects the printhead from the friction of the media. Because TT printing uses a ribbon, it also opens up other options regarding the type of ribbon and label media. More information on media is offered later.
Direct Thermal (DT): Direct Thermal printing is where the printhead comes in direct contact with the label media. There's a coating on the label media that turns black as heat is applied to it. Because of this, no ribbon is required.
You might be thinking that this would be a less-expensive method of printing because you don't have to buy ribbons. However, this method will also wear down the printhead faster than with thermal transfer. Paper is coarse and will break the printhead down over time. Also, the edge of each label strikes the printhead, causing further breakdown. You won't have to buy ribbons, but you'll have to buy more printheads, which are expensive. The bottom line is that there is little-to-no difference in the cost of operation between TT and DT.
Another downside to DT printing is that the labels will turn yellow over time, and the print will fade to a faint gray. Overnight carriers typically use DT labels because the labels only need to last a day or two. It is reasonable to expect a DT label to last about 6 months.
One last thing to remember - heat is what causes the label to change from white to black. Keep the labels from storefronts, jewelry cases, and lighting centers.
Dots Per Inch (DPI)
The quality of the print is many times directly related to the density of the printhead. An image appears on a label due to a single dot or series of dots being turned on. The greater the number of dots, the clearer the image.
Printheads come in five different densities: 152 dpi, 203 dpi, 300 dpi, 406 dpi, and 600 dpi. Be sure to get the printer that best suits your needs. For example, you may want to print "100% UPC." In this case, you would need a printer with at least a 152-dpi printhead. A barcode is measured in mils, which is 1/1000th of an inch. If you need to print 15 mil barcodes, then the width of the narrowest bar in the barcode would be 15/1000ths of an inch wide.
You need to know the width of a dot on a printhead to make sure that you get the proper printhead. Remember that dots are measured in mils and that an inch is 1000/1000. Consider the 203-dpi printhead. Take 1000/203 to calculate the width of a dot on a 203 dpi printhead, which is 4.926 (just round it up to 5) mils. Therefore, if you want to print a 15-mil barcode, a 203-dpi printhead would work. Each dot is 5 mils, turn three of them on, and you've got 15 mils! Think about a 300-dpi printhead. 1000/300 = 3.333, or just round down to 3. So, if you buy a printer with a 300-dpi printhead, then 3 mils x 5 = 15 mils!
If you don't care about printing barcodes, but want to print labels with pictures, then you'd want to get a printhead with the greatest density. If you are printing barcodes and don't care about the specific mil of the barcode, then 203 dpi would probably be your best bet.
To print an image, the printer must store a portion, or all, of that label image in its memory before it prints the label. There are different types of memory that serve different purposes. Manufacturers may use different terminology, but as long as you understand what those differences are, then you can apply their terminology to the memory's function.
SRAM / DRAM: A printhead may be the proper density to print a picture on a label, but the printer may not be able to store that entire image up in memory. This is where SRAM or DRAM comes into play. This gives the printer the ability to allow the printer to print a longer label, as well as store that large image in memory. Any data stored in SRAM or DRAM will be lost when the power to the printer is turned off.
Flash: "Flash is like a floppy." If the printer has to wait for the host to send an entire image down every time it wants to print it, the printing is going to be very slow. Having Flash memory will allow you to store the image on the printer, which will greatly speed up the printing of the label. It's like a floppy diskette because it is permanent storage and does not require power for the data to be maintained. In some cases, it is also portable.
Media Matching: Labels and ribbons come in different varieties. Labels can be paper, polyester, polyolefin, or polyproylene, to name just a few. Ribbons can be wax, a mix of wax and resin, or resin.
A printer with a serial port will almost always connect to the serial port of a PC. Serial ports on a PC are always male, and have 9 or 25 pins. Though the pinouts of the serial port on a PC are always the same, the pinouts for the serial port on a printer are not always predictable. Many times, a "null modem" cable is all that's needed, but other solutions may be required.
The parallel port on a PC is always 25-pin female. Again, most printers with a parallel port will have a Centronics interface, but may require other interfaces. You may wish to connect the printer to something other than the parallel port on the PC. There are devices available on the market that plug into the Centronics parallel port on the printer and convert the parallel ports to Ethernet or USB. More on Ethernet and USB options later.
Universal Serial Bus (USB):
This is new, but much needed technology. USB is faster than serial or standard parallel communications (ECP/EPP parallel is faster than USB), allows you to connect up to 127 devices to a single PC, and can go as far as 82 feet away from the PC. Serial is limited to about 50 feet and parallel to about 15 feet.
"10Base-T" and "10Base-2" are terms that you'll hear associated with Ethernet. 10Base-T uses phone jack (RJ) connections, while 10Base-2 uses coaxial (like your cable television cable) connections. Having an Ethernet port on the printer will allow you to connect the printer directly to your network, thus negating the need for a PC to function as a print server.
A Twinax (5250 emulation) interface is required for connecting a printer directly to an IBM AS/400 or IBM 3x System.
A coax (3270 emulation) interface is required for connecting a printer directly to an IBM mainframe system.
Regardless of the manufacturer, every thermal printer manufacturer has a proprietary printer language that they use for their printers. In some cases, the manufacturer has some printers that use one language and some printers that use a different language. Programming guides for these printers are generally available on the Internet, but will certainly be available in print.
There is software available that will enable you to design and print a label to a long list of printers from different manufacturers using a graphical user interface. Using these tools, you also have the ability to use incrementing fields (print the number 1, then the number 2, etc.), pull data from a database, automatically wrap text, and much more. Granted, it does take some savvy on the part of the user to be able to use all the features of these software packages, but it does not require the expertise of a programmer.
Finally, how many inches of labels a day would you like to print? Printer manufacturers make printers for different applications. Just like you wouldn't take your Honda Civic out to pick up a load of mulch or firewood, you wouldn't recommend a printer designed to create labels for a small boutique when you need a printer for a warehouse that will be printing 20,000 inches of labels every day. This also works hand-in-hand with print speed. If you need to print 20,000 inches of labels every day, you are probably going to want a printer that can print faster than 2 inches per second.