Thermal head - Mitsubishi P-91W Printer

Considering reviews I'd say price vs quality will make diference...
Also, you can buy ink cartridges for as low as 1 Usd each (recycled).

Check to see if your tags are meant for thermal transfer printing? Hope this helps!

clean thermal head roller with damp cloth or with isoprophil alcohol and dry it with dry cloth to remove static on the master and thermal head roller.

The following is from the Epson Users Manual:
Troubleshooting
No lights on the control panel
Check the power supply cable connections and the power outlet.
ERROR LED on (not flashing) with no printing
If PAPER OUT is on, the roll paper is not installed or is near the end.
If PAPER OUT is off, the printer cover is not closed properly.
ERROR LED flashing with no printing (and no paper jam)
Printing stops if the head overheats and resumes automatically when it cools.
If overheating is not the cause, turn the printer off, and after 10 seconds, back on.
Removing Jammed Paper
CAUTION:
Do not touch the thermal head because it can be very hot after printing.
1. Turn the printer off and press the cover open button.
2. Remove jammed paper, reinstall the roll, and close the cover.
3. If paper is caught in the cutter and you cannot open the printer cover, open
the cutter cover as shown in illustration J.
4. Turn the knob until you see a triangle in the opening. This returns the cutter
blade to the normal position. There is a label near the cutter to assist you. See
illustration K.
5. Close the cutter cover.
6. Open the printer cover and remove the jammed paper.
Cleaning the Thermal Head
CAUTION:
After printing, the thermal head can be very hot. Be careful not to touch it and
to let it cool before you clean it. Do not damage the thermal head by touching
it with your fingers or any hard object.
Turn off the printer, open the printer cover, and clean the thermal elements of the
thermal head with a cotton swab moistened with an alcohol solvent (ethanol, or
IPA).
Epson recommends cleaning the thermal head periodically (generally every
3 months) to maintain receipt print quality.

It sounds like your print head is overheating. Clean as instructed above.

• Thermal head — generates heat; prints on paper
• Platen — a rubber roller that feeds paper
• Spring — applies pressure to the thermal head, causing it to contact the thermo-sensitive paper
• Controller boards — for controlling the mechanism

I think that you may need to replace your thermal head, A line means there is a place that the head can not head or it cannot recieve data
http://www.youtube.com/watch?v=LWs74J7EfjM
How to matinence it and clean the head

your printer catridge has been faulty.so pls replace it.

Thermal heads wear out over time as the paper grates down the thermal head. You'll get to a point where the only thing you can do is to replace the head. Contact the manufacturer or service centers to where you can buy one

The printhead is a 300 dpi thermal. If you raise the head and can see the glass face, there are 2 rows of heating elements that are used in printing.
As in all thermal heads, do not use any sharp objects to scrape on the head. I usually use a non volitile citrus cleaner or iso alchohol.
The plate beneath the head should also be checked for wear and cleaned to provide positve drive for the stock.

Are you using thermal paper? Do you have the correct side up !

The thermal print head is damaged. You can try to clean it with a thermal printer head cleaner. That will only help if it is just clogged up with thermal print ink.