Inkjet printers are a fantastic invention however they can be problematic if
they are not used regularly or correctly. Most users will automatically
blame the ink cartridge if there's a printing defect however the truth is
that it is almost never the cartridge at fault.
Let's take a
detailed look at the inkjet printhead and discuss the causes of printhead
clogging and the cleaning solutions. We will also discuss ways in which you
can prevent your printhead from clogging in the first place. The image to
the left is of a typical Canon printhead. This is what they look like with
the cartridges removed and the individual nozzles exposed.
The Canon Printhead Explained ( Thermal Printhead )
The Canon printhead is whats known as a "Thermal or Bubblejet Printhead". It
uses thousands of micro size resistors in each colour nozzle to heat up the
ink and literally spit it out onto the paper. As the ink rapidly heats up
due to the increased temperature of each resistor it creates a series of
bubbles. This is much the same effect as boiling any type of liquid and
seeing the rush of bubbles coming to the surface and releasing the expanding
Once the bubble gets hot enough and explodes and has spat the ink onto the
paper the air starts to cool down as it rushes in to replace the expelled
air from the bursting bubble. In turn it starts to suck more ink into the
minute nozzle and again starts heating it untill it also explodes. This
process continues at a very high rate untill eventually the image is fully
printed. The higher the print resolution the more nozzles are used.
Printhead cleaning cycles utilise all of the nozzles.
As the printing process continues ink is continually drawn into the
printhead nozzles and the void or vacuum that is left after the bubbles
explode continues to suck ink from the cartridges into the printhead.
The amazing fact is
that each printhead nozzle is actually smaller in diameter than a human
hair. This is the reason that a printhead can be prone to clogging.
The Epson Printhead explained ( Piezo Printhead )
The "Piezo Electric" Printhead as it is known is what all Epson printers
use. It uses an entirely different process to the thermal printhead in that
it doesnt heat the ink but actually uses an element which kind of acts like
a micro pump to push the ink out onto the paper.
Many people love
the piezo printhead as it is capable of producing much higher print
resolutions. This is achieved due to the Piezo head being much more finely
controlled and the ink flow being able to be adjusted far more accurately
than the thermal printhead. The biggest drawback is the fact that the Piezo
printhead is far more prone to clogging or blocking up with Ink.
The diagram to the left shows how the Piezo printhead works. A charge is
applied to the piezo electric element above each nozzle which causes it to
This creates a
pressure behind the element which draws ink into the nozzle chamber ready
for printing. Next step is to actually push the ink out onto the paper
To actually push the ink out through the print nozzle we now have to get the
element to move in the opposite direction to force the ink out of the nozzle
and onto the paper. To do this the charge to the element is simply reversed
so instead of pulling away it now pushes towards the print nozzle and forces
the ink out of the tiny opening and onto the paper.
As with the thermal
printhead the entire process is electronically controlled from the printers
firmware which tells the printer exactly what to do.
An overview of the operation of a Printhead
Hopefully you are not totally confused after reading about the printheads
operation. A printhead wether thermal or piezo basically operates as
follows. The ink cartridges all sit directly above the printhead, each
colour above it's corresponding print nozzle.
When we hit the
print button an electronic signal is sent to the printer and once it gets to
the printing stage the above processes take place. Each colour nozzle is
either turned on or off to print minute coloured particles according to the
electronic signal which contains all of the complex orders for the print
nozzles to follow.
The 3 main colours
Cyan, Magenta and Yellow as well as the black all print minute dots as
required and similar to a TV they all combine to form the various colours
and complete the printing of the image. What an amazing fete to know that
this incredibly complex process all takes place within seconds and how dare
we get angry when the printing goes pear shaped ( HaHa ).
So now that you are
an expert on the operation of an inkjet printer lets take a look at why
printheads clog up and some tips on preventing this from occurring.
Why does a printhead clog or block up
There are numerous reasons as to why printheads block. The actual cause of
the blockage is that ink dries or congeals inside or on the outer surface of
the printhead. Due to the microscopic size of the print nozzles (smaller
than the diameter of a human hair) they can quite easily become blocked.
Blockages usually show up as either gaps or lines in the printing, incorrect
colour or in the worst cases no print at all.
are known for clogging. Epson are the leaders in clogging as the nozzles are
very small to achieve the high print resolution and they are just known for
clogging up. Brother printers have a common issue with the Black nozzle
clogging. As to why this occurs no one seems to know.
Here are the main
causes of printhead clogging:
Lack of printing - If
the printer sits around for long periods of time the ink can dry inside the
printhead and result in clogged nozzles.
cartridges when prompted by the printer - this is
also a leading cause of printhead clogs. If you print for too long on a near
empty cartridge you will start introducing air into the printhead which in
turn helps dry any remaining ink inside the printhead and results in clogged
grade generic cartridges - low grade cartridges with
the wrong ink viscosity can also quickly clog the printhead. Make sure that
you purchase your non genuine cartridges from a reputable source.
Dirty or faulty
purge pump or pads - If your printer has very dirty
pads on the purge pump then the printer will be unable to effectively run
cleaning cycles. During the automatic cleaning cycles that your printer does
periodically large amounts of ink are sucked through the printhead and out
into the waste pad. This helps to clear any dried ink or residue that may
cause printhead blockage. If either the pump is faulty or the pads very
dirty then little cleaning occurs and blockage is highly likely.
breathing correctly - If one or more cartridges do
not have the breather tape fully removed then the ink will not flow properly
from the cartridge and into the printhead.
And finally - How to clean a printhead
For printers with a removable printhead the easiest cleaning method is to
remove the printhead and flush it ( from the cartridge side ) under a hot
water tap. This is the easiest method for earlier Canon printers which have
removable printheads. Keep the water gently flowing untill all of the ink is
flushed out and the water comes out clear. If the blockage still occurs you
will need to soak the offending nozzles in a printhead
without a removable printhead you will need to open the printer as if you
were going to change inks. When it comes to the rest position and is
accesible quicly pull the power chord out so that the printhead remains in
an easy position to work on.
If possible lay
some blotting paper folded and soaked in cleaning fluid under the printhead
carriage and then move the printhead over the top of the blotting paper.
This helps to clean the outer surface of the printhead. You can gently run
the printhead carriage back and forth over the blotting paper to help clean
the printhead surface. Next insert around 2-3ml of cleaning solution into
each of the clogged nozzles and allow it to soak for an hour or so.
After this you can
replace the cartridges, run a printhead clean and then see if the problem
has been solved. If not you may need to repeat the process and let it soak
for a longer time.
If a certain colour
is clogged you can try putting the printer into its highest resolution print
mode and try to print a full page of that one solid colour. This is
basically the same method your printer uses when performing individual
It is extremely
common for a printhead nozzle to become blocked immediately after replacing
one or more cartridges. There are several reasons for this such as air
getting introduced into the nozzles, excessive ink pumped into the nozzles
straight after a cleaning cycle or the purge pads partly or fully blocked.
This prevents the purge pump from properly sucking the ink from the new
cartridge into the printhead therefore appearing as a partial or full
blockage of certain nozzles.
Cleaning the purge pads on your printer
The purge unit is usually situated on the right hand side of the printer
underneath the printhead carriage rest position. The image to the left shows
a typical Canon purge unit with a colour sponge and a Pigment black sponge.
These sponges are
surrounded by a rubber edging which forms a tight seal against the printhead
which helps the purge pump to suck ink through the printhead during cleaning
cycles. This excess ink is pumped directly into the waste pad below the
printhead carriage. To test if the purge unit is working correctly you can
fill each pad with a few ml of cleaning fluid untill you can see a small
pool form. If this pool of fluid leaks away within a few minutes then there
is an issue with the purge unit. ( a leak )
Close the printer
and let the printer run a cleaning cycle. Open the printer back up and check
that the fluid has all gone. If the purge unit is working correctly then the
fluid will all be gone as the pump will have sucked it all up and into the
waste pad below.
Many older printers
have faulty or dirty purge units and this is often a major cause of
printhead clogging. Make sure that you check the purge unit if you cant seem
to unblock the print nozzle and keep it clear.
Another thing you
can check is that the rubber surrounds around the purge pads are not damaged
or distorted. If they are not firmly sealing against the printhead then the
pump will not work correctly. If they are only distorted sometimes you can
reshape them a little by gently pressing them into shape with a pencil etc.
Types of printhead cleaning Solutions
There are various types of cleaning solutions on the market and they vary
greatly in their effectiveness. Many are purely detergent based which is
okay for cleaning printers using generic ink as all generic inks are water
based. For genuine ink blockages a more aggressive solution is needed.
At Ink Hub we have
experimented with various solutions and our current formula is from a
company called "Sensient" and we have simply added about 10% of Aqeous
Ammonia to give it a bit more of a kick. As much as I dont like using
ammonia it seems to have a better ability to break down dried ink.