| Whenever I enter an organization's
lobby or office I closely examine the plaques on the walls,
especially those made using laser sublimation. It amazes me
how many examples of bad laser sublimation work are sold professionally.
Most often I see fuzzy text, blurriness around the edges of
the characters and in general, an “out-of-focus”
appearance.
Laser sublimation should be very crisp. Text should not
have the slightest blur or fuzziness around the edges. Solid
areas should be solid black, with no unevenness or splotchiness.
Indeed that's one of the principal advantages of laser sublimation
(versus inkjet) is it's outstanding opacity and covering power.
This makes it the favorite choice when heat pressing images
onto metal.
It's not that difficult to produce perfect laser sublimation.
It's entirely a matter of adjusting a few variables and doing
a bit of fine tuning.
To demonstrate this point, let's make up a quick test image.
Workings in your usual text program, using a font like Times
Roman, write a line of six point text that reads, “This
is 6 point type.” Underneath that line of text make
a two inch line about 1/4" thick in solid black. This
little image will enable you to determine the correct pressing
time for your system. You can make test samples that are much
more elaborate, but it's really not necessary. Run off six
copies of this test image, and save the file for future use.
Set your heat press for 340º F. The controls and instrumentation
vary from press to press, so take a few minutes to really
understand what your press is doing. You'll need to watch
two complete cycles — from when it turns on to when
it turns off — and answer a few basic questions. At
what temperature does the press turn off, and then at what
temperature does it turn on? You need to know the range of
temperatures the press will allow, and the hottest and coolest
the press is likely to reach during the heat pressing cycle.
If the press allows a range of 15º or so between hottest
and coolest, this can dramatically affect the quality of your
outcome.
You want to set the press to 340º F in the middle of
your range. In other words, if your range is ten degrees,
then set the press to turn on at 335º F and off at 345º
F. A range of ten degrees isn't a problem if you set your
target temperature in the middle.
If your press has a fluctuation greater than 15º, you
need to watch the temperature every time you press sublimated
products, and make sure you're in the 335º to 345º
zone before pressing. Some people who have presses with wide
temperature ranges set their desired temperature at the low
end of the range, and wait until the press first turns off
before they use it.
Set your press for firm, solid pressure. This also is an
adjustment that varies from press to press, but for laser
sublimation work, you'll want a lot of pressure. On a clamp-type
press it should take considerable manual pressure to close
the press.
Sandwich the test print against a piece of sublimation-receptive
engraving metal. Make the test sample by pressing the job
through the protective plastic masking on the metal. For production
purposes you can press either way, with the plastic on or
off, but to calibrate your system, I'd suggest leaving it
on. Pressing with the plastic on requires a more exact time
than with it removed. By achieving an excellent result with
the plastic on, you'll yield the best possible result whether
you prefer to work with the plastic masking on or off.
Usually your sublimation toner supplier will provide a suggested
pressing time and temperature, based on their toner mixture.
For our toners, we suggest starting at 340º, with firm
pressure, for 15 seconds. If you've never calibrated your
system before, we'd suggest “bracketing” your
pressing time, for example — make one sample at 13 seconds,
one at 15 seconds and one at 17 seconds. Allow each test plate
to cool for about a minute.
Peel off the paper (with the plastic melted in) and place
the pieces of metal side by side. First of all, evaluate the
printed text. You may want to look through a magnifying loupe.
The characters should be clear and crisp, with no filling
in. Now look at the solid area. Is it really solid? “Bubbles,”
splotches or light spots are indications of insufficient heat
or time. Also, text with a purple or red cast is an indication
of “undercooking.” These symptoms usually go away
with one or two more seconds of pressing.
One of your tests should have produced a really perfect
sample. If not, you can probably figure out which direction
to try next, more time or less time. You'll need to keep fine
tuning until you've produced one perfect test sample. You
can add a second or subtract a second — whatever is
appropriate — until you have one perfect sample. You'll
want fine, crisp characters and dense, bold, solid black.
If changing pressing times doesn't produce a strong enough
black, you may need to go back and adjust the density setting
of your printer. Generally, we advise customers to set their
density at the lowest setting that makes an acceptably dark
print. This prevents wasting toner and extends the life of
the cartridge. But cartridges change during the course of
their lives. Density usually should be readjusted once, possibly
twice during the life of a long-life cartridge. If the cartridge
isn't printing dark enough, change the printer density setting.
Some printers have density settings on the printer; some
are controlled from the computer. Check your manual to determine
how to control your density setting. Now you should have a
perfect sample, and more importantly you should have a perfect
time and temperature for your system.
Let's assume its 340º for 15 seconds.
To consistently produce perfect laser sublimation you need
to know what can cause changes and what problems are likely
to happen.
First of all, you'll have to get to really know your heat
press. Do you have even heat distribution across the entire
platen or do you have hot spots and cool spots? The easiest
way to check this out is to make a grid, like a sheet of graph
paper, and sublimate it. I made my grid with 1/8" squares.
An easy way to do this step is to scan in a page of graph
paper and print it out with sublimation toner.
|
My press is 16" x 20", so I
made four 8" x 10" grid sheets and taped them down
to four 8" x 10" sheets of metal. I laid out all four
on the press and “cooked” them for my ideal time
plus two seconds. I added two seconds to compensate because
my press cools off quite a bit when it's fully loaded with metal.
There is a relationship between how much “cool”
material is put in a heat press and how long it takes to press
it all. It's like putting a frozen turkey in a preheated oven.
Don't expect the oven to stay at 350º with twelve pounds
of ice in it. The same principle applies to putting a lot of
“cool” metal in a heat press.
Pressing the grid pattern made a “map” of hot
and cold spots on my heat press. I was surprised to find I
had a cold spot on my press.
If you know that one spot in the back left corner of the
press is cold, a simple work-around is to simply avoid using
that area. But first you need to know where the cool spot(s)
is.
Many presses rapidly lose their heat when completely loaded
with metal, and won't recover within the usual pressing time.
How long you'll need to increase the time is something you'll
need to work out with your heat press. Pressing 20 name tags
is likely to require more time than pressing one name tag.
Selecting the paper you'll use for printing laser sublimation
transfers can be very important. Even more important is knowing
that a change in paper can change your pressing time. Going
from a 20 pound paper to a 28 pound paper can require a full
second additional pressing time in order to get the same result.
Changing your metal stock, even from satin finish to gloss
finish, can also affect your pressing time. To be certain,
press one of your sample images on different stocks for the
standard time and evaluate the result.
Changing toner cartridges is an event that needs more attention
than simply removing one cartridge and sliding another in.
First you'll need to check the image density without pressing.
Make a sample print and adjust the density to the lightest
setting that makes an acceptably dark print.
Now press the test sample for the standard time and make
certain it produces a perfect result. A new cartridge usually
necessitates some slight calibration and some pressing time
adjustment to produce a perfectly sublimated test print.
If you are printing very large, heavy solids you may experience
“cratering.” Laser printers (virtually all laser
printers) have difficulty with large solid areas, tending
to weaken toward the center. You may get an image that's dark
black around the edges but weak in the middle. The heart of
a laser printer is the drum, which typically has a top layer
of photoconductive material. To make an image print black
you have to strike the drum with a laser beam, which discharges
a 700V surface charge off the drum. Everything else around
that discharged area has a high voltage charge, but that area
has been discharged entirely and thus attracts toner. The
larger the area that has been discharged, the harder it is
for all of that area to maintain full discharge. In other
words, the center of that area tends to pick up loose charges
and print less dark.
This is true of virtually all laser printers. Some printers
manifest this problem by printing dark the first revolution
of the drum and then printing lighter thereafter. This looks
like two to three inches of dark black at the top followed
by lighter black or gray for the rest of the page.
This problem can be eliminated by introducing a slight pattern
within the solid. Instead of trying for 100% black, try for
95% black. Put in a very small dot pattern. A field of tiny
black dots can hold a full discharge much more efficiently
than a vast solid area.
Another problem common to almost all monochrome laser printers
(printers which print only one color at a time) is creating
halftone and grayscale images without introducing new patterns
or moiré effects. Monochrome laser printers were designed
as office (text) printers, not as art or graphics printers.
This isn't true of the color laser printers, such as the HP
4500/4550, which reproduce excellent photographic images.
After a few hundred pages, the magnetic roller of a toner
cartridge begins to develop a slight unevenness. If you were
printing a solid screen of dots, this would look like dark
or light streaks down the page. In text work, this isn't apparent,
but in graphics it does manifest itself. This isn't a cartridge
defect — don't complain to your cartridge maker about
it. It's a design defect and it's true of new, off-the-shelf
HP toner cartridges as much as it is of remanufactured cartridges.
After a few hundred pages, the mag roller will introduce some
patterns into dot screens. This means simply that the best
quality dot screen and halftone work comes from a new toner
cartridge. Many laser sublimation cartridge makers change
out the magnetic roller every time they build a cartridge
to ensure the highest quality out of the box. We also recommend
that users who do a lot of graphics and halftone work buy
cartridges with smaller amounts of toner. There's no sense
getting a 240 gram cartridge if you need graphics grade quality
that may last only for 120 grams. The actual rate of image
degradation depends on the type of cartridge, the processes
used in its manufacture, and how fast the cartridge is used.
But it's universally true: for the best graphics, use fresh
toner cartridges.
To achieve perfect laser sublimation, set your press at
a relatively low temperature, like 340º, and find your
perfect time using a test image that has both fine text and
a solid black area. Know your heat press, its cool or hot
spots and its heating cycle, and know how these can change
your image. Know the factors that can change your perfect
pressing time, such as change in paper or metal, or changes
in the toner cartridge. Expect some adjustment to be needed
in the middle of long-life cartridges. Be aware of changes
in the environment, particularly ambient temperature or humidity.
Most of all be fussy. Demand a really good product from
your system, and be willing to fiddle a little to get it.
If you understand what causes problems and what causes changes
you can adjust and get a perfect laser sublimated product.
|
Hilton
Images, Inc.
Finest Quality Laser Sublimation Products