Impressions - February 2015 - 55

or water-based inks, you will require hot
forced air to drive the water or moisture
content out of the ink ﬁlm and fabric.
From a production cost and efﬁciency
standpoint, gas dryers allow for greater
versatility in the use of different ink lines
and typically perform more efﬁciently
than other alternatives.
The objective of a dryer is to bring
the entire ink-ﬁlm thickness to the required cure temperature. I emphasize
the entire ink-ﬁlm thickness because not
everyone considers the temperature of
the ink where it contacts the fabric. The
interface between the fabric and the ink
also requires the correct curing temperature. Should this portion of the ink ﬁlm
not reach the required cure temperature,
the result will be poor washability, cracking, and possible bleeding/dye migration
on synthetics and 50/50 cotton/polyester
blends. (see Figure 3)
One major consideration in determining if you are achieving and maintaining
a proper cure is to know the temperature
of the ink throughout its run through the

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dryer. There are three different methods
for determining an approximate ink temperature when a printed garment emerges
from the dryer. The ﬁrst - and perhaps oldest - test method involves using Thermo
Tapes. With this method, you apply heat
strips to the surface of the garment being
cured and the individual strips will turn
black as the ideal temperature is reached.
Once you have determined the point at
which you have achieved a proper cure,
the heat strips also act as a good qualitycontrol tool to ensure that your dryer is
achieving consistent temperatures.
Second, and most popular, is the noncontact pyrometer, which is useful not
only as a quality-control tool, but also
for determining cool or dead spots on a
ﬂash unit's infrared panels or within a
dryer. This tool reads the ink ﬁlm's emitted heat energy, also known as emissivity. Although this is the most widely used
tool for monitoring ink ﬁlms and dryer
temperatures, it still doesn't indicate the
temperature of the ink that is in contact
with the fabric.

Finally, the donut probe also allows you
to monitor the substrate's temperature as
it passes through the dryer and plot out
the temperatures in multiple positions.
Currently, this is the most accurate process for reading the actual temperature of
the inside of the ink ﬁlm.
A donut probe's thermocouples allow
you to place the wires directly into the
ink ﬁlm to read its actual temperature as
it passes through the dryer chamber. The
advantage here is that you can monitor
and document the substrate's temperature every ﬁve or 10 seconds as the probe
passes through the dryer. Doing so on
the left, center and right sides of the dryer
allows you to plot a 3-D chart of your
dryer's history. Figure 4 shows what
documentation would look like for a
dryer with a 60-second retention time.
Once you have determined the proper
dryer settings in relation to achieving the
proper cure, you can use any of the previously mentioned tools to monitor and
maintain them.
One issue that occasionally surfaces

February 2015 | Impressions

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Impressions - February 2015

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