4.. Dyeing polyester with disperse dye(example of type III)
1) Characteristics of the rate of dyeing
In polyester dyeing, the thermal motion of the polymer chain and also the
dye-sites increase with the temperature rise then the dye uptake corresponding
to the dyeing temperature is determined as shown in Figure 6.
For example, when the absorption curve of a dye at X%(o.w.f.) dyeing is shown
as a, in the less than X%(o.w.f.) dyeing the dye uptake is the same as that of
at X%(o.w.f.) dyeing until this concentration of the dye is absorbed, and after
that the absorption ends due to the absence of the dye in the dyebath.
Therefore, the absorption curve is expected to be b, but the actual absorption
curve becomes c with a S-shaped curve, because of the decrease of the dye in
the dyebath.
| Figure 6 Relation between the concentration
of dye and rate of dyeing in disperse dyeing |
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Therefore, the absorption curve of the dye at X%(o.w.f.) or at X/2%%(o.w.f.)
is shown in curve a or curve c in Figure 6.
Dependency of absorption curve on the concentration of dye is shown in Figure
7, from which it is obvious that disperse dye is absorbed on the basis of the
principle shown in Figure 6, that is, in the paler shades the dyeing proceeds
at lower temperatures and at deeper shades it proceeds at higher temperatures.
| Figure 7 Relation between concentration
of dye and rate of dyeing curve |
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Changes of the rate of dyeing curve corresponding to the changes of the rate
of temperature rise are shown in Figure 8.
The dye uptake during the temperature rise depends on the dyeing temperature
in the range of normal temperature rise conditions (0.1～5℃/min.)
, but not on the time, therefore, the rate of absorption can be controlled by
the rate of temperature rise.
| Figure 8 Relation between the rate of
temperature rise and rate of absorption curve |
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From Figure 8, it is obvious that a reduction of rate of temperature rise
to half leads to a reduction of the rate of dyeing to half and an increase of
the rate of temperature rise to double leads to an increase of the rate of dyeing
to double.
Therefore, the rate of dyeing can be quantitatively controlled by the rate
of temperature rise, and the optimum rate of dyeing can be easily settled.
2) Dyeing cycle for level dyeing
It is very effective for rationalized dyeing to draw up a dyeing program by
settling the starting point and ending point of critical temperature range from
the rate of dyeing curve corresponding to the individual dye and its concentration.
In this case, the starting point is the temperature at which the absorption
is about 20% and the ending point is the temperature at which the absorption
is about 80%. In this critical temperature range, the temperature must be controlled
carefully.
It is complicated to determine the critical temperature range for individual
dyeing, therefore, the dyeing cycles are gathered up into three types for rationalized
dyeing as shown in Figure 9. One of these types is effectively applied to each
individual case of dyeing according to the dye used and its concentration.
| Remarks |
| (A) |
Water is poured into the vessel and material is loaded at lower than the
starting temperature of dyeing. After the addition of auxiliaries and pH adjustment,
dye is added and the temperature is raised according to the heating capacity. |
| (B) |
In this temperature range, an optimum rate of temperature rise should
be employed depending on the leveling capacity of the dyeing machine, referring
to the concepts of area exchange and circulation. |
| (C) |
In this temperature range, the temperature can be raised according to
the heating capacity because the levelness is hardly affected by the rate of
temperature rise. |
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