The dyeing temperature for these types of dyes is 800 C. If
the reactive group is monofunctional such as monochlorotriazine it will be
called hot brand dyes.
Typical Brand name for these dyes is Procion H E Dyes.
Why do dyes have different colour strengths between batches?
This can happen for a number of reasons. Dye manufacturers mix
the dyes with other compounds which are not colorants to give them various properties. The proportions that are added are not always identical from batch to batch.
Depending on the quantity of colorant or other compounds in the dye the colour
strength for a certain weight of dye will be different (so all new batches of
dye should be tested).
Does the quality of dye decrease over time?
Yes, the quality of dyes can decrease in two main ways. Firstly,
dyes can also absorb water which makes them heavier, so when they are weighted
out for a recipe, less colorant is actually weighted out than needed. Secondly,
dyes can react with water in the atmosphere and hydrolyze. This means that the
reactive group has reacted with the water and will not be able to react with
the cellulose (fabric), the desired depth of shade may not be achieved in the
dyeing. To address the problem test dyeings should be carried out in the
laboratory with dyes before they are used, especially if they are not used
regularly. The recipe may then need to be adjusted.
How do you prevent dye quality from decreasing?
Dyes should be kept in airtight containers and lids should
be replaced immediately after use. Storage rooms should be kept as cool and dry
as possible.
What are the requirements for selecting compatible dyes?
Compatible dyes are dyes which build up on shade in that
they increase in depth as the dyeing progresses to one single shade.
Incompatible dye mixtures build up off shade making shade matching very
difficult. The dye supplier should be able to specify which dyes in his range
are compatible.
Fixation should be what for reactive dyes?
Fixation for reactive dyes will depend on the type of
reactive group, dye quality, process parameters and process optimization. After
considering all these factors, fixation can typically be in the region of 77%.
How can fixation be measured?
Fixation can be determined by the analysis of the amount of
dye in the dye bath at the start and end of dyeing. The analysis requires the
use of a spectrophotometer which gives values of dye concentration within the
dye bath. The percent exhaustion and percent fixation can be calculated by
using the figures obtained from the spectrophotometer.
What are the parameters that a dye manager should consider
while selecting any dyeing process?
While selecting any dyeing process the parameters the dye
manager should consider:
- Whether the process is compatible with all the dyes he
has selected
- Whether the process is suited for the machine in terms
of temperature, pH, and material of construction and that he is able to
control these necessary parameters adequately that the dyes he has
selected give the fastness requirements specified by the buyer
What is uneven dyeing?
'Uneven' or
more correctly un level dyeing is a term used to describe the distribution of
dye over the whole substrate. If a dyeing is unlevel light and dark patches or
areas of dye can be seen when comparing different areas of the substrate. These
patches may be of the same hue being light and dark or of a different hue if an incompatible dye mixture has been used. Unlevel dyeing
may arise from a variety of causes, some are highlighted below:
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