Chemistry Reference
In-Depth Information
Dyeing composition may be introduced at any stage of polymer synthesis in the form of
powder, suspension, paste. For this type of dyeing the stage of paste production, containing
up to 30% of organic dyes and not more than 15% of pigments in different carriers
(monomers, oligomers and so on). This method is rational and economic while producing
large lots of synthetic fibres at large - tonnage continuous machines; however all this
prevents the production of wide range of dyed polymers because transition from one colour to
another is difficult and this requires technological equipment cleaning. Besides, long process
(6-12 hors) leads to the dyes destruction. This is shown in the two-tones of painting
throughout the whole technological process and requires application of very thermostable
dyes. Methods of PA-fibre dyeing in mass (before polymerization), in granules and in the
melt are considered in the work [87]. TiO2, pigments on the basis of
Fe, Cr, Cd
oxides,
ultramarine, phthalocyanine pigments are usually introduced before polymerization. PA
granules dyeing is carried out by direct mixing with pigment powder in dry and wet form.
Metallocomplex and acid dyes in ratio of 1:2 are used for such painting, but some part of the
dye gets into waste waters and this leads to economic problems. These defects may be
eliminated if the dye is introduced directly into finished polymer mass. Polymer dyeing in
mass through the stage of producing polymer concentrate of the dye (PCD) may be very
important [88]. In this case methods of dyeing at polymer synthesis and by introducing dyed
composition into polymer melt are coincided. Producing polymer concentrate of the dye is
fulfilled during the process of polymer synthesis in the presence of large amounts of the dye
(up to 50% from polymer mass).
Both initial granulate and ground industrial wastes of polymer may be used according to
this method (similar in similar). Dyeing may be carried out according to both periodic and
continuous scheme because more uniform distribution of the dye in polymer mass is achieved
here and this gives the opportunity to get the best monotone painting of the fibre throughout
the whole technological process. However, during this method only very thermostable dyes
may be included into the assortment, because the process is carried out at high temperatures
(250-280˚C) during the long time. But as PCD is the composition of resin-dye with the
dyeing component content from 10 to 50%. The role of dye thermal stability is high and it is
desirable that the nature of resin in PCD should be the same as of granulate being dyed.
Dyes for Polyamide Dyeing in Mass
Dyes, used for thermoplastic polymers dyeing, may be divided into two groups: dissolved
in spinning melt and high-dispersed pigments which must be uniformly distributed in
polymer melt and provide stable dispersions. Both groups have their advantages and
disadvantages. In the first case high demands are made on dyes solubility and in the second -
on the degree of dispersion of dye particles.
Use of dyes does not require fine dispersion and, being dissolved in polymer melt, they as
a rule do not influence physico-mechanical properties of the melt and dyed fibre but
sometimes improve them. Besides, the amount of dye, necessary to get bright tones of dyed
fibre is less than at using pigments. However, dyes are mainly less thermostable and that is
why they withstand less time of staying in melt. Light stability of the fibre, painted by these
dyes, is also less in most cases which shows feasibility of purposeful search and synthesis of
new dyes, especially meant for PA dyeing in mass.
As pigments, which are widely used in manufacture of dyed PA, titanium dioxide - first-
rate bleach; coloured mineral pigments, containing black or black with paraffin [89] have
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