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DYE QUANTITY EFFECT OF LUSTRE

It is known that, for a given quantity of dye, the appearance of a yarn greatly affects the colour obtained after dyeing.
The duller the yarn, i.e. the higher the percentage of titanium dioxide it contains, the lighter its subsequent appearance.
In practice full-dull yarns require a higher quantity of dye to obtain the same colour.
As a result the wet fastness of multifilament full-dull yarns is less than that found in standard filament semi-dull yarns.

EFFECT OF FILAMENT DTEX ON QUANTITY OF DYESTUFF REQUIRED FOR OBTAINING SHADE

EFFECT OF THE YARN LUSTRE ON THE QUANTITY OF DYE REQUIRED FOR OBTAINING A COLOUR

DYE KINETIC (DYE ABSORPTION RATE)

In general the dye kinetic of a material is affected by the specific surface area of the filaments.
For multifilament polyamide yarns the dye kinetic is distinctly faster than that of standard polyamide yarns in relation to the larger specific surface area of the filaments

Contrarily, parameters such as:

- titanium dioxide quantity
- section shape

have little or no influence on the dye kinetic.

The aforementioned different behaviour between multifilament and standard
filament yarns must be taken into account in the dyeing technique, in particular in the rise in temperature during heating of the dye bath, which in the case of multifilament yarns must be much slower and more gradual.


DYE FASTNESS

As mentioned previously, the increase in the quantity of dye required for multifilament polyamide yarns leads to a decrease in wet fastness of the dyes, above all with dark colours and more particularly on full-dull yarns. In order to obtain better wet fastness (washing,
perspiration, water etc.), selected dyes have to be used and a post-treatment with synthetic tannin performed. Contrarily, parameters such as:

- titanium dioxide quantity
- section shape

have little or no influence on the dye kinetic.

The aforementioned different behaviour between multifilament and standard
filament yarns must be taken into account in the dyeing technique, in particular in the rise in temperature during heating of the dye bath, which in the case of multifilament yarns must be much slower and more gradual.


SELECTING DYESTUFFS

The classes of dyes suitable for dyeing multifilament polyamide yarns are the same as those used for standard polyamide yarns.
The dyes to be selected for multifilament yarns must fulfil the following
specifications:

- good colour yield;
- good cover of differences in dye affinity;
- three-colour elements with comparable dye uptake rate and degree of migration;
- good fastness.

Thus a compromise has to be reached between the various requirements, accepting that some of them conflict.
It is however true that:
acid dyes cover dye affinity differences to a greater or lesser extent, but may have minimal fastness to wet treatments in the dark colours. Premetallised dyes have good fastness to wet treatments but a low degree of cover of affinity differences (like reactive dyes and some direct dyes).
Premetallised dyes can be used in certain cases (advisable for black), but for other colours dyeing is performed at the responsibility of the dyer (risk of stripes).
Thus the following are used:

For light colours:
acid dyes with good cover of affinity differences and excellent migration power.
For example:

Acidol E....................- Basf
Tectilon.....................- Ciba
Nylosan E.................- Clariant
Nylantrene B.............- Crompton
Telon........................- Dystar

For medium and dark colours:
acid dyes with good wet fastness but little cover of affinity differences.
For example:

Acidol X.....................- Basf
Erionyl.......................- Ciba
Polare........................- Ciba
Nylosan N..................- Clariant
Nylosan F..................- Clariant
Nylanthrene C............- Crompton
Telon A......................- Dystar
Supranol....................- Dystar


For black:
1 : 2 premetallised dyes
For example:

Colour Index Acid Black 194:
Acidol M-SRL black........- Basf
Erionyl M-RN black.........- Ciba
Lanasyn S-DL black........- Clariant

Colour Index Acid Black 63:
Erionyl M-BN black..........- Ciba

Colour Index Acid Black 172:
Lanasyn S-DB black........- Clariant
Neutrilan ARB black........- Crompton

DYEING PROCESS

Fabrics made in multifilament polyamide yarns are dyed at a maximum temperature of between 98°C and 110°C (98°C in the case of PA - elastomer fibre fabric mixtures).
Open-width beam dyeing is normally performed in a static pressure autoclave, on rope-dyeing in overflow.

A = Addition of auxiliary products (levelling and lubricating agents) and adjustment of pH.

B = Addition of pre-dissolved dyes.

C = Rinse.

D = Post-treatment with synthetic tannin

LEVELLING PRODUCTS

Both anionic products with affinity for polyamide yarn and slightly cationic products with affinity for the dyes, and products containing premixed anionic and cationic products are used, for example:

LUBRICATING PRODUCTS

For overflow dyeing, some types of fabric may be subject to creasing and therefore require the use of lubricating products which are added to the dye bath.
By acting as lubricants, these products prevent the creases which form during dyeing from fixing in specific points.
Examples of products: