Pretreatment of Nylon fabrics (Polyamide)

PREPARATIONS OF FABRICS FOR DYEING 
Preparation of fabrics for dyeing is very important as the final result depends on it. The main operations are:

- Scouring
- Drying - Heat-setting

SCOURING

Before heat-setting and dyeing it is advisable to remove the finishing oil from the polyamide yarn and, in the case of mixtures, that from the elastomer yarn. 

The finisher must know the type and quantity of finish on the polyamide yarn in order to decide on the best scouring conditions.
The quantity of finishing oil on Nylstar polyamide yarns is generally the following:

1% on flat cops yam (FDY)
1.2% on flat tubes yarn (FOY)

The main ingredients of the finish are lubricating, antistatic products and emulsifiers. The main purposes of finishing are the following:

- to ease sliding of the yarn on the mechanical parts of the looms
- to avoid electrostatic charges

On articles made in multifilament polyamide yarns removal of the finish does not entail particular problems as the products used are emulsionable and therefore easy to remove.

Scouring is carried out as for fabrics in standard polyamide yarns.
The scouring bath is prepared with:

0.5 - 1 g/l anionic or non-ionic detergent

Eg.
Diadawin EWN.....................- Bayer
Sandoclean PC....................- Clariant
Ultravon GP.........................- Ciba
Kieralon OL..........................- Basf
Veralon NKS........................- Rudolf

An alkaline agent
9- 11pH

e.g.
Sodium carbonate or
trisodium phosphate

If necessary, a 1 - 2 g/l dispersant

Eg.
Avolan IS............................- Bayer
Sandopan LFW...................- Clariant
Setamol WS.......................- Basf
Irgasol DAM........................- Ciba

Temperature:.........70°C - 80°C
Time:....................20 minutes

This is followed by rinsing in hot and cold water.
Scouring is carried out in continuous washing machines or in the open-width beam or overflow rope-dyeing machines.

 SCOURING OF PA MULTIFILAMENT AND ELASTOMER YARN FABRIC MIXTURES

Fabrics made in multifilament polyamide yarns in a mixture with elastomer yarns are scoured by techniques similar to those already used for fabrics made in standard and elastomer yarns.
Two processes are adopted:

A) Scouring in a solvent with perchloroethylene in continuous scouring machines (e.g. Sperotto machine). This is the best method of removing finishes from elastomer yarns with a silicone oil base.

B) Scouring in an aqueous bath in continuous washing machines, such as for example:
Eltex- Noseda
Arioli
Monfort
Babcock

In the above machines the process can be carried out as follows, e.g.:

1st beck: 
water (overflow washing)

2nd - 3rd becks:
80°C
pH 9-11..with trisodium phosphate or
..............sodium carbonate or
..............caustic soda

Detergent
eg..........Diadawin EWN........- Bayer
..............Hostapal FA...........- Hoechst
..............Sandoclean PC.......- Clariant
..............Ultravon GP............- Ciba
..............Tanaterge CW.........- Tanatex
..............Solvipol ELC...........- Lautex

Dispersant
eg..........Avolan IS..................- Bayer
..............Irgasol DAM.............- Ciba
..............Setamol WS............- Basf
..............Sandopan LFW........- Clariant

4th beck: 
rinsing in hot water

5th beck: 
rinsing in cold water and neutralisation with acetic acid

Note: a possible scouring product could be the Diadawin ESW detergent, from Bayer, which is specific for removing finishes from elastomer yarns.
(We advise consulting the technical information supplied by Bayer on this subject).

 HEAT - SETTING

This process is required for fixing the final dimensions of the fabrics (weight per
square meter, width) thus ensuring good dimensional stability.
Heat-setting is normally carried out before dyeing, although, the article permitting, it can also be performed at the end of the process.
The setting times and temperatures normally used for fabrics in multifilament polyamide yarns are the following:

..................Temperatures.........Times
PA 6..........180°C-190°C...........20-40 sec
PA 66........190°C-200°C...........20-40 sec

Note: in fabric mixtures with elastomer yarns the temperature and time conditions for setting these yarns are applied.
The temperature is normally between 180°C and 195°C and the times between 20 and 45 seconds.

BLEACHING

Polyamide yarns tend to yellow when heat-setting is performed on fabrics at a high temperature (over 180°C).
In order to obtain a good degree of white, bleaching with a chemical reducing bleach followed by bleaching with optical dyes are required. In some cases, particularly for nylon multifilament/elastomer fabrics, a protection agent may have to be used to reduce the possibility of yellowing during heat-setting (e.g. the product Spanscour GR - Sybron Tanatex may be applied for padding at the early stage of the process and before heat-setting).

A suitable process cycle is the following:

1 - Padding
with 10-20 g/l protection agent (e.g. Spanscour GR - Sybron - Tanatex)

2 - Heat-setting
in a stenter between 185°C and 195°C for 20-30 seconds. The temperature and process time should be regulated according to the following parameters: type of polyamide - PA6 or PA66 % elastomer yarn properties of the fabric (weight per sq. m).

3 - Preliminary scouring with non-ionic detergent - 1-2 g/l alkali
(e.g. sodium carbonate - trisodium phosphate) - 1-2 g/l
temperature:.....60°C - 80°C
time:................20 minutes

4 - Reducing optical bleaching in a single bath with:
stabilised sodium hydrosulphite - 2-3 g/l
e.g......Clarite PS........- Ciba
...........Blankit IN........- Basf
...........Arostit BLN.....- Clariant
x % optical dye
Possible addition of a bright blue or
violet acid dye in a minimum quantity, e.g. 0.0001%
pH = 4,5 - 5
Temperature:....90°C - 95°C
Time:..............30-45 minutes

4A - Reducing bleaching can be performed separately from optical bleaching for better whiteness.

Example of treatment:

-...First Bath
....5 g/l sodium hydrosulphite
....5 g/l sodium metabisulphite
....Temperature: 80°C - 85°C
....Time: 45 minutes

-...Neutralisation with cold hydrogen peroxide.

-...Second Bath
....2 g/l stabilised sodium hydrosulphite
....x % optical bleach
....Possible addition of acid dye,
....e.g. 0.0001%
....pH = 4,5 - 5
....Temperature: 98°C
....Time: 30 - 45 minutes

BLEACHING

Optical bleaches

Uvitex NFW.................- Ciba
Hostalux BN................- Hoechst
Leucophor PAT............- Clariant
Rucoblanc ADS...........- Rudolf
Blancophor CLE...........- Bayer

Optical bleach for
Padding - Heat-setting

This continuous process can be performed for fabrics which have to be printed
(for white backgrounds).
Dyeing must be preceded by preliminary scouring (e.g. in a solvent).
Padding is performed with:

optical dye x % gr/lt
organic acid pH = 5

The degree of whiteness with the method mentioned is less than that which can be obtained by the discontinuous process,
but may be adequate as a background for printing.

Suitable optical bleaches are:

Hostalux PR..................- Hoechst
Hostalux PN..................- Hoechst
Leucophor PAT..............- Clariant
Blancophor CLE.............- Bayer

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