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Polyamide pretreatment
GENERAL INFORMATION
Multifilament polyamide yarns were introduced and developed in response to a market demand for new articles with:
Multifilament polyamide yarns are used in warp knitting to manufacture various types of items for the following main sectors:
GENERAL INFORMATION ON FABRIC FINISHING CYCLES
The finishing cycles for multifilament PA and elastomer yarn fabric
mixtures are the following:
FINISHING CYCLE (A)
Finishing cycle with preliminary scouring 1 - Scouring in an aqueous bath or in solvent (perchloroethylene) in continuous washing machines; or double scouring: first in a solvent and later in an aqueous bath. During scouring simultaneous relaxation of the fabric occurs 2 - Drying 3 - Heat-setting in a hot-air stenter 4 - Dyeing open-width beam dyeing in an autoclave or in rope form in overflow 5 - Drying in a stenter 6 - Finishing
FINISHING CYCLE (B)
Finishing cycle with preliminary scouring 1 - Possible relaxation on table with steam (e.g. Sperotto or Arbach machine) or relaxation by steaming before entering the stenter 2- Heat-setting in a hot-air stenter 3 - Possible scouring before dyeing in the beam-dyeing machine in an autoclave or rope form in overflow 4 - Dyeing open-width beam dyeing in an autoclave or in rope form in overflow 5 - Drying in a stenter 6 - Finishing
FINISHING CYCLE (C)
Finishing cycle with pre-setting at low temperature and post-setting after dyeing In the case of dyeing in critical colours which require the use of acid dyes with high molecular weight and low levelling power, a finishing cycle can be adopted with pre-setting at a low temperature (normally between 150°C and 170°C) before dyeing. The dyed fabric must later be heat-set to achieve dimensional stability. This finishing cycle reduces the risk of possible stripes which in some cases may be influenced by the high heat-setting temperature. The dyer however, when formulating the dyeing recipe, must take account of possible colour change during final heat-setting. 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
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
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 .Courtersy Dystar
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