Q2: Dyeing Flashcards
Fibre dyeing:
The application of colour to fibres, before yarn construction
Piece dyeing:
The application of colour to fabric
Product dyeing:
The application of colour to a completed garment or other textile article
Solution dyeing:
The application of colour to manufactured fibres by adding the pigment to the spinning solution prior to extrusion
Yarn dyeing:
The application of colour to yarn before fabric construction
Fibre dyeing
This is also known as stock dyeing or loose-stock dyeing.
Both natural and manufactured fibres can be dyed while still in a loose fibre state.
The dye can penetrate each individual fibre, resulting in a uniform colour and excellent colourfastness.
Fibres that have been dyed different colours can be combined in a yarn to produce heather or tweed effects.
Solution dyeing
Solution dyeing is also called mass pigmentation or dope dyeing.
Obviously, it can only be used for manufactured fibres.
In solution dyeing, the dye is added to the spinning solution before it is forced through the spinneret.
The resulting colour is extremely even and colourfast.
It is practically impossible to remove the colour completely if solution dyeing has been used. It is therefore also not possible to change the colour of solution-dyed fibre if the colour is no longer in fashion.
Yarn dyeing
Yarn dyeing is one of the oldest methods used. It is usu- ally less labour-intensive than fibre dyeing.
Knitted fabrics are frequently dyed before the actual knitting process because piece dyeing can damage the knitted fabric.
Yarn can be dyed after spinning.
The major disadvantage of yarn dyeing is that fashion colours must be accurately predicted so that the manufacturer is not left with a large stock of fabric in an unfashionable colour, or with too little fabric in a highly popular colour.
It also allows the use of different coloured yarn in the same fabric, producing plaids, checks or stripes.
Piece dyeing
Piece dyeing means to dye in fabric form.
This is the easiest and least expensive way of dyeing and also the method most widely used.
Fabrics can be left undyed until fashion dictates a particular shade.
The dye does not penetrate the fabric as well as in the previous methods, but it is sufficient for most end uses.
To ensure a final uniform colour it may be necessary to use two or more dyes. The dyes can be applied simultaneously (one-bath process) or separately (two- bath process).
Problems can arise when a fabric consists of more than one type of fibre, each reacting differently to a dye.
Cross dyeing is achieved if a fabric contains more than one type of fibre, each reacting differently to a dye or mixture of dyes.
One fibre may not accept a dye at all and remain white. Depending on how the different fibres have been arranged, the result can be stripes, a plaid, check, tweed or heather effect.
Product dyeing
An article can be dyed after it has been completed. For many years this method was used mainly for dyeing sweaters and household items such as towels and bedspreads. The method used for this is called paddle dyeing.
These days, product dyeing is used on fully manufactured garments. The fabric is prepared for dyeing, cut and sewn into garments and then left until orders for specific colours arrive.
Garments can then quickly be dyed in the correct colour. This is known as garment dyeing.
The colour of garment-dyed clothing is more inclined to bleed or fade than that of clothing that has been dyed conventionally. Benetton garments are frequently garment-dyed.
Types of dyeing
fibre dyeing solution dyeing yarn dyeing piece dyeing product dyeing
Dye types and their properties Dye class Fibre types usually dyed Fastness to washing Fastness to light End uses Comments
Colourants used on textiles can be classified as dyes or pigments.
Pigments are insoluble in water and possess no specific attraction for any particular fibre type. Their major use is in printing.
Dyes were originally of natural extraction. Modern dyes, however, are usually synthetic organic colourants. Dyes can be classified in different ways including by application class. Generally, dyes with similar application methods are grouped in the same application class.
Details of the major application classes are given in the following table.
Two important properties of dyes are their fastness to washing and fastness to light. Dye fastness is defined as the ability of a shade (dye) to withstand external agencies (eg washing or light) without the loss of or a change in colour.
Dye class: Direct
Fibre types usually dyed: Cotton, rayon
Fastness to washing: Poor
Fastness to light: Poor – good
End uses: Low-quality apparel, fabrics, linings, curtains, socks
Comments: Cheap
After-treatment can improve fastness
Dye class: Acid
Fibre types usually dyed: Protein, polyamide
Fastness to washing: Poor – good
Fastness to light: Moderate – good
End uses: Carpet yarns, dress goods, suiting, overcoats, knitting yarns
Comments: Better fastness achieved on polyamide fibres
Dye class: Vat
Fibre types usually dyed: Cotton, rayon
Fastness to washing: Excellent
Fastness to light: Excellent
End uses: High-quality curtains, furnishings, shirts, towels, sewing threads, work-wear
Comments:
Expensive and often difficult to achieve bright colours
