Textile Product Dyeing and Finishing
Various methods, applications, and standards of coloring or dyeing of textile materials
When ‘colour’ is applied to a fabric it is termed as dyeing. Dyeing and printing of fabrics are usually done after routine or basic finishes but prior to the application of other finishes. It is mainly done to give color to the fabric and thus improve the appearance of the fabric.
Dyeing textile involved immersing or dipping a fibre, yarn or fabric in a colour pigment to change its colour. We have been doing this for centuries and will continue to dye fabrics for many centuries to come. Colour is known as a pigment and the way of keeping (fixing) the colour is to use a mordant, a chemical that fixes the dye to help prevent loss of colour when washing or wearing the product. To be successful at dyeing you must:
- Achieve the right colour
- Make sure the colour is fixed (often called colourfastness) so it does not run or wash out
- Make sure the colour is even throughout
- Make sure the dye does not damage the fibre, yarn, or fabric
- Make sure you can repeat the process and match the colour.
Stages of dye application
When we go to the market we find it is not only fabrics which are dyed but sewing threads and knitting yarns are also available as dyed materials.
This is the method that uses pigment (chemical dyes with salts added to fix the dye; these can be made up with water. The fibres, yarns or fabric are then immersed in the dye bath until the depth of colour is achieved.
Natural and vegetable dyes were the first-known dye pigments and with the move to be more environmentally friendly are becoming popular again. These work best with natural and regenerated fibres and fabrics and require a mordant to fix them to the fibres. With natural dye,s it is difficult to reproduce the exact shade each time.
Industrial dyeing can be done at the following stages:
Both natural and manmade fibres can be dyed at this stage. It gives very uniform dyeing and fast colours. But there is a lot of wastage during further processing of fibres. Fibres are dyed in vats until the dye has penetrated the fibre to give good uniform colour and fastness.
Sometimes yarns are also dyed, especially when they have to be sold as such. Hence in embroidery thread, sewing threads, and knitting yarn, dyeing is done at the yarn stage. Dye penetrates will but take-up may not be as uniform as when dyeing fibres then making them into yarns.
Liquid Polymer Stage
The polymer (artificial fibre) is coloured before extrusion so the dye is part of the fibre and gives excellent colourfastness.
This is the most popular stage of dying. Most of the fabrics which are dyed in a single solid colour are dyed at this stage. This method is a fast method and it is easy to match colours. Blended fabrics can also be dyed.
This is quite a cost-effective method because manufacturers can hold undyed fabric and dye it when needed, depending on changing fashions and demand. Cross-dyeing, where two different yarns have been used, which take up the dye at different rates, gives patterned effects such as stripes and checks.
Dyeing at the fabric sage is often known as pice dyeing, and the process can be batch (fabric pieces are held in the dye), continuous (fabric goes through dye pads and rollers) or semi-continuous (fabric goes through dye pads but is held for a time to set the colour).
Sometimes, after stitching the garment, there is a need to dye it, for example, dupattas for suits are dyed after making.
The fabric is dipped but not immersed to take up some dye on only part of the fabric or more depth of colour on part of the fabric; then it may be dipped again to get two or more colours blending together. This can be done in the classroom and achieves a popular patterned effect.
In resist dyeing a piece of fabric is dyed but part of the fabric is made to resist the absorption of dye as necessary to give a patterned effect.
In tie-dyeing, the fabric is wrapped, tied or folded in section to stop the absorption of the dye. The fabric is then put in the dye bath and left for the required time. A multi-coloured effect can be achieved if the fabric is untied after the first colour is set a and the re-tied and redyed in the second colour. Items such as buttons and pebbles can also be tied into to get further types of patterns. The tied dye effect is popular for T-shirts and soft furnishing.
Batik is the resist method of using melted wax, a flour mixture or gutta, which is applied to the fabric in patterns to resist the dye when dry. The item is either dipped into the dye bath or the fabric is stretched on a frame and dye is painted on to the fabric. Sometimes cracks appear in the resist giving a cracked effect. Silk and cotton fabrics are best for this method.
This is similar to Batik but the resist is made up of tightly pulled stitches instead of was. Again this method works best with cotton and silk.
This is a folding process, where dye is added to the folded fabric, which then steamed to set the dye. Unfolding the fabric reveals a sculptured effect.
Dyes and Sources of Dyes
The dyes which are used for colouring fabrics can be classified according to their sources.
These dyes are based on raw materials available in nature (plants, insects, and minerals) and are non–polluting.
These dyes are not received from natural sources. They are synthetically made by using various chemicals. Chemical dyes are cheap and easy to apply, with overall good colour fastness but cause environmental pollution.