Colour fastness of textiles
Many products - such as textiles, inks/paints/coatings, plastics, paper, - are coloured with dyes and pigments. These colours can fade or change when the products are exposed to water, light, rubbing, washing, perspiration etc.
Definitions and terms
Colour fastness is the resistance of a material to change in any of its colour characteristics, including the transfer of its colourants to adjacent materials;
Fading means the colour changes and lightens;
Bleeding is the transfer of one colour to another material. This is often expressed as soiling or staining.
Fastness properties respectively qualities are expressed in ratings. These fastness ratings are evaluated by grey scales for bleeding and fading. They consist of five different grey colour graduations and are compared with tested textile and its prescribed adjacent material. The ratings are:
- Very poor
Only light fastness ratings are evaluated with blue scales from 1 )very poor) to 8 for the best colour fastness.
How to improve colour fastness?
Various textile chemicals depending on fibre composition of the fabrics can be used. Generally dyed fabrics are undergoing a treatment after the washing process with chemicals for better fibre colour fixation.
- Cellulose fabrics dyed or printed with reactive dyestuffs are often washed at high temperature with chemicals that have dispersing and dissolving properties. Chemicals so-called colour transfer inhibitors might be used to improve the interaction between the dyestuff and the cellulose fibres. Excess of dyestuff from the fibre and in the wash water can be de-colourised by use of chemicals or enzymes. There is a risk of undesired chemical reactions during de-colourisation of the excess dyestuff resulting in toxic products caused by reactive azoic dyes that have remained in the fabric.
- Dyed polyester fabrics need treatment with chemicals. The died polyester fabric is washed with reductive agents to remove and destroy the unfixed or weakly fixed disperse dyestuffs on the fibre surface.
During textile dying and after-treatment washing restricted or banned chemicals can remain in the fabrics. This can be prevented by good manufacturing processes.
For the chemical risk assessment of materials this is essential information from your supply chain.