Pigment dyeing

Pigment Dyeing

1. PIGMENT DYEING

2. Introduction Pigments are finely-dispersed insoluble colourants and applied as insoluble particles on fibre Mainly used for printing rather than dyeing They do not have any affinity for the fibre They do not penetrate inside the fibre but remain on the surface of the fibre ; hence it is a surface dyeing They are held mechanically to the fabric by binders, which are then cured at higher temperature

3. For commercial application pigments should have very good heat resistance, dispersability, light & weather fastness, physiological harmless and should be available at affordable price (Heat resistance is required due to the usually high processing temperature)

4. Properties of Pigments Pigments are finely dispersed colourants insoluble in water They do not have any affinity towards the fibre Binders are require which binds both the fibre and pigments together Pigments have excellent light fastness property and weather fastness property The wash fastness and the rubbing fastness depends on the binder efficiency The rubbing fastness is however is not so good (Binders are very important during pigment dyeing)

5. Requirement of Binders used for Pigment Dyeing It should bond very effectively to the pigment It should have adhere well to the textile fibre It should form a clear colourless film on the layer of pigment particles It must have abrasion resistance, wash fastness and must be capable of being dry-cleaned It should display minimum tackiness of film …… cont

6. Requirement of Binders used for Pigment Dyeing It should not give a harsh handle It must not ‘ yellow’ on storage It should be resistant to mechanical and chemical agencies It must be compatible with other textile auxiliaries

7. Dyeing with Pigment Pigments can be used for dyeing of any fibres It consists of the following process Padding or application of the dye paste uniformly on the fabric Drying Curing (Done at around 150 C with hot air or steamed air at higher atmospheric pressure) Please note that no after treatment is required in case of pigment dyeing

8. Padding with Pigment Dye Drying Curing

9. Recipe Pigment x g/l (depending upon the depth of shade) Binder 80 – 100 g/l Migration inhibitor 10 – 20 g/l Acid liberating catalyst 60 – 70%

10. Process of Dyeing Dilute required quantity of binder + 5 times its weight of water + required quantity of 30% acetic acid Weight the pigment emulsion, paste with little water and dilute with 10 times its weight of water Add the pigment emulsion to the acidified binder emulsion with stirring Add required quantity of ammonium chloride to it Filter the dispersion through a fine cloth before padding Pad the fabric through this liquor using a padding mangle Dry the fabric in a hot drier and cure it at 150 C for 4 minutes

11. Test of Pigment Dyeing The most reliable method to test the pigment dyeing is by the microscopic test A fibre cross-section is viewed at a magnification of around 250 The evaluation is done on the basis of distribution of colour across the cross-section of the fibre If the colouration is evenly distributed over the total cross-section, the fibre has been dyed with a standard dye and not pigment dyed If only the fabric surface (i.e. the outermost layer in the fibre cross-section) shows deposition of pigment particles, the fibre is pigment dyed