Pigment Dyeing

Pigment dyeing is an electrical process whereby the textile to be dyed are first given an electrical charge and the pigments are given the opposite charge. Then when the charged textile material is introduced in the pigment bath, the opposite charges will attract and so the pigments will travel to the textile material surface.

In practice the pigments are given a slightly negative charge while the textile material is give a positive charge. Pigment dyeing process occurs in three steps.

1.    Cationisation: by cationisation the fabric is given a positive charge. This is achieved with the help of cation imparting agent and acetic acid.

2.    Dyeing: for dyeing, first the pigment is prepared by adding an anionic dispersing agent. This will give negative charge to the pigment. After preparation of the pigment, the textile material is then introduced in the bath where the opposite charges on pigment and textile material creates a force of attraction and so the pigment molecule travel towards the textile material and sit on the surface of the textile material.

3.    Fixation: by fixation the pigment is bound on to the textile material. This is done with the help of non-ionic or cationic binder. Curing is done at high temperatures.


To know about pigment dyeing procedure please follow the link below
http://texwiz101.blogspot.com/2012/04/pigment-dyeing-by-exhaust-process.html#axzz1sjnGgmbj

Pigment Binders

Binders are one of the most important chemicals for pigment printing and pigment dyeing. It is the chemical that helps to bind the fabric and the pigment together. The binder is one of the deciding factors of fastness properties of coloured fabric. Binder film property also influences the handle of the fabric. Therefore, for a Textile Technologist it is very important to know about binders.

Binders are usually co-polymers made up of two monomers that produce two distinct types to homo-polymers.

1.     One monomer produces homo-polymer that forms a hard and brittle film. This gives hardness and strength to the binder film. (Example: vinyl chloride, acrylonitrile, methyl acrylate, methyl methacrylate, etc.)

2.     The other monomer produces a homo-polymer that forms a soft and tacky film. This gives flexibility to the binder film. (Example: Butadiene, butyl acrylate, etc.)

Together with this two, there is a small amount of reactive component present in the binder polymer chain that contain reactive groups which are capable of reacting with each other or with other chemicals and thus form cross-linking between linear binder polymer molecule and also with the fibre molecules. Examples of such chemicals are acrylamide, meth acrylamide.

Example of a binder molecule is shown below.

There are two types of binder: Self-crosslinking binder and External crosslinking binder.

Self-crosslinking Binders: the binders that have N methylolacrylamide or N methylol methacrylamide as reactive groups in their polymer are self-crosslinking binders. These binder linear polymer chains react with one another and form crosslinking in the straight chains and thus form the binder film. Below is an example of self-linking polymer and how they react to form the cross-linking.

External crosslinking Binder: the binders that have acrylamide or meth acrylamide as reactive group is called external crosslinking binder. They require an ‘external’ chemical, most commonly know as fixer, for formation of the crosslinking between the linear chains. Usually methylolated methane or urea formaldehyde or melamine formaldehyde are used as fixers. Below is an example of external cross-linking polymer and how they react with fixer.

Characteristics of Dye Used in Textile Dyeing