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.