Printing Thickeners | Function or Object or Purpose of Thickener

Thickener:

Thickener is a thick mass which imparts stickiness and plasticity to the print paste so that it may be applied on the fabric surface without bleeding or spreading and be capable of maintaining the design out lines.

Thickener or Print pastes are traditionally made by weighing out and, if necessary, dissolving the colorants and auxiliary chemicals and then stirring them into the required weight of pre-prepared thickener. A thickener is a colourless, viscous paste made with one or more thickening agents. The use of terms such as thickener, and thin, long or short, to describe print pastes is of course descriptive rather than scientific, but is long established and a useful reminder that the materials being handled possess complex properties, not easily defined.The thickener must be stable and compatible with the dyes and dyeing auxiliaries to be used.

Function or Object or Purpose of Thickener:

1. To give the required viscosity to the printing paste. 
2. To prevent premature reactions between the chemicals contained in the print paste.
3. To hold the ingredients of the print paste on the fabrics

Four significantly different approaches may be used to produce thickeners, using:

1. A low concentration of a polymer of high relative molecular mass (r.m.m.)
2. A high concentration of a material of lower r.m.m. or of highly branched chain structure
3. An emulsion of two immiscible liquids, similar to the emulsions used as cosmetic creams, or a foam of air in a liquid
4. A dispersion of a finely divided solid, such as bentonite.

The first approach is the most important but all four have been used, sometimes in combination. Practical printers long ago discovered natural polymers with suitable properties and, by trial and error, acquired the art of using them. Because the natural products are variable materials and the requirements are complex and ill-defined, experience and subjective judgements were essential. Now that the chemistry and physics of polymers are better understood, it is possible to select and use them more scientifically. We also have available a wider range of thickening agents, including completely synthetic polymers, and this has increased our knowledge. It must not be assumed, however, that our understanding of these complex materials and their behavior is adequate.

In the selection of thickening agents, it is necessary to take into account requirements other than viscosity, which can usefully be classified in five categories: print paste stability, good adhesion of the dried thickener film, minimum effect on colour yield, ease of removal and acceptable cost.

Posted in: Wet process