Thickener is a thick, viscose substance that imparts stickiness and plasticity to the print paste, so that it may be applied on the fabric surface without bleeding or spreading and maintaining the printed design. Thickener gives the required viscosity to the printing paste to prevent premature reactions among the chemicals contained in the print paste. The main functions and objects are –
- To maintain a sharp outline of the printed design.
- To prevent bleeding or the spreading of color.
- To prevent premature reactions among the chemicals of the
- To hold the ingredients of the print paste on the surface
of the fabric and in the print
Examples: Starch, Na-alginate, fine gum, gum tragacanth,
British gum, C.M.C, etc.
Types of printing thickener
Basically, there are two types: Natural and synthetic
- Sodium Alginates
- British gum
- Locust bean gum
- Guar gum
- Gum tragacanth
- Polyvinyl alcohol (PVA)
- Polyvinyl amide
- Polyvinyl acid
- Polyvinyl chloride (PVC)
Natural polymers are renewable materials that are available in huge quantities. They are economically and environmentally attractive because of their low cost, biodegradability , and low toxicity. Similar to synthetic polymers, chemical modifications can be readily achieved on natural polymers, which can lead to materials
with highly interesting properties.
Most synthetic polymers are toxicologically safe but not biodegradable. They can be eliminated from wastewater by precipitation or adsorption to the sludge in sewage treatment facilities.
Factors to be considered when selecting/choosing
- Type and quality of material to be printed.
- Compatibility with dyes and auxiliaries chemicals.
- Printing paste stability and rheology.
- Styles and methods of printing.
- Properties of the dried thickener film.
- Effect on color yield, such as diffusion, and fixation.
- Preparation and removal of the thickener.
- Biological oxygen demand (BOD).
Essential quality of printing thickener
- Stability in printing paste should be good.
- It should have appropriate viscosity, flow property
- It must be compatible with the other ingredients of the
- It should dry properly on the fabric to
prevent the spreading of color.
- It should not have an affinity for the dye and
- During steaming, it should provide free space for the dye
molecules to move towards the fiber polymer.
- It should be cheap and available.
- It should be easily removed after completion
Thickener: Sodium Alginate
- Alginate is extracted from seaweeds
- The most satisfactory thickener for printing cotton fabric
with reactive dye
- Does not react with reactive dye
- Absence of primary reactive group
- Repulsion between COOof thickener and SO3- group of dye
- The thickener is usually made from wheat starch
- Nowadays, mostly modified carboxymethylated soluble
starches are used, which have a stable viscosity and are easier to rinse out of the
fabric and give reproducible favorable paste rheology.
Commercial name of Synthetic thickeners
Lutexal GP ECO (For pigment printing)
Lutexal F-RP (For reactive dye printing)
Merits of Synthetic
- No special storage requirements
- No fabric smell
Demerits of synthetic
- Slightly dull prints and harsh fabric feel
- Longer drying time
Suitable thickener for printing different fabrics
Combinations of cold-water-soluble carboxymethylated starch,
guar gum, and tamarind derivatives are most commonly used today in dispersed screen
printing on polyester, for cotton printing with reactive dyes and alginates is used, and
polyacrylates for pigment printing and with vat dyes on cotton, only carboxymethylated starch
Print paste rheology
Print paste rheology describes the properties of viscosity
of the print paste i.e. how the print paste viscosity changes as the pressure changes. Different materials deform differently under the same state of stress. The material stress response is known as rheology.
Measurement of print paste viscosity
Viscosity is a measure of a fluid’s resistance to flow
CGS: Poise or centipoise (cp)
SI: Pa.s = 1000 m Pa.s
1000 m Pa.s = 1 Pa.s = 1 Ns/m2
100 cP = 0.1 Pa.s = 100 m Pa.s = 1 dyne.s/cm2
Note: Viscosity is usually measured in Pascal seconds (Pa.
One pascal is equivalent to one newton (1 N) of force applied over an area of one meter
squared (1 m2). That is, 1 Pa = 1 N · m-2