Reactive textile printing

How it works

Reactive inks contain reactive dyes that form a chemical (covalent) bond with cellulose fibres such as cotton, viscose/rayon and linen. Once fixed, the colour is part of the fibre, so wash fastness is excellent and the fabric keeps its natural feel. It is the standard digital method for printed fashion fabric.

Process

1. Pre-treatment (padding): the fabric is coated with a recipe usually containing an alkali (soda ash or sodium bicarbonate), urea (keeps the dye moist for fixation) and a thickener such as sodium alginate (stops bleeding). Then dried.
2. Printing on the pre-treated fabric.
3. Drying straight after printing.
4. Steaming: saturated steam at about 100–102°C, typically 8–12 minutes in an atmospheric steamer. This is when the dye reacts with the fibre.
5. Washing: cold rinse, hot soaping wash (often near boiling), then rinses, to remove unfixed dye and thickener. Poor washing leaves loose dye that stains white areas.
6. Drying and finishing (softener, stentering to width).

Materials

Cotton, viscose/rayon, linen, modal; also silk. Not polyester. Silk, wool and nylon are often printed with acid inks instead, which use a similar steam-and-wash route.

Strengths

• Brightest and deepest colours on natural fibres, including true blacks.
• Excellent wash and rub fastness.
• Soft, natural hand; fabric can be cut and sewn like dyed fabric.

Limits

• Needs a full plant: padding, steamer, washing line, dryer, effluent treatment.
• Uses a lot of water and energy compared with pigment.
• Pre-treated fabric has a shelf life; store it cool and dry.

Common faults