Dyeing of hides and skins
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General description
The dyeing process is carried out to produce consistent colouring over the whole surface of each hide and skin, and for exact matching between hides in a commercial pack. Typical dyestuffs are water-based acid dyes. Basic and reactive dyes are less commonly used by the leather industry.
Emerging technologies
Continuous retanning and dyeing
Description
This is a manufacturing technique developed in Italy to perform retanning, dyeing and stuffing in a semi-continuous unit with low water requirements. The line is made up of three different modules.
- A roll machine for retanning and stuffing. Due to a system specially designed for the purpose, the machine facilitates the penetration of chemicals into the leather and then 'squeezes' the excess substances out of it. The special feature of the machine is that it includes a double basin for impregnation, so that leather can be processed on both sides simultaneously.
- A stabilising chamber where controlled pressure, humidity and temperature help chemicals diffuse and fix into leather.
- A soak-dyeing system, where leather can be dyed in a few seconds.
Both the roll machine and the soak system work in short-term washing mode: low volumes of
water contain high concentrations of chemicals, so that the amount of effluents is kept low. The
machines are provided with sensors to monitor the key parameters of the process (temperature,
pH and conductivity) and keep conditions stable.
Status of development
A prototype was built and used for pilot trials in 2008 to evaluate the emerging technique. The results were promising.
Source: (BAT) Reference Document for the Tanning of Hides and Skins, 2013
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