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KEEPING UP WITH THE FOOTWEAR MANUFACTURER
JULY/AUGUST 2012 | www.footwearbiz.com
SOFTER AND MORE REFINED LEATHERS
In line with a demand for more natural leathers, new
chemical products, suited to the demand for leather with
more natural characteristics, became available in the 1980s.
Polymeric agents, that could provide both filling of the
leather, and at the same time a softer handle, proved to be a
major advance in retanning systems. These products also
enabled the creation of leathers that could maintain a tight
break across the structure and suited the development of a
more uniform grain texture when subjected to milling
actions.
Improved fatliquors were also developed. These were
partially to meet the needs of vacuum drying operations and
avoid the migration of fats within the leather structure, but
also to ensure lightness in handle when high percentage
fatliquor offers were needed to provide softness. More
recently, greater selectivity has become possible with
retanning with the event of micro-spheres. Designed to
penetrate the leather structure, heat application can cause
these spheres to expand in-situ to a controlled degree. These
have the potential to provide filling, and to increase the
thicknesses and softness of leathers.
COMPATIBLE DYESTUFFS AND COLOUR CONTROL
There has been significant advance in the management of
dyestuffs within the tannery. This first started with the
introduction of ranges of dyestuffs that were compatible with
each other. They exhibited similar rates of penetration into
leather, exhausted from solution at similar rates, and
provided similar colour fastness. The outcome was that with
a relatively few dyes, a very broad range of colours could be
provided. The often very varied stocks in tanneries were
rationalised, and colour became more predictable.
This advantage was further enhanced by the use of
systems where colour became measurable with great
accuracy, causing less reliance on visual colour matching.
Leathers were produced at the dye stage where it was
possible to predict the final colour with reasonable accuracy
batch after batch.
LIGHTER FINISHES
Greater colour uniformity within crust leathers led to
radical changes within finishing. Unless a very high level of
finish was required to cover surface defects, the need for high
level of finish and pigments that were often required to
correct colour diminished. Finishing became a much lighter
operation, and it was possible for leathers to retain a softer
and more natural feel and handle.
At the same time the properties of the finishing film
improved: in general there was a shift from acrylic-based
resins to more expensive but better performing polyurethane
resins, or co-products that provided more defined properties.
There was also pressure to replace solvent-based finishes, so
better performing water-based and reactive finishes came
into wider use. It also became possible to apply lower
quantities of finish to the leather due to improvements in
roller coating developments.
THE UPGRADE OF INFERIOR MATERIALS
An advantage arising from these advances had led to a
better use of raw materials once viewed as inferior. For