Fashion, durability, comfort, performance - and at a price!6 August 2007
Also, requirements may vary around the world: for some 'eco-friendly' footwear is important. All these attributes have to be taken into consideration by retailers, footwear designers and leather manufacturers alike. The consumer's expectations are constantly moving upwards so, if want to make footwear that sells, innovation is crucial. In this article we look at how the leather industry is moving ahead with new and novel ideas for footwear leather.
Fashion is a fickle thing; one day fashion dictates something wild and outrageous, the next something subdued and sombre. For some, fashionable footwear must be the latest thing off the catwalk yet, for others, it may be a timeless classic style. So, the leather industry must be prepared to move fast on new effects never seen before, yet still be prepared to manufacture the more traditional leathers too.
Chemical suppliers work closely with the fashion industry and the likes of BASF, Clariant, Stahl, and TFL have all recently issued trend catalogues displaying their interpretation of next season's colours and effects for leather. There certainly were some unusual effects to be seen on leather at the recent Lineapelle fair in Bologna - gone are the days when surface effects came off the back of the embossing plate.
Leather was plaited, woven and embroidered for textural effects. It was made into flimsy lace with laser cut designs. Leather was also cut, shaved, curled, shrunk and quilted to produce some quite amazing effects - quite impractical, but amazing none the less.
Whilst shoe design and manufacture has the most influence over the comfort factor, leather certainly has its role to play. There is no doubt that an all-leather shoe (upper, sole, sock and lining) is far superior to synthetics. Leather will mould itself to the shape of your foot more easily and, most importantly, is breathable, thus allowing the perspiration from the foot to evaporate.
This creates a cooler, dryer atmosphere inside the shoe and helps prevent nasty odours and fungal infections developing. But this is not new you might say; this is why leather has been the chosen material for footwear for centuries. Well, there is always room for improvement.
TFL have recently launched their patented Cool technology for leather. These dyes and pigments reflect the sun's heat-generating Near Infra-red radiation away from the leather surface thus preventing the leather from heating up. In black leather (probably the most common colour for footwear) it is reported that up to a 20°C reduction in heat build-up can be achieved with the use of this Cool system.
Apart from the increased comfort value due to the reduction in heat build-up, since the rate of chemical reaction increases with temperature, it is envisaged that leather produced with the Cool system will also last longer due to the slowing down of various degradative processes; more comfort and increased durability - now that's really Cool!
Another comfort factor is the softness of the leather. Traditionally footwear was made from relatively firm leather and shoes had to be 'broken in' before they stopped giving us blisters on our heels. But fashion has in recent years steered us away from some of the traditional stiff footwear leathers towards the soft, more comfortable and casual look. But making soft footwear leather that retains a good grain break in use can be difficult.
Smit and Zoon recommend their Synthol UF 737 to replace combinations of fatliquors to achieve a high degree of softness without grain looseness. Their Syntan AM 656 is also reported to have good grain tightening properties on soft leathers, especially when combined with Syntan RS 540.
One of the keys to success in producing a soft comfortable leather that performs well in use and retains its good looks is to ensure that the fatliquor is well distributed, enabling the fibres to flex and move freely over one another without breaking. Trumpler's new range of Truposilk fatliquors claim to achieve better penetration, even into the smallest level of the leather structure (the fibrils), by producing extremely finely dispersed micelles of lubricant.
Price is always a sticking point - we know that manufacturing in Asia has kept the price of footwear on the High Street down, but the consumer wants it all - and cheaper. So, when it comes to leather manufacture, every little helps.
TFL have helped tanners squeeze just that little bit extra out of their leather with their Topcare system that is able to upgrade leather by concealing grain defects and producing a more even break over the hide. This enables increased cutting efficiency in the shoe factory and, therefore, cheaper shoes in the shops.
LANXESS's new formaldehyde-free resin retannage, Retingan ZF, is also reported to increase cutting efficiency by equalling out structural differences over the hide whilst maintaining elasticity required for good lasting properties and has the added advantage of being formaldehyde free.
The development of a formaldehyde-free resin retanning agent was driven by the strict consent limits on formaldehyde set by the automotive industry. But this is not the first time we have seen 'eco-friendly' technologies migrate from the automotive sector into other areas of leather usage; chrome-free leather is now emerging as the new vogue in the footwear. Many High Street brands are developing ranges of 'eco-leather' footwear based on wet-white or vegetable tanned leather to satisfy the call of the 'green' consumer.
Ecologically sound leather is not only dependent on the type of tannage or retannage used: finishing chemicals, surfactants etc, should also be considered. With this in mind, Stahl have launched a new water-borne activated polycarbodiimide crosslinking agent Crosslinker 5592 that is VOC-free. In the past, the use of more environmentally friendly chemicals has been driven by legislation, but increasingly it is now the consumer.
Whilst these individual step-wise movements to producing more environmentally friendly footwear leather are excellent in their own right, a more holistic approach could make more impact. Studies
1 have shown that compacting the leather making process and being mindful of energy, chemical and water consumption produces footwear leather of comparable quality but with real financial benefits for the tanner in terms of manpower and energy costs, and environmental benefits in the form of reduced water and chemical usage etc. But, like everything, there is always a price to pay. Chrome tanned leather was hailed as the answer to every shoe manufacturers' prayer when it was first developed; it enabled them to make a shoe that could withstand the rigors of modern shoe making processes and its resistance to perspiration ensured durability.
How will the new chrome-free upper leathers perform? One problem is that of waterproofing; the sites on the collagen molecule that the more successful waterproofing agents utilise are taken up by the tanning agent in wet-white production; it has not been possible to produce good waterproofness in chrome-free leather without the use of waterproofing agents based on metal salts, eg aluminium or zirconium. So, based on current technology, if we want waterproof leather it might be chrome-free, but it won't be metal free. Something for the future perhaps?