Today it is difficult to find tanneries that produce vegetable tanned sole leather as well as garment, upholstery and boxcalf leather under one roof. Companies have to develop into specialists and branch leaders.
Again the automotive industry was one of the main driving force which influenced this trend strongly. Driven by new regulations of complete recycling systems and the use of renewable resources, the automotive industry was forced to look for alternatives for the interior material which can withstand this new requirements.
In this market segment we face an increasing demand of so called ?FOC ? (free of Chrome) leathers which are produced from wet - white pretanned hides.
The production of FOC shoe leather is as old as the first tanning methods with vegetable extracts.
At the beginning of the last century the development of the chrome tannage gave new possibilities to produce a commercial trading product called wet - blue. This intermediate product is exported all over the world and we estimate that approx. 70 % of the whole leather production is based on chrome tanned material.
Especially in the automotive market we now observe a reverse trend towards full FOC leathers. This leather article has proved to have some major advantages :
- Full recycle shavings and end article
- Superior shrinkage behaviour of finished article compared to
leather processed from wet-blue (Dash board leather)
- No chrome containing sludge and waste water
- Possibilities to produce leathers with extreme low formaldehyde content.
- Brilliant dyeing of leather especially suitable for high fashion
articles.
- No risk of Cr VI formation
- Possibility to produce metal free articles for anti-allergy leather
Pretanned wet white material can be tanned and retanned in many different ways. Rechroming with TANNESCO® HN & CHROME 33 % bas. enables the tanner to produce semi chrome-leather with the advantages of chrome free shavings, possibility to sort in wet white and reduced amount of tanning and retanning chemicals. Wet white material pretanned with SELLATAN® CF New Liq. can be tanned with vegetable extracts like Mimosa, Chestnut, Quebracho etc.
In order to produce white leathers from pretanned material, the main tannage can be carried out with synthetic tanning agents like SELLATAN® RLS liq and SELLATAN® RBL gran.
This makes pretanned wet white material to a universally useable product, which offers the tanner a variety of possibilities to produce a large range of articles.
Today consumers are sensible to environmental issues and health regulations.The recent case of TBT in sport textiles put again the focus on chemicals in shoes and garment.
In some countries the free formaldehyde content in textile and leather is regulated already. We will see an increasing demand for ?Clean - materials ? in the future. Leathers on wet white basis can play a major part in modern footwear material. We could Already develop processes for FOC shoe leather where the content of Free formaldehyde in the crust is below the regulations, even for textiles for children under 2 years.
Institutes like the German Tanning School (LGR) in Reutlingen prepare labels for leathers which fulfill numerous tests, to prove that they are ? environmentaly friendly processed and tested for harmful substances?. The German Consumer Act from 1994 prohibits the use of certain azo dyes in Consumer Goods that come in repeated contact with the skin. TFL Dyestuff range complies with the German Consumers Goods Act. If Chrome - free leathers are processed, special care must be taken in the selection of suitable dyestuffs. Certain Dyestuffs are based on organic chrome complexes can so that TFL offers a selection of dyestuffs specially suitable for the dyeing of FOC Leathers.
One new marketing requirement is the use of modern, environmental friendly produced, recyclable, ?clean ? materials in leather and textile which underlines the health orientated, sporty lifestyle of the new millennium.
Articles for FOC Leather could be:
- White sport shoes , full pigmented / embossed
- Floater type / shrunken grain leather for casual shoes
- Tight grain semi - aniline natural leather for shoe & hand
bags
- Upper leather for children shoes in brilliant colours
TFL was approached by major shoe manufacturers to assist in the development of those articles.
Today the amount of wet white leather for footwear is still relatively small. 15 years ago, the automotive leather manufactures either did not believe in the importance of such articles. The ecological marketing concept and the technical benefits of FOC leather changed the demand dramatically. Today FOC leathers are not longer niche products but an important part of industrial leather production.
The same will happen to the shoe upper market. Millions of pairs of shoes are deposited in dumps every year. Recyclable materials would have enormous advantages for the industry and end user.
Shavings of wet white are accepted as nitrogenous organic fertilizer and a component of leather fiber products (LEFA).
In combination with natural latex as the sole material etc, FOC leathers can be used to produce fully recyclable footwear.
The pretanning of wet white leather is the key factor for the successful production of FOC leather. TFL established successful pretanning systems based on modified Glutardyaldehyde : SELLATAN® CF New liq.
2.5 - 3 % SELLATAN® CF -New liq. are added after the pickle at a pH of 2.9 - 3.2 in 2 steps. To assure the complete penetration of the product the process will run over night .The end pH of the pertannage after basification with sodium bicarbonate has an extreme influence on the colour of the wet white material. We recommed a pH of 4,0 - 4,3 to assure a complete fixation of the glutardyaldehyde.
We are constantly working on improving our processes. The addition of Syntans like SELLATAN® RLS liq. and polymers like MAGNOPAL® TGR in the pretannage improves the colour and the shavability of wet white.
For shoe upper leather where endsubstances of 1.4 - 2.0 mm are normal, the control of the shaving substance is important in order to guarantee constant thickness of the article.
Therefore SELLATAN® RLS liq. is added to the pretannage.
The main tannage with SELLATAN® RLS / RBL / FL can than be processed without the well known problem of irregular thickness in the end article due to unleveled plumping.
Comparing the dyeability of wet blue and wet white material, some major difference are obvious:
- The reflection curve of undyed wet white leather is more
linear compared to wet blue material (whiter = higher reflection)
- Wet white leather with synthetic tannage and retannage provides a clearer, whiter substrate for dyeing. This results in more brilliant dyeings of the crust leather. (Colouring is an additive process)
- Special care has to be taken by the selection of chrome - free
dyestuffs and low formaldehyde containing fixing agents.
- Due to the more anionic substrate of the FOC leather, fastness
properties of dyestuffs have to be checked.
TFL offers a range of special selected dyestuffs for FOC leathers.
We compared conventional pretanning methods based only on
Gluthardyaldehyde, with modified pretanning methods with increased
amounts of SELLATAN® RLS.
Some fundamental differences can be identified:
- Wet white pretanned with modified formulations show lighter, almost white colour. This makes it suitable for the production of white leather.
- Both systems reach shrinkage temperatures of 70°C and more.
- Tanning and retanning of modified pretanned material can be carried out faster and with reduced amounts of chemicals.
- Modified pretanning reduces the problem of irregular plumping in the tannage, therefore the final thickness can be adjusted during the shaving more precisely.
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