New ecological demands in leather finishing

One of the reasons for this is that the authorities have acknowledged the general hazards facing consumers and the environment, and they have acted accordingly. For instance, legislation governing food-contact and consumer goods in Germany (Lebensmittel- und Bedarfsgegenständegesetz) has led to a ban on azo dyes that are capable of releasing MAK amines. Other bans and demands for compulsory labelling in the making and marketing of leather have been introduced in the meantime. These include the following legislation: * European Council directive on VOCs (1999/13/EC) * California Proposition 65 * EU restrictions on the use of alkylphenol and its ethoxylates Another reason for the increased importance of ecological factors is that consumers are increasingly becoming more sensitive to environmental and health issues, as the discussion surrounding tributyl tin and other marine pollutants has shown. This has led to preventive action being taken to protect consumers and the environment. As far as the finishing of leather is concerned, attention not only needs to be paid to the general legislation and prohibitions covering the chemicals that are employed and the emissions that are generated, but the consumer-protection demands of the industries that purchase leather also have to be considered. These are enshrined in the following specifications: * Technical specifications issued by the automobile industry * Criteria defined in the German RAL quality guidelines for furniture * Technical specifications issued by retail footwear chains Virtually all types of leather are affected, but suppliers of chemicals to the leather industry have justifiably concentrated on a few selected issues because certain groups of products - and the leather manufactured with these products - have been at the focus of discussions. Ecological demands on automotive leather The ecological demands that are made on automotive leather and the solutions that have been devised to meet these demands can be illustrated by the following: * Changing over to water-based finishing systems * Pigmented finishes with very high fastness that are free of heavy metals * Labelling of N-methylpyrrolidone (NMP) according to California Proposition 65 * Reduction of emissions and elimination of residual VOCs Completely water-based finishes Low-solvent, water-based systems for finishing automotive leather, incorporating new chemicals and processes, were developed in the early 1990s in order to fulfil the standards demanded by the automobile industry. Nowadays, it can safely be said that it is possible to finish most of the leather destined for the automotive market with these systems, and the finished leather fulfils the technical and aesthetic demands that are made on it. It is possible to formulate the complete finish - consisting of a grounding coat, base coat and top coat - with a very low VOC content, and the requirements of the EU directive on VOCs can be fulfilled. Nevertheless, the discussion concerning emissions has led to demands being made to reduce VOC contents even further, and this is an issue that we are now working on intensively. Pigmented finishes free of heavy metals Another issue, which can now be considered as having been resolved, is the use of non-toxic pigmented finishes that are free of heavy metals. These pigmented finishes still have to meet high standards of fastness, ie they have to fulfil the required standards of lightfastness, heat resistance and resistance to migration etc, and at the same time allow the full range of desired colours to be matched. The pigments that are used in modern finishes can largely be divided up into two main groups. The first group consists of a few selected pigments with high coverage which are mainly inorganic, such as titanium dioxide for white, carbon black for black and iron oxides for various caramel and brown shades. The other group consists of organic pigments with high colour strength and high fastness, and these are necessary in order to enable the wide range of colours demanded by leather manufacturers to be matched exactly. Pigments containing heavy metals such as mercury, cadmium, lead, chromium(VI) and molybdenum(VI) are no longer used. NMP-free polyurethane dispersions Demands are increasingly being made in the interest of consumer protection for certain substances that are contained in finishing products to be labelled. These substances can be emitted from the finished leather. Special attention is currently being paid to N-methylpyrrolidone (NMP), which has been listed in Proposition 65 as a potential teratogen by the State of California. One of the main problems here is that, in the absence of reliable data, it is very difficult to assess the risk posed by the residual traces of NMP that are present in leather. In order to be on the safe side, demands have frequently been made that NMP contents should effectively be reduced to zero. Finishing products, especially polyurethane dispersions, are affected because NMP can be employed in the manufacturing process and the finished leather can contain residual traces of NMP. It is for this reason that BASF supplies an extensive range of NMP-free and low-NMP polyurethane dispersions and other products. Reducing emissions from auxiliaries The question of how to reduce VOC contents even further in order to reduce overall emissions is a constantly recurring topic. This is also desirable from the point of view of reducing odour. Attention, therefore, has to be paid to all of the substances emitted from leather, and the following questions asked: * What is the source of these emissions? * How can they be avoided? * Is any extra effort involved from the technical point of view? * Are there any other advantages or disadvantages? Finishing formulations have already largely been optimised to reduce their VOC contents and nowadays solvents are the only significant remaining volatile organic compounds in finishing formulations. For instance, solvents are added to crosslinker formulations to make them much easier to disperse when spray finishes are prepared manually. They make finishes much easier to process and enable high levels of fastness to be achieved. The only effective way to eliminate these solvents is to automate the metering and distribution system by such methods as in-line-activation. Here, viscous, low-solvent crosslinking agents are metered into the finish continuously with the aid of metering pumps and mixing equipment. Another advantage of this technique is that there are no restrictions on the pot life of the finish, because the crosslinking agent is only applied to the finish that is actually applied rather than to the whole batch. Methods such as these have made it possible to achieve a further significant reduction in emissions from leather finishing, as has been demonstrated in laboratory experiments. In summary, it can be said that the residual levels of VOCs that are still contained in finishes largely emanate from the auxiliaries used in the finishing process. However, it needs to be recognized that, rather than simply being undesirable impurities, the small residual quantities of VOC contained in finishes can sometimes make a decisive contribution to the processability of finishing systems. * Low-VOC products and formulations are mostly more sensitive in their technical performance, ie in terms of their levelling and wetting, etc * Greater care often needs to be taken when applying low-VOC finishes * Nevertheless, long-term cost advantages can be obtained by investing in technology and new developments Ecological demands on upholstery leather In principle, the ecological demands that apply to upholstery leather for furniture, and the finishes applied to this type of leather, are similar to the demands that apply to automotive leather. These are described in the German RAL RG 430 quality guidelines and test methods for furniture. Many of the advances that have been made in developing new products and processes for finishing automotive leather, such as low-VOC binders and top coats and pigments that are free of heavy metals, can be applied to upholstery leather. Nevertheless, specific products do have to be used on specific types of leather in order to obtain the required fastness at a cost-effective price. This is the reason why the focus has been placed on somewhat different products as far as the finishing of upholstery leather is concerned. Ecological demands on shoe upper leather Shoe upper leather and the finishes applied to shoe upper leather also have to fulfil high ecological standards. These standards apply to the manufacturing processes and the chemicals and finishing techniques that are employed, and the following regulations have to be observed. * Regulations in the EU concerning alkylphenol and alkylphenol ethoxylates * The EU directive on VOCs In future, attention may be paid to measures designed to reduce emissions of marine pollutants. Another factor that has to be considered is that shoe upper leather often comes into direct contact with the skin. This implies that leather manufacturers not only have to observe legislation covering materials that come into contact with the skin, but they also have to take into account the additional demands of their customers, ie the retailers and manufacturers of branded goods. These demands are usually orientated towards the criteria that have to be met to qualify for eco-labels. An example here is the problem with tributyl tin, which can affect some of the products employed in finishing. PU binders free of tributyl tin Tributyl tin compounds have already been banned in many applications in which they are employed exclusively as biocides. However, traces of tributyl tin can be present as impurities in the dibutyl tin-based catalysts employed in the production of polyurethane, and these can find their way into the polyurethane binders used to finish leather. It is possible to produce polyurethane dispersions without any organic tin catalysts. An example is the Astacin TF range supplied by BASF, which consists of polyurethane base coats and top coats that are free of organic tin compounds¹. APEO-free binders and auxiliaries Alkylphenol and its ethoxylates (APEO) have now become ubiquitous, and traces can be detected everywhere in the environment. The reason for this is that alkylphenol ethoxylates have been widely employed as nonionic emulsifiers in the past, and they are difficult to break down by natural means when they are released into the environment². Some of these compounds are also suspected of causing endocrine disruption, ie organisms react to them in the same way that they react to their own hormones. This has led to the current initiative to restrict the use of these substances within the European Union. In the latest draft directive, the use of nonylphenol and nonylphenol ethoxylates (NPEO) as auxiliaries in a variety of products, including products for leather finishing, has been reduced from 1% to 0.1%. These substances have been completely banned in Norway since January 1, 2002. The following products that are regularly employed in leather finishes are affected: * Pigment preparations * Acrylic binders * Auxiliaries such as wax emulsions However, there are many possibilities for replacing APEOs with other, more environmentally friendly emulsifiers, and modern finishing binders and auxiliaries can be produced free of APEOs. Low-VOC finishing systems The EU directive on volatile organic compounds has set the following limits for the emissions from new facilities for finishing leather: * max. 85g/m² at a total rate of emissions of 10 - 25 t/a * max. 75g/m² at a total rate of emissions of >25 t/a * max. 150g/m² for bag leather and aniline upholstery leather. These limits will also apply to existing facilities as from November 1, 2007. There is no difficulty in adhering to these limits if modern finishing formulations are employed. Chemical suppliers are developing and testing low-VOC systems for the following applications. * Lacquers * Printing pastes * Handle improvers * Pull-up waxes etc The aim here is to be able to react quickly to any possible tightening of restrictions that may be made at any time on the basis of new findings and new appraisals. Reduction of marine pollutants The Oslo-Paris Convention for the Protection of the Marine Environment of the North-East Atlantic (OSPAR)3 has drawn up a list of substances of possible concern. The list currently consists of 386 substances that are suspected of displaying adverse environmental behaviour. * Persistent in the environment (ie difficult to break down) * Bioaccumulating (ie build up in living organisms) * Toxic to aquatic organisms These substances include many plasticisers such as those still used in 'classical' lacquers, along with biocides and stabilisers etc. Twelve EU member states along with the EU Commission have signed up to the OSPAR Convention. The aim of this convention is to identify and reduce discharges of hazardous substances into the sea by 2020. Priority has been given to 45 substances and groups of substances. The findings will then be used as the basis for any restrictions that may be necessary, which would be implemented under the EU Water Framework Directive. Summary Because leather is a consumer product, leather manufacturers have a duty to take into account the growing ecological awareness and demands of consumers.The finishes that are nowadays applied to leather already fulfil the necessary ecological standards, provided careful attention is given to the selection of products and processes. Nevertheless, innovative new products and processes for finishing leather will always be needed in order to offer solutions to new ecological challenges in the future. We, therefore, consider it essential that our product range contains a complete set of products for use in environmentally friendly leather finishes in order for us to fulfil our responsibilities to customers and end-users in the spirit of Responsible Care and Sustainable Development.