Leather traceability and authentication26 June 2006
The 'intelligent' labelling of products (such as RFID - Radio Frequency Identification) is a suitable solution. However, it does not apply to specific needs in the leather sector, particularly in regards to the processing and use of leather as a material. The improvement of authentication systems is vital to guarantee traceability along the chain from the sourcing of raw materials at the abattoir to their use when manufacturing a finished product. In this article, the authors have set themselves the task of finding solutions in response to the industry's needs related firstly to leather authentication and secondly to finally assembled finished products. Technical guidelines: related to the improvement of a leather authentication system. In general, the integration of an additional step in leather processing that does not have a significant effect on the final performance of the material (therefore on the added value) must be carried out in the most hidden way possible. This is particularly the case when using a marker or labelling system for tracing raw materials. The main clauses to follow in the technical guidelines are related to the way leather is used as well as the way it is processed: * Leather as a finished product should not be modified. The colour, touch, thickness and handle characteristics should not be altered by the presence of the marker or label * When using leather, its appearance should remain constant. Cutting, glueing, sewing and shaping the material should not be affected by the marker or label * Applying the tracer should not modify the manufacturing process. The process involves physical and chemical operations which would be difficult to alter afterwards. However, the application should not need specific equipment, but that already existing within the company * The company signature or brand should not be visible to the naked eye; identification should be made possible within the factory with simple means (such as the control of batches throughout the process at the tannery or at the point of receipt by the end-user) * The signature or brand must be resistant to physical and chemical conditions during leather making operations carried out prior to tracing * The signature or brand should also be resistant to physical-chemical conditions during the manufacturing operations of the finished products manufacturer * Finally, cost accountability should be directly related to the technique of adding the marker or label. The extra cost of the marking treatment must be realistic. Especially to materials of strong added value such as luxury or technical leathers, some cost must be included The manufacturing process and possible entry points for application of the mark The transformation of raw materials into finished leather needs a certain number of consecutive operations: chemical, mechanical and thermal. These operations can be gathered in four main phases: beamhouse, tanning, post-tanning and finishing. Bearing in mind these main phases and the easy integration of the marking treatment, two entry points are possible: * following post-tanning at the end of the wet-end operations * during finishing at the end of the manufacturing process in the dry state Certain leather items are often not finished. In order to brand or mark the material, the treatment must include the whole cross section of the leather structure so that the smallest part of a cut element is marked. It is recommended to mark such items at the end of wet operations: this is called marking during the wet-end procedure. With regard to leather items that have been finished, the tracer may be incorporated along with the chemical agents (such as film formers on finishing coats): this is known as marking using a dry procedure. These two methods were required to be tested using compatible marking systems for both the wet and dry treatments. Both were investigated by CTC. Selection criteria according to the chosen tracer Depending on the above mentioned methods (dry and wet), some criteria will differ. Common criteria for both methods: * very thin grain with maximum particle sizes between 8-10m; * the leather as a product must contain no or little colour * compatible with the substrate * must remain stable with time * resistance to mechanical, thermal and chemical operations applied during leather making Specific criteria for the wet-end procedure: * Soluble product or able to emulsify or disperse in an aqueous environment * Product compatible with the chemical agents used prior to its application (such as fatliquors, dyes, retanning agents and formic acid etc) * pH stability around 3 to 5 * Resistance to rinsing pressure (100/200kg per cm2) * Thermal resistance when drying (80ºC maximum) * Mechanical resistance to glazing, polishing, stretching, milling and staking * Stability and resistance to physical-chemical conditions in the finishing process (see following paragraph) Specific conditions to the dry procedure: * Soluble products or able to disperse in finishing resins (in an aqueous environment or partially soluble) * Compatible with finishing agents (such as binders, pigments, touch modifiers etc) * Compatible with finishing equipment such as spray lines or rollercoaters * Thermal stability (hot air and/or IR) when drying the final film (80-90ºC) * Resistance to mechanical and thermal treatments applied to finished leather such as embossing, ironing and hot plating In addition to the criteria related to leather and its manufacturing and the end-use, the selection of tracing agents includes other parameters as follows: - It is harmless to the consumer - Producing an original ID code - Ease of applying the identification code in the procedure - Access to deciphering the code (for example at the application site or a specialised laboratory) - Unforgeable tracing system Analysis of the different procedures Following a series of initial trials carried out at CTC to find a suitable ID system, the most convincing results were obtained by using three different types of marking or tracing agents: 1. Procedure based on micro-spheres 2. Procedure based on DNA synthesis 3. Procedure using magnetic resonance 1. Micro-spheres procedure This procedure uses micro-spheres with polymeric envelopes with sizes between 2 and 10 microns. These micro-spheres present a variety of physical and chemical properties (nature and shape of the envelope) enabling a large application domain in the paper-carton, plastics, glue, ink and varnish, and textile industries. These products are inert, chemically stable and relatively resistant to thermal and mechanical constraints. These hollow micro-envelopes are made up of two types of fillers, firstly, a fluorophore agent and secondly a synthetic DNA filler. These have the potential to be used in the industry. With regards to the wet-end procedure, a method based on the use of only wet-blue which is then processed into crust and finished leather has been determined. A standard representation of the procedures used in tanneries as well as a control reference has been established and improved for the different test procedures. The operating mode has time constraints which were related to drum operations (approximately 4-5 hours of rotation) as well as to those from mechanical and thermal operations carried out on the leather under industrial conditions. The analysed parameters included the concentrations of the used tracer, the particle size, the contact time and the position of introduction of wet retanning agents as well as the influence of the final finishing in terms of detection possibilities of the tracer. In this type of application, reproducibility is not guaranteed and there are possibilities of contaminating the equipment (for example sammying felts). Also a heavily pigmented finish on the leather makes detection more difficult. As in the wet-end procedure, a method with a control has been determined for the analysis of the dry procedure. The application and finishing processes are entirely comparable to those used in the leather industry. They make it possible to check beyond the chemical compatibilities of each component, the behaviour of the tracer when applying a spraying gun (application pressure through the spraying valve etc) and mechanical finishing treatments such as ironing or embossing to flatten the grain (pressure and thermal effect). The analysed parameters were based on the concentrations used, the finishing types, the size of the particles and their position within the different layers of the finish. This procedure has a good reproducibility and needs relatively lighter concentrations of the tracer. There is no risk of contamination and the micro-spheres are resistant to spray gun applications as well as mechanical finishing operations such as ironing and embossing. Additionally, the use of pigments does not interfere in the detection. The process optimisation depends on a balance between particle size and its position within the film. 2. Process based on DNA synthesis DNA synthesis creates the base for a biological marking system with an almost unlimited coding capacity. These procedures are already being applied to banknote paper, perfumes and in general it can be added to all liquid and solid materials. DNA presents the advantage of great safety in terms of marking as well as total security towards the consumer. DNA can be used either in its free state directly mixed onto the area to mark or in micro-sphere capsules, particularly when conditions within the environment are less favourable. This process has been assessed with a view to its use for leather marking. The blending procedure is carried out with free DNA in a dry state which is mixed with the leather finishing preparation. The analysis of dry DNA has been developed in two ways: * Chemical compatibility with the finishing components * Application and detection of DNA in finished leather It was also necessary to check that leather containing natural DNA in itself was not interfering in the process. This analysis has been carried out for the first time and this particular experiment had never been studied before. For each case, the compatibility was analysed with the finishing preparations to apply before and after drying and with each component included in these preparations: * The DNA mixed with the compounds of acrylic-polyurethane preparations non-dried and polymerised is totally detectable and therefore compatible * In semi-aniline finishes of a proteic type, all analysed combinations show compatibility with DNA-finishing resins * Compatibility trials with a DNA/nitrocellulose fixation layer have led to positive results in all studied cases. These results give rise to the possibility of marking the surface layers Applications on leather have been carried out on semi-aniline and pigmented finished material. In all cases, the tracer concentration was analysed. The following trends were obtained: * The mixing of free DNA in proteic and acrylic finishes is completely feasible. Finishes based on polyurethane need further analysis in terms of the extraction of DNA from the dried and polymerised film and compatibility with certain components * For companies wishing to mark or brand their products, free DNA marking of finishing films will need further study to check the compatibility between the products used in manufacture and the DNA; certain mechanical operations on finished leather specific to each company will have to be assessed for reproducibility * Two level traceability on finished leather is feasible (combining micro-spheres, fluorophore and DNA) 3. Procedure based on magnetic resonance This process is based on an original technique sourced from the magnetic resonance of a material. The marking agent is a preparation made up of a micro-powder that can be mixed in most printing inks or added in the processing of raw ingredients. The potential in terms of detection reliability and non-falsification is very good. Current areas where magnetic resonance is used for brand protection include industrial sectors for perfume, wine and spirits, pharmaceutical, banking and other luxury products such as jewels, works of art etc. Magnetic resonance detection is carried out through a dedicated portable reader through contact or at a short distance of a few millimetres from the product. The detection readings can be made on the material or product without being physically destructive and monitoring can take place without direct visibility of the surface. This labelling system is compatible with other marking/branding technologies thus enabling a tanner or brand to monitor traceability on two levels. On the wet-end procedure, CTC noticed a better absorption of the tracer on the reverse (flesh side) of the leather. When thickness is less than or equal to 1.5mm, the detection is possible on the grain side, even if it contains hardly any marking agent. For thicker leathers, the tracer on the side to be monitored needs to be of a sufficient concentration to achieve an accurate result. A pigmented finish on leather treated in the wet-end does affect the final detection. With the finishing procedure, CTC found similar conclusions to the ones obtained with micro-spheres: ie the settled tracer quantities were well spread throughout the base coats and pigment finishing layers and were not adversely affected by applying via a spray gun. The only point to monitor when using this procedure is the desired distribution of the tracer in the finishing recipe to be added to the leather. Conclusion and future investigation In order to give a more complete answer for businesses in the leather sector, CTC will endeavour to carry out further analysis. Firstly, marking of pu finishes using free DNA is currently being tested. Secondly, CTC is looking at adding tracer elements to other components used with leather products such as threads and glues etc. The initial work which has been presented in this paper requires the acceptance of the three techniques investigated to go through a further validation phase before being commercially ready for use. Settling, compatibility, mixing, blending and detection (direct reading or laboratory analysis) all require further investigation. This involves not only adopting formulations of tracers specific to our industry's needs, but also sometimes the improvement of detection equipment suitable for the characteristics and manufacturing conditions of the treated materials and to those of individual companies.