Bonding, sustainable proposalsThe issue of adhesives and glues is central in footwear manufacturing. Some Italian companies propose innovative solutions that are able to transform the manufacturing processes and to provide the added value of sustainability to assembly lines.
Everyone knows that one of the characteristic traits of a footwear factory is the smell of glue that surrounds it. Nowadays, Italy and Europe are forced by law to progressively reduce the use of solvent-based adhesives in manufacturing process, like it happened in the automotive industry some years ago.
Even if in the rest of the world the environmental or, narrowly speaking, sustainable aspect is often less felt, regulations across the world are becoming increasingly restrictive, above all if we think about the main footwear manufacturing countries (China, Vietnam, India, Brazil…), where the attention of the people to these topics is growing.
We asked some Italian adhesive manufacturers how much this trend is actually underway and what kind of solutions can be adopted in order to make such a crucial stage of shoe manufacturing more sustainable.
The sales statistics of Industrie Chimiche Forestali speak quite clearly: the trend is there, but it still represents a niche. In fact, over 80% of the footwear market still asks for solvent-based adhesives (of which: 42% Italy, 30% Europe, 28% rest of the world), while the residual 20% (39% Italy, 37% Europe, 24% rest of the world) has converted to the water-based ones.
A thought: when we talk about adhesives we should not think only about glues, but also about other systems. For example, the hot-melt: a thermoplastic material that is solid at room temperature but that, in liquid (fused) state, makes surfaces adhesives. The advantages of this system, proposed among others by SIPOL®, lies in the ease of use, storage and transport; in the instant bonding strength, without dying or curing times; in the high viscosity compared to other adhesives, which allows their use on porous and non-porous surfaces; high mechanical strength and tolerance against aggression. Two SIPOL® products above all others, dedicated to lasting, folding, binding and coating for toe-puffs and counters:
- Technipol® Line: Copolyester based hot-melts. A catalytic system that has been tin-free since 2014, used to develop a range of copolyesters in which organotin compounds, which have a proven toxicity on the immune system of mammals, are totally absent.
- Technipol® PA Line: Polyamide based hot-melts. The raw materials of this line of adhesives are mostly (>80%) monomers that derive from renewable sources and vegetable biomasses not intended for human consumption.
And, keeping on talking about alternative systems to the traditional bonding “by brush” , let’s concentrate on KYOTEX, which over 10 years ago introduced an innovation in the process through the self-dimensioned coupling of 2 tapes (solid adhesive) for the application of insoles, heel covering and other items. A system that not only has progressively eliminated the workers’ health issues, expensive solvent extraction systems, and clean-ups carried out with hazardous products, but has also worked on a continual search for green raw materials. The Eco-Friendly Adhesive Tapes, anallergic and breathable, which have never seen a solvent or other hazardous agents even in the production stage, are the result of that.
Going back to the most traditional glues, it is necessary to identify the criticalities linked to the switch from traditional adhesives to sustainable adhesives in the sole – upper bonding. The use of sustainable (water-based) adhesives requires a more accurate preparation of substrates, which in some critical applications (for example, fatliquored leathers), would require the choice of solvent-based adhesives and primers in any case. Another criticality that has to be faced is the correct drying of the water-based adhesive, which needs suitable plant engineering, characterised by effective drying tunnels. We have also to consider the different crystallization rate of water-based polyurethane adhesives (slower) compared to the solvent-based ones: the assembly lines should necessary be equipped with refrigerated plants or tunnels in order to stabilise the bond in a short time.
In order to obviate these problems, INDUSTRIE CHIMICHE FORESTALI proposes:
- The Echo PU series: mono and bi-component polyurethane adhesives formulated for primary bondings (sole-upper) or for joining particularly critical synthetic materials. They can be reactivated between 50 and 55°C, and are characterised by a strong initial tack and high thermal resistance.
- The Echo P series: water-based polychloroprene adhesives that can be used for operations like folding, lining, heel and wedge covering, where leather or fabrics are used. Great open time, good initial tack and heat resistance are common characteristics of the series.
Continuing the discussion on the adhesive purposely studied for the most critical bonding in the footwear world (the one between the sole and the upper), we have to mention the water-based adhesives of KENDA FARBEN , which guarantee an endurance equal to that of a solvent (obviously if the modus operandi suggested by the company and the drying times are respected and if product pooling is avoided). Polychloroprene line ECOSAR 116 for Upper casting and general use, ECOSAR 470 for lasting and ECOSAR 405L for socks.
But how much does the use of “sustainable” adhesives affect costs? According to KENDA FARBEN “there’s no real impact on the cost of the material. By contrast, the performance is the same with the consumption of about one third of the product for the same use, making the switch from the solvent-based adhesive to the water-based one a cheaper choice”.
INDUSTRIE CHIMICHE FORESTALI has a similar position: “The greater impact is on plant engineering, because in order to use water-based adhesive you need drying tunnels and specially-made refrigerated systems. On the contrary, the problem of the greater cost of a water-based adhesive compared to a solvent-based one is irrelevant: the difference is erased by the greater performance of the sustainable adhesive in comparison with the traditional solvent-based”.
For the KYOTEX system by ALC the question is slightly different: “Surely, the main criticality in the introduction of Kyotex lies in the greater ease of use of hazardous glues (greater penetration into the surfaces): with the brush it is easier to obtain an effective bonding even if it is applied in a non-uniform way and not on the entire surface.
Attention, though: at what cost?! Leakages, cleaning operations, yellowing, greater need for employees, risks of occupational diseases… Kyotex adhesive tape obtains the same or even higher performances thanks to a simple application process that does not need qualified workforce. Besides: it offers certainty that each millimetre of the treated item will receive the same quantity of adhesive; the process can be carried out off line (so it is possible to produce, during dead times or externally, great quantities of insoles and store them in the warehouse for up to one year); it guarantees great productivity (up to 7000 insoles per day with only one operator); finally, it enables to calculate sure costs, easily determinable (contrary to the glue applied by hand)”.
SIPOL®’s vision is also different: “Sipol® chose, as much as possible, to follow a more sustainable path. This will lead to decisions that are not only ethical, but also economic. Costs for the development of the Technipol® project, but also an increase of about 10% on the cost of products, due to the choice of using raw materials from renewable sources. As well as in the energetic field, the choice to exploit 100% renewable energy led to a 5% increase in costs”.