Breathable and extremely durable: Modern adhesives for manufacturing building textiles
Demands on building projects in regard to energy efficiency are permanently growing. Heat insulation for roofs is taking up more space, which often goes at the expense of the ventilation system. Therefore, the requirements for building textiles such as roofing liners are also increasing. In addition to protecting the roofing frame, modern roofing liners also play a major role in facilitating a proper venting.
Requirements for roofing liners
Roofing liners are applied manually and therefore ease of installation plays an important role. The textiles, and in consequence the rolls, must be not too heavy for the roofer, as well as easy to transport and handle on the roof. In addition, the material has to be tear-resistant, provide a slip-resistant surface and be convenient to work with, for instance easy to cut. Once installed, the roofing liner protects the roofing frame and acts – often for extended periods – as temporary roof covering, taking over the function of tiles. Therefore, the material has to be impermeable and provide high and durable resistance against different climatic conditions and external influences. This includes rain, heat and UV resistance, flexibility at low temperatures and wind-tightness, as well as increased strength to resist stretching and tearing during installation. These characteristics are tested already during manufacturing in simulations to ensure that the necessary requirements are fulfilled. In addition to protecting the roof deck, the roofing liner has to be breathable to facilitate a proper venting of the roof truss and allow excess moisture to pass through the fabric for a proper moisture exchange. Fast drying and a high diffusion capacity are therefore a prerequisite for protecting the wooden roofing frame against mould – especially at higher temperature differences between inside and outside.
Powerful adhesives play a major role in the manufacture of functional building textiles. Modern Jowat hot melt adhesives based on polyolefin and polyurethane support the functional properties of those textiles, for instance strength paired with breathability.
Requirements for adhesives
Roofing liners consist of a multilayer structure of different nonwovens which are laminated with a breathable PU or PE membrane. Superior underlining may also include a PE netting which increases the strength of the material compound. The challenge which the adhesive has to master in the manufacture of these textiles, is the optimum adhesion to the different materials and a strong and durable lamination, without impairing the diffusion permeability of the textile. Good wetting properties are a prerequisite for optimum adhesion. The adhesive also has to compensate the different flexibility in the fleece and the membrane. Building textiles are sometimes manufactured of two layers of polyester fleece, which are laminated with a PO hot melt. The adhesive is extruded through a nozzle applicator and placed as a film similar to a curtain between the material compound, taking over the function of a membrane and having to provide the necessary tightness. In other cases, the material combination consists of polyester fleece and different membranes. The adhesive is applied by slot nozzles or by so-called curtain coating methods with the lowest application amount possible to ensure that the bonded substrates remain as open as possible. In this process, the substrate surface is coated only partially by interrupting the adhesive film; therefore, water vapour can diffuse through those “open” spots and escape. Another laminating method which is increasingly used, is the application of PUR hot melts with roller applicator systems. When used as a single unit, two roller applicator systems can laminate three layers in a single process step.
The powerful PO and PUR hot melt adhesives of Jowat are characterised by a wide spectrum of adhesion plus superior and permanent adhesive durability on all standard materials – also at low application amounts and high line speeds. Today, roofing liners are exposed to increasing temperatures due to changed climate conditions. A trend towards PUR hot melt adhesives can be observed, based on the growing requirements regarding heat resistance. PUR hot melts inherently come with the necessary high heat resistance. Even at high temperatures, the adhesive virtually does not soften, ensuring that the compound layers do not move under mechanical stress. For many years, EVA hot melts were the adhesive of choice for manufacturing building textiles. PO hot melts are the standard products today and, due to characteristics such as higher heat resistance and lower application amount which provides the same adhesion, increasingly also PUR adhesives. The suitable adhesive system has to be selected for each application based on the materials to be bonded, the manufacturing process and the individual requirements.
High breathability is an essential characteristic of adhesives in the manufacture of building textiles. Jowat has many years of experience in the development of breathable adhesives for clothing textiles. This experience is used to promote the development of polyolefin-based and of moisture-curing polyurethane adhesive systems for building textiles. The objective: Developing adhesives for building textiles with an increased water vapour diffusion permeability to replace foils with such adhesive films in the long term.
The professional article is published in the Melliand Newsletter of the magazine 'Technische Textilien'. You can download the original article in German language down below.