Adjusting the vertical for bulk benefits
This is particularly the case when materials are being employed for insulation, for cushioning, or for filling, in applications such as mattresses and bedding, furniture, automotive upholstery and construction materials.
Traditionally, the nonwovens produced for such functions have been made from self-crimping staple fibres and processed on drylaid, mechanical technologies. Crosslapping machines serve to successively layer loosely-bound nonwoven webs into the required thickness prior to them being consolidated, usually by needlepunch machines or thermobonding calendars.
But in addition to thickness, it’s also advantageous in many cases for thick nonwovens to contain a high percentage of air, making them lighter, more breathable and with greater resilience and recovery from compression.
These are some of the key advantages of so-called ‘high loft’ nonwovens, and specifically of the latest ‘vertically lapped’ materials, which are characterised by an extremely high uniformity due to the vertical orientation of their fibres.
Car manufacturers, for example, have been constantly looking to alternative energies and smaller cars for reduced fuel usage, but shedding the weight of components while achieving the same performance level can be just as critical. As a consequence, vertically-lapped nonwovens are now being employed by many of the leading car manufacturers in products such as door insulators, headliner pads and base materials, under-carpet insulators and bonnet and trunk liners.
They can also be equally effective solutions in other industrial areas such as building and construction and the furniture markets too, while in filtration, the unique structure of vertically-orientated webs improves both coarse particle holding on the surface and depth holding of the finer particles, resulting in filters with a very low pressure drop and excellent dust holding capacity.
The ability to provide increased bulk without adding weight provides for greater air circulation and a cooler feel than typical bonded nonwovens. Vertically-lapped products are more foam-like than other filling media, achieving a reduced weight/cost balance at comparable thicknesses, while delivering pressure relief, comfort and support properties.
In mattress construction, meanwhile, vertically-lapped high loft materials are used with strong scrims for spring pocket insulator materials, and as mattress topping materials which are much more foam-like than conventional crosslapped polyesters. The improved compression and recovery does not compromise the soft feel of these materials, while the ability to provide improved bulk without weight provides for much more air circulation and a ‘cooler’ feel.
But adding scrims – usually synthetic mesh materials – to these nonwovens to provide stability also adds cost, and in a further recent development, a new term has entered the nonwoven industry vocabulary – ‘skinning’.
“ ‘Skinning’ refers to running a web or fabric containing thermoplastic fibres under a heated calender roller that just rests gently on its surface – rather than squeezing it – so that only the fibres in the outer layer are compressed and fused together,” explains Professor Stephen Russell, director of the Nonwovens Research Group at the University of Leeds. “You might think of it as glazing the surface. You can achieve similar effects using other heat sources as long as they only act on the surface.”
Following investment in the latest technology for vertically lapped nonwovens production, the UK company John Cotton has this year commissioned a new thermal bonding line solely dedicated to the skinning process and employed to produce a range of glazed-surface materials, including its latest Airstream products.
Airstream nonwovens are the subject of a number of new patent applications in respect of their special ‘convoluted and zoned’ structures. They can be manufactured from a range of natural, synthetic, recycled and blended fibres at various web weights and product densities. In addition, they are odour free, contain no VOC’s (Volatile Organic Compounds) and are cradle-to-cradle recyclable. They are also hypo-allergenic and washable.
While voluminous high loft or vertically-lapped nonwovens have many advantages, however, their production has been restricted to self-crimping staple fibres and it has not been possible to manufacture them using the much faster spunbonding technology which now accounts for by far the highest percentage of all nonwovens manufactured worldwide.
This may be about to change.
Germany’s Reifenhäuser Reicofil reports success in the development of a spunbonding process exploiting bicomponent technology for the production of new high loft nonwovens.
This latest process is based on two filaments of different raw materials being extruded in a side-by-side structure.
Self-crimping of the filaments can be caused by the combination of the different materials or activated by thermal energy. The resulting nonwoven fabrics are subsequently bonded using hot air or a special embossing calender.
Reicofil says these thick, soft nonwovens are well suited for applications in which carded nonwovens are currently being employed and that in the future it expects to be able to offer the technology for producing high loft nonwovens much more cost-effectively.
It also sees possible new applications for such materials in the major hygiene market, as, for example, topsheets and backsheets in premium diapers.
As will be demonstrated at the 2017 edition of INDEX™ – the industry’s leading exhibition which next takes place at Palexpo in Switzerland from 4th-7th April 2017 – the technologies for producing nonwovens are in a constant state of evolution, and often the processes for one application can be successfully adopted by another.
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