|
Application |
Demands |
|
Adult incontinence Feminine hygiene Baby diapers |
Strength |
|
Filtration |
Porosity / air permeability |
|
Wipes |
Surface softness |
|
Table tops |
wipes softness Absorption capacity |
|
Hygiene- |
Low density air-laid Bulk |
|
Hygiene |
acquisition layers Absorption capacity |
|
Filtration |
low density air-laid Filtration Density |
|
Hygiene |
acquisition layer Resiliency |
|
Tabletops |
Printability |
Today the main share of air-laid products is still chemically bonded. However, the importance of chemical bonding has decreased during the past years because hydro-entanglement allows to produce more user-friendly products (Le. hygiene or cosmetics products without chemical additives, hence offering skin tolerance as well as wet wipes of first-class quality) and softer products of identical or higher strength. At the same time, the production methods themselves have become more environmentally friendly.
Thermal bonding with bonding fibers is also out for many products because the strength achieved is not sufficient and the products generate too much "dust" during making-up or use.
Hydro-entanglement has gained considerable importance lately as the developments in the field of hydro-entanglement also benefit the air-laid products. A reduced energy consumption per kg of raw material used, the reduction of material loss, the reduction of water consumption through the use of optimized filter systems as well as reliability and minimum maintenance requirements of the lines are decisive factors for the use of hydro-entanglement with air-laid products,
Especially worth mentioning is the next to ideal possibility of producing so-called composites by hydro-entanglement of various raw materials. In this process, the individual layers are assigned certain characteristics such as moisture absorption, moisture barrier, strength or softness. One example of many products are baby wipes.
In some cases, the lines for 2-layer and 3-layer composites are supplied with or also without pre-bonding stage. In the latter process, all web layers are placed one by one on top of each other and are then jointly hydro-entangled. The process used depends on the application of the respective product.
Fleissner has been delivering complete lines, Le. spunlacing including filtration, high-pressure and low-pressure components as well as complete process control systems since 1995. Continuous advancement and the experience gained with 70 production lines so far make it possible to run the Fleissner spunlacing line at production speeds of more than 300 m/min for working widths of up to 6 m.
As already mentioned, nonwovens produced by the air-Iaid/spunlace process offer products adapted in an optimum manner to the properties demanded at low raw material cost compared with pure air-laid webs.
A carding web is pre-bonded by hydro-entanglement in a first stage. Then woodpulp is spread on top by means of a forming head according to the air-lay technology. The fibers are deposited on the belt or in the case described on a carded PES web on the snowfall principle.
The quantity of biers supplied to the web formation belt and the speed of the belt determine the uniformity and thickness of the air-laid web.
After the carding web passed through the air-laid unit, the 2-layercomposite (carded PES/air-laid pulp) is fed to the subsequent hydro-entanglement system where the pulp layer is bonded with the PES web (2layer composite). 2-layer composites are at a disadvantage compared with 3-layer nonwovens because the pulp layer is at the surface. This can have a negative effect during use of the products, for instance, as wipes.
By addition of another fiber layer from a second card located before the above mentioned hydro-entanglement system, also 3-layer composites (carded PES/air-laid pulp/carded PES) can be produced. The cellulose fiber layer can also be supplied through tissue rolls instead of air-laid forming heads. This-means considerably reduced investment cost. Here also Fleissner has gained extensive know-how by the delivery of such lines. In addition, Fleissner has started a highly interesting development allowing to produce new product generations by combining the spunlace process with an air-lay machine.
Since all 3 processes (spun bond, air-laid and spunlace) can operate at high speeds (500 m/min), wiping cloths and hygiene products can be produced of various multi-layer composites in a highly cost-efficient manner.
Naturally it is also possible to use viscose or PP fibers or blends of these fibers with bi-component fibers instead of PES.
Therefore the following will be a comparison of energy and raw material cost for a 60 g/m2 web consisting of 50% PES/50% pulp or 70% PES/30% viscose. Investment and labor cost will not be taken into consideration, because essentially the yearly savings of energy and raw material cost are of interest here. The line for PES/viscose webs consists of two cards with fiber opening, a spunlace unit, a dryer and a winder. The PES/pulp line comprises two cards with fiber opening, an air-laid unit, one spunlace unit, a dryer and a winder.
The line speed is assumed to be identical for both lines although the PES/pulp line with one air-laid layer could be operated at a 1.5 times higher speed (higher fiber throughput possible).
The assumed production rate at 7000 hours and 3600 mm "'forking width is about 9000 tons/year in both cases. Calculations show that the specific energy cost for the carded/air-laid product are somewhat higher compared with a line for pure carding webs. However, the fiber costs clearly differ (pulp is much cheaper than staple fibers). A comparison therefore shows that the production cost for a pure carding web are essentially higher than for a carded/air-laid composite.
However, depending on the working width and the number of required air-laid forming heads, the investment cost for the air-laid composite may be higher, but this influence is only of minor importance considering the lower raw material costs.
As the raw material cost always represent the biggest share of the production cost the air-laid composite always has an advantage with respect to the production cost, however.
Moreover, the properties of a composite nonwoven are excellent. In conclusion, it can be said that air laid/carded composite nonwovens bonded by an AquaJet Spunlace line not only can be produced at lower cost than hydro-entangled all-fiber nonwovens, but also offer better qualities. This also particularly applies to the new generations of spunbond-airlaid-spunlaced composites or hydro-entangled composites in various combinations. Moreover, Fleissner offers protection for a number of products covered by Fleissner patents or exclusive licenses.
About the Author:
The author is the Director for Sales & Marketing of Fleissner GmbH.
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