The process of hydroentanglement was invented as a means of producing an entanglement similar to that made by a needle loom, but using a lighter weight batt. A successful process was developed during the 1960s by Du Pont and was patented.
However, Du Pont decided in the mid-1970s to dedicate the patents to the public domain, which resulted in a rush of new development work in the major industrial countries, Japan, USA, France, Germany and Britain. As the name implies the process depends on jets of water working at very high pressures through jet orifices with very small diameters. A very fine jet of this sort is liable to break up into droplets, particularly if there is any turbulence in the water passing through the orifice. If droplets are formed the energy in the jet stream will still be roughly the same, but it will spread over a much larger area of the batt so that the energy per unit area will be much less. Consequently, the design of the jet to avoid turbulence and to produce a needle-like stream of water is critical. The jets are arranged in banks and the batt is passed continuously under the jets held up by a perforated screen which removes most of the water. Exactly what happens to the batt underneath the jets is not known, but it is clear that fibre ends become twisted together or entangled by the turbulence in the water after it has hit the batt. It is also known that the supporting screen is vital to the process; changing the screen with all other variables remaining constant will profoundly alter the fabric
Although the machines have higher throughputs compared with most bonding systems and particularly compared with a needle loom, they are still very expensive and require a lot of power, which is also expensive. The other considerable problem lies in supplying clean water to the jets at the correct pH and temperature. Large quantities of water are needed, so recycling is necessary, but the water picks up air bubbles, bits of fibre and fibre lubricant/fibre finish in passing through the process and it is necessary to remove everything before recycling. It is said that this filtration process is more difficult than running the rest of the machine.
The fabric uses include wipes, surgeons’ gowns, disposable protective clothing and backing fabrics for coating. The wipes produced by hydroentanglement are guaranteed lint-free because it is argued that if a fibre is loose it will be washed away by the jetting process. It is interesting to note that the hydroentanglement process came into being as a process for entangling batts too light for a needle loom, but that the most recent developments are to use higher water pressures (400 bar) and to process heavier fabrics at the lower end of the needle loom range.