Nonwovens: Materials, Technologies & ApplicationsJohn Moot
Today, nonwovens are much more than just a fabric. Nonwovens are used in numerous markets such as the automotive or clothing industry, in the construction or medical sector, for numerous purposes. It is also used in the electrical industry: As phase insulation in the production of electric motors, as a resin carrier in laminates or as layer insulation in the production of transformers.
Advantages of nonwovens
Basically, nonwoven offers many advantages as a technical textile. Due to its composition of different fibers, the material can be adapted to its subsequent application in terms of composition, bonding of the fibers and manufacturing process. Spunbonded nonwovens, for example, are suitable as a material for manufacturing numerous hygiene articles such as baby diapers or bandages, but also for technical applications or the construction industry.
Production of nonwovens
Nonwovens are manufactured using innovative technologies and, depending on the production process, are perfectly tailored to the needs of the respective application areas. The product portfolio comprises numerous technical textiles and fabrics – including nonwovens such as staple fiber nonwovens, spunbond nonwovens, meltblown nonwovens or wetlaid nonwovens.
Differentiation of nonwovens
There are 4 types of nonwovens:
- Staple fiber nonwovens
- Spunbond nonwovens
- Meltblown nonwovens
- Wetlaid nonwovens
To the individual nonwoven types
Staple fiber nonwovens
Staple fiber nonwovens are used for technical textiles with high elasticity and variable basis weight. Staple fiber nonwovens are made from staple fibers that nonwoven manufacturers usually buy in. These fibers are opened and blended before processing. Nonwovens are formed on carding machines with rotating rolls. If high basis weights are to be achieved, crosslappers are used.
Depending on the application, a wide range of raw materials can be processed, e.g. synthetic fibers including viscose as well as natural, glass and carbon fibers.
Raw materials used for staple fiber nonwovens
Synthetic fibers including viscose, natural, glass and carbon fibers.
Meltblown nonwovens are very fine, melt-spun microfibers for a wide variety of applications. The meltblown process is similar to spunbond technology. At the nozzle tip, a hot gas stream flows at high velocity around the extruded, molten polymer. The turbulent hot gas flow below the nozzle scatters the filaments from about 500 microns below the nozzle to about 1 micron on the collection belt.
Compared to spunbond technology, the required melt flow index (MFI) value of the polymer is very high, and the throughput through the single spinneret is very low. The low throughput through very small nozzle holes and the high melt index provide the basis for spinning very fine fibers.
Unlike staple fiber nonwoven technology, spunbond technology eliminated the costly first process step of fiber spinning. In this process, synthetic polymers are extruded as granules of different geometries. The molten polymer, mainly polypropylene, polyester or polyethylene, is spun into continuous filaments using spinnerets.
These filaments are first cooled and stretched with air below the spinnerets, and finally deposited on a collecting belt – a process that takes place continuously. In this process, polyester must be spun at higher speeds than polypropylene in order to achieve the desired quality characteristics such as titer, strength, elongation and shrinkage.
In this process, staple fibers of up to 12 mm staple length are dispersed in water in large tanks, often blended with viscose or wood pulp. The water-fiber pulp dispersion is then pumped onto an inclined screen and continuously deposited. The water is extracted, filtered and returned to the process.
In addition to synthetic fibers, glass, ceramic and carbon fibers are also used in this process. To distinguish wetlaid nonwovens from papers, wetlaid nonwovens must process more than 30 percent by weight of fibers with a slenderness ratio greater than 300.
Contract slitting and cutting of nonwovens
We slit nonwovens from all manufacturers into narrow cut rolls on our slitting lines.