Several methods of nonwoven web formation

Nonwovens manufacturing starts by the arrangement of fibres in a sheet or web. The fibres can be staple fibres or filaments extruded from molten polymer granules.  

Illustrations of some of the methods used to form a nonwoven web

Drylaid-carded of nonwoven

1. Bale opener

2. Chute feed

3. Wind up

4. Drying

5. Pan with liquid binder

6. Binder impregnation

7. Card

8. Staple fibre from bale opener or blender

9. Bales of staple fibre

Carding is a mechanical process which starts from bales of fibres. These fibres are ‘opened’ and blended after which they are conveyed to the card by air transport. They are then combed into a web by a carding machine, which is a rotating drum or series of drums covered by card wire (thin strips with teeth). The precise configuration of cards will depend on the type of fibre and the basis weight to be produced. The web can be parallel-laid, where most of the fibres are laid in the machine direction, or they can be randomised. Typical parallel-laid carded webs result in good tensile strength, low elongation and low tear strength in the machine direction and the reverse in the cross direction. Machine parameters and fibre mix can be varied to produce a wide range of fabrics with different properties.

Wetlaid of nonwoven

1. Long fibre

2. Water

3. Fibre and water (slurry)

4. Webforming

5. Binder impregnation

6. Drying

7. Windup

8. Excess water removal

The principle of wetlaying is similar to paper manufacturing. The difference lies in the amount of synthetic fibres present in a wetlaid nonwoven. A dilute slurry of water and fibres is deposited on a moving wire screen, where the water is drained and the fibres form a web. The web is further dewatered by pressing between rollers and dried. Impregnation with binders is often included in a later stage of the process.

The strength of the random oriented web is rather similar in all directions in the plane of the fabric. A wide range of natural, mineral, synthetic and man-made fibres of varying lengths can be used.

Spunlaid of nonwoven

1. Polymer chips feed

2. Liquid polymer

3. Extrusion die

4. Filament attenuator (cooling and stretching)

5. Wind up

6. Calender bonding

7. Laydown

8. Fiber dispersion

9. Extruder

Spunmelt is a generic term describing the manufacturing of nonwoven webs directly from thermoplastic polymers. It encompasses 2 processes, spunlaid and meltblown, often run in combination.

Polymer granules are extruded into filaments through so called spinnerets. The continuous filaments are stretched and quenched before being deposited on conveyor belt to form a uniform web. The spunlaid process results into nonwovens with an increased strength compared to carding, due to the attenuation of the filaments. The downside is that the choice of raw materials is more restricted. Co-extrusion of two components leads to bico fibres, either adding more properties to the web or allowing air-through bonding. Please note that the word spunbonded is reserved for thermo bonded spunlaid.

Meltblown of nonwoven

Meltblown, like spunlaid, starts with extruding a low viscosity polymer. But instead of quenching the filaments when they leave the spinneret, the filaments are being attenuated by hot air streams, keeping the filaments in a partly molten state. This leads to much thinner filaments, with a low tensile strength. The filaments hit a belt or a conveyor belt where they form a web.