Airlaid Web Formation Techniques for Nonwovens
B.Tech, Dept. of Textile Engineering
Giani Zail Singh Punjab Technical University Campus,
Bathinda, Punjab, India
Airlaid and airlaid web formation:
Airlaid is a web formation process. Airlaying or airforming is a method of forming a web by mixing fibers with air to form a uniform air-fiber mixture that is then deposited on a moving air-permeable belt or wire. The process for making airlaid nonwovens involves three primary steps: fiber defibration, web formation and web bonding.
There are two main forming technologies used to produce airlaid webs. With the first, the fluff pulp and staple fibers are sifted through a coarse screen and deposited with the aid of a vacuum onto a forming wire below it. The second system employs formers – the fibers pass through a series of holes or slots in a large cylinder that spans the width of the forming wire.
There are three primary bonding technologies: latex, thermal and hydrogen bonding. The term multi-bonding is used when more then one of the above technologies are used in combination, generally latex and thermal bonding.
Airlaid wipes provide an efficient carrier for the effective and economical application of a variety of active ingredients. Over 40% of the webs are converted to wipes. Major airlaid nonwoven producers include Buckeye Technologies, Concert Industries, Georgia-Pacific Nonwovens, Rexcell (Duni), McAirlaid, Oji and BBA.
Principle of web formation in a simple airlaying process:
- Natural or man-made textile fiber (cut length >25 mm)
- Short cut fibers (generally <25 mm)
- Wood pulp (1.5–6 mm)
Airlaid fabric compared with carding technology has these features:
- The fibers are oriented randomly on the fabric surface – isotropic structure.
- Voluminious webs can be produced.
- The range of the area weight is wider (15 – 250 g/m2) but the mass uniformity of light air laid (up to 30 g/m2) is bad.
- Wide variety of processable fibers
Airlaid – production problems
- Low level of opening fiber material by licker-in roller. Thus is suitable to use pre-opened fibers or combine air-laid with card machine – Random card machine.
- Variable structures of web in width of layer due to irregular air flow close to walls of duct. This problem requires high quality design of duct.
- Possible entangling of fibers in air stream. This problem can be reduced by increasing the ratio air/fibers which nevertheless means decrease in performance and increase of energy consumption due to high volume of flowing air.
The relation between air flow and performance of device shows the importance of fiber length and fiber diameter. QA is air flow, K is device constant, P is performance of device (kg/hour), L is length of fiber staple (m) and D is fiber fineness (dtex).
QA = K.P.L2/D
Thus is suitable to use short fibers for this technology.
Random cards – combination of air laid and carding technology
A major objective of this combination is isotropic textile fabric (random orientation of fibers) with good mass uniformity of light fabrics and with high production speed.
- The first part – card machine opens perfectly fibrous material so single fibers are as a output.
- The second part – airlaid system uses the centrifugal force to strip the fibers off a roller and put them down on an air controlled scrim belt.
Main variations of random cards
Main variations of random cards I
Airlaid function of random card:
1) Random roller between main cylinder and doffer, which rotate in the opposite direction of the main cylinder.
Main variations of random cards II.
2) Centrifugal force of mean cylinder strips the fibers off.
Airlaid and random cards: used fibers
Synthetic fibers, viscose, cotton and blends there of; natural fibers such as flax, hemp, sisal fiber etc.; Reclaimed textile waste and shoddy, cellulose pulp 1.7 – 2000dtex. Max. 120 mm staple length
Feeding system of rando webber
Rando-webber systems with perforated screen
Rando webber systems with cylindrical condensers
- Relatively narrow widths up to about two metres
- Webs of 10– 3000 g/m2
- Virgin or recycled fibers
- Filtration, home furnishings, automotive fabrics, insulation and some medical specialties.
Random card K12 of Dr. E. Fehrer
High-production random card K21 of Dr. E. Fehrer
- K12 is more particularly suited to coarse fibers (10–110 dtex), Basic weight range 20– 2000 g/m2
- K21 is more particularly suited to synthetic and viscose rayon fibers of (1.7–3.3 dtex), Basic weight range 10–100 g/m2
Comparison of Card K12 and K21
|Working widths (m)||1.2 – 5.4||1.2 – 5.4|
|Production speeds (m/min)||150 m/min|
|Weight range (g/m2)||(20 to 2000 g/m 2 )||20 up to 130 g/m2|
|Capacity (kg/h/m)||450 kg/h/m||300 kg/h/m|
|Raw material||Cotton, reclaimed and recycled fibers of 1.7 to 200 dtex||Synthetic and viscose rayon 1.7 to 3.3 dtex|
|Applications||Insulating and mattress fabrics, filling material and mattress covers, under-carpets as well as wadding material for upholstery and automotive industry||Hygienic and sanitary applications, for interlinings and basic material for cleaning cloth as well as coating carriers|
Schematic view of the air laying system
Schematic view of the DOA airlaying system
Chicopee airlaying system
- Air velocity (140 m/s)
- Surface speed of the cylinder ( 20–60 m/s)
- Staple fibers ranging from 13–75 mm
Spinnbau airlaying system
Thibeau hybrid card airlaying machine
Thibeau hybrid system
- Typical MD/CD ratio of 1.2–1.5:1
- Production rate of 200–260 kg/h/m
- Web weights of 35–200 g/m 2
- Fiber types cotton, viscose rayon, PET, PP, PA
- Fiber length of 10–40 mm.
Turbo-card RC 2-6 TR
Turbo-Unit and Turbo-Card
- The turbo-unit TU is either fed by pre-carded webs via a feed plate intake or may be combined with a random card.
- The turbo-roll is equipped with carding segments.
- Aerodynamical web-forming by centrifugal force, doffer fan and suction conveyor.
- Lower to medium fiber fineness range.
- Staple length: approx. 10 – 80 mm.
- Web weight: approx. 25 – 450 g/m2
- Throughput depending on fiber fineness and fiber type: up to approx. 400 kg/h/m of working width.
- Working widths: up to 4.000 mm
- Web speed: approx. 20 – 120 m/min
Airlaid web formation machine 008-0445 of Laroche S.A.
- Web weight ranges from 300 to 3000 g/m 2
- Production speed of up to 10–15 m/min
- Fiber length should be in the range 20–75 mm
- Cotton, man-made, glass fibers
- Hemp, flax, sisal, coconut
- Bed covers, mats, upholstery and insulation material, carrier material for carpets, industrial and geotextiles as well as furniture textiles
General properties of airlaid fabrics
- High isotropicity
- High loft (if required)
- High porosity (95–>99%)
- High absorbency and wicking rate
- Soft handle
- Adequate tensile strength
- Good resiliency (compression recovery)
- High thermal resistance.
Airlaid and random cards: end products
- Chemical bonding: napkins, table cloths and wipes.
- Thermal bonding: nappies (different components, i.e., acquisition layer, distribution layer and absorption core), feminine hygiene/incontinence products and insulation.
- Spunlacing: wet and dry wipes for domestic and industrial applications, medical textiles (including disposable gowns, curtains, wound-care dressings, bed sheets), filtration media.
- Needle punching: interlinings and shoe linings, wadding, medical and hygiene products, geotextiles and roofing felts, insulation felts, automotive components, filters, wipes.
Combination of unidirectional and cross directional web
Cross lapper with horizontal laying device
Tasks of the web-laying machine
- Increasing the web mass
- Increasing the web width
- Determining the web strength in the length and cross directions
- Improving the end product quality
Lap drafter VSTG
Working width up to 7.000 mm. Individual servo-drives for 4 drafting zones with infinitely variable drafts. Only little changes of batt weight regularity by fiber re-orientation increase strength in md.
Merits and limitations of card – cross lapping and air laying
|Carding Cross lapping||Air Laying|
|Very wide widths of fabrics up to 15-20 metres are possible||Width is limited up to 2-3 metres|
|A wide range of fabric weights from 75 to 2500gsm are possible by varying take-off speed of laying lattice in relation to speed of delivery Lattice||GSM lower than 150 are not normally possible.|
|Highly uniform Fabrics can be made in respect of weight per unit length. Variations in weight per unit length in longitudinal and lateral directions are within 5%||It is difficult to achieve good uniformity in weight/unit length particularly in low weight nonwovens.|
|Ability to process a wide range of staple lengths||Mainly suitable for short fibers. With long fibers it is difficult to get satisfactory uniformity.|
|There is no randomisation between lateral and vertical planes. Anisotropy in strength is also present in the lateral plane. Strength is generally higher in cross direction than longitudinal direction though this is minimized to some extent by the use of randomising rollers in carding and web drafting prior to bonding||Fiber orientation is random in all the 3 dimensions though longitudinal direction strength is slightly higher than cross direction strength. The isotropic distribution gives a high degree of insulation properties. But strength is reduced as fibers in the vertical direction do not contribute to strength. Further anisotropic material cannot be made Batt formation involving carding.|
You may also like:
- Spunbonding Method for Nonwoven Fabric Production
- Hydroentanglement Bonding Process for Production of Nonwoven Fabric
- Spunbonding Technology with Types, Application (Bags) and Market Future
- Applications of Nonwoven Hygiene Materials
Founder & Editor of Textile Learner. He is a Textile Consultant, Blogger & Entrepreneur. He is working as a textile consultant in several local and international companies. He is also a contributor of Wikipedia.