wet laid nonwoven production process

1. J.N. Govt. Engg. College
SUNDERNAGAR
Presentation
Non-Woven Technology
TE-604
ABHISHEK RANA
10BTD5090001
Textile Engineering
Wet Laid Non-Wovens

2.  Wet laid nonwovens are nonwovens made by modified papermaking
process.
 The principle of wet laying is similar to paper manufacturing. The difference
lies in the amount of synthetic fibers present in a wet laid nonwoven. A dilute
slurry of water and fibers is deposited on a moving wire screen and drained
to form a web. The web is further dewatered, consolidated by pressing
between rollers and dried. Impregnation with binders is often included in a
large stage of process. This produce a web in which the fibers are randomly
oriented.
 Specialized paper machines are used to separate the water from the fibers
to form a uniform sheet of material, which is then bonded and dried.
 H. fourdrinier developed a papermaking machine that has been the basis
form the most modern papermaking machines employing very short fibers.
The schematic diagram of this machine is shown in figure.
Wet-laid Nonwovens

3.  The wood pulp and water in the ratio of 0.003-0.007 (w/w) are mixed to
make a good quality of suspension of fibers and water.
 The suspension is then pumped to the head bon which has a small opening,
often called as slice. Through the slice, the fiber-water suspension is
dropped onto the moving perforated Fourdeinier wires. These wires contain
a lot of perforations through which the water gets drained to the vacuum and
the fibers, deposited on the moving wires, formed a web. In this way, the
wet-laid paper is formed.

4.  But, by using this machine it was not possible to process relatively long
fibers as the mentioned dilution ration results in inadequate fiber dispersion
in water.
 In this regard, F. Osborne and C. H. Dexter proposed a solution.
 According to them, in order to process long fibers, the ration of weight of
fiber pulp and weight of water should be around 0.0005-0.00005 and in order
to handle such a huge quantity of water, the inclination of the forming wire to
the base is required to be equal to 20o.
 The modified machine has a large head box (slice) opening with inclined
wire machine is shown in Figure. This machine has been used to make
papers from long fibers and subsequently the basis for making nonwovens
also.

5. Process Description
 The fibers are mixed with water and it forms fiber-water suspension. It shows
two mixing tanks for preparation of better fiber-water suspension.
 This suspension is then pumped through the head box to the perforated
wire. The water is drained through the perforations and the fibers are laid on
the moving wire to form a web.
 The wet-laid web is then dried and bonded by using binder. It is again dried
and finally wound on a roll.

7. Special features of the wet-laid process and its features:
 Compared to the dry web-making practice such as card lying, aerodynamic
lying and the wet method are high efficient and wet-laid process are having
variety of end use.
 Given that short fibers are necessary, the web structure is closer, rigid and
less strong than in comparable web made from longer, warped fibers in dry
processes. Special cure is necessary to achieve analogous textile
properties.
 The basis weight commonly termed, as GSM (gram per square meter) is
variable within broad limits.
Web Forming
•Pulp line
•Synthetic
line
•Waste Line
Bonding
•Adding the
Binder
Fibers
•Adding
binding
dispersion to
the pulp
•Adding the
binder to the
nonwoven
pulp
Pressing
•Here the
web is
pressed.
Web Drying
•Contact
drying
•Circulating
all dryers.
•Radiation
drying
Batching

8. Raw Materials
▪ Cellulose Pulps
A wide range of materials.
▪ Man-made Fibers
Viscose rayon, polyester, nylon, polypropylene, poly-acrylate.
▪ Binder Fibers
PVA, co-polyesters, Bi-component fibers.
▪ High-tech fibers
Ceramic, aramid, polyuron, PTFE, carbon
▪ Bonding agents
latex, poly-acrylate, styrene-butadiene polymer, ethylene-vinyl acetates, vinyl
chlorides
▪ Natural fibers
jute, flax, hemp, kenaf, bast, peat, cotton, coir, ramie.

9. Merits and Demerits
The merits of wet-laid nonwovens are:
 High through put rate.
 Isotropic as well as anisotropic structures can be created.
 Too brittle fibers, generally not suitable for textile applications, can be
processes.
The demerits of wet-laid nonwovens are:
 High capital intensive process.
 High energy intensive process.
 High fiber quality requirements.

10. Applications of Wet-laid
Nonwovens
 Air filter paper, battery separators, bed linen, cigarette paper, liquid filter
paper, medical underwear, nonwoven for coating, nonwoven for mat,
sausage wrapping paper, synthetic fiber paper, table cloths, teabag paper,
vacuum cleaner bag paper, water proofing sheets, wet toilet paper.
 In addition, the wet-laid technical nonwovens are found to be used in many
specialized applications: glass fiber roofing substrate, glass fiber mat for
flooring, glass fiber mat for printed circuit boards, wall covering, insulation
materials, battery separators, RFI shielding veils etc.

11. Fabric Defects
Typically there exist three types of defects in the wet-laid nonwoven fabrics.
They are known as log, ropes and dumbbells.
 Logs are characterized by bundle of fibers with aligned cut ends that are
ever dispersed. They are normally considered to be a fiber supply problem
or can be the result of remarkably low under agitation of the initial
dispersion.
 Ropes are characterized by assemblages of fibers, with unaligned ends,
that are clearly more agglomerated than in the general dispersion. They are
formed when fibers are encountered a vortex that facilitates in entangling the
fibers to form ropes.
Logs Ropes

12. Dumbbells are characterized by paired clumps of fibers connected by one or
more long fibers. The formation of dumbbells requires an excessively long fiber
and a sang in he system piping. A long fiber snags in the system piping so that
its free end whips in the flow and accumulates normal fibers on each end and
these finer bundle becomes so large that the fluid drag plucks the dumbbells
from the snagged fiber. It is thus often said that the good quality of dispersion of
fibers in water is a key to the good quality of wet-laid webs.
Dumbbell

13. Continuous Filament Webs
Both the process, melt blown and spun laid are similar in principle but different
in technologies used. The two important polymer-extrusion based technologies
that are mainly used to convert the molten polymer into nonwoven fabric are:
Spun bond Webs: In the spun bond technology, usually thermoplastic fiber
forming polymer chips is extruded to form fine filament fibers direct of around
15-35 micrometer diameter. The filaments are attenuated collected on a
conveyer belt in the form of web. The filaments in web are then bonded to
make spun bond nonwoven fabric.
Melt blown Webs: The melt blown technology is based on melt blowing
process, where usually, a thermoplastic fiber forming polymer is extruded
through a line die containing several hundred small orifices. Convergent
streams of air (exiting from the top and bottom sides of the die nosepiece)
rapidly attenuate the extruded polymer stream to form extremely fine diameter
fibers (1-5 micrometer).the attenuated fibers are subsequently blown by high-
velocity air onto a collector conveyer, thus forming a fine fibered self-bonded
melt blown nonwoven fabric.

14. Spun Laid Webs
1) High molecular weight and broad molecular weight distribution such
polypropylene PP (polypropylene is mostly used primarily due to its low
price and advantageous properties such as low density, chemical
resistance, hydrophobicity, sufficient or even better strength. The fiber grade
polypropylene (mainly isotactic) is principal type of polypropylene which is
used in spun bond technology and polyester (PET).
2) Other polyolefin such as polyethylene of high density (HDPE) and linear
polyethylene of low density (LDPE) as well as a variety of polyamides (PA),
mainly PA^ and PA6.6 are found.
3) Bi-component fibers.
Applications
 Today they are used both for durable and disposable applications.
 The main application for spun bond nonwovens are in automobiles, civil
engineering, hygiene, medical, packaging and agriculture.

15. Process Sequence
 The spun bond technology, in its
simplest form, consists of four
processes namely, spinning, drawing,
web formation and web bonding.
 The spinning process largely
corresponds to the manufacture of
synthetic fiber materials by melt-
spinning process.
 In the drawing process, the filaments
are drawn in a tensionally locked way.
The web formation process forms a
nonwoven web.
 Web bonding is generally possible by
means of the web bonding processes
(mainly thermal calendar bonding)
 The sequence of processes is as follows: polymer preparation - polymer
feeding, melting, transportation and filtration – extrusion - quenching-drawing
– laydown – bonding - winding
Extrusion
Cooling & Filtering
Spinning
Drawing
Laydown on Forming Web
Autogenously Bonding
Roll Up
Polymer
Melt
Filament
Web
Fabric

17. Preparation of Polymer
It involves sufficient drying of the polymer pellets or granules and adequate
addition of stabilizers/additives. The stabilizers are often added to impart melt
stability to the polymers.
 Polymer pellets or granules are fed to an extruder hopper by gravity-feeding.
The pellets are then supplied to an extruder screw, which rotates within the
heated moves further to the screw. The screw is divided into feed,
transmission and metering zones.
 The feed zone preheats the polymer pellets in a deep screw channel and
conveys them into the transition zone.
 The transition zone gas a decreasing depth channel in order to compress
and homogenize the melting plastic.
 The melted polymer is discharged to the metering zone, which serves to
generate maximum pressure for pumping he molten polymer. The
pressurized molten polymer is the conveyed to the metering pump.
 A positive displacement volume metering device is used for uniform melt
delivery to the die assembly.

18. The molten polymer from the gear pump goes to the feed distribution system to
provide uniform flow to the die nosepiece in the die assembly.
From the feed distribution channel the polymer melt goes directly to the
spinneret having several thousands drilled orifice or holes. The spinnerets are
usually circular or rectangular in shape then it is solidified, drawn and entangle
the extruded filament from the spinneret and deposit them onto an air-
permeable conveyer belt or collector followed by spinnning.

19. The key process factors of spun bond nonwoven non-woven technology are
polymer throughput rate, polymer melting temperature, quench air
velocity, bonding parameters and lay-down velocity. These process factors
play important roles in deciding the morphology and diameter of the filament
which are the building block of any spun bond nonwovens.
 The filaments spun at lower throughput rate are thus more stable than those
spun at higher throughput rate. The filament diameter increases with
increasing throughput rate. Because the rheological conditions are more
favorable for crystallinity and orientation of the filaments spun at lower
throughput rate.
 The polymer melting temperature influences on the drawing of the
filaments through the spinneret that in turn decides the diameter of the
filament. The lower polymer melting temperature results in increase in melt
velocity of the polymer that leads to difficulty in drawing of the filaments.
 The lower quench air temperature results in increase of viscosity that leads
to slower drawn-down which finally resulting in higher filament diameter. As
the drawn-down takes place slowly, an increase in crystallinity and
orientation is observed.

20.  The quench air pressure has a role to decide filament diameter. Higher
quench air pressure increases spin line draw ratio that in turn reduces
filament diameter. The pressure drop is known to be proportional to air
velocity.
 The web is formed by the pneumatic deposition of the filament bundles onto
a moving belt. In order to obtain maximum uniformity and cover, the
individual filaments must be separated before reaching to the belt. This can
be accomplished by inducing an electrostatic charge onto the bundle while
under tension and before deposition. This can be achieved by high voltage
corona discharge. The belt is usually made of an electrically grounded
conducive wire, which discharge the filament upon deposition. Sometimes,
mechanical or aerodynamic forces can also separate filaments. If the lay-
down conveyer belt is moving and filaments are being rapidly traversed
across the direction of motion, the filaments are being deposited in a zig-zag
pattern on the surface of the moving belt.

21. Melt Blown Technology
The melt blown technology is based on melt blowing process, where usually a
thermoplastic fiber forming polymer is extruded through a liner die containing
several hundred small orifices. Convergent streams of hot air (exiting from the
top and bottom sides of the die nose piece) rapidly attenuate the extruded
polymer streams to form extremely fine diameter fiber (1 – 5 micrometer). The
attenuated fibers are subsequently blown by high-velocity air onto a collector
conveyer, thus forming a fine fibered self-bonded melt blown nonwoven fabric.
Raw Material:
 Polypropylene has been the most widely used polymer for melt blown
technology. Other polymers used are polyamide, polyester and polyethylene.
 It is known that polyethylene is more difficult to melt blown into fine fiber
webs than polypropylene, but polyamide 6 is easier to process and has less
tendency to make shot (particles of polymers that are large that fibers) than
polypropylene.
 In general, the requirements of polymers for melt blown technology are high
MFR or MFI (300-1500 g/10min), low molecular weight and narrow
molecular weight distribution.

22. Process Sequence
Melt blown technology converts polymeric resin to fine fibered nonwoven fabric.
Steps:
 Prepare polymer for extrusion.
 Extrude low viscosity polymer melt through fine capillaries.
 Blow high velocity hot air to the molten polymer and attenuate the polymer
melt.
 Cool the molten polymer by turbulent ambient air to form fine fiber.
 Deposit the fibers onto a collecting device to form useful articles like fiber.

23. As soon as the molten polymer is extruded from the die holes, high velocity hot
air streams (exiting from the die nosepiece) attenuate the polymer streams to
form microfibers. As the not air stream containing the micro fibers progresses
toward the collector screen, it draws in a large amount of surround air (also
called secondary air) that cools and solidifies the fibers. The solidified fibers get
laid randomly and entangled themselves onto the collecting screen, forming a
self-bonded nonwoven web due to the turbulence of the air.
 The extruder for melt blown technology is longer L/D (30+) so that more
external heating surface is available. The energy for melting comes costly
from barrel heating and practically no viscous shear heating when high MFR
resins are used.
 Also, the longer extruder can achieve a higher output rate and better melt
homogeneity than the shorter extruder thus offers good barrel support and
allowance for thermal expansion due to high screw speed and high barrel
temperature.
 The extruder should be able to provide heating and cooling. Air cooling for
barrel zones is usually sufficient for melt blown technology.

24.  The design of the extruder screw must be such that a deeper feed section
should be used for better feeding and it should have ability to receive
granules and pellets.
 A shallower metering section is required for higher shear and better
pumping. The compression ratio must be greater than 3.5.
 For melt filtration, a screen changer down stream of extruder is must. Fine
mesh screen (325 mesh screen) is recommended to remove undispersed
pigment, carbonized materials, etc.
 A metering pump is needed to maintain a constant output rate. This is
important for maintaining product quality.
 A static melt mixer may be used at the entrance of the die maintain good
melt temperature homogeneity.
 The die system is known to be one of the important components of the melt
blown technology.

25. There are generally two die systems used. The “Exxon” die (a coat hanger die
feeding a single row of capillaries and on e piece die tip construction where
there were 25-35 capillaries per inch of die width. The advantage of this system
is that higher quality web can be produced, but the disadvantage is that the
output per unit die width may be limited) and the “biax-fiberfilm” die
system(which has multiple rows of spinning nozzles and concentric air holes
having around 200 capillaries per inch of die width up to 12 rows to capillaries.
The advantage of this system is that higher output per unit die width may be
obtained (higher hole density), but the disadvantage is that it is more
challenging to maintain uniformity at each hole (air and polymer flow rate and
temperature) and it results in broader fiber size distribution.

26. Key Process Factors:
To decide the morphology and diameter of the fibers which are the building
blocks of the melt blown technology are:
 Polymer Melt Temperature
to control the melt viscosity of the polymer at die. Melt temperature decreases
with increasing screw speed/output rate, this needs to compensate for lower
temperature by using a higher barrel temperature at high screw speed/output
rate. Higher melt temperature results into finer fiber, more tendency to produce
“shots”, higher energy cost (heating and cooling), shorter tip life (degradation of
pigment, polymer etc.)
 Polymer Throughput Rate
It can be increased by increasing the screw speed. With higher output rate, it is
more difficult to achieve good quality web.

27.  Process (primary) air temperature, process (primary) air flow rate
The lower air temperature results in better fiber cooling, less shots, whereas
higher air temperature results in finer fiber diameter and more energy cost.
Increasing primary air flow rate generally increased global orientation of fibers
in the machine direction. Increasing primary air flow rate reduces pore cover in
the webs substantially. This is thought to occur because the increased air flow
decreases fiber entanglement and reduces fiber diameter.
 Die-to-collector distance
The higher distance results in higher fiber entangling, bulkier and softer web,
better fiber cooling, less tendency to disturb fiber lay down, less web uniformity
and is used for heavy basis weight fabric (sorbent products etc.). The lower
distance results in less fiber entangling, more compact/stiffer web, balance of
process air and suction capability, more uniformed web with better barrier
properties and is used for light basis weight fabric, especially light weight spun
melt composites.

28. Bonding in melt blown process:
Thermal bonding is most commonly used technique. The bonding can be either
overall (area bonding) or spot (pattern bonding).
Applications
 Owing to the smaller fibers and large surface area occupied by the fibers the
melt blown nonwovens offer enhanced filtration efficiency, good barrier
property and good wicking property. They are finding applications n filtration,
insulation and liquid absorption.
Characteristics of melt blown fabrics are:
Adjustable pores and capillary structures, excellent barrier properties, filament
size 1-3 µm, high elasticity, high filtration capability, isotropic formation – this
means the fibers are randomly distributed in the machine (MD) and cross-
machine direction(CD), large area-to-weight ratio, self-bonding, the weight of
the melt-blown fabrics in gram per square meter (GSM) should range from
4g/m2 to over 1000 g/m2, very good thermal insulation for apparel application,
weak tensile properties, wicking properties.

29. Defects in Melt Blown Process
There are three major defects that occur in melt-blown:
 Roping
It is caused by uncontrolled turbulence in the air-stream and by movement of
fibers during and after lay down.
 Shot
It is caused by excessively high temperatures or by too low a polymer
molecular weight.
 Fly
It is caused by too violent blowing conditions

30. Spun-bond v/s melt-blown
It is interesting to note the differences between the spun bond and melt blown
technologies and product thereof.
 The melt blown technology requires polymers with considerably lower melt
viscosity as compared to the spun bond technology.
 The initial investment for spun bond technology is three to four times higher
than that of melt blown technology.
 The melt blown technology consumes more energy than the spun bond
technology because of the usage of compressed hot air.
 The melt blown nonwoven is generally found to be costlier than the spun
bond nonwovens.

31. SMS, SMMS, SMMMS
 SMS is the abbreviation of “spun bond + melt blown + spun bond non
wovens”, that is a combined nonwoven fabric which two layer spun bond
have been combined with one layer melt blown nonwovens inside,
conforming them into a layered products called SMS nonwoven fabric (spun-
melt-spun) if combined with two layer melt blown nonwoven inside, it is
called SMMS nonwoven fabric (spun-melt-melt-spun) in the same way
combined with three layer melt blown nonwoven inside, it is called SMMMS
nonwoven fabric (spun-melt-melt-melt-spun).
 SMS, SMMS, SMMMMS are strong and offer the intrinsic benefits of fine
fibers such as fine filtration, low pressure drop as used in face masks or
filters and physical benefits such as acoustic insulation as used in
dishwashers. One of the largest users of SMS, SMMS, SMMMS materials is
the hygienic or medical industry such as disposable diaper, feminine care
products, facemask, surgical drape, surgical pack, surgical gown, etc.

32.  SMS, SMMS, SMMMS nonwoven fabrics can be treated by special
processes, including of repellency, anti-static, absorbent, flame Retardency,
anti-bacterial, UV resistance, fragrance treatment etc. the treated fabric will
be functioned with various features.
 This is a high coverage nonwoven fabric. Its low weight, high longitudinal
and transversal strength and soft feel make it suitable for use in the medical
and hygiene industry. It can be given special treatment to give it certain
properties (hydrophilic, anti-bacterial, oil-repellent, alcohol-repellent and
blood-repellent)

33. Spun Bond – Melt Blown – Spun Bond
(SMS)
Spun bond filament
Quenching
Stretching
Melt blown layer
forming
Spun bond filament
over laying
Calendaring
SMS fabric output
SMS Production Stage
Products
Baby diapers – standing cuff
Adult diapers
Medical products
Industrial protective apparel

34. Finishing Process
Finishes
Dry finishing process
Shrinkage
Wreching & creping
Perforating & slitring
Crabble, calendaring & pressure
Spliting
Wet finishing process
Washing
Dyeing
Printing
coating
Blocking
amanating
Dry
Wet