all dry laid nonwoven production processes

1. Presentation
Non-Woven Technology
TE-604
ABHISHEK RANA
10BTD5090001
Textile Engineering
Dry Laid Non-Wovens

2. It consists of four phases:
• Fiber Selection
• Fiber Preparation
• Web Formation and Layering
• Bonding and Stabilization Of Web

3. Fiber
Density
(kg/m3)
Moisture
Regain
(%)
Breaking
Force
(N/tex)
Breaking
Elongation
(%)
Initial
modulus
(N/tex)
Specific
flexural
rigidity
(mN
mm2/tex)
Co-efficient
of static
friction
Polypropylene 910 0 0.65 17 7.1 0.91
Polyester 1390 0.4 0.47 37 8.8 0.28 0.58
Nylon 6 1140 4.1 0.29 46 0.6 0.47
Nylon 6,6 1140 4.1 0.37 43 1.0 0.12-0.22 0.47
Acrylic 1190 1.2 0.27 28 6.2 0.33-0.48
Viscose Rayon 1490 1.2-1.4 0.21 15.7 6.8 0.05 0.43
Glass 2500 0 0.75 2.5 29.4 0.09
Cotton 1520 7-5 0.19-0.45 5.6-7.1 3.9-7.3 0.53 0.22
Flax 1520 7 0.54 3 18.0 0.19
Jute 1520 12 0.31 1.8 17.2 0.46
Wool 1310 14 0.11-0.12 29.8-42.5 21.3 0.24 0.14
Silk 1340 10 0.38 23.4 7.3 0.60 0.52

5. Fiber
Density
(kg/m3)
Moisture
Regain
(%)
Dry Breaking
Force
(Ntex)
Dry Breaking
Elongation
(%)
Wet Breaking
Force
(Ntex)
Wet Breaking
Elongation
(%)
Water
Inhibition
(%)
Cotton 1520 8.0 0.2-0.24 7-9 0.26-0.30 12-14 50
Abaca 1450 6.5 0.35 2.5
Viscose 1490 13.0 0.22-0.24 20-25 0.10-0.15 25-30 90-100
Tencel 1490 11.2 0.4-0.44 14-16 0.34-0.38 16-18 65-70
Polyamide 1140 4.1 0.29 46
Polyester 1390 0.4 0.55-0.60 25-30 0.54-0.58 25-30 3
Polypropylen
e
910 0 0.65 17
Glass 2500 0 0.75 2.5
It an be seen that viscose fibres have remarkably low wet breaking strength as
compared to their dry breaking strength, but they have excellent water absorption
capacity

8. 2. Blending
The blending feeders gently opens the tufts by the interaction of an inclined
needle lattice apron and an evener roller equipped with needles.
The opened tufts are deposited into a weigh pan controlled by load cells which
dumps the fibers onto a feed conveyer.

9. For coarse opening
Blending conveyers feeds fibers into an opening roll, which has a three lag pin
beater where coarse opening of the fiber takes place. (by kirschner beater)
Web Former Feeding
The feed system to the feed forming machine is selected based on the type of
fiber and the type of web former. Chute feeding is normally used to feed fibers
up to 60 millimeters in length. For longer length fibers, a hopper feed with a
shaker – type chute is used.

10. Web Formation
1. Mechanical Web Formation (carding and garneting)
2. Aerodynamic Web Formation (air lay)
3. Centrifugal Dynamic Web Formation (random card)

11. • To separate small tufts into
small fibers, to begin the
process of parallelization and
to deliver the fibers in the form
of a web.
• The principle of carding is the
mechanical action in which
fibers are held by one surface
while the other surface combs
the fibers causing individual
fiber separation.
• At its center is a large rotating
metallic cylinder covered with
card clothing. The card clothing
is comprised of needles, wires,
or fine metallic teeth embedded
in a heavy cloth or in a metallic
foundation.

12. • The fibers are fed by the chute feed or
hopper and condensed into the form of
a lap or batting.
• This is initially opened into small tufts
by a licker-in, which feeds the fibers to
the cylinder. The needles of the two
opposing surfaces of the cylinder and
flats or the rollers are inclined in
opposite directions and move at
different speeds.
• The main cylinder moves faster than
flats and, due to the opposing needles
and difference in speed, the fiber
clumps are pulled and teased apart. In
the roller-top card the separation occurs
between the worker roller and the
cylinder.
• The striping roller strips the larger tufts
and deposit them back on the cylinder.
• The fibers are aligned in the machine
direction and form a coherent web
below the surface of the needles of the
main cylinder.

13. • Garnetts are similar to roller-top cards.
• Garnett is defined as group “a group of rolls placed in an order
that allows a given wire configuration, along with certain speed
relationship, to level, transport, comb and interlock fibres to a
degree that a web is formed.
• Garnetts are mostly used to process wadding and form making
pads and automobiles and bedding industries.
• It delivers a more random web than a card. Most web from garnett
are layered by cross lapping to build up the desired finished
nonwoven weight.

14. Process:
• Lap or plied card webs are fed by feed
rollers.
• The fibers are separated by a licker-in or
spiked roller and introduced into an air-
stream.
• By the force generated by the
air stream (suck or blew),
single fibers are collected to
form a web on a perforated
surface of cylinder.
• The web is delivered to a
conveyer for transporting to
the bonding area.

16. Features of the Air-laid
• The length of fibres used varies from 2 to 6 cm.
• The shorter lengths allows higher production speeds. Longer fibres require
higher air volumes to avoid tangling.
• Due to uniformity problems, it has not been practical to make isotropic webs
lighter than 30 g/m2.
• Air-laying is slower than carding, hence more expensive.
Advantages
• Isotropic structure of the web.
• Vast webs can be produced.
• Wide variety of processable fibers such as natural, synthetic, glass, steel,
carbon etc.
• Possibility of processing waste fibers.
Disadvantages
• Low level of opening fiber material by licker-in.
• Variable structures of web in width of layer due to irregular air flow close to
walls of duct.
• Possible entanglement of fibers in air stream.

17. • The centrifugal dynamic random card forms a web by throwing off
fibers from the cylinder onto a doffer with fiber inertia, which is
subject to centrifugal force, in proportion to the square of the rotary
speed.
• Orientation in the web is three-dimensional and is random or
isotropic:
The production of random card is generally about 30 to 50% higher
than conventional cards. The machine direction versus the cross-
direction strength better than those produced in the conventional
card, but not as good as that of the air-laid webs.

18. Longitudinal Layering
More than one card is involved here. Carded webs from all the cards (placed
in a sequence one after the other) are laid above one another on a conveyer
belt and later bonded. Properties of the bonded webs are anisotropic in nature
because of the unidirectional arrangement of fibers. This technique can be
used for making light textiles.
Perpendicular Layering
This technique has an advantage over longitudinal and cross layering because
of the perpendicular and oriented fibers in the fabric. The bonded webs have
light resistance to compression and show better recovery after repeated
loading.
Cross layering
It can be done by using two different devices (cross lappers); vertical and
horizontal cross lapper. Vertical lapper consists of a pendulum conveyer
after the doffer roll on a card. Pendulum conveyer reciprocates and lays the
carded web in to the folds on another conveyer belt.

19. There are mainly three disadvantages of parallel laid web system viz.
a. Even though some width way stretching of the fleece is possible, it cannot be
increased more than the width of carding machine.
b. The fibers in the web lie predominately in the machine direction which means that
the web is five to six times stronger along its length than across its width.
c. The mass per unit area of the final fleece is limited because it is not economical to use
more than 12 cards.
Cross-lay Process
The cross lay process is very popular among the nonwoven industries. The function of
cross-lay process are as follows:
To obtain batt with higher basis weight than that of card web.
To obtain batt with higher width than that of card web.
To obtain batt with fibers preferentially oriented along the transverse direction of it.
To obtain batt with layered structure.

21. 1. Mechanical Bonding
a) Needle Punching
b) Stitch Bonding
2. Thermal Bonding
3. Chemical Bonding
4. Hydro Entanglement

22. Needle punching is a nonwoven process by which the fibers are mechanically
entangled to produce a nonwoven fabric by repeated penetration of barbed
needles through a performed dry fibrous web.
The machine which accomplishes this process is known as needle loom. The
fibrous web, which is unbounded and therefore thick and voluminous, is fed to
the machine by a pair of feed rollers. Needle punching is a process of bonding
non woven web structures by mechanically interlocking the fibers through the
web.
Barbed needles, mounted on a board, punch fibers into the web and then are
withdrawn leaving the fibers entangled.
The needles are spaced in a non-aligned arrangement and are designed to
release the fiber as he needle board is withdrawn.
The needle punch web offer a wide range of product characteristics such as :-
1. Unique physical properties i.e.,, elongation in all ( x, y & z ) directions for
mold able applications.
2. Ability to attach layers of different types of fiber webs to produce
composites.
3. High opacity per unit area.
4. High strength makes them overwhelming choice for geotextiles fabrics.

23. It then goes on working zone of the machine and passes in between a pair of
perforated bed plates. The needles are arranged in a needle board in width-
wise rows. The needle board is mounted on a beam which is then given an up
and down reciprocating motion by means of an eccentric crank mechanism. In
the down stroke mode, the needles descend through the perforations of the top
bed plate, through the web, and through the perforations of the bottom bed
plate. During the upstroke, the barbed needles withdraw upwards and the bed
plate strips the web off the needles. As a result, the fibres are mechanically
interlocked, thereby providing the mechanical strength. The needle bonded
nonwoven is delivered by a pair of delivery rollers.

25. Process Description:
Needle-punched nonwovens are manufactured by mechanically orienting and
interlocking the fibers of a carded web. This mechanical interlocking is
achieved with thousands of barbed felting needles repeatedly passing into and
out of the web. The major components of the needle punch line and brief
description of each are as follows:
Blender
The machine is where the raw materials are stored at a desired proportion of
different types fibers (e.g., 40% PP and 60% PET)
Opener
It is where the raw materials are fed from the blender in order to reduce the
size of fiber tufts from the blender to hopper feed.
Carding
The machine where the fibers are stored and are transferred for fiber carding.
Cross Lapper
The machine that continuously lays a web so that its fibers are oriented in
cross direction. The web is laid on the conveyer moving at right angles.
Needle Punching
The process in which the web is bonded mechanically to each other by a series
of needles. The designs of products are being controlled in this line. The
operations consists of a pre-needle, drafter and a finish needle loom.
Winding & Cutting
The final product is being wound into rolls and being cut into a specified width
in this line.

26. • Needles are the heart of the needle punching
process.
• A needle has the following parts: crank, shank,
taper, blade, barb and a point.
• The shank locates in the hole in the needle board
and the crank is clamped between upper surface
of the needle board and the needle beam, thus
holding it firmly and vertically aligned in the
loom.
• Traditionally, the cross-section of a needle is
triangular and carries a total of nine barbs, three
per apex. The dimensions of the barbs and their
relative arrangement vary depending upon the
application and machine operation.

27. • The nonwoven industry uses two types of
needles known as single reduction needle
and double reduction needle.
• The single reduction needle has two
sections, shank and blade.
• But the double reduction needle has an
intermediate section in-between the shank
and the blade. This is a transition stage
between the different diameters of the shank
and the blade.
• The single reduction needle is much stiffer
than the double reduction needle.
• The single reduction needle usually made
only for coarser gauge needles.
• The single reduction needle is used for stiff
fibers(waste fibers, shoddy etc.)

28. • The barb is known to the
main working component
of a needle.
• A barb is characterized
primarily by kick-up,
spacing, angle and depth.
• Based on the spacing,
the barbs are
categorized by
regular barb (RB),
medium barb (MB),
close barb (CB), and
high density barb
(HDB).

29. • As far as the kick-up is
concerned, there exist high kick-
up (‘K’ barb), low kick-up (‘NK’
barb), and non kick-up (‘B’
barb).
• The fiber carrying capacity
decreases from ‘K’ barb to ‘NK’
barb to ‘B’ barb.

30. • The high density barb
provides maximum
aggressive punching,
followed by the close barb,
medium barb and regular
barb.
• At the same time, he
surface of the fabric is
found to be maximum
uneven with the high
density barb, followed by
close barb, medium barb
and regular barb.
• Here exist barb with
different angles.

31. • In nonwoven industry, a wide variety of needles are used.
• They vary in their cross-sectional shape as well as the geometry of
the point of the needle.
• The blade cross-section of classical needles is triangular, with three
barbs formed on the apex as shown in (a).
• The star bladed needles have four apices and a cruciform cross-
section. This needle is intended to carry an increased number of
fiber per penetration as compared to the standard triangular
needle, which can increase fabric strength as shown in (b).
a b

32. The modern machine manufacturers offer various arrangements of needle
boards in needle loom.
Typical applications of these arrangements are filtration media, synthetic
leather, floor coverings, underlay, automotive headliners and blankets, geo-
synthetics, synthetic leather, waddings and paddings, floor coverings,
automotive fabrics, insulation, wipes, roofing etc.
Different arrangements of needle boards

33. Stitched bonding invariably uses a cross-laid web, which is fed directly to the stitch
bonder in a continuous process. The machine used in stitch bonding is basically a
modified warp knitting machine which bonds the fabric by knitting columns of stitches
down the length of the web.
In some cases, the web is fed initially to a needle puncher achieve a light needling
operation(known as tacking), before the rolls of fleece are passed to a stitched board.
Tacking enables the fleece to unroll easily and improves the mechanical interlocking
between fibers. This is of vital importance because a very serious shortcoming of many
stitch bonded fabrics is that under heavy or sever use, they tend to loose fibers from the
mobility of the knitted structure cannot provide sufficient anchorage of the fiber in the
fleece. Other steps minimize this weakness include the use of fibers of longer staple
length and the inclusion of some relatively low melting point fibers, which can provide
additional bonding during subsequent heat setting.
The wall matt stitch bonder is shown in figure. The web is fed to the machine in vertical
direction via a lattice arrangement. During stitch bonding it is normally supported, while
the needles contained to the needle bar penetrates the web. When the needle emerges
through the web, the yarn guide lay threads into the open hook and, as the needle
retract, the hook is closed by the tough. The closed needle draws the new loop through
the previous off course which held round the needle stream. Course spacing during
knitting is largely governed by the take-up tension applied to the fabric by the take-up
roller.

34. The structure and the performance of stitched bonded fabrics are affected by a
large number of variables, some of which are controllable, for instance web
area density, fiber characteristics and course spacing. Mall watt machines are
used to produce certain drapes, mattress thinking and fabrics for automotive
industry, such as surface covers for various molded components, parcel
shelves and headliners. Other types of machines available for the production of
specialized fabrics such as medical and electrical products.

35. Hydro entanglement, spun lacing, hydraulic entanglement, and water jet
needling are synonymous terms describing the process of mechanically
bonding the fibers in a web by means of high energy water jets. The machine
which accomplishes this is known as hydro entanglement or spun lace
machine.
Working:
A series of multiple high
pressure columnar water jets
is produced by pumping
water through a series of fine
nozzles in a jet strip clamped
into an injector (manifold).

36. The high velocity water jets are directed to the unbounded web, which
is supported on a moving perforated conveyer. The conveyer may have
a flat bed surface or cylindrical surface. The entanglement among the
fibers is introduced by the combined effects of the incident water jets
and the turbulent water created in the web which intertwines
neighboring fibers. The conveyer sleeve being permeable enables most
of the de-energized water to be drawn into the vacuum box for
recycling and reuse.

37. Selection of fibers
• Both natural fibers and synthetic fibers are used in the hydro
entanglement process.
• The wood pulp is often blended with staple fibers and used in
hydro entanglement process.
• Viscose fiber has been found to be mostly used.
• The important fiber properties for this process have been fiber
flexural rigidity and fiber hydrophobicity.
• Viscose rayon has a low wet modulus and this partly explains the
ease with which this fiber can be hydro entangled as compared to
polypropylene fiber that have higher modulus.
• As the coarser fibers offer higher flexural rigidity as compared to
the fine fiber, the former require more hydro entangling energy as
compared to the latter in order to have the same degree of bonding.
• Effective hydro entanglement requires uniform and rapid wetting
of the web. That is why the manmade fibers are often treated with
hydrophilic finishes before hydro entanglement.

38. Nozzles
The nozzles used in the hydro entanglement process are capillary cone nozzles,
where the nozzles are usually operated in the cone-down rather than the cone-
up position. This type of nozzles is known as cone-down nozzle. Besides the
cone-down nozzle where thee are one- up and cylindrical nozzles available. It
is of interest to know the discharge coefficient of the nozzles and the resulting
break-up length of its jets.
Discharge Coefficient
It is defined by the ratio of the actual mass flow rate to the ideal mass flow rate
of water. Break-up length is defined by the length of jet at which it breaks after
exiting from the nozzle. The higher is the break-up length, the higher is the
energy transmitted to the web. The cone-up nozzle has a remarkably higher
discharge coefficient than the cone-done and cylindrical nozzles. This can be
explained by the natural consequences of the geometry of the nozzles.
Figure:
The geometry of three
nozzle

39. Jet Streak
One of the major problem associated
with the quality of the hydro entangled
nonwoven is related to the jet marks or
jet strip. This is undesirable as it spoils
the aesthetic appearance of the fabric
and reduces the mechanical properties
of the fabric.
This effect can b reduced by having the
staggered arrangement of the nozzles
having one row with higher nozzle
diameter and other row with lower
nozzle diameter.
Applications
The hydro entangled nonwovens are used in a wide variety of
applications, including wipes, surgical fabrics, medical gauge, filter
cloths, artificial leather, automotive fabrics, lining and cloths, etc.

40. Thermal bonding is the process of using heat to bond or stabilize a
web structure that consists of a thermoplastic fiber. All part of the
fiber act as thermal binders, thus eliminating the use of latex and resin
binders.
Thermal bonding is the leading method used by the cover stock
industry for baby diapers.
Polypropylene has been the most suitable fiber with a low melting
point of approximately 165o C. It is also soft to touch.
The fiber web is passed between heated calendar rollers, where the
web is bonded. In most cases point bonding by the use of embossed
roll is the most desired method, adding softness and flexibility to the
fabric.
Use of smooth rolls bonds the entire surface to the fabric increasing
the strength, but reduced drape and softness.
The proportion of fibers that are melted can be controlled to prevent
the fabric from becoming too stiff or film-like. The temperature used
in bonding has to be selected according to the melting temperature of
the fibers.

41. The formation of a good bond during thermal bonding follows in
sequence through three critical steps:
(1) Heating the web to partially melt the crystalline region
(2) Repetition of the newly released chain segments across the fibre-
fibre interface
(3) Subsequent cooling of web to r-solidify it and to trap the chain
segments that diffused across the fibre-fibre interface.
Different methods of Thermal Bonding:
• hot calendaring
• Belt calendaring
• Through air thermal bonding
• Ultrasonic bonding
• Radiant heat bonding

42. Calendar Bonding Process
There are three main types of hot calendaring
a) Area Bonding
b) Point Bonding
c) Embossing
In thermal calendar bonding process, the fibrous web containing thermoplastic
fibers is passed through a heated calendar nip that is created by two rolls
(cylinders) pressed against each other.
One or both rolls are heated internally to a
temperature that usually exceeds the
melting point temperature of the binder
fibers to ensure there is sufficient heat
transfer to induce softening at prevailing
line speed.
As the web passes between the calendar nip, fibers are heated and compressed.
This causes the binder fibers to become soft and tacky and induces polymer
flow in and around the base fibers. The fluid polymer tends to collect at the
fiber crossover or contact points and bonding sites are formed. Cooling tends
to solidification of the polymer and bonding.

43. There exist two types of calendar rollers, that is, embossed and flat
calendar. It is generally known that the point bonding results in softer
fabric and the area bonding results n stiffer fabric.

44. Air Bonding Machine
Three types of through-air
bonding machines are used.
• Perforated drum through
air bonding machine.
• Perforated conveyer (flat
bed) through air bonding
machine.
• Impingement (air jetting)
through air bonding
machine.

46. The IR emitting bulbs (heaters) are used to radiate electromagnetic
energy in part of the IR wave length (0.7 -300 µm) which then
translates to heat by the receiving/absorbing materials
It does not require any medium, but does not penetrate deep into a
structure. For thinner webs, it is not economical.
This is mainly used for glazing the surface of thick nonwovens.

47. Here the web is compacted between an embossed patterned roller
(anvil) and an ultrasonic horn.
• Horn is vibrated at a frequency of
20-40 KHz.
• The friction between horn and web
surface heats fibers above the
raised points on the anvil.
• Mechanical energy is converted
into thermal energy. This is mostly
used for joining nonwoven
laminates.

48. Figure: Calendar Rollers Figure: Thermally Bonded
Fibers

49. • Bonding a web by means of a chemical is one of the most common
method of bonding.
• The chemical binder is applied to the web and is cured.
• The most commonly used binder is latex, because it is economical,
easy to apply and very effective.
• Several methods are used to apply the binder and include
saturation bonding, spray bonding, print bonding and foam
bonding.
• In chemical bonding, chemical binders ( adhesive materials) are
used to hold the fibers together in a nonwoven fabric. Chemical
binders are polymers that are formed by emulsion polymerization.
The mostly used binders today are water-borne latexes. They are
applied in a number o different ways to nonwovens and because of
their viscosity is close to that of water they can easily penetrate into
nonwoven structure by emulsion. After application of binder by,
for example, they are dried and the water evaporates. The binder
then forms an adhesive film across or between fiber intersections
and fiber bonding take place.

50. • There are various chemical binder polymers used including vinyl
polymers and copolymers, acrylic ester polyester and copolymers,
rubber and synthetic rubber, and natural binders, principally
starch.
• These are usually applied in aqueous dispersions but can be
supplied as polymer solutions providing they have sufficiently low
viscosity to allow penetration into the web.
• Commercially, latex polymers are the most commonly encountered
binder because of their availability, variety, versatility, ease of
application, and cost-effectiveness.
• The latex polymers are prepared by emulsion polymerization by
controlled addition of several components.
• These components include monomers (building block), water
(medium), initiator (decomposes to form free radicals to start the
polymerization process), surfactant (to prevent particle attraction
and thus stabilize the emulsion particles) and chain transfer agent
(to control the final polymer molecular weight).

51. • The process formation starts with a distribution f monomer
droplets in water, stabilized by emulsifiers that have accumulated
at the interface to the water phase. The emulsifier molecules have
the hydraulic heads and hydrophobic tails.
• In figure, the dot indicates the hydrophilic head and the line
represents the hydrophobic tail of emulsifier molecule. If the
concentration of the emulsifier is above a critical value, a
spheroidal collection of them is formed. This is called micelle and it
typically contains about a hundred emulsifier molecules.
• The initiator added is decomposed to form water-soluble free
radicals. When a free radical encounters monomer molecules
dissolved in water, it reacts successively with several to form a
short polymer chain.
• This short chain, called oligomer radical, is no longer soluble in
water. It precipitates and is stabilized by the emulsifier, which
accumulates at the newly formed interface. This is now called a
latex particle.
• When there are enough oligomer radicals formed they grow into
latex particles. Also, it is possible for a growing oligomer radical to
meet a monomer droplet and initiate polymerization to form a
latex particle. In this case, the latex particle would be large.

52. • In addition, when the oligomer radical meet an emulsifier micelle
where monomer molecules are diffused in, the monomer
polymerize and form another latex particle.
• This can only occur if the concentration of emulsifier is enough
high, that is, above the critical micelle concentration. Once the
formation of latex particles is completed, their growth starts. The
monomer flow from water to the latex particles where the
polymerization occurs. The latex particle grow longer and contains
hundreds of thousands of closely packed molecules in one particle.
As propagation proceeds more latex particles are added in layers to
form a large latex particle. Sometimes it is desirable to limit the
molecular weight of the polymer by introducing a chain transfer
agent. The growing polymer radical combines with the chain
transfer agent to stop the chain growth.

54. The most common methods of applying a binder to a dry-laid web
are:
• Saturation
• Foam
• Spray
• Print Bonding
For wet-laid nonwovens, most of the same methods can be used but
bonding must be applied after partial drying. For printing, the web
must be dry.

55. • Saturation chemical bonding involves complete
immersion of the nonwoven web in a bath
containing binder. The excess binder can be
removed by a pair of nip rolls.
• The basic method of saturation using horizontal
padding (a) and vertical padding (b).
• The nonwoven web is guided through the
saturation bath by rollers and then presses
between a pair of nip rolls to squeeze out excess
liquid. The amount of binder taken up by
nonwoven depends on the basis weight of the
non woven , length of time spent in the bath,
wettability of the fibers and nip pressure. This
method can provide higher binder to fiber levels
uniformly throughout the nonwoven. But as it
includes short wetting time, the method is more
suitable for lightweight and highly permeable
nonwovens.
This method also compresses
the nonwoven web, hence
reduces the thickness of the
ultimate fabric

56. Here, air or water is used to dilute the binder and as a mean to carry
the binder to the fibers. One advantage of diluting binder with air
rather than with water is that drying is faster and energy cost is
reduced remarkably. Foam is generated mechanically and can be
stabilized with a stabilizing agent to prevent collapse during
application.

57. • Foam can be applied so as to remain at the surface or can be made
to penetrate all the way through the fabric cross-section.
• One or two reciprocating foam spreaders are commonly used to
distribute the foam across the width of the fabric.
• The excess foam is sucked through the porous portion of the fabric
and the perforations of the web carrying medium to the vacuum
extractor.
• The key advantage of foam bonding is more efficiency drying and
the ability to control fabric softness.
• The disadvantages including the difficulty in achieving adequate
foaming and in controlling the process to give a uniform binder
distribution. Sometimes, non-stabilized foams, called froths, are
formed.

58. Here the binder is sprayed onto a moving web in fine droplet from through a
system of nozzles, which can be statically mounted across the machine or
transverse from one side to other side of the machine. It is used to make highly
porous and bulky products. This is possible because the substrate does not
need to pass between nip rollers. The liquid is atomized by air pressure,
hydraulic pressure or centrifugal force and is applied to the upper surfaces of
the web. The depth of penetration of the binder onto the substrate depends on
the wettability of the fibers, permeability of the web and amount of the binder.
The main advantage of this method is that
the nonwoven is not compressed and the
original bulk and structure is retained.
The disadvantages include lack of control
of the uniformly of spraying, poor binder
penetration, high level of overspray and
waste and possible lack of shear stability
of the binder.

59. The print bonding process applies the binder only in predetermined
areas as dictated by the pattern of the printing surfaces. Here the print
bonding process the latex is transferred to the web via feed roll and
engraved roll. As the web passes the engraved roll, it is pressed
against the surface by a rubber roll, transferring binder to the fabric.
The excess latex is
removed by a doctor
blade. This method is
suitable only for
applying low levels of
binder to the surface
where a textile like
handle is needed.

60. After the binder is applied, the web is dried to evaporate the latex
carrier (water) and allow the latex particles to bond the nonwovens.
Cross linking (if cross linking groups are presentation the binder
formulation) is usually carried out in the same dryer. During drying,
film forming or coagulation take place as well as evaporation of the
water and cross-linking occurs.
There are several types of dryers available such as :
Drum dryer
Flat bed dryer
Stenter-based dryer
Infrared dryer

61. • In drum or belt drying, the web is guided over a perforated
conveyer surface through which hot air pass.
• Air is then withdrawn from the inside of the drum or through the
perforations of the belt and mostly reused. The fabric shrinkage is
one of the important disadvantages of these methods.
• This can be overcome by stenter dryer.
• In infrared dryer, water is marked absorbed by infrared energy as
it rapidly converts water into heat leading to evaporation.
• It requires less capital investment but high running cost.
• They are often used for pre-dry the surface to prevent the coating
of binder on the first drum of a drum dryer to coagulate the binder
to prevent migration or post- dry the surface to complete cross-
linking.
Applications
The chemical bonding process is used to develop nonwovens used as
wipes, interlinings, hygiene and medical products, footwear, auto
motives and home furnishing products.