Huang and Xiao Gao
Spunbond fabrics are produced by depositing extruded,
spun filaments onto a collecting belt in a uniform random manner followed by
bonding the fibers. The fibers are separated during the web laying process
by air jets or electrostatic charges. The collecting surface is usually
perforated to prevent the air stream from deflecting and carrying the fibers
in an uncontrolled manner. Bonding imparts strength and integrity to the web
by applying heated rolls or hot needles to partially melt the polymer and
fuse the fibers together. Since molecular orientation increases the melting
point, fibers that are not highly drawn can be used as thermal binding
fibers. Polyethylene or random ethylene-propylene copolymers are used as low
melting bonding sites. Spunbond products are employed in carpet backing,
geotextiles, and disposable medical/hygiene products. Since the fabric
production is combined with fiber production, the process is generally more
economical than when using staple fiber to make nonwoven fabrics. 
The spunbond process consists of the following integrated operations:
- Polymer melting, transport and filtration of polymer melt
- Filament extrusion
- Filament drawing
- Filament deposition
Flowchart of Spunbonding
In general, high molecular weight and broad molecular
weight distribution polymers such as PP, PET, Polyamide,etc. can be
processed by spunbonding to produce uniform webs. Medium melt-viscosity
polymers, commonly used for production of fibers by melt-spinning, are used.
Isotactic polypropylene is the most widely used polymer
for spunbond nonwovens production. It provides the highest yield (fiber per
kilogram) and covering power at the lowest cost because of its low density.
Considerable advances have been made in the manufacture of polypropylene
resins and additives since the first spunbond polypropylene fabrics were
commercialized in the 1960s. Although unstabilized polypropylene is rapidly
degraded by UV light, improved stabilizers permit several years of outdoor
exposure before fiber properties deteriorate. To reduce cost, scrap or
polypropylene fibers of inferior quality may be repelletized and then
blended in small amounts with fresh polymer to produce first grade spunbond
fabrics. This is very advantageous and important in a highly competitive
Polyester is used in a number of commercial spunbond
products and offers certain advantages over polypropylene, although it is
more expensive. Unlike polypropylene, polyester scrap is not readily
recycled in spunbond manufacturing. Tensile strength, modulus, and heat
stability of polyester fabrics are superior to those of polypropylene
fabrics. Polyester fabrics are easily dyed and printed with conventional
Spunbond fabrics are made from both nylon-6, and
nylon-6,6. Nylon is highly energy intensive and, therefore, more expensive
than polyester or polypropylene. Nylon-6,6 spunbond fabrics are produced
with weights as low as 10 g/m2 and with excellent cover and
strength. Unlike olefins and polyester fabrics, those made from nylon
readily absorb water through hydrogen bonding between the amide group and
The properties of polyethylene fibers that are meltspun
by traditional methods are inferior to those of polypropylene fibers.
Advances in polyethylene technology may lead to the commercialization of
spunbond structures with characteristics not yet attainable with
polypropylene. A fiber grade polyethylene was announced in late 1986.
A new type of structure was announced in Japan with the
commercialization of spunbond fabrics based on thermoplastic urethanes.
Although spunbond urethane fabrics have been previously described, this
represents the first commercial production of such fabrics. Unique
properties are claimed for this product which appears to be well suited for
apparel and other applications requiring stretch and recovery.
Many type of rayons have been successfully processed into
usable spunbond webs. The main advantage of rayon is that it provides good
drape properties and softness to web.
Some fabrics are composed of several polymers. A lower
melting polymer can function as the binder which may be a separate fiber
interspersed with higher melting fibers, or two polymers may be combined
into a single fiber type. In the latter case the so-called bi-component
fibers possess a lower melting component, which acts as a sheath covering
over a higher melting core. Bicomponent fibers are also spun by extrusion of
two adjacent polymers. Polyethylene, nylon-6 and polyesters modified by
isophthalic acid are used as bicomponent (lower melting) elements.
SPINNING AND WEB FORMATION
Spunbonding combines fiber spinning with web formation by
placing the bonding device in line with spinning. In some arrangements the
web is bonded in a separate step which, at first glance, appears to be less
efficient. However, this arrangement is more flexible if more than one type
of bonding is applied to the same web.
The spinning process is similar to the production of
continuous filament yarns and utilizes similar extruder conditions for a
given polymer. Fibers are formed as the molten polymer exits the spinnerets
and is quenched by cool air. The objective of the process is to produce a
wide web and, therefore, many spinnerets are placed side by side to generate
sufficient fibers across the total width. The grouping of spinnerets is
often called a block or bank. In commercial production two or more blocks
are used in tandem in order to increase the coverage of fibers.
Before deposition on a moving belt or screen, the output
of a spinneret usually consists of a hundred or more individual filaments
which must be attenuated to orient molecular chains within the fibers to
increase fiber strength and decrease extensibility. This is accomplished by
rapidly stretching the plastic fibers immediately after exiting the
spinneret. In practice the fibers are accelerated either mechanically or
pneumatically. In most processes the fibers are pneumatically accelerated in
multiple filament bundles; however, other arrangements have been described
where a linearly aligned row or rows of individual filaments is
In traditional textile spinning some orientation of
fibers is achieved by winding the filaments at a rate of approximately 3,200
m/min to produce partially oriented yarns (POY). The POYs can be
mechanically drawn in a separate step for enhancing strength. In spunbond
production filament bundles are partially oriented by pneumatic acceleration
speeds of 6,000 m/min or higher. Such high speeds result in partial
orientation and high rates of web formation, particularly for lightweight
structures (17 g/m2). The formation of wide webs at high speeds
is a highly productive operation.
For many applications, partial orientation sufficiently
increases strength and decreases extensibility to give a functional fabric
(examples: diaper coverstock). However, some applications, such as primary
carpet backing, require filaments with very high tensile strength and low
degree of extension. For such application, the filaments are drawn over
heated rolls with a typical draw ratio of 3.5:1. The filaments are then
pneumatically accelerated onto a moving belt or screen. This process is
slower, but gives stronger webs.
The web is formed by the pneumatic deposition of the
filament bundles onto the moving belt. A pneumatic gun uses high-pressure
air to move the filaments through a constricted area of lower pressure, but
higher velocity as in a Venturi tube. In order for the web to achieve
maximum uniformity and cover, individual filaments must be separated before
reaching the belt. This is accomplished by inducing an electrostatic charge
onto the bundle while under tension and before deposition. The charge may be
induced triboelectrically or by applying a high voltage charge. The former
is a result of rubbing the filaments against a grounded, conductive surface.
The electrostatic charge on the filaments must be at least 30,000 esu/ m2.
The belt is usually made of an electrically grounded
conductive wire. Upon deposition, the belt discharges the filaments. This
method is simple and reliable. Webs produced by spinning linearly arranged
filaments through a so-called slot die eliminating the need for such bundle
Filaments are also separated by mechanical or aerodynamic
forces. The figure below illustrates a method that utilizes a rotating
deflector plane to separate the filaments by depositing them in overlapping
loops; suction holds the fiber mass in place.
For some applications, the filaments are laid down
randomly with respect to the direction of the lay down belt. In order to
achieve a particular characteristic in the final fabric, the directionality
of the splayed filament is controlled by traversing the filament bundles
mechanically or aerodynamically as they move toward the collecting belt. In
the aerodynamic method, alternating pulses of air are supplied on either
side of the filaments as they emerge from the pneumatic jet.
By proper arrangement of the spinneret blocks and the
jets, lay down can be achieved predominantly in the desired direction. The
production of a web with predominantly machine direction and cross-machine
direction filament lay down is shown in the figure below. Highly ordered
cross-lapped patterns can be generated by oscillating filament bundles, as
If the lay down belt is moving and filaments are being
rapidly traversed across this direction of motion, the filaments are being
deposited in a zig-zag or sine-wave pattern on the surface of the moving
belt. The effect of the traverse motion on the coverage and uniformity of
the web has been treated mathematically. The result is that relationships
between the collecting belt speed, period of traverse, and the width of
filament curtain being traversed determine the appearance of the formed web.
The following illustration shows the lay-down for a process where the
collecting belt travels a distance equal to the width of the filament
curtain x during one complete period of traverse across a belt width y. If
the belt speed is Vb and the traverse speed is Vt, the
number of layers deposited, z, is calculated by z = [x Vt/y Vb].
If the traverse speed is twice the belt speed and if x and y are equal, a
double coverage occurs over all areas of the belt.
Many methods can be used to bond the fibers in the spun
web. Although most procedures were developed for nonwoven staple fibers,
they have been successfully adapted for continuous filaments. These include
mechanical needling, thermal bonding, and chemical bonding. The last two may
bond large regions (area bonding) or small regions (point bonding) of the
web by fusion or adhesion of fibers. Point bonding results in the fusion of
fibers at points, with fibers between the point bonds remaining relatively
free. Other methods used with staple fiber webs, but not routinely with
continuous filament webs include stitchbonding, ultrasonic fusing, and
hydraulic entanglement. The last method has the potential to produce very
different continuous filament structures, but is more complex and expensive.
The choice of a particular bonding technique is dictated mainly by the
ultimate fabric applications, Occasionally, a combination of two or more
techniques is employed to achieve bonding.
SPUNBOND PROCESS SYSTEM
A number of spunbond processes can be fitted into one of
these three routes with appropriate modification. The following are three
successful spinning, drawing, and deposition systems merit a brief
This route was first developed by the Lurgi Kohle &
Mineral-Oltechnik GmbH of Germany in 1970. Many nonwoven companies have
licensed this route from the Lurgi Corporation for commercial production.
This route (chart 2 below) is based on the melt spinning technique. The melt
is forced by spin pumps through special spinnerets having a large number of
holes. By suitable choice of extrusion and spinning conditions, desired
filament denier is attained. The blow ducts located below individual
spinnerets continuously cool the filaments with conditioned air. The force
required for filament drawing and orientation is produced by a special
aerodynamic system. Each continuous filament bundle is picked up by a
draw-off jet operated on high pressure air and passed through a guide tube
to a separator which effects separation and fanning of the filaments .
Finally, the filament fan leaving the separators is deposited as a random
web on a moving sieve belt. The suction below the sieve belt enhances the
random lay down of the filaments.
This route has been developed by Reifenhauser GmbH of
Germany. Many nonwovens companies have licensed this route from the
Reiferihauser GmbH for commercial production. This route (Chart 3 below), is
based on the melt spinning technique. The melt is forced by spin pumps
through special spinnerets having a large number of holes. The primary blow
ducts, located below the spinneret block, continuously cool the filaments
with conditoned air. The secondary blow ducts, located below the primary
blow ducts, continuously supply the auxiliary room temperature air. Over the
line's entire working width, ventilator-generated underpressure sucks
filaments and mixed air down from the spinnerets and cooling chambers. The
continuous filaments are sucked through a venturi (high velocity, low
pressure zone) to a distributing chamber, which affects fanning and
entanglement of the filaments. Finally, the entangled filaments are
deposited as a random web on a moving sieve belt. The randomness is imparted
by the turbulence in the air stream, but there is a small bias in the
machine direction due to some directionality imparted by the moving belt.
The suction below the sieve belt enhances the random lay down of the
This route was first developed by Carl Freudenberg
Company of Germany in 1965. This process is proprietary and is not available
for commercial licensing. This route (Chart 4), is based on the melt
spinning technique. The melt is forced by spin pumps through special
spinnerets having a large number of holes. The primary blow ducts, located
below the spinneret block, continuously cool the filaments with conditioned
air. The secondary blow ducts, located below the primary blow ducts,
continuously supply controlled room-temperature air. The filaments are
passed through a special device, where high pressure tertiary air draws and
orients the filaments. Finally, the filaments are deposited as a random web
on a moving sieve belt.
CHARACTERISTICS AND PROPERTIES
The spunbonded webs represent a new class of man-made
product, with a property combination falling between paper and woven fabric.
Spunbonded webs offer a wide range of product characteristics ranging from
very light and flexible structure to heavy and stiff structure. 
Random fibrous structure
Generally the web is white with high opacity per unit area
- Most spunbond webs are layered or shingled structure, the number of
layers increases with increasing basis weight
Basis weights range between 5 and 800 g/m2, typically
10-200 g/ m2
Fiber diameters range between 1 and 50 um, but the preferred range is
between 15 and 35 um
web thicknesses range between 0. 1 and 4.0 mm, typically 0.2-1.5mm
High strength-to-weight ratios compared to other nonwoven, woven, and
High tear strength (for area bonded webs only)
Planar isotropic properties due to random lay-down of the fibers
Good fray and crease resistance
High liquid retention capacity due to high void content
High in-plane shear resistance, and low drapeability.
Spunbond fabrics are characterized by tensile, tear, and
burst strengths, elongation-to-break, weight, thickness, porosity and
stability to heat and chemicals. These properties reflect fabric composition
and structure. Comparison of generic stress-strain curves of thermally
bonded and needlepunched fabrics shows that the shape of the load-strain
curves is a function of the freedom of the filaments to move when the fabric
is placed under stress.
Some applications require special tests for sunlight,
oxidation, burning resistance, moisture vapor and liquid transport,
coefficient of friction, seam strength and aesthetic properties. Most
properties can be determined with standardized test procedures (INDA).
Typical physical properties are given below.
||Basis wt. g/m2
||Tensile St.a Nb
||Tear St. Nb
||Mullen burst KPac
aMD=machine direction; CD=Transverse direction.
bTo convert N to pound force, divide by 4.448.
cTo convert Kpa to psi, multiply by 0.145.
Today spunbonded webs are used throughout the automobile
and in many different applications. One of the major uses of spunbonded webs
in automobile is as a backing for tufted automobile floor carpets. The
spunbonded webs are also used for trim parts, trunkliners, interior door
panel, and seat covers.
The civil engineering market segment remains the largest
single market spunbond webs, constituting over 25% of the total. Spunbonded
civil engineering webs cover a multiple of related uses, such as, erosion
control, revestment protection, railroad beds stabilization, canal and
reservoir lining protection, highway and airfield black top cracking
prevention, roofing, etc.. The particular properties of spunbonded webs -
which are responsible for this revolution - are chemical and physical
stability, high strength/cost ratio, and their unique and highly
controllable structure which can be engineered to provide desired properties
The use of spunbond web as a coverstock for diapers and
incontinence devices has grown dramatically in the past decade. This is
mainly because of the unique structure of spunbond, which helps the skin of
the user stay dry and comfortable . Additionally, spunbond webs are cost
effective over other conventional nonwovens. Spunbond web, as coverstock, is
also widely used in sanitary napkins and to a limited extent in tampons.
In medical applications many traditional materials have
been replaced by high performance spunbonded webs. The particular properties
of spunbonded webs, which are responsible for medical use, are:
breathability; resistance to fluid penetration; lint free structure;
sterilizability; and, impermeability to bacteria. Medical applications
include: disposable operating room gowns, shoe covers and sterilizable
Spunbonded fabrics are widely used as packaging material
where paper products and plastic films are not satisfactory. The examples
include: metal-core wrap, medical sterile packaging, floppy disk liners,
high performance envelopes and stationery products.
Market and Producers
Recent developments in spunbonding equipment have aimed
at increasing the versatility of the technology. Today an increasing number
of machinery builders can offer spunbonding and meltblowing equipment to
facilitate the production of SMS, SMMA and other composite permutations. One
of the latest to enter sector is Kobelco, Japan. Kobelco is one of the main
Asian sources of spunbonding installations, but formerly concentrated on
developing lines for producing fine-denier spunbonds. However, an agreement
recently made with Accurate Products will permit Kobelco to adopt meltblown
technology developed by the US company to offer SMS lines.
Chart 5 shows a breakdown of the world's markets for fine
denier spunbond and SMS PP in tons. The North American market (excluding
Mexico) consumed 182,000 tons, representing 34% of global fine denier
consumption. It is expected that this market will grow about 6% per year to
231,000 tons per year (pty) by 2001.
Europe consumed 165,000 tpy in 1997 and accounted for 31
% of the world's fine denier PP consumption. As in North America, European
spunbond consumption grew rapidly between 1993 and 1997, propelled to a
large extent by the increasing use of spunbond and SMS PP materials by
absorbent products as capacity came onstream. We expect growth of the North
American and European spunbond and SMS markets will continue to grow in the
6-7% range per year.
The Rest of World (ROW) markets consumed about 94,000 tpy
in 1997. There is considerable spunbond capacity expansion in many world
Early marketing efforts centered on the substitution of
woven textile fabrics by spunbond fabrics. This was achieved where only
functionality was important. Where a more traditional textile like
appearance is required, progress has been slow. Nevertheless, spunbond
fabrics are recognized as a unique class of nonwoven fabrics. The area of
largest growth has been disposable diaper coverstock, which accounts for
more than 50% of the US coverstock market. There has been a steady increase
in the spunbond market and the trends show continuity of market growth.
Growth is forecast to exceed the growth of all nonwovens, which is expected
to grow at 7% per year. Additional growth is anticipated in geotextiles,
roofing, carpet backing, medical and durable paper applications.
West European output of spunbonds in 1970 was a mere
2,000 tonnes. In 1997, output had reached 318,000 tonnes. It is generally
accepted that 1998 statistics, when generally available, will show further
increases. In the 1970s, spunbonding expertise was virtually confined to a
handful of companies, mainly fiber producers, who had at great expense
developed their own proprietary technology and plant, or had acquired a
Docan process license and machinery from the Lurgi Group. Today only one
major fibre producer still operates a spunbonding facility in Western
Europe, and there are probably more sources of spunbonding machinery in the
region than builders of needlelooms.
 Encyclopedia of Polymer Science and Engineering
 Oldrich Jirsak and Larry C. Wadsworth:
Academic Press, ISBN: 0-89089-978-8, 1999
 Sanjiv R. Malkan and Larry C. Wadsworth:
A review on spunbond
technology, Part I
, INB, Nonwovens vol.3, 1992 , 4-14
 Sanjiv R. Malkan and Larry C. Wadsworth:
A review on spunbond
technology, Part II
, INB, Nonwovens vol.4, 1992 , 24-33
, Textile Month, March 1999, 16
 Poter K.;
Enzyclopedia of chemical technology
edition, 16, 72-104
 Smorada, R. L.;
Enzyclopedia of polymer science and engineering
New York, 227-253
 NRI, 135, 9, 1982, 7-10
 Ian Butler;
Worldwide prospects for spunbond
, nonwovens world,
September 1999, 59-63
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