Xiao Gao and Hsu-Yeh Huang
There are three major bonding types: chemical bonding /
thermal bonding/ mechanical bonding. The development of the past few years
has shown that the share of themally bonded webs is growing steadily. 
The first thermally bonded nonwovens were produced in
1940s. Initial products used rayon as the carrier fiber and plasticized
cellulose acetate or vinyl chloride as the binder fiber . The viability
of the thermal bonding process is rooted in the price advantage obtained
by lower energy costs. However, the thermal bonding process also addresses
the demanding quality requirements of the market place. The development of
new raw materials, better web formation technologies and higher production
speeds have made thermal bonding a viable process for the manufacture of
both durable and disposable
There are many materials that can be used as a binder for thermally
- Binding fibers
- Binding powder
- Binding web
The following are the essential characteristics of the binder polymer
- Efficient melt flow
- Good adhesion to the carrier fiber
- Lower melting point than the carrier fiber
- Appropriate stiffness/elasticity.
Single-component and bi-component fibers, as binder
fibers, are most widely used in thermal bonding of nonwovens .
Single-component fibers are the least sophisticated and most economical
because the fibers are often already in existence and low in cost. The
type bond that is formed is dependent on several factors including fiber
chemistry, morphology, linear density, staple length, crimp and processing
conditions. The major disadvantage encountered when using 100 percent
single-component fibers is the narrow temperature range that is necessary
when thermal bonding. If the temperature is too low, there is inadequate
bond strength. If the temperature is too high, the web will melt
excessively and lose its identity as a web.
When bi-component fibers are used to produce thermal
bonded nonwoven, the acceptable temperature range for bonding may be as
great as 25
C. When thermal bonding, the high melting portion of the fiber
maintains the integrity of the web, while the low melting point portion
melts and will bond with other fibers at the fiber cross-over points. The
product produced tends to have bulk and exceptional softness.
Powdered polymers are sometimes used in thermal bonding
of nonwovens. The most prevalent use is powdered polyethylene. The powder
can be applied between layers of fibers when cross-laying, air laying, or
as an after treatment. A short exposure in an oven is sufficient to melt
and fuse the powder. It is often used when a light weight and open
structure is required with a soft hand or when a reinforced, molded
product is necessary.
A very open-structured, low-melting-point thermoplastic
fabric is placed between the webs and, during thermal bonding between the
calender rolls, the fabric melts completely bonding the webs together. The
nonwoven produced by this technique is considerably soft and bulky.
Thermoplastic coatings and hot melt print bonding have been used to a
limited extent in controlled porosity filters, impermeable membranes and
other items. However, the use of this method of bonding is not expected to
achieve a high level of importance.
METHODS OF THERMAL BONDING
- Hot calendering
- Belt calendering
- Oven bonding
- Ultrasonic bonding
- Radiant-heat bonding, etc.
There are three main types of hot calendering.
This process involves the use of a calender with a hot
metal roll opposed by a wool felt, cotton or special composition roll.
Two, three or four roll calenders can be used, depending on the weight of
the web to be bonded and the degree of bonding desired. The three roll
calender has the heated roll in the middle while the four roll
configuration has the heated rolls on the top and bottom, with the two
composition roll in the middle. The amorphous or co-polymeric binder
fibers used in this process provide bonding at all cross-over points
between the carrier and binder fibers. The resultant product - commonly
used in electrical insulation and coating substrates - is smooth, thin and
stiff. The material is always two sided, but this effect is most apparent
in material processed through two and three roll calenders. Four roll
calenders minimize this effect.
The application of heat from the outside produces a
material whose inner area is less bonded than its outer surface. This
becomes more pronounced as the product weight increases beyond 35 g/m2
and can become detrimental unless corrective measures are taken. These
include increasing heat, slowing speed, or increasing the binder/carrier
fiber ratio. The two-roll calender is used for low-to-medium weight
products with light-to- medium bonding. The three-roll calender is used
for special bonding and finish effects on a single surface. The four roll
calender produces the widest weight range of materials because it provides
more flexibility in the application of heat.
Area-bond hot calendering is influenced by five factors:
Bonding occurs at the surface of the metal roll,
which obtains its heat by conduction from heated oil circulated through
its center or from restrictive heating. The composition rolls obtain
their heat from contact with the heated metal roll. Before the start of
a production run, the roll stacks are operated until the composition
rolls achieve dynamic heat equilibrium.
Bonding occurs through simultaneous application of
heat and pressure. The heat causes the fiber binder to become
thermoplastic. The pressure enhances mechanical bonding by forcing the
binder polymer to flow in and around the carrier fibers.
The speed at which the nonwoven passes through the
calender, combined with heat and pressure conditions, determines the
degree of bonding in the nonwoven. It also determines the throughput
rate of the entire nonwoven line and is a critical factor in product
cost. The faster the rate, the lower the cost. This is the primary
reason for the recent development of lower melting binders.
The only practical roll combination for area bonding
is a metal roll-felt roll. The metal roll applies the heat. The surface
resilience of the felt roll enables even application of pressure to all
the minute surface thickness variations throughout the product.
The product is warm and thermoplastic as it leaves
the calender nip. If the product were to be wound while it was still
hot, the tension applied to eliminate wrinkles would stretch the web and
introduce unrelieved stresses. This would lead to shrinkage whenever
post-heat treatments were used. A set of two cooling rolls placed
immediately after the calendering stage eliminates these unwanted side
Point-bond hot calendering is the main method of
thermally bonding in disposables as diaper, sanitary products, and medical
products. This method involves the use of a two-roll nip consisting of a
heated male patterned metal roll and a smooth or patterned metal roll (fig
1). This second roll may or may not be heated, depending on the
application. In a
typical production line, the web is fed by an apron
leading to a calender nip and the fiber temperature is raised to the point
at which tackiness and melting cause fiber segments caught between the
tips of engraved points and the smooth roll to adhere together. The
heating time is typically of the order of milliseconds. The fabric
properties are dependent on the process temperature and pressure and other
parameters like the contact time, quench rate and calender pattern.
Experimental results show that for a given nip line pressure and
calendering speed, the breaking strength reaches a maximum at a critical
bonding temperature; on keeping the nip line pressure constant, the
critical temperature was found to be a function of the calendering speed.
The maximum strength achieved is influenced by the nip
line pressure. This influence depends on the melting behavior of the
fiber. If the maxima occurs in the softening region, higher pressure
yields higher strength. On the other hand, if maximum occurs in the early
melting region, a low calendering pressure is desirable. The degree of
product bonding depends on the pattern of bond points on the roll surface.
Bonded areas are compressed and densely compacted. Unbonded area in
between are very open, breathable and porous. The products formed range
from thin, closed, inelastic, strong, and stiff to open, bulky, weak,
flexible and elastic depending on the number density, the size and the
pattern of the bond points.
This method is a figured or sculptured area-bond hot
calendering. In this case, though, the area bonding is three dimensional.
A "bulky but thin" product can be made in any pleasing or functional
construction, depending on the faces of the embossing rolls. The calender
roll combination has a male patterned heatable metal roll and a matching
female patterned felt roll.
Belt calendering is a modified form of hot roll
calendering. The two main differences are the time in the nip and the
degree of pressure applied. In belt calendering, time in the nip is 1-10
seconds. The pressure applied is about 1/10th of the pressure applied in
the hot calendering process. The belt bonder consists of a heated roll and
a rubber blanket. The nonwoven fabric is heat bonded by running it between
the roll and the blanket. Pressure is applied by varying:
- The tension on the blanket against the heated roll
- The pressure on the exit guide roll inside the rubber blanket.
Belt calendered products are much less dense and papery
compared to hot roll calendering. The belt bonder facilitates the use of
binders with sharp melting and flow properties. Such binders can present
difficulties in a hot roll calendering process.
Through air oven bonding involves the application of
hot air to the surface of the nonwoven fabric. The hot air flows through
holes in a plenum positioned just above the nonwoven. However, the air is
not pushed through the nonwoven, as in common hot air ovens. Negative
pressure or suction, pulls the air through the open conveyor apron that
supports the nonwoven as it passes thorough the oven. Pulling the air
through the nonwoven fabric allows much more rapid and even transmission
of heat and minimizes fabric distortion. (Fig.2)
Binders used in through air oven bonding include
crystalline binder fibers, bi-component binder fibers, and powders. When
using crystalline binder fibers or powders, the binder melts entirely and
forms molten droplets throughout the nonwoven's cross-section. Bonding
occurs at these points upon cooling. In the case of sheath/core binder
fibers, the sheath is the binder and the core is the carrier fiber.
Products manufactured using through-air ovens tend to be bulky, open,
soft, strong, extensible, breathable and absorbent. Through-air oven
bonding followed by immediate cold calendering results in thicknesses
between a hot roll calendered product and one that has been though-air
bonded without compression. Even after cold calendering, this product is
softer, more flexible and more extensible than area-bond hot calendered
This process involves the application of rapidly
alternating compressive forces to localized areas of fibers in the web.
The stress created by these compressive forces is converted to thermal
energy, which softens the fibers as they are pressed against each other.
Upon removal from the source of ultrasonic vibration, the softened fibers
cool, solidifying the bond points. This method is frequently used for spot
or patterned bonding of mechanically bonded materials.
No binder is necessary when synthetic fibers are used
since these are self-bonding. To bond natural fibers, some amount of
synthetic fiber must be blended with the natural fiber. Fabrics produced
by this technique are soft, breathable, absorbent, and strong. This
bonding method is used to make patterned composites and laminates, such as
quilts and outdoor jackets.
RADIANT HEAT BONDING
Radiant heat bonding takes place by exposing the web or
mat to a source of radiant energy in the infrared range. The
electromagnetic energy radiated from the source is absorbed by the web,
increasing its temperature. The application of radiant heat is controlled
so that it melts the binder without affecting the carrier fiber. Bonding
occurs when the binder resolidifies upon removal of the source of radiant
heat. Lower energy and equipment costs make this a favored method for
processing powder bonded nonwovens. Versatility and lower shipping costs
are also factors. Post-calendered rolls can be shipped in thin, compacted
form and rebulked by reapplication of heat, without pressure or
restraints, to the desired state at the time of use. Powder bonded
products made in this manner are soft, open, and absorbent with
low-to-medium strength. They also can be reactivated by heat for use in
the manufacture of laminated composites.
ADVANTAGES AND ENERGY COMPARISION
Compared to other bonding processes, thermal bonding and the products
thus obtained offer a number of advantages:
- Quality of product soft and textile-like.
High economic efficiency as compared to chemical bonding with binder
agents because no water evaporation is required, i.e., considerable
energy saving results. In comparison with chemical bonding, thermal
bonding only has a heat energy requirement of 1/4 to 1/6 (also in this
respect ecologically beneficial).
Less expensive machinery. The capital expenditure, maintenance and
operating costs are often lower because no binder preparation station
and no binder application units are required.
It is possible to bond even thicker webs uniformly and thoroughly to
the core which cannot be achieved by spraying. While a regular bonding
effect across the web cross- section can be achieved for a web with a
homogeneous distribution of the binding fibers, spraying only produces a
bonding effect in the outer layers of the web.
No binder agents are required and no curing process is needed.
Hence, there is no exhaust air or waste water problem. Objections
against certain chemicals can be dropped. Thus thermal bonding is
non-polluting. (Note: New developments of the binder producers in the
meantime have put on the market new dispersions which also can be
considered ecologically harmless).
As pure polymer fibers or blends can be used for thermal bonding
processes, a recyclability of practically 100 % is given.
- Fiber properties can be influenced in an ideal manner (e.g. flame-retardance,
nonwovens with high bulk and excellent resilience owing to fiber
crimping, heat-insulating characteristics due to hollow fiber, etc.).
It has to be mentioned, however, that not all nonwovens
can be processed by thermal bonding in such a way that the product obtains
the requested properties. It can be assumed therefore that binder bonding
can also secure its market share because the binder producers are trying
to develop polymer dispersions which are biodegradable and, in connection
with the fiber polymers using the same polymer basis, allow recycling of
the respective nonwovens.
THERMAL BONDED NONWOVENS
A variety of nonwovens made of staple fibers with
blends of matrix fibers and bicomponent fibers is produced on Fleissner
hot-air flow-through bonding installations. Other products are bicomponent
and bifilament spunbondeds. The following is a list of various
Colback by Akzo, for the production of carpet carrier webs, roofing
felts, geotextiles etc.
Lutradur by Freudenberg Spunweb for automobile construction, carpet
fabrication, civil engineering and building construction, roofing felt
production, furniture industry, filtering technology, electronic
industry, wall paper fabrication, horticulture and agriculture.
Lutrasil by Freudenberg Spunweb for sanitary products, medical
products, automobile construction, furniture, textile processing,
bedding, filters, protective clothes, agriculture, packing material.
Freudenberg Colmar Spunweb for roofing industry and many other
Celbond by Hoechst for personal products, f urniture, quilts,
needled webs made of spunbondeds for roofing felts, geotextiles etc.
- Cambrelle by ICI for insoles.
Terram by ICI, Exxon for spunbonded geotextiles.
Islands-in-the-Sea or Citrus by BASF for filtration and wiping
cloths, made of fibers that can easily be broken up into microfibers.
- ES fibers by Chisso or Danaklon for personal products up to paper
Danaklon for short staple fibers in the airlaid fabric sector, etc.
Corebond by DuPont for fiberfill webs, etc. Melty and Bellcombi by
Unitika, Kanebo for fiberfill webs, mattress substitutes etc.
- Sofil by Kuraray for various applications.
- TBS by Teijin as short staple for wet-laid webs.
Estranal by Toyobo for needle felts.
Wellbond by Wellman: clothing (ski outfits, interlinings), bedding
(comforters, mattresses), construction industry (insulating webs,
roofing), filters (industry, air, liquids, household), floor coverings
(needle felts), furniture (cushions, etc.)
The subsequent table lists the major applications for
thermobonded webs (carded webs, wet-laid webs, spunbonds) and the
respective preferred bonding method.
MERAKLON is introducing a new series of thermal bonding fibres,
S2000 for high speed nonwovens lines. These are available in hydophilic,
hydrophobic and durable strike-through types for both coverstock and the
production of cloth-like backsheets.
Thermal bonding is much less energy intensive, kinder
to the environment and more economical than latex bonding. A wide range of
products can be made with thermal bonding, depending on the options used
for processing. The bonding method has a significant effect on product
properties. Depending on the bonding method, product properties can vary
from nonporous, thin, nonextensible, and nonabsorbent to open, bulk,
extensible and absorbent. All thermal bonding methods provide strong bond
points that are resistant to hostile environment and to many solvents too.
 Alfred Watzi; "Fusion bonding, thermal bonding and
heat-setting of nonwovens-theoretical fundamentals, practical experience,
market trends", Melliand, English, 10/1994, E 217
Albert G. Hoyle, "Thermal bonding of nonwoven
fabrics", Tappi Journal, July '90, p 85-88.
 Other source
 "Thermal bonding", Textile progress vol ? p 3-11.date ?
 J. Robert Wagner, "The bonding nonwovens, The
Technical Needs: nonwovens for medical surgical and consumer uses", p
 Alfred Watzi; Fusion bonding, thermal bonding and
heat-setting of nonwovens-theoretical fundamentals, practical experience,
market trends", Melliand, English, 12/1994. P.E 270
 "Fibers and Fabrics-Thermal Bonding", Textile Month, March 1999, 20
Add Your Company Contact
Us About Us Advertise
News Letter Legal
1999-2001 Apparel Search Company. All Rights Reserved.
For The Holidays.