Secondary Backing Systems for Carpet
Once dyed, the carpet goes into the finishing department,
where the secondary backing is applied and the surface is sheared smooth.
The secondary backing is any material laminated to the
primary backing in a “marriage roller” for dimensional stability
while locking individual tufts in place.
The secondary backing is glued to the primary backing
with latex. The latex is a milky, rubbery fluid, usually styrene-butadiene
synthetic rubber (SBR) compounded with large quantities of powdered filler
such as chalk. The new carpet smell is from the chemical 4-PC, a by-product
of the latex.
Latex is applied to
the back of the carpet. As the carpet passes under the puddle of latex,
a blade forces the latex down and around all the yarn on the back of the
carpet, which locks the yarn into the backing. A second coat of latex is
applied to hold the secondary backing onto the tufted material, which gives
the carpet its dimensional stability.
After the primary and secondary backings are glued together
at the marriage roller, the carpet is sent to an oven to cure the latex.
;Dimensional stability, primarily imparted by the secondary
backing, is the ability of carpet to retain its size and shape after installation.
Most secondary backing today is woven polypropylene, such as Propex’s Action Bac®, which is a backing made of a leno weave of slit film and spun olefin yarns that forms a stretchable, all synthetic secondary backing fabric. It is shredded and spun into yarn,
which is then used.
The secondary backing might be made of jute, a material
high in lignin content derived from a fibrous plant native to India, Bangladesh,
and the Far East. Jute backing has several major problems, such as potential
for browning and rotting.
There are several other backing systems, including:
- AdBac®: A composite backing system whose key component is
an extruded polyethylene that’s processed into a spun-bonded fabric.
That fabric is sandwiched between the PolyBac® primary and the Action Bac
secondary backing. When heat is applied, the fabric melts to adhere the
primary and secondary backings. By eliminating the latex, this system eliminates
delamination and gives carpet lighter in weight, greater flexibility, easier
installation, and more easily recycled. Additionally, by eliminating the
latex, the “new carpet odor” is also eliminated. AdBac, PolyBac,
and ActionBac are registered trademarks of Propex® Fabrics.
- Attached cushion or cushion-backed carpet:
Carpet having a cushion or padding as an integral part of its backing.
- KangaBack®, a trademark of Textile Rubber & Chemical,
is an attached urethane cushion product for residential use.
- Moisture barrier backings: Most moisture barrier backings are
solid vinyl or urethane. Their purpose is to keep water-based spills from
penetrating through the carpet, affecting both the carpet and the surface
under the carpet. However, they can also have the disadvantage of trapping
any moisture trapped under them from evaporating. This can be especially
damaging to the concrete itself and to the glue if the carpet is glued
down. It can lead to failure of the carpet installation. Also, because
the pad does not absorb a spill, or pet urine, the material tends to spread
outward more, making wicking over a larger area more likely.
- Pet-Agree® Wear-Dated® carpet
from Solutia comes with a soft impervious polyethylene backing that traps
liquids (pet urine in
particular) where they can be found and cleaned thoroughly before soaking
into the padding and through to the floor. Pet-Agree keeps liquid from
seeping through the carpet into the cushion.
- Powerbond® ER3, made by Collins & Aikman Floorcoverings,
is a secondary backing that’s made from reclaimed carpet tile (which
includes the nylon tufted surface and vinyl backing).
- SoftBac® is a registered trademark
of Shaw Industries. It is a woven/non-woven combination backing system
that eliminates the harsh
surface of the backing that can scuff up walls and banisters. Additionally,
it results in a carpet that is more flexible and lighter. SoftBac provides
up to 3 times the delamination strength of ordinary backings.
- Polyurethane systems: A polymeric resin applied by the
mill in the finishing process. In the heat and curing chamber it reacts and creates
a foam-like texture. This backing encapsulates the yarn for extra tuft
bind (the force required to pull a tuft from the carpet) with a cushion
attached and also gives water repellency to provide a moisture barrier.
Additionally, urethane does not degrade the way latex can and it does not
give off the 4-PC “new carpet odor”.
- Dow’s Enhancer® system is the best-known urethane system.
The Enhancer system functions as both the adhesive and the secondary backing
and adheres to the back of the carpet by reacting with it. This system
provides a moisture barrier protection that protects sub-floors and reduces
wicking from spills. The Enhancer system protects the carpet against edge
ravel, pilling and fuzzing. It also provides a cushioned alternative in
direct glue down situations and increases the life of the carpet.
- PVC backing: Poly Vinyl Chloride. Sometimes used as a secondary
backing on carpet tiles and six-foot wide carpets because of its weight
- Sponge rubber cushion: Rubber carpet cushion backing that is
laminated to the back of a carpet.
- Unibond® backing: A hot-melt resin process that adheres the
primary and secondary backing offered by Lees Commercial Carpets.
- Unitary backing: A heavy application of back coating applied
to the carpet’s back without a secondary back. Used primarily with
loop pile carpet.
Additional Carpet and Fiber Manufacturing Information: