PVC (polyvinyl chloride) is a versatile polymeric plastic used in
many industries.
If you are into chemistry,
click here for a great, short presentation on the structure of a
PVC molecular chain by the Khan Institute.
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PVC, commonly called "vinyl", can be made softer and more flexible by
the addition of plasticizers, the most widely used being
phthalates, thus offering a strong, flexible, weather resistant,
and attractive finish for fabrics used in signs, banners, tents,
transportation, and many other applications. PVC is a
"thermoplastic" which means that it can be repeatedly
heated, softened, and rehardened. This property makes the
material highly suitable for various methods used to mold,
extrude, and shape many products and to weld
two PCV-coated surfaces together. |
One of the advantages delivered by
most PVC products is that their useful life is almost always long
and very dependable. For many applications, PVC is not a
one-time-use material. Thus, compared to many other products, PVC's
longevity is an environmental advantage. Nonetheless, PVC products
or their utility does not last forever and some waste (e.g. trimmed
pieces) also contributes to the need for recycling.
Recycling:
The Vinyl Institute offers expert
materials on the topic of PVC
characteristics, environmental
considerations and recycling. Please
visit their site at
http://www.vinylinfo.org/Environment.aspx.
Additionally, new methods for recycling
PVC are being developed regularly
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The Vinyloop Process
The relatively new
mechanical recycling process known as
Vinyloop® technology, developed by
Solvay Research & Technology, allows the
complete separation of PVC material from
the non-PVC materials that are often
combined with it, such as: Polyester
fibers; glass fibers; natural textiles;
polyurethane foam; metals; and rubber.
Ferrara PVC Recycling Plant, Italy
- Pretreatment:
The PVC is physically prepared to be
reverted back into a raw material.
These steps include cleaning or
washing, material size reduction by
cutting, grinding or milling and a
homogenization step.
- Dissolution:
The waste is combined with a
selective solvent in a closed
reactor that releases the PVC
compound matrix. Additives and other
materials are either dissolved or
remain suspended in the liquid.
- Separation:
Depending upon the insoluble
materials, techniques such as
centrifuging, decanting and
cycloning are used for separation.
Following the separation step, the
secondary materials are washed with
solvent to further remove any
remaining dissolved PVC compound.
- Precipitation:
Steam is injected to completely
evaporate the solvent. The PVC
compound formulation is recovered as
liquid slurry. The PVC resin
precipitates into microgranules.
- Drying: The
slurry from the precipitation, which
is a mixture of process water and
regenerated PVC compound, is dried
and the process water is treated
before discharge. The regenerated
PVC compound is now ready for use
and is packed to await shipment. The
solvent used in the process is
contained in a closed loop. More
than 99.9 percent of the solvent is
recovered and separated from the
process water, using condensation
and density separation.
The production of each component
needed for virgin PVC manufacturing
consumes more natural resources, uses
more energy, creates more air and water
pollution and, overall, has a greater
environmental effect than the Vinyloop
operation itself. Additionally, the end
product of the Vinyloop process is of
the same quality.
Creative Recycling
Inventors, recycling chemists, and
business people are seeking new ways to
make next-generation use of vinyl
billboard advertising materials that
would otherwise go into landfills.
Los Angeles Eco-Logical Art Gallery
focuses on a green solution to this
waste by creating functional art from
recovered vinyl billboards. The vinyl
sheets used in billboard advertising are
stretched so that the material can be
used as canvases. The vinyl canvases are
almost impervious to the elements with
little signs of fading, flaking or wear.
As a result, “eco-logical” artwork
appears on billboards around Los
Angeles. The gallery has also planned a
national “renewable imagery” billboard
art tour. The goal is to get the
material into public schools and provide
free mural walls to inner-city youths.
Welding
Methods:
Many industrial fabric companies use welding technology to
join panels using overlapped or butt seams. In overlap seams, one
sheet of vinyl-coated fabric is welded to another piece, usually of
the same type, by laying one sheet on the other along the intended
joint with anywhere from a one half to three inch wide contact area.
In a butt seam, the two primary sheets are aligned with no overlap
and an additional third piece, a narrow strip of a compatible
fabric, is welded behind the joint. By thus joining sheets of fabric
which are usually woven and coated in sizes no wider than five
meters (about 16 feet), fabricators can build many types of
industrial barriers, tarps and covers, tents and tensile structures,
grand format banners and building wraps, agricultural covers, and
other large structures.
To add the strength calculated for properly engineered structures, webbing
that is also PVC-coated can be added to seams and edges. Different
types of welding
equipment can be used for different seaming and edging operations.
But the chemical process of marrying two vinyl-coated surfaces is
based on having compatible coatings. Thus it is possible to join
fabrics with differing internal fabric weaves ("scrims") but with
similar outer PVC
surfaces. It is always advisable to be certain that surfaces to be
joined are clean before welding.
In cases where the scrim of a heavy webbing product is
considerably more dense than that of the broad fabric to which it is
being welded, it may be necessary to experiment with a variety of
intensity and dwell time settings to be sure that the amount of heat
needed to weld the webbing is not so great that it could cause
damage to the broad fabric.
Because the polyester webbing inside PVC-coated webbing is
essentially the same as regular polyester webbing, PVC-coated
webbing can also still be sewn using traditional stitching
machinery. This method is used in heavy applications such as
reinforcing fold-backs behind tent hardware and in lightweight
applications such as for smaller signs and banners where the
waterproof characteristics of the PVC-coating may be desired but
when welding is impractical. Once sewn, PVC-coated webbing offers
the advantage that if can be slightly re-melted with a heat gun to
seal needle holes.
In small sign shop applications, PVC-coated webbing can also be
applied using PVC-specific solvent adhesives or with double-sided banner tape without any welding at all..
Be familiar with four different methods for welding
PVC fabrics:
(information collected from various manufacturers) |
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Hot Air Welding
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| Two surfaces are pressed
together by a roller which follows a hot air nozzle. Air heated to over 400o F is
directed through a nozzle precisely into the space
between the fabrics. (Not from the outside as
in a heat press.) In smaller welding machines and
hand-held applications, the nozzle is moved along the
welding track. Larger machines can use either a moving
nozzle or a stationary nozzle with a carriage system
that feeds the fabric layers to be welded. |
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Hot Air Equipment Suppliers:
Production-Scale Machines:
Miller Weldmaster
Smaller Shop Tools:
Forsthoff (Abbeon Cal)
Leister
Mini-Hemme |
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| Electronic
Welding |
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| Compatible materials are pressed together
between a sealing bar and a bed plate. Thermoplastic
vinyl molecules are excited (heated) by radio frequency
waves or electronic pulses. Electronic controls manage
the duration and intensity of generated radio waves.
Bars can be stationary or can move along a track
delivering a series of similar welds without having to
move the positioned fabrics. |
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High Frequency Equipment Suppliers:
Cosmos/Kabar
Fiab
Forsstrom
Hall
Dielectric
JTE
Machine Systems
Zemat
Technology Group
Impulse Welding
Asco
Novaseal |
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Wedge Welding |
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| Heated fabrics are pressed together by a
trailing roller after passing between spaces
above and below a heated metal wedge. In smaller
machines and hand-held applications, the wedge is moved
along the welding track. Larger machines can use either
a moving wedge mechanism or a stationary wedge with a
carriage system that feeds the fabric layers to be
welded. |
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Wedge Equipment Suppliers:
Miller Weldmaster
Novaseal
Sinclair Equipment |
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| Solvent
Welding |
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| After a brief waiting
period during which a chemical solvent has had time to
soften the vinyl coatings, two compatible
materials can be joined with pressure at ambient (room)
temperature without additional heat. Prior to being
pressed, the chemical solvent is spread along the
surfaces to be joined. Consult manufacturer for
information on period required to be sure that the newly
joined surfaces are allowed to achieve a "tacky"
consistency and then clamped for sufficient time for
molecular bonding to be achieved. This method is useful
on many smaller projects such as banner edges and for
field repairs of any vinyl structure. |
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Fabric Adhesive Suppliers:
Adhesive Engineering & Supply
Chemical Concepts
H&H (Snyder Vinyl)
IPS
WELD-ON |
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