This story is an excerpt from an article which appeared in Sign Builder Illustrated magazine in 2006.
Sewing
is the traditional way to hem the edges of a vinyl banner. Today, you have many other
alternative finish methods. Many of these methods are just as reliable as
sewing and require less skill. These include banner tape, adhesives, chemical
welding, heat welding and RF welding. Each finishing method has its own
advantages and disadvantages. Considerations in evaluating each method include
equipment cost, floor space requirements, ease of fabrication, durability and
reliability of the finished product, as well as fabrication and raw material cost
and its impact on pricing.
Sewing
After
investing in a sewing machine, the cost of materials for stitching the edges of
banner with nylon thread is an insignificant factor in raw material cost of a
banner. If you decide to sew your own
banners, you will need a commercial sewing machine not your wife’s Singer.
A
high quality machine will allow you to sew through the heaviest of vinyl banner
material. Two commercial sewing machines commonly used for sewing banners are
the chain stitch machine and the lockstitch machine.
Chain Stitch Sewing Machines
The
chain stitch sewing machine only uses spools of thread mounted on the top of the
machine. The primary disadvantage of a chain stitch machine is that it can only
operate in the forward direction. That shortcoming makes it impossible for the
operator to sew around the corners of a banner. The chain stitch also unravels
easily which also makes it impractical.
Lockstitch Sewing Machines
A
lockstitch sewing machine uses a spool of thread on the top of the machine and
a bobbin of thread on the bottom. The
thread on the bottom “locks” the top thread to prevent it from unraveling,
hence the name “lockstitch”.
In
buying a sewing machine, many sign makers prefer the models that can sew in
both forward and backward directions. This will allow you to better negotiate
sewing the corners of a banner. Having the ability to sew back and forth also
allows you to sew over the stitching at the ends of the banner, which helps
prevent the stitching from unraveling.
Both
single needle and double needle machines are available. Sewing a double-stitch
hem provides additional reinforcement at the edges of the banner. Some double needle machines have two spools
of thread on the top and two on the bottom.
As
you might expect, the double needle sewing machines are more complex, more
expensive and more difficult to learn to use.
If you decide to buy a double needle machine, look for a model with needles
spaced a half of an inch or more.
If
you are sewing your own banners rather than buying the pre-made ones, use a
heavier material, reinforce the corners, and take care in installing the
banner. All banners that will be displayed outside for any length of time,
especially those exposed to high winds, should have the edges of the banner
stitched with an additional layer of
fabric sewn into the hem for reinforcement.
Banner Tape
Banner
tape is an acceptable alternative to stitching, whether you are making banners
for either indoor or outdoor use. Contrary to what many believe, banner tapes
provide sufficient holding power for outdoor applications if the tape is
applied properly.
Typically
4 to 8 mils thick, banner tape is a supported transfer adhesive, usually
consisting of a polyester or polypropylene carrier coated on both sides with an
aggressive acrylic adhesive. The
adhesive is specially formulated to withstand the effects of plasticizer in the
vinyl banner material.
Before
applying the tape to the fabric, clean the surface of the banner with isopropyl
alcohol to remove any contaminates, such as plasticizer. In hemming a banner, apply
the tape is along the edges of the banner material. Take care so that tunnels do not form in the
applied tape. After you have applied the
tape to the banner substrate, remove the release liner and fold the edges of
the banner over. In order to form a permanent bond, make sure that you use good
pressure. Remember, that banner tape is
a “pressure sensitive” and you need to apply pressure so that the adhesive
flows out and adheres.
Vinyl Cement
Another
method to hem a vinyl banner or to bond two pieces together is to use a vinyl
contact adhesive. Many sign makers use
HH-66 Vinyl Cement from R-H Products Co.
Before applying the vinyl cement, wipe the surfaces of the banner that
will be joined together with isopropyl alcohol.
As with any contact cement, the adhesive is applied to the two surfaces
that you are welding together. HH-66 can
either be brushed on the banner or applied with a roller.
After
waiting about three to five minutes for the adhesive to dry, the two coated
surfaces can be bonded together. At this
point the adhesive is no longer wet, so it won’t slip and slide. The two sections of vinyl material will bond
together instantly and permanently, which doesn’t leave you much margin for
error. In other words, once you’re stuck, you’re stuck.
To
ensure that the banner material is bonded well, use a roller to apply pressure
to the seam. The solvent-based vinyl adhesive will solvate or dissolve the two
sections of the vinyl banner, fusing the pieces together. This solvent cement
should form a waterproof bond that will stand up to the elements. To ensure
compatibility of the cement with the vinyl banner substrate, you should test
the components before using them on an actual job.
Heat Welding
As
the name implies, a heat welding machine utilizes high heat and pressure to
melt two surfaces of vinyl banner material together. It is a great way to
produce very durable seams and hems provided that the heat is set at the right
temperature. Many different types of hot air welding units are available from
small hand held machines to larger floor models.
RF Welding
RF
(Radio Frequency) Welding fuses two surfaces of vinyl banner material together
in a manner similar to hot air welding. Instead of using hot air to heat up and
melt the vinyl material, RF Welding uses high intensity radio frequency.
Whether
you are using a hot air welder or an RF welder, the keys to producing a
successful weld are time, temperature and pressure. Another key factor is the
quality of the vinyl banner material that you are using.
While
hot air and RF welding produces durable
and reliable seams, the only downside is the cost of the equipment. As
with other machinery purchases, shop owners need to have a solid base of business
to justify the equipment investment.
Grommets
To
strengthen the material at the hem additional fabric can be sewn under the
folded edges of the banner. Grommets
should be secured through these edges, because there is a double layer of
fabric for added strength. The corners
of the banner should be folded over so that there are four layers of fabric to
hold the grommet. The extra layers of
material at the corners, provides additional reinforcement, where it’s needed
most.
Some
banner experts recommend cutting a strip of banner material and laying it under
the folded edges that will form the hem of the banner. The extra material strengthens the edges
especially where it’s needed most – where the grommets are placed. Nothing can destroy a banner faster than wind.
Adding another layer of fabric gives the banner added strength, which prevents
tearing – especially in high wind conditions.
If you attach grommets along
the hemline of the banner, you can reinforce them by adding washers on both
sides of the banner under the grommets.
Grommets should be spaced two feet apart.
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About Jim Hingst: After fourteen years as Business Development Manager at RTape, Jim Hingst retired. He was involved in many facets of the company’s business, including marketing, sales, product development and technical service.
Hingst began his career 42 years ago in the graphic arts field creating and producing advertising and promotional materials for a large test equipment manufacturer. Working for offset printers, large format screen printers, vinyl film manufacturers, and application tape companies, his experience included estimating, production planning, purchasing and production art, as well as sales and marketing. In his capacity as a salesman, Hingst was recognized with numerous sales achievement awards.
Drawing on his experience in production and as graphics installation subcontractor, Hingst provided the industry with practical advice, publishing more than 150 articles for publications, such as Signs Canada, SignCraft, Signs of the Times, Screen Printing, Sign and Digital Graphics and Sign Builder Illustrated. He also posted more than 400 stories on his blog (hingstssignpost.blogspot.com). In 2007 Hingst’s book, Vinyl Sign Techniques, was published. Vinyl Sign Techniques is available at sign supply distributors and at Amazon.
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