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.
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 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.
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.
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 (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.
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.