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Notes on gluing Coroplast

The following paragraphs are from a series of emails posted on the alt.rec.bicycles.recumbent newsgroup. It may seem confusing at first because the posts were made over a period of time so please read to the end and everything should become clear. This thread was provided by our resident signmaker/Coroplast source, Dick Ludwig

Just found a site about RC Aircraft (Radio Controlled) - [coroplast & PVC constructed aircraft]. The guy talks about joining coroplast with glue, hot melt and epoxy. All of which worked only so-so at best. He then heard from a fellow that works in a big company that deals with plastics. This guy sent
the RC fellow this tip, which is reported to work really well. It uses Cyanoacrylate (CA) glue. SuperGlue is one form of CA, but there are many others with different properties. Most varieties can be found at hobby shops.

To glue coroplast [lap joint I guess] do this-----run the flame of a propane torch very quickly along the contact area of coroplast parts. This is supposed to burn away the oils in the coroplast [lots of practice for this] ----next, place little drops of CA about 1/8" apart and join parts. Don't glob the CA as this will not work. Small drops only. He said it joins the parts very well. Have not tried this yet but it sounds good to me. Will be trying it soon.

>>> We have discovered a new option for wing gluing you may wish to use, called "flashing". It involves using a small propane or butane torch. The object is to pass the flame across the area of Coroplast to be glued, slow enough to burn the manufacturing oils out of the pores, yet quick enough not to burn the plastic!

Once this is done, medium CA glue can be used, and it sticks like mad! The CA must be used sparingly (one drop every 1/8" or so). USING TOO MUCH GLUE IS THE BIGGEST MISTAKE HERE!!! WARNING! Practice this on a piece of scrap first, as there is a fine line between "flashing" and burning! If done correctly, the CA glue joints are stronger than epoxy! <<<<

The torch changes the surface energy of the polyethylene (PE) coroplast skin. AFAIK there are no 'oils' used in manufacturing coroplast. PE is a VERY inert material and has very low surface energy (measured in dynes). That's why water beads up when dropped on the surface of PE. PE is a very close chemical cousin of candle wax. After flame treating (or after the use of high energy discharge (corona (no, not the beer) treatment) a drop of water will sheet out if the treatment was correct. That's why the super glue will stick. There is a line of Double faced tape that is made by 3M called VHB (very high bond). The adhesive is formulated to work within specific dyne ranges. There is one formulated to stick to PE. These can usually be purchased from industrial distributors of adhesives and tapes. Works best if you can use an industrial purchasing account.

You may also want to look for some of the "No-Fumes" type of Cyano-Acrylate. This was used on models when you wanted to bond to foam or other sensitive material. It would be less likely to "eat" plastic than regular CA. BTW, purchasing this at model stores in the 2 oz sized is MUCH cheaper than just getting typical super glue. CA is like super glue and used a lot in model building.. Easy to find on the Internet or your local hobby store.

P.S. My (Dick's) recommendations would be to use the VHB Double Faced Tape. It is much easier to use. There is a real danger of dissolving/melting the coroplast if too much Super Glue is used. My other caution is NOT to OVER HEAT the coroplast. Too high a heat will structurally weaken the Coroplast and this point is passed very quickly when using a torch.

Note, all Coroplast used for signage is Corona treated before you buy it. However this treatment wears off/weakens with age. Within 6-12 months it needs to be redone. A good test to see if the Corona treatment is still good is to put some drops of water on the Coroplast. If the water beads up the treatment is old and needs to be redone. If the water spreads evenly across
the surface the treatment is still good.

Some info about gluing from 3M:

Bonding low surface energy (LSE) plastics such as polypropylene or other thermoplastic olefins with conventional tapes and adhesives typically requires the surfaces to be primed, flame treated or corona treated. These processes convert the low surface energy of these materials to a higher surface energy better suited for most bonding.

As design engineers and production engineers increasingly shift to LSE plastics, they need better and more efficient ways of attaching LSE plastics to themselves, to metals or to other materials. New adhesives and tapes can bond low surface energy plastics without pretreatment, ultimately reducing costs and improving manufacturing efficiencies.

According to Barry Kostyk, Ph.D., 3M Bonding Systems Division key account manager, the most recent advance in adhesive technology allows structural bonding (in excess of 1000 psi in overlap shear) of LSE plastics without priming or other pretreatment step. 3MT Scotch-WeldT Structural Plastic Adhesive DP-8005 uses a unique two-part solvent-free acrylic adhesive technology that does not require pretreating. "The structural bond that results is often greater than the strength of the substrates joined," Kostyk said. And because Scotch-Weld Adhesive DP-8005 cures at room temperature, it saves cost, time, oven-curing space, UV lamps and heaters. It also resists many chemicals, water, humidity and corrosion.

Why are low surface energy plastics difficult to bond? Surface energy defines the ability of adhesives and pressure sensitive adhesive tapes to "wet out" plastic surfaces and allow adhesion. Kostyk explained that surface wet out refers to how well a liquid or viscoelastic solid flows and intimately covers a surface. "Maximum adhesion develops when the adhesive or viscoelastic pressure sensitive adhesive tape thoroughly wets out the surface to be bonded," Kostyk said. "The greater the wet out, the better the surface contact and the greater the attractive force between the adhesive and the plastic surface." Surfaces with low surface energy are more difficult to bond because conventional adhesives and tapes cannot wet them out resulting in minimal contact with the plastic surface and unsatisfactory bonds. Plastics with high surface energy like ABS and polycarbonate are easier to bond because they are easier to wet with conventional adhesives and tapes than are low surface energy plastics.

For more information, contact, 3M, 800-362-3550 ext. 5160,

Source for the VHB tape:

Wensco Sign Supply

The tape you want is one of the following.

Scotch VHB Foam Tape Exterior:
# 4905 Clear 0.020" Foam thickness
# 4929 Black 0.025" Foam thickness
# 4950 White 0.045" Foam thickness

This company usually sells to just sign shops so you could yourself Recumbo

Happy gluing, Dick