Why is plastic hard to glue?

Many glues out there claim to do plastic. Krazy Glue and Gorilla Glue for example, claim to work on plastic. This statement is technically true, Krazy Glue and Gorilla Glue will work on modeling or PVC plastic. However, it will not work on any type of plastic and modeling plastic is not used for the overwhelming majority of plastic based products today. What is the most common type of plastic? The most common type of plastics are poly plastics. Examples of types of plastics referred to as poly’s are silicone, nylon, Teflon, Delrin, polyethylene, polypropylene and polyurethane. The second and third most common types of plastics are acrylic’s and resin’s. For all three of these commonplace plastics, poly’s resin’s and acrylic’s, priming is necessary. Surface preparation with Poly Prep Adhesion Promoter is a must, when dealing with literally every other type of plastic, except modeling plastic. The different molecular components of plastics make them almost impossible to glue on a superficial level; molecular bonding as well as priming, is required.

Why is Poly Prep Adhesion Promoter necessary?

Modern slippery plastics lack the surface tension necessary to create a strong bond by itself.

Priming the surface with Poly Prep Adhesion Promoter etches the surface of the plastic on a molecular level, thereby creating the necessary surface tension to create and maintain strong bonds. Priming each surface of the plastic to be bonded, is a critical first step when “gluing” plastics. What is the difference between gluing and bonding? Gluing joins the two surfaces together superficially with a glue join and nothing holding it together but the glue join. This join is penetrable and air and water permeate the join and degrade it over time. Gluing does not hold up with any amount of strength or permanence. Sometimes due to the slippery nature of the surface and to the age of the glue (which has likely been sitting on the shelf for years), a glue join may not even form. A bond however interlaces the surfaces on a molecular level and forms a covalent bond. A covalent bond shares molecular ions from each surface. Bonds cannot be permeated by air or water and are permanent. Bonds are so strong that substrate failure, is the result of strong overwhelming force or pressure. The material will actually break before the bond. We have seen this occur many times throughout our 20 year tenure, during applications of extreme stress or pressure. All of our Surface Insensitive Bonding Agents are made followed the Just In Time Inventory Process. Each bottle is fresh and we guarantee the shelf life for two years from the date of purchase.

When is Poly Prep Adhesion Promoter necessary?

To be safe, anytime you are working with plastic.

Often times it is hard to know just what type of plastic you are dealing with. Very little is made out of modeling plastic or PVC, which are the only type of plastics in which using the Adhesion Promoter is not necessary. Beyond those two exceptions, no matter what type of plastic is involved, the same solution is required.…….the Poly Prep Adhesion Promoter in conjunction with the Bonding Poly Process (BPP). If you happen to use the Poly Prep and the material turns out to be modeling plastic it will only increase the strength of the bond; there are no negative effects of its use when not required. There is a general rule of thumb when trying to identify through visual inspection alone, what type of plastic you are dealing with. If its slick and shiny, it is generally a poly and requires the Adhesion Promoter. If it is a dull, rough plastic it is most likely a modeling type plastic and the Adhesion Promoter is not required.

Substrate failure.

What is the Bonding Poly Process™(BPP)?

Throughout our long history with molecular bonding, we set out to solve the problem of gluing difficult plastics. It may have taken us over a decade of trial and error, but eventually we developed our patented Bonding Poly Process. The key to bonding hard to glue plastics is heat. Put in lay terms, heat expands the molecules in the plastic. When the surface temperature is warm to the touch or roughly 120 degrees Fahrenheit, bond your materials together. As the plastic cools, the molecules in the plastic constrict, strengthening the already interlaced covalent bond. This cohesion prevents bond degradation over time and provides a full seal. Don’t glue plastic, bond plastic. The result is a deep permanent bond.

How do you use the Poly Prep Adhesion Promoter and the Bonding Poly Process?

Step by step repair instructions.

The Bonding Poly Process™ for poly-plastics and other polymers begins at step 1.  The process for acrylic plastics and resin plastics begins with step 3.

  1. Begin by saturating both edges or surfaces* of the poly item to be repaired/bonded with the Poly Prep.
  2. Let the Poly Prep dry.
  3. Spray one edge/surface of the polymer or plastic with our solvent based AA.
  4. Let the AA dry.
  5. Warm both edges with a heat gun or hair dryer for 20 to 30 seconds (about degrees Fahrenheit. Warm not hot.)
  6. Apply the SI adhesive to the opposite edge from where you sprayed the Activator/Accelerator.
  7. Press the two edges together.
  8. Warm the seam with a heat gun or hair dryer for 15 – 20 seconds.
  9. Done, though full cure with plastics takes up to seven days.  All plastics and polymers are very slow curing.

When the repair is a crack, the repair procedure is slightly different.  Again polymer repair begins at step 1, other plastics at step 3.

  1. Spray the Poly Prep.
  2. Let the Poly Prep dry.
  3. Take a blow dryer or a heat gun and WARM both edges/surfaces.
  4. Apply a structural adhesive (Usually SI Blue) to the crack.
  5. Align the two edges/surfaces and press for fifteen to twenty seconds.
  6. Spray the seam with the Activator/Accelerator.
  7. Take the hair dryer or heat gun and warm the seam for thirty seconds.

* If you don’t have heat available, you will still get an excellent glue join by just using the Poly Prep, a solvent based AA and an SI adhesive.  If you don’t have either heat or the AA, the Poly Prep and SI adhesive will also work.

*Poly kits will bond any type of plastic to itself or any other substrate, except glass and stainless steel.

Specific Instructions For Individual Plastic Substrates and Respective Repair Videos:

The Bonding Poly Process works on all plastic substrates. In some instances of very extreme weight or pressure, there are tricks of the trade for specific types of plastic. For that reason, we have individual repair videos and pages, for certain plastics. While the repair techniques are all basically the same for each, some people find the individual videos and pages helpful.

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