The question of which glue is the best glue for rubber adhesion is a tough one. Rubber comes in dozens of forms and is used in even more applications. Furthermore, in these applications it can adhere to substrates ranging from hard to flexible, from metal to plastic, or even to another rubber itself. That’s why we decided to put our heads together here at Hotmelt.com to round up all the general rules of working with rubber, so you can pick the best glue for rubber adhesion that will meet the majority of your needs when it comes to adhering this material.
The General Rules of Rubber Adhesion
Identifying Your Type of Rubber
There are many kinds of rubber. It can be helpful to know which kind you are trying to adhere so you understand the flexibility and hold that will be required. These are likely the most common types of rubber you will be trying to bond:
- Nitrile rubber is a common rubber that’s often found in applications including hoses, o-rings, gaskets, conveyor belts, cable jacketing, and print rollers.
- Butyl rubber is very flexible and is used in items such as linings, inner tubes, seals and stoppers, and valve seating.
- Polyurethane rubber is used in molds and modeling.
- Natural rubber can be used for mountings, carpet backing, gaskets, and seals.
- Silicone rubber is very resistant to high heat, so it’s a popular choice for o-rings, gaskets, cookware, ovenware, medical devices, and prosthetics.
- EPDM rubber may be found in automotive hoses, seals, etc.
Prepping Rubber for Adhesion
Because of its variety of uses, your rubber could very well have mold release, slip additives, or other lubricants on it by the time you’re trying to bond it. So, whatever rubber you’re working with, it’s advisable to degrease it with a solvent before attempting any adhesion.
Choose isopropanol, as acetone can be too harsh for some types of rubber. Remember that your rubber may contain a plasticizer that will work its way to the surface and threaten your bond in the future. That’s why it’s important to try to identify your rubber and match it with the best adhesive for the job!
Picking the Best Glue for Your Rubber for Adhesion
Cyanoacrylate, also called “crazy glue” or “super glue,” is a good place to start when adhering rubber because it’s a great catchall for many substrates. Cyanoacrylate adhesive is an acrylic resin in which the main ingredient, cyanoacrylate, is an acrylic monomer that transforms to a plastic state after curing. While it requires the presence of moisture to cure, the bond will become very strong and rigid almost instantly.
While this is great in fast assembly line settings, it may pose a problem if your project requires a longer setting time to adjust your substrates or if you want any kind of flexibility at all. Cyanoacrylate also has a limited gap fill of 0.5mm max and can’t be used in a sprayer or roll coater for large areas due to its low open time. Learn how to use super glue the right way on our blog What Is Cyanoacrylate Glue?
If your joint simply isn’t sticking, your rubber could be of the EPDM or natural variety. For these substrates, we recommend a cyanoacrylate designed especially for “difficult” rubbers. Infinity Bond carries a special Rubber and Plastic Cyanoacrylate Super Glue that creates a lasting yet flexible bond.
Silicone-Based Adhesive
Thanks to elastomeric technology, silicone-based adhesives can be engineered to bond silicone rubber in a variety of applications ranging from household to transportation, to outer space. Silicone-based adhesives can be very flexible even after curing, and they resist extremely high temperatures and withstand chemicals and wetness. Different formulations can even provide electrical insulation or conductivity, depending on your needs.
While a two-component system does require mixing, it can cure in thicker sections than one-part systems, which might be necessary for certain applications. UV- or radiation-cured silicone adhesives use UV lamps or an electron beam to cure without additional heating or excessive heat generation.
One-component silicone adhesive systems are convenient—they require no mixing and cure at room temperature. Two-component silicone adhesive systems require the addition of a curing agent but can cure in thick layers, which is necessary for some situations. Silicone adhesive systems that cure with exposure to UV light or an electron beam are great for substrates that are sensitive to excessive heat or contact pressure.
Remember, when bonding silicone rubber, due to its slippery nature it can require extra care. If your bond just won’t hold, look for a primer to increase surface friction before applying an adhesive. View a wide selection of silicone and silicone-based adhesives at Hotmelt.com.
Two-Part Structural Acrylics
Two-part structural acrylics are often used to bond difficult plastics like polypropylene, polyethylene, and PTFE. Since EPDM rubber itself contains polypropylene, it makes sense that a two-part structural acrylic would bond well to this also “difficult” rubber substrate. While two-part acrylics, of course, take mixing to activate, this makes them more shelf stable than their one-part counterparts, so they can be purchased in bulk and stored for long periods of time.
Another benefit is that they cure more slowly than cyanoacrylates, so re-alignment and spreading over a large surface will be possible. Some varieties also have strong durability against harsh environments, even including being fully submerged in water. While two-part structural acrylics aren’t as convenient to use as super glue, they’re worth it to create a lasting bond if you’re working with a difficult rubber like EPDM.
Still a bit baffled about your type of rubber or which is the best glue for your specific rubber adhesion? No problem—we understand how many unique projects are out there! Just get in touch with the experts at Hotmelt.com online or by calling (877) 933-3343 any time.