The primary focus of this technical note is to document the importance of adhesive selection, preparation, and application to ensure a strong bond between the adhesive and coating adhesive interfaces.
Adhesive selection and application
The basic goal of adhesion testing is to produce coating failure. Coatings in test may experience interfacial disruption between substrates and coatings, or between individual coatings in multi-layer coatings. Coatings may also experience cohesive disruption within specific layers. The Perfect Adhesive is designed to provide a stronger bond in the Dolly Adhesive and Adhesive Coated Interface than the failure point of the coating test. This ensures that all test results are valid and meaningful.
Also remember: the adhesive needs to be pre-tested on the coating to ensure that it does not make a noticeable change in the properties of the coating. In the case of satisfactory results, this test should be performed from the time when the adhesive is fully mixed until the adhesive is fully cured. Any change in the properties of the coating may invalidate the results. Our lab tests have shown that some aggressive adhesives will be enough to weaken a particular coating, reducing its bond strength. In one case, the adhesive reacts with the coating, allowing the bond strength to increase when the new compound is fully cured.
Several experiments were carried out during the development cycle of the non-magnetic adhesion Tester. Some of these results and conclusions are cited throughout the technical note. An additional experiment was developed and implemented to quantify these results and facilitate the writing of this paper.
Considerations for the selection of adhesives
Curing Time – The recommended epoxy 2011 curing time is 24 hours for most applications. One experiment involved 24 carts after a 24-hour cure time and an additional 24 carts after a full 5 days of treatment. The result was an average adhesion force of 24 psi and 2729 psi after 5 hours and failure after 2706 days. This small increase may not be statistically significant, helping to show that epoxy 2011 is able to achieve maximum bond strength within the expected 24-hour window.
Work Life – Epoxy 2011 at room temperature has the potential to help the cart to put a larger 2 hours of work life.
The minimum curing time for epoxy resin curing can be reduced by 15 hours and 5 minutes, and the curing temperature can be increased to 302F 68F. Note: Applied heat may affect the substrate of coatings and bonds.
The mix ratio adheres to the ratio between the mixing resin and the curing agent is important when mixing the epoxy resin. The single plunger with built-in adhesive tubing is the perfect control of the mix ratio. The mixing process still requires the user's care to ensure that there is no clogging that can affect these quantities. It is also important to mix resins and hardeners effectively while avoiding air bubbles and impurities in the surrounding environment.
Application of epoxy resin thickness according to the manufacturer's instructions, for the epoxy resin 2011 core application thickness of 2~4 ml. By applying the right amount of epoxy resin to the surface of the trolley, the desired thickness can usually be achieved. By stretching until smooth, even across the surface, and then carefully placing the trolley on the surface, pushing straight down to extrude the excess epoxy, within the target adhesive thickness range, Dolly will tend to self-level.
Handling Strength – Epoxy 2011 has 7 hours to wait until full processing strength has been reached – this may require a cart to apply a partially cured coating of tape or similar material until.
Epoxy Handling and Storage Information – The temperature of the mixed material, the storage temperature between use and life is an important consideration when employing epoxy adhesives.
Whenever an unexpected or premature failure occurs, it is important to review how the adhesive has changed during use and during its application.
Difficult to adhere to surfaces
Independent of other aspects, the coating itself can be a decisive factor in the choice of adhesive. Various applications have been processed through the program for receiving samples from DeFelsko's customers.
When testing a sample, a thin UV-coated polycarbonate, epoxy resin is only able to reach 20% layer removal with 80% glue coating failure. The fault occurred around 400 psi. When the epoxy is pulled out with Loctite Glass Bonding glue it is required to replace 100% with the expected strength of 600 PSI.
In another sample, a smooth Teflon-like coated aluminum, a 100% adhesive coating on 100 psi epoxy and other adhesives experienced failure. Loctite Glass Adhesive was able to provide partial pull pins in excess of 1,500 pounds, but the repeatability was not enough to directly recommend. The advice to the user is to work with the adhesive manufacturer to find a more suitable alternative for the application.
Faster curing time
Many customers inquire about the use of cyanoacrylate, which is part of the adhesive often referred to as the "crazy glue", where the two-component epoxy is offered. Cyanoacrylates are known for their faster curing time, ease of application, and strong bond strength. The significant disadvantage is that they often experience bond failures at higher bond strength at the Dolly adhesive and coating bonding interface. They may still be acceptable, or even preferred, for specific low bond strength applications.
It should be noted that even fast-curing adhesives such as cyanoacrylate (working life in minutes and hours) are subject to a significant increase in the number of treatments resulting in an increase in bond strength. In a good Norwegian trial, all showed a significant increase in the bond strength of 4 different Zcyanoacrylates, and the number of treatments increased from 1 to room temperature for 5 hours. The increase ranged from 7 to 21 percent. In addition, the results of changes between cyanoacrylates tended to decrease and the number of treatments increased.
conclusion
While Epoxy 2011 is recommended as an industry-recognized multi-purpose adhesive, it is the user-selected adhesive that meets their application-specific adhesion testing requirements. If the adhesive chosen does not react with the coating, this is an acceptable option as long as most adhesion failures are limited to individual coats, between coatings, or between coatings and substrates.
