In part one of our series, we explored the first set of “screens” to help narrow the myriad of tape options that are available to manufacturers. These were:
- The type of assembly being considered
- The materials to be bonded (substrates)
- The manufacturing process itself
- What the product encounter during its’ life cycle(end use requirements)
- Cost considerations
Sometimes, it’s helpful to understand the basic pressure-sensitive adhesive chemistries and the physical performance tests that are used to characterize tapes. (Yes, I know this is kind of boring but bear with me and I’ll make it as easy as I can!)
Adhesive Chemistry 101
There are three basic pressure-sensitive chemistries:
- Rubber based or rubber/resin as it’s sometimes called
We’re going to limit our discussion to the very basic pros and cons to keep this simple:
The oldest type of pressure-sensitive adhesive consisting of a rubber (natural or synthetic) that is tackled by the addition of various resins.
- Can be easily formulated
- Adheres quickly to many surfaces
- Poor temperature resistance
- Poor chemical resistance
- Variable UV resistance
The “workhorse’ of the tape world.
- Tack, peel, and shear can be varied
- Good UV resistance
- Good temperature resistance
- May not adhere quickly
- More expensive than rubber
The most “specialized” of the three.
- Balanced peel and shear
- Excellent temperature resistance
- God UV resistance
- Low tack and quick stick
- Very expensive
Common Tape Test Methods
While many blogs could be written on this subject, we’ll keep to the basics.
Peel Adhesion– the force necessary to remove a tape sample from a surface after a specified time at a specified rate of removal, While stainless steel is the most common test surface, the tape can be tested on other application specific surfaces. The values are usually reported in ounces per inch width (or the metric equivalent) or pounds per inch width. Some tape companies use high medium or low designations ( Not as useful in my opinion)
Shear– a test to measure the internal or cohesive strength of the adhesive tape. Normally performed in the “static mode”, a weight is attached to a specified overlap and the time to failure is noted. The time to failure is a relative indication of shear strength. In the “dynamic mode” an overlap joint is placed in a tester and pulled apart at a specified rate. That value when the lap joint is sheared apart is the shear strength. Often report in pounds per square inch or metric equivalent.
Shear testing can also be performed at elevated temperatures which can be very useful information if the tape is expected to operate in such environments during use.
Well, that’s about it for Part 2. In Part 3, we’ll tie all of this information together using some real world examples. In the interim, if you have any questions on matching tapes to applications, just contact Tom Brown, Inc.