Back to the basics
How many times have you heard the complaint that “the tape just fell off” or it “didn’t stick to the part very well”?
Most people think that the product wasn’t the right one (and sometimes that can be the case!) or that tape is not a very good design solution for their problem. They couldn’t be more wrong!
Actually, the term “pressure sensitive self-adhesive tape” provides a number of clues as to how these products should be used. Self-adhesive tape is designed to stick to whatever surface to which it is applied. What is often overlooked is the importance of properly preparing and cleaning the surface to which you are applying the tape, as the tape will only stick to what is on the surface. This is particularly important when using high performance attachment tapes such as 3M VHB ® tape. Such products are much more effective at joining components than using mechanical methods of attachment such as screws or welds – but only if you prepare the surface properly.
Many surfaces look clean to the eye but at a microscopic level, they are not! Therefore, the importance of cleaning the surface first normally with a disposable wipe and a 50-70% mix of iso propyl alcohol (IPA) and water mix is essential. If a surface is heavily contaminated with oils, it may also be necessary to clean first with a compatible solvent – and then clean with the IPA mix next. Prior to doing that cleaning some surfaces may need to be abraded first – a finely abraded surface (approximately 180 to 320 grit scratch) can help adhesion to many paints and plastics. Very small scratches on the surface, generated with circular motion rather than straight-line motion, are most desirable.
Micro-scratches on a surface increases the available surface area to bond to resulting in greater initial adhesion and achieving higher ultimate strength. You need to maximise the surface area to which the tape is applied, and micro scratching helps to optimise that surface area.
Some surfaces may require the application of a very thin layer of adhesive promoter or primer first – some plastics such as propylene (PP) – which are commonly used today – have a low surface energy characteristic which requires the use of a promoter to enhance the surface energy level.
Having prepared the surface correctly, the next key element is to focus on the words “pressure sensitive”. Crudely put – the more pressure you apply through the tape itself when applying it will result in a better bond strength. As a pressure-sensitive adhesive, bond strength is dependent upon the amount of adhesive-to-surface contact developed. Firm application pressure develops better adhesive contact and helps improve bond strength. Generally, this means that the tape should experience >15 psi (>100 kPa) in roll down pressure using a handheld rubber roller – or flat platen pressure.
The final point to emphasise that some products like 3M VHB® tape will develop further bond strength over time as the adhesive “flows” properly into the surface (this is why micro scratching helps so much). This may take up to 72 hours to attain full bond strength – although the positive attribute of using tape is that the part can be instantly moved whilst this is happening.