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Duration of Bondings

A Friend for Life or only a Partner for a While?

Technologies

Bonding with adhesive tape is somehow similar to relationships bonded by love. Sometimes it lasts forever, sometimes only for a certain period of time and sometimes it stops and then starts again.

The nice thing about adhesive tapes is that you can determine in advance how stable the taping will be. Should it be permanent? Or only a quick flirt? Or perhaps a more temporary or reversible on-off relationship. We will explain what it's about.

Let's start with the basics: three forces act in an adhesive. The inner bond, the cohesion, determines the degree to which a substance is prevented from ripping. The adhesion, i.e. the stickiness of an adhesive, describes its ability to remain stuck to an non-sticky object. The tack is the strength with which an adhesive connects to a surface in a very short amount of time. So far, so good. But how do I set these three parameters in order to gain the right adhesive tape connection for my requirements?

The balance between T) tack, C) cohesion, and A) adhesion determinates the application field
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The balance between T) tack, C) cohesion, and A) adhesion determinates the application field
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When it comes to protect surfaces during transportation or painting works it is important that the tapes can be removed easily and without residues. Therefore the focus is set on cohesion rather than adhesion.

Temporary and Reversible Bonding

Tack and cohesion are tailored to each application. The adhesion is of secondary importance. In many applications in this area, it is critical that the relationship between the tack and inner solidity, cohesion, is balanced. Tack is necessary to ensure the immediate adhesion to the surface. Higher cohesion, the inner solidity of the adhesive, is required in particular if the product should be removed without residue. For many reversible applications, that is more important than a high specific adhesion, which would be seen, for example, in a high tack value (resistance to peeling).

One uses adhesive tapes with these properties, for example, to pre-mount in assembly processes, to cover sensitive surfaces in painting work, to protect against newly painted vehicles during transport or for the assembly of printing plates.

Permanent Bonding

If things should be connected permanently, adhesion and cohesion are in focus. They must be tailored to each application. The tack is of secondary importance for permanent attachments. Adhesives for this area are characterized above all by having a cohesion-adhesion relationship that is suited for the application. The significant part is the permanence of the bond. The tack, the stickiness at the moment of contact, is usually of secondary importance.

Areas of application include the assembly of façade components or furniture panels, decorative trims, profiles and emblems in the car industry or camera lenses in mobile phones. Or also the bundling and protection of cables in cars (wire harnessing). In all of these cases, a permanent bond and secure attachment is required and must be resistant to aging and have a long life.

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In newspaper printing the paper rolls are changed in high speed during the printing process. The end of the old roll is connected with the beginning of the new roll within a part of a second. High-tack is the prerequesite for this.

Quick Stick Bonds

Sometimes it has to be quick. That is where the right interplay of tack and adhesion is important. Both must be tailored to each application. The cohesion is of secondary importance in this case. The critical part for the adhesives in this area is that they stick immediately and firmly, i.e. they have good tack and/or high adhesion. Since generally no high loads need to be transferred and the adhesive doesn’t absolutely have to be removed without leaving residue, cohesion assumes a subordinate place here.

Splicing is a good example of this. It creates a bond at the end of one paper roll and the beginning of the next in paper production and newspaper printing. This bond must be achieved at full speed in a running operation. The end of one roll connects to the beginning of the next. This short touch must be sufficient in order to produce a solid connection. There is also a similar process in packaging printing with filmic webs. And also the famous tesafilm® is more of a quick stick product. It should stick quickly and doesn’t need to be removed without a trace. At the same time, the loads that it must hold over the long term are easily manageable.