How does tape stick?

‘Sticking’ is basically ‘adhesion’ which is defined as the ‘interaction that develops between two dissimilar bodies when they are in contact’. At the molecular level, adhesion is based on physical and in some cases, chemical bonding. For adhesive tapes, a ‘pressure sensitive adhesive’ (PSA) is used i.e. the adhesive characteristics are activated by pressure which causes the adhesive to ‘flow’ and ‘wet’ the surface of the substrate to which it is being applied. At this stage molecular interactions, such as Van de Waals’ forces begin to influence the bond and its ultimate strength.

Depending on the type of adhesive used the ultimate bond strength may take between 24 and 72 hours to be reached: an important consideration if the application for which the tape is being used is a critical one.

How strong a bond can be achieved?

In terms of quantitative values, double sided tapes can offer a bond strength in excess of 15N/cm and even up to 23N/cm depending on the substrate – strong enough to take the weight of a full-grown adult!

However, this is primarily this is down to two factors: good surface preparation and applied pressure. Firstly, it is essential that the surface to which the tape is being applied is clean, dry and free of any contaminants such as dust, oil etc. Secondly, the tape should be applied using firm, even pressure (remember they are ‘pressure sensitive adhesives!). Other factors such as the type of adhesive, the substrate(s) to which the tape is being applied and its surface characteristics (rough, smooth) also come into play, but without observing these two very simple rules to begin with, the chances of getting a good, strong bond are potentially greatly reduced.

What advantages do double sided tapes have?

All too often the traditional default when joining two substrates together is to use either a form of mechanical fixing, such as screws or nails, or ‘wet’ glues. However, in many cases a double sided tape can prove to be superior in terms of its ease of use and convenience, without suffering from lower bond performance.

For example, wet glues need to cure before progression to the next production stage can take place: double sided tapes don’t as up to 80% of the final bond strength is reached within a few minutes after application. There is also no risk of oozing around the joins when the substrates are compressed and stresses are displaced evenly over the area of the tape and not accentuated at the point of the bond as would be the case with nails or screws. Double sided tapes are also light and can absorb shock and vibration (depending on the carrier).

Why do masking tapes sometimes leave residue?

This is a very common question and there are usually two possible answers depending on the application. Firstly, the wrong tape is being used or secondly, the tape is being removed at too high a temperature when the adhesive is still ‘soft’.

Choosing the wrong tape is a common issue and is usually driven by a lack of knowledge of the construction of a masking tape – specifically the adhesive. With the exception of very high temperature masking tapes, such as for powder coating, a rubber adhesive is used. For general purpose masking tapes, if used indoors and kept out of direct sunlight, a good quality tape will remove cleanly after up to 3 days use, but there are others which will leave residue even after a few hours! As the process temperature increases (driven by the required curing temperature of the paint system) then it becomes even more important to match the masking tape to the application. This is because to provide the necessary temperature resistance, the amount of ‘cross-linking’ (or ‘curing’) of the polymer chains in the adhesive needs to be increased accordingly, and the greater the amount of cross-linking, the ‘harder’ the adhesive and the higher the temperature resistance. In manufacture, a process called ‘electron beam curing’ is used as the amount of cross-linking can be precisely controlled.

However, temperature and UV radiation (sunlight) can also initiate cross-linking, so if a masking tape with a stated temperature resistance of 80˚C is used when the required oven temperature is 140˚C, there is a very great chance further cross-linking will occur and the masking tape will cure onto the surface to which it has been applied.

So next time you’re at a DIY shop at the weekend and need a masking tape for painting windows and can’t decide between the more expensive, UV resistant option, and the cheaper version, think about how much time and frustration you’ll save by picking the recommended one compared to the few extra pounds out of your pocket.

What are tapes made of?

The ‘heart’ of any tape is the ‘carrier’ or ‘backing’ and this can be made from a variety of materials from paper to plastic films. For a double sided tape both sides of the carrier are coated with a pressure sensitive adhesive, and for a single sided tape just one side is coated. The coating weight and the type and formulation of the adhesive depend on the intended application the tape is designed for. To be able to unwind a double sided tape properly an ‘adhesive-repellent’ liner is used, usually glassine paper with a thin layer of silicon (about 1µm) which acts as a ‘release-coating’. For a single-side tape a similar principle is also used.

What are the different types of carrier and why are they used?

A carrier is primarily used as the means of getting the adhesive to where it is being used. However, depending on the application different types of carrier will be selected so their properties are often just as important as their main function. The different carriers used are divided into 5 groups. Firstly filmic tapes such as polypropylene (PP), polyester (PET) and polyvinyl chloride (PVC): these are dimensionally stable, chemically stable and heat resistant (PET) and are used in the construction of both double sided and single sided tapes. Next are cloth/fabric carriers which are used primarily in the form of single sided cloth tapes, such as duct and gaffer tapes, but they are also used for double sided tapes where their inherent strength makes them ideal for temporary applications such as carpet laying. In double sided tapes foam carriers are used e.g. for their ability to absorb shock and fill gaps between irregular surfaces: applications as a single sided tape are often used as a seal, for example as draught excluders (see tesamoll range – link to consumer page?). Non-woven (sometimes referred to as ‘tissue’) carriers are only used for double sided tapes: they are conformable, heat resistant and hand tearable. The last category again is only used for double-sided tapes, although they don’t actually have a carrier: these are transfer tapes and consist only of the adhesive on the liner.

What are the different types of adhesives used and why?

There are 3 main types of adhesive used: acrylic, natural rubber and synthetic rubber.

Acrylic adhesives are derived from oil and industrially synthesised (tesa polymerises and compounds its own acrylic adhesives meaning we retain control over the formulation and properties: most other manufacturers do not).

Advantages

• Stick well to high surface energy substrates (HSE) such as glass and metal.
• Temperature resistance
• Ageing resistance
• Environmental resistance
• High shear resistance

• Ultimate bond strength reached after up to 72 hours
• Low immediate peel adhesion (but can be repositioned)
• Lower adhesion on low surface energy (LSE) substrates such as PE and PP.

Synthetic rubber has very similar properties to natural rubber except that as with acrylic adhesives it is derived from oil.

Advantages

• High initial ‘tack’.
• High initial bond to substrate.
• Very good adhesion to LSE substrates such as PE and PP.
• Lower raw material costs than acrylics.

• Lower temperature resistance.
• Lower ageing resistance.
• Lower environmental resistance.
• Lower chemical resistance.
• Lower humidity resistance.