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Carrying adhesion to the peak. A brief look at backings
The tape backing turns an adhesive into adhesive tape. In other words: it is the backing that holds the adhesive in place. But it also has critical functional importance.
What is backing material? The backing material on adhesive tape not only holds the adhesive, but also contributes to the functioning of an adhesive tape. It is a little like a Sherpa: it does its work silently in the background. But just as Sherpas often take their rope team successfully to the peak, the perfect interaction of adhesive and backing material (plus primer and a separating layer) determines whether an adhesive tape will reach its goal.
Backing material and adhesive tape
The backing material initially has the job of holding the adhesive and the primer. It is fundamentally relatively thin, flexible and also smooth. That makes it perfectly suited for almost every application in every place of use and every design. The material itself can differ widely – and this is where it begins to play a critical role, depending on where, how long and for what purpose an adhesive tape should be used. Today’s backings are designed to withstand certain forces or to split at an exact defined force, to be optically clear or reflective, to be permeable or to function as a barrier (e.g. for humidity or oxygen), to be very thin (1.5 μm = 0.059 mils) or to be very thick (>3mm or 118 mils). Modern backings serve as gap fillers or noise dampeners, enable the tape to be machine-processed or die-cut. Due to the multiplicity of the available types of backings, it is worth discussing features and benefits of the different types.
Different backing materials we use
Filmic tapes (PP, PET, PVC)
Foam tapes (PE)
Dimensionally stable, chemically stable, heat-resistant (PET), transparent or white
Conformable, heat-resistant, hand-tearable, translucent
Dampens noise and vibration, adapts to rough substrates, compensates for different expansion factors (e.g. glass on metal), black or white
Conformable, tear-resistant, hand-tearable, for high coating weight
Differential adhesive coating weight on both sides of the backing. Strongly differing peel adhesion
No backing, only adhesive on liner, very conformable, very thin
Rip-proof: The film
Films make especially thin, rip-proof adhesive tapes possible. But there are even major differences when films are used as the backing material for adhesive tape. It depends on what they are produced of: PolyVinylChloride (PVC), PolyEthylene (PE), PolyPropylene (PP), PolyEthylene Terephthalate (PET) or another material.
PVC, for example, can be soft and is suited primarily to insulation applications and masking, for instance during plastering works. Very soft PVC is intended for insulating cable covers. Hard PVC, by contrast, is primarily stable in form and is used as packaging adhesive or for interior packaging. All PVC films share the fact that they are durable and do not ignite easily. They can be printed and embossed.
PE or PP films are used as backing for tesafilm® and other office adhesive tapes. They are also in demand as surface protection or for bundling materials (strapping).
Very different properties are involved in PET films. They primarily form the backing between two primers in double-sided adhesive tapes. Since they conduct heat, they are suitable for heat management in electronic devices. Their UV stability makes them attractive for exterior applications.
Besides the mentioned uses, polyurethane, polyimide, and cellophane/cellulose acetate are used in film backings, in particular because they are very elastic, weather-proof and immune to very high temperatures.
Strong: Fabric and fleece
Fabric and fleece such as cotton, viscose or PET provide mechanical advantages that make them exceptionally feasible for their specific area of application. The covering of cracks, the bundling of cables, sealing or splicing can be handled ideally with fabric and fleece as backing material.
Cotton and viscose have a high tensile strength but, in comparison to PET, are easy to rip by hand. Classical examples are adhesive tapes with fabric, such as duct tape or Gaffer tape. Cotton is a pure natural product and thus sustainable; viscose is more homogeneous and can be reproduced better. Fleece is especially supple and offers the advantage that it attenuates noise and vibrations exceptionally well.
Foam as backing material behaves as you would think: it is soft, voluminous and nestles very well into irregular surfaces. It also smooths out movements and stretched material well. Loads are absorbed well. In PVC windows, refrigerators, furniture, and decorative moulding, foams are used as backing materials – partly because they provide ideal support for very strong bonds.
One of its areas of specialism is the printing industry. The hardness of the foam in adhesive tape controls the contact pressure of the printing plate and ultimately the grid points on the paper for the printer. Foam adhesive tape also avoids stripes in the printing because it absorbs vibrations during the high printing speeds.
Produced out of pulp, hemp and synthetic fibres, it has different paper qualities that appear in the adhesive tapes.
Smooth papers are in demand when adhesive tape is required for packaging or as templates for sandblasting. Creped paper with different stretching is used for masking and painter's tapes. A higher degree of “crepe” to the paper allows for easier application of the tape to curves and contours. Especially fine Japanese paper prevents paint from running under the masking tape.
The special properties of paper as a backing material are seen in the ease with which it can be ripped by hand, its good suppleness and the possibility of stretching it by up to 50 percent. It is also resistant and absorbent up to over 180° C. There are more complex paper backings which are used in the paper industry for splicing or end tabbing large paper rolls. In this application, the paper needs to be re-pulpable (dissolvable without leaving any residues in the newly produced paper).
Elastic: the acrylic core
For high temperature applications (above 200º C) or for applications that require an even higher performance than a foam adhesive tape, acrylic core backings are the ideal solution. Since they consist of an acrylate polymer, they have outstanding viscoelastic properties. This means that they are capable of balancing out material tension, distributing forces and dissipating stress. Furthermore, they can compensate for temperature-related expansion – up to triple their thickness, depending on the backing structure. In combination with very high bonding strength, acrylic core tapes are the ideal solution for the gluing of distinct surfaces such as glass on metal or metal on plastic.
As an added benefit, acrylic backings are very resistant to many environmental elements, such as sunlight, ozone, temperature, and water. These characteristics make acrylic core tapes the ideal choice for long-lasting, high-performance outdoor applications. Application examples include bonding body side mouldings to car bodies (automotive); bonding framing of flat screens (electronics); bonding glass panels to metal frames; or joining photovoltaic panels onto back rails (solar panels). These and other appropriate applications demand high-bonding strength, long-term (up to 25 years) outdoor performance, and compensation of thermal differences.
Metallic backing materials are also resistant to ageing. Their primary qualities are unveiled when the matter involves electricity. Metallic backings consist of aluminium and copper, for example. They can conduct electricity and withstand temperatures of up to 140° C. They are used in electrical equipment as heat barriers.