How Is The Tape Made?

WHAT IS A PRESSURE SENSITIVE TAPE?

A pressure sensitive tape is any adhesive tape that will stick to a wide variety of clean dry surfaces with only the minimum of pressure applied. It is ready to use and does not need to be activated by water, solvent or heat.

A pressure sensitive tape consists of a relatively thin, flexible backing or carrier, coated with an adhesive, which is permanently sticky at room temperature. The tapes can be manufactured with the adhesive coating on one side (single-sided) or both sides (double-sided) of the carrier.

  Single Sided Tape                        Double Sided Tape

Backing / Carrier Materials

The tape carrier can be any one of a wide range of relatively thin flexible materials. Common materials include films (which are typically made from regenerated cellulose, polypropylene or PVC), paper tissues, cloth or even metal foils and can be clear, coloured or printed. The choice of material used as the carrier depends on what the tape is intended to do.

A tape for general use in the home and office uses regenerated cellulose as the carrier, which is strong but can be torn by hand and is easy to use. Packaging tapes will generally be made from a polypropylene film whereas electrical insulating tapes use soft PVC.

Masking tapes have a paper carrier, however other heavy-duty tapes for other DIY uses such as sealing or heating duct work are made from cloth.

Types of Adhesive

There are 2 main types of adhesives used for pressure sensitive tapes - rubber/resin and acrylic.

1. Rubber/resin adhesive is a mixture of a rubbery material and a hard resin. The rubber and the resin can come from natural or synthetic sources. The natural materials are usually extracted from trees while the synthetics come from the oil industry. Rubber/resin adhesives are relatively cheap but, unless they are specially formulated through curing or stabilising, do not have very good resistance to heat, ageing or exposure to light.

2. Acrylics are fully synthetic polymers, which are manufactured to give the specific adhesive properties required. Acrylic adhesives are more expensive but generally have better resistance to ageing and exposure to light.

HOW IS TAPE PRODUCED?

There are 2 processes in the production of pressure sensitive tape; coating and slitting. Coating is the application of the adhesive on to the carrier. Slitting is the cutting up of a huge 'jumbo' roll of coated carrier film into the large and small rolls of tape as we see them in the shops.

Coating

Since pressure sensitive adhesives are not runny liquids, they are not as easy to coat on to the thin flexible carriers, therefore they must be made less viscous (or thin) to make coating possible. There are 3 main ways to do this:-

1. Solvent Coating
The adhesive materials are dissolved into a suitable solvent. The resulting relatively runny solution is coated onto the carrier and the solvent removed by passing it through a heated oven.

2. Water-based Coating
The adhesive materials are mixed with water to form an emulsion or dispersion. This is then coated onto the backing and the water removed through a heated oven in the same way as for solvent coating.

3. Hot-melt Coating
The adhesive materials are heated until they melt and coated as a hot liquid. The coated tape is then simply cooled to give the finished tape.

These 3 coating techniques are frequently used to define pressure sensitive tape i.e. Solvent, Water-based or Hot melt. This is a loose description as it only refers to the technique used to coat the adhesive onto the carrier. It does not take account of the adhesive type and it is this that can have a considerable influence on the tape's performance.

Generally speaking, we manufacture our tape using the Hot-Melt technique because we believe that this method produces less waste and is more environmentally friendly. Any solvent used to make the release coating is destroyed in a thermal oxidiser which ensures that no dangerous or harmful gases are released into the atmosphere. In the process of converting any harmful gases into clean air, heat is produced from the thermal oxidiser. This heat is used to power the drying oven. This ensures that the process is not only very environmentally friendly but efficient. The following diagram shows the basics of the hot melt process:-

Why doesn't tape stick to itself on the Roll?
Pressure sensitive adhesives easily stick to a wide range of different surfaces including Cellulose film. So why does the tape not stick to itself? In order that we can use tape and easily pull it off the roll we need to treat the back of the carrier and coat it with a release coating. This may not be obvious straight away but it is a very important part of the tape. Without a release coat many tapes would be impossible to use.

The release coating not only ensures that the user can easily unwind the roll but it makes slitting, the second part of the process much more efficient.

Slitting
The process has now made a 'jumbo'. This is what we call a huge roll of tape, perhaps 1.5m wide x 6000m long. It is the slitting process that turns the large jumbo into rolls for sale, in the sizes we all know. These could be anything from 12mm x 4m to 50mm x 66m. The jumbo is unwound onto a machine that contains a number of razor blades. The number and distance between these blades determines the width of the tape. The carrier passes over these blades cutting the tape into narrower widths and these are then wound on to cores to give the appropriate length for the finished rolls.

GLOSSARY:

Regenerated Cellulose:
This film is made by dissolving wood pulp (Cellulose fibres) and regenerating it as a clear film

Polypropylene:
A polymer manufactured from propylene gas

PVC:
A polymer manufactured from vinyl/chlorine gas

Resin:
A hard brittle low molecular weight material

Polymer:
A solid made by joining a large number of small molecules to make one large one i.e. propylene gas into polypropylene solids

Solvent:
A liquid used to dissolve a solid e.g. coffee dissolving sugar

Curing / Stabilising:
Chemically modifying a material to make it more resistant to adverse conditions such as high temperature

Thermal Oxidiser:
Equipment operating at high temperature to break down environmentally unfriendly solvents into harmless water and carbon dioxide. The heat generated in this process can then used to heat the drying oven.

Jumbo:
The large roll of wide tape made on the coating machine

Cores:
Plastic or card rings at the centre of a roll of tape