Technicians have it taped

By
Thursday, 04 September, 2003


When the lights go out, chances are good that emergency crews will use vinyl electrical tape somewhere to help restore power. The same electricians might also use it to secure a broken latch on a lunch box.

Whatever you call it - 'black tape', 'electrician's tape', 'vinyl tape', or 'electrical insulating tape' - the glossy pressure-sensitive tape that electricians use by the carload is one of the most versatile tools in the industry.

Its more technical applications include: splicing, terminating, and harnessing wire and cable; providing electrical insulation and protective jacketing; and sealing electrical components such as split bolt connectors, motor leads and control connections.

But, as any electrician will tell you, rolls of black tape are used liberally on the job site as general purpose electrician's helpers.

However, black tape may be as misunderstood as it is versatile.

Widely considered a simple, expendable product, vinyl electrical tape is the result of over 50 years of research and development to achieve just the right combination of adhesion, cold-weather performance, stretch, conformity, and consistent quality.

It can be one of the most technologically complex products to come out of a manufacturer's lab, largely due to the interaction between ingredients of the backing and the adhesive.

Once that balance is struck in the 'perfect' tape, the ultimate challenge remains: how to manufacture it.

Tape tips

Although challenging in its make-up and manufacture, vinyl electrical tape is relatively straightforward in its use. Nevertheless, care should be taken to ensure the safest, most reliable use in critical electrical applications.

When using vinyl electrical tape, for example, you should always:

  • Apply tape with enough stretch to conform to the object you're wrapping. Be sure to let the last couple of inches relax before tabbing it down to prevent unwinding (sometimes called 'flagging').
  • Wrap an irregular mechanical connector, such as a split bolt, with rubber tape to pad sharp edges, before wrapping it with vinyl electrical tape.
  • Wrap cone-shaped (high-voltage splices) 'uphill' - that is, from the smallest to the largest point. This way you always secure the previous layer.
  • Cutting tape is preferable to tearing the tape as it will give the best adhesion and prevents 'flagging'.
  • When tearing tape is necessary keep fingers close together. The farther apart they are, the more the tape will stretch before it tears.
  • Use the right tape for the right conditions. Vinyl tapes are rated for cold-weather applications in two classes: 0°C and -18°C. Tapes formulated for high-temperature environments are typically rated 80°C or 105°C.
  • Think twice about viewing vinyl electrical tape as a cheap, throwaway consumable. More 'cheap' tape may end up in the scrap heap than on electrical components, and anticipated dollar savings may prove illusory. It's best to use a good quality tape for most applications.

History

Before the advent of vinyl electrical tape, technicians used friction tape made of tar-coated cotton and a vulcanised rubber adhesive.

Although it provided good mechanical protection, friction tape had a few drawbacks: it was subject to rotting, had low dielectric strength and the rubber adhesive - vulcanised with sulfur - caused corrosion under certain conditions.

Also, friction tape could not be used by itself when insulating a conductor and had to be applied over rubber tape. In the early 1940s, vinyl plastic emerged as a highly versatile material for a wide range of applications, from shower curtains to cable insulation.

Making it work for tape, however, was a different story. A major ingredient in vinyl was tricresyl phosphate (TCP), which was used as a plasticiser.

Unfortunately, TCP tended to migrate, giving the surface of the vinyl film an oily quality and degrading every tape adhesive known.

Research chemists and engineers at 3M set out to create a dependable, pressure-sensitive tape made of vinyl film that would have the required electrical, physical and chemical properties.

Experiments were conducted combining new plasticisers with the white, flour-like vinyl resin.

Finally, in January 1946, inventors Snell, Oace and Eastwood of 3M applied for a patent for a vinyl electrical tape with a plasticiser system and non-sulfur-based rubber adhesive that were compatible.

The first commercially available version of the tape was sold for use as a wire-harness wrapping.

Interestingly, this original black tape wasn't black at all. The first 3M tape sold was yellow and later versions were white.

White tape, because of its instability in ultraviolet light, was eventually replaced with black tape, although coloured vinyl tapes are still used as identification and marking tapes.

Black became the standard industry colour for vinyl electrical tape, primarily because of its ultraviolet resistance.

Thicknesses originally were 4 mil, 8 mil, 10 mil and 12 mil caliper. These were standardised to 7 mil and 10 mil in 1948.

Manufacturing

Vinyl tapes are by no means uncomplicated products. About 30 individual ingredients are involved in their manufacture.

When mixing these ingredients, manufacturing technicians must carefully control the formulation to achieve the right results.

For example, if the ingredients are mixed for too long or at the wrong temperatures, 'gapping' can occur in the finished roll (see glossary).

Other crucial steps are 'calendaring' (a calendar is a machine with hot rolls that forms the film to the right thickness and uniformity); properly preparing the vinyl surface for the adhesive; and making sure the adhesive is uniformly applied.

If the rolls aren't slit correctly, nicks can form in the edges, which can cause the tape to tear too soon during application.

Telescoping can result when the film is stretched before being wound into rolls.

Some of the more important ingredients of vinyl electrical tape are:

  • PVC, a major component, which imparts abrasion resistance and strength;
  • Plasticisers, which give the tape stretch, conformity, flexibility and integrity at high temperatures;
  • Stabilisers, which keep all the tape's ingredients in proper balance by eliminating heat sensitivity problems;
  • UV retardants that screen out ultraviolet rays and improve electrical properties;
  • Flame retardants that prevent the tape from contributing to an electrical fire;
  • Primers that prepare the backing surface and firmly anchor the adhesive to the backing;
  • Rubber polymers that provide the adhesive 'backbone';
  • Resins that provide 'tackiness' (see glossary) and adhesive strength; and
  • Curing agents that crosslink the adhesives to make them firm, resistant to plasticisers, and stable in applications.

R&D

Vinyl electrical tape has undergone continuous improvement since its invention 48 years ago.

After solving initial problems with the original yellow tape (which had a tendency to telescope, ooze, gap and peak-see glossary), researchers went on to improve its ageing, cold-weather handling and high-temperature capabilities.

Other qualities that have undergone continuous improvement include roll appearance, tensile profile, adhesion, dielectric strength, thermal stability, flame resistance, and flagging resistance.

No quality has received more R&D attention than temperature range.

Researchers came to envision the perfect vinyl electrical tape as one that could maintain its flexibility in cold weather and its stability in hot.

This can be important on the job site, as technicians struggle with gloved hands and brittle backings in the winter and temperatures high enough to melt adhesive in the summer.

Tape that goes on should stay on and be clean and easy to remove whether it's used to insulate a conductor or mark a junction box.

With that in mind, researchers have continually experimented with compounds and revised production techniques, until a single tape can now have an operating range from -18°C to 105°C.

No matter what the temperature, voltage, or application, vinyl electrical tape is one of the most useful tools for the electrician and electronics technician.

Ongoing research continues to widen the temperature range and improve handling characteristics. Researchers haven't been able to come up with a tape that will go on by itself, but we're working on it.

Glossary

The following are some of the electrical tape terms commonly used in the lab, and their definitions.

  • Adhesive - The medium that allows the backing to be quickly, positively and efficiently positioned to do its job.
  • Adhesion to backing - The bond produced by contact between a pressure-sensitive adhesive and the tape backing when one piece of tape is applied to the back of another piece of the same tape.
  • Backing - The material that performs the tape's desired function (insulation, protection, identification, holding).
  • Conformability - The ability of tape to fit snugly or make essentially complete contact with the surface of an irregular object without creasing or folding. Any tape can be applied to any surface, but it may not conform.
  • Dielectric strength - The voltage that a tape will withstand without allowing passage of current through it.
  • Elastic memory - A tendency of some tape backings to attempt to return to their original length after being elongated.
  • Electrolytic Corrosion factor - A measure of the tape's corrosive effect on a copper conductor. This is particularly important in the selection of tapes for use as electrical insulation.
  • Elongation - The distance a tape will stretch lengthwise before breaking, expressed in a percentage. Elongation is an indication of conformability.
  • Fish-eyes - Round, eye-shaped deformations in the adhesive.
  • Flagging - When the end of a length of tape peels away from the surface after the tape has been applied.
  • Gapping - Openings between layers of tape within a roll.
  • Holiday - A small defect that lowers the dielectric strength at the point of the defect.
  • Migration - The movement, over a long period of time, of an ingredient from one surface to another when the two are in contact. This may occur between tape components or between a tape and the surface to which it is applied.
  • Oozing - A 'squeezing out' of the adhesive from between the layers of tape so that the sides of the roll are very tacky.
  • Peaking - Large 'upheavals' in the outer layers of a roll of tape, when several layers bunch and protrude outward. Creates gapping within the roll.
  • Peel adhesion - The force required to pull a strip of tape from a surface at a specified angle and speed. Usually expressed in ounces per inch width.
  • Pressure sensitive - A term commonly used to designate a category of adhesion tapes that, in dry (solvent-free) form, are aggressively and permanently tacky at room temperature. They also firmly adhere to a variety of dissimilar surfaces upon contact without the need of more than finger or hand pressure. Despite their aggressive tackiness, however, these tapes can be handled with the fingers and removed from smooth surfaces without leaving residue.
  • Primer - Material applied to the underside of the backing that prevents the adhesive from adhering to both sides of the backing.
  • Tacky - A lab synonym for 'sticky', or highly adhesive. Sometimes used to express the idea of pressure sensitivity.
  • Telescoping - A sliding of the tape layers one over the other until the roll assumes a funnel shape.
  • Thermosetting - Adhesives that set up or harden on first exposure to heat and remain set regardless of subsequent temperature cycles.
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