Formulation 101: Wire and Cable Insulation and Jacket PVC Compounds

PVC is often used for electrical cable jacketing due to its excellent electrical insulating properties and dielectric constant.  PVC is commonly used in low voltage cable (up to 10 KV), telecommunication lines, and electrical wiring.

Basic formulation for the production of PVC insulation and jacket compounds for wire and cable is generally composed of the following:

1. PVC
2. Plasticizer
3. Filler
4. Pigment
5. Stabilizers and co-stabilizers
6. Lubricants
7. Additives (flame retardants, UV-absorbers, etc.)

Plasticizer Selection

Plasticizers are always added to wire & cable insulation and jacket compounds to increase flexibility and decrease brittleness.  It is important that the plasticizer used have a high compatibility with PVC, low volatility, good aging properties, and be electrolyte-free.   Beyond these requirements, plasticizers are selected with the requirements of the finished product in mind.  For example, a product intended for long-term outdoor use might require a plasticizer with better weathering properties than one would choose for an indoor use only product.

General purpose phthalate esters such as DOP, DINP, and DIDP are often used as primary plasticizers in wire and cable formulations due to their broad area of use, good mechanical properties, and good electrical properties.   TOTM is considered more suitable for high temperature compounds due to its lower volatility.  PVC compounds intended for low temperature use might do better with plasticizers such as DOA or DOS which retain low temperature flexibility better.  Epoxidized Soybean Oil (ESO) is often used as a co-plasticizer and stabilizer, since it adds a synergistic improvement of thermal and photo-stability when combined with Ca/Zn or Ba/Zn stabilizers.

Plasticizers in the wire and cable industry are often stabilized with a phenolic antioxidant in order to improve aging properties.  Bisphenol A is a common stabilizer used in a range of 0.3 – 0.5% for this purpose.

Commonly Used Fillers

Fillers are used in wire & cable formulations to reduce the price of the compound while improving electrical or physical properties.  Fillers can positively affect heat transfer and thermal conductivity.  Calcium Carbonate is the most common filler for this purpose.  Silicas are also sometimes used.

Pigments in Wire and Cable

Pigments are of course added to provide distinguishing color to compounds.  Titanium Dioxide is the most commonly used color carrier.

Lubricants

Lubricants for wire and cable can be either external or internal, and are used to aid in the reduction of the PVC sticking on the hot metal surfaces of the processing equipment.  Plasticizers themselves can act as an internal lubricant, as well as Calcium Stearate.  Fatty alcohols, waxes, paraffin and PEGs are can be used for additional lubrication.

Common Additives in Wire & Cable

Additives are used to impart special properties required for the end use of the product, for example, flame retardancy or resistance to weathering by the sun or by microbes.  Flame retardancy is a common requirement for wire and cable formulations.  Additives such as Antimony Trioxide (ATO) are effective flame retardants.   Plasticizers used such as phosphoric esters (i.e. TBP, TOF) can also impart flame retardant properties.   UV-absorbers may be added for exterior use applications to prevent weathering by the sun.  Carbon Black is effective at protection against light, but only if you are making a black or dark colored compound.  For brightly colored or transparent compounds, UV-Absorbers based on Benzotriazole or Benzophenone can be used.  Biocides are added to protect PVC compounds from degradation by fungus and microorganisms.  OBPA (10′,10′-0xybisphenoazine) is frequently used for this purpose and can be purchased already dissolved in plasticizer.

Example Formulation

Below is an example of a very basic starting point for a PVC wire coating formulation: