GOOD QUALITY VCI FILM SHOULD PROVIDE THE FOLLOWING BENEFITS.
- Vapour / Volatile corrosion protection.
- Contact corrosion protection.
- Barrier Protection.
Vapour / Volatile corrosion protection.
A volatile corrosion inhibitor (VCI) / Vapour Phase corrosion inhibitors (VPCI) agent/s are characterized as being primarily in the solid or liquid state at ambient temperatures and pressures, but with some fraction in the vapour phase at equilibrium.
The vapour phase corrosion inhibitor in the vapour stream adsorbs on the exposed metal surfaces forming a thin, protective layer that provides continuous protection against corrosion from exposure to moisture, salt, oxygen, carbon dioxide, or other corrosive elements.
Even if the layer is disturbed by moisture or other corrosive components entering the interior volume, the corrosion inhibiting characteristics remain effective.
In some embodiments, the VCI agent is supplied in a solid form. Solid-phase particles have diameters of less than 50 microns.
The VCI agent may be enclosed in a vapour permeable pouch or package.
VCI agents can also be added to the polymer melt intended for melt extrusion or blow molding, thus resulting in a packaging material (film or hard material) out of which the VCI components are able to sublime continuously because of the structurally induced porosity.
A VCI is a “noncontact inhibitor”. The performance of any VCI inhibitor depends on the effectiveness of the packaging seal around the metal object, i.e. to prevent the inhibitor from escaping into the atmosphere.
There are 3 Groups of Vapour Pressure Inhibitors
| Group I | Group II | Group III |
| Low vapour pressure inhibitors | Medium vapour pressure inhibitors | High vapour pressure inhibitors |
| Vapour pressure of less than 10-4 mm Hg at ambient conditions and 20° C | Vapour pressure of between 10-3 & 10-4 mm Hg at ambient conditions and 20° C | Vapour pressure above 10-3 mm Hg at ambient conditions and 20° C |
| Long term but slow effect as VCI | Medium Term effect and effect as VCI | Short term quick effect as VCI |
Some of the VCI Chemicals are as follows.
| Benzotriazole | Cyclohexylamine Benzoate |
| Cyclohexylamine carbonate | Cyclohexylammonium Benzoate |
| Dicyclohexyl ammonium benzoate | Dicyclohexyl ammonium cyclohexane carboxylate |
| Dicyclohexyl ammonium nitrite | Dicyclohexyl ammonium salicylate |
| Dicyclohexylamine Chromate | Dicyclohexylamine Nitrite |
| icyclohexylaminebenzotriazole | Diethanolamine Benzoate |
| Diisopropyl ammonium benzoate | Diisopropyl ammonium nitrite |
| Monoethanolamine Benzoate | Morpholine |
| Octylcaprilamide | Nitro naphthalene ammonium nitrite |
| Octylpalmamide | Octylstearamide |
| Tolyltriazole |
Contact corrosion protection.
Contact corrosion protection works only when the VCI product (film, paper, tape, and sheet) is in direct contact with the product which is to be protected. Most of the time the film, paper, or sheet is tightly wrapped around the object to prevent exposure to moisture, or corrosive environment. Contact corrosion inhibitors are transferred to the metal surface by creeping of the inhibitors from the wrapping material directly to the metal. This allows the corrosion inhibitor to remain with the metal even if the package is not sealed properly.
Contact corrosion inhibitors.
| Chemical Name | Chemical Name |
| Ammonium dimolybdate | Potassium benzoate |
| Cesium benzoate | Potassium Nitrite |
| Cesium Nitrite | Potassium Pyrophosphate |
| Lithium benzoate | Sodium Benzoate |
| Lithium Nitrite | Sodium Molybdate |
Barrier Protection
Any VCI film requires effective barrier protection to prevent corrosion from corrosive environment. One way to improve the barrier protection properties is by using additives to improve the film barrier properties.
Another option is to co-extruded VCI film with multiple layers of film with specific characteristics used to prevent corrosion, provide additional barrier protection, and increase durability and puncture resistance over mono-extruded VCI films. This additional protective layer serves as a barrier, preventing moisture, salt, dirt, oxygen, and other corrosion-causing materials from depositing directly on the metal. In addition, additives such as UV Inhibitors, Anti Static compound, low slip are added to prevent outer film degradation.
However there need to be a balance between barrier protection and film permeability to allow VCI components are able to sublime continuously because of the structurally induced porosity in the film. This can be achieved by either using 2 separate coatings to the 2 sides of the film or by using multiple layers. Selecting the correct Resin (HDPE, LDPE, PE, and PP) also helps in improvements in barrier properties of the VCI Film.
Masterbatch
Volatile corrosion inhibitor (VCI) / Vapour Phase corrosion inhibitors (VPCI) are supplied as Master Batch, which has the following typical processing combinations. Actual processing depends on the intended applications, type of resin to be used for preparation of the film and if the intended film is single layered or multiple layered.
Some examples
35 wt % of VCI mixture was mixed with 65 wt % of a conventional LD-PE and processed to yield a VCI master batch. A twin screw extruder is usually used. At cylinder temperatures of 150.degree. C. and a nozzle temperature of 158.degree. C., is administered. Intended VCI mixture is extruded at a screw speed of 65 to 80 rpm and granulated by cold chopping. This granulated VCI master batch was processed further by blow molding to yield VCI films, for which purpose the extruder was equipped with a single screw and a ring nozzle.
After thoroughly mixing 3 wt % of the VCI master batch with 97 wt % of a conventional LDPE granular batch, processing was continued at cylinder temperatures of 175.degree. C. and a nozzle outlet temperature of 180.degree. C. while the screw speed was varied between 80 and 85 rpm. A VCI film with an average layer thickness of 80 microns is produced.
Benefits of Sodium benzoate (Micronised) as Corrosion Inhibitor in VCI Films / VCI Papers.
Sodium Benzoate widely used as contact corrosion inhibitor in VCI Films. It is also used in Radiators & Engine coolants and metal treatment as corrosion inhibitor. Use of Sodium benzoate in VCI Films as effective contact corrosion inhibitor is well documented.
US Patent: 7763213 , 7588820, 6540959,6752934
Additional product references are available.
Trigon Chemicals Pvt Ltd supplies special grade of Sodium Benzoate called (Micronised VCI Grade) which is widely used to manufacture VCI Film and Paper.
Some of the benefits offered by Sodium Benzoate (Micronised VCI Grade) are as follows.
- Sodium Benzoate (Micronised VCI Grade) from Trigon Chemicals Pvt Ltd has very small micron particle size (D50 less than 5 microns) which enables complete, uniform dispersion in solid form in the VCI Film during extrusion.
- Better dispersion during extrusion means improvement in barrier properties and improvement in physical properties of VCI film. This is particularly useful where the VCI Packing has to be opened and closed several times during the usage cycle and effect of VCI additives is minimised due to constant opening and closing of the packing.
- Sodium Benzoate (Micronised VCI Grade) from Trigon Chemicals Pvt Ltd improves the flexural modulus without affecting the tensile strength of the film which can be verified by actual testing.
- Sodium Benzoate (Micronised VCI Grade) from Trigon Chemicals Pvt Ltd is thermally stable upto 400 degrees C making it preferred VCI additive for harsh weather conditions from sub zero to high temperatures applications.
- Compatible with almost all VCI Film grade polymers ( PP, LDPE, HDPE, PE, ETC)
- Sodium Benzoate does not react with other additives in the film.
- Sodium benzoate is cost effective & safe for the environment, as compared with other contact corrosion inhibitors used in VCI films.
Sodium Benzoate (Micronised VCI Grade) from Trigon Chemicals Pvt Ltd is available in 10 Kg paper bags with inner liners.