By Sinopec Online Technical Team
Introduction
Brightstock and heavy neutral base oils remain essential where high viscosity and good solvency are required. They contribute to film strength, additive response and stability in high viscosity lubricant formulations. Despite a global shift toward Group II and III production, Group I heavy neutrals and brightstocks continue to fill key roles where viscosity and solvency are critical.
Definitions
- Heavy neutral oils are high viscosity Group I neutrals such as 500N and 600N, typically produced through solvent refining and dewaxing of vacuum gas oil fractions.
- Brightstock is a very high viscosity Group I base oil derived from deasphalted vacuum residue using solvent extraction and dewaxing. It provides superior film thickness and solvency for heavy-duty lubricants.
Key properties
| Property | Heavy Neutral | Brightstock |
|---|---|---|
| KV at 100°C | 10–13 cSt | 28–35 cSt |
| Viscosity Index | ≈95 | ≈95 |
| Solvency | Good | Good |
| Pour Point | Higher than light grades | Higher than heavy neutrals |
Functions in blends
- Increase film thickness and load-carrying ability in high-duty lubricants.
- Provide solvency for additives, thickeners and dyes.
- Stabilise viscosity in high-temperature formulations.
- Support shear stability and maintain oil film under shock loading.
Typical uses
- Marine engine oils and industrial gear oils requiring strong film strength and resistance to oxidation.
- Greases where solvency supports thickener dispersion and additive response.
- Metalworking oils and process lubricants needing higher base viscosity and load tolerance.
Formulation notes
- Cold flow requires pour-point depressant and possibly blending with lighter neutrals such as 150N.
- Blends of 500N, 600N and brightstock are common for ISO VG 220 and above.
- For improved oxidation stability, heavy neutrals may be partially replaced with Group II 500N or Group II+ grades.
Illustrative viscosity comparison
The chart below shows approximate kinematic viscosity at 100°C for typical Group I neutrals and brightstock grades.
Cross-References
Relevant Base Oil Categories
Published by Sinopec Online Technical Team
