The differences between stand oils and blown oils
[ Manufacturing ] [ Properties ] [ General comparisons ] [ Use in surface coatings ] [ Historical notes ]
The difference in properties between the stand oils and blown oils results from the manufacturing processes used to produce them. The type of crude oil used also affects the oils' properties.
are produced at elevated temperatures in the absence of air. The oil polymerises by cross-linking across the double bonds which are naturally present in the oil. The bonds are of the carbon-carbon type. Stand oils are also known as thermally polymerised and heat polymerised oils.
are produced at elevated temperatures by blowing air through the oil. Again the oil polymerises by cross-linking across the double bonds but in this case there are oxygen molecules incorporated into the cross-linking bond. Peroxide, hydroperoxide and hydroxyl groups are also present. Blown oils are also known as oxidised, thickened and oxidatively polymerised oils.
Both types are, generally, manufactured to viscosity specifications.
are pale coloured and low in acidity. They can be produced with a wider range of viscosities than blown oils and are more stable in viscosity. In general, stand oils are produced from linseed oil and soya bean oil but can also be manufactured based on other oils. Stand oils are widely used in the surface coatings industry.
may be produced from a wider range of oils than stand oils. In general, blown oils are darker in colour and have a higher acidity when compared to stand oils. Because of the wide range of raw materials used, blown oils find uses in many diverse industries, for example blown linseed oils are used in the surface coatings industry and blown rapeseed oils are often used in lubricants.
When comparing blown linseed oils to their stand oil equivalents it is found that the oxygen cross links make the blown oils more reactive (they dry quicker but the viscosities are less stable due to auto-oxidation) and more soluble in a wider range of solvents.
Blown linseed oils are used in the surface coatings industry. The viscosities of blown rapeseed, castor and groundnut oils are more stable as these oils are less prone to auto-oxidation than blown linseed oils. These oils are therefore more suitable for applications which require "non drying oils" eg lubricants.
Use in surface coatings
Linseed and soyabean stand oils are used in the production of high quality paints and varnishes where gloss and durability are important. Blown (and boiled) linseed oils are often used in primers where quick drying times are important. Linseed oils may yellow with time (particularly stand oils with high acidity) and are often replaced with soyabean stand oil for the production of pale coloured paints.
Boiled linseed oils can be seen as low viscosity blown linseed oils with metal driers (siccatives) incorporated into the formulation. They are the quickest drying vegetable oil generally available and are used in primers and for direct application to wood. There are several grades available based on different drier combinations. There is no stand oil equivalent.
Before the industrial revolution, stand oils were made by placing the oil in large glass tanks exposed to sunlight (in order to promote UV catalysed polymerisation). This process was very slow; in some cases it took several years to reach the required viscosity. The name "stand" oil therefore derives from the fact that the oil had to "stand" in a tank for a long period of time.
Boiled linseed oil
Before the development of oil soluble metal driers, boiled oils were produced by reacting linseed oil with metal ores. This reaction was carried out at such high temperature that the linseed oil started to decompose - this process gave the appearance of the oil "boiling" hence the term "boiled".