Oil demand
Oil requirement , also oil number or oil absorption is an important pigment property and provides information about its behavior during dispersion . The oil requirement indicates the amount of oil with which a defined amount of the powder to be tested must be moistened in order to achieve a stiff, non-flowing putty-like paste . The powder is usually worked with the oil with a spatula . The paste should not break and should not separate, the paste should stick but not tear. This test method is preferably used for printing inks , artist paints and plasters in order to characterize pigments . Linseed oil is mainly used because of its good dispersing properties. In pigment production, it is also a quality feature in the production process. In addition to pigments, fillers are also tested.
The oil requirement can fluctuate due to external influences. In order to achieve comparable values, the standardized working method is specified in DIN EN ISO 787-5. Then two to five grams of pigment are precisely weighed in with a precisely measured amount of linseed oil according to ISO 150 and made into a paste on a glass plate using a spatula. Then more oil is added from a burette until the point is reached that the paste no longer breaks. The paste should no longer crumble and just stick to the plate.
The test result is stated as an indication of how much linseed oil with a density of 0.93 g / cm³ is needed to bind 100 grams of pigment.
A low oil number of around 10 g / 100 g means that the pigment is easy to disperse and thus a high amount of pigment with good flowability . For printing inks , a high pigment density per amount of colorant is aimed for. On the other hand, a high oil absorption of over 50 g / 100 g of the pigment means poor incorporation, a high degree of dispersion work and a limited pigment loading of the color. The high oil absorption of the pigment also creates poor flow properties in the printing process. The rheological properties also hinder the interruption of work and the restart of a printing process.
In general, inorganic pigments have a low to moderate oil requirement, while the organic pigments often have a moderate to high oil requirement. The color strength of a pigment can compensate for the disadvantage of a high oil requirement in the case of coloristically important pigment shades.
The oil requirement can also be used to assess the dispersing properties of oils. A preliminary assessment of starting products can be made in laboratories by choosing the appropriate pigment. Executed in the same way - but with alternating oil and defined pigment - comparative values are then obtained in order to assess the oil.
Web links
Individual evidence
- ↑ DIN EN ISO 787-5
- ^ Temple C. Patton: Pigment Handbook, Applications and Markets . John Wiley & Sons, London / Sydney, ISBN 047167124X .