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Oil is a fatty acid (C12 - C22), which has been esterified with glycerine, depending on the type of acid, the oil will be more or less drying.

Soja Colza

Drying oils have a high proportion of unsaturated fatty acids and when  they polymerize  giving a flim very strong and bright. The curing and drying process is done by air oxygen. All semi-drying oils and driers are thermally polymerizable

The way to determine whether an oil is drying, is by iodine (I2/100 g), the more higher the more drying, establishing the following scale:

  • Drying oil: from 140. Types of drying oils: safflower oil, wood  oil (Tung), dehydrated castor oil, linseed oil and standoils of both.
  • Semi-drying oil: between 110 - 140. Types of semi-drying oils: soybean oil, Rape oil refined.
  •  Non-drying oil: less than 110. Types of non-drying oils: olive oil, Castor first press.


The oils are a blend of fatty acids  and differ among themselves depending on the number of carbons and the double existing bonds.

 

Fatty acids
Number of carbons

Number of  double bonds

 Palmitic acid

16

0

 Stearic acid

18

0

Oleic acid

18

1

 Linoleic acid

18

2

Linolenic acid

18

3

Seeing from the above table, acids with double bonds (Iodine value), decide the drying rate of oil. The more quantity of oil the more drying rate.

However we can increase the viscosity of the oils through the following processes:

  • Thermal Polymerization: It is a physic process that keeps the starting conditions increasing only the oil viscosity, these oils are called: Polymerized / Standoils.
  • Oxipolymerization: It's a physical / chemical process that increases the viscosity and surface activity, these oils are called: Oxidized/ Blown.
Abstract

The oils used for industrial coatings can be divided into three sections, depending on the viscosity (drying) and surface activity.
  • Refined oils
  • Polymerized oils / standoils
  • Oxidized oils / Blown
 


2012/05
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