Drying oil

A fatty oil that easily forms a solid dry film by air oxidation. It generally has an iodine value of 130 or more. It contains polyunsaturated fatty acids such as linolenic acid and linoleic acid, such as linseed oil and perilla oil, or fatty acids with conjugated double bonds, such as eleostearic acid, such as tung oil, as its main components, and these are oxidized and polymerized to dry. Compared to polyunsaturated fatty acids, conjugated acids are more easily oxidized and have a higher degree of oxidative polymerization, so the dried film of tung oil and other oils has high water resistance and hardness, but if it dries too quickly, the film is prone to wrinkles. In addition to the natural drying oils mentioned above, there are synthetic drying oils, such as dehydrated castor oil, which are artificially changed from non-drying oils to drying oils. Drying oils are used in boiled oil, stand oil (both for paints), paints, printing inks, etc. Fatty oils with an iodine value of 130 to 100 are called semi-drying oils, and examples include soybean oil and rapeseed oil. Semi-drying oils dry more slowly than drying oils and are primarily used for edible purposes.

[Kazuo Fukuzumi]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

空気酸化により容易に固体乾燥膜を形成する脂肪油。一般にヨウ素価130以上。あまに油、荏油(えのあぶら)などのようにリノレン酸、リノール酸などの多不飽和脂肪酸か、桐油(きりゆ)のようにエレオステアリン酸などの共役二重結合を有する脂肪酸を主成分として含み、これらが酸化重合して乾燥する。多不飽和脂肪酸に比し、共役酸は酸化されやすく、酸化重合度が大であるために、桐油などの乾燥膜の耐水性や硬度は高いけれども、乾燥が速やかすぎる場合には、膜にしわができやすい。前述の天然乾性油のほかに、脱水ひまし油など人工的に不乾性油から乾性油に変化させた合成乾性油がある。乾性油はボイル油、スタンド油（いずれも塗料用）、塗料、印刷インキなどに用いられる。ヨウ素価130～100の脂肪油を半乾性油といい、大豆油、菜種油などがある。半乾性油の乾燥は、乾性油のそれに比し遅く、主として食用に供せられる。

［福住一雄］

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