漆の成分と硬化メカニズム Lacquer Urushi composition and curing mechanism


I will summarize from the references that scientifically analyze the composition of lacquer liquor. Lacquer does not have a mechanism that evaporates and dries solvents and water like other paints.

複雑な複合材料・漆 Complex composite material・Urushi



In the lacquer of liquid is quite complex composite material, is a material in a state in which water is mixed into the urushiol of lipids.

This is a stable mixture of two immiscible liquids such as water and oil, similar to woodworking bonds, acrylic paints and mayonnaise.

漆成分一覧 List of lacquer Urushi ingredients

漆液の成分は5つあります。↓There are five components of lacquer liquid. ↓

成分 component割合 ratio水溶性
Water soluble
Organic solvent soluble
ウルシオール Urushiol66~76% ×
②ゴム質(多糖)Rubber (polysaccharide)5~7%×
Nitrogen-containing substance (glycoprotein)
ラッカーゼ酵素 Laccase enzyme微量
Very small amount


Among the above ingredients, urushiol and laccase enzyme play an important role in the hardening of lacquer.

ウルシオールの特性 Characteristics of urushiol




→「キッチンの油汚れが茶褐色になる=油が自動酸化によって劣化する」 のと一緒です。



(1) Anti-acidity: Property to prevent oxidation (deterioration) due to oxygen in the air

→ This is a property represented by polyphenols in wine.

(2) Autoxidation: The property of reacting with oxygen in the air.

→ It is the same as “Oil stains in the kitchen turn brown = oil deteriorates due to autoxidation”.

Urushiol has two contradictory properties.

★ while the urushiol is holding the antioxidant properties of ① can not lacquer of liquid congeals hard.

ラッカーゼ酵素の特性 Characteristics of laccase enzyme



It is a component that has “the ability to oxidize phenols”.

The antioxidant properties (OH group) of urushiol correspond to these organic compound phenols.

塗膜になる複雑な化学反応メカニズム Complex chemical reaction mechanism that forms a coating film

簡単に3段階にまとめると。。。To briefly summarize in three stages. .. ..

1段階目 1st stage




Enzymatic oxidation polymerization: When a laccase enzyme is met at a certain temperature and humidity, it reacts to begin to exert its “ability to oxidize phenols”.

When the laccase enzyme works to its full potential and accumulates, the antioxidant properties of urushiol (corresponding to phenols) decrease. This will eliminate the barrier.

Put the lacquer liquid in a dryer that keeps the temperature at 20 to 25 ° C and the humidity at 70 to 75%. If you leave it for about one night and check it, it will be dry enough not to be sticky to the touch with your fingers. However, this is still a dry surface and is not completely cured.

2段階目 Second stage


Autoxidation: Since the barrier has disappeared, when autoxidation progresses due to oxygen in the air, the previously disjointed molecules are connected to polymerize and convert substances. When it is a liquid, the molecules are disjointed, and when they harden, they become solid and connected. It is said that the substance will be converted to a new polymer compound with a molecular weight of 20,000 to 30,000.

そして、硬い塗膜になる Then, it becomes an individual with a hard coating film.




The lacquer coating film cured in this way is said to be tough enough not to change even when immersed in sulfuric acid, hydrochloric acid, or aqua regia.

As the summary of the three stages of the above, goes through a curing reaction process of two-step in until completely cured.

That lacquer dries is that laccase enzyme is required oxygen suitable temperature and high humidity in the air to exhibit the ability.

漆を乾かす環境 Environment to dry lacquer Urushi


The higher the humidity, the faster the laccase enzyme, which is the enzyme oxidative polymerization, which is the first step of curing, is oxidized and the coating film is formed faster. Thick coating (the coating film becomes wrinkled) can be said to be a phenomenon that occurs because curing starts from the coating film on the surface first. When applying a thick coat, do not raise the room temperature too much, do not raise the humidity too much from the beginning, lower the humidity, dry slowly, and be careful not to hang down while the place is drying.



No matter how much the air conditioner is turned on on a hot summer rainy day or the rainy season, the outside air temperature is high and there is a high risk that the humidity will not drop easily, so it is not suitable for hardening thick coatings.

Also, in winter, the outside air temperature is too low, so no matter how high the humidity is, the lacquer will not dry easily.


In such as the adjustment of the air conditioner and humidifier and dry location of size, check the temperature and humidity, until the time of the coating can be confirmed is fully cured, it does not particularly missing care. In addition, the drying time varies from lot to lot of lacquer because the proportion of lacquer components varies depending on how the lacquer is refined.


Lacquer dry condition is, but you can control to some extent, is what difficult that must correspond to change as long as the change is the weather and seasonal daily. Therefore, I may be fascinated by lacquer forever.

参考文献 References

  • 国立歴史民俗博物館編『URUSHIふしぎ物語 –人と漆の12000年史–』,2017
  • 宮腰哲雄『漆学 植生、文化から有機化学まで』.明治大学出版会,2013
  • 山本勝巳『漆百科』.丸善株式会社,2008
  • 明治大学博物館編『漆器 文理融合型研究から見えてきた漆の過去・現在・未来』,2011


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