消泡剤(Defoamer)
Mechanism of action of defoamers
消泡剤とは、対象の発泡液に対してごく微量添加することによってその発泡を抑えることを目的としています。発泡とは液体が薄い膜になって空気を包むことであり、泡の生成には表面張力、泡の粘性などが重要な因子であると言われています。 従って、消泡剤とは泡膜の表面を部分的に不均衡な状態にし、泡を不安定化させるものと言えます。
(Foam collapse)
At the surface of a foam, surfactant molecules are arranged in an orderly manner with their hydrophobic tails oriented outward. In contrast, defoaming agents possess both hydrophilic and hydrophobic segments. When a defoamer is added, some of the surfactant molecules on the foam surface are replaced by defoamer molecules.
Normally, the thin film of a bubble maintains a certain thickness and exhibits high elasticity. However, the intrusion of the defoaming agent disrupts this structure, reducing the film’s elasticity and thinning it beyond its stability threshold, ultimately causing the film to collapse and the foam to break.
(Foam suppression)
By pre-dispersing defoaming agents into the foaming medium, the agents intrude into the surfactant layer aligned at the liquid surface, disrupting the interfacial structure. In addition, when bubbles reach the surface and attempt to form stabilized thin films, the defoaming agents hinder the film stability, effectively suppressing the formation of foam.
(Air release)
Defoaming components function as a coalescing agent within the foaming liquid, promoting the adhesion and merging of dispersed microbubbles. The resulting larger bubbles rise to the surface more quickly due to their higher buoyancy. Upon reaching the surface, these bubbles are eliminated through the two previously mentioned interactions—disruption of interfacial surfactant alignment and destabilization of the foam film.
Types of defoamers
Based-Oil
These defoamers are formulated by dispersing active defoaming components into mineral oil or similar carriers. They are particularly effective for quickly breaking surface foam. They also exhibit excellent thermal resistance, making them suitable for high-temperature applications. One of their major advantages is low cost.
However, their drawbacks include limited longevity despite their rapid initial action. Due to their strong oil-based nature, they may cause oil separation, which can pose environmental concerns—particularly in wastewater applications where discharge into rivers or other natural water bodies is involved.
Surfactant-Type Defoamer
界面活性剤の一種です。通常、洗剤などは親水性が高く、発泡性であるのに対して、このタイプの消泡剤は疎水性が高く油性です。水に入れるとある温度以上で白濁分散するため、自己乳化型消泡剤とも言われています。このときの温度を曇点（cloud point）と言います。有効成分が90～100%と高く、少量添加で高い消泡効果を発揮します。また、安定性に優れ長期保存が可能です。欠点としては、高価なことであり、添加量の厳密な管理が必要になります。また、被消泡液の温度が消泡剤の曇点以下の場合、消泡剤を添加することで発泡を助長する場合があります。
Structure of Surfactant type defoamers
R: Alkyl group
EO: Ethylene oxide
PO: Propylene oxide
n, m, a, b, c: Arbitrary integers (degree of polymerization or substitution)
上述した活性剤タイプの消泡剤の中でも特に代表的なものは高級アルコールにEO（エチレンオキサイド）、PO（プロピレンオキサイド）を付加させたものです。 （表中のエーテル型 Ｒ‐O‐EOn‐POm‐H に該当します） EO、POの付加モル数を変化させることによりあらゆる発泡条件に最適な消泡剤を設計することが出来ます。 また、このタイプの消泡剤は脱墨剤、洗剤等の界面活性剤と類似の構造をしています。（単純に述べるとEO、POの付加モル数が異なるだけです。）そのため、消泡剤を添加して逆に泡立ってしまうといった現象が見られるのはこのためでもあります。
Emulsion Type
This type of defoamer is an emulsion in which defoaming components (such as higher alcohols or esters) are dispersed in water. In order to activate its defoaming function, the active components are emulsified and dispersed in an aqueous medium, making it an O/W type (oil-in-water type) defoamer.
It offers excellent dispersibility in the target foaming system and is considered to have minimal impact on system properties such as particle size. It also demonstrates good deaeration performance.
However, one drawback is its sensitivity to storage conditions. Over time, thickening, solidification, or phase separation may occur, resulting in a decline in defoaming performance. To prevent such degradation, it is recommended to store the product indoors, away from direct sunlight.
消泡剤の種類別の特徴としては、一般的にオイルタイプが破泡性、活性剤タイプが抑泡性、エマルジョンタイプが脱気性に優れていると言われています。しかし、各タイプ単独だけで泡を消そうとする場合、その特徴だけでは消泡剤として満足な結果を得られない場合があります。このような時には違うタイプの消泡剤を併用して使用して頂いたり、予め他の特徴も併せ持つ消泡剤を使用して頂いたりしております。