In the previous article, we introduced that there are three types of industrial cleaning agents: "aqueous cleaning agents," "non-aqueous cleaning agents," and "semi-aqueous cleaning agents." Each has its specialized dirt and precautions, but in this article, we will introduce "aqueous cleaning agents" in detail.
The main component of aqueous cleaning agents is surfactants. Figure 1 shows the molecular structure of surfactants. Surfactants have both hydrophilic groups and lipophilic groups in their molecules. The hydrophilic group has a tendency to easily blend with water, while the lipophilic group has a tendency to easily blend with oil. These two characteristics enable surfactants to remove dirt.
Figure 2 shows the mechanism by which surfactants remove dirt. Here, "dirt" refers to oil and organic contaminants. When dirt and surfactants meet, many surfactant molecules first surround the "dirt." At this time, the surfactant binds its lipophilic group to the "dirt" and surrounds it with the hydrophilic group facing outward. By surrounding it with the hydrophilic group facing outward, this "dirt" can be dissolved in water. Using this action, dirt can be lifted and removed through cleaning.
Furthermore, for aqueous cleaning agents, to enhance cleaning effectiveness and clean special contaminants, it is necessary to select the appropriate cleaning agent from among: ① alkaline cleaning agents, ② neutral cleaning agents, and ③ acidic cleaning agents.
Alkaline cleaning agents refer to cleaning agents with a pH of approximately 10-14, with main components being alkaline substances such as sodium hydroxide, sodium carbonate, and sodium phosphate.
Alkaline cleaning agents excel at removing animal and vegetable oil stains. Oil stains contain oily substances called fatty acids. These fatty acids react with alkali to transform into water-soluble soap. Through this reaction, the dirt undergoes emulsification and solubilization, resulting in dirt removal.
For dirt caused by such fatty acids, the action of alkali is greater than the action of surfactants, and there are reports that alkaline solutions have higher cleaning performance for dirt with high fatty acid content.
※ Precautions
Alkaline cleaning agents cannot be used for cleaning amphoteric metals. The four amphoteric metals are aluminum, zinc, tin, and lead. These react with alkali and form complex ions, making them unsuitable for cleaning. Avoid using alkaline cleaning agents for cleaning items mainly composed of these amphoteric metals.
Acidic cleaning agents refer to cleaning solutions with a pH of approximately 0-6, containing inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid, as well as organic acids such as citric acid and acetic acid.
Acidic cleaning agents excel at cleaning rust and metal oxides. The principle is that acid action peels the metal surface, lifting rust stains for cleaning.
※ Precautions
Acidic cleaning agents require attention to corrosion of the cleaning object.
From the above mechanism, "rust" itself is not being dissolved; rather, the "metal surface" is being dissolved, so the cleaning object itself is somewhat etched.
Therefore, process design that takes into account the etching action of acidic cleaning agents is necessary for products being manufactured in the production process.
Neutral cleaning agents are cleaning agents with a pH of approximately 6-8 showing neutrality. They are used for cleaning objects that are weak against alkali.
The dirt that neutral cleaning agents excel at is oil stains. However, unlike alkaline cleaning agents and acidic cleaning agents, there is no accompanying chemical reaction, and the cleaning ability is mainly due to surfactants, so the cleaning power is not very high. However, the risk of corrosion to the cleaning object is small, and they are characterized by ease of handling.
Nickel and stainless steel form passive films in alkaline regions and have strong alkali resistance, so alkaline cleaning agents with strong cleaning power can be used.
On the other hand, aluminum and zinc dissolve in alkali, so alkaline cleaning agents are not suitable, and neutral cleaning agents should be selected.
Special attention is required for disposal methods of aqueous cleaning agents. Since the liquid properties show acidity or alkalinity, they cannot be discharged directly as waste liquid. Therefore, special treatment is necessary. Disposal methods are broadly divided into two types: incineration and neutralization treatment.
Incineration involves incinerating the waste alkaline cleaning agent that has been sprayed into a mist form in an incinerator. Neutralization treatment involves mixing acidic solutions with alkaline cleaning agents and alkaline solutions with acidic cleaning agents to bring them closer to neutral before disposal. Since toxic gases may be generated during this process, caution is required during the work.
It is necessary to use cleaning agents suitable for the cleaning machine being used. Cleaning machines can be broadly classified into two types: shower type and immersion type. When using shower-type cleaning machines, it is necessary to use cleaning agents containing defoaming agents. As mentioned above, the main component of aqueous cleaning agents is surfactants. Due to the action of these surfactants, in cleaning machines with strong jet streams such as showers, the cleaning agent in the tank will foam significantly.
As a countermeasure to this, shower-type cleaning machines require the use of cleaning agents containing defoaming agents. In this way, attention is required because it is necessary to select cleaning solutions designed to be suitable for the cleaning machine method in addition to liquid properties.
Aqueous Cleaning Machine
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