The bleaching oil of defoamers is an important factor affecting their normal use. In production applications, it is necessary to learn to identify the phenomenon of oil drifting and promptly solve the "oil drifting" phenomenon of defoamers.
What is float oil like?
Drifting oil "refers to the visible oil spots on the surface of the water dispersed by diluting the organic silicon defoamer with water, some of which are larger and have diameters ranging from a few millimeters to several millimeters; Some are very small, as big as needle points, with a diameter of less than 0.1 millimeters. Some of these oil spots do not disperse for a long time, while others disperse after a certain period of time, forming a thin oil film on the water surface. Some even stick to the walls of the container containing the water dispersion.
Harmful effects of floating oil:
Drifting oil is generally not good or harmful. Drifting oil has the following hazards:
1. May cause harm to the system being used
The oil floated out by organic silicon defoamers is polydimethylsiloxane, which has low surface tension, high viscosity, and is easily adhered to solid surfaces. If the adhered material is a textile, it will generate "silicone oil spots" on the textile, forming defective products; If the metal surface to be electroplated, sprayed, or painted is adhered, due to the anti adhesion of silicone oil (that is, any surface coated with silicone oil is difficult for other things to adhere to), plastic or paint will peel off at the area where silicone oil adheres, which will cause the scrap of the processed part. So much so that some industries, such as spraying, painting, and galvanizing, prohibit the use of defoamers containing organic silicon on steel surfaces, mainly for this reason.
2. Greatly reduce the defoaming performance of defoamers
As we all know, lotion particles with diameters of several microns to tens of microns are the basic defoamer unit of defoamer. Bleaching oil is the aggregation of lotion particles. The diameter of bleaching oil particles can reach several millimeters. It accumulates a large amount of active substances of defoamer, greatly reducing the number of defoaming active particles in lotion. An oil spot with a diameter of 1 mm contains active substances equivalent to the inactive substances contained in 1 million defoaming lotion particles with a diameter of 10 microns. The defoaming effect generated by an oil dot with a diameter of 1 millimeter is only equivalent to the defoaming effect of one or a few defoamer particles with a diameter of 10 microns. The direct consequence of the sharp decrease in the number of defoaming units is to affect the defoaming effect.
3. Reduce foam inhibition performance
The main function of defoaming is defoaming, and long-term defoaming is also known as foam suppression. The length of foam suppression time is the most important indicator of the quality of defoamers. It can be said that defoamers should actually be called foam suppressants. Because in the vast majority of cases, we use defoamers to utilize their anti foaming properties, rather than their initial defoaming properties.
The lotion particle of defoamer active substance is the basic unit of defoaming. Its quantity determines its defoaming property. The longer it exists in the defoaming system, the better the defoaming property of the system will be. Emulsification bleaching oil is the destruction of the state of defoaming particles and the aggregation of defoaming units. So the defoamers for bleaching oil generally have poor or extremely poor anti foaming properties.
How is float oil formed?
The stability of lotion defoamer depends on certain concentration of emulsifier and stabilizer and certain process methods. Although the oily substance in the lotion has a huge specific surface area and is an unstable system in terms of thermodynamics, the lotion itself is relatively stable due to the existence of sufficient emulsifiers and stabilizers. However, if diluted with water and working fluid, or added to the defoaming system, the stable environment of the defoamer is disrupted, and in the new environment, the defoamer is easily broken and bleached. In general working fluids and defoaming systems, there are organic and inorganic substances such as salts, alcohols, acids, and bases, which generally have a demulsification effect. Defoamers are added to the defoaming medium in small amounts, and the defoamers are completely in a completely new and different environment. If the technical level of defoamers is low and some ordinary or unsuitable emulsifiers or co emulsifiers are used, then such defoamers are easily able to break the emulsion and float the oil.
What is the evaluation method for float oil?
The following mainly analyzes defoamers through physical observation methods.
1. Check the original solution
To see if a defoamer floats oil, the first thing to consider is the original solution. The method is to take a container, preferably with a large diameter and a small depth, such as a drying dish or a 500ml beaker. Pour in a sufficient amount of defoamer solution (e.g. no less than 400ml should be poured into a 500ml beaker), hold the container by hand, and face the light. It is best to face the direction of the electric light indoors, so that the light shines from the front and above onto the defoamer liquid surface, and then reflects back to the eyes. By repeatedly adjusting the angle, you can clearly see the situation on the liquid surface. If the defoamer floats the oil, it can be seen on the liquid surface, especially for some low-quality products, you can see bright and obvious oil spots on the liquid surface. However, there are products with tiny floating oil that cannot be directly observed using the above methods, and further observation is needed using other methods.
2. Look at the diluent
After diluting the defoamer to a certain concentration, observing whether the diluted solution floats oil is also a method to judge whether the defoamer floats oil. Some poorly made defoamers can pass Method 1, but cannot pass Method 2. The specific dilution ratio is 99 parts of water for one defoamer, and the defoamer concentration of these dilutions is 1%. The observation method is the same as Method 1. At this time, some products with slight oil drift cannot be seen in the original solution, but small oil spots can be seen on the liquid surface in the diluent.
Different dilution ratios have significant differences in the occurrence of oil drift in defoamers. Generally speaking, high concentration defoaming diluents, such as 30%, 20%, and 10%, are most likely to produce bleaching oil. And the dilution solution of defoamer with very low concentration (1)&Permil is less likely to produce floating oil, and even some products that float oil at around 1% become non floating. This is because the surface tension of organic silicone oil is very low, and at very low concentrations, the oil dots gradually spread on the water surface, forming a thin oil film and disappearing.
3. Watch at operating temperature
If the ambient temperature is higher than room temperature, it is best to heat the diluted defoamer to the desired temperature before observation. Some defoamers do not float oil after dilution, but float oil at the operating temperature, indicating that this defoamer may float oil at the operating temperature and may cause problems due to oil bleaching during use.
Note:High temperature defoamers cannot be evaluated using this method. The evaluation method for high-temperature defoamers will be discussed in the specialized section on high-temperature defoamers.
It is particularly important to note that defoamers for bleaching oil cannot be used anymore. Because the bleaching oil has greatly reduced the defoaming and anti foaming functions of the defoamer, even if used, it cannot achieve the expected effect.
