Properties and classification of silicone oil (3)


1. Silicone oil emulsion defoamer


Silicone oil emulsion defoamer is generally water in oil (O / W) emulsion, that is, water is continuous phase, silicone oil is discontinuous phase. It is premixed with silicone oil, emulsifier and thickener, and then mixed with water gradually. Finally, it is grinded repeatedly in colloid mill until the required emulsion is obtained.


Silicone oil emulsion defoamer is one of the most widely used defoamers. It can be widely used as defoamer in aqueous system. When it is used, good defoaming effect can be obtained by adding emulsion directly into the foaming system. In order to improve the defoaming effect and the accuracy of measurement of the emulsion, it is generally not to directly use more than 10% concentrated silicone oil emulsion; instead, it is first used to dilute it to less than 10% with cold water or directly with foaming solution. Do not use superheated or supercooled liquid dilution, otherwise it will cause emulsion demulsification. The stability of the emulsion will be poor after dilution, and delamination (floating oil) may occur during storage, i.e. demulsification. Therefore, the diluted emulsion should be used up as soon as possible. If necessary, a thickener can be added to improve the stability of the emulsion. For the intermittent operation process, silicone oil emulsion can be added once before the operation of the system or in batches; for the continuous operation process, silicone oil emulsion should be added continuously or intermittently at appropriate parts of the system.


When using emulsion defoamer, especially consider the temperature of foaming system, acid, alkali and other conditions, because silicone oil emulsion is relatively delicate, beyond its scope of use, the emulsion will break prematurely and become inefficient or ineffective (the amount of silicone oil emulsion is generally 10-10oppm of the weight of foaming liquid (calculated by silicone oil). Of course, there are also less than 10 ppm and more than 100 ppm in special cases. The most suitable dosage is mainly determined by experiments.


Most of the general defoamers are oil in water. According to the different types of silicone oil, there are several types of silicone oil emulsion defoamers as follows:


1. Silicone oil emulsion with dimethyl silicone oil as the main body


This kind of defoamer is made up of dimethylsilicone oil, emulsifier and water. It can be widely used in fermentation, food, papermaking, fiber, pharmacy, synthetic resin and so on.






2. Silicone oil emulsion with methyl ethoxy silicone oil as the main body


This kind of defoamer is made of methyl ethoxy silicone oil and its compounding agent.


3. Silicone oil emulsion with ethyl silicone oil as the main body


Organosilicon defoamer is developing towards block copolymerization (or graft copolymerization) of organosilicon polyether. This kind of defoamer has the characteristics of both organosilicon and polyether, so the defoaming force is greatly improved; organosilicon polyether copolymer defoamer, also known as self emulsifying organosilicon defoamer, is a hydrophilic ethylene oxide chain or ethylene oxide propylene oxide chain block (or graft) in the organosilicon molecular chain, so that the hydrophobic siloxane part is combined with the hydrophilic polyether, As a defoamer, such a molecule has a large spreading coefficient, can disperse evenly in the foaming medium, and has a high defoamer efficiency. It is a new type of high-efficiency defoamer. This kind of self emulsified silicone oil does not need emulsifier. Its defoaming effect is quite satisfactory for some systems. It is especially suitable for those occasions where general silicone oil emulsion and general silicone oil emulsion are not suitable for use.






Pay attention to some points when finishing oil in softness


There are many kinds of silicone oil emulsion finishing agent with different quality. There are cationic, anionic, non-ionic, modified amino silicone oil and linear silicone oil. General silicone oil in soft finishing use should pay attention to the following points.


1. Control dosage:


For example, the amount of amino silicone oil with 20% solid content in 1.5-3% (o.w.f) is enough, and increasing the amount does not increase the softness.


2. Fixed speed:


When making some thin fabrics (such as chiffon, silk like, Balinese), the setting speed is very fast, sometimes it can reach 60 m / min. ordinary silicone oil is easy to stick to the roller due to poor permeability and reverse flow of silicone oil on the roller. Pay attention to change the working fluid in the groove and clean the roll frequently.


3. Problem of cylinder staining:


When the factory is doing impregnation and softness, the common silicone oil will stick to the cylinder wall. After a long time, some black oil spots will form on the cylinder wall and the silicone oil spots will form on the cloth surface.


4. Cohesion:


In the fabric containing short fibers (such as cotton cloth, viscose and cashmere), it is inevitable that some short fibers will fall down during the processing. The short fibers falling from the cloth will accumulate in the rolling groove, which will be agglutinated with common silicone oil. As the finishing solution goes up to the roller, it will be agglutinated with the extruded and demulsified silicone oil, which is easy to form sticking roller or silicon spot. Do a good job of cleaning before driving, and clean up in time in case of loose hair.


5. Hand feeling problems:


Due to the higher and higher hand feel requirements of fabrics in the market, and due to different seasons and customers' requirements, various fabrics need to show different style requirements, such as smooth and draping, smooth and flexible, fluffy and soft, pure elastic, etc. A silicone oil can only reflect one style. As a result, many factories have to use many kinds of silicone oil, resulting in confusion in production. Sometimes, they can't find the silicone oil suitable for customers' requirements, so they can only give up business and cause losses. We can choose different ammonia value, different kinds of silicone oil to control molecular weight and molecular distribution to synthesize silicone oil with different ammonia value viscosity and reaction, so as to meet the requirements of various fibers in soft and smooth elasticity.

6. Concentration problem:


It is not allowed to pour more than 20% (solid content) high concentration amino silicone oil emulsion directly into the running fabric. It should be diluted in advance and then poured into the container and stirred evenly before adding, so as to prevent rapid absorption and silicone oil speckles.


7. Temperature problem:


The use temperature should be 30-40 ℃, generally no more than 50-60 ℃. Although the temperature has no obvious influence on the softness and smoothness of hand feeling, the elasticity changes greatly when the temperature is too high, and the amino silicone oil is easy to produce roller sticking and demulsification.


8. PH value problem:


The pH value should be controlled around 5.5-6 when impregnating or rolling the working fluid, which is beneficial to improve the softness, drape and elasticity of the fabric handle.


9. Use time:


If the silicone oil emulsion is used for a long time, it will stick to the roller, especially if the quality is poor, and even skin will form on the roller, which will affect the driving. Cleaning should be strengthened. Generally, degreaser or cleaning agent can be used to scrub on the roller after dissolving in a certain proportion.


Transferred from rubber technology studio Li Xiuquan