Electret Charging Technology And Performance-related Research

Electret is named“yong dian ti”which is a kind of new functional material. It has thecharacteristics of lasting charged, widely been used in electronic products and sensor of functioncomponents. Since 1919, the first one electret was born, people had launched a series of researchabout electret and also made brilliant achievements. At present, whether the copy technology, orfiltering equipment, the electret microphone and all kinds of sensors or artificial organs and otherhigh-tech products and so on, for the development of society the electret products are theirreplaceable part. Along with the development of the technology, human’s life is constantlyimproved. The level of the characteristics of the product and the function of the demand is higherand higher. Usually there are many ways just like corona charging, electron beam charging, hotcharging, liquid contact method of charging, etc. Different charging way will make differentelectert. The charge storage situation of electret directly affected the performance of electretproducts. Therefore, the study of charging methods in an influence on the characteristic of electretis very important to the development and application of electret.The main work in this thesis is as follows:1. Use the traditional method of corona charging to charge the polypropylene film, includingnegative charging and positive charging. In the same condition, through recording the potentialattenuation of electret the figure can be drew. It was found that, the stability of electret whichcharged by negative corona charging is better than positive. Because of the different molecularstructure and amorphous of PP electret, the ability to capture charge is different. So it has dissimilarstability of performance.2. In order to study the relationship between the charge stability of electret and themorphology and crystallinity. In the room condition, using thermally stimulated discharge (TSD)technology study the PP electret sample. The charge storage characteristics of PP electret fordifferent morphology were studied by means of short-circuit thermally stimulated dischargetechnique. It is confirmed that there are two types of space charge traps, shallow and deep, in thefilm PP the peak temperature of the electret at 79℃and 117℃. While there was only one kindtrap-deep trap in the melt-blown PP web. When the crystallinity is 14.17%,the peak is 112℃，whilethe 36.64% one is 123℃.The peak temperature is higher with the increase of crystallinity inmelt-blown PP web.3. In the process of charging there is a phenomenon been found, that is the back of thepotential is higher than the charging surface. According to one of the electrodes plating PP film, using the way of corona charging respectively under room temperature and heat treatment in 80℃.The results found that after heating the stability becomes poor. This phenomenon and reason can beexplained by that the samples, air gap and the under electrode cause micro discharging. In this papershow the phenomenon that in the condition of positive and negative charging. Experiments showthat, when the charging is 5kV there is the polarity charging phenomenon. While if the power isnegative at -5.5kV will have a polarity charging. With the time passed by, the polarity phenomenonis more and more prominent. What is more, the higher of the charging voltage the more obvious ofthe polarity charge.4. The traditional corona charging methods such as needle to surface or line to surface getthe bell-shaped distribution of the electret surface potentials. In order to make the surface potentialmore uniform distribution on the electret surface, the idea of making use of dielectric barriercharging technology to improve the uniform distribution of electret surface potential is proposed.The results showed that surface potentials are the highest and uniformity is the best when PTFEfilm is used as dielectric barrier materials and by means of DC power.