Ionizer
As a metallic comb or sawtooth ionizer (also ionizers ) are devices called low power, the ions produced by means of high voltage. The oxygen ions are generated by electrical ionization of molecules .
Types and construction methods
Ionizers are devices for the partial ionization of air. If this ionized air is blown into rooms or directly onto surfaces, materials can be charged or discharged. The resulting radicals promote chemical breakdown processes, which can be used to remove odors and disinfect.
Ionizers work with high voltage, usually of a few thousand volts and an electrical discharge at the tips, or they contain sources of ionizing radiation ( ultraviolet emitters , radioactive isotopes ). The achievable currents are usually around 1 µA, which corresponds to several billion ions per second.
Corona discharge ionizers
Such metallic ionizers have conductive tips supplied with high voltage , which generate ions in the immediate vicinity by means of corona discharge and field emission . There are designs that continuously generate ions in an unregulated manner, and others in which the electrical field is regulated by measuring and targeted adjustment of the high voltage (regulated ionizer).
Regulated and unregulated ionizers are used both to build up defined charges and to dissipate unwanted charges (prevention of electrostatic charges and ESD).
In order to ensure that the ionizers can be set up at a greater distance from the material to be discharged (up to approx. 2 m), they are also offered with blown air nozzles or attached to existing nozzles. As a result, the ions are blown together with the air to the point of action (e.g. in printing machines).
Sawtooth ionizers are often designed as thin, comb-like strips. They are fed with direct or alternating voltage. In the case of alternating voltage, all comb tips are connected together to the voltage source. In the case of direct voltage, the metal tips arranged close to one another are alternately positively and negatively charged.
I.a. in Xerox - copiers and laser printers working with AC-superimposed DC voltage. Here the ionizers are used for contactless electrostatic charging of the image drum before exposure.
Ion generation by radiation
Ultraviolet radiation and other ionizing radiation ( alpha , beta , x-ray, and gamma radiation ) also produce ions. Ultraviolet emitters used to be used continuously in hospitals for disinfection. Today they can be found in drinking water treatment and for curing paints, resins and plastics. The main effect is not caused by ions.
Radioactive isotopes ( radionuclides ) are u. a. Used in ionization smoke detectors to detect substances that absorb ions (smoke gases, aerosols). The conductivity of the air caused by ionization is measured. This conductivity decreases in the presence of organic gases or aerosols.
Applications
Eliminate static electricity
One application of ionizers is the elimination of electrostatic charges (risk of electrostatic discharges , fire hazard, personal protection). It is used when the charged parts can only be insufficiently discharged by grounding alone.
Electrostatic discharges are a danger in systems in which electrically insulating products are moved (film production, film packaging, paper production, printing machines, textile production, flour mills, filling systems). There is a risk of fire and possibly explosion. Charge dissipation or air made weakly conductive by means of ionizers also prevents the processing goods from sticking to one another or to the transport tracks due to electrostatic charging, which would hinder the transport. Furthermore, the attraction of undesired particles can be prevented in this way. In machines that process paper sheets, electrostatic sticking is prevented when the sheets are separated from the stack, when the sheet is transported within machines and when it is stacked at the end of the machine with ionizers. In sheet-fed offset printing machines, ionization prevents drops of ink from prematurely jumping from the impression cylinder onto the sheet of the impression cylinder.
Ionizers are used at workplaces for the production and processing of electronic components ( wafers , circuits , light-emitting diodes , laser diodes , circuit board assembly) to ensure ESD protection of the components on the one hand and to prevent contamination from electrostatically attracted dust particles on the other.
To check the effectiveness of the ionizers used for ESD protection, there is the so-called Charged Plate Monitor (CPM), a measuring device with which the charge field between two defined plates can be determined as an image of the charge.
Corona treatment of plastic surfaces
Corona treatment is the superficial roughening and activation of non-conductive surfaces by means of corona discharges , mostly to improve bondability or adhesion. After such a treatment, plastic surfaces can be laminated or coated better or (with some plastics) at all.
air cleaner
Devices for ionizing room air come in different sizes and with different capacities. At the bottom of the power and size spectrum, microdevices find the car cigarette lighter or USB - Port . For use in the kitchen or on the desk, models with compact dimensions (about the size of a one-liter milk carton) are available. Often, ionizers are a sub-component of air purifiers which, in addition to the ionizer, have other approaches (e.g. filters and UV light) for cleaning the air.
The effect of the ionizer as an air purifier is mainly due to the dust-binding effect, which is based on the fact that charged ions attach to dust particles in the air and, through their electrostatic interaction, promote a merger with other particles to form a larger cluster. These clusters can be filtered better by an air purifier than individual particles. Accordingly, the degree of separation and the cleaning performance of the air cleaner can be increased by adding an ionizer.
In addition to the dust-binding effect, the ozone generated during room air ionization can also contribute to air purification. The highly reactive molecule splits many odor-causing molecules. The advantage of ozone lies in the fact that it penetrates substances that are already contaminated by odor and also causes the odor molecules to be broken down there.
The additional effect of the small appliances for household use, u. a. Increased well-being and fresher indoor air, which are supposed to be based on the generation of anions , have not been scientifically proven and are controversial. The basis of this discussion is the measurement of different ion concentrations (e.g. at the waterfall, on the beach, in the apartment) and the subjective well-being in these places.
Critical consideration
However, the breakdown products of nicotine and cigarette smoke, in addition to the ozone itself, harbor high health risks. B. the German Lung Foundation warns against removing the bad smell of smoky rooms with ozone-generating air purifiers.
Even with today's devices, ozone is produced during ionization. This reactive gas has a germicidal effect as a disinfectant and irritates the respiratory tract even in very low concentrations. The health department of the city of Zurich also warns of harmful by-products in the air that are caused by ozone.
Considerations on the effect and toxicological relevance of NTP air purification devices show that the use of non-thermal plasma is not recommended. In particular, warnings must be given against operation in rooms in which people are present.
Ionizers in household electrical appliances
Hair dryers , vacuum cleaners and notebooks with ionizers, which promise an antistatic effect, are also available in stores.
So-called water ionizers for the household are supposed to improve the quality of the drinking water .
safety
electric security
The operating voltages of corona ionizers do not pose a risk with proper insulation or a fault current protection circuit . The currents in laser printers and copiers are usually too small to cause damage to health when touched.
Since the electric fields to be eliminated are influenced by many factors such as B. natural ion clouds, open moving water, open fire, humidity, etc. are influenced, they occur in practice completely unpredictable. For example, processing goods that have been treated in exactly the same way can be charged differently in the same batch. Even the same processing item can be loaded differently when it is processed repeatedly. DC-superimposed ionizers for electrostatic discharge can functionally tip over under these circumstances and then charge instead of discharging. The distance between the tips and the applied voltage, possibly air flow and pulse times, must therefore be coordinated with one another.
See also
swell
- ↑ Rudi Riedl, Dieter Neumann, Jürgen Teubner: Technology of offset printing . P. 283 1st edition. VEB Fachbuchverlag Leipzig, Leipzig 1989, ISBN 3-343-00527-4 .
- ↑ DIN EN 100015-1: 1993-06 - Protection of electrostatically sensitive components - Part 1: General requirements.
- ↑ Room air purifier with ionizer. Retrieved July 28, 2017 .
- ↑ "Ion Concentration and Wellbeing" .
- ↑ Warning of air purifiers with ozone or ozone generators to remove odors
- ↑ Environment and Health Protection Zurich ( page no longer available ); Alternatively web link ( memento of the original from January 25, 2018 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ↑ Prof. H. Heberer, TOXICHEM, Leuna. Hazardous substances - keeping the air clean 65 (2005) No. 10
- ↑ M. Walter: Electrostatic charge . VEB Verlag der Technik, Berlin 1961.
