1.  Field of the Invention
The present invention relates to an air cleaner, and more particularly, to an air cleaner which further improves air cleaning performance through physical filtering and through filtering using an electrostatic force. 
2.  Background of the Related Art
An air cleaner is a device that operates to remove particulates such as fine dust, fine contaminants, etc.,  or remove bad odors or the like. 
Air cleaners can be divided into electric filtration types, electric dust collection types, anion generation types, mechanical filter types and others, according to a particulate removal mechanism.  Air cleaners can also be classified as ozone generation types and carbon adsorption types based on odor removal mechanism. 
While the electric filtration type and the electric dust collection type have high initial contaminant removal performance, in particular, a high CADR (clean air delivery rate), they have a disadvantage in that their performance is drastically reduced after a sustained period of continuous use.  The filters in such devices have to be frequently replaced.  The anion generation generally has low maintenance costs, but its filter performance is poor.  The mechanical filter type is high in clean air delivery rate, the life span of a filter is long, and its maintenance cost is low, but the filter size is large, which leads to a disadvantage that the volume of the entire system is large and it is difficult to make it compatible with other systems. 
FIG.  1 schematically illustrates an air cleaner according to a conventional electric dust collection mechanism.  An ionization unit 1 uses a high voltage discharge to ionize foreign materials such as dust and the like in the air passing through the ionization unit.  The ionized foreign materials are then collected in a dust collection unit 2 by an electrostatic force.  The dust collection unit 2 comprises a pair of cathode plates 4a and a dust collecting electrode plate 4b made of a cathode.  The ionization unit 1 comprises a discharge line 3a composed of a thin wire made of, for example, tungsten and forming an anode.  A pair of opposed discharge electrode plates 3b are mounted at upper and lower sides at a predetermined height gap from the discharge line 3a and form a cathode.  When a high voltage is applied to the discharge line 3a, current starts to flow due to a high potential difference formed between the discharge line 3a and the opposed discharge electrode plate 3b and a corona discharge takes place.  This discharge ionizes dust in the air flowing in the direction indicated by the arrows.  Typically, a plurality of discharge lines 3a and opposed discharge electrode plates 3b are formed side by side at regular intervals.