Electrophotographic imaging is the use of photons to generate a latent charge image on the photoconductor drum, and then use the electric field force between the developing device and the photoconductor drum to transfer the toner to the photoconductor drum , And then transfer the coloring agent from the photoconductor drum to the printing material. In ion imaging, a charge image is generated on the dielectric through an ion source, and the development and inking of the toner is the same as that of electrophotographic imaging. In these two imaging technologies, a charge latent image is first generated on an intermediate carrier, and then transferred to a common printing material without a special insulating coating through electrostatic attraction. The indirect electrostatic imaging technology.
If the charge image is directly generated in the electric field between the ink and the printing material, the ink transfer does not require other intermediate carriers. This technology is called direct electrostatic printing technology, which is called electronic imaging here.
The classification of definitions of electronic imaging terms is very difficult. If electronic imaging is defined as the use of electric fields to generate charge images and realize charge transfer (not photons), then it includes ion imaging. Because in ion imaging, charged particles are generated by an ion source, and printing is realized by charge transfer. As an independent digital printing technology, electronic imaging is defined as a charge image directly transferred to paper with a special insulating coating through electrodes, and then developed by electrostatic attraction between the paper and the coloring agent.
Electronic imaging uses an electric field to transfer image information to the substrate. The paper includes a dielectric coating, and the latent charge image can be directly written on the paper. The printing process only requires three steps of imaging, inking and fixing. Since there is an air gap between the paper and the printing electrode, a higher electric field strength is required in this type of system. In order to accurately and efficiently form charges during imaging, the printing electrode can be in contact with the paper coating. However, the imaging head and paper surface of this type of system must be wear-resistant and have good sliding characteristics. The imaging head of other electronic imaging systems is not in contact with the paper, but the imaging signal obtains a visible image through contact with a conductive liquid colorant.
In order to transfer charge across the width of the paper, the imaging system is configured as an electrode array. It can reach a resolution of 400dpi through the configuration of multiple columns of electrode heads.
The imaging electrode is in contact with the paper under lighter pressure, and the imaged web is in contact with the liquid coloring agent to obtain a stable color density. The charged area on the paper surface absorbs the liquid coloring agent for development. . Like other digital printing technologies that use liquid color formers, the color formers in the graphics and text parts must be fixed on the paper by melting and fixing.
Electronic imaging process
According to the contact mode of the writing electrode and the substrate, the electronic imaging process can be divided into three types to be discussed below.
(1) The imaging process where the write electrode does not contact the substrate
The figure (a) is the first type of electronic imaging working principle, and its basic feature is that the write electrode and the substrate The surface of the printing material does not touch. The printing material is composed of an insulating layer, a conductive paper layer and a back electrode. The insulating coating on the outer surface has a polarization effect under the action of an electric field, and it is possible to write the electrostatic latent image directly on the surface. Since the writing electrode is not in contact with the surface of the printing material, there is a layer of air gap (Air Gap) between the printing material and the writing electrode. For this reason, a high-intensity electric field is required between the writing electrode and the printing material to achieve Information writing. The intensity of the applied electric field should be high enough for the air gap to break down the air gap; the applied electric field should be moderately high to the insulating layer, so as not to cause the breakdown of the insulating layer, only the polarization of the dielectric occurs.
(2) The imaging process where the write electrode contacts the printing material
When the electronic imaging process where the write electrode contacts the printing material, the imaging signal from the grid image processor is still It is added between the writing electrode and the back electrode to control the writing electrode to directly "write" the latent image of the charge on the surface of the printing material. The electrostatic latent image formed corresponds to the image and text on the page. Therefore, the external electric field only needs to polarize the insulating layer.
In order to obtain effective and accurate charge distribution on the surface of the insulating layer during imaging, the action of the write electrode must be controlled by the imaging signal. The write head of the write electrode acts like an electronic engraving needle. The insulating coating of the printing material contacts, this is the imaging process given in the figure (b). But it should be noted that both the writing head and the surface of the printing material must have good abrasion resistance, and the writing head should have good sliding performance to extend the service life of the writing electrode.
(3) The imaging process in which the write electrode contacts the printing material through a conductive liquid
The figure (c) shows another electronic imaging process. The write electrode is electrically conductive. The layer generates an electrostatic latent image on the insulating surface of the printing material, that is, the writing electrode is in contact with the conductive layer, and the insulating layer is polarized under the action of an external electric field, and the charge from the writing hair is directed to migrate to the insulating layer. The conductive layer is usually liquid, and because it is conductive, it does not require an external electric field to break it down. In addition, there is also the problem of the selection of conductive liquid materials, which requires that the liquid does not cause the insulating layer on the surface of the printing material to wet, thereby affecting the imaging effect. Obviously, writing information through the conductive layer is also a non-contact electronic imaging replication process, which is similar to writing through an air gap, except that it does not require breakdown of the liquid layer.