Patent GB-919569-A (GB)
Title: Devices exhibiting persistent internal polarization and methods of utilizing the same
Inventor: KALLMANN HARTMUT P
IPC: G03G5/10
Filed: 1960-10-07
Abstract: 919,569. Electrophotography. RAVICH, L. E. Oct. 7, 1960, No. 34416/60. Class 98 (2). [Also in Group XXXVI] . An electrophotographic plate consists of a material 10 which exhibits persistent polarization effect deposited on a transparent electrode and provided with conductive islands secured to the polarizable material and insulated from each other. Fig. 1 shows such a polarizable material 10 (for example activated (Zn: Cd) S phosphors, alkali halides, anthracene, all of which exhibit a high dark resistance) deposited on an electrode 12 which consists of a coating 16 of silver on a glass backing plate 14. The removable electrode 18 consists of an aluminium sheet or foil but the Specification states that distortion of the charge pattern when this electrode is removed is avoided by providing conductive islands 36 secured to the photoconductor. In Fig. 2, these islands are formed by etching lines 34 in a conductive layer, in Fig 3 (not shown) they are applied as dots of conductive paint. In a further arrangement (Fig. 4, not shown), polarizable material is impressed into a heated thermoplastic tape of e.g. polyethylene or polystyrene. A continuous electrode such as silver is applied to one side of the tape while the island electrode layer is applied to the other. Three methods of producing a charge pattern on the islands which may produce a picture by conventional powder development techniques are described. In the first method removable electrode 18 is placed in contact with the islands, a de-polarizing voltage is applied between electrodes 18 and 12 at the same time as or after the radiation pattern. Internal polarization corresponding to the radiation pattern is thus produced. This pattern may be stored by connecting the electrodes together and earthing them. When the polarization is to be read out removable electrode 18 is taken off. Layer 10 is then uniformly irradiated leaving free charges on the conductive island and a positive may be produced by conventional powder development techniques. In another method, layer 10 is first uniformly irradiated and a polarizing voltage is then applied to produce a homogeneous polarization throughout. Electrodes 18 and 12 are connected together and the desired radiation pattern applied which reduces the internal polarization and corresponds to a negative image of the picture. Electrode 18 is removed and homogeneous radiation applied to release the rest of the polarization to transfer the image charge as a negative image to the island. In the third method layer 10 is homogeneously polarized either as in the second method or by applying uniform irradiation and polarizing voltage simultaneously. Electrodes 12 and 18 are grounded or otherwise connected together. Electrode 18 is removed and the polarization released by the radiation pattern to be depicted. The releasing radiation pattern is depicted by the charges which appear on the islands. Layer 10 may be formed of a powder deposited with a small amount of "Duco" (Trade Mark) cement or nitrocellulose as the binder. Alternatively, the powder on a support may be treated with an insulating material of high dielectric constant which interpenetrates the grains. Castor wax, polystyrene plastics and resins are suggested.