Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Charging simultaneous with imaging
Reexamination Certificate
2000-01-13
2002-08-27
Chapman, Mark (Department: 1753)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Charging simultaneous with imaging
C399S177000, C399S220000
Reexamination Certificate
active
06440625
ABSTRACT:
FIELD OF THE INVENTION
This invention is in the field of electrophotography and relates to a method for electrostatic recording on a cylindrical photoreceptor with dielectric coating and an electrophotographic apparatus for multiple-copy production utilizing this method. The invention is particularly useful in the creation of large-format copying equipment, as well as highly productive equipment for the manufacture of printed circuit boards (PCBs) and polygraphic matrices.
BACKGROUND OF THE INVENTION
The electrophotographic process is predominantly used for easy and quick image reproduction or copying. The ability of technology to reproduce/copy an image onto different materials serving as the final information carrier enables the use of electrophotographic methods of copying in different technical fields. One of these fields is the field of printed circuit boards (PCBs) production.
The PCB production process is the process of creating a pattern of conductors on a carrying dielectric basis. The traditional process of PCB production typically consists of the following main stages:
(1) depositing a special photoresist material onto the copper-foiled surface of a plate;
(2) applying optical means to form a required conductive pattern which is created due to the polymerization of the photoresist material within the image regions;
(3) removing the photoresist material from the non-exposed regions (i.e., spaces between the image regions);
(4) applying chemical etching to remove the copper foil from the non-exposed regions;
(5) removing the photoresist material from the image regions (stripping the current conductors).
There exists a number of technical solutions for pattern creation on a foil-coated plate by means of electrophotography. These solutions utilize either direct or indirect processes of electrophotographic copying. For example, U.S. Pat. Nos. 4,327,167 and 5,494,764 disclose a technique of PCBs production by means of a direct method of electrophotographic copying. For this purpose, a photo-semiconductive film is preliminary deposited on the foiled surface of a plate, which thereby is transformed into a photoreceptor. The printing process comprises the stages of electrostatic charging, exposure, development of a latent electrostatic image by a toner, and the toner fixation on the surface of the photo-semiconductive layer. Thereafter, the photo-semiconductive material is removed from the blanked regions, and selective chemical etching and stripping of the current conductors are carried out. It is evident that such cumbersome and relatively expensive technology has no essential advantages over the conventional one.
The application of the indirect process of electrophotographic copying using a photoreceptor as an intermediate image carrier is more effective. However, in this case, other problems arise associated mostly with the ability for high-quality reproduction of large-format images and the realization of a process of toner-image transfer from the photoreceptor surface onto a conductive information carrier. It is evident that a method of electrostatic transfer in the corona-discharge field which is widely used in the electrophotographic technique, as well as other known methods of the toner-image transfer onto a dielectric information carrier (paper, film, etc.) are not applicable for the manufacture of PCBs. For this reason, the known techniques of the kind specified utilize the adhesion-based transfer, wherein the forces of toner adhesion to the surface of a receiving material should exceed the forces of electrostatic attraction that hold the toner particles on the surface of the photoreceptor. These techniques are disclosed for example in U.S. Pat. Nos. 4,371,599; 5,470,644 and 5,576,135.
According to the technique disclosed in U.S. Pat. No. 5,470,644, the direct, adhesive toner transfer onto the PCB surface is used, wherein the PCB surface is coated with ink aimed at improving its adhesion properties. However, this technique suffers from the fact that the processes of preliminary PCB coating and subsequent ink removal before etching still remain. Additionally, this technique practically does not provide the full transfer of a toner-image, which may lead to intolerable defects in the image causing discontinuities in the conductive elements of the PCB.
The above drawbacks are eliminated to a considerable degree, when using a thermal method of the adhesive transfer of a thermoplastic toner, as disclosed, for example, in U.S. Pat. No. 4,371,599. In this case, the toner heating during the process of transfer increases the cohesion between the toner particles and its adhesion to the “bare” receiving surface of the PCB. However, such a thermal process is characterized by contradictory conditions of the process realization: On one hand, to provide the complete toner transfer, a high heating temperature of the receiving material should be provided (up to 250° C.), depending on the melting temperature of the toner and the given technological speed of the process. On the other hand, the photo-semiconductive layers used in photoreceptors are known as very sensitive to high temperatures, such that their parameters are sharply reduced even at temperatures of about 30° C.-40° C.
Furthermore, under such conditions that the photo-semiconductive surfaces of a photoreceptor directly contact the receiving surface of a rigid metal information carrier, unavoidable mechanical damages of the photo-semiconductive layer and sequential electrical breakage occur. This immediately makes the photo-semiconductive layer useless for further operation. The sources and kinds of damages can be different (pilling, scratches, etc.). For this reason, the thermal transfer based electrophotographic apparatuses usually utilize an intermediate, thermal, rubberized cylinder or a heated belt conveyor (as disclosed in U.S. Pat. No. 5,576,135), which is installed between a photoreceptor and the receiving surface of a final information carrier, and which should be equipped with a thermostatic system. In this case, the operational conditions of the photoreceptor are partially simplified, but the construction of the entire apparatus becomes significantly complicated, and the probability of the image quality degradation increases due to the double transfer process. Furthermore, to provide the required temperature mode for the toner image transfer from a heated drum onto a metal surface possessing high heat-conductivity, this surface should be preliminary heated. However, the combination of the thermal transfer processes with the simultaneous toner image fixation on the metal surface, does not guarantee the sufficient quality of the fixation, owing to the fact that these processes have different optimal temperature modes.
In view of the above, it appears that one of the main reasons limiting the application of an electrophotographic process for the manufacture of PCBs is the absence of an effective system for the toner-image transfer from the photoreceptor surface to the conductive receiving surface. For this reason, none of the existing electrophotography-based techniques for PCB production, is practically applied in industrial PCB production equipment.
The conditions of realization of the transfer process to a conductive surface can be significantly simplified when using a photoreceptor with a protective dielectric coating of the photo-semiconductive layer. This allows for carrying out the direct contact transfer of a toner-image from the surface of the photoreceptor directly onto the conductive surface of an information carrier.
Electrophotographic processes of the latent electrostatic image formation on a photoreceptor with a dielectric coating of the photo-semiconductive layer are known, such as Canon process, Katsuragawa process, Hall process). They are based on a certain sequence of the realization of separate stages of the electrostatic recording. In this case, the exposure process is carried out either by means of the conventional slot image projection technique, or by the beam scanning of the image along t
Chapman Mark
Elfotek Ltd.
Fitch Even Tabin & Flannery
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