Method and apparatus for curing receptor substrates in an enclosed planetary array

Abstract: An apparatus and method for curing cylindrical and belt-like substrates (18) include a curing chamber (410) defining a horizontal central axis (H); a support structure (14) selectively receivable within the curing chamber for supporting at least one substrate along a horizontal axis radially offset from and parallel to the central horizontal axis and for rotating the at least one substrate (18) about the offset horizontal axis; and a curing device (420) located within the curing chamber for expelling temperature controlled air toward the at least one substrate as the at least one substrates rotates about its offset horizontal axis. Preferably, the curing device is located along the central horizontal axis for expelling air radially outward. In a preferred embodiment, the support structure supports a plurality of substrates in a planetary configuration surrounding the central horizontal axis, each substrate being located along an offset horizontal axis radially spaced from and parallel to the central horizontal axis.

Description: The invention relates to a method and apparatus for curing coated drum and flexible belt charge receptors for photocopiers as defined by the features of the preamble of claim 1. A curing system comprising these features is known from US-A-4 008 401. A photoreceptor is a cylindrical or belt-like substrate used in a xerographic apparatus. The photoreceptor substrate is coated with one or more layers of a photoconductive material, i.e., a material whose electrical conductivity changes upon illumination. In xerographic use, an electrical potential is applied across the photoconductive layer and then exposed to light from an image. The electrical potential applied across the photoconductive layer decays at the portions irradiated by the light from the image, leaving a distribution of electrostatic charge corresponding to the dark areas of the projected image. The electrostatic latent image is made visible by development with a suitable powder. Better control of the coating quality yields better imaging performance. One method of coating substrates is to dip the substrate in a bath of the coating material. This method is disadvantageous because it usually results in a non-uniform coating. In particular, when the substrate is oriented vertically and dipped into a bath, the coating thickness tends to "thin" or decrease at the top of the substrate and "slump" or increase at the base of the substrate due to gravity induced flow of the coating material as the substrate is lifted from the bath. Thickness variations also occur even when the photoreceptor is oriented horizontally and dipped into the bath due to the formation of a meniscus as the substrate is removed from the bath. The variation in coating thickness causes variations in the performance of the photoreceptor In addition, the dipping process requires additional processing controls because the bath must be constantly maintained in a state suitable for coating. The bath increases the size of the entire processing apparatus and is not readily adaptable to rapid changes in coating formulations. Further, changing in coating formulations are inhibited due to incompatibilities between formulations for successive coatings or layers. It is also difficult to incorporate cleaning and curing operations that are compatible with the dipping process for efficient modular operation in a manufacturing process. In another method, an air assisted automatic a spray gun uses high velocity air to atomize the coating formulation which is sprayed onto a substrate. Due to high mass transfer rates intrinsic to the use of atomizing air, this method entails considerable evaporative loss of solvent from the spray droplets and requires the use of slow evaporating solvents to prevent excessive solvent loss before the droplets arrive at the substrate. It is difficult to use this method in a sealed environment, and thus difficult to control the solvent humidity surrounding the substrates prior to, during, or after the coating process. In addition, the air atomized spray method creates a considerable amount of overspray which results in higher material usage. Air spray guns also are less advantageous for batch processing of a number of substrates. It is thus an object of the invention to obviate the foregoing drawbacks of the prior art by providing a more efficient apparatus and process for fabricating rigid cylindrical or flexible belt photoreceptors. According to the invention, there is provided an apparatus for curing cylindrical or belt-like substrates, comprising: a curing chamber defining a horizontal central axis; a support structure selectively receivable within the curing chamber for supporting at least one substrate along a horizontal axis radially offset from and parallel to the central horizontal axis; curing means located along the central horizontal axis within the curing chamber wherein the support structure includes means for rotating the at least one substrate, relative to the support structure, about the offset horizontal axis, and the curing means comprises means for expelling temperature controlled air or for directing ultraviolet radiation toward the at least one substrate as the at least one substrate rotates about its offset horizontal axis. The invention also provides a method of drying cylindrical and belt-like substrates comprising the steps of: arranging a plurality of substrates in a planetary array on a support structure about a central horizontal axis, each substrate defining an offset horizontal axis radially spaced from and parallel to a curing mechanism along the central horizontal axis; with the additional steps of: rotating each substrate relative to the support structure about its offset horizontal axis; and expelling temperature controlled air or directing ultraviolet radiation from a curing mechanism, towards the substrates as the substrates rotate about their horizontal axes. The invention provides a method or apparatus which permits batch processing of a plurality of substrates in compatible cleaning, coating and curing operations. It has the advantage that it provides an apparatus or method which obtains high quality coatings of uniform thickness. The apparatus is modular and occupies a relatively small area per unit of production. It is automatic and adaptable to different coating material formulations and substrates of differing diameters. The apparatus operates in a sealed environment in which solvent humidity can be controlled. Preferably, the curing device is located along the central horizontal axis for expelling air radially outward. In a preferred embodiment, the support structure supports a plurality of substrates in a planetary configuration surrounding the central horizontal axis, each substrate being located along an offset horizontal axis radially spaced from and parallel to the central horizontal axis. The invention will be described in detail herein with reference to the following Figures in which like reference numerals denote like elements and wherein: Figure 1 is a schematic view of the substrate supporting structure Figure 2 is a schematic perspective view of the substrate supporting structure; Figure 3A is a schematic cross-sectional top view of a curing chamber; Figure 3B is a schematic cross-sectional side view of the curing chamber taken along the line Y-Y of Fig. 3A; Figure 3C is a schematic cross-sectional side view of an alternative nozzle structure for the curing chamber of Figure 3A; Figure 4A is a schematic cross-sectional top view of another embodiment of the curing chamber; and Figure 4B is a schematic cross-sectional side view of the curing chamber taken along the lines Z-Z of Fig. 4A. The invention will be described in relation to fabrication of cylindrical and belt-like substrates, and particularly rigid cylindrical and flexible belt photoreceptor substrates for photocopiers. The invention, however, is applicable to other coated substrates and/or coating processes. As best seen in Figures 1 and 2, the support structure 14 includes a planetary array of support arms 16, each defining an offset horizontal axis h radially spaced from a central horizontal axis H of the support structure 14. Each support arm 16 is capable of carrying at least one substrate 18 (and preferably two substrates) so that the support structure 14 provides a planetary arrangement of substrates 18, each substrate being parallel to but radially spaced from the central horizontal axis H. Preferably, the support arms are located in an annular array at equal radii relative to the central horizontal axis H so that the substrates are symmetrically positioned relative to the horizontal axis H. Further, the support structure 14 carries a mechanism for rotating each support arm 16 about its offset horizontal axis h while being secured in a position parallel to but radially spaced from the central horizontal axis H. The support structure 14 can include any mechanism for rotating the support arm 16 and securing a substrate along the horizontal axis h , such as an interior rod-like structure, a rotatable cap or collect structure grasping the exterior surface of an end of the substrate, or a rotatable interior expanding structure insertable into the substrate for grasping the interior surface. Further, while the substrates illustrated in Figure 1 can all have the same diameter (e.g., 84 mm), the support arms 16 are capable of supporting substrates of different diameters (e.g.m, 30 to 300 mm). The planetary arrangement of substrates 18 on the support structure 14 permits a large number of substrates to be processed simultaneously thereby increasing the throughput of the process and decreasing manufacturing costs. Each support arm 16 can carry multiple substrates and simple adjustments and/or modifications permit processing of substrates of varying diameters. Further, the curing stations described below can perform their operations from the central axis H radially outward while each substrate rotates about its offset axis h , so that each substrate is processed in an equal manner due to the radial symmetry thus ensuring uniformity and versatility in processing. In the operation of film curing or drying the support structure 14 is advanced to insert the planetary array of substrates 18 into a chamber 410. If there is solvent present in the coating film, it is removed by exposure to high velocity heated air (e.g., 113m³ min⁻¹ at 60-140°C for 1-5 minutes). If the film is photochemically reactive, the film is cured by exposure to ultraviolet light. When curing is complete the substrates are cooled by chilled air (if necessary) and then withdrawn from he chamber. In a preferred embodiment, the curing chamber includes a drying mechanism to remove solvent from the freshly coated film on the substrate by exposing the substrate to a heated stream of high velocity air as the substrate rotates. The drying mechanism includes (Figure 3A and 3B) a perforated air supply plenum 420 communicating with the source of temperature controlled air. The plenum 420 is located along the horizontal axis H of the chamber 410 so as to be surrounded by the planetary arrangement of substrates 18. Clean heated air flows radially outward through the perforated plenum 420 at high velocity, and impinges on the rotating surfaces of the coated substrate (rotating at about 20-100 RPM). The high velocity air minimizes the boundary layer, and the resultant high heat and mass transfer rates permit rapid solvent removal. Although a perforated plenum wall is shown in Figures 3A and 'B, other configurations such as an air-fed cylinder 425 located along the central axis H and having nozzles 430 (Fig. 3C) aligned axially with the individual substrates may be used to impart high velocity air to the substrate rotating at about 20-100 RPM. Alternatively, the curing chamber may include an array of dedicated nozzles, each being directed to expel air toward a particular substrate. The air supply temperature and flow rate are optimally controlled to minimize curing time without comprising coated surface quality and imaging performance. When the coated layer is cured adequately, the air supply temperature is lowered to below ambient temperature to rapidly cool the substrate to ambient temperature. The curing structure is compatible with the processing of substrates in a planetary configuration. In addition, the curing structure is versatile since the outward radial flow from the plenum to the substrate permits a single curing chamber to used with batches of coated substrates of differing diameters. The planetary arrangement of substrates with the central curing structure provides a synthetical system which reduces drying time and reduces temperature variations in the substrate. In another preferred embodiment, the curing station is capable of curing both substrates coated with a solvent based film by exposure to high velocity heated air, and substrates coated with photoreactive polymer films by exposure to ultraviolet light. For photoreactive polymer film coatings, the curing chamber 410 is equipped with an annular ultraviolet light source 450 (Figure 4) having an axis colinear with the central axis H. The light 450 is mounted within a concentric reflector 460 to provide a band b of light which radiates with equal intensity 360° around the reflector 460. The light 450 and reflector 460 are mounted on a carriage 470 which reciprocates along the central horizontal axis H as each substrate 18 rotates about the offset horizontal axis h. With this structure, a band b of ultraviolet light radiates outward and moves axially from end to end of the substrate 18 so that each substrate "sees" or is exposed to the band b of ultraviolet light several centimeters wide scanning along the axis of the substrate. Such exposure polymerizes the photochemically reactive coating on the substrate to produce a solid uniformly cured film. Optimum performance is obtained by matching reciprocation speed, rotational speed of the substrates, photochemistry of the film, intensity in wavelength of the ultraviolet lamp and width of the exposure band. The foregoing specification describes preferred embodiments of a novel method and apparatus for processing rigid drum and flexible belt charge receptors arranged in a planetary array which permits a large number of substrates to be processed simultaneously and uniformly. The planetary substrate array also permits each substrate to be processed in an equal manner due to the radial symmetry. The invention has been described with reference to the preferred embodiments thereof which are intended to be illustrative rather than limiting. Various changes and modifications may be made without departing from the scope of the invention as defined in the following claims.

Claims: An apparatus for curing cylindrical or belt-like substrates (18), comprising: a curing chamber (410) defining a horizontal central axis (H); a support structure (14) selectively receivable within the curing chamber for supporting at least one substrate (18) along a horizontal axis (h) radially offset from and parallel to the central horizontal axis, and curing means (420) located along the central horizontal axis (H) within the curing chamber, characterised in that the support structure includes means for rotating the at least one substrate, relative to the support structure, about the offset horizontal axis, and the curing means comprises means for expelling temperature controlled air, or for directing ultraviolet radiation, toward the at least one substrate (18) as the at least one substrate rotates about its offset horizontal axis (h). The apparatus of claim 1 wherein the support structure (14) includes means for supporting a plurality of substrates in a planetary configuration surrounding the central horizontal axis (H). The apparatus of claim 2, wherein the means for supporting the plurality of substrates (18) are symmetrically arranged in an annular array about the central horizontal axis (H), each substrate being equally radially spaced from the central horizontal axis. The apparatus of any one of claims 1 to 3 wherein the curing means is a perforated cylindrical plenum communicating with a source of heated air and supported along the central horizontal axis of the curing chamber. The apparatus of any one of claims 1 to 3 wherein the curing means (420) includes a conduit having a series of nozzles communicating with a source of temperature controlled air, the conduit being supported along the central horizontal axis of the curing chamber, and the nozzles being axially aligned with each substrate. The apparatus of any one of claims 1 to 5 further comprising control means to vary the temperature and flow rate of air expelled from the curing means. The apparatus of any one of claims 1 to 6 wherein the curing chamber includes a source of ultraviolet radiation arranged for movement along the central horizontal axis. The apparatus of claim 7 wherein the ultraviolet radiation source is annular, and is mounted within a concentric reflector. A method of drying cylindrical and belt-like substrates comprising the steps of: arranging a plurality of substrates (18) in a planetary array on a support structure (14) about a central horizontal axis (H), each substrate defining an offset horizontal axis (h) radially spaced from and parallel to a curing mechanism (420) along the central horizontal axis; characterised by rotating each substrate (18), relative to the support structure, about its offset horizontal axis; and expelling temperature controlled air, or directing ultraviolet radiation, from the curing mechanism towards the substrates as the substrates rotate about their horizontal axes.

Inventors: HAMMOND JOHN M, NOLLEY ROBERT W, HAMMOND, JOHN M., NOLLEY, ROBERT W.
Applicants: XEROX CORP, XEROX CORPORATION
Application year: 1990
Main classification: B05C9
IPC codes: F26B15, G03G5, B05C9, B05B3