A method and a device for cleaning drums

Abstract: In the cleaning of the outer circumferential surface of a drum by spraying a cleaning fluid thereon, the cleaning fluid is recirculated and is cleaned by a filter during its circulation. The cleaning fluid is passed through a primary filter having a relatively coarse porous structure at high pressure, after which the drum is cleaned with a cleaning fluid passed at lower pressure though a finishing filter having a fine porous structure.

Description: The present invention relates to a method and a device for cleaning drums, particularly photoconductor drums for use with image forming apparatus such as electrophotographic copying machines or the like. More particularly, this invention relates to a method and device for cleaning drums such as aluminum drums or the like, before applying a coating solvent containing a photoconductive substance to the outer circumferential surface of the drum in the manufacture of photoconductor drums having a photoconductive layer formed on the outer circumferential surface thereof. A photoconductor drum used with an image forming apparatus such as an electrophotographic copying machine or the like is manufactured by coating the outer circumferential surface of an aluminum drum with a photoconductive substance to form a photoconductive layer thereon. Prior to the coating of the photoconductive substance, the aluminum drum is cleaned to remove metal powder, grease, and other foreign matter adhering the surface thereof, so that the photoconductive substance can be applied in a uniform thickness onto the outer circumferential surface thereof. One method, known to the applicant, of cleaning such an aluminum drum is to spray a cleaning fluid onto the outer circumferential surface of the aluminum drum. In this cleaning method, as shown in accompanying Figure 2, a cleaning fluid is sprayed inwardly from nozzles 91 arranged in a circular configuration while an aluminum drum 10 is passed in rotating fashion through the inside space of the circular configuration toward which the cleaning fluid is sprayed. Thus, the cleaning fluid is sprayed onto the outer circumferential surface of the aluminum drum 10 to remove foreign matter adhering thereto. The cleaning fluid after being used for cleaning is collected in a storage tank 92 disposed beneath the nozzle 91 . The cleaning fluid 93 in the storage tank 92 is pressurized by means of a pump 94 to feed to a filter 95 through which the cleaning fluid is filtered and cleaned and recirculated to the nozzle 91 for use for cleaning the aluminum drum 10 . The cleaning fluid is thus effectively filtered and cleaned and recycled. With the above drum cleaning method, to assure complete removal of metal powder, grease, and other foreign matter adhering to the outer circumferential surface of the aluminum drum 10, the cleaning fluid usually has to be sprayed through the nozzles 91 under a high pressure of 30-50 kg/cm². Spraying the cleaning fluid through the nozzles 91 under a high pressure of about 50 kg/cm² requires that the pressure loss of cleaning fluid must be decreased at the filter 95 . Therefore, the filter 95 through which the cleaning fluid fed to the nozzle is passed through has a porous structure coarse enough to allow particles of 10 µm or larger size to pass through; otherwise, spraying the cleaning fluid under such a high pressure would not be possible because of a decrease in the pressure applied to the cleaning fluid due to the presence of the filter 95 . If the filter 95 having a porous structure coarse enough to allow particles of 10 µm or smaller size to pass through is used, the pressure loss of cleaning fluid must be decreased at the filter 95 , because the cleaning fluid cannot be sprayed under high pressure. After cleaning the aluminum drum 10 used as a photoconductor drum for an image forming apparatus, the maximum allowable size of foreign particles to be deposited on the outer circumferential surface of the aluminum drum 10 is generally said to be about 0.2 µm. When applying a coating solution containing a photoconductive substance on the cleaned drum surface, if any foreign particles larger than that size are left thereon, the coating solution cannot be applied uniformly where such particles are deposited, resulting in the formation of an image having missing portions on such areas. As described, when the filter 95 having a porous structure coarse enough to allow particles of 10 µm or larger size to pass through is used, particles larger than the allowable size may not be trapped by the filter 95 and may be redeposited on the outer circumferential surface of the aluminum drum 10 , thus resulting in a substantial drop in the cleaning effect even if the cleaning fluid is sprayed under high pressure. When fluid is to contact the cleaning filter under high pressure and several filters having a coarse porous structure are used in parallel with each other, the cleaning fluid can be sprayed under high pressure to the drum surface while reducing the size of foreign particles allowed to pass through the filters. However, such arrangement requires the provision of a large number of filters, which not only impairs economy but could result in failure to completely remove particles in the cleaning fluid which are larger than the allowable size. According to the present invention there is provided a method of cleaning a drum by spraying a cleaning fluid on the outer circumferential surface of the drum to remove particles of foreign matter larger than a prescribed size, the cleaning fluid being recirculated after being sprayed on the drum, the method comprising: a primary cleaning step in which the cleaning fluid is sprayed onto the outer circumferential surface of the drum at a first pressure and in which the cleaning fluid is passed through a primary filter, the primary filter having a porous structure in which the pore size is larger than the prescribed size; and a final cleaning step, following the primary cleaning step, in which the cleaning fluid is sprayed onto the outer circumferential surface of the drum at a second pressure which is lower than the first pressure, and in which the cleaning fluid is passed through a finishing filter, the finishing filter having a porous structure in which the pore size is substantially equal to the prescribed size. This invention is preferably applied to a photoconductive drum provided with a photoconductive layer on the circumferential surface thereof after cleaning. It is preferred that the primary filter have openings of about 10 µm so that said cleaning fluid passed through at a high pressure of about 50 kg/cm² does not lose much of the pressure thereof. It is preferred that the finishing filter has openings about 0.2 µm in size. In another aspect, this invention provides a device for cleaning a drum to remove particles of foreign matter larger than prescribed size, the drum being cleaned by spraying a cleaning fluid on the outer circumferential surface thereof and by circulating the cleaning fluid which has been sprayed, the device comprising: at least one nozzle for spraying the cleaning fluid on the outer circumferential surface of the drum; and a cleaning tank for accommodating the cleaning fluid which has been sprayed on the outer circumferential surface of the drum, characterized in that the device comprises: a primary fluid passage for circulating the cleaning fluid accommodated in the cleaning tank into the nozzle at a first pressure; a primary filter, disposed in the primary fluid passage, for allowing the cleaning fluid to pass through at a pressure substantially equal to the first pressure; a secondary fluid passage for circulating the cleaning fluid accommodated in the cleaning tank into the nozzle at a second pressure which is lower than the first pressure; and a finishing filter disposed in the secondary fluid passage, and having a porous structure in which the pore size is substantially equal to the prescribed size. In a preferred embodiment, the primary fluid passage is connected to a pump for circulating said cleaning fluid into said passage under a prescribed high pressure. The secondary fluid passage is preferably branched off the primary fluid passage upstream of the primary filter and re-joins said primary fluid passage at a location downstream of the filter, with said cleaning fluid flowing selectively through either said secondary fluid passage or said primary fluid passage. The primary fluid passage itself may be connected to a bypass branched off upstream of a position where said secondary passage is divided off, and a flow rate adjustment valve for adjusting the pressure of said cleaning fluid flowing inside said secondary fluid passage is provided in said bypass passage. The drum itself is typically a photoconductive drum having a photoconductive layer formed on the circumferential surface thereof after cleaning. Particularly with such drums, the primary filter has openings about 10µm in size, so that said cleaning fluid passing through at a high pressure of about 50 kg/cm² may not lose most of the pressure thereof. The finishing filter preferably has openings about 0.2µm in size. Thus, according to the drum cleaning method and device proposed by the present invention, a high-pressure cleaning fluid cleaned with a primary filter is sprayed onto the outer circumferential surface of a drum for effective removal of foreign particles adhering thereto. Furthermore, fine foreign particles passed through the primary filter and redeposited on the drum surface are easily removed using a low-pressure cleaning fluid cleaned with a finishing filter. Therefore, even fine foreign particles deposited on the drum surface can be completely removed by using a relatively small number of filters. For a better understanding of this invention and to show how the same can be carried into effect, reference will now be made by way of illustration only, to the accompanying drawings wherein: Figure 1 is a schematic diagram showing a device of the present invention used to carry out the method proposed by the invention. Figure 2 is a schematic diagram showing a prior drum cleaning device known to the applicant. The drum cleaning method and device proposed by the present invention is applied in the manufacture of a photoconductor drum having a photoconductive layer formed on the outer circumferential surface of an aluminum drum, and used to clean the outer circumferential surface of the aluminum drum on which the photoconductive layer is to be formed. Figure 1 is a schematic diagram showing the device of the present invention used to carry out the method proposed by the invention. As shown, a cleaning tank 30 which contains a cleaning fluid 40 is disposed beneath an aluminum drum 10 to be cleaned, which is held in a vertical position and is movable vertically. Disposed in a horizontal position in the upper part of the cleaning tank 30 are nozzles 20 arranged in a circular configuration having an inside space through which the vertically held aluminum drum 10 can be passed. The nozzles 20 are adapted to spray a cleaning fluid toward the inside space. Degreasing solvents such as dichloromethane, for example, are suitably used as cleaning fluid 40 for cleaning the aluminum drum 10 used in the manufacture of a photoconductor drum. The cleaning fluid 40 is sucked through a drain passage 31 by means of a pump 50 . The discharge pressure of the pump 50 is so set that the cleaning fluid is sprayed through the nozzles 20 under high pressure, for example, a pressure of about 50 kg/cm², is suitable for the cleaning of the aluminum drum 10 . A primary fluid passage 60 is provided for connection between the pump 50 and the nozzles 20 in the cleaning tank 30 . In the primary fluid passage 60 , a pair of solenoid valves 61 and 62 are disposed in this order in the flow direction of the cleaning fluid, and further downstream thereof, there are disposed a primary filter 63 and a solenoid valve 64 in this order in the flow direction of the cleaning solution, the solenoid valve 64 disposed downmost being made to communicate with the nozzles 20 . The primary filter 63 is a coarse filter, for example, having a pore size of about 10 µm and capable of withstanding a high pressure of about 50 kg/cm². A secondary fluid passage 70 branches from the primary fluid passage 60 position between the pair of solenoid valves 61 and 62 disposed in the upper stream section thereof, the opposite end of the secondary fluid passage 70 being connected to the primary fluid passage 60 position downstream of the solenoid valve 64 . In the secondary fluid passage 70 , there are disposed a solenoid valve 71 , a finishing filter 72 , and a solenoid valve 73 in this order down the current of the cleaning fluid. The finishing filter 72 is a fine filter having a pore size of about 0.2 µm, which is the maximum allowable size of foreign particles to be deposited on the aluminum drum 10 after cleaning. A bypass passage 80 branches from the primary fluid passage 60 at a position upstream of the solenoid valve 61 , the opposite end of the bypass passage 80 being connected to the lower part of the cleaning tank 30 . The bypass passage 80 is provided therein with a solenoid valve 81 capable of adjusting the flow rate. In the drum cleaning method of the present invention which is carried out utilizing the above device of the invention, a primary cleaning process is first performed in which the outer circumferential surface of the aluminum drum 10 is cleaned by spraying thereon a cleaning fluid under high pressure. In the primary cleaning process, the solenoid valves 61 , 62 , and 64 in the primary fluid passage 60 are all put in an open condition, while the solenoid valves 71 and 73 in the secondary fluid passage 70 and the solenoid valve 81 in the bypass passage 80 are put in a closed condition. When the pump 50 is driven, the pump 50 draws the cleaning fluid 40 contained in the cleaning tank 30 through the drain passage 31 . The pump 50 then pressurizes the thus drawn cleaning solution to a high pressure of about 50 kg/cm², for example, for discharging therefrom. Since the solenoid valves 61 , 62 , and 64 in the primary fluid passage 60 are all open while the other solenoid valves 71 , 73 , and 81 are all closed, the high-pressure cleaning fluid discharged from the pump 50 flows through the primary fluid passage 60 , passing through the primary filter 63 disposed therein, and is sprayed out of the nozzles 20 disposed in the cleaning tank 30 . Since the cleaning fluid passed through the primary filter 63 reaches the nozzles 20 with almost no pressure loss, the cleaning fluid is sprayed out of the nozzles 20 under a high pressure of about 50 kg/cm². The aluminum drum 10 is passed vertically through the space surrounded by the nozzles 20 while being rotated as necessary. Thus, the cleaning fluid is sprayed under a high pressure of about 50 kg/cm² onto the outer circumferential surface of the aluminum drum 10 . As a result, metal powder, grease, and other foreign particles adhering to the outer circumferential surface of the aluminum drum 10 are effectively removed by mechanical energy. The cleaning fluid used for cleaning the outer circumferential surface of the aluminum drum 10 is collected in the cleaning tank 30 , after which it is drawn by the pump 50 , flows through the primary fluid passage 60 , and is cleaned by the primary filter 63 for recirculation by the nozzles 20 . Relatively large foreign particles contained in the cleaning solution used for cleaning the outer circumferential surface of the aluminum drum 10 are removed when the cleaning solution passes through the primary filter 63 . Foreign particles unable to be trapped by the primary filter 63 may be redeposited on the drum 10 . In the meantime, the aluminum drum 10 is moved up and down a couple of times through the space surrounded by the nozzles 20 to complete the primary cleaning process. After that, to perform a final cleaning process, the solenoid valves 62 and 64 disposed opposite each other across the primary filter 63 in the primary fluid passage 60 are put in a closed condition, while the solenoid valves 71 and 73 in the secondary fluid passage 70 and the solenoid valve 81 in the bypass passage 80 are put in an open condition. This causes a portion of the cleaning fluid discharged from the pump 50 to pass through the bypass passage 80 and flow directly into the cleaning tank 30 , while the remainder of the cleaning fluid is caused to flow through the secondary fluid passage 70 under a reduced pressure. The cleaning fluid admitted into the secondary fluid passage 70 is cleaned by the finishing filter 72 and is fed to the nozzles 20 in the cleaning tank 30 . The solenoid valve 81 provided in the bypass passage 80 works to modulate the flow rate of the cleaning fluid branching into the bypass passage 80 in such a way that the cleaning fluid admitted into the secondary fluid passage 70 flows through the finishing filter 72 under a prescribed pressure. In these circumstances, the aluminum drum 10 is once again passed rotatingly through the inside space surrounded by the nozzles 20 . Thus, the cleaning fluid is sprayed under a relatively low pressure from the nozzles 20 onto the outer circumferential surface of the aluminum drum 10 . lf very fine foreign particles are deposited on the outer circumferential surface of the aluminum drum 10 , since these particles had already been partly removed from the outer circumferential surface of the aluminum drum 10 in the course of the preceding cleaning process using high-pressure cleaning fluid, such foreign particles can be completely removed from the aluminum drum 10 by the cleaning fluid sprayed from the nozzles 20 under a relatively low pressure. The cleaning fluid used for cleaning the aluminum drum 10 and collected in the cleaning tank 30 is cleaned by the finishing filter 72 while passing once again through the secondary fluid passage 70 . Since the finishing filter has a fine porous structure of about 0.2 µm which is the minimum size of foreign particles that must be removed after cleaning the aluminum drum 10 , the cleaned cleaning fluid does not contain fine foreign particles, the adherence of which to the aluminum drum 10 may cause a problem. Thus the possibility of redeposition to the outer circumferential surface of the aluminum drum 10 of foreign particles that may cause a problem when the aluminum drum 10 is cleaned with the cleaned cleaning fluid is eliminated. Further, since the cleaning fluid is passed through the finishing filter 72 under low pressure, there is no possibility of damage to the finishing filter 72 . By thus cleaning the aluminum drum 10 , even fine foreign particles adhering to the outer circumferential surface of the aluminum drum 10 are completely removed therefrom. Furthermore, the above method requires the provision of only two filters, the primary filter 63 and the finishing filter 72 , for cleaning the cleaning fluid. In the above embodiment, one pump is used to circulate the cleaning fluid by switching between the primary fluid passage 60 provided with the primary filter 63 and the secondary fluid passage 70 provided with the finishing filter 72 , but it will be appreciated that the application of the invention is not limited to the above embodiment. For example, a pump for circulating the cleaning fluid through the primary fluid passage 60 provided with the primary filter 63 may be provided separately from a pump for circulating the cleaning fluid through the secondary fluid passage 70 provided with the finishing filter 72 so that the cleaning fluid is circulated first through the primary fluid passage 60 for high-pressure cleaning and then through the secondary fluid passage 70 for high-precision cleaning.

Claims: A method of cleaning a drum (10) by spraying a cleaning fluid (40) on the outer circumferential surface of the drum (10) to remove particles of foreign matter larger than a prescribed size, the cleaning fluid (40) being recirculated after being sprayed on the drum (10), the method comprising: a primary cleaning step in which the cleaning fluid (40) is sprayed onto the outer circumferential surface of the drum (10) at a first pressure and in which the cleaning fluid (40) is passed through a primary filter (63), the primary filter (63) having a porous structure in which the pore size is larger than the prescribed size; and a final cleaning step, following the primary cleaning step, in which the cleaning fluid (40) is sprayed onto the outer circumferential surface of the drum (10) at a second pressure which is lower than the first pressure, and in which the cleaning fluid (40) is passed through a finishing filter (72), the finishing filter (72) having a porous structure in which the pore size is substantially equal to the prescribed size. A method of cleaning a drum according to claim 1, wherein the drum (10) is provided with a photoconductive layer on the outer circumferential surface thereof after cleaning. A method of cleaning a drum according to claim 1 or 2, wherein the size of each pore of the primary filter (63) is approximately 10 µm. A method of cleaning a drum according to any one of the preceding claims, wherein the size of each pore of the finishing filter (72) is approximately 0.2 µm. A device for cleaning a drum (10) to remove particles of foreign matter larger than prescribed size, the drum (10) being cleaned by spraying a cleaning fluid (40) on the outer circumferential surface thereof and by circulating the cleaning fluid (40) which has been sprayed, the device comprising: at least one nozzle (20) for spraying the cleaning fluid (40) on the outer circumferential surface of the drum (10); and a cleaning tank (30) for accommodating the cleaning fluid (40) which has been sprayed on the outer circumferential surface of the drum (10), characterized in that the device comprises: a primary fluid passage (60) for circulating the cleaning fluid (40) accommodated in the cleaning tank (30) into the nozzle (20) at a first pressure; a primary filter (63), disposed in the primary fluid passage (60), for allowing the cleaning fluid (40) to pass through at a pressure substantially equal to the first pressure; a secondary fluid passage (70) for circulating the cleaning fluid (40) accommodated in the cleaning tank (30) into the nozzle (20) at a second pressure which is lower than the first pressure; and a finishing filter (72) disposed in the secondary fluid passage (70), and having a porous structure in which the pore size is substantially equal to the prescribed size. A device according to claim 5, wherein the primary fluid passage (60) is connected to a pump (50) for circulating the cleaning fluid (40) into the primary fluid passage (60) under the first pressure. A device according to claim 5 or 6, wherein the secondary fluid passage (70) is branched off the primary fluid passage (60) upstream of the primary filter (63) and rejoins the primary fluid passage (60) downstream of the primary filter (63), means being provided for directing the cleaning fluid (40) selectively through either the primary fluid passage (60) or the secondary fluid passage (70). A device according to any one of claims 5 to 7, wherein a bypass passage (80) is branched off the primary fluid passage (60) upstream of a position where the secondary fluid passage (70) is branched off, and a flow rate adjustment valve (81) for adjusting the second pressure of the cleaning fluid (40) flowing inside the secondary fluid passage (70) is provided in the bypass passage (80). A device according to any one of claims 5 to 8, wherein the primary filter (63) has a plurality of pores, the size of each pore being approximately 10 µm. A device according to any one of claims 5 to 9, wherein the secondary filter (72) has a plurality of pores, the size of each pore being approximately 0.2 µm.

Inventors: GOTOH MASARU, GOTOH, MASARU
Applicants: MITA INDUSTRIAL CO LTD, MITA INDUSTRIAL CO., LTD.
Application year: 1990
Main classification: G03G5
IPC codes: B08B9, B08B3, G03G5, B01D35