Cleaning sheet for fixating rotational member and image forming apparatus having fixating rotational member

Abstract: A cleaning sheet for a fixating rotational member has a tacky layer provided on at least one surface of the cleaning sheet and having tackiness to toner at least when the cleaning sheet is conveyed to the fixating rotational member.

Description: The present invention relates to a printing apparatus according to the preamble of claim 1. In image forming apparatus such as copying apparatuses, laser beam printers and magnestylus printers, it is widely practised to form an unfixated toner image on a support material, and thereafter effect fixation by a fixating rotational member, particularly, a pair of rotational members. In order to prevent toner and paper powder adhering to the fixating rotational member(s) from spreading to the support material to deteriorate the quality of image, felt, a web or the like is brought into contact with the fixating rotational member(s) to thereby clean the latter. An example of such a fixating device is shown in Figure 3 of the accompanying drawings. The reference numeral 1 designates a fixating roller which comprises a mandrel 12 of aluminum, iron or like material and a resin layer 13 of good parting property such as PFA or PTFE provided on the mandrel 12 and the interior of which may be heated by a heater H. The surface temperature of the fixating roller 1 is detected by a temperature detecting element 19, and is controlled to a predetermined temperature by turning on or off the heater H by a temperature control circuit (not shown). On the other hand, the reference numeral 2 denotes a pressing roller which comprises a metallic mandrel 21 of iron, stainless steel or the like and an elastic material layer 22 of silicone rubber, fluorine rubber or the like having a heat resisting property and a good parting property and formed on the metallic mandrel 21. A recording material P carrying a toner image T thereon is directed to between the fixating roller 1 and the pressing roller 2 by an entrance guide 23, and is heated and pressed, whereby the image is fixated. Thereafter, the recording material P is peeled from the fixating roller 1 by a separating pawl 10. The reference numeral 18 designates cleaning felt which comprises a felt material such as Normex (the registered trademark of Du Pont, Inc.) impregnated with a parting agent such as silicon oil and serves to remove toner and paper powder adhering to the surface layer of the fixating roller 1. In recent years, however, as the tendency of the apparatus toward compactness and lower cost has progressed, the desire to eliminate the cleaning device has become stronger. For this reason, efforts have been made to improve the parting (mold releasing) property of the surface of the fixating rotational member and overcome the electrostatic problem, but it has been impossible to keep a good quality of image for a long period of time. Particularly, as regards the pair of rotational members, the stains of that rotational member which does not contact with the unfixated toner image have been serious and the problem of the stained back of the support material has occurred. According to document EP-A1-0 281 372, there is known a similar printing apparatus according to the preamble of claim 1. This generic apparatus is provided with a device which judges when a process unit has reached its life expiry by comparing the output of a sensor for detecting the density of toner contained in the developing device with a predetermined value and detecting when the output of this sensor is above the predetermined value. By means of this printing apparatus it is not possible to keep the surface of the fixating rotational member belonging to the fixing device clean for a long period of time and to maintain a good image quality. The "IBM Technical Disclosure Bulletin", vol. 25, no. 7B, December 1982, pages 3986-3987, discloses a heated fuser roll cleaning process, wherein the function of a cleaning member could not only be performed by a scrabble blade, but also by a cleaning sheet being a clean copy sheet, wherein the cleaning processes are performed by transferring to said clean copy sheet as much of the residual toner as possible. According to the "Research disclosure", no. 127, November 1974, pages 30-32, there is disclosed a method of cleaning a rotational member of an image forming apparatus by using a sheet copy provided with unfixated toner images. This method comprises, prior to the fixating or fusing the toner particles with a pressure member, the step of randomly distributing over generally the entire surface of the support material or copy and the toner particles on the support material are a finely-divided resinous powder, and thereafter impacting the support material surface, toner particles and powder with the pressure member having a temperature effective to adhere contaminants contained on said pressure member to the powder and to fuse the powder to the support material, thereby cleaning the pressure member. It is the object of the present invention to provide a printing apparatus by means of which it is possible to keep a good image quality for a long period of time. The object of the invention is achieved by means of the features indicated in claim 1. According to these features there are provided a ROM for storing an image signal corresponding to a pattern image and input means for inputting the pattern image signal which is output from the ROM to the image forming means to form a cleaning member consisting of a recording material on which the pattern image is formed, wherein, in use, the rotational members are cleaned by reversing and refeeding the cleaning member therebetween after the cleaning member has been discharged to the outside of the printing apparatus. Preferable embodiments of the invention are defined in the claims 2 to 6. In the following the invention is further illustrated by embodiments with reference to the enclosed figures. Figure 1 is a side view of a cleaning sheet. Figure 2 is a top plan view of the Figure 1. Figure 3 is a longitudinal cross-sectional view of a fixating device according to the prior art. Figure 4 is a longitudinal cross-sectional view of a laser beam printer according to an embodiment of the present invention. Figure 5 is a top plan view showing the test print pattern image by an embodiment of the present invention. Figure 6A is a top plan view showing the test print pattern image by another embodiment of the present invention. Figure 6B is an illustration of Figure 6A. Figure 7 is a top plan view showing the test print pattern image by still another embodiment of the present invention. The reference numeral 11 in Figure 1 designates a sheet substrate formed of paper or resin. The reference numeral 12 denotes a tacky layer provided on the sheet substrate 11, and the arrow A indicates the direction of conveyance during the use of the cleaning sheet. The tacky layer 12 is formed leaving the end portions of the sheet as viewed in the direction of conveyance. Therefore, the sheet can be reliably separated without twining around a fixating rotational member of a printing apparatus. Also, this cleaning sheet is provided at the maximum paper supply width size of the apparatus used and over the full width in a direction intersecting the direction of conveyance. (That is, it is provided at A4 width if the maximum paper supply size is A4). Therefore, there is no problem in the conveyance property, and it is possible to remove all stains which pose a problem. Further, the length of the tacky layer in the direction of conveyance is greater than the circumferential length of the rotational member to be cleaned. Therefore, the rotational member can be reliably cleaned over the full circumference thereof by the supply of a single cleaning sheet. In the heat fixating rollers of the fixating device of an electrophotographic apparatus, the fixating roller comprises a cylindrical aluminum alloy mandrel having an outer diameter of 20 mm and a thickness of 2 mm and having the surface thereof coated with PFA resin, and the pressing roller comprises a stainless steel mandrel having an outer diameter of 10 mm and an elastic layer of silicone rubber provided on the mandrel so that the outer diameter thereof is 20 mm. The fixating roller and the pressing roller are urged against each other with a predetermined pressure force of 60 kg. These are not provided with a cleaning device. The fixating roller is maintained at about 150 °C. When a predetermined number of sheets are used, paper powder and toner adhere to the surface of the pressing roller over a wide area thereof and the conveyance property and fixativeness are extremely aggravated. When in this state, said cleaning sheet was passed between the rollers with the coated surface of the cleaning sheet facing the pressing roller, the paper powder and toner adhering to the surface of the pressing roller all shifted to the surface of the cleaning sheet and the stains on the surface of the pressing roller were all removed and the surface of the pressing roller recovered its initial state. The cleaning sheet has no tackiness at room temperature, and it obtains tackiness by being heated by the fixating roller. Therefore, this cleaning sheet can be used in an apparatus having a member contacting with the tacky layer in the course of conveyance to the fixating roller, and is particularly effective for an image forming apparatus of the transfer type in which an unfixated toner image on a photosensitive member is transferred to a support member by a transfer device. Also, in this case, the material of the tacky layer may most preferably be the same material as the toner used in the image forming apparatus, from the viewpoint of the cleaning property of offset toner. Thus, offset toner or the like is removed by the cleaning sheet and therefore, without providing any special cleaning mechanism for the fixating rotational member, good fixated images can be obtained for a long period of time. Figure 4 is a cross-sectional view of a laser beam printer which is an electrophotographic apparatus of the digital recording type according to an embodiment of the present invention. Recording materials are piled in a cassette 62, and are fed one by one by a paper feed roller 63 with a print starting command input from a computer or the like, not shown. Register rollers 64 feed out the recording material in timed relationship with a photosensitive drum 41 so that the leading end edge of the image on the photosensitive drum 41 and the leading end edge of the recording material may be coincident with each other. On the photosensitive drum 41 uniformly charged by a charger 42, an electrostatic latent image conforming to an image signal is formed by the photosensitive drum being scanned by a laser beam emitted from a laser scanner 66 containing therein a semiconductor laser emitting a laser beam modulated in conformity with the image signal, a rotatable polygonal mirror for deflecting the laser beam emitted from the semiconductor laser etc. The reference numeral 67 designate a reflecting mirror for reflecting the laser beam. The electrostatic latent image thus formed on the photosensitive drum 41 is visualized into an unfixated toner image by a developing device 43 and transferred onto the recording material by a transfer charger 46. Any excess charges accumulated on the recording material are removed by a charge removing needle 47, and the unfixated toner image on the recording material is fixated by heat and pressure being applied thereto when the recording material is nipped and conveyed by a fixating roller 1 and a pressing roller 2. On the other hand, any toner and paper powder remaining on the photosensitive drum 41 are removed by a cleaner 45, and any charges remaining on the photosensitive drum 41 are also removed by a pre-exposure lamp 48. The photosensitive drum 41 is then utilized again for the primary charging and subsequent steps. These image forming processes, the control of the conveyance of the recording material, etc. are controlled by a CPU provided on an electrical base plate 68. An ROM for storing the image signal of a test pattern therein is also provided on the electrical base plate 68, and by depressing a test print switch 69, the laser beam is modulated by the image signal output from the ROM, whereby an image of predetermined pattern is formed on the recording material, which is then discharged. By reversing and refeeding the recording material on which this pattern has been formed, the cleaning of the pressing roller is accomplished. The image of the test pattern will now be described with reference to Figure 10. This pattern is endowed with blanks of ℓ₁ and ℓ₃ at the front end and rear end thereof, respectively. The blanks of ℓ₁ and ℓ₃ are for making it easy to separate the test pattern from the pressing roller during the resupply of paper, and according to the experiment, they may be 4 mm or more, and more preferably be 10 mm or more. The reason why such blanks are provided at the opposite ends is that the user may supply paper in any direction. Also, the solid painted portion has a length ℓ₂ with respect to the direction of feeding. This ℓ₂ may be equal to or greater than the circumferential length of the pressing roller, and may preferably be greater than the maximum circumferential length of the fixating roller and the pressing roller. The width w of the solid painted portion should be smaller than the width of a recording material of maximum size supplied and wider than the maximum printable area (the image area). This is for the purpose of making it possible to clean a widest possible area. Particularly, in the printer of the present embodiment, the right and left ends of the recording material are designed to limit a signal so that the image may not protrude. This is for the purpose of ensuring the quality of image because in the right and left end portions, the image is disturbed by curling or waving. In the case of this test pattern, it is not necessary to ensure the image in the opposite end portions and moreover, the width of the test pattern may preferably be as great as possible in order that it may be used as cleaning paper. Where the cassette 62 can be provided with means for detecting the size of the recording materials, the width w may be automatically set in accordance with the size of the recording materials. Usually, blanks of the order of 4 mm are provided at the right and left ends. In contrast, the width w may be determined so that the blanks may be 4 mm or less. Particularly, to clean a greatest possible width, it is preferable to use a transfer material of the greatest usable width as a cleaning sheet. The user can supply the test pattern output in this manner so that the printed surface thereof may contact with the pressing roller or the like having on the surface thereof an elastic layer having a parting property and a heat resisting property, thereby adsorbing and removing toner and paper powder offset to the surface of the roller. This is because there is good affinity between the solid painted portion and the offset toner and the offset toner can be adsorbed and removed. Particularly, immediately after a test print has been effected, the pressing roller is warm and the cleaning paper is also warm and therefore, the toner is ready to melt, and the cleaning effect becomes greater than when cleaning paper prepared in advance is passed. When the present invention was carried out and the cleaning of the roller was effected for each 10,000 prints, the service life of the pressing roller could be prolonged up to 150,000 sheets although in the past, the surface of the pressing roller was stained with toner for the order of 50,000 sheets and twining or jamming occurred to give rise to a problem. Another embodiment of the test pattern image will now be described. Figure 6A is a top plan view showing a test pattern image. In the present embodiment, solid painted portions and white ground portions are designed to be alternately printed in the direction of conveyance of the recording material. As shown in Figure 6B, the length ℓ₄ of the solid painted portion is made greater than the length ℓ₆ when the outer periphery of a roller to be cleaned is equally divided into 2n-1, and the length ℓ₅ of the blank portion is made so that ℓ₄ + ℓ₅ equals 2 ℓ₆ (n being a positive integer). The number of the solid painted portions is made greater than 2n-1. By supplying a recording material on which this pattern is printed so that the printed surface thereof may contact with the roller to be cleaned, the surface of the roller can be entirely cleaned. In the first embodiment, if small-dimensioned thin paper is used, because of its weak rigidity, the separability of the recording material of Figure 13 is improved from halfway of the recording material relative to the pressing roller and thus, it has become possible to prevent twining and at the same time, maintain the cleaning performance. The reason why in this embodiment, it is preferable that the outer periphery of the roller equally divided into 2n-1 be ℓ₆ is that if the recording material is so divided when twined around the roller, the solid painted portions will not overlap one another during the first and second rounds and cleaning can be accomplished efficiently. If the solid painted portions and the blank portions are formed at the same period when the outer periphery of the roller is equally divided into 2n, the solid painted portions will overlap one another during the first and second rounds and thus, portions which cannot be cleaned will be formed on the roller. In order to avoid this, there will arise the necessity of providing a blank between the first round and the second round and the procedure of memory or control will be required, and this means an economical disadvantage. Accordingly, the lengths ℓ₄ and ℓ₅ of the solid painted portion and the blank portion, respectively, may be arbitrary, but most preferably, design may be made such that as previously described, relative to the length ℓ₆ when the outer periphery of the roller is equally divided into 2n-1, 2 ℓ₆ = ℓ₄ + ℓ₅. A further preferred embodiment of the test pattern image will now be described with reference to Figure 12. This embodiment is such that as in the aforedescribed two embodiments, a solid painted portion is provided and a comment for the user is printed on a blank portion. The substance of this comment may be any if it instructs the user that the paper used is cleaning paper so that the user can rightly perform the cleaning operation by seeing the print on the blank portion which is indicative of the direction in which the cleaning paper should be placed on a paper supply cassette or a paper supply tray (not shown). Thus, although in the aforedescribed embodiment, it has sometimes happened that cleaning cannot be accomplished due to an erroneous operation and the pressing roller is stained and cannot keep its life, such a thing does not happen in the present embodiment and also, the apparatus could be made easy for the user to use.

Claims: A printing apparatus comprising: image forming means (66, 67) for forming an unfixated toner image on a recording material (P) in conformity with an image signal, and a pair of rotational members (1, 2) for nipping and conveying said recording material (P) therebetween and fixating the unfixated toner image on said recording material (P), said printing apparatus being characterized by ROM (68) for storing an image signal corresponding to a pattern image (A), and input means (69) for inputting said pattern image signal which is output from said ROM to said image forming means (66, 67) to form a cleaning member consisting of a recording material on which said pattern image (A) is formed, wherein, in use, said rotational members (1, 2) are cleaned by reversing and refeeding said cleaning member therebetween after said cleaning member has been discharged to the outside of said printing apparatus. A printing apparatus according to claim 1, characterized in that said input means comprises a test print switch (69) for inputting said pattern image signal from said ROM to said image forming means (66, 67) to form a cleaning member on which said pattern image (A) is formed by operation of said image forming means. A printing apparatus according to claim 2, characterized in that the length of said recording material (P) for said pattern image (A) in the direction of conveyance thereof is greater than the circumferential length of said rotational member (2) opposite to said rotational member (1) which contacts said unfixated toner image. A printing apparatus according to claim 2, characterized in that the width of said recording material (P) for said pattern image (A) in a direction orthogonal to the direction of conveyance thereof is greater than the image area. A printing apparatus according to claim 1, c haracterized in that said ROM furthermore stores an image signal corresponding to a comment, wherein both said pattern image (A) and the image of said comment are formed on the same recording material (P) by said output image signal from said ROM. A printing apparatus according to claim 1, characterized in that blank portions are provided on leading and trailing end portions of said recording material (P) on which said pattern image (A) has been formed by said output signal from said ROM, with respect to the direction of conveyance of said recording material (P).

Inventors: KISHINO KAZUO, MIYABAYASHI TOSHIYUKI, OHTSUKA YASUMASA, TAKAHASHI MASAAKI, TOMOYUKI YOJI, KISHINO, KAZUO, MIYABAYASHI, TOSHIYUKI, OHTSUKA, YASUMASA, TAKAHASHI, MASAAKI, TOMOYUKI, YOJI
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1989
Main classification: G03G15
IPC codes: G03G15