JP2018084708A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent abnormal vibration or turn-up during reverse rotation of a cleaning blade caused by an ozone product accumulated on an image carrier.SOLUTION: An image forming apparatus controls to rotate an image carrier having a certain area of concave parts in the reverse direction, and is provided with a configuration or a control mechanism to increase, during the rotation in the reverse direction, a hole inclination angle of the concave parts at the peripheral edge on the upstream side in the direction of rotation of the image carrier compared with a dynamic contact angle of a cleaning blade, in order to remove and store a causative agent obtained by polishing through a reverse rotation operation in the holes of the concave parts.SELECTED DRAWING: Figure 5

Description

  The present invention has a cleaning blade for cleaning a developer remaining on an image carrier having concave portions at a predetermined ratio on the surface, and after image formation is completed, the image carrier is rotated in a direction opposite to the rotation direction of the image carrier. A control mechanism that performs a rotation operation, and a configuration in which the recess hole inclination angle at the upstream peripheral edge of the rotation of the image carrier is larger than the dynamic contact angle of the cleaning blade during the reverse rotation control operation, or a control mechanism is provided. By this, the causative substance of abnormal blade vibration is ground and accommodated in the concave hole, and the inclination angle of the concave hole at the upstream peripheral edge of the rotation of the image carrier is controlled from the dynamic contact angle of the cleaning blade when controlling the normal rotation operation before image formation. An image forming apparatus characterized in that the causative substance accommodated in the recess hole is removed by providing a small configuration or a control mechanism.

  In recent years, a technique for increasing the mechanical strength of a surface layer has been developed for the purpose of improving the wear resistance and scratch resistance of an electrophotographic photosensitive member.

  However, in the case of an electrophotographic photosensitive member with high mechanical strength, it adheres to a photosensitive drum in a high-temperature and high-humidity environment due to energy saving and a drum heater-less operation in a high-temperature and high-humidity environment as image formation proceeds. Image blur due to poor charging (so-called image flow) starting from the ozone product is an important issue.

Furthermore, in recent years, it has been taken up as an urgent solution in conjunction with a decrease in the rubbing and polishing performance due to the cleaning member accompanying a reduction in the amount of toner on the drum for the purpose of reducing the toner consumption rate.
In contrast, conventional
1. Improve the polishing performance of the image carrier surface (reduce the content of lubricating fine particles)
2. Improved blade polishing ability (physical properties such as higher hardness, higher set pressure, etc.)
3. Increased abrasiveness by supplying toner band
4). Abrasiveness improvement by drum idle rotation sequence
Etc. have been implemented,
1. With regard to, there is a decrease in the life of the drum and a decrease in cleaning performance due to the rough surface of the drum
2. As for the abnormal vibration of the blade and the increase of turning over
3. As for the toner consumption rate UP, RC UP, development life reduction
4). However, important problems remain such as a reduction in image formation productivity.

  However, in order to remove the causative substances adhering to the surface, when the idle rotation sequence is performed, the collected toner deposited on the edge tip of the cleaning blade is depleted, and it is easy to cause abnormal vibration of the blade and turning over. Currently. In response to this problem, Patent Document 1 proposes a control configuration in which the image carrier is reversely rotated at a predetermined image forming interval.

JP 2011-150293 A

  However, the polishing powder after the reverse rotation is redeposited on the edge with the forward rotation of the image carrier, which causes a secondary problem that becomes the starting point of defective cleaning. Alternatively, in order to secure the assumed polishing amount, an excessive reverse rotation operation must be performed, and the collected toner deposited on the edge is depleted, and the same problem occurs.

On the other hand, in the present invention, for the purpose of improving the polishing property of the surface of the photosensitive drum, a solution is achieved by combining the photosensitive drum having a concave shape on the surface layer with the following mechanism or control mechanism. .
-A mechanism for predicting and detecting the occurrence of abnormal blade vibration due to the image carrier adhering matter is provided.
A mechanism is provided for controlling the reverse rotation of the photosensitive drum after completion of image formation when occurrence of abnormal blade vibration due to the image carrier adhering matter is predicted. (At this time, a physical action is generated such that the contact surface and the vicinity of the blade in the circumferential direction of the photosensitive drum can be slidably moved with the peripheral edge of the concave hole of the photosensitive drum.)
The cleaning blade has a two-layer structure, and the angle is set so that the surface layer having a high polishing power contacts the photosensitive drum during the reverse rotation control.

  In the image forming apparatus of the present invention, when the reverse rotation control is performed, the contact polishing surface of the cleaning blade contacts and moves to the peripheral edge of the recess hole, thereby polishing and removing the causative substance of the blade abnormal vibration, and It was possible to scrape into the recess hole, and it was possible to efficiently suppress the contamination of the blade and remove the causative substance.

Further, by using two cleaning blades, the causative substance at the time of reverse rotation can be efficiently removed in a shorter time.

  As described above, it is possible to ensure a long-term stable cleaning property.

FIG. 2 is a schematic cross-sectional view around the image carrier in the first embodiment of the present invention. It is principal sectional drawing in the 1st Example of this invention. It is the schematic diagram which looked at the recessed part shape of the image carrier surface in the 1st Example of this invention from right above. It is the schematic diagram which showed the recessed part cross-sectional shape of the image carrier surface in the 1st Example of this invention. In the first embodiment of the present invention, in the schematic diagram of the concave cross-sectional shape of the surface of the image carrier, it is a diagram defining the hole inclination angle of the upstream end portion of the concave hole at the time of reverse rotation of the image carrier. In the first embodiment of the present invention, in the schematic diagram of the cross-sectional shape of the concave portion on the surface of the image carrier, it is a diagram defining the hole inclination angle of the upstream end portion of the concave hole at the time of normal rotation of the image carrier. FIG. 5 shows the relationship between the image DUTY, the cleaning blade rubbing torque value, and the presence / absence of abnormal vibration / reversal turning of the cleaning blade in the first embodiment of the present invention. The relationship between the arbitrary image DUTY and the internal temperature / humidity region where the abnormal vibration of the blade occurs in the first embodiment of the present invention is shown. FIG. 3 is a schematic operation diagram of a reverse rotation control mechanism for an image carrier in the first embodiment of the present invention. FIG. 5 is a schematic cross-sectional view showing the sliding operation of the cleaning blade contact surface in the image carrier recess hole G in the first embodiment of the present invention. FIG. 5 is a schematic cross-sectional view showing the sliding operation of the cleaning blade contact surface in the image carrier recess hole G during the image carrier reverse rotation operation of the first embodiment of the present invention. FIG. 3 is a schematic diagram showing a rubbing operation of a blade contact surface during normal rotation of the image carrier of the first embodiment of the present invention. 2 shows the relationship between the rubbing torque between the image carrier and the cleaning blade and the number of images formed in the first embodiment of the present invention. FIG. 5 shows the relationship between the reverse rotation speed of the image carrier and the blade dynamic contact angle in the first embodiment of the present invention. FIG. FIG. 6 shows the relationship between the surface of the image carrier, the rubbing torque of the cleaning blade, and the number of images formed in the second embodiment of the present invention. FIG. 5 shows a layer structure of a two-layer blade member that contacts an image carrier in a third embodiment of the present invention. FIG. FIG. 6 shows the relationship between the rubbing torque between the image carrier and the cleaning blade and the number of sheets passing in the third embodiment of the present invention. FIG. 5 shows a blade in contact with an image carrier in which a chip-like rubber material having physical properties different from those of a base layer is arranged on the surface layer in a third embodiment of the present invention.

[Example 1]
FIG. 1 is a diagram showing a schematic cross-sectional configuration around an image carrier of an image forming apparatus according to an embodiment of the present invention. As a schematic configuration, the developing device 4 is an electrostatic image forming apparatus that rotates in the forward direction with respect to the photosensitive drum 1.

In the figure, reference numeral 1 denotes a photosensitive drum which is an image carrier, and 3 denotes a scanning optical unit and a polygon mirror constituting image exposure means for forming a latent image on the photosensitive drum 1. Here, as the photoreceptor drum 1 used in the present invention, a commonly used organic photoreceptor can be used. Preferably, a material having a resistance of 10E9 to 10E14 Ω · cm is formed on the organic photoreceptor. When a material having a surface layer is used, charge injection charging can be realized, which is effective in preventing ozone generation and reducing power consumption. In addition, the chargeability can be improved.
Hereinafter, the organic photosensitive drum used in the present embodiment will be schematically described.

<Support>
As the conductive support of the photoreceptor used in the present invention, for example, metals such as AL, Cr, Mo, Au, In, Nb, Te, V, Ti, Pt, Pd, Fe, and alloys thereof, For example, stainless steel, etc. In addition, at least light reception of an electrically insulating support such as polyester, polyethylene, polycarbonate, cellulose acetate, polypropylene, polyvinyl chloride, polystyrene, polyamide, or a synthetic resin film or sheet, glass, ceramic, etc. A support obtained by conducting a conductive treatment on the surface on which the layer is formed can also be used. Furthermore, it is more preferable to conduct the conductive treatment on the surface opposite to the side on which the photoconductive layer is formed.

<Photosensitive layer>
In this embodiment, as described above, a photosensitive layer having a carrier generation layer (CGL) as a charge generation layer and a carrier transport layer as a charge transport layer on the surface of a cylindrical aluminum substrate as a conductive support is used as a carrier. The transport layer (CTL) was coated to have a thickness of 30 μm, and a JIS surface roughness (B0601) with an Rz (10-point average roughness) of 2 μm or less in the initial state was used.

  As described above, the photosensitive layer of the electrophotographic photosensitive member used in the present invention includes at least the charge generation material constituting the carrier generation layer (CGL) here and the charge transport constituting the carrier transport layer (CTL) here. Material.

  Examples of charge generation materials other than this example include phthalocyanine pigments, polycyclic quinone pigments, azo pigments, perylene pigments, indigo pigments, quinacridone pigments, azulenium salt dyes, squarylium dyes, cyanine dyes, pyrylium dyes, thiopyrylium dyes, Examples thereof include xanthene dyes, quinoneimine dyes, triphenylmethane dyes, styryl dyes, selenium, selenium-tellurium alloys, amorphous silicon, and cadmium sulfide.

  Examples of charge transport materials include pyrene compounds, N-alkylcarbazole compounds, hydrazone compounds, N, N-dialkylaniline compounds, diphenylamine compounds, triphenylamine compounds, triphenylmethane compounds, pyrazoline compounds, styryl compounds, stilbene compounds, Examples thereof include polynitro compounds and polycyano compounds, and pendant polymers in which these compounds are fixed on the polymer.

  The photosensitive layer may have a single layer structure or a stacked structure as in this embodiment. In the case of a laminated structure, it is composed of at least a charge generation layer and a charge transport layer, and the charge polarity, the toner polarity to be used, etc., when the charge generation layer is provided on the conductive support 51 and when the charge transport layer is provided. Is different.

  In the case of a laminated structure, the thickness of the charge generation layer is 0.001 to 6 μm, preferably 0.01 to 2 μm. The content of the charge generation material contained in the charge generation layer is preferably 10 to 100% by mass, and more preferably 50 to 100% by mass.

  The film thickness of the charge transport layer is 5 to 40 μm, preferably 15 to 30 μm. The content of the charge transport material contained in the charge transport layer is preferably 20 to 80% by mass, more preferably 30 to 70% by mass.

  As the conductive support, metal or alloy such as iron, copper, gold, silver, aluminum, zinc, titanium, lead, nickel, tin, antimony and indium, oxide of the metal, carbon, conductive polymer, etc. are used. Possible shapes include drums such as cylinders and columns, belts, and sheets. The conductive material may be molded as it is, used as a paint, deposited, or processed by etching or plasma treatment. In the case of paint, the above-mentioned metal, alloy, paper, plastic, etc. are also used as a support.

  An undercoat layer that functions as a charge injection control at the interface or an adhesive layer may be provided between the conductive support and the photosensitive layer. The undercoat layer is mainly composed of a binder resin, but may contain these metals and alloys or their oxides, salts, surfactants and the like. The thickness of the undercoat layer is preferably 0.05 to 7 μm, more preferably 0.1 to 2 μm.

  Examples of the binder resin that forms the undercoat layer include polyester, polyurethane, polyarylate, polyethylene, polystyrene, polybutadiene, polycarbonate, polyamide, polypropylene, polyimide, phenol resin, acrylic resin, silicone resin, epoxy resin, urea resin. , Allyl resin, alkyd resin, polyamide-imide, polysulfone, polyallyl ether, polyacetal, butyral resin, and the like.

  In the present invention, the fluorine atom-containing resin fine particles are dispersed in a binder resin having film-forming properties, together with the charge generation material and charge transport material of the photosensitive layer formed as the surface layer, or Then, the dissolved solution is applied and dried to form a protective layer. Here, it applied as a protective layer on the surface of the photosensitive layer.

  Examples of the binder resin include polyester, polyurethane, polyarylate, polyethylene, polystyrene, polybutadiene, polycarbonate, polyamide, polypropylene, polyimide, phenol resin, acrylic resin, silicone resin, epoxy resin, urea resin, allyl resin, alkyd resin, Examples thereof include polyamide-imide, polysulfone, polyallyl ether, polyacetal, and butyral resin.

  Fluorine atom-containing resin particles include polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinylidene fluoride, polydichlorodifluoroethylene, tetrafluoroethylene, perfluoroalkyl vinyl ether copolymer, tetrafluoroethylene-hexafluoropropylene copolymer. Examples include polymers, tetrafluoroethylene-ethylene copolymers, and tetrafluoroethylene-hexafluoropropylene-perfluoroalkyl vinyl ether copolymers. These may be used alone or in combination of two or more. Also good.

  The molecular weight of these resin particles is preferably 3,000 to 5,000,000 in terms of weight average molecular weight, and the particle size is preferably 0.01 to 10 μm, particularly 0.05 to 2.0 μm. Is preferred.

  And in this invention, content of the fluorine atom containing resin particle of the protective layer 56 which is a surface layer is 5.0-45.0 mass% with respect to the surface layer 56 total mass, More preferably, it is 10.0. It is -35.0 mass%. If the content is less than 5.0% by mass, sufficient lubricity may not be obtained, and if it exceeds 45.0% by mass, it is not preferable from the viewpoint of film formability and sensitivity of the layer.

<Details of recess shape>
Here, the concave shape applied to the outermost layer of the photosensitive drum 1 will be described. FIG. 3 is a schematic view of the concave shape of the surface layer of the photosensitive drum 1 as viewed from directly above. FIG. 4 is a schematic diagram showing the cross-sectional shape of the recess on the surface of the image carrier in the first embodiment of the present invention. A specific concave portion and a flat portion are provided on the surface of the photosensitive drum 1. Plateau, when placing a square area of 500 um × 500 um at an arbitrary position of the photoreceptor surface, it is provided such that the area of the flat portion becomes 81000Um ² more ～240000Um ² or less. Incidentally, if the shape of the concave portion is too large, the cleaning property is deteriorated, so that the lower limit of the area of the flat portion is specified. If the shape of the concave portion is too small, the effect of preventing the image flow is reduced, and thus the upper limit is specified.

  As for the specific recess shape, the depth of the recess in the 500 μm × 500 μm square region is in the range of 0.5 μm to 6 μm, and the maximum opening diameter is in the range of 20 μm to 80 μm.

  In addition, a flat part and a specific recessed part shape can be observed using a laser microscope, an optical microscope, an electron microscope, etc. As a manufacturing method, a surface-treated mold having a convex shape corresponding to the concave shape to be formed is pressed against the surface of the photosensitive member 1 while the surface layer is heated on the surface of the photosensitive drum 1 to transfer the shape. Created by.

  FIG. 5 shows the inclination angle shape of the concave hole G at the upstream end JF of the concave hole G when the photosensitive drum rotates backward, which is the core of the present invention. The angle θ1 between the normal line perpendicular to the straight line connecting the end point of the contact NIP with the cleaning blade 61 and the rotation center of the photosensitive drum 1 and the contact surface of the cleaning blade 61 in the recess hole of the photosensitive drum 1, the recess The angle between the straight line connecting the upstream end JF of the hole and the rotation center of the photosensitive drum 1 and the normal line was set to satisfy θ2, θ1 = <θ2 (image carrier reverse rotation period).

  That is, when the photosensitive drum 1 rotates in the reverse direction, the inclination angle of the upstream recessed hole G is configured to be equal to or larger than the dynamic contact angle of the cleaning blade 61. In this embodiment, the angle θ1 is set to about 23 ° and the angle θ2 is set to 25 °.

  FIG. 6 shows an inclined angle shape of the recessed hole G at the upstream end KF of the recessed hole G when the photosensitive drum 1 is rotated forward. When the dynamic contact angle of the cleaning blade 61 is θ3, and the angle between the upstream end KF of the recessed hole G and the normal line is θ0, the shape satisfies θ0 <θ3. That is, when the photosensitive drum 1 is rotated forward, the inclination angle of the upstream recessed hole G is configured to be smaller than the dynamic contact angle θ3 of the cleaning blade 61.

  By the way, in this embodiment, θ0 = 10 ° and θ3> = 27 ° are set. Here, the constituent devices around the photosensitive drum 1 will be described with reference to FIG. 1, which is a schematic sectional view around the image carrier. In FIG. 1, reference numeral 2 denotes a charging device (hereinafter referred to as a charger) using a corona charging method. The corona charger 2 is fixed above the photosensitive drum 1 with a spacing of about 9 mm. In the present embodiment, the corona charger 2 is a 60 mm diameter gold plated tungsten wire.

  In the present embodiment, good chargeability is secured by applying to the corona charger 2 under the condition of DC-3 KV to -4 KV for the wire portion and DC-900 V for the control grit portion.

  In the present invention, the surface potential of the photosensitive drum 1 is set at the center of the photosensitive drum 1 and the end in the thrust direction. The detection operation is performed by performing the charging at the time of the pre-rotation or post-rotation of the photosensitive drum 1 and measuring the entire circumference of the photosensitive drum 1 in the circumferential direction.

FIG. 2 shows a main cross-sectional view related to image formation during the image formation period.
The current developing device 4 includes a developing sleeve, a developing sleeve magnet roller fixedly arranged in the developing sleeve, an agent conveying screw, an agent agitating screw, a regulating blade arranged for forming a thin layer of developer on the developing sleeve surface, developing A container is provided.

  Here, at least at the time of development, the developing sleeve is disposed so that the closest region to the photosensitive drum 1 is about 400 μm, and development can be performed in a state where the developer is in contact with the photosensitive drum 1. Is set to

  The two-component developer used in the present embodiment was obtained by externally adding 1% by weight of titanium oxide having an average particle diameter of 20 nm to a negatively charged toner having an average particle diameter of 6 μm manufactured as a toner particle by a pulverization method. And a magnetic carrier having a saturation magnetization of 205 emu / cm 3 and an average particle diameter of 35 μm was used. Further, a mixture of toner particles and magnetic carrier at a weight ratio of 6:94 was used as a developer.

  Next, after the developing process in which the electrostatic latent image formed on the photosensitive drum 1 is visualized by the two-component magnetic brush method using the developing device 4, and on the recording material P conveyed by the belt 7. The primary transfer charging roller 5 generates a pressing force from the inside of the intermediate transfer belt 7 in the direction of the photosensitive drum 1 and is supplied with power from a high voltage power source (not shown) so that the toner is transferred from the back side of the intermediate transfer belt 7. The toner image on the photosensitive drum 1 is electrostatically attached to the upper surface of the intermediate transfer belt 7 and transferred by charging with the opposite polarity.

  In the present embodiment, the intermediate transfer belt 7 is made of a polyimide resin having a film thickness of 75 μm. However, the material of the intermediate transfer belt 7 is not limited to polyimide resin, and may be polycarbonate resin, Plastics such as polyethylene terephthalate resin, polyvinylidene fluoride resin, polyethylene naphthalate resin, polyether ether ketone resin, polyether sulfone resin, and polyurethane resin, and fluorine-based and silicon-based rubbers can be suitably used. The thickness is not limited to 75 μm, and a thickness of about 25 to 2000 μm, preferably 50 to 150 μm can be suitably used.

  The electrical characteristics of the primary transfer charging roller 5 are those having a resistance of 1 × 10E5 to 1 × 10E7Ω, an outer diameter of Φ30 mm, and a length of 310 mm. A bias of +15 μA is applied to the primary transfer roller 5. Transfer was performed by applying constant current control.

  On the other hand, in FIG. 1, P is a recording material, and 20 and 21 are secondary transfer charging rollers which are secondary transfer means. The secondary transfer charging rollers 20 and 21 are transferred by the primary transfer charging roller 5. The toner image is transferred to a recording material P that is a transfer material. Note that the recording material P is conveyed from the paper feeding and conveying device to the transfer electric field nip portion in synchronization with the rotation of the intermediate transfer belt 7.

  Further, as a cleaning member for scraping and removing untransferred toner remaining on the surface of the intermediate transfer belt 7, a urethane blade is employed, and is configured to always abut in the counter direction with respect to the traveling rotation direction of the intermediate transfer belt 7. .

  The toner image thus transferred is transferred to the recording material P by the secondary transfer rollers 20 and 21, and the recording material P carrying the toner image is conveyed to a fixing device (not shown). After being heated and pressed in the fixing device, it is discharged.

  Details of the cleaning device 6 that forms the core of the present invention will be described below. The blade rubber member that is in contact with the photosensitive drum 1 has a hardness of JIS-A 73 ° (medium hardness) / thickness of 2 mm. The setting conditions of the cleaning blade 61 are as follows.

a) Cleaning blade free length: 7.5mm
b) Longitudinal length of the cleaning blade: 330 mm
c) Cleaning blade contact linear pressure: 3.1 N / cm
d) Cleaning blade contact angle: 30 °
e) Cleaning blade contact type: counter contact The contact NIP width of the cleaning blade 61 during the image forming operation (at the time of positive rotation of the photosensitive drum 1) was about 30 μm.

As a result, the relational expression between the blade NIP width during the image forming operation and the concave hole diameter of the surface layer of the photosensitive drum 1 is blade NIP width <photosensitive drum concave hole diameter, and the accumulated toner in the concave hole can be sufficiently removed by cleaning. Next, reverse rotation control after the image forming operation will be described. The friction coefficient on the surface of the photosensitive drum 1 is generally increased by a discharge product mainly composed of ozone or the like, which is generated by an ionization reaction of oxygen in the air, due to a high voltage generated by a charger generated during image formation. It is attributed to sticking to the surface. The discharge product adhering to the photosensitive drum 1 adsorbs minute external additives added through the cleaning blade 61 to form a film having a high friction coefficient. It has been found that this film is a causative substance that causes abnormal vibration and reversal of the blade 61 when the cleaning blade 61 rubs.

<Blade abnormal vibration occurrence prediction detection mechanism>
In the present invention, the temperature and humidity in the apparatus, the accumulated pixel value, and the rubbing torque value between the blade 61 and the photosensitive drum 1 are used as a predictive detection mechanism for abnormal vibrations that cause the cleaning blade 61 to turn over. Specifically, the in-machine temperature and humidity are detected by an environmental sensor (not shown) that monitors the in-machine temperature and humidity on the back of the main unit, and the accumulated pixel value is determined by a video counter (not shown) installed in the machine. The calculated value was used. As the rubbing torque between the photosensitive drum 1 and the blade 61, a load value by a torque limiter (not shown) connected to the photosensitive drum 1 drive shaft was used.

  FIG. 7 shows the result of examining the relationship between the image DUTY calculated based on the number of detected pixels and the start point of blade abnormal vibration while changing the temperature and humidity. ST in the figure indicates the abnormal vibration starting torque of the blade, and in the present example, it was in the vicinity of 4.0 kgf · cm. It was also found that there is a region where abnormal vibration occurs in the range of the image DUTY 0% (white background image) and the image DUTY 2.5% (low DUTY).

  FIG. 8 is a diagram showing a temperature / humidity range in which occurrence of abnormal blade vibration is predicted. SD1 and SD2 in the drawing indicate regions where abnormal blade vibration occurs in images DUTY 0% and 2.5%. It is shown.

<Photosensitive drum reverse rotation control operation>
The reverse rotation control operation of the photosensitive drum 1, which is the main component of the present invention, will be described. The outline of the reverse rotation control operation flow of the photosensitive drum 1 is as follows. Detects temperature and humidity inside the machine.
A pixel accumulated value is detected (image DUTY identification).

  The rubbing torque between the photosensitive drum 1 and the cleaning blade 61 is detected. When the internal temperature and humidity, the pixel accumulation value, and the rubbing torque of the photosensitive drum 1 exceed the threshold ST, the reverse rotation control operation of the photosensitive drum 1 is turned on. The operation is stopped after the photosensitive drum 1 is reversely rotated for a predetermined time.

(Blade dynamic abutment angle θ1 <= condition where the photosensitive drum recess hole downstream peripheral edge angle θ2)
Change to forward rotation operation during image forming operation (blade dynamic contact angle θ3> photosensitive drum recess hole downstream downstream peripheral edge tilt angle θ2> = photosensitive drum recess hole downstream peripheral edge tilt angle θ0)
Image Forming Operation Start FIG. 9 is a schematic operation diagram of the reverse rotation control mechanism that forms the core of the present invention. During the non-image forming period after the end of the image forming operation, (a) the reverse rotation operation is started, and (b) the reverse rotation operation is performed up to a predetermined area length L1.

  Details of the reverse rotation control operation mechanism will be described below.

  FIG. 10 is a schematic sectional view when the cleaning blade 61 slides in the recessed hole G of the photosensitive drum 1 according to the present invention. As can be seen from FIG. 5 described above, the inclination angle θ2 at the peripheral edge JF of the upstream recessed hole G is larger than the dynamic contact angle θ1 of the cleaning blade 61 during the reverse rotation operation period of the photosensitive drum 1. As a result, as shown in FIG. 10, the blade abnormal vibration causative substance KB is sandwiched between the edge of the cleaning blade 61 and the upstream side wall surface of the recessed hole G and compressed by the reverse rotation operation of the photosensitive drum 1.

  Thereafter, when the blade edge portion crawls up from the recess hole G, the causative substance KB is scraped off from the blade edge portion by the sliding action with the upstream peripheral edge JF of the recess hole G.

  FIG. 11 is a schematic diagram showing a rubbing state at the blade contact portion during the reverse rotation operation. As can be seen from FIG. 11, the reverse rotation operation is started, and the NIP region of the cleaning blade 61 rubs and polishes the surface of the photosensitive drum 1 while (a) sinking from the downstream peripheral edge KF of the recessed hole G toward the hole bottom. (B) An operation of scooping up from the hole bottom to the upstream peripheral edge JF is performed, and (c) the surface of the photosensitive drum 1 is moved again while being rubbed and polished.

  When the blade moves up, the dynamic contact angle θ1 of the blade is smaller than the recess hole G inclination angle θ2 of the upstream peripheral edge JF, so that the blade NIP region and a partial region of the contact surface are The rubbing hole upstream peripheral edge JF is rubbed. As a result, the rubbing torque UP causative substance KB that has been polished and removed by the reverse rotation operation can be scraped into the recess hole and accommodated.

  After rotating and conveying to a predetermined area length L1 (reverse rotation 1 circumference), a series of reverse rotation control operations are terminated. Thereafter, when the signal for starting the image forming operation is received, the rotation is changed to normal photosensitive drum normal rotation, and the rotation of the photosensitive drum 1 is started.

<Photosensitive drum forward rotation operation>
FIG. 12 is a schematic diagram showing the rubbing operation of the blade contact surface when the photosensitive drum 1 is rotated forward. As can be seen from FIG. 12, the angle θ2 at the downstream peripheral edge JF of the recess hole G is smaller than the dynamic contact angle θ3 of the cleaning blade 61 during forward rotation. (B) Sink into the bottom of the recess hole while rubbing against the downstream edge JF of the hole G.

  Thereafter, (c) when scooping up from the bottom surface of the recessed hole G to the upstream peripheral edge KF, as shown in FIG. 10, the inclination angle θ0 of the upstream recessed hole G peripheral edge KF is determined by the cleaning blade 61 is smaller than the dynamic contact angle θ1 of 61, the rubbing torque UP causative substance KB accumulated in the recessed hole G collected and accommodated by the reverse rotation operation control is scraped, and the collected toner is collected in the cleaner container. It will be stored and removed to the part.

  As described above, it is possible to remove the ozone product, which is a causative substance of the abnormal blade vibration, without contaminating the other component devices around the photosensitive drum 1, and it is possible to suppress the abnormal vibration of the blade. . In addition, the blade contact surface can be cleaned at the same time, and the long-term stability of the cleaning performance can be ensured.

  Incidentally, in the actual machine evaluation under the environmental conditions (temperature 35 ° C./humidity 85%), the photosensitive drum 1 is rubbed under the conditions of process speed 200 mm / s, image DUTY 0.1% / A4 size lateral feed / two-sheet intermittent image formation. When the torque exceeded 3.0 kgf · cm, the above-described reverse rotation control operation was performed every rotation / 100 sheets during the post-rotation of the photosensitive drum. As a comparative example, durability evaluation was performed in parallel with a process speed of 200 mm / s and a reverse rotation operation not mounted.

  As shown in FIG. 13, in the comparative example, as the image formation progresses, the blade abnormal vibration start torque ST is exceeded around 10K sheets of image formation, and the abnormal vibration of the cleaning blade 61 occurs. The blade was turned upside down, and the rotation of the photosensitive drum 1 of the image forming apparatus was stopped.

  On the other hand, in the embodiment of the present invention, the occurrence of abnormal vibration of the cleaning blade 61 was not confirmed even after 50K sheets.

  In this embodiment, the inclination angle θ2 of the peripheral edge JF of the concave hole G is set to be larger than the dynamic contact angle θ1 of the blade. However, the inclination angle of the concave hole G at the upstream and downstream peripheral edges is set. Even when the same shape is used, the same effect can be obtained even if the setting condition is such that the dynamic contact angle θ1 of the blade is smaller than θ2 to a desired value during reverse rotation. For example, the configuration may be such that the free length of the cleaning blade 61 is increased during reverse rotation (for example, a restriction member is provided to shorten the free length of the cleaning blade during normal rotation and increase the free length during reverse rotation). It goes without saying that it is good.

[Example 2]
In this embodiment, the configuration is the same as that of the first embodiment except that the rotational speed of the photosensitive drum 1 is set to be faster than the rotational speed during the forward rotation.

  FIG. 14 shows the relationship between the reverse rotation speed and the cleaning blade 61 dynamic contact angle θ1 during the reverse rotation control operation of the photosensitive drum 1. By increasing the reverse rotation speed of the photosensitive drum 1, the dynamic contact angle θ1 of the blade 61 is further reduced, and there is a region in which the causative substance KB of the rubbing torque UP adhering to the blade 61 edge contact surface is scraped off. As a result, the removal amount of the causative substance KB and the cleaning of the blade contact surface are further improved.

<Photosensitive drum reverse rotation control operation>
The reverse rotation control of the photosensitive drum 1, which is the main component of the present invention, will be described. The outline of the reverse rotation control operation flow of the photosensitive drum 1 is as follows. Detects temperature and humidity inside the machine.
Pixel cumulative value is detected (estimation of image DUTY).

The rubbing torque value between the photosensitive drum 1 and the cleaning blade 61 is measured. When the in-machine temperature and humidity, the pixel accumulation value, and the rubbing torque value of the photosensitive drum 1 exceed the threshold, the reverse rotation operation is turned ON after the reverse rotation speed of the photosensitive drum 1 is adjusted to a predetermined speed. The operation is stopped after the photosensitive drum 1 is reversely rotated for a predetermined time.
(Blade dynamic contact angle θ1 <= condition where photosensitive drum recess hole upstream peripheral edge angle θ2)
Changed to forward rotation during image formation.
(Blade dynamic contact angle θ3> photosensitive drum concave hole diameter downstream peripheral edge angle θ2 => photosensitive drum concave hole upstream peripheral edge angle θ0)
By the way, in actual machine evaluation under environmental conditions (temperature 35 ° C./humidity 85%), the process speed 200 mm / s when the photosensitive drum 1 is rotating forward, the process speed 300 mm / s when controlling the reverse rotation, The test was performed under the conditions of DUTY 0.1% / A4 size lateral feed / two-sheet intermittent image formation.

  In the present embodiment, as shown in FIG. 14, the dynamic contact angle of the cleaning blade 61 is set to be about 2 ° lower than that in the first embodiment.

  As shown in FIG. 15, in Example 2, the image was stabilized at a low torque equal to or lower than the abnormal blade vibration until 50K sheets or more of image formation, and no abnormal vibration of the cleaning blade 61 or reverse turning was confirmed. Further, it was found that the rubbing torque was more stable than in Example 1, and it was estimated that the latitude was ensured even in a severer temperature and humidity environment.

[Example 3]
In this embodiment, at least the contact edge portion of the cleaning blade 61 has the same configuration as that of the first embodiment except that the cleaning blade 61 has a two-layer configuration having different physical properties.

  In the present invention, the cleaning blade 61 is composed of two layers, and a rubber layer having high physical properties for cleaning and polishing is adopted as the surface layer in order to improve the ability to remove the causative substances adhering to the surface of the photosensitive drum 1. As a result, during the reverse rotation control operation period of the photosensitive drum 1, the surface layer portion of the blade 61 edge portion is rubbed and polished on the surface of the photosensitive drum 1, which is more efficient in a shorter time than in the first embodiment. Cleaning and polishing removal was made possible.

<Layer structure of cleaning blade>
FIG. 16 is a schematic view showing a layer structure of a two-layer cleaning blade which is a core part of the present invention, and details of the structure are as follows.
Surface layer NH (surface side facing photosensitive drum 1): Hardness JIS-A 77 ° (low hardness) / thickness 30 um / tan δ peak temperature = −3 ° C. Low temperature characteristics UP material next layer NK (with photosensitive drum 1 (Opposite surface side): Hardness JIS-A 73 ° (medium hardness) / thickness 1970 um / tan δ peak temperature = 8 ° C.

  Incidentally, the tan δ peak temperature is generally defined as the temperature at which the viscosity of the rubber material divided by the elastic modulus reaches a peak, and tan δ is called the loss tangent of energy. is there.

  In the present invention, by using a hard rubber material for the surface NH layer, the ability to polish and remove the causative substances adhering to the photosensitive drum 1 particularly in a high-temperature and high-humidity environment is higher than that of the first embodiment. Further improvement is possible. At the same time, by disposing a medium-hardness rubber in the next layer NK, it is possible to suppress the peak pressure of the high-hardness rubber layer of the surface layer H from being suppressed, and it is possible to maintain toner slip-through resistance.

  Incidentally, after 5K images were formed under the same setting conditions as in Example 1, the contact surface in the vicinity of the edge of the cleaning blade 61 was observed with a laser microscope (VK-8510, manufactured by KEYENCE). It was found that the blade surface layer NH rubbed the photosensitive drum 1 with a width of NIP of about 20 μm by the rotation operation. Since the NIP width at the time of reverse rotation of Example 1 which is a single layer blade is 25 μm, it can be inferred that in the present invention, the surface layer is almost in contact with rubbing.

  In the actual machine evaluation under the environmental conditions (temperature 35 ° C./humidity 85%), it was performed under the conditions of image DUTY 0.1% / A4 size lateral feed / 2 intermittent image formation. As a comparative example, image formation evaluation was performed in parallel with a process speed of 200 mm / s and a reverse rotation operation not mounted.

  As shown in FIG. 17, in the embodiment of the present invention, the occurrence of abnormal vibration of the cleaning blade 61 is not confirmed even around 50K sheets, and the friction torque of the first and second embodiments It was found that the transition was low and stable, suggesting the possibility of further improving the latitude and shortening the reverse rotation operation control time for the temperature and humidity environment conditions and the image DUTY.

  In this example, the two-layer blade shown in FIG. 16 was used. However, as shown in FIG. 18, the same applies to a blade in which a chip-like rubber material having different physical properties from the base layer is arranged on the surface layer NC. Needless to say, this effect can be obtained.

1 Photosensitive drum
2 Corona charger
3 Laser light emitting device
4 Developer
5 Primary transfer charging roller
6 Cleaning device
7 Intermediate belt
20 Secondary transfer charging roller
21 Secondary transfer charging roller
61 Cleaning blade
62 Fur Brush
63 Collected toner transfer screw
G Concave (image carrier surface)
Blade contact NIP when GF image is stopped
JF upstream peripheral edge (during reverse rotation)
KF downstream peripheral edge (during reverse rotation)
θ0 Inclination angle of upstream edge of recessed hole (during forward rotation)
θ1 Blade dynamic contact angle (during reverse rotation)
θ2 Upstream peripheral edge inclination angle of recessed hole (during reverse rotation)
θ3 Inclination angle of the downstream edge of the recessed hole (during forward rotation)
SD1 Blade abnormal vibration generation area (image DUTY 0%)
SD2 Blade abnormal vibration generation area (image DUTY 2.5%)
ST Blade abnormal vibration start torque
KB Cause of abnormal vibration (ozone product)
NH double layer blade surface
NK double-layer blade base layer
NC double layer blade surface (chip shape)
L1 photosensitive drum reverse rotation travel length

Claims (4)

In an electrostatic image forming apparatus that forms an electrostatic latent image on a traveling image carrier 1, develops toner, performs a transfer operation, and forms an image on a recording medium, the surface of the image carrier 1 has a flat portion. And a concave portion G which is independent at a predetermined ratio, and the surface shape and depth size of the concave portion G change with the progress of image formation, and the untransferred toner on the surface of the image carrier 1 is removed by cleaning. A cleaning device 6 for arranging
At least a mechanism for detecting the rotational torque and the number of pixels of the image carrier, and based on the detected value, the image carrier has a configuration for performing a reverse rotation operation satisfying the relationship of the formula (A). During the period in which the body rotates,
The dynamic contact between the normal line perpendicular to the straight line connecting the end point of the contact NIP with the cleaning blade 61 and the center of rotation of the image carrier 1 and the contact surface of the cleaning blade in the image carrier 1 recess hole. The contact angle is θ1, the angle between the straight line connecting the upstream end point of the concave hole and the rotation center of the image carrier and the normal is θ2, and the cleaning blade 61 is rotated during the normal rotation period of the image carrier 1. When the dynamic contact angle is θ3,
θ1 = <θ2 (image carrier reverse rotation period) (A)
θ2 <θ3 (image carrier normal rotation period) (B)
An image forming apparatus satisfying the requirements. 2. The image forming apparatus according to claim 1, further comprising a mechanism that controls a reverse rotation operation of the image carrier satisfying a relationship of Expressions (A) and (B) based on the detected value. The image forming apparatus according to claim 1, wherein the cleaning blade 61 has a two-layer configuration with different physical properties, and at least a surface layer contacts the image carrier 1 during the reverse rotation operation period. The surface shape of the concave portion G on the surface of the image carrier 1 has a depth of 0.5 μm or more and 5 μm or less and a maximum opening diameter of 20 μm to 80 μm is 0.5 to 5 μm. When a square area of 500 μm × 500 μm is arranged at an arbitrary position on the surface of the image carrier 1, the area of the recess G in the square area is 10,000 μ ^{2 to} 90000 μ ² , The area of the flat part included in the part other than G is 80000
um ² ～240000Um is ^2, in the forward rotation operation control period of said image bearing member 1, the image bearing member 1 recess hole G, the upstream end terminal point KF and the image bearing member rotation center of the recess hole G When the angle between the straight line connecting the two and the normal is θ0, the relational expression θ0 <θ2 (C) with θ2
The image forming apparatus according to claim 1, wherein the image forming apparatus satisfies the following.