JP4810124B2 - Image forming apparatus - Google Patents

Description

The present invention is a copying machine, a printer, it relates to an image forming equipment of the electrophotographic recording system such as a facsimile.

  When creating an image in an electrophotographic copying machine using an electrophotographic system, an electrostatic latent image is first formed on the surface of a photoconductor as an image carrier. Next, a charged toner (developer) is applied to the surface of the photoreceptor having the electrostatic latent image by a developing device and developed (visualized), and the obtained toner image is transferred and fixed on a sheet such as paper. To do. In a developing device used for such an electrophotographic copying machine, particularly a developing device using a non-magnetic toner as a one-component developer, it is important to supply a thin layer of a uniformly charged toner to the surface of the photoreceptor. .

  Conventionally, as such a developing device, a non-magnetic toner is supplied to a surface of an elastic developing roller as a developer carrying member by a developer supplying member, and a blade as a developer regulating member is pressed against the developing roller and the outer periphery of the developing roller There has been proposed a method of forming a toner image by forming a charged toner thin layer on the surface and bringing the charged toner thin layer into direct contact with the surface of the photoreceptor (see Patent Document 1).

  However, in the developing device of Patent Document 1, in order to form a charged toner thin layer on the surface of the developing roller, the blade needs to contact the developing roller with a certain level of pressing force. For this reason, the hardness required for the elastic developing roller is relatively high. However, on the contrary, the hardness required for the elastic developing roller is very low in order to prevent damage to the photoreceptor and destruction of the image at the contact portion with the photoreceptor. When a developing roller that satisfies the contact pressure is used, the contact pressure between the photosensitive member and the developing roller becomes high. For this reason, the toner deterioration is promoted due to a high level of contact and scratches on the photoreceptor. In a so-called “contact development type” developing device in which development is performed by bringing a photosensitive member and a developing roller into contact with each other, it is important that the photosensitive member and the developing roller are in contact with each other in order to form a uniform high electric field. Rather, the contact pressure is preferably the lowest contact pressure that can ensure stable contact.

  The specifications required for the developing roller to satisfy the contact pressure require a predetermined rubber hardness in order to secure a certain contact pressure in a portion that contributes to charging of the toner such as a supply member and a blade, The contact part with the body required a low hardness.

  However, there is no roller having such a contradictory property that the hardness is high and low, and either one of the requirements must be sacrificed.

  In order to solve this problem, development devices disclosed in Patent Document 2, Patent Document 3, and the like have been proposed.

  In these developing apparatuses disclosed in Patent Documents 2 and 3, a flexible thin film developing sleeve having a slight excess circumferential length with respect to the circumferential length of the roller is mounted on the driving roller, and the developing sleeve is pressed into contact with the driving roller from one side. In addition, the slack portion formed on the opposite side is brought into contact with the photosensitive member, and the toner regulating member is brought into contact with the developing sleeve from one side. In this developing device, the toner regulating member can be brought into contact with the developing sleeve supported by the driving roller with a certain pressure contact force, and the excessive slack portion of the developing sleeve can be brought into soft and uniform contact with the photosensitive member. it can. For this reason, the contact pressure between the developing sleeve and the photosensitive member can be very small.

Further, in order to supply toner to the developing sleeve and erase the history of the previous image, a sponge roller having a foam cell as a developer supplying member is preferably used, and this sponge roller is also similar to the toner regulating member. It is necessary to press the developing sleeve with a certain pressure.
JP 52-143831 A JP-A 63-226676 JP-A-64-65579

  However, in the developing devices of Patent Documents 2 and 3, since the excess slack portion of the developing sleeve is used to contact the photosensitive member, the means for transmitting the rotation of the driving roller to the developing sleeve is the surface of the driving roller and the inner surface of the developing sleeve. It was by friction. For this reason, the following problems have occurred.

  Unlike the magnetic toner, the nonmagnetic one-component toner is preferably provided with means for supplying toner to the surface of the developing sleeve. Further, it is desirable to provide means for removing the toner on the surface of the developing sleeve from the surface of the developing sleeve so as not to produce a so-called “ghost” image in which the previously output image appears in the next image. In order to satisfy these demands, as a contact member that contacts the developing sleeve, a developer supply / removal means that makes a sponge roller having foamed cells contact the developing sleeve with a peripheral speed difference is suitably used. In particular, since the toner adhering to the surface of the developing sleeve needs to be mechanically scraped off at the elastic portion forming the pores of the sponge, the surface of the developing sleeve and the surface of the sponge roller are generally brought into counter contact.

  As described above, in the conventional developing devices shown in Patent Documents 2 and 3, since friction is used as the drive transmission means of the developing sleeve, a sponge roller as a contact member is brought into counter contact with the surface of the developing roller. It is difficult to dispose the developing roller because the rotation of the developing roller is unstable or cannot be rotated. Therefore, the toner cannot be stably supplied to the developing sleeve, resulting in problems such as uneven density, and a ghost image due to the reasons described above.

  Further, even when a blade that is a developer regulating member is provided as a contact member that contacts the developing sleeve, the rotation of the developing sleeve may become unstable. Accordingly, the amount of developer carried on the developing sleeve becomes non-uniform, and density unevenness may occur.

The present invention is to stabilize the driving of the developer carrying member, e suppress the occurrence of uneven density were or, together with reducing the contact pressure between the image bearing member and the developing sleeve, those of the developing sleeve contact member properly coercive Chi contact pressure, that with a uniform amount of the developer carried on the current image-carrying member to prevent the occurrence of problems image such as density unevenness and ghost images over long term, to obtain a desired image density With the goal.

In order to achieve the above object, the present invention adopts the following configuration.
That is, an image carrier on which an electrostatic latent image is formed, a developer carrier that is rotatably provided and carries a developer for imparting to the electrostatic latent image , and the developer carrier. An image forming apparatus having a developing device including a contact member ;
The developer carrying member is a shaft portion and a developing sleeve that is provided on the outer peripheral side of the shaft portion and carries the developer. The developer carrying member is provided in contact with the image carrying member so that the developer is transferred to the electrostatic latent image. A flexible developing sleeve to be applied to an image; and a fixing portion provided between the developing sleeve and the shaft portion for fixing the developing sleeve at a longitudinal end portion, the shaft portion and the developing sleeve, A fixing portion for fixing the developing sleeve in a non-contact state,
The length of the contact member in the axial direction is a length that fits between the fixed portions. In the contact portion between the contact member and the development sleeve, the contact member bends the development sleeve by contacting the development sleeve. The inner surface of the developing sleeve in a region corresponding to the contact portion between the contact member and the developing sleeve is brought into contact with the shaft portion,
The axial length of the image carrier is an axial length that reaches the fixed portion. At the contact portion between the image carrier and the developing sleeve, the fixed portion is connected to the image carrier via the developing sleeve. The outer surface of the developing sleeve and the image carrier are brought into contact with each other, and the inner surface of the developing sleeve in a region corresponding to a contact portion between the image carrier and the developing sleeve is a region between the fixed portions. In the present invention, the shaft portion is configured to maintain a non-contact state.

  According to the present invention, the driving of the developer carrying member can be stabilized. Moreover, according to the present invention, it is possible to suppress the occurrence of density unevenness. Further, according to the present invention, the contact pressure between the image carrier and the developing sleeve can be reduced. In addition, according to the present invention, the contact pressure between the developing sleeve and the contact member can be maintained appropriately. Further, according to the present invention, the amount of developer carried on the developer carrying member can be made uniform. Further, according to the present invention, it is possible to prevent generation of defective images such as uneven density and ghost images over a long period of time and obtain a desired image density.

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. 1 is a detailed explanatory diagram of the image forming apparatus according to the first embodiment, FIG. 2 is an overall configuration diagram of the image forming apparatus according to the first embodiment, FIG. 3 is a configuration diagram of a developer carrier, and FIG. 4 is a developer. FIGS. 5A and 5B are diagrams for explaining a contact state between the carrier and other members, and FIGS.

  In the present embodiment, the developing roller as the developer carrying member includes a flexible thin film developing sleeve and an inner member having an outer peripheral length slightly smaller than the inner peripheral length of the developing sleeve. The inner member includes a cylindrical shaft portion having a constant outer diameter, and fixed portions having a larger outer diameter than the shaft portion at both axial ends of the shaft portion. The developing sleeve is fixed to the fixing portion at both axial ends, so that the developing sleeve and the inner member are rotated coaxially. Furthermore, the opposite portion of the developing roller and the photosensitive drum as the image bearing member has an axial length that reaches the fixed portion at both ends in the axial direction. Therefore, the developing sleeve comes into contact with the photosensitive drum with a small contact pressure. In order to minimize the contact pressure between the developing sleeve and the photosensitive drum, it is desirable that the inner surface of the developing sleeve is not in contact with the shaft portion at a position where the developing sleeve contacts the photosensitive drum. Further, in the contact between the developing roller and the developer regulating member (contact member) or the developer supplying member (contact member), the axial length of the developer regulating member or the developer supplying member is a length that fits between the fixed portions. Since the developing sleeve can be bent and pressed until the developing sleeve comes into contact with the shaft portion between the two fixed portions, the developer sleeve inner surface and the shaft portion of the inner member are in contact with each other. The member or the developer supply member can obtain a predetermined contact pressure from the developing roller.

  First, the image forming apparatus according to the present embodiment will be described with reference to FIG. The present embodiment is an image forming apparatus using a non-magnetic one-component developer in an electrophotographic image forming apparatus.

  In FIG. 2, a photosensitive drum 1, which is a rotatable image carrier, has a drum base that is electrically grounded, and rotates in the direction of arrow X at a rotational speed Vx. The photosensitive drum 1 is uniformly charged by a charging roller 2 as a primary charger, and an information signal is exposed thereto by a light emitting element 3 such as a laser to form an electrostatic latent image.

  The electrostatic latent image formed on the photosensitive drum 1 is provided with toner by a developing device 4 to be described later, and is developed to form a toner image. The developing device 4 contains a non-magnetic one-component toner T, and a developing roller 8 that is a developer carrying member is brought into contact with the photosensitive drum 1. The developing roller 8 is applied with a negative DC voltage and rotates in the arrow Y direction at a rotational peripheral speed Vy. Here, the rotational peripheral speed Vy of the developing roller 8 is higher than the rotational peripheral speed Vx of the photosensitive drum 1. Further, the developing device 4 includes a developing blade 10 as a developer regulating member (contact member), a supply roller 9 as a developer supply member (contact member) that rotates in the arrow Z direction, and an agitation that agitates the non-magnetic one-component toner T. A member 11 is provided. The developing blade 10 makes contact with the metal thin plate by utilizing the characteristics of the leaf spring. The supply roller 9 is constituted by a porous foam sponge bonded around a cored bar.

  The toner image formed on the photosensitive drum 1 is transferred to the transfer material P conveyed by the transfer roller 5, and then the toner is melted and fixed by applying heat and pressure by the fixing device 6 to form an image. . The transfer residual toner on the photosensitive drum 1 is removed by the cleaning device 7.

  Next, the arrangement of each component around the developing roller will be described. As described above, at the time of image formation, the developing blade 10, the supply roller 9, and the photosensitive drum 1 are disposed around the developing roller 8 in contact with the developing roller 8. Here, the photosensitive drum 1 may be configured to be separated from the developing roller 8 during non-image formation. As described above, the contact state at the time of image formation requires a certain amount of contact pressure between the supply roller 9 and the developing blade 10, but it is sufficient that the photosensitive drum 1 is in contact and does not deteriorate the toner. Therefore, it is desirable to reduce the contact pressure as much as possible.

Therefore, in the present embodiment, the developing roller 8 is configured as follows, so that the supply roller 9 and the developing blade 10 have a certain contact pressure, and the photosensitive drum 1 reduces the contact pressure. Yes. The contact pressure is measured by stacking three 20μm SUS 304 H thin plates and inserting them into the contact portion between the developing sleeve and the member in contact with the developing sleeve, and pulling out the central thin plate with a spring balance. The contact pressure was converted as a linear pressure from the force at that time.

  A possible configuration of the developing roller 8 will be described with reference to FIG. As shown in FIG. 3A, in the developing roller 8, a gap holding member 8c is first fitted on both ends of a shaft member 8b as a shaft portion. The gap holding member 8c has a D-cut shaft hole, and the D-cut shaft of the shaft member 8b is inserted into the shaft hole. Here, the outer diameters of the shaft member 8b and the gap holding member 8c are larger in the gap holding member 8c. That is, the shaft member 8b and the gap holding member 8c constitute an inner member, the shaft member 8b becomes a shaft portion having a constant outer diameter, and the gap holding members 8c fitted at both axial ends of the shaft member 8b are shaft portions. It is a fixed part at both ends in the axial direction.

  The shaft member 8b and the gap holding member 8c are wrapped by the flexible thin film developing sleeve 8a (FIG. 3B). Further, the gap holding member 8c and the developing sleeve 8a are bonded and fixed (FIG. 3C). Here, the developing sleeve 8a is fixed with a tension f when fixed to the gap holding member 8c at both axial ends. However, the tension f is sufficient so that the developing sleeve 8a does not bend due to its own weight.

A distance D between the outer peripheral surface of the shaft member 8b and the inner peripheral surface of the developing sleeve 8a is a radius difference between the gap holding member 8c and the shaft member 8b. The maximum value of the distance D is set in a range of 40 μm to 1 mm, more preferably 70 μm to 500 μm, in the state of the developing roller 8 alone in which the developing sleeve does not contact other members. If it is smaller than 40 μm, it is difficult to accurately manufacture the gap, and it is desirable that the gap be about 70 μm when many mass productions are taken into consideration. If the distance D is greater than 1 mm, an excessive force is applied to both ends when the developing blade 10 and the supply roller 9 are brought into contact with each other. Further, it is necessary to extend the developing sleeve 8a as much as the developing blade 10 and the supply roller 9 enter the developing roller 8. However, as the distance D increases, the developing sleeve 8a requires a greater tensile strength. The room for material selection will be narrowed. In addition, if the distance D is 500 micrometers or less, a resin film etc. can also be used.

  The developing sleeve 8a is fixed to the gap holding member 8c, and the gap holding member 8c and the shaft member 8b are prevented from rotating by a D-cut shaft and a shaft hole as shown in FIG. The developing sleeve 8a, the shaft member 8b, and the gap holding member 8c rotate integrally and synchronously.

  Further, since both ends of the developing sleeve 8a in the axial direction are fixed and held by the gap holding member 8c, the developing sleeve 8a is not in contact with the shaft member 8b, and the inner circumference and the gap of the developing sleeve 8a are located inside the developing sleeve 8a. A substantially cylindrical space surrounded by the side surface of the holding member 8c and the outer periphery of the shaft member 8b is formed.

  The contact state between the space formed inside the developing sleeve 8a as described above and the member that contacts the developing roller 8 will be described with reference to FIGS. In FIG. 4, when the supply roller 9 is brought into contact with the developing roller 8, the foamed sponge of the supply roller 9 is distorted and the developing sleeve 8a is also bent, and the inner peripheral surface of the developing sleeve 8a is formed on the shaft member 8b. Contact with the outer peripheral surface (part A in FIG. 1). Further, when the supply roller 9 is pushed in, the developing sleeve 8a cannot be bent because of the shaft member 8b, and the metal hardness of the shaft member 8b returns to the supply roller 9 as a repulsive force. As a result, the developing sleeve 8a and the supply roller 9 can have a contact pressure of about 15 to 80 g / cm, which is appropriate for supplying the developer to the developing sleeve.

  Similarly, at the abutting portion (B portion in FIG. 1) between the developing roller 8 and the developing blade 10, the flexible thin film developing sleeve 8a is bent by the abutting of the developing blade 10, and the inner peripheral surface of the developing sleeve 8a is a shaft member. By abutting against 8b and returning the repulsive force to the developing blade 10, it becomes possible to have a contact pressure of about 20 to 70 g / cm suitable for regulating the amount of developer by the developing blade.

  In contrast, at the contact portion (c portion in FIG. 1) between the photosensitive drum 1 and the developing roller 8, the contact pressure of the photosensitive drum 1 is received by the gap holding member 8c. Here, since the gap holding member 8c is formed of a rigid body, the inner peripheral surface of the developing sleeve 8a and the outer peripheral surface of the shaft member 8b do not contact each other.

  On the developing sleeve 8a, about 1 to 3 toner layers are formed when the developing blade 10 is passed. The height of the toner layer is about 7 to 20 μm when the toner particle size is about 7 μm. That is, at the contact portion between the developing sleeve 8a and the photosensitive drum 1, a toner layer of about 7 to 20 μm is sandwiched between the two. Here, since the photosensitive drum 1 is a rigid body and the developing sleeve 8a is flexible, the developing sleeve 8a is bent.

  However, as described above, since the developing sleeve 8a is fixed with the tension f when being fixed to the gap holding member 8c at both axial ends, a reaction force F acts against the bending of the developing sleeve 8a. . This reaction force F is very small because it has only a reaction force against the displacement of the developing sleeve 8a corresponding to the thickness of the toner layer. As a result, the contact pressure between the photosensitive drum 1 and the developing sleeve 8 becomes the tension of the developing sleeve 8a, and it is possible to ensure stable contact while securing about 1 to 50 g / cm. Then, it is possible to reduce the contact pressure due to the toner at the contact portion between the photosensitive drum 1 and the developing roller 8, and it is possible to prevent toner deterioration.

Here, as shown in FIG. 4, the photosensitive drum 1, the developing roller 8, and the supply roller 9 have the longest width (length in the axial direction) of the photosensitive drum 1, and then the developing roller 8 and the supply roller 9 in that order. Becomes shorter. The length of the supply roller 9 is smaller than the distance between the gap holding members 8c. However, the hardness of the supply roller is much lower than the hardness of the shaft member 8b of the developing roller and the rubber hardness of the supply roller 9. Therefore, even if the longitudinal widths of the developing roller 8 and the supply roller 9 are the same, it is possible to ensure an appropriate contact pressure.

  Further, in the longitudinal width (length in the axial direction), the developing blade 10 is not illustrated, but is configured to be equal to or shorter than the width of the developing roller 8. The toner carrying area is narrower than the width of the photosensitive drum 1 and the developing roller 8 and is the same as or wider than the width of the supply roller 9. The length of the developing blade 10 is smaller than the distance between the gap holding members 8c. In addition, the photosensitive drum 1 is disposed so as to reach the gap holding member 8c at both ends in the axial direction of the developing roller 8 and span between the interval holding members 8c to be in pressure contact with the developing roller 8. The supply roller 9 and the developing blade 10 are disposed so as to be accommodated between the gap holding members 8c at both ends in the axial direction of the developing roller 8 with respect to the developing roller.

  Further, as a secondary advantage, when an image having a low density (a so-called highlight image) is output, a problem that the density changes in the sheet passing direction with the rotation period of the developing roller 8 (hereinafter referred to as “density unevenness”). Is advantageous. The density unevenness is caused by a change in the toner coat amount by the developing blade 10, and the cause for changing the toner coat amount is a circumferential runout of the developing roller 8 in the radial direction.

  In the conventional elastic developing roller using rubber or the like, the circumferential runout in the radial direction is very large although it depends on the rubber manufacturing technology. This is because when the surface of the elastic developing roller is polished by post-processing or the like, circumferential runout occurs due to its softness. In other words, the more the toner deterioration is suppressed, the worse the circumferential runout becomes. When the core metal is inserted into a mold without post-processing on the surface of the developing roller, and then elastically molded in the mold, the position accuracy of the core metal at the center is difficult to be obtained, and the circumferential runout is also caused. Therefore, in the case of a developing roller using elasticity, it is necessary to strictly manage the circumferential runout accuracy.

  However, in the method of the present embodiment, the contact between the developing blade 10 and the developing roller 8 is mainly determined by the metal shaft member 8b and the developing blade 10 in the flexible thin film developing sleeve 8a. In the case of metal, naturally, the circumferential runout is higher than that of the elastic developing roller, and those with extremely high circumferential runout can be used at low cost. As a result, it is possible to suppress the occurrence of density unevenness without strictly managing the circumferential runout accuracy.

  Next, each component of the developing device 4 will be described.

(Development roller)
The shaft member 8b can be a rigid body such as stainless steel or aluminum. The shape may be solid or hollow. In the case of the solid shaft member 8b, it is obtained by cutting the bearing portions (D cut portions) at both axial ends from a solid steel material. When a hollow pipe is used, the shaft member 8b is obtained by bonding the bearing portions at both ends to the hollow pipe.

  In order to prevent excessive bending and deformation of the developing sleeve 8a due to contact with the developing blade 10 and the supply roller 9, it is more preferable that the shaft member 8b has an appropriate friction. As a method of increasing the friction, there is a method of covering the surface of the shaft member 8b with a flexible rubber, an uncrosslinked resin or the like.

Flexible and thin developing sleeve 8a is made of polyethylene terephthalate, polyamide, fluororesin resin tube, silicone rubber, urethane rubber, ethylene / propylene rubber (EPDM rubber), natural rubber, styrene / butadiene rubber and rubber and resin. A thin-layer tube mixed with the above, a thin film obtained by coating the resin on a metal thin film such as an iron thin film or a nickel electroformed thin film, a thin film obtained by laminating the rubber or a mixture of rubber and resin, rubber, etc. A tube in which the resin is coated on a thin layer tube can be used. The metal thin film alone is not preferable because contact with the photosensitive drum 1 becomes uneven.

  Since the developing sleeve 8a is in direct contact with the toner T, it is preferable that the charge imparting property to the toner is large. In the present embodiment, since a negatively chargeable toner is used, a silicone resin, a urethane resin, a polyamide resin, or the like that imparts a negative charge to the toner is selected as a material to be applied to the surface of the developing sleeve 8a. Is done.

  As the thickness of the developing sleeve 8a, when a metal thin film is used as the base layer, the thickness of the metal thin film is preferably about 10 to 100 μm. This is because if the metal thin film thickness of the developing sleeve 8a is smaller than 10 μm, the strength of the developing sleeve 8a is weakened, so that wrinkles and twists are likely to occur, and it is difficult to perform stable development. When the thickness of the metal thin film is larger than 100 μm, the flexibility of the developing sleeve 8a is lost, and the same operation as that of a rigid member is performed. As a result, light pressure is applied at the contact portion between the photosensitive drum 1 and the developing roller 8. It becomes difficult to contact.

  The thickness in the case of using a thin-layer tube such as a resin tube or rubber is preferably 30 μm to 800 μm. This is because when the thickness is smaller than 30 μm, the strength is insufficient and molding is difficult. Further, if it exceeds 800 μm, it is difficult to support at both axial ends.

The surface of the developing sleeve 8a preferably has an appropriate roughness so that the toner T in the developing device 4 is easily carried and conveyed. This surface roughness is 3 μm to 1 in terms of 10-point average roughness Rzjis.
5 μm is preferred. This is because if Rzjis is less than 3 μm, the toner conveyance amount is small and it becomes difficult to obtain a predetermined image density, and if it is 15 μm or more, density unevenness corresponding to the surface roughness of the developing sleeve 8a occurs in the output image. The ten-point average roughness Rzjis used the definition shown in JIS B0601, and a surface roughness tester “SE-30H” manufactured by Kosaka Laboratory was used for the measurement.

The electrical resistance of the developing sleeve 8a is preferably in the range of about 10 ³ Ω to 10 ⁹ Ω as a resistance value. If there is a pinhole or the like on the surface of the photosensitive drum 1, an overcurrent may flow. Therefore, it is preferable that the developing sleeve 8a has some resistance. When the developing sleeve 8a is composed of a plurality of layers, the development electric field is uniformly formed at the photosensitive drum contact portion by setting the lower layer to a low resistance and the surface layer side to a high resistance.

  The developing bias may be applied to the photosensitive drum contact portion (developing portion) from the shaft member 8 b through the contact portion between the developing blade 10 or the supply roller 9 and the inner peripheral surface of the developing sleeve 8 a at the contact portion of the developing roller 8. . As another method, the gap holding member 8c may be made of a conductive material, and the developing bias may be supplied from the shaft member 8b to the developing sleeve 8a through the gap holding member 8c.

  The gap holding member 8c is made of metal or hard resin. Hardness is required as a material for maintaining the contact pressure between the photosensitive drum 1 and the developing roller 8.

(Supply roller)
A supply roller 9 as a developer supply member supplies toner to the development roller 8. In order to adhere the one-component non-magnetic toner T accommodated in the developing device 4 to the developing roller 8, the toner T must be rubbed by the supply roller 9 and the developing roller 8 to be charged. As the material of the supply roller 9, known materials such as foamed urethane rubber, foamed EPDM rubber, and foamed silicone rubber are used. In the present embodiment, foamed urethane rubber is used.

(Toner regulating member)
The developing blade 10 as a developer regulating member regulates the layer thickness of the toner adhering to the outer peripheral surface of the developing roller 8 (regulates the amount of toner) and imparts an electric charge. Examples of the developing blade 10 include those using a leaf spring and those that press a fixing member. In the case of using a leaf spring, one end of the thin metal plate is used as a fixed end, and the other end is used as a free end, and the vicinity of the free end is brought into contact with the developing roller 8. In this embodiment, a 0.1 mm thick stainless steel plate was used. When it is desired to change the chargeability imparted to the toner, it is possible to use a material obtained by coating or molding a resin such as urethane or silicone or elastic rubber on the surface of the metal thin plate.

(toner)
The shape of the nonmagnetic one-component toner T (developer) accommodated in the developing device 4 may be a toner having irregularities formed by a pulverization method or the like, or a substantially spherical toner formed by a polymerization method or the like. Even if there is, there is no problem in use. However, the use of the substantially spherical toner facilitates the rolling of the toner at the contact portion between the developing roller 8 and the photosensitive drum 1, so that the toner is uniformly frictionally charged and is applied to the fogging and the non-image portion around the character. So-called scattering or the like to which toner adheres can be reduced, and the uniformity of the image is improved.

(Evaluation methods)
Whether a good image was obtained with the configuration of the present embodiment was evaluated according to the following evaluation. The results are shown in FIG.

(1) Density unevenness Using the above-mentioned image forming apparatus, a solid black image is drawn by A4 vertical feed, and the difference between the maximum value and the minimum value of the density is measured with a Macbeth densitometer RD-1255.
○: The difference between the maximum value and the minimum value is less than 0.2.
Δ: The difference between the maximum value and the minimum value is 0.2 to 0.3,
X: The difference between the maximum value and the minimum value of the density is greater than 0.3.
Evaluation was performed according to the above evaluation.

(2) Ghost Using the above-described image forming apparatus, a solid black image of 20 × 20 mm in the paper passing direction with A4 vertical feeding, and a highlight image having a density of about 0.2 from immediately below the solid black image. Output. And by the condition of the outline generated by the ghost of the solid image of 20 × 20 mm in the highlight image part,
○: No occurrence of a 20 × 20 mm contour in the highlight image part,
Δ: Although there is a slight occurrence of a 20 × 20 mm contour in the highlight image portion, there is no practical problem. ×: There is a 20 × 20 mm contour generation in the highlight image portion.
Evaluation was performed according to the above evaluation.

(3) Fog Using the above-described image forming apparatus, after leaving the image forming apparatus for one day in an environment of 30 ° C./80%, five solid white images are passed by A4 vertical feed, and the fifth image The surface was measured with a Tokyo Denki fog measuring instrument TC-6DS. Then, the same unused paper was similarly measured with a Tokyo Denki fog measuring instrument TC-6DS, and the difference between the measured values of the printed paper on the fifth sheet was obtained from the measured values of the unused paper. The difference is
○: The difference is smaller than 1.5.
Δ: Difference is 1.5 to 3.0,
X: The difference is larger than 3.0,
Evaluation was performed according to the above evaluation.

(4) White streaks Using the image forming apparatus described above, a solid black image is printed by A4 vertical feed, and it is checked whether a white spot parallel to the sheet passing direction occurs in the center of the image.
◯: No white spot ×: Evaluated according to the evaluation of white spot or higher.

(5) Development streaks Using the image forming apparatus described above, A4 vertical feed performed 1000 sheets at a printing rate of 4%, a solid image was passed at the time of 1000 sheets, and a width of 1 mm on the image. Whether or not the following thin streaks appear,
○: No fine streaks
Δ: Small streaks appear, but there is no practical problem.
×: Many fine streaks occur,
Evaluation was performed according to the above evaluation.

  As an example of this embodiment, the image was printed and evaluated in Examples 1 to 17 with different settings. Further, as Comparative Example 1, the image was printed with the supply roller 9 removed from the developing device 4 from the present embodiment, and the same evaluation was performed.

  As described above, the developing sleeve 8a is fixed to the gap holding member 8c at both ends in the axial direction and is rotated with the shaft member 8b, whereby the developing sleeve 8a and the shaft member 8b are driven to rotate coaxially. Further, the developing sleeve 8 a comes into contact with the photosensitive drum 1 with a small contact pressure at the facing portion between the developing roller 8 and the photosensitive drum 1. On the other hand, in the contact between the developing roller 8 and the developing blade 10 or the supply roller 9, a predetermined contact pressure is obtained by the contact between the inner peripheral surface of the developing sleeve 8a and the shaft member 8b. As a result, it is possible to prevent generation of defective images such as uneven density and ghost images over a long period of time, and to obtain a desired image density.

(Second Embodiment)
In the first embodiment, the contact between the photosensitive drum 1 and the developing roller 8 is performed by the gap holding member 8c. In the present embodiment, an intrusion adjusting member that adjusts the contact with the photosensitive drum 1 is provided at the end of the developing roller 12 in the axial direction, and the room for selecting the material of the gap holding member 12c used for the developing roller 12 is widened. . By using the elastic gap holding member 12c, a shock in contact or separation of the photosensitive drum 1 with respect to the developing roller 12 is reduced, and problems such as image blurring can be prevented.

FIG. 6 is a view showing a state in which the photosensitive drum 1 is in contact with and separated from the developing roller 8 in the second embodiment. 6A shows a separated state, and FIG. 6B shows a contact state. In FIG. 6, reference numeral 12 denotes a developing roller. The developing roller 12 includes a flexible thin film developing sleeve 12a, a shaft member 12b, and a gap holding member 12c. In the present embodiment, an elastic rubber member is used as the gap holding member 12c. Furthermore, an end roller 13 as an intrusion adjusting member is disposed at the longitudinal end (axial end) of the developing roller 12. The end roller 13 is formed of polyacetal resin. As shown in FIG. 6A, when the photosensitive drum 1 is separated from the developing roller 12, the end roller 13 is smaller than the outer diameter of the gap holding member 12c. As shown in FIG. 6B, when the photosensitive drum 1 comes into contact with the developing roller 12, the gap holding member 12 c in contact with the photosensitive drum 1 is distorted and the end roller 13 causes the photosensitive drum 1 to contact the developing roller 12. The amount of intrusion is adjusted. However, even if the gap holding member 12 c is compressed by the photosensitive drum 1, the back surface portion of the developing sleeve 12 a at the opposite portion of the photosensitive drum 1 does not contact the shaft member 12 b.

  In the first embodiment, when the developing roller 8 contacts or separates from the photosensitive drum 1, the developing sleeve 8a vibrates due to a shock when the gap holding member 8c contacts or separates from the photosensitive drum 1. It was. In the present embodiment, it is possible to suppress the vibration of the developing sleeve 12a by configuring the gap holding member 12c with an elastic member and restricting the amount of penetration of the photosensitive drum 1. As a result, it is possible to prevent image blurring caused by vibration of the developing sleeve 12a.

  Furthermore, in this embodiment, the effect can be further increased by using a rubber having a vibration-proofing property against vibration generated by the contact and separation between the developing roller 12 and the photosensitive drum 1 for the gap holding member 12c.

(Third embodiment)
In the above embodiment, the contact pressure from the developing roller to the photosensitive drum is formed by the reaction force of the tension that the developing sleeve is held at both ends in the axial direction and the force that pushes the toner layer from the photosensitive drum. Therefore, for example, when the outer diameter of the central portion in the longitudinal direction (axial direction) of the photosensitive drum is much smaller than the end portion, a region that is not developed at the central portion, so-called “white spot” occurs.

  The tolerance of the difference in the outer peripheral diameter between the longitudinal center portion and the longitudinal end portion of the photosensitive drum is determined by the layer thickness of the toner layer and the elastic range of the developing sleeve itself. That is, when the developing sleeve is a rigid body, it hardly distorts due to the contact of the photosensitive drum (is not elastically deformed), but when the developing sleeve has elasticity in the radial direction, the developing sleeve itself is elastically deformed and greatly distorted. Is possible.

  However, when the developing sleeve is a rigid body, it is almost determined by the thickness of the toner layer, so that the outer diameter difference between the central portion and the end portion in the longitudinal direction of the photosensitive drum is only allowed to be about 20 μm. This embodiment deals with the difference in the outer peripheral diameter difference in the longitudinal direction.

  In other words, in the present embodiment, the photosensitive drum and the developing roller can be brought into wide contact by abutting with a crossing angle in the contact state between the photosensitive drum and the developing roller, thereby preventing the above-mentioned “white spot”. It becomes possible.

  This embodiment will be described with reference to FIG. FIG. 7 is a diagram showing the arrangement of the photosensitive drum 1 and the developing roller 14 in the present embodiment. In FIG. 7, reference numeral 14 denotes a developing roller, and the developing roller 14 is brought into contact with the photosensitive drum 1 with an intersection angle θ. 14a is a flexible thin film developing sleeve, 14b is a shaft member, and 14c is a gap holding member. Since the photosensitive drum 1 and the developing roller 14 have the crossing angle θ, it is possible to form a stable contact nip between the photosensitive drum 1 and the developing roller 14. The intersection angle can be formed in the range of 0.2 degrees to 0.7 degrees. When the crossing angle is greater than 0.7 degrees, the load applied to the developing sleeve 14a increases, and the developing sleeve 14a is likely to be relied upon. If the angle is smaller than 0.2 degrees, there is no effect of setting the crossing angle.

  According to the present embodiment, when the developing roller 14 and the photosensitive drum 1 are brought into contact with each other, the contact length between the developing roller 14 and the photosensitive drum 1 is increased, but the developing sleeve 14a of the developing roller 14 is flexible. It will bend. Even if the developing sleeve 14a is bent, it does not come into contact with the shaft member 14b, so that the pressure increase due to the contact between the photosensitive drum 1 and the developing roller 14 is very small.

As described above, even when there is a difference in the outer peripheral diameter in the longitudinal direction of the photosensitive drum 1, it is possible to ensure a stable contact state according to the present embodiment. As a result, it is possible to prevent the occurrence of defective images by preventing “white spots” in the images.

Detailed explanatory view of the image forming apparatus according to the first embodiment 1 is an overall configuration diagram of an image forming apparatus according to a first embodiment. Configuration diagram of developer carrier according to first embodiment The figure explaining the contact state of the developer carrier and other members concerning a 1st embodiment The figure which shows the various evaluation results in the image forming apparatus of 1st Embodiment. The figure explaining the contact state of the developer carrier and the image carrier according to the second embodiment The figure which shows arrangement | positioning of the image carrier and developer carrier in 3rd Embodiment

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Charging roller 3 Light emitting element 4 Developing device 5 Transfer roller 6 Fixing device 7 Cleaning devices 8, 12, 14 Developing rollers 8a, 12a, 14a Flexible thin film developing sleeves 8b, 12b, 14a Shaft members 8c, 12c, 14c Gap holding member 9 Supply roller 10 Developing blade 11 Stirring member 13 End roller

Claims (7)

An image carrier on which an electrostatic latent image is formed;
A developing device comprising a developer carrying member that is rotatably provided and carries a developer for imparting to the electrostatic latent image ; and a contact member that contacts the developer carrying member ;
In an image forming apparatus having
The developer carrying member is a shaft portion and a developing sleeve that is provided on the outer peripheral side of the shaft portion and carries the developer. The developer carrying member is provided in contact with the image carrying member so that the developer is transferred to the electrostatic latent image. A flexible developing sleeve to be applied to an image; and a fixing portion provided between the developing sleeve and the shaft portion for fixing the developing sleeve at a longitudinal end portion, the shaft portion and the developing sleeve, A fixing portion for fixing the developing sleeve in a non-contact state,
The length of the contact member in the axial direction is a length that fits between the fixed portions. In the contact portion between the contact member and the development sleeve, the contact member bends the development sleeve by contacting the development sleeve. The inner surface of the developing sleeve in a region corresponding to the contact portion between the contact member and the developing sleeve is brought into contact with the shaft portion,
The axial length of the image carrier is an axial length that reaches the fixed portion. At the contact portion between the image carrier and the developing sleeve, the fixed portion is connected to the image carrier via the developing sleeve. The outer surface of the developing sleeve and the image carrier are brought into contact with each other, and the inner surface of the developing sleeve in a region corresponding to a contact portion between the image carrier and the developing sleeve is a region between the fixed portions. The image forming apparatus is configured to maintain a non-contact state with respect to the shaft portion . The image forming apparatus according to claim 1, wherein the fixing portion is formed of a rigid body. The fixing portion is formed of an elastic member, and further includes an intrusion amount adjusting member for adjusting an intrusion amount of the image carrier into the developer carrier due to elastic strain of the fixing portion. The image forming apparatus according to claim 1. The image forming apparatus according to claim 1, wherein the image carrier and the developer carrier are brought into contact with each other with a predetermined crossing angle. 5. The developing sleeve according to claim 1, wherein the developing sleeve is made of a resin, a mixture of rubber and a resin, or a laminate of a resin or a mixture of a rubber and a resin on a metal thin film. The image forming apparatus described. The image forming apparatus according to claim 1, wherein the contact member is a developer supply member that supplies a developer to the developer carrying member. The image forming apparatus according to claim 1, wherein the contact member is a developer regulating member that regulates the amount of developer carried on the developer carrying member.

Images