JP4885578B2 - Image forming unit and image forming apparatus - Google Patents

Description

  The present invention relates to an image forming unit and an image forming apparatus.

  2. Description of the Related Art Conventionally, in an image forming apparatus such as a printer, a copying machine, a facsimile machine, or a multifunction machine, for example, a printer, toner is attached to an electrostatic latent image formed on the surface of a photosensitive drum to form a toner image. An image forming unit (developing device) is disposed (see, for example, Patent Document 1).

  FIG. 2 is a conceptual diagram of a conventional printer.

  As shown in the figure, the electrophotographic process includes a charging roller 12 that uniformly charges the surface of the photosensitive drum 11, an exposure device 13 that exposes the surface of the photosensitive drum 11 to form an electrostatic latent image, The electrostatic latent image is developed with toner attached thereto, a developing roller 14 for forming a toner image, a toner supply roller 15 for charging the toner to be supplied to the developing roller 14, and a uniform toner layer on the developing roller 14 A developing blade 16, a transfer roller 17 for transferring the toner image on the photosensitive drum 11 onto the paper P, and a cleaning blade 18 for collecting the toner remaining on the photosensitive drum 11 without being transferred.

The photosensitive drum 11, the charging roller 12, the developing roller 14, the toner supply roller 15, the developing blade 16, the cleaning blade 18 and the like constitute an image forming unit.
JP 2001-305856 A

  However, in the conventional image forming unit, both ends of the developing roller 14 and both ends of the photosensitive drum 11 are rotatably fixed, so that the developing roller 14 is pressed against the photosensitive drum 11 by a certain amount (hereinafter referred to as “pressing amount”). When it is pressed with “nip amount”), the shaft of the developing roller 14 is deformed, and the nip amount in the central portion in the axial direction becomes smaller than the nip amount in the end portion, and the density in the horizontal direction of the image is reduced. There will be a difference.

  FIG. 3 is a view showing a pressure distribution between a conventional photosensitive drum and a developing roller. In the figure, the horizontal axis represents the axial position, and the vertical axis represents the pressure between the photosensitive drum 11 and the developing roller 14.

  As shown in the figure, the pressure at the center between the photosensitive drum 11 and the developing roller 14 is lower than the pressure at the end. Therefore, the nip amount at the central portion in the axial direction is smaller than the nip amount at the end portion.

  In this case, the central toner in the axial direction on the developing roller 14 is less likely to adhere to the photosensitive drum 11, and the toner at the end tends to adhere to the photosensitive drum 11. Will occur. As a result, the image quality is degraded.

  The present invention solves the problems of the conventional image forming unit and provides an image forming unit and an image forming apparatus capable of improving image quality without causing a density difference in the lateral direction of the image. With the goal.

  Therefore, in the image forming unit of the present invention, the image carrier, the developer carrier that is pressed against the image carrier, and attaches the developer to the image carrier, and the developer carrier are brought into contact with the image carrier. And a regulating member that regulates the amount of the developer on the developer carrying member.

  The regulating member is formed with a bent portion, and the portion of the bent portion having the smallest radius of curvature is defined as the apex portion, and the bending portion in the rotation direction of the developer carrying member. When a portion that is downstream from the apex and is in contact with the developer carrying member is a contact portion, a radius of curvature r of the contact portion is constant in the axial direction of the developer carrying member, and the apex portion Of the curvature radius R, the curvature radius Rc of the central portion in the axial direction of the developer carrying member is made smaller than the curvature radius Rt of the end portion.

  According to the present invention, in the image forming unit, the image carrier, the developer carrier that is brought into pressure contact with the image carrier, and the developer is attached to the image carrier, and the developer carrier are brought into contact with the image carrier. And a regulating member that regulates the amount of the developer on the developer carrying member.

  The regulating member is formed with a bent portion, and the portion of the bent portion having the smallest radius of curvature is defined as the apex portion, and the bending portion in the rotation direction of the developer carrying member. When a portion that is downstream from the apex and is in contact with the developer carrying member is a contact portion, a radius of curvature r of the contact portion is constant in the axial direction of the developer carrying member, and the apex portion Of the curvature radius R, the curvature radius Rc of the central portion in the axial direction of the developer carrying member is made smaller than the curvature radius Rt of the end portion.

  In this case, the curvature radius r of the contact portion is constant in the axial direction of the developer carrier, and the curvature radius Rc of the central portion in the axial direction of the developer carrier among the curvature radii R of the vertex portion is: The amount of toner adhering to the surface of the developer carrying member in the axial direction is uniform in the axial direction because it is smaller than the curvature radius Rt of the end portion, but the ratio of the toner having a large charge amount in the central portion of the developer carrying member And the ratio of toner with a large amount of charge at the edge decreases. Therefore, the development efficiency is high at the center of the developer carrying member, and the development efficiency is low at the end.

  Therefore, the difference in image density can be reduced between the center portion and the end portion of the developer carrier. As a result, the image quality can be improved.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In this case, a printer as an image forming apparatus will be described.

  FIG. 4 is a conceptual diagram of the printer according to the first embodiment of the present invention.

  As shown in the figure, an image forming unit 10 includes a photosensitive drum 11 as an image carrier, a charging roller 12 as a charging device that uniformly and uniformly charges the surface of the photosensitive drum 11, A developing roller 14 as a developer carrying member for forming a toner image as a developer image by attaching toner as a developer to the electrostatic latent image formed on the surface of the photosensitive drum 11 and developing the toner. A toner supply roller 15 as a developer supply roller that is charged and supplied to the developing roller 14, a developing blade 16 as a regulating member that forms a toner layer as a uniform developer layer on the developing roller 14, and a photosensitive drum 11 includes a cleaning blade 18 that collects toner remaining on the surface 11.

  An exposure device 13 is disposed above the image forming unit 10 so as to face the photosensitive drum 11. The exposure device 13 exposes the surface of the photosensitive drum 11 to form an electrostatic latent image as a latent image. Form an image. A transfer roller 17 as a transfer member is disposed below the image forming unit 10 so as to face the photoconductive drum 11, and the transfer roller 17 is a toner image formed on the photoconductive drum 11. Is transferred to a sheet P as a medium.

  The charging roller 12, the developing roller 14, the transfer roller 17, and the cleaning blade 18 are disposed in contact with the photosensitive drum 11. Then, both ends of the shaft (not shown) of the photosensitive drum 11 and both ends of the shaft 33 (FIG. 5) of the developing roller 14 are respectively rotatably fixed by a housing (not shown) which is an exterior of the image forming unit 10. The photosensitive drum 11 and the developing roller 14 are pressed by a nip amount as a predetermined pressure contact amount.

  In this embodiment, the left and right ends of the photosensitive drum 11 and the developing roller 14 are set to a nip amount of 0.10 [mm]. At this time, both ends of the shaft 33 (FIG. 5) of the developing roller 14 are urged toward the axial center of the developing roller 14 by the housing. Therefore, the developing roller 14 is bent, and the nip amount at the central portion of the photosensitive drum 11 and the developing roller 14 is smaller than the nip amount 0.10 [mm] at the end portion. Further, the developing blade 16 and the toner supply roller 15 are pressed against the developing roller 14.

  As shown in the drawing, the printer is provided with a paper cassette 21 as a medium accommodating portion for storing paper P, and a hopping roller 22 as a feeding roller for separating and transporting the paper P one by one. The Then, on the downstream side of the hopping roller 22 in the medium conveyance path, pinch rollers 23 and 24, a registration roller 25, and a conveyance roller 26 are arranged as conveyance members. Further, an image forming unit 10 is disposed in the medium conveyance path, and a fixing device 27 as a fixing device and the paper P that has passed through the fixing device 27 are discharged to the downstream side of the image forming unit 10 in the medium conveyance path. A pair of discharge rollers 28 is provided.

  Next, the operation of the printer having the above configuration will be described.

  In the printer, the sheets P stacked on the sheet cassette 21 are separated one by one by the hopping roller 22 and conveyed downstream. The skew is corrected by the registration roller 25 and the pinch roller 23 and further conveyed downstream.

  Subsequently, the transport roller 26 and the pinch roller 24 send the paper P to the image forming unit 10. The conveyed paper P passes between the image forming unit 10 and the transfer roller 17, and the toner image on the photosensitive drum 11 is transferred to the paper P. The paper P on which the toner image is transferred is sent to the fixing device 27, and the toner image is heated and pressurized in the fixing device 27 and fixed on the paper P. Thereafter, the paper P is discharged by a discharge roller 28 to a stacker unit (not shown).

  Next, the operation of the image forming unit 10 will be described.

  First, the photosensitive drum 11 is rotated clockwise (in the direction of the arrow) by a driving motor (not shown) as a driving unit, and the surface is uniformly and uniformly charged to a negative polarity by the charging roller 12. It is done. Then, the exposure device 13 irradiates the surface of the photosensitive drum 11 to form an electrostatic latent image on the surface of the photosensitive drum 11.

  Subsequently, the toner on the developing roller 14 is attached to the electrostatic latent image on the photosensitive drum 11, and the electrostatic latent image is developed to form a toner image. Then, the transfer roller 17 transfers the toner image onto the paper P. Note that toner remaining on the surface of the photosensitive drum 11 without being transferred is scraped off by the cleaning blade 18. As the photosensitive drum 11 is rotated clockwise, the charging roller 12, the developing roller 14, the toner supply roller 15, and the transfer roller 17 are rotated counterclockwise.

  FIG. 1 is a cross-sectional view of an end portion of a developing blade in the first embodiment of the present invention, FIG. 5 is a perspective view of a photosensitive drum, a developing roller, and a developing blade in the first embodiment of the present invention. FIG. 7 is a cross-sectional view of the central portion of the developing blade in the first embodiment of the present invention, and FIG. 7 is a diagram showing the radius of curvature of the developing blade in the first embodiment of the present invention. In FIG. 7, the horizontal axis represents the axial position, and the vertical axis represents the radius of curvature of the developing blade 16.

  In the figure, reference numeral 11 denotes a photosensitive drum. The photosensitive drum 11 is formed by coating a photosensitive layer 11a on an outer peripheral surface of a raw tube (not shown), and a photosensitive drum gear 35 is attached to one end of the raw tube. . Reference numeral 14 denotes a developing roller. The developing roller 14 is formed by coating a semiconductive elastic layer 34 on the outer peripheral surface of a cylindrical metal shaft 33, and a developing roller gear 36 is formed at one end of the shaft 33. Is attached.

  When the photosensitive drum gear 35 and the developing roller gear 36 are engaged with each other and the driving motor is driven, the photosensitive drum 11 and the developing roller 14 can be rotated. In this embodiment, urethane rubber is used as the material of the elastic layer 34, but silicone rubber can be used instead of urethane rubber.

  Reference numeral 16 denotes a developing blade. The developing blade 16 is formed by bending a plate-like elastic member into an “L” shape, and the bent portion, that is, the edge portion 30 is pressed against the developing roller 14. Arranged. The developing blade 16 extends toward the downstream side from the edge portion 30 in the rotation direction of the developing roller 14, and the first flat plate portion 16a extending toward the upstream side from the edge portion 30 in the rotation direction of the developing roller 14, A second flat plate portion 16b having a width Wb that is narrower than the width Wa of the first flat plate portion 16a, the tip of the first flat plate portion 16a being fixed to the main body of the image forming unit 10, and the second flat plate portion The tip of 16b is a free end. In the present embodiment, SUS (stainless steel) is used as the elastic member, but a metal material that is not easily worn can be used instead of SUS.

  The thickness of the developing blade 16 is preferably 0.05 [mm] or more and 0.5 [mm] or less from the viewpoint of easy folding. When the apex portion 31 is the point where the radius of curvature of the edge portion 30 of the developing blade 16 is the smallest, the curvature radius of the edge portion 30 is directed from the apex portion 31 toward the upstream side and the downstream side in the rotation direction of the developing roller 14. Is enlarged.

  In the present embodiment, the developing blade 16 is pressed against the developing roller 14 on the downstream side of the apex portion 31 in the rotation direction of the developing roller 14. If the developing blade 16 is brought into contact with the developing roller 14 on the upstream side of the apex portion 31 in the rotation direction of the developing roller 14, the developing blade 16 turns up as the developing roller 14 rotates. As a result, a toner layer having an appropriate thickness cannot be formed on the developing roller 14.

When the portion of the developing blade 16 that contacts the developing roller 14 is a contact portion 32, the radius of curvature at the apex portion 31 is R, and the radius of curvature at the contact portion 32 is r. The radius of curvature at the edge portion 30 is the minimum value at the apex portion 31 and increases with the downstream side in the rotation direction of the developing roller 14,
R <r
Be in a relationship.

If the radius of curvature R is large and the range of the edge portion 30 is wide,
r = R
However, the distance between the contact portion 32 and the apex portion 31 is close, and restrictions on the setting of the developing blade 16 become large, and it becomes difficult to make the thickness of the toner layer appropriate. Therefore,
R <r
Is preferable.

Further, as shown in FIG. 7, the curvature radius r is constant at each position in the axial direction of the developing blade 16, whereas the curvature radius R is varied depending on each position in the axial direction of the developing blade 16. As shown in FIGS. 1 and 6, the radius of curvature of the central portion of the developing blade 16 is made the smallest as Rc, and becomes larger as the distance from the central portion increases. When the radius of curvature of the end of the developing blade 16 is Rt,
Rt> Rc ≧ 0.7 Rt
And

  For this purpose, the mold used in the step of bending the developing blade 16 is formed so as to approach the values of the curvature radii Rc and Rt of the central part and the end part in the axial direction. When the developing blade 16 is bent, the developing blade 16 is wrinkled due to the bending. Therefore, polishing is performed to reduce the surface roughness to 1 [μm] or less. In this polishing step, the curvature radius Rt of the end portion in the axial direction of the developing blade 16 is adjusted. Similarly, the radius of curvature r of the contact portion 32 of the developing blade 16 may be adjusted to be uniform in the axial direction. Further, as a polishing method, there are buff polishing, sand blast polishing and the like. Sand blast polishing is more suitable for adjusting the curvature radius of the edge portion 30.

The relationship between the radius of curvature Rc at the center and the radius of curvature Rt at the end is Rc <0.8Rt
In this case, twisting occurs when the developing blade 16 is molded by a mold, and as a result, wrinkles are generated. In this case, even if polishing is performed, the surface roughness cannot be reduced to 1 [μm] or less. . As a result, an image defect occurs.

  By the way, when the developing roller 14 and the toner supply roller 15 are rotated counterclockwise in FIG. 4, the toner of the toner supply roller 15 is supplied to the developing roller 14. Variations occur in the thickness of the toner layer to be formed. Therefore, the edge portion 30 of the developing blade 16 scrapes off excess toner on the developing roller 14 to form a toner layer having a uniform thickness on the developing roller 14.

In this case, the thickness of the toner layer on the developing roller 14 after passing through the developing blade 16 is determined by the radius of curvature r of the contact portion 32 of the developing blade 16, and the larger the radius of curvature r is, Since the contact pressure with the developing roller 14 becomes lower, the toner layer on the developing roller 14 becomes thicker, and the smaller the radius of curvature r, the higher the contact pressure between the developing blade 16 and the developing roller 14, and the toner on the developing roller 14. The layer becomes thinner. The thickness of the toner layer on the developing roller 14 can be measured by the weight per unit area (1 [cm ² ]).

  In the present embodiment, since the radius of curvature r of the contact portion 32 is uniform in the axial direction, the thickness of the toner layer formed on the developing roller 14 is uniform in the axial direction.

  The toner on the developing roller 14 is charged as it passes between the developing blade 16 and the amount of charge depends on the radius of curvature R of the apex portion 31. An angle θ formed by a line connecting the apex portion 31 and the contact portion 32 and a tangent line of the developing roller 14 at the contact portion 32 is a toner entering angle.

  By the way, when the entering angle of the toner is large, the toner adhering on the developing roller 14 tends to enter between the developing roller 14 and the developing blade 16. That is, when the entrance angle of the toner is large, the ability of the developing blade 16 to scrape off the toner attached on the developing roller 14 is reduced. On the other hand, when the entrance angle of the toner is small, the toner adhering to the developing roller 14 hardly enters between the developing roller 14 and the developing blade 16. That is, when the entrance angle of the toner is small, the ability of the developing blade 16 to scrape off the toner attached on the developing roller 14 is increased. In addition, toner having a large charge amount is strongly held by the developing roller 14, but toner having a small charge amount is weakly held by the developing roller 14.

  Therefore, the smaller the radius of curvature R of the apex portion 31 of the developing blade 16, the smaller the toner entry angle. Therefore, toner with a large charge amount can enter, but toner with a small charge amount enters. It is scraped without being able to. That is, toner with a large amount of charge is attracted near the developing roller 14, and toner with a small amount of charge is separated from the developing roller 14.

  Further, the larger the radius of curvature R of the apex portion 31 of the developing blade 16, the larger the toner entering angle. Therefore, not only the toner having a large charge amount but also the toner having a small charge amount can enter without being scraped off. it can.

  The charge amount of the toner on the developing roller 14 can be obtained by connecting the shaft 33 of the developing roller 14 to a ground (not shown) and measuring the surface of the toner on the developing roller 14 with an electrometer. In this embodiment, since the radius of curvature r of the contact portion 32 is made uniform in the axial direction, the thickness of the toner layer on the developing roller 14 is also made uniform in the axial direction. Since the thickness of the toner layer on the developing roller 14 is uniform, the surface potential of the central portion and the end portion in the axial direction on the developing roller 14 is measured and compared to thereby charge the toner on the developing roller 14. The amount can be compared at the center and end in the axial direction.

  FIG. 8 is a diagram showing the flow of toner at the contact portion between the developing roller and the developing blade in the first embodiment of the present invention.

  Among the toners supplied from the toner supply roller 15 to the developing roller 14, the toner having a small charge amount is scraped off by the developing blade 16 at the central portion in the axial direction of the developing roller 14 because the curvature radius Rc is small. However, at the end of the developing roller 14 in the axial direction, the radius of curvature Rt is large, so that it is difficult to be scraped off. Therefore, the toner scraped off at the central portion in the axial direction of the developing roller 14 moves toward the end as shown in the drawing.

  On the other hand, among the toners supplied from the toner supply roller 15 to the developing roller 14, the toner having a large charge amount is not scraped off and gathers in the central portion having a small curvature radius Rc. Therefore, the ratio of the toner with a large charge amount is high at the central portion of the developing roller 14, and the ratio of the toner with a small charge amount is high at the end portion of the developing roller 14.

  In the image forming unit 10, when toner is attached from the developing roller 14 to the electrostatic latent image on the photosensitive drum 11, the amount of toner attached by the pressure between the photosensitive drum 11 and the developing roller 14 (hereinafter referred to as the toner adhesion amount) "Development efficiency") changes. The developing efficiency is affected by the charge amount of the toner on the developing roller 14 and is similarly affected by the pressure between the photosensitive drum 11 and the developing roller 14. Accordingly, the higher the ratio of toner having a large charge amount on the developing roller 14, the higher the development efficiency, and the more toner is attached to the photosensitive drum 11.

  Further, the development efficiency does not change when the pressure between the photosensitive drum 11 and the developing roller 14 is higher than a predetermined pressure, but the development efficiency is lower below the predetermined pressure. When the left and right end portions are pressed with the same nip amount as in the present embodiment, the pressure between the photosensitive drum 11 and the developing roller 14 is caused by the shaft 33 of the developing roller 14 being deformed. It changes by bending in a direction away from the photosensitive drum 11, and as a result, the central portion and the end portion in the axial direction are different.

  Then, the pressure is lowered at the central portion in the axial direction, and therefore the development efficiency is lowered, and the pressure is increased at the end portion, and thus the development efficiency is raised. If the charge amount of the toner on the developing roller 14 is uniform in the axial direction, when an image is formed, the density of the end portion with high development efficiency is high, and the density of the central portion with low development efficiency is low.

  Since the curvature radius Rc of the central portion of the apex portion 31 of the developing blade 16 is smaller than the curvature radius Rt of the end portion, toner having a small charge amount is scraped off at the central portion. Along with this, in the central portion, the ratio of toner having a large charge amount increases. The ratio of the toner having a large amount of charge at the central portion increases, so that the development efficiency increases, and the amount of toner adhering to the photosensitive drum 11 increases. Therefore, in the central portion, even if the nip amount between the photosensitive drum 11 and the developing roller 14 is small, the toner can be sufficiently adhered and development can be performed.

  FIG. 9 is a diagram showing the relationship between the ratio of the radius of curvature of the developing blade and the potential difference in the first embodiment of the present invention, and FIG. 10 is the ratio of the radius of curvature of the developing blade in the first embodiment of the present invention. It is a figure which shows the relationship with a density | concentration difference. In FIG. 9, the horizontal axis represents the ratio Rc / Rt of the curvature radius Rt to the curvature radius Rc of the developing blade 16, and the vertical axis represents the potential difference between the central portion and the end portion (the toner potential at the central portion minus the toner potential at the end portion). ) The absolute value of ΔV is taken. In FIG. 10, the horizontal axis represents the ratio Rc / Rt, and the vertical axis represents the difference in image density between the center portion and the end portion (end portion density−center portion density) ΔE.

  As shown in the figure, the smaller the ratio Rc / Rt (closer to zero (0)), the larger the difference between the radius of curvature Rc at the center and the radius of curvature Rt at the end, and the greater the absolute value of the potential difference ΔV. Become. Accordingly, the density difference ΔE of the image is reduced. Accordingly, there is no density unevenness in the axial direction, and image quality can be improved.

  Next, density difference determination was performed when the radii of curvature Rc and Rt of the apex portion 31 were changed.

  In the present embodiment, a solid black image (Duty 100 [%]) is formed, and the density of the image is measured with a reflection densitometer X-Rite 528 (manufactured by X-Rite). When the difference from the density is 0.4 or more, the density difference judgment is bad (×), and when it is 0.3 or more and less than 0.4, the density difference judgment is slightly good (Δ). When the density is less than 0.3, the density difference determination is good (◯).

When the ratio Rc / Rt is 1 (uniform radius of curvature in the axial direction), the density difference determination is poor, and as the ratio Rc / Rt decreases, the density difference determination becomes better. Become good. However,
Rc / Rt <0.8
In this case, twisting is likely to occur between the central portion and the end portion of the developing blade 16, and the twisting is increased by repeating image formation, and the thickness of the toner layer on the developing roller 14 is not uniform. Therefore, the life of the image forming unit 10 is shortened. Therefore, the ratio Rc / Rt is
Rc / Rt ≧ 0.8
Is preferable.

Further, the ratio Rc / Rt is
Rc / Rt <0.7
If this is the case, twisting occurs when the developing blade 16 is molded with a mold, wrinkles are formed, and the surface roughness cannot be reduced to 1 [μm] or less even after polishing. As a result, the image quality is degraded.

  Thus, in the present embodiment, the ratio Rc / Rt is set to 1 or less, so that the image density difference ΔE can be reduced between the central portion and the end portion of the developing roller 14. Therefore, the image quality can be improved.

  Next, a second embodiment of the present invention will be described. The image forming unit 10 in the present embodiment has the same structure as the image forming unit 10 in the first embodiment, and will be described with reference to FIG.

In the present embodiment, (r>) Rt> Rc in the first embodiment.
The developing blade 16 is used.

  FIG. 11 is a perspective view of the developing roller according to the second embodiment of the present invention.

  As shown in the figure, the developing roller 44 has a semiconductive elastic layer 45 formed on the outer peripheral surface of a cylindrical metal shaft 33, and the outer diameter increases at the central portion in the axial direction, and the outer surface at the end. It has a crown shape with a reduced diameter. It is preferable that at least a region for forming an image, that is, an image forming region has a crown shape. Further, although urethane rubber is used as the material of the elastic layer 45, silicone rubber can be used instead of urethane rubber.

  Next, the operation of the image forming unit 10 having the above configuration will be described.

  FIG. 12 is a sectional view of a developing roller and a developing blade in the second embodiment of the present invention.

  As shown in the figure, since the developing roller 44 has a crown shape, the position of the contact portion 32 of the developing blade 16 differs in the axial direction. The position of the developing blade 16 when the outer diameter is small, that is, when contacting the end 44a of the developing roller 44 is a, and the developing blade 16 when the outer diameter is large, that is, when the developing blade 16 contacts the central portion 44b of the developing roller 44 Let b be the position of. In this case, the developing blade 16 is lifted upward by the increase in the outer diameter of the central portion 44b (position b).

  Since one end of the developing blade 16 is fixed, the edge portion 30 of the developing blade 16 lifted upward is separated from the fixed portion fx in the horizontal direction. As a result, the contact portion 32 b where the developing blade 16 contacts the central portion 44 b of the developing roller 44 is in the direction away from the apex portion 31, that is, the downstream side in the rotating direction of the developing roller 44.

  On the contrary, the developing blade 16 is lowered downward by the amount of the outer diameter of the end portion 44a of the developing roller 44 (position a). Accordingly, the edge portion 30 of the developing blade 16 is closer in the horizontal direction than the fixed end portion in the longitudinal direction. Therefore, the contact portion 32 a where the developing blade 16 and the end portion 44 a of the developing roller 44 come into contact is in the direction approaching the fixed portion fx in the horizontal direction, that is, the upstream side in the rotating direction of the developing roller 44.

  As described above, the position of the contact portion 32 varies depending on the size of the outer diameter of the developing roller 44, and therefore, the distance between the line connecting the apex portion 31 of the developing blade 16 and the contact portion 32 and the tangent line of the developing roller 44. The entrance angle of the toner can be changed.

  FIG. 13 is a cross-sectional view of the central portion of the edge portion of the developing blade according to the second embodiment of the present invention.

  In the figure, ra is the radius of curvature of the end 44a of the developing roller 44, θa is the angle of entry of the end 44a of the developing roller 44, rb is the radius of curvature of the central portion 44b of the developing roller 44, and θb is the developing roller. 44, the approach angle of the central portion 44b, Rc is the radius of curvature of the apex portion 31.

  As shown in the figure, when the contact portion 32a is located near the apex portion 31, the toner entry angle θa is increased. As a result, the toner with a small charge amount is difficult to be scraped off, and the charge amount of the toner on the developing roller 44 is also reduced. Conversely, when the contact portion 32b is located at a position away from the apex portion 31, the toner entry angle θb is reduced. As a result, since the toner with a small charge amount is scraped off, the charge amount of the toner on the developing roller 44 is increased.

  Therefore, by using the developing roller 44 having a crown shape, the ratio of the toner having a large toner charge amount in the central portion 44a of the developing roller 44 having a large outer diameter is increased, and the end portion of the developing roller 44 having a small outer diameter is formed. In 44b, it is possible to increase the proportion of toner with a small amount of toner charge.

  Thus, in the present embodiment, the ratio Rc / Rt is set to 1 or less, so that the image density difference ΔE can be reduced between the central portion and the end portion of the developing roller 14. In addition, it is possible to increase the ratio of toner having a large amount of toner charge in the central portion 44a of the developing roller 44 and to increase the ratio of toner having a small amount of toner charge in the end portion 44b of the developing roller 44 having a small outer diameter. Therefore, the image quality can be further improved.

  Next, a third embodiment of the present invention will be described. The printer in this embodiment has the same structure as the printer in the first embodiment, and will be described with reference to FIG.

  In this embodiment, pulverized toner is used as the toner. However, polymerized toner can be used as long as it satisfies the conditions.

  Next, the definition of toner fluidity will be described.

The fluidity of the toner is
Fluidity [%] = 100-cohesion degree [%]
And the degree of aggregation is
Aggregation degree = (weight of toner remaining on sieve of 150 [μm] × 100) / 4
+ (Toner weight remaining on sieve of 75 [μm] mesh × 100) / 4 × (3/5)
+ (Toner weight remaining on sieve of 45 [μm] mesh × 100) / 4 × (1/5)
It is.

  When measuring fluidity, three types of sieves having different meshes of 150 [μm], 75 [μm], and 45 [μm] are stacked in three stages so that the coarser mesh is on the upper side. Then, 4.0 [g] of the toner to be measured is weighed and gently placed on the top 150 [μm] mesh screen. Subsequently, a three-tiered sieve with toner is set on a powder tester (Hosokawa Micron PT-N type), the vibration time is set to 15 [s], and the vibration ADJ dial is set to 1.5 (amplitude 1 [mm]). Gives vibration. Then, the sieve that has finished vibrating is divided into three, and the weight of the toner remaining on each sieve is measured. This measurement is repeated three times, and the average value is used as the fluidity value. Regarding the average particle diameter of the toner, the toner was measured using a Coulter Multisizer 3 (manufactured by Beckman Coulter, Inc.), and the toner was measured at 3000 counts with an aperture diameter of 100 [μm]. The particle size was taken.

  Since the surface area increases as the average particle size of the toner decreases, the amount of external additive added to make the fluidity 60% or more changes. Table 2 shows the relationship between the average particle diameter of the toner, the weight ratio of the toner, and the fluidity. In this embodiment, for example, an external additive having an average particle diameter of 5.5 [μm] and a toner weight ratio of 3.5 [%] or more is added.

  By the way, as the average particle diameter of the toner is smaller, the image quality can be improved. For example, the dot reproducibility, that is, how much reproducibility can be achieved on the image with respect to the dot pattern in the host device. It is shown in Table 3 when 2 × 2 printing (printing for forming 4 × 2 × 2 dots on 4 × 4 16 squares) is performed and the resolution (dpi) of 1 dot that can be printed is determined. It becomes like this.

  As can be seen from Table 3, in order to improve the image quality, the average particle diameter of the toner is preferably 6.0 [μm] or less.

  However, when the average particle size of the toner is reduced, the reproducibility of dots is increased, but the surface area per unit volume of the toner particles is increased, so that the adhesion between the toner particles is increased and the first embodiment is performed. Even when the developing blade 16 in the form is used, it becomes difficult for the toner to move from the center portion to the end portion side. Therefore, when the average particle diameter of the toner is 6.0 [μm] or less, it is preferable to use a toner having a fluidity of 60 [%] or more.

  Further, when the fluidity is lowered, it becomes difficult to separate the toner particles in a state where they adhere to each other. Therefore, only the toner having a large charge amount passes through the radius of curvature Rc of the apex of the edge portion 30 of the developing blade 16, and the charge amount is reduced. The separation of scraping off a small amount of toner becomes difficult.

  Accordingly, when the fluidity of the toner is set to 60% or more, the toners can be easily separated from each other, and the toner having a large charge amount and the toner having a small charge amount can be scraped and conveyed to the end portion.

  Next, density difference determination will be described.

  As in the first embodiment, the density difference in the horizontal direction is determined by forming a solid black image (Duty 100 [%]), measuring the density of the image with X-Rite, When the difference from the density of the part is 0.4 or more, the density difference determination is bad (x), and when it is 0.3 or more and less than 0.4, the density difference determination is slightly good (Δ ), And when it is less than 0.3, the density difference determination was good (◯).

  In addition, the dot reproducibility is determined by 2 × 2 printing (2 dots × 2 dots) and a resolution of 1 dot that can be printed [dpi]. The developing blade 16 having a radius of curvature Rc of 0.180 [mm], a radius of curvature Rt of 0.200 [mm], and a radius of curvature r of 0.236 [mm] Evaluation was made by combination with the fluidity of the toner. The evaluation results are shown in Table 4.

  As can be seen from Table 4, the use of toner having an average particle size of toner of 6.0 [μm] or less and toner fluidity of 60 [%] or more can eliminate uneven density in the lateral direction, Image quality can be improved.

  In the present embodiment, the evaluation was performed under the conditions that the curvature radius Rc is 0.180 [mm], the curvature radius Rt is 0.200 [mm], and the curvature radius r is 0.236 [mm]. The condition that the radius of curvature Rc is 0.158 [mm], the radius of curvature Rt is 0.197 [mm], the radius of curvature r is 0.235 [mm], and the radius of curvature Rc is the same as in the first embodiment. The results shown in Table 4 were also obtained when the conditions were 0.141 [mm], the radius of curvature Rt was 0.201 [mm], and the radius of curvature r was 0.237 [mm].

  When the curvature radius Rc is 0.199 [mm], the curvature radius Rt is 0.199 [mm], and the curvature radius r is 0.235 [mm], any toner shown in Table 4 or Table 5 can be used. Even if was used, the density difference judgment was poor (x).

  As described above, in this embodiment, by setting the average particle diameter of the toner to 6 [μm] or less, the dot reproducibility can be improved even when the resolution is large, and the toner fluidity is set to 60 [μm]. %] Or more can prevent density unevenness in the horizontal direction and improve image quality.

  Next, a fourth embodiment of the present invention will be described. The image forming unit 10 in the present embodiment has the same structure as the image forming unit 10 in the first embodiment, and will be described with reference to FIGS.

  FIG. 14 is a diagram showing the pressure distribution between the photosensitive drum and the developing roller in the fourth embodiment of the present invention, and FIG. 15 is a diagram showing the curvature radius of the developing blade in the fourth embodiment of the present invention. It is. In FIG. 15, the horizontal axis indicates the axial position, and the vertical axis indicates the radius of curvature of the developing blade 16.

  In the present embodiment, as shown in FIG. 14, the photosensitive drum 11 and the developing roller 14 are formed by a photosensitive drum gear 35 as a first gear and a developing roller gear 36 as a second gear. The nip amount on the processed side, that is, the gear side is increased to 0.15 [mm], and the nip amount on the side where the photosensitive drum gear 35 and the developing roller gear 36 are not formed, that is, the opposite gear side is set to 0.10 [mm]. ] And then pressed down.

  Further, as shown in FIG. 15, in this embodiment, the radius of curvature r is constant at each position in the axial direction of the developing blade 16, whereas the radius of curvature of the apex portion 31 of the developing blade 16 is set. Of R, the radius of curvature Rc of the central portion in the axial direction of the developing roller 14 is made smaller than the radius of curvature Rg of the end portion on the gear side and the radius of curvature Rh of the end portion on the opposite gear side in the axial direction of the developing roller 14. And the curvature radius Rh is made smaller than the curvature radius Rg. In the present embodiment, the radius of curvature Rg is 0.210 [mm], the radius of curvature Rh is 0.200 [mm], and the radius of curvature r is 0.236 [mm].

  Next, the operation of the image forming unit 10 having the above configuration will be described.

  When the photosensitive drum 11 and the developing roller 14 are rotated by a drive motor (not shown), a force that causes the photosensitive drum gear 35 and the developing roller gear 36 to escape with each other as the rotational speed increases, and rotates eccentrically. End up. As a result, the pressure between the photosensitive drum 11 on the gear side and the developing roller 14 is weakened with the period of the photosensitive drum 11.

  When the pressure between the photosensitive drum 11 and the developing roller 14 becomes low, the toner on the developing roller 14 becomes difficult to adhere to the photosensitive drum 11 and the photosensitive drum 11 and the developing roller 14 may be separated. is there. In that case, a white broach (a state in which no toner adheres) occurs. As a result, white spots occur in the drum cycle at the portion corresponding to the gear side on the image.

  Therefore, in the present embodiment, the occurrence of white broach can be suppressed by increasing the nip amount on the gear side. However, since the photosensitive drum 11 rotates eccentrically and the gear side pressure is low or high, the toner on the developing roller 14 is attached too much when the gear side pressure is high. As a result, the toner adheres to portions other than the electrostatic latent image on the surface of the photoconductive drum 11 and the background stain occurs.

  Therefore, in the present embodiment, the curvature radius Rg of the apex portion 31 of the developing blade 16 is made larger than the curvature radius Rh on the gear side than the curvature radius Rh on the counter gear side. Can increase the proportion of toner with a small amount of charge and increase the proportion of toner with a large amount of charge on the non-gear side. As a result, it is possible to prevent background contamination even if there is a difference in the nip amount between the photosensitive drum 11 and the developing roller 14 in the axial direction.

The radii of curvature r and R of the developing blade 16 are (r>) Rg> Rc
(R>) Rh> Rc
And
Rg> Rh
In the case of
Rg = Rh
And Rg <Rh
In the case of, there is generation of dirt,
The radius of curvature of the developing blade 16 is (r>) Rc> Rg
(R>) Rc> Rh
When this is, density unevenness occurs in the width direction as shown in the first embodiment regardless of the relationship between the curvature radii Rg and Rh.

In this embodiment,
r> R
Therefore, uneven density in the width direction can be prevented. further,
Rg> Rc
Therefore, the occurrence of white broach can be prevented.

  The present invention is not limited to the above embodiments, and various modifications can be made based on the gist of the present invention, and they are not excluded from the scope of the present invention.

It is sectional drawing of the edge part of the image development blade in the 1st Embodiment of this invention. It is a conceptual diagram of the conventional printer. It is a figure which shows the pressure distribution between the conventional photoreceptor drum and a developing roller. 1 is a conceptual diagram of a printer according to a first embodiment of the present invention. FIG. 3 is a perspective view of the photosensitive drum, the developing roller, and the developing blade in the first embodiment of the present invention. It is sectional drawing of the center part of the image development blade in the 1st Embodiment of this invention. 3 is a diagram illustrating a radius of curvature of the developing blade in the first embodiment of the present invention. FIG. 3 is a diagram illustrating a toner flow at a contact portion between a developing roller and a developing blade in the first embodiment of the present invention. It is a figure which shows the relationship between the ratio of the curvature radius of the image development blade in 1st Embodiment of this invention, and an electrical potential difference. It is a figure which shows the relationship between the ratio of the curvature radius of the image development blade and density difference in the 1st Embodiment of this invention. It is a perspective view of the developing roller in the 2nd embodiment of the present invention. It is sectional drawing of the developing roller and developing blade in the 2nd Embodiment of this invention. It is sectional drawing of the center part in the edge part of the image development blade in the 2nd Embodiment of this invention. It is a figure which shows the pressure distribution between the photoconductive drum and the developing roller in the 4th Embodiment of this invention. It is a figure which shows the curvature radius of the developing blade in the 4th Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Image forming unit 11 Photosensitive drums 14 and 44 Developing roller 16 Developing blade 30 Edge part 31 Apex part 32 Contact part 35 Photosensitive drum gear 36 Developing roller gear

Claims (8)

(A) an image carrier;
(B) a developer carrier that is brought into pressure contact with the image carrier and causes the developer to adhere to the image carrier;
(C) having a regulating member that is brought into contact with the developer carrying member and regulates the amount of the developer on the developer carrying member;
(D) The regulating member is formed with a bent portion, and a portion of the bent portion where the radius of curvature is minimized is a vertex portion, and the rotation direction of the developer carrier in the bent portion In this case, the radius of curvature r of the contact portion is constant in the axial direction of the developer carrier, and the portion that is downstream of the vertex portion and in contact with the developer carrier is a contact portion. The image forming unit, wherein a curvature radius Rc of a central portion in the axial direction of the developer carrying member is smaller than a curvature radius Rt of an end portion of the curvature radius R of the portion. The radii of curvature Rc and Rt are Rc ≧ 0.7Rt
The image forming unit according to claim 1. The ratio Rc / Rt of the radius of curvature Rt to the radius of curvature Rc is:
0.9 ≧ Rc / Rt ≧ 0.8
The image forming unit according to claim 1.   The image forming unit according to claim 1, wherein the developer carrying member has a crown shape in which an outer diameter decreases from a center portion toward an end portion in an axial direction.   The image forming unit according to claim 1, wherein the average particle diameter of the developer is 6.0 [μm] or less, and the flowability of the developer is 60 [%] or more. (A) an image carrier gear for transmitting rotation to one end of the image carrier;
(B) A developer carrier gear is disposed on a gear side of the end of the developer carrier on which the image carrier gear is disposed;
(C) The pressure contact amount between the image carrier and the developer carrier on the gear side is larger than the pressure contact amount on the non-gear side,
(D) Of the radius of curvature R of the apex, when the radius of curvature on the gear side is Rg and the radius of curvature on the opposite gear side is Rh,
Rg> Rh
The image forming unit according to claim 1.   The image forming unit according to claim 1, wherein a curvature radius R of the apex portion is smaller than a curvature radius r of the contact portion.   An image forming apparatus on which the image forming unit according to claim 1 is mounted.

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