JPH04336562A - Developing device - Google Patents

Abstract

PURPOSE:To keep the contact pressure between a developer carrier body and a latent image carrier body constant by forming the outer shape of the developer carrier body for press contact development to a crown shape. CONSTITUTION:A developer carrier body 9 is constituted by arranging an elastic layer 11 and a magnetic field generating layer 12 in concentric form on the outer circumference of a crown shaped shaft 10. Accordingly, even if a deflection is generated at the center part of the shaft 10 by an energizing force, the press contact pressure between the developer carrier body and a latent image carrier body can be kept constant, because the elastic deformation quantity at the edge part of the developer carrier body having a large thickness of the elastic layer is large. Accordingly, an image free from the density unevenness can be formed over the whole width in the image formation region.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a developing device that develops a latent image formed on a latent image carrier, and in particular, a developing device that forms a thin layer of developer on the developer carrier and transports the developer. It relates to a developing device.

0002

[Prior Art] A conventional developing device is
As disclosed in No. 867, a developer carrier is made of an elastic member, a thin toner layer regulated by an elastic blade is formed on the developer carrier, and the toner layer is pressed against the latent image carrier. The electrostatic latent image on the latent image carrier is developed and visualized using so-called pressure-contact development.

0003

[Problems to be Solved by the Invention] However, when a thin layer of toner is formed on a developer carrier and pressure development is carried out by holding and conveying the toner to a latent image carrier in the above-mentioned prior art, the developer carrier is Since the shaft of the image carrier is bent by the biasing force of the latent image carrier, the pressure of the developer carrier against the latent image carrier and the width of the development nip become uneven in the axial direction, resulting in the formation of a solid image over the entire surface. However,
There has been a problem in that the density of the image formed is different between a portion near the bearings that support both ends of the shaft of the developer carrier and a substantially central portion of the shaft, making it impossible to obtain a good printed image.

SUMMARY OF THE INVENTION The present invention is intended to solve these problems, and its object is to provide a developing device capable of printing with less density unevenness over the entire width of an image area.

[0005]

[Means for Solving the Problems] A developing device of the present invention forms a thin layer of developer on a developer carrier and develops a latent image formed on the latent image carrier with the developer. The developer carrier has a layered structure in which an elastic layer is provided around the outer periphery of the shaft, and the shaft has a crown shape.

Further, the developing device of the present invention is characterized in that the hardness of the elastic layer varies in the axial direction of the developer carrier.

[0007]

[Operation] According to the above structure of the present invention, the shaft of the developer carrier for pressure-contact development has a crown shape, and the diameter of the elastic layer disposed on the outer periphery of the shaft is constant in the axial direction of the developer carrier. In this case, the thickness of the elastic layer is thinnest at approximately the center of the shaft and thicker at the ends, and the amount of deformation of the elastic layer when pressure development is performed is smallest at approximately the center of the developer carrier, and becomes thicker at the ends. growing. Therefore, even if the shaft of the developer carrier is bent due to the biasing force, by keeping the shaft of the developer carrier in a crown shape, the pressure of contact between the developer carrier and the latent image carrier can be reduced to the developer carrier. Since it is possible to keep the density constant in the axial direction, it is possible to form an image with less density unevenness over the entire width of the image forming area.

[0008] According to the above structure of the present invention, the developer carrier is made of an elastic body or the like, and the hardness of the elastic body is set such that the hardness of the elastic body is highest at approximately the center of the developer carrier and becomes softer toward the ends. If the image bearing member is formed in such a manner that the shaft of the developer carrier is deflected by the biasing force when pressure contact development is performed, the distance between the shaft and the latent image carrier will be different between approximately the center and the ends of the shaft. Also, since the amount of elastic deformation of the developer carrier due to the urging force increases toward the ends depending on the hardness distribution of the elastic layer, the contact pressure between the developer carrier and the latent image carrier is adjusted in the axial direction of the developer carrier. The density can be kept constant, and an image with less density unevenness can be formed over the entire width of the image forming area.

The present invention will be explained in detail below with reference to Examples.

0010

【Example】

(Embodiment 1) FIG. 1 is a cross-sectional schematic view of a developer carrier in an embodiment of the present invention, in which a thin toner layer 8 regulated by an elastic blade is spread on the outer peripheral surface of a developer carrier 9. The developer carrier 9 is held against the latent image carrier 1 by a force applied to a bearing 17 that supports the shaft, and developed by being conveyed to a position facing the latent image carrier 1. It is being done. In FIG. 1(a), the developer carrier 9 is a roller in which an elastic layer 11 and a magnetic field generating layer 12 are arranged concentrically around the outer periphery of a shaft 10, and the diameter of the shaft is approximately at the center of the developer carrier. It is a so-called crown-shaped shaft that is largest and gradually becomes smaller as it approaches the end of the developer carrier, and the diameter at the center of the shaft is 11.
[mm] and 6 [mm] at the end. This is because if the developer carrier is biased against the latent image carrier when pressure development is performed, variations in the pressure in the axial direction of the developer carrier occur due to deflection of the shaft 10 due to the biasing force.
If the shaft diameter of the developer carrier is made larger at the center of the shaft where the pressure is lower and smaller at the ends where the pressure is higher,
Since the elastic layer thickness is thinner at the center and thicker at the ends, the amount of elastic deformation of the developer carrier in response to the biasing force is also smaller at the center and larger at the ends, and as a result, the pressure applied to the developer carrier increases. The density is almost constant in the axial direction of the body, making it possible to print with little density unevenness over the entire width of the image forming area.

In FIG. 1(b), the developer carrier 9 shown in FIG. 1(a) is pressed against the latent image carrier 1 for development. Diameter 20 [m
m], length 220 [mm], an elastic layer with an average hardness of 20 degrees in Asker type A (Kobunshi Keiki Co., Ltd.) is attached to the latent image carrier with a force of 2 [kg]. Forced. Shaft 1 with a length of 240 [mm] that supports the developer carrier
0 is bent due to the biasing force with the latent image carrier, but the diameter of the shaft is the largest at approximately the center of the developer carrier,
Since it gradually decreases as it approaches the end of the developer carrier, even if the shaft is deflected by the biasing force and the biasing force is concentrated at the end of the developer carrier, the amount of elastic deformation at the end will be reduced to the center. In comparison, it is about 30 [μm] larger, so the contact pressure at the part where the developer carrier and the latent image carrier face each other is 5 [g/g/m].
mm2], and the developing nip width was 2 [mm], which was almost constant over the entire width of the image forming area, and it was possible to form prints with little density unevenness.

In FIG. 1, the shaft 10 can be made of a highly rigid metal such as stainless steel or aluminum, and the outer diameter is preferably 6 mm or more in order to reduce deflection. The diameter difference (crown amount) is 2 to 10 [mm] in order to make a difference in the amount of elastic deformation of the elastic layer.
] is desirable. Further, for the elastic layer 11, polyurethane, fluorocarbon rubber, NBR, natural rubber, silicone rubber, etc. can be used in the form of rubber, foam, or a skin layer formed on the surface of the foam, and conductive powder such as carbon is dispersed to conduct the elastic layer 11. can be given gender. In addition, the thickness of the elastic layer is preferably 0.5 [mm] or more at the thinnest part in order to perform pressure development without damaging the latent image carrier, and the hardness is Asker A.
The desired hardness is about 5 to 50 degrees on a mold hardness tester. Furthermore, for the magnetic field generation layer 12, known magnetic recording materials and magnet materials can be used, and more specifically, Fe, Ni, Co,
A magnetic material containing at least one element of Mn, such as γ-Fe2O3, Ba-Fe, etc., can be used, and if it is dispersed in a resin to form a magnetic field generation layer, flexibility can be improved and the film thickness can be increased. is 100 [μm] or less, preferably 1
The film is thinned to around 0 [μm] and the minimum magnetization reversal pitch is 10
0 [μm] or less, fluctuations in the amount of toner conveyance are suppressed to a minute amount, and density fluctuations are reduced.

In addition, in FIG. 1, the toner transport performance is improved by performing surface treatments such as forming minute grooves in the circumferential direction or axial direction on the surface of the developer carrier 9, or forming minute irregularities by sandblasting or the like. You may also try to improve this. Furthermore, the layer structure of the developer carrier as shown in FIG.
Each can produce electrode effects, insulation effects, and wear resistance effects. Furthermore, an endless sleeve or the like is placed between the magnetic field generating layer and the elastic layer to improve the adhesion between the elastic layer and the magnetic field generating layer and to increase the smoothness of the base of the magnetic field generating layer, thereby improving the finishing accuracy of the magnetic field generating layer. You can improve your performance.

(Embodiment 2) FIG. 2 is a cross-sectional overview diagram and an explanatory diagram of the hardness distribution of a developer carrier in another embodiment of the present invention, in which members with substantially the same names and functions as those in FIG. are given the same number and the explanation will be omitted. In FIG. 2(a), the developer carrier 9 is a roller having an elastic layer 11 disposed around the outer periphery of the shaft 10, and the diameter of the shaft 10 is largest at approximately the center of the developer carrier. It has a so-called crown shape that gradually becomes smaller as it approaches the end, and is formed with a diameter difference of 10 [mm] between the shaft center and the end. The elastic layer 11 is the shaft 1
0 is integrally molded by foaming conductive silicone rubber around the outer periphery of the shaft, and has a skin layer 21 on the surface, and the cell density is high near the outer periphery of the shaft and the molding die of the elastic layer. The hardness is the hardest at the approximate center of the developer carrier, where there is less low cell density region, and becomes softer toward the edges.More specifically, as shown in FIG. 2(b), the center of the developer carrier has Asker type A hardness. 1 in total (manufactured by Kobunshi Keiki Co., Ltd.)
The angle is 5 degrees, and the ends are shaped to have an angle of 10 degrees. If pressure development is performed using the developer carrier 9 shown in FIG. 2, when the developer carrier is biased against the latent image carrier, the deflection of the shaft due to the biasing force causes pressure in the axial direction of the developer carrier. Even if variations occur, if the amount of elastic deformation of the developer carrier due to the biasing force is made larger toward the ends depending on the hardness distribution and elastic layer thickness of the elastic layer, concentration of the biasing force at the ends of the developer carrier can be reduced. It was possible to release the contact pressure to a constant value of approximately 2 [g/mm2] in the axial direction of the developer carrier, and form a printed image with little density unevenness over the entire width of the image forming area.

In FIG. 2, as a method of imparting a hardness distribution in the axial direction of the developer carrier, the elastic layer 11 is given a cell density distribution in the radial direction. It is also possible to obtain a desired hardness distribution by giving the skin layer thickness a distribution or by giving the skin layer thickness a distribution.

(Embodiment 3) FIG. 3 is a schematic cross-sectional view of a shaft in another embodiment of the present invention, in which an elastic layer or the like is provided around the outer periphery of the shaft 10 to serve as a developer carrier. It is. In FIG. 3(a), the shaft 10 has a gentle outer shape expressed by the following formula.

[0017]

[Equation 1] Dx=D+Cx Cx=C[1-(X/N)2] Dx: Shaft diameter at point X, Cx: Crown value at point X C: Specified crown value, X: Based on the center of the elastic roller Measurement position N: Number of divisions, D
: Crown portion minimum diameter d : Shaft minimum diameter Even when the shaft 10 is made of a rigid body such as stainless steel, it can withstand several tens of [kg] of biasing load of about 1 [kg].
μm], the shaft minimum diameter d is set to 6 [μm].
mm] or more is desirable. The designated crown value C is related to the difference in the thickness of the elastic layer provided on the outer periphery of the shaft, and this difference in thickness of the elastic layer controls the amount of elastic deformation of the elastic layer in response to the urging force, and the pressure is adjusted in the axial direction of the developer carrier. The hardness of the material itself that makes up the elastic layer is Asker A.
In the case of low hardness of 30 degrees or less on the mold hardness tester, the difference in the amount of elastic deformation due to the difference in elastic layer thickness becomes noticeable, so even if the specified crown value C is as small as 4 [mm] or less, it is difficult to press against the deflection of the shaft. Can compensate for pressure unevenness.

Although a quadratic equation is shown here as an equation for giving the external shape, the present invention is not limited to this, and various mathematical equations such as a quartic equation and a sine function can be applied.

In FIG. 3(b), the shaft 10 is made of stainless steel and has a length of 240 [mm], and its diameter is 10 mm over the central part of the shaft, which is about 140 [mm].
[mm] and 6 [mm] at both ends 20 [mm], and the hardness of the elastic layer is 15 on the Asker type A hardness tester.
When the amount of deflection of the shaft is small due to the hardness of
The concentration of biasing force generated at the ends of the developer carrier is relieved by increasing the thickness of the elastic layer only at the ends of the developer carrier.

Incidentally, the shaft 10 that can be used in the present invention is not limited to those shown in FIGS. 3(a) and 3(b), but also a shaft whose diameter is larger in the center as shown in FIG. 3(c). Any shape can be used as long as the pressure can be made uniform by changing the amount of elastic deformation of the developer carrier, such as one in which the shape is gradually changed so that the size becomes smaller toward the ends.

(Embodiment 4) FIG. 4 is a schematic cross-sectional view of an image forming apparatus using a developer carrier according to another embodiment of the present invention. A photosensitive layer 3 having organic or inorganic photoconductivity is coated thereon, and after the photosensitive layer 3 is charged using a charger 4 such as a corona charger or a charging roller, it is charged with a laser or an LED.
Light emitted from a light source such as the like is selectively irradiated onto the photosensitive layer 3 according to the image through the imaging optical system 6 to obtain a potential contrast and form an electrostatic latent image. On the other hand, the developing device 7 conveys and develops the magnetic toner 8, and the developer carrier 9 that conveys the toner 8 has an elastic layer 11 and a magnetic field generating layer 12 on the outer periphery of a crown-shaped shaft 10, respectively. They are arranged concentrically, and the magnetic toner 8 is held directly on the developer carrier 9 by leakage magnetic flux around the outer periphery of the magnetic field generating layer 12.
A thin layer of toner 8 is conveyed by rotating a developer carrier 9 while regulating the appropriate amount with a plate-shaped blade 13 made of non-magnetic or magnetic metal or resin. The developer carrier 9 is pressed against the latent image carrier 1 at a predetermined pressure, and when the toner 8 on the developer carrier 9 is conveyed to the pressure contact portion, the potential contrast of the latent image carrier 1 and the development The toner 8 charged according to the developing electric field by the bias applying means 14 adheres to the latent image carrier 1, and the electrostatic latent image is visualized. Further, a toner image is transferred onto the recording paper 16 using a transfer device 15 such as a corona charger or a transfer roller, and the toner is fixed onto the recording paper using heat or pressure to obtain a desired image on the recording paper. It is.

When 10,000 line images, character images, and solid images of 600 [DPI] were continuously formed using an image forming apparatus as shown in FIG. 4, the line images of 600 [DPI] became thicker. It is possible to stably form a high-density solid image with an OD value of 1.4 or higher without any density unevenness, without trailing at the edge of the image or with background fog, and with no background fog on the recording paper. Not only was there no background fog on the latent image carrier, the amount of waste toner could be significantly reduced. Further, by making the shaft 10 into a crown shape, even if the shaft is bent due to the urging force, the contact pressure between the developer carrier and the latent image carrier can be kept constant in the axial direction of the developer carrier, so that the image It is now possible to form a printed image with less density unevenness over the entire width of the area. Furthermore, since the magnetic toner 8 can be effectively held by the magnetic force generated by the magnetic field generating layer 12, stable toner transport is possible even when the amount of toner remaining in the developing device is as small as 50 [g] or less. We were able to obtain images with little variation in density over time.

Note that in FIG. 4, arrows indicate the direction of rotation of each member. Further, as toner suitable for the developer carrier of the present invention, all toners known as one-component magnetic toner or one-component non-magnetic toner can be used, as well as a mixture of non-magnetic toner and a small amount of magnetic particles. A 1.5-component toner or the like can also be used.

(Comparative Example 1) FIG. 5 is a schematic cross-sectional view of a developer carrier in a conventional developing device, and shows an elastic layer 1 having the same diameter and the same hardness in the axial direction on the outer periphery of the shaft 10.
1 is arranged to hold a thin toner layer 8 regulated by an elastic blade on the outer peripheral surface of the developer carrier 9,
It is conveyed to a position facing the latent image carrier 1 and developed.
The developer carrier 9 is urged against the latent image carrier 1 by a force applied to a bearing 17 that supports the shaft, and pressure development is performed. The shaft 10 has a bearing 1 that supports the developer carrier.
The shaft is bent due to the biasing force applied in step 7, and the approximately central portion of the shaft where the amount of deflection is the largest cannot maintain good pressure contact with the latent image carrier, and the developing nip width also decreases. The image density becomes lighter. Therefore, if the biasing force applied to the developer carrier is increased in order to obtain a sufficient density at the center of the image, background fog tends to occur at both ends of the image, making it impossible to obtain sufficient image quality.

[0025]

As explained above, according to the present invention, by making the shaft of the developer carrier for pressure-contact development into a crown shape, even if the shaft is deflected by the biasing force, it can be kept in contact with the developer carrier. In addition to keeping the contact pressure and nip width of the image carrier constant over the entire width of the image forming area, the amount of elastic deformation of the developer carrier can be controlled by machining the shaft, so the hardness of the material of the elastic layer itself can be changed. Since the hardness distribution can be imparted without using special polishing means, it is possible to provide a developing roller at a low cost that can control the pressing pressure with high accuracy.

Further, according to the present invention, by giving the developer carrier for pressure development a hardness distribution, even if the shaft is deflected by the urging force, the pressure is reduced due to the difference in the amount of elastic deformation of the developer carrier. can be kept constant over the entire width of the image forming area.

Therefore, in the present invention, the contact pressure between the developer carrier and the latent image carrier and the developing nip width are substantially uniform in the axial direction of the developer carrier, and an image with less density unevenness is produced over the entire width of the image forming area. It has the excellent effect of forming

[Brief explanation of drawings]

FIG. 1 is a cross-sectional schematic diagram of a developer carrier in an embodiment of the present invention.

FIG. 2 is a cross-sectional schematic diagram and an explanatory diagram of hardness distribution of a developer carrier in another embodiment of the present invention.

FIG. 3 is a cross-sectional schematic view of a shaft in another embodiment of the present invention.

FIG. 4 is a schematic cross-sectional view of an image forming apparatus using a developer carrier according to another embodiment of the present invention.

FIG. 5 is a cross-sectional schematic diagram of a developer carrier in a conventional developing device.

[Explanation of symbols]

1 Latent image carrier 8 Toner 9 Developer carrier 10 Shaft 11 Elastic layer 12 Magnetic field generation layer

Claims (2)

[Claims] 1. A developing device that forms a thin layer of developer on a developer carrier and develops a latent image formed on the latent image carrier with the developer, wherein the developer carrier is attached to a shaft. A developing device having a layered structure in which an elastic layer is disposed on the outer periphery, and the shaft has a crown shape. 2. The developing device according to claim 1, wherein the hardness of the elastic layer varies in the axial direction of the developer carrier.