JP3532480B2 - Developing device and manufacturing method thereof - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is provided in an image forming apparatus such as a copying machine or a printer for performing electrophotographic image formation, and uses an electrostatic latent image formed on the surface of an electrostatic latent image carrier as a toner. The present invention relates to a developing device that visualizes an image.

[0002]

2. Description of the Related Art In an image forming apparatus for forming an electrophotographic image, an electric charge of a single polarity is uniformly charged on the surface of an electrostatic latent image carrier, and then an image modulated by image data is formed. Irradiate with light. An electrostatic latent image is formed on the surface of the electrostatic latent image bearing member irradiated with the image light by the photoconductive action of the photosensitive layer, and after the electrostatic latent image is visualized as a toner image, the electrostatic latent image is formed. The image is transferred from the surface of the latent image carrier to the surface of the recording medium.

As described above, in the image forming apparatus for forming an electrophotographic image, as a means for visualizing an electrostatic latent image into a toner image, the electrostatic latent image is held after being irradiated with image light. There is one using a contact-developing type developing device provided with a toner carrier which is brought into pressure contact with the body surface. The developing device rotatably supports a toner carrier formed into a cylindrical shape by an elastic material, rotates the toner carrier carrying the toner on the surface at a predetermined speed, and holds an electrostatic latent image at a predetermined pressure. Contact the body surface.

As a conventional developing device, for example, Japanese Patent No. 2
Japanese Patent No. 760501 discloses a configuration in which the moving speed of the surface of a toner carrier having a surface roughness of 2 μm or less is set to 1.5 to 7.0 times the moving speed of the surface of an electrostatic latent image holding member. In Japanese Patent No. 2815888, the hardness is 15 to
A configuration is disclosed in which the peripheral speed of the elastic rubber roller of 60 degrees is set to 0.5 to 3 times the peripheral speed of the electrostatic latent image holding member.

Generally, the peripheral surface of the toner carrier formed of an elastic material in a cylindrical shape is elastically deformed in the radial direction at the portion by being brought into pressure contact with the surface of the electrostatic latent image carrier, and in the circumferential direction. A so-called developing nip that comes into contact with the surface of the electrostatic latent image holding member within a predetermined length range is formed, and the length (nip width) of the developing nip in the circumferential direction is equal to that of the electrostatic latent image holding member and the toner carrying member. Along with the pressure contact force (nip pressure), it affects the toner adhesion state to the electrostatic latent image, that is, the image forming state.

[0006]

However, the toner carrier and the electrostatic latent image carrier have a tolerance of several tens of μm in the radial direction for reasons of processing accuracy. While the image carrier rotates, the amount of radial deformation of the peripheral surface of the toner carrier fluctuates within a range of several tens of μm, and the nip width and nip pressure in the moving direction of the toner carrier and the electrostatic latent image carrier vary. There is a problem that it becomes non-uniform and unevenness occurs in the density of the formed image. Even when a toner carrier having excellent surface properties such as surface roughness and hardness is used, if the nip pressure becomes excessive due to the radial tolerance of the toner carrier and the electrostatic latent image carrier, the electrostatic latent image carrier will be retained. There is a problem that toner is mechanically attached to a non-image portion on the surface of the body, causing image fogging. Furthermore, when performing high-density image formation in which the electrostatic latent image density on the electrostatic latent image holder is 1200 dpi or more, the potential potential of the electrostatic latent image decreases, and once on the surface of the electrostatic latent image holder. There is a problem in that the adhered toner moves due to mechanical rubbing, which causes image distortion.

An object of the present invention is to improve the separability between the surface of the toner carrier and the toner so that the image density due to mechanical fluctuations in the contact portion between the toner carrier and the electrostatic latent image carrier. An object of the present invention is to provide a developing device capable of preventing the occurrence of unevenness, fog, and disorder and forming an image of good quality even when forming a high-resolution image.

[0008]

The present invention has the following structure as means for solving the above problems.

(1) A surface of the electrostatic latent image carrier is provided with a toner carrier that is in contact with the surface of the electrostatic latent image carrier over a predetermined length range. By supplying toner to the electrostatic latent image carrier through the toner carrier, the electrostatic latent image carrier is kept static. In a developing device for visualizing an electrostatic latent image formed on an electrostatic latent image carrier into a toner image, the contact force P per unit length of the toner carrier against the electrostatic latent image carrier and the electrostatic latent image The ratio P / δ with respect to the deformation amount δ in the contact direction of the surface of the holding body or the toner carrier is in the range of 3.4 to 123, and the ratio P / S of the contact force P and the contact width S. Is set in the range of 0.85 to 5 , and the contact force P is set to
A contact force P of 1 gf / mm or more, orthogonal to the above predetermined length range
The contact width S in the direction of contact is set to 2 mm or more.

In this structure, the ratio P / δ between the contact force (nip pressure) P at the developing position and the deformation amount δ in the contact direction of the toner carrier surface is set within the range of 3.4 to 123 , The ratio P / S between the contact force P and the contact width S is 0.85-5.
Range to Ru is set. Therefore, the change in the nip pressure P when the positional relationship between the electrostatic latent image holder and the toner carrier changes is smaller than the change in the deformation amount δ of the surface of the toner carrier in the contact direction.

[0011]

In this structure, the nip pressure at the developing position is set to a contact width (nip width) of 2 mm or more.
It is set to 0.5 to 7 times S. Therefore, the stress generated at the contact portion (nip portion) between the surface of the electrostatic latent image carrier and the surface of the toner carrier does not become too small or too large, and the surface of the electrostatic latent image carrier and the toner carrier do not become excessive. Adhesion with the surface is ensured and toner does not mechanically adhere to the surface of the electrostatic latent image holding member.

[0013]

[0014]

[0015]

[0016]

(2) The electrostatic latent image holding member has an endless belt shape, and has a flexible hollow space at a position where a part of the electrostatic latent image holding member is sandwiched between the electrostatic latent image holding member and the surface of the toner carrying member. An elastic member is arranged.

In this structure, a part of the electrostatic latent image carrier in the form of an endless belt is sandwiched between the surface of the toner carrier and the elastic member. Therefore, the desired developing condition is realized in a stable state without increasing the deformation amount in the contact direction of the surface of the electrostatic latent image holder or the surface of the toner carrier and the tension of the electrostatic latent image holder, and The durability of the electrostatic latent image carrier is improved, the occurrence of fogging and unevenness in the image is reduced, and the image quality of the high resolution image is improved. Further, the elastic member is composed of a flexible hollow body. Therefore, the gas present in the hollow portion bears the contact force acting on the electrostatic latent image holding member, and the amount of plastic deformation of the elastic member due to the continuous action of the compressing force is reduced, so that the toner carrier and the electrostatic latent image are electrostatically charged. The contact state with the latent image holder is maintained stable over a long period of time.

(3) The elastic member includes a pressure control mechanism for controlling the internal pressure.

In this structure, the internal pressure of the hollow elastic member is controlled by the pressure control mechanism. Therefore,
If the contact force acting on the electrostatic latent image holding member from the elastic member is appropriately adjusted by controlling the internal pressure of the elastic member, the toner carrier and the electrostatic latent image caused by changes in the use environment and changes in other members over time. The change in the contact state with the holder is corrected.

[0021]

FIG. 1 is a schematic diagram showing the configuration of the main part of an image forming apparatus to which a developing device according to an embodiment of the present invention is applied. The image forming apparatus 1 has a charging device 3, an exposure unit 4, a developing device 5, a transfer device 6 and a cleaner 7 arranged around a photosensitive drum 2 which is an electrostatic latent image holding member of the present invention. Photoreceptor drum 2 in the paper transport path
A fixing device 9 (not shown) is provided on the downstream side between the transfer device 5 and the transfer device 5. The photosensitive drum 2 has a photosensitive layer that produces a photoconductive effect on its surface, and rotates in the direction of arrow A at a predetermined speed. The charger 3 uniformly applies a single-polarity charge to the surface of the photoconductor drum 2. The exposure unit 4 irradiates the surface of the photosensitive drum 2 with the image light modulated by the image data to form an electrostatic latent image on the surface of the photosensitive drum 2.

The developing device 5 supplies toner to the surface of the photosensitive drum 2 via the developing roller 10 which is the toner carrier of the present invention, and visualizes the electrostatic latent image into a toner image. The transfer device 6 electrostatically attracts the toner adhering to the surface of the photosensitive drum 2 to the surface of the paper P. The cleaner 7 removes toner and the like remaining on the surface of the photoconductor drum 2 that has passed the position facing the transfer device 6. The electric charge remaining on the surface of the photoconductor drum 2 that has passed the position facing the transfer device 6 is removed by a static eliminator (not shown). Further, the paper P having the toner transferred onto the surface thereof passing between the photoconductor drum 2 and the transfer device 6 is heated and pressed by the fixing device, and the melted toner firmly adheres to the surface of the paper P.

The developing device 5 includes a doctor roller 12, a toner supply roller 13 and a stirring roller 14 in addition to the above-described developing roller 10, and contains a non-magnetic toner 15 inside. The agitating roller 14 agitates the non-magnetic toner 15 contained in the developing device 5, and the toner supplying roller 1
3 conveys the agitated non-magnetic toner 15 to the developing roller 10 side. As a result, the non-magnetic toner 15 electrostatically adheres to the surface of the developing roller 10. The doctor 12 controls the amount of toner electrostatically attached to the surface of the developing roller 10.
The developing roller 10 has a surface made of an elastic material, and is in contact with the surface of the photoconductor drum 2 and rotates at a predetermined speed in the direction of arrow B to form an electrostatic latent image on the surface of the photoconductor drum 2. Toner is supplied to.

FIG. 2 is a schematic view for explaining a contact state between the photosensitive drum and the developing roller in the image forming apparatus. As described above, the surface of the developing roller 10 is made of an elastic material and is more easily deformed than the surface of the photosensitive drum 2. For this reason, when the developing roller 10 is brought into contact with the surface of the photosensitive drum 2, the surface of the developing roller 10 is elastically deformed in a state where the surface of the photosensitive drum 2 bites into the surface of the developing roller 10, and the developing roller 10 develops. 10 contacts the surface of the photosensitive drum 2 with a nip width S in the direction orthogonal to the axial direction. When the amount of deformation of the surface of the developing roller 10 when a load (nip pressure) of P is applied to the developing roller 10 in the direction of the photosensitive drum 2 per unit length in the axial direction is δ, P / δ Is the spring constant at the developing position (the contact position between the photosensitive drum 2 and the developing roller 10).

FIG. 3 is a schematic view showing the structure of the main part of another image forming apparatus to which the developing device of the present invention is applied. Figure 3
The image forming apparatus 21 shown in (1) includes a photosensitive belt 22 instead of the photosensitive drum 2. The developing device 5 has the same configuration as the developing device 5 of the image forming apparatus 1 shown in FIG. In the image forming apparatus 21 configured as shown in FIG. 3, when the developing roller 10 is pressed toward the photosensitive belt 22 by the nip pressure P, the photosensitive belt 22 is displaced in the pressing direction as shown in FIG. The developing roller 10 contacts the surface of the photoconductor belt 22 with a nip width S in the direction orthogonal to the axial direction. At this time, assuming that the displacement amount of the photoconductor belt 22 is δ, P / δ is a spring constant at the developing position (the contact position between the photoconductor belt 22 and the developing roller 10). As described above, when the belt-shaped photoconductor is used, the spring constant P / δ at the developing position can be changed by adjusting the tension applied to the photoconductor belt 22, and the material having a high surface hardness and the elastic modulus can be used. The value of the spring constant can be reduced even when the material is made of a material having a large value.

Using the image forming apparatus 1 and the image forming apparatus 21 configured as described above, the spring constant P / δ, the relationship P / S between the nip pressure and the nip width, and the surface roughness of the developing roller and the toner are used. The results of experiments on the effect of the relationship with the particle size on the image will be described below.

A) Effect of spring constant P / δ on image Two developing rollers 10a and 1 having different spring constants P / δ
The development characteristics of 0b were compared. Developing rollers 10a and 10
b is an urethane rubber roller having an outer diameter of 32 mm, a thickness of 6 mm, and a JIS 10-point average roughness of 6 μm. The developing roller 10 a has an Asker C hardness of 55 degrees and a developing roller 10 b.
Has an Asker C hardness of 78 degrees. The developing roller 10a has a spring constant P / δ of 123, and the developing roller 10b has a spring constant P / δ of 278.

First, the developing rollers 10a and 10b are shown in FIG.
The toner image formed on the surface of the photoconductor drum 2 was observed by using the image forming apparatus 1 shown in FIG. The photoconductor drum 2 is formed by forming a photoconductive layer having a film thickness of 25 μm on the surface of an aluminum substrate having a diameter of 50 mm and a thickness of 1 mm. Is irradiated with the image light by the laser light. The toner 15 has a volume average particle diameter d50 of 5.5 μm and a particle diameter standard deviation σ of 1.
2 μm negatively charged toner. A developing bias Vb of −250 V was applied to the rotary shaft of the developing roller 10. The toner image formed in this state was peeled from the surface of the photosensitive drum 2 with a mending tape, and magnified and evaluated with a microscope for evaluation. As a result, when the developing roller 10a was used, dots with a uniform diameter were formed without fogging in the non-image area. On the other hand, when the developing roller 10b was used, the dot diameter became non-uniform.

As is clear from the above results, the developing characteristics are not the hardness of the surface of the developing roller 10 itself, but the developing characteristics.
The pressure contact state between the developing roller 10 and the photosensitive drum 2 represented by the spring constant P / δ of the developing roller 10 has a great influence. Therefore, even when a developing roller having a high Asker C hardness of about 78 degrees is used, good developing characteristics can be obtained by setting the spring constant P / δ of the developing roller 10 to a predetermined value. it can.

Next, in the image forming apparatus 21 shown in FIGS. 3 and 4, the tension of the photosensitive belt 22 is adjusted while the deformation amount δ is fixed at 0.5 mm to adjust the spring constant P / δ.
Was increased from 0.3 to 3.4 and the state of toner image formation on the photoconductor belt 22 was observed. As a result, in the range where the spring constant P / δ is less than 2, there are many image defects in the formed toner image, and there is a lot of fog due to the adhesion of toner to the non-image area.

From the above results, if the spring constant P / δ is too large, the dot diameter error becomes large, and if the spring constant P / δ is too small, dot missing and fogging in the non-image area increase, and the spring is increased. The constant P / δ should be set in the range of 2-200. Furthermore, as described later, from FIG.
Spring constant P / δ should be set in the range of 3.4 to 123
Is.

B) Relationship between Nip Pressure and Nip Width Effect of P / S on Image Quality First, in the image forming apparatus 1 shown in FIGS.
A developing roller 10a having an Asker C hardness of 55 degrees (P / δ = 123) was used, the nip pressure P was increased to change the nip width S variously, and a toner image was formed on the photosensitive drum 2.
As a result, when P = 10 gf / mm, the nip width S = 2
mm (P / S = 5), and a toner image with little variation in dot diameter was obtained. As the nip pressure P is further increased, the nip width S = 3 mm (P / S
= 7), the toner image on the photoconductor drum 2 did not change in the initial stage, but when images are continuously formed, filming occurs in which toner adheres to the surface of the developing roller 10a. However, the toner image is not formed on a part of the image. As a result, in order to prevent the deterioration of the image quality due to the occurrence of filming on the developing roller 10, P / S <7 should be adjusted. In addition,
As shown in FIG. 5, the P / S is in the range of 0.85 to 5
Should be set to.

Next, in the image forming apparatus 21 shown in FIGS. 3 and 4, the developing roller 1 having an Asker C hardness of 78 degrees.
0b is used to adjust the tension of the photosensitive belt 22 to set the spring constant P / δ = 3.4, and the nip pressure P is increased / decreased to change the nip width S about 2 mm. Formed an image. As a result, when the nip width S was narrower than 2 mm, the outline of the dots was unclear, but when the nip width S was in the range of 2 mm to 4 mm, dots with clear outlines were formed. At this time, P / S = 0.5 or more. Further, the tension of the photoconductor belt 22 is adjusted so that the spring constant P / δ = 0.6, and the nip pressure P = 0.
A toner image was formed on the photoconductor belt 22 under the conditions of 3 gf / mm and nip width S = 2 mm. As a result, the non-image area on the photoconductor belt 22 is fogged, and the variation in dot diameter becomes large. From these things, P / S> 0.5 should be adjusted in order to obtain a clear image. Furthermore
As described later, from FIG. 5, the P / S is 0.85.
It should be set in the range of ~ 5.

FIG. 5 shows the experimental results on the effect of the above spring constant P / δ and the relationship P / S between the nip pressure and the nip width on the image. As can be seen in FIG.
In order to maintain good image quality, with respect to the spring constant P / δ, 3.4 ≤ P / δ ≤ 123 ... Formula 1 Regarding the nip pressure P and the nip width S, P> 1, S> 2, 0. 85 <P / S < 5 ... Formula 2 is a condition.

C) Effect of Relationship between Surface Roughness of Developing Roller and Toner Particle Size on Image In the image forming apparatus 1 shown in FIGS. 1 and 2, the developing roller 10a having a spring constant P / δ = 123 used. A toner image was formed on the photosensitive drum 2 by variously changing the surface roughness and the particle size of the toner 15. Specifically, J on the surface
IS 10-point average roughness Rz is 1.4 μm, 3 μm, 6 μm
The three types of developing rollers 10a and the volume average particle diameter d5
0 is 7.1 μm, 5.5 μm, 4.1 μm, 3.1 μm
4 kinds of non-magnetic toner 15 are prepared, and 600 dp
Images were formed at densities of i and 1200 dpi. The result is shown in FIG. As is apparent from FIG. 6, when the surface roughness of the developing roller 10a is smaller than the toner particle size, the density of dots of the toner image on the photosensitive drum 2 is improved.

As described above, in order to accurately and reliably attach the toner to the high resolution minute latent image, the spring constant P / δ at the developing position is set to 2 to 200 and the nip width S is set to 2 mm or more. Therefore, it is desirable to use a developing roller whose surface roughness is smaller than the toner particle size. Also,
As described above, from FIG. 5, the spring constant P / δ is 3.
It should be set in the range of 4-123. Particularly, when the resolution is 1200 dpi or more, the toner particle size and the value of the specific charge thereof affect the dot reproducibility. Especially 1200d
The potential and electric field strength of the electrostatic latent image of pi or more are 6
It is extremely small compared to an electrostatic latent image of 00 dpi or less. Therefore, in order to surely attach the toner to the minute latent image in which the potential and the electric field strength are attenuated with time, it is necessary to bring the toner particles charged in an appropriate state sufficiently close to the electrostatic latent image.

At this point, as shown in FIG.
For a latent image having a pi resolution, if the volume average particle diameter d50 of the toner is 7 μm or more, unnecessary toner adheres to the vicinity of the dots. Further, the volume average particle diameter d50 of the toner is 4 μm.
If it is smaller than m, the specific charge of the toner becomes excessive,
The image force on the developing roller increases, the amount of toner adhered to the latent image decreases, and fogging in the non-image area becomes remarkable. Therefore, when forming a high-resolution image,
Volume average particle diameter d50 = 4 to 6 μm, specific charge Q / M = 30
~ 50 μC / g toner should be used.

FIG. 7 is a schematic view showing the arrangement of the main part of an image forming apparatus to which a developing device according to another embodiment of the present invention is applied. The developing device 35 according to this embodiment includes a developing roller 40 and an elastic member 41 that sandwich the photosensitive belt 32 stretched between the rollers 32a and 32b. The developing roller 40 is rotatably supported with its peripheral surface in contact with the surface of the photosensitive belt 32, and the elastic member 41 contacts with the rear surface of the photosensitive belt 32.

FIGS. 8A and 8B are views showing the relationship between the deformation amount of the developing position and the nip width in the above developing device. FIG. 8C is a diagram showing the relationship between the tension of the photoconductor belt and the spring constant in the image forming apparatus including the developing device. FIGS. 9A and 9B show the case where developing rollers having diameters of 20 mm and 32 mm are used, respectively. Further, FIGS. 9A to 9C show the measurement results when the tension distance L of the photosensitive belt is changed in the range of 50 to 300 mm. The same figure (A) and (B)
From the above, the stretching distance L of the photosensitive drum 32 is set to the developing roller 40.
When the diameter is about 10 times or more, the deformation amount δ at the developing position needs to be about 5 mm or more. The developing roller 4
The stretching distance L of the photoconductor belt 32 that is approximately 10 times the diameter of 0 is taken into consideration in the case where the photoconductor belt 32 is applied to a full-color image forming apparatus.
Is a value in the case of being provided in parallel with an appropriate interval. Also,
From FIG. 6C, in order to set the spring constant P / δ to 2 or more, the tension T of the photosensitive belt 32 needs to be 600 gf / mm or more.

This means that it is necessary to increase the deformation amount δ and the tension T, especially when the stretching distance L of the photosensitive belt 32 needs to be increased as in a full-color image forming apparatus. It is shown that the unevenness of the image is likely to occur due to the vibration of the photosensitive belt 32 and the increase of the driving torque.

FIGS. 9A and 9B are views showing the difference in the deformed state of the photosensitive belt depending on the presence or absence of the elastic member which abuts the back surface of the photosensitive belt. As shown in FIG. 3A, when the elastic member 41 that abuts on the back surface of the photoconductor belt 32 does not exist, the photoconductor belt 32 is displaced within the range of the stretching distance L due to the abutment of the developing roller 40. Then, the photosensitive belt 32 is separated from the peripheral surface of the developing roller 40 at the contact position on the peripheral surface of the developing roller 30. Therefore, when the stretching distance L becomes long, the nip width S becomes small even if the deformation amount δ is the same, and it is necessary to increase the deformation amount δ in order to secure a sufficient nip width S.

On the other hand, as shown in FIG.
When the elastic member 41 is brought into contact with the back surface of the photoconductor belt 32, the photoconductor belt 32 is deformed only in the range of the nip width S by the contact of the developing roller 40, and a sufficient nip width is obtained without increasing the deformation amount δ. S is obtained. That is, the elastic member 41 regulates the deformation of the photosensitive belt 32 on the both sides of the nip width S where the peripheral surface of the developing roller 3 is not in contact, and the elastic member 41 restricts the deformation of the developing roller 40 in the contact direction. The nip width S hardly changes even if the stretching distance L becomes long. Further, in the range of the nip width S, the repulsive force of the elastic member 41 can be added in addition to the force generated from the tension T of the photoconductor belt 32, so that the photoconductor belt 32 can receive the desired nip pressure P. It is not necessary to increase the tension T excessively. Further, since the photosensitive belt 32 is sandwiched between the developing roller 40 and the elastic member 41 at the developing position, the vibration of the portion of the photosensitive belt 32 other than the developing position is not transmitted to the developing position, and the nip pressure P is changed. Can be suppressed.

The experimental results for verifying the effect of the elastic member will be described below. FIG. 10 is a diagram showing the configuration of the image forming apparatus used in the experiment for verifying the effect of the elastic member. Like the image forming apparatus 31 shown in FIG. 7, the image forming apparatus 51 includes a photosensitive belt 32 stretched between a pair of rollers 32a and 32b, and a developing device 35 including a developing roller 40 and an elastic member 41. Including a charging unit 33 and an exposure unit 34 facing the peripheral surface of the photoconductor belt 32.
Is equipped with.

The developing roller 40 has a diameter of 32 mm, an Asker C hardness of 78 degrees, and a JIS 10-point average roughness Rz of 6 μ.
m is a carbon dispersion type rubber roller, rotates at a speed of 60 rpm, and has a peripheral speed of 100 mm / s. Developing device 3
The toner stored in No. 5 has a volume average particle diameter of 5 μm and a non-charge of −30 to −5 based on polymethacrysanmethyl.
It is a nonmagnetic toner of 0 μC / g. This toner is carried on the peripheral surface of the developing roller 40 at an adhesion amount of 0.33 mg / cm ² . A bias voltage of −350V is applied to the developing roller 40.

The photosensitive belt 32 is made of polyethylene terephthalate having a thickness of 0.1 mm as a base and has a thickness of 2 mm on the outer peripheral surface.
A photoconductive film having a thickness of 5 μm is applied and rotated at a peripheral speed of 66 mm / s by the rotation of the driving roller 32b. Therefore, the developing roller 4 with respect to the photosensitive belt 32 at the developing position
The peripheral speed ratio of 0 is 1.5. The tension roller 32a is locked at the other end of a tension spring 52, one end of which is fixed to a frame. The tension of the photosensitive belt 32 is adjusted to 10 to 1 by adjusting the elastic force of the tension spring 52.
It can be changed in the range of 00 gf / mm.

The elastic member 41 has a width of 50 mm in the developing direction,
A 5 mm thick urethane sponge is attached to the bottom surface of an aluminum flat plate having a thickness of 10 mm, and a polyethylene tape having a thickness of 25 μm is attached to the bottom surface of the urethane sponge as a smooth material. With the elastic member 41 in contact with the back surface, the photoreceptor belt 32 had an Asker C hardness on the front surface of 50 degrees and a spring constant of 104 gf / mm.

The charger 33 uniformly charges the surface of the photosensitive belt 32 to -1000V by corona discharge.
The exposure unit 34 drives the semiconductor laser based on signals from the laser driver and the oscillation control circuit,
The surface of the photoconductor belt 32 is irradiated with red image light modulated by the image data. Beam diameter of image light (1 / e
² diameter) is 80 μm as an example.

The image forming apparatus 51 configured as described above.
The developing device 35 is displaced in the vertical direction to change the deformation amount δ and the nip width S, and the electrostatic latent image of the dot pattern of 600 dpi formed on the surface of the photosensitive belt 32 is transferred to the developing device 35. After the toner image is visualized by a toner image, the toner image on the photoconductor belt 32 is peeled off with a mending tape, and the dot diameter of the toner image, the variation of the dot diameter, and the fog of the non-image area are observed by a microscope. evaluated. The result is shown in FIG.

The nip width S is set so that the photosensitive belt 3 and the developing roller 40 are stopped.
A value obtained by measuring the width of the toner image transferred to the photosensitive belt 32 when the potential difference between the developing roller 40 and the developing roller 40 is +100 is used.

Further, the tension distance L of the photosensitive belt 32 is set to 5
When the same evaluation was performed by changing the range of 0 to 300 mm, the same result was obtained regardless of the stretching distance L.

As is apparent from FIG. 11, the photosensitive belt 3
By providing the elastic member 41 that abuts on the back surface of 2,
Regardless of the stretching distance L of the photosensitive belt 32, the conditions of the above formulas 1 and 2 can be satisfied, and the image quality can be improved.

Next, the nip width S is set to 2 mm and the nip pressure P is set to 1.6 gf / mm, and an image is formed by the image forming apparatus not equipped with the elastic member 41 and the image forming apparatus equipped with the elastic member 41. The variations in dot diameter of the toner images formed on the photosensitive belt 32 and the dot reproducibility were compared. As a result, in the image forming apparatus that does not include the elastic member 41, the partial dot diameter variation is large, and fogging occurs in the non-image portion. On the other hand, in the image forming apparatus including the elastic member 41, the partial dot diameter variation is small, and a toner image without fog is obtained as a whole. The difference is that the elastic member 41 is brought into contact with the back surface of the photoconductor belt 32, thereby suppressing waviness and vibration of the photoconductor belt 32 and maintaining the contact state between the photoconductor belt 32 and the developing roller 40 constant. It was caused by being done.

Although the elastic member 41 is made of urethane sponge in the above example, other materials may be used as long as a repulsive force is generated to regulate the displacement of the photosensitive belt 32 before and after the developing position. Can be used.

FIG. 12 is a view showing another structure of the elastic member in the developing device. The developing device 35 includes an elastic member 61 configured to bring the flexible sheet into contact with the back surface of the photosensitive belt 32 by the compressed air filled in the housing. That is, the elastic member 61 is the same as the photosensitive belt 32.
A case 61 which is arranged at a position facing the developing roller 40 with the sheet sandwiched between the opening and the bottom, and which has an opening 61a formed on the bottom facing the back surface of the photosensitive belt 32 and covered with a flexible sheet 61b.
It is composed of c. As an example, the housing 61c
Is composed of a stainless flat plate having a thickness of 0.5 mm. The opening 61a has a rectangular shape that is longer than the developing roller 40 in the axial direction of the developing roller 40 and wider than the nip width in the direction orthogonal to the developing roller 40. The flexible sheet 61b is fixed to the bottom surface of the housing 61c via a mounting member, and does not leak air even when the internal pressure of the housing 61c exceeds 5 atm.

When the internal pressure of the casing 61c is equal to or lower than the atmospheric pressure, the flexible sheet 61b and the photosensitive belt 3 are
2 and the developing roller 40 are 1 mm so as not to contact each other.
It is arranged with a predetermined gap. 12
(B) shows a state in which the housing 61c is filled with compressed air. When the internal pressure of the housing 61c rises by introducing compressed air into the housing 61c, the flexible sheet 61
b expands downward and contacts the back surface of the photosensitive belt 32,
The photosensitive belt 32 is pressed against the developing roller 40 side. As a result, the surface of the photoconductor belt 32 comes into contact with the peripheral surface of the developing roller 40, and toner can be supplied to the electrostatic latent image formed on the photoconductor belt 32 via the developing roller 40. The latent image can be visualized as a toner image. In this configuration, the material of the flexible sheet 61b and the housing 61c
The nip width, the nip pressure and the spring constant at the developing position can be set to desired values by appropriately selecting the internal pressure of the.

As described above, by forming the elastic member 61 so that the flexible sheet 61b is expanded by the internal pressure of the housing 61c, the elasticity of the sponge body as in the case of using the elastic member having a multilayer structure including the sponge body. Even when the spring constant is small, the displacement of the photoconductor belt 32 before and after the developing position can be reliably regulated without causing deterioration of properties and deterioration with time such as peeling of each layer.

FIG. 13 is a diagram showing still another structure of the elastic member in the developing device. This developing device 35
In the elastic member 61 having the configuration shown in FIG. 12, the internal pressure of the housing 61c is controlled to control the contact condition between the photosensitive belt 32 and the developing roller 40 at the developing position, and the photosensitive belt 32. The contact / separation state between the developing roller 40 and the developing roller 40 is controlled. For this reason, one end of the housing 61c forming the elastic member 61 is
4 and an inlet 81 to which the other end of a pressure-resistant nylon tube 82 having an adjusting valve 83 in the middle is connected.
Is provided. The inside of the preliminary chamber 84 is connected to the compressor 85 and is opened to the outside through the opening valve 86. In addition, the internal pressure of the housing 61c and the auxiliary chamber 84
The internal pressure of is detected by the sensors 87 and 88.

In the above structure, when the surface of the photosensitive belt 32 is brought into contact with the peripheral surface of the developing roller 40, after the internal pressure of the auxiliary chamber 84 is appropriately adjusted via the compressor 85 and the adjusting valve 83, Tube 82 by adjusting valve 83
The housing 61c and the auxiliary chamber 84 are communicated with each other via. As a result, the internal pressure of the housing 61c becomes higher than the external pressure, the flexible sheet 61b expands, and presses the photosensitive belt 32 toward the developing roller 40 side. On the contrary, when the surface of the photosensitive belt 32 is separated from the peripheral surface of the developing roller 40, the inside of the housing 61c is opened to the outside through the adjustment valve 83. As a result, the internal pressure of the housing 61c becomes the same as the external pressure, and the flexible sheet 61b contracts due to the elastic force so that the photosensitive belt 32 is not pressed against the developing roller 40 side.

When a material having small elasticity is used as the flexible sheet 61b, even if the internal pressure of the housing 61c is changed, the variation of the expansion amount of the flexible sheet 61b is small and the nip width does not change so much. However, the spring constant at the developing position can be changed. In addition, the flexible sheet 61
When a material having large elasticity is used as b, the housing 61
By changing the internal pressure of the flexible sheet 61b
The variation in the expansion amount is large, the deformation amount δ in the contact direction between the photosensitive belt 32 and the developing roller 40 can be changed, and the nip width, the nip pressure, and the spring constant can be controlled.

As a result of performing image formation using the developing device having the above-mentioned structure, the conditions of the above formulas 1 and 2 can be satisfied, and the image quality can be improved.

[0061]

According to the present invention, the following effects can be obtained.

(1) Contact force (nip pressure) at the developing position
Ratio P of P and deformation amount δ of the surface of the toner carrier in the contact direction P /
By setting δ in the range of 3.4 to 123, the change in the nip pressure P when the positional relationship between the electrostatic latent image holding member and the toner carrying member changes can be measured in the contact direction of the surface of the toner carrying member. The deformation amount δ can be made smaller than the change, and the variation in dot diameter can be suppressed to form a uniform image. Ratio P / S of contact force P and contact width S at the developing position
Is set in the range of 0.85 to 5,
The contact area between the surface of the image carrier and the surface of the toner carrier
Prevents the stress generated in the upper part from becoming too small or too large
Between the surface of the electrostatic latent image carrier and the surface of the toner carrier.
The toner adheres to the surface of the electrostatic latent image carrier to ensure adhesion.
It is possible to prevent mechanical attachment. Because of this, the dot
It is possible to prevent omissions and fogging of non-image areas and improve image quality.
You can Part of the endless belt-shaped electrostatic latent image carrier is
By sandwiching it between the surface of the toner carrier and the elastic member.
The desired developing conditions on the surface of the electrostatic latent image carrier or toner
The amount of deformation of the surface of the holder in the contact direction and the electrostatic latent image holder
Realization in a stable state without increasing tension
Can improve the durability of the electrostatic latent image carrier and
High-resolution images that reduce the occurrence of fogging and unevenness in images
The image quality of can be improved. It also has flexibility
By forming an elastic member with a hollow body,
To act on the electrostatic latent image holder by the gas present in the
It can bear the contact force. Because of this, foams and sponges
Compressive force is continuously applied compared to the case where
The decrease in elastic force over time due to
The contact state between the holder and the electrostatic latent image holder is maintained for a long time.
It can be maintained in a stable state. Elastic part of hollow body
By controlling the internal pressure of the material by the pressure control mechanism,
The electrostatic latent image holder is controlled from the elastic member by controlling the internal pressure of the elastic member.
If the contact force acting on the
Toner carrier and electrostatic charge caused by aging of other members
It is possible to correct changes in the contact state with the latent image holder,
Make the contact state of both more stable over a long period of time
Can be maintained.

[0063]

[0064]

[0065]

[0066]

[0067]

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a configuration of a main part of an image forming apparatus to which a developing device according to an embodiment of the present invention is applied.

FIG. 2 is a schematic diagram illustrating a contact state between a photosensitive drum and a developing roller in the image forming apparatus.

FIG. 3 is a schematic diagram showing a configuration of a main part of another image forming apparatus to which the developing device of the present invention is applied.

FIG. 4 is a schematic diagram illustrating a contact state between a photosensitive belt and a developing roller in the image forming apparatus.

FIG. 5 is a diagram showing an experimental result of an influence of a spring constant and a relationship between a nip pressure and a nip width on an image.

FIG. 6 is a diagram showing experimental results on the influence of the relationship between the surface roughness of the developing roller and the toner particle size on an image.

FIG. 7 is a schematic diagram showing a configuration of a sheet unit of an image forming apparatus to which a developing device according to another embodiment of the present invention is applied.

FIG. 8 is a diagram showing a relationship between a deformation amount of a developing position and a nip width in the developing device, and a relationship between a tension of a photosensitive belt and a spring constant in an image forming apparatus including the developing device.

FIG. 9 is a diagram showing a difference in a deformed state of the photosensitive belt depending on the presence or absence of an elastic member that abuts on the back surface of the photosensitive belt.

FIG. 10 is a diagram showing a configuration of an image forming apparatus used in an experiment for verifying the effect of an elastic member.

FIG. 11 is a diagram showing the experimental results.

FIG. 12 is a diagram showing another configuration of an elastic member in the developing device.

FIG. 13 is a diagram showing still another configuration of the elastic member in the developing device.

[Explanation of symbols]

1, 21, 31, 51-Image forming apparatus 2-Photoreceptor drum (electrostatic latent image holder) 22, 32-photoreceptor belt (electrostatic latent image holder) 5,35-Developing device 10, 40-Developing roller (toner carrier)

Front page continued (72) Inventor Tadashi Iwamatsu 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka Prefecture Sharp Corporation (72) Inventor Yoshinori Muto 22-22 Nagaike-cho, Abeno-ku, Osaka City, Osaka Prefecture (56) ) Reference JP-A-4-336564 (JP, A) JP-A-3-273271 (JP, A) JP-A 1-219761 (JP, A) JP-A-6-149134 (JP, A) (58) Fields surveyed (Int.Cl. ⁷ , DB name) G03G 15/08 G03G 21/00

Claims (4)

(57) [Claims] 1. A toner carrier, which is in contact with the surface of the electrostatic latent image carrier over a predetermined length range, is provided, and toner is supplied to the electrostatic latent image carrier via the toner carrier.
In a developing device that visualizes an electrostatic latent image formed on an electrostatic latent image carrier into a toner image, the contact force P of the toner carrier against the electrostatic latent image carrier per unit length and the electrostatic latent image The ratio P / δ to the deformation amount δ in the contact direction of the surface of the image carrier or the toner carrier is in the range of 3.4 to 123, and the ratio P / of the contact force P and the contact width S is P / δ.
The contact force P is set so that S is in the range of 0.85 to 5 , and the contact force P is 1 gf / mm or more.
The contact width S in the direction orthogonal to the constant length range is 2 mm or more
A developing device characterized by being set . 2. The elastic latent image holding member is in the shape of an endless belt, and has a flexible hollow elasticity at a position where a part of the electrostatic latent image holding member is sandwiched between the electrostatic latent image holding member and the surface of the toner carrying member. The developing device according to claim 1, wherein members are arranged. 3. The developing device according to claim 2, wherein the elastic member includes a pressure control mechanism for controlling the internal pressure. 4. A toner carrier which is in contact with the surface of the electrostatic latent image carrier over a predetermined length range, and the toner is supplied to the electrostatic latent image carrier through the toner carrier.
In a method of manufacturing a developing device for visualizing an electrostatic latent image formed on an electrostatic latent image carrier into a toner image, a contact force P per unit length of a toner carrier with respect to the electrostatic latent image carrier is set. The contact force P is set so that the ratio P / δ with respect to the deformation amount δ in the contact direction of the surface of the electrostatic latent image carrier or the surface of the toner carrier is in the range of 3.4 to 123. P
The contact force P is set so that the ratio P / S between the contact width S and the contact width S is in the range of 0.85 to 5 , and the contact force P is 1 g.
f / mm or more, contact in the direction orthogonal to the above predetermined length range
A method for manufacturing a developing device, wherein the touch width S is set to 2 mm or more .