JPH0792792A - Developing device and image forming device with this developing device - Google Patents

Abstract

PURPOSE:To provide images with no image degrading such as printing density unevenness while generating no contamination on a photoreceptor drum, a developing device with a long service life and an image forming device equipped with the developping device. CONSTITUTION:This device is provided with a photoreceptor drum 1 for carrying latent images, a resilient developping roller 12 which is brought into contact with the drum 1 and supplies toner to develop latent images and a flexible blade which forms a thin toner layer on the roller 12 while being in contact with the roller 12. The roller 12 comprises a metal shaft 12a and a high- molecular resilient layer having the hardness of rubber (40 degrees or more) put on the metal shaft. Penetration holes along the longitudinal direction of the shaft 12a are formed on the high-molecular resilient layer over the circumference of the metal shaft 12a and the contact is made to the drum 1 with the contact pressure of 1-10g/mm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device applied to, for example, an electrophotographic apparatus and an image forming apparatus including the developing device.

[0002]

2. Description of the Related Art In recent years, research on contact development using magnetic or non-magnetic toner and commercialization of printers, fax machines, copying machines and the like have been actively conducted. The developing roller used in these contact developing methods can be roughly classified into a type in which a pipe made of a metal material is brought into contact with a photoconductor and a type in which a polymer elastic roller is used.

Among them, a developing roller using a polymer elastic body contaminates a photoconductor in contact with the developing roller with a plasticizer or the like used at the time of processing the roller, and a predetermined surface potential required for latent image formation. May not be obtained, or blurring of the latent image may occur.

Rubber hardness of 30 ° (JI
It is known that even when polyurethane near S-A) is used, the plasticizer, oil and the like added during roller processing contaminate the photoconductor. It is a well-known fact that further lowering of rubber hardness causes serious contamination of the photoreceptor.

It is also known that even when silicone rubber is used for the developing roller, low molecular weight oligomers elute on the rubber surface and contaminate the photoreceptor. In order to eliminate the above problems, the contact developing roller using a polymer elastic body is premised on that contaminants are not eluted from the rubber used.

When polyurethane or the like is used, it is about 4
It has been proved that when the hardness is increased to 0 ° or more, the amount of elution is relatively reduced, and it can be practically used. In addition, in order to eliminate the above problems, the developing roller has a hardness of low oligomer type 4
There is also an example in which a silicon rubber of about 0 ° is used.

Further, when the elastic polymer is used for the contact developing roller, the smoothness of the surface is required and the surface roughness Rz =
The thickness is required to be 10 μm or less, and if the surface is rough, a pattern corresponding to the surface roughness is generated in the image. To achieve this, a surface polishing step is required after the roller is molded, but when the surface is polished, the outer diameter of the roller is usually larger at the end portion than at the central portion.

By the way, regarding the positional relationship in the longitudinal direction of the photoconductor, the cleaning blade, and the developing roller arranged in the image forming apparatus, the length of the photoconductor, the cleaning blade, and the developing roller in the longitudinal direction is made smaller in this order. There is a need. In other words, the width of the cleaning blade that cleans the transfer residual toner on the photoconductor after the development-transfer step must be larger than that of the developing roller that performs development by bringing the toner into contact with the photoconductor, and the width with the photoconductor. In, the width is almost equal or less.

Therefore, due to the above-mentioned width relation, in order to bring the developing roller whose outer diameter at the end portion is larger than the central portion into contact with the photosensitive member and to perform uniform development in the longitudinal direction of the developing roller, the portion having the smaller outer diameter also serves as the photosensitive member. A predetermined nip width is required, and a predetermined pressure contact load is essential for this.

On the other hand, in addition to the outer diameter tolerance of the developing roller, the runout tolerance is also an important controlling factor for increasing the load. Especially, in the case of a shaft-to-axis fixing system in which the photoreceptor shaft and the developing roller shaft are fixed, the circumference of the photoreceptor is In order to obtain a uniform image in the direction, in the superimposition of the shake of the photoconductor and the shake of the developing roller,
Even in the case of the phase with the smallest overlap, the axial distance is required so that a developing nip larger than a predetermined value can be obtained.

[0011]

However, when a pressing force between the developing roller and the photosensitive member is applied in order to absorb the outer diameter tolerance and the runout tolerance, the toner is broken and agglomerated, and the initial toner particle diameter distribution is changed. The image is greatly deteriorated, image is fogged on the screen, lack of image sharpness, nonuniformity of solid black image, and the like, and image deterioration occurs, resulting in a device having an extremely short life.

As a toner layer forming member, a flexible member is brought into contact with a developing roller to form a thin toner layer on an elastic roller,
When developing an electrostatic latent image, the nip between the toner layer forming member and the developing roller is important, similar to the concept of the nip between the developing roller and the photoconductor.

The purpose of the toner layer forming member is to form a thin toner layer on the developing roller and at the same time to charge the toner when passing between the toner layer forming member and the developing roller. is necessary. Therefore 4
When a developing roller having a relatively high rubber hardness of 0 ° or more is used, it is necessary to apply a certain amount of pressure to the toner layer forming member, and if a load is applied too much, the toner will be destroyed like the developing roller and the photoconductor. In addition, aggregation may be caused, and a filming phenomenon may occur in which the toner is fused to the developing roller.

Therefore, according to the present invention, a developing device capable of forming an excellent image without causing image deterioration and a filming phenomenon in which a developer is welded to a developing roller, and an image provided with this developing device are provided. An object is to provide a forming device.

[0015]

In order to solve the above-mentioned problems, the present invention provides an image bearing member carrying a latent image and an elastic member which is brought into contact with the image bearing member and supplies a developer to develop the latent image. And a flexible developer layer forming member which is in contact with the developer supplying member and forms a thin layer of the developer on the developer supplying member. A core material and a polymer elastic body having a rubber hardness of 40 ° or more, which is coated on the core material, and a plurality of through holes along the longitudinal direction of the core material are provided in the polymer elastic body in the circumferential direction of the core material. One of them is provided and is brought into contact with the image carrier at a contact pressure of 1 to 10 g / mm.

Further, an image bearing member carrying a latent image, an image forming means for forming a latent image on the image bearing member, and the image bearing member are brought into contact with each other, and a developer is supplied to develop the latent image. An elastic developer supply member; and a flexible developer layer forming member that is in contact with the developer supply member and forms a thin layer of the developer on the developer supply member. Is composed of a core material and a polymer elastic body covering the core material with a rubber hardness of 40 ° or more, and a through hole along the longitudinal direction of the core material is provided in the polymer elastic body in the circumferential direction of the core material. A plurality of them are provided and are brought into contact with the image carrier at a contact pressure of 1 to 10 g / mm.

[0017]

The developer supplying member is composed of a core material and a polymer elastic body having a rubber hardness of 40 ° or more, which is covered with the core material. The polymer elastic body has a through hole extending in the longitudinal direction of the core material. Are provided along the circumferential direction of the core member, and the developer supply member is 1 to 10 g / mm with respect to the image carrier.
By contacting with the contact pressure of 1, the image carrier is not contaminated, and a good image is provided without image deterioration such as print density unevenness.

[0018]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 2 shows the internal structure of the electrophotographic apparatus. In FIG. 2, reference numeral 1 denotes a negatively chargeable organic photosensitive drum as an image carrier that rotates in the direction of arrow a. Around the photosensitive drum 1, a charging charger 2, a developing device 11, transfer and peeling chargers 3 and 4, and a cleaning blade 5 are arranged along the rotation direction.

The developing device 11 is a contact type one-component developing device, and the developing device 11 includes a developing roller 12 having conductivity and elasticity. A thin layer of non-magnetic toner is formed on the surface of the developing roller 12, and the thin layer of non-magnetic toner is brought into contact with the surface of the photosensitive drum 12 for development. The developing device 11 does not require a developer carrier, a magnet roller, a toner concentration control device, and the like, and is a developing device that can be downsized and reduced in cost.

The developing mechanism of the developing device 11 will be described below. The developing device 11 has a toner container 14, and the non-magnetic toner 15 in the toner container 14 is sent to a toner supply roller 17 while being agitated by a mixer 16, and the toner is supplied from the toner supply roller 17 to the developing roller 12. Supplied. The toner 15 is charged by friction with the surface of the developing roller 12, and electrostatically adsorbed on the surface of the developing roller 12 and conveyed. After that, the toner conveyance amount is regulated by the developer thin layer forming member (hereinafter referred to as a blade) 18, and at the same time, the toner 15 is triboelectrified by friction between the two. The blade 18 is held by the first blade holder 18a, the spacer 18b, and the second blade holder 18c, and is in contact with the developing roller 12.

In this embodiment, since the reversal development is carried out using the negatively chargeable organic photosensitive drum 1, a negatively charged toner is used as the toner 15 and a material that is easily negatively charged is used as the blade 18. Further, with respect to the photosensitive drum surface potential ( _VH ) -500v, the developing bias potential (V
_D ) -200v is supplied from the developing bias power source 12d to the metal shaft 12a of the developing roller 12. The developing roller 12 makes contact rotation (sliding contact) with the photosensitive member 1 at a speed of about 1 to 4 times that of the photosensitive drum 1 in the direction opposite to the rotation direction of the photosensitive drum 1 (direction of arrow a) (direction of arrow b). There is. Also,
Since the toner particles are triboelectrically charged even at the developing position, an extremely sharp image can be obtained with less fog. The undeveloped toner passes through the recovery blade (mylar film) 19 and returns to the toner container 14.

In FIG. 1, reference numeral 20 is a baffle plate attached to the first blade holder 18a, which is brought into contact with a foam material 21 made of maltoprene or the like attached to the back surface of the blade 18, The toner seal and the vibration of the blade 18 can be suppressed,
A good toner thin layer can be formed on the developing roller 12. The blade 18 is pressed against the developing roller 12 by the rotary shaft 22 of the first blade holder 18a and the plurality of compression springs 23 for pressurization. Since the plurality of compression springs 23 are lower than the spring constant of the thin leaf spring material of the blade 18, even if the abutting portion of the blade 18 is worn, there is almost no change in the pressing force, and a good toner thin layer can be maintained. Has become.

Next, details of main constituent members of the developing device 11 of the present invention will be described. 2 is a perspective view showing the developing roller 12, and FIG. 3 is a sectional view thereof. The first characteristic required of the developing roller 12 is that it has conductivity and elasticity, and the simplest configuration that satisfies this is a combination of a metal shaft and a conductive rubber roller.
Therefore, in the present invention, as shown in FIG. 3, since the toner is conveyed while being in pressure contact with the developing roller 12, the support 12a made of a metal shaft so as to satisfy the surface smoothness.
A two-layer structure of an elastic layer 12b and a surface conductive layer 12c is provided on the outer periphery of the.

There are two types of elastic layers 12b, one of which is electrically conductive and the other of which is not electrically conductive. In consideration of the case where the surface conductive layer 12c is peeled or scratched, the electrically conductive layer is preferable. The elastic layer 12b is the blade 1
8 and the photoconductor drum 13 are in pressure contact with each other, a large load is required to obtain a predetermined nip when the rubber hardness is large, which leads to an increase in the torque of the developing device. In addition, JISK63 due to being packed or left for a long time
The permanent strain (%) indicated by 01 also becomes a problem, and if it exceeds 10%, unevenness of the developing roller cycle occurs in the image. Therefore, the compression strain (%) of the elastic layer 12b is 10% or less, preferably 5%. Must be: Regarding the relationship between rubber hardness and permanent set (%), generally, the larger the rubber hardness is, the smaller the permanent set tends to be. Therefore, the balance between materials becomes important.

Since the surface conductive layer 12c is in direct contact with the toner and the photosensitive member 1, it must be one which does not contaminate the toner and the photosensitive member 1 due to the seeping out of the plasticizer, the vulcanizing agent, the process oil and the like. Further, the surface smoothness of the conductive layer 12c is preferably 10 μmRz or less, and when it is more than 10 μmRz, an uneven pattern on the surface is likely to appear in an image. In order to achieve a smoothness of 10 μmRz, it is conceivable to form a conductive layer 12c having a sufficiently large film thickness on the elastic layer 12b and then finish it to a predetermined outer diameter and surface roughness by post-processing (polishing). Since it is high, it is desirable to realize without processing. For that purpose, the surface roughness of the elastic layer 12b, the film thickness of the surface conductive layer 12c, and the viscosity of the coating material must be selected optimally. That is, the lower the viscosity and the higher the surface roughness of the elastic layer 12b,
The film thickness of the surface conductive layer 12c must be increased.
Further, the elongation (%) of the material itself of the surface conductive layer 12c also becomes a problem, and if it is 50% or less, the conductive layer 12c cannot follow the elastic deformation of rubber as described above, and cracks are likely to occur particularly at both ends where the elastic deformation becomes large. Become. Elongation (%) of the material of the elastic layer 12b and elongation (%) of the material of the surface conductive layer 12c itself
Also, if the difference is not more than 200%, the elastic deformation of the rubber cannot be followed, and cracks are generated or density unevenness is easily generated in one rotation of the developing roller as described above.
In the present embodiment, the material forming the surface conductive layer 12c is negatively charged with the toner. Therefore, a material that is easily frictionally charged positively and has excellent toner transportability is selected.

In order to confirm the electric characteristics required for the developing roller 12, the resistance between the surfaces of the support 12a made of a metal shaft and the conductive layer 12c is arbitrarily set between the developing bias power source 12d and the metal shaft 12a. A development experiment was conducted with a resistance 12e having a resistance value of 5 μm interposed. At a resistance value of 10 ⁷ Ω · cm or more, the surface potential of the developing roller 12 shows different values during development of a white solid image and a black solid image, and a white background latent image potential (V _H ) in a white solid image. To
The solid black image shows a tendency to approach the latent image potential ( _VL ) on the black background. That is, in an image having a large area image portion, the potential difference between the image latent image potential ( _VL ) and the surface potential of the developing roller 12 becomes small, resulting in a low density image. Then, the developing roller 12
Since the surface potential approaches the latent image potential (V _H ) on the white background and the potential difference from the image portion becomes large, the thin line becomes thick and the image is not sharp. Such potential fluctuations on the surface of the developing roller 12 are caused by the current flowing through the resistance during development. Since negatively charged toner particles are transferred from the developing roller 12 to the photosensitive drum 13 during solid black development,
The current flows from the developing roller 12 toward the bias power source 12d. At the time of solid white development, the surface charge of the photosensitive drum 13 is removed by the developing roller 12, so that the current flows from the developing bias power source 12d toward the developing roller 12. That is, such a current causes a potential difference between both ends of the protective resistance 12e, and causes the surface potential fluctuation of the developing roller 12 as described above. This tendency is the protection resistance 12
e is remarkable at 10 ⁸ Ω · cm or more, and in order to obtain a good image, the support 12a made of a metal shaft and the surface conductive layer 1
The resistance value with 2c is 10 ⁸ Ω · cm or less, preferably 10 ⁷
It was confirmed to be Ω · cm or less.

From the above, the developing roller 12 of the present invention is
In the above, in the elastic layer 12b, a conductive silicone rubber or a conductive urethane rubber having an elongation of about 250 to 500% and an electric resistance value of 10 ⁶ Ω · cm or less is used, and for the conductive layer 12c,
Electrical resistance 10 ^4-5 Ω · cm, extends from 100 to 400% of the conductive polyurethane paint were used: the product name spa Rex, Japan Miratotoron Co., Ltd.].

[0028] Now, the developing roller 12 is an electric resistance value 1x10 ⁶ to the conductive rubber layer 12b shown in FIG. 3 for use in the present invention
A conductive urethane rubber having an Ω · cm and a rubber hardness of 42 ° (JIS-A) is used, and a through hole 12 is formed in the conductive urethane rubber in parallel with the longitudinal direction of the cored bar and in the circumferential direction of the cored bar.
d ... is provided. Specifically, a urethane rubber layer 12b having a thickness of 5 mm is arranged on a metal shaft 12a having an outer diameter of 8 mm,
Twelve through holes 12d having an inner diameter of 2 mm are provided in the rubber layer 12b in parallel with the longitudinal direction of the shaft 12a.

[0029] on the surface of the conductive rubber layer 12b, the electrical resistance value 1x10 ^4-5 Ω · cm, extends from 100 to 400% of the conductive polyurethane paint [product name: Spa Rex, Japan Miratotoron Co., Ltd.] a A surface conductive layer 12c having a thickness of 30 to 100 μm was provided.

With the above construction, the overall rubber hardness of the roller is approximately 50 ° to 55 ° in ASKER-C hardness.
(JIS-A hardness is about 25 ° to 30 °), and the developing roller 12 having extremely high elasticity is realized.

The developing roller 12 is attached to the developing device 11, and the number distribution ratio of the volume average particle diameter of 10 μm or 5 μm or less using polyester as the main resin is 15%, 1%.
Printing was carried out using a negatively charged toner having a volume distribution ratio of 14% of 2.7 μm or more and a negatively charged organic photoreceptor as the photoreceptor.

When the image was output using the pressure contact force between the developing roller 12 and the photosensitive drum 1 as a parameter, a characteristic diagram as shown in FIG. 4 was obtained. The vertical axis in FIG. 4 represents the pressure applied between the developing roller 12 and the photosensitive drum 1, and the horizontal axis represents the print density unevenness in one image, which represents the difference between the maximum density and the minimum density.

In the region where the pressure contact load between the developing roller 12 and the photosensitive drum 1 is low, the print density unevenness is large, and conversely, in the region where the pressure contact load is high, the print density unevenness shows a low value.

This is because the developing roller 12 is used in the low pressure region.
This is because an appropriate developing nip is not locally obtained due to the influence of the outer diameter accuracy of the. Normally, it is necessary to suppress the print density unevenness to 0.2 or less, and if it is more than this value, the balance is visually unbalanced.

Further, FIG. 4 shows the ratio of toner particles having a volume distribution of 12.7 μm or more as one numerical value showing the degree of toner destructive aggregation at the time of printing 10,000 sheets on the horizontal axis. In the region where the pressure contact load is low, the degree of increase of the fine particle toner of 12.7 μm or more is slow, but when the pressure contact load is high, the increase of the fine particle toner is large, and particularly the linear pressure of 10 g /
It has increased remarkably from around mm. In the toner particle size distribution in this state, as the number of fine particles increases due to the destruction of the toner and the coarse particles increase due to the aggregation of the toner, fogging on the image and the sharpness of the image are significantly deteriorated. As a result of our study, it has been found that the number distribution of 12.7 μm or less due to fracture must be suppressed to 30% or less from the viewpoint of fog as an example.

From the above, the pressure contact load between the developing roller 12 and the photosensitive drum 1 of the present invention is in the range of 1 to 10 g / mm in the linear pressure. In the present invention, polyurethane rubber is used for the conductive rubber layer 12b of the developing roller 12, but the conductive silicone rubber or the like having a relatively low hardness and containing a small amount of low molecular weight oligomers, and thus the photosensitive drum 12 is less contaminated. May be adopted and the through holes 12d ... May be provided. Although the metal shaft 12a is used as the support, a resin shaft or the like may be used as long as the bias voltage can be supplied, and in the method of directly supplying the bias voltage to the elastic layer, the support need not be conductive. .

By the way, a developing roller was manufactured by using a conductive urethane rubber equivalent to the present invention for the conductive rubber layer, arranging a rubber having a thickness of 5 mm on a metal shaft having an outer diameter of 8 mm.
A rubber hardness of 42 ° was used, but the hardness after roller molding was about 46 ° (JIS hardness).

When this roller was attached to the contact type one-component developing device 11 and the same test as in the example was conducted, the result shown in FIG. 5 was obtained, and there was no load area compatible with the uneven print density and the toner destruction characteristics. In addition, print density unevenness is 0.2
When the printing was repeated under a load of 12 g / mm, the toner filming occurred on the photoconductor after about 3000 sheets, and remarkable noise was generated on the image.

FIG. 6 shows changes in toner particle size distribution due to stress. The solid line is the distribution map before receiving stress,
The dotted line shows the state where the toner is destroyed and aggregated due to the stress of the photoconductor 1 and the developing roller, and the distribution is largely changed.

FIG. 7 shows the influence of the toner whose distribution has been destroyed due to destructive aggregation on the fog during image formation. As an example of the parameter indicating the degree of distribution collapse, 12.5 is shown.
The volume distribution ratio of the toner of μm or more was used.

[0041]

As described above, according to the present invention, the developer supplying member is the core material, and the hardness of the rubber coated on the core material is 40.
And a plurality of through holes extending in the longitudinal direction of the core material are provided in the polymer elastic body in the circumferential direction of the core material, and the developer supply member is provided with the image carrying member. Since the image carrier is brought into contact with the body at a contact pressure of 1 to 10 g / mm, there is an effect that a good image can be provided without contaminating the image carrier and without image deterioration such as unevenness in printing density.

[Brief description of drawings]

FIG. 1 is a configuration diagram illustrating a part of an image forming apparatus that is an embodiment of the present invention.

FIG. 2 is a perspective view showing a developing roller of a developing device in the image forming apparatus of FIG.

FIG. 3 is a side sectional view showing the developing roller of FIG.

4 is a diagram showing a photosensitive member and a developing roller in the image forming apparatus of FIG.
FIG. 6 is a graph showing the relationship between the contact pressure with the toner, the print density unevenness, and the toner-volume distribution ratio of 12.7 μm or more.

FIG. 5 is a diagram illustrating a photosensitive member and a developing roller in a conventional image forming apparatus.
FIG. 6 is a graph showing the relationship between the contact pressure with the toner, the print density unevenness, and the toner-volume distribution ratio of 12.7 μm or more.

FIG. 6 is a graph showing toner-particle system distribution in a conventional image forming apparatus.

FIG. 7 is a graph showing the relationship between a coarse toner and image fog in a conventional image forming apparatus.

DESCRIPTION OF SYMBOLS 1 ... Photosensitive member (image bearing member), 12 ... Developing roller (developer supply member), 18 ... Blade (developer layer forming member), 12
a ... Metal shaft (core material), 12b ... Elastic layer (polymer elastic body), 12d ... Through hole.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshiyuki Fukuda 70, Yanagimachi, Saiwai-ku, Kawasaki-shi, Kanagawa Toshiba Intelligent Technology Co., Ltd.

Claims (2)

[Claims] 1. An image bearing member carrying a latent image, an elastic developer supplying member which is brought into contact with the image bearing member and supplies a developer to develop the latent image, and a developer supplying member. A flexible developer layer forming member for forming a thin layer of the developer on the developer supplying member, wherein the developer supplying member has a core material and a rubber hardness of 40%. And a plurality of through-holes extending in the longitudinal direction of the core material in the circumferential direction of the core material, and 1 to 10 g relative to the image carrier. A developing device which is contacted with a contact pressure of / mm. 2. An image bearing member carrying a latent image, an image forming means for forming a latent image on the image bearing member, and a developer supplied to the image bearing member to develop the latent image. An elastic developer supplying member; and a flexible developer layer forming member which is in contact with the developer supplying member and forms a thin layer of the developer on the developer supplying member. The member is composed of a core material and a polymer elastic body having a rubber hardness of 40 ° or more with which the core material is covered, and a through hole along the longitudinal direction of the core material is provided in the polymer elastic body in the circumferential direction of the core material. An image forming apparatus having a plurality of the above, and being brought into contact with the image carrier at a contact pressure of 1 to 10 g / mm.