JP2001235941A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of appropriately preventing a situation that developer put between an image carrier and a developer carrier is aggregated to deteriorate image quality. SOLUTION: In this image forming device 1, a toner image is formed and developed on the surface of a photoreceptor 2 by supplying toner to the photoreceptor 2 by the developing roller 5 of a developing part 3. The roller 5 abuts on the photoreceptor 2 through a toner layer on the roller 5. By pressing the roller 5 toward the photoreceptor 2 by an elastic member such as a spring, the roller 5 uniformly abuts on the photoreceptor 2 in the shaft direction of the roller 5. The roller 5 is formed in the shape of a cylinder obtained by sticking rubber material to the periphery of a core bar, provided with a surface layer whose surface is properly roughed and coated with coating material and an inner layer lower than the surface layer, and set so that the hardness of the surface layer may be higher than that of the inner layer. Therefore, the roller 5 uniformly abuts on the photoreceptor 2 and developing nip width is made small, so that a uniform and excellent-contrast image is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus, and more particularly, to an image forming apparatus capable of appropriately preventing deterioration of image quality due to aggregation of a developer interposed between an image carrier and a developer carrier. The present invention relates to a prevented image forming apparatus.

[0002]

2. Description of the Related Art In image forming apparatuses such as copying machines, printers and facsimile apparatuses using an electrophotographic system,
A uniformly charged image carrier is irradiated with writing light modulated by image data to form an electrostatic latent image on the image carrier, and the image carrier on which the electrostatic latent image is formed is formed. The developer is supplied to the body by the developing unit to develop the image carrier. The image forming apparatus transfers the developer image on the image carrier to recording paper at a transfer unit, and then heats and transfers the developer transferred onto the recording paper at a fixing unit.
The developer is pressed and fixed, and the developer remaining on the surface of the image carrier is collected by a method such as scraping off the developer with a cleaning blade at a cleaning unit.

[0003] To supply the developer from the developing section to the image carrier, a developer carrier such as a developing roller is provided in the developing section at a small interval from the image carrier on which the electrostatic latent image is formed. do it,
The developer of the developer carrier is supplied to a portion of the image carrier corresponding to the electrostatic latent image to develop the image carrier.

[0004]

However, in such a conventional image forming apparatus, a developer carrying member such as a developing roller is arranged at a minute interval on the image carrying member, and the developer carrying member is provided. Is supplied to the image bearing member to develop the image bearing member. Therefore, the image bearing member and the developer are opposed to each other (hereinafter referred to as a developing nip portion) between the image bearing member and the developer bearing member. The distance between the carrier and the carrier becomes uneven, the developer is sandwiched between the image carrier and the developer carrier, and the additive of the developer is buried and coagulated with the base resin of the developer over time. However, there has been a problem that the adhesive force between the developers increases, and the developing ability in a halftone image portion decreases.

[0005] In view of the above, the first aspect of the present invention provides a developer carrying member that contacts an image carrying member on which an electrostatic latent image is formed and develops the image carrying member with the carried developer. It has a surface layer to be supported and an inner layer inward of the surface layer, and the hardness of the surface layer is at least higher than the hardness of the inner layer, so that the developer carrier uniformly contacts the image carrier. And narrow the development nip width,
It is an object of the present invention to provide an image forming apparatus capable of forming a uniform and good-contrast image, particularly, an image with good image quality in a halftone portion.

According to a second aspect of the present invention, the surface layer and the inner layer are
An image forming apparatus that can form a more uniform and better-contrast image by forming a different member so that the developer carrier is brought into uniform contact with the image carrier and the developing nip width is reduced. It is intended to provide.

According to a third aspect of the present invention, by setting the coefficient of friction of the surface of the image carrier within the range of 0.1 to 0.4, the developer carrier is brought into uniform contact with the image carrier. It is another object of the present invention to provide an image forming apparatus capable of forming a more uniform and better contrast image by reducing a developing nip width.

According to a fourth aspect of the present invention, the developing nip width, which is the width in the rotation direction of the contact portion between the image carrier and the developer carrier, is set to 1 mm or less, so that the uniformity and contrast can be further improved. It is an object of the present invention to provide an image forming apparatus capable of forming an even better image.

According to a fifth aspect of the present invention, the hardness of the inner layer of the developer carrier is set in the range of 10 ° to 50 ° JISA so that the developer carrier is brought into more uniform contact with the image carrier. It is another object of the present invention to provide an image forming apparatus capable of forming an image with higher uniformity and higher contrast.

According to a sixth aspect of the present invention, by setting the thickness of the surface layer of the developer carrying member in the range of 5 to 20 μm, the width of the developing nip can be further reduced, and the uniformity and the contrast can be further improved. It is an object of the present invention to provide an image forming apparatus capable of forming a good image.

According to a seventh aspect of the present invention, the developer carrying member is provided
A first elastic member that presses the developer carrier toward the image carrier with a predetermined pressing force, and a developer carrier that is disposed between the image carrier and presses the developer carrier in a direction away from the image carrier. By pressing the image carrier with a predetermined pressing force by a difference between the pressing force of the second elastic member and the second elastic member, the developer carrier is brought into more uniform contact with the image carrier, and more uniform and high contrast is obtained. It is an object of the present invention to provide an image forming apparatus capable of forming an even better image.

[0012]

According to the first aspect of the present invention, the image forming apparatus is uniformly charged in advance while rotating, and then is irradiated with a writing light modulated based on image data to be electrostatically charged. The developer carrying the developer is brought into contact with the image carrier on which the latent image is formed, and development is performed. The developer image on the image carrier is transferred to a recording sheet to form the developer image. An image forming apparatus for fixing the transferred recording paper to form an image,
The developer carrier has at least a surface layer supporting the developer and an inner layer inner than the surface layer, and the surface layer has a hardness set to be higher than at least the hardness of the inner layer. By doing so, the above objective has been achieved.

According to the above construction, the developer carrying member which is in contact with the image carrying member on which the electrostatic latent image is formed and develops the image carrying member with the carrying developer is provided at least on the surface layer carrying the developer. And having an inner layer inner than the surface layer,
Since the hardness of the surface layer is at least higher than the hardness of the inner layer, the developer carrier can be uniformly brought into contact with the image carrier, and the developing nip width can be narrowed, so that uniform and contrast can be achieved. A good image, particularly an image with good image quality in the halftone portion can be formed.

In this case, for example, the surface layer and the inner layer may be formed of different members.

According to the above construction, since the surface layer and the inner layer are formed of different members, the developer carrier can be brought into more uniform contact with the image carrier, and the development nip width can be reduced. And a more uniform and better-contrast image can be formed.

Further, for example, the image bearing member has a surface having a friction coefficient of 0.1 to 0.1.
It may be set to a range of 0.4.

According to the above arrangement, since the coefficient of friction of the surface of the image carrier is set in the range of 0.1 to 0.4, the developer carrier can be brought into more uniform contact with the image carrier. And the development nip width can be narrowed, and an image with more uniform and better contrast can be formed.

Further, for example, a developing nip width, which is a width of the contact portion between the image carrier and the developer carrier in the rotation direction, is set to 1 mm or less. You may.

According to the above arrangement, the developing nip width, which is the width in the rotation direction of the contact portion between the image carrier and the developer carrier, is set to 1
mm or less, it is possible to form an image that is more uniform and has better contrast.

Further, for example, as described in claim 5, the inner layer of the developer carrier has a hardness of 10%.
° to 50 ° may be set in the range of JIS A.

According to the above configuration, since the hardness of the inner layer of the developer carrier is set in the range of 10 ° to 50 ° JIS A, the developer carrier is brought into more uniform contact with the image carrier. This makes it possible to form a more uniform and better-contrast image.

Further, for example, as described in claim 6, the surface layer of the developer carrier has a thickness of 5%.
It may be set in the range of up to 20 μm.

According to the above configuration, since the thickness of the surface layer of the developer carrier is set in the range of 5 to 20 μm, the width of the development nip can be further reduced, and the uniformity and contrast of the development can be further improved. An even better image can be formed.

Further, for example, as set forth in claim 7, the developer carrier includes a first elastic member that presses the developer carrier in a direction of the image carrier with a predetermined pressing force;
A predetermined pressing force is applied to the image carrier by a difference in pressing force between a second elastic member disposed between the image carrier and the second elastic member that presses the developer carrier in a direction away from the image carrier. May be pressed.

According to the above arrangement, the developer carrier is disposed between the first elastic member that presses the developer carrier in the image carrier direction with a predetermined pressing force, and the image carrier. Since the image carrier is pressed with a predetermined pressing force due to a difference between the pressing force of the second elastic member that presses the developer carrier in the direction away from the image carrier, the developer carrier is further pressed. The image can be uniformly brought into contact with the image carrier, and an image with higher uniformity and higher contrast can be formed.

[0026]

Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings. It should be noted that the embodiments described below are preferred embodiments of the present invention, and therefore, various technically preferable limitations are added. However, the scope of the present invention is not limited to the following description. The embodiments are not limited to these embodiments unless otherwise specified.

FIGS. 1 to 5 are views showing an image forming apparatus to which the first embodiment of the image forming apparatus according to the present invention is applied. This embodiment corresponds to claims 1 to 6. Is what you do.

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

Referring to FIG. 1, the image forming apparatus 1 has a developing unit 3 disposed close to a photoreceptor 2.
In the developing container 4, a developing roller 5, a supply roller 6, a regulating blade 7, an agitator 8, and the like are provided.

In the developing container 4, toner (developer) 9
(See FIG. 3), and the agitator 8 is
Is rotated clockwise, and the toner 9 in the developing container 4 is rotated.
Is supplied to the supply roller 6 with stirring.

The toner 9 includes polyester, polyol,
A charge control agent (CCA) and a coloring agent are mixed with a resin such as styrene acryl, and a substance such as silica or titanium oxide is externally added around the mixture. As the coloring agent, carbon black, phthalocyanine blue, quinacridone, carmine and the like are used.

In the toner (developer) 9, the above additives are externally added to a base toner in which CCA and a colorant are further dispersed and mixed in a polyester resin and a polyol resin, and in some cases, wax and the like. The particle size of the additive is 0.1 to
The range is 1.5 μm.

The range of the volume average particle size of the toner 9 is as follows.
Although 3 to 12 μm is preferable, in the present embodiment, it is preferable to set 7.
5 μm, which can sufficiently cope with a high-resolution image of 1200 dpi or more.

The supply roller 6 and the developing roller 5 are disposed in contact with each other, and are both rotated in the same direction (counter direction at the contact portion) in the counterclockwise direction indicated by an arrow in FIG. In this case, the linear velocity ratio between the rotation of the supply roller 6 and the developing roller 5 is 0.5 to 1.5 when the linear velocity of the developing roller 6 is 1 and the linear velocity is 1.
In the present embodiment, the linear velocity of the supply roller 6 is set to 0.9 with respect to the linear velocity of the developing roller 5. When the supply roller 5 rotates in the reverse direction (forward direction at the contact portion) with respect to the development roller 6, when the linear velocity of the supply roller 6 is set to 1 with respect to the development roller 6, the linear velocity of the supply roller 6 is: 0.8 to 1.5 is preferred.

The biting amount of the supply roller 6 with respect to the developing roller 5 is 0.5 to 1.5 mm, and the setting condition of the biting amount has a great effect on the charging characteristics and the supply property of the toner 9. It is set appropriately,
It is not limited to 1.5 mm. The amount of biting of the supply roller 6 into the developing roller 5 needs to be set in association with the characteristics of the motor and the gear head for driving the developing roller 5, and in the present embodiment, the unit effective width, the supply roller 6 and the developing roller The effective width of the roller 5 is 24
In the case of 0 mm (A4 length), the required torque is 1.
5 to 2.0 kg · fcm.

The supply roller 6 is formed of a foamed polyurethane or the like, has flexibility, and is formed in a cell having a diameter of 50 to 500 μm so as to easily hold the toner 9. The supply roller 6 has a relatively low hardness of 10 to 30 ° JIS A, and uniformly contacts the developing roller 5. The supply roller 6 holds the toner 9 supplied from the agitator 8 and supplies the toner to the developing roller 5 at a contact portion with the developing roller 5.

The developing roller (developer carrying member) 5 is formed in a cylindrical shape having a diameter of 10 to 30 mm with a rubber material adhered around a cored bar.
The roughness Rz (ten-point average roughness) is formed to be 1 to 4 μm. The value of the surface roughness of the developing roller 5 is 13 to 80% with respect to the volume average particle diameter of the toner 9, and the toner 9 is appropriately conveyed without being buried in the surface of the developing roller 5. This is the roughness value that can be obtained.

Silicone, butadiene, NBR (nitrile butadiene rubber),
Hydrin, EPDM (ethylene propylene diene rubber)
And the like. Further, on the surface of the developing roller 5, in order to stabilize the toner charging and the quality over time,
Coated with a coating material. As the coating material, silicon-based and Teflon-based coating materials are particularly preferable. The silicon-based coating material improves the charge of the toner 9, and the Teflon-based coating material improves the releasability. The coating layer of the developing roller 5 may appropriately contain a conductive material such as carbon black in order to improve conductivity, and the thickness of the coating layer is preferably in the range of 5 to 50 μm. If the thickness exceeds this thickness, defects such as cracks are likely to occur.

The developing roller 5 has a surface layer formed by the appropriately roughened surface and the coat layer, and an inner layer below the surface layer. That is, they are formed of different materials. And
The hardness of the surface layer of the developing roller 5 is set higher than that of the inner layer. When the coat layer is not formed, the surface layer of the developing roller 5 is formed only of the roughened rubber layer.

The hardness of the inner layer of the developing roller 5 is set in the range of 10 ° to 50 ° JIS A. That is, usually, the hardness of the surface of the developing roller 5 is 40 to 8
In most cases, the hardness is within the range of 0 ° JIS A. In order to make a difference with the hardness of the inner layer, in the image forming apparatus 1 of the present embodiment, the hardness of the inner layer of the developing roller
0 ° to 50 ° JIS A range, especially 10 ° to 40 °
JIS A is set so that uniform development can be performed without increasing the development nip width at the time of contact with the photoconductor 2.

Then, on the supply roller 6 or on the toner 9
The toner 9 existing inside the layer is sandwiched between the supply roller 6 and the developing roller 5 rotating in mutually opposite directions at the contact position, and a triboelectric charging effect is generated to obtain a negatively charged electric charge, thereby causing electrostatic force and development. The roller 5 is held on the developing roller 5 by a transport effect due to the surface roughness of the roller 5 and a non-electrostatic force acting on the surface. At this time, the toner 9 layer on the developing roller 5 is not uniform but adheres considerably excessively (1-2 mg / c).
m ² ), the 9 toner layers are made uniform and thinner by the regulating blade 7.

The regulating blade 7 has its base end fixed to the developing container 4 and its tip is directed upstream with respect to the rotation direction of the developing roller 5 (counter contact state).
The regulating blade 7 is arranged in such a manner that the central portion of the regulating blade 7 comes into contact with the developing roller 5, that is, the so-called belly contact. Note that the regulating blade 7 may be a so-called trailing contact or an edge contact. The regulating blade 7 has a thickness of 0.1 to 0.2 as its material.
mm such as SUS 304, a rubber material such as polyurethane rubber having a thickness of 1 to 2 mm, a silicone resin, and a fluorine-based material (for example,
Tetrafluoroethylene-ethylene copolymer (ETF
E), a resin material having relatively high hardness such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF) resin and the like.
The resistance can be reduced by mixing bon black or the like.
And a relatively strong electric field can be formed between them.

The regulating blade 7 preferably has a free end length in the range of 10 to 15 mm from the end attached to the developing container 4, and when the length exceeds the upper limit of this range, the free end length is increased. Is too long to increase the size of the developing container 4 and cannot be compactly stored. Conversely, if the free end length is shorter than the lower limit of the above range, contact with the surface of the developing roller 5 may occur. In addition, vibration due to natural vibration of both members is likely to occur, and an abnormal image such as horizontal unevenness tends to occur on the image. The contact pressure of the regulating blade 7 against the developing roller 5 is preferably in the range of 5 to 50 g · f / cm.
If the contact pressure of the regulating blade 7 on the developing roller 5 exceeds this preferred range, the amount of toner 9 adhered to the developing roller 5 decreases, and the charge amount of the toner 9 increases too much, so that the developing amount decreases. Image density is reduced. On the other hand, if the contact pressure falls below the preferred range, a thin layer of the toner 9 will not be formed uniformly, and the mass of the toner 9 will pass through the regulating blade 7, and the image quality will be significantly reduced.

As the photoreceptor (image carrier) 2, inorganic and organic photoreceptors can be used, and the coefficient of friction μ of the surface is 0.1 μm.
It is maintained in the range of 1 to 0.4. A method for maintaining the surface friction coefficient μ in the above range is disclosed in Japanese Patent Application Laid-Open No. Hei 4-3729.
No. 81, “When a toner having a volume average particle diameter of 4 to 10 μm is used, a substance that reduces the friction coefficient of the photoreceptor is supplied onto the photoreceptor. The member carrying the lubricant may be brought into contact with the photoconductor at all times or at regular intervals. "

The friction coefficient μ of the surface of the photosensitive member 2 can be measured by a predetermined method, for example, the Euler belt method.

In the Euler belt method, as shown in FIG. 2, a digital force gauge 12 is arranged on a measuring table 11 fixed to one end of a measuring table 10 and provided at the other end of the measuring table 10. Photoreceptor mounting table 13
The photoreceptor 2 to be measured is placed thereon. Paper 14 (in the experiment of this embodiment, RICOH TYPE 6200 A4
(Use the one with T cut to 297mm x 30mm)
The paper 14 of the measuring paper strip belt 16 having the yarns 15 attached to both ends of the measuring paper belt 16 is arranged in contact with the photoconductor 2, and one end of the yarn 15 of the measuring paper belt 16 is connected to the digital force gauge 12 via a hook or the like. At the same time, a predetermined weight, for example, a load 17 of 100 g (0.98 N) is connected to the other end of the thread 15 of the measuring paper strip belt 16 via a hook or the like in a state where gravity is appropriately applied. That is, in the Euler belt method, the digital force gauge 12 is connected in the horizontal direction of the measurement paper strip 16 via the cylindrical photoreceptor 2, and the load 45 is connected in the vertical direction bent at 90 degrees. I have.

In this state, the digital force gauge 12
To read the value F indicated by the digital force gauge 12 at the time when the measuring paper strip belt 16 starts moving, and calculate the friction coefficient μ of the surface of the photosensitive member 2 by the following equation (1), and Is measured.

Μ = In (F / 0.98) / (π / 2) (1) Then, in the image forming apparatus 1, the unprocessed case where the lubricant or the like measured in this way is not applied is used. The friction coefficient μ of the surface of the photoconductor 2 is set to 0.4 to 0.6, and the friction coefficient μ
Tends to increase over time. Also, when the photoconductor 2 coated with the lubricant is used, the friction coefficient μ of the surface of the photoconductor 2 is set in the range of 0.1 to 0.4.

The photoreceptor 2 is charged to a predetermined surface potential by a normal charging means, and an electrostatic latent image based on image data is formed by a normal optical writing means using a laser beam or the like.

The photosensitive member 2 includes a developing roller 5 and a developing roller 5.
It is in contact with a predetermined contact pressure via the upper 9 toner layers,
The photosensitive member 2 and the developing roller 5 are pressed against the photosensitive member 2 by an elastic member such as a spring (not shown) so that both ends of the developing roller 5, both ends supporting portions, or the entire developing container 4 are contacted.
In this case, as the number of the springs as the elastic members increases, the contact pressure can be made uniform in the longitudinal direction and the contact unevenness can be significantly reduced. A coil spring, a leaf spring, or the like can be used as an elastic member for bringing the photosensitive member 2 into contact with the developing roller 5. The contact pressure of the developing roller 5 against the photoreceptor 2 is preferably in the range of 0.5 to 4 gf / mm when the developing roller 5 having a hardness of 30 JIS A is used. When the contact pressure of the developing roller 5 with respect to the photoconductor 2 falls below the lower limit of the appropriate range, the state of contact of the developing roller 5 with the photoconductor 2 is easily affected by the straightness of the developing roller 5 in the width direction, Due to the uneven contact, the developing ability becomes non-uniform and white spots occur in the image. When the state of contact of the developing roller 5 with the photoconductor 2 exceeds the upper limit of the appropriate range, the toner 9 sandwiched between the developing roller 5 and the photoconductor 2 is compressed and aggregated, and the aggregated toner 9 is not developed. In this case, the solid image tends to remain on the developing roller 5 to cause uneven density in the solid image.

Next, the operation of the present embodiment will be described. In the image forming apparatus 1 of the present embodiment, the photoconductor 2 is charged to a predetermined surface potential by a charging unit (not shown) while rotating the photoconductor 2 in a clockwise direction, and a laser beam based on image data is written by an optical writing unit (not shown). And the like to form an electrostatic latent image.

The image forming apparatus 1 supplies the toner 9 to the photoreceptor 2 on which the electrostatic latent image is formed by the developing roller 5 rotating in the counterclockwise direction of the developing unit 3 to transfer the toner image to the surface of the photoreceptor 2. The toner image on the surface of the photoreceptor 2 is transferred to a recording paper conveyed between the photoreceptor 2 and a transfer unit (not shown), and the recording paper on which the toner image is transferred is fixed (not shown). The toner image is fixed on the recording paper by applying heat and pressure to the recording paper.

Further, the image forming apparatus 1 removes the toner remaining on the photoreceptor 2 by a cleaning unit (not shown) after the transfer of the photoreceptor 2 and charges the same again by a charging unit to form the next image. Offer.

The developing roller 5 is in contact with the photoreceptor 2 via the toner 9 layer on the developing roller 5, and the photoreceptor 2 and the developing roller 5 are supported at both ends of the developing roller 5, both ends supporting portions or The entire developing container 4 is pressed in the direction of the photoconductor 2 by an elastic member such as a spring (not shown), so that the developing roller 5
In the axial direction (longitudinal direction).

At this time, the photosensitive member 2, the developing roller 5, and the
A force as shown in FIG. That is, feeling
The toner 9 facing the dot latent image on the surface of the light body 2 has toner
Non-electrostatic adhesive force between the photoreceptor 2 and the surface of the photoreceptor 2
Acts on toner 9 on developing roller 5 facing the dot latent image
Force) F_{t ・ p}And the Coulomb force F acting on the toner 9_{q ・ e}
And F1 (F1 = F_{t ・ p}+ F_{q ・ e}) Is perpendicular to photoconductor 2
In the direction tangential to the surface of the photoreceptor 2
The direction opposite to the rotation direction of the light body 2 (the direction indicated by the arrow in FIG. 3)
The frictional force F between the toner 9 and the surface of the photoreceptor 2_{μ t ・ p}
= Μ_{t ・ p}F1 acts. Where μ_{t ・ p}Is toner 9
Coefficient of friction between the photoconductor 2 and the surface of the photoconductor 2. Also, the developing roller
5 and the toner 9, which are perpendicular to the surface of the developing roller 5.
Non-electrostatic adhesion between the toner 9 and the surface of the developing roller 5
Force F_{t ・ r}Acts on the tangential direction of the developing roller 5 and
Opposite to the rotation direction of the image roller 5 (the direction indicated by the arrow in FIG. 3)
Direction, the frictional force F between the toner 9 and the surface of the developing roller 5_{μ
t ・ r}= Μ_{t ・ r}・ F_{t ・ r}Works. Where μ_{t ・ r}Is developed
The coefficient of friction between the roller 5 and the toner 9. In addition, Tona
-9, the toner adhesion F_{t ・ t}Works
In the tangential direction, the frictional force F between the toner 9_{μ t ・ t}= Μ_{t ・ t}
・ F_{t ・ t}Works. Where μ_{t ・ t}Is the friction between toner 9
It is a friction coefficient. In FIG. 3, it is described on the photoconductor 2 side.
“× 1” described on the developing roller 5 side
“× 1.2” indicates that the linear velocity of the photoconductor 2 is “1”.
Shows that the developing roller 5 has a linear velocity 1.2 times that of the developing roller 5.
are doing.

Then, the toner 9 on the developing roller 5 is supplied to the dot latent image on the photoreceptor 2 and development is performed when the condition represented by the following equation (1) is satisfied.

[0057] _{F t · p + F q ·} e> F t · t + F t · r (1) By the way, by developing the toner images of halftone on the photosensitive member 2, and transfer the image of the half-tone recording paper When forming, the toner 9 of the developing roller 5 by the regulating blade 7 is used.
When the cohesive force between the toners 9 increases due to the contact pressure at the time of thinning and uniforming of the layer or at the time of development by the photoreceptor 2, the adhesion force _{Ft · t} between the toners of the above formula (1) partially increases, A phenomenon in which the halftone image is not developed may occur.

However, the image forming apparatus 1 of the present embodiment
The hardness of the developing roller 5 is J as described above.
A SUS plate having a thickness of 0.1 mm is used as a regulating blade 7 having an IS of 30 ° and the contact pressure of the regulating blade 7 on the developing roller 5 is set to 20 g · f / cm. I have. In this way, the amount of toner 9 adhering to the developing roller 5 can be made appropriate. According to an experiment, it has been found that the amount of toner 9 adhering to the developing roller 5 under the above conditions is zero. 0.4 to 0.8 mg / cm ² .

The contact angle of the regulating blade 7 with the developing roller 5 is 10 ° with respect to the tangential line of the developing roller 5 in a direction in which the tip of the regulating blade 7 faces the upstream side of the developing roller 5.
When the contact angle is set in this range, the toner 9 sandwiched between the regulating blade 7 and the developing roller 5 is unnecessary for forming a thin layer of the toner 9. The part is appropriately peeled off from the developing roller 5 to form a thin layer having a uniform thickness of 0.4 to 0.8 mg / cm ² per unit area. With this configuration, when the charge amount of the toner 9 is in the range of −8 to −30 μC / g, when the developing roller 5 having the toner 9 layer contacts the latent image on the photoconductor 2, The image is developed to develop the image.

When the photosensitive member 2 and the developing roller 5 are in contact with each other to perform development, the photosensitive member 2 and the developing roller 5 are pressed by a spring, which is an elastic member, and are in contact with a predetermined contact pressure. Therefore, if the surface layer is soft and highly flexible as in the conventional developing roller 5, the developing roller 5 is compressed in accordance with the bite, resulting in a developing region having a wide developing nip width.

However, the image forming apparatus 1 of the present embodiment
The developing roller 5 has a surface layer whose hardness is set higher than that of the inner layer.
The surface layer of the developing roller 5 behaves as if it is a resin having high hardness, and the contact area with the photoconductor 2, that is, the developing nip width is reduced. Further, since the inner layer inside the developing roller 5 has a low hardness, there is no occurrence of a density fluctuation or the like due to uneven contact.

As described above, the image forming apparatus 1 of the present embodiment includes the developing roller 5 that contacts the photosensitive member 2 on which the electrostatic latent image is formed and develops the photosensitive member 2 with the toner 9 carried thereon. It has at least a surface layer carrying the toner 9 and an inner layer inside the surface layer, and the hardness of the surface layer is higher than at least the hardness of the inner layer.

Therefore, the developing roller 5 can be brought into uniform contact with the photosensitive member 2 and the width of the developing nip can be reduced, so that a uniform and good-contrast image, particularly, an image quality in a halftone portion can be obtained. Can be formed.

In the image forming apparatus 1, the coefficient of friction of the surface of the photosensitive member 2 is set in the range of 0.1 to 0.4.

Accordingly, the developing roller 5 can be brought into uniform contact with the photosensitive member 2, and the width of the developing nip can be narrowed, so that a more uniform and better-contrast image can be formed.

The present inventor has set the diameter of the photoreceptor 2 to 50
mm, the diameter of the developing roller was 16 mm, and an experiment was performed using the above-described conventional developing roller. As a result, the developing nip width was 1.5 to 2 mm. When an experiment was performed using the developing roller 5 described above, the developing nip width between the developing roller 5 and the photosensitive member 2 was about 0.5 to 1 mm as shown in FIG. A uniform toner image could be formed on the photoreceptor 2 and developed without disturbing the nine layers, and a uniform toner image could be formed on the recording paper.

The developing nip width between the photosensitive member 2 and the developing roller 5 is preferably 1 mm or less. The inventor conducted an experiment using the image forming apparatus 1 under the following conditions.

The experimental conditions were as follows. The diameter of the photosensitive member 2 was 50 mm, the diameter of the developing roller 5 was 16 mm, and a hard drum made of an aluminum tube was used as the photosensitive member 2. The developing roller 5 used was one in which rubber was applied to a metal core and the surface layer had a hardness of 20 ° JIS A. The developing nip width between the developing roller 5 and the photosensitive member 2 is
When the hardness of the surface layer is 20 °, 30 °, and 40 °, FIG.
The relationship is as shown in FIG.

The developing unit 3 was urged from the rear toward the photoconductor 2 by a spring so that the contact pressure with the photoconductor 2 was 2.5 g / mm over the entire width of the developing roller 5. In this experiment, the developing roller 5 had a total length of 240 mm, and the pressing force for pressing the entire developing roller 5 was set to 600 g, and the contact pressure 2.5 g / mm, which was the above condition, was set. At this time, the developing nip width between the photosensitive member 2 and the developing roller 5 is 0.9 mm as can be seen from FIG.

Under these conditions, when the image was formed by the image forming apparatus 1, the image could be formed in good condition.

However, the pressing force of the developing roller 5 against the photosensitive member 2 is reduced to 6 g / mm (>) as in the conventional image forming apparatus.
3.2 g), the image was formed with the overall pressing force set to 1440 g and the development nip width set to 1.2 mm. As a result, the degree of aggregation of the toner 9 increased and the image quality deteriorated.

This is because when the developing nip width is 1.2 mm with a pressing force of 6 g / mm, the toner 9 is sandwiched between the photosensitive member 2 and the developing roller 5 to increase the cohesion degree. This is because the thin layer of the toner 9 on the surface 5 is disturbed and is not developed on the portion to be developed, or conversely, is developed on the portion that does not need to be developed and the toner 9 adheres.

However, the image forming apparatus 1 of the present embodiment
With a pressing force of 2.5 g / mm and a developing nip width of 0.
When the thickness is 9 mm, the toner 9 is
In this case, it is possible to suppress an increase in the degree of agglomeration between the toner and the toner 9 on the developing roller 5 and prevent the thin layer from being disturbed, thereby improving the image quality. Also, by narrowing the width of the development nip, the apparent development time is reduced, and the development process may be started or not completed before or after the development time, and the development process may be continued. Can be prevented, and the development can be performed with the contribution of the development electric field for a moment. As a result, uniform development characteristics can be obtained.

The hardness of the inner layer of the developing roller 5 of the image forming apparatus 1 according to the present embodiment is 10 ° to 50 ° JI.
It is set in the range of SA, in particular, in the range of 10 to 40 ° JIS A.

This is because the surface hardness of a normal developing roller is usually in the range of 40 ° to 80 ° JIS A, and the difference between the hardness of the surface layer of the developing roller 5 and the hardness of the inner layer is large. This is for performing uniform development without increasing the development nip width at the time of contact with the photoconductor 2.

Further, the overall hardness of the developing roller 5 depends on the hardness of the inner layer. When a photosensitive drum using an aluminum tube is used as the photosensitive member 2, the developing roller 5 is made of a low-hardness material. This is an inevitable direction, and uniform contact with the photoconductor 2 can be realized.

That is, if the hardness of the developing roller 5 is high, it is difficult to accurately contact the photosensitive member 2 with a uniform pressure over the entire surface. Is required, and the cost increases. Also,
Since the toner 9 sandwiched between the photoreceptor 2 and the developing roller 5 receives a very high pressure, the toner 9 is agglomerated, and the development at a low potential becomes insufficient, and sufficient image quality is obtained. Absent. Even if a sufficient image quality can be obtained at the initial stage, the degree of deterioration of the toner 9 progresses with time, and the degree of aggregation tends to increase after the additive is buried. Greater decline in performance.

However, uniform development can be realized by reducing the contact force between the photosensitive member 2 and the developing roller 5 in the development.

In the image forming apparatus 1 of the present embodiment, the thickness of the surface layer of the developing roller 5 is set to 5 to 20 μm. Usually, the thickness of the surface layer of the developing roller 5 can be considered to be about 1 μm, but in the image forming apparatus 1 of the present embodiment, it is set to be thicker than 5 μm.

When the thickness of the surface layer of the developing roller 5 is thinner than 5 μm, the flexibility with the inner layer of the developing roller 5 is improved, and the bite amount and the developing nip width largely depend on the hardness of the inner layer. Will be developed. For example, the developing roller 5
If the hardness of the inner layer is set to 10 ° JIS A, the developing nip width exceeds 2 mm, and the nine toner layers are disturbed when passing through the developing nip portion, so that uniform developing characteristics cannot be obtained. The thickness of the surface layer of the developing roller 5 is 40 μm
If the ratio exceeds the threshold value, there is a problem that cracks in the surface layer are likely to occur due to a difference in hardness between the developing roller 5 and the inner layer.

However, the image forming apparatus 1 of the present embodiment
Then, as described above, the hardness of the inner layer of the developing roller 5 is set to 1
0 ° to 50 ° JIS A range, especially 10 ° to 40 °
, The developing roller 5 can be brought into more uniform contact with the photosensitive member 2, and an image with higher uniformity and higher contrast can be formed.

FIG. 6 shows an image forming apparatus according to a second embodiment of the present invention. This embodiment corresponds to claim 7 of the present invention.

This embodiment is applied to an image forming apparatus similar to the image forming apparatus 1 according to the first embodiment, and is similar to the image forming apparatus 1 according to the first embodiment. The same reference numerals are given to the same components, and detailed description thereof will be omitted.

In FIG. 6, the image forming apparatus 20 includes a photosensitive member 2 similar to the image forming apparatus 1 of the first embodiment.
The developing unit 3 is provided with a developing roller 5, a supply roller 6, a regulating blade 7, an agitator 8, and the like in a developing container 4.

A toner 9 is stored in the developing container 4, and the agitator 8 is rotated clockwise in FIG. 6 to agitate the toner 9 in the developing container 4 and supply it to the supply roller 6. .

One end of an elastic body (first elastic member) 21 such as a spring is fixed to the developing container 4. The other end of the elastic body 21 is connected to a support member 22 such as a main body frame of the image forming apparatus 20. It is fixed to. The elastic body 21 presses the developing container 4 in the direction of the photoreceptor 2 with a constant pressing force, and the developing roller 5 is pressed against the photoreceptor 2 with a constant pressing force by the pressing of the developing container 4 by the elastic body 21. Have been.

On the other hand, the photosensitive member 2 has its rotating shaft 2 a rotatably supported by a support member 23.
An elastic body (second elastic member) is provided between the developing container 3 and the developing container 4.
24 are provided. The elastic body 24 is provided in the developing container 4 pressed by the elastic body 21 in the photoconductor 2 direction.
The developing container 4 is pressed with a constant pressing force in a direction away from the developing container 4.

In the image forming apparatus 20, the elastic member 2
1 and the elastic force of the elastic body 24 are set appropriately,
The contact pressure between the developing roller 5 and the photosensitive member 2 is set to 2.5 fg / m
m.

That is, in the image forming apparatus 20 using the photoreceptor 2 having a low friction coefficient, the contact pressure of the developing roller 5 with the photoreceptor 2 is reduced, so that the image forming apparatus 20 is free from the influence of the friction coefficient. An image can be formed.

However, when the developing roller 5 is pressed against the photosensitive member 2 by using only the elastic body 21,
If a spring is used as the elastic body 21 and its spring coefficient is reduced, the support of the developing container 4, that is, the developing roller 5 itself becomes unstable, and the image forming apparatus 1 is easily affected by vibration. Banding or the like may easily occur.

Therefore, the image forming apparatus 20 of the present embodiment
Is provided with an elastic body 24 between the photoreceptor 2 and the developing container 4 to prevent the developing roller 5 from excessively biting the photoreceptor 2, and between the developing roller 5 and the photoreceptor 2. The reference pressing force can be applied.

That is, the resultant force of the elastic bodies 21 and 24 acts as a contact pressure between the developing roller 5 and the photosensitive body 2.

For example, the pressing force of the elastic body 21 for urging the developing container 4 in the direction of the photosensitive member 2 is 5 gf / mm, and the elastic member provided between the supporting member 23 of the photosensitive member 2 and the developing container 4 is provided. Assuming that the pressing force of the body 24 is 2.5 fg / mm, the contact pressure between the developing roller 5 and the photoconductor 2 is 2.5 fg / mm.

Therefore, the image forming apparatus 20 of the present embodiment presses the developing roller 5 in the direction of the photosensitive member 2 in order to bring the developing roller 5 into contact with the photosensitive member 2 with a constant pressing force (contact pressure). And the elastic body 24 for pressing the developing roller 5 in a direction to separate the developing roller 5 from the photoreceptor 2. Therefore, if the action axes of the elastic body 21 and the elastic body 24 are shifted, the developing The roller 5 can be pressed from above and below, and the effect of holding the developing container 4 at an appropriate position can also be exhibited. The elastic body 21 and the elastic body 24
(When springs are used as the elastic members 21 and 24), a relatively large elastic coefficient can be used, and the contact pressure between the developing roller 5 and the photosensitive member 2 can be more accurately determined. It is possible to set even more uniform and good image quality image formation.

As described above, in the image forming apparatus 20 of the present embodiment, the developing roller 5 is connected to the photosensitive member 2.
An elastic body 21 that presses in a predetermined direction with a predetermined pressing force;
And an elastic body 24 that is disposed between the photosensitive member 2 and the developing roller 5 and presses the developing roller 5 away from the photosensitive member 2.
With a predetermined pressing force.

Therefore, the developing roller 5 can be brought into contact with the photosensitive member 2 more uniformly, and an image with more uniform and better contrast can be formed.

The invention made by the present inventor has been specifically described based on the preferred embodiments. However, the present invention is not limited to the above, and various modifications can be made without departing from the gist of the invention. It goes without saying that it is possible.

[0098]

According to the image forming apparatus of the first aspect of the present invention, the developer carrier that contacts the image carrier on which the electrostatic latent image is formed and develops the image carrier with the developer carried thereon. Has at least a surface layer carrying the developer and an inner layer inward of the surface layer, and the hardness of the surface layer is at least higher than the hardness of the inner layer. And the developing nip width can be narrowed, and an image with uniform and good contrast, particularly an image with good image quality in the halftone portion can be formed.

According to the image forming apparatus of the present invention, since the surface layer and the inner layer are formed by different members,
The developer carrier can be brought into more uniform contact with the image carrier, and the development nip width can be reduced.
An image with more uniform and better contrast can be formed.

According to the image forming apparatus of the present invention, since the friction coefficient of the surface of the image carrier is set in the range of 0.1 to 0.4, the developer carrier is supported by the image carrier. The contact can be made more evenly with the body, and the width of the developing nip can be narrowed, so that a more uniform and better-contrast image can be formed.

According to the image forming apparatus of the present invention, the developing nip width, which is the width in the rotation direction of the contact portion between the image carrier and the developer carrier, is set to 1 mm or less. It is possible to form an image with higher uniformity and better contrast.

According to the image forming apparatus of the present invention, the hardness of the inner layer of the developer carrying member is set to 10 ° to 50 ° JI.
Since it is set in the range of SA, the developer carrier can be brought into more uniform contact with the image carrier, and an image with more uniform and better contrast can be formed.

According to the image forming apparatus of the present invention, since the thickness of the surface layer of the developer carrying member is set in the range of 5 to 20 μm, the width of the developing nip can be further reduced. As a result, an image with higher uniformity and better contrast can be formed.

According to the image forming apparatus of the present invention, the first elastic member which presses the developer carrier with a predetermined pressing force in the direction of the image carrier and the image carrier. And a second elastic member that is disposed between the image carrier and the second elastic member that is disposed between the image carrier and the second elastic member. In addition, the developer carrier can be more uniformly contacted with the image carrier, and an image with more uniform and better contrast can be formed.

[Brief description of the drawings]

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

FIG. 2 is a diagram showing a state in which the coefficient of friction of the photoconductor surface is measured by the Euler belt method.

FIG. 3 is a diagram illustrating a force acting on a photoconductor, a developing roller, and toner at a developing nip portion between the photoconductor and a developing roller.

FIG. 4 is a diagram illustrating a relationship between a developing nip width between a photosensitive member and a developing roller and a contact force between the photosensitive member and a developing roller.

FIG. 5 is an enlarged front view of a developing nip portion between a photoconductor and a developing roller.

FIG. 6 is a schematic configuration diagram of a main part of an image forming apparatus to which a second embodiment of the image forming apparatus according to the invention is applied.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Photoreceptor 3 Developing part 4 Developing container 5 Developing roller 6 Supply roller 7 Regulator blade 8 Agitator 9 Toner 10 Measurement table 11 Measurement table 12 Digital force gauge 13 Photoconductor mounting table 14 Paper 15 Thread 16 Measurement paper strip belt 17 load

 ──────────────────────────────────────────────────の Continued on the front page F term (reference) 2H077 AB04 AC04 AD02 AD06 AD13 AD16 AD17 AE03 BA07 EA15 FA13 FA22 GA13

Claims (7)

[Claims] An image bearing member on which an electrostatic latent image is formed by irradiating a writing light modulated based on image data after being uniformly charged in advance while rotating is carried on a developer. An image forming apparatus for developing an image by bringing a developer carrier into contact with the developer, transferring the developer image on the image carrier to a recording sheet, and fixing the recording sheet on which the developer image has been transferred to form an image; Wherein the developer carrier has at least a surface layer that carries the developer and an inner layer that is inner than the surface layer, and the surface layer has a hardness set higher than at least the hardness of the inner layer. An image forming apparatus, comprising: 2. An image forming apparatus according to claim 1, wherein said surface layer and said inner layer are formed of different members. 3. The image bearing member has a surface having a friction coefficient of:
3. The image forming apparatus according to claim 1, wherein the value is set in a range of 0.1 to 0.4. 4. The developing nip width, which is a width in the rotation direction of a contact portion between the image carrier and the developer carrier, is set to 1 mm or less. Item 4. The image forming apparatus according to any one of Items 3. 5. The method according to claim 1, wherein the hardness of the inner layer of the developer carrier is set in a range of 10 ° to 50 ° JIS A. Image forming apparatus. 6. The image forming apparatus according to claim 1, wherein the thickness of the surface layer of the developer carrier is set in a range of 5 to 20 μm. apparatus. 7. The image forming apparatus according to claim 1, wherein the developer carrier is disposed between the image carrier and a first elastic member that presses the developer carrier with a predetermined pressing force in a direction of the image carrier. The image forming apparatus according to claim 1, wherein the developer carrier is pressed against the image carrier by a predetermined pressing force due to a difference between the pressing force and a second elastic member that presses the developer carrier in a direction away from the image carrier. The image forming apparatus according to claim 1.