JP2001034046A - Developing device, developing cartridge, processing cartridge and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a developing device where electrified charge amount of toner carried on a developing roll can be maintained high and an image with a superior gradation can be obtained even when contact developing is carried out and to provide an image forming device, etc. SOLUTION: In the developing device 4, a developing roll 5 brought into contact with a photoreceptor drum 1 and an elastic blade 7, etc., brought into contact with the roller 5 are provided in a developing container 14 storing a non magnetic toner 8 of negative polarity consisting of one component developer and the DC contact developing method where developing bias of DC voltage from a power source 18 is impressed on the developing roll 5 is adopted. An electrifying roll 20 that is in contact with the developing roll 5 is provided downstream of the blade 7 to further make electrified amount of the toner 8 on the developing roll 5 greater after a layer thickness restriction and electrifying is applied to the toner 8 on the developing roller 5 by the blade 7, electrifying bias of -1700 V is applied to the roll 20 and the toner 8 on the developing roll 5 is electrified at a potential difference of 1500 V from -200 V DC voltage of the developing bias.

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 such as an electrophotographic copying machine and an electrophotographic printer, and a developing device, a developing cartridge and a process cartridge provided in the image forming apparatus.

[0002]

2. Description of the Related Art Conventionally, in an electrophotographic image forming apparatus, an electric latent image is formed on a photoreceptor by various methods using a photosensitive material, and then the latent image is developed using toner. The toner image is visualized, the obtained toner image is transferred to a recording material such as paper as necessary, and fixed by heat, pressure, or the like, to obtain a copy.

At present, there is a demand for improvements in image resolution, sharpness, etc., and it is essential to develop a method for forming a thin layer of toner on a developer carrier of a developing device and a developing device. Several measures have been proposed.

As one of them, a one-component contact roller is used in which a semiconductive developing roller or a developing roller having an electric wire tied to the surface is used as a developer carrier, and development is performed by pressing the developing roller against the surface of a photoreceptor. A development method has been proposed. FIG.
1 shows a developing device of a one-component contact developing system.

The developing device 55 includes a developing roller 5 in a developing container 58 containing a non-magnetic toner 57 of a one-component developer.
4, an elastic roller 56, an elastic blade 59, and the like, and the elastic roller 56 pressed against the developing roller 54 on the upstream side of the elastic blade 59 in the direction of rotation of the developing roller.
The non-magnetic toner 57 contained in the container 57 is supplied to the developing roller 54 by rotating in the direction.

The toner 57 supplied to the developing roller 54
Is transported to the elastic blade 59 along with the rotation of the developing roller 54 in the direction of the arrow B, where triboelectric charges (triboelectric charges) are given by friction at a contact portion between the elastic blade 59 and the developing roller 54, and the layer thickness is increased. Is regulated to form a thin toner layer.

The thinned toner 57 is supplied to the developing roller 5
As the photosensitive drum 1 and the developing roller 54 come into contact with each other with the rotation of 4, the photosensitive drum 1 reaches a developing section where it is used for developing an electrostatic latent image on the photosensitive drum 1. The transfer residual toner remaining on the developing roller 54 without being used for developing the latent image is returned into the developing container 58 together with the developing roller 54, and is peeled off by the elastic roller 56 at the contact portion between the developing roller 54 and the elastic roller 56. Taken. At the same time, as described above, a new toner 57
Is supplied to the developing roller 54, and the above process is repeated.

For the elastic roller 56, a foam made of polyurethane foam, sponge, or the like, or a fur brush is used. The elastic blade 59 may use a thin metal plate. However, when the developing roller 54 is made of a metal material, it is not preferable in terms of abrasion of the developing roller 54,
In order to form a good toner thin layer, the elastic blade 5
9 must be formed of a rubber material such as urethane or silicone.

With such a developing device configuration, it is possible to form a thin toner layer of the non-magnetic toner 57 on the developing roller 54, and it is possible to obtain a sharper image without fogging by good development. became.

[0010]

However, the conventional one-component contact developing device 55 has the following problems.

FIG. 14 shows the relationship between the development contrast and the amount of developed toner transferred per unit area on the photosensitive member. When contact development is performed using a non-magnetic toner having a charge amount of about −40 to −20 μC / g, as shown in FIG. 14, the amount of toner transferred to the photoconductor (developed toner amount) is
It shows a sharp rise with low development contrast.

FIG. 15 shows an example of an image formed by the contact development, in which 64 of the image output at 600 dpi by the dither method.
4 shows the relationship between gradation and image density. As shown in FIG. 15, it is difficult to obtain the gradation of the highlight portion A which is a low density portion, and the gradation of the high density portion B cannot be obtained.

As described above, the conventional one-component contact developing device has a problem that it is difficult to obtain excellent gradation.

An object of the present invention is to provide a developing apparatus capable of maintaining a high charge amount of toner carried on a developing roller and capable of obtaining an image having excellent gradation even when performing contact development. , A developing cartridge, a process cartridge, and an image forming apparatus.

[0015]

The above object is achieved by a developing device, a developing cartridge, a process cartridge and an image forming apparatus according to the present invention. In summary, the present invention provides a non-magnetic one-component developer carried and conveyed on a rotating developer carrier, and a developer regulating member in contact with the developer carrier. After regulating the layer thickness,
At the developing section where the developer carrier contacts the rotating image carrier, the developer develops an electrostatic latent image on the image carrier while applying a developing bias to the developer carrier. In the developing device, in the rotation direction of the developer carrier,
On the downstream side of the developer regulating member and at the upstream side of the developing section, a developer charging member is provided which is in contact with the developer carrier, and at the time of development, the developer carrier is used as a developing bias with the developer. A DC voltage having the same polarity is applied, and a DC voltage having the same polarity as the developer is applied as a charging bias to the developer carrier by the developer charging member at a discharge starting voltage or higher for the developer. Is a developing device.

According to the present invention, the developer charging member comprises:
In a direction perpendicular to the rotation direction of the developer carrying member, an area corresponding to an image forming area in a direction perpendicular to the rotating direction of the image carrying member is in contact with the surface of the developer carrying member. The developer charging member is rotated at the same speed by being driven or driven by the developer carrier. The developer charging member comprises a conductive elastic roller. The developer charging member may be provided in non-contact with the developer carrier. Further, the shape factor SF-1 of the developer is 100 to 180,
The shape factor SF-2 is 100 to 140.

Further, the present invention is a developing cartridge having the above-mentioned developing device, which is detachable from an image forming apparatus main body.
A process cartridge having the developing device and detachable from an image forming apparatus main body.

Further, the present invention is an image forming apparatus having the above-mentioned developing device. A plurality of developing devices can be provided. An image forming apparatus having the developing cartridge detachably. The developing cartridge can be detachably provided for a plurality of colors. An image forming apparatus having the process cartridge detachably. The process cartridge can be detachably provided for a plurality of colors.

Further, according to the present invention, the image forming apparatus converts the toner image obtained on the image carrier by development by the developing device into
The image can be directly transferred onto the recording material. Alternatively, the toner image obtained on the image carrier by the development by the developing device can be transferred to the second image carrier, and then transferred to the recording material.

[0020]

Embodiments of the present invention will be described below in more detail with reference to the drawings.

Embodiment 1 FIG. 1 is a schematic structural view showing an embodiment of the image forming apparatus of the present invention, FIG. 2 is a sectional view showing a developing device installed in the image forming apparatus of FIG. 1, and FIG. FIG. 3 is a front view of the developing device.

As shown in FIG. 1, the image forming apparatus includes a drum-shaped electrophotographic photosensitive member that rotates in the direction of arrow A, that is, a photosensitive drum 1 as an image carrier.
Is uniformly charged by the charger 2 and the laser beam 3 from the laser exposure means 3A is exposed, and an electrostatic latent image is written on the surface of the photosensitive drum 1.

A developing device 4 is arranged close to the photosensitive drum 1. The developing device 4 is configured as a developing cartridge that is detachable from the image forming apparatus main body. The electrostatic latent image on the photosensitive drum 1 is developed by the developing device 4 and is visualized as a toner image. In the present embodiment, the developing by the developing device 4 is a so-called reversal developing system in which toner is adhered to an exposed portion on the surface of the photosensitive drum 1 to develop a latent image.

The toner image formed on the photosensitive drum 1 is
The image is transferred from the recording material cassette 22 to the paper 13 as the recording material supplied to the photosensitive drum 1 by the paper feed roller 47 by the action of the transfer roller 9. The paper 13 to which the toner image has been transferred is sent to the fixing device 12, where the toner image is fixed, and then discharged out of the apparatus as a copy image.

After the transfer, the photosensitive drum 1 is subjected to the next image formation after the transfer residual toner remaining on the surface is scraped off by the cleaning blade 10. The removed transfer residual toner is stored in a waste toner container 11 provided with a blade 10.

The developing device 4 will be described with reference to FIG.
The developing device 4 includes a developing container 5 containing a non-magnetic toner (one-component toner) 8 as a one-component developer,
The apparatus includes an elastic roller 6, an elastic blade 7, a toner stirring member 16, a toner charging roller 20, and the like.

The developing roller 5 serving as a developer carrier is disposed in an opening extending in the longitudinal direction of the developing container 14 facing the photosensitive drum 1, and its substantially right half peripheral surface protrudes into the container 14. Is exposed to the outside of the container 14 and is laterally provided. The surface of the developing roller 5 exposed outside the developing container 14 is in contact with the surface of the photosensitive drum 1 with a predetermined contact width. The developing roller 5 is driven to rotate in the forward direction of the arrow B in which the contact portion moves in the same direction with respect to the photosensitive drum 1 rotating in the direction of the arrow A.

The surface of the developing roller 5 is provided with appropriate irregularities in order to increase the degree of rubbing with the toner 8 and to give the toner 8 good transportability. In this embodiment, the developing roller 5 has a diameter of 16 mm, a length of 216 mm,
An acrylic / urethane resin was coated on a 5 mm thick silicone rubber cylinder. The roller resistance was 10 ⁴ to 10 ⁶ Ω. The photosensitive drum 1 was rotated at a peripheral speed of 80 mm / sec which was slightly faster than the peripheral speed of 50 mm / sec.

A developing power source 18 is connected to the developing roller 5, and a developing bias is applied from the power source 18 to the developing roller 5 during development. In this embodiment, a DC contact developing method is employed, and a DC voltage is applied as a developing bias.
The power supply 18 is connected to a toner charging roller 20,
The charging bias can be applied to the toner charging roller 20 by dividing the developing bias. The toner charging roller 20 will be described later.

The measurement of the resistance value of the developing roller 5
mm aluminum roller and the developing roller 5 are contacted with a contact load of 500 gf.
After rotating at m / sec, a DC voltage of 400 V was applied to the developing roller, the voltage across both ends of a 10 MΩ resistor attached to the ground side was measured to determine the flowing current, and then the resistance of the developing roller was calculated and implemented.

The elastic roller 6 is in contact with the lower surface of the developing roller 5 opposite to the photosensitive drum 1 and is rotatably supported. As the elastic roller 6,
A foamed skeleton-like sponge structure or a fur brush structure in which fibers such as rayon and nylon are planted on a cored bar are preferable from the viewpoint of supplying the toner 8 to the developing roller 5 and stripping off the undeveloped toner. In this embodiment, the elastic roller 6 has a foamed skeleton sponge structure in which a polyurethane foam is provided on a cored bar. The diameter of the elastic roller 6 is 16 m
m.

It is effective that the contact width of the elastic roller 6 with the developing roller 5 is 1 to 8 mm, and it is preferable that the developing roller 5 has a relative speed at the contact portion. In this embodiment, the contact width of the elastic roller 6 with the developing roller 5 is set to 3
mm, and the peripheral speed of the elastic row 6 is 50 m during the developing operation.
m / sec (the relative speed with the developing roller 5 is 130 mm / sec)
The rotation was performed by driving means (not shown) so that

The elastic blade 7 is supported by the supporting metal plate 15 at a position downstream of the elastic roller 6 in the rotation direction of the developing roller 5 so that the vicinity of the free end side tip is in surface contact with the outer peripheral surface of the developing roller 5. It is provided to be supported by the developing container 14. The elastic blade 7 uses a plate made of a rubber material such as silicone or urethane, or is based on a metal thin plate of SUS or phosphor bronze having spring elasticity, and a rubber material is formed on the contact surface side of the metal thin plate with the developing roller 5. A bonded product is used. The contact direction of the elastic blade 7 with respect to the developing roller 5 is a so-called counter direction in which the tip end is located upstream of the developing roller 5 in the rotation direction.

In this embodiment, the elastic blade 7 is formed by bonding a urethane rubber chip having a thickness of 1.0 mm to a SUS plate. The elastic blade 7 is attached to the developing container 14 by a supporting metal plate 15. The contact pressure against the developing roller 5 was set to a linear pressure of 25 to 35 g / cm. The linear pressure was measured by measuring three metal sheets with known friction coefficients.
The elastic blade 7 is inserted into the contact portion between the developing roller 5 and the elastic blade 7, a spring gauge is attached to one central metal plate, and the spring gauge is pulled to pull out the central metal plate from the load when the elastic blade 7 is pulled out. The conversion was performed per unit length in the longitudinal direction (the same direction as the longitudinal direction of the developing roller 5).

FIG. 3 shows the developing device 4 of FIG.
It is the front view seen from the direction. The developing roller 5 is omitted for convenience of understanding.

As shown in FIG. 3, on both sides of the opening of the developing container 14, an end sealing member 1 is provided to prevent toner from leaking from both ends of the developing roller 5 disposed in the opening.
9 are provided to seal both ends of the developing roller.

Both ends of the elastic blade 7 are formed so that the length in the same direction as the longitudinal direction of the developing roller 5 becomes shorter from the contact nip with the developing roller 5 shown by oblique lines in FIG. It is an inclined side that is cut toward. As well known, the thickness of the toner layer formed on the developing roller 5 under the control of the elastic blade 7 is
And the free end from the point upstream of the contact portion to the tip, the longer the distance, the thicker the layer, and the shorter, the thinner.

The non-magnetic toner 8 of the one-component developer includes:
A toner having an excellent transfer property and a property of high lubricity when it becomes a transfer residual toner, and thus has an advantage such that abrasion of the photosensitive drum 1 when cleaning with a cleaning means such as a blade or a fur brush is small. That is, a spherical toner having a smooth surface was used. The volume resistance was 10 ¹⁴ Ωcm or more.

The conditions for measuring the volume resistance of the toner were as follows: the diameter of the measurement electrode plate was 0.6 cm, the area was 0.238 cm ² , the weight of the weight was 1500 g, and the pressing force of the toner powder sample at the time of measurement was 980 gf / cm ^2. (96.1 kPa), the thickness of the toner sample powder layer is 0.5 to 1.0 mm, and the applied DC voltage is 400 V
And the amount of current flowing at that time is measured by a minute ammeter (YHP41
40pA METER / DC VOLTAGE SOU
CE), and the volume resistance (specific resistance) was calculated from the resistance value.

The toner 8 has a shape factor SF-1 of 100 to
At 180, the one having SF-2 of 100 to 140 is used.

The shape factors SF-1 and SF-2 were randomly sampled from 100 toner particle images using FE-SEM (S-800) manufactured by Hitachi, Ltd., and the image information was obtained via Nicole Corporation via an interface. Is introduced into an image analysis device (Lusex3) manufactured by FUJIFILM Corporation, and is defined as a value calculated by the following equation.

SF-1 = ｛(MXLNG) ² / ARE
A｝ × (π / 4) × 100 SF-2 = {(PERI) ² / AREA} × (4 / π)
× 100 where MXLNG: Absolute maximum length, AREA: Toner projection area, PERI: Perimeter The shape factor SF-1 of the toner indicates the degree of sphericity and is 1
As the size increases from 00, the shape gradually changes from a spherical shape to an irregular shape. SF-2 indicates the degree of unevenness, and as the value increases from 100, the unevenness of the toner surface becomes more conspicuous.

The method for producing the toner is not particularly limited as long as the toner falls within the range of the shape factor. In addition to the so-called pulverizing method,
No. 10231, a method of directly producing a toner using the suspension polymerization method described in JP-A-59-53856, and a method in which a monomer is soluble and a polymer obtained is an insoluble aqueous organic solvent. It is also possible to use a dispersion polymerization method for directly producing a toner, an emulsion polymerization method typified by a soap-free polymerization method for producing a toner by directly polymerizing in the presence of a water-soluble polar polymerization initiator, or the like.

In this embodiment, the shape factor SF is relatively easily
-1 can be adjusted to 100 to 180, SF-2 can be adjusted to 100 to 140, and a fine particle toner having a sharp particle size distribution and a particle size of 4 to 8 μm can be obtained by a suspension polymerization method under normal pressure or pressure. Styrene and n-butyl acrylate, a salicylic acid metal compound as a charge control agent, a saturated polyester as a polar resin, and a colorant, to produce colored suspension particles having a weight average particle size of about 7 μm. Then, 1.5 wt% of hydrophobic silica was externally added thereto, and used as the non-magnetic toner 8 having negative polarity. According to this toner, as described above, it is possible to exhibit characteristics that are excellent in transferability and can reduce abrasion of the photosensitive drum 1 at the time of cleaning the transfer residual toner.

In the developing device 4 described above, during the developing operation, the non-magnetic toner 8 in the developing container 14 is sent in the direction of the elastic roller 6 with the rotation of the stirring member 16 in the direction of arrow C. The toner 8 sent to the elastic roller 8 is conveyed to the vicinity of the developing roller 5 by the rotation of the elastic roller 8 in the direction of the arrow D, and is rubbed at the contact portion between the developing roller 5 and the elastic roller 6 by friction. It is charged and adheres and is carried on the developing roller 5 by the mirror force of the charged charge.

The toner 8 carried on the developing roller 5 is
As the developing roller 5 rotates in the direction of arrow B, it is sent under pressure of the elastic blade 7, and is further subjected to triboelectric charging and is formed on the developing roller 5 as a thin toner layer.

In the present embodiment, the contact pressure of the elastic blade 7 is set so that the charge amount is -40 to -20 μC / g,
A good toner coating amount of 4 to 1.0 mg / cm ² (10 to 20 μm in toner layer thickness) is obtained.

In the present invention, the non-magnetic toner 8
In order to maintain a high charge amount of the toner, the toner charging roller 20 is installed downstream of the elastic blade 7 with respect to the developing roller 5 so that the toner 8 regulated by the elastic blade 7 is charged to the charging roller 20. A bias was applied to discharge from the charging roller 20, and the toner 8 was further charged.

The toner charging roller 20 was a rubber roller, and was brought into contact with the developing roller 5 at a pressure of 100 to 200 gf by being supported by a pressing member 21 attached to the developing container 14. The deflection width of the charging roller 20 is set to 50 μm.
The following was used. The contact of the toner charging roller 20 with the developing roller 5 has a length (the elastic blade 7) that reliably covers the longitudinal portion (image developing area) of the developing roller 5 corresponding to the image forming area in the longitudinal direction of the photosensitive drum 1. In terms of the relationship, it is preferable that the elastic blade 7 has a length that surely covers the entire area of the toner coat portion which is the contact portion with the developing roller 5). The pressing of the toner charging roller 20 also has the effect of finely filling the toner on the developing roller 5 and uniformly coating.

A method of charging the toner by the charging roller will be described. When the resistance of the toner charging roller 20 is 10 ⁸ Ω, the surface potential of the charged toner 8 on the developing roller 5 with respect to the applied voltage behaves as shown in FIG.

That is, since the toner 8 on the developing roller 5 is frictionally charged by the elastic blade 7 or the like, the toner 8 has a surface potential of about -20 V even when the voltage applied to the charging roller 20 is 0 V. Excluding the surface potential, the discharge start voltage of the charging roller 20 and the toner 8 on the developing roller 5 rises at an inclination of 1 from −600 V as shown in FIG. Is shown.

As another method of applying and charging the toner, there is an injection charging method. In this method, the relationship between the toner charging roller voltage and the toner surface potential has a behavior as shown in FIG.

From the above results, it is considered that the application and charging of the toner by the toner charging roller 20 in the present invention utilizes the discharge phenomenon.

In general, the discharge starting voltage of the toner charging roller 20 and the toner 8 is determined by the intersection of two curves (including straight lines) represented by the following equations (1) and (2) with the space distance g as a variable. .

Vb = 312 + 6.2 × g (1) Vg = g × (Va−Vc) / {(Lt / Kt) + g} (2) where g: spatial distance, Vb: 8 μm <Approximate expression of Paschen's rule for g, Vg: gap voltage between toner charging roller and toner layer surface, Va: toner charging roller applied voltage, Vc: toner layer surface potential, Lt: toner layer thickness Kt: toner layer Relative Dielectric Constant The non-magnetic toner 8 used in the present embodiment is excellent in sharpness of particle size distribution and spherical in shape, so that the ratio of toner and air in the toner layer is constant. Therefore, the relative dielectric constant Kt of the toner layer in the equation (2) is stable, and it is possible to charge and charge the toner by stable discharge.

Then, the resistance range of the toner charging roller 20 in which the toner can be discharged was examined. If the resistance of the toner charging roller 20 is 10 ⁷ Ω or less, an abnormal discharge occurs between the toner charging roller 20 and the toner coat portion of the developing roller 5, and an optimum image cannot be obtained. On the other hand, when the resistance of the toner charging roller 20 is 10 ¹² Ω or more, the discharge starting voltage becomes too high, and the charging ability for the toner cannot be obtained.

From the above, the toner charging roller 2
A suitable range for a resistance of 0 is 10⁸-10^{1 1}Ω. This implementation
In the example, the resistance of the developing roller 5 is 10⁶Ω
However, the resistance of the developing roller depends on the toner charging roller 20.
Can be kept within the above-mentioned appropriate range.

The method of measuring the resistance of the toner charging roller 20 is as follows. An aluminum roller having a diameter of 16 mm and a toner charging roller were brought into contact with a contact load of 170 gf, the aluminum roller was rotated at a peripheral speed of 80 mm / sec, a DC voltage of 400 V was applied to the toner charging roller, and a 10 MΩ The voltage at both ends of the resistor is measured to find the flowing current, and then the resistance of the toner charging roller is calculated.

As shown in FIG. 6, the amount of charge of the toner on the developing roller 5 is such that the applied voltage between the charging roller 20 and the developing roller 5, that is, the applied bias of the charging roller 20 with respect to the developing roller 5 is-. It saturates from around 1200V. In this embodiment, in order to perform stable discharge, the potential difference between the developing roller 5 and the toner charging roller 20 is set to 1500V.
Set to. Since a DC voltage of -200 V was applied to the developing roller 5 as a developing bias, the DC voltage applied to the toner charging roller 20 was set to -1700 V.

As described above, in this embodiment, the developing roller 5 which has been regulated in the layer thickness by the elastic blade 7 and charged
The upper toner 8 is further charged by the charging roller 20, and then is conveyed to a developing unit which is a part facing the photosensitive drum 1. Then, in the developing section, the toner 8 on the developing roller 5 is adhered to the electrostatic latent image on the photosensitive drum 1 and developed by the DC voltage applied to the developing roller 5, and the latent image is visualized as a toner image.

The undeveloped toner not consumed in the developing section is collected into the developing device 14 from below the developing roller 5 with the rotation of the developing roller 5. A seal member 17 made of a flexible sheet is provided at the collecting portion to allow the undeveloped toner to pass into the developing container 14, and to allow the toner 8 in the container 14 to move from below the developing roller 5 to the outside. To prevent leakage.

The collected toner remaining after development is peeled off from the surface of the developing roller 5 at the contact portion between the elastic roller 6 and the developing roller 5. Most of the stripped toner is conveyed with the rotation of the elastic roller 6, mixed with the toner 8 in the container 14, and the charged charges are dispersed. At the same time, the rotation of the elastic roller 6 causes the developing roller 5
The supply of new toner is as described above.

In this embodiment, as described above, the toner charging roller 20 is provided on the downstream side of the elastic blade 7 so that the non-magnetic toner 8 on the developing roller 5 regulated by the elastic blade 7 is Because it is further charged
The charge amount of the toner can be kept high. Therefore, according to this embodiment, the coating amount on the developing roller 5 is 0.4 to 1.0 mg / cm ² (10 to 20 μm in layer thickness).
m) and the toner charge amount is −40 to −90 μC / g.
, A highly uniform thin toner layer can be stably formed, and an image with excellent gradation can be obtained.

In this embodiment, the toner charging roller 20
Charge of the non-magnetic toner 8 from -40 to-
When it was increased to 90 μC / g and DC contact development was performed using the same, FIG. 7 shows that the toner charge amount was −40 to −90 μm.
As shown by the dotted line at C / g, the curve of the development contrast—the amount of toner developed on the photoreceptor is made gentler than the case of the toner charge amount of −20 to −40 μC / g shown by the solid line. did it. Further, as shown by the dotted line in FIG. 8 in the case of the present embodiment, the gradation of the highlight portion which could not be expressed when the charge amount of the toner shown by the solid line was conventionally -20 to -40 μC / g is It is possible to reproduce the gradation of around 48 to 64 gradations.

In the above description, the developing device 4 is configured as a developing cartridge that is detachable from the image forming apparatus main body. However, the developing device 4 may be fixed to the image forming apparatus main body and configured to supply toner. it can. Developing device 4
The photosensitive drum 1 may be combined with the charging device 2, the cleaning blade 10, and the waste toner container 11 to form a process cartridge detachable from the image forming apparatus main body.

Embodiment 2 FIG. 9 is a sectional view showing a developing device according to another embodiment of the present invention.

In the developing device 14 shown in FIG. 2 of the first embodiment, the toner charging roller 20 is in contact with the developing roller 5, but in the present embodiment, the toner charging roller 20 is set apart from the developing roller 5. did. Other configurations of the present embodiment are basically the same as those of the first embodiment. In FIG. 9, the same reference numerals as those shown in FIG. 2 denote the same members.

Toner charging roller 2 for developing roller 5
0 is preferably about 50 to 600 μm,
If it is less than μm, it corresponds to the range of roller run-out, and the toner charging roller comes into contact with the developing roller, causing a decrease in charging ability due to toner adhesion. Due to the relationship between the bias and the gap as shown in FIG. 10, when an applied voltage of 3.5 kV or more is applied, an image abnormality due to an abnormal discharge occurs. In this embodiment, the interval between the toner charging rollers is set to 200 μm.

Further, from the relation of the equation (1), since g = 200 μm in this embodiment, the discharge starting voltage is −1552.
V, and the charge characteristic of the toner on the developing roller to the bias applied to the charging roller as shown in FIG. 11 can be obtained.

In this embodiment, similarly to the first embodiment, the potential difference between the developing roller 5 and the toner charging roller 20 is set to 1500 V
, A DC voltage of -200 V is applied to the developing roller 5 as a developing bias, and a DC voltage of -1700 V is applied to the toner charging roller 20 to control the layer thickness by the elastic blade 7 and to charge the developing roller 5. Non-magnetic toner 8
Was further charged.

As a result, the coating amount on the developing roller 5 is 0.4 to 1.0 mg / cm ² (10 to 20 μm in layer thickness).
m), a toner thin layer having a toner charge amount of −40 to −90 μC / g was stably formed, and an image having excellent gradation was obtained as in Example 1.

As described above, according to the present embodiment,
As in the first embodiment, a thin toner layer with a high toner charge amount can be stably formed on the developing roller, and good gradation can be obtained by performing good development. Further, according to the present embodiment, since the toner charging roller is provided in non-contact with the developing roller, there is also an effect of preventing a reduction in charging ability due to toner contamination.

Embodiment 3 FIG. 12 is a sectional view showing another embodiment of the image forming apparatus of the present invention.

The image forming apparatus of this embodiment is different from the monochromatic image forming apparatus of the first embodiment shown in FIG. 1 in that the image bearing member is not a drum-shaped photosensitive member but a belt-shaped photosensitive member, that is, a photosensitive member. A belt 34 is provided, and developing devices 4A, 4B, 4C, and 4D for four colors are arranged along the rotation direction. Further, an intermediate transfer belt 45 serving as a second image carrier is provided with respect to the photosensitive belt 34.
Is installed, and a four-color image can be formed by an intermediate transfer method.

The photosensitive belt 34 is a flexible belt having a surface coated or vapor-deposited with a photoconductor. The photosensitive belt 34 is wound around three rollers 38, 39, and 40, and rotates the rollers 38 to 40. Is rotated clockwise in the figure.

Around the photosensitive belt 34, a charging roller 36, a laser writing system unit 37 as exposure means, four-color developing devices 4A to 4D, an intermediate transfer belt 45, and a belt cleaner 35 are arranged along the rotating direction. Have been.

The photosensitive belt 34 rotates the charging roller 3 during the rotation process.
The laser beam 3 is exposed by a laser writing system unit 37 charged with a color signal from a signal processing unit (not shown) and formed into an electrostatic latent image corresponding to the first color, for example, yellow, on the surface of the photosensitive belt 34. Is done. The laser writing system unit 37 is an optical system that converges and scans the laser beam from the light emitting unit used here on the photosensitive belt 34 by a rotating polygon mirror or the like, and an optical system integrating the light emitting unit and a convergent light transmitter. A system or the like can also be used.

The electrostatic latent image corresponding to the first color, for example, yellow, formed on the photosensitive belt 34 is developed by the developing unit 44 by the yellow developing device 4D and is visualized as a yellow toner image. Developing devices 4A, 4B, 4C, 4
D contains toner of each color of black (K), cyan (C), magenta (M), and yellow (Y).

The yellow toner image formed on the photosensitive belt 34 in this manner is conveyed by the rotation of the photosensitive belt 34, and is transferred to the primary transfer section abutting the intermediate transfer belt 45 rotating in the direction of the arrow. The toner and the toner are transferred to the surface of the intermediate transfer belt 45 to which a reverse bias is applied (primary transfer).

Similarly, the second color on the photosensitive belt 34
The latent images of the third and fourth colors are formed, and the magenta developing device 4
C, magenta, cyan, and black toner images developed by the respective developing units 43, 42, and 41 by the cyan developing device 4B and the black developing device 4K are transferred onto the intermediate transfer belt 45. A color image formed by superimposing and transferring four color toner images of yellow, magenta, cyan, and black is formed on the image 45.

The four-color toner image thus superimposed and transferred is applied to the sheet conveyed from the recording material cassette 22 to the intermediate transfer belt 45 by the paper feed roller 47 by the transfer roller 46 applying a bias having the same polarity as the toner. (2)
Next transfer), and the paper is a fixing roller 4 which forms a fixing device.
8 and a pressure roller 49, where the four color toner images are fixed on paper to form a full-color print image, and then discharged onto a discharge tray 50 via a discharge roller 53.

The secondary transfer residual toner remaining on the surface of the intermediate transfer belt 45 on which the secondary transfer of the four color toner images has been completed is wiped off by the cleaner 60 to prepare for the next image formation. Each time the primary transfer of the toner image of each color is completed, the primary transfer residual toner remaining on the surface of the photosensitive belt 34 is scraped off by the cleaner 35, and the photosensitive belt 34 is prepared for image formation of the next color.

In this embodiment, the developing devices 4A to 4D
Is provided with a toner charging roller 20 that comes into contact with the developing roller 5 on the downstream side of the elastic blade 7 and applies a charging bias to the charging roller 20 so that the elastic blade 7 The toner 8 on the developing roller 5 which has been subjected to the layer thickness regulation and the charging is further charged.

As in Embodiment 1, the potential difference between the developing roller 5 and the toner charging roller 20 is set to 1500 V, a DC voltage of -200 V is applied to the developing roller 5 as a developing bias, and a DC voltage of -1700 V is applied to the toner charging roller 20. By applying the voltage, the non-magnetic toner 8 on the developing roller 5 that passed through the elastic blade 7 was further charged.

Thus, the coating amount on the developing roller 5 is 0.4 to 1.0 mg / cm ² (10 to 20 μm in layer thickness).
m), a toner thin layer having a toner charge amount of −40 to −90 μC / g could be formed stably, and as a result, a color image with excellent gradation could be obtained.

As described above, according to the present embodiment,
It is possible to stably form a thin toner layer having a high charge amount on the developing roller, and perform good development to obtain an image having excellent gradation.

[0087]

As described above, according to the present invention,
A toner charging roller is installed on the downstream side of the elastic roller with respect to the developing roller of the developing device so that the non-magnetic toner on the developing roller which has been regulated by the elastic roller and charged is further charged by the toner charging roller. As a result, the charge amount of the toner on the developing roller can be kept high, and an image with excellent gradation can be obtained even when performing the contact development in which the developing roller is in contact with the image carrier.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing one embodiment of an image forming apparatus of the present invention.

FIG. 2 is a cross-sectional view illustrating a developing device installed in the image forming apparatus of FIG.

FIG. 3 is a front view of the developing device.

FIG. 4 is a diagram showing the relationship between the voltage applied to the toner charging roller and the surface potential of the toner on the developing roller when the toner is charged by discharging with the toner charging roller provided in the developing device.

FIG. 5 is a diagram illustrating a relationship between an applied voltage of a toner charging roller and a surface potential of toner on a developing roller when charging is performed by an injection charging method.

FIG. 6 is a diagram illustrating a relationship between an applied bias of a toner charging roller with respect to a developing roller and a charge amount of toner on the developing roller.

FIG. 7 is a diagram illustrating a relationship between a development contrast and a developing toner amount on a photoconductor when charging is performed by a toner charging roller according to the present invention and when charging is not performed.

FIG. 8 is a diagram showing a gradation curve when charging is performed by a toner charging roller according to the present invention and when there is no charging.

FIG. 9 is a cross-sectional view illustrating a developing device according to another embodiment of the present invention.

FIG. 10 is an explanatory diagram showing a difference in charging ability depending on a gap between a developing roller and a charging member and a bias.

11 is a diagram illustrating a relationship between a charge amount of a toner on a developing roller and a bias applied to the charging roller in the developing device of FIG. 9;

FIG. 12 is a schematic configuration diagram showing still another embodiment of the image forming apparatus of the present invention.

FIG. 13 is a schematic view showing a conventional image forming apparatus.

14 is a diagram illustrating a relationship between a development contrast and a developing toner amount on a photoconductor in a developing device of the image forming apparatus of FIG. 13;

FIG. 15 is a diagram illustrating a gradation curve in the image forming apparatus of FIG. 13;

[Explanation of symbols]

 Reference Signs List 1 photosensitive drum 2 charging device 5 developing roller 6 elastic roller 7 elastic blade 8 non-magnetic toner 18 developing power supply 20 toner charging roller

Claims (19)

[Claims] 1. A non-magnetic one-component developer is carried and conveyed on a rotating developer carrier, and the layer thickness of the carried developer is reduced by a developer regulating member in contact with the developer carrier. After the regulation, the developer carrying member applies a developing bias to the developer carrying member at a developing portion in contact with the rotating image carrier, and the electrostatic latent on the image carrying member is applied. In a developing device that develops an image, a developer charging member that contacts the developer carrier at a position downstream of the developer regulating member and upstream of the developing unit in a rotation direction of the developer carrier. During development, a DC voltage having the same polarity as the developer is applied as a developing bias to the developer carrier, and the developer charging member applies a charging bias to the developer carrier as the developing bias. Polar DC voltage to the developer Developing device and applying in electric starting voltage or more. 2. The developer charging member is a region corresponding to an image forming area in a direction perpendicular to the rotation direction of the image carrier in a direction perpendicular to the rotation direction of the developer carrier.
The developing device according to claim 1, wherein the developing device contacts a surface of the developer carrier. 3. The developer charging member is rotated at the same speed by being driven or driven by the developer carrier.
Or 2 developing device. 4. The developing device according to claim 1, wherein said developer charging member comprises a conductive elastic roller. 5. A non-magnetic one-component developer is carried and conveyed on a rotating developer carrier, and the layer thickness of the carried developer is reduced by a developer regulating member in contact with the developer carrier. After the regulation, the developer carrying member applies a developing bias to the developer carrying member at a developing portion in contact with the rotating image carrier, and the electrostatic latent on the image carrying member is applied. In the developing device for developing an image, a developer is charged in a non-contact manner with the developer carrier at a position downstream of the developer regulating member and upstream of the developing unit in a rotational direction of the developer carrier. A member is provided, and at the time of development, a DC voltage having the same polarity as the developer is applied as a developing bias to the developer carrier, and the developer charging member applies a charging bias to the developer carrier by the developer charging member. DC voltage of the same polarity to the developer Developing device and applying in electric starting voltage or more. 6. The developer charging member is a region corresponding to an image forming area in a direction perpendicular to the rotation direction of the image carrier in a direction perpendicular to the rotation direction of the developer carrier.
The developing device according to claim 5, wherein the developing device faces the surface of the developer carrier. 7. The developer charging member is rotated at the same speed by driving the developer carrier.
Developing device. 8. The developing device according to claim 5, wherein said developer charging member comprises a conductive elastic roller. 9. The developer having a shape factor SF-1 of 100.
The developing device according to any one of claims 1 to 8, wherein the shape factor SF-2 is 100 to 140. 10. A developing cartridge having the developing device according to claim 1 and detachable from an image forming apparatus main body. 11. A process cartridge having the developing device according to claim 1 and detachable from an image forming apparatus main body. 12. An image forming apparatus having the developing device according to claim 1. 13. An image forming apparatus having the developing device according to claim 1 for a plurality of colors. 14. An image forming apparatus having the developing cartridge according to claim 10 detachably. 15. An image forming apparatus having the developing cartridge of claim 10 detachably for a plurality of colors. 16. An image forming apparatus having the process cartridge according to claim 11 detachably. 17. An image forming apparatus having the process cartridge according to claim 11 for a plurality of colors in a detachable manner. 18. The method according to claim 12, wherein the toner image obtained on the image carrier by the development by the developing device is directly transferred onto a recording material.
18. The image forming apparatus according to any one of items 17 to 17. 19. The image forming apparatus according to claim 12, wherein the toner image obtained on the image carrier by the development by the developing device is transferred to a second image carrier, and then transferred onto a recording material. Image forming apparatus.