JPH0619295A - Back exposure developing method - Google Patents

Abstract

PURPOSE:To provide the back exposure developing method which can form a sharp image even on a photosensitive body using, specially, a-Si by eliminating a ghost phenomenon, a fog, etc., due to an abrupt increase in the developer resistance in a low-electric-field area. CONSTITUTION:Even when a developer deteriorates as a result of the repetition of the contact electrostatic charging and exposure of the photosensitive body and a toner rubbing area 10, development can be performed within a range wherein the developer resistance after the deterioration satisfies Rt < (Vc/ Vs-Vc)Rh. In the inequality, Rt is the developer resistance (when a developable voltage Vc is applied), Vs a developing bias (voltage) applied to a developer carrier, Vc the developable voltage, and Rh the bright resistance of the photosensitive body.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backside exposure and development method applied to printers, facsimiles, copiers and the like, and in particular, while exposing the photoreceptor by exposing means arranged on the backside of the photoreceptor. The present invention relates to a backside exposure developing method which performs development almost simultaneously with

[0002]

2. Description of the Related Art Conventionally, for example, an exposing means for generating a light output corresponding to image information is provided in a photosensitive drum formed by laminating a transparent conductive layer and a photoconductive layer on a transparent support. At the same time as or immediately after forming the latent image on the photoconductor layer by converging the light output of the exposure means by interpolating the latent image, the latent image can be formed through the toner carrier facing the photosensitive drum. BACKGROUND ART An image forming apparatus is known in which it is possible to transfer a toner image onto a plain paper through a transfer roller or other transfer means after forming the image (toner image). (JP-A-58-153957, etc.)

In this type of image forming apparatus, in order to further simplify the structure, prevent ozone from being generated, and prevent fog from occurring, an independent charger is not provided to face the photosensitive drum. Conductive magnetic toner is carried on the developing sleeve arranged in parallel, and a so-called magnetic brush-like toner rubbing area is provided immediately before the developing position by utilizing the magnetic force of the fixed magnet assembly or the like contained in the sleeve. Charging was performed by injecting charges into the photosensitive layer of the drum through the rubbing area by using the developing bias applied to the developing sleeve side while rubbing the surface of the photosensitive drum with the rubbing area. After that, immediately after the charging, an exposure image is formed by using the exposure means included in the drum, and development is performed to form a predetermined image.

Therefore, it is premised that the toner used in the above apparatus is a conductive toner in order to inject charges from the developing sleeve side. However, when a conductive toner is used, the transfer efficiency is improved when a toner image is transferred onto a sheet. Badness becomes a problem.
In order to prevent such a defect, it is preferable to use an insulating toner instead of a conductive toner as the developer. However, when the insulating toner is used, the charging step of injecting charges from the developing bias cannot be performed, and only the triboelectric charging is performed. Therefore, smooth charging becomes difficult.

Therefore, in order to prevent the above-mentioned drawbacks, JP-A-63 / 1988
-214781, the toner resistivity is 10 ⁴
A conductive magnetic toner having a resistivity of 10 ⁹ Ω · cm and a triboelectrification type high resistance toner having a toner resistivity of 10 ¹⁴ Ω · cm or more and being charged to the number of poles determined by triboelectrification are mixed. It proposes a technology in which the resistance value is set to 10 ⁵ to 10 ¹⁰ Ω · cm.

[0006]

However, as described above, the conductive toner has a resistance value of 10 ⁴ to 10 ⁹ Ω · cm in the semi-conductive region, or 10 ⁵ to 10 ¹⁰ even in the case of a mixed toner.
It is a semiconductive region of Ω · cm, and the resistance value of a material in such a semiconductive region generally differs depending on the electric field strength, and the resistance value exponentially increases in a low electric field. Therefore, for example, 10
Even if a developer with a semi-conductive area of ⁵ to 10 ¹⁰ Ω · cm is created, if the photoconductor charging potential is charged close to the applied voltage of the development, the resistance of the developer existing in the developing space becomes high. , Smooth charge injection to the photoreceptor side, that is, charging is not performed. Therefore, when developing with the toner in the semiconductor region as described above, whether alone or mixed, it is not possible to impart a charge sufficient to erase the previous image at the time of recharging, and the history of image exposure in the subsequent developing process. Defects such as a ghost phenomenon caused by (the preceding latent image) and fog caused by insufficient recharging of the photoconductor become apparent.

The above-mentioned drawbacks caused by the sudden increase in the resistance of the developer in such a low electric field range are a-Si having a lower resistance than the conventional OPC and other organic semiconductors.
It becomes more prominent when other photoconductors are used,
In particular, a photoreceptor using a-Si has a relatively low resistance value as compared with the developer in the above-mentioned semiconductive region, so that the charging failure is further amplified and fogging and ghost are more likely to occur.

In view of the above-mentioned drawbacks of the prior art, the present invention eliminates the ghost phenomenon, fog, etc. that occur due to the rapid increase in developer resistance in the low electric field region, and in particular a-Si.
It is an object of the present invention to provide a backside exposure and development method which enables a clear image formation even on a photoreceptor using.

[0009]

In order to solve the above-mentioned drawbacks, the present invention does not require the developer resistance to be determined independently, but the developer resistance during development is always less than or equal to a resistance value determined by the following formula 1). In other words, even if the developer deteriorates due to repeated contact charging between the photoconductor and the toner rubbing area and repeated stirring of the developer, the developer resistance after the deterioration is 1) below.
It is characterized in that development is carried out within a range satisfying the formula. Rt <(Vc / Vs-Vc) Rh ... 1) Rt: developer resistance (developer resistance when a voltage of developable voltage Vc is applied) Vs: development bias (voltage) Vc applied to the developer carrier : Developable voltage (refers to the potential of (development bias-photoreceptor charging potential) when reversal development is started) Rh: Bright resistance of photoreceptor

[0010]

The function of the present invention will be described in detail. As shown in FIG. 1, the basic operation of the backside exposure development method is, as shown in FIG. 1, a light-transmitting conductive layer 1b, an injection blocking layer 1e, and a photosensitive layer composed of a photoconductor layer 1c and a surface layer 1f on a light-transmitting support 1a. On the developing sleeve 30 arranged to face the photosensitive drum 1 in which 1c / 1f is laminated, a developer composed of, for example, high resistance or insulating magnetic toner and a conductive magnetic carrier is carried, and, for example, both of the above 1 , 30 are rotated in the direction of the arrows with a relative speed difference, the magnetic force of the fixed magnet assembly 33 contained in the sleeve 31 is utilized to cause the so-called magnetic brush-like developer rubbing area 10 between the developing gaps. Form. In the developer rubbing area 10, the toner is once transferred and adhered to the photosensitive drum 1 side by the application of the developing bias Vs applied to the developing sleeve 30 side, and the surface of the photosensitive drum 1 is rubbed by the developer magnetic brush. Photoconductor drum 1
When the side surface is charged and the charging potential approaches the potential of the developing bias, the developer is pulled back to the developing sleeve 30 side by the magnetic force of the fixed magnet assembly 33. At this time, immediately after the charging, an exposure image is formed by using the exposure means 2 included in the drum 1, so that the charging potential is attenuated to near 0 V, and the toner is generated by the potential difference between the developing bias Vs and the photosensitive drum. Inverse development is carried out, and a predetermined image can be formed.

The relationship between the developing bias voltage Vs and the charging potential Vh in the rubbing area is represented by the equivalent circuit of FIG. Where Rh is the photoconductor resistance, Ch is the photoconductor capacity,
Rt is the developer resistance, and Ct is the developer capacity. Further, Rt and Ct refer to the total resistance and capacity of the developer obtained by mixing the toner and the carrier at a predetermined mixing ratio. Therefore, when the relation between the developing bias voltage Vs and the charging potential Vh is expressed by the equation from the equivalent circuit, the calculation equation of the equation 3) is obtained. Vh = Vs [(Rh / Rt + Rh) -A] ... 3) A = {(Ch ・ Rh-Ct ・ Rt) / (Ct + Ch) (Rt + Rh)} ・ exp [-{(Rt + Rh) t } / {Rt · Rh (Ct + Ch)} t: Development time. Now, in the calculation formula of 3) above, the resistance of the developer and the photoconductor
Unless Rt, Rh and capacities Ct, Ch are all small and the process time is not sufficiently short, Vh = Vs (Rh / Rt + Rh) ... 2) can be approximated.

On the other hand, FIG. 5 shows a development γ characteristic showing the relationship between (developing bias voltage Vs-photoconductor charge potential Vh) and development density. The charge potential of the photoconductor rises on the developer sliding area due to the developing bias. , (Vs-Vh) becomes Vc or less, the developer adheres only to the exposed non-charged portions by exposure, and smooth reversal development is performed.

FIG. 3 shows the relationship between the developer resistance Rt and the charging potential Vh. The solid line represents the resistance of the photoconductor (bright resistance) when the image is exposed, and the broken line represents the resistance (dark resistance) when the image is not exposed, which are measures of ghost and fog, respectively. When these curves exceed the development start voltage Vc (hatched portion in the figure), ghost and fog mainly occur in the former case and fog occurs in the latter case. Therefore, from FIG. 5, the resistance of the developer may be set so that the photosensitive member can be charged to at least the developable voltage Vc or higher.

On the other hand, since the dark resistance of the photoconductor is always equal to or higher than the light resistance, in other words, the resistance of the photoconductor does not become lower than the light resistance, so it can be set as the light resistance.
The term A in the above formula 3) is set under normal conditions, especially aS
In the case of the i photoconductor, it can be completely ignored. Therefore, by setting the developer resistance as described below, it is possible to prevent the occurrence of ghost and fog. Vh = Vs-Vc <Vs (Rh / Rt + Rh) ... 2 ') Rt <(Vc / Vs-Vc) Rh ... 1) can be derived by expanding the 2'formula.

FIG. 6 shows the electric field dependence of the developer resistance when a two-component developer is used in Examples described later,
(A) is the electric field dependence of the developer at the initial stage of development, (B)
Indicates the electric field dependence of the developer after printing a predetermined number of sheets (15,000 sheets), and shows that the resistance increases in a low electric field and that the developer resistance increases due to deterioration.
Therefore, even if the developer deteriorates due to repeated contact charging and stirring between the photoconductor and the toner rubbing region, it is necessary to carry out development within a range in which the developer resistance after the deterioration satisfies the expression 1). In this case, in the case of a two-component developer, since the toner is originally an insulator, it is considered that the cause of the high resistance due to the deterioration of the developer is the high resistance of the carrier.

Therefore, in the present invention, the developer is formed of a multi-component developer comprising a conductive magnetic carrier and a high-resistance or insulating magnetic toner. As shown in FIG. 7, the heat-melting conductive carrier 14 is formed by fixing the conductive fine particles 16 on the surface of the particles in which the magnetic material 15 is dispersed in the insulating resin 13, and the average of the carrier 14 is used. By setting the particle size within approximately 1 to 5 times the average particle size of the toner, the charge injection capacity of the photoconductor can be maintained sufficiently high.
When the carrier 14 becomes insulative due to its deterioration, the diameter ratio thereof is 1 to 5 times that of the toner. Therefore, the carrier 14 adheres to the latent image portion of the photosensitive drum together with the substantially insulative toner, and thus the rubbing area. Therefore, a fresh carrier is always supplied, and the above formula (1) can be maintained for a long period of time. In other words, a smooth image formation without fogging or ghost over a long period of time is possible. Is possible. Further, since the carrier is set as a resin carrier that can be melted by heat in the fixing step, it is treated in the same manner as the toner and does not affect the image quality at all. By setting the photoconductor to be an a-Si photoconductor, the item A can be completely ignored, and the object of the present invention can be achieved smoothly.

[0017]

Embodiments of the present invention will now be illustratively described in detail with reference to the drawings. However, the dimensions, materials, shapes, relative positions and the like of the components described in this embodiment are not intended to limit the scope of the present invention thereto, but are merely examples, unless otherwise specified. Not too much. Figure 2
1 is a schematic diagram showing a configuration of a printer according to an embodiment of the present invention. Reference numeral 1 denotes a photoconductor drum in which the LED unit 2 is inserted, and a developing sleeve 30 and a transfer roller 4 incorporated in the developing unit 3 are arranged along the rotation direction of the photoconductor drum 1 and the photoconductor drum 1 and the transfer roller. 4 from the upstream side along the tangential direction between the paper feed cassette 5, the paper detection sensor 6,
A fixing roller 8 is arranged with the registration roller 7 and the transfer roller 4 interposed therebetween.

Next, the construction of the photosensitive drum 1 and the developing unit 3 which are the essential parts of the present invention will be mainly described in detail with reference to FIGS. 2 and 1. Note that, in FIG. 1, the diameter of the photosensitive drum is set to be several steps larger than the diameter of the developing sleeve in order to facilitate the description, but in reality, the diameters of both are set to approximately 30 φ (mm) and the same diameter. . As shown in FIG. 1, the photoconductor drum 1 includes ITO (indium tin oxide) on the transparent support 1a made of glass or polyester from the inner surface side.
Translucent conductive layer 1 formed by active reaction vapor deposition method
b, a-Si (P ⁺ ) based injection blocking layer 1e, photoconductor layer 1
c and a-SiC surface layer 1f are formed by stacking, and the photoconductor layer 1c uses a photoconductor made of a-Si: H, and is non-doped or Va in order to enhance electron mobility. Contains a group element. And photoconductor layer 1
c has a thickness of 7.0 μm, a resistivity of 10 ⁸ Ω · cm (in the dark), 10 ¹¹ Ω · cm (bright), and the surface layer 1f has a thickness of 0.3 μm and a resistivity of 10 ¹² Ω.・ Cm (in the dark), 10
It is set to ¹² Ω · cm (middle). As a result, the photoconductor resistance Rh is 2.0 × 10 ⁶ Ω for bright resistance and 6.6 × for dark resistance.
It becomes 10 ⁶ Ω.

On the other hand, the LED inserted in the photosensitive drum 1
The unit 2 includes a head block 24 that integrally holds an LED chip row (not shown) arranged in one row along the drum axis direction and a converging lens array 23 (trade name: SELFOC lens). Formed and said LE
The exposure position of the D unit 2 is the closest contact point of the drum / sleeve, in other words, the photosensitive drum 1 and the developing sleeve 30.
The image is formed on the photoconductor layer 1c in the drum 1 by slightly deflecting it to the downstream side (about 4 °) in the rotation direction of the drum 1 from the center line connecting the axis centers of.

As the transfer roller 4, a medium resistance roller is used in order to increase transfer efficiency, a transfer bias having a polarity opposite to the charging potential of the toner is applied, and the photosensitive drum 1 is also used.
It is uniformly pressed against the peripheral surface and is rotatable in synchronization with the drum 1. The developing unit 3 includes a toner accommodating portion 32, a container body 31 accommodating a carrier and toner, and a developing sleeve 30 including a fixed magnet assembly 33 on the side of the container body 31 facing the photosensitive drum 1. The sleeve 30 has the same diameter as that of the photosensitive drum.
While being set to φ, it rotates in the clockwise direction opposite to the photosensitive drum 1, and preferably has a peripheral speed of 5 to 5 times the peripheral speed of the photosensitive drum.
The forward feed is possible at a rotation speed of about 10. The partition wall 3 is provided between the toner container 32 and the container body 31.
4, the supply roller 35 is arranged in the slit opening 34a provided in the center of the partition wall 34, and every time the carrier / toner mixture ratio (toner concentration) in the container body 31 is reduced based on the signal from the sensor 36. In addition, the replenishing roller 35 is rotated so that the proper mixing ratio is always maintained. A pair of mixers 37 are arranged in the container body 31 to maintain the carrier / toner compounding ratio in the container body 31 at a uniform concentration. Further, the container 31 on the upper surface side of the developing sleeve 30
A doctor blade 38 is attached to the outlet end,
The developer guided to the developing position can be regulated in a thin layer.

The fixed magnet assembly is set in a magnetic pole arrangement as shown in FIG. 2, and the main magnetic pole for forming the developer sliding area on the side facing the photosensitive drum 1 is the closest contact between the drum and the sleeve. It is arranged at a position displaced by about 2 ° on the upstream side of the drum rotation direction.

Next, the composition of the developer used in the developing unit 3 will be described with reference to FIG. FIG. 7 is a schematic view showing the structure of the carrier used in the present developer, and the magnetic material 1
Conductive fine particles 16 are fixed on the surface of carrier mother particles 13 in which 5 is uniformly dispersed in a binder resin to form a carrier 14.

The carrier 14 has an average particle diameter of 35 μm and a resistivity of 5 × 10 ² Ω · cm. In this case, the conductivity of the carrier 14 is mainly given by the conductive fine particles 16. In addition, the resistivity of the carrier 14 is as follows:
4 is 1.5 g, an electrode having an outer diameter of 20 mm is inserted, and a load of 1 kg is applied from above to measure. The magnetic force of the carrier 14 needs to be large to some extent or more, and the maximum magnetization in a magnetic field of 5 kOe (Oersted) is preferably 55 to 80 emu / g, and the maximum magnetization in a magnetic field of 1 kOe is 45 to 60 emu / g. Set to Settings.
If the magnetic force of the carrier 14 becomes too small, the developer carrying property deteriorates and the carrier 14 is developed together with the toner. The magnetic material used for the carrier 14 is, for example, magnetite (Fe ₃ O ₄ ), the conductive fine particles 16 are, for example, carbon black, and the binder resin used for the carrier mother particles 13 is a vinyl resin represented by polystyrene resin. Or polyester resin is used.

The conductive fine particles 16 are fixed to the surface of the carrier mother particles 13 by, for example, uniformly mixing the carrier mother particles 13 and the conductive fine particles 16 to form the carrier mother particles 13.
After attaching the conductive fine particles 16 to the surface of the carrier, a mechanical / thermal impact force is applied to the conductive fine particles 16 to form carrier mother particles 1.
It is carried out by fixing it so that it is driven in. The conductive fine particles 16 are not completely embedded in the carrier mother particle 13, but a part thereof is not embedded in the carrier mother particle 1.
It is fixed so that it projects from 3.

On the other hand, the toner is manufactured in the same manner as the conventionally known insulating toner. For example, a binder resin contains a coloring agent,
It is formed as a magnetic toner by adding a charge control agent, an offset preventing agent, and a magnetic substance, and the magnetic toner is set to have an average particle size of 7 μm and a resistivity of 10 ¹⁵ Ω · cm. The above carrier and toner are mixed in a predetermined ratio to set a developer having a photoreceptor resistance value described later.

In the present embodiment, for example, the photosensitive drum 1 is set to a rotational speed of 25 rpm, while the developing sleeve is set to a rotational speed of 200 rpm. Is 0.5 mm, and the magnetic pole position of the fixed magnet assembly 33 is 2 to 4 ° from the closest position between the drum and the sleeve as described above.
Swing to the upstream side of the photosensitive drum, and set the magnetic pole strength to 800 gauss. The LED head 2 has an exposure energy of 0.35 μJ / cm which is incident on the photosensitive drum 1.
^The drive current is set so as to be ² or more, and the time division drive is performed so that the light emission time is 5 to 50 μs.

Under such conditions, the conductive magnetic capacitor is
Carrier and the compounding ratio (weight ratio) of the rear and the insulating magnetic toner
/ Toner: Set to 85% / 15%, initial resistance of developer
Rt ₁= 1 x 10^FourΩ (resistivity ρ = 3 × 10⁶Ω / cm)
And a + 50V DC voltage is marked as the development bias Vs.
After printing 15,000 sheets, from the beginning of development
An image with an image density ID of 1.3 or more was obtained until the final printing.
In addition, no ghost or fogging was observed.

The resistance value of the developer after printing 15,000 sheets is Rt ₂ = 2 × 10 ⁵ Ω (resistivity ρ = 6 × 10 ⁷ Ω.
cm), and the developable voltage at this time is Vc = 8v
Therefore, the LED head 2 is slightly moved from the center line connecting the photosensitive drum 1 and the developing sleeve 30 to the drum 1 slightly.
Set on the downstream side (about 4 °) in the rotation direction. Next, in order to verify the effect of the present invention, Vc: 8v, V
Substituting s: 50, Rh (bright resistance): 2.0 × 10 ⁶ Ω, Vc / (Vs−Vc) Rh = {8 / (50−8)} 2.0 × 10 ⁶ Ω = 3.8 × It becomes 10 ⁵ Ω (limit value). The initial resistance Rt ₁ (1 × 10 ⁴ Ω) of the developer is also 1500
The resistance value Rt ₂ (2 × 10 ⁵ Ω) of the developer after printing 0 sheets is less than the above-mentioned limit value, which satisfies the present invention.

In order to further verify the effect of the present invention, the carrier / toner compounding ratio is changed and the initial resistance of the developer is set to Rt ₁ = 1 × 10 ⁵ Ω, and the other conditions are the same as above. When 15,000 sheets were printed below, an image with an image density ID of 1.3 or more was obtained in the early stage of development, and no ghost or fog was observed, but ghost or fog was observed from around several thousand sheets. Has occurred. Therefore, the above 15
After confirming the resistance value Rt ₂ of the developer after printing 000 sheets, 1
It was × 10 ⁶ Ω. Therefore, in this comparative example, the above expression 1) is satisfied at the initial stage of development, and the resistance value Rt ₂ of the developer after printing is satisfied.
Is understood to not satisfy the above formula 1), and the effect of the present invention was confirmed.

[0030]

As described above, according to the present invention, the developer resistance is set in the relationship between the developing bias voltage and the developable voltage voltage, in other words, the developer resistance is set corresponding to the developing electric field strength. Therefore, even when the developer deteriorates due to repeated contact charging and stirring, a clear image can be smoothly formed without causing a ghost phenomenon or fog. Since the developer resistance is set in correspondence with the light resistance of the photoconductor, it is smooth even when a-Si or other photoconductor having a lower resistance than the conventional OPC or other organic semiconductor is used. In addition, the above effect can be achieved.
It has various remarkable effects.

[Brief description of drawings]

FIG. 1 is a basic configuration diagram of a backside exposure developing device of the present invention.

FIG. 2 is a configuration diagram of a main part of an image forming apparatus to which the present invention is applied.

FIG. 3 is a graph showing the relationship between developer resistance Rt and charging potential Vh.

FIG. 4 is an equivalent circuit showing a relationship between a developing bias voltage Vs and a charging potential Vh.

FIG. 5 (Development bias voltage Vs-photoconductor charge potential V)
Development γ characteristic diagram showing the relationship between h) and development density ID

FIG. 6 shows the electric field dependence of the developer resistance when a two-component developer is used in this example, (A) is the electric field dependence of the developer at the initial stage of development, and (B) is the one after printing a predetermined number of sheets. The electric field dependence of the developer is shown.

FIG. 7 is a schematic diagram showing the structure of a carrier used for the developer of this embodiment.

[Explanation of symbols]

 1 Photoconductor 30 Development Sleeve 2 LED Unit 10 Developer Sliding Area

Claims (3)

[Claims] 1. A developer rubbing region is formed at a position where a photoconductor and a developer carrying member face each other, and a photoconductor is contacted through the developer rubbing region by a developing bias applied to the developer carrying member. In the backside exposure developing method, which exposes a predetermined position of the photoconductor on which the developer sliding area is formed from the backside of the photoconductor while being charged, and performs development almost simultaneously with the exposure, It is characterized in that development is carried out in such a range that the resistance always satisfies the following expression 1). Rt <(Vc / Vs-Vc) Rh Rt: Developer resistance (developer resistance when a voltage of developable voltage Vc is applied) Vs: Development bias (voltage) Vc applied to developer carrier Vc: Developable Voltage (refers to the potential of (development bias-photoreceptor charge potential) when reversal development is started.) Rh: Bright resistance of photoreceptor 2. The back exposure development method according to claim 1, wherein the developer is formed of a multi-component developer composed of a conductive magnetic carrier and a high-resistance or insulating magnetic toner. It is formed of a heat-melting conductive carrier formed by fixing conductive fine particles on the surface of particles in which a magnetic material is dispersed, and the average particle size of the carrier is about 1 to 5 times the average particle size of the toner. Back exposure development method set within 3. The back exposure development method according to claim 1, wherein the photoconductor is an a-Si photoconductor.