JP2895681B2 - Back exposure development method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a back exposure developing method applied to a printer, a facsimile, a copying machine, and the like, and more particularly, to a method of exposing a photosensitive member while exposing the photosensitive member by an exposing means provided on the back side of the photosensitive member. And a back exposure development method for performing development almost simultaneously.

[0002]

2. Description of the Related Art Conventionally, an exposure means for generating a light output corresponding to image information is provided in a photosensitive drum comprising a light transmitting conductive layer and a photoconductive layer laminated on a light transmitting support, for example. When the latent image is focused on the photoconductor layer by interpolating and converging the light output of the exposing means to form the latent image on the photoconductor layer, the latent image can be formed via a toner carrier facing the photosensitive drum at the same time or immediately thereafter. 2. Description of the Related Art An image forming apparatus in which a visible image (toner image) can be transferred to plain paper via a transfer roller or other transfer means after a toner image is formed is known. (JP-A-58-153957, etc.)

In this type of image forming apparatus, in order to further simplify the structure and prevent ozone generation and the like, and to prevent ground fogging, the image forming apparatus faces the photosensitive drum without providing an independent charger. The conductive magnetic toner is carried on the developing sleeve arranged in the manner described above, and a so-called magnetic brush-like toner rubbing area is provided immediately before the developing position by using a fixed magnet assembly or other magnetic force included in the sleeve. While the surface of the photosensitive drum was rubbed by the rubbing area, a charge was injected by injecting electric charge into the photosensitive layer of the drum through the rubbing area using a developing bias applied to the developing sleeve side. Then, immediately after the charging, an exposure image is formed by using an exposure unit included in the drum, and development is performed to form a predetermined image.

Therefore, it is premised that the toner used in the above-mentioned apparatus is a conductive toner in order to inject electric charge from the developing sleeve side. However, when the conductive toner is used, the transfer efficiency at the time of transferring a toner image to paper is increased. Is a problem.
In order to prevent such a defect, it is preferable to use an insulating toner without using a conductive toner as the developer. However, when an insulating toner is used, a charging step of charge injection from a developing bias cannot be performed, and only frictional charging is performed. As a result, smooth charging becomes difficult.

Therefore, in order to prevent the above-mentioned drawbacks, Japanese Patent Application Laid-Open
As shown in Japanese Patent No. 214781, the toner resistivity is 10 ⁴
A conductive magnetic toner of 〜１０10 ⁹ Ω · cm and a frictionally charged high-resistance toner having a toner resistivity of 10 ¹⁴ Ω · cm or more and charged to the number of poles determined by friction charging are mixed. A technique in which the resistance value is set to 10 ⁵ to 10 ¹⁰ Ω · cm is proposed.

[0006]

However, as described above, the conductive toner has a resistance value of 10 ⁴ to 10 ⁹ Ω · cm, which is in a semiconductive region, or 10 ⁵ to 10 ¹⁰ even in a mixed toner.
It is a semiconductive region of Ω · cm. The material of such a semiconductive region generally has a different resistance value depending on the electric field intensity, and in a low electric field, the resistance value increases exponentially. Therefore, for example, 10
Even if a developer having a semiconductive area of ⁵ to 10 ¹⁰ Ω · cm is prepared, if the photosensitive member charging potential is charged to near the applied voltage for development, the resistance of the developer existing in the developing space increases. Therefore, smooth charge injection to the photoconductor side, that is, charging is not performed. Therefore, if development is performed using the toner in the semiconductor region as described above singly or in a mixture, it is not possible to provide enough charge to erase the previous image at the time of recharging. A ghost phenomenon caused by the (leading latent image) and defects such as fogging caused by insufficient recharging of the photoconductor become apparent.

[0007] The disadvantage caused by the rapid increase in developer resistance in such a low electric field region is that a-Si having a lower resistance than conventional OPC and other organic semiconductors.
It becomes more noticeable when other photoconductors are used,
In particular, the photoreceptor using a-Si has a relatively low resistance value as compared with the developer in the semiconductive region, so that poor charging is further amplified and fogging and ghosting are more likely to occur.

In view of the drawbacks of the prior art, the present invention eliminates the ghost phenomenon, fogging, and the like that occur due to the rapid increase in developer resistance in a low electric field region.
It is an object of the present invention to provide a back-surface exposure and development method that enables a clear image to be formed even on a photoreceptor using the same.

[0009]

According to the present invention, in order to solve the above-mentioned disadvantage, the developer resistance at the time of development is always equal to or less than the resistance value determined by the following formula (1) without independently determining the developer resistance. In other words, even when the developer is deteriorated due to repeated contact charging of the photosensitive member and the toner rubbing area or repeated stirring of the developer, the developer resistance after the deterioration is 1)
It is characterized in that development is performed within a range satisfying the expression. Rt <(Vc / Vs−Vc) Rh 1) Rt: developer resistance (developer resistance when voltage of developable voltage Vc is applied) Vs: developing bias (voltage) applied to developer carrier Vc : Developable voltage (refers to the potential of (developing bias-photoconductor charging potential) when reversal development is started) Rh: light resistance of photoconductor

[0010]

The operation of the present invention will be described in detail. As shown in FIG. 1, the basic operation of the back exposure developing method is as follows: a light-transmitting conductive layer 1b, an injection blocking layer 1e, and a photosensitive layer composed of a photoconductive layer 1c and a surface layer 1f on a light-transmitting support 1a. On the developing sleeve 30 disposed opposite to the photosensitive drum 1 on which the layers 1c / 1f are formed, for example, a developer comprising a high-resistance or insulating magnetic toner and a conductive magnetic carrier is carried. , 30 are rotated with a relative speed difference in the direction of the arrow, so that a so-called magnetic brush-like developer rubbing area 10 is interposed between the developing gaps by utilizing the magnetic force of the fixed magnet assembly 33 contained in the sleeve 31. Form. In the developer rubbing area 10, the toner is once transferred and adhered to the photosensitive drum 1 by application of the developing bias Vs applied to the developing sleeve 30, and the developer magnetic brush brushes the surface of the photosensitive drum 1. Photoconductor drum 1
When the charged potential approaches the potential of the developing bias, the developer is pulled back to the developing sleeve 30 by the magnetic force of the fixed magnet assembly 33. At this time, the charged potential is attenuated to about 0 V by forming an exposure image using the exposure means 2 included in the drum 1 immediately after the charging, and the toner is generated by a potential difference between the developing bias Vs and the photosensitive drum. Is performed, and a predetermined image can be formed.

The relationship between the developing bias voltage Vs and the charging potential Vh in the rubbing region can be represented by an equivalent circuit shown in FIG. Here, Rh is the photoconductor resistance, Ch is the photoconductor capacity,
Rt is the developer resistance, and Ct is the developer capacity. Rt and Ct indicate the total resistance and capacity of the developer obtained by mixing the toner and the carrier at a predetermined compounding ratio. Therefore, when the relationship between the developing bias voltage Vs and the charging potential Vh is expressed by an equation from the equivalent circuit, 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. In the formula 3), the resistance of the developer and the photoreceptor is calculated.
Unless Rt and Rh and the capacities Ct and 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 .gamma. Characteristic showing a relationship between (developing bias voltage Vs-photoconductor charging potential Vh) and developing density. The charging potential of the photoconductor rises on the developer rubbing area by the developing bias. , (Vs-Vh) become equal to or less than Vc, the developer adheres only to the non-charged portion exposed, and smooth reversal development is performed.

FIG. 3 shows the relationship between the developer resistance Rt and the charging potential Vh. The solid line indicates the resistance of the photosensitive member (bright resistance) when the image is exposed, and the broken line indicates the resistance (dark resistance) when the exposure is not performed. When these curves exceed the development start voltage Vc (the hatched portion in the figure), ghosts and fogging mainly occur in the former, and fogging occurs in the latter. Therefore, as shown in 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.

On the other hand, the dark resistance of the photoreceptor is always equal to or higher than the light resistance. In other words, since the resistance of the photoreceptor does not become lower than the light resistance, it can be set as the light resistance.
Further, the term A in the above formula 3) can be obtained under a normal condition, especially a-S
In the case of the i photoreceptor, it can be completely neglected. Therefore, by setting the developer resistance as described below, ghost and fogging can be prevented. Vh = Vs−Vc <Vs (Rh / Rt + Rh) 2 ′) By expanding the equation 2 ′, Rt <(Vc / Vs−Vc) Rh 1) can be derived.

FIG. 6 shows, for example, the electric field dependency of the developer resistance when a two-component developer is used in the embodiment described later.
(A) is the electric field dependence of the developer in the early stage of development, (B)
Indicates the electric field dependence of the developer after printing a predetermined number of sheets (15,000 sheets), which indicates that the resistance increases at a low electric field and that the developer resistance increases due to deterioration.
Therefore, even when the developer is deteriorated due to repeated contact charging or agitation of the photosensitive member and the toner rubbing area, it is necessary to perform development within a range where the deteriorated developer resistance satisfies the expression (1). In this case, in the case of the two-component developer, since the toner is originally an insulator, it is considered that the cause of the increase in the resistance due to the deterioration of the developer is the increase in the resistance of the carrier.

According to the present invention, in the back exposure developing method according to the present invention, the developer is formed of a plurality of components consisting of a conductive magnetic carrier and a high-resistance or insulating magnetic toner. As shown in FIG. 7, a conductive material 14 is formed by fixing conductive fine particles 16 to the surface of particles in which a magnetic material 15 is dispersed in an insulating resin 13. By setting the particle size within approximately 1 to 5 times the average particle size of the toner, the charge injection ability of the photoreceptor is maintained sufficiently high,
When the carrier 14 becomes insulative due to deterioration, the diameter ratio is 1 to 5 times that of the toner. , The fresh carrier is always supplied, and the above-mentioned formula (1) can be maintained for a long period of time. In other words, the image can be formed smoothly without fogging or ghosting for a long period of time. Becomes possible. Since the carrier is set as a resin carrier which 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 an a-Si photoconductor, the above-mentioned item A can be completely ignored, and the object of the present invention can be achieved smoothly.

[0017]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of the present invention; However, unless otherwise specified, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention, but are merely illustrative examples. Not just. FIG.
1 is a schematic diagram illustrating a configuration of a printer according to an embodiment of the present invention. Reference numeral 1 denotes a photosensitive drum in which an LED unit 2 is inserted. A developing sleeve 30 and a transfer roller 4 incorporated in a developing unit 3 are arranged along the rotation direction of the photosensitive drum. 4, a paper feed cassette 5, a paper detection sensor 6,
A fixing roller 8 is provided with the registration roller 7 and the transfer roller 4 interposed therebetween.

Next, the configuration of the photosensitive drum 1 and the developing unit 3 which are main parts of the present invention will be described in detail with reference to FIGS. In FIG. 1, the diameter of the photosensitive drum is set to be several steps larger than the diameter of the developing sleeve for the sake of simplicity of explanation, but the diameters of both are actually set to approximately 30φ (mm). . As shown in FIG. 1, the photosensitive drum 1 is made of ITO (indium tin oxide) on a transparent support 1a made of glass or polyester from the inner side.
Light-transmitting conductive layer 1 formed by active reaction deposition
b, a-Si (P ⁺ ) -based injection blocking layer 1e, photoconductor layer 1
c and a-SiC surface layer 1f are laminated and formed, and photoconductor layer 1c is made of a photoconductor made of a-Si: H, and is non-doped or Va in order to increase electron mobility. Group element is contained. And the photoconductor layer 1
c has a thickness of 7.0 μm, a resistivity of 10 ⁸ Ω · cm (in the dark) and 10 ¹¹ Ω · cm (in the light), 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 (in the middle). As a result, the photoconductor resistance Rh has a light resistance of 2.0 × 10 ⁶ Ω and a dark resistance of 6.6 ×
10 ⁶ Ω.

On the other hand, an LED inserted in the photosensitive drum 1
The unit 2 includes a head block 24 integrally holding an unillustrated LED chip row and a converging lens array 23 (product name: Selfoc lens) arranged in a row along the drum axis direction. Formed and said LE
The D unit 2 has its exposure position closest to the drum / sleeve, in other words, the photosensitive drum 1 and the developing sleeve 30.
Is deflected slightly to the downstream side (about 4 °) in the rotation direction of the drum 1 from the center line connecting the axes of the optical axis, and forms an image on the photoconductor layer 1 c in the drum 1.

The transfer roller 4 uses a medium resistance roller to increase the transfer efficiency, applies a transfer bias having a polarity opposite to the charging potential of the toner and applies a transfer bias to the photosensitive drum 1.
It is configured to be uniformly pressed against the peripheral surface and to be rotatable in synchronization with the drum 1. The developing unit 3 includes a toner container 32, a container body 31 containing a carrier and toner, and a developing sleeve 30 containing a fixed magnet assembly 33 is provided on the side of the container body 31 facing the photosensitive drum 1. The diameter of the sleeve 30 is set to 30 in the same manner as the photosensitive drum.
Rotating clockwise in the opposite direction to the photoreceptor drum 1 while setting to φ, preferably the peripheral speed of the photoreceptor drum 5 to 5
It is configured to be able to forward feed at a rotation speed of about 10. A partition wall 3 is provided between the toner container 32 and the container body 31.
4, a supply roller 35 is disposed in a slit opening 34a provided in the center of the partition wall 34, and the carrier / toner mixture ratio (toner density) in the container main body 31 decreases based on a signal from the sensor 36. The replenishing roller 35 rotates so as to always maintain an appropriate blending ratio. A pair of mixers 37 are provided in the container body 31 to maintain the carrier / toner mixture ratio in the container body 31 at a uniform concentration. 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 restricted to a thin layer.

The fixed magnet assembly is set in a magnetic pole arrangement as shown in FIG. 2. In particular, the main magnetic pole for forming a developer rubbing area on the side facing the photosensitive drum 1 is closest to the drum / sleeve. It is disposed at a position displaced by about 2 ° on the upstream side in the drum rotation direction from the position.

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 a carrier used in the present developer.
The conductive fine particles 16 are fixed on the surface of carrier base particles 13 in which the particles 5 are uniformly dispersed in a binder resin to form a carrier 14.

The carrier 14 has an average particle size 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. The resistivity of the carrier 14 is determined by measuring the carrier 1 in a Teflon cylinder having an inner diameter of 20 mm and an electrode at the bottom.
4 is 1.5 g, an electrode having an outer diameter of 20 mm is inserted, and a value of 1 kg is applied from above and measured. The magnetic force of the carrier 14 needs to be larger than a certain level. Preferably, the maximum magnetization in a magnetic field of 5 kOe (Oersted) is 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 transportability of the developer 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 base particles 13 is a vinyl resin represented by a polystyrene resin. Or a polyester resin.

The conductive fine particles 16 can be fixed to the surface of the carrier base particles 13 by, for example, uniformly mixing the carrier base particles 13 and the conductive fine particles 16,
After the conductive fine particles 16 are adhered to the surface of the base material, a mechanical / thermal impact force is applied to the conductive fine particles 16 so that the carrier base particles 1
3 to be fixed. The conductive fine particles 16 are not completely embedded in the carrier base particles 13, and a part thereof is
3 so as to stick out.

On the other hand, the toner is manufactured in the same manner as a conventionally known insulating toner. For example, a colorant,
The magnetic toner is formed by adding a charge control agent, an anti-offset agent, and a magnetic material, and the magnetic toner has an average particle diameter of 7 μm and a resistivity of 10 ¹⁵ Ω · cm. The above-mentioned carrier and toner are mixed at a predetermined ratio to set a developer having a photoconductor resistance value described later.

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

Under such conditions, the conductive magnetic capacitor
The mixing ratio (weight ratio) of rear and insulating magnetic toner
/ Toner: 85% / 15%, initial resistance of developer
Rt ₁= 1 × 10^FourΩ (resistivity ρ = 3 × 10⁶Ω ・ cm)
And a DC voltage of +50 V is marked as a developing bias Vs.
After printing 15,000 sheets, from the beginning of development
Image density ID: 1.3 or more images are obtained until final printing
And no ghosting or fogging was observed.

Then, the resistance value Rt ₂ 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 = 8 V
Therefore, the LED head 2 is moved slightly from the center line connecting the photosensitive drum 1 and the axis of the developing sleeve 30 to the drum 1.
Set to 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
Each of the resistance values Rt ₂ (2 × 10 ⁵ Ω) of the developer after printing 0 sheets is below the above-mentioned limit value, which satisfies the present invention.

Further, in order to verify the effect of the present invention, the initial resistance Rt ₁ of the developer was set to 1 × 10 ⁵ Ω by changing the mixing ratio of the carrier / toner, and the other conditions were the same as those described above. When 15,000 sheets were printed below, an image having an image density ID of 1.3 or more was obtained in the early stage of development, and no ghost or fogging was observed. Has occurred. Therefore, the 15
When the resistance value Rt ₂ of the developer after printing 000 sheets was confirmed, 1
× 10 ⁶ Ω. Therefore, in this comparative example, the expression (1) is satisfied at the beginning of development, and the resistance value Rt ₂ of the developer after printing is satisfied.
Was not satisfied with the expression 1), and the effect of the present invention was confirmed.

[0030]

As described above, according to the present invention, since 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 according to the developing electric field strength. As a result, even when the developer is deteriorated due to the repetition of contact charging and stirring, a clear image can be formed smoothly without causing a ghost phenomenon or fogging. Further, since the developer resistance is set in correspondence with the light resistance of the photoreceptor, even when a-Si or other photoreceptor having lower resistance than conventional OPC or other organic semiconductors is used, the developer resistance is smooth. The above action can be achieved.
And so on.

[Brief description of the drawings]

FIG. 1 is a basic configuration diagram of a back exposure developing apparatus 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 a relationship between a developer resistance Rt and a 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 shows a relationship between (development bias voltage Vs—photoconductor charging potential V).
h) and development gamma characteristic diagram showing the relationship between the development density ID

FIGS. 6A and 6B show the electric field dependence of the developer resistance when a two-component developer is used in this embodiment, wherein FIG. 6A shows the electric field dependence of the developer in the initial stage of development and FIG. 4 shows the electric field dependence of the developer.

FIG. 7 is a schematic view illustrating a configuration of a carrier used for a developer according to the present exemplary embodiment.

[Explanation of symbols]

 Reference Signs List 1 photoconductor 30 developing sleeve 2 LED unit 10 developer rubbing area

Claims (3)

(57) [Claims] An image forming apparatus according to claim 1, wherein a developer rubbing area is formed at a position facing the photoconductor and the developer carrier, and the photoconductor is contacted via the developer rubbing area by a developing bias applied to the developer carrier. A back exposure developing method in which, while being charged, a predetermined position of the photoconductor on which the developer rubbing area is formed is exposed from the rear side of the photoconductor, and development is performed almost simultaneously with the exposure. The development is performed so that the resistance always satisfies the following expression (1). Rt <(Vc / Vs−Vc) Rh Rt: developer resistance (developer resistance when voltage of developable voltage Vc is applied) Vs: developing bias (voltage) applied to developer carrier Vc: developable Voltage (refers to the potential of (development bias-photoconductor charging potential) when reversal development is started) Rh: light resistance of photoconductor 2. The back exposure developing method according to claim 1, wherein said developer is formed of a multi-component developer comprising a conductive magnetic carrier and a high-resistance or insulating magnetic toner. The conductive particles are formed of a heat-fusible conductive carrier formed by fixing conductive fine particles on the surfaces of particles in which a magnetic material is dispersed, and the average particle size of the carrier is approximately 1 to 5 times the average particle size of the toner. Back exposure development method set within 3. The method according to claim 1, wherein the photoconductor is an a-Si photoconductor.