JP3146272B2 - Image forming method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming method used for a laser beam printer, a copying machine and the like.

[0002]

2. Description of the Related Art F. Since the invention of electrophotography by Carlson (U.S. Pat. No. 2,297,691),
Various improvements and developments have been made based on this method. An electrophotographic method represented by the Carlson method is widely used at present, and its basic process is to uniformly charge a photosensitive member, form a latent image by selective exposure, form a toner image with a developer, transfer and fix. In a conventional electrophotographic apparatus, a corona charging method, a roller charging method, and a brush charging method are mainly adopted as a charging method, and a photoconductor is charged to a charging potential of ± 400 to ± 800 volts to perform image exposure. The subsequent potential was ± 10 to ± 200 volts.

A particle charging method using conductive particles in contact with a photoreceptor is also known. The particle charging method is a method of forming a magnetic brush with magnetic particles and injecting electric charges through the magnetic particles, using magnetic particles of about 10 ³ to 10 ⁷ Ω · cm, and using a high bias of 1 KV or more. The photosensitive member was charged by applying a voltage. For example,
In JP-A-61-57958, a charging bias voltage of 2000 V is applied to magnetic particles of 10 ⁶ Ω · cm. In Japanese Patent Application Laid-Open No. 59-133569, a magnetic particle having a conductivity of 10 ^-7 V / cm is used to reduce
It is stated that a surface potential of 500 V can be obtained by applying a voltage of 0 V. However, in terms of charging the photoreceptor to a high potential, the conventional particle charging method is no different from the other charging methods described above.

[0004] As a developing method, one component or two components is used.
Components include a magnetic brush developer, a jumping development method, and a contact development method using a conductive elastic roller. A development bias voltage Vb of about ± 300 to ± 600 volts is applied, and an AC voltage is superimposed depending on the method.

[0005] However, the above image forming method includes
There are various disadvantages as described below, and further improvements have been made. (1) In the corona discharge method, there is a problem of generation of ozone, and the life of the charger was about 10,000 to 20,000 sheets. Further, in the a-Si type photoreceptor, a reaction deposit is generated on the surface of the photosensitive layer by corona discharge, which causes image deletion. (2) Even in the roller charging method and the brush charging method, ozone and corona products were not generated at all, and the life of those charging members was about 10,000 to 50,000 sheets or less. (3) Since the charging potential is high, the layer thickness of the photosensitive layer (hereinafter, also referred to as the photoconductor film thickness) needs to be increased.
An organic photoconductor (OPC) required 15 to 30 μm, and an a-Si photoconductor required 30 to 50 μm. (4) A photoreceptor with a small thickness cannot be used because of dielectric breakdown, and a photoreceptor with a small thickness has a large capacitance.
The corona charging method or the like having no sufficient charging ability is disadvantageous because the charging ability is reduced. (5) Since the a-Si photoreceptor forms a photosensitive layer by a plasma glow method or the like, the deposition rate of the photosensitive layer is low, and an increase in the thickness of the photoreceptor directly leads to an increase in cost. (6) The life of the OPC-based photoreceptor is shortened because the thickness of the photoreceptor decreases due to repeated use. Further, since the capacitance of the photosensitive layer increases as the film thickness decreases, the photoconductor cannot be charged to a set value within a predetermined time unless the charging current is increased according to the film thickness variation. For this reason, it is necessary to provide auxiliary means such as a correction circuit and a printed sheet counter to control the charging current according to the film thickness variation.

[0006]

SUMMARY OF THE INVENTION The present invention enables efficient use of low-pressure-pressure photoconductors and high-capacitance photoconductors, which have been difficult to use in the past, and stably displays images over a long period of time. It is an object of the present invention to provide an image forming method which can be formed, and which is safe, can be processed at high speed, and can be manufactured at low cost.

[0007]

According to the present invention, there is provided an image forming method comprising: a particulate charging agent comprising an aggregate of particles containing conductive particles;
By applying a charging bias voltage via
Latent to form a charging step of uniformly charging the optical material, an electrostatic latent image formed more as selective by light irradiation brought selectively lower the charge potential of the photoconductor low potential portions and high potential portions on the photoconductor An image forming step, by bringing a photosensitive member on which an electrostatic latent image is formed and a developer containing toner into contact with each other, and applying a developing bias voltage to the contact portion while selectively applying toner to the electrostatic latent image; In the image forming method for performing each step of a developing step of forming a toner image by attaching the particles , the particulate charging agent may be used in an amount of 10 ¹ to 10 ⁵
Ωcm low resistance magnetic particles and 10 ⁵ to 10 ¹⁵ Ωcm high resistance
By mixing the resistive magnetic particles, the total resistance value is 10 ² to 10 ⁸
The photoreceptor is charged to 400 volts or less (absolute value) using a particulate charging agent of Ωcm .

In consideration of the fact that the photosensitive layer of the photosensitive member is worn due to repeated use and the thickness of the photosensitive layer is reduced, the minimum usable layer thickness of the photosensitive layer is set in advance. Also, the resistance of the particulate charging agent is adjusted so that the charging current required to charge the photosensitive layer to a predetermined charging potential within the charging process time in the charging step flows into the photosensitive layer via the particulate charging agent. Set. Further, in the developing step, the developing bias voltage Vb and the low potential portion Vl of the electrostatic latent image are used.
Absolute value of the difference between | Vb-Vl | so becomes <br/> and 50 to 300 volts, it is possible to form a good image by applying a developing bias voltage to the photoreceptor.

[0009]

FIG. 1 is an explanatory view showing an embodiment of the image forming method of the present invention. Photosensitive layer 1 on conductive support 13
The charging unit 21 and the exposure unit (the LED exposure optical system 4)
1) A developing unit 51, a transfer unit 71, and a fixing unit 81 are provided. The photoconductor 11 may be a belt-shaped (sheet-shaped). As the photoconductor 11, an a-Si photoconductor, an OPC photoconductor (organic photoconductor), a Se photoconductor, or the like can be appropriately used. The photoconductor 11 rotates in the P direction, and is first charged in the dark by the charging unit 21.

The charging unit 21 includes a magnetic brush roller 23 (magnetic member) including a mag roller 25 and a conductive charging sleeve 27, a magnetic granular charging agent 29, and a charging bias power supply 31. Granular charging agent 2
9 is a charging bias power supply 31 via a charging sleeve 27.
Voltage is applied from the photoconductor 11 and contacts the photoconductor 11
The magnetic brush roller 23 is magnetically coupled to the magnetic brush roller 23 to form a so-called magnetic brush, and contacts with the photoreceptor 11 as the magnetic brush roller 23 rotates (in the M direction). While rotating. In addition, even if the magnetic brush roller 23 is not rotated, uniform charging is possible, and the granular charging agent can be stirred and moved only by rotating the photoconductor 11. The photoreceptor 11 whose surface is uniformly charged is then subjected to image exposure by the LED exposure optical system 41. By the image exposure, the surface potential of the exposed portion is selectively reduced, and an electrostatic latent image composed of a low potential portion and a high potential portion is formed.

In the embodiment shown in FIG. 1, the potential of a portion corresponding to a future image portion is reduced by the LED exposure optical system 41 in consideration of use as a printer. The LED exposure optical system 41 is a combination of an LED array in which LED chips are linearly arranged by the number of recording pixels and an imaging optical system such as a selfoc lens, but a rotating mirror is used instead of the LED exposure optical system. And a laser exposure optical system using an f-θ lens, or a copying optical system that irradiates reflected light from an original document when applied to a copying machine. Alternatively, the rear image may be exposed from the inside of the photoconductor 11.

The photosensitive member 11 on which the electrostatic latent image has been formed is developed by the developing unit 51. The developing unit 51 supplies the developer 91 to the surface of the photoconductor 11 by the developing roller 53 rotating in the S direction. A developing bias power source 59 for applying a developing bias voltage between the photoconductor 11 and the developing roller 53 is connected to the conductive developing sleeve 57 of the developing roller 53. The developing roller 53 includes a mag roller 55 having several magnetic poles (N and S poles) in a conductive developing sleeve 57.

At the time of development, a bias voltage is applied from a developing bias power source 59 to develop the developing roller 53 and the photosensitive member 1.
1, a developing bias electric field is generated. By the development, the toner 93 in the developer 91 selectively adheres to the electrostatic latent image on the photoconductor, and an image composed of the toner is formed on the photoconductor 11. The toner 93 is transferred to the transfer unit 7
At 3, the image is transferred onto the paper 95 by the transfer roller 73 to which a negative bias voltage is applied by the transfer bias power supply 75. Reference numeral 69 denotes a registration roller that sends out the paper 95.

Next, the transfer toner is supplied to the fixing unit 81.
Is fixed on the paper 95 by the fixing roller 83 (heating roller). Reference numeral 85 denotes a pressure roller. The residual toner remaining on the photoconductor 11 without being transferred at the time of transfer is removed by the cleaning blade 99. In the above description, the case where the photoconductor 11 is positively charged and an image is formed by reversal development using a two-component developer has been described. However, other developers such as a one-component developer, and other developments such as a regular development method Processes can also be applied.

In the present invention, electric charges are injected into the photosensitive layer 15 of the photosensitive member 11 via the particulate charging agent 29, which is an aggregate of charged particles (charge current is caused to flow), and the photosensitive layer 15 is exposed to light in the dark.
It is charged to a predetermined charging potential of less than 400 volts, preferably ± 250 volts or less, more preferably ± 30 to 250 volts. The photoreceptor can be stably and uniformly charged to a low potential by the particle charging method, and a reduction in image density due to uneven charging potential can be prevented, and the range in which latitude can be obtained can be widened.

Also, since the method is a particle charging method with a low charging potential, no harmful substances such as ozone and corona products are generated, it is safe for humans and photoconductors, and the charging bias power source is low. A voltage power supply is sufficient, there is no danger and the cost can be reduced. Further, according to the low charging potential and low electric field development process of the photoreceptor by the particle charging method according to the present invention, a low withstand voltage photoreceptor having a low dielectric breakdown potential (for example, a photosensitive layer having a thickness of 10 μm).
It is possible to form a stable image using an OPC-based photoreceptor having a thickness of about m or less, an a-Si-based photoreceptor having the same thickness, or a high-capacitance photoreceptor (for example, the above two examples). Become.

FIG. 2 is a graph showing an example of the relationship between the thickness of the photosensitive layer and its dielectric breakdown. The charge potential used in the conventional process is 500 to 1000 volts. For example, in the case of 900 volts, a photosensitive layer having a thickness of 10 μm causes dielectric breakdown, so that a photosensitive layer having a thickness smaller than this cannot be used. Even if the thickness of the photoconductor is 20 μm, the life of the photoconductor, such as the OPC photoconductor, whose layer thickness is reduced due to repeated use, is exhausted when the photoconductor is worn down to 10 μm.

On the other hand, in the process of the present invention using a charging potential of 400 volts or less, even a photosensitive layer of 5 μm or less can be sufficiently used without causing dielectric breakdown. Next, the relationship between the photosensitive layer thickness and the capacitance will be described. Since the photosensitive layer repeatedly charges and discharges like a capacitor, when the thickness d of the photosensitive layer decreases, the capacitance Cp increases in inverse proportion to the following equation (1).

[0019]

## EQU1 ## Cp = εo ・ εr ・ A / d Qp = Cp∝Vo I∝Qp = εo ・ εr ・ A ・ Vo / d = k / d Cp: Capacitance ｏo: Vacuum permittivity ｒr: Photoconductor A: Area d: Photosensitive layer thickness Qp: Surface charge of photoconductor Vo: Charge potential k: Constant

FIG. 3 is a graph showing an example of this relationship. In order to obtain a constant charging potential Vo in the photosensitive layer,
It is necessary to increase the charging current flowing into the photosensitive layer.
In the low charging potential process by the particle charging method of the present invention, following the increase in required charging current due to the decrease in the thickness of the photosensitive layer,
The photoconductor can be charged to the predetermined charging potential Vo in a short time. FIG. 4 is a graph showing this state, in which the predetermined charging potential Vo is set to -150 volts, the time required to charge an OPC-based photoconductor having an initial photosensitive layer thickness of 20 μm, and the photosensitive layer thickness due to abrasion. Shows the predetermined time when the value has decreased to 5 μm.

T ₀ : time during which the photosensitive member passes through the charging area s ₁ : time during which the charging potential is saturated by the corona charging method at a photosensitive layer thickness of 20 μm s ₂ : charging potential by the corona charging method at a photosensitive layer thickness of 5 μm P ₁ : Time during which the charging potential is saturated by the particle charging method at a photosensitive layer thickness of 20 μm p ₂ : Time during which the charging potential is saturated by the particle charging method at a photosensitive layer thickness of 5 μm Quick rise, layer thickness 20μm
Charged saturated until sometimes charging time p ₁ at 150 volts,
Even when the layer thickness is 5 μm and the required charging current is increased, the charge rises at time p ₂ , the difference between p ₁ and p ₂ is small, and the time t ₀ during which the photoreceptor passes through the charged area is set short to achieve a high-speed process. In addition, the charging potential can be made uniform. The corona charging method with respect to this, when the layer thickness 20μm in time s ₁ 1
It reaches 50 volts, but when the layer thickness reaches 5 μm, the saturation time s
₂ becomes extremely slow and cannot be processed any more in the actual charging processing time in the actual machine. Eventually, the charging potential decreases as the photosensitive layer thickness decreases, and stable image formation becomes impossible.

According to the present invention, when the charging area transit time t ₀ of the photosensitive member is determined in the design of the apparatus, p ₂ is set to t ₀ according to the final thickness of the used photosensitive member (5 μm in FIG. 4). The resistance of the particulate charging agent may be determined so that the charging current I can be supplied to the inside. Specifically, the upper limit value of the resistance is determined according to the photoconductor capacity of the final use layer thickness as described above, and the lower limit value is determined by the current flowing into the maximum pinhole within an allowable range when performing image evaluation. it can. In this case, the electrostatic capacity per unit area of the photoconductor is preferably 5.3 × 10 ⁻⁶ farad (F) or more.

The volume resistivity of the entire granular charging agent are those which can be appropriately set as described above, but 10 ² -
It is preferably about 10 ⁸ Ω · cm, more preferably 10 ³ Ω · cm or more.
10 ⁷ Ω · cm. In addition, when the resistance value of the particulate charging agent is set to be low, if the whole is made of the same conductive magnetic particles, injected charges may concentrate on minute defects in the photosensitive layer and abnormal charging current may flow to destroy the photosensitive layer. Occurs,
It is desirable to mix the magnetic particles having relatively low resistance and the magnetic particles having high resistance to obtain a particulate charging agent having a necessary resistance value as a whole.

In this case, the low-resistance magnetic particles have a density of 10 ⁵ Ω ·
cm or less, preferably 10 ¹ ~10 ⁵ Ω · cm, more preferably preferably set to a volume resistivity of 10 ² ~10 ⁴ Ω · cm, whereas, the high resistance magnetic particles 10 ⁵ Ω · c
m, preferably 10 ⁵ to 10 ¹⁵ Ω · cm, more preferably 10 ⁵ to 10 ¹² Ω · cm. The volume resistivity of the present invention was measured by placing 1.5 g of particles in a Teflon cylindrical body having an inner diameter of 20 mm and having an electrode at the bottom, inserting an electrode having an outer diameter of 20 mm, and applying a load of 1 kg from the top. Is the value of The granular charging agent is 40 em in a magnetic field of 1 kOe (KOe).
It preferably has a magnetic force of at least u / g, more preferably 50 to 100 emu / g.

The mixing ratio of the low-resistance magnetic particles A and the high-resistance magnetic particles B is generally in a range of A / B = 95/5 to 5/95 by weight, preferably 90/10. ~ 1
0/90, more preferably 80/20 to 20/80. The average particle size of the particulate magnetic particles is suitably 50 μm or less, preferably 5 to 45 μm. The photoreceptor charged to a charging potential Vo having an insulation value of 400 volts or less, preferably ± 30 to ± 250 volts, is then subjected to image signal exposure, and the post-exposure potential (low potential portion potential of the electrostatic latent image)
An electrostatic latent image of Vl is formed and developed with a developer.
The development is preferably performed under the condition of the following equation 2 while applying a development bias potential.

[0026]

ΔV = | Vb−Vl | = 400 volts or less, preferably 50 to 300 volts Vb: developing bias voltage Vl: low potential portion (exposed portion) potential of the electrostatic latent image

As the developer, a conductive magnetic developer is preferable, and in particular, a two-component conductive magnetic developer obtained by mixing a conductive magnetic carrier and a high-resistance toner is preferable. As the developer, those having a volume resistivity of 10 ³ to 10 ⁷ Ω · cm are suitable, and preferably 10 ³ to 10 ⁶ Ω · cm.
The conductive magnetic carrier has a volume resistivity of 10 ¹ to 10 ⁵ Ω.
Cm is suitable, preferably 10 ² to 10 ⁴ Ω · cm, and the average particle size is preferably 15 to 70 μm, and more preferably 25 to 40 μm.

[0028]

According to the image forming method of the present invention, the following effects can be obtained. (1) Since the photoreceptor is charged by the particle charging method, it does not generate harmful substances such as ozone and corona products, so it is safe for both the human body and the photoreceptor. And cost reduction is possible.
In addition, since there is no generation of corona products, there is no image flow, and there is no need to polish and clean the photoconductor surface.
It is possible to stabilize the characteristics of the photoconductor and prolong the service life. (2) The photoreceptor can be stably charged to a low potential by the particle charging method, and the latitude range can be widened without a decrease in image density due to uneven charging potential. (3) A low-withstand-voltage photoconductor and a high-capacitance photoconductor, which have been conventionally difficult to use, can be used. As a result,
For example, if an OPC-based photoconductor is used, the life can be extended,
In addition, the a-Si type photoreceptor can provide various benefits such as a thinner photosensitive layer. (4) The charge rise characteristics of the high-capacitance photoconductor can be improved, and a sufficiently fast rise time can be realized. As a result, a high-speed process can be performed, and uniform charging potential can be realized. (5) Even if the capacitance of the photosensitive layer greatly changes due to a decrease in the thickness of the photosensitive layer, the charging current is increased and the photosensitive member is charged to a predetermined potential in a short time without providing a special correction circuit. be able to.

[0029]

[Experimental example]

Experimental Example 1 Using the apparatus shown in FIG. 1, an image was formed using an OPC photoconductor having a photosensitive layer thickness of 5 μm as the photoconductor. In the charging step, 20% of low-resistance magnetic powder having an average particle diameter of 12 μm and a volume resistivity of 10 ² Ω · cm, an average particle diameter of 30 μm, and a resistivity of 10 ⁶
A charging bias voltage of -180 volts is applied using a granular charging agent having a volume resistivity of 1 × 10 ⁶ · cm mixed with 80% of high-resistance magnetic powder (iron-based) of Ω · cm, and the charging potential Vo of the photoconductor is adjusted. = -150 volts. The layer thickness is 5 μm
The dielectric breakdown voltage of the OPC photoreceptor was -500 volts in this particle charging method almost in the same manner as the corona charging, and it was found that the potential setting had no practical problem. An electrostatic latent image having a post-exposure potential Vl = -50 volts was formed by image exposure. In the development step, the average particle diameter is 35 μm, and the volume resistivity is 1
The average particle diameter of 7μm to 0 ³ Ω · cm, the volume resistivity 10 ¹³ Omega ·
cm of a negatively chargeable toner and 10% of a conductive magnetic developer, a developing bias voltage Vb = −120 volts,
That is, development is performed at ΔV = | Vb−Vl | = 70 volts,
When the image was transferred and fixed, a good image having an image density (ID) ≧ 1.3 was obtained.

Experimental Example 2 Using the apparatus shown in FIG. 1, an image was formed using an a-Si photosensitive member having a photosensitive layer thickness of 8 μm as the photosensitive member. In the charging step, 20% of low-resistance magnetic powder having an average particle diameter of 12 μm and a volume resistivity of 10 ² Ω · cm, an average particle diameter of 30 μm, and a resistivity of 10 μm.
^A charging bias voltage of +170 volts is applied using a granular charging agent having a volume resistivity of 1 × 10 ⁶ · cm mixed with 80% of a high-resistance magnetic powder (iron-based) of ⁶ Ω · cm, and a charging potential Vo of the photoreceptor is applied. = + 120 volts. In addition, a layer thickness of 8 μm
The dielectric breakdown voltage of the a-Si-based photoreceptor was +300 volts by this particle charging method, and it was found that the potential was set so as not to cause any practical problems. Post-exposure potential Vl = + by image exposure
A 5 volt electrostatic latent image was formed. In the development step, the average particle diameter is 35 μm, the volume resistivity is 10 ³ Ω · cm, and the average particle diameter is 7 μm.
m, positive charging toner having a volume resistivity of 10 ¹³ Ω · cm
Using a conductive magnetic developer mixed with 0%, a developing bias voltage Vb = + 100 volts, that is, ΔV = | Vb−V
When the image was developed at l | = 95 volts and transferred and fixed, a good image having an image density (ID) ≧ 1.3 was obtained.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an image forming method of the present invention.

FIG. 2 is a graph showing a relationship between a photosensitive layer thickness and a dielectric breakdown voltage.

FIG. 3 is a graph showing a relationship between a photosensitive layer thickness, a capacitance and a charging current required for charging.

FIG. 4 is a graph showing a rise time of a charging potential. t ₀ : Time during which the photoconductor passes through the charging process area s ₁ : Time during which the charging potential is saturated by the corona charging method at a photosensitive layer thickness of 20 μm s ₂ : Charging potential is saturated by the corona charging method at a photosensitive layer layer thickness of 5 μm Time p ₁ : Time at which the charging potential is saturated by the particle charging method at a photosensitive layer thickness of 20 μm p ₂ : Time at which the charging potential is saturated by the particle charging method at a photosensitive layer thickness of 5 μm

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Photoconductor 13 Conductive support 15 Photosensitive layer 21 Charging unit 23 Magnetic brush roller 25 Mag roller 27 Charging sleeve 29 Granular charging agent 31 Charging bias power supply 41 LED exposure optical system 51 Developing unit 53 Developing roller 55 Mag roller 57 Sleeve 59 Developing bias power supply 71 Transfer Unit 73 Transfer Roller 77 Transfer Bias Power Supply 81 Fixing Unit 83 Fixing Roller 85 Pressure Roller 91 Developer 93 Toner 95 Paper 99 Cleaning Blade

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shinji Yamane 2-14-9 Tamagawadai, Setagaya-ku, Tokyo Inside Kyocera Co., Ltd. Tokyo Yoga Office (72) Inventor Toshi Mukotaka 2-chome Tamagawadai, Setagaya-ku, Tokyo No. 9 Kyocera Corporation Tokyo Yoga Office (56) References JP-A-4-234063 (JP, A) JP-A-63-187267 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , (DB name) G03G 15/02 G03G 13/02

Claims (2)

(57) [Claims] 1. An aggregate of particles containing conductive particles
Applying a bias voltage for charging through the granular charging agent
A charging step of uniformly charging the photosensitive member, an electrostatic latent image formed more as selective by light irradiation brought selectively lower the charge potential of the photoconductor low potential portions and high potential portions are formed on a photosensitive member by A latent image forming step, by contacting the photosensitive member on which the electrostatic latent image is formed with a developer containing toner, and applying a developing bias voltage to the contact portion while selectively applying toner to the electrostatic latent image. An image forming method in which each step of a developing step of forming a toner image by adhering to a toner is carried out by using a low-resistance magnetic material of 10 ¹ to 10 ⁵ Ωcm as the particulate charging agent.
Particles and high-resistance magnetic particles of 10 ⁵ to 10 ¹⁵ Ωcm
And a granular band having an overall resistance of 10 ² to 10 ⁸ Ωcm
An image forming method , wherein a photoconductor is charged to 400 volts or less (absolute value) using an electric agent . 2. An absolute value | V of a difference between a developing bias voltage Vb and a low potential portion Vl of an electrostatic latent image in the developing step.
b-Vl | is such that 50 to 300 volts, an image forming method according to claim 1 for applying a developing bias voltage to the photoreceptor.