JPH11133707A - Contact electrifying member, image forming device and process cartridge - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve both the prevention of sand base due to too little discharge and the reduction of deterioration of a photoreceptive drum by specifying a discharge current flowing from a contact electrification member, and the varia tion coefficient of the discharge current. SOLUTION: The contact electrifying member 2 contacts an electrification body 1 and electrifies the surface of the electrification body 1 by the application of an AC voltage. At the time of the application of an AC voltage, a voltage between peaks, which is twice or more times lower than the electrification-start- voltage of the electrification body 1 obtained when a DC voltage is applied, a ratio of the AC voltage to an AC current flowing in the electrification body 1 is α. Further, an AC current flowing in the electrification body 1 when an AC voltage Vac, a voltage between peaks, which is twice or more times higher than the electrification-start-voltage is applied is I ac. A discharge current ΔIac yielded by the substitution of the ratio α, AC voltage Vac, and AC current Iac into the equation: ΔIac=Iac-α.Vac is 30 μA-150 μA, and the variation coefficient of the discharge current ΔIac of the AC current Iac to a relative humidity of 1% is below 0.5 μA.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a contact charging member, an image forming apparatus, and a process cartridge.

[0002]

2. Description of the Related Art Image forming apparatuses such as electrophotographic apparatuses (copiers, laser beam printers, etc.) and electrostatic recording apparatuses,
2. Description of the Related Art In a process cartridge detachably provided in an image forming apparatus main body, as a means for charging an image carrier (latent image carrier) such as a photoconductor and a dielectric, and other charged objects, a contact type has recently been used. (Contact charging) is widely used.

[0003] In contact charging, a voltage is applied to a charging member (contact charging member, conductive member) such as a roller type or a blade type, and the charging member is brought into contact with or in proximity to the charging member to charge the surface of the charging member. Is what you do.

Here, the charging member does not necessarily need to be in contact with the surface of the member to be charged, and even between the charging member and the surface of the member to be charged, a dischargeable area determined by the voltage between the gap and the correction Paschen carp is reliably guaranteed. Then, non-contact (proximity) may be used, and this case is also included in the category of contact charging.

[0005] Contact charging is more effective than non-contact type corona discharge devices. The applied voltage required to obtain a desired potential on the surface of the member to be charged is reduced. The amount of ozone generated during the charging process is very small, eliminating the need for an ozone removal filter. Therefore, the configuration of the exhaust system of the device is simplified. Maintenance free. It has advantages such as simple configuration.

In contact charging, an oscillating voltage (a voltage whose voltage value changes periodically with time, an AC application method) is often used as a voltage applied to a charging member.

Regarding the AC application method, as previously proposed by the present applicant (Japanese Patent Publication No. 3-52058), an oscillating voltage, particularly a charging start voltage (discharge) of a member to be charged when a DC voltage is applied. The method of applying an oscillating voltage having a peak-to-peak voltage that is twice or more the starting voltage) to the charging member to execute charging is effective because uniform charging (static elimination) processing can be performed.

More specifically, a charging member (contact charging member)
Is provided with a contact area in contact with the member to be charged and a separation surface region in which the distance from the surface of the member to be charged becomes larger downstream of the contact region in the moving direction of the member to be charged. A voltage having a peak-to-peak voltage component that is at least twice the applied voltage value of the charging member when the charging of the member to be charged is started by applying a DC voltage is applied between the member to be charged and the charging member. By forming an oscillating electric field between the surface of the member to be charged and the separation surface region of the charging member, the member to be charged is charged by the charging member.

The oscillating voltage is an oscillating voltage component (hereinafter, referred to as an AC component) or a superimposed voltage of the AC component and a DC voltage component (a voltage corresponding to a target charging potential; hereinafter, referred to as a DC component). Waveforms of sine wave, square wave,
A triangular wave or the like is appropriate. It may be a rectangular wave voltage formed by periodically turning on / off a DC power supply.

FIG. 11 shows a schematic configuration of an example of an image forming apparatus employing a contact charging member of an AC application type as a charging means. The image forming apparatus of this embodiment is a laser beam printer using an electrophotographic process.

Reference numeral 10 denotes a rotating drum type electrophotographic photosensitive member (hereinafter, referred to as a photosensitive drum) as a member to be charged (latent image carrier), for example, a drum base 10 made of aluminum.
organic photoconductor (OPC) 1 as a photosensitive layer on the outer peripheral surface of b
Oa is formed and has an outer diameter of 30 mm, and is driven to rotate at a predetermined peripheral speed (process speed) in the clockwise direction of arrow A.

Reference numeral 110 denotes a charging roller (conductive roller) as a contact charging member, which is composed of a core bar 111 and a conductive roller 112 made of conductive rubber or the like formed on the outer periphery thereof. The charging roller 110 is pressed against the surface of the photosensitive drum 10 with a predetermined pressing force by the pressing force of a pressing spring (pressing spring) 113 applied to both ends of the cored bar 111. Rotates following the rotation of the photosensitive drum 10.

Reference numeral 12 denotes a power supply for applying a voltage to the charging roller 110. The power supply 12 supplies a voltage between the peaks of twice or more the charging start voltage of the photosensitive drum 10 via a contact plate 114 which is brought into contact with a metal bar 111 of the charging roller 110. Voltage Vpp
A superimposed voltage (Vac + Vdc) of the AC component Vac and the DC component Vdc having the following is applied to the charging roller 110,
The outer circumferential surface of the rotating photosensitive drum 10 is uniformly contact charged by the AC application method.

On the other hand, a time-series electric digital pixel signal of target image (printing) information is input to a laser scanner (not shown) from a host device (not shown) such as a computer, a word processor, and an image reading device, and is inputted by a controller. The controlled laser scanner outputs a laser beam 50 image-modulated at a constant printing density DPI corresponding to the input pixel signal, and the output laser beam 50 is applied to the charged surface of the rotating photosensitive drum 10 by the output laser beam 50. By performing line scanning (main scanning exposure in the direction of the drum generatrix), target image information is written, and an electrostatic latent image of the image information is formed on the surface of the rotating photosensitive drum 10.

The latent image is visualized as a toner image by reversal development by a developing sleeve 61 of a developing device.

The toner image is transferred from a paper feed unit (not shown) to a pressure nip (transfer site) between the photosensitive drum 10 and the transfer roller 8.
Are sequentially transferred to the recording paper (transfer material) 7 fed at a predetermined timing.

The recording paper 7 to which the toner image has been transferred through the transfer portion is separated from the surface of the photosensitive drum 10 and is conveyed to fixing means (not shown), where the toner image is fixed and output as an image formed product.

After the transfer material is separated, the surface of the rotating photosensitive drum 10 is cleaned by a cleaning blade 91 of a cleaning device (cleaner) to remove residual deposits such as untransferred toner, and repeatedly used for image formation.

[0019]

Problems to be solved by the image forming apparatus using contact charging by the AC application method include the following.

That is, since positive and negative voltages are alternately applied as the applied voltage and discharge and reverse discharge are repeated, the surface of the photosensitive drum 1, which is the member to be charged, is greatly deteriorated by this discharge, and the deteriorated surface of the photosensitive drum is cleaned. It is scraped off by friction with a contact member such as the blade 91 (photosensitive drum scraping).

As a result, with the use of the apparatus, the photosensitive layer 10a of the photosensitive drum 1 gradually becomes thinner. When the photosensitive layer 10a reaches the limit film thickness, the function as the photosensitive layer is reduced, and minute charging unevenness may occur. In addition, poor charging occurs as the charge holding ability of the surface decreases. Therefore, the life of the image forming apparatus and the process cartridge is determined by the number of prints used until the photosensitive layer 10a is worn to the limit thickness.

Based on this, as a method of extending the life of the electrophotographic apparatus, a method of increasing the initial film thickness of the photosensitive layer 10a of the photosensitive drum 1 or a method of reducing the discharge amount of the charging member 110 to reduce the amount of discharge of the photosensitive drum 1 A method of reducing the deterioration of the photosensitive layer 10a can be considered.

However, when the thickness of the photosensitive layer 10a is simply increased, the holding power of the surface charge of the photosensitive layer is reduced, and the electrostatic image may be blurred.

It is also known that when the amount of discharge is excessively reduced, fine black spots called sand are generated on the image, and the discharge tends to be unstable.

Therefore, in order to achieve both high image quality and long life of the image forming apparatus and the process cartridge,
Using a photosensitive drum with a thickness that allows the thickness of the photosensitive layer to maintain the sharpness of the latent image, preventing sandy ground due to insufficient discharge, and
It is necessary to use a contact charging member such as a charging roller having an appropriate discharge amount to reduce the deterioration of the photosensitive drum.

As a method of controlling the voltage applied to the contact charging member, there is a method of controlling the amount of current flowing from the contact charging member such as a charging roller to the photosensitive drum to a constant value by a constant current control or the like. However, with this method alone, the amount of current itself is not a direct indicator of the amount of discharge, so that the amount of discharge is excessive for an actual charging device, which may accelerate the scraping of the photosensitive drum. For example, when the control current value is determined so as not to generate sand in a low-temperature and low-humidity environment, the discharge amount tends to be large under a high-temperature and high-humidity condition, and the photosensitive drum is easily scraped. As a result, the life of the entire image forming apparatus is shortened.

Therefore, it is necessary not only to control the current and voltage, but also to reduce the environmental fluctuation of the discharge amount during image formation as a charging device.

The present invention provides a contact charging unit employing an AC application method, and a sharpening and latent charging of a latent image in an image forming apparatus and a process cartridge using the contact charging unit. Aim.

[0029]

According to the present invention, there is provided a contact charging member, an image forming apparatus and a process cartridge having the following constitutions.

(1) A contact charging member that contacts an object to be charged and applies an AC voltage to charge the surface of the object to be charged, and is not more than twice the charging start voltage of the object to be charged when a DC voltage is applied. When the AC voltage that is the peak-to-peak voltage is applied, the ratio of the AC current flowing through the member to be charged with respect to the AC voltage is α, and the AC-to-peak voltage that is twice or more the charging start voltage When the AC current Iac flows through the member to be charged when the voltage Vac is applied, the above-described ratio α and the AC voltage Vac are applied.
ac, the discharge current △ Iac calculated by substituting the AC current Iac into Equation 1... △ Iac = Iac−α · Vac is 3
Within the range of 0 μA to 150 μA, the same alternating current Iac
Wherein the rate of change of the discharge current ΔIac with respect to 1% of relative humidity is 0.5 μA or less.

(2) Average surface roughness R of the contact charging member surface
The contact charging member according to (1), wherein a is 2 μm or less.

(3) In an image forming apparatus in which a latent image carrier is charged by a contact charging member and image information is written on the charged surface to execute image formation, the contact charging member is composed of (1)
Alternatively, the image forming apparatus is the contact charging member according to (2).

(4) The contact charging member is brought into contact with the latent image carrier at a predetermined pressure, and a gap formed at a contact portion between the contact charging member and the latent image carrier is set to 5 μm or less. The image forming apparatus according to (3).

(5) In a process cartridge having at least a contact charging member in addition to the latent image carrier and being detachably provided in the image forming apparatus main body, the contact charging member may be any of (1) and (2). A process cartridge comprising the contact charging member according to any one of the preceding claims.

(6) The contact charging member is brought into contact with the latent image carrier at a predetermined pressure, and a gap formed at a contact portion between the contact charging member and the latent image carrier is set to 5 μm or less. The process cartridge according to (5).

<Operation> That is, in the contact charging of the AC application method, the AC current when the AC voltage equal to or less than twice the charging start voltage (discharge start voltage) Vth of the member to be charged when the DC voltage is applied is applied. The AC voltage is α. Then, the contact charging member is supplied with an AC voltage Vac that is at least twice the charging start voltage.
Is applied to generate an AC current Iac, ΔIac =
The discharge current ΔIac calculated by Iac−α × Vac is 3
When the discharge current fluctuation value with respect to the relative humidity of 1% is 0.5 μA or less within the range of 0 to 150 μA, the discharge amount of the contact charging member is optimized, and the environmental fluctuation is small. The life of the image carrier is longer than that of the conventional one. This is because the amount of discharge was reduced, the deterioration of the member to be charged or the latent image carrier was reduced, and the amount of wear was reduced.

As a result, it is possible to increase the durability of the contact charging means based on the AC application method.

Further, in an image forming apparatus and a process cartridge image forming apparatus using the contact charging means, the generation of sand due to an insufficient discharge is prevented, and the latent image carrier (photosensitive drum) is reduced to reduce the length of the apparatus. A longer life can be achieved.

The contact charging member is discharged with a discharge current ΔIac 30-1.
The value within 50 μA can be adjusted by the set value of the applied current.

In order for the contact charging member to have a variation rate of the discharge current ΔIac relative to 1% relative humidity of 1% or less, the material of the contact charging member should have a small change in humidity. In addition, since the humidity changes due to the toner attached to the contact charging member, the releasability of the surface of the contact charging member is enhanced (the surface layer is made of a fluorine resin, the average surface roughness Ra is reduced, and the like).

The average surface roughness Ra of the contact charging member surface is J
According to the method of measuring the center line average roughness Ra of IS. As a measuring device, a contact type measuring instrument SE-3400 manufactured by Kosaka Corporation was used. Conditions were measured at a scan speed of 0.1 mm / s, an evaluation length of 2.5 mm, and a vertical magnification of 5000 times.

The contact charging member is brought into contact with the latent image carrier at a predetermined pressure, and the gap formed at the contact portion between the contact charging member and the latent image carrier is measured by measuring the distance between the contact charging member and the latent image carrier. It can be performed by following the contacted state, applying light horizontally to the contacting part, and measuring the amount of light leaking from the opposite side.

The reason why the gap is set to a predetermined value or less is that when the contact charging member is manufactured by a dipping method, the end portion tends to swell when the contact charging member is manufactured by a dipping method. In the vicinity of the section, the radius of the contact charging member is made substantially uniform.

[0044]

BEST MODE FOR CARRYING OUT THE INVENTION

<Embodiment 1> (FIGS. 1 to 6) In this embodiment, as in the apparatus of FIG. 11, the image forming apparatus employs an AC application type contact charging member as a charging means, and uses an electrophotographic process. Laser beam printer.

FIG. 1 shows a part of a rotary drum type electrophotographic photosensitive member (photosensitive drum) 1 as a member to be charged (latent image bearing member) and a contact charging member as a contact charging member which is brought into contact therewith. FIG. 3 is a model diagram of a charging roller 2.

In this embodiment, the photosensitive drum 1 is an organic photoconductor (OPC) drum having an outer diameter of 30 mm and an arrow A
Is rotated clockwise at a predetermined process speed (peripheral speed). The photosensitive drum 1 has an undercoat layer 1b on the surface of an aluminum cylinder (conductive drum base) 1a for suppressing interference of light and improving the adhesiveness of an upper layer.
The photo charge generation layer 1c and the charge transport layer 1d (thickness: t μm) are applied in order from the bottom.

The charging roller 2 according to the present embodiment includes a metal core (support member).
2a, a lower layer 2b, an intermediate layer 2c, and a surface layer 2d.
Are sequentially laminated from the bottom. The lower layer 2b is a foamed sponge layer for reducing charging noise,
Reference numeral c denotes a conductive layer for obtaining uniform resistance as a whole of the charging roller, and a surface layer 2d is a protective layer provided to prevent a leak even if a defect such as a pinhole exists on the photosensitive drum 1. It is. More specifically, the specifications of the charging roller 2 of this example are as follows.

A. Core 2a: diameter 6 mm, length 260
mm stainless steel round bar b. Lower layer 2b: foamed EPDM of carbon dispersion specific gravity 0.5 g / cm ³ volume resistance value 10 ² Ωcm to 10 ⁹ Ωcm layer thickness 3.0 mm, length 230 mm c. Intermediate layer 2c; NBR rubber dispersed with carbon Volume resistance value 10 ² Ωcm to 10 ⁵ Ωcm Layer thickness 700 μm d. Surface layer 2d; tin oxide and carbon dispersed in fluororesin resin resin Volume resistance value 10 ⁷ Ωcm to ^{10 10} Ωcm Surface roughness (average surface roughness Ra) 1.5 μm Layer thickness 10 μm This charging roller 2 has a core Both ends of the gold 2a are rotatably held by bearing members, respectively.
e, the photosensitive drum 1 is urged against the surface of the photosensitive drum 1 with a predetermined pressing force, and rotates following the rotation of the photosensitive drum 1. And power supply 12
A predetermined vibration voltage (bias voltage Vdc + Vac) obtained by superimposing an AC voltage having a frequency f on a DC voltage is applied to the charging roller 2 via the metal core 2a, so that the peripheral surface of the rotating photosensitive drum 1 has a predetermined potential. Is charged.

More specifically, in this embodiment, the voltage applied to the charging roller 2 is a current of 800 μA (constant current control), a frequency of 800 Hz, and a discharge current of 10 in a standard environment (temperature 15 ° C., humidity 50%).
0 μA.

The present invention is characterized by a contact charging member having a prescribed discharge amount. A method of calculating the discharge amount of the contact charging member will be described below.

First, the charging roller 2 as a contact charging member
[Experiment 1] described below was performed in order to check the amount of current flowing between the photosensitive drum 1 as a member to be charged (latent image carrier).

[Experiment 1] As shown in the schematic measurement diagram of FIG. 2, the charging roller 2 is pressed against the photosensitive drum 1 and the alternating current applied from the power source 12 to the charging roller 2 is rotated while the photosensitive drum 1 rotates. Change the voltage. At this time, the value of an alternating current flowing from the aluminum cylinder 1a, which is the conductive drum substrate of the photosensitive drum 1, to the ground is measured by the ammeter A. Details of the measurement environment and experimental conditions are shown below.

A. Measurement environment Under standard atmosphere (1 atm, temperature 15 ° C, relative humidity 50%)
And vacuum state (both in a dark room) b. Experimental conditions Rotation speed of photosensitive drum 1 (process speed): 5
0 mm / sec Applied AC voltage Vac: 0 to 3.0 kVpp Applied AC voltage frequency f: 600 Hz FIG. 3 shows an applied AC voltage V between the charging roller 2 and the photosensitive drum 1.
This is the relationship between ac (Vpp) and the measured current Iac.

In a vacuum, the current Iac with respect to the voltage Vac
Is linear. On the other hand, in the standard atmosphere (standard environment), the current Iac gradually shifts from the discharge threshold value 2 × Vth (V) to the current increase direction with respect to the voltage Vac.
Thus, it can be seen that this is the increment of the current involved in the discharge.

The VI curve is calculated from the following circuit model.

First, it is considered that the impedance Zc between the charging roller 2 and the photosensitive drum 1 is represented by an equivalent circuit shown in FIG. In FIG. 4, Rc is the resistance of the charging roller 2 Cc is the capacitance of the charging roller 2 Cd is the capacitance of the photosensitive drum 1 Cair is the capacitance of the minute air gap between the charging roller 2 and the photosensitive drum 1 is there.

In a vacuum, the following relationship is established between the applied AC voltage Vac (peak-to-peak voltage; Vpp) and the AC current Iac according to the impedance Zc.

Iac = Iz Iz = α · Vac α = 1 / (√2 · Zc) When discharge is occurring, that is, Vac (Vpp) ≧ 2 × V
In the case of th (V), the relationship deviates from the above relationship as shown in FIG. 3 and Iac ≧ Iz. Therefore, this Iac
ΔIac ΔIac = Iac−α · Vac (1) It is possible to define the discharge current amount.

By the way, in the process of charging the photosensitive drum as a member to be charged by discharging, such as contact charging as described above, discharge deterioration occurs on the surface of the photosensitive drum as described above. The charge transport layer 1d (FIG. 1) of the photosensitive drum 1 collides with charged particles (ions, electrons) generated by the discharge.
The molecular chains of the organic resin constituting the charge transport layer 1d are broken and become brittle, and are easily scraped off by the cleaning blade. As a result, the charge transport layer 1d is gradually removed.

FIG. 5 shows the relationship between the discharge current ΔIac and the scraping of the charge transport layer 1d (photoreceptor) per unit number. As described above, the charge transport layer 1d was scraped off at a discharge current of 150 μA.
Increase from degree.

Further, [Experiment 2] was performed to examine the relationship between the film thickness of the charge transport layer 1d and the image quality.

[Experiment 2] The thickness of the charge transport layer 1d was 10 μm.
The photosensitive drum 1 of m to 35 μm was prepared, and an image was formed by the laser beam printer as shown in FIG. 11 under the following experimental conditions.

The sharpness of the latent image was determined by taking a character image as an enlarged photograph and judging how the toner around the printing portion was separated. Table 1 shows the results.

Experimental conditions Rotation speed of photosensitive drum 1 (process speed): 5
0 mm / sec photosensitive drum dark area potential: -600 V photosensitive drum light area potential: -150 V applied AC voltage Vac: 2.0 kVpp applied AC voltage frequency f: 600 Hz

[0065]

[Table 1] The sharpness of the latent image decreases as the thickness t of the charge transport layer 1d increases. Therefore, in order to achieve a longer life of the photosensitive drum 1 while maintaining the sharpness of the latent image, the discharge current の of the charging roller 2 is reduced while the thickness t of the charge transport layer 1d of the photosensitive drum 1 is reduced as much as possible. Iac
Needs to be reduced. When the OPC photosensitive drum 1 of this example is used, if the thickness of the charge transport layer 1d is 25 μm or less, the sharpness of the latent image is satisfied.

When the applied voltage Vac is equal to or lower than a predetermined value, fine unevenness (sandy ground) in a sandy state may occur. This is because when the applied voltage Vac is low, an insufficient portion is generated in the discharge due to the resistance unevenness of the charging roller surface layer 2d, and a minute portion having a low potential on the photosensitive drum is developed to form a black spot-like image. It is.

Here, in order to examine the relationship between the discharge current ΔIac and the sand, an image was formed by changing the discharge current ΔIac under the apparatus and conditions of [Experiment 2], and the sand was evaluated. Table 2 shows the results. It can be seen that sand occurs when the discharge current is 25 μA or less, and disappears when the discharge current is 30 μA or more.

[0068]

[Table 2] By the way, the voltage of the charging roller 2 as a contact charging member
In general, the current characteristics are highly environment-dependent. In particular, humidity variability is high, and the discharge current may fluctuate greatly. Further, the toner tends to adhere to the charging port 2 due to the durability, and the discharge current tends to decrease. However, in a low-temperature and low-humidity environment, the resistance of the adhered toner is high and the decrease in the discharge current is remarkable. As a result, the environmental fluctuation difference of the discharge current further increases.

Therefore, in order to reduce the fluctuation in the durability and the fluctuation in the environment of the discharge current, the humidity variability of the charging roller 2 is reduced, and the surface layer 2d is reduced so that the toner adhesion during the running is reduced.
It is necessary to improve the mold releasability.

Table 3 shows the difference between the surface roughness (average surface roughness Ra) of the charging roller 2 and the discharge current before and after the endurance in a low-temperature and low-humidity environment.

[0071]

[Table 3] Thus, it can be seen that the surface roughness is 2 μm or less, and the difference in the durability variation of the discharge current is reduced.

The discharge current after the endurance is the discharge current of the charging roller 2 after passing through a laser beam printer (Apple Laser Writer 16 / 600ps, the same applies hereinafter) to 10,000 A4 sheets.

In this embodiment, an electron conductive material is used for the intermediate layer 2c of the charging roller 2, and the surface roughness of the surface layer 2d, ie, the surface roughness of the charging roller (average surface roughness Ra) is 2 μm.
m or less, and the surface layer 2d is made of a fluorine-based resin (a resin in which tin oxide and carbon are dispersed in a resin compound of a fluorine compound) to reduce environmental and durability fluctuations of the charging roller 2.

FIG. 6 shows the charging roller 2 of this embodiment in a high-temperature and high-humidity environment where the temperature and humidity are 30 ° C. and 80%, respectively.
It is a voltage and current characteristic under a low temperature and low humidity environment of 10 ° C. and 10%.

Table 4 shows the discharge current under the above-mentioned environment. The discharge current after the endurance is the discharge current of the charging roller 2 after setting the laser beam printer and passing up to 10,000 A4 sheets in each environment.

[0076]

[Table 4] As can be seen from this, when the AC current value when the image forming apparatus was used was 800 μA, the difference between the discharge currents in both environments could be 35 μA. Thus, the variation rate of the discharge current with respect to the relative humidity of 1% is preferably within 0.5 μA (35 μA / (80% -10%)).

As described above, the discharge current ΔIac of the charging roller 2 is set to 30 to 150 μA, and more preferably, the humidity variation rate of the discharge current is set to 0.5 μm for a relative humidity of 1%.
By setting the ratio to A or less, it is possible to prevent sandy ground and maintain high sharpness of the latent image and satisfy high environmental stability and high durability.

The charging roller 2 was set in a laser beam printer and used at room temperature up to 10,000 A4 papers. As a result, no image defect due to abrasion of the photosensitive drum 1 up to 10000 sheets occurred, and characters did not scatter, and the sharpness of the latent image could be maintained.

Although the charging roller 2 has been described as an example of the contact charging member in the present embodiment, the above-described effects can be obtained with other types of contact charging members such as a blade type.

As described above, for the contact charging member of the AC application type, the discharge current is set to 30 to 150 μA and the humidity variation rate of the discharge current is set to within 0.5 μA with respect to the relative humidity of 1%, whereby the insufficient charging is achieved. Therefore, it is possible to provide a laser beam printer capable of preventing a sand image due to the above-mentioned method and maintaining the high-quality image and extending the life of the photosensitive drum.

Second Embodiment (FIGS. 7 to 9) The second embodiment aims at further enhancing the effect of high durability of the image forming apparatus.

In the second embodiment, the image forming apparatus is the same as the first embodiment described above, except that AC is used as the contact charging member.
This is a laser beam printer using an electrophotographic process and employing an application type charging roller 2.

When the charging roller 2 is pressed against the photosensitive drum 1 by the load of the spring by the pressing spring 2e, a minute gap (gap) may be generated between the charging roller 2 and the photosensitive drum 1 due to the unevenness of the surface. In particular, a minute gap is often formed on the longitudinal end side of the charging roller due to unevenness caused by dripping when a solution for forming the intermediate layer 2c and the surface layer 2d is applied.

FIG. 7 is an exaggerated view of a gap G (hatched portion) formed between the charging roller 2 and the photosensitive drum 1 at the longitudinal end of the charging roller 2 when the charging roller 2 is pressed against the photosensitive drum 1. It is a model figure.

If a minute gap G is formed at the pressure contact portion between the charging roller 2 and the photosensitive drum 1, the photosensitive drum may be excessively scraped at this portion.

As described below, this gap G
This is due to an increase in the local discharge current of the charging roller 2 in the portion. FIG. 8 is an enlarged cross-sectional model diagram of the charging roller 2 and the photosensitive drum 1 at the cut surface L (gap G portion) in FIG. Here, the gap between the charging roller 2 and the photosensitive drum 1 at the cut surface L is G, the closest point between the photosensitive drum 1 and the charging roller 2 is the origin 0, and the displacement on the photosensitive drum downstream in the photosensitive drum rotation direction is x.

FIG. 9 shows the discharge current with respect to the displacement of the photosensitive drum calculated by using the above equation (1). Note that the profile of this discharge is
Although the calculated value is obtained when a DC voltage of 1.3 kV is applied, the relationship between the gap G of the press-contact portion and the discharge current may be considered to be the same when an AC voltage is applied.

As can be seen from FIG. 9, the discharge current of the charging roller 2 increases when the gap G at the press contact portion is 5 μm or more. Therefore, in order to further enhance the durability of the image forming apparatus, the gap amount between the charging roller 2 and the photosensitive drum 1 must be 5
It is understood that it is necessary to be not more than μm.

The charging roller 2 as described above was set in a laser beam printer (Apple Laser Writer 16 / 600ps), and up to 15,000 A4 paper sheets were used under the same charging roller application voltage conditions as in the first embodiment.

As a result, up to 15,000 photosensitive drums 1
No image failure due to local abrasion occurred, and high image quality could be maintained.

As described above, by setting the gap between the charging roller 2 and the photosensitive drum 1 to 5 μm or less, a sandy image due to insufficient charging can be prevented, and a high quality image can be maintained. It is possible to provide a laser beam printer capable of extending the life.

Third Embodiment (FIG. 10) In the third embodiment, an image using the contact charging member (charging roller) or the contact charging device described in the first embodiment as a charging unit for the image carrier is used. 6 is a process cartridge of the forming apparatus.

FIG. 10 is a schematic configuration diagram of the process cartridge PC. Process cartridge PC of this example
The four processes of a photosensitive drum 1 which is a rotating drum type electrophotographic photosensitive member as an image carrier (latent image carrier), a charging roller 2 as a contact charging member, a developing device 60 and a cleaning device 90 The device is integrally incorporated in the cartridge container 30.

A mounting means 100 for detachably mounting the process cartridge PC is provided on the side of the image forming apparatus main body to which the process cartridge PC is mounted.

The charging roller 2 is the same as that described in the first embodiment. The charging roller 2 is pressed against the photosensitive drum 1 by a pressure spring (not shown), and is driven to rotate as the photosensitive drum 1 rotates.

In the developing device 60, 61 is a developing sleeve, 63 is a container for storing the toner (developer) T, and 64 is a toner stirring rod in the container 63. And send it out. Reference numeral 62 denotes a developing blade for coating the developing sleeve 61 with a uniform thickness of toner.

In the cleaning device 90, reference numeral 91 denotes a cleaning blade, and 92 denotes a cleaning blade 91.
Is a toner reservoir for storing the collected toner 93.

Reference numeral 51 denotes a drum shutter of the process cartridge PC, which can be opened and closed from a closed state shown by a two-dot chain line to an open state shown by a solid line. When the process cartridge PC is removed from the image forming apparatus main body, the drum shutter 51 is in a closed state shown by a two-dot chain line, and protects the photosensitive drum 1 by concealing an externally exposed portion surface of the photosensitive drum 1.

When the process cartridge PC is mounted on the main body of the image forming apparatus, the drum shutter 51 is opened as shown by a solid line, or the process cartridge PC is opened.
The drum shutter 51 automatically opens during the mounting process of the process cartridge P into the process cartridge P.
When C is properly mounted, the outer exposed surface of the photosensitive drum 1 is brought into pressure contact with the transfer roller 8 on the image forming apparatus main body side.

When the process cartridge PC is properly mounted, the process cartridge PC and the image forming apparatus main body are mechanically and electrically coupled, and the driving mechanism of the image forming apparatus main body side drives the process cartridge PC side. Of the photosensitive drum 1, the developing sleep 61, the stir bar 64, and the like can be driven, and an electric circuit on the image forming apparatus main body side applies a charging bias to the charging roller 2 on the process cartridge PC side. It becomes possible to apply a developing bias or the like, and the image forming operation can be executed. Reference numerals 12, 13, and 14 denote bias application power supplies for the charging roller 2, the developing sleeve 61, and the transfer roller 8, respectively, which are located on the image forming apparatus main body side. Reference numeral 52 denotes an exposure window provided between the charging roller 2 and the developing device 60 in the process cartridge container 30, and an output laser beam 50 from a laser scanner (not shown) on the image forming apparatus main body side receives the exposure window. The light passes through 52 and enters the process cartridge PC, and the surface of the photosensitive drum 1 is scanned and exposed.

As described above, the charging roller 2 has a discharge current of 30 to 150 μA and a humidity variation rate of the discharge current of 0.5 μA or less with respect to a relative humidity of 1%. Thus, it is possible to configure a process cartridge that can extend the life of the photosensitive drum while maintaining high-quality images.

[0102]

As described above, in the contact charging of the AC application method, the discharge current ΔIac flowing from the contact charging member to the member to be charged or the latent image carrier is set to 30 to 150 μA, and the relative humidity at the same AC current Iac is set. The variation rate of the discharge current ΔIac with respect to
A or less can prevent a sandy image due to insufficient charging, enhance environmental stability, and maintain a high-quality image while maintaining a latent image carrier (photosensitive drum), an image forming apparatus, and a process cartridge. The service life can be extended.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating a configuration of a photosensitive drum and a charging roller in an image forming apparatus according to a first embodiment.

FIG. 2 is a schematic diagram of measurement in Experiment 1.

FIG. 3 is a graph of an AC applied voltage between a photosensitive drum and a charging roller and an AC current amount;

FIG. 4 is an equivalent circuit model of a photosensitive drum and a charging roller.

FIG. 5 is a graph of the discharge amount of the charging roller and the scraping of the charge transport layer.

FIG. 6 is an AC VI curve under high-temperature, high-humidity and low-temperature, low-humidity environments

FIG. 7 is an exaggerated model diagram showing a gap generated at a pressure contact portion between the photosensitive drum and the charging roller.

FIG. 8 is an enlarged schematic cross-sectional view taken along a section L in FIG. 7;

FIG. 9 is a calculation result of a discharge profile.

FIG. 10 is a schematic view of a process cartridge according to a third embodiment.

FIG. 11 is a schematic diagram of a conventional image forming apparatus.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 photosensitive drum (substrate to be charged, latent image carrier) 1a conductive drum substrate 1b undercoat layer 1c photocharge generation layer 1d charge transport layer 2 charging roller (contact charging member) 2a core metal 2b lower layer 2c intermediate layer 2d surface layer 12 Charging bias application power supply PC Process cartridge 50 Laser beam 60 Developing device 8 Transfer roller 90 Cleaning device

Claims (6)

[Claims] 1. A contact charging member that contacts an object to be charged and applies an AC voltage to charge the surface of the object to be charged, wherein a charging start voltage of the object to be charged when a DC voltage is applied is 2
When applying an AC voltage that is a peak-to-peak voltage of twice or less, the ratio of the AC current flowing through the member to be charged with respect to the AC voltage is α, and the peak-to-peak voltage is twice or more the charging start voltage. When the AC current Iac flows through the member to be charged when a certain AC voltage Vac is applied, the above ratio α, the AC voltage Vac, and the AC current Iac are substituted into Equation 1... △ Iac = Iac−α · Vac. The discharge current △ Iac calculated by
A contact charging member, wherein a variation rate of a discharge current △ Iac with respect to a relative humidity of 1% at the same alternating current Iac is 0.5 μA or less within a range of 0 μA to 150 μA. 2. The contact charging member according to claim 1, wherein the average surface roughness Ra of the surface of the contact charging member is 2 μm or less. 3. An image forming apparatus in which a latent image carrier is charged by a contact charging member and image information is written on the charging surface to execute image formation, wherein the contact charging member is according to claim 1 or 2. An image forming apparatus comprising a contact charging member. 4. A contact charging member is brought into contact with a latent image carrier at a predetermined pressure, and a gap formed at a contact portion between the contact charging member and the latent image carrier is set to 5 μm or less. Item 4. The image forming apparatus according to Item 3. 5. A process cartridge having at least a contact charging member in addition to a latent image carrier and detachably disposed in an image forming apparatus main body, wherein the contact charging member is according to claim 1 or 2. A process cartridge, which is a charging member. 6. A contact charging member is brought into contact with a latent image carrier at a predetermined pressure, and a gap formed at a contact portion between the contact charging member and the latent image carrier is set to 5 μm or less. The process cartridge according to claim 5, wherein: