JPH05232784A - Image forming device - Google Patents

Abstract

PURPOSE:To reduce fogs to such a degree as not presenting any problem in practical application when inversive development is made with an image forming device which performs primary electrostatic charging process for an electrostatic latent image carrier with contact system AC electrostatic charging. CONSTITUTION:Under the conditions that ¦VDC-Pr¦-VPP-Pr/2+550-¦VDC-DEV¦>0 or ¦VDC-Pr¦-VPP-Pr/2+550-¦VDC-DEV¦<=0, then vp/fPr<=0.20(mm) and Vp.(¦VDC-Pr¦-VPP-Pr/2+550-¦VDC-DEV¦)/fPr>-25(mm.V) must be met, where VDC-Pr is potential of DC bias component of the vibration voltage impressed on a charging member 2, VPP-Pr is amplitude of the potential of AC bias component, fPr is frequency, VDC-DEV is potential of DC bias component of the developing bias impressed on a developing member 3, and VP is the surface moving speed of latent image carrier.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming process means (electrophotographic process, electrostatic recording process, etc.) including charging means for primarily charging an electrostatic latent image carrier such as an electrophotographic photosensitive member or electrostatic recording dielectric. ), An electrostatic latent image of desired image information is formed on the surface of the electrostatic latent image carrier, and the electrostatic latent image is developed by developing means including a developing member to which a developing bias is applied.

More specifically, the present invention relates to an image forming apparatus which is a contact type charging device for charging the surface of an electrostatic latent image carrier by bringing a charging member to which the above-mentioned charging means applies an oscillating voltage into contact with the electrostatic latent image carrier. ..

[0003]

2. Description of the Related Art Conventionally, in an image forming apparatus such as an electrophotographic apparatus or an electrostatic recording apparatus, a non-contact type corona discharger is widely used as a charging processing means for an electrostatic latent image carrier as a charged body. It has been used.

In recent years, a charging member such as a roller type (charging roller), a blade type (charging blade), or a brush type (charging brush) to which a voltage is applied is brought into contact with the surface of the electrostatic latent image carrier to electrostatically charge it. A contact (direct) type charging device for charging the surface of the latent image carrier to a predetermined polarity and potential (for example, JP-A-63-16).
7380 gazette, etc.) has been put to practical use. The contact-type charging device has advantages over a corona discharger in that the power supply can be operated at a lower voltage, and the generation of corona discharge products such as ozone is extremely small (ozone-less).

A conductive roller (charging roller) as a charging member
The roller charging method using is preferably used from the viewpoint of charging stability.

A method of charging the surface of the member to be charged by applying only a DC voltage to the charging member (hereinafter, referred to as D
C charging) and a method of charging a charged member by applying an oscillating voltage (a voltage whose voltage value periodically changes with time) to a charging member (hereinafter referred to as AC charging,
JP-A-63-149669).

AC charging is a DC bias component of a desired potential, and preferably, a charging start voltage V of an electrostatic latent image carrier as a member to be charged when a DC bias is applied to a charging member.
_The electrostatic latent image bearing member is charged by applying a superposed oscillating voltage with an AC bias component having a peak-to-peak voltage V _PP that is at least twice _th to charge the electrostatic latent image carrier, and makes the charging more uniform than DC charging. Can be planned.

The waveform of the AC bias component is not limited to a sine wave, but may be a rectangular wave, a triangular wave, or a pulse wave. It includes a voltage generated by periodically turning the DC power supply on and off.

[0009]

An electrophotographic apparatus in which the primary charging of a photosensitive drum as an electrostatic latent image carrier is performed by AC charging will be described as an example.

When the photosensitive drum is charged by AC charging, the actual charging on the photosensitive drum follows the discharge law of Passion under normal pressure environment and between the charging roller as a charging member and the photosensitive member surface. Charging by discharge is performed in a state in which the potential difference of is 550 V or more.

Therefore, when an AC voltage is applied to the charging roller, the surface potential (that is, charging potential) on the photosensitive drum is as shown in FIG.
As shown in, it is considered that the potential is charged to a periodically changing potential having a voltage lower by 550 V from the peak voltage of the applied voltage, centering on the effective value of the AC waveform.

Therefore, for example, when performing so-called reversal development in which toner is adhered to the exposed portion of the electrostatic latent image of the photosensitive member (photosensitive exposed portion of the photosensitive member), so-called reversal development occurs, for the following reason. That is, the developing member of the developing device (developer carrier)
, The potential of the DC bias component of the developing bias applied to the developing sleeve is V _DC-DEV , and the potential of the AC bias component and the potential of the DC bias component of the charging vibration bias applied to the charging roller are V _PP-Pr , V, respectively. _{If DC-Pr} is set, | V _DC-Pr | -V _PP-Pr / 2 +550 <| V _DC-DEV | may occur depending on these settings.

This means that a region having a lower potential than the voltage of the DC bias component applied to the developing sleeve is periodically formed on the photoconductor, and this region is basically developed during reversal development. ..

In other words, there is a drawback that the surface of the photoconductor is soiled as so-called "fog" because it is developed regardless of whether the photoconductor is exposed or not.

The present invention aims to solve this problem.

[0016]

The present invention is an image forming apparatus having the following configuration.

(1) An electrostatic latent image of desired image information is formed on the surface of the electrostatic latent image bearing member by an image forming process means including a charging means for primarily charging the electrostatic latent image bearing member, and the electrostatic latent image is formed. An image forming apparatus for developing a latent image by a developing means including a developing member to which a developing bias is applied, wherein the charging means brings the charging member to which an oscillating voltage is applied into contact with the electrostatic latent image carrier to carry the electrostatic latent image. A contact type charging device for charging the body surface, wherein the potential of the DC bias component of the oscillating voltage applied to the charging member is V _DC-Pr , and the amplitude of the potential of the AC bias component is V _DC-Pr .
_{Where PP-Pr is} the frequency, f _{Pr is} the potential of the DC bias component of the developing bias applied to the developing member is _VDC-DEV , and the surface moving speed of the electrostatic latent image carrier is v _P , (1) | V _DC-Pr | -V _PP-Pr / 2 + 550- | V _DC-DEV |> 0 or (2) | V _DC-Pr | -V _PP-Pr / 2 + 550- | V _DC-DEV | ≤0 When v _P / f _Pr ≦ 0.20 (mm), and v _P · (| V _DC-Pr | -V _PP-Pr / 2 +550 − | V _DC-DEV |) / f _Pr > -25 An image forming apparatus characterized by being configured to satisfy (1) or (2) which is (mm · V).

(2) The image forming apparatus according to (1), characterized in that the developing means is a reversal developing device for adhering the developer to the exposed portion of the electrostatic latent image carrier on which the electrostatic latent image is exposed.

(3) The image forming apparatus according to (1), wherein the oscillating voltage is a superimposed voltage of a DC voltage and an AC voltage.

(4) The oscillating voltage is a direct current voltage having a desired potential,
(1) The image formation according to (1), which is a superimposed voltage with an AC voltage having a peak-to-peak voltage that is at least twice the charging start voltage of the electrostatic latent image carrier when a DC voltage is applied to the charging member. apparatus.

[0021]

That is, in the AC charging type image forming apparatus which performs the primary charging process of the electrostatic latent image carrier by applying the oscillating voltage to the charging member, the DC bias component potential V _{DC- of} the oscillating voltage applied to the charging member. _Pr , AC bias component potential V _PP-Pr ,
And the DC bias V _DC-DEV of the developing bias applied to the developing member is expressed by the formula (1), or even if the left side of the formula (1) becomes negative as in the formula (2), Surface moving speed v _{P of} the electrostatic latent image carrier, charging frequency f _pr
, V _P / f _pr ≦ 0.20 (mm), and v _P · (| V _DC-Pr |-V _PP-Pr / 2 + 550-| V _DC-DEV |) / f _pr > -25 By setting it to (mm · V), the fog that periodically occurs on the electrostatic latent image carrier due to the AC bias component being included in the charging bias is reduced and can be ignored on the transfer material. ..

[0022]

【Example】

<Embodiment 1> FIG. 1 is a schematic configuration diagram of an example of an image forming apparatus according to the present invention. The image forming apparatus of this example is a laser beam printer using a transfer type electrophotographic process.

Reference numeral 1 denotes a photosensitive drum, which is rotationally driven in a clockwise direction indicated by an arrow a at a predetermined peripheral speed (process speed) v _P. The photoconductor drum 1 of this example is formed by coating a layer of the OPC photoconductor 1a on the outer peripheral surface of a conductive drum substrate 1b made of aluminum or the like.

Reference numeral 2 denotes a charging roller as a primary charging member of the photosensitive drum 1, which comprises a core metal 1a, a conductive elastic layer (conductive rubber layer) 1b formed on the outer periphery thereof, and further formed on the outer periphery thereof. The high resistance layer 1c is formed. Core metal 2
Both end portions of a are supported by bearings in parallel with the photosensitive drum 1 and pressed against the surface of the photosensitive drum 1. In the case of this example, the photosensitive drum 1 is driven to rotate in accordance with the rotational driving of the photosensitive drum 1.

Reference numeral 2A denotes a charging bias application power source for the charging roller 2, which is composed of a DC power source 21 and an AC power source 22 in series, and a predetermined DC bias component potential is applied to the core metal 2a of the charging roller 2 by the power source 2A. The superposed oscillating voltage with the V _DC-Pr AC bias component potential V _PP-Pr is applied, and the peripheral surface of the photoconductor 1a of the rotary photoconductor drum 1 is uniformly and uniformly contact-charged to a predetermined polarity and potential.

Next, a laser beam L output from a laser beam scanner (not shown) on the charging surface of the rotary photosensitive drum 1 (a laser beam whose intensity is modulated in accordance with a time series electric digital pixel signal of target image information). By performing the scanning exposure by (1), the exposed portion of the surface of the photoconductor 1a is discharged and an electrostatic latent image of image information is formed on the surface of the photoconductor 1a.

Next, the latent image is subjected to reversal development by the reversal development device 4, that is, toner is attached to the exposure charge-eliminating portion (exposure bright portion) of the photoconductor 1a and is visualized (developed) as a toner image.

In the case of this embodiment, the reversal developing device 4 is a known jumping developing device using a one-component magnetic toner, and the developing sleeve 3 as a developing member has a developing bias composed of a DC power source 31 and an AC power source 32 in series. The superposed oscillating voltage with the DC bias component potential V _DC-DEV AC bias component potential V _PP-DEV is applied by the applied power source 3A.

When the toner image is at the position of the transfer roller 5,
The image is transferred onto a transfer material 7 fed at a predetermined timing from a sheet feeding mechanism (not shown) to a pressure contact nip portion (transfer portion) between the photosensitive drum 1 and the transfer roller 5.

A transfer bias applying power source 5 is applied to the transfer roller 5.
By A, a transfer bias having a polarity opposite to the toner polarity of the toner image is applied.

The transfer material 7 that has passed through the transfer portion is the photosensitive drum 1
The toner image is separated from the surface and sent to the fixing device 8, where the toner image is fixed by pressing and heating, and is output as an image formed product (print, copy).

After the transfer of the toner image, the surface of the photosensitive drum 1 is cleaned by a cleaning device 6 to remove residual toner such as untransferred toner and paper dust, and is repeatedly subjected to image formation.

In this embodiment, the charging bias for the charging roller 2 is a DC bias component V _DC-Pr : -550 V AC bias component V _PP-Pr : Frequency f _Pr = 300 Hz Swing V _PP-Pr = 1400 V Sine wave superposition It is an oscillating voltage.

Since the photoconductor drum 1 of this embodiment uses the OPC photoconductor 1a, the charging polarity is negative.

The developing bias applied to the developing sleeve 3 is a DC bias component V _DC-DEV : -400 V AC bias component V _PP-DEV : frequency = 1800 Hz amplitude = 1400 V rectangular wave superimposed vibration voltage.

In FIG. 2, the horizontal axis represents time t and the vertical axis represents voltage V.

V _L is the exposed portion potential of the photoconductor, V _DC-DEV is the DC component of the developing bias applied to the developing sleeve, and the sine wave is the bias power source waveform applied to the charging roller 2. It is called V _PP-Pr .

V _DC-Pr is a DC bias (effective value) superimposed on this sine wave. The waveform indicated by the dotted line represents the charging potential of the photoconductor 1a.

Since the AC frequency of the developing bias is 6 times that of the charging bias, the developing bias agrees with the experimental result if only the effective value is considered within one cycle of the charging AC.

AC bias component of charging bias V _PP-Pr
If the value of is less than 1100V, charging failure will occur, so that the value of 1100V or more is required. However, if this value is made too large, the dotted line waveform in FIG. 2, that is, the amplitude of the potential on the photoconductor becomes large, and the fog becomes worse as described in the above problem.

Therefore, even if the impedance of the charging roller 2 changes due to environmental changes or durability, V _PP-Pr becomes 110.
The minimum voltage not lower than 0V, that is, 1500V was selected.

In the reversal development, the development is performed on a region of low potential on the photoconductor. Therefore, the condition for not developing in the low potential region periodically generated on the photoconductor by using the charging roller 2 and applying an AC bias to it is │V _DC-Pr │-V _PP-Pr / 2 +550 − | V _DC-DEV |> 0 (1) When V _PP-Pr 1500 V of this embodiment is substituted into the above equation, | V _DC-Pr |-| V _DC-DEV |> 200 V.

That is, when V _PP-Pr = 1500 V, for example, when charging and developing are performed at V _DC-Pr = -700 V V _DC-DEV = -490 V, for example, the charging roller 2 to which an AC bias is applied is applied to the photosensitive member. Even in an image forming apparatus in which charging is performed and reversal development is performed, it is possible to perform development without fog caused by charging.

<Embodiment 2> When the primary charging roller 2 is used for charging, an AC bias component V of the charging bias is applied.
As described above, in order to enhance the effect of applying _PP-Pr and suppress charging failure, V _{PP of} at least 1100 V or more must be applied. It was also stated that it is practically sufficient to apply 1500 V to V _PP in order to absorb impedance changes caused by environmental changes and surface contamination.

However, in reality, it is desirable to apply V _PP of 1600 to 1700 V in consideration of variations in the resistance value of the conductive material of the charging roller 2 and the film thickness of the high resistance layer formed on the surface.

Further, the gist of the present invention can be easily achieved by setting the DC bias component V _DC-Pr of the charging bias high, but in the system in which the transfer is performed by the transfer roller 5, the developing portion and the non-developing portion of the photoconductor are used. If the potential difference between the parts is made too high, the degree of toner scattering may worsen, so it is also desirable to set this as low as possible.

The inventors of the present invention have found that when Vdεf = │V _DC-Pr │-V _PP / 2 + 550-│V _DC-DEV │ <0, the fogging caused by the charging roller is what is practically Vd εf. Was evaluated as acceptable.

It was also confirmed that the fog caused by the charging roller at this time also depends on the charging cycle formed on the photosensitive member. The results are shown in Table 1.

[0049]

[Table 1] Relationship between charging frequency, Vdεf ^{* 1} and fog In the table, the upper part shows the evaluation result of fog, and the lower part shows the value of v _P · Vdεf / f _Pr (mm · V) * 1 Vdεf = | V _DC-Pr | −V _PP / 2 +550 − | V
_DC-DEV | * 2 Process speed: v _P = 50 mm / sec ○ means that there is no periodic fog on the photoconductor due to the charging roller and it is at a level that is not recognized on the transfer material. In the figure, Δ indicates that the fogging was observed on the photoconductor, but the fog increased on the transfer paper was equivalent to the above level and no significant difference was observed, and x indicates the periodic fogging occurring on the photoconductor. It is shown that the fog on the transfer material is clearly increased due to the fog.

From this, when the charging pitch v _P / f _Pr (process speed divided by the charging frequency) is 200 μm or less, the charging pitch and Vdεf have an almost inversely proportional relationship with respect to fog, and the product of the two is obtained. Is -25
If it is larger, the fog caused by applying the AC bias to the charging roller is completely eliminated on the transfer material. That is, if the conditions of v _P / f _Pr ≦ 0.20 (mm) and v _P · Vdεf / f _Pr > −25 (mm · V) are satisfied, the charging potential formed on the surface of the photoconductor in the reversal development system is temporarily determined. Even if it becomes lower than the DC bias value applied to the developing sleeve periodically, that is, even if Vdεf <0, it is difficult to recognize the increase of fog on the transfer material due to this.

The present invention is not limited to contact charging using a roller as a charging member, but is effective for a contact charging system using a conductive blade, a conductive brush or the like as a charging member.

In the contact charging, the charging member can be charged in the same manner as when the charging member is brought into contact with the charged member even if the charging member is floated in a non-contact manner with a small gap. .. In the present invention, contact charging includes this aspect.

[0053]

As described above, according to the present invention, the occurrence of the fogging phenomenon at the time of reversal development in an image forming apparatus in which the primary charging process of the electrostatic latent image bearing member is performed by contact AC charging does not pose a practical problem. It can be reduced to a level below that, and high-quality image output becomes possible.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an image forming apparatus according to an embodiment.

FIG. 2 is a charging bias voltage applied to a charging roller,
FIG. 3 is a diagram for explaining the relationship between the photosensitive drum charging potential and the developing bias.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photoconductor drum as an electrostatic latent image carrier 2 Charging roller as a charging member L Laser light 3 Developing sleeve as a developing member 4 Developing device 5 Transfer roller 6 Cleaning device 7 Transfer material 8 Fixing device 2A Charging bias applying power source 3A Development bias application power supply 5A Transfer bias application power supply

Continuation of the front page (72) Inventor Erika Asano 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (4)

[Claims] 1. An electrostatic latent image of desired image information is formed on the surface of the electrostatic latent image carrier by an image forming process means including a charging means for primarily charging the electrostatic latent image carrier, and the electrostatic latent image is formed. An image forming apparatus that develops an image by a developing unit including a developing member to which a developing bias is applied, wherein the charging unit contacts the electrostatic latent image carrier with the charging member to which an oscillating voltage is applied, and the electrostatic latent image carrier surface Is a contact type charging device for charging the charging member, the potential of the DC bias component of the vibration voltage applied to the charging member is V _DC-Pr , the amplitude of the potential of the AC bias component is V _PP-Pr , the frequency is f _Pr , and the development The potential of the DC bias component of the developing bias applied to the member is V _DC-DEV , the surface moving speed of the electrostatic latent image carrier is v _P ,
Then, (1) | _VDC-Pr | -VPP _-Pr / 2 + 550- | _VDC-DEV |> 0 or (2) | _VDC-Pr | -VPP _-Pr / 2 + 550- | When V _DC-DEV | ≦ 0, v _P / f _Pr ≦ 0.20 (mm), and v _P · (| V _DC-Pr | −V _PP-Pr / 2 +550 − | V _DC-DEV An image forming apparatus characterized by being configured to satisfy (1) or (2) such that |) / f _Pr > −25 (mm · V). 2. The image forming apparatus according to claim 1, wherein the developing means is a reversal developing device for adhering the developer to the exposed portion of the electrostatic latent image carrier on which the electrostatic latent image is exposed. 3. The image forming apparatus according to claim 1, wherein the oscillating voltage is a superimposed voltage of a DC voltage and an AC voltage. 4. A superposition of a DC voltage having an oscillating voltage of a desired potential and an AC voltage having a peak-to-peak voltage that is at least twice the charging start voltage of the electrostatic latent image carrier when the DC voltage is applied to the charging member. The image forming apparatus according to claim 1, wherein the image forming apparatus is a voltage.