JPH02129655A - Developing method - Google Patents

Abstract

PURPOSE:To prevent the ground of an image from being stained by making the absolute value of the potential of DC pulses applied to a developing roll small than the absolute value of the surface potential of a photosensitive body by a main corona discharge and larger than the absolute value of the surface potential of the photosensitive body irradiated with light after exposure. CONSTITUTION:The developing roll 4 is applied with the DC pulses and the potential of the DC pulses is smaller than the absolute value of the surface potential of the photosensitive body 1 by the main corona discharger 2 and larger than the absolute value of the surface potential of the photosensitive body 1 irradiated with light after exposure. Therefore, a developer which is charged electrostatically to the same polarity with the potential applied to the developing roll is possible transferred from the developing roll to the photosensitive body side, but never attracted from the photosensitive body 1 back to the developing roll 4. Consequently, a sharp image is obtained without such an state that the image becomes thin or has its stained ground.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a developing method suitable for use in, for example, electrostatic copying machines.

2. Description of the Related Art In a typical electrostatic copying machine, a photoreceptor drum (1), which is rotatably provided on the machine body, is driven to rotate around its rotation axis, and as the photoreceptor drum surface is charged by a discharger and exposed to light. Light is irradiated in the area to form an electrostatic latent image corresponding to the information to be recorded. The electrostatic latent image on the surface of the photoreceptor drum is developed into a toner image by a developing device, and the toner image is transferred to a recording paper in a transfer area near where a transfer discharger is provided. The recording paper after transfer is
The recording paper is transported by a transport device to a fixing device for fixing the toner image on the surface of the recording paper.

In such an electrostatic copying machine, as a method for converting an electrostatic latent image formed on the surface of a photoreceptor drum into a toner image, the following developing method has been proposed. Toner, which has both the property of attracting magnetism and the property of charging electricity, is carried by magnetic adhesion on the outer circumferential surface of the developing roller containing a piece of permanent magnet, and the developing roller is held at a constant level with the surface of the photoreceptor drum. Rotate while maintaining the interval. A power source is connected to the developing roller, and a predetermined negative voltage is applied to the developing roller, thereby charging the toner to the same polarity as the applied voltage.

The charged toner is transferred to the surface of the photoreceptor drum according to the potential difference between the potential of the electrostatic ftI image on the surface of the photoreceptor drum and the potential of the developing roller, and is electrostatically attracted to the electrostatic latent image to form a toner image. do.

FIG. 3 is a diagram showing the relationship between the potential on the surface of the photosensitive drum and the alternating current voltage AP applied to the developing roller in the above-described developing method. FIG. 3 (1) is a diagram schematically showing the potential distribution near the boundary between the image forming area where the surface of the photoreceptor drum is charged and irradiated with light by an exposure means and the non-image forming area where no light is irradiated. be. The surface of the photosensitive drum is uniformly charged to a potential of, for example, 1,600 μm by a corona discharger. At the portion where the surface of the charged photoreceptor drum is irradiated with light by the exposure means, the charge escapes from the photoreceptor drum through the body which is grounded in advance, for example -
An image forming section whose potential is increased to 50V is formed.

Figure 3 (2) shows the waveform applied to the developing roller of the AC voltage AP, in which there is a negative potential period W3 and a positive potential period W4 with respect to the ground potential QV, with time as the horizontal axis. It is a diagram. This AC voltage AP is, for example, a sine wave AC voltage, and the peak value of the period W4 having a positive potential is +7
00V, and the peak value during the negative potential period W3 is -70V.
It is 0V. Therefore, the peak-to-peak value is 1400V
A sinusoidal alternating current voltage AP of is applied to the developing roller.

The negative value of the AC voltage AP applied to the developing roller with respect to the image forming part charged to, for example, -50V and the non-image forming part charged to, for example, -600V, shown in FIG. 3(1): For example, the peak value of period W3 at around rL -700
In (2), the negatively charged toner is transferred and attracted to both the image forming area and the non-image forming area on the surface of the photoreceptor drum.

The potential of the image forming portion formed on the surface of the photoreceptor drum is, for example, 150 V, whereas the peak value of the negative potential period W3 of the AC voltage AP applied to the developing roller is 17 V.
It is 00■. Therefore, the negatively charged toner is transferred to the image forming area on the surface of the photoreceptor drum in an amount proportional to the potential difference of 650 cm. On the other hand, to the non-image forming area on the surface of the photoreceptor drum, one of the non-image forming areas is
The potential of 00■ and the peak value of the AC voltage AP of the developing roller -
In proportion to the potential difference of 100V from 700V, a smaller amount of negatively charged toner than the amount of toner transferred to the image forming section is transferred.

On the other hand, even if the peak value of the positive potential period W4 of the AC voltage AP currently applied to the roller is +700V,
The positively charged toner is transferred and attracted to both the image forming area and the non-image forming area on the surface of the photoreceptor drum. The potential of the image forming portion formed on the surface of the photosensitive drum is, for example, 150 cm, whereas the peak value of the positive potential period W4 of the AC voltage AP applied to the developing roller is +700 cm. Therefore, the positively charged toner is transferred to the image forming area on the surface of the photoreceptor drum in an amount proportional to the potential difference of 750 cm.

On the other hand, the non-image forming area on the surface of the photoreceptor drum receives the image forming part in proportion to the potential difference of 1300 V between the potential of 1600 mm of the non-image forming area and the peak value of the AC voltage AP of the developing roller +700 mm. A larger amount of positively charged toner than the amount of toner transferred to the area is transferred.

Problems to be Solved by the Invention In the conventional developing method in which such an alternating current voltage is applied to the developing roller, for example, when the surface of the photoreceptor is charged to a negative potential and an electrostatic latent image is formed, the developing Some of the negatively charged toner in the toner image that is attracted to the surface of the photosensitive book and developed during the period when the AC voltage applied to the roller is at a negative potential is not developed during the period when the AC voltage is at a positive potential. The toner is pulled back toward the roller, and the toner density in the image forming area becomes thin. Therefore, the resulting image will be one-of-a-kind.

In particular, during the positive potential period of the AC pulse applied to the developing roller, more toner is transferred and adsorbed to the non-image forming area than the image forming area, causing stains on the background of the image. , Yo. Furthermore, a large amount of toner is adsorbed to the periphery of the image forming area where toner adheres to the surface of the photoreceptor in a so-called "solid black" pattern, resulting in an image where the periphery is emphasized. Put it away.

An object of the present invention is to solve the above-mentioned problems of the prior art, and to prevent the developer adsorbed on the surface of the photoreceptor from being pulled back toward the developing roller by the voltage applied to the developing roller, and to form an image. The electrostatic charge eliminates the undesirable situation in which more developer is adsorbed in the non-image forming areas than in the non-image forming areas, resulting in stains on the background of the image, and the resulting image is fine and has clear outlines. An object of the present invention is to provide a method for developing a latent image.

Another object of the present invention is to prevent the absolute value of the potential charged on the surface of the photoreceptor by the discharger from becoming sufficiently high due to deterioration of the photoreceptor due to continuous use on land for a long time.
It is an object of the present invention to provide a developing method that does not cause undesirable situations such as so-called "fogging", such as staining of the base of an image, and has a margin for "fogging".

Means for Solving the Problems The present invention provides a method for charging an 8-photo member in advance with a main corona discharger, and then exposing it to light to form an electrostatic latent image on the surface of the photoreceptor.
In a developing method in which development is then carried out using the developer carried on the outer circumferential surface of the developing roller, a DC power source that applies a DC pulse is connected to the developing roller, and the absolute value of the potential of this DC pulse is determined by the main corona. This developing method is characterized in that the absolute value of the surface potential of the photoreceptor is selected to be smaller than the absolute value of the surface potential of the photoreceptor produced by the discharger, and larger than the absolute value of the surface potential of the photoreceptor irradiated with the light after exposure.

Function According to the present invention, a DC pulse is applied to the developing roller, and the absolute value of the potential of this DC pulse is smaller than the absolute value of the surface potential of the photoreceptor due to the main corona discharger, and the is selected to be larger than the absolute value of the potential of the irradiated surface of the photoreceptor.

Therefore, for the entire range of voltage amplitude of the DC pulse applied to the developing roller, even if the developer charged to the same polarity as the potential applied to the developing roller is transferred from the developing roller to the photoreceptor, A situation where the developing roller side is pulled back from the body side does not occur. Furthermore, the developer is transferred and adsorbed only to the image forming area formed on the surface of the photoreceptor by the DC pulse applied to the developing roller, and the developer is not transferred or adsorbed to the non-image forming area.

As a result, a clear image can be obtained without causing undesirable situations such as the image becoming thinner or the base of the image becoming dirty. Furthermore, since the direct current applied to the developing roller is applied in a pulsed manner, the developer is densely adsorbed on the surface of the photoreceptor, resulting in fine image quality and clear outlines of the image.

Embodiment FIG. 1 is a diagram showing a basic configuration for carrying out a developing method which is an embodiment of the present invention. The photoreceptor 1 is constructed by forming a photosensitive layer of a photoconductive material such as amorphous selenium on the surface of a right cylindrical base made of a material such as aluminum. By grounding the base of the photoreceptor 1 to a machine such as a copying machine in advance, the base of the photoreceptor 1 is set equal to the ground potential OV.

As the photoreceptor 1 grounded to the machine body is rotated around its rotation axis, the surface of the photoreceptor 1 is uniformly charged to a potential of Vo by the main corona discharger 2, and the exposure means 3
For example, laser light is scanned and irradiated onto the surface of the photoreceptor 1, thereby forming an electrostatic latent image corresponding to the image to be recorded.

This electrostatic latent image on the surface of the photoreceptor 1 is formed at an image forming area where the potential is increased to, for example, V when laser light is irradiated, and when it is charged by the main corona discharger 2 without being irradiated with laser light. It consists of a non-magnetic acid moiety held at a potential of .

The electrostatic latent image formed on the surface of the photoreceptor 1 is driven to rotate about a rotation axis 1', J parallel to the rotation axis of the photoreceptor 1, and is arranged at a distance d from the surface of the photoreceptor 1. The image is visualized by the developer carried on the surface of the developing roller 4. Thereafter, the image is transferred onto the surface of the recording paper by a transfer/withdrawal device (not shown), and the recording paper is conveyed to a fixing device (not shown).

The developing roller 4 is constructed by enclosing a permanent magnet piece magnetized with a plurality of magnetic poles for magnetically adhering and supporting the developer on the outer surface of the sleeve, in a right cylindrical sleeve made of, for example, aluminum. be done.

The sleeve of the developing roller 4 includes a DC pulse generating means PG.
is connected. The DC pulse generating means PG consists of a switching means SW and a DC power supply 9.10. DC power supply 9
．． For example, the electromotive force of 10 is 100V and 600V, respectively.
It is. The sleeve of the developing roller 4 is connected via a line 11 to a common contact 8 of the switching means SW. This switching means SW has two individual contacts 6 and 7, and one individual contact 6 is connected to the negative electrode of a DC power supply 10. The positive electrode of the power source 10 is grounded to the aircraft body. Another individual contact 7 is connected to the negative electrode of the DC power supply 9. The positive electrode of the power source 9 is also grounded to the fuselage. Therefore, the DC power supply 9 is V a I with respect to the aircraft.

A potential of =-100 (V) is applied to the individual contact 7, and the DC power supply 10 applies a potential of =-600 (V) to the individual contact 6. The switching mode of the switching means SW is controlled by the control circuit 5.

The switching means SW of the DC pulse generating means PG having such a configuration is controlled by the control circuit 5 to switch the state in which the common contact 8 is electrically connected to the individual contacts 6 to the state in which the common contacts 8 are electrically connected to the individual contacts 7, and further to the state in which the common contacts 8 are electrically connected to the individual contacts 7. From individual contact 6
By performing a switching operation in which the conduction state is switched at a cycle of, for example, 1 kHz to 2 kHz, a DC pulse DP whose voltage waveform changes at one polarity, for example, a negative potential, as shown in FIG. 2 (2), is generated. can get. Therefore, there is a line 1 on the sleeve of the developing roller 4.
DC pulse DP with a period of 1 kHz to 2 kHz through 1
is applied. In this way, the sleeve of the developing roller 4 is energized with power in the range of -600V to -1100V, so
The developer carried on the outer surface of the sleeve of the developing roller 4 is negatively charged by a permanent magnet piece included in the developing roller 4 .

The surface of the photoreceptor 1 is uniformly exposed to Vo by the main corona discharger 2.
potential, for example V. --Charged to -650 (V).

The portion of the surface of the charged photoreceptor 1 that is irradiated with laser light by the exposure means 3 has a potential of VL, for example, V, = -50.
The potential rises to (V) to form an image forming area, while the part that is not irradiated with laser light is V, -1650
A non-image forming area is formed which is maintained at a potential of (V). According to the electrostatic latent image formed corresponding to the image to be recorded in this way and the DC pulse DP applied to the working roller 4,
The negatively charged developer is not electrostatically attracted to the non-image forming area, but is electrostatically attracted only to the image forming area, and visualization is performed.

FIG. 2 is a diagram showing the relationship between the potential on the surface of the photoreceptor 1 and the DC pulse DP applied to the developing roller 4 in a developing method according to an embodiment of the present invention. Figure 2 (1) shows the photoreceptor 1
is charged by the main corona discharger 2 and irradiated with laser light by the exposure means 3, so that the potential becomes, for example, V, = -5.
The potential distribution near the boundary between the image forming area, which has risen to 0 (V), and the non-image forming area, which is not irradiated with laser light and is maintained at a potential of -650 (V), is simply shown. It is a diagram. FIG. 2(2) is a diagram showing the waveform of the DC pulse DP generated by the DC pulse generating means PG described in connection with FIG. 1 and applied to the developing roller 4, with time plotted on the horizontal axis.

The surface of the photoreceptor 1 is uniformly set to a potential of Vo, for example ■, by the main corona discharger 2. --Charged to a potential of 650 (V). In the image forming section where the surface of the charged photoreceptor 1 is irradiated with, for example, laser light by the exposure means 3, the charges escape to the base of the photoreceptor 1 which is grounded to the machine body, and the potential of VL is increased.
For example, the potential increases to 50 (V). In this way, the potential ■ is charged by the main corona discharger 2 without being irradiated with laser light. The vicinity of the boundary between the non-image forming portion holding the image forming portion and the image forming portion exhibits the potential distribution shown in No. 211J(1).

The surface of the developing roller 4 carries a developer, and the first
A DC pulse DP in the form shown in FIG. 2(2) generated by the DC pulse generating means PG explained with reference to the figure is applied. Therefore, the developer on the surface of the developing roller 4 is also charged to the same polarity as the potential of the DC pulse DP.

The DC pulse DP is generated by switching the switching means SW of the DC pulse generating means PG at a cycle of, for example, 1 kHz to 2 kHz, so that the DC pulse DP has a period of Wl, which is an applied potential of 1, and a period of V+al. It is formed as a DC square wave with a period (Wl+W2) having alternating periods of W2, which is an applied potential of . Periods W1 and W2 are, for example, W1=W2
chosen for the relationship.

As mentioned above, the potential given by the DC power supply 10 ■1. V is, for example, V, , = -600 (V), and potential ■, - is, for example, V, given by the DC power supply 9.
, , --100 (V), respectively. As a result, the potential of the non-image forming part of the electrostatic latent image formed on the surface of the photoreceptor 1 is increased. absolute value vol and the potential V II a during the period W1 of the DC pulse DP applied to the developing roller 4
The difference between the absolute value of K and the absolute value IV, , l is Δ■-1■. I-IV,
,,l are set, for example, to Δ■-50 (V). This difference Δ■ is a potential difference set as a margin for so-called fog J, as will be described later.

As the photoreceptor 1 is rotationally driven, an electrostatic latent image formed on the surface of the photoreceptor 1 consisting of an image forming area and a non-image forming area carries developer on the surface and Figure 2 (2
) comes closest to the developing roller 4, which is rotated while being applied with a DC pulse DP having a waveform shown in FIG. In this transfer region, the developer carried on the surface of the developing roller 4 is transferred from the surface of the developing roller 4 to the photosensitive material according to the DC pulse DP applied to the surface of the developing roller 4 and the potential distribution of the electrostatic latent image on the surface of the photoreceptor 1. The electrostatic layer on the surface of the body 1 (transfers to the image forming part of the elephant and is attracted to it to form an image).

During the period W1 of the DC pulse DP applied to the developing roller 4, the potential of the image forming portion of the electrostatic latent image VL=s
The developer is transferred from the surface of the developing roller 4 to the surface of the photoreceptor 1 due to the potential difference between o (V) and V, . . . =-600 (V). Also in period W2, V L = -50 (V
) and V, , , = -100 (V), a relatively small amount of current (1 agent) is transferred compared to period W1. In this way, during both periods W1 and W2 of DC pulse DP, The developer is attracted to the image forming area on the photosensitive!*1 surface and forms an image.

On the other hand, the potential of the non-image forming part is Vo=650 (■), and the potential V in either period W1 or W2 of the DC pulse DP is
,,,=-600(V),V,,,=-100(V)
lower than. Therefore, the developer charged to the same negative polarity as the potential of the DC pulse DP is not attracted to the non-image forming area of the electrostatic latent image on the surface of the photoreceptor 1. Since the developer is adsorbed only to the image forming area and not to the non-image forming area, it is possible to obtain a clear image without background stains.

According to the research conducted by the present inventor, the following has been clarified. If the direct current applied to the developing roller 4 is constant and constant, the amount of developer adsorbed to the surface of the photoreceptor 1 will not be uniform when converting the electrostatic latent image into a ticket image, resulting in an uneven image. It gets rough. Furthermore, the contours that are the boundaries of the image become rough, and the clarity of the image is lost.

On the other hand, as described in the embodiment of the present invention, the developing roller 4 has a potential difference between the potential of the image forming part of the electrostatic latent image formed on the surface of the photoreceptor 1 and the non-image forming part. For example, a direct current pulse DP shown in FIG. 2 (2) is applied, which changes at the same potential as the potential of the part.

As a result, the electrostatic latent image is closely adsorbed, resulting in fine image quality and clear outlines of the image.

Furthermore, in the developing method of the present invention, it is possible to prevent staining of the image base, which is so-called "fogging", in which the developer adheres to the non-image forming portions 4 of the electrostatic latent image. That is, the potential (11) at which the absolute χ↑ value of the potential VL of the image forming area on the surface of the photoreceptor 1, the potential Vu of the non-image forming area, and the DC pulse DP applied to the developing roller 4 is the minimum. Regarding the potential V1□8 with the maximum absolute value, V
The values of O, V 1°V B @ y and V L are mutually set.

V, < V 1, < V,,,
< V 0 if V, = -50 (V)
,V,1. --100 (V), V, , = -600(
V), V. =-650 (■).

The developer charged to the same polarity as the potential applied to the developing roller 4 is expressed as (IV-+--l vt,
The developer is transferred from the surface of the developing roller 4 to the image forming area on the surface of the photoreceptor 1 and is attracted thereto in proportion to the value of 1 ) to (IV,, □! -IVLl >) and the amount of electricity charged to the developer.

And 1■. 1 and IVl,. When the difference from 1 is defined as Δ■, the following relationship holds true as is clear from the first equation.

ΔV= l Vol −1v,,,! −(2
)ΔV>O...(3) Therefore, from the first equation or the third equation, IV, .

<IV. There is a relationship of 1, V m I n or ■,
, 8 will not be transferred to the non-image forming area where the absolute value of the potential IV01 is larger than that of the developer.

By the way, when the photoreceptor 1 is used continuously for a long time, a phenomenon called deterioration of the photoreceptor occurs. When the photoreceptor 1 deteriorates, the potential v0 to be charged by the main corona discharger 2 becomes, for example, ■. Due to deterioration, what should be V = -650 (V) becomes, for example, V'' = -620 (V), or even V''.

= -610 (V) or the like.

Conventionally, this deterioration of the photoreceptor caused the background of the image to become stained.

However, in the developing method of the present invention, the potential V0■, 1.
is set so that it satisfies the relationship of the first or third equation, so that the background stain of the image is prevented.

For example, the surface of the photoreceptor 1 is brought to a potential ■ by the main corona discharger 2. = -650 (V), whereas
The potential Vs1 at which the absolute value of the DC pulse DP applied to the developing roller 4 is maximum is expressed by the relationship 1v-8I<lV, l
For example, V, . . . =-600 (V) is selected so as to satisfy the following. As a result, a potential difference of ΔV=50 (V), for example, is set between Vo and Vl-. This potential difference Δ■
This is used as a margin against the so-called "fogging", which is a stain on the background of an image.

The potential on the surface of the photoreceptor 1 is set by a corona discharger before exposure.

For example, even if the potential does not become sufficiently low to the desired V, -650 (V), as long as the fog margin Δ■ is kept at a positive value, that is, lV, , l is kept smaller than IVo. Since the developer charged to the same polarity as the potential of , V, , (or V, , ) does not transfer to the non-image forming area where the absolute value of the potential IV, l is larger than that, the non-image forming area An undesirable situation in which developer is adsorbed to the area does not occur.

Therefore, the developing method of the present invention can deal with the deterioration of the photoreceptor 1 with a margin, and even a slight deterioration of the photoreceptor 1 will not cause the background stain of the image, and a clear image can be developed.

As another embodiment of the present invention, it is also possible to set the potentials of the DC pulses applied to the electrostatic latent image on the surface of the photoreceptor 1 and the developing roller 4 to be all positive polarity potentials. Further, the absolute value of the potential of the DC pulse applied to the developing roller 4 is smaller than the absolute value of the surface potential of the photoreceptor 1 due to the main corona discharger, and the surface of the photoreceptor irradiated with the light after exposure is As long as the pulse has a mode selected to be larger than the absolute value of the electric potential, it may be a DC pulse with another appropriately selected shape, such as a sine wave or a sawtooth wave.

The developing method of the present invention can be suitably implemented not only in an electrostatic copying machine but also in a printer that prints an image signal output from a computer or the like.

Effects of the Invention According to the present invention, even though the charged developer is attracted to the image forming area on the surface of the photoreceptor, it is not attracted to the non-image forming area. Therefore, a clear image can be obtained without staining the background of the image.

Furthermore, the developer is finely adsorbed to the image forming area on the surface of the photoreceptor by the DC pulses applied to the developing roller, resulting in a fine image quality and an image with clear outlines.

Furthermore, according to the present invention, even if the photoconductor suffers from poor C, such as the absolute value of the potential on the photoconductor surface not being sufficiently high due to charging by the main corona discharger before exposure, the direct current pulse applied to the photoconductor Due to the pre-set "fogging" margin,
Adsorption of the developer to the non-image forming area of the electrostatic latent image is prevented, and a clear image without background stains can be obtained.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the basic configuration for carrying out the developing method which is an embodiment of the present invention, and FIG. 2 is a diagram showing the partial potential distribution on the surface of the photoreceptor 1 and the voltage applied to the developing roller 4 in the developing method of the present invention. FIG. 3 is a diagram showing the relationship between the partial potential distribution on the surface of the photoreceptor drum and the waveform of the AC pulse AP applied to the developing roller in a conventional developing method. It is. 1. Photoreceptor, 2. Main corona discharger, 3. Exposure means,
4...Developing roller, 5...Control circuit, 6.7...
Individual contact, 8...Common contact, 9, 10...DC power supply, AP...AC voltage, DP...DC pulse, L...
・Laser light, PG...DC pulse generation means, SW...
Switching means, ■. ...Potential of non-image forming area,■
,... Potential of the image forming section, V a a X... Potential with the maximum absolute value of the DC pulse DP, V a l R...
・Potential with the minimum absolute value of the DC pulse DP, Δ■... margin for "fogging" of the DC pulse DP, Wl... period of V 11 A X of the DC pulse DP, W2... ■ of the DC pulse DP ,,1 period agent Patent attorney Keiichi Nishikyo

Claims (1)

[Scope of Claims] A photoreceptor is charged in advance by a main corona discharger, and then exposed to light to form an electrostatic latent image on the surface of the photoreceptor, and then a developing image is carried on the outer peripheral surface of a developing roller. In a developing method in which development is performed using a developing agent, a DC power source that applies a DC pulse is connected to the developing roller, and the absolute value of the potential of this DC pulse is greater than the absolute value of the surface potential of the photoreceptor by the main corona discharger. A developing method characterized in that the absolute value of the surface potential of the photoreceptor is selected to be small and larger than the absolute value of the surface potential of the photoreceptor irradiated with the light after exposure.