JP3282190B2 - Image forming method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming method in a copying machine, a printer or the like, and more particularly to an image forming method using a contact charging device.

[0002]

2. Description of the Related Art In image formation by an electrophotographic method, a charging device for uniformly charging the surface of an electrostatic latent image carrier is used. Such charging devices are roughly classified into a corona charging device and a contact charging device. Examples of the contact charging device include a fixed or rotating brush charging device, a roller charging device, a blade charging device, a magnetic brush charging device, and the like. It has been known.

By the way, in the image formation by the electrophotographic system, in a developing device or the like, in addition to the toner charged to the original charging polarity, toner fragments charged to the opposite polarity may be generated. Further, shavings of the electrostatic latent image carrier having a polarity opposite to the original charge polarity of the toner may be generated. For example, when a contact-type charging device is used for a device for charging the surface of an electrostatic latent image carrier before forming an electrostatic latent image,
Such toner debris of the opposite polarity, shavings of the electrostatic latent image carrier, and the like adhere to the charging device, and as a result, poor charging occurs, and, in turn, image noise called brush streak noise occurs. Further, the life of the charging device is also reduced.

As a means for solving this problem, Japanese Patent Publication No. Sho 6
Japanese Patent Application Laid-Open No. 3-43750 discloses that during charging, a voltage including a DC component having the same polarity as the charging polarity of the electrostatic latent image carrier is applied to the charging device, and the polarity is opposite to the charging polarity of the electrostatic latent image carrier during non-charging. The method teaches that a voltage containing a DC component is applied to transfer fine dust adhering to the charging device to the electrostatic latent image carrier and thereby remove it. Japanese Patent Application Laid-Open No. 58-42067 teaches, as a similar technique, inverting the voltage applied to the charging brush when the photosensitive member passes through the non-image area.

Japanese Utility Model Laid-Open No. 57-65347 discloses that
It teaches that dirt adhering to the charging roller is removed by a roller that rotates in reverse in contact with the charging roller.

[0006]

However, according to the prior art disclosed in JP-B-63-43750 and JP-A-58-42067, in order to remove fine powder stains attached to a contact-type charging device. Therefore, the surface of the electrostatic latent image carrier is charged with a polarity opposite to its original charge polarity, and the charges of the opposite polarity at that time are accumulated on the surface or inside of the electrostatic latent image carrier, and as a result, When the surface of the electrostatic latent image carrier is charged to the original charge polarity during the next image formation, the charge cancels the original charge, and the charge amount decreases and uneven charging occurs. There is.

In the method disclosed in Japanese Utility Model Laid-Open No. 57-34747, the structure of the apparatus becomes large and the cost is increased. Therefore, the present invention relates to an electrophotographic image forming method using a contact-type charging device, wherein the fine powder stains adhered to the contact-type charging device are reduced in the amount of charge on the surface of the electrostatic latent image carrier, or uneven charging. It is an object of the present invention to make it possible to easily remove the problem without causing inconvenience such as generation of a problem.

[0008]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a contact type charging device for charging an electrostatic latent image carrier, and inverting an electrostatic latent image formed on the surface of the electrostatic latent image carrier. Present
A developing device for forming a toner image by forming an image and a transfer voltage.
Forming a charged area by charging a surface of an electrostatic latent image carrier by the contact-type charging device in an electrophotographic image forming method using a transfer device for transferring a toner image by adding
And applying a transfer voltage by the transfer device to the charging area.
Without contacting the contact-type charging device again, and applying a voltage having the same polarity as the surface potential of the charging area and an absolute value lower than the surface potential to the charging device at the time of re-contact.
There is provided an image forming method which comprises a degree.

In this specification, "voltage having the same polarity as the surface potential of the charging region by the contact-type charging device and having an absolute value lower than the surface potential" includes 0 V, that is, the ground potential. In this case, the charging of the electrostatic latent image carrier by the contact type charging device is, for example, 1 when the image carrier is a rotary type.
After the rotation, the applied voltage of the contact type charging device is switched to a voltage having an absolute value lower than the charging potential previously charged on the image carrier (including 0 volt), such as after one reciprocation when the image carrier is a reciprocating type. Do.

The contact-type charging device may be a rotary or fixed brush charging device, a roller charging device, a blade charging device, a magnetic brush charging device, a charging device using a film member, or the like. It is particularly effective for cleaning a brush-type charging device having a fibrous contact to which dirt is likely to adhere. In the image forming method according to the present invention, prior to
The electrostatic latent device which is not charged by the contact charging device.
During the passage of the image carrier surface, the surface of the electrostatic latent image carrier
Developing bar applied to the developing device so that the toner does not adhere.
The EAS may be switched.

[0011]

According to the image forming method of the present invention, the contact-type charging
The electrostatic latent image carrier is charged by the device, and is charged by the developing device.
Reverse development of the electrostatic latent image formed on the surface of the electrostatic latent image carrier
To form a toner image. Then, the transfer device
The toner image is transferred to a transfer material such as transfer paper by applying pressure.
In the reversal development, the polarity is the same as the charge potential of the electrostatic latent image carrier.
Is used for transferring the charged toner.
Transfer voltage negates the charged potential, and what is the polarity of the charged potential?
It is a voltage of the opposite polarity. When a regular charging voltage is applied to a contact-type charging device for removing stains for normal image formation, the absolute potential of the charging device is higher than the absolute potential of the surface of the electrostatic latent image carrier. Toner particles, shavings of the electrostatic latent image carrier, and the like, which are charged in a polarity opposite to the original charge polarity of the toner, adhere to the charging device. However, the surface of the electrostatic latent image carrier was charged by the contact-type charging device, and a voltage having the same polarity as the surface potential of the charged region and an absolute value lower than the surface potential was applied to the charged region. By contacting the contact type charging device again to remove the dirt,
Oppositely charged toner debris and the like attached to the contact type charging device migrate to the electrostatic latent image carrier side where the charged charge exists .
You. At this time, the transfer voltage by the transfer device is applied to the charging area.
The contact-type charging device does not
The charged area where the surface of the carrier is charged is
Contact-type band again without canceling the charged potential
Contact with the charging device and adhere to the contact charging device.
Stain that has been removed is reliably removed. Also, when cleaning the toner debris and the like from the contact charging device, the surface of the electrostatic latent image carrier is not charged with a polarity opposite to its normal charging polarity, so the surface of the electrostatic latent image carrier or the inside thereof is not charged. There is no accumulation of charge of the opposite polarity during the next image formation, and when a regular charging voltage is applied from the contact-type charging device in the next image formation, inconveniences such as a decrease in the charge amount and occurrence of uneven charging are caused. Absent.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an example of a printer for implementing the method of the present invention. This printer has a photosensitive drum 1 as an electrostatic latent image carrier at the center, and this drum is driven to rotate in the direction of arrow CW by driving means (not shown). Around the drum 1, a fixed brush charging device 2, a developing device 3, a transfer charger 4, a cleaning device 5, and an eraser 6 for erasing residual charges are sequentially arranged.

An optical system 7 is disposed above the photosensitive drum 1. This optical system is provided in a housing 71 with a semiconductor laser generator, a polygon mirror, a toroidal lens, a half mirror, a spherical mirror, a folding mirror, and a reflection mirror. A mirror or the like is arranged so that image exposure can be performed on the photosensitive drum 1 from an exposure slit on the floor of the housing 71.

On the right side of the photosensitive drum 1 in the figure, a pair of timing rollers 81, a pair of intermediate rollers 82, and a sheet cassette 83 are provided.
Are sequentially arranged, and a paper feed roller 84 faces the paper feed cassette 83. A pair of fixing rollers 91 and a pair of discharge rollers 92 are sequentially arranged on the left side of the photosensitive drum 1 in the drawing, and a discharge tray 93 faces the pair of discharge rollers 92.

The system speed of the printer (the peripheral speed of the photosensitive drum 1) is 3.5 cm / sec. The diameter of the photosensitive drum 1 is 30 mm. Therefore, one rotation of the drum 1 requires 2.7 seconds. The charging device 2 is shown in FIG.
As shown in FIG. 3, the power supply 220 is connected to the power supply 220 via the switch 210 or grounded. The voltage Vc applied to the charging device 2 is Vc = -1.1K when the power supply 220 is used.
V and Vc = 0 V when grounded. The developing device 3 is a contact-type developing device using a one-component developer. As shown in FIG.
To the power supply 32 or 33. The bias voltage Vb applied to the developing device is Vb = −250 V when the power supply 32 is used, and Vb = + 1 when the power supply 33 is used.
00V. This developing device 3 is used for normal image formation.
When the developing bias Vb = −250 V is applied, the drum 1
Reversal development is performed with a toner having the same charging polarity as the charging polarity.

As shown in FIG. 2C, the transfer charger 4 is connected to a power supply 42 via a switch 41 or is grounded. The voltage V _T applied to the transfer charger 4 is V _T = + 6.5 KV when the power supply 42 is used to transfer the toner image on the photoconductor onto the transfer paper, and V _T = 0 V when grounded. FIG. 3 is a block diagram showing the main points of the control circuit of the printer. This control circuit mainly includes a microprocessor CPU1 including a read-only memory ROM and a random access memory RAM, and the operation of the entire printer is controlled by the microprocessor CPU1.

The microprocessor CPU 1 has a rotation control unit 10a for the photosensitive drum 1, a control unit 10b for the transfer charger 4, a control unit 10c for the charging device 2, a development bias control unit 10d and others via the interface circuit I / O. Is connected, and further, a print command input unit 10f is connected. Microprocessor C
The processing program of PU1 is stored in the memory ROM in advance. The print command input unit 10f has a function of receiving a printer control signal from an external computer CP such as a personal computer and sending the signal to the microprocessor CPU1.

Further, since the memory ROM is input print command, time to time / stop start rotating the photosensitive drum 1, the time for switching the time / voltage V _T to apply a voltage V _T to the transfer charger 4 / time to turn off the voltage V _T, the charging device time to off-time / voltage Vc for switching time / voltage Vc and voltage Vc is applied to the 2, switches the time / voltage Vb applied to the developing bias Vb time / voltage V
The time for turning off b is stored in advance, and based on the time, an on / off / switch switching signal is transmitted via the interface I / O to the photoconductor rotation control unit 10a, the transfer charger control unit 10b, and the charging device control unit 10c. Are output to the developing bias controller 10d. Therefore, switching of the applied voltage Vc to the charging device 2 is performed by an instruction from the control unit 10c, and switching of the developing bias Vb to the developing device 3 is performed by an instruction of the control unit 10d.
Switching of _T is performed according to an instruction from the control unit 10b.

Also, the microprocessor CPU1 has:
An operation panel 10g is also connected, and a print key K for permitting the start of printing is mounted on this panel. In this example, the photoconductor drum 1 has a charge generation layer containing a τ-type metal-free phthalocyanine and a polyvinyl butyral resin formed on a cylindrical aluminum substrate having an outer diameter of 30 mm and a length of 240 mm, and a hydrazone compound and This is a negatively-charged function-separated organic photoreceptor having a charge transport layer containing a polycarbonate resin and having sensitivity to long wavelength light.

The toner used in the developing device 3 is a polyester-based negatively charged toner having an average particle diameter of 10 μm and a distribution of 80% by weight in a particle diameter range of 7 to 13 μm. The fixed type brush charging device 2 is shown in FIG. 4 and has a thickness of 6 denier containing 18 wt% of conductive carbon powder with respect to the total weight, and an electric resistance of 1 × 10 ⁵ Ωcm.
The conductive rayon fiber 21 is a bundle of 100 fibers.
W-woven on the warp of the base fabric 22 having a thickness of about 1 mm,
And 5000 / cm ^2, in which further coated with a conductive adhesive to the back surface of the base fabric 22, is formed by fixing the base fabric 22 to an aluminum back plate 23. Length L of brush part 20 = 240 mm, width W = 10
mm and height H = 5 mm.

According to this printer, in normal image formation, the surface of the photosensitive drum 1 is uniformly charged to a predetermined potential by the charging device 2 connected to the power supply 220, and the charged area is image-exposed from the optical system 7 to the charged area. Thus, an electrostatic latent image is formed. The electrostatic latent image thus formed is developed by the developing device 3 to become a toner image, and moves to a transfer area facing the transfer charger 4.

On the other hand, from the paper feed cassette 83 to the paper feed roller 8
The transfer paper is pulled out by 4 and reaches the timing roller pair 81 via the intermediate roller pair 82, where it is sent to the transfer area in synchronization with the toner image on the drum 1. Thus, in the transfer area, the toner image on the drum 1 is transferred onto the transfer paper by the action of the transfer roller 40, reaches the fixing roller 91, where the toner image is fixed, and is discharged by the discharge roller pair 92. The sheet is discharged to the paper tray 93.

However, the method of the present invention is carried out as follows at the timing shown in the timing chart of FIG.
First, after the printer receives the ON state of the print key K and the print command (1) from the external computer CP, the rotation of the photosensitive drum 1 is started (2). Thereafter, a voltage Vc = -1.1 KV is applied to the contact charging device 2 (3).
Then, the drum 1 is charged. Normally, the developing bias Vb is set to +100 V so that the developing is not performed even when the drum 1 has zero potential and passes through the surface.
It is switched to b = -250V (4). V _T = + 6.5 KV so that the transfer operation can be performed on the transfer charger 4.
Is applied (5).

A hatched line (for example, a line indicated by (ヲ)) shown in the timing chart indicates a time when one point of the drum 1 passes over each element (charging, developing, and transfer device) when attention is paid to the point. It is connected by a straight line. Also, (A)
The portion is charged but not affected by the transfer charger 4.

Now, (6), (8), (9), (11)
Charging as, transfer, applied voltage Vc of the devices, by switching the T _T, a. A portion which is negatively charged but is not affected by the transfer charger 4 (therefore, a negatively charged portion) (a) is formed. b. The portion (a) after the portion (a) on the drum 1 has made one rotation is negatively charged, and the contact charging device 2 applied with 0 V comes into contact therewith. At this time, the positively charged dirt attached to the brush of the charging device 2
The electric field works in the direction to move to. Thus, brush dirt is cleaned. FIG. 6 shows a state in which the positive polarity contamination in the charging device 2 moves onto the drum 1 by setting Vc = 0V.

In (7) and (10), the developing bias is switched so that the toner does not adhere to the drum 1 when the charging by the apparatus 2 is not performed. In the case of performing continuous printing, the charging device 2 can be operated even after the continuous printing is completed.
Vc = -1.1 KV is applied to form a portion (c) which is negatively charged but is not affected by the transfer charger 4 (thus a negatively charged portion). (C) The part (d) after one rotation is in a negatively charged state, and the contact charging device 2 to which 0 V is applied is brought into contact therewith to clean the device 2.

In this way, since the dirt attached to the charging device 2 is removed, it is possible to prevent the stripe-shaped charging failure due to the dirt inherent to the contact type charging device. As explained above,
Switching between the voltages applied to the charging device 2 and the transfer charger 4 to remove dirt from the charging device 2, and to repeat two-sheet intermittent printing (two continuous printings and a pause, two continuous printings and a pause) ), After printing 5000 sheets, evaluation of streak noise was good.

The evaluation of the streak noise is performed in order to evaluate whether or not the fine powder dirt in the brush charging device 2 has been successfully removed. That is, in the charging device 2, if there is fine dust on the brush bristles, charging unevenness occurs on the surface of the photosensitive drum 1 in a direction perpendicular to the traveling direction. Even after the exposure, the charge unevenness remains as unevenness of the potential (Vi) after the image exposure. That is, a portion having a partially high potential out of the potential (Vo) immediately after being charged by the charging device also has a partially high potential after image exposure (Vi).

When the reversal development is performed, a larger amount of toner adheres to the lower Vi portion. That is, Vo unevenness is caused by Vi unevenness, and finally, image unevenness, that is,
It becomes streak noise. Therefore, the evaluation of the removal of fine dust and dirt on the charging device 2 is performed by evaluating the streak noise. The streak noise was evaluated by the following method. FIG.
Vc = -1.1 KV on the drum 1
Then, a repetition pattern of 2 dots on (lighting) and 2 dots off (light off) is written in the main scanning direction by laser. The same 2-dot ON (lighting) is also applied to the sub-inspection direction.
The laser extinguishing timing is adjusted so that a dot-off (extinguishing) writing pattern is obtained. Thereafter, through a reversal development, transfer and fixing processes, a print image as shown in FIG. 7 was obtained.

[0030] The maximum width of the main scanning direction of the minimum solid black pattern of two dots × 2 dots on the image and W _M.
W of 30 minimal black solid patterns continuous in the main scanning direction
The standard deviation of _M was σ, and the streak noise was ranked according to the value of σ as follows. Standard deviation σ Evaluation symbol 10 μm ≦ σ <30 μm ○ 30 μm ≦ σ × In the evaluation, a mark “○” indicates a state where no streak noise exists or can be neglected, and a mark “X” indicates a state where there is a streak noise which cannot be ignored I have. That is, when σ is large, it means that the width of the fine black solid in the main scanning direction largely varies in the main scanning direction.

In this embodiment, the evaluation of the streak noise after the printing of 5000 sheets was good (「). In the comparative examples described below, the meanings of “O” and “X” in the evaluation of streak noise are the same as those of the present example. As a comparative example, using the printer shown in FIG. 1, switch the voltage Vc, the voltage V _T applied to the transfer charger 4 to be applied to the contact charging device 2 at the timing shown in FIG.

In this comparative example, the conditions (a), (a), (c) and (d) in the timing chart of the embodiment of FIG. That is, the voltage of the charging device 2 and the charging device 4 is not switched between the images, and the photosensitive drum is not rotated after the switching of the voltage applied to the charging device after the continuous printing. After 5000 sheets of two intermittent prints under these conditions, the evaluation of streak noise was "x" (poor).

In the above embodiment, when the optical erase is performed by the eraser 6, it is necessary to pay attention to the timing of turning on and off the light. That is, it is necessary to turn off the optical erase only at that time so as not to erase the electric charge previously charged on the electrostatic latent image carrier for cleaning the contact charging device. The present invention is not limited to the above embodiments, but can be implemented in various other modes.

The electrostatic latent image bearing member to which the present invention can be applied is not limited to the negatively charged photosensitive member, but may be applied to a positively charged photosensitive member. Further, not only a rotary type but also a reciprocating type can be considered. Furthermore, it is conceivable that the power supply is shared by making at least the switching timing (on / off) of the voltage applied to the charging device, the transfer device, and the developing device at the same time.

The switching of the developing bias may be performed as shown in the embodiment. However, the switching of the polarity of the developing bias and the switching of the voltage are determined by the characteristics of the developing device. Not a requirement. The bias switching is not limited to the negative polarity / positive polarity, but may be performed by any method such as negative polarity / negative polarity (voltage change), negative polarity / 0 V, and negative polarity / floating. In short, in order to save toner, it is desirable to prevent toner from adhering to the electrostatic latent image carrier at the time of cleaning the charging device.

AC may be superimposed on an image carrier charging device for cleaning the contact charging device. What is important is the reverse electric field region, whose presence determines the cleaning effect. The step of charging the electrostatic latent image carrier and cleaning the contact charging device is performed before starting printing, after printing, between printing and printing (between images), when the power of the image forming apparatus is turned on, and when jamming is performed. In addition, a means for monitoring the image quality may be provided, and the monitoring may be performed based on information from the means, or may be appropriately inserted by means for leaving the cleaning process to a user by a user switch or the like. Needless to say, the present invention is not limited to the above case.

[0037]

As described above, according to the present invention, in an electrophotographic image forming method using a contact-type charging device, fine dust adhered to the contact-type charging device is removed from the surface of the electrostatic latent image carrier. Can be easily removed without inconvenience such as lowering of the charge amount or generation of uneven charging.

[Brief description of the drawings]

FIG. 1 is a sectional view of an example of a printer used to carry out the method of the present invention.

FIG. 2A is an explanatory diagram of a voltage applying unit to a charging device, FIG. 2B is an explanatory diagram of a voltage applying unit to a developing sleeve, and FIG. 2C is an explanatory diagram of a voltage applying unit to a transfer charger.

FIG. 3 is a block diagram illustrating a main point of a control circuit of the printer in FIG. 1;

FIG. 4 is a perspective view of a charging device.

5 is a timing chart showing how the printer of FIG. 1 carries out the method of the present invention.

FIG. 6 is a diagram illustrating a state in which positively-charged dirt is transferred from a charging brush to a photosensitive drum.

FIG. 7 is a diagram showing an image pattern for performing image noise evaluation.

FIG. 8 is a timing chart showing a comparative example using the printer of FIG. 1;

[Explanation of symbols]

Reference Signs List 1 photosensitive drum 2 contact charging device Vc voltage applied to charging device 210 switch 220 power supply 3 developing device Vb voltage applied to developing device 31 switch 32, 33 power supply 4 transfer charger VT voltage applied to _T transfer device 41 switch 42 power supply

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Issei Osawa 2-3-1-13 Azuchicho, Chuo-ku, Osaka-shi Osaka International Building Minolta Camera Co., Ltd. (56) References JP-A-1-154175 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) G03G 15/02 G03G 15/16

Claims (2)

(57) [Claims] A contact charging device for charging an electrostatic latent image carrier, inverting an electrostatic latent image formed on the surface of the electrostatic latent image carrier;
Developing device to form toner image by developing and transfer voltage
The image forming method applied to an electrophotographic method using a transfer device for transferring the toner image to form a charging zone by charging the <br/> electrostatic latent image bearing member surface by the contact type charging device
And applying a transfer voltage by the transfer device to the charging area.
Without contacting the contact-type charging device again, and applying a voltage having the same polarity as the surface potential of the charging area and an absolute value lower than the surface potential to the charging device at the time of re-contact.
Image forming method, which comprises a degree. 2. The battery according to claim 1, wherein said charging device is charged by said contact charging device.
During the passage of the electrostatic latent image carrier surface,
The developing device so that toner does not adhere to the surface of the image carrier;
The image forming method according to claim 1, wherein a developing bias applied to the image forming apparatus is switched .