JP2789480B2 - Image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Object of the Invention (Industrial Application Field) The present invention includes an image forming apparatus using an electrostatic transfer process, such as an electrostatic copying machine and a printer, and particularly includes a contact-type transfer unit. Related to an image forming apparatus.

(Technical Means for Solving the Problems, Its Operation) The running image carrier is pressed against the running image carrier and runs synchronously.
A transfer roller of contact type such as a transfer roller is provided, and a transfer material such as paper is inserted into a transfer portion formed by abutting both of them, and a transfer bias is applied to the transfer unit,
Therefore, an image forming apparatus configured to transfer a toner image electrostatically formed in advance on the image carrier side by the action of an electric field formed to a transfer material has been widely used in the past.

FIG. 9 is a schematic side view showing a typical example of such an image forming apparatus, having an axis in a direction perpendicular to the paper surface,
Runs at a peripheral speed of 23 mm / sec in the direction of the arrow X shown in the figure, with OP
The photosensitive member 1 having the C photosensitive layer formed thereon is uniformly negatively charged by a power supply via a charging roller, and then irradiated with an image-modulated laser beam 7 so that the potential of the portion is reduced. Attenuates to form an electrostatic latent image.

Then, the latent image is visualized by negatively charged toner supplied from the developing device 9 to become a toner image, and the toner image is transferred as a nip portion formed by the photosensitive member 1 and the transfer roller 2 pressed against the photosensitive member 1. When the toner arrives at the portion, the transfer material P is supplied to the transfer portion in time with the toner image, and at the same time, a transfer bias having a polarity opposite to that of the toner is applied to the transfer roller by the power supply 5. The toner image is transferred to the transfer material P.

In the illustrated apparatus, the transfer means has a medium resistance value (10 ⁶
1010 ¹³ Ω) transfer roller was used.

A transfer unit using such a contact-type transfer unit does not require a high-voltage power supply as compared with a transfer unit using a corona discharger that has been widely used in the past, and is therefore advantageous in terms of cost. Since there is no contamination, there is no obstacle due to the contamination, and since there is no generation of ozone or nitride due to high-pressure discharge, there are various advantages such as no deterioration of image quality due to these.

On the other hand, the relationship (VI characteristics) between the voltage applied to the transfer roller and the current flowing through the transfer roller is inevitable to fluctuate greatly due to environmental changes, which affects the transferability and always provides good transferability. The reality is that it is difficult to obtain a good quality image.

 This will be briefly described.

In a low-temperature and low-humidity environment (15 ° C, 10% RH, hereinafter referred to as L / L), the resistance value of the transfer roller is normal temperature and normal humidity (23 ° C, 64% RH,
(Hereinafter referred to as N / N).

Conversely, in a high-temperature and high-humidity environment (32 ° C., 85% RH, hereinafter referred to as “H / H”), the value is reduced by one to two digits compared to N / N.

The change in the VI characteristic due to such an environmental change will be described with reference to FIG.

In the same figure, the solid line indicates that the voltage applied to the charging roller 3 is turned on in both AC and DC during the non-sheet passing operation such as the pre-rotation and the sheet interval, and the broken line indicates the sheet feeding when the A4 size transfer material is present at the transfer portion. The relationship between the voltage applied to the transfer roller 2 and the current flowing through the transfer roller when the power is on (1400 V peak-to-peak AC voltage, -700 V DC) is shown for each environment.

In the case of the known apparatus as described above, a transfer current of 0.5 to 4 .mu.A is required during paper passing in order to perform good transfer. If the transfer current exceeds 5 .mu.A, a non-transfer It has been experimentally found that a memory of a positive potential remains in the paper portion, and fogging occurs in subsequent images, which leads to deterioration of image quality.

From this, it is understood that the appropriate transfer bias in the known apparatus is about 300 to 500 V for H / H, about 400 to 750 V for N / N, and about 1250 to 2000 V for L / L.

In such an apparatus, when a constant voltage control is performed on the transfer roller, a transfer failure occurs due to an environment, and a transfer memory occurs. When a constant current control is performed, a small transfer material having a width equal to or less than a maximum usable width is used. If there is a part where the photoconductor and the transfer roller are in direct contact as always when paper is not passed,
Most of the current flows through the low resistance portion, which may cause inconveniences such as poor transfer and occurrence of transfer memory.

In order to avoid such a drawback, in an image forming apparatus having the above-mentioned contact-type transfer means, the transfer means is controlled at a constant current during non-sheet passing such as during pre-rotation, and the voltage at this time is held. The present applicant has proposed a transfer bias control system in which the transfer unit is controlled at a constant voltage by a voltage obtained by multiplying the voltage by a predetermined coefficient R (R> 1) during paper passing.

This configuration has a certain effect in correcting defects such as transfer failure as described above due to environmental changes, but has the following problems.

That is, when the voltage is detected at the time of the constant current control, if the insulating means is present on the opposite surface of the photoreceptor of the transfer means and is contaminated, the resistance value of the corresponding part is increased and the voltage to be held is also increased. Therefore, the voltage for the next constant voltage control also increases.

Further, when the constant voltage control is performed at the time of paper passing, if the transfer unit is contaminated with the insulating toner, the resistance value of the corresponding portion is high, so that the current density in the other portion increases and the transfer material corresponding to the portion is increased. The above-mentioned electric charge becomes excessive and discharges to the photoreceptor side to reverse the polarity of the toner to prevent transfer to the transfer material, thereby causing local transfer failure.

According to an experiment, it has been found that when the amount of toner per unit area of the surface of the transfer means is 0.1 mgr / cm ² , the above transfer failure occurs when the transfer current exceeds 3.5 μA. Also,
As the amount of toner increases, the limit value of the transfer current that causes transfer failure gradually decreases, and the toner amount becomes 1.0 mgr / c.
In m ^2, and it generates a transfer failure at 2.5 .mu.A.

The present invention has been made in order to cope with the situation as described above. In an image forming apparatus having the above-described contact-type transfer unit, not only the environment but also the contamination of the transfer unit is reduced. Nevertheless, an object of the present invention is to provide an image forming apparatus capable of always performing good transfer and obtaining a high-quality image, and in particular, to provide the transfer apparatus.

(2) Configuration of the Invention (Technical Means for Solving the Problems, Action of the Invention) In order to achieve the above object, the present invention provides an image carrier,
A transfer member that forms a nip portion of the image carrier, and a transfer member that transfers a toner image on the image carrier to a transfer material sent to the nip portion; When the transfer material is not present, a voltage / current characteristic of the transfer member is detected, and a voltage applied to the transfer member at the time of image transfer to the transfer material is determined based on the characteristic. An image forming apparatus (1), wherein a voltage of the same polarity of the toner image is applied to the transfer member in order to form an electric field for transferring toner from the transfer member to the image bearing member, or The image forming apparatus according to the above (1), wherein the detection of the voltage-current characteristic is performed by applying a voltage having a reverse polarity of the toner image to the transfer member. (1) (2) The image forming apparatus according to (2), wherein the detection of the voltage-current characteristic is performed by detecting a voltage generated in the transfer member when the transfer member is controlled at a constant current. Alternatively, in the above (1) or (2), the detection of the voltage-current characteristic is performed by detecting a current flowing through the transfer member when the transfer member is controlled at a constant voltage. In the apparatus (4) or the apparatus described in the above (3), the voltage applied to the transfer member at the time of transferring an image to a transfer material is a factor R times the voltage generated at the transfer member when the constant current control is performed. R> 1)
In the image forming apparatus (5) or any one of the above (1) to (5), the transfer member is controlled at a constant voltage when transferring an image to a transfer material. In the image forming apparatus (6) or any one of the above (1) to (6), the apparatus includes an image forming unit that forms the toner image on the image carrier, and the image forming apparatus includes: The image forming apparatus (7), wherein the forming unit includes a charging unit that charges the image carrier to the same polarity as the toner image, or any of the above (1) to (7). In the image forming apparatus (8), wherein the transfer member has a roller shape, or in any one of the above (1) to (8), the image carrier includes an electrophotographic photosensitive layer. An image forming apparatus (9) characterized in that is there.

With this configuration, good transfer can be performed irrespective of the environment, and transfer failure due to dirt on the transfer means using toner can be prevented, so that good transfer performance can always be stably obtained.

(Description of Embodiment) FIG. 1 is a schematic side view of an image forming apparatus showing an embodiment of the present invention. The configuration of the image forming apparatus itself, the image forming process, and the like are not particularly different from those of the known apparatus. Corresponding parts are denoted by the same reference numerals, and description thereof will be omitted.

A point bias power supply 5 is connected to the transfer roller 2,
The power supply 5 includes a minus constant voltage power supply 51, a plus constant current power supply 52, a plus constant voltage power supply 53, and changeover switches 54 and 55 as shown in the figure.

With such a configuration, in the illustrated apparatus, a bias voltage having the same polarity as that of the toner is applied to the transfer roller 2 during non-sheet passing such as pre-rotation and between sheets, and the transfer roller 2 facing the photoreceptor 1 at this time. When the surface of the transfer roller again faces the photoconductor 1, the transfer roller is controlled with a constant current, and the voltage generated at the transfer roller at this time is multiplied by a predetermined coefficient, and the transfer roller is controlled at a constant voltage when the paper is passed. It shall be.

Specifically, the diameter of the core metal is 6 m as the transfer roller 2.
m, having an outer diameter of 20 mm and having a medium resistance value adjusted to a hardness of 25 to 35 ° (Asker C) by dispersing carbon in EPDM.

To measure the resistance value of the transfer roller, it was pressed against a rotatable conductive drum having a diameter of 30 mm with an axial length of 220 mm and a nip width of 3 mm, and the drum was rotated at 23 mm / sec to transfer the transfer roller thereto. Following, applying a voltage of 2 KV between the drum and the core metal, 10 ⁸ ~ 10 ⁹ Ω for L / L, 10 ⁷ ~ 1 for N / N
0 ⁸ Omega, was H / H In 10 ⁶ ~10 ⁷ Ω.

FIG. 2 is a graph showing VI characteristics when the above roller is used and the roller is not contaminated with toner.

The solid line in the figure shows the characteristics when both components of the charging roller 3 are turned on (AC voltage peak-to-peak voltage 1400 V, DC voltage -700 V) at the time of non-sheet passing such as during pre-rotation and between sheets.
The broken lines show the characteristics when the A4 size transfer paper is passed for each environment H / H, N / N, and L / L.

FIG. 3 shows a part of the operation sequence of the above-described device, particularly in the vicinity of the pre-rotation, and the operation of the device will be described.

When the main motor is turned on, the charging roller 3
A charging bias in which a DC voltage of -700 V is superimposed on an AC voltage of 1400 V between peak voltages is applied.

At the same time, the transfer roller 2 is connected to the negative constant voltage electric wire 51 by the switch 54, and a DC voltage of -800 V is applied to the roller for t _CLN = 13 seconds.

During this time, the toner on the surface of the transfer roller 2 is transferred to the photoreceptor 1 and the surface is cleaned.

After the start of the pre-rotation, the time for the transfer roller 2 to make one rotation T _R = 2.
After a lapse of 7 seconds, the transfer rollers 2 are
Is connected to a positive constant current power supply 52 and performs constant current control of 2 μA during T _CLN . During this time, since the surface of the transfer roller 2 facing the photoreceptor 1 has been cleaned,
The I characteristic is the same as in the case of FIG.

Under the H / H environment, a voltage of 250 V is generated on the transfer roller 2, a voltage of 400 V on the N / N, and a voltage of 1300 V on the L / L (the voltage at this time is V ₁ ).

Then, at the time of paper passing the transfer of the transfer roller 2 is connected to the positive constant voltage power supply, the voltage V ₂ multiplied by the coefficient R (R> 1) to the voltages V ₁ and subjected to constant-voltage controlled by the switch 54, 55 Shall do.

The illustrated Δt is a time corresponding to a deviation between the latent image forming position and the transfer position. The coefficient R is appropriately set in consideration of the ability of the photoconductor to correspond to the memory and the uniformity of the resistance of the transfer roller. In this case, R = 1.5.

Therefore, the voltage during paper passing is 375 V for H / H, 1 μA, N
/ N is 600 V, 1.3 μA, and L / L is 1950 V, 1.8 μA.

With this apparatus, transfer failure does not occur even if the transfer roller is contaminated with the insulating toner.

Also, by increasing the resistance value of the transfer roller, the coefficient R can be set to 1 by reducing the difference between the transfer voltage generated during non-sheet passing and the sheet passing during the constant current control. In this case, since the constant voltage control can be performed as it is at the voltage at the time of the constant current control, the sequence can be simplified.

10 ⁹ to 10 ¹⁰ Ω in N / L environment, N / N
When a transfer roller with a resistance value of 10 ⁸ to 10 ⁹ Ω and H / H of 10 ⁷ to 10 ⁸ Ω is used, the transfer roller generates a constant current control of 2.5 μA when paper is not passed. Voltage is L /
It becomes 1900V in L, 850V in N / N, and 500V in H / H. By applying this voltage at the time of paper, 1.7μA in L / L and 1.6 in N / N
A transfer current of 1.5 μA was obtained at μA and H / H, and good transferability was obtained in each case.

FIG. 4 is a sequence diagram showing another embodiment of the present invention. In the apparatus shown in FIG. 1, a negative constant voltage is applied to at least 75% of the peripheral length of the transfer roller 2 so that the surface of the transfer roller 2 can be controlled. clean the, when the charged portion of the photosensitive member 1 passes through the transfer portion, there in that for detecting the transfer roller voltages V ₁ by applying a positive constant current bias to the substantially circumferential length of the transfer roller.

Thereby, or there is a variation in the resistance in the circumferential direction of the transfer roller, even if there is contamination with toner, it is possible to prevent improper transfer by increasing the transfer roller voltage detection accuracy of the V ₁ of the time plus the constant current bias It becomes possible.

 The operation will be described with reference to FIG.

In the apparatus shown in FIG. 1, the pre-rotation starts when the main motor is turned on, and the same charging bias is applied to the charging roller 3 as described above.
Is connected to the minus constant voltage power supply 51 by the switch 54, and a DC voltage of -800 V is applied for a period _tCLN .

Then, after the start of the pre-rotation, the time t _CT required for the charged portion of the photoreceptor 1 to reach the transfer site (t _CT = 1.
After the lapse of 8 seconds), the switches 54 and 5 are turned on for a time T _R (T _R = 2.7 seconds in this apparatus) required for the transfer roller 2 to make one round.
According to 5, the transfer roller 2 is connected to a positive constant current power supply, and constant current control is performed at 2 μA. At this time, the average value of the voltage generated in the transfer roller 2 is measured.

Based on the above measurement, the toner amount on the transfer roller
/ cm ² , 0.3 mgr / cm ² , and 0.5 mgr / cm ² were performed by changing the length of t _CLN . In the case where t _CLN exceeds t _CT , the rising timing of the voltage applied to the charging roller 3 is delayed by Δt _c as shown in the sequence of FIG. Was measured as t _CLN = t _CT + Δt _{c so} that the potential of the opposing photosensitive member 1 becomes almost 0 V when is applied.

 FIG. 6 shows the measurement results under the H / H environment.

The horizontal axis in t _CLN / t _R in the figure shows the percentage of the cleaning portion by a negative constant voltage bias of the transfer roller, the vertical axis represents the transfer voltages V _1, respectively.

Toner amount ^{0.1mgr / cm 2, 0.3mgr / cm} 2, in any case of 0.5mgr / cm ^2, the ratio t _CLN / t _R is the transfer voltages V ₁ to be 0.75 or more substantially converged, soiled with toner If not
It is close to 250 V (see FIG. 2), indicating that there is no practical problem.

Although not shown, even under the N / N and L / L environment, t _CLN
/ t _R detection accuracy of the transfer voltages V ₁ by 0.75 and was found to be sufficient.

According to this embodiment, the same effect as that of the first embodiment can be obtained, and after the transfer roller 2 is cleaned under the condition of t _CLN / t _R ≧ 0.75, the opposing photosensitive member 1 becomes negatively charged. cleaning portions of the transfer roller if time has does not need to synchronize to be opposed to the photosensitive member 1, detects the occurrence voltages V ₁ when the positive constant current control for almost one rotation of the transfer roller The detection sequence can be simplified.

Further, only when the transfer roller is to be cleaned, the time required for cleaning can be reduced by rotating the transfer roller at a high speed.

FIG. 7 shows still another embodiment of the present invention, in which parts of the image forming apparatus corresponding to those of the above embodiment are denoted by the same reference numerals.

In this apparatus, the charging roller 3 on the surface of the photoreceptor 1 is
The distance l _CT to the transfer roller 2 from the outer periphery L of the transfer roller 2 is, are constituted so as to be l _CT ≧ 0.75 L.

In the case of the illustrated device, the photosensitive member 1 having a diameter of 30 mm and the transfer roller having a diameter of 16.6 mm is used. In this case, l _CT = 42 m
m, 0.75L = 39mm.

At the start of the pre-rotation, the charging roller 3 has a peak-to-peak voltage of 1400.
A DC voltage of -700 V is superimposed on V and AC, and a negative constant voltage bias of -800 V is applied to the transfer roller.

Since this apparatus satisfies the condition of l _CT ≧ 0.75L, the circumferential length of the photoconductor 1 passing through the transfer site at approximately 0V is at least 75% of the outer circumference of the transfer roller. Therefore, 75% or more of the outer circumference of the transfer roller can be cleaned.

Therefore, unlike the case of FIG. 5 described above, there is no need to apply the charging voltage to the charging roller 3 with a delay after the main motor is turned on, and the pre-rotation time can be shortened.

Further, when applying the manner of this embodiment initially the above-described embodiment to detect the transfer voltages V ₁ performs a positive constant current control for the cleaning portion of the transfer roller 2, because the clean more than 75% of the transfer roller periphery This makes it easy to set the timing for performing the plus constant current control.

In the above embodiment, constant current control was performed on the cleaned portion of the transfer roller in the non-sheet passing portion, and the voltage generated at the transfer roller was detected at this time. Control may be performed to estimate the resistance value of the transfer roller by detecting the transfer current. In this case, the transfer voltage at the time of paper passing may be calculated from the detected transfer current by an analog arithmetic circuit, by a computer, or by using a look-up table.

FIG. 8 shows still another embodiment of the present invention. Also in this case, parts corresponding to the above-described embodiments are denoted by the same reference numerals.

An electrode 8 is in contact with the transfer roller 2 on the side opposite to the photoreceptor 1, and a constant voltage power supply 6 is connected to the electrode 8.

The transfer roller 2 can be selectively connected to the current detecting means 11 and the power supply 5 by a switch 57. The current source 5 includes a minus constant voltage power supply 51, a plus constant voltage power supply 53, and a power supply. Switch 56 that is switched to and connected to
Is provided.

In the non-sheet passing portion, the switches 56 and 57 connect the transfer roller 2 to the negative constant voltage power supply 51, apply a constant voltage bias of -800V, and clean the surface.

When the cleaned portion of the transfer roller 2 faces the electrode 8, for example, −2 KV
A constant voltage bias (regardless of polarity) is applied, and the switch 57 is connected to the current detecting means 11 to detect the current.

The resistance value of the transfer roller 2 is calculated by an appropriate means such as a computer and a look-up table based on the current value, and constant voltage control is performed by the plus constant voltage power supply 53 with the transfer voltage.

In the case of this embodiment, the current flowing into the photoreceptor 1 becomes small when the resistance value of the transfer roller is calculated and estimated, so that the occurrence of transfer memory of the photoreceptor can be prevented, and the transfer roller can be cleaned. Since the time required for the portion to reach the position where the resistance value is calculated can be shortened, the control can be speeded up.

Further, in this embodiment, when calculating the resistance value of the transfer roller 2, the resistance value may be separated from the photoconductor 1 so that no current flows into the photoconductor.

As described above, the embodiment using the transfer roller as the transfer unit has been described. However, the present invention is not limited to this. For example, the present invention can be applied to another contact type transfer unit such as a transfer belt. Of course.

(3) Effects of the Invention As described above, the image carrier is provided with the transfer unit that is in pressure contact with the image carrier. When paper is not passed, the voltage-current characteristics of the transfer unit are detected, and the paper is passed based on the characteristics. In the image forming apparatus that controls the bias applied to the transfer unit at the time, when a sheet is not passed, a voltage having the same polarity as the charging polarity of the toner is once applied to the transfer unit to clean the transfer unit, and then the voltage-current characteristics thereof are changed. Since the detection is performed, good transferability can be obtained in any environment, and transfer failure due to contamination of the transfer unit with toner is largely prevented, which contributes to obtaining a high-quality image.

[Brief description of the drawings]

FIG. 1 is a schematic side view of a main part of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a graph showing voltage and current characteristics of the image forming apparatus. FIG. 5 is a sequence diagram showing a modified embodiment of the above, FIG. 6 is an explanatory diagram showing the operation of the above by a graph, and FIG. 7 is an image forming apparatus as another embodiment of the present invention. FIG. 8 is a schematic side view of a main part of an image forming apparatus as still another embodiment, FIG. 9 is a schematic side view for explaining the operation of a known image forming apparatus, FIG. 10 is an operation sequence diagram of the above. 1 photoconductor, 2 transfer roller, 3 charging roller,
5 ... power supply, 6 ... current detection means, 8 ... electrodes, 9 ...
Developing unit, 51: minus constant voltage power supply, 52 ... plus constant current power supply, 53 ... plus constant voltage power supply.

Continuation of the front page (72) Inventor Koichi Suwa 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (72) Inventor Hideyuki Yano 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. ( 72) Inventor Takahiro Inoue 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (56) References US Patent 3837741 (US, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G03G 15/16

Claims (9)

(57) [Claims] An image carrier, and a transfer member for forming a nip portion with the image carrier, the transfer member transferring a toner image on the image carrier to a transfer material sent to the nip portion. In the image forming apparatus, when the transfer material is not present in the nip portion, a voltage / current characteristic of the transfer member is detected, and a voltage applied to the transfer member at the time of image transfer to the transfer material is determined based on the characteristic. A voltage having the same polarity as that of the toner image is applied to the transfer member to form an electric field for transferring the toner from the transfer member to the image carrier prior to the detection of the voltage-current characteristic. Image forming apparatus. 2. The image forming apparatus according to claim 1, wherein the detection of the voltage-current characteristic is performed by applying a voltage having a polarity opposite to that of the toner image to the transfer member. 3. The method according to claim 1, wherein the detection of the voltage-current characteristic is performed by detecting a voltage generated at the transfer member when the transfer member is controlled at a constant current. The image forming apparatus as described in the above. 4. The method according to claim 1, wherein the detection of the voltage-current characteristic is performed by detecting a current flowing through the transfer member when the transfer member is controlled at a constant voltage. The image forming apparatus as described in the above. 5. A voltage applied to the transfer member when transferring an image to a transfer material is a factor R (R> 1) of a voltage generated at the transfer member when the constant current control is performed. An image forming apparatus according to claim 3. 6. An image forming apparatus according to claim 1, wherein said transfer member is controlled at a constant voltage when transferring an image to a transfer material. 7. The apparatus according to claim 1, further comprising an image forming unit configured to form the toner image on the image carrier, wherein the image forming unit includes a charging unit configured to charge the image carrier to the same polarity as the toner image. The image forming apparatus according to any one of claims 1 to 6, wherein the image forming apparatus is provided. 8. An image forming apparatus according to claim 1, wherein said transfer member has a roller shape. 9. An image forming apparatus according to claim 1, wherein said image bearing member includes an electrophotographic photosensitive layer.