JP3112525B2 - Electrophotographic recording device - 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 recording apparatus, and more particularly, to a phenomenon in which a recording sheet is wound around a photoreceptor when a visible image on the surface of the photoreceptor is transferred to the recording sheet.
The present invention relates to an electrophotographic recording apparatus provided with a means for preventing occurrence of a drum wrap phenomenon.

[0002]

2. Description of the Related Art Conventionally, as an electrophotographic recording apparatus equipped with a means for preventing the occurrence of a drum wrap phenomenon (hereinafter referred to as a wrap preventing means), Japanese Patent Application Laid-Open No. 1-121879,
As disclosed in Japanese Patent Application Laid-Open Nos. 1-121878, 1-172986, etc., a separate contact corona charger is disposed upstream of a transfer corona charger in a recording paper transporting body. A recording paper and a recording paper transporting body are brought into close contact with each other immediately before transfer to the recording paper by a contact corona charger (hereinafter, this is referred to as a contact type).
Or, as disclosed in JP-A-55-9505,
Immediately before the recording paper is placed on the recording paper transport, the recording paper is charged with a polarity opposite to that of the recording paper transport, and when the recording paper is placed on the recording paper transport, both are charged. A plurality of small holes are provided in a recording paper transporting body, such as one that is made to be adsorbed (hereinafter referred to as a quasi-contact type) and that disclosed in Japanese Patent Application Laid-Open No. 61-5256. After the transfer of the recording paper, the recording paper is sucked toward the recording paper transporting body through a small hole by a vacuum suction device (hereinafter, this is referred to as a suction type). Note that the recording paper transport body used here must be one that retains the charge generated by the corona charger, and is made of a single layer or a multilayer of a plastic film such as urethane rubber or PVDF. is there.

[0003]

The above-mentioned drum wrap phenomenon which occurs in the electrophotographic recording apparatus has been found by the present inventors to be caused by the following factors.

[0004] One of them is a leading end portion of a recording sheet, in particular,
When a toner image is not formed in an area within at least 20 to 30 mm from the leading end, that is, when the area is a blank paper printing area, a drum wrap phenomenon is likely to occur. On the other hand, when the toner image is formed in the area, the toner in the area is interposed between the photosensitive member and the recording paper, and the drum wrap phenomenon is less likely to occur.

[0005] Second, when the recording paper is cut paper of A4 size or A3 size or the like, the cut paper is obtained by cutting a large paper into a predetermined size. At the time of cutting, a state in which the cutting portion of the recording paper (the leading end of the recording paper) bends in the cutting direction, that is, a so-called burr occurs. Further, even in a portion other than the cut portion, the leading end of the recording paper may be bent for some reason. As described above, if there is a large burr or bend at the leading end of the recording paper, the drum wrap phenomenon is likely to occur, and particularly,
When the burrs or bends are conveyed toward the recording paper conveying body, the frequency of occurrence of the drum wrap phenomenon becomes considerably large.

Third, even if the recording paper has burrs or bends of the same size, the frequency of occurrence of the drum wrap phenomenon depends on the type of the recording paper, for example, the thickness, the paper quality (the quality paper and the quality paper). This is particularly likely in the case of weak paper such as thin paper or recycled paper, depending on the type of recycled paper. The same applies to the case where not only ordinary paper but also an OHP sheet such as a plastic film is used as the transfer paper.

Fourth, the drum wrap phenomenon is more likely to occur as the humidity decreases, depending on the environmental conditions.
In particular, when the humidity is low at 30% RH or less, the frequency of occurrence of the drum wrap phenomenon increases.

As described above, the degree of occurrence of the above-described drum wrap phenomenon varies depending on various factors. Therefore, recently, a lap preventing means which is not affected by the variations of these factors has been demanded.

However, all of the above-mentioned conventional lap preventing means are not designed in consideration of the above-mentioned respective factors. In addition, the contact type and the quasi-contact type in the conventional lap prevention means described above are:
In addition to the corona charger for transfer, an extra corona charger for contact or an extra roller for charging is required, and the close-contact type is capable of transferring the visible image corresponding to a certain area at the leading end of the recording paper. It has the problem that it cannot be done.
In addition, the suction type of the conventional wrap prevention means,
There is a problem that an extra vacuum suction device is required, and it is difficult to set the timing for sucking the recording paper.

The object of the present invention is to eliminate these problems. The purpose of the present invention is to eliminate the drum wrap phenomenon with a simple structure irrespective of the presence or absence of burrs or bends at the leading end of a recording sheet and the type of recording sheet. It is an object of the present invention to provide an electrophotographic recording apparatus that can prevent occurrence of the occurrence and has no transfer failure.

[0011]

In order to achieve the above object, the present invention provides a photosensitive member which moves at a predetermined speed, an exposure device which exposes the photosensitive member, and an electrostatic latent image obtained by the exposure. And an electrophotographic recording apparatus having a transfer device for transferring the developed visible image to recording paper or the like, the transfer device includes a charging device that applies a charge to a recording paper conveyance body, The device applies a charge to the recording paper transport when the leading edge of the transported recording paper comes to the nip area, and at that time, gives a tip to an area corresponding to the leading edge of the recording paper of the recording paper transport. The supplied electric charge amount is smaller than the electric charge amount given to a region other than the front end portion of the recording paper of the recording paper transporting body, and the front end supplied electric charge amount is changed by the electric charge to the recording paper at the front end portion. For recording It comprises a first means for selecting a value that an electric field generated in the gap becomes less than the discharge start electric field of air between the carrier.

According to another aspect of the present invention, there is provided a photoconductor that moves at a predetermined speed, an exposure device that exposes the photoconductor, and a developing device that develops an electrostatic latent image obtained by the exposure. In an electrophotographic recording apparatus having a device and a transfer device for transferring the developed visible image to recording paper or the like,
The transfer device includes a conductive bias roller that presses a recording paper transport body toward the photoconductor, and the bias roller applies a voltage to the recording paper transport body when a leading end of the transported recording paper comes to a nip area. At that time,
The tip voltage applied to the recording sheet transporter corresponding to the leading edge of the recording sheet is smaller than the voltage applied to the recording sheet transporter corresponding to portions other than the leading edge of the recording sheet, and the tip applied voltage A second means for selecting an electric field generated in a gap between the recording sheet at the leading end and the recording sheet transporter by the voltage so as to be equal to or less than an electric field at which air starts to discharge.

[0013]

Before explaining the operation of the present invention, the mechanism by which a recording paper having burrs or bends causes a drum wrap phenomenon will be described.

FIG. 9 is an enlarged configuration diagram showing a lap area where the photoconductor and the recording paper transport body meet.

In FIG. 9, 101 is a drum, 102 is a photosensitive member on the surface of the drum 101, 103 is a toner, 104
Is a recording sheet, 105 is a burr at the leading end of the recording sheet 104, 1
Reference numeral 06 denotes a recording sheet conveying body, 107 denotes a gap, 108 denotes a pressing roller, 109 denotes a corona charger, 110 denotes a developing machine, 111 denotes a developing roller, and 112 denotes a constant current power supply.

The burrs 10 at the leading end of the recording paper 104
5, the burr 105 and the recording paper transport body 10
6 and a gap 1 having a width L of about 0.1 to 5.0 mm.
07 is formed, and the recording paper 104 including the burr 105 is formed.
Is a blank portion where no transfer is performed. Also, the current It from the constant current power supply 112 is supplied to the corona wire of the corona charger 109, and 10 to 30% of the current It flows from the corona wire to the recording paper transport body 106 as the charging current Ib, and the recording paper transport Positive charge Q (coulomb / cm)
^Two ) To accumulate. At this time, positive and negative charges are generated in the gap 107 based on the charge amount Q, thereby forming an electric field Eair.

Now, when the recording paper 104 having the burrs 105 at the leading end is conveyed to the recording paper transport 106 and reaches the nip area, the corona charger 109 accumulates positive charges on the back surface of the recording paper transport 106, and this positive charge is accumulated. The toner 103 having a negative charge attached to the surface of the photoconductor 102 due to the electric charge is sucked onto the recording paper 104, and the visible image formed on the surface of the photoconductor 102 is changed to the recording paper 10.
4 is transferred.

In this case, as shown in FIG.
When the recording paper 104 approaches the nip area, the transfer current Im flows through the corona charger 109, and the burrs 105 at the leading end of the recording paper 104, as shown by the curve in FIG. Before the portion of the burr 105 reaches the input end La of the corona charger 109, charge starts to be accumulated, and thereafter, the amount of this charge is determined while the portion of the burr 105 is moved from the inlet end La to the outlet end Lc of the corona charger 109. Gradually increase. When the portion of the burr 105 reaches a position Lp between the inlet end La and the outlet end Lc, the gap 1
The electric field Eair of 07 reaches a discharge starting electric field Eb of air (30 kv / cm at atmospheric pressure), and a discharge is generated in the gap 107. When this discharge occurs, a positive charge and a negative charge are generated. The positive charge is attracted by the negative charge on the photoconductor 102 and is injected into the recording paper 104, and the negative charge is injected into the recording paper transport 106. . As a result, an electrostatic attraction force acts between the recording paper 104 and the photoconductor 102, and the recording paper 1
A phenomenon in which the sheet 04 wraps around the photoconductor 102, that is, a so-called drum wrap phenomenon occurs.

By the way, as shown by the curve in FIG. 10B, electric charge starts to be accumulated before the portion of the burr 105 reaches the entrance end La of the corona charger 109, and thereafter, the portion of the burr 105 is removed. The entrance end L
a, while the amount of the electric charge gradually increases while being conveyed to the outlet end Lc of the corona charger 109, the amount of the electric charge is increased by the electric field Eai of the air gap 107.
If r does not exceed the amount of charge Qb corresponding to the discharge start electric field Eb of air, no discharge occurs in the gap 107,
Therefore, the aforementioned drum wrap phenomenon does not occur.

The present invention has been made based on such a principle. The first means is to use a charger (corona charger) 109 for injecting electric charge into the recording paper transporting body 106. The charger 109 applies a tip to the leading end of the recording paper 104 having a burr 105 at the leading end.
The end supply charge amount is changed to the charge amount Qj smaller than the charge amount Qb.
And apply it to the recording paper 104 except for the leading end.
The obtained charge amount is selected as the charge amount Qm that maximizes the transfer efficiency.

The second means uses a bias roll for applying a voltage to the recording paper transporting body 106,
With this bias roll, the leading end applied voltage applied to the leading end of the recording paper 104 having the burrs 105 at the leading end becomes a voltage Vj smaller than the voltage that generates the charge amount Qb .
Select urchin, electrostatic <br/> load volume giving in addition to the leading end of the recording paper 104 is Elect voltage Vm to generate the charge amount Qm such as transfer efficiency is maximized.

If the first or second means described above is employed, even if the burr 105 is present at the leading end of the recording paper 104, the amount of charge supplied to the leading end supplied to the recording paper transport 106 corresponding to the leading end Alternatively, the tip applied voltage is
7 is set so as to be smaller than the electric discharge start electric field Eb of the air, no discharge occurs in the gap 107, and therefore, the recording paper 104 is
02 and no drum wrap phenomenon occurs.

FIG. 8 shows the charge amount Q applied to the recording sheet transport 106, the transfer efficiency (%), and the recording sheet 104.
6 is a graph showing the relationship between the drum wrap occurrence rate (%) of FIG.

As shown by the curve of this graph, if the amount of charge Q given to the recording sheet transporter 106 is equal to or less than the amount of charge Qb, the drum wrap occurrence rate is 0,
When the charge amount Q exceeds the charge amount Qb, the drum wrap generation rate sharply increases. On the other hand, as shown by the curve in the graph, the transfer efficiency when the charge amount Q given to the recording paper transport body 106 is equal to or less than the charge amount Qb is lower than when the transfer charge amount Qm is given. But, for example,
If a charge amount Qj as shown in the figure is selected as the charge amount Q, a transfer efficiency of about 60% can be obtained. Incidentally, the transfer efficiency when no charge amount Q is given to the recording sheet transporting body 106 is 20% or less. At this time, the density of the transferred image is low, image unevenness occurs, and image deterioration is inevitable.

In the present invention, the recording paper transporting body 106 corresponding to the leading end has a transfer charge or a voltage having the same polarity as the transfer voltage, even if the transfer is insufficient.
The leading end supplied charge amount or the leading end applied voltage is given, and the charge amount Q
j, a transfer electric field acts between the surface of the photoconductor 102 and the recording paper transporting body 106, and a visible image on the surface of the photoconductor 102 is also transferred at the leading end of the recording paper 104. You. In addition, since a transfer charge or a transfer voltage sufficient for performing transfer is applied to the portion other than the leading end portion of the recording paper 104, clear transfer can be performed as in the related art.

When selecting the charge amount Qj, it is sufficient to select a value such that the transfer efficiency is 60% or more, preferably about 60 to 70%. There is no problem.

As described above, according to the present invention, the transferred image is not deteriorated at the leading end of the recording
An electrophotographic recording apparatus in which the so-called drum wrapping phenomenon does not occur, which does not wrap around the photosensitive member 102, can be obtained.

[0028]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings. Prior to describing the following embodiments, an outline of the overall configuration of an electrophotographic recording apparatus to which the present invention is applied will be described. The configuration is, for example, as shown in FIG.

Referring to FIG. 11, an electrophotographic recording apparatus includes a photosensitive drum 201, a charger 202, and an exposure device 203.
, Developing machine 204, transfer device 205, recording paper 206
, A fixing device 207, an erase lamp 208, and a cleaner 209.

The outline of the operation of this electrophotographic recording apparatus is as follows.

The photosensitive drum 201 is rotated at a constant speed by a driving device (not shown). First, the surface of the photosensitive drum 201 is uniformly charged by a negative charge in the charger 202. Next, the surface is exposed in an exposure device 203 including a laser light emitter, a polygon mirror, and the like, and an electrostatic latent image is formed thereon. Next, this electrostatic latent image is
At 04, the toner is developed by attaching the negatively charged toner, and a visible image corresponding to the electrostatic latent image is formed on the surface. Subsequently, this visible image is transferred to the transfer unit 205.
At this time, the recording paper 206 transported to a recording paper transport (not shown) arrives at the nip area, and the recording paper 206 is transferred to the transfer unit 205 together with the recording paper transport. , The recording paper 206 is charged in this nip area.
The visible image is transferred by attaching toner on the top. Subsequently, toner is fixed on the recording paper 206 to which the visible image has been transferred in the fixing device 207, and predetermined recording is performed. Further, after the transfer, the toner remaining on the surface of the photosensitive drum 201 is erased by the erase lamp 2.
08 and the cleaner 209, and the above steps are repeated again.

Here, an embodiment of the present invention will be described.
First, FIG. 1 is a main part configuration diagram showing a first embodiment of an electrophotographic recording apparatus according to the present invention, and particularly shows a peripheral portion of a transfer unit 205 shown in FIG.

In FIG. 1, 1 is a drum, 2 is a photoreceptor,
Reference numeral 3 denotes toner, 4 denotes recording paper, 5 denotes burrs at the end of the recording paper 4, 6 denotes a recording paper transport body, 7 denotes a gap, 8 denotes a pressing roller, 9 denotes a driving roller, 10 denotes a registration roller, and 11 denotes a paper position detection sensor. , 12 is a corona charger, 13 is a corona wire, 14 is a constant current source, 15 is a control circuit,
6 is a paper quality sensor, 17 is a humidity sensor, and 18 is a measurement circuit.

Then, the recording paper transport body 6 is driven by a driving roller 9.
Is moved in the direction of the arrow shown in FIG. 1 to convey the recording paper 4 supplied via the registration roller 10. The corona wire 13 of the corona charger 12 is a constant current source 14
And generates an electric charge as shown in FIG. A paper position detection sensor 11 disposed near the registration roller 10 detects the leading end of the recording paper 4 supplied from the registration roller 10 and sends the detection output Vs obtained here to a control circuit. Also,
The paper quality sensor 16 detects the type of the recording paper 4, for example, the thickness, the difference between high-quality paper and recycled paper, and the humidity sensor 17 detects the surrounding humidity, and outputs these detection outputs via the measurement circuit 18. It is sent to the control circuit. In this embodiment, the recording paper transporting body 6 has a thickness of 500 mm.
A three-layer urethane rubber belt having a thickness of about 650 μm and a fluorine-based film formed on both sides of the belt is used.

The operation of this embodiment is as described below.

Now, when the recording paper 4 is supplied through the registration roller 10 and its leading end is detected by the paper position detection sensor 11, the detection signal Vs is supplied to the control circuit 15. When receiving the signal Vs, the control circuit 15 sets the timing of the current It flowing through the corona wire 13 and the value of the current It. Then, when the leading edge of the recording sheet 4 reaches the inlet end La corona charger 12, the control circuit 15, as shown in FIG. 2, the size is generated the current It I _1, recording as described below The operation for giving the leading end supply charge amount Q1 to the paper transporting body 6 is started. continue,
When the leading end of the recording paper 4 is conveyed to the exit portion Lno of the nip area, the control circuit 15 generates a current It having a magnitude Im as shown in FIG.
Is transferred to the normal transfer operation.

Here, the moving speed of the recording paper transporting body 6 is set to U
b, the time Tc at which the leading end of the recording paper 4 receives the charge from the corona charger 12 is Tc ≒ (Lno−L
a) It is represented by / Ub. Then, among the size of the control circuit 15 generates the current It of I _1, when the average value of the current flowing into the recording paper conveying member 6 and I1v, corresponding to the leading edge of the recording sheet 4 recording sheet conveying member 6 Tip to be given to
Feed charge amount Q1 is expressed by Q1 = Tc × I1v. Therefore, the tip supply charge amount Q1 is changed to the charge amount Qb shown in FIG.
If the recording paper 4 is selected to be smaller, the recording paper 4 will not be wound around the photoreceptor 2, and the drum wrap phenomenon will not occur.

The above-described example is for the case where the current It supplied to the corona charger 12 is changed in two stages of I ₁ and Im. As shown in FIG. The tip of the paper 4 is the corona charger 12
Of when it is conveyed to the intermediate point, a large value I ₂ of current It magnitude which has been supplied from the current It I ₁ until it
Then, when the leading end of the recording paper 4 is conveyed to the exit portion Lno of the nip area, a current It having a magnitude Im is generated as before, that is, the current is changed in three stages. You can also.

[0039] Here, among magnitude control circuit 15 generates the current It of I _2, an average value of the current flowing into the recording paper conveying member 6 When I2v, the leading edge of the recording sheet 4 in this case The leading edge provided to the corresponding recording paper transport 6
Feed charge amount Q12 is, Q12 = Tc (I1v + I2v ) /
It will be represented by 2. Therefore, also in this case, if the leading end supply charge amount Q12 is selected to be smaller than the charge amount Qb shown in FIG. The wrap phenomenon will not occur.

Further, as described above, the drum wrap phenomenon depends on the type of the recording paper 4 or the surrounding environment, particularly, the humidity. Therefore, when the type of the recording paper 4 is changed, when the humidity is considerably changed. For example, the detection output from the paper quality sensor 16 or the humidity sensor 17 is appropriately processed by the measurement circuit 18 and then supplied to the control circuit 15 to control the magnitude of the current It supplied to the corona charger 12. .

In FIG. 2, when the leading edge of the recording paper 4 reaches the entrance end La of the corona charger 12, the size I ₁ of the corona charger 12 starts.
Is applied, but when it is difficult to detect when the leading end of the recording paper 4 reaches the entrance end La, the leading end of the recording paper 4 reaches the entrance end La. previously the size I ₁ of the current it may be energized.

FIG. 3 is a block diagram showing a detailed configuration of the constant current source 14 and the control circuit 15 used in the embodiment of FIG.

In FIG. 3, 14a is a low current source, 14b
Denotes a high current source, and the same components as those shown in FIG. 1 are denoted by the same reference numerals.

The constant current source 14 comprises a low current source 14a for generating a small current and a high current source 14b for generating a large current. The control circuit 15 is connected to the low current source 14a and the high current source 14b. Control signals Vsl and Vsh from
Are supplied respectively.

The operation of the constant current source 14 will be described with reference to the operation explanatory diagram of FIG. However, in this figure, each signal is shown in negative logic.

[0046] First, in (a) of FIG. 4, now, the time when the sheet position detecting sensor 11 to t ₀ detects the leading end of the recording sheet 4, the detection signal Vs which becomes High level from time t ₀ to time t ₁ Occurs. The control circuit 15, when the detection signal Vs becomes Low level, and generates a control signal Vsl becomes Low level from the time t ₃ after a lapse of time Ts to time t _4, the low within the application period of the control signal Vsl current source 14a generates a current It small value I _1. Next, at time t ₄ , the control circuit 15 generates a control signal Vsh which becomes a low level from time t ₄ to time t ₅ , and the high current source 14 b becomes large during the application period of the control signal Vsh. A current It having a value Im is generated. Subsequently, at time t ₆ , the sheet position detection sensor 11 detects the leading edge of the recording sheet 4 again, generates a detection signal Vs that goes low from time t ₆ to time t ₇ , and the above-described operation is repeated. . In FIG. 3, Ts is the time from when the leading edge of the recording paper 4 is detected by the paper position detection sensor 11 to when it reaches the entrance end La of the corona charger 12, and Te is when the leading edge of the recording paper 4 is Is the time from the input end La to the exit end Lno of the nip area, Tr is the time during which the transfer current of a large value Im flows, and Tq is the time for one recording paper 4.
And the time during which the next recording paper 4 is respectively conveyed.

Thus, the current It generated by the constant current source 14 has a small value I from time t ₃ to time t _4.
1, the time t ₄ from the time t ₅ to a large value Im becomes the prevention of the drum wrap phenomenon as described above, the conventional transfer takes place.

Next, FIG. 4B shows one recording paper 4
And also between the next recording sheet 4, a case that energized the current small value I _1, in this example, the timing of the control signal Vsh to the control circuit 15 generates the 4 ( a) Same as Vsl, except that control signal V
sl is a voltage waveform from time t ₄ as shown in FIG. 4 (b) to time t ₅ becomes Low level.

[0049] Thus, current It constant current source 14 occurs, the larger the value Im next to the time t ₅ from the time t _4, the other time to a low value I _1, previous as well as the drum wrap phenomenon And normal transfer is performed. However, in this example, the low current source 14a
Although it is not necessary to take into account the rise time of the current It, the life of the recording sheet transport 6 is slightly shortened because the recording sheet transport 6 is constantly exposed to the corona.

At the time of actual operation, the transfer speed of the recording paper transport body 6 is 10 ips, the width of the corona charger 12 is 20 mm, and the width of the nip area (this is (Lno-L
b) Equivalent to × 2) at 10 mm, 20 ° C., 20% R
Under the environmental condition of H, the current It shown in FIG. 4A is supplied, and the time Tc is set to 69 ms.
The conduction current I ₁ of the corona charger 12 is 10 to 30
When μA and Im are set to 300 μA, the current flowing into the leading end of the recording paper 4 becomes 5 to 20 μA, and the current flowing into the portion excluding the leading end of the recording paper 4 becomes about 50 μA. The transfer efficiency of the area within about 5 mm was 60 to 80%, and recording of relatively high image quality could be performed. At the same time, the photosensitive member 2 of the recording paper 4
It was also confirmed that there was no winding around.

The leading end of the recording paper 4 is positioned at the center point of the corona charger 12 (the point where the corona wire 13 exists) Lb.
, The current (I ₁ = approximately 70 μA) to the corona charger 12 is started. When the leading edge of the recording paper 4 reaches the exit Lno of the nip area, the current to the corona charger 12 is increased (Im = I.sub.m). About 300μA)
As a result, the transfer efficiency in a region from the leading end of the recording paper 4 to about 3 mm was 60 to 80%, and the transfer efficiency in a portion other than the above-described region of the recording paper 4 was about 80% or more, and there was no particular problem in image quality. . Further, also in this case, it was confirmed that the recording paper 4 was not wound around the photoconductor 2.

Next, as environmental conditions, 20 ° C., 40% R
H, the small value I ₁ was set to 200 μA and the large value Im was set to 300 μA.
There was no occurrence of wrap around, and a transfer efficiency of about 80% or more could be obtained over the entire recording paper 4.

FIG. 5 is a block diagram showing a second embodiment of the electrophotographic recording apparatus according to the present invention.

In FIG. 5, reference numeral 19 denotes a conductive bias roller for pressing the recording sheet transport body 6 toward the photosensitive member 2, reference numeral 20 denotes a pressure applying means, reference numeral 21 denotes a voltage source, and the other components are the same as those shown in FIG. The components have the same reference numerals.

The conductive bias roller 19 is a metal roller or a metal roller having a low resistance film formed on the surface of the metal roller. In addition to pressing, a voltage is applied to the recording sheet transporting body 6 by a voltage supplied from the voltage source 21.

The operation of this embodiment is to apply a voltage to the recording paper transporting body 6 via the conductive bias roller 19 and to generate a positive charge on the recording paper transporting body 6 by the voltage. Is different from that of the first embodiment, but the other points are almost the same as those of the first embodiment.

The means for applying a voltage to the recording paper transporting body 6 will now be described with reference to FIG. 6 which shows a temporal change in the voltage applied to the bias roller 19.

[0058] After the recording paper 4 is detected by the sheet position detection sensor 11, when the tip reaches the entry point Lni of the nip region, control circuit 15, a voltage of lower value V ₁ by controlling the voltage source 21 When the leading end reaches the exit point Lno of the nip area, the control circuit 15 supplies a large value Vm necessary for normal transfer.
Is supplied to the bias roller 19.

In this case, the voltage applied to the leading end of the small value V ₁ is such that the burrs 5 are provided at the leading end of the recording sheet 4, and the gap 7 is formed between the leading end recording sheet 4 and the recording sheet transport body 6. Has been formed, the small value V ₁
Tip even added tip applied voltage, the discharge gap within 7 is selected to a value that does not cause, in other words, generated the recording paper feed member 6 by the supply of small value V ₁ The small value V ₁ is selected so that the supplied charge amount Q is equal to or less than the aforementioned charge amount Qb, and the leading end supplied charge amount Q generated by the small value V ₁ makes the transfer efficiency at least 60% or more. Is chosen to be

Therefore, also in this embodiment, the recording paper 4 is not wrapped around the photoreceptor 2 and the transferred image at the leading end of the recording paper 4 is not deteriorated.

FIG. 7 is a block diagram showing a third embodiment of the electrophotographic recording apparatus according to the present invention.

In FIG. 7, reference numeral 22 denotes a current source, reference numeral 23 denotes a shield inflow current detection circuit, and other components which are the same as those shown in FIG. 1 are denoted by the same reference numerals.

The shield inflow current detection circuit 23 is a circuit for detecting the current Is flowing in the shield of the corona charger 12 from the current It flowing in the corona wire 13 of the corona charger 12, and the current source 22 is a shield inflow current detection circuit. 23, the output current value It is changed based on the detection result.

That is, a part of the current It supplied from the current source 22 to the corona wire 13 of the corona charger 12 flows into the recording sheet transporting body 6 and is supplied as the current Ib, while the remaining part is supplied as the shield current Is. It flows to the shield of the corona charger 12. At this time, even if the current It is constant, the magnitude of the shield current Is changes depending on environmental conditions and the like.
Although the inflow current Ib is no longer constant, in the present embodiment, the shield inflow current detection circuit 23 detects the value of the shield current Is, and when the value of the shield current Is changes, the polarity of the change and A signal corresponding to the amount is fed back to the current source 22, and the current It is made variable according to the amount of feedback, so that the flowing current Ib can be kept constant.

The other operations are the same as those of the first embodiment, so that further explanation is omitted.

According to this embodiment, since the current Ib flowing into the recording paper transporting body 6 is directly related to the amount of electric charge applied to the recording paper transporting body 6, the control is performed as in the first embodiment. , The transfer current It of the corona charger 12
Can be controlled with higher precision than the control of

In each of the above embodiments, the case where a drum-shaped photosensitive member 2 is used has been described. However, the present invention is not limited to the drum-shaped photosensitive member 2. Alternatively, the photoreceptor sheet may be used by being wound around the drum surface, or the photoreceptor sheet may be applied to the belt-like photoreceptor 2 as long as the photoreceptor sheet has a relatively large curvature.

[0068]

According to the present invention, the leading end supply charge of the same polarity as the transfer charge, which is smaller than the transfer charge amount Qm, is applied to the recording sheet transporter 6 corresponding to the leading end of the recording sheet 4. Since the amount Qj is given, regardless of the presence or absence of burrs at the leading end of the recording sheet 4, the type of the recording sheet 4, and the environmental condition, the recording sheet 4 is wound around the photoconductor 2, that is, the so-called drum wrap phenomenon occurs. There is an effect that can be prevented.

Even if the leading end charge amount Qj is insufficient for normal transfer, it has the same polarity as the transfer charge. Has an effect that a visible image on the surface of the photoreceptor 2 is transferred also at the leading end of the recording paper 4.

Since a sufficient amount of transfer charge for transferring is applied to the portion of the recording paper 4 other than the leading end, clear transfer can be performed as in the conventional case.

As described above, according to the present invention, the recording paper 1
An electrophotographic recording apparatus in which the transferred image is not deteriorated at the leading end of the photoconductor 04 and the recording paper 4 is not wrapped around the photoconductor 2, that is, the so-called drum wrap phenomenon does not occur can be realized by a simple configuration. There is.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a first embodiment of an electrophotographic recording apparatus according to the present invention.

FIG. 2 is an explanatory diagram showing a time change of a transfer current of a corona charger.

FIG. 3 is a block diagram showing an internal configuration of a constant current power supply.

FIG. 4 is an explanatory diagram showing a time change of a transfer current output from a constant current power supply.

FIG. 5 is a configuration diagram showing a second embodiment of the electrophotographic recording apparatus according to the present invention.

FIG. 6 is an explanatory diagram showing a time change of an applied voltage of a bias roller.

FIG. 7 is a configuration diagram showing a third embodiment of the electrophotographic recording apparatus according to the present invention.

FIG. 8 is a characteristic diagram showing a relationship among a charge amount, a transfer efficiency, and a wrap ratio.

FIG. 9 is a schematic configuration diagram illustrating a mechanism of drum wrap generation.

FIG. 10 is a characteristic diagram showing a relationship between a leading end position of a recording sheet, a charge amount, and a gap electric field.

FIG. 11 is a configuration diagram illustrating an outline of the overall structure of an electrophotographic recording apparatus.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 drum 2 photoreceptor 3 toner 4 recording paper 5 burr 6 recording paper transporter 7 gap 8 pressing roller 9 drive roller 10 registration roller 11 paper position detection sensor 12 corona charger 13 corona wire 14 constant current source 15 control circuit 16 paper quality sensor 17 Humidity sensor 18 Measurement circuit 19 Bias roller 20 Pressure applying means 21 Voltage source 22 Current source 23 Shield inflow current detection circuit

──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Yasuo Takuma 4026 Kuji-cho, Hitachi City, Ibaraki Prefecture Within Hitachi Research Laboratory, Hitachi, Ltd. (72) Inventor Tatsuo Igawa 4026 Kuji-cho, Hitachi City, Ibaraki Prefecture Hitachi Research, Ltd. In-house (72) Inventor Masato Miwa 1060 Takeda, Katsuta-shi, Ibaraki Hitachi Koki Co., Ltd. (56) References JP-A-3-177852 (JP, A) JP-A-1-121879 (JP, A) JP JP-A-4-314075 (JP, A) JP-A-4-326385 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03G 15/16 G03G 15/14 101

Claims (10)

(57) [Claims] 1. A photoconductor that moves at a predetermined speed, an exposure device that exposes the photoconductor, a developing device that develops an electrostatic latent image obtained by the exposure, and a recording paper that develops the developed visible image In the electrophotographic recording apparatus having a transfer device for transferring to the like, the transfer device includes a charger for applying a charge to a recording sheet transporter, and the charger is configured such that a leading end of the transported recording sheet is located in a nip area. When a charge is supplied to the recording sheet transporter, a tip supply charge amount applied to an area corresponding to a leading end of the recording sheet of the recording sheet transporter is supplied to the recording sheet transporter. An electric field generated in a gap between the recording paper at the front end and the recording paper transporter due to the electric charge is set to be smaller than the amount of electric charge applied to a region other than the front end, and the electric charge supplied to the front end is reduced by air. Discharge starting power An electrophotographic recording apparatus characterized in that the value is selected to be below the field. 2. The electrophotographic recording apparatus according to claim 1, wherein the amount of charge supplied to the leading end is set to a value that allows a visible image of a photoconductor to be transferred to recording paper. 3. The electrophotographic recording apparatus according to claim 1, wherein said charger is a corona charger capable of adjusting a charge current amount. 4. The corona charger according to claim 1, wherein a current flowing through the corona wire when the leading end of the recording sheet is in the nip region is smaller than a current flowing through the corona wire when the leading end leaves the nip region. 4. The electrophotographic recording apparatus according to claim 3, wherein the power is supplied so as to be small. 5. The electrophotography according to claim 1, wherein the charging device is a corona charger, and starts energizing the corona wire when the leading end of the recording paper reaches the vicinity of the corona wire. Recording device. 6. The electrophotographic recording apparatus according to claim 3, wherein the corona charger is controlled such that a current flowing into a recording sheet transporter is always constant. 7. A photoconductor that moves at a predetermined speed, an exposure device that exposes the photoconductor, a developing device that develops an electrostatic latent image obtained by the exposure, and a recording paper that prints the developed visible image. In the electrophotographic recording apparatus having a transfer device for transferring to the photoconductor, the transfer device includes a conductive bias roller that presses a recording paper transport body toward the photoconductor, and the bias roller is configured to transfer the recording paper that has been transported. When the leading edge comes to the nip area, a voltage is applied to the recording paper transport body,
At this time, the leading end applied voltage applied to the recording sheet transporter corresponding to the leading end of the recording sheet is smaller than the voltage applied to the recording sheet transporter corresponding to other than the leading end of the recording sheet, and The electrophotographic recording apparatus according to claim 1, wherein the voltage applied to the leading end is selected so that an electric field generated in a gap between the recording sheet at the leading end and the recording sheet transporter by the voltage is equal to or less than an electric field for starting air discharge. 8. The electrophotographic recording apparatus according to claim 7, wherein the voltage applied to the front end is set to a value at which a visible image on a photosensitive member can be transferred to a recording sheet. 9. A length of a leading end portion of a recording sheet for applying the leading end supplied electric charge amount or the leading end applied voltage to the recording sheet transporting body is at least 0.1 mm to 5 mm from the leading end. The electrophotographic recording device according to claim 1. 10. An electrophotographic recording apparatus according to claim 1, wherein said recording sheet transporter is a dielectric belt.