JPH03100578A - Image forming device - Google Patents

Abstract

PURPOSE:To secure sufficient transfer efficiency even under a very humid environment by impressing bias voltage on a guiding means formed with an electro conductive member conducting a transfer material to a transfer part. CONSTITUTION:Paper (material to be transferred) is guided to a pair of resisting rolls 19 through paper guiding paths 17 or 18, and is guided in contact with the paper guide 70 which is consisted of electro conductive material to the transfer part. A bias power source 71 is connected between the paper guide 70 and an earthing, the material to be transferred is electrified by having the bias voltage of an opposite polarity as toner impressed by the bias power source 71, that is, when the toner of negative polarity is utilized, positive bias voltage is impressed against the paper guide 70, and the transfer current is prevented from being earthed through the material to be transferred. Thus, even in the very humid environment, sufficient transfer efficiency can be secured.

Description

DETAILED DESCRIPTION OF THE INVENTION [Purpose of the Invention (Industrial Application Field) The present invention relates to an image forming apparatus such as an electronic copying machine that forms an image by electrostatic transfer.

(Prior Art) Generally, in the case of an electronic copying machine that uses an electrostatic transfer method, paper (
It has been known for a long time that humidity has a great effect on image quality during transfer to a transfer material. This is because, as shown in FIG. 9, the surface resistance of the paper decreases as the humidity increases. That is, when the surface resistance of the paper is reduced, the transfer current is transmitted through the paper and grounded, resulting in a reduction in transfer efficiency.

Therefore, in the vicinity of the transfer section, for example, the paper guide (guiding means) for guiding the paper to the transfer section may be insulated (floated) with an insulating material such as Mylar, or the paper guide 70 and ground may be grounded as shown in FIG. A method is used to create a potential difference by inserting a resistor 90 between the two. Furthermore, various methods have been devised to increase transfer efficiency, such as using a varistor or a Zener diode instead of the resistor 90.

However, when the humidity exceeds 70%, the moisture content of paper reaches 8.0%, as shown in FIG. Further, the surface resistance of the paper at this time is 1×10 10 Ω (ohm) or more (see FIG. 9).

Therefore, no matter how much the paper guide 70 is insulated or a potential difference is created between the paper guide 70 and the ground as described above, the transfer efficiency is as shown in FIG. 12. As such, it had the drawback that it could only be improved by about 50% at most.

(Problem to be solved by the invention) As mentioned above, in the conventional device, the humidity is 70%.
If it exceeds 100%, there is a drawback that good transfer efficiency cannot be obtained.

Therefore, an object of the present invention is to provide an image forming apparatus that can ensure sufficient transfer efficiency even in a humid environment.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, in the image forming apparatus of the present invention, a developer image formed on a photoconductor is transferred to a transfer section. In an apparatus for transferring onto a material, a supply means for supplying the material to be transferred, a guide means for guiding the material to be transferred supplied by the supply means to the transfer section and formed of a conductive member; and an application means for applying a bias voltage to the guide means.

(Function) This invention uses the above-described means to charge the transfer material and prevent the transfer current from being transmitted through the transfer material and grounded.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

4 and 5 schematically show, for example, an electronic copying machine as an image forming apparatus of the present invention. That is,
A document table (transparent glass) 2 for supporting a document is fixed to the top surface of the copying machine main body 1.

The document table 2 is provided with a fixed scale 2 that serves as a reference for setting the document, and furthermore, a document cover 11 that can be opened and closed and a work table 1□ are provided near the document table 2. The document placed on the document table 2 is exposed and scanned by an optical system consisting of an exposure lamp 4 and a mirror 5°6.7 being reciprocated in the direction of arrow a along the lower surface of the document table 2. It is supposed to be done. In this case, the mirror 67 is moved at half the speed of the mirror 5 so as to maintain the optical path length. The light reflected from the original by the scanning of the optical system, that is, the light reflected from the original by the light irradiation of the exposure lamp 4, is reflected by the mirrors 5, 6, 71:
By passing through the variable magnification lens block 8, being further reflected by the mirror 9, and being guided to the photoreceptor drum 10,
An image of the original is formed on the surface of the photosensitive drum 10.

The photosensitive drum 10 is rotated in the direction of arrow C in the figure, and the surface thereof is first charged by the charging device 11 . Thereafter, the image is subjected to slit exposure in the exposure section ph, thereby forming an electrostatic latent image on the surface. This electrostatic latent image is made visible by applying toner by the developing device 12.

On the other hand, the paper (transfer material) P is taken out one by one from the selected upper paper feed cassette 13 or lower paper feed cassette 14 by the delivery roller 15 or 16, and the taken out paper P is taken out from the paper guide path 17 or 18 and is guided to a pair of registration rollers (supply means) 19. The paper is then guided to the transfer section by being sent in contact with a paper guide (guiding means) 70 made of a conductive member.

Here, the paper feed cassettes 13 and 14 are removably provided at the lower right end of the main body 1, and one of them can be selected from an operation panel to be described later. Note that each of the paper feed cassettes 13 and 14 has a cassette size detection switch 60. ．． 602, the paper size is detected. This cassette size detection switch 60. ．． 60□ is composed of a plurality of microswitches that are turned on/off in accordance with the insertion of cassettes of different sizes.

The paper P sent to the transfer section is brought into close contact with the surface of the photoreceptor drum 10 at the transfer charger 20, and
0, the toner image (developer image) on the photosensitive drum 10 is transferred. The transferred paper P is electrostatically peeled off from the photosensitive drum 10 by the action of a peeling charger 21, and is sent by a conveyor belt 22 to a fixing roller 23 as a fixing device provided at the end thereof. The transferred image is fixed by passing through this, and the fixed paper P is transferred to a tray 25 outside the main body 1 by a pair of paper ejection rollers 24.
is discharged.

Further, the photoreceptor drum 10 after the transfer is transferred to a charger 26 for removing static electricity.
After the charge is removed by the cleaner 27, residual toner on the surface is removed, and the afterimage is erased by the charge removal lamp 28, so that the initial state is restored. Note that 29 is a cooling fan for preventing the temperature inside the main body 1 from rising.

FIG. 6 shows the operation panel 30 provided on the main body 1. That is, 301 is a copy key for commanding the start of copying, 302 is a numeric keypad for setting the number of copies, etc. 3
0. 304 is a display section that displays the operating status of each section, paper jam, etc., and 304 is an upper section.

Cassette selection key to select lower paper feed cassette 13.14 30. 306 is a magnification setting key for setting the enlargement/reduction magnification of copying in a predetermined relationship. 307 is a zoom key 30B for setting the enlargement/reduction magnification steplessly. A magnification display section 309 is a density setting section for setting copy density.

FIG. 7 shows a drive mechanism for reciprocating the optical system. That is, the mirror 5 and the exposure lamp 4 are supported by the first carriage 411, and the mirror 6.7 is supported by the second carriage 412.
．． Second carriage 41, . 41□ is the guide rail 421.
It is guided by 42□ and can freely move in parallel in the direction of arrow a.

Further, the four-phase pulse motor 33 drives a pulley 43. This pulley 43 and idle pulley 44
An endless belt 45 is stretched between the belt 45 and the first carriage 4 that supports the mirror 5.
One end of 11 is fixed.

On the other hand, on the guide portion 46 of the second carriage 41□ that supports the mirror 6.7, two boobies 947, 47 are rotatably provided at a distance in the axial direction of the rail 42□, and these pulleys 47, A wire 48 is stretched between the wires 47. One end of this wire 48 is fixed to a fixed part 49, and the other end is fixed to the fixed part 49 via a coil spring 50. Further, one end of a first carriage 411 is fixed to a midway portion of the wire 48. therefore,
As the motor 33 is rotated, the belt 45 rotates and the first carriage 41. is moved, and the second carriage 412 is also moved accordingly. At this time, since the pulleys 47, 47 serve as movable pulleys, the second carriage 41□ is moved in the same direction with respect to the first carriage 411 at 1/2 the speed. In addition, 1. The direction of movement of the second carriage 411.41□ is controlled by switching the direction of rotation of the motor 33.

FIG. 1 shows a peripheral portion of the photosensitive drum 10.

As shown in this figure, a bias power source (applying means) 71 is connected between the paper guide 70 and the ground. The bias power supply 71 applies a bias voltage having a polarity opposite to that of the toner to the paper guide 70. That is, when a selenium photoreceptor is used as the photoreceptor drum 10, for example, a toner of - (minus) polarity is used. Therefore, in this case, a + (plus) bias voltage is applied to the paper guide 70 by the bias power supply 71.

Further, the paper guide path 17, 18 and the registration roller pair 19 are each connected to ground.

Next, the operation in the above configuration will be explained.

For example, if the photoreceptor drum 10 is made of a selenium photoreceptor and negative polarity toner is used, a bias voltage of 10 is applied to the paper guide 70 by the bias power supply 71.

In this state, when the image forming operation by the copying machine main body 1 is started, the paper P taken out from the upper paper feed cassette 13 or the lower paper feed cassette 14 is guided to the transfer section by the registration roller pair 19. At this time, the paper P comes into contact with the paper guide 70 and becomes fully charged.

Then, by sending this paper P to the transfer section, the toner image on the photoreceptor drum 10 is transferred as described above.

The relationship between humidity, bias voltage, and transfer efficiency will be explained below.

Figure 2 shows the results of evaluating transfer efficiency by varying the bias voltage applied to the paper guide 70 using sheets of paper that were exposed to 80% humidity for 24 hours. be.

As is clear from this figure, the bias voltage is 50V (
volt), the transfer efficiency can be improved up to 50%, and 1
When it exceeds 00OV, a high transfer efficiency of 80% or more can be obtained. However, when the paper has a high resistance such as a Mylar sheet for 0HP (overhead projector), when the bias voltage exceeds 2000V, hollow characters and pockmarks appear in halftone areas. Therefore, when the photoreceptor drum 10 is made of a selenium photoreceptor and negative polarity toner is used, it is desirable that a positive bias voltage of 500V to 2000V be applied to the paper guide 70 by the bias power supply 71. .

FIG. 3 shows changes in transfer efficiency due to differences in humidity when a bias voltage of, for example, +1400 V is applied to the paper guide 70.

When a bias voltage of +1400 V was applied, as shown by the solid line in FIG. 3, the transfer efficiency hardly changed even when the humidity exceeded 80%, and a high transfer efficiency of nearly 90% was obtained. In other words, when a bias voltage of +1400V is applied, when the guide 70 shown in Figure 11 is grounded as shown by the dotted chain line, or when it is insulated with a 100 MΩ (megaohm) resistor shown by the double dotted chain line in the diagram, or when the guide 70 is 85 indicated by the dotted chain line
Compared to floating with a 0V varistor, the humidity is 70
Stable and good transfer efficiency can be ensured even in a humid environment exceeding 50%.

As mentioned above, the paper supplied to the transfer section is charged,
This is to prevent the transfer current from being transmitted through the paper and grounded.

That is, by applying a bias voltage to the paper guide, the paper being fed through the paper guide is charged. This makes it possible to prevent the transfer current from being grounded through the paper even if the surface resistance of the paper decreases as the humidity increases. Therefore, it is possible to improve the transfer efficiency when the humidity is 70% or more.

Although the above embodiments have been described using an electronic copying machine as an example, the present invention is not limited to this, and can be applied to various image forming apparatuses that use electrostatic transfer, for example.

Also, it is most effective to apply the bias voltage immediately before the transfer section, and it is sufficient if a part of the paper guide comes into contact with the paper, and on the upstream side, for example, on the paper transport path 17.
．． Even if the registration roller pair 18 and the registration roller pair 19 are not connected to the ground, the transfer efficiency will not be reduced.

Furthermore, in order to prevent characters from being hollowed out or pocked in halftone areas in low humidity conditions (low humidity environment), the application of bias voltage to the paper guide is selectively controlled according to the humidity. You can do it like this. in this case,
For example, as shown in FIG. 8, a switch 72 is provided between a paper guide 70 and a bias power source 71, and a control unit determines whether or not the humidity detected by a humidity sensor (detection means) 80 is greater than a reference value. The switch 72 may be turned on/off by making a determination using the control means 81 and controlling the relay circuit 82 according to the result.

It goes without saying that various other modifications can be made without departing from the gist of the invention.

[Effects of the Invention] As described in detail above, according to the present invention, it is possible to provide an image forming apparatus that can ensure sufficient transfer efficiency even in a humid environment.

[Brief explanation of drawings]

1 to 7 show an embodiment of the present invention,
Fig. 1 is a diagram showing the main parts of an electronic copying machine according to the present invention, Fig. 2 is a diagram showing changes in transfer efficiency due to differences in bias voltage, and Fig. 3 is a diagram showing changes in transfer efficiency due to differences in humidity. Figure 4 shown to explain changes in transfer efficiency.
The figure is an external perspective view showing the configuration of the electronic copying machine, Figure 5 is a side sectional view showing the configuration of the copying machine, Figure 6 is a plan view showing an example of the operation panel, and Figure 7 is the drive mechanism of the optical system. FIG. 8 is a schematic diagram showing another embodiment of the present invention, and FIGS. 9 to 12 show the prior art and m points therebetween. is a diagram shown to explain the change in paper surface resistance due to differences in humidity, Figure 10 is a configuration diagram illustrating the case where the paper guide is floated using a resistor, and Figure 11 is a diagram showing the change in paper surface resistance due to differences in humidity. FIG. 12, a diagram shown to explain changes in moisture content, is a diagram comparing changes in transfer efficiency due to differences in humidity between cases where the paper guide is insulated and cases where the paper guide is grounded. 1... Copying machine main body, 10... Photosensitive drum, 12.
...Developer, 19...Register roller pair (supply means)
, 70... paper guide (guiding means), 71... bias power supply (applying means), 72... switch, 80...
- Humidity sensor (detection means), 81...control unit (control means), 82...relay circuit. Bell it: + ◆500 +1000 +1500 +2000 ByTs (V) Figure 0 0 0 3 degrees (RH'n) 0 0 0 Humidity (RH'/,) Figure 10 Figure 2゜0 0 Turbidity Degree (RH'/,) Figure 1

Claims (2)

[Claims] (1) In an image forming apparatus that transfers a developer image formed on a photoreceptor onto a transfer material in a transfer section, a supply means for supplying the transfer material; and a transfer material supplied by the supply means. What is claimed is: 1. An image forming apparatus comprising: a guide means formed of a conductive member, and an application means for applying a bias voltage to the guide means. (2) In an image forming apparatus that transfers a developer image formed on a photoreceptor onto a transfer material in a transfer section, a supply means for supplying the transfer material; and a transfer material supplied by the supply means. a guide means formed of a conductive member for guiding the image to the transfer section; an application means for applying a bias voltage to the guide means; a detection means for detecting humidity within the image forming apparatus; An image forming apparatus comprising: a control means for selectively controlling the operation of the applying means according to a detection result of the applying means.