JPH05134564A - Image forming device - Google Patents

Abstract

PURPOSE:To make transfer electrification to paper constant. CONSTITUTION:A grid 10 electrically insulated from a shield case 5C is provided in an opening part 5H of the shield case 5C forming a transfer device 5 faced to an image carrier 1, an electrical power source device 20 for the grid impressing grid voltage Vg to the grid 10 is provided, and furthermore, the electrical power source device 20 for the grid is constituted of a device generating grid voltage Vg which is the same polarity as the transfer voltage Vd of an electrical power source device 5P for transferring.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus having an image carrier and a transfer device.

[0002]

2. Description of the Related Art FIG. 5 shows a general structure of an image forming apparatus. In the figure, reference numeral 1 denotes an image carrier, which is formed by applying a photosensitive agent on the surface of a cylindrical body made of, for example, an aluminum alloy, and rotates in a predetermined direction. On the peripheral surface of the image carrier 1,
A charging device 2, an optical unit 3, a developing device including a developing roller 4, a transfer device 5, a waste toner box including a blade 6, and a discharging lamp 7 are provided. Further, the paper P is conveyed along the guide 8 between the image carrier 1 and the transfer device 4.

In such an image forming apparatus, the surface of the image carrier 1 is uniformly negatively charged by the charger 2. Then, the optical unit 3 draws an electrostatic latent image, that is, an invisible image on the surface thereof. This invisible image is developed when passing through the developing roller 4, and becomes a visible toner image.

On the other hand, the paper P conveyed along the guide 8
One surface (lower surface) is positively charged by the transfer device 5 at a position interposed between the image carrier 1 and the transfer device 5.
That is, the electric charge generated by the corona discharge is directly applied to the paper P. Therefore, the visible toner image is transferred from the image carrier 1 to the other surface (upper surface) of the paper P by the action of the electric field.
Is transcribed to. After that, heat fixing is performed by a fixing device (not shown).

The toner remaining on the surface of the image carrier 1 is cleaned by the blade 6. The cleaned surface is discharged by exposure with the lamp 7, and the charger 2 is charged again.
Move to.

Here, the transfer device 5 has a structure in which a corona wire 5W is arranged in a shield case 5C having an opening 5H facing the image carrier 1. This corona wire 5
The transfer device power supply device 5P is connected to W, and the shield case 5C is grounded. Also, the transfer voltage Vd
Is a high voltage of, for example, +4.6 KV.

Therefore, in order to form a uniform and clear image on the paper P, it is necessary to set the transfer voltage Vd to an optimum value. In addition, a constant voltage power supply device (5P) may be adopted in order to keep a value that is carefully examined and set constant.

[0008]

However, the transfer device 5 (5
No matter how carefully the C, 5W, 5P) structure and the transfer voltage Vd are selected and set, the demand for diversification of the operating environment due to expansion and spread, stable operation over a long period of time, and higher image quality will be satisfied. There are cases where you can't.

That is, since the charging of one surface of the paper is influenced by the corona discharge, if the corona wire 5W is soiled or deteriorated due to toner adhesion or the like, the corona discharge is insufficient and the paper is insufficiently charged. That is, transfer blurring and transfer loss occur. Further, when the constant voltage power supply device (5P) is adopted, corona discharge is air discharge even in the main body of the device. Therefore, if the temperature, humidity, and air density change, the paper P cannot be charged in a predetermined manner. I will end up. For example, as shown in FIG. 6, if the altitude (m) of the installation location changes,
Transfer voltage Vd (4.6KV, 4.9KV, 5.2KV)
Even if is kept constant, the transfer current changes in inverse proportion to its electrical air resistance.

Therefore, when the set transfer current is changed to the decreasing side, the transfer charge is insufficient, and in this case as well, image unevenness and image missing occur, and high image quality cannot be guaranteed. Further, since the amount of toner remaining on the image carrier 1 also increases, the subsequent charging action of the charger 2 is hindered, and this also leads to further deterioration in image quality. In particular, an image forming apparatus of the cleaning and developing simultaneous cleaning type which does not have the blade 6 (for example, JP-A-3-797).
No. 2) has a strong possibility of causing a fatal defect.

On the other hand, when the set transfer current changes to the increasing side, the image carrier 1 is positively charged to the opposite polarity, so that not only the smooth transfer action is hindered but also the life of the image carrier 1 is extremely extended. It causes harmful effects such as shrinking.

An object of the present invention is to provide an image forming apparatus capable of controlling a transfer charging voltage to a sheet at a predetermined value and stably maintaining high image quality.

[0013]

[Means for Solving the Problems] The present invention is based on a number of actual machine delivery operation results, especially the following test and research results.
It is a new one created.

That is, as shown in FIG. 2, the state where the photosensitizer is peeled off from the image carrier 1, that is, the aluminum alloy tube 1S is assumed to be the paper P indicated by the two-dot chain line, and the sheet is transferred to this tube 1S. A charging equivalent voltage, that is, a tube applied voltage Vp is applied, and the tube inflow current Id is monitored. Then, Fig. 3
As shown in, the higher (lower) the transfer voltage Vd is, the larger (smaller) the elementary tube inflow current Id is. If the transfer voltage Vd is constant, the elementary tube inflow current becomes higher (lower) as the elementary tube applied voltage Vp increases. It can be seen that Id becomes large (small). That is, in the conventional configuration shown in FIG. 5, no matter how carefully the transfer voltage Vd is set, or whatever value the charging voltage of the paper P is selected, as shown in FIG. It can be seen that when the deterioration or the electrical air resistance, the temperature, the humidity, or the like changes, the charging voltage of the paper P changes due to their electrical balance.

In FIG. 2, a grid 10 is provided between the tube 1S and the corona wire 5W, and the grid 10 has the same polarity as the transfer voltage Vd and the tube applied voltage Vp.
Grid voltage Vg (eg + 1.2K)
V) is applied. Then, as shown in FIG. 4, the transfer voltage V
Even if d is changed to high or low, the set tube applied voltage Vp (+
At 1.2 KV), the bare tube inflow current Id becomes zero (0) and stabilizes. In other words, when the grid voltage Vg equivalent to the voltage (Vp) to be charged on one surface (lower surface) of the paper P is applied, the paper charging voltage can be kept constant at the set value and the image carrier is reversely charged. There is no current that causes this.

Incidentally, the grid voltage Vg is applied to the grid 10.
If the voltage is not applied, the grid 10 apparently acts in the same manner as the corona wire 5W, the ions (charges) generated by the corona discharge are dispersed in a wide range, and the nearby guide 8 is also charged. Therefore, the toner image transferred to the paper P is disturbed and the image quality is deteriorated. In addition, it pollutes the inside of the device.

Here, in the image forming apparatus according to the present invention, a sheet is interposed between an image carrier carrying a visible toner image and a transfer device, and one side of the sheet is charged while the other side is charged. In an image forming apparatus for forming an image by transferring a visible toner image, a grid electrically insulated from the shield case is provided in the opening of the shield case forming the transfer device, the opening facing the image carrier. A grid power supply device for applying a grid voltage is provided, and the grid power supply device is configured to generate a grid voltage having the same polarity as the transfer voltage of the transfer device power supply device.

[0018]

In the present invention having the above construction, the grid voltage corresponding to the transfer charging voltage for charging the sheet is applied to the grid to start the operation. Then, when the transfer voltage is constant and the environment changes and a current tries to flow from the power supply device for the transfer device to the paper or the image carrier, the grid blocks the current flow and sets the paper to a predetermined value. Can be charged.

[0019]

Embodiments of the present invention will be described below with reference to the drawings. This image forming apparatus has the same basic configuration as the conventional example (FIG. 5) and, as shown in FIG.
A grid 10 and a power supply device 20 for the grid are provided between the two, and the transfer charge to the paper can be controlled.

In FIG. 1, the transfer device 5 comprises a corona wire 5W made of gold-plated tungsten wire having a diameter of 60 μm and a metallic shield case 5C, and the shield case 5C is grounded. Also, the power supply device 5P for the transfer device
Can apply a high voltage of +6 KV to the corona wire 5W.

Here, the image carrier 1 of the shield case 5C.
An electrically conductive grid 10 is provided through a support member 15 in the opening 5H that faces the. This support member 1
5 has a volume resistivity of 10 ¹² to 10 ¹⁶ Ω. cm of electrically insulating material. In this example, it is made of ABS resin. That is, the grid 10 is electrically insulated from the shield case 5C.

Next, the grid power supply device 20 is connected so that a high voltage (Vg) having the same polarity as that of the transfer device power supply device 5P can be applied to the grid 10. Output voltage (Vg)
Is possible from 500V to 2.5KV. However, in the case of a reversal development method using a magnetic 1.5-component developer (toner), it is sufficient to be able to variably set between 800V and 2.2KV.

In the case of such an embodiment, when the transfer charging voltage to the paper P is set to 1.2 KV, for example, as shown in FIG. 4, the grid power supply device 20 is adjusted to set the grid voltage Vg to 1 It is applied to the grid 10 as about 0.2 KV. At this time, the set voltage (transfer voltage) Vd of the power source device 5P for the transfer device is the transfer charging voltage of the paper P as described in 1.
For example, it is set to 4.6 KV which is set to 2 KV.

Here, when the corona discharge is reduced due to dirt on the grid wire 5W or the like, even if the transfer voltage Vd is increased, or the ambient temperature, humidity and air density (electrical resistance) change, the above-mentioned diagram Inflow current Id described in 2 above
That is, even if the current to the paper P or the image carrier 1 tends to increase (decrease), the charging voltage of the paper P can be controlled to a predetermined value by the action of the grid (10).

However, according to this embodiment, the transfer device 5
The shield case 5C is provided with the grid 10 electrically insulated from the opening 5H of the shield kale 5C for forming the grid, and the grid power supply device 20 for applying the grid voltage Vg is provided. Since the transfer voltage of is controlled to be a predetermined value and constant, the corona wire 5W becomes dirty and deteriorates,
Or even if there is a change in ambient temperature, air density, etc., the paper P
Since a predetermined charge can be charged, a high-quality image can always be formed. Further, since the toner unstable movement due to static electricity when overcharged does not occur, transfer unevenness and missing can be prevented, and from this point also higher image quality can be achieved. Moreover, since the image carrier 1 is not charged with the opposite polarity, the life of the image carrier 1 can be prevented from being shortened.

Since the grid 10 has the same polarity as the transfer voltage Vd, the peripheral guide 8 is not charged, so that toner scattering and dirt in the apparatus can be prevented.

Further, since the grid power supply device 20 only needs to be able to apply the grid voltage Vg in charge of the paper charging voltage and the grid current is close to zero (0), it is economical with a small capacity.

Further, since the grid voltage Vg can be set and changed in the grid power supply device 20, the transfer voltage Vd and the sheet charging voltage can be optimally adjusted, so that the adaptability is wide. Further, since it is not necessary to use a constant voltage power source, the cost can be reduced.

[0029]

According to the present invention, a grid connected to the grid power supply device is provided between the image carrier and the transfer device,
Because the transfer charging voltage to the paper can be controlled, even if the corona wire is soiled with toner, deteriorates, or the ambient temperature or air density changes, the paper transfer charging voltage will not exceed the specified value. In addition, the image carrier can be prevented from being reversely charged. Therefore, stable and highly efficient transfer can always be performed, and a high-quality image can be stably formed.

[Brief description of drawings]

FIG. 1 is a diagram for explaining an essential part of an embodiment of the present invention.

FIG. 2 is likewise a diagram for explaining the operating principle.

FIG. 3 is a diagram for explaining a problem of a conventional example (without grid).

FIG. 4 is a diagram for explaining an operation when a grid is present and a grid voltage is applied.

FIG. 5 is a diagram illustrating a conventional image forming apparatus.

FIG. 6 is a diagram for explaining a change in transfer current in a conventional example.

[Explanation of symbols]

 1 Image Carrier 1S Element Tube 2 Charging Device 3 Optical Unit 4 Developing Roller 5 Transfer Device 5C Shield Case 5H Opening 5W Corona Wire 5P Transfer Device Power Supply Device 6 Blade 7 Elimination Lamp 10 Grid 15 Supporting Member 20 Grid Power Supply Device P Paper Vd Transfer voltage Vg Grid voltage

Claims (1)

[Claims] 1. A sheet is interposed between an image carrier carrying a visible toner image and a transfer unit, and the visible toner image is transferred to the other side while being charged from one side of the sheet to form an image. In the image forming apparatus, a grid power supply device is provided, in which a grid electrically insulated from the shield case is provided in an opening portion of the shield case forming the transfer device, the opening facing the image carrier. An image forming apparatus, wherein the image forming apparatus is provided, and the grid power supply device is configured to generate a grid voltage having the same polarity as the transfer voltage of the transfer device power supply device.