JPH07114273A - Image forming device - Google Patents

Abstract

PURPOSE:To prevent the scattering of toner and the generation of ozone and to provide an excellent image without a transfer fault and retransfer in an image forming device provided with a roller shape or belt shape transfer/ separation means. CONSTITUTION:An insulating sheet 9 is arranged between a transfer roller 2 and a separation roller 3, and further, when a DC component absolute value of a current between the transfer roller 2 and a transfer material 4, a photoreception drum 1 is defined ¦I1¦(muA), also, the DC component absolute value of the current between the separation roller 3 and the transfer material 4, the photoreceptor drum 1 as ¦I2¦(muA) and the DC component absolute value of the current between the transfer roller 2 and the separation roller 3 as ¦I3¦(muA) respectively, this device is controlled so that the relation ¦I1¦>¦I2¦>¦I3¦ is satisfied while the transfer material 4 passes through a transfer part and a separation part.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a copying machine, an LBP, etc.
The present invention relates to an electrophotographic image forming apparatus utilizing an electrostatic transfer / separation process.

[0002]

2. Description of the Related Art Heretofore, a corotron charger, a needle-shaped electrode, a roller-shaped electrode, a belt-shaped electrode, etc. have been used in an electrostatic transfer / separation type electrophotographic image forming apparatus.

On the other hand, in recent years, roller transfer and belt transfer have been developed from the viewpoint of ozone-less, which is related to environmental problems, and roller-shaped, belt-shaped electrodes and needle-shaped electrodes are also used as separating means. Among them, the roller-shaped or belt-shaped electrode is not deteriorated corresponding to the discharge deterioration of the needle tip in the needle-shaped electrode, and thus it is known that it is more advantageous than the needle-shaped electrode in terms of durability.

Further, since the roller-shaped and belt-shaped electrodes are rotatable, the cleaning effect of the cleaning member can be expected, and the durability is taken into consideration. Is advantageous.

[0005]

However, the roller-like or belt-like separating member generally does not reach the needle-like electrode in terms of separating performance. This is because the larger the radius of curvature of the electrode, the smaller the discharge efficiency and the smaller the amount of separated charges for the same applied voltage.

Therefore, in order to improve the separation performance, it is effective to bring the separating member closer to the image bearing member. However, since the transfer paper may come into contact with the separating member, it is closer to the transfer member side while moving toward the image bearing member. Measures have been taken to get closer to. Alternatively, the separation performance has been improved by increasing the voltage applied to the separation member.

In both of the above measures, a leak current is apt to occur between the transfer member and the separating member, and the electric field between both members causes the toner adhering to the surfaces of both members to scatter into the machine or the backside of the transfer paper. There was an adverse effect such as pollution. Also,
When the leak current is large, a large amount of ozone is generated due to discharge, and the balance of the amount of current from the transfer member and separation member to the transfer paper and the image carrier easily changes, resulting in poor transfer or retransfer due to excessive separation discharge. May occur.

Next, these problems will be specifically described with reference to an enlarged view of the transfer / separation portion in the conventional image forming apparatus shown in FIG. A transfer roller 2 and a separation roller 3 are arranged in proximity to the photosensitive drum 1 which is an image carrier, and the transfer power source 10 is connected to the transfer roller 2 and the separation power source 11 is connected to the separation roller 3. The toner image formed on the photosensitive drum 1 is transferred onto the transfer paper 4 by the voltage applied to the transfer roller 2 while passing between the photosensitive drum 1 and the transfer roller 2. The transfer paper 4 is separated by the voltage applied to the separation roller 3 and fixed by a fixing device (not shown).

The closest distance between the transfer roller 2 and the separation roller 3 is set to d, and the center of the photosensitive drum 1
2 connecting the centers of the transfer roller 2 and the separation roller 3
The distance of the line of the book on the peripheral surface of the photosensitive drum is set to L.

FIG. 9 shows the equivalent circuit of FIG. 8. The resistance value of the transfer roller is R _r1 or R ′ _r1 , the resistance of the space between the transfer roller and the transfer paper, and the electrostatic capacity are R _a1. ,
C _a1 , the resistance of the space between the separation roller and the transfer paper, the electrostatic capacity is R _a2 , C _a2 , the resistance of the space between the transfer roller and the separation roller, the electrostatic capacity is R _a3 , C _a3 , the resistance of the transfer paper, The capacitance is R _p or R ′ _p , C _p , and the capacitance of the photosensitive drum is R _d
Alternatively, R ′ _d and C _d are used (the space between the transfer paper and the photosensitive drum is omitted).

In addition, the transfer roller transfers the transfer paper, the direct current component of the photosensitive drum direction is I ₁ , the separation roller transfers the transfer paper,
The direct current component in the direction of the photosensitive drum is I ₂ , and the current in the direction from the separation roller to the transfer roller (not through the transfer paper) is I ₃ .

In the conventional image forming apparatus, the values of L and d in FIG. 8 are set small in order to secure the separation performance as described above. Therefore, the resistance R _{a3 in} the space between the transfer roller and the separation roller in FIG. 9 decreases, and the current I _{3 in the} direction from the separation roller to the transfer roller increases, and the DC component I of the current in the direction from the separation roller to the transfer paper and the photosensitive drum. _It may be larger than ₂ . That is, a leak current from the separation roller toward the transfer roller may occur.

The balance of I ₁ and I ₂ is important in the transfer and separation process. In FIG. 9, I ₃ is a discharge current, which is largely variable due to the environment, dirt on the transfer roller, separation roller, change in surface shape, etc., and the balance between I ₁ and I ₂ collapses as I ₃ changes. , | I ₁ | <|
When it was I ₂ |, transfer failure or retransfer occurred.

Therefore, an object of the present invention is to provide a roller-shaped or belt-shaped transfer / separation means capable of preventing toner scattering and ozone generation and obtaining a good image without transfer failure or retransfer. An image forming apparatus having the same is provided.

[0015]

The above object can be achieved by an image forming apparatus according to the present invention. In summary, the present invention is
An image carrier that carries a toner image, a roller-shaped or belt-shaped transfer unit that transfers the toner image on the image carrier to a transfer material at a transfer unit, and the transfer in which the toner image is transferred by the transfer unit. In an image forming apparatus having a roller-shaped or belt-shaped separating unit that separates a material from the image carrier at a separation unit, a DC absolute value of a current between the transfer unit and the transfer material and the image carrier. | I ₁ | (μA), the absolute value of the direct current component of the current between the separating means and the transfer material and the image carrier is | I ₂ | (μA), between the transferring means and the separating means. When the absolute value of the direct current component of the current is | I ₃ | (μA), the relational expression of | I ₁ |> | I ₂ |> | I ₃ | while the transfer material is passing through the transfer section and the separation section. The image forming apparatus is characterized by satisfying:

It is preferable to install a member having a volume resistance value of 10 ⁵ Ωcm or more and a thickness of 5 μm or more between both the transfer means and the separating means including the closest position.

Preferably, the voltage supplied to the transfer means and the separation means is direct current or direct current superimposed with alternating current.

Preferably, the alternating voltage supplied to the transferring means and the separating means has the same frequency and substantially the same phase.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An image forming apparatus according to the present invention will be described below in more detail with reference to the drawings.

FIG. 1 is a schematic configuration diagram of an image forming apparatus according to the present invention. In the figure, the photosensitive drum 1 which is an image bearing member rotated in the direction of the arrow is uniformly charged by a primary charging roller 8, and then an information signal is exposed by a light emitting element 7 such as a laser to form an electrostatic latent image. Form and develop device 5
To form a toner image with toner. The toner image is transferred to the transfer paper 4 by the transfer roller 2, the transfer paper 4 is separated by the separation roller 3, and the transferred toner image is fixed to the transfer paper 4 by a fixing device (not shown). On the other hand, the image carrier 1
The residual toner on the top is removed by the cleaner 6.

The photosensitive drum 1 is equipped with an a-Si photosensitive member having a diameter of 100 mm and a photosensitive layer thickness of 25 to 35 μm. The transfer roller 2 is made of foamed EPDM and has a diameter of 20 mm.
It has a volume resistivity of about 10 ⁷ to 10 ¹¹ Ωcm.
The separating roller 3 is made of SUS and has a diameter of 20 mm. The toner is a one-component dry magnetic toner with a particle size of 4
It is about 10 μm. Tribo is −10 to −15 μc / g on the photosensitive drum 1, and toner layer thickness is 30 when solid black.
It is about 60 μm. Although not shown, a guide is provided so that the transfer paper and the separation roller do not come into contact with each other so that the electric current does not leak from the transfer paper that has absorbed moisture. The process speed is 300 mm / sec, and the maximum sheet width in the longitudinal direction is 300 mm.

FIG. 2 is an enlarged view showing the transfer / separation unit of the image forming apparatus of FIG. 1, and shows a configuration similar to that of the transfer / separation unit shown in FIG. 8 and an equivalent circuit shown in FIG. I have it. The different point is that the distance between the transfer roller 2 and the separation roller 3 is set to be extremely small, and the insulating sheet 9 is arranged between them.

The transfer roller 2 has a total pressure of 100 g and the photoconductor 1
And rotates at the same peripheral speed as the photoconductor 1 by gear drive. The separation roller 3 is rotated at a distance of 3 mm from the photoconductor and is rotated at the same speed as the photoconductor 1 in the same direction as the transfer paper 4 is traveling.

The material of the insulating sheet 9 is PET, the volume resistivity is about 10 ¹⁴ Ωcm, and the thickness is 100 μm. The closest distance in the circumferential direction between the transfer roller 2 and the separation roller 3 is 2 m.
The insulating sheet 9 is fixed to the block 12 so as to be substantially equidistant from both rollers and is installed between the rollers.

The transfer power source 10 has a maximum output of +7 kV, +20
With 0 μA, as a control method, +15 μA constant current control is performed during pre-rotation, and constant current control is performed during transfer with a value obtained by adding a constant voltage to the voltage at that time. The current at this time is about +80 μA.

The separated power supply 11 has a maximum output of -3KV, -40
As a control method, a constant current control of −30 μA is performed during paper feeding in μA.

FIG. 3 is a diagram showing the relationship between the separation current I ₂ and the transfer efficiency when the transfer current I ₁ is kept constant at +80 μA. The transfer current I ₁ all flows toward the transfer paper and the photosensitive drum, and the separation roller The current I _{3 in the} direction is almost zero.

FIG. 4 is a diagram showing the relationship between the transfer current I ₁ and the transfer efficiency when the separation current I ₂ is zero. The highest transfer efficiency is obtained when the separation current I ₂ is about +80 μA. In the present invention, the transfer current I ₁ is +80 μA. Control so that

In FIG. 3, the separation current I ₂ is -50 μA.
It can be seen that the transfer efficiency decreases from the above level. It is considered that this is because the toner once transferred is returned to the photosensitive drum again by the separation electric field.

Assuming a practical transfer efficiency of 80%, FIG.
Therefore, the separation current I ₂ is 80 μA or less, that is, | I ₂ |> |
It can be seen that I ₁ |

In the present embodiment, I ₁ = 80 (μA), I
_{Since 2} = −30 (μA) and I ₃ ≈0 (μA), | I ₁ |> | I ₂ |> | I ₃ |.

By setting the respective current values as described above, it is possible to prevent the toner from scattering and the generation of ozone, and it is possible to obtain a good image without transfer defects or retransfer.

Next, another embodiment of the image forming apparatus according to the present invention will be described.

In this embodiment, a direct current voltage in which an alternating current is superposed is applied to both the transfer roller and the separation roller.

The apparatus is the same as that of the first embodiment, and the transfer bias is a DC voltage V ₁ = 7.0 KV, an AC voltage having a peak-to-peak voltage of about 6 KV and a frequency of 1000 Hz is applied. The phases are the same as shown in FIG.

At this time, the direct current components of the currents are I ₁ = 70 (μA) I ₂ = −30 (μA) I ₃ ≈0 (μA), respectively. That is, | I ₁ |> | I ₂ |> | I ₃ |. By setting the waveforms of both to have the same frequency and the same phase, I
It is possible to keep ₃ close to zero.

However, depending on the resistance values of the transfer roller and the separation roller, it may be more effective to slightly shift the phase at the same frequency, but it goes without saying that the present invention includes this case.

Therefore, also in this embodiment, it is possible to obtain the same effect as that of the above embodiment.

Further, in the present invention, as shown in FIG. 6, a transfer belt 22 may be used instead of the transfer roller,
Further, as shown in FIG. 7, a separation belt 33 may be used instead of the separation roller, and transfer and separation may be performed by a combination of the belt and the roller. In this case, it is possible to shorten L while keeping the closest distance d large by making one of them into a belt shape, and | I ₁ |> | I ₂ |> without an insulating member between both rollers. | I ₃ |
The separation performance is satisfied, and there is no scattering in the machine due to toner stains on the insulating member, which saves space.

[0040]

As is apparent from the above description, the image forming apparatus provided with the roller-shaped or belt-shaped transfer / separation means according to the present invention is capable of applying the current between the transfer means and the transfer material and the image carrier. The absolute value of the direct current component is | I ₁ | (μA), and the absolute value of the direct current component between the separating means and the transfer material and the image carrier is |
I ₂ | (μA), | I ₃ | (μA) is the absolute value of the direct current component of the current between the transfer means and the separation means, | I ₁ while the transfer material is passing through the transfer part and the separation part. |> | I ₂ |> | I
By satisfying the relational expression of ₃ |, it is possible to prevent toner scattering and ozone generation, and obtain a good image without transfer failure or retransfer.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of an image forming apparatus according to the present invention.

FIG. 2 is an enlarged view of a transfer / separation unit in FIG.

FIG. 3 is a graph showing the relationship between separation current I ₂ and transfer efficiency when the transfer current is constant.

FIG. 4 is a graph showing the relationship between transfer current I ₁ and transfer efficiency when the separation current is set to zero.

FIG. 5 is a graph showing an applied voltage waveform in another example.

FIG. 6 is an enlarged view of a transfer / separation unit showing a modification of the embodiment.

FIG. 7 is an enlarged view of a transfer / separation unit showing another modification of the embodiment.

FIG. 8 is a configuration diagram showing a transfer / separation unit of a conventional image forming apparatus.

9 is an equivalent circuit diagram of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photosensitive drum (image bearing member) 2 Transfer roller (transfer means) 3 Separation roller (separation means) 4 Transfer paper (transfer material) 9 Insulating sheet (insulating member)

Claims (4)

[Claims] 1. An image carrier that carries a toner image, a roller-shaped or belt-shaped transfer unit that transfers the toner image on the image carrier to a transfer material at a transfer unit, and the toner image is transferred by the transfer unit. In an image forming apparatus having a roller-shaped or belt-shaped separation unit that separates the transferred transfer material from the image carrier at a separation unit, a current flowing between the transfer unit and the transfer material and the image carrier. Absolute value of DC component of | I ₁ | (μA), absolute value of DC component of current between the separating unit and the transfer material and the image carrier is | I ₂ | (μA), the transferring unit and the separating unit. When the direct current absolute value of the current between the transfer means and the means is | I ₃ | (μA), | I ₁ |> | I ₂ |> | I while the transfer material is passing through the transfer part and the separation part. An image forming apparatus characterized by satisfying the relational expression ₃ |. 2. An insulating member having a volume resistance value of 10 ⁵ Ωcm or more and a thickness of 5 μm or more is provided between the transfer means and the separating means, including the closest position to each other. Image forming device. 3. The image forming apparatus according to claim 1, wherein the voltage supplied to the transfer means and the separation means is direct current or direct current superimposed on alternating current. 4. The image forming apparatus according to claim 3, wherein the AC voltages supplied to the transfer means and the separation means have the same frequency and substantially the same phase.