JP2003098854A - Image forming device - Google Patents

Abstract

(57) [Problem] To transfer an optimum transfer current to a toner image when an image is electrostatically transferred to two surfaces of a transfer material. SOLUTION: The transfer current of the second side of the transfer material is controlled based on the relative position between the first side image and the second side image during the transfer of the second side of the transfer material.

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.

[0002]

2. Description of the Related Art FIG. 5 and FIG. 6 show a conventional example.

In an electrophotographic image forming apparatus such as a copying machine, a printer or a facsimile, the surface of a photoreceptor 1 which is an image carrier is uniformly charged and electrostatically generated by light 3 carrying image information thereon. A latent image is formed, a toner image is formed on the photoconductor 1 by the developing device 4, and the toner image is directly formed on the transfer material 5 by the electrostatic transfer process or on the transfer material 5 via the intermediate transfer body 10. Images are formed by electrostatic transfer.

In the electrostatic transfer process, a corona transfer charging system has been conventionally used, but from the viewpoint of environmental protection in recent years, a contact transfer charging system in which ozone generation is extremely small is increasing. . Examples of the contact transfer charging method include roller transfer and blade transfer. In this transfer method, a transfer material, or a transfer material and a transfer material carrying member, or an intermediate transfer member is passed through a nip portion formed by pressing a conductive rubber roller or a conductive rubber blade to which a voltage is applied to a photosensitive member. Then, the toner image on the photoconductor is transferred to a transfer material or an intermediate transfer body. Similarly, when a toner image is formed on a transfer material via the intermediate transfer body, a transfer material is similarly applied to a nip portion formed by pressing a conductive rubber roller or a conductive rubber blade to which a voltage is applied to the intermediate transfer body. To transfer the toner image on the intermediate transfer member onto a transfer material.

Since the volume resistivity of these conductive rubber rollers or conductive rubber blades changes greatly depending on the environment, a constant current is applied in order to cope with resistance fluctuations due to resistance changes of these transfer charging members due to environmental changes. In some cases, a constant current method is used.

On the other hand, however, the constant current application method has the following problems.

That is, comparing the portion with the toner image and the portion without the toner image in the longitudinal direction of the photosensitive drum, a large amount of transfer current flows in the portion without the toner image due to the resistance of the toner itself, and the portion with the toner image is transferred. It is difficult for current to flow. Therefore, in order to obtain an optimal image, an image having a high longitudinal image ratio requires a small transfer current, but an image having a low longitudinal image ratio requires a larger transfer current. . In such an image forming apparatus, if the transfer current is set so that an optimum image is obtained when the image ratio in the longitudinal direction is high, for example, when the image ratio in the longitudinal direction is low, the transfer current becomes insufficient and transfer failure occurs. I will end up. Conversely, if the transfer current is set so that an optimal image is obtained when the image ratio in the longitudinal direction is low, excessive transfer current flows into the toner image area when the image ratio in the longitudinal direction is high, and the polarity of the toner changes. Will result in a transfer failure such as being reversed.

In such a situation, Japanese Unexamined Patent Publication No. 08-08
As described in Japanese Laid-Open Patent Publication No. 3006, it is conceivable to control the transfer current by the image ratio so that the transferability does not change due to the difference in the image ratio.

[0009]

However, in the case of printing on both sides of the transfer material, when the toner image on the photoconductor is transferred to the second surface of the transfer material or the toner image on the intermediate transfer material is transferred to the second surface of the transfer material. A toner image already exists on the first surface of the transfer material, and when only the image ratio at the time of transfer is taken into consideration as described in JP-A-08-083006, transfer failure may occur.

An example is shown in FIG.

FIGS. 1A and 1B are diagrams in which the toner image on the photosensitive member or the intermediate transfer member is about to be transferred to the second surface of the transfer material 5. The difference between FIGS. 1A and 1B is whether or not there is a toner image on the first surface.

In Japanese Patent Laid-Open No. 08-083006, the transfer current is determined in consideration of only the image ratio at the time of transfer, so that the toner images in FIGS. 1A and 1B have the same image ratio. (B) In both situations, the transfer current applied to the transfer charger 12 on the second side is the same. However, the current flowing in the toner image of FIG. 1A is suitable, but in FIG. 1B, the toner image exists on the first surface and the resistance of the toner image causes the toner image of FIG. As a result, an overcurrent occurs, which causes a transfer failure such as the polarity of the toner being reversed. That is, the optimum transfer current for the second surface differs depending on the relative position of the images on the first and second surfaces. In the special registration 02921066, the transfer current of the second surface is controlled depending on whether the image of the first surface is single or multiple, and the transfer current of the second surface is controlled by the relative position of the images of the first surface and the second surface. However, the above problem is not solved.

[0013]

In order to solve the above problems, the invention relating to the present application is directed to an image carrier on which a visible image is formed by means for forming a latent image and means for developing the latent image with toner. And a transfer charging member to which a transfer high voltage is applied, and the transfer charging member is in contact with a transfer material carrier carrying a transfer material or a transfer material at least at the time of transfer, and the transfer material is attached to the transfer material on the image carrier. In an image forming apparatus for electrostatically transferring an image to the transfer material, a storage device for storing image information of the image is provided, and an image A on the image carrier is placed on a surface α of the transfer material in contact with the image carrier. At the time of transfer, the transfer high voltage applied to the transfer charging member is controlled based on the information of the image B already transferred onto the back surface β of the surface α and the information of the image A. .

The information of the image A includes the relative position information of the image A and the image B.

The transfer high voltage applied to the transfer charger is controlled by a constant current.

The transfer charging member is provided with a second image carrier on which the image on the first image carrier is primarily transferred and carries the image, and a transfer charging member to which a transfer high voltage is applied. At least at the time of transfer, in a transfer material carrying member carrying a transfer material or in an image forming apparatus for contacting the transfer material and electrostatically transferring the image on the second image carrier to the transfer material, image information of the image A transfer device for storing the image A on the second image carrier, and when the image A on the second image carrier is transferred to the surface α of the transfer material in contact with the second image carrier, the image is transferred onto the surface β of the back surface of the surface α. It is characterized in that the transfer high voltage applied to the transfer charging member is controlled based on the information of the image B already transferred and the information of the image A.

The information of the image A includes the relative position information of the image A and the image B.

The transfer high voltage applied to the transfer charger is controlled by a constant current.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION (Embodiment 1) FIG.
About.

FIG. 2 is a schematic block diagram of an electrophotographic image forming apparatus showing one embodiment of the present invention.
Is a charging device, 3a is exposure for carrying image information, 4a is a developing device, 9a is a transfer charger, 7 is a registration roller, 1a
Is a photosensitive drum as an image carrier, 5 is a transfer paper, 15 is a transfer material carrier, 13 is a controller for controlling exposure for carrying image information, and 14 is a position and an image ratio of a toner image on the transfer material. The storage devices are shown respectively.

When an image is formed on both sides of a transfer sheet in an electrophotographic image forming apparatus as shown in FIG. 2, the photosensitive drum 1a is first uniformly charged to a negative polarity by the charging device 2a. In that state, an electrostatic latent image is formed on the photosensitive drum 1a by the exposure 3a.

Next, the electrostatic latent image formed on the photosensitive drum 1a by the exposure 3a is developed with the toner of the developing device 4a to obtain a toner image. Here, the developing device 4a is a developing device that performs reversal development.

The toner image formed on the photosensitive drum 1a through the respective steps in this manner is transferred to the transfer paper 5 by the transfer charger 9a whose constant current is controlled, and the fixing device 11
And the image is formed on the first surface of the transfer material. Next, the transfer material is automatically inverted, and an image is formed on the second surface of the transfer material with a transfer current controlled by the storage device 14.

The transfer charging system includes a non-contact charging device such as corona discharge or a contact charging device using a transfer charging member such as a blade, a roller or a brush. The non-contact charger has problems that ozone is generated, and that it is charged via air, so that it is vulnerable to fluctuations in the temperature and humidity environment of the atmosphere and an image is not stably formed. On the other hand, in the contact charger, the contact transfer charging blade is used in the present embodiment because it has advantages such as ozone less, resistance to temperature and humidity environment variation, and high image quality. Transfer blade member 9a
Is provided with a base material made of a rectangular plate-shaped conductive rubber, and a conductive electrode provided along the lower end of the base material in order to uniformly apply a voltage in the longitudinal direction. Linear pressure of 120g on photosensitive drum via recording material or recording material and conveyor belt
/ Cm is pressed. The material of the base material of the transfer blade is generally isoprene rubber, styrene rubber, butadiene rubber, nitrile rubber, ethylene propylene rubber,
Rubber materials such as butyl rubber, silicone rubber, chloropyrene rubber, chlorosulfonated polyethylene, acrylic rubber, hydrin rubber, urethane rubber, and fluororubber, or synthetic rubbers in which these are compounded, or synthetic resins such as nylon, urethane, and polyester, A mixture of conductive agents such as tin oxide and carbon black can be used, and the resistance value is about 10 ³ to 10 ¹⁰ Ω · cm and the hardness is 5
The blade member 9a was used by using a blade having a thickness of about 80 degrees (JIS A) and setting the thickness of the base material to about 2 mm. The transfer blades used are connected to a transfer high-voltage power supply (not shown).

In the image forming apparatus according to the present embodiment, the ratio of the second surface image in the longitudinal direction of the photosensitive drum immediately before the second surface transfer, the transfer position of the second surface toner image onto the transfer material, and the already transferred longitudinal direction 1 Surface image ratio and transfer material 1
The optimum transfer current changes depending on the position of the toner image on the surface.

This will be described with reference to FIG. As an example, consider the transfer in the image forming unit 8a in FIG.

The two drawings in FIG. 3 are cross-sections in the longitudinal direction of the image forming portion (transfer portion) 8a seen from upstream or downstream in the transfer material conveying direction when the toner image is being transferred onto the second surface of the transfer material. It is a figure. At the time of transferring the second surface of the transfer material, a portion where the toner image on the second surface is transferred to a portion on the second surface where the toner image is on the first surface is defined as a length in the longitudinal direction. At the time of transfer of the second surface of the transfer material, a portion where the toner image of the second surface is transferred to a portion of the second surface where the toner image is not present on the first surface is defined as a length b in the longitudinal direction. At the time of transferring the second surface of the transfer material, a portion where the toner image is not transferred is defined as a portion of the second surface where the toner image is present on the first surface and has a length c in the longitudinal direction. At the time of transferring the second surface of the transfer material, a portion where the toner image is not transferred on the first surface is a portion where the toner image is not transferred on the second surface and has a length of d in the longitudinal direction. When the second surface of the transfer material is transferred, the entire area in the longitudinal direction is defined as L in the case where the first surface is the entire solid in the longitudinal direction or white solid and the second surface is the entire solid in the longitudinal direction. Further, there is a relation of L = a + b + c + d.

The table of FIG. 3 will be described. When a certain second surface transfer current Itr is applied, the currents flowing in the entire portion or in the longitudinal direction are I ₁ , I ₂ , I ₃ , respectively.
I ₄ and I ₀ . The resistance of the part of R ₁ , R
₂ , R ₃ , R ₄ and R ₀ . Second side transfer current It
In each part when r is applied, the transfer current per longitudinal unit length is i ₁ , i ₂ ,
i ₃ , i ₄ , and i ₀ .

In this embodiment, the following formulas are established. i₁<I_Two<I_Four  … (1) i₁* R₁= I_Two* R_Two= I_Three* R_Three= I_Four* R_Four  … (2) Itr = I₁＋ I_Two＋ I_Three＋ I_Four= A * i₁+ B * i_Two+ C * i_Three+ D * i_Four   … (3) If there is a toner image, the resistance will increase, so
I flowing₁, I_Two, I _FourBecomes like the inequality in (1)
It

Equation (2) is based on Ohm's law.

Equation (3) is based on Kirchhoff's law.

In the present embodiment, i ₀ [A
/ M] becomes a transfer current with a transfer efficiency of 95% or more on the second side. It is good to let i ₀ flow in both parts of, but it is impossible from equation (1).

Suppose i ₀ is substituted for i ₁ . Then (2)
From the formula, i ₁ = i ₀ (4-1) i ₂ = (R ₁ / R ₂ ) * i ₀ (4-2) i ₃ = (R ₁ / R ₃ ) * i ₀ (4-) 3) i ₄ = (R ₁ / R ₄ ) * i ₀ (4-4).

When the expression (4-1) is established, the second surface transfer current Itr ₁ is (3) (4-1) (4-2) (4-3).
From the formula (4-4), Itr = (a + b * (R ₁ / R ₂ ) + c * (R ₁ / R ₃ ) + d * (R ₁ / R ₄ )) * i ₀ (5) On the other hand, suppose i ₂ Substitute i ₀ for Then, from the formula (2), i ₁ = (R ₂ / R ₁ ) * i ₀ (6-1) i ₂ = i ₀ (6-2) i ₃ = (R ₂ / R ₃ ) * i ₀ (6-3) i ₄ = (R ₂ / R ₄ ) * i ₀ (6-4)

Second surface transfer when expression (6-2) is established
Current Itr_TwoIs (3) (6-1) (6-2) (6-3)
From equation (6-4)   Itr_Two= (A * (R_Two/ R₁) + B + c * (R_Two/ R_Three) + D * (R_Two/ R _Four )) * I₀  … (5) That is, the transfer current Itr on the second surface is
i₁, I_TwoIn which of i₀Itr depending on the current flow₁，
Itr_TwoWill be selected. However, Itr = It
r₁, I₁= I₀When R₁/ R_Two> 1 i_Two> I₀
Overcurrent occurs in the area next to it.

On the other hand, when Itr = Itr ₂ and i ₂ = i ₀ , the current becomes insufficient at the portion where i ₁ <i _{0 because of} R ₂ / R ₁ <1.

Therefore, the optimum transfer current Itr for the second surface is determined by proportionally distributing Itr ₁ and Itr ₂ by the lengths a and b in the longitudinal direction of the portion. That is, Itr = (a * Itr ₁ + b * Itr ₂ ) / (a + b).

In the case of a laser printer system, the image information is binarized at the position of the transferred or transferred toner on the transfer material, and it is determined from the bitmap data of the controller controlling the writing device. You can ask. That is, a certain sampling interval s [s]
The position of the toner on the transfer material is detected every time. Regarding the first surface, the sampled toner position of the first surface is stored in the storage device 14. At the time of transfer of the second surface, the optimum transfer current is calculated from the toner position on the second surface to be transferred and the toner position on the first surface stored in the storage device 14, and the transfer current is controlled.

Further, the resistances R ₁ , R ₂ , and
R ₃ and R ₄ are obtained as follows.

The resistance _RA when transferring the entire solid on the first surface of the transfer material having the length L in the longitudinal direction and then transferring the entire solid on the second surface is measured.

R ₁ = _RA * (a / L) The first surface of the transfer material having a length L in the longitudinal direction is a white solid, and then,
The resistance R _B at the time of transferring the entire solid on the second surface is measured.

R ₂ = R _B * (b / L) The resistance R _C when the entire solid is transferred to the first surface of the transfer material having the length L in the longitudinal direction and then the white solid is transferred to the second surface is measured. .

R ₃ = R _C * (c / L) The first surface of the transfer material having a length L in the longitudinal direction is white solid, and then,
The resistance R _D when a solid white image is transferred to the second surface is also measured.

R ₄ = R _D * (d / L) In an image forming apparatus that forms a full-color image using toner of a plurality of colors, calculation of the optimum transfer current becomes more complicated.

(Second Embodiment) FIG. 4 shows a second embodiment.

FIG. 4 is a schematic configuration diagram of an electrophotographic image forming apparatus showing one embodiment of the present invention.
Is a charging device, 3b is exposure for carrying image information, 4b is a developing device, 9b is a primary transfer charging device, 10 is an intermediate transfer belt, 7 is a registration roller, 1b is a photosensitive drum as an image carrier, and 9x is Secondary transfer body electric device, 5 is a transfer paper, 13 is a controller for controlling exposure for carrying image information, and 14 is a storage device for storing the image ratio.

When images are formed on both sides of the transfer paper in the electrophotographic image forming apparatus as shown in FIG. 4, first, the photoconductor drum 1b is uniformly charged to, for example, a negative polarity by the charging device 2b. In that state, an electrostatic latent image is formed on the photosensitive drum 1b by the exposure 3b.

Next, the electrostatic latent image formed on the photosensitive drum 1b by the exposure 3b is developed by the toner of the developing device 4b to obtain a toner image on the photosensitive drum. Here, the developing device 4b is a developing device that performs reversal development.

The toner image formed on the photosensitive drum 1a through the respective steps in this manner is primarily transferred onto the intermediate transfer belt by the transfer charger 9b, and the toner image on the intermediate transfer body is subjected to a constant current. The image is formed on the first surface of the transfer material by being secondarily transferred to the transfer paper 5 by the controlled transfer electric device 9x and conveyed to the fixing device 11. Next, the transfer material is automatically inverted, and an image is formed on the second surface of the transfer material with a transfer current controlled by the storage device 14 in the same process.

The setting method of the optimum transfer current of the transfer charger 9x of the secondary transfer portion when printing is performed on the second surface of the transfer material is the same as the setting method described with reference to FIG. 3 in the first embodiment.

In an image forming apparatus that forms a full-color image by using toners of a plurality of colors, calculation of the optimum transfer current becomes more complicated.

[0052]

As described above, according to the first and second inventions of the present application, when the image is electrostatically transferred to the second surface of the transfer material, an optimum transfer current is applied to the toner image. You can

[Brief description of drawings]

FIG. 1 is a diagram for explaining a situation of a problem to be solved.

FIG. 2 is a sectional view of the image forming apparatus according to the first embodiment of the present invention.

FIG. 3 is a diagram for explaining an embodiment of the present invention.

FIG. 4 is a sectional view of an image forming apparatus according to a second embodiment of the present invention.

FIG. 5 is a sectional view of a conventional image forming apparatus.

FIG. 6 is a sectional view of a conventional image forming apparatus.

Claims (6)

[Claims] 1. A means for forming a latent image and an image carrier on which a visible image is formed by means of developing the latent image with toner.
A transfer charging member to which a transfer high voltage is applied is provided, and the transfer charging member is brought into contact with a transfer material carrier carrying a transfer material or a transfer material at least at the time of transfer, and an image on the image carrier is transferred to the transfer material. An image forming apparatus for electrostatically transferring to the transfer material, comprising a storage device for storing image information of the image, and transferring the image A on the image carrier to a surface α of the transfer material in contact with the image carrier. Sometimes, based on the information of the image B already transferred onto the back surface β of the surface α and the information of the image A,
An image forming apparatus which controls a transfer high voltage applied to the transfer charging member. 2. The image forming apparatus according to claim 1, wherein the information of the image A includes relative position information of the image A and the image B. 3. The image forming apparatus according to claim 1, wherein the transfer high voltage applied to the transfer charger is controlled by a constant current. 4. An image on the first image carrier is primarily transferred, and a second image carrier for carrying the image and a transfer charging member to which a transfer high voltage is applied are provided, and the transfer charging member is provided. An image forming apparatus that contacts a transfer material carrying member or a transfer material at least at the time of transfer, and electrostatically transfers the image on the second image carrier to the transfer material; A transfer device for storing the image A on the second image carrier, and when the image A on the second image carrier is transferred to the surface α of the transfer material in contact with the second image carrier, the image is transferred onto the surface β of the back surface of the surface α. An image forming apparatus characterized in that the transfer high voltage applied to the transfer charging member is controlled on the basis of the information of the image B already transferred and the information of the image A. 5. The image forming apparatus according to claim 4, wherein the information of the image A includes relative position information of the image A and the image B. 6. The image forming apparatus according to claim 4, wherein the transfer high voltage applied to the transfer charger is controlled by a constant current.