JP2003114582A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To cause an optimum transfer current to flow in a toner image during the transfer of it. SOLUTION: During the transfer of a toner image, a transfer current is controlled according to a position relative to a toner image transferred previously.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic type and electrostatic recording type image forming apparatus.

[0002]

2. Description of the Related Art FIG. 7 and FIG. 8 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. The transfer material is electrostatically transferred, and the transfer material is conveyed to a fixing unit (not shown), where the toner is melted and fixed on the transfer material to form an image.

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.

However, the constant current application method has the following problems.

In the longitudinal direction of the photosensitive drum, comparing a portion with a toner image with a portion without a toner image, a large amount of transfer current flows in a portion without a toner image due to the resistance of the toner itself, and a transfer current flows in a portion with a toner image. Is hard 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, when there is another toner image already transferred or fixed on the transfer material at the time of transfer, the toner image on the photoconductor is transferred to the transfer material or the intermediate transfer material. When transferring to a body, the above-mentioned JP-A-0
If only the image ratio at the time of transfer is taken into consideration as described in JP-A-8-083006, transfer failure may occur.

An example is shown in FIG.

FIGS. 2A and 2B are diagrams in which the toner image on the photoconductor is about to be transferred to the transfer material 5. Figure 2
The difference between (a) and (b) is whether or not there is another toner image already transferred or fixed on the transfer material.

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. Therefore, the toner images in FIGS. 2A and 2B have the same image ratio, and therefore the toner image in FIG. (B) In either situation, the transfer high voltage applied to the transfer charger 12 is the same. But Figure 2
The current flowing in the toner image of (a) is appropriate, but FIG.
In FIG. 2B, a toner image is present and the resistance of the toner image causes an overcurrent in the toner image in FIG. 2B, resulting in a transfer failure such as the polarity of the toner being reversed. Wake up. That is, the optimum transfer current differs depending on whether there is another toner image already transferred onto the transfer material or another toner image fixed at the time of transfer.

The same applies when images are formed on both sides of the transfer material. That is, when the toner image is transferred to the second surface of both surfaces, the toner image formed on the first surface is localized, so that the optimum transfer current is different as in the above case.

[0014]

A photosensitive member, latent image means for forming an electrostatic latent image on the photosensitive member according to image information, and the electrostatic latent image is developed with toner to form a toner image. An image having a developing means for contacting the photoconductor and a transfer charging means for electrostatically transferring the toner image to the transfer material by applying a charge having a polarity opposite to that of the toner, the developing means being in contact with the photoreceptor via the transfer material. The forming apparatus has means for measuring the resistance of the transfer material by dividing in the width direction perpendicular to the transfer material conveying direction, and based on the position information of the image and the result of the resistance measurement, An image forming apparatus characterized by controlling a transfer high voltage applied to a transfer charging member.

An image forming apparatus wherein the transfer high voltage applied to the transfer charger is controlled to a constant current.

An image forming apparatus wherein the means for measuring the resistance of the transfer material is a roller pair or a needle electrode divided in a direction perpendicular to the transfer material conveying direction.

A photosensitive member, a latent image means for forming an electrostatic latent image according to image information on the photosensitive member, a developing means for developing the electrostatic latent image with toner to form a toner image, and an intermediate portion. A first transfer charging unit, which is disposed in contact with the photosensitive member via the transfer member so as to be electrostatically primary-transferred to the intermediate transfer member by applying a charge having a polarity opposite to that of the toner; An image provided with a second transfer charging unit which is arranged to face the intermediate transfer member via a material and electrostatically secondarily transfers the toner image to the transfer material by applying a charge having a polarity opposite to that of the toner. The forming apparatus has means for measuring the resistance of the intermediate transfer member by dividing the intermediate transfer member in the width direction perpendicular to the conveying direction, and the primary image of the image from the photosensitive member to the intermediate transfer member is provided. At the time of transfer, based on the image information of the image and the result of the resistance measurement, Image forming apparatus and controls the transfer high voltage to be applied to the serial first transfer charging member.

An image forming apparatus characterized in that the transfer high voltage applied to the first transfer charger is controlled to a constant current.

The means for measuring the resistance of the intermediate transfer member is a roller pair or a needle electrode which is parallel to the surface of the intermediate transfer member and is divided in a direction perpendicular to the transfer material conveying direction. A characteristic image forming apparatus.

Intermediate between a photoconductor, a latent image means for forming an electrostatic latent image on the photoconductor according to image information, a developing means for developing the electrostatic latent image with toner to form a toner image, A first transfer charging unit, which is arranged to face the photosensitive member via a transfer member and electrostatically primary-transfers the toner image to the intermediate transfer member by applying a charge having a polarity opposite to that of the toner; An image provided with a second transfer charging unit that is disposed so as to face the intermediate transfer member via a sheet and electrostatically secondarily transfers the toner image to a transfer material by applying a charge having a polarity opposite to that of the toner. The forming apparatus has means for measuring the resistance of the transfer material by dividing the transfer material in the width direction perpendicular to the transfer material conveyance direction, and at the time of the secondary transfer of the image from the intermediate transfer body to the transfer material. The second information based on the image information of the image and the result of the resistance measurement. Image forming apparatus and controls the transfer high voltage to be applied to the transfer charging member.

An image forming apparatus characterized in that the transfer high voltage applied to the second transfer charger is controlled to a constant current.

An image forming apparatus wherein the means for measuring the resistance of the transfer material is a roller pair or a needle electrode divided in a width direction perpendicular to the transfer material conveying direction.

When the surface of the transfer material that comes into contact with the image carrier at the time of transferring the image is represented by the table, the image is formed on the back surface when the resistance of the transfer material is measured. apparatus.

[0024]

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

FIG. 6 is a schematic configuration 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 charging device, and 7 is 2.5 m in a direction horizontal to the transfer material and perpendicular to the transfer material conveying direction as shown in FIG.
A resistance measuring device for measuring the resistance of the transfer material by dividing the rollers into 128 at m intervals and applying a high voltage to each of the divided rollers to monitor the current value at that time. As the material of the base material of the roller of the resistance measuring device 7, isoprene rubber, styrene rubber, butadiene rubber, nitrile rubber, ethylene propylene rubber, butyl rubber, silicone rubber, chloropyrene rubber, chlorosulfonated polyethylene, acrylic rubber, hydrin rubber, urethane. Rubber,
A rubber material such as fluororubber, a synthetic rubber obtained by compounding them, or a synthetic resin such as nylon, urethane or polyester mixed with a conductive agent such as tin oxide or carbon black can be used. 10 ³ ~ 1
A material having a hardness of about 0 ¹⁰ Ω · cm and a hardness of about 5 to 80 degrees (JISA) is used. Reference numeral 1a denotes a photosensitive drum, which is an image carrier, 5 denotes a transfer sheet, 15 denotes a transfer material carrier, and 13 denotes a controller for controlling exposure for carrying image information.

In the electrophotographic image forming apparatus as shown in FIG. 6, first, the photosensitive drum 1a is uniformly charged with, for example, 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
Then, the image is formed by being transported to.

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 image ratio in the longitudinal direction of the photosensitive drum immediately before transfer, the transfer position on the transfer material, the image ratio in the longitudinal direction of the toner image already transferred, and the transfer material on the transfer material. Depending on the position of the toner image,
The optimum transfer current changes.

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

The two figures in FIG. 3 are longitudinal sectional views 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 transfer material. is there.

At the time of transfer, a portion where the toner image is transferred to a portion where the toner image is already present on the transfer material is defined as a length a in the longitudinal direction.

At the time of transfer, a portion where the toner image is transferred to a portion where the toner image is not present on the transfer material is defined as a length b in the longitudinal direction.

At the time of transfer, the portion where the toner image is not transferred to the portion where the toner image is present on the transfer material is defined as the length c in the longitudinal direction.

At the time of transfer, a portion where the toner image is not transferred is set to a portion where the toner image is not transferred on the transfer material, and the length is set to d in the longitudinal direction.

At the time of transfer, the entire solid or white solid has already been transferred on the transfer material in the longitudinal direction, and the entire area in the longitudinal direction when transferring the entire solid in the longitudinal direction is defined as L. .

Further, there is a relation of L = a + b + c + d.

The table of FIG. 3 will be described. A certain transfer current It
When r is applied, the currents flowing in the part or the entire region in the longitudinal direction are I ₁ , I ₂ , I ₃ , I ₄ , and I ₄ , respectively.
I ₀ . The resistance of the part of R ₁ , R ₂ , R
₃ , R ₄ and R ₀ . At each portion when a certain transfer current Itr is applied, the transfer currents per unit length in the longitudinal direction are i ₁ , i ₂ , i ₃ , i ₄ , i _{0, respectively.}
Is.

In this embodiment, the following equations are established.

[0041]   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 an equation 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 that 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).

Transfer current I when equation (4-1) holds
tr ₁ is (3) (4-1) (4-2) (4-3) (4-
4) From the equation, 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 that i ₂ is i _0. Is substituted. 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)

Transfer current I when equation (6-2) holds
tr_TwoIs (3) (6-1) (6-2) (6-3) (6-
From equation 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 is i₁, I_Twoof
Where i₀Itr depending on the current flow₁, Itr_TwoChoose
Will be selected. However, Itr = Itr₁, I₁
= I₀  When R₁/ R_TwoI from> 1_Two> I₀  Tona
Overcurrent will occur in the lower part.

On the other hand, Itr = Itr ₂ , i ₂ = i ₀
In this case, the current becomes insufficient in the portion where i ₁ <i _{0 because} R ₂ / R ₁ <1.

Therefore, the optimum transfer current Itr 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).

The position of the already transferred toner image can be known by the resistance measuring device 7 divided in the width direction perpendicular to the transfer material conveying direction. FIG. 4 is a schematic view of the resistance measuring device 7 divided in the width direction perpendicular to the transfer material conveyance direction, as viewed from upstream or downstream in the transfer material conveyance direction.
If the toner image is already present before the transfer, the resistance becomes high, and the resistance distribution in the longitudinal direction can be known by the divided resistance measuring device 7, and the position of the toner image already transferred can be known.

Further, the position in the longitudinal direction of the toner image to be transferred on the photosensitive drum at the time of transfer can be known as follows. That is, in the case of a laser printer system or the like, the image information is binarized and can be known from the bitmap data of the controller controlling the writing device. Sampling interval s for bitmap data
Sampling is performed every [s] to detect the position of the toner image on the photosensitive drum in the longitudinal direction during transfer.

Therefore, a, b, c, d in the table of FIG. 3 are known from the result of the resistance measurement and the result of the sampling of the bitmap data described above, and the optimum transfer current is calculated to calculate the transfer current. To control.

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

The entire solid is transferred to a transfer material having a length L in the longitudinal direction, and the resistance _RA at the time of transferring the entire solid is measured.

R ₁ = R _A * (a / L) _A white solid is transferred to a transfer material having a length L in the longitudinal direction, and then,
The resistance R _B when transferring all solids is measured.

R ₂ = R _B * (b / L) All solids are transferred to a transfer material of length L in the longitudinal direction, and then
The resistance R _C when transferring a white solid is measured.

R ₃ = R _C * (c / L) A white solid is transferred to a transfer material having a length L in the longitudinal direction, and the resistance R _D at the time of transferring the white solid is measured.

R ₄ = R _D * (d / L) In the image forming apparatus for forming a full-color image, the combination of toner layers transferred and laminated as shown in FIG. 3 is a in the table of FIG. , B, c, and d, the calculation becomes more complicated.

When the surface of the transfer material on which the toner image is to be transferred is represented, even if the already transferred toner image is on the back surface of the transfer material at the time of transfer, the optimum transfer current of the present invention is calculated. Is applicable.

(Second Embodiment) FIG. 5 shows a second embodiment.

FIG. 5 is a schematic configuration diagram of an electrophotographic image forming apparatus showing an embodiment of the present invention, and is denoted by reference numeral 2b in the figure.
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, and 7 is horizontal and intermediate to an intermediate transfer member or transfer material as shown in FIG. Rollers divided into 128 at intervals of 2.5 mm in the direction perpendicular to the transfer body or the transfer material conveyance direction. High voltage is applied to each of the divided rollers, and the current value at that time is monitored to detect an intermediate transfer body or transfer. A resistance measuring device for measuring the resistance of materials. As the material of the base material of the roller of the resistance measuring device 7, isoprene rubber, styrene rubber, butadiene rubber, nitrile rubber, ethylene propylene rubber, butyl rubber, silicone rubber, chloropyrene rubber, chlorosulfonated polyethylene, acrylic rubber, hydrin rubber, urethane. Rubber materials such as rubber and fluororubber, or synthetic rubber compounded with them, or nylon,
A synthetic resin such as urethane or polyester mixed with a conductive agent such as tin oxide or carbon black can be used, and has a resistance value of about 10 ³ to 10 ¹⁰ Ω · cm and a hardness of 5 to 80 degrees (JISA). Use something of a degree. 1b
Is a photoconductor drum which is an image carrier, 9x is a secondary transfer electric device, 5 is a transfer paper, and 13 is a controller which controls exposure for carrying image information.

In the electrophotographic image forming apparatus as shown in FIG. 5, first, the photosensitive drum 1b is uniformly charged with, 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 with 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 fed with a constant current. The image is secondarily transferred onto the transfer paper 5 by the controlled transfer body electric device 9x and conveyed to the fixing device 11 to form an image on the transfer material.

The method of setting the optimum transfer currents of the transfer charger 9b of the primary transfer portion and the transfer charger 9x of the secondary transfer portion when printing on the transfer material is the setting described in Embodiment 1 with reference to FIG. The method is similar.

In the image forming apparatus for forming a full-color image using toners of a plurality of colors, the combinations of toner layers transferred and laminated as shown in FIG. 3 are a, b, c in the table of FIG. , D, which makes the calculation of the optimum transfer current complicated.

Regarding the secondary transfer portion, when the surface of the transfer material to which the toner image is to be transferred is shown as a table, even if the toner image already transferred is on the back surface of the transfer material at the time of transfer, the present invention can be used. The calculation of the optimum transfer current is applicable.

[0068]

As described above, according to the invention of the present application, when an image is electrostatically transferred to a transfer material or an intermediate transfer member, an optimum transfer current can be applied to a toner image, and a transfer failure occurs. Does not happen.

[Brief description of drawings]

FIG. 1 is a diagram for explaining a divided resistance measuring device of the present invention.

FIG. 2 is a diagram for explaining a situation of a problem to be solved.

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

FIG. 4 is a diagram for explaining the first embodiment of the present invention.

FIG. 5 is a diagram for explaining a second embodiment of the present invention.

FIG. 6 is a sectional view of the image forming apparatus according to the first embodiment of the present invention.

FIG. 7 is a sectional view of a conventional image forming apparatus.

FIG. 8 is a sectional view of a conventional image forming apparatus.

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Claims (10)

[Claims] 1. A photoconductor, a latent image means for forming an electrostatic latent image on the photoconductor according to image information, and a developing means for developing the electrostatic latent image with toner to form a toner image. In an image forming apparatus including a transfer charging unit that is arranged in contact with the photoconductor via a transfer material to electrostatically transfer the toner image to the transfer material by applying a charge having a polarity opposite to that of the toner, The transfer charging member has means for measuring the resistance of the transfer material by dividing it in the width direction perpendicular to the transfer material conveying direction, and based on the position information of the image and the result of the resistance measurement, the transfer charging member is An image forming apparatus characterized by controlling a transfer high voltage applied. 2. The image forming apparatus according to claim 1, wherein the transfer high voltage applied to the transfer charger is controlled to a constant current. 3. A means for measuring the resistance of the transfer material, wherein the roller pair is divided in a direction perpendicular to the transfer material conveying direction,
Alternatively, the image forming apparatus according to claim 1 or 2, which is a needle electrode. 4. A photoconductor, a latent image means for forming an electrostatic latent image according to image information on the photoconductor, and a developing means for developing the electrostatic latent image with toner to form a toner image. A first transfer charging unit that is disposed in contact with the photoconductor via the intermediate transfer member and that electrostatically primary-transfers the toner image to the intermediate transfer member by applying a charge having a polarity opposite to that of the toner. And a second transfer charging unit which is arranged to face the intermediate transfer member via a transfer material and electrostatically secondarily transfers the toner image to the transfer material by applying a charge having a polarity opposite to that of the toner. In the image forming apparatus, a unit for measuring the resistance of the intermediate transfer member by dividing the intermediate transfer member in the width direction perpendicular to the transport direction is provided, and the image transfer from the photosensitive member to the intermediate transfer member is performed. During the primary transfer, based on the image information of the image and the result of the resistance measurement Image forming apparatus and controls the transfer high voltage to be applied to the first transfer charging member. 5. The image forming apparatus according to claim 4, wherein the transfer high voltage applied to the first transfer charger is controlled to a constant current. 6. A means for measuring the resistance of the intermediate transfer member,
The image forming apparatus according to claim 4, wherein the image forming apparatus is a roller pair or a needle electrode divided in a width direction perpendicular to the conveyance direction of the intermediate transfer member. 7. A photoconductor, a latent image means for forming an electrostatic latent image on the photoconductor according to image information, and a developing means for developing the electrostatic latent image with toner to form a toner image. A first transfer charging unit that is arranged to face the photoconductor through an intermediate transfer member and electrostatically primary-transfers the toner image to the intermediate transfer member by applying a charge having a polarity opposite to that of the toner. A second transfer charging unit that is disposed in contact with the intermediate transfer member via a transfer material so as to electrostatically secondarily transfer the toner image to the transfer material by applying a charge having a polarity opposite to that of the toner. In the image forming apparatus described above, the image forming apparatus includes means for measuring the resistance of the transfer material by dividing the transfer material in the width direction perpendicular to the transfer material conveying direction, At the time of transfer, based on the image information of the image and the result of the resistance measurement, the first
An image forming apparatus, wherein the transfer high voltage applied to the transfer charging member is controlled. 8. The image forming apparatus according to claim 7, wherein the transfer high voltage applied to the second transfer charger is controlled to a constant current. 9. The means for measuring the resistance of the transfer material is a roller pair or a needle electrode divided in a width direction perpendicular to the transfer material conveying direction.
Alternatively, the image forming apparatus according to Item 9. 10. The surface of the transfer material, which is in contact with the image carrier at the time of transferring an image, is represented as a surface, and when the resistance of the transfer material is measured, the image is already transferred to the back surface. The image forming apparatus according to claim 1.