KR100312571B1 - Image transferring method using an intermediate transfer body and image forming apparatus for practicing the same - Google Patents

Abstract

In the image forming apparatus, the potential caught on the back side of the transfer member is selected to be zero or selected to have the same polarity as the charge of the image carrier at least part of the gripping point formed for image transfer. In this state, an image transfer condition that can minimize toner scattering during image transfer can be set to prevent change of storage of the transfer member over time, and thus an image with minimum toner scattering can be obtained.

Description

IMAGE TRANSFERRING METHOD USING AN INTERMEDIATE TRANSFER BODY AND IMAGE FORMING APPARATUS FOR PRACTICING THE SAME}

The present invention relates to an image transfer method using an intermediate transfer member and an image forming apparatus for implementing the same.

More specifically, the present invention provides an image transfer method for transferring a toner image from a photoreceptor element or similar image carrier to a paper or such a recording medium through an intermediate transfer member, and can transfer paper from the photoreceptor element or the like image carrier. An image transfer method for transferring a toner image onto paper or a similar recording medium using a belt, and a copying machine, printer, facsimile or similar image forming apparatus for performing any one of these methods.

In electrophotographic image forming apparatuses, especially full-color image forming apparatuses, it is common to transfer the second toner stage, that is, the first transfer stage and the second transfer stage, the raw toner image from the photosensitive member element to the paper.

In the first transfer step, successive toner images of different colors are transferred from the photosensitive member to an intermediate transfer member such as a belt, for example.

In the second transfer step, the toner image transferred to the transfer member is transferred to the paper in a concentrated manner. For the first transfer, an electric field is formed by a bias applied to one or both of the two rollers through which the transfer body passes.

The two rollers are located on both sides of the photoreceptor element.

Optionally the two rollers can be grounded, in which case a bias will be applied to the contact member located centrally between the nip between the photoreceptor element and the transfer member.

The intermediate transfer member may be often formed with an average volume resistance 10 ⁸ Ω㎝ ~ 10 ¹³ Ω㎝ or average surface resistance of 10 ⁷ Ω ~ 10 ¹² Ω material.

In this kind of intermediate transfer member, it is possible to discharge the transfer charge applied from the charge applying means during image transfer or to reduce the required static discharge output even when such discharge means are used, without using a corona discharger or similar discharge means.

However, a problem of the image forming apparatus in the form of performing the first and second image transfers is that the images tend to blur due to toner scattered around in the two image transfer steps.

Such toner scattering changes depending on the transfer voltage and the transfer current.

In general, transfer current, transfer voltage, and other transfer conditions are initially set to minimize toner scattering while performing maximum toner transfer efficiency before shipment of the apparatus, but transfer to realize both high transfer efficiency and satisfactory toner scattering reduction. The range of conditions is very narrow.

It is difficult to reduce toner scatter significantly because the optimum transfer condition is related to the changing ambient conditions and the characteristics of the changing photosensitive element and the intermediate transfer belt.

In particular, when the ambient conditions such as temperature and humidity change, the amount of charge adhering on the toner and the resistance of the transfer member also change, so that constant transfer conditions lower the transfer efficiency or cause the toner to scatter around.

In particular, when the storage of the transfer body decreases, the transfer voltage exceeds its optimum value and further promotes toner scattering due to discharges generated at the image transfer position.

To overcome the changing ambient conditions, the temperature and humidity sensors have been provided to the image forming apparatus. Transfer conditions measured in advance experimentally were selectively set according to the output of the sensor, thereby compensating for environmental changes. On the other hand, the average resistance material made of resin and carbon black or similar conductive filler dispersed in the resin tends to decrease its resistance with time.

For the intermediate transfer material made of such an average resistance material, the deterioration over time is roughly experimentally estimated for the deterioration trend and compensated by changing the transfer condition according to the estimated tendency.

Japanese Patent Laid-Open Publication No. 4-45470 discloses an image forming apparatus of a type in which a preliminary transfer is omitted by using an image transfer conveyance belt and causing the paper and the photoreceptor element to contact each other at the upper portion of the image transfer portion.

Japanese Patent Laid-Open No. 4-186387 discloses an image forming apparatus including a transfer drum and eliminating preliminary transfer by providing a means for shielding the electric field at an upper position of the electric field forming means.

However, each of the above conventional image forming apparatuses corrects based on experimental data or empirical data. Therefore, such a device cannot end users easily overcome the operating conditions or make accurate corrections.

Toner scattering is particularly noticeable during image transfer when the intermediate transfer member or transfer member for conveying paper is made of the average resistive material. That is, when the intermediate transfer member is formed of the average resistance material, the transfer charge applied from the charge applying means can be moved to the transfer member portion outside the nip where the image carrier and the transfer member come into contact with each other. As a result, a potential gradient and an electric field are formed on the surface of the intermediate transfer body outside the holding point. In particular, the electric field formed at the inlet of the gripping point acts on the toner in the image carrier at an upper position of the gripping point in the direction of movement of the intermediate transfer member. As a result, the toner image is partially transferred from the image carrier to the intermediate transfer member (preliminary transfer) before reaching the gripping point, resulting in deterioration of the image quality.

Further, in some types of image forming apparatuses, an undesirable electric field is formed at a position downstream of the gripping point, thereby spoiling the toner image preferably transferred to the intermediate transfer member. This also causes toner scattering, uneven image density, localized runoff and many other problems.

It is therefore an object of the present invention to provide an image forming apparatus capable of preserving transfer conditions for minimum toner scattering, for example, such as changes in transfer body resistance due to elapsed time, and always keeping toner scattering to a minimum. .

It is another object of the present invention to provide an image forming apparatus capable of reducing toner scatter during image transfer and thus obtaining a desired image from image carriers to intermediate transfer members or from paper carriers to sheets of paper placed on a transfer belt.

Another object of the present invention is to provide an image forming apparatus capable of setting an optimum transfer condition based on a potential attached to the rear of the transfer member or a current flowing behind the transfer member.

It is still another object of the present invention to provide an image transfer method capable of reducing an undesirable electric field between an image carrier and an intermediate transfer member, and an image forming apparatus for implementing the same.

1 is a schematic diagram schematically showing an image carrier and an intermediate transfer member included in a conventional image forming apparatus and a member coupled thereto;

2A and 2B show that toner is scattered in the conventional apparatus shown in FIG.

3 is a schematic diagram showing a first embodiment of an image forming apparatus according to the present invention;

4 is a partially enlarged view in which the gripping point between the photosensitive drum and the intermediate transfer belt included in the first embodiment of the present invention is enlarged;

5 is a graph showing the relationship between the transfer voltage applied from the transfer bias power source to the exit roller and the voltage measured in each of the first and third embodiments.

6 is a graph showing that toner scattering and toner efficiency change according to the transfer voltage change in the first embodiment;

7 is a graph comparing the first embodiment and the second side with respect to the first side with respect to the transfer voltage applied to the exit roller and the potential caught on the rear face of the intermediate transfer belt.

8 is a graph showing changes in toner scattering level and transfer efficiency with respect to the transfer voltage in the first embodiment;

9 is a graph showing a change in toner scattering level and transfer efficiency with respect to a transfer voltage in a second aspect;

10 and 11 are flowcharts showing the control procedure in the third embodiment.

12 is a schematic view showing a photosensitive member, an intermediate transfer belt, and elements associated therewith included in a fourth embodiment of the present invention;

13 is a schematic view showing a fourth aspect

14 is a graph showing the relationship between the current flowing from the conductive brush to the ground and the voltage applied to the exit roller and measured in the fourth and fifth embodiments.

15 is a graph showing the relationship between the gripping point brush current and the transfer bias

FIG. 16 is a diagram of a current flowing through a gripping point

17 shows an intermediate transfer belt and a photosensitive member element included in a second example according to the fourth embodiment.

18 is a flowchart showing a control procedure showing the fifth embodiment

19 and 20 show the sixth and seventh embodiments of the present invention, respectively;

21 and 22 show a seventh embodiment

23 shows the advantages of the seventh embodiment

24A and 24B show a specific image according to the seventh embodiment

25 is a view showing an accurate contact angle of the shock brush included in the seventh embodiment

26 shows an eighth embodiment of the present invention.

27 is a view showing an intermediate transfer belt included in the eighth embodiment of the present invention.

FIG. 28 is a view illustrating a position where an antistatic brush included in the eighth embodiment is located

29 and 30 show ninth and tenth embodiments of the present invention, respectively;

31 is a view showing a position where a brush included in the tenth embodiment is located.

Explanation of symbols on the main parts of the drawings

10, 30 image forming apparatus

12, 32 ... photoconductive drum

14, 44 ... belt (intermediate image transfer body)

16, 46 ... bias roller

18.ground roller

34.Charger

36.laser beam

42 ... sensor

60 ... cleaning blade

N ... nip

According to the present invention, a method of transferring a toner image from an image carrier to a transfer member in contact with the transfer member or to a recording medium supported by the transfer member performs image transfer by electrical manipulation at a contact portion where the image carrier and the transfer member come into contact with each other. To form an electric field.

At least a portion of the contact portion has a reduction operation for reducing the electric field so that the potential of the transfer member becomes zero or has the same polarity as the charge attached to the image carrier.

Further, according to the present invention, the image forming apparatus includes an image carrier for forming a toner image thereon by charging.

The transfer member maintains contact with the image carrier at the contact portion for transferring the toner image onto the recording medium by the image transfer electric field formed at the contact portion.

At least a portion of the contact portion causes the reduction electrode to bring the potential on the transfer member to zero or to the same polarity as the charge attached to the image carrier.

Furthermore, according to the present invention, the image forming apparatus includes an image carrier for forming a toner image by charging. The transfer member is held in contact with the image carrier at a position where the toner image is transferred to the recording medium by the image transfer electric field formed at the contact position.

The reduction electrode is grounded to reduce the transfer electric field.

The current Inip flowing from the reduction electrode to the ground is selected to be zero or less when the image carrier is chargeable with negative polarity, or to be zero or more when the image carrier is chargeable with positive polarity.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

Conventional image forming apparatus to aid the understanding of the present invention; In particular, an apparatus in which toner scattering is caused during image transfer will be briefly described.

As shown in Fig. 1, a conventional image forming apparatus 10 includes an image carrier in the form of a photosensitive drum 12.

An intermediate image transfer member having an intermediate resistance is provided as the belt 14 and is in contact with the drum 12.

The bias roller 16, which is an image transfer and serves as a charge application means, is located downstream of the grip point N between the drum 12 and the belt 14 in the direction in which the belt 14 moves.

For example, a bias of 800 V (absolute value) is applied to bias roller 16.

A ground roller 18 is located downstream of the grip point N in the direction of movement of the belt 14.

Ground roller 18 is grounded but this is a specific type of electrode that is grounded or applied with a predetermined bias.

Since the belt 14 has an intermediate resistance, a potential gradient 24 (indicated by shading) occurs in the belt 14 and extends from the downstream side toward the upstream side of the gripping point N in the direction of movement of the belt 14.

The potential gradient 24 is 300 V (absolute value) at inlet 20 at grip point N and 600 V (absolute value) at outlet 22 of grip point N.

As a result, the image transfer electric field is formed at the holding point N.

In Fig. 1, the gradient 24 is shown by a straight line extending from the charge application position to the antistatic position. In practice, however, because the gradient contacts drum 12 at grip point N, the slope of the straight line changes at grip point N, or the straight line is partially replaced by the curve of FIG. 2 or a similar nonlinear gradient.

In other particular arrangements, corona dischargers, rollers, image transfer brushes or braids or similar charge application means are located at gripping point N.

A grounded or biased electrode is located upstream of the gripping point N in the direction of movement of the belt 14. In this arrangement, it is also possible to generate a potential gradient 24 on the belt 14 based on the intermediate resistance of the belt 14.

Gradient 24 extends upstream from the charge application position in gripping point N.

The problem with such a device 10, however, is that the charge applied by the bias roller 16 can be transferred to the belt 14 portion outside of the grip point N due to the intermediate resistance of the belt 14. As a result, an electric field is also generated in the above portion of the belt 14, thereby degrading the quality of the resultant toner image.

In particular, the electric field formed at inlet 20 of gripping point N acts on gripping point N on the toner formed on drum 12 at position 26, which is different from the expected image transfer position, such that a portion of the toner at position 26 moves from drum 12 to belt 14. Let the soldier die

As a result, the toner is scattered around.

As a result, text, lines or images are contaminated or image quality is degraded. 2A shows a contaminated image 28a transferred from drum 12 to belt 14.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

First embodiment

3 shows an electrophotographic image forming apparatus embodying the present invention, which is shown at 30. In summary, the apparatus 30 has one photoconductive element or image carrier and, for example, four developing units facing the photoconductive element and each assigned a specific color. The toner images, which are made of different colors and are continuously formed on the photoconductive element, are successively transferred to intermediate image transfer belts arranged in an overlapping manner. As a result, the synthetic toner images are collectively transferred onto one sheet or similar recording medium. As a result, a color image is formed on the sheet.

As shown in FIG. 3, the photoconductive element is comprised as a drum 32. The drum 32 comprises a hollow core formed as aluminum, although not particularly shown in detail, and a functionally separated photoconductive layer formed on the core. Although not shown, the photoconductive layer includes a base layer, a charge generation layer, a charge transfer layer, and the like. The photoconductive layer has a thickness of approximately 28 μm and a capacity of approximately 90 pF / cm ² . During image formation, the drum 32 is rotated in the direction of the arrow in FIG. 3 by a drive source (not shown). The charger 34 consists of a scorotron charger and uniformly charges the surface of the drum 32 to approximately -650V to -700V. The laser beam 36 scans the charged surface of the drum 32 according to the image data, and electrostatically forms a latent image of -100V to -500V. This process is repeated to successively form latent images corresponding to four different colors: black (BK), cyan (C), magenta (M) and yellow (Y).

The potential sensor 38 detects the charge potential of the drum 32 and the potential of the exposed portion of the drum 32. A controller not shown controls the charged state, the exposed state, and the like based on the output value of the potential sensor 38. The developing units 40BK, 40C, 40M, and 40Y constitute one developing unit, each storing toner of a specific color. Each of the developing units 40BK-40Y develops a latent image of an associated color formed on the drum 32 to form a toner image. In particular, each of the developing units 40BK-40Y stores a dry two-component developer, i.e., a toner and a carrier mixture, and adheres the negative toner to the low potential of the drum 32. Developing units of this type are generally referred to as reversal type developing units.

A bias power source (not shown) for development applies a bias voltage of approximately -500V to -550V to each development unit 40BK-40Y. If necessary, an AC component can be superimposed on the bias. The sensor 42 detects the amount of toner adhered on the drum 32. The sensor 42 is configured as an optical sensor capable of detecting the amount of toner adhered based on the optical reflectance of the drum 32. The controller controls process conditions in response to the output of the sensor 42.

The toner image on the drum 32 is successively transferred onto the intermediate transfer belt 44 of the endless track. Transfer of the toner image from the drum 32 to the intermediate transfer belt 44 is referred to as belt transfer for simplicity. The belt 44 passes through the drive roller 46, the driven roller 48, the roller 50 facing the belt cleaning unit 66, the inflow roller 52 and the discharge roller 54. A drive source (not shown) rotates the belt 44 through the drive roller 46. . A moving mechanism (not shown) moves the portion of the belt 44 between the inlet roller 52 and the outlet roller 54 to contact or separate the drum 32. When the belt 44 and the drum 32 are in contact with each other, they form a recess N for image transfer therebetween.

In the illustrated embodiment, the belt 44 portion between the inlet roller 52 and the outlet roller 54 is 36 mm, but the belt 44 is 350 mm in its longitudinal direction. The belt 44 is composed of a resistive layer of a single medium consisting of a fluorine-containing resin and carbon black dispersed in the resin. In this embodiment, the belt 44 has a thickness of approximately 150 μm, and if it is new, has a surface resistance of approximately 5 × 10 ⁹ Ω / cm ² and a volume resistance of approximately 1 × 10 ¹¹ Ωcm. The volume resistance (ρv) is 10 using a measurement unit Hiresta IP (MCP-HT260) (trade name), probe HRS Robe (trade name) available from Mitsubishi Petrochemical, and a bias voltage of 100 V (ρv) and 500 (ρs). Measured for seconds. If necessary, the volume resistance is measurable in the manner described in JIS (Japanese Industrial Standard) K6911.

The surface resistance was measured by the use of Hiresta IP (trade name) available from Yuka Denshi, which can also be made in the manner described in JIS K6911.

The belt 44 may be made of polycarbonate or a similar resin. In this embodiment, the inlet roller 52 is formed as a conductive material, connected to ground, and the discharge roller 54 is connected to a transfer bias power source (not shown) for image transfer. The transfer bias power source applies a positive voltage Vt to the discharge roller 54. In other words, an indirect transfer voltage application system is used. A power source control means (not shown) controls the voltage Vt to be applied to the discharge roller 54 from the transfer bias power source.

The precleaner 56 controls the charge of the toner remaining on the drum 32 after belt transfer. The cleaning blush 58 and the cleaning blade 60 constituting the drum cleaning device remove the residual toner whose charge is controlled by the precleaner 56. The discharge lamp 62 then dissipates the remaining charges on the drum 32. The charger or charging means 34, the exposing portion or the exposure means, the developing unit or the developing means 40BK-40Y, the belt or the transfer member 44, and the transfer bias power source together constitute a toner image forming means.

In order to form a toner image of the first color BK, the drum 32 is uniformly charged by the charger 34 and exposed by the exposed portion. The resulting BK latent image is developed by the developing unit 40BK and transferred to the belt 44. As a result, a BK toner image is formed on the belt 44. The toner remaining on the drum 32 after the image transfer is removed by the precleaner 56, the sweep blush 58, and the sweep blade 60. Subsequently, the charge remaining on the drum 32 is dissipated by the discharge lamp 62.

The process for forming the toner image of the second color C is the same as the above process up to the step of developing a latent image formed on the drum 32. The resulting C toner image is transferred from the drum 32 to the belt 44 onto the BK toner image present on the belt 44. Thereafter, the toner and charge on the drum 32 are removed by the preliminary cleaner 56, the sweep brush 58, the sweep blade 60 and the discharge lamp 62, respectively.

The process for forming the toner image of the third color M is also the same as the above process up to the step of developing a latent image formed on the drum 32. The resulting M toner image is transferred from the drum 32 onto the BK and C toner images held in writing with the belt 44. Thereafter, the toner and charge on the drum 32 are removed in the manner described above.

The process for forming the toner image of the fourth color (Y) is also the same as the above process up to the step of developing the latent image formed on the drum 32. The resulting Y toner image is transferred from the drum 32 onto the BK, C, and M toner images existing in the state written on the belt 44, thereby completing the entire color image. Thereafter, the drum 32 is cleaned by the precleaner 56, the sweep brush 58, the sweep blade 60 and the discharge lamp 62. The voltage Vt applied from the transfer bias power source to the discharge roller 54 can be continuously increased whenever the toner image is transferred from the drum 32 to the belt 44.

Sheet S is fed from the sheet supply to the point between the belt 44 and the roller 64, the leading edge of which meets the leading edge of the full color image on the belt 44. The roller 64 is pressed to the driving roller 46 through the belt 44, and forms a concave portion N between the roller 64 and the belt 44. A bias power source (not shown) applies both transfer voltages to roller 54. This transfer voltage is applied from the rear of the sheet S to the sheet S between the roller 64 and the belt 44. As a result, the full color image is transferred from the belt 44 to the sheet S. The image transfer from the belt 44 to the sheet is called sheet transfer. In this respect, the roller 64 will be referred to as sheet transfer roller 64. The image of all colors on the sheet S is fixed by a fixing unit (not shown). The belt cleaning unit 66 mentioned above removes the toner remaining on the belt 44 after sheet transfer.

The intermediate transfer body embodied as belt 44 allows the process units around the belt 44 to be arranged more freely, which makes it possible to reduce the overall size of the device 30. However, the advantage of this embodiment is that it can be achieved even with an intermediate transfer body in the form of a drum or roller.

In the above-mentioned embodiment, when the charged state, the resistance of the belt or the intermediate transfer member 44, the output value of the transfer bias power source, and the like are measured at least in part of the concave portion N, the rear side of the belt (the portion not contacting the drum 32). Is selected such that the potential Vnip of the phase is of zero polarity or of the same polarity as the charge attached to the drum 32. The manner in which the potential on the rear of the belt 44 accumulates will be described below. Essentially, it is desirable that the potential on the front part of the belt 44 should be described as the charge potential of the belt 44. In practice, however, the potential on the front part of the belt 44 (the part in contact with the drum 32) cannot be measured directly at the N part. When measured at the recess N, the correlation between the electric potential on the rear part of the belt 44 and the electric potential on the front part of the belt 44 will be described below with reference to FIG.

As shown in FIG. 4, assuming that the resistance of the belt 44 and the transfer bias voltage are as mentioned above, the front portion of the belt 44 facing the drum 32 is charged with negative tens of volts in the vicinity of the N portion. And a few hundred volts negative in the vicinity of the transfer bias roller 54. This is because the distance between the roller 54 and the front portion of the belt 44 and the distance between the roller 54 and the rear portion of the belt 44 decrease with increasing distance from the roller 54. In the vicinity of the concave portion N, the front part of the belt 44 is charged to the negative side rather than the rear part due to the negative charge of the drum 32. Thus, if the potential on the rear part of the belt 44 is zero or negative, The negative potential is reliably attached to the front part of the belt 44. This entails the reduction of the electric field attributable to the dispersion of the toner at the inlet of the recess N. It is assumed that the correlation between the front part and the rear part of the belt 44 is maintained even when the resistance of the belt 44 and the transfer bias is changed under the condition of actually implementing image transfer. As shown in FIG. 4, a conductive brush 70 and a transfer bias power source 72 are shown.

The range in which the potential Vnip on the rear portion of the belt 44 is zero or the same polarity as the charge of the drum 32 should be changed according to the mechanical conditions different from the width l of the recess N and the transfer characteristics of the toner itself. In this case, the electric field must be reduced at the position preceding the front portion N in order to remove the blurred image. Another prerequisite is that the width of the effective portion should be made as long as possible to prevent the transfer rate from lowering. It is assumed that the drum 32 and the belt 44 initiate contact with each other at position 0 shown in FIG. 4 and are separated from each other at position L shown in FIG. 4. Then, in order to satisfy the preceding conditions, the charging condition, the resistance of the belt 44, the output of the transfer bias power source, etc. are optimally selected so that the potential Vnip on the rear part of the belt 44 is zero or at the recess N, 0 ≦ X ≦ L It has the same polarity as the charge of the drum 32 at position X over the range of / 2. As long as this range satisfies the preceding condition, the embodiment is practical even when the position X does not fall within such a certain range due to the charging condition and developing condition of the drum 32.

Hereinafter, the optimum image transfer condition will be described. In this embodiment, the distance between the inlet roller 52 and the position O was selected to be 8 mm. The width l of the recess N was chosen to be 20 mm. The distance between the position L and the discharge roller 54 was selected as 8 mm. As shown in FIG. 3, the potential sensor 68 is located at the rear side of the belt 44 at the recess N. FIG. The potential sensor 68 measures the potential Vnip on the rear portion of the belt 44 over a range of approximately 4 mm of the portion whose center is located 7 mm away from position O. Thus, the sensor 68 measures the average value of the rear potential Vnips of the belt 44 over a range of 5 mm ≦ X ≦ 9 mm.

FIG. 5 is a graph showing the correlation between the transfer voltage Vt applied from the transfer bias power source to the discharge roller 54 and the rear potential of the belt 44. FIG. In particular, the rear potential of the belt 44 was measured while the charged portion of the drum 32 was passed through the transfer position without being exposed (same as the image of the blank sheet). The rear potential of the belt 44 changes due to non-uniformity of the belt 44 resistance. In this regard, the rear potential of the belt 44 was measured over one complete wheel of the belt 44, and the average value of the measured potentials was determined. The measurements showed that the rear potential Vnip of the belt 44 is zero or the same polarity as the charge of the drum 32 when the transfer voltage Vt includes the portion below 800V. Therefore, in the above embodiment, it is possible to implement a transfer condition that minimizes toner dispersion while preventing the transfer efficiency from lowering when the transfer voltage Vt includes a portion of 800 V or less.

6 shows how the toner dispersion and the transfer efficiency change in relation to the transfer voltage Vt. As shown, the toner dispersion was evaluated by observing the toner image transferred to the belt 44 (a linear image approximately 0.3 mm wide) as an enlarged scale. Grade 5 and Grade 1 represent the smallest and largest variances, respectively. The transfer efficiency was determined as the weight value of the toner measured by the suction mechanism before and after the transfer of the solid toner image.

As shown in Fig. 6, although the dispersion seems to increase with an increase in the transfer voltage Vt, it is placed in class 4 or higher when the voltage Vt includes a portion of 800V or less; Classes 4 and 5 are acceptable in practical use. Further, although the transfer efficiency decreases with the decrease in the transfer voltage Vt, 90% or more transfer efficiency is achieved when the voltage Vt is about 500V or more. Therefore, the dispersion of the toner was successfully reduced when the transfer condition was selected such that the rear potential Vnip of the belt 44 contained less than zero. More preferably, when the transfer conditions were selected to establish a relationship of -100 V ≦ Vnip ≦ 0, not only the reduction of the toner dispersion but also sufficient transfer efficiency was achieved.

As long as the drum 32 included in the above embodiment can be negatively charged, it is possible to use a positively chargeable drum. If the drum 32 is bipolarly chargeable, the toner will be bipolarly charged and the transfer bias of the negative electrode will be applied. In this case, the transfer conditions will be selected such that the potential Vnip on the rear portion of the belt 44 is greater than zero at position X over a range of 0 ≦ X ≦ L / 2. This also successfully reduces toner dispersion. . In this embodiment, the output value of the transfer bias power source is controlled by the power source control means to change the rear potential Vnip of the belt 44. Alternatively, the output value of the charger 34 or the resistance of the belt 44 can be adjusted for the same purpose.

A first comparative example will be described below in connection with the above embodiment. The comparative example differs from the above embodiment in that the inflow roller 52 and the discharge roller 54 are rearranged to change the width l of the concave portion N. In the comparative example, the distance between the inflow roller 52 and the contact start position O was selected as 12 mm, the width l was selected as 10 mm, and the distance between the separation start position and the discharge roller 54 was selected as 14 mm. The measuring range of the potential sensor 68 is approximately 4 mm. Thus, the sensor 68 calculates the average value of the rear potential Vnips of the belt 44 over a range of 1 mm ≦ X ≦ 5 mm.

Fig. 7 shows a correlation between the transfer voltage Vt applied to the discharge roller 54 and the rear potential Vnip of the belt 44, which is specified in the first comparative example. As shown, the rear potential Vnip is only zero or less when the transfer voltage Vt is zero. 8 shows a correlation between the transfer voltage Vt, the toner dispersion level and the transfer efficiency, which is also specified in the comparative example. As shown, a range in which the toner dispersion level was 4 or more and the transfer efficiency was 90% or more was not obtained at all.

Second embodiment

This embodiment is the same as the first comparative example with respect to the width L of the concave portion N, but differs from the latter with respect to the resistance of the belt 44. In the present example, when the belt 44 was new, it had a volume resistance of approximately 1 × 10 ¹¹ Ωcm. It should be noted that the image transfer body applicable to this embodiment has a resistance range determined by the output and the capacity of the transfer power source. For example, even if the resistance of the transfer member is as low as 1 × 10 ⁷ Ωcm, the transfer member can be used when a power source capable of allowing a strong current to flow is used. As long as the commonly used transcript allows a current of approximately tens of microamps, even a low resistance transcript can be used if the current is increased to several microamps.

Also, several kilovolts of transfer bias is typically applied to the transfer body. Even a high resistance transcript may be used if it is implemented in a single layer and a transfer bias of approximately 10 kV is applied. It is assumed that the transcript has a double layer structure. Then, even if the volume resistance of the entire transfer member in the thickness direction is approximately 1 x 10 ¹³ Ωcm, the transfer member has a general voltage and a general voltage if the surface layer is approximately 1 x 10 ¹³ Ωcm and the base layer is 1 x 10 ¹⁰ Ωcm. It can be used within the range of current. Thus, the embodiment described above is practical in the volume resistivity range of 1 x 10 ⁷ Ωcm to 1 x 10 ¹³ Ωcm. The volume resistivity range useful in this embodiment can be formed in the range of 1 x 10 ⁸ Ωcm to 1 x 10 ¹² Ωcm in the case of a single layer or 1 x 10 ¹³ Ωcm in the case of a double layer from the cost point of view of the power source.

The correlation specific to the second embodiment and between the transfer voltage applied to the discharge roller 54 and the rear potential Vnip on the belt 44 is also shown in FIG. As shown, in the present embodiment, when the transfer voltage Vt is 1,600 V or less, the rear potential Vnip was less than zero. Fig. 9 shows how the toner dispersion level and the transfer efficiency change in accordance with the transfer voltage Vt.

In the second embodiment, as in the first embodiment, although the toner dispersion tends to increase with an increase in the transfer voltage Vt, an actually acceptable grade 4 or more is obtained when the voltage Vt is 1,600V or less. Was achieved. Although the transfer efficiency decreases with the decrease in the transfer voltage Vt, a transfer voltage of 90% or more was obtained when the voltage Vt was approximately 1,200 V or more. Therefore, it was possible to reduce toner dispersion by selecting the transfer condition for implementing the rear potential Vnip to be less than zero. Preferably, a correlation of −60 V ≦ Vnip ≦ 0 was set to reduce toner dispersion and increase transfer efficiency.

As explained above, each of the first and second embodiments has new various advantages as listed below.

(1) The image forming apparatus includes toner image forming means having a photoconductive drum or a movable image carrier 32. The charger 34 and the exposed portion constitute image forming means for electrostatically forming a latent image on the drum 32. The developing unit 40BK-40Y serves as a developing means for developing the latent image to produce a toner image corresponding thereto. The intermediate transfer belt or crawler transfer member 44 passes through a plurality of rollers 46, 48, 50, 52 and 54. The belt 44 contacts the drum 32 between two 52 and 54 of the rollers 46-54 to form a concave portion N. The toner image is transferred from the drum 32 to the belt 44 in the recess portion N. The bias power source applies an opposite polarity charge to the toner to at least one of the two rollers 52 and 54. In this structure, the potential on the rear of the belt 44 within at least a portion of the concave portion N is selected as zero or the same polarity as the charge attached on the drum 32. Thus, the electric field for image transfer in the portion of the N portion is weakened, so that the generation of the electric field in the gap preceding the N portion is reduced. This is to successfully prevent the movement of the toner at the position preceding the front portion N, and thus to allow the minimum toner to be dispersed during image transfer.

(2) Assume that the position where the drum 32 and the belt 44 start contacting each other is position O, and the position where they start to separate from each other is position L. Then, the potential on the rear portion of the belt 44 is selected as the same polarity as the charge of the drum 32 at any position X of the recess N located at zero or in the range 0 ≦ X ≦ LK / 2. This is to reduce the intensity of the electric field in the portion adjacent to the inlet of the recess N, thus preventing the movement of the toner at the position preceding the recess N, and allowing the minimum toner to disperse during image transfer.

(3) The potential sensor or the potential measuring means 68 detects the potential Vnip on the rear of the belt 44 at the specific position X mentioned above. Therefore, an optimum image transfer condition can be set based on the output of the sensor 68, thereby reducing the toner dispersion during image transfer.

Third embodiment

This embodiment additionally includes a control unit that affects the measurement of the rear potential Vnip at power up of the device and whenever the imaging cycle is repeated a predetermined number of times compared to the first embodiment. They are similar to each other except they are included. When the power rises, the charging and developing conditions are optimized, and the transfer voltage Vt applied from the transfer bias power source to the belt 44 is optimized.

In particular, as shown in Fig. 10, the charging condition and developing condition at the time of power up are optimized as in general process control. Such optimizations are known and therefore will not be described in particular detail. Successively, the voltage Vt applied from the transfer bias power source to the belt 44 is optimized. Immediately at this time, the drum 32 rotated by the drive source is charged to approximately -650V by the charger 34 and passed through the developing unit 40BK-40Y without being exposed. The developing unit 40BK-40Y using a reversal developing system does not operate in the same way as when they form an image of a blank sheet. When the charging section of the drum 32 reaches the belt transfer position, the potential sensor 68 detects the rear potential of the belt 44. Thereafter, the accumulated number of sheet outputs is reset to zero after the final setting of the transfer voltage Vt. This leads to a stand-by state. If the preset number of sheets is an output value after power rise, the transfer voltage Vt is set. This too leads to a standby state.

In order to eliminate the influence of the non-uniform resistance distribution of the belt 44, the sensor 68 detects the rear potential Vnip of the belt 44 obtained from a single transfer voltage Vt over the complete round of the belt 44, and the average value of the measured potential Vnips is It is desirable to be used as a numerical value for control. In particular, as shown in Fig. 11, after the start of formation of the white sheet image, the transfer voltage Vt is applied. In this condition, the rear potential Vnip is measured. If the rear potential Vnip is zero, it will be possible to increase the voltage Vt. Thus, the voltage Vt is increased to Vt + DELTA V by one step DELTA V, and the potential Vnip is measured again. This process is repeated until the rear potential Vnip exceeds zero. Since the potential Vnip exceeding zero is excessive, the voltage Vt 'is generated one step ago, that is, Vt' = Vt-DELTA t is set as the optimal transfer voltage. The transfer voltage Vt shown in FIG. 5 has an initial value of 0 V and increases continuously in steps of 200 V, and the initial value can be selected to be several hundred volts to reduce the voltage set time. Then, the interval between the steps of the voltage Vt can be reduced to 50V to perform more precise control over the voltage Vt.

In this embodiment, the transfer voltage Vt is controlled so that the maximum voltage within the range for implementing the rear potential Vnip below zero at the position X is set as the optimum transfer voltage. In particular, the power source control means controls the output value of the transfer bias power source so that the transfer voltage Vt matches the optimum transfer voltage. When the belt 44 is new, the voltage Vt of 800 V is set as the optimum voltage as described above.

Again, the range where the rear potential Vnip is zero or the same polarity as the charge of the drum 32 does not have to be within 0 ≦ X ≦ L / 2 depending on the transfer condition.

Then, when the normal image forming cycle was repeated for 5,000 sheets without setting any of the optimum transfer voltages described above, the toner dispersion grade was lowered from 4.0 to 3.5 in the halftone region first. The volume resistance of the belt 44 was lowered to approximately 5 x 10 ⁹ Ωcm. When the optimum transfer voltage setting was executed again in the above-mentioned manner, the characteristic shown by the dotted line in Fig. 5 was obtained; The optimal transfer voltage was set at 600V. Under these conditions, a uniform image with minimum toner dispersion was obtained from the halftone region to the solid area. Each time the image forming cycle is repeated according to the preset number of sheets, the control unit performs the rear potential measurement and sets the optimum transfer voltage based on the result of the measurement.

When the volume resistance of the belt 44 is about 1 × 10 ⁸ Ωcm or less, the current output flowing through the belt 44 from the transfer bias power source increases. As a result, a condition that implements a back potential of less than zero cannot be obtained. In this case, 90% or more of transfer efficiency did not occur in the range in which the dispersion grade 4 or more was realized.

As described above, the third embodiment has the following advantages.

(1) Assume that the position where the drum 32 and the belt 44 start contacting each other is position O, and the position where they start to separate from each other is position L. Then, the potential sensor or the potential detecting means 68 measures the rear potential of the belt 44 at an arbitrary position X of the recess N located in the range 0 ≦ X ≦ L / 2. The control unit causes the sensor 68 to detect the potential Vnip at the recess N during image transfer. The control unit controls the operation of the toner image forming means so that the potential Vnip is zero or of the same polarity as the charge of the drum 32. Therefore, by periodically measuring the dislocation Vnip and setting a condition to reduce toner dispersion, it is possible to maintain a transfer condition such that minimum dispersion occurs against a change in resistance of the belt 44 due to aging, and thus at least To ensure an image with toner dispersion of

(2) The means for controlling the operation of the toner image forming means is implemented as power source control means for controlling the output of the transfer bias power source. Therefore, the transfer conditions that generate the minimum toner dispersion can be maintained while ensuring an image with the minimum toner dispersion against the resistance change of the belt 44 due to aging.

Fourth embodiment

In the fourth embodiment, as in the first embodiment, the distance between the inlet roller 52 and the contact start position O is set to 8 mm, the width l of the concave portion N is selected to be 20 mm, and the separation start position L and the discharge roller are The distance between 54 was chosen as 8mm. In this embodiment, as shown in Fig. 12, the conductive brush 70 is located on the rear side of the belt 44 at the N-side. The brush 70 remains in contact with the rear portion of the belt 44 over a range of its center 7 mm away from the contact starting position O.

The brush 70 is 340 mm wide in its longitudinal direction and approximately 4 mm wide in the movement direction of the belt 44. The brush 70 is in contact with the rear portion of the belt 44 at position X over a range of 5 mm <X <9 mm. The position X is located in the range 0 ≦ X ≦ L / 2 of the N part.

The inlet roller 52 is connected to ground by a conductor. The transfer bias power source 72 applies a transfer bias to the discharge roller 54. The brush 70 consists of 24 carbon-containing 360 denier acrylic filaments. The filament has a resistance of approximately 1 × 10 ⁷ Ωcm.

As shown in Fig. 13, in the production of the device, an ammeter 74 is connected between the brush 70 and ground to set the transfer voltage. The ammeter 74 is connected such that the brush 70 side and the ground side are respectively formed as an anode and a cathode. In this state, the power source control means varies the transfer voltage applied from the power source 72 to the discharge roller 54, and the ammeter 74 measures the current Inip flowing from the brush 70 to ground. The optimal transfer current is determined based on the measurement result, and the transfer voltage is controlled to the optimum voltage.

Fig. 14 shows the correlation between the transfer voltage Vt applied to the discharge roller 54 and the current flowing from the brush 21 to the ground and determined by the above measurement. For this measurement, the charging section of the drum 32 passed through the exposed position without being exposed (blank sheet image). Since the current flowing from the brush 70 to ground changes due to the uneven distribution of resistance of the belt 44, the current flowing from the brush 70 to ground was measured over one complete wheel of the belt 44, and the average value of the current Obtained. The measurements showed that the current Inip flowing from the brush 70 to ground is less than 800V within the range of Vt ≤ 800V (current flowing from ground to the brush 70 or electrons flowing from ground to the brush 70). In the above-described embodiment, the transfer condition that produces the minimum toner dispersion can be obtained in the above range Vt? 800V.

The current Inip will be described using experimental data. The first belt was formed with carbon dispersion ETFE (ethylene tetrafluoroethylene) and a thickness of 150 μm. The first belt had a surface resistance of 10 ⁹ Ω to 10 ¹⁰ Ω, a volume resistance of 10 ¹⁰ Ωcm to 10 ¹¹ Ω, and had a specific induction capacity of 11 ± 3. The second belt was formed with a carbon dispersed polycarbonate to a thickness of 150 μm. The second belt had a surface resistance of 10 ⁸ Ω to 10 ⁹ Ω and a volume resistance of 10 ⁸ Ωcm to 10 ⁹ Ωcm.

The electric current flowing through the brush 70 and the potential attached to the inlet roller 52 during image transfer were measured, and compared to investigate the deterioration of toner dispersion due to the decrease in resistance of the belt 44. 15 shows the current flowing through the brush 70. For the measurement, a nip ground bias application system, Method D, was used. In Fig. 15, the ordinate indicates the current flowing through the brush 70 (닢 brush current), and the abscissa indicates the transfer bias voltage.

As shown in Fig. 16, two different current components, i.e., the omnidirectional current I1 drawn from the positive transfer bias and applied to the discharge roller 54, and the negative charge attached on the non-imaging region of the drum 32, Reverse current I2 flowing toward it flows hypothetically through the brush 70. The current Inip and the toner dispersion level change according to the correlation between the currents I1 and I2. For the first belt, the current Inip becomes negative because the current I2 becomes greater than the current I1 over the transfer bias range from 0V to approximately + 800V. However, the current I1 increases when the transfer voltage exceeds +800 V, resulting in a bipolar current Inip. It is noteworthy that the transfer bias which balances the two currents I1 and I2 and thus reduces the wet brush current to zero corresponds to the optimal transfer bias determined in a different way than above.

When the current Inip is negative, the negative charge is prominent in the belt 44 around the brush 70 to reduce the electric field around the inlet of the N. As a result, toner dispersion during image transfer is reduced. Conversely, when the current Inip is bipolar, a positive charge increases in the periphery electric field of the inlet portion N, which is noticeable in the portion of the belt 44 and worsens toner dispersion.

Under optimum transfer conditions, the current flowing through the first belt is 0 μA, while the current flowing through the second belt is as large as approximately 20 μm. This is simply due to the low resistance of the second belt which increases the current I1. When the transfer bias is 0 V, the current flowing through the second belt increases toward the positive side than the current flowing through the first belt. This indicates that the low resistance belt somewhat worsens the toner dispersion level when compared to other belts.

In this embodiment, the toner scattering and the transfer efficiency were changed as in the first embodiment (Fig. 6) with respect to the transfer voltage V _t . When the power supply control means set the transfer voltage so as to satisfy the relationship of Inip ≤ 0, a scattering grade of 4.0 or higher was obtained. Preferably, by setting a transfer voltage satisfying the relationship of −3 ㎂ ≦ 0, a scattering rank of 4.0 or more and 2 or more and 90% or more of transfer efficiency can be obtained.

If desired, the conductive brush or conductive member 70 can replace the conductive roller. In any case, it is desirable to use a low hardness conductive brush or roller that can reduce the pressure acting on the belt 44. If the mechanical pressure acting on the belt 44 in the nip N is excessive, defects occur in image transfer.

If the drum 32 can be positively charged, the current Inip flowing from the brush to ground becomes greater than zero.

The second comparative example is the same as the fourth embodiment except for the position of the brush 70. In the comparative example, the brush 70 was kept in contact with the rear face of the belt 44 over an area 12 mm away from the contact starting position 0 of the nip N. The brush 70 was held in contact with the rear face of the belt 44 at position X, which had a width of about 4 mm in the direction of movement of the belt and was in the region of 10 mm <X <14 mm. In particular, as shown in FIG. 17, the brush 70 contacts the back of the belt 44 at a position X greater than L / 2, which in the fourth embodiment causes the brush 70 to be O ≦ X ≦ L / 2. Contact with the rear face of the belt 44 at position X in the region of.

Compared to the case in which the transfer voltage V _t had a scattering rating of 4.0 or 2 or higher at 1000 V or less, the nip width depending on a sufficient electric field was reduced, and the image transfer efficiency dropped to 85%.

The fourth embodiment has the following advantages.

(1) The conductive member 70 is kept in contact with the rear surface of the belt or transfer member 44 and is connected to ground. The transfer bias power source 72 is only in the direction of movement of the nip N

Connected downstream. This weakens the electric field around the inlet of the nip N to eliminate the inflow of toner at the position passing through the nip N. As a result, toner scattering can be successfully reduced during image transfer.

(2) The conductive member 70 is located at position X in the region of O ≦ X ≦ L / 2. This prevents the transfer efficiency from lowering and reduces toner scattering.

(3) The current Inip flowing from the conductive member 70 to the ground may be selected to be smaller than O when the drum 32 is charged with a negative polarity, or greater than O when the drum 32 is charged with a positive polarity. You can choose. As a result, a condition is established in which the electric current flows to the rear surface of the belt 44 in the first half of the nip N.

This reduces the magnitude of the electric field around the inlet of the nip (N) and thus passes through the nip (N).

Remove the toner spill in position. As a result, toner scattering is successfully reduced during image transfer.

(4) An ammeter or current measuring means 74 is provided to measure the current Inip flowing from the conductive member 70 to ground.

Thus, an optimal transfer condition is set based on the measurement result to reduce toner scattering.

(5) The conductive member 70 is made of an acrylic resin containing carbon fine particles

It is implemented as a brush with conductive filaments. Usually acrylic fibers can be used for a long time without breaking or breaking. This reduces toner scattering for a long time and eliminates image transfer defects due to aging. Containing carbon

Acrylic resin filament is stainless steel with diameter of about 5 to 8 micrometers

Filament, acrylic resin, nylon, polyester, rayon or similar resin

Steel plated as filaments, resin and carbon fine particles, materials of similar conductivity dispersed in steel or resin can be replaced by those made by carbonization as constructed filaments or carbon filaments or similar conductive or semiconductive filaments. Such conductive filaments and semiconductive filaments may be used separately or in combination. Furthermore, conductive, semiconductive filaments can be used in acrylic, nylon, polyester, and rayon to control the strength of the brush and the resistance of the tip of the filament.

Can be used in combination with filament.

Fifth Embodiment

This embodiment is similar to the fourth embodiment except that it is controlled by measuring the current Inip flowing from the brush 70 to the ground when the power supply to the additional device and the image forming cycle are repeated a predetermined number of times. It includes a control unit.

When the power is turned on, the charging condition and the transfer condition are optimized and the transfer voltage V _t applied to the belt 44 in the transfer bias power source is optimized.

In particular, as shown in Fig. 18, charging conditions and developing conditions at power-on are optimized by general process control. This optimization is not new and will not be specifically described. As a result, the voltage V _t applied from the transfer bias power source to the belt 44 is optimized. At this moment, the drum 32, which is rotated by the drive source, is charged to about -650V by the charger 34 and passes through the developing unit 40BK-40Y without being exposed. The developing unit 40BK-40Y using the inverse developing system does not operate as it does when developing a blank paper image. The ammeter 74 measures the current Inip flowing from the brush 70 to the ground when the charged portion of the drum 32 reaches the belt transfer position.

In order to eliminate the influence of the irregular resistance distribution of the belt 44, the ammeter 74 measures the back current induced from the single transfer voltage V _t over one rotation of the belt 44 and controls the average value of the measured current. It is preferable to use for. In particular, as shown in Fig. 18, a transfer voltage V _t is applied after starting to form an image of a blank sheet of paper. In this condition, the current Inip is measured. If the rear potential is less than 0, it is possible to increase the voltage V _t .

Therefore, the voltage Vt is increased by one step by Vt + DELTA V, and the current Inip is measured again.

This process continues until the current Inip exceeds zero.

Since the current Inip over zero is excessive, the voltage Vt 'occurs one step before. That is, Vt '= Vt- DELTA t is set to the optimum transfer voltage.

While the transfer voltage Vt shown in FIG. 14 has an initial value of 0 V and is sequentially increased by 200 V, the initial value may be selected to be several hundred volts to reduce the voltage setting time.

Furthermore, the interval between the steps of the voltage Vt can be reduced to 50V for more accurate control of the voltage Vt.

The transfer voltage Vt is controlled to implement the current Inip flowing from the brush 70 to the ground and to set the maximum voltage to an optimum transfer voltage in the range of 0 or less. In particular, the power supply control means controls the output of the transfer bias power so that the transfer voltage Vt becomes equal to the optimum transfer voltage. If the belt 44 is new, the voltage Vt of 800 V is set to the optimum voltage as mentioned above.

Thus, if the normal image forming cycle was repeated 5000 times without setting the optimum transfer voltage described above, the toner scattering grade dropped from the initial 4.0 to 3.5 in the midtone region.

The volume resistance of the belt 44 dropped to about 5 × 10 ⁹ cm 3.

When the optimum transfer voltage setting was made again in this method, the characteristic shown by the dotted line in Fig. 14 was obtained;

The optimal transfer voltage was measured at 600V and set based on Inip≤0.

Under this condition, a uniform image with minimum toner scattering was obtained in the midtone region to the dark region.

Each time a predetermined number of image forming cycles is repeated, the control unit performs current measurement and then sets the optimum transfer voltage according to the measurement result.

The third comparative example is the same as the fifth embodiment except that the brush 70 is embodied as an SUS brush having a diameter of about 20 μm.

This comparative example was preferred as in Example 5 with respect to the initial transfer voltage setting, but scratches occurred on the rear surface of the belt 44 when the image forming cycle was repeated for several hundred sheets.

The powder due to the scratches accumulated on the roller surface in the form of protrusions. As a result, defective transfer occurred on the belt transfer portion and the sheet transfer portion.

The fifth embodiment has the following advantages.

(1) The ammeter or current measuring means 74 measures the current Inip flowing from the conductive member 70 to the ground.

The operation of the toner image forming means is controlled so that the drum 32 is equal to or less than zero when the drum 32 can be charged with the negative electrode and more than zero when the drum 32 can be charged with the positive electrode.

In this state, the current flowing to the back of the belt or to the transfer member 44 is measured periodically to set transfer conditions that can reduce toner scattering. This minimizes the toner scattering due to the transfer condition, for example, the resistance change of the belt 44 over time, so that there is no noticeable toner scattering on the toner.

(2) The transfer condition for minimizing toner scattering, for example, against change in resistance of the belt 44 over time, by the operation of the toner image forming means being controlled by the power supply control means for controlling the output of the transfer bias power source 72. This results in a noticeable toner scatter on the toner.

(3) Since the conductive member 70 is embodied as a brush composed of an acrylic resin and a carbon-containing fine conductive filament dispersed in the resin, toner scattering is reduced during image transfer and eliminates defective image transfer due to time.

In the first to fifth embodiments, the transfer member 44 is embodied as an intermediate transfer belt in which the toner image is transferred from the drum 32 to the paper in the nip portion N. FIG. Therefore, the apparatus is small in size and reduces toner scattering from the drum 32 to the transfer member 44 during image transfer.

The foregoing embodiment focuses on an image forming apparatus using an intermediate image transfer system, but the present invention is not limited thereto.

Example 6

A sixth embodiment of the present invention will be described with reference to FIG. As shown, the image forming apparatus 80 includes a conveyance belt or transfer belt 82 for supporting and conveying paper.

The photoreceptor element is embodied in drum 84.

Drum 84 consists of a hollow core of aluminum and a functionally separated photosensitive layer formed on the core (not shown).

The photosensitive layer consists of a base layer, a charge generating layer and a charge transfer layer (not shown).

The photosensitive layer is about 28 μm thick and has a volume of about 90 pF / cm 2. During image formation, the drum 32 is rotated by a driving source not shown.

Charger 86 is implemented as a scorotron charger and charges the surface of drum 84 to about -650 V to -700 V.

The laser beam 88 scans the charged surface of the drum 84 in accordance with the image data to form an electrostatic latent image of -100V to -500V.

The developing unit 90 develops the latent image to produce a corresponding toner image. The developing unit 90 stores the dry two-component developer and attaches the negatively charged toner to the low potential portion of the drum 84 (reverse phenomenon).

The developing bias power supply applies a bias voltage of about -500 V to -550 V to the developing unit 90 with or without the AC component superimposed on the top.

The endless belt 82 passes through the driving roller 92 and the driven roller 94 and is rotated by a driving source not shown through the driving roller 92.

The sheet S is conveyed from the sheet feeding unit, not shown, to the register roller pair 96.

The register roller pair 96 drives the sheet S toward the belt 82 so that its leading end meets the leading end on the toner on the drum 84.

The drum 84 and the belt 82 are in contact with each other to form a nip N therebetween.

The bias roller 98 is held in contact with the rear portion of the belt 82 located below the nip N in the rotational direction of the belt 82. A part of the belt 82 between the bias roller 98 and the driven roller 94 is held in contact with the drum 84.

Nip N has a width of about 10 mm and belt 82 has a width of 350 mm in its length direction.

The conductive brush 100 is in contact with the rear face of the belt 82 between the position where the drum 84 and the belt 82 start to contact each other and a position 5 mm away from the position.

Brush 100 is embodied with 24 360 denier carbon-containing acrylic filaments. The filament has a resistance of 1 × 10 ⁷ Ωcm. Brush 100 is grounded by a conductor.

The belt 82 is composed of a rubber layer having an intermediate resistance and a fluorine-based coating layer formed on the rubber layer.

The rubber layer is composed of chloroprene rubber and EDPM mixture and carbon black dispersed in the mixture.

The rubber layer has a thickness of about 500 μm and has a volume resistance of about 1 × 10 ¹⁰ cm 3 when the belt is new.

The coating layer has a thickness of about 10㎛ and the new surface resistance is 1 x 10 ¹¹ Ωcm / ㎠.

The driven roller 94 and the brush 100 are grounded.

A transfer bias power source (not shown) is connected to the bias roller 98 to apply a positive transfer voltage Vt to the roller 98.

The transfer voltage Vt is controlled by a power supply control means (not shown).

The paper S driven by the register roller pair 96 is conveyed to the nip N by the belt 82.

In the nip N, the toner image is transferred from the drum 84 to the paper S.

Since the paper is held electrostatically on the belt, it is easily separated from the drum 84 when moving from the nip N. Thus, the belt 82 can reduce paper jams and other problems.

The cleaning brush 102 and the cleaning braid 104 remove the toner remaining on the drum 84 after image transfer.

The discharge lamp 106 also disperses the remaining charge on the drum 84. The sheet S having the toner image is separated from the belt 82 by bending at the position where the driving roller 92 is located.

The toner image is then fixed to the sheet S by the fixing unit 108.

The charger or charging means 86, the exposing portion or the exposure means, the developing unit or the developing means 90, the paper or the recording medium S, the belt 82, and the bias power supply constitute toner image forming means.

When a bias voltage of 2600 V was applied from the bias power supply to the bias roller 98 under normal image forming conditions, the output current of the bias power supply was about +150 mA. As a result, the toner scattering grade was 4.5.

As described above, the transfer member 82 of the present embodiment is embodied as a conveyance belt for temporarily supporting the sheet S on the upper side. The toner image formed on the drum or the image carrier is transferred from the paper S in the nip N.

The conveying belt then conveys the paper to the next step. This reduces paper jams and also reduces toner scattering from the drum 84 to the paper S placed on the belt 82 during image transfer.

Since the volume resistance of the belt 82 is 10 ⁷ Ωcm-10 ¹³ Ωcm, it is possible to control the transfer condition based on the potential on the rear surface of the belt 82 or the current flowing to the rear surface of the belt 82.

Seventh embodiment

This embodiment is applied to a color copying machine. Fig. 20 shows the general structure of the color copying machine and Fig. 21 shows the photoconductor, the intermediate transfer belt and its peripheral device. As shown, the color copier (usually 110) is composed of a color image reading apparatus (hereinafter referred to as a color scanner) 112 and a color image recording apparatus (hereinafter referred to as a color printer) 114.

In the color scanner 112, the lamp 118 irradiates light on the document 116 placed on the glass plate 125. The image reflected from the document 116 is concentrated on the color image sensor 124 through the mirror group 120 including the mirrors 120a, 120b, 120c and the lens 122. The color image sensor 124 separates instantaneous color information into R (red), G (green), and B (blue) components and converts them into electrical image signals. In an embodiment, the image detector 124 is comprised of R, G, B color separation means and a charge coupled device (CCD) or similar photoelectric converter to read three colors simultaneously. R, G, and B image signals output from the image detector 124 are BK (black), C (cyan), M (magenta), and Y (yellow) colors according to their intensity by an image processor (not shown). It is converted into image data. In particular, the optical system including the lamp and the mirror in response to the scanner start signal synchronized with the operation of the color printer 114 scans the document 116 from right to left as indicated by the arrow in FIG. Output

The optical system repeatedly scans the document 116 four times and sequentially outputs BK, C, M, and Y image data.

The optical recording unit 126 converts the color image data included in the color printer 114 and received from the color scanner 112 into an optical signal, and scans the optical signal to the photoconductive drum or the image carrier 128 to electrostatically. As a result, a latent image is formed on the drum 128.

The recording unit 126 includes a semiconductor laser 126a, a laser controller (not shown), a polygon mirror 126b, a motor 126c for rotating the mirror 126b, an f / θ lens 126d, and a mirror 126e. It includes.

The drum 128 rotates counterclockwise as indicated by the arrow in FIG. Around the drum 128, a drum cleaning unit 130 including a pre-cleaner, a charge lamp 132 charger or a main charger 134, a potential detector 136, a BK (black) development unit ( 138), a C (cyan) developing unit 140, an M (magenta) developing unit 142, a Y (yellow) developing unit 144, a density pattern detector 146, and an intermediate transfer belt 148 are provided. .

The developing units 138, 140, 142, and 144 include developing sleeves 138a, 140a, 142a and 144a, paddles 138b, 140b, 142b and 144b, and toner-containing sensors 138c, 140c, 142c and 144c, respectively. Doing.

The developing sleeves 138a-144a are rotatable with a developer attached thereon to develop a latent image while surface contacting the drum 128.

Paddles 138b-144b are rotatable to scoop up the developer while stirring it. Toner-containing sensors 138c-144c respond to toner-containing of the developer. In the ready state, the developer of all the developing units is in the inoperative position.

The intermediate transfer belt 148 passes through the driving roller 150, the belt transfer bias roller 152, the ground roller 154, and the plurality of driving rollers.

A motor (not shown) causes the belt to rotate through the drive roller 150 as described below. The belt cleaning unit 150 and the sheet transfer unit 158 are installed around the belt 140.

The belt cleaning unit 156 includes a brush roller 156a, a rubber blade 156b, and a mechanism 156c for moving the unit 156 to contact and remove the belt 148. The sheet transfer unit 158 includes a sheet transfer bias roller 158a, a roller cleaning blade 158b, and a mechanism 158c for moving the unit 158 to contact or remove the belt.

The printer 114 additionally includes a pickup roller 160 for transporting the sheet S between the sheet transfer unit 158 and the belt 148, a register roller 162, and a paper cassette 164 for storing paper of a specific size. 166, 168, 170), manual feed trays for overhead project (OHP) paper and rather thick paper.

20 also shows a paper conveying unit 174, a fixing unit 176, and a copy tray 178.

The operation of the color copying machine 110 is described under the assumption that BK pictures, C pictures, M pictures, and Y pictures are sequentially formed in this order.

When the operation starts, the color scanner 112 starts reading the BK image at a predetermined time. The formation of a latent image using a laser beam is started based on the BK image data. A latent image based on BK image data is called a BK latent image. This is also the same for the other colors C, M and Y. Before the leading edge of the BK latent image reaches the developing position assigned to the BK developing unit 138 (hereinafter referred to as the BK developing position), the developing sleeve 138a starts rotating to develop from the leading edge of the BK latent image to the distal edge. .

As a result, the BK toner attached to the sleeve 138a develops the BK latent image and produces a corresponding BK toner image. As soon as the terminal edge of the BK latent image leaves the BK developing position, the developer of the sleeve 138a returns to the non-operating position. This is completed before at least the leading edge of the C latent image based on the C image data reaches the BK developing position. The sleeve 138a rotates in the reverse direction to deactivate the developer.

The BK toner image is transferred from the drum 128 to the front surface of the belt that rotates at the same speed as the drum 128. For this belt transfer, a predetermined bias voltage is applied to the belt transfer bias roller 152 and the drum 128 and the belt 148 are in contact with each other.

In parallel with the belt transfer, a process of forming a C toner image on the drum 128 is performed. In particular, the color scanner 112 starts reading the C image data at a predetermined time.

Latent image formation using a laser beam is started based on the C image data. After the end edge of the BK latent image deviates from the developing position assigned to the C developing unit 140 (hereinafter referred to as the C developing position), the developing sleeve 140a is the front of the C latent image before the leading edge of the C latent image reaches the C developing position. It begins to rotate to develop from the edge to the distal edge. As a result, the C toner attached to the sleeve 140a develops a C latent image and produces a corresponding C toner image.

As soon as the end edge of the C latent image leaves the C developing point, the developer of the sleeve 140 goes to the non-operational position. This is also completed before at least the C latent image based on the M image data reaches the C developing position. The C toner image is transferred from the drum 128 to the belt 148 and is accurately resisted with the BK toner image present on the belt 148.

The M toner image and the Y toner image are also formed in the same way as the BK and C toner images. As a result, the BK, C, M, and Y toner images are sequentially transferred from the drum 128 to the belt 148 to complete the four-color composite image.

After being completely transferred to the belt 148 on the first or BK toner image, the belt 148 is controlled by any one of a constant speed forward system, a skip forward system, a forward and backward (or quick return) system or an effective combination thereof. It is driven to harmonize with the copy size according to the copy speed. The constant speed forward system allows the belt 148 to rotate at a low speed in a predetermined direction during image transfer.

The skipping advance system releases the belt 148 from the drum 128, and the belt 148 skips forward until the image forming position of the belt returns to the toner image position of the drum 128, and then the belt 148 again. Is brought into contact with the drum 128. This process is then repeated. The forward and backward system releases the belt 148 from the drum 128, stops the forward operation of the belt 148, until the image forming position of the belt 148 returns to the toner image position of the drum 128. The belt 148 is moved in the reverse direction, the belt 148 is advanced again, and this process is repeated.

During belt transfer of the second, third and fourth colors, the belt cleaning unit 156 is spaced apart from the surface of the belt 148 by the mechanism 156c. The paper transfer bias roller 158a is usually spaced apart from the belt 148. The mechanism 156c causes the roller 158a to contact the belt 148 when the four color composite image is transferred from the belt 148 to the paper S. FIG.

In this condition, a predetermined bias voltage is applied to the roller 158a. As a result, the composite toner image is transferred from the belt 148 to the paper S. FIG. The paper S is supplied from one of the designated paper cassettes 166-170 via an operation panel (not shown), and when the leading edge of the composite image conveyed by the belt 148 reaches the paper transfer position, a register roller ( 160).

The paper S for conveying the composite toner image is conveyed to the fixing unit 176 by the conveying unit 174. In the fixing unit 176, the heating roller 176a and the pressure roller 176b operate together to fix the toner image onto the paper. The paper S from the fixing unit 176 is copied in full color to the tray 178.

The drum cleaning unit 130 (pre-cleaner, brush roller, rubber blade) removes toner remaining in the drum 128 after the belt transfer, and the antistatic lamp 132 charges remaining in the drum 128. The instrument 156c contacts the belt cleaning unit 156 belt 148 to clean the surface of the belt.

In the repeat copy mode, the operation of the color scanner 112 and the image formation on the drum 128 precede the second BK (first color) step after the first Y (fourth color) step at a predetermined timing.

After the composite toner image is transferred from the belt 148 to the paper S, the second BK toner image is transferred from the drum 128 to the area of the belt 148 cleaned by the cleaning unit 156.

The following description focuses on the four-color copy mode, and the three- or two-color mode is also possible by repeating the above process by the number corresponding to the desired number of colors and the desired number of copies. In monochrome copy mode, only the development unit assigned to the desired color is kept running until the desired number of copies have been made. In this case, the belt 148 is driven forward at a constant speed in contact with the drum 128 and the belt cleaner 156 is kept in contact with the belt 148.

The characteristic device of this embodiment is described as follows. As shown in FIG. 22, the belt transfer bias roller 152 is located downstream of the nip between the drum 128 and the belt 148. A bias is applied to the bias roller 152. In this sense, the bias roller 152 serves as a charge applying means. The ground roller 154 connected to the ground is located upstream of the nip N. The bias roller 152 and the ground roller 154 support the belt 148 and press the belt against the drum 128.

The brush or nip contact member 18 contacts the back of the belt 148 at the center of the nip N to prevent the toner of the drum 128 from being transferred before it reaches the nip N. Brush 180 is implemented with conductive filaments and connected to ground.

In an embodiment, the transfer charge applied from the bias roller 152 to the belt 148 is discharged by the brush 180. As a result, the transfer charge applied to the belt does not move or moves almost upstream in the direction of operation of the belt 148 from the position where the brush 180 contacts the belt 148. Thus, at the inlet of the nip where drum 128 and belt 148 are not in contact with each other, there is no charge or basically no charge at belt 148. Thus, at the inlet of the nip N, there is no electric field that affects the image since the dislocation slope does not exist or is basically present. As shown in FIG. 23, the potential warp 182 (shown in hatching) in the belt 148 extends only to the brush 180. This is in contrast to the potential gradient 24 shown in FIG.

Under the above conditions, the potential of the upstream belt 148 at the position where the brush 180 contacts the belt 148 is basically zero or of the same polarity as the charge potential of the drum 128. How brush 180 staticizes belt 148 has already been described in detail.

As mentioned above, in the image forming apparatus of the type in which the toner image is transferred from the photoconductive element to the paper as the intermediate transfer member passing through the roller, the seventh embodiment is provided on both sides of the nip between the photoconductive element and the intermediate transfer member. This eliminates the problems caused by the transfer bias applied to the downstream rollers of the two rollers located.

Such transfer bias causes excessive electric field inclination so that the electric field extends to the upstream roller, causing pre-transfer of the toner. For example, the seventh embodiment successfully reduced the scattering of the toner shown in FIG. 2B by experiments. The term 'conspicuous' substantially means that the drum 128 and toner have a negative electric field and cause transfer or pre-transfer to occur. But this kind of pre-transcription doesn't get in the way of burns.

A seventh embodiment if the process conditions as described in connection with the conventional configuration shown in FIG. 1 are assumed and include the electrical properties and other properties and materials of the intermediate transfer body, the moving speed of the intermediate transfer body, and the properties and materials of the toner. The example has a low transfer efficiency compared with the conventional configuration. To obtain the same transfer efficiency as the voltage at the outlet of the nip shown in FIG. 23 to 60V as in the configuration of FIG. 1, a transfer bias (1kV) higher than the conventional bias 800V is applied. Alternatively or additionally, the nip N area between the drum 128 and the belt 148 may be increased. For example, a portion of the upstream nip of brush 180 may extend in addition to the application of a higher transfer bias. Instead of changing the transfer bias and nip area of the related art, various process conditions including the electrical characteristics and the moving speed of the belt 148 can be appropriately selected.

When the brush 180 included in the apparatus of FIG. 23 exerts excessive pressure on the drum 128, the contact pressure acting between the drum 128 and the belt 148 in the nip N increases, which results in a tortuous state. Thin lines are omitted.

FIG. 24A shows a specific image 184 formed on the drum 128, and FIG. 24B shows an image corresponding to the image 184, which is transferred to the belt 148 under a tortuous condition.

In this regard, excessive pressure of the brush 180 is controlled to a sufficient value. Optionally, the brush 180 is an angle of contact between the brush 18 and the belt 148, that is, the angle of the brush 180 and the line perpendicular to the line of the belt 148 contacting the drum 128 in the nip N. If the pressure is in the range of 20 degrees to 60 degrees, the above pressure can be reduced.

Eighth Embodiment

The color copier described includes a color scanner similar to the color copier shown in FIG. 20 and basically operates in the same manner as the copier of FIG. The copier of this embodiment differs mainly in the configuration and operation of the color printer from that of FIG.

As shown in FIG. 26, the color printer 190 according to the present embodiment includes a photoconductive drum 192. In the periphery of the drum 192 there is a parking lot or charging means 194, a drum cleaning unit 196 including a cleaning blade and a brush, an optical recording unit or an exposure means (not shown), a rotational development unit (hereinafter referred to as a "reverb"). Or the developing means 198 or the like. The printer 190 additionally includes an intermediary transfer unit 200, a fixing unit 204 implemented by a roller pair, a paper feeder (not shown), and a controller (not shown).

In full color copy mode the copier 190 assumes that the color scanner sequentially reads BK, C, M, Y in this order.

Then, at the beginning of the imaging cycle, a motor (not shown) rotates the drum 192 counterclockwise as shown by the arrow in FIG. The parking bottom 194 starts to uniformly charge the drum 192 with negative polarity by Cocona discharge. The intermediary transfer belt 206 included in the intermediary transcription unit 200 rotates at the same speed as the drum 192 in the direction indicated by the arrow.

The belt 206 has a main transfer bias roller 208 serving as a main charge applying means, a driving roller 210, a tension roller 212, a sub-transfer count roller 214, a belt cleaning count roller 216, and an antistatic It passes through a roller or main transfer prestatic means (218). The rollers 208-218 are each formed of a conductive material and are grounded except for the main transfer bias roller 208. The main transfer power supply 220 is controlled with a constant current or constant voltage bias and applies a preselected transfer bias to the bias roller 208.

The color scanner starts reading the BK color image data at a predetermined timing. The optical recording unit scans the surface of the drum 192 with a laser beam in accordance with BK image data, in particular by raster scanning. As a result, a BK latent image by BK image data is formed in the drum 192.

The BK developing unit 198BK included in the rebarr 198 develops the BK latent image by inverse development using a toner having a negative polarity stored therein. As a result, a BK toner image corresponding to the BK latent image is formed in the drum 192.

At the main transfer position where the drum 192 and the belt 206 contact each other, the BK toner image is transferred from the drum 192 to the belt 206 by a transfer electric field. This electric field is formed by the electric charge applied to the belt 206 at the main transfer bias roller 208.

After the image transfer, the cleaning unit 196 removes the toner remaining in a part of the drum 192 which is out of the main transfer position.

The rotating belt 206 again carries the BK toner image to the main transfer position. During this transportation, the toner image BK must be protected from being disturbed.

To this end, the transfer charger or transfer charging unit (hereinafter referred to as PTC) 224, the paper transfer unit 202, the belt cleaning charger 226, the belt cleaning blade 228, and the belt 206 Brush 230 installed around the periphery is maintained in an inoperative state. That is, the PTC 224 and the belt static eliminator 226 are prevented from being discharged. The paper transfer unit 202 includes three support rollers 232, 234, 236 and a negative transfer bias roller or negative transfer charge applying means 238. The second transfer belt 240 is located at the upstream end of the unit 202 so that the second transfer belt or conveying belt 240 is in contact with the counter roller 214.

While carrying the BK toner image, the support roller 232 and the sub-transfer bias roller or sub-transfer charge application means 238 are spaced apart from the belt 206 by a mechanism (not shown), so that the sub-transfer belt or record carrier 240 is spaced apart from the belt 206. The subordinate transfer power source 242 does not apply any voltage to the subordinate transfer bias roller 238.

Moreover, the belt cleaning blade 228 and the lubrication brush 230 are spaced apart from the belt 206 by a mechanism (not shown).

These conditions also hold when the toner image is sequentially transferred to the belt 206.

The C image forming step is continued following the BK image forming step made with the drum 192.

In the C image forming step, the color scanner starts reading the C image data at a predetermined timing. The C latent image is formed in the drum 192 according to the C image data. As soon as the distal edge of the BK latent image deviates from the developing position assigned to the reverberator 198, the reverberator 198 starts to rotate. Before the leading edge of the C latent image reaches the developing position, the rotation of the reverberator 198 is stopped and the C developing unit 198c is positioned at the developing position. The C latent image is developed by the C toner stored in the C developing unit 198c. This process is repeated for M image data and Y image data to sequentially form M and Y toner images. As a result, BK, C, M, and Y toner images are sequentially transferred to the belt 206, and a composite color image is formed on the belt 206. FIG.

The belt 206 carries the composite color image formed thereon to the subtranscription position and causes the image to be uniformly charged by the PTC 224. The paper is fed to the sub-transfer position where the paper transfer unit 202 and the belt 206 contact each other so that the leading edge of the paper meets the leading edge of the image carried on the belt 206. At this moment, the paper transfer unit 202 is operated. The transfer bias is applied to the negative transfer bias roller 238 of the paper transfer unit 202 to form a transfer electric field. As a result, the composite image of the belt 206 is transferred to the paper as a whole. The paper transfer eliminator 246 carries the toner image and is operated when the paper conveyed by the belt 240 meets the static eliminator 246, so that the paper is separated from the belt 240. The paper separated from the belt 240 is conveyed to the fixing roller pair 204. The roller pair 204 heats and presses the paper to fix the toner image of the paper. Finally, the paper from the copier is placed in the copy tray by an exit roller pair (not shown).

After the negative transfer, the belt static eliminator 226 staticizes the surface of the belt 206.

In addition, the belt cleaning blade 228 is pressed against the belt 206 by the aforementioned mechanism to remove toner remaining on the belt 206. Moreover, in order to improve the cleaning of the belt 206 and the transfer to the paper of the toner image, a mechanism (not shown) presses the lubrication brush 230 against the belt 206 to apply the lubricant 247 to the belt. .

Lubricant 247 is embodied in platelets of fine particles of zinc stearate.

After separation of the paper, the belt static eliminator 248 removes the electric charge remaining in the subsidiary transfer belt 240 and the cleaning blade 250 cleans the surface of the belt 240.

The following technique is focused on four-color copy mode, but repeating the above process by the desired number of colors and the desired number of copies is possible in three- or two-color copy mode.

In the monochromatic color copy mode, only the developing portion of the reverberator 198 assigned to the desired color is kept in operation until the desired number of copies are made. The belt cleaning blade 228 as well as the other members are maintained in operating conditions.

As shown in Fig. 27, in this embodiment, the belt 206 is provided in a laminated structure and consists of a surface layer 206a, an intermediate layer 206b, and a base layer 206c. The surface layer 206a and the base layer 206c respectively form an outermost layer and an innermost layer in contact with the drum 192. The adhesive layer 206d adheres them between the intermediate layer 206b and the base layer 206c.

In the main transfer position, the belt 206 passes through the main transfer bias roller 208 and the belt antistatic roller 218 and is pressed against the drum 192. In this condition, the drum 192 and the belt 206 form a nip N having a predetermined width.

The belt antistatic brush or main transfer static eliminator 252 is connected to ground and held in contact with the back of the belt 206 at the nip N.

The belt antistatic brush 252 prevents an unwanted electric field from forming at the inlet of the main transfer position where the belt 206 approaches the drum 192. As shown in FIG. 28, the main transfer position has a nip width Wn and the brush 252 is positioned at a distance spaced from the downstream end of the nip N by a distance L in the direction of movement of the belt 206. Contact 206. The nip width Wn and the distance L are selected to satisfy a preselected transfer condition.

Specific examples of the eighth embodiment are as follows. The intermediate transfer belt 206 has a thickness of 0.15 mm, a width of 368 mm, and a length of 565 mm in terms of the inner peripheral length. The belt 206 moves at a speed of 200 mm / sec.

The surface layer 206a of the belt 206 is implemented with an insulating layer having a thickness of about 1 μm. The intermediate layer 206b is made of PVDF (polyvinylidene fluoride) and consists of an insulating layer of about 75 탆 thickness having a volume resistivity of about 10 ¹³ Ωcm. The base layer 206c is formed of PVDF and titanium oxide, and is made of an intermediate resistance layer of about 75 μm having a volume resistance of 10 ⁸ cm 3 to 10 ¹¹ cm 3. The belt 206 having such a laminated structure had a volume resistivity in the range of 10 ⁷ cm 3 to 10 ¹² cm ^{3 as a} whole.

The volume resistance was measured by the method according to JIS K6911, and a voltage of 100 V was applied for 10 seconds. The surface layer 206a had a surface resistance of 10 ⁷ GPa-10 ¹² GPa as measured by the aforementioned Hiresta IP. For the measurement of surface resistance, the surface resistance measurement method according to JIS K6911 can be used.

The first transfer bias roller 208 was performed by a metal roller plated with nickel. Belt discharge roller 218 was also performed by a metal roller.

For other rollers, metal rollers or conductive resin rollers were used.

An appropriately sized DC transfer bias is applied to the bias roller 208. In particular, 1.0 kV, 1.3 kV to 1.4 kV, 1.6 kV to 1.8 kV and 1.9 kV to 2.2 kV were applied successively to the bias roller 208 for the first, second, third and fourth colors, respectively.

The nip width Wn of the first transfer position was chosen to be 10 mm while the distance L was chosen to be 7 mm (shown in FIG. 28).

The belt discharge brush 252 has a conductive filament formed of a resin containing carbon.

For PTC 226, a charger with a grid was used.

The power supply 254 applied a DC bias voltage of a pole, such as the charge of the toner image carried from the belt 206 to the PTC 224.

More specifically, while a DC voltage in the range of 0 kV to -3 kV was applied to the grid electrode 224b, a DC voltage controlled at a constant current of -500 mA was applied to the main wire 225a included in the PTC 224.

The second transfer bias roller 238 has a surface layer formed of conductive sponge or conductive rubber and has a core layer formed of metal or conductive resin.

A transfer bias controlled by a constant current of 10 mA to 20 mA was applied to the roller 238.

The second transfer belt 240 is 100 μm thick, formed of PVDF, and has a volume resistance of 10 ¹⁰ μm cm to 10 ¹³ μm cm.

The paper transfer discharger 246 was performed by a discharger in which an AC voltage or an AC + DC voltage was applied from a power supply (not shown).

The cleaning blade 250 was held in contact with a portion of the second transfer belt 240 in contact with the support roller 236.

9th embodiment

Referring to Fig. 29, the ninth embodiment of the present invention is similar to the seventh embodiment except for adding cost saving features.

In Fig. 29, elements having the same structure as the elements in Fig. 26 are denoted by the same element numbers, and detailed description is not made to avoid duplication.

In the color copying machine 260 of FIG. 29, the intermediate layer 206b of the intermediate transfer belt 206 is formed of a material having an intermediate resistance. In addition, the entire belt 206 is configured to have an intermediate resistance.

The belt 206 with intermediate resistance causes minimal random charge distribution to occur on the belt 206 after the first transfer. For this reason, the copier 260 does not include the PTC 224.

The drive roller 210 for driving the belt 206 is in a position where the belt 206 moves from the second transfer position to the first transfer position, and at the same time serves as a belt cleaning counter roller.

For the purpose of reducing manufacturing costs, the second transfer belt 240 of FIG. 26 uses a portion of the belt 206 in contact with the second transfer bias roller 238 and the second transfer counter roller 214 to hang paper therebetween. Replaced by an array

In addition, there is no paper static eliminator 246, belt eliminator 248, cleaning blade 250.

A detailed example of the ninth embodiment is as follows. The example is similar to the eighth embodiment except for the following.

The entire belt 206 and the intermediate layer 206b of the belt 206 have a volume resistivity of 10 ⁸ cm 3 to 10 ¹⁰ cm 3.

The intermediate layer 206b, such as the base layer 206c, is composed of PVPF and titanium oxide.

The distance L (shown in FIG. 28) was chosen to be 6 mm to 7 mm. The belt 206 was allowed to move at a speed of 156 mm / sec.

The appropriate sized DC transfer bias is supplied to the first transfer bias roller 208.

In particular, 1.2 kV, 1.3 kV, 1.4 kV and 1.6 kV were continuously supplied to the bias roller 208 for the first, second, third and fourth colors, respectively.

The second transfer bias roller 238 was formed of a conductive rubber.

Tenth embodiment

Fig. 30 shows a tenth embodiment of the present invention provided in an image forming apparatus of a type including a similar supporting member OHP paper or a similar recording medium for supporting a belt or paper.

As can be seen, the image forming apparatus, generally 270, comprises a transfer belt 272 which serves as a silver record carrier support member.

The toner image is formed on the photoconductive drum or image carrier 274 by a conventional electro-optical graphics process.

The drum 274 and the belt 272 contact each other and form a nip N therebetween.

The transfer bias roller 276 is located downstream of the nip N in the direction of movement of the belt 272.

The toner image formed on the drum 274 is a transfer charge supplied through the bias roller 276.

It is transferred to the paper S by change.

Belt 272 is provided with an intermediate resistance (10 ⁸ Ωcm ~ 10 ¹³ Ωcm or Ω~ 10 ⁷ 10 ¹² Ω) for the purposes such as the one described in connection with the preceding embodiment.

The potential difference slope is formed on the belt 272 due to the transfer difference provided through the bias roller 278.

The potential difference slope creates an electric field at the inlet of the nip (N).

As a result, the toner image performed on the drum 274 before the paper reaches the nip N due to the electric field (transfer) above is partly easy to be transferred to the paper.

Such occurrences lower the quality of the resulting burn.

In this respect, the discharge brush 280 or similar discharge means is disposed in the nip N.

The discharge brush 280 prevents from causing the potential difference of preliminary transfer at the inlet of the nip N from the beginning.

In the seventh to tenth embodiments, the discharge means is performed with a discharge brush. If desired, the discharge brush may be replaced with a blade, roller, or similar discharge member.

The position where the discharge means is present is not limited to the one included in the tenth embodiment.

The key point is that the discharge position is located upstream of the charge application means 152, 208, 276 in the direction of movement of the intermediate transfer belt except for the bias roller or nip N.

Referring to the arrangement of FIG. 26 or FIG. 27 as an example, FIG. 31 shows the inclination of the potential difference V of the belt 206 particular to positions A-E and A-E in the nip N where the discharge brush 252 is located. Nip N starts at position A.

Position B is intermediate between position A and the middle C of nip N. Position P is halfway between position C and position E which is the end of nip N.

The potential difference of the upstream belt 206 at the position where the discharge brush 252 and the belt 206 meet in the moving direction of the belt 206 is a pole equal to the charge on the drum 192.

In particular, the charge potential difference of the belt 206 measured at the contact position is OV or under some conditions approximately OV.

The charge potential difference of the belt 206 continuously approaches the charge potential difference of the drum 192 toward the upstream side by where it is affected by the drum 192.

The charge potential difference of the belt 206 changes back to approximately OV or OV.

As shown in FIG. 31, the discharge member may interfere with the formation of an electric field at the inlet of the nip N at any point in positions A-E.

If desired, the plurality of discharge means are arranged side by side, each having a special configuration.

The other discharging means is located upstream of the nip N in the direction of movement of the belt 206 in addition to the discharging means arranged in the nip N.

For example, the discharging means independent of the discharging means present in the nip N is located upstream or downstream of the nip N with respect to the upward direction.

While the discharge brush of the tenth embodiment is grounded, a bias opposite to the transfer charge can be applied to the discharge brush so as not to affect the transfer charge required for image transfer in the nip N.

The photoconductive drum, which can be seen everywhere in the seventh to tenth embodiments, can be replaced with another suitable kind of image carrier, for example an endless light conducting belt passing through two rollers.

The intermediate transfer belt, which can be seen everywhere in the seventh to ninth embodiments, can be replaced with other suitable forms of intermediate transfer bodies.

The intermediate transfer belt can have a suitable thickness and structure (single layer, double side or the like) and is formed of a suitable material that matches the desired image forming conditions.

In the seventh to tenth embodiments, the bias roller is only a unique form of the transfer charge applying means.

If the position placed in the nip is downstream of the portion where the discharge brush or similar transfer discharging means is located, the transfer charge applying means may apply the transfer charge at the position placed in the nip.

In the seventh to tenth embodiments, the ground roller serving as the preliminary transfer digitizing means can be replaced by a blade, a brush or the like.

The second transfer bias roller included in the seventh to ninth embodiments may be replaced by a blade, a brush or other suitable second transfer charge applying means.

In the eighth embodiment, the supporting member for supporting the recording medium is performed as a belt. If desired, a drum or similar support member may be substituted for the belt.

In the seventh to ninth embodiments, the photoconductive drum is filled with a cathode and the developing unit performs reverse development using two component types, a developer.

Embodiments can also be practiced with a foldable developing system using a photoconductive drum and / or a single component type developer chargeable to the anode.

In one embodiment, the voltage and current of the first transfer applied to the first transfer charge applying means are merely illustrative and may be replaced with other voltages and currents meeting the desired image forming conditions.

In summary, it can be seen that the present invention achieves various benefits as follows.

(1) The potential difference placed in the vicinity of the transcript is zero or at least a pole, such as the charge of the image carrier, in a portion of the nip formed for image transfer.

Therefore, the electric field of the image transfer is weakened at least in part of the nip. This prevents the toner from moving in a position prior to the nip and thereby reduces totter scattering at image transfer time.

(2) Suppose that the image carrier and the transcript start to contact each other at position 0 of the nip and they begin to separate from each other at position L.

The potential difference near the transcript is then zero or a pole equal to the charge of the image carrier at position X in the range 0 ≦ X ≦ L / 2 of the nip.

Therefore, the effective nip width can be made as large as possible to prevent the transfer efficiency from lowering. At the same time the electric field for the image transfer weakens near the entrance of the nip.

This prevents the toner from moving in front of the entrance of the nip and reduces toner scattering.

(3) A potential difference measuring means is provided for measuring the potential difference V _nip lying behind the transfer body.

Therefore, the transfer condition can be set optimally based on the measurement result and reduces toner scattering in the image transfer time.

(4) Control means are provided for causing the potential difference measuring means to be activated at the image transfer time in the nip.

The control means controls the operation of the toner image forming means of which the potential difference V _nip is of the same polarity as zero or the charge of the image carrier.

This allows the transfer condition to always occur with minimal toner scattering against the changing resistance of the transfer body due to aging.

As a result, an image with minimal toner scattering can always be obtained.

(5) The measurement occurs at the image transfer time at the position of the nip within the range of 0 ≦ X ≦ 1/2.

This also makes the effective nip width as large as possible and prevents poor transfer efficiency.

(6) The power supply control means serves as a means for controlling the output of the transfer bias power supply and controlling the operation of the toner image forming means.

This also ensures transfer conditions such that a minimum amount of toner scattering occurs due to aging and changes in the transfer body always occur with respect to resistance.

As a result, an image with a minimum amount of toner scattering can be obtained at any time.

(7) The conductive member is held in contact with the back of the transfer member and grounded.

The transfer bias power supply is only connected to the downstream shaft in the direction of movement of the nip. As a result, the electric field near the inlet of the nip weakens.

This prevents the toner from moving forward of the nip and reduces toner scattering at image transfer time.

(8) The current I _nip flowing from the conducting member to ground is selected to be less than zero, including when the image carrier is charged to the cathode, or greater than zero, including when the image carrier can be charged to the anode.

As a result, the transfer condition is set so that a current flows behind the transfer body in the first half of the nip.

This weakens the electric field near the entrance of the nip and prevents the movement of the toner in front of the nip.

(9) Current measuring means for measuring the current I _nip is provided.

Therefore, the optimum transfer condition can be set based on the measurement result and reduces the toner scattering to the time of image transfer.

(10) The features mentioned in the above items (8) and (9) are combined to ensure the transfer condition causing the minimum toner scattering against the changing resistance of the transfer member due to aging.

(11) The conductive member is performed with a brush having conductive filaments composed of an acrylic resin and fine carbon particles dispersed therein.

Therefore, the conductive member can reduce toner scattering for a long time and prevent incomplete image transfer due to aging.

(12) The transfer member is performed with an intermediate transfer belt for temporarily supporting the toner image transferred from the image carrier in the nip and transferring it to paper or a similar recording medium.

Therefore, the apparatus is compact and reduces toner scattering in the image transfer time from the image carrier to the belt.

(13) The transfer member temporarily holds the sheet and is carried out by a conveying belt for conveying the sheet to the next step after the image is transferred from the image carrier to the sheet.

Therefore, the transfer member reduces the paper jam while reducing the toner scattering at the image transfer time from the image carrier to the paper.

(14) Since the transfer member has a volume resistance of 10 ⁷ mA to 10 ¹³ mA, the transfer conditions can be controlled based on the potential difference behind the transfer member or the current flowing behind the transfer member.

(15) Assume the position where the image carrier is in contact with the intermediate transfer member or the recording medium support member.

The influence of the electrical manipulations to form the transfer electric field in the gap which is extremely close to the position where the two members are in contact can then be preferably reduced,

This operation can be compared with the case where the two members are affected at a position apart from each other.

This prevents the image quality from being reduced due to preliminary transfer.

(16) Compared with the case where the contact pressure acting between the image carrier and the intermediate transfer member is prevented from increasing to a critical degree and the electrode member contacts a part of the transfer member in contact with the image carrier.

This prevents burn quality from being reduced by such contact pressures.

The phenomenon of the electrode member is rarely transferred to the image carrier when the electrode member is performed by the rotating body. Otherwise, development adversely affects the step of forming a toner image on the image carrier.

(17) The electrode member absorbs the change in contact conditions between the elastically deformable contact portion and the intermediate transfer member and the electrode member influencing the contact pressure continuously.

Therefore, the electrode member can be positioned relative to the transfer body in a manner of setting a desired contact pressure by a simple positioning mechanism, and can be compared when the electrode member has a firm contact portion.

(18) The influence of the electric charges which failed to dissipate in the gap between the electrode members is reduced, and compared with the case where electric charges disperse where the image carrier and the intermediate transfer member come into contact with each other.

This more preferably reduces the deterioration of the image quality due to preliminary transfer than when the charge starts to disperse where the image carrier and the transfer body begin to contact each other.

(19) The charges on the intermediate transfer member can be sufficiently dispersed than when the charges are scattered only at the place where the image carrier and the transfer member contact each other.

This is also successful in achieving the gain 18.

Various modifications will be possible without departing from the scope of the invention.

The present invention selects a potential on the back of the transfer member to be zero or has the same polarity as the charge of the image carrier on at least a part of the gripping point formed for image transfer, thereby minimizing toner scatter during image transfer. It is also possible to prevent the change of storage of the transfer material over time, thereby minimizing toner scattering.

Claims (53)

A method of transferring a toner image from an image carrier to a transfer member in contact with the transfer member or to a recording medium supported by the transfer member, Forming an image transfer electric field by an electrical operation on a contact portion where the image carrier and the transfer member come into contact with each other; Measuring a potential of the rear side of the transcript at a minimum of the contact portion; and Performing a reduction operation to reduce the electric field so that the potential on the transfer member becomes zero or is the same polarity as the charge on the image carrier; And it include, characterized in that it has a surface resistivity of said transfer member is 10 10 ~ ^{13 7} Ω㎝ Ω㎝ volume resistivity and 10 ⁷ Ω ~ 10 ¹² Ω of the. 2. The method of claim 1 wherein said reducing operation removes charge from said transcript while said electrical manipulation comprises applying charge to said transcript. 3. The method of claim 2, wherein said charge is applied to said transcript at a position downstream of said position at which said charge is removed from said transcript relative to the direction of movement of said transcript. The electric charge according to claim 2, wherein when the image bearing member and the transfer member start to contact each other at position 0 in the moving direction of the transfer member, and when they start to move away from each other at position L in the direction, the charge is zero at the contact position. Characterized in that it is removed from the transcript at position X in the range ≦ X ≦ L / 2. The method of claim 1, wherein the charge on the transfer member is a potential on the side of the transfer member opposite to the side in contact with the image carrier. The electric potential on the transfer member according to claim 1, wherein when the image bearing member and the transfer member start to contact each other at a zero position in a moving direction of the transfer member and start to disengage from each other at a position L in that direction, And the same polarity as the charge attached to the image carrier at the X position within the range of 0 ≦ X ≦ L / 2 of the contact portion. The method of claim 1, wherein the transfer member comprises an intermediate transfer member for temporarily supporting a toner image transferred from the image carrier and then transferring the toner image to a recording medium. 2. The transfer member according to claim 1, wherein the transfer member includes a transfer member for supporting the recording medium and transferring the recording medium to the next step after the toner image is transferred from the image carrier to the recording medium at the contact portion. Way. The method according to claim 1, wherein the intensity of the electric field or the length of the contact portion is adjusted according to the suppression operation. An image carrier for forming a toner image thereon by charging; 10 ⁷ Ωcm to 10 ¹³ Ωcm volume resistance for holding and contacting the image carrier at the contact portion to transfer the toner image to the recording medium by an electric field for image transfer formed on the contact portion by electrical operation. ^{A transfer member} having a surface resistance of ⁷ kPa to 10 ¹² kPa; And A reduction electrode configured to perform a reduction operation such that at least a portion of the contact position causes a potential on the transfer member to become zero or a charge such as a charge attached to the image carrier; Image forming apparatus comprising a 11. The apparatus of claim 10, wherein said reducing operation comprises removing said charge from said transcript, while said electrical manipulation comprises applying a charge to said transcript. 12. The apparatus according to claim 11, wherein the potential caught on the transfer member is a potential caught on a side of the transfer member opposite to an axis in contact with the image carrier. 12. The potential of the transfer member according to claim 11, wherein if the image carrier and said transfer member start to contact each other at a position 0 in a moving direction of said transfer member and are separated from each other at a position L in that direction, Wherein the device is of the same polarity as the charge selected or attached to the image carrier at the X position within the range of 0 ≦ X ≦ L / 2 of the contact position. 11. An apparatus according to claim 10, further comprising a transfer electrode for applying charge to the transfer body at a position downstream of the position at which the charge is removed from the transfer body in the direction of movement of the transfer body. 11. The apparatus of claim 10, further comprising a transfer electrode for applying charge to the transfer member side opposite to a side contacting the image carrier. 11. The apparatus of claim 10, wherein the suppression (reduction) electrode contacts the transfer body side opposite to the side contacting the image carrier. 17. The reduction electrode according to claim 16, wherein if the image bearing member and the transfer member start contacting each other at a zero position in a moving direction of the transfer member and are separated from each other at a position L in that direction, the reduction electrode is 0? Wherein the device is located at position X in the range X≤L / 2. 18. The apparatus of claim 17, further comprising an electrode in contact with a side of the transfer member opposite to a side in contact with the image carrier at a position ahead of the contact position. The apparatus of claim 18, wherein the electrode is made of a rotating body or a flat member made of a metal or a conductive resin. The image carrier of claim 16, wherein the surface of the image carrier and the surface of the transfer member are sequentially approached with each other, move in contact with each other, move in contact with each other, move a predetermined distance, and then move away from each other. A device located on the opposite side of the surface in contact with and in contact with a portion of the surface of the transfer body that has traveled a predetermined distance as short as the predetermined distance 17. The apparatus of claim 16, wherein the reduction electrode is grounded. 17. The apparatus of claim 16, wherein the reduction electrode contacts at least a portion of the transfer body made of an elastic material. 23. The apparatus of claim 22, wherein the reduction electrode portion is installed with a brush. 24. The device of claim 23, wherein the brush comprises a conductive filament made of acrylic resin containing fine carbon particles. 23. The apparatus of claim 22, wherein the reduction electrode portion is installed as a plate. The apparatus of claim 16, wherein the reduction electrode comprises a rotating body. 27. The apparatus of claim 26, wherein the rotating body has an elastic surface layer. An apparatus according to claim 10, wherein said transfer member comprises an intermediate transfer member which temporarily supports a toner image transferred from said image carrier at said contact position, and then transfers said toner image to a recording medium. 11. The method according to claim 10, wherein the transfer agent includes a transfer member for supporting the recording medium after transferring the toner image from the image carrier to the paper (recording medium) at the contacting position and transferring to the next step. Characterized in that the device. 11. An apparatus according to claim 10, further comprising a potential measuring means for measuring a potential Vnip at said contact. 31. The potential measurement means according to claim 30, wherein when the image bearing member and the transfer member start contacting each other at position 0 in the transfer direction of the transfer member and deviate from each other at position L in the direction, And measure the potential Vnip at position X in the range X ≦ L / 2. 31. The apparatus according to claim 30, further comprising a first operation control means for causing the potential measurement means to perform the measurement in the image transfer step, and the potential Vnip becomes zero or a charge equal to the charge attached to the image carrier. And second operation control means for controlling the operation of the image forming means. 33. The potential measurement means according to claim 32, wherein if the image bearing member and the transfer member initiate contact with each other at position 0 in the moving direction of the transfer member and deviate from each other at position L in the direction, Wherein the potential Vnip is measured at position X in the range 0 ≦ X ≦ L / 2. 33. An apparatus according to claim 32, further comprising power control means for controlling the output of the transfer power source. An image carrier for forming a toner image thereon by charging; A transfer member held in contact with the image carrier at a contact position to transfer the toner image onto the recording medium by an image transfer electric field formed at the contact portion; And And a reduction electrode grounded to reduce the transfer electric field. The current Inip flowing from the reduction electrode to the ground is selected to be zero or less if the image carrier is chargeable with (-) polarity, and zero or more if the image carrier is chargeable with (+) polarity. . 36. The apparatus of claim 35, wherein the reduction electrode causes the potential on the transfer member to be at zero or at least a portion of the contact portion to be the same polarity as the charge attached to the image carrier. 37. The apparatus of claim 36, wherein the potential on the transfer member is a potential caught on a side of the transfer member opposite to a side contacting the image carrier. 37. The potential on the transfer member according to claim 36, wherein if the image carrier and said transfer member start to contact each other at position 0 in the direction of movement of said transfer member and are separated from each other at position L in that direction, the potential on said transfer member is selected to be zero. Device selected from the same polarity as the charge attached to the image carrier at position X or in the range 0 ≦ X ≦ L / 2 of the contact region. The apparatus according to claim 38, further comprising an electrode in contact with the transfer member side surface opposite to the side contacting the image carrier at a position preceding the contact position. 40. The apparatus of claim 39, wherein the electrode comprises a rotating body or a flat member made of metal or conductive resin. 37. The apparatus of claim 36, wherein the reduction electrode has at least a portion in contact with the transfer member made of an elastic material. 42. The apparatus of claim 41, wherein the reduction electrode portion is installed with a brush. 42. The apparatus of claim 41, wherein the reduction electrode portion is installed as a plate. 37. The apparatus of claim 36, wherein the reduction electrode comprises a rotating body. 45. An apparatus as in claim 44 wherein said rotating body has an elastic surface layer. 37. The apparatus of claim 36, further comprising current measuring means for measuring a current Inip flowing from the reduction electrode to the ground. 47. The device of claim 46, wherein the current Inip is less than or equal to zero when the image carrier is charged with a negative polarity and is greater than or equal to zero when charged with a positive polarity 48. An apparatus according to claim 47, further comprising power control means for controlling the output of the transfer power. The apparatus of claim 36, wherein the transfer member includes an intermediate transfer member which temporarily supports a toner image transferred from the image carrier at the contact position, and then transfers the toner image onto a recording medium. . 37. The transfer device according to claim 36, wherein the transfer member includes a transfer member for supporting a recording medium, and transferring the paper to the next step after the toner image is transferred from the image carrier to the paper at the contact position. Device. 37. The apparatus of claim 36, wherein the volume resistance of the transfer member is between 10 ⁷ cm 3 and 10 ¹³ mm 3. 36. The reduction electrode as set forth in claim 35, wherein the image bearing member and the transfer member initiate contact with each other at a zero position in a moving direction of the transfer member and deviate from each other at a position L in that direction. Wherein the device is located at position X in the range X ≦ L / 2. 36. The method of claim 35, wherein the surface of the image carrier and the surface of the transfer member sequentially approach each other, move in contact with each other and move in contact with each other by a certain distance, and then move away from each other, the reduction electrode and the image carrier And is located in contact with a portion of the surface of the transfer body that is opposite the contacting surface and travels a predetermined distance shorter by the predetermined distance.

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