JP3679928B2 - Image forming apparatus - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile, and more particularly to an image forming apparatus provided with a wet developing device and an intermediate transfer member.
[0002]
[Prior art]
Conventionally, in an image forming apparatus using a wet developing device, a toner image is formed on an image carrier by developing using a liquid developer in which toner is dispersed, and the toner image is transferred to a transfer material. Thus, image formation is performed. In this apparatus, a phenomenon of electrophoresis of toner particles charged with a liquid carrier is used to cause toner to adhere to the surface of the image carrier during development or to move toner from the surface of the image carrier to the transfer material during transfer. Is used.
[0003]
Conventionally, in an image forming apparatus using an intermediate transfer member, a primary transfer that superimposes and transfers a toner image formed on an image carrier onto the intermediate transfer member and an overlap on the intermediate transfer member. Secondary transfer is performed in which toner images are collectively transferred onto a transfer material. Since the toner image formed on the image carrier in this manner can be superimposed on the intermediate transfer member, a color image forming apparatus for forming a color image on a transfer material, using a dry developing device, is not used. Widely applied.
[0004]
However, in the case of performing primary transfer in which a plurality of colors (for example, four colors) are superimposed on the intermediate transfer member, the toner image developed on the image carrier by the wet developing device is subjected to secondary transfer from the intermediate transfer member to the transfer material. The problem is that the rate drops.
[0005]
As a result of intensive studies to solve the problem of such a decrease in the secondary transfer rate, the present inventors have developed the image on the intermediate transfer member every time the toner image of each color of the primary transfer is transferred. It was found that the solid content concentration in the agent was increased, and the apparent charge amount as a dense toner particle group was smaller than the total charge possessed by each toner particle. For this reason, the electric charge contributing to the secondary transfer electrophoresis is reduced, and the toner is less likely to move to the transfer material, resulting in a decrease in the secondary transfer rate.
[0006]
[Problems to be solved by the invention]
The present invention has been made in view of the above problems, and an object thereof is to provide an image forming apparatus capable of improving the transfer rate from an intermediate transfer member to a transfer material and obtaining a high-quality image. It is to be.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, an image forming apparatus according to claim 1 is a wet developing apparatus in which an electrostatic latent image on a surface of an image carrier is used as a toner image by using a liquid developer carried on the developer carrier. And an intermediate transfer member to which the toner image formed on the image carrier is transferred, the toner image is formed on the toner image transferred on the intermediate transfer member a charge assigning means for assigning the same polarity as the charging polarity of the charge of the toner particles, is characterized in that used as the volume resistivity is less than 10 [Omega cm or more 10 ³ Omega cm as intermediate transfer member.
[0008]
According to a second aspect of the present invention, in the image forming apparatus of the first aspect, a corona charger is used as the charge applying unit.
[0009]
According to a third aspect of the present invention, there is provided the image forming apparatus according to the first aspect, wherein a charger composed of a thin wire conductor is used as the charge applying means.
[0010]
According to a fourth aspect of the present invention, there is provided the image forming apparatus according to the first aspect, wherein a rotating roller charger that contacts the intermediate transfer member is used as the charging means.
[0011]
According to a fifth aspect of the present invention, in the image forming apparatus of the first aspect, an ion flow charger is used as the charge applying unit.
[0012]
An image forming apparatus according to a sixth aspect is the image forming apparatus according to the first to fifth aspects, wherein the solid content concentration of the liquid developer is 5% or more and 70% or less.
The image forming apparatus according to claim 7 is the image forming apparatus according to any one of claims 1 to 5, wherein the charge applying unit is arranged downstream of a contact facing portion between the image carrier and the intermediate body in the rotation direction of the intermediate transfer body. And at a position upstream of the contact facing portion between the intermediate transfer member and the transfer material.
The image forming apparatus according to claim 1 to 7, to the intermediate toner image transferred onto the transfer member, a charging unit for imparting the same polarity as the charging polarity of the charge of the toner particles forming the toner image By providing the toner image, a sufficient charge can be given to the toner image for good transfer, so that the secondary transfer rate can be improved.
Then, the by the volume resistivity of the intermediate transfer member and below 10 [Omega cm or more 10 ³ Omega cm, prevents the charging of the intermediate transfer member itself, the intermediate transfer body charge imparted by the charge applying unit Since it is difficult to remain, transfer unevenness at the time of secondary transfer can be prevented. Further, it is possible to easily apply a transfer bias at the time of secondary transfer.
[0013]
In particular, in the image forming apparatus according to the second aspect, since the corona charger which is the most common charge applying means is used as the charge applying means, it can be easily incorporated into the apparatus.
[0014]
In particular, in the image forming apparatus according to the third aspect, since an inexpensive charger composed of a thin wire conductor is used as the charge supplying means, the cost can be reduced.
[0015]
In particular, in the image forming apparatus according to the fourth aspect, since the rotary roller charger contacting the intermediate transfer member is used as the charge applying unit, it is advantageous in terms of ozone reduction and power saving.
[0016]
In particular, in the image forming apparatus according to the fifth aspect, an ion flow charger is used as the charge imparting unit. Therefore, a toner image on the intermediate transfer member is formed in a state where the charger is not in contact with the intermediate transfer member. Charge can be imparted, which is advantageous in that the intermediate transfer member has no influence other than the impartment of charge. The charger is also advantageous in that the amount of generated corona ions can be easily adjusted.
[0018]
In particular, in the image forming apparatus according to the sixth aspect , when the solid content concentration of the liquid developer is 5% or more and 70% or less, that is, the reduction in the charge amount due to toner concentration on the intermediate transfer member becomes significant. When the density is high, the above-described charge imparting to the toner image is particularly effective, so that the effect can be further improved for improving the secondary transfer rate.
[0022]
In particular, in the image forming apparatus according to claim 7 , the charge applying unit is disposed downstream of the contact facing portion (primary transfer region) between the image carrier and the intermediate member in the rotation direction of the intermediate transfer member. In addition, the charge applying means is placed upstream of the primary transfer area and downstream of the secondary transfer area by installing it at a position upstream of the contact facing portion (secondary transfer area) between the intermediate transfer member and the transfer material. Compared with the case where it is provided, the time from the end of the primary transfer to the start of the secondary transfer can be shortened. When the charge applying unit is provided at the former position, the toner image on the intermediate transfer member after the final primary transfer is completed is charged by the charge applying unit before reaching the secondary transfer region. Secondary transfer can be performed. On the other hand, when the toner image is provided at the latter position, the toner image passes through the secondary transfer area and is given charge by the charge applying means, and then reaches the secondary transfer area again. This is because secondary transfer is performed, so that it takes extra time for the intermediate transfer member to make one rotation.
[0023]
In the image forming apparatus according to claim 7 , the charge applying unit is connected to the intermediate transfer member and the transfer member on the downstream side of the contact facing portion between the image carrier and the intermediate member in the rotation direction of the intermediate transfer member. It is desirable to provide it upstream of the contact facing portion with the material and immediately before the secondary transfer region. According to this, charge attenuation of the charged toner image is prevented, so that the secondary transfer rate can be further improved.
[0024]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment in which the present invention is applied to a color electrophotographic copying machine (hereinafter referred to as a copying machine) which is an image forming apparatus will be described.
FIG. 1 is a schematic configuration diagram of a copying machine according to the present embodiment. Around a photosensitive drum (hereinafter referred to as a photosensitive member) 10 as an image carrier, a charging roller 20 as a charging device, an exposure device 30, a cleaning device 60 having a cleaning blade, a static elimination lamp 70 as a static elimination device, and a wet type. A developing device 40 and an intermediate transfer belt 50 as an intermediate transfer member are disposed. The intermediate transfer belt 50 is suspended by a plurality of suspension rollers 51 and travels endlessly in the direction of the arrow by a driving unit such as a motor (not shown). A part of the suspension roller 51 also serves as a transfer bias roller for supplying a transfer bias to the intermediate transfer belt, and a predetermined transfer bias voltage is applied from a power source (not shown). A cleaning device 90 having a cleaning blade for the intermediate transfer belt 50 is also provided. Further, a transfer roller 80 is disposed as a transfer means for transferring the developed image onto the transfer paper 100 as a final transfer material, facing the intermediate transfer belt 50, and the transfer roller 80 is transferred by a power supply device (not shown). Supplied.
Around the intermediate transfer belt 50, a corona charger 52 as a charge applying unit is provided.
[0025]
The wet developing device 40 includes a developing belt 41 as a developer carrier, a black (hereinafter referred to as Bk) developing unit 45K, a yellow (hereinafter referred to as Y) developing unit 45Y, and a magenta provided around the developing belt 41. It comprises a developing unit 45M (hereinafter referred to as magenta) and a cyan (hereinafter referred to as C) developing unit 45C. Further, the developing belt 41 is stretched between a plurality of belt rollers, and is configured to run endlessly in a direction indicated by an arrow by a driving unit such as a motor (not shown). Moves at approximately the same speed as 10.
[0026]
Since the configuration of each developing unit is common, the following description will be given only for the Bk developing unit 50Bk, and for the other developing units 50Y, 50M, and 50C, the portions corresponding to those in the Bk developing unit 50Bk in the figure are as follows. Y, M, and C are appended to the numbers given to those in the unit, and the description is omitted.
The developing unit 50Bk is disposed so that a developing tank 42Bk containing a high-viscosity, high-concentration liquid developer containing toner particles and a carrier liquid component, and a lower part is immersed in the liquid developer in the developing tank 42Bk. And a coating roller 44Bk that thins the developer pumped from the pumping roller 43Bk and applies it to the developing belt 41. The application roller 44Bk has conductivity, and a predetermined bias is applied from a power source (not shown).
[0027]
In addition to the apparatus configuration as shown in FIG. 1, the apparatus configuration of the copying machine according to the present embodiment is an apparatus configuration in which development units 45 for each color are provided around the photoconductor 10 as shown in FIG. It may be.
[0028]
Next, the operation of the copying machine according to the present embodiment will be described.
In FIG. 1, the photosensitive member 10 is uniformly charged by the charging roller 20 while being driven to rotate in the direction of the arrow, and then the reflected light from the original is imaged and projected by an optical system (not shown) by the exposure device 30 on the photosensitive member 10. An electrostatic latent image is formed on the surface. The electrostatic latent image is developed by the wet developing device 40 to form a toner image as a visible image. The developer thin layer on the developing belt 41 is peeled off from the belt 41 in a thin layer state by contact with the photosensitive member in the developing region, and moves to a portion where a latent image is formed on the photosensitive member 10. The toner image developed by the wet developing device 40 is transferred to the surface of the intermediate transfer belt 50 at a contact portion (primary transfer region) between the photoreceptor 10 and the intermediate transfer belt 50 moving at a constant speed (primary transfer region). Primary transfer). When transferring three or four colors to be superimposed, this process is repeated for each color, and a color image is formed on the intermediate transfer belt 50.
[0029]
The corona charger 52 for applying an electric charge to the superimposed toner image on the intermediate transfer belt is arranged at the contact facing portion between the photoconductor 10 and the intermediate transfer belt 50 in the rotation direction of the intermediate transfer belt 50. It is installed on the downstream side and on the upstream side of the contact facing portion between the intermediate transfer belt 50 and the transfer paper 100. The corona charger 52 gives the toner image a true charge having the same polarity as the charge polarity of the toner particles forming the toner image, and is sufficient for good transfer to the transfer paper 100. Charge is applied to the toner image.
The toner image is charged by the corona charger 52, and then transferred to the transfer paper 100 conveyed in the direction of the arrow from a paper supply unit (not shown) by a transfer bias from the transfer roller 80 (two). Next transfer). Thereafter, the transfer paper 100 onto which the toner image has been transferred is separated from the photoconductor 10 by a separation device (not shown), and after a fixing process is performed by a fixing device (not shown), the transfer paper 100 is discharged from the device. On the other hand, after the transfer, the untransferred toner is collected and removed by the cleaning device 60, and the residual charge is discharged by the discharging lamp 70 in preparation for the next charging.
[0030]
Next, in this embodiment, a liquid developer having a solid content concentration of 15% and an endless belt having a volume resistance of about 10 Ω · cm as the intermediate transfer belt 50 are used, and the amount of charge given by the corona charger 52 is determined. The result of changing and developing and transferring is shown. First, at the time of the primary transfer from the photosensitive member 10 to the intermediate transfer belt 50, the solid content concentration of the developer moved onto the intermediate transfer belt 50 is about 25% in the case of monochromatic image formation. In the case of color, it increased to 30-40%. This indicates that the toner density on the intermediate transfer belt 50 becomes more prominent in the case of four-color color copying.
Next, FIG. 7 shows the secondary transfer rate in the case of four-color color copying. The vertical axis of the graph represents the secondary transfer rate, and the horizontal axis represents the effective current value. Here, the effective current represented by the horizontal axis of the graph is an effective current value Ie emitted from the corona charger 52 to the toner image on the intermediate transfer belt 50 as shown in FIG. Is represented by a relationship of Ie = Is−Ir, where Is is the current value flowing from the casing and Ir is the current flowing into the casing of the corona charger 52. The current value Is flowing from the constant current source 53 is controlled so that the effective current value Ie is constant.
In FIG. 7, when the effective current value is 0 μA, that is, when charge is not applied to the toner image by the corona charger 52, the secondary transfer rate is low, and in the case of four colors shown in FIG. The transfer rate was about%. A significant increase in the transfer rate is observed up to an effective current value of 20 μA, and the effect of applying charges by the corona charger 52 can be confirmed.
Further, when the effective current is 20 μA or more, the transfer rate hardly increases, and it can be seen that the effective current of 20 μA is a saturation current for improving the transfer rate. If this saturation current value of 20 μA is the minimum necessary current value that sufficiently improves the secondary transfer rate, 2.4 × 10 ⁻³ C / g is obtained as the amount of charge imparted per unit developer mass. .
[0031]
As described above, in this embodiment, the corona charger 52 applies a true charge having the same polarity as the charged polarity of the toner particles forming the toner image to the toner image on the intermediate transfer belt 50. As a result, the secondary transfer rate could be improved.
[0032]
Further, in addition to the corona charger 52 used in the present embodiment, a charger 52a made of a thin wire conductor may be used as the charge applying means, for example, as shown in FIGS. The leading end of the thin linear conductor extends in a direction perpendicular to the toner image carrying surface on the intermediate transfer belt 50, and discharges from the leading end of the thin linear conductor toward the toner image. Since a true charge sufficient for the transfer can be given, the toner is easily transferred to the transfer paper 100, and the secondary transfer rate can be improved. Further, since the charger 52a is less expensive than other chargers, the cost can be reduced.
[0033]
For example, as shown in FIG. 5, a rotary roller charger 52b that contacts the intermediate may be used as the charge applying means. When the roller charger 52b is used, a true charge can be uniformly applied to the toner image on the intermediate transfer belt 50, so that the toner is easily transferred to the transfer paper 100 and the secondary transfer rate is improved. be able to. Further, it is advantageous in terms of ozone reduction and power saving.
[0034]
Further, for example, as shown in FIG. 6, an ion flow charger 52c may be used as the charge applying means. When this ion flow charger 52c is used, the charger can give a true charge sufficient for good transfer to the toner image in a non-contact state with the intermediate transfer belt 50. The secondary transfer rate can be improved without affecting the intermediate transfer member other than the charge application. The charger also has an advantage that the amount of generated corona ions can be easily adjusted.
[0035]
Further, since the charge applying means as described above is installed on the downstream side of the primary transfer area and the upstream side of the secondary transfer area in the rotation direction of the intermediate transfer member, the charge applying means is disposed on the primary transfer area. Compared with the case where it is provided on the upstream side of the region and on the downstream side of the secondary transfer region, the time from the end of the primary transfer to the start of the secondary transfer can be shortened. When the charge applying unit is provided at the former position, the toner image on the intermediate transfer member after the final primary transfer is completed is charged by the charge applying unit before reaching the secondary transfer region. Secondary transfer can be performed. On the other hand, when the toner image is provided at the latter position, the toner image is once charged through the secondary transfer region and then charged by the charge applying unit, and then reaches the secondary transfer region again. This is because the next transfer is performed, so that it takes extra time for the intermediate transfer member to make one rotation.
[0036]
By the way, with respect to the liquid developer, when the solid content concentration is 5% or more, a problem of a decrease in transfer rate occurs. In this embodiment, a developer having a solid content concentration of 15% is used for ease of handling. However, in practical use, charging is performed by toner concentration on the intermediate transfer belt 50 within a range of 5 to 70%. Since the decrease in the amount becomes remarkable, the charge application to the toner image as described above is particularly effective, and the effect can be more effectively exhibited in improving the secondary transfer rate.
[0037]
In the present embodiment, the intermediate transfer belt 50 having a low resistance is used. This prevents the surface of the intermediate transfer belt 50 from being charged, and the charge imparted by the charge imparting means is transferred to the intermediate transfer belt 50. Therefore, uneven transfer during secondary transfer can be prevented. In addition, there is an effect that transfer bias application at the time of secondary transfer becomes easy. In the present embodiment, an example in which the endless intermediate transfer belt 50 is used as an intermediate transfer member has been described. However, the present invention can also be applied to intermediate transfer members having other shapes, such as a roller. it can.
[0038]
【The invention's effect】
According to the first to fifth aspects of the present invention, the charge imparting means imparts sufficient charge to the toner image on the intermediate transfer member so that a good transfer can be made, so that the secondary transfer rate can be improved. And high-quality images can be obtained.
Further, the volume resistivity of the intermediate transfer member is not more than 10 [Omega cm or more 10 ³ Omega cm, prevents the charging of the intermediate transfer member itself, the charge imparted by the charge applying unit is remaining on the intermediate transfer member It is possible to prevent uneven transfer during secondary transfer. Further, it is possible to easily apply a transfer bias at the time of secondary transfer.
[0039]
In particular, according to the second aspect of the present invention, since the most common corona charger is used as the charge applying means, it can be easily incorporated into the apparatus.
[0040]
In particular, according to the invention of claim 3, since the charger constituted by the thin wire conductor is less expensive than other charge applying means, the cost can be reduced.
[0041]
In particular, according to the invention of claim 4, since the rotary roller charger that contacts the intermediate transfer member is used, it is advantageous in terms of ozone reduction and power saving.
[0042]
In particular, according to the invention of claim 5, since the ion flow charger is used, the charge can be imparted to the toner image on the intermediate transfer member while the charger is not in contact with the intermediate transfer member. This is advantageous in that the intermediate transfer member is not affected other than the charge application. The charger is also advantageous in that the amount of generated corona ions can be easily adjusted.
[0043]
According to the invention of claim 6, since the solid content concentration of the liquid developer is as high as 5% or more and 70% or less, the charge application by the charge application means is particularly effective, and the secondary transfer rate is improved. More effective, and image quality can be improved.
[0045]
According to the seventh aspect of the present invention, since the charge applying means is installed at a position downstream of the primary transfer area and upstream of the secondary transfer area in the rotation direction of the intermediate transfer member, the charge applying means is provided. Compared with the case where the means is provided on the upstream side of the primary transfer area and on the downstream side of the secondary transfer area, the time from the end of the primary transfer to the start of the secondary transfer can be shortened.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing a configuration of a copier according to an embodiment.
FIG. 2 is a schematic configuration diagram showing another configuration of the copying machine according to the embodiment.
FIG. 3 is a configuration diagram showing another configuration of the charge providing unit in the embodiment.
FIG. 4 is a configuration diagram showing a configuration of the charge applying means.
FIG. 5 is a configuration diagram showing still another configuration of the charge providing unit in the embodiment.
FIG. 6 is a configuration diagram showing still another configuration of the charge providing unit in the embodiment.
FIG. 7 is a graph showing the relationship between the secondary transfer rate and the effective current of the charge applying unit.
FIG. 8 is an explanatory diagram for explaining the effective current.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Photoconductor 20 Charging roller 30 Exposure apparatus 40 Wet developing device 41 Developing belt 42 Developing tank 43 Pumping roller 44 Coating roller 45 Developing unit 50 Intermediate transfer belt 51 Suspension roller 52 Corona charger 53 Constant current source 60 Cleaning device 70 Static elimination lamp 80 Transfer roller 90 Cleaning device 100 Transfer paper

Claims (7)

A wet developing device that uses a liquid developer carried on a developer carrying body as a toner image from an electrostatic latent image on the surface of the image carrying body;
In an image forming apparatus provided with an intermediate transfer body to which a toner image formed on the image carrier is transferred,
Against intermediate transferred toner image on the transfer member, a charging unit that applies toner particles of the same polarity charge which forms the toner image is provided,
An image forming apparatus characterized by using what volume resistivity is less than 10 [Omega cm or more 10 ³ Omega cm as intermediate transfer member. The image forming apparatus according to claim 1.
An image forming apparatus using a corona charger as the charge applying means. The image forming apparatus according to claim 1.
An image forming apparatus using a charger composed of a thin linear conductor as the charge applying means. The image forming apparatus according to claim 1.
An image forming apparatus using a rotary roller charger in contact with the intermediate as the charge applying means. The image forming apparatus according to claim 1.
An image forming apparatus using an ion flow charger as the charge applying means. 6. The image forming apparatus according to claim 1, wherein:
An image forming apparatus, wherein the liquid developer has a solid content concentration of 5% to 70%. 6. The image forming apparatus according to claim 1, wherein:
The charge applying means is disposed on the downstream side of the contact facing portion between the image carrier and the intermediate member and on the upstream side of the contact facing portion between the intermediate transfer member and the transfer material in the rotation direction of the intermediate transfer member. An image forming apparatus installed at a position.

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