JP2017076101A - Transfer device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a transfer device that can satisfactorily transfer a toner image in a special color even with the use of a developer deteriorated over time.SOLUTION: An image forming apparatus 1 comprises an image forming unit 110S that forms a toner image in a special color (S), such as gold and silver, in addition to image forming units 110Y, M, C, and K that form toner images in process colors including yellow (Y), magenta (M), cyan (C), and black (K). The image forming apparatus 1 performs correction of gradually decreasing a primary transfer bias for a special color for transferring the toner image in a special color (S) to an intermediate transfer belt 131 in an S mode of performing image formation by using only a special color toner according to the degree of deterioration of a developer forming the toner image in a special color (S), and gradually increasing the primary transfer bias for a special color in an FCS mode of forming images with all colors.SELECTED DRAWING: Figure 7

Description

  The present invention relates to a transfer device and an image forming apparatus including the transfer device.

There is known an image forming apparatus that forms an image by transferring toner images formed on a plurality of image carriers (latent image carriers) onto a transfer material such as a recording material or an intermediate transfer material.
For example, Patent Document 1 describes a monochrome image forming apparatus that forms an image by directly transferring a toner image from a single image carrier (photosensitive drum) to a transfer target (paper). In this image forming apparatus, the number of printed sheets or the number of printed sheets corresponding to developer agitation is measured, and the transfer bias is set so that the optimum transfer current is inversely proportional to the change in the toner charge amount over time according to the measurement result. Is corrected. By correcting in this way, even if the toner charge amount becomes low overall due to the deterioration of the developer over time, the transfer current is corrected accordingly, so that the image quality is deteriorated due to the deterioration of the developer over time. Is described in Patent Document 1.

Even in an image forming apparatus that forms an image by transferring toner images formed on a plurality of image carriers to an intermediate transfer body as a transfer target, the degree of deterioration of the developer (which has a correlation with the degree of deterioration of the developer). It is preferable to correct the transfer current according to a certain parameter.
In addition, as an image forming apparatus provided with a plurality of image carriers, the following toner images are provided in addition to a plurality of image forming units that form toner images of four process colors of yellow, magenta, cyan, and black. There is also known an image forming unit that forms
The image forming unit forms a toner image having a color different from a process color, that is, a colored or colorless color such as at least one kind of gold or silver, that is, a so-called special color toner image.

However, the present inventor conducted verification for correcting the transfer current in the same manner in accordance with the degree of developer deterioration in any color toner image in an image forming apparatus having an image forming unit for forming a special color toner image. As a result, it has been found that the effect of suppressing image quality deterioration differs depending on the toner image.
In particular, when an image forming unit that forms a special color toner that has deteriorated over time is used, the transfer rate of the special color toner image varies significantly more than when only an image forming unit that forms a toner image of the process color is used. As a result, the effect of suppressing image quality deterioration has been reduced.

  In order to solve the above-described problem, the invention according to claim 1 is a transfer device used in an image forming apparatus that forms an image by transferring toner images formed on a plurality of image carriers to an intermediate transfer member. The image forming apparatus includes an image forming unit that forms at least one kind of colored or colorless spot color toner image, in addition to the plurality of image forming units that form process color toner images. The transfer bias for transferring the toner image to the intermediate transfer member is lowered in the special color mode in which the image is formed using only the special color toner according to the degree of deterioration of the special color toner forming the special color toner image, and the image is formed in all colors. In the all color mode, correction is performed to increase.

  According to the present invention, it is possible to provide a transfer device capable of transferring a good spot color toner image even when a developer deteriorated with time is used.

A schematic configuration diagram of an image forming apparatus according to an embodiment. 5 is a graph showing a relationship between a primary transfer rate and a primary transfer current for toner images having different image area ratios in the main scanning direction for each of an initial time when the developer is not deteriorated and a time when the developer is deteriorated. 6 is a graph showing the relationship between the number of formed images (number of printed sheets) and the toner charge amount (Q / M). 6 is a graph showing the relationship between developer transport distance and toner charge amount (Q / M). 3 is a graph showing the relationship between the degree of developer deterioration and the toner charge amount (Q / M) in Example 1. 5 is a flowchart illustrating an example of determining an environmental correction amount (environment correction coefficient) in the first embodiment. 6 is a flowchart illustrating an example of determining a temporal correction amount (a temporal correction coefficient) in the first embodiment. 9 is a flowchart illustrating an example of determining a time correction amount (time correction coefficient) in the second embodiment.

Hereinafter, an embodiment of an electrophotographic image forming apparatus (hereinafter referred to as an image forming apparatus 1) will be described as an image forming apparatus provided with a transfer device to which the present invention is applied.
FIG. 1 is a schematic configuration diagram of an image forming apparatus 1 according to the present embodiment.

An image forming apparatus 1 shown in FIG. 1 is a photoconductor as an image carrier (latent image carrier) capable of forming an image of a color corresponding to color separation of image information sent from an image reading unit 10 or an external device. A tandem configuration in which a plurality of 112 are juxtaposed is provided. A toner image formed on each photoconductor 112 is superimposed and transferred onto an intermediate transfer belt 131, and then the superimposed image is collectively transferred to a sheet material such as recording paper as a recording material to form a multicolor image. It is a possible full-color copier.
The image forming apparatus according to the present embodiment is not limited to a full-color copying machine, but includes a printer, a facsimile apparatus, a printing machine, and the like that support full-color.

An image forming apparatus 1 shown in FIG. 1 is a full-color copying machine that forms a color image by a tandem type image forming unit (hereinafter referred to as an image forming unit 11). The image reading unit 10, the image forming unit 11, The paper unit 12, the transfer unit 13, the fixing unit 14, the paper discharge unit 15, the control unit 16, and the like are included.
The image reading unit 10 is for reading an image of a document and generating image information. It comprises a contact glass 101 and a reading sensor 102. The image reading unit 10 irradiates the original with light, receives the reflected light with a sensor such as a CCD (charge coupled device) or a CIS (contact image sensor), and the electrical colors of RGB which are the three primary colors of light. Read color separation signal.

The image forming unit 11 forms and outputs a toner image of a special color (S) such as gold or silver, in addition to four process colors of cyan (C), magenta (M), yellow (Y), and black (K). It is composed of five image forming units 110S, Y, M, C, and K. The five image forming units 110S, Y, M, C, and K use S, Y, M, C, and K toners of different colors as image forming materials, but the other configurations are the same. It will be replaced when the life is reached. Each of the image forming units 110S, Y, M, C, and K is configured to be detachable from the image forming apparatus main body 2, and constitutes a so-called process cartridge.
Hereinafter, the common configuration of the image forming units 110S, Y, M, C, and K will be described using the image forming unit 110K for forming a K toner image as an example.

The image forming unit 110K includes a charging device 111K, a photoconductor 112K as an image carrier or a latent image carrier, a developing device 114K, a charge eliminating device 115K, a photoconductor cleaning device 116K, and the like. These devices are held by a common holding body, and can be exchanged at the same time by being integrally attached to and detached from the image forming apparatus main body 2.
The photoreceptor 112K has a drum shape with an outer diameter of 60 [mm] in which an organic photosensitive layer is formed on the surface of the substrate, and is driven to rotate counterclockwise by a driving unit.

  The charging device 111K generates a discharge between the charging wire and the outer peripheral surface of the photoconductor 112K by applying a charging bias to a charging wire that is a charging electrode of a charging charger (charger), and thereby the surface of the photoconductor 112K. Is uniformly charged. In this embodiment, the toner is charged to the same negative polarity as that of the toner. As the charging bias, one in which an AC voltage is superimposed on a DC voltage is employed. Instead of the charging charger, a method using a charging roller provided in contact with or close to the photosensitive member 112K may be employed.

  An electrostatic latent image for K is formed on the surface of the uniformly charged photoreceptor 112K by optical scanning with a laser beam emitted from an exposure device 113K described later. Of the entire area of the uniformly charged surface of the photoconductor 112K, the potential of the portion irradiated with the laser light is attenuated, and the potential of the laser irradiated portion is smaller than the potential of the other portion (background portion). Become a statue. The electrostatic latent image for K is developed by a developing device 114K using K toner, which will be described later, to become a K toner image. Then, primary transfer is performed on an intermediate transfer belt 131 described later.

  The developing device 114K has a container for storing a two-component developer containing K toner and a carrier, and supports the developer on the surface of the developing sleeve by the magnetic force of a magnet roller inside the developing sleeve provided in the container. A developing bias having the same polarity as the toner and larger than the electrostatic latent image of the photosensitive member 112K and smaller than the charging potential of the photosensitive member 112K is applied to the developing sleeve. In the meantime, a developing potential from the developing sleeve toward the electrostatic latent image acts. Further, a non-developing potential that moves the toner on the developing sleeve toward the sleeve surface acts between the developing sleeve and the background portion of the photoreceptor 112K. By the action of these development potential and non-development potential, K toner on the development sleeve is selectively attached to the electrostatic latent image on the photoconductor 112K and developed, so that a K-color toner image is formed on the photoconductor 112K. It is formed.

The neutralization device 115K neutralizes the surface of the photoreceptor 112K after the toner image is primarily transferred to the intermediate transfer belt 131.
The photoconductor cleaning device 116K includes a cleaning blade and a cleaning brush, and removes transfer residual toner and the like remaining on the surface of the photoconductor 112K that has been neutralized by the neutralization device 115K.
In the image forming units 110S, Y, M, and C shown in FIG. 1, S, Y, M, and C toner images are respectively formed on the photosensitive members 112S, Y, M, and C in the same manner as the image forming unit 110K. It is formed.

  Above the image forming units 110S, Y, M, C, and K, an exposure device 113 as a latent image writing unit or an exposure unit is disposed. The exposure device 113 optically scans the photoconductors 112S, Y, M, C, and K with a laser beam emitted from a laser diode based on image information sent from an external device such as the image reading unit 10 or a personal computer. . The exposure device 113 is configured such that a laser beam emitted from a light source is polarized in the main scanning direction by a polygon mirror that is rotationally driven by a polygon motor, and the photosensitive elements 112S, Y, M, C, and the like are passed through a plurality of optical lenses and mirrors. K is irradiated. However, instead of laser light, a configuration may be adopted in which optical writing and irradiation are performed using LED light emitted from a plurality of LEDs.

  The paper feed unit 12 supplies a sheet material such as recording paper as a recording material to the transfer unit 13. The paper feed unit 12 includes a paper storage unit 121, a paper feed pickup roller 122, a paper feed belt 123, and a registration roller 124. I have. The paper feed pickup roller 122 is provided to rotate in order to move the sheet material accommodated in the paper accommodating portion 121 toward the paper feed belt 123. The sheet feed pickup roller 122 provided in this way takes out the sheet material at the top of the stored sheet materials one by one and places it on the sheet feed belt 123. The sheet feeding belt 123 conveys the sheet material taken out by the sheet feeding pickup roller 122 to the transfer unit 13. The registration roller 124 feeds the sheet material at a timing when a portion where the toner image is formed on the intermediate transfer belt 131 reaches a secondary transfer nip as a transfer nip of the transfer unit 13.

The transfer unit 13 is disposed below the image forming units 110S, Y, M, C, and K. The transfer unit 13 includes a drive roller 132, a driven roller 133, an intermediate transfer belt 131, primary transfer rollers 134S, Y, M, C, and K, a secondary transfer roller 135, a secondary transfer counter roller 136, a toner adhesion amount sensor 137, A belt cleaning device 138 is provided.
The intermediate transfer belt 131 functions as an endless intermediate transfer member, and a driving roller 132, a driven roller 133, a secondary transfer counter roller 136, and primary transfer rollers 134S, Y, M, and C disposed inside the loop. , K, etc. Here, the term “arrangement” means to arrange and provide, or the position to be determined, and the “tension” means to hang around in a tensioned state.

The intermediate transfer belt 131 is endlessly moved and traveled in the same direction by a driving roller 132 that is driven to rotate in the clockwise direction in the drawing by the driving means, and the photoreceptors 112S, Y, M, C, Move while touching K.
The intermediate transfer belt 131 has a thickness of 20 to 200 [μm], preferably about 60 [μm]. Further, the volume resistivity is about 10 ⁶ to 10 ¹² [Ω · cm], preferably about 10 ⁹ [Ω · cm] (measured with a Hirester UP MCP HT45 manufactured by Mitsubishi Chemical under the condition of an applied voltage of 100 [V]. ) Is preferable.

A toner adhesion amount sensor 137 is disposed in the vicinity of the intermediate transfer belt 131 wound around the driving roller 132. The toner adhesion amount sensor 137 functions as a toner amount detection unit that detects the amount of a specific toner image transferred onto the intermediate transfer belt 131. The toner adhesion amount sensor 137 includes a light reflection type photosensor. The toner adhesion amount sensor 137 detects the amount of reflected light from a specific toner image (special color toner such as a colorless and transparent clear toner) adhered and formed on the intermediate transfer belt 131 to thereby detect the specific toner image. It measures the amount of adhesion.
Here, the toner adhesion amount sensor 137 may also be used as a toner concentration sensor or the like as a toner concentration detecting means for detecting and measuring a toner concentration that has been generally used from the above function. In this case, since it is possible to avoid the provision of a new toner amount detecting means, it is possible to reduce the number of parts and contribute to cost reduction.

The primary transfer rollers 134S, Y, M, C, and K are arranged to face the photoconductors 112S, Y, M, C, and K, respectively, with the intermediate transfer belt 131 interposed therebetween so as to move the intermediate transfer belt 131. Followed rotation. As a result, a primary transfer nip is formed in which the front surface (outer peripheral surface) of the intermediate transfer belt 131 and the photoconductors 112S, Y, M, C, and K are in contact (meaning that they are in contact with each other). Is done. A primary transfer bias is applied to the primary transfer rollers 134S, Y, M, C, and K from a primary transfer bias power source. As a result, a primary transfer electric field is formed between the S, Y, M, C, and K toner images on the photoreceptors 112S, Y, M, C, and K and the primary transfer rollers 134S, Y, M, C, and K. Then, the toner images of the respective colors are primarily transferred to the intermediate transfer belt 131 sequentially.
That is, the S, Y, M, C, and K toner images on the photoreceptors 112S, Y, M, C, and K are intermediately transferred by the primary transfer rollers 134S, Y, M, C, and K, the intermediate transfer belt 131, and the like. A primary transfer means for primary transfer onto the belt 131 is configured.

  The S toner image formed on the surface of the S photoconductor 112S enters the S primary transfer nip with the rotation of the photoconductor 112S, and is intermediated from above the photoconductor 112S by the action of the primary transfer electric field and nip pressure. Primary transfer is performed on the transfer belt 131. The intermediate transfer belt 131 on which the S toner image has been primarily transferred in this way then passes sequentially through the primary transfer nips for Y, M, C, and K, and the Y and Y on the photoconductors 112Y, M, C, and K, respectively. The M, C, and K toner images are primarily transferred on the S toner image while being sequentially superimposed. By this primary transfer of superposition, a superposed toner image including a color toner image and a special color toner image is formed on the intermediate transfer belt 131.

The primary transfer rollers 134S, Y, M, C, and K are made of an elastic roller having a metal core and a conductive sponge layer fixed on the surface, and have an outer diameter of 16 [mm]. The core metal diameter is 10 [mm].
Here, in a state where a grounded metal roller having an outer diameter of 30 [mm] is pressed against the sponge layer with a force of 10 [N], the core of the primary transfer roller 134S, Y, M, C, K is 1000 [ The resistance value R of the sponge layer was calculated from the current I flowing when the voltage V] was applied. Specifically, the resistance value R of the sponge layer calculated based on Ohm's law (R = V / I) from the current I flowing when a voltage of 1000 [V] is applied to the core metal is about 3 × 10 ⁷ [Ω]. A primary transfer bias output from the primary transfer bias power source by constant current control is applied to such primary transfer rollers 134S, Y, M, C, and K. However, instead of the primary transfer rollers 134S, Y, M, C, and K, a transfer charger, a transfer brush, or the like may be employed.

The secondary transfer roller 135 rotates with the intermediate transfer belt 131 and a sheet material such as recording paper as a recording material sandwiched between the secondary transfer counter roller 136. As a result, a secondary transfer nip where the front surface of the intermediate transfer belt 131 and the secondary transfer roller 135 abut is formed. The secondary transfer roller 135 functions as a nip forming member and a transfer member, and the secondary transfer counter roller 136 functions as a nip forming member and a counter member. The secondary transfer roller 135 is grounded, whereas the secondary transfer counter roller 136 is applied with a secondary transfer bias by a secondary transfer bias power source.
The output terminal of the secondary transfer bias power source is connected to the core of the secondary transfer counter roller 136, and the potential of the core of the secondary transfer counter roller 136 is the output voltage value from the secondary transfer bias power source. And almost the same value.

By applying a secondary transfer bias to the secondary transfer counter roller 136, a negative polarity toner is transferred between the secondary transfer counter roller 136 and the secondary transfer roller 135 from the secondary transfer counter roller 136 side to the secondary transfer counter roller 136. A secondary transfer electric field that is electrostatically moved toward the roller 135 is formed. Thereby, the negative polarity toner on the intermediate transfer belt 131 can be moved from the secondary transfer counter roller 136 side to the secondary transfer roller 135 side.
That is, the secondary transfer counter roller 136, the intermediate transfer belt 131, and the like constitute secondary transfer means for secondary transfer of the superimposed toner image on the intermediate transfer belt 131 onto a sheet material such as recording paper.

  Here, as the secondary transfer bias power source, a DC component having the same negative polarity as that of the toner is used, and the same negative polarity as that of the toner is used. However, instead of grounding the secondary transfer roller 135 while applying the secondary transfer bias to the secondary transfer counter roller 136, the secondary transfer counter roller 136 is applied while applying the secondary transfer bias to the secondary transfer roller 135. In this case, the polarities of the DC voltage and DC component are made different.

The secondary transfer counter roller 136 of the present embodiment is formed by laminating a resistance layer on a metal core made of stainless steel, aluminum, or the like, and has the following characteristics.
That is, the outer diameter is about 24 [mm], and the diameter of the cored bar is about 16 [mm]. The resistance layer is made of polycarbonate, fluorine rubber, silicon rubber in which conductive particles such as carbon or metal complex are dispersed, rubber such as NBR or EPDM, rubber of NBR / ECO copolymer, polyurethane Made of conductive rubber or the like. The volume resistance is 10 ⁶ to 10 ¹² [Ω], preferably 10 ⁷ to 10 ⁹ [Ω]. Further, the rubber hardness (ASKER-C) may be a foam type of 20 to 50 degrees or a rubber type of 30 to 60 degrees, but since it contacts the secondary transfer roller 135 via the intermediate transfer belt 131, a small contact pressure is obtained. However, a sponge type that does not generate a non-contact portion is desirable. This is to prevent characters and fine lines from being easily lost as the contact pressure between the intermediate transfer belt 131 and the secondary transfer counter roller 136 increases.

On the intermediate transfer belt 131 after the secondary transfer that has passed through the secondary transfer nip, residual transfer toner that has not been transferred to a sheet material such as a recording paper as a recording material remains. This is removed and cleaned from the surface of the intermediate transfer belt 131 by a belt cleaning device 138 having a cleaning blade in contact with the surface of the intermediate transfer belt 131.
The fixing unit 14 is a belt fixing method, and is configured by pressing a pressure roller 142 against a fixing belt 141 that is an endless belt. The fixing belt 141 is wound around a fixing roller 143 and a heating roller 144, and at least one of the rollers is provided with a heat source / heating means (a heater, a lamp, an electromagnetic induction heating device, or the like). The fixing belt 141 forms a fixing nip between the fixing belt 141 and the pressure roller 142 in a state where the fixing belt 141 is sandwiched and pressed between the fixing roller 143 and the pressure roller 142.

A sheet material such as recording paper, which is a recording material sent to the fixing unit 14, is sandwiched between the fixing nips in a posture in which the carrying surface of the unfixed toner image is in close contact with the fixing belt 141. Since the toner in the toner image is softened by heating or pressurization, the toner image is fixed, and the sheet material is discharged outside the apparatus. Further, in the configuration in which an image is formed also on the surface of the sheet material opposite to the surface to which the toner image is transferred, a sheet material reversing mechanism is provided, and after fixing the toner image, the sheet material is conveyed to the provided sheet material reversing mechanism The sheet material is reversed by the sheet material reversing mechanism. Thereafter, a toner image is formed on the opposite surface in the same manner as the image forming process described above.
Then, the sheet material on which the toner is fixed by the fixing unit 14 is discharged from the image forming apparatus main body 2 to the outside of the apparatus via a discharge roller constituting the discharge unit 15, and is a discharge storage unit such as a discharge tray. 151.

Next, the characteristics of the image forming apparatus 1 of the present embodiment will be described with reference to a plurality of examples.
However, in each of the embodiments described below, an example in which the transfer bias is controlled by a current value is shown, but the case where the transfer bias is controlled by a voltage value is the same and is not particularly limited.

Example 1
First, Example 1 of the image forming apparatus 1 of the present embodiment will be described.
In an image forming apparatus such as the image forming apparatus 1 of this embodiment, a toner image on an image carrier is transferred to an intermediate transfer body as a transfer target body by applying a transfer bias from a transfer unit included in the transfer apparatus. However, of the toner constituting the toner image on the image carrier such as the photoconductor 112, the ratio (transfer rate) of the toner transferred to the intermediate transfer body such as the intermediate transfer belt 131 is determined by the amount of charge of the toner and the transfer bias. It changes depending on the size.
Generally, as the current value of the transfer current increases, the transfer efficiency improves and more toner is transferred to the intermediate transfer body. However, if the transfer current is increased more than necessary, the transfer rate may decrease or transfer Degradation of image quality such as density unevenness occurs in the toner image. This is the same for both primary transfer and secondary transfer. In this type of image forming apparatus, the developer deteriorates as the image forming operation is repeated.

  When the developer deteriorates with time, the toner charge amount (specifically, specific charge: Q / M, which is the charge amount per unit mass of the developer) gradually decreases, and the overall situation becomes low. Is common. Therefore, even if an appropriate transfer bias is set according to the toner charge amount in the initial stage of use where the developer is not deteriorated (hereinafter simply referred to as the initial), the toner charge amount is reduced over time when the developer is deteriorated. Therefore, the transfer bias is not appropriate. For this reason, if the transfer bias as it is at the initial stage is used even when the developer has deteriorated, the transfer rate decreases with time, causing image quality deterioration.

As described above, when the toner charge amount is decreased, the preferable value of the transfer current (primary transfer current) necessary for transferring the toner image from the photosensitive member to the intermediate transfer member is changed. Therefore, it is desirable to correct the primary transfer current according to the degree of deterioration of the developer and to suppress image quality deterioration according to the degree of deterioration of the developer.
Further, it has been found by the inventor's earnest study that the transfer rate also changes depending on the image pattern to be formed (image area ratio in the main scanning direction), and that it is greatly influenced particularly in a state where Q / M is lowered.

The transfer rate includes the size, thickness, material, temperature, humidity, charge amount (Q / M) of developer on the photosensitive member 112, toner adhesion amount, transfer portion 13 of the intermediate transfer belt 131 and the sheet material. The transfer means, the moisture content of each transfer means, the contact state between the photosensitive member 112 and the intermediate transfer belt 131 and the intermediate transfer belt 131 and the sheet material, the rotational speed of the photosensitive member 112, and the conveying speed of the sheet material. It varies depending on etc. For this reason, it is necessary to make adjustments in consideration of these various conditions, but as described above, the influence on the transfer due to the change in the charge amount of the developer is particularly large.
When the charge amount of the developer changes, for example, the optimum value of the primary transfer bias applied to the primary transfer roller 134 in order to transfer the toner image from the photoconductor 112 to the intermediate transfer belt 131 changes. For this reason, conventionally, the transfer bias value (current value or voltage value) supplied to the transfer body is controlled according to the number of printed sheets (for example, Patent Document 1).

However, in the conventional configuration as described above, the transfer bias corresponding to the change in the charge amount of the developer that has deteriorated over time can be set, but the influence of the pattern of the image to be formed is not taken into consideration. The effect of the image pattern to be formed is that, for example, the image quality is unstable depending on the image area ratio such as whether the image is a full-color image, a line-shaped vertical band image, or a patch-shaped image. There is a case.
The image quality may be unstable depending on the image area ratio because the amount of toner or the like forming the image differs depending on whether the image is a solid image or a line image. It is considered to be caused. In particular, it has been proved by the present inventors that the instability of image quality due to the image area ratio is greatly influenced by a change in the charge amount (Q / M) of the developer.

Specifically, the charge amount (Q / M) of the developer decreases as it deteriorates with time depending on the use environment and the number of sheets used. When the charge amount (Q / M) of the developer decreases, the transfer rate changes depending on the image area ratio. For example, transfer performance (transfer rate) is good at a low image area at a certain transfer bias, but transfer is insufficient at a high image area. End up. That is, since the transfer rate is shifted by the image area rate, the transfer good current value is shifted by the image pattern.
On the other hand, various utilization methods have been considered for full-color image forming apparatuses such as copying machines and printers. For example, a home party guide using a full-color printer, a small shop flyer, and advertisement creation.

Therefore, in addition to conventional process color toners such as yellow, magenta, cyan, and black, transparent toner for the purpose of high gloss images, fluorescent toner for obtaining fluorescent images, red for the purpose of expanding the color reproduction region, Colored toners such as green, so-called special color toners (spot color toners) are beginning to be adopted.
Among them, in fields where decorativeness is required (for example, certificate frames, printed paper, celebration bags, etc.), there are cases where gold or silver electrophotographic copies or printed materials are required, and gold or silver features. There is a need for toner. This is because a normal color printer overlays yellow, magenta, and cyan colors to express metallic luster, but the image quality obtained is gold with low reflectivity, and is not of a quality that satisfies customer requirements. .

As a gold or silver special color toner, for example, Patent Document 2 describes that a pigment obtained by coating scaly mica (mica) in a thin film with titanium dioxide and iron oxide is used as a colorant. Has been.
Patent Document 2 describes that the reproduction of golden color can be obtained by using fine powder of an alloy mainly composed of copper, zinc and aluminum as a colorant.
However, since such pigments are generally conductive, they have a feature that they have a low electrical resistance value and are difficult to hold as a problem in a toner having a low volume resistivity. This is presumed to be because the apparent capacitance decreases as the resistance decreases.
For this reason, when the charging ability of the carrier decreases with time, the charge amount of the toner is likely to decrease as compared with the conventional process color toner having a high volume resistivity.
In addition, since the toner charge amount decreases with time, the optimum transfer current in an image with a large image area (such as a full solid image) shifts between the initial time and time, and with a constant transfer current, The problem is that overtransfer occurs and the transfer rate decreases and the image becomes thin.

Accordingly, a first object of the present embodiment is to provide a transfer device (transfer unit 13) that can transfer a good special color toner image even when a developer deteriorated with time is used.
The second purpose of the present embodiment is also good for a toner whose amount of charge (Q / M) of the toner has deteriorated due to deterioration with time, especially for special color toners such as gold and silver, regardless of the image pattern. An image forming apparatus 1 capable of forming a clear image is provided.

FIG. 2 is a graph showing the relationship between the primary transfer rate and the primary transfer current for toner images having different image area ratios in the main scanning direction for each of the initial time when the developer is not deteriorated and the time when the developer is deteriorated. is there.
FIG. 2 shows the relationship between the primary transfer rate and the primary transfer current for the patch image and the solid image for each of the initial time when the developer is not deteriorated and the time when the developer is deteriorated. The patch image is a monochromatic all-solid image whose size is set to a maximum density of 20 mm in the vertical direction (main scanning direction) × 10 mm in the horizontal direction (sub-scanning direction). On the other hand, the solid image is a monochromatic all-solid image whose size is set to a maximum density of 20 mm in length × 300 mm in width. As shown in FIG. 2, each graph shows a relationship in which there is a primary transfer current value (peak) at which the maximum primary transfer rate can be obtained. The relationship is different.

  At the initial stage when the developer is not deteriorated, the primary transfer current value is such that the primary transfer rate is as high as possible (97%) within the range where the same primary transfer rate can be obtained for both the patch image and the solid image. Is set as the initial optimum value (25 μA) shown in FIG. On the other hand, over time when the developer has deteriorated, the relationship between the primary transfer rate and the primary transfer current in the patch image and the solid image is as shown in FIG. Here, when looking at the primary transfer current value (peak) at which the maximum primary transfer rate of the solid image over time is obtained, it can be seen that the primary transfer current (absolute value) is greatly shifted compared to the initial time. .

  If the image forming operation is executed with the primary transfer current value (25 μA) as it is at the initial time even over time, a primary transfer rate of about 93% is obtained for the patch image as shown in FIG. For solid images, the primary transfer rate falls to about 85%. The optimal value of the primary transfer current so that the primary transfer rate is as high as possible (93%) within the range where the same primary transfer rate can be obtained for both the patch image and the solid image over time is the optimal for time shown in FIG. Value (15 μA). As described above, the optimum value of the primary transfer current over time is greatly shifted to the side where the absolute value is lower than the initial value. Therefore, it is desired to correct the primary transfer current so as to decrease the primary transfer current in accordance with the degree of deterioration of the developer. .

Here, the degree of deterioration of the developer, that is, the degree of deterioration of the developer indicating the degree of decrease in the toner charge amount can be calculated using various parameters. For example, the degree of deterioration of the developer, such as the number of printed sheets, the developer transport distance information, the information on the amount of toner consumed from the developing device 6, and the elapsed time since the new developer was set in the developing device 6. One or more of various correlated parameters can be used in combination. In addition, since the slope of the development amount with respect to the development bias (development γ) during image quality adjustment control (during process control) has a correlation with the degree of developer deterioration, it is a parameter for calculating the degree of developer deterioration. Can be used.
Further, it is known that the transfer rate shift from the initial time to the time has a large correlation with Q / M.

FIG. 3 is a graph showing the relationship between the number of formed images (number of printed sheets) and the toner charge amount (Q / M).
This graph shows the transition of the toner charge amount (Q / M) when images having an image area ratio (coverage) of 0.5%, 5%, and 20% are continuously formed. According to the graph shown in FIG. 3, it can be seen that as the image is formed with a low image area ratio (low coverage), the toner charge amount (Q / M) decreases more rapidly. This is presumably because the lower the image area ratio, the smaller the amount of toner consumed in the developing device 6, and therefore the larger the amount of toner staying in the developing device 6, the more stress on the toner.

FIG. 4 is a graph showing the relationship between the developer transport distance and the toner charge amount (Q / M).
This graph shows the transition of the toner charge amount (Q / M) when images having an image area ratio of 0.5%, 5%, and 20% are continuously formed. According to the graph shown in FIG. 4, the toner charge amount (Q / M) decreases rapidly not only in the case of a low image area ratio (0.5%) but also in the case of a high image area ratio (20%). Here, as the developer transport distance, an estimated value calculated by multiplying the process linear velocity (photosensitive linear velocity) by the operating time of the developing device can be used.

  Comparing FIG. 3 and FIG. 4, the transition of the toner charge amount is simply estimated from only the number of formed images (number of printed sheets) or only the developer transport distance, and the primary transfer current is changed according to the toner charge amount. When the correction is performed, there is a large error in the estimated value of the toner charge amount depending on the state of the image forming operation (difference in the image area ratio), and there is a possibility that appropriate primary transfer current correction cannot be performed. Therefore, it is preferable that the degree of deterioration of the developer takes into account not only the number of image forming sheets (number of printed sheets) and the developer transport distance but also the state of image forming operation (difference in image area ratio).

Therefore, the value calculated by the following formula 1 is used as an example of the deterioration degree of the developer in this embodiment.
Degradation degree of developer = (developer transport distance) ² / (toner consumption) Formula 1

FIG. 5 is a graph showing the relationship between the deterioration degree of the developer and the toner charge amount (Q / M) in this embodiment.
According to this, the Q / M transition decreases at a constant rate regardless of the printing conditions (image area ratio). This graph shows the transition of the toner charge amount (Q / M) when images having an image area ratio of 0.5%, 5%, and 20% are continuously formed. According to the graph shown in FIG. 5, it can be seen that the toner charge amount (Q / M) changes in the same manner at any image area ratio. Therefore, by using the degree of deterioration of the developer calculated from Equation 1 above, even if there is a difference in the image forming operation status (even if there is a difference in the image area ratio), the transition of the toner charge amount can be appropriately adjusted. The reflected deterioration degree of the developer can be obtained. Therefore, by correcting the primary transfer current according to the degree of deterioration of the developer, an appropriate primary transfer current can be corrected without being affected by the state of the image forming operation.

The set value of the primary transfer current in this embodiment is calculated from the following equation 2.
Set value = Reference current value × Environmental correction factor × Temporal correction factor Equation 2
The reference current value is a reference primary transfer current value determined by the paper type, paper thickness, and the like.
The environmental correction amount is a correction coefficient due to environmental changes such as temperature and humidity.
The time-dependent correction amount is a correction amount calculated according to the degree of developer deterioration calculated from Equation 1 above.

  In this embodiment, a temperature / humidity sensor of TDK / CHS-CSC-18 is used as the temperature / humidity sensor 17 which is the environment information acquisition means, temperature information is acquired from the thermistor output in the temperature / humidity sensor 17, and Humidity information is acquired from the humidity sensor output in the humidity sensor 17. The detection timing of temperature / humidity information is sampled every 1 min from the time of power-on. The timing for performing environmental correction on the reference current value is performed in the same cycle as the temperature and humidity detection timing. Further, the installation location of the temperature / humidity sensor 17 is not particularly limited, but is preferably a place away from a heat source such as the fixing unit 14. Therefore, in the present embodiment, as shown in FIG.

FIG. 6 is a flowchart illustrating an example of determining the environmental correction amount (environment correction coefficient) in the present embodiment.
First, the thermistor output in the temperature / humidity sensor is detected, and the temperature is determined from the thermistor output-temperature conversion table based on the correlation between the thermistor output and temperature (S1). Next, the humidity sensor output in the temperature / humidity sensor is detected, and the relative humidity is determined from the temperature obtained above and the humidity sensor output-relative humidity conversion table (S2). This table obtains the relative humidity by setting the temperature to the horizontal and the humidity to the vertical. Next, the absolute humidity is calculated from the relative humidity obtained above and the relative humidity-absolute humidity conversion table (S3). In this table, relative humidity is set horizontally and temperature is set vertically, and absolute humidity is obtained. However, the absolute humidity can also be obtained from the temperature and relative humidity by a calculation formula.

  Next, the current environment is determined from the absolute humidity obtained above and the absolute humidity-current environment conversion table (S4). In the determination of the current environment, for example, L / L (19 ° C. 30%), M / L (23 ° C. 30%), M / M (23 ° C. 50%), M / H (23 ° C. 80%), H It is determined which of the predetermined environmental classifications, such as / H (27 ° C., 80%). However, the temperature and humidity values and combinations of the environmental classifications are not limited to this. Finally, an environmental correction coefficient (environment correction amount) corresponding to the current environment obtained as described above is determined (S5). Since the detection by the temperature / humidity sensor does not require any mechanical operation, it can always be monitored and sequential control can be performed against environmental fluctuations.

FIG. 7 is a flowchart illustrating an example of determining the temporal correction amount (temporal correction coefficient) in the present embodiment.
The temporal correction amount of the present embodiment is calculated according to the deterioration degree of the developer calculated from Equation 1 above. The degree of decrease in the toner charge amount indicated by the degree of deterioration of the developer is not only the deterioration of the developer itself, but also the deterioration of the configuration for charging the developer and the toner charge amount constituting the toner image on the intermediate transfer belt 131. It is caused by various factors that decrease over time. However, the main factor is considered to be stirring in the developing device 114. That is, the developer transport distance, which can be estimated from the process linear velocity and the developing unit operating time.

  Another main factor that affects the degree of decrease in the toner charge amount is the amount of toner consumed in the developing device 114. As the toner consumption is smaller, the toner stays in the developing device 114 for a longer time, and is repeatedly subjected to sliding and friction with the developing sleeve, the photoconductor 112 and the like, and the deterioration progresses. The toner consumption amount is calculated by the control unit 16 based on the image area ratio of each formed toner image.

  In this embodiment, by using the developer transport distance and the toner consumption value that influence the degree of decrease in the toner charge amount, the developer deterioration degree (toner deterioration degree) (toner deterioration degree) is calculated from the above formula 1. An index value indicating the degree of decrease in charge amount is calculated. In this embodiment, the deterioration degree of the developer calculated in this way is compared with predetermined threshold values K1, K2, and K3, and a temporal correction coefficient (temporal correction amount) is determined. The toner consumption amount used for calculating the deterioration degree of the developer is the toner consumption amount used for image formation up to the previous time. However, it is reset when the process cartridge constituting the image forming unit is replaced.

Specifically, as shown in FIG. 7, it is determined whether or not the degree of deterioration of the developer is smaller than the threshold value K1 (S11), and when it is determined that the degree of deterioration is smaller than the threshold value K1 ( YES in S11), the deterioration classification is classified as “no deterioration”, and the temporal correction coefficient is determined to be 100% (S12).
If it is determined that the degree of deterioration is greater than or equal to the threshold K1 (NO in S11), it is next determined whether or not the degree of deterioration of the developer is smaller than the threshold K2 (S13). In this determination, if it is determined that the degree of deterioration is smaller than the threshold value K2 (YES in S13), the deterioration classification is classified as “deterioration 1” and the temporal correction coefficient is determined to be 92% (S14).
If it is determined that the degree of deterioration is greater than or equal to the threshold K2 (NO in S13), it is next determined whether or not the degree of deterioration of the developer is smaller than the threshold K3 (S15). In this determination, when it is determined that the degree of deterioration is smaller than the threshold value K3 (YES in S15), the deterioration classification is classified as “deterioration 2” and the temporal correction coefficient is determined as 84% (S16).
If it is determined that the degree of deterioration is greater than or equal to the threshold value K3 (NO in S15), the deterioration classification is classified as “deterioration 3” and the temporal correction coefficient is determined to be 76% (S17).

In this embodiment, for example, K1 = 10000, K2 = 30000, and K3 = 70000 can be used as the above-described thresholds, but the present invention is not limited to this. In addition, the developer deterioration degree is divided into four deterioration categories using three threshold values, but may be divided into fewer deterioration categories or more deterioration categories, or continuously according to the deterioration degree. Alternatively, the time correction count value may be changed. Further, the timing for performing the temporal correction is performed at an appropriate timing, for example, every print job or every time the number of image formation reaches a predetermined number.
In this embodiment, the control unit 16 functions as a developer deterioration degree detecting means for detecting the deterioration degree of the developer, a toner density detecting means for detecting the toner density on the intermediate transfer belt 131, and a transfer bias. The operation function of the transfer unit 13 such as a control function is controlled. However, the present invention is not limited to such a configuration, and a transfer unit control means (control unit) that controls the operation function of the transfer unit 13 is provided in the transfer unit 13 separately from the control unit 16 for controlling the entire apparatus. It may be provided.

Here, the toner used in this embodiment will be described.
Conventionally, it is preferable to use a toner having a volume resistivity larger than 10.7 [log Ωcm] so that charging in the developing device 6 and charging by charge-up (charge injection) in the transfer unit can be obtained. I was thinking.
However, in the configuration including the image forming unit 110S for the special color toner as in the image forming apparatus 1 of the present embodiment, the volume resistivity may be 10.7 [log Ωcm] or less in the special color toner such as gold or silver. Therefore, it is necessary to make full use of these toners. A problem with toners having a low volume resistivity is that it is difficult to maintain a charge.

  Also, in fields where decorativeness is required (for example, certificate frames, printed paper, celebration bags, etc.), there are cases in which gold and silver electrophotographic copies and printed materials are required. There is a need for toner. This is because a normal color printer overlays the three colors of yellow (Y), magenta (M), and cyan (C) to express metallic luster, but the image quality obtained is gold or silver with low reflectivity. This is because the quality does not satisfy the customer's request. In general, the electrical properties of these special color toners vary greatly depending on the pigment used. For example, pigments such as gold and silver toners are electrically conductive and thus become toners with low volume resistivity.

  In particular, it is presumed that special color toners such as gold and silver have a feature that it is difficult to hold a charge because an apparent capacitance decreases due to a decrease in electric resistance. For this reason, during the time when the developer has deteriorated, the toner charge amount of the toner having a low volume resistivity tends to be lower than that of the conventional toner having a high volume resistivity. Further, as described above, the optimum primary transfer current in an image with a high image area ratio shifts between the initial time and the time elapsed as described above due to the decrease in the toner charge amount with time. And the problem that the image density becomes thin becomes remarkable.

Therefore, when the volume resistivity is different, the ease of reduction of the charge amount of the toner is different, and the degree of the problem is also different. For this reason, each image forming unit 110S, Y, M, C, K (for each toner color) is compared with the optimum threshold value, and the primary transfer current is corrected over time, so that good transfer can be performed regardless of the image area. It can be performed.
Therefore, in the image forming apparatus 1 of the present embodiment, when the special color toner (image forming unit 110S) is not used, the image forming units 110Y, 110M, 110C, and 110K use the above-described time correction coefficient (time correction amount). The correction is performed to lower the primary transfer current (in steps) over time.
When the special color toner is used, in the image forming unit 110S, in the S mode (special color single color) using only the special color toner, the primary transfer bias is lowered (stepwise) over time, and the FCS mode in which all the image forming units 110 are used. In (all colors), correction is performed to increase the transfer bias (stepwise).

As described above, when the special color toner is used, the primary transfer bias is controlled differently in the S mode using only the special color toner and the FCS mode using all the image forming units 110 for the following reason.
Because the secondary transfer bias in the FCS mode is set higher than that in the S mode, there is a phenomenon that the special color toner that has become lowly charged over time becomes overtransferred only in the secondary transfer during the FCS mode and becomes thin on the image. To do. On the other hand, in the S mode, the secondary transfer bias is not set as high as in the all-color mode, so there is no concern that the special color toner will be over-transferred in the secondary transfer and lightened on the image.
For these reasons, in the S mode, the primary transfer current is lowered over time, and good transfer is performed regardless of the image area ratio. In the FCS mode, the primary transfer bias is increased with time in order to prevent thinness of the spot color toner in the secondary transfer, and the charge amount is increased by charge-up (charge injection) in the primary transfer portion. In this case, the density of the special color toner is reduced.

As described above, by controlling the primary transfer current of the image forming unit 110S, it is possible to provide a transfer unit (transfer device) 13 that can transfer a good color toner image even with a developer that has deteriorated over time.
In addition, by controlling the primary transfer current of the image forming unit 110S as described above, it is also possible for toners that have deteriorated with time and whose toner charge amount (Q / M) has fluctuated, especially for special color toners such as gold and silver. Thus, it is possible to provide the image forming apparatus 1 capable of forming a good image regardless of the image pattern.

  In addition, when transferring yellow (Y), magenta (M), cyan (C), and black (K) process color toner images, the configuration is the same as when transferring the above-described gold or silver special color toner. Thus, even when a developer that has deteriorated over time is used, better transfer can be performed regardless of the image area ratio.

Here, an example of increasing the primary transfer bias over time, which is performed in the FCS mode in order to prevent the density of the special color toner from being thinned in the secondary transfer, will be described.
In the FCS mode, the timing and method for increasing the primary transfer current over time are the same as those for decreasing in the S mode. For example, as shown in the following Table 1, the time-dependent correction coefficient to be decreased for each degradation category in the S mode is set. Raise in steps.

Specifically, in the flowchart shown in FIG. 7, it is determined whether or not the degree of deterioration of the developer is smaller than the threshold value K1 (S11), and if it is determined that the degree of deterioration is smaller than the threshold value K1. (YES in S11), the temporal correction coefficient is determined to be 100% (S12).
If it is determined that the degree of deterioration is greater than or equal to the threshold K1 (NO in S11), it is next determined whether or not the degree of deterioration of the developer is smaller than the threshold K2 (S13). If it is determined in this determination that the degree of deterioration is smaller than the threshold value K2 (YES in S13), the temporal correction coefficient is determined to be 105% (S14).
If it is determined that the degree of deterioration is greater than or equal to the threshold K2 (NO in S13), it is next determined whether or not the degree of deterioration of the developer is smaller than the threshold K3 (S15). In this determination, when it is determined that the degree of deterioration is smaller than the threshold value K3 (YES in S15), the temporal correction coefficient is determined to be 110% (S16).
If it is determined that the degree of deterioration is equal to or greater than the threshold value K3 (NO in S15), the temporal correction coefficient is determined to be 120% (S17).

  In this way, in the FCS mode, by increasing the primary transfer current over time, the charge amount can be increased by charge-up (charge injection) in the primary transfer portion, and the density of the special color toner in the secondary transfer can be prevented.

  The volume resistivity of the toner described above can be measured, for example, as follows. The toner particle powder 3 [g] is formed into a pellet having a thickness of about 3 [mm] with an electric press, and the pellet is set in a TR-10C type dielectric loss measuring instrument (manufactured by Ando Electric Co., Ltd.). It is calculated from the result of measuring the specific resistance.

(Example 2)
Next, Example 2 of the temporal correction of the primary transfer current in the present embodiment will be described.
This embodiment is different from the first embodiment described above only in the following points.
In Example 1, as the degree of developer deterioration, the degree of developer deterioration (developer transport distance ² / toner consumption) calculated from the above formula 1 was used. In contrast, in this embodiment, the image density detection result of the image quality adjustment pattern obtained at the time of image quality adjustment control (during process control) is used instead of the degree of deterioration (developer transport distance ² / toner consumption). It is a point concerning.
Therefore, the configuration and effects similar to those of the first embodiment described above will be omitted as appropriate.

First, image adjustment control (process control) in the present embodiment will be described.
In the image quality adjustment control, image density control and position shift control are performed based on the result of detecting and detecting a test pattern. In the image density control, for example, a toner adhesion amount (image density) of a density control pattern (image quality adjustment pattern) obtained by developing a predetermined pattern latent image is detected, and in the developing device according to the detection result. The setting values such as the toner concentration in the developer, the writing condition (exposure power, etc.) of the exposure device 113, the charging bias and the developing bias are changed. In the positional deviation control, for example, the latent image writing timing of each color toner image is adjusted by the detection timing of the positional deviation control pattern (image quality adjustment pattern).

  Such image quality adjustment pattern is detected on the photosensitive member 112 between the development area and the primary transfer portion, or on the intermediate transfer belt 131 after the primary transfer of the density control pattern. Etc. However, when the diameter of the photoconductor 112 is small, it is difficult to detect it on the photoconductor 112 due to the installation space of the detection sensor. Therefore, it is preferable to detect it on the intermediate transfer belt 131. On the other hand, regarding the positional deviation control pattern, it is necessary to observe the positional deviation between the color toner images due to the variation in the distance between the photoconductors or the positional deviation due to the writing timing of each color latent image. The above detection is essential. In this embodiment, both the density control pattern and the positional deviation control pattern are detected on the intermediate transfer belt 131.

  In general, image quality adjustment control (process control) is performed in a non-image forming operation period other than an image forming operation period such as when a predetermined number of images are formed before or after the start of a print job (image forming operation) when the power is turned on. Done. However, to further stabilize the image quality, an image quality adjustment pattern is created in the non-image area between the image area (image portion transferred to one recording material) and the image area even during the image forming operation period. The image quality adjustment control may be performed by detecting this. Such image quality adjustment control performed during the image forming operation period is mainly used when controlling the toner density control reference value Vref of the toner density sensor.

  Further, the image quality adjustment pattern includes two types of patterns for each color: a horizontal strip pattern having a long length in the main scanning direction and a patch pattern having a short length in the main scanning direction. Then, the image density (toner adhesion amount) ID of the horizontal band pattern and the patch pattern for each color is detected by the detection sensor, and the image density difference value ΔID between the horizontal band pattern and the patch pattern is calculated for each color. This is used as the degree of deterioration of the developer. As will be described below, the image density difference value ΔID has a relationship that the larger the value is, the greater the degree of decrease in the toner charge amount is.

  That is, as shown in the graph of FIG. 2, when primary transfer is performed using an optimal primary transfer current value (initial optimal value) at the initial stage when the developer is not deteriorated, the initial patch image and For solid images, the primary transfer rate is approximately 97%, which is almost the same. On the other hand, the patch image and the solid image over time when the developer is deteriorated, the primary transfer rate of the patch image is about 94%, whereas the primary transfer rate of the solid image is about 84%. There is a large difference in the primary transfer rate between the two. That is, there is a correlation that as the developer deteriorates and the toner charge amount decreases, the difference in the primary transfer rate between the patch image and the solid image increases. From this correlation, as the image density difference value ΔID between the two obtained from the image density result between the horizontal band pattern and the patch pattern on the intermediate transfer belt 131 increases, the degree of developer deterioration (the toner charge amount) increases. The relationship that the degree of reduction) is large is obtained. That is, when the image density difference value ΔID is small, the correction amount can be reduced, and when the difference ΔID is large, the correction amount can be increased to reduce the difference in transfer rate due to the difference in image area ratio.

In this embodiment, depending on the execution timing of the process control, the following image adjustment pattern for correction of transfer current over time is represented by special colors (S), yellow (Y), magenta (M), cyan (C), black (K ) For each color. The patch-like pattern is a pattern that has a size of 20 [mm] × 10 [mm] in width and becomes a solid image of a single color set to the maximum density, and the horizontal belt-like pattern has a size of 20 [mm] × vertical This is a pattern that forms a solid monochrome image with a horizontal density of 300 mm and a maximum density. The image density (toner adhesion amount) of these patterns is detected on the intermediate transfer belt 131 by a detection sensor (optical sensor). However, the image quality adjustment pattern for calculating the deterioration degree of the developer is not limited to this.
Subsequently, the density of the toner transferred to the intermediate transfer belt 131 is measured by a detection sensor disposed on the intermediate transfer belt 131.

FIG. 8 is a flowchart illustrating an example of determining the temporal correction amount (temporal correction coefficient) in the present embodiment.
As described above, the temporal correction amount of the present embodiment is calculated using the image density difference value ΔID between the horizontal band pattern and the patch pattern as the developer deterioration degree.
Specifically, as shown in FIG. 8, it is determined whether or not the difference value ΔID is smaller than the threshold value L1 (S21), and when it is determined that the difference value ΔID is smaller than the threshold value L1 (YES in S21). ), The time correction coefficient is determined to be 100% (S22).
If it is determined that the difference value ΔID is equal to or greater than the threshold value L1 (NO in S21), it is next determined whether or not the difference value ΔID of the developer is smaller than the threshold value L2 (S23). . In this determination, when it is determined that the difference value ΔID is smaller than the threshold value L2 (YES in S23), the temporal correction coefficient is determined to be 92% (S24).

On the other hand, if it is determined that the difference value ΔID is greater than or equal to the threshold value L2 (NO in S23), it is next determined whether or not the difference value ΔID of the developer is smaller than the threshold value L3 (S25). . In this determination, if it is determined that the difference value ΔID is smaller than the threshold value L3 (YES in S25), the temporal correction coefficient is determined to be 84% (S26).
If it is determined that the difference value ΔID is equal to or greater than the threshold value L3 (NO in S25), the temporal correction coefficient is determined to be 76% (S27).
That is, when the image density difference value ΔID between the horizontal band pattern and the patch pattern is large, it means that Q / M decreases and the image area ratio greatly depends, and when the density difference is small, Q / M is so small. This means a state in which the image area ratio does not decrease and the dependence on the image area ratio is small. For this reason, a good transfer can be performed regardless of the image area by setting the optimum correction amount according to the dependency of the image area ratio due to the decrease in the density difference ΔID (= Q / M) between the horizontal band pattern and the patch pattern. It can be carried out.

  In the present embodiment, for example, L1 = 0.08, L2 = 0.14, and L3 = 0.20 can be used as the above-described threshold values, but the present invention is not limited to this. Further, although the difference value ΔID of the developer is divided into four sections using three threshold values, the difference value ΔID of the developer may be divided into fewer sections or more sections. The time correction count value may be continuously changed according to the value.

  In addition, when transferring yellow (Y), magenta (M), cyan (C), and black (K) process color toner images, the configuration is the same as when transferring the above-described gold or silver special color toner. Thus, even when a developer that has deteriorated over time is used, better transfer can be performed regardless of the image area ratio.

Here, an example of increasing the primary transfer bias over time, which is performed to prevent the density of the special color toner from being thinned in the secondary transfer in the FCS mode of the present embodiment, will also be described.
In the FCS mode of the present embodiment, the timing and method for increasing the primary transfer current with time are the same as when decreasing in the S mode of this embodiment, and the temporal correction coefficient to be decreased in the S mode is increased stepwise.

Specifically, in the flowchart shown in FIG. 8, it is determined whether or not the difference value ΔID is smaller than the threshold value L1 (S21), and when it is determined that the difference value ΔID is smaller than the threshold value L1 (S21). YES), the degradation category is classified as “no degradation” and the temporal correction coefficient is determined to be 100% (S22).
If it is determined that the difference value ΔID is equal to or greater than the threshold value L1 (NO in S21), it is next determined whether or not the difference value ΔID of the developer is smaller than the threshold value L2 (S23). . In this determination, if it is determined that the difference value ΔID is smaller than the threshold value L2 (YES in S23), the deterioration classification is classified as “deterioration 1” and the temporal correction coefficient is determined to be 105% (S24). .

On the other hand, if it is determined that the difference value ΔID is greater than or equal to the threshold value L2 (NO in S23), it is next determined whether or not the difference value ΔID of the developer is smaller than the threshold value L3 (S25). . In this determination, when it is determined that the difference value ΔID is smaller than the threshold value L3 (YES in S25), the deterioration classification is classified as “deterioration 2” and the temporal correction coefficient is determined to be 110% (S26). .
If it is determined that the difference value ΔID is equal to or greater than the threshold value L3 (NO in S25), the deterioration classification is classified as “deterioration 3” and the temporal correction coefficient is determined to be 120% (S27).
In this way, in the FCS mode, by increasing the primary transfer current over time, the charge amount is increased by charge-up (charge injection) in the primary transfer part, and in this embodiment also, the density of the special color toner in the secondary transfer is prevented. can do.

(Example 3)
Next, a description will be given of an example 3 of the temporal correction of the transfer current in the present embodiment.
This embodiment is different from the first and second embodiments described above only in the following points.
In Examples 1 and 2, the primary transfer bias was corrected over time according to the degree of deterioration of the developer. On the other hand, in the present embodiment, the secondary transfer bias is also corrected over time by the primary transfer bias correction over time according to the deterioration degree of the developer.
Therefore, the same configurations and effects as those of the first and second embodiments will be omitted as appropriate.

In this embodiment, as described above, the secondary transfer bias is also corrected over time by correcting the primary transfer bias over time. This is due to the following reason.
When the toner that has deteriorated with time is secondarily transferred to the paper, it is affected when the Q / M of the toner decreases, and the secondary transfer rate is slightly shifted to the low bias side. Furthermore, if correction is performed to reduce the primary transfer bias by temporal correction at the time of primary transfer, the amount of charge due to charge-up is difficult to improve, so that it is more susceptible to influence. For this reason, it is possible to obtain a more optimal secondary transfer bias by correcting the secondary transfer bias to be lowered according to the temporal correction amount at the time of primary transfer. Transfer can be performed. In addition, by lowering the secondary transfer bias, it can be expected to suppress image quality deterioration due to an afterimage and increase the life of the transfer member.

Example 4
Next, Example 4 of the temporal correction of the primary transfer current in this embodiment will be described.
This embodiment is different from the first to third embodiments described above only in that the present embodiment is different from the deterioration degree (deterioration with time) of the developer and the change in the correction amount of the transfer bias with time depending on the use environment. .
Therefore, the configurations and effects similar to those of the first to third embodiments described above will be omitted as appropriate.

Specifically, the toner Q / M decreases when the usage environment is high temperature, high humidity, or low temperature, low humidity, and the developer usage environment is more severe and easily deteriorates. The degree of reduction in charge amount varies depending on the usage environment. . For this reason, by changing the correction amount according to the use environment, it is possible to obtain an optimum transfer bias according to the use environment, and good transfer can be performed.
Here, an example of changing the correction amount of the primary transfer bias depending on the use environment, that is, the temperature / humidity and the environment is shown in Table 2 below.

The current environment (use environment) is the environment determined by the flowchart of FIG. Here, the current environment indicates temperature / humidity and environment, and L / L (19 ° C. 30%), M / L (23 ° C. 30%), M / M (23 ° C. 50%), M / H ( 23 ° C., 80%), H / H (27 ° C., 80%), etc. However, temperature, humidity values, combinations, and the like are not limited thereto.
In the example shown in Table 2, when correction is performed to lower the primary transfer bias according to the degree of deterioration of the developer, the correction amount of the primary transfer bias is greatly changed as the use environment becomes higher temperature and humidity. ing. By changing in this way, when performing a correction to lower the primary transfer bias, it is possible to obtain an optimum transfer bias according to the use environment, and good transfer can be performed.

  Further, when the primary transfer bias is corrected according to the degree of deterioration of the developer, the primary transfer bias is changed step by step. Thereby, when the correction amount is determined by the control unit 16 as the correction amount determination means, the correction amount can be determined by easily combining the deterioration degree of the developer and the use environment.

(Example 5)
Next, Example 5 of the temporal correction of the primary transfer current in this embodiment will be described.
This embodiment differs from the first to fourth embodiments described above only in that this embodiment is related to changing the amount of correction over time due to the resistance change of the transfer member.
Therefore, the configurations and effects similar to those of the first to fourth embodiments described above will be omitted as appropriate.

Specifically, the temporal correction amount is determined by detecting the electrical resistance of the transfer member and combining the detected resistance value and the temporal correction value. This is due to the following reason.
The transfer resistance (transfer rate) is largely related to the electrical resistance of transfer members such as the primary transfer roller 134 and the intermediate transfer belt 131. That is, when the resistance of the transfer member is too low, the influence of the resistance of the toner layer increases, and the voltage applied to the primary transfer roller 134 or the like, which is a transfer means, varies greatly depending on the image area, often when the image area is small. Sometimes transfer efficiency changes.

In addition, even when the resistance of the transfer member is too high, if the applied voltage becomes too high, current leaks and disturbs the image, or the voltage increases to the upper limit of the power supply performance. It stops flowing. If the current does not flow in this way, there is a risk that the transfer may not be performed sufficiently, or the risk that the power supply is broken increases.
In general, the members of the transfer means such as the intermediate transfer belt 131 and the primary transfer roller 134 are gradually changed in resistance by applying a transfer voltage such as a primary transfer voltage. For this reason, when the resistance of the member constituting the transfer means included in the transfer apparatus changes with time, the above-described problems may occur.

Therefore, in order to suppress the occurrence of the above-described problems, the electrical resistance of the transfer member is detected, and the temporal correction amount is determined by combining the detected resistance value and the temporal correction value. did. Hereinafter, the configuration of the present embodiment will be described more specifically.
In the configuration of this example, the primary transfer bias applied to the primary transfer roller 134 is controlled at a constant current, and the resistance of the intermediate transfer belt 131 and the primary transfer roller 134 constituting the primary transfer unit is detected by detecting the applied voltage. It has electrical characteristic detection means for detecting the value.
Here, the voltage detection of the primary transfer unit may be any of voltage detection of only the primary transfer roller 134, voltage detection of only the intermediate transfer belt 131, and voltage detection of the primary transfer roller 134 and the intermediate transfer belt 131. .

この表３に示すように、一次転写ローラ１３４のローラ抵抗によって転写電圧は異なり、ローラ抵抗が高いほど検知電圧は高くなっているため、検知電圧によって、転写部材である一次転写ローラ１３４のローラ抵抗、つまり抵抗値が分かる。 When the current used for detection is, for example, 25 [μA], the detection voltage is as shown in Table 3 below.

As shown in Table 3, the transfer voltage varies depending on the roller resistance of the primary transfer roller 134, and the detection voltage increases as the roller resistance increases. Therefore, the roller resistance of the primary transfer roller 134, which is a transfer member, depends on the detection voltage. That is, the resistance value is known.

Next, when the roller resistance of the primary transfer roller 134 is changed, the primary transfer rate, which is the ratio between the toner adhesion amount on the intermediate transfer belt 131 and the toner adhesion amount on the photoconductor 112, is different. Table 4 below shows the roller resistance of the primary transfer roller 134 and the primary transfer bias that maximizes the primary transfer rate.

From Table 4, for example, if the reference roller resistance is 7.5th power (1 × 10 ^7.5 [Ω]), the appropriate transfer bias is 25 [μA], and the roller resistance is 7.0th power. In this case, the bias value is corrected by +4 [μA] to 29 μA. It can also be seen that when the roller resistance becomes 8.0 power (1 × 10 ^8.0 [Ω]), the bias value is corrected to −4 μA to 21 μA.
On the other hand, when the roller resistance becomes 9.0 power (1 × 10 ^9.0 [Ω]), image disturbance due to discharge occurs at 21 [μA], and does not occur at 17 [μA]. The transfer rate was almost the same regardless of [μA] or 17 [μA]. From this, it can be seen that when the roller resistance becomes 9.0 power (1 × 10 ^9.0 [Ω]), the bias value is corrected by −8 [μA] to 17 [μA].

表５に示したように補正量を変化させることにより、一次転写ローラのローラ抵抗やトナーのＱ／Ｍが変わっても、一次転写率が最大となる一次転写バイアスを設定（選択）することができ、画像不良の発生も抑制（防止）できる。 The time-dependent correction based on the roller resistance of the primary transfer roller 134 of these primary transfer biases can be determined based on whether the detected voltage is lower or higher than the voltage threshold. It is possible to set a more optimal primary transfer current.
Here, an example is shown in Table 5 below.

By changing the correction amount as shown in Table 5, the primary transfer bias that maximizes the primary transfer rate can be set (selected) even when the roller resistance of the primary transfer roller and the Q / M of the toner change. And the occurrence of image defects can be suppressed (prevented).

In the above description, the resistance of the primary transfer roller 134 (roller resistance) is changed. However, the same change is shown when the resistance of the intermediate transfer belt 131 is changed. Therefore, the same effect can be obtained by performing the same primary transfer bias correction in accordance with the resistance of the intermediate transfer belt 131.
Here, the correction control of the primary transfer bias performed based on the above-described electrical characteristic detection means (method) and a predetermined threshold is performed by the above-described control unit 16, and the control unit 16 also serves as a correction amount determination unit. It is functioning. Further, in this embodiment, correction is performed by voltage detection of constant current control, but it can be similarly performed by current detection of constant voltage control.

That is, the following effects can be achieved by changing the amount of correction of the transfer bias with time based on the change in resistance of the transfer member constituting the transfer means.
The electrical resistance of the transfer member is also greatly involved in the transferability. For this reason, by detecting the electrical resistance of the transfer member and combining the resistance value and the correction value with time, a more optimal transfer bias can be obtained, and good transfer can be performed.

  Further, in the example shown in Table 5, when the correction for lowering the primary transfer bias is performed according to the degree of deterioration of the developer, the resistance change amount from the reference resistance value of the transfer member constituting the transfer unit. The larger the is, the larger the primary transfer bias correction amount is changed. By changing in this way, when correcting to lower the primary transfer bias, it is possible to obtain an optimum primary transfer bias according to the degree of deterioration of the developer and the resistance of the primary transfer roller 134, and good transfer can be achieved. It can be carried out.

Here, the voltage detection as described above generally needs to be accompanied by a mechanical operation in which a transfer current is passed for a certain period of time to read the voltage, and therefore, the production capacity of the machine by the voltage detection operation is lowered.
On the other hand, the image quality adjustment process control in the image forming apparatus 1 of the present embodiment is often performed with a dedicated time other than during image formation. For this reason, when performing the image quality adjustment process control, the above-described voltage detection is also performed, so that it is possible to suppress a reduction in the production capacity of the machine due to the voltage detection alone.
Therefore, in this embodiment, the above-described voltage detection operation is performed when the image quality adjustment process control is performed.

  Further, when the primary transfer bias is corrected according to the degree of deterioration of the developer, the primary transfer bias is changed step by step. Thereby, when the correction amount is determined by the control unit 16 as the correction amount determining means, the correction amount can be determined by easily combining the deterioration degree of the developer and the roller resistance of the primary transfer roller 134. It becomes.

The preferred embodiment of the present embodiment has been described with reference to a plurality of examples. However, the present embodiment is not limited to the specific embodiment, and is not particularly limited in the above description. Various modifications and changes can be made within the scope of the gist of the present invention described in the claims.
For example, the detection of the developer deterioration level and the determination as to whether the developer deterioration level has reached a level that requires correction of the primary transfer current over time is performed from the viewpoint of facilitating control. May be performed only for the image forming unit used for image formation at that time. The primary transfer current may be controlled not by controlling the current value but by controlling the voltage value. The developer may be a two-component developer containing toner and carrier as described above, or a one-component developer composed of toner. A detection sensor that detects a horizontal belt-like pattern or a patch-like pattern may be provided in each image forming unit.

Further, the preferred image forming apparatus of the present embodiment is not limited to the tandem type image forming apparatus, and the toner images of the respective colors are sequentially formed on one photosensitive drum, and the respective color toner images are sequentially superimposed. So-called. The same applies to the one-drum type.
Further, the image forming apparatus is not limited to a copying machine, and may be a single unit such as a printer or a facsimile, or a complex machine having at least two of these functions.
Further, the effects described in the present embodiment are merely enumerated the most preferable effects resulting from the present embodiment, and the effects are not limited to those described in the present embodiment.

What was demonstrated above is an example, and there exists an effect peculiar for every following aspect.
(Aspect A)
Toner images such as S, Y, M, C, and K toner images formed on a plurality of image carriers such as photoreceptors 112S, Y, M, C, and K are transferred to an intermediate transfer member such as an intermediate transfer belt 131. In the transfer device such as the transfer unit 13 used in the image forming apparatus such as the image forming apparatus 1 that forms an image such as a multicolor image, the image forming apparatus includes cyan (C), magenta (M), yellow ( In addition to a plurality of image forming units such as image forming units 110Y, 110M, 110C, and 110K that form process color toner images such as Y) and black (K), special color (S) toner images such as gold and silver An image forming unit such as an image forming unit 110S that forms at least one kind of colored or colorless spot color toner image is provided, and a primary color transfer bias for spot colors that transfers the spot color toner image to the intermediate transfer body. In accordance with the degree of deterioration of the developer that forms the spot color toner image, the transfer bias is lowered stepwise in the spot color mode such as the S mode in which an image is formed using only the spot color toner to form an image with all colors. In all color modes such as the FCS mode, correction is performed by increasing the level stepwise.

According to this, as described in the present embodiment, the following effects can be achieved.
In general, the electrical characteristics of special color toners vary greatly depending on the pigment used. For example, pigments such as gold and silver toners are electrically conductive and thus become toners with low volume resistivity. A problem with toners having a low volume resistivity is that it is difficult to maintain a charge. This is presumed to be because the apparent capacitance decreases as the resistance decreases.
For this reason, when the charging ability of the carrier decreases with time, the charge amount of the toner is likely to decrease as compared with the conventional process color toner having a high volume resistivity.
As the toner charge amount decreases over time, the optimum transfer current for an image with a large image area (all solid images) shifts between the initial time and time, and overtransfer occurs over time at a constant transfer current. The problem that the transfer rate decreases and the image becomes thin becomes remarkable. In this case, it is particularly effective to lower the transfer bias so as to lower the transfer current over time.

However, when transferring a special color toner image, since the secondary transfer bias is set higher in the all color mode than in the special color mode, the special color toner that has become lowly charged over time becomes overtransferred in the secondary transfer and becomes thin on the image. There is a phenomenon of becoming. On the other hand, in the special color mode, the secondary transfer bias is not set as high as in the full color mode, so there is no concern that the special color toner will be overtransferred in the secondary transfer and lightened on the image.
For these reasons, in the spot color mode, the primary transfer bias is lowered over time, and good transfer is performed regardless of the image area ratio. In the all-color mode, the primary transfer bias is increased to prevent thinness in secondary transfer, the charge amount is increased by charge-up (charge injection) in the primary transfer part, and the density of special colors in secondary transfer is reduced. To prevent.
Therefore, it is possible to provide a transfer device that can transfer a good spot color toner image even when a developer deteriorated with time is used.

(Aspect B)
In (Aspect A), the special color toner forming the special color toner image is a toner such as a special color (S) toner image such as gold or silver with metallic luster.
According to this, as described in the present embodiment, the following effects can be achieved.
The demands of luxurious customers who do not have dullness with a metallic luster that cannot be obtained with metallic luster that overlays process color toners such as yellow (Y), magenta (M), cyan (C), and black (K). A transfer device capable of transferring a metallic gloss image satisfying the above can be provided.

(Aspect C)
In (Aspect A) or (Aspect B), the transfer bias for transferring the special color toner image to the intermediate transfer member is a formula using the transport distance of the developer forming the special color toner image and the amount of toner consumption. The correction is performed in accordance with the value of a calculated value such as the value calculated in 1.

According to this, as described in the present embodiment, the following effects can be achieved.
The toner deteriorated with time decreases in Q / M. When Q / M decreases, the dependency of the primary transfer rate on the image area ratio in the main scanning direction (image ratio in the main scanning direction) increases, and the transfer ratio shifts depending on the image area in the main scanning direction. Specifically, when the toner deteriorates with time, an image with a small image area ratio (for example, a patch image) is not so much affected, but when an image with a large image area ratio (for example, a solid image) is obtained, it becomes over-transferred and becomes thin. (The transfer rate shifts to the low current side, and the transfer rate becomes overtransferred and the transfer rate is lowered). Further, the condition for lowering Q / M tends to decrease under the conditions of low duty and low coverage. In view of this, the correction of lowering the transfer current based on the calculated value using the developer travel distance (duty) and the toner consumption (coverage) shown in Equation 1 allows the image area ratio to be large even for toner that has deteriorated over time. Make sure the image does not fade. In addition, the correction amount is corrected to the extent that the density of the patch is not affected, and an optimal correction amount in which the patch and all the solids are compatible with each other enables good transfer regardless of the image area.
Therefore, even if a developer that has deteriorated with time is used, a good special color toner image can be transferred regardless of the image area ratio.

(Aspect D)
In (Aspect C), the transfer bias for transferring the process color toner image to be transferred to the transfer target, the transport distance of the developer forming the respective process color toner image, and the toner consumption amount are set. The correction is performed in accordance with the value of the calculated value used.
According to this, as described in the present embodiment, it is possible to provide a transfer device that can perform good transfer regardless of the image area ratio even when a developer that has deteriorated with time is used.

(Aspect E)
In (Aspect A) or (Aspect B), the image forming apparatus determines the density of a toner adhesion pattern such as an image adjustment pattern for image adjustment formed on a non-image area of the image carrier on the intermediate transfer member. Control means for performing process control for changing the image forming condition in accordance with the value detected by the detection sensor detected in step (a), wherein the toner adjustment pattern for image adjustment extends at least in a patch-like pattern and in the main scanning direction. The control means includes a process color for transferring a difference such as an image density difference value ΔID between the density of the toner image of the patch-like pattern and the density of the toner image of the horizontal-band pattern, and The transfer bias that is calculated for each spot color and transfers the spot color toner image to the intermediate transfer member is set according to the calculated difference value of the spot color. And performing correction to decrease.

According to this, as described in the present embodiment, the following effects can be achieved.
When the image density is small (patch) toner density and image area is large (horizontal band) by adding a horizontal band pattern extending in the main scanning direction to the conventional patch-like image adjustment pattern The toner density can be measured. When the difference ΔID between the density (patch) when the image area ratio is small and the density (horizontal band) when the image area ratio is large, the correction amount is small, and when the difference ΔID is large, the correction amount is large. Thus, the difference in transfer rate due to the difference in image area rate can be reduced. That is, when the density difference between the patch and the horizontal band is large, it means that Q / M is lowered and the image area ratio is highly dependent. When the density difference is small, Q / M is not so lowered. This means that the dependence on the image area ratio is small. Therefore, the difference between the amount of adhesion between the patch and the horizontal band = the optimum correction amount according to the dependence of the image area ratio due to the Q / M reduction, regardless of the image area. Good transfer can be performed.
Therefore, even if a developer that has deteriorated with time is used, a good special color toner image can be transferred regardless of the image area ratio.

(Aspect F)
(Embodiment E) wherein correction is performed to lower each transfer bias for transferring a process color toner image to be transferred to the intermediate transfer body in accordance with the calculated difference value of each process color. And
According to this, as described in the present embodiment, it is possible to provide a transfer device that can perform good transfer regardless of the image area ratio even when a developer that has deteriorated with time is used.

(Aspect G)
In any one of (Aspect A) to (Aspect F), primary transfer means including a primary transfer roller 134 and an intermediate transfer belt 131 that primarily transfer a toner image formed on an image carrier to an intermediate transfer member; A secondary transfer unit that secondary-transfers the toner image transferred to the transfer body to a transfer-receiving body such as a sheet material, and the secondary transfer counter roller 136 and the intermediate transfer roller 136 according to the correction amount when correcting the primary transfer bias. Correction of the secondary transfer bias composed of the transfer belt 131 and the like is also performed.

According to this, as described in the present embodiment, the following effects can be achieved.
Even when the toner that has deteriorated with time is secondarily transferred to a transfer medium such as paper, the toner is affected if the Q / M of the toner is lowered, and the secondary transfer rate is also shifted to the low bias side. Furthermore, during primary transfer, for example, if correction with time is performed to lower the primary transfer bias, the amount of charge due to charge-up is difficult to improve, so that it is more susceptible to influence.
For this reason, it is possible to obtain an optimal secondary transfer bias by performing a correction that lowers the secondary transfer bias according to the temporal correction amount at the time of primary transfer, and good transfer can be performed.
Further, by lowering the secondary transfer bias, it can be expected that image quality deterioration is suppressed by the residual image and that the life of the transfer member such as the primary transfer roller 134 and the intermediate transfer belt 131 is extended.

(Aspect H)
In (Aspect G), when the correction for lowering the primary transfer bias is performed, the correction for lowering the secondary transfer bias is performed according to the correction amount.

According to this, as described in the present embodiment, the following effects can be achieved.
Even when the toner that has deteriorated with time is secondarily transferred to a transfer medium such as paper, the toner is affected if the Q / M of the toner is lowered, and the secondary transfer rate is also shifted to the low bias side. Furthermore, if correction with time is performed to lower the primary transfer bias during primary transfer, the amount of charge due to charge-up is difficult to improve, and this is more susceptible to influence.
For this reason, by correcting the secondary transfer bias to be lowered by the temporal correction amount for lowering the primary transfer bias at the time of primary transfer, the optimum secondary transfer bias can be obtained, and good transfer can be performed.
Further, by lowering the secondary transfer bias, it can be expected that image quality deterioration is suppressed by the residual image and that the life of the transfer member such as the primary transfer roller 134 and the intermediate transfer belt 131 is extended.

(Aspect I)
In any one of (Aspect A) to (Aspect H), a correction amount for correcting a transfer bias such as a primary transfer bias and a secondary transfer bias according to a change in a use environment such as a temperature / humidity of the current environment and an environment. It is characterized by changing.
According to this, as described in the present embodiment, the following effects can be achieved.
The toner Q / M decreases when the usage environment is high temperature, high humidity, or low temperature, low humidity. The developer usage environment is more severe and easily deteriorates, and the degree of decrease in the charge amount varies depending on the usage environment. For this reason, by changing the correction amount according to the use environment, it is possible to obtain an optimum transfer bias according to the use environment, and good transfer can be performed.

(Aspect J)
In (Aspect I), when the correction for lowering the primary transfer bias is performed according to the degree of deterioration of the developer, the correction amount of the primary transfer bias is greatly changed as the use environment becomes higher in temperature and humidity. Features.
According to this, as described in the present embodiment, when correction for lowering the primary transfer bias is performed, an optimum transfer bias according to the use environment can be obtained, and good transfer can be performed.

(Aspect K)
In any one of (Aspect A) to (Aspect J), transfer members such as a primary transfer roller 134, a secondary transfer roller 135, and an intermediate transfer belt 131 that constitute transfer means such as a primary transfer means and a secondary transfer means. The correction amount for correcting the transfer bias is changed by changing the resistance.
According to this, as described in the present embodiment, the following effects can be achieved.
The electrical resistance of the transfer member is also greatly involved in the transferability. Therefore, by detecting the electrical resistance of the transfer member and combining the resistance value and the time-dependent correction value, a more optimal transfer bias can be set, and good transfer can be performed.

(Aspect L)
In (Aspect K), when correction for lowering the primary transfer bias is performed according to the degree of deterioration of the developer, the transfer member constituting the transfer unit is set to the 7.5th power (1 × 10 ^{7.5) as a reference.} As the resistance change amount from the resistance value such as [Ω]) is larger, the correction amount of the primary transfer bias is largely changed.
According to this, as described in the present embodiment, when performing the correction for lowering the primary transfer bias, the optimum primary transfer bias according to the deterioration degree of the developer and the resistance of the transfer member can be obtained. Good transfer can be performed.

(Aspect M)
In any one of (Aspect A) to (Aspect L), when the transfer bias is corrected according to the deterioration degree of the developer, the transfer bias is changed stepwise.
According to this, as described in the present embodiment, when the correction amount is determined by the correction amount determination unit such as the control unit 16, the deterioration degree of the developer and other conditions such as the use environment and the transfer member resistance are determined. Can be easily combined to determine the correction amount.

(Aspect N)
Toner images such as S, Y, M, C, and K toner images formed on a plurality of image carriers such as the photoreceptors 112S, Y, M, C, and K are transferred to an intermediate transfer member such as the intermediate transfer belt 131. In the image forming apparatus such as the image forming apparatus 1 including a transfer device for transferring, the transfer device includes a transfer device such as the transfer unit 13 of any one of (Aspect A) to (Aspect M). To do.
According to this, as described in the present embodiment, it is possible to provide an image forming apparatus that can achieve the same effects as the transfer apparatus of any one of (Aspect A) to (Aspect M).
That is, it is possible to provide an image forming apparatus that performs good transfer even with toner that has deteriorated over time, regardless of the image area ratio.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Image forming apparatus main body 10 Image reading part 11 Image forming part 12 Paper feed part 13 Transfer part 14 Fixing part 15 Paper discharge part 16 Control part 17 Temperature / humidity sensor 110 Image forming unit 111 Charging device 112 Photoreceptor 113 Exposure Device 114 Developing device 115 Neutralizing device 116 Photoconductor cleaning device 121 Paper storage portion 131 Intermediate transfer belt 134 Primary transfer roller 135 Secondary transfer roller 136 Secondary transfer counter roller 137 Toner adhesion amount sensor

JP-A-5-158357 Japanese Examined Patent Publication No. 6-073028 JP-A-9-160298

Claims (14)

In a transfer device used for an image forming apparatus that forms an image by transferring toner images formed on a plurality of image carriers to an intermediate transfer member,
The image forming apparatus includes an image forming unit that forms at least one kind of colored or colorless spot color toner image, apart from a plurality of image forming units that form process color toner images.
The transfer bias for transferring the special color toner image to the intermediate transfer body is lowered in the special color mode in which an image is formed using only the special color toner according to the degree of deterioration of the developer that forms the special color toner image, and is created in all colors. A transfer apparatus that performs correction to be raised in an all-color mode for imaging. The transfer device according to claim 1,
The transfer device, wherein the special color toner forming the special color toner image is a metallic glossy toner. In the transfer device according to claim 1 or 2,
Correction is performed to lower the transfer bias for transferring the special color toner image to the intermediate transfer body in accordance with a calculated value using a transport distance and a toner consumption amount of the developer forming the special color toner image. A transfer device characterized by that. The transfer device according to claim 3, wherein
Calculated value using each transfer bias for transferring the process color toner image to be transferred to the intermediate transfer member, and the transport distance of the developer and the toner consumption for forming the respective process color toner image The transfer device is characterized in that the correction is performed according to the above. In the transfer device according to claim 1 or 2,
In the image forming apparatus, the image forming condition is determined according to the value of the detection value of the detection sensor that detects the density of the toner adhesion pattern for image adjustment formed on the non-image area of the image carrier on the intermediate transfer body. Control means for performing process control to change the
The image adjustment toner adhesion pattern comprises at least a patch-like pattern and a horizontal belt-like pattern extending in the main scanning direction,
The control means calculates the difference between the density of the toner image of the patch-like pattern and the density of the toner image of the horizontal belt-like pattern for each process color and spot color to be transferred,
A transfer apparatus that performs correction to lower the transfer bias for transferring the spot color toner image to the intermediate transfer body according to the calculated difference value of the spot color. The transfer device according to claim 5, wherein
A transfer apparatus that performs correction to lower each transfer bias for transferring a toner image of a process color to be transferred to the intermediate transfer body in accordance with a calculated difference value of each process color. In the transfer device according to any one of claims 1 to 6,
A primary transfer unit that primarily transfers a toner image formed on the image carrier to an intermediate transfer member; and a secondary transfer unit that secondarily transfers the toner image transferred to the intermediate transfer member to a transfer target.
A transfer apparatus, wherein a secondary transfer bias is also corrected according to a correction amount for correcting the primary transfer bias. The transfer device according to claim 7,
A transfer apparatus, wherein when performing correction to lower the primary transfer bias, correction to lower the secondary transfer bias is performed according to the correction amount. In the transfer device according to any one of claims 1 to 8,
A transfer apparatus, wherein a correction amount for correcting a transfer bias is changed according to a change in a use environment. The transfer device according to claim 9, wherein
A transfer apparatus characterized in that, when correction is performed to lower the primary transfer bias in accordance with the degree of deterioration of the developer, the correction amount of the primary transfer bias is greatly changed as the use environment becomes higher temperature and humidity. The transfer device according to any one of claims 1 to 10,
A transfer apparatus, wherein a correction amount for correcting a transfer bias is changed by a change in resistance of a transfer member constituting a transfer unit. The transfer device according to claim 11, wherein
When performing correction to lower the primary transfer bias according to the degree of developer deterioration,
A transfer apparatus characterized in that the correction amount of the primary transfer bias is largely changed as the resistance change amount from the reference resistance value of the transfer member constituting the transfer means is larger. The transfer device according to any one of claims 1 to 12,
A transfer apparatus that changes the transfer bias stepwise when correcting the transfer bias in accordance with the degree of deterioration of the developer. In an image forming apparatus comprising a transfer device for transferring toner images formed on a plurality of image carriers to an intermediate transfer member,
An image forming apparatus comprising the transfer device according to claim 1 as the transfer device.

Images