JP6891524B2 - Image forming device - Google Patents

Description

The present invention relates to an image forming apparatus such as a copier or a printer using an electrophotographic method.

In an electrophotographic image forming apparatus, a charged latent image obtained by forming optical image information on an image carrier such as a photoconductor uniformly charged in advance is visualized by toner from a developing apparatus. Then, the visible image is transferred directly onto a recording material such as transfer paper or via an intermediate transfer body such as an intermediate transfer belt, and fixed on the recording material to form an image.

In such an image forming apparatus, a method of controlling a DC transfer bias applied to a transfer means by a constant current using a DC power supply has been widely adopted. However, in recent years, a wide variety of papers have come to be used as recording materials used in image forming apparatus, and those having a high-class leather pattern image and Japanese paper-like ones are commercially available.

Such paper has irregularities on its surface due to embossing or the like in order to give a high-class feeling. Toner is less likely to be transferred to the concave portion than to the convex portion, and particularly when the toner is transferred to a recording material having large irregularities, the toner may not be sufficiently transferred to the concave portion and an image may be lost.

Regarding transfer defects to the recesses of recording materials, it is known that by superimposing an AC voltage on a DC voltage, it is possible to improve the transfer rate and improve abnormal images such as hollows. For example, Japanese Patent Application Laid-Open No. 2006-267486 (Patent). It has been proposed in Japanese Patent Application Laid-Open No. 1), Japanese Patent Application Laid-Open No. 2008-058585 (Patent Document 2), Japanese Patent Application Laid-Open No. 09-146381 (Patent Document 3), Japanese Patent Application Laid-Open No. 04-0867878 (Patent Document 4), and the like.

Further, Japanese Patent Application Laid-Open No. 2013-237592 (Patent Document 5) discloses that a better image can be obtained by making the output time of a voltage closer to the transfer direction longer than the output time closer to the opposite polarity as a voltage waveform. ing.

Further, in such an image forming apparatus, a method of detecting the temperature and humidity of the operating environment and determining and controlling (correcting) the transfer current (voltage) value according to the detection result is described, for example, Japanese Patent Application Laid-Open No. 2013-231936. (Patent Document 6).

An object of the present invention is to provide an image forming apparatus capable of performing image transfer with an optimum bias of a DC component and an AC component.

In order to solve the above problems, the present invention presents a transfer bias output means for outputting a bias including a DC component and an AC component in order to transfer the image carrier and the toner image on the image carrier to the recording material. An environment detecting means for detecting at least one of the temperature and humidity in the apparatus, and a controlling means for controlling the transfer bias output means, which occupies one cycle of the bias waveform of the bias. The area on the side where the toner is returned from the recording material to the image carrier is A from the center value (Voff) of the maximum and minimum values of the voltage, and from the center value (Voff) of the maximum and minimum values of the voltage of the bias. When the area on the side where the toner is transferred from the image carrier to the recording material is B and the bias duty (Duty) = A / (A + B) × 100 [%], the control means is the environment. The DC component and the AC component are resized according to at least one of the temperature and humidity detected by the detection means and whether the duty is less than 50% or greater than 50%. It is characterized by controlling the transfer bias output means.

Further, in order to solve the above-mentioned problems, the present invention has a transfer bias that outputs a bias including a DC component and an AC component in order to transfer the image carrier and the toner image on the image carrier to the recording material. It has an output means, the transfer bias output means, and a control means for controlling the printing speed, and is larger than the center value (Voff) of the maximum and minimum values of the bias voltage in one cycle of the bias waveform. The area on the side where the toner is returned from the recording material to the image carrier is A, and the side where the toner is transferred from the image carrier to the recording material rather than the center value (Voff) of the maximum and minimum values of the bias voltage. When the area of the bias is B and the duty of the bias is A / (A + B) × 100 [%], the control means obtains the printing speed, the value of the duty, and the DC. It is characterized in that the transfer bias output means is controlled so as to change the size of the component and the AC component.

Further, in order to solve the above-mentioned problems, the present invention outputs a bias including a DC component and an AC component in order to transfer the image carrier and the toner image on the image carrier to the recording material by the transfer unit. It has a transfer bias output means for detecting the resistance of the transfer unit, a resistance detecting means for detecting the resistance of the transfer unit, and a control means for controlling the transfer bias output means, and the voltage of the bias occupied in one cycle of the bias waveform. The area on the side where the toner is returned from the recording material to the image carrier is A, which is larger than the center value (Voff) of the maximum and minimum values, and the area is larger than the center value (Voff) of the maximum and minimum values of the bias voltage. When the area on the side where the toner is transferred from the image carrier to the recording material is B and the bias duty (Duty) = A / (A + B) × 100 [%], the control means is the resistance detection means. Controlling the transfer bias output means so as to change the magnitude of the AC component according to the resistance of the transfer unit detected by the above and whether the duty is less than 50% or greater than 50%. It is a feature.

According to the image forming apparatus of the present invention, it is possible to perform image transfer with the bias of the optimum DC component and AC component, so that a good transferred image can be obtained.

It is a figure which shows the schematic structure of the electrophotographic color printer which is an example of the image forming apparatus which concerns on embodiment of this invention. It is a block diagram which shows the image formation unit. It is a schematic block diagram which shows another example of an image forming apparatus. It is a schematic diagram which shows the mode of switching a DC bias and a superimposition bias and applying it to a secondary transfer part. It is a block diagram which shows the configuration example which switches a DC bias and a superimposition bias by using two relays. It is a block diagram which shows the configuration example which switches a DC bias and a superimposition bias without providing a relay. It is a waveform diagram explaining the action of superimposition bias. It is a waveform diagram which shows an example of the superimposition bias waveform of low duty. It is a waveform diagram which shows an example of the superimposition bias waveform of high duty. It is a waveform figure which shows another example of the superimposition bias waveform of low duty. It is a waveform diagram which shows another example of the superimposition bias waveform of high duty.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a diagram showing a schematic configuration of an electrophotographic color printer (hereinafter, simply referred to as “printer”) which is an example of an image forming apparatus according to an embodiment of the present invention. The printer shown in this figure is a color image forming apparatus adopting an intermediate transfer method, and has an endless belt (intermediate transfer belt 51) as an intermediate transfer body. Four image forming units 1Y, 1M, for forming each color toner image of yellow (Y), magenta (M), cyan (C), and black (K) along the upper running side of the intermediate transfer belt 51. 1C and 1K are arranged side by side to form a tandem image formation unit.

Since each of the image forming units 1Y, 1M, 1C, and 1K has the same configuration except for the color of the toner to be handled, only one image forming unit will be described with reference to FIG. As shown in FIG. 2, the image forming unit includes a photoconductor drum 11 as an image carrier, a charging device 21 that charges the surface of the photoconductor drum 11 with a charging roller, and a development that visualizes a latent image on the photoconductor drum 11. The apparatus 31 includes a transfer roller 55 as a primary transfer means for transferring a toner image from the photoconductor drum 11 to an intermediate transfer belt 51, a cleaning device 41 for cleaning the surface of the photoconductor drum 11, and the like. In this embodiment, the image forming units 1Y, 1M, 1C, and 1K are detachably provided with respect to the printer main body.

The photoconductor 11 of this example has a drum shape with an organic photosensitive layer formed on the surface of the drum substrate and has an outer diameter of about 60 mm, and is rotationally driven clockwise in the drawing by a driving means (not shown). The charging device 21 uniformly charges the surface of the photoconductor by generating an electric discharge between the charging roller and the photoconductor 11 while bringing the charging roller to which the charging bias is applied into contact with or close to the photoconductor drum 11. .. In the present embodiment, the toner is uniformly charged to the same negative polarity as the normal charging polarity. As the charging bias, the one in which the AC voltage is superimposed on the DC voltage is adopted. Instead of the method using a charging roller, a method using a charging charger may be adopted.

The developing device 31 includes a developing sleeve 31a as a developing agent carrier and two screw members as a stirring member that conveys the developing agent while stirring in a container containing a two-component developer composed of toner and a carrier. It includes 31b and 31c. It is also possible to use a developing device that uses a one-component developer.

The cleaning device 41 includes a cleaning blade 41a and a cleaning brush 41b. The cleaning blade 41a is in contact with the photoconductor drum 11 from the counter direction with respect to the rotation direction of the photoconductor drum 11, and the cleaning brush 41b is in contact with the photoconductor drum 11 while rotating in the opposite direction. Clean the surface of the photoconductor drum 11 with.

Returning to FIG. 1, an optical writing unit 80, which is a latent image writing means, is arranged above the image forming units 1Y, 1M, 1C, and 1K. The optical writing unit 80 lightly scans the photoconductors 11Y, 11M, 11C, and 11K with a laser beam emitted from a laser diode based on image information sent from an external device such as a personal computer. By this optical scanning, electrostatic latent images for Y, M, C, and K are formed on the photoconductors 11Y, 11M, 11C, and 11K. Specifically, in the entire area of the uniformly charged surface of the photoconductor 11, the portion irradiated with the laser beam attenuates the potential. As a result, the potential of the laser-irradiated portion becomes an electrostatic latent image smaller than the potential of the other portion (ground portion). The optical writing unit 80 irradiates the photoconductor through a plurality of optical lenses and mirrors while polarized the laser beam L emitted from the light source in the main scanning direction by a polygon mirror rotationally driven by a polygon motor. Is. An LED array may be used in which light writing is performed by LED light emitted from a plurality of LEDs in the LED array.

Below the image forming units 1Y, 1M, 1C, and 1K, a transfer unit 50 as a transfer device that moves endlessly in the counterclockwise direction in the drawing while stretching an endless intermediate transfer belt 51 is arranged. .. In addition to the intermediate transfer belt 51 which is an image carrier, the transfer unit 50 includes a drive roller 52, a secondary transfer back surface roller 53, a cleaning backup roller 54, four primary transfer rollers 55, a nip forming roller 56, and a belt cleaning device 57. It has a potential sensor 58 and the like.

The intermediate transfer belt 51 is stretched by a drive roller 52, a secondary transfer back surface roller 53, a cleaning backup roller 54, and four primary transfer rollers 55 arranged inside the loop. The rotational force of the drive roller 52, which is rotationally driven in the clockwise direction, causes endless movement in the same direction. As the intermediate transfer belt 51, a belt having the following characteristics is used. That is, the thickness is about 20 [μm] to 200 [μm], preferably about 60 [μm]. The volume resistivity is about 1e6 [Ωcm] to 1e13 [Ωcm], preferably 1e7.5 [Ωcm] to 1e12.5 [Ωcm], and more preferably about 1e9 [Ωcm] (Mitsubishi Chemical High Leicester, Inc.). Measured with UP MCP HT45 and HRS probe under the condition of applied voltage 100V and 10sec value). Further, as the material, PI (polyimide), PVDF (vinylidene fluoride), ETFE (ethylene-ethylene tetrafluoride copolymer), PC (polycarbonate), etc. may be used as a single layer or a plurality of layers. It is possible. If necessary, the surface of the belt may be coated with a release layer. Materials used for coating include ETFE (ethylene-ethylene tetrafluorinated copolymer), PTFE (polytetrafluorinated ethylene), PVDF (vinyl fluoride), PEA (perfluoroalkoxyfluororesin), and FEP (four-fluorine). Fluororesin such as ethylene oxide-propylene hexafluoride copolymer) and PVF (vinyl fluoride) can be used, but the present invention is not limited thereto. The belt manufacturing method includes a casting method, a centrifugal molding method, and the like, and the surface thereof may be polished if necessary. Further, a belt material (endless belt) having a three-layer structure of a base layer, an elastic layer and a coat layer may be used. In the case of a belt having a three-layer structure, the base layer is made of, for example, a fluororesin having low elongation or a rubber material having large elongation combined with a material having difficulty in stretching such as canvas. The elastic layer is made of, for example, a fluorine-based rubber or an acrylonitrile-butadiene copolymer rubber, and is formed on the base layer. Further, the coat layer is formed by coating the surface of the elastic layer with, for example, a fluororesin. The resistivity is adjusted by dispersing a conductive material such as carbon black.

The four primary transfer rollers 55 sandwich the intermediate transfer belt 51, which is endlessly movable, between the photoconductor 11 (Y, M, C, K). As a result, a primary transfer nip for Y, M, C, K is formed in which the front surface of the intermediate transfer belt 51 and the photoconductor 11 (Y, M, C, K) come into contact with each other. A primary transfer bias is applied to each of the primary transfer rollers 55 by a transfer bias power supply (not shown). As a result, a transfer electric field is formed between each color toner image on the photoconductor 11 (Y, M, C, K) and each color primary transfer roller 55, and the transfer electric field and nip pressure act on the photoconductor 11. The toner image is primarily transferred onto the intermediate transfer belt 51. By sequentially superimposing the M, C, and K toner images on the Y toner image and performing primary transfer, a four-color superimposed toner image is formed on the intermediate transfer belt 51.

When forming a monochrome image, the support plates supporting the primary transfer rollers 55Y, M, C for Y, M, C in the transfer unit 50 are moved to move the primary transfer rollers 55Y, M, C. Keep away from the photoconductors 11Y, M, and C. As a result, the front surface of the intermediate transfer belt 51 is separated from the photoconductors 11Y, M, and C, and the intermediate transfer belt 51 is brought into contact with only the photoconductor 11K for K. In this state, of the four image forming units 1Y, M, C, and K, only the image forming unit 1K for K is driven to form a K toner image on the photoconductor 11K.

The primary transfer roller 55 is composed of an elastic roller provided with a metal core metal and a conductive sponge layer fixed on the surface of the core metal, and has the following characteristics in this example. .. The outer shape is 16 [mm]. The diameter of the core metal is 10 [mm]. The volume resistance of the roller is measured by rotation. A load of 5 [N] / one side is applied, a bias of 1 [kV] is applied to the transfer roller shaft, and the roller is rotated during 1 minute measurement (roller rotation speed is For example, the resistance value was measured while rotating (30 rpm), and the average value was taken as the volume resistance. The resistance R of the sponge layer calculated based on Ohm's law (R = V / I) is 1e6Ω to 1e9Ω, preferably about 3E7Ω. A primary transfer bias is applied to such a primary transfer roller 55 under constant current control. A transfer charger, a transfer brush, or the like may be used instead of the transfer roller.

The nip forming roller 56 of the transfer unit 50 is arranged outside the loop of the intermediate transfer belt 51, and sandwiches the intermediate transfer belt 51 with the secondary transfer back surface roller 53 inside the loop. As a result, a secondary transfer nip is formed in which the front surface of the intermediate transfer belt 51 and the nip forming roller 56 come into contact with each other. While the nip forming roller 56 is grounded, the secondary transfer bias is applied to the secondary transfer back surface roller 53 by the secondary transfer bias power supply 200. As a result, a secondary transfer electric field is formed between the secondary transfer back surface roller 53 and the nip formation roller 56 to electrostatically move the toner from the secondary transfer back surface roller 53 side toward the nip formation roller 56 side.
In the present embodiment, the temperature / humidity sensor 106 is provided as an environment detecting means for detecting the temperature / humidity around the secondary transfer unit.

Below the transfer unit 50, a paper feed cassette 100 that houses a plurality of recording papers P (recording materials) in a stack of paper bundles is arranged. The paper feed cassette 100 has a paper feed roller 101 in contact with the recording paper P at the top of the paper bundle, and by rotating the paper feed roller 101 at a predetermined timing, the recording paper P is brought into the paper feed path. Send it toward. A resist roller pair 102 is arranged near the end of the paper feed path. The resist roller pair 102 stops the rotation of both rollers as soon as the recording paper P sent out from the paper feed cassette 100 is sandwiched between the rollers. Then, the rotation drive is restarted at a timing when the sandwiched recording paper P can be synchronized with the toner image on the intermediate transfer belt 51 in the secondary transfer nip, and the recording paper P is sent out toward the secondary transfer nip. The toner image on the intermediate transfer belt 51, which is brought into close contact with the recording paper P by the secondary transfer nip, is collectively secondary transferred onto the recording paper P by the action of the secondary transfer electric field and the nip pressure. When the recording paper P on which the full-color toner image or the monochrome toner image is formed on the surface in this way passes through the secondary transfer nip, the curvature is separated from the nip forming roller 56 and the intermediate transfer belt 51.

The secondary transfer back surface roller 53 is formed by laminating a resistance layer on a core metal made of stainless steel, aluminum, or the like. The resistance layer is made of polycarbonate, fluororubber, silicon rubber, etc. with conductive particles such as carbon or metal complex dispersed, or rubber such as NBR or EPDM, NBR / ECO copolymer rubber, or polyurethane semi-conductive. It is made of rubber or the like. Its volumetric resistance is 10 ⁶ to 10 ¹² [Ω], preferably 10 ⁷ to 10 ⁹ [Ω]. Further, a foam type having a hardness of 20 to 50 degrees or a rubber type having a rubber hardness of 30 to 60 degrees may be used, but since it contacts the nip forming roller 56 via the intermediate transfer belt 51, it is a non-contact portion even with a small contact pressure. A sponge type that does not cause This is to prevent the characters and fine lines from being hollowed out as the contact pressure between the intermediate transfer belt 51 and the secondary transfer back surface roller 53 increases.

Further, the nip forming roller 56 is formed by laminating a resistance layer made of conductive rubber or the like and a surface layer on a core metal made of stainless steel, aluminum or the like. In this example, the outer diameter of the roller is 20 [mm], and the core metal is stainless steel with a diameter of 16 [mm]. The resistance layer is a rubber having a hardness of 40 to 60 degrees [JIS-A] made of an NBR / ECO copolymer. The surface layer is made of a fluorine-containing urethane elastomer, and its thickness is preferably 8 to 24 [μm]. The reason is that the surface layer of the roller is often manufactured by the coating process, so if the thickness of the surface layer is 8 μm or less, the effect of resistance unevenness due to coating unevenness is large, and there is a possibility that leaks will occur in places with low resistance. Yes, not preferable. Further, the problem that the surface layer is cracked due to wrinkles on the roller surface is likely to occur. On the other hand, when the thickness of the surface layer becomes thicker than 24 μm, the resistance increases, and when the volume resistance is high, the voltage when a constant current is applied to the core metal of the secondary transfer back surface roller 53 may increase, which is constant. If the current falls below the target current because it exceeds the voltage variable range of the current power supply, or if the voltage variable range is sufficiently high, the high-voltage path from the constant current power supply to the secondary transfer back surface roller core metal or the secondary transfer back surface Leakage is likely to occur due to the high voltage of the roller core metal. Further, if the thickness of the surface layer of the nip forming roller 56 is thicker than 24 μm, the hardness becomes high, and there is a problem that the adhesion to the recording medium (paper or the like) or the intermediate transfer belt is deteriorated. The surface resistance of the nip forming roller 56 is 10 ^6.5 [Ω] or more, and the volume resistance of the surface layer of the nip forming roller 56 is 10 ¹⁰ [Ω cm] or more, more preferably 10 ¹² [Ω cm] or more.

The nip forming roller 56 can be a foam type roller in which the surface layers are not laminated. In that case, the volume resistance of the nip forming roller is 6.0 logΩ to 8.0 logΩ, preferably 7.0 logΩ to 8.0 logΩ. At this time, the secondary transfer back surface roller 53 may be a foam type, a rubber type, or a metal roller such as SUS, and its volume resistance is preferably 6.0 logΩ or less, which is lower than that of the nip forming roller. .. The volume resistance measurement method of the nip forming roller 56 and the secondary transfer back surface roller 53 is based on the rotation measurement as in the case of the primary transfer roller 55, and 5 [N] / one-sided load is applied to 1 [ A bias of [kV] was applied, and the resistance value was measured while rotating the roller (roller rotation speed is, for example, 30 rpm) during the measurement for 1 minute, and the average value was taken as the volume resistance.

The potential sensor 58 is arranged outside the loop of the intermediate transfer belt 51. Then, in the entire area of the intermediate transfer belt 51 in the circumferential direction, the intermediate transfer belt 51 faces the grounded drive roller 52 with respect to the hanging portion via a gap of about 4 [mm]. Then, when the toner image primaryly transferred onto the intermediate transfer belt 51 enters a position facing itself, the surface potential of the toner image is measured. As the potential sensor 58, EFS-22D manufactured by TDK Corporation is used. The potential sensor can also be a toner image detection sensor. The toner image detection sensor is an optical sensor of 1 light emission and 2 light receiving type, and detects the amount of adhesion of the toner image primaryly transferred on the intermediate transfer belt by converting the received output into the amount of adhesion.

A fixing device 90 is arranged on the right side of the drawing of the secondary transfer nip. The fixing device 90 forms a fixing nip by a fixing roller 91 including a heat generating source such as a halogen lamp and a pressure roller 92 that rotates while contacting the fixing roller 91 with a predetermined pressure. The recording paper P fed into the fixing device 90 is sandwiched between the fixing nips in a posture in which the surface supporting the unfixed toner image is brought into close contact with the fixing roller 91. Then, the toner in the toner image is softened by the influence of heating and pressurization, and the full-color image is fixed. The recording paper P discharged from the fixing device 90 is discharged to the outside of the machine after passing through the transport path after fixing.

Instead of the nip forming roller 56, a configuration using a secondary transfer unit 41 having an endless secondary transfer belt 36 as shown in FIG. 3 can also be adopted. The secondary transfer unit 41 of FIG. 3 includes a secondary transfer belt 36, a secondary transfer roller 400, and support rollers 401, 402, 403. The secondary transfer belt 36 is supported by the secondary transfer roller 400 and the support rollers 401, 402, 403. The secondary transfer roller 400 is electrically grounded. A secondary transfer nip N is formed between the secondary transfer belt 36 and the intermediate transfer belt 51.

The secondary transfer bias power supply 200 as the secondary transfer bias output means included in the printer of the present embodiment is a DC power supply that outputs a DC component and an AC power supply (superimposed power supply) that outputs a DC component superposed with an AC component. As the secondary transfer bias, it is possible to output a DC voltage (hereinafter referred to as DC bias) and a DC voltage overlaid with an AC voltage (hereinafter referred to as superimposition bias). ..

FIG. 4 is a schematic view showing how the DC bias and the superimposition bias are switched and applied to the secondary transfer unit (in this example, the secondary transfer back surface roller 53). In this figure, the secondary transfer bias power supply 200 is composed of a DC power supply 201 and an AC power supply (superimposed power supply) 202.

The figure (a) shows a state in which a DC bias is applied from the DC power supply 201, and the figure (b) shows a state in which a superimposed bias is applied from the AC power supply 202. Note that FIG. 4 shows switching between the DC power supply 201 and the AC power supply 202 with a switch in order to conceptually show the switching, but in the specific configuration example illustrated in FIG. 5, switching is performed using two relays. It is configured as follows. Further, as illustrated in FIG. 6, a configuration in which the switching means is not provided is also possible.

FIG. 5 is a configuration example in which the DC bias and the superimposition bias are switched by using two relays. As shown in this figure, the DC power supply 201 applies a DC bias to the secondary transfer back surface roller 53 via the relay 1. Further, the AC power supply 202 applies a superimposition bias to the secondary transfer back surface roller 53 via the relay 2. The connection and disconnection of the two relays (relay 1 and relay 2) are controlled by the control means 300 via the relay drive means 205, and the DC bias or the superimposition bias as the secondary transfer bias is switched. The DC power supply 201 has a voltage detecting means 203, and inputs the detected feedback voltage to the control means 300.

FIG. 6 is a configuration example for switching between DC bias and superimposition bias without providing a relay. As shown in this figure, the bias power supply 200 includes a DC power supply 201 and an AC power supply 202'. The AC power supply 202'applies an AC bias to the secondary transfer back surface roller 53. Further, the DC power supply 201 applies a DC bias to the secondary transfer back surface roller 53 via the AC power supply 202'. When a DC bias is applied to the secondary transfer back surface roller 53 as the secondary transfer bias, the DC power supply 201 is made to output the DC bias, and the output of the AC power supply 202'is turned off. When a superimposition bias is applied to the secondary transfer back surface roller 53 as the secondary transfer bias, the DC power supply 201 outputs the DC bias and the AC power supply 202 ′ outputs the AC bias. As a result, the bias power supply 200 applies a superimposed bias in which the AC bias is superimposed on the DC bias to the secondary transfer back surface roller 53. Switching between the DC bias and the superimposed bias is controlled by the control means 300. The DC power supply 201 has a voltage detecting means 203, and inputs the detected feedback voltage to the control means 300.

The form (configuration) of the transfer power supply and the voltage supply is not limited to those illustrated here, and various forms are possible. These will be explained later with an example.
Next, the action of the superimposition bias will be described with reference to the waveform diagram of FIG.

In the figure, the offset voltage Voff is the value of the DC component of the superimposition bias. Further, the peak toe peak voltage Vpp is the peak toe peak voltage of the AC component of the superposition bias. The superimposition bias is a superposition of the offset voltage Voff and the peak topeak voltage Vpp, and the time average value thereof is the same as the offset voltage Voff. As shown in the figure, the superimposed bias has a sinusoidal shape and has a positive peak value and a negative peak value. Of these two peak values, Vt is the peak value of the one that moves the toner from the belt side to the recording paper side (minus side in this example) in the secondary transfer nip. Further, what is indicated by Vr is the peak value of the direction in which the toner is returned from the recording paper side to the belt side (plus side in this example). By applying a superposition bias containing a DC component and setting the offset voltage Voff, which is the time average value, to the same polarity as the toner (minus in this example), the toner is reciprocated and recorded relatively from the belt side. It is possible to move it to the paper side and transfer it to the recording paper. As the AC voltage, a sine wave-shaped waveform is adopted, but a rectangular wave-shaped waveform may be used.

Although FIG. 7 shows a symmetrical waveform, a waveform in which the time for moving the toner of the AC component from the belt side to the recording paper side and the time for returning the toner from the recording paper side to the belt side are different times. It can also be used. In the embodiment, the latter waveform is adopted.

Here, the duty in the superimposed bias in which the AC voltage (that is, the peak-to-peak voltage Vpp) is superimposed on the DC voltage (that is, the time average voltage Vave) will be described with reference to FIGS. 8 and 9. The transfer using the superimposition bias (superimposition voltage) is referred to as "AC transfer".

As a value indicating the relationship between the center voltage value Voff of the superposition bias and the time average value Vave of the voltage, the ratio of the area on the return direction side of the center voltage value Voff to the entire AC waveform was set as the return time [%]. .. That is, when the area on the return direction side of the center voltage value (Voff) is A and the area on the transfer direction side of the center voltage value (Voff) is B in one cycle of the voltage waveform that switches alternately. A / (A + B) × 100 [%] is defined as duty.

In other words, the time during which the voltage in the transfer direction and the voltage on the opposite polarity side (voltage on the side that returns the toner) is output from the center voltage value (Voff) that occupies one cycle of the voltage waveform that switches alternately. The ratio can also be called duty.

The waveform of FIG. 8 has a duty of less than 50%, and the waveform of FIG. 9 has a duty of more than 50%. In the present specification, a duty (Duty) of less than 50% is referred to as a low duty, and a duty (Duty) of more than 50% is referred to as a high duty.

In the low-duty AC transfer mode using the low-duty superposition bias, the time average value (Vave) of the voltage in the AC component of the secondary transfer bias is higher than the center voltage value (center value of the maximum and minimum values of the voltage) Voff. Is also required to be on the transcription side. In order to realize this, it is necessary to make the waveform smaller in the area on the return direction side than the area on the transfer direction side with the center voltage value Voff of the AC component in between. The time average value is the time average value of the voltage, which is the integrated value of the voltage waveform over one cycle divided by the length of one cycle.

As one form for achieving this, for example, as shown in FIG. 8, a trapezoidal shape in which the slopes of the rising and falling edges of the voltage on the return direction side are smaller than the slopes of the rising and falling edges of the voltage on the transfer direction side. The form of the waveform of is conceivable.

The form of the waveform is not limited to the trapezoidal waveform, and may be a triangular waveform, a rectangular waveform, or a waveform in which these are combined, and the shape of the waveform is not limited.

As another form for achieving low duty, for example, the waveform shown in FIG. 10 may be used. In the case of the waveform of FIG. 10, the duty is reduced by adjusting the time on the return direction side and the time on the transfer direction side. That is, in FIG. 10, the period: T, the time on the return direction side: t1, and the time on the transfer direction side: t2. In the illustrated example, t1 <t2, and the return side area A <transfer side area B. That is, duty = A / (A + B) × 100 [%] has a low duty of 50% or less.

When using recording paper with large surface irregularities (surface irregularities larger than a predetermined value) such as Japanese paper-like paper or embossed paper, the duty is low as shown in FIGS. 8 and 10. By applying the superimposition bias, as described above, the toner is reciprocally moved and relatively moved from the belt side to the recording paper side to be transferred onto the recording paper, thereby improving the transferability to the paper recess. , It is possible to improve the transfer rate and abnormal images such as hollows. The paper having a large surface unevenness includes a paper having a maximum unevenness depth of 60 μm or more, for example, rezac, embossing, linen, and the like.

As the low-duty superposition bias, the polarity (negative polarity in the present embodiment) acting in the direction of transferring the toner image to the recording material (paper) and the opposite polarity (positive polarity in the present embodiment) are alternately switched. Is preferably used. By using such a bias, the toner electrostatically reciprocates between the paper surface (particularly the recess) and the surface of the intermediate transfer belt 51, and the transferability to the paper recess can be improved. By using a low-duty superposition bias, the magnitude of (i) the voltage peak value (Vt) in the transfer direction can be suppressed and (i) the magnitude of the voltage peak value (Vt) in the transfer direction can be suppressed as compared with the case where a high-duty one with a duty of 50% is used. ii) The absolute value of the time average voltage (Vave) can be increased while satisfying the condition that the peak value (Vr) in the return direction is increased. As a result, it is possible to prevent the generation of electric discharge due to the voltage peak value (Vt) in the transfer direction being made too large, and the toner can be sufficiently reciprocated by the peak value (Vr) in the return direction. By increasing the absolute value of the time average voltage (Vave), the toner image can be sufficiently transferred to the paper.

In the high-duty AC transfer mode using a high-duty superposition bias, the time average value (Vave) of the voltage in the AC component of the secondary transfer bias is higher than the center voltage value (center value of the maximum and minimum values of the voltage) Voff. Is also required to be on the return side. In order to realize this, it is necessary to make a waveform in which the area on the return direction side is larger than the area on the transfer direction side with the center voltage value Voff of the AC component in between.

As one form for achieving this, for example, as shown in FIG. 9, a trapezoidal shape in which the slopes of the rising and falling edges of the voltage on the return direction side are made larger than the slopes of the rising and falling edges of the voltage on the transfer direction side. The form of the waveform of is conceivable.

The form of the waveform is not limited to the trapezoidal waveform, and may be a triangular waveform, a rectangular waveform, or a waveform in which these are combined, and the shape of the waveform is not limited.

As another form for achieving high duty, for example, the waveform shown in FIG. 11 may be used. In the case of the waveform shown in FIG. 11, the duty is increased by adjusting the time on the return direction side and the time on the transfer direction side. That is, in FIG. 11, the period: T, the time on the return direction side: t1, and the time on the transfer direction side: t2. In the illustrated example, t1> t2, and the return side area A> the transfer side area B. That is, duty = A / (A + B) × 100 [%] has a higher duty than 50%.

By applying a high-duty superposition bias as shown in FIGS. 9 and 11, the charge acting in the transfer direction is reduced, and the decrease in the toner charge amount Q / M due to charge injection in the secondary transfer nip is suppressed. Will be possible. As a result, it is possible to suppress the occurrence of insufficient image density due to a decrease in secondary transferability due to a decrease in the toner charge amount Q / M. Even if the duty exceeds 50 [%], the secondary transfer of the toner image is possible by performing the following. That is, by making the area of the graph portion on the plus side based on 0 [V] smaller than the area of the graph portion on the minus side, the average potential becomes negative polarity and the toner is recorded relatively from the belt side. It can be electrostatically moved to the paper side.

As the high-duty superposition bias, the polarity (negative polarity in the present embodiment) acting in the direction of transferring the toner image to the recording material (paper) and the opposite polarity (positive polarity in the present embodiment) are alternately switched. Or the one whose polarity is not reversed (in the present embodiment, the polarity remains negative). In any case, the secondary transferability due to the decrease in the toner charge amount Q / M is compared with the case where a bias consisting only of a DC component, that is, a bias in which a high voltage is maintained on the negative polarity side is applied. It is possible to suppress the occurrence of insufficient image density due to the decrease in image density.

In the present embodiment, as the AC transfer mode using the superposition bias, the low-duty AC transfer mode having a duty of 50% or less as shown in FIGS. 8 and 10 and the duty as shown in FIGS. 9 and 11 are more than 50%. It also has a large high-duty AC transfer mode, and both are switchable. Then, by switching the transfer mode to the low-duty AC transfer mode or the high-duty AC transfer mode according to the type of paper to be passed, good image transfer is performed on both paper with small unevenness and paper with large unevenness. be able to.

The transfer mode may be switched between the low-duty AC transfer mode, the high-duty AC transfer mode, and the DC transfer mode according to predetermined conditions such as the type of paper to be passed and the temperature and humidity. The color printer shown in FIGS. 1 and 3 includes an optical sensor 600 provided so as to face the paper cassette 100. The optical sensor 600 is detected by a light emitting unit that irradiates light toward the surface of the paper loaded on the paper feed cassette 100, a light receiving unit that receives the light reflected from the surface of the paper, and the light emitting unit and the light receiving unit. It is provided with a discriminating unit for discriminating unevenness on the paper surface based on the shape (cross-sectional curve) of the paper surface. The optical sensor 600 measures the shape (cross-sectional curve) of the paper surface by irradiating light toward a region of a predetermined length (for example, 20 mm) of the paper loaded on the paper feed cassette 100 and receiving the light. To do. The discriminating unit obtains the maximum cross-sectional height Pt (JIS B 0601: 2001) of the cross-sectional curve. In the present embodiment, the maximum cross-sectional height Pt (μm) is defined as the surface unevenness of the paper. The transfer mode of the paper surface is switched based on the information on the surface unevenness of the paper determined by the discriminating unit of the optical sensor 600. When the surface unevenness is equal to or more than a predetermined value, the low-duty AC transfer mode is selected. If the surface unevenness is less than a predetermined value, the high-duty AC transfer mode is selected. The transfer mode may be switched automatically depending on the paper type setting (that is, the setting of whether or not the paper is uneven).

Alternatively, the transfer mode may be specified by the user. These settings can be set from the operation panel 500 (see FIGS. 1 and 3) of the image forming apparatus. When the user specifies the transfer mode from the operation panel 500, it is preferable to provide, for example, a "recessed priority mode" and a "halftone image priority mode" on the operation panel so as to be selectable. The control means 300 transfers the image to the paper in the low-duty AC transfer mode when the "recessed priority mode" is selected, and transfers the image in the high-duty AC transfer mode when the "halftone image priority mode" is selected. The power supply 200 is controlled so as to transfer to paper.

That is, the image forming apparatus uses a recess priority mode for transferring the toner image from the intermediate transfer belt 51 to the paper using a bias having a duty of less than 50%, and a toner image using a bias having a duty greater than 50%. The operation panel 500 is provided for selecting one of the halftone image priority mode for transferring the image from the intermediate transfer belt 51 to the paper. Then, the control means 300 outputs the power supply 200 so as to output either a duty of less than 50% or a duty of more than 50% as a bias according to the mode selected by the user on the operation panel 500. To control.

There are recesses on the surface of the paper regardless of the type of paper, and an image including a halftone image may be output regardless of the type of paper. When transferring an image to any type of paper, the user selects the transfer mode from the operation panel 500 depending on whether the transferability of the concave portion of the paper is to be prioritized or the transferability of the halftone image is to be prioritized. It is possible to do. By outputting the superimposition bias according to the selected mode by the control means 300, it is possible to output an image suitable for the user's needs by a simple method.

Alternatively, the user may be able to select the type (paper type) of the recording material from the operation panel 500. In this case, the control means 300 outputs either a duty of less than 50% or a duty of more than 50% as a bias, depending on the type of recording material selected on the operation panel 500. The next transfer bias power supply 200 is controlled. The control means 300 selects the low-duty AC transfer mode when the surface unevenness of the recording material selected by the user is equal to or greater than a predetermined value. When the surface unevenness of the recording material is less than a predetermined value, the high-duty AC transfer mode is selected. Even with such a configuration, it is possible to output an image suitable for the user's needs by a simple method. The configuration for selecting the type (paper type) of the recording material from the operation panel 500 may be a configuration for directly selecting the brand of the recording material or a configuration for selecting whether or not the recording material is uneven paper. May be good.

As a configuration of the secondary transfer unit, in the form of FIG. 1, a configuration in which an AC component is superimposed on a DC component (superimposition bias) is applied to the secondary transfer back surface roller 53, but either a DC bias or an AC bias is applied. Is applied to the secondary transfer back surface roller 53 and the other is applied to the nip forming roller 56, or a superimposed bias in which an AC component is superimposed on a DC component is applied to the nip forming roller 56. In the embodiment shown in FIG. 3, the secondary transfer bias power supply 200 is configured to apply the secondary transfer bias to the secondary transfer back surface roller 53, but even if the secondary transfer bias is applied to the roller 400 as the secondary transfer roller. Good. In these cases, it is necessary to make the toner to be used and the polarity of the applied bias correspond to each configuration. When a paper having a small surface unevenness such as plain paper is used, a transfer bias consisting of only a DC component (DC bias) may be applied. On the other hand, when using paper having a large surface unevenness, it is preferable to switch the transfer bias from the one containing only the DC component to the superimposition bias.

Next, the secondary transfer bias will be described in detail. In this embodiment (Example 1), the DC component (DC component) of the secondary transfer bias is controlled by a constant current, and the peak to peak (Peak to Peak) voltage of the AC component (AC component) is controlled by a constant voltage. ing.

In the case of the form shown in FIG. 5, the AC direct current superimposition power supply 202 includes a DC output unit that outputs a DC component (DC component) and an AC output unit that outputs an AC component (AC component). The DC output unit outputs the time average voltage Wave as a DC component. The AC output unit outputs an AC voltage. The AC direct quantity superimposition power supply 202 generates a superimposition bias as shown in FIGS. 7 to 11 by superimposing the AC voltage on the time average voltage Wave, and applies this to the secondary transfer unit.

On the other hand, in the case of the form shown in FIG. 6, the DC power supply 201 outputs the time average voltage Vave as a DC component. The AC power supply 202 outputs an AC voltage. The power supply 200 generates a superimposition bias as shown in FIGS. 7 to 11 by superimposing an AC voltage on the time average voltage Vave, and applies this to the secondary transfer unit.
In the following, the time average voltage is defined as a DC component (DC component), and the AC voltage superimposed on the time average voltage is defined as an AC component (AC component).

The superimposition bias for both the DC component and the AC component was corrected according to the device environment (environmental correction), correction according to the printing speed of the device (line speed correction), and paper conditions, respectively, for each standard value. The output value is calculated by multiplying the correction (referred to as paper size correction), that is, the width in the main scanning direction of the paper, the correction according to the thickness of the paper, and the correction according to the resistance of the transfer unit.

When an elastic belt having a multi-layer structure is used as the image carrier (intermediate transfer belt 51) for supporting the toner image, and a material having good surface smoothness such as plain paper or coated paper is used as the recording material, It was found that the image density is likely to be insufficient due to the secondary transfer failure. Then, as a result of diligent research on the cause, the following was found. In the secondary transfer nip, a secondary transfer current flows between the contact roller sandwiching the intermediate transfer belt and the back surface roller. If a multi-layer structure is used as the intermediate transfer belt, the secondary transfer current flows in the belt thickness direction while wrapping around the belt circumferential direction at the interface between the layers. As a result, in the secondary transfer nip, the secondary transfer current is circulated not only at the center position of the nip where the nip pressure is highest, but also near the inlet and outlet of the nip, and the toner image on the belt in the secondary transfer nip is formed. However, a secondary transfer current is passed over a long period of time. Then, a large amount of charge having a polarity opposite to the charge polarity is injected into the toner to reduce the toner charge amount Q / M at the normal polarity, so that the secondary transferability is lowered and the image density is insufficient. It turned out to cause.

The present inventors output a secondary transfer bias having a duty of more than 50 [%] to inject a reverse charge into the toner at the secondary transfer nip, resulting in a toner charge amount Q / M. It has been found that the deterioration can be suppressed and the occurrence of insufficient image density can be suppressed by satisfactorily secondary transfer of the toner image.

However, when such a high-duty transfer bias is used, the higher the temperature and humidity, the stronger the peak peak of the AC voltage and the time average voltage must be applied to obtain the effect. On the other hand, when a low-duty transfer bias is used for the purpose of improving transferability to uneven paper, discharge will occur and white spots will occur unless the peak peak of the AC voltage and the time average voltage are weakened at high temperature and high humidity. appear. That is, it was found that since the correction direction differs depending on whether the transfer bias duty is high or low, it is necessary to perform different corrections instead of a single correction. It was also found that the required correction differs depending on the bias duty for changes in roller resistance and linear speed (printing speed).

In the above, the injection of electric charge into the toner has been described as a problem when the image carrier having a multilayer structure is used, but this is only an example. Even when an image carrier having no multilayer structure is used, if the width of the secondary transfer nip N (width in the paper transport direction) is large, or if the device has a high transfer nip pressure, the secondary transfer unit Similarly, when the intermediate transfer belt is wound around the secondary transfer member (belt or roller) by a predetermined amount, or when the device has a slow linear velocity, the image density may be insufficient. Similarly, the image density may be insufficient depending on the type of toner used and the material of the image carrier (belt).

However, the required correction values differ between the low-duty AC transfer mode and the high-duty AC transfer mode. For example, the high-duty AC transfer mode has no effect unless the peak peak of the AC voltage and the time average voltage are strongly applied as the temperature and humidity increase. On the other hand, in the low-duty AC transfer mode, which is a countermeasure against uneven paper, discharge occurs and white spots occur unless the peak peak of the AC voltage and the time average voltage are weakened at high temperature and high humidity, so a single correction is sufficient. No effect can be obtained.

[Example 1]
The calculation method of each correction in this embodiment is described below, but these calculation methods are examples and are not limited in any way. Further, in this embodiment, all three corrections described later are used, but it is not a premise that all three of them are used. For example, it is possible to obtain a sufficient effect by using only one or two of the three corrections described later.

First, for the environmental correction, the environmental classification based on the temperature and / and the humidity is set in advance, and the temperature or the temperature detected by the temperature / humidity sensor 106 (see FIGS. 1 and 3) installed in the main body of the device as the environmental detection means. / And the environmental classification is judged from the relative humidity, and the correction value is decided according to the judged environmental classification. Table 1 shows an example of the environmental classification set based on the temperature and relative humidity. Alternatively, an environment classification based on absolute humidity is set, the absolute humidity is calculated from the temperature and relative humidity detected by the temperature / humidity sensor, and the environment classification is determined based on the calculated absolute humidity to determine the correction value. Good. Table 2 shows an example of environmental classification based on absolute humidity. Environment classifications in Tables 1 and 2: MM is a normal temperature environment (normal temperature and humidity environment), LL is a low temperature environment (low temperature and low humidity environment), and HH is a high temperature environment (high temperature and high humidity environment). For example, when it is 23 ° C. and 50% RH, it is determined to be a normal temperature and humidity environment, when it is 10 ° C. and 15% RH, it is determined to be a low temperature and low humidity environment, and when it is 27 ° C. and 80% RH, it is determined to be a high temperature and high humidity environment.

The temperature / humidity sensor 106 in the present embodiment detects temperature and relative humidity, but the type of sensor is not limited to this. Instead of the temperature / humidity sensor 106, a temperature sensor capable of detecting only the temperature may be used. Further, instead of the temperature / humidity sensor 106, a humidity sensor capable of detecting only relative humidity may be used.

The linear velocity correction is determined according to the printing speed of the apparatus. In this embodiment, it has three line speeds of standard speed, medium speed (70% of standard speed), and low speed (50% of standard speed).
The paper size correction is roughly divided into three judgment items: the width in the main scanning direction of the paper, the thickness of the paper, and the combined resistance of the secondary transfer portion, and as shown in Tables 3 to 5, all three levels are provided. ing. In this embodiment, the width in the main scanning direction of the paper and the thickness of the paper are obtained from the paper feed tray setting conditions.

The combined resistance of the secondary transfer section (in the form of FIG. 1, the resistance of the current path including the secondary transfer back surface roller 53, the intermediate transfer belt 51, and the nip forming roller 56. In the form of FIG. 3, the secondary transfer The back surface roller 53, the intermediate transfer belt 51, the secondary transfer belt 36, and the resistance of the current path including the secondary transfer roller 400) are used in an adjustment operation such as during manufacturing or by a serviceman, or during automatic adjustment operation such as printing. The output voltage when a constant current (-50 μA in this embodiment) is applied is calculated, and the resistance classification is determined from the calculation result. The resistance detecting means 203 shown in FIGS. 5 and 6 detects the output voltage when a constant current is passed through the secondary transfer unit (secondary transfer nip N). Then, the resistance of the secondary transfer unit is detected based on the relationship between the current and the voltage. The combined resistance of the secondary transfer unit is calculated in a state where the paper is not sandwiched between the secondary transfer nip N. In Table 5, RL indicates that the combined resistance is low, RM indicates that the combined resistance is standard, and RH indicates that the combined resistance is high.

Subsequently, each correction value in this embodiment is shown below, but this correction value is also an example and is not limited in any way. In the following, the correction value shall be indicated as a percentage (%) with respect to the standard value. Specific specifications of standard values (values such as voltage and current) are appropriately set according to the device configuration.

The environmental correction values in this embodiment are shown in Table 6 according to the above environmental classification.
The control means 300 controls the power supply 200 so as to change the magnitude of the DC component and the AC component according to at least one of the temperature and humidity detected by the temperature / humidity sensor 106, the duty value, and the value of the duty. To do.

The toner used in this embodiment is negatively charged, and the amount of charge increases in absolute value as the environment becomes lower in temperature (example: -25 μC / g → -40 μC / g). Therefore, DC in the low-duty AC transfer mode. Both the component and the AC component are corrected (in the positive direction) so as to be larger than the standard value in the low temperature environment (LL environment) with respect to the normal temperature environment (MM environment). This makes it possible to prevent insufficient density in the recesses of the paper. On the contrary, the higher the temperature environment, the smaller the toner charge amount in absolute value. Therefore, when both the DC component and the AC component are in a high temperature environment (HH environment) with respect to a normal temperature environment (MM environment), they are lower than the standard value. Correct it so that it becomes smaller (in the negative direction). This makes it possible to prevent the generation of an abnormal image due to the discharge of toner.

On the other hand, in the high-duty AC transfer mode, the toner charge amount is high in a low temperature environment (LL environment), so no correction is performed, and the peak peak (AC component) and time average voltage (DC component) of the AC voltage are in the normal temperature environment (DC component). Same as (MM environment), that is, the standard value is left as it is. This makes it possible to secure the bias required for transfer in a low temperature environment (LL environment) and improve the transferability. On the other hand, in a high temperature environment (HH environment), the peak peak (AC component) and the time average voltage (DC component) of the AC voltage are corrected so as to be larger than the standard values. That is, in a high temperature environment (HH environment), the absolute values of the peak peak (AC component) and the time average voltage (DC component) of the AC voltage are made larger than those in the normal temperature environment (MM environment). With this correction, the peak voltage value Vr (see FIGS. 9 and 11) in the return direction becomes larger on the positive polarity side, that is, on the polarity side opposite to the polarity at which the toner is transferred to the paper. .. In a high temperature environment (HH environment), the amount of charge of the toner is smaller than that in a normal temperature environment (MM environment), but by increasing the Vr value to the positive side, the injection of charge of the same polarity as the toner into the toner is promoted. It is possible to more reliably suppress the decrease in the toner charge amount Q / M. As a result, it is possible to more reliably prevent the occurrence of insufficient image density on the paper in a high temperature environment (HH environment).

In a low temperature environment (LL environment), the peak peak (AC component) and the time average voltage (DC component) of the AC voltage may be corrected so as to be smaller than the standard values. The peak peak (AC component) and the time average voltage (DC component) of the AC voltage may be reduced as long as the bias required for transfer is secured.

Further, when correcting the bias according to the temperature and humidity, the time average voltage (DC component) is kept constant regardless of the temperature and humidity, and only the peak peak (AC component) of the AC voltage is corrected as described above. You may.

Next, the linear velocity correction values in this embodiment are as shown in Table 7 according to the printing speed of the above apparatus. Medium speed is 70% faster than standard speed, and low speed is 50% faster than standard speed. The printing speed is the transport speed of the paper passing through the secondary transfer nip N.

The control means 300 controls the power supply 200 and the printing speed of the paper. The printing speed of the paper is controlled by controlling the speed of the paper sent out by the resist roller pair 102.

The control means 300 controls the power supply 200 so as to change the magnitudes of the DC component and the AC component according to the printing speed, the duty value of the superposition bias, and so on.

In the low-duty AC transfer mode, the DC component is controlled by a constant current, so when the printing speed is slower than the standard speed, it is corrected to be smaller than the standard bias. Since the AC component is controlled by a constant voltage, correction according to the printing speed is not necessary, and the setting is the same as the standard speed. The value of the AC component may be corrected according to the printing speed as long as it does not affect the transferability.

In the high-duty AC transfer mode, the basic concept of correction is the same, but the lower the speed, the longer the toner stays in the transfer nip, and the longer the charge is injected into the toner. That is, the secondary transfer bias tends to affect the amount of charge of the toner. Therefore, in the present embodiment, when the image is transferred at a slow printing speed (medium speed or low speed), the DC component is corrected so that the absolute value becomes smaller than that at the standard speed, and the low-duty AC transfer mode is used. The DC component is corrected so as to be smaller than that of.

For example, when transferring in the low-duty AC transfer mode and at low speed, the DC component is corrected to 50%, whereas when transferring in the high-duty AC transfer mode and at low speed, the DC component is adjusted to 40% (that is, more than 50%). Is also corrected to a small percentage). In other words, the reduction rate of the DC component according to the printing speed when the duty is greater than 50% (when comparing the standard speed and the low speed in the high duty transfer mode in Table 7, the reduction rate of the DC component is 100%-. 40% and 60%) is the rate of decrease of the DC component according to the printing speed when the duty is less than 50% (when comparing the standard speed and the low speed in the low duty transfer mode in Table 7). The reduction rate of the DC component is 100% -50%, which is larger than 50%).

By controlling the bias in this way, when the image is transferred at a slow printing speed, the peak value Vr in the return direction of the transfer bias becomes a value on the more positive side. As a result, it is possible to prevent the toner from being injected with a charge having a polarity opposite to the charge polarity of the toner, and to prevent the occurrence of insufficient image density.

Next, the paper size correction values in this embodiment are as shown in Tables 8 to 13 below according to the detection method (low-duty AC transfer mode: Tables 8 to 10, high-duty AC transfer mode: Table). 11 to Table 13).

In both the low-duty AC transfer mode and the high-duty AC transfer mode, the DC component has a large correction (large correction%) when the width in the main scanning direction of the paper is small, when the thickness of the paper is thick, and when the combined resistance is low. To do. This is because the DC component is controlled by a constant current, and the current that leaks out of the paper area increases under any of the above conditions. Therefore, in order to secure the current required for transfer to the paper, it depends on each condition. The correction is increased.

Since the AC component has a constant voltage, there is no effect of leakage outside the paper area, so the correction is the same regardless of the paper size and thickness.
If the AC component and DC component correction of the main scanning direction width correction of the paper are made the same and the DC component correction is applied to the AC component, the AC component will be overcorrected and a whiteout image due to discharge will occur. Resulting in. The value of the AC component may be corrected according to the printing speed as long as it does not affect the transferability.

However, regarding the correction for the combined resistance of the AC component, the low-duty AC transfer mode corrects the applied bias so that it becomes smaller (smaller than the reference value) when the combined resistance is low, and applies it when the combined resistance is high. Correct so that the bias to be applied becomes large (larger than the reference value). This is because the voltage required for the secondary transfer nip when transferring toner to paper is the same regardless of the combined resistance, so if the combined resistance (especially the resistance of the secondary transfer backside roller) is high, the voltage drops. This is because a high voltage is required in consideration of the above.

On the other hand, in the high-duty AC transfer mode, when the combined resistance is low, the effect is not obtained unless the peak peak of the AC voltage and the time average voltage are increased. Therefore, when the combined resistance is low, the correction is increased and the combined resistance is increased. If it is high, reduce the correction.

The correction according to the combined resistance may be performed independently of the correction according to the paper thickness and the paper size. In this case, as shown in Tables 8 to 10, in the low-duty AC transfer mode, the higher the synthesis resistance, the larger the AC component. On the other hand, as shown in Tables 11 to 13, in the high-duty AC transfer mode, the lower the synthesis resistance, the larger the AC component.

As a result, in the low-duty AC transfer mode, it is possible to prevent insufficient density in the recesses of the paper when the synthesis resistance is high, as in the case of correcting the DC component and the AC component according to the temperature and humidity. It is possible to prevent the occurrence of an abnormal image due to discharge when the combined resistance is low. On the other hand, in the high-duty AC transfer mode, the transferability when the combined resistance is high can be improved, and the decrease in the toner charge amount Q / M when the combined resistance is low can be more reliably suppressed.

As described above, by setting different corrections for the low-duty AC transfer mode and the high-low-duty AC transfer mode, image transfer can be performed with the optimum DC component and AC component according to each condition. it can.

Further, in the correction of the AC component, the amount of change when the transfer portion resistance is large when the thickness of the recording paper is large is smaller than the amount of change when the transfer portion resistance is large when the thickness of the recording paper is small. , It is preferable to use a correction factor. Thereby, the optimum DC component and AC component can be output according to the thickness and resistance of each recording paper.

For comparison with the present invention, a low-duty AC transfer mode and a high-duty AC transfer mode in which the same correction is applied in the transfer bias are shown below as Comparative Example 1. Since the device configuration and the detection method of various corrections are the same as those in the embodiment, the description is omitted.

[Comparative Example 1]
Comparative Example 1 is a case where the correction values of the AC component and the DC component of the environmental correction coefficient of the high-duty AC transfer mode are the same as the correction values of the low-duty AC transfer mode, and the correction values are shown in Table 14. The settings other than the environmental correction are the same as in the first embodiment (Tables 7 to 13).

In Example 1 and Comparative Example 1, images were printed under the following conditions to confirm the effect.
Printing speed of the device: Standard speed Secondary transfer synthesis resistance classification: RM
Environment: 10 ° C 15% (environment classification: LL), 23 ° C 50% (environment classification: MM), 27 ° C 80% (environment classification: HH)
Width in the main scanning direction of paper: A4 width (297 mm: size 1)
Paper 1: Rezac 66, ream weight: 100 kg (basis weight: 116 gsm) (paper thickness 1)
Paper 2: POD gloss coat 100 (basis weight: 100 gsm) (paper thickness 1)
Chart: Full solid image (blue), full halftone image (cyan)
Transfer mode: Low-duty AC transfer mode is used for Rezac 66, and high-duty AC transfer mode is used for POD gloss coat.

The effect confirmation results are shown in Table 15. In Table 15, "◯" indicates no abnormal image, and "x" indicates an abnormal image.
Both "Rezac" and "POD Gloss Coat" are product names. The POD gloss coat is a coated paper whose surface is coated. The surface unevenness of the POD gloss coat is smaller than the surface unevenness of the Rezac 66.

In the case of Example 1 (having different correction tables for low duty and high duty), no abnormal image was generated in each environment, but in the case of Comparative Example 1 (same correction for low duty and high duty), it was low. Since the correction was unified to the duty AC transfer mode, no abnormal image was generated for the Rezac 66, but the correction was insufficient for the POD gloss coat in the HH (high temperature and high humidity) environment, and the toner was charged. As a result, the transfer rate decreased, and white spots occurred due to insufficient transfer. As a result, it was confirmed that the low-duty AC transfer mode and the high-duty AC transfer mode have different environment correction tables.

[Comparative Example 2]
Comparative Example 2 is a case where the linear velocity correction coefficient of the high-duty AC transfer mode is the same as the correction value of the low-duty AC transfer mode, and the correction values are shown in Table 16. The settings other than the linear velocity correction are the same as in the first embodiment (Tables 6 and 8 to 13).

In Example 1 and Comparative Example 2, images were printed under the following conditions to confirm the effect.
Printing speed of the device: Refer to the "Paper" item below. Secondary transfer synthesis resistance classification: RM
Environment: 23 ° C 50% (Environment classification: MM)
Width in the main scanning direction of paper: A4 width (297 mm: size 1)
Paper 1: Rezac 66, ream weight: 130 kg (basis weight: 151 gsm) (paper thickness 2: medium speed printing)
Paper 2: POD gloss coat 128 (basis weight: 128gsm) (paper thickness 2: medium speed printing)
Paper 3: Made by Conqueror, LAID Unwatermarked Hi White 300gsm (Paper thickness 3: Low speed printing)
Paper 4: MagnoStar 300gsm (Paper thickness 3: Low speed printing)
Chart: Full solid image (blue), full halftone image (cyan)
Transfer mode: Low-duty AC transfer mode is used for papers 1 and 3, and high-duty AC transfer mode is used for papers 2 and 4.

The effect confirmation results are shown in Table 17. In Table 17, “◯” indicates no abnormal image, and “x” indicates an abnormal image.
Both "LAID Unwatermarked Hi White" and "Magno Star" are product names.

In the case of Example 1 (having different correction tables for low duty and high duty), no abnormal image was generated at each printing speed, but in the case of Comparative Example 2 (same correction for low duty and high duty). Printing speed: When the high-duty AC transfer mode was used in both medium and low speeds, the DC component was insufficient, so the effect of preventing charge injection was weak, and white spots occurred due to insufficient transfer. As a result, it was confirmed that the low-duty AC transfer mode and the high-duty AC transfer mode have different linear velocity correction tables.
[Comparative Example 3]

Comparative Example 3 is a case where the correction value is unified to the value of the low-duty AC transfer mode in the correction of the paper main scanning direction width of the paper size correction with the resistance classification: RL and the paper thickness 1, and the correction value is shown in the table. It is shown in 8 (already mentioned). The settings other than the paper size correction are the same as in the first embodiment (Tables 6 to 13).

In Example 1 and Comparative Example 3, images were printed under the following conditions to confirm the effect.
Printing speed of the device: Standard speed Secondary transfer synthesis resistance classification: RL
Environment: 23 ° C 50% (Environment classification: MM)
Width in the main scanning direction of paper: A4 width (297 mm: size 1), A5 length (148.5 mm: size 3)
Paper 1: Rezac 66, ream weight: 100 kg (basis weight: 116 gsm) (paper thickness 1)
Paper 2: POD gloss coat 100 Basis weight 100 gsm (paper thickness 1)
Chart: Full solid image (blue), full halftone image (cyan)
Transfer mode: Low-duty AC transfer mode is used for Rezac 66, and high-duty AC transfer mode is used for POD gloss coat.

The effect confirmation results are shown in Table 18. In Table 18, "◯" means no abnormal image, and "x" means that there is an abnormal image.

In the case of Example 1 (having different correction tables for low duty and high duty), no abnormal image was generated in any of the paper sizes, but in the case of Comparative Example 3 (same correction for low duty and high duty). In Rezac 66, no abnormal image was generated, but in POD gloss coat, the AC component was insufficient, and white spots occurred due to insufficient transfer in solid and halftone. From this, it was confirmed that among the paper size corrections, the correction of the width in the main scanning direction of the paper has the effect of having different correction tables in the low-duty AC transfer mode and the high-duty AC transfer mode.

As described above, the configuration of the power supply that outputs the superposition bias and the method of correcting the power supply output by the control means are as follows. The power supply outputs a superimposed bias in which an AC voltage having a predetermined duty and a predetermined peak-to-peak voltage Vpp is superimposed on the time average voltage Wave to the secondary transfer unit. That is, the power supply includes a DC power supply that outputs a time average voltage Vave and an AC power supply that outputs an AC voltage, and the DC power supply and the AC power supply are connected in series. Then, the control means controls the output of the power supply so as to change the time average voltage Vave and the magnitude Vpp of the AC voltage according to the magnitude of the duty.

On the other hand, instead of this, the power supply outputs a superimposed bias in which an AC voltage having a predetermined duty and a predetermined peak-to-peak voltage Vpp is superimposed on the center value (Voff) to the secondary transfer unit. There may be. That is, the power supply has a DC power supply that outputs a center value (Voff) and an AC power supply that outputs an AC voltage, and the DC power supply and the AC power supply are connected in series. Then, the center value (Voff) and the AC voltage are corrected according to the temperature and humidity, the paper thickness, the paper size, the resistance of the transfer portion, and the center value (Voff) and the AC voltage are corrected according to the duty. It is a configuration that makes the correction method of. Even with such a configuration, the same effect as that of the form described above can be obtained.

As described above, according to the image forming apparatus of the present invention, it is possible to perform image transfer with the bias of the optimum DC component and AC component according to various conditions, so that a good transferred image can be obtained. Can be done.

Further, it has an environment detecting means for detecting an environmental state in the apparatus, and the control means transfers the transfer so as to change the sizes of the DC component and the AC component according to the detection result of the environment detecting means. By controlling the bias output means, a good transfer image can be obtained regardless of the environmental condition.

Further, when the time average value (Vave) of the bias voltage is closer to the transfer side than the center value (Voff), the lower the temperature and / or humidity detected by the environmental detection means, the more standard the bias is. By correcting the value to be larger than the value, the bias required for transfer can be secured even in a low temperature environment.

Further, when the time average value (Vave) of the bias voltage is closer to the transfer side than the center value (Voff), the higher the temperature and / or humidity detected by the environmental detection means, the more standard the bias is. By correcting the value so that it is smaller than the value, the transfer bias can be made suitable for the amount of toner charged in a high temperature environment.

Further, when the time average value (Vave) of the bias voltage is on the returning side of the center value (Voff), the temperature and / and humidity detected by the environment detecting means are in a predetermined low temperature environment. By leaving the bias at a standard value, the transfer bias can be made suitable for the amount of toner charged in a low temperature environment.

Further, when the time average value (Vave) of the bias voltage is on the returning side of the center value (Voff), the higher the temperature and / or humidity detected by the environmental detection means, the higher the standard value of the bias. By correcting it so that it becomes larger, the effect of superimposition bias can be exhibited even in a high temperature environment.

Further, by changing the sizes of the DC component and the AC component according to the printing speed, a good transfer image with an optimum transfer bias corresponding to the printing speed can be obtained.

Further, as the printing speed becomes slower than the standard speed, the DC component of the bias is corrected to be smaller than the standard value, and the AC component of the bias remains at the standard value, so that the DC component becomes a constant current. In the case of control, a good transfer image can be obtained by the optimum transfer bias corresponding to the printing speed.

Further, the time average of the bias voltage is the amount of correction of the DC component according to the decrease in the printing speed when the time average value (Vave) of the bias voltage is on the return side of the center value (Voff). By making the value (Vave) larger than the correction amount of the DC component corresponding to the decrease in the printing speed when the value (Vove) is on the transfer side of the center value (Voff), the influence of charge injection in the transfer portion is suppressed. can do.

Further, by changing the sizes of the DC component and the AC component according to the conditions of the recording material, a good transfer image with an optimum transfer bias can be obtained regardless of the conditions of the recording material.

Further, as the width of the recording material in the main scanning direction becomes smaller, the DC component of the bias is corrected to be larger than the standard value, and the AC component of the bias is left at the standard value, so that the paper can be printed. The current required for transfer can be secured, and a good transfer image can be obtained.

Further, as the thickness of the recording material increases, the DC component of the bias is corrected to be larger than the standard value, and the AC component of the bias remains at the standard value for transfer to paper. The required current can be secured and a good transfer image can be obtained.

Further, as the resistance value of the transfer unit becomes smaller, the DC component of the bias is corrected to be larger than the standard value, and the AC component of the bias remains at the standard value for transfer to paper. The required current can be secured and a good transfer image can be obtained.

When a low-duty bias is used when the surface unevenness of the recording material is larger than a predetermined value, and a high-duty bias is used when the surface unevenness of the recording material is smaller than the predetermined value. By using the above, a good transfer image can be obtained on both papers having large irregularities and papers having small irregularities.

Further, the image carrier is composed of a plurality of layers including a base layer and an elastic layer laminated on the base layer, so that the elastic layer is flexibly deformed by the elasticity in the transfer nip, and the paper has large surface irregularities. The adhesion between the toner and the image carrier is improved, and the transferability of the toner image on paper having large surface irregularities can be further improved.

Although the present invention has been described above with reference to the illustrated examples, the present invention is not limited thereto. An appropriate configuration can be adopted for the configuration of the transfer unit and the power supply.
Further, the configuration of the image forming apparatus is also arbitrary, and the arrangement order of each color image forming unit in the tandem type is arbitrary. Further, the present invention can be applied not only to a four-color machine but also to a full-color machine using five or more colors of toner or three-color toner, a multi-color machine using two-color toner, or a monochrome device. The present invention can also be applied to a device that does not include an intermediate transfer body and directly transfers a toner image from an image carrier such as a photoconductor to paper, a so-called direct transfer method device. Of course, the image forming apparatus is not limited to a printer, and may be a copying machine, a facsimile, or a multifunction device having a plurality of functions.

As the secondary transfer bias, a bias in which the DC component is controlled by a constant voltage may be used. Similarly, as the secondary transfer bias, a bias in which the AC component is controlled by a constant voltage may be used.

In the above embodiments, as shown in Table 6, an example in which the DC component and the AC component of the secondary transfer bias are changed in three stages according to the temperature and humidity has been described, but the DC component and the AC component of the secondary transfer bias may be changed in only two stages. It may be finely changed in 4 steps or more. The same applies to the case where the DC component and the AC component are changed according to the printing speed. The same applies to the case where the DC component and the AC component are changed according to the resistance of the transfer unit.

1 Image forming unit 11 Photoreceptor drum 50 Transfer unit 51 Intermediate transfer belt (image carrier)
53 Secondary transfer backside roller 56 Nip forming roller 80 Optical writing unit 90 Fixing device 106 Temperature / humidity sensor (environmental detection means)
200 Secondary transfer bias power supply 300 Control means

Japanese Unexamined Patent Publication No. 2006-267486 Japanese Unexamined Patent Publication No. 2008-058585 Japanese Unexamined Patent Publication No. 09-146381 Japanese Unexamined Patent Publication No. 04-0867878 Japanese Unexamined Patent Publication No. 2013-237592 Japanese Unexamined Patent Publication No. 2013-231936

Claims (14)

Image carrier and
In order to transfer the toner image on the image carrier to the recording material, a transfer bias output means for outputting a bias including a DC component and an AC component, and a transfer bias output means.
An environmental detection means that detects at least one of the temperature and humidity inside the device,
It has a control means for controlling the transfer bias output means, and has
The area on the side where the toner is returned from the recording material to the image carrier from the center value (Voff) of the maximum and minimum values of the voltage of the bias in one cycle of the bias waveform is A, and the area of the bias is Let B be the area on the side where the toner is transferred from the image carrier to the recording material rather than the center value (Voff) of the maximum and minimum values of the voltage.
Bias duty = A / (A + B) × 100 [%]
When
The control means has at least one of the temperature and humidity detected by the environment detection means and the magnitude of the DC component and the AC component, depending on whether the duty is less than 50% or greater than 50%. An image forming apparatus, characterized in that the transfer bias output means is controlled so as to change the above. Claim 1 is characterized in that when the duty is less than 50%, the absolute value of the DC component and the AC component increase as at least one of the temperature and humidity detected by the environment detecting means is lower. The image forming apparatus according to. Claim 1 is characterized in that when the duty is greater than 50%, the higher the temperature and humidity detected by the environmental detection means, the larger the absolute value of the DC component and the AC component. Or the image forming apparatus according to 2. When the duty is greater than 50%
(1) When at least one of the temperature and humidity detected by the environmental detection means is equal to or higher than a predetermined value, the higher the temperature and humidity, the larger the absolute value of the DC component and the AC component. ,
(2) When at least one of the temperature and humidity detected by the environmental detection means is lower than a predetermined value, the absolute value of the DC component and the AC component are not affected by at least one of the temperature and humidity. The image forming apparatus according to claim 1 or 2, wherein the image forming apparatus is constant. Image carrier and
In order to transfer the toner image on the image carrier to the recording material, a transfer bias output means for outputting a bias including a DC component and an AC component, and a transfer bias output means.
It has the transfer bias output means and the control means for controlling the printing speed.
The area on the side where the toner is returned from the recording material to the image carrier from the center value (Voff) of the maximum and minimum values of the voltage of the bias in one cycle of the bias waveform is A, and the area of the bias is Let B be the area on the side where the toner is transferred from the image carrier to the recording material rather than the center value (Voff) of the maximum and minimum values of the voltage.
Bias duty = A / (A + B) × 100 [%]
When
The control means controls the transfer bias output means so as to change the magnitudes of the direct current component and the alternating current component according to the printing speed, the duty value, and the image. Forming device. The image forming apparatus according to claim 5, wherein the control means reduces the absolute value of the DC component of the bias as the printing speed is slower. The reduction rate of the DC component according to the printing speed when the duty is greater than 50% is larger than the reduction rate of the DC component according to the printing speed when the duty is less than 50%. The image forming apparatus according to claim 6. Image carrier and
A transfer bias output means that outputs a bias including a DC component and an AC component in order to transfer the toner image on the image carrier to the recording material by the transfer unit.
A resistance detecting means for detecting the resistance of the transfer unit and
It has a control means for controlling the transfer bias output means, and has
The area on the side where the toner is returned from the recording material to the image carrier from the center value (Voff) of the maximum and minimum values of the voltage of the bias in one cycle of the bias waveform is A, and the area of the bias is Let B be the area on the side where the toner is transferred from the image carrier to the recording material rather than the center value (Voff) of the maximum and minimum values of the voltage.
Bias duty = A / (A + B) × 100 [%]
When
The control means changes the size of the AC component according to the resistance of the transfer portion detected by the resistance detection means and whether the duty is less than 50% or greater than 50%. An image forming apparatus characterized by controlling a transfer bias output means. The image forming apparatus according to claim 8, wherein when the duty is less than 50%, the higher the resistance of the transfer portion, the larger the AC component. The image forming apparatus according to claim 8 or 9, wherein when the duty is larger than 50%, the lower the resistance of the transfer portion, the larger the AC component. When the surface unevenness of the recording material is larger than a predetermined value, the toner image is transferred from the image carrier to the recording material by using a bias having a duty of less than 50%.
When a recording material having a surface unevenness smaller than a predetermined value is used, the toner image is transferred from the image carrier to the recording material by using a bias having a duty of more than 50%. Item 2. The image forming apparatus according to any one of Items 1 to 10. The toner image is transferred from the image carrier to the recording material using a bias having a duty of less than 50%, and the toner image is transferred to the toner image using a bias having a duty of more than 50%. It is equipped with an operation unit for selecting one of the mode of transferring from the image carrier to the recording material.
The transfer bias is such that the control means outputs either a duty of less than 50% or a duty of more than 50% as the bias according to the mode selected by the operation unit. The image forming apparatus according to any one of claims 1 to 10, wherein the output means is controlled. Equipped with an operation unit for selecting the type of recording material
The control means outputs either a duty of less than 50% or a duty of more than 50% as the bias, depending on the type of recording material selected by the operation unit. The image forming apparatus according to any one of claims 1 to 10, wherein the transfer bias output means is controlled. The image forming apparatus according to any one of claims 1 to 12, wherein the image carrier is composed of a plurality of layers including a base layer and an elastic layer laminated on the base layer.

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