JP5799773B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus.

  Conventionally, as the image forming apparatus, for example, a plurality of photosensitive drums on which toner images of different colors are formed are provided, and toner images of each color formed on the plurality of photosensitive drums are intermediated by a primary transfer roll. After multiple primary transfer to the transfer belt, each color toner image transferred onto the intermediate transfer belt is collectively transferred to a recording sheet by a secondary transfer roll to form a full color image. There is something.

  In such an image forming apparatus, in order to supply toner as a lubricant to the cleaning blade of the photosensitive drum, the cleaning blade of the secondary transfer roll, or the cleaning blade of the intermediate transfer belt, the image forming apparatus is positioned between adjacent images of the photosensitive drum. A toner band is formed as necessary in the non-image area.

  As a technique for forming a toner band in an image forming apparatus, for example, those disclosed in Japanese Patent Application Laid-Open Nos. 2000-231274 and 2007-65007 have been proposed.

  In the image forming apparatus according to the above Japanese Patent Laid-Open No. 2000-231274, the transfer at the secondary transfer position on the surface of the intermediate transfer member is performed in order to suppress the occurrence of damage such as chipping or reversal (turning) in the cleaning elastic blade. A toner layer forming means for forming a toner layer in a non-passing region of the member, and a cleaning means for pressing the surface of the intermediate transfer body at a predetermined timing to remove the deposits attached to the surface of the intermediate transfer body. It is comprised so that it may be equipped with.

  In addition, the image forming apparatus according to the above Japanese Patent Application Laid-Open No. 2007-65007 includes a lubricant containing an appropriate amount of toner according to the type and process speed of transfer paper such as transfer paper having good surface smoothness and recycled paper that easily generates paper dust. In order to prevent damage to the cleaning blade due to friction with the photosensitive member, the control means transfers the image to the transfer material according to at least one of the type of transfer material and the process speed for forming the image. The non-transferred toner image is formed in the non-image portion of the photoreceptor by changing the toner amount.

Japanese Patent Laid-Open No. 2000-231274 JP 2007-065007 A

  By the way, the problem to be solved by the present invention is to lubricate the intermediate transfer body and the secondary transfer means even when a belt-like toner image cannot be formed in a non-image area located between adjacent images on the image carrier. An object of the present invention is to provide an image forming apparatus capable of supplying toner as an agent.

That is, the invention described in claim 1 includes a single or a plurality of image holding members for holding a toner image,
An intermediate transfer member onto which a toner image is transferred from the image carrier;
Primary transfer means to which a primary transfer bias voltage is applied to transfer a toner image from the image carrier to the intermediate transfer member;
Secondary transfer means to which a secondary transfer bias voltage is applied to transfer a toner image from the intermediate transfer member to a recording medium;
A belt-like toner image forming means for forming a belt-like toner image in a non-image area located between adjacent images of the image carrier;
Whether or not the belt-like toner image formed in the non-image area of the image carrier can pass through the primary transfer means in a state where the primary transfer bias voltage is cut off or a bias voltage lower than a normal value is applied. If it is determined that the toner cannot pass, the toner image forming unit does not form a belt-like toner image, but the toner attached to the non-image area of the image carrier or the image carrier The toner having a lower density than the belt-shaped toner image attached to the non-image area is primarily transferred to the intermediate transfer body, and the covering toner or the low density toner transferred to the intermediate transfer body is transferred to the secondary transfer body. An image forming apparatus comprising control means for controlling the primary transfer bias voltage and the secondary transfer bias voltage so as to perform secondary transfer to a transfer means.

  According to a second aspect of the present invention, when the control means determines that the image can pass, the belt-like toner image forming means forms a belt-like toner image in a non-image area of the image carrier, and the image The primary transfer bias voltage is controlled so that the belt-like toner image formed on the holding member is not transferred to the intermediate transfer member, and the transfer toner transferred to the intermediate transfer member is transferred to the secondary transfer unit. The image forming apparatus according to claim 1, wherein the secondary transfer bias voltage is controlled so as not to occur.

  According to a third aspect of the present invention, when it is determined that the control means can pass, the length of the non-image area of the image carrier, the response time of the primary transfer bias voltage, and the image carrier 3. The image forming apparatus according to claim 1, wherein the belt-like toner image having a length determined based on the moving speed is controlled to be formed by the belt-like toner image forming unit.

  According to a fourth aspect of the present invention, when the control unit determines that it can pass, the secondary transfer bias voltage applied to the secondary transfer unit has the same polarity as that during normal image formation. 4. The image forming apparatus according to claim 2, wherein the voltage is controlled to a voltage having a small absolute value.

  According to the first aspect of the present invention, in comparison with the case where this configuration is not provided, in the case where a belt-like toner image cannot be formed in a non-image area located between adjacent images on the image carrier. Even in such a case, toner as a lubricant can be supplied to the intermediate transfer member or the secondary transfer unit.

  According to the second aspect of the present invention, it is possible to prevent the intermediate transfer member and the secondary transfer unit from being soiled by the belt-like toner image, as compared with the case where this configuration is not provided.

  According to the third aspect of the present invention, a band-like toner image can be reliably formed in the non-image area located between the adjacent images on the image carrier, as compared with the case without this configuration. .

  According to the invention described in claim 4, it is possible to suppress the adhesion of the discharge product to the intermediate transfer member as compared with the case where this configuration is not provided.

It is explanatory drawing which shows operation | movement of the image forming apparatus which concerns on Embodiment 1 of this invention. 1 is a configuration diagram illustrating an image forming apparatus according to Embodiment 1 of the present invention. It is explanatory drawing which shows operation | movement of the image forming apparatus which concerns on Embodiment 1 of this invention. 6 is a timing chart showing control of a primary transfer bias voltage and a secondary transfer bias voltage. 6 is a graph showing the relationship between the productivity of the image forming apparatus and the length of a non-image area. 6 is a chart showing the lengths of toner bands that can be formed. 6 is a chart showing control of a primary transfer bias voltage and a secondary transfer bias voltage. 6 is a timing chart showing control of a primary transfer bias voltage and a secondary transfer bias voltage. It is a block diagram which shows the image forming apparatus which concerns on Embodiment 2 of this invention. It is explanatory drawing which shows operation | movement of the image forming apparatus which concerns on Embodiment 2 of this invention.

  Embodiments of the present invention will be described below with reference to the drawings.

Embodiment 1
FIG. 2 shows a tandem full-color image forming apparatus as an image forming apparatus according to Embodiment 1 of the present invention. However, the present invention is not limited to a tandem image forming apparatus, and can be applied to a so-called four-cycle full color image forming apparatus having a single photosensitive drum.

  In the image forming apparatus main body according to this embodiment, as shown in FIG. 2, as a plurality of image forming means, for example, transparent toner (CT), yellow (Y), magenta (M), cyan (C ), And five image forming units 1CT, 1Y, 1M, 1C, and 1K corresponding to the respective colors of black (K) are arranged in parallel at regular intervals along the horizontal direction. The transparent toner (CT) is obtained, for example, by removing a pigment from a color toner, and is used to improve glossiness by being uniformly formed on the surface of an image region as necessary. Note that the image forming apparatus does not include the transparent toner (CT) image forming unit 1CT, and has four images corresponding to yellow (Y), magenta (M), cyan (C), and black (K). Even if the forming units 1Y, 1M, 1C, and 1K are provided, high saturation cyan (HC) and high saturation magenta are provided for each color of yellow (Y), magenta (M), cyan (C), and black (K). Of course, it may be provided with five or more (for example, six) image forming units to which (HM) or the like is added. In addition, the order of arrangement of the image forming units 1Y, 1M, 1C, and 1K of yellow (Y), magenta (M), cyan (C), and black (K) is also yellow (Y), magenta (M), and cyan. The order is not limited to (C) and black (K).

  The transparent toner (CT), yellow (Y), magenta (M), cyan (C), and black (K) image forming units 1CT, 1Y, 1M, 1C, and 1K are belt-shaped toner images (hereinafter, referred to as “tonal toner images”). , Also referred to as “toner band”).

  The transparent toner (CT), yellow (Y), magenta (M), cyan (C), and black (K) image forming units 1CT, 1Y, 1M, 1C, and 1K are individually integrated. The image forming units 1CT, 1Y, 1M, 1C, and 1K are independently attached to the main body of the image forming apparatus in a replaceable manner.

  These five image forming units 1CT, 1Y, 1M, 1C, and 1K are basically configured in the same manner except for the type of toner to be used, as shown in FIG. And photosensitive drums 2CT, 2Y, 2M, 2C, and 2K as image carriers that are rotationally driven at a predetermined speed along the surface of the photosensitive drums 2CT, 2Y, 2M, 2C, and 2K. Charge rolls 3CT, 3Y, 3M, 3C, and 3K as primary charging means that uniformly charge negative polarity, and images corresponding to the respective colors are exposed on the surfaces of the photosensitive drums 2CT, 2Y, 2M, 2C, and 2K. Image exposure apparatuses 4CT, 4Y, 4M, 4C, and 4K as latent image forming means for forming electrostatic latent images and electrostatic latent images formed on the photosensitive drums 2CT, 2Y, 2M, 2C, and 2K. For negative polarity of corresponding color Developing devices 5CT, 5Y, 5M, 5C, and 5K as developing means for reversal development with charged toner, and a cleaning device 6CT that removes transfer residual toner and the like remaining on the photosensitive drums 2CT, 2Y, 2M, 2C, and 2K , 6Y, 6M, 6C, 6K.

  Examples of the image exposure apparatuses 4CT, 4Y, 4M, 4C, and 4K include, for example, transparent toner (CT), yellow (Y), magenta (M), cyan (C), and black (K) image forming units 1CT. Laser light LB-CT, LB-Y, LB-M, LB-C, LB-K is emitted according to image data from a semiconductor laser (not shown) provided corresponding to 1Y, 1M, 1C, 1K, The laser beams LB-CT, LB-Y, LB-M, LB-C, and LB-K are deflected and scanned along the axial direction of the corresponding photosensitive drums 2CT, 2Y, 2M, 2C, and 2K. What performs exposure is used. The image exposure apparatuses 4CT, 4Y, 4M, 4C, and 4K are apparatuses that perform image exposure by deflecting and scanning the laser beams LB-CT, LB-Y, LB-M, LB-C, and LB-K. For example, an apparatus using an LED eyelet or the like in which a large number of LED light emitting elements are arranged along the axial directions of the photosensitive drums 2CT, 2Y, 2M, 2C, and 2K may be used. In the case of image exposure devices 4CT, 4Y, 4M, 4C, and 4K using LED eyelets, image exposure is performed by deflecting and scanning laser beams LB-CT, LB-Y, LB-M, LB-C, and LB-K. Compared with the image exposure apparatuses 4CT, 4Y, 4M, 4C, and 4K that perform the image exposure, the image exposure apparatuses 4CT, 4Y, 4M, 4C, and 4K can be significantly downsized, and the entire image forming apparatus can be downsized. This is desirable.

  Image forming units 1CT, 1Y, 1M, 1C, and 1K of image forming units 4CT, 4Y, and 4M for the respective transparent toner (CT), yellow (Y), magenta (M), cyan (C), and black (K) colors. For 4C and 4K, image data corresponding to each color is sequentially output from an image processing apparatus (not shown). Laser beams LB-CT, LB-Y, LB-M, LB-C, and LB-K emitted from the image exposure apparatuses 4CT, 4Y, 4M, 4C, and 4K in accordance with image data correspond to the corresponding photosensitive drums 2CT. 2Y, 2M, 2C, and 2K surface image areas are scanned and exposed along the main scanning direction (axial direction of the photosensitive drum), and electrostatic latent images are exposed on the surfaces of the photosensitive drums 2CT, 2Y, 2M, 2C, and 2K. An image is formed. The electrostatic latent images formed on the surfaces of the photosensitive drums 2CT, 2Y, 2M, 2C, and 2K are respectively transferred to transparent toner (CT) and yellow (Y) by developing devices 5CT, 5Y, 5M, 5C, and 5K. , And reversal development as toner images of respective colors of magenta (M), cyan (C), and black (K).

  Transparent toner (CT), yellow (Y), magenta (M), sequentially formed on the photosensitive drums 2CT, 2Y, 2M, 2C, and 2K of the image forming units 1CT, 1Y, 1M, 1C, and 1K, respectively. As shown in FIG. 2, the cyan (C) and black (K) toner images are transferred to intermediate transfer belts as intermediate transfer members arranged below the image forming units 1CT, 1Y, 1M, 1C, and 1K. 7 is primarily transferred in a state of being superposed on each other by primary transfer rolls 8CT, 8Y, 8M, 8C and 8K as primary transfer means to which a primary transfer voltage is applied.

  The intermediate transfer belt 7 has a predetermined tension between a plurality of rolls including a drive roll 10, a driven roll 11, a sensor roll 12, a tension applying roll 13, and a back support roll 14 of the secondary transfer portion. It is laid over. The intermediate transfer belt 7 is rotated in the direction of the arrow B along the photosensitive drums 1CT, 1Y, 1M, 1C, and 1K by a drive roll 10 that is rotated by a dedicated drive motor that is not illustrated and has excellent constant speed. It is driven to circulate at a predetermined speed substantially equal to the speed (circumferential speed). As the intermediate transfer belt 7, for example, a flexible synthetic resin film such as polyimide or polyamideimide formed in an endless belt shape is used.

  The transparent toner (CT), yellow (Y), magenta (M), cyan (C), and black (K) toner images transferred onto the intermediate transfer belt 7 are transferred to the back support roll 14 in the middle. Secondary transfer is collectively performed on a recording sheet 16 as a recording medium by a secondary transfer bias voltage applied to a secondary transfer roll 15 as a secondary transfer unit that is in pressure contact with the transfer belt 7. The recording paper 16 on which the toner images of these colors are transferred is peeled off from the intermediate transfer belt 7 by the peeling slow-down device 17 and then transferred to the fixing device 20 as fixing means by the transport belt 19 through the guide member 18. Be transported. The recording paper 16 to which the unfixed toner images of the respective colors are transferred is subjected to a fixing process with heat and pressure by the heating roll 21 and the pressure roll 22 of the fixing device 20 and then provided outside the image forming apparatus main body. The paper is discharged onto a discharge tray (not shown).

  As shown in FIG. 2, for example, the recording paper 16 has a predetermined size or material from any one of a plurality of paper feed trays 23 and 24, and a paper feed roll 25 and a paper transport roll. The paper is once transported to the registration roll 28 in a state of being separated one by one through the paper transport path 27 formed of the pair 26. The recording paper 16 supplied from any one of the paper feed trays 23 and 24 is synchronized with the toner image on the intermediate transfer belt 7 by a registration roll 28 that is rotationally driven at a predetermined timing. It is sent out to the transfer position 29.

  Note that the surface of the photosensitive drum 2 after the primary transfer of the toner image has been completed, the residual toner is removed by the cleaning blade 6a of the cleaning device 6. Further, the intermediate transfer belt 7 after the secondary transfer of the toner image is completed, residual toner, paper dust, and the like are removed by the cleaning blade 30a of the belt cleaning device 30 whose surface is opposed to the drive roll 10. Is done. Further, residual toner, paper dust, and the like are removed from the surface of the secondary transfer roll 15 by the cleaning blade 31a and the cleaning brush 31b of the cleaning device 31.

  By the way, the above-described image forming apparatus is sensitive to each of the image forming portions 1CT, 1Y, 1M, 1C, and 1K for transparent toner (CT), yellow (Y), magenta (M), cyan (C), and black (K). The process speed, which is the rotational speed of the body drums 2CT, 2Y, 2M, 2C, and 2K, is 308 mm / sec, 255 mm / sec, and 200 mm / sec depending on the type of the recording medium 16 such as plain paper and cardboard and the image forming mode. , 103 mm / sec.

  Further, in the image forming apparatus, depending on the type of image such as when low density images are continuously formed on the recording paper 16, the photosensitive drums 2CT of the image forming units 1CT, 1Y, 1M, 1C, and 1K, In some cases, the transfer residual toner is hardly supplied to the cleaning devices 6CT, 6Y, 6M, 6C, and 6K of 2Y, 2M, 2C, and 2K, the cleaning device 30 of the intermediate transfer belt 7, and the cleaning device 31 of the secondary transfer roll 15. is there. Residual toner remains on the cleaning devices 6CT, 6Y, 6M, 6C, and 6K for the photosensitive drums 2CT, 2Y, 2M, 2C, and 2K, the cleaning device 30 for the intermediate transfer belt 7, and the cleaning device 31 for the secondary transfer roll 15. When the state where almost no supply continues, the cleaning blade 6a and the photosensitive drum 2 of the cleaning device 6, the cleaning blade 30a and the intermediate transfer belt 7 of the cleaning device 30, or the cleaning blade 31a of the cleaning device 31 and the secondary transfer are performed. The sliding force with the roll 15 becomes excessive, and there is a possibility that the cleaning blades 6a, 30a, 31a may be worn, chipped or turned up.

  Therefore, in this embodiment, as shown in FIG. 3, the image 41 corresponding to the adjacent preceding recording sheet and the image 42 corresponding to the succeeding recording sheet of each photosensitive drum 2CT, 2Y, 2M, 2C, 2K. At a predetermined timing such as after printing on a predetermined number of recording sheets 16 in a non-image area 43 positioned between and a predetermined number of low-density images. A toner band 44 is formed. The toner band 44 has, for example, a predetermined density (for example, Cin = 25%) and a full width of the image area (photosensitive drum 2 over a predetermined length L along the rotation direction of the photosensitive drum 2). In the axial direction).

  At that time, in the image forming apparatus, the toner bands 44 formed in the non-image areas 43 of the photosensitive drums 2CT, 2Y, 2M, 2C, and 2K are transferred to the intermediate transfer belt 7 and the secondary transfer roll 15 with a normal image. If the transfer is performed in the same manner as described above, the surfaces of the intermediate transfer belt 7 and the secondary transfer roll 15 may be soiled by the toner of the toner band 44, and the back surface of the recording paper 16 may be stained.

  Therefore, in the image forming apparatus, as shown in FIGS. 3 and 4, when the toner band 44 is formed on the surface of the photosensitive drum 2, the primary transfer is performed on the primary transfer rolls 8CT, 8Y, 8M, 8C, and 8K. The high-voltage power supply circuit that applies the bias voltage is controlled to turn off (shut off) the primary transfer bias voltage applied to the primary transfer rolls 8CT, 8Y, 8M, 8C, and 8K and to apply the secondary transfer roll 15 to the secondary transfer roll 15. The transfer bias voltage is set to have a polarity opposite to that at the time of normal image formation or to turn off (cut off). In FIG. 4, for the sake of convenience, the primary transfer bias voltage and the secondary transfer bias voltage are shown corresponding to the upper and lower sides, but the primary transfer bias voltage is shown in the non-image area 43 of the photosensitive drum 2 as the primary transfer roll. The secondary transfer bias voltage indicates the state in which the region of the intermediate transfer belt 7 corresponding to the non-image region 43 of the photosensitive drum 2 is moved to the position of the secondary transfer roll 15. Yes.

  In this way, most of the toner band 44 on the surface of the photosensitive drum 2 is supplied to the surface of the photosensitive drum 2 without being transferred to the intermediate transfer belt 7, and the toner band 44 supplied to the surface of the photosensitive drum 2 is supplied. The toner is removed by the cleaning blade 6 a of the cleaning device 6. Further, the transfer toner of the toner band 44 that has been transferred from the surface of the photosensitive drum 2 to the intermediate transfer belt 7 is not transferred to the secondary transfer roll 15 but is left on the intermediate transfer belt 7, so that the cleaning device 30. The transfer toner of the toner band 44 removed by the cleaning blade 30 a and transferred to the secondary transfer roll 15 is removed by the cleaning blade 31 a of the cleaning device 31.

  It is desirable that a small amount of toner is always supplied to the cleaning blade 31a of the secondary transfer roll 15. If the supply amount of the toner is too small, the cleaning blade 31a may be turned over. If the amount is too large, the back side of the recording paper 16 may become dirty.

  As described above, in the image forming apparatus, the toner band 44 is formed in the non-image area 43 of the photosensitive drum 2, and the toner band 44 formed in the non-image area 43 of the photosensitive drum 2 is The recording sheet 16 is transferred to the secondary transfer roll 15 to prevent the recording paper 16 from being stained.

  At that time, in the image forming apparatus, the system for forming the toner band 44 is shared among a plurality of models having different productivity determined by the number of recording sheets 16 that can be printed per unit time, or the same model. Even in such a case, the productivity determined by the number of recording sheets 16 that can be printed per unit time may be different depending on the difference in the image forming mode and the user's needs.

  In the image forming apparatus, if the process speed is kept constant at the maximum speed of 308 mm / sec and the productivity determined by the number of recording sheets 16 that can be printed per unit time is to be improved, the minimum size When the recording paper 16 having a length of 8.5 inches (= 215.9 mm) as the recording paper 16 is conveyed in the conveying state with the highest productivity, the non-image area along the rotation direction of the photosensitive drum 2 is obtained. As shown in FIG. 5, the length L of 43 becomes shorter as the productivity increases.

  In the image forming apparatus, for example, when the productivity of a full-color image is 70 (Paper Per Minuit: hereinafter abbreviated as “PPM”) while the process speed is kept constant at the maximum speed of 308 mm / sec. Is set to 75 (PPM).

  At this time, in order to prevent the toner band 44 formed in the non-image area 43 of the photosensitive drum 2 from being primarily transferred to the intermediate transfer belt 7, the toner band 44 passes through the primary transfer roll 8. 3 and 4, the primary transfer bias voltage applied to the primary transfer roll 8 is turned off (cut off) immediately after the preceding image 41 passes, and the next image 42 passes through the primary transfer roll 8. The primary transfer bias voltage needs to be turned on (applied) by the time before, but a certain response time is required to turn on and off the primary transfer bias voltage. In this embodiment, the case where the primary transfer bias voltage applied to the primary transfer roll 8 is turned off (cut off) will be described. However, the primary transfer bias voltage applied to the primary transfer roll 8 needs to be turned off (cut off). For example, the present invention can be applied even when the primary transfer bias voltage applied to the primary transfer roll 8 is switched to a bias voltage lower than a normal value and applied.

  The response time required to turn on and off the primary transfer bias voltage is determined by a switching element such as a transistor and a circuit element such as a resistor or a capacitor constituting a high voltage power supply circuit as a power source for the primary transfer bias voltage. In addition, by using a circuit element having a short time constant, for example, it is possible to shorten a response time as long as about 200 msec to about 20 msec of 1/10 in 20 msec increments if necessary. As the response time decreases, the cost increases accordingly.

  The response time of the high-voltage power supply circuit used in the image forming apparatus is already known, but the response time of the high-voltage power supply circuit as well as the productivity per unit time, such as when the toner band formation system is shared by multiple models. It is desirable to be able to handle models with different

  Therefore, depending on the response time required to turn on / off the primary transfer bias voltage, the primary transfer bias voltage is increased while the toner band 44 formed in the non-image area 43 of the photosensitive drum 2 passes through the primary transfer roll 8. May not be able to be turned on / off.

  Now, the process speed, which is the rotational speed of the photosensitive drums 2CT, 2Y, 2M, 2C, and 2K, is 308 mm / sec, and the productivity determined by the number of recording sheets 16 that can be printed per unit time is the length in the transport direction. When the recording paper 16 of 8.5 inches is 70 PPM, the length L of the non-image area 43 along the rotation direction of the photosensitive drum 2 is 48.1 mm as shown in FIG. On the other hand, when a high-voltage power supply circuit having a response time of 100 msec that is required to turn on / off the primary transfer bias voltage is used, the process speed is 308 mm / sec, so the primary transfer bias voltage is turned on / off. As shown in FIG. 3, the toner band 44 cannot be formed in a region having a length of 100 (msec) × 308 (mm / sec) = 30.8 mm. As a result, the theoretically formable length L of the toner band 44 is determined from the length L ′ (48.1 mm) of the non-image area 43 of the photosensitive drum 2 by the response time of the primary transfer bias voltage. The value obtained by subtracting the length that cannot be formed (30.8 mm) is 48.1-30.8 = 17.3 mm.

  On the other hand, when the productivity determined by the number of recording sheets 16 that can be printed per unit time is improved to 75 PPM while the process speed remains at 308 mm / sec, as shown in FIG. The length L ′ of the non-image area 43 along the rotation direction of the body drum 2 is 30.5 mm, and the length L of the toner band 44 that can be theoretically formed is the length of the non-image area 43 of the photosensitive drum 2. A value obtained by subtracting a length (30.8 mm) at which the toner band 40 cannot be formed by the response time of the primary transfer bias voltage from the length L ′ (30.5 mm) is 30.5-30.8 = −0. Therefore, the toner band 44 cannot be formed in the non-image area 43 of the photosensitive drum 2.

  Therefore, if the toner band 44 is formed in the non-image area 43 of the photosensitive drum 2 with the productivity corresponding to 70 PPM, the toner band 44 on the surface of the photosensitive drum 2 is primarily transferred to the intermediate transfer belt 7. As a result, the amount of toner reaching the secondary transfer portion 29 where the secondary transfer roll 15 is located from the intermediate transfer belt 7 increases from an assumed amount. In this case, the amount of toner adhering to the secondary transfer roll 15 from the intermediate transfer belt 7 is larger than the amount assumed in advance, and there is a high possibility that the back surface of the recording paper 16 will be stained.

  In order to solve such a problem, as shown in FIG. 6, it is conceivable to use a high-voltage power supply circuit having a short response time required to turn on and off the primary transfer bias voltage. It is necessary to use an expensive power supply circuit, which causes a new problem that leads to an increase in cost.

  Further, when the toner band 44 is not formed in the non-image area 43 of the photosensitive drum 2 in order to avoid the backside contamination of the recording paper 16, the process speed is 308 mm / sec and the response time of the high voltage power supply circuit is 100 msec. When the property is improved to 75 PPM, the toner is not supplied to the secondary transfer unit 29, a load is applied to the cleaning blade 31a of the cleaning device 31 for cleaning the surface of the secondary transfer roll 15, and the cleaning blade 31a is turned over. The risk of occurrence increases.

  Therefore, in this embodiment, whether or not the toner band 44 formed in the non-image area 43 of the photosensitive drum 2 can pass through the primary transfer roll 8 with the primary transfer bias voltage cut off, that is, recording is performed. It is determined whether or not the toner band 44 can be formed while avoiding the occurrence of the backside contamination of the paper 16, and the toner band 44 formed in the non-image area 43 of the photosensitive drum 2 is subjected to the primary transfer bias voltage. When it is determined that it is possible to pass through the primary transfer roll 8 and the toner band 44 can be formed, the normal control is performed and the photosensitive drum 2 is not A toner band 44 is formed in the image area 43.

  On the other hand, the toner band 44 formed in the non-image area 43 of the photosensitive drum 2 cannot pass through the primary transfer roll 8 in a state where the primary transfer bias voltage is cut off, and the toner band 44 can be formed. If it is determined that it is not possible, as shown in FIGS. 7 and 8, the control of turning on / off the primary transfer bias voltage is not performed, and the photosensitive drum is kept in the state where the primary transfer bias voltage is kept on. When the non-image area 43 of the photosensitive drum 2 passes through the developing device 5 without forming the toner band 44 in the second non-image area 43, so-called covered toner 45 is applied to the non-image area 43 of the photosensitive drum 2. The toner 45 is adhered and primarily transferred to the intermediate transfer belt 7, and the secondary transfer bias voltage is kept at the same normal bias voltage as that during normal image formation. Actively fog toner 45 is transferred is obtained by configured to transfer to the secondary transfer roll 15.

  Note that the toner 45 that adheres to the surface of the photosensitive drum 2 has, for example, a density of about 1 to 2% and is much lower in density than the toner band 44. Therefore, the toner 45 is transferred to the intermediate transfer belt 7. However, there is no possibility that the back surface of the recording paper 16 is stained.

  FIG. 2 is a block diagram showing a control circuit of the image forming apparatus according to this embodiment together with a block diagram.

  In FIG. 2, reference numeral 100 denotes a control circuit including a CPU or the like as a control unit that controls the operation of the image forming apparatus. The control circuit 100 is used for programs stored in the ROM 101 in advance, parameters stored in the RAM 102, and the like. Based on this, the operation of the image forming apparatus is controlled. The parameters shown in FIGS. 5 and 6 are stored in advance in the RAM 102 as nonvolatile data including a look-up table (LUT). Reference numeral 103 denotes a primary transfer roll 8CT for each of the image forming units 1CT, 1Y, 1M, 1C, and 1K for transparent toner (CT), yellow (Y), magenta (M), cyan (C), and black (K). A high-voltage power supply circuit that applies a primary transfer bias voltage to the 8Y, 8M, 8C, and 8K and also applies a secondary transfer bias voltage to the secondary transfer roll 15, and based on a control signal from the control circuit 100, the primary transfer bias The voltage and secondary transfer bias voltage are turned on / off and the voltage value is switched.

  In the above configuration, in the image forming apparatus according to this embodiment, even when a belt-like toner image cannot be formed in a non-image area located between adjacent images on the image carrier, It is possible to supply toner as a lubricant to the intermediate transfer member or the secondary transfer unit.

  That is, in the image forming apparatus according to this embodiment, as shown in FIG. 2, each image forming unit of transparent toner (CT), yellow (Y), magenta (M), cyan (C), and black (K) is formed. In 1CT, 1Y, 1M, 1C, and 1K, toner images of colors corresponding to the surfaces of the photosensitive drums 2CT, 2Y, 2M, 2C, and 2K are formed. Transparent toner (CT), yellow (Y), magenta (M), cyan (C), and black (K) toners formed on the surfaces of the photosensitive drums 2CT, 2Y, 2M, 2C, and 2K. The images are successively primary transferred in multiples onto the intermediate transfer belt 7 by primary transfer bias voltages applied to the primary transfer rolls 8CT, 8Y, 8M, 8C, and 8K, and then at the secondary transfer position 29, the secondary transfer roll 15 Are secondary-transferred collectively onto the recording paper 16 from the intermediate transfer belt 7 by the secondary transfer bias voltage applied to.

  The recording paper 16 on which the toner images of each color of transparent toner (CT), yellow (Y), magenta (M), cyan (C), and black (K) are secondarily transferred at once is shown in FIG. Then, after being separated from the intermediate transfer belt 7, it is conveyed to the fixing device 20 by the conveying belt 19 through the guide member 18, heated and pressurized by the fixing device 20, and the unfixed toner image is fixed. The paper is discharged onto a discharge tray (not shown) provided outside the forming apparatus.

  By the way, in the image forming apparatus, depending on the type of image such as when low density images are continuously formed on the recording paper 16, the photosensitive drums 2CT of the image forming units 1CT, 1Y, 1M, 1C, and 1K, In some cases, the transfer residual toner is hardly supplied to the cleaning devices 6CT, 6Y, 6M, 6C, and 6K of 2Y, 2M, 2C, and 2K, the cleaning device 30 of the intermediate transfer belt 7, and the cleaning device 31 of the secondary transfer roll 15. is there.

  Therefore, in this embodiment, as shown in FIG. 3, the image 41 corresponding to the adjacent preceding recording sheet and the image 42 corresponding to the succeeding recording sheet of each photosensitive drum 2CT, 2Y, 2M, 2C, 2K. At a predetermined timing such as after printing on a predetermined number of recording sheets 16 in a non-image area 43 positioned between and a predetermined number of low-density images. A toner band 44 is formed.

  As shown in FIGS. 3 and 4, the toner band 44 formed in the non-image area 43 of each of the photosensitive drums 2CT, 2Y, 2M, 2C, and 2K has the toner band 44 formed by the primary transfer rolls 8CT, 8Y, When passing through 8M, 8C, and 8K, the primary transfer bias voltage applied to the primary transfer rolls 8CT, 8Y, 8M, 8C, and 8K is turned off, and the respective photosensitive members are not transferred to the intermediate transfer belt 7 without being primarily transferred. Cleaning is performed by the cleaning devices 6CT, 6Y, 6M, 6C, and 6K of the drums 2CT, 2Y, 2M, 2C, and 2K.

  Even when the primary transfer bias voltage is turned off as described above, a small amount of toner that has been primarily transferred from the photosensitive drums 2CT, 2Y, 2M, 2C, and 2K to the intermediate transfer belt 7 is secondary to When passing through the transfer roll 15, the secondary transfer bias voltage applied to the secondary transfer roll 15 is turned off, and the secondary transfer roll 15 is not transferred to the secondary transfer roll 15 by the cleaning device 30 for the intermediate transfer belt 7. To be cleaned.

  Finally, even when the secondary transfer bias voltage is turned off, only a very small amount of toner that has been secondarily transferred from the intermediate transfer belt 7 to the secondary transfer roll 15 is transferred to the secondary transfer roll 15. The cleaning device 31 performs cleaning.

  On the other hand, in the image forming apparatus, for example, when the maximum process speed is set to 308 mm / sec, the high-voltage power supply circuit 103 with a response time of 100 msec is used, and the productivity is increased from 70 PPM to 75 PPM, FIG. As shown in FIG. 6, the toner band 44 may not be formed in the non-image area 43 of the photosensitive drums 2CT, 2Y, 2M, 2C, and 2K.

  Therefore, as shown in FIG. 5, the control circuit 100 sets the length L of the non-image area 43 of the photosensitive drums 2CT, 2Y, 2M, 2C, and 2K and the primary transfer bias voltage when the process speed is 308 mm / sec. , And the photosensitive drums 2CT, 2Y, 2Y, 2D, 2C, 2D, and 2D with reference to the table shown in FIG. It is determined whether or not the toner band 44 can be formed in the non-image area 43 of 2M, 2C, and 2K.

  When the process speed is 308 mm / sec, the response time of the high-voltage power supply circuit 103 is 100 msec, and the productivity is 70 PPM to 75 PPM, the control circuit 100 refers to the table shown in FIG. The length L is obtained, the length L of the toner band 44 is −0.3 mm, and the toner band 44 blocks the primary transfer bias voltage in the non-image area 43 of the photosensitive drums 2CT, 2Y, 2M, 2C, and 2K. When it is determined that the primary transfer rolls 8CT, 8Y, 8M, 8C, and 8K cannot be passed, the following control is performed.

  The control circuit 100 passes through the primary transfer rolls 8CT, 8Y, 8M, 8C, and 8K with the toner band 44 blocking the primary transfer bias voltage in the non-image area 43 of the photosensitive drums 2CT, 2Y, 2M, 2C, and 2K. If it cannot be determined, the toner band 44 is not formed in the non-image area 43 of the photosensitive drums 2CT, 2Y, 2M, 2C, and 2K as shown in FIGS. 7 and 8, and the photosensitive drums 2CT, 2Y are not formed. 2M, 2C, 2K surface non-image area 43 is charged to the same charging potential as that for normal image formation by charging rolls 3CT, 3Y, 3M, 3C, 3K, and developing devices 5CT, 5Y, 5M, 5C, By applying a developing bias voltage similar to that during normal image formation to 5K, the toner 45 covers the non-image area 43 of the photosensitive drums 2CT, 2Y, 2M, 2C, and 2K. Adhered to.

  Next, as shown in FIG. 7 and FIG. 8, the control circuit 100 causes the toner to be adhered to the non-image areas 43 of the photosensitive drums 2CT, 2Y, 2M, 2C, and 2K to be transferred to the primary transfer rolls 8CT, 8Y, 8M, When passing through 8C and 8K, a primary transfer bias voltage similar to that during normal image formation is applied to the primary transfer rolls 8CT, 8Y, 8M, 8C, and 8K by the high-voltage power supply circuit 103, and the photosensitive drums 2CT, 2Y, The toner 45 attached to the 2M, 2C, and 2K non-image areas 43 is primarily transferred onto the intermediate transfer belt 7.

  The untransferred remaining toner 45 remaining in the non-image areas 43 of the photosensitive drums 2CT, 2Y, 2M, 2C, and 2K is the cleaning devices 6CT, 6Y, and 6K of the photosensitive drums 2CT, 2Y, 2M, 2C, and 2K. It is cleaned by 6M, 6C, 6K.

  Further, as shown in FIGS. 7 and 8, the control circuit 100 performs secondary transfer by the high-voltage power supply circuit 103 when the toner 45 that has been primarily transferred onto the intermediate transfer belt 7 passes through the secondary transfer roll 15. A normal secondary transfer bias voltage is applied to the roll 15, and the fog toner primarily transferred onto the intermediate transfer belt 7 is transferred to the secondary transfer roll 15.

At this time, the secondary transfer bias voltage applied to the secondary transfer roll 15 by the high-voltage power supply circuit 103 may be a normal secondary transfer bias voltage, but as shown by a broken line in FIG. It is desirable to control the voltage so that it has the same polarity as that at the time of formation and has a small absolute value (for example, about several hundred volts). In this way, when the secondary transfer bias voltage applied to the secondary transfer roll 15 is controlled so as to be switched to a voltage having the same polarity as that of normal image formation and a small absolute value, the secondary transfer roll 15 can suppress the generation of nitrogen oxide (NO _x ) generated when a high voltage of 2 to 8 KV, which is normally applied to the electrode 15, is applied, and the nitrogen oxide (NO _x ) adheres to the surface of the intermediate transfer belt 7. It is possible to reduce the occurrence of image defects due to the above.

  As described above, the control circuit 100 performs the primary transfer rolls 8CT, 8Y, 8M, and 8C in a state where the toner band 44 blocks the primary transfer bias voltage in the non-image areas 43 of the photosensitive drums 2CT, 2Y, 2M, 2C, and 2K. , 8K cannot be passed through, the covering toner 45 is attached to the non-image areas 43 of the photosensitive drums 2CT, 2Y, 2M, 2C, and 2K, and the covering toner 45 is primarily applied to the intermediate transfer belt 7. By transferring and secondary transfer to the secondary transfer roll 15, toner can be supplied to the cleaning blade 31 a of the cleaning device 31 of the secondary transfer roll 15, and the cleaning blade 31 a can be turned over. Can be suppressed.

  Further, since the covering toner 45 adhering to the non-image areas 43 of the photosensitive drums 2CT, 2Y, 2M, 2C, and 2K has a toner concentration of 1 to 2%, the covering toner passes through the intermediate transfer belt 7 two times. Even if secondary transfer is performed on the next transfer roll 15, it is possible to avoid the possibility that the back surface of the recording paper 16 is stained.

  Even when the toner band 44 is formed in the non-image area 43 of the photosensitive drums 2CT, 2Y, 2M, 2C, and 2K, the non-image area 43 of the photosensitive drums 2CT, 2Y, 2M, 2C, and 2K is formed. It is not always necessary to form toner bands 44 of transparent toner (CT), yellow (Y), magenta (M), cyan (C), and black (K) for each color, and the photosensitive drums 2CT, 2Y, 2M, 2C, Of course, the toner band 44 may be formed every other one or a plurality of non-image areas 43 of 2K.

  Further, instead of attaching the toner 45 to the non-image areas 43 of the photosensitive drums 2CT, 2Y, 2M, 2C, and 2K, the density is lower than that of the toner band 44 by the image exposure devices 4CT, 4Y, 4M, 4C, and 4K. For example, after the image exposure with a highlight of about 3 to 4% is performed and then developed with the developing devices 5CT, 5Y, 5M, 5C, and 5K, the density is about 3 to 4% that is lower than the toner band 44. The toner may be uniformly adhered.

  In this case, the image exposure amount is controlled by the image exposure devices 4CT, 4Y, 4M, 4C, and 4K to be supplied to the secondary transfer roll 15 as compared with the case where the covering toner is attached to the non-image area 43. It is possible to control the amount of toner to be applied.

Embodiment 2
FIG. 9 shows an embodiment of the present invention. The same reference numerals are given to the same parts as those in the first embodiment. In the second embodiment, a single image carrier is provided. And is configured to determine and control whether or not a belt-like toner image can be formed in a non-image area of the single image carrier.

  That is, in the second embodiment, as shown in FIG. 9, a single photosensitive drum 2 is provided, and an electrostatic charge formed on the surface of the photosensitive drum 2 is formed on one side of the photosensitive drum 2. Rotating developing devices 5Y, 5M, 5C, and 5K are provided that develop the latent image with toner of each color of yellow (Y), magenta (M), cyan (C), and black (K). The rotation type developing devices 5Y, 5M, 5C, and 5K correspond to yellow (Y), magenta (M), cyan (C), and black (K) colors that are sequentially formed on the surface of the photosensitive drum 2. The electrostatic latent image is developed by rotating the corresponding color developing devices 5Y, 5M, 5C, and 5K to a developing position facing the photosensitive drum 2, and developing the electrostatic latent image.

  As shown in FIG. 10, for example, two images 41 and 42 are continuously formed on the surface of the photosensitive drum 2 and formed on the surface of the photosensitive drum 2. Two images 41 and 42 are sequentially primary transferred onto the intermediate transfer belt 7 by the primary transfer roll 8.

  For example, a toner image corresponding to the first yellow color of the images 41 and 42 is formed on the surface of the photosensitive drum 2, and the yellow toner image is formed on the intermediate transfer belt 7 by the primary transfer roll 8. Primary transcription. Next, a toner image corresponding to the second magenta color of the images 41 and 42 is formed on the surface of the photosensitive drum 2, and the magenta toner image is transferred onto the intermediate transfer belt 7 by the primary transfer roll 8. Primary transcription. Similarly, a cyan toner image of the third color and a black toner image of the fourth color formed on the surface of the photosensitive drum 2 are sequentially primary-transferred onto the intermediate transfer belt 7 by the primary transfer roll 8.

  The yellow (Y), magenta (M), cyan (C), and black (K) toner images of the images 41 and 42 that have been primary-transferred multiple times onto the intermediate transfer belt 7 are the primary colors of the final color. Secondary transfer roll 15 performs secondary transfer collectively on recording paper 16 fed in synchronization with transfer, and images 41 and 42 are continuously formed on the two recording papers 16.

  At this time, in the second embodiment, as in the first embodiment, it is determined whether or not the toner band 44 can be formed in the non-image region 43 between the adjacent images 41 and 42 on the photosensitive drum 2, and When it is determined that the toner band 44 formed in the non-image area 43 of the drum 2 can pass through the primary transfer roll 8 with the primary transfer bias voltage cut off, the toner band 44 is formed and cannot pass through. If it is determined that there is a toner band 44, the toner is applied to the non-image area 43 of the photosensitive drum 2 without forming the toner band 44, and the toner is transferred to the secondary transfer roll 15. Yes.

  In the second embodiment, the cleaning device 30 for the intermediate transfer belt 7 is configured to move to a position separated from the surface of the intermediate transfer belt 7 until the secondary transfer is completed.

  Since other configurations and operations are the same as those of the first embodiment, description thereof is omitted.

  1CT, 1Y, 1M, 1C, 1K: Transparent toner (CT), yellow (Y), magenta (M), cyan (C), black (K) image forming unit, 2CT, 2Y, 2M, 2C, 2K: Photosensitive drum, 41, 42: Image, 43: Non-image area, 44: Toner band, 45: Covered toner, 100: Control circuit, 103: High voltage power supply circuit.

Claims (4)

A single or a plurality of image carriers for holding a toner image;
An intermediate transfer member onto which a toner image is transferred from the image carrier;
Primary transfer means to which a primary transfer bias voltage is applied to transfer a toner image from the image carrier to the intermediate transfer member;
Secondary transfer means to which a secondary transfer bias voltage is applied to transfer a toner image from the intermediate transfer member to a recording medium;
A belt-like toner image forming means for forming a belt-like toner image in a non-image area located between adjacent images of the image carrier;
Whether or not the belt-like toner image formed in the non-image area of the image carrier can pass through the primary transfer means in a state where the primary transfer bias voltage is cut off or a bias voltage lower than a normal value is applied. If it is determined that the toner cannot pass, the toner image forming unit does not form a belt-like toner image, but the toner attached to the non-image area of the image carrier or the image carrier The toner having a lower density than the belt-shaped toner image attached to the non-image area is primarily transferred to the intermediate transfer body, and the covering toner or the low density toner transferred to the intermediate transfer body is transferred to the secondary transfer body. An image forming apparatus comprising: a control unit that controls the primary transfer bias voltage and the secondary transfer bias voltage so as to perform secondary transfer to a transfer unit.   When it is determined that the control unit can pass, the belt-like toner image is formed on the non-image area of the image carrier by the belt-like toner image forming unit, and the belt-like toner image formed on the image carrier is formed. The primary transfer bias voltage is controlled so as not to be transferred to the intermediate transfer member, and the secondary transfer bias voltage is set so as not to transfer the transfer toner transferred to the intermediate transfer member to the secondary transfer unit. The image forming apparatus according to claim 1, wherein the image forming apparatus is controlled.   When it is determined that the control unit can pass, the control unit determines the length determined based on the length of the non-image area of the image carrier, the response time of the primary transfer bias voltage, and the moving speed of the image carrier. The image forming apparatus according to claim 1, wherein the belt-shaped toner image is controlled to be formed by the belt-shaped toner image forming unit.   When it is determined that the control unit can pass, the control unit controls the secondary transfer bias voltage applied to the secondary transfer unit to a voltage having the same polarity as that of normal image formation and a small absolute value. The image forming apparatus according to claim 2, wherein the image forming apparatus is an image forming apparatus.

Images