JP2014035464A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device configured to stabilize image quality of a transfer image, while preventing reduction in printing quality.SOLUTION: An image forming device 100 includes: an intermediate transfer belt 31 for carrying a toner image; a counter roller 32 on which the intermediate transfer belt 31 is stretched; a secondary transfer belt 41 forming a transfer position with the intermediate transfer belt 31; a secondary transfer roller 42 facing the counter roller 32 across the transfer position; a first power supply part 63 that applies a secondary transfer voltage having a polarity opposite to a charging polarity of the toner image to the secondary transfer roller 42; a second power supply part 64 that applies a secondary transfer voltage having the same polarity as the charging polarity of the toner image to the counter roller 32; and a CPU 71. The CPU 71 controls the first and second power supply parts 63, 64 so as to apply the secondary transfer voltage to the secondary transfer roller 42 or the counter roller 32. When applied with the secondary transfer voltage, the counter roller 32 and the secondary transfer roller 42 secondarily transfers the toner image on the intermediate transfer belt 31 to a sheet passing through the transfer position.

Description

  The present invention relates to an electrophotographic image forming apparatus including an intermediate transfer member.

  In an electrophotographic image forming apparatus, a toner image primarily transferred from the surface of an image carrier to the surface of an intermediate transfer member is secondarily transferred onto a sheet passing between the intermediate transfer member and the secondary transfer member. There are some (for example, refer to Patent Document 1).

  As a secondary transfer method in which the toner image is secondarily transferred from the surface of the intermediate transfer member to a sheet, a transfer voltage having a polarity opposite to the charged polarity of the toner image is applied to the secondary transfer member, and the intermediate transfer member is grounded. And a second secondary transfer method in which a transfer voltage having the same polarity as the charging polarity of the toner image is applied to the intermediate transfer member to ground the secondary transfer member. Either the secondary transfer method or the second secondary transfer method is employed. In the first secondary transfer method, the toner image is secondarily transferred from the surface of the intermediate transfer body to the sheet by the suction force of the charge applied to the secondary transfer body. In the second secondary transfer method, the toner image is secondarily transferred from the surface of the intermediate transfer member to the sheet by the repulsive force of the charge applied to the intermediate transfer member.

JP 2006-10882 A

  However, when the apparatus main body is installed in a humid installation environment, the sheet absorbs moisture and the resistance value of the sheet is lowered. Therefore, in the first secondary transfer method, a part of the charge attached to the secondary transfer body is removed. The toner image cannot be sufficiently attracted to the paper by energizing the members of the apparatus main body through the paper. For this reason, in the first secondary transfer method, since the suction state of the toner image onto the paper changes according to the moisture absorption of the paper and the amount of toner adhering to the paper changes, the image quality of the transferred image is stabilized. I can't.

  Further, in the second secondary transfer method, when the toner image is secondarily transferred to a paper having a non-uniform surface resistance value, the toner image is changed to the surface resistance value of the paper by the repulsive force of the charge applied to the intermediate transfer member. Therefore, the transfer image is disturbed and the print quality is deteriorated. The paper having a non-uniform surface resistance value is a paper whose surface has been subjected to water repellent processing or lamination processing, or a paper on which a frame for a certificate or a company name is printed.

  For this reason, in an image forming apparatus that employs only one of the first secondary transfer method and the second secondary transfer method, the image quality of the transferred image on the moisture-absorbed paper is disturbed or the surface resistance value is not uniform. Deterioration of print quality on fresh paper.

  An object of the present invention is to select a secondary transfer method according to the state of the sheet indicating the moisture absorption of the sheet, the type of sheet, and the like, thereby preventing a decrease in print quality and stabilizing the image quality of the transferred image. An image forming apparatus is provided.

  The image forming apparatus of the present invention includes a first power supply unit, a second power supply unit, and a control unit, and primarily transfers a toner image formed on the surface of the image carrier onto the surface of the intermediate transfer member, thereby intermediate transfer member The toner image is secondarily transferred from the surface of the sheet to a sheet passing between the intermediate transfer member and the secondary transfer member. The first power supply unit selectively applies a transfer voltage having a polarity opposite to the charging polarity of the toner image to the secondary transfer member. The second power supply unit selectively applies a transfer voltage having the same polarity as the charging polarity of the toner image to the intermediate transfer member. The control unit sets the first power supply unit and the second power supply unit so as to apply a transfer voltage to only one of the secondary transfer member and the intermediate transfer member according to the state of the sheet when the toner image is secondarily transferred to the sheet. Control.

  When the toner image is secondarily transferred to the sheet, the control unit sets the first power supply unit and the second power supply unit so as to apply a transfer voltage to only one of the secondary transfer member and the intermediate transfer member depending on the state of the sheet. Control. When a transfer voltage is applied only to the secondary transfer member, a transfer voltage having a polarity opposite to the charged polarity of the toner image is applied to the secondary transfer member, and the intermediate transfer member is grounded, thereby providing the secondary transfer member. The toner image is secondarily transferred to a sheet by the suction force of the charge applied to the sheet. When the transfer voltage is applied only to the intermediate transfer member, the transfer voltage having the same polarity as the charging polarity of the toner image is applied to the intermediate transfer member, and the secondary transfer member is grounded to be applied to the intermediate transfer member. The toner image is secondarily transferred to the paper by the repulsive force of the charge.

  In the configuration further comprising an acquisition unit that acquires the type of paper on which the toner image is secondarily transferred, the control unit, when the paper type acquired by the acquisition unit is a paper type with a non-uniform surface resistance value, It is preferable to control so that the transfer voltage is applied only to the secondary transfer body.

  When the toner image is secondarily transferred to a sheet having a non-uniform surface resistance value, the control unit applies a transfer voltage having a polarity opposite to the charging polarity of the toner image to the secondary transfer body. Control the second power supply unit. When a transfer voltage is applied to the secondary transfer body, the toner image is sucked from the intermediate transfer body and secondarily transferred to the paper. The image forming apparatus can prevent the print quality from being deteriorated even in the secondary transfer onto a sheet having a non-uniform surface resistance value.

  In the configuration further comprising a detection unit for detecting the moisture absorption of the sheet on which the toner image is secondarily transferred as the state of the sheet, the control unit detects whether the sheet type is other than the sheet type having a non-uniform surface resistance value. It is preferable to control so that the transfer voltage is applied only to the intermediate transfer member when the part detects moisture absorption of a predetermined value or more.

  The sheet having absorbed moisture has a low resistance value. When the toner image is secondarily transferred to a sheet having a low resistance value, the control unit sets the first power supply unit and the second power supply unit so as to apply a transfer voltage having the same polarity as the charging polarity of the toner image to the intermediate transfer member. Control. When a transfer voltage is applied to the intermediate transfer member, the toner image is repelled from the surface of the intermediate transfer member and secondarily transferred onto the paper. The image forming apparatus can stabilize the image quality of the transferred image even when the sheet absorbs moisture.

  The detection unit is preferably a sensor that detects the humidity inside the apparatus main body.

  The higher the humidity inside the apparatus body, the more the paper absorbs moisture. For this reason, application of the transfer voltage to the secondary transfer body or the intermediate transfer body can be appropriately controlled by detecting the humidity inside the apparatus main body.

  According to the present invention, by selecting a secondary transfer method suitable for the paper state indicating the paper type, the moisture absorption of the paper, etc. from the two types of secondary transfer methods, it is possible to prevent deterioration in print quality. It is possible to stabilize the image quality of the transferred image.

1 is a diagram illustrating a schematic configuration in the vicinity of an image forming unit of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a diagram illustrating a schematic configuration in the vicinity of a secondary transfer unit included in the image forming apparatus. 2 is a block diagram illustrating a partial function of the image forming apparatus. FIG. 3 is a flowchart of an image forming process of a CPU in the image forming apparatus. 3 is a flowchart of a transfer process in the image forming process of the CPU.

  As shown in FIG. 1, the image forming apparatus 100 according to the embodiment of the present invention includes, as an example, a scanner, an image forming unit 10, and a sheet conveyance path S (not shown), and based on image data read by the scanner. Multi-color or single-color image forming processing is performed on a sheet by electrophotography.

  The image forming unit 10 irradiates image light based on the image data from the exposure unit 1 to form toner images on the surfaces of the photosensitive drums (corresponding to the image carrier of the present invention) 2A to 2D. The image forming unit 10 primarily transfers the toner images formed on the surfaces of the photosensitive drums 2 </ b> A to 2 </ b> D to the surface of the intermediate transfer belt 31 in order. On the surfaces of the photoconductive drums 2A to 2D, toner images of hues of black, cyan, magenta, and yellow are formed, respectively. The image forming unit 10 secondarily transfers the toner image on the surface of the intermediate transfer belt 31 onto a sheet passing through a secondary transfer position formed between the intermediate transfer belt 31 and the secondary transfer belt 41, and a fixing roller. 5 to fix.

  The sheet conveyance path S is moved from a sheet feeding unit (not shown) to a sheet discharge tray (not shown) via the secondary transfer position between the intermediate transfer belt 31 and the secondary transfer belt 41 in the image forming unit 10 and the fixing roller 5. It is formed everywhere.

  As shown in FIG. 2, the intermediate transfer belt 31 is stretched between a counter roller 32 and a drive roller 33, and moves along a circulation path that passes through the photosensitive drums 2D, 2C, 2B, and 2A in this order. Primary transfer rollers 34 </ b> A to 34 </ b> D are arranged on the inner peripheral surface of the intermediate transfer belt 31 so as to face the photoreceptor drums 2 </ b> A to 2 </ b> D, respectively. Each of the primary transfer rollers 34 </ b> A to 34 </ b> D receives the photosensitive drums 2 </ b> D and 2 </ b> C when a primary transfer voltage having a polarity opposite to the charging polarity of the toner image is applied while the intermediate transfer belt 31 moves along the circulation path. The toner images are primarily transferred onto the surface of the intermediate transfer belt 31 in order from the surfaces 2B and 2A.

  The secondary transfer belt 41 is stretched around a plurality of rollers including the drive roller 43 and moves along a predetermined circulation path. The secondary transfer roller 42 is disposed so as to face the opposing roller 32 with the secondary transfer belt 41 and the intermediate transfer belt 31 interposed therebetween. The secondary transfer roller 42 is connected to the first power supply unit 63, and a secondary transfer voltage having a polarity opposite to the charging polarity of the toner image is selectively applied by the first power supply unit 63. The counter roller 32 is connected to the second power supply unit 64, and a secondary transfer voltage having the same polarity as the charging polarity of the toner image is selectively applied by the second power supply unit 64. When a secondary transfer voltage is applied to one of the secondary transfer roller 42 and the counter roller 32, the toner image is transferred from the surface of the intermediate transfer belt 31 to a sheet that passes to the secondary transfer position. The intermediate transfer belt 31 and the counter roller 32 correspond to the intermediate transfer member of the present invention, and the secondary transfer belt 41 and the secondary transfer roller 42 correspond to the secondary transfer member of the present invention.

  In addition to the above, the image forming apparatus 100 includes a humidity sensor 61, a motor 62, a first power supply unit 63, a second power supply unit 64, a third power supply unit 65, and an operation unit (corresponding to the acquisition unit of the present invention) 70. CPU 71, ROM 72, and RAM 73 are provided.

  The humidity sensor 61 is an existing sensor that detects the humidity inside the apparatus main body. The humidity sensor 61 is not limited to an existing sensor that detects the humidity of the apparatus main body, and may be a sensor that detects the humidity of the paper feed unit that stores the paper, or a sensor that detects the moisture absorption of the paper. There may be.

  The motor 62 is connected to a plurality of transport rollers (not shown) that transport the paper along the paper transport path S and the drive rollers 33 and 43. The plurality of transport rollers and the drive rollers 33 and 43 may be connected to different motors 62, respectively.

  The first power supply unit 63 and the second power supply unit 64 are connected to the secondary transfer roller 42 and the counter roller 32, respectively. The third power supply unit 65 is connected to the primary transfer rollers 34A to 34D and selectively applies the primary transfer voltage.

  The operation unit 70 accepts operation inputs such as settings relating to the image forming process and an instruction to start the image forming process. The setting relating to the image forming process includes selection of the type of paper to be subjected to the image forming process. The paper types include special papers with non-uniform surface resistance values. Special paper is, for example, paper that has been subjected to water-repellent processing or lamination processing on a part of its surface, or paper that has a frame for award certificate or company name printed on its surface.

  The CPU 71 executes the control program recorded in the ROM 72 by using the RAM 73 as a working area. The CPU 71 selectively supplies power to the motor 62 via a power supply unit (not shown). The CPU 71 controls the first power supply unit 63 and the second power supply unit 64 so as to apply the secondary transfer voltage only to either the secondary transfer roller 42 or the opposing roller 32. The CPU 71 controls the third power supply unit 65 so as to apply the primary transfer voltage to the primary transfer rollers 34A to 34D.

  The image forming process performed by the CPU 71 will be described with reference to FIG.

  As shown in FIG. 4, the CPU 71 waits until the operation unit 70 accepts selection of the type of paper to be subjected to image forming processing (S11). When the CPU 71 accepts the selection of the paper type, the CPU 71 waits until the operation unit 70 accepts an instruction to start the image forming process (S12). When the CPU 71 receives the start instruction, the CPU 71 performs image forming processing for forming toner images on the surfaces of the photosensitive drums 2A to 2D (S13). The CPU 71 performs a transfer process for transferring the toner images from the surfaces of the photosensitive drums 2A to 2D to the sheet (S14). The CPU 71 performs a fixing process for fixing the toner image on the sheet (S15).

  Transfer processing by the CPU 71 will be described with reference to FIG.

  As shown in FIG. 5, the CPU 71 waits until the start timing of the transfer process (S21). At the start timing, the CPU 71 supplies power to the motor 62 (S22). When electric power is supplied to the motor 62, the plurality of transport rollers and the drive rollers 33 and 43 rotate. As the plurality of transport rollers rotate, the paper is transported on the paper transport path S along a predetermined transport direction. Further, as the drive roller 33 and the drive roller 43 rotate, the intermediate transfer belt 31 and the secondary transfer belt 41 move along their circulation paths.

  The CPU 71 controls the third power supply unit 65 so as to apply the primary transfer voltage to each of the primary transfer rollers 34A to 34D (S23). The primary transfer rollers 34 </ b> A to 34 </ b> D primarily transfer the toner images from the surfaces of the photosensitive drums 2 </ b> A to 2 </ b> D to the surface of the intermediate transfer belt 31 when a primary transfer voltage is applied.

  The CPU 71 determines whether or not the sheet to be subjected to the image forming process is a special sheet having a non-uniform surface resistance value (S24). The CPU 71 controls the second power supply unit 64 so that the opposing roller 32 is grounded when the paper to be subjected to the image forming process is a special paper (S25), and applies the secondary transfer voltage to the secondary transfer roller 42. The first power supply unit 63 is controlled to apply (S26), and the process proceeds to S30. When a secondary transfer voltage is applied, the secondary transfer roller 42 charges the secondary transfer belt 41 with a polarity opposite to the charging polarity of the toner image, and the toner image is transferred from the surface of the intermediate transfer belt 31 by the suction force of the charge. Is transferred to the paper.

  Further, the CPU 71 determines whether or not the humidity detected by the sensor of the humidity sensor 61 is equal to or higher than the threshold value when the paper to be subjected to the image forming process is other than the special paper (S27). The CPU 71 controls the first power supply unit 63 so as to ground the secondary transfer roller 42 when the humidity sensor 61 detects a humidity equal to or higher than a threshold (for example, 70%) (S28). The second power supply unit 64 is controlled to apply the secondary transfer voltage (S29), and the process proceeds to S30. When the secondary transfer voltage is applied, the opposing roller 32 charges the intermediate transfer belt 31 to the same polarity as the charging polarity of the toner image, and transfers the toner image from the surface of the intermediate transfer belt 31 to the sheet by the repulsive force of the charge. To do. Further, when the humidity sensor 61 detects the humidity below the threshold, the CPU 71 proceeds to the process of S25.

  In the process of S30, the CPU 71 determines whether image data exists. If the image data exists, the CPU 71 proceeds to the process of S23. When there is no image data, the CPU 71 controls the third power supply unit 65 to stop applying the primary transfer voltage to the primary transfer rollers 34A to 34D (S31). The CPU 71 controls the first power supply unit 63 and the second power supply unit 64 so as to stop the application of the secondary transfer voltage to the opposing roller 32 or the secondary transfer roller 42 (S32). The CPU 71 stops power supply to the motor 62 (S33).

  As described above, when the toner image is secondarily transferred to a special sheet having a non-uniform surface resistance value, the image forming apparatus 100 applies the secondary transfer voltage to the counter roller 32, and the toner is applied to a portion where the surface resistance value is low. Therefore, a secondary transfer voltage is applied to the secondary transfer roller 42. When a secondary transfer voltage is applied, the secondary transfer roller 42 charges the secondary transfer belt 41 to a polarity opposite to the charging polarity of the toner image, and sucks the toner image from the surface of the intermediate transfer belt 31. Secondary transfer to paper. As a result, the image forming apparatus 100 can prevent the print quality from being deteriorated even in the secondary transfer onto the special paper having a non-uniform surface resistance value.

  Further, when the humidity inside the apparatus main body increases, the moisture absorption of the sheet increases and the resistance value of the sheet decreases. When the toner image is secondarily transferred to a sheet having a low resistance value, when the secondary transfer voltage is applied to the secondary transfer roller 42, the image forming apparatus 100 leaks current to the apparatus body through the sheet. A secondary transfer voltage is applied to the roller 32. When a secondary transfer voltage is applied, the counter roller 32 charges the intermediate transfer belt 31 to the same polarity as the charging polarity of the toner image, and repels the toner image from the surface of the intermediate transfer belt 31 to secondary the paper. Transcript. As a result, the image forming apparatus 100 can stabilize the image quality of the transferred image even when the moisture absorption of the sheet is high.

  In the above-described embodiment, the operation unit 70 that receives selection of the type of paper including whether or not the surface resistance value of the paper is uniform is the acquisition unit of the present invention. However, a paper type including whether or not the surface resistance value of the paper is uniform is assigned in advance to each of the plurality of paper feed units, and the operation unit 70 that receives selection of the paper feed unit is used as the acquisition unit of the present invention. Also good. The present invention also provides a detection unit that is provided in a line in a direction orthogonal to the conveyance direction and on the sheet conveyance path S, and that detects a current value flowing through the sheet by applying a voltage to the sheet being conveyed. It is good also as an acquisition part. The CPU 71 determines whether or not the surface resistance value of the sheet is uniform based on the detection result of the detection unit.

  In the above-described embodiment, the image forming unit 10 primarily transfers the toner image from the surface of the photosensitive drums 2A to 2D to the intermediate transfer belt 31, but may be configured to perform primary transfer to the intermediate transfer drum. In addition, the image forming unit 10 does not include the secondary transfer belt 41 and the plurality of rollers that stretch the secondary transfer belt 41, and toner is applied to a sheet that passes between the intermediate transfer belt 31 and the secondary transfer roller 42. A configuration in which the image is secondarily transferred may be used.

  The above description of the embodiment is to be considered in all respects as illustrative and not restrictive. The scope of the present invention is shown not by the above embodiments but by the claims. Furthermore, the scope of the present invention is intended to include all modifications within the meaning and scope equivalent to the scope of the claims.

2A to 2D ... photosensitive drum 31 ... intermediate transfer belt 32 ... opposed rollers 34A to 34D ... primary transfer roller 41 ... secondary transfer belt 42 ... secondary transfer roller 63 ... first power source 64 ... second power source 71 ... CPU
100: Image forming apparatus

Claims (4)

A sheet on which the toner image formed on the surface of the image carrier is primarily transferred to the surface of the intermediate transfer member, and the toner image passes between the intermediate transfer member and the secondary transfer member from the surface of the intermediate transfer member. An image forming apparatus for secondary transfer to
A first power supply unit that selectively applies a transfer voltage having a polarity opposite to the charging polarity of the toner image to the secondary transfer member;
A second power supply unit that selectively applies a transfer voltage having the same polarity as the charging polarity of the toner image to the intermediate transfer member;
When the toner image is secondarily transferred to the sheet, the first power supply unit and the second power supply unit are configured to apply a transfer voltage to only one of the secondary transfer body or the intermediate transfer body according to the state of the sheet. An image forming apparatus comprising: a control unit that controls a power supply unit. An acquisition unit that acquires the type of paper on which the toner image is secondarily transferred as the state of the paper;
2. The control unit according to claim 1, wherein the control unit performs control so that a transfer voltage is applied only to the secondary transfer body when a paper type acquired by the acquisition unit is a paper type having a non-uniform surface resistance value. The image forming apparatus described. A detection unit that detects moisture absorption of the paper on which the toner image is secondarily transferred as the state of the paper;
The control unit applies a transfer voltage only to the intermediate transfer body when the type of the sheet is other than the type of the sheet having a non-uniform surface resistance value and the detection unit detects the moisture absorption of a predetermined value or more. The image forming apparatus according to claim 2, which is controlled as described above.   The image forming apparatus according to claim 3, wherein the detection unit is a humidity sensor that detects humidity inside the apparatus main body.

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