JP5589676B2 - Transfer mechanism and image forming apparatus - Google Patents

Description

  The present invention relates to a transfer mechanism and an image forming apparatus.

  There is an image forming apparatus that transfers a toner image formed on a photosensitive drum onto a transfer material by pressing the transfer material against the photosensitive drum with a transfer roll. In such an image forming apparatus, a technique is disclosed in which the pressing force of the transfer roll is varied depending on certain conditions for the purpose of preventing an image defect caused by an inappropriate pressing force of the transfer roll. For example, Patent Document 1 discloses a technique for varying the pressing force of a transfer roll according to the image pattern of a toner image. Patent Document 2 discloses a technique for varying the pressing force of the transfer roll in accordance with the type and thickness of the transfer material.

Japanese Patent Laid-Open No. 10-11607 JP 2002-214943 A

  An object of the present invention is to suppress toner image transfer failure.

In order to solve the above problem, the transfer mechanism according to claim 1 of the present invention is a first mechanism in which a first toner image representing the image is formed by toner of the first color constituting the image to be output. A first transfer means for pressing the transfer body against the holding body and transferring the first toner image to the transfer body; and a second color toner different from the first color toner. The transfer body is pressed against the second holding body on which the toner image is formed, and before the first toner image is transferred to the transfer body, the first toner image is transferred to the transfer body. A second transfer means for transferring the second toner image to an area to be transferred; a pressing force by which the first transfer means presses the transfer body against the first image carrier; and the second transfer. It means for adjusting and a pressing force for pressing the transfer member to said second image holding member adjustment And stage, by controlling the adjusting means, the first transfer means in addition to increasing the pressing force for pressing the transfer member to said first image holding member, the second transfer means and the second lowering the pressing force for pressing the transfer member to the image carrier, and a control unit to be smaller than the pressing force which the first transfer means for pressing the transfer member to said first image holding member, in that it comprises Features.

Further, the transfer mechanism according to claim 2 is the transfer mechanism according to claim 1, wherein the control means is configured to transfer the first toner image only in a region where the first toner image is to be transferred . In addition to increasing the pressing force by the first transfer unit, the pressing force by the second transfer unit is lowered and made smaller than the pressing force by the first transfer unit.

According to a third aspect of the present invention, in the transfer mechanism according to the first or second aspect, the control means determines in advance the type of transfer material onto which the first toner image is transferred and fixed. In addition to increasing the pressing force by the first transfer means, the pressing force by the second transfer means is lowered and made smaller than the pressing force by the first transfer means. Features.

According to a fourth aspect of the present invention, there is provided the transfer mechanism according to any one of the first to third aspects, in which the control unit uses a plurality of colors of toner for a line segment image included in the first toner image. In the case of a multi-colored color used , in addition to increasing the pressing force by the first transfer unit, the pressing force by the second transfer unit is lowered and more than the pressing force by the first transfer unit. Is also made smaller.

The transfer mechanism of claim 5, in the transfer mechanism according to claim 1, wherein, when the humidity of the ambient measured by the measurement means is higher than the threshold, the In addition to increasing the pressing force by the first transfer means, the pressing force by the second transfer means is lowered and made smaller than the pressing force by the first transfer means.

  According to a sixth aspect of the present invention, there is provided the image forming apparatus according to the sixth aspect, wherein the first toner image representing the image is formed on the first holding body using the color toner constituting the image to be output. , Second forming means for forming a second toner image on the second holding body using a second color toner different from the first color toner, the first toner image, and the second toner image. The transfer mechanism according to any one of claims 1 to 5, which functions as a primary transfer unit that primarily transfers the toner image to a transfer body, and the first toner image primarily transferred to the transfer body by the transfer mechanism; Secondary transfer means for secondary transfer of the second toner image to a transfer material, and fixing the first toner image and the second toner image secondarily transferred by the secondary transfer means to the transfer material And a fixing means for making it possible.

  According to a seventh aspect of the present invention, in the image forming apparatus according to the sixth aspect of the present invention, the image forming apparatus includes a specifying unit that specifies an area including a line segment image in the first toner image, and the second formation. The means forms the second toner image at a position corresponding to the area specified by the specifying means on the second image holding member.

  The image forming apparatus according to claim 8 is the image forming apparatus according to claim 6 or 7, wherein the second toner image is a dot-like toner image arranged at a predetermined interval. It is characterized by that.

  The image forming apparatus according to claim 9 is the image forming apparatus according to claim 6 or 7, wherein the second toner image is a linear toner image arranged at a predetermined interval. It is characterized by that.

  According to a tenth aspect of the present invention, in the image forming apparatus according to the sixth or seventh aspect, the second toner image is a toner image arranged in a lattice pattern.

1 shows an internal configuration of an image forming apparatus. The concept of a laminated structure of a first toner image and a second toner image is shown. The appearance of the primary transfer mechanism is shown. The side of a primary transfer mechanism is shown. The front of the primary transfer mechanism is shown. 2 shows an example of a toner image transferred to an intermediate transfer belt. 6 shows a change in toner density distribution accompanying a change in pressing force of a primary transfer roll. 6 shows a change in toner density distribution accompanying a change in pressing force of a primary transfer roll. The change of the character missing level accompanying the change of the pressing force of the primary transfer roll is shown. The change of the character missing level accompanying the change of the pressing force of the primary transfer roll is shown.

(First embodiment)
The first embodiment of the present invention will be described below. First, the internal configuration of the image forming apparatus 1 will be described. FIG. 1 shows an internal configuration of the image forming apparatus 1. The image forming apparatus 1 includes image forming units 2Y, 2M, 2C, and 2K, and a tandem type full color printer in which the image forming units 2Y, 2M, 2C, and 2K are arranged in parallel along the intermediate transfer belt 10. It is. Hereinafter, the image forming units 2Y, 2M, 2C, and 2K are collectively referred to as an “image forming unit 2YMCK”, and the image forming unit 2 includes the image forming unit 2S in addition to the image forming units 2Y, 2M, 2C, and 2K. Collectively. Y (yellow), M (magenta), C (cyan), and K (black) are colors necessary for forming a color image, and are referred to as standard colors here. The image forming unit 2YMCK is formed according to image data with toners of standard colors of Y (yellow), M (magenta), C (cyan), and K (black), which are examples of the first color toner. And a first forming unit for forming each toner image (hereinafter, referred to as “first toner image”). This first toner image is, for example, an image such as a document instructed to be printed out or copied by the user.

  Each of the image forming units 2YMCK includes a photosensitive drum 4 and a developing device 5. An image exposure device 6 is provided below the image forming unit 2. The image exposure device 6 irradiates the photosensitive drum 4 with a laser beam corresponding to the image data. The laser beam emitted from the image exposure device 6 scans the surface of the photosensitive drum 4 to form an electrostatic latent image on the photosensitive drum 4. The electrostatic latent image formed on the photosensitive drum 4 is developed by the developer 5 with a developer containing toner of a color corresponding to the image forming unit 2 to be a first toner image. The first toner image formed on the photosensitive drum 4 is transferred to the first holder by a primary transfer roll 110 which is an example of a first transfer unit of the primary transfer mechanism 100 provided to face the photosensitive drum 4. Primary transfer is performed from a photosensitive drum 4 as an example to an intermediate transfer belt 10 as an example of a transfer body. The intermediate transfer belt 10 is a belt-like member that is stretched by a plurality of rolls such as a drive roll 12, a tension roll 13, and an idler roll 14. The intermediate transfer belt 10 is driven by a drive roll 12 to move in a predetermined direction (direction A in FIG. 1).

  Here, the image forming apparatus 1 is provided with an image forming unit 2S. The image forming unit 2S is a second forming unit that forms a second toner image formed of a second color toner different from the standard colors Y, M, C, and K (first color toner). It is an example. The color of the toner of the image forming unit 2S is, for example, a color having higher transparency than the standard color or a lighter color than the standard color. The second toner image of such a color is for improving the transfer performance when the first toner image is primarily transferred to the intermediate transfer belt 10. If the pressing force by the primary transfer roll 110 when transferring the first toner image is increased, the occurrence of problems such as uneven toner density distribution and toner scattering can be suppressed. However, if the pressing force by the primary transfer roll 110 is too high, an image defect (character omission) occurs in which toner is not transferred in a line-shaped image area constituting the character. Therefore, in order to prevent the occurrence of character omission while maintaining the pressing force of the primary transfer roll at a high level to the extent that problems such as uneven toner density distribution and toner scattering do not occur. This toner image is transferred to the portion of the intermediate transfer belt 10 where the first toner image is transferred. In the first embodiment, the second toner image uses a transparent toner and has a halftone dot shape.

  Here, the concept of the laminated structure of the first toner image and the second toner image will be described with reference to FIG. FIG. 2 shows the concept of the laminated structure of the first toner image and the second toner image. FIG. 2 shows an example in which the toner image 310 is transferred to the front surface of the intermediate transfer belt 10 and the toner image 320 is transferred to a region where the toner image 310 is transferred. In FIG. 2, a toner image 310 is a first toner image. As described above, if the load when transferring the toner image 310 to the intermediate transfer belt 10 is increased, the occurrence of problems such as uneven toner density distribution and toner scattering can be suppressed. However, if the load applied when the toner image 310 is transferred to the intermediate transfer belt 10 is increased by increasing the pressing force by the primary transfer roll 110, a transfer failure occurs. Therefore, as shown in FIG. 2, a toner image 320, which is a second toner image, is transferred to an area where the toner image 310 is transferred. As a result, even if the pressing force by the primary transfer roll 110 is not increased, a high load is applied to the toner image 310 as much as the total toner thickness is increased by the toner image 320. Therefore, the occurrence of defects such as uneven toner density distribution and toner scattering is suppressed without causing transfer defects. In particular, in the example shown in FIG. 2, a halftone dot toner image is used as the toner image 320. As a result, when the toner image 310 is pressed, the load applied to the toner image 310 is dispersed by the presence of the toner image 320, and an equal load is applied over a wide range of the toner image 310.

  Similar to the image forming unit 2YMCK, the image forming unit 2S includes a photosensitive drum 4 (second holding body) and a developing device 5. The configuration and operation until the image forming unit 2S forms the second toner image on the photosensitive drum 4 are the same as the configuration and operation until the image forming unit 2YMCK forms the first toner image on the photosensitive drum 4. Therefore, the description is omitted. The second toner image formed on the photosensitive drum 4 of the image forming unit 2S is transferred by a primary transfer roll 110, which is an example of a second transfer unit of the primary transfer mechanism 100 provided to face the photosensitive drum 4. Then, primary transfer is performed from the photosensitive drum 4 which is an example of the second holding body to the intermediate transfer belt 10 (transfer body). As described above, the second toner image is transferred to the intermediate transfer belt 10 before the first toner images formed by the image forming units 2Y, 2M, 2C, and 2K are transferred to the intermediate transfer belt 10. . Therefore, the image forming unit 2S for forming the second toner image is provided upstream of the image forming units 2Y, 2M, 2C, and 2K in the moving direction of the intermediate transfer belt 10.

  The transfer paper 18 (transfer material) is stored in the tray 24 in advance, and is taken out from the tray 24 when image formation is performed, and is transported to the secondary transfer position by the transport roll 25 and the resist roll 28. At the secondary transfer position, a secondary transfer roll 17 is provided as an example of secondary transfer means for secondary transfer of the toner image to the transfer material. The secondary transfer roll 17 is pressed by a pressing means such as a spring (not shown) to press the transfer paper 18 against the intermediate transfer belt 10 from the back side of the transfer paper 18. In this state, a secondary transfer bias supplied from a power supply (not shown) is applied between the secondary transfer roll 17 and a roll facing the secondary transfer roll 17, thereby being transferred onto the surface of the intermediate transfer belt 10. The existing toner image is secondarily transferred to the transfer paper 18. Thereafter, the transfer paper 18 is heated and pressed by a fixing device 19 (fixing means) that is an example of a fixing unit that fixes the toner image to the transfer paper 18, and the toner image is fixed. It is discharged outside the main body of the forming apparatus 1. The so-called residual toner remaining on the intermediate transfer belt 10 without being secondarily transferred to the transfer paper 18 is recovered by the toner recovery unit 50.

  Next, the configuration of the primary transfer mechanism 100 will be described. 3 to 5 show the configuration of the primary transfer mechanism 100. Among these, FIG. 3 shows the external appearance of the primary transfer mechanism 100. FIG. 4 shows a side view of the primary transfer mechanism 100. FIG. 5 shows the front of the primary transfer mechanism 100. Here, the “side surface of the primary transfer mechanism 100” indicates the primary transfer mechanism 100 when the axial direction of the primary transfer roll 110 is the direction of the line of sight. The “front surface of the primary transfer mechanism 100” indicates the primary transfer mechanism 100 when the traveling direction of the intermediate transfer belt 10 is the direction of the line of sight.

  The primary transfer mechanism 100 transfers the toner image formed on the photosensitive drum 4 to the intermediate transfer belt 10. The primary transfer mechanism 100 includes a primary transfer roll 110, an adjustment unit 120, and a control circuit 140. The primary transfer mechanism 100 includes a primary transfer roll 110 and an adjustment unit 120 corresponding to each of the image forming units 2Y, 2M, 2C, 2K, and 2S. One of them will be described.

  The primary transfer roll 110 sandwiches the intermediate transfer belt 10 between the intermediate transfer belt 10 and the photosensitive drum 4 from the back surface (the surface on which the toner image is not transferred). The primary transfer roll 110 is pressed against the photosensitive drum 4 via the intermediate transfer belt 10, and is supplied between a primary transfer roll 110 and the photosensitive drum 4 from a power supply (not shown). When the transfer bias is applied, the toner image formed on the surface of the photosensitive drum 4 is primarily transferred to the intermediate transfer belt 10.

  The adjusting unit 120 adjusts the pressing force of the primary transfer roll 110 against the photosensitive drum 4 by adjusting the vertical position of the shaft portion 112 of the primary transfer roll 110. Specifically, in the primary transfer roll 110, both one end 112A and the other end 112B of the shaft portion 112 are supported in a rotatable state by a bearing portion or the like (not shown). The adjusting unit 120 adjusts the pressing force of the primary transfer roll 110 by adjusting the vertical positions of both the end 112A and the end 112B. The “up and down direction” here refers to the direction in which the pressing force of the primary transfer roll 110 is increased (that is, the direction in which the primary transfer roll 110 is brought close to the photosensitive drum 4) as “upward”, and the pressing force of the primary transfer roll 110 is the same. The direction of weakening (that is, the direction of moving the primary transfer roll 110 away from the photosensitive drum 4) is “downward”.

  The adjusting unit 120 includes a pressing spring 122, a support plate 124, and a cam 126. The pressing spring 122 presses the shaft portion 112 from below. The support plate 124 supports the lower end portion of the pressing spring 122. The cam 126 is in contact under the support plate 124 and adjusts the vertical position of the support plate 124. In the adjustment means 120 configured as described above, the vertical position of the support plate 124 is adjusted by rotating the cam 126 by driving a motor (not shown). As a result, the elasticity of the pressing spring 122 whose lower end is supported by the support plate 124 is adjusted, and as a result, the pressing force of the primary transfer roll 110 is adjusted.

  The control circuit 140 functions as a control unit that controls the adjusting unit 120 to control the pressing force of the primary transfer roll 110. For example, the control circuit 140 controls the adjusting unit 120 to move the shaft portion 112 upward, thereby increasing the pressing force of the primary transfer roll 110. Further, the control circuit 140 controls the adjusting unit 120 to move the shaft portion 112 downward, thereby weakening the pressing force of the primary transfer roll 110. The control circuit 140 is realized by, for example, an IC (Integrated Circuit) configured by a CPU (Central Processing Unit), a memory, and the like.

  Here, the control circuit 140 uses the primary transfer roll 110 (hereinafter referred to as “primary transfer roll 110 </ b> S”) for transferring the second toner image as the primary transfer roll for transferring the first toner image. The pressing force of the primary transfer roll 110S is controlled to be lower than the pressing force of 110 (hereinafter collectively referred to as “primary transfer roll 110YMCK”). At this time, the control circuit 140 controls the pressing force of the primary transfer roll 110 </ b> S so that the toner that forms the second toner image is not crushed and the second toner image can be sufficiently transferred to the intermediate transfer belt 10. . Since the pressing force of the primary transfer roll 110S that satisfies such conditions varies depending on the properties such as the viscosity of the toner that forms the second toner image, an appropriate value is determined by conducting an experiment in advance. Good.

  The control circuit 140 also functions as a specifying unit that specifies an area (hereinafter, referred to as “target area”) that includes a line segment image forming a character, a table, or the like in the first toner image. For example, the control circuit 140 analyzes the image data of the first toner image, recognizes the line segment image in the first toner image, and specifies the area including the recognized line segment image as the target area. When the control circuit 140 specifies the target area, the image forming unit 2S forms a second toner image at a position corresponding to the specified target area on the photosensitive drum 4. The primary transfer roll 110 </ b> S transfers the second toner image to the position of the specified target area on the intermediate transfer belt 10. That is, the primary transfer roll 110 </ b> S does not transfer the second toner image to a portion of the intermediate transfer belt 10 where the region other than the target region is transferred. An area other than the target area can be said to be an area in which character omission is unlikely to occur. Therefore, by not transferring the second toner image to a portion where such an area is transferred, the toner used for the second toner image is not transferred. Consumption is reduced.

  FIG. 6 shows an example of a toner image transferred to the intermediate transfer belt 10. In FIG. 6, a toner image 200 is formed by transferring and superimposing four toner images Y, M, C, and K on the intermediate transfer belt 10 by image forming units 2Y, 2M, 2C, and 2K. Is. The upper half of the toner image 200 is an area including text, and the lower half is an area including a photograph. Therefore, the upper half toner image 200 is the target area 202 described above.

  A halftone dot toner image 210 is transferred to the intermediate transfer belt 10 by the primary transfer roll 110S before the toner image 200 is transferred by the primary transfer roll 110YMCK. The toner image 210 is for suppressing the occurrence of transfer defects such as missing characters by dispersing the transfer load when the toner image 200 is transferred. In the toner image 210, the shape, size, interval, and arrangement of each halftone dot are determined in advance based on test results, simulation results, and the like so that the transfer load is suitably dispersed. Here, as shown in FIG. 6, the toner image 210 is transferred to the intermediate transfer belt 10 only in the portion where the target area 202 is transferred. This is because, when the toner image 200 is transferred to the intermediate transfer belt 10, character omission is likely to occur in a portion where the character or line is transferred. As described above, the primary transfer mechanism 100 according to the present embodiment transfers the halftone dot toner image 210 to the portion of the surface of the intermediate transfer belt 10 to which the target area is transferred, so that the toner image 200 is transferred. The transfer load when the image is transferred is dispersed to prevent the occurrence of transfer defects such as missing characters.

  For example, if the primary transfer roll 110S presses the toner image 210 with the same pressing force as the primary transfer roll 110YMCK, the halftone dot toner image 210 is transferred before the primary transfer roll 110YMCK transfers the toner image 200. The effect of applying a uniform load over a wide range of the toner image 310 is reduced. However, if the pressing force by the primary transfer roll 110S is too low, the toner image 210 may be peeled off from the intermediate transfer belt 10 before the primary transfer roll 110YMCK transfers the toner image 200. End up. Therefore, the pressing force when the primary transfer roll 110S transfers the toner image 210 to such an extent that the toner image 210 does not peel from the intermediate transfer belt 10 is the pressing force when the primary transfer roll 110YMCK transfers the toner image 200. It is set lower than the pressure. In particular, the primary transfer mechanism 100 of this embodiment sets the pressing force of the primary transfer roll 110S to be lower than the pressing force of the primary transfer roll 110YMCK only while the primary transfer roll 110S is transferring the toner image 210. While the primary transfer roll 110S is not transferring the toner image 210, it is preferable that the pressing force of the primary transfer roll 110S is equal to the pressing force of the primary transfer roll 110YMCK because the intermediate transfer belt 10 is pressed evenly. Because.

  7 and 8 show changes in toner density distribution accompanying changes in the pressing force of the primary transfer roll 110YMCK. Here, for each of the cases where the pressing force (linear pressure (gf / cm)) of the primary transfer roll 110YMCK is changed from “13” to “30”, the current value of the primary transfer bias supplied to the primary transfer roll 110YMCK is calculated. Experiments were performed to detect the toner density at each of the detection positions of “IN”, “CENTER”, and “OUT” while changing. FIG. 7 shows the experimental results before changing the pressing force of the primary transfer roll 110YMCK. FIG. 8 shows the experimental results after changing the pressing force of the primary transfer roll 110YMCK. “CENTER” indicates a center detection position in the width direction on the surface of the intermediate transfer belt 10. “IN” indicates a detection position on the back side as viewed from the front of the image forming apparatus 1 with respect to the center in the width direction on the surface of the intermediate transfer belt 10. “OUT” indicates a detection position on the front side of the image forming apparatus 1 from the center in the width direction on the surface of the intermediate transfer belt 10.

  7 and 8 show that increasing the pressing force of the primary transfer roll 110YMCK suppresses uneven toner density distribution at each detection position. The toner density referred to here is an index value of the ratio (area coverage) that the toner covers the unit area of the toner image. For example, focusing on the case where the current value of the primary transfer bias supplied to the primary transfer roll 110YMCK is “45 (μA)”, FIG. 7 showing the experimental results before increasing the pressing force of the primary transfer roll 110YMCK shows each detection. It is shown that the toner density at the position is discrete in the range of “1.65 to 1.77”. This indicates that the toner density distribution of the transferred toner image is uneven on the surface of the intermediate transfer belt 10. On the other hand, FIG. 8 showing experimental results after increasing the pressing force of the primary transfer roll 110YMCK shows that the toner density at each detection position converges in the range of “1.72 or more and 1.77 or less”. ing. This indicates that the toner density distribution of the transferred toner image is substantially uniform on the surface of the intermediate transfer belt 10.

  FIG. 9 shows a change in the missing character level accompanying a change in the pressing force of the primary transfer roll 110YMCK. Here, when the second toner image is not transferred, when the second toner image is transferred with the same pressing force as the first toner image, and when the second toner image is pressed lower than the first toner image. For each of the cases where the image was transferred by pressure, an experiment was conducted to measure the character missing level while changing the pressing force of the primary transfer roll 110YMCK for transferring the first toner image. FIG. 9 shows the experimental results. Here, the “character missing level” indicates that the higher the numerical value, the more characters are missing.

  FIG. 9 shows that the character omission level increases as the pressing force of the primary transfer roll 110YMCK increases. For example, in FIG. 9, when the second toner image is not transferred, characters are lost when the linear pressure of the primary transfer roll 110YMCK is changed from “10 (gf / cm)” to “30 (gf / cm)”. It is shown that the level changes from “1” to “4”.

  FIG. 9 shows that the character omission level is lower when the second toner image is transferred than when the second toner image is not transferred. For example, in FIG. 9, focusing on the case where the linear pressure of the primary transfer roll 110YMCK is set to “30 (gf / cm)”, the character missing level is “4” when the second toner image is not transferred. When the second toner image is transferred, it is shown that the character missing level is “3.5”.

  Further, in FIG. 9, it is better to transfer the second toner image with a lower pressing force than the first toner image, rather than transferring the second toner image with the same pressing force as the first toner image. It is shown that the omission level is lowered. For example, in FIG. 9, focusing on the case where the linear pressure of the primary transfer roll 110YMCK is set to “30 (gf / cm)”, when the second toner image is transferred with the same linear pressure as the first toner image, Although the character missing level is “3.5”, it is indicated that the character missing level is “2” when the second toner image is transferred with a lower pressing force than the first toner image. .

  FIG. 10 shows a change in the missing character level accompanying a change in the pressing force of the primary transfer roll 110YMCK. Here, when the linear pressure of the primary transfer roll 110S for transferring the second toner image is “5 (gf / cm)”, “4 (gf / cm)” is “3 (gf / cm)”. In each case, an experiment was conducted to measure the character missing level while changing the pressing force of the primary transfer roll 110YMCK that transfers the first toner image. FIG. 10 shows the experimental results.

  FIG. 10 shows that the character omission level decreases as the pressing force of the primary transfer roll 110S decreases. For example, paying attention to the case where the linear pressure of the primary transfer roll 110YMCK is “30 (gf / cm)”, the character omission level is low when the linear pressure of the primary transfer roll 110S is “5 (gf / cm)”. Although it is “2.5”, when the pressing force of the primary transfer roll 110S is “4 (gf / cm)”, it is shown that the character missing level is “2 (gf / cm)”. .

  Further, FIG. 10 shows that when the pressing force of the primary transfer roll 110S becomes lower than a certain level, the character missing level suppressing force is saturated. For example, paying attention to the case where the pressing force of the primary transfer roll 110YMCK is “30 (gf / cm)”, when the linear pressure of the primary transfer roll 110S is “4 (gf / cm)”, the character missing level is Although it is “2”, it is shown that the character omission level is “2” even when the pressing force of the primary transfer roll 110S is “3 (gf / cm)”.

  From these experimental results, as in the image forming apparatus 1 of the present embodiment, by increasing the pressing force of the primary transfer roll 110YMCK, while suppressing unevenness in the toner density distribution on the surface of the intermediate transfer belt 10, Further, it has been clarified that the occurrence of character omission is suppressed by making the pressing force of the primary transfer roll 110S lower than the pressing force of the primary transfer roll 110YMCK.

(Modification)
The present invention is not limited to the embodiment described above, and may be modified as follows. Further, the following modifications may be combined.

(Modification 1)
In the embodiment, when the control circuit 140 determines whether or not a character dropout is likely to occur and determines that a character dropout is likely to occur, the pressing force of the primary transfer roll 110S is applied to the primary transfer roll 110YMCK. The pressing force of the primary transfer roll 110S may be controlled so as to be lower than the pressing force.

  For example, the ease of missing characters varies depending on the type of transfer material onto which the first toner image is secondarily transferred. The higher the smoothness of the surface of the transfer material, the easier it is for missing characters. Accordingly, the control circuit 140 determines that the pressing force of the primary transfer roll 110S is the primary transfer roll 110YMCK when the type of transfer material onto which the first toner image is secondarily transferred is predetermined. The pressing force of the primary transfer roll 110S is controlled so as to be lower than the pressing force. For example, in this embodiment, the transfer paper 18 is used as a transfer material onto which the first toner image is secondarily transferred. In view of this, the control circuit 140 uses the pressing force of the primary transfer roll 110 </ b> S as the pressing force of the primary transfer roll 110 </ b> YMCK when the transfer paper 18 used for the secondary transfer uses glossy paper or OHP having high surface smoothness. The pressing force of the primary transfer roll 110S is controlled so as to be lower. Generally, since the type of transfer paper 18 used for secondary transfer is set in the image forming apparatus 1, the control circuit 140 determines in advance that the transfer paper 18 used for secondary transfer is based on this setting. What is necessary is just to judge whether it is what is defined.

  In addition, the ease of occurrence of character omission varies depending on whether the character or line is of primary color or multi-color. If the characters or lines are of primary color, missing characters are unlikely to occur. Therefore, the control circuit 140 determines that the pressing force of the primary transfer roll 110 </ b> S is greater than the pressing force of the primary transfer roll 110 </ b> YMCK when the characters or lines included in the first toner image are of a multi-color that easily causes missing characters. Also, the pressing force of the primary transfer roll 110S is controlled so as to be low. In this case, the control circuit 140 may determine, for example, from the image data of the first toner image whether the character or line is of a primary color or a multi-color.

  In addition, the ease of missing characters varies depending on the ambient humidity. The higher the humidity is, the easier it is for missing characters. Therefore, when the ambient humidity measured by a measuring unit such as a humidity sensor (not shown) is higher than a predetermined threshold and is likely to cause missing characters, the control circuit 140 causes the primary transfer roll 110S. The pressing force of the primary transfer roll 110S is controlled so that the pressing force is lower than the pressing force of the primary transfer roll 110YMCK. Further, the control circuit 140 determines that the pressing force of the primary transfer roll 110S is primary when the ambient temperature measured by a measuring unit such as a temperature sensor (not shown) is a predetermined temperature at which characters are easily lost. The pressing force of the primary transfer roll 110S may be controlled so as to be lower than the pressing force of the transfer roll 110YMCK.

(Modification 2)
In a general image forming apparatus, a user sets an arbitrary image quality mode. Therefore, when the selected image quality mode is to form an image with a higher quality than a predetermined image quality, the control circuit 140 makes the pressing force of the primary transfer roll 110S lower than the pressing force of the primary transfer roll 110YMCK. The pressing force of the primary transfer roll 110S may be controlled. For example, it is assumed that the “low image quality mode”, “medium image quality mode”, and “high image quality mode” are provided in the image forming apparatus 1. In this case, when the user selects the “high quality mode”, the control circuit 140 sets the pressing force of the primary transfer roll 110S so that the pressing force of the primary transfer roll 110S is lower than the pressing force of the primary transfer roll 110YMCK. For example, it is controlled.

(Modification 3)
In the embodiment, the control circuit 140 may specify an area including a character or a line whose line width is smaller than a predetermined threshold as a target area. This is because the thinner the line width, the easier the occurrence of missing characters, and the greater the line width to a certain extent, the less likely the missing characters. In such a configuration, the line width at which character omission is less likely to occur differs depending on the model of the image forming apparatus 1, the nip width, and the like. Therefore, an appropriate threshold value is set in advance based on experimental results, simulation results, and the like. It is good to keep.

(Modification 4)
In the embodiment, the second toner image is a dot-like toner image arranged at a predetermined interval. However, the present invention is not limited to this, and the second toner image can disperse the transfer load. Any shape may be used as long as it has a shape. For example, the second toner image may be a linear toner image arranged at a predetermined interval or a toner image arranged in a grid.

(Modification 5)
In the embodiment, the transparent toner is used as the toner for forming the second toner image. However, the present invention is not limited to this, and the toner for forming the second toner image improves the transfer performance of the first toner image. Any color can be used as long as it does not affect the appearance of the first toner image. For example, a light color toner of Y, M, C, or K may be used as the toner for forming the second toner image.

(Modification 6)
In the embodiment, as shown in FIG. 6, the second toner image is transferred only to the portion of the surface of the intermediate transfer belt 10 to which the target area specified by the control circuit 140 is transferred. However, the present invention is not limited to this, and it is sufficient that the second toner image is transferred to at least a portion to which the target region is transferred. Therefore, for example, the second toner image may be transferred to the entire area on the surface of the intermediate transfer belt 10 where the first toner image is transferred.

(Modification 7)
In the embodiment, an example in which the transfer mechanism of the present invention is employed in an image forming apparatus that employs an intermediate transfer belt as a transfer member has been described. However, the transfer mechanism of the present invention is capable of transferring images other than the intermediate transfer belt, such as an intermediate transfer roll. You may employ | adopt for the image forming apparatus which employ | adopted the body. The image forming apparatus employing the transfer mechanism of the present invention is not limited to the one described in the embodiment, and at least transfers the first toner image made of standard color toner from the holding body to the transfer body. Any other configuration may be used as long as the configuration is used.

(Modification 8)
In the embodiment, the functions of the control unit and the specifying unit are realized by the control circuit 140. However, the present invention is not limited to this. For example, the main control device already installed in the image forming apparatus 1 may be configured to realize the functions of the control unit and the specifying unit without providing the control circuit 140. In short, as long as the functions of the control means and the specifying means are realized, the operation subject may be any hardware or software.

(Modification 9)
In the embodiment, the pressing force of the primary transfer roll 110S is set lower than the pressing force of the primary transfer roll 110YMCK only during the period in which the primary transfer roll 110S transfers the second toner image. The pressing force of the primary transfer roll 110S is not limited to this, and the pressing force may be set low even in the period before and after transferring the second toner image.

(Modification 10)
In the embodiment, the adjusting unit 120 includes the pressing spring 122, the support plate 124, and the cam 126, but is not limited thereto. The adjusting means 120 may have any configuration as long as it adjusts at least the vertical position of the shaft portion 112.

  DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 4 ... Photosensitive drum, 10 ... Intermediate transfer belt, 100 ... Primary transfer mechanism, 110 ... Primary transfer roll, 112 ... Shaft part, 120 ... Adjustment means, 140 ... Control circuit

Claims (10)

The transfer body is pressed against the first holding body on which the first toner image representing the image is formed by the first color toner constituting the image to be output, and the first toner image is First transfer means for transferring to a transfer body;
The transfer body is pressed against a second holding body on which a second toner image is formed with a second color toner different from the first color toner, and the first toner image is transferred to the transfer body A second transfer means for transferring the second toner image to an area where the first toner image is to be transferred on the transfer body before being transferred to the body;
Adjusting the pressing force, the pressing force which the second transfer means presses the transfer medium to said second image holding member, the said first transfer means for pressing the transfer member to said first image holding member Adjusting means to
In addition to controlling the adjusting means to increase the pressing force with which the first transfer means presses the transfer body against the first image holding body, the second transfer means has the second image holding body. Control means for lowering the pressing force for pressing the transfer body and for making the first transfer means smaller than the pressing force for pressing the transfer body against the first image holding body ,
A transfer mechanism comprising: The control means includes
Only in the region of the transfer body where the first toner image is to be transferred , in addition to increasing the pressing force by the first transfer means, reducing the pressing force by the second transfer means , and The transfer mechanism according to claim 1, wherein the pressing force is smaller than the pressing force by the first transfer unit. The control means includes
When the type of transfer material on which the first toner image is transferred and fixed is predetermined , in addition to increasing the pressing force by the first transfer unit, the second transfer unit causes the second transfer unit to increase the pressing force. The transfer mechanism according to claim 1 , wherein the pressing force is lowered and is smaller than the pressing force by the first transfer unit. The control means includes
In addition to increasing the pressing force by the first transfer means when the line segment image included in the first toner image is a multi-color image using a plurality of colors of toner , the second transfer means transfer mechanism according to claim 1, wherein the lower the pressure, and is characterized in that smaller than the pressing force by the first transfer means by. The control means includes
When the ambient humidity measured by the measuring means is higher than the threshold value , in addition to increasing the pressing force by the first transfer means, the pressing force by the second transfer means is reduced, and the first transfer means The transfer mechanism according to claim 1, wherein the transfer force is smaller than the pressing force due to. First forming means for forming, on the first holding body, a first toner image representing the image by using the color toner constituting the image to be output;
Second forming means for forming a second toner image on the second holding body using a second color toner different from the first color toner;
The transfer mechanism according to any one of claims 1 to 5, which functions as a primary transfer unit that primarily transfers the first toner image and the second toner image to a transfer body;
Secondary transfer means for secondary transfer of the first toner image and the second toner image, which are primarily transferred to the transfer body by the transfer mechanism, onto a transfer material;
An image forming apparatus comprising: a fixing unit that fixes the first toner image and the second toner image secondarily transferred by the secondary transfer unit to the transfer material. Specifying means for specifying an area including a line segment image in the first toner image;
The image according to claim 6, wherein the second forming unit forms the second toner image at a position corresponding to the area specified by the specifying unit on the second image holding member. Forming equipment. The image forming apparatus according to claim 6, wherein the second toner image is a dot-like toner image arranged at a predetermined interval. The image forming apparatus according to claim 6, wherein the second toner image is a line-shaped toner image arranged at a predetermined interval. The image forming apparatus according to claim 6, wherein the second toner image is a toner image arranged in a lattice pattern.

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