JP2021081499A - Image forming apparatus - Google Patents

Abstract

To easily prevent, even when an endless intermediate transfer belt manufactured by extrusion molding is used, stick-slip vibration of the belt without newly adding a component, such as vibration prevention means, and easily prevent the generation of abnormal noise caused by the stick-slip vibration.SOLUTION: An image forming apparatus includes: an endless intermediate transfer belt that moves along a plurality of image forming units; a backup roller that is located on the upstream side of an image carrier located on the most upstream side in the direction of movement of the intermediate transfer belt, and changes the direction of movement of the intermediate transfer belt before and after winding; and a tension roller that is located on the upstream side of the backup roller. The arithmetic average roughness of an inner peripheral surface of the intermediate transfer belt is larger in the movement direction than that in a width direction of the intermediate transfer belt. The distance of movement of the intermediate transfer belt from the tension roller to the backup roller is 26 mm or more.SELECTED DRAWING: Figure 6

Description

The present invention relates to an electrophotographic image forming apparatus such as a copying machine, a printer, and a facsimile. In particular, after primary transferring a toner image formed on an image carrier to an intermediate transfer belt, the present invention further transfers the toner image from the intermediate transfer belt to a recording medium. The present invention relates to an intermediate transfer type image forming apparatus for secondary transfer.

Conventionally, various intermediate transfer type image forming devices have been proposed. In this type of image forming apparatus, when an endless intermediate transfer belt stretched by a plurality of support rollers repeatedly adheres to and slips on the support rollers (this phenomenon is also called a "stick slip phenomenon"). The intermediate transfer belt resonates between adjacent support rollers (stick slip vibration occurs), and this resonance causes abnormal noise. Further, the vibration of the intermediate transfer belt causes a positional shift or the like in the toner image transferred on the intermediate transfer belt, which causes deterioration of image quality.

Therefore, in Patent Document 1, the vibration generated in the belt member is suppressed by contacting the endless belt member with a contact roll as a vibration suppressing means. Further, in Patent Document 2, by providing a dynamic vibration absorber in a tension roller that applies tension to the intermediate transfer belt, vibration of a specific frequency by the dynamic vibration absorber is reduced and high image quality is achieved. Further, in Patent Document 3, the back surface of the belt stretched by a plurality of rollers is provided with an uneven shape, and the maximum dynamic friction coefficient of the back surface of the belt and the difference between the maximum dynamic friction coefficient and the minimum dynamic friction coefficient are appropriately defined. This suppresses the generation of abnormal noise when the belt is running.

Japanese Unexamined Patent Publication No. 2004-109872 Japanese Unexamined Patent Publication No. 2008-76499 Japanese Unexamined Patent Publication No. 2015-132799

However, in the configuration of Patent Document 1, since it is necessary to provide a contact roll as a means for suppressing the vibration of the belt member, the cost of the apparatus increases and the configuration of the apparatus becomes complicated. Similarly, Patent Document 2 also requires a dynamic vibration absorber that reduces vibrations of a specific frequency, which increases the cost of the device and complicates the configuration of the device. Further, if the tension roller is provided with a dynamic vibration absorber, the tension roller may become large and the intermediate transfer unit may become large. Therefore, it is not desirable to add new parts to suppress the vibration of the belt as in Patent Documents 1 and 2. Further, since the maximum dynamic friction coefficient is a value peculiar to the material and it is not easy to control it, it is practically difficult to suppress the generation of abnormal noise when the belt is running by the method of Patent Document 3. is there.

Further, as a method for producing an intermediate transfer belt, extrusion molding and centrifugal molding are known. Extrusion molding is a method of extruding molten resin from a die to manufacture a tubular belt. Centrifugal molding is a method of manufacturing an endless belt by supplying a resin solution to the inner surface of a rotating cylindrical mold.

When an endless belt is manufactured by extrusion molding, innumerable streaky concave scratches along the width direction of the belt are generated on the inner peripheral surface of the belt due to extrusion during manufacturing (the circumferential direction of the belt). No concave scratches along the belt). The concave scratches on the inner peripheral surface of the belt are formed on the belt with respect to the support roller (for example, the backup roller) located further upstream than the image carrier arranged on the most upstream side in the moving direction of the belt in the image forming apparatus. It is known that a stick-slip phenomenon occurs, and as a result, a belt resonates between a backup roller and a support roller (for example, a tension roller) located further upstream thereof, and an abnormal noise is generated.

On the other hand, it is known that when an endless belt is manufactured by centrifugal molding, the difference in surface unevenness on the inner surface of the belt becomes small in the width direction and the circumferential direction of the belt, and the abnormal noise becomes small. However, in centrifugal molding, the productivity of the belt is lower than that in extrusion molding, so that the unit price of the belt increases. Therefore, in terms of cost, it is desirable to use a belt manufactured by extrusion molding. Therefore, it is desired to realize a configuration using the belt to suppress stick-slip vibration and suppress the generation of abnormal noise. However, such a configuration has not yet been proposed, including the above-mentioned Patent Documents 1 to 3.

In view of the above problems, the present invention facilitates stick-slip vibration of the belt without adding new parts such as vibration suppressing means even when an endless intermediate transfer belt manufactured by extrusion molding is used. It is an object of the present invention to provide an image forming apparatus capable of suppressing the generation of abnormal noise caused by stick-slip vibration.

In order to achieve the above object, the image forming apparatus according to one aspect of the present invention includes an image carrier and a developing apparatus that supplies toner to the image carrier, and forms images of different colors. An endless intermediate transfer belt that is stretched by a plurality of support rollers and moves along the plurality of image forming portions, and an endless intermediate transfer belt that faces the image carrier with the intermediate transfer belt interposed therebetween. A plurality of primary transfer members that primarily transfer the toner image formed on the image carrier onto the intermediate transfer belt, and the toner image that is primarily transferred onto the intermediate transfer belt are secondarily transferred to a recording medium. It is provided with a next transfer member. The plurality of support rollers are the drive roller arranged to face the secondary transfer member with the intermediate transfer belt interposed therebetween, and the image carrier of the plurality of image forming portions, which is the most in the moving direction of the intermediate transfer belt. A backup roller located upstream of the image carrier located on the upstream side and changing the moving direction of the intermediate transfer belt before and after winding by winding the intermediate transfer belt around the peripheral surface, and a backup roller further than the backup roller. It includes a tension roller located on the upstream side and applying tension to the intermediate transfer belt. The arithmetic mean roughness of the inner peripheral surface of the intermediate transfer belt is larger in the moving direction perpendicular to the width direction than in the width direction of the intermediate transfer belt. The moving distance of the intermediate transfer belt from the tension roller to the backup roller is 26 mm or more.

In the intermediate transfer belt manufactured by extrusion molding, the arithmetic mean roughness of the inner peripheral surface is larger in the moving direction than in the width direction (because the extrusion direction at the time of manufacture corresponds to the width direction of the belt). In such a configuration using an intermediate transfer belt, if the moving distance of the intermediate transfer belt from the tension roller to the backup roller is 26 mm or more, even if the intermediate transfer belt slips on the peripheral surface of the backup roller and vibrates. , The vibration is dampened by the time it is transmitted to the tension roller. As a result, string vibration (stick slip vibration) is suppressed between the tension roller and the backup roller. Therefore, it is possible to suppress the generation of abnormal noise caused by the stick-slip vibration.

Therefore, even if the arithmetic mean roughness of the inner peripheral surface of the intermediate transfer belt is large in the moving direction as described above (even when an endless intermediate transfer belt manufactured by extrusion molding is used), the conventional method is used. It is possible to easily suppress the stick-slip vibration of the intermediate transfer belt without newly adding a component such as a vibration suppressing means. As a result, it is possible to easily suppress the generation of abnormal noise caused by the stick-slip vibration.

It is the schematic sectional drawing of the color printer which is an example of the image forming apparatus which concerns on one Embodiment of this invention. It is sectional drawing which shows the structure around the intermediate transfer unit mounted on the said color printer. It is a partial cross-sectional view which shows the laminated structure of the intermediate transfer belt which the said intermediate transfer unit has. It is explanatory drawing which shows typically the calculation method of the arithmetic mean roughness Ra. It is explanatory drawing which shows typically the calculation method of the maximum height Rz. It is explanatory drawing which enlarges and shows the vicinity of the backup roller on the upstream side in the said intermediate transfer unit. It is explanatory drawing which shows typically the positional relationship between the said backup roller and the said intermediate transfer belt. It is explanatory drawing which shows typically the change of the moving speed of the inner peripheral surface and the outer peripheral surface of the said intermediate transfer belt when the said intermediate transfer belt moves while winding around the peripheral surface of the said backup roller. It is a graph which shows the relationship between the moving distance of the said intermediate transfer belt from the tension roller of the said intermediate transfer unit to the said backup roller, and the level of the generated sound.

[Structure of image forming apparatus]
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view of a tandem color printer 100, which is an example of an image forming apparatus according to an embodiment of the present invention. In the main body of the color printer 100, four image forming portions Pa, Pb, Pc and Pd are arranged along the moving direction of the intermediate transfer belt 8 from the upstream side (left side in FIG. 1) to the downstream side (right side in FIG. 1). Are arranged in order. These image forming units Pa to Pd are provided corresponding to images of four different colors (yellow, cyan, magenta, and black), and are respectively charged, exposed, developed, and transferred to yellow and cyan, respectively. , Magenta, and black images are formed in sequence.

Photoreceptor drums 1a, 1b, 1c and 1d (image carriers) carrying visible images (toner images) of each color are arranged on these image forming portions Pa to Pd, respectively. The photoconductor drums 1a to 1d are, for example, organic photoconductors in which an organic photosensitive layer (OPC) is laminated on the outer peripheral surface of an aluminum drum tube, and are rotationally driven by a main motor (not shown). Further, in FIG. 1, an intermediate transfer belt 8 that rotates in the counterclockwise direction is provided. The intermediate transfer belt 8 moves along the image forming portions Pa to Pd (particularly along the photoconductor drums 1a to 1d) by the rotation of the drive roller 11. The drive roller 11 is rotationally driven by a belt drive motor 41 (see FIG. 2). Further, the secondary transfer roller 9 (secondary transfer member) is arranged at a position facing the drive roller 11 with the intermediate transfer belt 8 interposed therebetween.

When image data is input from a higher-level device such as a personal computer, first, the surfaces of the photoconductor drums 1a to 1d are uniformly charged by the charging devices 2a to 2d. Next, the exposure apparatus 5 irradiates light according to the image data to form an electrostatic latent image according to the image data on each of the photoconductor drums 1a to 1d. The developing devices 3a to 3d are filled with a predetermined amount of a two-component developer (hereinafter, also simply referred to as a developing agent) containing toners of each color of yellow, cyan, magenta, and black by toner containers 4a to 4d. The toners in the developer are supplied onto the photoconductor drums 1a to 1d by the developing devices 3a to 3d and are electrostatically adhered. As a result, a toner image corresponding to the electrostatic latent image formed by the exposure from the exposure apparatus 5 is formed.

The charging devices 2a to 2d have a charging roller 21 (see FIG. 2) that comes into contact with the photoconductor drums 1a to 1d to charge the surface of the photoconductor drums 1a to 1d. In the present embodiment, in order to reduce the amount of ozone generated and to reduce the cost of the charging voltage power supply (not shown), a charging voltage consisting of only a DC voltage is applied to the charging roller 21.

The developing devices 3a to 3d include a developing roller 30 (see FIG. 2) facing the photoconductor drums 1a to 1d. A two-component developer composed of a carrier and a toner is housed in the developing devices 3a to 3d, and the two-component developing agent is supplied to the developing roller 30 by a stirring and transporting member (not shown) and is placed on the developing roller 30. A magnetic brush is formed. Further, a developing voltage obtained by superimposing an AC voltage on a DC voltage is applied to the developing roller 30 from a developing voltage power supply (not shown).

When the developing roller 30 to which the developing voltage is applied rotates in the counterclockwise direction of FIG. 2, the magnetic brush supported on the surface of the developing roller 30 due to the potential difference between the developing potential and the potential of the exposed portion of the photoconductor drums 1a to 1d. The toner is supplied to the photoconductor drums 1a to 1d. The toner sequentially adheres to the exposed portion on the photoconductor drums 1a to 1d rotating in the clockwise direction, and the electrostatic latent image on the photoconductor drums 1a to 1d is developed into a toner image.

Then, an electric field is applied between the primary transfer rollers 6a to 6d and the photoconductor drums 1a to 1d by the primary transfer rollers 6a to 6d (primary transfer member) at a predetermined transfer voltage, and the electric field is applied on the photoconductor drums 1a to 1d. Yellow, cyan, magenta, and black toner images are primarily transferred onto the intermediate transfer belt 8. Toner and the like remaining on the surfaces of the photoconductor drums 1a to 1d after the primary transfer are removed by the cleaning devices 7a to 7d.

The cleaning devices 7a to 7d include a cleaning blade 71 (see FIG. 2) that removes toner remaining on the surfaces of the photoconductor drums 1a to 1d. As the cleaning blade 71, for example, a blade made of polyurethane rubber is used.

As shown in FIG. 1, the transfer paper P (recording medium) on which the toner image is transferred is housed in the paper cassette 16a arranged at the lower part of the color printer 100, or arranged on the side surface of the color printer 100. It is placed on the bypass tray 16b. The transfer paper P in the paper cassette 16a or on the bypass tray 16b passes through the paper transport path 17 at a predetermined timing via the paper feed roller 12a and the resist roller pair 12b, and the nip of the secondary transfer roller 9 and the intermediate transfer belt 8. It is conveyed to a section (secondary transfer nip section N, see FIG. 2). The transfer paper P on which the toner image is secondarily transferred is conveyed to the fixing portion 13. Toner and the like remaining on the surface of the intermediate transfer belt 8 are removed by the belt cleaning unit 19.

The transfer paper P conveyed to the fixing portion 13 is heated and pressurized by the fixing roller pair 13a to fix the toner image on the surface of the transfer paper P, and a predetermined full-color image is formed. The transfer paper P on which the full-color image is formed is directly (or after being distributed to the reversing transport path 18 by the branch portion 14 and the images are formed on both sides) from the paper transport path 17 via the discharge roller pair 15 and the discharge tray 20. Is discharged to.

Further, the image density sensor 45 is arranged to face the intermediate transfer belt 8 at a position further downstream than the photoconductor drum 1d on the most downstream side. As the image density sensor 45, an optical sensor including a light emitting element made of an LED or the like and a light receiving element made of a photodiode or the like is generally used. When measuring the amount of toner adhering to the intermediate transfer belt 8, when the measurement light is irradiated from the light emitting element to each reference image formed on the intermediate transfer belt 8, the measurement light is the light reflected by the toner and the belt surface. It is incident on the light receiving element as light reflected by.

The reflected light from the toner and the belt surface includes specularly reflected light and diffusely reflected light. The specularly reflected light and the diffusely reflected light are separated by a polarization separation prism and then incident on separate light receiving elements. Each light receiving element photoelectrically converts the specularly reflected light and the diffusely reflected light received and outputs an output signal to a control unit (not shown). Then, the amount of toner is detected from the characteristic change of the output signals of the specularly reflected light and the diffusely reflected light, and the density correction (calibration) is performed for each color by adjusting the characteristic value of the developing voltage in comparison with a predetermined reference density. ) Is performed.

FIG. 2 is a cross-sectional view showing the configuration around the intermediate transfer unit 31 mounted on the color printer 100 of the present embodiment. The intermediate transfer unit 31 is a primary transfer roller that comes into contact with the photoconductor drums 1a to 1d via the intermediate transfer belt 8 spanned by the tension roller 10 on the upstream side and the drive roller 11 on the downstream side, and the intermediate transfer belt 8. It has 6a to 6d, backup rollers 22a and 22b, a belt cleaning unit 19, and a roller attachment / detachment mechanism 32. A belt drive motor 41 is connected to the drive roller 11 via a gear train (not shown).

The tension roller 10, the drive roller 11, and the backup rollers 22a and 22b each constitute a plurality of support rollers SR for tensioning the intermediate transfer belt 8. Further, it is assumed that the backup rollers 22a and 22b are rollers located on the upstream side and the downstream side of the intermediate transfer belt 8 in the moving direction, respectively. The backup roller 22a is arranged to ensure (stable) contact the intermediate transfer belt 8 with the photoconductor drum 1a located on the most upstream side from the horizontal direction. The backup roller 22b is arranged to move the intermediate transfer belt 8 whose contact with the photoconductor drum 1d has been released in the horizontal direction, and then change the moving direction toward the drive roller 11.

FIG. 3 is a partial cross-sectional view showing the laminated structure of the intermediate transfer belt 8. The intermediate transfer belt 8 is, for example, a conductive belt having a three-layer structure including a base material layer 81, an elastic layer 82, and a coat layer 83, and the coat layer 83 comes into contact with the photoconductor drums 1a to 1d. The base material layer 81 serves as a basic material constituting the intermediate transfer belt 8 and imparts a predetermined rigidity, and at the same time, withstands the processing conditions when laminating the elastic layer 82 and the coat layer 83, and further manufactures the intermediate transfer belt 8. In this case, it is preferable that the product is excellent in processing workability, heat resistance, slipperiness, and other physical properties. As the material of such a base material layer 81, for example, PVDF (polyvinylidene fluoride) is preferably used.

The elastic layer 82 is provided to impart elasticity to the intermediate transfer belt 8 to prevent an image hollow phenomenon due to stress concentration. As the material of the elastic layer 82, for example, hydrin rubber, chloroprene rubber, thermoplastic polyurethane rubber called TPU (Thermoplastic Polyurethane), or the like is used. The coat layer 83 is provided to protect the elastic layer 82. As the material of the coat layer 83, acrylic, silicon, fluororesin (for example, polytetrafluoroethylene (PTFE)) or the like is used. The intermediate transfer belt 8 can be obtained by extrusion molding of three layers (base material layer 81, elastic layer 82, and coat layer 83) by coextrusion.

In addition, the intermediate transfer belt 8 may have a structure that does not include the base material layer 81 or a structure that includes other layers other than the base material layer 81, the elastic layer 82, and the coat layer 83, and is not limited to the laminated structure. A single-layer structure having only the elastic layer 82 may be used.

As shown in FIG. 2, the belt cleaning unit 19 includes a fur brush 23, a recovery roller 25, a scraper 27, and a transport spiral 29 in a housing. The fur brush 23 is arranged to face the tension roller 10 via the intermediate transfer belt 8. The fur brush 23 rotates in the counter direction (counterclockwise direction in FIG. 2) with respect to the moving direction of the intermediate transfer belt 8, so that foreign matter such as toner and paper dust remaining on the intermediate transfer belt 8 (hereinafter referred to as “foreign matter”) remains on the intermediate transfer belt 8. (Toner, etc.) is scraped off. The brush portion of the fur brush 23 that comes into contact with the recovery roller 25 is formed of conductive fibers having an electric resistance value of about 1 to 900 MΩ.

The recovery roller 25 collects the toner and the like adhering to the fur brush 23 by rotating in the direction opposite to the fur brush 23 (clockwise in FIG. 2) while contacting the surface of the fur brush 23. A belt cleaning voltage power supply 55 is connected to the recovery roller 25, and a cleaning voltage having a polarity opposite to that of the toner (here, negative electrode) is applied when cleaning the intermediate transfer belt 8. Further, the tension roller 10 is grounded to the ground. As a result, the toner or the like scraped from the intermediate transfer belt 8 is electrically and mechanically recovered by the brush portion of the fur brush 23, and further electrically transferred to the recovery roller 25. The transport spiral 29 transports the toner or the like scraped off from the recovery roller 25 by the scraper 27 to a waste toner recovery container (not shown) outside the housing.

The roller contact / disengagement mechanism 32 corresponds to a four-color pressing state (color printing mode) in which four primary transfer rollers 6a to 6d are pressed against the photoconductor drums 1a to 1d via an intermediate transfer belt 8 and black. Only the primary transfer roller 6d is pressed against the photoconductor drum 1d via the intermediate transfer belt 8 in a three-color separation state (monochrome printing mode), and all four primary transfer rollers 6a to 6d are removed from the intermediate transfer belt 8. It is possible to switch between the four-color separation state (maintenance mode) and the separation state. The four-color separation state is used when performing maintenance work such as replacement of a unit (for example, a process unit including a photoconductor drum) included in the image forming unit Pa or the like.

[Countermeasures against abnormal noise]
Next, measures for suppressing the generation of abnormal noise caused by the stick-slip vibration of the intermediate transfer belt 8 will be described.

As described above, when an endless belt is manufactured by extrusion molding, concave scratches are generated on the inner peripheral surface of the belt, and these concave scratches increase the stick slip vibration of the belt and cause abnormal noise. It's a street. The depth of the concave scratch can be evaluated by substituting the surface roughness such as the arithmetic mean roughness Ra and the maximum height Rz.

Here, FIG. 4 is an explanatory diagram schematically showing a calculation method of the arithmetic mean roughness Ra. The arithmetic mean roughness Ra is a value defined by JIS B0601-1994 or JIS B0601-2001. That is, the arithmetic average roughness Ra is obtained by extracting only the reference length L from the roughness curve in the direction of the average line m, the X axis in the direction of the average line m of the extracted portion, and the Y axis in the direction of the longitudinal magnification. When the roughness curve is expressed by y = f (x), the value obtained by the formula in the figure is expressed in micrometers (μm). JIS is an abbreviation for Japanese Industrial Standards.

On the other hand, FIG. 5 is an explanatory diagram schematically showing a method of calculating the maximum height Rz. The maximum height Rz is a value defined in JIS B 0601-2001. That is, for the maximum height Rz, only the reference length L is extracted from the roughness curve in the direction of the average line m, and the distance between the peak line and the valley bottom line of the extracted portion is measured in the direction of the vertical magnification of the roughness curve. However, this value is expressed in micrometers (μm).

As a result of various studies on the relationship between the abnormal noise caused by the stick-slip vibration of the belt and the surface roughness of the inner peripheral surface of the belt, it was found that the arithmetic average roughness Ra has the highest correlation with the above abnormal noise. .. Furthermore, the arithmetic mean roughness Ra in the circumferential direction of the belt (here, the average value when the belt is divided into 18 equal parts in the circumferential direction and Ra at 18 points is measured) is reduced to less than 0.32 μm. If it was kept small, the sound level of the generated abnormal noise was allowed. However, when the surface roughness is controlled so that Ra <0.32 μm, the yield is poor in the production of the belt, and Ra of 0.6 μm at the maximum may be generated.

On the other hand, it occurs when the surface roughness in the width direction (direction perpendicular to the circumferential direction) of the belt is increased to the same level as the circumferential direction (when the difference between the surface roughness in the circumferential direction and the width direction is reduced). It is known that the level of abnormal noise becomes smaller. It is considered that this is because the vibration source of the roller (the contact portion with the belt on the roller surface) is finely dispersed in the circumferential direction and the width direction, so that the vibration is reduced as a whole. Such belts can be manufactured by using centrifugation. However, since centrifugal molding is less productive than extrusion molding, the unit price of the belt increases in centrifugal molding.

In consideration of the above points, in the present embodiment, the intermediate transfer belt 8 is a belt in which concave scratches are formed in the width direction by extrusion molding (a belt having a lower surface roughness in the width direction than the circumferential direction) and in the circumferential direction. A belt having an arithmetic mean roughness Ra of 0.32 μm or more was used. In such an intermediate transfer belt 8, it can be said that the arithmetic mean roughness Ra of the inner peripheral surface 8a (see FIG. 6) is larger in the circumferential direction (movement direction) than in the width direction. Then, a configuration capable of suppressing the generation of abnormal noise caused by the stick-slip vibration of the intermediate transfer belt 8 was examined.

The tension roller 10 and the backup rollers 22a and 22b are metal rollers formed by anodizing an aluminum core metal, respectively, while the drive roller 11 is an elastic roller having an elastic layer. Therefore, even if the intermediate transfer belt 8 slips and vibrates between the backup roller 22b and the drive roller 11 located on the downstream side in the moving direction of the intermediate transfer belt 8, the elastic layer of the drive roller 11 is used. Since vibration is absorbed and attenuated, abnormal noise is unlikely to occur. On the other hand, since the backup roller 22a and the tension roller 10 located on the upstream side in the moving direction are both metal rollers and do not have an elastic layer that absorbs vibration, the sticks described above are located between these two metal rollers. Slip vibration is likely to occur. Therefore, in the present embodiment, a configuration capable of suppressing the generation of abnormal noise due to the stick-slip vibration generated between the tension roller 10 and the backup roller 22a on the upstream side has been examined.

FIG. 6 shows an enlarged view of the vicinity of the backup roller 22a of the intermediate transfer unit 31. The backup roller 22a is located upstream of the photoconductor drums 1a located on the most upstream side in the moving direction of the intermediate transfer belt 8 among the photoconductor drums 1a to 1d of the plurality of image forming portions Pa to Pd. .. Then, the backup roller 22a changes the moving direction of the intermediate transfer belt 8 before and after winding by winding the intermediate transfer belt 8 around the peripheral surface. Due to the arrangement of the backup roller 22a, the intermediate transfer belt 8 moves horizontally toward between the photoconductor drum 1a and the primary transfer roller 6a when the intermediate transfer belt 8 is separated from the peripheral surface of the backup roller 22a.

Further, the tension roller 10 is located further upstream than the backup roller 22a, and is urged by a tension spring (not shown) on the side opposite to the drive roller 11 (on the left side in FIG. 6). As a result, a predetermined tension is applied to the intermediate transfer belt 8 and the intermediate transfer belt 8 is stretched.

Here, the angle formed by the intermediate transfer belt 8 and the horizontal plane S between the tension roller 10 and the backup roller 22a is θ (°). The above angle θ is the angle formed by the moving direction of the intermediate transfer belt 8 toward the contact position (corresponding to the point P1 described later) of the peripheral surface of the backup roller 22a, which is sent out from the tension roller 10, and the horizontal plane S. It can be said that. Further, the horizontal plane S is a plane perpendicular to the facing direction (vertical direction in FIG. 6) between the photoconductor drum 1a located on the most upstream side and the primary transfer member 6a in the above-mentioned four-color pressing state (color printing mode). equal. In the present embodiment, the positional relationship between the tension roller 10 on which the intermediate transfer belt 8 is stretched and the backup roller 22a is set so that the angle θ is 25 ° or less. As described above, since the backup roller 22a is arranged to bring the intermediate transfer belt 8 into contact with the photoconductor drum 1a from the horizontal direction, θ> 0 °.

Further, the moving distance of the intermediate transfer belt 8 from the tension roller 10 to the backup roller 22a is Lb (mm). The moving distance Lb is defined as P3 at a point where the intermediate transfer belt 8 is sent out from the tension roller 10 (a point where the intermediate transfer belt 8 is separated) in a plane perpendicular to the rotation axis of the tension roller 10 or the backup roller 22a. Between points P3 and P1 when the point at which the intermediate transfer belt 8 sent out from the tension roller 10 first abuts on the peripheral surface of the backup roller 22a (the point at which the intermediate transfer belt 8 begins to wind) is P1. Is equal to the distance of.

When the moving distance Lb is long, even if the intermediate transfer belt 8 slips on the peripheral surface of the backup roller 22a and vibrates, the vibration is transmitted from the point P1 (vibration point) of the backup roller 22a to the tension roller 10. Decays to. As a result, the string vibration between the tension roller 10 and the backup roller 22a, that is, the stick slip vibration of the intermediate transfer belt 8 is suppressed. As a result, it is possible to suppress the generation of abnormal noise caused by the stick-slip vibration of the intermediate transfer belt 8. From the examination results in the examples described later, it was confirmed that the generation of abnormal noise can be suppressed if Lb ≧ 26 mm.

Therefore, even if the arithmetic average roughness Ra of the inner peripheral surface 8a of the intermediate transfer belt 8 is larger in the moving direction than in the width direction as in the present embodiment, in other words, the intermediate transfer belt 8 is extruded as the intermediate transfer belt 8. Even in the configuration using the manufactured endless belt, the stick-slip vibration of the intermediate transfer belt 8 can be suppressed without newly adding parts such as vibration suppressing means. That is, with a simple configuration in which the moving distance Lb is set to 26 mm or more, the stick-slip vibration of the intermediate transfer belt 8 can be easily suppressed without adding new parts. As a result, the generation of abnormal noise caused by the stick-slip vibration can be easily suppressed.

Further, since it is not necessary to add parts such as vibration suppressing means, it is possible to reduce the cost of the apparatus, simplify the configuration of the apparatus, and reduce the size of the intermediate transfer unit 31 as compared with the configuration in which such parts are provided. it can. Further, by setting the angle θ, the stick-slip vibration of the intermediate transfer belt 8 can be suppressed regardless of the material of the intermediate transfer belt 8 used, and the generation of abnormal noise can be suppressed.

In particular, from the viewpoint of suppressing the string vibration of the intermediate transfer belt 8 to be less and suppressing the generation of abnormal noise due to the stick slip vibration, the moving distance Lb is preferably 30 mm or more, and is 40 mm or more. Is more desirable. Further, when the moving distance Lb becomes large, the tension roller 10 and the backup roller 22a are arranged apart from each other, so that the intermediate transfer unit 31 becomes large and the color printer 100 becomes large. Therefore, from the viewpoint of miniaturizing the intermediate transfer unit 31, the moving distance Lb is preferably 69 mm or less, more preferably 60 mm or less, and even more preferably 50 mm or less. The appropriate range of the moving distance Lb can be defined by a combination of any of the above-mentioned lower limit and any of the upper limit.

Further, FIG. 7 schematically shows the positional relationship between the backup roller 22a and the intermediate transfer belt 8. In the plane perpendicular to the rotation axis of the backup roller 22a, the point at which the intermediate transfer belt 8 sent out from the tension roller 10 first abuts on the peripheral surface of the backup roller 22a is designated as P1 as in FIG. Let P2 be the point at which the contact (wrapping) with the peripheral surface of 8 is released. In this case, between the points P1 and P2 on the peripheral surface of the backup roller 22a, an area around which the intermediate transfer belt 8 is wound is shown on the peripheral surface of the backup roller 22a. From the figure, it can be seen that the above angle θ is equal to the winding angle θ'corresponding to the central angle of the region where the intermediate transfer belt 8 is wound around the peripheral surface of the backup roller 22a. From FIG. 7, it can be said that the above-mentioned angle θ is an angle formed by the tangent plane 8S of the intermediate transfer belt 8 and the horizontal plane S at the point P1 on the peripheral surface of the backup roller 22a.

Further, FIG. 8 schematically shows a change in the moving speeds of the inner peripheral surface 8a and the outer peripheral surface 8b of the intermediate transfer belt 8 when the intermediate transfer belt 8 moves while being wound around the peripheral surface of the backup roller 22a. .. The moving speeds of the inner peripheral surface 8a and the outer peripheral surface 8b before the intermediate transfer belt 8 is wound around the peripheral surface of the backup roller 22a are set to V2a (mm / s), respectively. Further, the moving speeds of the inner peripheral surface 8a and the outer peripheral surface 8b after the winding of the intermediate transfer belt 8 around the peripheral surface of the backup roller 22a is released are set to V2b (mm / s), respectively. Further, the moving speeds of the inner peripheral surface 8a and the outer peripheral surface 8b in a state where the intermediate transfer belt 8 is wound around the peripheral surface of the backup roller 22a are set to V1 (mm / s) and V3 (mm / s), respectively. In addition, V2a = V2b, and V2a and V2b are collectively referred to as V2.

As shown in the figure, the moving speeds of the inner peripheral surface 8a and the outer peripheral surface 8b of the intermediate transfer belt 8 when the intermediate transfer belt 8 moves while being wound around the peripheral surface of the backup roller 22a are V3> V2> V1. Relationship is established. When the thickness of the intermediate transfer belt 8 is constant and the outer diameter of the backup roller 22a is constant, the larger the winding angle θ', the larger the difference between V1 and V3, and the larger the difference between V1 and V2. .. The larger the difference between V1 and V2, the easier it is for the intermediate transfer belt 8 to slip with respect to the peripheral surface of the backup roller 22a, and as a result, the stick-slip vibration of the intermediate transfer belt 8 tends to occur. As described above, since the winding angle θ'is equal to the angle θ, it can be said that the larger the angle θ, the larger the difference between V1 and V2, and the stick-slip vibration of the intermediate transfer belt 8 is likely to occur.

In the present embodiment, by reducing the angle θ to 25 ° or less, the intermediate transfer belt 8 comes into contact with the peripheral surface of the backup roller 22a at an angle close to horizontal. As a result, the moving speed V1 of the inner peripheral surface 8a when the intermediate transfer belt 8 is in contact with the peripheral surface of the backup roller 22a (when it is wound) and the moving speed V2 of the inner peripheral surface 8a when it is not in contact with each other. The difference between the two can be reduced to prevent the intermediate transfer belt 8 from slipping on the peripheral surface of the backup roller 22a. As a result, the stick-slip vibration of the intermediate transfer belt 8 can be further suppressed, and the generation of abnormal noise caused by the stick-slip vibration can be further suppressed. As the angle θ approaches 0 °, the difference between V1 and V2 approaches 0, and slipping of the intermediate transfer belt 8 is less likely to occur, so that the effect of suppressing stick slip vibration becomes higher.

Further, even if the arithmetic mean roughness Ra in the moving direction on the inner peripheral surface 8a of the intermediate transfer belt 8 exceeds 0.6 μm, by setting the moving distance Lb to 26 mm or more, the stick slip vibration of the intermediate transfer belt 8 and It has the effect of suppressing the generation of abnormal noise, but in particular, when the arithmetic mean roughness Ra in the moving direction is 0.6 μm or less, the stick-slip vibration of the intermediate transfer belt 8 is set by setting the moving distance Lb. The effect of suppressing the noise is enhanced, which makes it possible to surely suppress the generation of abnormal noise.

Further, from the viewpoint of suppressing the stick slip vibration and the generation of abnormal noise of the intermediate transfer belt 8, it is desirable that the arithmetic average roughness Ra in the moving direction on the inner peripheral surface 8a of the intermediate transfer belt 8 is small, but as described above. When Ra <0.32 μm, Ra is too small, and it becomes difficult to control such surface roughness in the production of the intermediate transfer belt 8. By using the intermediate transfer belt 8 having the arithmetic mean roughness Ra in the moving direction of 0.32 μm or more, the surface roughness can be easily controlled, and the present embodiment described above with the configuration using such the intermediate transfer belt 8. The effect of the morphology can be obtained.

Further, in the present embodiment, the intermediate transfer belt 8 has an elastic layer 82. In this configuration, the vibration generated by the intermediate transfer belt 8 can be absorbed and damped by the elastic layer 82. As a result, the stick-slip vibration of the intermediate transfer belt 8 can be further suppressed, and the generation of abnormal noise due to the stick-slip vibration can be further suppressed.

Further, since the tension roller 10 and the backup roller 22a are both metal rollers and do not have an elastic layer that absorbs vibration, the intermediate transfer belt 8 resonates between these two metal rollers to cause stick-slip vibration. It will be easier. Therefore, by defining the moving distance Lb of the intermediate transfer belt 8 between these two metal rollers, the effect of the present embodiment that suppresses the generation of stick-slip vibration and abnormal noise can be surely obtained.

〔Example〕
Hereinafter, the movement distance Lb was changed according to the configuration of FIG. 6, and the state of generation of abnormal noise caused by the stick-slip vibration of the intermediate transfer belt 8 was specifically investigated. The results are shown below.

FIG. 9 shows the moving distance Lb (mm) of the intermediate transfer belt 8 from the tension roller 10 to the backup roller 22a, and the sound level generated in the vicinity of the backup roller 22a when the intermediate transfer belt 8 is moved (circulated). It shows the result of investigating the relationship between. Here, the moving distance Lb was changed between 22 mm and 69 mm. The above sound level is obtained for each frequency obtained when the sound generated near the backup roller 22a is detected by a sensor and the detection signal is analyzed by an FFT (Fast Fourie Transform) with a Fourier transform analyzer. Corresponds to the maximum value of the amplitude of.

The other conditions are as follows.
-Intermediate transfer belt: Belt with elastic layer (manufactured by Okura Industrial Co., Ltd., thickness 0.37 mm)
-Belt with elastic layer: base material (PVDF) + elastic layer (TPU) + coat layer (PTFE)
・ Intermediate transfer belt inner peripheral surface arithmetic average roughness Ra (moving direction): 0.6 μm
-Intermediate transfer belt inner peripheral surface arithmetic average roughness Ra (width direction): 0.1 μm
-Ra measurement method: Using a surface roughness measuring machine (Mitutoyo Co., Ltd., SJ210), 18 points of Ra were measured in the moving direction or the width direction of the inner peripheral surface of the intermediate transfer belt, and the average value was adopted.
-Backup roller: Outer diameter 13 mm (aluminum core metal + alumite processing)
-Tension roller: outer diameter 24 mm (aluminum core metal + alumite processing)
・ Tension spring: 60N (horizontal direction)
・ Angle θ: 25 °
・ Intermediate transfer belt transfer speed: 130 mm / s

Assuming that the sound level is 4 or less and the OK level (range in which abnormal noise can be tolerated), it can be seen from FIG. 9 that the generated abnormal noise can be tolerated if Lb ≧ 26 mm. Further, as the Lb becomes longer, the generated abnormal noise becomes smaller. Therefore, from the viewpoint of suppressing the generation of the abnormal noise, it is desirable that the Lb is 30 mm or more, and more preferably 40 mm or more.

Further, if Lb = 69 mm, the abnormal noise is the smallest, which is most desirable from the viewpoint of suppressing the generation of the abnormal noise. However, if the Lb is too long, the tension roller 10 and the backup roller 22a are arranged apart from each other. As a result, the intermediate transfer unit 31 may become large. Therefore, from the viewpoint of avoiding an increase in the size of the intermediate transfer unit 31, it is desirable that Lb ≦ 69 mm, more preferably Lb ≦ 60 mm, and even more preferably Lb ≦ 50 mm.

The appropriate range of Lb may be set by appropriately selecting the upper limit and the lower limit in consideration of the allowable range of the generated sound level and the size required for the intermediate transfer unit 31.

It was experimentally confirmed that even when the outer diameter of the backup roller is other than 13 mm, the same result as in this example can be obtained as long as it is within the range of 10 mm or more and 18 mm or less. Further, it was experimentally confirmed that even when the thickness of the intermediate transfer belt is other than 0.37 mm, the same result as in this example can be obtained as long as it is within the range of 0.2 mm or more and 0.5 mm or less.

Further, it was experimentally confirmed that, for example, when the angle θ was set to 20 °, the level of the generated abnormal noise was further reduced. Further, it was experimentally confirmed that when Lb ≧ 26 mm, the level of the generated abnormal noise becomes small even when an intermediate transfer belt in which Ra in the moving direction of the inner peripheral surface is, for example, 0.7 μm is used.

The present invention can be used in an intermediate transfer type image forming apparatus using an intermediate transfer belt.

1a-1d Photoreceptor drum (image carrier)
3a to 3d developing equipment 6a to 6d primary transfer roller (primary transfer member)
8 Intermediate transfer belt 8a Inner peripheral surface 9 Secondary transfer roller (secondary transfer member)
10 Tension roller 11 Drive roller 22a Backup roller 82 Elastic layer 100 Color printer (image forming device)
Pa to Pd image forming part SR support roller

Claims (11)

A plurality of image forming portions having an image carrier and a developing device for supplying toner to the image carrier and forming images of different colors.
An endless intermediate transfer belt that is stretched by a plurality of support rollers and moves along the plurality of image forming portions.
A plurality of primary transfer members that are arranged so as to face the image carrier with the intermediate transfer belt interposed therebetween and that primary transfer the toner image formed on the image carrier onto the intermediate transfer belt.
An image forming apparatus comprising a secondary transfer member for secondary transfer of the toner image primary transfer on the intermediate transfer belt to a recording medium.
The plurality of support rollers
A drive roller arranged so as to face the secondary transfer member with the intermediate transfer belt interposed therebetween.
Among the image carriers of the plurality of image forming portions, the intermediate transfer belt is located on the upstream side of the image carrier located on the most upstream side in the moving direction of the intermediate transfer belt, and the intermediate transfer belt is wound around the peripheral surface. A backup roller that changes the movement direction of the intermediate transfer belt before and after winding,
A tension roller located further upstream than the backup roller and applying tension to the intermediate transfer belt, and the like.
The arithmetic mean roughness of the inner peripheral surface of the intermediate transfer belt is larger in the moving direction perpendicular to the width direction than in the width direction of the intermediate transfer belt.
An image forming apparatus characterized in that the moving distance of the intermediate transfer belt from the tension roller to the backup roller is 26 mm or more. The image forming apparatus according to claim 1, wherein the moving distance is 30 mm or more. The image forming apparatus according to claim 1 or 2, wherein the moving distance is 40 mm or more. The image forming apparatus according to any one of claims 1 to 3, wherein the moving distance is 69 mm or less. The image forming apparatus according to any one of claims 1 to 4, wherein the moving distance is 60 mm or less. The image forming apparatus according to any one of claims 1 to 5, wherein the moving distance is 50 mm or less. The image forming apparatus according to any one of claims 1 to 6, wherein the angle formed by the intermediate transfer belt and the horizontal plane between the tension roller and the backup roller is 25 ° or less. When the arithmetic mean roughness in the moving direction on the inner peripheral surface of the intermediate transfer belt is expressed by Ra,
The image forming apparatus according to any one of claims 1 to 7, wherein Ra ≦ 0.6 μm. The image forming apparatus according to claim 8, wherein Ra ≧ 0.32 μm. The image forming apparatus according to any one of claims 1 to 9, wherein the intermediate transfer belt has an elastic layer. The image forming apparatus according to any one of claims 1 to 10, wherein the tension roller and the backup roller are both metal rollers.

Images