Patent Application
20220113658
The present disclosure relates to an image forming apparatus performing an electrophotographic method such as a laser printer, a copying machine, or a facsimile.
A conventional image forming apparatus adopting an electrophotographic method includes a drum-shaped electrophotographic photosensitive member (hereinbelow, referred to as a photosensitive member) for bearing a toner image and forms an image on a transfer material such as paper or an overhead projector (OHP) sheet via a charge process, an exposure process, a development process, a transfer process, and a fixing process. In the transfer process, the image forming apparatus electrostatically transfers the toner image from the photosensitive member to the transfer material by applying a voltage to a transfer member facing the photosensitive member. In recent image forming apparatuses, contact type transfer members which come into contact with photosensitive members are often used, and generation of ozone can be suppressed by adopting the contact type transfer member.
In a case where the contact type transfer member is used, at the time of transferring a toner image from a photosensitive member to a transfer material sandwiched between the photosensitive member and a transfer member, a current is concentrated and flows in an end portion at which the transfer material does not intervene in a width direction of the transfer material orthogonal to a conveyance direction of the transfer material in some cases. This is because a resistance is higher in a position in which the transfer material intervenes than in a position in which the transfer material does not intervene in an area in which the photosensitive member and the transfer member face each other in the width direction of the transfer material. If the current is concentrated in the end portion in which the transfer material does not intervene, an electrostatic history is generated at an end portion of the photosensitive member during the transfer process, which makes it easier for toner to excessively adhere to the end portion of the photosensitive member, and there is a risk that an end portion of the transfer material is soiled during image forming.
According to Japanese Patent Application Laid-Open No. 10-268671, a contact type transfer member is discussed which is configured with a conductive shaft and a semiconductive member surrounding the conductive shaft. According to Japanese Patent Application Laid-Open No. 10-268671, a high resistance member is provided between the conductive shaft and the semiconductive member at an end portion of a transfer member in a width direction of a transfer material in order to suppress occurrence of the above-described soiling in the end portion.
In a configuration of the transfer member in which the high resistance member is provided between the conductive shaft and the semiconductive member as discussed in Japanese Patent Application Laid-Open No. 10-268671, there is a concern that a manufacturing process of the transfer member is complicated because the high resistance member is provided.
The present disclosure provides for a contact type transfer member which is used in an image forming apparatus and can suppress occurrence of soiling in an end portion in a width direction of a transfer material.
According to an aspect of the present disclosure, an image forming apparatus includes an image bearing member configured to bear a toner image, and a transfer member configured to transfer the toner image born by the image bearing member to a transfer material in a transfer portion which faces the image bearing member, the transfer member comprising a rotatable conductive shaft and an elastic portion which covers a periphery of the shaft, wherein, when the shaft is viewed from a direction orthogonal to a rotation axis direction of the shaft, the shaft includes a first contact portion which is provided on an end portion side of the elastic portion in the rotation axis direction and in which the shaft and the elastic portion are in contact with each other and a second contact portion which is provided on a more center side of the transfer portion than the first contact portion in the rotation axis direction and in which the shaft and the elastic portion are in contact with each other, the first contact portion is provided on a more end portion side of the elastic portion than an end portion of a transfer material having a maximum size which can pass through the transfer portion, the transfer member includes a void between the first contact portion and the second contact portion in the rotation axis direction, and the void is arranged on a more center side of the transfer portion than the end portion of the transfer material having the maximum size.
Further features of the present disclosure will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
Various exemplary embodiments of the present disclosure will be described below with reference to the attached drawings. However, components described in the following exemplary embodiments can be appropriately modified in their dimensions, materials, shapes, and relative arrangement considering the configuration and various conditions of an apparatus to which the present disclosure is applied, and they are not to be construed as intended to restrict the scope of the present disclosure.
The charging roller 2 abuts on and can charge the photosensitive drum 1 to a uniform potential (approximately −600 V according to the present exemplary embodiment) by being applied with a voltage from a charging power supply E1. The development unit 4 stores toner, and the development roller 4a is applied with a voltage having a polarity opposite to a normal charge polarity of the toner from a non-illustrated development power supply and thus can bear the toner stored in the development unit 4
A transfer roller 5 as a contact type transfer member which forms a transfer portion Nt by coming into contact with the photosensitive drum 1 is arranged at a position facing the photosensitive drum 1. The transfer roller 5 includes a core metal and an elastic member such as rubber which is conductive and is formed on a surface of the core metal, and is connected to a transfer power supply E2. A configuration of the transfer roller 5 according to the present exemplary embodiment is described in detail below.
In a conveyance direction of a transfer material P, a sheet feeding cassette 50 which stores the transfer material P such as paper or an overhead projector (OHP) sheet, a feeding unit 51 which feeds the transfer material P stored in the sheet feeding cassette 50 to the transfer portion Nt, and a conveyance roller 52 as a conveyance member are arranged on an upstream side of the transfer portion Nt.
A fixing unit 60 including a heating member 61 and a pressing member 62 is arranged on a downstream side of the transfer portion Nt in the conveyance direction of the transfer material P. Further, a sheet discharge tray 54 which loads the transfer material P on which an image is formed and which is discharged from the image forming apparatus 100 thereon and a sheet discharge roller 53 which discharges the transfer material P to the sheet discharge tray 54 are arranged on the downstream side of the fixing unit 60.
If a controller circuit (not illustrated) receives an image signal, and an image forming operation is started, the photosensitive drum 1 is rotationally driven and uniformly charged to a predetermined potential by the charging roller 2 which is applied with a voltage having a predetermined polarity (a negative polarity according to the present exemplary embodiment) in a rotation process. Then, an electrostatic latent image corresponding to a target image is formed on a surface of the photosensitive drum 1 by being subjected to exposure according to the image signal by the exposure unit 3. The electrostatic latent image is developed at a development position by the development roller 4a bearing the toner and is visualized as a toner image by the photosensitive drum 1. According to the present exemplary embodiment, the normal charge polarity of the toner stored in the development unit 4 is the negative polarity, and reversal development is performed on the electrostatic latent image with the toner charged to a polarity same as the charge polarity of the photosensitive drum 1 by the charging roller 2. However, the present disclosure can also be applied to an image forming apparatus which positively develops an electrostatic latent image with toner charged in a polarity opposite to the charge polarity of the photosensitive drum 1 without being limited to the above-described configuration.
A voltage having a polarity (the positive polarity according to the present exemplary embodiment) opposite to the normal charge polarity of the toner is applied from the transfer power supply E2 to the transfer roller 5 (the transfer member), and thus the toner image formed on the photosensitive drum 1 is transferred to the transfer material P fed from the sheet feeding cassette 50 at the transfer portion Nt. The transfer roller 5 is urged toward the photosensitive drum 1 by a non-illustrated urging unit and is rotated by following rotation of the photosensitive drum 1 at the time when the toner image is transferred from the photosensitive drum 1 to the transfer material P.
The transfer material P on which the toner image is transferred from the photosensitive drum 1 in the transfer portion Nt is conveyed to the fixing unit 60 along a path indicated by a dotted arrow in
As illustrated in
As illustrated in
The elastic portion 5b as a semiconductive member according to the present exemplary embodiment includes rubber, a cross-linking component for cross-linking the rubber, a foaming component for foaming the rubber, and potassium salt of an anion including a fluoro group and a sulfonyl group in a molecule. The rubber includes conductive rubber composition including at least one selected from a group including styrene-butadiene rubber (SBR) and nitrile-butadiene rubber (NBR) and epichlorohydrin rubber.
A manufacturing method of the transfer roller 5 according to the present exemplary embodiment is as follows. First, an adjusted conductive rubber composition is continuously extruded into a tube shape through a mouthpiece of a head of an extrusion machine, and the extruded tube passes through a microwave cross-linking device and then a hot air cross-linking device without being cut. Accordingly, the conductive rubber composition is continuously foamed and cross-linked to form a tube-shaped foam. Then, the tube-shaped foam is cut to a predetermined length. A conductive shaft (the shaft 5a) is inserted into the obtained tube-shaped foam having the predetermined length (the elastic portion 5b) and cooled, and then an outer circumferential surface of the tube-shaped foam is polished to be a predetermined outer diameter. Accordingly, the transfer roller 5 is obtained. As a polishing method for the elastic portion 5b, various polishing methods such as dry traverse polishing can be adopted.
The transfer roller 5 according to the present exemplary embodiment is a conductive roller having an outer diameter of 14.0 mm which is configured with the conductive shaft 5a having an outer diameter of 5 mm and the elastic portion 5b as the semiconductive member having a thickness of 4.5 mm. A longitudinal width (a width in the rotation axis direction) of the elastic portion 5b is set to 216 mm which is the same as a width of a letter (LTR) size sheet which is a maximum size transfer material P that can be used in the image forming apparatus 100. Further, an electric resistance value of the transfer roller 5 is a resistance value calculated from a current value measured by applying a voltage of 2.0 KV to the conductive shaft 5a and is approximately 5.0*107Ω. The electric resistance value of the transfer roller 5 was measured by rotating the transfer roller 5 at a circumferential speed of approximately 120 mm/sec in a state in which the transfer roller 5 was pressed against a grounded aluminum drum with a load of 400 g under a normal temperature and humidity environment.
The voltage is applied as described above, and thus a current necessary for transferring the toner image flows from the second contact portion a3 on the shaft 5a of the transfer roller 5 toward the photosensitive drum 1 via the elastic portion 5b and the transfer material P through paths Ia illustrated by solid arrows in
The non-sheet passing area is an area in which the elastic portion 5b and the photosensitive drum 1 are in direct contact with each other without intervention of the transfer material P in the longitudinal direction. If an excessive current flows into the non-sheet passing area 13, the surface of the photosensitive drum 1 in the non-sheet passing area 13 is charged, and a local electrostatic history (hereinbelow, referred to as a transfer memory) is formed on the photosensitive drum 1 after transfer. In a case where the transfer memory is formed on the photosensitive drum 1, charging becomes insufficient in a position at which the transfer memory is generated on the surface of the photosensitive drum 1 in the charge process in a next image forming operation, and thus the toner adheres to the position. Then, in a case where a position of the transfer material P in the longitudinal direction is deviated even a little in the transfer process, toner unrelated to an image to be originally formed adheres to the end portion of the transfer material P and causes an image defect (hereinbelow, referred to as end portion soiling).
Therefore, according to the present exemplary embodiment, the concave portion a1 is formed on the shaft 5a of the transfer roller 5 in order to suppress the current from flowing into the non-sheet passing area 13 of the photosensitive drum 1. A width of the concave portion a1 is secured from the first contact portion a2 between the elastic portion 5b and the shaft 5a in the first region Re to a more inner side than the end portion of the transfer material P in the sheet passing area in the longitudinal direction. The reason is described below. According to the present exemplary embodiment, the concave portion a1 is formed from the end portion of an A4 size transfer material P to the inside of the sheet passing area by about 10 mm within a range in which transfer property of the toner image can be ensured at the end portion of the transfer material P. Further, a depth of the concave portion a1 is approximately 0.5 mm in the radial direction of the shaft 5a.
The shaft 5a arranged in the first region Re, namely the first contact portion a2 of the shaft 5a which is in contact with an inner circumferential surface of the elastic portion 5b on an end portion side of the elastic portion 5b in the longitudinal direction serves as a pillar for supporting the elastic portion 5b at both ends. A width of the first contact portion a2 in the first region Re in the longitudinal direction is set to about 2 mm according to the present exemplary embodiment as a minimum width necessary for fulfilling the function of the pillar. Accordingly, in a case where the transfer roller 5 is urged toward the photosensitive drum 1, the void 10 is formed without contact between an inside (the inner circumferential surface) of the elastic portion 5b and the shaft 5a, and the amount of current flowing from the shaft 5a toward the non-sheet passing area 13 in the first region Re is suppressed to a minimum.
As described above, the current flowing into the non-sheet passing area 13 of the photosensitive drum 1 can be suppressed by forming the void 10 between the shaft 5a and the elastic portion 5b on the end portion side of the elastic portion 5b in the longitudinal direction on the shaft 5a in which the concave portion a1 is formed.
Regarding the transfer roller 25 according to the first comparative example and the transfer roller 35 according to the second comparative example, widths in the longitudinal direction, electric resistance values, and materials of the elastic portions are the same as those according to the present exemplary embodiment, and only shapes of the shafts of the transfer rollers are different from the present exemplary embodiment. The configurations of the transfer rollers 25 and 35 according to the respective first and second comparative examples are described in details below.
As illustrated in
The current flowing to the non-sheet passing area 13 was measured in a state in which an A4 size insulation sheet 15 simulating a high resistance sheet was sandwiched between an aluminum drum 14 for resistance measurement and the transfer roller which was pressed against the aluminum drum 14 with a load of a total pressure of 400 g as illustrated in
As illustrated in
As illustrated in
In a case where the transfer roller 35 is used in the present measurement, the current flows from the shaft 35a to the area 16 through paths Id indicated by solid arrows in
As described above, according to the present measurement, it is desirable that the shaft of the transfer roller is provided with the concave portion, and the void formed by the concave portion between the shaft and the elastic portion is provided to the inside of sheet passing area, more desirably to the inside of about 10 mm of the sheet passing area as a method for suppressing the current flowing to the non-sheet passing area. The current flowing toward the non-sheet passing area by avoiding the end portion of the transfer material P tends to be larger in a case where an electric resistance value of the transfer roller is low or in a case where a resistance value of the transfer material P is high. Therefore, in a case where various conditions are taken into consideration, it is desirable that the above-described concave portion and void are provided to the inside of the sheet passing area in the longitudinal direction as much as possible in a range in which the transfer property of the toner image at the end portion of the transfer material P can be ensured.
Table 1 indicates results of evaluating levels of the end portion soiling of the transfer materials P in a case where the A4 size transfer materials P (basis weight 68 g/m2) passed using the respective transfer rollers according to the present exemplary embodiment, the first comparative example, and the second comparative example. As conditions for performing the present evaluation, an evaluation environment was set to a low temperature and low humidity environment of a room temperature of 10° C. and a humidity of 15% RH as a condition in which the end portion soiling is more likely to occur, and image forming was continuously performed on 500 sheets of the transfer materials P in a double-sided print mode. Further, in order to make a width of the non-sheet passing area uniform in the longitudinal direction for each evaluation, the transfer material P was conveyed to the transfer portion Nt in a center reference in which centers of the transfer roller and the transfer material P in the longitudinal direction are substantially in the same positions. The level of the end portion soiling was evaluated on a side of which the soiling level was worse in both end portions of the transfer material P in the longitudinal direction. In the tables below, a level A is a level at which the end portion soiling cannot be visually recognized, a level B is a level at which the end portion soiling can be visually recognized but hardly noticeable, and a level C is a level at which the end portion soiling can be clearly visually recognized.
As indicated in Table 1, in the configurations according to the first and the second comparative examples, the levels of the end portion soiling increased as the number of passing sheets increased. On the other hand, according to the configuration of the present exemplary embodiment, occurrence of the end portion soiling could not be visually confirmed even if the number of passing sheets increased. This is because, the amount of current flowing into the non-sheet passing area was suppressed by providing the concave portion a1 and the void 10 associated therewith on the shaft 5a of the transfer roller 5 as described above.
Further, there is a tendency that the end portion soiling becomes worse as the number of continuously passing sheets increases regardless of a type of the transfer roller in Table 1. This is because the resistance of the transfer roller gradually decreased during the continuous sheet passing, and the current sneaking into the non-sheet passing area from an inside in the longitudinal direction of the A4 size sheet passing area increased. Particularly, in a case of double-sided sheet passing, the transfer material P in a high temperature state after passing through the fixing unit on a first surface passes through the transfer portion Nt again on a second side thereof. Therefore, a roller temperature significantly rises during continuous sheet passing due to repeating of the process, and the resistance value of the transfer roller tends to decrease more than that in single-sided sheet passing. In addition to the above-described decrease of the resistance value of the transfer roller, if the transfer material P having a higher resistance passes along the transfer roller, the current flowing into the non-sheet passing area is further increased. Therefore, as a method for suppressing the current flowing into the non-sheet passing area, it is desirable to provide the concave portion and the void associated therewith on the shaft of the transfer roller about 10 mm inside the sheet passing area in the longitudinal direction. It is further desirable to provide the concave portion and the void associated therewith to the inside of the sheet passing area as much as possible in the range in which the transfer property at the end portion of the transfer material P can be ensured in the longitudinal direction.
Table 2 indicates results of evaluating the levels of end portion soiling of the transfer materials P in a case where A5 size transfer materials P (basis weight 68 g/m2) of which a non-sheet passing area is wider than that of the A4 size transfer material P passed using the respective transfer rollers according to the present exemplary embodiment, the first comparative example, and the second comparative example. Conditions for performing the present evaluation were set to the same as the conditions for the evaluation using the A4 size transfer material P.
As indicated in Table 2, the levels of the end portion soiling were improved in the configurations according to the first and the second comparative examples in the case of using the A5 size transfer material P compared with the case of using the A4 size transfer material P. This is related to a fact that the A5 size transfer material P has a wider non-sheet passing area in the longitudinal direction than the A4 size transfer material P. More specifically, the non-sheet passing area is wider, so that the current flowing from the shaft provided on the sheet passing area side to the non-sheet passing area is widely dispersed in the longitudinal direction of the non-sheet passing area regardless of the configuration of the used transfer roller. In the configuration in which a width of the non-sheet passing area is narrow, it is considered that the level of the end portion soiling tends to be worse since the current is concentrated in the narrow area.
In other words, such current concentration in the non-sheet passing area is influenced by a width of the transfer material P in the longitudinal direction, a conveyance position of the transfer material P in the transfer portion Nt, a width of the elastic portion of the transfer roller in the longitudinal direction, and the like. The current concentration is remarkable in a case where the transfer material P is used which is shorter than the width of the elastic portion 5b of the transfer roller 5 in the longitudinal direction and has a maximum size width of which the sheet passing area is the widest. Alternatively, even if the transfer material P does not have the maximum size, the current concentration is remarkable in a case where the conveyance position of the transfer material P is shifted in the longitudinal direction, and the width of non-sheet passing area generated between the elastic portion 5b of the transfer roller 5 and the photosensitive drum 1 becomes narrow. In these cases, occurrence of the end portion soiling can be effectively suppressed by adopting the configuration according to the present exemplary embodiment.
As described above, according to the configuration of the present exemplary embodiment, the shaft 5a of the transfer roller 5 is provided with the concave portion a1, and thus the void 10 is formed between the first contact portion a2 and the second contact portion a3 in the end portion side of the elastic portion 5b. Further, according to the configuration of the present exemplary embodiment, at least the void 10 is formed on a more center side of the sheet passing area (namely, a more inner side than the end portion of the transfer material P) than the end portion of the transfer material P having the maximum size which can be used in the image forming apparatus 100 in the longitudinal direction. Accordingly, occurrence of the end portion soiling caused by an excessive current flowing from the transfer roller 5 toward the non-sheet passing area 13 of the photosensitive drum 1 can be suppressed.
According to the configuration of the present exemplary embodiment, the transfer roller 5 is described which is obtained by inserting the shaft 5a which has the concave portions a1 on both end portions into the elastic portion 5b which is the tube-shaped semiconductive member. Such a transfer roller 5 can be simply molded using a commonly used extrusion machine. In other words, according to the configuration of the present exemplary embodiment, occurrence of the end portion soiling can be suppressed by a simpler configuration without complicating a manufacturing process.
According to the present exemplary embodiment, an organic photosensitive drum having a laminated structure is used as an image bearing member, but the present exemplary embodiment is not limited to this configuration. As the image bearing member, a belt-shaped one or a configuration in which a latent image is written on a single layer photosensitive member, an inorganic photosensitive member, a dielectric material, or the like can be used.
Further, according to the present exemplary embodiment, the image forming apparatus 100 which transfers a toner image from the photosensitive drum 1 as the image bearing member to the transfer material P is used in the description. However, the present disclosure can also be applied to an image forming apparatus which transfers a toner image to the transfer material P via an intermediate transfer member or the like without being limited to the above-described configuration. In this case, a configuration similar to the transfer roller 5 described according to the present exemplary embodiment can be applied to a transfer member which is arranged in contact with an inner circumferential surface side of the intermediate transfer member in order to transfer a toner image from the photosensitive drum to the intermediate transfer member. In this case, at least an end portion of the intermediate transfer member is arranged to overlap with the void 10 formed by the concave portion a1 in the longitudinal direction, so that an effect similar to that according to the present exemplary embodiment can be obtained.
According to the first exemplary embodiment, the configuration is described in which the concave portion a1 having a predetermined shape is provided in the shaft 5a of the transfer roller 5. In contrast, according to a second exemplary embodiment, a shape of a concave portion Sal of a transfer roller 55 is different from that of the transfer roller 5 according to the first exemplary embodiment. The configuration and operations according to the second exemplary embodiment are substantially the same as those according to the first exemplary embodiment except that the concave portion Sal is different from the concave portion a1 according to the first exemplary embodiment. Therefore, in the following description, the portions common to those according to the first exemplary embodiment are denoted by the same reference numerals, and the descriptions thereof are omitted.
The concave portion 5a1 according to the present exemplary embodiment is not a single and wide concave portion like the concave portion a1 of the transfer roller 5 according to the first exemplary embodiment, but is configured with a plurality of concave portions having different widths in the longitudinal direction. As illustrated in
A width of the concave portion Sal in the longitudinal direction is different in the non-sheet passing area and in the sheet passing area. The concave portion Sal corresponding directly below the non-sheet passing area 13 is formed to have a wide width in the longitudinal direction in order to block a current path of a current which flows from the shaft 55a into the non-sheet passing area 13 in the shortest path. Meanwhile, regarding the concave portions Sal located on a more center side of the sheet passing area (namely, a more inner side than the end portion of the transfer material P) than the end portion of the transfer material P, the concave portion located closer to the center of the sheet passing area is formed to have a narrower width in order to secure paths Ig through which the current necessary for the transfer property of a toner image at the end portion of the transfer material P flows.
Further, the concave portion 5a1 is provided from the end portion on the sheet passing area side of a first contact portion 5a2 between the shaft 55a and the elastic portion 55b in the first region Re to a position corresponding to 15 mm inside from the end portion of the A4 size transfer material P toward the center side of the sheet passing area in the longitudinal direction. In other words, the concave portion 5a1 is extended by about 5 mm on the sheet passing area side in the longitudinal direction than the concave portion a1 according to the first exemplary embodiment, and, according to the configuration of the present exemplary embodiment, the transfer property of the toner image at the end portion of the transfer material P is ensured by providing the convex portions to secure the current flowing through the paths Ig. The first contact portion 5a2 serves as a pillar for supporting the elastic portion 55b at both ends of the shaft 55a and has a width of about 2 mm which is the same as that of the first contact portion a2 according to the first exemplary embodiment.
The non-sheet passing area 13 is an area in which the elastic portion 55b and the photosensitive drum 1 are in direct contact with each other. A minute current flowing from the first contact portion 5a2 through a path Ie and a minute current flowing through a path If by wrapping around from the inside of the sheet passing area of the A4 size transfer material P flow into the non-sheet passing area 13. A total amount of currents flowing into the non-sheet passing area 13 through the paths Ie and If is almost the same as that according to the first exemplary embodiment. More specifically, the width of the first contact portion 5a2 in the longitudinal direction is the same as the first contact portion a2, so that the amount of current flowing into the non-sheet passing area 13 through the path Ie is about the same as that according to the first exemplary embodiment. On the other hand, as for the amount of current flowing into the non-sheet passing area 13 through the path If, the current branched from the paths Ig excessively flows thereinto as compared with that according to the first exemplary embodiment, but, since the concave portion 5a1 is provided in a wide range up to 15 mm inside the sheet passing area, the total amount of current is about the same as that according to the first exemplary embodiment.
Table 3 indicates results of evaluating the levels of the end portion soiling of the transfer materials P in a case where the A4 size transfer materials P (basis weight 68 g/m2) passed using the respective transfer rollers according to the present exemplary embodiment, the first comparative example, and the first exemplary embodiment. The conditions for performing the present evaluation were set to the same as the evaluation conditions according to the first exemplary embodiment.
As indicated in Table 3, according to the present exemplary embodiment, the end portion soiling at a visible level could not be confirmed, and the evaluation results were good as with the first exemplary embodiment. As described above, the concave portion Sal according to the present exemplary embodiment has the shape different from that according to the first exemplary embodiment. However, the voids 70 are formed between the shaft 55a and the elastic portion 55b, and thus the current flowing into the non-sheet passing area 13 can be suppressed, and occurrence of the end portion soiling can be suppressed to the same extent as in the first exemplary embodiment.
According to the present exemplary embodiment, the concave portions Sal and the convex portions are alternately divided and formed with a relatively narrow width in the longitudinal direction of the transfer roller 55, so that the elastic portion 55b can be suppressed from largely bending even in the configuration in which a pressure for urging the transfer roller 55 toward the photosensitive drum 1 is high. Accordingly, the voids 70 formed between the shaft 55a and the elastic portion 55b can be stably secured. Accordingly, even in the configuration in which the pressure for urging the transfer roller 55 is high, the current concentration in the non-sheet passing area 13 can be reduced, and occurrence of the end portion soiling can be more effectively suppressed with respect to the configuration according to the first exemplary embodiment.
The above-described functions and effects obtained according to the present exemplary embodiment are not limited to a case in which the pressure for urging the transfer roller 55 is high and can be exerted under conditions in which the elastic portion 55b is easily bent, and there is a concern that the voids 70 may be crushed, for example, in a case where hardness of the elastic portion 55b is low or a thickness thereof is small.
The transfer roller 55 according to the present exemplary embodiment can also be obtained by press-fitting the shaft 55a on which the concave portions Sal are formed, into a tube-shaped elastic portion 55b, so that the transfer roller 55 can be easily obtained without complicating the manufacturing process.
According to the first and the second exemplary embodiments, the configuration is described in which a concave portion which has a ring shape in a circumferential direction of the shaft and is concaved in a radial direction of the shaft is provided. However, the shape of the concave portion to be provided on the shaft is not limited to the one according to the above-described exemplary embodiments. For example, the configuration of the concave portion as illustrated in
As illustrated in
According to the first exemplary embodiment, the configuration is described in which the concave portion a1 is provided in the shaft 5a of the transfer roller 5, and the void 10 having a predetermined range is formed between the shaft 5a and the elastic portion 5b. In contrast, according to a third exemplary embodiment, a configuration is described in which a high resistance member 79 is provided to a concave portion 78 of a shaft 76. In the following description, the portions common to those according to the first exemplary embodiment are denoted by the same reference numerals, and the descriptions thereof are omitted.
As described above, in the configuration according to the present exemplary embodiment, the high resistance member 79 is formed on the outside in the longitudinal direction of an A4 size area, and thus a current path of a current flowing from the shaft 76 to the non-sheet passing area 13 in the shortest path is blocked. Further, there is no support member which supports a void as in the first and the second exemplary embodiments, so that there is no current flowing from the support member at the end portion of the shaft 76. Only the current which wraps around from the inside in the longitudinal direction of the sheet passing area through a path 111 indicated by an arrow in
Further, the configuration according to the present exemplary embodiment does not include a void due to a concave portion and thus does not need to assume bending of the elastic portion and crushing of the void accompanying the concave portion as described in the second exemplary embodiment. Therefore, an effect equal to or higher than that according to the second exemplary embodiment can be obtained even for the end portion soiling caused by the transfer memory in a case where a pressure for urging the transfer roller is high as an evaluation condition according to the second exemplary embodiment.
According to the present exemplary embodiment, the example is described in which a single and wide concave portion is provided on the shaft, and the high resistance member is provided in the concave portion. However, the shape of the concave portion according to the third exemplary embodiment is not limited to that according to the above-described exemplary embodiments. For example, the transfer property of the toner image at the end portion of the transfer material P may be optimized by providing the high resistance member in the concave portions divided in the longitudinal direction as illustrated in
According to the present disclosure, a form of a contact type transfer member can be provided which is used in an image forming apparatus and is able to suppress occurrence of soiling in an end portion in a width direction of a transfer material.
While the present disclosure has been described with reference to exemplary embodiments, it is to be understood that the disclosure is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of priority from Japanese Patent Application No. 2020-171283, filed Oct. 9, 2020, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2020-171283 | Oct 2020 | JP | national |
