JP2015138205A - Image formation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image formation device which can suppress reduction in transfer efficiency in such a case that a resistance-lowered recording material is used, and can suppress toner contamination to the recording material.SOLUTION: An image formation device 100 comprises: an image carrier 1; a transfer member 5; a guide member 50 provided to contact a recording material P held between the image carrier 1 and the transfer member 5, which guides the recording material P to a contact portion Nt of the image carrier 1 with the transfer member 5; and a power source 50a which applies a voltage to the guide member 50. The guide member 50 has an electrically conductive part 51 which contacts with the recording material P and to which the voltage from the power source 50a is applied, and the electrically conductive part 51 is configured to be arranged inside an area W1 where the recording material P whose width in the direction approximately orthogonal to a conveyance direction of the recording material P is maximum among the usable recording materials P in the image formation device 100 passes.

Description

  The present invention relates to an image forming apparatus such as a copying machine, a laser beam printer, or a facsimile using an electrophotographic system or an electrostatic recording system.

  Conventionally, in an image forming apparatus such as an electrophotographic copying machine, a toner image formed on an image carrier such as a photosensitive drum is formed by contacting the image carrier and a transfer member such as a transfer roller. Is transferred to the recording material at the transfer nip. At this time, a predetermined transfer voltage having a polarity opposite to the charging polarity (normal charging polarity) of the toner at the time of development is applied to the transfer roller. The recording material onto which the toner image has been transferred is heated and pressed in a fixing nip formed by contact between the heating body and the pressure body in the fixing device, and the toner image is fixed thereon.

  Here, in order to stably supply the recording material to the transfer nip, a pre-transfer guide may be disposed as a guide member on the entrance side of the transfer nip. The recording material is conveyed to the transfer nip while being guided by the pre-transfer guide. A conductive member is used as a part of the pre-transfer guide in order to prevent frictional charging caused by rubbing against the recording material, and electric charges are released by electrically grounding the member. However, if a recording material with increased moisture content and reduced electrical resistance is introduced into the transfer nip in a high-temperature, high-humidity environment, etc., part of the transfer current passes through the recording material to the fixing device or pre-transfer guide. Flowing. As a result, the transfer current flowing to the image carrier is insufficient, the toner on the image carrier cannot be transferred sufficiently, and good transfer efficiency may not be obtained.

  Therefore, as described in Patent Document 1, a pre-transfer guide for transfer current is applied to a conductive pre-transfer guide by applying a voltage having the same polarity as the transfer voltage (opposite to the normal charging polarity of the toner). There has been proposed a method of obtaining a desired transfer efficiency by cutting off the route to the above.

JP-A-7-239617

  However, in the configuration described in Patent Document 1, since a voltage having a polarity opposite to the normal charging polarity of the toner is applied to the pre-transfer guide, the toner scattered in the image forming apparatus is electrostatically applied to the pre-transfer guide. Easy to adhere to.

  Since such toner is very small, it does not immediately affect the latest printed image. In a region where the recording material on the pre-transfer guide passes in a direction substantially perpendicular to the conveyance direction of the recording material, when the recording material passes through the pre-transfer guide, the adhered toner goes out of the image forming apparatus together with the recording material. And vomited. On the other hand, the adhering toner is not discharged together with the recording material except in the region where the recording material on the pre-transfer guide passes, and therefore is deposited on the pre-transfer guide every time the printing operation is repeated. Therefore, by continuing to use the image forming apparatus, a large amount of toner accumulates on the pre-transfer guide, and in the course of transporting the recording material, the end of the recording material in the direction substantially perpendicular to the recording material transport direction becomes soiled with toner. Sometimes.

  Accordingly, an object of the present invention is to provide an image forming apparatus capable of suppressing a decrease in transfer efficiency when using a recording material with a low resistance, and suppressing toner contamination of the recording material. It is.

  The above object is achieved by the image forming apparatus according to the present invention. In summary, the present invention provides an image carrier that carries a toner image and a recording material that is provided so as to be in contact with the image carrier and is sandwiched between the image carrier and a voltage applied thereto. A transfer member for transferring a toner image from the image carrier, and a contact portion between the image carrier and the transfer member, provided to be in contact with a recording material sandwiched between the image carrier and the transfer member. In an image forming apparatus having a guide member for guiding a recording material and a power source for applying a voltage to the guide member, the guide member is a conductive conductor that contacts the recording material and is applied with a voltage from the power source. The conductive portion is disposed inside a region through which a recording material having the maximum width in the direction among the recording materials usable in the image forming apparatus passes in a direction substantially orthogonal to the conveyance direction of the recording material. A picture characterized by being A forming apparatus.

  According to the present invention, it is possible to suppress a decrease in transfer efficiency when using a recording material with reduced resistance, and to suppress toner contamination of the recording material.

1 is a schematic configuration diagram of an image forming apparatus. It is a schematic diagram for demonstrating the effect of the voltage applied to a pre-transfer guide. It is a graph for demonstrating the relationship between transfer efficiency and a transfer voltage. FIG. 3 is a schematic diagram illustrating a positional relationship between a pre-transfer guide (electrode portion) and a recording material in Example 1. It is a graph which shows the experimental result of the transfer efficiency in Example 1 and a prior art example. FIG. 6 is a schematic diagram illustrating a positional relationship between an electrode portion of a pre-transfer guide and a recording material in Example 2. FIG. 6 is a schematic diagram illustrating a positional relationship between an electrode portion of a pre-transfer guide and a recording material in Example 3. FIG. 10 is a schematic flowchart of a process for applying a voltage to a pre-transfer guide in Embodiment 3.

  The image forming apparatus according to the present invention will be described below in more detail with reference to the drawings.

Example 1
1. Image Forming Apparatus FIG. 1 shows a schematic configuration of an image forming apparatus 100 according to an embodiment of the present invention. The image forming apparatus 100 of this embodiment is a laser beam printer using an electrophotographic system.

  First, the configuration of the image forming apparatus 100 will be described. The image forming apparatus 100 includes a photosensitive drum 1 that is a drum-type (cylindrical) electrophotographic photosensitive member as an image carrier that carries a toner image. The photosensitive drum 1 is configured by providing a layer of a photosensitive material such as OPC (organic optical semiconductor), amorphous selenium, or amorphous silicon on a cylindrical drum base formed of aluminum, nickel, or the like. The photosensitive drum 1 is rotatably supported by the apparatus main body M, and is rotationally driven at a predetermined process speed (circumferential speed) in the direction of arrow R1 in the figure by a drive source (not shown).

  Around the photosensitive drum 1, the following units are arranged in order along the rotation direction. First, a charging roller 2 which is a roller-shaped charging member as a charging unit is disposed. Next, an exposure apparatus 3 as an exposure unit is arranged. Next, a developing device 4 as a developing unit is arranged. Next, a transfer roller 5 which is a roller-like transfer member as a transfer unit is disposed. Next, a cleaning device 6 as a cleaning means is arranged.

  A paper feed cassette 7 that stores a recording material P such as paper is disposed below the apparatus main body M. A paper feed roller 8, a transport roller 9, a top sensor 10, and a pre-transfer guide 50 are arranged in this order along the transport path of the recording material P from the paper feed cassette 7 on the upstream side of a transfer nip Nt described later. . Further, on the downstream side of the transfer nip Nt, a conveyance guide 11, a fixing device 12, a paper discharge sensor 13, a conveyance roller 14, a paper discharge roller 15, and a paper discharge tray 16 are disposed in order along the conveyance path of the recording material P. ing.

  Next, the operation of the image forming apparatus 100 configured as described above will be described. The photosensitive drum 1 that is rotationally driven in the direction of arrow R1 in the figure by a driving source (not shown) is charged substantially uniformly by the charging roller 2 to a predetermined polarity (negative polarity in this embodiment) and a predetermined potential. The charged photosensitive drum 1 is subjected to an image exposure L based on image information by an exposure device 3 such as a laser optical system on the surface thereof, and the charge of the exposed portion is removed to form an electrostatic latent image (electrostatic image). It is formed. The electrostatic latent image is developed by the developing device 4. The developing device 4 has a developing roller 4a, and a developing voltage (developing bias) is applied to the developing roller 4a to attach the toner to the electrostatic latent image on the photosensitive drum 1 and develop it as a toner image (visualization). To do. In this embodiment, the charging polarity (normal charging polarity) of the toner during development is negative. The toner image is transferred to the recording material P such as paper by the transfer roller 5. The transfer roller 5 is pressed against the photosensitive drum 1 by a transfer pressure spring (not shown), and forms a transfer nip Nt that is a contact portion between the photosensitive drum 1 and the transfer roller 5 between the transfer roller 5. The transfer roller 5 is an example of a transfer member that is provided so as to be in contact with the image carrier and to which a toner image is transferred from the image carrier to a recording material that is sandwiched between the image carrier and a voltage applied thereto. .

  The recording material P is stored in a paper feed cassette 7, fed one by one by a paper feed roller 8, and conveyed by a conveyance roller 9. Thereafter, the recording material P is conveyed to the transfer nip Nt between the photosensitive drum 1 and the transfer roller 5 while being guided by the pre-transfer guide 50. At this time, the leading edge of the recording material P is detected by the top sensor 10 and synchronized with the toner image on the photosensitive drum 1. A transfer voltage (transfer bias), which is a DC voltage having a polarity opposite to the normal charging polarity of the toner, is applied to the transfer roller 5 from a transfer power source (transfer high voltage generator) 5a. As a result, the toner image on the photosensitive drum 1 is transferred to a predetermined position on the recording material P. The transfer voltage applied from the transfer power source 5a is determined by ATVC (Active Transfer Voltage Control) control by the transfer voltage control device 5b as transfer voltage control means.

  Here, the ATVC control will be briefly described. During rotation before printing, a voltage is applied to the transfer roller 5, the voltage value is controlled so that a predetermined current flows through the charged photosensitive drum 1, and the voltage value at the stage when the target current value is reached is recorded as V0. To do. Based on the value of V0, the transfer voltage value Vt during the actual image forming operation is determined by multiplying a predetermined coefficient, for example. As a result, it is possible to determine a suitable transfer voltage value in accordance with variations in the electric resistance value of the transfer roller 5 and electric resistance fluctuations.

  The recording material P carrying the unfixed toner image on the surface by transfer is transported to the fixing device 12 along the transport guide 11, where the unfixed toner image is heated and pressurized and fixed on the surface of the recording material P. The In this embodiment, the fixing device 12 is a pressure roller driving type fixing device using a flexible endless belt as a fixing film. The fixing device 12 includes the following elements as main components. That is, the fixing device 12 includes a fixing film 12a which is a film-like fixing rotating body, and a pressure roller 12b as a pressure member in contact with the fixing film 12a. The fixing device 12 includes a ceramic heater (hereinafter referred to as “heater”) 12 c that heats the toner through the fixing film 12 a and a heater holder 12 d that is a heater support member. The pressure roller 12b is provided with a heat-resistant elastic layer having elasticity such as silicone rubber on the outer peripheral surface of a metal core, and the outermost layer is made of a material having high releasability such as fluororesin. A layer is provided. The pressure roller 12b presses the fixing film 12a against the heater 12c from below on the outer peripheral surface of the release layer by a pressure spring (not shown) to form a fixing nip Nf with the fixing film 12a. When the pressure roller 12b is rotationally driven in the direction of arrow R12b in the figure by a drive source (not shown), a rotational force acts on the fixing film 12a due to the pressure frictional force of the fixing nip Nf between the pressure roller 12b and the fixing film 12a. . Then, the fixing film 12a is driven to rotate in the direction of the arrow R12a in the figure while the inner surface of the fixing film 12a slides in close contact with the downward surface of the heater 12c. In the fixing device 12, the pressure roller 12b is rotationally driven, and the fixing film 12a is in a driven rotational state, and electric power is supplied to the heater 12c. The heater 12a rises in temperature and rises to a predetermined temperature. The state is adjusted. In this state, the recording material P carrying an unfixed toner image is introduced between the fixing film 12a and the pressure roller 12b in the fixing nip Nf. Then, in the fixing nip Nf, the toner image carrying surface side of the recording material P is in close contact with the outer surface of the fixing film 12a, and the fixing nip Nf is nipped and conveyed together with the fixing film 12a. In this nipping and conveying process, the heat of the heater 12c is applied to the recording material P through the fixing film 12a, and the unfixed toner image on the recording material P is heated and pressurized on the recording material P and melted and fixed. The recording material P that has passed through the fixing nip Nf is separated in curvature from the fixing film 12a.

  The recording material P on which the toner image has been fixed is conveyed by the conveying roller 14 and is discharged onto the discharge tray 16 on the upper surface of the apparatus main body M by the discharge roller 15.

  On the other hand, toner remaining on the surface of the photosensitive drum 1 without being transferred to the recording material P after transfer of the toner image (transfer residual toner) is removed and collected by the cleaning blade 6a in the cleaning device 6. Thereafter, the photosensitive drum 1 is used for the next image formation.

  By repeating the above operation, image formation can be performed one after another.

2. Pre-transfer guide A pre-transfer guide 50 serving as a guide member (guide member) is disposed upstream of the transfer nip Nt in the conveyance direction of the recording material P in order to stably introduce the recording material P into the transfer nip Nt. It is arranged in the vicinity. The pre-transfer guide 50 is disposed at a position where the tip protrudes with respect to the conveyance surface (conveyance path) of the recording material P so as to come into contact with the back surface of the recording material P.

  In order to prevent frictional charging due to rubbing with the recording material P, the pre-transfer guide 50 has an electrode portion which is a conductive portion made of a conductive member on all or part of the pre-transfer guide 50. In this embodiment, the entire pre-transfer guide 50 is an electrode portion 51 (FIG. 4). As the conductive material, a metal such as iron or stainless steel (SUS) can be preferably used. In this example, SUS was used. Further, the guide 50 before transfer (more specifically, the electrode portion 51) is connected to a guide member power source (herein, also simply referred to as “high voltage generator”) 50a, and has the same polarity as the transfer voltage (regular toner). The guide member voltage (guide member bias) having a desired value of the opposite polarity to the charging polarity of (1) is applied. The guide member voltage applied from the guide member power supply 50a is controlled by a guide member voltage control device (herein simply referred to as “control device”) 50b as control means.

  The effect of applying a voltage to the pre-transfer guide 50 will be described with reference to FIGS.

  FIG. 2 is a schematic diagram showing the vicinity of the transfer nip Nt when the recording material P is conveyed to the transfer nip Nt and the current flow at that time. Since the toner used in this embodiment is charged with a negative polarity, the voltage of the transfer power supply 5 is set to a positive polarity so that the transfer current flows into the photosensitive drum 1. FIG. 2A shows a state in which the pre-transfer guide 50 is directly grounded and the recording material P has a high resistance. FIG. 2B shows a case where the pre-transfer guide 50 is directly grounded and the recording material P has a low electrical resistance. FIG. 2C shows a configuration in which the high-voltage generating device 50a and the control device 50b are connected to the pre-transfer guide 50 (configuration of the present embodiment), and the electrical resistance of the recording material P is low. Yes.

  FIG. 3 is a diagram showing the relationship between transfer efficiency and transfer voltage when the electrical resistance of the recording material P is different. (A), (b), and (c) in FIG. 3 correspond to the configurations of (a), (b), and (c) in FIG. 2, respectively.

  Here, the transfer efficiency is defined by Equation 1 below.

  First, in the case of FIG. 2A, in a state where the recording material P having a high electric resistance is conveyed to the transfer nip Nt, a transfer voltage having a polarity opposite to the normal charging polarity of the toner is applied to the transfer roller 5, and the photosensitive material is exposed. The toner on the drum 1 is transferred onto the recording material P. At this time, even if the recording material P is in contact with the pre-transfer guide 50 and the fixing device 12, the recording material P has a high electric resistance, so that the pre-transfer guide 50 and the fixing device 12 pass through the recording material P. The current flowing through is small. Therefore, most of the transfer current flows to the photosensitive drum 1. FIG. 3A shows the relationship between the transfer voltage and the transfer efficiency in this state. Let Va be the transfer voltage value at which the transfer efficiency is highest. Here, when the transfer efficiency is lower than 80%, the toner image on the photosensitive drum 1 is not sufficiently transferred to the recording material P and density unevenness and line missing occur. A defective transfer efficiency level is set, and when the transfer efficiency is higher, a good level is set. In this case, the transfer voltage becomes a good level in the range of VaL to VaH. When the transfer voltage is lower than VaL, a phenomenon of transfer omission in which the current value necessary for transfer is insufficient occurs, and the transfer efficiency becomes a defective level. On the other hand, when the transfer voltage is higher than VaH, an excessive transfer current flows to the photosensitive drum 1, and the phenomenon of retransfer in which the polarity of the toner is reversed and the toner is not transferred occurs, and the transfer efficiency becomes a defective level. As described above, when the resistance value of the recording material P is high, good transfer efficiency can be obtained when the transfer voltage is in the range of VaL to VaH.

  However, in the case of FIG. 2B, since the moisture content increases in a high humidity environment or the like and the recording material P whose resistance has been lowered is conveyed to the transfer nip Nt, the transfer current passes through the recording material P and before transfer. It becomes easy to flow to the guide 50 and the fixing device 12. In this state, when the transfer voltage is controlled with the same voltage as in the state of FIG. 2A in which the recording material P has a high electric resistance value, a large amount of current flows through the pre-transfer guide 50, so that the current flowing through the transfer roller 5 To increase. When the current flowing through the transfer roller 5 increases, the voltage drop due to the electrical resistance of the transfer roller 5 increases and the potential of the transfer nip Nt decreases, so that the transfer electric field becomes weaker than in the state of FIG. For this reason, at the same transfer voltage as when the electrical resistance of the recording material P is high, transfer omission occurs, and the transfer efficiency becomes a defective level. In a state where the recording material P has a low resistance, the transfer efficiency is as shown in FIG. That is, the transfer voltage becomes maximum at Vb higher than Va, and a range from VbL to VbH is required to obtain good transfer efficiency. At this time, since the value of VbL is higher than VaH, there is no transfer voltage value suitable for both the low-resistance and high-resistance recording materials when the electric resistance value of the recording material P is wide, and the transfer efficiency is not satisfactory. Occurs. In order to improve this state, in this embodiment, a voltage having the same polarity as the transfer voltage is applied to the pre-transfer guide 50.

  As shown in FIG. 2C, when a voltage having the same polarity as the transfer voltage is applied to the pre-transfer guide 50, the potential of the transfer nip Nt is compared with FIG. 2B where the pre-transfer guide 50 is directly grounded. And the potential difference between the pre-transfer guide 50 is reduced. Therefore, even when the recording material P has a low resistance, the transfer current flowing through the recording material P and flowing into the pre-transfer guide 50 can be suppressed. If the transfer current flowing through the recording material P and flowing to the pre-transfer guide 50 is suppressed, the transfer current flowing to the transfer roller 5 can be appropriately maintained. Therefore, a drop in the potential of the transfer nip Nt can be prevented, so that the transfer electric field can be maintained appropriately. As a result, the transfer efficiency is as shown in FIG. That is, transfer efficiency is improved in a region where the transfer voltage is low, and good transfer efficiency can be obtained up to VcL lower than VbL. Here, since VcL is lower than VaH, even when the transfer voltage is the same as that in the case of FIG. As described above, by applying a voltage having the same polarity as the transfer voltage to the pre-transfer guide 50, both the low resistance and the high resistance recording material P can be used even when the recording material P has a wide electric resistance value. Therefore, a good transfer efficiency can be obtained.

  Here, depending on the voltage value applied to the pre-transfer guide 50, the current flowing to the pre-transfer guide 50 may not be prevented, or conversely, an excessive current may flow through the photosensitive drum 1, and good transfer efficiency may be achieved. There are things you can't get. The optimum voltage value to be applied to the pre-transfer guide 50 differs depending on the charging characteristics of the toner and the latent image setting of the photosensitive drum 1, but in this embodiment, good transfer efficiency can be obtained in the range of + 300V to 500V. it can.

  Further, the position of the pre-transfer guide 50 in the conveyance direction of the recording material P is preferably set to a position within 5 mm upstream from the upstream end of the transfer nip Nt. This is less than or equal to the conveyance direction dimension of the non-image forming portion that is generally provided at the front end portion and the rear end portion of the recording material P, and the image forming portion of the recording material P always has both the transfer nip Nt and the pre-transfer guide 50. This is because it is in contact with.

3. Recording Material Contamination Due to Pre-Transfer Guide Toner Accumulation Next, recording material contamination due to toner pre-transfer guide 50 toner accumulation will be described. When a voltage having the same polarity as the transfer voltage is applied to the pre-transfer guide 50 in order to improve the transfer efficiency of the recording material P whose resistance has been reduced, the pre-transfer guide 50 has a polarity opposite to the normal charging polarity of the toner. Become. Therefore, the toner floating in the apparatus and the toner on the photosensitive drum 1 before transfer are easily attached to the pre-transfer guide 50 electrostatically. When one sheet of recording material P passes, the amount of toner adhering to the pre-transfer guide is very small and does not immediately affect the latest printed image. Then, in a region (hereinafter also referred to as “recording material passage region”) through which the recording material P passes on the pre-transfer guide 50 in a direction substantially orthogonal to the conveyance direction of the recording material P (hereinafter also referred to as “thrust direction”). The adhered toner is discharged out of the image forming apparatus 100 together with the recording material P. However, the toner adhering to the area other than the recording material passage area on the pre-transfer guide 50 is not discharged out of the apparatus but gradually accumulates. When the image forming apparatus 100 is used for a long period of time, a large amount of toner accumulates outside the recording material passage area on the pre-transfer guide 50, and the end portion of the recording material P in the thrust direction eventually becomes dirty. In this embodiment, since the recording material P is conveyed with the center reference, both end portions in the thrust direction become dirty.

4). Arrangement of Pre-Transfer Guide FIG. 4 is a schematic diagram showing the positional relationship between the pre-transfer guide 50 and the recording material P in this embodiment. In this embodiment, in the configuration in which a voltage having the same polarity as the transfer voltage is applied to the pre-transfer guide 50 using a conductive material, the pre-transfer guide 50 is disposed inside the recording material passage region in the thrust direction. More specifically, the recording material passage area for the recording material P having the maximum size (that is, the maximum width in the thrust direction) that can be used (conveyed) by the image forming apparatus 100 in the thrust direction. Place inside.

  The effect of this embodiment when a letter size Business 4200 made by Xerox (hereinafter referred to as “letter paper”) is used as the recording material P will be described. In this case, the width W1 of the recording material passage area is 215.9 mm. Therefore, in this embodiment, the width W2 in the thrust direction of the pre-transfer guide 50 is set to 100 mm. The pre-transfer guide 50 is disposed inside the recording material passage area in the thrust direction. In the present embodiment, since the recording material P is conveyed on the basis of the center, the pre-transfer guide 50 is disposed at the center of the recording material passage region in the thrust direction.

  In order to examine the effect of the present embodiment, a configuration in which the width in the thrust direction of the pre-transfer guide 50 (more specifically, the electrode portion 51 to which a voltage is applied) is 230 mm wider than the width of the recording material passage area (conventional example). A comparative experiment was conducted on the configuration of this example. The conveyance speed of the recording material P was set to 150 mm / sec, the voltage value applied to the pre-transfer guide 50 was set to +300 V, and the transfer efficiency and the contamination at the end of the recording material P were confirmed when 1000 sheets of the recording material P were passed. . As the recording material P, letter paper left for 48 hours in a high temperature and high humidity environment of 32.5 ° C./80% was used. The results are shown in FIG. FIG. 5 shows the result of the transfer efficiency for every 100 sheets, and Table 1 shows the stain on the edge of the recording material P every 100 sheets.

  Here, the transfer efficiency was obtained by averaging the transfer efficiencies when five strip images having a width of 3 cm were printed at equal intervals in the conveyance direction of the recording material P in the print range. A transfer efficiency of 80% or more is a good level, and a transfer efficiency lower than that is a defective level. Further, “O (good level)” indicates that there is no contamination at the end of the recording material P, and “x (defect level)” indicates that even a slight amount of contamination is attached.

  First, regarding the transfer efficiency, as shown in FIG. 5, since the voltage having the same polarity as the transfer voltage is applied to the pre-transfer guide 50 in both the conventional example and the present embodiment, the recording material P is in a high temperature and high humidity environment. Even if the resistance is lowered, there is no shortage of transfer current and good transfer efficiency can be obtained.

  Next, stains at the end of the recording material P will be described with reference to Table 1. In the conventional example, the width in the thrust direction of the pre-transfer guide 50 is wider than the width of the recording material passage area. Therefore, when a voltage having the same polarity as the transfer voltage is applied to the pre-transfer guide 50 and the toner is likely to adhere electrostatically, the toner gradually moves outside the recording material passage area on the pre-transfer guide 50 in the thrust direction. Accumulate. For this reason, the edge of the recording material P is contaminated from 500 sheets by increasing the number of sheets to be passed and increasing the amount of accumulated toner. On the other hand, in this embodiment, the pre-transfer guide 50 is disposed inside the recording material passage area in the thrust direction. Accordingly, even when a voltage having the same polarity as the transfer voltage is applied to the pre-transfer guide 50 and the toner is easily electrostatically attached to the pre-transfer guide 50, the toner does not accumulate on the pre-transfer guide 50. Or small enough to be acceptable. Therefore, the edge of the recording material P does not get dirty even when the number of sheets passed increases, and a good image can be obtained even when 1000 sheets are passed.

  Thus, in this embodiment, the electrode portion 51 of the pre-transfer guide 50 is disposed inside the recording material passage region in the thrust direction. Thus, even when a voltage having the same polarity as the transfer voltage is applied to the pre-transfer guide 50 and the toner is likely to adhere electrostatically, the toner accumulation on the pre-transfer guide 50 can be suppressed. Therefore, a good image can be obtained even for the recording material P whose resistance has been reduced, and toner contamination at the end of the recording material P can be suppressed. In addition, by arranging the electrode portion 51 of the pre-transfer guide 50 inside the recording material passage area for the recording material P having the maximum width in the thrust direction, a recording material that can be used, such as a recording material P that is normally used. The above-described effects can be obtained with at least part of P.

Example 2
Next, another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus of this embodiment are the same as those of the first embodiment. Therefore, elements having the same or corresponding functions and configurations as those of the image forming apparatus according to the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  FIG. 6 is a schematic diagram showing the positional relationship between the electrode portion 51 of the pre-transfer guide 50 and the recording material P in this embodiment. In the present embodiment, the pre-transfer guide 50 has a width wider than the width of the recording material passage area, and has an electrode portion 51 that is a conductive portion formed of a conductive member in a part thereof. More specifically, the pre-transfer guide 50 has a width wider than the width of the recording material passage area for the recording material P having the maximum width in the thrust direction among the recording materials P usable in the image forming apparatus 100. Yes. The electrode portion 51 is disposed inside the recording material passage area for the recording material P having the maximum width in the direction of the recording material P usable in the image forming apparatus 100 in the thrust direction. As the conductive material, a metal such as iron or SUS can be preferably used. In this example, SUS was used. Further, a portion other than the electrode portion 51 of the pre-transfer guide 50 is a non-conductive portion 52 made of a non-conductive member. In the present embodiment, the non-conductive portion 52 also contacts the recording material P. As the non-conductive material, a synthetic resin such as PET can be preferably used. In this example, PET was used. The electrode portion 51 is disposed inside the recording material passage region in the thrust direction, and the non-conductive portion 52 is disposed on both ends of the electrode portion 51 in the thrust direction. A voltage having the same polarity as the transfer voltage is applied to the electrode unit 51.

  The effect of this embodiment when letter paper is used as the recording material P will be described. In this case, the width W1 of the recording material passage area is 215.9 mm. Therefore, in this embodiment, the width W2 in the thrust direction of the pre-transfer guide 50 is set to 230 mm, and the width W3 in the thrust direction of the electrode portion 51 is set to 100 mm. And this electrode part 51 was arrange | positioned inside the recording material passage area | region in the thrust direction. In the present embodiment, since the recording material P is transported on the basis of the center, the electrode portion 51 is disposed at the center of the recording material passage region in the thrust direction.

  In order to examine the effect of the present embodiment, a configuration in which the width in the thrust direction of the pre-transfer guide 50 (more specifically, the electrode portion 51 to which a voltage is applied) is 230 mm wider than the width of the recording material passage area (conventional example). A comparative experiment was conducted on the configuration of this example. The conveyance speed of the recording material P was set to 150 mm / sec, the voltage value applied to the pre-transfer guide 50 was set to +300 V, and the transfer efficiency and the contamination at the end of the recording material P were confirmed when 1000 sheets of the recording material P were passed. . As the recording material P, letter paper left for 48 hours in a high temperature and high humidity environment of 32.5 ° C./80% was used. Table 2 shows the transfer efficiency and the contamination of the edge of the recording material P when 1000 sheets of letter paper are passed.

  Here, the transfer efficiency was obtained by averaging the transfer efficiencies when five strips of 3 cm width were printed at equal intervals in the conveyance direction of the recording material P every 100 sheets in the print range. As for transfer efficiency, 80% or more is “◯ (good level)”, and even one sheet has a lower value than “× (defect level)”. Further, “O (good level)” indicates that there is no contamination at the end of the recording material P, and “x (defect level)” indicates that even a slight amount of contamination is attached.

  First, since the voltage having the same polarity as the transfer voltage is applied to the pre-transfer guide 50 in both the conventional example and the present embodiment, even if the recording material P absorbs moisture and the resistance is reduced, the transfer current is reduced. There is no shortage, good transfer efficiency can be obtained, and good transfer efficiency can be obtained.

  On the other hand, in the conventional example, the width in the thrust direction of the pre-transfer guide 50 to which the voltage is applied is longer than the width of the recording material passage area. Therefore, when a voltage having the same polarity as the transfer voltage is applied to the pre-transfer guide 50 and the toner easily adheres electrostatically, the toner accumulates outside the recording material passage area of the pre-transfer guide 50 in the thrust direction. After 1000 sheets have passed, the recording material P is smeared at the end.

  On the other hand, in this embodiment, an electrode portion 51 for applying a voltage having the same polarity as the transfer voltage is disposed on a part of the pre-transfer guide 50 having a width wider than the width of the recording material passage region. 51 is arranged inside the recording material passage region in the thrust direction. Therefore, even when a voltage having the same polarity as the transfer voltage is applied to the electrode portion 51 and the toner is likely to adhere electrostatically, the toner does not accumulate or is sufficiently small to an acceptable level, 1000 sheets Even when the paper is passed, the end of the recording material P is not soiled.

  As described above, in this embodiment, the electrode portion 51 is provided on a part of the pre-transfer guide 50 that is equal to or larger than the width of the recording material passage area, and the electrode 51 is disposed inside the recording material passage area in the thrust direction. Thus, even when a voltage having the same polarity as the transfer voltage is applied to the pre-transfer guide 50 and the toner is likely to adhere electrostatically, the toner accumulation on the pre-transfer guide 50 can be suppressed. Therefore, a good image can be obtained even for the recording material P whose resistance has been reduced, and toner contamination at the end of the recording material P can be suppressed. Further, since the pre-transfer guide 50 is wider than the recording material passage area, more specifically, wider than the recording material passage area for the recording material P having the maximum width in the thrust direction, the recording material P is guided more stably. can do.

Example 3
Next, another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus of this embodiment are the same as those of the first embodiment. Therefore, elements having the same or corresponding functions and configurations as those of the image forming apparatus according to the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  In an apparatus corresponding to recording materials P of various sizes, a recording material P having a large size such as a letter size may be passed after a recording material P having a small size such as a postcard is passed. . In this case, the toner may adhere on the pre-transfer guide outside the area through which the postcard-sized recording material P passes. For this reason, even when the number of sheets to be passed is small, toner may adhere to the letter-size recording material P wider than the postcard size, and the recording material P may be soiled.

  Therefore, in this embodiment, the position of the electrode unit 51 to which the voltage is applied is selected from the plurality of electrode units 51 corresponding to the plurality of types of recording materials P having different sizes that can be used in the image forming apparatus 100. It can be changed (switched).

  FIG. 7 is a schematic diagram showing the positional relationship between the electrode portion 51 of the pre-transfer guide 50 and the recording material P in this embodiment. In this embodiment, the pre-transfer guide 50 is wider than the width of the recording material passage area (maximum passage area) for the recording material P having the maximum width in the thrust direction among the recording materials P that can be used in the image forming apparatus 100. It has a width. The pre-transfer guide 50 is provided with a plurality of electrode portions 51 made of a conductive member in the thrust direction. As the conductive material, a metal such as iron or SUS can be preferably used. In this example, SUS was used. Further, a portion other than the plurality of conductive portions of the pre-transfer guide 50 is a non-conductive portion 52 made of a non-conductive member. In the present embodiment, the non-conductive portion 52 also contacts the recording material P. As the non-conductive material, a synthetic resin such as PET can be preferably used. In this example, PET was used. Each of the plurality of electrode portions 51 is disposed inside the maximum passage region in the thrust direction, and the non-conductive portion 52 is disposed between the adjacent electrode portions 51 and on the outer end side of the electrode portions 51 at both ends. A voltage having the same polarity as the transfer voltage is selectively applied to the plurality of electrode portions 51 in accordance with the width of the recording material P to be used in the thrust direction.

  In the present embodiment, a high voltage generator 50a is connected to the plurality of electrode portions 51 via switches S1 to S5 that switch ON / OFF of voltage application. The control device 50b is connected to the electrode unit 51 so that the electrode unit 51 to which a voltage is applied is always inside the recording material passage region in the thrust direction according to the width in the thrust direction of the recording material P to be used. The switches S1 to S5 are switched as appropriate. The width of the recording material P to be used in the thrust direction is detected by the detecting means 60. As an example of the detection unit 60, an input unit provided in the image forming apparatus 100 or the image forming apparatus 100 that inputs information related to the type (that is, size) of the recording material P designated by the user or the like to the control device 50 b. The input unit is connected to be communicable.

  FIG. 8 is a schematic flow diagram for explaining the flow of voltage application processing for the pre-transfer guide 50 in the present embodiment. This figure shows an example in which letter paper or a postcard is used as the recording material P in accordance with a specific example described later. When the printing operation is started, the control device 50b inputs the type of the recording material P designated for use in image formation, which is input from the input unit of the operation panel provided in the apparatus main body M of the image forming apparatus 100. The information concerning is read (step 1). Next, the control device 50b determines whether the designated recording material P is letter paper or postcard (step 2). When the control device 50b determines that the recording material P designated in step 2 is letter paper, the control device 50b turns on the switches S1 to S5 (step 3) and applies a voltage to all the electrode portions 51 from the high voltage generator 50a. (Step 5). On the other hand, when the control device 50b determines that the recording material P designated in step 2 is a postcard, the control device 50b turns on the switches S2 to S4 (step 4), and the high voltage generator is applied to the three electrode portions 51 on the center side. A voltage is applied from 50a (step 5). Thus, image formation is performed with the voltage applied to the pre-transfer guide 50.

  As the recording material P, letter paper which is the largest recording material P usable in the image forming apparatus 100 of this embodiment and postcard which is the smallest recording material P usable in the image forming apparatus 100 of this embodiment. The effect of the present embodiment when using is described. In this embodiment, since the width W1L of the recording material passage area for letter paper is 215.9 mm, the width W2 in the thrust direction of the pre-transfer guide 50 is set to 230 mm or more. In the present embodiment, the pre-transfer guide 50 has five electrode portions 51 arranged at substantially equal intervals in the thrust direction as the plurality of electrode portions 51. The plurality of electrode portions 51 are all arranged inside the recording material passage area for letter paper. Each of the electrode portions 51 is connected to switches S1 to S5 that switch ON / OFF of voltage application. The control unit 50b switches the electrode unit 51 to which a voltage is applied from the high voltage generator 50a in accordance with the width in the thrust direction of the recording material P specified at the time of printing. In the present embodiment, since the recording material P is conveyed on the basis of the center, at least the central electrode portion 51 among the five electrode portions 51 is the smallest recording material that can be used in the image forming apparatus 100 of the present embodiment. The width is smaller than the width W1S of the recording material passage area (minimum passage area) for P. And at least the center electrode part 51 is arrange | positioned inside the minimum passage area | region. In the present embodiment, the width W1S of the minimum passage region is a postcard size of 100 mm. Therefore, the width of the five electrode portions 51 in the thrust direction is 25 mm and the interval between the electrode portions 51 is 10 mm, and the three electrode portions 51 on the center side are inside the recording material passage area for the postcard-sized recording material P. Is arranged. The two electrode portions 51 on both ends are disposed outside the recording material passage area for the postcard-sized recording material P. Therefore, when letter paper is used, a voltage having the same polarity as the transfer voltage is applied to all electrode portions 51, and when using a postcard, a voltage having the same polarity as the transfer voltage is applied to the three central electrode portions 51. The

  In order to examine the effect of the present embodiment, the configuration in which the width in the thrust direction of the pre-transfer guide 50 (more specifically, the electrode portion 51 to which a voltage is applied) is 230 mm (conventional example) and the configuration of the present embodiment are described. A comparative experiment was conducted. The conveyance speed of the recording material P is 150 mm / sec, the voltage value applied to the pre-transfer guide 50 is +300 V, the transfer efficiency when 100 postcards are passed, and the letter when 10 letter papers are passed. Check for paper smudges. As the postcard and letter paper, those left for 48 hours in a high temperature and high humidity environment of 32.5 ° C./80% were used. Table 3 shows the transfer efficiency when 100 postcards are printed, and the result of smearing of the recording material P when the letter paper is subsequently passed.

  Here, the transfer efficiency was obtained by averaging the transfer efficiencies when five strip images having a width of 3 cm were printed at equal intervals in the conveyance direction of the recording material P in the print range. As for transfer efficiency, 80% or more is “◯ (good level)”, and even one sheet has a lower value than “× (defect level)”. In addition, letter paper stains after small size are not marked at all, “◯ (good level)”, and even if a slight amount of stains are adhered, “x (defective level)”.

  First, since the voltage having the same polarity as the transfer voltage is applied to the pre-transfer guide 50 in both the conventional example and the present embodiment, even if the recording material P absorbs moisture and the resistance is reduced, the transfer current is reduced. There is no shortage, good transfer efficiency can be obtained, and good transfer efficiency can be obtained.

  On the other hand, in the conventional example, the width of the pre-transfer guide 50 to which the voltage is applied is longer than the width of the postcard. Toner accumulates on the outside. The edge of the postcard is not smeared when passing about 100 sheets, but when using letter paper wider than the postcard, the accumulated toner adheres to the letter paper and is outside of the recording material passage area of the postcard. As a result, the recording material P becomes dirty.

  On the other hand, in this embodiment, when postcards are used according to the width of the recording material P used in the thrust direction, S2 to S4 are turned on, S1 and S5 are turned off, and letter paper is used. When being performed, S1 to S5 are switched to ON. Thereby, the electrode part 51 to which a voltage is applied becomes inside the recording material passage region. Therefore, even when a voltage having the same polarity as the transfer voltage is applied to the pre-transfer guide 50 and the toner is likely to be electrostatically attached to the pre-transfer guide 50, there is no toner accumulation on the electrode portion 51 or Small enough to be acceptable. For this reason, even if the letter paper having a larger size is passed after passing the postcard, the recording material P is not stained.

  As described above, in this embodiment, a voltage is applied to the electrode portion 51 located inside the recording material passage area according to the width in the thrust direction of the recording material P designated at the time of printing. As a result, when the recording material P having a reduced resistance is used, a voltage having the same polarity as the transfer voltage is applied to the pre-transfer guide, and the pre-transfer guide can be used even when the toner is likely to adhere electrostatically. 50 can suppress toner accumulation. Therefore, even when the recording material P having a different size is used, the recording material P can be prevented from being contaminated by toner.

  In this embodiment, the electrode to which the voltage is applied is switched according to the size of the designated recording material. However, the present invention is not limited to this. For example, a sensor for detecting the width of the recording material P in the thrust direction is provided as the detection means 60 upstream of the pre-transfer guide 50 in the conveyance direction of the recording material P, and a voltage is applied according to the width detected by the sensor. You may switch the electrode part 51 to apply. Further, the number and size of the electrode portions 51 may be set more finely according to the type of the recording material P. That is, for example, by reducing the size of each electrode portion 51 and increasing the number of electrode portions 51, it is possible to cope with more types of recording materials (sizes of recording materials having more stages). .

Other Embodiments Although the present invention has been described with reference to specific embodiments, the present invention is not limited to the above-described embodiments.

  For example, in the above-described embodiment, the case where the present invention is applied to the guide member that guides the recording material to the transfer nip formed by the photosensitive member as the image carrier and the transfer member has been described. However, the present invention is not limited to this, and the present invention can also be applied to a guide member that guides a recording material to a transfer nip formed by an intermediate transfer member serving as an image carrier and a transfer member. . In other words, the toner image formed on the photosensitive member as the first image carrier is transferred (primary transfer) to the intermediate transfer member as the second image carrier, and then the toner image conveyed by the intermediate transfer member. There is an intermediate transfer type image forming apparatus that transfers (secondary transfer) to a recording material. An endless belt or the like is used as the intermediate transfer member. Secondary transfer is performed by applying a secondary transfer voltage to a secondary transfer member that forms a transfer nip (secondary transfer nip) in contact with the intermediate transfer member. A voltage can be applied to the guide member that guides the recording material to the secondary transfer nip, thereby suppressing reduction in secondary transfer efficiency. In that case, in order to suppress toner contamination of the recording material, the same configuration as in the above-described embodiment can be applied to the guide member that guides the recording material to the secondary transfer nip, and the same effect as described above can be obtained. Can be obtained.

  In addition, the present invention solves a common problem in monochrome / color image forming apparatuses, and the effect of this embodiment is not limited to monochrome image forming apparatuses, but is similar to color image forming apparatuses. It is obtained.

  Further, the transfer member is not limited to a roller-shaped transfer member, and may be any transfer member such as a brush shape or a blade shape.

  In the above-described embodiment, the recording material is transported on the basis of the center. However, the recording material may be transported on the basis of one end portion in the thrust direction. In this case, the electrode part of the guide member of Example 1 and the guide member of Example 2 may be arrange | positioned rather than one edge part of a thrust direction. In this case, in the guide member of Example 3, when a small-sized recording material is used, a voltage may be applied to a plurality of electrode portions on one end side in the thrust direction.

  In the above-described embodiment, the entire area of the guide member is in contact with the recording material in the thrust direction. However, a part of the thrust direction is recorded in one or both of the electrode portion and the non-conductive portion. The shape may not be in contact with the material. For example, in the guide member of Example 3, the plurality of electrode portions may have a shape that protrudes toward the recording material conveyance path side with respect to the non-conductive portion. In this case, the non-conductive portion is formed on the recording material. There is no need to contact. However, the recording material can be guided more stably by being configured such that the guide member is in contact with substantially the entire recording material passage region in the thrust direction.

1 Photosensitive drum (image carrier)
5 Transfer roller (transfer member)
5a Transfer power supply 50 Guide before transfer (guide member)
50a High pressure generator (power supply)
50b Control device (control means)
51 Electrode part 52 Non-conductive part Nt Transfer nip

Claims (12)

An image carrier for carrying a toner image;
A transfer member that is provided so as to be in contact with the image carrier and to which a toner image is transferred from the image carrier to a recording material sandwiched between the image carrier and a voltage applied thereto;
A guide member that is provided so as to contact a recording material held between the image carrier and the transfer member and guides the recording material to a contact portion between the image carrier and the transfer member;
A power source for applying a voltage to the guide member;
In an image forming apparatus having
The guide member has a conductive conductive portion that contacts a recording material and to which a voltage from the power source is applied, and the conductive portion is arranged in the image forming apparatus in a direction substantially orthogonal to the recording material conveyance direction. An image forming apparatus, wherein the usable recording material is disposed inside a region through which a maximum width in the direction passes.   The image forming apparatus according to claim 1, wherein the guide member is configured such that all of the portions in contact with the recording material are the conductive portions.   The image forming apparatus according to claim 1, wherein the conductive portion is made of metal.   The guide member has a width that is wider than a region through which a maximum width in the direction among recording materials usable in the image forming apparatus passes in a direction substantially orthogonal to the conveyance direction of the recording material, A non-conductive non-conductive portion that contacts the recording material is provided on both ends in a direction substantially perpendicular to the recording material conveyance direction, and the conductive portion is provided between the non-conductive portions on both ends. The image forming apparatus according to claim 1.   The image forming apparatus according to claim 4, wherein the conductive portion is made of metal, and the non-conductive portion is made of synthetic resin.   The image forming apparatus according to claim 1, wherein the guide member includes a plurality of the conductive portions in a direction substantially orthogonal to a recording material conveyance direction. Detecting means for detecting the width of the recording material in a direction substantially orthogonal to the conveying direction;
In accordance with the width detected by the detecting means, the voltage from the power source is applied only to the conductive portion arranged inside the region through which the recording material of the width passes among the plurality of conductive portions. Control means for controlling;
The image forming apparatus according to claim 6, further comprising: All of the plurality of conductive portions are disposed inside a region through which a recording material having the maximum width in the direction among recording materials usable in the image forming apparatus passes in a direction substantially orthogonal to the conveyance direction of the recording material. And
In the image forming apparatus, at least one of the plurality of conductive portions in the direction substantially orthogonal to the conveyance direction of the recording material or at least one conductive portion on one end side thereof is substantially orthogonal to the conveyance direction of the recording material. The image forming apparatus according to claim 7, wherein the usable recording material is disposed outside a region through which a minimum width in the direction passes.   The image forming according to any one of claims 6 to 8, wherein the conductive portion is formed of a metal, and a portion in contact with the recording material other than the conductive portion is formed of a synthetic resin. apparatus.   The image forming apparatus according to claim 1, wherein the image carrier is a photoconductor.   10. The image bearing member according to claim 1, wherein the image bearing member is an intermediate transfer member that conveys the toner image primarily transferred from the photosensitive member for secondary transfer to a recording material. Image forming apparatus.   The voltage applied to the transfer member for the transfer and the voltage applied to the guide member by the power source have the same polarity.

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