JP4967332B2 - Image forming apparatus - Google Patents

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile, or a complex machine to which an electrophotographic method is applied. In particular, a developed image formed on an image carrier is transferred using a transfer unit. The present invention relates to an improvement of an image forming apparatus of a transfer type.

JP 2005-275212 A JP 2004-013032 A

  In such an image forming apparatus, a guide member for guiding a transfer material is provided at a nip portion between the photosensitive drum and the transfer member and a nip portion between the belt-shaped or drum-shaped intermediate transfer member and the transfer member. However, if the transfer material is not guided to the nip portion in an appropriate posture by the guide member, the transfer material is transported to the transfer member side and an excessive transfer electric field acts, or the rear end of the transfer material is the guide member When it passes through, the rear end of the transfer material jumps up, and the image is disturbed.

  Therefore, in order to solve such a problem, prior arts for suppressing image disturbance accompanying the above-described phenomenon have been proposed (see, for example, Patent Documents 1 and 2).

  Here, Patent Document 1 discloses an image forming apparatus in which a sheet that is charged with the same polarity as a resin sheet or toner made of polyethylene terephthalate is pasted on a paper guide surface.

  Patent Document 2 discloses an image forming apparatus in which an intermediate portion of a paper guide is disposed on the photosensitive drum side with respect to a transfer nip tangent, and the paper guide is configured by a member that is charged with the same polarity as a semiconductive material or toner. It is disclosed.

  However, each of the above prior arts has the following problems.

  For example, in each of the prior arts disclosed in Patent Documents 1 and 2, since the tip portion (edge portion) of the sheet member is used as a functional surface, there has been a problem that the effect decreases with time.

  Specifically, as schematically shown in FIG. 4, the front end portion 105 t (edge portion) of the sheet member 105 attached to the side surface of the support member 101 is supported in sliding contact with the recording paper P, and Since the recording paper P is guided to the transfer nip region N so as to have a predetermined posture, the front end portion 105t of the sheet member 105 is worn by the sliding contact between the sheet member 105 and the recording paper P, and the front end of the recording paper P is slid. The contact position changes or the tip 101t of the support member 101 is exposed and comes into sliding contact with the recording paper P.

  When the position of the leading end portion 105t of the sheet member 105 changes, the posture of the recording paper P also changes, and the effect of suppressing image scattering (blurring) or the like due to gap transfer at the portion immediately before the transfer nip region N is achieved. Decreases over time.

  In particular, the support member 101 is inevitably made of an ordinary resin having good moldability (for example, ABS resin) in consideration of size, rigidity, cost, and the like, and is molded with such a resin. When the support member 101 rubs against the recording paper P, the support member 101 is easily charged to a high potential (for example, about 4000 V), and an improper discharge such as a gap discharge occurs, resulting in an image defect. There was a problem of letting it go. Further, when the sheet member 105 is bonded to the side surface of the support member 101 and the both are configured as functional surfaces, toner is added to the bonding portions of the tips 101t and 105t of the support member 101 and the sheet member 105. There has also been a problem of accumulation and toner contamination.

  Further, in the prior art disclosed in Patent Document 2, the intermediate portion (101t, 105t) of the guide member 100 is arranged on the photosensitive drum PR side with respect to the transfer nip tangent to suppress the trailing edge splash of the recording paper P. Therefore, it is inevitably necessary to dispose the guide member 100 in the vicinity of the transfer nip region N, and a part of the guide member 100 is a movable region of the transfer roll Rt (moving region of the transfer roll Rt during disassembly / assembly). ) And the workability during assembly is greatly impaired. In order to improve such assemblability, problems such as cost increase due to addition of special jigs and assembly man-hours, and problems such as restrictions on design / assembly freedom have arisen. Further, when the guide member 100 (the support member 101 and the sheet member 105) itself is integrally formed of a semiconductive material or a member that is charged with the same polarity as the toner, molding is difficult, and there is a problem such as molding failure and cost increase. Was produced.

  Therefore, the present invention has been made in view of the above-described problems of the prior art, and a simple image forming apparatus that prevents discharge defects due to excessive charging of the guide member and image defects due to sheet trailing edge splashing. The purpose is to provide a low-cost configuration.

  In order to achieve the above object, an image forming apparatus according to the present invention includes a drum-shaped image carrier on which a toner image is formed, a pressure-contacting and opposed arrangement of the image carrier, A transfer roll that forms a transfer nip region for transferring the toner image onto the transfer material, and a guide member that guides the transfer material to the transfer nip region, the guide member facing the image carrier And a support member which is disposed outside the moving region at the time of disassembly / assembly of the transfer roll, and at least a part thereof extends to the image carrier side of the transfer nip tangent line, and the support member And a sheet member that is bent so as to cover the opposite end portion of the support member.

  Generally, for a guide member that guides the recording paper to the transfer area, the guide member is used to suppress the trailing edge splash of the recording paper when the recording paper comes out of the guide member, and to transport the recording paper to the transfer area in a stable posture. It must be placed as close as possible to the transfer area. When the guide member is disposed in the moving area when the transfer roll is disassembled / assembled, the assembling workability when the transfer roll is assembled to the apparatus is greatly impaired.

  Further, since the recording paper is conveyed while being pushed and bent toward the image carrier such as the photosensitive drum by the guide member, when the recording paper is guided to the transfer area, the leading end of the guide member slides on the recording paper. The wear part comes into contact and wears, and the wear part is easily triboelectrically charged. When charges are accumulated at the tip of the guide member that is easily frictionally charged, the tip of the guide member is disposed close to the image carrier and the transfer roll, so that discharge easily occurs.

  Therefore, according to the image forming apparatus of the present invention configured as described above, since the support member constituting the guide member is disposed outside the moving area during disassembly / assembly of the transfer roll, Interference between the roll and the support member can be prevented, and workability during assembly can be improved. In addition, the sheet member bent so as to cover the end of the support member facing the image carrier sufficiently supports the recording sheet to prevent the trailing edge of the sheet from being splashed, and by sliding contact with the recording sheet. Since the support member is not overcharged, it is possible to prevent image defects such as white spot-like image omission due to discharge due to abnormal charging (excessive charging) and image scattering due to paper trailing edge splashing at a low cost with a simple configuration. it can.

  In addition, the downstream end of the sheet member is in a moving area when the transfer roll is disassembled / assembled, and the angle between the downstream end and the transfer nip tangent extends to an area within 0 to 90 °. May be present.

  When configured in this manner, the downstream end of the sheet member is in the moving area during disassembly / assembly of the transfer roll, and the angle formed between the downstream end and the transfer nip tangent is within 0 to 90 °. The recording paper is more stably supported up to the transfer nip area without impairing the workability when the transfer roll is assembled by the flexible sheet member. It is possible to reliably prevent the rear end splash when the sheet is pulled out from the sheet member.

  Further, the downstream end of the sheet member extends to a region on the transfer nip tangent or on the transfer roll side with respect to the transfer nip tangent, and at an angle of 90 ° or less with the transfer nip tangent. You may do it.

  When configured in this manner, the downstream end of the sheet member is on the transfer nip tangent or on the transfer roll side with respect to the transfer nip tangent, and the angle formed with the transfer nip tangent is within 90 °. Since it extends, the recording paper is sufficiently supported at the downstream end of the sheet member to the vicinity of the transfer roll, and the recording paper is stably guided to the transfer area along the transfer nip tangent. It is possible to suppress high-frequency vibration when the sheet member comes out from the downstream end portion, and to more reliably prevent image defects due to sheet trailing edge splashing.

  The sheet member may be formed of a member that is charged to the same polarity as the toner.

  In such a configuration, since the sheet member is formed of a member that is charged to the same polarity as the toner, even if the sheet member is charged by rubbing against the recording paper, the toner image or the image carrier Therefore, the occurrence of discharge can be suppressed and image defects such as white spot-like transfer omission can be prevented.

In the above, the sheet member may have a volume resistance of 10 ¹² to 10 ¹⁶ Ωcm.

In this case, since the volume resistance of the sheet member is 10 ¹² to 10 ¹⁶ Ωcm, the sheet member becomes difficult to be charged by sliding contact with the recording paper, and image defects due to abnormal discharge are more effectively prevented. Can be prevented.

  According to the present invention, it is possible to realize an image forming apparatus that prevents discharge defects due to overcharging and image defects due to paper trailing edge splashing with a simple configuration at low cost.

  Hereinafter, an embodiment according to the present invention will be described with reference to the drawings.

  First, a schematic configuration of an embodiment of an image forming apparatus to which the present invention can be applied will be described with reference to FIG.

  In FIG. 1, an image forming apparatus (digital copying machine) U having a unit configuration includes an image forming apparatus main body U1 and an automatic document feeder U2. The image forming apparatus main body U1 includes an image forming unit IOT and a document reading unit IIT, and is sent from image information of a document read by the document reading unit IIT, a personal computer (not shown), an image data input device, or the like. Image information or the like is input, and image processing is performed on the input image information.

  The automatic document feeder U2 is supported on a transparent platen glass PG on the upper surface of the document reading unit IIT, and is configured to be rotatable upward. The automatic document feeder U2 has a document feed tray TG1 on which a plurality of documents Gi to be copied are placed and placed thereon, and a plurality of documents placed on the document feed tray TG1. Each document Gi sequentially passes the copy position on the platen glass PG and is discharged to the document discharge tray TG2.

  On the other hand, the image forming apparatus main body U1 has a UI (user interface) through which a user inputs an operation command signal such as a copy start, and a sheet discharge tray between the image forming unit IOT and the image reading unit IIT. TRh is provided.

  An exposure optical system A for reading a document image is disposed below the platen glass PG, and is placed on the platen glass PG manually or manually on the platen glass PG by the automatic document feeder U2. Reflected light from a document (not shown) is converted into an electrical signal by a CCD (solid-state imaging device) via an exposure optical system A. Thereafter, the electrical signal output from the CCD is converted into image data and temporarily stored by the image processing system IPS, and the image data is transmitted to the laser drive circuit DL as image data for forming a latent image at a predetermined timing. Is output. The laser drive circuit DL outputs a laser drive signal to the latent image forming unit ROS according to the input image data. The operation of the user interface UI, the image processing system IPS, the laser drive signal output device DL, the power supply circuit E for applying a bias voltage to the developing roll Ga and the transfer roll Rt, which will be described later, is controlled by the controller C.

  Further, on the left side of the latent image forming unit ROS, a toner image forming unit (process unit) Up configured to be detachable from the image forming apparatus main body U1 and forming a black toner image is disposed. The toner image forming unit Up includes a photosensitive drum PR that is an image carrier that rotates in a predetermined direction, a charging roll CR, a developing device G, a cleaner CL, and the like, and is not shown in the latent image forming unit ROS. The laser beam L emitted from the laser diode is incident on the photosensitive drum PR.

  The developing device G includes, for example, a developing roll Ga to which a developing bias of about −500 V is applied, and a plurality of developer agitating members that convey the developer containing polymerized toner charged to negative (minus) polarity to the developing roll while stirring. A developing container V that rotatably supports the developer and stores the developer, and the electrostatic latent image on the photosensitive drum PR passing through the developing area is developed into a toner image by the developing roll Ga. Yes.

  In addition, a transfer area is formed on the downstream side of the development area formed by the photosensitive drum PR and the developing roll Ga so as to be opposed to the photosensitive drum PR so as to form a transfer nip area with the photosensitive drum PR. A roll Rt is provided.

  The transfer roll Rt is urged so as to come into pressure contact with the photosensitive drum PR by a spring. When the recording paper P as a transfer material passes through the transfer area, the transfer roll Rt is controlled by the controller C. For example, a transfer bias voltage of about +1000 V is applied from the power supply circuit E at a predetermined timing, and the toner image on the photosensitive drum PR is transferred onto the recording paper P by the transfer roll Rt.

  Further, on the downstream side of the transfer roll Rt, a fixing roll F that includes a heating roll Fh and a pressure roll Fp that rotate in pressure contact with each other and heat-presses and fixes the toner image on the recording paper P is disposed. . On the other hand, in the lower part of the main body of the image forming apparatus, paper feed trays TR1 to TR4 that accommodate recording paper P so as to be fed are disposed.

  Next, an outline of the operation of the image forming apparatus according to the present invention configured as described above will be described below.

  First, in the present embodiment, the surface of the photosensitive drum PR is uniformly charged to a negative (minus) polarity of about −700 V by the charging roll CR, and then exposed and scanned by the laser beam L of the latent image forming unit ROS. Thus, an electrostatic latent image is formed. Here, the charged potential of the photosensitive drum PR in the portion irradiated with the laser beam L is lowered to about −200 to −300V. Then, the surface of the photosensitive drum PR on which the electrostatic latent image is formed rotates and moves, and the electrostatic latent image formed on the photosensitive drum PR is converted into a toner image in the developing area facing the developing roll Ga. . Thereafter, the toner image formed on the photosensitive drum PR is transferred to the recording paper P in a transfer region facing the transfer roll Rt.

  On the other hand, the recording paper P taken out from the paper feed trays TR1 to TR4 by the pickup roll Rp is separated one by one by the separation roll Rs having the retard roll and the paper feed roll, and is arranged along the paper transport path SH. The paper is transported by a plurality of paper transport rollers Ra. The recording paper P transported by the paper transporting roll Ra is transported to a transfer region where the transfer roll Rt and the photosensitive drum PR face each other at a predetermined timing by a pair of resist rolls Rr. Then, as described above, the toner image formed on the photosensitive drum PR is transferred to the recording paper P by the pressure contact force and electrostatic attraction force between the photosensitive drum PR and the transfer roll Rt in the transfer region. Here, the resist roll Rr can be constituted by a roll in which a base made of ABS (acrylonitrile butadiene styrene) resin is coated with urethane rubber.

  The recording paper P to which the toner image has been transferred is conveyed to the fixing device F, and the toner image is fixed on the recording paper P by heat and pressure in a fixing area formed by the heating roll Fh and the pressure roll Fp. Then, the fixed recording paper P is discharged to the discharge tray TRh via the discharge roll Rh. The transfer residual toner on the photosensitive drum PR is collected by the cleaner CL, and the photosensitive drum PR is charged again by the charging roll CR to prepare for the next image formation.

  Next, the detailed configuration around the guide member according to the present invention will be further described with reference to FIG. FIG. 2 is an enlarged view of a main part of the paper guide unit according to the present invention.

As shown in FIG. 2, a photosensitive drum side guide member is disposed between a transfer region N formed by a pressure contact portion between the transfer roll Rt and the photosensitive drum PR and the resist roll pair Rr ₁ and Rr _2. (Hereinafter also referred to as a right guide member) 10 and a transfer roll side guide member (hereinafter also referred to as a left guide member) 20 are disposed. The recording paper P sent out by the resist roll pair Rr ₁ , Rr ₂ is guided by the right guide member 10 and the left guide member 20 and conveyed to the transfer area N.

The right guide member 10 includes a straight portion 11 extending from the right resist roll Rr ₂ toward the transfer roll Rt, a connecting portion 13 formed so as to be substantially orthogonal to the tip of the straight portion 11, and the connecting portion. 13 and a straight line portion 15 extending from one end to the transfer roll Rt.

On the other hand, the transfer roll side guide member (left guide member) 20 which is a guide member according to the present invention includes a linear portion 21L extending from above the left resist roll Rr ₁ toward the surface of the photosensitive drum PR, and a transfer portion. A support member 21 having an arc portion 21B extending along the surface shape of the transfer roll Rt so as to cover the lower surface of the roll Rt, and a sheet member attached to the side surface of the linear portion 21L of the support member 21 23.

  Specifically, as schematically shown in FIG. 3, the support member 21 is disposed outside the moving region (movable region of the transfer roll Rt along the pressure contact direction) S when the transfer roll Rt is disassembled / assembled. The straight portion 21L of the support member 21 has a front end portion 21t that is a facing end portion that opposes the photosensitive drum PR with the front end thereof exceeding the arc portion 21B. The leading end 21t is disposed so as to be located on the photosensitive drum PR side with respect to the nip tangent Ln in the transfer region N, and the separation distance from the photosensitive drum PR is set to approximately 2 mm. Yes.

  As described above, the tip 21t of the support member 21 is arranged so as to be positioned on the photosensitive drum PR side with respect to the nip tangent Ln. Therefore, when the recording paper P enters the transfer region N, the transfer roll It is not too close to the Rt side, the transfer electric field is not excessive, gap transfer does not occur, and image defects such as image scattering (blur) and transfer leak (white spot missing) are prevented in advance. be able to. In addition, since the support member 21 is disposed outside the moving region S when the transfer roll Rt is disassembled / assembled, the workability when the transfer roll Rt is assembled to the apparatus is not impaired, and the cost due to the reduction in work man-hours, etc. Can contribute to down.

  In the present embodiment, the support member 21 can be formed of, for example, an ABS (acrylonitrile butadiene styrene) resin from the viewpoint of moldability, ensuring rigidity and reducing costs.

  On the other hand, the sheet member 23 is a flexible member having a thickness of about 0.25 mm. The distal end of the sheet member 23 is folded so as to cover the distal end portion 21t of the support member 21, and the sheet member 23 is folded. The distal end portion 23t is arranged and formed so as to extend in the moving region S when the transfer roll Rt is disassembled / assembled. Specifically, the distal end portion 23t is arranged and formed so as to extend within an area range where the angle θ formed with the nip tangent Ln is 0 to 90 °.

  By arranging and forming the leading end portion 23t of the flexible sheet member 23 in such a region range, when assembling the transfer roll Rt to the apparatus, the assembling workability is not impaired, and recording is performed. When the paper P is guided to the transfer area N, the recording paper P is smoothly guided along the rotation of the photosensitive drum PR, and the paper when the rear end of the recording paper P comes out of the front end portion 23t of the sheet member 23 is used. It is possible to prevent the trailing edge of the sheet from splashing due to the trailing edge falling to the transfer roll Rt, and to achieve both improvement in assemblability and prevention of image defects.

  Note that the recording paper P is stably supported along the nip tangent Ln until just before the transfer area N, and vibrations when the rear edge of the paper slips out from the front end portion 23t of the sheet member 23 are further suppressed, thereby causing an image defect. From the viewpoint of more effectively preventing the occurrence of the toner image, the front end portion 23t of the sheet member 23 is further on the nip tangent line Ln from the front end portion 21t of the support member 21 or in a region closer to the transfer roll Rt than the nip tangent line Ln. In addition, it is more preferable to form and arrange so that the angle θ formed with the nip tangent Ln extends within a range of 90 ° or less.

  By disposing and forming the leading end portion 23t of the sheet member 23 in such a region, the recording paper P is sufficiently supported by the downstream end portion 23t of the sheet member 23 up to the vicinity of the transfer roll Rt and the transfer nip tangent Ln. The recording paper P is stably guided to the transfer area N along the line A, and high-frequency vibration is suppressed when the recording paper P is pulled out from the downstream end 23 t of the sheet member 23, and image defects caused by splashing of the rear edge of the paper are more reliably performed. Can be prevented.

Further, the sheet member 23 in the present embodiment is less likely to be charged compared to a normal resin (for example, ABS resin used for the support member 21) when in sliding contact with the recording paper P, and has the same polarity as the toner. It is preferably formed of a member that is electrically charged, for example, flexible PET (polyethylene terephthalate).
Furthermore, from the viewpoint of preventing the sheet member from being charged easily by sliding contact with the recording paper and more effectively preventing image defects due to abnormal discharge, the volume resistance of the sheet member is preferably 10 ¹² to 10 ¹⁶ Ωcm. .

In the guide member 20 according to the present invention configured as described above, the recording paper P conveyed from the pair of resist rolls Rr ₁ and Rr ₂ is along the sheet member 23 of the left guide member 20 and the surface of the photosensitive drum PR. Toward the transfer area N along the rotation of the photosensitive drum PR. At this time, since the recording paper P is once fed to the photosensitive drum PR side beyond the nip tangent Ln, the recording paper P is conveyed to the transfer region N while being in close contact with the surface of the photosensitive drum PR. Excessive proximity to Rt can be prevented, and thereby gap discharge due to a transfer electric field can be effectively prevented.

  Further, since the opposing end portion (tip end portion) 21t of the support member 21 is covered with the sheet member 23, the discharge characteristics of the guide member 20 may change over time due to sliding with the recording paper P. Absent. That is, in the guide member 20 according to the present embodiment, the recording paper P and the support member 21 are not immediately brought into sliding contact with each other due to wear of the sheet member 23 corresponding to the tip portion 21t of the support member 21. Compared with the guide member 100 having the conventional configuration shown in FIG. 4, the life of the guide member 20 can be significantly increased. Further, since the sheet member 23 is affixed to the support member 21, maintenance and replacement can be easily performed, and the life of the guide member 20 can be further extended easily. Further, since the support member 21 and the sheet member 23 can be made of different materials, the sheet member 23 is less likely to be charged by sliding with the recording paper P and charged to the same polarity as the polarity of the toner image and the photosensitive drum PR. In addition, it is possible to easily realize the support member 21 that enables moldability, rigidity, and cost reduction, and it is possible to widen the selection range of the constituent materials of the members 21 and 23.

  Further, the tip end portion 23t of the sheet member 23 is in the moving region S when the transfer roll Rt is disassembled / assembled, and is an area where the angle formed with the nip tangent Ln is within 0 to 90 °, more preferably the nip tangent. Since it extends to a region on the transfer roll Rt side with respect to Ln, the angle formed with the nip tangent Ln is within 90 °, the recording paper P can be transferred without impairing workability during assembly. When guiding to the area N, the trailing edge of the recording paper P is sufficiently supported up to the transfer area, and the image scattering due to the trailing edge of the recording paper P falling to the transfer roll Rt side (paper trailing edge splashing). The occurrence of image defects such as (blur) and transfer leakage (white spot missing) can be more reliably prevented.

  Further, since the sheet member 23 is formed of a member that is charged with the same polarity as the charging polarity of the toner image at the time of frictional charging with the recording paper P, even if charge is accumulated on the sheet member 23, The potential difference is not so large. Accordingly, the discharge between the toner image and the photosensitive drum PR can be reduced, thereby reducing the reverse charging of the toner due to the discharge, the scattering of the toner due to the discharge, and the transfer of the white spots. Occurrence of image defects such as omission can be suppressed. Even when polymerized toner is used, the occurrence of toner scattering due to discharge can be reduced.

  When the image forming apparatus according to the present invention as described above (see FIG. 3) and the image forming apparatus having the conventional configuration as shown in FIG. In FIG. 1, image defects such as image scattering and transfer leak occurred at 100 to 150k sheets. However, in the image forming apparatus according to the present invention, the occurrence of the image defects was not confirmed even when the number of sheets exceeded 300k sheets.

  As a result, according to the image forming apparatus of the present invention, it has been confirmed that image defects based on excessive charging of the guide member and sheet trailing edge splashing can be prevented at a low cost with a simple configuration.

1 is a schematic configuration diagram showing an embodiment of an image forming apparatus according to the present invention. It is a principal part enlarged view which expands and shows the structure of the guide member periphery which concerns on this invention. It is a schematic diagram which shows the structure of the guide member which concerns on this invention. It is a schematic diagram which shows the structure of the conventional guide member.

Explanation of symbols

  10: Right guide member, 20: Left guide member, 21: Support member, 21B: Arc part, 21L: Straight line part, 21t: Tip part, 23: Sheet member, 23t: Tip part, 100: Guide member, 101: Support Member, 105: sheet member, 101t, 105t: leading end, Ln: transfer nip tangent, N: transfer nip region, P: recording paper, PR: photosensitive drum, Rr: registration roll, Rt: transfer roll, S: disassembly / Moving area during assembly

Claims (3)

A drum-shaped image carrier on which a toner image is formed;
A transfer roll that is disposed opposite to and in contact with the image carrier, and forms a transfer nip region that transfers the toner image to a transfer material with the image carrier;
A guide member for guiding the transfer material to the transfer nip region;
The guide member includes a rigid support member and a flexible sheet member,
The support member is disposed outside the moving area during disassembly / assembly of the transfer roll so that the tip of the support member extends to the image carrier side with respect to the transfer nip tangent, whereas the sheet member Affixed to the support member, is bent so as to cover the front end of the support member and intersect the transfer nip tangent, and the front end is on the transfer roll side with respect to the transfer nip tangent, and the transfer roll is disassembled / assembled. An image forming apparatus, wherein the image forming apparatus is arranged so as to extend in a moving region of time . The sheet member, an image forming apparatus according to claim 1 or 2, characterized in that it is formed by a member is charged to the same polarity as the toner. The sheet member, an image forming apparatus according to any one of claims 1 to 3, characterized in that the volume resistivity is 10 ¹² ~10 ¹⁶ Ωcm.

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