JP2003122142A - Toner image transfer device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a toner image transfer device capable of excellently transferring a toner image to a recording sheet by preventing the occurrence of such a phenomenon that the trailing edge of the recording sheet whose leading edge has already rushed into a transfer part springs up just before the transfer part. SOLUTION: This transfer device for transferring the toner image to the recording sheet P from an image carrier 5 on which the toner image is formed or transferred is constituted of a transfer roll 8 press-contacting with the image carrier 5, a just-before carrying roll 10 feeding the sheet P to a toner image transfer position formed by the image carrier 5 and the roll 8, and a pair of guiding members 20 and 21 provided between the roll 10 and the transfer position and guiding the sheet P. Then, the 1st guiding member 20 arranged on the image carrier side is provided with a restraining means 22 releasing a situation that the trailing edge of the sheet P getting out of the member 20 springs up toward the image carrier 5 stepwise.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a toner image transfer device for forming a recorded image by transferring a toner image formed on the surface of a photosensitive layer onto a recording sheet, such as an electrophotographic copying machine or a laser beam printer. More specifically, the present invention relates to an improvement for preventing the disorder of the transferred image when the toner image is transferred to a recording sheet having a strong rigidity such as thick paper.

[0002]

2. Description of the Related Art In an image forming apparatus such as a color copying machine or a color printer for forming a full-color image, yellow, magenta, cyan and black formed on an image bearing member such as a photosensitive drum according to image information. It is necessary to transfer each toner image on the recording sheet in an overlapping manner, but in recent years, each color toner image is not directly transferred from the image carrier to the recording sheet, but is first transferred to the intermediate transfer belt and then transferred to the recording sheet. It is known that the secondary transfer is performed. In this way, when the toner images are indirectly transferred from the image carrier to the recording sheet via the intermediate transfer belt, the toner images of the respective colors can be superposed on each other on the intermediate transfer belt. It is possible to superimpose toner images of a plurality of colors without being affected by the variation in the resistance value of the recording sheet, and it becomes easy to control the transfer conditions of the toner images when forming a color image. Can be easily transported, and there is an advantage that the occurrence of sheet jam can be prevented as much as possible.

In an image forming apparatus using such an intermediate transfer belt, a transfer roll to which a transfer bias is applied is used for secondary transfer of a toner image. This transfer roll is arranged so as to face a backup roll arranged on the back surface side of the intermediate transfer belt, abuts against the intermediate transfer belt under a predetermined pressure, and a predetermined transfer is performed between the backup roll and the backup roll. A bias voltage is applied, and the toner image on the intermediate transfer belt is transferred to a recording sheet inserted between the intermediate transfer belt and the transfer roll for use. Further, in order to prevent the recording sheet that has passed through the secondary transfer portion from sticking to the intermediate transfer belt, the discharge direction of the recording sheet at this secondary transfer portion should be slightly closer to the transfer roll, that is, slightly downward. Is set to.

On the other hand, the recording sheet is unloaded from the paper feed tray at a predetermined timing in synchronization with the rotation timing of the intermediate transfer belt, and is transported toward the secondary transfer section. A registration roll (hereinafter referred to as "registration roll") is provided immediately before the secondary transfer portion, and the conveyed recording sheet hits the registration roll and is temporarily locked.
Skew generated during the transportation is corrected. And
The registration roll starts rotating at a predetermined timing, and the recording sheet is sent to the secondary transfer portion.

When the recording sheet that has entered the secondary transfer portion is sandwiched between the transfer roll and the backup roll, the recording sheet in front of the secondary transfer portion is wavy along the width direction due to the influence of the pressure distribution. When the recording sheet passes through the secondary transfer portion in the deformed state, the recording sheet may be wrinkled or a toner image may be missing. For this reason, conventionally, a pair of guide members is provided between the secondary transfer portion and the registration roll, with the conveyance path of the recording sheet interposed therebetween, and the recording sheet is formed between the first and second guide members. It is configured to reach the secondary transfer portion through the gap. With such a configuration, the trailing edge of the recording sheet protruding into the secondary transfer portion is restricted from being deformed by the guide member, so that the above-mentioned wavy deformation of the recording sheet can be suppressed. Therefore, it is possible to effectively prevent the occurrence of wrinkles and the occurrence of transfer omission.

[0006]

Since the guide member provided in front of the secondary transfer portion plays a role of preventing the deformation of the recording sheet passing through the secondary transfer portion, the secondary transfer portion is thus prevented. It can be said that it is preferable to exist at a position as close as possible to. However, in the first guide member located on the image receiving surface side of the toner image, the tip on the secondary transfer portion side is likely to interfere with the intermediate transfer belt. I had no choice but to make it shorter.

Therefore, when the toner image is secondarily transferred to a recording sheet having a strong rigidity such as a postcard, the trailing edge of the recording sheet that has passed through the first guide member suddenly jumps upward. However, there is a problem that the toner image secondarily transferred to the recording sheet is disturbed by the impact. Particularly, in order to improve the peelability of the recording sheet from the intermediate transfer belt, when the leading edge of the recording sheet passing through the secondary transfer portion is guided toward the transfer roll as described above, the trailing edge of the recording sheet is A force toward the intermediate transfer belt, which is opposite to the tip, tends to act on the sheet, and such a problem of jumping up tends to occur remarkably.

JP-A-10-221973 and JP-A-10-232567 mention that the trailing edge of the recording sheet that has exited the registration roll jumps up and the trailing edge collides with the first guide member. In the former case, a part of the first guide member is cut out to correspond to the recording sheet of a specific size, and in the latter case, a guide member corresponding to the recording sheet of a specific size is provided on the lower surface side of the first guide member. Is disclosed. However, these prior examples do not take into consideration the jumping up that occurs when the trailing edge of the recording sheet leaves the first guide member, and these prior examples cannot overcome the above-mentioned problems. .

In the above description, the case where the toner image is transferred from the intermediate transfer belt to the recording sheet has been described as an example. However, such a problem is caused by the toner formed on the photosensitive drum or the photosensitive belt. The same applies to a toner image transfer device for directly transferring an image to a recording sheet. In the above description, the case where the recording sheet is conveyed in the horizontal direction has been described as an example, but the same problem occurs in the vertical direction.

The present invention has been made in view of the above problems, and an object of the present invention is to prevent a phenomenon in which the trailing edge of a recording sheet, the leading edge of which has already entered the transfer section, jumps up immediately before the transfer section. It is an object of the present invention to provide a toner image transfer device capable of preventing the occurrence of the toner image and thus favorably transferring the toner image onto the recording sheet.

[0011]

That is, the present invention is a transfer device for transferring a toner image from an image carrier on which a toner image is formed or transferred onto a recording sheet, which is in pressure contact with the image carrier. Transfer roll, a transport roll immediately before feeding the recording sheet to the transfer position of the toner image formed by the image carrier and the transfer roll, and a pair provided between this transport roll and the transfer position to guide the recording sheet. And a first guide member disposed on the upper side is provided with a suppressing unit that gradually releases the trailing edge of the recording sheet that exits the first guide member from jumping up toward the image carrier. It is characterized by that.

According to the above technical means, the transfer of the toner image from the image carrier to the recording sheet proceeds, and when the recording sheet completely exits the first guide member, the image is transferred to the image carrier at the rear end. Since the upward jump is gradually released by the suppressing means, sudden jump does not occur, and it is possible to avoid the inconvenience of disturbing the toner image during transfer due to the shock of the jump.

Here, as a means for suppressing the recoil of the trailing edge of the recording sheet in a stepwise manner, first of all, the trailing edge of the recording sheet is located at the downstream end of the first guide member in the recording sheet conveying direction. It is conceivable to form a notch having an inclined side with respect to, for example, a notch having a substantially triangular shape.
Since the opening width of the cutout portion having such a shape gradually expands as the recording sheet advances, the jumping of the recording sheet gradually opens as the opening width increases, It is possible to prevent such a sudden jump of the trailing edge of the recording sheet.

At this time, the notch may be formed corresponding to a recording sheet of a specific size such as a postcard, or may be formed over the entire width direction of the recording sheet. However, from the viewpoint that a pair of guide members are provided to prevent the corrugated deformation that occurs at the trailing edge of the recording sheet that has entered the transfer portion, the notch is formed in the entire widthwise direction of the recording sheet. It is not preferable that the notches are not formed at least at the positions corresponding to both ends of the maximum size recording sheet in the width direction, and at this position, the first guide member has the maximum length along the recording sheet conveyance direction. It is preferable to have. By forming the cutout portion in this way, it is possible to feed at least the maximum size of the recording sheet to the transfer portion while suppressing the deformation of the recording sheet regardless of the formation of the cutout portion.

Further, the size of the cutout portion required to gradually release the jumping up of the trailing edge of the recording sheet depends on the size of the recording sheet desired to prevent such jumping up, and the jumping up is also caused. Since it occurs only when the toner image is transferred to a recording sheet having a strong rigidity such as thick paper, from the viewpoint of more effectively implementing the present invention, it may depend on the type and / or size of the recording sheet used. It is preferable to be configured so that the cut amount of the cutout portion along the recording sheet conveying direction and the opening width along the width direction of the recording sheet can be changed.

For example, a cutout portion is formed in the entire width direction of the recording sheet with respect to the first guide member, and the cutout portion is appropriately covered with a movable adjustment plate attached to the first guide member. By moving the movable adjusting plate, it is possible to change the cut amount and the opening width of the cutout portion. At this time, the movable adjusting plate may be capable of manually adjusting the setting position, or may be automatically set by taking in information regarding transfer conditions such as the size and type of recording sheet to be used.

On the other hand, as another means for restraining the jumping up of the trailing edge of the recording sheet in a stepwise manner, recording is performed at the downstream end of the first guide member in the recording sheet conveying direction without forming a notch. It is conceivable to form an inclined portion that gradually widens the distance from the second guide member on the back side of the sheet along the conveyance direction of the recording sheet. In this way, if the distance between the first guide member and the second guide member gradually expands along the recording sheet conveying direction, the jumping of the recording sheet gradually increases as the distance between the pair of guide members increases. Therefore, it is possible to prevent such a sudden jump of the trailing edge of the recording sheet.

Further, in order to prevent the trailing edge of the recording sheet that has come out of the first guide member from jumping up, it is possible to separate the end portion of the first guide member on the transfer portion side from the transfer portion by a certain distance or more. It is an effective means. This is because it is considered that as the end portion of the first guide member is separated from the transfer portion, the force for flipping up the trailing end of the recording sheet is weakened. However, if the tip of the first guide member on the transfer portion side is too far from the transfer portion, the wavy deformation that occurs on the recording sheet during the passage of the transfer portion cannot be effectively suppressed by the pair of guide members, as described above. However, there is a concern that wrinkles may occur on the recording sheet after transfer, or transfer omission may occur.

According to the results confirmed by the inventors of the present application through experiments, the distance between the toner image transfer position and the end of the first guide member on the downstream side in the recording sheet conveyance direction is L, and the transfer roll to the image carrier is When the angle formed by the tangential direction and the conveying direction of the recording sheet immediately before the transfer position is θ, these θ and L are expressed by the following equation, that is, 0.43 ≦ θ / L ≦ 0.55
Within the range satisfying the condition, the transfer image was not disturbed due to the jumping up of the trailing edge of the recording sheet, and the undulation of the recording sheet was suppressed during transfer, and the recording sheet could be satisfactorily conveyed.

In the present invention, the image carrier for transferring the toner image onto the recording sheet is a concept including a photosensitive drum, a photosensitive belt, an intermediate transfer drum and an intermediate transfer belt.

[0021]

DETAILED DESCRIPTION OF THE INVENTION The toner image transfer device of the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 shows an example of a color laser beam printer that transfers a toner image onto a recording sheet using the toner image transfer device of the present invention. In the figure, reference numeral 1 is a photosensitive drum as an image carrier, reference numeral 2 is a charging roll for pre-charging the surface of the photosensitive drum 1, and reference numeral 3 is an electrostatic charge on the photosensitive drum 1 charged by the charging roll 2. A laser beam scanner for writing a latent image, reference numeral 4 is four developing units 40K, 40Y, 40M, 40C for accommodating each toner image of black (K), yellow (Y), magenta (M), and cyan (C). Is a rotary developing unit that is rotatably disposed and is appropriately switched and selected.

On the other hand, reference numeral 5 designates a plurality of transport rolls 6a to 6a.
The intermediate transfer belt stretched by d. The toner images of respective colors sequentially formed on the photosensitive drum 1 are transferred to the intermediate transfer belt 5 in a multiplex manner, and then the intermediate transfer belt 5 and the recording sheet P are collectively transferred. Is secondarily transcribed. Also,
Reference numeral 7 is a primary transfer roll that electrostatically transfers the toner image from the photosensitive drum 1 to the intermediate transfer belt 5, reference numeral 8 is a secondary transfer roll that electrostatically transfers the toner image to the recording sheet P, and reference numeral 9 is the intermediate transfer belt 5. It is a belt cleaner that cleans the paper dust and toner adhering to the.

Further, reference numeral 10 is a registration roll for feeding the recording sheet P fed from the paper feed cassette 11 to the secondary transfer position of the toner image at a predetermined timing, for example, a full-color image on the recording sheet P. If it is to be formed, after the toner images of all four colors are primarily transferred to the intermediate transfer belt 5, the recording sheet P is fed to the secondary transfer position where the secondary transfer roll 8 is arranged.

Reference numeral 12 is a heat fixing device for inserting the recording sheet P on which the toner image is transferred and fixing an unfixed toner image on the recording sheet P. The heating fixing device 12 has a heater inside. It is composed of a built-in heating roll and a pressure roll arranged in pressure contact with the heating roll.

In the color laser beam printer of this embodiment constructed as described above, the laser beam scanner 3 exposes the photosensitive drum 1 on the basis of image information, and the photosensitive drum 1 corresponds to yellow Y. The electrostatic latent image is written. On the other hand, in the rotary developing unit 4, the yellow developing device 40Y is set at a position facing the photosensitive drum 1, and the electrostatic latent image is developed by the yellow developing device 40Y with a slight delay from the writing timing. The yellow Y toner image thus formed is primarily transferred onto the intermediate transfer belt 5 by the primary transfer roll 7, and the intermediate transfer belt 5 rotates while carrying the toner image. Further, when the developing process by the yellow developing device 40Y is completed, the developing device is exchanged until the intermediate transfer belt 5 completes one rotation cycle, and the magenta developing device 40M is rotated by 90 ° rotation of the rotary developing unit 4. It is set at a position facing the photosensitive drum 1.

Thereafter, these operations are repeated every one rotation cycle of the intermediate transfer belt 5, and magenta M,
The cyan C and black K toner images are transferred from the photosensitive drum 1 to the intermediate transfer belt 5, and a superposed toner image of four color toner images is formed on the intermediate transfer belt 5. The full-color multi-transfer toner image thus formed is secondarily transferred to the recording sheet P sent from the registration roll 10 at a predetermined timing, and the unfixed toner image is transferred to the recording sheet P.
Is discharged to the discharge tray 13 via the heat fixing device 12.

On the other hand, after the toner image is secondarily transferred to the recording sheet P, the intermediate transfer belt 5 passes through the belt cleaner 9, whereby the residual toner adhering to the surface of the intermediate transfer belt 5 is removed, and the belt cleaner is removed. The toner image can be primarily transferred again to the surface of the intermediate transfer belt that has passed through.

FIG. 2 shows the structure of the secondary transfer portion for transferring the toner image from the intermediate transfer belt 5 to the recording sheet P. Secondary transfer roll 8 with the intermediate transfer belt 5 in between
The transport roll 6c facing the is a backup roll having a function as a counter electrode of the secondary transfer roll 8. The backup roll 6c is formed by covering the surface of an insulating roll with a semi-conductive rubber layer, and a conductive contact roll 15 to which a predetermined transfer bias is applied is in contact with the surface. On the other hand, the secondary transfer roll 8 in contact with the back surface side of the recording sheet P presses the recording sheet P against the intermediate transfer belt 5 with a predetermined nip width to enhance transfer efficiency. It is formed by filling urethane foam having an adjusted resistivity and further covering the periphery with a semiconductive rubber layer, and the shaft core member is grounded. Therefore, when a transfer bias having the same polarity as that of the toner image is applied to the contact roll 15 in contact with the backup roll 6c and charges are applied to the front surface of the backup roll 6c, the secondary transfer located on the back surface side of the recording sheet P is performed. A transfer electric field is formed between the roll 8 and the backup roll 6c located on the back side of the intermediate transfer belt 5, and the toner image T held on the intermediate transfer belt 5 is electrostatically transferred onto the recording sheet P.

Further, since this color printer is a so-called 4-cycle system and a full color image is formed by four rotations of the intermediate transfer belt 5, when forming a full color image, the toner image of the fourth color is intermediately transferred. Belt 5
It is necessary to separate the secondary transfer roll 8 from the intermediate transfer belt 5 until it is transferred to. Therefore, the secondary transfer roll 8 is supported by the retract mechanism. In this retract mechanism, the secondary transfer roll 8 is provided at one end of a support arm 81 which is swingably supported by a support shaft 80.
The other end of is pulled by a spring 82 for urging the secondary transfer roll 8 toward the intermediate transfer belt 5. An eccentric cam 83 is in contact with the support arm 81, and the rotational position of the eccentric cam 83 pushes up the secondary transfer roll 8 toward the intermediate transfer belt 5 or resists the urging force of the spring 82. Then it is forcibly pushed down.

Further, the position of the secondary transfer roll 8 is regulated on the side of the backup roll 6c so that a predetermined nip width is always formed between the secondary transfer roll 8 and the intermediate transfer belt 5 which are in pressure contact with each other. A stop member (not shown) is provided, and the secondary transfer roll 8 pushed up toward the intermediate transfer belt 5 is positioned by this locking member. Therefore, when the secondary transfer roll 8 is brought into contact with the intermediate transfer belt 5, the axial distance between the secondary transfer roll 8 and the backup roll 6c becomes a predetermined value regardless of the biasing force of the spring 82. Is set.

After the recording sheet P is carried out from the paper feeding cassette 11, the recording sheet P is temporarily locked by the registration roll 10 to perform skew correction, and the timing at which the toner image on the intermediate transfer belt 5 reaches the secondary transfer portion is set. After being checked, it is sent to the secondary transfer section. A pair of a first guide member 20 and a second guide member 21 are provided between the registration roll 10 and the secondary transfer portion so as to sandwich the conveyance path of the recording sheet P from above and below. Guide member 20,
It passes through the gap formed between 21 and reaches the secondary transfer portion. Although a nip region is formed between the intermediate transfer belt 5 and the secondary transfer roll 8, it is difficult to make the pressure distribution in this nip region uniform along the axial direction of the transfer roll 8. , Wavy deformation, that is, waviness is likely to occur at the rear end of the recording sheet P whose front end has entered the secondary transfer portion, and when the recording sheet P passes through the secondary transfer portion with this deformation occurring, the toner Wrinkles and transfer omissions occur on the recording sheet after the image transfer. First mentioned above
The guide member 20 and the second guide member 21 suppress the occurrence of this waviness and fulfill the function of feeding the recording sheet P to the secondary transfer portion in a state where the rear end of the recording sheet P is extended. In order to fully exhibit this function, the tips of these guide members on the side of the secondary transfer portion are as close to the secondary transfer portion as possible within the range where they do not interfere with the peripheral members. However, since the intermediate transfer belt is stretched toward the backup roll in the secondary transfer portion, in order to avoid interference with the intermediate transfer belt, the first guide member is more than the second guide member in the secondary transfer portion. Away from.

Further, the first and second guide members 20, 21
Is formed of a conductive material in order to prevent the recording sheet P passing between them from being triboelectrically charged.

On the other hand, when the recording sheet P passes through the secondary transfer portion in this manner, charges of opposite polarities are injected into the back surface of the recording sheet P and the back surface of the intermediate transfer belt 5, so that the secondary transfer is performed. An electrostatic attraction force acts between the intermediate transfer belt 5 and the recording sheet P, which are in close contact with each other at the portion.
For this reason, the recording sheet P, which should originally be separated from the intermediate transfer belt 5 immediately after passing through the secondary transfer portion, may stick to the intermediate transfer belt 5 without being separated, and such a POB (Paper If a jam occurs, the recording sheet P may rush into the belt cleaner 9 as the intermediate transfer belt 5 rotates.

In order to prevent the occurrence of such a POB jam, the intermediate transfer belt 5 is wound around the backup roll 6c at a relatively large wrap angle, and the leading end of the recording sheet P passing through the secondary transfer portion itself. It is designed to be peeled off from the intermediate transfer belt 5 by the strength of the waist. Further, the intermediate transfer belt 5 of the secondary transfer roll 8 is arranged so that the recording sheet passing through the secondary transfer portion is discharged slightly downward, that is, discharged in a direction along the peripheral surface of the secondary transfer roll 8 rather than the intermediate transfer belt 5. The pressure contact position for is the backup roll 6c
Is displaced upstream of the contact point of the intermediate transfer belt 5 with respect to the rotational direction of the intermediate transfer belt 5. Specifically, as shown in FIG. 3, the first plane is a plane that is perpendicular to the intermediate transfer belt 5 stretched from the upstream side of the backup roll 6c and that includes the rotation center O of the backup roll 6c.
On the other hand, when the plane including the rotation center O of the backup roll 6c and the rotation center P of the secondary transfer roll 8 is the second virtual plane m, the first virtual plane and the second virtual plane are formed. The angle α is set to 12 °. As a result, the recording sheet P that has passed the secondary transfer portion is discharged in the direction along the peripheral surface of the secondary transfer roll 8 rather than the intermediate transfer belt 5, and the occurrence of the POB jam described above is prevented as much as possible. You can

However, when the recording sheet does not pass through the secondary transfer portion in a straight line as described above and the traveling direction after passing through the secondary transfer portion is displaced in the direction close to the peripheral surface of the secondary transfer roll, The trailing edge of the recording sheet passing through the secondary transfer portion tends to be displaced in the direction opposite to the leading edge, that is, in the direction close to the intermediate transfer belt. Such a behavior of the recording sheet remarkably occurs when the toner image is secondarily transferred to a thick paper such as a postcard. Therefore, when a stiff recording sheet such as a postcard is sent from the registration roll to the secondary transfer section, as soon as the trailing edge of the recording sheet passing through the secondary transfer section comes out of the first guide member, There is a problem that the edge jumps upward, that is, jumps up toward the intermediate transfer belt, and the impact at this time disturbs the toner image being transferred.

Therefore, in the printer of this embodiment, the first
In order to prevent the trailing edge of the recording sheet P that has passed through the guide member 20 from jumping up suddenly, as shown in FIG. 4, the end portion of the first guide member 20 on the secondary transfer portion side is cut in a substantially triangular shape. The notch 22 is provided. FIG. 5 is a plan view showing the cutout portion 22. The notch 22 is formed smaller than the maximum size recording sheet width a, and in the printer of this embodiment, the opening width b corresponds to the size of the officially made postcard P0 and is slightly larger than the short side of the officially made postcard. Has been formed. Further, the printer of this embodiment is configured to convey recording sheets of various sizes with a so-called side register, that is, one side edge of the conveying path as a reference, and the cutout portion 22 has an end portion of its opening width. It is provided to match the side registration reference position. Further, the cut amount of the substantially triangular cutout portion 22 with respect to the first guide member 20 is 0 on the side registration reference side, and the cut amount gradually increases toward the opposite side in the width direction. There is.

Therefore, when the officially made postcard is conveyed from the registration roll to the secondary transfer portion, as shown in FIG. 6, the rear end of the postcard gradually comes from below the first guide member 20 as it approaches the secondary transfer portion. It will appear and will gradually lift up without suddenly jumping toward the intermediate transfer belt 5. Therefore, even if the trailing edge of the postcard passes through the first guide member 20, no impact is exerted on the postcard itself during the secondary transfer of the toner image, and the toner image during the transfer is disturbed. Is something that can be avoided.

Even when such a cutout portion 22 is provided in the first guide member 20 only for postcards, as long as a recording sheet P having a size larger than the postcard P0 is used, it is necessary. At positions corresponding to both ends of the recording sheet P in the width direction, the first guide member 20 has the maximum length along the recording sheet conveyance direction. Therefore, with the first guide member 20 shown in FIG. 3, it is possible to suppress the undulation that occurs at the trailing edge of the recording sheet P other than the postcard up to the vicinity of the secondary transfer portion. It is possible to improve the transportability to the transfer portion, and effectively prevent wrinkles from being generated on the recording sheet after passing through the transfer portion, or occurrence of transfer omission of the toner image.

FIG. 7 shows a second example of the first guide member 20. In the first guide member 20 shown in FIG. 3, the triangular notch portion 22 is fixedly provided, but in the first guide member 20 shown in FIG. 6, the movable adjustment plate 23 that can move forward and backward on the notch portion 22. Is provided, and by moving the movable adjusting plate 23, the cutout portion 2 along the conveyance direction of the recording sheet P is formed.
The cut amount of 2 can be changed. With this configuration, the cut amount of the cutout portion 22 can be adjusted according to the strength of the recording sheet P, and the trailing edge of the recording sheet P passing through the transfer portion is the intermediate transfer belt 5. It is possible to more smoothly release the bounce toward. Further, such a movable adjusting plate 23,
For example, if a user wants to print on a postcard,
It is also possible for the user to manually move it to the open position before giving a print instruction, which is a very convenient measure when using thick paper as the recording sheet P. Furthermore, when printing on plain paper, the cutout portion 22 can be completely covered by the movable adjusting plate 23, which is also effective in terms of preventing the undulation of the recording sheet P while passing through the transfer portion.

In the example shown in FIG. 7, the setting position of the movable adjusting plate 23 is manually changed. However, based on the information such as the size and type of the recording sheet P input to the printer, It is also easy to automatically change the set position of the movable adjusting plate 23 by a power means such as a solenoid or a motor.

Next, FIG. 8 shows a third example of the first guide member. The first guide member 25 is not provided with the notch as described above, but the inclined portion 26 is formed at the trailing end on the downstream side in the transport direction of the recording sheet P, that is, the leading end on the secondary transfer portion side. There is. The inclined portion 26 is provided so that the distance from the second guide member 21 gradually widens as it goes downstream in the transport direction of the recording sheet P, and is formed over the entire width direction of the recording sheet P. .

Therefore, the trailing edge of the recording sheet P, which is about to jump toward the intermediate transfer belt 5, is located at the first guide member 2.
When it exits 5, it is gradually released toward the intermediate transfer belt 5 while being prevented from being suddenly jumped up by the inclined portion 26. Therefore, even when a strong recording sheet such as thick paper is used, the rear end of the first guide member 2
It does not suddenly jump up when exiting 5, and like the first guide member 20 provided with the cutout portion 22, it is possible to prevent the occurrence of problems such as disturbance of the toner image being transferred.

On the other hand, such a phenomenon that the trailing edge of the recording sheet P jumps up when it comes out of the first guide member occurs remarkably and rapidly as the edge of the first guide member approaches the secondary transfer portion. , As the edge part moves away from the secondary transfer part, the way it jumps up becomes gentle. Therefore, the first
If the end portion of the guide member is sufficiently distant from the secondary transfer portion, it is possible to prevent the recording sheet P from jumping up to such an extent that the transfer of the toner image is not affected even if the recording sheet has a strong rigidity. is there. However, it is presumed that as the first guide member moves away from the secondary transfer portion, the original purpose of the guide member, that is, the purpose of suppressing the undulation generated at the trailing edge of the recording sheet during the passage of the transfer portion cannot be achieved.

Further, the jumping up of the trailing edge of the recording sheet P in question is closely related to the change in the advancing direction of the recording sheet P before and after the secondary transfer portion, and the change angle in the advancing direction is large. It is considered that the jumping up is remarkable and rapid.

Therefore, the inventors of the present application associate the above two parameters, that is, the amount of change in the moving direction of the recording sheet P before and after the secondary transfer portion and the distance between the first guide member and the secondary transfer portion, with each other, and The occurrence of defective transfer of the toner image due to the jumping up of the trailing edge of P, and the occurrence of wrinkles and missing transfer due to the waviness of the trailing edge of the recording sheet P were investigated. Specifically, as shown in FIG. 9, the first guide member 2
7, the distance between the downstream end of the recording sheet in the conveying direction and the transfer position of the toner image is L, and the recording sheet P before and after the transfer portion is P.
When the change angle of the advancing direction of the recording sheet is θ and f = θ / L is changed, the occurrence of the waviness at the trailing edge of the recording sheet and the occurrence of toner image disturbance during transfer were observed. The tangential direction of the secondary transfer roll 6c to the intermediate transfer belt 5 was used as the conveying direction of the recording sheet P after the transfer. The results are shown in Table 1 below.

[0046]

[Table 1]

According to this result, f = θ / L is 0.43
If it is smaller than (f <0.43), undulation occurs at the trailing edge of the recording sheet P that is passing through the transfer portion, and wrinkles are formed on the recording sheet P after the toner image transfer due to poor conveyance of the recording sheet P. Occurred, or the toner image was not transferred. It is presumed that this is because the distance L between the first guide member 27 and the secondary transfer portion becomes too large, and the first guide member 27 could not perform the original function of suppressing the undulation of the trailing edge of the recording sheet.

On the other hand, when f = θ / L is larger than 0.55 (f> 0.55), when a thick paper such as a postcard is used as the recording sheet P, the trailing edge of the recording sheet P passing through the transfer portion is used. Immediately jumped out of the first guide member 27, and suddenly jumped up, and the impact caused a disturbance in the toner image being transferred. This is the distance L between the first guide member 27 and the secondary transfer portion.
On the other hand, it is considered that the conversion angle θ in the traveling direction becomes too large.

Therefore, θ and L are 0.43 ≦ θ / L ≦
In order to satisfy the range of 0.55, the first guide member 27
If the arrangement position of the recording sheet P and the angle of change in the conveyance direction of the recording sheet P before and after the secondary transfer portion are determined, the conveyance failure due to the undulation of the trailing edge of the recording sheet can be performed without any modification to the shape of the first guide member 27. It has been found that it is possible to avoid the toner image disturbance due to the jumping up of the trailing edge of the recording sheet.

[0050]

As described above, according to the toner image transfer device of the present invention, the transfer of the toner image from the image carrier to the recording sheet proceeds, and the recording sheet completely covers the first guide member. When exiting, the trailing edge toward the image carrier is released in a stepwise manner, preventing the trailing edge of the recording sheet, which already has its leading edge protruding into the transfer section, from jumping up immediately before the transfer section. Therefore, it becomes possible to favorably transfer the toner image onto the recording sheet.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a configuration example of a full-color laser beam printer including a toner image transfer device of the present invention.

FIG. 2 is an enlarged view showing a secondary transfer portion of a toner image in the printer shown in FIG.

FIG. 3 is a diagram showing a pressure contact position of a secondary transfer roll with respect to an intermediate transfer belt.

FIG. 4 is a perspective view showing a first embodiment of a first guide member to which the present invention is applied.

FIG. 5 is a plan view showing the position of a notch formed in the first guide member according to the first embodiment.

FIG. 6 is a perspective view showing a state where the officially made postcard has come out of the first guide member according to the first embodiment.

FIG. 7 is a perspective view showing a second embodiment of the first guide member.

FIG. 8 is a perspective view showing a third embodiment of the first guide member.

FIG. 9 is a diagram showing an angle change θ in a traveling direction of a recording sheet before and after a secondary transfer portion and a distance L between a first guide member and the secondary transfer portion.

[Explanation of symbols]

5 ... Intermediate transfer belt (image carrier), 8 ... Secondary transfer roll (transfer roll), 10 ... Registration roll (previous conveyance roll), 20 ... First guide member, 21 ... Second guide member, 22
… Notch, P… Recording sheet

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Koji Hamabe             Fujize, 3-7-1, Fuchu, Iwatsuki City, Saitama Prefecture             Rocks Co., Ltd. Iwatsuki Office F-term (reference) 2H200 FA17 GA23 GA34 GA47 GA51                       GA52 GB22 HA03 HB12 HB22                       JA02 JA04 JA21 JB10 JB12                       JB17 JB20 JB46 JC03 JC12                       MB01                 3F101 FA00 FB04 FC01 FC14 LA02                       LB03

Claims (9)

[Claims] 1. A transfer device for transferring a toner image from an image carrier on which a toner image is formed or transferred to a recording sheet, the transfer roll being in pressure contact with the image carrier, and the image carrier. The image carrier is composed of a conveyance roll immediately before feeding the recording sheet to the transfer position of the toner image formed by the transfer roll, and a pair of guide members provided between the conveyance roll and the transfer position to guide the recording sheet. The toner is characterized in that the first guide member arranged on the body side is provided with a suppressing means for gradually releasing the trailing edge of the recording sheet exiting the first guide member from jumping up toward the image carrier. Image transfer device. 2. The toner image transfer according to claim 1, wherein the suppressing unit is a substantially triangular notch formed at an end of the first guide member on the downstream side in the recording sheet conveying direction. apparatus. 3. The first guide member has the maximum length along the conveyance direction of the recording sheet at the positions corresponding to both ends of the maximum size recording sheet in the width direction. The toner image transfer device described. 4. The recording sheet is conveyed between a pair of guide members at a side register with one end in the width direction as a reference, and the cut amount of the notch is from the end on the side register side to the opposite end. 4. The toner image transfer device according to claim 3, wherein the toner image transfer device gradually increases in size. 5. The toner image transfer device according to claim 2, wherein the cut amount of the cutout portion along the conveying direction of the recording sheet is variable. 6. The toner image transfer device according to claim 5, wherein the cut amount is changed according to the type and / or size of the recording sheet. 7. The restraint means is formed at an end of the first guide member on the downstream side in the recording sheet conveying direction, and is spaced apart from the second guide member on the back side of the recording sheet along the conveying direction of the recording sheet. The toner image transfer device according to claim 1, wherein the toner image transfer device is an inclined portion that gradually expands. 8. A transfer device for transferring a toner image from an image carrier on which a toner image is formed or transferred to a recording sheet, the transfer roller immediately before feeding the recording sheet to a transfer position of the toner image, and The distance between the transfer position of the toner image and the end of the first guide member on the downstream side in the recording sheet conveyance direction is constituted by a pair of guide members that are provided between the immediately preceding conveyance roll and the transfer position and guide the recording sheet. Is L, and the angle formed by the tangential direction of the transfer roll to the image carrier and the conveying direction of the recording sheet immediately before the transfer position is θ, 0.43 ≦ θ / L ≦ 0.55 is satisfied. Toner image transfer device. 9. The toner image transfer device according to claim 1, wherein the first guide member is electrically conductive.