JP3942615B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus used in an electrophotographic printer, an electronic copying machine, an electrophotographic color electronic copying machine, a color printer, and the like, and more particularly to a transfer device.

  In general, as a transfer device constituting an electrophotographic image forming apparatus, conventionally, a transfer technique using a corona charger has been widely used. However, since it has been found that some harmful ozone is generated, an ozone-less transfer technique is used. Development is underway.

  Therefore, a contact-type transfer technique has been considered. This is achieved by arranging a semiconductive transfer belt and a transfer roller on the back of the transfer belt, and applying a transfer bias to the transfer roller. A transfer brush or a power supply blade is known as a transfer apparatus that has a large size, takes up a large space in the apparatus, and is a high cost factor. In this case, a transfer bias is applied to a power supply member such as a power supply brush or a power supply blade to form a transfer electric field.

At this time, if the flat brush is oriented perpendicularly to the axis of the photosensitive drum and the tip of the flat brush is brought into contact with the photosensitive drum, the durability of the brush will be damaged due to long-term use. There is a technology to move away from the photosensitive drum when the power supply member is not used, because the transfer electric field nip width is likely to fluctuate and the contact is insufficient, resulting in transfer failure. A technology that eliminates positioning accuracy, always maintains a constant transfer electric field forming nip width, and adopts a tandem transfer method, as high accuracy is required for positioning of the contact portion of the member end and leads to cost increase. It is disclosed (for example, see Patent Document 1).
Japanese Patent Laid-Open No. 10-232574

  However, when a brush-like material is used as the transfer means, the brush is inclined to the downstream side in the conveying direction due to the movement of the conveying means, and the inclined tip is a point where the transfer material is peeled off from the photosensitive member, that is, Beyond the end of the nip formed by the conveying means and the photosensitive member, it easily contacts the conveying member. In this case, scattering of the developer electrostatically attracted to the transfer material or reverse transfer to the photosensitive member occurs. .

As described above, when the brush-like transfer unit is used, the developer electrostatically attracted to the transfer material and the reverse transfer to the photosensitive member are generated, and the image is disturbed, the density is lowered, and the fog is formed. It has an adverse effect on the image that should be.
In addition, in a color image forming apparatus configured by a tandem method or the like, the above-described adverse effect is likely to be remarkable, and new problems such as color mixing of developers also arise.

  The present invention has been made in view of the above problems, and its main purpose is to define a transfer area of a transfer apparatus.

In order to achieve the above object, the present invention has the following configuration.
According to a first aspect of the present invention, an electrostatic latent image is formed on a photosensitive member, a developer is supplied to the photosensitive member to visualize the electrostatic latent image, and the visible image is transferred to a transfer device. In the image forming apparatus in which the transfer image is transferred to the transfer material and the visible image on the transfer material is fixed by the fixing device, the transfer device is a belt-shaped conveyance member that conveys the transfer material while contacting the photosensitive member. It has a brush portion that is charged in contact with the back surface, and is provided so that the brush tip of the brush portion at the time of image formation does not exceed a nip portion range that is an overlapping region of the photosensitive member and the conveying member. In the image forming apparatus.

The second gist of the present invention is that the transfer device is supported by an elastic member so that the distance D1 from the conveying member is substantially constant, and the distance between the brush root and the end of the nip portion is D2. The image forming apparatus according to claim 1, wherein the brush length L1 satisfies the following relational expression.
D2 ≧ L1 ≧ D1

According to a third aspect of the present invention, the transfer device includes a member having rigidity on the downstream side in the transport direction of the transport member of the brush portion, and the length from the brush-side upper end portion of the rigid member to the brush upper end is set. 2. The image forming apparatus according to claim 1, wherein the following relational expression is satisfied, where D3 is a distance between L2 and the brush-side upper end of the rigid member and the end of the nip portion.
D3 ≧ L2> 0

  The fourth gist of the present invention is the image forming apparatus according to claim 1, wherein the brush portion of the transfer device is formed to be inclined in the advancing direction of the conveying member with respect to the normal axis of the conveying member. .

  The fifth gist of the present invention resides in the image forming apparatus according to claim 1, wherein the brush portion has a roller shape.

  The sixth aspect of the present invention is the image according to claim 5 or 6, wherein the transfer device operates in a direction relatively opposite to a traveling direction of the conveying member on a contact surface with the conveying member. In the forming device.

Seventh aspect of the present invention, the curvature radius of the nip portion of the conveying member R1, the center angle looking into the nip and 2 [Theta] _1, the radius of curvature of the portion where the transfer device opposes the conveying member and R2, 7. The image forming apparatus according to claim 5, wherein the following relational expression is satisfied when a central angle at which the facing portion is viewed is 2θ ₂ .
sinθ ₂ ≦ (R1sinθ ₁ ) / R2

  According to the first aspect of the invention, even when the brush portion of the transfer device falls down in the transfer material conveyance direction, the developer does not come into contact with any portion other than the nip portion of the conveyance member, It prevents reverse transcription.

  According to the second aspect of the invention, by defining the brush length of the brush portion of the transfer device, even if the brush falls down in the transport direction, it does not come into contact with any portion other than the nip portion of the transport member. In this case, the developer on the transfer material is prevented from scattering and reverse transfer.

  According to the invention of the third aspect, the guide is provided on the downstream side in the transport direction of the brush portion of the transfer device, the density of the brush portion that actually contacts the transport member is improved, and the scattering of the developer on the transfer material is reversed or reversed. This will prevent copying.

  According to the invention of the fourth aspect, the contact area to the conveying member is increased by arranging the brush in an inclined manner in advance, thereby improving the transfer efficiency and not contacting any part other than the nip portion of the conveying member. In addition, it prevents scattering of the developer and reverse transfer.

  According to the invention of the fifth aspect, the total contact area per unit time is increased, and transfer unevenness due to the brush and the specific variation is prevented, so that the transfer efficiency is improved and the contact of the conveying member other than the nip portion is performed. By not doing so, scattering of the developer and reverse transfer are prevented.

  According to the invention of the sixth aspect, the total contact area per unit time between the conveying member and the roller-shaped brush portion or the endless belt is increased, transfer unevenness due to the brush and the specific variation is prevented, and transfer efficiency is further improved. This prevents the developer from scattering and reverse transfer by preventing contact other than the nip portion of the conveying member.

  According to the seventh aspect of the invention, the curvature of the transfer device relative to the curvature of the nip portion of the conveying member is defined. By making the transfer device a roller or an endless belt whose surface is a brush, By increasing the total contact area and preventing contact other than the nip portion of the conveying member, it is possible to prevent the developer from scattering and reverse transfer.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows a color image forming apparatus as an image forming apparatus, and image stations B and M that form images for respective colors of black (B), magenta (M), cyan (C), and yellow (Y). , C, and Y are formed on a sheet of paper and the like, and a conveyor 7 that is in close contact with the image stations B, M, C, and Y and sequentially conveys a medium to be transferred such as a sheet toward each image station. The image forming apparatus includes a fixing device 8 that heats and fixes the image.

With this configuration, the sheet or the like forms one color image by superimposing the images at the image stations B, M, C, and Y arranged in cascade from the upstream side while controlling the position. Further, the image can be fixed on paper or the like by sending it to the fixing device 8.
The image stations B, M, C, and Y are different in toner type but have substantially the same configuration, so that the image station B will be described below as a representative.

  Around the photosensitive drum 6B of the image station B, a charging device 1B, an exposure device 2B, a developing device 3B, a transfer device 4B, and a cleaning device 5B are arranged along the rotation direction to constitute a process unit.

  The charging device 1B is a charging device 1B that is positioned above the photosensitive drum 6B and that contacts the surface of the photosensitive drum 6B to uniformly charge the photosensitive drum 6B to, for example, a negative potential.

  The exposure device 2B is located downstream of the charging device 1B in the rotation direction of the photosensitive drum 6B, and is a signal from an image data input means (not shown) (for example, an optical system such as a scanner device in a copying machine, or an image signal). Then, the charged photosensitive drum 6B is exposed to form an electrostatic latent image.

  The developing device 3B is located further on the photosensitive drum rotation direction side than the exposure device 1B, and visualizes the electrostatic latent image by supplying a developer to the electrostatic latent image formed on the photosensitive drum 6B. The developer accommodated in the developing device 3B of the image station B is, for example, black toner.

The transfer device 4B is provided at a position on the back side (lower surface side) of the conveying belt 7 provided for conveying the sheet as a transfer material to the photosensitive drum 6B, and a visible image carried on the photosensitive drum 6B is transferred. A bias voltage is applied so that the developer is transferred to the paper side at the same time as it is in close contact with the paper conveyed by the conveyance belt 7.
More details will be described later.

  The cleaning device 5B is provided on the downstream side in the rotation direction of the photosensitive drum 6B from the transfer position, and collects residual toner on the surface of the photosensitive drum 6B, for example, by scraping it with a blade or the like.

The conveyor belt 7 is a belt that sequentially conveys a sheet as a transfer material from the photosensitive drum 6B of the first image station B to the photosensitive drum 6Y of the fourth image station Y. And a driven roller 11.
The width of the conveyance belt 7 (the direction orthogonal to the sheet conveyance direction) is formed to have a length that is substantially equal to the length of the photosensitive drum 6 in the longitudinal direction.
The transport belt 7 is an endless belt made of polyimide, and the transport speed is 116 [mm / sec].

  The nip portion, which is a contact area formed by the contact between the photosensitive drum 6B and the conveyor belt 7, has an arc length of about 3 [mm].

  The fixing device 8 is located on the downstream side of the driven roller 11 of the conveyor belt 7 and heats and fixes the toner image on the paper formed by superimposing at the first to fourth image stations on the paper. Is what you get.

Next, the transfer device 4B will be described in detail with reference to FIG.
FIG. 2 is an explanatory diagram showing the mutual relationship among the photosensitive drum 6B, the conveyance belt 7, and the transfer device 4B.
The transfer device 4B includes a base 4B1 and a brush 4B2, and the brush 4B2 is uniformly formed in the longitudinal direction with a predetermined width on the base 4B1 having substantially the same length as the width direction of the transport belt 7. A bias voltage is applied.

The brush 4B2 is made of rayon / ETFE (Ethylene Tetrafluoroethylene), and the length of the bristle is adjusted between 2 and 5 [mm]. Moreover, the thickness shall be adjusted to 3-6D (Denier: Denier), and the flocking density shall be adjusted to 8-24 [10,000 / inch < ² >]. Further, the transfer device 4B is urged by an urging means (not shown) (for example, an elastic member such as a spring or rubber) so as to be urged to the conveying belt 7 by a pressure of 10 to 20 [g / cm ² ]. Yes.

The transfer device 4B is supported by the elastic member so that the distance D1 from the conveying belt 7 is substantially constant, and the maximum length L1 from the root to the tip of the brush 4B2 is expressed by the following relational expression ( It is configured to satisfy 1).
D2 ≧ L1 ≧ D1 Formula (1)
D2: Distance between the brush root and the rear end of the nip portion.

  Specifically, when the distance D1 from the root of the brush 4B2 to the transport belt 7 is 2 [mm] and the length L1 of the brush 4B2 is 2.3 [mm], the nip of the transport belt 7 from the root of the brush 4B2 The distance D2 to the rear end portion is about 2.5 [mm], and the brush 4B2 is provided so as not to contact the downstream side beyond the nip portion.

  By making the length L1 of the brush 4B2 longer than the distance D1 from the root of the brush 4B2 to the transport belt 7, the brush 4B2 falls down along the transport direction of the sheet and the contact area (transfer area) is as described above. Increases and transfer is ensured. Further, since the tip of the fallen brush 4B2 does not contact beyond the nip portion of the transport belt 7, a bias voltage other than transfer is not applied to the developer on the paper, and the transfer is formed on the paper. It is possible to prevent scattering of the developer and reverse transfer.

(Comparative Example 1)
As a comparative example to the first embodiment, if the distance D1 from the brush root of the transfer device to the conveyor belt 7 is 2 [mm] and the brush length L1 is 3 [mm], the brush root Since the distance D2 to the rear end portion of the conveying member nip is about 2.5 [mm], the relational expression (1) is not satisfied, and the brush comes in contact with a portion other than the nip portion.

Next, a second embodiment of the transfer device will be described with reference to FIG.
The transfer device 4B ₂ shown in FIG. 3 has a predetermined height (with the transfer belt 7) on the downstream side in the transfer direction of the transfer belt 7 from the mounting position of the brush 4B2 of the base 4B1 in the transfer device 4B of the first embodiment. the rigid member 9 provide a gap D3) is fixed along the longitudinal direction of the base 4 B 1, it is intended to longer brush 4B 2 ₂ of the transfer apparatus 4B of the first embodiment which can cope.

In this case, in order to obtain the same effect as that of the first embodiment, the length from the brush side end portion (upstream side surface upper end side) of the rigid member 9 to the brush tip portion (the rigidity member 9 and the brush When the distance difference (L2) is L2 and the distance from the brush side end of the rigid member 9 to the rear end of the nip is D3, the following relational expression (2) is satisfied.
D3 ≧ L2> 0 Formula (2)

Specifically, the distance from the brush root to the transfer member nip end was about 2.5 [mm] in the same manner as in the first embodiment, when the length of the brush 4B 2 ₂ and 3 [mm] If the height of the rigid member 9 is about 1.5 [mm] and the distance between the rigid member 9 and the conveyor belt 7 is 1 [mm], L2 = 1.5 [mm] and D3 = 1.6 [ mm], which satisfies the above relational expression (2).

By providing the rigid member 9 so as to satisfy the above relational expression (2), the brush 4B ₂ 2 is bent halfway along the way, so that the brush 4B ₂ 2 contacts the part other than the nip part beyond the nip part. There is no.
Thus, the transfer apparatus in the downstream side of the brush 4B 2 ₂ By providing the rigid member (guide member) 9 that exerts a guiding effect 4B _2, the brush 4B 2 ₂ that actually contacts the conveyor belt 7 The density is improved and the developer on the transfer material is prevented from scattering and reverse transfer.
In addition, the attachment position and shape of the rigid member 9 are not limited to those described above, and may be attached to other parts or in a plate shape as long as the effect as a guide member of the brush is obtained. It is not limited to a linear one.

Next, a third embodiment of the transfer apparatus will be described with reference to FIG.
The transfer device 4B ₃ shown in FIG. 4 has the brush 4B ₃ 2 inclined with respect to the normal axis of the transport belt 7 in the traveling direction of the transport belt 7, and the tip of the brush 4B ₃ 2 contacts the transport belt 7. It is.

Specifically, the inclination angle of the brush 4B ₃ 2 implanted in the transfer device 4B ₃ with respect to the normal axis of the transport belt 7 is set to 45 °, and the base 4B1 of the transfer device 4B ₃ is the most on the transport belt 7. The distance between the upstream side of the approaching transport belt 7 in the moving direction and the transport belt 7 was 1 [mm], and the length of the bristle was 3 [mm]. Also in this case, the brush 4B ₃ 2 does not come into contact with anything other than the nip portion.

With the above configuration, the brush 4B ₃ 2 is inclined in advance to increase the contact area between the brush 4B ₃ 2 and the conveying belt 7 to increase the transfer efficiency, and contact other than the nip portion of the conveying belt 7 This prevents the developer from scattering and reverse transfer.

(Comparative Example 2)
As a comparative example with respect to the third embodiment, the inclination angle of the transfer device 4B ₃ is set to 45 [°], and the upstream side in the moving direction of the conveying belt 7 where the base 4B1 is closest to the conveying belt 7 is used. If the distance between the side base and the conveyor belt 7 is 1 [mm] and the length of the bristle is 4 [mm], the brush comes into contact with other than the nip portion.

Next, a fourth embodiment of the transfer apparatus will be described with reference to FIG.
Transfer device 4B ₄ shown in FIG. 5 has a brush roller BR and planted uniformly brush 4B ₄ 2 in the axial S having rotatable toward the circumferential direction, the nip portion of the conveyance belt 7 contacting the blanking Rashirora BR Te odor within the whole range, and is rotated so as to contact the opposite direction to the transporting belt 7 in the contact portion (photosensitive drum 6B the same direction of rotation). Incidentally, wherein the embodiment similarly to the brush 4B ₄ 2, and at the same time a visible image carried on the photosensitive drum 6B comes into close contact with the sheet conveyed by the conveying belt 7, the developer is transferred onto the sheet side Thus, a bias voltage is applied.

  As described above, the brush roller BR is in operation contact with the contact surface with the transport belt 7 in the direction opposite to the transport traveling direction, so that the extended contact area per unit time between the brush roller BR and the transport belt 7 is reduced. In addition, transfer unevenness due to brush-specific variations is prevented, and transfer efficiency is further increased.

Further, the brush roller BR is the curvature radius of the nip portion of the conveyance belt 7 R1, the center angle looking into the nip and 2 [Theta] _1, the radius of curvature of the portion where the brush roller BR is opposed to the conveyor belt 7 and R2 The brush 4B ₄ 2 and the like are provided so as to satisfy the following relational expression (3) when the central angle at which the facing portion is expected is 2θ ₂ .
sin θ ₂ ≦ (R1 sin θ ₁ ) / R2 Formula (3)

Specifically, the radius of curvature of the brush roller BR is set to 5.00 [mm], the distance between the shaft S and the photosensitive drum 6B is set to 24.73 [mm], and the nip in the photosensitive drum 6B is set. The central angle 2θ ₁ for viewing the portion is 8.59 [°], and the central angle 2θ ₂ for viewing the portion of the brush roller BR facing the conveying member is 33.68 [°]. In other words, the axis S of the brush roller BR is arranged at a position where the bisector of the center angle 2θ _{1 and} the bisector of the center angle 2θ ₂ coincide with each other in the nip range, so that the nip portion of the transport belt 7 The brush roller BR can contact the entire range. Also at this time, the brush roller BR does not come into contact with anything other than the nip portion.

  The above configuration increases the total contact area per unit time and prevents uneven transfer due to brush-specific variations, increasing transfer efficiency and avoiding contact with parts other than the nip of the conveying member. By doing so, the scattering of the developer and the reverse transfer are prevented.

Further, when the brush roller BR satisfies the relational expression (3), the curvature of the brush roller BR with respect to the curvature of the nip portion of the transport belt 7 is defined.
By using a brush roller BR in the form of a rotating roller as a bias voltage application means of the transfer device, the total contact area per unit time is increased, and contact other than the nip portion of the transport member is avoided, so It prevents reverse transcription.

(Comparative Example 3)
As a comparative example to the fourth embodiment, a brush roller is used for the transfer device 4B ₄ , the radius of curvature is 5.00 [mm], the radius of the photosensitive drum 6B is 20.00 [mm], Further, the distance between the two axes is 24.70 [mm], the central angle 2θ ₁ for looking at the nip portion on the photosensitive drum 6B is 8.59 [°], and the portion facing the conveying belt 7 in the transfer device 4B ₄ is expected. When the central angle 2θ ₂ is set to 36.08 [°], the brush comes into contact with other than the nip portion.

  As described above, in Comparative Examples 1 to 3, the brush as the bias voltage applying means contacts other than the nip portion, and the produced copy sample is scattered by the developer and fogged, and can be used further. Also, the color mixing of the developer has been seen.

  However, in the copy samples in the first to fourth embodiments, no developer scattering or fogging was observed, and no image disturbance occurred.

  In addition, although the embodiment example about the color image forming apparatus has been given this time, it goes without saying that the present invention is also applicable to a normal monocolor image forming apparatus.

  According to the present invention described above, when the brush portion of the transfer device falls in the transfer material conveyance direction, or when the belt portion rotates in a predetermined shape in advance, the transfer member is placed on a portion other than the nip portion of the conveyance member. It is possible to prevent the developer on the transfer material from scattering and reverse transfer without contacting them.

1 is an overall schematic front view of an image forming apparatus according to a first embodiment of the present invention. It is an operational explanatory view of the transfer device concerning a 1st embodiment of the present invention. It is an operational explanatory view of a transfer device concerning a 2nd embodiment of the present invention. It is an operational explanatory view of a transfer device concerning a 3rd embodiment of the present invention. It is an operational explanatory view of a transfer device concerning a 4th embodiment of the present invention.

Explanation of symbols

1B charging apparatus 3B developing device _{4B, 4B 2, 4B 3,} 4B 4 transfer device 6B photosensitive drum 7 conveyor belt 8 fixing device 4B2,4B ₂ 2,4B _{3 2} brushes BR brush roller

Claims (1)

An electrostatic latent image is formed on the photosensitive member, a developer is supplied to the photosensitive member to visualize the electrostatic latent image, and the visible image is transferred to a transfer material by a transfer device. In an image forming apparatus for fixing a visible image on a material by a fixing device,
The transfer device has a brush portion that is charged by contacting a back surface of a belt-like conveyance member that conveys a transfer material while being in contact with the photosensitive member, and a brush tip of the brush portion at the time of image formation is Provided so as not to exceed the nip portion range, which is the overlapping region of the photosensitive member and the conveying member,
The brush part is in a roller shape,
The brush tip of the roller-shaped brush part operates in a direction opposite to the advancing direction of the conveying member on the contact surface with the conveying member,
The rotation center axis of the brush portion includes a bisector of a central angle at which the nip portion of the photosensitive member is seen and a bisector of a central angle at which the brush portion faces the conveying member. Place it at the same position in the nip area,
The curvature radius of the nip portion of the conveying member R1, the center angle looking into the nip and 2 [Theta] _1, the transfer device and the radius of curvature of the portion facing the conveying member R2, a central angle looking into the facing portion 2 [Theta] when _2, an image forming apparatus which satisfy the following relational expression.
sinθ ₂ ≦ (R1sinθ ₁ ) / R2

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