JP2005107419A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To save space and to form images of stable image quality. <P>SOLUTION: One among the rolls stretching a conveying belt is concurrently used as a roll for transfer. It is preferable that the hardness of the roll be 70 degrees or lower in Asker C, and the composite hardness of the roll and the conveying belt stretched by the roll be 78 degrees or lower in the Asker C. This eliminates the conventional need to attach a roll dedicated for transfer to the flat face of a conveying belt, and accordingly, space saving is achieved. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a technique for transferring a toner image to a recording medium in an image forming apparatus.

In an electrophotographic image forming apparatus, first, a toner image formed on an image carrier such as a photoreceptor is primarily transferred to an intermediate transfer belt, and then the toner image is transferred from the intermediate transfer belt to a recording sheet. The toner image is further transferred and fixed on the recording paper.
Here, FIG. 7 is a diagram showing a configuration around the transfer portion where the toner image is secondarily transferred. In FIG. 7, the intermediate transfer belt 1 on which the toner image has been primarily transferred is rotated in the direction of arrow A. A transfer roll 2 for performing secondary transfer is disposed on the inner periphery of the intermediate transfer belt 1. On the other hand, the conveying belt 3 for conveying the recording paper P is stretched by two stretching rolls 4a and 4b. A counter transfer roll 5 is provided at a position facing the transfer roll 2 with the intermediate transfer belt 1 and the conveyance belt 3 interposed therebetween. A voltage is applied between the transfer roll 2 and the counter transfer roll 5 by a power source (not shown), and thereby, between the transfer roll 2 and the counter tension roll 5, that is, the intermediate transfer belt 1 and the conveyance belt 3. A transfer electric field is formed in a region (hereinafter referred to as a transfer region) in contact with. The toner image is secondarily transferred from the intermediate transfer belt 1 to the recording paper P by the action of the transfer electric field thus formed.

  By the way, in the image forming apparatus, various devices have been devised in order to further reduce the size of the entire apparatus, and it is preferable to further reduce the space for the configuration of the transfer unit as described above. Therefore, for example, as shown in FIG. 8, if one roll 4 a plays a role as a tension roll that stretches the conveyor belt 3 and a role as an opposing transfer roll that forms a transfer electric field, It should be possible to save space by the space surrounded by the dotted line. Such a configuration similar to that shown in FIG. 8 is disclosed, for example, in the drawings of Patent Documents 1 to 7.

  However, the stretching rolls 4a and 4b for stretching the conveying belt 3 are generally formed of metal for the purpose of stably moving the conveying belt 3 around the conveying belt 3, so that they are directly transferred as opposed to each other. When used as a roll, the following problems may occur. That is, since the roll formed of metal hardly deforms, if the roll mounting position is slightly shifted, the transfer region as described above cannot be formed properly, and transfer failure may occur.

JP-A-1-234874 JP-A-3-231273 JP-A-5-333723 Japanese Patent Laid-Open No. 10-74000 Japanese Patent Laid-Open No. 10-319741 Japanese Patent Laid-Open No. 11-23679 JP 2003-91132 A

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus capable of saving space and forming an image with stable image quality.

In order to solve the above problems, the present invention provides a transfer belt to which a toner image is transferred while being rotated, a conveyance belt for conveying a recording medium, and a position at which the toner image is transferred from the transfer belt to the recording medium. And a transfer roll disposed so as to be in contact with the inner periphery of the transfer belt, and a position facing the transfer roll across the transfer belt and the transport belt so as to be in contact with the inner periphery of the transport belt. A transfer tension roll, and at least a surface of the roll is formed of a material having a predetermined elasticity, and the transfer tension roll stretches the conveyance belt to stretch the conveyance belt. Provided is an image forming apparatus arranged at a position where a belt conveying direction is changed.
According to this image forming apparatus, since the transfer stretching roll plays the role of stretching the conveyance belt and the role of forming the transfer electric field as a single unit, space saving in the apparatus can be achieved. Further, since the transfer tension roll has a predetermined elasticity, it is possible to appropriately form a region (transfer region) where the intermediate transfer belt and the transport belt are in contact with each other.

  In a preferred aspect of the present invention, the conveyor belt has a predetermined elasticity. When the conveyance belt has elasticity like a rubber belt, for example, it is softer than a resin belt, so that the transfer region can be appropriately formed.

The hardness of the transfer stretch roll is Asker C 70 ° or less, and the combined hardness of the roll hardness and the belt hardness at the portion where the transfer belt is stretched by the transfer stretch roll is Asker C78. It is desirable that the angle is below. In order to obtain such hardness, a roll may be constituted by a foam layer. For example, the transfer tension roll may be constituted by a single foam layer, or at least one of the plurality of layers constituting the transfer tension roll may be a foam layer.
When the tension transfer roll is a relatively soft roll having an Asker C of 70 ° or less, the transfer area can be appropriately formed. Further, when an elastic belt such as a rubber belt is used as the conveying belt, if the Asker C of the transfer stretch roll is 78 ° or less from above the belt portion stretched by the transfer stretch roll, the transfer area is appropriately set. Can be formed.
Further, in order to appropriately form the transfer region, it is desirable that the outer diameter of the transfer stretch roll is 16 mm or more.

  If the electrical resistivity per unit volume of the transport belt is lower than the electrical resistivity per unit volume of the transfer stretch roll, current does not flow to the transfer stretch roll, but to the nearby stretch roll via the transport belt. It will flow. Thus, when current flows in the direction of the belt surface of the conveyor belt, image quality defects occur. Therefore, it is desirable that the electrical resistivity per unit volume of the transfer tension roll is equal to or lower than the electrical resistivity per unit volume of the transport belt.

  Further, a force is applied to the transfer stretching roll that stretches the conveyor belt by the action of the tension applied to the conveyor belt. At this time, the roll portion to which the largest force is applied to the transfer tension roll is crushed by the force, and the effective hardness increases. If the hardness of the transfer tension roll increases as described above, there is a possibility that the transfer region cannot be formed properly. Therefore, it is desirable that the conveyance belt and the transfer belt are in contact with each other at a portion other than the portion where the largest force is applied from the conveyance belt to the transfer tension roll when the conveyance belt is stretched by the transfer tension roll.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
In the present embodiment, a belt formed of an elastic body is used as the conveyance belt, and a roll formed of an elastic body is used as the stretching roll used for secondary transfer. Conventionally, when the stretch roll is formed of an elastic soft material, the drive of the transport belt is not stable, and so-called walk (meandering) may occur. Only rolls made of a very hard material have been used. However, the inventors have found through experiments to be described later that the above-mentioned problem is within an allowable range as long as the tension roll has elasticity even if it has elasticity. .

  First, the configuration of the image forming apparatus 100 according to the present embodiment will be described with reference to FIG. The image forming units 10Y, 10M, 10C, and 10K form toner images of yellow (Y), magenta (M), cyan (C), and black (K) colors, respectively. The intermediate transfer belt 20 is stretched around a plurality of various rolls 30, and is rotated around these rolls 30 in the direction of arrow a. The toner images formed by the image forming units 10Y, 10M, 10C, and 10K are primarily transferred onto the intermediate transfer belt 20 that is moved in this manner so as to overlap.

  The recording paper sent out from the storage tray 40 is conveyed in the direction of arrow b along the conveyance path Path by a plurality of conveyance rolls 50. The transfer device 60 secondarily transfers the toner image primarily transferred to the intermediate transfer belt 20 onto a recording sheet conveyed on the conveyance path Path. The fixing device 70 fixes the toner image secondarily transferred to the recording paper on the paper surface by heating and pressing. The recording paper on which the toner image is fixed is discharged to the discharge tray 80 along the direction of arrow c.

Next, FIG. 2 is a diagram illustrating a configuration of the transfer device 60.
The transfer device 60 includes a transfer roll 61 disposed so as to be in contact with the inner periphery of the intermediate transfer belt 20, a power supply 65 connected to the shaft 61a of the transfer roll 61, a conveyance belt 62 for conveying recording paper, In order to stretch the conveyor belt 62, stretching rolls 63 and 64 are provided so as to be in contact with the inner periphery of the belt. The term “stretching” as used herein means that the tensioning rolls 63 and 64 are arranged at positions that change the transporting direction (moving direction) of the transporting belt 62, so that tension is applied to the transporting belt 62. It means a state that is. In the example shown in FIG. 2, the moving direction of the conveyor belt 62 is reversed by each of the stretching rolls 63 and 64, so it can be said that it is “stretched”. On the other hand, for example, the counter transfer roll 5 shown in FIG. 7 does not change the conveyance direction of the conveyance belt 3 and is merely in contact with the inner circumference of the belt. I can't say that.
Of these stretching rolls 63 and 64, the stretching roll 63 is provided at a position facing the transfer roll 61 with the intermediate transfer belt 20 and the conveyance belt 62 interposed therebetween, and is used for secondary transfer of the toner image. Therefore, it is hereinafter referred to as “transfer stretch roll 63”. The metal shaft 63a of the transfer tension roll 63 is grounded and is driven to rotate by a motor (not shown). On the other hand, the tension roll 64 plays a role for peeling the recording sheet onto which the toner image has been secondarily transferred from the conveyance belt 62, and hence will be referred to as a “stretch tension roll 64” hereinafter. The peeling tension roll 64 is rotatable around a grounded metal shaft 64a.

  The intermediate transfer belt 20 and the conveyance belt 62 are in contact with each other by being pressed against each other by the transfer roll 61 and the transfer stretching roll 63. This contact area is the transfer area G. Due to the frictional force generated in the transfer region G and the driving force of the motor described above, the conveying belt 62 is rotated in the direction of the arrow d in synchronization with the circular movement of the intermediate transfer belt 20. Further, a voltage is applied between the transfer roll 61 and the transfer tension roll 63 by the power source 65 to form an electric field therebetween, and the toner image is transferred from the intermediate transfer belt 20 onto the recording paper by the action of the electric field. Transcribed.

  It should be noted that the transfer region G and the belt winding center of the transfer tension roll 63 are preferably not at the same position. Here, “the belt winding center of the transfer tension roll 63” refers to the circumferential direction of the transfer tension roll from the positions P1 and P2 at which the transfer tension roll 63 and the conveyance belt 62 start to contact, as shown in FIG. It is the position P that is at an equal distance along. The force F applied to the transfer tension roll 63 by the tension (tension) T applied to the transport belt 62 is the largest at the position P. Therefore, the amount that the transfer tension roll 63 itself collapses due to elastic deformation in the direction of the force F should be the largest at this position P. If the transfer tension roll 63 is crushed, its effective hardness increases. Therefore, if the position P and the transfer area G overlap with each other, the elasticity of the transfer tension roll 63 does not function properly, It becomes difficult to form a simple transfer region. Therefore, in the present embodiment, the transfer region G and the belt winding center (position P) of the transfer tension roll 63 are prevented from overlapping.

The inventors conducted an experiment using the image forming apparatus 100 configured as described above under the following conditions.
The intermediate transfer belt 20 is formed of a resin in which a conductive material such as carbon black as a resistance adjusting agent is dispersed in polyimide. The thickness of the intermediate transfer belt 20 is 100 (μm). The transfer roll 61 is made of conductive EPDM (Ethylene Propylene Diene Methylene Linkage) in which carbon black as a resistance adjusting agent is dispersed. The hardness of the transfer roll 61 is Asker C75 °. The conveyance belt 62 is formed of a mixed rubber of chloroprene and EPDM in which carbon black as a resistance adjusting material is dispersed, has a thickness of 450 (μm), and has a belt length of 264 (without tension). mm) and a durometer hardness of 73 °. The transfer tension roll 63 is formed of a material having at least a roll surface having a predetermined elasticity. Here, it is a single-layer foamed rubber roll in which resistance of epichlorohydrin rubber or urethane rubber is adjusted with an ionic conductive material and / or carbon black, the diameter of the shaft 63a is φ14 (mm), and the outer diameter of the roll is φ28 (mm). is there. In order to appropriately form the transfer region G, the outer diameter of the transfer tension roll 63 is desirably φ16 (mm) or more. As such a transfer stretching roll 63, several rolls having a hardness in the range of Asker C5 ° to 100 ° were prepared. In order to obtain the transfer tension roll 63 having such hardness, the transfer tension roll 63 is constituted by a single foam layer as described above, or the transfer tension roll 63 is constituted by a plurality of layers. At least any one of them may be a foam layer. However, as the transfer tension roll 63 with Asker C 100 °, the one formed of SUS was used. The peeling tension roll 64 is made of SUS (Steel Use Stainless) and has an outer diameter of φ15 (mm).

  Here, FIG. 4 is a diagram showing the magnitude relationship between the electrical resistances of the transport belt 62 and the transfer tension roll 63 configured as described above, with the current density as the horizontal axis. Here, the symbol ◇ indicates the electrical resistance of the conveying belt 62, and the symbol □ indicates the electrical resistance of the transfer tension roll 63. In addition, a dotted line obtained by extending a solid line connected with ◇ marks and a dotted line obtained by extending a solid line connected with □ marks indicate the electric resistance expected from the inclination of the solid line portion. When the electrical resistivity per unit volume of the transport belt 62 is lower than the electrical resistivity per unit volume of the transfer tension roll 63, current does not flow to the transfer stretch roll 63, It flows to the tension roll (here, the peeling tension roll 64). As described above, when an electric current flows in the belt surface direction of the conveying belt 62, an image quality defect occurs. Therefore, it is desirable that the electrical resistivity per unit volume of the transfer tension roll 63 is equal to or lower than the electrical resistivity per unit volume of the transport belt 62. Referring to FIG. 4, when the current densities are equal, it can be confirmed that the above-described experiment is performed in a state where the relationship of the electrical resistivity of the conveying belt> the electrical resistivity of the transfer stretch roll is satisfied.

In this experiment, first, the transfer roll 61 and the transfer stretching roll 63 are pressed against each other so that the amount of biting into the other roll is adjusted to 0.8 (mm) as a standard. Next, the image quality of the image formed on the recording sheet is confirmed while gradually making a difference in the amount of biting between the one end side and the other end side of the roll shaft. Then, the maximum value of the difference in the amount of biting that can maintain good image quality (hereinafter referred to as the allowable maximum biting amount) is specified. A larger allowable maximum bite amount is preferable because the allowable range is wider.
In the experiment, a 100% blue full-color chart and 8-point lines (vertical and horizontal crosses in red, blue, green, and black) were placed at both ends and the center in the recording paper feed direction. Two types of line charts were used. The full chart is used for verifying general transferability, and the line chart is used for verifying an image quality defect called “worm-eaten” generated by pressure concentration in the transfer region G.

  Table 1 shows the results of performing the above-described experiment using the transfer tension roll 63 having various hardness (Asker C5 ° to 100 °). For example, when the hardness of the transfer tension roll 63 is Asker C20 °, even if the difference in the biting amount at both ends in the roll axis direction is ± 0.5 (mm) at the maximum (that is, the biting amount on one end side of the roll shaft is 0.3 (mm) and the amount of biting on the other end side was 1.3 (mm)), and good image quality could be realized. Further, no walk of the conveyor belt 62 occurred. Therefore, in the “determination” column in Table 1, “◎” meaning “good” is written. Note that “the combined hardness of the transfer tension roll and the conveyance belt” in Table 1 means the hardness of the transfer tension roll 63 and the conveyance belt 62 at the portion where the conveyance belt 62 is stretched by the transfer tension roll 63. It is the synthetic hardness with the hardness.

  On the other hand, when the hardness of the transfer tension roll 63 is Asker C 70 °, the difference in the amount of biting at both ends in the roll axial direction is ± 0.1 (mm) at the maximum, and a very good image quality can be realized. . Therefore, in the “determination” column in Table 1, “Δ” meaning “ordinary” is written. When the hardness of the transfer tension roll 63 is Asker C100 °, good image quality cannot be realized even when there is no difference in the amount of biting in both ends in the roll axis direction. Therefore, “x” meaning “bad” is written in the “determination” column in Table 1.

  From the above experimental results, when the hardness of the transfer stretch roll 63 is lower than Asker C70 °, or when the combined hardness of the transfer stretch roll and the conveyance belt is lower than Asker C78 °, good image quality is realized. It can be said that it is preferable because it is possible. In addition, as a transfer roll 61, an experiment was conducted using a two-layer roll in which EPDM (thickness: 2 mm) made of carbon black on a foamed layer was used to conduct conductivity. I was able to.

  The image forming apparatus 100 described above is a type that performs transfer using the intermediate transfer belt 20 (hereinafter referred to as a belt transfer type), but in addition to this, as shown in FIG. A type in which a toner image is transferred onto a recording sheet on the conveyance transfer belt 62 (hereinafter referred to as drum transfer type) is also conceivable. However, since the belt transfer type has the following advantages over the drum transfer type, it is desirable to adopt the belt transfer type.

  When the toner image is transferred to the recording paper, the recording paper is peeled off from the transfer conveyance belt 62 and then conveyed toward the next conveyance path. The ease of peeling at this time is determined by the degree of adsorption of the recording paper to the conveyance belt and the curvature of the intermediate transfer member (the intermediate transfer belt 20 or the intermediate transfer drum 101). The former factor is the same for both the belt transfer type and the drum transfer type, but the latter factor is different for both types.

  Since the recording paper has a so-called stiffness, the end of the recording paper is more easily separated from the intermediate transfer member as the curvature radius of the intermediate transfer member is smaller. That is, in the belt transfer type, as shown in FIG. 6A, the radius of curvature of the intermediate transfer belt 20 (that is, the radius of the transfer roll 61) is relatively small. That is, after the transfer region G, the intermediate transfer belt 20 and the conveyance belt 62 are suddenly separated at an angle θ. On the other hand, in the drum transfer type, as shown in FIG. 6B, since the radius of curvature of the intermediate transfer drum 101 is relatively large, the intermediate transfer drum 101 and the conveyance belt 62 pass from the angle θ after passing the transfer region G. Will be separated by a small angle θ ′. As described above, the recording paper is subjected to the electric attraction between the own belt and the conveying belt 62, so that the belt transfer type is easier to peel off the recording paper from the intermediate transfer member. Accordingly, the recording paper can be conveyed promptly. Of course, in the drum transfer type, the radius of curvature of the drum may be reduced. However, considering the efficiency of the image forming process, it is impossible to make the curvature (radius) of the intermediate transfer drum 101 too small. Therefore, it is desirable to apply the present invention to an image forming apparatus that performs transfer using an intermediate transfer belt.

According to the embodiment described above, one of the rolls around which the conveyor belt 62 is stretched is used as a transfer roll. In this way, while a dedicated roll for transfer is conventionally attached to the flat surface of the conveyor belt, it is not necessary to attach such a dedicated roll, so that space can be saved. Further, since the intermediate transfer belt 20 is used, it is preferable from the viewpoint of ease of peeling of the recording paper.
In the above description, the recording paper has been described as an example of the recording medium to which the toner image is transferred. However, in addition to this, various materials such as plastic such as an OHP film, wood, and cloth are recorded. It can be used as a medium.

1 is a diagram illustrating a configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a diagram illustrating a configuration around a transfer device provided in the image forming apparatus. FIG. 6 is a diagram for explaining a positional relationship between a belt winding center of a transfer tension roll 63 and a transfer region. It is a figure which shows the electrical resistivity per unit volume of a conveyance belt and a transfer tension roll. FIG. 4 is a diagram illustrating a configuration around a transfer portion when an intermediate transfer drum is used instead of the intermediate transfer belt in the embodiment. FIG. 6 is a diagram for explaining a difference between when an intermediate transfer belt is used and when an intermediate transfer drum is used. It is a figure which shows the structure of the conventional transfer part periphery. It is a figure which shows the structure improved aiming at space saving from the past.

Explanation of symbols

  10Y, 10M, 10C, 10K ... Image forming unit, 20 ... Intermediate transfer belt, 40 ... Recording paper tray, 60 ... Transfer device, 61 ... Transfer roll, 62 ... Conveyor belt 63 ... Transfer tension roll, 64 ... Release tension roll, 65 ... Power supply, 70 ... Fixing device.

Claims (9)

A transfer belt on which the toner image is transferred while being rotated,
A conveying belt for conveying a recording medium;
A transfer roll disposed so as to contact the inner periphery of the transfer belt at a position where a toner image is transferred from the transfer belt to the recording medium;
A transfer tension roll disposed at a position facing the transfer roll across the transfer belt and the transport belt so as to be in contact with the inner periphery of the transport belt;
The transfer tension roll is
At least the roll surface is made of a material having a predetermined elasticity,
An image forming apparatus disposed at a position where the transfer tension roll changes the conveying direction of the conveying belt by stretching the conveying belt.   The image forming apparatus according to claim 1, wherein the conveyor belt has predetermined elasticity.   The image forming apparatus according to claim 1, wherein the transfer tension roll has an Asker C of 70 ° or less.   The image forming apparatus according to claim 2, wherein a combined hardness of the hardness of the roll and the hardness of the belt in a portion where the conveyance belt is stretched by the transfer stretch roll is Asker C of 78 ° or less.   The image forming apparatus according to claim 2, wherein an outer diameter of the transfer tension roll is 16 mm or more.   The image forming apparatus according to claim 1, wherein an electrical resistivity per unit volume of the transfer tension roll is equal to or lower than an electrical resistivity per unit volume of the transport belt.   The image forming apparatus according to claim 3, wherein the transfer tension roll is configured by a single foam layer.   The image forming apparatus according to claim 3, wherein at least one of the plurality of layers constituting the transfer tension roll is a foam layer. The conveyance belt and the transfer belt are in contact with each other at a portion other than a portion where the largest force is applied from the conveyance belt to the transfer tension roll when the conveyance belt is stretched by the transfer tension roll. The image forming apparatus according to 1.

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