JP2017026777A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of outputting deliverables having a high image quality in which voids are not generated by abnormal discharge due to a gap caused between an intermediate transfer body and a paper in the upper stream side of the secondary transfer part when a thick paper is fed.SOLUTION: An image forming apparatus includes: an image carrier 1Y; toner image forming means 3Y, 4Y, and 5Y for forming toner images on the image carrier 1Y; an intermediate transfer body 40; primary transfer means 6Y for primarily transferring the toner image on the image carrier 1Y to an intermediate transfer body 40; secondary transfer means 10 for transferring the toner image primarily transferred on the intermediate transfer body 40 onto a transfer material P; a high voltage power source 11 for applying a transfer high voltage to the secondary transfer means 10; and a secondary transfer counter material 42 arranged opposed to the secondary transfer means 10 by sandwiching the intermediate transfer body 40. The image forming apparatus further includes a backup member 21 abutting against the inner side of the intermediate transfer body along the surface of the intermediate transfer body in the upper stream of the secondary transfer counter material 42.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an image forming apparatus for transferring a toner image carried on an image carrier onto a recording material by using an electrophotographic technique such as a copying machine or a laser printer, and more specifically, electrostatically transferring a toner image onto a transfer material. The present invention relates to a technique that enables high-quality image formation during transfer.

  Each color toner image formed on an image carrier such as a photosensitive drum is sequentially primary-transferred to an intermediate transfer body such as an intermediate transfer belt to form a multicolor toner image, and then the multicolor toner image is collectively applied to a recording material. Thus, a color image forming apparatus that performs secondary transfer onto a recording material has been put into practical use. The intermediate transfer method can transfer the toner image stably because the transfer of the toner image to the recording material whose state is easy to change is only one time.

  The toner image on the intermediate transfer belt is secondarily transferred electrostatically to a recording material such as paper by applying a transfer high voltage having a reverse polarity to the toner to a secondary transfer unit such as a secondary transfer roller. Since the transfer high pressure used at this time is a very high pressure of several kV, the space near the secondary transfer nip formed by the secondary transfer roller and the secondary transfer counter roller via the intermediate transfer belt. A large electric field is formed on the surface and abnormal discharge is likely to occur.

  If an abnormal discharge occurs between the intermediate transfer belt and the paper before the toner on the intermediate transfer belt is transferred to the paper upstream of the secondary transfer nip, the electric charge of the toner image on the intermediate transfer belt is caused by the discharge. It will be lost. In this state, even if a high transfer voltage is applied to the secondary transfer nip portion, the toner image cannot be moved electrostatically onto the paper, resulting in an image defect in which a portion where a large discharge occurs is white.

  In order to prevent white spots caused by discharge occurring in the upstream portion of the secondary transfer nip, it is effective to substantially eliminate the gap between the intermediate transfer belt and the paper upstream of the secondary transfer nip. The reason for this is that when the gap between the intermediate transfer belt and the paper becomes small in the vicinity of the secondary transfer nip portion where the transfer electric field is strong, the electric field between the intermediate transfer belt and the paper becomes small and abnormal discharge hardly occurs. It is to become.

  As a means for substantially eliminating such a gap between the intermediate transfer belt and the paper, for example, Patent Document 1 proposes a method of offsetting the secondary transfer roller upstream of the secondary transfer counter roller. .

  As an effect of offsetting the secondary transfer roller to the upstream side, when the paper is nipped by the secondary transfer portion, the direction perpendicular to the line connecting the centers of the secondary transfer roller and the secondary transfer counter roller is set. When defined as a nip line, the paper attempts to maintain a posture substantially along the nip line. In other words, since the paper moves toward the nip line in the direction of biting into the intermediate transfer belt upstream of the secondary transfer nip, the intermediate transfer belt restrains the paper, so that the gap between the intermediate transfer belt and the paper is almost eliminated. Can do. That is, in a portion where a large electric field is formed in the vicinity of the secondary transfer nip, the secondary transfer roller is offset upstream so that there is almost no gap between the intermediate transfer belt and the paper. Therefore, white spots caused by this discharge are also suppressed.

JP 2011-22466 A

  By offsetting the secondary transfer roller in the upstream direction with respect to the secondary transfer counter roller, it is possible to suppress the gap that causes discharge while the paper is stably nipped in the secondary transfer nip. It is. However, as shown in FIG. 2, when a thick paper having a strong stiffness is passed, the paper pushes up the intermediate transfer belt, and between the intermediate transfer belt and the paper in the vicinity of the secondary transfer nip where the electric field is strong. A gap such as the middle B portion was formed, and white spots due to discharge at the rear end portion, and white spots at the rear end occurred.

  SUMMARY OF THE INVENTION In view of the above circumstances, the present invention provides an image forming apparatus capable of outputting a high-quality product that suppresses white-out at the trailing edge of a paper, which occurs remarkably when a thick paper is passed while maintaining a basic density. The purpose is to provide.

In order to achieve the above object, an image forming apparatus according to the present invention includes:
An image carrier (1), toner image forming means (3, 4, 5) for forming a toner image on the image carrier (1), an intermediate transfer member (40), and the image carrier (1) A primary transfer means (6) for primarily transferring the upper toner image onto the intermediate transfer member (40), and a toner image primarily transferred onto the intermediate transfer member (40) as a transfer material (P ) Secondary transfer means (10) for transferring up, high voltage power source (11) for applying a transfer high voltage to the secondary transfer means (10), and secondary transfer means (10) with the intermediate transfer body (40) interposed therebetween. 2) a secondary transfer opposing member (42) disposed opposite to each other.
A backup member (21) is provided on the inner side of the intermediate transfer member upstream of the secondary transfer opposing member (42) and abuts along the surface of the intermediate transfer member.

  According to the image forming apparatus of the present invention, the deflection preventing member prevents the intermediate transfer belt from bending inward. Thereby, it is possible to prevent a gap from being formed in the portion B in FIG. As a result, it is possible to suppress the trailing edge white spot phenomenon that is caused by the discharge at the trailing edge portion. That is, it is possible to provide an image forming apparatus that can output a high-quality product.

  As a conventional example close to the configuration of the present invention, there is JP-A-2002-82543, which deals with a problem that is not related to the thickness of paper and the stiffness of toner scattering and white spots where the toner image shifts. On the other hand, the problem of the present invention is that it is abnormal discharge that occurs because the stiffness of the cardboard is strong. The solution means is also configured to project the intermediate transfer belt outward, whereas the present invention is different in that the intermediate transfer belt is prevented from bending inward.

  In JP-A-2002-82543, the distance along the moving direction of the image carrier belt of the contact portion where the transfer material comes into close contact with the surface of the image carrier belt before reaching the press contact portion is set to 2 mm or more and 30 mm or less. The image forming apparatus according to claim 2, wherein the deflection of the belt at the distance along the moving direction of the image bearing belt, that is, the portion described by the distance D is not described. In addition, there is no description of the guide member over the entire portion.

  On the other hand, the present invention is different in that the intermediate transfer belt is bent inward over an area of the distance D.

FIG. 3 is a diagram illustrating Example 1. It is a figure explaining the problem which invention is going to solve. FIG. 3 is a diagram illustrating Example 1. 1 is a block diagram of Example 1. FIG. 3 is a flowchart of the first embodiment. FIG. 6 is a diagram illustrating Example 2. 6 is a block diagram of Embodiment 2. FIG. 10 is a flowchart of Example 2. FIG. 6 is a diagram for explaining a third embodiment. It is a figure explaining the combination of control of Example 1, Example 2, and Example 3. FIG.

<Example 1>
FIG. 1 is an explanatory diagram of the configuration of the image forming apparatus of this embodiment.

  Reference numerals 1Y, 1M, 1C, and 1k denote photosensitive drums (latent image carriers) that rotate in the direction of arrow A, and their surfaces are uniformly charged by primary charging devices 3Y, 3M, 3C, and 3k. Reference numerals 4Y, 4M, 4C, and 4k denote exposure apparatuses that perform exposure based on image information. An electrostatic latent image corresponding to image information is formed on the photosensitive drums 1Y, 1M, 1C, and 1k by a known electrophotographic process.

  The developing devices 5Y, 5M, 5C, and 5k include yellow (Y), magenta (M), cyan (C), and black (k) toners, which are chromatic toners, respectively. The aforementioned electrostatic latent images are developed by the developing devices 5Y, 5M, 5C, and 5k, and toner images are formed on the respective photosensitive drums 1Y, 1M, 1C, and 1k. A reversal development method is used in which toner is attached to the exposed portion of the electrostatic latent image for development.

The electrostatic latent image formed by the exposure device 4 is an aggregate of small dot images, and the density of the toner image formed on the photosensitive drum 1 can be changed by changing the density of the dot images. it can. In this embodiment, each color toner image has a maximum density of about 1.5 to 1.7, and the applied amount of toner at the maximum density is about 0.4 to 0.6 mg / cm ^2. Reference numeral 40 denotes an intermediate transfer belt disposed so as to be in contact with the surface of the photosensitive drum 1, and is stretched between a plurality of stretching rollers 41, 42, and 43 in the direction of arrow G to 250. It is designed to rotate at 300 mm / sec. In this embodiment, the intermediate transfer belt stretching roller 41 is a tension roller that controls the tension of the intermediate transfer belt 40 to be constant, and the intermediate transfer belt stretching roller 43 is a driving roller for the intermediate transfer belt 40, and the intermediate transfer belt. The stretching roller 42 is a secondary transfer counter roller that forms a secondary transfer nip N against the secondary transfer roller 10 through the intermediate transfer belt 40.

  As the intermediate transfer belt 40, an appropriate amount of carbon black as an antistatic agent is contained in resins such as polyimide and polycarbonate, or various rubbers, and the volume resistivity is 1E + 9 to 1E + 14 Ω · cm, and the thickness is 0.07 to 0.3 mm. We use what we did.

  Further, as the intermediate transfer belt 40, a rubber in which an appropriate amount of carbon black is contained as an antistatic agent in various rubbers on a base material having a thickness of 0.07 to 0.2 mm made of a resin such as polyimide or polycarbonate. It is also possible to use a belt having a three-layer structure in which a layer is formed with a thickness of 0.05 to 0.5 mm and a surface layer is coated with a material containing a fluororesin or the like with a thickness of 5 to 30 μm.

  At that time, the volume resistivity is preferably 1E + 9 to 1E + 14 Ω · cm.

  The transfer material P is temporarily stopped here by the registration roller 13, and the paper P is supplied to the secondary transfer nip N in synchronization with the toner image on the intermediate transfer belt 40 being conveyed to the secondary transfer nip N. The secondary transfer upstream upper guide 14 and the paper P are intermediate transfer belts as the secondary transfer upstream upper guide member that regulates the behavior of the paper P approaching the surface of the intermediate transfer belt 40 on the surface side of the intermediate transfer body upstream of the secondary transfer nip. 40 has a secondary transfer upstream lower guide 15 as a secondary transfer upstream lower guide member that regulates the behavior away from the surface side. The conveyance path is regulated by these guide members until the paper P is conveyed from the registration roller 13 to the secondary transfer nip N.

  The paper P supplied from the registration roller 13 passes between the secondary transfer upstream upper guide 14 and the secondary transfer upstream lower guide 15 and is formed by the secondary transfer counter roller 42 and the secondary transfer roller 10. Passes through the transfer nip N. At this time, a secondary transfer current having a polarity opposite to that of the toner is applied by the secondary transfer roller 10, whereby the toner image on the intermediate transfer belt 40 is collectively transferred onto the paper P and the supplied electrostatic force. As a result, the paper is adsorbed to the secondary transfer belt 12. For example, in this embodiment, a current of +40 to 60 uA is passed.

  The secondary transfer roller 10 is made of an elastic layer of an ion conductive foamed rubber (NBR rubber) and a metal core, has an outer diameter of 24 mm, a roller surface roughness Rz = 6.0 to 12.0 (μm), and a resistance value of N. / N (23 ° C., 50% RH) measurement A transfer roller of 1E + 5 to 1E + 7Ω with 2 kV applied is used. A secondary transfer high-voltage power supply 11 having a variable supply bias is attached to each of the secondary transfer rollers 10.

  After passing through the secondary transfer nip N, the paper P on which the unfixed toner image is placed is conveyed to the fixing device 60, where the toner image is fixed, and then discharged out of the machine.

  On the other hand, the intermediate transfer belt 40 after the secondary transfer is subjected to an image forming process after the transfer residual toner, paper powder and the like are cleaned by the intermediate transfer belt cleaning device 44.

  The secondary transfer roller 10 is disposed so as to have an offset amount of 0 to 4 mm upstream from the secondary transfer counter roller 42 along the surface of the intermediate transfer belt 40.

  The reason why the offset amount 0 mm is included is that, as shown in FIG. 3, the secondary transfer counter roller 42 is harder than the secondary transfer roller 10 even when the offset amount is 0 mm. Since the paper is bent so as to wind around the secondary transfer counter roller 42, the paper is bent so as to wind around the intermediate transfer belt, so that the nip line enters the inside of the intermediate transfer belt upstream of the secondary transfer portion as indicated by the dotted line. It is because it can be set as a simple structure.

  The backup roller 20 has an image formed when the front end of the paper comes into contact with the intermediate transfer belt, the rear end of the paper comes out of the entrance guide 14 and jumps to the intermediate transfer belt, or the intermediate transfer belt bounces and vibrates. It is installed so as not to shake.

  Here, the tension roller of the intermediate transfer belt immediately upstream of the secondary transfer counter roller is defined as a backup roller.

  With such a configuration, when a process speed of 300 mm / s and Oji Paper's Bon Ivory +310 g / m 2 were passed, white spots occurred at the trailing edge at a secondary transfer current of 40 μA.

  As described above, this phenomenon is a phenomenon in which discharge occurs when the electric field in the area where the transfer electric field is strong, that is, the electric field of about 2 to 10 mm upstream of the secondary transfer nip is large. By narrowing the gap, the electric field can be reduced and countermeasures can be taken.

  Therefore, as shown in FIG. 4, a backup member 21 is provided on the upstream inner side of the secondary transfer portion so that the intermediate transfer belt does not bend.

  The backup member 21 is preferably installed so that there is no gap between the paper and the intermediate transfer belt during the sheet passing. The intermediate transfer when the secondary transfer roller is not in contact with the backup member 21 being absent. It was installed so as to follow the position of the belt. That is, if the intermediate transfer belt is pushed strongly outward, the rubbing force is increased. Conversely, if the intermediate transfer belt is installed away from the intermediate transfer belt, the intermediate transfer belt may bend.

  As the backup member 21, a resin whose resistance is adjusted to a medium resistance is used. If the resistance is low, a secondary transfer current may flow and transfer failure may occur. If the resistance is high, friction charging occurs and the intermediate transfer belt is attracted to prevent rotation of the belt. There is a risk that such issues will occur. The thickness was 3 mm, and the length along the rotation direction of the intermediate transfer belt was 25 mm. The gap with the secondary transfer counter roller 42 was 2 mm. The gap with the backup roller 20 was 5 mm.

  If the distance between the secondary transfer counter roller and the backup member 21 is short, they may come into contact with each other, which may cause wear, vibration, or an image defect.

  In addition, if the gap is long, the effect is reduced.

In general, the image formable area is narrower than the size of the recording material. Such a portion where image formation is not performed on the front, back, left, and right of the paper is referred to as a margin. The margin is designed to be about 1 to 4 mm.
The margin on the rear side with respect to the paper traveling direction is called the trailing edge margin.

  If the image defect is within the trailing edge margin, since there is no image originally, even if white spots occur, it does not become obvious.

That means
The backup member (21) has a distance from the secondary transfer counter roller,
0 ≦ D ≦ L
Here, it is preferable that D: distance L between the backup member (21) and the two-rolling opposed roller;

  Now, with such a configuration, when Oji Paper's Bon Ivory + 310 g / m 2 was passed, no white spots occurred even at a secondary transfer current of 50 μA.

  The backup member 21 is not limited to this, and any material that is sufficiently rigid as compared with paper may be used. For example, a metal plate may be used. Further, in order to prevent the intermediate transfer belt from being worn by rubbing, a sheet of a fluorine-based material or an ultrahigh molecular weight polyethylene sheet may be attached to the surface. In addition, a resistance-adjusted material may be used to prevent electrical charging. In addition, electric elements such as varistors, resistors, and diodes may be connected to prevent charging.

  The optimal position of the backup member 21 changes depending on the offset amount and hardness of the secondary transfer roller.

If the offset amount of the secondary transfer roller is large, the secondary transfer roller tends to lift the intermediate transfer belt inward, so that the optimal backup member 21 position changes. Also, if the hardness of the secondary transfer roller is soft, the force to lift the intermediate transfer belt inward is weakened.
Further, the optimum position of the backup member 21 varies depending on the outer diameters of the secondary transfer roller and the secondary transfer counter roller.

  According to such a situation, the position of the backup member 21 can be adjusted as appropriate.

As described above, by providing the backup member 21 on the inner side upstream of the secondary transfer portion so that the intermediate transfer belt does not bend, this occurs remarkably when the thick paper is passed while maintaining the basic density. Thus, an image forming apparatus capable of outputting a high-quality product with the trailing edge of the paper suppressed.
<Example 2>

  In the first embodiment, the backup member 21 is configured to contact and separate.

  Since the backup member 21 rubs against the intermediate transfer belt, the backup member 21 is worn or the intermediate transfer belt is worn.

  Therefore, the backup member 21 is movable so that it contacts the intermediate transfer belt only when necessary.

  More specifically, as shown in FIG. 5, the backup member 21 is fixed to the backup roller 20, and the lever attached to the back side of the backup roller 20 is moved by the solenoid 22, so that the backup member 21 has a dotted line and a solid line. It can be abutted and separated like the part written in.

As a paper type to be contacted, a paper having a basis weight of 200 g / m ² or more was used.

  The operation of the backup member 21 is controlled by the control circuit 50. A block diagram of the control circuit 50 is shown in FIG. FIG. 7 is a flowchart showing a control flow performed by the control circuit 50. Details of the flow of control performed by the control circuit 50 will be described below with reference to FIGS.

  First, the user designates the paper basis weight as the paper type information to be used by the user operation unit 51. This basis weight information is written in the RAM 53 of the control circuit 50 (S2).

The basis weight of the user-specified paper written in ROM 53 is recorded in ROM 52.
The basis weights of the reference papers for operating the backup member 21 are compared. In this embodiment, this reference value is set to 200 g / m ² .

It is determined whether or not the backup member is in contact with the intermediate transfer belt based on the basis weight of the output paper (S3).
When the basis weight of the paper is 200 g / m ² or more, the backup member solenoid is turned on in order to bring the backup member into contact with the intermediate transfer belt (S4).

  When the image formation is completed and the image formation is completed (S6), the state is returned to the original state even if the solenoid of the backup member is turned OFF, and the process ends (S7).

S4: When the basis weight of the paper is less than 200 g / m ² , the solenoid of the backup member is turned off to perform image formation (S5).

  With such a configuration, when Oji Paper's Bon Ivory + 310 g / m 2 was passed, no white spots occurred even at a secondary transfer current of 50 μA.

As described above, by providing the backup member 21 on the inner side upstream of the secondary transfer portion so that the intermediate transfer belt does not bend, this occurs remarkably when the thick paper is passed while maintaining the basic density. Thus, an image forming apparatus capable of outputting a high-quality product with the trailing edge of the paper suppressed.
<Example 3>

  In this embodiment, the distance between the secondary transfer counter roller and the backup roller is reduced and the tension of the intermediate transfer belt is increased to take measures.

  As shown in FIG. 7, the gap B shown in FIG. 2 is weighted as a configuration in which a load is applied to point E on the intermediate transfer belt stretched between the secondary transfer counter roller 42 and the backup roller 20. Perform the calculation.

Here, when the orientation is rotated in an easy-to-understand manner, the result is as shown in FIG.
L = Horizontal span length (m)
f = Deflection (m)
m, n = horizontal distance from both ends to point x (m)
W = mass of belt unit length (t)
P = concentrated load (kg)
H = Belt horizontal tension (kg)
θ = Belt inclination angle (°)
T = Belt tension = Hxsecθ (kg)
If the load due to the weight of the intermediate transfer belt is ignored, the deflection amount f due to the concentrated load P is expressed by the following equations (1) and (2).
Deflection at point X
f = Pxmxn / (LxH) (1)
Deflection amount at the center point
f = PxL / (4xH) (2)
It is expressed as

  When the amount of deflection is large, the gap between the intermediate transfer belt and the paper also increases, and white spots due to abnormal discharge are likely to occur.

Since the maximum deflection is at the center point, looking at equation (2), the deflection f is proportional to L = horizontal span length (m) and H = belt horizontal tension (kg). I understand that.
Rewriting equation (2), H = PxL / (4xf) = αxL (3)
Then α = P / (4f)
It becomes.

  On the other hand, FIG. 9 shows the occurrence of white spots when the distance between the secondary transfer counter roller and the backup roller and the tension of the intermediate transfer belt are changed at a secondary transfer current of 50 μA using Bon Ivory +310 g / m2. , X is plotted.

Considering this result corresponding to L = horizontal span length (m),
9 is expressed by the equation H = 1.1 × L + 5, and when the distance between the direction roller and the backup roller (mm), the relationship between H = belt horizontal tension (N) is
H (N) ≧ 1.1 × L (mm) +5
If so, white spots do not occur.

  As described above, by providing the backup member 21 on the inner side upstream of the secondary transfer portion so that the intermediate transfer belt does not bend, this occurs remarkably when the thick paper is passed while maintaining the basic density. Thus, an image forming apparatus capable of outputting a high-quality product with the trailing edge of the paper suppressed.

1 photosensitive drum, 2 exposure lamp, 3 primary charging device, 4 exposure device, 5 developing device,
6 primary transfer roller, 7 cleaning device, 10 secondary transfer roller,
11 Secondary transfer high-voltage power supply, 12 Secondary transfer belt, 13 Registration roller,
14 Secondary transfer upstream upper guide, 15 Secondary transfer upstream lower guide, 16 Oscillating shaft,
17 Secondary transfer roller swing motor, 18 Lower guide cam,
19 Lower guide cam motor, 20 Backup roller, 21 Backup member,
22 Backup member solenoid, 40 Intermediate transfer belt,
41 Intermediate transfer belt stretching roller (tension roller),
42 intermediate transfer belt stretching roller (secondary transfer counter roller),
43 Intermediate transfer belt stretching roller (drive roller),
44 Intermediate transfer belt cleaning device, 50 control circuit, 51 user operation unit,
52 CPU, 53 RAM, 54 ROM, 60 fixing device,
P transfer material, paper, paper, A rotation direction of the photosensitive drum,
B, the gap between the intermediate transfer belt and paper, G, the rotation direction of the intermediate transfer belt,
N secondary transfer nip, S secondary transfer roller offset relative to the secondary transfer counter roller,
L Distance from the tip of the secondary transfer upstream guide to the intermediate transfer belt

Claims (3)

An image carrier (1), toner image forming means (3, 4, 5) for forming a toner image on the image carrier (1), an intermediate transfer member (40), and the image carrier (1) A primary transfer means (6) for primarily transferring the upper toner image onto the intermediate transfer member (40), and a toner image primarily transferred onto the intermediate transfer member (40) as a transfer material (P ) Secondary transfer means (10) for transferring up, high voltage power source (11) for applying a transfer high voltage to the secondary transfer means (10), and secondary transfer means (10) with the intermediate transfer body (40) interposed therebetween. 2) a secondary transfer opposing member (42) disposed opposite to each other.
An image forming system comprising a backup member (21) that contacts the surface of the intermediate transfer member on the inner side of the intermediate transfer member upstream of the secondary transfer opposing member (42) and satisfies the following formula (1): apparatus.
The backup member (21) has a distance from the secondary transfer counter roller,
0 ≦ D ≦ L (1)
Here, D: distance L between the backup member (21) and the secondary transfer counter roller; rear end margin of the apparatus   The image forming apparatus according to claim 1, wherein the backup member is in contact with or separated from the paper according to a paper type. The distance of the backup member (21) and H = belt horizontal tension (N) are:
The image forming apparatus according to claim 1, wherein the following expressions (1) and (2) are satisfied.
The backup member (21) has a distance from the secondary transfer counter roller,
0 ≦ D ≦ L (1)
Here, D: distance between the backup member (21) and the secondary transfer counter roller; L: rear edge margin of the apparatus; distance between the secondary transfer counter roller and the backup roller; and H = belt horizontal tension (N) Is
H (N) ≧ 1.1 × L + 5 Formula (2)
L: Distance between the secondary transfer counter roller and the backup roller (mm)
H (N) = Intermediate transfer belt horizontal tension