JPH05313510A - Image forming device - Google Patents

Abstract

PURPOSE:To perform satisfactory transfer free from image disturbance by keeping the potential of the surface of a recording carrier stable before transfer. CONSTITUTION:In an image forming device which is provided with an image carrier 1, a transfer roller 8, which comes into pressure-contact with this, an upper pretransfer sheet carrying member 11 and a lower pretransfer sheet carrying member 12, and which passes the recording carrier 6 between the upper and lower pretransfer sheet carrying members 11 and 12 and introduces it between the image carrier 1 and the transfer roller 8 to carry out transfer, either the upper pretransfer sheet carrying member 11 or the lower pretransfer sheet carrying member 12 is made conductive and unselected one is made insulated. Therefore, even when an amount of moisture of the recording carrier 6 changes because of the environmemt where it is used, and when toner on the image carrier 1 is brought into direct contact with the transfer roller 8, the potential of the surface of the recording carrier is made stable by the upper and lower pretransfer sheet carrying members 11 and 12 immediately before the transfer, and the satisfactory transfer with the stable transfer efficiency can thereby be achieved in the simple structure.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus utilizing an electrophotographic process in a copying machine, a printer or the like, and more particularly to a transfer device using an electrostatic transfer process.

[0002]

2. Description of the Related Art A printing apparatus using a transfer roller in an electrophotographic process uses a transfer roller provided with a conductive member on the outer periphery of a shaft and a bias in order to transfer a toner image formed on an image carrier to a record carrier. It is provided with a bias control device for applying and a transfer device including a paper conveying member for guiding the record carrier to the transfer roller.

The transfer roller of such a transfer device is made of an elastic material such as rubber foam and is connected to a drive source.

According to such an apparatus, when the toner image formed on the image carrier is transferred, the record carrier passed by the paper conveying member is guided to the transfer roller, and the transfer roller is elastic. By elastically deforming, a contact area with the record carrier can be secured, and an electric field required for transfer can be formed between the toner image surface and the record carrier to perform transfer.

[0005]

However, the record carrier used in such a printing apparatus is classified as follows depending on the environment in which it is used. FIG. 7 shows the relationship between the relative humidity and the water content of the record carrier in the environment of 35 ° C. Generally, the relative humidity used in the image forming apparatus using the electrophotographic process is about 20% RH to 70% RH, so that it can be said that the amount of water content of the record carrier used is about 2% to 8%.
FIG. 8 shows the relationship between the water content of the record carrier and the resistance in the thickness direction. From the above, the resistance in the thickness direction of the record carrier between 2% and 8% of the water content of the record carrier is about 10 ⁶ to 10 ^10.
It can be said that it is between Ω. Therefore, depending on the environment in which the record carrier is used, ordinary plain paper and high-humidity paper, which has a large amount of moisture in the air and has a low electric resistance, are used.
Furthermore, it can be seen that there is a paper called a low-moisture paper, which has a low water content and a high electric resistance value.

Further, the paper carrying member is generally formed of a conductive member made of metal or the like. When the high-humidity paper is passed there and conveyed to the transfer roller, the electric charge given from the transfer roller does not flow to the image carrier via the toner image surface, but to the well-known toner image surface. There occurs a phenomenon that the particles flow through the surface of the record carrier having a resistance value lower than the resistance value to the pre-transfer sheet conveying member made of a conductive member.
Therefore, the electric field strength for transferring the toner on the image carrier to the recording carrier is lowered. Therefore, there is a problem that image dropout occurs.

In order to avoid such a problem, there is a means of forming the pre-transfer sheet conveying member with an insulating member.
It is proposed in JP-A-49-134334. But,
This method improves and prevents the escape of electric charge from the transfer roller to the pre-transfer paper conveying member in high-humidity paper.
In the case of low-moisture paper, frictional electrification occurs between the low-moisture paper and the low-moisture paper, and between the low-moisture paper and the paper conveying member made of an insulating member, and the paper is unevenly electrified. Therefore, there is a problem that the image is scattered. This is because the electric potential on the record carrier becomes unstable due to uneven charging of the paper before transfer,
This is because the electric field is unstable even if electric charges are applied by the transfer roller.

The present invention has been made in view of such circumstances, and in an image forming apparatus formed by a pre-transfer sheet conveying member and a transfer roller, all the record carriers in a use environment have a simple structure. Then, there is a need to provide a novel transfer device capable of obtaining a good image without image dropouts and scattering. Still another object is to provide a transfer device which is easy to manufacture and low in cost.

[0009]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention is directed to an image carrier, an elastic transfer roller which is in pressure contact with the image carrier, a pre-transfer upper sheet conveying member, and a pre-transfer lower sheet conveying member. An image forming apparatus for transferring a record carrier between the pre-transfer upper sheet conveying member and the pre-transfer lower sheet conveying member, and guiding and transferring the image carrier between the image carrier and the transfer roller. At least the paper passing portion of the front upper paper conveying member is formed of a conductive member, and at least the paper passing portion of the pre-lower paper conveying member is formed of an insulating member.

Further, an image carrier, an elastic transfer roller in pressure contact with the image carrier, and a pre-transfer paper conveying member forming a plurality of record carrier conveying paths are provided, and the record carrier is conveyed by the pre-transfer paper conveying member. In an image forming apparatus that passes through a path and guides and transfers between the image carrier and the transfer roller, a pre-transfer paper carrying member has a record carrier carrying path formed with an insulating member on at least the paper passing surface, and a pre-transfer carrying path. At least the paper passing surface of the paper carrying member has a recording carrier carrying path formed of a conductive member.

[0011]

【Example】

(Embodiment 1) Therefore, details of the present invention will be described below based on illustrated embodiments.

FIG. 1 is a schematic sectional view showing a main part of an electrophotographic printing apparatus using a transfer roller of the present invention.
Reference numeral 1 in the drawing is an image carrier, which is rotated in a direction of an arrow D in the drawing, that is, in a direction of moving the record carrier 6 to the left side, and an optical signal generator 2 for generating a light beam is provided on an upper portion thereof. There is.

A charging unit 3, a developing device 4, and an erase unit 5 are arranged around the image carrier 1. Below the image carrier 1, a transfer device 7 for transferring the toner image to the recording carrier 6 is arranged, which is a feature of the present invention.

FIG. 2 shows an embodiment of the transfer device of the present invention, in which reference numeral 11 is a pre-transfer top paper conveying member.
Reference numeral 2 is a pre-transfer lower sheet conveying member, and 13 is a pair of sheet conveying rollers. In the figure, reference numeral 8 is a transfer roller, and 14 is a bias controller for applying a bias to the transfer roller, which is connected to a transfer roller shaft 9. Also, the transfer roller 8 is a bearing 1.
5, the pressure spring 16 is further supported by the bearing 15
The transfer roller 8 is disposed so as to come into pressure contact with the image carrier 1 via the. Further, the transfer roller 8 is configured to be connected to a drive source via a drive gear (not shown).

Next, the pre-transfer upper sheet conveying member 11 and the pre-transfer lower sheet conveying member 12 will be described. The pre-transfer top paper conveying member 11 is configured by pressing a conductive member such as a metal plate. Regarding the material of the pre-transfer top paper conveying member 11, the same effect can be obtained even if the base is an insulating member such as resin and only the rib surface of the recording carrier 6 through which the paper is passed is made of a conductive member.

The above-mentioned pre-transfer top paper conveying member 11 is
The pair of paper transport rollers 13 are erected so as to be coincident with or substantially parallel to the nip tangent line A, and then the recording carrier 6 is disposed in the transfer nip so as to pass below the pre-transfer upper paper transport member 11.

The nip tangent line A of the pair of paper conveying rollers 13 is arranged so that the recording medium 6 intersects with the image carrier 1 slightly upstream of the transfer nip as in the present embodiment. Is common. As is well known, when the recording medium 6 directly enters the transfer nip, the transfer nip becomes unstable due to the outer shape fluctuation of the transfer roller 8 or the transfer nip is caused by the wobbling of the recording medium 6 itself. The reason is that the transfer of the record carrier 6 becomes unstable and a transfer failure occurs.

Next, the pre-transfer lower sheet conveying member 12 is formed by molding an insulating member such as resin. Regarding the material of the pre-transfer lower sheet conveying member 12, the same effect can be obtained even if the base is made of a conductive member such as metal and only the rib surface of the record carrier 6 through which the sheet is passed is made of an insulating member.

Such a pre-transfer lower sheet conveying member 12 is
The image carrier 1 and the transfer roller 8 are erected so as to be coincident with or substantially parallel to the tangent B of the transfer roller 8, and then the recording carrier 6 is arranged so as to be guided to the transfer nip.

Next, the elastic body forming the transfer roller 8 will be described. A foam member is formed around the transfer roller shaft 9. Further, as the method for producing the foamed member, besides the reaction injection molding method, a gas mixing method, a foaming agent decomposition method, a solvent vaporization method, a chemical reaction method, a sintering method, an elution method or the like can be used. With either manufacturing method, it is possible to manufacture a light-weight and low-cost transfer roller.

Furthermore, since the foam member is preferably a low hardness member that does not cause a hollowing phenomenon, polyurethane foam, polystyrene foam, polyethylene foam, which is a material that can be manufactured to have a relatively low hardness even when a conductive agent is dispersed, is used. Polyester foam, elastomer foam, silicone foam, synthetic rubber foam and the like can be used. The material of the transfer roller 8 may be a low hardness solid member such as rubber.

The foamed member is made conductive by dispersing conductive fine powder such as carbon black or metal.

In this embodiment, when a print command is input, the record carrier 6 is sent to a pair of paper carrying rollers 13 from a stacker (not shown). The record carrier 6 sent out is transferred by the paper carrying roller 13 to the pre-transfer top paper carrying member 1
1 or the pre-transfer lower sheet conveying member 12 and conveys it to the image carrier 1. On the image carrier 1, a toner image is formed in the order of charging by the charging unit 3, electrostatic latent image formation by the optical signal generator 2, and toner adhesion to the electrostatic latent image by the developing device 4. The toner image on the image carrier 1 and the recording carrier 6 sent from the stacker are transferred to the transfer roller 8.
And moves to the transfer nip portion formed by the image carrier 1.

Next, the bias controller 14 applies an electric field necessary for transfer onto the transfer roller shaft 9 to the toner image and the record carrier 6.
A bias is applied to form between. The applied bias is applied from the transfer roller shaft 9 to the elastic body 10 made of a conductive member. As a result, a constant transfer electric field is obtained between the recording carrier 6 and the toner layer, and good transfer can be performed.

FIG. 3 shows the relationship between the paper moisture content and the flexure amount when plain paper is used as the record carrier.
The amount of deflection is the amount of deflection of the tip of the record carrier due to its own weight when the record carrier projects 100 mm.

As a result, as can be seen from FIG. 3, when the water content of the record carrier exceeds about 7%, the amount of deflection sharply increases. This is the amount of deflection of the record carrier, which is considered to be caused by the softening of the fibers due to the entry of water into the record carrier.

Furthermore, FIG. 4 is a diagram showing the relationship between the amount of water in the record carrier and the image disturbance due to abnormal charging of the record carrier when the paper conveying member is made of a conductive member and when made of an insulating member. Is.

As a result, when the paper carrying member composed of the conductive member is used, the image disturbance does not occur, but when the paper carrying member composed of the insulating member is used, the water content of the record carrier is reduced. It can be seen that when the amount is about 3% or less, image distortion occurs. This is because in the process before transfer, non-uniform electrification occurs due to friction between the record carrier and the record carrier and between the record carrier and the paper conveying member composed of an insulating member, resulting in image disturbance. However, even if the record carrier is unevenly charged before transfer, the surface potential of the record carrier is stabilized and good transfer can be realized by contacting with the conductive member immediately before transfer.

FIG. 5 is a diagram showing the relationship between the water content of the record carrier and the good transfer start voltage when the paper conveying member is a conductive member and when it is an insulating member.

As a result, when the paper carrying member made of the insulating member is used, the paper carrying member made of the conductive member rises at a substantially constant good transfer start voltage regardless of the water content of the record carrier. It can be seen that, when is used, the good transfer start voltage also rises as the water content of the record carrier rises. This is particularly noticeable when the water content of the record carrier is 7% or more. This is because the electric charge given from the transfer roller flows to the paper conveying member through the surface of the record carrier having a low resistance value. Therefore, an electric field necessary for transfer is not formed between the recording carrier and the toner layer, and therefore transfer cannot be performed unless a high voltage is applied, as compared with low wet paper.

As described above, from the above data, for the low-moisture paper having a water content of 3% or less, the paper conveying member made of the conductive member is better, and for the high-wet paper, especially the record carrier having a water content of 7% or more, It can be said that good transfer can be achieved by using a paper conveying member made of an insulating member.

Further, as described above, the paper conveying member is constructed by taking into consideration the characteristics of the low-moisture paper and high-humidity paper by utilizing the relationship between the water content of the record carrier and the deflection amount, that is, the strain of the record carrier. This is the present embodiment. First, since the low-moisture paper has a strain on the record carrier 6 itself, the nip tangent line A of the paper transport roller 13 is used.
Try to proceed in the direction. Therefore, immediately after that, the pre-transfer sheet conveying member 11 made of a conductive member is formed, and the pre-transfer sheet conveying member 11 is brought into contact with the pre-transfer sheet conveying member 11 and is guided to the transfer nip. Can be transcribed.

Further, since the high-humidity paper has no strain on the record carrier 6 itself, the nip tangent line A of the paper carrying roller 13 is caused by its own weight.
Proceed while flexing downward. Therefore, immediately after that, the pre-transfer lower-paper conveying member 12 made of an insulating member is formed, and the pre-transfer lower-paper conveying member 12 is moved while being in contact with the pre-transfer lower paper conveying member 12, so that the charge from the transfer roller 8 does not escape efficiently. Good transfer can be realized.

(Embodiment 2) FIG. 6 is a view showing another embodiment. In the image forming apparatus, the record carrier transport path is
The pre-transfer upper sheet conveying member 11 constitutes a record carrier conveying path and the pre-transfer lower sheet conveying member 12 constitutes a record carrier conveying path. The pre-transfer top paper transport member 11 is the paper transport roller 1
3, the recording medium 6 is set up at a position substantially parallel to the nip tangent line A or closer to the transfer nip.
Is arranged so as to pass through the upper part of the sheet and be guided to the transfer nip.

As the pre-transfer top paper conveying member, other than the paper guide shape, a member such as a roller or a roller that can be used for conveying the record carrier 6 can be applied. Further, the pre-transfer top paper conveying member 11
Is a conductive member.

Next, regarding the lower sheet conveying member before transfer,
This is the same as in the first embodiment.

With such a structure, the recording carrier conveying paths for low-moisture paper and high-moisture paper are clearly separated, so that the recording carrier 6 does not fluctuate in the recording carrier conveying path due to fluttering or the like. Therefore, the electric potential of the record carrier 6 is stable and more reliable transfer is possible.

In the present embodiment, the recording carrier transport path is constituted by the pre-transfer upper paper transport member 11 and the pre-transfer lower paper transport member 12 separately. If the paper conveying member made of a member is formed, and the paper conveying member made of an insulating member is formed above the pre-transfer lower paper conveying member 12, and the two paths are completely separated, the potential of the record carrier 6 is further stabilized. I have also confirmed that. Also, in the case of forming a record carrier transport path for double-sided printing in addition to the above-described normal record carrier transport path for single-sided printing, the same effect can be obtained with the same configuration.

Further, in the present embodiment, the recording carrier 6 is separated by using a strainer of the recording carrier 6, and the recording carrier carrying path consisting of the pre-transfer upper paper carrying member 11 and the pre-transfer lower paper carrying member 12 is carried. Although the sheet is being conveyed to the path, the sheet conveying direction switching means using an electromagnetic clutch is used as the sheet conveying roller 1.
3 is installed immediately after and is forced to transfer the pre-transfer top paper conveying member 11
Record carrier transporting path and a pre-transfer lower sheet transporting member 1
It is obvious that the same effect can be obtained even if the recording medium is separated and conveyed to the record carrier conveying path.

In this case, since the recording carrier conveying direction can be forcibly switched, the pre-transfer upper paper conveying member 11 is composed of an insulating member, high-humidity paper is passed through, and the pre-transfer lower paper conveying member 12 is used. Is composed of a conductive member, and even if low-moisture paper is passed through,
Similar effects can be obtained.

[0041]

As described above, according to the present invention,
An image carrier, an elastic transfer roller in pressure contact with the image carrier, a pre-transfer upper paper conveying member, and a pre-transfer lower paper conveying member are provided, and the recording carrier is the pre-transfer upper paper conveying member and the pre-transfer lower paper conveying member. In an image forming apparatus which passes between the image carrier and the transfer roller between the image carrier and the transfer roller, at least the sheet passing portion of the pre-transfer upper sheet conveying member is formed of a conductive member, and Since at least the paper passing portion of the lower paper conveying member is formed of an insulating member, even the record carrier that changes depending on the usage environment, the low-moisture paper passes through the pre-transfer upper paper conveying member made of a conductive member, and the high wet paper moves from the insulating member. By passing the following pre-transfer lower sheet conveying member, the potential on the surface of the record carrier before transfer can be stabilized, and thus good transfer with stable transfer efficiency can be configured with a simple structure.

Further, in the image forming apparatus for transferring the recording carrier through the recording carrier conveying path formed of the pre-transfer paper conveying member and guiding between the image carrier and the transfer roller, the pre-transfer paper conveying member is used. Since it has a record carrier transport path having at least a paper passing surface formed of an insulating member and a record carrier transport path having at least a paper passing surface of the pre-transfer paper transport member formed of a conductive member, the record carrier can be clearly separated and transported. Since the electric potential on the surface of the record carrier will not become unstable due to the flapping of the record carrier,
The transfer efficiency is stable.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of an image forming apparatus of the present invention.

FIG. 2 is a sectional view of the transfer device according to the first embodiment of the present invention.

FIG. 3 is a diagram showing the relationship between the amount of water and the amount of deflection of the record carrier.

FIG. 4 is a diagram showing the relationship between the amount of water on the record carrier and the image disturbance due to the difference in the material of the paper conveying member.

FIG. 5 is a diagram showing the relationship between the water content of the record carrier and the transfer start voltage depending on the material of the paper transport member.

FIG. 6 is a sectional view of a transfer device according to a second embodiment of the present invention.

FIG. 7 is a relationship diagram of relative humidity and water content of a record carrier in an environment of 35 ° C.

FIG. 8 is a relationship diagram between the water content of the record carrier and the resistance value in the thickness direction.

[Explanation of symbols]

 1 Image Carrier 2 Optical Signal Generator 3 Charging Unit 4 Developing Device 5 Erase Unit 6 Record Carrier 7 Transfer Device 8 Transfer Roller 9 Transfer Roller Shaft 10 Elastic Body 11 Pre-Transfer Upper Paper Conveying Member 12 Paper Before Transfer Lower Paper Conveying Member 13 Paper Conveyor roller 14 Bias control device 15 Bearing 16 Pressure spring 17 Drive gear

Claims (2)

[Claims] 1. An image carrier, an elastic transfer roller that is in pressure contact with the image carrier, a pre-transfer upper paper conveying member, and a pre-transfer lower paper conveying member, and a recording carrier for the pre-transfer upper paper conveying member and the transfer medium. In an image forming apparatus that passes between front lower paper conveying members and guides and transfers between the image carrier and the transfer roller,
An image forming apparatus, wherein at least a sheet passing portion of the pre-transfer upper sheet conveying member is formed of a conductive member, and at least a sheet passing portion of the pre-transfer lower sheet conveying member is formed of an insulating member. 2. An image carrier, an elastic transfer roller that is in pressure contact with the image carrier, and a pre-transfer paper transport member that forms a plurality of record carrier transport paths, and the record carrier transports the pre-transfer paper transport member. In an image forming apparatus that passes through a path and guides and transfers between the image carrier and the transfer roller, a pre-transfer paper carrying member has a record carrier carrying path formed with an insulating member on at least the paper passing surface, and a pre-transfer carrying path. An image forming apparatus, comprising: a paper carrying member, and a record carrier carrying path in which at least a paper passing surface of the paper carrying member is formed of a conductive member.