JPH0830110A - Image forming device - Google Patents

Abstract

PURPOSE:To provide an image forming device capable of obtaining a high transfer efficiency, and also, capable of improving black solid density shortage due to a middle missing in a character and an edge effect, and defective transfer caused by an environmental fluctuation. CONSTITUTION:A transfer member 81 for transferring a toner layer developed on an electrostatic latent image carrier to a printing medium 11 passing through a nip part between the electrostatic latent image carrier and the transfer member 81 is constituted of an elastic roller 13, a seamless thin film member 14 and a supporting member 15. The seamless thin film member 14 is supported and pressed against the outer circumferential surface of the elastic roller 13 by the supporting member 15. The circumferential length of the member 14 is made longer than the circumferential length of the elastic roller 13, and a supporting member is not arranged outside the member 14 on the side coming contact with the printing medium 11, then, the surplus length part of the member 14 is attracted toward the contact part with the printing medium 11, then, a space part 16 is formed between the elastic roller 13 and the seamless thin film member 14.

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, and more particularly to a printer, a facsimile or the like using an electrophotographic process for transferring a toner layer developed on an electrostatic latent image carrier onto a print medium such as paper. The present invention relates to an image forming apparatus.

[0002]

2. Description of the Related Art Conventionally, as an image forming apparatus using an electrophotographic process, a rotary roller-shaped or endless belt-shaped transfer member that comes in contact with an electrostatic latent image bearing member (photosensitive member) has been provided, and the nip portion of both members has A so-called contact transfer, in which the toner layer developed on the electrostatic latent image carrier is attracted to the transfer member side and transferred to the print medium while passing the print medium and applying a voltage having a polarity opposite to that of the toner to the transfer member. System image forming apparatuses are known (JP-A-4-278977, JP-A-2-2).
No. 21040).

As the above-mentioned rotary roller-shaped transfer member, there is a foamed roller made of urethane or the like in which metal oxide or carbon powder is dispersed to have semiconductivity, and as the above-mentioned endless belt-shaped transfer member. In some cases, a rubber belt is coated with polyester, or a polyamide endless belt is supported by a plurality of rollers.

[0004]

However, in the above-mentioned contact transfer type image forming apparatus, in order to obtain a good transfer effect, a sufficient nip between the electrostatic latent image carrier, the print medium and the transfer member is obtained. The width was required, and the pressure contact force between them had to be increased. Therefore, in the above conventional device, the surface of the electrostatic latent image carrier or the transfer member is easily damaged,
In addition, there is a defect that the torque of the device increases.

Further, in the above-mentioned conventional apparatus, when the pressure contact force is large, the toner once transferred to the print medium returns to the electrostatic latent image carrier, and the characters and the solid black image are distorted or hollow. There is also a problem to do.

Further, in the above conventional apparatus, when a print medium smaller than the developed toner image is used, for example, when A4 paper is fed for A3 size image data, the presence of the print medium is present. There is a problem that the toner on the electrostatic latent image carrier is transferred to the transfer member in the non-printing area, which causes the back stain of the next print medium. Further, in normal printing as well, there is a problem that fog toner or the like migrates to the transfer member between the pages where the electrostatic latent image carrier and the transfer member are in direct contact with each other, and the fog toner is accumulated to stain the back of the print medium.

[0007] The present invention has been made in view of the above points,
Even if the nip between the transfer member and the electrostatic latent image carrier is non-uniform due to respective mounting errors, twists, etc., the error can be absorbed by a simple method and a high transfer efficiency can be obtained. The purpose is to provide.

Another object of the present invention is to provide an image forming apparatus capable of improving defective printing caused by hollow characters, lack of solid black density due to edge effect, and environmental change.

Another object of the present invention is to provide an image forming apparatus capable of preventing the transfer member and the print medium from being contaminated and extending the life of the transfer member.

[0010]

In order to achieve the above object, the present invention allows a print medium to pass through a nip portion between an electrostatic latent image carrier and a transfer member which face each other, and a bias voltage is applied to the transfer member. In an image forming apparatus for transferring a toner layer developed on an electrostatic latent image carrier to a print medium by applying, an elastic roller having a circumference longer than that of a rotating elastic roller and the elastic roller A tubular seamless thin film member provided to have inside, and by pressing and supporting a part of the seamless thin film member from the outer side to the outer peripheral surface of the elastic roller, a space is formed between the seamless thin film member and the elastic roller. A transfer member is formed by a support member that is formed to bring the outer surface of the seamless thin film member into contact with the electrostatic latent image carrier and the print medium.

Further, according to the present invention, as the supporting member, a member having a cleaning property for the seamless thin film member is used.

[0012]

In the present invention, since the elastic roller supports the seamless thin film member by the supporting member so as to contact the electrostatic latent image carrier and the print medium through the space and the seamless thin film member, The contact pressure between the electrostatic latent image carrier and the print medium can be made weaker than in the case where a conventional rotating roller or an endless belt is used as the transfer member.

Further, since a space is formed between the seamless thin film member and the elastic roller, the electrostatic latent image carrier and the elastic roller are not uniform due to warping, twisting and the like. However, the error can be absorbed by the bulge portion of the seamless thin film member including the space portion. Further, the seamless thin film member has a feature that resistance unevenness is small, and can contact the electrostatic latent image carrier and the print medium with a sufficient nip width.

Further, since the supporting member is made of a member having a cleaning property with respect to the seamless thin film member, it is possible to clean the seamless thin film member which is soiled with fog toner or jam.

Further, in the present invention, the surface roughness is set so that the dynamic friction coefficient between the elastic roller and the seamless thin film member is larger than the dynamic friction coefficient between the seamless thin film member and the support member. The roller and the seamless thin film member can rotate without slipping.

[0016]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 shows a block diagram of an embodiment of the device of the present invention.
In this embodiment, the toner hopper 1, the supply member 4, the toner carrier 5, the thin layer forming member 6, the drum-shaped electrostatic latent image carrier 7,
The transfer member 8 is arranged to face the electrostatic latent image carrier 7, the charging member 9 and the cleaner unit 10 are arranged to face the electrostatic latent image carrier 7. There is a feature in the configuration.

The toner hopper 1 is disposed so as to face the electrostatic latent image carrier 7, stores the toner 2 and stirs the toner 2 by the stirring member 3. Supply member 4 and toner carrier 5
Are rollers that rotate counterclockwise, respectively. The toner carrier 5 is composed of, for example, a metal roller made of stainless steel, aluminum or the like, and an elastic portion such as silicone, nitrile / butadiene copolymer, urethane rubber or the like provided on the outer periphery of the metal roller, which is provided with conductivity.

In consideration of the contact pressure between the thin layer forming member 6 and the electrostatic latent image carrier 7, the elastic portion of the toner carrier 5 has a rubber hardness of 30 ° to 40 ° in JIS A hardness tester. It is preferable that the resistance value between the surface of the metal roller and the shaft is 10 ⁵ Ω or more in consideration of leakage to the electrostatic latent image carrier 7 due to the low resistance of the toner carrier 5 and fogging due to high resistance.
It is preferably 10 ⁶ Ω.

Further, the negatively chargeable polyester type toner used in this embodiment has a particle size of about 10 μm, and the toner 2
In order to uniformly charge the toner carrier 5, the ten-point average surface roughness Rz of the toner carrier 5 is preferably 10 μm.

The thin layer forming member 6 is a member for forming the toner 2 supplied to the toner carrier 5 into a uniform thin layer, and is made of stainless steel,
The spring member is made of a thin metal plate of phosphor bronze or the like, or is formed by applying silicone rubber to the contact portion with the toner carrier 5. The electrostatic latent image carrier 7 is a drum-shaped photosensitive member, which is rotationally driven in the clockwise direction in the figure, is uniformly charged by a charging member 9, and is exposed to image data by light from a laser or the like to form an electrostatic latent image. To form.

The transfer member 8 is a member forming the essential part of this embodiment, and as will be described later, an elastic roller and a cylindrical seamless thin film member provided so as to have the elastic roller therein, and supports the same. It is composed of a support member. Further, the transfer member 8 has a structure in which a voltage is applied to the shaft of the elastic roller from a power source (not shown). At the time of non-transfer from the end of transfer to the passage of the next print medium, cleaning of toner on the transfer member 8 and transfer of toner on the electrostatic latent image carrier 7 to the transfer member 8 are prevented during transfer. And the opposite polarity (that is, the same polarity as the toner).

In this embodiment, since a non-chargeable non-magnetic toner is used, a positive voltage is supplied to the transfer member 8 during transfer and a negative voltage is used as a bias voltage during non-transfer. The charging member 9 uniformly charges the electrostatic latent image carrier 7 with electric charges. The cleaner unit 10 removes residual adhesion of toner on the electrostatic latent image carrier 7.

Next, the operation of this embodiment will be described.
Electric charges are uniformly applied to the surface of the electrostatic latent image carrier 7 rotating clockwise by the charging member 9. When the charged portion of the electrostatic latent image carrier 7 moves to a position between the charging member 9 and the toner carrier 5, light modulated by image data from a light source (not shown) enters. It is exposed to light and forms an electrostatic latent image.

On the other hand, the toner 2 in the toner hopper 1 is supplied to the toner carrier 5 which rotates counterclockwise by the toner supply member 4 which is stirred by the stirring member 3 and is driven to rotate counterclockwise. The toner 2 supplied to the toner carrier 5 is triboelectrically charged and regulated by the thin layer forming member 6 to form a more uniform thin layer. In this way,
The charged toner formed as a thin layer on the toner carrier 5 is carried to the portion where the toner carrier 5 and the electrostatic latent image carrier 7 face each other as the toner carrier 5 rotates.

When the portion of the electrostatic latent image carrier 7 on which the electrostatic latent image is formed reaches the position facing the toner carrier 5, the surface potential of the electrostatic latent image carrier 7 and the toner carrier. By the electric field based on the potential difference from the bias voltage applied to the electrostatic latent image carrier 7
It moves to the electrostatic latent image on the surface to form a toner image.

The toner image developed as described above on the electrostatic latent image carrier 7 is carried to a position facing the transfer member 8 as the electrostatic latent image carrier 7 rotates clockwise. At this time,
A print medium 11 such as paper is conveyed and passes through a nip portion between the electrostatic latent image carrier 7 and the transfer member 8. The transfer member 8 applies a bias voltage having a polarity opposite to that of the toner from the back side of the print medium 11 to transfer and transfer the developing toner layer on the electrostatic latent image carrier 7 side to the front side of the print medium 11.

The transferred portion of the electrostatic latent image carrier 7 moves to a position facing the cleaner unit 10 in accordance with the clockwise rotation of the electrostatic latent image carrier 7 and is cleaned there. Thereafter, the same operation as above is repeated.

Next, each embodiment of the transfer member 8 forming the essential part of the present invention will be described. FIG. 2 shows a cross-sectional view of the first embodiment of the transfer member 8. In the figure, a transfer member 81 has a cylindrical elastic roller 13, a peripheral length longer than the peripheral length of the elastic roller 13, and a seamless thin film member 14 mounted on the elastic roller 13 and the seamless thin film member 14 elastically. By pressing the outer peripheral surface of the roller 13, the seamless thin film member 14
And a pair of rod-shaped support members 15 provided to face each other.

The elastic roller 13 comprises a metal shaft 13a made of stainless steel, aluminum or the like, and a foam material such as silicone, urethane, nitrile, ethylene / propylene copolymer, or a rubber material provided with conductivity on the outer periphery of the metal shaft 13a. Has been done. A voltage is applied to the metal shaft 13a from a power source (not shown).

The seamless thin film member 14 is a sheet-shaped member obtained by adding carbon or metal oxide to fluororesin such as PFA or polyamide, or a seamless electroformed sleeve of nickel or stainless. Here, the print medium 11
The resistance value of the transfer member 8 (81) is, for example, 10 ^{8 in} order to cope with short-circuiting and damage to the electrostatic latent image carrier 7 due to the sheet width, environmental fluctuations, pinholes, etc. Ω
It is set to -10 ⁹ Ω.

The support member 15 has the same length in the width direction as the seamless thin film member 14 and has a cleaning property, and has elasticity such as fine polyester fiber or felt made of a binder of polyester and polyurethane. Composed of pads. Further, when the dynamic friction coefficient between the elastic roller 13 and the seamless thin film member 14 is μ ₁ and the dynamic friction coefficient between the seamless thin film member 14 and the support member 15 is μ ₂ , the elastic roller 13 is such that μ ₁ > μ _2. The surface roughness of the seamless thin film member 14 and the support member 15 is adjusted. This is to rotate the elastic roller 13 and the seamless thin film member 14 without causing slip, as described later.

According to this embodiment, the seamless thin film member 14 is moved to the elastic roller 13 by the pair of supporting members 15 facing each other.
Is pressed and supported on the outer peripheral surface of the. At this time, the seamless thin film member 14 is formed on the outer peripheral portion of the elastic roller 13 opposite to the print medium 11.
Hold them in close contact.

As a result, the seamless thin film member 14 has a peripheral length longer than the peripheral length of the elastic roller 13, and there is no support member outside the seamless thin film member 14 on the side in contact with the print medium 11. Furthermore, the seamless thin film member 14
Has such a rigidity that it does not come into contact with the outer peripheral portion of the elastic roller 13 on the print medium 11 side due to its own weight. Therefore, as shown in FIG. 2, the extra long portion of the seamless thin film member 14 is provided at the contact portion with the unsupported print medium 11. And a space 16 is formed between the elastic roller 13 and the seamless thin film member 14.

Next, the operation of this embodiment will be described.
The elastic roller 13 is rotated counterclockwise in the figure by a drive mechanism (not shown) substantially in synchronization with the rotation of the electrostatic latent image carrier 7. As a result, the seamless thin film member 14 rotates following the rotation of the elastic roller 13, and the seamless thin film member 14 having the space 16 is applied to the electrostatic latent image carrier 7 and the print medium 11 with an appropriate nip width. On the other hand, compared with the case where the conventional rotating roller or the endless belt is used as the transfer member, the contact is made with a weak contact pressure.

As a result, the surface of the electrostatic latent image carrier 7 will not be damaged and the torque of the apparatus will not increase. Further, the voltage applied to the metal shaft 13a of the elastic roller 13 is evenly applied as a transfer bias voltage on the print medium 11 via the elastic roller 13 and the seamless thin film member 14, and as a result, the electrostatic latent image carrier is formed. As the toner image transferred from 7 to the print medium 11, it is possible to obtain an image without missing characters and distortion of characters, and the electrostatic latent image carrier 7 is not damaged.

When the foaming roller is directly used as the transfer means, it is technically difficult to manufacture the foaming roller by uniformly adding the conductive material such as carbon powder to the foaming material such as urethane. Resistance unevenness in the width direction of A3
When printing on narrow paper, where there is a portion where the electrostatic latent image carrier 7 and the transfer member (foaming roller) are in direct contact, such as when performing postcard printing with a size-compatible machine, and environments such as low temperature and low humidity, high temperature and high humidity When it fluctuates, transfer failure due to insufficient transfer current or insufficient transfer bias to the print medium is observed, but since the seamless thin film member 14 used in this embodiment does not use carbon particles, resistance unevenness is small, and therefore the above problems can be improved. .

Further, in this embodiment, since the supporting member 15 has a cleaning property, it is possible to clean the surface of the seamless thin film member 14 contaminated with fog toner, jam, etc., and thus, the same as the toner when the paper is not passed. Could not be prevented by the polarity bias (cleaning bias),
It is possible to prevent the back surface of the print medium from being smeared due to a jam or print running. Furthermore, since the surface of the seamless thin film member 14 can be cleaned, the life of the seamless thin film member 14 can be extended.

FIG. 3 is a sectional view of a second embodiment of the transfer member 8 of the essential part of the present invention. 2, those parts which are the same as those corresponding parts in FIG. 2 are designated by the same reference numerals, and a description thereof will be omitted. Second shown in FIG.
The transfer member 82 of the embodiment is characterized in that a pair of roller-shaped support members 17 are used as the support members.

The roller-shaped support member 17 is an elastic roller 13.
The seamless thin film member 14 is pressed and supported by the outer peripheral surface of the elastic roller 13 at the same height as the metal shaft 13a of the above, and is rotated in the clockwise direction in the figure in synchronization with the rotation of the elastic roller 13. ing.

The roller-like support member 17 is made of foam such as urethane or ethylene / propylene copolymer and has cleaning properties. The transfer member 82 of this embodiment is also similar to the transfer member 81 shown in FIG.
The print medium 11 and the electrostatic latent image carrier 7 having the space 16
Since the contact can be made with a weak contact pressure, the same effect as that of the first embodiment can be obtained. Further, in this embodiment, since the support member 17 rotates together with the elastic roller 14, the cleaning property is less deteriorated as compared with the first embodiment.

Next, a third embodiment of the essential part of the present invention will be described. FIG. 4 is a sectional view of a third embodiment of the transfer member 8 which is the main part of the present invention. 2, those parts which are the same as those corresponding parts in FIG. 2 are designated by the same reference numerals, and a description thereof will be omitted.

The transfer member 83 of the third embodiment shown in FIG.
As a supporting member, a characteristic is that a support member 18 having a semicircular cross section concentric with the elastic roller 13 is used, in which the seamless thin film member 14 is weakly pressed against the elastic roller 13 from below to above.

The support member 18 is composed of a polyester fiber having a slidability and has a cleaning property. Similarly to the transfer members 81 and 82 shown in FIGS. 2 and 3, the transfer member 83 of this embodiment has the seamless thin film member 14 having the space 16 and is weak against the print medium 11 and the electrostatic latent image carrier 7. Since they can be contacted with each other with contact pressure, the same effect as in the first embodiment can be obtained.

[0044]

As described above, according to the present invention,
The contact pressure between the transfer member, the electrostatic latent image carrier and the print medium is
By using a seamless thin film member, the contact pressure was made weaker than in the case where a conventional rotating roller or an endless belt was used as a transfer member, so that the surface of the electrostatic latent image bearing member was damaged or the torque of the device was reduced. It can be prevented from becoming large.

Further, according to the present invention, even if the electrostatic latent image carrier and the elastic roller are non-uniform due to warp, twist, etc., the error is caused by the bulge portion of the seamless thin film member including the space portion. Since the transfer bias voltage can be uniformly applied to the print medium because it can be absorbed, the transfer efficiency can be obtained by a simple method, and the seamless thin film member is sufficient for the electrostatic latent image carrier and the print medium. Since the contact is made with a wide nip width, it is possible to improve the deterioration of the image quality such as missing characters, image distortion, and uneven density.

Further, according to the present invention, since the seamless thin film member has the characteristic that the resistance unevenness is small, it is possible to improve the transfer failure due to the shortage of the transfer current or the shortage of the transfer bias caused by the environmental change.

Further, according to the present invention, the support member is
Since the seamless thin film member is made of a material that has cleaning properties to clean the seamless thin film member that is contaminated with fog toner or jam, it is prevented by the bias (cleaning bias) of the same polarity as the toner when the paper is not fed. It is possible to prevent jamming and back stain of the print medium due to print running, which could not be achieved.

Furthermore, since the surface of the seamless thin film member can be cleaned, the life of the seamless thin film member can be extended.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention.

FIG. 2 is a sectional view of the first embodiment of the essential part of the present invention.

FIG. 3 is a sectional view of a second embodiment of the main part of the present invention.

FIG. 4 is a sectional view of a third embodiment of the main part of the present invention.

[Explanation of symbols]

 1 toner hopper 2 toner 4 supply member 5 toner carrier 6 thin layer forming member 7 electrostatic latent image carrier 8 transfer member 9 charging member 11 printing medium 13 elastic roller 13a shaft 14 seamless thin film member 15, 17, 18 support member 16 space Part 81 Transfer Member of First Example 82 Transfer Member of Second Example 83 Transfer Member of Third Example

Claims (3)

[Claims] 1. A printing medium is passed through a nip portion between an electrostatic latent image carrier and a transfer member, which are opposed to each other, and a bias voltage is applied to the transfer member to develop on the electrostatic latent image carrier. In an image forming apparatus for transferring a toner layer onto the print medium, a cylindrical roller having a rotating elastic roller and a peripheral length longer than the peripheral length of the elastic roller and having the elastic roller inside. And a part of the seamless thin film member is pressed and supported from the outer side to the outer peripheral surface of the elastic roller to form a space between the seamless thin film member and the elastic roller. An image forming apparatus, wherein the transfer member is constituted by a support member that makes the outer surface of the member contact the electrostatic latent image carrier and the print medium. 2. The image forming apparatus according to claim 1, wherein the supporting member is made of a member having a cleaning property with respect to the seamless thin film member. 3. The surface roughness of each of the elastic rollers is set so that the dynamic friction coefficient between the elastic roller and the seamless thin film member is larger than the dynamic friction coefficient between the seamless thin film member and the support member. The image forming apparatus according to claim 1 or 2.