JPH05134568A - Image forming device - Google Patents

Abstract

(57) [Summary] [Purpose] Output image (transfer image) in a transfer type image forming apparatus adopting non-magnetic one-component non-contact AC applied development.
To improve the image quality by reducing the negative phenomenon and hollowing out phenomenon. [Structure] Means 2 for forming an electrical latent image on the surface of an image carrier 1
L and a developer carrier 4b that carries a non-magnetic one-component developer T and faces the surface of the image carrier 1 in a non-contact manner, and develops a latent image on the surface of the image carrier 1 under an alternating electric field. Means 4 for performing Tb
And a transfer bias having a polarity opposite to the charging polarity of the developer T is applied, and the transfer material P is brought into pressure contact with the surface of the image carrier 1 and the image carrier 1
An image forming apparatus comprising: a contact-type transfer unit 5 that transfers the developer image Tb on the surface to the transfer material P.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention uses an appropriate image forming process such as an electrophotographic process or an electrostatic recording process to electrically transfer target image information to the surface of an image carrier such as an electrophotographic photosensitive member or an electrostatic recording dielectric. The present invention relates to an image forming apparatus such as a copying machine or a printer, which forms a latent image, develops the latent image with a developer (charged particles, toner), transfers the developer image to a transfer material, and outputs an image formed product. .. More specifically, the present invention relates to an image forming apparatus that employs a developing unit that develops a latent image using a dry non-magnetic one-component developer.

[0002]

2. Description of the Related Art A thin layer of a dry non-magnetic one-component developer is formed and carried on a developer carrier to face the surface of the image carrier in a non-contact manner, and the developer on the developer carrier is exposed under an alternating electric field. A developing means (non-magnetic one-component non-contact AC application development) for developing the latent image by selectively transferring it to the surface of the image bearing member corresponding to the electric latent image on the surface of the image bearing member is known.

This developing means is smaller in size than the developing means using a two-component developer composed of toner and carrier.
The cost can be reduced, and the image quality can be improved.

[0004]

However, there are the following problems as problems. That is, in consideration of tribo-down of a developer (hereinafter referred to as toner) due to moisture absorption in a high humidity environment, the toner layer on the developer carrier is further thinned and carried, and then the image carrier (hereinafter referred to as a photoconductor). When the above solid image latent image was developed, the following so-called "negative phenomenon" and "middle void phenomenon" occurred.

(1) Negative phenomenon When the difference between the photoconductor potential (Vs) and the developing DC bias (V _DC ) becomes larger than a certain value, the developed image density decreases and the solid image density becomes lower than the halftone density. Lower phenomenon occurs.

(2) Pixel void phenomenon In a large area solid image, the edge (peripheral) portion of the developed image is extremely density-enhanced as compared with the central portion of the image.

FIG. 3 is an explanatory model diagram of this phenomenon.
In FIG. 6A, Tb is a toner development image of a solid image latent image on the surface of the photosensitive member 1, and the toner amount in the central portion of the image is small with respect to the edge portion of the image,
The above-mentioned negative phenomenon or hollow phenomenon occurs, and this developed image Tb
Is transferred to the transfer material P only by the action of an electric field such as corona transfer, the transfer becomes inefficient as shown in FIG. 7C, and in this transfer image Td, the negative phenomenon and the hollow phenomenon are further promoted and the image quality is deteriorated. It will be what you did.

According to the present invention, in the transfer type image forming apparatus adopting the non-magnetic one-component non-contact AC applied development as described above, the negative phenomenon and the hollow defect phenomenon of the output image (transferred image) are reduced and the image quality is improved. The purpose is to improve.

[0009]

The present invention is an image forming apparatus having the following configuration.

(1) A means for forming an electrical latent image on the surface of the image bearing member and a developer bearing member that bears a non-magnetic one-component developer and faces the surface of the image bearing member in a non-contact manner. Means for developing a latent image on the surface of the image carrier and a transfer bias having a polarity opposite to the charging polarity of the developer are applied, and the transfer material is pressed against the surface of the image carrier to transfer the developer image on the surface of the image carrier. An image forming apparatus comprising: a contact-type transfer unit that transfers the image onto the image forming apparatus.

(2) The developing means has a rotating developer carrying member and an end portion biased so as to come into contact with the developer carrying member, and the non-magnetic one-component developing is carried out on the developer carrying member. A developer regulating member that forms a thin layer of the developer, and rotates while being in contact with the developer carrying member at a position upstream of the contact portion of the developer regulating member on the developer carrying member in the rotation direction of the developer carrying member. The image forming apparatus according to (1), further including an elastic roller that is freely supported.

(3) The image forming apparatus according to (1), wherein the contact type transfer means is a rotary transfer roller.

(4) The image forming apparatus according to (1), wherein the contact type transfer means is a rotary transfer drum having a dielectric sheet stretched around the outer peripheral portion.

(5) The image forming apparatus according to (1), wherein the contact type transfer means is a rotary transfer belt formed by suspending an endless transfer material carrying member on a plurality of support rollers.

[0015]

The transfer of the developer image Tb ((a) in FIG. 3) formed and carried on the image carrier 1 by non-magnetic one-component non-contact AC application development to the transfer material P is defined as the charge polarity of the developer. By applying a transfer bias of reverse polarity, the transfer material is pressed against the surface of the image carrier, and a contact-type transfer means for transferring the developer image on the surface of the image carrier to the transfer material is used. In addition to the transfer of the developer image to the side by the same electric field action as the corona transfer means, the transfer is performed by the physical adhesion of the transfer material to the surface of the image carrier by the mechanical pressing pressure contact force, as shown in FIG. , The transfer efficiency is improved as compared with the case of transfer by only the action of an electric field (corona transfer), and as a result, the negative phenomenon of the developer image Tb on the image carrier, which occurs in the non-magnetic one-component non-contact AC application development, The hollow phenomenon is promoted on the transfer material P. Can be reduced, also transferred image density itself be able to improve (in FIG. 3 (c) →
(B)), the image quality of the output image can be always made good and stable.

Further, the developing means has a rotating developer carrying member and an end portion biased so as to come into contact with the developer carrying member, and the non-magnetic one-component developer is provided on the developer carrying member. And a developer regulating member that forms a thin layer, and is rotatable while contacting the developer bearing member at a position on the upstream side in the rotation direction of the developer bearing member with respect to the contact portion of the developer regulating member on the developer bearing member. By having the elastic roller supported on the developer carrier, it becomes possible to form and carry a thin layer of non-magnetic one-component developer which is uniform in the longitudinal direction on the developer carrier, and to prevent abnormal charge up of the developer. It has become possible to prevent even this, and a more stable and good image can be output.

[0017]

【Example】

Example 1 (FIGS. 1 to 4) FIG. 1 is a schematic configuration diagram of an example of an image forming apparatus according to the present invention. The image forming apparatus of this example is a transfer type electrophotographic apparatus.

Reference numeral 1 denotes an electrophotographic photosensitive drum as an image bearing member, which is rotationally driven in a clockwise direction indicated by an arrow a at a predetermined peripheral speed (process speed).

In the case of the apparatus of this embodiment, the peripheral surface of the photosensitive drum 1 is uniformly negatively charged by the charging device 2 in the drum rotating process, and then the image exposure 3 of the target image information is received by the image exposure means (not shown). An electrostatic latent image corresponding to the exposure pattern is formed on the drum peripheral surface. The latent image is non-magnetic one-component non-contact A
Regular development Tb is performed by the C application type developing device 4.

The developer image (toner image) Tb is supplied to a pressure contact nip portion (transfer site) 6 between the photosensitive drum 1 and a transfer roller 5 as a contact type transfer means which is pressed against the photosensitive drum 1. Transfer Tc is performed on the transfer material P fed at a predetermined timing from the paper mechanism section.

The transfer material P that has passed through the transfer portion 6 is separated from the surface of the photosensitive drum 1 and is introduced into an image fixing device (not shown) to undergo image fixing, and is output as an image-formed product.

After the image is transferred, the surface of the photosensitive drum 1 is cleaned by a cleaning device 7 to remove adhering residues such as transfer residual developer and the like, and is repeatedly used for image formation.

FIG. 2 is an enlarged view of the main part of the developing device 4. The developing device 4 includes a developer supply container 4a, a non-magnetic one-component developer (toner) T contained in the container, and a developer carrying member. The body includes a developing sleeve 4b made of a non-magnetic material such as aluminum, an elastic blade 4c made of rubber or metal as a developer regulating member, an elastic roller 4d, and the like.

The developer supply container 4a has an opening extending in the longitudinal direction of the developing device (a direction perpendicular to the plane of the drawing), and the developing sleeve 4b is inserted into the opening with its right half peripheral surface projecting into the container 4a. The left approximately half-circumferential surface is exposed to the outside of the container, is rotatably supported by a bearing, and is laterally installed, and is rotationally driven in the direction of arrow b. The developer carrying member 4b is not limited to the sleeve (cylindrical body), and may be in the form of an endless belt that is rotationally driven. Alternatively, a conductive rubber roller may be used. The developing sleeve 4b
The exposed surface outside the container is facing or in contact with the surface of the photosensitive drum 1 with a small gap α.

The elastic blade 4c is provided with the tip end thereof in a slight pressure contact with the outer surface of the developing sleeve 4b in the direction of rotation of the sleeve toward the counter.

The elastic roller 4d is the elastic blade 4c.
Is softly contacted with the outer surface of the sleeve and rotatably supported on the upstream side of the contact point with the developing sleeve 4b in the sleeve rotation direction.

As the developing sleeve 4b rotates, the toner T passes through the contact nip portion between the developing sleeve 4b and the elastic blade 4c while being regulated, and a thin layer Ta of the toner T is formed on the developing sleeve 4b. Moreover, the friction there provides the toner with sufficient tribo.

The thin toner layer Ta formed on the developing sleeve 4b is carried and conveyed to the portion (developing portion) facing the photosensitive drum 1 by the rotation of the sleeve 4b, and is conveyed between the developing sleeve 4b and the photosensitive drum 1. By the AC developing bias applied from the power source 8, the latent image pattern is selectively transferred to the surface of the photosensitive drum 1 corresponding to the latent image pattern and is used for developing Tb of the latent image.

The toner not used for the development is continuously carried on the developing sleeve 4b, returned to the container 4a, peeled off from the surface of the developing sleeve 4b by the elastic roller 4d, and new to the surface of the developing sleeve 4b. Toner is supplied.

With the above-described structure of the developing device, it is possible to form the toner thin layer Ta which is uniform in the longitudinal direction on the developing sleeve 4b, and the abnormal charge-up can be prevented, so that a more stable and good image can be obtained. In addition to being able to obtain the same, it is possible to reduce the size and cost of the device as compared with a developing device using a two-component developer composed of toner and carrier.

The transfer roller 5 is pressed against the photosensitive drum 1 with a predetermined pressing force, and rotates in the forward direction of the rotation of the photosensitive drum 1 and at substantially the same peripheral speed as the drum 1. The transfer material P is supplied to the transfer portion 6 which is a pressure nip portion between the photosensitive drum 1 and the transfer roller 5, and a transfer bias having a polarity opposite to that of the toner T is applied to the transfer roller 5 from the power source 9. As a result, the toner image Tb on the surface of the photosensitive drum 1 is sequentially transferred Tc to the surface of the transfer material P by the action of the electric field due to the applied transfer bias and the pressure contact force of the transfer roller 5.

As described above, in the large area solid image Tb on the surface of the photosensitive drum 1 developed by the developing device 4, the edge portion is emphasized and the density of the central portion is reduced as shown in FIG. There is a negative phenomenon / hollow phenomenon. This phenomenon occurs remarkably in the non-magnetic one-component non-contact AC application phenomenon method, and particularly easily occurs when the toner is charged up.

When such a toner image Tb is transferred onto the transfer material P only by corona transfer (electric field action), the upper layer toner of the edge portion of the toner image Tb has a low charge amount, that is, the mirror image power. However, since the toner in the center of the toner image Tb has a high charge amount and has a strong adhesion to the surface of the photosensitive drum 1, as shown in (c) of FIG.
In the transferred toner image Td on the transfer material P, the essence portion is further emphasized as compared with the toner image Tb on the photoconductor drum 1, and the toner amount in the central portion is small so that the image density is low. That is, the image quality becomes poor due to the promotion of the negative phenomenon and the void phenomenon.

This phenomenon naturally occurs even under a transfer bias that maximizes the transfer efficiency, so that it is difficult to prevent it in the transfer only by the action of the electric field such as corona transfer.

However, by transferring the above-mentioned developing toner image Tb onto the transfer material P by the contact type transfer roller 5 to which a transfer bias is applied as in the present embodiment, in addition to the same electric field action as corona transfer, pressure contact is performed. By applying the transfer force due to the force, the toner portion having a high charge amount in the central portion of the developed toner image Tb is easily transferred to the transfer material P side, and the overall transfer efficiency is improved (see FIG. 4). As shown in FIG. 3B, the transfer toner image Tc on the transfer material P is reduced in degree of emphasis at the edge portion as compared with the transfer toner image Td when the corona transfer is only performed (FIG. 3B).

When a thin layer of toner is coated Ta on the developing sleeve 4b in a low humidity environment to develop a large area solid image with the toner, as the contrast potential (drum surface potential-developing DC bias potential) increases, the developing toner The negative phenomenon in which the image density is lowered becomes less noticeable as the transfer efficiency of the toner image to the transfer material P side is increased as described above, and the image density is improved, and a good image-formed product having no practical problem is output. Can be made This effect can be more remarkable when PVDF or the like is dispersed on the surface of the photoconductor to improve the releasability of the toner image on the surface of the photoconductor.

Specifically, each of the developing device 4 and the transfer device 5 has the following specifications.

(1) Developing device 4 a. Development sleeve 4b: φ16 aluminum sleeve, the surface of which is subjected to a standard sandblast treatment with glass beads.

B. Elastic blade 4c; JIS hardness 65
゜ urethane blade. As the material of the elastic blade 4c, for example, a rubber having JIS hardness of 40 to 80 °, preferably 50 to 70 ° is preferable for the stable formation of the thin developer layer.

The end of the blade 4c is the developing sleeve 4
It is urged to abut b. Here, the blade end is the blade tip, the vicinity including the tip, or the tip not including the tip.

The set pressure of the blade 4c is 5 to 200
g / cm (line pressure in the sleeve generatrix direction) is effective, and in this embodiment, it is set to 30 g / cm.

The linear pressure is measured by stacking three thin plates having a friction coefficient of 1 and inserting them into the blade abutting portion, and pulling out the central thin plate with a spring, and the pulling force at that time is taken as the linear pressure. did.

C. Elastic roller 4d; a core rod wound with a urethane foam having a thickness of 3 mm and a density of 0.025 g / cm ³ .

As the material of the elastic roller 4d, a sponge roller having a skeleton structure having a relatively low degree of foaming (having a relatively high density) is preferable.

The elastic roller 4d comes into soft contact with the developing sleeve 4b, and the effective contact width is 1 to 10 mm. In this embodiment, it is 3 mm.

It should be noted that the container 4 is not subjected to development at the development site.
In order to improve the peeling of the residual toner layer on the developing sleeve 4b returned to the inside of a, it is preferable that the elastic roller peripheral speed and the developing sleeve peripheral speed have a relative speed, and the relative speed is 5 to 600 mm. / Sec is effective, and in this embodiment, it is set to 45 mm / sec.

D. Developer T: 1.5% of colloidal silica in toner powder having an average particle size of 12 μm, which is composed of a copolymer of styrene / acrylic resin and styrene butadiene resin and a pigment.
Externally added toner.

By storing this toner in the container 4a and rotating the developing sleeve 4b, the developing sleeve 4b is rotated.
A uniform toner coating layer Ta having a thickness of about 50 μm was formed thereon. When the charge amount of the toner coating layer Ta was measured by the blow-off method, the charge amount was +15 μc / g, which is a sufficient value.

E. Gap between the photosensitive drum 1 and the developing sleeve 4b α: 250 μm f. Development bias: The AC + DC bias application method described in JP-B-58-32375 is preferred. In this embodiment, an AC voltage; a frequency of 1800 Hz Vpp 1200 V DC voltage; an AC + DC superimposed voltage of −300 V.

(2) Transfer device a. Transfer roller 5; core metal having a diameter of 7 mm and a volume resistance of 10 ⁶ Ωcm by foamed EPDM in which carbon black is dispersed.
Of 100 μm thick PVdF is subjected to a conductive treatment on its surface to form a surface layer having a volume resistance of 10 ⁹ Ωcm.

B. Contact pressure / contact width: The contact pressure (linear pressure) of the transfer roller 5 to the photosensitive drum 1 is effectively 10 to 50 g / cm. In this embodiment, the amount is 30 g / cm. Contact width is 1
It was set to 1.5 mm.

C. Transfer bias: -4 KV The developing device and the transfer device having the above specifications were incorporated into a modified FC-3 or FC-5 copying machine manufactured by Canon Inc., and the surface potential of the latent image on the photoconductor drum 1 was changed to a dark area- When the image was output at 600V bright part -150V, the edge enhancement (middle void) was not noticeable even in the solid image, and the reflection density was 1.
A good image without the negative phenomenon of No. 3 was output.

<Embodiment 2> (FIGS. 5 and 6) In this embodiment, the contact type transfer means is the transfer drum 5A.
FIG. 5 is a multi-color image (or full-color) copying machine using a transfer type electrophotographic process, FIG. 5 is a schematic configuration diagram thereof, and FIG. 6 is a partially cutaway perspective view of a transfer drum 5A.

Reference numerals 4A, 4B, and 4C are first to third nonmagnetic one-component non-contact AC developing type developing devices that store different color toners, respectively.

A latent image of the image of the first color is formed on the surface of the rotary photosensitive drum 1, the latent image is developed by the first color developing device 4A, and the developed toner image is formed on the outer peripheral surface of the rotary transfer drum 5A. It is transferred to the transfer material P which is gripped by the grip 5d and held in a wound state.

The transfer material P is continuously held in a wound state on the surface of the transfer drum 5A until the transfer of the second and third color toner images.

Next, the latent image of the second color image is formed, the latent image is developed by the second color developing device 4B, the developed toner image is transferred to the transfer material P surface, and further the third color image is formed. Latent image is formed, the latent image is developed by the third color developing device 4C, and the developed toner image is transferred to the surface of the transfer material P. That is, the toner image is transferred onto the transfer material P three times, so that a multicolor image is transferred and formed on the surface of the transfer material P.

When the transfer material P receives the final color toner transfer, the gripper 5d releases the grip on the surface of the transfer drum 5A, separates it from the surface of the transfer drum 5A, and conveys it to an image fixing device (not shown).

The transfer drum 5A is pressed against the surface of the photosensitive drum 1 with a predetermined pressing force and rotates in the forward direction of the rotation of the photosensitive drum 1 at substantially the same peripheral speed as the peripheral speed of rotation of the drum 1.
Reference numeral 5e denotes a transfer discharger disposed in the transfer drum 5A toward a transfer portion 6 which is a pressure contact nip portion between the photosensitive drum 1 and the transfer drum 5A.

The transfer material P held in a state of being wound around the transfer drum 5A is the toner on the surface of the photosensitive drum 1 due to the pressure contact force of the transfer drum 5A against the surface of the photosensitive drum 1 and the electric field action of the transfer discharger 5e. Upon receiving the image transfer, as in the case of the first embodiment, a good image in which the negative phenomenon and the void phenomenon are reduced is output.

Reference numerals 5f, 5g, and 5h are static eliminators disposed inside and outside the transfer drum 5A. Reference numeral 5i is a transfer material separating claw.

As shown in FIG. 6, the transfer drum 5A has cylinders 5a, 5a at both ends thereof, a connecting portion 5b connecting the cylinders 5a, 5a, and a transfer material carrier stretched between the cylinders 5a, 5a. It has a dielectric sheet 5c as a member, a gripper 5d for grasping the transfer material provided on the connecting portion 5b, and the like. The dielectric sheet 5c as the transfer material carrying member is
Usually, it is, for example, polyethylene terephthalate or polyvinylidene fluoride resin.

<Embodiment 3> (FIG. 7) This embodiment is a copying machine using a transfer type electrophotographic process, in which the contact type transfer means is an endless transfer belt 5B.

The endless transfer belt 5B is stretched around a plurality of supporting rollers 5j, 5k, and 5l. The endless transfer belt 5B is in pressure contact with the photosensitive drum 1 at the transfer portion 6, and the photosensitive drum 1 rotates. The drum 1 is rotationally driven in the forward direction at a peripheral speed substantially equal to the rotational peripheral speed of the drum 1. A transfer discharger 5m is arranged in the endless transfer belt 5B toward a transfer portion 6 which is a pressure nip portion between the photosensitive drum 1 and the transfer belt 5B.

The transfer material P fed from a paper feed mechanism (not shown) is carried on the rotary transfer belt 5B and conveyed to the transfer portion 6, where the transfer belt 5B makes contact with the surface of the photosensitive drum 1 by pressure. A toner image on the surface of the photoconductor drum 1 is transferred by the electric field effect of the transfer discharger 5m, and a good image in which the negative phenomenon and the hollow defect are reduced is obtained as in the case of the first and second embodiments. Is output. 5n is the transfer material P from the transfer belt 5B.
This is a discharger for eliminating static electricity.

For the purpose of obtaining a multicolor image (or full color), a plurality of photosensitive drums are arranged in contact with one transfer belt so that the toner images are sequentially transferred onto the same transfer material to perform multiple transfer. The effect is the same when it is performed.

[0067]

As described above, according to the present invention, the non-magnetic 1
In a transfer-type image forming apparatus adopting component non-contact AC applied development, the degree of negative phenomenon and edge enhancement (blank phenomenon) of the developer image generated by the above-described developing method is reduced on the transfer material, and It is possible to improve the image quality of the output image by improving the density itself.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an image forming apparatus according to a first embodiment.

FIG. 2 is an enlarged view of a main part of the developing device.

[FIG. 3] (a), (b), and (c) are explanatory model diagrams of a negative phenomenon and a hollow defect phenomenon.

FIG. 4 is a graph showing the relationship between the toner charge amount per unit mass and the transfer efficiency in the case of only corona transfer and in the case of transfer by press contact force.

FIG. 5 is a schematic configuration diagram of an image forming apparatus according to a second embodiment.

FIG. 6 is a partially cutaway perspective view of a transfer drum.

FIG. 7 is a schematic configuration diagram of an image forming apparatus according to a third embodiment.

[Explanation of symbols]

1 Photoconductor drum 4 (4A to 4C) as image carrier Non-magnetic one-component non-contact AC application type developing device 5.5A / 5B Transfer roller or transfer drum or transfer belt as contact type transfer means

Claims (5)

[Claims] 1. A means for forming an electric latent image on the surface of an image carrier, and a developer carrier which carries a non-magnetic one-component developer and faces the surface of the image carrier in a non-contact manner. A means for developing a latent image on the surface of the image carrier and a transfer bias having a polarity opposite to the charging polarity of the developer are applied, and the transfer material is pressed against the surface of the image carrier to transfer the developer image on the surface of the image carrier to the transfer material. An image forming apparatus comprising: a contact-type transfer unit for transferring. 2. The developing means includes a rotating developer carrier,
A developer regulating member having an end portion biased so as to abut against the developer bearing member and forming a thin layer of a non-magnetic one-component developer on the developer bearing member, and the developer regulating member. 2. An elastic roller rotatably supported while being in contact with the developer carrier at a position on the upstream side of the abutting portion on the developer carrier in the rotating direction of the developer carrier. Image forming device. 3. The image forming apparatus according to claim 1, wherein the contact type transfer means is a rotary transfer roller. 4. The image forming apparatus according to claim 1, wherein the contact-type transfer means is a rotary transfer drum having a dielectric sheet stretched around an outer peripheral portion thereof. 5. The image forming apparatus according to claim 1, wherein the contact type transfer means is a rotary transfer belt formed by suspending an endless transfer material carrying member on a plurality of support rollers.