JPH05303249A - Image forming device - Google Patents

Abstract

PURPOSE:To provide smooth electrostatic charging and to form a high definition image even when the diameter of a photosensitive drum is made smaller by making the circumferential speed of a developing sleeve higher than that of the photosensitive drum and setting an exposing position to a downstream side in a drum rotating direction from a position where developer comes closest. CONSTITUTION:An exposing means 2 is arranged on the back surface side of the photosensitive drum 1 facing to the developing sleeve 30, and the drum 1 is electrostatically charged through a developer rubbing area formed between the sleeve 30 and the drum 1, so that development is executed simultaneously with exposure. The rotating direction and the speed of the sleeve 30 are set to forward feeding rotation and the circumferential speed 5-10 times as high as that of the drum, respectively. The exposing position by the exposing means 2 is set to the downstream side in the drum rotating direction from the position where the developer comes closest. Namely, the circumferential speed of the sleeve 30 is made high, the density of the developer is made very large in an electrostatic charging area, the exposing position is set to the downstream side, and the density of the developer is relatively made small in an exposing and developing area. Therefore, the smooth electrostatic charging is attained and the high definition image is obtained.

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 applied to a printer, a facsimile, a copying machine or the like, and more particularly, it exposes a photoconductor while exposing the photoconductor by exposing means provided on the back side of the photoconductor. The present invention relates to an image forming apparatus that develops substantially at the same time.

[0002]

2. Description of the Related Art Conventionally, for example, an exposing means for producing a light output corresponding to image information is provided in a photosensitive drum formed by laminating a transparent conductive layer and a photoconductive layer on a transparent support. At the same time as or immediately after forming the latent image on the photoconductor layer by converging the light output of the exposure means by interpolating, the latent image is visualized through the developing sleeve facing the photosensitive drum. An image forming apparatus is known in which after the image is formed (toner image), the toner image can be transferred onto plain paper through a transfer roller or other transfer means. (JP-A-58-153957, etc.)

In this type of image forming apparatus, in order to further simplify the configuration, prevent ozone generation, etc., and prevent background fogging, the image forming apparatus does not have an independent charger and faces the photosensitive drum. The conductive magnetic toner is carried on the developing sleeve arranged in the above-mentioned manner, and a so-called magnetic brush-shaped toner sliding area is provided near the developing position by utilizing the magnetic force of the fixed magnet assembly or the like contained in the sleeve. While rubbing the surface of the photosensitive drum 1 with the rubbing area, a developing bias applied to the developing sleeve side is used to inject charge into the photoconductive layer of the drum through the rubbing area to perform charging. After that, immediately after the charging, an exposure image is formed by using the exposure means included in the drum, and the development is performed to form a predetermined image.

In this apparatus, it is preferable to maximize the time for passing through the rubbing area in order to charge the photosensitive drum side by utilizing the toner rubbing area. However, in the apparatus, in order to make full use of the merit that the miniaturization can be achieved by inserting the exposing means in the drum, the diameter of the photosensitive drum is made as small as possible together with the LED constituting the exposing means. However, in order to obtain a paper feed speed that satisfies the function of a printer or a facsimile machine of 10 or 6 sheets, the peripheral speed of the drum is inversely proportional to the drum diameter. However, as a result, there arises a problem that the charging cannot be performed sufficiently.

In order to solve such a drawback, the present applicant first sets the moving direction of the photoconductor in the rubbing area in the direction opposite to the toner carrying direction (in this case, the photoconductor drum and the developing sleeve are used for formation). In either case, the movement direction in the rubbing region can be set to the opposite direction by setting the same rotation direction such as clockwise or counterclockwise. This will be referred to as a counter feed hereinafter). Attempts have been made to increase the amount of toner to be charged, in other words, to increase the toner density, and consequently increase the charging efficiency in a short time. However, in the case where the rubbing area is formed between the photosensitive drum and the developing sleeve, the closest position between them becomes a substantial weir, and in many cases, in the rubbing area on the toner inflow side, that is, on the downstream side of the drum. Toner is accumulated and the toner density becomes large, and the toner density at the upstream side of the closest position becomes relatively coarse, so that the toner density in the charging area can be made sufficiently dense from the upstream side in the rotation direction of the photosensitive drum. Therefore, the desired effect cannot always be expected.

In order to solve such a drawback, the inventors of the present invention set the developing sleeve to the forward feed in which the moving direction in the rubbing area is the forward direction without counter feeding the photosensitive drum and the developing sleeve. By increasing the peripheral speed of the roller relative to the peripheral speed of the drum, the toner density supplied to the charging area on the upstream side of the drum from the closest position of the sliding area is increased. Now, in the above apparatus, in order to facilitate the injection of charges to the drum side, conductive toner is generally used. However, when conductive toner is used while increasing the relative peripheral speed and setting the toner density to a large value, In the process of simultaneous development with exposure after charging, the toner once attached to the latent image is likely to be recharged due to the toner rubbing on the rubbing area, and the image density is likely to be lowered.

In order to eliminate such a defect, the photosensitive drum and the developing sleeve are set to the forward rotation at the same speed, and the magnet assembly is made relatively faster than the peripheral speed of the drum, so that It is also possible to increase the toner density supplied to the charging area on the upstream side of the drum from the closest position. However, as described above, since the toner rubbing region is stably magnetically held by the magnetic poles of the magnet assembly, it is not preferable to rotate the magnetic pole because the position and density of the rubbing region tend to vary.

In view of the above technical problems, the present invention provides an image forming apparatus capable of smoothly charging and forming a clear image even when the diameter of the drum is reduced while maintaining a predetermined printing speed. The purpose is to do.

[0009]

SUMMARY OF THE INVENTION According to the present invention, the peripheral speed of the developing sleeve is relative to the peripheral speed of the drum without counter-feeding the rotational directions of the drum and the sleeve and without rotating the magnet assembly. The first feature is that the sleeve is rotated by the forward feed at a high speed. In this case, the sleeve peripheral speed is preferably set to 5 to 10 times the drum peripheral speed. That is, if it is 5 times or less, charging due to the rubbing is not sufficiently performed, and as a result, charging failure is likely to occur and ghost and density decrease are likely to occur. Again 10
If it is more than twice, not only the inside contamination of the machine due to the increase of the relative rubbing speed and the life of the developer are shortened but also the developing nipple after the exposure (the end of the rubbing area) is increased due to the increase of the rubbing speed.
Is easily destabilized.

With the above construction, as described above, the toner density in the developer rubbing area increases and the charging efficiency increases, but the increase in the toner density causes a problem of recharging at the time of exposure / development. In some cases, the effects of the present invention cannot be achieved smoothly. Therefore, the second feature of the present invention is that the developer density is sufficiently increased in the charging region, and the developer density is relatively coarsened in the exposure and development region to effectively eliminate the above-mentioned defects. It is in the point that I aimed. That is, more specifically, the above-described configuration can be obtained by setting the exposure position of the exposure means to the downstream side of the developer closest position in the drum rotation direction. In order to further increase the developer density on the charged area side, in the preferred embodiment of the present invention, the main magnetic pole of the magnet assembly included in the developing sleeve may be set on the upstream side of the exposure position.

Even if the above construction is adopted, if the toner is a conductive toner, the problem of recharging at the time of exposure / development cannot be completely solved. Therefore, the present invention separates the charge and the development even in the developer, and does not use the developer as a one-component conductive toner, but the conductive carrier and the high-resistance or insulating toner (hereinafter, substantially insulating toner including both of them). That is) a two-component developer composed of a combination of According to this invention, in the charging area, the conductive carrier can smoothly charge, and at the portion where the insulating toner is adhered by exposure / development, recharging from the upper surface side of the adhered portion is prevented, and the smooth exposure is performed. / Development becomes possible. Incidentally, it is preferable to set the content of the substantially insulating toner higher than that of the conventional two-component developer, and set to 10 to 20%.

Further, by using a high-resistance or insulating toner, stable and smooth transfer is possible, and since charge injection is performed by using a conductive carrier, it is independent of the transfer condition on the downstream side of the developing position. In addition, the conductivity of the carrier can be set to a high value, which makes it possible to shorten the charging time. In this case, by setting the average particle diameter of the carrier within about 1 to 5 times the average particle diameter of the toner, it is possible to more finely charge the drum side.

Further, in the above construction, the developer density is high in the charging region and the relative peripheral speed of the sleeve is high.
Carrier deterioration easily occurs. Therefore, the present invention is characterized in that, as the carrier, a heat-melting conductive carrier having a color similar to that of the toner, which is formed by fixing conductive fine particles to the surface of particles in which a magnetic material is dispersed in an insulating resin, is used. And
That is, when the conductive fine particles are peeled off due to the deterioration of the carrier and the carrier is deteriorated, the carrier becomes insulative and the diameter ratio thereof is 1 to 5 times that of the toner. A fresh carrier is always supplied by mixing a carrier that adheres to the latent image portion of the drum and is detached from the rubbing area and newly replenished with toner that supplements the deteriorated carrier amount, which is preferable. .. Further, by setting the detached carrier to be a resin carrier which has a color similar to that of the toner and is heat-meltable in the fixing step, it is treated in the same manner as the toner and does not affect the image quality at all.

Further, with the above construction, the diameter of the photosensitive drum can be reduced while maintaining the predetermined feeding speed. However, when the drum diameter is set to 50 φ or less, the distance between the developing sleeve and the photosensitive drum is reduced. It is preferable to set the developing gap at the closest position to the range of 0.3 to 0.55 mm.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described in detail below as an example with reference to the drawings. However, unless otherwise specified, the dimensions, materials, shapes, relative positions, etc. of the components described in this embodiment are not intended to limit the scope of the present invention thereto, but are merely illustrative examples. Not too much.

FIG. 1 is a schematic diagram showing the configuration of a printer according to an embodiment of the present invention. Reference numeral 1 denotes a photoconductor drum in which the LED unit 2 is inserted, and a developing sleeve 30 and a transfer roller 4 incorporated in the developing unit 3 are arranged along the rotation direction thereof, and the photoconductor drum 1 and the transfer roller 1 are arranged. 4 from the upstream side along the tangential direction between the sheet feeding cassettes 5,
Paper detection sensor 6, registration roller 7, and transfer roller 4
A fixing roller 8 is arranged with the sheet sandwiched therebetween. A conductive roller is used as the transfer roller 4 in order to improve transfer efficiency, a transfer bias having a polarity opposite to the charging potential of the toner is applied, and the transfer roller 4 is uniformly pressed against the peripheral surface of the photosensitive drum 1.
It is configured to be rotatable in synchronization with the drum 1.

Next, as shown in FIG. 2, the construction of the photosensitive drum 1 and the developing unit 3, which are essential parts of the present invention, will be mainly described in detail. The photoconductor drum 1 is formed by laminating a transparent conductive layer 1b, an injection blocking layer 1e, a photoconductive layer 1c, and a surface layer 1f on a transparent support 1a from the inner surface side.
The translucent support 1a is formed of a transparent inorganic material such as glass or a transparent resin such as polyester. In this embodiment, the thickness is 2 mm and the outer diameter is set to 30 mm. Form a transparent cylindrical glass substrate having a length of 300 mm in the axial direction. The transparent conductive layer 1b is formed by depositing an ITO (indium tin oxide) layer on the support by an active reaction vapor deposition method to a thickness of 1000 liters. The photoconductor layer 1c uses a photoconductor made of a-Si: H, and contains a non-doped or Va group element in order to increase electron mobility when the developing bias is positive, and the developing bias is negative. In this case, it is preferable to contain a Group IIIa element in order to enhance the mobility of holes. The photoconductor layer 1c is formed of two layers, that is, a photoexcitation layer region 1c1 having a function of generating photocarriers from the back side and a layer region 1c2 having a function of carrier transport. The voltage can be increased.

The LED units 2 inserted in the photosensitive drum 1 are LEs arranged in a line along the axial direction of the drum.
The head block 2 is composed of a converging lens array 23 (trade name: SELFOC lens) arranged on a printed circuit board on which the D chip row 21 and the like are mounted.
4, the pixel information is output for one scanning line while the LED chip is time-divisionally driven in units of 64 bits. By repeating the above operation, the image information for one page can be output. And the LE
The exposure position of the D unit 2 is the closest contact point of the drum / sleeve, in other words, the photosensitive drum 1 and the developing sleeve 30.
The image is formed on the photoconductor layer 1c in the drum 1 by slightly deflecting it to the downstream side (about 4 °) in the rotation direction of the drum 1 from the center line connecting the axis centers of.

As shown in FIG. 1, the developing unit 3 comprises a toner replenishing container 32 and a developing container 31 containing a carrier and toner, and a fixed magnet assembly is provided on the side of the container body 31 facing the photosensitive drum 1. A developing sleeve 30 containing a body 33 is provided, and the diameter of the sleeve 30 is set to 30φ similarly to the photosensitive drum, and the photosensitive drum 1 is provided.
And the forward feed is rotated in the counterclockwise direction, preferably at a rotation speed of about 5 to 10 of the peripheral speed of the photosensitive drum. The fixed magnet assembly 33 is set to have a magnetic pole arrangement as shown in FIG. 1, and in particular, the main magnetic pole for forming the rubbing area is displaced about 2 ° upstream from the closest position between the drum and the sleeve in the drum rotation direction. It is located at the specified position.

Next, the composition of the developer used in the developing unit 3 will be described. FIG. 2 is a schematic diagram showing the structure of the carrier used in the present developer, in which the conductive fine particles 16 are fixed on the surface of the carrier mother particle 13 in which the magnetic material 15 is uniformly dispersed in the binder resin, and the carrier 14 is It is configured.

The carrier 14 has a volume resistivity of 10 ⁸
Ω · cm or less, more preferably 10 ⁴ · Ω · cm or less. If the volume resistivity becomes too large, the characteristics as a conductive carrier are impaired. For example, in the case of using the simultaneous charging exposure method, the charge injection is not performed promptly and the photoreceptor is insufficiently charged. The conductivity of the carrier 14 is mainly given by the conductive fine particles 16. The volume resistivity of the carrier 14 is the inner diameter having an electrode on the bottom.
1.5g of carrier 14 is put in a 20mm Teflon cylinder,
It is a value when an electrode having an outer diameter of 20 mm is inserted and a load of 1 kg is applied from above to measure. The magnetic force of the carrier 14 needs to be large to some extent or more, and preferably 5 k
The maximum magnetization in the magnetic field of Oe (Oersted) is 55 em
u / g or more, more preferably 55 to 80 emu / g. The maximum magnetization in a magnetic field of 1 kOe is 45 emu.
/ G or more is suitable, more preferably 45 to 60 em
u / g. If the magnetic force of the carrier 14 becomes too small, the developer transportability deteriorates, and the carrier 14 is developed together with the toner.

The average particle size of the carrier 14 is 10 to 100.
μm is suitable, and more preferably 15 to 50 μm. If the carrier 14 is too large, it becomes difficult to uniformly charge the photoconductor, and the toner concentration T / C cannot be increased. On the other hand, if it is too small, the transportability of the developer on the developing sleeve deteriorates, and it becomes difficult to apply a constant potential. In addition, the carrier 14
The true density of is preferably in the range of 3.0 to 4.5 g / cm ³ . Magnetite (Fe ₃ O ₄ ), ferrite (Fe ₂ O ₃ ) and the like are used as the magnetic substance, and magnetite is particularly preferable, but the magnetic substance is not limited thereto.

As the conductive fine particles 16, carbon black, tin oxide, conductive titanium oxide (titanium oxide coated with a conductive material), silicon carbide or the like is used, and conductivity is obtained by oxidation by oxygen in the air. Those that do not lose are desirable. As the binder resin used for the carrier mother particles 13, a vinyl resin represented by polystyrene resin, a polyester resin, a polyamide (trade name nylon) resin, a polyolefin resin, or the like is used.

The conductive fine particles 16 are fixed to the surface of the carrier mother particles 13 by, for example, uniformly mixing the carrier mother particles 13 and the conductive fine particles 16 and attaching the conductive fine particles 16 to the surface of the carrier mother particles 13. After that, a mechanical and thermal impact force is applied and the conductive fine particles 16 are driven into the carrier mother particles 13 and fixed. The conductive fine particles 16 are not completely embedded in the carrier mother particles 13, but are fixed so that a part thereof protrudes from the carrier mother particles 13. Carrier 1 like this
By fixing the conductive fine particles 16 to the surface of 4, the carrier 14 can be efficiently provided with high conductivity. Also,
Since it is not necessary to mix the conductive fine particles 16 in the carrier mother particles 13, a larger amount of the magnetic material 15 can be mixed in the carrier mother particles 13 and the magnetic force of the carrier 14 can be increased.

The above carrier and toner are mixed to obtain a developer. As the toner, a usual insulating toner is used, preferably having a volume resistivity of 10 ¹⁴ Ω · cm or more, more preferably 10 ¹⁶ Ω · cm or more. For example, a binder resin, a colorant, Charge control agent,
It is preferable to add a magnetic substance together with an offset preventive agent to obtain a magnetic toner.

The operation of this embodiment will be briefly described below. The photosensitive drum 1 is set at a rotation speed of 25 rpm, while the rotation speed of the developing sleeve is sequentially changed in the range of 0 to 300 rpm, and a developed image is obtained. The relationship between the concentration and the rotation speed of the sleeve was examined. Incidentally, a DC voltage of +50 V is applied as the developing bias Vi, the drum and the developing sleeve are each 30φ, the gap between them is 0.5 mm, and the magnetic pole position of the fixed magnet assembly 33 is the drum / It is swung to the upstream side of the photosensitive drum by 4 ° from the closest position between the sleeves, and the magnetic pole strength is set to 800 gauss. The LED head 2 sets the drive current so that the exposure energy incident on the photosensitive drum 1 is 0.35 μJ / cm ² or more, and the light emission time is 5 to 50 μm.
and the transfer roller 4
Bias Vt of is set to -300V.

Based on the above condition setting, the relationship between the developed image density and the rotational speed of the sleeve was obtained as shown by the broken line in FIG. As is apparent from this figure, it was confirmed that the development density increased until the relative peripheral speed between the sleeve and the drum reached 5 times, stabilized at 5 to 9 times, but decreased rapidly after 10 times. It was Next, when the same experiment was performed by narrowing the developing gap to 0.4 mm, it was confirmed that the stable region was extended to about 10 times as shown by the solid line in FIG. From the above results, it is considered that the developing density decreases due to poor charging until the relative peripheral speed between the sleeve and the drum reaches 5 times, and also due to rubbing or recharging after development exceeding 10 times. From the above results, it is considered that the developing density decreases due to poor charging until the relative peripheral speed between the sleeve and the drum reaches 5 times, and also due to rubbing or recharging after development exceeding 10 times.

Further, an aluminum tube is used instead of the drum, the sleeve is 200 rpm, the doctor blade gap is 0.5 mm, and the relationship between the developing gap (sleeve / drum distance at the closest position) and the image density is examined. .. As a substitute characteristic of the image density, the variation of the current value in each of the areas 1 to 8 in the grid of FIG. 5 is examined. That is, FIG.
As is clear from the result, when the development gap was changed and the development nip width on the downstream side (exposure / development area) and the development density were examined, the development nip width decreased when the development gap became 0.6 mm or more. In addition, it was confirmed that the current value affecting the image formation on the upstream side of the exposure position was significantly reduced. Further, it was confirmed that when the developing gap was 0.4 mm, the developing nip width and the current value were sufficient, and from this viewpoint, it is presumed that sufficient developing density can be obtained even when the developing gap is 0.3 mm.

Next, the relationship between the magnetic pole position of the fixed magnet assembly contained in the sleeve and the developing density is examined under the same conditions as described above. As is apparent from FIG. 5, when the main magnetic pole of the fixed magnet assembly is swung to the left and right with the closest position between the drum and the sleeve sandwiched, the exposure position is upstream (charging area) and downstream (exposure / developing area). Of the developing nipple width of the developing nipple width, the developing nipple width on the downstream side (exposure / developing area) that influences image formation is forward feed rotation, so the developer flow rate is regulated at the closest contact point It was confirmed that the amount of fluctuation was small and stable image formation was performed, and there was little fluctuation when the main magnetic pole was located upstream of the exposure position, but when set on the downstream side of the exposure position, the nipple width It was confirmed that the image quality was sharply decreased, and as a result, the image formation was adversely affected.

[0030]

As described above, according to the present invention, even when the diameter of the drum is reduced while maintaining a predetermined printing speed, it is possible to smoothly charge and form a clear image, and particularly, the developing sleeve. By clarifying the relationship between the photoconductor drum and the photosensitive drum, it was possible to easily and smoothly achieve the conflicting demands for downsizing, sharpening and stabilizing the image. And so on.

[Brief description of drawings]

FIG. 1 is an overall schematic diagram of an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a schematic diagram showing the structure of a carrier used in the present developer.

FIG. 3 is a relationship diagram between image density and sleeve rotation speed.

FIG. 4 is a relational diagram showing variations in current value in each region as a substitute characteristic of a developing gap, a developing nip width, and a developing density.

FIG. 5 is a relational diagram showing the fluctuation of the main magnetic pole position of the fixed magnet assembly and the developing nip width.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photoconductor 2 Exposure means 30 Toner carrier 10 Developer sliding area

Claims (8)

[Claims] 1. A photosensitive member is arranged on the back side of a photosensitive drum facing the developing sleeve, and a developing bias is applied through a developer sliding area formed between the developing sleeve and the photosensitive drum. In an image forming apparatus in which a body is charged and then developed almost at the same time as or immediately after exposure, the rotation direction and speed of a developing sleeve including a fixed magnet assembly are set in relation to the photosensitive drum in the rubbing area. An image characterized by being set so as to be forward feed rotation and a peripheral speed relatively higher than the peripheral speed of the drum, and the exposure position of the exposing means is set on the downstream side in the drum rotation direction from the closest position of the developer. Forming device 2. The peripheral speed of the sleeve is 5 relative to the peripheral speed of the drum.
The image forming apparatus according to claim 1, wherein the image forming apparatus is set to 10 times. 3. The photosensitive drum is set to 50 mmφ or less, and the developing gap at the closest position between the developing sleeve and the photosensitive drum is set to 0.3 to 0.55 mm. Item 1. The image forming apparatus according to item 1. 4. The image forming apparatus according to claim 2, wherein the main magnetic pole of the fixed magnet assembly included in the developing sleeve is set on the upstream side of the exposure position. 5. An image forming apparatus characterized in that a two-component developer comprising a conductive carrier and a high resistance or insulating toner is used as a developer supplied to the sleeve. 6. The image forming apparatus according to claim 1, wherein the high-resistance or insulating toner is set to approximately 10 to 20% of the conductive carrier. 7. The developer is composed of a carrier whose surface is at least conductively treated and a high resistance or insulating toner, and the average particle size of the carrier is approximately 1 of the toner average particle size.
The image forming apparatus according to claim 1, wherein the setting is within 5 times. 8. The carrier is a heat-melting conductive carrier having a color similar to that of the toner, which is formed by fixing conductive fine particles to the surface of particles in which a magnetic material is dispersed in an insulating resin. Image forming apparatus according to item 6.