JP3180995B2 - Image forming method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic process applicable to a printer, a facsimile, a copying machine, and the like. The present invention relates to an image forming method in which a body is exposed and developed.

[0002]

2. Description of the Related Art Conventionally, a so-called Carlson process, in which process means for charging, exposing, developing, transferring, cleaning and discharging are arranged on the outer peripheral surface of a photosensitive drum to form an image by a predetermined electrophotographic process, is well known. Technology.

According to such an apparatus, each process means must be independently disposed on the outer peripheral surface of the photosensitive drum, and a high voltage is required for charging and developing bias voltages. The device configuration becomes complicated and large.

In order to solve such a drawback, a developing device is provided by a developing device disposed on the surface of a photosensitive drum in which a light-transmitting conductive layer and a photoconductive layer are laminated on a cylindrical light-transmitting support. While forming the agent rubbing area, the light output of the exposure head built in the photosensitive drum is selectively imaged on the photoconductor layer toward the rubbing area, and development is performed simultaneously with or immediately thereafter. An image forming process has been proposed in which an image is formed on a sheet of paper and transferred to plain paper via a transfer roller or other transfer means (JP-A-58-44445).

In the case where the developer used in such a process is used as a one-component developer, it is premised that the toner used is a conductive toner in order to inject electric charges from the developing sleeve side to the photosensitive member. However, when conductive toner is used, electrostatic transfer means by corona discharge cannot be used as in the case where insulating toner is used in transfer means. The transfer efficiency is increased by applying heat, magnetic force, etc. in addition to applying a transfer bias to the transfer roller using the transferred transfer roller, but the resistance value on the recording paper side tends to fluctuate due to moisture and other environmental factors. However, stable high-efficiency transfer cannot be performed, and it is difficult to form a high-quality image.

In order to solve such a drawback, the applicant of the present application has previously filed an application for a process capable of performing high-quality printing using a two-component developer composed of a combination of a high-resistance or insulating toner and a conductive carrier (Japanese Patent Application Laid-Open (JP-A) No. Heisei 9 (1994) -207). 5-6060). These use a developer containing a conductive resin carrier formed by fixing conductive particles to the surface of particles in which a magnetic material is dispersed in a binder resin. The resin carrier is subjected to mechanical stress when mixed with toner. The developer is likely to be degraded due to peeling of the conductive fine particles of the resin carrier or breakage of the resin due to long-term use.

Therefore, the applicant of the present application has proposed a so-called 3
(Japanese Patent Application No. 4-105).
13). These are added by adding an insulating carrier,
The insulating toner is electrostatically attracted and attracted around the insulating carrier, thereby reducing the toner around the conductive carrier and increasing the contact probability between the conductive carriers. Even if the developer is deteriorated due to a mechanical stress, an electric conduction path is easily secured, and a stable resistance value of the developer can be obtained for a long time.

[0008]

Therefore, the so-called three-component developer carries the toner on the developing sleeve and conveys it to the photosensitive member without greatly affecting the magnetic properties of the insulating toner itself due to the electrostatic force of the insulating carrier. Is possible,
As a result, it is possible to obtain a good image with little fog on the non-exposed area.

However, in the conventional reversal developing method, the toner adhered to the non-exposed portion is attracted to the developing device side by the force generated by the potential difference between the developing bias voltage and the surface potential in the non-exposed portion, and the fog is removed. In the process, charge is injected from the developing sleeve side via the developer, charged with the developer in contact with the photoconductor, and exposure and development are performed almost simultaneously, so that the surface potential of the photoconductor is applied to the developing sleeve. The force is hardly applied in the direction toward the developing device that returns the toner adhering to the unexposed portion of the photoreceptor surface to the sleeve side because the potential is substantially equal to or lower than the electric potential. It depended on the magnetic force of the toner.

However, mixing the magnetic powder into the toner has a problem that the process cannot be applied to a color printer because the magnetic powder itself is non-transparent.

The present invention has been made in view of the above-mentioned drawbacks of the prior art, and has as its object to provide an image forming method capable of forming a clear image without fogging by devising a developing bias voltage.

[0012]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention is to dispose an exposing means on the back side of a belt-shaped or drum-shaped photosensitive member facing a developing sleeve, and to provide the developing sleeve with the developing sleeve. Reversal development in which the photoreceptor is charged while a voltage is applied by a developing bias voltage generating means through a developer rubbing area formed between the photoreceptors, and toner is attached to the exposed portion almost simultaneously with or immediately after exposure. The developing bias voltage generating means applies an intermittent oscillating electric field including an oscillating electric field centered on a DC offset voltage, and the non-oscillating period of the intermittent oscillating electric field is の of the oscillating period. | Va |> | V0 | Va: average value of applied developing bias voltage V0: DC off during non-oscillation period of the intermittent oscillation electric field Tsu G Voltage | V1 |> | ΔV | V1: amplitude [Delta] V of the oscillating electric field that oscillates around the V0: a structure for applying a DC electric field having a relationship of the pedestal voltage.

Further, the present invention can be solved by applying a period of time equal to or longer than 1/2 of the oscillation period during the non-oscillation period of the intermittent oscillation electric field.

[0014]

Since the present invention employs the reversal developing method in which the toner adheres to the exposed portion of the photoreceptor, the background portion has the charged potential and the image portion has the exposed potential. For electrophotography are conventional commonly done, with respect to the surface potential S _p of the background portion, the relationship between the developing bias voltage _{V b | S P |> |} V b | With background section Although fogging can be prevented by generating an electric field force that pulls back toner adhered to the surface, the present invention performs charging, exposure, and development by using the rubbing area of the developer as described above.
Since the developing bias voltage _Vb is almost equal to the surface potential | _Sp |, it is impossible to set | _Sp |> | _Vb |. Therefore, fogging can be prevented by applying the developing bias voltage of the present invention with an intermittent oscillating electric field for each of the vibration period and the non-vibration period for a predetermined time.

The operation of the present invention will be described in detail with reference to FIGS. FIG. 2 shows a developing bias voltage applied to the developing sleeve, where V ₀ is a DC offset voltage, ΔV is a pedestal voltage, V ₁ is an amplitude of an oscillating electric field oscillating around the DC offset voltage V ₀ , and V ₁ is a photoconductor exposure. The subsequent surface potential _, T _1, is the application time of the oscillation period, and T ₂ is the application time of the DC voltage during the non-oscillation period.

[0016] shows the average value V _a when applying such a developing bias voltage in FIG. 2, specifically become general formula as follows, is sufficiently broad developer rubbing area of the charging unit photoreceptor is charged substantially to the mean value V _a time.

[0017]

(Equation 1)

Here, as shown in FIG. 3, the post-exposure potential V
electrodeposition contributes to the development potential is indicated by an arrow A1~A3 respect l
This is equal to the difference between the developing bias voltage and the post-exposure potential Vl during the pressure application period . Therefore, when the pedestal voltage ΔV is applied for T2 time, it is understood that the development amount is larger by an amount corresponding to T2ΔV than when a mere DC offset voltage V0 is applied, thereby improving the image density. it can.

On the other hand, during the period of applying the voltage indicated by the arrow A4, a force due to an electric field acts from the developing sleeve toward the photosensitive drum, so that the toner in the developer moves toward the photosensitive drum as a whole, that is, so-called fogging occurs. Act on the side.
However, during the period in which the voltage indicated by arrow A5 is applied, the toner adhered to the exposed portion is held as it is by the electrostatic force, but in the other background portion (non-exposed portion), the toner is transferred from the photosensitive drum to the developing sleeve. The force by the electric field acts on the side, and the force acts in a direction to remove fog.

[0020] Here, a voltage integral value is indicated by an arrow A4 of the developing bias voltage in the period that gives the voltage indicated by the arrow A5
Than the integrated value of the developing bias voltage during the given period (T1
It will be larger by T2 / (T1 + T2)) ΔV. This means that it acts as a fog removal voltage, and therefore
At this time T1, fog removal is performed.

Next, the fog removal voltage ( A5-A4 )
FIG. 4 shows a relationship in which the magnitude of the voltage indicated by the arrow A6 is expressed as a function of T2. Here, the magnitude of the voltage indicated by the arrow A6 is (T1 / (T1 + T2)) [Delta ] V. In this period, the voltage acts on the fogging direction in the same manner as the voltage indicated by A4. Originally, in order to obtain a good image, it is preferable to apply a developing bias voltage having a sufficiently low fog generation voltage indicated by arrow A6 and a sufficiently high fog removal voltage (A5-A4) .

FIG. 4 shows that the fog elimination voltage (A5-A4) is indicated by an arrow A6 at the intersection of the curves, that is, at least when the time T2 is longer than T1 / 2 or sufficiently longer than T1 / 2.
The fog generation voltage becomes larger than the fog generation voltage shown , and a good image can be obtained by taking the value of the developing bias voltage having this time relationship.

[0023]

An embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic diagram showing the configuration of the image forming apparatus of the present invention. Reference numeral 1 denotes a photosensitive drum including an LED unit 2, and a developing sleeve 30 and a transfer roller 4 incorporated in a developing unit 3 are disposed along a rotation direction of the photosensitive drum. A paper feed cassette 5, a paper detection sensor 6, a registration roller 7, and a fixing roller 8 are arranged from the upstream side along the tangential direction of the arrow.

The transfer roller 4 uses a low-resistance roller to increase transfer efficiency, applies a transfer bias having a polarity opposite to the charge of the toner, and is disposed in pressure contact with the photosensitive drum 1.
It is configured to be rotatable in synchronization with the photosensitive drum 1.

Next, the structure of the photosensitive drum 1 and the developing unit 3 which are characteristic parts of the present invention will be described. The photosensitive drum 1 is formed by laminating a light-transmitting conductive layer 1b, a charge injection blocking layer 1e, a photoconductor layer 1c, and a surface protection layer 1f on a light-transmitting support 1a from the inside. In the example, the outer diameter is set to 30 mm, and the translucent conductive layer 1b is grounded.

The LED unit 2 installed in the photosensitive drum 1 has a printed board on which LED chip rows 21 and the like arranged in a row along the drum axis are mounted, and a converging lens array arranged on the front surface thereof. 23 (trade name: Selfoc lens), which are integrally held by a head block 24. Then, the LED unit 2 deflects the light to a position slightly downstream from the closest contact point of the drum / sleeve, that is, the center line connecting the photosensitive drum 1 and the developing sleeve 30 with respect to the rotation direction of the photosensitive drum 1. It is configured to form an image on the conductor layer 1c.

The developing unit 3 includes a toner supply container 32, a developing container 31 containing a conductive carrier and an insulating toner.
A developing sleeve 30 containing a fixed magnet assembly 33 is disposed on the side of the container 31 facing the photoconductor drum, and the diameter of the sleeve 30 is set to 30 mm similarly to the photoconductor drum 1. ing. As the rotation direction, the photosensitive drum 1 is rotated in the opposite direction. The developing sleeve 30 is connected to the developing bias voltage generating means Vi of the present invention, so that an intermittent oscillating electric field can be applied. As shown in FIG. 2, the intermittent oscillating electric field repeatedly applies an oscillating period and a non-oscillating period. The developing bias voltage generating means of the present invention first applies an oscillating electric field having an amplitude V1 superimposed on a DC voltage for a time T1. The oscillating electric field oscillates around the DC offset voltage V0. In this embodiment, the oscillating electric field has been described as a rectangular wave. However, the oscillating electric field is not limited to this, and may be a sine wave, a triangular wave, or another waveform. The peak voltage of the amplitude V1 is set so as not to exceed the dielectric breakdown voltage of the photoconductor.
Next, during a non-oscillation period, a DC electric field having a pedestal voltage is applied. At this time, the relationship between the average value Va of the developing bias voltage and the DC offset voltage V0 is such that the developing bias voltage is applied for T2 so that | Va |> | V0 | is satisfied. What
As shown in FIG. 3, | V1 |> | ΔV | is satisfied.
I also do. The relationship between the time T1 and the time T2 is, as described in the above operation section, at least T2 is equal to T1.
It is set to be 1/2 times or more. In this case, T1 is set sufficiently larger than the surface potential charging time constant of the photoconductor. The fixed magnet assembly 33 is set in the magnetic pole arrangement as shown in FIG. , Located at a slightly displaced position. On the other hand, the developing container 31 has an opening on the peripheral surface side below the developing sleeve 30 facing the photosensitive drum 1, and both sides of the opening are concavely formed in an arc shape, and the photosensitive drum is stored in the concave portion. The transfer roller 4 is rotatably brought into contact with the photosensitive drum 1 on the bottom surface side of the photosensitive drum 1. In the drawing, 35 is a toner supply roller, 34a is a slit opening, 36 is a density control sensor, and 37 is a stirring roller.

Next, the composition of the developer will be described. In the present embodiment, description will be made on the assumption that a two-component developer of a conductive magnetic carrier and an insulating toner is used. Although the conductive magnetic carrier is not particularly limited, for example, a magnetite, which is a magnetic substance, is uniformly dispersed in a polyethylene resin or other binder resin to form a base particle of the carrier, and the conductive fine particles are fixed on the surface thereof. Carrier having an average particle size of 15 μm to 50 μm, preferably 20 μm to 40 μm, and a volume resistivity of 10 ⁵ Ω · cm or less, preferably 10 ¹ Ω · cm to 10 ⁴ Ω · cm. As the insulating toner, one having the same configuration as that of the related art is used, and for example, a binder resin, a coloring agent, a charge controlling agent, an offset preventing agent, and the like can be compounded. A volume resistivity of 10 ¹⁴ Ω · cm is appropriate. A developer is prepared by mixing a conductive magnetic carrier and an insulating toner, and has a volume resistivity of 10 ⁵ Ω · c as a whole.
m, preferably 10 ³ Ω · cm to 10 ⁵ Ω · cm. This resistor has an inner diameter of 20 mm with an electrode at the bottom.
1.5 g of developer is placed in a Teflon cylindrical body of
Are measured when a load of 1 kg is applied from above with the electrode inserted.

(Experimental Example 1) Using the electrophotographic apparatus having the structure described in the above embodiment, an image evaluation experiment was conducted under the following conditions of the developer and the developing bias voltage.

Volume resistivity of developer: 10 ⁴ Ω · c
m DC offset voltage V _0: 50 V of the oscillating electric field amplitude V _1: 20 V pedestal voltage [Delta] V: 10 V developing bias voltage average value V _{a of: 57V T 1: 2 msec T} 2: using a 5 msec the developer Exposure, development, transfer, fixing
As a result of performing image evaluation after printing a total of 200 sheets,
An image with good image density and fog level was obtained.

COMPARATIVE EXAMPLE The apparatus used in Experimental Example 1 was the same, and an experiment was conducted by changing only the application time of the developing bias voltage.

T ₁ : 4 msec T ₂ : 5 msec Similarly, as a result of image evaluation after a total of 200 sheets, an image having a poor evaluation of the fog level on the background portion was obtained in any of the prints.

(Experimental example 2) Developing bias voltage application time T
_1, T ₂ respectively to change the by pedestal voltage ΔV is 10
The fog level at V and 15 V was evaluated. Note that the experimental conditions were set in the same manner as in Experiment 1.

FIG. 5 shows the results of the fog evaluation. T ₂ is the head when T ₂ is understood that the level of the head is improved is less than twice the T ₁ according to become larger than T ₁ level becomes 2.5 or less, less good image fogging It is understood that it can be obtained.

[0035]

As described above, according to the present invention,
In an image forming method in which an exposing unit is installed in a transparent drum-shaped or belt-shaped photoreceptor drum, and the photoreceptor is exposed by the exposing unit, development is performed almost simultaneously with or immediately after exposure. By using the applying means, a clear image with reduced fog can be formed. This makes it possible to use a non-magnetic toner, which facilitates application of colorization.

[Brief description of the drawings]

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

FIG. 2 is a diagram showing a waveform of a developing bias voltage according to the present invention.

FIG. 3 is an explanatory diagram of a main part of a waveform of a developing bias voltage according to the present invention.

FIG. 4 is a diagram showing a relationship between a fog removal voltage and a fog occurrence voltage.

FIG. 5 is a diagram showing a relationship between a fog level and T ₂ / T ₁ .

[Explanation of symbols]

1: photosensitive drum 2: LED unit 3: a developing unit V _a: mean value V ₀ which is the developing bias voltage: offset voltage [Delta] V: pedestal voltage

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-58-44445 (JP, A) JP-A-60-53968 (JP, A) JP-A-60-53969 (JP, A) JP-A-60-53969 134262 (JP, A) JP-A-61-239253 (JP, A) JP-A-61-239254 (JP, A) JP-A-4-2533071 (JP, A) JP-A-5-6060 (JP, A) JP-A-5-257347 (JP, A) JP-A-5-35063 (JP, A) JP-A-6-167847 (JP, A) JP-A-6-230652 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G03G 15/24 G03G 15/06-15/095 G03G 15/05

Claims (1)

(57) [Claims] An exposing means disposed on the back side of a belt-shaped or drum-shaped photoconductor facing the developing sleeve;
After charging the photoconductor while applying a voltage by the developing bias voltage generating means through the developer rubbing region formed between the developing sleeve and the photoconductor, the toner is transferred to the exposed portion almost simultaneously with or immediately after the exposure. In the image forming method of performing reversal development, the developing bias voltage generating means applies an intermittent oscillating electric field including an oscillating electric field centered on a DC offset voltage, and vibrates during a non-oscillating period of the intermittent oscillating electric field. 1/2 or more of the period
An image forming method , wherein the above time is applied, and a non-oscillating period of the intermittent oscillating electric field is applied by a DC electric field having the following relationship. | Va |> V0 | Va: average value of applied developing bias voltage V0: DC offset voltage | V1 |> | ΔV | V1: amplitude of oscillating electric field oscillating around V0 ΔV: pedestal voltage