JP3014133B2 - Image forming device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus that forms a multicolor image on an electrostatic latent image carrier and transfers the image to a transfer material.

(Prior Art) Japanese Patent Application Laid-Open No. 63-60471 discloses a conventional method for obtaining a multicolor image by one transfer after superimposing and developing a color-separated image on an electrostatic latent image carrier. The techniques described in JP-A-63-63061 and JP-A-63-85578 are known.

The technique described in Japanese Patent Application Laid-Open No. 63-60471 is a system in which a plurality of developing means are provided around a latent image carrier to obtain a multicolor image, and the downstream developing means comprises: a. Is opposite to the developing means on the upstream side.

b. The toner layer is not in contact with the latent image carrier.

c. At the time of development, the AC electric field is used to develop this toner.
During non-development, an electric field for developing the toner on the upstream side is applied.

d. The thickness of the toner layer is 30 to 500 μm.

e. The upstream side is composed of a two-component developer having a chromatic color toner, and the downstream side is composed of a one-component developer of a black toner.

Etc.

The technique described in Japanese Patent Application Laid-Open No. 63-63061 discloses a technique in which a photosensitive layer having a thickness of 35 to 90 μm and a capacitance of 20 to 170 pF / cm ² is provided around a photoreceptor made of selenium or arsenic selenide. A method of obtaining a color image on the same photoreceptor by repeating charging, exposure and development a plurality of times, wherein a. DC bias development.

b. The donor roller not contributing to the development is stopped, and the toner on the surface is attached outside the image area to prevent color mixing.

c. The photoreceptor is made of 15-50 μm OPC, and development is reversal development.

d. Set the potential contrast to 400 V or more.

e. The thickness of the toner layer on the photoreceptor is 5 to 30 μm.

f. The charging was Scorotron.

Etc.

The technique described in JP-A-63-85578 is to obtain a multicolor image by arranging a plurality of developing means on a recording medium in a non-contact state. To make the peripheral speed faster than that of the recording medium by rotating in the same direction, to apply black development, and to apply an AC bias biased by DC.

b. The second and subsequent developing means downstream are set to constant speed development,
Apply only DC bias in color development.

Etc.

(Problems to be Solved by the Invention) When a multi-color image is to be formed on the electrostatic latent image carrier, the first color toner image is formed on the electrostatic latent image carrier during the development of the second color. Has already been formed, it is necessary to use the non-contact development in the development method for the second and subsequent colors.

Therefore, the developing method is an image forming method using a non-magnetic toner that can be developed by making the toner layer and the latent image carrier face each other in a non-contact manner, and is easy to colorize. The one-component method which is advantageous to the above is preferred.

However, when an AC bias is applied as a developing bias as in the method described in the above-mentioned conventional Japanese Patent Application Laid-Open No. 63-60471, the toner reciprocates between the latent image surface and the toner carrier surface. In addition, not only the first color toner image is disturbed, but also the second color toner is mixed into the second color developing device, so that the second color toner gradually becomes cloudy.

In order to solve this problem, as in the systems described in JP-A-63-63061 and JP-A-63-85578, the development of the second and subsequent colors is performed by causing the nonmagnetic toner to fly by a DC electric field. What should I do?

However, in order to transfer the toner layer under a DC electric field, it is necessary to control the amount of charge of the toner to be low so that the electric field acting on the toner layer is directed toward the flight.

For this reason, as the toner layer, a toner layer having a charge amount of 5 μC / g or less as measured by a suction method is preferable in terms of its flying efficiency.

However, when the toner having such a low charge amount is fly-developed, the toner does not fly faithfully along the electric field, and the sharpness of the image becomes insufficient.

Further, in the flying phenomenon caused by the DC electric field, the toner does not fly unless it becomes equal to or higher than the electric field at which the toner starts to fly in the development area, that is, the threshold electric field.

The threshold electric field is a value that depends on the amount of charge of each toner, van der Waals force, and the like, and has a large variation. I can't get it.

In addition, since the toner having a low charge has a weak electrostatic high-speed force, there is a problem that the toner scatters from the toner carrier and contaminates the inside of the apparatus.

The present invention has been made in view of the above points,
The purpose is to superimpose and develop toner images of two or more colors on the electrostatic latent image carrier, and to develop the first and second and subsequent colors of the developing bias, the toner charge amount, or the toner particle shape, the charge amount,
An object of the present invention is to provide an image forming apparatus which solves the above-mentioned problem by optimally combining a toner carrier.

(Means for Solving the Problems) In order to solve the above-described problems, the present invention sequentially develops latent images on an electrostatic latent image carrier with toners of different colors and transfers the latent images to a transfer material at one time. In the image forming apparatus in which a multicolor image is obtained by using a two-component magnetic brush in which a carrier and a toner are mixed, a developing device for the first color is used, and the developing device for the second and subsequent colors is a one-component developing device. In the case of the non-contact developing method using a thin layer of non-magnetic toner, the absolute value of the charge per unit mass by the blow-off method of the toner used in the developing means of the first color is 10 μC / g or more, and the second and subsequent colors are used. The amount of charge per unit mass of the toner layer used in the developing means by the suction method is in the range of 5 to 20 μC / g, and the toner used in the developing means for the second and subsequent colors has the same polarity as the latent image and has a negative charge. Pulse applied when Voltage portion on the range type is 0 to-600V of bias and -600
A voltage portion below the range of -2000V, wherein the time of the lower voltage portion in one cycle is 50% or less, preferably approximately 30%.
%, The frequency is in the range of 500 to 5000 Hz,
The ratio v / f of the moving speed v of the electrostatic latent image to the bias frequency f is 0.5
In the following, when the toner has a positive charge, the bias type is symmetric with respect to the ground potential.

Further, according to the present invention, in order to solve the above-mentioned problem, a latent image on an electrostatic latent image carrier is sequentially developed with toners of different colors, and transferred to a transfer material at a time to obtain a multicolor image. In the above-described image forming apparatus, the toner used for the developing means of the first color is spherical particles, and the electrostatic latent image is formed during the development of the second and subsequent colors per unit mass by the suction method of the toner of the first color. The absolute value of the charge amount is 20 μC / g or more,
When the developing means for the second and subsequent colors is a non-contact developing method using a thin layer of one-component non-magnetic toner, the toner used for the developing means for the second and subsequent colors is irregular shaped particles, Charge per unit mass by suction method at 5
~ 20μC / g, a roller for holding the irregular toner used in the developing means for the second and subsequent colors in multiple layers on a roller and transporting it to the developing area, and a plurality of rollers having different characteristics of the surface of the roller. At least one of the portions has a charge holding function, and a roller configured to hold the toner by an electric field formed between the different portions is used.

(Operation) According to the present invention, when a toner image of two or more colors is superimposed and developed on an electrostatic latent image carrier, the first color developing means contacts with a two-component magnetic brush in which a carrier and a toner are mixed. When the developing means for the second and subsequent colors is a non-contact developing method using a thin layer of one-component non-magnetic toner,
The absolute value of the charge per unit mass of the toner used in the first color developing means by the blow-off method is 10 μC / g or more, and the charge per unit mass by the suction method of the toner layers used in the second and subsequent color developing means is 5 μC / g. And the type of the pulse bias applied when the toner used for the developing means for the second and subsequent colors has the same polarity as the latent image and has a negative charge is in the range of 0 to -600 V. It consists of a voltage part and a voltage part below the range of -600 to -2000 V, and the time of the lower part of the voltage in one cycle is 50% or less, preferably about 30%, and the frequency is 500 to 5000 Hz. And the ratio v / f of the moving speed v of the electrostatic latent image to the bias frequency f.
Is 0.5 or less, and when the toner has a positive charge, the bias type is symmetric with respect to the ground potential. Therefore, the optimal combination of the developing bias for the first and second colors and the toner charge amount is Becomes

Further, according to the present invention, when a toner image of two or more colors is superimposed and developed on the electrostatic latent image carrier, the toner used for the developing means of the first color is a spherical particle, and when developing the second and subsequent colors, The absolute value of the amount of charge per unit mass of the toner of the first color forming the electrostatic latent image by the suction method is 20 μC / g or more, and the developing means of the second and subsequent colors is a non-magnetic toner of one component. When a non-contact developing method using a thin layer is used,
The toner used in the developing means for the second and subsequent colors is an irregular particle, and the amount of charge per unit mass by suction on the toner carrier is in the range of 5 to 20 μC / g. A roller for holding the fixed toner in a multilayer on a roller and transporting the toner to a development area, wherein at least one of a plurality of portions having different characteristics of the roller surface has a charge holding function, and Since a roller configured to hold the toner by an electric field formed therebetween is used, the developing bias for the first and second colors and the toner particle shape, charge amount, and toner carrier are optimized. It becomes a combination.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

However, the configuration and operation of the range that can be clearly recalled from the description of the present specification, and the above and other objects and novel features of the present invention are omitted from illustration and disclosure in order to avoid complication of description. Or simplify it.

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

In FIG. 1, first, the surface of the drum-shaped photoconductor 1 is charged by the first charger 2.

Next, an electrostatic latent image is formed on the photoconductor 1 by the first exposure unit 3, and a first toner image is formed by the first developing unit 4.

As the first developing means 1, a contact developing method using magnetic or non-magnetic toner using a magnetic brush of a two-component developer in which charging of the toner is reliably performed by friction with the carrier is used.

Next, the photoreceptor 1 is recharged from above the first color toner image by the second charger 5, and the potential state of the portion where the first exposure has been performed is made equal to that of the surroundings.

Then, a second electrostatic latent image is formed on the photoconductor 1 by the second exposure unit 6.

At this time, by not exposing the portion where the first color toner is adhered, it is possible to prevent the second color toner and the first color toner from overlapping on the photoreceptor 1 to make the color turbid. .

Next, the second electrostatic latent image is developed by the second developing means 7.

As the second developing means 7, a non-magnetic toner which is easy to color is suitable, and a one-component non-contact developing method which is particularly advantageous for miniaturization and cost reduction is used.

Through the above process, a two-color image or a multi-color image of two or more colors is formed on the photoreceptor 1, and the multi-color image is transferred by the transfer charger 9 onto the transfer material 8 (recording material) on the transport path at one time. Is done.

The multicolor toner image transferred to the transfer material 8 is
After being fixed on the transfer material 8 by 10, it is discharged as a completed copy image.

On the other hand, the untransferred toner remaining on the photoreceptor 1 is scraped off from the photoreceptor 1 by the cleaning unit 11 so as not to hinder the next image formation.

Next, a non-contact developing method for the first color, the second color and the subsequent colors will be described in detail.

FIG. 2 is a schematic view of a developing device using a non-magnetic one-component toner used in this developing method.

In FIG. 2, a toner 26 of a color different from the first color is supplied into the hopper 25, and the toner 26 is stirred by the agitator 24.

Then, the toner 26 transferred to the supply member 22 is frictionally charged with the developing roller 21 and adheres to the developing roller 21.

The toner 26 attached to the developing roller 21 is transported to the developing area by the toner layer forming member 23 as a uniform toner layer.

The toner layer and the photoreceptor 1 face each other without contact, and are moved at substantially the same speed.

At this time, it is necessary to develop the first color toner image formed on the photoconductor 1 without disturbing it.
The distance between the photoconductor 1 and the photoconductor 1 is 0.05 to 0.5 mm, preferably 0.1 to 0.5 mm.
A range of ~ 0.2 mm is suitable.

At the time of this development, a development bias is applied by the power supply 27.

Here, when a negatively chargeable organic photoconductor is used as the electrostatic latent image carrier, the potential of the toner image portion of the first color is −700 to −900 V, and the potential of the latent image of the second color is , -1
The background potential is about -800V, and the background potential is about -800V.

Further, the developing bias at this time is such that the toner of the first color does not fly back into the developing device of the second color and is mixed, and the toner of the non-magnetic toner layer is satisfactorily transferred to the latent image potential portion of the second color. Must be a value to fly.

The following Table 1 shows that when the developing interval between the developing roller 21 of the developing device and the photoconductor 1 is 0.15 mm,
This is a result of examining the presence or absence of reverse flight of the first color toner by the developing bias applied to the developing roller 21 on which the color toner layer is formed.

In Table 1 above, the results of ○ indicate no color mixing, Δ indicates slight color mixing, and × indicates color mixing.

As is apparent from this result, if the latent image of the first color is formed by the toner charged sufficiently by friction with the carrier, a pulse bias having a portion of -600 V or less is applied as the developing bias of the second color. No color mixing occurs.

The charge amount of the first color toner in Table 1 indicates a value obtained by measuring the charge amount when the toner attached to the carrier is blown off.

FIG. 3 shows how the development γ curve changes depending on the charge amount of the toner layer when a DC bias of −800 V is applied as a developing bias when the non-magnetic toner layer is subjected to flight development. Indicated.

The amount of charge of the toner layer on the roller 21 is a value measured by a suction method, and is approximately 10 g in a Faraday gauge of about 30 g.
The amount of charge is measured by suctioning about g of toner.

In FIG. 3, a curve A represents a charge amount per unit mass (Q /
M) is the result when a toner of −3 μC / g was used, and the image density was sufficient but the sharpness of the line portion was insufficient.

Curve B shows that the charge per unit mass (Q / M) is -12.
As a result of using μC / g toner, the image density is insufficient.

Therefore, if the first color toner is prevented from flying back to the second color developing device by the DC electric field, a good image cannot be obtained as the second color image.

Therefore, a developing bias in which a direct current is superimposed on an alternating current is used as the developing bias of the second color.

For example, VP-P to 800V, 1000Hz frequency, -50
The use of a developing bias superimposed with a direct current of 0 V can substantially prevent the reverse flight of the toner of the first color and fly the toner layer having a charge per unit mass (Q / M) of -12 μC / g. Can be.

However, the development γ curve at this time is as shown by curve A in FIG.

This indicates that the non-magnetic toner layer does not fly with a normal sine wave alternating current according to the intensity of the electric field, and a good image cannot be obtained.

Therefore, the following DC bias pulse bias is used for non-contact development of the second and subsequent colors.

That is, the type of the pulse bias is made up of a voltage portion above the range of 0 to -600 V and a voltage portion below the range of -600 to -2000 V, and the time of the lower voltage portion in one cycle is 50%. Below, it is preferably about 30%, and the frequency is
The frequency is in the range of 500 to 5000 Hz, preferably about 800 to 1500 Hz. Here, if there is a portion of 0 V or more, the reverse flight of the toner of the first color cannot be prevented, and if there is a portion of -2000 V or less, there is a risk of discharge between the photoconductor 1 and the toner.

Further, if the frequency is in the range of 500 Hz to 5000 Hz, the mirror image force and van der Waals force that restrain the non-magnetic toner on the developing roller 21 are reduced, and the charge amount per unit mass (Q /
A toner layer having M) in the range of -5 to -20 µC / g can be used for flight development.

Further, the ratio of the moving speed v of the electrostatic latent image carrier to the frequency f,
By setting v / f to 0.5 or less, cycle unevenness can be prevented.

If the time of the lower voltage portion in one cycle of the applied pulse bias is 50% or less, preferably approximately 30%, the developing γ curve at this time is as shown by curve B in FIG. That is, the nonmagnetic toner layer flies in accordance with the intensity of the electric field, so that an image with high fidelity to the latent image can be obtained.

Further, since the charge amount per unit mass (Q / M) of the toner layer used at this time was −20 μC / g, an image with high definition was obtained.

Here, when a toner and a photoreceptor having a positive charge are used, if the above-described pulse bias type is used symmetrically with respect to the ground potential, the same effect as described above can be obtained.

Further, the charge amount per unit mass (Q / Q) of the first color toner and the second and subsequent color toners on the electrostatic latent image carrier by the suction method.
M) is approximately the same in the range of −20 to −30 μC / g, so that there is no difference in toner in the transfer rate to the transfer material, and a good multicolor image can be obtained.

As a more specific embodiment of the present invention, a drum-shaped organic photoreceptor is used as an electrostatic latent image carrier, and black development of the first color is performed by two-component magnetic brush development.

The charge amount of the black toner is −18 μC / g as measured by a blow-off method.

Then, the photoconductor on which the black toner image is formed is recharged, a second electrostatic latent image is formed by the second exposure unit, and the second color development is performed.

At this time, the photoconductor potential at the portion where the black toner adheres is -900 V, the background portion is -800 V, and the exposed portion is -100 V. The linear speed between the photoconductor and the toner carrying roller is 120 mm / sec.

In addition, the non-magnetic toner layer used for the development of the second color has Q /
M is -15 μC / g, M / A on the toner carrying roller is 1.2 mg / c
m ² , the gap between the toner carrying roller and the photoconductor is 0.16 mm
And

Further, the type of the applied pulse bias is -400 V, 0.5 m
It consists of a part between sec and a part between -1000V for 0.25 msec.

 The frequency is approximately 1330Hz.

According to the present invention, under the above-described conditions, the reverse flight of the toner of the first color is prevented, and a good color image of the second color is obtained.

Next, another embodiment of the present invention will be described in detail with reference to the drawings.

Since the image forming apparatus of this embodiment has substantially the same configuration as the image forming apparatus of the above embodiment, the configuration will be described with reference to FIGS. 1 and 2.

In this embodiment, first, in FIG. 1, the surface of the drum-shaped photoconductor 1 is charged by the first charger 2.

Next, an electrostatic latent image is formed on the photoconductor 1 by the first exposure unit 3, and a first toner image is formed by the first developing unit 4.

Since the first developing means 1 often develops a character image with black toner, a method with good image resolution is required.

Therefore, by using a spherical magnetic or non-magnetic toner for the first developing means 1, it is possible to reduce blurring or blurring of fine lines of an image.

Next, the photoreceptor 1 is recharged from above the first color toner image by the second charger 5, and the potential state of the portion where the first exposure has been performed is made equal to or higher than the surroundings.

Then, a second electrostatic latent image is formed on the photoconductor 1 by the second exposure unit 6.

At this time, by not exposing the portion where the first color toner is adhered, it is possible to prevent the second color toner and the first color toner from overlapping on the photoreceptor 1 to make the color turbid. .

Next, the second electrostatic latent image is developed by the second developing means 7.

As the second developing means 7, a non-magnetic toner which is easy to color is suitable, and a one-component non-contact developing method which is particularly advantageous for miniaturization and cost reduction is used.

Then, an amorphous toner having excellent fluidity and good flight efficiency is used.

Through the above process, a two-color image or a multi-color image of two or more colors is sequentially formed on the photoreceptor 1, and the multi-color image is once transferred onto the transfer material 8 (recording material) on the transport path by the transfer charger 9. Transfer to

The multicolor toner image transferred to the transfer material 8 is
After being fixed on the transfer material 8 by 10, it is discharged as a completed copy image.

On the other hand, the untransferred toner remaining on the photoreceptor 1 is scraped off from the photoreceptor 1 by the cleaning unit 11 so as not to hinder the next image formation.

Next, a non-contact developing method for the first color, the second color and the subsequent colors will be described in detail.

In FIG. 2, a toner 26 of a color different from the first color is supplied into the hopper 25, and the toner 26 is stirred by the agitator 24.

Then, the toner 26 transferred to the supply member 22 is frictionally charged with the developing roller 21 and adheres to the developing roller 21.

The toner 26 attached to the developing roller 21 is transported to the developing area by the toner layer forming member 23 as a uniform toner layer.

At this time, the toner adhesion amount on the developing roller 21 is preferably such that a sufficient image density can be obtained even when the developing roller 21 and the photoconductor 1 move in a non-contact manner and move at a substantially constant speed.

Here, if the developing roller 21 and the photosensitive member 1 have a speed difference,
The phenomenon of "toner trailing edge" occurs and the density of the solid portion becomes non-uniform, which is a problem in a color image.

For this reason, the mass per unit area (M /
A), forming a multi-layered toner layer in the range of 0.8 to 1.2 mg / cm ² and the absolute value of the charge per unit mass (Q / M) of 5 to 20 μC / g maintains the image quality. Needed above.

As such a toner holding roller, a roller obtained by subjecting an aluminum elemental surface to sandblasting is known.

However, when multi-layered toner is conveyed by mechanical irregularities like this roller, the toner on the surface scatters and contaminates the inside of the apparatus, or the irregularities are clogged with toner. There is a problem with durability.

Therefore, in this embodiment, the toner holding roller is configured as follows.

That is, the toner holding roller used in this embodiment is
Among the parts having different characteristics on the roller surface,
At least one of the rollers is configured to retain toner by applying an electric charge to a portion having a charge retaining function, so that an electric field is formed between the portions having different characteristics.

As a specific example, as shown in FIGS. 5 and 6, a lattice-shaped or iris-shaped knurled groove is formed on the aluminum surface of the roller surface, and a dielectric material is embedded in the groove. Is done.

By using the roller configured as described above as a toner holding roller, it is possible to easily form a multilayer thin layer of amorphous toner having excellent fluidity and a high flying rate, and to provide the toner for development.

At this time, it is necessary to develop the first color toner image formed on the photoconductor 1 without disturbing it.
The distance between the photoconductor 1 and the photoconductor 1 is 0.05 to 0.5 mm, preferably 0.1 to 0.5 mm.
A range of ~ 0.2 mm is suitable.

At the time of this development, a development bias is applied by the power supply 27.

Here, when a negatively chargeable organic photoconductor is used as the electrostatic latent image carrier, the potential of the toner image portion of the first color is −700 to −900 V, and the potential of the latent image of the second color is , -1
The background potential is about -800V, and the background potential is about -800V.

Further, the developing bias at this time is such that the toner of the first color does not fly back into the developing device of the second color and is mixed, and the toner of the non-magnetic toner layer is satisfactorily transferred to the latent image potential portion of the second color. Must be a value to fly.

The following Table-2 shows that when the developing interval between the developing roller 21 and the photoreceptor 1 of this developing device is 0.15 mm,
This is a result of examining the presence or absence of reverse flight of the first color toner by the developing bias applied to the developing roller 21 on which the color toner layer is formed.

In Table 2, however, the results of ○ indicate no color mixing, Δ indicates slight color mixing, and × indicates color mixing.

As is evident from the results, if the latent image of the first color is formed by a spherical toner having a Q / M of −20 μC / g or more by the suction method using the photoreceptor-shaped recharged toner, the development of the second color is performed. Even if a pulse bias having a portion of 600 V or less is applied as a bias, reverse flight is prevented and color mixing of toner does not occur.

This suction method measures Q / M by measuring the amount of charge by suctioning about 10 mg of toner into a
It is what was asked.

FIG. 7 shows how the development γ curve changes depending on the amount of charge of the toner layer on the roller when a DC bias of −800 V is applied as a developing bias when the non-magnetic toner layer is subjected to flight development. showed that.

In FIG. 7, a curve C represents a charge amount per unit mass (Q /
M) is the result when the toner layer of -3 μC / g was used, and the image density was sufficient but the sharpness of the line portion was insufficient.

Curve D shows that the charge per unit mass (Q / M) is -12.
As a result of using μC / g toner, the image density is insufficient.

Therefore, if the first color toner is prevented from flying back to the second color developing device by the DC electric field, a good image cannot be obtained as the second color image.

Therefore, a developing bias in which a direct current is superimposed on an alternating current is used as the developing bias of the second color.

For example, 800V or less VP-P, 1000Hz frequency,
The use of a developing bias on which a direct current of -500 V is superimposed can substantially prevent the toner of the first color from flying backward and fly the toner layer having a charge per unit mass (Q / M) of -15 μC / g. be able to.

However, the development γ curve at this time is as shown by a curve D in FIG.

This indicates that the non-magnetic toner layer does not fly with a normal sine wave alternating current according to the intensity of the electric field, and a good image cannot be obtained.

Therefore, the following DC bias pulse bias is used for non-contact development of the second and subsequent colors.

That is, the type of the pulse bias is made up of a voltage portion above the range of 0 to -600 V and a voltage portion below the range of -600 to -2000 V, and the time of the high voltage portion in one cycle is 50 hours. %, Preferably about 30%, and a frequency in the range of 500 to 5000 Hz, preferably 800 to 1500 Hz.
Set to about Hz.

Here, if there is a portion of 0 V or more, the reverse flight of the toner of the first color cannot be prevented, and if there is a portion of -2000 V or less, there is a risk of discharging between the photoconductor 1 and the portion.

Further, if the frequency is in the range of 500 Hz to 5000 Hz, the mirror image force and van der Waals force that restrain the non-magnetic toner on the developing roller 21 are reduced, and the charge amount per unit mass (Q /
A toner layer having M) in the range of -5 to -20 µC / g can be used for flight development.

Further, the ratio of the moving speed v of the electrostatic latent image carrier to the frequency f,
By setting v / f to 0.5 or less, cycle unevenness of the applied pulse bias can be prevented.

When a pulse bias that satisfies the above conditions is applied, the non-magnetic toner layer flies in accordance with the strength of the electric field, as shown by curve D in FIG. An image with high fidelity can be obtained.

Further, the charge amount per unit mass (Q / M) of the toner layer used at this time was −15 μC / g, so that an image with high definition was obtained.

Here, when a toner and a photoreceptor having a positive charge are used, if the above-described pulse bias type is used symmetrically with respect to the ground potential, the same effect as described above can be obtained.

Further, the charge amount per unit mass (Q / Q) of the first color toner and the second and subsequent color toners on the electrostatic latent image carrier by the suction method.
M) is approximately the same in the range of −20 to −30 μC / g, so that there is no difference in toner in the transfer rate to the transfer material, and a good multicolor image can be obtained.

As a specific image forming apparatus of this embodiment, a drum-shaped organic photoconductor is used as an electrostatic latent image carrier, and black development of the first color is performed by contact development using a two-component magnetic brush.

As the black toner, a spherical toner having a volume average particle diameter of 7 μm prepared by a polymerization method is used.

Then, the photoreceptor on which the black toner image is formed is recharged so that the second exposure unit can form a second electrostatic latent image.

The charge amount Q / M of the black toner on the photoreceptor after this recharging
Is −25 μC / g.

At this time, the potential of the photoconductor at the portion where the black toner adheres is -900 V, the background portion is -800 V, and the exposed portion is -100 V.

On the other hand, the color development of the second color is performed using an irregular toner having a volume average particle diameter of 10 μm prepared by a pulverization method.

At this time, the linear velocity between the photoconductor and the toner carrying roller is:
Equally 120 mm / sec.

The roller carrying the nonmagnetic one-component toner layer is configured as follows.

In other words, this roller has a horizontal groove of 0.
After applying a silicon-based resin to each groove knurl of 1 mm and depth of 0.2 mm cut at a pitch of 0.3 mm and an angle of 45 degrees, the surface of this roller is cut to expose the aluminum surface It is formed.

Therefore, according to this roller, a positive charge is accumulated in the resin portion due to friction with the toner supply member, so that a fringe electric field is formed between the roller and the aluminum surface, and the negatively charged toner is removed. It can be transported in multiple layers.

The nonmagnetic toner layer used for the development of the second color is Q / M
Is -15 μC / g, M / A on the toner carrying roller is 1.2 mg / cm
² , the gap between the toner carrying roller and the photoconductor is 0.1
6 mm.

The type of applied pulse bias is -400V, 0.5m
It consists of a part between sec and a part between -1000V for 0.25 msec.

 Further, the frequency is approximately 1330 Hz.

According to the present embodiment, by setting the above conditions, it is possible to prevent the toner of the first color from flying backward and obtain a good color image of the second color.

As described above, in the case where a multicolor toner image is formed on a photoconductor and transferred to a transfer material at one time, the toner used for development of the first color is frictionally charged with the carrier,
Since the Q / M measured by the blow-off method is -10 μC / g or more, the development of the second and subsequent colors is non-contact development using a thin layer of non-magnetic toner, and even if a DC bias pulse bias is applied as a development bias. And a good multicolor image without color mixture can be obtained.

Further, in this apparatus, since the Q / M of the toner layer used for non-contact development is in the range of 5 to 20 μC / g in absolute value, a clear image can be obtained despite non-contact development, and the transfer of multicolor toner is performed. The conditions can be the same.

When the toner used for the development of the second and subsequent colors has the same polarity as the latent image and has a negative charge, when the applied pulse bias is applied to a voltage portion in the range of 0 to -600 V,
It consists of a voltage part below the range of 0 to -2000V, and the frequency is
Since it is in the range of 500 to 5000 Hz, it is possible to prevent the reverse flight of the toner of the first color and to use a non-magnetic toner layer having a Q / M in the range of -5 to -20 μC / g for the flight development. .

Further, in this device, the time of the lower voltage portion in one cycle is 50% or less, preferably approximately 30%, so that the toner can fly according to the intensity of the electric field, and a good image can be obtained. can get.

Further, in this apparatus, when a toner having a positive charge is used, the same effect as described above can be obtained if the bias type is used symmetrically with respect to the ground potential.

On the other hand, in the case where a multicolor toner image is formed on a photoconductor and transferred to a transfer material at one time, the toner used for the first color development is spherical particles, Absolute value of Q / M of toner by suction method on body is 20μC
/ g or more, it is possible to obtain a first-color image with high definition and good resolution.

In this apparatus, since the development of the second and subsequent colors is non-contact development using a thin layer of non-magnetic toner, even if a DC bias pulse bias is applied as the development bias, color mixing of the toner does not occur, and the development over time does not occur. A good multicolor image without any color turbidity can be obtained.

Further, in this apparatus, the toner used for non-contact development is irregular particles having good flying efficiency, and the Q / M on the toner carrier is in the range of 5 to 20 μC / g in absolute value. Thus, a clear and smooth image can be obtained in spite of non-contact development, and the transfer conditions of the multicolor toner can be made the same.

Also, the surface of the toner carrying roller used for the development of the second and subsequent colors has at least one of a plurality of portions having a charge holding function, and holds the toner charged by an electric field formed between the different portions. Because of this, it is possible to form a multilayer thin layer with amorphous toner with high fluidity and high flying efficiency, and to obtain sufficient image density even when the linear speed between the photoconductor and the toner carrying roller is almost equal. This makes it possible to obtain a good color image with uniform density without "toner deviation near the toner".

Further, when the toner used for the development of the second and subsequent colors has the same polarity as the latent image and has a negative charge, the applied pulse bias is changed to a low voltage portion in the range of 0 to -600 V,
It consists of a high voltage part in the range of 0 to -2000 V, and has a frequency of 50
Since it is in the range of 0 to 5000 Hz, it is possible to prevent reverse flight of the toner of the first color and to use a non-magnetic toner layer having a Q / M in the range of -5 to -20 μC / g for flight development. .

Also, in this device, the time of the high voltage portion in one cycle is 50% or less, preferably approximately 30%.
The flying of the toner according to the intensity of the electric field becomes possible, and a good multicolor image can be obtained.

Further, in this apparatus, when a toner having a positive charge is used, the same effect as described above can be obtained if the bias type is used symmetrically with respect to the ground potential.

(Effects of the Invention) According to the present invention, when a toner image of two or more colors is superimposed and developed on an electrostatic latent image carrier, the developing bias of the first color and the second and subsequent colors, the toner charge amount, or the toner Since the optimal combination of particle shape, charge amount, and toner carrier,
A good and clear multicolor image without toner color mixture can be obtained, and the transfer conditions of the multicolor toner can be made the same.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of an image forming apparatus showing an embodiment of the present invention, FIG. 2 is a schematic sectional view of a developing device in the image forming apparatus, and FIG. 3 has a nonmagnetic toner layer in the embodiment. FIG. 4 is a graph showing the change in the development γ curve depending on the charge amount. FIG. 4 is a graph showing the change in the development γ curve depending on the charge amount of the non-magnetic toner layer when a direct current is superimposed on an alternating current as a developing bias for the second color. FIG. 5 is a perspective view of a toner holding roller according to another embodiment of the present invention, FIG. 6 is an enlarged view of the surface of the toner holding roller, and FIG. 7 is a non-magnetic toner according to the other embodiment. FIG. 8 is a diagram showing a change in the development γ curve depending on the charge amount of the layer. FIG. 8 is a diagram showing the charge of the non-magnetic toner layer when a direct current is superimposed on an alternating current as a developing bias of the second color in the other embodiment. FIG. 4 is a diagram showing a change in a development γ curve depending on an amount. DESCRIPTION OF SYMBOLS 1 ... Photoconductor, 2 ... 1st charger, 3 ... 1st exposure means, 4 ... 1st developing means, 5 ... 2nd charger, 6
... Second exposure means, 7 second developing means, 8 transfer material, 9 transfer charger, 10 fixing device, 11 cleaning unit, 21 developing roller, 22 ... toner supply member,
23 ... toner layer forming member, 24 ... agitator, 25 ... hopper, 26 ... toner, 27 ... power supply for applying a developing bias.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G03G 15/06-15/09 101 G03G 15/01-15/01 117

Claims (3)

(57) [Claims] 1. An image forming apparatus in which a latent image on an electrostatic latent image carrier is sequentially developed with toners of different colors and transferred to a transfer material at a time to obtain a multicolor image. When the developing means is a contact developing method using a two-component magnetic brush in which a carrier and a toner are mixed, and the developing means for the second and subsequent colors is a non-contact developing method using a thin layer of a one-component non-magnetic toner, The absolute value of the charge per unit mass of the toner used in the first color developing means by the blow-off method is 10 μC / g or more, and the charge per unit mass by the suction method of the toner layers used in the second and subsequent color developing means. Is 5
20 μ / g, and the type of pulse bias applied when the toner used for the developing means for the second and subsequent colors has the same polarity as the latent image and has a negative charge is in the range of 0 to −600 V. Consisting of a voltage part and a voltage part below the range of -600 to -2000V, the time of the lower voltage part in one cycle is 50%
Hereinafter, it is preferably approximately 30%, and the frequency is 500 to 5
When the toner has a positive charge, the ratio of the moving speed v of the electrostatic latent image to the bias frequency f is 0.5 or less, and when the toner has a positive charge, the bias type is symmetric with respect to the ground potential. An image forming apparatus characterized in that: 2. An image forming apparatus in which a latent image on an electrostatic latent image carrier is sequentially developed with toners of different colors and transferred to a transfer material at a time to obtain a multicolor image. The toner used in the developing means is spherical particles, and the absolute value of the charge per unit mass of the toner of the first color, which forms an electrostatic latent image during the development of the second and subsequent colors, is 20 μC /
g or more, and when the developing means for the second and subsequent colors is a non-contact developing method using a thin layer of one-component non-magnetic toner, the toner used for the developing means for the second and subsequent colors is irregular particles. The charge amount per unit mass by the suction method on the toner carrier is in the range of 5 to 20 μC / G, and the amorphous toner used for the developing means for the second and subsequent colors is held in multiple layers on a roller to form a developing area. Wherein at least one of a plurality of portions having different characteristics of the roller surface has a charge holding function, and holds the toner with an electric field formed between the different portions. An image forming apparatus using the roller configured as described above. 3. A low-voltage portion in which the type of pulse bias applied when the toner used in the developing means for the second and subsequent colors has the same polarity as the latent image and has a negative charge is 0 to -600V. It consists of a high voltage portion in the range of -600 to -2000V, the time of the high voltage portion in one cycle is 50% or less, preferably approximately 30% or less, and the frequency is 500 to 5000Hz.
When the ratio v / f of the moving speed v of the electrostatic latent image to the bias frequency f is 0.5 or less and the toner has a positive charge, the bias type is symmetric with respect to the ground potential. The image forming apparatus according to claim 2, wherein: