JPH0777858A - Image forming device - Google Patents

Abstract

PURPOSE:To provide an image forming device capable of obtaining an image having high quality and no roughness by using an intermediate transfer medium, and also capable of obtaining a highly definite color image whose color reproducibility is stabilized and not causing toner scattering, etc., even in the case of forming a full color image. CONSTITUTION:The main scanning beam diameter of a laser beam is 30 to 45mum, and also, the volume average particle diameter of the toner used is 3 to 8mum. Furthermore, provided that (a) denotes the amount of the toner lying on a transfer material, (t1) and (t2) denote each transfer efficiency of 1st and 2nd, A denotes the amount of the toner lying on a photoreceptive drum 3 and M denotes the volume average particle diameter of the toner used, the relation represented by the equation is satisfied.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention forms a latent image on an image bearing member (photosensitive medium) by means of latent image forming means using laser light,
This latent image is made into a visible image (toner image) by the developing means, this toner image is transferred to the intermediate transfer medium, and then the toner image on the intermediate transfer medium is recorded on the transfer material which is the final image carrier. The present invention relates to an image forming apparatus and is applied to a copying machine, a printer and the like.

[0002]

2. Description of the Related Art FIG. 1 shows an example of an electrophotographic color printer using an intermediate transfer medium. According to this example, the rotary developing device 1 including the electrophotographic photosensitive drum 3 as a photosensitive medium that rotates in the direction of the arrow and the charger 4 and the developing devices 1M, 1C, 1Y, and 1BK around the photosensitive drum 3 is provided. An image forming unit including an intermediate transfer belt 10 as an intermediate transfer medium, a cleaning unit 12, and a laser beam scanner arranged above the photosensitive drum 3 in the drawing is provided.

The sequence of the entire color printer will be briefly described by taking the case of the full color mode as an example.
First, the photosensitive drum 3 is uniformly charged by the charger 4. Next, image exposure is performed by a laser beam E modulated by a magenta image signal of a document (not shown), an electrostatic latent image is formed on the photosensitive drum 3, and then magenta development that is previously set at a developing position. Development is performed by the container 1M.

On the other hand, the intermediate transfer belt 10 is rotating in the direction of the arrow in the figure in synchronization with the photosensitive drum 3, and the visible image, that is, the toner image developed by the magenta developing unit 1M is biased at the transfer portion. Transferred onto the intermediate transfer belt 10 by the transferred transfer roller 9. Intermediate transfer belt 10
Continues to rotate in preparation for the transfer of the next color (cyan in FIG. 1).

On the other hand, the photosensitive drum 3 is cleaned by the cleaning means 12, is charged again by the charger 4, and is exposed as described above by the next cyan image signal.

During this time, the developing device 1 rotates and the cyan developing device 1C is fixed at a predetermined developing position to perform predetermined cyan development.

Subsequently, the above steps are carried out for yellow and black respectively, and when the transfer of four colors is completed, the toner images of four colors on the intermediate transfer belt are image-formed by the paper feed cassette. The transfer roller 11 collectively transfers the transferred material onto the transferred transfer material in accordance with the timing.
The transfer roller 11 is brought into pressure contact with the intermediate transfer belt 10 according to the timing of sheet feeding, and transfers a four-color toner image on the intermediate transfer belt 10 onto a transfer material by applying a bias. The transfer material after the transfer is sent to the fixing device (heat pressure roller fixing device) 17 by the conveyor belt 16 and the series of full-color printing sequence is completed to form a required full-color print image.

In the color printer having such a structure, the toner images formed on the photosensitive drum 3 are transferred onto the intermediate transfer belt 10 so as to be sequentially superposed, and then the toner images on the intermediate transfer belt 10 are transferred. Since it is configured to transfer the material to the material all at once, for example, in the case of a multiple transfer type printer in which the transfer material is held on the transfer drum and the toner images on the photosensitive drum are transferred so as to be sequentially superimposed to obtain an image. The problem of stable holding of the transfer material on the transfer drum that has occurred is solved, and cardboard such as postcards can be used as the transfer material.

[0009]

However, it was very difficult to obtain a high-quality and clear image with the above-mentioned conventional color printer. This is the intermediate transfer belt 1
This is due to the use of an intermediate transfer medium such as 0.

That is, in the transfer using the intermediate transfer medium, the magenta, cyan, yellow, and black toner images formed on the photosensitive drum, that is, the photosensitive member are sequentially superposed on the intermediate transfer medium and then collectively transferred. The toner image on the photoconductor is required to undergo the first transfer onto the intermediate transfer medium and the second transfer from the intermediate transfer medium to the transfer material. The image deteriorates.

This is because when developing a latent image on the photosensitive member 3, the toner adheres by acting on a confining electric field called a latent image.
This is because the transfer is performed with a non-restraining electric field, so that the toner image is blurred every time the transfer is repeated.

In order to solve this problem, it has been necessary to optimize the amount of blurring from the time of latent image formation on the photosensitive member.

Further, since the transfer is performed twice, the image is formed by one transfer. For example, as compared with the multiple transfer system,
Therefore, it is necessary to form a toner image in such a manner that a large amount of toner is attached to the photosensitive drum 3 by an extra amount.

Therefore, it is an object of the present invention to obtain a high quality image free from rubbing using an intermediate transfer medium, and to obtain a high definition image with no toner scattering even when forming a full color image. An object of the present invention is to provide an image forming apparatus capable of obtaining a color image with stable color reproducibility.

[0015]

The above object can be achieved by an image forming apparatus according to the present invention. In summary, the present invention is
An electrostatic latent image is formed on a photosensitive medium by a latent image forming means using a laser light source and having a control means for controlling the lighting time of the laser light per pixel according to a recorded image signal. Is developed with a developer containing toner to form a toner image, then the toner image formed on the photosensitive medium is transferred to an intermediate transfer medium (first transfer), and then this intermediate transfer medium is transferred. In an image forming apparatus for transferring the above image to a transfer material (second transfer), the spot diameter in the scanning direction of the laser light is set to spot size (1 / e ² ) <pixel size 0.7, and the toner volume average is When the particle diameter is M and the toner particle diameter is r, 90% by volume or more of the toner is included in the range of (1/2) M <r <(3/2) M in the toner volume distribution. Within the range of 0 <r <2M, 99% by volume or less of the toner Further, the main scanning beam diameter of the laser light is 30 μm to 45 μm, the volume average particle diameter of the toner is 3 μm to 8 μm, preferably 5 μm to 6 μm, and on the transfer material. Amount of toner is a, transfer efficiencies of the first transfer and the second transfer are t _1, t _2.
And the amount of toner on the photosensitive drum is A,

[0016]

[Equation 2] The image forming apparatus has the following relationship.

Preferably, the toner to be used has an average charge amount of 10 μC / g or more and 30 μC / g or less, and the maximum amount of toner to be loaded on the photosensitive drum at one time is 1.5 mg / cm ^2. It is said that

Further, according to the present invention, toner images formed on a photosensitive medium using yellow, magenta, cyan and black toners are held on the intermediate transfer medium and are collectively transferred to the transfer material. As a result, a full-color image can be obtained.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An image forming apparatus according to the present invention will be described below in more detail with reference to the drawings. In the embodiment described below, the present invention is applied to, but is not limited to, an electrophotographic color printer using the intermediate transfer medium described with reference to FIG.

In this embodiment, the image forming apparatus of the present invention is
A rotary developing device 1 including an electrophotographic photosensitive drum 3 as a photosensitive medium that rotates in the arrow direction, and a charging device 4 and developing devices 1M, 1C, 1Y, and 1BK around the photosensitive drum 3.
An image forming unit including an intermediate transfer belt 10 as an intermediate transfer medium, a cleaning unit 12, and a laser beam scanner as an exposing unit disposed above the photosensitive drum 3 in the drawing is provided.

The sequence of the entire color printer will be briefly described by taking the case of the full color mode as an example.
First, the photosensitive drum 3 is uniformly charged by the charger 4. Next, image exposure is performed by a laser beam E modulated by a magenta image signal of a document (not shown), an electrostatic latent image is formed on the photosensitive drum 3, and then magenta development that is previously set at a developing position. Development is performed by the container 1M.

On the other hand, the intermediate transfer belt 10 rotates in the direction of the arrow in the figure in synchronization with the photosensitive drum 3, and the visible image, that is, the toner image developed by the magenta developing device 1M is biased at the transfer portion. Transferred onto the intermediate transfer belt 10 by the transferred transfer roller 9. Intermediate transfer belt 10
Continues to rotate in preparation for the transfer of the next color (cyan in FIG. 1).

On the other hand, the photosensitive drum 3 is cleaned by the cleaning means 12, is charged again by the charger 4, and is exposed as described above by the next cyan image signal.

During this time, the developing device 1 rotates and the cyan developing device 1C is fixed at a predetermined developing position to perform predetermined cyan development.

Subsequently, the above steps are carried out for yellow and black respectively, and when the transfer of four colors is completed, the toner images of four colors on the intermediate transfer belt are image-formed by the paper feed cassette. The transfer roller 11 collectively transfers the transferred material onto the transferred transfer material in accordance with the timing.
The transfer roller 11 is brought into pressure contact with the intermediate transfer belt 10 according to the timing of sheet feeding, and transfers a four-color toner image on the intermediate transfer belt 10 onto a transfer material by applying a bias. The transfer material after the transfer is sent to the fixing device (heat pressure roller fixing device) 17 by the conveyor belt 16 and the series of full-color printing sequence is completed to form a required full-color print image.

In the present embodiment, the laser beam scanner forming the exposure means has a semiconductor laser section 102 and a polygon mirror 10 rotating at a high speed, as shown in FIG.
5, the f-θ lens 106, and the semiconductor laser unit 102 receives a time-series digital pixel signal that is arithmetically output by an electronic calculator or the like of the image reading apparatus, and performs PWM modulation in accordance with the signal. The generated laser beam is oscillated to expose the surface of the photosensitive drum 3.

More specifically, referring to FIG.
Solid-state laser device 1 as a laser light source that is a light source unit
Reference numeral 02 is connected to a laser driver 500, which is a light emission signal generator for sending a light emission signal for generating a laser beam, and the light intensity is decreased according to the light emission signal of the laser driver.
The laser light flux emitted from the solid-state laser element 102 is made into substantially parallel light by the collimator lens system 103. The collimator lens system 103 includes a focus adjusting means 10 described later.
4 allows movement by a predetermined amount in the direction of arrow A, which is the optical axis direction of the laser light.

Polygon mirror, that is, rotary polygon mirror 105
Rotates in the direction of arrow B at a constant speed, reflects parallel light emitted from the collimator lens system 103, and scans in the direction of arrow C, which is a predetermined direction. An f-θ lens group 106 (106a, 106a) provided in front of the rotary polygon mirror 105.
b and 106c) form an image of the laser light beam deflected by the polygon mirror 105 on the surface to be scanned, that is, a predetermined position on the photosensitive drum 3, and make the scanning speed constant on the surface to be scanned.

The laser beam L is guided through a reflecting mirror 107 onto a CCD (solid-state image pickup device) 108 as a detecting means, and is scanned on a photosensitive drum 3 as a surface to be scanned. The CCD 108 is configured by arranging a large number of photodetectors in the direction of arrow C at positions substantially optically equivalent to the surface of the photosensitive drum 3 and the light source section. The CCD 108 is connected to the control unit 100 that controls the laser driver 500 and the focus adjusting means 104.

An image processing section 111 is connected to the laser driver 500 and the control section 100.

In the above structure, when forming a desired image, first, the image output signal P is input from the image processing section 111 to the control section 100, and the laser driver 500 is used.
The image signal S is input to and the solid-state laser element 102 is turned on and off at a predetermined timing.

Laser light emitted from the solid-state laser element 102 is converted into substantially parallel light by the collimator lens system 103, and is further rotated in the direction of arrow B.
5 is scanned in the direction of arrow C, and an image is formed in a spot shape on the photosensitive drum 3 by the f-θ lens group 106. An exposure distribution for one scanning of the image is formed on the surface of the photosensitive drum 3 by the scanning of the laser beam L as described above, and the photosensitive drum 3 is rotated by a predetermined amount for each scanning to generate an image signal S on the drum 3. A latent image having an exposure distribution corresponding to is formed and recorded as a visible image on a transfer material by a well-known electrophotographic process.

The image output signal P is output from the image processing unit 111 prior to the image signal S, and the output is finished after the output of the image signal S is finished. Further, the control unit 100 stops its operation while the image output signal P is input from the image processing unit 111. Therefore, the pixel size and the contrast can be kept constant during the image forming operation.

Next, the operation of the focus position adjusting means 104 for the laser beam L will be described.

When the image output signal P is deenergized, the control unit 1
The operation signal is input to the laser driver 500 from 00,
From the laser driver 500, a rectangular wave that turns on and off at regular intervals as shown in FIG. 16A is generated for a predetermined period, and the laser element 102 blinks in response to this test signal. The laser light modulated by the test signal is reflected by the reflecting mirror 107, and projected and scanned on the CCD 108 arranged at a position optically equivalent to the photosensitive drum 3.

The control unit 100 resets the accumulated charges of each photoelectric conversion element of the CCD 108 before the laser beam L scans the CCD 108, and scans one line of the photoelectric conversion element of the CCD 108 by the beam modulated by the test signal. After the electric charge is accumulated in, the electric charge is read out as an electric signal.

As shown in FIG. 17, the exposure distribution on the surface of the CCD 108 shows a strong and weak distribution shape according to the spot diameter of the laser beam L. Therefore, the output of each pixel of the CCD 108 has a distribution as shown in FIG. 16B, and the signal is sent to the control unit 100. In the control unit 100,
The maximum value of the output of the CCD 108 is θmax, and the minimum value is θm.
In, the contrast V is

[0038]

[Equation 3] It is calculated and measured by the formula.

In this case, the contrast V becomes larger as the spot diameter in the scanning direction becomes smaller. Therefore, when the preset value Vo is compared with V calculated by the equation (1), V is not equal to the predetermined value Vo. The control unit 100 sends a drive signal to the focus adjustment unit 104 to move the collimator lens system 103 in the direction of arrow A by a predetermined amount. Then, the contrast V is measured at each position where the collimator lens system 103 is moved, and the collimator lens system 103 is fixed at a position where this value is equal to Vo. The scanning spot diameter of L can be minimized.

FIG. 3 is a circuit diagram of the PWM circuit, and FIG. 4 is a PWM.
6 is a timing chart showing the operation of the circuit.

In FIG. 3, the PWM circuit includes TTL latch circuits 401 and TTL for latching an 8-bit image signal.
A level converter 402 for converting a logic level into a high-speed ECL logic level, an ECL D / A converter 403, an ECL comparator 404 for generating a PWM signal, and a level converter 40 for converting an ECL logic level into a TTL logic level.
5, a clock signal 2 having twice the frequency of the pixel clock signal f
clock oscillator 406 for generating f, clock signal 2f
A triangular wave generator 407 that generates a substantially ideal triangular wave signal in synchronism with the clock signal, and 1/2 that divides the clock signal 2f by 1/2.
It has a frequency divider 408. Moreover, in order to operate the circuit at high speed, ECL logic circuits are arranged everywhere.

The operation of this structure will be described with reference to FIG.

The signal (a) shows the clock signal 2f, and the signal (b) shows the pixel clock signal f having a double period thereof, which is related to the pixel number as shown in the figure. Triangle wave generator 407
Internally, in order to keep the duty ratio of the triangular wave signal at 50%, the triangular wave signal (c) is generated after dividing the clock signal 2f by 1/2. Further, the triangular wave signal (c) is converted into the ECL level (0 to -1V) to become the triangular wave signal (d).

On the other hand, the pixel signals are OOH (white) to FFH.
It changes in 256 gradation levels up to (black). The symbol H is hexadecimal. The image signal (e) represents the ECL voltage level obtained by D / A converting some image signal values. For example, the first pixel is a black pixel level FFH,
The second pixel shows the voltage of the intermediate tone level of 80H, the third pixel shows the intermediate tone level of 40H, and the fourth pixel shows the intermediate tone level of 20H. The comparator 404 compares the triangular wave signal (d) with the image signal (e) to obtain PWM such as pulse widths T, t ₂ , t ₃ and t ₄ according to the pixel density to be formed.
Generate a signal. And this PWM signal is 0V or 5V
Is converted to the TTL level of and becomes the PWM signal (e),
Input to the laser drive circuit 500.

In the circuit of FIG. 3, the latch circuit 401
A lookup table (not shown) is provided in the front stage of the. This look-up table is for performing γ correction of image data, and is a memory in which the data of the result of γ correction is stored, and the memory is accessed by using an image signal of 8 bits per pixel as address data to obtain a desired γ The image signal of the corrected data is output. Normally, one specific γ correction table is used in one screen, but a plurality of types of γ correction tables can be switched and used in one screen as needed. That is, for example, three types of tables are sequentially and repeatedly used for each line scanning by the beam, and the γ correction in the sub-scanning direction can be changed for each line to perform gradation correction.

The look-up table is a so-called standing γ table when the toner density is low so that it is not affected by the density unique to each color, for example, four colors of yellow, magenta, cyan, and black. When the density is set and the density is high, a γ table having the opposite characteristic is set and provided for each forming color. The turbidity of the color of each color toner is corrected before the look-up table. A non-linear color masking circuit, for example a secondary color masking circuit, can be provided for this purpose.

The above-mentioned PWM method is characterized in that the area gradation of dots is performed for each pixel and halftone can be expressed at the same time without reducing the density of pixels to be recorded.

However, even in this PWM method, it was found that the exposure distribution on the surface to be scanned 3 is affected by the spot diameter of the laser and changes as shown in FIG. 5, as shown in FIG.

This has a recording pixel density of 400 dpi (pixel size 63.5 μm) and a laser spot diameter of 70 μm.
For (main scanning Gaussian distribution spot 1 / e ² ), 1/4 pixel equivalent per pixel, 1/2 pixel equivalent time, and the exposure distribution on the scanned surface when the laser drive time is pulse width modulated Show.

For example, even if the laser beam is turned ON / OFF with a 50% pulse width, the exposure distribution on the surface of the photosensitive drum is as shown in FIG. 5B, and the contrast at the maximum and minimum values of the exposure amount is However, only about 30% can be obtained, and gradation reproduction due to a change in dot area of each pixel obtained by the subsequent development process cannot be performed stably.

In order to stabilize the dot area gradation expression by pulse width modulation, various experiments by the present inventors have revealed that, for example, a laser beam with a pulse width of 50%
It was found to be possible if about 80% or more of the contrast in the exposure distribution on the drum surface was obtained when N / OFF was performed.

Therefore, the spot diameter on the drum surface is set to the spot diameter (Gaussian distribution spot 1
/ E ² ) <pixel size × 0.7.

FIG. 6 shows that when the recording density is set to 400 dpi (pixel size 63.5 μm), the laser beam spot diameter is 50 μm, which is 0.8 times the pixel size.
(A), 0.7 times 42 μm (B), 0.55 times 35
The exposure distribution on the drum surface when μm (C) is shown.

From FIG. 6, ON / OF with a pulse width of 50%
The exposure distribution contrast when F is about 60 each
% (A), about 80% (B), about 90% (C), and it became possible by setting the laser beam spot diameter (1 / e ² ) to 0.7 times the pixel size or less.

Therefore, in each spot diameter, when the driving pulse width of the laser is changed from 10% to 100%, the change in the dot shape obtained by the subsequent developing process is shown in FIG. 7A. (B). At this time, the spot diameter in the sub-scanning direction is 1.1 times as large as the conventional pixel size in order to make the exposure distribution in the sub-scanning direction uniform.
It was set to 0 μm.

In general, a well-known developing system using a powder of about 8 μm, as shown in FIG. 8, is such that rapid development is performed from a certain potential with respect to the surface potential of the photosensitive member.
It has the characteristic of having a threshold value.

Therefore, in the case where the contrast of the exposure distribution when the laser is turned ON / OFF in one pixel is low as shown in FIG. 6A, the surface potential of the photosensitive drum is also shown in FIG.
According to the exposure distribution of (A), the surface potential is changed as a whole with respect to the driving pulse width of the laser. Therefore, according to the V-D characteristic of the developing system of FIG. From the point where the threshold value is exceeded, the image is rapidly developed. As a result, as shown in FIG. 7A, the developed dot diameter is also rapidly increased to a large dot shape from a certain gradation number. Will tend to The graph (A) in FIG. 9 shows the change in the drive pulse width within one pixel at this time and the image density after development obtained at that time. It can be seen that it is strongly affected by the VD characteristics of the developing system.

On the other hand, in the example of the present invention in which the laser spot diameter is set to 0.55 times the pixel size and the contrast of the exposure distribution when the laser is turned ON / OFF in one pixel is increased to at least 80% or more, The latent image formed on the drum also has an ON / OFF pattern with high potential contrast according to this exposure distribution. Therefore, even if developed with a developing system having a certain threshold characteristic, the peak of the exposure distribution immediately rises from the short region of the drive pulse, and since it exceeds the development threshold value, it is stable as dots. Developed (Figure 7)
(B)). As a result, it is possible to stably reproduce the change in dot diameter from a region where the ON / OFF ratio of the drive pulse is small,
It is possible to reproduce a stable area gradation during development.

The graph (B) in FIG. 9 shows the relationship between the image density and the laser driving pulse when the spot size according to the present invention is used. As is clear from the figure,
It can be seen that stable area gradation is possible with respect to the pulse width without being affected by the developing system.

Here, the image deterioration when the intermediate transfer medium used in the present invention undergoes the first transfer and the second transfer will be described.

FIG. 10 shows a line-shaped toner image (A) formed on a photoconductor on a intermediate transfer medium (B) after the first transfer and on a transfer material (C) after the second transfer. Is a schematic representation.

Assuming that the line width on the photosensitive member is a, the line width b after the first transfer is: b = k · ak = 1.1 to 1.3 Similarly, the line width c after the second transfer is , C = k · b = k ² · a k = 1.1 to 1.3.

From this, in order to obtain a line width equivalent to that of an apparatus which does not use an intermediate transfer medium, if it is attempted to use only the laser beam diameter, the beam diameter reduced by 1 / k from the conventional beam diameter is used. Is good.

However, even if the density reproducibility is obtained by the development, the roughness in the highlight portion due to the scattering after transfer and fixing may not be erased by the developer.

As a result of numerous experiments, it was found that the above problems can be solved by adjusting the particle size distribution of the toner contained in the developer and / or the volume average particle size of the toner.

Specifically, according to the present invention, when the volume average particle diameter of the toner is M and the particle diameter of the toner particle is r, (1/2) M <r <(3/2) The range of M (ie M
A toner containing 90% by volume or more of toner particles in the range (± (1/2) M) and 99% by volume or more of the toner particles in the range of 0 <r <2M (that is, the range of M ± M) is an image. Used in forming method.

Further, according to the present invention, the volume average particle size is 1
Less than 2 μm, preferably 9 μm or less, more preferably 8 μm
Toner having a particle size of not more than μm is used in the image forming method.

In the present invention, the volume distribution and volume average particle diameter of the toner are those measured by the following measuring method, for example.

As a measuring device, a Coulter counter T
A-II type (manufactured by Coulter, Inc.)
Interface that outputs volume average distribution (made by Nikkaki)
And CX-i personal computer (Canon) are connected, and the electrolyte is 1% Na using primary sodium chloride.
An aqueous Cl solution is prepared.

As the measuring method, the electrolytic aqueous solution 100 to 1 is used.
0.1 to 5 ml of a surfactant (preferably alkylbenzene sulfonate) as a dispersant is added to 50 ml, and 0.5 to 50 mg of a measurement sample is further added.

The electrolytic solution in which the sample was suspended was treated with an ultrasonic disperser for about 1 to 3 minutes. The Coulter Counter TA
According to the type II, a particle size distribution of particles of 2 to 40 μm is measured using a 100 μm aperture as an aperture to obtain a volume distribution.

The volume average particle size of the sample can be obtained from the obtained volume distribution.

If the toner has a volume distribution exceeding the above range, the effect cannot be sufficiently exhibited even if the particle size is changed.

When the number of particles having a large particle size increases, toner particles having a large particle size, which causes scattering in transfer, exist even if the average particle size is decreased. It is difficult to reduce the rustiness in the field. On the other hand, when the number of toner particles having a small particle size increases, the amount of toner that adheres to the magnetic particles and does not separate increases, and the magnetic particles cannot efficiently give triboelectric charge to the toner, which increases scattering and fogging from the developing device. Further, a toner having a small particle diameter is apt to cause fusion, and is fused around the magnetic particles (carrier), so that fogging and scattering due to carrier deterioration also increase.

From the above points, it is necessary to use those having a sharp particle size as shown in FIG. 11 as the volume distribution.

In the image forming apparatus shown in FIG. 1, the spot diameter of the laser beam is 70 μm in the sub-scanning direction.
m, an elliptical spot having a beam diameter of 42 μm in the scanning direction was used to write on the photosensitive drum in the same manner as in the following example, and then volume average particles of the toner when development, transfer, and heat-pressure roller fixing were performed. FIG. 12 shows a graph showing the relationship between the diameter and the diameter of the minimum reproduced dot of the image after fixing.

Here, as a developing condition, an AC bias and a DC bias are superposed for each particle diameter of the toner, or a DC bias is applied.
Only the bias was used, and the type of magnetic particles (carrier), the sleeve-drum, and the sleeve-blade were changed, but the diameter of the smallest reproduced dot was hardly affected. This is explained as follows.

That is, in the method of writing a latent image by controlling the emission time of the laser beam, the density gradation of development can be obtained by decreasing the spot diameter. However, after a process of transferring and fixing a plurality of times to obtain a full-color image, toner having a large particle diameter scatters, resulting in a broad dot diameter, but toner having a small particle diameter does not scatter. No image distortion. Toner with a small particle size is a thin layer on the paper after transfer, and the attraction force with the paper is also large. Therefore, even if the toner image is exposed to the transfer electric field that is transferred to the intermediate transfer belt a plurality of times and once to the transfer material, it is considered that the toner image does not easily scatter.

The reproducibility of a full-color image in a portion where the image density is low significantly changes the impression of the image. When trying to obtain a high-quality image having gradation with a full-color image, the impression of the image is remarkably different depending on whether or not dots around 25 μm are faithfully reproduced.

Considering the thickening of the toner image in two times of transfer when the above-mentioned intermediate transfer medium is used, on the photosensitive member,
A toner image with a width of about 16 μm must be formed.

25 μm / k ₁ k ₂ , when the maximum weight is
With k ₁ = 1.3 and k ₂ = 1.3, from FIG. 12, the volume average particle diameter of the toner is 6 μm or less that satisfies the above content, but 5 μm or less is less than the reproduced dot diameter. This is because there is little effect and it can be said that the range of 5 μm to 6 μm is a practical range.

Although not described in detail, it is the current situation that a toner having a particle size of 4 μm or less cannot be mass-produced for practical use due to a problem in the toner manufacturing method by the pulverization method.

According to another manufacturing method, for example, a polymerization method, it is possible to manufacture a toner having a particle diameter of up to about 1 μm or even smaller. Therefore, if these are put into practical use, the image formation using them does not depart from the scope of the present invention.

The main scanning diameter of the laser beam of the present invention is applied in the range of 30 μm to 45 μm.
It is preferably 35 μm or less.

That is, the toner volume average particle diameter is 5 μm to 6 μm.
m, the main scanning diameter of the laser beam is 30 to 35 μm,
It can be said that, as a practical configuration, the effect of the present invention is the largest.

Therefore, when the recording density is set to 400 dpi, the laser beam spot diameter in the scanning direction is 42 μm or less, preferably the volume average particle diameter is 9 μm or less, more preferably 8 μm or less. As shown in, the dots around 50 μm are faithfully reproduced, and the scattering in the transfer is extremely reduced.
The gradation of full-color and low image density, which could not be obtained by the conventional method, is sufficient, and a high-definition image with less blurring and blurring can be obtained.

Due to the above-mentioned effects, especially when the toner having the volume average particle diameter of 8 μm or less is used, the dots of 50 μm or less are faithfully reproduced, and the image is less likely to be disturbed even when exposed to the transfer electric field a plurality of times. . In particular, this tendency has a good influence on the roughness and reproducibility in the portion where the image density is low.

For example, when the toner used in the present invention has a volume average particle size of 6 μm, the toner has a volume distribution of more than 3 μm and less than 9 μm.
Contains toner particles of volume% or more and is larger than 0 and 1
It is important to contain 99% by volume or more of toner particles in the range of less than 2 μm.

In order to produce a toner having a sharp particle size distribution according to the present invention, for example, a predetermined toner material is melt-kneaded, the kneaded product is cooled and then pulverized, and the pulverized powder is precisely classified to obtain a predetermined toner. A method of preparing a toner having a particle size distribution and / or a volume average particle size can be mentioned.

As a method for precisely classifying the pulverized powder, it is classified by a classifying means such as a fixed wall type air classifier, and the obtained classified powder is further divided into a multi-division classifying device utilizing the Coanda effect, for example, Japanese A method of preparing a toner having a predetermined particle size distribution and / or a volume average particle size by simultaneously precisely removing fine powder and coarse powder by a multi-division classifying means such as an elbow jet classifier manufactured by Iron Mining Co., Ltd. . In the present invention, the toner means colored resin particles (binder resin, colorant,
(Including other additives as necessary) itself, and colored resin particles to which an external additive such as a hydrophobic colloidal silica fine powder is externally added.

Examples of the binder resin used in the toner include styrene-based polymers such as styrene-acrylic acid ester resins or styrene-methacrylic acid ester resins or polyester resins. In particular, when considering the color mixture when fixing color toner,

[0092]

[Chemical 1] (Wherein R is an ethylene or propylene group, x and y are positive integers of 1 or more, and the average value of x + y is 2 to 10.) or a bisphenol derivative represented by the formula or a substituted product thereof. And a carboxylic acid component such as a divalent or higher carboxylic acid or an acid anhydride thereof, or a lower alkyl ester thereof (eg, fumaric acid, maleic acid, maleic anhydride, phthalic acid, terephthalic acid). The copolycondensed polyester resin is more preferable because it has sharp melting characteristics.

Coloring agents suitable for the purposes of the present invention include the following pigments or dyes. In the present invention, the light resistance of CI Disperse Y164, CISolvent Y77 and CISo is poor.
Colorants such as lvent Y93 are not recommended.

Examples of the dye include C.I. I. Direct Red 1, C.I. I. Direct Red 4, C.I. I. Acid Red 1, C.I. I. Basic Red 1, C.I. I.
Modant Red 30, C.I. I. Direct Blue 1,
C. I. Direct Blue 2, C.I. I. Acid Blue 9, C.I. I. Acid Blue 15, C.I. I. Basic Blue 3, C.I. I. Basic Blue 5, C.I. I. There is Modant Blue 7.

Examples of pigments include Naphthol Yellow S, Hansa Yellow G, Permanent Yellow NCG, Permanent Orange GTR, Pyrazolone Orange, Benzidine Orange G, Permanent Red 4R, Watching Red Calcium Salt, Brilliant Carmine 3B, First Violet B, Methyl Violet. There are rake, phthalocyanine blue, fast sky blue, and indanthrene blue BC.

In particular, disazo yellow, insoluble azo and copper phthalocyanine are preferable as the pigment, and basic dye or oil-soluble dye is preferable as the dye.

Particularly preferably, C.I. I. Pigment Yellow 17, C.I. I. Pigment Yellow 15, C.I. I. Pigment Yellow 13, C.I. I. Pigment Yellow 1
4, C.I. I. Pigment Yellow 12, C.I. I. Pigment Red 5, C.I. I. Pigment Red 3, C.I. I.
Pigment Red 2, C.I. I. Pigment Red 6,
C. I. Pigment Red 7, C.I. I. Pigment Blue 15, C.I. I. Pigment Blue 16 or a copper phthalocyanine-based pigment which is a Ba salt in which 2 to 3 carboxybenzamidomethyl groups are substituted on the phthalocyanine skeleton.

As the dye, C.I. I. Solvent Red 4
9, C.I. I. Solvent Red 52, C.I. I. Solvent Red 109, C.I. I. Basic Red 12, C.I.
I. Basic Red 1, C.I. I. Basic red 3
b.

The content of the colorant is 12 parts by weight or less, and preferably 0.5 to 7 parts by weight, based on 100 parts by weight of the binder resin for the yellow toner which sensitively reflects the transparency of the OHP film. Parts by weight are desirable. When it is 12 parts by weight or less, the reproducibility of green, red and flesh color, which are mixed colors of yellow, is poor.

With respect to magenta toner and cyan toner, 15 parts by weight or less relative to 100 parts by weight of the binder resin,
It is more preferably 0.1 to 9 parts by weight or less.

In the case of a black toner which is used in combination with two or more colorants, the addition of 20 parts by weight or more of the total amount of colorants tends to cause spent on the carrier, and moreover, many colorants are exposed on the toner surface. As a result, the fusion of the toner on the photosensitive drum increases, and the fixing property becomes unstable. Therefore,
In the black toner, the amount of the colorant is preferably 3 to 15 parts by weight with respect to 100 parts by weight of the binder resin.

A preferable combination of colorants for forming a black toner is a combination of a disazo yellow pigment, a monoazo red pigment and a copper phthalocyanine blue pigment. The mixing ratio of each pigment is such that the ratio of yellow pigment, red pigment and blue pigment is 1: 1.5 to 2.5 :.
0.5 to 1.5 is preferable.

When the toner used in the present invention is negatively chargeable, it is also preferable to blend a charge control agent in order to stabilize the negatively chargeable characteristics. At that time, a colorless or light-colored negatively chargeable control agent that does not affect the color tone of the toner is preferable.
Examples of the negatively charged control agent include metal complexes of alkyl-substituted salicylic acid, for example, organic attributional complexes such as chromium or zinc complexes of ditertiarybutylsalicylic acid. When the negative charge control agent is blended with the toner, it is added in an amount of 0.1 to 10 parts by weight, preferably 0.5 to 8 parts by weight, based on 100 parts by weight of the binder resin.

In the present invention, when the developer used is a two-component developer, the carrier is preferably magnetic particles.
The magnetic particles have a particle size of 30 to 100 μm, preferably 40.
˜80 μm, electric resistance value is 10 ⁷ Ωcm or more, preferably 10 ⁸ Ω or more, more preferably 10 ⁹ to 10 ¹² Ω.
The ferrite particles (maximum magnetization 60 em
Resin coating on u / g) can be preferably used.

The resistance value of magnetic particles, for example, ferrite particles or resin-coated ferrite particles, was measured by using a sandwich type cell having a measuring electrode area of 4 cm ² and an electrode gap of 0.4 cm. An applied voltage E (V / cm) between both electrodes is applied under pressure,
It is a value obtained by measuring the resistance value of the magnetic particles from the current flowing in the circuit.

The present invention will be further described below with reference to Examples.

FIG. 13 is an enlarged sectional view of the vicinity of one developing device of the rotary developing device 1 used in the laser beam printer shown in FIG. 1, and the developing device is arranged at the developing position facing the photosensitive drum 3. Has been done.

The developing device has a developing sleeve 22 which is located close to the photosensitive drum 3. The developing sleeve 22
Is made of a non-magnetic material such as aluminum or SUS316. The developing sleeve 22 is a developing container 36.
The right substantially semi-peripheral surface is projected into the container 36 in a laterally long opening formed in the lower left wall of the container in the longitudinal direction of the container, and the left substantially semi-peripheral surface is exposed to the outside of the container so as to be rotatably supported by the arrow, b
Driven to rotate.

In the developing sleeve 22, a fixed permanent magnet (magnet) 23 as a fixed magnetic field generating means positioned in the illustrated position and orientation is arranged. The magnet 23 includes an N-pole magnetic pole 23a, an S-pole magnetic pole 23b, an N-pole magnetic pole 23c,
It has four magnetic poles, that is, an S-pole magnetic pole 23d. The magnet 23 may be an electromagnet instead of the permanent magnet.

The base is fixed to the side wall of the container on the upper edge side of the developer supply device in which the developing sleeve 22 is disposed, and the tip end side is projected to the inside of the container 36 from the upper edge position of the opening so that the upper edge of the opening becomes longer. Along the side, a non-magnetic blade 24 as a developer regulating member is arranged. The blade 24 is, for example, SUS3
16 is bent so that the cross section has a V shape. Further, a magnetic particle limiting member 26 is provided in which the upper surface is in contact with the lower surface side of the non-magnetic blade 24 and the front end surface is the developer guide surface 261. The portion formed by the non-magnetic blade 24, the magnetic particle limiting member 26, and the like is the restriction portion.

The developer is magnetic particles 27 and non-magnetic toner 37.
Contains. A seal member 40 is provided to seal the toner accumulated in the lower portion of the developing container 36. The seal member 40 has elasticity, is bent in the rotation direction of the sleeve 22, and elastically presses the surface side of the sleeve 22. The seal member 40 has an end portion on the downstream side in the sleeve rotation direction in the contact area with the sleeve so as to allow the developer to enter the inside of the container.

In the developing container, a floating toner generated in the developing process is further applied with a voltage of the same polarity as that of the toner to adhere to the photosensitive drum side to prevent scattering.
0, and a toner replenishing roller 60 that operates according to an output obtained by a toner concentration detection sensor (not shown) is arranged. As the sensor, for example, a developer volume detection method, a piezoelectric element, an inductance change detection element, an antenna method using an alternating bias, or a method for detecting optical density can be used. The non-magnetic toner 37 is replenished by stopping the rotation of the roller 60. The fresh developer supplied with the toner 37 is mixed and stirred while being conveyed by the screw 61. Therefore, tribo is applied to the replenished toner during this conveyance. The cutout plate 63 is notched at both ends in the longitudinal direction of the developing device, and the fresh developer conveyed by the screw 61 is transferred to the screw 62 at this portion.

The S pole 23d is a carrier pole. The collected developer after the development is collected in the container, and the developer in the container is conveyed to the regulation unit. In the vicinity of the S pole 23d, the fresh developer conveyed by the screw 62 provided close to the sleeve and the recovered developer after development are exchanged.

The carrying screw 64 is for equalizing the amount of the developer in the developing sleeve axial direction, and the developer carried on the sleeve in accordance with the rotation of the sleeve is carried in the sleeve axial direction by the screw 64. A part of the developer layer on which the "convex" is formed in the axial direction on the sleeve is pushed back by reversing the direction in which the developer is conveyed on the sleeve through the space M in FIG. The screw 64 conveys the developer in the opposite direction to the screw 62.

The construction of such a developing device is also effective when magnetic particles and non-magnetic or weakly magnetic toner are mixed in the developer container.

The distance d ₂ between the end of the non-magnetic blade 24 and the surface of the developing sleeve 22 is 50 to 900 μm, preferably 1
It is 50 to 800 μm. If this distance is less than 50 μm, magnetic particles are clogged between them and the developer layer is liable to be uneven, and the developer necessary for good development cannot be applied, resulting in only a developed image with a thin density and unevenness. It tends not to be obtained. The distance d ₂ is preferably 400 μm or more in order to prevent the blade from being clogged by unnecessary particles such as toner aggregates and dust mixed in the developer. If it is larger than 900 μm, the amount of the developer coated on the developing sleeve 22 increases and the predetermined developer thickness cannot be regulated, the magnetic particles adhere to the photosensitive drum more, the developer circulates, and the developer limiting member 26. Due to this, the regulation of development is weakened, toner tribo is insufficient, and fog tends to occur.

The angle θ ₁ in the figure is -5 ° to 35 °, preferably 0 ° to 25 °. When θ ₁ <−5 °, the developer thin layer formed by the magnetic force, the mirror image force, and / or the cohesive force acting on the developer tends to be sparse and uneven.
When θ> 35 °, the non-magnetic blade increases the amount of developer applied, making it difficult to obtain a predetermined amount of developer.

In this magnetic particle layer, the sleeve 22 has an arrow b.
Even if the sleeve 22 is rotationally driven in the direction, the movement becomes slower as the distance from the sleeve surface increases due to the balance between the restraining force based on the magnetic force and the gravity and the conveying force in the moving direction of the sleeve 22. Of course, some of them fall under the influence of gravity.

Therefore, by appropriately selecting the positions where the magnetic poles 23a and 23d are arranged and the fluidity and magnetic characteristics of the magnetic particles 27, the magnetic particle layer is transported toward the magnetic pole 23a toward the sleeve to form a moving layer. Due to the movement of the magnetic particles, the magnetic particles and the toner are conveyed to the developing area with the rotation of the sleeve 22, and are provided for the development.

In this example, A using ferrite particles was used.
Although the C bias plus DC bias development system is used, DC bias development using normal iron powder may be used.

Even when the developing device having the structure shown in FIG. 13 was used and the development was carried out with the photosensitive drum and the counter in the rotating direction of the developing sleeve, the same effect was obtained with the toner having an average particle diameter of 8 μm or less.

Particle size distribution and particles satisfying the conditions of the present invention
Use a toner having a diameter, for example, a volume average particle diameter of 6 μm
The end of the non-magnetic blade 24 and the surface of the developing sleeve 22.
Distance d ₂ Is 600 μm, and the surface of the developing sleeve 22
The distance between the optical drums 3 was 450 μm.

In the above embodiment, the photosensitive drum 3 is a laminated organic photoconductive (OPC) drum, and is -600V.
Of the charged latent image. Frequency of 17 as bias power supply
Development was performed using a rectangular wave alternating voltage having a peak-to-peak value of 1500 V at 00 Hz and a DC voltage of −300 V superposed thereon.

To write the latent image, the original image is color-separated, and the spot diameter of the laser beam is set to 42 μm in the main scanning direction 1 / e ² using the semiconductor laser as a light source in the order of magenta, cyan, yellow, and black on the photosensitive drum. Scanning direction 1 /
With e ^{2 set} to 70 μm, the emission time is controlled by the PWM control described above, an image of 256 gradations is written at 200 lines / inch, development and transfer are repeated in sequence, and finally fixed to obtain a full-color image. As a result, even a portion with a low image density was faithfully reproduced, and a high-definition and high-quality image free of shakiness was obtained.

On the other hand, when a laser beam spot diameter was 70 μm in the main scanning direction and an image was formed under the same conditions with a toner having a volume average particle diameter of 12 μm, it was compared with a toner having a volume average particle diameter of 6 μm. The reproducibility was poor in the area where the image density was low, and only an image with outstanding roughness was obtained.

As described above, the original image is color-separated, the latent image is formed on the photosensitive drum for each color using the light beam of the laser as the light source, and the toner image of each color visualized by the development using the toner is formed. In a multicolor electrophotographic apparatus that sequentially transfers and transfers a multicolor image onto a transfer member,
The spot size in the scanning direction of the beam spot is the spot size (1 / e ² ) with respect to the recording pixel size in the scanning direction.
<Pixel size x 0.7, a toner having a particle size distribution of 8 μm or less with a sharp particle size distribution is used as a developer, and a light beam is pulse-width modulated with an image signal as a halftone forming method. By using (1), sufficient gradation can be obtained in a portion having a low image density, and (2) the entire image including a portion having a low image density can be greatly reduced, and a high-quality full-color image can be obtained. There is an effect that an image can be obtained.

Here, in the case of using an intermediate transfer medium, the amount of toner a on the transfer material a, the transfer efficiencies t ₁ and t _{2 of} the first transfer and the second transfer, the toner particle size and the toner coverage are shown. Describe the relationship.

According to various experiments, when the image density on the transfer material is required to be 1.5 by using the toner and the development described later, the toner carrying amount is about 0.8 m for the toner having the particle diameter of 8 μm.
It was g / cm ² . In the case of a full-color image, the maximum density needs to be about 2.0. The amount of toner applied at this time was about 1.1 mg / cm ² .

The transfer efficiency of the first transfer and the second transfer was 85 to 95% as measured by the present inventors.

From this, the maximum amount of toner A on the photosensitive drum is set to the maximum value of the transfer efficiency,

[0131]

[Equation 4] It was found that about 1.5 mg / cm ^{2 was} necessary.

Further, when the relationship between the toner amount for reproducing the same density and the toner particle size was examined, it was found that the toner amount required for reproducing the same density is proportional to the volume average particle size for the toner of the same prescription. I understood.

As an example, when a toner having a volume average particle size M = 6 μm is used in comparison with the above-mentioned toner having M ₀ = 8 μm, the toner usage amount used for reproducing the same density is M /
It was proportional to M ₀ .

Therefore, the above equation (2) indicating the amount of toner on the photosensitive drum is

[0135]

[Equation 5] Can be For 6 μm toner, about 1.1
It is mg / cm ² .

Furthermore, the relationship between the amount of tribo and the transfer efficiency was examined for toners having a volume average particle size of 6 μm and 8 μm. FIG. 15 shows this relationship. In each case, the amount of toner on the photosensitive drum was set to the maximum amount described above according to the equation (3), and the tribo of the toner at this time, the transferability, and the image-forming toner were examined.

According to this, it was found that the defect occurred in either of the intermediate transfer medium and the transfer material at 30 μC /
Tribo of g or more, which hardly depended on the toner particle size.

Although the reason for this is not fully understood, it is considered that this is because the tribo value is further changed by changing the toner amount required for maximum density reproduction.

For confirmation, when the toner amount was made the same and the toner tribo was changed, the transfer became more difficult as the particle size became smaller.

On the other hand, in the low tribo example, the larger the particle size is, the more severe the toner image is scattered and deteriorated by transfer.

Further, in the drawing, the toner particle size and the limit in image reproduction described above are shown, and further, in the current state, the area where experimental production of toner is difficult is shown. Overall, regardless of the particle size, it was judged that using toner of about 20 μC / g was a stable tribo in terms of the device configuration.

Specific examples of the present invention will be described below.

Example 1 Polyester resin obtained by condensing 100 parts by weight of propoxylated bisphenol and fumaric acid (weight average molecular weight 15,000, number average molecular weight 3300) Rhodamine pigment ... 3 parts by weight Load Electrostatic control agent (dialkyl-substituted salicy ... 4 parts by weight metal complex of acid)

The above materials are melt-kneaded, the melt-kneaded product is cooled, the cooled product is crushed, classified by a fixed wall type air classifier, and further classified by a multi-division classifier utilizing the Coanda effect,
A negatively chargeable magenta toner having a volume average particle diameter of 6 μm was prepared. The magenta toner obtained is over 3 μm and 9 μm
It had a sharp particle size distribution of 95% by volume in the range of less than 100 μm and substantially 100% by volume in the range of more than 0 μm and less than 12 μm.

100 parts by weight of the magenta toner and 0.4 part by weight of negative triboelectrically-charged hydrophobic colloidal silica were mixed to prepare a magenta toner having silica added thereto. Next, 94 parts by weight of ferrite magnetic particles coated with a styrene-acrylic acid ester-based copolymer and having a weight average particle size of 50 μm (electrical resistance value of 10 ¹⁰ Ωcm) were mixed with 6 parts by weight of the above magenta toner having silica added thereto. Then, a two-component developer for forming a magenta toner image was prepared.

Similarly, using the following colorants, a two-component developer for forming a cyan toner image, a two-component developer for forming a yellow toner image, and a two-component developer for forming a black toner image are prepared. did.

[0147]

[Table 1]

Each two-component type developer was placed in a polyethylene container having a volume of 100 ml, and after vigorous stirring by hand for about 30 times, the triboelectric charge amount of the toner was measured. The value of each color toner was about -30 μc / g. Indicated.

The above two-component type developer was introduced into the developing device of the color image forming apparatus shown in FIG. In this embodiment, in the developing device, the distance d ₂ between the end of the non-magnetic blade 24 and the surface of the developing sleeve 22 is set to 600 μm, and the developing sleeve 2
The distance d ₁ between the two surfaces and the photosensitive drum 3 was 450 μm.

The photosensitive drum 3 is a laminated organic photoconductive (O
PC) drum was used, and the charged latent image potential was -600V.

As a bias power source, a frequency of 1700 Hz,
-30 for rectangular wave alternating voltage with peak-to-peak value 1500V
Development was carried out using a superposed DC voltage of 0V.

To write the latent image, the original image is color-separated, and the spot diameter of the laser beam is 42 μm in the main scanning direction 1 / e ² with the semiconductor laser as a light source on the photosensitive drum in the order of magenta, cyan, yellow, and black. Scanning direction 1 /
With e ^{2 set} to 70 μm, the above-mentioned PWM control is performed to control the light emission time, an image of 256 gradations is written at 200 lines / inch, and reversal development and electrostatic transfer are repeated in order, and finally heat compression is performed. It was fixed by a roller fixing device to obtain a full-color image. Area where image density is low (highlight area)
Was reproduced faithfully, and a high-definition, high-quality image with no shakiness was obtained.

When the full-color image was observed, it was 50
Dots around μm were faithfully reproduced corresponding to the latent image.

Examples 2 to 4 In the same manner as in Example 1, the volume average particle size is 5 μm and 6.8 μm.
m and 8 μm, the toners shown in Table 2 were prepared, and Example 1 was used.
When a full-color image was formed in the same manner as, good results were obtained.

[0155]

[Table 2]

[0156]

[Table 3]

Comparative Example In the same manner as in Example 1, Table 3 having a volume average particle diameter of 12 μm was used.
Toners of respective colors shown in are obtained.

A two-component type developer was prepared in the same manner as in Example 1 and a color image was formed in the same manner as in Example 1. As a result, as compared with the case of Example 1, in a portion where the image density was low, Although it has reproducibility, only an image with a noticeable roughness was obtained.

Further, the above two-component type developer was put in a polyethylene container having a volume of 100 ml, and after vigorous stirring by hand for about 30 times, the triboelectric charge amount of the toner was measured. As a result, each color toner was -16 to -18 μc / Example 1 showing the value of g
It was lower than the case.

Observation of the obtained full-color image revealed that the smallest dot faithfully reproducing the latent image was about 90 μm.
It was m. The dots below that were very scattered.

Example 5 Toners of respective colors shown in Table 4 having a volume average particle diameter of 9 μm were prepared in the same manner as in Example 1, and a two-component type developer was prepared in the same manner as in Example 1.

When a color image was formed in the same manner as in Example 1, a portion with a low image density (highlight portion) was faithfully reproduced although it was slightly inferior to that in Example 1, and high definition and high image quality with less shading were obtained. An image was obtained.

When the full-color image was observed, it was 60 μm.
The dot in front of m is faithfully reproduced corresponding to the latent image.
Dots around m were also reproduced with relative fidelity corresponding to the latent image.

[0164]

[Table 4]

[0165]

The image forming apparatus according to the present invention configured as described above has a main scanning beam diameter of laser light of 30 μm.
A ～45Myuemu, also the volume average particle diameter of the toner to be used 3Myuemu～8myuemu, further the toner bearing amount on the transfer material a, first, the second the transfer efficiency of t _1, t _2, Let A be the amount of toner on the photosensitive drum and M be the volume average particle size of the toner used.

[0166]

[Equation 6] Since it is configured to have a relationship of, it is possible to obtain a high-quality image with no roughness even when using an intermediate transfer medium,
Further, even when a full-color image is formed, it is possible to obtain a color image with high definition and stable color reproducibility without scattering of toner.

[Brief description of drawings]

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

2 is a perspective view of a scanning optical device used in the apparatus of FIG.

FIG. 3 is a timing chart showing a PWM circuit used in the device of FIG. 1 and its operation.

FIG. 4 is a timing chart showing a PWM circuit used in the device of FIG. 1 and its operation.

FIG. 5 is an exposure distribution diagram on a photosensitive medium according to a conventional example.

FIG. 6 is a comparison diagram of an exposure distribution chart on a photosensitive medium according to the present invention and a conventional example.

FIG. 7 is a comparison diagram between a gradation expression according to a dot area change according to the present invention and a conventional example.

FIG. 8 is a graph showing a typical example of VD characteristics of a known developing system.

FIG. 9 is a graph showing the relationship between the pulse width modulation method according to the present invention and the image density.

FIG. 10 is a diagram illustrating transfer and image deterioration in the image forming apparatus according to the present invention.

FIG. 11 is a graph showing a particle size distribution chart of the toner used in the present invention.

FIG. 12 is a graph showing the relationship between the average particle diameter of toner and the minimum reproduced dot diameter.

FIG. 13 is a schematic sectional view of an example of a developing device.

FIG. 14 is a schematic sectional view of another embodiment of the developing device.

FIG. 15 is an explanatory diagram showing an applicable range of toner used in the present invention.

FIG. 16: ON / OFF state of laser light source and CCD
3 is an output distribution diagram of each pixel of FIG.

FIG. 17 is a distribution state diagram of laser spot diameters.

[Explanation of symbols]

3 image carrier (photosensitive drum) 10 intermediate transfer medium (intermediate transfer belt) 1 (M, C, Y, BK) developing device 101 laser drive circuit 102 laser light source 104 polygon mirror

 ─────────────────────────────────────────────────── ─── Continued front page (72) Inventor Jun Koide 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Tatsuo Takeuchi 3-30-2 Shimomaruko, Ota-ku, Tokyo Kya Non non corporation

Claims (3)

[Claims] 1. An electrostatic latent image is formed on a photosensitive medium by a latent image forming means including a laser light source and a control means for controlling a lighting time of a laser light per pixel according to a recorded image signal. Then, this latent image is developed with a developer containing toner to form a toner image, and then the toner image formed on the photosensitive medium is transferred to an intermediate transfer medium (first transfer). In an image forming apparatus for transferring an image on the intermediate transfer medium to a transfer material (second transfer), the spot diameter of the laser beam in the scanning direction is set to spot size (1 / e ² ) <pixel size 0.7, When the volume average particle diameter of the toner is M and the particle diameter of the toner particle is r, in the toner volume distribution, (1 /
2) 90% by volume of toner in the range of M <r <(3/2) M
In the range of 0 <r <2M, 99% by volume or more of the toner is included, and the main scanning beam diameter of the laser light is 30 μm to 45 μm.
And the volume average particle diameter of the toner is 3 μm to 8 μm,
Further, when the toner amount on the transfer material is a, the transfer efficiencies of the first transfer and the second transfer are t _{1 and} t _2, and the toner amount on the photosensitive drum is A, An image forming apparatus having the following relationship. 2. The average charge amount of the toner used is 10 μC.
/ G or more and 30 μC / g or less, 1 on the photosensitive drum
Maximum toner loading amount is 1.5 mg for each toner image formation
The image forming apparatus according to claim 1, wherein the image forming apparatus has a thickness of 1 / cm ² . 3. The toner used is yellow, magenta, cyan, and black, and the toner image formed on the photosensitive medium is held on the intermediate transfer medium and transferred to the transfer material all at once to obtain a full-color image. The image forming apparatus according to claim 1, wherein an image is obtained.