JP3416310B2 - Image forming device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic type or electrostatic recording type image forming apparatus such as a copying machine or a printer, and is characterized by a developing device.

[0002]

2. Description of the Related Art In an electrophotographic type or electrostatic recording type image forming apparatus, it is general to perform development by making a developing sleeve carrying a developer correspond to an image carrying body carrying an electrostatic image.

A developing bias is applied to the developing sleeve to form a developing electric field between the image carrier and the developing sleeve.

As the developing bias, DC shown in FIG. 2 is used.
A component in which an AC component is superimposed has been used.

Further, the rectangular wave shown in FIG. 2 can obtain high developing efficiency with a small peak-to-peak voltage.

However, the developing bias as shown in FIG. 2 has a drawback that the highlight portion of the image is “gritty”. For the purpose of improving this drawback, for example, FIG.
The applicant has proposed a developing bias in which an AC component is intermittently superposed on a DC component as shown in FIG.

However, the developing bias as shown in FIG. 3 has the following problems.

The developing bias as shown in FIG. 3 (blank pulse bias; hereinafter referred to as BP bias) is more developable than the developing bias as shown in FIG. 2 (hereinafter referred to as rectangular bias). On the other hand, on the other hand, lower contrast (difference between the potential of the electrostatic latent image on the electrostatic latent image carrier and the DC component of the developing bias; hereinafter V _{co nt}
The image density (hereinafter referred to as OD) will appear, and the problem is that unevenness in the potential of the electrostatic latent image appears as unevenness on the image.

In an experiment conducted by the inventors of the present application, γ (= ΔOD / ΔV when the BP bias shown in FIG. 3 is used.
_cont ) is γ when the rectangular bias shown in FIG. 2 is used.
Was 1.8 to 2.3 times (depending on environmental temperature and humidity). That is, the density unevenness that appears with respect to the same potential unevenness is 1.8 to 2.3 times larger in the BP bias shown in FIG. 3 than in the rectangular bias shown in FIG.

Therefore, when the BP bias is used, it is required to suppress the unevenness of the potential of the electrostatic latent image to be smaller than that when the rectangular bias is used.

By the way, the photosensitive member as the electrostatic latent image bearing member is mainly scraped by the cleaning step of the electrophotographic process while being repeatedly used. At this time, the amount of abrasion depends on the pressure distribution of the cleaning device on the photoconductor, the distribution of the toner image developed on the photoconductor, and so on. It is difficult to configure, and unevenness inevitably occurs in the surface layer thickness of the photoconductor.

Generally, when the surface layer thickness of the photoconductor becomes uneven, the electrostatic latent image formed on the photoconductor becomes uneven.

Therefore, when the same photoreceptor having the same surface layer is used, the BP bias is about 1.8 to 2.3 times faster than the rectangular bias (with a small number of image outputs). Further, there is a problem that unevenness exceeding the allowable range occurs, and the replacement period of the photoconductor, that is, the life of the photoconductor is shortened by that amount.

On the other hand, the inclusion of a fluorine-based resin in the surface layer of the photoconductor is effective in improving the surface smoothness, and is therefore effective in improving the cleaning property and suppressing the abrasion amount of the photoconductor. It is known.

However, the inclusion of the fluorine-based resin in the surface layer of the photoconductor has a drawback that "roughness" occurs in the highlight portion of the image. Since the “sharpness” in the highlight portion is increased by the repeated use of the developer, the image quality has been maintained by the conventional regular replacement of the developer.

That is, by including a fluorine-based resin in the surface layer of the photoconductor, the amount of abrasion of the photoconductor can be suppressed, while on the other hand, the life of the developer is shortened due to deterioration of "roughness" in the highlight portion of the image. There was another problem of shortening.

Therefore, a first object of the present invention is to provide an image forming apparatus having a developing device which prevents uneven density.

A second object of the present invention is to provide an image forming apparatus having a developing device which prevents the highlight portion from being rough.

A third object of the present invention is to provide an image forming apparatus in which the cleaning property is improved and the amount of abrasion of the photoconductor is reduced.

[0020]

The above object of the present invention relates to the present invention.
This is achieved by the image forming apparatus. In summary, the present invention is
An image carrier having a surface layer containing a fluororesin,Tona
And carrierFaces the image carrier with the developer
Formed on the image bearing member, which is provided with a developer bearing member for carrying to
The developing device for developing the electrostatic image and the developer carrier.DC component
AC component was intermittently superimposed onApply development bias
And an image forming apparatus having a bias applying unit.
The peak-to-peak value of the development bias and the frequency.
Each V_pp[V], V_f[Hz], image contrast potential
To V_cont[V], the average tribo of the toner is Q [C / k
g], and the distance between the image bearing member and the developer bearing member is d [m].
Then, | V_pp-2V_cont｜ / 16V_f ²<D²/ | Q | SatisfiedAnd The time of the vibration part of the developing bias is T
₁ [Sec], the time of the rest part is T ₂ [Sec], Fluorine tree
If the fat content is F [wt%], 6- (F / 10) ^1/2 > T ₂ / T ₁ > (F / 10) ^1/2 10 <F <40 The image forming apparatus is characterized in that

According to one embodiment of the present invention, the fluorine
The primary particle size of the resin is 0.3 μm or less.

According to another embodiment, the developing bias is
The waveform of the vibrating part is substantially a rectangular wave.

[0023]

[0024]

[0025]

[0026]

[0027]

[0028]

[0029]

[0030]

[0031]

Embodiments of the image forming apparatus according to the present invention will be described below in more detail with reference to the drawings.

Embodiment 1 FIG. 1 is a schematic configuration diagram showing an embodiment of an image forming apparatus to which a developing device according to the present invention is applied. In FIG. 1, a photosensitive drum 131 as an electrostatic latent image carrier rotates in the direction of arrow R in the figure, and its surface is uniformly charged by a primary charger 132. Then, the photosensitive drum 131 is exposed to laser light (arrow L in the figure) corresponding to the image, and an electrostatic latent image is formed. The electrostatic latent image is developed and visualized by the developing device 133 containing a two-component developer containing toner and carrier inside. The visualized toner image is transferred by the transfer charging device 134 onto the paper conveyed by a paper conveying device (not shown), and then fixed by the fixing device 135 and output as an image. In the transfer step, the transfer residual toner remaining on the photosensitive drum 131 is the photosensitive drum 1
Cleaning is performed by the cleaning device 136 having the cleaning blade 161 pressed against 31.
After that, the photosensitive drum 131 is destaticized by the pre-exposure device 137, and is used for another image formation.

FIG. 4 shows a schematic layer structure of the photosensitive drum of this embodiment. As shown in FIG. 4, the photosensitive drum is a conductive base material 5.
1, a charge generation layer 52 coated thereon, and a charge transport layer 53 further coated thereon. In this embodiment, the charge transport layer 53 which is the surface layer of the photosensitive drum.
30% of Teflon (trade name), which is a fluororesin, is dispersed in (main binder; polycarbonate).

The developing bias in this embodiment is the same BP bias as that shown in FIG. 3, which has a vibrating portion and a rest portion in one cycle.

The following table shows the results of comparison between the life of the photosensitive drum and the life of the developer when repeated image output (hereinafter referred to as a durability test) is performed using the image forming apparatus configured as described above. Shown in 1. In Table 1, the photosensitive drum life and the developer life when the photosensitive drum in which Teflon (trade name) is not dispersed and the rectangular bias shown in FIG. 2 are used are set to 1.

[0036]

[Table 1]

As shown in Table 1, only by changing the developing bias from the rectangular bias shown in FIG. 2 to the BP bias shown in FIG. 3, the developer life becomes 2.5 to 3 times longer, but the photosensitive drum life becomes longer. Is 0.5 times to 0.7 times, resulting in an increase in running cost, which is dominated by service cost.

On the other hand, if the rectangular bias shown in FIG. 2 is used as the developing bias and the Teflon is dispersed by 30% on the surface layer of the photosensitive drum, the life of the photosensitive drum becomes 3 to 3.5 times longer. Developer life is 0.7-0.8
This will also increase the running cost, as it will be twice as short.

However, when Teflon is dispersed in the surface layer of the photosensitive drum by 30% and the developing bias is changed from the rectangular bias shown in FIG. 2 to the BP bias shown in FIG. 3, the photosensitive drum life is 1.5 to 2. 4 times longer, and the life of the developer is 1.7 times to 2.4 times longer.

As described above, when the photosensitive drum having the surface layer containing the fluorine resin is used, the BP bias is used as the developing bias, and when the BP bias is used as the developing bias, the photosensitive drum is exposed. It was effective from the running cost point of view to include a fluororesin in the drum surface layer.

Further, if the photosensitive drum and the developer are exchanged at the same cycle as the conventional one, the "sharpness" of the highlight portion of the image is less than that in the conventional one, and the unevenness of the photosensitive drum causes less image unevenness. It becomes possible to maintain a high image.

Second Embodiment Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 5 shows a schematic layer structure of the photosensitive drum used in this embodiment. It is to be noted that the elements having the same numbers as those in FIG.

As shown in FIG. 5, the photosensitive drum of this embodiment has a conductive base material 51, a charge generation layer 52 coated thereon, and a charge transport layer 63 further coated thereon. Further, it has a protective layer 64 coated thereon. still,
Teflon is not dispersed in the charge transport layer 63 in this embodiment. Instead, 30% of Teflon (trade name) is dispersed in the protective layer 64 (main binder; polycarbonate).

Using the image forming apparatus shown in FIG. 1 using such a photosensitive drum, the same durability test as in the first embodiment was conducted and the results are shown in Table 2 below.

[0045]

[Table 2]

As is clear from Table 2, the life of the photosensitive drum is extended by about 15% as compared with the above-mentioned examples by providing the protective layer (containing 30% Teflon).

It is considered that this is because the amount of unevenness of the potential of the electrostatic latent image with respect to the amount of abrasion of the photosensitive drum is reduced.

By using such a photosensitive drum, it is possible to obtain the effect that the roughness and the image unevenness are small as in the first embodiment.

Embodiment 3 In the first and second embodiments, the BP bias shown in FIG. 3 was used as the developing bias, but the developing bias effective in the present invention is limited to the BP bias shown in FIG. Not a thing.

FIG. 6 shows the developing bias used in this embodiment. In the developing section shown in FIG. 6, the vibrating section vibrates a plurality of times. This developing bias has an advantage over the developing bias shown in FIG. 3 in that the amount of change in image density with respect to the change in toner concentration in the developer is smaller.

By using such a developing bias, it is possible to obtain the effect that the image is rough and the image unevenness is small as in the first and second embodiments.

Fourth Embodiment Next, a fourth embodiment of the image forming apparatus according to the present invention will be described. FIG. 7 is a sectional view showing the image forming apparatus.

The color image forming apparatus shown in FIG. 7 has a digital color image reader section in its upper part and a digital color image printer section in its lower part.

In the reader unit, the reflected light image from the original 30 obtained by placing the original 30 on the original table glass 31 and exposing and scanning with the exposure lamp 32 is focused on the full color sensor 34 by the lens 33, and the color image is obtained. Obtain a color separated image signal. The color-separated image signal is amplified by an amplifier circuit (not shown), processed by a video processing unit (not shown), and sent to the printer section.

In the printer section, the photosensitive drum 1, which is an image bearing member, is a photosensitive member having a surface protective layer, which will be described later, and is rotatably carried in the direction of the arrow in the figure. Around the photosensitive drum 1, a pre-exposure lamp 11 for initializing the surface of the photosensitive drum 1, a charger 2 (corona charger in this example) for uniformly charging the surface of the photosensitive drum 1, A laser exposure optical system 3 for forming an electrostatic latent image according to image information, a potential sensor 12 for detecting the potential on the surface of the photosensitive drum 1, and an electrostatic latent image formed on the photosensitive drum 1 is developed into a visible image. A developing device having a fixed arrangement of four developing devices 4C, 4M, 4Y, and 4K for accommodating developers (toners) of different colors, a light detecting means 13 for detecting the amount of toner on the photosensitive drum 1, a recording material carrier. A transfer device 5 including a transfer drum 5a, a cleaner 6 for removing the developer remaining on the photosensitive drum 1, and the like are provided.

In this example, the laser exposure optical system 3 is composed of a polygon mirror 3a, a lens 3b, a mirror 3c, etc., and is modulated by a color image signal of each color separated from the reader section, and is output to a laser output section. Is converted into an optical signal for image scan exposure, the converted laser light E is reflected by the polygon mirror 3a, and the lens 3b and the mirror 3c are reflected.
Through to project on the surface of the photosensitive drum 1 to form an electrostatic latent image corresponding to the color image signal of each color.

At the time of image formation in the printer section, the photosensitive drum 1 is rotated in the direction of the arrow shown in the figure, and first the pre-exposure lamp 1
The surface of the photosensitive drum 1 is neutralized and initialized by 1 and then the surface of the photosensitive drum 1 is uniformly negatively charged by the charger 2, and an optical image E corresponding to the image signals of the respective colors separated by the image exposing means 3 is obtained. Is sequentially irradiated onto the surface of the photosensitive drum 1 to form an electrostatic latent image in a predetermined color order.

Next, a predetermined developing device is operated in the order of predetermined development of cyan (C), magenta (M), yellow (Y), and black (K) to form a latent image on the photosensitive drum 1. After development, a toner image is formed on the photosensitive drum 1 with a negative toner having a resin as a base in order. Here, each of the developing devices 4C, 4M, 4Y, 4K of the developing device has an eccentric cam 24C,
By the operations of 24M, 24Y, and 24K, a required developing device is selectively brought close to the photosensitive drum 1 to perform the developing operation according to the color of the latent image formed.

On the other hand, the recording material cassette 7a, 7b, or 7
From c (may be manually fed), pickup roller,
A recording material such as a transfer sheet fed by a conveying system including a sheet feed guide and a sheet feed roller is wound around the transfer device 5 in synchronization with a predetermined timing. This transfer device 5
In this example, a transfer drum 5a having a diameter of 180 mm as a recording material carrier, a transfer corona charger 5b for transferring the toner image on the photosensitive drum 1 to the recording material, and the recording material are attracted to the transfer drum 5a. Corona charger 5c for adsorption, which is an adsorption charging means, and for adsorption as an opposite electrode (for contact)
A transfer drum 5a, which has a roller 5g, an inner corona charger 5d, and an outer corona charger 5e, and is rotatably supported, has a peripheral surface opening area made of a dielectric material serving as a recording material carrying means. The recording material carrying sheet 5f is integrally stretched in a cylindrical shape. A dielectric sheet such as a polycarbonate film is used as the recording material carrying sheet 5f.

The transfer drum 5a is rotated in the direction of the arrow in the figure in synchronization with the photosensitive drum 1, and the cyan toner image developed by the cyan developing device 4C is carried on the recording material carrying sheet 5f by the transfer charging device 5b at the transfer portion. It is transferred to the recorded recording material. The transfer drum 5b continues to rotate and prepares for transfer of an image of the next color (for example, magenta).

Further, the photosensitive drum 1 on which the toner image is transferred
The cleaner 6 cleans the adhering substances such as residual toner and the like, and the charger 2 again uniformly charges the same, and the above-mentioned image exposure is performed by the laser light modulated by the next magenta image signal. This magenta latent image is developed by the magenta developing device 4M to form a magenta toner image, and this magenta toner image is transferred to the recording material carried on the recording material carrying sheet 5f by the transfer charging device 5b at the transfer portion. , The magenta toner image is transferred onto the cyan toner image. The transfer drum 5b continues to rotate and is ready for transfer of an image of the next color (for example, yellow).

Subsequently, the above-described process is performed for yellow and black image formation and transfer, and when the superimposing transfer of the four color toner images is completed, the recording material is discharged by the separating charger 5h, Next, the separation push-up roller 8
It is separated from the transfer drum 5a by the action of b and the separation claw 8a, and is fixed by a conveying means (heat roller fixing device in this example).
It is sent to the printer 9 and fixed in a batch, and is discharged onto the external tray 10. Thus, the series of full-color print sequences is completed, and the required full-color print image is formed.

Next, when images are to be formed on both sides of the recording material, immediately after the recording material is ejected from the fixing device 9, the conveying path switching guide 19 is driven and the recording material is conveyed along the vertical path 20. After that, it is once guided to the inversion path 21a. After that, the reversing roller 21b reversely rotates the recording material as it is fed, with the trailing end of the recording material as the leading end, and the recording material is withdrawn in the direction opposite to the feeding direction and is stored in the intermediate tray 22. Then, the recording material is again conveyed from the intermediate tray 22 to the transfer device 5, and an image is formed on the other surface by the above-described image forming process.

Further, in order to prevent scattering and adhesion of powder on the recording material carrying sheet 5f of the transfer drum 5a and adhesion of oil on the recording material, the fur brush 14 and the recording material carrying sheet 5f are used to interpose the fur. Cleaning is performed by the action of the backup brush 15 facing the brush 14, and the backup brush 17 facing the oil removing roller 16 via the oil removing roller 16 and the recording material carrying sheet 5f. Such cleaning is performed before or after image formation, and at any time when a jam (paper jam) occurs.

Further, in this example, the eccentric cam 25 is operated at a desired timing and the cam follower 5i integrated with the transfer drum 5a is operated, so that the gap between the recording material carrying sheet 5f and the photosensitive drum 1 is reduced. It has a configuration that can be set arbitrarily. For example, during standby (standby) or when the power is off, the transfer drum 5a and the photosensitive drum 1 are separated from each other.

Next, referring to the block diagram of FIG.
The image processing process of 0 will be described.

The digital image data 42 is the D / A converter 4
It is converted into an analog image signal 403 by 02 and is input to one terminal of the comparator 411. A timing signal generation circuit 407 inputs the reference clock signal 43 and creates and outputs the pixel clock 404 and the screen clock 408 to the pattern signal generator 409. The pattern signal generator 409 outputs the pattern signal 410 based on the screen clock 408, and inputs it to the other terminal of the comparator 411.

The digital image data 42 is the pixel clock 4
04, and the D / A converter 402 outputs the analog image signal 403 in synchronization with the pixel clock 404. Screen clock 408 is pixel clock 404
Is a clock signal that is an integer multiple of, and defines the cycle of the pattern signal 410 that is, for example, a triangular wave.

Analog image signal 403 and pattern signal 4
10 is compared by the comparator 411, and when the analog image signal 403 is larger, it is set to 0, and when it is smaller, the pulse width modulated binarized image data 41 is created and output.

Further, the image processing process will be described with reference to the timing chart shown in FIG. 9 which shows the timing of each part of FIG.

Here, the screen clock 408 is a clock having a cycle twice that of the pixel clock 404.
Digital image signal is hexadecimal 00 (white) to FF
The pulse waveform of the binarized image data 41 pulse-width-modulated by the pattern signal 410 is shown when changing stepwise to (black). By changing the amplitude of the pattern signal 410 in this way, the relationship between the input level of the digital image data 42 and the pulse width of the binarized image data 41 can be changed.

The binarized image data of the data 41 is inputted to the image forming section of the full-color copying machine, the exposure width by the laser light is controlled, and a laser spot having an exposure width corresponding to the image data is formed on the photoconductor. It is projected and a latent image is formed. These latent images are the above-mentioned developing devices 4Y, 4C, 4M,
Developed by 4K.

Next, the developing step which is a characteristic part of the present invention will be described in detail. As the developer, a two-component developer composed of non-magnetic toner and magnetic particles (carrier) is used. The mixing ratio was such that the nonmagnetic toner was about 5% by weight. The non-magnetic toner has a volume average particle diameter of about 8 μm.
The magnetic particles are resin-coated ferrite particles (maximum magnetization 60 emu / g), the weight average particle size is 50 μm, and the resistance value is 10 ⁸ Ωcm or more. The magnetic permeability of the magnetic particles is about 5.0.

An opening is provided in a portion of the developing container near the photosensitive drum 1, and the developing sleeve projects to the outside from the opening. The developing sleeve is rotatably incorporated in the developing container. The outer diameter of the developing sleeve is 25 mm
And the peripheral speed is 280 mm / sec. The developing sleeve is arranged so that the distance between it and the photosensitive drum 1 is 500 μm.

In this embodiment, as the developing bias, V _PP : peak-to-peak voltage [V] of alternating voltage applied to the developer carrying member V _f : frequency of alternating voltage [H] applied to the developer carrying member
z] V _cont : image contrast potential [V] (potential difference from latent image potential when maximum image density is output from DC voltage of developing bias) Q: toner average tribo [C / Kg] d: developer carrier - when the distance of the latent image bearing member _{[m], | V PP -2V} cont | / 16V f 2 <d 2 / | Q | alternating voltage to satisfy an alternating electric field of are formed intermittently is Is applied.

The toner used in this example has a triboelectric charge amount of about 2.0 × 10 ^-2 C / kg and that of about 3.0 × 10 ^-2 C.
/ Kg of 2 kinds were used.

Next, a method of measuring the triboelectric charge amount (two-component developer) of toner will be described with reference to FIG. Figure 1
0 is an explanatory diagram of an apparatus for measuring the amount of triboelectric charge of toner.

First, a two-component developer whose triboelectric charge is to be measured is placed in a metal measuring container 142 having a 500-mesh screen 143 in a polyethylene bottle having a capacity of 50 to 100 ml, and a container of about 10 to 40 is charged. Shake for 2 seconds by hand, add about 0.5 to 1.5 g of the developer, and cover with a metal lid 144. The weight of the entire measuring container 142 at this time is measured and set to W ₁ (kg). Next, in the suction device 141 (at least the portion in contact with the measurement container 142 is an insulator),
Suction is performed from the suction port 147, the air flow rate control valve 146 is adjusted, and the pressure of the vacuum gauge 145 is set to 250 (mmAq). In this state, suction is carried out sufficiently, preferably for 2 minutes, to remove the resin by suction. The potential of the electrometer 149 at this time is V (V). Here, 148 is a capacitor, and the capacitance is C (F). Also, weigh the entire measuring container 142 after suction
₂ (kg) Triboelectric charge amount of this toner (C / k
g) is calculated by the following formula.

Frictional charge amount of resin (C / kg) = C × V ×
10 ⁻³ / (W ₁ −W ₂ ) In this embodiment, a highlight halftone image having an image density of about 0.2 and a solid image are output, and the smoothness of the highlight halftone image and the solid image are obtained. The concentration was evaluated. The electrostatic latent image formation for outputting the above image is as follows. First, the photosensitive drum is uniformly charged to 650V. Here, when a highlight halftone image is output, PWM exposure (pulse width modulation) is performed by a semiconductor laser to reduce the surface potential to about 450 V, and when a solid image is output, it is reduced to about 100 V (V _cont = 400V). (This example was performed by reversal development.)

Next, the developing process performed by using the developing device having the above-mentioned structure and the toner having the above charge amount will be described.

In this embodiment, the DC voltage is 500V.
And the amplitude V _{pp of the} alternating voltage applied intermittently is set to 200.
It is fixed at 0 V, the frequency V _f is changed, and the toner tribo is about 2.0 × 10 ^-2 c / kg and about 3.
The image quality of output images under the above-mentioned latent image conditions was evaluated for two types of 0 × 10 ^-2 c / kg. (At this time,
As shown in FIG. 11, the time period during which the alternating electric field was cut off was set to one cycle for each cycle of the alternating electric field. )

As a result, as can be seen from Table 3 below,
A = | V _PP −2V _cont | / 16V _f ² and B = d ² / | Q
Only when the relationship of | was A <B, the high density was maintained in the solid state and the reproducibility of highlight was good.

[0083]

[Table 3]

This was very effective for the drum of the present invention having an increased content of fluororesin powder.

As an example, in FIG. 12, the amplitude V _{pp of the} alternating voltage intermittently applied by the bias of FIG. 11 is 2000 V, and the frequency V _f is 8 kHz. Fluorine resin powder content and highlight image level in the case of using the developing bias (bias 1) in this example and the conventional rectangular wave bias (bias 2) having an amplitude V _pp of 2000 V and a frequency V _f of 2 kHz Shows the relationship.

When the bias of this example is used, the level of the highlight image is higher than that of the conventional bias even when the fluorine content is 0%, but the characteristic point is to implement this example. Even when a drum having an increased content of fluororesin powder is used, the deterioration of the image is almost negligible.

This has a deep relationship with the condition of A <B shown in Table 3, which will be described below.

17 and 18 are views showing the force applied to one toner on the developing sleeve. In the figure, q is the charge amount,
m is the mass, a is the acceleration, ΔV is the potential difference between the photosensitive drum and the developing sleeve, and d is the gap between the photosensitive drum and the developing sleeve.

Alternating voltage is applied to the toner from the developing sleeve for 1 / (2V _f ) seconds per cycle. The distance X that the toner can move during this time is calculated by the following mathematical expression (1).

[0090]

[Equation 1]

The distance X ₊ that the toner can move from the developing sleeve toward the photosensitive drum is obtained by the following mathematical expression (2).

[0092]

[Equation 2]

Further, the distance X ₋ that the toner can move from the photosensitive drum to the developing sleeve is obtained by the following mathematical expression (3).

[0094]

[Equation 3]

Here, by setting the condition that the toner developed on the photosensitive drum is not returned to the developing sleeve at the moving distance X ₋ when the stripping voltage is applied for one cycle, the toner is exposed to light. Repeated biased vibration on the drum. This is because X ₊ > X ₋ .

The condition at this time is a condition represented by the following formula (4) in which X ₋ is smaller than the gap d between the photosensitive drum and the developing sleeve.

[0097]

[Equation 4]

When the development is performed under such conditions, the reciprocating motion between SD cannot be sufficiently performed by the alternating electric field of one cycle, and the DC component is a latent image when the alternating voltage is cut off. Since it works so as to attract an amount of toner corresponding to the potential to the photosensitive drum, dot loss does not occur. Further, since the toner is concentrated on the latent image portion and the dots are faithfully reproduced on the photosensitive drum by repeating the vibration intermittently, only a non-uniform image is obtained by the conventional rectangular bias. A uniform image can be output even with a shallow latent image that does not exist. Thus, for example, a uniform image can be obtained even on a drum containing 30% of fluororesin.

Further, in the non-image portion, in order to remove a normal fog, the DC component of the developing bias is set higher as in this embodiment. Therefore, in the non-image part,
Since V _cont in Equation 2 and Equation 3 becomes negative,
X ₊ <X ₋ . Also, because the alternating voltage is cut off, D
C component works to attract the toner to the sleeve side,
Further, the toner is biased toward the developing sleeve, and fogging on the photosensitive drum does not occur.

In this embodiment, the applied alternating electric field is set as shown in FIG. 11, but the present invention is not limited to this. For example, as shown in FIG. 13, application of two wavelengths,
5 wavelength pause, or 1 wavelength application as shown in FIG. 14, 10
The wavelength may be stopped, and a rectangular wave is used in the embodiment, but various kinds of application such as a triangular wave and a sine wave can be applied, and the most appropriate application method can be selected according to the copying speed and the developing conditions. The ratio of bias application time and rest time is 1: 1.
When / 2 to 1:15, favorable results were obtained.

Next, a method of manufacturing the photoconductor in this example will be described.

50 parts by weight of conductive titanium oxide powder coated with tin oxide containing 10% antimony oxide, 25 parts by weight of phenol resin, 20 parts by weight of methyl cellosolve, 5 parts by weight of methanol and silicone oil (polydimethylsiloxane poly 0.002 parts by weight of the oxyalkylene copolymer (number average molecular weight 3000) was dispersed for 2 hours with a sand mill using φ1 mm glass beads to prepare a conductive coating material. Aluminum cylinder (φ180mm × 3
60) dip-coating the above-mentioned paint on 140),
And dried for 300 minutes to form a conductive layer having a film thickness of 20 μm.

Next, 30 parts by weight of methoxymethylated nylon resin (number average separation amount 32000) and 10 parts by weight of alcohol-soluble copolymerized nylon resin (number average separation amount 29000) were mixed with 260 parts by weight of methanol and 40 parts by weight of butanol as a mixed solvent. The liquid dissolved therein was applied on the above conductive layer by a dipping coating machine to form an undercoat layer having a film thickness after drying of 1 μm.

Next, the following structural formula [I]

[0105]

[Chemical 1] 4 parts by weight of disazo pigment, 2 parts by weight of benzal resin, and 40 parts by weight of tetrahydrofuran were dispersed for 60 hours in a sand mill using φ1 mm glass beads, and then diluted with a cyclohexanone / tetrahydrofuran mixed solvent to prepare a charge generation layer coating material. .

This coating solution was applied onto the undercoat layer by a dipping coating machine to form a charge generation layer having a film thickness of 0.1 μm after drying.

Next, the following structural formula [II]

[0108]

[Chemical 2] 10 parts by weight of the charge transport material and 10 parts by weight of a polycarbonate resin (number average molecular weight 25,000) were added to dichloromethane.
It was dissolved in a mixed solvent of 0 parts by weight and 40 parts by weight of monochlorobenzene, and this solution was dip-coated on the charge generation layer and dried at 120 ° C. for 60 minutes to form a charge transport layer having a thickness of 20 μm.

Next, 6 parts by weight of a polycarbonate resin (number average molecular weight 25,000), 2 parts by weight of the above charge transport material, and polytetrafluoroethylene (average primary particle size 0.3 μm) 2
Part by weight is dissolved in a mixed solvent of 200 parts by weight of dichloromethane and 300 parts by weight of monochlorobenzene, and this solution is spray coated on the above charge transport layer and dried at 120 ° C. for 60 minutes to form a surface protective layer having a thickness of 5 μm. Then, a photoconductor is prepared. In this case, the content of the fluorinated resin is 20% by weight based on the weight of the surface solid content.

Image formation was carried out under the conditions of ⊚ shown in Table 3 as a combination of toner and bias. In all cases, a clear image was obtained in the highlight portion without any greasiness, and the cleaning property was included. It was also possible to confirm durability stability.

Further, as the fluorine-based resin body applied to the present invention, tetrafluoroethylene resin, trifluoroethylene chloride resin, tetrafluoroethylene hexafluoropropylene resin, vinyl fluoride resin, difluorochloroethylene resin. And one or more of these copolymers are appropriately selected. Especially, it is a low molecular grade and has a primary particle of 0.3 μm.
The following are preferred.

Example 5 Next, as Example 5, the electrophotographic photoreceptor was prepared without a surface protective layer, and polytetrafluoroethylene particles (average primary particle size 0.3 μm) were contained in the charge transport layer in a weight ratio of 15%. Except that it was included, the same conditions as in Example 1 were used, and similarly images were displayed and evaluated. In this case, it was confirmed that stable image quality can be obtained over a long period of time.

Sixth Embodiment Next, a sixth embodiment will be described. The present embodiment is characterized in that a binder resin or a curable resin in which a fluororesin is dispersed in a photoconductor is used for the surface layer.

The binder resin for forming the surface layer may be a polymeric substance having film-forming properties, but it is preferable that the binder resin is a polymer substance having a certain degree of hardness when used alone and does not interfere with carrier transportation. Methacrylic acid ester, polystyrene, methacrylic acid ester / styrene copolymer,
Polycarbonate, polyester, polysulfone and the like are preferable.

As the curable resin, thermosetting resins such as polyurethane resin, epoxy resin, melamine resin, or guanamine resin, and photocurable resins typified by polyacrylates are used. However, when these resins are used alone for the surface layer, the surface slipperiness is poor and the cleaning property is poor. Therefore, a fluorine-based resin is dispersed in these resins to improve surface lubricity and form a surface layer satisfying the above characteristics.

FIG. 15 shows an explanatory diagram in the case where a protective layer is provided on the photoconductor. As shown in FIGS. 15A and 15B, when a protective layer of a binder resin or a curable resin is provided on the surface layer of the photoconductor, the light exposed on the drum is not scattered inside the protective layer and The exposure distribution of 1 does not spread much as compared with the case where no protective layer is provided.

However, when the surface slipperiness improving particles are contained, the exposure distribution in the photosensitive layer is widened.

The content of the fluororesin is preferably 10% or more of the surface solid content weight.

FIG. 16 shows the relationship between the weight ratio of the fluorine-based resin to the solid content of the surface layer, the photoreceptor life and the highlight image level. The photoreceptor life is the life until scratches occur on the drum or cleaning failure occurs. Although it depends on the cleaning configuration, the content has an inflection point around 10%, and it gradually saturates above 10%. Tend. This is considered as follows.

It is considered that the fluorine-based resin serves as a lubricant to improve the surface lubricity, but unless the resin is sufficiently dispersed on the surface, the friction coefficient does not decrease and the durability cannot be improved. For this reason, the fluororesin relative to the surface solid content weight,
By containing 10% or more by weight ratio, the effect of containing the fluorine-based resin is exhibited. That is, it is necessary to contain the fluorine-based resin in an amount of at least 10% in order to obtain a sufficient effect on durability.

Although the fluorine-based resin used here has the primary particles selected to be 0.3 μm or less, the scattering of the incident light cannot be prevented, and as shown in FIGS. 15 (C) and 15 (D). The light incident on is scattered by the influence of the fluorine resin of the protective layer, and the exposure distribution on the photoconductor layer is broadened, resulting in a latent image with a shallow potential.

Next, the content of the fluororesin and the developing bias will be described in more detail.

As the content of the fluororesin increases, the latent image is formed only shallowly as described above. Therefore, in the toner having low tribo, the alternating voltage is cut off when the alternating voltage is cut off for a short time until the pullback voltage is applied. The latent image cannot be transferred during the period of time, and the non-uniformity of the tribo reflects the non-uniformity of the dot as it is, resulting in a non-uniform image.

Here, instead of prolonging the time for cutting off the alternating voltage, it seems that the time for applying the alternating voltage in the direction in which the developer is transferred from the developing sleeve to the photosensitive drum is made longer, but this time is simply set. If the length is simply increased, the toner is transferred to the non-image area, and a uniform image can be obtained, but fogging occurs, and this cannot solve the problem.

If the time for which the alternating voltage is cut off becomes too long, sufficient vibration will not occur during development. The higher the content of the fluororesin in which the latent image becomes shallow, the more uniform the image cannot be obtained unless the number of vibrations is increased. Therefore, the upper limit of the time for cutting off the alternating voltage is also limited.

The relationship between the application time of the alternating voltage and the time when the alternating voltage was cut off, and the fluororesin content, at which uniform dot reproducibility was obtained, was varied by varying the frequency within the range of the condition A <B described above. Upon examination, the following relationships were obtained.

That is, the time for applying the alternating voltage is T ₁
[Sec], T ₂ [sec] is the time for which the alternating voltage is cut off, and F [wt%] is the fluororesin content. 6- (F / 10) ^1/2 > T ₂ / T ₁ > (F / 10) Within the range of ^1/2, the image quality of highlight was sufficiently uniform. Further, as described above, stable cleaning properties cannot be obtained unless the fluororesin content is 10% or more, and the latent image is completely blurred when the fluororesin content is 40% or more. It becomes impossible to obtain a good image. Therefore, if a range of 10 <F [wt%] <40 is selected, a uniform image can be stably obtained.

The graph of FIG. 19 shows the relationship between the content of fluororesin and the ratio T ₂ / T ₁ of the time T ₂ for cutting off the alternating voltage and the time T ₁ for applying the alternating voltage, and the optimum developing conditions in this embodiment. Indicates the range of. In the figure, the shaded area is the applicable range of the present invention, and if this condition is satisfied, a stable image can be obtained without highlight shading. Also, ◎, ○, △, × shown in the figure are A = | V _PP -2V _cont |
The relationship between / 16V _f ² and B = d ² / | Q | is the level of a highlight image when an image is generated under the conditions of some figures at a frequency satisfying the condition of A <B.

The dotted line L ₁ shown in FIG. 19 is the condition for the developing bias of FIG. 11, and the relationship between the image quality of this portion and the fluororesin content is as shown in the graph of FIG.

The non-image portion is set higher than the DC component of the developing bias in this embodiment in order to remove the normal fog. Therefore, in the non-image part, V
_{for cont} becomes negative, X ₊ <X _- to become. Also,
Since the alternating voltage is cut off, the DC component works to attract the toner toward the sleeve side, and the toner is biased toward the developing sleeve side, and fogging on the photosensitive drum does not occur.

Although the embodiments of the present invention have been described above, the present invention is not limited to these embodiments and various modifications can be made within the technical idea.

[0132]

As described above, according to the present invention,
Even though the surface layer is configured to contain a fluororesin in order to prolong the life of the image bearing member, it is possible to prevent uneven density and roughness of the highlight portion and obtain a sufficiently uniform image . Therefore, it is possible to achieve both reduction of running cost and improvement of image quality.

[Brief description of drawings]

FIG. 1 is an electrophotographic image forming apparatus in which the present invention can be embodied.

FIG. 2 is a waveform diagram showing a rectangular bias.

FIG. 3 is a waveform diagram showing a BP bias.

FIG. 4 is an explanatory diagram showing a schematic layer structure of a photosensitive drum applied in the first embodiment.

FIG. 5 is an explanatory diagram showing a schematic layer structure of a photosensitive drum applied in a second embodiment.

FIG. 6 is a waveform diagram of a developing bias applied in the third embodiment.

FIG. 7 is a sectional view of another image forming apparatus to which an embodiment of the present invention can be applied.

8 is a block diagram showing an image processing unit of the color image forming apparatus of FIG.

9 is a timing chart of the image processing unit in FIG.

FIG. 10 shows a measuring device for measuring the triboelectric charge amount of a two-component developer.

FIG. 11 is a waveform chart showing an example of a developing bias voltage in Example 4.

FIG. 12 is a graph showing the relationship between the fluorine content and the image quality.

FIG. 13 is a waveform chart showing another example of the developing bias voltage in the fourth embodiment.

FIG. 14 is a waveform diagram showing still another example of the developing bias voltage in the fourth embodiment.

FIG. 15 is an explanatory diagram for explaining light scattering due to fluorine on a photoconductor.

FIG. 16 is a graph showing the relationship between the fluorine content and the photoreceptor life and image quality.

FIG. 17 is an explanatory diagram showing a force that acts on toner.

FIG. 18 is an enlarged explanatory diagram of FIG. 17.

FIG. 19 is a graph showing the optimum developing conditions in the relationship between the fluorine content and the ratio of the time to turn off the alternating voltage and the time to apply the alternating voltage.

[Explanation of symbols]

1, 131 Photosensitive drum (image bearing member) 4, 133 Developing device 51 Conductive base material 52 Charge generation layer 53 Charge transport layer containing Teflon (surface layer) 63 Charge transport layer containing no Teflon 64 Contains Teflon Protective layer (surface layer)

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hisashi Fukushima 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (56) References JP-A-60-134262 (JP, A) JP-A-60 -53968 (JP, A) JP 60-53969 (JP, A) JP 4-315181 (JP, A) JP 5-35063 (JP, A) JP 4-12365 (JP, A) ) JP-A-5-34979 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G03G 15/06 101 G03G 15/08

Claims (3)

(57) [Claims] 1. An image carrier comprising: an image carrier having a surface layer containing a fluororesin; and a developer carrier carrying a developer containing toner and carrier and conveying the developer to a portion facing the image carrier. An image forming apparatus comprising: a developing device for developing the electrostatic image formed on the developing device; and a bias applying means for applying a developing bias in which a DC component and an AC component are intermittently superposed on the developer carrying member. Peak-to-peak value and frequency are V _pp [V] and V _f [Hz], respectively, and the image contrast potential is V
_cont [V], the average tribo of toner is Q [C / kg], and the distance between the image carrier and the developer carrier is d [m], then | V _pp −2V _cont | / 16V _f ² <d ² / | Q | is satisfied , and the time of the vibrating portion of the developing bias is T ₁ [sec], the rest portion is
Is T ₂ [sec], and the content of fluororesin is F [weight]
%]], The image forming apparatus is characterized by satisfying 6- (F / 10) ^1/2 > T ₂ / T ₁ > (F / 10) ^1/2 and 10 <F <40 . 2. The primary particle size of the fluororesin is 0.3 μm.
The image forming apparatus according to claim 1, wherein: 3. The waveform of the vibration portion of the developing bias is substantially
3. The image according to claim 1, wherein the image is a rectangular wave.
Image forming device.