JPH0962028A - Image forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device in which splashing of a toner around characters caused by an excess amt. of toner coating in a developing zone can be prevented, and both of prevention of voids in characters and improvement in printing accuracy can be obtd. by using a fine particulate toner without making the difference in the rotation speed between the transfer roll and the photosensitive drum. SOLUTION: This image forming device has such properties that the SF2 value of a toner defined by SF2 = (peripheral length)<2> /(projected area ×4π))×100 ranges 100 to 150 and that the amt. of toner coating (mass/area) on a developer carrying body ranges 0.5 to <=1.5mg/cm<2> . Further, the image forming device has such properties that the SF2 value of the toner ranges 100 to 150, the weight average particle size of the toner is 4.5 to 8μm, and the relative velocity of a transfer roller to a photosensitive drum is 95 to 110%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus using an electrophotographic system such as a printer and a digital copying machine.

[0002]

2. Description of the Related Art Conventionally, an image forming apparatus using an electrophotographic system such as a printer or a digital copying machine uses a known charging roller or the like to uniformly charge an electrophotographic photosensitive member (photosensitive drum), Image exposure is performed by a semiconductor laser or the like modulated by an image signal to form an electrostatic latent image on the image carrier (photosensitive drum). As a developing device for developing this electrostatic latent image, a developer (toner) is transferred to an electrostatic latent image on the image bearing member from a developer bearing member which is in contact with the image bearing member or faces the image bearing member with a minute gap. Then, by giving
It is known to develop an electrostatic latent image. As a result, the electrostatic latent image is developed and a toner image is formed and visualized.

The toner image thus formed is transferred to a transfer material such as paper by a known transfer means such as a transfer roller. The transfer material to which the toner image is transferred is separated from the image carrier and sent to a known heat fixing means or the like, where the toner image is fixed to the transfer material. The toner remaining on the image carrier after the completion of transfer is removed by a known cleaning means such as a cleaning blade.

To supply the toner to the image carrier, first, the toner is carried out of the toner container by the rotating developer carrier and carried out on the developer carrier, and is conveyed to the developing area facing the photosensitive drum. . As the developer carrying member, a developing sleeve in which the outer peripheral surface of the aluminum tube is sandblasted with alundum abrasive grains, or an NBR rubber layer which is an elastic body is about 2 mm on the outer surface of the aluminum tube. An elastic developing roller or the like having a resistance value of about 10 ⁴ to 10 ¹² Ωcm and having a thickness of 10 to 10 ¹² Ωcm is used.

Now, a developer regulating member for regulating the amount of toner conveyed to the developing area to an optimum amount will be described. The thickness of the developer layer on the developer carrying member is regulated by the developing blade that is a regulating member. The developing blade, for example, fixed by a steel plate holder,
An elastic developing blade made of an elastic material such as urethane rubber having a thickness of 1 to 1.5 mm and a free length of about 10 mm is used.
The elastic developing blade is brought into contact with a developing sleeve or a developing roller, which is a developer bearing member, with a contact pressure of about 30 g / cm. As a result, a developer layer (toner coat layer) is formed on the developer carrier such as the developing roller described above.

In the toner coating method using such a regulating member, the thickness of the toner coat layer on the developer carrying member is
Mainly determined by the shape of the magnetic field and electric field,
It has the advantage of being less susceptible to instability factors such as tribo and cohesive force. Also, the coated toner is
Since it is attracted onto the developer carrying member by the magnetic force of the magnet or the like installed therein, there is also an advantage that toner scattering is small.

However, in the above-mentioned conventional example, since the toner coating amount on the developer carrying member such as the elastic developing roller in the developing area is as large as 1.5 to 2.5 mg / cm ² , the development at the developing portion is performed. There has been a problem that the amount of toner coat on the surface of the agent carrier becomes too large and scattering around characters occurs.

On the other hand, it is possible to reduce the amount of toner coating that contributes to the development by weakening the polarity at the development pole position, which is the development site, to lower the toner spike. In this method, the toner holding power is weakened, and the fog on the white background portion of the image and the toner scattering around the developing device are deteriorated, which is not a good solution.

Further, in the above-mentioned conventional example, in particular, in order to prevent character dropout which is likely to occur when an OHP sheet or a thick paper is used as the transfer material, the gear ratio of the transfer roller to the photosensitive drum and the photosensitive drum are applied. It is a value calculated from the outer diameter of the transfer roller without contact, and the transfer roller is rotated 110% faster than the photosensitive drum, and the actual paper feed speed is about 1% faster than the photosensitive drum. I am trying to do it. However, this causes another problem that a deviation occurs due to the paper type and the thickness of the paper, resulting in an image with poor printing accuracy.

However, due to the trend toward higher image quality required of printers in recent years, the toner particle size is 12
Since the particle size has been reduced from about μm to about 6 to 8 μm, the problem of hollow characters has become particularly noticeable.
As described above, it is necessary to increase the speed difference between the transfer roller and the photosensitive drum. That is, if the speed difference of the transfer roller with respect to the photosensitive drum is increased, the character dropout is improved, but the printing accuracy is deteriorated. On the other hand, if the speed difference of the transfer roller with respect to the photosensitive drum is decreased, the printing accuracy is improved. However, the character dropout is aggravated, and it is difficult to satisfy both the problem of character dropout and the problem of printing accuracy in the obtained recorded image.

[0011]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an image forming apparatus which prevents the scattering of toner around characters which is caused by an excessively large toner coat amount at a developing portion. Especially. Another object of the present invention is to use a toner having a fine particle diameter, without causing a peripheral speed difference between a transfer roller and a photosensitive drum, without causing a character dropout, and for printing. An object of the present invention is to provide an image forming apparatus that can obtain a printed matter with good accuracy.

[0012]

The above object can be achieved by the present invention described below. That is, the first invention of the present invention is to expose a uniformly charged photosensitive drum to form an electrostatic latent image, and develop the electrostatic latent image with toner coated on a developer carrier. Then, in an electrophotographic image forming apparatus that transfers a toner image onto a transfer material using a transfer roller, heat-fixes it, and outputs the toner, when the shape factor SF ₂ is defined by the following formula, The SF ₂ value is 100 or more and 150 or less, and the toner coat amount on the developer carrying member (mass /
The image forming apparatus is characterized in that the area) is 0.5 mg / cm ² or more and 1.5 mg / cm ² or less. SF ₂ = {(perimeter) ² / (projected area × 4π)} × 100

In a second aspect of the present invention, the toner used in the image forming apparatus is a toner shape factor S.
The F ₂ value is 100 or more and 150 or less, and the weight average particle diameter is 4.
Calculated from the gear ratio of the transfer roller to the photosensitive drum, which is 5 μm or more and 8 μm or less, and the outer diameter of the transfer roller alone, which is not in contact with the photosensitive drum.
The relative speed of the transfer roller to the photosensitive drum is 95% or more and 110% or less. SF ₂ = {(perimeter) ² / (projected area × 4π)} × 100

[0014]

According to the action of the first invention of the present invention, the toner coat amount on the surface of the developer carrying member in the developing region is kept appropriately thin, so that the toner coat amount becomes large in the developing region. It is possible to effectively prevent the toner from scattering around the characters caused by the passing, and to improve the image quality of the obtained recorded image. Further, since the toner used in the second aspect of the present invention has a small particle size and a small surface area, it is effective in preventing the toner from being charged more than necessary. Further, since the toner has a small surface area, the effect of silica added externally is great, the level of voids in characters is very good, and it is not necessary to provide the transfer roller with a peripheral speed difference with respect to the photosensitive drum. The printing accuracy is also greatly improved, and both prevention of character dropout and improvement of printing accuracy are achieved.

The present invention will be described in more detail below with reference to preferred embodiments. FIG. 1 is an enlarged configuration diagram of a developing device portion of an image forming apparatus showing an embodiment of the present invention. The basic configuration of the image forming apparatus is basically the same as that of the conventional image forming apparatus described above, and the description thereof will be omitted unless necessary.

As shown in FIG. 1, the developing device 10 of the present invention is provided with a developing container 12 containing, for example, a magnetic toner 11 which is an insulating one-component magnetic developer, and the like. A developing sleeve 17 is arranged in contact with the photosensitive drum 1 in the opening facing the photosensitive drum 1. The magnetic toner 11 in the developing container 12 is carried on the developing sleeve 17 by the magnet roller 15 provided inside the developing sleeve 17. The developing sleeve 1
The toner carried on 7 is triboelectrically charged and thin-layer coated by a developing blade 16 as a regulating member, and is conveyed to a developing area 13 facing the photosensitive drum 1 as the developing sleeve 17 rotates. It

The development carrier used in the present invention includes:
As described above, a conventionally known development sleeve made of a sandblasted aluminum base pipe or an NBR rubber layer having a thickness of about 2 mm is provided on the outer periphery of the aluminum base pipe to have a resistance of 10 ⁴ to 10 ¹² An elastic developing sleeve provided with an elastic member having an Ωcm may be used. As the developing blade 16, a conventionally known one is used, but for example, an elastic developing blade made of an elastic member such as urethane rubber fixed to a steel plate holder is used, and the developing blade is the above-described developing blade. It is provided in contact with a sleeve or an elastic developing sleeve.

First, the first aspect of the present invention will be described with reference to preferred embodiments. In the first aspect of the present invention, the developing blade 16 as described above is used to appropriately thin the toner on the developer carrying member 17 such as the developing roller, that is, the toner coating amount is 0.5 to 1.5 mg / cm ² . A developer layer (toner coat layer) needs to be formed. That is, when the toner coat amount is more than 1.5 mg / cm ² ,
Toner scattering is exacerbated and the image quality is inferior.
If it is less than / cm ² , there is an adverse effect that the density becomes low due to solid black or the like, which is not preferable.

As a method of forming such a thin toner coat layer, for example, the surface roughness of the developer carrying member 17 such as the developing sleeve and the developing roller described above is determined by the center line average roughness Ra = 0. It is necessary to configure so as to maintain the thickness of 1 to 0.5 μm. When the surface roughness is rough, the toner coating amount becomes about 2.0 mg / cm ² , and the toner scattering is deteriorated, which is not preferable. Further, in the case of the elastic developing roller provided with the elastic member as described above, it is necessary to polish the surface of the roller so as to have the surface roughness as described above.

The toner coat layer 11a conveyed to the developing area 13 by such a developer carrying member 17 is used for developing the electrostatic latent image formed on the photosensitive drum 1,
The electrostatic latent image is developed into a toner image and visualized. still,
At the time of development, the bias power source 50 is applied to the developing sleeve 17.
AC voltage (peak-to-peak voltage of 1,600 V, frequency of 2 kHz) to DC developing bias of about -400 to -600 V.
Bias is applied. The toner image thus developed on the photosensitive drum 1 is then transferred to a transfer target material (not shown) by the transfer roller 5 and fixed by a heat fixing device (not shown). Also, the transfer residual toner remaining on the drum after the transfer is collected by the cleaner 7.

Next, the toner used in the image forming apparatus of the first aspect of the present invention has a toner shape factor SF ₂ of 1
It is necessary to be 00 or more and 150 or less. Here, the toner shape factor SF ₂ is defined by the following formula from the perimeter of the toner particles, and as is clear from the formula, SF
_{When the binary} value is 100, the toner particles have a spherical shape. SF ₂ = {(peripheral length) ² / (projected area × 4π)} × 100 Therefore, when the shape factor SF ₂ is larger than 150, the shape of the toner becomes far from a sphere, and the shape of the toner is indefinite. Is bad and the distribution of charge is broad,
A smooth developing sleeve having the above-mentioned surface roughness does not have a carrying force and is coated only with an excessively charged toner, which causes a decrease in density in printing several tens to several hundreds of sheets, which is preferable. Absent. On the other hand, when the toner having a shape factor SF ₂ according to the present invention and having a shape close to a sphere having a shape factor SF ₂ of 150 or less is used, the toner has good fluidity and the charge distribution is sharp (uniform). No problem occurs even with a developing sleeve having such a surface roughness.

Next, the second aspect of the present invention will be described with reference to preferred embodiments. In the image forming apparatus of the second invention of the present invention, as the toner, as in the first invention,
The toner has a shape factor SF ₂ value of 100 or more and 150 or less, and a nearly spherical toner is used. Further, in the second invention, the weight average particle diameter of the toner is 4.5 μm or more and 8 μm or more.
The following fine particle toner is used. That is, when a toner having a weight average particle diameter of 8 μm or more is used, good reproducibility of the minimum dot at a high resolution of about 600 dpi cannot be obtained,
On the other hand, if the weight average particle diameter is less than 4.5 μm, adverse effects such as white background fog and low density due to poor fluidity of the toner occur remarkably. Therefore, in the second aspect of the present invention, in order to improve the reproducibility of the smallest dot and prevent the adverse effects of white background fog and low density,
The toner particle size is set to 4.5 μm or more and 8 μm or less.

Further, in the second aspect of the present invention, the transfer roller is calculated from the gear ratio of the transfer roller to the photosensitive drum and the outer diameter of the transfer roller alone which is not in contact with the photosensitive drum. The relative speed with respect to the photosensitive drum is set to 95% or more and 110% or less. That is, in the second aspect of the present invention, for example, the transfer roller is driven by the photosensitive drum via a gear (not shown), or is a transfer roller which is a transfer device by driven transfer without using the gear. An image forming apparatus is used in which the peripheral speed is set to be substantially equal to the peripheral speed of the photosensitive drum.

In the above-mentioned transfer, the peripheral speed of the transfer roller with respect to the drum becomes a little less than 100%, and the printing accuracy is greatly improved. However, as will be described later, when the conventional toner is used, characters are not printed. It is the range where the void is a problem.
However, in the second invention of the present invention, the use of a toner having a shape close to a sphere greatly improves the level of voids in characters, so that the weight average particle diameter is 4.5 μm or more and 8 μm or less. Even if toner is used, the result may be obtained in which the transfer roller may be set to rotate at a substantially constant speed on the drum.

[0025]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. Example 1 FIG. 1 shows a partially enlarged view of a developing device of an image forming apparatus used in this example. The basic configuration of the device is the same as that described above. The developing device of this embodiment is a non-contact developing device, and the developing blade 16 has a hardness of 65 ° (JIS
A) An elastic developing blade having an elastic member made of urethane rubber having a thickness of 1.2 mm and a free length of 10 mm, which elastic member is in contact with a developing sleeve (developing roller) at a contact pressure of about 30 g / cm. used. For the developing sleeve 17 in contact with the elastic developing blade 16, an aluminum tube was used as it was. At the time of development, a bias power supply 50 applied to the developing sleeve 17 a bias in which an AC bias (a peak-to-peak voltage of 1,600 V, a frequency of 2 kHz, a rectangular wave) was superimposed on a DC developing bias of -500 V. Further, in this embodiment, as the toner, the magnetic toner which is the insulating one-component magnetic developer is used, but the weight average particle diameter of the magnetic toner is about 12 μm and the shape factor SF ₂ value is 120. It was used. Then, the toner coating amount on the elastic developing blade 16 was measured and found to be 0.8 mg / cm ² . The image obtained by the image forming apparatus of this example has a good image quality without toner scattering.

Next, in order to investigate the relationship between the toner coating amount on the elastic developing blade 16 and the toner scattering in the obtained image, the toner coating amount was set to 0. 3 mg / cm ^{2 to} 2.0
Images were formed by changing to mg / cm ² . With respect to the obtained image, toner scattering was measured by the method described below, and the results are shown in Table 1. As a result, it was found that when the toner coat amount was 1.5 mg / cm ² or less, toner scattering was improved and a good image quality was obtained. on the other hand,
If the toner coat amount is less than 0.5 mg / cm ² ,
This is not preferable because another problem that the image density becomes low in an image of solid black or the like occurs. That is, in the image forming apparatus of the present invention, the toner coat amount on the developing blade 16 is set to 0.5
Since the thin layer coat is formed by controlling the amount to be not less than mg / cm ^{2 and not} more than 1.5 mg / cm ² , it is possible to obtain an image with good image quality without toner scattering.

Table 1: Relationship between toner coat amount and toner scattering

The method for measuring the toner scattering of the image will be described below. As shown in FIG. 2, in measuring the scattering rate T, the difference in the area (S1) of the character portion with respect to the predetermined area (S) around the character is obtained, and how much toner is applied to the portion that should originally be a white background. In each case, the area ratio is expressed as a percentage. That is, S = S1 + S2 + S3 S: predetermined area (square portion) S1: area of character A portion S2: area of scattered portion around character S3: actual white portion area Can be obtained from T = S2 / (S−S1) × 100 Incidentally, the measuring device for image evaluation used for measuring the toner scattering is Luzex (manufactured by Nireco Co.). If the scattering rate T measured in this manner is 5% or less, there is no practical problem, but if it exceeds 5%, the characters on the image have a dirty impression when visually observed.

Embodiment 2 The basic structure of the image forming apparatus of this embodiment is basically the same as that of the conventional image forming apparatus described above, but the peripheral speed of the transfer roller 5 which is the transfer device is set to the photosensitive drum 1. It was set to be equal to. The transfer roller 5 is driven by the photosensitive drum 1 via a gear (not shown). In this embodiment, the relationship between the toner particle size and the image quality was considered. First, in the above image forming apparatus, an image having a toner shape factor SF ₂ value of 120 was used, and an image was formed by variously changing the weight average particle diameter of the toner as shown in Table 2 below. Then, with respect to the obtained image, the minimum dot reproducibility at 600 dpi and 300 dpi was examined. The results obtained are shown in Table 2. In the table, those in which the smallest dot could be reproduced were evaluated as ○, and those in which the smallest dot could not be reproduced properly were evaluated as ×.

Table 2: Relationship between toner particle size and image quality (minimum dot reproducibility)

As a result of the above test, as shown in Table 2, 30
With a resolution as low as 0 dpi, the smallest dot could be reproduced even with toner having a particle diameter of 12 μm.
It has been found that at a high resolution of 600 dpi, the smallest dot cannot be properly reproduced unless the toner has a small particle size of 8 μm or less. On the other hand, as the lower limit of the particle size,
It is not necessary that the toner particle size is as small as possible. In particular, when the toner particle size is smaller than 4.5 μm, adverse effects such as white background fog and low density occur remarkably due to deterioration of toner fluidity, which is not preferable. . Therefore, in the present invention, a fine particle size toner having a toner particle size of 4.5 μm or more and 8 μm or less is used.

Next, with respect to the toner having a fine particle diameter within the above range, the influence of the difference in shape on the image quality was examined. First, toners each having a weight average particle diameter of 6 μm are used, and a toner having a toner shape factor SF ₂ of 160 and an irregular shape are used as a conventional example, and a toner having a toner shape factor SF ₂ of 120 and a high sphericity are used in this embodiment. Two types of toner having different shapes were used. An image was formed using these toners using the image forming apparatus used in the above-described embodiment.
An OHP sheet and plain paper were used as the transferred material.
In addition, the transfer roller 5 for the photosensitive drum 1 is adjusted by adjusting the gear.
The peripheral speed of 90%, 95%, 100%, 105%, 11
Images were formed by changing them to 0% and 115%, respectively, and the obtained images were evaluated for character dropout and printing accuracy. Table 3 shows the results.

Table 3: Relationship between difference in toner shape and peripheral speed ratio of transfer roller / photosensitive drum

[0034] As shown in Table 3, in this embodiment, the conventional example
Compared to the case of using the irregular toner of
By using toner, it is especially
I was able to improve Le significantly. In the conventional example
Is a character dropout that occurs when using fine toner particles.
To prevent this, the peripheral speed of the transfer roller 5 is set to the photosensitive drum 1.
It is necessary to increase it to 110% or more of the peripheral speed.
However, if it is too fast (115% or more), the characters will be skipped.
Was good, but there was a problem in printing accuracy. Against this
However, as is clear from the results of Table 3, in the case of this embodiment,
Gives the transfer roller a peripheral speed difference with respect to the photosensitive drum
It is possible to achieve both missing characters and printing accuracy.
Was completed. Further, in the present embodiment, the fineness of 6.0 μm
Since toner particles are used, it is possible to
A high quality image excellent in actuality was obtained.

Embodiment 3 The basic structure of the image forming apparatus of this embodiment is basically the same as that of the conventional image forming apparatus described above, but the transfer roller, which is the transfer device, is not driven but is driven by the drum. It was set so that it was driven to contact and rotated, and rotated at substantially the same peripheral speed. Example 2 using this image forming apparatus
An image was formed using a spherical toner having the same shape factor (SF ₂ = 120) and the average weight particle diameter (6.0 μm). For comparison, an image was formed using a conventional amorphous toner having a weight average particle diameter of 6.0 μm.

An image was formed using an OHP sheet. In this example as well, since the spherical toner was used to improve the level of voids in the characters as in Example 2, the weight average particle size was 6. Good results could be obtained even if the toner having a fine particle diameter of 0 μm was used and the transfer roller 5 was set so as to be driven and contact-rotated with the photosensitive drum 1. On the other hand, when the conventional irregular toner is used, the peripheral speed of the transfer roller 5 with respect to the photosensitive drum 1 becomes a little less than 100% in the driven transfer, and the conventional toner causes a blank character.

[0037]

As described above, according to the present invention, the coat amount of the developer on the surface of the developer carrying member at the developing portion is maintained at an appropriate level, so that the toner coat amount becomes too large at the developing portion. It is possible to provide an image forming apparatus in which the occurrence of scattering around characters caused by the above is effectively prevented and the image quality is improved. Further, according to the present invention, it is possible to form an image by using the toner having a fine particle diameter without providing the transfer roller with a peripheral speed difference with respect to the photosensitive drum. Provided is an image forming apparatus in which the improvement of the image quality is achieved and the image quality is greatly improved.

[Brief description of drawings]

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

FIG. 2 is a diagram illustrating a method of measuring toner scattering.

[Explanation of symbols]

 1: Photosensitive drum 2: Charging roller 3: Exposure device 5: Transfer roller 7: Cleaner 10: Developing device 11: Magnetic toner 11a: Toner coat layer 12: Developing container 13: Developing area 15: Magnet roller 16: Developing blade 17: Developing sleeve 50: Bias power supply N1, N2, S1, S2: Electrode S: Predetermined area (square portion) S1: Area of character A portion S2: Area of scattered portion around character S3: Actual white portion area

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Yozo Horita 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Yuko Ogama 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Within the corporation

Claims (2)

[Claims] 1. A uniformly charged photosensitive drum is exposed to form an electrostatic latent image, the electrostatic latent image is developed with toner coated on a developer carrier, and a transfer roller is used. In an electrophotographic image forming apparatus in which a toner image is transferred onto a transfer target material, heated and fixed, and output, the toner has a shape factor SF ₂
Is defined by the following equation, the SF ₂ value of the toner is 10
0 or more and 150 or less, and the toner coating amount (mass / area) on the developer carrying member is 0.5 mg / cm ² or more and 1.
An image forming apparatus characterized by being 5 mg / cm ² or less. SF ₂ = {(perimeter) ² / (projected area × 4π)} × 100 2. A uniformly charged photosensitive drum is exposed to form an electrostatic latent image, the electrostatic latent image is developed with toner coated on a developer carrier, and a transfer roller is used. In an electrophotographic image forming apparatus in which a toner image is transferred onto a transfer target material, heated and fixed, and output, the toner has a shape factor SF ₂
Is defined by the following formula, the SF ₂ value of the toner is 1
00 or more and 150 or less, the weight average particle diameter is 4.5 μm or more and 8 μm or less, and the gear ratio of the transfer roller to the photosensitive drum, and the outer diameter of the transfer roller alone which is not in contact with the photosensitive drum. The relative speed of the transfer roller to the photosensitive drum calculated from is 95% or more 11
An image forming apparatus characterized by being 0% or less. SF ₂ = {(perimeter) ² / (projected area × 4π)} × 100