JP2001281934A - Image forming device and image forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance image quality by improving the reproducibility of a line width and dot diameter as well as image density of a digital image forming device using a dry process two-component developer for which an iron powder carrier is used. SOLUTION: The carrier current value at impressed voltage of 200 V of the digital image forming device using the carrier consisting of iron powder as a core material is selected at 20 to 50 μA and the volume average grain size of the carrier at 50 to 70 μm. The resolution thereof is selected at >=600 dpi and the volume average grain size of the toner at 6 go 9 μm. The ratio of the minimum beam diameter D0 and minimum effective spot diameter Dr of a laser device is selected at 7<=Dr/D0<=1.0. The circumferential speed ratio of a linear speed R1 of a photoreceptor and a linear speed R2 of a developing roller is selected at R1/R1>=2.5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image forming apparatus and an image forming method using a dry two-component developer, such as a copying machine and a printer.

[0002]

2. Description of the Related Art Conventionally, a dry two-component digital image forming apparatus includes, for example, a magnetic carrier coated with a silicone resin, at least a binder resin, a colorant, and other additives selected as necessary. A two-component developer including a toner is used.

The toner in the electrostatic charge developer used for such a two-component developer is used in a fixing section of a dry two-component digital image forming apparatus.

FIG. 1 is a block diagram showing a conventional dry two-component digital image forming apparatus together with the present invention. The image forming apparatus includes a photoconductor, a laser device 5 for forming an electrostatic latent image on the photoconductor 1, a developing device 9 for developing the electrostatic latent image into a toner image, and fixing the toner image to paper. And a fixing unit 2. The fixing section 2 is provided with a heat roller 4 having a heater lamp built in a silicone-coated aluminum tube, and a pressure roller 6 whose outer peripheral portion is made of silicone rubber and whose core is iron. In the fixing unit 2, when the paper is passed vertically between the heat roller 4 and the pressure roller 6, the toner on the paper is fused and fixed to the paper by heat and pressure.

As the toner, for example, an acrylic styrene resin is used as a main resin, a gold-containing azo compound and bischromate as a charge control agent, carbon black as a coloring agent, and polyethylene wax (PEWAX) and polypropylene wax (PPWAX) as wax. There was something. The toner is prepared by mixing these materials, kneading them with a twin-screw kneading extruder, roughly crushing them into flakes with a cooling roller, classifying them with a jet mill, and producing raw toner. Produced by mixing silica and magnetite as a resistance modifier. The generated toner is used as a two-component developer by, for example, stirring and mixing the core material with a carrier coated with silicone with iron powder.

In recent years, various studies have been made to improve image quality. Japanese Unexamined Patent Application Publication No. 7-271133 discloses an electrostatic latent image holding member, a developer holding member, and a magnetic field generating means built therein. An image forming method using a developing device including a magnet roller as an image forming apparatus is described. In this image forming method, a developer is rotated while a magnet roller is fixed, and in particular, a two-component developer containing at least a ferrite carrier and a color toner is circulated and conveyed on the developer carrier to form a latent image. In this method, a latent image is developed with a color toner in a developing region of a holding member and a developer carrying member opposed thereto, and a toner image formed on the latent image carrying member is transferred onto a transfer material. In this image forming method, the carrier has a carrier core material surface coated with at least a resin, a weight average particle diameter of 25 to 60 μm, and a current value of 20 to 150 μA when a voltage of 500 V is applied. It has been proposed to improve the image quality.

It is important that the carrier current value be within the above range. If the current value is larger than 150 μA, a leak occurs when a specific toner scattering prevention electric field is applied, and the developing electric field is disturbed. Unevenness occurs, 20μ
If the particle diameter is smaller than A, the carrier strongly adheres to the electrode plate when a specific toner scattering prevention electric field is applied, and the toner scattering prevention effect is drastically reduced. In addition, by applying a specific toner scattering prevention electric field, the development characteristics are improved, that is, the image density is improved, fog is reduced, highlight reproduction is improved,
An improvement in line width reproducibility and the like are shown.

When the characteristics of the carrier are set as described above,
For example, in a carrier coated with silicone using iron powder as a core material, when the current value is 90 μA, the line width of one line becomes too thin, and a phenomenon that the dot diameter of the dot cannot be measured occurs. When the current value is 20 μA, both the line width of one line and the dot diameter of one dot can be compatible, but the image density is not satisfied.

In the above publication, 96% or more of Cu—Zn—F is preferably used as a core material of a carrier.
There is also a description that ferrite particles having a specific composition of e are preferable because they can be easily homogenized and spheroidized and have stable charging ability.

FIG. 2 is an enlarged view showing a part of the developing device 9 in the image forming apparatus shown in FIG. The developing device 9 includes a developing roller 18, a doctor blade 14 and the developer 12. The developing roller 18 includes a developing sleeve 16 and a magnet roll 17 as a magnetic shaft member.
, And are arranged close to each other with a distance D1 therebetween, and are configured to be rotatable in a rotation direction 10 opposite to the rotation direction 3 of the photoconductor 1.
The doctor blade 14 is a spike height control plate that controls the spike height. The doctor blade 14 is opposed to the developing roller 18 at a distance D2 upstream of the photoconductor 1 in the developer flow path. The ear height means that the developer 12 is applied to the developing roller 1.
The height from the surface of the developing roll 18 of the developer 12 to the top of the developer, which is put on the surface in contact with the photoconductor 1 when rotated at 8.

Using a ferrite carrier having a current value of 20 to 150 μA as described above, for example, the diameter of the developing roller 18 is 20 mm, and the distance D between the photosensitive member 1 and the developing roller 18 is D.
1 is 2 mm, the distance D2 between the developing roller 18 and the doctor blade 14 is 1.5 mm, and the process speed is 88 mm.
Under the development conditions set at mm / sec, the spikes of the ferrite carrier are small, so that the image density becomes extremely low and cannot be said to be sufficient as a good electrostatic charge developer.

Under these circumstances, there is a demand for development of an electrostatic charge developer capable of obtaining high quality and stable image quality while maintaining the carrier physical properties of the developer design.

[0013]

When an image is formed by using a silicone-coated iron powder carrier according to the contents described in the above-mentioned publication, there arises a problem that the density of the original document decreases as the carrier current increases. The higher the resolution of the image, the more remarkable the phenomenon.

In a dry two-component electrophotographic apparatus using an inexpensive iron powder-based carrier, in order to improve line width and dot diameter reproducibility and image density which cannot be influenced by high image quality, the following is required. As in the publication, it is conceivable to use a carrier having a weight average particle size of 25 to 60 μm and a current value of 20 to 150 μA when a voltage of 500 V is applied. However, it is difficult to obtain an output image with high image quality, which is the subject, and reproduced with a line width of one line of 83 μm or more and a dot diameter of one dot of 60 μm or more by using only these characteristics.

That is, the weight average particle size is 25 to 60 μm,
When a carrier having a current value of 20 to 150 μA when a voltage of 00 V is applied is used, a line width and a dot diameter of one dot are difficult to reproduce at a current value of 50 μA or more, and there is a problem that measurement cannot be performed. This problem has been confirmed in Examples and Comparative Examples of the present invention.

Further, when the toner volume average particle diameter in the electrostatic charge developer changes, and when the image forming apparatus uses dp,
When the i (dot per inch) resolution changes, a change occurs in the line width of one line, the dot diameter of one dot, and the image density such as solid density. That is, even if the carrier current of the developer is 40 μA and the carrier volume average particle size is 60 μm, the toner used for this has a volume average particle size of 10 μm.
m, the width of one line becomes narrower,
The dot diameter of one dot becomes so thin that it cannot be reproduced, resulting in image degradation. However, the solid image density is satisfied. As a cause, as the particle diameter of the toner in the developer increases, the chargeability decreases, the charge amount decreases, the edge effect decreases, and the reproduction of the line width and the dot diameter deteriorates.

The image forming apparatus has a dpi resolution of 600.
When the resolution changes to 300 dpi or less, the line width of one line becomes too large, and the dot diameter of one dot also becomes large.
Visually, a phenomenon such as collapse occurs and the image quality cannot be said to be good.

In the image forming apparatus shown in FIG.
When the ratio between the minimum beam diameter D0 and the minimum effective spot diameter Dr of the laser device 5 is out of the range of 0.7 ≦ Dr / D0 ≦ 1.0, if Dr / D0 is small, an edge effect in development occurs. Since it is difficult, the dot diameter becomes small. If Dr / D0 is large, the dot diameter becomes large, and the dot is crushed and clear dots cannot be reproduced. A phenomenon that cannot be said to be high image quality occurs. Note that the minimum beam diameter D0 refers to the minimum beam diameter used in the laser device 5 among the beams irradiated on the photoconductor 1,
The minimum effective spot diameter Dr refers to a spot diameter that can be used for a latent image on the photoconductor 1 among spot diameters formed on the photoconductor 1 by a beam applied to the photoconductor 1.

An object of the present invention is to provide a digital image forming apparatus and method using a dry two-component developer using an inexpensive iron powder-based carrier to reproduce the line width and dot diameter which are indispensable for high image quality. Performance and image density.

[0020]

SUMMARY OF THE INVENTION The present invention provides a photosensitive member for forming an electrostatic latent image, an electrostatic latent image forming means for irradiating the surface of the photosensitive member with light to form an electrostatic latent image, and a core. A two-component developer including a carrier and a toner, the surface of which is coated with iron powder, and a developing roller including a developing sleeve that covers an outer peripheral portion of a magnetic shaft member; A developing roller for transporting the developer to the photoreceptor, and a developing unit for visualizing an electrostatic latent image on the photoreceptor.
The carrier current value at an applied voltage of 00 V is 20 to 50
μA, and the carrier volume average particle size is 50 to 70.
μm.

According to the present invention, the carrier current value is 50 μm.
When A is larger than A, the edge effect is reduced and the line width and the dot diameter are reduced, and when the current value is smaller than 20 μA, the edge effect is improved and the line width and the dot diameter are reproduced, but the image density is extremely large. The problem of falling can be avoided. Further, the carrier volume average particle diameter is 70.
When the particle size is larger than μm, the charge amount of the developer becomes low, and the line width becomes difficult to be reproduced.
When it is smaller than 0 μm, it is possible to avoid the problem that the charge amount increases and the image density tends to decrease.
Therefore, an image satisfying the reproducibility of the line width and the dot diameter and the image density can be obtained.

The present invention is characterized in that the resolution of the digital image forming apparatus is 600 dpi or more, and the volume average particle diameter of the toner is selected to be 6 to 9 μm.

According to the present invention, even if the carrier current value and the carrier volume average particle size are specified, the resolution is 60%.
If the value falls below 0 dpi, it is possible to prevent the line width and the dot diameter from increasing and becoming crushed. Also, when the toner particle size is increased, the charge amount of the developer is reduced and the dot diameter is not reproduced because the dot diameter cannot be reproduced, and measurement cannot be performed. When the toner particle size is reduced, the charge amount increases and the solid density tends to be reduced. Can be. Therefore, an image that further satisfies the reproducibility of the line width and the dot diameter and the image density can be obtained.

The present invention can be used to form a latent image based on the minimum beam diameter D0 of light applied to the photoreceptor and the spot diameter of light formed on the photoreceptor in the electrostatic latent image forming means. When the ratio of the light to the minimum effective spot diameter Dr is 7 ≦ D
r / D0 ≦ 1.0.

According to the present invention, when Dr / D0 is smaller than 0.7, the dot diameter becomes small as an image and it is difficult to reproduce the image. When Dr / D0 is larger than 1.0, the dot diameter becomes large as an image. By avoiding the problem that the image is easily collapsed, the line width and the dot diameter on the image are reproduced, and high image quality with satisfactory solid image density can be obtained.

According to the present invention, the photosensitive member preferably has an outer diameter of 35 mmφ.
The following is characterized in that the peripheral speed ratio between the photoconductor linear speed R1 and the developing roller linear speed R2 is selected to be R2 / R1 ≧ 2.5.

According to the present invention, even if the carrier current, the carrier volume average particle diameter, the resolution of the image forming apparatus, the toner particle diameter, and the ratio between the minimum beam diameter and the minimum effective spot diameter of the laser apparatus are specified, the line width is not changed. It is not easy to reproduce the dot diameter and optimize the solid image density, and the peripheral speed ratio R2 / R between the photoconductor linear speed R1 and the developing roller linear speed R2.
By controlling the developing condition and the process condition by setting 1 to 2.5 or more, a further optimal image can be obtained.

According to the present invention, there is provided a two-component developer containing a carrier and toner in which a surface of a photoreceptor is irradiated with light to form an electrostatic latent image and a surface of iron powder as a core material is coated with silicone. The electrostatic latent image on the photoconductor is visualized by being conveyed to the photoconductor by a developing roller including a developing sleeve that covers the outer peripheral portion of the magnetic shaft member, and the visualized toner image is transferred to recording paper. A digital image forming method for fixing the transferred toner image to recording paper, wherein the carrier comprises:
Carrier current value at an applied voltage of V is 20 to 50 μA
And the carrier volume average particle size is 50 to 70 μm
An image forming method characterized by being selected from the group consisting of:

According to the present invention, an image satisfying the reproducibility of the line width and the dot diameter and the image density can be obtained by specifying the optimum carrier current value and the carrier volume average particle diameter.

According to the present invention, in the image forming method, the resolution is set to be 600 dpi or more, and the volume average particle diameter of the toner is selected to be 6 to 9 μm.

According to the present invention, in addition to the carrier current value and the carrier volume average particle size, the optimum resolution and the toner volume average particle size are defined to further improve the reproducibility of the line width and dot diameter, and the image density. A satisfactory image can be obtained.

According to the present invention, the minimum beam diameter D0 of the light irradiated to the photoconductor when forming the electrostatic latent image and the spot diameter of the light formed on the photoconductor are used for forming a latent image. The ratio of the light generated to the minimum effective spot diameter Dr is 7 ≦ Dr.
/D0≦1.0.

According to the present invention, a further optimum Dr / D0
Is defined, the line width and the dot diameter on the image are reproduced, and high image quality with a satisfactory solid image density can be obtained.

According to the present invention, the outer diameter of the photoreceptor is 35 mmφ.
The peripheral speed ratio between the photoconductor linear speed R1 and the developing roller linear speed R2 is selected as R2 / R1 ≧ 2.5.

According to the present invention, a more optimal image can be obtained by controlling the development conditions and the process conditions.

[0036]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an image forming method using an electrostatic charge developer according to the present invention will be described. First, a carrier current measuring method, a carrier particle size measuring method, a toner particle size measuring method, a line width and dot diameter measuring method, an image density measuring method, and a charge amount measuring method performed in the image forming method will be described. These measuring methods are not limited to the methods described below.

(A) Method of Measuring Toner Particle Size The particle size distribution of the toner was measured with a Coulter Multisizer measuring device. The volume average particle diameter D50 value was taken.

(B) Carrier current measuring method About 1000 g of a carrier sample was collected, and the room temperature was 20 to 2
Exposure to the environment between 6 ° C. and 50-60% RH for 15 minutes or more.

FIG. 3 is a view for explaining a method of measuring a carrier current in the developing device 9 shown in FIG. Developing device 9 incorporating developing roller 18 shown in FIG.
At a predetermined distance D facing the conductive developing sleeve 16.
1 was provided with a counter electrode using a drum cable 21 which is a photosensitive drum without a photosensitive member, instead of the photosensitive member 1. The carrier exposed between the developing sleeve 16 and the drum tube 21 is magnetically attracted, and the magnet roll 17 in the developing sleeve 16 is rotated to apply a DC voltage of 200 V between the drum cable 21 as the counter electrode. , A resistor was inserted between them, and the current was detected. The unit of the detected current value is μA.

(C) Method for Measuring Carrier Particle Size About 100 g of a carrier sample is weighed to the order of 0.1 g, and five types of sieves having sieve openings of 149 μm to 44 μm are used. They were stacked in the order of 63,44 μm in size, and a tray was placed at the bottom. The stacked sieves are shaken by a vibrator at a horizontal rotation speed of 285 rpm and a vibration frequency of 150 rpm for 15 minutes. After sieving, the carriers on each sieve and on the pan were weighed. Calculated by weight percentage, JI
Performed according to S-H2601.

(D) Method for Measuring Charge Amount About 0.2 g of a developer in which a carrier and a toner were mixed at a toner concentration of B% was weighed and sampled. The collected developer Cg was immediately measured by a blow-off machine (TB-200: manufactured by Toshiba Chemical Corporation). Blow off pressure is 1.0kg /
Assuming that the blow-off value after 30 seconds was A and the charge amount was determined by the following equation. Charge amount (μC / g) = A × 100 / (B × C)

(E) Measuring Method of Line Width and Dot Diameter The line width and the dot diameter were measured using microscope image data. Measurement and analysis were performed in the processes of image input, calibration, processing range setting, extraction, measurement, and data display. Digital Hi-Vision Microscope (BS) as an image input and calibration device
Using a 200 × lens with a -7800 (manufactured by CSK), an image sample was taken into the data and calibration was performed. Next, this data is analyzed by the analysis software (Win
(ROOF: manufactured by MITANNI CORPORATION) to set a processing range for extraction, and calculate the area of a target line or dot. The line width was determined by dividing the area of the line by the denominator using the distance in the longitudinal direction as the denominator, and the dot diameter was determined from the horizontal Feret diameter of the dot object and the vertical Feret diameter of the object.

(F) Image Density Measurement Method Image density was measured using a Macbeth densitometer (manufactured by Macbeth).

The image forming method using the electrostatic charge developer according to the present invention will be described with reference to Examples and Comparative Examples. The electrostatic charge developer in the present invention is not limited to the materials described below. By way of example, some examples will be addressed in order to determine what is appropriate.
Please fill in the blanks below.

To obtain the developers used in Examples and Comparative Examples, toners were first prepared. A mixture of 91 parts by weight of acrylic styrene as a main resin of a toner, 2 parts by weight of a gold-containing azo compound as a charge control agent, 6 parts by weight of carbon black as a coloring agent, and 1 part by weight of polyethylene wax as a wax. After pre-mixing using a machine,
The mixture was kneaded with a screw extruder. The kneaded product was cooled by a cooling roller, crushed into flakes by a crusher, and classified by a jet mill to obtain two types of raw toner having a volume average particle size of 7.5 μm and 10 μm. The volume average particle size of the raw toner is
It was measured by the above-mentioned (a) toner particle size measuring method. To each raw toner, 0.5 part by weight of silica as a fluidizing agent and 1 part by weight of magnetite as a resistance modifier were externally added by a mixer, and two kinds of toners having a volume average particle diameter of 7.5 μm and 10 μm were added. Obtained.

Next, a developer was prepared using the obtained toner. The obtained toner and each carrier having a core material of iron powder coated with silicone and having carrier properties shown in Table 1 below are stirred and mixed at a toner concentration of 8% by weight, and the charge amount is 35 μC. The mixture was stirred until it was secured, thereby obtaining a developer having various toner properties and carrier properties. Specifically, dimethyl silicon was used as the silicone on which the carrier was coated. The carrier current value and the carrier volume average particle diameter of the carrier physical properties are measured by the above-mentioned (b) carrier current measurement method and (c) carrier particle diameter measurement method, respectively. It was measured by the method. The carrier current value was adjusted by adjusting the silicone coating amount (resin amount) as a carrier coating agent.

As the main resin of the toner, in addition to the above-mentioned acrylic styrene, styrene, α-methylstyrene, halogenated styrene, styrenesulfonic acid, sulfonamidestyrene, methyl methacrylate, ethyl methacrylate, propyl methacrylate And butyl methacrylate.

As the charge control agent, bischromates and the like can be used in addition to the above-mentioned gold-containing azo compounds.

Examples of the coloring agent include acetylene black and aniline black in addition to the above-mentioned carbon black.

As the wax, a polyolefin wax other than the polyethylene wax, for example, a polypropylene wax may be used.

The materials of the toner of the above embodiment include a wax, a resistance adjusting agent and a fluidizing agent, but these additives are not essential, and the toner contains other additives as necessary. Is also good.

The developer obtained as described above is used as a digital copier (AR machine: manufactured by Sharp Corporation) having a resolution of 600 dpi or a copier having a resolution of 300 dpi (AR modified machine:
(Manufactured by Sharp Corporation).
The dot diameter reproducibility, solid image density and image quality were evaluated. The developing condition in the copying machine is the printer mode, as shown in FIG.
0 mm, the diameter of the developing roller 18 is 20 mm, the distance (D1) between the photosensitive member 1 and the developing roller 18 is 2 mm,
(D2) of 1.5 mm and the process speed of 88 mm / sec.

(Example 1) In a carrier coating agent for coating the surface of a core material of iron powder, the amount of silicone coating was adjusted to 4.5, which is slightly smaller than the amount of resin, and the current value of the carrier was adjusted to 48 μA. Then, a carrier having a carrier volume average particle size of 60 μm was prepared. Using the carriers set to these carrier properties, the developer obtained as described above was used in the copying machine and evaluated under the developing conditions.

(Example 2) In a carrier coating agent for coating the surface of a core material of iron powder, the silicone coating amount was slightly increased to 7.5 in terms of the resin amount, and the current value of the carrier was 2%.
Adjusted to 2 μA, carrier volume average particle size was 6
A 0 μm carrier was produced. Using the carriers set to these carrier properties, the developer obtained as described above was used in the copying machine and evaluated under the developing conditions.

(Comparative Example 1) In a carrier coating agent for coating the surface of a core material of iron powder, the amount of silicone coating was reduced to 2 which is a small amount of resin, and the current value of the carrier was adjusted to 55 μA. A carrier having an average particle size of 60 μm was prepared. Using the carriers set to these carrier properties, the developer obtained as described above was used in the copying machine and evaluated under the developing conditions.

(Comparative Example 2) In the carrier coating agent for coating the surface of the core material of the iron powder, the silicone coating amount was increased to a relatively large amount of 8, and the current value of the carrier was adjusted to 18 μA. A carrier having a volume average particle size of 60 μm was prepared. Using the carriers set to these carrier properties, the developer obtained as described above was used in the copying machine and evaluated under the developing conditions.

(Comparative Example 3) In the carrier coating agent for coating the surface of the core material of the iron powder, the amount of the silicone coat was set to 4 slightly smaller than the amount of the resin, and the current value of the carrier was 48.
μA, and the carrier volume average particle size is 80
A μm carrier was prepared. Using the carriers set to these carrier properties, the developer obtained as described above was used in the copying machine and evaluated under the developing conditions.

(Comparative Example 4) In a carrier coating agent for coating the surface of a core material of iron powder, the amount of silicone coating was set to 4, which was slightly smaller than the amount of resin, and the current value of the carrier was 48.
μA, and the carrier volume average particle size is 30
A μm carrier was prepared. Using the carriers set to these carrier properties, the developer obtained as described above was used in the copying machine and evaluated under the developing conditions.

(Example 3) In a carrier coating agent for coating the surface of a core material of iron powder, the silicone coating amount was set to 6 in resin amount, and the current value of the carrier was adjusted to 30 μA. A carrier having a particle size of 60 μm was prepared. A developer was obtained as described above using a carrier having these carrier properties and a toner having a volume average particle size of 7.5 μm. The obtained developer was used in the above-mentioned copier having a resolution of 600 dpi, and evaluated under the above-mentioned developing conditions.

Example 4 A developer was obtained as described above using a carrier having the same carrier properties as in Example 3 and a toner having a volume average particle diameter of 10 μm. The obtained developer was used in the above-mentioned copier having a resolution of 600 dpi, and evaluated under the above-mentioned developing conditions.

Example 5 A developer was obtained as described above using a carrier having the same carrier properties as in Example 3 and a toner having a volume average particle size of 7.5 μm. The obtained developer was used in the above-mentioned copier having a resolution of 300 dpi, and evaluated under the above-mentioned developing conditions.

Example 6 A developer was obtained as described above using a carrier having the same carrier properties as in Example 3 and a toner having a volume average particle diameter of 10 μm. The obtained developer was used in the above-mentioned copier having a resolution of 300 dpi, and evaluated under the above-mentioned developing conditions.

Example 7 A developer was obtained as described above using a carrier having the same carrier properties as in Example 3 and a toner having a volume average particle diameter of 7.5 μm. The obtained developer was used in a copier having a resolution of 600 dpi as described above. In addition to the above-mentioned development conditions, the laser apparatus was evaluated by setting the minimum effective spot diameter / beam diameter = 0.6.

Example 8 A developer was obtained as described above using a carrier having the same carrier properties as in Example 3 and a toner having a volume average particle size of 7.5 μm. The obtained developer was used in a copier having a resolution of 600 dpi as described above. In addition to the above-mentioned developing conditions, the laser apparatus was evaluated by setting the minimum effective spot diameter / beam diameter = 0.7.

Example 9 A developer was obtained as described above using a carrier having the same carrier properties as in Example 3 and a toner having a volume average particle diameter of 7.5 μm. The obtained developer was used in a copier having a resolution of 600 dpi as described above. In addition to the above-mentioned development conditions, the laser device was evaluated by setting the minimum effective spot diameter / beam diameter to 1.

Example 10 A developer was obtained as described above using a carrier having the same carrier properties as in Example 3 and a toner having a volume average particle diameter of 7.5 μm. The obtained developer was used in a copier having a resolution of 600 dpi as described above. In addition to the above-described development conditions, the laser apparatus was evaluated by setting the minimum effective spot diameter / beam diameter to 1.1.

(Example 11) In addition to the developer, the copying machine and the developing conditions, the evaluation was made by setting the peripheral speed ratio (developing roller linear speed / drum linear speed) between the photosensitive member and the developing roller to 3.

Example 12 In addition to the developer, the copying machine, and the developing conditions, the evaluation was performed by setting the peripheral speed ratio (developing roller linear speed / drum linear speed) between the photosensitive member and the developing roller to 2.2.

(Evaluation Criteria) One line line width reproducibility: 83 μm or more Δ: 75 μm or more and 83 μm or less ×: less than 75 μm 1 dot diameter reproducibility: 60 μm or more Δ: 50 μm or more and 60 μm or less ×: less than 50 μm Solid image density (ID) : 1.35 or more Δ: 1.28 or more and less than 1.35 ×: less than 1.28 γ characteristics (gradation) The formed photographic image was visually judged as follows. : Good △: normal ×: bad fog (whiteness meter): 0.8 or less △: 0.8 to 1.2 ×: 1.2 or more

FIG. 4 is a graph showing the reproducibility of the line width or the image density at the carrier current value of each of Examples and Comparative Examples. FIG. 5 is a graph showing the reproducibility of the dot diameter or the image density at the carrier current value in each of the examples and the comparative examples.

The results of Examples 1 to 12 and Comparative Examples 1 to 4 evaluated according to the above evaluation criteria are shown in Table 1 below.

[0072]

[Table 1]

(Evaluation Results) From Table 1, FIG. 4 and FIG.
Examples 1, 2 and Comparative Examples 1 and 2 show the effect of a change in carrier current on a constant carrier volume average particle diameter. As in Comparative Example 1, the carrier current was 55
In the case of μA, only solid image density is present, and line and dot reproducibility, γ characteristics, and fog are poor.
When the current value is 48 μA as in the first embodiment, the γ characteristic is slightly poor. When the current value was 22 μA as in Example 2, there was almost no problem with any of the evaluation items. When the current value is 18 μA as in Comparative Example 2, the solid density is low.

Examples 1 and Comparative Examples 3 and 4 show the effect of a change in the carrier volume average particle diameter when the carrier current is constant. When the current value is 48 μA and the carrier volume average particle diameter is 80 μm as in Comparative Example 3, the reproducibility of lines and dots, γ characteristics, and fog are poor. Comparative Example 4
The current value is 48 μA and the carrier volume average particle size is 3
At 0 μm, the solid density is insufficient.

Examples 3 to 6 show the effects of changes in resolution and toner particle size when the physical properties of the carrier are appropriate as in Examples 1 and 2. When the resolution was 600 dpi and the toner particle size was 7.5 μm as in Example 3, an image having almost no problem was obtained for any of the evaluation items. When the resolution was 600 dpi and the toner particle size was 10 μm as in Example 4, the reproducibility of lines and dots and the γ characteristics were slightly inferior. As in Example 5, the resolution is 300 dpi, and the toner particle size is 7.5 μm.
At this time, the reproducibility of lines and dots was slightly inferior. When the resolution was 300 dpi and the toner particle size was 10 μm as in Example 6, the reproducibility of lines and dots and the γ specification were slightly inferior. Examples 4 to 6 had slightly poor evaluation results, but were not particularly problematic.

In the seventh to tenth embodiments, when the physical properties of the carrier, the resolution and the toner particle diameter are appropriate as in the third embodiment, the change of the minimum effective spot diameter (Dr) / minimum beam diameter (D0) of the laser device is obtained. The effect is shown. When Dr / D0 was 0.6 as in Example 7, the reproducibility of lines and dots was slightly inferior. When Dr / D0 was 0.7 and 1.0, respectively, as in Examples 8 and 9, good and problem-free image quality was obtained for all evaluation items. When Dr / D0 was 1.1 as in Example 10, the reproducibility of lines and dots was slightly inferior.

In Examples 11 and 12, when the physical properties of the carrier, the resolution, the toner particle diameter and the minimum effective spot diameter (Dr) / minimum beam diameter (D0) of the laser device are appropriate as in Examples 8 and 9, The effect of a change in the peripheral speed ratio of development / process is shown. When the peripheral speed ratio was 3 as in Example 11, images satisfying all the evaluation items were obtained. When the peripheral speed ratio was 2.2 as in Example 12, only the solid density was slightly inferior.

[0078]

According to the present invention, an image satisfying the reproducibility of the line width and the dot diameter and the image density can be obtained by defining the optimum carrier current value and the carrier volume average particle diameter.

According to the present invention, in addition to the carrier current value and the carrier volume average particle size, the optimum resolution and the toner volume average particle size are defined to further improve the reproducibility of the line width and dot diameter, and the image density. A satisfactory image can be obtained.

According to the present invention, more optimal Dr / D0
Is defined, the line width and the dot diameter on the image are reproduced, and high image quality with a satisfactory solid image density can be obtained.

According to the present invention, a more optimal image can be obtained by controlling the development conditions and the process conditions.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a conventional dry two-component digital image forming apparatus together with the present invention.

FIG. 2 is an enlarged view showing a part of a developing device 9 in the image forming apparatus shown in FIG.

FIG. 3 is a diagram for explaining a method of measuring a carrier current in the developing device 9 shown in FIG.

FIG. 4 is a graph showing a relationship between a carrier current value and line width reproducibility or image density.

FIG. 5 is a graph showing a relationship between a carrier current value and dot diameter reproducibility or image density.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photoconductor 2 Fixing part 5 Laser device 9 Developing device

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G03G 15/08 501 G03G 15/04 120 507 15/08 507X 15/09 (72) Inventor Takahiro Bito Osaka 22-22 Nagaikecho, Abeno-ku, Osaka F-term in Sharp Corporation (reference) 2H005 BA06 CA12 EA01 EA05 FA02 2H031 AC08 AC15 BA09 2H068 AA54 FC05 FC08 2H076 AB02 AB09 2H077 AD02 AD06 BA03 EA03 FA19

Claims (8)

[Claims] A photosensitive member for forming an electrostatic latent image; an electrostatic latent image forming means for irradiating the surface of the photosensitive member with light to form an electrostatic latent image; and a surface of iron powder as a core material. A two-component developer including a carrier and a toner coated with silicone, and a developing roller including a developing sleeve that covers an outer peripheral portion of a magnetic axis member, wherein the developer is applied to the photoconductor in a region close to the photoconductor. A digital image forming apparatus comprising: a developing roller for transporting; and a developing unit for visualizing an electrostatic latent image on the photoconductor, wherein the carrier has a carrier current value of 20 to 50 μA at an applied voltage of 200 V. Wherein the carrier volume average particle diameter is selected to be 50 to 70 μm. 2. The resolution of the digital image forming apparatus is 6
00 dpi or more, and the toner volume average particle diameter is 6
The image forming apparatus according to claim 1, wherein the thickness is selected from a range of 9 to 9 μm. 3. A minimum beam diameter D0 of light radiated to a photoconductor in the electrostatic latent image forming means, and a spot diameter of light formed on the photoconductor and used for forming a latent image. 3. The image forming apparatus according to claim 2, wherein the ratio to the minimum effective spot diameter Dr is selected to be 0.7 ≦ Dr / D0 ≦ 1.0. 4. The photosensitive member has an outer diameter of 35 mmφ or less, and a peripheral speed ratio between a linear speed R1 of the photoconductor and a linear speed R2 of the developing roller is selected to be R2 / R1 ≧ 2.5. The image forming apparatus according to claim 3. 5. A two-component developer containing a carrier and toner in which the surface of a photoreceptor is irradiated with light to form an electrostatic latent image, and the surface of iron powder as a core material is coated with silicone. The electrostatic latent image on the photoreceptor is visualized by being conveyed to the photoreceptor by a developing roller including a developing sleeve that covers the outer peripheral portion of the shaft center member, and the visualized toner image is transferred to recording paper. A digital image forming method for fixing the formed toner image to recording paper, wherein the carrier has a carrier current value of 20 to 50 μA at an applied voltage of 200 V and a carrier volume average particle size of 50 to 70 μm. Image forming method. 6. In the image forming method, the resolution is set to 6
00 dpi or more, and the volume average particle diameter of the toner is 6 to 9 μm.
The image forming method according to claim 5, wherein m is selected. 7. A light beam which is a minimum beam diameter D0 of light irradiating the photosensitive member when forming the electrostatic latent image and a spot diameter of light formed on the photosensitive member and which can be used for forming a latent image. 7. The image forming method according to claim 6, wherein the ratio of the minimum effective spot diameter to the minimum effective spot diameter is selected to be 0.7 ≦ Dr / D0 ≦ 1.0. 8. The method according to claim 1, wherein an outer diameter of the photoconductor is selected to be 35 mmφ or less, and a peripheral speed ratio between a linear speed R1 of the photoconductor and a linear speed R2 of the developing roller is selected to be R2 / R1 ≧ 2.5. The image forming method according to claim 7.