JP2009294546A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of improving an image density and a dot reproducibility, and reducing fogging. <P>SOLUTION: A developing device 1 develops an electrostatic latent image formed on a photoreceptor 51 with toner by applying alternating voltage superposed on DC voltage to a developing roller 3. Bias voltage waveform superposed at this time has an original cycle (first cycle) in which developing side potential and reverse developing side potential are applied by once, and a cycle (second cycle) in which Vpp is gradually increased from an initial value to a maximum value. When duty on the same polarity side as the toner is defined as x(%), and frequency of the first cycle is defined as y(kHz), the duty and the frequency of the first cycle are set within a range satisfying 39≤x≤49, y≤0.5x-2.5, y≤-1.25x+76 and y≥-0.05x+13. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus including a developing device that develops an electrostatic latent image formed on an electrostatic latent image carrier with toner by applying an alternating voltage superimposed on a DC voltage to the developer carrier. .

  In an electrophotographic image forming apparatus, the surface of an electrostatic latent image carrier (for example, a photoreceptor) is charged, and an image is exposed to the charged area to form an electrostatic latent image. A developing method for developing and visualizing (developing) is employed.

  As such a developing method, generally, a one-component developer containing toner or a two-component developer containing carrier and toner is used, and the toner is frictionally charged to carry an electrostatic latent image. A developing method is used in which the electrostatic latent image on the surface of the body is attracted by the electrostatic force to develop the electrostatic latent image to form a toner image.

  For example, when a two-component developer is used, a magnetic brush is formed by a carrier on a developer carrier (for example, a developing roller) in the developing device, and a bias is applied between the developer carrier and the electrostatic latent image carrier. A method of developing an electrostatic latent image while applying a voltage is employed.

  Regardless of the one-component or two-component developer, development is performed using toner charged to a polarity opposite to the surface potential charged on the electrostatic latent image carrier, or electrostatic latent image carrier There are cases where reversal development is performed using toner charged to the same polarity as the surface potential charged on the body.

  Furthermore, an electrostatic latent image formed on the electrostatic latent image carrier can be developed with the toner by applying a vibration bias voltage between the developer carrier and the electrostatic latent image carrier. is there. This vibration bias voltage is applied to the toner to be charged from the developing side potential that can exert a force in the direction from the developer carrier to the electrostatic latent image carrier, and from the electrostatic latent image carrier to the toner. The reverse development side potential capable of exerting a force in the direction toward the developer carrying member is alternately switched. For example, the development side potential is applied with respect to the application time of one cycle in which the development side potential and the reverse development side potential are applied. In general, a rectangular wave having a ratio of application time (duty ratio) of 50% is used.

  By the way, in such a conventional developing method, it is desirable to increase the charge amount of the toner in order to obtain smooth image quality with little roughness. However, if the charge amount of the toner is increased, for example, when a two-component developer is used, the electrostatic force between the carrier and the toner is proportional to the square of the charge amount, so the rate of separation of the toner from the carrier decreases. To do. As a result, the toner utilization efficiency is lowered, and the image density is lowered.

  In order to increase the image density, the vibration bias voltage Vpp (peak-to-peak voltage) may be increased. However, if this Vpp is increased, the electric field in the direction in which the toner returns from the electrostatic latent image carrier to the developer carrier becomes stronger, so that the toner image once attached to the electrostatic latent image carrier is peeled off. Dot adheres cleanly. That is, so-called dot reproducibility tends to deteriorate.

  The developing device described in Patent Document 1 can suppress fogging by controlling the three elements of the frequency, amplitude, and duty of the alternating voltage to a predetermined range value. For example, the three elements have a frequency of 1.0 kHz to 2.5 kHz, an amplitude of 500 V to 1000 V, and a duty of 40% to 6%.

In the developing device described in Patent Document 2, the frequency of the AC voltage applied to the developing roller is 5 to 12 kHz, the peak-to-peak voltage is 0.5 to 1.1 kV, the duty is 30 to 40%, and the background potential is 100 to 100. 150 V, development gap is 0.30 to 0.45 mm, two-component developer pumping density is 1.0 to 1.5 mg / mm ³ , and the linear speed ratio of the developing roller to the photosensitive member is 1.4 to 2.1. Prevents carrier adhesion and half-tone white spots.

JP-A-11-65270 JP 2004-101640 A

  Under the development conditions described in Patent Document 1 and Patent Document 2, it is difficult to achieve all of solid image density, dot reproducibility, and fog reduction.

  An object of the present invention is to provide an image forming apparatus capable of realizing all of improvement in image density, dot reproducibility, and reduction of fog.

The present invention relates to an image forming apparatus including a developing device that develops an electrostatic latent image formed on an electrostatic latent image carrier with toner by applying an alternating voltage superimposed on a DC voltage to the developer carrier. ,
The alternating voltage to be applied includes a development side potential for transferring toner from the developer carrier to the electrostatic latent image carrier, and a reverse development side potential for transferring toner from the electrostatic latent image carrier to the developer carrier. And having an alternating voltage waveform applied so as to switch alternately,
The alternating voltage is a first period in which the development-side potential and the reverse development-side potential are applied once, and the peak-to-peak voltage is gradually increased from the initial minimum value to the maximum value. And applying a maximum peak-to-peak voltage in the second period, and then applying an initial minimum peak-to-peak voltage,
When the duty on the same polarity side as the toner in the alternating voltage is x (%) and the frequency of the first cycle is y (kHz),
39 ≦ x ≦ 49 (1)
y ≦ 0.5x−2.5 (2)
y ≦ −1.25x + 76 (3)
y ≧ −0.05x + 13 (4)
In the image forming apparatus, the duty and the frequency of the first period are set within a range satisfying the above.

The present invention also provides
y ≧ −0.05x + 13 (4)
41 ≦ x ≦ 45 (5)
y ≦ x−25 (6)
y ≧ x−31 (7)
The duty and the frequency of the first cycle are set within a range satisfying the above.

Further, according to the present invention, the alternating voltage includes n first periods in one period of the second period, and each of the alternating voltage from the initial minimum peak-to-peak voltage to the maximum peak-to-peak voltage. When the peak-to-peak voltage is changed to V (1), V (2),... V (n) over time, each peak-to-peak voltage is expressed by the following formula (A). It is characterized by satisfying.
V (i) ≦ V (i + 1)
V (1) <V (n) (A)
1 ≦ i ≦ n−1 (i is an integer)

In the present invention, the alternating voltage is characterized in that the peak-to-peak voltage V (n) applied at the end of the second period satisfies the following formula (8).
1.5 kV ≦ V (n) ≦ 2.5 kV (8)

Further, according to the present invention, the alternating voltage is characterized in that the peak-to-peak voltage V (1) applied at the beginning of the second period satisfies the following expression (9).
0.3 kV ≦ V (1) ≦ 0.5 kV (9)

  Further, according to the present invention, the alternating voltage is characterized in that the number of periods of the first period included in the second period is 3 or more and 7 or less.

  In the invention, the developer is a two-component developer including a toner and a carrier.

  According to the present invention, an image forming apparatus includes a developing device that develops an electrostatic latent image formed on an electrostatic latent image carrier with toner by applying an alternating voltage superimposed on a DC voltage to the developer carrier. Device. At this time, the alternating voltage to be applied is the development side potential for transferring the toner from the developer carrying member to the electrostatic latent image carrying member, and the reverse for transferring the toner from the electrostatic latent image carrying member to the developer carrying member. It has an alternating voltage waveform applied so that the development side potential is alternately switched. Further, the alternating voltage is gradually increased from the initial minimum value to the maximum value in the first period in which the development side potential and the reverse development side potential are applied once each, and the peak-to-peak voltage is gradually increased. And applying a maximum peak-to-peak voltage in the second period and then applying an initial minimum peak-to-peak voltage.

Further, when the duty on the same polarity side as the toner in the alternating voltage is x (%) and the frequency of the first period is y (kHz),
39 ≦ x ≦ 49 (1)
y ≦ 0.5x−2.5 (2)
y ≦ −1.25x + 76 (3)
y ≧ −0.05x + 13 (4)
The duty and the frequency of the first period are set within a range satisfying the above.

  Since the image density is determined by the maximum peak-to-peak voltage, the same image density as when the maximum peak-to-peak voltage is continuously applied can be obtained.

  The dot reproducibility can be improved by periodically increasing the peak-to-peak voltage, and the dot reproducibility can be further improved by setting the duty to 49% or less.

  Although the fog tends to increase by periodically increasing the first period, the image density and the dot reproduction are set by setting the duty to 39% or more and setting the frequency in a range of about 11 kHz or more. It is possible to reduce the fog while maintaining the property.

Also according to the invention,
y ≧ −0.05x + 13 (4)
41 ≦ x ≦ 45 (5)
y ≦ x−25 (6)
y ≧ x−31 (7)
By setting the duty and the frequency of the first cycle within a range that satisfies the above, dot reproducibility can be further improved and fogging can be reduced.

According to the invention, the alternating voltage includes n first periods in one period of the second period, from the initial minimum peak-to-peak voltage to the maximum peak-to-peak voltage. Each peak-to-peak voltage is changed to V (1), V (2),... V (n) over time, and each peak-to-peak voltage is expressed by the following formula (A Is satisfied.
V (i) ≦ V (i + 1)
V (1) <V (n) (A)
1 ≦ i ≦ n−1 (i is an integer)

  When a peak-to-peak voltage close to the maximum is applied after the minimum peak-to-peak voltage, dot reproducibility deteriorates. Therefore, dot reproducibility can be improved by gradually increasing the peak-to-peak voltage from the minimum peak-to-peak voltage to the maximum peak-to-peak voltage.

  According to the invention, the peak-to-peak voltage V (n) applied at the end of the second period satisfies 1.5 kV ≦ V (n) ≦ 2.5 kV.

  By setting V (n) to 1.5 kV or more, the image density can be further improved. However, if it exceeds 2.5 kV, almost no improvement can be seen, so V (n) is set within such a range. It is preferable.

  According to the present invention, the alternating voltage is such that the peak-to-peak voltage V (1) applied at the beginning of the second period satisfies 0.3 kV ≦ V (1) ≦ 0.5 kV.

  By setting V (1) within this range, dot reproducibility can be improved and fogging can be reduced.

  According to the invention, the number of periods of the first period included in the second period is 3 or more and 7 or less.

  If it is 8 or more, when the second period is constant, the first period is shortened, and as a result, the dot reproducibility is lowered. Therefore, the number of periods of the first period is set within this range. By doing so, dot reproducibility can be improved.

According to the invention, the developer is a two-component developer containing a toner and a carrier.
Since the maximum peak-to-peak voltage is increased, the toner is easily separated from the carrier, and the use efficiency of the toner is increased. As a result, unevenness of the heading becomes inconspicuous, which is suitable for development of a two-component developer.

  Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In the present specification and drawings, components having substantially the same functional configuration are denoted by the same reference numerals, and redundant description is omitted.

  FIG. 1 is a longitudinal sectional view schematically showing an outline of the entire configuration of an image forming apparatus 100 according to an embodiment of the present invention. FIG. 1 is an example that is simplified and described mainly with respect to main components of the image forming apparatus of the present embodiment, and is not limited to the configuration of the image forming apparatus that performs the developing method according to the present invention. It is not something.

  The image forming apparatus 100 includes color images including a plurality of photosensitive members 51 (four in this embodiment, for yellow images, for magenta images, for cyan images, and for black images) that serve as electrostatic latent image carriers. This is a tandem color image forming apparatus that can be formed. The image forming apparatus 100 includes image data transmitted from various terminal devices (not shown) such as a PC (Personal Computer) connected via a network (not shown), and a document reading device (not shown) such as a scanner. And a printer function for forming a color image or a monochrome image on a sheet P as a transfer material (recording medium).

  As shown in FIG. 1, the image forming apparatus 100 is formed on an image forming station unit 50 (50Y, 50M, 50C, 50B) having a function of forming an image on a sheet P, and is formed on a recording medium P by the image forming station unit 50. A fixing device 40 having a function of fixing the toner image, and a transport unit 30 having a function of transporting the recording medium P from a supply tray 60 on which the recording medium P is placed to the image forming station unit 50 and the fixing device 40. ing.

  The image forming station section 50 includes four image forming stations 50Y, 50M, 50C, and 50B for yellow image, magenta image, cyan image, and black image, respectively.

  Specifically, between the supply tray 60 and the fixing device 40, the yellow image forming station 50Y, the magenta image forming station 50M, the cyan image forming station 50C, and the black image forming station 50B are arranged in this order from the supply tray 60 side. It is installed side by side.

  The image forming stations 50Y, 50M, 50C, and 50B for the respective colors have substantially the same configuration, and yellow, magenta, cyan, and black images are obtained based on image data corresponding to the respective colors. It is formed and transferred onto the paper P that will eventually become the transfer material (recording medium).

  Note that the reference numerals of the components of each image forming station in FIG. 1 are representatively shown for the image forming station 50Y for yellow images, and the reference numerals of the components of the other image forming stations 50M, 50C, 50B are omitted. It is.

  Each of the image forming stations 50Y, 50M, 50C, and 50B includes a photoconductor 51 serving as a latent image carrier on which an electrostatic latent image is formed, and a charging device 52 is provided around the photoconductor 51 in the circumferential direction. An exposure device 53, a developing device 1, a transfer device 55, and a cleaning device 56 are disposed.

  The photoconductor 51 has a substantially cylindrical drum shape having a photosensitive material such as OPC (Organic Photoconductor) on its surface, is disposed below the exposure unit 1, and is predetermined by a drive unit and a control unit. It is controlled to rotate in the direction (arrow F direction in the figure).

  The charging device 52 is a charging means for uniformly charging the surface of the photoconductor 51 to a predetermined potential, and is disposed above the photoconductor 51 and in the vicinity of the outer peripheral surface thereof. In this embodiment, a contact-type charging roller is used, but a charger-type or brush-type charging device may be used instead.

  The exposure device 53 irradiates the surface of the photoconductor 51 charged by the charging device 52 by irradiating it with laser light based on the image data output from the image processing unit (not shown), thereby exposing the surface. It has a function of writing and forming an electrostatic latent image according to image data. The exposure device 53 receives image data corresponding to yellow, magenta, cyan, or black according to each of the image forming stations 50Y, 50M, 50C, and 50B, so that an electrostatic latent image corresponding to the corresponding color is obtained. Is supposed to form. As the exposure device 53, a laser scanning unit (LSU) including a laser irradiation unit and a reflection mirror, or a writing device (for example, a writing head) in which light emitting elements such as EL and LED are arranged in an array can be used. .

  The developing device 1 includes a developing roller 3 serving as a developer latent image bearing a developer. The developing roller 3 is configured to convey the developer to a developing area where the toner can move to the photoreceptor 51. In this embodiment, the developing device 1 uses a two-component developer containing toner and a carrier, and uses the toner to convert an electrostatic latent image formed on the surface of the photoreceptor 51 by the exposure device 53. A toner image (visible image) is formed by reversal development.

  The developing device 1 contains yellow, magenta, cyan, or black developer according to the image formation of each of the image forming stations 50Y, 50M, 50C, and 50B. This developer contains toner charged to the same polarity as the surface potential charged to the photoreceptor 51. In this embodiment, the polarity of the surface potential charged on the photoconductor 51 and the charging polarity of the toner to be used are both negative.

  The transfer device 55 transfers the toner image on the photosensitive member 51 onto the transfer material P conveyed by the conveyance belt 33, and has a polarity opposite to the charging polarity of the toner (in this embodiment, a positive polarity). ) Is applied to the transfer roller 55.

  The cleaning device 56 removes and collects toner remaining on the outer peripheral surface of the photoreceptor 51 after development and image transfer onto the paper P as a transfer material. In the present embodiment, the photosensitive member 51 is disposed substantially horizontally (on the left side in FIG. 1) at a position substantially opposite to the developing device 1 across the photosensitive member 51.

  The conveyance unit 30 includes a driving roller 31, a driven roller 32, and a conveyance belt 33, and conveys a transfer material P to which a toner image of each color is transferred at each of the image forming stations 50Y, 50M, 50C, and 50B. is there. The transport unit 30 has a configuration in which an endless transport belt 33 is stretched between the driving roller 31 and the driven roller 32, and becomes a transfer material (recording medium) fed from the supply tray 60. The paper P is sequentially conveyed to the image forming stations 50Y, 50M, 50C, and 50B.

  The fixing device 40 includes a heating roller 41 and a pressure roller 42, and conveys the transfer material P to these nip portions so that the toner image transferred onto the paper P is thermocompression bonded onto the paper P. It is to fix.

  The image forming apparatus 100 according to the present embodiment also applies a bias voltage application that applies an oscillating bias voltage to the developing roller 3 so that the potential difference between the developing roller 3 and the photoreceptor 51 changes continuously and periodically. A bias voltage application unit 110 serving as means is provided. The vibration bias voltage has a development-side potential that can exert a force in the direction from the developing roller 3 toward the photoconductor 51 on the charged toner, and a direction in the direction from the photoconductor 51 toward the developing roller 3 with respect to the charged toner. This is an alternating voltage at which the reverse development side potential capable of exerting force is alternately switched. Details of the application of the vibration bias voltage will be described later.

  In the image forming apparatus 100 configured as described above, when the paper P conveyed by the conveyance unit 30 passes through the position facing the photoconductor 51 of each of the image forming stations 50Y, 50M, 50C, and 50B, At the facing position, the toner images on the respective photoreceptors 51 are sequentially transferred onto the paper P by the action of the transfer electric field by the transfer roller 55 disposed below via the conveying belt 33. As a result, the toner images of the respective colors overlap on the paper P, and a desired full-color image is formed on the paper P. The sheet P as a transfer material onto which the toner image has been transferred in this manner is subjected to a fixing process of the toner image by the fixing device 40 and then sent to a paper discharge tray (not shown).

  FIG. 2 is a side view showing a schematic configuration of the developing device 1 in each image forming station shown in FIG. Note that FIG. 2 is an example that is simplified and described mainly with respect to main components of the developing device 1 of the present embodiment, and is not limited to the configuration of the developing device that performs the developing method according to the present invention. It is not a thing.

  As shown in FIG. 2, in addition to the developing roller 3 described above, the developing device 1 of the present embodiment includes a regulating blade 6 that serves as a regulating member that regulates the layer thickness of the developer on the developing roller 3, and a developer. A pair of agitating / conveying screws 4 and 5 serving as an agitating / conveying member for conveying the developer to the developing roller 3 and agitating the developer; Is provided.

  In the developing tank 2, a pair of agitation / conveyance screws 4 and 5 are arranged substantially in parallel. A partition wall 7 is provided between the agitating / conveying screws 4 and 5 except for both ends in the axial direction. By providing the partition wall 7 in the developing tank 2 in this way, an independent developer transport path is formed in the developing tank 2 with the partition wall 7 as a boundary. In the developing device 1, the toner in the developer accommodated in the developing tank 2 is agitated with the carrier and frictionally charged by the agitating operation of the agitating / conveying screws 4 and 5 disposed in the developing tank 2. It has become so.

  Further, a developing opening Q is provided at a position facing the photosensitive member 51 in the developing tank 2, and the developing roller 3 has a developing gap (about 0.3 to 1.0 mm) between the developing roller 3 and the photosensitive member 51. ) And is disposed in the developing tank 2 so as to be partially exposed from the opening Q of the developing tank 2.

  The developing roller 3 includes a magnet roller 8 including a plurality of magnetic pole members arranged in parallel along the circumferential direction, and is externally fitted to the magnet roller 8 so as to be rotatable in a certain direction (G direction in FIG. 2). And a non-magnetic developing sleeve 9 formed of a substantially cylindrical aluminum alloy and brass or the like. The developing sleeve 9 is controlled in a predetermined direction (arrow G in the figure) by a control means / driving means not shown. Direction).

  The developer contains toner and a carrier made of a magnetic material. The developer is attracted to the surface of the developing sleeve 9 by the magnetic force of the magnet, and is conveyed on the developing sleeve 9 along the rotation direction G of the developing sleeve 9. At this time, the carrier is attracted to the surface of the developing sleeve 9 by the magnetic force of the magnet roller 8 to form a magnetic brush, and the toner adheres to the carrier by Coulomb force due to frictional charging.

  Further, on the upstream side in the rotation direction G of the developing sleeve 9 in the developing opening Q, the tip end portion of the regulating blade 6 is disposed so as to face the developing sleeve 9. In the present embodiment, the regulating blade 6 is configured to regulate the layer thickness of the developer formed on the surface of the developing roller 3.

  By configuring the developing device 1 of the present embodiment as described above, the developing device 1 is supplied with a certain amount of developer at a position facing the photoconductor 51, and the development supplied to the facing position. The toner in the agent is attracted by the electrostatic force of the electrostatic latent image formed on the surface of the photoreceptor 51, and the electrostatic latent image is developed to form a toner image. Further, the developing device 1 is configured such that, of the developer supplied to the above-described facing position, the carrier and the toner that has not been used for development are returned to the developing tank 2 again by the rotation of the developing sleeve 9. .

  The bias voltage application unit 110 is a vibration in which a development-side potential that exerts a force for directing toner from the developing roller 3 to the photoconductor 51 and a reverse development-side potential that exerts a force for directing toner from the photoconductor 51 to the developing roller 3 are periodically switched. A bias voltage having a waveform as shown in FIG. 3 is applied to the developing sleeve 9 of the developing roller 3 as the bias voltage.

  As shown in the waveform of FIG. 3, in the present embodiment, the peak-to-peak voltage (hereinafter referred to as Vpp) of the bias voltage is gradually increased from the initial Vpp, and after a certain number of cycles have elapsed, The Vpp is gradually decreased to Vpp and then gradually increased again. By gradually increasing Vpp, the toner is easily separated from the carrier, and the toner flies most from the carrier at the maximum Vpp. The amount of flight at this time is almost the same as when the same Vpp is always repeated. Further, the dot reproducibility is improved by once decreasing Vpp from the maximum Vpp state to the initial minimum Vpp. This is presumably because the toner flying at the maximum Vpp moves slowly to the dot latent image to form stable dots.

  As described above, the bias voltage waveform of the present invention has an original cycle (first cycle) in which the development-side potential and the reverse development-side potential are applied once, and Vpp is maximized from the initial value. And a cycle (second cycle) that gradually increases until

In other words, the development bias voltage in the present invention includes n first periods in one period of the second period, and from the initial minimum peak-to-peak voltage to the maximum peak-to-peak voltage. When each peak-to-peak voltage is changed to V (1), V (2),... V (n) over time, each peak-to-peak voltage is expressed by the following formula (A). Will be satisfied.
V (i) ≦ V (i + 1)
V (1) <V (n) (A)
1 ≦ i ≦ n−1 (i is an integer)

Further, when the duty on the same polarity side as the toner in the alternating voltage is x (%) and the frequency of the first period is y (kHz),
39 ≦ x ≦ 49 (1)
y ≦ 0.5x−2.5 (2)
y ≦ −1.25x + 76 (3)
y ≧ −0.05x + 13 (4)
Set the duty and frequency in a range that satisfies the above conditions.

(Example)
Examples 1 to 16 and Comparative Examples 1 to 13 were output using a multifunction machine MX-7001N manufactured by Sharp Corporation. However, various development bias waveforms are represented using an arbitrary waveform generator (trade name: HIOKI 7075, manufactured by Hioki Electric Co., Ltd.) and an amplifier (trade name: HVA4321, manufactured by NF Circuit Design Block Co., Ltd.). The output of the development bias voltage waveform shown in FIG. The toner used in the experiment was a volume average particle diameter of 6.8 μm, and the carrier was a volume average particle diameter of 40 μm. The toner charge amount during the experiment was about 25 μC / g.

  As the development bias waveform, the duty, the frequency of the first period, V (n), V (1), and the number of periods were changed as shown in Table 1 below to give Examples 1 to 16 and Comparative Examples 1 to 13.

  The duty indicates a duty ratio (%) on the same polarity side as the toner in the first period. V (n) represents Vpp of the first period applied at the end of the second period. V (1) represents Vpp of the first period applied at the beginning of the second period. The number of periods indicates the number of first periods included in the second period.

  Image density, dot reproducibility, and fog were evaluated for Examples 1 to 16 and Comparative Examples 1 to 13.

-Image density The image density is printed on the entire surface of A4 paper, and the image density of the printed solid image is measured with a portable spectrophotometric densitometer (trade name: X-Rite 939, manufactured by X-Rite). It was measured.

  As an evaluation standard of image density, a density of 1.6 or higher, which is not faint, is judged as good, ◯, 1.4 or higher, which is hardly seen in fading, and less than 1.6, can be used practically, and faint is noticeable 1 Less than 4 was marked as x for practical use.

  For dot reproducibility and fogging, a pattern image consisting of dots as shown in FIG. 4 is printed, and the paper on which the pattern image is printed is placed on a microscope (trade name: DIGITAL MICROSCOPE VHX-200, manufactured by Keyence Corporation). The image was magnified at a magnification of 100 and judged visually.

  As an evaluation standard for dot reproducibility, a dot that can clearly recognize the shape of the dot is good. ○ The outline of the dot is blurred. Was marked as x for practical use.

As an evaluation standard for fogging, less than 10 dots by toner (amount that cannot be recognized with the naked eye) in a 1 mm ² area where dots are not printed are good, and 10 or more and less than 20 (amount that can be recognized with the naked eye) Δ for practical use, 20 or more (amount that can be easily recognized with the naked eye) as x for practical use.

  Comprehensive evaluation is の も の for all evaluations of image density, dot reproducibility, and fogging, ◎, any one evaluation is △, and the remaining two evaluations are ◯, any one evaluation is ○ Then, the remaining two evaluations were Δ, and one or more evaluations were ×, where X was ×.

  In Example 1, the duty is 39.0% and the frequency is 11.5 kHz. At this time, the image density is ◯, the dot reproducibility and fog are △, and the overall evaluation is △. In Example 2, the duty is 39.0. %, Frequency 17.0 kHz, image density and fogging are ◯, dot reproducibility is Δ, and overall evaluation is ◯.

  In Comparative Example 1, the duty is 38.0% and the frequency is 11.5 kHz. At this time, the image density and dot reproducibility are ◯, the fog is ×, and the overall evaluation is ×. In Comparative Example 2, the duty is 38. 0%, frequency 17.0 kHz, image density is ◯, dot reproducibility is x, fog is Δ, and overall evaluation is x.

  Thus, even if the frequency is the same, if the duty is 38%, the overall evaluation is x, so the duty needs to be 39% or more.

  In Example 4, the duty is 49.0%, the frequency is 15.0 kHz, the image density and the fog are ◯, the dot reproducibility is Δ, and the overall evaluation is ◯. In Example 5, the duty is 49.0. %, Frequency is 11.0 kHz, image density is ◯, dot reproducibility and fog are Δ, and overall evaluation is Δ.

  In Comparative Example 6, the duty is 50.0%, the frequency is 15.0 kHz, the image density is ◯, the dot reproducibility is ×, the fog is Δ, and the overall evaluation is ×.

  Thus, even if the frequency is the same, if the duty becomes 50%, the overall evaluation becomes x, and therefore the duty needs to be 49% or less.

From the above evaluation results, the duty x (%) is
39 ≦ x ≦ 49 (1)
It is necessary to satisfy.

  In Example 2, the duty is 39.0%, the frequency is 17.0 kHz, the image density and fog are ◯, the dot reproducibility is Δ, and the overall evaluation is ◯. In Example 3, the duty is 45.0%, The frequency is 20.0 kHz, the image density and fog are ◯, the dot reproducibility is Δ, and the overall evaluation is ◯.

  In Comparative Example 2, the duty is 38.0%, the frequency is 17.0 kHz, the image density is ○, the dot reproducibility is ×, the fog is Δ, and the overall evaluation is ×, and in Comparative Example 3, the duty is 41.0. %, Frequency is 18.5 kHz, image density and fog are ◯, dot reproducibility is x, and overall evaluation is x. In Comparative Example 4, the duty is 45.0% and the frequency is 21.0 kHz. Density and fog are ◯, dot reproducibility is x, and overall evaluation is x.

When the duty x (%) and the frequency y (kHz) are assumed, an approximate straight line is obtained by using the least square method for x and y in Examples 2 and 3, and y = 0.5x−2.5. From the above evaluation results, it is preferable that y is smaller (lower frequency) than this approximate line,
y ≦ 0.5x−2.5 (2)
It is necessary to satisfy.

  In Example 3, the duty is 45.0% and the frequency is 20.0 kHz, the image density and the fog are ◯, the dot reproducibility is Δ, and the overall evaluation is ◯. In Example 4, the duty is 49.0%, The frequency is 15.0 kHz, the image density and fog are ◯, the dot reproducibility is Δ, and the overall evaluation is ◯.

  In Comparative Example 4, the duty is 45.0%, the frequency is 21.0 kHz, the image density and fog are ◯, the dot reproducibility is ×, and the overall evaluation is ×. In Comparative Example 5, the duty is 47.0%. The frequency is 17.5 kHz, the image density is ○, the dot reproducibility is ×, the fog is Δ, the overall evaluation is ×, and in Comparative Example 6, the duty is 50.0% and the frequency is 15.0 kHz. The image density is o, the dot reproducibility is x, the fog is Δ, and the overall evaluation is x.

When the duty x (%) and the frequency y (kHz) are used, an approximate straight line is obtained by using the least square method for x and y in Examples 3 and 4, and y = −1.25x + 76. From the above evaluation results, it is preferable that y is smaller (lower frequency) than this approximate line,
y ≦ −1.25x + 76 (3)
It is necessary to satisfy.

  In Example 1, the duty is 39.0%, the frequency is 11.5 kHz, the image density is ◯, the dot reproducibility and fog are Δ, and the overall evaluation is △. In Example 5, the duty is 49.0%, The frequency is 11.0 kHz, the image density is ◯, the dot reproducibility and fog are Δ, and the overall evaluation is Δ.

  In Comparative Example 1, the duty is 38.0%, the frequency is 11.5 kHz, the image density and the dot reproducibility are ○, the fog is ×, and the overall evaluation is ×. In Comparative Example 7, the duty is 49.0%, The frequency is 10.0 kHz, the image density is o, the dot reproducibility is x, the fog is Δ, and the overall evaluation is x.

When the duty x (%) and the frequency y (kHz) are used, an approximate straight line is obtained by using the least square method for x and y in Examples 1 and 5, and y = −0.05x + 13. From the above evaluation results, it is preferable that y is larger (higher frequency) than this approximate line,
y ≧ −0.05x + 13 (4)
It is necessary to satisfy.

  From the above results, when the duty x (%) and the frequency y (kHz) are set, the duty and the frequency of the first period are set so as to be within the range surrounded by the above formulas (1) to (4). There is a need.

  In Example 6, the duty is 41.0% and the frequency is 11.0 kHz, the image density, the dot reproducibility, and the fog are ○, and the overall evaluation is ◎. In Example 7, the duty is 41.0% and the frequency is 16 0.0 kHz, image density, dot reproducibility, fogging are good, and overall evaluation is good.

  In Example 1, the duty is 39.0%, the frequency is 11.5 kHz, the image density is ◯, the dot reproducibility and the fog are Δ, and the overall evaluation is △. In Example 2, the duty is 39.0%, The frequency is 17.0 kHz, the image density and fog are ◯, the dot reproducibility is Δ, and the overall evaluation is ◯.

  In Example 3, the duty is 45.0% and the frequency is 20.0 kHz, the image density and the fog are ◯, the dot reproducibility is Δ, and the overall evaluation is ◯. In Example 8, the duty is 45.0. %, Frequency 14.0 kHz, image density, dot reproducibility, fogging are good, and overall evaluation is good. In Example 4, the duty is 49.0%, the frequency is 15.0 kHz, the image density and fog are ◯, the dot reproducibility is Δ, and the overall evaluation is ◯. In Example 5, the duty is 49.0%, The frequency is 11.0 kHz, the image density is ◯, the dot reproducibility and fog are Δ, and the overall evaluation is Δ.

From the above table results, the duty x (%) is
41 ≦ x ≦ 45 (5)
Is a more preferable range.

  In Example 3, the duty is 45.0%, the frequency is 20.0 kHz, the image density and the fog are ◯, the dot reproducibility is Δ, and the overall evaluation is ◯. In Example 7, the duty is 41.0%, The frequency is 16.0 kHz, the image density, the dot reproducibility, and the fog are ◯, and the overall evaluation is ◎.

  In Example 2, the duty is 39.0%, the frequency is 17.0 kHz, the image density and fog are ◯, the dot reproducibility is Δ, and the overall evaluation is ◯.

When the duty x (%) and the frequency y (kHz) are assumed, an approximate straight line is obtained by using the least square method for x and y in Examples 3 and 7, and y = x−25. From the above evaluation results, it is more preferable that y is smaller (frequency is lower) than this approximate line.
y ≦ x−25 (6)
Is a more preferable range.

  In Example 8, the duty is 45.0% and the frequency is 14.0 kHz, the image density, the dot reproducibility, and the fog are ◯, and the overall evaluation is ◎. In Example 9, the duty is 42.0% and the frequency is 11 0.0 kHz, image density and dot reproducibility are good, fog is Δ, and overall evaluation is good.

  In Example 5, the duty is 49.0%, the frequency is 11.0 kHz, the image density is ◯, the dot reproducibility and the fog are Δ, and the overall evaluation is Δ.

When the duty x (%) and the frequency y (kHz) are assumed, an approximate straight line is obtained by using the least square method for x and y in Examples 8 and 9, and y = x−31. From the above evaluation results, it is more preferable that y is larger (higher frequency) than this approximate line.
y ≧ x−31 (7)
Is a more preferable range.

  In Example 6, the duty is 41.0% and the frequency is 11.0 kHz, the image density, the dot reproducibility, and the fog are ◯, and the overall evaluation is ◎. In Example 9, the duty is 42.0% and the frequency is 11 0.0 kHz, image density and dot reproducibility are good, fog is Δ, and overall evaluation is good. In Example 10, the duty is 43.0%, the frequency is 15.0 kHz, the image density, the dot reproducibility, and the fog are ◯, and the overall evaluation is ◎.

  In Comparative Example 8, the duty is 42.0%, the frequency is 10.0 kHz, the image density and the dot reproducibility are ◯, the fogging is ×, and the overall evaluation is ×.

When the duty x (%) and the frequency y (kHz) are used, an approximate straight line is obtained by using the least square method for x and y in Examples 6 and 9, and y = −0.05x + 13. From the above evaluation results, it is more preferable that y is larger (higher frequency) than this approximate line.
y ≧ −0.05x + 13 (4)
Is a more preferable range.

  From the above results, when the duty x (%) and the frequency y (kHz) are set, the duty and the frequency of the first period are set so as to be within the range surrounded by the above formulas (4) to (7). It turns out that it is more preferable.

  In Example 12, V (n) = 1.5 kV, image density is Δ, dot reproducibility and fog are ◯, and overall evaluation is ◯. In Example 13, V (n) = 2.5 kV. The image density, dot reproducibility, and fog are all good, and the overall evaluation is good.

  In Example 11, V (n) = 1.4 kV, image density and dot reproducibility are Δ, fogging is ◯, and overall evaluation is Δ. In Example 14, V (n) = 2.6 kV. The image density is Δ, the dot reproducibility and fog are ◯, and the overall evaluation is ◯.

From the above evaluation results, V (n) is
1.5 kV ≦ V (n) ≦ 2.5 kV (8)
It is preferable that

  In Example 16, V (1) = 0.3 kV, image density and dot reproducibility are ◯, fog is Δ, and overall evaluation is ◯. In Example 17, V (1) = 0.5 kV. The image density, the dot reproducibility, and the fog are all good and the overall evaluation is good.

  In Example 15, V (1) = 0.2 kV, dot reproducibility is good, image density and fog are Δ, and overall evaluation is Δ, and V (1) in Example 18 is 0.6 kV. The image density and fog are ◯, the dot reproducibility is Δ, and the overall evaluation is ◯.

From the above results, V (1) is
0.3 kV ≦ V (1) ≦ 0.5 kV (9)
It is preferable that

  In Example 19, the number of cycles is 3, the image density and dot reproducibility are ○, the fog is Δ, and the overall evaluation is ○, and in Example 20, the number of cycles is 7, and the image density and fog are Is ◯, dot reproducibility is Δ, and overall evaluation is ◯.

  In Example 21, the number of cycles is 8, the fog is ◯, the image density and dot reproducibility are Δ, and the overall evaluation is Δ.

  From the above results, it is preferable to set the waveform so that the first period includes 3 times or more and 7 times or less in the second period.

  FIG. 5 is a graph illustrating a range satisfying the expressions (1) to (7). The vertical axis represents the frequency (kHz) of the first period, and the horizontal axis represents the duty (%).

  The frequency (kHz) and duty (%) of the first period must be set within a range that satisfies the expressions (1) to (4), and a range that satisfies the expressions (4) to (7). It is more preferable that the setting is within the range.

  In the above description, the two-component development has been described. However, the present invention is not limited to the two-component development as long as the toner is developed by the development bias, and the same effect can be obtained in the one-component development. .

1 is a longitudinal sectional view schematically showing an outline of the overall configuration of an image forming apparatus 100 according to an embodiment of the present invention. FIG. 2 is a side view illustrating a schematic configuration of a developing device 1 in each image forming station illustrated in FIG. 1. FIG. 4 is a diagram showing a developing bias voltage waveform applied to the developing roller 3; It is a figure which shows the pattern image which consists of a dot for evaluating dot reproducibility and fog. It is the graph which illustrated the range which satisfy | fills Formula (1)-Formula (7).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Developing device 2 Developing tank 3 Developing roller 4, 5 Agitating / conveying screw 6 Restricting blade 30 Conveying unit 40 Fixing device 50 Image forming station unit 60 Supply tray 100 Image forming device

Claims (7)

In an image forming apparatus including a developing device that develops an electrostatic latent image formed on an electrostatic latent image carrier with toner by applying an alternating voltage superimposed on a DC voltage to the developer carrier.
The alternating voltage to be applied includes a development side potential for transferring toner from the developer carrier to the electrostatic latent image carrier, and a reverse development side potential for transferring toner from the electrostatic latent image carrier to the developer carrier. And having an alternating voltage waveform applied so as to switch alternately,
The alternating voltage is a first period in which the development-side potential and the reverse development-side potential are applied once, and the peak-to-peak voltage is gradually increased from the initial minimum value to the maximum value. And applying a maximum peak-to-peak voltage in the second period, and then applying an initial minimum peak-to-peak voltage,
When the duty on the same polarity side as the toner in the alternating voltage is x (%) and the frequency of the first cycle is y (kHz),
39 ≦ x ≦ 49 (1)
y ≦ 0.5x−2.5 (2)
y ≦ −1.25x + 76 (3)
y ≧ −0.05x + 13 (4)
An image forming apparatus, wherein the duty and the frequency of the first cycle are set within a range satisfying the above. y ≧ −0.05x + 13 (4)
41 ≦ x ≦ 45 (5)
y ≦ x−25 (6)
y ≧ x−31 (7)
The image forming apparatus according to claim 1, wherein the duty and the frequency of the first cycle are set within a range that satisfies the above. The alternating voltage includes n first periods in one period of the second period, and each peak-to-peak from the initial minimum peak-to-peak voltage to the maximum peak-to-peak voltage. When the voltage is changed to V (1), V (2),... V (n) over time, each peak-to-peak voltage satisfies the following formula (A). The image forming apparatus according to claim 1 or 2.
V (i) ≦ V (i + 1)
V (1) <V (n) (A)
1 ≦ i ≦ n−1 (i is an integer) The alternating voltage is a peak-to-peak voltage V (n) applied at the end of the second period satisfying the following formula (8). Image forming apparatus.
1.5 kV ≦ V (n) ≦ 2.5 kV (8) The alternating voltage has a peak-to-peak voltage V (1) applied at the beginning of the second period satisfying the following formula (9). Image forming apparatus.
0.3 kV ≦ V (1) ≦ 0.5 kV (9)   6. The image forming apparatus according to claim 1, wherein the alternating voltage has a period number of the first period included in the second period of 3 or more and 7 or less.   The image forming apparatus according to claim 1, wherein the developer is a two-component developer including a toner and a carrier.

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