JP2004295148A - Digital image developing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a digital image developing device capable of making the rear end part of an image part denser than the front end part thereof in order to make inconspicuous concentration unevenness caused by the front-to-rear difference in a developing direction. <P>SOLUTION: In the digital image developing device, the level of a toner non-development side bias V<SB>L</SB>in one cycle of pulse-shaped AC development bias to be applied to a development roller and a preliminarily set development bias in an applying time T<SB>L</SB>is defined as two stages V<SB>L1</SB>and V<SB>L2</SB>, and the difference between the toner development side bias V<SB>H</SB>in one cycle of the pulse-shaped AC development bias and the bias V<SB>L1</SB>just before the applying time T<SB>H</SB>is made larger than the difference between the toner development side bias V<SB>H</SB>in one cycle of the pulse-shaped AC development bias and the bias V<SB>L2</SB>just after the applying time T<SB>H</SB>. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a digital image developing device that develops an electrostatic latent image on the surface of an image carrier using a developing roller that is a rotating member that carries a thin layer of dry developer, and more particularly, to a laser beam or the like. The present invention relates to a digital image developing device for developing a latent image formed by dots on the surface of an image carrier with a developer.

  A method for visualizing image information of an electrostatic latent image by an electrophotographic method is currently used in various fields. In the electrophotographic method, an electrostatic latent image is formed on a photoconductor by a charging and exposing process, and the electrostatic latent image is developed with a developer containing toner, transferred, and fixed to be visualized by a process of fixing. The developer used here includes a two-component developer composed of a toner and a carrier, a one-component developer used alone with a toner such as a magnetic toner containing a magnetic material, and a single component developer that does not further contain a magnetic material. There are non-magnetic one-component developers used. Each developer is subjected to a developing process by a magnetic brush developing method using a roll member having a magnet as a developing roller. 2. Description of the Related Art In an image forming apparatus using an electrophotographic method, in recent years, there has been a strong demand for high-quality images without distinction between color images and monochrome images. In an image forming apparatus, charging, exposure, development, and transfer steps are usually repeated. In this step, the development step particularly affects the quality of an image. And a developing device are required.

  In order to solve such a problem, a method of performing development by applying an AC electric field while maintaining the latent image carrier and the developer in a non-contact state by using a roll member as a developer carrier, and a method using only a DC electric field. There is a method in which development is performed by applying the above method. However, from the viewpoint of the image quality of a line image, particularly, the reproducibility of fine lines, the former method in which the development is performed by applying an AC electric field is considered to be advantageous. Furthermore, in this developing method, in order to keep the magnetic brush layer formed by the developer in a non-contact state with respect to the latent image carrier, the magnetic brush layer is thinner than in the conventional contact developing method. Therefore, the amount of toner that can be supplied to the developing space becomes relatively small, and if the toner in the developing space is not transferred to the latent image with higher efficiency than the contact developing method, the image density is high and the image quality is high. Can not get. Also, for example, in Japanese Patent Application Laid-Open No. H11-163, an AC electric field is applied to obtain a good halftone image, no fog in the image, an appropriate image density, and a fine-textured image. Period and the alternating electric field rest period alternately, and the directions of the first and last electric fields of the alternating electric field operation period are reversed, and the first electric field of the alternating electric field in the next operation period after the rest period has elapsed. In the same direction as the direction of the last electric field of the AC electric field in the previous operation period, and the length of the operation period of the AC electric field becomes ２ times or more the length of the idle period. There has been proposed a developing device for such a configuration. Further, in Japanese Patent Application Laid-Open No. H11-163, in order to appropriately adjust the density with an inexpensive configuration, a time for supplying a predetermined level of a developing bias and a zero level are supplied according to a density reference indicating a reference operation of the developing density. An image recording apparatus and method including means for adjusting a time ratio have been proposed.

JP-A-10-78694 JP-A-10-97127

  However, the above-described developing device has the following problems. In the developing device, fine and good images can be obtained at an appropriate density without fog, and in the image recording device, the density can be appropriately adjusted with an inexpensive configuration. In the alternating current (AC) bias development in the image forming apparatus, there is a problem that the toner visualized image tends to spread rather than the electrostatic latent image, and an image with high resolution cannot be obtained in the sub-scanning direction.

  The present invention has been made in view of the above-described problems, and in order to make density unevenness caused by a front-to-back difference in the developing direction less noticeable, a digital image in which a rear end of an image portion is darker than a front end is provided. An object of the present invention is to provide a developing device. Another object of the present invention is to provide a developing device for a digital image in which the front end of an image portion is darker than the rear end in order to make density unevenness caused by a front-back difference in a developing direction less noticeable.

In order to solve the above problem, the invention according to claim 1 includes a developing roller that carries a developer movably endlessly, and a developer roller that transports the developer to a developing area facing the image carrier, and In a digital image developing apparatus having a power supply for performing development by applying a pulsed AC developing bias between a roller and a photoreceptor, an opposing portion in a developing area of the developing roller is in the same direction as a moving direction of the photoreceptor. moves and more quickly, with pulsed AC development bias first toner undeveloped side in bias V _L and the applied time T _L in period, the level of the developing bias to be set in advance as the two-stage V _L1, V _L2, and the difference between the toner developing side bias V _H and the applied time T _H immediately before side bias V _L1 of the pulsed AC development bias one cycle, the next pulsed AC toner present in the developing bias 1 cycle It is greater than the difference between the side bias V _H and the applied time T _H after side V _L2 is a developing device of a digital image, characterized in.

According to a second aspect of the present invention, there is provided a developing roller for carrying the developer movably endlessly, and the developing roller conveys the developer to a developing area facing the image carrier, and forms a pulse-like state between the developing roller and the photosensitive member. In a developing device provided with a power supply for performing development by applying an AC developing bias, a portion of the developing roller opposite to a developing region of the developing roller is moved in a direction opposite to a moving direction of the photoconductor, so that a pulse-shaped AC developing bias within one cycle. toner undeveloped side bias V _L application time T _L two-stage development bias level in V _L1, and V _L2, and toner development-side bias V _H and the applied time T _H after the pulsed AC development bias 1 cycle Patent that the difference between the side bias V _L2, larger than the difference between the toner developing side bias V _H and the applied time T _H immediately before the side V _L1 of the next pulsed AC development bias 1 cycle This is a digital image developing device.

  According to the present invention, it is possible to provide a digital image developing apparatus capable of making the rear end of an image portion darker than the front end and preventing density unevenness due to a front-back difference in a developing direction. Further, the present invention can provide a digital image developing apparatus in which the front end of the image portion is made darker than the rear end, and density unevenness caused by a front-back difference in the developing direction can be prevented.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. According to the present invention, a developing roller that carries the developer 5 movably endlessly, and the developer roller conveys the developer 5 to a developing area facing the image carrier, and applies a pulsed AC bias between the developing roller and the photoconductor. in the developing device of a digital image comprising a power source 6 for developing by applying the toner developing side bias V _H and the applied time in one cycle of the pulse-shaped AC development bias applied to the developing roller 2 T _H, the dots the following sub-scanning direction minimum diameter _d developing roller passing time _{T 1} of the _y, and a developing device of a digital image duty eta satisfies a relation of 0.5K _L ≦ η ≦ 1.5K _H.

  FIG. 1 is a schematic configuration diagram showing a one-component developing device according to one embodiment of the present invention. Here, the present invention will be described using a one-component developing apparatus, but the present invention is not limited to the conditions described below. The one-component developing device is provided at a position facing an image carrier (hereinafter, referred to as a “photosensitive drum”) capable of forming an electrostatic latent image by a difference in potential due to electrostatic charges charged on the surface. The developer 5 is stored in the one-component developing device, and a developer accommodating section 4 for supplying toner to the developing roller 2 as necessary, and a toner adhered to the surface and conveyed, and is brought close to the photosensitive drum 1. A developing roller 2; a developer thin layer blade 3 for regulating the amount of toner adhering to the surface of the developing roller 2 to form five layers of developer; and an electrostatic latent image formed on the surface of the photosensitive drum 1. A developing bias circuit capable of applying a DC and AC developing bias is provided. The developing roller 2 is rotatably supported, and a voltage is applied between the photosensitive drum 1 and the developing roller 2 from a developing bias circuit. As a result, an electric field is formed between the developing roller 2 and the photosensitive drum 1, and the developer 5 can develop the electrostatic latent image on the photosensitive drum 1 into a visible image. At this time, the applied voltage is a voltage in which DC and AC are superimposed. In particular, here, in order to maintain the developer layer stably for a long period of time, the surface of the developing roller 2 can be appropriately and uniformly roughened by blasting with fine particles. It is possible to use the developing roller 2 in which the problem of the deterioration of the developer conveying ability of the developing roller 2 with time due to the surface scraping of the roller 2 is improved by adding a simple and inexpensive developing roller processing method and conditions.

  The developer 5 used in this one-component developing device is a magnetic one-component developer 5, which is a magnetic material and a pigment in a thermoplastic resin such as a styrene-based resin, an acryl-based resin, a polyester-based resin, or a resin in which these are mixed. , Wax and the like can be appropriately selected and contained. Further, in addition to the above, an azo metal-containing dye for negative charging and a nigrosine dye for positive charging may be contained in accordance with the charging property of the developer 5. Further, it may contain fine particles of silica, alumina, titanium oxide, etc., which have been pulverized to 5 to 20 μm and then subjected to a hydrophobic treatment. Further, in this one-component developing device, a non-magnetic magnetic one-component developer 5 from which the magnetic material is removed from the above-described magnetic one-component developer 5 can also be used.

FIG. 2 is a diagram schematically showing an embodiment of the present invention. FIG. 2A is a diagram showing an electrostatic latent image formed on the photoconductor drum, and FIG. 2B is applied between the photoconductor drum and the developing roller by a developing bias circuit. FIG. 2C is a diagram schematically illustrating an AC bias, and FIG. 2C is a diagram schematically illustrating a developer developed on a photosensitive drum. This one-component developing device operates as follows to form the visible image 8. The developer 5 supplied from the developer accommodating portion 4 adheres to the surface of the developing roller 2, and a part of the adhered developer 5 receives the pressing force of the developer thin layer blade 3 by the rotation of the developing roller 2. While passing between the developer thin layer blade 3 and the developing roller 2, five layers of the developer are formed on the developing roller 2. At this time, the developer 5 can be frictionally charged to a desired polarity by coating the surface of the developer thin layer blade 3 with a fluorine resin or a silicone resin. The five layers of the developer formed on the developing roller 2 are transported to a developing area facing the photosensitive drum 1 by the rotation of the developing roller 2. At this time, as shown in FIG. 2A, an electrostatic latent image corresponding to one dot in the sub-scanning direction is formed on the photosensitive drum 1 by a laser beam from a laser light emitting element. A developing bias is applied between the photosensitive drum 1 and the developing roll, as shown in FIG. Here, V ₀ -V _H is set to the level of the potential difference at which most (67% or more) of the toner on the developing roller 2 adheres to the photosensitive drum 1 when the same level of the developing bias is applied only for the DC current. However, it is necessary to set them in consideration of the developer 5 to be used, the magnetic field of the developing roller 2, the gap between the photosensitive drum 1 and the developing roller 2, and the like. V _D -V _L is set to the level of the potential difference at which most of the toner (95% or more) on the developing roller 2 stays at the developing roller 2 when only the DC is applied at the same level of the developing bias. Similarly to the above, it is necessary to set in consideration of the developer 5 to be used, the magnetic field of the developing roller 2, the gap between the photosensitive drum 1 and the developing roller 2, and the like.

Developing bias, a pulse-like alternating current bias applied to the developing roller 2, the developing roller transit time in the sub-scanning direction minimum diameter d _y dot application time T _H of the toner developing side bias V _H T ₁ or less within 1 cycle to, by duty eta (ratio of T _H for 1 period of the AC bias) and 0.5K _L ≦ η ≦ 1.5K _H, the minimum dot image pattern could developing faithfully without excess or deficiency to the latent image pattern . At this time, eta <When the 0.5 K _L, the minimum dot toner visible image pattern tends to be insufficient density and area shortage from the latent image pattern, eta> when 1.5K _H is the minimum dot toner visible image pattern Tends to have an excessively large density or an excessively large area than the latent image pattern. Further, more preferably duty eta, good range of the K _L ≦ η ≦ K _H.

However, the developing roller transit time _{T 1,} the following equation (1)
_{T 1 = d y / | V} R -V P | −−−−−− (1)
In expressed, wherein, V _R is the developing roller linear velocity, V _P represents the photoreceptor linear velocity. Further, T _L represents the application time of the bias V _L without developing the toner within one period of pulse-like alternating current bias, T _H, the bias V _H for developing the toner in one cycle of the pulse-shaped AC bias T _L + _H represents the time of one cycle of the AC bias, and the following equation (2)
_{T L + H = T L +} T H ------ (2)
expressed. The duty η is given by the following equation (3)
_{η = T H / T L +} H <1 ------ (3)
Is represented by The code KL is _calculated by the following equation (4).
_{K L = (m P - MIN} × V P) / (m R - MAX × V R) --- (4)
Where m _P - _MIN is the minimum permissible amount of toner per unit area per unit area on the photosensitive drum, and m _R - _MAX is the maximum permissible toner per unit area per unit area on the developing roller immediately before development. And represents. The code KH is _calculated by the following equation (5).
_{K H = (m P - MAX} × V P) / (m R - MIN × V R) --- (5)
Where m _P - _MAX is the permissible maximum amount of solid per unit area per unit area on the photosensitive drum, and m _R - _MIN is the permissible minimum amount of per unit area per unit toner on the developing roller immediately before development. And represents.

  This is based on the following concept. If the amount of toner adhering to the photoconductor drum 1 is too small, the image density becomes low and the image quality deteriorates. If the amount is too large, the image quality rises because the image rises or spreads in the fixing process and the image quality deteriorates. Requires a certain amount of toner adhesion. In order to obtain this constant toner adhesion amount, the developing conditions must be considered together with the amount of toner conveyed on the developing roller 2. As the developing condition, the application time of the developing-side bias for developing the toner of the developing bias on the photosensitive drum 1 is most important. It is necessary to further consider the size of one dot to be reproduced, and this application time is at least one pulse or more for one dot, and a developing bias sufficient for developing the toner on the developing roller 2 is applied. It is necessary to. In order to obtain high-quality digital images composed of dots, the present invention relates to the relationship between the necessary amount of adhered toner, the amount of toner transported by the developing roller 2 and the pulse period to be further applied. It is specified.

Was examined image with one-component developer 5, to obtain a high-quality image, unit area equivalent solid portion permissible minimum deposited amount on the photosensitive drum 1 _- as (m P _MIN) is, 0.6 mg / cm ^2, the unit area equivalent solid portion permissible largest deposition amount on the photosensitive drum 1 _- the _{(m M MAX),} was found to be required 0.8 mg / cm ^2. Further, in order to confirm the developing performance of the digital image developing device, an image output test is performed under the following conditions.
Photosensitive drum image portion surface potential V ₀ = -100 V, the non-image portion surface potential V _D = -800 V, the image unit 1 dot d _y = 22μm (1200dpi equivalent), the circumferential speed V _P = 200mm / sec, the developing roller peripheral speed V _R = 300 mm / sec, AC bias V _L = −0 V, V _H = −1000 V Further, in order to obtain the stability of conveyance by making the one-component developer 5 on the developing roller 2 about 1 to 1.5 layers. a developing roller 2 on unit area equivalent allowable minimum toner adhesion amount immediately before development _- the _{(m R MIN),} a 0.8 mg / cm ^2, and the upper unit area developing roller 2 immediately before developing those permissible largest toner attached amount _- the _{(m R MAX),} which is 1.0 mg / cm ^2.

Application time _{T H} of the toner developing side bias _{V H,} considering the peripheral speed _{V R} of the developing roller 2 and the circumferential speed _{V P} of the photosensitive drum 1, become less 0.220Msec, also Deti eta, is _{K L} in 0.400, because _{K H} is 0.677, and 1.0 or less 0.2 or more. From this, the time _TL + _H of one cycle of the AC bias is 0.22 msec to 1.1 msec, and the frequency corresponds to 0.9 kHz to 4.5 kHz. Therefore, when an image is output at a frequency of 3.0 kHz and a duty η of 0.3, a high-quality image can be obtained. Further, as shown in FIG. 1, a solid portion having a predetermined size is provided on the photosensitive drum 1, and an amount of toner adhered to the solid portion is detected by an optical sensor 9, and a control unit (not shown) is provided. The processing may be performed by controlling the amount of toner to be developed on the photosensitive drum 1 by correcting the duty η.

Further, the present invention is a digital image developing device for correcting the duty η by detecting the amount of toner adhered to the photoconductor formed on the photoconductor in the above-mentioned developing device. FIG. 3 is a diagram showing the relationship between the duty η and the image density. Here, without the development of exposed portion (image portion) potential V ₀ photosensitive drum 1 changes the V _H portion duty η is the application time T _H when the developing bias side missing 0.3 developing pulse bias By increasing the frequency of the duty η, the amount of adhered toner to be developed can be increased. Regardless of before and after the correction of the amount of adhered toner to be developed, the one-dot image pattern can be developed faithfully to the latent image pattern and the amount of adhered toner can be developed without excess or deficiency, and high-quality image quality can be obtained.

The present invention also provides a developing device of the digital image, wherein a developer 5 is a one-component developer 5, and a unit area on the developing roller 2 of the developing immediately preceding those permissible largest amount of toner adhesion m _R - _MAX is a developing device of a digital image to 1.5 times the product of the toner volume average particle diameter 2r _t and the toner true density [rho _t and unit area. FIG. 4 is a diagram showing the relationship between the amount of toner attached to the developing roller and the amount of toner charge immediately before development. This is because, when an excessive toner layer is formed on the developing roller 2 of the one-component developing device, the amount of toner charge becomes insufficient, causing problems such as toner scattering and background contamination. For this reason, as the toner of the one-component developer 5 on the developing roller 2, it is necessary to maintain the toner charge amount of | -10 | [mu] C / g or more, which is an allowable lower limit. Therefore, by setting the toner adhesion amount on the developing roller 2 to within 1.5 layers, it is possible to maintain the toner charge amount of | −10 | μC / g or more. As a result, background contamination of the non-image area due to a decrease in the toner charge amount and toner scattering can be prevented, development can be performed faithfully with the latent image pattern, and the amount of adhered toner can be developed without excess or shortage, and high-quality image quality can be obtained. . Further, the digital image developing device of the present invention is not limited to the one-component developer 5 but can be applied to the two-component developer 15.

  Further, according to the present invention, in the digital image developing apparatus, the developer is a two-component developer 15 and the number of toner layers formed on the carrier surface on the developing roller 12 immediately before development is reduced to one or less. It is a digital image developing device. FIG. 5 is a schematic configuration diagram showing the two-component developing device. The two-component developing device is provided at a position facing the photoconductor drum 11 that can form an electrostatic latent image by a difference in potential due to electrostatic charges charged on the surface. A developer storage unit 14 for storing toner and supplying toner to a stirring roller as necessary; a developing roller 12 which conveys a carrier having toner adhered to the surface thereof as a developer 15; A developer thin-layer blade 13 for controlling the amount of the developer 15 attached to the surface of the developing roller 12 to form the developer 15 layer, and further, a DC and AC electrostatic latent image formed on the surface of the photosensitive drum 11 It has a developing bias circuit to which a developing bias can be applied. Here, the developer thin layer blade 13 is formed by coating a resin containing a charge control agent or the like on the surface of aluminum or stainless steel to charge the toner or the like on the surface.

The developer 15 used in the two-component developing device is composed of a carrier and a toner. The toner in the two-component developer 15 includes a thermoplastic resin, a pigment, a wax, and a charge control agent. The thermoplastic resin can be selected from a styrene-acrylic type, a polyester type, and an epoxy type. The pigment can be selected from carbun black, dyes and pigments. Further, the toner may contain fine particles of silica, alumina, titanium oxide, etc., which have been subjected to hydrophobic treatment after pulverizing the toner. As the carrier, a magnetic material such as ferrite, magnetite, Fe, Ni, Co or the like coated with a resin on the surface is used. The resin to be coated can be selected from among styrene-acrylic type, corn type and fluorine type. The weight average particle diameter of the toner can be 5 to 20 μm, and the weight average particle diameter of the carrier can be 20 to 100 μm. When the toner concentration C is coated up to the fully coated toner concentration C _MAX (% by weight) and then brought into contact with the carrier, the toner can be triboelectrically charged. However, when the toner concentration C exceeds a certain level, the uncharged toner rapidly increases, and the problem such as toner scattering becomes noticeable. Become. For this reason, the toner concentration C (% by weight) must be equal to or less than one toner layer relative to the carrier surface.

FIG. 6 is a model diagram when the toner is more completely covered on the carrier surface with the two-component developer 15. The complete coverage toner concentration C _MAX (% by weight) at that time is given by the following equation (6):
C _MAX = 100 × Nr ³ ρ _t / (Nr ³ ρ _t + R ³ ρ _C )-(6)
Is represented by Here, N represents the number of toners in the two-component developer 15 when one layer of the toner completely covers the carrier surface. The number N of toners is given by the following equation (7):
^{_{N = 2π (r t + R}} ) 2/3 1/2 r t 2 ---- (7)
In, represented, respectively numerals [rho _t: true specific gravity of the toner [rho _C: true specific gravity r _t of _carrier: toner having a volume average radius R: represents the volume average radius of the carrier. The volume average radius _{r t} of the toner, 5 [mu] m, a true specific gravity [rho _t of the toner, 1.15, volume average radius R of the carrier, 30 [mu] m, a true specific gravity [rho _C of the carrier is, in the case of 5, toner carrier Assuming that the surface is completely covered with one layer, the toner concentration C _MAX (% by weight) is 15.9% by weight from the equations (6) and (7). Further, the toner concentration C (% by weight) is preferably 70% or less based on the surface area of the carrier. Therefore, the toner concentration C (% by weight) is preferably set to 12.4 wt.% Or less. Thereby, the contact between the toner and the carrier can be ensured, the charge amount can be kept constant, and a toner having a narrow charge amount distribution can be obtained, whereby a high quality image can be obtained.

  Further, the present invention is the digital image developing device, wherein a pulsed AC developing bias is applied for (1 / η) cycles or more while the photoconductor passes through the developable region. 7A and 7B are diagrams showing an embodiment of the present invention. FIG. 7A is a diagram showing the relationship between a photosensitive drum and a developing roller, and FIG. 7B is a waveform of an AC developing bias. FIG. While the photosensitive drum 1 passes through a developable area (a range in which an electrostatic latent image portion to which toner is to be adhered can be developed with a predetermined developing bias), an AC developing bias on a pulse is applied at (1 / η) cycles or more. The developer 5 on the developing roller 2 is developed. As a result, uneven development caused by pulsation of the developing bias can be completely prevented.

In order to confirm the developing performance of the digital image developing device, an image forming test is performed using a one-component developer under the following conditions.
Photosensitive drum image portion surface potential V ₀ = -100 V, the non-image portion surface potential V _D = -800 V image unit 1 dot d _y = 22μm (1200dpi equivalent), the circumferential speed V _P = 100mm / sec developing roller circumferential speed V _R = 300 mm / sec AC bias _VL = -0 V, _VH = -1000 V Developing area 1 = 0.5 mm, the developing area adjusts the distance between the photosensitive drum 1 and the developing roller 2 and the voltage of the AC developing bias. Can be controlled. The duty η is 0.3, and the pulse _TL + _H of the AC developing bias is 0.367 msec. Now, the time point on the photosensitive drum 1 passes through the developing area in 5 msec, an application time _{T H} of the developing side bias in 0.110Msec, the number of applications is about 13 times. As a result, the one-dot image pattern can be developed with faithfulness to the latent image pattern and without an excess or deficiency in the amount of adhered toner, and high-quality image quality can be obtained. When the pulse _TL + _H of the AC developing bias is adjusted and the AC developing bias is applied to the latent image at a duty ratio (1 / η) or more, a high quality image can be obtained. Here, the duty η can When 0.3, the application time T _H of the development-side bias to obtain a high-quality image quality is applied at least three times or more.

  Further, the present invention is the digital image developing device, wherein the pulsed AC developing bias is a developing bias that reciprocates between a preset level and a zero level. FIG. 8 is a diagram showing a waveform of a pulsed AC developing bias of the present invention. The developing bias is reciprocated between zero volts and a preset level on the negative polarity side, so that the developing bias generating means configuration is simpler and less expensive than the developing bias generating means that requires both positive and negative polar outputs. can do.

Further, the present invention provides a developing roller 2 that carries the developer 5 movably endlessly, and the developer roller 2 transports the developer 5 to a developing area facing the image bearing member, and the developing roller 2 and the photosensitive drum 1 In a digital image developing apparatus provided with a developing bias circuit 6 for performing development by applying a pulsed AC developing bias to the developing device, a portion of the developing area of the developing roller 2 facing the moving direction of the photosensitive drum 1 is in the same direction. in moves and more quickly, with pulsed AC development bias first toner undeveloped side in bias V _L and the applied time T _L in period, the level of the developing bias to be set in advance as the two-stage V _L1, V _L2, and the difference between the toner developing side bias V _H and the applied pressure time T _H immediately before side bias V _L1 of the pulsed AC development bias one cycle, bets for the next pulsed AC development bias 1 cycle A developing device of a digital image to be larger than the difference between the over development-side bias V _H and the applied time T _H after side V _L2.
9A and 9B are diagrams showing an embodiment of the present invention. FIG. 9A is a diagram showing a waveform of an AC developing bias, and FIG. It is a figure which shows the state visualized typically.

As in the image forming apparatus shown in FIG. 1, the opposing portion of the developing roller 2 in the developing region is in the same direction with respect to the moving direction of the photosensitive drum 1 and is moved faster, so that the developing roller 2 is moved within one cycle of the developing pulse / bias. the developing bias level a two-phase _{V L1, V L2} toner non-development side _{V L} applied within a time _{T L,} the difference between the developing pulsed bias one period in the toner developing side _{V H} application time _{T H} immediately before the side _{V L1} and _{V H} the toner conveyed to the crests of the _V 0 -V _H becomes the development potential of the image portion the rear end to be larger than the difference between the next pulse of _{T H} after side _{V L2} and _{V H} becomes all _V D _{-V L1} developing This is a digital image developing apparatus in which the rear end of the image portion is darker than the front end so as to pass through a deep potential valley so as to make the density unevenness caused by the front-back difference in the developing direction inconspicuous. This is because even if the developing bias circuit 6 applies a pulse-like AC bias with a rapid rise and fall of the pulse, the falling edge is caused by the characteristics of the developing bias circuit 6 and the resistance between the developing bias circuit 6 and the developing roller 2. And the state where the developing bias is applied continues. Therefore, at the end of developing the solid portion, the fall is further delayed so that a large amount of toner on the developing roller 2 is developed, and the image density at the rear end portion is increased to reduce density unevenness. It is less noticeable, and a high-quality image can be obtained.

The present invention relates to a developing roller 2 that carries a developer 5 movably endlessly, a developer 5 that conveys the developer 5 to a developing area facing an image carrier, and a pulse between the developing roller 2 and the photosensitive drum 1. In a developing device provided with a developing bias circuit 6 for performing development by applying an AC developing bias in the shape of an arrow, a portion of the developing area of the developing roller 2 opposed to the moving direction of the photosensitive drum 1 is moved in a direction opposite to the direction of the pulse. the developing bias level Jo of the AC developing bias one period in the toner non-development side bias V _L in the application time T _L and a two-stage V _L1, V _L2, and toner development side bias of the pulsed AC development bias 1 cycle the difference between the V _H and the applied time _{T H} after side bias _{V L2,} and the toner developing side bias _{V H} and the applied time _{T H} immediately before the side _{V L1} of the next pulsed AC development bias 1 cycle This is a digital image developing device that makes the difference larger than the difference. 10A and 10B are diagrams illustrating an embodiment of the present invention. FIG. 10A is a diagram illustrating a waveform of an AC developing bias, and FIG. It is a figure which shows the state visualized typically.

The opposing portion of the developing roller 2 in the developing region is moved in the opposite direction to the moving direction of the photosensitive drum 1, and the developing bias level is changed within the toner non-developing side _VL application time _TL within one cycle of the developing pulse / bias. and step _{V L1, V L2,} the difference between the developing pulsed bias one period in the toner developing side _{V H} application time _{T H} immediately before the side _{V L1} and _{V H,} from the difference _{T H} after side _{V L2} and _{V H} of the next pulse By reducing the size, the toner transported to the peak of the developing potential V ₀ -V _H at the tip of the image portion passes through the deep valley of the developing potential V _D -V _L2 , so that the difference between the front and rear in the developing direction is reduced. This is a digital image developing device in which the front end of the image area is darker than the rear end in order to make the resulting density unevenness less noticeable. This is because even with the developing bias circuit 6 that applies a pulsed AC bias with a rapid rise and fall of the pulse, the rising and falling of the pulse are caused by the characteristics of the developing bias circuit 6 and the resistance between the developing bias circuit 6 and the developing roller 2. Would. However, in the early stage of development, since the toner is sufficient on the developing roller, the development tends to be excessive even if the rising is slow. Therefore, at the beginning of developing the solid portion, the rise is further delayed so that the toner on the developing roller is developed less, and the image density at the front end portion is reduced, so that the density unevenness is conspicuous. Thus, a high-quality image can be obtained.

FIG. 1 is a schematic configuration diagram illustrating a one-component developing device according to an embodiment of the invention. It is a figure showing one embodiment of the present invention typically. FIG. 2A is a diagram showing an electrostatic latent image formed on the photoconductor drum, and FIG. 2B is applied between the photoconductor drum and the developing roller by a developing bias circuit. FIG. 2C is a diagram schematically illustrating an AC bias, and FIG. 2C is a diagram schematically illustrating a developer developed on a photosensitive drum. FIG. 6 is a diagram illustrating a relationship between a duty η and an image density. FIG. 6 is a diagram illustrating a relationship between a toner adhesion amount on a developing roller and a toner charge amount immediately before development. FIG. 1 is a schematic configuration diagram illustrating a two-component developing device according to an embodiment of the present invention. FIG. 4 is a model diagram when a toner is more completely coated on a carrier surface with a two-component developer. FIG. 7A is a diagram illustrating an embodiment of the present invention, FIG. 7A is a diagram illustrating a relationship between a photosensitive drum and a developing roller, and FIG. 7B is a diagram illustrating a waveform of an AC developing bias. is there. FIG. 4 is a diagram illustrating a waveform of a pulsed AC developing bias of the present invention. FIG. 9A is a diagram showing an embodiment of the present invention, FIG. 9A is a diagram showing a waveform of an AC developing bias, and FIG. It is a figure which shows the state in which it was folded. FIG. 10A is a diagram showing an embodiment of the present invention, and FIG. 10A is a diagram showing a waveform of an AC developing bias, and FIG. 10B is a diagram showing an image developed by toner developed on a photoconductor. It is a figure which shows the state in which it was folded.

Explanation of reference numerals

Reference numerals 1, 11 Photoreceptor drum 2, 12 Developing roller 3, 13 Developer thin layer blade 4, 14 Developer accommodating section 5, 15 Developer 6, 16 Developing bias circuit 6-1, 16-1 DC power supply 6-2, 16-2 AC power supply 7 Electrostatic latent image 8 Visual image 9 Optical sensor

Claims (2)

A developing roller that carries the developer movably endlessly, and the developing roller conveys the developer to a developing area facing the image carrier, and applies a pulsed AC developing bias between the developing roller and the photoconductor to perform development. In a digital image developing apparatus provided with a power supply, a portion of a developing roller opposed to a developing area in the moving direction of the photosensitive member is moved in the same direction and earlier, so that the toner within one cycle of a pulsed AC developing bias is moved. in a non-developing side bias V _L application time T _L, the level of the developing bias to a two-stage V _L1, V _L2, and the application time of the toner developing side bias V _H of the pulsed AC development bias one cycle T _H the difference between the immediately preceding side bias V _L1, larger than the difference between the application time of the toner developing side bias V _H of the next pulsed AC development bias one cycle T _H after side V _L2 child A developing device of a digital image, characterized in. A developing roller that carries the developer movably endlessly, and the developing roller conveys the developer to a developing area facing the image carrier, and applies a pulsed AC developing bias between the developing roller and the photoconductor to perform development. In a developing device provided with a power supply, a portion of the developing roller opposite to the developing region in the moving direction of the photoconductor is moved in the opposite direction, and a non-toner developing bias _VL within one cycle of a pulsed AC developing bias is applied. the developing bias level within the time _{T L} and a two-stage _{V L1, V L2,} and a difference between the toner developing side of the pulsed AC development bias one cycle bias _{V H} and the applied time _{T H} after side bias _{V L2,} development of the digital image, characterized by greater than the difference between the toner developing side bias V _H and the applied time T _H immediately before the side V _L1 of the next pulsed AC development bias 1 cycle Location.

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