JP5494256B2 - Development device - Google Patents

Description

  The present invention relates to a developing device, and more particularly to a developing device for developing an electrostatic latent image formed on a photoreceptor in image formation by electrophotography.

  In recent years, in the field of image formation by electrophotography, as a developing method of an electrostatic latent image formed on a photoconductor (image carrier), a one-component developing method using only toner and agitation / A hybrid development system that has the advantages of a mixed two-component development system has attracted attention. In this hybrid development system, the toner and carrier are agitated / mixed to charge the toner, and then the developer carrying roller for carrying the developer (mixture of toner and carrier) and the toner are supplied to the photosensitive member The toner is separated from the carrier by the action of a separation electric field formed between the developing (toner carrying) roller and the toner alone is held on the developing roller, and one-component development is performed on the electrostatic latent image on the photoreceptor. Like to do.

  In the hybrid development, in order to cope with high-speed development, a plurality of development rollers are arranged along the rotation direction with respect to the photosensitive member to expand the development area (see Patent Documents 1 and 2).

  In such a hybrid developing device having a plurality of developing rollers, an AC electric field is formed in the developing region between the photosensitive member and the developing roller, and the toner is moved back and forth between the developing roller and the photosensitive member for development. It is common to do it. In order to perform development that maintains uniformity in fine density (development toner amount), a sufficient number of times of reciprocation of the toner is required, but under the present circumstances, development time is insufficient as speed increases. To compensate for this, the frequency of the AC bias voltage is increased. However, with this countermeasure, the reproducibility of lines and dots is reduced with an edge electric field.

  In addition, in the low development potential portion where the toner adheres to a low amount on the photoconductor, the toner moved on the photoconductor is easily collected by the developing roller, so the characteristics of the development toner amount with respect to the development potential are not linear, S-shaped characteristics in which the amount of toner is reduced at the low development potential portion. Therefore, there is inevitably a region in which the inclination of the developing toner amount becomes large, the sensitivity to the potential unevenness of the electrostatic latent image is high, and the density unevenness is likely to occur in the low potential portion. .

JP 2005-37523 A JP 2006-276853 A

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a hybrid type developing device capable of improving reproducibility of fine lines and fine dots and suppressing toner density unevenness and fogging.

A developing device according to an aspect of the present invention is:
A plurality of toner carriers that carry toner on the outer peripheral surface and are arranged in non-contact with the image carrier along the rotation direction with respect to the image carrier;
A developer carrier that carries a developer composed of toner and a carrier, and supplies the toner to the plurality of toner carriers;
With
In a developing device for attaching toner to an electrostatic latent image by an electric field formed between a voltage of an electrostatic latent image formed on the image carrier and an AC bias voltage applied to the toner carrier,
The peak-peak voltage of the AC bias voltage applied to the first toner carrier disposed on the upstream side in the rotation direction of the image carrier and the second toner carrier disposed on the downstream side in the rotation direction are the same value. In addition, the central value of the peak-to-peak voltage, where the central value applied to the first toner carrier has a potential difference that moves the toner closer to the image carrier than the central value applied to the second toner carrier. Yes, and developed toner amount after passing through the developing region by the first toner carrying member, it larger than the developing amount of toner after passing through the developing region by the second toner carrier,
A developing device.

  In the developing device, the peak-peak voltage of the AC bias voltage applied to the first toner carrier disposed on the upstream side in the rotational direction of the image carrier and the second toner carrier disposed on the downstream side in the rotational direction. Since the central value applied to the first toner carrier has a potential difference that moves the toner toward the image carrier compared to the central value applied to the second toner carrier, the rotation of the image carrier The development toner amount after passing through the development area on the upstream side in the direction is larger than the development toner amount after passing through the development area on the downstream side in the rotation direction, and the toner is excessively developed on the photoconductor in the development area on the upstream side. The toner is collected in the developing area on the downstream side in the rotation direction (collection is promoted). As a result, the reproducibility of fine lines and fine dots is improved, and toner density unevenness and fogging in a low density portion are suppressed.

  According to the present invention, it is possible to improve reproducibility of fine lines and fine dots and to suppress toner density unevenness and fogging.

1 is a cross-sectional view illustrating a developing device, a photosensitive drum, and peripheral devices thereof according to a first embodiment. FIG. 7 is a chart showing a bias voltage applied to the developing roller, where (A) shows a relationship between an AC bias voltage applied to the upstream developing roller and a solid latent image potential on the photosensitive member; Indicates the relationship between the developing roller on the downstream side and the solid latent image potential on the photoreceptor. FIG. 5 is a chart showing a relationship between an average voltage value of an AC bias voltage applied to the developing roller and a DC bias voltage applied to the developer carrying roller. FIG. 6 is an explanatory diagram illustrating a state of toner adhesion on a photoreceptor. FIG. 6 is a cross-sectional view illustrating a developing device, a photosensitive drum, and peripheral devices thereof according to a second embodiment. It is a block diagram which shows the 1st example of an electrical potential difference generation means. It is a block diagram which shows the 2nd example of an electrical potential difference generation means.

  Embodiments of a developing device according to the present invention will be described below with reference to the accompanying drawings. In addition, in each drawing, the same code | symbol is attached | subjected to the same member and part, and the overlapping description is abbreviate | omitted.

(Refer to the first embodiment of the developing device, FIGS. 1 to 4)
The developing device 2A according to the first embodiment visualizes the electrostatic latent image formed on the photoreceptor (image carrier) 1 with toner. As shown in FIG. 1, the photosensitive member 1 is uniformly charged to a predetermined potential by the charging roller 6 along with the counterclockwise rotation indicated by an arrow, and is emitted from a laser scanning device (not shown). Then, an electrostatic latent image is formed, developed by the developing device 2A, the toner image is transferred to the recording paper S by the electric field applied from the transfer roller 8, and the residual toner is removed by the blade 9. Further, residual electrification is removed by an eraser (not shown). The process of forming an image by electrophotography using this type of image forming means is well known, and detailed description thereof is omitted.

  The charging unit and the transfer unit may be a corotron type or scorotron type discharger instead of the roller 6 or the roller 8, and the exposure apparatus may use light other than laser.

  The developing device 2A includes a toner supply bottle 3, a developer tank 28 containing a developer 25 composed of toner and a carrier, and a first and a second that carry the developer 25 on its outer peripheral surface and convey it in the rotation direction. Developer carrying rollers 23a, 23b, and first and second developments (toners) that separate toner from the outer circumferential surfaces of the rollers 23a, 23b, carry the toner on their outer circumferential surfaces, and convey them in the rotation direction (clockwise direction). Support) rollers 21a and 21b, which perform hybrid development. The first and second developer carrying rollers 23a and 23b are connected to high voltage power supply circuits 4a and 4b, and the first and second developing rollers 21a and 21b are connected to high voltage power supply circuits 5a and 5b.

  The toner is supplied from the toner supply bottle 3 to the developer tank 28 by a predetermined amount based on the rotation of the toner supply roller 27. Two stirring and conveying rollers 26 are disposed at the bottom of the developer tank 28. The replenished toner is agitated / mixed with the carrier based on the rotation of the roller 26, charged to a predetermined potential, and conveyed to the lower portion of the first developer carrying roller 23a. The agitating / mixing action of the developer 25 by the agitating / conveying roller 26 is the same as that of the conventional developing device, and a detailed description thereof is omitted.

  The first and second developer carrying rollers 23a and 23b are composed of a sleeve that is rotationally driven in the direction of the arrow, and a magnet roller that is built / fixed in the sleeve. The sleeve of the first developer carrying roller 23a rotates in the counterclockwise direction, and the sleeve of the second developer carrying roller 23b rotates in the clockwise direction. Each magnet roller has a north pole and a south pole along the rotation direction of the sleeve.

  The developer 25 conveyed to the vicinity of the first developer carrying roller 23a by the agitating and conveying roller 26 is first supplied to the first developer carrying roller 23a with the layer thickness (passage amount) regulated by the regulating blade 24, Approximately half of the amount of toner held on the first developer carrying roller 23a is supplied to the second developer carrying roller 23b by the action of the magnetic force generated by the built-in magnet at the portions facing the rollers 23a and 23b. Thereafter, the toner is supplied from the rollers 23a and 23b to the developing rollers 21a and 21b.

  The first developing roller 21a is disposed on the upstream side in the rotation direction (counterclockwise direction) of the photoreceptor 1, and is driven to rotate clockwise as indicated by an arrow. The second developing roller 21b is disposed on the downstream side in the rotation direction of the photoconductor 1, and is driven to rotate clockwise as indicated by an arrow.

  In a region where the first and second developer carrying rollers 23a, 23b and the first and second developing rollers 21a, 21b are opposed to each other, the toner is electrically separated from the developer 25 by the high-voltage power supply circuits 4a, 4b. , 21b is formed on the outer peripheral surface. Further, in the developing areas a and b where the first and second developing rollers 21a and 21b and the photoconductor 1 face each other, an electric field for moving the toner to the outer peripheral surface of the photoconductor 1 is formed by the high voltage power supply circuits 5a and 5b. The

  The toner carried in the form of a layer on the outer peripheral surface of the first developing roller 21a from the first developer carrying roller 23a is conveyed to the developing area a facing the photoreceptor 1 based on the rotation of the first developing roller 21a. These toners are formed on the photosensitive member 1 and the developing roller by an electric field formed between the voltage of the electrostatic latent image formed on the photosensitive member 1 and the AC bias voltage applied to the developing roller 21a from the high-voltage power supply circuit 5a. The electrostatic latent image is developed while reciprocating between 21a. The toner carried in a layered manner on the outer peripheral surface of the second developing roller 21b from the second developer carrying roller 23b is conveyed to the developing area b facing the photoreceptor 1 based on the rotation of the second developing roller 21b. The These toners are formed on the photosensitive member 1 and the developing roller by an electric field formed between the voltage of the electrostatic latent image formed on the photosensitive member 1 and the AC bias voltage applied to the developing roller 21b from the high-voltage power supply circuit 5b. The electrostatic latent image is developed while reciprocating between 21b.

  The developing rollers 21a and 21b are composed of a conductive roller made of a metal material, for example, an aluminum roller having an anodized surface. Even if the roller base is coated with polyester resin, polycarbonate resin, polyethylene resin, polyamide resin, polyimide resin, polysulfone resin, silicone resin, fluororesin, or coated with silicone rubber, urethane rubber, etc. Good.

  By the way, in the developer which is a mixture of toner and carrier, as a toner, a commonly used binder resin contains a colorant and, if necessary, a charge control material or a release material, and an external additive is added. The processed one can be used. The toner particle size is preferably about 3 to 10 μm. As the carrier, generally used binder type carriers, coat type carriers, and the like can be used. The carrier particle size is preferably about 15 to 100 μm. The mixing ratio of the toner and the carrier may be adjusted so as to obtain a desired toner charge amount, and is actually set so that the coverage of the toner on the surface of the carrier is about 20 to 40%. .

  Here, the bias voltage applied to the developing rollers 21a and 21b will be described. An AC electric field is formed between the developing rollers 21a, 21b and the developer carrying rollers 23a, 23b by the high voltage power supply circuits 4a, 4b, 5a, 5b, and the developer carrying rollers 23a, 23b to the developing rollers 21a, 21b. The potential relationship is such that toner is supplied. In the development areas a and b, the toner is ejected by the electric field force in the space between the development rollers 21a and 21b and the photoconductor 1 so that the electrostatic latent image on the photoconductor 1 is faithfully developed. , 21b and the photosensitive member 1 are configured in a non-contact manner, and an alternating electric field is formed.

  FIG. 2A shows the relationship between the AC bias voltage applied to the upstream first developing roller 21a and the solid latent image potential on the photoreceptor 1, and FIG. 2B shows the downstream second developing. The relationship between the roller 21b and the solid latent image potential on the photoreceptor 1 is shown. FIG. 3 shows the relationship between the average voltage value of the AC bias voltage applied to the developing rollers 21a and 21b and the DC bias voltages V2 (A) and V2 (B) applied to the developer carrying rollers 23a and 23b. The photosensitive member 1 and the toner are negatively charged.

  Here, in the developing device 2A, as shown in FIG. 4, the developing toner amount M1 after passing through the developing area a of the first developing roller 21a on the upstream side becomes the developing area of the second developing roller 21b on the downstream side. The AC bias voltage applied from the high-voltage power supply circuits 5a and 5b is set so as to be larger than the developing toner amount M2 after passing b. That is, the peak-peak voltage (V1 (A) pp, V1 (B) pp) of the AC bias voltage applied to the first developing roller 21a disposed on the upstream side and the second developing roller 21b disposed on the downstream side. The central value applied to the first developing roller 21a has a potential difference that moves the toner closer to the photoreceptor 1 side than the central value applied to the second developing roller 21b.

  As shown in FIGS. 2A and 2B, a rectangular wave AC bias voltage is applied to the developing rollers 21a and 21b (the peak-peak voltage values are both V1 (A) pp and V1 (B) pp. 2500V), the center value (V1 (A) dc: -250V for roller 21a, V1 (B) dc: -150V for roller 21b) and the solid electrostatic latent image portion potential Vi. An amount of toner corresponding to the potential difference is transferred to the photoreceptor 1. The toner moves to the photosensitive member 1 when the applied bias voltage is at the minimum value, and moves to the developing rollers 21a and 21b when the bias voltage is at the maximum value. The ratio of the minimum value period in one cycle is called a development duty ratio, and in this embodiment, the development duty ratio is set to 50%.

  In this embodiment, the central value (V1 (A) dc) in the developing area a of the upstream developing roller 21a is the central value (V1 (V1 (A) dc) in the developing area b of the downstream developing roller 21b. B) The absolute value is set larger than dc). Therefore, as shown in FIG. 4, the developing toner amount M1 after passing through the developing region a of the upstream developing roller 21a is equal to the developing toner amount M2 after passing through the developing region b of the downstream developing roller 21b. More than.

  Incidentally, in the conventional developing device, the target developing toner amount is achieved by accumulating the developing toner amounts in the developing regions a and b. On the other hand, in this embodiment, the developing toner amount M1 after passing through the upstream developing area a is increased, so to speak, the developing toner is excessively developed and passed through the downstream developing area b. The amount M2 is reduced, and the excessively developed toner is collected in the downstream development area b. As a result, the reproducibility of fine lines and fine dots is improved, and toner density unevenness and fogging in a low density portion are suppressed.

(See the second embodiment of the developing device, FIG. 5)
As shown in FIG. 5, the developing device 2B according to the second embodiment comprises the first and second developer carrying rollers 23a and 23b shown in the first embodiment as a single developer carrying roller 23. Is. The developer carrying roller 23 includes a sleeve that is rotationally driven in an arrow direction (clockwise direction) and a magnet roller that is built in / fixed to the sleeve, and is connected to the high-voltage power circuit 4. The magnet roller has magnetic poles N1, S1, N2, S2, S3, N3, and S4 along the rotation direction of the sleeve. The rotation direction of the sleeve is the same as the rotation direction of the first and second developing rollers 21a and 21b, and the sleeves move in opposite directions at the opposed portions.

  The developer 25 conveyed to the vicinity of the developer carrying roller 23 by the stirring and conveying roller 26 is carried on the outer peripheral surface of the sleeve by the magnetic force of the magnetic pole S3 of the magnet roller, and the layer thickness (passage amount) is regulated by the regulating blade 24. To the first and second developing rollers 21a and 21b. The main magnetic poles N1 and S1 of the magnet roller are arranged to face the first and second developing rollers 21a and 21b, respectively, and the toner is separated from the developer 25 and supplied to the developing rollers 21a and 21b. The magnetic poles S2 and S3 are disposed immediately above the developer tank 28 and generate a repulsive magnetic field for separating the developer 25 carried on the sleeve from the sleeve.

  As described in the first embodiment, the toner is electrically separated from the developer 25 by the high-voltage power supply circuit 4 in the opposite region between the developer carrying roller 23 and the first and second developing rollers 21a and 21b. As a result, an electric field that is transferred to the outer peripheral surfaces of the rollers 21a and 21b is formed. Further, in the developing areas a and b where the first and second developing rollers 21a and 21b and the photoconductor 1 face each other, an electric field for moving the toner to the outer peripheral surface of the photoconductor 1 is formed by the high voltage power supply circuits 5a and 5b. The

  Other configurations and operations are the same as those of the first embodiment shown in FIG. 1, and the application of an AC bias voltage for development is as shown in FIG. Accordingly, in the developing device 2B according to the second embodiment, the reproducibility of fine lines and fine dots is improved as well as the first embodiment, and toner density unevenness and fogging in a low density portion are suppressed.

(Potential difference generating means, see FIGS. 6 and 7)
Here, means for generating a potential difference between the center values (V1 (A) dc, V1 (B) dc) of the AC bias voltage will be described with reference to FIGS. In the first example shown in FIG. 6, a Zener diode D is inserted between a parallel resonant circuit LC composed of a resistor R and a capacitor C and a power output Vout, and the first developing roller 21a is connected to the AC from the connection point A. A voltage is applied, and an AC voltage is applied from the connection point B to the second developing roller 21b. The peak-peak voltage value V1 (B) dc of the AC bias voltage applied to the second developing roller 21b is different from the peak-peak voltage value V1 (A) dc of the AC bias voltage applied to the first developing roller 21a. Value.

  In the second example shown in FIG. 7, Zener diodes D1 and D2 are inserted between parallel resonant circuits LC1 and LC2 composed of a resistor R and a capacitor C and a power output Vout, and are connected to the first developing roller 21a. An AC voltage is applied from the point A, and an AC voltage is applied from the connection point B to the second developing roller 21b. The peak-peak voltage value V1 (B) dc of the AC bias voltage applied to the second developing roller 21b is the same as the peak-peak voltage value V1 (A) dc of the AC bias voltage applied to the first developing roller 21a. Value.

(Experimental example)
The following experiments (Invention Examples 1 to 17 and Comparative Examples 1 to 6) were performed using the developing device 2A of the first example. The system speed (paper conveyance speed) is 700 mm / sec. The developing bias conditions are as shown in Table 1 below for each experimental example (both the inventive example and the comparative example).

As a fixing condition, an AC bias voltage having a frequency of 5 kHz was applied to the developing rollers 21a and 21b as a rectangular wave shown in FIG. 2 at a gap Ds of 250 μm at the closest portion between the photosensitive member 1 and the developing rollers 21a and 21b. The bias voltage applied to the developer carrying rollers 23a and 23b was adjusted so that the developer transport amount per unit area on the developer carrying rollers 23a and 23b was 6 g / m ² . The background potential of the electrostatic latent image formed on the photoreceptor 1 is −450 V, and the solid image portion potential is −50 V. Further, the rotation speeds of the developing rollers 21a and 21b were set so that the ratio of the rotation peripheral speed of the developing rollers 21a and the rotation peripheral speed of the photosensitive member 1 was 1.5: 1.

  The following were used as developers. In the toner, 100 parts by weight of a toner base material having a volume average particle diameter of about 6.5 μm prepared by a wet granulation method is used, and 0.2 parts by weight of the first hydrophobic silica and 0.5 parts of the second hydrophobic silica are used. A negative electrode having an external addition treatment of 0.5 parts by weight of hydrophobic titanium oxide and 0.5 parts by weight of hydrophobic titanium oxide was used. The carrier used is a coated carrier in which an acrylic resin coat is applied to carrier core particles made of a magnetic material and has an average particle diameter of about 33 μm. The toner ratio in the developer (ratio of the toner amount to the total amount of developer) was 8 wt%.

  Each item shown in Table 1 will be described below.

  The item “Vpp1 / Ds” is a value (V / μm) obtained by dividing the peak-to-peak voltage value V1 (A) pp of the upstream developing roller 21a by the developing gap Ds. Although the bias setting of the downstream developing roller 21b is not described, when the first example of the potential difference generating means (see FIG. 6) is used, a potential difference is provided at the center values V1 (A) dc and V1 (B) dc. There is also a difference in the peak-peak voltage value V1 (A) pp. When the second example (see FIG. 7) is used, no difference occurs in the peak-peak voltage value V1 (A) pp even if a potential difference is provided in the center values V1 (A) dc and V1 (B) dc. In Table 1, the item “bias setting” is “setting 1” when the first example is used, and “setting example 2” is when the second example is used.

  The item “development duty 1 and 2” is the development duty ratio of the AC bias voltage applied to the upstream developing roller 21a and the downstream developing roller 21b, and is set to a common value for both the rollers 21a and 21b.

  The item “Vdc1” is the center potential V1 (A) dc of the voltage V1 (A) pp applied to the upstream developing roller 21a, and the item “Vdc2” is the voltage V1 ( B) The central potential V1 (B) dc of pp.

  The item “relationship between development amounts” is a magnitude relationship between the development toner amount M1 after passing through the development region a and the development toner amount M2 after passing through the development region b.

  Based on the various conditions described above, the central values Vdc1 and Vdc2 of the developing bias applied to the developing rollers 21a and 21b are set as follows while keeping the toner supply potential difference between the developing rollers 21a and 21b and the developer carrying roller 23 constant. The printing process was carried out with variations as shown in Examples 1 to 17 and Comparative Examples 1 to 6 in Table 1. In Table 1, fine line reproducibility, density unevenness, and fog are listed as evaluation items, and comprehensive evaluation was also performed.

  The fine line reproducibility was evaluated by printing an oblique line of 1 dot at 600 dpi and evaluating the image from the highest rank of 5 to 1. The rank that is practically good is set to 3, rank 3 or higher is marked with ◯, rank 2 or lower is marked with x. For density unevenness, a halftone image was printed, and the image was evaluated from the highest rank of 5 to 1. The rank that is practically good is set to 3, rank 3 or higher is marked with ◯, rank 2 or lower is marked with x. The fog printed a blank paper image and evaluated the degree of unnecessary adhesion of toner from the highest rank of 5 to 1. The rank that is practically good is set to 3, rank 3 or higher is marked with ◯, rank 2 or lower is marked with x.

  In Examples 1 to 17 of the present invention, the development toner amounts M1 and M2 all satisfied the relationship of M1> M2, and good evaluation was obtained for all image quality, that is, evaluations that were practically good in comprehensive evaluation.

  On the other hand, all of Comparative Examples 1 to 6 are in a relationship of M1 <M2, and both the fine line reproducibility and the density unevenness were evaluated to ranks that are not preferable.

(Other examples)
The developing device according to the present invention is not limited to the above-described embodiment, and can be variously modified within the scope of the gist thereof.

  For example, the rotation direction of the photosensitive member, the developer roller, and the first and second developing rollers is not limited to the direction described in the above embodiment. Various rollers can be made of various materials. Various materials can also be used for the toner and the carrier. The developing method may be either normal development or reversal development that is conventionally known.

  As described above, the present invention is useful for a developing device, and is particularly excellent in that the reproducibility of fine lines and minute dots is improved and toner density unevenness and fog can be suppressed.

DESCRIPTION OF SYMBOLS 1 ... Photosensitive body 2A, 2B ... Developing apparatus 5a, 5b ... High voltage power supply circuit 21a ... 1st developing roller 21b ... 2nd developing roller 23, 23a, 23b ... Developer carrying roller a, b ... Developing area M1, M2 ... Developing Toner amount D, D1, D2 ... Zener diode

Claims (2)

A plurality of toner carriers that carry toner on the outer peripheral surface and are arranged in non-contact with the image carrier along the rotation direction with respect to the image carrier;
A developer carrier that carries a developer composed of toner and a carrier, and supplies the toner to the plurality of toner carriers;
With
In a developing device for attaching toner to an electrostatic latent image by an electric field formed between a voltage of an electrostatic latent image formed on the image carrier and an AC bias voltage applied to the toner carrier,
The peak-peak voltage of the AC bias voltage applied to the first toner carrier disposed on the upstream side in the rotation direction of the image carrier and the second toner carrier disposed on the downstream side in the rotation direction are the same value. In addition, the central value of the peak-to-peak voltage, where the central value applied to the first toner carrier has a potential difference that moves the toner closer to the image carrier than the central value applied to the second toner carrier. Yes, and developed toner amount after passing through the developing region by the first toner carrying member, it larger than the developing amount of toner after passing through the developing region by the second toner carrier,
A developing device. A power supply circuit for applying an AC bias voltage to the first and second toner carriers is provided, and a zener diode is used in the power supply circuit to change the center value of the peak-peak voltage of the AC bias voltage. The developing device according to claim 1 .

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