JP2006220967A - Developing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing device and an image forming apparatus which can suppress the deterioration of image quality. <P>SOLUTION: A voltage level to be applied on a layer thickness regulating blade 44 is controlled in such a manner that a toner image formed by developing an electrostatic latent image formed in accordance with a preliminarily determined density data on an image carrying body 12 reaches the density in accordance with the density data. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a developing device used in an image forming apparatus such as a copying machine, a printer, a facsimile, and a composite machine that combines these, and an image forming apparatus using the developing device.

  Conventionally, as an image forming apparatus, an electrostatic image on an image carrier is transferred by transferring the developer from a developer carrier carrying a developer such as toner in a layer form to an image carrier on which an electrostatic latent image is formed. An image forming apparatus using a developing method for developing a latent image is known.

In such an image forming apparatus, a layer thickness regulating member is formed on the surface of the developer carrying member until the developer carrying member carries the toner in a layered state and shifts to the image carrying member on which the electrostatic latent image is formed. By applying a constant voltage to the layer thickness regulating member so that an electric field in the direction of moving to the image carrier is generated between the image carrier and the developer carrier on the developer carrier. A technique for regulating the layer thickness of the developer carried on the toner and charging the toner is known (see, for example, Patent Document 1 and Patent Document 2).
JP 2002-258602 A JP 2002-162825 A

  However, in the above prior art, if the charge amount of the developer fluctuates according to the environmental fluctuation around the image forming apparatus, the layer thickness of the developer carried on the image carrier fluctuates, particularly at high temperature and high humidity. In such an environment, the charge amount of the developer is lowered, and there is a problem that the density of the formed image is deteriorated and the image quality is deteriorated such as fog.

  SUMMARY An advantage of some aspects of the invention is that it provides a developing device and an image forming apparatus capable of suppressing deterioration in image quality.

  In order to achieve the above object, the developing device of the present invention supports the developer accommodated in the developer accommodating portion in a layer form on the image bearing member on which the electrostatic latent image is formed according to predetermined density data. The developing means for developing the electrostatic latent image and the layer thickness of the developer carried on the developing means are regulated, and the layer thickness of the developer carried on the developing means is regulated. And a layer thickness regulating member to which a voltage is applied so that an electric field in the direction of moving the developer toward the developing unit is generated between the developing unit and the density of the image developed by the developing unit. Detection means for detecting, and control means for controlling the voltage applied to the layer thickness regulating member so that the density of the image detected by the detection means becomes a density corresponding to the predetermined density data. Composed of including That.

  When the density of the image obtained by developing the electrostatic latent image according to the predetermined density data by the developing means is detected by the detecting means, the control means of the developing device of the present invention detects the density of the detected image. The voltage applied to the layer thickness regulating member is controlled so that the concentration corresponds to the data. When a voltage is applied to the layer thickness regulating member, the layer thickness of the developer carried on the developing unit is regulated according to the applied voltage, and the developer is applied in a direction to move the developer toward the developing unit. An electric field corresponding to the voltage is generated between the developing means and the layer thickness regulating member.

  In this manner, the voltage applied to the layer thickness regulating member can be controlled so as to obtain a density corresponding to the density data of the electrostatic latent image of the image according to the detection result of the density of the developed image. In addition, image quality deterioration due to environmental fluctuations can be suppressed.

  Further, the image forming apparatus of the present invention is configured to divide the voltage by the developing device according to claim 1, a voltage supply unit for supplying a voltage to a charging unit for charging the image carrier, and a voltage by the voltage supply unit. And a voltage dividing means for applying the voltage to the layer thickness regulating member, so that a power source for supplying a voltage to each of the image carrier and the layer thickness regulating member can be shared. In addition, it is possible to provide an image forming apparatus that can suppress an increase in cost due to the addition of a new dedicated power source and can suppress deterioration in image quality.

  As described above, according to the developing device of the present invention, the layer thickness regulating member has a density corresponding to the density data of the electrostatic latent image of the image according to the density detection result of the developed image. Since the voltage to be applied to is controlled, the image quality deterioration due to environmental fluctuations can be suppressed.

  In addition, according to the image forming apparatus of the present invention, since the power supply for supplying the voltage to each of the image carrier and the layer thickness regulating member is shared, the image forming apparatus is increased in size and cost. And an image forming apparatus capable of suppressing image quality deterioration can be obtained.

  An embodiment of an image forming apparatus of the present invention will be described with reference to the drawings.

  As shown in FIG. 1, the image forming apparatus 10 includes an image carrier 12, a charging device 14 for charging the image carrier 12 to a predetermined potential, a semiconductor laser that is modulated and irradiated based on image data, and rotated. A light beam scanning device 18 for forming an electrostatic latent image corresponding to image data by irradiating a charged image carrier 12 with a laser beam scanned by a polygon mirror 16 through a mirror 16. The developing device 34 for developing the formed electrostatic latent image with toner as a developer, the transfer roll 24 for transferring the toner image on the image carrier 12 to the paper P, and the toner from the outer peripheral surface of the image carrier 12 It includes a cleaning device 20 for removal and an image processing unit 19 for performing image processing.

  Further, the image forming apparatus 10 is provided with a paper storage unit 28 for storing the paper P. The uppermost paper P of the paper storage unit 28 is fed to a predetermined paper transport path by a delivery roll (not shown). Sent out. The paper P sent to the paper transport path is transported through the paper transport path by a plurality of transport rolls such as the transport roll 22 and reaches the vicinity of the transfer roll 24, and the paper P passes between the transfer roll 24 and the image carrier 12. Is nipped and conveyed, the toner image formed on the image carrier 12 is transferred onto the paper P. The paper P onto which the toner image has been transferred is conveyed to the fixing device 26 by a conveyance roll (not shown). After the fixing process is performed by the fixing device 26, the paper P is discharged to a paper tray (not shown).

  The charging device 14 includes a charger 32 for charging the image carrier 12 and a voltage supply power source 30 for supplying a voltage to the charger 32. When the voltage from the voltage supply power source 30 is applied to the charger 32, the charger 32 charges the image carrier 12.

  The charger 32 includes a shield case in which an insulating block (not shown) is disposed, and a discharge wire for charging the surface of the image carrier 12 by corona discharge is stretched on the shield case. It is configured as a scorotron in which a plurality of grids are stretched to uniformly disperse the corona discharge caused by the above and improve the image quality. The charger 32 charges the surface of the image carrier 12 by applying a voltage to the grid electrode simultaneously with applying a high voltage to the discharge wire.

  The developing device 34 includes a toner container 36 for storing toner, an agitator mechanism 38 for stirring and conveying the toner stored in the toner container 36 by rotating, and the toner conveyed from the agitator mechanism 38 as a developer. A supply roll 40 for supplying to the carrier 42, a developer carrier 42 that elastically contacts with the supply roll 40 and carries the supplied toner in a layered manner to be transferred to the image carrier 12, and the developer carrier 42 A layer thickness regulating blade 44 for regulating the layer thickness of the carried toner is included. Further, the developing device 34 includes a sensor 46 for detecting the density of the toner image formed on the image carrier 12, and an image density detecting unit 48 for detecting the density of the toner image based on the detection result of the sensor 46. , And a bias voltage dividing control means 50 for controlling the voltage applied to the layer thickness regulating blade 44 based on the detection result by the image density detection means 48. The bias voltage dividing control unit 50 divides the voltage of the voltage supply power source 30 for supplying a voltage to the charger 32 and also applies a voltage level corresponding to the density of the toner image detected by the image density detecting unit 48. Control is applied to the thickness regulating blade 44. In this embodiment, as the sensor 46 and the image density detection means 48, a case where X-Rite 404A (product name) manufactured by X-Rite is used will be described.

  The developer carrier 42 is a roll having a diameter of 16 mm, an elastic layer made of silicon rubber having a thickness of 4 mm in which carbon black is mixed in an SUS shaft having a diameter of 8 mm, and a surface layer having a thickness of 20 μm made of butadiene / acrylonitrile rubber. Are laminated. The supply roll 40 is configured by laminating a 4 mm thick urethane foam roll on a 4 mm diameter SUS shaft. The layer thickness regulating blade 44 is a phosphor bronze blade having a thickness of 0.1 mm, and is in contact with the developer carrier 42 with a linear pressure of 20 g / cm.

  The case where the toner of the present embodiment employs a one-component non-magnetic toner having a particle diameter of 5.8 μm made of styrene / acrylic by polymerizing fine particles by an emulsion polymerization method will be described. An elastic roll is used for the developer carrier 42, a metal blade is adopted as the layer thickness regulating blade 44, and the layer thickness regulating blade 44 is disposed so as to contact the developer carrier 42 with a low linear pressure. Therefore, the toner produced by the emulsion polymerization method having a very soft and fragile property can be prevented from cracking.

  When the toner stored in the toner storage unit 36 is supplied to the developer carrier 42 by the supply roll 40, the developer carrier 42 supports the toner in layers. The toner carried on the developer carrier 42 is charged to a predetermined polarity by friction between the supply roll 40 and the developer carrier 42, and is regulated to a predetermined layer thickness by the layer thickness regulating blade 44. The regulation of the layer thickness is performed according to the level of the voltage applied to the layer thickness regulation blade 44. When the voltage adjusted by the control of the bias voltage dividing control means 50 is applied to the layer thickness regulation blade 44, the layer thickness is regulated. A potential difference is generated between the thickness regulating blade 44 and the developer carrier 42, and an electric field is formed in the direction in which the toner is directed toward the developer carrier 42, and the toner layer thickness on the developer carrier 42, that is, development The toner transport amount per unit area on the agent carrier 42 is adjusted according to the applied voltage.

  For example, when the developer carrier 42 is grounded and a DC bias of 10 V to 200 V is applied to the layer thickness regulating blade 44 when the peripheral speed of the developer carrier 42 is 120 mm / s, as shown in FIG. When the voltage applied to the layer thickness regulating blade 44 is in the range of 10V to 120V, that is, the potential difference between the developer carrying body 42 and the layer thickness regulating blade 44 is in the range of 10V to 120V, the developer carrying body 42 increases as the potential difference increases. It can be seen that the amount of toner transport per unit area increases.

  In this way, by adjusting the potential difference between the developer carrier 42 and the layer thickness regulating blade 44 by the voltage applied to the layer thickness regulating blade 44, the layer thickness (unit area) of the toner carried on the developer carrier 42 is adjusted. Per transport amount) can be adjusted.

  In the present embodiment, the image processing unit 19 controls the light beam scanning device 18 so as to form an electrostatic latent image corresponding to predetermined density data. As the predetermined density, in this embodiment, the density when formed on the paper P is the density of an image having an image density of 100% (hereinafter referred to as a solid density), and the density of an image having an image density of 20%. The light beam scanning device 18 is controlled so as to form an electrostatic latent image corresponding to density data indicating density (hereinafter referred to as halftone) and image density 0% (hereinafter referred to as white portion).

  Next, processing executed by the bias voltage dividing control unit 50 will be described. In the bias partial pressure control means 50, the light beam scanning device 18 is controlled by control of a control unit (not shown) of the image forming apparatus 10, and an electrostatic latent image corresponding to predetermined density data is displayed on the image carrier 12. If it is determined that the predetermined time has elapsed in step 100, the process proceeds to step 102. The determination in step 100 may determine whether or not a predetermined number of image formations have been executed in the image forming apparatus 10. Whether or not a predetermined number of images has been formed is determined by inputting a signal indicating that a predetermined number of images have been formed from the image processing unit 19 every time a predetermined number of images are formed. You just have to do it.

  In step 102, the detection result of the density of the toner image formed on the image carrier 12 is read from the image density detection means 48.

  In the next step 104, based on the density detection result detected in step 104, the level of the voltage applied to the layer thickness regulating blade 44 is set so that the density of the toner image becomes a density corresponding to the density data. . For example, when the electrostatic latent image formed on the image carrier 12 is an electrostatic latent image corresponding to the solid density, it is applied to the layer thickness regulating blade 44 so as to have a density corresponding to the solid density. Set the voltage level to be used. Similarly, when the electrostatic latent image formed on the image carrier 12 is an electrostatic latent image corresponding to halftone, the layer thickness regulating blade 44 is adjusted so that the density corresponds to halftone. Sets the level of voltage to be applied. Similarly, when the electrostatic latent image formed on the image carrier 12 is an electrostatic latent image corresponding to the white part, the layer thickness regulating blade 44 is adjusted so that the density corresponds to the white part. Sets the level of voltage to be applied.

  In the next step 106, the voltage obtained by dividing the voltage of the voltage supply power source 30 for supplying the voltage to the charger 32 is controlled to be the voltage level set in step 104, and the voltage at this level is controlled. After application to the layer thickness regulating blade 44, this routine is terminated.

  When the processing routine of FIG. 3 is executed in a high-temperature and high-humidity environment with a temperature of 28 ° C. and a humidity of 85%, the toner image on the image carrier 12 with respect to an increase in the number of images formed (number of printed sheets) in the image forming apparatus 10. The density of the toner, the fog grade, the toner conveyance amount per unit area on the image carrier 12, and the toner charge amount on the developer carrier 42 after the layer thickness is regulated by the layer thickness regulating blade 44 are shown in FIG. The experimental results shown by the diagrams 70, 72, 74, and 76 (output condition B) in FIGS. 5, 6, and 7 respectively were obtained.

  The fog grade indicates the degree of dirt on a non-image part (hereinafter referred to as a background part) other than the toner image forming part on the image carrier 12, and is graded according to the degree of dirt in advance, and the numerical value increases. This indicates that the degree of contamination is large.

  In this experiment, the rotational speed of the image carrier 12 is set to 100 mm / s (the rotational speed ratio of the developer carrier 42 to the image carrier 12 is 1 to 2), and the discharge wire of the charger 32 is −4 kV. A DC bias of minus 650 V was applied to the grid electrode, and a DC bias of −340 V was applied to the developer carrier 42 by a power source (not shown). That is, the potential of the electrostatic latent image forming unit on the image carrier 12 by the light beam scanning device 18 was −140 V, and the potential of the non-electrostatic latent image forming unit was −640 V (potential difference −300 V). . As the image carrier 12, an organic photoreceptor having a diameter of 40 mm was used, and the amount of biting between the image carrier 12 and the developer carrier 42 was 0.1 mm.

  In addition, as a comparative example, the same experiment was performed under the above-described environment even when no voltage was applied to the layer thickness regulating blade 44 (output condition A). Experimental results indicated by 62, 64, and 66 (output condition A) were obtained.

  When no voltage is applied to the layer thickness regulating blade 44, the toner image density decreases as the number of prints in the image forming apparatus 10 increases as shown in the diagram 60 of FIG. In this case, the density was lower than 1.35 or more which is the density range corresponding to the density data of the solid density. Further, as shown in the diagram 62 of FIG. 5, the fog grade to the background portion increases as the number of printed sheets increases, and when the number of printed sheets reaches 4 kPV or more, the degree of fog that does not affect the image quality obtained in advance. The occurrence rate exceeded the acceptable range of grades. Also, as shown in the diagram 64 of FIG. 6, the toner transport amount decreases as the number of printed sheets increases, and when the number of printed sheets reaches 2 kPV or more, the toner transport amount measured in advance corresponding to the density data of the solid density. As a result, it was less than the allowable range. Further, as shown in a diagram 66 in FIG. 7, the toner charge amount decreases as the number of printed sheets increases, and when the number of printed sheets reaches 5 kPV or more, the toner charge amount measured in advance corresponding to the solid density data is displayed. As a result, the result was less than the permissible range (allowable value is 10 μC / g or less).

  However, the processing routine of FIG. 3 is executed by the bias voltage dividing control means 50, and the density of the toner image on the image carrier 12 is changed every 0.5 kPV of the solid density image printed in the processing of step 100. In accordance with the measurement result, the voltage level supplied to the layer thickness regulating blade 44 is adjusted so that the amount of toner transported on the developer carrier 42 is 0.5 mg / cm 2 corresponding to the solid density. 4 to 8, as shown in each of the diagrams 70, 72, 74, and 76, the density of the toner image on the image carrier 12, the fog grade to the background, and the unit area on the image carrier 12 Good results were obtained in all of the toner conveyance amount and the toner charge amount on the developer carrier 42 after the layer thickness was regulated by the layer thickness regulating blade 44.

  Specifically, by adjusting the level of the voltage applied to the layer thickness regulating blade 44 according to the density detection result of the toner image, the number of prints in the image forming apparatus 10 increases as shown in the diagram 70 of FIG. Even in this case, the toner image density was 1.35 or more, which is the density range corresponding to the density data of the solid density. Further, as shown in the diagram 72 of FIG. 5, even when the number of prints is increased, the fog grade to the background portion is an allowable value indicating a fog grade that does not affect the image quality obtained in advance. The results were within the allowable range. Further, as shown in a diagram 74 in FIG. 6, the toner conveyance amount maintains a desired value as a pre-measured toner conveyance amount corresponding to the density data of the solid density even when the number of printed sheets is increased. The results were obtained. Further, as shown in the diagram 76 of FIG. 7, the toner charge amount decreases with an increase in the number of printed sheets, but an allowable range (allowance) as a pre-measured toner charge amount corresponding to solid density data. A value within the allowable range was always obtained without falling below 10 μC / g).

  As described above, in the image forming apparatus 10 and the developing apparatus 34 of the present invention, the static image formed according to the predetermined density data on the image carrier 12 by executing the processing routine of FIG. Since the level of the voltage applied to the layer thickness regulating blade 44 can be controlled so that the density of the toner image obtained by developing the electrostatic latent image becomes a density corresponding to the density data, the toner on the developer carrier 42 can be controlled. Since the toner layer having the density corresponding to the density data can be formed on the image carrier 12, the developer carrier caused by environmental fluctuations or changes in the toner over time can be used. It is possible to suppress the occurrence of uneven density, fogging, and the like due to the change in the toner layer thickness 42. Therefore, it is possible to suppress a decrease in image quality.

  Further, since the voltage from the voltage supply power source 30 for supplying the voltage to the charger 32 is divided and applied to the layer thickness regulating blade 44, a dedicated power source for applying a voltage to the layer thickness regulating blade 44 is provided. Since the voltage can be applied to the layer thickness regulating blade without increasing the size of the image forming apparatus 10, the manufacturing cost can be reduced.

  In the present embodiment, the case where a scorotron or a contact charger is adopted as the charger 32 has been described, but a non-contact charger may be used.

  The developing method by the developing device 34 includes a non-contact method in which the image carrier 12 and the developer carrier 42 are provided in a non-contact manner, and development is performed by flying toner to the image carrier 12 with a strong vibration electric field, and an image. Any of the contact methods in which the carrier 12 and the developer carrier 42 are provided in contact with each other and developed by a DC electric field may be used.

  In the present embodiment, a non-magnetic one-component toner is used as a developing method, a supply roll 40 is pressed against the developer carrying member 42, and toner having no magnetic force is supplied onto the developer carrying member 42. In the above description, the non-magnetic one-component development method is used in which the toner is held by electrostatic force and the layer thickness of the held toner is regulated by the layer thickness regulating blade 44. However, the magnetic one-component development method may be adopted. Good. In this case, for example, magnetic field generating means such as a magnet is provided inside the developer carrier 42, and magnetic toner containing a magnetic material such as magnetite is held on the developer carrier 42, and The layer thickness may be regulated by the layer thickness regulating blade 44.

  When the image bearing member 12 is made to withstand a voltage as the charger 32 by superimposing the AC component on the DC component, the voltage from the power source for supplying the DC voltage to the charger 32 is divided to control the layer thickness. What is necessary is just to make it apply to the blade 44. Further, the voltage from both the power source and the power source for supplying the AC voltage to the charger 32 may be divided and applied to the layer thickness regulating blade 44. In this case, an electric field in which the toner vibrates is formed between the layer thickness regulating blade 44 and the developer carrier 42, and the number of contact between the toner and the developer carrier 42 and the toner and the layer thickness regulating blade 44 increases. An effect of assisting frictional charging of the toner is obtained, and image quality deterioration can be further suppressed.

  In particular, polymerized toners produced by polymerizing fine particles that are widely used in connection with higher image quality tend to aggregate, but the toner is between the layer thickness regulating blade 44 and the developer carrier 42. By forming an oscillating electric field, an effect of preventing toner aggregation can be obtained, generation of layer spots and white streaks can be suppressed, and image quality deterioration can be suppressed. At this time, the voltage and duty ratio of the AC component supplied to the layer thickness regulating blade 44 may be adjusted by the bias voltage dividing control means 50.

  Further, even when the non-contact method is used as the developing method, the layer thickness regulating blade is obtained by dividing the voltage from the power source for supplying the DC voltage to the charger 32 and applying the voltage to the layer regulating blade 44. An electric field in which the toner vibrates is formed between 44 and the developer carrying member 42, and an effect of assisting frictional charging of the toner is obtained. The AC voltage having the same phase as the AC component of the voltage applied to the developer carrier 42 is divided from the power source for supplying the AC voltage to the charger 32 and applied to the layer regulating blade 44. You may do it.

  As described above, the power supply for supplying voltage to the charger 32 is common as the power supply for supplying to the layer thickness regulating blade 44 regardless of the developing method and the charging method of the image carrier 12 by the charger 32. Can be used.

1 is a schematic configuration diagram illustrating an image forming apparatus including a developing device according to an embodiment of the present invention. FIG. 6 is a diagram illustrating an example of a relationship between a toner conveyance amount on a developer carrying member and a voltage level applied to a layer thickness regulating blade. 6 is a flowchart showing processing executed by a bias partial pressure control unit of the developing device of the present invention. FIG. 4 is a diagram showing the relationship between the number of images formed in an image forming apparatus and the density of a toner image on an image carrier. FIG. 4 is a diagram showing a relationship between the number of image formations and fog grade in the image forming apparatus. FIG. 4 is a diagram showing the relationship between the number of images formed in the image forming apparatus and the toner conveyance amount per unit area on the image carrier. FIG. 5 is a diagram showing the relationship between the number of images formed in the image forming apparatus and the toner charge amount on the developer carrier after the layer thickness is regulated by the layer thickness regulating blade.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Image forming apparatus 34 Developing apparatus 42 Developer carrier 44 Layer thickness control blade 46 Sensor 48 Image density detection means 50 Bias partial pressure control means

Claims (2)

The electrostatic latent image is developed by transferring the developer stored in the developer storage layer in a layered manner to an image carrier on which the electrostatic latent image is formed according to predetermined density data. Developing means,
Layer thickness control for regulating the layer thickness of the developer carried on the developing unit and for applying a voltage so that an electric field is generated between the developing unit and the developer in the direction of the developing unit. Members,
Detecting means for detecting the density of the image developed by the developing means;
Control means for controlling the voltage applied to the layer thickness regulating member so that the density of the image detected by the detection means becomes a density corresponding to the predetermined density data;
A developing device. A developing device according to claim 1;
Voltage supply means for supplying a voltage to a charging means for charging the image carrier;
A voltage dividing means for dividing a voltage by the voltage supply means and applying the divided voltage to the layer thickness regulating member;
An image forming apparatus.

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