JP4642451B2 - Contact resistance measurement method - Google Patents

Description

This invention relates to contact resistance measuring method for measuring the contact resistance of the liquid developer layer a latent image of the latent image bearing member at the developing nip of a developing device performing development using a liquid developer.

  In Patent Document 1, Patent Document 2 and Patent Document 3, an electrostatic latent image is formed by uniformly charging the surface of a photoconductor with a charging unit and then exposing the surface of the photoconductor with a writing unit according to image data. There has been proposed an image forming apparatus that develops and visualizes an electrostatic latent image by a developing device using a liquid developer having a high viscosity and a high concentration.

  In a developing device using a high-viscosity, high-concentration liquid developer provided in image forming apparatuses such as Patent Document 1, Patent Document 2, and Patent Document 3, for example, a developer made of an insulating liquid such as dimethylpolysiloxane oil A high-viscosity liquid developer having a viscosity of 50 to 10,000 mPa · s obtained by dispersing toner in a high concentration in a solvent. The liquid developer stored in the storage tank is applied to the developing roller and the developing belt with a uniform thickness to form a liquid developer thin layer, and the liquid developer thin layer applied to the developing roller and the developing belt is the photoreceptor. When the toner passes through the development region in the vicinity of the toner, the electrostatic latent image on the photosensitive member is developed with a thin toner layer of a liquid developer to form a toner image. The liquid developer remaining on the developing roller and the developing belt that has passed through the developing region is removed by a scraping blade and collected in a storage tank.

  The liquid developer is formed by dispersing a solid content of a resin and a pigment in a carrier liquid that is an insulating liquid. At the time of development, the charged toner moves in the insulating liquid by electrostatic force to develop the electrostatic latent image. The development efficiency improves as the moving distance of the toner is shorter. In order to shorten the moving distance of the toner, a thin layer of a micron unit of liquid developer is formed on a developer carrier such as a developing roller, and the thinned liquid developer is brought into contact with the photosensitive member for development. It is desirable to use a liquid developer having a high viscosity of 50 to 10,000 mPa · s.

  When developing with a thin layer of a liquid developer, the density is determined by the thickness of the thin layer, so that it is important to form the thin layer uniformly.

  Patent Document 4 discloses an image forming apparatus that measures the amount of liquid developer by bringing a doctor blade into contact with a coating roller having engraved grooves formed on the surface thereof, and makes a thin layer of the liquid developer formed on the developing roller uniform. Has been proposed. In Patent Document 5 and Patent Document 6, by inserting an intermediate roller between the application roller and the developing roller, the life of the developing roller whose specifications are strict and the selection range is narrow and it is difficult to make a highly durable part is improved. In addition, by applying to the developing roller the liquid developer that has passed between the nip between the intermediate roller and the coating roller, the developing device can eliminate streaks due to clogging of foreign matter by eliminating contact of the doctor blade to the coating roller. Has been proposed.

In Patent Document 7, the volume resistivity of the developing roller is set in a range of 0 to 10 ⁷ Ω · cm to prevent density unevenness in a visible image after development due to instability of electric field strength during development. Development devices have been proposed.

JP 7-152254 A Japanese Patent Laid-Open No. 7-209922 JP 7-219355 A Japanese Patent Laid-Open No. 11-265122 JP 2002-287513 A JP 2003-156938 A JP 2001-194912 A

  The developing electric field that effectively acts on the movement of the toner in the developing nip is an electric field formed between the developing roller surface and the photoreceptor surface. The strength of the electric field formed between the surface of the developing roller and the surface of the photoconductor varies depending on the thickness of the conductive layer of the developing roller and the resistance of the liquid developer layer to be developed even when the applied voltage is the same. To do. Furthermore, the resistance value varies with time and the environment, and may vary depending on the situation even if the initial state or a certain condition is sufficient. The substantial strength of the developing electric field varies depending on the thickness of the roller and the resistance value of the liquid developer layer, and a sufficient electric field strength cannot be obtained stably only by defining the volume resistivity of the developing roller.

The present invention aims at providing a contact resistance measuring method for measuring the contact resistance of the liquid developer layer in the developing nip of the current image device.

  The contact resistance value measuring method of the present invention is such that a developer carrier carrying a liquid developer is opposed to a latent image carrier carrying a latent image on the surface, and the surface of the latent image carrier and the surface of the developer carrier While applying a voltage, a voltage is applied between the developer carrier and the latent image carrier, and a developing electric field is applied to the liquid developer layer formed between the developer carrier and the latent image carrier. A contact resistance value measuring method for measuring a contact resistance value of a liquid developer layer in a developing device for developing a latent image, wherein the latent image carrier is exposed on the whole surface without being charged, and the latent image carrier is exposed on the whole surface. The current flowing between the developer carrier and the developer carrier is measured, and the voltage applied between the developer carrier and the latent image carrier is divided by the measured current to obtain the resistance value obtained by dividing The contact resistance value of the area including the developer carrier and the liquid developer layer is obtained by multiplying the nip width and the total length of the Contact resistance of a region including a carrying member and the liquid developer layer, obtaining the contact resistance of the liquid developer layer in the developing nip by subtracting the contact resistance value of the developer carrying member.

According to the contact resistance measuring method of this invention, by a latent image bearing member is entirely exposed without being charged, the contact resistance value by eliminating the complexity of the measured current value subtracting the impact of charging It can be measured easily.

  As shown in the configuration diagram of FIG. 1, the image forming apparatus 1 according to the first embodiment sequentially includes a charger 11, an exposure device 12, a developing device 13, a photoconductor sweep device 14, and an intermediate transfer around the photoconductor 10. The body 15, the charge-removing lamp 16, and the photoconductor cleaning device 17 are disposed. The secondary transfer roller 18 and the intermediate transfer body cleaning device 19 are disposed around the intermediate transfer body 15. A device 21 and a paper discharge unit 22 are provided. The image forming apparatus 1 is not limited to the electrophotographic copying machine described below, but may be various image forming apparatuses such as a printing apparatus, a copying apparatus, a FAX, and a multifunction machine. Moreover, it is not restricted to what uses reversal development.

  The surface of the photoconductor 10 is formed of a-Si, OPC, or the like, and is driven to rotate in the direction of the arrow at a constant speed during copying by a driving unit such as a motor, and functions as a latent image carrier that forms an image by reversal development. The photoreceptor 10 is desirably formed of amorphous silicon on the surface, and the photoreceptor 10 formed of amorphous silicon on the surface is more stable than the organic photoreceptor (OPC) because it has stable electrical characteristics. Even if it is used, the charging characteristics do not change, and a stable developing electric field can be formed. The charger 11 uniformly charges the surface of the photoreceptor 10 in the dark with a roller, a charger, or the like. The exposure device 12 forms an electrostatic latent image by irradiating an original light image onto the charged photoreceptor 10 with an LED, a laser scanning optical system, or the like.

  The developing device 13 includes a storage tank 30, a stirring screw 31, a coating device 32, and a developing roller 33. The developing device 13 supplies liquid developer to a portion where the developing roller 33 and the photoconductor 10 face each other, and passes through the developing roller 33. The toner image is developed from the electrostatic latent image.

  The storage tank 30 stores a liquid developer. Liquid developers include, for example, a toner composed mainly of a binder composed of a colorant and a resin, and a charge control agent added in a carrier liquid mainly composed of a solvent having a high insulating property and a low dielectric constant. It is not a liquid developer with a low viscosity of about 1 cSt and a low concentration of about 1% using Isopar (trademark) as a carrier, but a viscosity of 50 to 10,000 mPa · S and a concentration of 5 It is preferable to use a high-viscosity and high-concentration liquid developer of about 40% to 40%. A volatile or non-volatile liquid developer is selected according to the purpose, and the toner particle size is from submicron to about 6 μm. Select according to your purpose. As the carrier liquid, a highly insulating material such as silicone oil, normal paraffin, IsoparM (trademark), vegetable oil, mineral oil or the like is used. The stirring screw 31 is stirring the liquid developer stored in the storage tank 30.

  The coating device 32 includes a coating roller 34, an intermediate roller 35, and a cleaning member 36. The application roller 34 draws up and applies the liquid developer stored in the storage tank 30 to the intermediate roller 35 while rotating. As shown in the front view of FIG. 2A, the application roller 34 is preferably composed of an anilox roller having a uniform pattern of engraving grooves on the surface. An oblique line type as shown in b), a turtle shell type as shown in FIG. 2C, a lattice type as shown in FIG. The excess liquid developer on the surface of the coating roller 34 is scraped off by a doctor blade or a doctor roller, and the liquid developer is accurately measured by the engraving groove and transferred to the intermediate roller 35 to transfer the liquid developer. A uniform thin layer can be formed.

  The intermediate roller 35 carries a liquid developer measured according to the volume of the engraving groove of the application roller 34 at the nip portion with the application roller 34, and the reverse direction in which the moving direction of the surface is reversed with respect to the development roller 33. The surface of the developing roller 33 is rotated at a peripheral speed equal to or higher than the peripheral speed of the developing roller 33, and the pattern of the engraving groove remaining on the intermediate roller 35 when the liquid developer is transferred from the coating roller 34 is leveled. To form a uniform thin layer. By providing the intermediate roller 35, a mechanical load is applied to the surface of the developing roller 33 and the life of the developing roller 34 is shortened as compared with the case where the coating roller 34 is directly brought into contact with the developing roller 33 for coating. Can be prevented.

  The cleaning member 36 is composed of a blade, a roller, or the like formed by a metal blade, a rubber blade, or the like, and comes into contact with the intermediate roller 35, passes through a contact portion with the developing roller 33, and again comes into contact with the application roller 34. The liquid developer adhering to the surface of the intermediate roller 35 is removed.

When the thickness of the liquid developer applied to the developing roller 33 is such that the pigment content in the toner carried per 1 cm ² of the surface of the developing roller 33 is less than 3 μg, the liquid developer is formed on the photoreceptor 10. Since a sufficient amount of pigment cannot move to the image portion of the electrostatic latent image, the image density of the image portion is reduced. On the other hand, when the thickness of the liquid developer applied to the developing roller 33 is such that the pigment content in the toner carried per 1 cm ² of the surface of the developing roller 33 is greater than 60 μg, Since a lot of excess toner remains on the background portion of the photoconductor 10, the removal of the excess toner by the photoconductor sweep device 14 becomes incomplete. The thin film of the liquid developer on the developing roller 33 may be 3 to 12 μm thick so that the pigment content in the toner carried per 1 cm ² of the surface of the developing roller 33 is 3 μg or more and 60 μg or less. desirable.

  By providing the coating device 32, the liquid developer thin film can be uniformly applied to the surface of the developing roller 33, and the thickness of the liquid developer layer in the developing nip can be made uniform. In addition, the contact resistance value of the liquid developer layer can be stabilized and fluctuations in the electric field strength at the development nip can be prevented.

  The developing roller 33 has a cored bar 37 and an elastic body layer 38. The elastic body layer 38 is formed of an elastic body having conductivity such as urethane rubber on the outer peripheral surface around the core metal 37, and is elastically deformed by being brought into contact with the photoconductor 10 with an appropriate pressure. A developing nip is formed with the body 10. A developing bias is applied between the developing roller 33 and the photoreceptor 10. The thin layer of liquid developer formed on the surface of the developing roller 33 by the intermediate roller 35 passes through the developing nip and develops the toner image from the electrostatic latent image on the photoreceptor 10.

  The surface hardness of the elastic layer 38 is desirably 50 degrees or less in terms of JIS-A hardness so that a developing nip can be efficiently formed with the photoreceptor 10. The material of the elastic layer 38 is not limited to urethane rubber as long as it is conductive and does not swell and dissolve with a liquid developer containing a carrier liquid. Means for imparting conductivity to the elastic layer 38 of the rubber member include an electronic conductivity type in which carbon is added and an ion conductivity type. As shown in the relationship diagram between the environmental variation and the electrical resistance of the ion conductive type elastic body layer 38 in FIG. 3, the resistance value is larger than that of the ion conductive type elastic body layer 38 whose resistance value largely varies due to the environmental variation. It is preferable to use an electron conductive type elastic body layer 38 to which carbon is added which is not easily affected by the strength of the developing electric field.

  By forming the developing nip, it is possible to secure a certain developing time required for the liquid developer toner to move and adhere to the photoconductor 10 by the developing electric field in the developing region. The nip width, which is the width of the developing nip in the direction of surface movement, is set to be equal to or greater than the product of the linear velocity of the developing roller 33 and the development time constant by adjusting the pressure at which the developing roller 33 and the photoreceptor 10 abut. The development time constant is the time required for the development amount to saturate, and is the minimum required nip width divided by the process speed. For example, during development when the required minimum nip width is 5 mm and the process speed is 500 mm / sec. The constant is 10 milliseconds.

Here, the contact resistance value (Ω · cm ² ) of the elastic layer 38 does not exceed the contact resistance value of the liquid developer layer in the development nip. The contact resistance value is obtained based on the formula (1) using the applied voltage and current value between the photoconductor 10 and the developing roller 33 and the total length and nip width in the developing nip. When the contact resistance value is divided by the thickness of the elastic layer 38, a volume resistivity indicating the physical property value of the material is obtained. Here, the resistance between the elastic layer 38 and the liquid developer is compared using the contact resistance value including the information in the thickness direction without using the volume resistivity that does not include the information in the thickness direction. The contact resistance value of the elastic layer 38 can be set by adjusting the thickness of the elastic layer 38 of the developing roller 33 and the volume resistance value of the material.

  Contact resistance value = (applied voltage / current value) x total length x nip width (1)

  A method for measuring the contact resistance value of the elastic layer 38 will be described. As shown in FIG. 4, a positive potential with respect to the photosensitive member 10 is applied to the core 10 of the developing roller 33 in a state where the developing roller 33 is brought into contact with the photosensitive member 10 on which a solid image is formed in the same manner as during development. Then, the current flowing through the developing nip is measured, and the contact resistance value of the elastic layer 38 is obtained by substituting the applied voltage and the measured current value into the equation (1). The positive potential with respect to the photoreceptor 10 applied to the developing roller 33 is the same as the developing bias at the time of development.

  Next, a method for measuring the contact resistance value of the liquid developer layer at the development nip will be described. In a state where the developing roller 33 in which a thin film of liquid developer is formed is in contact with the photoconductor 10 while being pressed in the same manner as during development, a positive potential with respect to the photoconductor 10 is applied to the cored bar 37 of the developing roller 33 to develop. The current flowing through the nip is measured, and the applied voltage and the measured current value are substituted into Equation (1) to obtain the contact resistance value of the region including the elastic layer 38 and the liquid developer layer in the development nip. The contact resistance value of the liquid developer layer in the development nip is obtained by subtracting the contact resistance value of the elastic layer 38 from the obtained contact resistance value.

  FIG. 5 shows how the voltage ratio changes depending on the contact resistance ratio of the elastic layer 38. The contact resistance ratio indicates the ratio of the contact resistance value of the elastic layer 38 to the contact resistance value of the liquid developer layer in the development nip. The voltage ratio indicates the ratio of the voltage acting on the liquid developer layer in the development nip to the applied voltage.

  By making the contact resistance value of the elastic body layer 38 smaller than the contact resistance value of the liquid developer layer in the developing nip and reducing the contact resistance ratio, the voltage drop in the elastic body layer 38 can be reduced, acting on the liquid developer layer. Density unevenness due to insufficient strength of the developing electric field can be prevented. On the other hand, when the contact resistance value of the elastic body layer 38 is made larger than the contact resistance value of the liquid developer layer in the development nip to increase the contact resistance ratio, the voltage drop in the elastic body layer 38 is increased and is generated in the development nip. The strength of the developing electric field is insufficient. In order to prevent the voltage drop in the elastic layer 38 from affecting the voltage ratio, it is desirable that the contact resistance ratio is 1/100 or less. By making the contact resistance value of the elastic layer 38 smaller than the contact resistance value of the liquid developer layer in the development nip and reducing the contact resistance ratio, a high voltage is applied to generate a development electric field necessary for the development nip. This eliminates the need to reduce the burden on the power supply.

  The contact resistance value of the elastic layer 38 is preferably as small as possible. However, when the power source is controlled at a constant voltage, the developing roller 33 does not contact the photoreceptor 10 and cause damage in an unexpected situation such as running out of liquid developer. It is desirable to make it a level. Note that the power source has a constant current if a control method that prevents the intensity of the developing electric field from changing due to a change in the current value depending on the image area, for example, a control method that controls the current value that flows according to the image area. It may be controlled.

  With the developing device 13 mounted on the image forming apparatus 1, the contact resistance value of the elastic layer 38 and the contact resistance value of the liquid developer layer in the development nip are measured to thereby determine the contact state during actual image formation. In addition, the application amount of the liquid developer can be accurately reproduced, and errors between the actual image formation and the measurement can be reduced. Note that when the photoconductor 10 is measured by charging, exposing and developing as in actual image formation, there is the complexity of subtracting the effect of charging from the measured current value. The value may be measured, and the contact resistance value can be easily evaluated by developing without charging.

If the contact resistance of the liquid developer layer on the measured development nip is 10 ⁷ Ω · cm ^2, using a developing roller A contact resistance value of the measured elastic layer 38 is 10 ⁷ Ω · cm ² When developed, the development characteristics were poor, the image density was low, and image unevenness occurred. When development was performed using the developing roller B having a measured contact resistance value of the elastic layer 38 of 10 ⁶ Ω · cm ² , image unevenness due to slightly insufficient development electric field strength occurred. When development was performed using the developing roller C having a measured contact resistance value of the elastic layer 38 of 10 ⁵ Ω · cm ^2, a good image with no image unevenness could be formed.

  By managing the gap and pressure of the development nip, the thickness of the liquid developer layer in the development nip is controlled to make the contact resistance value of the liquid developer layer constant, or excessive pressure is applied to the development nip. In order to prevent the liquid developer layer formed on the developing roller 33 from passing through the developing nip, it is preferable to control so as not to exceed the upper limit of the set pressure value.

The developer carrier of the developing device 13 is not limited to the roller-type developing roller 33, and may have other forms such as a belt-type developing belt. When the developer carrier is a developing belt, the resistance value obtained by multiplying the surface resistance (Ω / cm ² ) of the developing belt by the belt width and the distance from the electrode roller that applies a voltage to the belt to the developing portion However, the conductivity of the material of the developing belt is determined so as to be lower than the resistance value of the contact portion of the liquid developer layer. In the case of the belt form, there is no point in applying the nip width as in the case of the roller form, so the conductivity of the material is defined by a direct resistance value comparison. In either the roller form or the belt form, the developer carrier is resisted against the resistance of the liquid developer layer so that the developing electric field acting on the liquid developer layer to be developed is sufficiently strong. It is the same in terms of defining.

  In the photoconductor sweep device 14, the sweep roller 40 having the sweep roller 40 and the cleaning member 41 has an elastic layer having conductivity on the outer peripheral surface in the same manner as the development roller 33, and is more photosensitive than the development roller 33. 10 is disposed so as to press the photosensitive member 10 with the developed toner layer interposed therebetween, and the surface is moved with the surface of the photosensitive member 10 at a substantially constant speed. When the sweep roller 40 is brought into contact with the photosensitive member with an appropriate pressure, the elastic layer of the sweep roller 40 is elastically deformed to form a removal nip. By adjusting the contact pressure, the nip width that is the width in the surface moving direction at the nip portion can be adjusted. The nip width is set to be equal to or greater than the product of the linear speed of the sweep roller 40 and the development time constant, like the developing roller 33.

  During development, toner is moved to the photoreceptor 10 in the image portion, while toner is moved to the surface of the developing roller 33 by the electric field formed by the developing bias potential and the photoreceptor potential in the background portion (non-image portion). The toner is prevented from adhering to the background portion. The sweep roller 40 can remove the so-called fog toner that causes the fog to remain on the surface of the photoreceptor 10 without moving to the surface of the developing roller 33 in the background portion.

  The cleaning member 41 is configured by a blade, a roller, or the like formed by a metal blade, a rubber blade, or the like, and removes the liquid developer attached to the surface in contact with the sweep roller 40. By removing the liquid developer from the sweep roller 40, the sweep performance of the sweep roller 40 can be maintained. The liquid developer removed from the sweep roller 40 is collected in the adjustment tank, and is sent again to the developing device 13 after the density adjustment. In the adjustment tank, a stirring means for making the concentration in the adjustment tank uniform, a concentration detection means for detecting the concentration in a uniform state, and a liquid amount detection means for detecting the liquid amount are provided. The concentration is adjusted by replenishment of the agent and carrier. The amount of liquid developer supplied from the adjustment tank into the developing unit is set slightly larger than the amount of liquid developer used, so the liquid developer is constantly circulated by returning the overflow to the adjustment tank. .

  The intermediate transfer member 15 is applied with a transfer bias and rotates in conjunction with the photosensitive member 10 while being in contact therewith. The toner image formed on the photoconductor 10 is primarily transferred to the intermediate transfer member 15 at a contact portion with the intermediate transfer member 15. The neutralization lamp 16 removes residual potential remaining on the photoconductor 10 after primary transfer. The photoconductor cleaning device 17 removes the liquid developer remaining on the photoconductor 10 after the primary transfer.

  The secondary transfer roller 18 disposed facing the intermediate transfer member 15 conveys the toner image formed on the intermediate transfer member 15 on the transfer material while conveying the transfer material with the intermediate transfer member 15 interposed therebetween. Secondary transfer. The intermediate transfer body cleaning device 19 removes residual toner remaining on the intermediate transfer body 15 after the secondary transfer. The secondary transfer method may be a method using a corona discharge, an adhesive transfer method, a thermal transfer method, or the like.

  The paper feed unit 20 feeds transfer materials such as copy sheets and OHP sheets loaded on the paper feed tray by paper feed rollers, temporarily stops them by registration rollers, and matches the position and timing of the toner image on the intermediate transfer member 15. Then, the secondary transfer roller 18 and the intermediate transfer member 15 are sent out to the contact portion. The fixing device 21 heats and pressurizes the transfer material onto which the toner image is secondarily transferred, fixes the toner image on the transfer material, and discharges it to the paper discharge unit 22. The fixing device 21 may use a thermal transfer method, solvent fixing, UV fixing, pressure fixing, or the like.

  According to the image forming apparatus 1 including the developing device 13, it is possible to eliminate image unevenness due to insufficient development electric field and form an image with high image quality.

1 is a configuration diagram of an image forming apparatus. It is a figure which shows the example of a block diagram of an application | coating roller, and an engraving groove pattern. FIG. 5 is a relationship diagram between an environmental change and an electrical resistance of an ion conductive type elastic body layer. FIG. 3 is a cross-sectional view of a developing roller and a photoreceptor, and a diagram illustrating a voltage application state. It is a figure which shows the relationship between the contact resistance ratio of an elastic body layer, and a voltage ratio.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1; Image forming apparatus, 10; Photoconductor, 11: Charger, 12: Exposure apparatus, 13: Developing apparatus,
14; photoconductor sweep device, 15; intermediate transfer member, 16; static elimination lamp,
17; Photoconductor cleaning device, 18; Secondary transfer roller,
19; intermediate transfer member cleaning device; 20; paper feed unit; 21; fixing device; 22; paper discharge unit;
30; Developer storage tank, 31; Stir screw, 32; Coating device, 33; Developing roller,
34; coating roller, 35; intermediate roller, 36; cleaning member, 37; cored bar,
38; elastic layer, 40; sweep roller, 41; cleaning member.

Claims (1)

The image bearing member configured to bear a latent image on the front surface, a developer carrying member for carrying the liquid developer is opposed, while moving the surface and the surface of the developer carrying member of the latent image carrier, the developing A voltage is applied between the developer carrier and the latent image carrier and a developing electric field is applied to the liquid developer layer formed between the developer carrier and the latent image carrier to In a developing device for developing an image, a contact resistance value measuring method for measuring a contact resistance value of the liquid developer layer,
Exposing the entire surface without charging the latent image carrier,
Measure the current flowing between the latent image carrier and the developer carrier that are exposed on the entire surface,
The developer is obtained by multiplying the resistance value obtained by dividing the voltage applied between the developer carrier and the latent image carrier by the measured current and the nip width and total length of the development nip. Obtain the contact resistance value of the region including the carrier and the liquid developer layer,
The contact resistance value of the liquid developer layer in the developing nip is obtained by subtracting the contact resistance value of the developer carrier from the contact resistance value of the region including the developer carrier and the liquid developer layer. A characteristic contact resistance value measuring method.

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