JP2014092586A - Image forming apparatus, image forming method, charging device, and charging method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of suppressing the occurrence of density unevenness in an image, even when insulating materials such as an external additive, shaved powder of a drum, and toner are attached to a charging member.SOLUTION: An image forming apparatus includes an image carrier 1 charged by charging means 100 that contacts the image carrier 1, and exposes the image carrier 1 to form an electrostatic latent image. The image forming apparatus then attaches a developer to the electrostatic latent image to form a developed image, and transfers the developed image onto a recording medium to form an image on the recording medium. The charging means can be applied with a conductive liquid with liquid application means.

Description

  The present invention relates to an image forming apparatus in which a latent image is formed on an image carrier charged by a charging member, and a visible image formed by attaching toner to the latent image is transferred to a recording medium to form an image. The present invention relates to a charging device.

  In general, there is known an electrophotographic image forming apparatus that forms an image through a series of electrophotographic processes such as charging, exposure, development, transfer, cleaning, and fixing using a photosensitive drum as an image carrier.

  An electrophotographic image forming apparatus is provided with a charging device that charges an image carrier (photosensitive drum) as a member to be charged. As this charging device, a corotron method is known in which a high voltage of 5 to 6 kV is applied to a tungsten wire to perform corona discharge to charge a member to be charged. However, since this system handles a high voltage, the power supply device is expensive and there are safety problems. Therefore, in recent years, a contact charging method has been adopted in which charging is performed while a conductive charging member is in contact with a member to be charged. In this charging method, a voltage of 1 to 2 [kV] is applied to a roller-shaped conductive charging member, and the surface of the charging member is rotated by contact with a photosensitive drum as a member to be charged to 0.5 [kV]. It is generally known that it can be charged to a degree. This roller charging method is attracting attention because it has advantages such as a relatively low voltage and a significantly smaller amount of ozone generated than the corotron method.

  In general, a cleaning blade is disposed on the upstream side in the movement direction of the peripheral surface of the member to be charged at the position where the charging member is disposed, and the residual toner on the surface of the member to be charged after the transfer by this cleaning blade. Is being removed. However, paper dust attached to the member to be charged at the time of transfer or a minute external additive peeled off from the toner cannot be completely removed from the member to be charged.

  In the charging roller method, since the charging roller is always in contact with the member to be charged, the external additive of the small diameter toner that has passed through the cleaning blade adheres to and contaminates the surface of the charging roller, adversely affecting the charging operation. . In the case of reversal development, the developer adhesion portion of the image carrier is not charged, and the adhesion force of the developer to the image carrier is mainly a mirror image force. However, at this time, if the developer has a small particle size of 8 μm or less, the adhesive force becomes very large, and cleaning defects due to an elastic cleaning blade tend to occur. Furthermore, external additives having a particle size smaller than that of a developer can be easily rubbed between the elastic blade and the image carrier in a cleaning device using an elastic blade. The cleaning property decreases. Further, since the contact charging means is always in contact with the image carrier, the toner is easily contaminated by toner that has passed through the cleaner, paper dust, dust, and floating toner in the apparatus, and has adhered to the surface of the charging roller. It was inevitable that the deposits would cause problems such as uneven charging and potential reduction, and the resulting deterioration in image quality. In order to deal with such a problem, a method is generally used in which the cleaning member is brought into contact with the surface of the charging roller in various ways to remove dirt on the surface (Patent Documents 1, 2, and 5). 3 and 4).

Japanese Patent Laid-Open No. 3-130787 Japanese Patent Laid-Open No. 5-188738 JP 2005-195950 A JP-A-6-289759

  However, in the technique disclosed in any of the above cited references, the cleaning capability of the cleaning member itself for cleaning the charged body is also reduced due to the adhesion of external additives, drum shavings, and toner. In general, a method of removing the adhering material by abutting is used. However, in this case, a container for collecting the removed substance is required, and due to damage of the cleaning member and uneven cleaning ability, a sufficient cleaning state cannot be obtained, resulting in poor charging. It was extremely difficult to suppress for a long time.

  The present invention has been made in view of the above problems. Even when an external additive, drum scraping powder, or an insulator such as toner adheres to the charging member, it is possible to suppress the occurrence of density unevenness and the like for a long time. An object of the present invention is to provide an image forming apparatus capable of forming a good image over a wide range.

  In order to achieve the above object, the present invention comprises the following arrangement.

  In the first aspect of the present invention, the surface of the image carrier is charged by a charging means that contacts the image carrier, and an electrostatic latent image is formed by exposing the image carrier that is a charged member to be charged. An image forming apparatus configured to form an image on a recording medium by transferring an image visualized by attaching a developer to the electrostatic latent image onto the recording medium, wherein a conductive liquid is applied to the charging member. It is characterized by comprising a liquid applying means for applying a liquid.

  According to a second aspect of the present invention, in the charging device including a charging member that charges the charging surface while being in contact with the charging surface of the member to be charged, a conductive liquid is applied to the charging member that is in contact with the charging surface. The liquid supply means which can be provided is provided.

  As described above, according to the present invention, by supplying a conductive liquid to the charging member according to the temperature and humidity conditions, an insulator such as an external additive, drum scraping powder, or toner is supplied to the charging member. Even if the toner adheres, a good image can be formed over a long period of time.

  In addition, according to the charging device of the present invention, even if an insulator adheres to the charging member, the charging surface of the member to be charged can be uniformly charged.

1 is a schematic diagram illustrating an overall configuration of an image forming apparatus according to a first embodiment of the present invention. It is sectional drawing which shows the structure of the charging roller used for this embodiment. It is a fragmentary sectional view of the image carrier used for this embodiment. It is a schematic diagram of the humidifier provided in this embodiment. (A) is explanatory cross-sectional view which shows the arrangement | positioning state of the electrothermal conversion element in this embodiment, The figure (b) is a vertical side view of the figure (a). (A) is a voltage waveform diagram of a drive pulse applied to the electrothermal conversion element in the present embodiment, and (b) is an electric diagram when the drive pulse shown in (a) is applied to the electrothermal conversion element. It is a wave form diagram which shows the thermal characteristic of a heat conversion element. It is a block diagram which shows schematic structure of the control apparatus which controls the humidification apparatus etc. which are provided in this embodiment. It is a flowchart which shows the operation | movement implemented by the control apparatus of this embodiment. It is explanatory drawing which shows the microparticles | fine-particles of the insulating substance adhering to a charging roller, and the water molecule adhering to the circumference | surroundings. It is a figure which shows the 2nd Embodiment of this invention, (a) is a humidification apparatus, (b) is the open state of the shutter shown to the figure (a), (c) is the closed state of a shutter, Each is shown. It is a perspective view which shows the 3rd Embodiment of this invention typically.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that the apparatus configuration, components, dimensions, materials, shapes, and other relative arrangements described in the following embodiments do not limit the scope of the present invention.

[First Embodiment]
First, a first embodiment of the present invention will be described. In the following description regarding the first embodiment, the overall configuration of the image forming apparatus will be described first, and then each part will be described in more detail.

[overall structure]
FIG. 1 is a schematic diagram schematically showing the overall configuration of the image forming apparatus of the present invention. This image forming apparatus is a contact charging type / transfer type electron using an image carrier (hereinafter also referred to as a photosensitive drum) 1 as a rotatable cylindrical charged member for forming an electrostatic latent image. This is a photographic image forming apparatus.

  The image carrier 1 is supported and disposed so as to be rotatable about an axis, and is rotated at a predetermined speed in a clockwise direction indicated by an arrow by a drive mechanism (not shown).

  The surface of the rotating image carrier 1 is uniformly charged to a predetermined polarity and potential by a charging means. In this example, the charging means is a contact charging device (roller charging device) using the charging roller 2 as a charging member. The charging roller 2 is a conductive elastic roller having a roller shaft (conductive support, cored bar). Then, both end portions of the roller shaft body are rotatably supported via bearing members, respectively, and the roller axis is arranged substantially parallel to the axis of the image carrier 1 so that a predetermined pressing force is applied to the image carrier 1. Are arranged in contact with each other. In this example, the charging roller 2 rotates following the rotation of the image carrier 1. In addition, the charging roller 2 is characterized in that surface irregularities are formed by mixing resin particles in the surface layer. The configuration of the charging roller 2 will be described in detail later.

  A charging bias is applied to the roller shaft of the charging roller 2 from the charging bias application power source S1 by a predetermined DC voltage (DC charging method) or a voltage obtained by superimposing a predetermined AC voltage on a predetermined DC voltage (AC + DC charging method). As applied. As a result, the surface of the rotating image carrier 1 is uniformly contact-charged to a predetermined polarity and potential.

  Then, the image exposure unit 3 performs image exposure on the charged surface of the image carrier 1. As a result, the exposed bright part on the surface of the photosensitive drum is attenuated, and an electrostatic latent image corresponding to the image exposure pattern is formed on the surface of the image carrier. The image exposure means 3 may be an analog exposure device that performs image projection exposure of a document image, or may be a digital exposure device such as a laser scanner or an LED array. In this example, a laser scanner that performs laser scanning exposure L with a wavelength λ = 780 nm is used as the image exposure means 3.

  The electrostatic latent image formed on the surface of the image carrier as described above is developed as a toner image by the developing means. In this example, the developing means uses a jumping reversal developing device 4 using a one-component magnetic negative polarity toner as a developer. However, other developing methods can be used as the developing means. For example, a method (two-component contact development) in which toner particles mixed with a magnetic carrier are used as a developer, and the developer is conveyed by magnetic force and developed in contact with an image carrier. Is also possible. Further, a method of developing the two-component developer in a non-contact state with respect to the image carrier 1 (two-component non-contact development method) can also be suitably used. The developing device 4 includes a developing sleeve 5 that is driven to rotate, and a hopper 6 that supplies developer to the developing sleeve 5. The developing sleeve 5 is disposed between the image carrier 1 and the image carrier 1 so as to maintain a constant interval of 0.3 mm in the longitudinal direction of the apparatus. A voltage obtained by superimposing a predetermined AC component and DC component is applied to the developing sleeve 5 from the developing bias applying power source S2. Thereby, the electrostatic latent image on the surface of the image carrier is reversed by jumping by the developing device 4.

  The toner image (developed image) visualized by the toner on the surface of the photosensitive drum reaches the transfer portion T which is a contact nip portion between the image carrier 1 and the transfer roller 7 by the subsequent rotation of the image carrier 1. The image is transferred to the recording medium P fed to the transfer portion T. The transfer roller 7 is a conductive elastic roller having a roller shaft (conductive support, cored bar). Then, both end portions of the roller shaft body are rotatably supported via bearing members. The roller axis is arranged substantially in parallel with the axis of the image carrier 1 and is arranged to contact the image carrier 1 with a predetermined pressing force. In this example, the transfer roller 7 rotates following the rotation of the image carrier 1. The recording medium P is fed from a paper feed mechanism (not shown) at a predetermined control timing, is synchronized with the image formation on the image carrier 1 by the registration roller 8, and is introduced into the transfer unit T at an appropriate timing. It is conveyed while being sandwiched between the image carrier 1 and the transfer roller 7. While the recording medium P passes through the transfer portion T, a DC voltage having a predetermined potential opposite to the charging polarity of the toner is applied to the transfer roller 7 from the transfer portion T. In this example, a positive polarity DC voltage having a predetermined potential is applied. As a result, a positive charge is applied to the back side of the recording medium P at the transfer portion T (the side opposite to the surface opposite to the image carrier 1), and the toner image on the surface of the image carrier 1 is sequentially transferred to the recording medium P. It is electrostatically transferred to the surface.

  When the recording medium P that has received the transfer of the toner image exits the transfer portion T, it is separated from the surface of the image carrier 1 and introduced into the fixing device 11 by the conveying belt 10. The fixing device 11 of this example is a heat fixing device having a pressure-contact rotating roller pair of a heat roller 12 and a pressure roller 13. The recording medium P introduced into the fixing device 11 enters the fixing portion N which is a pressure nip portion of the roller pair 12 and 13 and is conveyed while being nipped. As a result, the unfixed toner image on the recording medium P is fixed as a fixed image on the surface of the recording medium by heat and pressure, and then the recording medium is discharged outside the apparatus main body as an image formed product.

  On the other hand, the surface of the image carrier 1 after separation of the recording medium is cleaned by removing residuals such as transfer residual toner and paper dust by the cleaning device 14 and repeatedly used for image formation. In this example, the cleaning device 14 is a blade cleaning device using a chip-type cleaning blade 15 as a cleaning member. The cleaning blade 15 rubs the surface of the image carrier to scrape residues from the surface of the image carrier. The scraped residue is stored in the collected toner storage unit 16. The series of image forming processes in the image forming apparatus has been described above. Next, the configuration and operation of each unit for performing the image processing will be described in more detail.

[Charging roller]
An example of the charging roller 2 used in this embodiment will be described with reference to FIG.

  The charging roller 2 in the figure includes a shaft body 201, a conductive elastic body layer 202 formed on the outer periphery thereof, a softener transition preventing layer 203 on the outer periphery thereof, and a resistance adjusting layer (or dielectric layer formed on the outer periphery thereof). ) 204 and a protective layer 205.

  The shaft body 201 is not particularly limited, and for example, a metal core made of a metal columnar body or a metal cylinder body hollowed out inside is used. Examples of the metal material include stainless steel, aluminum, copper, and iron plated.

  The conductive elastic body layer 202 formed on the outer periphery of the shaft body is not particularly limited, and examples thereof include polyurethane foam, polynorbornene rubber, ethylene-propylene-diene rubber (EPDM) and the like. These may be used alone or in combination of two or more.

  In addition to the rubber, the material for the conductive elastic body layer 202 may be blended with a foaming agent, a conductive agent, a crosslinking agent, a crosslinking accelerator, oil, and the like as necessary.

  Examples of the foaming agent include inorganic foaming agents, organic foaming agents, and the like, and are used alone or in combination of two or more.

  Examples of the conductive agent include carbon black, graphite, potassium titanate, iron oxide, conductive titanium oxide, conductive zinc oxide, conductive tin oxide, ionic conductive agent (quaternary ammonium salt, borate, interface And the like.

  Examples of the crosslinking agent include sulfur and peroxide.

Such a conductive elastic layer is usually set to have a conductivity of about 10 ⁻¹ to 10 ⁻⁴ Ω and considerably lower than the resistance adjustment layer. The thickness is usually set to about 1 to 10 mm, preferably about 2 to 4 mm.

  Next, as the softening agent migration preventing layer 203 formed on the outer periphery of the conductive elastic layer 202, the exudation of the softening agent such as oil contained in the conductive elastic layer is prevented. Therefore, it is particularly preferable that the layer mainly composed of N-methoxymethylated nylon is configured.

The thickness of the softener migration preventing layer 203 is generally set to 3 to 20 μm, preferably 4 to 10 μm. And the electrical resistance of this softening agent transfer prevention layer is set to about 10 ^<-2 > (omega ^| ohm).

  The N-methoxymethylated nylon (8-nylon) is not particularly limited, and conventionally known ones are used. The softener migration preventing layer 203 also contains carbon black such as ketjen black as a conductive agent.

  Further, the resistance adjusting layer 204 formed on the outer periphery of the softener migration preventing layer 203 is formed using a composition mainly composed of a conductive agent and one or both of epichlorohydrin rubber (CHR) and acrylic rubber (ACM). It is what is done. And the thickness needs to be normally set to 50-400 micrometers, Most preferably, it is 200-350 micrometers. If the thickness is smaller than 50 μm, the resistance adjustment layer 204 is less affected and the function as a charging roller is difficult to be achieved. On the other hand, if the thickness is larger than 400 μm, the influence of the resistance adjustment layer 204 becomes too great, and the voltage must be used in a considerably high state, so that it is difficult to use a general power source for an electrophotographic apparatus. Here, the epichlorohydrin rubber is a homopolymer or copolymer that does not contain ethylene oxide as a copolymerization component. In the present invention, the term “subject” is intended to include the case where the entirety is composed of only the subject.

As described above, one or both of the above CHR and ACM and the conductive agent are used in a form including the softener migration preventing layer 203, which may cause charging unevenness, but is essential for taking advantage of the charging characteristics. It is not allowed. The resistance adjustment layer 204 has an electric resistance in the range of 10 ⁵ to 10 ⁸ Ω.

  The blending amount of the conductive agent is preferably set to 0.5 to 5 parts with respect to 100 parts by weight (hereinafter abbreviated as “part”) of the rubber component composed of CHR and ACM. That is, when the blending amount of the conductive agent is less than 0.5 parts, the unevenness is very good, but the electric resistance cannot be adjusted, and this also requires an excessive voltage to be applied. On the other hand, if it exceeds 5 parts, the conductive agent unevenness leads to resistance unevenness, and image unevenness easily occurs within the scope of the present invention.

  In addition to the conductive agent, a vulcanizing agent, a filler, and the like are appropriately blended in the material for forming the resistance adjusting layer 204. Note that a conductive filler such as carbon black is liable to cause dielectric breakdown when used under a high voltage, and therefore should be used in an amount of 10% by volume or less based on the rubber component.

  The protective layer 205 formed as the outermost layer on the outer periphery of the resistance adjusting layer 204 may be a known layer used on the surface of the charging roller.

When the conductive agent such as the above-described carbon black is mixed and dispersed in the protective layer 205, environmental characteristics including conductivity at low temperature and low humidity are good, and good performance is exhibited even in a low temperature and low humidity environment. become. Such a protective layer 205 is usually preferably set to a thickness of 5 to 30 μm, and a particularly preferable range is 7 to 23 μm. Moreover, the electrical resistance of this protective layer is set to 10 ³ to 10 ⁵ Ω. The conductive agent is not limited to carbon black, and a conventionally known conductive agent can be used in place of the carbon black.

  The charging roller formed of the material described above exhibits environmental dependency. For example, the resistance value of the charging roller may increase in a low temperature environment. The reason why the current flows in the charging roller is that the movement of charges occurs in the charging roller due to the carbon black used as the conductive material, but the resistance value is reduced due to a decrease in the mobility of the charges in a low temperature environment. To rise. On the other hand, in a high temperature environment, the resistance value tends to decrease because the mobility of the charges increases.

  The charging roller has not only temperature dependency as described above but also humidity dependency. For example, the resistance value tends to be lower in a high humidity environment than in a low humidity environment. Usually, in the charging roller, electric current is generated by the movement of electric charge in the charging roller 2 due to the carbon black contained therein. Furthermore, when moisture in the environment is contained in the charging roller, a phenomenon occurs in which the amount of current increases due to the movement of charges in the moisture itself and the resistance value decreases.

  When the charging roller 2 deteriorates in durability, an increase in the entire resistance value of the charging roller 2 or uneven resistance value in the longitudinal direction occurs, which may become uneven charging and cause image defects. In order to prevent such a situation from occurring, it is indispensable to suppress the entire charging roller to a low resistance and to make the resistance value uniform.

[Image carrier]
Here, a schematic configuration of the image carrier 1 will be described with reference to FIGS. 2A is a schematic configuration of the single-layer image carrier 1, and FIG. 2B is a schematic configuration of the multilayer image carrier 1. FIG.

  The single-layer type (a) includes a conductive substrate (support, image carrier substrate) 51 having an outer diameter of, for example, 30 mm, and a charge generation material and a charge transport material in the same layer (photosensitive layer) 53. This is a layer structure. The stacked type (b) has a configuration in which a charge generation layer 54 containing a charge generation material and a charge transport layer 55 containing a charge transport material are laminated in order or in reverse order. Layers 54 + 55 are photosensitive layers. Further, it is possible to form a surface protective layer 56 on the photosensitive layer 53 or 54 and 55.

  Further, in order to optimize the film thickness of the electron transport layer, it is preferable to use the surface protective layer 56 in order to provide a width of the film thickness. At least the surface layer of the image carrier 1 only needs to contain a compound that can be polymerized or crosslinked and cured by heat, light such as visible light, ultraviolet light, or radiation.

  Then, from the viewpoint of the characteristics as the image carrier 1, particularly the electrical characteristics such as the residual potential and the durability, the laminated type image carrier (b) is preferable. That is, a surface protective layer 56 is further formed on the functional separation type photoreceptor structure in which the charge generation layer 54 and the charge transport layer 55 are sequentially laminated, or on the photosensitive layer laminated in this functional separation type photoreceptor structure. A configuration is preferable.

  Further, an undercoat layer 52 having a barrier function and an adhesive function can be provided on the surface of the conductive support 51.

  When the photoreceptor is a function separation type photoreceptor, the charge generation layer 54 and the charge transport layer 55 are laminated.

The ratio of the conductive metal oxide particles in the surface protective layer 56 is one of the factors that directly determines the resistance of the surface protective layer. Therefore, the specific resistance of the protective layer is desirably in the range of 10 ⁸ to 10 ¹³ Ωm (10 ¹⁰ to 10 ¹⁵ Ωcm).

  The configuration of the general image carrier 1 has been described above. The image carrier 1 described here is conscious of long life, but the configuration of the image carrier 1 is not limited to this. For example, it is possible to configure the image carrier without providing the surface protective layer 56 described this time.

[Humidifying device]
Next, a humidifier as a liquid applying means provided in the present embodiment will be described with reference to FIG.

  The humidifier in the present embodiment is provided in the vicinity of the charging roller 2 and configured to discharge the liquid to the charging roller 2 to humidify it. In FIG. 4, the humidifier 100 includes a droplet discharge unit (droplet discharge means) 110 that discharges droplets to the charging roller 2 and a liquid storage container 120 that stores liquid to be supplied to the droplet discharge unit. In addition, the humidifier 100 includes a liquid supply path 130 for supplying the liquid in the liquid storage container 120 to the droplet discharge unit 110. Note that the liquid used in this embodiment is water, and the water stored in the liquid storage container 120 is discharged from the droplet discharge unit 110 toward the charging roller 2 as water droplets.

  The humidifying apparatus 100 used in the present embodiment employs a droplet discharge method in an ink jet recording apparatus. Various droplet ejection methods used in the ink jet recording apparatus are currently proposed. Here, an electrothermal conversion element, which is a typical ink ejection method, is used as an ejection energy generating element. Technology is cited as an example. In the humidifying device 100 using this ink ejection method, the electrothermal conversion element 104 is provided in the pressurizing chamber, and by applying an electrical pulse as an ejection signal to the electrothermal conversion element 104, thermal energy is supplied to the supplied water. Is granted. This thermal energy causes a phase change in the water, and water droplets are ejected from the droplet ejection unit 110 shown in FIG. 4 toward the charging roller 2 by the bubble pressure when the water is foamed (at the time of film boiling).

  Further, as shown in FIG. 4, the droplet discharge unit includes a recording element substrate 103 in which a support member 101 in which a liquid supply channel 101a is formed and a recording liquid supply port 103a in communication with the liquid supply channel 101a is formed. And a discharge port plate 104 fixed to the recording element substrate 103. Further, the recording element substrate 103 is provided with an electrothermal conversion element (heater) 102 as the ejection energy generating element (recording element). Further, the ejection port plate 104 is formed with ejection ports 104 a that eject liquid droplets (water droplets) at positions facing the respective recording elements 102. In the present embodiment, the discharge port 104a is arranged over a range approximately the same as the entire length of the charging roller 2 in the longitudinal direction (center axis direction), thereby enabling the entire area of the charging roller 2 to be humidified. In addition to the electrothermal conversion element, an electromechanical conversion element (piezo) or the like is known as the discharge energy generating element.

  FIG. 5A is an explanatory transverse cross-sectional view showing an arrangement state of the electrothermal conversion element, and FIG. 5B is a longitudinal side view of FIG. As shown in FIG. 5, a plurality of signal electrodes 113 and a common electrode 114 are formed on the element substrate 103, and a plurality of ejection energy generating elements 102 having a predetermined area are further formed. Each discharge energy generating element 102 is formed with a discharge port 104 a that penetrates the substrate 103 and the electrothermal conversion element 102. In the present embodiment, only one discharge port 104a is provided for each electrothermal conversion element 102, but a plurality of discharge ports 104a may be provided.

  6A is a voltage waveform diagram of a drive pulse applied to the electrothermal transducer 102, and FIG. 6B is a diagram in which the drive pulse shown in FIG. 6A is applied to the electrothermal transducer 102. It is a wave form diagram which shows the thermal characteristic (temperature change with respect to time) of the electrothermal conversion element at the time.

  As shown in FIG. 6A, when a predetermined drive pulse 36 is applied to an arbitrary signal electrode 113, a current flows through the electrothermal transducer 102, and a heat pulse 37 is generated as shown in FIG. 6B. To do.

  That is, by selectively inputting the drive pulse 36, the ejection energy generating element 102 can be selectively heated, and the liquid (water) can be ejected by the thermal energy.

  In the droplet discharge unit 110 having the above-described configuration, the liquid (water) supplied from the liquid storage container 120 via the liquid supply path 130 is supplied into the liquid flow path 101a and then into the pressurizing chamber via the supply port 103a. It reaches. The liquid supplied to the pressurizing chamber receives the discharge energy of the discharge energy generating element 105 (for example, thermal energy in the case of the electrothermal conversion element) and is discharged as droplets from the discharge port 104a. The driving of the ejection energy generating element 105 is controlled by a control device described later.

  FIG. 7 is a block diagram showing a schematic configuration of the control device 20 that performs control of the humidifier provided in the present embodiment.

  As shown in the figure, the control device 20 in the present embodiment is a main control unit 21 having a CPU 22, a ROM 23, a RAM 24, and the like, and a humidifier control unit that controls the discharge energy generation element 105 to control the discharge of water droplets. The humidification control circuit 25 is provided. The main control unit 21 in the present embodiment controls the operation of the entire image forming apparatus, and controls not only the humidification control circuit but also the drive circuit that drives other actuators. The CPU 22 performs processing such as this control and calculations and determinations necessary for the control. A ROM (first storage means) 23 stores a processing program executed by the CPU 22, liquid ejection data corresponding to the humidification amount, and the like. Further, the RAM (second storage means) 24 temporarily stores various data, and is also used as a work area for processing executed by the CPU 22. Further, a temperature / humidity detector (temperature detection means, humidity detection means) 26 for detecting the temperature environment and the humidity environment around the charging roller 2 is connected to the CPU 22 of the main control unit 21. As described above, since the electrical resistance value of the charging roller 2 varies depending on the surrounding temperature environment and humidity environment, the temperature and humidity detected by the temperature / humidity detector 21 determines the electrical resistance value of the charging roller 2. It is also used as information. That is, it can be said that the temperature detector 26 functions as an estimation means for estimating the electrical resistance value of the charging roller 2, in other words, conductivity.

  In the present embodiment, a cover member 28 that covers the periphery of the charging roller 2 is provided, and the discharge port of the humidifier 20 is also disposed in the cover member 28. For this reason, it becomes possible to mitigate that the humidity in the charging roller 2 humidified by the humidifier 20 and the surrounding atmosphere rapidly change. In addition, it is possible to protect the water droplets discharged from the humidifying device 20 from the influence of an air current and the like, and to appropriately discharge the water droplets on the peripheral surface of the charging roller 2.

  Next, the operation of the image forming apparatus having the above configuration will be described.

  When an insulating material such as an external additive adheres to the surface of the charging roller 2 due to durability deterioration, a local resistance value rises, and this appears on the image as uneven charging in the conveyance direction of the recording medium. However, when water droplets are applied to the peripheral surface of the charging roller 20 by the humidifying device 20 and the charging roller 2 is humidified, as shown in FIG. Surrounds and works to suppress local increase in resistance. At this time, the charging roller 2 is rotated so that the charging roller 2 absorbs moisture uniformly. By doing so, charging unevenness due to local increase in resistance value can be prevented.

  On the other hand, the surface of the image carrier 1 after separation of the recording medium is cleaned by the cleaning device 14 after removing residuals such as transfer residual toner and paper dust, and repeatedly used for image formation. Residual toner and paper dust that cannot be cleaned may be generated. The residual toner / paper powder adheres to the surface of the charging roller 2.

  For example, when local toner contamination occurs on the charging roller 2, the insulating material such as strontium titanate, which is a kind of external filler, inhibits charging in the portion where the toner contamination occurs. Defects occur. As a result, a non-uniform charging state (hereinafter referred to as charging unevenness) in which a charged portion and an uncharged portion exist is generated on the peripheral surface of the charging roller 2. This uneven charging causes black streaks or density unevenness on the printed image.

  Therefore, in the present embodiment, as shown in FIG. 9, water molecules H are attached around the fine particles I of the attached insulating material such as strontium titanate, so that the periphery of the insulating material is made conductive. As a result, it is possible to suppress the occurrence of local resistance unevenness on the peripheral surface of the charging roller 2, and to uniformly charge the entire peripheral surface of the charging roller 2, thereby preventing the occurrence of image defects. can do.

  Therefore, by supplying moisture to the charging roller 2 according to the temperature and humidity conditions and adjusting the moisture content of the charging roller 2, external additives, scraping powder of the image carrier 1, toner, etc. are applied to the charging roller 2. Even if it adheres, a good image can be obtained over a long period of time.

  The actual humidification control is performed by the control device 20 according to the flowchart shown in FIG.

  When the image forming process is started, the temperature / humidity detecting unit 26 detects the humidity of the environment around the charging roller 2 (step S1), and the detection result is sent to the CPU 22 of the main control unit 21. Upon receiving the temperature / humidity detection signal representing the temperature and humidity output from the temperature / humidity detector 26, the CPU 22 determines whether or not a humidification operation is necessary (step S2). Various criteria can be considered for this criterion. For example, when it is determined that the detected temperature is equal to or higher than a predetermined threshold temperature and lower than the threshold humidity, it is determined that a humidifying operation is necessary. Alternatively, if the detected temperature corresponds to at least one of the threshold temperature and the detected humidity is less than the threshold humidity, it is determined that the humidifying operation is necessary. Furthermore, it is possible to define various criteria such as determining that the humidification operation is performed when the combination of the detected temperature and the detected humidity is a combination that satisfies a certain condition.

  The result determined by the CPU 22 as described above is sent to the humidifier control circuit 25. The humidifier control circuit 25 that has received the humidification signal instructing the execution of the humidification operation from the CPU 22 drives the electrothermal conversion element 102 provided in the humidifier 20 and discharges water droplets toward the peripheral surface of the charging roller 2. (Step S4). As a result, water droplets adhere to the peripheral surface of the charging roller 2 and are humidified.

  The amount of water supply (the number of water droplets discharged) during this humidification control operation can be varied according to the temperature and humidity values detected by the temperature / humidity detector 26. For example, the amount of water droplets discharged from the humidifier 20 is controlled according to the difference between the above-described threshold temperature and the detected temperature, or the difference between the above-described threshold humidity and the detected humidity. That is, even when it is determined that the humidification operation is to be performed, if the detected temperature is much higher than the threshold temperature, more water droplets are discharged, and if the detected humidity is much lower than the threshold humidity, more Of water drops.

  In this embodiment, the discharge amount is controlled by the ratio of the discharge ports to be driven ((the number of discharge ports in the entire discharge port array) in the discharge port array including a plurality of discharge ports arranged along the longitudinal direction of the charging roller. The discharge driving rate corresponds to the amount of water droplets supplied to the charging roller 2, that is, the humidification amount. In this case, it is possible to supply moisture evenly in the longitudinal direction of the peripheral surface of the charging roller 2 by selecting the discharge ports to be driven so that the intervals between the discharge ports for discharging are substantially equal. The charging roller 2 is evenly humidified.

  Thus, in this embodiment, moisture is supplied to the charging roller 2 according to the temperature and humidity conditions, and the amount of moisture contained in the charging roller 2 is adjusted. For this reason, even if an external additive, shaving powder of the image carrier 1 or an insulator such as toner adheres to the charging roller 2, a constant electric resistance value is maintained that suppresses fluctuations in the electric resistance value in the charging roller 2. be able to. Therefore, if this charging roller 2 is used, the drum (image carrier) 1 can be uniformly charged without causing uneven charging, and an image of good quality can be formed.

  Here, the influence which the change of the environment at the time of image formation has on the image and the amount of water to be supplied in the humidifying operation for eliminating the influence will be described using a specific example.

  When the external filler (strontium titanate) adheres to the peripheral surface of the charging roller as streak-like stains in an environment where the temperature is 25 ° C./humidity 20% in an electronic conductive charging roller, the image has a high density. Striped density unevenness (black streaks) occurred.

  On the other hand, when the outer filler adheres to the peripheral surface of the charging roller as streak-like dirt as described above, the environment around the charging roller 2 is changed to a temperature of 25 ° C./humidity of 50 by the humidifier 100 described above. %. In this case, since the chargeability was improved, density unevenness did not appear on the image.

In the present embodiment, the charging roller 2 has a diameter of φ25, a length in the central axis direction (length in the longitudinal direction) of 300 mm, a cored bar diameter of φ5, and the entire sponge constituting the outer peripheral portion of the charging roller. It is assumed that the volume is 9.4 × 10 ⁴ (mm ³ ) and the sponge bubble rate is 30%. In this case, the volume of the bubble portion of the sponge is 2.8 × 10 ⁴ (mm ³ ).

  In the charging roller 2, when the environment in which density unevenness occurs due to contamination on the peripheral surface is a temperature of 25 ° C./humidity of 20%, the amount of water contained in the bubble portion is 0.13 g. On the other hand, when the environment in which streaks are not generated in the same charging roller 2 is a temperature of 25 ° C./humidity of 50%, the amount of water contained in the bubble portion is 0.32 g.

  Therefore, when there is an environment in which density unevenness occurs as described above (for example, in an environment with a temperature of 25 ° C./humidity of 20%), the humidifier 100 uses the amount of water and concentration when the density unevenness occurs. A difference (for example, 0.19 g) from the amount of water when unevenness does not occur is supplied to the charging roller 2. In order to perform this water supply, when water supply is performed using a 7 pl droplet with a resolution of 1200 dpi, the water droplets may be discharged at a discharge drive rate (duty) of 65% in both the longitudinal and circumferential directions.

  When the charging roller 2 is humidified, even if the charging roller 2 absorbs moisture and external additives, drum scraping powder, toner, etc. adhere to the charging member, image defects such as streaky density unevenness occur. There is no need to do it. In this humidification operation, it is desirable to rotate the charging roller 2 so that the charging roller 2 absorbs moisture uniformly.

  As described above, according to the present embodiment, even when the external additive, drum scraping powder, toner, or the like adheres to the charging roller and streaky density unevenness occurs, By humidifying the roller, the electric resistance value of the charging roller can be kept constant. For this reason, it is possible to form a good image without density stripes over a period.

[Second Embodiment]
Next, a second embodiment of the present invention will be described with reference to FIG. In addition, the same code | symbol is attached | subjected to the part which is the same as that of the said 1st Embodiment, or an equivalent part.

  As in the first embodiment, the image forming apparatus according to the second embodiment uses a contact charging method / transfer method using a rotatable cylindrical image carrier 1 for forming an electrostatic latent image. An electrophotographic image forming apparatus. However, in this 2nd Embodiment, the structure of the humidification apparatus 200 differs from the humidification apparatus 100 in the said 1st Embodiment. That is, the humidifier 200 includes a liquid container 202 that is provided in the vicinity of the charging roller 2 and has a water vapor outlet 204 a at a position facing the charging roller 2. Further, the liquid container 202 includes an electrothermal converter (heater) 205 provided therein, a shutter 206 that opens and closes the discharge port 204a, a first atmospheric pressure detector 207a that detects an external air pressure, and a liquid container. A second atmospheric pressure detector 207b for detecting atmospheric pressure. The first atmospheric pressure detector 207a as the first atmospheric pressure detection means is arranged outside (external space) inside the liquid container 201, and the second atmospheric pressure detection means 207b as the second atmospheric pressure detection means is inside the liquid container 201. Has been placed.

  Various configurations can be adopted as the shutter 206 for opening and closing the discharge port 204a. In this embodiment, as an example, a plate-like member that can reciprocate along the surface of the side liquid container 202 where the discharge port 204a is formed is provided as a shutter, and the shutter 206 is provided by a predetermined actuator for driving the shutter. Move back and forth. As the actuator, various configurations such as those using the rotational force of the rotary motor, those using a linear motor, and those using a solenoid can be applied. The shutter 206 and the shutter driving actuator that reciprocates the shutter 206 constitute the opening / closing means of the present invention.

  Also in the second embodiment, a temperature / humidity detector (temperature / humidity detection means) 26 for detecting the humidity and temperature around the charging roller 2 is provided. Then, based on the temperature and humidity detected by the temperature / humidity detector 26, it is determined whether or not the control device 20 performs the humidifying operation as in the first embodiment, and the humidifier is controlled based on the determination result. To do.

  Further, the heater 205 can keep the atmospheric pressure in the liquid container 202 at or above the external atmospheric pressure by heating the liquid (water) in the liquid container 201 in advance before the humidifying operation. The discharge ports 204a disposed in the humidifying device 200 are disposed at regular intervals over a range approximately the same as the entire length of the charging roller 2. Therefore, by discharging water vapor from the discharge port 204a, the entire atmosphere including the charging roller 2 can be humidified substantially uniformly.

  Furthermore, also in the second embodiment, a CPU 22 that performs determination processing such as whether or not to perform a humidifying operation, arithmetic processing and control, a main control unit 21 that includes a ROM 23 and a RAM 24, a humidifier control circuit 25, A control device 20 is provided. However, in the second embodiment, a signal (atmospheric pressure detection signal) representing the atmospheric pressure detected by the first atmospheric pressure detector 207a and the second atmospheric pressure detector 207b is input to the CPU 22, and the CPU 22 205 and the shutter driving actuator 29 are controlled.

  Next, the humidification control implemented in 2nd Embodiment is demonstrated.

  When the image forming process is started, the temperature / humidity detector 21 detects the temperature and humidity of the environment, and sends the detection results (humidity detection signal and temperature detection signal) to the CPU 22. The CPU 22 determines whether or not to perform a humidification operation based on the temperature detection signal and the humidity detection signal, and sends a control signal to the humidifier control circuit 25 based on the determination result. Based on this control signal, the humidifier control circuit 25 controls the drive (heat generation operation) of the heater 205 and the operation of the shutter as follows.

  First, the humidifier control circuit 25 drives a heater 205 provided in the liquid container 201 of the humidifier 200 to heat the liquid (here, water) stored in the liquid container 201. The CPU 22 obtains a differential pressure between the pressure in the liquid container 201 detected by the second atmospheric pressure detector 207b and the pressure detected by the first atmospheric pressure detector 207a. Then, a control signal for driving the shutter drive actuator 29 is sent to the humidifier driving circuit 25 when the differential pressure reaches a certain value or more. Upon receipt of the control signal, the shutter drive actuator 29 moves the shutter 206 from the state shown in FIG. 10C to the state shown in FIG. That is, the shutter moves from the position where the discharge port 204a is closed to the position where it is opened. Thereby, water vapor generated in the liquid container 201 is discharged from the plurality of discharge ports 204a toward the outer peripheral surface of the charging roller 2, and the charging roller 2 is humidified. As described above, since the discharge ports 204a are arranged uniformly along the longitudinal direction of the charging roller 2 with a constant interval, the charging roller 2 is evenly humidified.

  By humidifying the charging roller 2 as described above, the electric resistance of the charging roller 2 can be kept constant also in the second embodiment, and the image carrier 1 is uniformly charged. It becomes possible to keep.

  By the way, in the second embodiment, the amount of water supplied to the charging roller 2 by the humidifying operation is adjusted by controlling the opening time of the discharge port 204 by the shutter 206 and the pressure difference between the inside and outside of the liquid container 201. To do. That is, the greater the pressure difference in the liquid container 201, the greater the amount of water vapor released per unit time, and the longer the opening time of the discharge port 204, the greater the amount of water vapor released. Accordingly, the CPU 200 obtains a necessary water supply amount based on the difference between the detected temperature / humidity and the threshold temperature / humidity as in the first embodiment, and then, according to the water supply amount, the discharge port 204. And the pressure difference between the inside and outside of the liquid container 201 is determined. For example, the opening time of the discharge port 204 is determined based on the current pressure difference inside and outside. Alternatively, the air pressure in the liquid container 201 is increased by the heater 205 until a constant pressure difference is reached, and when the pressure difference from the external pressure becomes equal to or greater than a certain pressure, the discharge port is opened for an opening time corresponding to the pressure difference. An opening time of 204 may be determined. In addition, a table representing the relationship between the combination of the opening time and the atmospheric pressure and the supply amount of water is stored in the ROM 23 or the like in advance, and when the humidifying operation becomes necessary, the opening time is referred to by referring to the table. A combination with atmospheric pressure may be determined.

In this embodiment, the charging roller 2 has a diameter of φ5, a length in the central axis direction (length in the longitudinal direction) of 300 mm, a cored bar diameter of φ5, and the entire sponge constituting the outer peripheral portion of the charging roller. It is assumed that the volume is 9.4 × 10 ⁴ (mm ³ ) and the sponge bubble rate is 30%. In this case, the volume of the bubble portion of the sponge is 2.8 × 10 ⁴ (mm ³ ).

  The amount of moisture contained in the bubble portion of the sponge is the amount of moisture contained in the bubble portion when the environment in which density unevenness occurs due to dirt on the peripheral surface of the charging roller 2 is temperature 25 ° C./humidity 20%. Is 0.13 g. On the other hand, when the environment where the streak is not generated in the charging roller 2 is a temperature of 25 ° C./humidity of 50%, the amount of water contained in the bubble portion is 0.32 g.

  Therefore, in an environment where uneven density occurs (for example, temperature 25 ° C./humidity 20%), the humidifier 100 has a moisture content when the uneven density occurs and a moisture content when the uneven density does not occur. The difference (for example, 0.19 g) is supplied to the charging roller 2. Now, it is assumed that the size of the discharge port 204a is 20 μm × 20 μm wide, and the difference between the atmospheric pressure in the liquid container 201 and the external atmospheric pressure is maintained at 30 hPa. Here, when water supply is performed, the circumferential surface of the charging roller 2 is divided every 1 mm, and the humidifying operation time for each divided section, that is, the opening time of the discharge port 204a by the shutter 206 is set to 100 μsec. Thus, a predetermined amount (0.19 g) of moisture can be applied evenly on the entire circumferential surface of the charging roller 2 by rotating the charging roller 2 once.

  As described above, according to the second embodiment, even if insulating foreign matter such as external additives, drum scraping powder, and toner adheres to the charging roller 2 at low humidity, the peripheral surface of the charging roller 2 By humidifying the charging roller, the electric resistance of the charging roller 2 can be kept substantially uniform. For this reason, it is possible to suppress the occurrence of density unevenness in the image, which has been caused by the adhesion of insulating foreign matter to the charging roller 2 when the humidity is low, and a good image can be obtained over a long period of time. Is possible.

[Third Embodiment]
Next, a third embodiment of the present invention will be described with reference to FIG.

  As in the first and second embodiments, the image forming apparatus according to the third embodiment is a contact charging system that uses a rotatable cylindrical image carrier 1 for forming an electrostatic latent image. 1 is a transfer type electrophotographic image forming apparatus. However, in this 3rd Embodiment, the structure of the humidification apparatus 300 differs from the humidification apparatuses 100 and 200 in the said 1st Embodiment.

  The humidifier 20c in the third embodiment includes a liquid supply container 301 having a liquid supply sheet 302 that exhibits liquid absorbability, a liquid flow path 304, and a liquid storage container 303, which are provided in the vicinity of the charging roller 2. In the present embodiment, the liquid stored in the liquid storage container 303 is water, and the liquid supply sheet 302 uses a water supply sheet made of polystyrene foam material. As the liquid supply sheet 302, one made of another material can be used. One end of the liquid channel 304 is attached to the liquid supply sheet, and the other end is immersed in water in the liquid storage container 303. Water is always supplied to the liquid supply sheet 302 by capillary action. The width of the liquid supply sheet 302 in the liquid supply container 301 is approximately the same as the entire length of the charging roller 2 so that the entire atmosphere of the charging roller 2 is humidified.

  When the atmosphere around the charging roller 2 is in a low humidity environment, the liquid supply sheet 302 is also in a low humidity state. For this reason, the water stored in the liquid storage container 303 is supplied to the liquid supply sheet 302 via the liquid channel 304 by the capillary phenomenon of the liquid supply sheet 302. Since water supplied to the liquid supply sheet 302 evaporates from the liquid supply sheet 302, the atmosphere around the charging roller 2 is humidified, and the charging roller 2 is humidified. On the other hand, when the atmosphere environment of the charging roller 2 is in a high humidity state and the charging roller 2 itself is in a high humidity state, the liquid supply sheet 302 is also in a high humidity state. For this reason, water supply using a capillary phenomenon as in a low humidity environment is not performed, and the temperature and humidity around the charging roller 2 is not changed by the humidifier 300.

  As described above, in the third embodiment, when the atmosphere around the charging roller 2 is a low humidity environment, the liquid supply sheet 302 absorbs moisture by capillary force to humidify the atmosphere, and humidifies the charging roller 2. Therefore, even if external additives, drum scraping powder, toner, or the like adheres to the charging roller 2, the electric resistance of the charging roller 2 can be kept constant, and the image carrier 1 is uniformly charged. be able to. Therefore, also in the third embodiment, high-quality image formation can be performed over a long period of time.

  In the third embodiment, the liquid supply sheet 302 containing moisture is used to gradually humidify the atmosphere and the charging roller 2 by natural evaporation according to the humidity of the atmosphere. It is not configured. For this reason, it becomes possible to manufacture cheaply and easily, and it becomes possible to suppress the increase in the cost of an apparatus.

[Fourth Embodiment]
Next, a fourth embodiment of the present invention will be described.

  The image forming apparatus according to the fourth embodiment is characterized in that, in the image forming apparatus according to the first embodiment, the amount of water supplied by the humidifier is varied in accordance with the average printing rate of the printed matter on which the image is formed. It is what. Here, the printing rate means the area of the adhesion portion of the developer (toner) per unit area. Therefore, the higher the printing ratio, the larger the amount of toner per unit area. Conversely, the lower the printing ratio, the smaller the amount of toner per unit area.

  When the charging roller 2 is not subjected to the humidification operation as in the above embodiments, streaky density unevenness starts to occur in the image due to the adherence of an insulator such as toner or external filler to the charging roller 2. The number of prints varies depending on the average value of the print rate (print duty) of the print image. For example, in the environment of a temperature of 25 ° C./humidity of 20%, when a toner filler (strontium titanate) adheres to the charging roller 2 where the humidifying operation is not performed, a low printing rate with an average printing rate of 3% The number of prints that appear as black stripes on the image is 90k. On the other hand, in the case of a high printing rate with an average printing rate of 10%, the number of prints appearing as black stripes on the image is 50k, and black stripes occur earlier than in the case of an average printing rate of 3%. .

  For this reason, in the image forming apparatus shown in the present embodiment, the amount of water supply is adjusted by the humidifier in accordance with the average printing rate of the printed matter that has been printed out. For example, the amount of water supply is adjusted according to the average printing rate by using the following formula 1. In this case, in an environment of a temperature of 25 ° C./humidity of 50%, the charging property of the charging roller 2 is improved by the humidity around the charging roller 2, so that no streak-like density unevenness appears on the image.

Here, when the charging roller 2 to be used is a φ25, (longitudinal 300 mm) charging roller (core metal diameter φ5), the entire sponge volume is 9.4 × 10 ⁴ (mm ³ ), and the sponge bubble rate is 30%. If there is, the volume of the bubble part of the sponge is 2.8 × 10 ⁴ (mm ³ ).

  If an environment where streaky density unevenness occurs due to adhesion of an insulator such as an external filler to the charging roller 2 is a temperature of 25 ° C./humidity of 20%, moisture contained in the bubble portion The amount is 0.13 g. On the other hand, when the environment in which streaky density unevenness occurs due to adhesion of an insulator such as an external filler to the charging roller 2 is a temperature of 25 ° C./humidity of 50%, the amount of water contained in the bubble portion is 0.32 g.

Based on the above conditions, the amount of water supplied to the charging roller 2 is determined as follows.
Water supply amount = (Ideal water amount of charging roller−Moisture amount of charging roller in current environment) × Standard water amount (%) ÷ Average printing rate = (Ideal water amount [0.32] − (0.0188 × Environment) Absolute water content +0.1031)) x standard printing rate (%) ÷ average printing rate (%)

For example, in the environment of temperature 25 ° C./humidity 20%, the water supply amount when the average printing rate is 3% is calculated as follows.
Water supply amount = (Ideal moisture amount of charging roller−Charging roller moisture amount in current environment) × Reference moisture amount (%) ÷ Average printing rate (ideal moisture amount [0.32] − (0.0188 × environmental absolute Water content + 0.1031)) x standard printing rate (%) ÷ average printing rate (%)
= (0.32- (0.0188 × 0.19 + 0.1031)) × 5 ÷ 3 = 0.21 g
It becomes.

  Therefore, by applying a water supply amount (0.21 g) of water to the peripheral surface of the charging roller 2, the electric resistance of the charging roller can be kept uniform, and streaky density unevenness occurs on the image. Can be reduced. In addition, 0.21 g of water supply is realized by applying droplets to the peripheral surface of the charging roller 2 at a resolution of 1200 dpi using 7 pl droplets at a printing rate of 72% in both the longitudinal direction and the circumferential direction. it can. Note that it is desirable to rotate the charging roller 2 during the humidifying operation by the humidifier 100 so that the charging roller 2 absorbs moisture uniformly.

  As described above, in the fourth embodiment, in addition to the environmental temperature and humidity around the charging roller 2, the amount of water supplied to the charging roller 2 is more accurately based on the average value of the printing ratio during image formation. It becomes possible to control. For this reason, according to the present embodiment, even when an external additive, drum shaving powder, toner, or the like adheres to the charging roller 2, water can be supplied to the charging roller 2 without excess or deficiency. Uniform electrical resistance can be obtained. For this reason, it is possible to realize image formation without density unevenness over a long period of time.

[Other Embodiments]
In each of the embodiments described above, water is used as the liquid. However, as the liquid for humidifying the charging roller 2 in order to make the electric resistance of the charging roller 2 uniform, a conductive material that does not adversely affect other members ( (Liquid) etc. are also applicable.

Further, the humidifier is approximately the same as the entire length of the charging roller, and the entire area of the charging roller is humidified.
Further, the humidifier is not limited to those shown in the above embodiments. For example, as in the fourth embodiment, instead of humidifying the atmosphere and the charging roller 2 by natural evaporation, the charging roller is humidified using an ultrasonic humidification method in which water vapor is generated by ultrasonic addition. Also good.

  In each of the above embodiments, the case where a charging roller is used as the charging member for charging the image carrier 1 has been described as an example. However, the charging member is not limited to a roller type, but a blade type, a rod type, It can be of an appropriate shape and form such as a pad type.

  Furthermore, the charging device according to the present invention can be applied to configurations other than the configuration in which the charging member charges the image carrier as shown in the above-described embodiment. For example, a contact type in which a transfer material is introduced between an image carrier and a transfer member to which a voltage is applied, the back surface of the transfer material is charged, and the transfer image on the image carrier side is electrostatically transferred to the transfer material side. The present invention can also be applied to a transfer charging device. Furthermore, the charging device according to the present invention can be widely used as a device for charging a member to be charged.

DESCRIPTION OF SYMBOLS 1 Carrier 2 Charging roller 3 Exposure means 4 Developing device 7 Transfer roller 20 Controller 21 Main controller 22 CPU
25 Humidification control circuit 26 Temperature / humidity detector 100 Humidifier 104a Discharge port 110 Droplet discharge unit 200 Humidifier 204a Discharge port 206 Shutter

Claims (11)

The image carrier as a member to be charged is charged by charging means that contacts the image carrier, and an electrostatic latent image is formed by exposing the charged image carrier, and a developer is attached to the electrostatic latent image. An image forming apparatus configured to form an image on the recording medium by transferring the developed image to the recording medium,
An image forming apparatus comprising: a liquid applying unit that applies a conductive liquid to the charging member.   The image forming apparatus according to claim 1, wherein the liquid application unit applies the liquid to the charging member according to conductivity of the charging member.   The image according to claim 1, wherein the liquid applying unit is configured to estimate a change in conductivity of the charging member, and to apply liquid to the charging member according to the estimated conductivity. Forming equipment. The estimation means includes humidity detection means for detecting at least one of a humidity environment and a temperature environment around the charging member,
The image forming apparatus according to claim 3, wherein the liquid application unit controls application of the liquid to the charging member according to at least one of humidity and temperature detected by the humidity detection unit. apparatus.   The image according to claim 1, wherein the liquid application unit includes a droplet discharge unit that discharges a droplet from the discharge port toward the charging member by thermal energy generated by the electrothermal conversion element. Forming equipment. The liquid applying means includes a liquid container provided in the vicinity of the charging member;
An outlet for releasing water vapor generated from the liquid container;
Opening and closing means for opening and closing the discharge port;
The image forming apparatus according to claim 1, further comprising: The liquid applying means includes a liquid supply sheet having liquid absorbency provided in the vicinity of the charging member, and a liquid supply means capable of supplying liquid to the liquid supply sheet,
The image forming apparatus according to claim 1, wherein the charging member is humidified by a liquid that naturally evaporates from the liquid supply sheet.   The image forming apparatus according to claim 3, wherein the estimation unit estimates the average according to an average value of a printing rate of an image formed on the image carrier. The image carrier as a member to be charged is charged by charging means that contacts the image carrier, and an electrostatic latent image is formed by exposing the charged image carrier, and a developer is attached to the electrostatic latent image. An image forming method for forming an image on the recording medium by transferring the developed image to the recording medium,
An image forming method comprising a step of applying a conductive liquid to the charging member. In a charging device including a charging member that charges the charging surface while being in contact with the charging surface of the member to be charged,
A charging device comprising: a liquid applying unit capable of applying a conductive liquid to the charging member that contacts the charging surface. In the charging method of charging the charging surface while being in contact with the charging surface of the member to be charged,
A charging method comprising applying a conductive liquid to the charging member in contact with the charging surface.