JP2024083787A - Image forming device - Google Patents

Abstract

To provide an image forming apparatus that uses a non-magnetic one-component developing system, and can prevent the occurrence of a reversely electrified toner when the toner is frictionally electrified and can prevent image fogging.SOLUTION: An image forming apparatus comprises an image carrier, an electrifying device, an exposure device, and a developing device. The developing device has a developer container storing a non-magnetic one-component developer, a developer carrier having a toner layer formed on its outer peripheral surface, and a regulation blade regulating the layer thickness of the toner layer formed on the developer carrier. When the peripheral speed of the developer carrier is defined as Sd [mm/sec], the peripheral speed of the image carrier as Sp [mm/sec], and the drive time of the developer carrier required for printing one sheet as Td [sec], 0≤(Sd-Sp)*Td≤400 is satisfied.SELECTED DRAWING: Figure 2

Description

The present invention relates to image forming devices using electrophotographic processes, such as copiers, printers, and facsimiles, and in particular to image forming devices equipped with a non-magnetic single-component development device.

The developing devices used in image forming devices such as electrophotographic copiers, printers, facsimiles, and multifunction machines are of two types: two-component developing devices that use toner and carrier as the developer, and one-component developing devices that use only toner without a carrier.

In a developing device that uses a non-magnetic one-component development method that uses non-magnetic toner, a regulating blade, which acts as a developer regulating member, is arranged so that it comes into contact with the surface of the developing roller, which is the developer carrier. The toner is transported by the fine irregularities on the surface of the developing roller, and excess toner is scraped off by the regulating blade, forming a thin layer of toner. When the toner passes under the regulating blade, it becomes charged by friction with the regulating blade and the surface of the developing roller. The photoconductor and the developing roller are then rotated in contact with each other, and the toner on the surface of the developing roller is developed onto the photoconductor by an electric field.

In the non-magnetic one-component development method described above, when the toner is triboelectrically charged, it may become charged with a polarity opposite to the normal charging polarity. As a result, reversely charged toner is generated, and the toner adheres to the white parts of the image, causing the problem of so-called image fogging.

As a method for suppressing image fog in a non-magnetic one-component development method, for example, Patent Document 1 discloses an image formation method in which a non-magnetic one-component toner is used in which the charge amount Q1 imparted in the first toner thinning is 65 to 95% (preferably 75 to 95%) of the charge amount Q2 at saturation, and the absolute value of the charge amount Q1 is 3 μC/g to 20 μC/g (preferably 4 μC/g to 15 μC/g), and the surface speed of the toner layer carrier is set to 160 mm/sec or more, or a toner with a volume average particle size of 0.1 to 8.5 μm is selected as the non-magnetic one-component toner.

Japanese Patent Application Laid-Open No. 9-211986

The image forming method of Patent Document 1 does not limit whether it is contact development or non-contact development, but in a contact development type image forming device in which the photoconductor and toner are charged with a polarity opposite to the normal charging polarity when they are frictionally charged, there is a problem that the generation of oppositely charged toner and image fogging cannot be suppressed even if the method of Patent Document 1 is used.

In view of the above problems, the present invention aims to provide an image forming device that uses a non-magnetic single-component development method and is capable of suppressing the generation of reversely charged toner when toner is triboelectrically charged, thereby suppressing image fog.

In order to achieve the above object, the first configuration of the present invention is an image forming apparatus including an image carrier, a charging device, an exposure device, and a developing device. The image carrier has a photosensitive layer formed on its surface. The charging device charges the image carrier to a predetermined surface potential. The exposure device exposes the surface of the image carrier charged by the charging device to form an electrostatic latent image in which the charge is attenuated. The developing device has a developing container that contains a non-magnetic one-component developer consisting of only toner, a developer carrier that is pressed against the image carrier with a predetermined pressing force and carries toner on its outer circumferential surface to form a toner layer, and a regulating blade that contacts the outer circumferential surface of the developer carrier to regulate the layer thickness of the toner layer formed on the outer circumferential surface of the developer carrier, and supplies toner to the image carrier on which the electrostatic latent image is formed. The image forming apparatus uses a toner whose charge polarity when triboelectrically charged with the image carrier and the charge amount [μC/g] are measured is opposite to the normal charge polarity. If the peripheral speed of the developer carrier is Sd [mm/sec], the peripheral speed of the image carrier is Sp [mm/sec], and the drive time of the developer carrier per print is Td [sec], then 0≦(Sd-Sp)*Td≦400 is satisfied.

According to the first configuration of the present invention, by setting (Sd-Sp)*Td, which indicates the distance (reverse charging distance) that the toner rubs against the image carrier when one sheet is printed, to the range of 0≦(Sd-Sp)*Td≦400, it is possible to suppress the generation of reversely charged toner and the associated image fog while ensuring the amount of toner charge required for development.

FIG. 1 is a side cross-sectional view showing a schematic configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 1 is a side cross-sectional view showing a schematic configuration of an image forming unit 30 of an image forming apparatus 1 according to an embodiment of the present invention. FIG. 3 is a plan view of the contact area between the photoconductor drum 31 and the developing roller 331 of the developing unit 33, viewed from above. FIG. 1 is an enlarged cross-sectional view of the vicinity of a contact portion between a developing roller 331 and a regulating blade 334 in a developing unit 33; An enlarged cross-sectional view of a contact portion between the developing roller 331 and the supply roller 332. FIG. 1 is a block diagram showing an example of a control path used in an image forming apparatus according to an embodiment of the present invention. Graph showing the change in fog density when (Sd-Sp)*Td is changed Graph showing the relationship between the developing voltage applied to the developing roller 331 and the image density when the surface free energy of the developing roller 331 is changed

(1. Overall configuration of image forming apparatus 1)
Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a side cross-sectional view showing a schematic configuration of an image forming apparatus 1 according to an embodiment of the present invention. In Fig. 1, the right side is the front side of the image forming apparatus 1, and the left side is the rear side.

The image forming device 1 (here, a monochrome printer) includes a main housing 10 having a substantially rectangular parallelepiped casing structure, a paper feed section 20, an image forming section 30, and a fixing section 40 housed within the main housing 10. A front cover 11 is provided on the front side of the main housing 10, and a rear cover 12 is provided on the rear side. The top surface of the main housing 10 is provided with a paper discharge section 13 into which sheets after image formation are discharged. Each unit of the image forming section 30 can be inserted or removed from the top side of the main housing 10 by lifting the paper discharge section 13 to open the top. In the following description, the term "sheet" refers to copy paper, coated paper, overhead projector sheets, cardboard, postcards, tracing paper, or other sheet material that undergoes image formation processing.

The paper feed section 20 includes a paper feed cassette 21 that stores sheets on which image formation processing is performed. A portion of the paper feed cassette 21 protrudes further forward from the front surface of the main housing 10. The upper surface of the portion of the paper feed cassette 21 that is stored inside the main housing 10 is covered by a paper feed cassette top plate 21U. The paper feed cassette 21 is provided with a paper storage space that stores a stack of sheets, a lift plate that lifts up the stack of sheets for feeding, and the like. A paper feed section 21A is provided at the top of the rear end side of the paper feed cassette 21. A paper feed roller 21B is arranged in this paper feed section 21A to feed the topmost sheet of the stack of sheets in the paper feed cassette 21 one by one.

The image forming unit 30 performs an image forming operation to form a toner image (developer image) on a sheet fed from the paper feed unit 20. The image forming unit 30 includes a photoconductor drum 31, and a charging unit 32, an exposure unit 35, a developing unit 33, and a transfer roller 34 arranged around the photoconductor drum 31.

The photosensitive drum 31 (image carrier) has a rotating shaft and an outer peripheral surface (drum body) that rotates around the rotating shaft. The outer peripheral surface of the photosensitive drum 31 is made of, for example, a known organic (OPC) photosensitive material, and a photosensitive layer made of a charge generation layer, a charge transport layer, etc. is formed on the outer peripheral surface. The photosensitive layer is uniformly charged by the charging unit 32 described below, and then irradiated with light by the exposure unit 35 to form an electrostatic latent image with the charge attenuated, and the developing unit 33 develops the electrostatic latent image into a toner image that is carried.

The charging section 32 (charging device) is disposed at a predetermined interval from the outer peripheral surface of the photosensitive drum 31, and charges the outer peripheral surface of the photosensitive drum 31 uniformly without contact. Specifically, the charging section 32 has a charge wire 321 and a grid electrode 322 (see FIG. 2 for both). The charge wire 321 is a linear electrode extending in the direction of the rotation axis of the photosensitive drum 31, and generates a corona discharge between the charge wire 321 and the photosensitive drum 31. The grid electrode 322 is a lattice-shaped electrode extending in the direction of the rotation axis of the photosensitive drum 31, and is disposed between the charge wire 321 and the photosensitive drum 31. The charging section 32 generates a corona discharge by passing a current of a predetermined current value through the charge wire 321, and applies a predetermined voltage to the grid electrode 322 to uniformly charge the outer peripheral surface of the photosensitive drum 31 facing the grid electrode 322 to a predetermined surface potential.

The exposure section 35 (exposure device) has a laser light source and optical equipment such as mirrors and lenses, and irradiates the outer peripheral surface of the photoconductor drum 31 with light modulated based on image data provided from an external device such as a personal computer. As a result, the exposure section 35 forms an electrostatic latent image on the outer peripheral surface of the photoconductor drum 31 that corresponds to the image based on the image data.

The developing unit 33 (developing device) is detachable from the main housing 10, and develops the electrostatic latent image formed on the outer peripheral surface of the photosensitive drum 31 by supplying non-magnetic single-component toner (developer) to the outer peripheral surface of the photosensitive drum 31. Developing an electrostatic latent image means forming a toner image (developer image) that manifests the electrostatic latent image. The detailed configuration of the developing unit 33 will be described later.

The transfer roller 34 is a roller for transferring the toner image formed on the outer peripheral surface of the photosensitive drum 31 onto a sheet. Specifically, the transfer roller 34 rotates around its axis, and has an outer peripheral surface that faces the outer peripheral surface of the photosensitive drum 31 at a position downstream of the developing roller 331 in the rotation direction of the photosensitive drum 31. The transfer roller 34 transfers the toner image carried on the outer peripheral surface of the photosensitive drum 31 to a sheet that passes through a nip portion between the transfer roller 34 and the outer peripheral surface of the photosensitive drum 31. During this transfer, a transfer voltage of the opposite polarity to that of the toner is applied to the transfer roller 34.

The fixing unit 40 performs a fixing process to fix the toner image transferred to the sheet onto the sheet. The fixing unit 40 has a fixing roller 41 and a pressure roller 42. The fixing roller 41 has an internal heating source and heats the toner transferred to the sheet to a predetermined temperature. The pressure roller 42 is pressed against the fixing roller 41 to form a fixing nip between the fixing roller 41. When the sheet onto which the toner image has been transferred is passed through the fixing nip, the toner image is fixed onto the sheet by heating from the fixing roller 41 and pressure from the pressure roller 42.

The main housing 10 is provided with a main transport path 22F and a reverse transport path 22B for transporting sheets. The main transport path 22F extends from the paper feed section 21A of the paper feed section 20, through the image forming section 30 and the fixing section 40, to the paper discharge port 14 provided opposite the paper discharge section 13 on the top surface of the main housing 10. The reverse transport path 22B is a transport path for returning a sheet that has been printed on one side to the upstream side of the image forming section 30 on the main transport path 22F when performing double-sided printing on the sheet.

The main transport path 22F extends from below to above the transfer nip formed by the photosensitive drum 31 and the transfer roller 34. A pair of registration rollers 23 is disposed upstream of the transfer nip on the main transport path 22F. The sheet is temporarily stopped by the pair of registration rollers 23, and after skew correction is performed, it is sent to the transfer nip at a predetermined timing for image transfer. A plurality of transport rollers for transporting the sheet are disposed at appropriate positions on the main transport path 22F and the reverse transport path 22B. A pair of paper discharge rollers 24 is disposed near the paper discharge outlet 14.

The reverse transport path 22B is formed between the outer surface of the reversing unit 25 and the inner surface of the rear cover 12 of the main housing 10. The transfer roller 34 and one of the pair of registration rollers 23 are mounted on the inner surface of the reversing unit 25. The rear cover 12 and the reversing unit 25 can each rotate around the axis of the fulcrum 121 provided at their lower ends. If a jam (paper jam) occurs in the reverse transport path 22B, the rear cover 12 is opened. If a jam occurs in the main transport path 22F, or if the photosensitive drum 31 unit or the developing unit 33 is removed to the outside, the reverse unit 25 is opened in addition to the rear cover 12.

(2. Configuration of Image Forming Unit 30)
Fig. 2 is a cross-sectional view of the image forming unit 30 in the image forming apparatus 1 of this embodiment. Fig. 3 is a plan view seen from above of the periphery of the contact portion between the photoconductor drum 31 and the developing roller 331 of the developing unit 33. Fig. 4 is an enlarged cross-sectional view of the periphery of the contact portion between the developing roller 331 and the regulating blade 334 in the developing unit 33. Fig. 5 is an enlarged cross-sectional view of the abutment portion between the developing roller 331 and the supply roller 332.

As shown in Figures 2 and 3, the developing unit 33 includes a developing housing 330 (developing container), a developing roller 331 (developer carrier), a supply roller 332, an agitating paddle 333, and a regulating blade 334.

The developing housing 330 contains a non-magnetic single-component developer consisting only of toner, and also contains a developing roller 331, a supply roller 332, a regulating blade 334, etc. The developing housing 330 has an agitation chamber 335 that contains the developer (toner) in an agitated state. An agitation paddle 333 is disposed in the agitation chamber 335. The agitation paddle 333 agitates the toner in the agitation chamber 335.

The developing roller 331 includes a rotating shaft 331a and a roller portion 331b. The rotating shaft 331a is rotatably supported by a bearing portion (not shown) of the developing housing 330. The roller portion 331b is a cylindrical member laminated on the outer circumferential surface of the rotating shaft 331a, and is configured by laminating a coating layer of a coating material having an uneven surface such as urethane on the surface of a base rubber (e.g., silicone rubber). The roller portion 331b rotates integrally with the rotating shaft 331a as the rotating shaft 331a rotates. A toner layer (developer layer) of a predetermined thickness is formed on the surface of the roller portion 331b. The layer thickness of the toner layer is regulated (adjusted uniformly to a predetermined thickness) by the regulating blade 334 described later. The toner layer is charged by static electricity generated by the contact (friction) between the regulating blade 334 and the roller portion 331b.

When facing the photosensitive drum 31, the developing roller 331 rotates in a direction from the upstream side to the downstream side (counterclockwise direction in FIG. 2) in the rotation direction of the photosensitive drum 31 (clockwise direction in FIG. 2). In other words, when facing the photosensitive drum 31, the developing roller 331 rotates in the same direction as the photosensitive drum 31.

The supply roller 332 is disposed opposite the developing roller 331. The supply roller 332 holds the developer contained in the stirring chamber 335 on its outer circumferential surface. The supply roller 332 also supplies the developer held on its outer circumferential surface to the developing roller 331.

At a position facing the developing roller 331, the supply roller 332 rotates in a direction from downstream to upstream in the rotation direction of the developing roller 331 (counterclockwise direction in FIG. 2). In other words, at a position facing the developing roller 331, the supply roller 332 rotates in the opposite direction to the developing roller 331. In order to move toner from the supply roller 332 to the developing roller 331, a predetermined supply voltage (DC voltage) is applied to the supply roller 332.

The developing roller 331 receives developer from the supply roller 332 and holds a toner layer on its outer circumferential surface. The developing roller 331 then supplies developer to the photoconductor drum 31. The axial length (direction perpendicular to the paper surface of FIG. 2) of the developing roller 331 and the supply roller 332 is approximately the same as the axial length of the photoconductor drum 31. To move the toner from the developing roller 331 to the photoconductor drum 31, a predetermined developing voltage (DC voltage) is applied to the developing roller 331.

In the image forming unit 30, a pressing mechanism 36 consisting of a pressing member 361 and a pressing spring 362 is arranged on the opposite side of the photosensitive drum 31 (lower right side in FIG. 2, lower side in FIG. 3) across the developing housing 330. The pressing mechanism 36 is arranged at two locations in the longitudinal direction of the developing housing 330 (85 mm from the axial center of the photosensitive drum 31, respectively). When the developing unit 33 is attached to the image forming unit 30, the pressing member 361 is pressed against the developing housing 330 and pressed in a direction approaching the photosensitive drum 31 (upper left direction in FIG. 2, upper direction in FIG. 3), and the developing roller 331 is pressed against the photosensitive drum 31 with a predetermined pressing force. In this embodiment, the developing unit 33 and the photosensitive drum 31 do not have a mechanism for regulating the distance between the developing roller 331 and the photosensitive drum 31, i.e., a mechanism for regulating the pressing force of the developing roller 331 against the photosensitive drum 31. However, a mechanism may be provided to regulate the pressure of the developing roller 331 against the photoconductor drum 31.

The regulating blade 334 is a thin plate-like member made of metal. The regulating blade 334 is configured so that the base end 334a is fixed to the developing housing 330 and the tip end 334b is a free end. The regulating blade 334 contacts the outer peripheral surface of the developing roller 331 at a position upstream in the rotation direction of the developing roller 331 from the position where the photoconductor drum 31 and the developing roller 331 face each other.

The regulating blade 334 is flexible and deformable, and there is a contact portion (regulating nip) between the regulating blade 334 and the developing roller 331 in the circumferential direction of the developing roller 331. The regulating blade 334 abuts against the outer peripheral surface of the developing roller 331 (roller portion 331b) with a predetermined regulating pressure and regulating nip width W. Note that, as described below, the regulating blade 334 may be configured to apply a predetermined regulating voltage (DC voltage).

The material of the regulating blade 334 is, for example, stainless steel (SUS304), and in this embodiment, the free length is 10 mm. The tip 334b of the regulating blade 334 is bent to form a curved portion 334c. This curved portion 334c abuts against the outer circumferential surface of the developing roller 331. The radius of curvature of the curved portion 334c is 0.1 mm or more.

As shown in FIG. 4, the regulating blade 334 contacts the developing roller 331 with a constant regulating pressure (contact line pressure), so that the toner layer carried on the outer peripheral surface of the developing roller 331 is adjusted to a uniform thickness. In this way, the regulating blade 334 regulates the amount of toner on the outer peripheral surface of the developing roller 331. The regulating blade 334 also charges the toner carried on the outer peripheral surface of the developing roller 331 by rubbing the toner. The contact line pressure of the regulating blade 334 against the developing roller 331 is the contact pressure per unit length of the regulating blade 334 at the contact position between the regulating blade 334 and the outer peripheral surface of the developing roller 331.

As shown in FIG. 5, the developing roller 331 is configured to bite into the supply roller 332 at the contact portion (supply nip N) between the developing roller 331 and the supply roller 332. In addition, a toner pool T is formed downstream of the supply nip N in the rotation direction of the developing roller 331 (upper right side in FIG. 5).

It is known that if the developing roller 331 and the supply roller 332 are in line contact at the supply nip N, toner pool T is not formed and toner supply performance is significantly reduced. Therefore, it is necessary to design the axial distance, diameter, and hardness of the developing roller 331 and the supply roller 332 so that the developing roller 331 and the supply roller 332 are appropriately biting into each other. The developing roller 331 is designed to have an Asker C hardness of about 50 to 80 because it comes into contact with the photosensitive drum 31, a hard member. Therefore, in order to configure the developing roller 331 to bite into the supply roller 332, it is necessary to make the hardness of the supply roller 332 lower than that of the developing roller 331.

By generating a potential difference between the supply roller 332 and the development roller 331, electric field energy is generated in the direction in which the toner moves from the supply roller 332 to the development roller 331. In addition, van der Waals force acts between toner particles regardless of the potential difference. This electric field energy and van der Waals force supply the toner from the supply roller 332 to the development roller 331. In order to improve the density tracking of a solid image (no density difference between the leading and trailing ends of the image), it is also important to set the compression load, which is the force that presses the supply roller 332 against the development roller 331, in an optimal range.

(3. Control Path of Image Forming Apparatus 1)
6 is a block diagram showing an example of a control path used in the image forming apparatus 1 of this embodiment. Note that, since various controls are performed on each part of the image forming apparatus 1 when the image forming apparatus 1 is used, the control path of the entire image forming apparatus 1 becomes complicated. Therefore, the following description will focus on the parts of the control path that are necessary for implementing the present invention.

The main motor 50 drives the paper feed roller 21B, the photosensitive drum 31, the developing roller 331 in the developing unit 33, the supply roller 332, the stirring paddle 333, the fixing roller 41 in the fixing unit 40, etc. to rotate at a predetermined rotational speed in response to an output signal from the control unit 90.

The voltage control circuit 51 is connected to the charging voltage power supply 52, the developing voltage power supply 53, and the transfer voltage power supply 54, and operates each of these power supplies according to an output signal from the control unit 90. According to a control signal from the voltage control circuit 51, the charging voltage power supply 52 applies a charging voltage to the charge wire 321 in the charging unit 32. The developing voltage power supply 53 applies a developing voltage to the developing roller 331 in the developing unit 33, and applies a supply voltage to the supply roller 332. When applying a regulating voltage to the regulating blade 334 in the developing unit 33, the developing voltage power supply applies the regulating voltage to the regulating blade 334. The transfer voltage power supply 54 applies a transfer voltage to the transfer roller 34.

The image input unit 60 is a receiving unit that receives image data sent from a personal computer or the like to the image forming device 1. The image signal input from the image input unit 60 is converted into a digital signal and then sent to the temporary storage unit 94.

The internal temperature and humidity sensor 61 detects the temperature and humidity inside the image forming device 1, particularly the temperature and humidity around the developing unit 33, and is located near the image forming unit 30.

The operation unit 70 is provided with an LCD display 71 and an LED 72 that indicates various states, and is configured to indicate the state of the image forming device 1, the image formation status, and the number of copies to be printed. Various settings for the image forming device 1 are made using the printer driver of the computer.

The control unit 90 includes at least a CPU (Central Processing Unit) 91 as a central processing unit, a ROM (Read Only Memory) 92 as a read-only memory unit, a RAM (Random Access Memory) 93 as a readable and writable memory unit, a temporary memory unit 94 that temporarily stores image data and the like, a counter 95, and multiple (here, two) I/Fs (interfaces) 96 that transmit control signals to each device in the image forming device 1 and receive input signals from the operation unit 70.

ROM 92 stores control programs for image forming device 1, numerical values necessary for control, and other data that will not change while image forming device 1 is in use. RAM 93 stores necessary data that is generated during the control of image forming device 1, data that is temporarily required for the control of image forming device 1, and the like.

The temporary storage unit 94 temporarily stores the image signal that is input from the image input unit 60, which receives image data sent from a personal computer or the like and converted into a digital signal. The counter 95 accumulates and counts the number of printed sheets.

The control unit 90 also transmits control signals from the CPU 91 through the I/F 96 to each part and device in the image forming apparatus 1. Furthermore, signals indicating the state and input signals are transmitted from each part and device to the CPU 91 through the I/F 96. Examples of parts and devices controlled by the control unit 90 include the image forming unit 30, the fixing unit 40, the main motor 50, the voltage control circuit 51, the image input unit 60, and the operation unit 70.

(4. Setting of the developing unit in the image forming operation)
The setting of the developing unit 33 during image formation (development), which is a characteristic part of the image forming apparatus 1 of this embodiment, will be described below. As described above, in the non-magnetic one-component development method, when the photoconductor drum 31 and the toner are triboelectrically charged, the toner is charged to a polarity (negative polarity) opposite to the normal charging polarity (positive polarity in this embodiment). More specifically, when the photoconductor drum 31 and the toner are triboelectrically charged and the charge amount [μC] of the toner is divided by the total weight [g] of the toner to measure the charge amount [μC/g] of the toner, the charge polarity of the toner becomes the polarity opposite to the normal charging polarity (positive polarity). This toner charged to the opposite polarity (oppositely charged toner) adheres to the white background part of the photoconductor drum 31, causing image fogging.

Therefore, in this embodiment, when the circumferential speed of the developing roller 331 is Sd [mm/sec], the circumferential speed of the photosensitive drum 31 is Sp [mm/sec], and the driving time of the developing roller 331 per printed sheet is Td [sec], the following formula (1) is satisfied.
0≦(Sd−Sp)*Td≦400 (1)

Formula (1) shows the distance (reverse charging distance) over which the toner rubs against the photoconductor drum 31 when one sheet is printed, and affects the likelihood of reverse charging toner occurring when the toner is charged to the opposite polarity when frictionally charged against the photoconductor drum 31. If (Sd-Sp)*Td is smaller than 0, the distance over which the toner rubs against the photoconductor drum 31 is too small, and the toner is not sufficiently charged. On the other hand, if (Sd-Sp)*Td is too large, the distance over which the toner rubs against the photoconductor drum 31 becomes too large, and the occurrence of reverse charging toner becomes prominent. By setting (Sd-Sp)*Td in the range of 0 to 400, the occurrence of reverse charging toner and the associated occurrence of image fog can be suppressed while ensuring the amount of toner charge required for development.

Furthermore, as shown in the examples described later, by making (Sd-Sp)*Td satisfy the following formula (2), the reverse charge distance can be further reduced within a range in which the toner charge can be maintained, and the occurrence of image fog can be suppressed even in a high-temperature, high-humidity environment after endurance printing.
0≦(Sd−Sp)*Td≦200 (2)

Furthermore, by adding spacer particles to the toner, the frequency of contact between the photoconductor drum 31 and the toner base particles is reduced. As a result, the frictional charging between the toner and the photoconductor drum 31 is optimized, so the generation of reversely charged toner can be more effectively suppressed.

In this specification, the spacer particles refer to particles that have a larger particle diameter than external toner additives such as silica and have the function of suppressing the embedding of silica into the toner base particles. In this embodiment, electrostatically charged resin particles are used as the spacer particles.

If the particle diameter of the spacer particles is too small, it is not possible to sufficiently reduce the frequency of contact between the photoconductor drum 31 and the toner base particles. On the other hand, if the particle diameter of the spacer particles is too large, it becomes difficult to uniformly add the spacer particles to the surface of the toner base particles. Therefore, in this embodiment, the number average particle diameter of the spacer particles is set to 0.05 to 0.8 μm.

Furthermore, as shown in the examples described later, by making the polarity of the spacer particles the opposite polarity to the charge polarity of the toner (negative polarity in this case), it is possible to further suppress reverse charging of the photoconductor drum 31 and the toner. This is thought to be because the spacer particles, which have a polarity opposite to the charge polarity of the toner that has detached from the toner base particles, adhere to the photoconductor drum 31, suppressing the generation of reversely charged toner due to frictional charging between the photoconductor drum 31 and the toner.

The amount of triboelectric charge of the toner caused by friction with the photosensitive drum 31 can be measured by using a rotating disk tool to sandwich the toner between photosensitive sheets (the photosensitive layer of the photosensitive drum in sheet form) and frictionally charging it for a specified period of time (10 to 20 seconds), then sucking in the toner. Generally, toner that is triboelectrically charged with the photosensitive drum 31 is charged to the normal polarity (positive polarity in this case), but if it is reversely charged, image fog can be suppressed by using the above configuration.

In this embodiment, it is assumed that a low-temperature fixing toner is used as the non-magnetic toner. More specifically, the melt viscosity [Pa·s] of the toner contained in the development housing 330 at 95°C is preferably in the range of 10,000 to 200,000. When the melt viscosity exceeds the upper limit of 200,000, image quality can be easily maintained even without setting the conditions of the peripheral speed ratio Sd/Sp and the development ratio Mp/Md according to this embodiment, but the power required for the fixing process becomes larger than in this embodiment. In addition, it is difficult to use a toner with a viscosity below the lower limit of 10,000 for manufacturing reasons. Below, a manufacturing example of the toner used in the development unit 33 of this embodiment will be described.

(Production Example 1)
In a 1000 mL four-neck flask equipped with a stirrer, a cooling tube, a thermometer, and a nitrogen inlet tube, 80 g of butyl methacrylate (BMA) as an acrylic acid monomer, 80 g of styrene as a styrene monomer, 40 g of divinylbenzene (DVB) as a monomer having two or more vinyl groups, 15 g of sodium lauryl sulfate (SLS) as an emulsifier, 15 g of benzoyl peroxide (BPO) as a polymerization initiator, and 600 g of ion-exchanged water were added while stirring. While introducing nitrogen gas into the flask, the contents of the flask were reacted (copolymerized) at 90° C. for 3 hours under stirring. The number average primary particle diameter of the resulting resin fine particles was adjusted by adjusting the stirring conditions. As a result, an emulsion of the reaction product (resin fine particles) was obtained. The emulsion of resin fine particles was cooled, washed, and dehydrated. The copolymer particles were separated from the emulsion to obtain negatively charged resin fine particles (number average primary particle diameter 50 nm).

(Production Example 2)
Ion-exchanged water, an emulsifier (e.g., ammonium perfluorohexanoate, etc.), and paraffin wax were charged into the autoclave. Next, the inside of the autoclave was replaced with nitrogen gas and a raw material gas for the fluororesin (e.g., tetrafluoroethylene gas, etc.) while maintaining the temperature inside the autoclave at 40° C. or higher and 90° C. or lower.

Next, an aqueous solution of a polymerization initiator (e.g., an aqueous solution of ammonium persulfate, an aqueous solution of disuccinic acid peroxide, etc.) was injected into the autoclave, and the raw material gas of the fluororesin was continuously supplied into the autoclave to carry out the polymerization reaction. During the polymerization reaction, the temperature inside the autoclave was maintained at 40°C or higher and 90°C or lower, and the contents of the autoclave were stirred at a rotation speed of 200 rpm or higher and 300 rpm or lower. Then, after a predetermined time (e.g., 30 minutes or higher and 150 minutes or lower) has elapsed since the start of injection of the aqueous solution of the polymerization initiator (start of stirring the contents of the autoclave), the supply of the raw material gas was stopped and the stirring of the contents of the autoclave was stopped, and the polymerization reaction was terminated.

Next, concentrated nitric acid was added to the dispersion liquid (autoclave contents) after the polymerization reaction, and the dispersion liquid to which the concentrated nitric acid was added was stirred at a rotation speed of 200 rpm to 600 rpm for a predetermined time (e.g., 30 minutes to 2 hours) to coagulate the polymer. Next, the dispersion liquid after the coagulation was subjected to solid-liquid separation, and the obtained solid was dried to obtain a powder of fluororesin particles.

(Production Example 3)
To 100 parts of the cyan toner not containing any external additives, 2.0 parts of silica (CAB-O-SIL (registered trademark) TG-308F, manufactured by Cabot Corporation), 0.5 parts of alumina (AKP-20, manufactured by Sumitomo Chemical Co., Ltd.), 0.5 parts of the negatively charged resin fine particles (spacer particles) manufactured in Production Example 1, and 0.5 parts of the fluorine fine particles manufactured in Production Example 2 were externally added to produce a toner.

(6. Image Evaluation by Development Unit Settings)
The following describes the image evaluation results when the developing unit 33 is set as in this embodiment. First, a durability printing test was performed by changing the printing conditions (the peripheral speed Sd of the photoconductor drum 31, the peripheral speed Sp of the developing roller 331, and the driving time Td of the developing roller 331 per printed sheet) to verify the effect on the occurrence of image fog. The image forming apparatus 1 (manufactured by Kyocera Document Solutions Inc.) shown in FIG. 1 was used as the test machine.

The developing roller 331 has a rotating shaft 331a with a shaft diameter of 6 mm, and a roller portion 331b with an outer diameter of 13 mm and an axial length of 232 mm, coated with a silicone rubber layer with a thickness of 3.5 mm as a base layer, and has an Asker C hardness of 55°. The coating was 5 μm thick, with 100 parts by weight of copolymer nylon resin to which 1 part by weight of carbon black or quaternary ammonium salt was added, and with no addition, and the roller resistance was adjusted to 9 to 11 [log Ω]. The roller resistance was measured by applying a DC voltage of 100 V between the developing roller 331 and the metal roller while a load F of 1 kg was applied to the metal roller M and the metal roller M was stopped in contact with the developing roller 331.

The photoconductor drum 31 was a positively charged single-layer OPC photoconductor drum (manufactured by Kyocera Document Solutions, Inc.) with an outer diameter of 24 mm and a photosensitive layer thickness of 22 μm.

(Relationship between (Sd-Sp)*Td and image fog)
The relationship between the value of (Sd-Sp)*Td and image fog was investigated. As a test method, an image forming apparatus 1 was prepared in which the toner produced in Production Example 3 was filled in the developing section 33. Using these image forming apparatuses 1, (Sd-Sp)*Td was changed within the ranges of Sp: 118 to 122 [mm/sec], Sd: 130 to 180 [mm/sec], and Td: 9 to 10.5 [sec], and 1500 sheets of standard data (character pattern with a print rate of 3.9%) specified in ISO/IEC19752 were printed as test images in succession. Then, the fog density when a blank image (print rate of 0%) was output in a normal temperature and normal humidity environment (NN environment, 25°C, 50% RH) or a high temperature and high humidity environment (HH environment, 32.5°C, 80% RH) was measured with a reflection densitometer (FD-9, manufactured by Konica Minolta, Inc.). The results are shown in Figure 7.

As shown in Figure 7, by setting (Sd - Sp) * Td ≦ 400, the fog density in the NN environment after durable printing (data series marked with circles in the figure) was 0.01 or less (shaded area), and no image fog occurred. Also, the fog density in the HH environment (data series marked with circles in the figure) was 0.01 to 0.015 or less (dot area), and although image fog occurred, it was within a range that did not cause any problems in practical use.

In addition, by setting (Sd-Sp)*Td≦200, the fog density in both the NN and HH environments after endurance printing was 0.01 or less (shaded area), further improving the effect of suppressing image fog.

(7. Other Configurations)
8 is a graph showing the relationship between the developing voltage applied to the developing roller 331 and the image density (1D) when the surface free energy of the developing roller 331 is changed. Surface free energy corresponds to the surface tension of a liquid in a solid, and is the molecular energy of the solid surface itself. In FIG. 8, the case where the surface free energy of the developing roller 331 is 12 mJ/ ^m2 is shown by the data series of ◇, the case where it is 21 mJ/ ^m2 is shown by the data series of □, and the case where it is 30 mJ/ ^m2 is shown by the data series of △.

8, the usable development voltage range OW tends to become narrower as the surface free energy of the developing roller 331 increases. This is because the upper limit of the pressing force of the developing roller 331 at which blank areas occur in a halftone image decreases as the surface free energy of the developing roller 331 increases. The surface free energy of the developing roller 331 is preferably 5 mj/ ^m2 or more and 27 mj/ ^m2 or less.

The amount of toner regulated by the regulating blade 334 also varies depending on the contact area ratio of the outer peripheral surface of the developing roller 331. The contact area ratio of the outer peripheral surface of the developing roller 331 is the ratio of the area of the outer peripheral surface of the developing roller 331 excluding recesses (non-contact areas). In other words, the contact area ratio of the outer peripheral surface of the developing roller 331 represents the true contact area relative to the apparent contact area between the outer peripheral surface of the developing roller 331 and the regulating blade 334. The contact area ratio is preferably 4.5 to 10%, and more preferably 6 to 8%.

The regulating pressure of the regulating blade 334 is preferably 10 to 60 N/m, and more preferably 20 to 40 N/m. The manufacturing method of the developing roller 331 is not particularly limited, and the surface roughness of the developing roller 331 may be adjusted by coating with a coating layer containing particles, or the roughness may be adjusted by polishing alone.

In addition, in this embodiment, both toner produced by a pulverization method (pulverized toner) and toner produced by a polymerization method (polymerized toner) can be used. Polymerized toner has a highly circular, true spherical shape, so it has low adhesion and good developability, so it has a wide usable range OW. Therefore, the present invention is particularly effective in non-magnetic one-component development methods that use pulverized toner, which is less expensive than polymerized toner.

In addition, in this embodiment, it has been confirmed that good results are obtained with toner having a median particle size of 6.0 to 8.0 μm. The reason for selecting this range of median particle size is that a median particle size smaller than 6.0 μm leads to increased toner manufacturing costs, while a median particle size larger than 8.0 μm increases toner consumption and deteriorates fixability, which is undesirable.

In addition, in this embodiment, it has been confirmed that good results are obtained with toner having a circularity of 0.93 to 0.97. If the circularity is 0.93 or less, image quality tends to decrease. If the circularity is 0.97 or more, the manufacturing costs increase significantly, so neither is preferable.

In addition, in this embodiment, it has been confirmed that good results are obtained with a toner having a melt viscosity of 100,000 Pa·s or less at 90°C. If the melt viscosity at 90°C exceeds 100,000 Pa·s, the fixing properties of the toner deteriorate, which is not preferable from the viewpoint of energy saving.

It has also been confirmed that similar results can be obtained when the surface potential V0 of the photoconductor drum 31 is in the range of 500 to 800 V and the post-exposure potential VL is in the range of 70 to 200 V.

In addition, the present invention is not limited to the above embodiment, and various modifications are possible within the scope of the present invention. For example, in the above embodiment, a monochrome printer has been described as an example of the image forming device 1, but the present invention can also be applied to, for example, tandem or rotary color printers. The present invention can also be applied to image forming devices such as copiers, facsimiles, or multifunction devices equipped with these functions. However, it is necessary to have a photoconductor drum 31 and a developing unit 33 that uses a non-magnetic single-component development method. In the above embodiment, a configuration in which non-magnetic toner is stored inside the developing housing 330 of the developing unit 33 has been described, but a toner container or toner cartridge that contains non-magnetic toner may be provided separately from the developing housing 330.

In addition, the photoconductor drum 31 in the above embodiment uses a cylindrical tube as the support, but other shapes of support may be used. Other shapes may include a plate shape or an endless belt shape. In addition, the photoconductor drum 31 in the above embodiment uses amorphous silicon as the photosensitive layer, but may have, for example, a charge injection blocking layer that blocks the injection of charge from the support.

The present invention can be used in an image forming apparatus equipped with a developing device that uses a non-magnetic one-component development method with non-magnetic toner. By utilizing the present invention, it is possible to provide an image forming apparatus that uses a non-magnetic one-component development method, in which stable image formation is possible even if the image area potential of the photoreceptor changes, and which can also ensure the uniformity of solid images.

1 Image forming apparatus 30 Image forming section 31 Photoconductor drum (image carrier)
32 Charging section (charging device)
33 Development section (developing device)
330 Development housing (developing container)
331 Developing roller (developer carrier)
331a Rotating shaft 331b Roller portion 332 Supply roller (toner supply member)
334 Regulating blade 35 Exposure section (exposure device)
53 Development voltage power supply 61 In-machine temperature and humidity sensor (temperature detection device)
90 Control unit

Claims (5)

an image carrier having a photosensitive layer formed on its surface;
a charging device for charging the image carrier to a predetermined surface potential;
an exposure device that exposes the surface of the image carrier charged by the charging device to light and forms an electrostatic latent image by attenuating the charge;
a developing container that contains a non-magnetic one-component developer consisting of only toner;
a developer carrier that is pressed against the image carrier with a predetermined pressing force and that carries the toner on its outer circumferential surface to form a toner layer;
a regulating blade that comes into contact with an outer peripheral surface of the developer carrier to regulate a thickness of the toner layer formed on the outer peripheral surface of the developer carrier;
a developing device for supplying the toner to the image carrier on which the electrostatic latent image is formed;
Equipped with
In an image forming apparatus using the toner, the charge polarity of which is opposite to a normal charge polarity when the charge amount [μC/g] is measured by frictionally charging the toner with the image carrier,
An image forming apparatus characterized in that, when a peripheral speed of the developer carrier is Sd [mm/sec], a peripheral speed of the image carrier is Sp [mm/sec], and a drive time of the developer carrier per printed sheet is Td [sec], the following formula (1) is satisfied:
0≦(Sd−Sp)*Td≦400 (1) 2. The image forming apparatus according to claim 1, wherein the following formula (2) is satisfied:
0≦(Sd−Sp)*Td≦200 (2) The image forming apparatus according to claim 1 or 2, characterized in that the toner has externally added spacer particles made of a resin having electrostatic properties. The image forming apparatus according to claim 3, characterized in that the number average particle diameter of the spacer particles is 0.05 to 0.8 μm. The image forming apparatus according to claim 3, characterized in that the spacer particles have a charge polarity opposite to that of the toner.

Images