JP2011007887A - Liquid-jetting developing device, and image forming apparatus equipped with liquid-jetting developing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid-jetting developing device and an image forming apparatus, preventing developer liquid droplets from splitting or scattering upon landing by suppressing a large increase in a jetting speed of developer liquid droplets.SOLUTION: The developing device 6 includes a developing tank 63 that reserves a liquid developer dv, a developing roller 66 that produces charged developer liquid droplets F from the developer dv and carries and conveys the developer liquid droplets F, and a metal roller 66b and a rotation shaft 66c that generate a jetting electric field to supply the developer liquid droplets F from the developing roller 66 to a photoreceptor belt 1 where an electrostatic latent image D is formed. The developing device is also provided with a developing roller surface layer 66a that suppresses induction of charges on the metal roller 66b by the developer liquid droplets F carried on the surface of the developing roller 66.

Description

  The present invention relates to a liquid flying development device that develops an electrostatic latent image by flying droplets made of a liquid developer, and an image forming apparatus including the liquid flying development device.

  In general, an image forming apparatus using an electrophotographic method is configured to charge a surface of an image carrier such as a photoconductor, and to irradiate the charged image carrier with light based on image data, thereby to form an image carrier. The electrostatic latent image is developed by bringing an electrostatic latent image on the surface of the toner and an electrostatic latent image on the image bearing member into contact with the developer carried on the surface of the developing roller of the developing device. A development process (forming a toner image), a transfer process for transferring the toner image onto the recording paper, and a fixing process for heating and fixing the toner image onto the recording paper are performed to form a desired image.

  An image forming apparatus that performs the fixing process consumes a large amount of power to melt the toner. With respect to this problem, Patent Literature 1 and Patent Literature 2 disclose an image forming apparatus including a developing device that performs development using a liquid developer. An image forming apparatus using a liquid developer forms a developer image with a liquid developer on an image carrier, transfers the developer image to a recording sheet, and permeates the developer image into the recording sheet. An image is formed by drying the developer image. Therefore, this image forming apparatus does not require heating and fixing of the toner image, and does not require a large amount of power.

  As an image forming apparatus using a liquid developer, Patent Document 3 discloses an image including a developing device that develops an electrostatic latent image by causing the liquid developer on the developing roller to fly by a Coulomb force with the electrostatic latent image. A forming apparatus is described. According to the developing device described in Patent Document 3, since the developing droplets stably fly from the surface of the developing roller subjected to the water repellent treatment, the development with the liquid developer can be stably performed.

JP 2003-5456 A JP 2004-341140 A JP-A-6-295131

  However, the developing device described in Patent Document 3 has several problems. The developing device described in Patent Document 3 forms developing droplets on the developing roller by bringing a regulating member such as a liquid supply roller into pressure contact with the developing roller. When the pressing force of the regulating member is weakened, the developing droplets aggregate and become coarse. Further, when the pressing force of the regulating member is increased, the number density of the developing droplets is reduced. Therefore, in the developing device described in Patent Document 3, it is difficult to carry developing droplets having a small droplet diameter at a high number density on the developing roller, and a high-density and high-definition image cannot be obtained.

  Further, in the developing device described in Patent Document 3, in order to stably form a droplet, the surface of the developing roller is provided with irregularities, and a developer droplet is formed by pushing a liquid developer into the concave portion. . However, when developing droplets are formed in this way, the droplet diameter of the developing droplets formed and the spacing between the developing droplets are determined by the shape of the unevenness. Therefore, the surface of the developing roller needs to be unevenly formed with high density at equal intervals. However, since it is difficult to form unevenness on the surface of the developing roller at equal intervals and high density, it is difficult to obtain a high-density and high-definition image as a result.

  Furthermore, the developing device described in Patent Document 1 has a problem that a developing droplet cannot be obtained because a developing droplet is split at the time of flight or scattered at the time of landing on an image carrier. This problem will be described in more detail with reference to FIG. 9 and FIG.

  In the developing device described in Patent Document 3, it is considered that the development droplet breaks up because the flying speed of the development droplet is too high. Therefore, the applicant of the present application obtained a predicted value of the flying speed of the developing droplet immediately before landing on the image carrier by simulation 1 below. FIG. 9 is a diagram illustrating a simulation model. 9A is a diagram for explaining the simulation model, FIG. 9B is a diagram for explaining the primary mirror image charge, and FIG. 9C is a diagram explaining the secondary mirror image charge. It is a figure for doing.

<Simulation 1>
(Conditions for simulation 1)
A conductive belt provided with a photosensitive layer B having a dielectric constant of 3 and a thickness of 20 μm on a conductive substrate A, and a conductive layer provided at a position 200 μm vertically below the photosensitive layer B of the photosensitive belt. Consider an image forming apparatus provided with a developing roller C having The photosensitive belt is charged to −600 V and then exposed to form a predetermined electrostatic latent image D. A voltage is applied between the developing roller C and the photosensitive belt, and a uniform flying electric field E _f is generated between the developing roller C and the surface perpendicular to the developing roller C and between the developing roller and the photosensitive belt. To do.

(Simulation model)
Consider a two-dimensional model in which the photosensitive belt and the developing roller C are parallel plates as shown in FIG. The x direction is a direction parallel to the surface of the developing roller C, and the y direction is a direction perpendicular to the surface from the surface of the developing roller C to the surface of the photosensitive belt. The position of the surface of the developing roller C is the origin in the y direction.

One developing droplet F (diameter R = 8 [μm], charge amount Q = −5.36 × 10 ⁻¹⁵ [C], density ρ = 1.0 [g / cm ³ ] carried on the developing roller C , Mass m = 2.68 × 10 ⁻¹⁰ [g] is considered to fly toward the electrostatic latent image, where the developing droplet F is treated as a rigid sphere. In the case of negative reversal development in which a negative charge is present in the unexposed portion of the photosensitive layer B and no charge is present in the electrostatic latent image D, in order to simplify the calculation in the simulation, a state in which there is negative charge in the exposed area, by replacing the condition that there is a positive charge P ₁ to the electrostatic latent image D, and the reversal development equivalent to the state of negative charge. here, the electrostatic latent image D The width L is 5.0 mm, the relative permittivity ε _S = 3.0 of the photosensitive member, the film thickness is 20 μm, and the charging potential is −600 V. The linear density of the load _{P 1,} and -8.0 × ¹⁰ -4 C / m.

(Calculation of force applied to developing droplets)
The Coulomb force applied to the developing droplet F by the flying electric field E _f is a Coulomb force | Q · E _f | in the y direction. In addition to this, there is a Coulomb force applied to the developing droplet F. The first Coulomb force is a Coulomb force between the developing droplet F and a positive charge induced on the surface of the substrate A and the developing roller C by the developing droplet F. Since direct calculation of the positive charge induced on each surface requires complicated calculation, an approximation of the Coulomb force between the induced positive charge and the developing droplet F is used by using a mirror image method instead of direct calculation. Find the value. According to the mirror image method, as shown in FIG. 9B, it can be assumed that a positive mirror image charge Q ′ ₁ exists at a position symmetrical to the developing droplet F with the surface of the developing roller C as the center. Further, it can be assumed that the positive mirror image charge Q ″ ₁ exists at a position symmetrical to the developing droplet F with the surface of the substrate A as the center. The mirror image charges Q ′ ₁ and Q ″ ₁ are charges having the same absolute value as the negative charge Q of the developing droplet F.

Further, according to the mirror image method, negative charges are induced on the surface of the substrate A and the surface of the developing roller C by the primary mirror image charges Q ′ ₁ and Q ″ ₁ . Accordingly, as shown in FIG. 9 (c), around the developing roller C surface, 'to ₁ and symmetrical position, a negative mirror image charge Q is a secondary mirror image charge' primary mirror image charges Q _'2 is It can be assumed that it exists. Further, it can be assumed that a negative mirror image charge Q ″ ₂ that is a secondary mirror image charge exists at a position symmetrical to the primary mirror image charge Q ′ ₁ with the surface of the substrate A as a center. The secondary mirror image charges Q ′ ₂ and Q ″ ₂ are also charges having an absolute value equal to the negative charge Q of the developing droplet F.

Thus, the approximate value of the Coulomb force between the true positive charge induced on the surface of the substrate A and the surface of the developing roller C and the developing droplet F is obtained by sequentially obtaining the mirror image charge which is a virtual charge. Can be requested. In simulation 1, an approximate value F ₁ of the Coulomb force in the y direction between the positive charge induced on the surface of the substrate A and the surface of the developing roller C and the developing droplet F in consideration of the mirror image charge up to the 10th order. (Y) was calculated. F ₁ (Y) is a force depending on the y coordinate Y of the developing droplet F. When 0 [μm] ≦ Y << 100 [μm], F (Y) <0, that is, the developing droplet F is attracted to the surface of the developing roller C. When 100 [μm] << Y ≦ 200 [μm], F (Y)> 0, that is, the developing droplet F is attracted to the surface of the photosensitive layer B.

The second Coulomb force applied to the developing droplet F is a Coulomb force F ₂ (Y) in the y direction generated between the positive charge P ₁ of the electrostatic latent image D and the developing droplet F. F ₂ (Y) is a force depending on the y coordinate Y of the developing droplet F. F ₂ (Y) is always positive. That is, the developer drops F by the positive charge P ₁ of the electrostatic latent image D, is always attracted to the photosensitive layer B surface. F ₂ (Y) increases as Y increases.

Coulomb force third according to the developing droplet F a developing solution and droplet F, by the positive charge P ₁ of the electrostatic latent image D between the negative charge induced in the base material A surface and the developing roller C surface , Y direction Coulomb force F ₃ (Y). Similarly to F ₁ (Y), F ₃ (Y) is calculated as an approximate value by using the mirror image method and taking into consideration the mirror image charges up to the 10th order. F ₃ (Y) is a force depending on the y coordinate Y of the developing droplet F.

From the flying electric field E _f and the three Coulomb forces described above, the electric field E (Y) in the y direction applied to the developing droplet F is E (Y) = E _f + (F ₁ (Y) + F ₂ (Y) + F ₃ (Y)) / | Q |, and the total of the Coulomb forces in the y direction applied to the developing droplet F is Q · E (Y). Although flying in the horizontal direction is not a problem, when the developing droplet F is caused to fly in the vertical direction, the downward gravity y · g acting on the developing droplet F acts as a deceleration force (gravity acceleration). g = 9.8 [m / s ² ]). Accordingly, the sum of the forces applied to the developing droplet F is Q · E (Y) −m · g. Here, the flying electric field E _f is set so that the developing droplet F can fly and the flying velocity V _f of the developing droplet F is as small as possible. That is, the flying electric field E _f is such that the sum Q · E (Y) −m · g of the force applied to the developing droplet F in the vicinity of the developing roller C is close to 0 and is in a direction away from the developing roller C. Set to Further, when the surface of the developing roller C is not sufficiently water-repellent and an intermolecular force acts between the surface and the developing droplet F and the intermolecular force cannot be ignored, the same as gravity. Considering the intermolecular force.

(simulation result)
FIG. 10 is a diagram illustrating a result of the simulation 1. FIG. 10A shows E (Y), E _f , and E _Q (Y) = (F ₁ (Y) + F ₂ (Y) + F ₃ (Y)) / | Q | The relationship with the y coordinate Y is shown. Graph _{G 1} represents an electric field E (Y), the graph _{G 2} is shown an electric field _{E f,} the graph _{G 3} are showing the electric field _E Q (Y). The vertical axis represents the magnitude [V / m] of the electric field with the direction from the developing roller C toward the photosensitive belt being positive, and the horizontal axis represents the y coordinate Y [μm] of the developing droplet F.

Since the electric field E _Q (Y) is positive in the vicinity of the surface of the developing roller C, the developing droplet F having the negative charge Q cannot fly from the surface of the developing roller C unless the flying electric field E _f is formed. . In order to cause the developing droplet F to fly, in the simulation 1, a flying electric field E _f = 1.5 × 10 ⁶ [V / m] is formed. Thus, as the graph shows _{G 1, E (Y) =} - a ^{2.0 × 10 5 [V / m} ]. Accordingly, the total Coulomb force applied to the developing droplet F becomes | Q · E (Y) | = 1.08 × 10 ⁻⁹ [N] in the direction away from the developing roller C, and the developing droplet F is moved vertically. It will be the flying power when flying. On the other hand, the gravity applied to the developing droplet F when the developing droplet F flies in the vertical direction is m · g = 2.63 × 10 ⁻¹² [N] in the direction toward the developing roller C. Therefore, the developing droplet F can fly in the vertical direction.

FIG. 10B shows the relationship between the flying speed V _f of the developing droplet F, the y coordinate Y, the y coordinate Y, and the time t from the start of flying. In FIG. 10B, the left vertical axis represents the flight speed V _f [m / s], the right vertical axis represents the time t [sec], and the horizontal axis represents the y coordinate Y [μm] of the developing droplet F. Represents. Graph G ₄ are a graph showing the relationship between the flight speed V _f and time t, the graph G ₅ is a graph showing the relationship between the y-coordinate Y and time t. Graphs G ₄ and G ₅ solve the equation of motion m · dV _f / dt = −Q · E (Y) −m · g for the developing droplet F using the electric field E (Y) shown in the graph G _1. Can be obtained. As the graph _{G 4,} the developer drops F, in the landing just prior to the photosensitive layer B, the flying speed _{V f} satisfies has a 4.3 m / s.

In the simulation 1, the flying speed _Vf is calculated on the assumption that the developing droplet F is a rigid sphere. Actually, however, the developing droplet F is not a rigid body but a droplet having a predetermined surface energy. Therefore, when the surface energy Us = τ × π × R ² of the developing droplet F is obtained with the surface tension τ = 55 [dyn / cm], it becomes Us = 1.11 × 10 ⁻¹¹ J. On the other hand, the kinetic energy Uv of the developing droplet F is Uv = 1/2 × ρ × π / 6 × R ³ × V _f ² = 2.48 × 10 ⁻¹² J.

Thus, when the kinetic energy Uv of the developing droplet F approaches the surface energy Us, it is considered that the developing droplet F that is not a rigid body is split during the flight. When the developing droplets F are split, the landing positions of the developing droplets F on the photosensitive belt are shifted due to the splitting, or the image is soiled by the satellite droplets generated along with the splitting. Further, depending on variations in the mass and charge of the developing droplet F, it is considered that the flying speed _Vf is further increased and that the kinetic energy Uv exceeds the surface energy Us. For example, the kinetic energy Uv when the flying speed V _f is 10.0 m / s is Uv = 1.34 × 10 ⁻¹¹ J, and the surface energy Us = 1.11 × 10 ⁻¹¹ is larger than J. . In such a case, it is considered that the developing droplet F is finely divided and scattered in a wide range. As described above, the developing device described in Patent Document 3 forms a high-definition image because the developing droplet flying speed _Vf is too high, and the developing droplet F is split and scattered when landing. I can't.

Further, from the result of the simulation 1, a significant increase in the flying speed V _f is formed by the electric field E _Q (Y), in particular, the charges induced on the surface of the substrate A and the surface of the developing roller C by the developing droplet F. It can be seen that this is due to the electric field, F ₁ (Y) / | Q |.

As described above, the electric field F ₁ (Y) / | Q | is an electric field that draws the developing droplet F toward the developing roller C in the vicinity of the developing roller C, and the developing droplet F is exposed to the photosensitive layer in the vicinity of the photosensitive layer B. The electric field attracts the B side. From such a characteristic of the electric field F ₁ (Y) / | Q |, as shown in FIG. 10A, the electric field E _Q (Y) becomes a positive value in the vicinity of the developing roller C, and from the developing roller C As the distance increases, the absolute value becomes a large negative value.

Therefore, in order to fly a developer drops F a as possible small flying speed V _f, to adjust the flying electric field E _f, developing roller according to the developer drops F near C forces sum Q · E (Y) Even when −m · g is adjusted to be close to 0 and away from the developing roller C, as the developing droplet F leaves the developing roller C, the force applied to the developing droplet F is It will be a great force away from C. As a result, the developing droplet F is greatly accelerated toward the photosensitive layer B, and as a result, splitting or the like occurs.

The breakage of the developing droplet F is actually observed by strobe observation. The kinetic energy Uv and the surface energy Us are calculated by performing strobe observation on the flying developing droplet F and measuring the shape and flying speed _Vf of the developing droplet F. Measured mass of the developer drops F from the shape is calculated, the kinetic energy Uv is calculated from the said mass and the flying speed V _f. Further, the surface area of the developer droplet F is calculated from the measured shape, and the surface energy Us is calculated from the surface area and the surface tension τ of the liquid developer obtained in advance by a surface tension meter.

  The present invention has been made in order to solve the above-described problem, and is a liquid that prevents the development droplets from flying apart by suppressing a significant increase in the flying speed of the development droplets, and preventing the development droplets from being scattered during landing. An object is to provide a flying developing device and an image forming apparatus.

The present invention comprises a developer tank for storing a liquid developer containing a colorant;
A developing roller that forms charged developer droplets from the developer and conveys the developer droplets while carrying the developer droplets;
A flying electric field generating means for generating a flying electric field, which is an electric field for flying and supplying the developer droplets from the developing roller to an image carrier on which an electrostatic latent image is formed,
The developing roller has a developing roller charge suppressing unit that suppresses the development droplet carried on the surface of the developing roller from inducing charge in the developing roller.

Further, in the present invention, the developing roller has a conductive developing roller base material, and a developing roller surface layer made of a dielectric provided on the surface of the developing roller base material,
The developing roller charge suppressing means is the developing roller surface layer.

  Further, the invention is characterized in that the surface of the developing roller has liquid repellency with respect to the developer.

The present invention also provides a developer tank for storing a liquid developer containing a colorant;
A supply roller that forms charged developer droplets from the developer and conveys the developer droplets while supporting the developer droplets;
A developing roller for transporting the developer droplets supplied from the supply roller while carrying;
Intermediate flying electric field generating means for generating an intermediate flying electric field, which is an electric field for flying and supplying the developer droplets from the supply roller to the developing roller;
A flying electric field generating means for generating a flying electric field, which is an electric field for flying and supplying the developer droplets from the developing roller to an image carrier on which an electrostatic latent image is formed,
The supply roller is a liquid flying developing device characterized by having supply roller charge suppressing means for suppressing development droplets carried on the surface of the supply roller from inducing charge in the supply roller.

In the present invention, the supply roller has a conductive supply roller base material, and a supply roller surface layer made of a dielectric material provided on the surface of the supply roller base material,
The supply roller charge suppression means is the supply roller surface layer.

  Further, the invention is characterized in that the surface of the supply roller has liquid repellency with respect to the developer.

  In the invention, it is preferable that the developing roller has a developing roller charge suppressing unit that suppresses the development droplet carried on the surface of the developing roller from inducing charge in the developing roller.

In the present invention, when the peripheral speed of the supply roller is S1 [m / s] and the peripheral speed of the developing roller is S2 [m / s], the supply roller and A first circumferential speed ratio control means for controlling the developing roller is provided.
| S1 / S2 |> 1 (1)

In the present invention, the surface energy of the developing droplet is Us [J], the mass of the developing droplet is M [kg], and the maximum flying speed of the developing droplet is V _max [m / s]. In some cases, a flying electric field control means for controlling the flying electric field so as to satisfy the following formula (2) is provided.
Us> (1/2) MV _max ² (2)

The present invention also provides an image carrier having a photosensitive layer,
An image forming apparatus comprising a first-stage liquid flying developing device.

The present invention also provides an image carrier having a conductive base material having conductivity and a photosensitive layer,
A liquid flying developing device that is supplied from the liquid developer containing the colorant and that is supplied to the image carrier by flying charged developer droplets;
The image carrier is an image forming apparatus having an intermediate layer that suppresses the development droplets flying to the surface of the photosensitive layer from inducing charges on the conductive substrate.

  The image forming apparatus according to the present invention is characterized in that the intermediate layer is a dielectric provided between the photosensitive layer and the conductive substrate.

  In addition, an image forming apparatus according to the present invention includes the above-described liquid flying developing device as the liquid flying developing device.

Further, the image forming apparatus according to the present invention satisfies the following expression (3) when the peripheral speed of the developing roller is S2 [m / s] and the peripheral speed of the image carrier is S3 [m / s]. As described above, the image forming apparatus includes a second peripheral speed ratio control unit that controls the developing roller and the image carrier.
| S2 / S3 |> 1 (3)

  According to the present invention, the developing roller has the developing roller charge suppressing means. As a result, the developing roller can suppress the induction of charge on the developing roller due to charged developing droplets on the surface of the developing roller. That is, the developing roller can reduce the so-called mirror image charge with respect to the charge of the developing droplet. Therefore, the developing roller can reduce the electric field formed by the mirror image charge (developing roller mirror image electric field), so that the minimum electric field required for the developer droplets to separate from the surface of the developing roller can be reduced. it can.

  Therefore, the liquid flying development apparatus according to the present invention can reduce the magnitude of the flying electric field, and thus can prevent a significant increase in the flying speed (development flying speed) of the developing droplets during development. . Therefore, the liquid flying developing device according to the present invention can prevent the development droplets from being split when flying from the developing roller (developing flying) and the developing droplets from being scattered when landing on the image carrier. As a result, an image forming apparatus capable of obtaining an image with good image quality can be realized.

  According to the invention, the surface layer of the developing roller made of a dielectric functions as a developing roller charge suppressing unit. Therefore, the developing roller surface layer can reduce the developing roller mirror image field. Therefore, it is possible to provide a liquid flying developing device that can relieve the developing roller mirror image field stably and at low cost.

  According to the invention, the developing roller surface has liquid repellency with respect to the developer. As a result, the surface of the developing roller can reduce the electric field required for the developer droplets to separate from the surface of the developing roller. Therefore, the liquid flying developing device according to the present invention can further reduce the magnitude of the flying electric field. As a result, the liquid flying developing device according to the present invention can further prevent a significant increase in the developing flying speed of the developing droplet.

  According to the invention, the supply roller has supply roller charge suppression means. Thereby, the supply roller can suppress the induction of the electric charge to the supply roller by the charged developing droplet on the surface of the supply roller. That is, the supply roller can reduce the mirror image charge with respect to the charge of the developing droplet. Therefore, the supply roller can reduce the electric field (supply roller mirror image electric field) formed by the mirror image charge, so that the minimum electric field required for the developer droplets to fly from the surface of the supply roller can be reduced. it can.

  Therefore, the liquid flying developing device according to the present invention can reduce the magnitude of the intermediate flying electric field, so that the developing droplet flying speed (intermediate flying speed) at the time of flying from the supply roller (intermediate flying) can be reduced. A significant increase can be prevented. Therefore, the liquid flight developing device according to the present invention can prevent the development droplets from being split during intermediate flight and the development droplets from being scattered when landing on the development roller. As a result, an image forming apparatus capable of obtaining an image with good image quality can be realized.

  According to the invention, the supply roller surface layer made of a dielectric functions as supply roller charge suppression means. Therefore, the supply roller surface layer can reduce the supply roller mirror image field. Therefore, it is possible to provide a liquid flying developing device that can relieve the supply roller mirror image field stably and at low cost.

  According to the invention, the surface of the supply roller has liquid repellency with respect to the developer. As a result, the surface of the supply roller can reduce the electric field required for the developer droplets to separate from the surface of the supply roller. Therefore, the liquid flying developing apparatus according to the present invention can further reduce the magnitude of the intermediate flying electric field. As a result, the liquid flight developing apparatus according to the present invention can further prevent a significant increase in the intermediate flight speed of the developer droplets.

  According to the invention, the developing roller has the developing roller charge suppressing means. As a result, the developing roller can reduce the developing roller mirror image field, so that the minimum electric field required for the developer droplets to separate from the surface of the developing roller can be reduced. Therefore, the liquid flying development apparatus according to the present invention can reduce the magnitude of the flying electric field, and thus can prevent a significant increase in the developing flying speed of the developing droplet. Therefore, the liquid flight developing device according to the present invention can prevent the development droplets from being split during the development flight and the development droplets from being scattered when landing on the image carrier.

  In addition, since the developing roller can reduce the developing roller mirror electric field generated when the developing droplet approaches the developing roller, the intermediate flying speed is greatly increased when the developing droplet reaches the developing roller. It is possible to prevent the increase. Therefore, the liquid flying developing device according to the present invention can prevent the development droplets from being split just before landing on the developing roller and the developing droplets from being scattered when landing on the developing roller.

  According to the invention, the first peripheral speed ratio control means controls the absolute value of the peripheral speed S1 of the supply roller to exceed the absolute value of the peripheral speed S2 of the developing roller. As a result, the liquid flying developing apparatus according to the present invention can closely adhere the developing droplets onto the surface of the developing roller. Therefore, the liquid flying developing device according to the present invention can increase the image density of the image formed on the developing roller.

According to the present invention, the flying electric field control means controls so that the maximum value (1/2) MV _max ² of the developing droplet kinetic energy at the time of developing flying is less than the surface energy Us of the developing droplet. To do. As a result, the liquid flying development apparatus according to the present invention can prevent the development droplets from being split during the development flight and the development droplets from being scattered when landing on the image carrier.

  Further, according to the present invention, the liquid flight developing device can prevent the development droplets from being split during the development flight or the intermediate flight, and the development droplets from being scattered when landing on the image carrier or the development roller. Therefore, it is possible to provide an image forming apparatus that can obtain an image with good image quality.

  According to the invention, the image carrier has an intermediate layer. As a result, the image carrier can suppress the induction of electric charges on the conductive substrate due to the developing droplet approaching the surface of the photosensitive layer. That is, the image carrier can reduce the mirror image charge with respect to the charge of the developing droplet. Therefore, the image carrier can reduce the mirror image electric field (image carrier mirror image electric field) formed by the mirror image charge.

  As a result, the image carrier can prevent the development flying speed from significantly increasing when the developer droplet reaches the image carrier, so that the developer droplet immediately before landing on the image carrier can be prevented. It is possible to prevent splitting and scattering of developer droplets upon landing on the image carrier. Therefore, it is possible to realize an image forming apparatus that can obtain an image with good image quality.

  According to the invention, the intermediate layer is made of a dielectric. Therefore, the image carrier can reduce the mirror image electric field of the image carrier while ensuring the charging characteristics and exposure characteristics of the image carrier.

  Further, according to the present invention, the liquid flight developing device can prevent the development droplets from being split during the development flight or the intermediate flight, and the development droplets from being scattered when landing on the image carrier or the development roller. Therefore, the image forming apparatus according to the present invention can obtain an image with good image quality.

  According to the invention, the second peripheral speed ratio control means controls the absolute value of the peripheral speed S2 of the developing roller to exceed the absolute value of the peripheral speed S3 of the image carrier. As a result, the image forming apparatus according to the present invention can closely adhere the developing droplets onto the surface of the developing roller. Therefore, the image forming apparatus according to the present invention can increase the image density of the image formed on the developing roller.

1 is a schematic diagram schematically showing a cross section of an image forming apparatus 100. FIG. 2 is a schematic diagram schematically showing a cross section of a photoreceptor belt 1 and an image forming unit 3. FIG. FIG. 6 is a plan view and a cross-sectional view of the uppermost portion in the vertical direction of the supply roller 64. It is a figure which shows the result of the simulation 2. FIG. It is a schematic diagram which shows roughly the cross section of the developing device 6a. 2 is a schematic diagram schematically showing a cross section of the image forming apparatus 200. FIG. 2 is a cross-sectional view showing a part of the cross section of the photoreceptor belt 1. FIG. It is a figure which shows the result of the simulation. It is a figure which shows a simulation model. It is a figure which shows the result of the simulation.

  An image forming apparatus according to the present invention includes the liquid flying development apparatus according to the present invention. In the following, with reference to FIG. 1, FIG. 2, and FIG. 3, the image forming apparatus 100 as the first embodiment of the image forming apparatus according to the present invention and the first embodiment of the liquid flight developing apparatus according to the present invention will be described. A certain developing device 6 will be described. FIG. 1 is a schematic diagram schematically showing a cross section of the image forming apparatus 100. FIG. 2 is a schematic diagram schematically showing cross sections of the photosensitive belt 1 and the image forming unit 3. FIG. 3 is a plan view and a cross-sectional view of the uppermost portion in the vertical direction of the supply roller 64.

  The image forming apparatus 100 includes a photosensitive belt 1, support rollers 2a and 2b, image forming units 3y, 3m, 3c, and 3k, a photosensitive member cleaning unit 7, a pickup roller 8, transport rollers 9a and 9b, A transfer roller 10 and a control unit (not shown) are provided. The image forming apparatus 100 forms an image on the recording paper P based on the image information stored by the control unit.

The photoreceptor belt 1 is an endless belt-shaped image carrier having a photosensitive layer 1c and a conductive substrate. The photosensitive belt 1 is stretched around the support rollers 2 a and 2 b so that the photosensitive layer 1 c is on the outer peripheral side of the photosensitive belt 1 and the conductive substrate is on the inner peripheral side of the photosensitive belt 1. The photosensitive layer 1c is made of transparent OPC (Organic PhotoConductor, organic photoconductor) having a relative dielectric constant ε _s 3.0 and a thickness of 20 μm. Here, the term “transparent” means that light emitted from the exposure unit 5 described later can be transmitted. The transparent OPC may be either a laminated type photoreceptor in which a charge transport layer and a charge generation layer are laminated, or a single layer type photoreceptor in which a charge generation layer is dispersed in a binder.

  The conductive substrate includes a conductive layer 1b having conductivity and a dielectric layer 1a provided on the inner peripheral side of the conductive layer 1b. The conductive layer 1b is a transparent electrode made of ITO (Indium Tin Oxide). In the present embodiment, the conductive layer 1b is grounded. The conductive layer 1b may be set to a predetermined potential instead of being grounded. The dielectric layer 1a is made of a transparent polyester film. The meaning of transparency is as described above.

  The support rollers 2a and 2b are roller-like members that stretch the photosensitive belt 1 in the horizontal direction. The support rollers 2a and 2b are provided so as to rotate clockwise by driving means (not shown). As the support rollers 2a and 2b rotate clockwise, the lower portion of the photosensitive belt 1 in the vertical direction moves in the image conveying direction indicated by an arrow b.

  The image forming units 3y, 3m, 3c, and 3k are provided in a line in this order from the upstream in the image transport direction b. The image forming units 3y, 3m, 3c, and 3k have the same configuration except that the liquid developer used for forming the developer image is different. The image forming unit 3y forms a yellow (y) developer image from the yellow liquid developer, the image forming unit 3m forms a magenta (m) developer image from the magenta liquid developer, and the image forming unit 3c is cyan. A cyan (c) developer image is formed from the liquid developer, and the image forming unit 3k forms a black (k) developer image from the black liquid developer. Any one of y, m, c, k representing each color only when the members constituting the image forming units 3y, 3m, 3c, 3k and the image forming units 3y, 3m, 3c, 3k are distinguished for each color. The alphabet is appended to the end of the reference sign.

  The image forming unit 3 includes a charging unit 4, an exposure unit 5, a developing device 6, a coating roller power source 11, a supply roller power source 12, a neutralizing roller power source 13, a developing roller power source 14, and a cleaning blade power source 15. And a concentration detector 16.

  The charging unit 4 is a scorotron charger for uniformly charging the surface of the photosensitive layer 1c to a predetermined potential. The charging unit 4 is provided on the outer peripheral side of the photosensitive belt 1 and is separated from the photosensitive belt 1. In the present embodiment, the photosensitive layer 1 c is charged to −500 V to −600 V by the charging unit 4.

  The exposure unit 5 is a member that is provided on the inner peripheral side of the photosensitive belt 1 and spaced from the photosensitive belt 1 and that irradiates the photosensitive layer 1 c with predetermined light from the inner peripheral side of the photosensitive belt 1. The exposure unit 5 exposes the charged photosensitive layer 1c based on the image information input from the control unit, thereby releasing the charged state only in the exposed portion. As a result, an electrostatic latent image D corresponding to the image information is formed on the surface of the photosensitive layer 1c. The exposure unit 5y forms an electrostatic latent image D corresponding to yellow, the exposure unit 5m forms an electrostatic latent image D corresponding to magenta, and the exposure unit 5c performs an electrostatic latent image D corresponding to cyan. The exposure unit 5k forms an electrostatic latent image D corresponding to black.

  The potential of the electrostatic latent image D is preferably −100V or higher. In the present embodiment, the potential of the electrostatic latent image D is about −50V. As the exposure unit 5, a writing device (for example, writing) in which light emitting elements such as a laser scanning unit (LSU), an EL (Electro Luminescence), or an LED (Light Emitting Diode) are arranged in an array. Head) or the like.

  The developing device 6 is a liquid flying developing device that is provided so as to be separated from the lower portion of the photosensitive belt 1 in the vertical direction and downward in the vertical direction. The developing device 6 includes a coating roller 61, a regulating member 62, a developing tank 63, a supply roller 64, a charge removing roller 65, a developing roller 66, a cleaning blade 67, a collection container 68, and a flying electric field control (not shown). Means, an intermediate flying electric field control means (not shown), a first peripheral speed ratio control means (not shown), and a second peripheral speed ratio control means (not shown).

  The developing device 6 forms charged developer droplets F from a liquid developer containing a colorant (liquid developer dv) and causes the developer droplets F to fly, thereby electrostatically charging the surface of the photosensitive layer 1c. The latent image D is supplied. As a charging method of the developing droplet F, a spontaneous charging method in which a charge appears in the developing droplet F based on the zeta potential by forming the droplet from the liquid developer dv, a discharging method in which the droplet is corona charged, The charge injection method may induce a charge on the droplet surface by applying a voltage to the conductive droplet.

  In the present embodiment, the developing device 6 employs a spontaneous charging method. Therefore, when the developing droplet F is formed on the supply roller 64, the developing droplet F is charged. In the case where the developing device 6 adopts the discharge method, colorant deposition and electrodeposition of the deposited colorant to the supply roller 64 are likely to occur with corona discharge. The roller 64 may be cleaned.

  The developing tank 63 is a container-like member that stores the liquid developer dv. The liquid developer dv stored in the developing tank 63 is adjusted so as to be maintained at a predetermined liquid level. As the liquid developer dv, a liquid in which a pigment negatively charged by a pigment dispersant is dispersed in an insulating solvent can be used. For example, a solvent (a mixture of 60 parts by weight of palm palm fatty acid ester and 25 parts by weight of a naphthenic solvent), a pigment (carbon black or 5 parts by weight of titanium black), and a pigment dispersant (AgriSperse DFA (Kaneda Corporation) 10 weights) Can be used as a black liquid developer. The black liquid developer has a viscosity of about 300 cp at 20 ° C.

  The application roller 61 is a roller-like member that carries the liquid developer dv and applies the liquid developer dv to a supply roller 64 described later. The application roller 61 is formed by coating a stainless steel rotating shaft 61b with an elastic layer 61a made of a rubber member such as EPDM (ethylene / propylene / diene rubber), silicon rubber, or fluorine resin. The elastic layer 61a may be a metal or the like. The rotating shaft 61b is connected to the application roller power supply 11 and is adjusted to a predetermined potential. The potential of the rotating shaft 61b may be the same as that of the supply roller 64, may have a potential difference with the supply roller 64 in order to control the charge amount of the developing droplet F, or may be floating.

  The application roller 61 is provided in pressure contact with the supply roller 64 with a predetermined linear pressure. The application roller 61 is rotated clockwise by a driving unit (not shown) so that the surface of the application roller 61 and the surface of the supply roller 64 move in opposite directions in the proximity region between the application roller 61 and the supply roller 64. Is provided. As a result, a developing droplet F having a predetermined droplet diameter and droplet density is formed on the surface of the supply roller 64.

  If the surface of the application roller 61 has liquid repellency, which will be described later, and it is difficult to form the developing droplet F when the application roller 61 rotates so that each surface moves in the opposite direction, each surface is the same. The developing droplet F may be formed by rotating the application roller 61 at a predetermined peripheral speed so as to move in the direction.

  A regulating member 62 is provided in pressure contact with the surface of the application roller 61. The regulating member 62 is a blade-like member that regulates the liquid developer dv carried on the application roller 61 so as to be a predetermined amount or less.

  The supply roller 64 is a member that forms development droplets F charged from the liquid developer dv and conveys the development droplets F while being carried. The supply roller 64 includes a supply roller base material having a rotating shaft 64c and a metal roller 64b, and a supply roller surface layer 64a. The supply roller 64 is provided such that a lower portion in the vertical direction is immersed in the liquid developer dv.

  The rotating shaft 64c is a metal rod-like member that rotates clockwise by a supply roller driving unit (not shown). The rotating shaft 64c is an intermediate flying electric field generating means. The rotating shaft 64c, which is an intermediate flying electric field generating means, is connected to the supply roller power supply 12 so as to cause the developing droplet F to fly (intermediate flying) to be supplied from the supply roller 64 to the developing roller 66 described later. An intermediate flying electric field, which is an electric field, is generated. By applying a supply bias voltage to the rotating shaft 64c, an intermediate flying electric field is stably formed. The supply bias voltage applied to the rotating shaft 64c is −850V to −900V when a margin of 50 to 100V is provided, for example, when the intermediate flight start voltage is −800V.

  The metal roller 64b is a metal roller-like member that is fixed to the rotary shaft 64c via a metal bearing (not shown). Therefore, the metal roller 64b rotates clockwise as the rotation shaft 64c rotates. Further, the metal roller 64b and the rotating shaft 64c are electrically connected via a metal bearing. Stainless steel can be used for the metal roller 64b, the rotation shaft 64c, and the metal bearing.

  The supply roller surface layer 64a is a dielectric that covers the surface of the metal roller 64b. The supply roller surface layer 64a is supply roller charge suppression means. The supply roller surface layer 64a serving as supply roller charge suppression means suppresses the induction of charge on the surface of the metal roller 64b by the developing droplets F carried on the surface of the supply roller 64. For the supply roller surface layer 64a, fluororesin, for example, PETFE (tetrafluoroethylene-ethylene copolymer), PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer), PFE (tetrafluoroethylene-perfluoro). Alkoxyethylene copolymer), PTFE (polytetrafluoroethylene), and the like can be used. Moreover, you may use in the state in which either of these was piled up.

  The thickness of the supply roller surface layer 64a is preferably 50 μm to 500 μm. When the thickness is less than 50 μm, the function as the supply roller charge suppressing means is lowered, and it is difficult to suppress the induction of charge on the surface of the metal roller 64b. If the thickness exceeds 500 μm, the proximity region (intermediate flying region) between the supply roller 64 and the developing roller 66 becomes too wide, and it becomes difficult to cause the developing droplet F to fly to the developing roller 66 with high positional accuracy. In this embodiment, PTFE having a dielectric constant of 2.1 and a thickness of 210 μm is used as the supply roller surface layer 64a.

  The supply roller surface layer 64a is surface-treated so as to have liquid repellency with respect to the liquid developer dv. Here, having liquid repellency means that the contact angle between the surface of the member carrying the developing droplet F (here, the surface of the supply roller surface layer 64a) and the developing droplet F is 90 degrees or more. Means. The contact angle is an angle between the bottom surface and the side surface of the developing droplet F. If the volume of the developing droplet F is the same, the bottom area of the developing droplet F decreases as the contact angle increases. Such surface treatment can be performed using, for example, a photosensitive coating / fluorine resin “AL-Polymer” manufactured by Asahi Glass Co., Ltd.

The supply roller surface layer 64a is provided with droplet formation holes H. In the present embodiment, the droplet forming hole H has a regular quadrangular pyramid shape with a side l ₁ of 2.83 μm and a height l ₂ of 2 μm. As shown in FIG. 3, the droplet formation holes H are provided in a staggered arrangement, and the pitch p in the image transport direction b is 35 μm. The size and pitch of the droplet formation holes are not limited to this, and the depth l ₂ can be selected from the range of ₂ μm to ₂₀ μm, and the pitch p can be selected from the range of 35 μm to 340 μm (about 725 DPI to 75 DPI). Further, the droplet formation holes H may be provided not in a staggered arrangement but in a close-packed arrangement. In the close-packed arrangement, the center of each droplet forming hole H is arranged on the vertex of an equilateral triangle. In this case, the distance between the centers of the closest droplet formation holes H is defined as the pitch.

  Further, the droplet forming hole H may be provided in the application roller 61 instead of the supply roller 64. The droplet formation hole H does not have to be a regular quadrangular pyramid shape, and may be a valley shape having a curved surface or a cylindrical shape having a side surface roughened to several μm.

  The developing roller 66 is a member that conveys the developing droplet F developed from the supply roller 64 while carrying it. The developing roller 66 includes a developing roller base material having a rotating shaft 66c and a metal roller 66b, and a developing roller surface layer 66a. The developing roller 66 is provided such that the lowest vertical portion of the developing roller 66 is located 200 μm above the vertical uppermost portion of the supply roller 64 in the vertical direction. Further, the developing roller 66 is provided such that the uppermost portion in the vertical direction of the developing roller 66 is located at a position 200 μm vertically below the lowermost portion in the vertical direction of the photosensitive belt 1. Although the supply roller 64 and the developing roller 66 may be provided so as to be aligned in the horizontal direction, the electrostatic latent image D of the photosensitive belt 1 is provided by being provided so as to be aligned in the vertical direction as in the present embodiment. It is possible to suppress the development droplet F from adhering to other portions (fogging of the development droplet F).

  The rotating shaft 66c is a metal rod-like member that is rotated counterclockwise by a developing roller driving unit (not shown). The rotating shaft 66c is a flying electric field generating means. The rotating shaft 66c, which is a flying electric field generating means, is connected to the developing roller power supply 14 to fly the developing droplet F from the developing roller 66 to the photosensitive belt 1 on which the electrostatic latent image D is formed (developing flying). ) To generate a flying electric field that is an electric field to be supplied. By applying a developing bias voltage to the rotating shaft 66c, a flying electric field is stably formed. When the development start voltage is −600 V, the development bias voltage applied to the rotating shaft 66 c is −650 V to −700 V with a margin of −50 to −100 V.

  The metal roller 66b is a metal roller-like member that is fixed to the rotary shaft 66c via a metal bearing (not shown). Therefore, the metal roller 66b rotates counterclockwise with the rotation of the rotating shaft 66c. The metal roller 66b and the rotating shaft 66c are electrically connected via a metal bearing. Stainless steel can be used for the metal roller 66b, the rotation shaft 66c, and the metal bearing.

  The developing roller surface layer 66a is a dielectric covering the surface of the metal roller 66b. The developing roller surface layer 66a is a developing roller charge suppressing unit. The developing roller surface layer 66a, which is a developing roller charge suppressing means, suppresses the induction of charges on the surface of the metal roller 66b by the developing droplets F carried on the surface of the developing roller 66. For the developing roller surface layer 66a, a fluororesin such as PETFE, PFA, PFE, or PTFE can be used. Moreover, you may use in the state in which either of these was piled up.

  The thickness of the developing roller surface layer 66a is preferably 50 μm to 500 μm. If the thickness is less than 50 μm, the function as the developing roller charge suppressing means is lowered, and it is difficult to suppress the induction of charge on the surface of the metal roller 66b. If the thickness exceeds 500 μm, the proximity area (flying area) between the developing roller 66 and the photosensitive belt 1 becomes too wide, and it becomes difficult to fly the developing droplet F to the electrostatic latent image D with high positional accuracy. . In the present embodiment, PTFE having a relative dielectric constant of 2.1 and a thickness of 210 μm is used as the developing roller surface layer 66a.

  The developing roller surface layer 66a is surface-treated so as to have liquid repellency with respect to the liquid developer dv. Such surface treatment can be performed using, for example, a photosensitive coating / fluorine resin “AL-Polymer” manufactured by Asahi Glass Co., Ltd.

  The static eliminating roller 65 is a roller-like member disposed so as to be in contact with the supply roller 64. In order to prevent the charge removing roller 65 from repeatedly accumulating charges on the supply roller 64 during the formation of the development droplet F and during the intermediate flight of the development droplet F, the surface of the supply roller 65 is prevented. 64a is subjected to AC (alternating current) charge removal. The static eliminating roller 65 is formed by coating a stainless steel rotating shaft 65b with an elastic layer 65a made of a rubber member. The rotating shaft 65b is connected to the static elimination roller power source 13 and is applied with an alternating current. The static elimination roller 65 is not limited to this, and may be a member that performs static elimination without contact, or may be a member that performs both static elimination and cleaning.

  The cleaning blade 67 is a blade-like member provided in pressure contact with the developing roller surface layer 66a. The cleaning blade 67 discharges the developing roller surface layer 66a and removes the developing droplets F remaining on the developing roller surface layer 66a after the development, thereby enabling a stable continuous operation of the developing device 6. The leaning blade 67 is made of conductive urethane rubber, and removes the developing droplet F by scraping the developing roller surface layer 66a. Below the cleaning blade 67 in the vertical direction, a collection container 68 that is a container-like member for collecting the developing droplets F removed by the cleaning blade 67 is provided. In addition, the cleaning blade 67 is connected to the cleaning blade power supply 15, and an AC current is applied from the cleaning blade power supply 15, so that the developing roller surface layer 66 a is discharged with AC.

  The density detector 16 is a member for measuring the image density of the image on the surface of the developing roller 66 and the image density of the image on the surface of the photosensitive belt 1. The concentration detection unit 16 includes a light emitting unit and a light receiving unit. The density detection unit 16 measures the image density by irradiating the developing droplet F that forms an image with the light emitting unit with light, and receiving the light reflected by the developing droplet F with the light receiving unit.

The developing operation by the developing device 6 configured as described above will be described. When a command to perform development is input from the control unit, first, the application roller 61 and the supply roller 64 start to rotate. In this embodiment, when the peripheral speed of the application roller 61 and the supply roller 64 is S1, | S1 | = 1200 mm / s (in the following, the peripheral speed is a positive value in the clockwise direction and a negative value in the counterclockwise direction) Value.) As a result, on the surface of the supply roller 64, a development droplet F having a mass m = 2.7 × 10 ⁻¹⁰ g / piece and a charge amount Q = −5.4 × 10 ⁻¹⁵ C / piece has a pitch of 35 μm. formed by p. At this time, the droplet diameter of the developing droplet F is equal to or smaller than the size of the droplet forming hole H.

The ratio of charge amount Q to mass m per developing droplet F | Q / m | varies depending on the type of liquid developer dv and the droplet diameter of developing droplet F, but is 5 μC / g to 50 μC / g. It is preferable to be within the range. In this embodiment, the ratio | Q / m | = 20 μC / g. Further, when the droplet formation holes H are provided in a close-packed arrangement, if the distance (pitch) between the centers of the droplet formation holes H is 35 μm, the mass m of each development droplet F is 2.7 × 10. ^{From -10} g, the mass of the liquid developer dv per unit area is
2.7 × 10 ⁻¹⁰ g / (35 × 10 ⁻⁴ cm × 35 × 10 ⁻⁴ cm × √3 / 2)
= 2.53 × 10 ⁻⁵ g / cm ²
= 0.0253 mg / cm ²
It becomes.

  Next, the developing roller 66 rotates so as to synchronize the arrival of the electrostatic latent image D to the flying area and the arrival of the developing droplet F to the flying area. In the present embodiment, when the peripheral speed of the developing roller 66 is S2, | S2 | = 200 mm / s. At this time, a supply bias voltage and a developing bias voltage are applied to the rotating shaft 64c and the rotating shaft 66c, respectively, and an intermediate flying electric field is generated in the intermediate flying region.

  The developing droplet F flies from the supply roller 64 to the developing roller 66 by the intermediate flying electric field. As described above, the absolute value of the peripheral speed S1 of the supply roller is 1200 mm / s, and the magnitude of the peripheral speed S2 of the developing roller 66 is 200 mm / s. Therefore, the peripheral speed ratio | S1 / S2 | = 6. That is, the peripheral speed ratio | S1 / S2 |> 1. The first peripheral speed ratio control means is a means for controlling the peripheral speed ratio | S1 / S2 |> 1 as described above. The first peripheral speed ratio control unit may be a part of the control unit of the image forming apparatus 100 or may be provided in the developing device 6.

As a result, the developing droplets F having a number density six times that of the developing droplets F on the surface of the supply roller 64 adhere to the surface of the developing roller 66. At this time, the droplet diameter of the developing droplet F on the developing roller 66 is the same as the droplet diameter of the developing droplet F on the supply roller 64. Further, the mass of the liquid developer dv per unit area on the developing roller 66 is 0.15 mg / cm ² .

At this time, the intermediate flying electric field control means uses Us [J] as the surface energy of the developing droplet F, M [kg] as the mass of the developing droplet F, and performs flying (intermediate flying) from the supply roller 64. When the maximum value of the flying speed (intermediate flying speed) of the developing droplet F is V ′ _max [m / s], the supply roller power supply 12 and the developing roller power supply 14 are controlled so as to satisfy the following formula (1). Control the intermediate flying electric field.
Us> (1/2) MV ′ _max ² (1)

  At this time, the intermediate flying electric field control means controls the intermediate flying electric field so that the sum of the forces applied to the developing droplets F on the supply roller 64 becomes a force close to 0 and away from the supply roller 64. This facilitates the intermediate flight of the developing droplet F while satisfying the above formula (1). The intermediate flying electric field control means may be part of the control unit of the image forming apparatus 100 or may be provided in the developing device 6.

  Further, the intermediate flying electric field control means controls the intermediate flying electric field so that the image density on the developing roller 66, which varies depending on environmental factors, the state of the supply roller 64, and the density of the liquid developer dv, always becomes a predetermined value. Correct. This correction is performed when the density detector 16 detects the image density of the test pattern formed on the surface of the developing roller 66 in a state where the developing operation is stopped. The detection signal from the density detector 16 is transmitted to the intermediate flying electric field control means, and the intermediate flying electric field control means determines whether or not the image density is within a predetermined range. The intermediate flying electric field control means increases the intermediate flying electric field when the image density is lower than the lower limit value. The intermediate flying electric field control means decreases the intermediate flying electric field when the image density is higher than the upper limit value.

  Finally, the electrostatic latent image D on the photosensitive belt 1 is developed by causing the development droplet F to fly from the development roller 66. In this embodiment, when the peripheral speed of the photosensitive belt 1 is S3, | S3 | = 100 mm / s. At this time, a developing bias voltage is applied to the rotating shaft 66c, and the conductive layer 1b is grounded. As a result, a flying electric field is generated in the flying region.

  The developing droplet F flies from the developing roller 66 to the photosensitive layer 1c by a flying electric field. As described above, the absolute value of the peripheral speed S2 of the developing roller is 200 mm / s, and the absolute value of the peripheral speed S3 of the photosensitive belt 1 is 100 mm / s. Therefore, the peripheral speed ratio | S2 / S3 | = 2. That is, the peripheral speed ratio | S2 / S3 |> 1. The second peripheral speed ratio control means is a means for controlling the peripheral speed ratio | S2 / S3 |> 1 as described above. The second peripheral speed ratio control unit may be a part of the control unit of the image forming apparatus 100 or may be provided in the developing device 6.

As a result, the developing droplets F having a number density twice that of the developing droplets F on the surface of the developing roller 66 adhere to the surface of the photosensitive belt 1. At this time, the droplet diameter of the developing droplet F on the photosensitive belt 1 is the same as the droplet diameter of the developing droplet F on the developing roller 66. Further, the mass of the liquid developer dv per unit area on the photosensitive belt 1 is 0.30 mg / cm ² .

Further, at this time, the flying electric field control means uses Us [J] as the surface energy of the developing droplet F, M [kg] as the mass of the developing droplet F, and develops when developing from the developing roller 66 (developing flight). When the maximum value of the flying speed of the droplet F (development flying speed) is V _max [m / s], the developing roller power source 14 is controlled to control the flying electric field so as to satisfy the following formula (2).
Us> (1/2) MV _max ² (2)

  At this time, the flying electric field control means controls the flying electric field so that the sum of the forces applied to the developing droplets F on the developing roller 66 is close to 0 and becomes a force in a direction away from the developing roller 66. This makes it easy to develop and fly the developing droplet F while satisfying the above formula (2). The flying electric field control unit may be a part of the control unit of the image forming apparatus 100 or may be provided in the developing device 6.

  Further, the flying electric field control means controls the flying electric field so that the image density on the photosensitive belt 1 that varies depending on environmental factors, the state of the developing roller 66, and the density of the liquid developer dv always becomes a predetermined value. to correct. This correction is performed by the density detector 16 detecting the image density of the test pattern formed on the surface of the photoreceptor belt 1. The detection signal from the density detector 16 is transmitted to the flying electric field control means, and the flying electric field control means determines whether or not the image density is within a predetermined range. The flying electric field control means increases the flying electric field when the image density is lower than the lower limit value. The flying electric field control means reduces the flying electric field when the image density is higher than the upper limit value.

  In general, a solid image pattern is used as the test pattern. However, since it is difficult to ensure stable fine line reproducibility with a solid image pattern, it is preferable to use a thin line or sea-island pattern instead of a solid image pattern.

  According to the developing device 6 that performs the developing operation as described above, the supply roller surface layer 64a can suppress the induction of charge on the metal roller 64b by the charged developing droplet F on the surface of the supply roller 64. . That is, the supply roller surface layer 64a can reduce the so-called mirror image charge with respect to the charge of the developing droplet F. Accordingly, the supply roller surface layer 64a can reduce the electric field formed by the mirror image charge (supply roller mirror image electric field), and therefore, the minimum electric field required for the developing droplet F to leave the surface of the supply roller 64. Can be reduced. Therefore, the developing device 6 can reduce the magnitude of the intermediate flying electric field. Thus, the developing device 6 can prevent a significant increase in the intermediate flight speed. Therefore, the developing device 6 can prevent the development droplet F from being split during the intermediate flight and the development droplet F from being scattered when landing on the development roller 66.

  In the developing device 6, the supply roller surface layer 64a made of a dielectric functions as supply roller charge suppression means. This makes it possible to provide a low-cost liquid flying developing device that can relieve the supply roller mirror image field stably.

  It is also possible to use a high-resistance semiconductive layer made of a resin to which an ionic conductive agent is added instead of the dielectric, for the supply roller surface layer 64a. However, in the semiconductive layer, the resistance value varies in the high resistance portion, or the resistance value varies due to environmental changes or deterioration over time. Variations and fluctuations in the resistance value adversely affect the flying electric field. Therefore, it is preferable to use a dielectric for the supply roller surface layer 64a.

  Further, the surface of the supply roller 64 has liquid repellency with respect to the liquid developer dv. As a result, the supply roller surface layer 64a can further reduce the electric field required for the developing droplet F to separate from the surface of the supply roller 64. Therefore, the developing device 6 can further reduce the magnitude of the intermediate flying electric field. Therefore, the developing device 6 can further prevent a significant increase in the intermediate flying speed of the developing droplet F.

  Further, according to the developing device 6, the first peripheral speed ratio control means performs control so that the peripheral speed ratio | S1 / S2 |> 1. More preferably, the first circumferential speed ratio control means performs control so that 1 <| S1 / S2 | ≦ 6. At this time, the peripheral speed | S1 | is selected from the range of 100 mm / s to 4800 mm / s, and the peripheral speed | S2 | is selected from the range of 100 mm / s to 800 mm / s.

  As described above, the first peripheral speed ratio control unit controls the absolute value of the peripheral speed S1 of the supply roller 64 to exceed the absolute value of the peripheral speed S2 of the developing roller 66. As a result, the developing device 6 can closely adhere the developing droplet F onto the surface of the developing roller 66. At this time, as described above, since the intermediate flying speed is suppressed, even if the pitch p of the droplet forming holes H is too small or the absolute value of the peripheral speed S1 of the supply roller 64 is too large, the developing device 6 Can avoid aggregation and combination of the developing droplets F due to electrostatic repulsion between the developing droplets F. Therefore, the developing device 6 can form a high-density, high-definition image on the developing roller 66.

Further, according to the developing device 6, the intermediate flying electric field control means has the maximum value (1/2) MV ′ _max ² of the kinetic energy of the developing droplet F during the intermediate flying as the surface energy Us of the developing droplet F. Control to be less than. Thus, the developing device 6 can prevent the development droplet F from being split during the intermediate flight and the development droplet F from being scattered when landing on the development roller 66.

  Further, according to the developing device 6, the developing roller surface layer 66 a can suppress the induction of charge on the metal roller 66 b by the charged developing droplet F on the surface of the developing roller 66. That is, the developing roller surface layer 66a can reduce the mirror image charge with respect to the charge of the developing droplet F. Therefore, since the developing roller surface layer 66a can reduce the electric field formed by the mirror image charge (developing roller mirror electric field), the minimum electric field required for the developing droplet F to separate from the surface of the developing roller 66. Can be reduced. Therefore, the developing device 6 can reduce the magnitude of the flying electric field. As a result, the developing device 6 can prevent a significant increase in the developing flight speed. Therefore, the developing device 6 can prevent the development droplets F from being split during the development flight and the development droplets F from being scattered when landing on the photosensitive belt 1.

  Further, since the developing roller surface layer 66a can reduce a developing roller mirror image field generated when the developing droplet F approaches the developing roller 66, when the developing droplet F reaches the developing roller 66, the developing roller surface layer 66a is intermediate. A significant increase in flight speed can be prevented. Therefore, the developing device 6 can prevent breakage of the developing droplet F just before landing on the developing roller 66 and scattering of the developing droplet F when landing on the developing roller 66.

  In the developing device 6, the developing roller surface layer 66a made of a dielectric functions as a developing roller charge suppressing unit. This makes it possible to provide a low-cost liquid flying developing device that can stably reduce the developing roller mirror image field.

  It is also possible to use a high-resistance semiconductive layer made of a resin to which an ionic conductive agent is added instead of the dielectric for the developing roller surface layer 66a. However, in the semiconductive layer, the resistance value varies in the high resistance portion, or the resistance value varies due to environmental changes or deterioration over time. Variations and fluctuations in the resistance value adversely affect the flying electric field. Therefore, it is preferable to use a dielectric for the developing roller surface layer 66a.

  Further, the surface of the developing roller 66 has liquid repellency with respect to the liquid developer dv. As a result, the developing roller surface layer 66a can reduce the electric field required for the developing droplet F to separate from the surface of the developing roller 66. Therefore, the developing device 6 can further reduce the magnitude of the flying electric field. Therefore, the developing device 6 can prevent a significant increase in the developing flying speed of the developing droplet F.

  Further, according to the developing device 6, the second peripheral speed ratio control means performs control so that the peripheral speed ratio | S2 / S3 |> 1. More preferably, the second peripheral speed ratio control means performs control so that 1 <| S2 / S3 | ≦ 4. At this time, the peripheral speed | S2 | is selected from the range of 100 mm / s to 800 mm / s, and the peripheral speed | S3 | is selected from the range of 100 mm / s to 200 mm / s.

  As described above, the second peripheral speed ratio control unit controls the absolute value of the peripheral speed S2 of the developing roller 66 to exceed the absolute value of the peripheral speed S3 of the photosensitive belt 1. As a result, the developing device 6 can closely adhere the developing droplet F onto the surface of the photosensitive belt 1. At this time, as described above, since the development flying speed is suppressed, even if the pitch p of the droplet forming holes H is too small or the absolute value of the peripheral speed S2 of the developing roller 66 is too large, the developing device 6 is used. Can avoid aggregation and combination of the developing droplets F due to electrostatic repulsion between the developing droplets F. Therefore, the developing device 6 can form a high-density, high-definition image on the photosensitive belt 1.

Further, according to the developing device 6, the flying electric field control means is such that the maximum value (½) MV _max ² of the developing droplet F during the developing flight is less than the surface energy Us of the developing droplet F. Control to be. As a result, the developing device 6 can prevent the development droplets F from being split during the development flight and the development droplets F from being scattered upon landing on the photosensitive belt 1.

<Simulation 2>
In order to confirm the effect of the developing device 6, a simulation 2 was performed. FIG. 4 is a diagram illustrating a result of the simulation 2. In the simulation 2, the developing roller surface layer 66a having the same dielectric constant as air and a thickness of 100 μm is provided on the surface of the developing roller C under the conditions of the simulation 1 described in [Problems to be Solved by the Invention]. This was done under the condition that

FIG. 4A shows the relationship between E (Y), E _f , and E _Q (Y) and the y coordinate Y of the developing droplet F in the simulation 2. Graph _{G 6} shows the electric field E (Y), the graph _{G 7} is shows the electric field _{E f,} the graph _{G 8} shows the electric field _E Q (Y). The vertical axis represents the magnitude [V / m] of the electric field with the direction from the developing roller C toward the photosensitive belt being positive, and the horizontal axis represents the y coordinate Y [μm] of the developing droplet F. As shown in FIG. 4 (a), the by is provided a developing roller surface layer 66a, as compared with the case of the graph G _1, a sharp change of the electric field E in the developing roller C vicinity (Y) is eliminated I understand that.

FIG. 4B shows the relationship between the flying speed V _f of the developing droplet F, the y coordinate Y, the y coordinate Y, and the time t from the start of the flight in the simulation 2. In FIG. 4B, the left vertical axis represents the flight speed V _f [m / s], the right vertical axis represents the time t [sec], and the horizontal axis represents the y coordinate Y [μm] of the developing droplet F. Represents. Graph G ₉ is a graph showing the relationship between the flight speed V _f and time t, the graph G ₁₀ is a graph showing the relationship between the y-coordinate Y and time t. The graph G ₉ and the graph G ₁₀ solve the equation of motion m · dV _f / dt = −Q · E (Y) −m · g for the developing droplet F using the electric field E (Y) shown in the graph G _6. Can be obtained. As shown graph G ₉ is flying speed V _f, as compared to the case of the graph G _4, significantly reduced in the developing roller C vicinity, it is changing gently in the whole.

In simulation 2, immediately before landing on the photosensitive layer B, the flying speed _Vf is 3.6 m / s. The kinetic energy Uv is 1.74 × 10 ⁻¹² J, which is smaller than the kinetic energy Uv in the simulation 1. Thus, it was confirmed that the increase in the flying speed _Vf can be suppressed by providing the developing roller surface layer 66a.

  The image forming unit 3 performs development in the order of the image forming units 3y, 3m, 3c, and 3k, and stacks a developer image of a predetermined color on the photosensitive belt 1. Four color developer images are stacked on the photoreceptor belt 1 to form a full color developer image. The full-color developer image is conveyed to a region (transfer region) between a transfer roller 10 and a support roller 2a described later.

  The pickup roller 8 is a roller-like member that sends out the recording paper P stored in the image forming apparatus 100 one by one to the transport rollers 9a and 9b. The pickup roller 8 sends out the recording paper P so as to synchronize the arrival of the full color developer image to the transfer area and the arrival of the recording paper P at the transfer area. The conveyance rollers 9a and 9b are a pair of roller-like members that sandwich the recording paper P sent out by the pickup roller 8 and send it to the transfer area.

  The transfer roller 10 is a roller-like member that adheres and transfers the developer image to the recording paper P conveyed by the pickup roller 8 and the conveyance rollers 9a and 9b. At the time of adhesive transfer, the transfer roller 10 is pressed against the surface of the recording paper P opposite to the surface to which the full color developer image is transferred. At the time of adhesive transfer, the transfer of the developer image onto the recording paper P may be made more reliable by applying a predetermined voltage to the transfer roller 10. The transfer roller 10 sends out the recording paper P on which the full-color developer image is transferred to the outside of the image forming apparatus 100.

  The liquid developer dv transferred to the recording paper P penetrates the recording paper P and then dries. As a result, an image is formed on the recording paper P. The image forming apparatus 100 may include a heater or a dryer for promoting the penetration and drying of the liquid developer dv.

  The photoconductor cleaning unit 7 is a member that cleans the surface of the photoconductor belt 1 after the developer image is transferred to the recording paper P. The photoreceptor cleaning unit 7 is provided in the vicinity of the support roller 2a. The photoreceptor cleaning unit 7 includes, for example, a urethane rubber cleaning blade that scrapes off the liquid developer dv remaining on the surface of the photoreceptor belt 1 and a developer collection container that collects the scraped liquid developer dv.

  In this embodiment, an image is formed by superimposing liquid developers dv of a plurality of colors on a single photoreceptor belt 1, but other embodiments include, for example, four colors corresponding to each color. The image forming apparatus may include a photosensitive member and an intermediate transfer belt, and a liquid developer dv is superimposed on the intermediate transfer belt.

  Next, a developing device 6a that is a second embodiment of the liquid flying developing device according to the present invention will be described. FIG. 5 is a schematic diagram schematically showing a cross section of the developing device 6a. The image forming apparatus 100 can include a developing device 6 a instead of the developing device 6.

  The developing device 6 a is a liquid flying developing device that is provided so as to be spaced apart from the lower portion in the vertical direction from the photosensitive belt 1 downward in the vertical direction. The developing device 6 includes a coating roller 71, a regulating member 72, a developing tank 73, a developing roller 74, a charge removing roller 75, a flying electric field control unit (not shown), and a second peripheral speed ratio control unit (not shown). .

  The developing device 6a forms charged developer droplets F from the liquid developer dv, and supplies the developer droplets F to the electrostatic latent image D on the surface of the photosensitive layer 1c by flying. In the present embodiment, as in the developing device 6, a spontaneous charging method is adopted.

  The developing tank 73 is a container-like member that stores the liquid developer dv. The liquid developer dv stored in the developing tank 73 is adjusted so as to be maintained at a predetermined liquid level. As the liquid developer dv, the one used in the developing device 6 can be used, but a developer in which fine particles of a binder resin in which a pigment is dispersed is dispersed in a solvent can also be used. The liquid developer dv used in the present embodiment can also be used in the developing device 6. Below, the manufacturing method of the liquid developer dv used for this embodiment is shown.

<Method for Producing Liquid Developer dv>
Composition obtained by adding 40% by weight of pigment to a polyester resin (binder resin) having the characteristics of glass transition temperature Tg = 60 ° C. and 1/2 flow softening temperature Tm = 110 ° C. (master) The batch-treated composition), the polyester resin, and the charge control agent (alkyl salicylate metal salt) are charged into a Henschel mixer and mixed for 10 minutes to form a mixture (raw material mixture). In producing the mixture, each composition material satisfying the following conditions is charged according to the desired pigment concentration N of the color toner to be produced.

(Input amount of raw materials when producing color toner with pigment concentration of N wt%)
Polyester resin: (98-Z) parts by weight Composition: Y parts by weight Charge control agent: 2 parts by weight However, N / 100 = 0.4 × Z / 100 is satisfied.

Moreover, the following products are used for the pigment.
(Pigment)
Yellow pigment: C.I. I. Pigment Yellow 74 “FAST YELLOW FGOK (manufactured by Sanyo Dye)”
Magenta pigment ... C.I. I. Pigment Red 122 “Toner Magennta E-02 (manufactured by Clariant Japan)”
Cyan pigment: C.I. I. Pigment Blue 15: 3 “Hosteaperm Blue B2G (manufactured by Clariant Japan)”

  A mixture having a pigment concentration of 20% by weight is melt-kneaded with a Niedix MOS140-800 manufactured by Mitsui Mining Co., Ltd. and uniformly dispersed to obtain a master batch. The above master batch, carrier liquid (silicon oil “KF-96” manufactured by Shin-Etsu Silicon Co., Ltd.), and a dispersing agent are prepared, and wet pulverized by a ball mill, and a toner dispersion liquid having a particle diameter of 2 μm and a solid content concentration of 20% (liquid development Agent dv) is obtained.

  The application roller 71 is a roller-like member that carries the liquid developer dv and applies the liquid developer dv to the development roller 74 described later. The application roller 71 is formed by coating a stainless steel rotating shaft 71b with an elastic layer 71a made of a rubber member such as EPDM, silicon rubber, or fluororesin. The elastic layer 71a may be a metal or the like. The rotating shaft 71b is connected to the application roller power supply 11 and adjusted to a predetermined potential. The potential of the rotating shaft 71b may be the same as that of the developing roller 74, may have a potential difference with the developing roller 74 in order to control the charge amount of the developing droplet F, or may be floating.

  The application roller 71 is provided in pressure contact with the developing roller 74 with a predetermined linear pressure. The application roller 71 is rotated clockwise by a driving unit (not shown) so that the surface of the application roller 71 and the surface of the development roller 74 move in the opposite direction in the proximity region between the application roller 71 and the development roller 74. Is provided. As a result, a developing droplet F having a predetermined droplet diameter and droplet density is formed on the surface of the developing roller 74.

  If the surface of the application roller 71 has liquid repellency and it is difficult to form the developing droplet F when the application roller 71 rotates so that each surface moves in the opposite direction, each surface is in the same direction. The developing droplet F may be formed by rotating the application roller 71 at a predetermined peripheral speed so as to move.

  A regulating member 72 is provided in pressure contact with the surface of the application roller 71. The restricting member 72 is a blade-like member that restricts the liquid developer dv carried on the application roller 71 to be a predetermined amount or less.

  The developing roller 74 is a member that forms a developing droplet F charged from the liquid developer dv and conveys the developing droplet F while carrying it. The developing roller 74 includes a developing roller base having a rotating shaft 74c and a metal roller 74b, and a developing roller surface layer 74a. The developing roller 74 is provided such that the lower portion in the vertical direction is immersed in the liquid developer dv. Further, the developing roller 74 is provided such that the uppermost portion in the vertical direction of the developing roller 74 is located at a position 200 μm vertically below the lowermost portion in the vertical direction of the photosensitive belt 1.

  The rotating shaft 74c is a metal rod-like member that is rotated counterclockwise by a developing roller driving unit (not shown). The rotating shaft 74c is a flying electric field generating means. The rotating shaft 74c, which is a flying electric field generating means, is connected to the developing roller power supply 14 to fly the developing droplet F from the developing roller 74 to the photosensitive belt 1 on which the electrostatic latent image D is formed (developing flying). ) To generate a flying electric field that is an electric field to be supplied. By applying a developing bias voltage to the rotating shaft 74c, a flying electric field is stably formed. For example, when the development start voltage is −600 V, the development bias voltage applied to the rotating shaft 74 c is −650 V to −700 V with a margin of −50 to −100 V added.

  The metal roller 74b is a metal roller-like member that is fixed to the rotary shaft 74c via a metal bearing (not shown). Therefore, the metal roller 74b rotates counterclockwise as the rotating shaft 64c rotates. Further, the metal roller 74b and the rotating shaft 74c are electrically connected via a metal bearing. Stainless steel can be used for the metal roller 74b, the rotating shaft 74c, and the metal bearing.

  The developing roller surface layer 74a is a dielectric that covers the surface of the metal roller 74b. The developing roller surface layer 74a is a developing roller charge suppressing unit. The developing roller surface layer 74a, which is a developing roller charge suppressing means, suppresses the induction of charge on the surface of the metal roller 74b by the developing droplet F carried on the surface of the developing roller 74. For the developing roller surface layer 74a, a fluororesin such as PETFE, PFA, PFE, PTFE, or the like can be used. Moreover, you may use in the state in which either of these was piled up.

  The thickness of the developing roller surface layer 74a is preferably 50 μm to 500 μm. When the thickness is less than 50 μm, the function as the developing roller charge suppressing means is lowered, and it is difficult to suppress the induction of charge on the surface of the metal roller 74b. If the thickness exceeds 500 μm, the proximity area (flying area) between the developing roller 74 and the photosensitive belt 1 becomes too wide, and it becomes difficult to fly the developing droplet F to the electrostatic latent image D with high positional accuracy. . In the present embodiment, PTFE having a relative dielectric constant of 2.1 and a thickness of 210 μm is used as the developing roller surface layer 74a.

  The developing roller surface layer 74a is surface-treated so as to have liquid repellency with respect to the liquid developer dv. Such surface treatment can be performed using, for example, a photosensitive coating / fluorine resin “AL-Polymer” manufactured by Asahi Glass Co., Ltd.

  The developing roller surface layer 74a is provided with a droplet forming hole. In this embodiment, the droplet forming hole has a regular quadrangular pyramid shape with a side of 2.83 μm and a height of 2 μm. The droplet formation holes are provided in a staggered arrangement, and the pitch in the image transport direction b is 35 μm. The size and pitch of the droplet formation holes are not limited to this, and the depth can be selected from the range of 2 μm to 20 μm, and the pitch can be selected from the range of 35 μm to 340 μm (about 725 DPI to 75 DPI).

  Further, the droplet forming hole may be provided in the application roller 71 instead of the developing roller 74. The droplet formation hole does not have to be a regular quadrangular pyramid, and may be a valley having a curved surface or a cylinder having a side surface roughened to several μm.

  The static eliminating roller 75 is a roller-like member disposed so as to be in contact with the developing roller 74. In order to prevent the charge removal roller 75 from repeatedly accumulating charges on the developing roller 74 during the formation of the developing droplet F and the development flight of the developing droplet F, the surface of the developing roller 75 is prevented. 74a is AC neutralized. The static elimination roller 75 is a member that serves as both static elimination and cleaning. The static eliminating roller 75 is formed by covering a stainless steel rotating shaft 75b with an elastic layer 75a made of a rubber member. The rotating shaft 75b is connected to the static elimination roller power source 13 and is applied with an alternating current. The static eliminating roller 75 is not limited to this, and may be a member that performs static elimination without contact.

The developing operation by the developing device 6a configured as described above will be described. When a command to perform development is input from the control unit, first, the application roller 71 and the development roller 74 are rotated. In this embodiment, when the peripheral speed of the application roller 71 and the developing roller 74 is S2, | S2 | = 1200 mm / s. Thus, on the surface of the developing roller 74, a development droplet F having a mass m = 2.7 × 10 ⁻¹⁰ g / piece and a charge amount Q = −5.4 × 10 ⁻¹⁵ C / piece has a pitch of 35 μm. Formed with. At this time, the droplet diameter of the developing droplet F is equal to or smaller than the size of the droplet formation hole.

The ratio of charge amount Q to mass m per developing droplet F | Q / m | varies depending on the type of liquid developer dv and the droplet diameter of developing droplet F, but is 5 μC / g to 50 μC / g. It is preferable to be within the range. In this embodiment, the ratio | Q / m | = 20 μC / g. Further, from the mass m and the pitch, the mass of the liquid developer dv per unit area is 0.0253 mg / cm ² .

  Next, the electrostatic discharge image D on the photosensitive belt 1 is developed by causing the development droplet F to fly from the development roller 74. In this embodiment, when the peripheral speed of the photosensitive belt 1 is S3, | S3 | = 100 mm / s. At this time, a developing bias voltage is applied to the rotating shaft 74c, and the conductive layer 1b is grounded. As a result, a flying electric field is generated in the flying region.

  The developing droplet F flies from the developing roller 74 to the photosensitive layer 1c by a flying electric field. As described above, the absolute value of the peripheral speed S2 of the developing roller is 1200 mm / s, and the absolute value of the peripheral speed S3 of the photosensitive belt 1 is 100 mm / s. Therefore, the peripheral speed ratio | S2 / S3 | = 12. That is, the peripheral speed ratio | S2 / S3 |> 1. The second peripheral speed ratio control means is a means for controlling the peripheral speed ratio | S2 / S3 |> 1 as described above. The second peripheral speed ratio control unit may be a part of the control unit of the image forming apparatus 100 or may be provided in the developing device 6a.

As a result, the developing droplets F having a number density 12 times that of the developing droplets F on the surface of the developing roller 74 adhere to the surface of the photosensitive belt 1. At this time, the droplet diameter of the developing droplet F on the photosensitive belt 1 is the same as the droplet diameter of the developing droplet F on the developing roller 74. Further, the mass of the liquid developer dv per unit area on the photosensitive belt 1 is 0.30 mg / cm ² .

At this time, the flying electric field control means uses Us [J] as the surface energy of the developing droplet F, M [kg] as the mass of the developing droplet F, and develops when developing from the developing roller 74 (developing flight). When the maximum value of the flying speed of the droplet F (development flying speed) is V _max [m / s], the developing roller power supply 14 is controlled so as to satisfy the above formula (2), and the flying electric field is controlled.

  At this time, the flying electric field control means controls the flying electric field so that the sum of the forces applied to the developing droplets F on the developing roller 74 is close to 0 and becomes a force in a direction away from the developing roller 74. This makes it easy to develop and fly the developing droplet F while satisfying the above formula (2).

  Further, the flying electric field control means controls the flying electric field so that the image density on the photosensitive belt 1 that varies depending on environmental factors, the state of the developing roller 74, and the density of the liquid developer dv is always a predetermined value. to correct. This correction is performed by the density detector 16 detecting the image density of the test pattern formed on the surface of the photoreceptor belt 1. The detection signal from the density detector 16 is transmitted to the flying electric field control means, and the flying electric field control means determines whether or not the image density is within a predetermined range. The flying electric field control means increases the flying electric field when the image density is lower than the lower limit value. The flying electric field control means reduces the flying electric field when the image density is higher than the upper limit value. As the test pattern, it is preferable to use a fine line or sea-island pattern.

  According to the developing device 6a that performs the developing operation as described above, the developing roller surface layer 74a can suppress the induction of charge on the metal roller 74b by the charged developing droplet F on the surface of the developing roller 74. . That is, the developing roller surface layer 74a can reduce the mirror image charge with respect to the charge of the developing droplet F. Therefore, the developing roller surface layer 74a can reduce the electric field formed by the mirror image charge (developing roller mirror image electric field), and therefore, the minimum electric field required for the developing droplet F to leave the surface of the developing roller 74. Can be reduced. Therefore, the developing device 6a can reduce the magnitude of the flying electric field. As a result, the developing device 6 can prevent a significant increase in the developing flight speed. Therefore, the developing device 6 can prevent the development droplets F from being split during the development flight and the development droplets F from being scattered when landing on the photosensitive belt 1.

  In the developing device 6a, the developing roller surface layer 74a made of a dielectric functions as a developing roller charge suppressing unit. This makes it possible to provide a low-cost liquid flying developing device that can stably reduce the developing roller mirror image field.

  It is also possible to use a high-resistance semiconductive layer made of a resin to which an ionic conductive agent is added instead of the dielectric for the developing roller surface layer 74a. However, in the semiconductive layer, the resistance value varies in the high resistance portion, or the resistance value varies due to environmental changes or deterioration over time. Variations and fluctuations in the resistance value adversely affect the flying electric field. Therefore, it is preferable to use a dielectric for the developing roller surface layer 74a.

  Further, the surface of the developing roller 74 has liquid repellency with respect to the liquid developer dv. As a result, the developing roller surface layer 74a can further reduce the electric field required for the developing droplet F to separate from the surface of the developing roller 74. Therefore, the developing device 6a can further reduce the magnitude of the flying electric field. Therefore, the developing device 6a can further prevent a significant increase in the developing flight speed of the developing droplet F.

  Further, according to the developing device 6a, the second peripheral speed ratio control unit controls the peripheral speed ratio | S2 / S3 |> 1. More preferably, the second peripheral speed ratio control means performs control so that 1 <| S2 / S3 | ≦ 24. At this time, the peripheral speed | S2 | is selected from the range of 100 mm / s to 4800 mm / s, and the peripheral speed | S3 | is selected from the range of 100 mm / s to 200 mm / s.

  As described above, the second peripheral speed ratio control unit controls the absolute value of the peripheral speed S2 of the developing roller 74 to exceed the absolute value of the peripheral speed S3 of the photosensitive belt 1. As a result, the developing device 6a can closely adhere the developing droplets F onto the surface of the photoreceptor belt 1. At this time, as described above, since the development flying speed is suppressed, even if the pitch of the droplet forming holes is too small or the absolute value of the peripheral speed S2 of the developing roller 74 is too large, the developing device 6a The electrostatic repulsion between the developing droplets F can avoid the aggregation and combination of the developing droplets F. Therefore, the developing device 6a can form a high-density, high-definition image on the photoreceptor belt 1.

Further, according to the developing device 6a, the flying electric field control means is such that the maximum value (1/2) MV _max ² of the kinetic energy of the developing droplet F at the time of developing flying is less than the surface energy Us of the developing droplet F. Control to be. As a result, the developing device 6a can prevent the development droplet F from being split at the time of development flight and the development droplet F from being scattered at the time of landing on the photosensitive belt 1.

  Further, the developing device 6a draws up the liquid developer dv from the developing tank 73 by the developing roller 74, and supplies the developing droplet F formed thereby directly to the photosensitive belt 1 without passing through the supply roller. Therefore, the configuration of the developing device 6a is simpler than that of the developing device 6, and there is an advantage that the developing device can be downsized. On the other hand, since the developing device 6 performs the development via the supply roller 64, the developer droplet F can be adhered more closely on the surface of the photosensitive belt 1 than the developing device 6a. There is.

  Next, an image forming apparatus 200 that is a second embodiment of the image forming apparatus according to the present invention will be described. FIG. 6 is a schematic diagram schematically showing a cross section of the image forming apparatus 200. The image forming apparatus 200 has the same configuration as the image forming apparatus 100 except that the configuration of the photosensitive belt 1 and the arrangement position of the exposure unit 5 are different. Therefore, the description other than the photosensitive belt 1 and the exposure unit 5 is omitted.

  FIG. 7 is a cross-sectional view showing a part of the cross section of the photosensitive belt 1. In this embodiment, the photoreceptor belt 1 is an endless belt-like image carrier having a photosensitive layer 1c, a conductive base material, and an intermediate layer 1d. In the photosensitive belt 1, the photosensitive layer 1c is on the outer peripheral side of the photosensitive belt 1, the conductive substrate is on the inner peripheral side of the photosensitive belt 1, and the intermediate layer 1d is between the photosensitive layer 1c and the conductive substrate. It is stretched around the support rollers 2a and 2b.

The photosensitive layer 1c is made of OPC having a thickness of 20 μm. The OPC may be either a laminated type photoreceptor in which a charge transport layer and a charge generation layer are laminated, or a single layer type photoreceptor in which a charge generation layer is dispersed in a binder. The conductive substrate includes an opaque conductive layer 1b in which carbon black is dispersed and imparted conductivity, and a dielectric layer 1a provided on the inner peripheral side of the conductive layer 1b. Here, the term “opaque” means that light emitted from the exposure unit 5 is not transmitted.
The conductive layer 1b is an electrode made of a polycarbonate resin in which carbon black is dispersed. In the present embodiment, the conductive layer 1b is grounded. The dielectric layer 1a is made of polycarbonate resin.

The intermediate layer 1d is a member that suppresses the development droplet F flying to the surface of the photosensitive layer 1c from inducing charges in the conductive layer 1b. The intermediate layer 1d is a dielectric having a relative dielectric constant of 3, a volume resistivity of 2 × 10 ⁹ [Ω · m], a thickness of 200 μm, and a time constant of 53 msec. As the dielectric, a semiconductive resin such as polycarbonate can be used. The thickness can be selected from a range of 100 μm to 200 μm.

  Here, the time constant of the intermediate layer 1d is measured as follows. First, only the intermediate layer 1d is provided on the conductive substrate. The photosensitive layer 1c is not provided. Using a scorotron charger, the gap between the grid (grid voltage is -500V) and the intermediate layer 1d is set to 1.0 mm, and the intermediate layer 1d is uniformly charged to -510V. The surface potential of the intermediate layer 1d after charging is measured with a surface potentiometer, the time taken for the surface potential to decay 0.368 times is determined, and this time is taken as the time constant of the intermediate layer 1d.

  The exposure unit 5 is a member that is provided on the outer peripheral side of the photosensitive belt 1 and is separated from the photosensitive belt 1 and that irradiates the photosensitive layer 1 c with predetermined light from the outer peripheral side of the photosensitive belt 1. In the present embodiment, since the photosensitive belt 1 is opaque, the exposure unit 5 is provided on the outer peripheral side of the photosensitive belt 1 unlike the image forming apparatus 100. However, the photosensitive belt 1 may be transparent.

  Except for the above points, the image forming apparatus 100 and the image forming apparatus 200 have the same configuration, and thus the image forming apparatus 200 performs the same developing operation as the image forming apparatus 100. Therefore, the peripheral speed S3 of the photosensitive belt 1 is 100 mm / s. At this time, it takes 140 msec for the photosensitive belt 1 to pass through a region where the charging unit 4 performs charging (charging region). This value is larger than the time constant of the intermediate layer 1d. Accordingly, since the dielectric polarization proceeds in the intermediate layer 1d, the surface of the photosensitive layer 1c is charged to a target voltage.

  Thereafter, the photosensitive belt 1 on which the electrostatic latent image D is formed by the exposure unit 5 reaches the flying region. In the flying region, the photosensitive belt 1 is supplied with developing droplets F from the developing roller 66. At this time, the flying time until the developing droplet F separated from the developing roller 66 reaches the photosensitive belt 1 is 0.1 msec to 0.3 msec. This time is smaller than the time constant of the intermediate layer 1d. Therefore, during the flight of the developing droplet F, the dielectric polarization of the intermediate layer 1d does not proceed.

  As described above, the intermediate layer 1d having a time constant larger than the flight time can suppress the induction of charge on the conductive layer 1b by the developing droplet F approaching the surface of the photosensitive layer 1c. That is, the intermediate layer 1d can reduce the mirror image charge with respect to the charge of the developing droplet F. Therefore, the intermediate layer 1d can reduce the mirror image electric field (image carrier mirror image electric field) formed by the mirror image charge. As a result, the image forming apparatus 200 can prevent the development flying speed from significantly increasing when the developing droplet F reaches the photosensitive belt 1. Therefore, the image forming apparatus 200 can prevent the development droplets F from being split just before landing on the photosensitive belt 1 and the development droplets F to be scattered when landing on the photosensitive belt 1. Images can be obtained.

  Further, as described above, since the time constant of the intermediate layer 1d is smaller than the charging region passage time, the photosensitive belt 1 can maintain the charging characteristics and exposure characteristics of the photosensitive belt 1 while maintaining the mirror image electric field of the image carrier. Can be reduced.

<Simulation 3>
In order to confirm the effect of the image forming apparatus 200, a simulation 3 was performed. FIG. 8 is a diagram illustrating a result of the simulation 3. In simulation 3, the conditions of simulation 2 are as follows: between the substrate A and the photosensitive layer B, the relative dielectric constant ε _s = 1.0, the volume resistivity ρ _v = 10 ¹⁰ Ωm, the thickness is 100 μm, This is performed under the condition that an intermediate layer 1d having a constant of 89 msec is provided.

FIG. 8A shows the relationship between E (Y), E _f , and E _Q (Y) and the y coordinate Y of the developing droplet F in the simulation 3. Graph _{G 11} represents an electric field E (Y), the graph _{G 12} shows the electric field _{E f,} the graph _{G 13} shows the electric field _E Q (Y). The vertical axis represents the magnitude [V / m] of the electric field with the direction from the developing roller C toward the photosensitive belt being positive, and the horizontal axis represents the y coordinate Y [μm] of the developing droplet F. As shown in FIG. 8 (a), the by intermediate layer 1d is provided, as compared with the case of the graph G _1, that rapid change of the electric field E (Y) of the photosensitive belt vicinity is eliminated Recognize.

FIG. 8B shows the relationship between the flight speed V _f of the developing droplet F, the y coordinate Y, the y coordinate Y, and the time t from the start of the flight in the simulation 3. In FIG. 8B, the left vertical axis represents the flight speed V _f [m / s], the right vertical axis represents the time t [sec], and the horizontal axis represents the y coordinate Y [μm] of the developing droplet F. Represents. Graph G ₁₄ is a graph showing the relationship between the flight speed V _f and time t, the graph G ₁₅ is a graph showing the relationship between the y-coordinate Y and time t. Graphs G ₁₄ and G ₁₅ solve the equation of motion m · dV _f / dt = −Q · E (Y) −m · g for the developing droplet F using the electric field E (Y) shown in the graph G _11. Can be obtained. As shown the graph G ₁₄ is, the flying speed V _f, as compared to the case of the graph G _4, significantly reduced in the photoreceptor belt near, it is changing gently in the whole.

In simulation 3, the flying speed _Vf is 2.6 m / s immediately before landing on the photosensitive layer B. The kinetic energy Uv is 0.91 × 10 ⁻¹² J, which is smaller than the kinetic energy Uv in the simulation 1. Thus, it was confirmed that the increase in the flying speed _Vf can be suppressed by providing the intermediate layer 1d.

DESCRIPTION OF SYMBOLS 1 Photosensitive belt 1a Photosensitive layer 1b Conductive layer 1c Dielectric layer 1d Intermediate layer 3, 3c, 3k, 3m, 3y Image forming part 4, 4c, 4k, 4m, 4y Charging part 5, 5c, 5k, 5m, 5y Exposure Part 6, 6a, 6c, 6k, 6m, 6y Developing device 61, 71 Application roller 63 Developing tank 64 Supply roller 64a Supply roller surface layer 64b, 66b, 74b Metal roller 64c, 66c, 74c Rotating shaft 66, 74 Development roller 66a 74a Developing roller surface layer 100, 200 Image forming apparatus

Claims (14)

A developing tank for storing a liquid developer containing a colorant;
A developing roller that forms charged developer droplets from the developer and conveys the developer droplets while carrying the developer droplets;
A flying electric field generating means for generating a flying electric field, which is an electric field for flying and supplying the developer droplets from the developing roller to an image carrier on which an electrostatic latent image is formed,
The liquid flying developing device, wherein the developing roller has a developing roller charge suppressing unit that suppresses the development droplet carried on the surface of the developing roller from inducing charge in the developing roller. The developing roller has a conductive developing roller base material, and a developing roller surface layer made of a dielectric provided on the surface of the developing roller base material,
The liquid flying developing device according to claim 1, wherein the developing roller charge suppression unit is a surface layer of the developing roller.   The liquid flying developing device according to claim 1, wherein the surface of the developing roller has liquid repellency with respect to the developer. A developing tank for storing a liquid developer containing a colorant;
A supply roller that forms charged developer droplets from the developer and conveys the developer droplets while supporting the developer droplets;
A developing roller for transporting the developer droplets supplied from the supply roller while carrying;
Intermediate flying electric field generating means for generating an intermediate flying electric field, which is an electric field for flying and supplying the developer droplets from the supply roller to the developing roller;
A flying electric field generating means for generating a flying electric field, which is an electric field for flying and supplying the developer droplets from the developing roller to an image carrier on which an electrostatic latent image is formed,
The liquid flying developing device according to claim 1, wherein the supply roller has supply roller charge suppression means for suppressing development droplets carried on the surface of the supply roller from inducing charge in the supply roller. The supply roller has a conductive supply roller base material and a supply roller surface layer made of a dielectric provided on the surface of the supply roller base material.
The liquid flying developing device according to claim 4, wherein the supply roller charge suppression unit is a surface layer of the supply roller.   6. The liquid flying developing device according to claim 4, wherein a surface of the supply roller has liquid repellency with respect to the developer.   7. The developing roller according to claim 4, further comprising a developing roller charge suppressing unit that suppresses the development droplet carried on the surface of the developing roller from inducing charge in the developing roller. Or a liquid flying developing device according to any one of the above. When the peripheral speed of the supply roller is S1 [m / s] and the peripheral speed of the developing roller is S2 [m / s], the supply roller and the developing roller are controlled so as to satisfy the following formula (1). The liquid flying developing device according to claim 4, further comprising a first peripheral speed ratio control unit configured to perform the first peripheral speed ratio control unit.
| S1 / S2 |> 1 (1) When the surface energy of the developing droplet is Us [J], the mass of the developing droplet is M [kg], and the maximum value of the flying speed of the developing droplet is V _max [m / s], the following formula ( 9. The liquid flying developing device according to claim 1, further comprising flying electric field control means for controlling the flying electric field so as to satisfy 2).
Us> (1/2) MV _max ² (2) An image carrier having a photosensitive layer;
An image forming apparatus comprising: the liquid flying developing device according to claim 1. An image carrier having a conductive base material having conductivity and a photosensitive layer;
A liquid flying developing device that is supplied from the liquid developer containing the colorant and that is supplied to the image carrier by flying charged developer droplets;
The image forming apparatus according to claim 1, wherein the image bearing member includes an intermediate layer that suppresses the development droplets flying to the surface of the photosensitive layer from inducing charge in the conductive substrate.   The image forming apparatus according to claim 11, wherein the intermediate layer is a dielectric provided between the photosensitive layer and the conductive substrate.   The image forming apparatus according to claim 11, wherein the liquid flying developing device includes the liquid flying developing device according to claim 1. When the peripheral speed of the developing roller is S2 [m / s] and the peripheral speed of the image bearing member is S3 [m / s], the developing roller and the image bearing member satisfy the following expression (3). The image forming apparatus according to claim 10, further comprising a second peripheral speed ratio control unit configured to control the rotation.
| S2 / S3 |> 1 (3)

Images