JP4563742B2 - Liquid developer coating apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to a liquid developer coating apparatus and an image forming apparatus.

  As an image forming apparatus, the surface of the photoconductor is uniformly charged by a charging unit, and the surface of the photoconductor is exposed according to image data by an optical writing unit to form an electrostatic latent image. There is an electrophotographic type in which a visible image is developed after developing with a transfer member (including an intermediate transfer member).

In such an image forming apparatus, as a developing device for visualizing an electrostatic latent image, for example, a high-viscosity and high-concentration liquid developer is used as disclosed in Patent Documents 1, 2, and 3. Some use a liquid developing device.
JP 7-152254 A Japanese Patent Laid-Open No. 7-209922 JP 7-219355 A

  This liquid developing device uses a high-viscosity liquid developer of 50 to 10,000 mPa · s in which a toner as a visualized particle is dispersed at a high concentration in a developer solvent made of an insulating liquid such as dimethylpolysiloxane oil. use. Then, the liquid developer stored in the storage tank is applied to the developing roller and the developing belt with a uniform thickness, and the thin layer of the liquid developer applied to the developing roller and the developing belt is close to the photoconductor to open the developing area. As it passes, the electrostatic latent image on the photoconductor is developed with a thin layer of toner of the liquid developer to form a toner image, and the liquid developer remaining on the development roller and development belt that has passed through the development area is scraped off. It is removed with a blade and collected in a storage tank.

  By the way, the liquid developer used for this image formation is formed by dispersing a solid content (toner) composed of a resin and a pigment in an insulating liquid (carrier liquid) as described above, and is charged during development. Since the toner moves in the insulating liquid by electrostatic force to develop the electrostatic latent image, the developing efficiency is improved as the moving distance of the charged toner is shorter.

  Therefore, in order to increase the development efficiency, a thin layer of a micron unit of liquid developer is formed on a developer carrying member such as a developing roller, and the thinned liquid developer is brought into contact with the photoconductor for development. It is preferable. This is particularly noticeable when a high-viscosity liquid developer having a viscosity of 50 to 10,000 mPa · s as described above is used.

  Thus, when developing with a thin layer of liquid developer, the concentration is determined by the thickness of the layer of the liquid developer. It is necessary to form a stable and uniform thin layer of liquid developer on the body.

Therefore, conventionally, as disclosed in Patent Document 4, using a coating roller (anilox roller) whose surface is regularly engraved, a predetermined amount of liquid developer is carried on the coating roller, The developing roller, which is a developer carrying member, is brought into direct contact with the coating roller, and the developing roller is rotated in a direction opposite to the coating roller at a peripheral speed equal to or higher than the peripheral speed of the coating roller. And a uniform heat layer is formed on the developing roller by leveling the engraving pattern on the coating roller during transfer.
Japanese Patent Laid-Open No. 11-265122

  However, when the coating roller is brought into direct contact with the developing roller and rotated in the opposite direction as described above, the surface of the developing roller always comes into contact with the engraving pattern on the surface of the coating roller with a large linear velocity. There is an inconvenience that the surface of the developing roller is scratched and the life is shortened.

  In a coating apparatus that transfers the liquid developer by bringing the coating roller and the developing roller into direct contact with each other, scratches on the developing roller as the developer carrying member and the durability of the developing roller depend on the quality of the formed image. Therefore, strict conditions are required in terms of the specifications, and the selection range of the developing roller forming member is narrow, making it difficult to produce a highly durable part.

  The specifications of the developing roller are as follows: (1) low hardness for forming a developing nip with the photoconductor, (2) at least the surface being a conductive material for bias application, (3) Have mechanical strength of the surface for abrasion resistance against the coating roller, (4) have mechanical strength of the surface for abrasion resistance of the cleaning blade, (5) uniform coating Therefore, strict characteristics such as having smoothness are required, so that it is difficult to manufacture highly durable parts.

  Among these, the requirements of (3) and (4) are deeply related to the durability of the developing roller, and the life of the developing roller is determined depending on how this is satisfied. For example, the surface of the developing roller is electrically conductive. Even when a PFA tube is used, the durable life of the developing roller is only about 50,000 printed sheets.

Therefore, as disclosed in Patent Document 5, an intermediate roller is interposed between the coating roller and the developing roller, the intermediate roller is rotated at a constant speed with respect to the coating roller, and the developing roller is Some have attempted to extend the life of the developing roller by avoiding direct contact between the developing roller and the coating roller by employing a configuration that rotates in the reverse direction.
JP 2002-287513 A

  In other words, in this configuration, the developing roller does not come into direct contact with the coating roller, so that it is not damaged by the engraving pattern of the coating roller, and is in contact with the intermediate roller in the reverse direction, but the surface of the intermediate roller is uneven. Since the developing roller surface is not held, the surface of the developing roller is not damaged, the mechanical stress applied to the developing roller is reduced, and the life of the developing roller can be extended.

  The intermediate roller is in contact with the application roller, but the mechanical stress received from the application roller is reduced because of the constant speed. The liquid developer layer transferred from the coating roller to the intermediate roller is the same as the engraving pattern on the surface of the coating roller transferred as it is. By making the peripheral speed of the roller equal to or higher than the peripheral speed of the developing roller, it can be stretched and the pattern can be leveled to form a uniform coating surface.

  In addition, when foreign matter enters the liquid developer, not only does the streaks appear on the liquid developer coating surface starting from the foreign matter, but when foreign matter with a hardness higher than that of the roller enters, the roller surface is damaged and the life of the roller Will be reduced.

Therefore, as disclosed in Patent Document 6, there is a device in which the coating device and the developing roller are stored in a sealed container, and an opening is provided only at a contact portion with the latent image carrier.
JP 2003-156938 A

  In addition, for example, foreign matters such as dust may be clogged at the tip of the cleaning blade used when removing unnecessary liquid developer from the roller surface, and scratches may occur on the roller surface starting from this foreign matter.

As described above, when scratches occur on the roller surface, it leads to a decrease in image quality and a decrease in roller life, so as disclosed in Patent Document 7, a continuous test for performing durability evaluation is performed. Based on this result, it is known that the surface roughness of the intermediate roller is rough to some extent, and the 10-point average surface roughness Rz is 3 μm or more to reduce scratches on the roller surface and extend the life of the roller. It has been.
JP 2004-037963 A

  However, even in the apparatus described in Patent Document 7, the state of occurrence of short streaks (referred to as “ribs”) in the rotation direction of the developing roller varies depending on the surface roughness of the intermediate roller. Further, it has been found that the occurrence of such ribs and the change in the state of the occurrence of the ribs causes a streak-like density unevenness on the image, particularly in the highlight portion, and there is a problem that the image quality is significantly lowered.

  The present invention has been made in view of the above-described problems, and includes a liquid developer coating apparatus that can stably apply a liquid developer to a developer carrying member with high quality, and the coating apparatus. An object is to provide an image forming apparatus capable of forming a high quality image.

In order to solve the above problems, a liquid developer coating apparatus according to the present invention includes:
A coating member that rotates while carrying a predetermined amount of liquid developer on the surface;
In a liquid developer coating apparatus comprising an intermediate coating member interposed between the coating member and a rotating coated member to which the liquid developer is coated,
On the surface of the intermediate application member,
Convex and concave portions are formed in which the inclined surface with a small inclination angle is located on the front side in the rotational direction of the intermediate coating member, with a mountain shape having a different cross-sectional shape and a inclined surface in the circumferential direction,
An elastic layer and a slipping layer coated on the surface of the elastic layer were used.

An image forming apparatus according to the present invention includes the liquid developer coating apparatus according to the present invention.

According to the liquid developer coating apparatus of the present invention, the surface of the intermediate coating member has a mountain shape with a cross-sectional shape and a different inclined surface in the circumferential direction, and an inclined surface with a small inclination angle is in the rotational direction of the intermediate coating member. Since it has an uneven surface located on the front side and has an elastic layer and a slipping layer coated on the surface of this elastic layer, it suppresses unevenness (ribs) on the application surface of the liquid developer and stabilizes it. And high-quality coated surfaces can be formed.

According to the image forming apparatus of the present invention, since the liquid developer coating apparatus according to the present invention is provided , a high-quality image can be stably formed.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a schematic configuration diagram of a main part of an image forming apparatus provided with a developing device including a liquid developer coating device according to the present invention.

  The image forming apparatus includes a charger 2 using a charging charger (or a charging roller or the like) around a drum-shaped photoreceptor 1 that is a latent image carrier using amorphous Si, OPC, or the like. A developing device 4 including such a liquid developer coating device, a transfer device 5 and a cleaning device 7 are arranged.

  In this image forming apparatus, the photosensitive member 1 is rotated in the direction of the arrow at a constant speed by a driving means such as a motor (not shown), and the surface of the photosensitive member 1 is uniformly charged in the dark by the charger 2 to perform LED or laser scanning. An optical writing unit (not shown) composed of an optical system or the like is exposed by irradiating a laser beam 3 in accordance with a document image to form an electrostatic latent image on the surface of the photoreceptor 1.

  Then, a developer (toner) is applied to the electrostatic latent image on the surface of the photoreceptor 1 by the developing device 4 including the liquid developer coating device according to the present invention, and the toner image is indicated by an arrow of the transfer device 5. The image is transferred to an intermediate transfer roller 51 that rotates in the direction, and further transferred from the intermediate transfer roller 51 to the transfer paper 9 that is conveyed in the transfer paper conveyance direction while being pressed by the secondary transfer roller 52 that rotates in the direction of the arrow. As the transfer device 5, for example, an apparatus that performs transfer by an electrostatic roller method, a corona discharge method, an adhesive transfer method, a thermal transfer method, or the like can be used.

  The transfer paper 9 onto which the toner image has been transferred passes through a fixing device (not shown) and is fixed, and then is discharged outside the apparatus. As a fixing device (not shown), for example, a device that performs a fixing process such as a thermal transfer method, solvent fixing, UV fixing, and pressure fixing can be used.

  On the other hand, after the transfer, the photosensitive member 1 is removed from the residual potential by the charge eliminating lamp 6 and the residual toner is removed by the cleaning device 7 to be ready for the next image formation.

Next, details of the developing device 4 of the image forming apparatus will be described.
The developing device 4 is attached to the surface of the photoconductor 1 on the downstream side of the developing roller 12, a developer containing tank 11 that contains the liquid developer 10 therein, a developing roller 12 that is a developer carrying member. A sweep roller 13 for scraping off the developer and a liquid developer coating device 14 according to the present invention for coating the developer roller 12 with the liquid developer 10 are provided.

  The liquid developer 10 is not a low-viscosity (about 1 cSt), low-concentration (about 1%) liquid developer using Isopar (registered trademark) as a carrier, which is generally used in the past, but a high-viscosity, high-concentration liquid. Developer. As the viscosity and density range of the developer, for example, a viscosity of 50 to 10,000 mPa · s and a density of 5% to 40% are used. As the carrier liquid, a highly insulating material such as silicone oil, normal paraffin, Isopar M (registered trademark), vegetable oil or mineral oil is used. Volatile and non-volatile can be selected according to the purpose, and the particle size of the toner can be selected from submicron to about 6 μm according to the purpose.

  The liquid developer 10 is fed from a not-shown adjustment tank to the developer storage tank 11 in the developing device 4 by the stirring / conveying screw 15 and stirred by the stirring / conveying screw 15.

  The developing roller 12 and the sweep roller 13 are each provided with an elastic body layer formed of urethane rubber or the like having conductivity on the outer peripheral surface thereof. The surface hardness of the elastic layer is preferably 50 degrees or less in terms of JIS-A hardness so that a nip can be efficiently formed with the photoreceptor 1. The material of the elastic body layer is not limited to urethane rubber, and may be any material that has conductivity and does not swell or dissolve with the carrier liquid or developer of the liquid developer 10. . Furthermore, the developing roller 12 and the sweep roller 13 have a surface having a smoothness of 3 μm or less with a ten-point average surface roughness Rz by using a coating or a tube.

  The developing roller 12 and the sweep roller 13 may be configured such that the surfaces thereof are conductive and do not swell or dissolve with the liquid developer, and the liquid developer does not contact the inner layer. For example, the material of the inner layer is not limited to the above-mentioned conductivity and swelling and dissolution, and may be elastic. In this case, it is necessary to apply the developing bias voltage to the developing roller 12 and the sweep bias voltage to the sweep roller 13 from the surface, not from the shaft of the developing roller 12 sweep roller 2.

  In addition, an elastic body layer may be provided on the surface of the photosensitive member 1 instead of an elastic body layer provided on the developing roller 12 or the sweep roller 13 side.

  The developing roller 12 and the sweep roller 13 are brought into contact with the photoreceptor 1 with an appropriate pressure, respectively, and elastic layers of the rollers 12 and 13 are elastically deformed to form a developing nip and a removal nip, respectively. ing. In particular, by forming the developing nip portion, it is possible to ensure a certain developing time for the developer toner to move and adhere to the photoreceptor 1 by the developing electric field in the developing region.

  Moreover, the nip width which is the width | variety of the surface moving direction in each nip part can be adjusted by adjusting a contact pressure. Each nip width is set to a numerical value equal to or greater than the product of the linear speed of each of the rollers 12 and 13 and the development time constant. Here, the development time constant is the time required until the development amount is saturated, and is obtained by dividing the necessary minimum nip width by the process speed. For example, if the required minimum nip width is 5 mm and the process speed is 500 mm / sec, the development time constant is 10 msec.

  Further, a cleaning blade 16 for removing the developer on the surface of the sweep roller 13 is provided. The cleaning blade 16 is composed of a metal blade or a rubber blade and is in contact with the surface of the sweep roller 13. A roller may be used instead of the blade.

In this developing device, during the developing operation, the liquid developer 10 is applied to the developing roller 12 by the coating device 14 to form a thin layer of the liquid developer 10. At this time, the liquid developer 10 is applied from the coating device 14 to the developing roller 12 so that the pigment content in the toner carried per 1 cm ² of the surface of the developing roller 12 is 3 μg or more and 60 μg or less. Therefore, the thin layer of the liquid developer has a thickness of 3 to 12 μm.

That is, when the coating thickness of the liquid developer 10 is such that the pigment content in the toner carried per 1 cm ^{2 of the} surface of the developing roller 12 is less than 3 μg, a sufficient amount of pigment is present on the photoreceptor 1. There is a risk that the image density of the image portion will become lighter without moving to the image portion of the latent image formed on the surface. On the other hand, when the pigment content in the toner carried per 1 cm ^{2 on the} surface of the developing roller 12 is larger than 60 μg, excess toner remains on the background after development, and the sweep roller 13 removes the toner. May be incomplete.

  The thin layer of the liquid developer 10 formed on the surface of the developing roller 12 develops the latent image on the photosensitive member 1 when passing through the developing nip formed by the photosensitive member 1 and the developing roller 12. . That is, in the image portion, the toner in the liquid developer 10 moves onto the photosensitive member 1, and in the background portion (non-image portion), the surface of the developing roller 12 is generated by an electric field formed by the developing bias potential and the photosensitive member potential. The electrostatic latent image is developed when the toner moves to the side and the toner does not adhere to the background portion.

  The developing portion of the photosensitive member 1 developed by the developing roller 12 faces the sweep roller 13 and does not move to the surface of the developing roller 12 at the background portion, but remains on the photosensitive member 1 side and causes toner (which causes fogging). Hereinafter, the “fog toner” is swept (cleaned) by the sweep roller 13.

  As described above, the sweep roller 13 is disposed downstream of the developing roller 12 in the rotation direction of the photosensitive member 1 and pressed against the photosensitive member 1 so as to sandwich the developed toner layer. The surface of the sweep roller 203 removes fog toner from the background while moving at a substantially constant speed with the surface of the photoreceptor 1.

  The liquid developer removed by the sweep roller 12 is removed by the cleaning blade 16 in order to maintain the sweep performance, and collected in an adjustment tank, where it is sent again into the developing unit after adjusting the density. It has become.

  In the adjustment tank, a part of the agitating / conveying screw 15 described above, concentration detection means and liquid amount detection means (not shown) are provided, and the concentration and liquid amount are detected with the concentration in the tank uniform. The density is adjusted by replenishing new liquid developer or replenishing carrier. The supply amount of the liquid developer into the developing device 4 from here is set so as to be slightly larger than the use amount of the liquid developer, and the overflow amount is returned to the adjustment tank. The agent always circulates.

  In addition, the developing device 4 includes a pre-development charger 17 that applies an electric field to the liquid developer 10 on the developing roller 12 before development in order to improve the developing ability of the liquid developer 10. A roller or the like can be used as means for applying an electric field before development.

  By applying an electric field to the liquid developer before such development, the liquid developer layer on the developer carrying member can be compressed and separated by the carrier layer during development. In this case, if there is a fine non-uniformity such as a rib in the thin layer of the liquid developer 10 on the developing roller 12 which is a developer carrying member, it is compressed as it is, and the non-uniformity is more emphasized. Therefore, in the method of performing pre-development charging, it is important to suppress the ribs and form a uniform thin layer of liquid developer.

Next, the coating device 14 for applying the liquid developer 10 to the surface of the developing roller 12 to form a thin layer will be described.
The coating device 14 is in contact with the coating roller 21 that is a coating member that carries the liquid developer 10 in the developer storage tank 11 and rotates in the direction of the arrow, and the coating roller 21 and the developing roller 12. Rotating in the direction indicated by the arrow of the developing roller 12 rotating in the direction indicated by the arrow in the direction opposite to the direction of rotation 21, the liquid developer 10 is transferred from the application roller 21 to the developing roller 12 for liquid development. An intermediate roller 22 which is an intermediate application member for retransfer applying the agent 10 and a cleaning blade 23 are provided.

  Here, as shown in FIG. 2, the application roller 21 is a roller in which fine engraving grooves 21a are formed in a uniform pattern on the surface thereof. As the shape of the engraving groove 21a, an oblique engraving groove 21a1 as shown in FIG. 3A, a turtle-shaped engraving groove 21a2 as shown in FIG. 3B, and as shown in FIG. 3C. The shape may be a lattice-shaped engraving groove 21a3 or the like.

  The application roller 21 rotates in the direction indicated by the arrow in FIG. 1 to attach the liquid developer 10 stored in the developer storage tank 11 to the surface, and an excess of the liquid developer 10 attached to the surface is removed. The liquid developer 10 is scraped off by the intermediate roller 22 which also serves as a doctor roller, and the liquid developer 10 is accurately measured in the engraving groove 21 a and transferred to the intermediate roller 22.

  That is, in a mechanism that uses a roller having a fine pattern with a uniform pattern on the surface as an application roller, and measures the amount of application by bringing a restriction member into contact therewith, a doctor blade and a doctor roller are used as the restriction member. May be used. The doctor blade has a disadvantage that it is worn and causes coating unevenness due to foreign matter mixed into the tip. However, since the doctor blade has a relatively simple structure, it is suitable for downsizing the apparatus. On the other hand, the doctor roller is more advantageous than the blade in terms of wear and clogging of foreign matter, but has a disadvantage that the apparatus becomes larger.

  Therefore, in the present embodiment, as described above, the intermediate roller 22 is also used as a doctor roller, and the intermediate roller 22 is contacted with a pressure sufficient to measure the pressure at the contact portion between the application roller 21 and the intermediate roller 22. The roller 22 is caused to function as a doctor roller.

  As described above, the intermediate roller 22 is interposed between the application roller 21 and the developing roller 12, and allows the liquid developer 10 attached to the surface of the application roller 21 to be applied to the application roller 21 at the same speed as the application roller 21. The liquid developer 10 is transferred onto the developing roller 12 which is a developer carrying member rotating in the same direction as the intermediate roller 22 while rotating in the opposite direction, and a uniform thin layer of the liquid developer 10 is transferred. Form.

  As shown in FIG. 4 (b), which is an enlarged view of part A in FIG. 4 (a), the intermediate roller 22 is provided with a fine convex part 22a having a mountain-shaped cross section continuously in the circumferential direction of the surface. By forming them at intervals, fine irregularities 22A (between the convex portions 22a become concave portions 22b) are formed.

  Here, the convex portion 22a has a first inclined surface 22a1 and a second inclined surface 22a2, and the inclination angle θ1 of the first inclined surface 22a1 is smaller than the inclination angle θ2 of the second inclined surface 22a2 ( θ1 <θ2) is formed, and the first inclined surface 22a1 is formed to be positioned on the front side in the rotation direction of the intermediate roller 22. Further, the unevenness 22A is formed so that the height (height of the step) h of the convex portion 22a is 10 μm or less and the pitch (pitch of the step) P of the convex portion 22a is 3 μm or less.

  The cleaning blade 23 is for removing the liquid developer 10 remaining on the surface of the intermediate roller 22, and this cleaning blade 23 is constituted by a metal blade or a rubber blade and comes into contact with the surface of the intermediate roller 22. I am letting. A roller may be used instead of the blade.

  As described above, in the coating device 14, the coating roller 21 that rotates while carrying a predetermined amount of the liquid developer 10 on the surface, and the surface that contacts the surface of the coating roller 21 and contacts the surface of the coating roller 21. The surface that moves at the same speed in the same direction as the surface of the application roller 21 and that contacts the surface of the development roller 12 to which the liquid developer 10 is applied and contacts the surface of the development roller 12 is the surface of the development roller 12. Since the intermediate roller 22 moving in the reverse direction is provided and the fine irregularities 22A are formed in the circumferential direction of the surface of the intermediate roller 22, the occurrence of short stripes (ribs) in the roller rotation direction can be suppressed. It becomes like this.

  That is, when a continuous test was performed on a coating apparatus having a configuration in which the intermediate roller 22 is used as a doctor roller with respect to the coating roller 21 as in the prior art, mechanical stress was found even after the end of 200,000 sheets. However, when the continuous test was continued, the surface of the intermediate roller 22 was scratched earlier than the surface of the developing roller 12. It turned out that the image quality was degraded and the rollers had to be replaced.

  Therefore, as described above, when a continuous test was performed by setting the surface roughness of the intermediate roller 22 to 3 μm or more with a 10-point average surface roughness Rz, scratches generated on the roller surface were rapidly reduced, and the life of the roller was extended. On the other hand, depending on the state of the roller surface, the state of occurrence of short streaks (ribs) in the roller rotation direction changes, and such ribs cause streak-like density on the image, particularly in the highlight portion. It has been found that unevenness may occur and image quality may be significantly reduced.

  Therefore, as a result of the present inventors outputting an image sample using an intermediate roller having various surface shapes, it is understood that the surface property of the surface of the intermediate roller has a great influence on the occurrence of this rib. It has been found that the ribs are hardly noticeable by forming fine irregularities 22A in the circumferential direction of the intermediate roller 22 as in the present embodiment.

  The reason why the rib becomes inconspicuous is assumed as follows. That is, as shown in FIG. 5, the liquid developer 10 that has passed through the nip between the application roller 21 and the intermediate roller 22 remains on the application roller 21 and the liquid developer 10 a that is transferred to the intermediate roller 22 at the exit of the nip portion. The liquid developer 10b is divided into two layers. At this time, it is considered that the trace of the liquid developers 10a and 10b attracting each other causes the rib. Therefore, if the surface of the intermediate roller 22 has fine irregularities 22A in the circumferential direction, it is presumed that the traces are cut off by the convex portions 22a and thus become inconspicuous.

  However, depending on the shape of the fine unevenness 22A on the surface of the intermediate roller 22, the shape of the unevenness 22A sometimes appears in the image.

  Therefore, a plurality of intermediate rollers 22 having different steps (height h of the protrusions 22a) and pitches (pitch P of the protrusions 22a) are produced to generate ribs and display the unevenness on the image. We evaluated the outing. The results are shown in Table 1.

  From the results in Table 1, the unevenness 22A that does not affect the image is a case where the height (step) h of the convex portion 22a is 10 μm or less and the pitch P of the convex portion 22a is 3 μm or less. I understand. That is, when the level difference h exceeds 10 μm, the difference in coating amount between the concave portion 22b and the convex portion 22a increases, and as a result, a pattern corresponding to the concave and convex portions 22A appears on the image. In addition, when the pitch P of the convex portions 22a of the irregularities 22 exceeds 3 μm, the pattern corresponding to the irregularities 22 is easily noticeable.

  As described above, since the liquid developer coating apparatus according to the present invention has fine irregularities formed in the circumferential direction of the surface of the intermediate coating member, the occurrence of ribs can be suppressed, and the quality can be stabilized stably. Thus, a thin layer of liquid developer can be applied and formed on the member to be coated.

  In this case, the fine unevenness of the intermediate coating member is such that the level difference is 10 μm or less and the pitch is 0.3 mm or less, so that a thin layer of liquid developer can be reliably and stably produced with high quality. Can be formed.

  In addition, when this liquid developer coating apparatus was used for the developing device 4 of the image forming apparatus and a continuous test was performed, the developing roller 12 showed that the intermediate roller 22 caused by mechanical stress even after completion of 400,000 sheets. It was confirmed that there was no image degradation due to scratches or image quality degradation due to ribs, and sufficient durability quality was obtained.

  In this case, as an image carrier, by using a photoconductor whose surface is formed of amorphous silicon (a-Si), it exhibits a mechanical strength superior to that of an organic photoconductor (OPC), The lifetime of the photoreceptor can be extended, and high-quality image formation can be stably performed.

Next, the relationship between the surface property of the application roller 21 and the ribs appearing on the image will be described.
As described above, when the liquid developer 10 is transferred from the application roller 21 to the intermediate roller 22, ribs are generated due to the two-layer division peculiar to the liquid generated at the nip portion. This rib is formed only by the surface shape of the intermediate roller 22. In addition, it is also affected by the groove shape (engraving groove 21a) of the anilox roller that is the application roller 21.

  That is, the engraving groove 21a of the application roller 21 can be formed in various shapes as described above because the application amount can be determined by its volume if it is a uniform pattern, as shown in FIG. In addition, the hatched engraving groove 21a1 (many groove patterns are formed in the 45 degree direction, but there are also those in the 60 degree direction), the turtle shell shaped engraving groove 21a2, and the lattice engraving groove 21a3 (30 In many cases, a groove pattern is formed in the direction of 60 degrees or 60 degrees).

  Using these application rollers 21 having different groove patterns, the occurrence of ribs on the application surface on the intermediate roller 22 was examined. As a result, the generation of ribs on the application surface was less noticeable in the order of inclined type, lattice type, and turtle shell type. It was confirmed that

  This is presumed that the more the patterns are arranged, the more the ribs are canceled out and the less noticeable. That is, if there is a directivity of the pattern, it is presumed that the ribs are canceled out and become inconspicuous.

  Therefore, at this time, the angle of the pattern of the inclined engraving groove 21a1 is also affected. That is, when the inclination angle is small and approaches the direction of the rib, the generation of the rib is promoted, and as the angle increases, the rib becomes less conspicuous.

  On the other hand, when the angle of inclination becomes large, the trace of the groove pattern of the application roller 21 (this is referred to as “platelet”) becomes conspicuous. Normally, when the plate is applied from the intermediate roller 22 to the developing roller 12 as a developer support, the surface of the intermediate roller 22 is moved in the direction opposite to the surface of the developing roller 12. In addition, the intermediate roller 22 is made inconspicuous by making the moving speed faster.

  However, if the angle of inclination increases, it becomes difficult to form a uniform coating surface even if a speed difference is made between the intermediate roller 22 and the developing roller 12, so that the angle of inclination is 30 degrees to 60 degrees. By making it within the range of the degree, the influence of the rib and the plate can be reduced.

  Therefore, in the present embodiment, by using the application roller 21 on which a 45-degree oblique line pattern is formed, the influence of ribs on the surface of the intermediate roller 22 can be suppressed as compared with other shapes.

  As described above, the application member is an anilox roller having a uniform groove on the surface thereof, and the groove pattern is an oblique line type, so that the generation of ribs can be further reduced.

Next, the relationship between the inclined surface of the irregularities 22A of the intermediate roller 22, the rotation direction, and the cleaning blade 23 will be described with reference to FIG.
As described above, the intermediate roller 22 has a function of applying the liquid developer 10 to the developing roller 12 that is a developer carrying member, and for removing the liquid developer 10 remaining on the developing roller 12 after development. It also has a function as a cleaning member.

  Since the solid concentration of the liquid developer 10 changes during development, high-quality image formation cannot be performed if the next development is performed with the liquid developer remaining on the developing roller 12 as it is. For example, if it is used for the next development without removing the remaining liquid developer, a so-called ghost phenomenon occurs in which the pattern of the image is reversed and placed on the image in the period of the developing roller 12, and the image quality is improved. Will be reduced.

  Therefore, the liquid developer 10 remaining on the surface of the developing roller 12 is removed using the intermediate roller 22, and further, the liquid developer transferred to the intermediate roller 22 is removed from the surface of the intermediate roller 22 by the cleaning blade 23. And collect.

  At this time, the cleaning blade 23 extends the edge 23a from the direction opposite to the rotation direction of the intermediate roller 22 as shown in FIG. In order to scrape off the liquid developer 10 on the surface of the intermediate roller 22 in contact with the surface of the intermediate roller 22, when the fine unevenness 22A is formed on the surface of the intermediate roller 22, if the edge 23a of the cleaning blade 23 is caught by the unevenness 22A, the intermediate roller 22 As a result of the rotation, not only abnormal noise is generated or a driving load of the intermediate roller 22 is generated, but also the edge 23a of the cleaning blade 23 is damaged and the cleaning performance is deteriorated.

  Therefore, in the present embodiment, as shown in FIG. 6B, the first inclined surface having a small inclination angle among the first and second inclined surfaces 22a1 and 22a2 of the convex portion 22a constituting the unevenness 22A. The unevenness 22A is formed so that 22a1 is positioned on the front side in the rotation direction of the intermediate roller 22, so that the cleaning blade 23 is not caught by the unevenness 22A.

  As described above, the fine unevenness of the intermediate coating member is a mountain shape with a cross-sectional shape and a different inclined surface, and the inclined surface with a small inclination angle is positioned on the front side in the rotation direction of the intermediate coating member, so that the cleaning blade can be used. Even in such a case, the intermediate application member can be smoothly rotated, and the edge of the cleaning blade is not damaged, so that the cleaning performance can be maintained.

  This also makes it easy to always apply a new liquid developer. Therefore, when used in an image forming apparatus, it is possible to remove the developer remaining on the developing roller from the intermediate coating member, thereby preventing ghosts and reducing the mechanical burden on the developing roller. Therefore, high quality images can be obtained stably.

Next, a specific configuration of the intermediate roller 22 will be described with reference to FIG. In addition, the figure is sectional explanatory drawing which shows the structure of the intermediate roller.
The intermediate roller 22 is formed by laminating an elastic layer 122b made of an elastic material such as rubber and a slipping layer 122c made of a material of a low friction member covering the surface of the elastic layer 122b around the core metal 122a. It has a two-layer structure.

  That is, it is preferable that the intermediate roller 22 is in uniform contact with the application roller 21 in the axial direction in order to uniformly deposit the liquid developer 10. Therefore, for example, an elastic layer 122b having elasticity such as rubber is provided. On the other hand, the intermediate roller 22 rotates in such a direction that the surfaces thereof move in opposite directions at the contact portion with the developing roller 12 that is a member to be coated, so that the elastic layer 122b made of rubber or the like having a large friction coefficient. If the surface is exposed to the surface as it is, a large frictional resistance is generated at the contact portion, which increases the load on the drive system and the life of the roller. Therefore, it is preferable to cover the surface of the elastic layer 122b with a slipping layer 122c made of a low friction member.

  In the present embodiment, the intermediate roller 22 has a coating agent containing fluororesin, for example, PTFE, PFA, PVDF, PVF, etc. on the surface of an elastic layer (hardness JIS-A 40 degrees) 122b formed of urethane resin. A film in which a sliding layer 122c is formed by coating with a thickness of ˜50 μm is used. As a method for coating the slipping layer 122c, there are dipping and spraying, but the method may be selected according to the material of the elastic material and the material of the coating material.

  The slipping layer 122c can be formed by covering with a PFA tube or the like, but in this case, the fine uneven shape on the surface of the intermediate roller 22 is determined by the surface property of the tube. However, it is difficult to control the fine shape of the surface of such a tube material, and as a result, it becomes difficult to control the fine shape of the surface of the roller.

  As described above, the intermediate roller has an elastic layer and a slipping layer coated on the surface of the elastic layer, thereby maintaining the uniformity of the contact surface between the intermediate roller and the application roller, and the application target member. The mechanical load caused by sliding can be reduced. Moreover, it becomes easy to make the surface into a fine concavo-convex shape by forming the surface slipping layer by coating instead of a tube.

Next, a method for manufacturing the intermediate roller 22 having such a two-layer structure will be described.
In order to form fine irregularities 22A on the surface of the intermediate roller 22 having a two-layer structure, fine irregularities are formed on the surface of the inner elastic layer, and an outer slipping layer is formed following the irregularities. A method of causing fine irregularities 22A to appear on the surface of the intermediate roller 22, or a method of forming the irregularities 22A by a coating method of a slipping layer or processing after coating may be considered.

  The intermediate roller 22 according to the present embodiment forms irregularities by processing the surface of the elastic layer 122b, and forms a slipping layer 122c on the surface of the elastic layer 122b, thereby corresponding to the irregularities on the surface of the elastic layer 122b. Concavities and convexities 22A are formed on the surface of the slipping layer 122c.

  That is, in order to manufacture the intermediate roller 22, a rubber layer serving as the elastic layer 122b is formed around the core metal 122a, and then the surface of the rubber layer is polished to form irregularities on the surface. Accordingly, as shown in FIG. 8, one of the surface irregularities can be formed into a gentle inclined surface depending on the polishing direction.

  At this time, since the surface shape after coating the slipping layer 122c changes substantially in proportion to the surface shape of the elastic layer 122b before coating, the elastic layer 122b is polished in advance in consideration of the amount of change. Thus, by coating the surface of the elastic layer 122b with the slippery layer 122c, the surface shape of the slippery layer 122c follows the surface shape of the male layer 122b, and the required fine irregularities 22A are formed on the surface of the intermediate roller 22. be able to.

  On the other hand, it is conceivable that the surface is formed in an uneven shape when coating the slipping layer, but in general, since the coating layer is formed in accordance with the underlying shape, the film It is practically difficult to form unevenness by locally controlling the thickness. In addition, it is conceivable to process the surface into an uneven shape after coating the slipping layer, but the slipping layer that is the coat layer may be peeled off by processing (for example, polishing) of the slipping layer. The top is difficult.

  Therefore, as described above, after forming fine irregularities on the surface of the elastic layer, coating the slippery layer and forming the slippery layer following the irregularities on the surface of the elastic layer, the surface of the intermediate roller By forming the unevenness, the step shape can be controlled stably, and the fine unevenness can be formed relatively easily.

  Further, in order to improve the developing ability of the liquid developer, the developing device 4 applies an electric field to the pre-development charger 17 and the pre-development 10 such as a roller (not shown) with respect to the liquid developer on the developer carrying band. Means are provided.

  With such a configuration, the liquid developer layer can be compressed and separated by the carrier layer during development.

  As described above, by providing a means for applying an electric field before development on the developer support, the fine non-uniformity generated on the coated surface is maintained by the rib generated on the developer support. It is possible to suppress the non-uniformity from being emphasized by compressing the image as it is.

  The inventor manufactured an image forming apparatus using the above-described liquid developer coating apparatus as a developing device, and applied an electric field from the pre-development charger 17 to the thin layer of the liquid developer 10 on the developing roller 12 before development. However, when a continuous test was performed, image quality deterioration due to scratches on the intermediate roller 22 of the coating device 13 due to mechanical stress and image quality degradation due to ribs were not observed even after completion of 400,000 sheets, and sufficient durability quality was achieved. It was confirmed that it was obtained.

1 is a schematic configuration diagram of a main part of an image forming apparatus according to the present invention. It is front explanatory drawing of the coating roller used for the coating device which concerns on this invention of the image forming apparatus. It is expansion perspective explanatory drawing which shows the example from which the shape of the engraving groove | channel of the surface of the coating roller of the coating device differs. It is explanatory drawing with which it uses for description of the surface shape of the intermediate | middle roller of the coating device. It is a principal part expansion explanatory drawing used for description of the generation | occurrence | production process of the rib in the coating device. It is explanatory drawing with which it uses for description of the relationship between the same intermediate | middle roller and a cleaning blade. It is sectional explanatory drawing which shows an example of a structure of the same intermediate | middle roller. It is explanatory drawing with which it uses for description of the manufacturing process of the intermediate roller.

Explanation of symbols

1 ... Photoconductor (latent image carrier)
DESCRIPTION OF SYMBOLS 2 ... Charger 3 ... Exposure apparatus 4 ... Developing apparatus 5 ... Transfer apparatus 6 ... Static elimination lamp 7 ... Cleaning apparatus 11 ... Liquid developer storage tank 12 ... Developing roller (developer carrier)
13 ... Sweep roller 14 ... Application device 21 ... Application roller 22 ... Intermediate roller

Claims (2)

A coating member that rotates while carrying a predetermined amount of liquid developer on the surface;
In a liquid developer coating apparatus comprising an intermediate coating member interposed between the coating member and a rotating coated member to which the liquid developer is coated,
On the surface of the intermediate application member,
Convex and convexities are formed in which the inclined surface with a small inclination angle is located on the front side in the rotation direction of the intermediate coating member in a mountain shape with a different cross-sectional shape in the circumferential direction,
An apparatus for applying a liquid developer, comprising: an elastic layer; and a slipping layer coated on the surface of the elastic layer . An image forming apparatus characterized by comprising a coating equipment of the liquid developer according to claim 1.

Images