JP2007171601A - Image forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming method for obtaining an image of high quality by appropriately determining a voltage to be applied to a compression roller and a voltage to be applied to a developing roller. <P>SOLUTION: In the image forming method by the image forming apparatus equipped with the developing roller that carries liquid toner with toner dispersed in carrier liquid, a photoreceptor for forming a latent image to be developed by the developing roller, the compression roller for compressing the liquid toner on the developing roller in a position before the image on the photoreceptor is developed by the developing roller, and an intermediate transfer body to which the toner image on the photoreceptor is transferred, data with the combination of the apply voltage value of the compression roller and the apply voltage value of the developing roller are stored in a plurality of memories, and referring to the memories, a patch is formed on the intermediate transfer body while changing a set of the apply voltage value of the compression roller and the apply voltage value of the developing roller, then, the voltage value to be applied to the compression roller and the voltage value to be applied to the developing roller are set based on the patch density. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming method using liquid toner in which toner is dispersed in a carrier liquid.

As a prior art of an image forming method using liquid toner, Japanese Patent Laid-Open No. 2002-278291 discloses a developing roller before development in an image forming method in which a latent image on a photoreceptor is developed by a developing roller carrying liquid toner. A compression roller for compressing the liquid toner is applied, and independent voltages are applied to the developing roller and the compression roller, respectively, so that the applied voltage of the compression roller is greater than the applied voltage of the developing roller. An image forming method that prevents density unevenness and obtains a high-quality image is disclosed.
JP 2002-278291 A

  As shown in FIGS. 3 and 5-C, the toner layer on the developing roller is compressed to form a film, so that the toner layer is easily moved in the subsequent development / transfer process, and high development / transfer efficiency is achieved. A turbulent image can be obtained. In order to obtain an appropriate compressed state, it is necessary to adjust the voltage difference between the developing roller and the compressing roller and appropriately set the strength of the electric field that presses the toner from the compressing roller to the developing roller. On the other hand, toner characteristics may change due to toner deterioration due to long-term operation, environmental influences, or when toner of a different manufacturing rod is replenished, and the manner in which the electric field is compressed changes. For this reason, if the potential difference between the compression roller and the developing roller is constant (unless adjusted), the compression state changes due to a change in toner characteristics. As a result, problems such as density unevenness due to ribs, poor cleaning, and poor development occur.

If the electric field pressing the toner from the compression roller to the developing roller is too weak, the compression is insufficient and the following problems occur.
As shown in FIG. 4A, the movement of the toner particles to the developing roller side is insufficient, and part of the toner particles adhere to the compression roller, and the toner particles on the developing roller are insufficient. At this time, since toner particles are present at the interface where the liquid crys at the exit of the compression roller nip, the liquid containing the toner particles causes stringing, and striped unevenness called a rib occurs.
Even when the toner particles are properly compressed as shown in FIG. 3 and there are no toner particles at the interface, it seems that stringing has occurred. However, in this case, only the carrier liquid that does not contain toner particles causes stringing. Must not. In addition, since the carrier liquid has a low viscosity, the stringing is fine, and since it is almost Newtonian and has high fluidity, the unevenness is immediately flattened. However, since the liquid containing toner particles has a higher viscosity than that of the carrier liquid alone, the unevenness due to stringing is large and difficult to flatten, so that the unevenness remains as striped unevenness.
As shown in FIG. 4-B, the electric field of the compression roller is a little stronger, and even if the toner particles move to the developing roller side to such an extent that the toner particles do not adhere to the compression roller, the toner particles are insufficiently compressed to the developing roller side. If this is the case, toner particles are present near the tearing interface of the carrier liquid at the exit of the compression roller nip, so that ribs are also formed by thread drawing.
Even if the rib does not occur in the compression roller nip, the pressed toner layer is diffused again, and the rib may be generated in a downstream process (development or primary transfer nip).

When the electric field that presses the toner from the compression roller to the developing roller is too strong, the compaction is excessive and the following problems occur.
As shown in FIG. 5D, the toner particles are excessively pressed against the developing roller, and the toner particles adhere firmly to the surface of the developing roller. As a result, some of the toner particles are not peeled off from the developing roller at the developing nip, resulting in poor development.
For the same reason, toner particles are not peeled off from the developing roller at the cleaning portion of the developing roller, resulting in poor cleaning.
In addition, the movement behavior of the toner layer formed into a film after compaction may fluctuate due to the change in the toner characteristics, and it is necessary to apply an appropriate development voltage accordingly.
If the voltage of the developing roller is too low, the amount of development is insufficient, or the pressing force of the toner on the photosensitive member at the developing nip is insufficient, so that toner particles are present near the tearing interface of the liquid at the developing nip exit. The image is disturbed by the ribs. Due to these problems, the patch density is lower than specified.

  An object of the present invention is to provide an image forming method for obtaining a high-quality image by setting an appropriate compression roller applied voltage and developing roller applied voltage to solve the above-mentioned problems.

  In order to solve the above problems, the first invention provides a developing roller for carrying a liquid toner in which a toner is dispersed in a carrier liquid, a photoreceptor on which a latent image developed by the developing roller is formed, and the developing In an image forming method by an image forming apparatus, comprising: a compression roller that compresses liquid toner of the developing roller at a position before development of the roller on the photosensitive member; and an intermediate transfer member to which the toner image of the photosensitive member is transferred. An intermediate transfer member having a plurality of combinations of roller application voltage values and development roller application voltage values in a memory, and referring to the memory while changing the compression roller application voltage value and the development roller application voltage value as a set. A patch is formed thereon, and an applied voltage value of the compression roller and an applied voltage value of the developing roller are set based on the patch density.

  The second invention is characterized in that, in the image forming method of the first invention, the position for detecting the density of the patch is located downstream of the squeeze roller of the intermediate transfer member.

  According to the third aspect of the present invention, in the image forming method according to the first or second aspect of the present invention, the applied voltage of the compression roller is a combination of the applied voltage value of the compression roller and the applied voltage value of the developing roller that provides a predetermined patch density. A combination is adopted in which the voltage difference between the value and the applied voltage value of the developing roller is as low as possible.

  According to a fourth aspect of the present invention, in the image forming method according to any one of the second to third aspects of the present invention, an applied voltage difference between the electrode facing the squeeze roller and an applied voltage difference between the compression roller and the developing roller is made smaller. Features.

According to the configuration of the first aspect of the present invention, the compression roller application voltage value and the development roller application voltage value are simultaneously changed as a set with respect to fluctuations in toner characteristics, thereby maintaining an appropriate compression state and an appropriate development condition. Therefore, it is possible to obtain a high-quality image without causing the problem described in the above problem.
With the configuration of the second invention, it is possible to remove the excess carrier with a squeeze roller, and further perform the patch density sensing in a state where the toner particles are firmly formed into a film by pressing the floating toner particles in the carrier against the substrate. Stable measurement is possible.
With the configuration of the third aspect of the invention, the following problems can be prevented from occurring. That is, even if the patch density is appropriate, if the voltage difference between the compression roller application voltage value and the development roller application voltage value is too large, the toner particles are pressed too hard against the development roller and are difficult to peel off from the development roller, resulting in poor development or cleaning. May cause defects. Therefore, the occurrence of these problems can be prevented by selecting a voltage value as low as possible from the voltage value range in which an appropriate concentration can be obtained.
According to the configuration of the fourth aspect of the invention, appropriate squeezing can be performed without pressing the toner layer too much.

  Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram illustrating a main configuration of an image forming apparatus according to an embodiment of the present invention.

The intermediate transfer belt 70 is an endless belt stretched around a belt driving roller 82 and a driven roller 85, and is rotationally driven while being in contact with the photoreceptors 20Y, 20M, 20C, and 20K. Four primary transfer units 60Y, 60M, 60C, and 60K including the intermediate transfer belt 70, the primary transfer backup rollers 61Y, 61M, 61C, and 61K and the photoconductors 20Y, 20M, 20C, and 20K are arranged on the intermediate transfer belt 70. The color liquid toners are sequentially superimposed and transferred to form a full color liquid toner image. A squeeze roller 15, a squeeze roller blade 16, a squeeze roller cleaning liquid recovery unit 17, and a backup roller 18 are arranged at a position before the secondary transfer of the intermediate transfer belt 70, and a patch sensor 19 is arranged downstream thereof.
The squeeze roller 15 may be provided not only after the K unit as shown in the figure but also after the primary transfer of each color unit. Further, it may be provided on the photoreceptor.

  The secondary transfer unit 80 includes a secondary transfer roller 81, an intermediate transfer belt driving roller 82, a secondary transfer roller blade 83, and a secondary transfer roller cleaning liquid recovery unit 84, and is formed on the intermediate transfer belt 70. A liquid toner image or a full-color liquid toner image is transferred to a paper recording medium.

  A fixing unit (not shown) is a device for fusing a single color liquid toner image or a full color liquid toner image transferred onto a recording medium onto the recording medium to form a permanent image.

  The developing units 50Y, 50M, 50C, and 50K have a function of developing a latent image with yellow (Y) liquid toner, magenta (M) liquid toner, cyan (C) liquid toner, and black (K) liquid toner, respectively. ing.

  The developing units 50Y, 50M, 50C, and 50K are roughly supplied with developing toner containers 53Y, 53M, 53C, and 53K that store the liquid toners, and supply the liquid toners from the developing toner containers to the developing rollers 54Y, 54M, 54C, and 54K. Toner supply rollers 51Y, 51M, 51C, 51K, photoconductors 20Y, 20M, 20C, 20K charging units 30Y, 30M, 30C, 30K, and exposure unit 40Y for forming an electrostatic latent image on the charged photoconductor , 40M, 40C, 40K.

  Since the developing units 50Y, 50M, 50C, and 50K have the same configuration, the developing unit 50K will be described below.

  As shown in FIG. 1, a charging unit 30K, an exposure unit 40K, and a primary transfer unit 60K are mainly arranged along the rotation direction of the photoconductor 20K. The photoconductor 20K includes a cylindrical base material and a photosensitive layer formed on the outer peripheral surface thereof, and can rotate around a central axis. In the present embodiment, the photoconductor 20K rotates clockwise.

  The charging unit 30K is a device for charging the photoconductor 20K. The exposure unit 40K has a semiconductor laser, a polygon mirror, an F-θ lens, and the like, and irradiates the modulated laser onto the charged photoconductor 20K to form a latent image.

  The developing unit 50K is a device for developing the latent image formed on the photoconductor 20K using black (K) liquid toner. The developing unit 50K will be described later.

  The primary transfer unit 60K is a device for transferring the black liquid toner image formed on the photoreceptor 20K to the intermediate transfer belt 70.

  FIG. 2 is a cross-sectional view showing main components of the developing unit 50K. The developing toner container 53K contains black liquid toner for developing the latent image formed on the photoreceptor 20K. In the liquid toner used in this embodiment, solid particles having an average particle diameter of 1 μm in which a colorant such as a pigment is dispersed in a thermoplastic resin are dispersed in a liquid solvent such as an organic solvent, silicon oil, mineral oil, or edible oil. It is a non-volatile liquid toner at room temperature with a high viscosity (about 30 to 10000 mPa · s) that is added together with the agent and has a toner solid content concentration of about 25%.

  Liquid toner is supplied from the developing toner container 53K to the developing roller 54K by the toner supply roller 51K. The toner supply roller 51K is a cylindrical member, and is an aniloc roller that rotates clockwise as shown in FIG. 2 and has fine and uniform spiral grooves formed on the surface. The groove dimensions are such that the groove pitch is about 130 μm and the groove depth is about 30 μm.

  The toner regulating blade 52K includes a rubber portion made of urethane rubber or the like that contacts the surface of the toner supply roller 51K, and a metal plate that supports the outer rubber portion, and scrapes off the liquid toner remaining on the toner supply roller 51K. Remove.

  The developing roller 54K is a cylindrical member, and rotates counterclockwise around the central axis as shown in FIG. The developing roller 54K is provided with an elastic body such as conductive urethane rubber, a resin layer, and a rubber layer on the outer periphery of an inner core made of metal such as iron. The developing roller 54K is provided with a developing roller blade 58K and a developing roller cleaning liquid recovery unit 59K. The developing roller blade 58K is made of rubber or the like that contacts the surface of the developing roller 54K, and scrapes and removes the liquid toner remaining on the developing roller 54K. The developing roller cleaning liquid recovery unit 59K is a container for storing liquid toner scraped off by the developing roller blade 58K.

  The compression roller 55K is a cylindrical member, rotates around the central axis, and includes a conductive resin or rubber layer on the surface layer of the metal roller. As shown in FIG. 2, the rotation direction is clockwise in the direction opposite to the developing roller 54K. A voltage is applied to the compression roller 55K separately from the developing roller 54K, and a potential difference is provided between the two rollers. The compression roller blade 56K is made of rubber or the like that contacts the surface of the compression roller 55K, and scrapes off and removes the liquid toner remaining on the compression roller 55K. The compression roller cleaning liquid recovery unit 57K is a container for storing liquid toner scraped off by the compression roller blade 56K.

  The photoconductor 20K is a cylindrical member that is wider than the developing roller 54K and has a photosensitive layer formed on the outer peripheral surface thereof, and rotates clockwise around the central axis as shown in FIG. The photosensitive layer of the photoreceptor 20K is composed of an organic photoreceptor or an amorphous silicon photoreceptor.

  The charger 30K is provided upstream of the nip portion between the photoconductor 20K and the developing roller 54K. The charger 30K is applied with a bias having the same polarity as the liquid toner from a power supply device (not shown), and charges the photoconductor 20K. The charged photoconductor 20K is irradiated with laser from the exposure unit 40K to form a latent image. The formed latent image is developed by the developing roller 54K and is primarily transferred to the intermediate transfer belt 70 in the primary transfer unit 60K.

  Next, the operation of such an image forming apparatus will be described. Subsequently, the developing unit will be described by taking the developing unit 50K of the four developing units as an example.

  The liquid toner in the developing toner container 53K has a solid content concentration of 25%, a viscosity of 30 to 10,000 mPa · s, and the toner particles have a positive charge. The liquid toner is pumped up from the developing toner container 53K as the toner supply roller 51K rotates. The toner regulating blade 52K is in contact with the surface of the toner supply roller 51K, leaves the developer in the groove formed on the surface of the toner supply roller 51K, and scrapes off other excess developer. The amount of liquid toner supplied to the developing roller 54K is regulated. According to this regulation, the film thickness of the liquid toner applied to the developing roller 54K is quantified so as to be 6 μm. The liquid toner scraped off by the toner regulating blade 52K falls into the developing toner container 53K due to gravity.

  The developing roller 54K coated with liquid toner contacts the compression roller 55K downstream of the nip portion with the toner supply roller 51K. A voltage of +300 to +500 V is applied to the developing roller 54K. A voltage 200 to 500 V higher than the applied voltage of the developing roller 54K is applied to the compression roller 55K. That is, if the applied voltage of the developing roller 54K is + 400V, the applied voltage of the compression roller 55K is +600 to + 900V. Therefore, when the toner on the developing roller 54K passes through the nip with the compression roller 55K, the toner moves to the developing roller 54K side, and only the carrier liquid containing almost no toner particles is collected in the compression roller 55K. As a result, the toner particles are gently coupled to form a film. As a result, the toner moves quickly in the developing unit, and the image density is improved.

  The compression roller 55K rotates in the follower direction at a constant speed with respect to the surface of the developing roller 54K. However, the rotational speed and direction of the compression roller 55K may be different from the rotational speed of the developing roller 54K, or may be rotated in the counter direction facing the surface of the developing roller 54K. The compression roller blade 56K contacts the compression roller 55K. However, the compression roller blade 56K may not be provided. In this case, the carrier having a constant film thickness is held on the compression roller 55K, and the carrier amount of the toner layer on the developing roller 54K does not change before and after the nip with the compression roller 55K.

  The photoreceptor 20K uses amorphous silicon, and charges the surface to about +600 V by applying about +5.5 kV to the wire of the corona charger 30K upstream of the nip portion with the developing roller 54K. After charging, a latent image is formed by the exposure unit 40K so that the potential of the image portion becomes + 25V. In the developing nip portion formed between the developing roller 54K and the photoconductor 20K, a bias + 400V applied to the developing roller 54K and a latent image (image portion + 25V, non-image portion + 600V) applied to the photoconductor 20K are formed. According to the electric field, the toner particles selectively move to the image portion on the photoconductor 20K. Thereby, a toner image is formed on the photoconductor 20K. Since the carrier liquid is not affected by the electric field, it is separated at the exit of the developing nip between the developing roller 54K and the photoconductor 20K, and adheres to both the developing roller 54K and the photoconductor 20K.

  The photosensitive member 20K that has passed through the developing nip portion passes through the nip portion with the intermediate transfer belt 70, and primary transfer is performed. The primary transfer backup roller 61K is applied with a voltage of about −200 V having the opposite polarity to the charging characteristics of the toner particles, and the toner particles on the photoconductor 20K are primarily transferred to the intermediate transfer belt 70 and transferred to the photoconductor 20K. Only the carrier liquid remains. The carrier liquid remaining on the photoconductor 20K is scraped off by the photoconductor blade 21K downstream of the primary transfer unit and collected by the photoconductor cleaning liquid collection unit 22K.

  The toner image primarily transferred onto the intermediate transfer belt 70 by the primary transfer unit 60K is directed to the secondary transfer unit 80. However, as shown in FIG. 1, before the secondary transfer nip portion, the toner image is transferred onto the intermediate transfer belt 70. A squeeze roller 15, a squeeze roller blade 16, a squeeze roller cleaning liquid recovery unit 17, and a backup roller 18 are disposed for scraping off excess carriers. A voltage of +150 V is applied to the squeeze roller 15 and the backup roller 18 is maintained at 0 V, and an electric field that presses the toner particles against the intermediate transfer belt 70 is generated. Therefore, only the carrier liquid that does not have toner particles attached to the squeeze roller 15 and is not affected by the electric field is cried and collected between the intermediate transfer belt 70 and the squeeze roller 15. If the voltage difference between the squeeze roller 15 and the backup roller is smaller than the voltage difference between the compression roller 55K and the developing roller 54K, appropriate squeezing can be performed without excessively pressing the toner layer against the intermediate transfer belt 70.

  In the secondary transfer unit 80, a voltage of −1000 V is applied to the secondary transfer roller 81, and the intermediate transfer belt drive roller 82 is maintained at 0 V. The toner particles on the intermediate transfer belt 70 are paper or the like. Secondary transferred to a recording medium.

  In the image forming process by such an image forming apparatus, toner characteristics may change due to toner deterioration due to long-term operation, environmental influences, toner supplied from different manufacturing rods, etc. Will change. For this reason, if the potential difference between the compression roller 55K and the development roller 54K is constant (unless adjusted), the compression state changes due to a change in toner characteristics, causing problems such as density unevenness due to ribs, cleaning failure, and development failure. . In addition, the movement behavior of the toner layer formed into a film after compression may change due to the change in the toner characteristics, and it is necessary to apply an appropriate development voltage accordingly.

  In order to solve such problems, in the image forming method of the present invention, combinations shown in Table 1 are held in the memory with respect to the applied voltage value of the compression roller 55K and the applied voltage value of the developing roller 54K.

With reference to Table 1, the applied voltage values of the developing roller 54K and the compression roller 55K are changed as a set, and a solid pattern patch as shown in FIG. 6A is formed on the intermediate transfer belt 70. By measuring the patch density by the patch sensor 19 downstream of the squeeze roller 15 of the intermediate transfer belt 70, the excess carrier is removed by the squeeze roller 15, and the floating toner particles in the carrier are pressed against the base material. The patch concentration can be measured while the particles are firmly formed into a film, and stable measurement is possible.
The patch density at that time, that is, the signal intensity of the patch sensor is as shown in FIG. The measurement results shown in FIG. 7 are shown in Table 2 below.

  Among the combinations C, D, E, and F of the applied voltage value of the developing roller 54K and the applied voltage value of the compression roller 55K that have obtained the specified density shown in FIG. That is, an applied voltage value of 350 V for the developing roller 54K and an applied voltage value of 650 V for the compression roller 55K are selected.

  Setting of the applied voltage value of the compression roller 54K and the applied voltage value of the developing roller 54K by creating a patch in the image forming method of the present invention is normally performed when the apparatus is activated and after printing a certain number of sheets. In the present embodiment, the patch is executed every time 100 sheets are printed in A4 conversion. Also, it may be operated at regular intervals, or may be operated by user selection, or temperature and humidity may be monitored and operated according to changes. Further, it may be operated when the toner is replenished from the outside.

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Explanation of symbols

15: squeeze roller, 16: squeeze roller blade, 17: squeeze roller cleaning liquid recovery unit, 18: (squeeze unit) backup roller, 19: patch sensor 20Y, 20M, 20C, 20K: photoconductor 21K: photoconductor blade, 22K : Photoconductor cleaning liquid recovery unit 30Y, 30M, 30C, 30K: Corona charger 40Y, 40M, 40C, 40K: Exposure unit 50Y, 50M, 50C, 50K: Development unit 51Y, 51M, 51C, 51K: Toner supply roller 53Y 53M, 53C, 53K: Development toner containers 54Y, 54M, 54C, 54K: Development roller 52K: Toner regulating blade, 55K: Compression roller, 56K: Compression roller blade, 57K: Compression roller cleaning recovery unit, 58K: Development roller blur 59K: Development roller cleaning liquid recovery unit 60Y, 60M, 60C, 60K: Primary transfer unit 61Y, 61M, 61C, 61K: Primary transfer backup roller 70: Intermediate transfer belt

Claims (4)

A developing roller carrying liquid toner in which toner is dispersed in a carrier liquid; a photosensitive member on which a latent image developed by the developing roller is formed; and the developing roller at a position of the developing roller before development on the photosensitive member In an image forming method using an image forming apparatus comprising a compression roller for compressing the liquid toner and an intermediate transfer member to which the toner image of the photosensitive member is transferred, a combination of an applied voltage value of the compression roller and an applied voltage value of the developing roller Data is stored in a plurality of memories, and patches are formed on the intermediate transfer member while changing the applied voltage value of the compression roller and the applied voltage value of the developing roller as a set by referring to the memory, and the compression roller is based on the patch density. And an applied voltage value of the developing roller are set. 2. The image forming method according to claim 1, wherein a position at which the density of the patch is detected is located downstream of a squeeze roller of the intermediate transfer member. Among the combinations of the applied voltage value of the compression roller and the applied voltage value of the developing roller that have obtained a predetermined patch density, a combination in which the voltage difference between the applied voltage value of the compressing roller and the applied voltage value of the developing roller is as low as possible is adopted. The image forming apparatus according to claim 1, wherein: 4. The image forming method according to claim 2, wherein an applied voltage difference between the squeeze roller and an electrode facing the squeeze roller is made smaller than an applied voltage difference between the compression roller and the developing roller.

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