JP2008262085A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of forming an image of high image quality even onto a recording member that has large recesses and projections as in an embossed surface, by forming, with a simple method, a latent image corresponding to a toner image to be transferred onto the recording member, thereby uniformizing the action of pressure and an electric field between the intermediate transfer belt and the recesses and projections of the recording member. <P>SOLUTION: The image forming apparatus is configured so that toner images formed on an electrostatic latent image carrier are primarily transferred onto an intermediate transfer belt in or near a primary transfer nip, formed between the electrostatic latent image carrier and a primary transfer member via the intermediate transfer belt, by the application of electric field and pressure, and then the toner images transferred onto the intermediate transfer belt are transferred to a recording member in a secondary transfer section all at once by the application of electric field and pressure. This image forming apparatus includes a charge application member 12 disposed upstream of the secondary transfer nip in order to apply charges of the same polarity as toner to the projecting part of the toner image forming face of the recording member 8 according to image data. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to control of a transfer process for improving image quality of an image forming apparatus using an intermediate transfer belt in a copying machine, a printer, a facsimile machine or a complex machine using an electrophotographic system.

  In a conventional color electrophotographic image forming apparatus using an intermediate transfer belt, toner formed on a plurality of electrostatic latent image carriers is transferred to each electrostatic latent image carrier and each intermediate transfer belt. In the vicinity of the primary transfer nip, pressure and electric force are applied to the toner to sequentially superimpose and transfer onto the intermediate transfer belt, and then secondary transfer is performed collectively on a recording member such as paper, followed by pressurization and heating. After passing through the fixing work, a final color image is obtained.

  By the way, in order to obtain a high-quality image, the toner image formed on the electrostatic latent image carrier is not excessively or deficient, and is accurately superimposed on the latent image on the electrostatic latent image carrier to accurately transfer the intermediate image. It is necessary to transfer onto the belt and finish the fixing process while maintaining this state.

  The so-called intermediate transfer belt method, in which the toner image formed on the electrostatic latent image carrier is once transferred onto the intermediate transfer belt and then collectively transferred onto the recording member, the so-called intermediate transfer belt method has a recording member in comparison with the direct transfer method. Generally, the image quality is good.

  However, in the case of a recording member whose surface has been embossed and has concavities and convexities, the transfer of toner is difficult to occur in the recesses, image loss may occur, and image quality may be greatly impaired. As one of the causes, it is conceivable that transfer from the intermediate transfer belt to the recording member (secondary transfer) hardly occurs because the pressure during the secondary transfer is insufficient in the concave portion. Therefore, several methods have been proposed as countermeasures for this (Patent Documents 1 and 2).

  In Patent Document 1, in order to improve the followability of the intermediate transfer belt with respect to the concave portion of the recording member, the transferability to a recording member having large irregularities is improved by adjusting the Young's modulus and hardness of the constituent members of the intermediate transfer belt. However, in this method, in order for the intermediate transfer belt to follow the unevenness of the image forming surface of the recording member, the width of the concave portion needs to be larger than a certain value, so that it is not possible to cope with any recording member. Absent.

In Patent Document 2, the toner charge amount on the intermediate transfer belt is adjusted by discharge before secondary transfer to increase the secondary transfer rate, improve transferability to non-smooth paper, and improve image quality. In this method, the transferability to a recording member having large irregularities (for example, irregularities of about 50 μm) cannot be sufficiently improved.
JP 2006-267951 A JP 2004-109575 A

  The present invention has been made in view of the above-described conventional problems, and an object thereof is to form a latent image corresponding to a toner image transferred onto a recording member by a simple method. This makes it possible to achieve high image quality even on recording members with large irregularities, such as those with embossed surfaces, by uniformizing the action of the electric field and pressure created on the concave and convex portions of the intermediate transfer belt and recording member. An object of the present invention is to provide an image forming apparatus capable of forming an image.

  In order to achieve the above object, the invention described in claim 1 is directed to transferring a toner image formed on an electrostatic latent image carrier through an intermediate transfer belt between the electrostatic latent image carrier and a primary transfer member. In the primary transfer nip formed in the vicinity of the intermediate transfer belt, the toner image transferred onto the intermediate transfer belt is subjected to primary transfer using an electric field and pressure on the intermediate transfer belt. In the image forming apparatus that collectively transfers to the recording member using pressure, the toner image forming surface of the recording member has the same polarity as the toner on the upstream side of the secondary transfer nip according to the image data. It is characterized by comprising a charge imparting member that imparts a charge.

  According to a second aspect of the present invention, each color toner image formed on a plurality of electrostatic latent image carriers is formed between each of the electrostatic latent image carriers and each primary transfer member via an intermediate transfer belt. In each of the primary transfer nips and in the vicinity thereof, after the primary transfer is sequentially superimposed on the intermediate transfer belt using an electric field and pressure, each color toner image superimposed on the intermediate transfer belt is transferred to 2 In a tandem type image forming apparatus that collectively transfers to a recording member using an electric field and pressure at the secondary transfer unit, on the upstream side of the secondary transfer nip, on the convex portion of the toner image forming surface of the recording member according to image data A charge imparting member is provided that gives a charge having the same polarity as that of the toner.

  According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, the charge applying member is a planar electrode formed with a size and a pitch corresponding to the maximum resolution of the image forming apparatus. It is characterized by. According to a fourth aspect of the present invention, in the image forming apparatus according to the first or second aspect, the charge applying member is a needle electrode formed with a size and a pitch corresponding to the maximum resolution of the image forming apparatus. It is characterized by. According to a fifth aspect of the present invention, in the image forming apparatus according to any one of the first to fourth aspects, the charge applying member is perpendicular to the outermost surface of the recording member regardless of the thickness of the recording member. It is installed to keep the distance constant.

  According to the first aspect of the present invention, the toner image formed on the electrostatic latent image carrier is transferred between the electrostatic latent image carrier and the primary transfer member. The toner image transferred onto the intermediate transfer belt is transferred to the intermediate transfer belt using the electric field and pressure in and around the primary transfer nip formed through the intermediate transfer belt. In an image forming apparatus that collectively transfers to a recording member using an electric field and pressure in a secondary transfer unit, the toner image forming surface of the recording member is provided on a convex portion on the upstream side of the secondary transfer nip according to image data. Since the charge imparting member for applying the charge having the same polarity as that of the toner is provided, the discharge charge having the same polarity as that of the toner can be applied to the convex portion of the recording member, and the toner and the convex to be transferred to the concave portion of the recording member. Gives the same transferability to the toner transferred to the part It becomes possible, there is excellent effect that it is possible to form a high-quality image even on a large recording member irregularities. Moreover, the discharge between the charge imparting member and the recording member is determined by the potential difference and the distance between the two members. In the present invention, however, the discharge is less likely to occur as the distance increases. For example, the unevenness of the recording member is several tens of μm. In the above case, assuming that the surface of the recording member is equipotential, the convex portion is close to the charge-providing member, the discharge is likely to occur between the charge-providing member, and the concave portion does not cause the discharge. It becomes possible to do. Accordingly, there is no discharge charge having the same polarity as that of the toner in the concave portion, and there is a discharge charge in the convex portion, and toner transfer is more easily performed in the concave portion. However, since sufficient pressure is applied to the convex portions, the combined transfer effect of the two is aligned between the concave portions and the convex portions, so that the toner can be transferred cleanly even if there are irregularities.

  An embodiment of the present invention will be described with reference to the accompanying drawings. However, the arrangement, types, and the like of components used in the embodiments (examples) described below do not limit the scope of the present invention.

[Example 1]
FIG. 1 shows a main configuration of an example of a tandem type image forming apparatus having a plurality of electrostatic latent image carriers. In the drawing, 1a to 1d are developing devices, 2a to 2d are electrostatic latent image carriers, 3a to 3d are corona discharge devices, 4a to 4d are primary transfer rollers, 5 is an intermediate transfer belt, and 6 is secondary transfer. Roller, 7 is a secondary transfer counter roller, 8 is a recording member, 9 is a fixing device, 10a to 10d are cleaning devices, 11a to 11d are lubricating oil supply devices, 12 is a charge applying member, and 13 is a cleaning blade for an intermediate transfer belt. 14 and 14 respectively indicate recording member conveyance belts.

  In the developing devices 1a to 1d, toners of different colors are held with a carrier in a negatively charged state (charge amount Q / M = −30 μC / g), respectively. There is no restriction on the order in which the toner colors are arranged, but yellow is desirable for the first color so that it is not noticeable when pre-transfer dust occurs in the first color. In this embodiment, the order is yellow, magenta, cyan, and black.

The electrostatic latent image carriers 2a to 2d, in which the organic photoreceptor layer is formed on the electrically grounded metal core, are held rotatably in the directions of arrows A1 to A4, respectively, and are surfaced by the corona discharge devices 3a to 3d. Is uniformly negatively charged (−600 V), and then the light corresponding to the image is irradiated by a light emitting means including a laser diode (not shown) to form an electrostatic latent image. In this embodiment, the writing resolution is 600 dpi. After the toner is developed on the electrostatic latent image carriers 2a to 2d, the toner image is a contact area between the primary transfer rollers 4a to 4d to which the positive voltage and pressure are applied and the electrostatic latent image carriers 2a to 2d. The image is transferred onto the intermediate transfer belt 5 in and near the primary transfer nip formed. In this embodiment, a polyimide belt (80 μm thickness) having a volume resistivity of 10 ⁷ Ω · m was used as the intermediate transfer belt 5. Further, as the primary transfer rollers 4a to 4d, those in which a foamed rubber layer (volume resistivity 10 ⁵ Ω · m) having a thickness of 2 mm was formed around a core metal having a diameter of 10 mmφ were used.

After the toner image of the fourth color is formed on the intermediate transfer belt 5, each of the toners superimposed on the intermediate transfer belt includes a grounded secondary transfer roller 6 and a secondary transfer counter roller to which a negative voltage is applied. 7 is transferred to the recording member 8 which is conveyed in the C direction in the secondary transfer nip formed by 7 and has a latent image of the same polarity as the toner formed on the surface by the charge applying member 12 to which a bias corresponding to image data is applied in advance. After that, the image is fixed on the recording member 8 by the fixing device 9. In this embodiment, a foamed rubber (volume resistivity: 10 ⁵ Ω · m) having a thickness of 3 mm was used as the secondary transfer counter roller 7 on a 10 mmφ cored bar. The toner remaining on the electrostatic latent image carriers 2a to 2d is collected and reused by the cleaning devices 10a to 10d. A certain amount of zinc stearate is supplied as a lubricating oil from the lubricating oil supply devices 11a to 11d onto the electrostatic latent image carriers 2a to 2d, and the static friction coefficients on the surfaces of the electrostatic latent image carriers 2a to 2d are kept constant. ing.

  Next, a method for forming a negative charge at the toner image transfer site on the recording member 8 will be described. The charge applying member 12 is spaced a certain distance upward from the uppermost surface of the recording member 8 that is the toner image forming surface (the surface is equivalent to a convex portion), and upstream from each secondary transfer nip. It is installed at a location 40 mm away so that a negative potential (a charge having the same polarity as the toner) can be variably applied. The distance between the uppermost surface of the charge applying member 12 and the recording member 8 varies depending on the voltage applied to the charge applying member 12, but a negative charge is supplied only to the uppermost surface of the recording member 8 due to the discharge, and a discharge occurs in the recess. Adjust so that there is no.

  Further, as the electrode formed on the charge applying member 12, a planar electrode as shown in FIG. 2 was formed and used with a size and a pitch corresponding to the maximum resolution of the image forming apparatus. That is, according to the writing resolution of 600 dpi of the present embodiment, 7021 plane electrodes of 40 μm × 35 μm are formed at a pitch of 42.3 μm so that a print area with a width of 297 mm can be accommodated. Image data written on each of the electrostatic latent image carriers 2a to 2d is also transferred to the charge applying member 12, and a negative charge latent image is formed on the surface of the recording member 8 on the upstream side of the secondary transfer portion by discharge. The The timing of forming the negative charge latent image is obtained from the separation distance in the recording member conveyance direction of the secondary transfer nip and the charge applying member 12, the positions of the electrostatic latent image carriers 2 a to 2 d, and the linear speed of the intermediate transfer belt 5. Can do. In order to cope with subtle variations in the linear velocity of the transport system, a signal for a normal transfer alignment mechanism is used for correction to improve the accuracy of the negative charge latent image forming position.

  Next, the formation of a latent image on the recording member 8 by the charge applying member 12 will be described in more detail with reference to FIG.

  3A and 3B are cross-sectional views of the secondary transfer portion. The recording member 8 has an embossed surface, and has an unevenness of about 100 μm. Image data formed at the secondary transfer nip is transferred line by line to the charge applying member 12 having the planar electrodes formed in an array, and corresponds to the image data portion when the recording member 8 passes directly below. A negative potential is applied to the planar electrode. This negative potential is set so that discharge occurs between the uppermost surface of the recording member 8 but no discharge occurs in the embossed recess. On the recording member 8 after passing through the charge applying member 12, for example, negative charges are given only to the convex portions corresponding to the image portion (for example, letter F style) shown in FIG. 4. Due to the negative charge of the convex portion, a strong transfer electric field can be formed in the concave portion in the secondary transfer nip, and transfer conditions including the effect of the transfer pressure can be brought closer to the concave portion and the convex portion. . For this reason, by setting the optimized secondary transfer bias in the concave portion, that is, by changing the secondary transfer current by the same method as in the case of optimizing the normal secondary transfer current at the time of designing, the concave and convex portions of the recording medium 8 are set. By setting a secondary transfer bias in which toner adheres evenly to the portion, it is possible to transfer the same amount of toner as that of the convex portion, and it is possible to form a high-quality image along the uneven shape. If there is no negative charge on the convex part, it is conceivable to increase the secondary transfer bias in order to increase the transfer rate to the concave part. In this case, however, the transfer defect due to the discharge to the toner at the convex part becomes remarkable. As a result, a good image cannot be formed.

  In order to verify the effects of Example 1, an evaluation image was output and image quality was evaluated at 600 dpi output using a modified machine based on IPSioCX400 as an evaluation image output machine. As the recording member 8, an FC white 220 (A3 / thickness 250 μm) embossing having a width of about 100 μm and a depth of about 100 μm formed perpendicularly to the recording member transport direction was used. Also, images for evaluation are recorded in yellow, magenta, cyan, black, red (yellow + magenta), green (yellow + cyan), blue (magenta + cyan), and three-color black (yellow + magenta + cyan). 10 lines each having a width of 4 dots in the member conveyance direction (the maximum length in the width direction of the intermediate transfer belt) were used. For 100 final images after fixing, rank 5 is an image with no omission along the unevenness of the surface of the recording member 8, and rank 1 is the case where omission is not significant as an image. It was.

  As Comparative Example 1, the same evaluation was performed when the potential applying member 12 was not provided (other image forming conditions are the same as those in Example 1). In addition, since a desired discharge was observed when the distance between the top surface of the charge applying member 12 and the recording member 8 was 100 μm and the applied voltage to the flat electrode of the charge applying member was −930 V, evaluation was performed using this set value. .

  As shown in FIG. 5, in Comparative Example 1, the rank was 1 or 2, and almost no image could be formed in the recesses. However, in Example 1, a sufficiently high quality image having a rank average of 4 or more was obtained. I was able to get it.

[Example 2]
Another embodiment 2 is described below. Although the basic configuration is the same as that of the first embodiment, in this embodiment, the uppermost surface of the recording member 8 and the electrode of the charge applying member 12 are separated by a separation distance adjusting device using a stepping motor (not shown). It has a mechanism for keeping the distance between them constant regardless of the recording member thickness (preliminarily input together with the image data).

  In addition, as the electrode formed on the charge imparting member 12, a needle electrode having a height of 1 mm and a tip thickness of 20 μm as shown in FIG. 6 formed at a pitch of 42.3 μm was used. The charge applying member 12 was installed at a location 40 mm away from the corresponding secondary transfer nip upstream. The distance between the top surface of the charge applying member 12 and the recording member 8 is 100 μm regardless of the paper type, and a desired discharge was observed when the applied voltage to the needle electrode of the charge applying member 12 was −840 V. Evaluation was performed. As recording member 8, FC white 220 (A3 / thickness 250 μm) and FC white 135W (A3 / thickness 180 μm) embossed each with a width of about 100 μm and a depth of about 50 μm formed perpendicular to the recording member conveyance direction. Was used.

  In order to verify the effect of the second embodiment, a modified machine based on IPSioCX400 is used as an image output machine for evaluation, and FC white 220 and FC white 135W are output 50 sheets alternately at 600 dpi output. The image quality evaluation similar to 1 was performed.

  As Comparative Example 2, the same evaluation was performed for the case without the charge imparting member 12. As shown in FIG. 7, in the comparative example 2, both the FC white 220 and the FC white 135W have a rank of 1 or 2 (there is only one rank 3), and almost no image can be formed in the recess. However, in Example 2, a sufficiently high quality image having a rank average of 4 or more could be obtained regardless of the paper thickness.

  In the above embodiment, only the case where the secondary transfer portion is a repulsive force transfer (transferred by applying a bias having the same polarity as the toner to the secondary transfer counter roller 7) has been described. Needless to say, the transfer roller 6 may be transferred by applying a bias having a polarity opposite to that of the toner. Moreover, the shape of the electrode formed on the charge providing member 12 is also arbitrary. For example, the shape of the planar electrode on the charge providing member 12 of Example 1 may be square. Further, when smooth paper is used as the recording member 8, a mechanism for stopping the charge applying member 12 may be provided. In the above embodiment, the tandem image forming apparatus having a plurality of electrostatic latent image carriers has been described. However, the tandem image forming apparatus is not necessarily required.

  Next, a characteristic effect of the invention described in claim 2 and the following claims will be described. According to claim 2, each color toner image formed on a plurality of electrostatic latent image carriers is formed between each of the electrostatic latent image carriers and each primary transfer member via an intermediate transfer belt. In each of the primary transfer nips and in the vicinity thereof, the primary transfer is sequentially superimposed on the intermediate transfer belt using an electric field and pressure, and then each color toner image superimposed and transferred on the intermediate transfer belt is subjected to secondary transfer. In the tandem type image forming apparatus that collectively transfers to the recording member using an electric field and pressure at the portion, the toner is formed on the convex portion of the toner image forming surface of the recording member on the upstream side of the secondary transfer nip according to the image data. Since the charge imparting member that gives the charge having the same polarity as that of the recording member is provided, a discharge charge having the same polarity as that of the toner can be given to the convex portion of the recording member, and transferred to the concave portion of the recording member and the convex portion. Gives toner equivalent transferability It becomes possible, it is possible to form a high-quality image even on a large recording member irregularities.

  According to the third aspect, since the charge imparting member is a planar electrode formed with a size and a pitch corresponding to the maximum resolution of the image forming apparatus, the charge imparting member can be produced by a simple method, A high-quality image can be formed even on a recording member having large irregularities at a low cost.

  According to the fourth aspect of the present invention, since the charge imparting member is a needle electrode formed with a size and a pitch corresponding to the maximum resolution of the image forming apparatus, a generally distributed needle electrode can be used, and the unevenness can be reduced at a low development cost. It becomes possible to form a high-quality image even on a large recording member.

  According to claim 5, since the charge applying member is installed so as to keep the distance in the vertical direction from the recording member outermost surface constant regardless of the thickness of the recording member, regardless of the thickness of the recording member, It becomes possible to form a high-quality image on a recording member having large irregularities.

1 is a schematic diagram illustrating a configuration of a main part of an example (Example 1) of an image forming apparatus according to an embodiment of the present invention. It is the schematic which shows the plane electrode formed in a charge provision member same as the above. (A), (B) is sectional drawing explaining the effect | action of the charge provision member in a secondary transfer part. It is an enlarged view of the primary transfer nip part same as the above. It is a table | surface which shows the evaluation result of Example 1 same as the above. 6 is a schematic diagram showing needle electrodes formed on a charge imparting member of Example 2. FIG. It is a table | surface which shows the evaluation result of Example 2 same as the above.

Explanation of symbols

1a to 1d Developing devices 2a to 2d Electrostatic latent image carriers 3a to 3d Corona discharge devices 4a to 4d Primary transfer roller 5 Intermediate transfer belt 6 Secondary transfer roller 7 Secondary transfer counter roller 8 Recording member 9 Fixing device 10a to 10d Cleaning devices 11a to 11d Lubricating oil supply device 12 Charge applying member

Claims (5)

The toner image formed on the electrostatic latent image carrier is transferred to the intermediate portion in and near the primary transfer nip formed through an intermediate transfer belt between the electrostatic latent image carrier and the primary transfer member. An image forming apparatus that performs primary transfer on a transfer belt using an electric field and pressure and then collectively transfers the toner image transferred on the intermediate transfer belt to a recording member using an electric field and pressure at a secondary transfer unit. In
An image forming apparatus, comprising: a charge imparting member that applies an electric charge having the same polarity as the toner to a convex portion of a toner image forming surface of the recording member according to image data on an upstream side of a secondary transfer nip. Each color toner image formed on a plurality of electrostatic latent image carriers is transferred into each primary transfer nip formed via an intermediate transfer belt between each electrostatic latent image carrier and each primary transfer member, and In the vicinity, primary transfer is performed by sequentially superimposing on the intermediate transfer belt using an electric field and pressure, and then each color toner image superimposed and transferred on the intermediate transfer belt is subjected to an electric field and pressure at the secondary transfer unit. In a tandem image forming apparatus that collectively transfers to a recording member,
An image forming apparatus, comprising: a charge imparting member that applies an electric charge having the same polarity as the toner to a convex portion of a toner image forming surface of the recording member according to image data on an upstream side of a secondary transfer nip.   3. The image forming apparatus according to claim 1, wherein the charge applying member is a planar electrode formed with a size and a pitch corresponding to the maximum resolution of the image forming apparatus.   3. The image forming apparatus according to claim 1, wherein the charge applying member is a needle electrode formed with a size and a pitch corresponding to a maximum resolution of the image forming apparatus.   5. The image forming apparatus according to claim 1, wherein the charge imparting member is installed so as to keep a distance in a vertical direction from the outermost surface of the recording member constant regardless of a thickness of the recording member. An image forming apparatus.

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