JP4807991B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a copying machine, a facsimile machine, or a printer, and more specifically, a charging unit that charges an image carrier and an electrostatic latent image formed by exposure of the image carrier charged by the charging unit. The present invention relates to an image forming apparatus including at least an exposure unit that forms, a developing unit that develops the electrostatic latent image, and a transfer unit that transfers the developed image. More specifically, the present invention relates to an image forming apparatus including an effective lubricant application device using a charging unit for charging an image carrier.

In an image forming apparatus using a general electrophotographic system having a charging member that is close or in contact, the occurrence of toner filming (fusion) of the image carrier is prevented by applying a lubricant to the image carrier. It is considered that the transfer efficiency is improved by reducing the friction coefficient of the image carrier, the wear of the image carrier is prevented by reducing the friction coefficient of the image carrier, and the hazard due to the discharge of the image carrier is suppressed. However, it has been found that the above effect is not always sufficient by simply applying a lubricant as has been done so far.

For example, it is known that an image carrier is charged and the electrostatic charge is selectively erased or reduced by exposure to form an electrostatic latent image on the image carrier. As the charging means for charging the image bearing member, those using corona discharge have been the mainstream. However, the charging means using the corona discharge has a problem that a large amount of ozone is generated, and a high voltage power source for applying a high voltage of 5 to 10 kV is necessary to perform the corona discharge. It has been difficult to reduce the cost of the image forming apparatus. Therefore, in recent years, many contact-type charging units that contact a charging member with an image carrier without using corona discharge have been proposed as charging units that can be employed in an image forming apparatus. In this contact-type charging unit, many of the problems mentioned in the case of the charging unit using the corona discharge are solved, while an abnormal image called image flow is generated and the wear amount of the image carrier is increased. The problem has also occurred. In addition, when alternating current is used as the applied voltage, noise is also a problem. In addition, since the charging means rubs toner or paper dust between the image carrier and the charging member, contamination is promoted, and contamination due to this also becomes a problem.
However, until now, there has been no idea that these problems are caused by lubricants. Therefore, in Patent Document 1, in an image forming apparatus having a contact charging roller that performs primary charging by superimposing an AC voltage on a DC voltage, lubrication dispersed in a resin binder at a contact portion between the photosensitive member and the cleaning blade. An image forming apparatus for applying an agent is disclosed.
In Patent Document 2, an application brush roller for applying a fatty acid metal salt is disposed in contact, and a film of the fatty acid metal salt is formed on the surface of the photosensitive drum via the transfer roller. This improves the recoverability of the transfer residual toner, and prevents the transfer residual toner from adhering to the photosensitive drum or the charging device.
However, there is no description regarding the deterioration of the lubricant due to the discharge of the charging member, and there is no description that an abnormal image is generated due to this.

JP 2002-258987 A JP 2004-101551 A

  Therefore, the present invention has been made in view of the above problems, and its problem is to grasp the deterioration state of the lubricant that has not been grasped so far, and to prevent the wear of the image carrier and the cleaning blade. When the deteriorated lubricant remains on the image carrier, an image forming apparatus that prevents the occurrence of an abnormal image such as an image flow and efficiently applies the lubricant is provided.

The features of the present invention, which is a means for solving the above problems, are listed below.
The image forming apparatus of the present invention, at least an image bearing member, a charging means having a charging member proximity or contact with the image bearing member, a coating means for applying a lubricant to the image bearing member, the friction of the image bearing member An image forming apparatus having a coefficient of friction measurement unit, wherein the image forming apparatus has a value measured by the coefficient of friction measurement unit equal to or greater than a predetermined value in response to a command to start an image forming operation. The cleaning unit performs a cleaning mode in which the voltage applied to the charging unit is a voltage whose frequency (f) or peak-to-peak voltage (Vpp) is higher than that during image formation, and the surface of the image carrier is removed by the cleaning unit. Then, after the lubricant is applied to the image carrier, image formation is performed .
In the image forming apparatus of the present invention, the friction coefficient measuring unit further measures a current of a motor that drives the image carrier, and calculates a friction coefficient of the image carrier based on the current value. It is a measuring means .
In the image forming apparatus according to the present invention, the friction coefficient measuring unit may further include a torque measurement for calculating a friction coefficient of the image carrier based on a value of a strain sensor attached to a shaft driven by the image carrier. it characterized in that it is a means.

Alternatively, the image forming apparatus of the present invention is characterized in that the image carrier has a protective layer on the surface layer.
Alternatively, the image forming apparatus of the present invention is characterized in that the binder resin of the protective layer has a crosslinked structure.
Alternatively, the image forming apparatus of the present invention has a charge transporting site in the structure of the binder resin having the cross-linked structure.
Alternatively, the image forming apparatus of the present invention comprises a unit including at least an image bearing member, characterized in that it comprises a detachable process cartridge in the image forming apparatus main body.

  As described above, according to the present invention, the wear of the image carrier and the cleaning blade can be prevented, and the life of the machine body can be extended. Furthermore, the occurrence of abnormal images can be prevented. In addition, the waste of paper and energy generated when an abnormal image occurs can be reduced.

  The best mode for carrying out the present invention will be described below with reference to the drawings. Note that it is easy for a person skilled in the art to make other embodiments by changing or correcting the present invention within the scope of the claims, and these changes and modifications are included in the scope of the claims. The following description is an example of the best mode of the present invention, and does not limit the scope of the claims.

FIG. 1 is an overall view of an image forming apparatus and is an embodiment of the present invention. The image forming apparatus 1 shown here has an image carrier 2 arranged in the main body of the image forming apparatus 1. The image carrier 2 is composed of a drum-like photosensitive member having a photosensitive layer on the outer peripheral surface of a cylindrical conductive base. The image carrier 2 is an endless belt-like image carrier that is wound around a plurality of rollers and rotated. The body 2 can also be used.
The image carrier 2 shown in FIG. 1 is rotated in the clockwise direction during the image forming operation. At this time, the image carrier 2 is charged to a predetermined polarity by the charging means 3. Although the non-contact charging roller is used in FIG. 1, the invention is not limited to this, and a contact charging roller may be used.
The image carrier 2 charged by the charging unit 3 is irradiated with light-modulated laser light emitted from a laser writing unit 4 which is an example of an exposure unit, whereby an electrostatic latent image is formed on the image carrier 2. Is done. In the example shown in the figure, the absolute value of the potential of the surface portion of the image carrier 2 irradiated with the laser beam decreases, and this becomes an electrostatic latent image (image portion), and the absolute value of the potential without being irradiated with the laser beam. The part where is kept high becomes the background part. Next, the electrostatic latent image is visualized as a toner image by toner charged to a predetermined polarity when passing through the developing means 5. An exposure unit having an LED array, an exposure unit 4 that illuminates a document surface and forms an image of the document on the image carrier 2 can also be used.
On the other hand, a transfer material made of, for example, transfer (recording) paper is sent out from the paper supply unit 18, and the transfer material is placed at a predetermined timing between the transfer unit 6 and the image carrier 2 facing the image carrier 2. Sent in. At this time, the toner image formed on the image carrier 2 is electrostatically transferred onto the transfer material. The transfer material on which the toner image has been transferred continues to pass through the fixing means 10, and at this time, the toner image is fixed on the transfer material by the action of heat and pressure. The transfer material that has passed through the fixing unit 10 is discharged to a paper discharge unit. The transfer residual toner that is not transferred to the transfer material and remains on the surface of the image carrier 2 is removed by the cleaning unit 7. The fixing unit 10 has a two-roller configuration in the figure, but there is no problem with other configurations such as a belt and a roller.

The developing means 5 shown in FIG. 1 has a developing case that contains a dry developer and a developing roller that carries the developer while carrying it. As the developer, for example, a dry developer having a toner and a carrier, or a one-component developer having no carrier can be used. The developing roller is rotationally driven in the direction of the arrow. At this time, the developer is carried and conveyed on the peripheral surface of the developing roller, and the toner in the developer carried to the developing area between the developing roller and the image carrier 2 is statically discharged. The electrostatic latent image is electrostatically transferred to the electrostatic latent image, and the electrostatic latent image is visualized as a toner image.
The transfer means 6 shown in FIG. 1 is constituted by a transfer roller to which a transfer voltage having a polarity opposite to the charging polarity of the toner on the image carrier 2 is applied, and a transfer brush, transfer blade or corona wire is used. It is also possible to use a transfer means comprising a corona discharger. Further, instead of directly transferring the toner image on the image carrier 2 to a transfer material as a final recording medium, the toner image on the image carrier 2 is transferred onto a transfer material made of an intermediate transfer member, and the toner It can also be configured to transfer the image to the final recording medium.
The cleaning means 7 shown in FIG. 1 has a cleaning member composed of a fur brush and a cleaning blade rotatably supported by the cleaning case, and these cleaning members abut on the surface of the image carrier 2. The transfer residual toner adhering to the surface is removed.
For the cleaning blade as a cleaning means, for example, a known material such as polyurethane rubber, silicone rubber, nitrile rubber, chloroprene rubber or the like is appropriately selected, and its elastic modulus, thickness, contact angle with respect to the image carrier 2 and the like are appropriately set. Can be used.
Although not shown in FIG. 1, a charge removal unit may be provided on the downstream side of the cleaning unit 7, the upstream side of the charging unit, or the like to remove the residual charges on the image carrier 2.

The image forming apparatus 1 of the present invention has a friction coefficient measuring means (not shown) for measuring the friction coefficient of the image carrier 2, and the surface of the image carrier 2 is charged according to the measured value of the friction coefficient measuring means. 3 and the cleaning means 7, and then the lubricant is applied by the lubricant application device 102.
FIG. 2 is a flowchart for explaining the operation of the image forming apparatus of the present invention. Hereinafter, a description will be given with reference to FIG. When the image forming apparatus 1 receives the print command signal, the image forming apparatus 1 performs a preparatory rotation for performing normal image formation, and then performs an image forming operation. Thereafter, the friction coefficient of the image carrier is measured. If the measured friction coefficient exceeds a predetermined value (A), a cleaning mode for removing the lubricant on the image carrier 2 is entered, and the lubricant is removed. Then, post-preparation rotation is performed to form a lubricant film on the image carrier 2 and the series of operations is completed. Further, when the measured friction coefficient does not exceed the predetermined value (A), the cleaning mode is not entered, the post-preparation rotation is performed, and the series of operations is terminated.

FIG. 3 is a flowchart for explaining the operation of the image forming apparatus of the present invention. Hereinafter, a description will be given with reference to FIG. When the image forming apparatus 1 receives the print command signal, the friction coefficient of the image carrier 2 is measured. If the measured friction coefficient exceeds a predetermined value (A), a cleaning mode for removing the lubricant on the image carrier 2 is entered, and the lubricant is removed. Then, a preparatory rotation is performed to form a lubricant film on the image carrier 2. If the measured friction coefficient does not exceed the predetermined value (A), the cleaning mode is not entered and the preparatory rotation is performed to form a lubricant film on the image carrier 2. Thereafter, an image forming operation is performed, a post-preparation rotation is performed, and the series of operations is completed.
There are mainly two methods for measuring (estimating) the friction coefficient of the image carrier 2 in the image forming apparatus 1. One is a method of measuring the current of the motor that drives the image carrier 2 and estimating the friction coefficient based on the value of the current measuring means, and the other is the distortion affixed to the rotating shaft or the like of the image carrier 2. This is a method of estimating the friction coefficient based on the gauge value. There is no problem even if the friction coefficient is measured by a friction coefficient measurement method other than the above. The first measurement method will be described in detail. The friction coefficient is estimated from the current of the motor that drives the image carrier 2. First, the friction coefficient of the image carrier 2 is measured. There are two measuring methods, the Euler belt method and the HEIDON measuring device, but HEIDON is preferable in that the contact with the object to be measured is stable. At least an image carrier 2 having a low friction coefficient and a high friction coefficient measured by one of the measurement methods described above is prepared. It is preferable that there are as many friction coefficients as possible between the low friction coefficient and the high friction coefficient.
4 and 5 are electrical block diagrams for operating the image forming apparatus of the present invention.
The image carrier 2 having a low friction coefficient is set in the image forming apparatus 1 and the current value at that time is measured. Thereafter, the image carrier 2 is replaced with one having a high friction coefficient, and the current value is measured. Thereafter, a current value (a) corresponding to a predetermined friction coefficient (A) is calculated from a straight line connecting the two points. When the intermediate friction coefficient is measured, the current value (a) corresponding to the friction coefficient (A) is calculated from a straight line or curve connecting multiple points. The friction coefficient may be estimated based on the value of the strain gauge as in the case of the current.

FIG. 6 shows the change in the friction coefficient according to the number of discharges of the image carrier 2 when the image carrier is charged by using a charging roller after the lubricant is applied to the image carrier. As the number of discharges increases, it can be seen that the lubricant on the image carrier 2 changes and the friction coefficient increases. It is presumed that the same phenomenon occurs in the actual image forming apparatus 1.
FIG. 7 shows a case where only the image carrier and a lubricant are applied (hereinafter referred to as an application state), a case where discharge is applied (hereinafter referred to as a discharge deterioration state), and a case where discharge is applied again. The results of measuring the respective friction coefficients when a lubricant is applied (referred to as reapplying state) are shown. It is not a measurement result in the normal image forming apparatus 1. If the image carrier 2 (photoreceptor) of the image forming apparatus 1 can always be maintained at the friction coefficient in the applied state, it is possible to prevent or reduce the wear of the photoreceptor and the cleaning blade caused by the discharge of the charging roller. Is known. However, even if the lubricant is always applied in the image forming apparatus 1, the friction coefficient tends to increase mainly due to discharge by the charging roller. Therefore, it is necessary to remove the deteriorated lubricant when the friction coefficient becomes a certain value (A) or more. The value (A) of the friction coefficient is somewhat different depending on the image carrier 2 (photosensitive member), but is preferably OPC, more preferably 0.3, and more preferably 0.2.
When the cleaning mode was applied to the image carrier 2 with weak discharge, and then a lubricant was applied, the friction coefficient increased from about 0.14 to about 0.2. Next, when the cleaning mode was performed on the image carrier 2 during discharge and then a lubricant was applied, the coefficient of friction dropped from about 0.24 to about 0.1. Next, when the cleaning mode was performed on the image carrier 2 having a strong discharge, and then the lubricant was applied, the friction coefficient was significantly reduced from about 0.45 to about 0.1. As is clear from the above results, it can be seen that the cleaning mode is not effective when the friction coefficient is low, and is effective when the friction coefficient exceeds a certain level. Although the lubricant that has not deteriorated can be removed by a cleaning blade, a brush, or the like, the deteriorated lubricant is difficult to remove. Further, if the deteriorated lubricant remains on the image carrier 2, an abnormal image such as an image flow tends to occur. Therefore, it is necessary to remove the deteriorated lubricant by using both the charging roller as the charging unit 3 and the cleaning unit 7. The voltage applied to the charging roller used in the cleaning mode for removing the lubricant may be a normal voltage. However, since the cleaning time becomes longer, the frequency (f) is increased or the peak-to-peak voltage is increased compared to the time of image formation. The time is shortened by increasing (Vpp).

As the image carrier 2 used in the image forming apparatus 1 of the present invention, it is preferable that the image carrier 2 has a protective layer on the surface layer, and the binder resin of the protective layer has a crosslinked structure.
Regarding the formation of a cross-linked structure, a reactive monomer having a plurality of cross-linkable functional groups in one molecule is used to cause a cross-linking reaction using light or thermal energy to form a three-dimensional network structure. is there. This network structure functions as a binder resin and exhibits high wear resistance. From the viewpoint of electrical stability, printing durability, and life, it is a very effective means to use a monomer having a charge transporting ability in whole or in part as the reactive monomer. By using such a monomer, a charge transporting site is formed in the network structure, and the function as a protective layer can be sufficiently expressed. The reactive monomer having charge transporting ability includes a compound containing at least one charge transporting component and a silicon atom having a hydrolyzable substituent in the same molecule, and a charge transporting component in the same molecule. A compound containing a hydroxyl group, a compound containing a charge transporting component and a carboxyl group in the same molecule, a compound containing a charge transporting component and an epoxy group in the same molecule, a charge transporting component in the same molecule And a compound containing an isocyanate group. These charge transport materials having a reactive group may be used alone or in combination of two or more.
More preferably, a reactive monomer having a triarylamine structure is effectively used as the monomer having a charge transporting ability because of high electrical and chemical stability and high carrier mobility. In addition to this, monofunctional and bifunctional polymerizable monomers and polymerizable oligomers are used in combination for the purpose of viscosity adjustment during coating, stress relaxation of the cross-linked charge transport layer, low surface energy, and reduction of friction coefficient. be able to. As these polymerizable monomers and oligomers, known ones can be used.
In the present invention, the hole transporting compound is polymerized or cross-linked using heat or light. When the polymerization reaction is performed by heat, the polymerization initiator may be used in the case where the polymerization reaction proceeds only with thermal energy. Although it may be necessary, it is preferable to add an initiator in order to advance the reaction efficiently at a lower temperature.

  In the case of polymerization by light, it is preferable to use ultraviolet light as light, but the reaction rarely proceeds only by light energy, and a photopolymerization initiator is generally used in combination. The polymerization initiator in this case mainly absorbs ultraviolet rays having a wavelength of 400 nm or less to generate active species such as radicals and ions, and initiates polymerization. In the present invention, the aforementioned heat and photopolymerization initiator can be used in combination. The charge transport layer having a network structure formed in this manner has high wear resistance, but has a large volume shrinkage during the crosslinking reaction, and if it is too thick, it may cause cracks. In such a case, the protective layer may be a laminated structure, a low molecular dispersion polymer protective layer may be used for the lower layer (photosensitive layer side), and a protective layer having a crosslinked structure may be formed on the upper layer (surface side). good.

Examples of the image carrier 2 using the above-mentioned crosslinking type protective layer are shown below.
In the image carrier 2, the first image carrier 2 was prepared in the following manner with respect to the protective layer coating solution, film thickness, and preparation conditions.
<First image carrier>
182 parts of methyltrimethoxysilane, 40 parts of dihydroxymethyltriphenylamine, 225 parts of 2-propanol, 106 parts of 2% acetic acid, and 1 part of aluminum trisacetylacetonate were mixed to prepare a coating solution for a protective layer. This coating solution was applied onto the charge transport layer and dried, and then heat-cured at 110 ° C. for 1 hour to form a protective layer having a thickness of 3 μm.

<Second image carrier>
In the image carrier 2, a second image carrier 2 was produced in the same manner as the first image carrier 2 except that the protective layer coating solution and the film thickness / creation conditions were changed as follows.
30 parts of a hole transporting compound (the following structural formula (I)), 0.6 part of an acrylic monomer (the following structural formula (II)) and a photopolymerization initiator (1-hydroxy-cyclohexyl-phenyl-ketone) It was dissolved in a mixed solvent of 50 parts of chlorobenzene / 50 parts of dichloromethane to prepare a coating material for the surface protective layer. This paint was applied on the previous charge transport layer by spray coating, and cured for 30 seconds with a light intensity of 500 mW / cm ² using a metal halide lamp to form a surface protective layer having a thickness of 5 μm.

  Further, the image bearing member 2 has characteristics of an organic photoreceptor having a surface layer reinforced with a filler such as alumina powder of 0.1 μm or less, an organic photoreceptor using a cross-linked charge transport material, or both. When the organic photoconductor is configured, the surface hardness is increased and the wear resistance is improved, so that the life can be greatly extended.

FIG. 8 is a schematic view showing the configuration of the process cartridge of the present invention. In the image forming apparatus 1 shown in FIG. 1, a casing that rotatably supports the charging unit 3 and a cleaning case that supports the cleaning unit 7 are configured as an integral unit case, and the image carrier 2 is mounted on this unit. The process cartridge can be assembled rotatably.
In this way, the process cartridge 20 in which the charging unit 3 and the image carrier 2 are integrally assembled is configured, and the process cartridge 20 is detachably mounted on the main body of the image forming apparatus 1. The charging member 3 and the image carrier 2 are incorporated in the process cartridge 20 with the minute gap G kept constant, and the process cartridge 20 is held in the main body of the image forming apparatus 1 while keeping the minute gap G constant. It can be attached to and detached from. For this reason, it is possible to prevent a problem that the size of the minute gap G greatly fluctuates when the process cartridge 20 is attached or detached. The image carrier 2 and the charging member 3 may be configured to be detachable separately from the main body of the image forming apparatus 1. However, according to this configuration, the minute gap G changes when the image carrier 2 and the charging member 3 are attached and detached. There is a risk that uniform charging may not be possible. Further, the process cartridge 20 of the present example has a contact member that contacts the image carrier 2 in addition to the charging unit 3. In the example shown in FIG. 6, as described above, the cleaning means 7 and the casing are formed as an integral unit case, and the lubricant supply means 9 is assembled to the unit case. The charging member 3 constitutes a contact member that contacts the image carrier 2, and these contact members may be configured to be mounted on the process cartridge 20 separately from the charging member 3. When the contact member is attached or detached, these members move while being in contact with the image carrier 2, so that a large external force is applied to the image carrier 2, which may cause the minute gap G to fluctuate. On the other hand, if the contact member is also an element of the process cartridge 20, when the process cartridge 20 is attached to or detached from the main body of the image forming apparatus 1, the contact member including the cleaning blade 7 and the lubricant applying unit 9 is also attached and detached. Therefore, these members do not move relative to the image carrier 2, so that there is no possibility that the minute gap G will fluctuate greatly, and it is possible to prevent the image carrier 2 from being damaged due to contact.

1 is an overall view of an image forming apparatus and is an embodiment of the present invention. FIG. 6 is a flowchart illustrating the operation of the image forming apparatus of the present invention. FIG. 6 is a flowchart illustrating the operation of the image forming apparatus of the present invention. FIG. 2 is an electrical block diagram for operating the image forming apparatus of the present invention. FIG. 2 is an electrical block diagram for operating the image forming apparatus of the present invention. This figure shows the change in the friction coefficient according to the number of discharges of the image carrier when the image carrier is charged by using a charging roller after the lubricant is applied to the image carrier. The results of measuring the respective friction coefficients when only the image carrier, the lubricant is applied, when the discharge is applied, and when the lubricant is applied again after the discharge is applied are shown. It is the schematic which shows the structure of the process cartridge of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Image carrier 3 Charging means 4 Exposure means 5 Developing means 6 Transfer means 7 Cleaning means 9 Lubricant application means 10 Fixing means 15 Recording paper 16 Conveying belt 17 Intermediate transfer body 20 Process cartridge

Claims (7)

At least an image carrier;
A charging means having a charging member proximity or contact with the image bearing member,
Application means for applying a lubricant to the image carrier;
In an image forming apparatus having a friction coefficient measuring means for measuring a friction coefficient of an image carrier,
In response to a command to start an image forming operation, the image forming apparatus
When the measured value of the friction coefficient measuring unit is equal to or greater than a predetermined value, the voltage applied to the charging unit is a voltage that is higher in frequency (f) or peak-to-peak voltage (Vpp) than during image formation, An image forming apparatus, wherein a cleaning mode in which a lubricant is removed from a surface of an image carrier by a cleaning unit is performed, and then an image is formed after applying the lubricant to the image carrier . The image forming apparatus according to claim 1.
The friction coefficient measuring unit is a current measuring unit that measures a current of a motor that drives the image carrier and calculates a friction coefficient of the image carrier based on the current value. . The image forming apparatus according to claim 1.
The image forming apparatus according to claim 1, wherein the friction coefficient measuring means is a torque measuring means for calculating a friction coefficient of the image carrier based on a value of a strain sensor attached to a shaft driven by the image carrier . The image forming apparatus according to any one of claims 1 to 3,
An image forming apparatus, wherein the image carrier has a protective layer on a surface layer . The image forming apparatus according to claim 4 .
An image forming apparatus , wherein the binder resin of the protective layer has a crosslinked structure . The image forming apparatus according to claim 5 .
An image forming apparatus comprising a charge transporting site in the structure of the binder resin having a crosslinked structure . The image forming apparatus according to claim 1 ,
An image forming apparatus comprising a process cartridge which is composed of a unit including at least an image carrier and is detachable from an image forming apparatus main body .

Images