JP4369689B2 - Color image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a color image forming apparatus such as a laser printer or a copying machine using an electrophotographic method, and in particular, after a toner image formed on an electrostatic latent image carrier is once transferred to a belt-like intermediate transfer member. The present invention relates to a color image forming apparatus using a method of transferring to a recording medium.
[0002]
[Prior art]
[Patent Document 1]
JP-A-1-288880
[Patent Document 2]
JP-A-6-289737
[Patent Document 3]
JP-A-8-292664
[Patent Document 4]
JP-A-9-96973
[Patent Document 5]
JP-A-10-123860
[Patent Document 6]
JP 11-119572 A
[Patent Document 7]
JP-A-9-236964
[Patent Document 8]
JP-A-8-328312
Image forming apparatuses such as laser printers and copiers using electrophotography are uniformly charged with an electrostatic latent image carrier made of an inorganic or organic material using a charging roller or a discharge electrode. An electrostatic latent image is formed by charging and irradiating light with a semiconductor laser, a gas laser, an LED array, or the like, and a toner image is obtained by visualizing the electrostatic latent image with toner having a particle size of several μm. . Thereafter, the toner image is directly transferred to a recording medium such as paper, or is primarily transferred to a semiconductive intermediate transfer member and then secondarily transferred to the recording medium to form an image.
A method in which a toner image on an electrostatic latent image carrier is primarily transferred to an intermediate transfer member and then secondarily transferred to a recording medium to form an image is disclosed in Patent Document 1 (Japanese Patent Laid-Open No. 1-288880). ing. As disclosed in Patent Document 1, a belt is also used for the intermediate transfer member. The primary transfer of the toner from the electrostatic latent image carrier to the intermediate transfer belt can be performed by a method in which a charge opposite to that of the toner is applied to the back of the belt with a corona discharger (Patent Documents 2, 3, and 4), or a semiconductive transfer. 2. Description of the Related Art For a long time, methods using a roller and transferring with an electric field and pressure formed by a potential difference provided between the transfer roller and the electrostatic latent image carrier have been known (Patent Documents 5, 6, and 7).
[0003]
Also, the secondary transfer of toner on the intermediate transfer body to the recording medium is formed between the secondary transfer roller and the opposing roller by sandwiching the recording medium between the secondary transfer roller and the opposing roller that supports the intermediate transfer body. A method of performing the voltage and pressure is disclosed in the above-mentioned patent document.
[0004]
FIG. 2 shows a specific example. Developing units 101 to 104 corresponding to yellow (Y), magenta (M), cyan (C), and black (K) are arranged around the photosensitive drum 100, and toner images of respective colors are made for each rotation of the photosensitive drum 100. 105 is formed and superimposed on a belt-shaped or drum-shaped intermediate transfer member 106. Further, the toner image 105 on the intermediate transfer member 106 is transferred onto a recording medium 107 to obtain an image.
[0005]
Further, as shown in FIG. 3, a photosensitive drum 100 is provided for each color, and four-color toner images 111 to 114 are formed by one rotation, superimposed on the intermediate transfer member 106, and further transferred onto a recording medium 107. There is also a method for obtaining an image.
[0006]
In these apparatuses, the transfer of the toner image from the photosensitive drum 100 to the intermediate transfer member 106 is performed by a semiconductive primary transfer roller 108 disposed on the back surface of the intermediate transfer member. When the base tube of the photosensitive drum 100 is grounded and a voltage having a polarity opposite to that of the toner is applied to the primary transfer roller 108, a transfer electric field is formed, and the toner images 111 to 114 are transferred to the intermediate transfer member 106 by the transfer electric field and pressure. . Transfer of the toner image from the intermediate transfer member 106 to the recording medium 107 is performed by a secondary transfer roller 109 disposed on the back surface of the recording medium 107. A transfer electric field is formed by applying a voltage having a reverse polarity to the toner to the secondary transfer roller 109 and grounding the opposing roller 110 disposed at a position facing the secondary transfer roller 109. The image is transferred to the recording medium 107 (Patent Document 8).
[0007]
In addition, as shown in FIG. 4, there is a system in which the secondary transfer roller 109 is grounded and a voltage having the same polarity as the toner is applied to the opposing roller 110 to perform transfer (Patent Document 3).
[0008]
However, in the secondary transfer method using the contact transfer method as described above, the secondary transfer roller 109 is pressed against the opposing roller 110 via the intermediate transfer member 106 or the recording medium 105, and thus the toner image 105 is recorded. When transferring to the medium 107, an image defect called a void occurs. In particular, when a thick recording medium is used, the hollowing out phenomenon becomes remarkable. As a method for preventing the hollowing out phenomenon, a countermeasure is taken in many patent documents such as Patent Document 8 by specifying the shape factor of the toner, but this is not always sufficient.
[0009]
[Problems to be solved by the invention]
SUMMARY OF THE INVENTION An object of the present invention is to provide a color image forming apparatus provided with a transfer unit that is less likely to cause voids regardless of the shape of the toner.
[0010]
Another object of the present invention is to provide a color image forming apparatus capable of improving transfer efficiency by making it difficult for voids to occur, thereby reducing the amount of waste toner and reducing waste.
[0011]
Another object of the present invention is to provide a color image forming apparatus that is less likely to cause voids even when transferring onto thick paper.
[0012]
[Means for Solving the Problems]
In order to solve the above problems, the present invention provides a developing unit that forms a toner image on an electrostatic latent image carrier, a primary transfer unit that transfers the toner image onto a belt-shaped intermediate transfer member, and the intermediate unit. In a color image forming apparatus having a secondary transfer means for transferring a toner image on a transfer body to a recording medium, the intermediate transfer body is stretched by first and second rollers, and the stretched intermediate transfer body is A secondary transfer roller is pressed against the surface to wind the intermediate transfer member around the secondary transfer roller , and a charge having the same polarity as the toner is applied to the intermediate transfer member at a position facing the secondary transfer roller across the intermediate transfer member. A first corona discharger for applying to the transfer member is provided, and a second corona discharger for adsorbing the recording medium to the intermediate transfer member is provided upstream of the secondary transfer roller . 2 corona discharger, the first row Wherein a point at which the intermediate transfer member is in contact with the recording medium sandwiched between the recording medium, as the discharge electrode at a position on approximately an extension line of said first roller line connecting the center of that position and It has one feature in the arrangement .
[0013]
Another feature of the present invention is that a third corona discharger is provided on the downstream side of the secondary transfer roller,
Corona discharger said third said recording medium and said intermediate transfer member and that is peeled off, placed so that the second roller discharge electrode on the downstream side of the extension line of the line connecting the centers of position It is to have done.
[0014]
Another feature of the present invention is that an alternating current is applied to the discharge electrode of the third corona discharger.
[0016]
Another feature of the present invention is that the volume resistance value of the intermediate transfer member is set to 10 ⁷ to 10 ¹² Ωcm, and the volume resistance value of the secondary transfer unit is selected to be smaller than the resistance value.
[0017]
Another feature of the present invention resides in that the secondary transfer means is constituted by a secondary transfer roller having a volume resistance smaller than that of the intermediate transfer body and a surface made of an elastic body.
Other features and advantages of the present invention will be more clearly understood from the following description.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 5 is a schematic view showing an embodiment of a color image forming apparatus according to the present invention. In FIG. 5, reference numeral 106 denotes an intermediate transfer belt, which runs at a constant speed in the direction of the arrow. Four image forming units are arranged around the intermediate transfer member 106. Reference numeral 100 denotes a photosensitive drum included in each image forming unit. Reference numeral 1 denotes a charger for uniformly charging the photosensitive drum 100. An exposure apparatus 2 exposes the surface of the uniformly charged photoreceptor 100 and forms an electrostatic latent image on the surface. Reference numerals 101 to 104 denote developing machines that develop electrostatic latent images to form toner images, and form a yellow toner image 111, a magenta toner image 112, a cyan toner image 113, and a black toner image 114, respectively.
[0019]
Reference numeral 115 denotes a transfer device for transferring the toner images 111 to 114 to the intermediate transfer member 106. In this embodiment, a transfer device using corona discharge is used as the transfer device 115. Reference numeral 3 denotes a cleaning unit for removing the toner remaining on each photoconductor 100 after the toner image is transferred to the intermediate transfer body 106.
[0020]
Reference numeral 107 denotes a recording medium such as paper or OHP. Reference numeral 109 denotes a secondary transfer roller for transferring the toner image from the intermediate transfer member 106 to the recording medium 107, and is pressed against the surface formed by the two rollers 5 and 6 for stretching the intermediate transfer member 106. Use. Reference numeral 4 denotes a secondary transfer roller which is disposed at a position opposite to 109 and is a corona discharger for charging the intermediate transfer body 106 from the back surface to form a transfer electric field. Reference numeral 7 denotes a cleaning unit for removing the toner remaining on the intermediate transfer member 106.
[0021]
Next, a color image forming operation by this apparatus will be described. First, after the power is turned on, an image information signal is sent for each color from an information processing apparatus (not shown) to an image forming apparatus that is in a print standby state, and each exposure apparatus 2 emits a laser beam corresponding to a toner image according to the image information signal. Irradiation is performed on each photosensitive drum 100 uniformly charged by each charger 1, and an electrostatic latent image is formed on each photosensitive drum 100.
[0022]
Next, the electrostatic latent images formed by the respective exposure devices 2 on the respective photosensitive drums 100 are developed by the developing units 101 to 104 to form toner images 111 to 114 of the respective colors. The transfer unit 115 applies a charge having a polarity opposite to that of the toner to the back surface of the intermediate transfer member. By grounding the photosensitive drum, the toner images 111 to 114 of each color receive a force moving in the direction of the intermediate transfer member 106 and are transferred to the intermediate transfer member 106. The toner that cannot be completely transferred by the primary transfer and remains on each photosensitive drum 100 is removed from each photosensitive drum 100 by each cleaning unit 3.
[0023]
Next, the color image formed on the intermediate transfer member 106 is conveyed to the secondary transfer unit, and the recording medium 107 is also sent to the secondary transfer unit at a timing that matches the color image. The present invention is characterized by the configuration of the secondary transfer portion. Examples of the secondary transfer unit in the apparatus of the present invention will be described below.
(Example 1)
FIG. 1 is a schematic diagram showing the configuration of an embodiment of a secondary transfer unit in an image forming apparatus according to the present invention.
In the figure, reference numeral 8 denotes a corona discharger, which supplies the recording medium 107 with charges for adsorbing the recording medium 107 to the intermediate transfer member 106. Reference numeral 109 denotes a secondary transfer roller in which the periphery of the metal roller is covered with a semiconductive material, and the metal roller is grounded. The corona discharger 4 disposed at a position facing the secondary transfer roller 109 applies a charge having the same polarity as that of the toner to the back surface of the intermediate transfer member 106 and forms a transfer electric field between the secondary transfer roller 106 and the secondary transfer roller 106. The corona discharger 4 is discharged by constant voltage control. As a result, the toner image is transferred to the recording medium 107.
[0024]
Reference numeral 9 denotes a corona discharger, whereby the recording medium 107 is easily peeled from the intermediate transfer member 106. Thereafter, the recording medium 107 is fixed by a fixing device (not shown) to become a printed matter.
[0025]
In this embodiment, the intermediate transfer member 106 is an endless belt-like material, and carbon black is contained in a polyimide resin so that the volume resistance value is 10 ⁷ to 10 ¹² Ωcm, and the thickness thereof is 70 to 110 μm. It is. The secondary transfer roller 109 is a foam having a volume resistance set to a value lower than that of the intermediate transfer member.
[0026]
As described in the conventional example, a hollowing out phenomenon frequently occurs in the method in which the secondary transfer roller 109 is pressed against the opposing roller 110 (a metal roller or a roller having a metal roller covered with a rubber layer) as shown in FIGS. In particular, it tends to be prominent in an electrophotographic apparatus that performs high-speed printing. In an electrophotographic apparatus that performs high-speed printing, there is a tendency that the toner is softly designed in order to secure the fixability of the toner image in the fixing device. As a result, when pressure is applied at the secondary transfer portion, the toner tends to aggregate.
[0027]
FIG. 6 shows an example of the relationship between the degree of toner aggregation and the occurrence rate of voids. Here, about 1 g of toner is put in a container and a predetermined load (g / cm ² ) is added thereto, then the toner is transferred to a 75 μm mesh sieve, and a vibration with a width of 3 mm is given in the left and right directions for 1 minute, and then the mesh This is a value obtained by multiplying 100 by the value obtained by dividing the weight of the toner remaining on the toner by the weight of the toner in the container.
[0028]
In addition, the amount of voids generated was transferred by using an electrophotographic apparatus having a process speed of 314 mm / sec by applying the same load as that applied when measuring the degree of aggregation to the convex image of 10 dots per side shown in FIG. This is the rate of occurrence of voids in the convex image. A value obtained by multiplying the value of the number of convex images in which voids were recognized by the total convex image and multiplying by 100 was defined as the void occurrence rate. It can be seen from FIG. 6 that when the degree of aggregation of the toner increases, the void phenomenon tends to occur.
[0029]
FIG. 8 is a graph showing the relationship between the load (g / cm ² ) applied to the toner and the toner aggregation degree. Regarding the relationship between the load and the degree of aggregation, the larger the load is, the larger the degree of aggregation is. Therefore, the transfer load cannot be increased so much. However, if the load is small, a transfer nip cannot be formed and transfer efficiency is deteriorated. That is, in the contact between the secondary transfer roller 109 and the counter roller 110 as shown in FIGS. 2 to 4, if the force applied to the secondary transfer roller 109 is increased, the elastic layer of the secondary transfer roller also increases the strain contact area. Since the force applied to the transfer roller 109 is increased, there is almost no effect of reducing the load, and it is difficult to reduce the void. On the other hand, if the force applied to the secondary transfer roller 109 is reduced in order to reduce voids, transfer efficiency cannot be obtained, so it is difficult to achieve both void and transfer efficiency.
[0030]
If a soft transfer roller is used, a wide transfer nip can be formed with a small pressing force, so that the load (g / cm ² ) is small and an image with good transfer efficiency can be obtained without being hollow out, but the life of the transfer roller is shortened. .
[0031]
For the same reason, when a drum-shaped intermediate transfer member is used and the transfer is performed with a roller member, a hollow portion is likely to occur. Therefore, in order to use a hard transfer roller and secure a transfer nip width, the secondary transfer roller is configured so that the intermediate transfer body 106 is wound around the secondary transfer roller 109 and a load is not locally applied. A configuration in which the facing roller 110 is not provided at the 109 facing position is desirable.
[0032]
Based on the above consideration, in the present invention, the secondary transfer roller is pressed against the surface formed by being stretched by the two rollers, and a corona charger is provided at a position facing the secondary transfer roller. A charge having the same polarity as that of the toner is applied.
[0033]
With this configuration, the transfer nip width can be widened without applying a large transfer load (g / cm ² ) as compared with the method of FIGS. As a result, as shown in FIGS. 2 to 4, in the method of transferring between the secondary transfer roller 109 and the opposing roller 110, even if toner that has lost voids is used, the degree of aggregation can be kept small and no voids are lost. In addition, an image with good transfer efficiency can be obtained. Further, even if thick paper is used, it is difficult for the hollows to occur.
(Example 2)
FIG. 9 is a schematic diagram showing the configuration of another embodiment of the secondary transfer unit in the image forming apparatus according to the present invention.
This transfer portion presses a secondary transfer roller 109 having a volume resistance smaller than that of the intermediate transfer body 106 and having a surface made of an elastic body against the surface of the intermediate transfer body 106 formed by the two rollers 5 and 6, so The toner is transferred to the recording medium 107 by providing the intermediate transfer body charger 4 for applying a charge having a reverse polarity to the toner to the back surface of the intermediate transfer body 106.
[0034]
In this configuration, the recording medium 107 is attracted to the intermediate transfer member 106 by the corona discharger 8 that discharges charges having a polarity opposite to that of the toner. The corona discharger 8 was installed so that the discharge electrode for performing corona discharge was substantially on the extended line of the center of the roller 5 and the contact point between the intermediate transfer member 106 and the recording medium 107. If the corona discharger 8 is provided extremely upstream or downstream from the contact point between the center of the roller 5 and the intermediate transfer member 106 and the recording medium, the suction cannot be performed efficiently.
[0035]
In this configuration, the recording medium 107 is peeled from the intermediate transfer member 106 by the corona discharger 9 in which an alternating constant current is applied to the discharge electrode. The corona discharger 9 is installed on the downstream side of the center of the roller 6, and substantially on the extended line of the separation point of the intermediate transfer member 106 and the recording medium 107. When the corona discharger 9 is installed on the upstream side of the center of the roller 6 and on the substantially extended line of the peeling point between the intermediate transfer member 106 and the recording medium 107, the recording medium is given an excess charge more than the charge necessary for peeling, and conversely the peeling. Can not be done well. The discharge may be direct current + alternating current, but the alternating current alone is easier to peel off the recording medium 107.
[0036]
【The invention's effect】
As is apparent from the above description, the color image forming apparatus according to the present invention does not press the secondary transfer roller against the opposing roller, but the surface of the intermediate transfer member that runs over the first and second rollers. In addition to pressing the secondary transfer roller, and means for charging the intermediate transfer member at a position facing the secondary transfer roller across the intermediate transfer member, a toner dropout phenomenon occurs regardless of the toner shape. There is an effect that can be difficult. In addition, since it becomes difficult for voids to occur, there is an effect that transfer efficiency is improved and the amount of waste toner and waste can be reduced.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a secondary transfer unit of an image forming apparatus of the present invention.
FIG. 2 is a schematic configuration diagram of a secondary transfer unit of a conventional image forming apparatus.
FIG. 3 is a schematic configuration diagram of a secondary transfer unit of a conventional image forming apparatus.
FIG. 4 is a schematic configuration diagram of a secondary transfer unit of a conventional image forming apparatus.
FIG. 5 is a schematic configuration diagram showing an embodiment of the image forming apparatus of the present invention.
FIG. 6 is an explanatory diagram illustrating an example of a relationship between the degree of aggregation of toner and a void phenomenon.
FIG. 7 is a view showing an image obtained by evaluating a void.
FIG. 8 is an explanatory diagram showing a relationship between a transfer roller load and a toner aggregation degree.
FIG. 9 is a schematic configuration diagram showing another embodiment of the secondary transfer portion in the image forming apparatus of the present invention.
[Explanation of symbols]
1 charger, 2 exposure device, 3 cleaning means, 4 intermediate transfer body charger, 5 rollers, 6 rollers, 7 cleaning means, 8 corona discharger, 9 corona discharger, 100 photosensitive drum, 101 yellow developing machine, 102 Magenta developing machine, 103, cyan developing machine, 104 black developing machine, 105 toner image, 106 intermediate transfer member, 107 recording medium, 108 primary transfer roller, 109 secondary transfer roller, 110 facing roller, 111 yellow toner image, 112 magenta Toner image 113, cyan toner image 114 black toner image 115 transfer device

Claims (5)

Developing means for forming a toner image on the electrostatic latent image carrier;
Primary transfer means for transferring the toner image onto a belt-like intermediate transfer member;
In a color image forming apparatus having secondary transfer means for transferring a toner image on the intermediate transfer member to a recording medium,
The intermediate transfer member is stretched by the first and second rollers, the secondary transfer roller is pressed against the surface of the stretched intermediate transfer member, the intermediate transfer member is wound around the secondary transfer roller, and the intermediate transfer member is A first corona discharger for applying a charge of the same polarity as the toner to the intermediate transfer member at a position facing the secondary transfer roller with the transfer member interposed therebetween;
A second corona discharger for adsorbing the recording medium to the intermediate transfer member is provided upstream of the secondary transfer roller ;
The second corona discharger includes a line connecting a point where the intermediate transfer body, which is sandwiched between the first roller and the recording medium , contacts the recording medium, and a center of the first roller. A color image forming apparatus, wherein the discharge electrode is disposed substantially at a position on an extension line. The third corona discharger is provided on the downstream side of the secondary transfer roller according to claim 1,
Corona discharger said third said recording medium and said intermediate transfer member and that is peeled off, placed so that the second roller discharge electrode on the downstream side of the extension line of the line connecting the centers of position the color image forming apparatus according to claim 1, wherein the the. The color image forming apparatus according to claim 2, wherein an alternating current is applied to a discharge electrode of the third corona discharger. 2. The color image forming apparatus according to claim 1, wherein the volume resistance value of the intermediate transfer member is 10 ⁷ to 10 ¹² Ωcm, and the volume resistance value of the secondary transfer unit is smaller than the resistance value.   2. A color image forming apparatus according to claim 1, wherein said secondary transfer means is constituted by a secondary transfer roller having a volume resistance smaller than that of said intermediate transfer body and having a surface made of an elastic body.

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