JP2006267486A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance transfer performance of a toner image to embossed paper. <P>SOLUTION: In a printer 10, positive charges are given to a transfer surface of the embossed paper P by a charging roll 34 before transfer and a transfer bias formed by superimposing AC voltage on DC voltage is impressed to a secondary transfer roll 11 at the time of transfer. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus in which a toner image carried on an image carrier is transferred to a recording medium by a transfer unit.

  In an image forming apparatus employing an electrophotographic system, when an image is formed on a recording medium having a low surface smoothness such as embossed paper, the transfer potential of the concave portion on the surface of the recording medium is lower than the transfer potential of the convex portion. Thus, there is a problem in that the toner is not sufficiently transferred to the concave portion, and the image is white. For this reason, conventionally, a method has been devised that detects the smoothness and texture of the surface of the recording medium, changes the transfer current and transfer pressure, and changes other image forming conditions (for example, patents). References 1 to 3).

  In Patent Document 1, the transfer performance of a special recording medium is improved by changing the transfer pressure in accordance with the surface smoothness of the recording medium. In Patent Document 2, the type of recording medium and the surface smoothness are improved. Accordingly, the image quality of the special recording medium is improved by changing the voltage value of the transfer bias or changing the fixing temperature. Further, in Patent Document 3, unevenness appearing in an image on a special recording medium is suppressed by changing various image forming parameters such as the amount of toner according to the texture of the recording medium.

However, in the image forming apparatus of the type that directly transfers the toner image from the photoconductor to the recording medium, the transfer performance to the embossed paper has been improved by using the above-described conventional technology. In the image forming apparatus of the type in which the toner image is transferred to the body and the toner image is transferred from the intermediate transfer member to the recording medium, the transfer performance to the embossed paper is not improved even when the above-described conventional technology is used. . On the other hand, when the toner amount was increased, the white spots of the image deteriorated.
JP 2002-156839 A JP 2002-202638 A Japanese Patent Laid-Open No. 2001-337496

  The present invention has been made in consideration of the above facts, and an object thereof is to improve the transfer performance of a toner image onto a recording medium having a low surface smoothness.

  The image forming apparatus according to claim 1, comprising: an image carrier that carries a toner image; and a transfer unit that transfers the toner image carried on the image carrier to a recording medium. A transfer bias in which an alternating voltage is superimposed on a DC voltage is applied to the transfer means.

  In the image forming apparatus according to the first aspect, the toner image carried on the image carrier is transferred to the recording medium by the transfer means. Here, a transfer bias in which an alternating voltage is superimposed on a DC voltage is applied to the transfer means. For this reason, when the smoothness of the surface of the recording medium is low, the toner reciprocates between the concave portion on the surface of the recording medium and the image carrier and contacts the concave portion on the surface of the recording medium. It is possible to suppress the transfer failure of the toner to the concave portion on the surface, and it is possible to suppress the whiteout of the image on the recording medium having a low surface smoothness.

  An image forming apparatus according to a second aspect is the image forming apparatus according to the first aspect, wherein the detecting means detects the smoothness of the transfer surface of the recording medium, and the transfer of the recording medium detected by the detecting means. When the smoothness of the surface is lower than a predetermined value, a transfer bias in which an alternating voltage is superimposed on a DC voltage is applied to the transfer unit, and the smoothness of the transfer surface of the recording medium detected by the detection unit is higher than a predetermined value In this case, the transfer unit includes a first control unit that applies a transfer bias of a DC voltage to the transfer unit.

  In the image forming apparatus according to claim 2, when the smoothness of the surface of the recording medium is detected by the detection unit and the smoothness of the surface of the recording medium detected by the detection unit is lower than a predetermined value, the first control unit Then, a transfer bias in which an alternating voltage is superimposed on a DC voltage is applied to the transfer means. When the smoothness of the surface of the recording medium detected by the detection unit is higher than a predetermined value, the control unit applies a transfer bias of a DC voltage to the transfer unit.

  As a result, it is possible to suppress white spots in an image with respect to a recording medium having a surface smoothness lower than a predetermined value, and to suppress toner scattering with respect to a recording medium with a surface smoothness higher than a predetermined value. Can be suppressed.

  An image forming apparatus according to a third aspect of the present invention includes an image carrier that carries a toner image, a transfer unit that transfers the toner image carried on the image carrier to a recording medium, and an upstream side in the transport direction of the transfer unit. And charging means for charging the surface of the recording medium to a polarity opposite to the polarity of the toner.

  In the image forming apparatus according to the third aspect, the toner image carried on the image carrier is transferred to the recording medium by the transfer means. The surface of the recording medium is charged to a polarity opposite to the polarity of the toner by a charging unit upstream of the transfer unit in the transport direction.

  Here, the amount of charge applied to the surface of the recording medium is proportional to the size of the gap between the image carrier and the surface of the recording medium. It becomes higher than the potential.

  For this reason, since the transfer potential of the concave portion on the surface of the recording medium is higher than the transfer potential of the convex portion on the surface of the recording medium, transfer failure of the toner to the concave portion on the surface of the recording medium can be suppressed, and the smoothness of the surface Can suppress white spots in an image with a low recording medium.

  An image forming apparatus according to a fourth aspect is the image forming apparatus according to the third aspect, wherein a detecting means for detecting the smoothness of the surface of the recording medium, and a surface of the recording medium detected by the detecting means. And second control means for operating the charging means when the smoothness is lower than a predetermined value.

  In the image forming apparatus according to claim 4, when the smoothness of the surface of the recording medium is detected by the detection unit and the smoothness of the surface of the recording medium detected by the detection unit is lower than a predetermined value, the second control unit Activating the charging means.

  As a result, white spots in the image can be suppressed for a recording medium having a surface smoothness lower than a predetermined value. Further, when a recording medium having a high surface smoothness and capable of being transferred satisfactorily without being charged before being transferred, power consumption can be reduced by stopping the charging means.

  The image forming apparatus according to claim 5, wherein an image carrier that carries a toner image, a transfer unit that transfers the toner image carried on the image carrier to a recording medium, and a surface smoothness of the recording medium are detected. And detecting means for detecting the toner, and when the smoothness of the surface of the recording medium detected by the detecting means is lower than a predetermined value, the toner flying property is higher than when the smoothness of the surface of the recording medium is higher than the predetermined value. And a control means.

  In the image forming apparatus according to claim 5, when the smoothness of the surface of the recording medium detected by the detection unit is lower than a predetermined value, the third control unit performs recording by the method according to claims 1 to 4 described above. The flying property of the toner is made higher than when the surface smoothness of the medium is higher than a predetermined value. As a result, white spots in the image on the recording medium having a low surface smoothness can be suppressed.

  Since the present invention is configured as described above, it is possible to improve the transfer performance of a toner image onto a recording medium having a low surface smoothness.

  Embodiments of the present invention will be described below with reference to the drawings.

  As shown in FIG. 1, the printer 10 is a full-color laser beam printer that performs full-color printing with yellow (Y), magenta (M), cyan (C), and black (K) toners that do not contain an infrared absorbing material. Further, the printer 10 includes print engines 12Y, 12M, 12C, and 12K (hereinafter, referred to as 12Y to K) that use Y, M, C, and K toners along the flat surface 14A on the upper side of the intermediate transfer belt 14. In the so-called tandem type printer arranged, the print engines 12Y to 12K sequentially transfer and superimpose the Y to K toner images on the intermediate transfer belt 14 while the intermediate transfer belt 14 makes one round, and are full color toners. Form an image.

  The intermediate transfer belt 14 is stretched by rolls 11A, 13, 15, 16, and 18, and is rotated in the direction of arrow A in the figure (counterclockwise direction in the figure). The rolls 16 and 18 are arranged in the horizontal direction, and the flat surface 14 </ b> A described above is stretched between the rolls 16 and 18. The rolls 13 and 15 are arranged in the horizontal direction below the rolls 16 and 18, and the roll 11 </ b> A is disposed below the rolls 13 and 15. A roll 11B provided on the outer peripheral side of the intermediate transfer belt 14 is in contact with the roll 11A with the intermediate transfer belt 14 in between, and the secondary transfer roll 11 is configured by the roll 11A and the roll 11B. A secondary transfer nip N <b> 2 is formed with the transfer roll 11. The recording paper P is fed from the paper feed cassette 13 to the secondary transfer nip N2, and at the same time, a transfer bias is applied to the secondary transfer roll 11, so that a full-color toner image formed on the intermediate transfer belt 14 is obtained. Is transferred to the recording paper P.

  A fixing device 20 is disposed on the downstream side in the transport direction of the secondary transfer nip N2. When the recording paper P passes through the fixing device 20, the toner on the recording paper P is heated and pressed to perform recording. It is fixed on the paper P. Then, the recording paper P is discharged from the printer 10.

  Next, the print engines 12Y to 12K will be described. The print engines 12Y to 12K include a photosensitive member 22, a cleaner 24, a charging roll 26, an exposure head 28, and a developing device that are sequentially arranged around the photosensitive member 22 in the rotation direction of the photosensitive member 22 (in the direction of arrow B in the figure). 30. The photosensitive member 22 abuts on the outer peripheral side of the flat surface 14A of the intermediate transfer belt 14, and a primary transfer roll 32 provided on the inner peripheral side of the intermediate transfer belt 14 is interposed between the photosensitive member 22 and the intermediate transfer belt 14. The primary transfer nip N1 is formed by the photoconductor 22 and the primary transfer roll 32.

  In the print engines 12Y to 12K, first, a charging bias in which an AC voltage is superimposed on a DC voltage is applied to a charging roll 26 that rotates in contact with the photosensitive member 22, so that the photosensitive member 22 is uniformly charged. Next, an exposure head 28 such as an LED array exposes the charged surface of the photosensitive member 22 to form an electrostatic latent image corresponding to the image data.

  Next, a developing bias is applied to the developing roll 30A of the developing device 30, and the toner adhering to the developing roll 30A moves onto the electrostatic latent image on the photoconductor 22, so that the electrostatic latent image on the photoconductor 22 is formed. Developed. Then, a transfer bias is applied to the primary transfer roll 32, and the toner image is transferred from the photoreceptor 22 to the intermediate transfer belt 14 at the primary transfer nip N1. Finally, the cleaner 24 cleans the surface of the photoconductor 22 by scraping off toner remaining on the photoconductor 22 without being transferred to the intermediate transfer belt 14.

  A charging roll 34 is disposed upstream of the secondary transfer nip N2 in the transport direction. The charging roll 34 includes a first roll 34A that contacts the transfer surface (front surface) of the recording paper P, and a second roll 34B that contacts the back surface of the recording paper P. The positive electrode 36 is connected, and the negative electrode of the AC power source 36 is connected to the second roll 34A.

  A sensor 38 that detects the smoothness of the transfer surface of the recording paper P is disposed on the upstream side of the charging roll 34 in the transport direction. The sensor 38 includes a light projecting sensor (not shown) that projects light toward the transfer surface of the recording paper P, and a light receiving sensor (not shown) that receives the light emitted from the light projecting sensor and reflected by the transfer surface of the recording paper P. The light quantity received by the light receiving sensor is converted into a signal and output.

  A control unit 40 is connected to the output of the sensor 38, and a light amount detection signal is input to the control unit 40. The controller 40 determines the smoothness of the transfer surface of the recording paper P according to the light amount detection signal. That is, when the smoothness of the transfer surface of the recording paper P is high, the amount of light reflected by the transfer surface of the recording paper P increases, and when the smoothness of the transfer surface of the recording paper P is low, the recording paper P Since the amount of light reflected on the transfer surface of the recording paper P is reduced, the control unit 40 determines that the smoothness of the transfer surface of the recording paper P is high when the light receiving amount of the light receiving sensor is large, and the light receiving amount of the light receiving sensor is small. Furthermore, it is determined that the smoothness of the transfer surface of the recording paper P is low.

  Further, a power source 42 for transfer bias is connected to the secondary transfer roll 11. The power source 42 includes a DC power source 42A and an AC power source 42B, the positive electrode of the DC power source 42A is connected to the roll 11B, the negative electrode of the DC power source 42A is connected to one pole of the AC power source 42B, and The other pole of the AC power source 42B is connected to the roll 11A.

  Here, a control unit 40 is connected to the power sources 36 and 42, and on / off of the power sources 36 and 42 is controlled by the control unit 40. Hereinafter, a method of controlling the power sources 36 and 42 will be described with reference to the flowchart of FIG.

  First, when a print job is started, a processing routine is started and the process proceeds to step 100. In step 100, the negative determination is repeated until a light amount detection signal is received from the sensor 38. If the determination is affirmative, the process proceeds to step 101. In step 101, it is determined whether the amount of light received by the sensor 38 is lower than a predetermined value, that is, whether the smoothness of the transfer surface of the recording paper P is lower than a predetermined value. Then, the process proceeds to step 102. In step 102, the DC power source 42 </ b> A of the power source 42 is turned on, a DC voltage is applied to the secondary transfer roll 11, and the toner image is transferred from the intermediate transfer belt 14 to the recording paper P. Then, the process proceeds to Step 105.

  On the other hand, in step 103, the power source 36 is turned on, a DC voltage is applied to the charging roll 34, and a positive charge is applied to the transfer surface of the recording paper P. Next, in step 104, the DC power source 42 </ b> A and the AC power source 42 </ b> B of the power source 42 are turned on, and a transfer bias in which the AC voltage is superimposed on the DC voltage is applied to the secondary transfer roll 11. The toner image is transferred to P. Then, the process proceeds to step 105, the negative determination is repeated until the print job is completed, the process returns to step 100, and if the determination is affirmed, the processing routine is ended.

Here, the predetermined value of the amount of light received by the sensor 38 in step 101 is a numerical value when embossed paper P (Rezac 66 (product name), 151 g / m ² , maximum surface roughness is 80 to 100 μm) is passed. It is set slightly higher. That is, when the embossed paper P is passed, a DC voltage is applied to the charging roll 34 to impart a positive charge to the transfer surface of the embossed paper P, and an AC voltage is superimposed on the DC voltage on the secondary transfer roll 11. The transfer bias applied is applied.

  As shown in FIG. 3, the charging roll 34 imparts a positive charge to the transfer surface of the embossed paper P before transfer, so that the flying property of the negatively charged toner is increased, and the toner is transferred onto the transfer surface of the embossed paper P. It becomes easy to adsorb electrostatically. That is, the transfer potential of the toner is improved by increasing the transfer potential of the transfer surface of the embossed paper P.

  Here, the gap between the concave portion P1 on the transfer surface of the embossed paper P and the intermediate transfer belt 14 is larger than the gap between the convex portion P2 and the intermediate transfer belt 14. Further, since the discharge start voltage is proportional to the gap in the discharge region, the amount of charge applied to the embossed paper P is proportional to the size of the gap between the surface of the embossed paper P and the intermediate transfer belt 14. For this reason, the charge amount imparted to the concave portion P1 is larger than the charge amount imparted to the convex portion P2. For this reason, since the transfer potential at the concave portion P1 is higher than the transfer potential at the convex portion P2, transfer failure of the toner to the concave portion P1 can be suppressed.

  On the other hand, at the time of transfer, toner is reciprocated between the intermediate transfer belt 14 and the transfer surface of the embossed paper P by applying a transfer bias in which an AC voltage is superimposed on a DC voltage to the secondary transfer roll 11 to form a concave portion. Since it is in contact with P1, transfer failure of the toner to the recess P1 can be suppressed.

  Further, when a recording paper P such as plain paper having a smoothness of the transfer surface higher than that of the embossed paper P is passed, only the DC voltage is applied to the secondary transfer roll 11, thereby scattering toner. The image quality can be improved. Note that a highly uniform charge can be imparted to the transfer surface of the recording paper P having high transfer surface smoothness simply by applying a DC voltage to the secondary transfer roll 11. Therefore, toner transfer failure does not occur.

  Next, the results of experiments conducted to confirm the effects of the present invention will be described. In addition, as shown in the table of FIG. 4, the degree of white spots in the recesses P1 was ranked from grade 1 to grade 6.

  First, in a state where only a DC voltage of 2.0 kV is applied to the secondary transfer roll 11 without applying a DC voltage to the charging roll 34, a blue 20 mm × 20 mm patch with a toner amount of 200% is applied to the embossed paper P described above. As a result, grade 4 was obtained in which the toner did not get much on the recess P2.

  Next, with a DC voltage of −2.0 kV applied to the roll 34 </ b> B of the charging roll 34 and only a DC voltage of 2.0 kV applied to the secondary transfer roll 11, blue 20 mm × 20 mm with a toner amount of 200%. When the above-mentioned patch was formed on the embossed paper P described above, the concave portion P2 became a slightly white grade 2. That is, by applying a positive charge to the transfer surface of the embossed paper P before transfer, the white spots of the image on the embossed paper P are improved.

  Finally, in a state where a DC voltage is not applied to the charging roll 34 but a DC voltage of 1 kv and 2 kHz is applied to the secondary transfer roll 11 and a DC voltage of 1 kv and 2 kHz, 20% × 20 mm of blue having a toner amount of 200%. 5 is formed on the above-described embossed paper P. As shown in the graph of FIG. 5, the degree of whiteout in the image is intermediate between grades 3 and 4, and when the AC voltage is increased to 2 kv, the whiteout in the image The grade was grade 3 with white grooves. That is, by applying a transfer bias in which an AC voltage is superimposed on a DC voltage to the secondary transfer roll 11, white spots of the image on the embossed paper P are improved.

  In the present embodiment, the embossed paper P has been described as an example, but the same effect can be obtained by the present invention for other recording media having a low surface smoothness.

  In the present embodiment, the detection means for detecting the smoothness of the surface of the recording medium is a sensor. However, instead of the sensor, the determination for determining the smoothness of the surface of the recording medium from a preset type of the recording medium. Means are also applicable. In this case, although there is a disadvantage that the smoothness of the surface of the recording medium cannot be automatically detected, there is an advantage that a sensor is not required and the cost of parts can be reduced.

1 is a diagram illustrating an outline of a printer according to an embodiment. 5 is a flowchart for explaining a method for controlling the power source of the printer according to the embodiment. It is sectional drawing which expanded the recessed part periphery of the embossed paper. It is a table | surface of the grade of the outline of the image of embossed paper. It is a graph which shows the relationship between the AC voltage of a secondary transfer roll, and the white-out grade of the image of embossed paper.

Explanation of symbols

10 Printer (image forming device)
11 Secondary transfer roll (transfer means)
14 Intermediate transfer belt (image carrier)
38 sensor (detection means)
40 control unit (first control means, second control means, third control means)
P Recording paper (recording medium)

Claims (5)

An image carrier for carrying a toner image;
An image forming apparatus comprising: transfer means for transferring a toner image carried on the image carrier to a recording medium;
An image forming apparatus, wherein a transfer bias in which an alternating voltage is superimposed on a DC voltage is applied to the transfer unit. Detection means for detecting the smoothness of the surface of the recording medium;
When the smoothness of the surface of the recording medium detected by the detection means is lower than a predetermined value, a transfer bias in which an alternating voltage is superimposed on a DC voltage is applied to the transfer means, and the recording medium detected by the detection means A first control means for applying a DC voltage transfer bias to the transfer means when the surface smoothness is higher than a predetermined value;
The image forming apparatus according to claim 1, further comprising: An image carrier for carrying a toner image;
Transfer means for transferring the toner image carried on the image carrier to a recording medium;
A charging unit for charging the surface of the recording medium to a polarity opposite to the polarity of the toner on the upstream side in the transport direction of the transfer unit;
An image forming apparatus comprising: Detection means for detecting the smoothness of the surface of the recording medium;
A second control unit that operates the charging unit when the smoothness of the surface of the recording medium detected by the detection unit is lower than a predetermined value;
The image forming apparatus according to claim 3, further comprising: An image carrier for carrying a toner image;
Transfer means for transferring the toner image carried on the image carrier to a recording medium;
Detection means for detecting the smoothness of the surface of the recording medium;
Third control means for increasing toner flying performance when the smoothness of the surface of the recording medium detected by the detection means is lower than a predetermined value, than when the smoothness of the surface of the recording medium is higher than a predetermined value;
An image forming apparatus comprising:

Images