JP2016090622A - Image formation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image formation device that allows application of a voltage having a reverse polarity of a transfer voltage to more properly secure separability of a sheet.SOLUTION: In an image formation device comprising: an image carrier body that carries a toner image, and forms a transfer area between a belt conveying a sheet and the image carrier body; an electric charging unit that electrically charges the belt in response to the applied voltage; and a voltage control unit that applies to the electric charging unit a transfer voltage having a reverse polarity with respect to the toner image, in which the sheet is conveyed so as to pass through the transfer area, and application of the transfer voltage causes the toner image to be transferred to the sheet in the transfer area, the voltage control unit is configured to execute reverse voltage application processing of applying to the electric charging unit a reverse voltage having a reverse polarity of the transfer voltage when a part from a tip end in the sheet to a first interval therein passes through the transfer area; detect a second interval from the tip end of the sheet to a start position of the toner image to be transferred on the sheet; and set the first interval on the basis of a result of the detection.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an image forming apparatus such as a printer.

  In general, an image forming apparatus (printer, copier, facsimile, etc.) using an electrophotographic process technology generates an electrostatic latent image by irradiating (exposing) a charged photoconductor with a laser beam based on image data. Form. Then, by supplying toner from the developing device to the photosensitive member on which the electrostatic latent image is formed, the electrostatic latent image is visualized to form a toner image (development). Further, after the toner image is transferred to a sheet, the image is formed on the sheet by fixing by heating and pressing.

  In the above-described image forming apparatus, a transfer nip portion is formed between the photosensitive member and the transfer belt, and the conveyed paper is formed so as to pass through the transfer nip portion. In addition, for example, a transfer roller (charging unit) is disposed at a position facing the photoconductor across the nip portion, and a transfer voltage having a polarity opposite to that of the toner image is applied to the transfer roller, so that the toner on the photoconductor. The image is transferred to the paper.

  Japanese Patent Application Laid-Open No. H10-228561 discloses a technique for changing the transfer bias application timing based on image processing information. In this technique, in order to prevent a transfer memory, when a predetermined condition is satisfied, a transfer bias is applied after the leading edge of the transfer material has passed through the transfer nip.

  Japanese Patent Application Laid-Open No. 2004-228561 discloses a technique in which a voltage to be applied is switched to a voltage on the transfer polarity side after a voltage having a polarity opposite to that at the time of transfer is applied to the leading edge of the paper until the machine-specific image area reaches the transfer position. ing. Patent Document 3 discloses a technique for changing the application timing of a transfer voltage based on humidity environment information. In this technique, in order to improve the separation of the paper, the application timing is set closer to the image leading end side of the transfer material in the case of high humidity than in the case of appropriate humidity.

JP 2001-154505 A JP-A-11-174860 JP 2000-227745 A

  In the belt transfer type image forming apparatus described above, in a high humidity environment, due to a decrease in resistance of the transfer belt or the paper, a positive charge for transferring an image is transferred to the leading edge of the paper as indicated by an arrow in FIG. By attracting to a negatively charged photoconductor, separation failure is likely to occur. In particular, when the apparatus is left in a high humidity environment for a long time, the transfer belt absorbs moisture and the resistance is further lowered, so that it is very difficult to ensure the sheet separation.

  For this reason, it is conceivable to apply a voltage having a polarity opposite to the transfer voltage corresponding to the vicinity of the leading edge of the sheet to ensure the separation of the sheet. In the above-described device of Patent Document 2, such a reverse polarity voltage is applied, but the reverse polarity voltage is applied at a uniform timing regardless of the start position of the image transferred to the paper. There is a possibility that the paper separation property cannot be ensured. Also, in the devices according to other patent documents, the applied voltage is not controlled in accordance with the start position of the image transferred to the paper, and there is a possibility that the paper separation property cannot be secured properly.

  SUMMARY OF THE INVENTION In view of the above-described problems, an object of the present invention is to provide an image forming apparatus that can secure a paper separation more appropriately by applying a voltage having a polarity opposite to a transfer voltage.

  An image forming apparatus according to the present invention includes an image carrier that forms a transfer region with a belt that carries a toner image and conveys a sheet, a charging unit that charges the belt according to an applied voltage, A voltage control unit that applies a transfer voltage having a polarity opposite to that of the toner image to the charging unit, conveys the sheet through the transfer region, and applies the transfer voltage to the transfer region in the transfer region. In the image forming apparatus for transferring a toner image to the sheet, the voltage control unit is configured such that when the portion from the leading edge to the first interval on the sheet passes through the transfer region, the charging unit has a polarity opposite to the transfer voltage. A reverse voltage application process for applying a reverse voltage is performed, wherein a second interval from the leading edge of the sheet to the start position of the toner image transferred to the sheet is detected, and a first interval is detected based on the detection result. Set interval Configuration to that.

  According to this configuration, it is possible to more appropriately ensure the separation of the paper by applying a voltage having a polarity opposite to the transfer voltage.

  More specifically, the voltage control unit sets the first interval at least shorter than the second interval, and sets the first interval to a shorter interval as the second interval is shorter. It is good also as a structure.

  More specifically, the voltage control unit may omit the reverse voltage application process when the second interval is shorter than a predetermined reference interval.

  More specifically, the above-described configuration further includes a humidity detection unit that detects humidity, and the voltage control unit executes the reverse voltage application process when the detected humidity falls below a predetermined reference humidity. A configuration may be omitted.

  More specifically, as the above-described configuration, a basis weight detection unit that detects the basis weight of the paper is provided, and the voltage control unit, when the detected basis weight exceeds a predetermined reference basis weight, It is good also as a structure which abbreviate | omits execution of a reverse voltage application process.

  According to the image forming apparatus of the present invention, it is possible to more appropriately ensure the separation of paper by applying a voltage having a polarity opposite to the transfer voltage.

1 is a block diagram illustrating a schematic configuration of an image forming apparatus according to an exemplary embodiment. It is a block diagram of the image forming transfer part which concerns on this embodiment. It is explanatory drawing regarding control of an applied voltage. It is a flowchart regarding the control procedure of an applied voltage. It is explanatory drawing regarding the generation | occurrence | production factor of a separation defect.

  Embodiments of the present invention will be described below with reference to the drawings. However, the content of the present invention is not limited to the embodiment.

[Configuration of image forming apparatus]
FIG. 1 is a block diagram illustrating a schematic configuration of an image forming apparatus X according to the present embodiment. As shown in the figure, the image forming apparatus X includes a paper feeding unit 1, an image forming transfer unit 2, a fixing unit 3, and a control unit 4. The image forming apparatus X is an electrophotographic image forming apparatus (for example, a printer). As a basic operation, the image forming apparatus X receives input of image data from the outside (for example, a PC), prints the image on paper, and discharges the image to the outside. Do.

  The paper feeding unit 1 includes a tray for storing paper, and supplies the paper to the image forming transfer unit 2 in accordance with the transfer timing of the toner image. The image forming transfer unit 2 performs processing (image forming processing) for creating a toner image based on input image data and processing (transfer processing) for transferring the toner image to a sheet. The sheet on which the toner image is transferred by the image forming transfer unit 2 is conveyed to the fixing unit 3.

  The fixing unit 3 plays a role of fixing the toner image transferred to the sheet to the sheet. Printing is achieved by fixing the toner image, and the fixed (printed) paper is discharged from the image forming apparatus X to the outside. The control unit 4 is constituted by, for example, a CPU and controls the operation of each unit in the image forming apparatus X.

  Next, a specific configuration of the image forming transfer unit 2 will be described with reference to FIG. In FIG. 2, a photosensitive drum (one form of image carrier) 211 is a rotatable member that carries a toner image. A charging device 212, an exposure device 213, a developing device 214, a transfer belt 215 for transferring a toner image formed on the photosensitive drum 211 to a sheet, and a PCC (cleaning) along the rotation direction (arrow direction) of the photosensitive drum 211. A pre-charger 216 and a cleaning device 217 (including a brush 217a and a blade 217b) for removing toner remaining on the photosensitive drum 211 are provided.

  The charging device 212 uniformly charges the surface of the photoconductive drum 211 with a negative polarity. The exposure device 213 is composed of, for example, a semiconductor laser, and irradiates the photosensitive drum 211 with laser light corresponding to an image. A positive charge is generated in the charge generation layer of the photosensitive drum 211 and is transported to the surface of the charge transport layer, whereby the surface charge (negative charge) of the photosensitive drum 211 is neutralized. An electrostatic latent image is formed on the surface of the photosensitive drum 211 due to a potential difference from the surroundings.

  The developing device 214 is, for example, a two-component developing type developing device, and forms a toner image by visualizing an electrostatic latent image by attaching toner to the surface of the photosensitive drum 211 (developing operation). The toner consumed by the developing operation is supplied by a toner supply mechanism (not shown).

  The transfer belt 215 has a two-layer structure of a semiconductive belt base material made of chloroprene rubber or the like and an insulating layer provided as a surface layer. The transfer belt 215 is stretched between the driven roller 223, the driving roller 222, and other rollers, and the surface of the transfer belt 215 is in contact with a part of the outer peripheral surface of the photosensitive drum 211 below the photosensitive drum 211. Are arranged as follows. That is, a transfer nip portion as a transfer region is formed between the transfer belt 215 and the photosensitive drum 211. The sheet is conveyed while being pressed against the photosensitive drum 211 by the transfer belt 215 at the transfer nip portion.

  A transfer roller 220 (one form of charging unit) is disposed inside the transfer belt 215 that contacts a part of the outer peripheral surface of the photosensitive drum 211. A power supply (not shown) for applying a transfer voltage Vt and a reverse voltage Vr, which will be described later, is connected to the transfer roller 220, and the voltage applied to the transfer roller 220 is controlled by the control unit 4.

  The control unit 4 basically has a positive polarity (reverse polarity to the toner) to the transfer roller 220 so that the transfer belt 215 has a predetermined transfer potential (positive polarity) when the paper passes through the transfer nip portion. A transfer voltage Vt is applied. As a result, the negative toner image on the photosensitive drum 211 is transferred to the sheet in contact with the photosensitive drum 211 in the transfer nip portion.

  However, the control unit 4 improves the separability of the sheet from the photosensitive drum 211, and therefore, when the transfer nip portion corresponds to the vicinity of the leading end of the sheet, the transfer roller 220 has a reverse voltage Vr having a polarity opposite to the transfer voltage Vt. Can be executed (hereinafter referred to as “reverse voltage application process”). Specific details regarding the control of the applied voltage will be described later.

  The PCC 216 removes unnecessary residual charges on the photosensitive drum 211. The cleaning device 217 serves to remove (clean) deposits such as residual toner adhered to the surface of the photosensitive drum 211 after transfer.

[Control of applied voltage]
Next, control of the applied voltage in this embodiment will be described. As described above, the control unit 4 executes the reverse voltage application process in order to improve the separation of the paper from the photosensitive drum 211. In this reverse voltage application process, the reverse voltage Vr is applied to the transfer roller 220 when a range from the leading edge on the paper to a certain interval (hereinafter, this interval is referred to as “first interval”) passes through the transfer region. It is processing.

  Then, when performing the reverse voltage application process, the control unit 4 refers to an interval from the leading end of the sheet to the start position (image start position) of the toner image transferred to the sheet (hereinafter, this interval is referred to as a “second interval”). ) And the first interval is set based on the detection result. A region from the leading edge of the paper to the second interval corresponds to a region where the toner image is not transferred. The detection of the second interval can be executed based on, for example, print contents received from an external device such as a PC, or a print margin setting by the user.

  The control unit 4 sets the first interval to be shorter than at least the second interval, and sets the first interval to a shorter interval as the second interval is shorter. That is, in this embodiment, the farther the image start position is from the front end of the paper, the longer the range on the paper (reverse voltage application range) where the reverse voltage Vr is applied when passing through the transfer nip portion.

  By making the reverse voltage application range as long as possible, it is generally more reliably prevented that the transfer charge of the image forming transfer unit 2 shifts to the front end of the paper, and the paper separation property is improved. However, when the reverse voltage application range reaches the portion where the toner image is transferred, the transfer of the toner image is lost. Therefore, in the present embodiment, consideration is given so that the first interval is at least shorter than the second interval. .

  FIG. 3 shows a specific example of how the applied voltage is controlled when (A) the second interval is relatively small and (B) the second interval is relatively large. In FIG. 3, the vertical axis represents the applied voltage, and the horizontal axis represents the positional relationship between the transfer nip portion and the paper or toner image (that is, the timing at which the positional relationship is realized). As shown in the figure, the first interval is controlled not to exceed the second interval, and the range to which the reverse voltage Vr is applied is controlled to be larger as the first interval is larger.

  As shown in FIG. 3, the first interval is a voltage switching position on the leading edge of the sheet and the sheet (when the position passes through the transfer nip portion, the applied voltage is switched from the reverse voltage Vr to the transfer voltage Vt). It can be said that this is the interval. The applied voltage is preferably a voltage value larger than the transfer voltage Vt immediately after switching from the reverse voltage Vr to the transfer voltage Vt, and is preferably set to the transfer voltage Vt immediately before the toner image start position. By such applied voltage control, the rise from the reverse voltage to the transfer voltage is accelerated, and the reverse voltage Vr can be applied for a longer time immediately before the toner image start position.

  Moreover, the control part 4 may abbreviate | omit a reverse voltage application process in the condition where the necessity of performing a reverse voltage application process is small. For example, when the second interval is very small, a sufficient effect of the reverse voltage application process cannot be obtained (or a reverse phenomenon occurs as will be described later), so the reverse voltage application process may be omitted. good.

  In addition, a humidity detecting unit is provided, and when the humidity is sufficiently low, the sheet separation property is unlikely to deteriorate, and therefore the reverse voltage application process may be omitted. Also, a means for detecting the basis weight of the paper may be provided, and the reverse voltage application process may be omitted because the paper separability is unlikely to deteriorate even when the basis weight is sufficiently high.

  Here, on the assumption that the image forming apparatus X is provided with a means for detecting the humidity and the basis weight of the paper, a specific example of the control procedure of the applied voltage based on the above description will be described with reference to the flowchart shown in FIG. While explaining.

  Upon receiving the print instruction, the control unit 4 detects the second interval in the current printing (step S11), and determines whether or not the second interval is shorter than a predetermined reference interval (that is, when the second interval is very small). (Step S12). As a result, if it is determined that it is not short (No in step S12), the control unit 4 next determines whether or not the detected humidity is lower than a predetermined reference humidity (step S13).

  As a result, if it is determined that it does not fall (No in step S13), the control unit 4 next determines whether or not the detected basis weight exceeds a predetermined reference basis weight (step S14). As a result, when it is determined that it does not exceed (No in step S14), the control unit 4 sets the first interval based on the second interval (step S15). Thereafter, the control unit 4 executes a reverse voltage application process based on the first interval set this time (step S16).

  However, when the second interval is shorter than the reference interval (Yes in Step S12), when the detected humidity is lower than the reference humidity (Yes in Step S13), or the detected basis weight is the above reference When exceeding a basic weight (Yes of step S14), the control part 4 abbreviate | omits a reverse voltage application process (step S17). After the process of step S16 or S17, the process after step S11 is repeated when the next sheet is printed.

[Correspondence between first interval and second interval]
As described above, the first interval is set according to the second interval. Here, an appropriate correspondence between the first interval and the second interval can be determined in advance through experimental evaluation or the like. For example, by preparing an experimental apparatus equivalent to the image forming apparatus X, assigning various first intervals to the second interval, performing printing on a trial basis, and evaluating the separability, etc. It is possible to find a relationship.

Hereinafter, conditions and results of the experiment evaluation performed by the applicant will be described. In the experimental evaluation, a device of a predetermined model (Symphony machine) was appropriately modified, and a device capable of controlling the applied voltage and allocating the first interval and the second interval was used. The specifications of the transfer belt are as follows.
・ Base material: Chloroplane rubber ・ Thickness: 0.5 mm (including the coating layer, the coating layer is a PTFE material with a thickness of 3 μm)
Volume resistance: 9.5 log Ωm (when 20 ° C./50% RH / 500 V is applied)
・ Surface resistance: 10.5 logΩ / □ (when 20 ° C / 50% RH / 500V is applied)

In the experiment, a position (voltage switching position) for switching the applied voltage from the reverse voltage Vr to the transfer voltage Vt is determined based on the detected image start position of the document, and print output is performed according to this determination. As a specific procedure, under the conditions of 80% RH at 30 ° C. and 65% RH at 30 ° C., each condition shown in Tables 1 and 2 (voltage polarity at the front end of the paper, first interval, second interval) 1,000 sheets of 40 g / m ² basis weight were printed on each sheet, and the items shown in the table (separation jam occurrence rate, separability, density of the top image) were evaluated. The reverse voltage Vr was set to −20 μA, and the transfer voltage Vt was set to +100 μA (the same for the image portion).

  The results of the experimental evaluation under each of the above conditions are as shown in Tables 1 and 2. In the table, ○ indicates that the result is good, △ indicates that the result is within the allowable range, and × indicates that the result is out of the allowable range (such as “○ △”). If two are listed, this is an intermediate result). Hereinafter, the result will be described in more detail.

  First, the results under the condition of 30% and 80% RH will be described with reference to Table 1. In Comparative Examples 1 and 2 and Examples 1 to 3, the second interval (the interval from the leading edge of the paper to the image start position) was 6 mm. First, in the first comparative example, the first interval (the interval from the front end of the sheet to the voltage switching position) is as very short as 2 mm. For this reason, when the positive charge is transferred to the leading edge of the sheet, the electrostatic adsorption force between the sheet and the photosensitive drum 211 is increased, and the separation jam frequently occurs so as to exceed the allowable range.

  In Examples 1 to 3, the first charge interval was increased to increase the application range of the reverse voltage Vr, so that the transfer of positive charges to the leading edge of the sheet was suppressed, and the separability was improved as compared with Comparative Example 1. As the end of the application range of the reverse voltage Vr approaches the image start position and the range becomes longer, the jam occurrence rate can be reduced. Further, since the applied voltage is switched to the transfer voltage Vt at a position closer to the front than the image start position (at an early timing), the transferability of the leading image (image start portion) is also good.

  In Comparative Example 2, good results were obtained in the same manner as in Examples 1-3. However, since the applied voltage is switched to the transfer voltage Vt at a position behind the image start position (at a later timing), the density (transferability) of the leading image deviates from the allowable range.

  Next, in Comparative Example 3 and Example 4, the second interval was set to 12 mm. First, in Comparative Example 3, as in Comparative Example 1, the first interval is very short. Therefore, the positive charge is transferred to the leading edge of the paper, so that the electrostatic attractive force between the paper and the photosensitive drum 211 is increased. As a result, the separation jam occurred so frequently as to exceed the allowable range.

  On the other hand, in Example 4, since the application range of the reverse voltage Vr was longer than that in Example 1, the separability was further improved. Good results were also obtained for the density of the leading image.

  Next, in Examples 5 and 6, the second interval was 4 mm. First, in Example 5, since the image start position is close to the leading edge of the paper, the application range of the reverse voltage Vr is shorter than that in Example 1, and the separation jam is slightly increased although it is within the allowable range.

  In Example 6, by applying the transfer voltage Vt between the leading edge of the sheet and the image start position, a better result was obtained for the separation than in the case of Example 5. When the image start position is closer to the leading edge than the predetermined position, a reverse phenomenon occurs in which separation is better when the transfer voltage Vt is applied than when the reverse voltage Vr is applied to the leading edge of the sheet. This reverse phenomenon occurs at a position farther from the leading edge of the paper as the humidity is higher.

  Next, the results under the condition of 65% RH at 30 ° C. will be described with reference to Table 2. In Comparative Example 4 and Examples 7 to 9, the second interval was 6 mm. First, in Comparative Example 4, as in Comparative Example 1, the first interval is very short, and the positive charge is transferred to the leading edge of the paper, thereby increasing the electrostatic attraction between the paper and the photosensitive drum 211. Conceivable. Compared to Comparative Example 1, although the occurrence rate of separation jam was lowered due to low humidity, a satisfactory result could not be obtained.

  In Examples 7 to 9, as in Examples 1 to 3, it was possible to decrease the jam occurrence rate as the first interval was increased and the application range of the reverse voltage Vr was increased. Since the absolute humidity is lower than those in the first to third embodiments, the separability is improved as a whole, and the required application range of the reverse voltage Vr is also reduced. Since the effect of improving the separability by increasing the application range of the reverse voltage Vr becomes significant in a high humidity environment, it can be said that this control may be performed when the humidity is higher than a predetermined humidity. Further, the required application range of the reverse voltage Vr varies depending on the physical properties, basis weight, curl state, and the like of the paper.

  From the result of the experimental evaluation exemplified above, it is possible to specify an appropriate correspondence between the first interval and the second interval. For example, according to the results of Comparative Example 1 and Examples 1 to 3, the first interval corresponding to the case where the second interval is 6 mm in an environment at 30 ° C. and 80% RH is in the range of 3 mm to 5 mm. The value (for example, 4 mm) is an appropriate value. By using such information and setting the operation of the image forming apparatus X (control unit 4) so as to apply an appropriate first interval according to the second interval at that time, the image forming apparatus X Can be operated appropriately.

[Others]
As described above, the image forming apparatus X according to the present embodiment has a photosensitive drum 211 (image carrier) that forms a transfer area between the transfer belt 215 that carries a toner image and conveys paper. A transfer roller 220 (charging unit) that charges the transfer belt 215 according to the applied voltage, and a control unit 4 (voltage control unit) that applies a transfer voltage Vt having a polarity opposite to that of the toner image to the transfer roller 220 are provided. ing.

  Further, the image forming apparatus X conveys the paper so as to pass through the transfer area, and transfers the toner image onto the paper in the transfer area by applying the transfer voltage Vt. Then, when the portion from the leading edge to the first interval on the sheet passes through the transfer region, the control unit 4 executes a reverse voltage application process for applying a reverse voltage Vr having a polarity opposite to the transfer voltage Vt to the transfer roller 220.

  The control unit 4 detects the second interval from the leading end of the sheet to the start position of the toner image transferred to the sheet, and sets the first interval based on the detection result. For this reason, it is possible to apply a voltage having a polarity opposite to the transfer voltage to more appropriately ensure the sheet separation. The control unit 4 sets the first interval to be shorter than at least the second interval. The shorter the second interval, the shorter the first interval is set.

  As mentioned above, although the specific example was given and demonstrated about embodiment of this invention, this invention is not limited to the content. The present invention can be implemented in various specific forms without departing from the spirit of the present invention.

  The present invention is applicable to various image forming apparatuses.

X Image forming apparatus 1 Paper feeding section 2 Image transfer section 3 Fixing section 4 Control section 211 Photosensitive drum 212 Charging apparatus 213 Exposure apparatus 214 Development apparatus 215 Transfer belt 216 PCC
217 Cleaning device 217a Brush 217b Blade 220 Transfer roller 222 Drive roller 223 Driven roller

Claims (5)

An image carrier that carries a toner image and forms a transfer region with a belt that conveys paper; and
A charging unit that charges the belt according to an applied voltage;
A voltage control unit that applies a transfer voltage having a polarity opposite to that of the toner image to the charging unit;
In the image forming apparatus that conveys the paper through the transfer area and transfers the toner image to the paper in the transfer area by applying the transfer voltage.
The voltage controller is
When a portion from the leading edge to the first interval on the sheet passes through the transfer region, a reverse voltage application process is performed in which a reverse voltage having a reverse polarity to the transfer voltage is applied to the charging unit,
An image forming apparatus comprising: detecting a second interval from a leading end of the sheet to a start position of a toner image transferred to the sheet; and setting the first interval based on the detection result. The voltage controller is
Setting the first interval to be at least shorter than the second interval,
The image forming apparatus according to claim 1, wherein the first interval is set to be shorter as the second interval is shorter. The voltage controller is
The image forming apparatus according to claim 2, wherein execution of the reverse voltage application process is omitted when the second interval is shorter than a predetermined reference interval. It has a humidity detector that detects humidity,
The voltage controller is
The image forming apparatus according to claim 2, wherein when the detected humidity is lower than a predetermined reference humidity, the execution of the reverse voltage application process is omitted. A basis weight detection unit for detecting the basis weight of the paper;
The voltage controller is
The image forming apparatus according to any one of claims 2 to 4, wherein when the detected basis weight exceeds a predetermined reference basis weight, the execution of the reverse voltage application process is omitted.