JP5294564B2 - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus for reducing image defects, such as transfer defect, even if using a feeding device adopting the separating and feeding method of blowing air. <P>SOLUTION: The image forming apparatus includes an image carrier which carries a toner image; a transfer means which transfers the toner image on the image carrier to a transfer portion, when a transfer voltage is applied; a recording material feeding unit which includes a stacking portion, where recording materials are stacked and an air blowing device for blowing air to the recording material stacked in the stacking portion, and feeds the recording material to the transfer portion; and a transfer bias control portion which controls the transfer bias, according to at least one of air-received time per one sheet among the air blowing unit, air pressure and air temperature. <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

  The present invention relates to an image forming apparatus including a feeding device that blows air onto a recording material and feeds the recording material, and a transfer device that electrostatically transfers a toner image to the recording material.

  In conventional image forming apparatuses such as copiers and printers, sheets stacked on a sheet stacking unit are sequentially fed one by one from the uppermost one by a pickup roller, and then separated one by one by a separation unit to form an image. A sheet feeding device for feeding to the section.

  Here, in such a sheet feeding apparatus, when continuous feeding of sheets is performed, a cut sheet is used. However, such a cut sheet is usually used on high-quality paper or plain paper designated by a copying machine manufacturer. It was limited. Further, in order to reliably separate and feed such sheets one by one, various separation methods have been conventionally employed. As such a separation method, for example, a friction member is provided on a feed roller. There is a separation pad type that abuts with a pressure of 2 to prevent double feeding.

  As another separation method, the separation unit includes a feed roller that rotates in the sheet conveyance direction, and a separation roller that is driven with a predetermined torque in a direction opposite to the sheet conveyance direction and that contacts the feed roller with a predetermined pressure. Configure. A retard separation system that prevents the multi-feeding by passing only the uppermost sheet of the sheet bundle fed by the pickup roller and returning the other sheet fed to the uppermost sheet to the sheet stacking means side by the separation unit. There are things.

  Here, in order to reliably separate and feed the sheet by these separation methods, for example, in the case of the retard separation method, optimization is performed in consideration of the return torque of the separation roller and the frictional force of the sheet to be fed. This makes it possible to reliably separate the sheets one by one.

  By the way, with the diversification of sheets (recording materials and recording media) in recent years, in addition to ultra-thick paper, OHP sheets, art films, etc., the surface of the sheet has been subjected to a coating process in order to obtain whiteness and gloss from the market demand for colorization. There is a growing demand for image formation on coated sheets such as coated paper.

  However, when trying to feed ultra-thick paper, the weight of the super-thick paper becomes a conveyance resistance and cannot be picked up, resulting in jamming. In addition, a sheet made of a resin material that is easily charged, such as an OHP sheet or an art film, is gradually charged when the sheet is rubbed during a feeding operation in a low humidity environment. Then, since the sheets stick to each other due to the Coulomb force, pick-up cannot be performed or double feeding occurs.

  Also, coated paper with a coating material such as paint on the paper surface has the property of adsorbing sheets when loaded in a highly humid environment. There is a problem that sending frequently occurs.

  This is because, in the case of a special sheet as described above, the frictional force itself between the sheets is equal to or less than that of plain paper or the like, but the adsorption force is high. In other words, in the case of resin material sheets, the force is much higher than the friction force between sheets due to the adsorption force due to frictional charging in a low-humidity environment, and in the case of coated paper due to the adsorption force in a high-humidity environment. This is because it cannot be separated by the conventional separation method.

  In other words, in the case of the conventional separation method, only the frictional force between the sheets is taken into consideration, and therefore, when an adsorption force other than such a frictional force acts, the sheet cannot be reliably separated.

  Therefore, in order to solve such a very high adsorbing force between sheets, a separation feeding method using air blowing is used in the printing industry and some copying machines. This is because air is blown from the side of the sheet bundle in advance, the sheets are picked up one by one from the upper sheet without any adsorption between the sheets, and one sheet is picked up at the separation section provided downstream thereof. In this method, separation is performed each time (Japanese Patent Laid-Open No. 11-005643).

  In the separation and feeding method provided with means for blowing air from the side surface of such a sheet bundle, even a sheet having a high adsorbing power as described above is unrolled by unloading the sheet prior to feeding. Separation performance is improved compared to the method using only the frictional force described above.

  In addition, in the separation and feeding method in which air is blown from the side of the sheet bundle as described above, the sheet is dehumidified by heating the blown air with a heater, particularly for coated paper in a high humidity environment. There is one in which the adsorption force is relaxed (Japanese Patent Laid-Open No. 2001-48366).

JP-A-2005-330079 JP 01-265282 A JP 09-197734 A JP 2004-118019 A JP 09-58902 A JP 2002-32817 A JP-A-11-005643 JP 2001-48366 A

  However, in the feeding device that employs the separation feeding method in which air is blown as described above, when air is blown, the moisture content of the sheet gradually changes. Along with this change in the amount of water, the transferability with respect to the applied bias changes in the secondary transfer portion, and an image defect occurs in the middle of the job. In particular, in the case of an electrophotographic system in which the image forming unit transfers a toner image onto a sheet using static electricity, the transfer performance is greatly affected by the resistance value of the sheet. For this reason, when the resistance value fluctuates in the sheet, transfer unevenness occurs, and the image deterioration due to it is remarkable, which causes an image quality problem.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an image forming apparatus capable of reducing image defects such as transfer defects even by using a feeding device employing a separation feeding method in which air is blown. .

In order to achieve the above object, a typical configuration according to the present invention includes an image carrier that carries a toner image and a transfer voltage for transferring the toner image to a recording material. Transfer means for transferring the toner image at the transfer section, a stacking section on which recording materials are stacked, a recording material feeding means for feeding the uppermost stacked recording material to the transfer section, and stacking on the stacking section Air blowing means for assisting in feeding the recording material by blowing air toward the side surface of the recording material, and the recording material in a predetermined range from the uppermost recording material to the recording material loaded below the predetermined position The cumulative time for which the air of each recording material is blown is obtained from the number of sheets and the time during which air is blown from the air blowing means to the recording material within the predetermined range for each feeding of each recording material. When wind time When continuously in successive imaging performs feeding of the same type of the recording material by the recording material feeding means, the cumulative target air time of each recording material in the image formation, than the first cumulative target air time Each recording material has a second transfer voltage higher than the first transfer voltage when the accumulated wind time is the first accumulated wind time when the second accumulated wind time is long. And transfer voltage setting means for setting each transfer voltage when passing through the transfer portion .

  In the present invention, it is possible to reduce image defects such as transfer defects even if a feeding device adopting a separation feeding method in which air is blown is used.

  Next, an image forming apparatus according to an embodiment of the present invention will be specifically described with reference to the drawings.

[First Embodiment]
The present embodiment relates to a tandem type image forming apparatus provided with an image carrier composed of four photosensitive members.

{Overall configuration of image forming apparatus}
First, the overall configuration of the image forming apparatus will be described together with the image forming operation. In the image forming apparatus of the present embodiment, image forming portions Pa, Pb, Pc, and Pd that form toner images of yellow, magenta, cyan, and black are arranged substantially horizontally from the left in FIG. Each image forming unit has the same configuration except that the color of the toner is different. Therefore, the following explanation will be made by omitting the symbols a, b, c, and d attached to the drawings.

  As shown in FIG. 1, the image forming apparatus of this embodiment includes a belt-like elastic intermediate transfer member, that is, an endless elastic intermediate transfer belt 181. The intermediate transfer belt 181 is wound around a driving roller 125, a tension roller 126, and a backup roller 129 as a support. Four image forming portions P are arranged in series along the horizontal portion of the intermediate transfer belt 181.

  Each image forming unit P includes a drum-shaped electrophotographic photosensitive member (hereinafter referred to as “photosensitive drum”) 101 which is an image carrier that is rotatably arranged. Around the photosensitive drum 101, process means such as a primary charging roller 122, a developing device 123, and a cleaning device 112 are arranged.

  The developing devices 123 arranged in the image forming units Pa to Pd store yellow toner, magenta toner, cyan toner, and black toner, respectively.

  The photosensitive drum 101 is uniformly charged to a negative polarity by the primary charging roller 122, and an image signal is projected from the exposure device 111 onto the photosensitive drum 101 via a polygon mirror or the like to form an electrostatic latent image. Next, toner is supplied from the developing device 123, and the electrostatic latent image is developed as a toner image. When the toner image arrives at the primary transfer portion T1 where the photosensitive drum 101 and the intermediate transfer belt 181 come into contact with the rotation of the photosensitive drum 101, a positive transfer is performed from a bias power source (not shown) to the primary transfer roller 124. A bias is applied. As a result, the toner images on the respective photosensitive drums 101 are transferred in a state of being sequentially superimposed on the intermediate transfer belt 181 to form a color image.

  A sheet S which is a recording material fed from the paper deck 401 by a sheet feeding device described later is fed to the secondary transfer portion T2 so as to synchronize with the transfer of the toner image onto the intermediate transfer belt 181. A positive transfer bias is applied from the bias power supply 141 to the secondary transfer roller 140, and the toner image on the intermediate transfer belt 181 is transferred onto the sheet S by the electric field.

  A method for determining the transfer bias will be described later.

  Then, the sheet S to which the toner image is transferred is conveyed to the fixing unit 211, and the toner image is fixed on the sheet S by heat and pressure, and is discharged to the discharge tray 212.

  On the other hand, the residual transfer toner that could not be transferred from the photosensitive drum 101 to the intermediate transfer belt 181 in the primary transfer portion T1 is cleaned by the cleaning device 112. Further, in the secondary transfer portion T2, the transfer residual toner that could not be transferred from the intermediate transfer belt 181 to the sheet S is cleaned by the belt cleaning device 116.

{Sheet feeding device}
Next, a sheet feeding device (recording material feeding means) for feeding a sheet (recording material) to the secondary transfer portion T2 will be described. The sheet feeding apparatus in the present embodiment uses an air feeding type separation feeding system.

  FIG. 2 is a perspective explanatory view of the paper deck 401. The paper deck 401 is configured to stack and store the sheet bundle S on an intermediate plate 403 that is a sheet stacking unit provided in the storage 402 so as to be movable up and down. Rails 404 and 405 (rails 404 are shown in FIG. 1) are provided on the lower edge portions on both sides of the storage case 402, and can be pulled out to the front side (the front side in FIG. 1) with respect to the apparatus main body. The sheet bundle S loaded and stored in the storage 402 has its front end portion (downstream end in the sheet feeding direction) at the front end thereof by the pre-separation plate 406, and the rear end portion (upstream end at the sheet feeding direction) at the rear end. It is regulated by the plate 412. Further, the sheet side end portion is regulated at a predetermined position by the side regulating plates 410 and 411.

  On the downstream side of the stacked sheet bundle S in the sheet feeding direction, a sheet feeding unit 409 is provided as a sheet sucking and conveying unit for sucking and feeding the uppermost sheet with air. The sheet feeding unit 409 includes a suction duct 408 that is connected to a suction unit (not shown) and can generate a static suction pressure above the sheet bundle, and has a plurality of holes so as to surround the suction duct 408. Reference numeral 407 denotes a sheet that can be rotated in the sheet feeding direction.

  The sheet feeding unit 409 feeds the sheet by causing the suction duct 408 to suck the sheet onto the suction belt 407 and rotating the suction belt 407.

(Air blowing means)
The sheet feeding apparatus according to the present embodiment separates and feeds air by blowing air on the side surface of the sheet bundle stacked on the sheet stacking unit using an air blowing unit. Here, the structure of the air floating means will be described with reference to FIG. 3 is a cross-sectional explanatory view of the air blowing means when FIG. 2 is viewed from the sheet feeding direction.

  Here, the wind pressure of air received per sheet and the time for receiving air (winding time) are changed depending on the basis weight and surface property of the sheet. That is, when the basis weight of the sheet is large, the rotational pressure of the blowing fan 417 is increased to increase the wind pressure in order to cope with the weight of the sheet. On the contrary, when the basis weight of the sheet is small, in order to prevent the sheet from being wrinkled by air, the rotational speed of the blowing fan 417 is decreased to reduce the wind pressure. Further, when using a sheet having a high surface adhesion, such as coated paper, the wind pressure is increased. In addition, when the basis weight of the sheet is small, the number of sheets that receive air by one blowing increases, so that the total time for receiving air becomes long before the sheets stacked on the paper deck 401 are fed. The temperature of the air sent by the blowing fan 417 changes according to the ambient temperature.

  Air blowing means is provided inside the side regulating plate 410. This air blowing means is connected to a blowing fan 417 (illustrated in FIG. 2) that is an air supply source, and one end is opened toward the side edge of the sheet bundle S loaded and stored in the storage 402. A blowing duct 413 having an aperture 414 formed therein is provided. As a result, air is blown from the opening 414 toward the side edge of the sheet bundle S, and the sheet is rolled. Note that the air supply source of the air blowing means may be a fan such as a sirocco fan or a compressor.

  Further, as shown in FIG. 3, a shutter 415 that is a wind time variable means that can be moved between a side end of the sheet bundle S and the opening 414 in a substantially vertical direction by a drive source (not shown) (for example, a motor or a solenoid). Is arranged. When the shutter 415 is moved upward, air can be blown from the shutter opening 416 to the side of the stacked sheet bundle. On the other hand, as shown in FIG. 3D, when the shutter opening 416 is displaced from the opening 414 of the blowing duct 413, air does not hit the side of the stacked sheet bundle. Therefore, by moving the shutter 415 up and down (opening and closing), it is possible to adjust the time for blowing air on the stacked sheet bundle, that is, the wind time. The wind pressure can be adjusted by controlling the rotational speed of the blowing fan 417 as shown in FIG.

(Transfer bias changing means)
A method for determining the transfer bias Vt of the image forming apparatus of this embodiment will be described. The transfer voltage Vt is obtained as the sum of the shared voltage Vb of the secondary transfer portion T2 and the shared voltage Vp of the recording material P.

  In the secondary transfer roller 140, it is difficult to suppress variations in resistance at the time of manufacture, and the resistance changes due to changes in temperature and humidity in the ambient environment and deterioration of durability. Therefore, the current value at which a predetermined voltage is applied to the secondary transfer roller 140 is detected at a timing other than normal secondary transfer, and the shared voltage Vb of the secondary transfer portion T2 is obtained.

  Further, the sheet is affected by the blowing air in the paper deck 401, and the moisture content of the sheet decreases. At this time, as shown in FIG. 5, if the same bias value transfer bias is applied in the secondary transfer portion, there is a possibility that a transfer failure due to a transfer bias mismatch may occur and a transfer defect that becomes a bulge image may occur. is there.

  Therefore, bias changing means is provided for correcting the predetermined shared voltage Vp of the recording material P based on the temperature, air volume, and air receiving time (winding time) received by each sheet. It has been.

  First, details of a method for determining the shared voltage Vb of the secondary transfer portion T2 will be described.

  When the secondary transfer is not performed, the intermediate transfer belt 181 is rotated, and +1 kV and +2 kV are applied to the secondary transfer roller 140 as monitor voltages. At this time, the current detection unit 204 detects the current value flowing through the secondary transfer roller 140.

  In addition, a target current value, which is a current value to be passed through the secondary transfer roller 140 in order to perform good secondary transfer, is set in the memory 205 in advance. The transfer bias control unit 203 obtains the shared voltage Vb of the secondary transfer unit T2 for flowing the target current value based on the detection result of the current detection unit 204. In this example, the current value when +1 kV was applied was 30 μA, and the current value when +2 kV was applied was 60 μA. From these relationships, the voltage-current value relationship shown in FIG. 5 is obtained. Based on the relationship of FIG. 5, 1700 V is obtained as Vb corresponding to the target current value of 50 μA of this embodiment.

  Next, a method for determining the shared voltage Vp of the recording material P will be described.

  Specifically, as shown in FIG. 6, the bias changing means is provided with a temperature sensor 200 for detecting the temperature of the blowing air and a wind pressure sensor 201 for detecting the wind pressure of the blowing air. Further, a wind time sensor 202 for detecting the air wind time of the stacked sheet bundle by the upper and lower sides of the shutter 415 is provided. Table 1 is a table showing the relationship between the sheet type and the shared voltage Vp of the sheet.

そして、前記各センサの検知信号を受け、検知結果に基づいて転写バイアスを変更する転写バイアス制御部203が設けられる。なお、風圧は、図４に示す様に、吹き付けファン411の回転数に応じて変化し、風圧センサ201は吹き付けファン411の回転数から風圧を検知する。ここで、図４に示される風圧は、ＫＡＮＯＭＡＸ製クリモマスター風速計（Model 6551）を用いて測定した。

A transfer bias control unit 203 that receives the detection signals of the sensors and changes the transfer bias based on the detection result is provided. As shown in FIG. 4, the wind pressure changes according to the rotational speed of the blowing fan 411, and the wind pressure sensor 201 detects the wind pressure from the rotational speed of the blowing fan 411. Here, the wind pressure shown in FIG. 4 was measured using a Kurimax Kurimo Master anemometer (Model 6551).

  Then, as shown in FIG. 7, as the water content decreases, the sheet sharing voltage Vp is increased (absolute value, hereinafter the same expression is used), and the transfer bias applied to the secondary transfer roller 140 is increased. . More specifically, as shown in FIG. 8, when an image recording job is started (S1), the wind time per sheet on which air is blown by the blowing fan 417, air pressure, and air temperature information Is acquired (S2). Based on these pieces of information, an appropriate correction value is added to the shared voltage Vp to change the secondary transfer bias value (S3). As a result, a secondary transfer bias having a value suitable for the moisture content of the sheet is applied, thereby preventing image defects.

  Here, specific examples of transfer bias values at the secondary transfer unit when the wind pressure and wind time by the blowing fan 417 are changed in the image forming apparatus of the present embodiment will be described with reference to Tables 2 and 3. . It is the table | surface which showed the relationship between a wind pressure, wind time, air temperature, and a correction value.

  In the image forming apparatus according to the present embodiment, air is blown for 2 seconds near the top of the sheet bundle every time one sheet is fed from the sheet bundle stacked on the paper deck 401. Further, the height at which the sheet bundle receives air is kept constant in the height direction of the sheet bundle. Therefore, the thinner the sheet (the smaller the basis weight), the greater the number of sheets (floating number) on which air is blown in order to feed one sheet from the sheet bundle. The time during which air is blown, that is, the wind time becomes longer.

  As shown in Table 4, the air pressure of the air and the number of floating sheets that are affected by the air during the job have preset values in the main body for each type of sheet. Table 4 shows the relationship between the sheet type and the number of flying sheets.

また、被風時間、風圧、エアーの温度と、補正値の関係は、表２及び表３に示すとおりである。上述の様に、シート束から１枚のシートを給送するごとに、シートの種類に関わらず、シート束の最上部近傍にエアーを２秒吹き付ける。したがって、シートの最も上にあるシートの被風時間は２秒である。また、上から２番目にあるシートは、給送されるまでに、２回、エアーを吹き付けられるので、被風時間は４秒となる。同様に、シートの位置が１枚下がるごとに、被風時間は２秒づつ加算される。シートの位置が浮上枚数に達するまで、２秒ずつ加算される。

Tables 2 and 3 show the relationship between wind time, wind pressure, air temperature, and correction values. As described above, every time one sheet is fed from the sheet bundle, air is blown for 2 seconds near the top of the sheet bundle regardless of the type of sheet. Therefore, the wind time of the uppermost sheet is 2 seconds. In addition, since the second sheet from the top is blown with air twice before being fed, the wind time is 4 seconds. Similarly, every time the sheet position is lowered, the wind time is incremented by 2 seconds. It is incremented by 2 seconds until the sheet position reaches the number of flying sheets.

  A. When the air temperature is 25 ℃

  (1) When the sheet is plain paper with a basis weight of 80 g

  The wind pressure is set to 400 Pa. In addition, the number of flying surfaces is 20. Every time the wind time increases by 2 seconds, the correction value added to the shared voltage Vp of the sheet is increased by + 20V.

  The shared voltage Vp of plain paper with a basis weight of 80 g is 500V. Therefore, the shared voltage Vp of the uppermost sheet in the sheet bundle in which the wind time is 2 seconds is set to + 520V (= 500V + 20V). The shared voltage Vp of the second sheet from the top of the sheet bundle in which the wind time is 4 seconds is +540 V (= 500 V + 20 V × 2).

  (2) When the sheet is plain paper with a basis weight of 209 g

  The wind pressure is set to 600 Pa. The number of levitating is 10. Every time the wind time increases by 2 seconds, the correction value added to the shared voltage Vp of the sheet is increased by 30V.

  (3) When the sheet is coated paper with a basis weight of 209 g

  The wind pressure is set to 800 Pa. The number of levitating is 10. Every time the wind time increases by 2 seconds, the correction value added to the shared voltage Vp of the sheet is increased by 40V.

  B. When the temperature of the air is 40 ° C., it is controlled as follows according to Table 3.

  (1) When the sheet is plain paper with a basis weight of 80 g

  The wind pressure is set to 400 Pa. In addition, the number of flying surfaces is 20. Every time the wind time increases by 2 seconds, the correction value added to the shared voltage Vp of the sheet is increased by + 30V.

  (2) When the sheet is plain paper with a basis weight of 209 g

  The wind pressure is set to 600 Pa. The number of levitating is 10. Every time the wind time increases by 2 seconds, the correction value added to the shared voltage Vp of the sheet is increased by + 45V.

  (3) When the sheet is coated paper with a basis weight of 209 g

  The wind pressure is set to 800 Pa. The number of levitating is 10. Every time the wind time increases by 2 seconds, the correction value added to the shared voltage Vp of the sheet is increased by + 60V.

  In this embodiment, the wind pressure is changed according to the basis weight and surface property of the sheet. However, every time one sheet is fed from the sheet bundle while the wind pressure is fixed, the wind pressure is changed near the uppermost part of the sheet bundle. It is also possible to change the time for blowing air. When the wind pressure is fixed at 400 Pa, the spraying time for feeding one plain paper with a basis weight of 80 g is 2 seconds, plain paper with a basis weight of 209 g is 3 seconds, and coated paper with a basis weight of 209 g is 4 seconds. You can also.

In the present embodiment, the case of continuous paper feeding is described. However, in intermittent mode or when a user adds a sheet in the middle, the sheet surface position detection sensor disposed in the main body and the time when the sheet is loaded into the paper deck and the current sheet surface position are stored and transferred. The bias controller 203 can control the transfer bias.

  Since the air blowing history of a single sheet can be known from the time when it was put into the paper deck and the current sheet surface position, the bias applied in the secondary transfer unit can be controlled, and good transferability can be obtained. It becomes possible.

  In this embodiment, the air blowing fan 417 detects the wind time, wind pressure, and air temperature received by each sheet, and the transfer bias is changed based on the detected information. However, even if the transfer bias at the secondary transfer portion is changed according to at least one of the wind time, wind pressure, and air temperature, it is possible to set the transfer bias according to the moisture content of the sheet. .

[Second Embodiment]
Next, an apparatus according to a second embodiment will be described with reference to FIGS. Note that the basic configuration of the apparatus of this embodiment is the same as that of the above-described embodiment, and thus a duplicate description is omitted. Here, a configuration that is a feature of this embodiment will be described. Moreover, the same code | symbol is attached | subjected to the member which has the same function as embodiment mentioned above.

  In this embodiment, as shown in FIGS. 9A and 9B, a blowing duct 413 and a vertically movable shutter 415 are provided on the sheet bundle leading end side in the sheet feeding direction (downstream side end side in the sheet feeding direction). .

  A separation nozzle 419 is provided in a separation duct 418 connected to a separation fan (not shown), and separation air is supplied obliquely toward the suction belt 407 by the separation nozzle 419. This separation air works effectively for adsorbing only the uppermost sheet on the adsorption belt 407 and separating and dropping the next and subsequent sheets.

  The air pressure of the present embodiment is 400 Pa, the temperature is 25 ° C., and the number of sheets that the sheet used in this embodiment (basis weight 80 g plain paper) floats by air is 20. In order to feed one sheet, air is blown onto the sheet bundle for 2 seconds.

  In the present embodiment, a blowing duct 413, a vertically movable shutter 415, and a separation nozzle for supplying separation air are provided on the sheet bundle leading end side in the sheet feeding direction. For this reason, as shown in FIG. 10, among the stacked sheets, the water content at the front end side of the sheet bundle to which air is blown is significantly reduced, and the water at the rear end side of the sheet bundle (upstream end side in the sheet feeding direction) There is almost no change in quantity. Therefore, from the leading end side of the sheet bundle to the portion where the amount of water decreases due to the influence of the blowing air, an image defect is caused by the mismatch of the bias applied at the secondary transfer portion T2.

  Therefore, by increasing the applied bias from the front end side of the sheet bundle to the location where the amount of moisture decreases due to the air, no correction value is added to the shared voltage Vp on the rear end side of the sheet bundle that is not affected by the air. In addition, it is possible to obtain a uniform transfer property within the surface of the sheet.

  Specifically, as shown in FIG. 11, when an image recording job is started (S21), the wind time per sheet to which air is blown by the blowing fan 417, air pressure, and air temperature information Is acquired (S22). Also, information on the boundary region for changing the secondary transfer bias is acquired (S23). Note that this boundary region can be set in advance corresponding to the wind pressure or the like. Based on this information, a correction value to be added to the shared voltage Vp of the sheet is determined, and the secondary transfer bias value is changed (S24). As a result, a secondary transfer bias having a value suitable for the moisture content of the sheet is applied, thereby preventing image defects.

  This will be described using specific numerical values as examples. Changes in the wind time per sheet and the amount of moisture during continuous sheet passing, and the set values of the bias applied to the secondary transfer portion are the values shown in FIG. 10 as in the first embodiment. As shown in FIG. 10, the secondary transfer bias to be applied to the location (based on the boundary region information acquired in step S23) until the moisture content on the sheet bundle front end side significantly decreases with the moisture content change is changed. . The secondary transfer bias applied to the portion where the moisture content on the trailing edge side of the sheet does not change is not changed.

  A large difference in bias occurs between the portion where the transfer bias is changed and the portion where the transfer bias is not changed. However, by changing the bias value in, for example, five steps, there is no density step when the secondary transfer bias is switched in the plane. For this reason, it becomes possible to apply an appropriate bias to each sheet having different wind times.

  For example, the case of plain paper with a basis weight of 80 g and a wind pressure of 400 Pa, an air temperature of 25 ° C., and a wind time of 40 seconds will be described. The air blowing time for feeding one sheet is 2 seconds. With a wind of 20 seconds, the bias from the leading edge of the sheet bundle to the location where the moisture content decreases due to the air is increased by 400 V from FIG. Then, the bias is lowered in five steps every 80 V (= 400 V / 5) at the boundary between the portion where the moisture content is lowered and the portion where the moisture amount is not lowered (each bias is switched at 50 mmsec). As a result, uniform transferability can be obtained in the surface without density difference. Note that the switching boundary in the present embodiment is a position 50 mm from the leading edge of the sheet. As shown in FIG. 12, the boundary is controlled by the control unit for each wind pressure.

  The air wind pressure, the wind time per sheet, and the number of floating sheets that are affected by air during a job have preset values in the control unit for each apparatus environment and sheet type.

  In this embodiment, the bias is changed in five steps. However, any number of steps may be used as long as the density difference is eliminated. An example of using the same sheet as above is shown below. In the present embodiment, the wind pressure is controlled by the rotational speed of the fan, and the wind time per sheet is adjusted by the height of the shutter.

  The change in the secondary transfer bias value will be described in detail when other types of sheets are used and the wind pressure and wind time received by the stacked sheets change.

(1) When air with a wind pressure of 600 Pa and a temperature of 25 ° C. is blown onto plain paper with a basis weight of 209 g The number of floating sheets shall be 10. The air blowing time for feeding one sheet is 2 seconds.

  Winding time received by one sheet is integrated every 2 seconds. In order to cope with the change in the moisture content, the bias applied at the secondary transfer portion is incremented by 30 V every time the wind time increases by 2 seconds. As shown in FIG. 12, the boundary between the portion where the moisture content decreases and the portion where the moisture amount does not decrease is 75 mm from the leading edge of the sheet. The boundary is 5 for every ΔVtotal (= ((winding time / 2 seconds) × 30 V) / 5). By reducing the bias in stages, mismatch of applied bias can be suppressed.

  (2) When air with a wind pressure of 800 Pa and temperature of 25 ° C is sprayed on coated paper with a basis weight of 209 g

  The number of levitation shall be 10. The air blowing time for feeding one sheet is 2 seconds.

  Winding time received by one sheet is integrated every 2 seconds. In order to cope with a change in the amount of moisture, the bias applied at the secondary transfer portion is incremented by 40 V every time the wind time increases by 2 seconds. As shown in FIG. 12, the boundary between the portion where the moisture content decreases and the portion where the moisture amount does not decrease is 75 mm from the leading edge of the sheet, and is 5 for every ΔVtotal (= ((winding time / 2 seconds) × 40 V) / 5) at the boundary. By reducing the bias in stages, mismatch of applied bias can be suppressed.

  As described above, an image with no transfer failure can be obtained on the entire sheet by changing the secondary transfer bias only at the location where the blowing air hits and the moisture content of the sheet is reduced.

  In this embodiment, the time for blowing air to feed one sheet is fixed, and the wind pressure is changed according to the sheet type. However, the time for blowing air with the wind pressure fixed is set as the sheet type. The configuration of the present embodiment can also be applied when changing accordingly.

[Third Embodiment]
Next, an apparatus according to the third embodiment will be described with reference to FIG. 13 and Table 5. Table 5 is a simplified table showing the relationship between temperature and wind time. The basic configuration of the apparatus according to the present embodiment is also the same as that of the above-described embodiment, and thus redundant description is omitted. Here, a configuration that is a feature of the present embodiment will be described. Moreover, the same code | symbol is attached | subjected to the member which has the same function as embodiment mentioned above.

  As shown in FIG. 13, a heat source 421 is provided in the air blowing portion of the paper deck of this embodiment. And it is comprised so that the temperature of blowing air may be adjusted by operating the said heat source according to the temperature in an apparatus. By blowing the air heated by the heat source 421 onto the sheet bundle and drying the sheets, the adhesion between the sheets can be reduced and the sheets can be fed stably.

  The wind pressure of the blown air in this embodiment is 400 Pa, and the number of sheets (the number of sheets subjected to wind) of the sheets used in this embodiment (basis weight 80 g plain paper) floats by air is 20 sheets (2 seconds). / Sheet).

  In this embodiment, the temperature of the blowing air is set to 30 ° C. Table 5 shows changes in wind time and moisture content per sheet during continuous paper feeding, and set values of applied bias at the secondary transfer portion. As shown in Table 5, every time the wind time per sheet increases by 2 seconds, the bias applied to the secondary transfer portion is increased by 30 V, so that an appropriate bias is applied to each sheet having different wind times. It becomes possible. As a result, transfer failure due to transfer bias mismatch can be suppressed, and good transferability can be obtained. The table in Table 5 shows the case where the wind pressure is 400 Pa.

  Note that the air wind pressure, air temperature, wind time per sheet, and the number of floating sheets that are affected by air during a job have preset values in the main body for each environment and paper type.

  The change in the secondary transfer bias when the air temperature and the wind time change when the wind pressure of the air blown onto the stacked sheets is set to 400 Pa will be specifically described with reference to Table 5.

  (1) When the air temperature is 40 ° C, the wind time is accumulated every 2 seconds (2 seconds of air is fed into one sheet) / wind pressure is 400Pa / the number of floating is 10 sheets

  Winding time received by one sheet is integrated every 2 seconds. In order to cope with the change in the amount of moisture, the applied bias mismatch can be suppressed by adding the applied bias at the secondary transfer portion by 40 V every time the wind time increases by 2 seconds.

  (2) When the temperature is 40 ° C and the wind time is 4 seconds each (air feeding for 4 seconds to feed one sheet) / wind pressure 400Pa / sheet (floating 10 sheets)

  Winding time received by one sheet is integrated every 4 seconds. In order to cope with the change in the amount of moisture, the applied bias mismatch can be suppressed by adding the applied bias at the secondary transfer portion by 80 V every time the wind time increases by 4 seconds.

  (3) When the temperature is 50 ° C and the wind time is 2 seconds at a time (2 sheets of air is blown for 1 sheet feeding) / wind pressure is 400 Pa / the number of levitation is 10 sheets

  Winding time received by one sheet is integrated every 2 seconds. In order to cope with a change in the amount of moisture, mismatch of the applied bias can be suppressed by adding the applied bias at the secondary transfer portion by 50 V every time the wind time increases by 2 seconds.

  As described above, the higher the temperature of the air to be blown, the greater the decrease in the moisture content of the sheet even during the same wind time, so the secondary transfer bias is changed higher. As a result, an image having no transfer failure can be obtained.

[Fourth Embodiment]
Next, an apparatus according to a fourth embodiment will be described with reference to FIGS. Note that the basic configuration of the apparatus of this embodiment is the same as that of the above-described embodiment, and thus a duplicate description is omitted. Here, a configuration that is a feature of this embodiment will be described. Moreover, the same code | symbol is attached | subjected to the member which has the same function as embodiment mentioned above.

  The sheet is affected by air in the paper deck 401, and the moisture content of the sheet decreases. In particular, when a portion with a large change in curl amount is located at the rear end of the secondary transfer portion, as shown in FIG. 14B, the area a in FIG. 14A has a transfer bias mismatch if the same transfer bias is applied during the secondary transfer. As a result, there is a possibility that the transferability is lowered and a marginal image (transfer defect) is generated. Further, as shown in FIG. 14C, the curl amount gradually changes in the b region. As a result, the discharge characteristics are different, and there is a possibility that an image defect due to discharge unevenness occurs due to a mismatch of the transfer bias.

  Therefore, in order to suppress the image defect, in the present embodiment, as the moisture amount decreases and the curl amount increases, the secondary transfer portion T2 in the region a in FIG. The transfer bias to be applied is increased (absolute value, hereinafter the same expression is used). 14A, the transfer bias applied to the secondary transfer roller 140 is sequentially lowered. Specifically, as shown in FIG. 15, when an image recording job is started (S1), the wind time per sheet to which air is blown by the blowing fan 417, the wind pressure of the air Air temperature and sheet type information are acquired (S2). Based on these pieces of information, in the area a of FIG. 14A, a correction value is added to the shared voltage Vp of the sheet to increase the transfer bias. In the area b of FIG. 14A, the transfer bias is sequentially lowered by subtracting the correction value from the transfer bias applied to the area a of FIG. 14A (S3). As a result, a secondary transfer bias having a value suitable for the moisture content of the sheet is applied, thereby preventing image defects.

  Here, specific examples of transfer bias values at the secondary transfer portions in the regions a and b of FIG. 14A when the wind pressure and wind time by the blowing fan 417 are changed in the image forming apparatus of this embodiment are shown in Table 6. This will be described with reference to Tables 7 and 8. Tables 6, 7, and 8 are tables showing the relationship among the wind pressure, wind time, curl amount, and correction value.

  In the image forming apparatus of this embodiment, the air pressure of the blowing fan 417 is 400 Pa, and the temperature is 25 ° C. And, the number of sheets (the number of sheets subjected to wind) of the sheets (basis weight 80 g plain paper) used in this embodiment floats by air is 20 sheets (2 seconds / sheet).

  As shown in Table 6, each time the wind time per sheet increases by 2 seconds, the transfer bias in the region a in FIG. 14A is increased by 20 V, so that an appropriate bias is applied to each sheet with different wind times. It becomes possible to apply.

  Further, when the wind time increases by 2 seconds, the curl amount in the region b in FIG. 14A increases by 0.2 mm (see Table 7). Therefore, the transfer bias applied to the region b in FIG. 14A is 25 V every time the wind time is increased by 2 seconds from the transfer bias applied to the region a in FIG. 14A (a value obtained by adding a correction value to the shared voltage Vp). Decrease the value. (See Table 8). By this control, transfer defects due to transfer bias mismatch can be reduced, and good transferability can be obtained.

  Note that the air wind pressure, the wind time per sheet, and the number of floating sheets that are affected by air during a job have preset values in the main body for each environment and type of sheet.

  When a sheet similar to the above is used, the secondary transfer bias value in the areas a and b in FIG. 14A is changed when the wind pressure received by the stacked sheets changes.

  (1) When wind pressure is 600Pa, wind time is accumulated every 2 seconds, air temperature is 25 ℃, and the number of levitation is 10

  Winding time received by one sheet is integrated every 2 seconds. In order to cope with a change in the amount of moisture, an applied bias at the secondary transfer portion in the region a in FIG. The transfer bias applied to the area b in FIG. 14A is 37.5 V for every 2 seconds of wind time from the transfer bias applied to the area a in FIG. 14A (a value obtained by adding a correction value to the shared voltage Vp). Reduced value. (See Table 8).

  (2) When wind pressure is 600Pa, wind time is accumulated every 4 seconds, air temperature is 25 ℃, and the number of levitation is 20

  The wind time received by a certain sheet is integrated every 4 seconds. In order to cope with the change in the amount of moisture, the transfer bias applied to the region a in FIG.

  The transfer bias applied to the area b in FIG. 14A is decreased by 75 V from the transfer bias applied to the area a in FIG. 14A (a value obtained by adding a correction value to the shared voltage Vp) every 2 seconds of wind time. Value. (See Table 8).

  (3) When the wind pressure is 800 Pa, the wind time is accumulated every 2 seconds, the air temperature is 25 ° C, and the number of levitation is 10

  The wind time received by a certain sheet is integrated every 2 seconds. In order to cope with the change in the moisture content, the transfer bias applied to the region a in FIG.

  The transfer bias applied to the area b in FIG. 14A is reduced by 50 V for every 2 seconds of wind time from the transfer bias applied to the area a in FIG. 14A (a value obtained by adding a correction value to the shared voltage Vp). Value. (See Table 8).

[Fifth Embodiment]
Next, an apparatus according to the fifth embodiment will be described with reference to FIG. 14, FIG. 15, Table 9, and Table 10. Note that the basic configuration of the apparatus of this embodiment is the same as that of the above-described embodiment, and thus a duplicate description is omitted. Here, a configuration that is a feature of this embodiment will be described. Moreover, the same code | symbol is attached | subjected to the member which has the same function as embodiment mentioned above.

  In the present embodiment, as in the fourth embodiment, the transfer bias applied to the trailing edge of the sheet is reduced in consideration of the curl of the sheet. In this embodiment, a case where the air temperature changes will be described.

  The transfer bias control method follows the flowchart of FIG. 15 as in the fourth embodiment.

  Specific examples of transfer bias values in the areas a and b in FIG. 14A according to the air temperature and wind time by the blowing fan 417 in the image forming apparatus of this embodiment are shown in Table 9, Table 10, and Table 8. explain. Tables 9, 10, and 8 are tables showing the relationship between the air temperature, wind time, curl amount, and correction value.

  In the image forming apparatus of the present embodiment, the air pressure of the blowing fan 417 is 400 Pa. First, the case where the temperature of air is 30 degreeC is demonstrated. It is a sheet (basis weight 80 g plain paper) used in this embodiment, and the number of sheets that float by air is 20.

  As shown in Table 9, every time the wind time per sheet increases by 2 seconds, the transfer bias applied to the region a in FIG. 14A is increased by 30 V, so that it is appropriate for each sheet having different wind times. It is possible to apply a proper bias. At this time, the curl amount in the region b in FIG. 14A increases by 0.3 mm (see Table 8).

  Therefore, the transfer bias applied to the region b in FIG. 14A is 37.5% every increase of the wind time 2 seconds from the transfer bias applied to the region a in FIG. 14A (a value obtained by adding a correction value to the shared voltage Vp). The value is decreased by V (an intermediate value between 25 V when the curl amount is 0.2 mm and 50 V when the curl amount is 0.4 mm) (see Table 8).

  Note that the air wind pressure, the wind time per sheet, and the number of floating sheets that are affected by air during a job have preset values in the main body for each environment and type of sheet.

  When the temperature of the air received by the stacked sheets changes, the secondary transfer bias value in the areas a and b in FIG. 14A is changed.

  (1) When the air temperature is 40 ° C, the wind time is accumulated every 2 seconds, the wind pressure is 400 Pa, and the number of sheets floating is 10

  Winding time received by one sheet is integrated every 2 seconds. In order to cope with the change in the amount of moisture, every time the wind time increases by 2 seconds, the applied bias at the secondary transfer portion in the region a in FIG. The transfer bias applied to the area b in FIG. 14A is reduced by 50 V for every 2 seconds of wind time from the transfer bias applied to the area a in FIG. 14A (a value obtained by adding a correction value to the shared voltage Vp). (See Table 8).

  (2) When the temperature is 40 ° C and the wind duration is 4 seconds / wind pressure 400Pa / sheet (floating 20 sheets)

  The wind time received by a certain sheet is integrated every 4 seconds. In order to cope with the change in the amount of moisture, the transfer bias applied to the region a in FIG.

  The transfer bias applied to the area b in FIG. 14A is decreased by 100 V every 4 seconds of wind time from the transfer bias applied to the area a in FIG. 14A (a value obtained by adding a correction value to the shared voltage Vp). (See Table 8).

  (3) When the temperature is 50 ° C and the wind time is 2 seconds at a time / sheet (floating 10 sheets)

  The wind time received by a certain sheet is integrated every 2 seconds. In order to cope with the change in the amount of moisture, a transfer bias applied to the region a in FIG.

  The transfer bias applied to the region b in FIG. 14A is 87.5 V every 4 seconds of wind time increase from the transfer bias applied to the region a in FIG. 14A (a value obtained by adding a correction value to the shared voltage Vp). The lowered value (an intermediate value between 75 V when the curl amount is 0.6 mm and 100 V when the curl amount is 0.8 mm) (see Table 8).

  [Other Embodiments]

  Similarly, in an image forming apparatus that directly transfers a toner image on a photosensitive drum to a sheet to form an image, at least one of the air exposure time, wind pressure, and air temperature received by a sheet loaded with a transfer bias. You may make it change according to one.

1 is a cross-sectional explanatory diagram of an image forming apparatus. It is a perspective explanatory view of a paper deck. It is sectional explanatory drawing of the air spraying means when seeing from a sheet feeding direction. It is sectional explanatory drawing of the air spraying means when seeing from a sheet feeding direction. It is sectional explanatory drawing of the air spraying means when seeing from a sheet feeding direction. It is sectional explanatory drawing of the air spraying means when seeing from a sheet feeding direction. It is a figure which shows the relationship between the rotation speed of a fan, and a wind pressure. It is a figure which shows the electric current when a voltage is applied to a secondary transfer roller. It is a block diagram which shows the control structure which changes a transfer bias. It is a simplified diagram of moisture content and transfer bias. 6 is a control flowchart for changing a transfer bias in the first to third embodiments. It is the simplified sectional view showing the paper deck. It is the simplified sectional view showing the paper deck. It is the simple figure which showed the relationship of the moisture content distribution of the sheet | seat. 5 is a control flowchart for changing a transfer bias. It is the graph which showed the boundary of a wind pressure and bias switching. It is a simplified sectional view showing a paper deck provided with a heater. It is a simplified sectional view showing a paper deck provided with a heater. FIG. 6 is a diagram illustrating a transfer failure and a state of occurrence of curling of a recording material. FIG. 6 is a diagram illustrating a transfer failure and a state of occurrence of curling of a recording material. FIG. 6 is a diagram illustrating a transfer failure and a state of occurrence of curling of a recording material. 7 is a control flowchart for changing a transfer bias in Examples 4 and 5;

Explanation of symbols

401… Paper deck
402… Storage
403 ... Middle plate
406… Pre-separation plate
407… Suction belt
408… suction duct
409… Sheet feeding section
410, 411 ... Side regulating plate
412… rear end regulating plate
413… Blowing duct
414… Opening
415 ... Shutter
416… Shutter opening
417… Blowing fan

Claims (5)

An image carrier for carrying a toner image;
A transfer means for transferring a toner image on the image carrier at a transfer portion by applying a transfer voltage for transferring the toner image to the recording material;
A loading section on which recording materials are loaded;
A recording material feeding means for feeding the stacked recording material at the uppermost position to the transfer unit;
Air blowing means for assisting in feeding the recording material by blowing air toward the side surface of the recording material loaded on the loading section;
Air from the air blowing means is applied to the number of recording materials in a predetermined range from the recording material at the uppermost position to the recording material stacked below the predetermined position and to the recording material in the predetermined range for each recording material feeding. When the cumulative time during which the air of each recording material is blown is obtained from the sprayed time as the cumulative wind time of each recording material, the same type of recording by the recording material feeding means is continuously performed during continuous image formation. when performing the feeding of the wood, the accumulated the wind time of each recording material in the image formation, when the first accumulation a long second cumulative target air time than the wind time, the accumulated the wind time the Transfer voltage setting means for setting each transfer voltage when each recording material passes through the transfer section so that the second transfer voltage is higher than the first transfer voltage in the case of one accumulated wind time. And
An image forming apparatus comprising: The image forming apparatus further includes a sensor for detecting the accumulated wind time,
A recording material surface position detection sensor;
A storage unit for storing the time when the recording material was put into the stacking unit and the recording material surface position;
With
2. The image according to claim 1, wherein the transfer voltage setting unit sets each transfer voltage when each recording material passes through the transfer unit according to information stored in the sensor and the storage unit. Forming equipment. The image forming apparatus further includes a wind pressure sensor that detects a wind pressure of the air received by the air blowing means on the recording material in the stacking unit,
When the accumulated wind time is the same for the same type of recording material, the transfer voltage setting means is configured to use the first wind pressure when the wind pressure is a second wind pressure higher than the first wind pressure. 3. The image forming apparatus according to claim 1, wherein the transfer voltage is set to be a fourth transfer voltage higher than a third transfer voltage in a certain case. The image forming apparatus further includes a temperature sensor that detects the temperature of the air that the recording material has received by the air blowing means in the stacking unit,
When the accumulated wind time is the same for the same type of recording material, the transfer voltage setting means is configured such that when the temperature is a second temperature higher than the first temperature, the temperature is the first temperature. 4. The image forming apparatus according to claim 1, wherein the transfer voltage is set to be a sixth transfer voltage higher than a fifth transfer voltage in a certain case. 5. The air blowing means blows air from the downstream end portion in the feeding direction of the recording material loaded on the stacking portion to the side surface of the recording material,
The transfer voltage setting means is configured such that the transfer voltage when the leading end portion of the recording material in the feeding direction passes through the transfer portion, and the trailing end portion of the recording material in the feeding direction passes through the transfer portion. 5. The image forming apparatus according to claim 1, wherein the transfer voltage is set so as to be higher than the transfer voltage when the image is transferred.

Images