JP4932270B2 - Image forming apparatus and image forming system - Google Patents

Description

  According to the present invention, a corona transfer unit is provided opposite to the photosensitive drum, and the toner image formed on the surface of the photosensitive drum is statically placed on a recording medium conveyed to a transfer region between the photosensitive drum and the corona transfer unit. The present invention relates to an image transfer apparatus that is electrically transferred, and in particular, is excellent in transferability to rough paper with large irregularities on the surface, and in the double-sided printing process, wrinkles are generated due to heat at the time of fixing a toner image on the first side. The present invention relates to an image forming apparatus and an image forming system capable of good transfer without image defects even when transferring to a second surface of a sheet.

  FIG. 7 shows a configuration example of a conventional electrophotographic continuous paper printer. Charge is applied to the surface of the photosensitive drum 1 by the charger 20, and an exposure pattern based on the print data is irradiated by the exposure light source 21, thereby forming an electrostatic latent image on the surface of the photosensitive drum. The electrostatic latent image on the surface of the photosensitive drum is developed by the developer on the developing roll of the developing machine 22, and a toner image 9a is formed on the drum. The continuous paper 7 (paper with feed holes provided on both sides of the paper in FIG. 1) is conveyed to the transfer section by the tractor 8a, and the toner image 9a is transferred onto the paper by the corona transfer device 3. When the transferred toner image 9b passes through the pre-heater 24, it is heated to near the glass transition temperature of the toner resin, and is then melted and fixed to the paper by a fixing machine comprising a heating roller 25a and a backup roller 25b incorporating the heater. Reference numeral 23 denotes a photosensitive drum cleaning mechanism.

  Conventionally, such continuous paper printers have been often used for computer output printing on forms, but recently, the functions of high-speed variable information printers have been utilized to print direct mail, invoices, manuals, books, etc. Came to be used. In addition, it has become necessary to deal with a wide variety of paper types, from thin paper with a thickness of around 50 μm to thick paper with a thickness of around 135 μm, and paper types from fine paper to rough paper. Further, from the viewpoint of resource saving, there is an increasing need for printing on both sides of paper (double-sided printing).

  For example, as shown in FIG. 8, after using the two continuous paper printers 26a and 26b to print the first surface by the first printer (26a), the paper reversing mechanism 27 reverses the paper surface. There is a double-sided printing method on continuous paper by a tandem operation method in which printing is performed on the second side by a second printer (26b).

  The transfer performance dominates the image quality when dealing with such applications. In general, there are many paper fibers on the paper surface. FIG. 9 shows the cross-sectional shapes of fine paper (a) and rough paper (b). The fine paper has a paper fiber spacing of about 50 μm, while the rough paper has a wide paper fiber spacing of about 100 μm and a recess depth of about 20 μm. For this reason, in both cases of printing on the first side and printing on the second side, in the case of rough paper, the adhesion between the rough paper and the photosensitive drum surface is poor in the transfer section, and the surface of the rough paper An image defect due to transfer failure occurs in the recessed area. Even if the transfer current (charge) is increased, discharge occurs in the gaps in the recesses, resulting in image deterioration such as toner scattering.

  In the case of double-sided printing shown in FIG. 8, when fixing the toner image on the first sheet with the first printer (26a), a pre-heater (80 ° C. entrance, 120 ° C. outlet) and a fixing device are used. Since the paper passes through (the high-temperature heat roll 25a and backup roller 25b near 190 ° C.), the paper is deformed and the paper resistance is increased due to the rapid evaporation of moisture contained in the paper. For this reason, there is a problem that the transfer performance of the second surface is lowered and the image quality is deteriorated.

  As a solution, a method has been proposed in which a sheet is pressed against a photosensitive member with a blade (hereinafter referred to as a transfer assist blade) so that the sheet and the surface of the photosensitive member are in close contact with each other. (See Patent Document 1, Patent Document 2, and Patent Document 3.) For example, in Patent Document 1, when performing double-sided printing on continuous paper in tandem operation, the paper is pressed against the photosensitive drum only in the printing width range during the second side printing, and away from the photosensitive drum outside the printing width range. In addition, a configuration has been proposed in which the transfer assist blade is divided in the paper width direction and a retract mechanism is provided in each divided portion. Further, in a printer that supports cut sheets, a transfer assist blade that presses the sheet against the photoconductor is provided according to the timing at which the sheet passes, and the transfer assist blade does not come into contact with the surface of the photoconductor layer to cause damage. As described above, a configuration has been proposed in which the transfer assist blade can be retracted by a solenoid mechanism in the inter-sheet portion.

JP-A-4-321062 JP-A-9-171308 Japanese Patent Application Laid-Open No. 11-65328 Japanese Patent Publication No. 7-17773

  In the continuous paper printer, printing is performed by transporting perforated box paper or perforated roll paper at a high speed (0.5 to 2 m / sec). Unlike cut paper, there is no break in the paper.

  Problems when the transfer assist blade is applied to a continuous paper printer will be described with reference to FIGS. FIG. 10A shows a configuration in which the transfer assist blade 28 is employed. Reference numeral 1 denotes a photosensitive drum, on which a photoconductor layer 2b is formed on a substrate a. A transfer assist blade 28 such as a plastic plate, a film, or a metal plate is provided on the upstream side of the corona transfer unit 3 when viewed from the sheet conveying direction. The sheet 7 conveyed by the tractor 8a reaches the transfer unit housing 6 along the frame 6a of the transfer unit housing 6, and is pressed against and closely adhered to the surface of the photoconductor layer 2b of the photosensitive drum 1 by the transfer assist blade 28. Then, the position reaches the position facing the corona transfer device 3. The toner image 9a is transferred onto the paper 7 by the application of electric charge from the corona transfer device 3, and then comes out of the housing 6 along the frame 6b of the housing 6, and then sent to a fixing device (not shown) by the tractor 8b. It is done. Even in the case of rough paper or the like having a large surface roughness, the transfer assist blade 28 reduces the gap between the surface of the rough paper and the photosensitive drum. .

  On the other hand, in FIG. 10B, the toner image is printed on the second surface which is the back surface of the paper 7 on which the toner image 11 is formed on the first surface by the continuous paper printers 26a and 26b having the tandem configuration shown in FIG. Shows the case where double-sided printing is performed. In this case, there is paper deformation due to evaporation of moisture when passing through the fixing unit (preheater, fixing machine) of the continuous paper printer 26a and an increase in paper resistance, and the second surface is difficult to transfer. Further, since the transfer assist blade 28 is in direct contact with the toner image, the toner image 10 formed on the first surface is scraped off, and image deterioration such as missing toner image occurs. In general, when printing on the second side, the sheet is deformed due to the heat history in the fixing process at the time of printing on the first side. Therefore, in order to improve the adhesion, the pressing pressure of the transfer assist blade 28 is increased. It needs to be larger, which will further promote image quality degradation.

As described above, the continuous paper printer has a high need for printing on various types of paper, but the width of the paper to be used can be used depending on the application. For this reason, recently, long (21 to 22 inches) photosensitive drums have been used, and the width of the paper used varies widely, such as 12 inches, 16 inches, and 22 inches. The form is 12 to 16 inches wide, and when printing manuals, books, etc., it is cut after printing, so it is a 17- inch width that can be two-sided in A4 size, and a 22-inch paper that is three-sided in B5 size.

  FIG. 12A shows a case where continuous paper 7 having a narrow width is passed through the length of the photosensitive drum for printing. At this time, the transfer assist blade 28 presses the sheet 7 against the surface of the photoconductor layer 2b to bring them into close contact so that no gap is generated between the sheet and the photoconductor layer.

  Here, an area where the sheet 7 exists is an area a, and an area where the sheet is not present and the transfer assist blade 24 directly contacts the photoconductor layer 2b of the photosensitive drum is an area b.

  FIG. 12B shows a transfer state in the region a. Since the transfer assist blade 28 does not directly contact the photoconductor layer 2b, the surface of the photoconductor layer 2b is not damaged. On the other hand, FIG. 9C shows a state in the region b. Since the transfer assist blade 28 directly contacts the surface of the photoconductor layer 2b, the photoconductor layer is damaged. As a method for dealing with such different paper widths, Patent Document 2 proposes a method in which a plurality of transfer assist blades are provided and combined according to the paper width. However, there is a problem that the configuration is complicated and the size of the transfer assist mechanism is increased.

  The object of the present invention is to transfer a second surface of a paper wrinkled by heat at the time of fixing a toner image on the first surface, even when the surface is transferred to a rough paper having a large unevenness or the surface is relatively flat. An object of the present invention is to provide an image forming apparatus corresponding to continuous paper, which can be satisfactorily transferred without image defects even when transferring to a surface.

  The outline of typical ones of the inventions disclosed in the present application will be briefly described as follows.

A corona transfer unit is provided opposite to the photosensitive drum, and the toner image formed on the surface of the photosensitive drum is electrostatically transferred to a recording medium conveyed to a transfer region where the photosensitive drum surface and the transfer unit are opposed to each other. In the image forming apparatus, the recording medium is continuous paper conveyed by a tractor, and a semiconductive rubber layer, a semiconductive resin layer, or a semiconductive layer is formed on the surface of the metal roller near the entrance of the transfer region. A transfer assist roller coated with a laminate composed of a conductive rubber layer and a semiconductive resin layer is disposed, and when the background potential of the photosensitive drum at the mounting position of the transfer assist roller is Vd, the metal the rollers, the pulse width Tp, the peak value and 2Vd, by applying a pulse voltage to less 0.1ms to Tp, the photosensitive Dora the surface of the transfer assist roller Between the surfaces of, alternately changes positive and negative in the same peak value Vd, comprising a first power source for applying an alternating electric field, the transfer and print the toner image on the photosensitive drum onto the recording medium when performing, the transfer assist roller, the recording medium was rotated by the driving of the recording medium with is brought into close contact with the photosensitive drum surface, and, between the photosensitive drum and the surface of the transfer assist roller, toner An image forming apparatus, wherein a voltage is applied to the transfer assist roller so that the alternating electric field whose polarity changes in a short time that does not move .

Hereinafter, some features of the present invention will be described.
(1) A roller structure that rotates as the recording medium travels as means for bringing the recording medium into close contact with the photosensitive drum surface without damaging the toner image formed on the first surface printing surface during duplex printing in tandem operation. The transfer assist roller is provided.

  (2) When one transfer assist roller supports different paper widths, and the paper width is shorter than the transfer assist roller length, a part of the transfer assist roller surface comes into contact with the photosensitive drum, and transfer assist It is anticipated that toner, paper dust, etc. will adhere to the surface of the roller, resulting in contamination. For this reason, when printing is performed by changing to a paper having a wide paper width, there is a problem in that the dirt in the region that has been in contact with the photosensitive drum surface is transferred to the paper.

  FIG. 11 shows toner adhering to the photosensitive drum surface in the reversal development process using a positively charged photosensitive drum. A region G is a regular image forming region, and the potential is lowered by exposure, and development is performed by a developing machine, so that a positively charged toner 9a is formed on the drum. On the other hand, the region NG is a background potential portion of the non-image portion, and the positively charged toner 9a does not adhere to this region, but the reverse polarity (negatively charged) toner 10a in the developing device adheres. Note that the positively charged toner 9a may shift to the region NG due to toner scattering. For this reason, positively charged and negatively charged toners are formed on the surface of the photosensitive drum.

  Therefore, in order to prevent electrical adhesion of the toner to the surface of the transfer assist roller, it is necessary to electrically repel the bipolar toner, and the positive polarity and the negative polarity are alternately provided between the transfer assist roller surface and the photosensitive drum. An alternating electric field that changes to is applied.

  Specifically, as a transfer assist roller, the surface of a metal roll is covered with a semiconductive rubber layer, a semiconductive resin layer, or a laminate composed of a semiconductive rubber layer and a semiconductive resin layer. When the background potential of the photosensitive drum surface at the transfer assist roller mounting position is Vd, a potential difference between the surface of the transfer assist roller and the photosensitive drum is applied by applying a pulse voltage having a peak value of 2 Vd to the metal roller. Becomes an AC voltage of ± Vd. In other words, an alternating electric field is applied between the two.

As the coating layer of the transfer assist roller, a semiconductive layer having a relatively wide volume resistivity can be used. This is because, unlike the transfer roll, the toner is electrically repelled, the charge leaks due to frictional charging with the paper, and the toner or paper powder attached to the surface of the transfer assist roller is charged with the same polarity. It is because it is the purpose. As a result of the experiment, it was found that a volume resistivity of 10 ³ to 10 ⁹ Ω · cm can be used.

  (3) Since the transfer assist roller is in contact with the surface of the photosensitive drum, the toner on the surface of the photosensitive drum may be physically or mechanically in the long term even if it is not electrically attached by the measure (2). It is expected to adhere to the roller surface. As measures to reduce the adhesion of the toner, from the material aspect, a treatment for improving the releasability of the surface of the semiconductive rubber or a carbon-containing fluororesin having a releasability as the semiconductive resin layer is used. be able to.

Methods have also been proposed for reducing the friction and improving the non-stickiness of the surface of synthetic rubber moldings capable of crosslinking sulfur. (See Patent Document 4)
On the other hand, it is also necessary to clean the surface of the transfer assist roller. As a cleaning method, before the printing operation is finished and a new recording medium is loaded, the surface of the transfer assist roller is brought into close contact with the surface of the photosensitive drum, and the metal roller of the transfer assist roller is opposite to the charged polarity of the photosensitive drum. The charged photosensitive drum is rotated in a state where a polar DC voltage is applied and no voltage is applied to the corona transfer means, and foreign matters such as toner and paper dust adhering to the surface of the transfer assist roller are removed from the surface of the photosensitive drum. , The foreign matter is removed by the cleaning member of the photosensitive drum. This eliminates the need for a transfer assist roller cleaning member.

  (4) Pressing pressure against the photoconductor layer on the surface of the photosensitive drum of the recording medium by the transfer assist roller, which depends on the material of the coating layer, the type of the recording medium, and the surface condition, but if the pressing pressure is too weak, the adhesion force If the strength is too high and too strong, there is a problem that the coating layer is worn and the roller cannot be rotated.

As a result of the experiment, it is set in the range of 5 to 60 g / cm ² , preferably 13 g / cm ^{2 to} 40 g / cm ² .

  (5) Further, duplex printing is performed on continuous paper by an image forming system including a plurality of the image forming apparatuses.

  (1) The transfer assist roller rotates following the running of the recording medium in a state where the recording medium is pressed against the photosensitive drum surface with a predetermined pressure. For this reason, the adhesion between the recording medium and the photoconductor surface is improved, the voids are reduced, and the transfer performance is improved. Further, since the transfer assist roller follows the running of the recording medium, the recording medium is not deformed such as wrinkles. In addition, the toner image on the first surface is not damaged even during the second surface transfer. By applying an alternating electric field whose polarity changes in such a short time that the toner does not move between the surface of the transfer assist roller and the photosensitive drum surface, the toner on the surface of the photosensitive drum is electrically attached to the surface of the transfer assist roller. Can be prevented.

  (2) Since the surface of the transfer assist roller has releasability, it is difficult for toner to adhere to it. In addition, after the printing operation is completed and the recording medium is loaded, the transfer assist roller surface is brought into close contact with the photosensitive drum surface, and a DC roller having a polarity opposite to the charging polarity of the photosensitive drum is placed on the metal roller of the transfer assist roller. By applying a voltage, a DC charge having a polarity opposite to the charged polarity of the photosensitive drum is injected into the positive and negative toners physically or mechanically attached to the surface of the transfer assist roller. The toner and paper dust on the roller has a charge opposite to the charged polarity of the photosensitive drum. As a result, foreign matter such as toner and paper dust attached to the surface of the transfer assist roller can be transferred to the surface of the photosensitive drum, and the foreign matter can be removed by the cleaning member of the photosensitive drum.

  (3) In double-sided printing by tandem operation, even if the first continuous paper printer causes deformation of paper or an increase in paper resistance due to heat at the time of fixing the image on the first surface, the second continuous paper printer A good image can be formed without deteriorating the transfer performance during the second side printing.

As a transfer assist roller, it is desirable to satisfy the following performance.
(1) Excellent adhesion between the metal roll and the coating layer, and no peeling occurs at the interface between the metal roll and the coating layer even when the recording medium is pressed against the photosensitive drum and rotated at high speed.

  (2) The coating material has a releasability that prevents the toner or the like from adhering, has excellent wear resistance, and is installed in the vicinity of the corona transfer device and is exposed to ozone. To be excellent.

(3) The coating layer of the metal roll is preferably a semiconductive type from the viewpoint that the charging potential on the surface of the transfer assist roller can be controlled to a predetermined value, and the volume resistivity is preferably 10 ³ to 10 ⁹ Ω · cm.

  As the best mode that can clear the above performance, the surface of a metal rod made of stainless steel or aluminum is covered with a heat shrinkable tube such as resin or rubber, or a non-shrinkable tube is covered with heat fusion or adhesive. Form.

  According to the present invention, an image forming apparatus and an image forming system that satisfy the above performance are provided. Hereinafter, embodiments will be described in detail with reference to the drawings.

An embodiment of the present invention will be described with reference to FIGS. FIG. 1A shows the structure of a transfer portion according to an embodiment of the present invention. In this embodiment, a case will be described in which a positively charged OPC photosensitive member is used as the photosensitive drum 1, a developing method is a reversal developing method, and a positive toner is used. The transfer unit stores a transfer assist roller 5, a negatively charged corona transfer unit 3, and an AC static eliminator 4 in a transfer unit housing 6. The corona transfer device 3 has a discharge wire 3a, and the AC static eliminator 4 has a discharge wire 4a. As shown in FIG. 1B, the transfer assist roller 5 is made by covering a stainless steel round bar 5a having a diameter of 10 mm with a heat-shrinkable tube made of ethylene propylene rubber, heat-treating at 120 to 160 ° C., and polishing the surface. And flattened (± 50 μm). The thickness of the ethylene propylene rubber layer 5b is 1 mm. Carbon is added to the ethylene propylene rubber, the volume resistivity is 10 ⁵ Ω · cm, and the rubber hardness is 80 degrees (JIS).

  The cored bar 5a of the transfer assist roller 5 is selectively connected to either a first power source 13 made of, for example, a pulse power source or a second power source made of, for example, a negative power source, and a predetermined power is applied. In the example of FIG. 1, a pulse voltage Va <b> 1 is applied to the metal core 5 a of the transfer assist roller 5 by the first power supply 13. When the potential Vp of the background area of the photosensitive drum at the mounting position of the transfer assist roller 5 is Vd, the pulse voltage Va1 is a pulse waveform having a peak value 2Vd and a pulse width Tp as shown in FIG. Voltage. This voltage waveform is a waveform obtained by offsetting the direct current Vd to a rectangular wave alternating current having a peak value Vd and a period of 2 Tp. Since the surface potential of the photosensitive drum surface is Vd, the potential difference Vk between the roller surface and the photosensitive drum 1 at the mounting position of the transfer assist roller 5 is a rectangular wave AC voltage having a peak value Vd shown in FIG. (Vk).

Next, a transfer operation sequence using the transfer assist roller 5 will be described. After the recording medium 7 on which the toner image is formed on the first surface (the contactor side in FIG. 1) is pressed against the photoconductor layer 2b of the photosensitive drum 1 by the transfer assist roller 5, and is in close contact with the photoconductor layer 2b. , And a corona transfer unit 3 and a transfer unit composed of a static eliminator 4. In order to ensure adhesion with the photoconductor layer 2b and to follow and rotate, it is necessary to optimize the pressing pressure of the transfer assist roller 5. Results of printing run, pressing pressure of the recording medium by the roller member is found to be set in the range of ^{13g / cm 2 ~40g / cm 2} .

  FIG. 3 is a view of FIG. 1 viewed from the photosensitive drum surface side. 3A is a region where the surface of the transfer assist roller 5 is in contact with the recording medium 7, and region b is a region where the surface of the transfer assist roller 5 is directly in contact with the photoconductor layer 2b of the photosensitive drum.

  The used photosensitive drum is positively charged OPC, and the potential Vd of the background area of the photosensitive drum 1 at the position of the transfer assist roller 5 is about + 400V. As described with reference to FIG. 1C, when the voltage waveform Va1 of the power source 13 is a pulse voltage having a peak value of 800 V (= 2 Vd) and a pulse width Tp, the transfer assist roller 5 and the photosensitive drum 1 are connected with each other as shown in FIG. A rectangular wave AC voltage Vk having a peak value of 400 V and a pulse width Tp as shown in c) is applied. FIG. 3B shows the behavior of the toner at this time. The positively charged toner 9a in the region a and the positively charged toner 9d in the region b2 where there is no paper are repelled from the transfer assist roller side when Vk is positive, and are attracted to the transfer assist roller side when Vk is negative.

  On the other hand, the negative fog toner 10a is attracted to the transfer assist roller side when Vk is positive, and repels from the transfer assist roller side when negative. As described above, the toners 9a, 9d, and 10a reciprocate at a cycle of 2Tp. As a result of the experiment, it was found that when the peak value is 400 V, Tp can be prevented from being electrically attached to the transfer assist roller surface and the back surface of the paper 7 by setting the Tp to 0.1 ms or less, that is, 5 kHz or more. The toner image formed on the photosensitive drum is transferred to the paper 7 that has passed the transfer assist roller 5 by the corona transfer device 3 to which a negative DC voltage is applied, and the paper is discharged by the static eliminator 4 to which an AC voltage is applied. Is peeled off from the drum surface.

  Since the surface of the transfer assist roller 5 is a rubber layer of ethylene propylene (EPDM) and is driven by the recording medium, the toner image 11 on the first surface is not damaged. Even if the recording medium is a rough surface paper or the like, the gap is reduced by the pressing effect and the adhesion to the surface of the photosensitive drum is improved, so that a good transfer can be performed. . When limiting the current value from the photosensitive drum to the transfer assist roller, a DC resistance may be connected as a current limiting resistor between the power supply 13 and the assist roller.

  In this embodiment, the case where a positively charged OPC photoconductor is used has been described. However, a selenium photoconductor can be used as the same positively charged photoconductor. On the other hand, the same concept can be applied to a negatively charged OPC photoreceptor. In this case, in FIG. 1C, Va1 may be a peak value of −2Vd, a pulse width Tp, and Vp may be −Vd.

  As a result, Vk becomes a rectangular wave AC voltage having a peak value Vd, as in FIG. In the embodiment, the configuration using the photosensitive drum has been described, but it is needless to say that the present invention can be applied to the photosensitive belt.

  Further, since an AC electric field is applied between the surface of the transfer assist roller 5 and the photosensitive drum surface, the width of the recording medium is narrower than the width of the photosensitive drum, and the transfer assist roller directly contacts the photoconductive layer. Also, the toner can be prevented from adhering to the surface of the transfer assist roller.

  A configuration example of a transfer portion according to another embodiment of the present invention will be described with reference to FIGS. Here, a method of cleaning the surface of the transfer assist roller before a series of printing operations are completed and a recording medium such as box paper or roll paper is loaded will be described. The same photosensitive drum 1 and transfer assist roller 5 as those used in Example 1 were used. When thousands of pages are printed, as shown in FIG. 2B, the positively charged toner 9d, paper dust, and negatively charged fog toner 10a in the area without the paper adhere to the surface of the transfer assist roller 5. In order to remove this, the surface of the transfer assist roller is brought into close contact with the surface of the photosensitive drum, and a negative DC voltage Va2 is applied from the second power source 14 to the metal core 5a of the roller 5.

  When Va2 is −Vs, the potential difference Vm between the transfer assist roller 5 and the photosensitive drum 1 becomes a negative DC voltage of − (Vs + Vd) as shown in FIG. 2 (c-3). Vd was 400 V, and Vs was set to −400 V in the experiment. When the transfer assist roller 5 is brought into contact with the surface of the photosensitive drum 1 in such a state, as shown in FIG. 4, the electrons from the negative power source 14 pass through the conductive rubber layer, and the toner 9 d, 10 a, paper dust The toner 9d and the paper powder 19 injected into the toner 19 and charged positively have a negative polarity. When the positively charged photosensitive drum is rotated, foreign matters such as toner and paper dust adhering to the surface of the transfer assist roller are transferred to the surface of the photosensitive drum by electrostatic force.

  Foreign matters such as toners 9c and 10b and paper dust 19 transferred to the surface of the photosensitive drum are removed by the cleaning unit 12 of the photosensitive drum. Accordingly, the transfer assist roller can be cleaned relatively easily without requiring a new cleaning member. Further, there is an effect that a space for mounting the roller is small.

  In this embodiment, the case where a positively charged OPC photoconductor is used has been described. However, the same concept can be applied to a negatively charged OPC photoconductor. In this case, in FIG. 2C, Va2 may be a + Vs DC voltage and Vp may be a -Vd DC voltage. As a result, Vm becomes a DC voltage of (Vs + Vd).

FIG. 5 is a diagram showing another configuration example of the transfer assist roller of the present invention. The transfer assist rollers used in Examples 1 and 2 were formed by forming a semiconductive ethylene propylene rubber layer on the surface of the metal roll. A semiconductive Teflon (registered trademark) resin layer 18 is formed on the outside. A stainless steel metal roll with a diameter of 10 mm is covered with a heat-shrinkable tube of a semiconductive ethylene propylene rubber having a volume resistivity of 10 ⁵ Ω · cm and a rubber hardness of 40 degrees, and a heat-shrinkable tube is covered with heat treatment at 120 to 160 ° C. Thereafter, the surface was polished and flattened (± 50 μm). The rubber layer thickness is 2 mm. Next, a heat-shrinkable tube of semiconductive Teflon (volume resistivity is 10 ⁷ Ω · cm) is put on and heat-treated with hot air at 120 to 150 ° C., so that the outer half of the rubber layer has a thickness of 0.5 mm. A conductive resin layer 18 was formed. Since the time required for the heat treatment is short and the heat resistant limit temperature of the ethylene propylene rubber is 140 ° C., there is no problem in heat treatment.

  Since Teflon resin is excellent in releasability, it is difficult for foreign matters such as toner and paper powder to adhere to it. This configuration is a function-separated transfer that provides a semiconductive ethylene propylene rubber with a relatively low rubber hardness for elastic function to ensure a nip during pressing, and a semiconductive Teflon resin layer for cleanability. It is an assist roller.

  According to the present embodiment, even when the paper is transferred to rough paper having a large unevenness on the surface, or the paper having a relatively flat surface, the first surface of the paper on which wrinkles are generated due to heat at the time of fixing the toner image on the first surface. It is possible to provide an image forming apparatus corresponding to continuous paper that can perform good transfer without image defects even when transferring to two sides.

FIG. 6 is a diagram showing another configuration example of the transfer assist roller of the present invention. Although it has the same configuration as the transfer assist roller used in Examples 1 and 2, the surface of the coating layer 5b (semiconductive ethylene propylene rubber layer) of the core metal 5a of the transfer assist roller 5 is chemically treated to reduce the friction. The layer 5c which gave the property and non-adhesiveness is formed. As a forming method, there is a method such as “(1) Addition reaction of halogen such as chlorine. (2) Treating the surface with a sulfur dispersion to form a cured rubber film having a thickness of several μm on the surface”.

  In any case, since the treatment layer 5c is formed integrally with 5b, there is no peeling or cracking, and there is an effect that a highly reliable transfer assist roller excellent in cleanability can be obtained.

  FIG. 8 shows an image forming system that performs duplex printing by operating the image forming apparatuses of Embodiments 1 and 2 in tandem. The description of the tandem operation is omitted because it has been described above.

  Since the transfer assist roller 5 is driven with respect to the continuous paper 7, the toner image 11 on the first surface was not damaged.

  Further, even if the continuous paper 7 is a rough paper or the like having an uneven surface, good transfer can be performed because the gap is reduced and the adhesion to the surface of the photoreceptor 1 is improved. Further, since an AC electric field is applied between the transfer assist roller 5 and the photosensitive drum, two types of toner (regular toner image 9a and fog toner 10a having a polarity opposite to that of 9a) adhering to the surface of the photosensitive member 1 are Since both are electrically repelled from the surface of the transfer assist roller, it is possible to prevent electrical adhesion of both toners to the transfer assist roller 5. In addition, even if toner adheres to the surface of the transfer assist roller during long-term printing, a process of transferring the toner adhering to the surface of the transfer assist roller to the photosensitive drum when there is no sheet on the drum surface, such as when a new sheet is loaded. By adding, printing on a new sheet can be started with the surface of the transfer assist roller being cleaned.

  When fixing the image on the first surface with the first continuous paper printer 26a, the paper passes between the high-temperature heat roll 25a and the backup roller 25b near 190 ° C. Even if the paper resistance increases due to the formation of the toner image 11 on the first surface and the evaporation of moisture, the transfer performance at the time of the second surface printing by the second continuous paper printer 26b does not deteriorate and a good image is obtained. Been formed.

The transfer assist roller 5 of the present invention has excellent adhesion between the metal roll 5a and the coating layer 5b, and even at high speed rotation with the recording medium pressed against the photoreceptor 1, at the interface between the metal roll 5a and the coating layer 5b. It is desirable that peeling does not occur. Since the coating layer 5b is installed in the vicinity of the corona transfer device 3 and is used in a state exposed to ozone, it is desirable that the coating layer 5b is excellent in ozone resistance and wear resistance. The coating layer 5b of the metal roll 5a is preferably a semiconductive type from the viewpoint that the charging potential on the surface of the transfer assist roller 5 can be controlled to a predetermined value, and the volume resistivity is particularly preferably 10 ³ to 10 ⁹ Ω · cm. .

  Electrophotographic printers can be used in a wide range of fields from commercial printing to personal use, taking advantage of the ability to print variable information on recording media such as paper at high speed. In particular, continuous paper printers do not generate paper jams during paper conveyance, such as cut paper, so that various types of paper (from thin paper to thick paper, from fine paper to rough paper) can be conveyed and printed at high speed. Recently, printing needs for individuals such as direct mail and fee schedules have increased, and it is required to print faster, in large quantities, and at lower prices. In addition, from the viewpoint of protecting the global environment, reduction of paper usage by double-sided printing, use of recycled paper and roughened paper using recycled pulp, and the like are desired. The present invention can solve the transfer failure of the second side during double-sided printing and can improve the transferability to low-priced paper such as recycled paper and roughened paper. It can also contribute to resource saving. In the specification, the continuous paper printer has been described, but it goes without saying that the transfer assist roller of the present invention can also be applied to a cut paper printer.

The figure explaining the structure and operation | movement at the time of the printing of the transfer part which become one Example of this invention. The figure explaining the structure and operation | movement at the time of the cleaning of the transfer part which become one Example of this invention. FIG. 4 is a diagram illustrating an effect when printing on a recording medium having a width smaller than the width of the photosensitive drum according to the present invention. The figure explaining the mechanism at the time of the cleaning in one Example of this invention. The figure explaining the 2nd structural example of the transfer assist roller of this invention. The figure explaining the 3rd structural example of the transfer assist roller of this invention. FIG. 3 is a diagram illustrating a configuration of a continuous paper compatible printer. The figure which shows the state which performs double-sided printing by the tandem operation | movement of the continuous paper corresponding | compatible printer. The figure which shows the cross section of a paper. The figure which shows the transcription | transfer part using a transcription | transfer assist blade. FIG. 3 is a diagram illustrating toner adhered on a photoconductor. The figure explaining the subject at the time of the printing to a narrow recording medium in the transfer part using a transfer assist blade.

Explanation of symbols

1: Photosensitive drum 2: Photoconductor layer 3: Corona transfer device 4: Static eliminator 5: Transfer assist roller 6: Transfer housing 7: Recording medium 9: Toner 10: Fog toner (reverse polarity charged toner)
12: photosensitive drum cleaning mechanism 13: first power source (voltage source applied to the transfer assist roller during printing)
14: Second power source (voltage source applied to the transfer assist roller during cleaning)
19: Paper dust 22: Developer 28: Transfer assist blade

Claims (9)

A corona transfer unit is provided opposite to the photosensitive drum, and the toner image formed on the surface of the photosensitive drum is electrostatically transferred to a recording medium conveyed to a transfer region where the photosensitive drum surface and the transfer unit are opposed to each other. In the image forming apparatus to
The recording medium is continuous paper conveyed by a tractor;
Near the entrance of the transfer area, the surface of the metal roller was covered with a semiconductive rubber layer, a semiconductive resin layer, or a laminate composed of a semiconductive rubber layer and a semiconductive resin layer. A transfer assist roller is arranged,
When the background potential of the photosensitive drum at the mounting position of the transfer assist roller is Vd , a pulse voltage with a pulse width Tp, a peak value of 2 Vd, and Tp of 0.1 ms or less is applied to the metal roller. A first power source for applying an alternating electric field that alternately changes between positive polarity and negative polarity at the same peak value Vd between the surface of the transfer assist roller and the surface of the photosensitive drum;
When the toner image on the photosensitive drum is transferred to the recording medium for printing, the transfer assist roller causes the recording medium to closely contact the surface of the photosensitive drum and rotates as the recording medium travels. In addition, a voltage is applied to the transfer assist roller between the surface of the transfer assist roller and the photosensitive drum so that the AC electric field whose polarity is changed in a short time such that toner does not move. Image forming apparatus. A second power source for applying a DC voltage to the metal roller ;
When cleaning the transfer assist roller , the surface of the transfer assist roller is brought into close contact with the surface of the photosensitive drum, and the DC voltage having a polarity opposite to the charging polarity of the photosensitive drum is applied to the surface of the transfer assist roller. 2. The image forming apparatus according to claim 1, wherein foreign matter such as toner or paper dust attached to the surface of the assist roller is transferred to the charged photosensitive drum surface, and the foreign matter is removed by a cleaning member of the photosensitive drum. apparatus. Wherein the paper conveying direction downstream side of the corona transfer means, the image forming apparatus according to claim 1, wherein the dividing collector is provided.   3. The transfer assist roller according to claim 1, wherein a vulcanizable semiconductive rubber molding member is formed on a surface of a metal roller, and the surface of the rubber molding member is subjected to sulfur treatment. Image forming apparatus.   3. The image forming apparatus according to claim 1, wherein the coating layer of the transfer assist roller is a semiconductive resin layer and is a fluorine resin having releasability.   The image forming apparatus according to claim 1, wherein the semiconductive resin layer or the semiconductive rubber layer has a volume resistivity of 103 to 109 Ω · cm.   The image forming apparatus according to claim 1, wherein both the corona transfer unit and the transfer assist roller are configured to be retractable with respect to the photosensitive drum surface.   3. The image forming apparatus according to claim 1, wherein a pressure for pressing the recording medium against the photosensitive drum by the transfer assist roller is in a range of 13 g / cm 2 to 40 g / cm 2.   9. An image forming system comprising a plurality of image forming apparatuses according to claim 1 and capable of duplex printing on continuous paper.

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