JP2000194168A - Electrophotographic system both-side printer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a small-sized ecological electrophotographic both-side printer by constituting the printer so that a bias roller may be brought into contact with a photoreceptor drum and also a bias whose polarity is opposite to the electrostatically charged polarity of unfixed toner on the 1st side of a paper may be applied within a specified value. SOLUTION: The bias roller 95 facing the photoreceptor drum 91 as a 2nd image forming means across a paper P7 carrying path is brought into contact with the photoreceptor drum 91, and also, the bias of 1000 to 6000 V whose polarity is opposite to the electrostatically charged polarity of the unfixed toner on the 1st side of the paper P7 is applied by such the constitution, in the case the applied voltage of the bias roller 95 is controlled within the extent of 1000 to 6000 V, the electrostatically charged polarity of the unfixed toner on the 1st side of the paper is converted without the sticking of the toner on the 1st side to the bias roller 95, irrespective of the kind of rollers, and also, without the occurrence of irregularities in the image on the 1st side of the paper, and the toner image is transferred from the photoreceptor drum 91 to the 2nd side of the paper.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a copying machine, a laser printer, a facsimile, and the like, and more particularly, to a transfer device of a printing apparatus capable of performing double-sided printing using electrophotographic technology.

[0002]

2. Description of the Related Art Conventionally, in an electrophotographic double-sided printing apparatus in which an unfixed toner image is transferred onto both sides of a sheet and then fixed, the charging polarities of the photoconductors of a first image forming unit and a second image forming unit are known. And the toner must have different charging polarities. However, the need for photoconductors and toners with different charging polarities means that there are two types of photoconductors,
It is necessary to prepare two types of toner, and inevitably two or more types of peripheral devices are necessary.

[0003]

As a means for solving such a problem, a technique disclosed in Japanese Patent Application Laid-Open No. HEI 8-212664 is disclosed. Means for charging the unfixed toner image transferred to the sheet by the first image forming means by the corotron method in the transport path of the first image forming means so as to have the same polarity as the voltage polarity of the second transfer means. However, according to this method, since discharge products such as ozone and nitrogen oxides are generated from the discharge wire, it is not environmentally friendly. Furthermore, the addition of an extra device on the transport path hinders miniaturization of the entire machine.

An object of the present invention is to provide a first image forming means for forming an unfixed toner image on a first surface of a sheet, and a second image forming means for downstream of the first image forming means in a sheet conveying direction. A second image forming means for forming an unfixed toner image on the surface, wherein the photoconductor of the first image forming means and the photoconductor of the second image forming means have the same charge polarity, and In the electrophotographic double-sided printing apparatus, which has the same polarity as the charged polarity of the toner and has a means for changing the charged polarity of the unfixed toner on the first side of the sheet, it is environmentally friendly and prevents miniaturization of the entire machine. It is another object of the present invention to provide a means for converting the charging polarity of the unfixed toner on the first surface of the sheet.

[0005]

According to the present invention, there is provided a first image forming means for forming an unfixed toner image on a first surface of a sheet, the first image forming means comprising: A second image forming unit for forming an unfixed toner image on the second surface of the sheet is provided downstream of the sheet in the conveying direction, and a photosensitive member of the first image forming unit and a photosensitive member of the second image forming unit are provided. The charge polarity of the body is the same polarity, and the charge polarity of the toner is also the same polarity, and the transfer means of the second image forming means is transferred via the photosensitive drum of the second image forming means and the paper conveyance path. The bias roller opposes the photosensitive drum, and applies a bias of 1,000 V to 6,000 V having a polarity opposite to the polarity of the unfixed toner on the first surface of the sheet.

[0006]

The sheet on which the unfixed toner image has been transferred to the first surface by the first image forming means passes through a transport path, and the unfixed toner image is transferred to the second surface of the sheet by the second image forming means. When the unfixed toner image is transferred to the second surface of the sheet while being conveyed, the unfixed toner image on the first surface of the sheet simultaneously contacts the transfer unit of the second image forming unit. Since a high voltage having a polarity opposite to the charging polarity of the toner of the image transferred to the first surface is applied to the bias roller as the second transfer means of the image forming means, Corona discharge occurs in a minute gap immediately before the one surface comes into contact, the charge polarity of the unfixed toner on the first surface of the paper is converted, and becomes the same polarity as the voltage applied to the bias roller. Thereafter, the unfixed toner on the first surface of the sheet comes into contact with the bias roller with the same charge polarity as the voltage polarity applied to the bias roller. The unfixed toner on the first surface of the sheet does not adhere to the bias roller.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A printing apparatus capable of double-sided printing to which an embodiment of the present invention is applied will be described with reference to FIG. In the drawing, sheets fed one by one from a sheet feeding cassette 1 by a sheet feeding roller 2 pass through a vertical transport path 3, and are aligned at a registration unit 4, and wait for a first image. The toner image formed by the first image forming unit 6 is conveyed to the forming unit, and the first transfer unit 65 transfers the toner image to the first surface of the sheet. The sheet on which the unfixed toner image has been transferred to the first surface is conveyed through the conveyance path 7, and the toner image formed by the second image forming unit 9 is transferred to the second surface of the sheet by the second transfer unit 95. Is done. Thereafter, the sheet having the unfixed toner image transferred on both sides thereof is conveyed to the fixing device 10 and the unfixed toner images on both sides of the sheet are simultaneously fixed, and is discharged to the sheet discharge tray 12 via the sheet discharge unit 11.

Further, a configuration of a printing apparatus capable of performing double-sided printing to which the embodiment of the present invention is applied will be described in detail with reference to FIGS.

The first image forming means 6 has a generally used electrophotographic process. In the embodiment of the present invention, a positive charge is applied to the surface of the photoreceptor by a main charging section 62, and a laser beam is applied. The electrostatic latent image exposed and formed by the laser beam of the unit 63 is visualized by the positively charged toner of the developing device 64. The visual image formed by the positively charged toner is transferred to the first surface of the sheet by the first transfer unit 65. The first transfer unit 65 uses a corotron method in the embodiment of the present invention, but may use any of a bias roller method, a transfer belt method, and the like.

The sheet on which the toner image has been transferred to the first surface by the first image forming means 6 carries a positively charged toner image on the transport path 7.

The second image forming means 9 has an electrophotographic process which is also generally used. In the embodiment of the present invention, a positive charge is applied to the surface of the photoreceptor by a main charging portion 92. The electrostatic latent image exposed and formed by the laser light of the laser unit 93 is visualized by the positively charged toner of the developing device 94. The visual image formed by the positively charged toner is transferred to the second transfer unit 95 on the second surface of the sheet.
Is transferred.

The second transfer means 95 comprises a bias roller 95 and a voltage applying means 953. More specifically, the axis of the bias roller 95 is a conductive metal roller, its periphery is made of rubber or resin, and polyester is used. System elastomer,
An elastic body such as a polyurethane elastomer mixed with an inorganic ion such as conductive carbon black or lithium perchlorate or an organic ion such as a quaternary ammonium salt, and has a volume resistivity of 10 ² to 10 ¹⁰ Ω · cm. It is preferable that the outer circumference is coated with fluorine. What can be applied to the present invention is not limited to the above, but may be a roller generally used as a transfer roller, and an optimum roller may be appropriately selected according to peripheral conditions.

Although the bias roller 95 and the photosensitive drum 91 are in contact with each other and face each other, they may face each other at a distance of one sheet or more, that is, at a distance of about 0.5 mm. Almost the same effects can be obtained.

The voltage of the bias roller 95 is applied to the axis of the bias roller 95 by a DC power supply 953.

In the present embodiment, the image on the first surface and the bias roller 95 are driven by driving means (not shown) because they must not rub against the unfixed toner image on the first surface of the sheet. In order to avoid drive unevenness, it is preferable to transmit the drive by a helical gear.

Conventionally, when the charged polarity of the unfixed toner on the first surface of the sheet and the voltage polarity of the bias roller 95 that comes into contact with the toner have opposite polarities, the unfixed toner on the first surface of the sheet adheres to the bias roller 95. Was considered one. However, as shown in Tables 1 to 9, depending on the setting of the voltage applied to the bias roller 95, the unfixed toner on the first surface of the sheet does not adhere to the bias roller 95, and the first surface of the sheet does not adhere. It was found that when the charging polarity of the unfixed toner was changed, the toner image of the second image forming means 9 could be transferred to the second surface of the sheet. This is because the conversion of the charging polarity of the unfixed toner on the first surface of the sheet is performed upstream of the nip position between the bias roller 95 and the sheet in the sheet conveyance direction. The polarity and the charging polarity of the unfixed toner on the first surface of the paper are the same, and the unfixed toner on the first surface of the paper and the bias roller 9
Due to the repulsion of 5, the unfixed toner on the first surface of the sheet does not adhere to the bias roller 95.

The roller used in the experiment for determining the voltage applied to the bias roller 95 according to the first aspect of the present invention is as follows: Roller A: Lithium perchlorate added to polyurethane elastomer, volume resistance 10 ⁴ Ω · cm, Asker C hardness 6
8 °, elastic layer 5 mm, outer diameter φ 20 mm, length 230 mm, shaft core is aluminum Roller B: Lithium perchlorate added to polyester elastomer, volume resistance 10 ⁵ Ω · cm, Asker C hardness 6
2 °, elastic layer 5mm, outer diameter φ20mm, length 230mm, shaft core is aluminum Roller C: conductive carbon black added to urethane rubber, volume resistance 10 ⁶ Ω · cm, Asker C hardness 75 °, elastic layer 5mm, The outer diameter is φ20 mm, the length is 230 mm, and the shaft core is made of aluminum.

A bias roller 95 as a second transfer means
And the photosensitive drum 91 of the second image forming means has 0,0.
They face each other at a distance of 2,0.5 mm.

Tables 1 to 9 show the results under each condition.

[0020]

[Table 1]

[0021]

[Table 2]

[0022]

[Table 3]

[0023]

[Table 4]

[0024]

[Table 5]

[0025]

[Table 6]

[0026]

[Table 7]

[0027]

[Table 8]

[0028]

[Table 9]

Here, when the voltage applied to the bias roller 95 is a relatively low voltage of 200 to 900 V, an image can be transferred to the second surface of the paper, but the toner on the first surface of the paper adheres to the bias roller 81. , Get dirty.

When the voltage applied to the bias roller 95 is in the range of 1,000 to 6,000 V, the toner on the first surface adheres to the bias roller 95 in any type of roller. The charging polarity of the unfixed toner on the first side of the sheet is converted without disturbing the image on the first side of the sheet, and the toner image from the photosensitive drum 91 is transferred to the second side of the sheet without disturbing the image on the first side of the sheet. It is possible.

When the voltage applied to the bias roller 95 is 6,000
When the voltage slightly exceeds 0 V, an arc discharge is generated from the bias roller 95 to the sheet, so that the polarity conversion of the toner is not performed normally. Further, the images on both sides of the sheet are disturbed, and image defects occur.

From the above results, it is found that the bias roller 95 as the second transfer means has a voltage of 1,000 V to 6,000 V
Must be applied. Further, the type of the bias roller 95 and the distance between the bias roller 95 and the photosensitive drum 91 seem to have little effect as long as the normal transfer conditions are satisfied.

The fixing device 10 includes a first fixing roller 10
1, first fixing heater 1011, second fixing roller 10
And a second fixing heater 1021, and the first fixing roller 101 is formed by applying a fluorine-coated outer periphery of a roller made of aluminum or the like having good heat conductivity. By incorporating the first fixing heater 1011, the temperature is controlled to a predetermined temperature required for fixing. The second fixing roller 102 also has a heat-conductive urethane rubber covered with an elastic layer made of heat-resistant urethane rubber, and further has an outer periphery having a release layer made of a fluorine-based resin such as PTFE. Used. In consideration of simultaneous double-sided fixing, the second fixing roller 102 also has a built-in fixing heater 1021 and is controlled to a predetermined temperature required for fixing.

[0034]

According to the present invention, a first image forming means for forming an unfixed toner image on a first surface of a sheet,
A second image forming unit that forms an unfixed toner image on the second surface of the sheet downstream of the image forming unit in the sheet conveyance direction, wherein the first image forming unit and the second image In an electrophotographic double-sided printing apparatus in which the charging polarity of the photosensitive member of the forming unit and the charging polarity of the toner are the same,
It is possible to provide a small-sized, environmentally friendly electrophotographic double-sided printing apparatus.

[Brief description of the drawings]

FIG. 1 shows a printing apparatus capable of performing double-sided printing to which an embodiment of the present invention is applied.

FIG. 2 is a detailed view of a transfer unit of a printing apparatus capable of performing double-sided printing according to an embodiment of the present invention.

FIG. 3 is a printing apparatus capable of performing both-side printing according to a conventional technique.

[Explanation of symbols]

 P1 to P9: paper 5: transport path 66: first separating charger 67: first cleaning device 68: second discharging lamp 86: second separating charger 87: second cleaning device 88: second discharging lamp

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H028 BA16 BB04 BC01 2H032 AA05 BA01 BA19 BA23 BA27 CA01

Claims (1)

[Claims] A first image forming means for forming an unfixed toner image on a first surface of a sheet, and an unfixed toner image on a second surface of the sheet downstream from the first image forming means in a sheet conveying direction. A second image forming unit for forming an image is provided, and the photoconductor of the first image forming unit and the photoconductor of the second image forming unit have the same charge polarity, and the toner has the same charge polarity. Polarity, the transfer means of the second image forming means is a bias roller opposed to the photosensitive drum of the second image forming means via a sheet conveying path, and is in contact with the photosensitive drum, An electrophotographic double-sided printing apparatus, wherein a bias of 1,000 V to 6,000 V having a polarity opposite to the polarity of the unfixed toner on the first surface of the sheet is applied.