JP2929111B2 - Image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Object of the Invention (Industrial Application Field) The present invention relates to an image forming apparatus using an electrostatic transfer process, such as an electrostatic copying machine and a printer, and particularly to a contact type transfer unit. The present invention relates to an image forming apparatus to be used.

(Prior art and problems to be solved) An image-modulated laser beam, an LED array, or the like is irradiated on the charged surface of the image carrier to form an electrostatic latent image, and the toner is charged to the same polarity as the latent image. To form a toner image by the reversal development method, and a transfer member in the form of a sheet such as paper is transferred to a transfer portion formed by abutting transfer means such as a conductive transfer roller and a transfer belt on the image carrier. There has already been proposed an image forming apparatus configured to supply a toner image and a timing together, apply a transfer bias to the transfer unit, and transfer the toner image on the image carrier side to a transfer material.

The transfer unit as described above is based on discharge unevenness due to contamination of a discharge line due to dust and floating toner in the device, as compared with a transfer unit using a corona discharge device widely used in this type of device. There are various advantages such as less occurrence of transfer unevenness, scattering of unfixed toner, image blur due to instability of transfer material support at the transfer site, and extremely low generation of ozone and nitrogen oxide due to high pressure discharge. On the other hand, when transfer means such as a transfer roller is contaminated with toner, it is difficult to clean the transfer means. For example, in a method using a known blade or a felt material for cleaning the transfer roller, the transfer roller or the like is flexible, and paper dust or the like is clogged between the transfer member and the cleaning material such as the blade, so that cleaning failure may occur. As a result, the back surface of the transfer material is easily stained, and particularly in the case of continuous printing, the stain is remarkable.

The present invention has been made in order to cope with such a situation. In an image forming apparatus using a transfer unit such as a transfer roller, which is in contact with an image carrier, an interval for feeding a transfer material, Provided is an image forming apparatus that can perform good cleaning without providing a special cleaning member in a transfer unit by setting a relationship between an outer circumference, a width of a nip portion between the two, and a speed of each of the portions facing each other. It is intended to do so.

(2) Configuration of the Invention (Technical Means for Solving the Problems and Their Functions) In order to achieve the above-mentioned object, the present invention comprises a traveling image carrier and a transfer unit traveling in contact with the image carrier, and performs reversal development. An image forming apparatus for performing development by a method, wherein a transfer material is continuously passed through a transfer portion where the image carrier and the transfer means abut, and the distance between adjacent transfer materials is d. , the image bearing member and the speed of the image carrier at the site and the transfer means is in contact V, speed V _t of the transfer means, the length as viewed in the transfer material running direction of the abutting nip portion of both m, Assuming that the circumference of the transfer means is l, a means for applying (1 + m) × V / V _t <d <5l and applying a bias voltage having the same polarity as the latent image to the transfer means in a portion where no transfer material exists is provided. An image forming apparatus (1), In the above (1), an image forming apparatus which uses a laser beam as a light source for forming an electrostatic latent image and controls the amount of light by exposing the light source during pre-rotation or between sheets of paper. Assuming that the distance between the exposure portion for controlling the light amount on the body and the subsequent transfer material after passing the transfer portion is d ', this is set to (l + m) × V / V _t <d'<5l. An image forming apparatus (2),
Alternatively, the image forming apparatus according to the above (1) or (2), wherein the average particle diameter of the toner is 8 μm or less.

With this configuration, a high-quality image can always be obtained without providing a special cleaning unit in the transfer unit.

FIG. 1 is a schematic side view of a laser beam printer according to an embodiment of the present invention. An image-modulated laser beam emitted from a scanner unit 1 passes through a reflecting mirror 2. The surface is previously negatively charged to about -700 V by the primary charger 4 and is projected onto the OPC photoreceptor 3 disposed so as to extend in the direction perpendicular to the paper, and the potential of the projected portion is attenuated to about -100 to 200 V. Thus, an electrostatic latent image is formed.

When the latent image arrives at a development site close to the developing device 5 with the rotation of the photoconductor 3, toner having the same polarity as that of the latent image, that is, a negatively charged toner is supplied from the latent image. The toner adheres to the portion to form a toner image.

Further, when the photoconductor 3 rotates and the toner image reaches a transfer portion, which is a press-contact nip portion between the photoconductor 3 and the transfer roller 6 that presses the photoconductor 3, the transfer material supplied from the cassette 7 The transfer roller 6 is guided to the transfer portion at the same timing as the image. At this time, a positive transfer bias having a polarity opposite to that of the toner is applied to the transfer roller 6 by a power source (not shown), and the toner image on the photosensitive member is transferred to the transfer material. Transfer.

Thereafter, the transfer material passes through a fixing portion (not shown) to fix and fix the toner image, and then is discharged outside the apparatus.

After the transfer is completed, the residual toner remaining on the photoconductor is removed by the cleaner 9 and the residual charge is removed by the discharging lamp 10, so that the photoconductor is ready for the next step.

Next, the configuration of the transfer roller will be described with reference to FIGS.

FIG. 2 shows an example in which the core 21 is provided with a urethane sponge,
Layer 22 whose volume resistance is adjusted to 10 ⁴ to 10 ⁹ Ωcm by dispersing carbon or metal powder in sponge such as NBR
It is formed to have a thickness of about 50 mm.

A bias voltage having a polarity opposite to that of the toner, that is, a plus voltage in the case of the above-described apparatus, is applied to the transfer roller 6 during transfer. The applied voltage depends on the resistance value of the transfer roller and the process speed.
It shall be determined appropriately in the range of 500 to 4000 V, and generally,
A current of several μA needs to flow to the transfer roller.

The rollers shown in FIGS. 3 and ⁴ are made of urethane sponge, silicon sponge, or NB in which carbon or metal powder is dispersed outside the metal core 21 to adjust the volume resistance to about 10 ⁴ to 10 ⁹ Ωcm.
R sponge, and an inner layer 22 having a thickness of 3 to 50 mm formed of a rubber having a low hardness, etc., and Teflon (trade name), nylon, polyurethane rubber, polyethylene, polyester, silicone rubber, NB formed outside the inner layer 22
R, a resin selected from acryl, etc., preferably made of a material that is charged to the opposite polarity to the toner by friction with the transfer material, having a thickness of 0.01 to 0.3 mm and a volume resistance of 1
It consists adjusted outer layer 23 to have 0 ⁹ [Omega] cm or more insulating. In this case, for example, Teflon, polyethylene, polyester and the like are easily charged to a negative polarity, and nylon is easily charged to a positive polarity. Further, since the transfer roller is disposed in contact with or close to the photoconductor, it is necessary to select a material of the surface that does not adversely affect the photoconductor.

The bias voltage applied to the transfer roller 6 at the time of transfer depends on the resistance value of the transfer roller and the process speed.
It is also possible to apply a voltage obtained by superimposing an alternating current of V and a frequency of 500 Hz to 3 KHz.

FIG. 4 is an enlarged view of the vicinity of a transfer portion formed by abutting the photosensitive member 3 and the transfer roller 6 of the apparatus of FIG. 1, wherein the photosensitive member 3 and the transfer roller 6 are brought into pressure contact with each other. A nip portion having a length m is formed when viewed in the traveling direction of the transfer material.

Photoreceptor 3, the transfer roller 6, respectively _{Vmm / sec, V t mm /} sec
It is assumed that the roller 6 is traveling in the direction of the arrow at a peripheral speed of r, the diameter of the transfer roller 6 is r, the peripheral length thereof is l, and a predetermined bias voltage is applied to the roller 6 by the power supply 35.

The distance between the rear end of the preceding transfer material 32 and the front end of the succeeding transfer material 31 adjacent thereto is d.

Since the transfer material of various widths arrives at the transfer portion within a range narrower than the photosensitive member and the transfer roller, the toner supplied from the developing device remains attached for some reason, and this is the photosensitive member. It is inevitable that the toner is present on the surface of the toner, and the toner is inevitable to adhere to the transfer roller.
If it is left as it is, the back surface of the transfer material will be stained.

It has been found that the following conditions are required to avoid such a situation. In the illustrated device,
Nip also approximately one turn (l + m) time required to move the consideration to the transfer roller, a _{(l + m) / V t} , the distance of the photoconductor that moves in this time is _{(l + m) / V t} + V and (l + m) × V / V t, the relationship between the distance d of the transfer material is set so that the (l + m) × V / V t <d.

Further, as shown in FIG. 5, the bias applied to the transfer roller is applied from the time when the transfer material passes through the transfer portion to the time when the next transfer material passes, that is, the transfer material While the toner is not present at the transfer site, its polarity is inverted to negative so that the toner on the transfer material roller is electrostatically returned to the photoconductor. However, in addition to the toner charged to a negative polarity as a predetermined polarity, there is a so-called reversal fog toner charged to a positive polarity as an opposite polarity, which is a transfer material and a next transfer material. If a bias voltage of the same polarity as that of the latent image is applied to the transfer roller for a long time, the reverse fog toner may adhere to the transfer roller. is there.

According to the experiment, the time for applying the bias having the same polarity as the latent image to the transfer roller is 5 to 10 rotations, preferably 5 rotations or less at the upper limit of the number of transfer rollers. That is, it is preferable that d <5l.

In the sequence of FIG. 5, the transfer bias is +500 to 4000 when the transfer material exists at the transfer site.
V, when the transfer material is not present at the transfer site and is in direct contact with the photoconductor, -1000 to +300 V, preferably -1000 to
About 0V is preferable.

As can be understood from the above description, the photoconductor, the speed of the transfer roller, the length of the nip portion as the transfer portion, the circumferential length of the transfer roller, and the interval between adjacent transfer materials are represented by (l + m) × V / V _t <d By setting as described above, the transfer roller can always be kept clean without using a special cleaning member.

The above-mentioned phenomenon is the case of the toner having an average particle diameter of 10 to 15 μm. However, fine toner having an average particle diameter of about 4 to 8 μm which has come to be used recently to improve the image quality, It is easy to adhere to the transfer roller, and once adhered, separation is difficult. In such a case, it has been found that the present invention is extremely effective.

FIG. 6 is an operation sequence showing another embodiment of the present invention.

In a laser beam printer, in order to keep the light intensity of the beam constant, a laser beam intensity is illuminated between papers where no transfer material exists at a transfer portion to correct and control the intensity of the laser beam (APC: Automatic Power Control). Something like that has been done.

In this APC exposure section, the photoconductor is exposed and then developed.As shown in the figure, when the APC exposure section reaches the development position, the AC component of the development bias is cut, but slightly. It is inevitable that the toner will adhere.

Of course, in this case, it is natural that it is more effective to cut the direct current component, but the rise and fall times of the voltage at that time are several tens of milliseconds, and the nip of the transfer roller, that is, the transfer area Is practically difficult to control in view of the fact that is about 1 to 3 mm.

Therefore, in such a case, the toner remains in the form of a streak between the paper sheets.However, while applying a voltage having the opposite polarity to the toner between the paper sheets, the APC portion passes through the transfer portion, and then the transfer material of the succeeding transfer material is transferred. By setting the interval d 'to (l + m) × V / V _t <d ′ <5l, the toner adhering to the transfer roller can be
The next time it comes into contact with the photoconductor, it can be returned to the photoconductor.

As mentioned above, although the example which applied the present invention to a transfer roller was explained, the present invention is not limited to this,
It can be easily understood that the present invention can be applied to a transfer belt, and also to a structure in which an intermediate transfer member is used to transfer a toner image to the toner image.

(3) Effects of the Invention As described above, according to the present invention, the transfer of the transfer material is adjusted in an image forming apparatus such as a printer using a so-called image exposure or reversal development method that exposes a portion where toner is to be adhered. By changing the developing bias, back stains are reduced, image blurring and poor separation of the transfer material are prevented as much as possible, and there is a remarkable effect in obtaining a high quality image.

[Brief description of the drawings]

FIG. 1 is a side view of a main part showing an embodiment in which the present invention is applied to a printer, FIG. 2 and FIG. 3 are cross-sectional views showing the structure of a transfer roller, and FIG. FIG. 5 is an enlarged side view, FIG. 5 is a diagram showing an operation sequence of the apparatus shown in FIG. 1, and FIG. 6 is an operation sequence showing another embodiment of the present invention. 3 ... Photoconductor, 6 ... Transfer roller.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Masaki Ojima 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (56) References JP-A-63-247780 (JP, A) JP-A-63-247780 JP-A-63-286878 (JP, A) JP-A-63-56674 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G03G 15/16

Claims (3)

(57) [Claims] 1. An image forming apparatus comprising a traveling image carrier and a transfer unit traveling in contact with the image carrier, and performing development by a reversal developing method, wherein the image carrier and the transfer unit are in contact with each other. In the transfer method in which the transfer material is continuously passed through the transfer portion to perform the transfer, the distance between adjacent transfer materials is d, the speed of the image carrier at the portion where the image carrier and the transfer unit are in contact is V, When the speed of the means is V _t , the length of the abutting nip portion of the two in the transfer material running direction is m, and the circumferential length of the transfer means is l, (l + m) × V / V _t <d <5l And a means for applying a bias voltage having the same polarity as that of the latent image to the transfer means in a portion where no transfer material is present. 2. An image forming apparatus which uses a laser beam as a light source for forming an electrostatic latent image and controls the amount of light by exposing the light source during pre-rotation or between sheets. 'when a, which (l + m) × V / V t <d' exposure unit for the spacing between the transfer material subsequent after passed through the transfer portion d and wherein <be set to 5l Claims to be made (1)
The image forming apparatus as described in the above. 3. The image forming apparatus according to claim 1, wherein the average particle diameter of the toner is 8 μm or less.