JPH03171079A - Image forming device - Google Patents

Abstract

PURPOSE:To impress inexpensive and stable electric charges without adversely affecting transfer action by providing an elastic body layer, conductive layer and resistance layer on the outer peripheral surface of a metal shaft in this order and constituting a transfer roller. CONSTITUTION:The transfer roller 5 is constituted of a metal shaft 1 on which the transfer voltage is impressed, the elastic body layer 2 with which the peripheral surface of the metal shaft 1 is covered, the conductive layer 3 with which the outer peripheral surfaces of the elastic body layer 2 and the metal shaft 1 are covered, and the resistance layer 4 with which the outer peripheral surface of the conductive layer 3 is covered. At this time, without scattering conductive grains on the elastic body layer 2 of the transfer roller 5, the transfer voltage can be impressed and the flexibility of the elastic body layer 2 can be preferably maintained. Thus, an inexpensive and stable transfer voltage can be impressed without adversely affecting the transfer action, and therefore, a preferable image without transfer omission nor transfer uneveness can be obtained.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention applies a transfer voltage to an elastic transfer roller provided so as to sandwich a transfer material and press against an image carrier. The present invention relates to an image forming apparatus that transfers toner from an image carrier to a transfer material using pressure and electrostatic force.

(Prior Art) A method using a corona charger (corona transfer method) is known. This method uses a corona charge to generate charges from the back side of the transfer material, and uses the electric field formed by the charges attached to the transfer material to transfer the toner from the toner image carrier to the transfer material, and the 'gcW configuration is simple. Because of this, it is widely used in copiers, printers, etc. However, the corona transfer method has problems such as image scattering, transfer defects when the transfer material absorbs the mixture in a humid environment, and the need for an expensive power source because it uses high voltage. . For this purpose, there is a method in which a transfer roller is pressed against a toner image carrier and the toner image is transferred by pressure, and a method in which an elastic roller is pressed against the toner image carrier and a transfer voltage is applied to transfer the toner image by pressure and electrostatic force. has been devised.

In particular, a method in which an elastic roller is pressed onto a toner image carrier, a transfer voltage is applied, and a toner image is transferred using pressure and electrostatic force can perform extremely good transfer without image scattering, even in a humid environment. It is possible.

However, in order to impart electrical conductivity to the elastic roller, it is generally necessary to use rubber or sponge whose resistance has been reduced by dispersing electrically conductive particles such as electrically conductive carbon black. Rubbers and sponges treated in this manner are expensive, generally lack flexibility, and have large residual strain due to compression, which causes transfer omissions and uneven transfer due to roller deformation.

(Problems to be Solved by the Invention) The present invention has been made to solve these problems in the conventional technology, and it is possible to apply a stable transfer voltage at low cost without adversely affecting the transfer action. An object of the present invention is to provide an image forming apparatus that can form good images without transfer omissions or uneven transfer.

[Structure of the Invention] (Means for Solving the Problems) In order to solve the above problems, the first invention provides a transfer roller with a metal shaft to which a transfer voltage is applied, and a coating on the outer peripheral surface of the metal shaft. an elastic body layer, and this elastic body r
The above-mentioned metal◆ is characterized by comprising a conductive layer covering the outer peripheral surface of the shaft and a resistance layer covering the outer peripheral surface of the conductive layer, and the second invention has a transfer roller. a metal shaft to which a transfer voltage is applied; an elastic layer covering the outer peripheral surface of the metal shaft; a conductive layer continuously covering the outer peripheral surface and end surfaces of the elastic layer; A third aspect of the present invention is characterized in that the transfer roller includes a conductive member connecting the metal shaft and a resistive layer covering the outer periphery of the conductive layer. an elastic layer that covers the surface, a conductive layer that continuously covers the outer peripheral surface and end surfaces of the elastic layer, and an electrode that is connected to the end surface of the conductive layer and applies a transfer voltage;
It is characterized by comprising a resistance layer covering the outer peripheral surface of the conductive layer.

(Function) With the above means, it is possible to apply a transfer voltage and maintain good flexibility of the elastic layer of the transfer roller without performing a process such as dispersing conductive particles in the elastic layer of the transfer roller.

(Example) Examples of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a perspective sectional view showing an embodiment of a transfer roller used in the first invention.

In the figure, reference numeral 1 denotes a metal shaft, and an elastic layer 2, a conductive layer 3, and a resistive layer 4 are sequentially provided on the outer periphery of the metal shaft 1 to form a transfer roller 5. The metal shaft 1 is made of stainless steel and has a diameter of 8W. The elastic layer 2 is made of an elastic material that can be compressed and deformed, such as foamed rubber sponge, foamed polyethylene, or foamed urethane. As shown in FIG. 3, the transfer roller 5 is partially pressed against the photosensitive drum 21 as a toner image carrier, so the elastic layer 2 deforms flexibly when the pressure is applied, and quickly returns to its original shape when the pressure is released. It is necessary to restore the system to the original state, and it is necessary to be able to operate stably against repeated repetitions. In other words, a material with excellent creep resistance and plastic deformation resistance is desirable. As the foam structure, any structure can be used, such as an open cell structure (open cell) or a closed cell structure, but the open cell structure is optimally used because its shape is stable regardless of the ambient temperature. . The flexibility of the elastic layer 2 can be changed to any desired flexibility by changing the constituent materials, foam structure, degree of foaming, etc., and a hardness equal to or lower than the hardness of closed-cell sponge rubber of 30 is optimal. used for.

In this example, foamed urethane is used, and JIS standard K
6301 type A hardness tester. It has a hardness of 20 degrees and an outer diameter of 18 mm.

The conductive layer 3 can be made of a thin sheet of conductive resin metal in which conductive fine particles such as conductive carbon are dispersed in polyurethane resin, or a conductive adhesive, and must have conductivity and flexibility. , and the volume resistance value is the resistive layer 1
It must be lower than that of 105Ω・0 or less.

In this example, conductive polyurethane paint was applied to the surface and side surfaces of the elastic layer 2 made of urethane foam in the following steps, and after drying, it was heat-treated. First, as a conductive polyurethane paint, the trade name "Subarex DH202313" manufactured by Nippon Miractran Co., Ltd. was used. This is combined with methyl ethyl ketone (MEK) and tetrahydrofuran (T
HF) in a 1:1 ratio is added in an equal amount. “Sparex DH20231B” is a solution type conductive polyurethane paint based on thermoplastic polyurethane.

After thoroughly stirring this diluted paint, it is applied by dipping to the surface and side surfaces of the elastic layer 2 made of foamed urethane that has been washed with a solvent. The pulling speed of the foamed urethane roller was 5 + n/see. Approximately 30 minutes after application
It was dried in air for a minute, and then heat-treated at 100°C for 20 minutes. The thickness of the conductor layer 3 thus created was approximately 50 mm, and the resistance value was 5×10′Ω·mark. The conductive layer 3 was also formed on the surface of the metal shaft 1 near the side surface of the conductive layer 2, so that a transfer voltage was applied from the metal shaft 1.

The resistive layer 4 is made of resin such as polyester, polyethylene, or vinyl chloride, or rubber in which conductive fine particles such as conductive carbon, copper, or nickel fine metal particles are dispersed.
Alternatively, a highly flexible resistive sheet such as a conductive polymer resin may be used. Volume resistance value is 105~1
The range of 0.015 Ω·W is desirable, especially the range of 107 to 10 I2
A range of Ω·(7) is preferably used. Such volume resistance value can be easily controlled by changing the mixing ratio of conductive fine particles to the resin or rubber. Further, it is desirable that the volume resistivity value of the resistive layer does not change or changes only slightly in response to changes in environmental conditions such as external pressure, temperature, and humidity.

Further, it is desirable that the surface of the resistive layer 4 be smooth. If unnecessary toner accumulates on the surface of the resistive layer 4, it will stain the back surface of the transfer material, but the smoother the surface of the resistive layer 4, the easier it is to remove this toner. The thickness of the resistive layer 4 is preferably as thin as possible in order not to impair the flexibility of the elastic layer 2, preferably in the range of <0.02 to 2 times. In this example, conductive carbon is dispersed in a polyester resin, adjusted to a volume resistivity of 1010Ω·(1), and cast to a thickness of 50 mm.

FIG. 3 shows an embodiment of an image forming apparatus using the present invention. In this figure, the transfer roller 5 is the same as the transfer roller shown in FIG. 1, and the explanation of the parts common to those in FIG. 1 will be omitted. The photoreceptor drum 21 serving as an image carrier is a chloro drum made of an aluminum tube coated with an organic photoreceptor.

The surface potential of the photoreceptor drum 21 is charged to about -600V by a scorotron charger (not shown), and image exposure is performed by an LED array (not shown), so that an electrostatic latent image is formed on the photoreceptor drum 21. Formally imposing. This electrostatic latent image is developed by a two-step developing device 22 to be visualized, and a toner image 23 is formed on the photoreceptor drum 21. A paper 24 as a transfer material, on which toner has negative polarity and reverse development is performed, is supplied and conveyed from a cassette (not shown) and inserted between the photosensitive drum 21 and the transfer roller 5. No transfer voltage is applied to the transfer roller 5 until the paper 24 enters between the photosensitive drum 21 and the transfer roller 5. This is because if a transfer voltage is applied from the leading edge of the paper 24, the paper 24 will wrap around the photoreceptor drum 21 after transfer, and a peeling means must be used to separate the paper 24, making the machine expensive. . Therefore, in this embodiment, the leading edge of the paper 24 is 3' mr.
The transfer voltage is turned ON when the transfer voltage enters the s transfer section. However, with this method, an image cannot be formed on the tip and the tip peels off.

Therefore, a transfer bias is applied from the leading edge of the paper 24, and A
It is also possible to use a method such as peeling off the paper 24 using a C corona charger or gradually increasing the transfer bias voltage. Here, the polarity of the transfer voltage applied to the transfer roller 5 is opposite to the polarity of the toner, and in this embodiment, it is +700V.
~2000V is applied. In the transfer section, the transfer roller 5 is pressed against the photosensitive drum 21 with a predetermined pressure.

The toner image on the photoreceptor drum 21 is transferred onto the paper 24 by pressure and electrostatic force in the transfer nip width formed by the photoreceptor drum 21 and the transfer roller 5 . In this embodiment, the transfer roller 5 does not have a drive system and rotates as the photosensitive drum 21 rotates. The paper 24 is naturally peeled off by its own weight, guided by a conveyor belt 25 to a fixing device (not shown), where the toner image is fixed, and then discharged. When the paper 24 is not present in the transfer nip, no transfer voltage is applied, but the toner may adhere to the roller due to physical adhesion force, or the width of the paper 24 is narrower than the width of the roller, so the toner may adhere to the roller. A transfer roller cleaning blade 26 for cleaning the toner and a cleaning box 27 for storing the cleaned toner are arranged.

The untransferred toner remaining on the photoreceptor drum 21 without being transferred is cleaned by a cleaning device (not shown), and the charge on the photoreceptor drum 21 is removed by a charge removal lamp (not shown), completing one cycle of the process. ends. Note that the method of forming an image on the photosensitive drum 21, the method of fixing the transferred image to the transfer material, the fixing method, etc. are outside the scope of the present invention, and any known method may be used.

In the above image forming apparatus, plain paper is used as the transfer material, and the pressing force of the transfer roller 5 on the photosensitive drum 21 is 90 g.
/c! When the image was transferred, an extremely good transferred image was obtained with no hollow character images or uneven transfer. next,
A life test of 10,000 sheets was conducted using this image forming apparatus, and even at the end of the life test, there was no conduction failure between the metal shaft 1 and the conductive layer 3 due to peeling of the conductive layer 3, etc. This is caused by deformation of the roller. It was possible to obtain a transferred image as good as the initial one without hollow spots or unevenness in the transferred image.

FIG. 4 is a perspective sectional view of a transfer roller used in the second invention.

An elastic layer 2 made of foamed urethane is formed on the outer periphery of a metal shaft 1 made of stainless steel, and a conductive layer 3 and a resistive layer 4 are sequentially formed on the outer periphery of the elastic layer 2. Further, the conductive layer 3 is also formed on the surface and end side surfaces of the amenophobic layer 2 by coating.

In this embodiment, the conductive polyurethane paint applied to the metal shaft 1 is peeled off, and the annular conductor 6 is wound around the metal shaft 1 and brought into contact with the side surface of the roller.
is adhered to the end side surface of the conductive body layer 2 and the metal shaft 1 with a conductive adhesive. The conductor 4 is made by dispersing and impregnating urethane foam with carbon, etc., and has a volume resistivity of 10 3 Ω·. Other materials and the like are the same as those of the transfer roller shown in FIG.

Using this transfer roller, a life test was conducted using the image forming apparatus shown in Fig. 3 (the conditions were the same as in the above-mentioned example). There was no conduction failure between the shaft and the conductive layer, and it was possible to obtain a good transferred image without voids or unevenness in the transferred image caused by conduction failure or deformation of the edges.

FIG. 6 is an oblique sectional view of the transfer roller used in the third invention.

An elastic layer 2 made of foamed urethane is formed on the outer periphery of a metal shaft 1 made of stainless steel, and a conductive layer 3 and a resistive layer 4 are sequentially formed on the outer periphery of the elastic layer 2. Further, the barrel electric body layer 3 is also formed on the surface and end side surfaces of the electric body layer 2 by coating.

In this embodiment, the conductive polyurethane paint applied to the metal shaft 1 is peeled off, the electrode wheel 7 is brought into contact with the side surface of the end of the roller, and the transfer bias is directly supplied from the DC power source 9 through the lead wire 8.

Using this transfer roller, a life test was conducted using the image forming apparatus shown in Fig. 3 (the conditions were the same as in the above-mentioned example). There was no conduction failure between the shaft 1 and the conductive layer 3, and a good transferred image could be obtained without voids or unevenness in the transferred image caused by conductivity failure or roller deformation.

[Effects of the Invention] As explained above, according to the present invention, a transfer voltage can be applied without dispersing conductive particles in the elastic layer of the transfer roller, and the flexibility of the elastic layer can be maintained well. .

Therefore, it is possible to apply an inexpensive and stable transfer voltage without adversely affecting the transfer action, and it is possible to provide a good image without transfer omissions or transfer unevenness.

[Brief explanation of the drawing]

FIG. 1 is a perspective cross-sectional view showing an example of a transfer roller used in the first invention, FIG. 2 is a partial cross-sectional view of the end of this transfer roller, and FIG. 3 is an electrophotograph using this transfer roller. 4 is a perspective sectional view showing an example of a transfer roller used in the second invention; FIG. 5 is a partial sectional view of the end of the transfer roller; FIG. is a perspective cross-sectional view of a main part showing an example of a transfer roller used in the third invention;
FIG. 7 is a partial sectional view of this transfer roller. DESCRIPTION OF SYMBOLS 1... Metal shaft, 2... Elastic body layer, 3... Electric conductor layer, 4... Resistive layer, 5... Elastic transfer roller,
6... Electric conductor, 7... Electrode ring, 21... Photosensitive drum (image carrier).

Claims (3)

[Claims] (1) An image carrier that carries an image, and the image on the image carrier is transferred to the transfer material by being pressed against the image carrier via a transfer material and applying a transfer voltage. In an image forming apparatus comprising a transfer roller, the transfer roller includes a metal shaft to which the transfer voltage is applied, an elastic layer covering an outer peripheral surface of the metal shaft,
An image forming apparatus comprising: a conductive layer covering the elastic layer and the outer peripheral surface of the metal shaft; and a resistive layer covering the outer peripheral surface of the conductive layer. (2) An image carrier that carries an image, and a transfer that transfers the image of the image carrier to the transfer material by being pressed against the image carrier via a transfer material and applying a transfer voltage. an image forming apparatus comprising: a metal shaft to which the transfer voltage is applied to the transfer roller; an elastic layer covering an outer peripheral surface of the metal shaft;
A conductive layer that covers the elastic layer, a conductive member that connects an end surface of the conductive layer to the metal shaft, and a resistance layer that covers the outer peripheral surface of the conductive layer. image forming device. (3) An image carrier that carries an image, and a transfer that transfers the image of the image carrier to the transfer material by being pressed against the image carrier via a transfer material and applying a transfer voltage. In the image forming apparatus comprising a roller, the transfer roller includes a metal shaft, an elastic layer covering the outer peripheral surface of the metal shaft, a conductive layer covering the elastic layer, and an end surface of the conductive layer. An image forming apparatus comprising: an electrode connected to the electrode for applying a transfer voltage; and a resistive layer covering the outer peripheral surface of the conductive layer.