JPH03202885A - Elastic roller - Google Patents

Abstract

PURPOSE:To obtain stable transfer characteristic extending over a wide environmental range and high transfer efficiency by specifying resistance per unit area between a core bar and the outer surface of an elastic roller and the resistivity of an elastic layer. CONSTITUTION:The elastic roller 1 is formed with the core bar 2, the elastic layer 3, and a surface coating layer 4 which covers the elastic layer 3. By setting the resistivity of the elastic layer 3 of the roller 1 at 103-108 OMEGAcm<2>, the transfer efficiency can be improved. Also, by setting the resistance per unit area between th core bar 2 and the outer surface of the roller 1 at 10<6>-10<9>OMEGA/cm<2>, the stable transfer characteristic can be obtained extending over respective environmental condition.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to an elastic roller, and particularly to a transfer roller used in an electrophotographic apparatus.

(Prior Art) Currently, in image forming apparatuses using an electrophotographic process, a corona charger is mainly used as a method for transferring an image formed on an image carrier such as a photoreceptor to a transfer material such as paper. method (corona transfer method) is used. However, the corona transfer method has problems such as image scattering, transfer failures when the transfer material absorbs moisture in a humid environment, and the need for an expensive power source to generate high voltage. Ta.

Therefore, as a transfer method to replace the corona transfer method, there is a method in which a transfer roller is pressed against an image carrier and the image is transferred by pressure, and a method in which an elastic roller is pressed against the image carrier, a bias voltage is applied, and pressure and static electricity are transferred. A method of transferring by force has been devised. In particular, a method in which an elastic roller is pressed against the image carrier, a bias voltage is applied, and the image is transferred using pressure and electrostatic force can eliminate image scattering, make the contours of images such as characters and lines clear, and improve image quality. There is an advantage that good transfer can be performed without damaging the carrier.

For use in this roller transfer method, a functionally separated transfer roller has been proposed, the internal structure of which consists of a core metal, an elastic layer fixed around the core metal, and a surface coating layer covering the elastic layer. ing.

In this function-separated transfer roller, the elastic layer deforms elastically when the roller comes into pressure contact with the image carrier, improving the adhesion between the image carrier and the image-receiving sheet such as paper or OHP sheet during transfer, and improving the adhesion of the transferred image. It stabilizes the The surface coating layer is generally made of a material with high electrical resistance, which provides an appropriate transfer electric field near the transfer surface, and also makes it easy to remove untransferred toner with a blade or brush if it adheres to the surface of the roller. It has surface properties that allow it to

(Problem to be solved by the invention) However, the transfer characteristics are significantly influenced by changes in the environment.
In particular, the resistance of the paper changes greatly depending on the humidity, and the resistance of the transfer roller itself also changes, so there is a problem in that it is difficult to stabilize the transfer characteristics, that is, the transfer efficiency, without being affected by the environment.

Therefore, an object of the present invention is to provide an elastic roller that can obtain stable transfer characteristics and high transfer efficiency even in a wide environmental range from high temperature and high humidity to low temperature and low humidity.

[Structure of the Invention] (Means for Solving the Problems) In order to solve the above problems, the present invention provides a first layer (elastic layer) consisting of a core metal and an elastic body fixed around the core metal.
and a second layer (surface layer) made of a high-resistance resin formed on the first layer, the elastic roller comprising:
The resistance per unit area between the core metal and the outer surface of the second layer is in the range of 106 Ω/cm2 to 109 Ω/ci, and the resistivity of the first layer is 103 Ω·cm to 1
03 Ω・cm, and the resistivity of the second layer is 1
Provided is an elastic roller characterized in that the resistance is in the range of 0.07 Ω·cm to 10 12 Ω◆cm.

In the elastic roller of the present invention, the resistance per unit area between the core metal and the outer surface of the second layer is preferably in the range of 10 6 Ω/cm 2 to 10 9 Ω/cd. Also,
The resistivity of the first layer is 103Ω·cm to 103Ω·c
Preferably, the resistivity of the second layer is in the range 10
It is preferably in the range of 3 Ω·cm to 10 12 Ω·cm.

(Function) As described above, in the elastic roller of the present invention, the resistance per unit area between the core bar and the outer surface of the second layer, the resistivity of the first layer, and the resistivity of the second layer are determined. The resistivity is defined within a predetermined range. When such an elastic roller is applied to a transfer roller of an electrophotographic apparatus, stable transfer characteristics can be obtained in a wide environmental range from high temperature and high humidity to low temperature and low humidity.

(Example) Hereinafter, the present invention will be explained in detail using the drawings.

FIG. 1 is a schematic diagram showing the internal structure of an elastic roller according to the present invention.

In FIG. 1, reference numeral 1 indicates an elastic roller, and the second elastic roller 1 has a core bar 2 made of metal such as stainless steel or brass, an elastic layer 3 made of an elastic body, and an elastic layer 3.
It is composed of a surface coating layer 4 covering the surface.

As the material of the elastic layer 3, for example, silicone rubber, polyurethane rubber, etc. are used. As the material for the surface coating layer 4, fluorine resin, rubber, or the like is used. By dispersing conductive fine particles in the rubber constituting the elastic layer 3, the elastic layer itself can be made conductive.

The rubber hardness on the surface of the elastic roller 1 is ASKER-C.
The hardness is preferably in the range of 20 degrees to 60 degrees, and when used as a transfer roller under this condition, an appropriate nip width with the photoreceptor can be obtained.

Several so-called functionally separated elastic rollers having an internal structure of two or more layers as in the present invention have been proposed in the past.

As an example of an elastic roller used as a transfer roller, there is one in which a conductive layer made of conductive resin or the like is further provided between the elastic layer and the surface coating layer. In this type of roller, the conductive layer and the metal core are electrically connected, and the conductive layer often functions as an electrode during transfer. Methods for establishing electrical conductivity between this conductive layer and the core metal include covering both ends of the roller with a conductive layer and bringing it into contact with the core metal, or providing a conductive layer on the surface of the roller and around the core metal and using an elastic layer to conduct the conductive layers. Some have a conductor made of the same material as the conductive layer that penetrates through the layer.

However, these elastic rollers provided with a conductive layer have a complicated internal structure, and in terms of the manufacturing method of the roller, there are problems in that the manufacturing process is increased and the cost is increased.

Since the elastic roller of the present invention consists of only two layers, the elastic layer 3 and the surface coating layer 4, the manufacturing cost is relatively low.

Another feature of the present invention is that the elastic layer 3 itself has electrical conductivity.

In addition, some other rollers have an internal structure made of a single material with only an elastic layer, but when used as a transfer roller, toner adheres to the roller surface due to the surface roughness and stickiness of the elastic layer. It is difficult to remove attached toner with a blade or the like.

Therefore, as in the present invention, such a problem can be solved by providing a surface coating layer separately from the elastic layer and selecting a material having low surface roughness and to which toner does not easily adhere.

In this embodiment, the surface coating layer 4 is made of fluorine resin, latex, or the like.

FIG. 2 is a schematic diagram of the apparatus used for evaluating the elastic roller of the present invention. In this example, this elastic roller was used as a transfer roller of a copying machine for evaluation. In the following explanation,
The elastic roller of the present invention is referred to as a transfer roller.

In FIG. 2, the toner image 8 on the toner image carrier 6 is
As the toner image bearing member rotates (in the direction of the arrow), the toner image bearing member is transferred to the contact portion with the transfer material 7 pressed against the toner image bearing member 6 by the transfer roller 1, that is, the toner transfer portion.

In the toner transfer section, a high voltage having a polarity opposite to the charge polarity of the toner image 8 supplied by the high voltage generation circuit 5 via the transfer roller 1 acts on the transfer material 7, and the toner image 8 is electrostatically The image is transferred onto a transfer material 7, and an image 9 is formed on the transfer material.

By the way, the contact width between the transfer roller 1 and the transfer material 7 is 1
~2mm.

However, the toner image 8 on the toner image carrier is not completely transferred to the transfer material 7 as the image 9, and a small amount remains on the image carrier as residual toner 10.

The efficiency with which this toner is transferred from the image carrier to the transfer material is
It was calculated using the following calculation method.

The relationship between the optical density of the toner image transferred onto the transfer material 7 and the toner transfer amount, and the relationship between the transfer remaining toner concentration on the image carrier and the toner amount are measured in advance, and based on these, the relationship is measured in advance. The amount of transferred toner and the amount of remaining transfer toner were calculated by converting the density of the transferred image and the density of the remaining transfer toner, respectively. The transferred image density is determined by measuring the sample after the toner has adhered to a certain level using a reflection densitometer, and the remaining transferred toner density is determined by measuring the remaining transferred toner 10 on the image carrier with a mending tape.
It was pasted on PC paper and measured from above.

Next, the resistance per unit area between the core bar 2 of the transfer roller 1 and the outer surface of the roller was measured. A voltage of 1.0 OOV was applied to the core metal 2, a metal probe was brought into contact with the surface of the roller, the current at that time was detected, and the resistance value was determined.

In this example, transfer rollers with four different resistance values were manufactured and evaluated. The results are shown in Figures 3-6.

In Figure 3, the resistance value of the transfer roller is 105Ω/cj.

106Ω/cd, 103Ω/cl, IQIOΩ/c
d shows changes in transfer efficiency with respect to changes in transfer voltage applied to the transfer roller.

However, the measurements were conducted under environmental conditions of a temperature of 25° C. and a humidity of 55%.

From Figure 3, the resistance value of the transfer roller is 1010Ω/cm2.
In this case, it can be seen that in order to obtain high transfer efficiency, the transfer voltage needs to be a high voltage of 4 KV or more. Also, 10
At 5 Ω/cd, a high transfer efficiency can be obtained around 1 Kv, but the maximum transfer efficiency is slightly lower at about 80% compared to transfer rollers with other resistance values. Transfer roller resistance is 103Ω
/cd or less is not suitable because electric discharge may occur between the image bearing member and the roller.

FIG. 4 shows the relationship between transfer voltage and transfer efficiency when measurements were made under environmental conditions of a temperature of 30° C. and a humidity of 85%.

From FIG. 4, it can be seen that the range of high transfer efficiency is narrower than when the temperature is 25° C. and the humidity is 55%. Furthermore, in the case of 1010Ω/cj, the overall transfer efficiency is lower.

FIG. 5 shows the transfer efficiency of the transfer roller of each resistance value when measurements were made under environmental conditions of a temperature of 10° C. and a humidity of 20%. Compared to other environmental conditions, the area with high transfer efficiency becomes wider, but in the case of 103Ω/cl, the transfer efficiency is considerably lower.

Considering the results under each of the above environmental conditions, the resistance per unit area of the transfer roller is 106Ω/cd to 109Ω/cd.
The range of cj is suitable for high transfer efficiency over various environmental conditions.

Next, selection of the resistance values of the elastic layer and surface coating layer of the transfer roller of the present invention will be explained.

The results shown in Figures 3 to 5 were obtained by adjusting the resistivity of the elastic layer and surface coating layer and changing the resistance per unit area of the entire roller, but the results were obtained by adjusting the resistivity of each layer. There are conditions. In this embodiment, the diameter of the transfer roller 1 is 28 mm.
Measurements were made as follows. The diameter of the core bar 2 is 10 mm, the thickness of the elastic layer 3 is 13.1 mm, and the thickness of the surface coating layer 4 is 0.1 mm.
It is mm.

The thickness of the surface coating layer 4 is 0.05 mm (50 μm) to 0.2 mm (0.05 mm (50 μm) to 0.2 mm (50 μm) in order to fully utilize the function of the elastic layer to provide an appropriate nip width when pressed against the image carrier.
200 μm) is desirable.

The resistivity of the surface coating layer 4 is set to 108Ω・Cm, and the elastic layer 3
When the resistivity of 102 Ω·cm was changed significantly, the resistance was too low, causing an excessive current to flow between the image carrier and the image carrier, destroying the surface of the image carrier. Therefore, it is appropriate that at least the resistivity of the elastic layer 3 is greater than 10<3 >[Omega].cm.

Further, it was found that if the resistance is 109 Ω·cm or more, the resistance of the entire transfer roller becomes too high, and it is difficult to increase the transfer efficiency to about 190% unless the transfer voltage is increased to nearly 5 KV.

On the other hand, the resistivity of the elastic layer 3 was set to 10 5 Ω·cm, the resistivity of the surface coating layer 4 was varied, and the appropriate resistance value of the surface coating layer was investigated.

FIG. 6 shows the change in transfer efficiency when the resistivity of the surface coating layer is changed.

From FIG. 6, it can be seen that the range of resistance values at which the transfer efficiency is 90% or more is from 10<7 >Ω.cm to 10<12 >Ω.cm. In the case of 10'3 Ω·cm, the transfer efficiency suddenly decreases. This is considered to be because the resistance is too high and sufficient transfer efficiency cannot be obtained unless the voltage applied to the transfer roller is considerably high. Further, in areas where the resistivity is low, the transfer efficiency is thought to decrease because a transfer electric field is not applied to the transfer surface portion.

From these facts, the resistivity of the elastic layer 3 of the transfer roller 1 is
The resistivity of the surface coating layer 4 is in the range of 103Ωcm to 108Ωcm, and the resistivity of the surface coating layer 4 is in the range of 103Ωcm to 1012Ωcm.
A range of m is appropriate.

By using the elastic layer 3 and the surface coating layer 4 having resistivities specified in this way, and by setting the resistance per unit area of the transfer roller in the range of 106 Ω/cm2 to 109 Ω/d, it is possible to withstand fluctuations in environmental conditions. High transfer efficiency can also be obtained.

In this embodiment, a case is shown in which the elastic roller of the present invention is used as a transfer roller, but since the internal structure of the roller is relatively simple and environmental stability is good, a charging roller that charges an image carrier, so-called a photoreceptor, It can be said that it is also effective to apply it as a.

[Effects of the Invention] As explained above, according to the present invention, in an elastic roller composed of a core metal, an elastic layer, and a surface coating layer, per unit area of the surface of the core metal and the surface of the surface coating layer. resistance 106
The resistivity of the elastic layer is in the range of 103Ω·cm to 107Ω·cm, and the resistivity of the surface coating layer is in the range of 107Ω·cm to 10!
By setting it in the range of 2 Ω·cm, stable transfer characteristics can be obtained over a wide range of environmental conditions.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of the elastic roller of the present invention, FIG. 2 is a schematic diagram of the apparatus used for evaluating the elastic roller of the present invention, and FIGS. 3 to 5 show the elastic roller of the present invention as a transfer roller. FIG. 3 is a graph showing the relationship between transfer voltage and transfer efficiency in the case where the temperature is 25° C. and the humidity is 55%, FIG. 4 is the temperature at 30° C. and the humidity is 85%, and FIG. , humidity 20
% under environmental conditions, and FIG. 6 is a graph showing the relationship between the resistivity of the surface coating layer and the transfer efficiency. 1... Elastic roller, 2... Core metal, 3... Elastic layer,
4...Surface coating layer.

Claims (1)

[Claims] An elastic roller comprising a core metal, a first layer made of an elastic body fixed around the core metal, and a second layer made of a high-resistance resin formed on the first layer. The resistance per unit area between the core metal and the outer surface of the second layer is in the range of 10^6 Ω/cm^2 to 10^9 Ω/cm^2, and The resistivity is in the range of 10^3 Ω·cm to 10^8 Ω·cm, and the resistivity of the second layer is in the range of 10^7 Ω·cm to 10^1^2 Ω·cm. elastic roller.