JP3410277B2 - Charging device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for charging a flat surface or a curved surface. For example, in an image forming apparatus such as a copying machine, a fax machine or a printer, a photoreceptor is charged or a visible image (toner image) on a recording paper. It is used for the transfer of.

[0002]

2. Description of the Related Art In an electrophotographic image forming apparatus, a charged photoconductor is exposed to image light to form an electrostatic latent image, and the electrostatic latent image is developed by a toner to visualize the latent image. ) To the recording paper. Recently, there is an image forming apparatus that uses a charging roller for charging a photoreceptor and / or transferring a visible image onto a recording paper.

The charging roller has a conductive rubber supported by a cored bar of a conductive material, but uneven charging potential is likely to occur. The cause of this uneven charging has been studied, and it has been reported that the surface condition, temperature, humidity, etc. of the conductive rubber affect the uneven charging or the fluctuation of the charging potential.

In Japanese Patent Laid-Open No. 4-186381, in order to prevent a decrease in charging potential at low humidity, the temperature of a charging roller is detected and charging is applied according to the temperature (humidity estimated from the temperature). There is a suggestion to adjust the voltage. JP-A-3-3866
Japanese Patent Laid-Open No. 3-77759 and Japanese Patent Laid-Open No. 4-77759 propose that the surface of a conductive rubber is coated with a resin to reduce uneven charging. In addition, there is a proposal to coat the surface of the conductive rubber to reduce the humidity dependence of the charging potential, and a surface coating to reduce toner stains or toner adhesion.

[0005]

The temperature distribution of the entire charging roller including the surface layer becomes non-uniform due to the influence of the environment in which the charging roller is used. For example, the temperature distribution inside the charging device is not uniform for a while after the image forming apparatus is powered on, and for example, the fixing device is heated by turning on the heater power,
The temperature around it rises relatively quickly, but the temperature of the photosensitive drum is low. When the photoconductor drum has a preheating heater, the temperature of the photoconductor gradually rises. Although there are many mechanical elements in the apparatus, the temperature rises from those near the heat source (fixing heater, preheating heater, etc.), but even the same member has different temperatures depending on the location. Since the elastic rubber of the charging roller has low thermal conductivity, temperature unevenness is likely to occur.

Further, in the case of a large-sized sheet passing after a continuous transfer of a small-sized transfer sheet, the temperature distribution in the longitudinal direction and the circumferential direction of the photosensitive member becomes non-uniform depending on the recording size. The roller temperature distribution is affected.

If the temperature distribution of the surface layer of the charging roller becomes non-uniform, the volume resistance of the surface layer becomes non-uniform, causing uneven charging on the photosensitive member. This uneven charging deteriorates the image quality.

An object of the present invention is to suppress uneven charging due to uneven temperature of the charging roller.

[0009]

A charging device according to the present invention comprises a charging roller having an elastic layer on a cored bar, and a temperature-adjusting roller having a high thermal conductivity which comes into contact with the charging roller . Of charging roller
The releasability of the toner against the toner on the surface of the temperature control roller
It is higher than the releasability .

According to this, when the temperature unevenness in the longitudinal direction of the charging roller comes into contact with the temperature controlling roller, the heat of the high temperature portion propagates to the low temperature portion through the temperature controlling roller, and the temperature fluctuation occurs. The difference becomes smaller. That is, the temperature control roller functions as a heat transfer medium and eliminates temperature unevenness. The temperature control roller functions as a heat absorber against temperature unevenness in the direction of rotation of the roller, and when the high temperature part comes into contact with the temperature control roller, the temperature control roller charges the charging roller.
The heat of the roller is absorbed, and when the low temperature portion comes into contact, the temperature control roller gives heat to the charging roller. As a result, temperature unevenness in the rotating direction of the charging roller is also eliminated. Furthermore, the charging roller surface
The releasability of the toner against the toner on the surface of the temperature control roller
Is higher than the releasability of the charging roller.
Toner (dirt) moves to the temperature control roller, and the charging roller cleans.
And does not cause charging failure.

In a preferred embodiment of the present invention, the charging roller has, as a surface layer, a surface layer made of a material different from the material of the elastic layer on the elastic layer, and the releasability of the surface layer from the toner is temperature controlled. Higher than that of the roller surface. The temperature control effective length of the temperature control roller is longer than the charging effective width of the charging roller, and the temperature control roller has a roller base having a high thermal conductivity such as a copper material or an aluminum material. In some embodiments of the present invention, the temperature controlled roller has a heat pipe inside the roller substrate. Further, in one embodiment of the present invention, the roller base of the temperature control roller is a heat pipe. All of the embodiments of the present invention include means for pressurizing the temperature control roller against the charging roller.

According to these embodiments, by a temperature control effective length of the temperature control roller is made longer than the charging effective width of the charging roller over charging effective width throughout the temperature of the surface layer of the charging roller becomes uniform . Since the roller base of the temperature control roller is made of copper or aluminum having a high thermal conductivity, the heat transfer inside the temperature control roller is smooth and the temperature of the surface layer of the charging roller is uniformized. high. In the embodiment in which the heat pipe is inserted inside the temperature control roller, the movement of heat in the temperature control roller becomes smoother, and the effect of equalizing the temperature of the charging roller is high. In the embodiment in which the temperature control roller is a heat pipe,
Since the pipe directly contacts the charging roller, the temperature uniformizing effect is higher. Since the temperature control roller is pressed against the charging roller by the pressing means, the contact area between the temperature control roller and the charging roller is large, and the heat transfer between the temperature control roller and the charging roller becomes smoother. The uniformity effect of is further improved.

Other objects and features of the present invention will become apparent from the following description of embodiments with reference to the drawings.

[0014]

DETAILED DESCRIPTION OF THE INVENTION

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment FIG. 1 is a side view of a first embodiment of the present invention, FIG. 2 is a front view, and FIG. Referring to these drawings, the charging roller 2 is pressed against the photoconductor 3 and the photoconductor 3 rotates clockwise, so that the charge roller 2 is driven to rotate counterclockwise. The core metal 21 of the charging roller 2 is connected to the power supply device 4. A charging bias is applied to the cored bar 21 by the power supply device 4, whereby the cored bar 2 of the charging roller 2 is applied.
A charging current flows from the cored bar 21 to the photoconductor 3 (or in the opposite direction) through the elastic layer supported by 1 and its surface layer, whereby the photoconductor 3 is charged.

The temperature control roller 1 is in contact with the charging roller 2, and the temperature control roller 1 is pressed against the charging roller 2 by the compression coil springs 5a and 5b via the bearings 17a and 17b. ing. When the charging roller 2 is driven to rotate counterclockwise with respect to the photoconductor 3, the temperature adjusting roller 1 is driven to rotate clockwise. The charging roller 2 and the temperature control roller 1 are supported by bearings 7a, 7b and 17a, 17b, respectively. These bearings 7a, 7b and 17a, 17b
Is made of highly insulating resin. Bearings 7a and 1
Reference numeral 7a is supported by a support arm 6a, and bearings 7b and 17b are supported by a support arm 6b so as to be movable in the radial direction around the rotation center of the photoconductor 3.

Since the bearings 7a, 7b and 17a, 17b are insulators, the heat transfer from the charging roller 2 and the temperature control roller 1 to the arms 6a, 6b is small.

The temperature control roller 1 and the charging roller 2 shown in FIG.
In the positional relationship of, the relationship between the effective length L ₂ of the temperature control roller 1 and the effective charging width L ₁ is L ₂ ≧ L _1, and the surface temperature of the charging roller 2 is uniform in the range of the effective charging width L _1. Is realized.

Referring to FIG. The charging roller 2 is a core metal 2
1 is coated with an elastic layer 22 and further the elastic layer is coated with a surface layer 23. The toner releasing property of the surface layer 23 is the toner releasing property of the temperature control roller 1. Higher than sex. Residual toner -T ₁ of the photosensitive member 3 is charged at the nip portion _{N 1} b - La 2
The toner T ₂ transferred to the charging roller 2 moves to the temperature control roller 1 (at the nip portion N ₂ ) when it is pressed against the temperature control roller 1. The toner transferred to the temperature control roller 1 is indicated by T ₃ .
Thus temperature control B - La 1 has the effect of cleaning the surface of the charging roller 2.

Since the roller base of the temperature control roller 1 is an aluminum pipe (which may be made of copper, brass, or another material having a high thermal conductivity), it has a high thermal conductivity and the temperature of the charging roller 2 is high. In the nip N ₁ of the adjusting roller 1, heat is quickly exchanged between the two, so that the distribution of the surface temperature of the charging roller 2 becomes uniform.

-Second Embodiment- FIG. 4 shows a vertical cross section of a temperature control roller 1 used in a second embodiment of the present invention. The temperature control roller 1 is a solid aluminum rod (a shaft made by cutting a shaft 11 into an aluminum round rod). The other structure is similar to that of the first embodiment described above. In the second embodiment, since the heat capacity of the temperature control roller 1 is large, the charging roller 2
The heat exchange between the temperature control roller 1 and the temperature control roller 1 is fast, and the effect of uniformizing a relatively large temperature unevenness is high.

-Third Embodiment- FIG. 5 shows a temperature control roller 1 used in a third embodiment of the present invention. 5A is a side view, and FIG. 5B is a vertical sectional view. This temperature control roller 1 is an aluminum roller of the second embodiment.
In the la, three holes penetrating between both shaft ends are opened in parallel and at equal pitches, and heat pipes 8a, 8b, 8c are press-fitted and fixed therein. The other structure is similar to that of the first embodiment described above. The heat pipes 8a, 8b, 8c are thin-walled copper pipes having a high thermal conductivity and a working liquid having a low vaporization temperature sealed therein. In this third embodiment, the heat pipe 8
The heat pipes 8a, 8 are exchanged between the heat of vaporization and the latent heat when the working fluid is vaporized and liquefied inside a, 8b, 8c.
b and 8c make the temperature of the temperature control roller 1 uniform. The aluminum base (roller base) into which they are press-fitted is a charging roller 2.
Exchange heat with. Since the heat pipe has a high effect of uniformizing the temperature of the aluminum substrate, the effect of rapidly uniforming a relatively large temperature unevenness is high. The relationship between the effective length L ₃ of the heat pipe and the effective charging width L ₁ of the charging roller 1 is L ₃ ≧
It is L ₁ . The number and arrangement of the heat pipes 8a, 8b, 8c may be determined according to the required performance.

-Fourth Embodiment- FIG. 6 shows a temperature control roller 1 used in the fourth embodiment of the present invention.
Indicates. In this temperature control roller 1, a through hole is formed in the center of a solid roller, and a heat pipe 8 is press-fitted therein. The other structure is similar to that of the first embodiment described above. The fourth embodiment is a modification of the third embodiment, and the same effect as the third embodiment can be obtained.

-Fifth Embodiment- FIG. 7 shows a front view of a fifth embodiment of the present invention. In this fifth embodiment, the temperature control roller 1 uses the heat pipe 8 as a roller base, and the heat pipe 8 is pressed against the charging roller 2.
At both ends of the heat pipe 8, shafts 11a, 1 with flanges are provided.
1b are fixed, and the flanges thereof have holes for receiving the pipe ends, and the ends of the pipes 8 are inserted therein. The pipe member of the heat pipe 8 is a copper pipe plated with a metal for rust prevention and wear resistance, and has a high heat exchange efficiency between the working liquid in the heat pipe 8 and the charging roller 2.

In any of the embodiments described above, in order to make the temperature distribution of the surface layer of the charging roller 2 uniform, the temperature distribution of the surface layer of the charging roller 2 is changed by bringing the temperature adjusting roller 1 into contact with the surface layer. It is possible to obtain a stable, high-quality image without causing uneven charging on the photoconductor 3 by homogenizing. Since the releasability of the charging roller surface with respect to the toner is higher than the releasability of the temperature adjusting roller surface with respect to the toner, the toner adhering to the charging roller surface is cleaned by the temperature controlling roller 1 and charging failure does not occur. By the effective length L _2, L ₃ of the temperature control roller 1 is made longer than the charging effective width L ₁ of the charging roller 2, the charge across the effective width L ₁ throughout the temperature of the surface layer of the charging roller 2 becomes uniform. Since the temperature control roller 1 is made of a material having a high thermal conductivity, the heat in the temperature control roller 1 can move smoothly, and the temperature of the surface layer of the charging roller 2 can be made uniform. Since the temperature adjusting roller 1 and the charging roller 2 are pressed against each other by the compression coil springs 5a and 5b which are pressurizing means, the contact area between them (the contact area at the nip N2) is increased.
The transfer of heat between the temperature control roller 1 and the charging roller 2 becomes smooth, and the effect of making the temperature of the surface layer of the charging roller 2 uniform is further enhanced.

In the third and fourth embodiments, the temperature control roller 1
Since the heat pipe is inserted into the inside of the roller base body, the movement of heat in the temperature control roller 1 is smoother, and the effect of uniformizing the temperature of the surface layer of the charging roller 2 is high.

In the fifth embodiment, since the roller base of the temperature control roller 1 is a heat pipe, the structure for uniformizing the temperature of the surface layer of the charging roller 2 is simpler than the third and fourth embodiments. Is.

[Brief description of drawings]

FIG. 1 is a side view of a first embodiment of the present invention.

FIG. 2 is a front view of the first embodiment.

FIG. 3 is a cross-sectional view of the first embodiment.

FIG. 4 is a solid temperature control roll used in the second embodiment of the present invention.
It is a longitudinal cross-sectional view of la.

5A is a side view of a temperature control roller used in a third embodiment of the present invention, and FIG. 5B is a vertical sectional view.

FIG. 6A is a side view of a temperature control roller used in a fourth embodiment of the present invention, and FIG. 6B is a vertical sectional view.

FIG. 7 is a front view of a fifth embodiment of the present invention.

[Explanation of symbols]

1: Temperature control roller 2: Charging roller 3: Photoconductor 4: Power supply devices 5a, 5b: Compression coil springs 6a, 6b: Arms 7a, 7b: Bearings 8, 8a, 8b, 8c: Heat pipes 11a, 11b: Bearing 17a, 17b: Bearing 21: Core 22: Elastic layer 23: Surface layer L ₁ : Effective charging width L ₂ : Effective length of temperature control roller L ₃ : Effective length of heat pipe N ₁ , N ₂ : Nip T ₁ , T ₂ , T ₃ : Toner

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Claims (7)

(57) [Claims] 1. A mold releasability of a charging roller from a toner, comprising a charging roller having an elastic layer on a cored bar and a temperature control roller having a high thermal conductivity in contact with the charging roller. Is the temperature control roller table
A charging device that has higher releasability than the toner on the surface. 2. The charging roller comprises a surface layer on the elastic layer,
The charging device according to claim 1, further comprising a surface layer made of a material different from that of the elastic layer. 3. The charging device according to claim 1, wherein the temperature control effective length of the temperature control roller is longer than the effective charging width of the charging roller. 4. The charging device according to claim 1, wherein the temperature control roller has a roller base having a high thermal conductivity such as a copper material or an aluminum material. 5. The charging device according to claim 4, wherein the temperature control roller has a heat pipe inside the roller base. 6. The roller substrate is a heat pipe.
The charging device described. 7. Furthermore, adjustment Yutakaro - charging a La b - comprises means for pressurizing La claim 1, claim 2, claim 3, claim 4, charging of claim 5 or claim 6, wherein apparatus.