JP3117983B2 - Image forming device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as an electrophotographic apparatus and an electrostatic recording apparatus, and more particularly, to an image having a pair of conveying members for pinching and fixing an unfixed image. The present invention relates to a forming apparatus.

[Prior Art] FIG. 9 shows a heat roller fixing device used in a conventional image forming apparatus.

Pressing with an elastic layer of silicone rubber or fluorine rubber on a core metal as well as the fixing roller 1 with a resin layer of heat resistance and release properties such as PFA and PTFE on a core metal of aluminum, iron, etc. The roller 2 is brought into pressure contact with the recording material P on which a toner image Q is placed between the pair of rollers, and is heated and pressed to fix the toner image Q.

The fixing roller 1 is heated by the internal heater 3, the surface temperature is detected by the temperature detecting element 4, and the power supply to the heater 3 is turned ON / OFF based on the detected output to maintain the predetermined temperature.

The recording material P is guided between the pair of rollers by the entrance guide 6, is separated from the fixing roller 1 by the separation claw 5, and is sent out of the apparatus by the discharge guide 7.

When fixing is performed by nipping and conveying the recording material in this manner,
Due to frictional charging between the roller and the recording material, the fixing roller 1
There has been a problem that electric charges accumulate on the surface of the pressure roller 2 to adsorb the toner, or electric charges accumulate on the surface of the pressure roller 2 to repel the toner and cause an electrostatic offset to the fixing roller 1. For this reason, Japanese Patent Application Laid-Open No. 55-96970 proposes supplying a bias voltage to the fixing roller 1 by a power supply.

In this method, the toner Q is repelled from the fixing roller 1 by applying a voltage having the same polarity as that of the toner Q to the core metal of the fixing roller 1.

[Problems to be Solved by the Invention] However, when a bias voltage is applied to a fixing roller from a power supply, a voltage of 500 V or more is required to sufficiently prevent electrostatic offset.

In this case, in a high-temperature and high-humidity environment, a current may flow through the recording material P and adversely affect transfer.

In particular, as shown in FIG. 2, when transferring from a photoconductor to a recording material using a contact charging member such as a transfer roller, the recording material P
Then, a current having a polarity opposite to that of the transfer flows from the transfer roller 9 to the transfer roller 9 and the voltage of the transfer is lowered, so that there is a disadvantage that the transfer is omitted.

Means for Solving the Problems In order to solve the above problems, the present invention provides an image carrier that carries an unfixed image, and a transfer unit that transfers the unfixed image on the image carrier onto a recording material at a transfer unit. A charging member, a fixing member that contacts the recording material carrying the unfixed image at the fixing unit and fixes the unfixed image on the recording material, and a power supply that applies a bias voltage to the fixing member; In the image forming apparatus in which the distance between the fixing unit and the fixing unit is shorter than the maximum length of the recording material, the power supply and the fixing member are connected via a first resistor, and between the first resistor and the fixing member. It is characterized by being branched and grounded via a second resistor.

[Example] Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a simplified diagram showing a main part of an image forming apparatus according to an embodiment of the present invention.

The toner image formed on the photosensitive drum 8 serving as an image carrier is transferred to a recording material by a transfer roller 9 which contacts and charges the recording material.

A power supply 13 is provided to the transfer roller 9 serving as the contact transfer charging member.
Thus, a voltage having a polarity opposite to that of the toner is applied.

The recording material to which the toner image has been transferred is nipped and conveyed by the fixing roller 1 and the pressure roller 2 and is fixed by heat and pressure.

As shown in FIG. 1, the distance between the transfer unit and the fixing unit is
It is shorter than the maximum recording material length in the transport direction.

The fixing roller 1 is formed by applying PFA12, which is a fluororesin, on a surface of a conductive core 11 made of aluminum, iron or the like by electrostatic coating.

The pressure roller 2 is one in which an elastic layer of silicon rubber, fluorine rubber or the like is provided on a cored bar.

In this embodiment, the output voltage of the same polarity as the toner from the constant voltage power supply 10 is divided by a plurality of resistors R ₁ and R ₂ , and the divided voltage V ₁ is applied to the core metal 11 of the fixing roller 1. ing.

That As shown in FIG. 1, the fixing roller 1 and the power supply 10 is connected through a resistor R ₂ is a first resistor, and the resistor
A resistor R ₁ is branched between R ₂ and the fixing roller and is a second resistor.
Grounded.

A pinhole is provided in the PFA on the surface layer of the fixing roller 1, and a current flows through the recording material through the pinhole.

FIG. 3 (a) shows the amount of current flowing through the paper with respect to the bias voltage under a high temperature and high humidity environment, and FIG. 3 (b) under a low temperature and low humidity environment. From these, the resistance between the core of the fixing roller and the recording material can be seen.

From Fig. 3 (a), the resistance value in a high temperature and high humidity environment is 200 V
It becomes 33MΩ at the time. It is 23MΩ at 400v. In this case, a fixing roller having an outer diameter of 30 mm was used, and a pressure roller having a high resistance was used. The nip was changed from 4.5mm to 6.0mm.

In FIG. 3A, an offset occurs in a region on the left side of the broken line A. On the other hand, in a region on the right side of the broken line B, transfer failure occurs. In FIG. 3B, an offset occurs on the left side of the broken line c. Therefore, in a high-temperature, high-humidity environment, the bias of the fixing roller
Must be limited to between 400V and 400V, and in low temperature and low humidity environments, a voltage of 1000V or more is required. From the intersection of the broken line and the curve, the resistance between the fixing roller and the recording material is between 23 MΩ and 33 MΩ in a high temperature and high humidity environment. In low-temperature, low-humidity environments
2500MΩ or more is required.

In FIG. 1, the resistance between the fixing roller and the recording material is represented by R
And the power supply voltage is 2000v.

 Assuming that the voltage applied to the fixing roller at this time is V1, V1 = 2000 (1−R2 (R + R1) / (RR1 + RR2 + R1R2)).

Based on FIG. 3 (a), if the condition is determined to be on the right side of the dashed line A, V1 = 200, so that 2000 (1-R2 (R + R1) / (RR1 + RR2 + R1R2)) ≧ 20
It becomes 0. Since R = 33MΩ when V1 = 200v, R1 and R
The relationship of 2 can be expressed as R2 ≦ 297R1 / (33 + R1).

This is because R1 and R2 are in the lower right area of the curve D in FIG.
Is present. On the other hand, the condition on the left side of the dashed line B is expressed as V1 ≦ 400.
It becomes 0.

Since R = 23 MΩ when V1 = 400 V, the relationship between R1 and R2 can be expressed as R2 ≧ 184R1 / (46 + 2R1).

This is because R1 and R1 are located in the upper left area of the curve E in FIG.
R2 is coming.

Similarly, from FIG. 3 (b), the condition on the right side of the dashed line c is expressed as V1 ≧ 1000, so that (1−R2 (R + R1) / (RR1 + RR2 + R1R2)) ≧ 1000.

Since R = 2500 MΩ when V1 = 1000 V, the relationship between R1 and R2 is expressed as R2 ≦ 2500R1 (2500 + R1).

This means that R1 and R2 are below the curve F in FIG.

From FIG. 4, as such a combination of R1 and R2, R1
= 120 MΩ and R2 = 100 MΩ are possible.

With this combination, in a high-temperature and high-humidity environment, as shown in FIG. 5A, the resistance R between the fixing roller and the transfer material and the curve of the voltage-current characteristic with respect to the combined resistance of R1 = 100 MΩ.
M1 and the line N1 of the voltage drop due to R2 = 120MΩ from 200V
It can be seen that there is a balancing intersection in a region where an offset between 400 V and transfer failure does not occur.

Further, as shown in FIG. 5 (b), in a low-temperature and low-humidity environment, the resistance R between the fixing roller and the transfer material and the voltage-current characteristic curves M2 and R2 = 120 MΩ for the combined resistance of R1 = 100 MΩ. Since the intersection point between the straight line N2 and the straight line is 1000 V or more, no offset occurs.

As described above, in this embodiment, the fixing roller 1
Is corrected to a range in which offset and transfer omission do not occur, so that stable image formation can be performed even if an environmental change occurs.

In order to prevent offset from occurring in a low-temperature and low-humidity environment, a high pressure (1000 V or more in this embodiment) is preferable. However, in a high-pressure environment, a relatively large hole is formed due to the rupture of a pinhole in the surface layer of the fixing roller. An excessive current may flow there.

However, in this embodiment, by providing the resistor R1,
The current can be controlled so that the voltage becomes lower in the range exceeding 00V, and the offset can be prevented.

In the above-described embodiment, PFA was coated by electrostatic coating as a release layer of the fixing roller.However, a PFA tube was coated on a cored bar, and heated and bonded to a temperature higher than the melting temperature of PFA to form a fixing roller. An example will be described.

The fixing roller coated with this tube has an advantage that the number of pinholes on the surface layer is small, and transfer loss is less likely to occur in proportion to the above embodiment.

FIGS. 6 (a) and 6 (b) show the results of measuring the current actually flowing from the fixing roller to the recording material and examining the occurrence limits of transfer omission and offset. It can be seen that the range of the bias potential that can be used is wider than that of the above-described embodiment, and that a lower potential is sufficient.

FIG. 6A shows current-voltage characteristics under a high-temperature and high-humidity environment. FIG. 6B shows current-voltage characteristics under a low-temperature and low-humidity environment.

According to FIG. 6 (a), in the area on the right side of the dashed line H, the transfer omission occurs, but the bias voltage at this time is 1300 V or more, which indicates that the combined resistance of the fixing roller and the recording material is 38 MΩ.
It is the following time. Conversely, although an offset occurs on the left side of the broken line G, the bias voltage at this time is 200 V,
This is when the combined resistance of the fixing roller and the recording material is 133 MΩ or more.

In the same manner as in the above-described embodiment, the resistance division as shown in FIG. 1 was performed to examine what combination of R1 and R2 is possible.

From FIG. 6 (a), since the offset prevention condition of the right side of the broken line G can be written as V1 ≧ 200, 2000 (1−R2 (R + R1) / (R1R2 + RR1 + RR2)) ≦ 20
It becomes 0. Since R1 = 133MΩ when V1 = 200V, the relationship between R1 and R2 is expressed as R2 ≦ 1197R1 / (R1 + 133).

This indicates that R2 must be below curve K in FIG.

On the other hand, the transfer omission prevention condition on the left side of the broken line H can be expressed as V1 ≦ 1300. This is 2000 (1−R2 (R + R1) / (R1R2 + RR1 + RR2)) ≧ 13
00.

Since R = 38 MΩ when V1 = 1300 V, the relationship between R1 and R2 can be expressed as R2 ≧ 20.5R1 / (38 + R1).

This indicates that in FIG. 7, R2 must be above curve J.

From FIG. 6 (b), in a low-temperature and low-humidity environment, the offset prevention condition can be expressed as V1 ≧ 300.

That is, 2000 (1−R2 (R + R1) / (R1R2 + RR1 + RR2)) ≦ 13
It becomes 00.

When V1 = 300V, R = 3000MΩ, so R1 and R2
Can be expressed as R2 ≦ 2550R1 / (0.15R1 + 450).

This indicates that in FIG. 7, R2 must be below the curve L.

A point satisfying the above results is R1 = R2 = 500 MΩ.

Fig. 8 (a) in a high temperature and high humidity environment by this combination
As shown in the figure, the resistance R between the fixing roller and the recording material and R1
= Curve S1 and R2 of the voltage power supply characteristic for the combined resistance of 500MΩ
= The linear drop T1 of 500MΩ is from 200V to 1300V
It can be seen that there is a balance intersection in a region where no offset and transfer failure occur.

Also, as shown in FIG. 8 (b), in a low-temperature and low-humidity environment, a curve R2 of the resistance between the fixing roller and the recording material and a voltage-current characteristic with respect to a combined resistance of R1 = 500 MΩ, and a straight line of a voltage drop due to R2 = 500 MΩ. Intersection with T2 begins to generate offset
No offset occurs because it is over 300v.

The high temperature and high humidity environment described above is 32.5 ° C, 85%,
The low-temperature and low-humidity environment is a condition of 15 ° C. and 10%.

As described above, PFA is used as the release layer in the embodiment of the present invention, but an elastic body such as fluororesin such as PTFE or PFA, silicon rubber, or fluororubber can be used.

In the above-described embodiment, a bias voltage having the same polarity as the toner is applied to the fixing roller in contact with the unfixed toner image.
A bias voltage having a polarity opposite to that of the toner may be applied to the pressing roller that is in pressure contact with the fixing roller, or a bias voltage may be applied to both the fixing roller and the pressing roller.

Further, when a bias voltage is applied to the roller, if the resistance of the roller is low, it is difficult for the roller surface to hold a potential. The volume resistivity of the surface layer is preferably 10 ¹¹ Ωcm or more.

Further, the transporting body for nipping and transporting the recording material and fixing it is not limited to the roller shape but may be an endless belt shape or an endless shape.

[Effects of the Invention] As described above, according to the present invention, it is possible to provide an image forming apparatus that does not cause transfer omission even under a high-temperature and high-humidity environment and does not generate an offset even under a low-temperature and low-humidity environment.

[Brief description of the drawings]

FIG. 1 is a simplified view of an image forming apparatus according to an embodiment of the present invention, FIG. 2 is a simplified view of an image forming apparatus as a background of the present invention, and FIGS. 3 (a) and 3 (b) are fixings coated with PFA. FIG. 4 is a diagram showing a correlation between a current flowing between a roller and a recording material and a bias voltage. FIG. 4 is a diagram showing an appropriate region of a resistor dividing resistor. FIGS. 5 (a) and (b) are diagrams showing a case where a dividing resistor is used. PFA
FIG. 5 is a diagram showing a current flowing through a fixing roller coated with a recording material and a recording material and a voltage actually applied. 6 (a) and 6 (b) are diagrams showing a correlation between a current flowing between a fixing roller covering a PFA tube and a recording material and a bias voltage. FIG. 7 is a diagram showing an appropriate region of the resistance dividing resistor. FIGS. 8 (a) and 8 (b) show currents actually flowing through the fixing roller coated with the PFA tube and the recording material when the divided resistance is used. FIG. 9 is a longitudinal sectional view of a conventional example. 1 is a fixing roller 2 is a pressure roller 10 is a power supply R1 and R2 are split resistors

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hideo Nanataki 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Hideyuki Yano 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (72) Inventor Takayasu Yuminomo 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Hiroshi Sasame 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Hiroto Hasegawa 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (56) References JP-A-59-34573 (JP, A) JP-A-55-96970 (JP, A) (58) Fields surveyed (Int. Cl. ⁷ , DB name) G03G 15/20 G03G 15/16

Claims (1)

(57) [Claims] An image carrier for carrying an unfixed image, a transfer charging means for transferring an unfixed image on the image carrier onto a recording material at a transfer section, and fixing the recording material carrying the unfixed image to the recording material A fixing member for fixing an unfixed image on a recording material in contact with the recording medium, and a power supply for applying a bias voltage to the fixing member, wherein a distance between the transfer unit and the fixing unit is the largest. In the image forming apparatus shorter than the length, the power supply and the fixing member are connected via a first resistor,
The image forming apparatus is characterized in that a portion between the first resistor and the fixing member is branched and grounded via a second resistor.